Method for operating a hydraulic system of a transmission for a motor vehicle

Abstract

The invention relates to a method for operating a hydraulic system (10) for a motor vehicle transmission, wherein the hydraulic system (10) comprises a hydraulic pump (12), a first hydraulic valve (26), a second hydraulic valve (28) and a sump (32).In a first method step, a diagnosis of the first hydraulic valve (26) is carried out, wherein if a defect in the first hydraulic valve (26) is detected in the first method step, a second method step is carried out for the purpose of reducing the pressure in a working pressure line (36), wherein in the second method step the second hydraulic valve (28) is briefly brought into a second actuating position in which a connection is established between a second working pressure connection (44) of the second hydraulic valve (28) and a second actuating connection (46) of the second hydraulic valve by means of the second hydraulic valve (28), wherein subsequently in the course of a third method step the second hydraulic valve (28) is brought into a second rest position in which a connection exists between the second actuating connection (46) and the sump (32).

Description

The invention relates to a method for operating a hydraulic system of a transmission for a motor vehicle.DE 10 2018 214 427 A1 discloses a hydraulic system for a dual clutch transmission of a motor vehicle. This hydraulic system comprises a hydraulic pump and piston-cylinder units, each for the actuation of two friction clutches of a dual clutch and a separating clutch upstream of the dual clutch. Each piston cylinder unit is assigned a hydraulic valve, as a result of which in each case an actuating chamber of the respective piston cylinder unit can be supplied with actuating fluid of the hydraulic system as required. The actuating fluid is provided by a working pressure line connected to the hydraulic valves and the hydraulic pump.It is the object of the present invention to present a method for operating a hydraulic system of this type known from the prior art, wherein particularly safe operation of the hydraulic system is to be made possible.The object is achieved by a method according to claim 1. advantageous developments of the method are described by claims dependent on claim 1.Known methods for operating a hydraulic system for a motor vehicle transmission are used as the basis, wherein the hydraulic system comprises a hydraulic pump, a first piston-cylinder unit, a second piston-cylinder unit, a first hydraulic valve, a second hydraulic valve and a sump. In this case, an output of the hydraulic pump is connected in a known manner to a working pressure line, wherein a first working pressure connection of the first hydraulic valve and a second working pressure connection of the second hydraulic valve are each connected to the working pressure line. Furthermore, a first actuation connection of the first hydraulic valve is connected to a first actuation chamber of the first piston-cylinder unit by means of a first feed line. In addition, a second actuation connection of the second hydraulic valve is connected to a second actuation chamber of the second piston-cylinder unit by means of a second feed line. A first sump connection of the first hydraulic valve and a second sump connection of the second hydraulic valve are each connected to the sump.The first feed line is advantageously connected at its one end directly to the first actuation connection and at its other end directly to the first actuation chamber. Advantageously, the second feed line is connected at its one end directly to the second actuation connection and at its other end to the second actuation chamber.The term of the direct connection of two hydraulic elements means that no further valve is arranged between said hydraulic elements, wherein it is not excluded that throttle elements could be arranged between said hydraulic elements.The hydraulic pump is advantageously designed as an electric motor-driven hydraulic pump. By means of the hydraulic pump, hydraulic fluid is conveyed from the sump, which serves as a type of storage container, into the working pressure line.The piston-cylinder units are designed to actuate clutches of the motor vehicle transmission. Particularly advantageously, the piston-cylinder units are designed to actuate friction clutches of the motor vehicle transmission. For this purpose, actuating pistons of the piston-cylinder units are advantageously arranged in such a way that a respective actuating piston of a respective piston-cylinder unit can act, for example, on a disk pack of a multi-disk clutch. The respective actuating pistons are partially arranged in a respective cylinder of the piston-cylinder units in a known manner. The actuating pistons divide a respective inner volume of the respective piston-cylinder units into an actuating chamber and a centrifugal oil chamber in a known manner.The hydraulic valves are designed in the above-mentioned manner to connect