Method and controller for operating hydraulic system, and motor vehicle having hydraulic system

Abstract

The invention relates to a method and a controller for operating a hydraulic system and a motor vehicle with the hydraulic system. The hydraulic system has a hydraulic pump (10), which is driven by an electric motor (11), for drawing in hydraulic oil from an oil reservoir (6) and for supplying the hydraulic oil to at least one component (8) that needs to be cooled and / or lubricated by the hydraulic oil, depending on the temperature of the hydraulic oil and on the actual current of the electric motor (11) driving the hydraulic pump (10) and / or on the actual rotational speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump, it is ascertained whether a sufficiently high oil supply to the at least one component (8) requiring cooling and / or lubrication has been ensured.

Description

Technical Field

[0001] The invention relates to a method and a control unit for operating a hydraulic system and to a motor vehicle having a hydraulic system. Background Art

[0002] Motor vehicles have a large number of components that must be supplied with cooling fluid for cooling and / or lubrication. In motor vehicles designed as electric vehicles or hybrid vehicles, these components include electric machines, which can be supplied with hydraulic oil as cooling fluid for cooling, for example. For this purpose, the respective components to be cooled and / or lubricated are connected to a hydraulic system. The hydraulic system of the motor vehicle, to which the components to be cooled and / or lubricated by hydraulic oil are connected, has a hydraulic pump, which draws hydraulic oil from an oil reservoir and supplies it to the components to be cooled and / or lubricated by hydraulic oil, respectively. The hydraulic pump is operated by an electric motor.

[0003] Leaks may form in the area of ​​the hydraulic system, which can lead to oil losses. If there is no longer enough hydraulic oil in the hydraulic system, this will lead to a drop in the system pressure in the hydraulic system, which in extreme cases will lead to dry running of the hydraulic pump. This makes it impossible to ensure sufficient cooling and / or lubrication of the respective components that need cooling and / or lubrication. It is also possible that in production, in particular the plugs at the hydraulic lines are not removed, so that a sufficiently high oil supply to the components that need lubrication and / or cooling cannot be ensured afterwards. For example, in the event of production errors, such as the failure to perform drilling in the hydraulic system or the failure of drilling, or in the presence of foreign particles in the hydraulic system, it is also possible that a sufficiently high oil supply to the components that need lubrication and / or cooling cannot be ensured. There is a need to reliably check whether a sufficiently high oil supply to at least one component that needs cooling and / or lubrication can be ensured using a simple mechanism, more precisely without the need for a level sensor or oil pressure sensor in the oil storage container.

[0004] DE 10 2017 210 885 A1 discloses a method for detecting dry-running of a pump system. A dry-running check step is activated as a function of a pump characteristic variable and as a function of a timer. Summary of the invention

[0005] Based on this, the object of the present invention is to provide a novel method and a control unit for operating a hydraulic system and a motor vehicle having a hydraulic system.

[0006] This object is achieved by a method according to claim 1 , a control unit according to claim 14 and a motor vehicle according to claim 15 .

[0007] According to the invention, it is determined, depending on the temperature of the hydraulic oil and on the actual current of the electric motor driving the hydraulic pump and / or the actual rotational speed of the hydraulic pump or of the electric motor driving the hydraulic pump, whether a sufficiently high oil supply is ensured for at least one component requiring cooling and / or lubrication.

[0008] The invention proposes to use the temperature of the hydraulic oil to determine whether a sufficiently high oil supply is ensured for at least one component that requires cooling or lubrication. In this case, not only the temperature of the hydraulic oil but also the actual current of the electric motor driving the hydraulic pump and / or the actual rotational speed of the hydraulic pump or of the electric motor driving the hydraulic pump are taken into account.

[0009] The present invention is based on the recognition that an actual current of an electric motor driving a hydraulic pump and / or an actual rotational speed of the hydraulic pump or of the electric motor driving the hydraulic pump can advantageously be used, in a temperature-dependent manner, to determine whether a sufficiently high oil supply is ensured for at least one component requiring cooling and / or lubrication.

[0010] Therefore, depending on the temperature of the hydraulic oil, either the actual current of the electric motor driving the hydraulic pump or the actual speed of the hydraulic pump or the electric motor driving the hydraulic pump is better suitable for the above-mentioned determination. In addition, depending on the temperature of the hydraulic oil, both the actual current of the electric motor driving the hydraulic pump and the actual speed of the hydraulic pump or the electric motor driving the hydraulic pump can also be used to determine whether a sufficiently high oil supply is ensured for at least one component that needs to be cooled and / or lubricated.

