Electrically driven clutch actuator

Abstract

The invention relates to an electrically driven clutch actuators (1) for actuating the clutch of a transmission of a vehicle. An actuator comprises a spindle nut (11) on a spindle (9) and a pressure piece (13) displaceable relative to the spindle nut (11) and coupled to the spindle nut by a biasing spring (15). By rotation of the threaded spindle under a driving force of an electric motor (5), the spindle nut (11) compresses the biasing spring (15) and displaces the pressure piece (13) to disengage the clutch. A latching mechanism (16) is configured to limit displacement of the spindle nut away from the pressure piece under the force of the expanding biasing spring when the driving force is reduced below a predetermined level. Further, a control unit is described that reduces the driving force in response to a trigger condition to reduce power consumption in the clutch disengaged state.

Claims

1. An electrically driven clutch actuator for actuating a clutch of a transmission of a vehicle, comprising: a pressure piece that is axially movable between a first position and a second position corresponding to engaging and disengaging of the clutch, respectively, wherein the pressure piece is driven from the first position into the second position by a spindle drive that comprises a threaded spindle rotationally driven by an electric motor, and a spindle nut mounted on the threaded spindle and being axially displaceable by rotation of the threaded spindle; wherein the spindle nut and the pressure piece are displaceable relative to each other in an axial direction, and are coupled to each other by a biasing spring interposed between the spindle nut and the pressure piece such that by rotation of the threaded spindle under a driving force of the electric motor, the spindle nut compresses the biasing spring and displaces the pressure piece towards the second position to disengage the clutch, wherein when the driving force provided by the electric motor is reduced below a predetermined level, the pressure piece is returned to the first position by the restoring force of the clutch and the biasing spring expands to displace the spindle nut away from the pressure piece, wherein a latching mechanism that is configured to limit displacement of the spindle nut away from the pressure piece under the force of the expanding biasing spring such that the biasing spring is held in a preload state, the latching mechanism comprises first latching means and second latching means, wherein the first latching means are firmly connected to the rotatable threaded spindle or the axially displaceable spindle nut.

2. The clutch actuator according to claim 1, wherein the latching mechanism comprises a detent recess and a detent lug, wherein one of the detent recess and the detent lug is biased in the direction of engagement with the other of the detent recess and the detent lug.

3. The clutch actuator according to claim 1, wherein the latching mechanism comprises a detent portion that is firmly connected to or provided on the threaded spindle and that has at least one detent recess, preferably more than one detent recess, on its outer circumferential surface to retain the threaded spindle in a rotational position by engagement with a detent lug.

4. The clutch actuator according to claim 1 further comprising a sensor arrangement to detect the rotational position of the threaded spindle and/or the axial position of the spindle nut and/or the axial position of the pressure piece.

5. The clutch actuator according to claim 4, wherein the sensor arrangement includes a rotary encoder to detect rotations of the threaded spindle.

6. The clutch actuator according to claim 1, wherein the latching mechanism is releasable by the driving force provided by the electric motor.

7. An electrically driven clutch actuator for actuating a clutch of a transmission of a vehicle, comprising: a threaded spindle supported by one or more roller bearings and rotationally driven by an electric motor, a spindle nut mounted on the threaded spindle and being axially displaceable by rotation of the threaded spindle from a clutch engaging position into a clutch disengaging position corresponding to engaging and disengaging of the clutch, respectively, against a restoring force of the clutch, and a control unit for activating the electric motor to apply a driving force to the threaded spindle, wherein the control unit is configured to hold the spindle nut in the clutch disengaging position with a first value of the driving force, wherein the control unit is configured to, when the spindle nut is held in the clutch disengaging position with the first value of the driving force, reduce the driving force in response to a trigger condition sensed by the control unit to a second value, the second value of the driving force being above a threshold value at which the spindle nut moves toward the clutch engaging position.

8. The clutch actuator according to claim 7, wherein the control unit is configured to adjust the driving force of the electric motor.

9. The clutch actuator according to claim 7, wherein the trigger condition is associated with predetermined driving or stationary conditions of the vehicle.

