Method and control unit for operating a motor vehicle

Abstract

Method for operating a motor vehicle, comprising a drive unit (1), a transmission (2) and an output (3), wherein the transmission (2) is connected between the drive unit (1) and the output (3) and is designed as an automatic transmission, the transmission (2) comprises several switching elements (4), of which in each engaged, traction-transmitting gear a first number of switching elements (4) are closed and a second number of switching elements (4) are open, the transmission (2) comprises a hydraulic system (5) with a primary circuit (13) for controlling the shift elements (4), a secondary circuit (14) for cooling and / or lubricating the transmission, a system pressure valve (12), a main pump (8) and a pressure-controlled, electric auxiliary pump (9), depending on at least one operating condition of the motor vehicle, a sailing mode is entered, in which the transmission (2) decouples the drive unit (1) from the output (3) by opening a switching element (4) closed in the respective traction-transmitting gear, and in which, depending on at least one operating condition of the motor vehicle, the sailing mode is subsequently exited, wherein, when the drive unit (1) is stopped in sailing mode, the electric auxiliary pump (9) is switched on to ensure a hydraulic oil supply to the transmission (2), characterized in that, for functional testing of the hydraulic oil supply during active sailing mode, after the drive unit (1) has been switched off and the electric auxiliary pump (9) has been switched on, a system pressure request is increased by the control system above the current delivery pressure of the electric auxiliary pump (9), so that all hydraulic oil delivered by the electric auxiliary pump (9) is delivered into the primary circuit (13), wherein, after a defined period of time following the control system's increase of the system pressure request, the current speed of the electric auxiliary pump (9) is determined and compared with a threshold value, wherein, if the current speed of the electric auxiliary pump (9) is greater than the threshold value, it is concluded that the hydraulic oil supply via the electric auxiliary pump (9) is defective.

Description

[0001] The invention relates to a method for operating a motor vehicle. Furthermore, the invention relates to a control unit for implementing the method.

[0002] Motor vehicles whose drivetrain comprises a drive unit and an automatic transmission connected between the drive unit and an output are well known in practice. The drive unit can comprise an internal combustion engine and / or an electric motor. Furthermore, it is known in practice that, when at least one defined operating condition is met, the motor vehicle can enter a coasting mode and subsequently exit from coasting mode depending on at least one further operating condition. Furthermore, it is already known in practice that, in coasting mode, the motor vehicle can be operated with the drive unit running on the one hand and with the drive unit switched off on the other.When a drive unit is stopped, its speed is zero or approximately zero, thus reducing it below a limit so that the main pump of a transmission's hydraulic system, which is mechanically driven by a transmission shaft, cannot maintain the transmission's hydraulic oil supply. The main pump then does not deliver any hydraulic oil. When the vehicle's drive unit is stopped in coasting mode, the hydraulic oil supply is typically ensured by an electric auxiliary pump driven by an electric motor.Although such an electric auxiliary pump can be monitored for an electrical defect in practice, namely by monitoring the electrical control of the electric motor that drives the electric auxiliary pump, it has not yet been possible to provide a functional check of the hydraulic oil supply via the electric auxiliary pump during active coasting mode after the drive unit has been shut down in such a way that a potentially critical undersupply of hydraulic oil to the transmission via the electric auxiliary pump can be easily and reliably detected. Therefore, there is a need for a method for operating a motor vehicle with which such a functional check of the hydraulic oil supply can be provided in the coasting mode of the motor vehicle.

[0003] DE 10 2010 039 173 A1 discloses a method for operating a motor vehicle during an active coasting mode. Based on the operating parameters of the drivetrain, the hydraulic oil supply status of the transmission is determined. Based on the determined supply status, a critical lubrication and / or cooling deficiency of the transmission is detected. If a critical lubrication and / or cooling deficiency is detected, a different coasting mode can be selected or the coasting mode can be terminated.

