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Title:
CONTROL DEVICE FOR A MOTOR FOR A HYDRAULIC SYSTEM
Document Type and Number:
WIPO Patent Application WO/2019/034317
Kind Code:
A1
Abstract:
A control device (100) for a motor (210) for a hydraulic system (200) is provided. The control device comprises at least one first sensor (120, 130) for measuring a pump pressure of the hydraulic system and a load pressure of 5 the hydraulic system, and at least on second sensor (135) for measuring at least one operating condition of at least one of the motor and a pump (220) of the hydraulic system. The control unit further comprises a processing unit (110) configured to control an rpm setting for the motor. The processing unit may control the rpm based on a difference in pressure, Δp, between the 10 pump pressure and the load pressure measured by the at least one first sensor, a predetermined preferred difference, Δp_pref, in pressure between the pump pressure and the load pressure, and at least one of the at least one operating condition.

Inventors:
SUNDIN, Mats (Hudiksvall, 824 01, SE)
WEISBJERG, Sigvard (Hudiksvall, 824 01, SE)
Application Number:
EP2018/067667
Publication Date:
February 21, 2019
Filing Date:
June 29, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SUNFAB HYDRAULICS AB (Varvsgatan 2-4, Hudiksvall, 824 01, SE)
International Classes:
F04B17/03; F04B17/05; F04B23/00; F04B49/06; F04B49/08; F04B49/20
Domestic Patent References:
WO2014189445A12014-11-27
Foreign References:
US20140046552A12014-02-13
EP2081788B12011-08-31
US6748739B12004-06-15
US20100058752A12010-03-11
EP0796952A11997-09-24
US20100264885A12010-10-21
Other References:
None
Attorney, Agent or Firm:
AWA SWEDEN AB (Box104 30 Stockholm, 104 30, SE)
Download PDF:
Claims:
CLAIMS

1 . A control device (100) for a motor (210) for a hydraulic system (200), the motor being adapted for driving a vehicle, the control device comprising: at least one first sensor (120, 130) for measuring a pump pressure of the hydraulic system and a load pressure of the hydraulic system;

at least one second sensor (135) for measuring at least one operating condition of at least one of the motor and a pump (220) of the hydraulic system;

a processing unit (1 10) configured to control a revolutions per minute setting, rpm, for the motor based on:

a difference in pressure, Δρ, between the pump pressure and the load pressure measured by the at least one first sensor;

a predetermined preferred difference, Ap_pref, in pressure between the pump pressure and the load pressure; and

at least one of the at least one operating condition measured by the at least one second sensor. 2. A control device according to claim 1 , wherein the at least one operating condition is at least one of the rpm setting for the motor, a change in the rpm setting for the motor, an operation of a motor throttle, a motor sound level, a temperature of the motor, a temperature of a motor oil, a motor oil pressure, a motor oil viscosity, a temperature of a hydraulic oil, a pump sound level, a temperature of the pump, a pump oil pressure, and a pump oil viscosity.

3. A control device according to claim 1 or 2, wherein the processing unit is further configured to control the rpm setting for the motor based on an ambient temperature.

4. A control device according to any preceding claim, wherein the control device further comprises at least one sensor configured to detect a vibration frequency of at least one of the motor and the pump,

and wherein the processing unit is further configured to control the rpm setting for the motor based on the detected vibration frequency.

5. A control device according to claim 4, wherein the processing unit is further configured to control the rpm setting for the motor based on a predetermined resonance frequency of at least one of the motor and the pump.

6. A control device according to any preceding claim, wherein the processing unit is further configured to:

control an electrical bypass of the hydraulic system for controlling a flow of the hydraulic system, and

control the rpm setting for the motor based on a state of the electrical bypass.

7. The control device according to any preceding claim, wherein the control device further comprises an interface (140), and wherein the processing unit is coupled to the interface and configured to control the rpm setting for the motor based on information received from the interface.

8. The control device according to claim 7, wherein the interface is configured to receive information via a wireless communication link.