[0011] With the invention it is possible to monitor the ensuring of a sufficiently high oil supply, depending on the temperature of the hydraulic oil, based on already existing measured variables, namely the actual current of the electric motor driving the hydraulic pump and / or the actual rotational speed of the hydraulic pump or of the electric motor driving the hydraulic pump. Thus, an oil level sensor in the region of the oil reservoir or an oil pressure sensor in the hydraulic system can be omitted. Although the invention can be used particularly advantageously in hydraulic systems of motor vehicles, it can also be used in other hydraulic systems.

[0012] Preferably, when the temperature of the hydraulic oil is greater than a first temperature limit value, it is determined whether a sufficiently high oil supply to at least one component requiring cooling and / or lubrication is ensured depending on the actual current of the electric motor driving the hydraulic pump. In the case of a relatively high temperature of the hydraulic oil, it is determined whether a sufficiently high oil supply is ensured based on the temperature of the hydraulic oil and the actual current of the electric motor driving the hydraulic pump. This is based on the recognition that, in the case of a relatively high oil temperature, the current of the electric motor driving the hydraulic pump is particularly suitable for determining whether the hydraulic pump provides sufficient oil.

[0013] Preferably, when the temperature of the hydraulic oil is less than the second temperature limit value, it is determined whether a sufficiently high oil supply to at least one component requiring cooling and / or lubrication is ensured based on the actual rotational speed of the hydraulic pump or the electric motor driving the hydraulic pump. In the case of a relatively low temperature of the hydraulic oil, it is determined whether a sufficiently high oil supply is ensured based on the actual rotational speed of the hydraulic pump or the electric motor driving the hydraulic pump. This is based on the recognition that, in the case of a low temperature of the hydraulic oil, the actual rotational speed is more suitable than the actual current for determining whether a sufficiently high oil supply is ensured.

[0014] The first temperature limit value and the second temperature limit value may be identical. If the first temperature limit value and the second temperature limit value deviate from one another and if the temperature of the hydraulic oil is less than the first temperature limit value and greater than the second temperature limit value, it is preferably determined based on the actual current of the hydraulic pump and also based on the actual rotational speed of the hydraulic pump or of the electric motor driving the hydraulic pump whether a sufficiently high oil supply is ensured for at least one component to be cooled and / or lubricated. According to this refinement of the invention, when the oil temperature is in an intermediate temperature range, i.e. less than the first temperature value but greater than the second temperature limit value, a sufficiently high oil supply can be determined based on the actual current and based on the actual rotational speed, preferably for a plausibility check. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Preferred improvements are derived from the dependent claims and the following description. Embodiments of the invention are explained in more detail in conjunction with the accompanying drawings, but are not limited thereto. Among them:

[0016] Figure 1 A simplified diagram of the drive train of a motor vehicle is shown;

[0017] Figure 2 A simplified diagram of the hydraulic system is shown;

[0018] Figure 3 shows a first diagram for explaining the present invention; and

[0019] Figure 4 A second diagram for explaining the present invention is shown. DETAILED DESCRIPTION

[0020] Figure 1 A simplified diagram of a drive train for a motor vehicle is shown very schematically. Figure 1 The drive train of the invention comprises a drive unit 1 and a transmission device 3 connected between the drive unit 1 and a driven end 2. The drive unit 1 may be an electric motor. Figure 1 Also shown are a motor controller 4 for controlling and / or regulating the operation of the drive unit 1 and a transmission controller 5 for controlling and / or regulating the operation of the transmission 3. Figure 1The motor controller 4 exchanges data with the drive unit 1, and the transmission controller 5 exchanges data with the transmission 3. In addition, the motor controller 4 and the transmission controller 5 exchange data with each other.

[0021] Motor vehicles have a number of components that must be supplied with hydraulic oil for cooling and / or lubrication. Figure 1 In the drive train, these structural components include a transmission device 3 and a drive unit 1.

