阅读说明：本技术 液压系统以及机动车变速器 (Hydraulic system and motor vehicle transmission ) 是由 多米尼克·居尔登舒 于 2019-07-11 设计创作，主要内容包括：本发明涉及液压系统以及机动车变速器。液压系统(12)、尤其是用于机动车变速器(10)的液压系统具有促动器(18；18’)、阀(24)、压力供应线路(26)和箱线路(28)。促动器(18；18’)具有能被加载压力以操纵促动器(18；18’)的第一压力室(20)和第二压力室(22),其中,压力室(20、22)、压力供应线路(26)和箱线路(28)分别与阀(24)的接口(A、B、P、T)联接。阀(24)具有多个不同的切换位置,其中,压力室(20、22)有选择地与压力供应线路(26)或箱线路(28)相互连接或彼此断开。至少在阀(24)的起始位置中,在压力室(20、22)之间存在流体连接。(The invention relates to a hydraulic system and a motor vehicle transmission. A hydraulic system (12), in particular for a motor vehicle transmission (10), has an actuator (18; 18'), a valve (24), a pressure supply line (26) and a tank line (28). The actuator (18; 18') has a first pressure chamber (20) and a second pressure chamber (22) which can be pressurized in order to actuate the actuator (18; 18'), wherein the pressure chambers (20, 22), the pressure supply line (26) and the tank line (28) are each coupled to an interface (A, B, P, T) of the valve (24). The valve (24) has a plurality of different switching positions, wherein the pressure chambers (20, 22) are selectively interconnected or disconnected from a pressure supply line (26) or a tank line (28). At least in the starting position of the valve (24), a fluid connection is present between the pressure chambers (20, 22).)

1. A hydraulic system (12), in particular for a motor vehicle transmission (10), having an actuator (18; 18'), a valve (24), a pressure supply line (26) and a tank line (28), wherein the actuator (18; 18') has a first pressure chamber (20) and a second pressure chamber (22) which can be pressurized to actuate the actuator (18; 18'), wherein the pressure chambers (20, 22), the pressure supply line (26) and the tank line (28) are each coupled to a connection (A, B, P, T) of the valve (24), wherein the valve (24) has a plurality of different switching positions in which the pressure chambers (20, 22) are selectively interconnected or disconnected from the pressure supply line (26) or the tank line (28), and wherein, in at least one starting position of the valve (24), a fluid connection is present between the pressure chambers (20, 22).

2. The hydraulic system (12) of claim 1, wherein the valve (24) is loaded toward a starting position by a recall device (59).

3. The hydraulic system (12) according to claim 1 or 2, characterized in that the actuator (18; 18') has a cylinder (30; 30') and an actuator piston (32; 32') accommodated in the cylinder (30; 30'), wherein the actuator piston (32; 32') divides the cylinder (30; 30') into the first pressure chamber (20) and the second pressure chamber (22), in particular wherein a switching element (58) of the actuator (18; 18') is connected with the actuator piston (32; 32').

4. The hydraulic system (12) of claim 3, characterized in that the actuator (18; 18') has at least one annular piston (54, 56; 54') which is arranged around at least one portion (44, 46; 44') of the actuator piston (32; 32') and which seals the first pressure chamber (20) from the second pressure chamber (22).

5. The hydraulic system (12) as claimed in claim 4, characterized in that a stop is provided in the cylinder (30; 30'), against which the annular piston (54, 56; 54') rests in the first switching position of the valve (24).

6. The hydraulic system (12) as claimed in one of claims 3 to 5, characterized in that the cylinder (30; 30') has at least one first section (34; 34') and a second section (36; 36'), wherein the first section (34; 34') forms the first pressure chamber (20) and the second section (36; 36') forms the second pressure chamber (22), and wherein the actuator piston (32; 32') has at least one first section (44; 44') and a second section (46; 46'), wherein the first section (44; 44') of the actuator piston (32; 32') is assigned to the first pressure chamber (20) and the second section (46; 46') of the actuator piston (32; 32') is assigned to the second pressure chamber (22).