9. The control device according to claim 7 or 8, wherein the interface is configured to receive information from an operator via the interface for determining the rpm setting for the motor.

10. The control device according to any preceding claim, wherein the processing unit comprises a microcontroller.

1 1 . A system comprising:

a vehicle motor (210, 310, 410);

a hydraulic system (200, 300) driven by the vehicle motor;

an electrical bypass (205, 305); and

a control device according to any preceding claim;

wherein the control device is communicatively coupled to the vehicle motor and configured to control the rpm setting for the vehicle motor.

12. The system according to claim 1 1 , wherein the vehicle motor comprises a combustion engine. 13. The system according to claim 12, wherein the combustion engine is a diesel engine.

14. The system according to any one of claims 1 1 -13, wherein the vehicle motor comprises an electric motor.

15. The system according to any one of claims 1 1 -14, wherein the vehicle motor is a hybrid motor.

16. The system according to any one of claims 1 1 -15, wherein the processing unit is configured to send a preferred rpm setting for the vehicle motor to the vehicle motor via a communication means, and

the vehicle motor is configured to adjust the rpm setting for the vehicle motor to the preferred rpm setting for the vehicle motor sent by the

processing unit.

17. The system according to any one of claims 1 1 -16, further comprising an axial piston pump coupled to the vehicle motor.

18. The system according to claim 17, wherein the axial piston pump has a fixed displacement.

19. The system according to any one of claims 1 1 -18, wherein the control device is communicatively coupled to the vehicle motor via a CAN bus.

20. A vehicle (400) comprising a system according to any one of claims

Description:
CONTROL DEVICE FOR A MOTOR FOR A HYDRAULIC SYSTEM

Field of the invention

The present invention generally relates to control devices or units for a motor driving a hydraulic system.

Background

Hydraulic systems are used in various mobile applications, such as in cranes, on trucks or in forestry. It is common that many of the hydraulic systems have pumps with a fixed displacement, but it is becoming more and more popular to use hydraulic systems with a variable displacement. It will be appreciated that a variable displacement allows for a better control of the flow in the system, and thereby increases the efficiency.

However, there are some drawbacks with the use of variable displacement pumps. For example, systems having variable displacement pumps may not be as robust as systems having a fixed displacement.

Further, variable displacement pumps are often more expensive than pumps with a fixed displacement.

On the other hand, hydraulic systems with a fixed displacement pump may be less energy efficient than a system with a variable displacement, as there is a relatively high flow in the system even if it is not needed.

Hence, there is a need for providing improved hydraulic systems.

Summary

An object of the present disclosure is therefore to mitigate at least some of the drawbacks described above. To achieve this, a control device for a motor for a hydraulic system is provided, wherein the motor is adapted for driving a vehicle. Further embodiments are defined in the dependent claims.

Hence, according to a first aspect, a control device for a motor for a hydraulic system is provided. The motor is further adapted to drive a vehicle. The control device comprises at least one first sensor for measuring a pump pressure of the hydraulic system and a load pressure of the hydraulic system. The control device further comprises at least one second sensor for measuring at least one operating condition of at least one of the motor and a pump of the hydraulic system. Furthermore, the control device comprises a processing unit configured to control a revolutions per minute setting, rpm, for the motor. The processing unit may control the rpm based on a difference in pressure between the pump pressure and the load pressure measured by the at least one first sensor, a predetermined preferred difference in pressure between the pump pressure and the load pressure, and at least one of the at least one operating condition measured by the at least one second sensor.

In this way, the flow in the system created by the pump may be adjusted or controlled via the control device controlling the rpm setting for the motor. With this control device, fixed displacement pumps may be used while avoiding having a high flow in the system when not needed, which may require a more robust system in comparison with a system with a variable displacement pump.

