Method for establishing hydraulic readiness of a fluid device in a motor vehicle

Abstract

The invention relates to a method for producing a hydraulic readiness of a fluid device (10) in a motor vehicle

Description

[0001] The invention relates to a method for establishing a hydraulic readiness of a fluid device in a motor vehicle according to the preamble of claim 1.

[0002] The ever-increasing complexity of vehicles requires the flawless function and interaction of all components. The functioning of electrical components is particularly important for enabling purely electric driving and increasing efficiency. Failure or defects of certain electronic components can have serious consequences for the vehicle.

[0003] DE 10 2021 116 688 A1 discloses a method for controlling a hybrid head of a hybrid powertrain.

[0004] DE 10 2020 119 189 A1 discloses a method for controlling a friction clutch in a drive train.

[0005] DE 10 2021 117 344 A1 discloses a method for controlling a drive train.

[0006] DE 10 2020 111 970 A1 describes a hydraulic device that supplies a clutch actuation device with an actuating fluid pressure. A hybrid disconnect clutch is actuated depending on the actuating fluid pressure. A relief valve is actuated to open the hybrid disconnect clutch, resulting in a pressure drop in the actuating fluid pressure.

[0007] DE 10 2022 113 487 A1 describes a fluid device for a hydraulic actuator. Valves are activated by actively applying a current. A return to the rest position occurs passively through a reduction in current and forces applied by a built-in spring. It cannot be ruled out that the valve may jam, meaning the rest position is not reached. Therefore, it is possible to diagnose the position of a drain valve. The drain valve either allows the hydraulic fluid to drain from the hybrid disconnect clutch into a fluid reservoir (rest position of the non-defective drain valve) so that existing pressure is reduced, or it blocks the drain (position of the energized drain valve) so that the existing pressure is not reduced.The diagnosis consists in observing the pressure: If the pressure does not reduce when the drain valve is energized, the drain valve is not in the rest position and is therefore jammed or defective, meaning that no fluid can drain from the separating clutch.

[0008] DE 10 2022 103 384 A1 discloses that hydraulic actuators located outside or above the oil level can run dry during idle times. To ensure operational readiness and the desired performance, for example, for engaging a parking lock, the system must be filled, since air in the hydraulic system results in reduced rigidity and consequently poorer performance, particularly in terms of dynamics. The aim of DE 10 2022 103 384 A1 is therefore to pre-fill the actuator to ensure subsequent actuation with maximum performance. Depending on the idle time and the ambient temperature, a filling routine is initiated, for example, when unlocking the vehicle. After a predetermined termination criterion is met, the system's operational readiness is reported back, and the subsequent actuation can be carried out.

[0009] DE 10 2018 131 117 A1 describes that an electrically operated reversing pump is responsible for actuating the parking lock and the disconnect clutch, as well as pumping the coolant in the transmission. In one direction of rotation, the coolant is pumped through the cooling circuit; in the other direction of rotation, the pressure required to actuate the disconnect clutch or parking lock is provided. The pump is not located in the fluid sump, but is mounted at a distance above the sump. After a long wait, for example when the vehicle's ignition is switched off, the intake pipes may be empty. An initial filling of the intake pipes after the ignition is switched on in the transmission control unit is therefore provided. For this purpose, a 2-way valve in the drain line between the pump and the disconnect clutch is set to flow. The pump pumps fluid towards the disconnect clutch, but this is not actuated because the fluid flows back into the fluid sump via the drain valve.The pump thus pumps the fluid from the sump toward the separating coupling and back through the valve in the drain pipe into the fluid sump. Due to the low air resistance within the pump, the pump speed is high at a constant voltage. The speed decreases as more fluid is drawn in and the air content decreases. Once the air has been completely pumped out of the intake pipe, the speed remains constant at a low level.