7. The hydraulic system (12) of claim 6, wherein an inner cross-sectional area of the first section (34') of the cylinder (30') is greater than an inner cross-sectional area of the second section (36') of the cylinder (30') forming a step (40'), and/or wherein a cross-sectional area of the first section (44') of the actuator piston (32') is less than a cross-sectional area of the second section (46') of the actuator piston (32') forming another step (50').

8. The hydraulic system (12) according to claim 6 or 7, characterized in that the cylinder (30) has a third section (38) between the first section (34) and the second section (36) of the cylinder (30) and having an inner cross-sectional area that is smaller than the inner cross-sectional area of the first section (34) and/or of the second section (36) of the cylinder (30).

9. The hydraulic system (12) according to claim 8, characterized in that the actuator piston (3) has a third section (48) between the first section (44) and the second section (46) of the actuator piston (32) and having a cross-sectional area which is larger than the cross-sectional area of the first section (44) and/or of the second section (46) of the actuator piston (32).

10. The hydraulic system (12) of claim 9, characterized in that two annular pistons (54, 56) are provided, wherein a first annular piston (54) is disposed around the first section (44) of the actuator piston (32) and a second annular piston (56) is disposed around the second section (46) of the actuator piston (32).

11. The hydraulic system (12) as claimed in any one of the preceding claims, characterized in that the pressure chambers (20, 22) are neither connected with the pressure supply line (26) nor with the tank line (28) in the first switching position of the valve (24), wherein the pressure chambers (20, 22) are fluidically connected to one another by means of a bypass line (60).

12. The hydraulic system (12) of claim 11, characterized in that the bypass line (60) is disposed within an actuator (18; 18'), particularly wherein the bypass line (60) is configured to pass through a bore of the actuator piston (32; 32').

13. The hydraulic system (12) as claimed in one of the preceding claims, characterized in that the pressure chambers (20, 22) are each connected with the pressure supply line (26) in a starting position of the valve (24).

14. The hydraulic system (12) of any one of the preceding claims, wherein the valve (24) is a four-position, four-way reversing valve or a four-position, five-way reversing valve.

15. The hydraulic system (12) of any one of the preceding claims,

-in a second switching position of the valve (24), the first pressure chamber (20) is connected with the pressure supply line (26) and the second pressure chamber (22) is connected with the tank line (28);

-in a third switching position of the valve (24), the pressure chambers (20, 22) are each connected to the tank line (28); and/or

-in a fourth switching position of the valve (24), the first pressure chamber (20) is connected with the tank line (28) and the second pressure chamber (22) is connected with the pressure supply line (26).

16. Motor vehicle transmission (10) having a hydraulic system (12) according to one of the preceding claims, a pressure source (14), a tank (16), wherein a pressure supply line (26) is fluidically connected to the pressure source (14) and a tank line (28) is fluidically connected to the tank (16), and/or wherein the motor vehicle transmission (10) has a shift lever which is connected to an actuator piston (32; 32') for force transmission.

Technical Field

The invention relates to a hydraulic system, in particular for a motor vehicle transmission, and to a motor vehicle transmission.

Background

The hydraulic system is used in known motor vehicle transmissions, in particular for controlling clutch devices. In a dog clutch, the axial movement of the dog teeth can be effected, for example, via a hydraulically actuated piston which is connected to a shift lever of the dog clutch.

The fastening of the gripper in the neutral position (the gripping of the gripper) is frequently effected here by mechanical means or by hydraulic locking of the piston. However, additional components are required for mechanical fastening, which require additional installation space and therefore lead to additional costs. When the piston is hydraulically fixed in the neutral position, a leak in the valve can lead to the piston being unintentionally adjusted and thus, for example, an unintentional gear being engaged.

Disclosure of Invention

The task of the invention is therefore: a hydraulic system and a motor vehicle transmission are provided that eliminate the disadvantages from the prior art.