This is based on the realization that the required flow for a hydraulic system may be controlled based on a difference between a pump pressure and a load pressure and one or more operating conditions of the motor and/or a pump of the hydraulic system. In load sensing systems, there is a difference between the pump pressure and the load pressure, as measured after the hydraulic system. By monitoring the difference in pressure between a pump pressure and a load pressure and comparing that with a predetermined preferred pressure difference, the flow may be adjusted accordingly. For example, if the difference calculated is lower than the preferred pressure difference, the control device may increase the rpm setting for the motor, and thereby increase the rpm for the pump, and thereby the flow in the system, which may lead to a higher difference in pressure. Furthermore, the control device may control the rpm setting for the motor based on one or more operating conditions of the motor and/or a pump of the hydraulic system. In this way, more robust systems with pumps with a fixed displacement may be used in a more energy-efficient way. This may also advantageously be used with variable displacement pumps.

With this control device according to the present invention, the rpm setting for the motor, and thereby in a corresponding manner also for the pump, may be determined based on the flow currently needed in the system. The control device may hereby increase the rpm when a higher flow is needed, and decrease the rpm when a lower flow is needed. In this way, the flow generated by the motor is adapted to the need of the system, which may lead to lower energy losses and allow for a higher efficiency. Furthermore, the control of the rpm setting or the motor is even further improved by performing the control based on one or more motor and/or pump conditions measured by the second sensor(s). Hence, dependent on one or more operating conditions of the motor and/or a pump of the hydraulic system such as the rpm of the motor, the motor and/or pump sound level, the motor and/or pump

temperature, etc., the rpm setting for the motor can be controlled to even further improve the efficiency, robustness and/or energy conservation of hydraulic systems.

With previous fixed displacement systems, the flow of the system is constant, and the rpm of the motor driving the system is constant. This may lead to energy losses as the flow in the system will not be decreased when the system is subjected to a relatively low load or no load. Similarly, the flow in the system will not be increased when more power is needed. In the previous fixed displacement systems, to avoid too high energy losses, the pump and the engine may not be used at a maximum capacity, but rather at a slightly lower rpm sufficient to perform what is needed and low enough to avoid excessive energy losses. As the present control device may increase the rpm of the pump when needed, the system may provide more hydraulic power when needed, in comparison with previous fixed displacement systems, allowing for faster movements of the hydraulic system.

The control device of the present invention is advantageous in that it may be installed with minimal changes to already existing hydraulic systems with fixed displacement pumps. In this way, the control device is relatively easy to install in or together with existing systems, which may lead to lower installation or upgrade costs. Further, as the motor is adapted to drive the vehicle, an installation on a vehicle may utilize the already existing motor, instead of using another motor for the hydraulic system. This also allows for lower installation and/or upgrade costs.

Further, varying the rpm of the motor may decrease the noise from the motor. This may contribute to a better working environment for an operator of the application of the hydraulic system.

By the term "motor" it may be meant any motor or engine suitable for driving a hydraulic system, e.g. an electric motor (electric engine), a combustion engine (for example powered by gasoline of diesel), or a hybrid engine. Hence, the motor may be coupled to the hydraulic system. The motor may also be adapted to drive a vehicle.

The term "hydraulic system" may be a load-sensing hydraulic system.

Typically, hydraulic systems comprise at least one pump and at least one hydraulic valve for determining or altering the current flow of a fluid in the hydraulic system, and thereby the pressure, in the system.

By "load pressure" it is meant the pressure as measured on the hydraulic system. For example, the "load pressure" may be the pressure measured on a load sensing connection of the hydraulic system after the hydraulic valve of the hydraulic system.

By "pump pressure" it is meant the pressure created by the pump. More specifically, the "pump pressure" may be construed as the pressure of the hydraulic fluid in the hydraulic system exerted via the pump.

By the phrasing "operating condition of at least one of the motor and a pump of the hydraulic system" it is meant substantially any condition, state, or the like of the motor and/or the pump during their respective operation. For example, one or more of a rpm, a sound level, a temperature, etc., of the motor and/or the pump may constitute (an) operating condition(s) of the motor and/or pump. By "rpm" it is meant a revolutions per minute setting or rate. This may apply either to the pump or to the motor. The rpm sent to the motor by the control device may correspond to the rpm for the pump. For example, the minimal rpm for the pump may correspond to an idle running of the motor.