the respective piston-cylinder units in each case on the one hand to the working pressure line and on the other hand to the sump. The hydraulic valves are advantageously designed as electromagnetically actuated proportional valves.The first hydraulic valve is advantageously and in a known manner configured such that, in a first actuation position of the first hydraulic valve, a connection is established between the first working pressure connection of the first hydraulic valve and the first actuation connection of the first hydraulic valve. The first hydraulic valve is furthermore advantageously designed in such a way that, in a first rest position of the first hydraulic valve, a connection is produced between the first actuating connection and the first sump connection.The second hydraulic valve is designed in such a way that in a second actuation position of the second hydraulic valve a connection is produced between the second working pressure connection and the second actuation connection and that in a second rest position of the second hydraulic valve a connection is produced between the second actuation connection and the second sump connection.The respective actuation positions are advantageously valve positions which bring about a closing of the respective friction clutches by corresponding supply of the respective piston-cylinder units with hydraulic fluid.In the method according to the invention, it is provided that a diagnosis of the first hydraulic valve is carried out in a first method step, wherein a second method step is carried out in the first method step for the purpose of a pressure reduction in the working pressure line when a defect of the first hydraulic valve is detected, wherein the second hydraulic valve is brought briefly into the second actuation position in the second method step, wherein the second hydraulic valve is then brought into the second rest position in the course of a third method step.The diagnosis is a method known per se, in which it is checked whether a fault-free function of the hydraulic valve is present. The diagnosis is advantageously carried out or controlled by an electronic open-loop and closed-loop control unit of the hydraulic system. The diagnosis is, for example, a plausibility diagnosis, in which it is checked whether, when the first hydraulic valve is actuated in the form of the first actuation position, a system reaction takes place in such a way that it is possible to infer, for example, a closed friction clutch operatively coupled to the first hydraulic valve. If the expected system response does not occur, a fault may be inferred, for example. In other words, a defect can be detected in this way. When such a defect is detected, firstly advantageously fault information is stored in a fault memory of the electronic open-loop and closed-loop control unit of the hydraulic system in the immediate sequence.On the other hand, when the defect is detected, a protective reaction advantageously takes place. The advantageous protective reaction has the effect, in the manner described above, that hydraulic fluid is discharged as quickly as possible from the working pressure line to the sump, to be precise at least to the extent that there is no longer any overpressure in the working pressure line.The fact that the second hydraulic valve is brought briefly into the second actuation position in the second method step means that the duration for which the second hydraulic valve is moved into the second actuation position is so short that no perceptible displacement of the second actuation piston of the second piston-cylinder unit takes place. During the briefly established second actuation position, a small amount of hydraulic fluid is thus conducted from the working pressure line into the second feed line, whereupon a hydraulic pressure in the working pressure line falls slightly and the hydraulic pressure in the second feed line rises slightly. If a connection is then subsequently established between the second feed line and the sump in the third method step, a small quantity of hydraulic fluid is thus conducted from the second feed line into the sump. By means of the second method step and the third method step, a discharge of hydraulic fluid from the working pressure line into the sump can thus be effected.Particularly advantageously, after the third method step, a fourth method step takes place, in which the second hydraulic valve is again brought briefly into the second actuation position. In the fourth method step, therefore, the method is exactly the same with the second hydraulic valve as in the second method step. A fifth method step then advantageously takes place, in which the second hydraulic valve is used to method exactly the same as in the third method step. This procedure is particularly advantageously repeated at least until an overpressure in the working pressure line has been completely reduced or until at least a certain pressure threshold in the working pressure line is undershot.An