[0004] DE 10 2011 077 552 A1 discloses a hydraulic arrangement for a transmission comprising a primary circuit, a secondary circuit, a main pump, an auxiliary pump, and a system pressure valve. The primary circuit and the secondary circuit are coupled via the system pressure valve, which ensures that the primary circuit is supplied first and that hydraulic oil only reaches the secondary circuit when the primary circuit is sufficiently supplied. The auxiliary pump is an auxiliary pump driven on the output side, for example, by the vehicle's output or a transmission output shaft. If the hydraulic oil supply via the main pump cannot be maintained during coasting operation, the auxiliary pump can be activated.

[0005] The further documents DE 10 2005 013 137 A1, DE 10 2010 039 173 A1, DE 10 2011 077 552 A1 and DE 10 2014 201 922 A1 also disclose methods for operating a motor vehicle, having a drive unit, a transmission and an output, wherein the transmission is connected between the drive unit and the output and is designed as an automatic transmission, the transmission comprising a plurality of shift elements, of which a first number of shift elements is closed and a second number of shift elements is open in each engaged, traction-transmitting gear.

[0006] Based on this, the invention is based on the object of creating a novel method for operating a motor vehicle and a control device for operating a motor vehicle.

[0007] This object is achieved by a method according to patent claim 1.

[0008] According to the invention, in order to check the function of the hydraulic oil supply during the active sailing mode, after the drive unit has been stopped and after the electric auxiliary pump has been switched on, a system pressure requirement is raised on the control side above the current delivery pressure of the electric auxiliary pump so that all hydraulic oil delivered by the electric auxiliary pump is pumped into the primary circuit.

[0009] After a defined period of time has elapsed after the control-side increase in the system pressure requirement, a current speed of the electric auxiliary pump is determined and compared with a threshold value. If the current speed of the electric auxiliary pump is greater than the threshold value, a defect in the hydraulic oil supply via the electric auxiliary pump is concluded.

[0010] If the current speed of the electric auxiliary pump, which is determined after the defined period of time has elapsed after the control-side increase of the system requirement above the current delivery pressure of the electric auxiliary pump, is greater than the threshold value, it can be concluded that the hydraulic oil supply via the electric auxiliary pump is defective, for example a defect in the electric auxiliary pump as such or an undesirable leak in the hydraulic system, which means that the electric auxiliary pump cannot provide the hydraulic oil supply at a speed below the threshold value.

[0011] If the initial diagnosis above indicates a defect in the hydraulic oil supply via the electric auxiliary pump, a backup measure can be initiated to ensure a sufficient hydraulic oil supply to the transmission and eliminate the risk of damage. Preferably, if a defect in the hydraulic oil supply via the electric auxiliary pump is identified, the drive unit is started or its speed is increased to ensure the hydraulic oil supply via the main pump. This is particularly preferred as a backup measure if a defect in the hydraulic oil supply via the electric auxiliary pump is detected.

[0012] According to a further development of the invention, a second diagnosis is furthermore determined, depending on this determined current speed of the electric auxiliary pump and a maximum available speed of the electric auxiliary pump, whether the secondary circuit can be supplied with a defined hydraulic oil volume flow via the electric auxiliary pump.

[0013] If it is determined that the secondary circuit cannot be supplied with the defined hydraulic oil volume flow via the electric auxiliary pump, the drive unit is started or its speed is increased in order to ensure the hydraulic oil supply via the main pump.

[0014] If, however, it is determined that the secondary circuit can be supplied with the defined hydraulic oil volume flow via the electric auxiliary pump, the system pressure requirement is subsequently reduced until the resulting increase in the speed of the electric auxiliary pump supplies the secondary circuit with the defined hydraulic oil volume flow. At the end of the reduction in the system pressure requirement, a third diagnosis can be used to determine, depending on the determined current speed of the electric auxiliary pump and the current speed of the electric auxiliary pump, whether the secondary circuit is being supplied with a defined hydraulic oil volume flow via the electric auxiliary pump.