[0010] DE 10 2018 130 700 A1 describes that with so-called open hydraulic circuits, there is a fundamental risk that the pump's intake line may run dry, which can delay the availability of hydraulic functions until the line is vented and the pump begins to draw in air. DE 10 2018 130 700 A1 therefore proposes the following measures: • Test whether hydraulic readiness is present by turning the pump in the actuation direction. • Turn the pump in the direction of the cooling oil to supply or fill the suction line. • Bleed the actuating section by turning the pump towards the actuation and switching the valves accordingly.

[0011] It should be noted that the measures mentioned can be carried out in different order, combination and / or number of repetitions depending on the boundary conditions.

[0012] Many automated clutch systems have an actuator that contains a movable piston, for example a master cylinder with a master cylinder piston and a slave cylinder CSC (Concentric Slave Cylinder) with a slave cylinder piston, whereby the pistons interact with each other via a hydraulic fluid in a hydraulic line. Thus, a certain volume of fluid is displaced when the clutch is actuated. If the pressure is to be kept constant, the piston remains in one position. If too low or too high a pressure is detected, it is regulated by moving the piston in the actuator. When no more pressure is required, the piston moves to its original position and the pressure drops to 0 bar. The clutch is actuated with a clutch actuation device, also referred to below as the actuation device. The hydraulic fluid is also referred to below as oil.

[0013] According to the invention, a parking lock, like a clutch, is actuated by a pump actuator comprising a fluid pump. The pump actuator provides the required fluid flow to actuate both systems (parking lock and clutch), and a switching valve distributes the fluid flow to the parking lock or the clutch as needed. By default, the switching valve is in the "clutch" position. This means that as long as the switching valve is not energized, fluid pumped by the fluid pump is directed toward the clutch to close the clutch, while the switching valve blocks the line to the parking lock.

[0014] The operation of the fluid device, such as that used in Fig. 1 is shown, is carried out, among other things, by means of a method for establishing a hydraulic readiness of a fluid device, hereinafter also referred to as the control method, which controls, for example, the fluid pump, the switching valve and the drain valve (pressure relief valve DV) but also the other valves and processes data from sensors, such as a pressure sensor and a position sensor.

[0015] The clutch, for example a “closed” or “normally open” clutch, is therefore not actuated by a master cylinder piston, but by a pump actuator that has a fluid pump. If the target “clutch engagement” is requested, for example by a higher-level or other conventional control method, the drain valve, also referred to below as the pressure relief valve DV, closes. The fluid pump supplies the fluid volume flow towards the slave cylinder piston of the CSC (Concentric Slave Cylinder) until the pressure, also referred to below as the CSC pressure or the actuating fluid pressure of the clutch actuation device, has reached a predetermined value for the target pressure. The CSC pressure can then be maintained for a desired time if requested. If the CSC pressure is to be reduced, the pressure relief valve DV is opened completely.For this purpose, the pressure relief valve is no longer energized and the pressure relief valve opens automatically, for example by means of a spring mechanism.

[0016] The clutch and the parking lock are operated with an actuator device, also referred to as a fluid device or actuator, as in Fig. 1, is actuated hydraulically via the fluid volume flow provided by the fluid pump. It is important that the actuation time of the clutch, i.e. the time between the control command from a control unit to the actuator to actuate the clutch and the actual onset of actuation, does not exceed a maximum time. In general, it is permissible to have free air in the hydraulic system, since the fluid pump supplies an almost "infinite" volume for actuating the clutch. However, the more air there is in the system, the more delayed the clutch is actuated, because the air must first be compressed by the actuator. During driving, if the clutch is engaged several times in succession, the air can escape or dissolve in the oil.

[0017] A hydraulic system is never 100% leak-proof. In the fluid device, as used in Fig. As shown in Figure 1, the advantage of this fluid device, namely providing a virtually infinite displacement, is utilized to the extent that a higher leakage is permitted at the CSC. This minimizes friction during actuation. However, after extended downtimes, e.g., overnight, the hydraulic line to the clutch can run dry. This would mean that the clutch would take a very long time to close upon initial start-up. Since the clutch is only supposed to close at a speed of more than 50 km / h during purely electric driving, the delayed closing of the clutch has a significantly negative effect.

