SYSTEM FOR ACTUATING A CLUTCH

Abstract

In a drive train for a motor vehicle, which has a permanently driven primary drive train and a secondary drive train which can be connected to the primary drive train when necessary or decoupled therefrom, in order to couple or decouple from the primary drive train, there is provision for actuating a clutch apparatus of a device for power transmission and/or power distribution, in which the disengagement unit when providing the clutch actuation force which is required for the actuation of the clutch apparatus is operationally connected to secondary drive members or in which there is provided a drive clutch which, in order to provide the clutch actuation force required for the actuation of the clutch apparatus, is capable of producing an operational connection between the primary drive members or the secondary drive members and a manipulated variable unit of the disengagement unit.

Claims

1.-14 (canceled)

15. A system for actuating a clutch apparatus of a power transmission/distribution device for at least one of power transmission and power distribution of the drive power of a motor vehicle that has a permanently driven primary drive train and a secondary drive train which can be connected to the primary drive train, the system comprising the power transmission/distribution device, including primary drive members which during correct installation of the power transmission/distribution device are permanently driven or towed on the motor vehicle during travel, and secondary drive members which, during correct installation of the power transmission/distribution device on the motor vehicle are couplable to, and decouplable from, the primary drive members by the clutch apparatus; wherein the clutch apparatus has a clutch actuation device having a disengagement unit for decoupling primary drive members and secondary drive members; wherein the disengagement unit for the provision of clutch actuation force to actuate of the clutch apparatus is operationally connected to the secondary drive members.

16. The system as claimed in claim 15, wherein there is provided a drive clutch which in order to provide the clutch actuation force is arranged to produce an operational connection between the primary drive members or the secondary drive members and a manipulated variable unit of the disengagement unit.

17. The system as claimed in claim 15, wherein the clutch apparatus is a clutch which acts in a positive-locking manner.

18. The system as claimed in claim 16, wherein the drive clutch is a clutch which can be switched on demand and which can be controlled electrically.

19. The system as claimed in claim 16, wherein the drive clutch is a clutch which operates in a contactless manner.

20. The system as claimed in claim 16, wherein the drive clutch is a magnetic clutch or an eddy current clutch.

21. The system as claimed in claim 16, wherein the drive clutch acts as a pressure limitation device for a manipulated variable unit which produces hydraulic pressure.

22. The system as claimed in claim 15, further comprising an engagement unit that has a pretensioning element which stores potential energy for the engagement operation.

23. The system as claimed in claim 15, wherein the clutch apparatus comprises a retention element which is arranged for retaining an engagement member which produces the positive-locking connection of the clutch in a permanently disengaged position.

24. The system as claimed in claim 15, wherein the clutch apparatus is a bi-stable clutch apparatus.

25. The system as claimed in claim 23, wherein the retention element is formed by an electrically controllable magnetic retention member or an electrically controllable switching detent.

26. The system as claimed in claim 15, wherein the retention element is configured such that, during operation of the motor vehicle with the clutch disengaged or engaged, the respective switching state of the clutch apparatus can be kept permanently in an energy-supply-free state.

27. The system as claimed in claim 23, further comprising a bi-stable retention element which, starting from a first position which is stable per se, can be moved into a second position which is stable per se if it is urged counter to an internal resistance beyond an indifferently stable zero position.

Description

SUMMARY OF THE DRAWINGS

[0031] In the drawings:

[0032] FIG. 1 is a schematic illustration of an entire drive train of a motor vehicle according to the prior art with a permanently driven primary drive train and with a secondary drive train which can if necessary be connected to the primary drive train or be decoupled therefrom,

[0033] FIG. 2 shows a PTU (Power Takeoff Unit) according to the prior art and how it can be used in the drive train shown in FIG. 1,

[0034] FIG. 3 shows an RDU (Rear Drive Unit) according to the prior art and how it can be used in the drive train shown in FIG. 1,

[0035] FIG. 4 is a schematic illustration of a bi-stable clutch actuation device with a disengagement unit and an engagement unit and a drive clutch which operates between a primary or secondary drive member and a manipulated variable unit,

[0036] FIG. 5 is a schematic illustration of a modification of the embodiment shown in FIG. 4 with a direct connection between the secondary drive member and the manipulated variable unit and with an additional pressure limitation valve,

[0037] FIG. 6 is a schematic illustration of a bi-stable clutch actuation device with a dual-action clutch actuator and a bi-stable retention element and a drive clutch which operates between a primary or secondary drive member and a manipulated variable unit, and

[0038] FIG. 7 is a schematic illustration of a modification of the embodiment shown in FIG. 6 with a direct connection between the secondary drive member and the manipulated variable unit and with an additional pressure limitation valve.

DESCRIPTION

[0039] FIG. 1 shows a drive train construction known from the prior art with a permanently driven primary drive trainin FIG. 1 by way of example the portion of the overall drive train which is permanently driven by a front engine and which directs the drive power to the front wheelsand a secondary drive train which is driven only as required and via which the drive power is also directed as necessary to the secondary drive wheels. Of course, other drive train configurations, in which the primarily driven axle is, for example, the rear axle and/or in which a rear or central motor is used, are also conceivable.