[0015] If the first diagnosis discussed above determines that there is no defect in the hydraulic oil supply via the electric auxiliary pump, the second diagnosis is preferably carried out subsequently. This is dependent on the current speed of the electric auxiliary pump, which is determined after the defined period of time has elapsed after the control-side increase in the system pressure requirement, and also dependent on a maximum available speed of the electric auxiliary pump. This results in a speed difference that is suitable for providing a defined hydraulic oil volume flow that can be pumped into the secondary circuit. If the hydraulic oil volume flow that can be provided to the secondary circuit via the electric auxiliary pump is too low, an alternative measure is initiated, for example by switching on the drive unit in order to then ensure the hydraulic oil supply via the main pump.If, on the other hand, the secondary circuit can be supplied with the defined hydraulic oil volume flow via the electric auxiliary pump, the system pressure requirement is subsequently reduced in order to indirectly increase the speed of the auxiliary pump and supply the secondary circuit with the defined hydraulic oil volume flow.

[0016] If the first and second diagnoses discussed above determine that there is no defect in the hydraulic oil supply via the electric auxiliary pump, the third diagnosis is preferably subsequently performed, namely depending on the current speed of the electric auxiliary pump, which is determined after the defined time period has elapsed after the control-side increase in the system pressure requirement, as well as depending on the current speed of the electric auxiliary pump. This results in a speed difference (identical to the speed difference determined during the second diagnosis) that is suitable for providing a defined hydraulic oil volume flow, which is pumped into the secondary circuit.If the hydraulic oil flow rate available for the secondary circuit via the electric auxiliary pump is too low, an alternative measure is initiated, for example, by switching on the drive unit to ensure the hydraulic oil supply via the main pump. If, however, the secondary circuit can be supplied with the defined hydraulic oil flow rate via the electric auxiliary pump, the system pressure requirement is subsequently maintained to indirectly fix the speed of the auxiliary pump and supply the secondary circuit with the defined hydraulic oil flow rate. Ultimately, this ensures that the electric auxiliary pump operates at an adjusted speed while reducing its power consumption.

[0017] According to a further development of the invention, a hydraulic oil temperature-dependent and / or sail-gear-dependent threshold value and / or a hydraulic oil temperature-dependent and / or sail-gear-dependent hydraulic oil volume flow are used for the functional test of the hydraulic oil supply. This allows the method to be optimally adapted to the prevailing hydraulic oil temperature and the sail gear engaged in the transmission.

[0018] The control device according to the invention is defined in claim 11.

[0019] Preferred developments emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1 a drive train diagram of a motor vehicle; Fig. 2 assemblies of a hydraulic system of a transmission of the motor vehicle; and Fig. 3 a timing diagram to illustrate the invention.

[0020] Fig. Figure 1 shows a highly schematic drive train diagram of a motor vehicle with a drive unit 1, a transmission 2, and an output 3, wherein the transmission 2 is connected between the drive unit 1 and the output 3 and provides the tractive force of the drive unit 1 to the output 3. The drive unit 1 can be an internal combustion engine, an electric motor, or a hybrid drive with an internal combustion engine and an electric motor. The transmission 2 is an automatic transmission with several shift elements 4, wherein Fig. 1 shows only one such shifting element 4 by way of example. In each traction-transmitting gear of the transmission 2, a first defined number of shifting elements 4 are closed and a second defined number of shifting elements 4 are open. To execute a gear change in the transmission 2 from a traction-transmitting actual gear to a traction-transmitting target gear, at least one previously closed shifting element 4 must be opened and at least one previously open shifting element 4 must be closed.

[0021] Fig. 1 further shows a highly schematic hydraulic system 5 of the transmission 2, in which Fig. 2 selected components of the hydraulic system 5 of the transmission 2 are shown. Fig. 2 a main pump 8 of the hydraulic system 5 and an electric auxiliary pump 9 of the hydraulic system 5. The main pump 8 is driven mechanically by the transmission 2, in particular from a transmission shaft of the transmission 2. The electric auxiliary pump 9, on the other hand, is driven by an electric motor, namely via an electric motor 10 of the hydraulic system 5. The main pump 8 and the electric auxiliary pump 9 are connected in parallel and can both pump hydraulic oil from an oil reservoir 11. A so-called system pressure valve 12 of the hydraulic system 5 interacts with the main pump 8 and the auxiliary pump 9 and can pump pumped hydraulic oil into a primary circuit 13 of the hydraulic system 5 and into a secondary circuit 14 of the hydraulic system 5. The primary circuit 13 serves to control the switching elements 4 of the transmission 2 in order to close and open them. The secondary circuit 14, on the other hand, serves to cool and lubricate the transmission 2.