[0018] The separating clutch and the parking lock are hydraulically actuated via the flow rate provided by the pump (SHA). It is important that the clutch actuation time does not exceed the maximum. To remove unwanted air from the hydraulic system, a demand-based pre-fill routine is initiated, as already described in the as yet unpublished German patent application 10 2024 101 116.5.

[0019] The mechatronic release valve plays a key role here. It ensures that the hydraulic pressure is released after the clutch is actuated, allowing the clutch to be opened.

[0020] There are also already methods for detecting faults in the drain valve, as described in the as yet unpublished German patent application 10 2023 132 699.6.

[0021] While previous patent applications ensure that a fault in the drain valve is detected early, this "early" detection still occurs during operation. However, opening the coupling has the highest safety requirements. Therefore, a potential fault must be detected before operation.

[0022] The object of the present invention is a method for early fault detection on the pressure relief valve DV (drain valve) before driving.

[0023] These objects are achieved by a method for producing a hydraulic readiness of a fluid device in a motor vehicle having the features according to claim 1.

[0024] The fluid device may be a hydraulic device. The fluid may be a hydraulic fluid. The fluid may be an oil, in particular a hydraulic oil.

[0025] The vehicle may be a motor vehicle, in particular a hybrid vehicle or electric vehicle.

[0026] The fluid pump can be a gear pump. The fluid pump can be a reversing pump. In a first pumping mode, the fluid pump can generate the fluid volume flow to build up the actuating fluid pressure. In a second pumping mode, the fluid pump can supply at least one cooling device with a fluid volume flow. The fluid pump can be alternately switchable between the first and second pumping modes. The fluid pump can be driven by an electric motor.

[0027] The clutch may be a friction clutch or a dog clutch. The clutch may be a separating clutch, particularly a K0 clutch in a hybrid powertrain. The clutch actuation device may have a concentric slave cylinder (CSC) actuation.

[0028] The actuating fluid pressure may be a clutch actuation pressure.

[0029] The first actuation state can result in a closed clutch. The second actuation state can result in an open clutch.

[0030] The pressure relief valve can be a drain valve.

[0031] The first relief valve state may correspond to a fully closed pressure relief valve. The second relief valve state may correspond to a fully open pressure relief valve. The third relief valve state differs from a fully open and fully closed relief valve state, respectively.

[0032] A pressure relief valve may not be provided in the fluid device, at least for limiting the actuating fluid pressure.

[0033] The objects are therefore achieved by a method for establishing a hydraulic readiness of a fluid device in a motor vehicle, comprising the fluid device with a fluid pump, an actuating device which is switchable depending on an actuating fluid pressure which is built up by a fluid volume flow provided by the fluid pump and which is switchable between a first actuating state in which the actuating device is actuated and a second actuating state in which the actuating device is not actuated, and with a controllable pressure relief valve which is switchable at least between a first relief valve state in which the pressure relief valve is closed and a second relief valve state in which the pressure relief valve is open,is switchable and which has the first relief valve state in the first actuation state and, to assume the second actuation state, assumes the second relief valve state from the first actuation state, and a control unit which controls at least the pressure relief valve and the fluid pump, wherein, when the control unit wakes up, an actuation fluid pressure-dependent pre-filling of a hydraulic path of the fluid device, at least between the fluid pump and the actuation device, with hydraulic fluid by means of the fluid pump takes place at a constant, predetermined pump speed (PumpSpeedTar), and the pressure relief valve is opened until a predetermined, first actuation fluid pressure (PrThdFillingDct) is reached. It is provided that, after a specified first period of time after reaching the specified first actuating fluid pressure (PrThdFillingDct), the pressure relief valve is closed until a specified second actuating fluid pressure (PrThdDVCheck) is reached and the pressure relief valve is reopened for a second specified period of time (TimeDvRectangle) when the specified second actuating fluid pressure (PrThdDVCheck) is reached, and the pressure at the end of the second specified period of time (TimeDvRectangle) is determined and wherein after expiry of the second predetermined period of time (TimeDvRectangle), the pressure relief valve is closed again until the predetermined second actuating fluid pressure (PrThdDVCheck) is reached.

