The invention relates to energy supply system for vehicles, and especially to electrical and hydraulic systems for agricultural vehicles.

It is well known in the vehicle industry to provide electrical energy to power vehicle propulsion systems such as electric motors driving the vehicle wheels from, for example, rechargeable batteries, fuel cells or a combustion engine combined with a generator and associated battery.

Typically such a vehicle will, in addition to the propulsion system, also have an internal DC voltage network (12V or 24V) for supplying vehicle components and external systems such as trailer lights etc.

Tractors differ considerably from trucks, vans and passenger cars as their primarily requirement is not simply to drive over the ground but to power attached implements such as trailers, balers, seed drills or ploughs etc.

These implements include functions which are currently commonly powered by hydraulic systems or from a Power Take-Off (PTO) shaft driven from an engine of the vehicle. Such drives for attached implements can be of constant speed type, e.g. to lift the boom of a sprayer, or of variable speed type, e.g. to drive a metering system of a seeder. Constant speed type drives may be today driven by the PTO shaft whilst variable speed type drives may be powered by hydraulics using regulators to vary flow and thereby speed of a fluid motor or ram.

It is also known to power functions on a trailed implement (such as flywheels for the pressing plunger of a baler and powered axles) by electric motors from an electrical supply on the towing vehicle. As is well understood, when electric motors rotate without an applied driving current they act as generators feeding current back into the energy supply of the towing vehicle. This may occur for example during hill descent or under braking, and the resulting surplus energy must be managed to avoid damage to components on the vehicle electrical supply circuit. It is an object of the present invention to provide a means for managing surplus electrical energy fed back into the electrical supply circuit of a vehicle. Thus according to the present invention there is provided an energy supply system for a vehicle, including electric and hydraulic supply systems, comprising:

- monitoring means configured to detect a predetermined overload condition in the electric supply system; and

- control means arranged to controllably dissipate or store energy in the hydraulic supply system in response to detection of an overload condition by the monitoring means.

Thus, whilst the electric supply system will typically have some capacity to handle an energy surplus, the means provided (such as extra batteries or a brake chopper) tend to be specified as small as possible for reasons of size and cost, and by handling any surplus beyond what the electric system can accommodate through the hydraulic system results in a compact and efficient arrangement.

Where the electric supply system includes means to dissipate surplus electrical energy fed into the supply system including a brake chopper having a known dissipation capability, the monitoring means may be arranged to determine an overload condition when the surplus electrical energy reaches or exceeds the brake chopper dissipation capability, as may be indicated by a temperature sensor located proximate the brake chopper. Additionally, or alternately, the electric supply system may include electrical storage means (such as batteries or capacitor devices) having a known storage capability to store surplus electrical energy fed into the supply system, with the monitoring means being arranged to determine an overload condition when the surplus electrical energy reaches or exceeds the storage means capability.

The control means arranged to controllably dissipate or store energy in the hydraulic supply system suitably includes an electrically driven pump driving hydraulic fluid against a flow resistance, such as a flow limiter or pressure limiting valve, with the surplus energy being dissipated as heat. Alternately, flow resistance in the form of an accumulator into which the pressurised fluid is pumped may be provided, with the stored energy thereby being available when subsequently required.

Further features and advantages of the present invention are recited in the attached claims to which reference should now be made.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates the voltage branch (related to the voltage supply system) of a vehicle energy supply system embodying the present invention;

Figure 2 schematically illustrates a first arrangement of the hydraulic branch (related to the hydraulic supply system) of a vehicle energy supply system embodying the present invention;

Figure 3 schematically shows a further embodiment of the hydraulic branch of a vehicle energy supply system embodying the present invention;

Figure 4 schematically shows a still further embodiment of the hydraulic branch of a vehicle energy supply system embodying the present invention; and

Figure 5 schematically shows a yet further embodiment of the hydraulic branch of a vehicle energy supply system embodying the present invention.

Referring to Fig. 1 this shows an electric supply system 1 for a tractor 2. The system has a combustion engine 10, an electric generator 1 1 driven by the engine crank shaft 10a and an electronic power unit 12 (insulated-gate bipolar transistor) connected to the electric generator by wiring 1 1 a. As will be understood, in an alternative arrangement the source of electrical energy may be a fuel cell and/or a battery. Electronic power unit 12 is connected to Tractor control unit 3 which connects the control system of the electric supply system to other systems of the tractor, including the hydraulic supply system shown in Figure 2.

The generator 1 1 produces AC power with an AC frequency dependent on the combustion engine speed. The electronic power unit 12 converts the AC power output of the generator 1 1 to a DC voltage with the defined DC-link voltage level to provide all units connected to DC-link 15.

