The invention also relates to a computer program for performing the method and a device according to the preamble to claim 22.

The vehicle consists preferably of a working machine, such as a wheel-mounted loader, or a dumper.

There is a desire to reduce the emissions from diesel engines. This desire is driven not least by increasingly stringent legislation. A consequence of this is that a number of engines have too low a torque at low engine speeds. A mechanical loader, with a torque converter in the drive line and a hydraulic system for supplying among other things the lifting and tilting cylinders of the loader's loading unit and shovel and control cylinders for the steering, requires high torque even at low engine speeds. If the driver utilizes the power from the engine at low engine speeds to drive the vehicle's half shafts at the same time as the hydraulic system is activated, then there is a danger that the engine will cut out or that the engine

will"stick", that is it will not be able to increase the engine speed when the driver depresses the accelerator pedal. The driver can, of course, adjust the power consumption via various controls, but this can be problematical, particularly when the engine suddenly cuts out.

BACKGROUND ART In US 5,996, 701 a control device is described for a working vehicle which is equipped with a hydraulic system for operating a piece of equipment, for example a shovel, and for turning the vehicle. The control device is intended to prevent the engine cutting out during operation. A first hydraulic pump is driven by the vehicle's engine and is arranged to raise or lower the piece of equipment. A second hydraulic pump with variable displacement is also driven by the vehicle's engine and is arranged to turn the body of the vehicle.

A load on the piece of equipment is detected and when the load exceeds a predetermined value, the maximum displacement for the second pump is reduced. By this means, the load is reduced which arises from the turning of the vehicle and the engine is prevented from cutting out. In other words, the handling of the vehicle's piece of equipment is given priority over the steering of the vehicle, by the displacement of the second pump being reduced.

DISCLOSURE OF INVENTION A first aim of the invention is to achieve a method for controlling a vehicle which solves the problem of the engine cutting out and which makes possible more cost-effective operation and/or a more cost-effective system.

This aim is achieved by the power limitation being carried out by the maximum available movement of at least one flow-regulating valve in the hydraulic system

being limited. By a limited movement of the valve is meant that it can only be moved a certain limited amount, or in other words that the opening for the through-flow of the hydraulic oil is limited. In the existing hydraulic system of the working vehicle, there is already a plurality of movable flow-regulating valves. By controlling one or more of these, it is possible to achieve a cost-effective system/vehicle in a simple way. The flow-regulating valve can, for example, consist of a directional valve.

According to a preferred embodiment of the invention, the consumed power is determined by a flow being determined that is supplied from the pump, and in particular to said hydraulic component, and by the determined flow value being multiplied by a special pressure value, with the product giving a value for the consumed power. The determination of the flow and the pressure value can be carried out in a plurality of more or less accurate ways.

According to an example, a movement is detected of a first movable control means, such as a control lever, which is arranged to regulate said hydraulic component, and the size of the movement is utilized to determine the flow value to said component. More specifically, the signal from the control lever is sent to a computer unit and processed there, after which the computer unit sends a signal to the flow-regulating valve to control this. This is particularly advantageous when the hydraulic system is of a so-called load-detecting type.

With such a load-detecting system, the pressure drop across a valve is in principle constant, which means that the flow is only dependent upon the movement of the movable control means.

According to a further embodiment, the pressure is measured in the flow that is supplied to said hydraulic

component, and the measured pressure is utilized as the special pressure value for the determination of the consumed power. According to an alternative embodiment, a pressure value is utilized which is characteristic of the hydraulic component. According to yet another alternative embodiment, the pressure value is changed depending upon the operational application. In addition, an estimated average value can be utilized for several different hydraulic components or operational applications.

A second aim of the invention is to achieve a device for controlling a vehicle that solves the problem of the engine cutting out and that makes possible more cost-effective operation and/or a more cost-effective system/vehicle.

This aim is achieved by a device for controlling a vehicle, which device comprises a hydraulic system comprising at least one pump which is arranged to supply at least a first hydraulic component with hydraulic oil, the pump being connected to the vehicle's engine for driving the pump, the device comprising means for determining the power consumed by the hydraulic system, means for comparing the determined consumed power with a reference value, and means for limiting the maximum available power for the hydraulic system, said power-limiting means consisting of a flow-regulating valve in the hydraulic system.

According to a preferred embodiment of the invention, the device comprises a computer unit which comprises software for said determination of the power consumed by the hydraulic system and said comparison of the determined consumed power with a reference value, and comprises the computer unit being connected to said first flow-regulating valve.

Further preferred embodiments of the invention and associated advantages are apparent from the additional subsidiary claims and the following description.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following, with reference to the embodiments that are illustrated in the enclosed drawings, in which Figure 1 shows schematically a wheel-mounted loader in a side view, Figure 2 shows schematically the drive-line of the wheel-mounted loader, and Figure 3 shows a device for controlling the wheel- mounted loader.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a wheel-mounted loader 1. The body of the wheel-mounted loader 1 comprises a front body section 2 and a rear body section 3, which sections each have a pair of half shafts 12,120. The body sections are connected to each other in such a way that they can pivot. The body sections 2,3 can pivot in relation to each other around an axis by means of two first hydraulic components in the form of hydraulic cylinders 4,5 arranged between the two sections. The hydraulic cylinders 4,5 are thus arranged to turn the wheel-mounted loader 1.

