METHOD FOR DETECTING A SAFE STATE OF A VALVE OF A HYDRAULIC SYSTEM

Abstract

A method for detecting a safe state of a switchable valve of a hydraulic system of an actuator in a motor vehicle includes the at least one first switchable valve, which is actuated by being energized, a pump, and a controller which controls at least the first switchable valve and the pump. The pump delivers the fluid to a first load in a first rotational direction and to at least one second load in a second rotational direction.

Claims

1. A method for detecting a safe state of a switchable valve of a hydraulic system of an actuator in a motor vehicle having at least one first switchable valve which is actuated by being energized, a pump and a controller which controls at least the first switchable valve and the pump, comprising: delivering fluid, via the pump, to a first consumer in a first rotational direction and delivering fluid, via the pump, to at least one second consumer in a second rotational direction, and having a line system through which the pump can be connected to the at least one second consumer with the first switchable valve being interposed, wherein the line system has a hydraulic pressure line connected to the pump and a first pressure line branch actuating a parking lock and a second pressure line branch actuating a friction clutch, wherein the two pressure line branches can be alternately connected to the hydraulic pressure line by means of the first switchable valve, wherein a pressure sensor connected to the controller is mounted in the pressure line branch actuating the friction clutch, wherein the energization of the first switchable valve is deactivated by the controller and the pump is activated with an increasing speed ramp in the second rotational direction, and in that the safe state of the first switchable valve is detected when a pressure difference at the pressure sensor since a start of the speed ramp reaches a predetermined limit value within a predetermined time period since the start of the speed ramp.

2. The method according to claim 1, wherein a second switchable valve controlled by the controller and actuated by being energized is introduced into the pressure line branch actuating the friction clutch, by means of which the pressure line branch actuating the friction clutch can be alternately connected to a reservoir via a discharge line, wherein the safe state of the first switchable valve is detected and the pump is deactivated and the safe state of the second switchable valve is detected when the pressure difference at the pressure sensor falls back to the value from before the start of the speed ramp.

3. The method according to claim 1, wherein the pump is activated from standstill with the increasing speed ramp in the second rotational direction.

4. The method according to claim 2, wherein the first switchable valve is a 4/2 valve and the second switchable valve is a 2/2 valve.

5. A device for detecting a safe state of a switchable valve of a hydraulic system of an actuator in a motor vehicle comprising: at least one first switchable valve which is actuated by being energized, a pump and a controller which controls at least the first switchable valve and the pump, wherein the pump delivers fluid to a first consumer in a first rotational direction and delivers fluid to at least one second consumer in a second rotational direction, and having a line system through which the pump can be connected to the at least one second consumer with the first switchable valve being interposed, wherein the line system has a hydraulic pressure line connected to the pump and a first pressure line branch actuating a parking lock and a second pressure line branch actuating a friction clutch, wherein the two pressure line branches can be alternately connected to the hydraulic pressure line by means of the first switchable valve, wherein a pressure sensor connected to the controller is mounted in the pressure line branch actuating the friction clutch, and wherein a second switchable valve controlled by the controller and actuated by being energized is introduced into the pressure line branch actuating the friction clutch, by means of which the pressure line branch actuating the friction clutch can be alternately connected to a reservoir via a discharge line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The disclosure is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 and 2. In the figures:

[0020] FIG. 1 shows a hydraulic diagram of a hydraulic system

[0021] FIG. 2 shows a schematic representation of the method according to the disclosure for detecting the safe state of the valve 21 in the hydraulic system of FIG. 1.

[0022] Left: Valve 21 is OK (valve is in safe state)

[0023] Right: Valve 21 is not OK (safe state of the valve 21 not confirmed)

[0024] FIG. 3 shows a flow diagram of the method according to the disclosure for detecting the safe state of the valve 21 and/or the valve 24 in the hydraulic system of FIG. 1.

DETAILED DESCRIPTION

[0025] FIG. 1 shows a schematic representation of the hydraulic system 1 of the actuator. The hydraulic system 1 has a pump 2 designed as a reversing pump. The pump 2 can be driven in a first rotational direction 3. In the first rotational direction 3, the pump 2 delivers fluid to the first consumer 4, such as a cooling device, and provides a volume flow function.