The DC-link or components such as the generator 1 1 or the electronic power unit 12 of the DC-link 15 are provided with electrical storage means, respectively network capacitors 15a, which store energy to feed back into the DC-link to stabilise the supply on a level to ensure standard operation. These network capacitors 15a are very small and limited in their storage capacity but are suitable to balance e.g.

voltage variations of the generator 1 1 caused by variations of the engine speed.

A brake chopper 13 is provided to avoid a voltage rise in the DC-link 15 if energy is fed back into the system from other sources than the generator. The chopper comprises an oscillating switch in series with a resistor and, depending on the input voltage overshoot (coming from e.g. the implement via the internal network) the switch is oscillated to guide the excess voltage into the resistor transforming the voltage into heat. The oscillation is necessary to keep the network active and supplying energy. If the switch was to be closed completely over a longer period, the complete voltage supplied by the system would be cut and all consumers would be non operative. By oscillating the switch, only the peaks of the voltage are destroyed and the system is still operative. In addition, the resistors are generally designed to be quite small so they are not capable of receiving a constant high load. Using oscillation enables them to cope with the load. For example, if the nominal voltage of the network is 700 V, with an overshoot limitation of 900 V, then if peaks of > 900 V occur the switch is closed in an oscillatory manner.

An insulation monitoring system 14 is provided to monitor the resistance in the network to detect electrical malfunctions in the medium voltage system. This is necessary to protect the life of potential users of the system and to prevent damage in electric components of the tractor or implement or other consumers connected to the system. Internal medium voltage DC-link 15 (>400V, 150 kW) is provided for supplying tractor components such as a battery/supply network 16 via DC/DC converter 16a reducing voltage >400 V into, for example, the standard 12V supply.

An electronic unit 17 for supplying a heating/ventilating/air conditioning (HVAC) compressor 17 via DC/DC converter 17a is also provided. Similarly a variable cooling fan drive 18 is supplied via a DC/AC inverter 18a to provide a variable frequency to vary fan speed.

In the shown embodiment, the tractor is not driven by electric motors but is provided with a standard transmission driven by crankshaft 10a. If the drive system is a diesel- electric drive system, further motor(s) may be provided which drive axles or wheels. These are similar to those described with reference to 16, 17 or 18.

The system may also be equipped with an additional electric storage means 19 which can be a battery or double-layer capacitor device (also known as a

supercapacitor). Compared to the network capacitors 15a described above, these storage means 19 are of higher storage capacity or can deal with higher overload referring to time and voltage. While batteries in vehicles are mainly used to

constantly provide supply to electric consumers due to their constant charge/high capacity nature, supercapacitors are more suited to the storage of high peaks but with reduced capacity, e.g. for recuperation during braking (such as KERS in

Formula One motor racing).

To supply external consumers (e.g. on implements/ front loaders /stationary devices supplied by the tractor) additional supply means are provided. For example, a DC/AC branch 30 which includes an electronic unit 31 for inverting high power DC into high power AC at fixed frequency for the supply of one motor or other rotating device is provided. An associated outlet terminal 20 is supplied from electronic unit 31 via a power switch 32 to deactivate the supply connector pins 30a, 30b, 30c. In parallel, the DC-link 15 is directly forwarded to the connector 20 by branch 33 via switch 34 to deactivate DC supply from DC branch to connector pins 30d and 30e.

The branches are equipped with a potential equalisation function (indicated generally at 35) in order to equalise potentials between different metal parts that can be touched simultaneously, or to reduce differences of potential which can occur during operation between the bodies of electrical devices and conductive parts of other objects. For example, the tractor stands on rubber tyres while the plough is contacting ground via steel parts. Thus, as the tyres and metal plough parts have different earthing properties and thus different electric potential, if the operator were to touch both simultaneously, the potential difference would pass through him and he could be injured badly.

Further DC/AC branches and/ or DC branches may be provided as shown in commonly-assigned patent application WO 12/010489. These supply systems may offer DC or AC, or DC and AC. The design of the AC and/or DC supply system may vary. Further explanations are given in the above mentioned WO12/010489.

As will be appreciated the above AC/DC supply system enables AC/DC electrical power to be provided simultaneously for a wide range implements and other consumers.

An implement/trailer 100 is schematically shown in Figure 1 which comprises different consumers driven by the energy supplied by tractor 2.