The at least one first sensor may be any sensor or device capable of measuring or determining a pressure of any of a pump pressure and a load pressure. Analogously, the at least one second sensor may be any sensor or device capable of measuring or determining one or more operating conditions of the motor.

According to an embodiment of the present invention, the at least one operating condition is at least one of the rpm setting for the motor, a change in the rpm setting for the motor, an operation of a motor throttle, a motor sound level, a temperature of the motor, a temperature of the motor oil, a motor oil pressure, a motor oil viscosity, a temperature of the hydraulic oil, a pump sound level, a temperature of the pump, a pump oil pressure, and a pump oil viscosity. Hence, the processing device of the control device may be configured to control the rpm setting for the motor based on one or more of these operating conditions of the motor and/or pump. The present

embodiment is advantageous in that the control device may hereby even further improve the efficiency, robustness and/or energy saving of hydraulic systems.

According to an embodiment of the present invention, the processing unit is further configured to control the rpm setting for the motor based on an ambient temperature. By "ambient temperature", it is meant (the) outdoor temperature. The present embodiment is advantageous in that the control device may even further optimize its control of the rpm setting for the motor based on the ambient temperature to which the motor and/or hydraulic system is exposed. For example, in case of a relatively high ambient temperature, the control device may be configured to set a lower rpm setting for the motor in order to mitigate the risk of a motor breakdown. According to an embodiment of the present invention, the control device may further comprise at least one sensor configured to detect a vibration frequency of the motor and/or the pump, and wherein the processing unit may further be configured to determine the rpm setting for the motor based on the detected vibration frequency.

According to an embodiment of the present invention, the processing unit may further be configured to control the rpm setting for the motor based on a predetermined resonance frequency of the motor and/or the pump.

According to an embodiment of the present invention, the processing unit may be further configured to control an electrical bypass of the hydraulic system for controlling a flow of the hydraulic system, and control the rpm setting for the motor based on a state of the electrical bypass. By "electrical bypass" it may be meant an electrical shunt. The electrical bypass may be any type of bypass for controlling a flow of hydraulic fluid in the hydraulic system. For example, by changing the state of the electrical bypass the pressure may be increased in one portion of the hydraulic system, and be decreased in another portion of the hydraulic system.

By controlling the rpm setting for the motor based on a state of the electrical bypass, the flow of the hydraulic system may be controlled with a combination of the state of the electrical bypass and the rpm setting of the motor. For example, if the pressure of the flow in the hydraulic system is decreasing, instead of only adjusting the rpm of the motor, the control device may control both the rpm setting of the motor and the state of the electrical shunt in combination. In this way, the flow and the pressure in the hydraulic system may be better and faster controlled.

According to an embodiment of the present invention, the processing unit may be further configured to determine the rpm setting for the motor based on a minimum rpm setting for the motor or a maximum rpm setting for the motor. By using a minimum rpm setting or a maximum rpm setting for the motor, the control device may adapt the current rpm setting to the possible rpm settings for the motor, thereby avoiding the motor stopping or overloading the motor.

According to an embodiment of the present invention, the control device may further comprise an interface, and wherein the processing unit may be coupled to the interface and configured to control the rpm setting for the motor based on information received from the interface. In this way, information regarding the system, the motor or other relevant data may be conveyed to the processing unit via the interface, and the control device may use the information to control the rpm setting of the motor. Thereby, the control of the rpm of the motor may be improved even further, which, for example, may lead to an increased energy-efficiency.

According to an embodiment of the present invention, the interface may be configured to receive information via a wireless communication link. It will be appreciated that the use of a wireless link may increase the flexibility and/or operation of the control device.

According to an embodiment of the present invention, the interface may be configured to receive information from an operator via the interface for the rpm setting of the motor. The information may, for example, comprise parameters which the control device may use to set and/or control the rpm setting for the motor, such that the control may be even further improved.