This object is achieved according to the invention by a hydraulic system, in particular for a motor vehicle transmission, having an actuator, a valve, a pressure supply line and a tank line. The actuator has a first pressure chamber and a second pressure chamber which can be pressurized for actuating the actuator, wherein the pressure chambers, the pressure supply line and the tank line are each connected to a connection of the valve. The valve has a plurality of different switching positions, wherein the pressure chambers and the pressure supply line or the tank line are selectively connected to each other or disconnected from each other, wherein, at least in a starting position of the valve, a fluid connection exists between the pressure chambers.

Via this fluid connection, a pressure equalization between the two pressure chambers can be achieved in a defined manner. This makes it possible to compensate for leaks, in particular valve leaks, which may lead to a pressure drop in one of the two pressure chambers. In spite of the potential leakage in both pressure chambers, the same pressure is always generated at least in the starting position of the valve, so that the actuator is not unintentionally actuated.

According to one embodiment of the invention, the valve is loaded by the return device toward the starting position. The return means are in particular springs. The valve is thus configured as a spring-loaded valve. If the valve is not actuated, i.e. not acted upon by an external force, the valve returns to the starting position on the basis of the control-back device, in which, as explained above, an equilibrium pressure in the two pressure chambers is always generated. In other words, the non-actuated valve always returns, in the absence of external forces, into a switching position in which the actuator is not actuated unintentionally.

The valve may be a solenoid operated valve or a valve that is pre-controlled. Correspondingly, the valve is actuated by means of an electromagnet or by means of hydraulic or pneumatic pressure.

In a further embodiment of the invention, the actuator has a cylinder and an actuator piston accommodated in the cylinder, wherein the actuator piston divides the cylinder into a first pressure chamber and a second pressure chamber, in particular wherein a switching element of the actuator is connected to the actuator piston. The shift element is in particular a shift lever of a motor vehicle transmission, for example a shift lever of a clutch device, such as a dog clutch.

Preferably, the actuator piston is in a neutral position when the valve is in the starting position. In particular, a clutch device of the motor vehicle transmission, which is connected to the actuator piston via the shift element, is disengaged in the neutral position of the piston. In the case of dog clutches, this means that the dog is pulled out.

In a further aspect of the invention, it is provided that the actuator has at least one annular piston which is arranged around at least one section of the actuator piston and which seals the first pressure chamber from the second pressure chamber. Unintentional leakage and thus unintentional pressure equalization between the two pressure chambers is effectively prevented by the annular pistons. In particular, the annular piston is movable relative to the actuator piston and may therefore also be referred to as a floating piston.

A stop is preferably provided in the cylinder, against which the annular piston rests in the first operating position of the valve. The first switching position of the valve is in particular the starting position of the valve. When a pressure equalization occurs between the two pressure chambers, the annular piston bears at least against the stop. In other words, the annular piston rests against the stop in the neutral position of the actuator piston. The stop can limit the movement of the annular piston in the cylinder to a predefined extent in a simple manner. The annular piston is fixed to the first or second pressure chamber, in particular by a stop. Furthermore, a seal is provided by the stop and the annular piston which bears against it.

According to a further embodiment of the invention, the cylinder has at least one first section and one second section, wherein the first section forms a first pressure chamber and the second section forms a second pressure chamber, and wherein the actuator piston has at least one first section and one second section, wherein the first section of the actuator piston is assigned to the first pressure chamber and the second section of the actuator piston is assigned to the second pressure chamber. In the neutral position of the actuator piston, the first and second sections of the actuator piston are located in the first pressure chamber or in the second pressure chamber. If one of the two pressure chambers is loaded with a higher pressure, the actuator piston is moved in the direction of the lower pressure. Thereby operating the actuator.

According to a further embodiment of the invention, it is provided that the inner cross-sectional area of the first section of the cylinder is greater than the inner cross-sectional area of the second section of the cylinder, so that a step is formed, and/or wherein the cross-sectional area of the first section of the actuator piston is smaller than the cross-sectional area of the second section of the actuator piston, so that a further step is formed.