advantageous development of the method is proposed below, which can be used when the hydraulic system has a third piston cylinder unit and a third hydraulic valve, wherein a third working pressure connection of the third hydraulic valve is connected to the working pressure line, wherein a third actuation connection of the third hydraulic valve is connected to a third actuation chamber of the third piston cylinder unit by means of a third feed line, and wherein a third sump connection of the third hydraulic valve is connected to the sump, wherein the third hydraulic valve is designed such that, in a third actuation position of the third hydraulic valve, there is a connection between the third working pressure connection and the third actuation connection and that, in a third rest position of the third hydraulic valve, there is a connection between the third actuation connection and the third sump connection. In the course of the third method step, the third hydraulic valve is brought briefly into the third actuation position, wherein subsequently in the course of the fourth method step the third hydraulic valve is brought into the third rest position. Thus, in this development, the third hydraulic valve is moved with the same time offset with respect to the sequence of the method steps as with the second hydraulic valve.A further development provides that, in the course of the second method step, the hydraulic pump is brought into a non-delivery state. For example, the hydraulic pump, which is advantageously designed as an electric hydraulic pump, is switched to the zero current state for this purpose.A further development of the method provides that the second hydraulic valve and the third hydraulic valve each have not only one actuation connection but also a return connection. In both cases, the respective return connection is permanently connected to the respective actuation chamber by means of a respective return line. In other words, in both cases, the respective return connection is advantageously permanently connected to the respective actuating connection by means of the respective return line. In both cases, the respective hydraulic valve is advantageously designed internally in such a way that a connection can be established between the respective return connection and the respective sump connection internally of the hydraulic valve, that is to say without further external lines.The invention will now be described in detail with reference to the figures mentioned below.The following are shown: FIG. 1 shows a schematic illustration of a hydraulic system, and FIG. 2 shows a schematic flow diagram of a method for operating the hydraulic system.FIG. 1 shows a schematic illustration of a hydraulic system 10 for a motor vehicle transmission, in particular for a hybrid dual clutch transmission. The hydraulic system 10 is part of an overall hydraulic system for the motor vehicle transmission, not shown in full. The part relevant to the method according to the invention is shown here.The hydraulic system 10 has an electrically operated hydraulic pump 12 by means of which a hydraulic fluid can be conveyed from a sump 32 into a working pressure line 36. For this purpose, an outlet 34 of the hydraulic pump 12 is connected to the working pressure line 36.The hydraulic system 10 further comprises a first piston cylinder unit 14, a second piston cylinder unit 16 and a third piston cylinder unit 18. The second piston-cylinder unit 16 is designed to actuate a second multiplate clutch, not shown in detail, of the dual clutch of the hybrid dual clutch transmission. The third piston-cylinder unit 18 is designed to actuate a separating clutch, not shown in more detail, of the hybrid dual clutch transmission, which is designed as a third multiplate clutch. The separating clutch is arranged in this case with respect to a force flow between an input shaft, not shown, of the hybrid dual clutch transmission and the dual clutch.For the supply of the piston-cylinder units 14, 16, 18 with hydraulic fluid as required, the hydraulic system has a first hydraulic valve 26, a second hydraulic valve 28 and a third hydraulic valve 30.The hydraulic valves 26, 28, 30 are advantageously designed as electromagnetically actuated proportional valves.The hydraulic valves 26, 28, 30 advantageously have electromagnetic actuators 80, 82, 84, namely a first electromagnetic actuator 80 of the first hydraulic valve 26, a second electromagnetic actuator 82 of the second hydraulic valve 28 and a third electromagnetic actuator 84 of the third hydraulic valve 30.The hydraulic valves 26, 28, 30, in particular their electromagnetic actuators 80, 82, 84, are advantageously connected to an electronic control and regulating unit, not shown here.The first hydraulic valve 26 has a first working pressure connection 38 which is connected directly to the working pressure line 36. The direct connection means that no further hydraulic valve is arranged between the working pressure line 36 and the hydraulic