[0022] The electrically driven auxiliary pump 9 is pressure-controlled, which means that it is operated at a speed such that the auxiliary pump 9 provides a requested delivery pressure.

[0023] Depending on a control-side system pressure requirement, the system pressure valve 12 of the hydraulic system 5 ensures that, if the delivery pressure of the respective pump of the hydraulic system 5 is lower than the system pressure requirement, all delivered hydraulic oil is initially pumped into the primary circuit 13. Only when the delivery pressure of the respective hydraulic pump is greater than the system pressure requirement does the system pressure valve 12 direct a corresponding excess amount of oil into the secondary circuit 14.

[0024] Fig. 1 further shows a transmission control unit 6, which serves to control and / or regulate the operation of the transmission 2. In particular, the transmission control unit 6 controls and / or regulates the switching elements 4 and the hydraulic system 5 and, for this purpose, exchanges the Fig. 1 with the gearbox 2 data.

[0025] An engine control unit 7 regulates and / or controls the operation of the drive unit 1 and exchanges the Fig. 1 with the drive unit 1 data.

[0026] Furthermore, the engine control unit 6 and the transmission control unit 7 exchange data with each other.

[0027] As already explained, in each engaged, tractive force-transmitting gear of the transmission 2, a first defined number of the shift elements 4 of the transmission 2 are closed and a second defined number of the shift elements 4 of the transmission 2 are open. Depending on at least one operating condition of the motor vehicle, the vehicle can be entered into a coasting mode in which the transmission 2 decouples the drive unit 1 from the output. For this purpose, a so-called coasting gear is engaged in the transmission 2, in which one shift element 4 is more open than in a tractive force-transmitting gear, so that in the coasting mode the transmission 2 no longer transmits tractive force towards the output 3.

[0028] When, in such a coasting mode of the motor vehicle, the drive unit 1, which is decoupled from the output 3, is stopped, i.e. is operated at a speed of zero or approximately zero, the hydraulic oil supply to the transmission 2 cannot be maintained via the mechanically driven main pump 8, so that the electrically driven auxiliary pump 9 is then switched on in order to ensure the hydraulic oil supply to the transmission 2 via this auxiliary pump 9. The present invention now relates to such details with the aid of which, when the coasting mode is active, a functional test of the hydraulic oil supply is enabled after the drive unit 1 has been stopped in order to determine whether the transmission 2 can be supplied with sufficient hydraulic oil via the electrical auxiliary pump 9 in order to avoid damage to the transmission 2.When the drive unit is stopped, its speed is zero or approximately zero, i.e. the speed of the drive unit 1 is so low that the hydraulic oil supply cannot be maintained via the main pump 8 or the main pump 8 does not deliver any hydraulic oil.

[0029] To check the functionality of the hydraulic oil supply during active sailing mode after the drive unit 1 has been shut down and the electric auxiliary pump 9 has been switched on, a system pressure requirement is raised on the control side above the current delivery pressure of the electric auxiliary pump 9. This ensures that all hydraulic oil delivered by the electric auxiliary pump 9 is pumped into the primary circuit 13 of the hydraulic system 5, but no hydraulic oil enters the secondary circuit 14.

[0030] After a defined period of time following the control-side increase in the system pressure requirement, the current speed of the electric auxiliary pump 9 is determined and compared with a threshold value as part of an initial diagnosis. If the current speed of the electric auxiliary pump 9 is greater than the threshold value, it is concluded that the hydraulic oil supply via the electric auxiliary pump 9 is defective, and a substitute measure is initiated to ensure the hydraulic oil supply to the transmission 2.

[0031] If, however, the current speed of the electric auxiliary pump 9 determined here is lower than the threshold value, the first diagnosis concludes that the hydraulic oil supply via the electric auxiliary pump 9 is not defective, so that a subsequent second diagnosis checks whether the available speed reserve of the electric auxiliary pump is sufficient to supply the secondary circuit 14 with a defined hydraulic oil volume flow. If this is not the case, i.e. the speed reserve of the electric auxiliary pump 9 is insufficient, an alternative measure is initiated to ensure the hydraulic oil supply to the transmission. If, however, the speed reserve of the electric auxiliary pump 9 is sufficient, the system pressure requirement is subsequently reduced, thereby indirectly increasing the speed of the pressure-controlled, electric auxiliary pump in order to then supply a corresponding hydraulic oil quantity orto provide the corresponding defined hydraulic oil volume flow to the secondary circuit.

