This disclosure relates to a mobile machine having an engine and a pressurised fluid supply system, and/or to a combination of such a mobile machine and an attached implement. The disclosure also relates to a method of operating such a mobile machine and/or combination. The disclosure relates in particular to an agricultural mobile machine and/or combination such as a tractor ad/or agricultural implement.

BACKGROUND

Pressurised fluid (hydraulic) supply systems are widely used to drive consumers on agricultural or construction mobile machines, e.g. a tractor or a self-propelled harvester, or on implements attached thereto. Such mobile machines will be referred to hereinafter simply as machines and are sometimes referred to as vehicles. These hydraulic systems are mostly provided with a pump supply, consumers, control means (respectively control valves) and a tank to provide a fluid reservoir. The term “consumer” is used in the further description to encompass hydraulic drives such as rotary motors or linear rams but also for the respective control valves assigned to these drives. The term “control” in relation to supply systems hereby includes any adjustment of the supply system regarding direction, supply time or pressure of the fluid flow or the delivery of the pump used to supply the system. The term “pump supply” includes the pump and all valve means which are needed to adjust the fluid flow and/or fluid pressure supplied by said pump to a pump supply line. The pressure of the fluid provided by the pump supply being referred to herein as the pump supply pressure PSP.

In a hydrostatic hydraulic system, a pressure differential is needed to provide hydrostatic work (an output). This pressure differential between the pump supply (source) and consumer results in a fluid flow which is sufficient to undertake work, such as to lift a tractor three-point hitch or a operate a rotary drive on an implement or in a hydrostatic drive for example. Furthermore, a stand-by or static pressure differential AP _s t is also needed when the system is otherwise in idle mode to keep control valves (assigned to consumers) responsive so that the spool of the valve can be moved on demand.

Hydraulic losses are present whenever oil circulates within a hydraulic system even when no consumer is operated. To mitigate this problem, it is known to provide means to forward a demand of a consumer to the pump supply. These systems are generally called load sensing systems (the term load sensing is abbreviated to LS). In such systems, a load induced pressure demand of the consumers, hereafter referred to as a “load sensing pressure” LSP, is hydraulically fed back to the pump supply via pipes or hoses so that pump supply oil flow/pressure can be adjusted according to the needs of the consumers. This load sensing pressure LSP feedback signal is typically generated by the control valve assigned to a consumer and the highest load sensing pressure LSP of all the consumers supplied by the pump is used to adjust the pump supply.

In general there are two different types of hydraulic supply systems with LS demand feedback available on the market - closed-centre load sensing systems (CC-LS systems) and open-centre load sensing systems (OC-LS systems).

CC-LS systems are equipped with variable displacement pumps whereby the demand of the consumers is hydraulically fed back to the pump supply including an adjustment means for the pump so that the displacement of the pump is adjusted according to the needs of the consumers.

To ensure that a stand-by pressure differential AP _st is maintained in the supply to support fast system response, the pump is kept on low displacement to compensate for losses/leakage resulting in a stand-by pressure even if there is no demand by consumers. As a result of the reduction of the hydraulic fluid circulation, losses and power input required by the pump are reduced.

Figure 1 illustrates part of a simplified known CC-LS hydraulic circuit. A pump supply 10 includes a variable displacement pump 12 which draws fluid from a tank 14 and forwards pressurised fluid to consumers (not shown) via a pump supply line P. Fluid is returned to the tank from the consumers via a return or tank line T. The pump 12 can be any suitable variable displacement pump and could, for example, be a swash plate axial piston pump in which the displacement of the pump is changed by pivoting the swash plate by means of a pump actuator 16 to vary the piston stoke. In the arrangement illustrated, actuator 16 is biased by a spring to pivot the swash plate in a direction to increase pump displacement and hence the output of the pump.

Pressurised fluid introduced into a chamber 20 of the actuator opposes the force of the spring and if the force of the fluid is greater than that of the spring the swash plate is pivoted to reduce the delivery of the pump. Operation of the actuator 16 is controlled by a flow control valve 22 and a pressure limiting valve 24, which together with the actuator 16 form a pump controller and form part of the pump supply 10. Each of the valves is biased by a respective spring 26, 28 to the position shown in which the actuator chamber 20 is connected to the tank 14. Each of the valves has a pump pressure port 30, 32 connected to the pressure line P of pump so that the fluid pressure acting on the valve spool through the pump pressure port 30, 32 opposes the force of the respective spring 26, 28. The flow control valve 22 also has a LS pressure port 34 to which a load sensing pressure signal line LS is connected. The highest consumer load sensing pressure LSP of the various consumers in the hydraulic LS system is fed into the LS pressure signal line so that the load sensing pressure LSP is added to the force of the spring to move the valve spool towards the position shown. The spring 26 in the flow control valve sets the stand-by pressure differential AP _s t which is typically in the region of 10 to 30 bar for tractor applications. The spring force may be adjustable to enable the stand-by pressure differential AP _s tto be adjusted. The spring 28 of the pressure limiting valve sets the maximum operating pressure of the system, which could be in the region 250 bar in the present example. Again, the spring force may be adjustable to enable the maximum operating pressure to be adjusted.

In normal operation when the system is at idle with no demand from the consumers, the pump supply pressure PSP acting through the pump pressure port 30 of the flow control valve 22 moves the spool against the force of the spring 26 to introduce pressurised fluid in to the chamber 20 of the actuator. This causes the actuator to pivot the swash plate and reduce the output of the pump until the pump supply pressure PSP balances the force of the spring 26 so that the output of the pump is held at the stand-by pressure AP _s t.

When a load sensing pressure signal LSP (or an increasing load sensing pressure signal) is reported to the LS pressure port 34 via the LS sensing line, this is added to the force of the spring 26 moving the valve spool so that the fluid pressure in the chamber 20 of the actuator is reduced. In response, the actuator 16 moves the swash plate to increase the output of the pump until the pump supply pressure PSP balances the force of the spring 26 and the load sensing pressure signal LSP. The pump therefore delivers a pump supply pressure PSP that is higher than the load sensing pressure LSP by the stand-by pressure differential AP _s t.

The pressure limiting valve 24 is usually held in the position shown by the spring 28 so that fluid passes into and out of the actuator chamber 20 under the control of the flow control valve 22. However, should the pump supply pressure PSP exceed the maximum permitted system pressure, as defined by the spring 28, the spool of the pressure limiting valve 24 is moved against the spring force to admit pressurised fluid into the chamber 20 of the actuator. This reduces the output of the pump until the pump supply pressure PSP it is brought back below the maximum permitted system pressure.

Generally, CC-LS systems are more expensive and complex than OC-LS systems but they have the advantage that the pump is only delivering above the stand-by pressure AP _s t on demand. This has a positive effect on the overall system efficiency. These systems are mainly used in high performance and high specification tractors (e.g. >100kW) used to supply complex and powerful implements.

In contrast to CC-LS systems, OC-LS systems are provided with a fixed displacement pump. Figure 2 illustrates part of a simplified OC-LS hydraulic circuit. A constant displacement pump 12’ draws hydraulic fluid from a tank 14 and delivers it to various consumers (not shown) via a pump supply or pressure line P. Fluid is returned to the tank 14 from the consumers via a return or tank line T. A proportional pressure compensator valve 40 forms part of the pump supply and is operative to selectively connect the pump supply line P to the tank 14. The spool of the valve 40 is biased by a spring 44towards a closed position, as shown, in which pump supply line P is not connected to the tank. This spring sets a static or stand-by pressure differential APstand the spring force may be adjustable to enable the stand-by pressure differential APstto be adjusted. The pump supply pressure PSP is applied to the opposite end of the spool via a pressure port 46 to oppose the force of the spring. The valve also has an LS pressure port 48 through which a consumer load sensing pressure signal LSP is applied to the valve spool to act in addition to the spring force.

In an idle mode where there is no consumer demand, the pump supply pressure PSP opposes the spring force to open the valve and connect the pump supply line P to the tank. The pump supply pressure PSP in the pump supply line falls until it balances the spring force and is then held at the stand-by pressure differential AP _s t. If a consumer load sensing pressure signal LSP is forwarded to the valve 40 via the LS pressure port 48, this adds to the spring force tending to close the valve so that the pump supply pressure PSP increases until it balances the combination of the spring force and the load sensing pressure LSP. The pump supply pressure PSP is thereby held a level which is higher than the load sensing pressure LSP by the stand-by pressure differential AP _s t defined by the spring 44. A further trend can be seen related to the supply and control means used on implements attached to an agricultural machine, such as a tractor. Due to increasing automation in agricultural work, implements are provided with more and more control functions which require complex control strategies. While in the past implements were equipped with only a few controllable drives (e.g. hydraulic cylinders or motors) which were controlled by valves on the tractor, today implements are provided with numerous controllable drives which cannot be controlled by the valves installed on the tractor. To address this, tractors are often equipped with power beyond systems (which may also be referred to in the art as high-pressure carry over). As the name suggests, these systems supply an uncontrolled (at the tractor) fluid flow from the pump supply to the implement via a respective interface, such as quick couplers. The implement itself is then equipped with control means in form of valves to adjust the parameters of the fluid supply. Similar to internal consumers on the tractor, these power beyond systems also include a LS function so that the load sensing pressure of consumers on the implement can be fed back to the pump supply on the tractor via a hydraulic LS line.

A typical power beyond interface 50 is illustrated in Figure 1 and includes quick release hydraulic couplings 50a, 50b, 50c for releasably connecting a pump supply line P, a return or tank line T, and an LS signal line on the tractor to equivalent hydraulic lines Pi, Ti, LSi on the implement. As illustrated, the LS line (LS _P b)from the power beyond interface which reports a LS signal from the consumers on the implement and an LS line (LSt) which reports a LS signal from the consumers on the tractor are connected to the LS pressure port 34 on the flow control valve 22 though a shuttle valve 52 or other functionally similar arrangement. This ensures that the highest LS load sensing pressure signal from the implement or the tractor is used to control the output of the pump. Where there are a number of consumers on the implement, shuttle valves are used to ensure the highest LS load sensing pressure signal LSP of the implement consumers is fed through to the power beyond LS connection 50c. Similarly, where there are a number of consumers on the tractor, shuttle valves or other functionally similar arrangements are used to feed the highest LS load sensing pressure signal LSP of the tractor consumers to the LSt line and hence to the shuttle valve 52.