valve 26, or between the two mentioned directly connected elements. The second hydraulic valve 28 has a second working pressure connection 44, which is connected directly to the working pressure line 36.The third hydraulic valve 30 used in an advantageous embodiment of the method according to the invention described below has a third working pressure connection 50, which is connected directly to the working pressure line 36.A first actuation connection 40 of the first hydraulic valve 26 is connected directly to a first actuation chamber 20 of the first piston-cylinder unit 14 via a first feed line 74. A second actuation connection 46 of the second hydraulic valve 28 is connected directly to a second actuation chamber 22 of the second piston-cylinder unit 16 via a second feed line 76. A third actuation connection 52 of the third hydraulic valve 30 is connected directly to a third actuation chamber 24 of the third piston-cylinder unit 18 via a third feed line 78.The first actuating chamber 20 is a chamber enclosed by a cylinder of the first piston-cylinder unit 14 and by a first actuating piston 68 of the first piston-cylinder unit 14. If hydraulic fluid is supplied to the first actuating chamber 20 via the first feed line 74, the first actuating piston 68 is moved in such a way that the first multiplate clutch is closed.Analogously, a supply of hydraulic fluid to the second actuating chamber 22 via the second feed line 76 brings about a movement of a second actuating piston 70 in such a way that a closing of the second multiplate clutch is brought about. Analogously, a supply of hydraulic fluid to the third actuating chamber 24 via the third feed line 78 brings about a movement of a third actuating piston 72 in such a way that a closing of the third multiplate clutch is brought about.The first hydraulic valve 26 has a first sump connection 62. The first sump connection 62 is connected, preferably directly, to the sump 32.The first hydraulic valve 26 is designed such that at least two valve positions can be realized, namely a first actuation position and a first rest position. In the first actuation position of the first hydraulic valve 26, there is a connection, advantageously internal to the valve, between the first working pressure connection 38 and the first actuation connection 40.Advantageously, the first hydraulic valve 26 has a first return connection 42. The first return connection 42 is connected to the first actuation chamber 20 by means of a first return line 56. The first return connection 42 is advantageously connected directly to the first feed line 74. The first hydraulic valve 26 is particularly advantageously designed such that, in the first rest position, there is a valve-internal connection between the first return connection 42 and the first sump connection 62.The second hydraulic valve 28 has a second sump connection 64. The second sump connection 64 is connected, preferably directly, to the sump 32.The second hydraulic valve 28 is designed such that at least two valve positions can be realized, namely a second actuation position and a second rest position. In the second actuation position of the second hydraulic valve 28, there is a connection, advantageously internal to the valve, between the second working pressure connection 44 and the second actuation connection 46.Advantageously, the second hydraulic valve 28 has a second return connection 48. The second return connection 48 is connected to the second actuation chamber 22 by means of a second return line 58. The second return connection 48 is advantageously connected directly to the second feed line 76. The second hydraulic valve 28 is particularly advantageously designed such that, in the second rest position, there is a valve-internal connection between the second return connection 48 and the second sump connection 64.The third hydraulic valve 30 has a third sump connection 66. The third sump connection 66 is connected, preferably directly, to the sump 32.The third hydraulic valve 30 is designed such that at least two valve positions can be realized, namely a third actuation position and a third rest position. In the third actuation position of the third hydraulic valve 30, there is a connection, advantageously internal to the valve, between the third working pressure connection 50 and the third actuation connection 52.The third hydraulic valve 30 advantageously has a third return connection 54. The third return connection 54 is connected to the third actuation chamber 24 by means of a third return line 60. The third return connection 54 is advantageously connected directly to the third feed line 78. The third hydraulic valve 30 is particularly advantageously designed such that, in the third rest position, there is a valve-internal connection between the third return connection 54 and the third sump connection 66.FIG. 2 shows a schematic flow diagram of a method for operating the hydraulic system 10.For carrying out or controlling the method, the hydraulic system 10 has a control