10. The clutch actuator according to claim 7, wherein the trigger condition is a specific period of time over which the clutch remains disengaged.

11. The clutch actuator according to claim 7, wherein the control unit is configured to perform the steps of: 1) holding the spindle nut in the clutch disengaging position with the first value of the driving force; 2) monitoring displacement of the threaded spindle or the spindle nut and gradually reducing the driving force until reaching a threshold value of the driving force at which the spindle nut begins to displace relative to the threaded spindle under the restoring force of the clutch; 3) gradually increasing the driving force above the threshold value until the spindle nut is stopped and/or returned to the clutch disengaging position.

12. The clutch actuator according to claim 11, wherein the control unit determines the second value of the driving force of the electric motor by performing the steps 1-3 and saving the value of the driving force required for stopping and/or returning the spindle nut into the clutch disengaging position in a memory as second value for later operations of the clutch associated with the trigger condition.

13. The clutch actuator according to claim 7, wherein a pressure piece is provided that is axially movable between a first position and a second position corresponding to engaging and disengaging of the clutch, respectively, wherein the spindle nut and the pressure piece are displaceable relative to each other in an axial direction, and are coupled to each other by a biasing spring interposed between the spindle nut and the pressure piece such that by rotation of the threaded spindle under a driving force of the electric motor, the spindle nut compresses the biasing spring and displaces the pressure piece towards the second position to disengage the clutch.

14. The clutch actuator according to claim 13, wherein the biasing spring is provided in a recess portion of the spindle nut and/or the pressure piece such that the spindle nut makes contact with the pressure piece when the biasing spring is compressed.

15. The clutch actuator according to claim 5, wherein the rotary encoder is an absolute encoder to detect absolute rotations of the threaded spindle.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will now be described referring to exemplary embodiments of the invention shown in the Figures in which

(2) FIG. 1 is a schematic illustration of a clutch actuator;

(3) FIG. 2 is detailed view of a section of the clutch actuator in FIG. 1

(4) FIG. 3 is another schematic illustration of the clutch actuator of FIG. 1.

(5) FIG. 1 is a schematic illustration of a clutch actuator 1 for engaging and disengaging a clutch (not shown) connected to clutch actuation means in the form of a clutch lever 2 mounted in a vehicle to pivot about a pivot axis 3. The upper section of the clutch lever 2 is coupled to the disengagement bearing of the clutch and by swiveling motion of the clutch lever 2 (indicated by bend arrows), the disengagement bearing of the clutch is displaced to switch between the clutch engaged state and the clutch disengaged state.

(6) Swiveling motion of the upper section of the clutch lever 2 to the right (clockwise) engages the clutch. Swiveling motion of the upper section of the clutch lever 2 to the left (counterclockwise) disengages of the clutch. The lower end of the clutch lever 2 is connected to a push-rod 4 serving as a force transmitting element that couples the clutch lever 2 to the clutch actuator 1.

(7) The clutch actuator 1 comprises an electric motor 5 with an output shaft 6 connected to the sun gear of a planetary gear set 7, which is mounted in a housing 8 of the clutch actuator 1. For illustration purposes, only sections of the housing 8 are shown. The planetary gear set 7 is connected with its planet gears to a threaded spindle 9 with an outer thread section 10. On the outer thread section 10 is mounted a spindle nut 11 which has an inner thread meshing with the outer thread 10 of the threaded spindle 9.

(8) The threaded spindle 9 is rotationally supported by a roller bearing 12 mounted in the housing 8. For illustration purposes, only one roller bearing is shown, however, other roller bearings (not shown) are also mounted to support the threaded spindle. The threaded spindle 9 may rotate about is longitudinal axis but is locked against axial displacement. In contrast, the spindle nut 11 is rotatably fixed relative to the housing 8 by a longitudinal guidance (not shown) provided in the housing so that the spindle nut 11 is axially displaceable in the housing 8 but locked against rotation. Rotation of the threaded spindle 9 under the driving force provided by the electric motor 5 and transmitted through the planetary gear set 7 drives the spindle nut 11 in axial direction along the threaded spindle 9.