A first consumer 101 may be an electric motor 101 which drives the axles or wheels of the implement (not shown). This configuration may be used in forestry and on hilly terrain to improve the traction of the overall vehicle. First consumer 101 is connected to connector pins 30a, 30b, 30c of DC/AC branch 30. The speed of the motor 101 can thereby controlled by electronic unit 31 on tractor 2 which is advantageous to control the traction of the vehicle and implement.

A second consumer 102 may be an electric motor 102 which operates other drives of the implement (not shown).These may be pumps to deliver fertilizer or motors to pivot or move frames of the implement. Second consumer 102 is connected to connector pins 30d, 30e to DC branch 33. The speed of the motor 102 can thereby controlled by electronic unit 103 (including DC/AC converter) on the implement 100 which is advantageous if there are a lot of motors on the implement.

The function of the system is now explained for the case that energy is charged back from consumers on the vehicle or the trailer as occurs, for example, if the vehicle with a trailer having one or more electric driven axles is driven downhill . The installed motors 101 , 102 (wheel or axle driving motor on the trailer) are then working as an electric generator and would generate electric power which is fed via connector 20 into the tractor internal medium voltage DC-link 15. If the motors 101 , 102 are normally provided with a power of say 50kW to drive the axle, a similar electric power is generated then. The electric power is then forwarded to the generator 1 1 which would work as an electric motor driving the combustion engine 10. This may result in the speed of combustion engine 10 exceeding a maximum level causing serious damage as the capability of the combustion engine 10 to bear input torque is limited.

Presuming that the generator 1 1 has a maximum power of 100 kW this level has to be considered for charge back protection as, especially in downhill driving, the combustion engine may already reach maximum engine speed (driven by vehicle and trailer weight) and then the surplus charged back electrically would result in massive overload.

To protect the combustion engine 10, the electric power could firstly forwarded (by control of electronic power unit 12) to network capacitors 15a and then to storage means 19. As a battery which is capable to take the full energy charged back would require an enormous size, a smaller battery or array of supercapacitors is likely to be installed. If the storage means 15a or 19 reaches its capacity limit (as may be determined by sensing load condition/temperature/energy input) the brake chopper 13 may be used to dissipate the remaining electrical energy in the form of heat. However, a brake chopper 13 which is capable to bear maximum possible energy would require a size, for about 100 kW , which cannot be installed in a vehicle. Accordingly it is a vital requirement to reduce the brake chopper. A suitable chopper size (for installation) may be capable of handling 20 kW permanent load and 200kW for 5 seconds. This requires that the brake chopper 13 is monitored referring to its capacity, and monitoring means such as a temperature sensor is provided to forward a signal to electronic power unit 12 if the limit is reached.

The installation of a brake chopper 13 requires space and increase production costs. Applications may be possible wherein the network capacitors 15a can cope with parts of the surplus energy without the need of a brake chopper 13.

As a storage means may not be present or also be limited in capacity, means are required to bear electric load surplus to the capacity of the electric supply system. Figure 2 shows the hydraulic supply system 40. The main supply pump 50 is a variable displacement type swash plate piston pump (where the swash plate is pivoted for adjusting displacement) and operable to generate a fluid pressure of up to 200 bar. Pump 50 supplies the different consumers (different consumers 60 on the tractor, for example front and/or rear linkages and main valve manifold) via main supply circuit MC.

The displacement (and thereby mass-flow) of main supply pump 50 is controlled by a load-sensing circuit LSC. Generally, the load-sensing circuit LSC is connected to the major consumers 60 (work hydraulics and steering system) to adapt delivery of main pump 50 according to current needs. These systems are very efficient as the pump 50 only delivers hydraulic fluid on demand (in comparison with fixed displacement pumps).

The control of the displacement is now explained assuming that the pump 50, and load sensing (LS) port 50a are directly connected for better clarity. If the combustion engine 10, or any prime mover, is running, the pump 50 is driven and delivers a very small oil flow rate into MC which is not capable to supply consumers 60 (e.g. a lifting cylinder of a three-point linkage system), but supplies oil e.g. to the pilot pressure supply system which is used to control/move hydraulically operated valves to control different consumers 60. This small oil flow rate ensures a stand-by condition with an initial pressure level of about 20 bar (depending on pump setting) of the system. Due to the small flow rate, losses in stand-by mode are very small (as hydraulic output is proportional to flow Q and pressure p).