and regulating unit, not shown in FIG. 1.In a first method step S 1 of the method for operating the hydraulic system 10, a diagnosis of the first hydraulic valve 26 is carried out. The sequence of the diagnosis is not explained in more detail here. The diagnosis can be a diagnosis method known per se for hydraulic valves. For example, the diagnostic may include an electrical test of the first electromagnetic actuator 80. For example, the diagnosis can also comprise a plausibility check of the first hydraulic valve 26. The first method step has a first test step P 1, in which it is checked whether or not a defect of the first hydraulic valve 26 is present. If a defect of the first hydraulic valve 26 is present, a second method step S 2 is carried out. If the test in the test step P 1 reveals that there is no defect in the first hydraulic valve 26, the first method step S 1 is carried out again.In the second method step S 2, for the purpose of a pressure reduction in the working pressure line 36, the second hydraulic valve 28 is brought briefly into the second actuation position. The term "short-term" means here that a time duration for which the second hydraulic valve 28 is moved into the second actuation position during the second method step S 2 is so short that no noticeable displacement of the second actuation piston 70 takes place. In the second method step S 2, a slight flow of hydraulic fluid from the working pressure line 36 into the second feed line 76 thus takes place.During the second method step, the hydraulic pump 12 is advantageously brought into a non-delivery state, so that the pressure in the working pressure line 36 no longer rises any further.Advantageously, immediately after the second method step S 2, a third method step S 3 takes place. During the third method step, the second hydraulic valve 28 is brought into the second rest position, advantageously briefly. As a result, in the third method step S 3, a slight flow of hydraulic fluid from the second feed line 76, advantageously via the second return line 58, into the sump 32 takes place.Particularly advantageously, during the third method step S 3, the third hydraulic valve 30 is brought briefly into the third actuation position, so that a slight flow of hydraulic fluid takes place from the working pressure line 36 into the third feed line 78. The third method step is advantageously carried out quickly, that is to say overall with a short period of time, so that no noticeable movement of the third actuating piston 72 takes place during the third method step S 3.After the third method step S 3, a fourth method step S 4 is advantageously carried out. During the fourth method step S 4, the third hydraulic valve 30 is brought into the third rest position, so that a slight flow of hydraulic fluid from the third feed line 78, advantageously via the third return line 60, into the sump 32 takes place. During the fourth method step, the second hydraulic valve 28 is once again advantageously brought briefly into the second actuation position, in the same way as is also moved with the second hydraulic valve 28 in the second method step S 2.After the fourth method step S 4, a second test step P 2 is advantageously carried out. During the second test step P 2, a check is carried out as to whether a pressure in the working pressure line 36 has been sufficiently reduced. The check can be carried out by means of a suitable and suitably arranged pressure sensor and the electronic control and regulating unit. If it is determined in the course of the second test step P 2 that the pressure in the working pressure line 36 is higher than a pressure threshold value, the third method step S 3 is carried out again next. If, on the other hand, it is determined in the course of the second test step P 2 that the pressure in the working pressure line 36 is less than or equal to the pressure threshold value, the method is ended, or the first method step is carried out next.List of reference characters10 Hydraulic system 12 Hydraulic pump 14 First piston cylinder unit 16 Second piston cylinder unit 18 Third piston cylinder unit 20 First actuation chamber 22 Second actuation chamber 24 Third actuation chamber 26 First hydraulic valve 28 Second hydraulic valve 30 Third hydraulic valve 32 Sump 34 Outlet 36 Working pressure line 38 First working pressure connection 40 First actuation connection 42 First return connection 44 Second working pressure connection 46 Second actuation connection 48 Second return connection 50 Third working pressure connection 52 Third actuation connection 54 Third return connection 56 First return line 58 Second return line 60 Third return line 62 First sump connection 64 Second sump connection 66 Third sump connection 68 First actuation piston 70 Second actuation piston 72 Third actuation piston 74 First supply line 76 Second supply line 78 Third supply line 80 First electromagnetic actuator 82 Second Electromagnetic actuator 84 Third electromagnetic actuator P 1 First test step P 2 Second test step S 1 First method step S 2 Second method step S 3 Third method step S 4 Fourth method step