[0032] If the second diagnosis concludes that the hydraulic oil supply via the electric auxiliary pump 9 is not defective, a subsequent third diagnosis is carried out to check whether, after the system pressure requirement has been reduced, the expected differential speed at the electric auxiliary pump is established in order to supply the secondary circuit 14 with a defined hydraulic oil volume flow. If this is not the case, i.e. the differential speed of the electric auxiliary pump 9 is not established, an alternative measure is again initiated to ensure the hydraulic oil supply to the transmission. If, on the other hand, the differential speed of the electric auxiliary pump 9 that is established is sufficient, the system pressure requirement is subsequently maintained and this indirectly causes the speed of the pressure-controlled, electric auxiliary pump to be maintained in order to then supply a corresponding hydraulic oil quantity orto provide the corresponding defined hydraulic oil volume flow to the secondary circuit.

[0033] Further details of the invention will be explained below with reference to the timing diagram of the Fig. 3, where Fig. 3 Several temporal curves 15, 16, and 17 are plotted over time t. Curve 15 represents the temporal progression of the speed of drive unit 1. Curve 16 represents the temporal progression of a system pressure demand. Curve 17 represents the temporal progression of the speed of auxiliary pump 9.

[0034] In Fig. 3, it is assumed that before time t1, the motor vehicle is already operating in a coasting mode with the drive unit 1 decoupled from the output 3 but still running. Accordingly, before time t1, the speed of the drive unit 1 (curve 15) is sufficient to ensure the hydraulic oil supply to the transmission 2 via the main pump 8. Therefore, before time t1, as can be seen from the speed curve of the auxiliary pump 9 (curve 17), the electrically driven auxiliary pump 9 is shut down.

[0035] At time t1, Fig. 3, the drive unit 1 is shut down, whereby between times t1 and t2, the speed of the drive unit 1 (curve 15) runs out and at time t2 is so low that the hydraulic oil supply to the transmission 2 cannot be maintained via the main pump 8. Therefore, when the drive unit 1 is shut down on the control side at time t1, the electrically driven auxiliary pump 9 is switched on according to curve 17, so that it is running at time t2 at the latest and can supply the transmission 2 with hydraulic oil.

[0036] Then, if at time t2 the speed of the drive unit 1 (curve 15) falls below a limit value, i.e. if starting at time t2 the hydraulic oil supply to the transmission 2 cannot be maintained via the main pump 8, in the preferred embodiment a delay time T1 is started at time t2 in order to ensure that after the delay time T1 has elapsed at time t3 the drive unit is safely at a standstill, i.e. its speed is zero or approximately zero, so that accordingly the main pump 8 is also at a standstill or is not delivering any hydraulic oil at time t3.

[0037] At time t3, i.e. during the active sailing mode after the drive unit 1 has been stopped and after the electric auxiliary pump 9 has been switched on and after the time period T1 has elapsed, the system pressure requirement is increased according to the curve 16, in steps to a level which is above the current delivery pressure of the pressure-controlled, electric auxiliary pump 9, so that at time t3 all of the hydraulic oil delivered by the electric auxiliary pump 9 is delivered exclusively into the primary circuit 13 of the hydraulic system 5, but no hydraulic oil reaches the secondary circuit 14 of the hydraulic system 5.

[0038] Starting at time t3, a further delay time T2 is started. After the time period defined by this delay time T2 has elapsed, after the control-side increase in the system pressure request 16 at time t4, the current speed of the electric auxiliary pump 9 is determined and compared with a threshold value. This threshold value, with which the current speed of the electric auxiliary pump 9 determined at time t4 is compared, is preferably dependent on the hydraulic oil temperature and the non-traction-transmitting coasting gear currently engaged in the transmission 2.