In addition, the wheel-mounted loader 1 has a load-arm unit 6 and a piece of equipment in the form of a shovel 7 fitted on the load-arm unit. The load-arm unit 6 can be raised and lowered relative to the front section 2 of the vehicle by means of two second hydraulic components in the form of two hydraulic cylinders 8,9, each of which is connected at one end to the front vehicle section 2 and at the other end to the load-arm unit 6. The shovel 7 can be tilted relative to the load-arm unit 6 by means of a third hydraulic component

in the form of a hydraulic cylinder 10, which is connected at one end to the front vehicle section 2 and at the other end to the shovel 7 via a link-arm system.

Figure 2 shows in a simplified sketch the drive line of the wheel-mounted loader 1. The vehicle 1 has a diesel engine 11, which is arranged to drive the front pair of half shafts 120 and the rear pair of half shafts 12 via a hydrodynamic torque converter 27, a gearbox 32 and a differential 33. The engine 11 also drives at least one pump 15 for supplying a hydraulic system.

Figure 3 illustrates a device 13 for controlling the wheel-mounted loader 1. The solid lines show the hydraulic hoses and the broken lines show the paths for 'electrical signals. The control device 13 comprises the hydraulic system 14 comprising the pump 15 which is arranged to supply said hydraulic components 4,5, 8,9, 10 with hydraulic oil.

The hydraulic system 14 comprises a first flow- regulating valve 16 in the form of a control valve, which is arranged to regulate the control cylinders 4,5. The hydraulic system 14 comprises in addition a second flow-regulating valve 17 in the form of a loading valve, which is arranged to regulate the lifting and tilting cylinders 8,9, 10.

The control device 13 comprises a computer unit 18 which is connected to said first and second valves 16,17 for regulating/moving these. The control device comprises in addition a set of manually movable control means 19, in the form of levers, which are arranged to be accessible to the driver inside the cab of the wheel-mounted loader 1. The movable control means 19 are connected to the computer unit 18.

The hydraulic system 14 is of the load-detecting type, which means that the pump 15 only supplies oil when it is required and where it is required. This means that more engine power remains for driving the half shafts.

In addition, this leads to a reduced fuel consumption.

The pump 15 detects the pressure from the hydraulic cylinders via a shuttle valve 20 and via the valve that is activated. The pump thereafter sets a pressure that is a specific number of bar higher than the pressure of the cylinders. The number of bar by which the pressure is higher is determined by the constant pressure drop across the valve in question. Accordingly, there is an oil flow out to the cylinders, the level of which depends on by how much the activated control valve is adjusted.

The hydraulic system 14 comprises, in addition, a prioritizing means 21, which is arranged to ensure that the steering has a higher priority than the loading, that is to say if the control cylinders 4,5 and the loading/tilting cylinders 8,9, 10 are used simultaneously, it is the control cylinders that have priority. The prioritization is carried out completely hydraulically.

An additional valve 22 is shown in Figure 3. This valve 22 is intended to regulate the supply of hydraulic oil to a hydraulic unit for a piece of equipment and is connected hydraulically to the pump 15 via the prioritizing valve 21 and electrically to the computer unit 18. In the description above, the piece of equipment has been a shovel 7, but it can however consist, for example, of a fork or gripping arms. Said hydraulic unit for the piece of equipment can, for example, consist of an operating cylinder for the gripping arms for moving these in relation to each other or an operating cylinder for a fork for moving the two prongs in relation to each other. The

prioritizing valve is also arranged to give the steering hydraulics priority over the hydraulics for the piece of equipment in question.

As mentioned above, the engine 11 drives both the pairs of half shafts 12,120 and the pump or pumps 15 for the hydraulic system 14. In certain operating situations, it is desirable to limit the maximum available power for the hydraulic system 14 so that sufficient power is available for driving the half shafts 12,120. The computer unit 18 therefore comprises software for determining or estimating the instantaneous power consumed by the hydraulic system 14 and for comparison of the determined consumed power with a reference value. If the detected consumed power exceeds the reference value, the maximum available power for the hydraulic system is limited by the maximum available movement of at least one of said flow-regulating valves 16,17 being limited.

The reference value for the hydraulic power corresponds to the engine's speed being able to be increased, or at least to the engine not cutting out in the event of attempted acceleration. In other words, it is ensured by the reference value for the hydraulic power that the engine can provide sufficient power to the half shafts.

Said reference value can also include a set of reference values, which, for example, defines a curve for power consumption dependent upon the engine speed.

