METHOD FOR ACTUATING A DECOUPLING UNIT

Abstract

The disclosure relates to a method for actuating a decoupling unit in a powertrain which comprises at least one driven axle. The aim of the disclosure is to simplify the actuation of the decoupling unit. This is achieved in that the decoupling unit is passively actuated in an actuation direction using an actuation force, which is provided in a hydraulic system, via a first hydraulic functional surface, and the decoupling unit is passively actuated in a restoring direction using a restoring force via a second hydraulic functional surface.

Claims

1. Method A method for actuating a decoupling unit in a drive train which comprises at least one driven axle, the method comprising: passively actuating the decoupling unit with an actuation force present in a hydraulic system in an actuation direction via a first hydraulic functional surface, and passively actuating the decoupling unit with a restoring force in a restoring direction via a second hydraulic functional surface.

2. The method according to claim 1, wherein the restoring force is generated by two transmission elements.

3. The method according to claim 2, wherein a hydraulic resistance is arranged in respective tank lines of the two transmission elements to generate the restoring force.

4. The method according to claim 1, wherein the restoring force is tapped off via an OR valve.

5. The method according to claim 1, wherein passively actuating the decoupling unit is accomplished via signal amplification.

6. The method according to claim 1, wherein passively actuating the decoupling unit with a restoring force is accomplished via signal amplification.

7. The method according to claim 1, wherein a first hydraulic control surface for restoring the decoupling unit is larger than a second hydraulic control surface for actuating the decoupling unit.

8. The method according to claim 1, wherein the decoupling unit comprises a double-acting hydraulic cylinder configured to be actuated and reset via a decoupling valve.

9. The method according to claim 8, wherein the decoupling valve is configured as a 4/2-way valve which is controlled via two OR valves.

10. The method according to claim 9, wherein the decoupling valve is configured as a proportional valve.

11. The method according to claim 1, wherein the decoupling unit comprises a double-acting hydraulic cylinder having the first hydraulic functional surface and the second hydraulic functional surface.

12. A method for actuating a decoupling unit configured to deactivate a driven axle within a drive train of a vehicle, the method comprising: providing a hydraulic system including: a first actuating branch comprising a first clutch or brake, a second actuating branch comprising a second clutch or brake, a decoupling unit, a first OR valve, a second OR valve, and passively actuating the decoupling unit via the first OR valve with a hydraulic actuation force present within the hydraulic system configured to actuate the first clutch or brake or the second clutch or brake, and passively actuating the decoupling unit with a hydraulic restoring force via the second OR valve.

13. The method according to claim 12, wherein the decoupling unit is configured as a cut-out clutch.

14. The method according to claim 12, wherein the hydraulic system further comprises a first hydraulic branch configured to fluidly connect the first actuating branch to the second actuating branch, and the first hydraulic branch includes the first OR valve.

15. The method according to claim 12, wherein the first actuating branch further comprises a first pressure reducing valve corresponding to the first clutch or brake, and the second actuating branch further comprises a second pressure reducing valve corresponding to a second clutch or brake.

16. The method according to claim 15, wherein the hydraulic system further comprises a second hydraulic branch configured to fluidly connect the second OR valve to: i) a first tank line of the first pressure reducing valve, and ii) a second tank line of the second pressure reducing valve.

17. The method according to claim 16, wherein each one of the first tank line and the second tank line includes a hydraulic resistance configured as an orifice.

18. The method according to claim 15, wherein the hydraulic system further comprises a hydraulic pressure source configured to supply: the first clutch or brake, the second clutch or brake, the first pressure reducing valve, and the second pressure reducing valve.