(9) The clutch actuator 1 further comprises a pressure piece 13 in the form of a plunger, which extends about the threaded spindle 9 but which is not engaged with the threaded spindle as the spindle nut 11. The pressure piece 13 is displaceable in axial direction 14 along the longitudinal axis of the threaded spindle 9, analogously to the spindle nut 11, wherein the pressure piece 13 is also guided in axial direction by a linear guidance (not shown) in the housing 8.

(10) The pressure piece 13 is further connected to the push-rod 4. When the pressure piece 13 is displaced in axial direction 14, along the axis of the threaded spindle 9, it displaces the push-rod 4 which, in turn, actuates the clutch lever 2 to rotate the same about the pivot axis 3.

(11) Pressure piece 13 and spindle nut 11 are movable relative to each other in the axial direction 14 so that the spindle nut 11 and the pressure piece 13 may approach each other and may move away from each other. A biasing spring 15 is interposed between the spindle nut 11 and the pressure piece 13 and couples the two elements with each other. The spindle nut 11 has at one end facing the pressure piece 13 a flange section 23 with a pocket 24 in the form of a recessed portion. The biasing spring 15 is inserted into the recess portion 24 and extends toward the pressure piece 13. The pressure piece 13 has in correspondence to the spindle nut 11 a flange section 25 that faces the flange section 23 of the spindle nut 11. In the illustrated embodiment, the flange section 25 of the pressure piece 13 is flat. Alternatively, the recess portion 24 may be provided on the flange section 25 or both flange sections 23 and 25 may be provided with a recess portion to receive a respective end of the biasing spring 15.

(12) As indicated above, the position of the pressure piece 13 is linked to the condition of the clutch. The pressure piece 13 is axially moveable relative to the threaded spindle 9 between a first position A corresponding to the engaged state of the clutch and a second position B that corresponds to the disengaged state of the clutch. Similar, the spindle nut 11 is axially moveable relative to the threaded spindle 9 between a clutch engaging position C corresponding to the engaged state of the clutch and a second position D corresponding to the disengaged state of the clutch. The displacements between the positions A-B and C-D is respectively indicated by an arrow.

(13) FIG. 1 illustrates the clutch actuator in a state that corresponds to the clutch engaged state. The clutch (not shown) has a clutch spring (not shown) which exerts a restoring force against the clutch lever, indicated by F, upon actuation of the clutch. When the electric motor 5 provides a driving force and rotates the threaded spindle 9 in a first direction, the spindle nut 11 is displaced in axial direction due to the thread engagement with the driving threaded spindle 9, approaches the pressure piece 13 and begins to compress the biasing spring 15 and then to displace the pressure piece 13 from position A to position B against the restoring force of the clutch. As the biasing spring 15 is being compressed into the recess portion 24, the spindle nut 11 approaches the pressure piece 13 until the flange section 23 of the spindle nut 11 engages the flange section 25 of the pressure piece 13 so that axial force is directly transmitted via the flange sections 23 and 25. The pressure piece 13 displaces the push rod 4 and the clutch lever 2 is rotated counterclockwise against the restoring force F of the clutch spring to disengage the clutch. In the disengaged state of the clutch, the restoring force of the clutch acts against the driving torque of the electric motor 5 on the threaded spindle 9 through the push rod 4, the pressure piece 13, the biasing spring 15 and the spindle nut 11.

(14) When the driving force is reduced below a predetermined level, the clutch lever 2 begins to rotate in clockwise direction and the pressure piece is moved backward from position B to position A and the spindle nut 11 is moved backward toward position C. Displacement of the spindle nut 11 toward position C rotates the spindle 11 and causes rotation of the threaded spindle 9. When the pressure piece 13 has reached position A the biasing spring expands and displaces the spindle nut 11 away from the pressure piece 13 toward position C.

(15) In order to prevent displacement of the spindle nut beyond position C and full relaxation of the biasing spring 15, a latching mechanism 16 is provided to limit displacement of the spindle nut 11 away from the pressure piece 13 under the force of the expanding biasing spring 15 and to hold the biasing spring in a preloaded state.