If the operator activates a consumer, e.g. to lift the rear linkage, the oil flow is forward via the consumers control valve (not shown) to e.g. one side of a piston of a lifting cylinder. If the oil flow is not capable to lift the cylinder, the pressure in the cylinder (or any rotational motor) is increased. The pressure difference (between pressure applied by the load and pressure supplied by air flow of the system) is forwarded as LS signal pressure via load sensing circuit LSC to port 50a of the pump 50. If now the LS signal pressure signal is say 100 bar, the pressure within the pump is increased to a pressure of LS signal pressure plus initial pressure level of about =100 bar + 20 bar=120 bar and this pressure then pivots the swash plate to increase the oil flow and pressure level to 120bar in the main circuit MC.

If the consumer is in the desired position, the LS signal goes back to 0 bar. If e.g. a rotation hydraulic motor is used, the oil flow is constantly controlled so swash plate is permanently readjusted. In this way, the pump is permanently readjusted to bear the demand of the consumers. If more then one consumer is installed, the highest demand is forwarded to adjust main pump 50. These systems are known in the art and a complete hydraulic system used in a tractor is described in applicants unpublished application GB1209109.6 filed 24 May 2012.

Referring back to Figure 1 and the situation that energy is charged back into the electric network 15, and network capacitors 15a , the brake chopper 13 or storage means 19 are not capable to dissipate or store the complete energy, means are provided in the hydraulic supply system 40 to support the function.

If the electronic power unit 12 recognizes that the capacity of network capacitors 15a, storage means 19 or brake chopper 13 regarding the transformation of surplus charge is reached, an overload condition exists and a signal is sent to tractor control unit 3. A first control valve 70 (Figure 2) is controlled by the tractor control unit 3 and has two positions: in position 70a (supported by spring 70c) load sensing circuit LSC is connected with LS port 50a and pump 50 supplies the consumers 60. This position is supported by spring means so that if no signal is present, position 70a is kept.

If the first control valve 70 is moved, by tractor control unit 3, to its position 70b, the pump 50 is directly connected to LS port 50a. As described before, the stand-by pressure in the system is permanently 20 bar, so if this pressure is charged to port 50a, the LS signal pressure plus initial pressure level of about =20 bar + 20 bar=40 bar and this pressure than pivots the swash plate to increase the oil flow and pressure level to 40bar in the main circuit MC. This is again charged to port 50a so that the swash plate of the pump is stepwise pivoted to maximum pressure of

200bar, whereby this adjustment occurs very rapidly.

So the first control valve 70 serves the purpose to increase the pump output independent from LS signals from consumers.

A second control valve 71 is provided which is simultaneously controlled with first control valve 70 by tractor control unit 3. The second control valve 71 has two positions wherein position 71 a (supported by spring 71 b) is closed, while position 71 c is an opened position. In position 71 c the oil flow in MC is redirected to the tank 72 of the hydraulic system through a flow limiter in the form of an orifice 73 in which the energy of the oil flow is transferred into temperature of the oil (and the orifice). The oil is then cooled by an internal oil cooling circuit.

In this way, the electric energy charged back into the electric supply system 1 is dissipated (transferred into heat) by increasing the oil flow of the pump 50. As the pump 50 is drivingly connected to the combustion engine 10, additional torque supplied by the generator 1 1 (working as an electric motor) can be supported without damaging the engine.

Figure 3 shows a further embodiment whereby the flow limiter is replaced by a pressure limiting valve 74. As the oil flow must counteract a defined spring force of valve spring 74a, adjusted to 190 bar, the energy of the oil flow is again transferred into temperature of the oil (and the valve). The oil is then cooled by the internal oil cooling circuit As will be recognised, the dissipation arrangements of Figures 2 and 3 still enable the hydraulic system to supply oil flow to consumers which would also result in energy reduction.

Figure 4 shows a further embodiment which contains the feature of hydraulic recuperation. Hydraulic recuperation, similar to electric recuperation, transfers excessive load to a storage means. Excessive load can be generated as described above, or for example by braking. In loaders, for example, hydraulic recuperation is used to store hydraulic overload when the vehicle is braked especially as loaders mainly move on a v-shaped path to load the bucket and unload on a truck and lower the boom. Therefore, a means is provided which redirects hydraulic oil to a storage means, e.g. an accumulator (piston or gas accumulator). These systems are known for construction machinery.

According to the present invention, similar means may also be used to support overload in the electric supply system.

Referring to Figure 4, a gas membrane type accumulator 80 is additionally provided, together with third 81 , fourth 82 and fifth 83 switching valves, check valve 84 and pressure monitoring means (pressure sensor) 85. The accumulator is connected to the line to flow limiter 73 or pressure limiting valve 74 (according to Figure 3) via the third 81 and fifth 83 valves, with check valve 84 in the line between them acting to prevent the accumulator discharging to the tank 72 via the flow limiter 73.