[0022] In order to supply hydraulic oil to components which require cooling and / or lubrication, motor vehicles have a hydraulic system in which: Figure 2 A simplified diagram of the hydraulic system is shown. Figure 2 An oil storage container 6, a motor-pump unit 7 consisting of a hydraulic pump 10 and an electric motor 11 driving the hydraulic pump, and a structural component 8 requiring cooling and / or lubrication are shown, wherein the hydraulic pump 10 is used to draw hydraulic oil from the oil storage container 6 and supply it to the structural component 8 requiring cooling and / or lubrication. Figure 2 The component 8 shown in FIG. 8 that needs to be cooled and / or lubricated can be, for example, a drive unit 1 configured as an electric machine 1 or Figure 1 The transmission 3 in the embodiment of the invention. The electric motor 11 and thus the hydraulic pump 10 are designed in this case in a speed-controlled manner.

[0023] Figure 2 Also shown is a controller 9. The controller 9 exchanges data with the components 8 that require cooling and / or lubrication and with the motor-pump unit 7. Figure 1 In the case of a motor vehicle, the controller 9 may be the motor controller 4 or also the transmission controller 5 .

[0024] During operation, oil leakage, i.e. oil loss, may occur. This can result in a lack of sufficient oil in the hydraulic system and a sufficiently high oil supply to the components 8 that require cooling and / or lubrication. In extreme cases, the hydraulic pump 7 may even run dry.

[0025] It is also possible that the oil line of the hydraulic system is blocked due to an assembly or production error, because, for example, the shipping plug has not been removed. In this case, a sufficiently high oil supply to the components that require cooling and / or lubrication cannot be ensured either. The present invention now relates to a method and a control device in order to determine whether a sufficiently high oil supply to at least one component that requires cooling and / or lubrication is ensured by the hydraulic system, more precisely without requiring a fill level sensor for the oil reservoir 6 and without requiring an oil pressure sensor in the hydraulic system.

[0026] According to the invention, it is determined depending on the temperature of the hydraulic oil and on the actual current of the electric motor 11 driving the hydraulic pump 10 and / or on the actual rotational speed of the hydraulic pump 10 or of the electric motor 11 driving the hydraulic pump 10 whether a sufficiently high oil supply is ensured for at least one structural component 8 requiring cooling and / or lubrication.

[0027] The present invention is based on the recognition that, depending on the temperature of the hydraulic oil, either the actual current of the electric motor 11 driving the hydraulic pump 10 or the actual rotational speed of the hydraulic pump 10 or of the electric motor 11 driving the hydraulic pump or both actual variables (i.e. the actual current and the actual rotational speed) are particularly suitable for determining whether a sufficiently high oil supply to at least one component 8 requiring cooling and / or lubrication is ensured or can be ensured via the hydraulic system.

[0028] If the temperature of the hydraulic oil measurable by means of at least one temperature sensor is greater than a first temperature limit value, it is determined whether a sufficiently high oil supply is ensured for at least one component 8 requiring cooling and / or lubrication, depending on the actual current of the electric motor 11 driving the hydraulic pump 10. The actual current of the electric motor 11 driving the hydraulic pump 10 is a variable known, measurable or calculable on the control side, wherein the actual current is in particular the actual phase current of the electric motor 11.

[0029] In order to determine whether a sufficiently high oil supply is ensured, when the temperature of the hydraulic oil is greater than a first temperature limit value, not only the actual value of the actual current itself but also the time gradient of the actual current can be taken into account. Thus, if the actual value of the actual current of the electric motor 11 is less than the rated current and / or the time gradient of the actual current of the electric motor 11 is greater than the first gradient limit value when the temperature of the hydraulic oil is defined and the rated speed of the electric motor 11 driving the hydraulic pump 10 in a speed-controlled manner is defined, it is determined that a sufficiently high oil supply is not provided or is not ensured for at least one component 8 that requires cooling and / or lubrication.

[0030] When the temperature T of the hydraulic oil is greater than the first temperature limit value, Figure 3 The diagram shows the dependence of the oil pressure p provided by the hydraulic pump 10 on the actual current I of the electric motor 11 driving the hydraulic pump 10 for different temperatures T of the hydraulic oil when the rated speed of the hydraulic pump 10 is predetermined. Figure 3 It can be seen that when the temperature T of the hydraulic oil is high (the temperature is greater than the first temperature limit value), there is an almost linear correlation between the actual current I of the electric motor 11 driving the hydraulic pump 10 and the oil pressure p provided by the pump 10. Figure 3 Comprehensive characteristic curves can be stored on the control side for multiple rated speeds.