A major advantage of the power beyond system is that the costs involved with fluid supply control are moved from the tractor to the implement so that a wider range of applications can be handled by tractors with reduced hydraulic control capability. These power beyond systems have mainly been the reserve of tractors with higher performance (>100kW) and CC-LS systems. However, a demand has been recognized for smaller tractors with OC-LS systems to provide power beyond, for example vineyard tractors with about 70 kW have to provide a supply to complex implements such as fruit harvesters equipped with many hydraulic drives to be controlled.

A drawback with purely hydraulic LS arrangements is that the hydraulic load sensing pressure signal LSP has to be forwarded to the pump supply by hydraulic lines. Where the load sensing pressure signal LSP comes from a consumer on an implement, a coupling is required to releasably connect the implement hydraulic LS signal line with a hydraulic LS signal line on the tractor. Furthermore, the various hydraulic LS signal lines from different consumers must be connected via shuttle valves to ensure that the highest consumer load sensing pressure LSP is forwarded to the pump supply. This all involves considerable additional expense and takes up valuable installation space. To overcome these drawbacks, electrohydraulic load sensing (E-LS) arrangements have been developed.

US 20070151238 A1 discloses a hydrostatic drive system in which a variable displacement pump controller is actuated electronically by an electronic control device. A pressure sensor is used to detect a hydraulic consumer load sensing pressure LSP and provides an input to the electronic control system. The electronic control system generates an electronic control signal for actuating the displacement pump controller via a LS control valve to set the pump supply pressure PSP so that it is higher than the sensed load sensing pressure LSP by a set amount APst. The system avoids the need for lengthy hydraulic LS load sensing pressure signal lines.

DE 102014 103 932 B3 discloses an E-LS system for an implement towed by a tractor. The towed implement has an electronic control device which determines the difference between the pump supply pressure PSP and the highest load sensing pressure LSP of the consumers on the towed implement. An electronic signal indicative of the pressure difference is forwarded to a hydraulic control module coupled to a LS connection of a variable displacement pump on the tractor. The hydraulic control module converts the electronic signal to a hydraulic control signal for controlling the pump displacement.

US2019345694 A1 discloses a further E-LS system for a tractor and towed implement which does not necessarily require an electronic controller on the implement. In the arrangement disclosed, a pressure sensor is provided on the tractor to detect a hydraulic LS load sensing pressure signal LSP provided by the implement via a power beyond LS coupling. The pressure sensor forwards an electronic load sensing pressure signal ELSPS representative of the hydraulic load sensing pressure LSP to an electronic control unit on the tractor which controls a transducer (e.g. a solenoid actuated pressure limiting valve) to provide a hydraulic pump supply control signal HPSCS having a pressure P _se t for forwarding to a variable displacement pump controller. A further pressure sensor may be provided to forward an electronic load sensing pressure signal ELSPS representative of the highest load sensing pressure LSP of a number of consumers on the tractor. In this case, the electronic control unit selects the highest of the electronic load sensing pressure signals to use as a basis to control the transducer. The hydraulic pump supply control signal HPSCS output from the transducer may be connected with the pump controller via a shuttle valve, with a hydraulic load sensing pressure signal LSP from a steering system providing a further input to the shuttle valve. In this case, the highest pressure of the hydraulic pump supply control signal HPSCS from the transducer or the load sensing pressure LSP from the steering system is forwarded to the pump controller. This illustrates how E-LS and traditional hydraulic LS can be combined.

Arrangements for adjusting the pump supply pressure PSP in an E-LS system can be similar to those illustrated in either of Figures 1 and 2, except that a hydraulic pump supply control signal HPSCS for application to the LS pressure port 34, 48 of a flow control valve 22 or pressure compensator valve 40 is produced using a suitable transducer in dependence on an electronic pump supply control signal EPSCS from the controller. The transducer may be a solenoid controlled pressure limiting valve, for example. The solenoid valve is actuated by the controller as a function of the hydraulic load sensing pressure demand LSP detected by a pressure sensor.

Figure 3 illustrates how a pump supply 10 including a variable displacement pump 12 similar to that described above in relation to Figure 1 can be adapted to incorporate a solenoid controlled pressure limiting valve for use with an E-LS system. The pump supply 10 includes a flow control valve 22’ to control the flow of fluid between the pump supply line P, the chamber 20 of the pump control actuator 16 and the tank 14. As in the hydraulic LS system of Figure 1, a spring 26 sets the stand-by or static pressure differential and is opposed by the pressure in the pump supply line P connected to the pressure port 30 of the flow control valve 22’. However, for use in an E-LS system, the fluid pressure P _se t supplied to the LS pressure port 34 is set by a solenoid controlled pressure limiting valve 54. When no current is provided to the solenoid 56 of the pressure limiting valve 54, the LS pressure port 34 is fully connected to the tank 14 and the pump supply pressure PSP at port 30 is opposed only by the force of the spring 26 in the flow control valve 22’ so that the pump output is maintained at the stand-by pressure AP _s t. When a consumer load sensing pressure LSP is detected by a pressure sensor and forwarded to a controller, the controller generates an electronic pump supply control signal EPSCS which is forward to the solenoid of the pressure limiting valve 54. The electronic pump supply control signal EPSCS actuates the pressure limiting valve 54 so that a hydraulic pump supply control signal HPSCS at a pressure P _se t is applied at the LS port 34 of the flow control valve 22’ in addition to the spring force. This causes the pump displacement to be increased until the pump supply pressure PSP balances the combination of the spring force and the pressure P _se t of the hydraulic supply control signal HPSCS.

As illustrated in US2019345694 A1, the hydraulic pump supply control signal HPSCS generated by the pressure limiting valve 54 may be forwarded to the LS port 34 via a shuttle valve with a conventionally generated hydraulic load sensing pressure signal LSP provided as second input to the shuttle valve. This arrangement enables an E-LS system to be integrated with a conventional hydro-mechanical hydraulic LS system.

For use with a fixed displacement pump arrangement such as that illustrated in Figure 2, a solenoid actuated pressure limiting valve 54 can be used to generate a hydraulic pump supply control signal HPSCS for application to the LS pressure port 48 of the pressure compensator valve 40.

Other electronically controlled transducer arrangements can be used to convert an electronic pump supply control signal EPSCS into a hydraulic pump supply control signal HPSCS.

Demands for increased efficiency and environmental protection have resulted in the development of low engine speed concepts for mobile agricultural machines such as tractors. However, a drawback of such arrangements is that the low engine speeds maintained may be insufficient to enable a pump driven by the engine to meet an increase in hydraulic demand.

There is a need for a mobile machine having a pressurised fluid supply system which overcomes, or at least mitigates the drawbacks of the known machines.

There is also a need for an alternative method of operating a mobile machine having a hydraulic supply system which overcomes, or at least mitigates, some or all of the drawbacks of the known methods. SUMMARY OF THE INVENTION

Aspects of the invention relate to a mobile machine, to a combination of a mobile machine and an attached implement, and to a method of controlling a mobile machine or a mobile machine and attached implement combination.

In accordance with a first aspect of the invention, there is provided a mobile machine having an engine and a hydraulic supply system, wherein the hydraulic supply system comprises a pump supply including a pump driven by the engine for supplying a pressurised fluid to at least one consumer on the mobile machine and/or an implement attached to the mobile machine, the mobile machine having a control system comprising one or more controllers configured to: receive, from a pressure sensor of a load sensing LS system associated with the at least one consumer, a first pressure signal indicative of a sensed load sensing pressure LSP demand associated with the at least one consumer; generate a pump supply control signal for adjusting the pump supply pressure in dependence the load sensing pressure LSP demand; receive or obtain data representative of the pump supply pressure PSP; and receive or obtain data representative of engine speed; wherein, the one or more controllers are selectively operable in at least one operating mode to generate one or more control signals for regulating the speed of the engine and wherein the one or more controllers configured when operating in the at least one operating mode to monitor the load sensing pressure LSP demand and the pump supply pressure PSP and determine whether the pump supply is able to meet a load sensing pressure LSP demand, and to regulate the engine speed in dependence on the determined ability of the pump supply to meet the load sensing pressure LSP demand of the at least one consumer.

Advantageously, in a mobile machine according to the invention the one or more controllers can be programed to maintain the engine speed as constant as possible but to allow an increase in engine speed to meet a hydraulic demand when operating in the at least one mode. This enables the hydraulic supply system to operate dynamically whilst still keeping fuel consumption and exhaust emissions down.

A determination that the pump supply is not able to meet the load sensing pressure LSP demand may be made when the pump supply pressure PSP is lower than the sensed load sensing pressure LSP demand. Such a determination might be made if the pump supply pressure PSP remains below the sensed load sensing pressure LSP demand for a given amount of time. This is indicative that the load sensing system is unable raise the pump supply pressure PSP sufficiently to meet the hydraulic demand at the speed the engine is being operated at. The one or more controllers may also, or alternatively, receive data relating to operating parameters of the pump supply control which can be used to determine if the pump supply pressure PSP can be increased at the present engine speed.

In an embodiment, the one or more controllers configured, when operating in the at least one mode of operation, to determine whether the pump supply is able to meet the load sensing pressure LSP demand at the present engine speed, and, in the event a determination is made that the pump supply cannot meet the load sensing pressure LSP demand at the present engine speed, to compute and generate one or more control signals to increase the engine speed to a value at which the pump supply is able meet the load sensing pressure LSP demand.

In an embodiment the mobile machine has a continuously variable transmission, the one or more controllers being selectively operable in a ground speed control mode to generate control signals regulating operation of the CVT to maintain the ground speed of the mobile machine substantially constant whilst regulating the engine speed so as to enable the pump supply to meet a load sensing pressure LSP demand of the at least one consumer.

Advantageously, the engine speed is kept as low and constant as possible but can be increased to meet a load sensing pressure LSP demand whilst adjusting the CVT to keep the ground speed constant. This enables the hydraulic supply system to operate dynamically whilst still keeping fuel consumption and exhaust emissions down.

