Hydraulic clutch actuation with on-demand clutch oiling

Abstract

In a hydraulic clutch actuation system for controlling in particular a clutch-controlled compensation unit of a drivetrain of a motor vehicle, in which hydraulic clutch actuation system a hydraulic pump is used for generating hydraulic pressure in a hydraulic fluid for the purposes of clutch actuation by means of a hydraulic clutch actuation device, provision is made whereby the hydraulic fluid is supplied as clutch oil to the friction members of the friction clutch which are to be oiled with clutch oil (cooling and/or lubricating oil). In this way, improved and more reliable oiling of the clutch can be made possible even at low vehicle speeds and under heavy clutch load, wherein, despite this, very rapid dry-running of the cutches, and low power losses generated by the clutch oiling, are ensured.

Claims

1. A hydraulic clutch actuation system for actuation of at least one friction clutch of a clutch-controlled compensation unit for a motor vehicle, comprising: a hydraulic pump operable independently of a driving state for generating hydraulic pressure in a hydraulic fluid, wherein at least one clutch actuation device is provided for actuating the at least one friction clutch, on which the hydraulic pressure generated by the hydraulic pump by means of the hydraulic fluid may act as a clutch pressure via a clutch pressure line, and wherein the compensation unit comprises assembly components, which are to be oiled with cooling and/or lubricating oil for lubrication and/or cooling via an oiling line, and at least one clutch control valve via which the clutch pressure is controlled, wherein the clutch pressure line is formed by a line portion running between the at least one clutch control valve and the clutch actuation device, and wherein the oiling line branches off the clutch pressure line downstream of the clutch control valve; wherein a volume flow conveyed by the hydraulic pump is conducted at least partially to the assembly components as cooling or lubricating oil.

2. The system of claim 1, wherein the clutch actuation system is configured for at least one of (a) under a high hydraulic pressure provided by the hydraulic pump, a supply of cooling and lubricating oil to the assembly components of the at least one friction clutch is guaranteed, or (b) such that it is able to provide a high oil volume flow for clutch oiling when the hydraulic pump provides a high-pressure for transmission of a high torque.

3. The system of claim 1, wherein at least one oiling diaphragm is provided in the oiling line.

4. The system of claim 3, wherein the at least one oiling diaphragm is dimensioned such that under the operating pressures and operating temperatures prevailing in the clutch actuation system in proper use, it allows a volume flow in the oiling line of between 0 l/min and 1.5 l/min.

5. The system of claim 1, wherein the clutch actuation system is configured such that the oiling line is supplied with cooling and/or lubricating oil only if the clutch pressure line is also loaded with clutch pressure.

6. The system of claim 1, wherein the oiling line has one or more oiling branches, and a main oiling diaphragm is arranged in the oiling line upstream of the oiling branches.

7. The system of claim 6, wherein a further oiling diaphragm is provided in at least one oiling branch in addition to the main oiling diaphragm provided in the oiling line.

8. The system of claim 1, wherein an oiling control valve is arranged in the oiling line.

9. The system of claim 8, wherein one or more component oiling lines branch off the oiling line.

10. The system of claim 9, wherein the oiling control valve is connected upstream of the branch point of the one or more component oiling lines.

11. The system of claim 1, wherein a shut-off valve is arranged in the oiling line and only opens the oiling line if an adequate opening pressure threshold has been reached.

12. The system of claim 11, wherein an oiling control valve is connected upstream of the shut-off valve.

13. The system of claim 1, wherein a first clutch pressure line is provided for a first friction clutch, and a second clutch pressure line is provided for a second friction clutch, to load the clutch actuation devices of the two clutches with clutch pressure, wherein the first clutch pressure line and the second clutch pressure line are each connected to an input of a changeover valve, and wherein the shut-off valve is connected on the control side to the output of the changeover valve via a control line.

14. The system of claim 1, wherein a shut-off valve is connected on a control side to a distribution line via a control line, wherein the control line branches off the distribution line at a branch point, and wherein an oiling control valve is arranged between the branch point and the shut-off valve.

15. The system of claim 1, wherein the hydraulic pump is controlled by rotation speed or regulated by pressure and driven in rotation via an electric motor.