[0039] If it is determined that the current speed of the electric auxiliary pump 9 determined at time t4 is greater than the corresponding threshold value (first diagnosis), a defect in the hydraulic oil supply via the electric auxiliary pump 9 at time t4 is concluded. Such a defect in the hydraulic oil supply can be caused, for example, by a defect in the electric auxiliary pump 9 as such, for example, by a mechanical defect in the electric auxiliary pump 9. Furthermore, such a defect can also be caused by a leak in the hydraulic oil system 5. If it is determined at time t4 that the current speed of the electric auxiliary pump 9 is greater than the corresponding threshold value, i.e. if a defect in the hydraulic oil supply via the electric auxiliary pump 9 is concluded, an alternative measure is initiated in order to nevertheless ensure the hydraulic oil supply to the transmission 2, preferably by starting the drive unit 1 or increasing its speed in order to then ensure the hydraulic oil supply to the transmission 2 via the main pump 8.

[0040] In Fig. 3 it is assumed that at time t4 the speed of the electric auxiliary pump 9 is lower than the corresponding threshold value, so that no defect in the hydraulic oil supply via the electric auxiliary pump 9 is concluded at time t4. In this case, in addition to the previously performed diagnosis based on the comparison of the current speed of the electric auxiliary pump 9 with the threshold value, a further diagnosis is carried out (second diagnosis), specifically depending on the current speed of the electric auxiliary pump 9 determined at time t4 and on the basis of a maximum available speed of the electric auxiliary pump 9, wherein the maximum available speed of the electric auxiliary pump 9 and the current speed of the electric auxiliary pump 9 determined at time t4 determine a speed reserve of the electric auxiliary pump 9.

[0041] Depending on this speed reserve, it can be mathematically determined whether the secondary circuit 14 of the hydraulic system 5 can be supplied with a defined hydraulic oil volume flow via the electric auxiliary pump 9, which typically depends on the hydraulic oil temperature and the coasting gear currently engaged in the transmission 2. If it is determined that the secondary circuit 14 of the hydraulic system 5 cannot be supplied with the defined hydraulic oil volume flow via the auxiliary pump 9 due to the available speed reserve, an alternative measure is taken to ensure the hydraulic oil supply via the main pump 8, for which purpose the drive unit 1 is preferably started again or its speed is increased.

[0042] Then, however, if at time t4 it is determined during the second diagnosis that the secondary circuit 14 can be supplied with the defined hydraulic oil volume flow via the electric auxiliary pump 9 due to the available speed reserve of the same, the system pressure requirement is subsequently reduced starting at time t4 according to the curve 16, namely initially in steps at time t4 and subsequently in a ramp-like manner between times t4 and t5.

[0043] The system pressure requirement is reduced between times t4 and t5 to below the delivery pressure of the auxiliary pump 9 until an increase in the speed of the pressure-controlled, electric auxiliary pump 9, indirectly caused by the reduction in the system pressure requirement, supplies the secondary circuit 14 with the defined hydraulic oil volume flow. As already explained, the electric auxiliary pump 9 is a pressure-controlled or pressure-regulated auxiliary pump whose speed is automatically adjusted so that it provides the delivery pressure requested by the control system.

[0044] If it is determined at time t5 during the third diagnosis that the secondary circuit 14 is supplied with the defined hydraulic oil volume flow via the electric auxiliary pump 9 as a result of the current speed of the same, the system pressure requirement is subsequently maintained starting at time t5 according to the curve 16.

[0045] If at time t5 during the third diagnosis it is determined that the secondary circuit 14 is not supplied with the defined hydraulic oil volume flow via the electric auxiliary pump 9 due to the current speed of the same, an alternative measure is again taken to ensure the hydraulic oil supply via the main pump 8, for which purpose the drive unit 1 is preferably started again or its speed is increased.

[0046] As soon as at time t5, using the available speed reserve of the electric auxiliary pump 9, the speed of the electric auxiliary pump 9 has been increased by the difference Δn from the speed at time t4 to such an extent that, due to this increased speed level of the electric auxiliary pump 9, the same supplies the secondary circuit 14 with the defined hydraulic oil volume flow, the system pressure requirement is kept constant at time t5, so that the speed of the auxiliary pump 9 (curve 17) subsequently also remains constant.