[0031] Therefore, if the actual value of the actual current I of the electric motor 11 driving the hydraulic pump 10 is less than the rated current (which can depend on the desired pressure p, for example, via a pressure control function according to the invention) when the temperature T of the hydraulic oil is greater than the first temperature limit value and the rated speed of the electric motor 11 driving the hydraulic pump 10 is defined, the actual value of the actual current I of the electric motor 11 driving the hydraulic pump 10 is less than the rated current (which can depend on the desired pressure p, for example, via a pressure control function according to the invention). Figure 3 If the temperature-dependent characteristic curve of the oil flowmeter is known), it can be concluded that a sufficiently high oil supply is not ensured.

[0032] Similarly, when the temperature T of the hydraulic oil is greater than the first temperature limit value, the time gradient of the actual current of the electric motor 11 driving the hydraulic pump 10 can be evaluated to determine whether a sufficiently high oil supply is ensured. If the actual current I of the electric motor 11 is subject to strong fluctuations (i.e., the time gradient of the actual current is greater than the first gradient limit value) when the rated speed of the electric motor 11 driving the hydraulic pump 10 is limited, it can also be determined that a sufficiently high oil supply is no longer ensured. Both the actual current itself and the time gradient of the actual current can be continuously evaluated by the controller 9.

[0033] In a further development of the invention, it is possible to take at least one alternative measure, i.e., to issue an alarm, or even to initiate an emergency operation of the hydraulic system, depending on the deviation between the actual value of the actual current of the electric motor 11 driving the hydraulic pump 10 and the rated current determined as a function of the temperature of the hydraulic oil and the desired rated pressure and / or depending on the deviation of the time gradient of the actual current from the first gradient limit value. If the respective deviation is small, i.e., less than the corresponding limit value, only an alarm is generated. However, if the respective deviation is large, i.e., greater than the corresponding limit value, an emergency operation of the hydraulic system can also be initiated in addition, for example, in order to protect the hydraulic pump 10 from damage.

[0034] When the temperature T of the hydraulic oil is greater than the first temperature limit value, the hydraulic oil temperature T, the actual current I of the electric motor 11 driving the hydraulic pump 10, and the defined rated speed of the electric motor 11 (at which the electric motor is to be operated) can also be used to determine the hydraulic oil temperature T. Figure 3 The resulting actual pressure p is calculated from the characteristic curve shown in , and is compared with the desired setpoint pressure. If the deviation between the actual pressure and the setpoint pressure is greater than a corresponding limit value, it can be concluded that a sufficiently high oil supply can no longer be ensured. Depending on the deviation between the actual pressure and the setpoint pressure, at least one countermeasure can then be taken.

[0035] When the temperature of the hydraulic oil is less than the second temperature limit value, it is determined whether a sufficiently high oil supply is ensured based on the actual rotational speed of the hydraulic pump 10 or the electric motor 11 driving the hydraulic pump. This is preferably done based on the time gradient of the actual rotational speed.

[0036] If the time gradient of the actual speed is greater than the second gradient limit value for a defined temperature of the hydraulic oil and a defined setpoint speed of the speed-controlled electric motor 11 for driving the hydraulic pump 10 , it is detected that the hydraulic pump 10 no longer ensures a sufficiently high oil supply. Figure 4 The present invention describes a processing method for determining whether a sufficiently high oil supply is ensured when the temperature of the hydraulic oil is less than a second temperature limit value (ie, when the hydraulic oil has a relatively low temperature). Figure 4 1 shows a plurality of curves with respect to time, namely, the rated speed of the electric motor 11 driving the hydraulic pump 10 is shown by the curve 12, and the actual speed of the electric motor is shown by the curve 13. Figure 4 In FIG. 1 , curve 14 shows the actual current of the electric motor 11 driving the hydraulic pump 10 .

[0037] Before time t1, due to the high viscosity of the hydraulic oil at the low temperature of the hydraulic oil, the actual speed 13 of the motor 11 driving the hydraulic pump 10 is less than the rated speed 12. Starting from time t1, the actual speed 13 of the electric motor 11 driving the hydraulic pump 10 increases sharply in the direction of the rated speed 12, that is, with a high time gradient. Since the load exerted on the hydraulic pump 10 and thus on the electric motor 11 due to the high viscosity of the oil is eliminated, the electric motor 11 and thus the hydraulic pump 10 accelerates towards its rated speed 12 with a large time gradient. During the acceleration phase of the electric motor 11 between time t1 and t2, the actual current 14 of the electric motor remains almost unchanged. Only after the acceleration phase after time t2 does the actual current 14 drop. Therefore, at a relatively low hydraulic oil temperature less than the second temperature limit value, the evaluation of the time gradient of the actual speed 13 of the electric motor 11 driving the hydraulic pump 10 is primary for knowing whether a sufficiently high oil supply is ensured.

