Method for controlling a park lock

Abstract

The invention relates to a method for controlling a park lock (20) for a motor vehicle having a control unit which controls a slave cylinder (13) which, controlling the travel path, moves the park lock (20) from an engaged state into a disengaged state and to which system pressure is applied by a pump (3) controlled by the control unit, and having an electrically actuated holding device (18) which is controlled by the control apparatus and form-fittingly holds the park lock (20) in the disengaged state. In order to prevent the motor vehicle from unintentionally rolling away from a stationary state or blocking the park lock during travel in the event of a defective holding device (18), the function of the holding device (18) is checked before the park lock (20) is disengaged, and the park lock (20) is prevented from being disengaged in the event of a malfunction of the holding device (18).

Description

[0001] P241199 DE

[0002] - 1 -

[0003] Method for controlling a parking barrier

[0004] The invention relates to a method for controlling a parking lock for a motor vehicle with a control unit which controls a slave cylinder which moves the parking lock from an engaged to an extended state and which is pressurized by a pump controlled by the control unit and carries out system pressure, and an electrically actuated holding device controlled by the control unit which holds the parking lock positively in the extended state.

[0005] German patent application DE 10 2020 117 020 A1 discloses a device for actuating a parking lock by means of a slave cylinder and a method for controlling the actuation by means of this device. To keep the parking lock in the open state, and thus actuated by the slave cylinder, regardless of the system pressure acting on the slave cylinder, a holding device with an auxiliary cylinder is provided, the locking pin of which engages positively when the parking lock is actuated. Furthermore, the applicant's unpublished German patent application No. 10 2023 103 469.3, which is hereby incorporated in its entirety into the present disclosure, contains a device for actuating a parking lock in which the parking lock is held positively in both the actuated and open states by means of an electrically operated holding device.

[0006] The object of the invention is the further development of a method for controlling a parking lock which is hydraulically actuated by means of a slave cylinder and positively locked in the actuated state by means of a holding device. In particular, the object of the invention is to propose a method for controlling such a parking lock, P241199 DE

[0007] - 2 - which prevents the motor vehicle from rolling away unintentionally and / or the parking lock from closing unintentionally.

[0008] The problem is solved by the subject matter of claim 1. The dependent claims describe advantageous embodiments of the subject matter of claim 1.

[0009] The proposed method serves to control a parking lock for the powertrain of a motor vehicle, for example, a hybrid or purely electric vehicle. A control unit is provided for actuating the parking lock. This unit controls an electrically operated pump, thereby regulating system pressure, and simultaneously controls a slave cylinder along the travel of its piston. To actuate the parking lock, the slave cylinder is pressurized with system pressure, so that a movement of its piston actuates and thus opens the parking lock, whether it is engaged or disengaged. Therefore, the parking lock is closed when not actuated and open when actuated.To keep the parking lock open regardless of the state of the slave cylinder in the actuated position, an electrically actuated and control-controlled holding device is provided, which holds the parking lock positively in the deployed, actuated and open state.

[0010] The proper functioning of the parking lock, and thus the safe operation of the vehicle, depends significantly on the function of the holding device. It is therefore recommended to check the function of the holding device before engaging or disengaging the parking lock and to prevent the parking lock from engaging if it malfunctions. In the event of a malfunction, the primary measure is to prevent movement of the vehicle; further steps to at least partially restart the vehicle can be taken as described below. P241199 DE

[0011] - 3 - written. A malfunction can occur, for example, if the holding device cannot be released when the parking lock is engaged. In this way, the parking lock can no longer be switched to the locked state, i.e., the unengaged state in this configuration, by, for example, the slave cylinder being returned to its unpressurized zero position by the action of a spring device pre-tensioned when the parking lock is engaged. The parking lock therefore fails to function, and the vehicle can roll unintentionally. Alternatively, if the parking lock is engaged and the holding device is not functioning, the parking lock can be at least partially engaged, for example, while driving, if the system pressure drops.By monitoring the holding device and, if necessary, intervening in the operation of the parking lock, this prevents potential hazardous situations in the event of a malfunction of the holding device.

[0012] For example, the holding device can include a slave cylinder piston of the slave cylinder that moves axially and actuates the parking lock along an actuation path, or a locking element that engages positively with this component and is controlled by a magnetic switch controlled by the control unit, whereby electrical parameters are checked by the control unit before the parking lock is deployed.