[0026] The pump 2 can be driven in a second rotational direction 5 opposite to the first rotational direction 3. In the second rotational direction 5, the pump 2 delivers the fluid to the two consumers 6. In this regard, an operating pressure is built up in order to actuate them. In the exemplary embodiment shown, the pump 2 delivers the fluid to two second consumers 6, in this case to a slave cylinder of the parking lock 7 and to a slave cylinder of the friction clutch 8.

[0027] The pump 2 is driven by the electric motor 9. The electric motor 9 is controlled by the controller 10. The first pump inlet 11 of the pump 2 is connected to the first consumer 4 by means of the cooling line 12 with the check valve 14 being interposed and to the first intake branch 16 drawing in from the reservoir 15 by means of the check valve 13. The check valve 13 prevents the fluid from being pumped back into the reservoir 15.

[0028] The opposite pump inlet 17 of pump 2 is connected to the intake branch 20 with the check valve 19 being interposed. The pump inlet 17 is also connected to the line system 30, which contains the hydraulic pressure line 18, the pressure line branches 22, 23, the valves 21, 24, the check valve 25 and the discharge lines 27, 28. The pressure line branches 22, 23 are followed by the consumers 6, which are each actuated, for example, by means of a slave cylinder, not shown, connected to one of the pressure line branches 22, 23. Depending on the rotational directions 3, 5, the pump 2 draws in fluid from the reservoir 15 from one of the intake branches 16, 20 in each case.

[0029] The hydraulic pressure line 18 can be alternately connected to the pressure line branch 22 supplying the slave cylinder of the parking lock 7 or the pressure line branch 23 supplying the slave cylinder of the friction clutch 8 by means of the switchable valve 21, in this case a 4/2 valve. The switchable valve 24, in this case a 2/2 valve, is introduced into the pressure line branch 23 and connects it to the reservoir 15 via the discharge line 27. With the valve 21 connected between the hydraulic pressure line 18 and the pressure line branch 23, the pressure line branch 22 is connected to the reservoir 15 by means of the discharge line 28, so that the parking lock 7 is disengaged. With the hydraulic pressure line 18 connected to the pressure line branch 22, the pressure line branch 23 is decoupled. A pressure built up at the slave cylinder of the friction clutch in order to actuate the friction clutch 8 is maintained by means of the check valve 25, so that the friction clutch 8 remains engaged, for example, regardless of the energization of the valve 21 or the operation of the pump 2, and only the pressure loss due to leakage has to be compensated for. The friction clutch 8 is disengaged by opening the valve 24.

[0030] The pressure sensor 26 connected to the controller 10 is connected to the pressure line branch 23.

[0031] FIG. 2 shows the basic sequence of the method according to the disclosure. It is assumed, in this regard, that the valve 24 is switched to the open position.

[0032] FIG. 2, right (top) shows the case in which the valve 21 does not fall back from the actuated state (connection to the parking lock) to the rest state, for example because the valve 21 is jammed, although the valve 21 is intended to fall back to the rest state in accordance with step 50 (FIG. 3).

[0033] FIG. 2, left (top) shows the case in which the valve 21 falls back from the actuated state to the rest state, as intended in accordance with step 50 (FIG. 3).

[0034] In both cases, the pump 2 is now operated in the direction of the pump inlet 17, i.e., in the direction of reference sign 5, with an increasing speed ramp of, for example, 20 rpm/ms (cf. step 70 in FIG. 3) (FIG. 2, bottom).

[0035] According to FIG. 2, right (center), the pressure at the pressure sensor 26 does not increase, as there is no hydraulic connection to this pressure line branch 23 due to the jammed valve 21.

[0036] According to FIG. 2, right (bottom), the pump reaches its maximum speed with the speed ramp and stops after the predetermined time period t of 200 ms, for example, has elapsed (cf. step 80 in FIG. 3).

[0037] According to FIG. 2, left (center), the pressure at pressure sensor 26 increases up to a predetermined pressure difference p compared to the pressure before the start of the speed ramp of the pump 2, which is determined in step 60, since the valve 21 is not jammed and has fallen back to the safe state.

[0038] According to FIG. 2, left (bottom), the pump does not reach its maximum speed at all with the speed ramp and stops when the predetermined pressure difference of, for example, 0.3 bar is reached (cf. step 80 in FIG. 3).

[0039] FIG. 3 shows the entire sequence of the method with exemplary values. This also includes the optional detection of the discharge valve 24.