16. The system of claim 1, wherein the compensation unit comprises friction members of the at least one friction clutch.

17. The system of claim 1, wherein the oiling line is a clutch oiling line.

18. A method for operating a clutch-controlled compensation unit including a hydraulic clutch actuation system for actuation of at least one friction clutch of the clutch-controlled compensation unit for a motor vehicle, comprising a hydraulic pump operable independently of a driving state for generating hydraulic pressure in a hydraulic fluid, wherein at least one clutch actuation device is provided for actuating the at least one friction clutch, on which the hydraulic pressure generated by the hydraulic pump by means of the hydraulic fluid may act as a clutch pressure via a clutch pressure line, and wherein the compensation unit comprises assembly components, which are to be oiled with cooling and/or lubricating oil for lubrication and/or cooling via an oiling line, wherein a volume flow conveyed by the hydraulic pump is conducted at least partially to the assembly components as cooling or lubricating oil, the method comprising: generating a hydraulic pressure in a hydraulic fluid by means of a hydraulic pump which can be driven independently of driving state; loading a clutch actuation device of the at least one friction clutch comprising friction members with a hydraulic clutch pressure via a clutch pressure line, and oiling assembly components of the compensation unit, including the friction members of the at least one friction clutch, with cooling and/or lubricating oil via an oiling line for the purpose of lubricating and/or cooling the assembly components including the friction members, wherein the hydraulic fluid is supplied as cooling or lubricating oil to the assembly components, including the friction members, for oiling, and wherein the clutch actuation system further comprises at least one clutch control valve via which the clutch pressure is controlled, wherein the clutch pressure line is formed by a line portion running between the at least one clutch control valve and the clutch actuation device, and wherein the oiling line branches off the clutch pressure line downstream of the clutch control valve.

19. The method of claim 18, wherein under the operating pressures and operating temperatures prevailing in proper use, the volume flow of the hydraulic fluid supplied to the assembly components is between 0 l/min and 1.5 l/min per clutch.

20. The method of claim 18, wherein the oiling line is only supplied with cooling or lubricating oil if the clutch pressure line is also loaded with pressure, and wherein a shut-off valve is arranged in the oiling line and only opens the oiling line if an adequate opening pressure threshold has been reached, and wherein a high oil volume flow is provided for the clutch oiling when the hydraulic pump provides a high pressure for transmitting a high torque.

Description

SUMMARY OF THE DRAWINGS

(1) Further features and advantages of the invention arise from the subclaims and from the following description of preferred exemplary embodiments with reference to the drawings.

(2) The drawings show:

(3) FIG. 1: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit with a clutch and a positive-action differential;

(4) FIG. 2: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit working without differential, with two clutches and a clutch control valve per clutch;

(5) FIG. 3: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit working without differential, with two clutches, a clutch control valve per clutch, and a main oiling diaphragm in a clutch oiling line;

(6) FIG. 4: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit with a clutch and positive-action differential, with an oiling control valve in a clutch oiling line;

(7) FIG. 5: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit working without differential, with two clutches, a clutch control valve per clutch, and an oiling control valve in a clutch oiling line and an additional component oiling;

(8) FIG. 6: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit with a clutch and positive-action differential with an oiling control valve and a shut-off valve in a clutch oiling line and with an additional component oiling;

(9) FIG. 7: a diagrammatic depiction of a hydraulic clutch actuation system of a clutch-controlled transverse compensation unit working without differential, with two clutches, a clutch control valve per clutch, and an oiling control valve and a shut-off valve controlled via clutch pressure in a clutch oiling line, and an additional component oiling: and

(10) FIG. 8: an embodiment corresponding to FIG. 7 in which the shut-off valve is controlled via the pressure prevailing in a distribution line.

DESCRIPTION

(11) In the figures described below, description is provided with reference to a clutch-controlled transverse compensation unit. The letters L and R assigned to specific reference signs in some figures stand respectively for the left (L) and right (R) component of the partially symmetrical basic structure of the embodiment shown in some of the figures.

(12) The figures show two different variants of a clutch-controlled transverse compensation unit, of which one is equipped with a clutch and a differential, and the other works without a differential and has two clutches K.sub.L and K.sub.R, wherein the clutch K.sub.L transmits the drive power to the left drive wheel and the clutch K.sub.R transmits the drive power to the right drive wheel. The clutch actuation systems depicted for the respective compensation units, and the respective oiling architecture and the use of the components used here, may be transferred accordingly from the one variant to the other taking into account the omission or addition of a clutch.

(13) In FIG. 1, a clutch-controlled transverse compensation unit 1 of an axle of a car is shown together with a clutch actuation system in a simplified, diagrammatic view. Depending on the clutch state, the transverse compensation unit shown in FIG. 1 may transmit torque to both drive wheels. When the clutch is open, no torque is transmitted; when the clutch is closed, torque is transmitted, wherein the amount of the transmitted torque is dependent on the set clutch slip which is regulated via the level of hydraulic clutch pressure provided by a pump P. If the clutch is closed completely (slip-free), the transverse compensation unit shown works like a conventional positive-action differential.