According to an embodiment of the present invention, the processing unit may comprise a microcontroller. Alternatively, the processing unit may comprise a computer.

According to an embodiment of the present invention, the control device may be comprised in a system. The system may further comprise a vehicle motor, a hydraulic system driven by the motor, and an electrical bypass. The control device may be communicatively coupled to the vehicle motor and configured to control the rpm of the vehicle motor. The vehicle motor is adapted to drive a vehicle.

According to an embodiment of the present invention, the vehicle motor comprises a combustion engine. According to an embodiment, the vehicle motor is or comprises a diesel engine, i.e. a combustion engine powered by diesel. As combustion engines and diesel engines are commonly used, the process of installing the control device may be easier as compared to a control device not suitable for a diesel engine, which may lead to a need for switching engines or motors.

According to an embodiment of the present invention, the vehicle motor comprises an electric motor. This allows for a relatively easy process of installation when the vehicle is driven by an electric motor. By using the electric motor of the vehicle, in comparison with using the batteries of the electric motor, the interface between the motor and the hydraulic system may be kept simpler, as one interface may work for several different types of vehicle motors. Further, by using an electric motor in comparison with a combustion engine, the rpm of the motor may be kept relatively low while still delivering enough power to drive the hydraulic pump. This allows for an energy efficient system.

According to an embodiment of the present invention, the vehicle motor is a hybrid motor. The hybrid motor may be a motor comprising an electric motor and a combustion engine, for example, a diesel engine.

According to an embodiment of the present invention, the processing unit is configured to send a preferred rpm to the motor via a communication means, and the motor is configured to adjust the rpm of the vehicle motor to the preferred rpm sent by the processing unit.

According to an embodiment of the present invention, comprising an axial piston pump coupled to the vehicle motor.

According to an embodiment of the present invention, the axial piston pump has a fixed displacement. By using the control device in a system which has a fixed displacement pump, the system may be more energy efficient in comparison to previous systems.

According to an embodiment of the present invention, the axial piston pump has a variable displacement. According to an embodiment of the present invention, the control device is communicatively coupled to the vehicle motor via a CAN bus. As CAN-buses are commonly used for communications between systems or parts of systems on, for example, trucks or forestries, it may be beneficial that the control device may communicate over a CAN-bus as the need for a separate communication system is decreased. Further, having the control device coupled to a CAN-bus increases the ease of installation as CAN-buses are commonly existing on vehicles.

According to an embodiment of the present invention, the system is comprised in a vehicle.

Further objectives of, features of, and advantages with the present inventive concept will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present inventive concept can be combined to create embodiments other than those described in the following.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present inventive concept, with reference to the appended drawings. In the drawings like reference numeral will be used of like elements unless stated otherwise. Figure 1 shows a schematic view of a control device in a system with a fixed displacement pump;

Figure 2 shows a schematic view of a control device in a system with a variable displacement pump;

Figure 3 illustrates a control device in a system arranged in a vehicle. All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted. Detailed description

Detailed embodiments of the present inventive concept will now be described with reference to the drawings. The present inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the inventive concept to those skilled in the art.

Embodiments of the present inventive concept generally relate to a control device 100 for a motor 210 driving a pump 220 in a hydraulic system 200, now described with reference to Figure 1 . Hydraulic systems 200 of this kind generally comprise a hydraulic valve 230, a pump 220 for providing a flow to the hydraulic valve 230 and a control device 100. Here, the motor 210 is coupled to the hydraulic system 200, and the control device 100 is coupled to the hydraulic system 200 and to the motor 210.

The motor 210 is configured to drive the pump 220 for the hydraulic valve 230. The motor 210 may, for example, be a vehicle motor, such as an electric motor, a combustion engine, a diesel engine, a hybrid motor, or another motor suitable for driving the pump 220. The motor 210 may also be adapted to drive the vehicle. In case of a hybrid motor, any one of the motors in the hybrid motor may be used for driving the pump 220.