[0034] In a preferred embodiment, it is provided that the time period (TimeDVCheck) is determined while the pressure relief valve is closed until the predetermined second actuating fluid pressure (PrThdDVCheck) is reached.

[0035] In a further preferred embodiment, it is provided that the predetermined second actuating fluid pressure (PrThdDVCheck) is lower than a predetermined fourth actuating fluid pressure (PrThdMinCluStOpen), from which the clutch is no longer considered to be open.

[0036] In a particularly preferred embodiment, it is provided that the actuating pressure determined at the end of the second predetermined period (TimeDvRecline) is lower by the predetermined third actuating fluid pressure (PrThdDVCheck - PrHystDvCheck) compared to the predetermined second actuating fluid pressure (PrThdDVCheck) at the beginning of the second predetermined period (TimeDvRecline).

[0037] In a further preferred embodiment, it is provided that the fluid pump has a constant, predetermined pump speed (PumpSpeedTar) until an error (Error) in the pressure relief valve or a fault-free state of the pressure relief valve is detected.

[0038] In a preferred embodiment, it is provided that at the beginning of the pre-filling, a switching valve assumes the switching position that the fluid pump is hydraulically connected to the actuating device via a hydraulic pressure line and a pressure line branch.

[0039] In a further preferred embodiment, it is provided that the actuating pressure in the hydraulic path to the actuating device is determined by means of a pressure sensor (58).

[0040] Further advantages and advantageous embodiments of the invention emerge from the description of the figures and the illustrations.

[0041] The invention is described in detail below with reference to the figures. They show in detail: Fig. 1: A fluid device 10 in a specific embodiment of the invention. Fig. 2: Course of a pre-filling of the fluid device 10 according to the prior art Fig. 3: Course of the method for establishing the hydraulic readiness of the fluid device 10 according to a specific embodiment of the invention with a fault-free fluid device 10 (DV: pressure relief valve 52) Fig. 4: Course of the method for establishing the hydraulic readiness of the fluid device 10 according to a special embodiment of the invention in the case of a faulty fluid device 10: pressure relief valve DV 52 does not close. Fig. 5: Course of the method for establishing the hydraulic readiness of the fluid device 10 according to a special embodiment of the invention in the case of a faulty fluid device 10: pressure relief valve DV 52 does not open.

[0042] Fig. Figure 1 shows a fluid device 10 in a specific embodiment of the invention. The fluid device 10 is arranged in a vehicle and is designed as a hydraulic device 12 containing a hydraulic fluid. The fluid device 10 comprises a fluid pump 14 driven by an electric motor 16, which in turn is electrically controlled by a motor controller 18.

[0043] The fluid device 10 further comprises an actuating device 20 for a clutch 28, hereinafter referred to as the clutch actuating device 26, which, depending on an actuating fluid pressure p, which is built up by a fluid volume flow provided by the fluid pump 14, can be switched between a first actuating state 22, in which the clutch actuating device 26 is actuated (shown here in the dashed area), and a second actuating state 24, in which the clutch actuating device 26 is not actuated. The actuating fluid pressure p is a clutch actuation pressure, which is also referred to as the CSC pressure in this document. The clutch actuating device 26 comprises a CSC actuation, which has a slave cylinder piston 30 that can be displaced depending on the actuating fluid pressure p.

[0044] The fluid volume flow is drawn by the fluid pump 14 from a fluid reservoir 32. A suction-side filter 34 is arranged between the fluid reservoir 32 and the fluid pump 14. The fluid pump 14 is designed as a reversing pump, which, with a first pumping operation, builds up the fluid volume flow to build up the actuating fluid pressure p and, with a second pumping operation, builds up a fluid volume flow to supply additional vehicle components, for example, cooling devices 36, in particular for cooling a ring gear 38, a hollow shaft bearing 40, and one or more electric motors 42. The fluid is cooled by a heat exchanger 44.