The one or more controllers may be configured, when operating in the ground speed control mode to maintain the engine speed as low as possible consistent with maintaining a required ground speed and meeting a load sensing pressure LSP demand of the at least one consumer. The one or more controllers may be configured, when operating in the ground speed control mode, to determine whether the pump supply is able to meet the load sensing pressure LSP demand at a present engine speed, and, in the event a determination is made that the pump supply has excess capacity to meet the load sensing pressure LSP demand at the present engine speed, to compute and generate control one or more signals to reduce the engine speed to a minimum value at which the load sensing pressure LSP demand and the required ground speed can both be met.

Advantageously, the one or more controllers are programmed to lower the engine speed where this is possible whilst meeting the hydraulic demand and maintaining the required ground speed. Thus, after initially raising the engine speed following a temporary increase in hydraulic demand, the one or more controllers can be programmed to reduce the engine speed once the hydraulic demand has reduced. This helps to maintain fuel efficiency and reduce emissions.

In an embodiment, the one or more controllers are configured to receive, from a pressure sensor of the hydraulic supply system associated with the pump supply, data representative of the pump supply pressure PSP in the form of a second pressure signal indicative of a sensed pump supply pressure PSP.

The one or more controllers may be configured to compute and generate an electronic pump supply control signal EPSCS, the control system comprising a transducer for converting the electronic pump supply control signal EPSCS to a hydraulic pump supply control signal HPSCS at a set point pressure value P _se t for forwarding to a hydraulic pump supply adjustment system. In an embodiment, the one or more controllers may be configured to determine the pump supply pressure PSP from the electronic pump supply control signal EPSCS. The one or more controllers may be configured to determine the pump supply pressure PSP from the electronic pump supply control signal EPSCS, say by reference to a characteristic map or look up table accessible to the one or more controllers from which a correlation between the electronic pump supply control signal EPSCS and pump supply pressure PSP (or a related pressure such as P _se t) can be derived.

The hydraulic system of the mobile machine and/or implement may include more than one consumer and more than one pressure sensor, each pressure sensor for sensing a load sensing pressure LSP demand associated with one or more of the consumers, in which case, the one or more controllers may be configured to receive pressure signals indicative of sensed load sensing pressure LSP demand from each of the pressure sensors and the control system configured to adjust the pump supply pressure in dependence on the pressure signal indicative of the highest load sensing pressure LSP demand received by the one or more controllers at any given time when operating in a load sensing mode for controlling the pump supply.

In an embodiment, the mobile machine has an implement attached to it, the implement having at least one consumer supplied with pressurised fluid by the pump supply. In an embodiment, the one or more controllers may be configured to receive, from a pressure sensor of a load sensing LS system associated with the at least one consumer on the implement, a pressure signal indicative of a sensed load sensing pressure LSP demand associated with the at least one consumer on the implement. In an embodiment, the one or more controllers comprise at least a first controller on the mobile machine and a second controller on the implement; the first and second controllers being in communication with one another. The mobile machine may be an agricultural mobile machine, such as a tractor or harvester, and the implement, where present, may be an agricultural implement.

In an embodiment, the control system comprises a user input actuatable by an operator to initiate the at least one operating mode which may be a constant ground speed mode.

In an embodiment, the pump is a variable displacement pump having a pump controller including a flow control valve for regulating movement of an actuator to adjust the pump displacement. In this embodiment, the one or more controllers may be configured to compute and generate an electronic pump supply control signal EPSCS, the control system comprising a transducer for converting the electronic pump supply control signal to a hydraulic pump supply control signal HPSCS for forwarding to an LS pressure port of the flow control valve. The transducer may be a solenoid controlled pressure limiting valve.

In an alternative embodiment, the pump is a fixed displacement pump, the pump supply comprising a pressure compensator valve for selectively connecting a pump supply line to a reservoir (tank) to vary the pump supply pressure PSP. In this embodiment, the one or more controllers may be configured to compute and generate an electronic pump supply control signal EPSCS, the control system comprising a transducer for converting the electronic pump supply control signal EPSCS to a hydraulic pump supply control signal HPSCS for forwarding to an LS pressure port of the pressure compensator valve. The transducer may be a solenoid controlled pressure limiting valve. The one or more controllers may collectively comprise an input (e.g. an electronic input) for receiving one or more input signals (e.g. the pressure signal and signals from engine speed, ground speed and CVT sensors) indicative of a sensed load sensing pressure LSP, pump supply pressure PSP, engine speed, ground speed, and operational parameters of the CVT. The one or more controllers may collectively comprise one or more processors (e.g. electronic processors) operable to execute computer readable instructions for controlling operation of the control system, for example to determine whether the pump supply is able to meet the load sensing pressure LSP demand at the present engine speed. The one or more processors may be operable to generate one or more control signals for controlling the pump supply pressure PSP, engine speed, and operation of the CVT. The one or more controllers may collectively comprise an output (e.g. an electronic output) for outputting the one or more control signals such as a pump supply control signal EPSCS, an engine speed control signal, and one or more CVT control signals.

In accordance with a further aspect of the invention, there is provided a method of operating a mobile machine having an engine and a hydraulic supply system, wherein the hydraulic supply system comprises a pump supply including a pump driven by the engine for supplying a pressurised fluid to at least one consumer on the mobile machine and/or an implement attached to the mobile machine, the mobile machine having a control system comprising one or more controllers configured to: receive, from a pressure sensor of a load sensing LS system associated with the at least one consumer, a first pressure signal indicative of a sensed load sensing pressure LSP demand associated with the at least one consumer; generate a pump supply control signal for adjusting the pump supply pressure in dependence the load sensing pressure LSP demand; receive or obtain data representative of the pump supply pressure PSP; and receive or obtain data representative of engine speed; wherein, the method comprises operating the mobile machine in at least one mode of operation in which the speed of the engine is automatically regulated in dependence on the ability of the pump supply to meet a load sensing pressure LSP demand of the at least one consumer. Advantageously, the method enables the engine speed to be kept as constant as possible but allows an increase in engine speed to meet a hydraulic demand. This enables the hydraulic supply system to operate dynamically whilst still keeping fuel consumption and exhaust emissions down. In an embodiment, the method comprising determining from the first pressure signal, the data relating to pump supply pressure, and the data relating to engine speed a required engine speed to meet the hydraulic demand LSP of the at least one consumer.

In an embodiment, the method comprising, determining whether the pump supply is able to meet the load sensing pressure LSP demand at the present engine speed, and, in the event a determination is made that the pump supply cannot meet the load sensing pressure LSP demand at the present engine speed, increasing the engine speed to enable the pump supply to meet the load sensing pressure LSP demand.

A determination that the pump supply is not able to meet the load sensing pressure LSP demand may be made when the pump supply pressure PSP is lower than the sensed load sensing pressure LSP. Such a determination might be made if the pump supply pressure remains below the sensed load sensing pressure LSP demand for a given amount of time. This is indicative that the load sensing system is unable raise the pump supply pressure sufficiently to meet the hydraulic demand at the speed the engine is being operated at.

Data relating to operating parameters of the pump supply control may also be used to determine if the pump supply pressure can be increased at the present engine speed.

In an embodiment for use where the mobile machine has a continuously variable transmission, the method comprising operating the mobile machine in a ground speed control mode in which operation of the CVT is regulated to maintain the ground speed of the mobile machine substantially constant whilst adjusting the speed of the engine in order to enable the pump supply to meet a load sensing pressure LSP demand of the at least one consumer.

When operating the mobile machine in the ground speed control mode, the method may comprise maintaining the engine speed as low as possible consistent with maintaining a required ground speed and meeting the load sensing pressure LSP demand of the at least one consumer. In an embodiment, the method comprising, when operating the mobile machine in the ground speed control mode, determining whether the pump supply is able to meet the load sensing pressure LSP demand at the present engine speed, and, in the event a determination is made that the pump supply has excess capacity to meet the load sensing pressure LSP demand at the present engine speed, reducing the engine speed to a minimum at which the load sensing pressure LSP demand and the required ground speed can both be met.

Advantageously, the engine speed is lowered where this is possible whilst meeting the hydraulic demand and the required ground speed. Thus after initially raising the engine speed following a temporary increase in hydraulic demand, the engine speed can be reduced, say back to its default value, once the hydraulic demand as reduced. This helps to maintain fuel efficiency and reduce emission.

In an embodiment, the method comprises receiving, from a pressure sensor of the hydraulic supply system associated with the pump supply, data representative of the pump supply pressure PSP in the form of a second pressure signal indicative of a sensed pump supply pressure PSP. Alternatively, the method may comprise determining the pump supply pressure PSP from the pump supply control signal, say by reference to a characteristic map or look up table from which a correlation between the pump supply control signal and pump supply pressure (or a related pressure such as P _se t) can be derived.

A further aspect of the invention provides a computer readable storage medium comprising the computer software of any of the preceding aspects of the invention. Optionally, the storage medium comprises a non-transitory computer readable storage medium.

Within the scope of this application it should be understood that the various aspects, embodiments, examples and alternatives set out herein, and individual features thereof may be taken independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that such features are applicable to all aspects and embodiments unless otherwise stated or where such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the further accompanying drawings, in which:

Figure 4 is a schematic side view of an agricultural machine and implement combination embodying aspects of the invention;

Figure 5 is a schematic representation of an embodiment of a hydraulic system in accordance with the invention which is embodied in the combination of Figure 4.

Figure 4 illustrates a combination comprising a mobile agricultural machine 60 and an implement 62 attached to the rear of the machine, which combination embodies aspects of the present invention. The implement 62 can be any suitable agricultural implement attachable to an agricultural machine having hydraulic consumers supplied with pressurised hydraulic fluid from a hydraulic supply system on the machine 60. The implement 62 will be referred to as a rear implement 62 and a further or alternative implement having hydraulic consumers fed by the supply on the machine, not shown in Figure 4 but see Figure 5, may be attached to the front of the tractor and will be referred to as a front implement 63.

The agricultural machine in the embodiment shown in the drawings and described below is specifically an agricultural tractor 60 and the rear implement 62 is a baler. Other types of agricultural implement commonly used with tractors, and which fall within the scope of the invention, include without limitation: a loading wagon, a towed sprayer, and a towed potato harvester. Furthermore, the invention is not limited to application on tractors or other mobile agricultural machines but can be adapted for use with other mobile machines having a hydraulic supply system whether connected with an implement or not.

The tractor 60 has an engine 60A and a continuously variable transmission 60B for transmitting drive from the engine to at least the rear wheels 60C of the tractor. Rather than wheels, the tractor may have other types of ground engaging members such as endless tracks through which drive is transmitted from the engine to move the tractor across the ground.