19. The method according to claim 12, wherein the decoupling unit comprises a double-acting hydraulic cylinder.

20. The method according to claim 19, wherein the first OR valve is fluidly connected to a first functional surface of the double-acting hydraulic cylinder and the second OR valve is fluidly connected to a second functional surface of the double-acting hydraulic cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further advantages, features and details of the disclosure are apparent from the following description, in which various exemplary embodiments are described in detail with reference to the drawing. In the figures:

[0028] FIG. 1 shows a schematic representation of a motor vehicle with two driven axles;

[0029] FIG. 2 shows two exemplary embodiments of a functional chain in a drive in different positions of a decoupling unit;

[0030] FIG. 3 shows a hydraulic system for actuating and restoring a decoupling unit in a drive train of a motor vehicle according to a first exemplary embodiment;

[0031] FIG. 4 shows an exemplary embodiment similar to that in FIG. 3 with an additional decoupling valve which is assigned to the decoupling unit; and

[0032] FIG. 5 shows an exemplary embodiment similar to that in FIG. 4, wherein the decoupling valve is designed as a proportional valve with a reversing system.

DETAILED DESCRIPTION

[0033] In FIG. 1, a motor vehicle 1 with a drive train 2 is shown schematically. The drive train 2 comprises two driven axles 3, 4. The driven axles 3, 4 are each equipped with two wheels 5, 6 and 7, 8.

[0034] An axle drive 9 is assigned to the driven axle 3. An axle drive 10 is assigned to the driven axle 4. When the motor vehicle 1 is in operation, both axle drives 9, 10 do not always have to be active at the same time. In order to avoid losses, one of the axle drives 9, 10 can be switched off during normal driving.

[0035] In FIG. 2, two options for a functional chain with a drive 11, a transmission ratio device 12, a decoupling unit 13 and a wheel 14 are shown schematically. The transmission ratio device 12 is, for example, a transmission. In order to avoid unwanted losses during operation of the drive 11, the drive 11 can be decoupled with the decoupling unit 13. As a result, losses to the wheel 14 can be reduced.

[0036] Vehicles with classical drives have transmissions with clutches and gears. Losses to the wheel can usually be adequately decoupled here using the clutches and the selection of the gears.

[0037] In vehicles with so-called e-axles, shiftable transmissions are often not installed. Here, the decoupling unit 13 can be used advantageously in order to reduce losses during operation when the respective drive 11 is not required.

[0038] Vehicles with e-axles can also have multiple gears, in particular double gears. Here, too, the decoupling unit 13 can be used advantageously in order to minimize losses. The upper functional chain of FIG. 2 provides for the decoupling unit 13 to be arranged closer to the wheel 14.

[0039] An appropriate actuator can be used to actuate the decoupling unit 13. Conventional actuators include at least one active element with an electric motor or at least with an electric valve.

[0040] FIGS. 3 to 5 show how the desired decoupling function can be implemented with a hydraulic system 60 without an additional active element being required for the decoupling unit. In the exemplary embodiments of the hydraulic system 60 in FIGS. 3 to 5, a decoupling unit 27 is connected to existing active elements in such a way that the decoupling unit 27 can be actuated effectively without additional active elements. The same reference signs are used in FIGS. 3 to 5 to designate the same or similar parts. Common features are described only once. The hydraulic system 60 includes a hydraulic pressure source 15. The hydraulic pressure source 15 includes, for example, at least one hydraulic pump.

[0041] In the FIGS. 3 to 5, an actuation force line 16 is connected to the outlet of the hydraulic pressure source 15. A hydraulic consumer, such as a parking lock, can be connected to an upper end of the actuation force line 16, which is cut off in FIGS. 3 to 5. In the actuation force line 16, two branching points 17, 18 are provided.

[0042] A first actuating branch 19 is connected to branching point 17. A second actuating branch 20 is connected to branching point 18. A first transmission element 21 is assigned to the first actuating branch 19. A second transmission element 22 is assigned to the second actuation branch 20. A pressure reducing valve 23, 25 is arranged in each of the actuating branches 19, 20.

[0043] A hydraulic branch 24, 26 is additionally provided between the pressure reducing valve 23, 25 and the transmission element 21, 22. An OR valve 29 is connected between branching points 24 and 26.