The pump 220 is connected to the hydraulic valve 230, and the pump

220 may create a flow 270 from the pump 220 to the hydraulic valve 230. In this example, the pump 220 is an axial piston pump and has a fixed

displacement. The pump 220 is driven by the motor 210.

The hydraulic valve 230 is in this example a load sensing hydraulic valve and has an inlet, into which the pump 220 creates a flow, and a load sensing connection 231 which is configured to indicate the highest load pressure in the system 200. The hydraulic valve 230 is connected to a tank 250. The hydraulic system 200 may be of a closed-center type.

The control device 100 comprises at least one first sensor 120, 130. The pump 220 creates a flow 270, i.e. a pressure in the hydraulic fluid, in the hydraulic system. In this example, the at least one first sensor 120, 130 comprises a pressure sensor 120 for measuring a pump pressure, i.e. the pressure on the connection 221 between the pump and the hydraulic valve 230, and pressure sensor 130 for measuring a load pressure, i.e. the pressure on the load-sensing connection 231 . The first pressure sensors 120, 130 are located at different positons of the hydraulic system 200.

The hydraulic system 200 may comprise at least one electrical bypass 205 or electrical shunt 205 for controlling a flow of the hydraulic system 200. The electrical bypass may be connected to the control device 100, and the control device 100 may be adapted to control the function of the electrical bypass. In this way, the control device 100 may control a flow of the hydraulic system 200 and thereby control the flow of the hydraulic system 200. By controlling the electrical bypass 205, the amount and direction of the flow 270 through the hydraulic system 200 is controlled.

The control device 100 further comprises at least one second sensor 135a, 135b. The second sensor(s) 135a, 135b is (are) configured to measure at least one operating condition of the motor 210 and/or the pump 220.

According to the example of Figure 1 , a second sensor 135a is coupled to the motor 210 and a second sensor 135b is coupled to the pump 220.

The control device 100 further comprises an interface 140 which is configured to receive data from an input means 150. The input means 150 may, for example, be a touch display, and may be used by an operator to enter configuration data based on which the processing unit may determine a rpm setting for the motor 210.

The control device 100 further comprises a processing unit 1 10. The processing unit 1 10 may, for example comprise a microcontroller, a single- board computer or a general purpose computer. The processing unit 1 10 may comprise a PID-regulator. The PID- regulator creates a preferred rpm that is sent to the motor 210. The PID- generator has a maximum rpm limit, which the preferred rpm may not exceed.

The processing unit 1 10 is configured to receive or determine a difference in pressure, Δρ, between the pump pressure as measured by the pressure sensor 120, and the load pressure as measured by the pressure sensor 130. The processing unit 1 10 is further configured to compare the Δρ with a preferred difference in pressure, Ap_pref. The processing unit 1 10 may, based on the difference, and on the one or more operating conditions of the motor 210 and/or the pump 220, determine a rpm setting for the motor 210 to either decrease, increase, or keep the rpm on the same level as before.

For example, if the Δρ is lower than Ap_pref, the processing unit 1 10 may determine that the rpm should increase. When the rpm increases the pressure created by the pump 220 increases, and if the load is constant, the load pressure as measure by pressure sensor 130 increases. In this way, when the load on the hydraulic system 200 is increasing, i.e. there is a need for more pressure or flow to operate it, the Δρ will decrease, causing the processing unit 1 10 to determine that a higher rpm is needed. In the same way, when the load on the hydraulic system 230 is decreasing, i.e. the need for a pressure or flow for operating the hydraulic system decreases, the Δρ will increase, causing the processing unit 1 10 to determine that a lower rpm is needed. Furthermore, the processing unit 100 may determine that the rpm of the motor should increase or decrease dependent on one or more operating conditions of the motor 210 and/or pump 220. For example, the processing unit 100 may control the rpm based on a sound level, temperature, oil pressure, oil viscosity, etc., of the motor 210 and/or pump 220.

