SE1650082A1

SE1650082A1 - Clutch actuator for a vehicle

Info

Publication number: SE1650082A1
Application number: SE1650082A
Authority: SE
Inventors: Norum Viggo
Original assignee: Kongsberg Automotive As
Priority date: 2016-01-25
Filing date: 2016-01-25
Publication date: 2017-07-26
Also published as: SE541641C2; WO2017129610A3; WO2017129610A2

Abstract

The present invention relätes to a clutch actuator for a combustion engine, comprising. a motor for generating a motor torque. transmission means for transforming said motor torque into a force for generating a. movement able to act on a clutch operating mechanism, and. a brake able to generate a braking force for braking said means, wherein the maximum braking force able to be generated by said brake is less than the maximum force for generating a movement.The invention also relätes to a vehicle comprising a clutch actuator and a method for failsafe operation of a clutch actuator.Publ. Fig. 1

Description

CLUTCH ACTUATOR FOR A VEHICLETECHNICAL FIELD The present invention relates to a clutch actuator for a vehicle and to a method for failsafe operationof such a clutch actuator.

BACKGROUND Within many fields, such as for instance combustion engines, a clutch is needed to allow thetransmission to engage and disengage from the engine, thereby enabling gear shifts as well assmooth starting. The driver generates a signal that an activation of the clutch is desired, oftenthrough pushing a pedal in a vehicle with manual transmission or moving the shift lever in a vehiclewith automatic transmission, and this signal, sometimes together with a signal from the transmissioncontroller software for automatic shifting, is used by a clutch actuator to activate the clutch itself.

Clutch actuators may be of different types, for instance hydraulic or electric. They are necessary forthe reliable operation of the vehicle and must be sturdy and reliable to ensure a safe operation andavoid accidents. lf they break or suffer power failure, there must be a failsafe operating mode thatallows the engine to remain connected to the transmission so that the vehicle can be driven toanother location thereby avoiding blocking other traffic.

Electric clutch actuators are generally driven by a small electric motor and are reliable and suitablefor manual as well as automatic transmission. The motor drives a transmission means in a forward ora backward direction and allow a disengagement or engagement of the clutch. Generally, a clutchoperating mechanism that is in contact with the clutch itself can act with a linear force against thetransmission means, so that the motor only needs to drive the transmission means in the forwarddirection, and a brake is supplied to prevent the clutch operating mechanism from pushing thetransmission means in the backward direction when the motor does not deliver a torque. However,in the event of a power loss that prevents the electric motor from operating the clutch in thebackward direction it may be locked in the disengaged position and prevent the vehicle from beingdriven. Also, during normal operation the motor will suffer excessive wear due to heat generationand may break for this reason.

There is a need for improved clutch actuators that reduce the wear on the components and also havea failsafe mode to ensure that the vehicle can be operated even in the event of a power failure.

SUMMARY The object of the present invention is to eliminate or at least to minimize the problems describedabove. This is achieved through a clutch actuator according to the appended independent claim.Thanks to the invention, a clutch actuator that allows for reduced wear of the motor as well as afailsafe operation is achieved.

Many additional benefits and advantages of the invention will become readily apparent to theperson skilled in the art in view of the detailed description below.

FIGURES The invention will now be described in more detail with reference to the appended drawings, wherein Fig. 1 discloses a cross-sectional view of an actuator for operating a vehicle clutch accordingto a preferred embodiment of the present invention; Fig. 2 discloses an exploded view of the actuator of Fig. 1; Fig. 3 discloses a cross-sectional view of a first end of the actuator of Fig. 1; Fig. 4 discloses a schematic cross-sectional view of a the actuator of Fig. 1 in an installationposition; Fig. 5 discloses a schematic cross-sectional view of the actuator of Fig. 1 in a first operationposition; Fig. 6 discloses a schematic cross-sectional view of the actuator of Fig. 1 in a secondoperation position; Fig. 7 discloses a schematic cross-sectional view of the actuator of Fig. 1 in a third operationposition; Fig. 8a discloses a perspective view of an alternative embodiment of the brake of the actuatoraccording to the invention; Fig. 8b discloses an exploded view of the alternative embodiment of Fig. 8a; Fig. 9 discloses schematically method steps for normal operation of the actuator of Fig. 1; Fig. 10 discloses schematically method steps for failsafe operation of the actuator of Fig. 1;and Fig. 11 discloses a diagram relating motor torque to pushrod position for the actuator according to the invention.DETAILED DESCRIPTION Fig. 1 and 2 show an actuator 1 for operating a vehicle clutch according to a preferred embodimentof the present invention, said actuator 1 comprising a torque producing motor 3 connected by amotor output 5 to and driving a reduction gear 9, which can be for example, as shown here, aplanetary gear. A brake means such as return brake 10 is connected to the reduction gear andthereby to the motor as will be described in detail further below. An output shaft 11 of the reductiongear 9 is connected to transmission means in the form of an actuator 13 with a stationary support,arranged for transforming the torque from motor 3 into a force for generating a movement able toact on a clutch operating mechanism. The transmission means 13 are illustrated here as a ball screw15, the rotation of which can drive a movable body, e.g. ball nut 17 linearly along it, and themovement able to act on the clutch operating mechanism is therefore a linear movement. lt is to be noted, however, that rotary movement or other movements may also be used in a similar way as the|inear movement described herein with reference to this preferred embodiment.