[0045] An electrically controllable switching valve 46, here a 4 / 2-way valve, is arranged between the fluid pump 14 and the clutch actuating device 26. The switching valve 46 controls the fluid volume flow between the fluid pump 14 and the clutch actuating device 26, as well as a parking lock actuating device 48, which has a displacement sensor 56 and is associated with a parking lock device 50.

[0046] The parking lock 50, like the clutch 28, is actuated by the fluid pump 14 of the fluid device 10. The fluid pump 14 provides the required fluid volume flow to actuate the respective system, and the switching valve 46 distributes the fluid volume flow, as needed, either entirely to the parking lock actuating device 48 of the parking lock 50 or entirely to the clutch actuating device 26 of the clutch 28, but not to both simultaneously. By default, i.e. in the fault-free, non-energized basic setting determined only by mechanical conditions such as springs, the switching valve 46 is in the "clutch" position and not in the "parking lock" position if the switching valve 46 is not jammed, blocked, or otherwise defective. As long as the switching valve 46 is not defective and is not energized, the oil is passed on to the slave cylinder piston 30 of the CSC of the clutch 28 to close the clutch.

[0047] The fluid device 10 comprises a controllable pressure relief valve (DV) 52, here a 2 / 2-way valve, which can be switched at least between a first relief valve state C1, in which the pressure relief valve (DV) 52 is closed, and a second relief valve state C2, in which the pressure relief valve (DV) 52 is open. In the first actuation state 22, the pressure relief valve (DV) 52 has the first relief valve state C1, i.e., the pressure relief valve (DV) 52 is closed. To assume the second actuation state 24, starting from the first actuation state 22, the pressure relief valve (DV) 52 has the second relief valve state C2, i.e., it is opened, thus reducing the actuation fluid pressure p and disengaging the clutch 28, since it is a "compressed" or "normally open" clutch.

[0048] In the first actuation state 22, the clutch 28 is closed, and the actuation fluid pressure p remains above a first actuation pressure value due to the closed pressure relief valve (DV) 52, from which the first actuation state 22 exists. The check valve 54 prevents a backflow of the fluid into the fluid reservoir 32 and a reduction in the actuation fluid pressure p. Temperature influences can cause pressure increases in the actuation fluid pressure p.

[0049] Fig. 2 shows a method for pre-filling the fluid device 10 - hereinafter also referred to as pre-filling routine or pre-filling process - as shown, for example, in the as yet unpublished German patent application 10 2024 101 116.5.

[0050] Each time the control unit 18 wakes up from a sleep mode after a longer standstill of the vehicle, a pre-filling routine should be given the highest priority, and all hydraulic lines, especially the hydraulic line from the fluid pump 14 to the clutch 28, should be filled depending on the pressure p in the fluid.

[0051] The prefill routine is given the highest priority only if there are no calls with a higher priority than "clutch actuation" at the same time. For example, the priority of "parking lock release" is higher than the priority of "clutch actuation."

[0052] A longer vehicle standstill time is longer than the duration of a stop at a red light or a stop during a traffic jam. During a longer vehicle standstill time, the deviation from the duration of the control unit's sleep mode is generally only slight, since the control unit enters sleep mode after a short vehicle standstill.

[0053] The invention is not directed to the waking up of the control unit 18 Fig. 1, but can refer to any other predefined control unit, the so-called predetermined control unit. A group of several vehicle control units can also be predefined, whereby a wake-up occurs when at least one of the control units in the group wakes up. This group is then considered the predetermined control unit, even though the group includes multiple control units.

[0054] A control unit can be woken up, for example, by unlocking the vehicle using a transponder, either automatically from a distance, or by manually activating the transponder. It is also possible that only opening a vehicle door triggers a control unit to wake up.