[0044] FIG. 3 shows the simplest variant of the hydraulic system 60. The decoupling unit 27 is connected directly to the OR valve 29, which in turn is connected between the branching points 24 and 26. The decoupling unit 27 is, for example, a cut-out clutch. The transmission elements 21 and 22 are, for example, clutches or brakes.

[0045] The transmission elements 21 and 22 are actuated via the pressure reducing valves 23, 25. In the non-actuated state, the transmission elements 21, 22, in particular the clutches 21, 22, do not transmit any torque. This means that the decoupling unit 27 can also be open when the clutches 21, 22 are open.

[0046] During operation of the hydraulic system 60, it must be ensured that the decoupling unit 27 designed as a cut-out clutch 28 is securely closed before one of the transmission elements, in particular one of the clutches 21, 22, transmits torque.

[0047] Therefore, the cut-out clutch 28 is to be designed in such a way that the cut-out clutch 28 is securely closed at a low pressure before one of the clutches 21, 22 begins to transmit torque. In order to achieve this, the pressure range of a so-called ventilation path of one of the clutches 21, 22 is used to close the cut-out clutch 28. An actuation path up to a touch point is designated the ventilation path. When the touch point is exceeded, torque is transmitted in a targeted manner.

[0048] A symbol 30 in FIG. 3 indicates that the decoupling unit 27 designed as a cut-out clutch 28 comprises a double-acting cylinder. In the double-acting cylinder 30, a piston in FIG. 3 is guided back and forth to the left and to the right. The piston comprises a first hydraulic functional surface 31 on the left in FIG. 3 and a second hydraulic functional surface 32 on the right in FIG. 3. The first hydraulic functional surface 31 is designed as a circular surface. The second hydraulic functional surface 32 is designed as an annular surface.

[0049] The first hydraulic functional surface 31 is acted upon by an actuation force from the first actuating branch 19 or from the second actuating branch 20 via the OR valve 29. The second hydraulic functional surface 32 can be acted upon by a restoring force from a tank line 34 or from a tank line 35 via an OR valve 33.

[0050] The tank line 34 is connected to the pressure reducing valve 23. The tank line 35 is connected to the pressure reducing valve 25. A hydraulic resistance 41 is arranged in the tank line 34. A hydraulic resistance 42 is arranged in the tank line 35.

[0051] The decoupling unit 27 is engaged via the first, circular hydraulic functional surface 31 and the OR connection of the actuating branches 19 and 20. The disengagement is initiated via the second annular hydraulic functional surface 32. The working pressure, referred to as the restoring force, is tapped off via the OR connection of the tank lines 34, 35.

[0052] In contrast to the engagement process, the working pressure must first be generated during the disengagement process. As shown in FIG. 3, this can be done by the hydraulic resistances 41, 42 in the tank lines 34, 35. The hydraulic resistances 41, 42 are designed, for example, as orifices. The pressure signal for the disengagement process is tapped off between the pressure reducing valve 23, 25 and the hydraulic resistance 41, 42 and fed to the OR valve 33.

[0053] The working pressures, signal pressures or restoring forces for disengagement should be relatively low in order to only slightly influence the dynamic opening of the transmission elements 21, 22 designed as clutches. Reliable disengagement of the decoupling unit 27 is therefore only possible with a very large hydraulic functional surface 32.

[0054] It is therefore proposed with the exemplary embodiment in FIG. 4 that both engagement and disengagement take place with signal amplification. Ideally, this takes place with a passive decoupling valve 45, which is arranged in an actuating branch 37. The actuating branch 37 is connected to a branch 38 of the actuation force line 16. In this way, the decoupling valve 45 is supplied from the actuation force line 16 with an actuation force or system pressure which is provided at the outlet of the hydraulic pressure source 15.