(14) The drive power of the vehicle drive is transferred via an input member 2, such as a cardan shaft, and an associated drive wheel 3 to a crown wheel 4, and from there transmitted to an input plate carrier 5 (in FIG. 1, the outer plate carrier), to which axially displaceable input plates are assigned in a rotationally fixed fashion. These input plates cooperate with output plates, which in turn are assigned in an axially displaceable but rotationally fixed fashion to an output plate carrier 6 (in FIG. 1, the inner plate carrier). The resulting clutch unit K constitutes a multiplate clutch known in principle.

(15) A clutch actuation device with a hydraulically actuated clutch actuator A is assigned to the clutch unit, and is supplied with pressurized oil by a hydraulic pump P driven in rotation by a speed-controlled electric motor M, wherein the clutch device delivers oil permanently during operation in order to build up the clutch actuation pressure, creating a return volume flow.

(16) A branch point which opens into a clutch oiling line 9.sub.1 provided with an oiling diaphragm 10 is arranged in the hydraulic line leading from the hydraulic pump to the clutch actuator; said clutch oiling line supplies the clutch K with clutch oil (cooling or lubricating oil) since the return volume flow occurring on hydraulic clutch actuation is conducted via the clutch oiling line to the clutch K as clutch oil (cooling and/or lubricating oil for the clutch plates).

(17) Depending on the pressure level provided by the pump P, which can build up rapidly when the pump P or the motor M driving the pump P is switched on, despite the basically open oiling diaphragm 10 with its very limited passage cross-section, at the same time as the build-up of the pressure level for switching the clutch, the clutch K is supplied with clutch oil which is used for lubricating and cooling the friction plates.

(18) When the motor M and hence the pump P are switched off, the pressure in the oil lines 8 and 9fed by the same pump P and belonging to the same oil circuitrapidly falls, the clutch opens and at the same time, without further measures, the clutch oiling also stops so that the clutch runs dry quickly with a rapid reduction of any hydrodynamic friction effects.

(19) FIG. 2 shows a structure of a transverse compensation unit working solely by frictional locking, in which the torque to be distributed to the two drive wheels is transmitted exclusively via two friction clutches K.sub.L and K.sub.R to the drive wheels assigned to the respective clutches. In contrast to FIG. 1, there is no differential with positively intermeshing drive members. The compensation unit constitutes a clutch-controlled transverse compensation unit working without differential.

(20) The pressure provided by the hydraulic pump P is conducted to the respective clutch actuator 7 of the respective clutch via two normally closed VFS (Variable Force Solenoid) control valves 11.sub.L and 11.sub.R via the clutch pressure lines 8.sub.L and 8.sub.R. By corresponding control of the control valves 11.sub.R and 11.sub.L, the pressure is regulated clutch-specifically to the pressure level required for the respective driving state, so that the drive power transmitted via the clutches can be set individually for each drive wheel.

(21) Each of the two clutches has an assigned clutch oiling line 9, by means of which the oil required for clutch oiling is conducted to the respective clutch via a respective oiling diaphragm 10. The clutch oiling lines 9.sub.L and 9.sub.R are arranged behind the control valves 11.sub.L and 11.sub.R, viewed from the hydraulic pump P, and branch off the clutch pressure lines 8.sub.L and 8.sub.R. This guarantees that each clutch is supplied with clutch oil exclusively when the control valves apply clutch pressure to the clutch actuators 7 for closing the clutches.

(22) The exemplary embodiment shown in FIG. 3 largely corresponds to the exemplary embodiment shown in FIG. 2 with regard to the configuration of the clutch-controlled compensation unit, wherein the clutch control system has a clutch oiling line 9, which however, in contrast to the oiling lines 9 shown in FIGS. 1 and 2, branches off before the clutch control valves when viewed from the hydraulic pump P. A main oiling diaphragm 13 is provided in the clutch oiling line 9, across which in operation a differential pressure exists which can effectively limit and reduce the maximum oiling pressure occurring at the individual oiling points.

(23) An oiling branch 12 is provided which branches off the clutch oiling line leading to the clutches downstream of the main oiling diaphragm, and via which for example gearwheels or bearings can be oiled. Also, the oiling points supplied by this oiling branch 12 are provided with oiling diaphragms 10 which are adapted to the oiling demand at the respective oiling point.

(24) FIG. 4 illustrates a clutch actuation system for a transverse compensation unit as also shown in FIG. 1. In contrast to FIG. 1, an oiling control valve 14 is provided in the clutch oiling line 9 in the form of a VBS (Variable Bleed Solenoid, preferably normally open). The oil volume flow available for clutch oiling can be significantly increased in comparison with the use of a main oiling diaphragm in the clutch oiling line, with simultaneously lower power consumption of the hydraulic pump. The clutch oil volume flow may furthermore be set independently of the vehicle speed, the torque demand of the clutch, and the differential rotation speed between the two drive wheels.