[0055] If the predetermined control unit in the vehicle wakes up again after a long period of inactivity, for example because the vehicle was turned off overnight or because the vehicle was turned off for a long time in a parking lot while shopping, etc., a pre-fill routine should be initiated. As long as no higher priority activities, such as service activities or end-of-line teach-in processes or parking lock release, are required, the pre-fill routine starts automatically. The pressure relief valve DV 52 (drain valve) and the switching valve 46, which ensures the supply of fluid, remain open in the hydraulic path to the clutch; for this purpose, a voltage of 0 V is applied to both valves. It must not happen that the clutch 28 is inadvertently closed during the pre-fill routine due to the pressure relief valve 52 closing unintentionally.Subsequently, the fluid pump 14 of the fluid device 10 receives a pump speed specification, which is determined from a stored characteristic curve for the prefilling process. The characteristic curve, and thus the specified speed, depends on both the oil sump temperature and the previous duration of a currently running prefilling process, i.e., the duration of the already running prefilling process (active filling time). After the pump 14 begins to pump fluid toward the clutch 28, the pressure p is monitored in parallel, for example, with a pressure sensor 58 in the hydraulic line to the clutch 28.

[0056] If the pressure p exceeds the pressure limit for pre-filling PrThdFillingDct stored in the control unit 18, whereby the pressure limit PrThdFillingDct is also dependent on the oil sump temperature, this means that the hydraulic path to the clutch 28 is sufficiently filled and that the pre-filling routine process can be terminated.

[0057] If the pressure limit PrThdFillingDct has not yet been reached while the pressure p is building up for a period of time that is shorter than the maximum prefill time, pump 14 should continue to pump the fluid. However, if the pressure limit PrThdFillingDct has not yet been reached, but the prefill time exceeds the maximum prefill time, an error has occurred. The process should be aborted, and an error should be reported to a designated control unit.

[0058] The Fig. 3 to 5 show the course of the method for establishing the hydraulic readiness of the fluid device 10 according to a specific embodiment of the invention.

[0059] Fig. Figure 3 shows the procedure for a faultless pressure relief valve DV 52.

[0060] Fig. 4 shows the process flow when the pressure relief valve DV 52 does not close.

[0061] Fig. 5 shows the procedure when the pressure relief valve DV 52 does not open.

[0062] The pre-filling method as described, for example, in the as yet unpublished German patent application 10 2024 101 116.5 is to be extended by a further function in order to check the drain valve (pressure relief valve DV) 52 before the vehicle is started.

[0063] The prefilling process, as described, for example, in the as yet unpublished German patent application 10 2024 101 116.5, ensures that the prefilling process is executed each time the control unit wakes up, and the hydraulic system is filled with oil. During this process, the drain valve (pressure relief valve DV) 52 remains in its initial, open position. Counterpressure is generated solely by the volume flow toward the CSC (clutch actuation device 26). As soon as this counterpressure reaches a defined threshold PrThdFillingDct, the system is considered filled.

[0064] According to the invention, a further pressure threshold is to be incorporated and taken into account in the method for establishing the hydraulic readiness of the fluid device 10. FillingPressure = PrThdDvCheck is to be an additional pressure threshold between FillingPressure = PrThdFillingDct and FillingPressure = PrThdMinCluStOpen, whereby from a pressure FillingPressure > PrThdMinCluStOpen, the clutch is no longer considered open.

[0065] After the fluid device 10 is detected as filled (Filling-State = Filled) by the above-mentioned pre-filling routine, after a defined, ie predetermined, time delay Δ_t ( Fig. 3 to 5, reference number 3) at constant pump speed (PumpSpeed ​​= PumpSpeedTar) the pressure relief valve DV 52 (drain valve) must be closed ( Fig. 3, reference numeral 4). This ensures that the pressure increases faster and, above all, further.

[0066] If the pressure threshold FillingPressure = PrThdDvCheck is reached ( Fig. 3, reference numeral 1), the pressure relief valve DV 52 (drain valve) opens for the period TimeDvRectangle. During this period, the pressure should be less than or equal to (PrThdDvCheck - PrHystDvCheck) ( Fig. 3, reference numeral 2). In addition, the time period TimeDVCheck between closing the pressure relief valve DV 52 (drain valve) and reaching the pressure threshold FillingPressure = PrThdDvCheck can be determined.