Figure 5 is a simplified representation of a hydraulic supply system 64 suitable for use on the tractor 60 and implement 62, 63 combination. The hydraulic supply system 64 incorporates an E- LS system and is configured in accordance with one or more aspects of the invention. Hydraulic Network

The hydraulic supply system 64 has pump supply 66 including main pump MP which is of variable displacement type and a pump output controller 68 for adjusting the displacement of the pump. In an embodiment, the pump output controller 68 is configured in a manner similar to that illustrated in Figure 3. However, in other embodiments, alternative pump output controller arrangements can be adopted including any of those currently used with E-LS systems which enable an electronic controller to regulate and adjust the flow and/or pressure output of the pump supply 66.

The pump MP draws fluid from a tank 69 and supplies pressurised hydraulic fluid at a pump supply pressure PSP to consumers on the tractor and the implement via a pump supply line P. The tank 69 provides a reservoir for the hydraulic supply system in which the fluid is held generally at ambient pressure. The tank 69 is illustrated schematically in Figure 5. In practice in any given hydraulic supply system 64 there may a single tank 69 or multiple tanks 69.

The consumers on the tractor 60 include a hydraulic steering system SS, a central valve manifold CVM, and a rear valve manifold RVM.

The steering system SS may include a hydraulic cylinder and control valve designated tractor consumer TC1 for moving the steered wheels. The control valve is connected to the pump supply line via a pressure port P and to the tank via a tank port T.

The central valve manifold CVM is installed generally in or towards the middle of the tractor and includes a number of functional valves for controlling a corresponding number of hydraulic consumers located usually in or towards the middle and front area of the tractor. In the example illustrated, the central valve manifold CVM includes three functional valves CMV1 , CMV2, CMV3 assembled together and connected to the pump supply line via a common pressure port P and to a return line to the tank at a common return port T. Each valve is assigned to a specific consumer and the valves CMV1 , CMV2, CMV3 may have different configurations (e.g., ON/OFF, proportional valves, 3/2 valves, 4/2 valves) according the functional needs of their respective consumer. The valves CMV1 , CMV2, CMV3 are solenoid valves and each has a valve controller VC for controlling the solenoid. The number and configuration of the valves in the CVM may be varied to meet the requirements of the tractor manufacturer and/or the end customer. There may, for example, be more or fewer than three functional valves in the CVM. The CVM has a common load sensing port LS1 and each of the valves CMV1 , CMV2, CMV3 have LS ducts connected to the common LS port LS1 by means of shuttle valves so that the highest load sensing pressure LSP generated by the various valves CMV1 , CMV2, CMV3 at any given point in time is forwarded to the LS port.

The CVM can be used to supply hydraulic fluid to various consumers such as, without limitation, a front linkage actuator FLC and an axle suspension system indicated as tractor consumer TC2. Valves in the CVM can also be used to supply consumers on a front implement 63 attached to the tractor indicated as FIC1. Each consumer on the front implement 63 being hydraulically connected to a respective valve CMV2 via front valve couplings FVC.

The RVM is installed in the rear of the tractor and is provided to supply consumers which are mainly in the rear area of the tractor and/or on a rear implement 62. The RVM is similar to the CVM in terms of design and variability and contains a number of functional valves indicated as RMV1 to RMV5 assembled together and connected to the pump supply line via a common pressure port P and to a return line to the tank at a common return port T. At least some of the valves in the RVM may be used to supply consumers on a rear implement 62 and/or on the tractor 60. In the exemplary embodiment illustrated, three of the valves, RMV3, RMV4, and RVM5, are connected with respective consumers RIC1 , RIC2, RIC3 on the rear implement 62 via rear valve couplings RVC. The RVC may be directly flanged to the RVM as described in EP2886926. As it is common to attach complex implements to the rear of a tractor, there may be more than three valves in the RVM for connection to consumers on a rear implement 62.There may, for example, be as many as six, seven, eight or more valves in the RVM assigned for connection to consumers on rear implements. At least some of the valves in the RVM may be assigned to consumers located at or towards the rear of the tractor such as actuators on a rear linkage system. In the exemplary embodiment shown, valve RMV1 is assigned to a pair of lower link hydraulic cylinders LLC being supplied in parallel and valve RMV2 is assigned to a hydraulically driven top link actuator cylinder TLC. In an alternative embodiment, the top link actuator may be a mechanical actuator and the valve RMV2 used for other purposes.

Each valve RMV1 to RMV5 in the RVM is a solenoid actuated valve and is provided with a valve controller VC which moves the solenoid and provides a pilot pressure. Each valve is configured according to the requirements of its respective consumer (e.g., ON/OFF, proportional valves, 3/2 valves, 4/2 valves). The RVM has a common load sensing port LS2 and LS ducts of the valves RMV1 , RMV2, RMV3, RMV4, RMV5 are all connected to the common LS port LS2 by means of shuttle valves so that the highest load sensing pressure LSP generated by the various valves at any given point in time is forwarded to the common LS port LS2.

As with the CMV, the RVM can be configured to have any required number and configuration of valves depending on the number and requirements of the hydraulic consumers on the tractor and any implements that are expected to be attached to the tractor. It should be understood, therefore, that the configuration of the CVM and RVM shown in Figure 5 is for illustrative purposes only and can be varied.

The hydraulic supply system 64 includes a power beyond interface 70 to provide an “uncontrolled” supply of pressurised fluid to a rear implement 62 which requires more hydraulic functions than can be controlled using the available valves on the tractor. Such a complex implement 62 may be a baler, for example. The power beyond interface 70 includes quick release couplings 70a, 70b to connect the pump supply line P and a return tank line T on the tractor to a pump pressure supply line PI and a return line Tl respectively on the implement 62. The power beyond interface provides a pressurised fluid supply to an implement which is at the pump supply pressure PSP but which is otherwise uncontrolled on the tractor.

In a typical arrangement, the rear implement 62 has an implement valve manifold IVM similar to the CVM and RVM as described above. The IVM has a number of functional control valves IMV1 to IMV3 which are each connected to the implement pump supply pressure line PI through a common pressure port P and to the implement return line Tl via a common return port T. The IVM also has a common LS pressure signal port LS3 to which LS ducts of each of the valves IMV1 to IMV3 are connected via a series of shuttle valves or the like arranged so that the highest consumer load sensing pressure LSP from the various valves in the IVM at any given point in time is reported to the common LS port LS3. Each valve IMV1 to IMV3 is connected to a respective consumer (e.g. a hydraulic cylinder or hydraulic motor) which are schematically designated RIC4 to RIC6. Each valve is configured according to the requirements of its respective consumer (e.g., ON/OFF, proportional valves, 3/2 valves, 4/2 valves). The valves are all solenoid controlled valves and each is provided with an electronic valve controller VC which moves the solenoid and provides a pilot pressure (supplied via pump connection to support the valve slider movement). The number of valves in the IVM is selected depending on the number of consumers on the implement that are to be supplied via the power beyond interface and can be varied as required. Furthermore, there may be more than one valve manifold on the implement and/or one or more separate valves not incorporated into a manifold can be connected to the power beyond interface via suitable hydraulic lines.

In the embodiment shown, the tractor has a further hydraulic consumer in the form of a hydraulic motor 72 for driving a cooling fan CF. The hydraulic motor 72 is controlled by a cooling fan valve CFV which regulates the cooling fan motor to vary the speed of the fan. The CFV is a solenoid controlled valve having an electronic valve controller VC which is operably connected with an electronic controller 102 on the tractor. The controller is configured to actuate the CFV in order to adapt the motor speed to the cooling demand.

As illustrated in Figure 3, the hydraulic supply system may also be provided with a main pressure limiting valve MLV which opens to vent the pump supply P to the tank 69 if the pressure exceeds a predetermined pressure. The MLV is set to open at a pressure above the maximum permitted operating pressure of the system. This provides an additional level of safety in case the limitation of the pump supply pressure PSP through the pump controller should fail. For use with current tractor hydraulic supply systems, the MLV may be set to open a pressure value of around 250 bar, for example. However, the pressure at which the MLV opens can be selected as appropriate for any given system.

The hydraulic supply system 64 illustrated in Figure 5 is exemplary only and the invention can be modified for use with hydraulic supply systems which have alternative layouts, including an alternative number and type of consumers and control valves. For example, the tractor 60 may have more than one pump and may have a fixed displacement pump in addition to the main pump MP for supplying other consumers such as a lubrication system for the driveline, a transmission (of hydrostatic-mechanical split type) or a hydraulic brake system, for example. These are not shown in Figure 5 as they are not included in the E-LS control arrangements which are the subject of the present invention.

Electronic Network

Figure 5 also illustrates an electronic control system network 100 for the hydraulic supply system 64. As shown, the control network 100 includes a controller 102 on the tractor having an electronic processor 104. The processor 104 is operable to access a memory 106, which may be part of the controller 102, and execute instructions stored therein to perform the steps and functionality according to aspects of the present invention. The memory 106 may include any one or a combination of volatile memory elements (e.g., random-access memory RAM, such as DRAM, and SRAM, etc.) and non-volatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). The memory 106 may store a native operating system, one or more native applications, emulation systems, or emulated applications for any of a variety of operating systems and/or emulated hardware platforms, emulated operating systems, etc. The memory 106 may furthermore store parameters or settings needed to operate the control systems and/or perform the methods as described below.

It should be appreciated by one having ordinary skill in the art that in some embodiments, additional or fewer software modules (e.g., combined functionality) may be stored in the memory 106 or additional memory. In some embodiments, a separate storage device may be coupled to the data bus, such as a persistent memory (e.g., optical, magnetic, and/or semiconductor memory and associated drives). In a further embodiment, the memory 106 may be connectable with an off-board network architecture (via mobile communication or WLAN) to provide parameters or settings.

The processor 104 may be embodied as a custom-made or commercially available processor, a central processing unit (CPU) or an auxiliary processor among several processors, a semiconductor based microprocessor (in the form of a microchip), a macro processor, one or more application specific integrated circuits (ASICs), a plurality of suitably configured digital logic gates, and/or other well-known electrical configurations comprising discrete elements both individually and in various combinations to coordinate the overall operation of the controller 102.