[0047] This ensures that the electric auxiliary pump 9 is operated at an optimally adjusted speed in order to supply the secondary circuit 14 and the primary circuit 13 with a defined hydraulic pressure, on the one hand, so that switching elements 4 can be properly closed or opened with the system pressure via the primary circuit 13 and, on the other hand, proper lubrication and cooling of the transmission 2 is possible via the secondary circuit 14.

[0048] In Fig. 3, an exit condition from sailing mode exists at time t6, so that the drive unit 1 is started at time t6. Subsequently, the auxiliary pump 9 is shut down and the hydraulic oil supply is ensured via the main pump 8.

[0049] The invention further relates to a control unit for implementing the method according to the invention, this control unit being the transmission control unit 6. The transmission control unit 6 is designed to execute the method on the control side. For this purpose, the transmission control unit 6 comprises means for implementing the method according to the invention, namely hardware means and software means. The hardware means include interfaces for exchanging data with the modules involved in the method according to the invention. Furthermore, the hardware means include a processor for data processing and a memory for data storage. The software means include program modules for implementing the method according to the invention.

[0050] With the method according to the invention, it can be checked during sailing with the drive unit 1 shut down whether the transmission can be supplied with sufficient hydraulic oil via the electric auxiliary pump 9. If this is not the case, an alternative measure can be initiated to then ensure the hydraulic oil supply via the main pump 8. If this is the case, the speed of the electric auxiliary pump 9 can be adjusted such that both the primary circuit 13 and the secondary circuit 14 of the hydraulic system 5 are optimally supplied with hydraulic oil with the lowest possible power consumption, i.e., with the lowest possible speed of the electric auxiliary pump 9.

[0051] As explained above, two diagnoses are performed at time t4, i.e., a defined period of time after the system pressure request 16 has been increased. A first diagnosis is based on a comparison of the current speed of the electric auxiliary pump 9 determined at time t4 with a threshold value that is preferably dependent on the oil temperature and the sail speed.

[0052] Based on the first diagnosis, a leak in the hydraulic system or a defect in the auxiliary pump 9 can be detected.

[0053] The second diagnosis at time t4 calculates, on the basis of the currently available speed reserve of the auxiliary pump 9, whether the secondary circuit for lubricating and / or cooling the transmission 2 can be supplied with a defined hydraulic oil volume flow by the auxiliary pump 9.

[0054] The third diagnosis at time t5 is based on the difference between the speed determined at time t4 and the current speed of the electric auxiliary pump 9 with a preferably oil temperature-dependent and sail speed-dependent threshold value as to whether the secondary circuit for lubrication and / or cooling of the transmission 2 is supplied with a defined hydraulic oil volume flow by the auxiliary pump 9. Reference symbol 1 drive unit 2 gearboxes 3 Downforce 4 Switching element 5 Hydraulic system 6 Transmission control unit 7 Engine control unit 8 Main pump 9 Auxiliary pump 10 Electric motor 11 oil storage tanks 12 System pressure valve 13 Primary circuit 14 Secondary circulation 15 Curve of drive unit speed 16 Curve system pressure requirement 17 Curve speed of auxiliary pump