The first section of the piston delimits, for example, a first pressure chamber, and the second section of the piston delimits a second pressure chamber. In particular, the second section of the actuator piston is then configured substantially complementary to the inner wall of the second section of the cylinder on the outside. Furthermore, an annular piston is provided on the first section, which annular piston is configured substantially complementary on the outside to the inner wall of the first section of the cylinder and on the inside to the outer wall of the first section of the actuator piston.

"substantially complementary" is understood here and below as: the gap between the components is designed such that fluid can flow through the gap with little or no volume flow.

In particular, a stop can be formed by the step and/or the further step, against which the annular piston rests at least in the starting position of the valve. Preferably, the annular piston in each switching position of the valve rests at least against the step or the further step. The pressure chambers can thus be efficiently sealed with respect to each other.

In a further aspect of the invention, it is provided that the cylinder has a third section which is located between the first section and the second section of the cylinder and whose inner cross-sectional area is smaller than the inner cross-sectional area of the first section and/or of the second section of the cylinder. The internal cross-sectional areas of the first and second sections may be the same or different, preferably the same, from each other. Since the third section of the cylinder has a smaller inner cross section than the other two sections of the cylinder, a step is formed between the first section and the third section and between the third section and the second section, respectively. These steps in particular each form a stop.

The actuator piston may have a third section which is located between the first section and the second section of the actuator piston and whose cross-sectional area is greater than the cross-sectional area of the first section and/or of the second section of the actuator piston. The third section of the actuator piston is assigned in particular to the third section of the cylinder and, in the neutral position of the actuator piston, is located in the third section of the cylinder. The third section of the actuator piston is preferably configured substantially complementary to the inner wall of the third section of the cylinder.

In one embodiment of the invention, two annular pistons are provided, wherein a first annular piston is arranged around a first section of the actuator piston and a second annular piston is arranged around a second section of the actuator piston. The first and second pressure chambers are separated from each other in a fluid-tight manner by two annular pistons.

The first annular piston is preferably configured substantially complementary on the outside to the inner wall of the first section of the cylinder and/or the second annular piston is configured substantially complementary on the outside to the inner wall of the second section of the cylinder. Thereby further improving the sealing effect of the annular piston.

It is further preferred that the first annular piston is configured substantially complementarily to the outer wall of the first section of the actuator piston on the inside and/or that the second annular piston is configured substantially complementarily to the outer wall of the second section of the actuator piston on the inside. The sealing effect is thus also improved.

In particular, the pressure chambers are not connected to the pressure supply line nor to the tank line in the first switching position of the valve, wherein the pressure chambers are fluidically connected to one another by a bypass line. The bypass line allows pressure equalization between the two pressure chambers to be achieved at a predefined speed, which can be determined by selecting the cross section of the bypass line. If a pressure loss occurs in one of the pressure chambers, for example due to a leak in the valve, the same pressure is again generated in both pressure chambers on the basis of the bypass line.

The bypass line is preferably arranged within the actuator, in particular wherein the bypass line is configured as a bore through the actuator piston. No additional ports and/or lines are therefore required on the cylinders to provide a bypass line.

According to a further aspect of the invention, the pressure chambers are each connected to a pressure supply line in the initial position of the valve. The fluid connection between the two pressure chambers is established in this variant within the valve by a connection common to both pressure chambers to the pressure supply line. Correspondingly, the same pressure is always present in the two pressure chambers, which pressure is provided by the pressure source via the pressure supply line. This also compensates for leaks, in particular in the valve, so that the actuator is not unintentionally actuated.

The valve is preferably a four-position, four-way (4/4) or a four-position, five-way (5/4) reversing valve. Correspondingly, the valve has four possible switching positions, wherein the first switching position is the starting position. In the case of a four-position, five-way directional valve, an additional port is then preferably assigned to the tank line.

One possible embodiment of the invention provides that,

in a second switching position of the valve, the first pressure chamber is connected to the pressure supply line and the second pressure chamber is connected to the tank line;

in a third switching position of the valve, the pressure chambers are each connected to the tank line; and/or

In a fourth switching position of the valve, the first pressure chamber is connected to the tank line and the second pressure chamber is connected to the pressure supply line.