Electronic communications among the various components of the control network 100, as indicated by the dashed lines, may be achieved over a controller area network (CAN) bus or via a communications medium using other standard or proprietary communication protocols (e.g., RS 232, Ethernet, etc.). Communication may be achieved over a wired medium, wireless medium, or a combination of wired and wireless media.

The controller 102 is in communication with each of the electronic solenoid valve controllers VC of the various valves on the tractor, with the pump output controller 68, and with various user interfaces such as a steering wheel SW, valve rockers represented as UI1 and UI2, a linkage control represented as UI3, and a touch screen TS. The touch screen is typically located within a cab of the tractor to provide information to the driver and receive input (e.g. to select, adjust and/or save settings). The touch screen TS may alternatively be replaced or enhanced by a keyboard to receive input. Indeed, any input or presentation of information whether by manual, speech or gestures may be included herein. Each user interface III may be permanently assigned to one consumer of the tractor or the implement. Alternatively, one or more of the user interfaces may be variably assignable to any one of two or more consumers by the operator. Such an assignment might be effected via the touch screen, for example.

The controller 102 may also receive further data, such as from a GPS receiver to determine the current position of the tractor, and/or may be operative to control further devices.

The rear implement 62 may also be connected to the tractor controller 102, say via the standardized agricultural ISOBUS for example, to exchange data and control between the implement and tractor as described later on. For this purpose, the implement 62 may be provided with an implement controller 110 which communicates with the tractor controller 102. Where present, an implement controller 110 may have an electronic processor 114 which is operable to access a memory 112 of the implement controller 110 and execute instructions stored therein to perform the steps and functionality according to one or more aspects of the present invention.

The memory 112 may include any one or a combination of volatile memory elements (e.g., random-access memory RAM, such as DRAM, and SRAM, etc.) and non-volatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). The memory 112 may store a native operating system, one or more native applications, emulation systems, or emulated applications for any of a variety of operating systems and/or emulated hardware platforms, emulated operating systems, etc. The memory 112 may furthermore store parameters or settings needed to operate the control systems as described below.

It should be appreciated by one having ordinary skill in the art that in some embodiments, additional or fewer software modules (e.g., combined functionality) may be stored in the memory 112 or additional memory. In some embodiments, a separate storage device may be coupled to the data bus, such as a persistent memory (e.g., optical, magnetic, and/or semiconductor memory and associated drives). In a further embodiment, the memory 112 may be connectable with an off-board network architecture (via mobile communication or WLAN) to provide parameters or settings. The processor 114 may be embodied as a custom-made or commercially available processor, a central processing unit (CPU) or an auxiliary processor among several processors, a semiconductor based microprocessor (in the form of a microchip), a macro processor, one or more application specific integrated circuits (ASICs), a plurality of suitably configured digital logic gates, and/or other well-known electrical configurations comprising discrete elements both individually and in various combinations to coordinate the overall operation of the controller 102.

Load Sensing

Returning to the hydraulic supply system, at any given time, a highest of the load sensing pressure demands LSP from the consumers on the tractor 60 and any attached implements 62 is used to regulate the pump output controller 68 by means of a load sensing LS system. The load sensing system includes an electronic (electrohydraulic) load sensing (E-LS) system including a number of pressure sensors for sensing load sensing pressure demand signals LSP from consumers which are part of the E-LS system. Each of the pressure sensors is in communication with a controller 102 or 110 and forwards to the controller an electronic load sensing pressure signal ELSPS (a pressure signal) representative of the sensed consumer load sensing pressure LSP.

The electronic load sensing pressure signal ELSPS may be an analogue signal in which a characteristic of the signal is modulated in dependence on the pressure of the hydraulic load sensing pressure signal LSP. In an embodiment, the current of the ELSPS is modulated in dependence on the pressure of the hydraulic load sensing pressure signal LSP but in another embodiment it is the voltage. In an embodiment where the ELSPS is an analogue signal, the controller 102, 110 converts the ELSPS into a pressure value by reference to data stored in the controller (or to which the controller has access) which provides a correlation between the modulated characteristic and pressure for the sensed load sensing pressure LSP. This data may be provided in the form of a characteristic map or a look up table assigned to the sensor. In another embodiment, the pressure sensor has a CPU and communicates with the controller through a CAN interface. In this case, conversion of the analogue signal to a pressure value is made at the sensor and the pressure value forwarded to the controller 102, 110.

In the embodiment illustrated, a first pressure sensor 122 is connected with the LS port LS1 on the CVM where it is subject to the highest consumer load sensing pressure signal LSP of the valves in the CVM. A second pressure sensor 124 is connected with an LS port LS2 on the RVM where it is subject to the highest consumer load sensing pressure signal LSP of the valves in the RVM. A third pressure sensor 125 is connected with an LS port LS4 on the cooling fan valve CFV to sense the load sensing pressure of the cooling fan motor.

A fourth pressure sensor 126 on the tractor is connected with a LS coupling 70c of the power beyond interface. On the implement, the LS power beyond coupling may be hydraulically connected with the common LS port LS3 of the IVM so that the highest load sensing pressure demand LSP from the various valves in the IVM is forwarded to the fourth pressure sensor 126 when the implement is coupled to the tractor. However, for implements which have a controller 112, an implement pressure sensor 128 can be connected with the common LS port LS3 of the IVM. In this case, the implement pressure sensor 128 communicates with the implement controller 112 and forwards to the implement controller 112 an electronic load sensing pressure signal ELSPS representative of the sensed consumer load sensing pressure LSP at the IVM common LS port LS3. The implement controller 112 forwards data relating to the sensed load demand pressure LSP to the tractor controller 102. The implement controller 110 may process the load sensing pressure demand data and forward to the tractor controller 102 data which is modified or a signal which is a function of the sensed load sensing pressure signal LSP.

The load sensing pressure demand LSP of the steering system is also sensed electronically to form part of the E-LS system. Figure 5 illustrates two alternative arrangements. In one embodiment, an LS port LS5 of the steering system actuator/control valve TC1 is hydraulically connected by a LS signal line to an LS input port LS6 on the CVM. The LS input port LS6 is connected together with the LS ducts of each of the valves in the CVM to the common LS port LS1 by a suitable cascade of shuttle valves so that the highest load sensing pressure demand LSP from the steering system and the various valves CMV1 To CMV3 is reported to the common LS port LS1 to be sensed by the first pressure sensor 122. In an alternative embodiment, a dedicated pressure sensor 130 is provided to sense the load demand pressure LSP of the steering system. The steering system pressure sensor 130 may be hydraulically connected to the LS port of the steering system and electronically connected to the tractor controller 102 to forward to the controller an electronic load sensing pressure signal ELSPS representative of a sensed consumer load sensing pressure LSP of the steering system.

The tractor controller 102 is configured to select an electronic load sensing pressure signal ELSPS representative of the highest consumer load sensing pressure LSP forwarded to it, either directly from a pressure sensor or from the implement controller 112. The controller processes the selected signal and forwards an electronic pump supply control signal EPSCS to the output controller 68 of the main pump MP to vary the output of the pump MP in dependence on the highest sensed load sensing pressure LSP. Where the pump output controller 68 comprises a solenoid controlled pressure limiting valve 54 as illustrated in Figure 3, the tractor controller 102 forwards an electronic pump supply control signal EPSCS to actuate the solenoid of the pressure limiting valve 54 in order to vary the output of the main pump. Typically, the current of the electronic pump supply control signal EPSCS will determine the extent of movement of the solenoid and so will determine the pressure P _se t of the resulting hydraulic pump supply control signal HPSCS applied to the LS port 34 of the flow control valve 22’ and hence the supply pressure PSP of the main pump. The resulting pump supply pressure PSP can be calculated by equation 1 :

PSP = AP _s t + Pset Equation 1

Where

APst is the static or stand-by pressure differential defined by the spring 26 in the flow control valve 22’, and

Pset is the pressure of the hydraulic pump supply control signal HPSCS provided at the LS pressure port of the flow control valve.

Where the implement has an electronical controller 110, communication between the tractor controller 102 and electronic components of the LS pressure control system on the implement, such as valve controllers VC and pressure sensors 128 of the IVM, is typically made via the implement controller 110, with data and instructions being transmitted between the implement controller 110 and the tractor controller 102 via a standardized ISOBUS connection.

In an embodiment, the controller 102 converts a target pressure value for P _se t to a current value for forwarding to the solenoid controlled pressure limiting valve 54 (or other transducer) as an analogue electronic pump supply control signal EPSCS. In another embodiment, the pump output controller 68 has a CPU and communicates with the controller 102 through a CAN interface. In this case, the controller 102 forwards the target set point pressure value P _se t to pump controller 66 in an electronic pump supply control signal EPSCS through a CAN interface and the pump CPU converts the pressure value to an analogue signal for controlling the pressure limiting valve 54 or other transducer. Conversion of the target pressure value for P _se t to a current value may be made by reference to data which provides a correlation between a current value and the resulting pressure P _se t generated by the solenoid controlled pressure limiting valve 54 or other transducer. This data may be stored in, or is otherwise accessible to, the controller 102 or pump controller CPU and may be provided in a characteristic map or a look up table assigned to the valve 54 and/or the pump MP for example. In other embodiments it may be a voltage of the analogue which is modulated to control the output of the solenoid controlled pressure limiting valve 54.

The pressure sensors, the one or more controllers 102, 110, and the pump output controller 68 can all be considered as part of a control system for the hydraulic supply system.

Pressure Differential Set in Dependence on the Rate of Increase of Load Pressure Demand LSP

In accordance with an embodiment, the tractor controller 102 is programmed and configured to control adjustment of the output of the main pump MP in dependence not only on the value of the sensed load sensing pressure LSP but also in dependence on the rate of change of an increasing load sensing pressure demand LSP (referred to as the LSP pressure gradient).