[0040] A routine for execution after a valve actuation of the valve 21 is disclosed, which checks whether the valve is back in the rest position. If not, preventive replacement reactions are possible in order to prevent the activation of undesired, safety-critical functions in the vehicle.

[0041] In the rest position, the valve 21 is in the clutch 8 position, as shown in FIG. 1. The valve 21 thus connects the hydraulic pressure line 18 and the pressure line branch 23. The valve 21 is therefore not in the alternative parking lock 7 position. The pressure sensor 26 present in the pressure line branch 23 is used to detect this valve position of the valve 21. Due to the characteristics of the present hydraulic system, it is possible to build up a dynamic pressure p at the pressure sensor 26, as there is a fluid flow from the pump 2 to the tank 15 when the discharge valve 24 is open, but this does not actuate the clutch 8. In this regard, the following requirements exist with regard to the method: The pressure p must exceed a predetermined value that is greater than the sensor accuracy of the pressure sensor 26 in order to have a meaningful result. On the other hand, however, the pressure p must not become too high in order to ensure that no leakage towards the clutch 8 or even an undesired clutch actuation occurs. In addition, only a certain amount of time is available for the entire method. The method should be carried out after each actuation (disengagement of parking lock 7) and subsequent actual falling back of the valve 21 as shown in FIG. 2 on the left, or as shown in FIG. 2 on the right, in the event that a falling back of the valve 21 was intended but has not actually occurred due to a fault or damage to be detected by means of the method according to the disclosure (FIG. 3, step 50). The speed of the hydraulic pump 2 should then be increased in the form of a ramp (FIG. 3, step 70) and the pressure p in the clutch pressure line branch 23 be monitored by the pressure sensor 26 (FIG. 3, step 60). If the pressure increases by a predetermined pressure difference p (FIG. 3, step 80) within a predetermined time period t (FIG. 3, step 90), the method evaluates the falling back of the valve 21 into the safe state as successful (FIG. 3, step 120). Otherwise, the falling back of the valve 21 into the safe state is evaluated as having failed (FIG. 3, step 100) and a replacement reaction must be carried out in order to prevent any further damage. This replacement reaction is defined on a project-specific basis.

[0042] For the exemplary case described here, a reduced functionality would be conceivable, while the parking lock 7 is disengaged with all functions switched off as soon as the parking lock 7 is engaged. The system can then only be actuated again if replacement reactions are available on the vehicle side and are actually present. (A brake application by the driver, for example).

[0043] The use of a speed ramp offers the advantage of optimized detection. The goal in this regard is to optimize the time and reduce noise from the actuator as much as possible. Depending on the system and temperature, the speed at which a predetermined pressure is exceeded also varies. This therefore no longer needs to be taken into account. In addition, the speed ramp significantly reduces the probability of exceeding the upper limit for the permitted pressure p.

[0044] In practice, it has been shown that it is possible to detect the pressure increase for all relevant system temperatures. In addition, the time criterion was also met in all tests.

[0045] It is also possible to diagnose the position of the other switching valve 24 as part of the method according to the disclosure. This either allows a volume flow from the clutch into the tank (rest position) or blocks it so that pressure can build up. The method step now consists of continuing to monitor the pressure: If the pressure is not reduced after the pump has stopped (FIG. 3, step 110), this valve 24 is then not in the rest position (FIG. 3, step 120).

LIST OF REFERENCE SIGNS

[0046] 1 Hydraulic system [0047] 2 Pump [0048] 3 Rotational direction [0049] 4 Consumer [0050] 5 Rotational direction [0051] 6 Consumer [0052] 7 Parking lock [0053] 8 Friction clutch [0054] 9 Electric motor [0055] 10 Controller [0056] 11 Pump inlet [0057] 12 Cooling line [0058] 13 Check valve [0059] 14 Check valve [0060] 15 Reservoir [0061] 16 Intake branch [0062] 17 Pump inlet [0063] 18 Hydraulic pressure line [0064] 19 Check valve [0065] 20 Intake branch [0066] 21 Valve [0067] 22 Pressure line branch [0068] 23 Pressure line branch [0069] 24 Valve [0070] 25 Check valve [0071] 26 Pressure sensor [0072] 27 Discharge line [0073] 28 Discharge line [0074] 29 Connection node [0075] 30 Line system [0076] 50 Method step [0077] 60 Method step [0078] 70 Method step [0079] 80 Method step [0080] 90 Method step [0081] 100 Method step [0082] 110 Method step [0083] 120 Method step