[0067] The pressure relief valve DV 52 (drain valve) is then closed again ( Fig. 3, reference numeral 5) to verify the condition. The pressure should rise again to FillingPressure = PrThdDvCheck and as soon as this pressure threshold is reached ( Fig. 3, reference numeral 1), the pressure relief valve DV 52 (drain valve) opens again, and the pressure should drop again. Here, too, the time period TimeDVCheck between the closing of the pressure relief valve DV 52 (drain valve) and reaching the pressure threshold FillingPressure = PrThdDvCheck can be determined.

[0068] If this target condition has been verified at least twice, the pressure relief valve DV 52 (drain valve) is considered fault-free and therefore fully functional, and the vehicle can now be put into operation without restrictions, at least with regard to the pressure relief valve DV 52 (drain valve). ( Fig. 3)

[0069] The following error scenarios can occur: • When the pressure relief valve DV 52 is closed for the first and second time, the pressure does not rise to PrThdDvCheck: As a result, an error is detected (ErrorState = Error), because the pressure relief valve DV 52 (drain valve) does not close sufficiently. ( Fig. 4, reference number 7) • When the pressure relief valve DV 52 is closed for the first time, the pressure does not rise. When the pressure relief valve DV 52 is closed for the second time, the pressure rises to PrThdDvCheck. Verification should be performed a third time. If the pressure does not rise again, an error is set (ErrorState = Error). If the pressure does rise, a WARNING is set, and the status of the pressure relief valve DV 52 is monitored. • When the pressure relief valve DV 52 is closed for the first time, the pressure rises as expected. However, when the pressure relief valve DV 52 is opened, the pressure drops too little before rising again the second time. An error is set (ErrorState = Error) because the pressure relief valve DV 52 appears to be stuck or is not opening properly, or the pressure relief valve DV 52 may be clogged. • When the pressure relief valve DV 52 is closed for the first time, the pressure does increase, but the pressure does not decrease when the pressure relief valve DV 52 opens again. Instead, the pressure continues to rise and exceeds the pressure threshold PrThdMinCluStOpen. The clutch is now considered closed. An error is set (ErrorState = Error), because the pressure relief valve DV 52 is stuck and does not open again ( Fig. 5, reference number 9).

[0070] Additionally, the TimeDVCheck measured during the first and second closing of the pressure relief valve DV 52 can be compared. If both measured values ​​are sufficiently similar, this confirms that the pressure relief valve DV 52 (drain valve) is fault-free.

[0071] In the method for establishing hydraulic readiness of the fluid device 10, the fluid pump 14 maintains the pump speed PumpSpeed ​​constant at a constant, predetermined value PumpSpeedTar from the start of the fluid device during the aforementioned prefilling process. The pump is only stopped again when an error (7, 9) is detected or the pressure relief valve DV 52 (drain valve) is correct. List of reference symbols 1 If the pressure increase and decrease is proportional to the state of the pressure relief valve DV 52 (DV-State), then this is an indication that the pressure relief valve DV 52 is functioning correctly. 2 PrThdDvCheck - PrHystDvCheck 3 Δ_t: Time delay after the “Filled” state has occurred until the pressure relief valve DV 52 closes. 4 By closing the pressure relief valve DV 52, a targeted check is carried out to see whether the pressure (FillingPressure) continues to rise. 5 The closing and reopening of the pressure relief valve DV 52 is repeated at least twice (DV check) to verify the result. 6 Although the pressure relief valve DV 52 closes and reopens, the pressure (FillingPressure) does not change. This indicates that the pressure relief valve DV 52 is blocked and the actual state of the pressure relief valve DV 52 does not change. 7 After closing and reopening the pressure relief valve DV 52 (DV-Check) twice, an error is detected. 8 Although the pressure relief valve DV 52 should open, the pressure (FillingPressure) continues to rise and reaches the critical limit (PrThdMinCluStOpen), at which the clutch is no longer in the open state. 9 The second closing and reopening (DV check) of the pressure relief valve DV 52 is aborted and an error is set (ErrorState = Error) 10 Fluid device 12 Hydraulic device 14 Fluid pump 16 electric motor 18 Control unit 20 Actuating device 22 first operating state 24 second operating state 26 Clutch operating device 28 Clutch 30 slave cylinder pistons 32 fluid reservoirs 34 filters 36 cooling devices 38 ring gear teeth 40 hollow shaft bearings 42 electric motor 44 heat exchangers 46 Switching valve 48 Parking lock actuation device 50 Parking lock device 52 Pressure relief valve DV 54 check valve 56 displacement sensor 58 Pressure sensor C1 first relief valve state C2 second relief valve state p Actuating fluid pressure