The switching positions are preferably passed through in ascending order when the actuator is actuated. The valve is therefore first in the starting position, then in the second switching position, then in the third switching position and finally in the fourth switching position.

A shut-off device may be provided which allows the return from the fourth switching position to the starting position without a change in the pressure chamber. The shut-off device is preferably designed as a switchable shut-off valve, which is arranged, for example, in the pressure supply line. Correspondingly, in the blocking position of the shut-off valve, regardless of the switching position of the valve, one of the two pressure chambers is prevented from being pressurized via the pressure supply line. Correspondingly, the valve can be switched from the fourth switching position to the starting position without renewed application of load to the actuator piston in the direction of the second pressure chamber in the second switching position.

The object is also achieved according to the invention by a motor vehicle transmission having the above-described hydraulic system, a pressure source and a tank, wherein a pressure supply line is fluidically connected to the pressure source and a tank line is fluidically connected to the tank, and/or wherein the motor vehicle transmission has a selector lever which is connected to an actuator piston for force transmission. Reference is made to the above explanations as to advantages.

Drawings

Further advantages and features of the invention emerge from the following description and the figures with reference to the figures. In the drawings:

fig. 1 schematically shows a section of a motor vehicle transmission according to the invention with a hydraulic system according to the invention;

fig. 2 schematically shows the motor vehicle transmission according to the invention of fig. 1 with an alternative variant of the hydraulic system according to the invention;

fig. 3(a) to (d) show four different switching positions of the valve of the hydraulic system according to the invention of fig. 1;

fig. 4(a) to (c) show three different switching positions of the actuator of the hydraulic system according to the invention of fig. 1; and

fig. 5(a) to (c) show three different switching positions of an alternative variant of the actuator of the hydraulic system according to the invention.

Detailed Description

Fig. 1 and 2 each show a section of a motor vehicle transmission 10. The motor vehicle transmission 10 includes a hydraulic system 12, as well as a pressure source 14 and a tank 16 for hydraulic fluid.

The hydraulic system 12 has an actuator 18 with a first pressure chamber 20 and a second pressure chamber 22, which can be pressurized for actuating the actuator 18.

In addition, hydraulic system 12 includes a valve 24 having four ports A, B, P, T. Here, the first pressure chamber 20 is coupled to the first port a, the second pressure chamber 22 is coupled to the second port B, the pressure source 14 is coupled to the third port P via a pressure supply line 26, and the tank 16 is coupled to the fourth port T via a tank line 28.

The actuator 18 has a cylinder 30, inside which two pressure chambers 20, 22 are arranged. Furthermore, the actuator 18 comprises an actuator piston 32 accommodated in the cylinder 30, which actuator piston divides the cylinder 30 into the first pressure chamber 20 and the second pressure chamber 22.

The cylinder 30 has a first section 34, a second section 36 and a third section 38. Wherein the third section 38 is arranged between the first section 34 and the second section 36.

The inner cross-sectional area of the third section 38 is less than the respective inner cross-sectional areas of the first section 34 and the second section 36, thereby forming a first step 40 between the first section 34 and the third section 38, and a second step 42 between the third section 38 and the second section 36.

The internal cross-sectional areas of the first section 34 and the second section 36 of the cylinder 30 are preferably the same size. But may also be different from each other.

Similarly, the actuator piston 32 has three sections 44, 46, 48, wherein the third section 48 is arranged between the first section 44 and the second section 46.

The cross-sectional area of the third section 48 is greater than the respective cross-sectional areas of the first section 44 and the second section 46, such that a third step 50 is formed between the first section 44 of the actuator piston 32 and the third section 48 of the actuator piston 32, and a fourth step 52 is formed between the third section 48 and the second section 46 of the actuator piston 32.

The cross-sectional areas of the first section 44 and the second section 46 of the actuator piston 32 are preferably the same. But may also be different from each other.

A first annular piston 54 is disposed around the first section 44 of the actuator piston 32. The first annular piston 54 at least partially fills the gap between the first section 44 of the actuator piston 32 and the first section 34 of the cylinder 30 and thus substantially prevents fluid flow between the first pressure chamber 20 and the second pressure chamber 22.