[0055] A dashed circle in FIG. 4 indicates a further hydraulic pressure source 50, which can be provided in the hydraulic system 60 to supply the actuating branch 37 with the actuation force or system pressure. In this case, the hydraulic connection between branching points 18 and 38 is omitted in FIG. 4. In contrast to what is shown in FIG. 4, the signal-amplified engagement and disengagement can also take place with one passive valve for engagement and disengagement, respectively.

[0056] The engaged operating situation is shown in FIG. 4, in which the system pressure is connected to the first hydraulic functional surface for engagement. The decoupling unit 27 is engaged from a pressure threshold that must be reached once. This is done by varying the system pressure before the transmission elements 21 or 22 are activated or torque is transmitted with the transmission elements 21, 22 designed as clutches.

[0057] Opening of the decoupling unit 27 designed as a cut-out clutch 28 takes place in the reverse order. If the transmission element 21 designed as a clutch or the transmission element 22 designed as a clutch reaches its touch point when opening, the force ratios at the decoupling valve 45 are coordinated in such a way that the decoupling valve 45 switches over and the hydraulic functional surface 32 is acted upon for disengagement.

[0058] As shown symbolically or schematically in FIG. 4, this is done by means of pressure control surfaces of different sizes on the decoupling valve 45. Here, the pressure control surface for the opening valve position is larger than that for closing. The pressure level for switching the decoupling valve 45 is typically lower than the two touch pressures of the clutches 21, 22.

[0059] This in turn is important when torque is transferred from clutch 21 to clutch 22, since the decoupling unit should remain securely closed here. With such a design, the decoupling can take place only when one of the two clutches 21, 22 is already open and the second passes through the touch point when opening.

[0060] An optional spring on the decoupling valve 45, which reliably guarantees a position of the decoupling valve 45 in the depressurized state, is not shown. Depending on the boundary conditions, such as a suitable control strategy, the first or second valve position of the decoupling valve 45 can be advantageous.

[0061] FIG. 5 shows a detailed variant of the decoupling valve 45. Switching from one valve position to the other is proportional to the respective pressure signal size. The respective load pressures are fed back to the decoupling valve 45, which is designed as a proportional valve. A transitional position between the two end positions is designed in such a way that both pressure chambers of the double-acting cylinder 30 of the decoupling unit 27 are located on the tank. This has the advantage that there can never be pressure on both pressure chambers of the double-acting cylinder 30 at the same time.

[0062] Variants in which only one of the two pressure chambers of the double-acting cylinder 30 of the decoupling unit 27 is fed back to the decoupling valve 45 are not shown. It could be advantageous to dispense with the return when opening the decoupling unit 27 in order to make the decoupling more robust or more dynamic.

LIST OF REFERENCE SYMBOLS

[0063] 1 Motor vehicle [0064] 2 Drive train [0065] 3 Driven axle [0066] 4 Driven axle [0067] 5 Wheel [0068] 6 Wheel [0069] 7 Wheel [0070] 8 Wheel [0071] 9 Axle drive [0072] 10 Axle drive [0073] 11 Drive [0074] 12 Transmission ratio device [0075] 13 Decoupling unit [0076] 14 Wheel [0077] 15 Hydraulic pressure source [0078] 16 Actuation force line [0079] 17 Branching point [0080] 18 Branching point [0081] 19 First actuating branch [0082] 20 Second actuating branch [0083] 21 First transmission element [0084] 22 Second transmission element [0085] 23 Pressure reducing valve [0086] 24 Branching point [0087] 25 Pressure reducing valve [0088] 26 Branching point [0089] 27 Decoupling unit [0090] 28 Cut-out clutch [0091] 29 OR valve [0092] 30 Double-acting cylinder [0093] 31 First hydraulic functional surface [0094] 32 Second hydraulic functional surface [0095] 33 OR valve [0096] 34 Tank line [0097] 35 Tank line [0098] 37 Actuating branch [0099] 38 Branching point [0100] 41 Hydraulic resistance [0101] 42 Hydraulic resistance [0102] 45 Decoupling valve [0103] 50 Other hydraulic pressure source