The third valve 81 has two positions: in the first position 81 a (as illustrated) the connection to load the accumulator 80 is opened. Position 81 a is supported by valve spring 81 b such that the default setting has oil flow charging the accumulator. If position 81 c of the third valve 81 is selected by tractor control unit 3, the accumulator begins to discharge, with oil flow directed to main circuit MC to support pump 50. As will be recognised, the third valve 81 can also be used independently from handling overload in the electric supply system. If valve 71 is opened, any pressure overload applied to pump 50 (as described above for a loader when lowering boom or braking) could be charged to the accumulator as the alternative to discharging it to the tank 72.

Fourth valve 82 is a two-position valve provided between third valve 81 and main circuit MC. In the first position 82a of the valve (as shown) the load sensing signal pressure is higher than the pressure available from the accumulator 80 as

determined by the pressure sensor 85. The LS signal is forwarded to the pump 50 to adjust displacement. The connection of accumulator 80 to main circuit MC is then blocked so that only the main pump 50 supplies the consumers 60. An additional check valve 87 is positioned in the main circuit MC between the fourth valve 82 and the main pump 50.

If the pressure in the accumulator 80 is higher than a load request coming from consumers, the connection to main circuit MC is opened (valve position 82b) so that the accumulator 80 is supplying to consumers. The load sensing signal is then blocked so that the pump 50 is only adjusted if the accumulator is not able to provide the load demand coming via LSC.

The fifth valve 83 is positioned between the valve 71 and the flow limiter 73 or pressure relief valve 74 and is controlled by the tractor control unit 3. In a first position 83a of the valve (as shown) to which it is biased by spring 83b, oil flow from valve 71 discharges to the tank 72 via the limiter 73 (or valve 74). In the second position 83c of the fifth valve 83, the path to the tank is blocked and instead the oil flow is directed via check valve 84 and third valve 81 to charge the accumulator 80.

The systems described above are provided with a variable displacement pump which is pivoted to dissipate electric surplus energy. A similar system may also be provided with a fixed displacement type pump including means to dissipate energy as shown in Figure 5. Figure 5 shows the hydraulic supply system 41 . The main supply pump 51 is a fixed displacement type piston pump and operable to generate a fluid pressure of up to 200 bar. Pump 51 supplies the different consumers (different consumers 60 on the tractor, for example front and/or rear linkages and main valve manifold) via main supply circuit MC. Compared to the hydraulic systems described in Figures 2 to 4, there is no load-sensing circuit LSC to feedback consumer demand to the pump. This type of hydraulic supply system is used for low-cost or low-specification tractors but with the major disadvantage that the pump 51 constantly supplies fluid even if there is no demand by the consumers 60.

If there is no demand from the consumers 60, a pressure limiting valve 90 discharges the oil flow to the tank 72 assuming that the pump 51 and pressure limiting valve 90 are directly connected, which is achieved by a sixth control valve 91 as described below.

Compared to the pressure limiting valve 74 shown in Figure 3 serving the purpose to dissipate energy by high flow resistance and heat transfer, pressure limiting valve 90 is designed to discharge the oil flow with minimum resistance. The sixth control valve 91 is connected to the tractor control unit 3 and has two positions: in position 90a (supported by spring 91 c) the oil flow is discharged to the tank 72 via pressure limiting valve 90 with minimum resistance to increase efficiency in normal operation. This position 91 a is supported by spring means 91 c so that if no signal is present, position 91 a is kept.

Referring back to Figure 1 and the situation that energy is charged back into the electric network 15, and network capacitors 15a, the brake chopper 13 or storage means 19 are not capable to dissipate or store the complete energy, sixth control valve 91 is provided with a further position 91 b to enable the hydraulic supply system 41 to support the function in similar manner to the systems described in Figures 2 to 4.

If the sixth control valve 91 is switched to position 91 b by tractor control unit 3 detecting an overload condition as described in the Figures above, the oil flow is discharged to tank 72 via an orifice 92 working exactly the same way as orifice 73 (Fig. 2). Alternatively the orifice 92 may be replaced by further pressure limiting valve (not shown) with a specification similar to pressure limiting valve 74 to dissipate energy (transfer into heat).

The system shown in Figure 5 may also be combined with am accumulator as described in Figure 4.

From reading the present disclosure, it will be understood that additions or modifications are possible. For example, in the hydraulic circuit of Figure 4, the combination of the pressure sensor 85 and fifth valve 83 may be replaced by a purely hydraulic solution. The scope of the present invention is defined by the attached claims.