(25) Inside the clutch oiling line 9 with the oiling branch 12, the oil volume flow is distributed in the same way as in FIG. 3 via the hydraulic resistances of the oiling diaphragms provided upstream of the individual oiling points.

(26) FIG. 5 shows the clutch actuation system shown in FIG. 4 for a transverse compensation unit working without differential, as has already been shown in FIGS. 2 and 3.

(27) FIG. 6, FIG. 7 and FIG. 8 illustrate a further possible embodiment of a clutch actuation system with a shut-off valve 15 in the clutch oiling line, via which the oiling line leading to the clutches can be blocked or opened depending on operating state.

(28) The shut-off valve can be formed by a seat-type valve and can be pressure-controlled so that it opens the clutch oiling line when a predefined opening pressure threshold is exceeded. Also, spool-type valves may be used, wherein seat valves are preferred because of their simpler structure, higher load-bearing capacity, lower susceptibility to leakage and low sensitivity to contamination in the hydraulic system. The shut-off valve may however also be electronically controllable. The shut-off valve can be normally closed. The switching point or opening pressure threshold may lie between 2 bar and 4 bar.

(29) By providing such a shut-off valve, it is possible for a component oiling line 17 to branch off the clutch oiling line at a branch point downstream of the oiling control valve but upstream of the shut-off valve, and supply oil to components which may require oiling independently of the oiling demand of the clutches. The arrangement shown in the figures, with the oiling control valve 14, the shut-off valve 15 and the position of the branch point for the component oiling line 17, allows targeted oiling of components independently of any oiling demand at the clutches.

(30) Thus with the embodiment shown in FIGS. 6, 7 and 8, by closing the oiling control valve 14, the component oiling can be stopped completely or set to a specific volume flow, while the oiling line leading to the clutches is opened only if the clutch pressure (FIG. 6 and FIG. 7), or the system pressure prevailing in a distribution line 18 upstream of the clutch control valves 11.sub.L and 11.sub.R, exceeds the opening pressure threshold of the shut-off valve 15.

(31) In FIG. 6 and FIG. 7, the pressure-controlled shut-off valve 15 is connected on the control side to the clutch pressure line or lines 8 via a control line 16. In this way, the pressure prevailing in the clutch pressure lines is decisive for determining whether or not the opening pressure threshold has been exceeded.

(32) In the exemplary embodiment shown in FIG. 7, the clutch pressure lines 8.sub.L and 8.sub.R are connected to the control line via a changeover valve 19, so that always the higher pressure prevailing in the two clutch control lines is decisive for determining whether or not the pressure-controlled shut-off valve 15 opens the oiling line.

(33) In the exemplary embodiment shown in FIG. 8, the control line 16 is connected to a distribution line 18. Here, it is not the clutch actuation pressure set by the clutch control valves 11.sub.L or 11.sub.R in the clutch pressure lines which is decisive for determining whether or not the opening pressure threshold of the switchover valve 15 has been exceeded, but the system pressure supplied by the hydraulic pump into the distribution line 18.

(34) The embodiments shown in FIGS. 6, 7 and 8 enable the oil volume flow for the clutches to be controlled independently of the vehicle speed, differential rotation speeds at the drive wheels, and the amount of clutch torque. The oil volume flow, in particular the clutch oil volume flow but also any volume flow for any other component oiling, may therefore be adapted directly to the respective requirements depending on operating state, and allows a rapid and complete stoppage of clutch oiling even during oiling of other components which must be oiled independently of the clutches.

LIST OF REFERENCE SIGNS

(35) 1 Transverse compensation unit

(36) 2 Input member

(37) 3 Drive wheel

(38) 4 Crown wheel

(39) 5 Input plate carrier

(40) 6 Output plate carrier

(41) 7.sub.(L,R) Clutch actuator

(42) 8.sub.(L,R) Clutch pressure line

(43) 9.sub.(L,R) Clutch oiling line

(44) 10.sub.(L,R) Oiling diaphragm

(45) 11.sub.(L,R) Clutch control valve

(46) 12 Oiling branch

(47) 13 Main oiling diaphragm

(48) 14 Oiling control valve

(49) 15 Shut-off valve

(50) 16 Control line

(51) 17 Component oiling line

(52) 18 Distribution line

(53) 19 Changeover valve

(54) K Clutch

(55) M Electric motor

(56) P Hydraulic pump