Similarly, a second annular piston 56 is arranged around the second section 46 of the actuator piston 32, which at least partially fills the gap between the second section 46 of the actuator piston 32 and the second section 36 of the cylinder 30 and thus prevents a fluid flow between the first pressure chamber 20 and the second pressure chamber 22.

The first annular piston 54 and/or the second annular piston 56 are movable relative to the actuator piston 32. The first annular piston 54 and/or the second annular piston 56 may accordingly also be referred to as floating pistons.

A shift element 58 of the motor vehicle transmission 10 is arranged on the actuator piston 32. The shift element 58 is in particular a shift lever of the motor vehicle transmission 10, which is used to actuate the clutch device. The clutch device is designed, for example, as a claw clutch or another clutch type.

The operation of the hydraulic system 12 will be explained in detail below with reference to fig. 1 to 5.

For actuating the switching element 58, the actuator piston 32 is moved in its axial direction R in such a way that one of the two pressure chambers 20, 22 is acted upon by a higher pressure. The actuator piston 32 is then displaced in the direction of a lower pressure.

The control of the actuator 18 is effected here via a valve 24, which for this purpose has four different switching positions, which are indicated schematically in fig. 1 to 3 by respective blocks in the valve 24, wherein the arrows symbolize the fluid flow direction in each case. The valve 24 is accordingly a four-position, four-way reversing valve in the embodiment shown.

The valve 24 is acted upon by the return device 59 in the direction of the starting position. The return means 59 are in particular springs. The valve 24 is thus configured as a spring-loaded valve. If the valve 24 is not actuated, i.e. is not loaded with external force, the valve returns into the starting position on the basis of the reset device 59.

The valve 24 may also be a solenoid operated or pre-controlled valve 24. Correspondingly, the valve 24 is actuated by means of an electromagnet or by means of hydraulic or pneumatic pressure.

Alternatively, the valve 24 can also be designed as a four-position, five-way directional valve, wherein an additional port is preferably assigned to the tank 16.

In each of the switching positions of the valve 24, the pressure chambers 20, 22 are in each case fluidically connected to the pressure source 14, to the tank 16 or fluidically disconnected from the pressure source 14 and the tank 16.

In the starting position of the valve 24, see fig. 1 to 3(a), there is a fluid connection between the two pressure chambers 20, 22. This fluid connection is realized differently in the two variants of the hydraulic system 12 illustrated in fig. 1 and 2.

According to the variant of fig. 1, in the initial position of the valve 24, both the first pressure chamber 20 and the second pressure chamber 22 are connected to the pressure source 14.

In the starting position of the valve 24, the same pressure prevails in both pressure chambers 20, 22, so that the actuator piston 32 remains in its neutral position.

According to the variant shown in fig. 2, none of the four ports A, B, P, T of the valve 24 are connected to one another. The two pressure chambers 20, 22 are thus disconnected from both the pressure source 14 and the tank 16, respectively.

In order to nevertheless ensure the same pressure in the two pressure chambers 20, 22 in this switching position, a bypass line 60 is provided, which is designed in particular as a bore hole through the actuator piston 32.

The pressure drop in one of the pressure chambers 20, 22 can be equalized by the bypass line 60, so that the actuator piston 32 is also left in its neutral position in this case.

The further explanation applies to both variants described above, since in particular the further switching position of the valve 24 is the same in both variants.

In the neutral position of the actuator piston 32, the first annular piston 54 bears against the first step 40 on the first cylinder 30 and against the third step 50 of the actuator piston 32. Similarly, the second annular piston 56 bears against the second step 42 on the cylinder 30 and against the fourth step 52 of the actuator piston 32. The first step 40 and the third step 50 thus together form a stop for the first annular piston 54, and the second step 42 and the fourth step 52 form a stop for the second annular piston 56.

In the case of the same pressure in the pressure chambers 20, 22, the actuator piston 32 is held safely in its neutral position, since, when the actuator piston 32 is displaced out of its neutral position, a restoring force toward the neutral position always occurs, as discussed for the following example of a rightward displacement in the axial direction R.