[0040] In 4WD mode or Connect mode, via a PTU 1 which is shown in detail in FIG. 2, drive power is tapped at the primary drive train and directed via a cardan shaft to an RDU 2 which is shown in detail in FIG. 3 and which takes up the function of transverse compensation and transmits the drive power to both secondary drive wheels. PTU and RDU each constitute a device for power transmission and/or power distribution of the drive power in the context of this disclosure.

[0041] Both on the PTU 1 and on the RDU 2, there is provided a clutch apparatus 3 which acts in a positive-locking manner and by means of which the primary drive members 4 and secondary drive members 5 of the PTU or the RDU can be coupled to each other or decoupled from each other. To this end, a hydraulic actuation 7 displaces as a portion of a disengagement unit of the clutch actuation device a sliding sleeve 6 between a connect position (primary and secondary drive members are coupled to each other) and a disconnect position (primary and secondary drive members are decoupled from each other).

[0042] FIGS. 4 to 7 are schematic illustrations of a clutch actuation device according to example embodiments, as can be used in a drive train or one of the devices for power transmission and/or power distribution of the drive power as shown in FIG. 2 or FIG. 3. The sliding sleeve 6 shown in FIGS. 4 to 7 corresponds in terms of its function to the sliding sleeve 6 shown in FIG. 2 and FIG. 3 and can be displaced by means of a hydraulic actuation 7 from a connect position into a disconnect position (indicated by the double-headed arrow below the sliding sleeve 7). Non-hydraulically acting actuators can also be used.

[0043] The hydraulic actuation 7 is provided with a hydraulic pressure produced by a hydraulic pump 8 in order to displace the sliding sleeve 6 counter to the force of a spring 9 which acts as a pretensioning element from a connect position into a disconnect position and thus to complete a disengagement operation of the clutch. The hydraulic pump 8 represents as a component of a disengagement unit a manipulated variable unit which provides a manipulated variable (in this instance: hydraulic pressure) which is used to produce a clutch disengagement force. Of course, the use of other types of different manipulated variable units which provide different types of manipulated variables is also conceivable in principle. In particular, in place of a hydraulic pump which is driven by a drive clutch, an electromagnetic clutch which drives a ramp mechanism may be provided.

[0044] The hydraulic pump 8 (the manipulated variable unit of the clutch apparatus) is operationally connected by an operational connection 10 and an interposed drive clutch 11 to a secondary drive member 5 so as to transmit power. The secondary drive member, with which the manipulated variable unit is operationally connected, may be formed by any desired drive member of the portion of the secondary drive train which is stopped in 2-WD mode and which rotates in 4-WD mode, for example, from the cardan shaft or an input or output shaft of the device for power transmission and/or power distribution of the drive power.

[0045] The drive clutch 11 is preferably a magnetic or eddy current clutch which operates in a contactless manner, which can be switched on demand and which can be controlled in an electrical manner. The use of such a clutch which limits the torque which can be transmitted has the advantage thatas a result of the contactless running and the torque which can be transmitted only in a limited mannerit also acts as a pressure limiter because the pressure produced by the hydraulic pump is directly dependent on the torque transmitted to the hydraulic pump. Consequently, when such a drive clutch 11 is used, the pressure limitation valve can be dispensed with. The clutch only has to be configured with respect to the torque transmission potential thereof in such a manner that the hydraulic pressure produced is sufficient to force the sliding sleeve during a disconnect operation into the disconnect position. Furthermore, the power which is intended to be transmitted via the drive clutch to the hydraulic pump can be varied by means of corresponding control of the pump and where necessary can be reduced to zero.

[0046] The described arrangement enablesapart from the respective switching operationsoperation both in 4-WD mode or connect mode and in 2-WD or disconnect mode without significant towing losses and without consuming electrical energy.

[0047] Whilst the components and operations described above with respect to FIG. 4 relate to the disengagement unit or the function thereof for the disconnect operation, the engagement operation or the components and operations which relate to the engagement operation are described below.

[0048] The spring 9 which acts as a pretensioning element stores a large portion of the energy which is introduced into the system during the disengagement operation in order to produce the clutch operation. The resilient force urges or biases the sliding sleeve 6 from the disconnect position back into the connect position but it is retained in the disconnect position by means of a magnetic retention member 12 which acts as a retention element during operation in 2-WD mode. The magnetic retention member 12 is sized in such a manner that the retention force thereof is greater than the resilient force of the pretensioning element which acts in the opposing direction.

[0049] The magnetic retention member 12 is electrically switchable and has a permanent magnet 13 to which current can be applied. In order to initiate the connect operation, the permanent magnet is electrically controlled, whereby it loses its magnetic force. The retention force is thus cancelled or reduced and the magnetic switch releases the restoring force of the pretensioning element 9 in order to initiate the connect operation. In the connect mode, there is an air gap (gap width, for example, >2 mm) between the permanent magnet 13 and the component of the magnetic retention member 12 keeping it in the disconnect mode so that, even when the current supply is switched off, the permanent magnet is not pulled back into the disconnect position.