[0038] When the temperature of the hydraulic oil is less than the first temperature limit value and greater than the second temperature limit value, it is determined whether a sufficient supply of hydraulic oil is ensured, depending on the temperature of the hydraulic oil, on the actual current of the electric motor 11 driving the hydraulic pump 10, and additionally on the actual speed of the hydraulic pump 10 or the electric motor 11 driving the hydraulic pump. Here, for temperatures greater than the first temperature limit value, the actual current can be evaluated as described above. For temperatures below the second temperature limit value, the actual speed can be evaluated as described above. These determined results can be used for plausibility checks, wherein only when the actual current is less than the rated current and / or the time gradient of the actual current is greater than the first gradient limit value and the time gradient of the actual speed is greater than the second gradient limit value, it is inferred that a sufficiently high oil supply is no longer ensured.

[0039] Alternatively, it is also possible to evaluate the two evaluation criteria based on the actual current and based on the actual speed in an OR logic, i.e., if the actual current is less than the rated current and / or the time gradient of the actual current is greater than a first gradient limit value or the time gradient of the actual speed is greater than a second gradient limit value, it is inferred that there is no longer a sufficiently high oil supply. The above-mentioned evaluation criteria can also be weighted in a temperature-dependent manner.

[0040] The first temperature limit value and the second temperature limit value can be identical. In particular, the first temperature limit value is +20° C. and the second temperature limit value is 0° C. However, these temperatures are purely exemplary in nature.

[0041] The above evaluation can be performed during continuous operation of the hydraulic system and thus the motor vehicle at different temperatures.

[0042] The above-described monitoring can also be used at the end of production in order to check whether the hydraulic system is installed in accordance with the specification and is therefore functional. Therefore, at the end of the production line, a defined temperature of the hydraulic oil is typically present that is greater than a first temperature limit value. Depending on this temperature of the hydraulic oil and the predetermined rated speed for the hydraulic pump 10, the actual current of the electric motor 11 driving the hydraulic pump 10 can be evaluated in order to check whether the hydraulic pump 10 provides an adequate oil supply. Therefore, as described above with reference to Figure 3 As described, the hydraulic pressure provided by the hydraulic pump 10 can be determined based on the actual current for a defined temperature of the hydraulic oil and a defined rated speed of the hydraulic pump based on the map stored in the controller. If this hydraulic pressure is high enough, a sufficiently high oil supply can be inferred.

[0043] At the end of production, during the functional check of the hydraulic system for the electric motor 11 driving the hydraulic pump 10, a speed ramp can also be run through in order to determine a reference characteristic curve for the current of the electric motor 11 for a speed selected along the speed ramp. If it is determined over the service life that the actual current of the electric motor 11 driving the hydraulic pump 10 deviates from the determined reference characteristic curve at a defined speed and at a temperature for which the reference characteristic curve has been determined, then aging or a defect of the hydraulic pump 10 or the electric motor 11 can be inferred.

[0044] The invention also relates to a control unit for operating a hydraulic system, in particular a hydraulic system of a motor vehicle. The control unit is configured to implement the above method on the control side. Furthermore, the invention also relates to a motor vehicle having a hydraulic system and such a control unit.

[0045] The controller set up to implement the above method can be a transmission controller 5. It is preferably an electronic controller here, which has a hardware-side mechanism and a software-side mechanism for executing the method according to the present invention. The hardware-side mechanism includes a data interface to exchange data with the structural components involved in the implementation of the method according to the present invention, that is, for example, with a sensor for detecting the temperature of the hydraulic oil, with a sensor for detecting the actual current of the electric motor driving the hydraulic pump and / or for detecting the actual speed of the hydraulic pump or the electric motor driving the hydraulic pump. The mentioned sensors can be integrated in the motor-pump unit 7, for example. The data to be exchanged can be transmitted via a data bus, for example, via a CAN bus (controller area network). In addition, the hardware-side mechanism includes a processor for data processing and a memory for data storage. The software-side mechanism includes a program module implemented in the controller for executing the method according to the present invention.