In accordance with a suitable algorithm, the tractor controller 102 determines the LSP pressure gradient of a highest of the load sensing pressure signals LSP forwarded to it by the various pressure sensors in the E-LS network. Where the LSP pressure gradient is below a threshold value Tr, the controller 102 regulates the main pump output so that the supply pressure PSP is maintained above the load sensing pressure LSP by a first differential. In an embodiment, the first differential is the stand-by or static pressure differential AP _s t defined by the spring 26 in the flow control valve 22’ and the tractor controller 102 forwards an electronic pump supply control signal EPSCS to the pressure limiting valve 54 calibrated to generate a hydraulic pump supply control signal HPSCS having a pressure P _se t that is the same as (or equivalent to) the load demand pressure LSP. The resulting pump supply pressure PSP under these circumstance can be derived from equation 1 where P _se t = LSP so that equation 1 can be re-written as:

PSP = APst + LSP Equation 2

Accordingly, when the rate of change of an increasing consumer load sensing pressure LSP is below the threshold value Tr, the E-LS system operates broadly in the same manner as a conventional E-LS system. However, when the rate of increase of a consumer load sensing pressure LSP is at or above the threshold value Tr, the controller 102 is programmed and configured to regulate the main pump output so that the supply pressure PSP is maintained above the load sensing pressure LSP by a second differential larger than the first pressure differential AP _s t. The second pressure differential can be considered to be made up of the static or stand-by pressure differential AP _s t regulated by the spring 26 in the flow control valve 22’ plus an additional dynamic pressure differential APd _yn which is applied by the controller 102 through the hydraulic pump supply control signal HPSCS generated by the pressure limiting valve 54. In this case, the tractor controller 102 forwards to the pressure limiting valve 54 an electronic pump supply control signal EPSCS calibrated to generate a hydraulic pump supply control signal HPSCS having a pressure P _se t that is higher than the load demand pressure LSP by the amount of the dynamic pressure differential APd _yn , such that P _se t is equal to the load demand pressure LSP plus the dynamic pressure differential APd _yn (Pset = LSP + APd _yn ). Equation 1 in this case can be re-written as:

PSP = P _s t + LSP + APd _yn Equation 3

By providing an increased pressure differential when the rate of increase of the load sensing pressure LSP is at or above a certain threshold Tr, the dynamic response of the system is increased. The dynamic pressure differential APd _yn may be applied for a set time period once it is triggered as discussed below

In a first example, AP _s t is set at 20 bar, the threshold value Tr of the LSP pressure gradient is set at 5 bar/50 ms (a pressure increase of 5 bar in 50 ms), and the dynamic pressure differential APd _yn is set at 20 bar.

The following tables compare the dynamic performance of a conventional E-LS system and an E- LS system in accordance with the embodiment described above when a consumer valve is opened to produce a consumer load sensing pressure LSP rapidly increasing to 140 bar. Table 1 below illustrates a typical dynamic response of a conventional E-LS control system in these circumstances.

Table 1 - pressure differential increased by LSP in accordance with prior art

As illustrated in table 1 , at each cycle the pressure P _se t of hydraulic pump supply control signal HPSCS forwarded to the pump controller is equal to the consumer load sensing pressure signal LSP at that time. In the arrangement illustrated, it takes seven cycles for the system to increase the pump supply pressure PSP to 160 bar as required to maintain the pump supply pressure higher than the final consumer load sensing pressure LSP of 140 bar by the static pressure differential AP st Table 2 below shows the effect of increasing the pressure P _se t of the hydraulic pump supply control HPSCS to include a dynamic pressure differential APd _yn of 20 bar when the rate of increase of LSP reaches the threshold value Tr of 5 bar/50 ms.

Table 2 - Pressure differential increased depending on rate of change of LSP in accordance with an aspect of the invention

It can be seen from table 2 that increasing P _se t to include an additional dynamic pressure differential APd _yn when the rate of increase of the load sensing pressure LSP reaches the threshold Tr, fewer cycles (four in this case) are required to increase the pump supply pressure PSP to 160 bar using the method according to the invention. This considerably increases the speed of response of the system in adapting the pump supply pressure PSP to meet a rapidly rising consumer load.

In the above example, once application of a dynamic pressure differential APd _yn has been triggered by the rate of increase of the load sensing pressure reaching the threshold Tr, the dynamic pressure differential APd _yn is applied continuously until the consumer demand is met, that is to say when the pump supply pressure PSP equals the sum of the load sensing pressure LSP, the static pressure differential AP _s t , and the dynamic pressure differential APd _yn . However, in an alternative embodiment, the dynamic pressure differential APd _yn is only applied for a limited time period after its application is triggered by the rate of increase of the load sensing pressure LSP reaching the threshold Tr and is then ramped down. The time period over which the dynamic pressure differential APd _yn is applied will be referred to as an application period (AP). Applying a dynamic pressure differential APd _yn for a time limited application period AP has been found to provide a dynamic response to a rapidly increasing load sensing pressure LSP but in a more efficient way than applying a dynamic pressure differential APd _yn continuously. The relatively brief application of a dynamic pressure differential APd _yn gives the pump output supply an initial boost to meet the hydraulic load demand but without over supplying the hydraulic system. The application period AP can be selected to meet system requirements but the applicant has found an application period AP in the range of 50 to 300 ms, or in the range of 80 to 200 ms, or in the range of 90 to 150 ms, or in the region of 100 ms to be effective. The system may be configured to apply a dynamic pressure differential APd _yn for different application periods AP depending on operational requirements, say for different consumers.

In embodiments where the dynamic pressure differential APd _yn is applied for a time limited application period AP, the system may also be configured to set a delay period DP following one application of a dynamic pressure differential APd _yn before a subsequent application of a dynamic pressure differential APd _yn is permitted. The application of a delay period DP between applications of dynamic pressure differential APd _yn helps to maintain system stability, reducing the risk that oscillations in a load sensing pressure LSP signal are unduly amplified by the addition of a dynamic pressure differential APd _yn . The delay period DP is timed from the point at which a dynamic pressure differential APd _yn is first applied. In other embodiments, the delay period DP is timed from the point at which application of a dynamic pressure differential APd _yn is stopped. Indeed, the delay period DP can be timed from any suitable point in relation to an application of a dynamic pressure differential APd _yn . Once the delay period DP has expired, a dynamic pressure differential APd _yn can be applied again for the set application period AP if the operating conditions meet the criteria for application of a dynamic pressure differential APd _yn . For example, if at the end of the delay period DP following a one application of a dynamic pressure differential APd _yn the rate of increase of the load sensing pressure LSP is at or above the threshold Tr, the controller 102 will again apply a dynamic pressure differential APd _yn for a further application period AP and a further delay period DP begins. The delay period DP can be selected to meet system requirements but the applicant has found that where the delay period DP is timed from the start of a dynamic pressure differential APd _yn being applied, a delay period DP in the range of 600 to 1400 ms, or in the range of 800 to 1200 ms, or in the region of 1000 ms to be effective. The delay period DP is longer than the application period AP and once a dynamic pressure differential APd _yn has been ramped down, no dynamic pressure differential APd _yn is applied for at least the remainder of the delay period DP. Thus the delay period DP defines a minimum interval between applications of a dynamic pressure differential APd _yn .

In other embodiments, once application of a dynamic pressure differential APd _yn is triggered by the rate of increase of the load sensing pressure LSP reaching the threshold Tr, the dynamic pressure differential APd _yn is applied continuously until the rate of rate of increase of the load sensing pressure LSP falls below a threshold value Tr*. This threshold value Tr* may be the same as the threshold value Tr which triggers the application of a dynamic pressure differential APd _yn or it may be a different value. Again the system may apply a delay period DP following one application of a dynamic pressure differential APd _yn before another application is permitted.

A delay period DP between applications of dynamic pressure differential APd _yn can be adopted in any of the embodiments disclosed herein.

The performance of the hydraulic supply system will be influenced by the choice of dynamic pressure differential APd _yn and threshold value Tr broadly as follows:

1. A higher value for the dynamic pressure differential APd _yn will increase the system dynamics as it leads to a faster reaction time to change the pump supply pressure PSP once the rate of increase of the consumer load sensing pressure LSP has reached the threshold value. A lower APd _yn value would tend to lead to a slower response but perhaps a smoother and less abrupt change in pump supply pressure PSP.

2. Lowering the threshold value Tr will increase system dynamics as it causes the dynamic pressure differential APd _yn to be applied sooner when an increase in load sensing pressure LSP occurs, whilst a higher threshold will delay application of the dynamic pressure differential APd _yn , leading to a less dynamic system response.

Increasing the dynamic pressure differential APd _yn and/or lowering the threshold value Tr of the rate of increase of the load sensing pressure LSP can both be used to provide higher system dynamics. However, use of a lower threshold value Tr is dependent on the ability of the system to sense the load sensing pressure to the tolerances required for reliable control with a smaller threshold value Tr. In view of this it is generally preferred to increase the dynamic pressure differential APdyn in order to increase the dynamic performance of a hydraulic system. However, a lower threshold value Tr can be used to increase system dynamics where the value selected and the system permits reliable operation.

As both the dynamic pressure differential APd _yn and the threshold value Tr of the rate of increase of consumer load sensing pressure LSP influence the dynamic behaviour of the pump adjustment based on consumer load sensing pressure LSP, they are collectively referred to as “LS dynamic parameters”.

The actual values for the threshold Tr and the dynamic pressure differential APdyn are selected as appropriate to any given hydraulic system and the person skilled in the art will be able to establish suitable values by, for example, trial and error. However, in trials with a typical hydraulic supply system on a tractor having a pump MP with a maximum delivery rate of about 229.5 l/min at an engine speed of 2700 RPM and a maximum pump supply pressure of about 230 bar, the applicant has found that a dynamic pressure differential APd _yn in the range of 10 bar to 40 bar and a threshold value Tr in the range of 4 to 10 bar/50ms are generally suitable. Values outside of these ranges though might also be applicable in some hydraulic systems.

Values for the LS dynamic parameters may be stored in the memory 106 of the tractor controller 102 or be otherwise accessible to the electronic processor 104. LS dynamic parameters may be provided as a default setting permanently saved to the memory 106 or the system may be configured so the values of the LS dynamic parameters can be set or modified via a user interface, such as the touch screen. This would enable the parameters to be input or adjusted by a driver or other user. Where the LS dynamic parameters can be input or modified, this would enable a driver to set the LS dynamic parameters to provide a suitable dynamic performance for a particular job or task and/or enable different values for the parameters to be used for different implements. For example, use of a particular implement may be improved by a more dynamic response whilst a different type of implement may be better suited to a less dynamic response. The ability to vary the value of one or more of the LS dynamic parameters enables the driver to adapt the hydraulic supply system accordingly. In a further alternative, instead of entering respective values for the threshold Tr and/or the dynamic pressure differential APdyn, the system may be configured to operate in different LS modes which may be optionally selected by a user. The system could, for example, be configured to be operable in a “dynamic mode” or an “efficiency mode”, with the values of the LS dynamic parameters being set to provide a faster response to increases in consumer load sensing pressure LSP in the dynamic mode and to provide a slower response time in efficiency mode to reduce power consumption. The system may be further configured to enable selection of a “balanced mode” with the values of the LS dynamic parameters set in-between the dynamic and efficiency modes. The use of predefined, selectable modes require less skill and experience by the driver whilst still providing an ability to customize the hydraulic supply system settings.