Claims

[1] Method for operating a motor vehicle, with a drive unit (1), a transmission (2) and an output (3), wherein the transmission (2) is connected between the drive unit (1) and the output (3) and is designed as an automatic transmission, the transmission (2) comprises a plurality of shift elements (4), of which a first number of shift elements (4) are closed and a second number of shift elements (4) are open in each engaged, traction-transmitting gear, the transmission (2) comprises a hydraulic system (5) with a primary circuit (13) for controlling the switching elements (4), a secondary circuit (14) for cooling and / or lubricating the transmission, a system pressure valve (12), a main pump (8) and a pressure-controlled, electric auxiliary pump (9), depending on at least one operating condition of the motor vehicle, a sailing mode is entered in which the transmission (2) decouples the drive unit (1) from the output (3) by opening a switching element (4) closed in the respective traction-transmitting gear, and wherein the sailing mode is subsequently exited depending on at least one operating condition of the motor vehicle, wherein when the drive unit (1) is stopped in sailing mode, the electric auxiliary pump (9) is switched on to ensure a hydraulic oil supply to the transmission (2), characterized byin that, in order to check the function of the hydraulic oil supply during the active sailing mode, after the drive unit (1) has been stopped and after the electric auxiliary pump (9) has been switched on, a system pressure requirement is raised on the control side above the current delivery pressure of the electric auxiliary pump (9) so that all of the hydraulic oil delivered by the electric auxiliary pump (9) is delivered into the primary circuit (13), wherein after a defined period of time has elapsed after the system pressure requirement has been raised on the control side, a current speed of the electric auxiliary pump (9) is determined and compared with a threshold value, wherein if the current speed of the electric auxiliary pump (9) is greater than the threshold value, it is concluded that the hydraulic oil supply via the electric auxiliary pump (9) is defective. [2] Method according to claim 1, characterized bythat if a defect in the hydraulic oil supply via the electric auxiliary pump (9) is detected, the drive unit (1) is started or its speed is increased in order to ensure the hydraulic oil supply via the main pump (8). [3] Method according to claim 1 or 2, characterized by that then, the current speed of the electric auxiliary pump (9) is less than the threshold value, no defect in the hydraulic oil supply via the electric auxiliary pump (9) is concluded. [4] Method according to one of claims 1 to 3, characterized by that a hydraulic oil temperature-dependent and / or sail speed-dependent threshold value is used for the functional test of the hydraulic oil supply. [5] Method according to one of claims 1 to 4, characterized bythat furthermore, depending on the determined current speed of the electric auxiliary pump (9) and a maximum available speed of the electric auxiliary pump (9), it is determined whether the secondary circuit (14) can be supplied with a defined hydraulic oil volume flow via the electric auxiliary pump (9). [6] Method according to claim 5, characterized by that if it is determined that the secondary circuit (14) cannot be supplied with the defined hydraulic oil volume flow via the additional pump (9), the drive unit (1) is started or its speed is increased in order to ensure the hydraulic oil supply via the main pump (8). [7] Method according to claim 5 or 6, characterized bythat when it is determined that the secondary circuit (14) can be supplied with the defined hydraulic oil volume flow via the additional pump (9), the system pressure requirement is subsequently reduced until, as a result of an increase in the speed of the electric additional pump (9), the pump supplies the secondary circuit (14) with the defined hydraulic oil volume flow. [8] Method according to claim 7, characterized by that the system pressure requirement is subsequently kept constant. [9] Method according to one of claims 5 to 8, characterized by that a hydraulic oil temperature-dependent and / or sail speed-dependent hydraulic oil volume flow is used. [10] Method according to one of claims 1 to 9, characterized by that the functional check during the active sailing mode is only carried out when the speed of the drive unit (1) is zero or approximately zero. [11] Control unit (6) for operating a motor vehicle with a drive unit (1) and a transmission (2), wherein the control unit activates a sailing mode of the motor vehicle depending on at least one operating condition of the motor vehicle, wherein the control unit subsequently deactivates the sailing mode depending on at least one operating condition of the motor vehicle, and wherein the transmission (2) comprises a hydraulic system (5) with a primary circuit (13) for controlling shift elements (4) of the transmission, with a secondary circuit (14) for cooling and / or lubricating the transmission, with a system pressure valve (12), with a main pump (8) and with a pressure-controlled, electric auxiliary pump (9), characterized byin that, in order to check the function of the hydraulic oil supply during the active sailing mode, after the drive unit (1) has been stopped and after the electric auxiliary pump (9) has been switched on, the control unit raises a system pressure request above the current delivery pressure of the electric auxiliary pump (9) on the control side, so that all of the hydraulic oil delivered by the auxiliary pump (9) is delivered into the primary circuit (13), wherein the control unit determines a current speed of the electric auxiliary pump (9) after a defined period of time has elapsed after the system pressure request has been raised on the control side and compares it with a threshold value, wherein if the current speed of the electric auxiliary pump (9) is greater than the threshold value, the control unit concludes that the hydraulic oil supply via the electric auxiliary pump (9) is defective. [12] Control device according to claim 11, which carries out the method according to one of claims 1 to 10.

Images