(16) FIG. 2 shows in cross section the latching mechanism 16 in a cross-sectional view along the axial direction 14. The latching mechanism comprises a disc 17 attached to the threaded spindle 9 in a rotatably fixed manner. The disc 17 is provided with a number of detent recesses 18 on its outer circumferential surface. A spring biased detent cam 19 is urged into engagement with detent disc 17 by means of a spring element 20. When the threaded spindle 9 rotates, the detent cam moves from one detent recess 18 into the adjacent detent recess 18. When the driving force of the electric motor is reduced under predetermined value and the detent cam 19 is engaged with one of the detent recesses 18, the spring force provided by the spring element 20 retains the threaded spindle 9 against rotation under the force of the biasing spring 15. As further rotation of the threaded spindle 9 is prevented, the spindle nut 11 is prevented from further displacement away from the pressure piece 13 so that the biasing spring 15 is not allowed to fully expand and is held in pre-load state. Thereby, the disengagement bearing of the clutch is loaded with a preload when the spindle nut 11 is in the clutch engaging position. Further, when the vehicle is turned off and the electric motor is not energized, the spindle nut remains in that position.

(17) The electric motor is activated by the control unit 21 which can adjust the output driving force of the electric motor. The threaded spindle is further provided with an absolute rotary encoder 22, e.g. a magnet element of a Hall-effect sensor. The corresponding sensor part is mounted on the housing but not shown.

(18) FIG. 3 shows the clutch actuator in a state corresponding to the disengaged stated of the clutch. The pressure piece 13 is in the second position B corresponding to the disengaged state of the clutch and the spindle nut 11 is in the clutch disengaging position D. The biasing spring 15 between the spindle nut 11 and the pressure piece 13 is compressed and the restoring force of the clutch acts on the pressure piece and through the compressed spring and the spindle nut 11 as an axial load on the threaded spindle 9. The biasing 15 is fully compressed and received in the recess portion 24. Due to the recess portion 24, the flange section 23 of the spindle nut 11 is in engagement with the flange section 25 of the pressure piece 13.

(19) The roller bearing 12 is of the type that supports radial and axial loads applied to the threaded spindle 9. The clutch is held in the disengaged state and the spindle nut 11 and the pressure piece 13 are retained in positions D, B by a driving force having a first value. The control unit 21, which controls the electric motor 5, is configured to measure the time the clutch is in the disengaged state. For that purpose, the above described rotary encoder may be used to provide the control unit with information if the spindle nut is in the clutch engaging or the clutch disengaging position and an internal timer of the control unit may measure the time. When a predetermined time has lapsed without the clutch reengaging, the control unit considers this condition to be a trigger condition that triggers a specific action by the control unit. The trigger control unit begins to reduce the driving force to a second value that is lower than the first value but that is above a threshold value at which the spindle nut leaves its position and begins to moves along the threaded spindle under the restoring force of the clutch.

(20) Even though the driving force is reduced to the second value, the threaded spindle 9 remains stationary. This is due to the fact that the restoring force of the clutch exerts an axial load through spindle nut 11 into the threaded spindle 9 and into the roller bearing 12. As the components of the clutch actuator are stationary, the roller bearings as well as other sections of the clutch actuator, e.g. the meshed engagement between the spindle nut and the threaded spindle, generate static friction. This static friction assists the driving force in providing a counter force against the restoring force of the clutch and the control unit may reduce the driving force to a second value which is lower than the first value of the driving force whilst the clutch actuator components remain stationary. Thereby, energy consumption is significantly reduced.

REFERENCE NUMERALS

(21) 1 clutch actuator 2 clutch lever 3 pivot axis 4 push-rod 5 electric motor 6 shaft 7 planetary gear set 8 housing 9 threaded spindle 10 outer thread 11 spindle nut 12 roller bearing 13 pressure piece 14 axial direction 15 biasing spring 16 latching mechanism 17 detent disc 18 detent recess 19 detent cam 20 spring element 21 control unit 22 rotary encoder 23 flange section of spindle nut 24 recess portion 25 flange section of pressure piece A first position of pressure piece B second position of pressure piece C clutch engaging position of spindle nut D clutch disengaging position of spindle nut