Claims

[1] Method for establishing a hydraulic readiness of a fluid device (10) in a motor vehicle, comprising the fluid device (10) with a fluid pump (14), an actuating device (20) which is switchable depending on an actuating fluid pressure (p) which is built up by a fluid volume flow provided by the fluid pump (14) and which is switchable between a first actuating state (22) in which the actuating device (20) is actuated and a second actuating state (24) in which the actuating device (20) is not actuated, and with a controllable pressure relief valve (52) which is switchable at least between a first relief valve state (C1) in which the pressure relief valve (52) is closed and a second relief valve state (C2) in which the pressure relief valve (52) is open,is switchable and which has the first relief valve state (C1) in the first actuation state (22) and, to assume the second actuation state (24), assumes the second relief valve state (C2) starting from the first actuation state (22), and a control unit (18) which controls at least the pressure relief valve (52) and the fluid pump (14), wherein, when the control unit (18) wakes up, an actuation fluid pressure-dependent pre-filling of a hydraulic path of the fluid device (10), at least between the fluid pump (14) and the actuation device (20), with hydraulic fluid by means of the fluid pump (14) takes place at a constant, predetermined pump speed (PumpSpeedTar), and the pressure relief valve (52) is opened until a predetermined, first actuation fluid pressure (PrThdFillingDct) is reached, , characterized by , that after a predetermined first period of time (Δ_t) after reaching the predetermined first actuating fluid pressure (PrThdFillingDct), the pressure relief valve (52) is closed until a predetermined second actuating fluid pressure (PrThdDVCheck) is reached and the pressure relief valve (52) is reopened for a second predetermined period of time (TimeDvRectangle) upon reaching the predetermined second actuating fluid pressure (PrThdDVCheck), and the pressure at the end of the second predetermined period of time (TimeDvRectangle) is determined and wherein after expiration of the second predetermined period of time (TimeDvRectangle), the pressure relief valve (52) is closed again until the predetermined second actuating fluid pressure (PrThdDVCheck) is reached. [2] Method according to claim 1, characterized bythat the time period (TimeDVCheck) is determined while the pressure relief valve (52) is closed until the predetermined second actuating fluid pressure (PrThdDVCheck) is reached. [3] Method according to claim 1 or 2, characterized by that the specified second actuating fluid pressure (PrThdDVCheck) is less than a specified fourth actuating fluid pressure (PrThdMinCluStOpen), above which the clutch is no longer considered to be open. [4] Method according to one of claims 1 to 3, characterized by that the actuating pressure determined at the end of the second predetermined period (TimeDvRecline) is lower by the predetermined third actuating fluid pressure (PrThdDVCheck - PrHystDvCheck) compared to the predetermined second actuating fluid pressure (PrThdDVCheck) at the beginning of the second predetermined period (TimeDvRecline). [5] Method according to one of claims 1 to 4, characterized bythat the fluid pump (14) has a constant, predetermined pump speed (PumpSpeedTar) until an error (Error) in the pressure relief valve (52) or a fault-free state of the pressure relief valve (52) is detected. [6] Method according to one of the preceding claims, characterized by that at the beginning of the pre-filling a switching valve (46) assumes the switching position that the fluid pump (14) is hydraulically connected to the actuating device (20) via a hydraulic pressure line and a pressure line branch. [7] Method according to one of the preceding claims, characterized by that the actuating pressure (p) in the hydraulic path to the actuating device (20) is determined by means of a pressure sensor (58).

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