[0050] A retention device which is provided with such a magnetic retention member enables a high restoring force (F >1000 Newtons (N)) at low current strengths (I<2 Amps (A)), wherein, according to current requirements, it should be assumed that the magnetic retention member only has to be capable of securely maintaining a resilient force of the pretensioning element greater than 300 N. In addition, such a magnetic retention member has only a small structural spatial requirement.

[0051] It should be mentioned that, when the drive clutch 11 which is shown in FIG. 4 and which operates in a base-loss-free manner is used, a power transmitting operational connection of the disengagement unit with the primary drive members 4 is also possible because in this instance, any towing losses are also prevented.

[0052] FIG. 5 shows a slight modification of the embodiment which is shown in FIG. 4 and in which the drive clutch whichas described abovealso performs the function of a pressure limiter, is dispensed with. Consequently, a portion of the disengagement unit is also a pressure limitation valve 16 which allows the pressure which is produced by the hydraulic pump 8 not to exceed an appropriate maximum value. In order to keep the power loss as low as possible in connect mode, the pressure limiter in this travel mode can be adjusted to low pressure, e.g., to zero.

[0053] Furthermore, FIG. 5 shows an alternative embodiment of a retention element in the form of a switching detent 14 in which an electromagnetically actuated locking detent engages in a catch groove and is thus capable of holding the sliding sleeve in an energy-supply-free manner in the disconnect position. Also in this instance, there is provision for the switching detent 14 to have to be controlled in order to release the pretensioning force applied by the pretensioning element 9 for the engagement operation.

[0054] Of course, the switching detent 14 may also be used in the embodiment shown in FIG. 4 in place of the magnetic switch 12 which is illustrated therein and vice versa.

[0055] FIG. 6 shows a variant in which a pretensioning element 9 which stores potential energy, as shown in FIG. 4 and FIG. 5, is dispensed with. Instead, a bi-stable retention element 17 in the manner of a plate spring is used. Such a retention element can be moved starting from a first position which is stable per se into a second position which is stable per se if it is urged counter to an inner resistance beyond an indifferently stable zero position. Consequently, when such a retention element is used, a generally bi-stable clutch apparatus is also ensured and, neither during operation of the motor vehicle in 2-WD mode nor during operation thereof in 4-WD mode, requires an energy supply in order to maintain the respective clutch state. This is required only for the actual clutch operation.

[0056] In order to control a hydraulic actuation there is again provided a hydraulic pump 8 which can be operationally connected, via an interposed drive clutch 11 which limits the torque which can be transmitted, to a secondary drive member 5 (where applicable also to a primary drive member 4) so as to transmit power. The hydraulic pump 8 controls in the example shown in FIG. 6 a dual-action hydraulic actuation and has a control valve 15 which is required for this purpose.

[0057] FIG. 7 finally shows an embodiment of a system for controlling a clutch apparatus in which, in comparison with the embodiment shown in FIG. 6, a drive clutch 11 by means of which the torque which can be transmitted to the hydraulic pump 8 can also be limited is dispensed with. Also in this instance, there is therefore provided a pressure limitation valve which does not allow the pressure produced by the hydraulic pump 8 to exceed a suitable maximum value.

[0058] When the clutch actuation device is constructed in such a manner that the disengagement unit for the provision of the clutch actuation force which is required for the actuation of the clutch apparatus is operationally connected to the secondary drive membersregardless of whether this takes place via a drive clutch 11 (FIG. 4 and FIG. 6) or without such a drive clutch (FIG. 5 and FIG. 7)there may further be provision for the drive torque which is tapped via the operational connection from the secondary members in order to provide the manipulated variable for the clutch actuation force to be used, after the disengagement operation as a brake torque for the secondary drive members. In particular, by adjusting a high manipulated variable (for instance, a high hydraulic pressure) there can be requested a high drive torque which, after completing the disengagement operation, acts as a brake torque. It is thus possible to prevent even for a slowed further rotation of the secondary drive members which may occur, for example, as a result of hydrodynamic effects, in multiple-disc clutches, a disconnect mode.

[0059] The use of an electrically controllable magnetic switch as a retention element and component of a clutch actuation device, in particular as a component of an engagement unit of a clutch actuation device, is, separately from the features of the above-described disengagement unit, is considered to be part of this disclosure.

LIST OF REFERENCE NUMERALS

[0060] 1 Power Takeoff Unit (PTU)

[0061] 2 Rear Drive Unit (RDU)

[0062] 3 Clutch apparatus

[0063] 4 Primary drive members

[0064] 5 Secondary drive members

[0065] 6 Sliding sleeve (engagement member)

[0066] 7 Hydraulic actuation

[0067] 8 Manipulated variable unit (hydraulic pump)

[0068] 9 Pretensioning element (resilient element)

[0069] 10 Operational connection

[0070] 11 Drive clutch

[0071] 12 Retention element (magnetic retention member)

[0072] 13 Permanent magnet

[0073] 14 Retention element (switching detent)

[0074] 15 Control valve

[0075] 16 Pressure limitation valve

[0076] 17 Bi-stable retention element