[0013] The proposed method can, for example, be implemented in a hydraulic system with a hydraulic actuator, which may include a pump that pumps a pressure medium into a pressure line, thereby generating system pressure. The pump may be driven by an electric motor, for example a contactless commutated electric motor, which drives the pump at a controlled speed, so that P241199 DE

[0014] - 4 - the pumping capacity of the pump is adjusted by means of the speeds of the electric motor.

[0015] The slave cylinder is connected to the pressure line. Its piston is moved along an actuation path depending on the system pressure, thereby driving an actuating mechanism that engages a parking pawl, such as a wheel clamp, parking pawl, or similar device. This engages or disengages a drive element connected directly to the drive wheels or, for example, via a gearbox. The parking pawl has two states: an engaged state, in which it is effectively activated, and a disengaged state, in which it is ineffective and the vehicle is driven normally. When system pressure is applied, the parking pawl is disengaged, meaning it is inactive if there is insufficient system pressure, and the slave cylinder is in its neutral position.To hold the parking lock in the engaged position when system pressure is applied, a holding device is provided that positively locks the actuating mechanism in this state, both when the parking lock is deployed and when actuated. For the positive locking connection of the actuating mechanism, a locking element is provided, for example, a locking pin or pawl that can be displaced in a locking sleeve. In the case of a locking pin, this element is displaceable within a housing-fixed locking sleeve, while in the case of a pawl, it is fixed to the housing and rotatable. It engages positively in a detent recess of the slave cylinder piston or the actuating mechanism effectively associated with it. To release the positive locking connection, a solenoid such as a magnetic switch is provided, which displaces the locking element (e.g., the locking pin) within the locking sleeve and releases it from the corresponding position. P241199 DE.

[0016] - 5 - pulls out the detent recess so that the actuating mechanism can again be moved along the actuating path depending on the pressure. For example, the locking element can be spring-loaded into a detent recess that defines at least one state by means of a spring device and pulled out of the detent recess by the lifting magnet against the action of the spring device.

[0017] The correct displacement of the actuating mechanism can be detected. For example, a displacement sensor can be arranged on the actuating mechanism or on a piston rod of the slave cylinder piston, where the detent recess may also be provided. Alternatively, a displacement transducer can be fixed to the housing, which detects corresponding displacement markings on the displaced component – ​​piston rod or actuating mechanism – for example, displacement increments, and converts them into a displacement signal.

[0018] For example, to check the functionality or malfunction of the holding device, the electrical properties of a coil in the magnetic switch can be examined. For instance, a fault can be detected if the coil's electrical resistance falls outside a predefined range. Depending on the resistance, a short circuit or an open circuit in the electrical line may be present, leading to malfunction of the holding device.

[0019] Alternatively or additionally, a fault can be detected, for example, if the current draw of the coil under load is within a predefined range. If the current draw is outside the range, for example, jamming of the locking element in the detent recess can lead to an increased current draw. P241199 DE

[0020] - 6 - This can lead to problems. If the current draw is too low, a broken wire may be the cause, for example.

[0021] A single detected error can trigger a malfunction of the holding device.

[0022] To increase the robustness of the monitoring of the holding device's malfunction, any occurring error can be subjected to a reproducibility or plausibility check. For example, an error counter can be provided, whereby a malfunction is triggered after a predetermined number of detected errors. Additional plausibility checks of the parking lock's activation can be performed, for example, in accordance with the disclosure of the aforementioned German patent application No. 10 2023 103 469.3.

[0023] Alternatively or additionally, to ensure the reproducibility of a detected fault, a persistent fault can be identified after at least one automated or driver-initiated reset of the control unit. This can involve checking the holding device when the vehicle is started, such as when restarting after being parked by the driver, and / or before each automated or driver-initiated activation of the parking lock.

[0024] In the event of a malfunction, the control unit switches to an emergency operating mode. This means, for example, that the driver is informed of the driver's unavailability and / or further measures are initiated automatically or by the driver. For example, the parking lock can be temporarily replaced by an electrically activated parking brake or electrically operated service brakes to prevent the vehicle from rolling away. In emergency operating mode, the control unit can allow the vehicle to be driven at a limited speed, for example, to the nearest repair shop. P241199 DE

[0025] - 7 -

[0026] The invention is explained in more detail with reference to the embodiment shown in Figures 1 to 3. These show:

[0027] Figure 1 shows a hydraulic diagram of a hydraulic system for operating a parking lock,

[0028] Figure 2 shows a diagram during an activation of the parking lock of Figure 1 over time, and

[0029] Figure 3 shows a flowchart for carrying out the proposed method. Figure 1 shows a schematic representation of the hydraulic diagram of the hydraulic system 1 used, for example, to carry out the proposed method. The possible additional actuation of a friction clutch is not shown here. The hydraulic system 1 contains the actuator 2, which in this case consists of the pump 3 and the electric motor 4 that drives it. The pump sensor 5 is associated with the pump 3. This sensor detects the speed of the electric motor 4, for example, for its electronic commutation, and, given the pump characteristics, enables the measurement of the pump power. In the illustrated embodiment, the pump 3 pumps fluid such as pressure medium, hydraulic fluid, for example, oil, from the unpressurized tank 6 to the branch 7.