If the actuator piston 32 is shifted to the right (see, e.g., fig. 4(b) and 5(b)), the fourth step 52 carries the second annular piston 56 with it. The composite structure formed by the second annular piston 56 and the second section 46 of the actuator piston 32 has a larger total cross-sectional area than the first section 44 of the actuator piston 32, so that the restoring force acts towards the neutral position of the actuator piston 32 with the same pressure in the two pressure chambers 20, 22.

In the second switching position of the valve 24, which is shown in fig. 3(b), the first pressure chamber 20 is connected to the pressure source 14, while the second pressure chamber 22 is connected to the tank 16.

The resulting movement of the actuator piston 32 is shown in fig. 4(b) and 5 (b). On the side assigned to the first pressure chamber 20, a greater force acts on the actuator piston 32 than on the side assigned to the second pressure chamber 22, so that the actuator piston 32 is moved to the right in its axial direction R.

The movement of the first annular piston 54 is limited in this case by the first step 40 of the cylinder 30, which forms a stop for the first annular piston 54, while the second annular piston 56 is carried along by the fourth step 52.

In the third switching position of the valve 24, which is shown in fig. 3(c), the two pressure chambers 20, 22 are connected to the tank 16, so that the actuator piston 32 is substantially freely movable.

In the fourth switching position of the valve 24, which is shown in fig. 3(d), the first pressure chamber 20 is connected to the tank 16, while the second pressure chamber 22 is connected to the pressure source 14.

The resulting movement of the actuator piston 32 is shown in fig. 4(c) and 5 (c). On the side assigned to the first pressure chamber 20, a smaller force acts on the actuator piston 32 than on the side assigned to the second pressure chamber 22, so that the actuator piston 32 is moved to the left in its axial direction R.

In the switching process, the starting position, the second switching position, the third switching position and the fourth switching position are typically passed successively, wherein after that, the starting operating position should be returned directly from the fourth switching position.

For this purpose, a shut-off device 62 can be provided, which allows a return from the fourth switching position to the starting position without significant pressure changes in the pressure chambers 20, 22. The shut-off device 62 is preferably designed as a switchable shut-off valve, which is arranged, for example, in the pressure supply line 26. Correspondingly, in the blocking position of the shut-off valve, irrespective of the switching position of the valve, one of the two pressure chambers 20, 22 is prevented from being pressurized via the pressure supply line 26. Correspondingly, the valve 24 can be switched from the fourth switching position to the starting position without renewed application of load to the actuator piston 32 in the direction of the second pressure chamber 22 in the second switching position.

Fig. 5(a) to (b) show an alternative variant of the actuator 18', in which the remaining structure of the hydraulic system 12 can be kept unchanged.

The cylinder 30 'of the actuator 18' has only a first section 34 'and a second section 36', wherein the second section 36 'has a smaller inner cross-sectional area, thereby forming a first step 40'.

The actuator piston 32 'also has only a first section 44' and a second section 46', wherein the second section 46' has a larger cross section than the first section 44', forming a second step 50'.

In this case, the second section 46 'of the actuator piston 32' is configured substantially complementarily on the outside to the inner wall of the second section 36 'of the cylinder 30'.

Furthermore, a first annular piston 54' is provided on the first section 44' of the actuator piston 32', as also in the case described above.

In other respects, the actuator 18' operates in a similar manner to the actuator 18 described above.

List of reference numerals

10 motor vehicle speed variator

12 hydraulic system

14 pressure source

16 boxes

18 actuator

20 first pressure chamber

22 second pressure chamber

24 valve

26 pressure supply line

28-box line

30 jar

32 actuator piston

34 first section of cylinder

36 second section of cylinder

38 cylinder third section

40 first step

42 second step

44 first section of the actuator piston

46 second section of the actuator piston

48 third section of the actuator piston

50 third step

52 fourth step

54 first annular piston

56 second annular piston

58 switching element

59 callback device

60 bypass line

62 stop device

A first interface

B second interface

Pthird interface

Tth interface

R axial direction