Claims

Method for operating a hydraulic system (10) for a motor vehicle transmission, wherein the hydraulic system (10) comprises a hydraulic pump (12), a first piston cylinder unit (14), a second piston cylinder unit (16), a first hydraulic valve (26), a second hydraulic valve (28) and a sump (32), wherein an outlet (34) of the hydraulic pump (12) is connected to a working pressure line (36), wherein a first working pressure connection (38) of the first hydraulic valve (26) is connected to the working pressure line (36), wherein a second working pressure connection (44) of the second hydraulic valve (28) is connected to the working pressure line (36), wherein a first actuation connection (40) of the first hydraulic valve (26) is connected to a first actuation chamber (20) of the first piston cylinder unit (14), wherein a second actuation connection (46) of the second hydraulic valve (28) is connected to a second actuation chamber (22) of the second piston-cylinder unit (16), wherein a first sump connection (62) of the first hydraulic valve (26) and a second sump connection (64) of the second hydraulic valve (28) are each connected to the sump (32), wherein the second hydraulic valve (28) is designed such that, in a second actuation position of the second hydraulic valve (28), there is a connection between the second working pressure connection (44) and the second actuation connection (46), and that, in a second rest position of the second hydraulic valve (28), there is a connection between the second actuation connection (46) and the second sump connection (64), characterized in that, in a first method step (S 1), a diagnosis of the first hydraulic valve (26) is carried out, wherein, upon detection of a defect of the first hydraulic valve (26) in the first method step (S 1) for the purpose of a pressure reduction in the working pressure line (36), a second method step (S 2) is carried out, wherein in the second method step (S 2) the second hydraulic valve (28) is briefly brought into the second actuation position, wherein subsequently in the course of a third method step (S 3) the second hydraulic valve (28) is brought into the second rest position.Method according to Claim 1, characterized in that the hydraulic system (10) has a third piston cylinder unit (18) and a third hydraulic valve (30), wherein a third working pressure connection (50) of the third hydraulic valve (30) is connected to the working pressure line (36), wherein a third actuating connection (52) of the third hydraulic valve (30) is connected to a third actuating chamber (24) of the third piston cylinder unit (18), and wherein a third sump connection (66) of the third hydraulic valve (30) is connected to the sump (32), wherein the third hydraulic valve (30) is designed such that, in a third actuating position of the third hydraulic valve (30), there is a connection between the third working pressure connection (50) and the third actuating connection (52), and in that, in a third rest position of the third hydraulic valve (30), there is a connection between the third actuating connection (52) and the third sump connection (66), wherein, in the course of the third method step (S 3), the third hydraulic valve (30) is brought briefly into the third actuation position, wherein subsequently, in the course of a fourth method step (S 4), the third hydraulic valve (30) is brought into the third rest position.Method according to Claim 2, characterized in that, in the course of the fourth method step (S4), the second hydraulic valve (28) is brought briefly into the second actuation position.Method according to one of the preceding claims, characterized in that, in the course of the second method step (S2), the hydraulic pump (12) is brought into a non-conveying state.Method according to one of the preceding claims, characterized in that a first piston (68) of the first piston-cylinder unit (14) is designed as an actuating piston for a first friction clutch of a dual clutch of a dual clutch transmission, wherein a second actuating piston (70) of the second piston-cylinder unit (16) is designed as an actuating piston for a second friction clutch of the dual clutch of the dual clutch transmission.Method according to Claim 2 and Claim 5, characterized in that a third actuating piston (72) of the third piston-cylinder unit (18) is designed as an actuating piston for a separating clutch of the dual clutch transmission which is mounted upstream of the dual clutch.Method according to one of the preceding claims, characterized in that the second hydraulic valve (28) has a second return connection (48) connected to the second actuation chamber (22), wherein the second hydraulic valve is designed in such a way that, in the second rest position, there is a connection between the second return connection (48) and the second sump connection (64).

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