[0030] Valve 8, for example a switching valve controlled by a control unit, is located downstream of branch 7 in the fluid flow. Valve 8 is electromagnetically actuated and biased in the open position shown. Via a control pressure line with the optional hydraulic resistance 9, valve 8 is supplied with the system pressure present at branch 7. P241199 DE

[0031] - 8 -

[0032] The first hydraulic consumer 10, indicated only as a coupling, can be effectively connected to the valve 8 for cooling and / or lubrication, particularly when consumers 11 and 12 do not require a supply. Cooling and / or lubrication constitutes a subordinate hydraulic consumer in the hydraulic system 1.

[0033] The hydraulic system 1 supplies the consumers 11 and 12, for example, the slave cylinder of a disconnect clutch in consumer 11 and the slave cylinder 13 of the parking lock 20 (not shown in detail). The slave cylinder piston 14 is mounted in the slave cylinder 13 so as to be displaceable along the actuation stroke s. The slave cylinder piston 14 is pre-tensioned at a zero position of the actuation stroke s (shown here) by means of the spring element 26 and is displaced along the actuation stroke s against the action of the spring element 26 by means of the system pressure applied to the slave cylinder 13. The valve 24 serves to control the system pressure.

[0034] The piston rod 15, belonging to the actuating mechanism 16, is connected to the slave cylinder piston 14 and has detent recesses 28, 29. The position sensor 17 is associated with the piston rod 15. The actuating mechanism 16 acts, for example, on a parking claw, a parking latch, or the like of the parking lock 20, which is designed according to the prior art.

[0035] The parking lock 20 can, for example, have a parking lock wheel that is rotatable when the parking lock 20 is open and locked when the parking lock 20 is closed or locked. For example, the closed parking lock 20, i.e., the parking pawl engaging positively in the parking lock wheel, can be engaged by means of the actuating mechanism 16 when system pressure is applied, thus closing the parking lock 20 as if it were engaged. P241199 DE

[0036] - 9 -

[0037] The slave cylinder 13 can be pressurized, for example, by means of valve 23, such as an electrically controlled switching or proportional valve, with the system pressure supplied by actuator 2 and switched by means of valve 8. The system pressure at the slave cylinder 13 is controlled by adjusting the pump speed of pump 3. At the beginning of the actuation process of the parking lock 20 – here for opening and extending the parking lock 20 – a high pump speed is set at the zero position, which is then reduced to a predetermined switching point near the end position when the parking lock 20 is fully open. From the switching point, the pump speed is increased slightly again to ensure that the end position is reached despite any disturbances that may be present, such as leakage, changes in fluid viscosity, mechanical friction, manufacturing tolerances, and / or the like.

[0038] The holding device 18 contains the locking element 19, designed here as a locking pin, which is mounted in the housing-fixed locking sleeve 21 and is displaceable perpendicular to the piston rod 15 against the action of the spring element 27. Due to the preload of the spring element 27, the locking element 19 is biased against the piston rod 15. The locking element 19 can be displaced against the action of the spring element 27 by means of the magnetic switch 22 when the spring element 27 is energized, thereby releasing the contact with the piston rod 15.

[0039] The locking element 19 engages in one of the two detent recesses 28, 29 when the piston rod 15 is displaced accordingly, thus positively locking the piston rod 15 and therefore the actuating mechanism 16 in the engaged or disengaged state of the parking lock 20. To release the piston rod 15, the locking element 19 is disengaged from the locking sleeve 21 by means of the electrically controlled magnetic switch 22.

[0040] - 10 - is displaced from the relevant detent recess 28, 29 due to the action of the spring element 27.

[0041] Due to tolerances such as variations in the coefficient of friction, extreme system temperatures, and / or the like in the holding device 18, the locking element 19 may not be pulled out of the corresponding detent recess 28, 29 by the switching magnet 22 when the parking lock 20 is engaged or disengaged. Furthermore, the magnetic switch 22 itself may be damaged. This leads, on the one hand, to a situation where, if the locking element 19 is jammed in the detent recess 28, the parking lock 20 can no longer be activated by the spring element 26 when the system pressure decreases and remains permanently disengaged, which can lead to unintended rolling of the vehicle. On the other hand, if the holding device 18 is faulty, the locking element 19 does not engage in the detent recess 28 when the parking lock 20 is actuated, so that if the system pressure decreases due to system factors, the parking lock 20 may engage unintentionally.