The hydraulic power is obtained by the pressure being multiplied by the flow. According to a first embodiment, it is assumed that the machine operates on average with a particular pressure. This means that it is sufficient for the computer unit 18 to keep track of which flows go to different functions. As mentioned above, the machine has a load-detecting system, which means that the pressure drop across a valve is in

principle constant. This means that the flow is only dependent upon the movement of the lever, which the computer unit 18 receives as an input signal from the control levers 19. The computer unit 18 thus sends out suitably processed signals to the flow-regulating valve.

In particular at lower engine speeds, the pump capacity is insufficient for satisfying the functions that are activated. The control device 13 comprises means 23 for detecting the speed of the engine 11. The computer unit 18 can determine the flow from the pump 15 by means of the detected engine speed which, together with the pump's predefined maximum displacement, gives the pump speed, and by the movement of the lever.

The pressure value is set to a particular average pressure, which can be set differently for different functions or the same for all functions.

Thereafter the computer unit 18 calculates the consumed hydraulic power by multiplying the determined flow (which is determined by the movement of the lever, if necessary reduced due to the pump capacity) by the pressure value.

The computer unit 18 thereafter limits the output signals to the valves 16,17, 22 so that the sum of all the calculated hydraulic power does not exceed a specific level. The specific level is dependent upon the engine speed produced by the engine, which the computer receives as an input signal from the detecting means 23.

A plurality of further developments of the embodiment described above are described below, with regard to the determination of the hydraulic power, which can be used

either as a supplement or an alternative to the methods described above.

According to a first further development, the device comprises one or more pressure sensors 24 in the hydraulic system for measuring a pressure value that is then used for the calculation of the consumed hydraulic power. The pressure sensor 24 is therefore connected to the computer unit 18. The pressure sensor 24 is located, for example, at the outlet of the pump. If several independent pumps are used, then sensors are located at each pump. The sensor 24 can alternatively be located out in the functions, for example in a hydraulic cylinder.

According to a second further development, for certain functions, for example those that are not controlled electrically, a position sensor 25 is located on a cylinder or other mechanically movable part. The position sensor 25 is connected to the computer unit 18. The computer unit 18 thus receives the position of the function as an input signal and calculates the speed and thereby also the flow for these functions.

According to a third further development, the device comprises means 26 for detecting the power consumption to the pair of half shafts 12. This means 26 comprises, for example, sensors for detecting the respective speeds of the incoming shaft and outgoing shaft of the torque converter 27. The detecting means 26 is connected to the computer unit 18. By this means, the maximum power consumption of the hydraulic system is determined, also depending upon the instantaneous power consumption of the transmission.

According to a fourth further development, the device comprises means 28 for detecting the position of a throttle control fitted in the vehicle, in the form of

an accelerator pedal. The detecting means 28 is connected to the computer unit 18. Using this, the computer unit 18 records whether the driver wants to remain at the current instantaneous engine speed or whether the driver depresses the accelerator pedal further with the aim of increasing the engine speed.

The power limitation for the hydraulics can thereby be increased if the driver, for example, depresses the accelerator pedal to the floor, which means that the engine increases its speed more quickly.

According to a fifth further development, the device comprises means 29 for measuring the speed of the vehicle. The speed measuring means 29 is connected to the computer unit 18. The power limitation for the hydraulics can thereby also be made to be dependent upon the speed of the machine, which means that the power limitation can be made indirectly dependent upon the type of handling.

According to a sixth further development, the device comprises means 30 for measuring the temperature of the hydraulic oil. The temperature measuring means 30 is connected to the computer unit 18. The hydraulic oil temperature is used with the aim of obtaining greater precision when the flow is determined, and accordingly when the hydraulic power consumption is calculated.

According to a seventh further development, the device comprises means 31 for measuring the temperature of the transmission oil. The temperature measuring means 31 is connected to the computer unit 18. The transmission oil temperature is used with the aim of obtaining greater precision when calculating the power consumption of the torque converter.

The vehicle's computer unit 18 comprises a memory, which in turn comprises a computer program product with

computer program segments, or program code, for carrying out all the steps according to the method described above when the program is run. The computer program product can be the actual software for performing the method or a piece of hardware on which the software is stored, that is a disk or the like.

By the expression hydraulic component is meant not only a hydraulic cylinder for straight-line movement, but also, for example, a hydraulic motor for rotating movements.

The invention is not to be regarded as being limited to the embodiments described above, a number of further variants and modifications being possible within the framework of the following claims. For example, it would be possible for the vehicle only to drive one pair of half shafts, either temporarily or permanently.

In addition, vehicles with more than two pairs of half shafts are included, for example three pairs of half shafts, which is the case with a dumper, that is to say an articulated vehicle.

According to an alternative to the embodiments described above, certain functions can be controlled directly mechanically or hydraulically by the levers, without going via the computer unit.

There are various alternatives for how one or more functions are to be limited. It will not always be desirable to limit certain functions or else these can be limited to a certain extent. Such a function is, for example, steering of the machine. The computer thus prioritizes certain functions initially. Thereafter, secondary prioritizations can be carried out and finally the remaining functions can be limited by a certain percentage in relation to the maximum flow or also by a certain percentage in relation to the movement of the lever that the driver is making at that instant.