[0046] Reference numerals list

[0047] 1 Drive system

[0048] 2 drive unit

[0049] 3. Driven end

[0050] 4 Motor Controller

[0051] 5 Transmission controller

[0052] 6 Oil storage container

[0053] 7 Motor-Pump Unit

[0054] 8 Structural components

[0055] 9 Controller

[0056] 10Hydraulic pump

[0057] 11 Electric Motor

[0058] 12 Curve trend of rated speed

[0059] 13 Actual speed curve trend

[0060] 14 Actual current curve trend

Claims

1. A method for operating a hydraulic system, in particular a hydraulic system of a motor vehicle, comprising a hydraulic pump (10) driven by a speed-controlled electric motor (11) for drawing hydraulic oil from an oil reservoir (6) and supplying it to at least one component (8) which requires cooling and / or lubrication with hydraulic oil, It is characterized in that depends on the hydraulic oil temperature, and depending on the actual current of the electric motor (11) driving the hydraulic pump (10) and / or the actual rotational speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump, To determine whether a sufficiently high oil supply is ensured for at least one component (8) which requires cooling and / or lubrication.

2. The method according to claim 1, characterized in that When the temperature of the hydraulic oil is greater than a first temperature limit value, it is determined whether a sufficiently high oil supply is ensured by relying on the actual current of the electric motor (11) driving the hydraulic pump (10).

3. The method according to claim 2, characterized in that The determination is based on an evaluation of an actual value of the actual current and / or an evaluation of a time gradient of the actual current.

4. The method according to claim 3, characterized in that: When the temperature of the hydraulic oil is limited and the rated speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump is limited, the actual value of the actual current is less than the rated current and / or the time gradient of the actual current is greater than a first gradient limit value, it is detected that a sufficiently high oil supply to the at least one component requiring cooling or lubrication is not ensured.

5. The method according to claim 4, characterized in that At least one alternative measure is taken as a function of a deviation between an actual value of the actual current and the setpoint current and / or as a function of a deviation of a time gradient of the actual current from the first gradient limit value.

6. The method according to any one of claims 1 to 5, characterized in that When the temperature of the hydraulic oil is less than a second temperature limit value, it is determined whether a sufficiently high oil supply is ensured depending on the actual rotational speed of the hydraulic pump (10) or the electric motor (11) driving the hydraulic pump.

7. The method according to claim 6, characterized in that The determination is based on an evaluation of the time gradient of the actual rotational speed.

8. The method according to claim 7, characterized in that If the time gradient of the actual speed is greater than a second gradient limit value when the temperature of the hydraulic oil is defined and the rated speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump is defined, it is detected that a sufficiently high oil supply to the at least one component requiring cooling or lubrication is not ensured.

9. The method according to claim 8, characterized in that At least one alternative measure is taken as a function of the deviation of the time gradient of the actual rotational speed from the second gradient limit value.

10. The method according to any one of claims 2 to 5 and any one of claims 6 to 9, characterized in that When the temperature of the hydraulic oil is less than the first temperature limit value and greater than the second temperature limit value, it is determined whether a sufficiently high oil supply is ensured depending on the actual current of the hydraulic pump (10) and on the actual rotational speed of the hydraulic pump or of the electric motor (11) driving the hydraulic pump.

11. The method according to claim 10, characterized in that When, when the temperature of the hydraulic oil is limited and when the rated speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump is limited, on the one hand the actual value of the actual current is less than the rated current and / or the time gradient of the actual current is greater than the first gradient limit value and on the other hand the time gradient of the actual speed is greater than the second gradient limit value, it is detected that the hydraulic pump (10) does not ensure a sufficiently high oil supply.

12. The method according to claim 10, characterized in that When, when the temperature of the hydraulic oil is limited and when the rated speed of the hydraulic pump (10) or of the electric motor (11) driving the hydraulic pump is limited, either the actual value of the actual current is less than the rated current and / or the time gradient of the actual current is greater than the first gradient limit value, or the time gradient of the actual speed is greater than the second gradient limit value, it is detected that the hydraulic pump (10) does not ensure a sufficiently high oil supply.

13. The method according to any one of claims 1 to 12, characterized in that The method is carried out during continuous operation of the hydraulic system and / or, in the case of production of the hydraulic system, at the end of production.

14. A control unit for operating a hydraulic system, in particular a hydraulic system of a motor vehicle, characterized in that The controller is configured to automatically carry out the method according to any one of claims 1 to 13 on the control side.

15. A motor vehicle having a hydraulic system and a controller according to claim 14.

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