[0042] This malfunction is detected by continuously checking and validating the electrical parameters of the magnetic switch 22, particularly before the vehicle is started and / or before the parking lock 20 is activated. For example, the electrical resistance and / or, when the magnetic switch 22 is in operation, its load, such as its current, are determined. If these electrical parameters are outside of predefined or predefinable ranges, a malfunction of the magnetic switch 22 or the holding device 18 is concluded, and further operation of the vehicle is prevented for safety reasons.

[0043] It may be provided that, if the parking lock can no longer be activated or engaged, the vehicle is automatically controlled by the control unit or initiated by the driver, either temporarily or alternatively by means of a possible pre-handle. P241199 DE

[0044] - 11 - The vehicle is prevented from rolling away by the electric parking brake and / or electrically operated service brakes. A corresponding driver warning to visit a workshop is issued as a matter of priority.

[0045] Figure 2 shows, with reference to the hydraulic system 1 of Figure 1, diagram 100 of the actuation of the parking lock 20, based on sub-diagrams I, II, III, and IV over time t. Sub-diagram I shows the current i of the magnetic switch 22, sub-diagram II the voltage U across the magnetic switch 22, sub-diagram III the actuation stroke s of the piston rod 15, and sub-diagram IV the switching signal P over time t. At time t=0, the parking lock 20 is engaged, the vehicle is stationary with the parking lock 20 closed, the switching signal P is in the low position LOW, the actuation stroke is s=0 (i.e., the slave cylinder piston 14 of the slave cylinder 13 is in the zero position), and the voltage U and current i of the magnetic switch are U=0, i=0.

[0046] At time t1, switching the switching signal P to HIGH initiates the opening of the parking lock 20. Applying system pressure to the slave cylinder 13 causes the slave cylinder piston 14, the piston rod 15, and the actuating mechanism 16 to move along the actuating path s into the deployed position s(a), in which the parking lock 20 is open, i.e., not actuated. Due to the overlap of the detent recess 28 with the locking element 19, the latter, assisted by the spring element 27, automatically engages in this recess and positively locks the piston rod 15 in place.

[0047] At time t2, switching the switching signal P to LOW initiates the closing and disengaging of the parking lock 20. For this purpose, the system pressure is reduced, and the insertion voltage U(e) is applied to the magnetic switch 22. The target current i(setpoint) specified for proper function is applied to the insertion voltage P241199 DE

[0048] - 12 -

[0049] The resulting input current i(e) is almost reached and is above the range i(limit), so that the locking element 19 is retracted against the action of the spring element 27 by means of the magnetic switch 22 and the slave cylinder piston 14 returns to its zero position with the support of the spring element 26 and the parking lock 20 effectively holds the vehicle in rest position.

[0050] At time t3, the parking lock 20 is reopened as designed, corresponding to time t1. During the subsequent engagement of the parking lock 20 at time t4, the engagement voltage U(e) fails, for example, due to a broken wire or similar fault. Consequently, the magnetic switch 22 is not energized, and the locking element 19 remains in the detent recess 28. The reduction of the system pressure has no effect on the actuation travel s, and the parking lock 20 remains open despite the switching signal P being LOW, creating a risk of the vehicle rolling away. Therefore, before the parking lock 20 is engaged, an electrical parameter, such as the engagement current i(e), is pre-checked by actuating the magnetic switch 22. If this current is below the limit i(limit), engagement of the parking lock 20 is prevented.Alternatively, the vehicle can be temporarily prevented from rolling away by appropriately controlling an electric parking brake and / or electrically controlled service brakes. Figure 3 shows, with reference to the preceding figures, the flowchart 200 for monitoring the holding device 18 of Figure 1. For this purpose, routine 201 is implemented in a control unit of the vehicle, for example, a control unit integrated into the hydraulic system 1.

[0051] Routine 201, for example, is started externally in block 202 via a start signal from the vehicle, for example via CAN. For this purpose, the control unit's processor is initialized in block 203. Branch 204 checks whether a P241199 DE error code is present.

[0052] - 13 -

[0053] The status ST(22) of magnetic switch 22 is implausible (NOT_VALID). If this is the case, the switching signal P in block 208 is held LOW, activation of the parking lock 20 is prevented and the parking lock 20 remains in the park position.