In a further optional refinement, the method may utilise more than one threshold value Tr for the rate of increase of load sensing pressure LSP and more than one dynamic pressure differential APdyn so as to enable a stepped ramp up of the dynamic pressure differential Pdyn depending on the rate of increase of the load sensing pressure LSP. Accordingly, in an embodiment the system may configured to apply a first dynamic pressure differential Ap1d _yn , for example 20 bar, when the rate of increase of the load sensing pressure LSP is at or above a first threshold value Tr1 but below a second threshold value Tr2, and to apply a higher, second dynamic pressure differential AP2dyn, for example 40 bar, when the rate of increase of the load sensing pressure LSP is at or above the second threshold value Tr2. For example, a first threshold value Tr1 could be set at 5bar/50ms and a second threshold value Tr2 set at 10bar/50ms. It will be appreciated that the values for Tr1, Tr2, AP1d _yn , and AP2d _yn mentioned above are illustrative only and that the values used can be selected as desired to suit any particular hydraulic supply system and performance requirements. It should also be appreciated that more than two different dynamic pressure differentials can be utilized and implemented at suitable threshold values for the rate of increase of the load sensing pressure.

In a yet still further optional refinement, different settings for the LS dynamic parameters are adopted depending on the value of the load sensing pressure LSP. For example, a first dynamic pressure differential AP1d _yn and/or threshold value Tr1 for the LSP pressure gradient is/are applied when the load sensing pressure LSP is below a first threshold pressure TP1 and a second dynamic pressure differential AP2d _yn and/or threshold value Tr2 for the LSP pressure gradient is/are applied if the load sensing pressure LSP is equal to or above the first threshold pressure TP1. In an embodiment, the LS dynamic parameters may be selected to provide a less dynamic response at higher load sensing pressures. Thus the LS dynamic parameters can be set to provide a fast reaction initially (e.g. to overcome internal inertia in the pump controller when starting to pivot the pump) but then provide a smoother control of the pump supply pressure as the dynamic behaviour of the pump increases. This also provides a tiered dynamic response and it will be appreciated that more than two ranges of load sensing pressure LSP in which different LS dynamic parameters are adopted can be defined. In one example, different LS dynamic parameters are applied in two ranges:

Range 1 : a first dynamic pressure differential AP1d _yn , say in the region of 10-20 bar, is applied when the rate of increase of the load sensing pressure is at or above a threshold value Tr1 of 7 bar/50ms and the load sensing pressure LSP is below a first pressure threshold TP1 , say in the region of 40-45 bar.

Range 2: a second dynamic pressure differential AP2d _yn , say in the region of 5-10 bar, is applied when the rate of increase of the load sensing pressure is at or above a second threshold value Tr2 of 5 bar/50ms and the load sensing pressure LSP at or above the first pressure threshold TP1 , say in the region of 40-45 bar.

It will be noted that the threshold value Tr1 of the rate of increase of the load sensing pressure is slightly higher in the first range than the second range. The means that the system will wait for a higher increase per time of the load sensing pressure LSP before applying the first dynamic pressure differential AP1d _yn . Nevertheless, since the dynamic pressure differential AP1d _yn applied in the first range is significantly higher than that applied in the second range, the dynamic response is higher overall in the first range than the second. In tests it has been found that the control system is less prone to oscillation by applying a slightly higher threshold value Tr initially. However, there may be circumstances where the threshold Tr for the load sensing pressure LSP gradient is the same in all LSP pressure ranges or where a lower threshold Tr is used for a range where the LSP pressure is lower than in a later range where the LSP pressure is higher.

Additional ranges could be added with a second, a third or more threshold pressures TP2, TP3,...TPn with a different dynamic pressure differentials AP23d _yn , AP4d _yn , ... APnd _yn and/or threshold value(s) Tr for the LSP pressure gradient being applied in each range.

In one embodiment, no dynamic pressure differential APd _yn is applied once the LSP reaches a threshold pressure TP. Thus in the above example, in a third range where the LSP pressure is at or above a threshold value TP2 of 70 bar, no dynamic pressure differential APd _yn is applied regardless of the rate of increase of the load sensing pressure LSP. The actual values for the dynamic pressure differential(s) AP1d _yn , AP2d _yn , the threshold value(s) Tr for the LSP pressure gradient, and threshold pressure(s) TP can be selected to meet system requirements and are not limited to the above examples.

In an embodiment, the controller 102 is configured to require that the conditions for a particular range are met for a set period of time, referred to as a range delay period RDP, before a dynamic pressure differential APd _yn for that range is applied. The range delay period RDP may be in the region of 150 to 450 ms, or in the range of 200 to 400 ms, or in the range of 250 to 350 ms, for example. Thus if the system is operating in range 1 and the load sensing pressure LSP increases to or above the threshold value TP1 indicating a change to range 2, the controller 102 waits for the range delay period RDP to expire before the dynamic pressure differential AP2d _yn for range 2 can be applied. During this time delay, no dynamic pressure differential APd _yn is applied to control the output of the pump. If after expiry of the range delay period RDP the conditions for range 2 are still met, the dynamic pressure differential AP2d _yn for range 2 is adopted and can be applied if the appropriate threshold Tr2 for the load sensing pressure LSP gradient in that range is met. However, if during the range delay period RDP the load sensing pressure LSP indicates a further change of range, say back to range 1 , a further range delay period RDP is applied from the moment the new range is triggered before the dynamic pressure differential AP1d _yn for the new range can be applied.

Where the system is configured to apply a dynamic pressure differential APd _yn for a limited application period AP when triggered and to apply a minimum delay period DP between applications of a dynamic pressure differential APd _yn , the system can be configured to apply the both a minimum delay period DP and a range delay period RDP. In this case, the controller 102 may be configured to apply the delay period DP and the range delay period RDP concurrently should a change of range occur whilst a delay period DP is still running following an earlier application of dynamic pressure differential APd _yn in the previous range. Typically, the delay period DP will be longer than the range delay period RDP.

To further clarify concurrent running of the delay period DP the range delay period RDP, two examples are considered where the delay period DP is set to 1000 ms and the range delay period RDP is set to 300 ms. In the examples, a change from range 2 to range 1 takes place after the dynamic pressure differential AP2d _yn for range 2 has been applied but before the end of the delay period DP triggered by that application. In a first example, the change of range takes place 600 ms after the delay period DP began. In this case, the range delay period RDP ends 900 ms after the delay period DP had begun. Accordingly, when the delay period DP expires after 1000 ms, the LS dynamic parameters for range 1 are adopted and the dynamic pressure differential AP1d _yn for range 1 can be applied, provided the conditions for range 1 are still met and the rate of increase of the load sensing pressure is at or above the threshold value Tr1 for range 1 at the time. If the dynamic pressure differential AP1d _yn is subsequently applied, this will be applied for the application period AP and a further delay period DP is commenced.

In a second example the change in range takes place 800 ms after the delay period DP has begun. In this case, the delay period DP expires 100 ms before the end of the range delay period RDP. Accordingly, application of the LS dynamic parameters for range 1 is delayed for a further 100 ms after the end of the delay period DP. After the range delay period RDP has expired (1100 ms after the previous application of dynamic pressure differential AP2d _yn when the system was operating in range 2) the dynamic pressure differential AP1d _yn for range 1 can be applied, provided the conditions for range 1 are still met and the rate of increase of the load sensing pressure is at or above the threshold value Tr1 for range 1 at the time. If the dynamic pressure differential AP1d _yn is applied, this will be applied for the application period AP and a further delay period DP is commenced.

Should a change of range occur during the application period AP, the controller continues to apply the dynamic pressure differential APd _yn until the end of the application period AP. The controller will also concurrently apply the delay period DP and the range delay period RDP before any further dynamic pressure differential APd _yn is applied.

Use of the delay periods in this way helps to maintain system stability when changing between ranges and smooths reaction when a range is maintained.

It is expected that varying the LS dynamic parameters in discreet ranges of load sensing pressure LSP will offer smoother control with less risk of oscillation. However, in some systems, the LS dynamic parameters may be varied in proportion (e.g. a linear or other mathematical relationship) to the value of pressure of the load sensing pressure LSP, at least over a certain range of pressures.

Regulation of Engine Speed in Dependence on LS Parameter The engine speed of a tractor or other mobile machine can often be set at a fixed value in order to meet certain targets. This may be carried out automatically, say by a controller 102, or a fixed speed selected or input manually by the driver. The engine speed setting function is typically accessible via an HMI interface, such as a touch screen TS and stored in the controller 102. One such target is to operate the engine at the lowest possible engine speed to minimize fuel consumption. A further target is to ensure that supply systems driven by the engine are able to function optimally. One of such supply system is the hydraulic supply system 64. Performance of the hydraulic supply system is dependent (amongst other things) on the speed of the engine which provides a drive input to at least the main pump MP. In a typical hydraulic supply system used on tractors, a pump might be expected to provide a maximum delivery rate at a minimum engine speed of 700 RPM in the region of 44 l/min while at maximum engine speed of say 1700 RPM, the maximum delivery rate may be in the region of 170 l/min. Since a sufficiently high deliver rate is required to enable the hydraulic supply system to maintain a pressure differential AP _s t above any hydraulic demand LSP made by the consumers, the engine speed has a major impact on the performance of the hydraulic supply system.

Where the engine speed is set relatively low with increased fuel efficiency in mind, the set engine speed may not be sufficient to enable the pump MP to provide a delivery rate needed to ensure the required static pressure differential AP _s t in all circumstances. In a known solution to this problem the hydraulic supply control system is configured to compare the delivery rate of the pump at the set engine speed with the current valve settings in terms of delivery. If the overall delivery demand of the valves exceeds the capacity of the pump at the set engine speed so that required pressure differential AP _s t cannot be provided, the controller is operative to reduce the delivery rates of the valves to balance the delivery demand of the valves with the delivery capacity of the pump. As a consequence, the speed at which the consumers connected to valves are operated is restricted. This negatively impacts the dynamic performance of the hydraulic system.