Further, the control unit 100 may control a state of an electrical bypass 205 in the hydraulic valve 230, and control the rpm setting based on the state of the electrical bypass 205. The determined rpm of the motor 210 is communicated by the processing unit 1 10 to the motor 210. The processing unit 1 10 and the motor 210 may be communicatively coupled 240, for example via a CAN-bus, a control device for the motor 210, or they may be directly coupled.

The motor 210 may, based on the preferred rpm communicated by the processing unit 1 10, increase or decrease the rpm for the pump 220.

The processing unit 1 10 may base the determination of the preferred rpm on further parameters, such as a minimum rpm setting for the motor 210, a maximum rpm setting for the motor 210, a model identifier for the hydraulic system 200 or the motor 210, or another parameter which may be relevant for determining the rpm setting for the motor 210. The processing unit 1 10 may receive the parameters via an interface 140. The interface may, for example, be accessible via Bluetooth or USB. An input means 150 may be coupled to the processing unit 1 10 via the interface. The input means 150 may be comprised in the control device 100. The input means 150 may, for example, be a touch display, a smartphone, a computer, or another device with which an operation may interact to set the parameters.

The parameters received by the processing unit 1 10 may further affect the communications message sent by the processing unit 1 10 to the motor 210. For example, the parameters may affect which protocol the processing unit 1 10 uses to communicate with the motor 210.

The control device 100 may also be applied in a system 300 with a variable displacement pump, and will now be described with reference to Figure 2. The system 300 comprises a control device 100, a motor 310, a pump 320 and a hydraulic valve 330. The control device 100, the motor 310 and the pump 320 has the same features as the corresponding devices described with reference to Figure 1 .

The hydraulic system 300 comprises a load-sensing hydraulic valve 330 and a pump 320. A load sensing connection 331 is connected to the pump 320. The pump 320 may be an axial piston pump. The pump 320 is connected to the motor 310. The motor 310 may be a diesel engine or another type of motor.

In this example, the rpm for the pump 320 is affected by both the load- sensing connection 331 and the rpm determined by the motor 310. If the load pressure decreases, it will be sensed by a pressure sensor 130 and communicated to the processing unit 1 10. The pump 320 receives the load pressure via the load-sensing connection 331 and may adjust the

displacement. The rpm of the pump 320 is affected by the motor 310 in the same way as described with reference to Figure 1 .

A vehicle 400 comprising a hydraulic system as described above is now described with reference to Figure 3. Figure 3 shows a schematic view of a hydraulic system comprised in a vehicle 400. The vehicle 400 may, for example, be a forestry or a truck, but also other applications are envisaged. The vehicle 400 comprises a hydraulic driven crane 450 arranged on the vehicle 400. A cab 480 of the vehicle 400 is arranged at the crane 450.

Actuating levers 460 and a control panel 490 for allowing an operator to operate the crane 450 are located in the cab 480.

The vehicle 400 further comprises a motor 410, for example a diesel engine, another combustion engine, an electric motor or a hybrid motor. The vehicle 400 further comprises a hydraulic system for driving the crane 450. The hydraulic system comprises a control device 440, a valve 470, and a pump 420.

The motor 410, or a sub-motor of the motor 410 in case of a hybrid motor, drives the pump 420 which creates a pressure in the hydraulic system. The pressure is used to control the crane 450 via hydraulic actuators.

The control device 440, or parts thereof, may be arranged in the cab 430. It will be appreciated that the control device 440 or parts thereof may be arranged at any location in or on the vehicle 400. The control device 440 may comprise a display arranged so that an operator may enter data to the control device 440. The control device 440 is connected to the valve 470. A part of the control device 440, for example a sensor (not shown in Figure 3), may be arranged at the valve 470 for measuring pressure. The control device 440 may comprise a processing unit (not shown in Figure 3) comprised in the control device 440 arranged in the cab 430 of the vehicle 400. The processing unit may receive the pressure measurements from the sensor. The control device 440 is connected to the motor 410 and may send a message to the motor 410 indicating a preferred rpm. The motor 410 may affect the rpm accordingly.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements of steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot me used to advantage.