[0054] If the status ST(22) is plausible, for example the input current is greater than the range i(limit), a counter C in block 205 is incremented by one.

[0055] Branch 206 checks whether a request to activate the parking lock 20 has been received, i.e., whether the switching signal P is HIGH. If not, branch 207 checks whether counter C is greater than zero. If so, the system branches back to branch 206. If counter C is zero, the system branches to branch 204.

[0056] If a request is made to activate the parking lock 20, branch 209 checks, in accordance with branch 204, whether the status ST(22) of the magnetic switch 22 is implausible (NOT_VALID). If this is the case, i.e., if there is a malfunction of the holding device 18, for example, if the range i(limit) has been undershot, block 208 prevents the activation of the parking lock 20 by setting P=L0W. If the status ST(22) of the holding device 18 is plausible, block 210 enables the activation of the parking lock 20 by changing the switching signal to P=HIGH.

[0057] P241199 DE

[0058] - 14 -

[0059] List of reference signs

[0060] 1 Hydraulic system

[0061] 2 Actuator

[0062] 3 Pump

[0063] 4 electric motor

[0064] 5 Pump sensor

[0065] 6 Tank

[0066] 7 branching

[0067] 8 valve

[0068] 9 hydraulic resistance

[0069] 10 consumers

[0070] 11 consumers

[0071] 12 consumers

[0072] 13 slave cylinders

[0073] 14 slave cylinder pistons

[0074] 15 Piston rod

[0075] 16 Actuation mechanism

[0076] 17 Position sensor

[0077] 18 Holding device

[0078] 19 Locking element 0 Parking lock 1 Locking sleeve 2 Magnetic switch 3 Valve 4 Valve 6 Spring element 7 Spring element 8 Detent recess 9 Detent recess

[0079] 100 Diagram 00 Flowchart 01 Routine P241199 DE

[0080] - 15 -

[0081] Block 202

[0082] Block 203

[0083] 204 branch

[0084] 205 Block

[0085] 206 branch

[0086] 207 Branching

[0087] 208 Block

[0088] 209 branch

[0089] Block 210

[0090] C Meter i Current i(e) Input current i(limit) Range i(set) Set current

[0091] P switching signal

[0092] ST(22) Status magnetic switch s Actuation path s(a) Disengagement position

[0093] U voltage

[0094] U(e) Input voltage t Time t1 Time t2 Time t3 Time t4 Time

[0095] Part I subdiagram

[0096] II Subdiagram

[0097] III Subdiagram

[0098] IV Subdiagram

Claims

P241199 DE - 16 - Patent claims 1. Method for controlling a parking lock (20) for a motor vehicle with a control unit which controls a slave cylinder (13) which moves the parking lock (20) from an engaged to a disengaged state and is pressurized by a pump (3) controlled by the control unit, and an electrically actuated holding device (18) controlled by the control unit which holds the parking lock (20) positively in the disengaged state, characterized in that the function of the holding device (18) is checked before the parking lock (20) is disengaged and disengagement of the parking lock (20) is prevented in the event of a malfunction of the holding device (18).

2. Method according to claim 1, characterized in that the holding device (18) includes a locking element (19) which engages in a form-fitting manner in an axially displacing slave cylinder piston (14) of the slave cylinder (13) which actuates the parking lock (20) along an actuation path (s), and which is controlled by means of a magnetic switch (22) controlled by the control unit, wherein electrical parameters of the holding device (18) are checked by the control unit before the parking lock (20) is deployed.

3. Method according to claim 2, characterized in that electrical properties of a coil of the magnetic switch (22) are checked.

4. Method according to claim 3, characterized in that an error is detected when an electrical resistance of the magnetic switch (22) lies outside a predetermined range.

5. Method according to claim 3 or 4, characterized in that a fault is detected if the current consumption of the magnetic switch (22) under load is outside a predetermined range.

6. Method according to one of claims 1 to 5, characterized in that a malfunction is detected in the event of one or more successive malfunctions. P241199 DE - 17 - 7. Method according to claim 6, characterized in that, after at least one automated or driver-performed reset of the control unit, a continuing fault is detected as a malfunction.

8. Method according to one of claims 1 to 7, characterized in that a check of the holding device (18) is carried out when the motor vehicle is started.

9. Method according to one of claims 1 to 7, characterized in that the control unit switches to an emergency operating mode in the event of a malfunction.

10. Method according to claim 9, characterized in that the motor vehicle is made to roll away by means of actuation of an electrically controlled parking brake and / or electrically controlled service brakes.

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