To address the above issue in accordance with aspects of the invention, when the mobile machine is operating with a set engine speed which potentially limits the pump supply (in terms of delivery rate and/or pump pressure), the machine is operable in a mode in which the controller 102 is configured to compare the actual pump supply pressure PSP with the load sensing pressure LSP and to determine, with reference say to stored data such as a characteristic map or look up table for the pump, whether the pump supply is capable of meeting the load sensing pressure LSP demand at the speed the engine is operating at. If the controller 102 determines that the pump supply cannot meet the load sensing pressure LSP demand at the present engine speed, the controller is configured to increase the engine speed by an amount necessary to enable the pump supply delivery/pressure PSP to be raised to meet the hydraulic demand as indicated by the load sensing pressure LSP.

Data regarding the actual pump supply pressure PSP is provided in the form of a pressure signal provided by a pressure sensor 132 of the hydraulic supply system which is located so as to measure the pump supply pressure PSP. This pressure signal will be referred to as a second pressure signal to differentiate it from a pressure signal indicative of a sensed load sensing pressure LSP, which is referred to as a first pressure signal. Alternatively, the controller 102 may be configured to determine the pump supply pressure based on the electronic pump supply control signal EPSCS. The controller having access to data, say in the form of a look up table for characteristic map, from which the pump supply pressure can be derived from the electronic pump supply control signal EPSCS. Such data may provide a correlation between the current of the electronic pump supply control signal EPSCS and the pressure P _se tof the hydraulic pump supply control signal HPSCS, which is related to the pump supply pressure PSP. Engine speed data is also provided to the controller 102, say in the form of an engine speed signal from an engine speed sensor (additional sensors such as the ground speed sensor or engine speed sensor are indicated schematically at 103 in Fig. 5). By monitoring and comparing the load sensing pressure LSP demand and the pump supply pressure PSP, the controller is able to determine whether the load sensing pressure LSP demand is higher than the pump supply pressure PSP at any given time. The controller 102 is also programmed to determine, in accordance with a predefined algorithm, whether the pump supply has sufficient capacity to meet the sensed load sensing pressure LSP with the engine operating at its present set engine speed and, if not, to determine by how much the engine speed needs to be increased to enable the pump supply to meet the hydraulic demand indicated by the load sensing pressure LSP. The controller 102 is thus able to increase the engine speed in order that the pump supply is able to meet the hydraulic demands of the various consumers

In an example, a pump has a maximum delivery capacity of 120 l/min at a set engine speed of 1200 RPM but is capable of a maximum delivery of 170 l/min at an engine speed of 1700 RPM. If the hydraulic consumers have a delivery demand which is increased to 150 l/min and so cannot be met by the pump at the set engine speed of 1200RPM, the controller 102 is configured to raise the engine speed to balance pump supply pressure PSP and the load sensing pressure LSP. This may result in the engine speed being increased to say 1500 RPM, where the pump is capable of delivering 150 l/min. Increasing the engine speed rather than reducing the delivery rates of the valves has the advantage of not slowing down consumer supply, though at the expense of reduced fuel economy.

It is also known to enable a driver to set engine speeds depending on specific operating conditions which require use of hydraulic consumers in order to meet expected hydraulic demands. In one example, the driver can set an engine speed when electrohydraulic linkage/hitch control EHR or functions thereof, like the draft control mode as described in applicant's granted patent EP 2 765 844, is activated. In this operating condition the actuators LLC of a rear linkage system, supplied by valve RMV1 , are automatically adjusted to move the implement only within a small range while avoiding excessive draft or pull force, e.g. when a plough runs on a stone in the ground.

The engine speed in this mode of operation is set predicatively to meet an expected hydraulic demand. However, this set engine speed may be higher than is necessary during periods when there is no or reduced consumer demand, having a negative impact on overall efficiency. To address this issue in accordance with aspects of the invention, the controller 102 is selectively operated in a control mode in which it is configured to adapt or overwrite engine speed settings chosen for an operating condition such as the EHR mode based on a comparison of the pump supply pressure PSP with the load sensing pressure LSP demand. The controller 102 makes a determination whether the pump supply PSP exceeds or undercuts the load sensing pressure LSP demand at the chosen engine speed and is configured to adapt the engine speed accordingly. For example, the controller can automatically increase the engine speed when the maximum available pump pressure PSP is reached at the present engine speed but the load sensing pressure LSP demand is higher. The controller may also lower the engine speed when the pump supply has excess capacity to meet the current hydraulic demand.

The controller 102, may be programmed to determine whether the pump supply is capable of meeting the load sensing pressure LSP demand at the speed the engine is operating at using a predefined algorithm stored in a memory accessible to the controller 102.

In either of the embodiments described above, it is further envisaged that the controller 102 may generate a signal to the driver before changing the engine speed or require a confirmation from the driver before proceeding. This may be required when the tractor is operating an implement which is driven via PTO wherein the PTO speed must be kept constant, for example to maintain a constant application rate of a fertilizer spreader driven by PTO. Alternatively, the controller 102 may determine the PTO mode is engaged and prohibit engine speed variation based on a comparison of pump pressure PSP and load sensing pressure LSP demand. The control system may be configured to enable the driver to selectively engage an operating mode in which hydraulic demand and supply are monitored and a set engine speed is automatically overridden to meet the hydraulic demand, say in circumstances where hydraulic performance is more important than fuel efficiency.

In a further embodiment, the tractor has a continuously variable transmission CVT 60B and the controller 102 is part of an overall control system for the tractor and is in communication with sensors and actuators associated with the engine 60A and CVT 60B. The controller 102 is operable in a ground speed control mode in which it automatically regulates the engine speed and operation of the CVT in order to maintain a constant ground speed of the tractor at a substantially constant engine speed, which may be about 1000 RPM at 40 km/h. For this purpose, the controller 102 receives engine speed data, say in the form of an engine speed signal from an engine speed sensor (103) and ground speed data for the mobile machine, say in the form of a signal from a ground speed sensor (103). The controller 102 also receives data regarding one or more operational parameters of the CVT, say in the form of one or move CVT signals from one or more sensors (not shown) associated with the CVT. The controller 102 is configured to monitor and analyze the received data and to compute and generate control signals which are forwarded to one or more actuators for automatically regulating the engine speed and operation of the CVT. Typically in a ground speed control mode, the controller 102 is programmed to maintain a constant ground speed, which may be input or selected by an operator, using the lowest possible compatible engine speed. This reduces fuel consumption and reduces harmful engine emissions.

The CVT may be any suitable type and may be of the hydrostatic-mechanical split type as described applicant's published patent applications EP 1 990 230 and EP 2 935 948. However any other type of CVT may be used instead, e.g. pulley-based CVT's or planetary CVT.

For the reasons discussed, when the engine is being operated at a constant low speed, the pump MP driven by the engine 60A may not be able to satisfy a large and/or rapidly increasing hydraulic load. Accordingly, attempts by the load sensing control system to increase the pump supply pressure PSP in response to an increasing load sensing pressure LSP demand may not be successful if, at a certain engine speed, the maximum delivery of the pump is reached and no further increase of the delivery rate is possible. To address this issue, the controller 102 is configured, at least when operating in a ground speed control mode, to compare the pump supply pressure PSP with the load sensing pressure LSP and to determine whether the pump supply is capable of meeting the load sensing pressure demand LSP at the speed the engine is operating at. If the controller 102 determines that the pump supply cannot meet the load sensing pressure LSP demand at the present engine speed, the controller is configured to increase the engine speed to enable the pump supply pressure to be raised to meet the hydraulic demand as indicated by the load sensing pressure LSP whilst at the same time controlling the CVT to maintain the ground speed of the tractor substantially constant. The controller 102, may be programmed to determine whether the pump supply is capable of meeting the load sensing pressure demand at the speed the engine is operating at using a predefined algorithm stored in a memory accessible to the controller.

The controller is thus able to increase the engine speed in order that the pump supply is able to meet the hydraulic demands of the various consumers whilst maintaining a constant ground speed of the tractor and keeping the engine speed as low as possible. Should the load sensing pressure LSP (hydraulic demand) fall after the engine speed has been increased and the controller determines that the pump supply has excessive capacity to meet the current hydraulic demands at the increased engine speed, the controller is configured to lower the engine accordingly whilst again regulating the CVT to maintain a consent ground speed. The controller 102 may be programmed to maintain the lowest possible engine speed consistent with maintaining a required ground speed and meeting the hydraulic demand. Data regarding the maximum output of the pump at different engine speeds may be stored in a look up table or characteristic map accessible by the controller 102.

In one example, if when operated in a constant ground speed mode the tractor 60 has to execute a turn leading to an increase increasing hydraulic demand from the steering system SS, the controller 102 is operative to increase the engine speed whilst the turn is executed to meet the increased hydraulic demand and then lower the engine speed once the hydraulic demand of the steering system has reduced, all whilst maintaining a constant ground speed. In other examples, a temporary increase in hydraulic demand might arise form the need to actuate a hydraulic ram to lift an implement 62 attached to the tractor or to carry out some other function on an implement 62 or the tractor 60.

It will be appreciated, the controller 102 can be programmed to maintain the engine speed as constant as possible whilst enabling the hydraulic demands of the consumers to be met and the selected ground speed maintained. Where an increase in engine speed is necessary to enable the pump supply to meet a load sensing pressure LSP, the increase is preferably kept to a minimum necessary and the engine speed dropped once the hydraulic demand reduces.

Various modifications to the mobile machine and methods according to the invention will be apparent to those skilled in the art, without departing from the scope of the invention. For example, the main pump MP may be a fixed displacement pump and the pump supply may be configured as illustrated in Figure 2. In this case, the pump supply pressure PSP can be regulated by directing a hydraulic LS pump supply control signal P _se t from a solenoid controlled pressure limiting valve 54 to the load sensing port 48 of the proportional pressure compensator valve 40. The solenoid controlled pressure limiting valve 54 being controlled by the electronic pump supply control signal EPSCS from the tractor controller 102.