A clutch preload plunger 19 is also mounted on the ball screw 15 and is able to translate freely alongthe ball screw 15. A helical preload spring 21 with an inner diameter between the coils which isgreater than the outer diameter of the ball nut is mounted concentrically around the ball screw andball nut. ln this embodiment of the invention the proximal end 23 of the preload spring 21 isattached by a spring holder 25 to or near the proximal end 27 of the ball nut and the distal end 29 ofthe preload spring is attached to or pushes on the proximal end surface 31 of the preload plunger,thereby exerting a force on the preload plunger which pushes the preload plunger towards the distalend 33 of the ball screw.

The transmission means could alternatively comprise other components for translating a rotarymovement into a |inear movement, such as a lead screw or a roller screw for example. Theadaptations required to alter the preferred embodiment to use such alternatives will be readilyapparent to the person skilled in the art.

Other arrangements of the preload spring are also conceivable, for example it may have an innerdiameter and an outer diameter which both are less than the diameter of the ball nut and in this caseit can be positioned between the distal end of the ball nut and the proximal end of the preloadplunger. ln this case it must be collapsed completely in order for the high clutch disengaging force tobe transmitted from the ball nut to the preload plunger.

The preload plunger is preferably provided with a longitudinally extending guide arm 35 which isoffset from, and parallel with, the central longitudinal axis of the preload plunger and which cancooperate with an optional housing 37 which can at least partially surround the actuator to protect itfrom dust and other contamination. The guide rail is arranged parallel to the central longitudinal axisof the ball screw in order to ensure that the preload plunger is maintained parallel to the ball screwas it moves along it. The distal end surface 39 of the preload plunger further comprises a clutchpushrod receiving cup 41 with an open end 43. The cup is offset from the central axis of the preloadplunger which reduces the overall length of the actuator. The open end faces away from the preloadplunger and the interior of the clutch pushrod receiving cup is provided with gripping means 45 forgripping the proximal end 47 of a clutch operating mechanism 49, here in the form of a clutchpushrod 49. Preferably the gripping means and the proximal end of the clutch pushrod are arrangedto allow angular movement of the pushrod, for example as a ball on the end of the pushrod and acorresponding socket in the cup. During use the distal end 57 of the pushrod is intended to bepressed in contact with the release bearing operating arm of a clutch with a continuous preload forcewhich is generated by the preload spring.

The clutch operating mechanism 49 is thus arranged to perform a |inear movement in a distaldirection for disengaging and a proximal direction for engaging the clutch of the vehicle, and themovement is performed in response to a |inear movement by the transmission means 13 driven bythe motor 3. The brake 10 is arranged to generate a braking force for braking the transmission means13, i.e. in this embodiment the ball screw 15 and ball nut 17, and to prevent a rotary movement thatcan be translated into a |inear movement of the ball nut 17.

The brake 10 is preferably a one-way brake that is able to brake the transmission means 13 to halt orto slow a movement in a proximal direction but is not able to brake a movement in the distaldirection. Generally, the motor 3 serves to provide a torque for generating a movement in both theproximal and the distal direction, while the clutch operating mechanism 49 provides a clutch force ina proximal direction that must be counteracted by the motor 3 to create the movement of the clutchoperating mechanism 49 in the distal direction. Thus, when the clutch has been dis-engaged and themotor 3 is no longer providing a torque to generate the movement in the distal direction, thetransmission means 13 are pushed back in the proximal direction by the clutch operating mechanism49, and the brake 10 may then serve to brake this proximal movement. ln the preferred embodimentthe brake 10 is a wrap spring brake. The maximum braking force that can be generated by the brake10 is less than the maximum force for generating a linear movement by the motor 3. Thereby, thebrake 10 is unable to lock the transmission means 13 and prevent a movement when the motor 3 isoperated to generate a torque. The maximum braking force is also preferably smaller than the clutchforce applied by the clutch via the clutch operating mechanism 49, so that the clutch operatingmechanism 49 can push the transmission means 13 in the proximal direction when the motor 3 doesnot deliver a torque to overcome this. Thereby, the brake 10 is able to slow movement in theproximal direction but is not able to prevent it.

Fig. 3 discloses the proximal end of the clutch actuator 1 with the motor 3 connected via an output 5to the reduction gear 9. The motor 3 is also attached to the housing 37, and to the brake 10 by ashaft 51 that extends through a brake disk 52 and a proximal part 53 of the brake 10. The brake 10 isin this preferred embodiment in the form of a wrap spring brake with a brake spring 55 surroundingthe proximal part 53 and a distal part 54 that is connected to the transmission means 13, in thisembodiment to the ball screw 15 in order to be able to brake said ball screw 15 when the brake 10 isactivated. Fig. 3 also discloses the ball nut 17 and the preload spring 21 mounted on the proximalend of the ball nut 17.

The operation of the clutch actuator 1, and in particular of the brake 10, will now be described inmore detail with reference to Figs. 4-7, where the clutch actuator 1 is shown schematically indifferent operation positions.

Fig. 4 discloses an installation position where the ball nut 17 is located in a proximal position adjacentto the reduction gears 9. Via the motor output 5 and reduction gear 9, the transmission means 13 inthe form of the ball screw 15 and ball nut 17 may be operated so that a rotation of the ball screw 15results in a linear movement of the ball nut 17 in the distal direction towards the plunger 19. ln the first operation position shown in Fig. 5, the ball nut 17 has been moved in the distal directionand is situated at a distance d from the plunger 19. This is the position where the clutch is engagedand the clutch actuator 1 is not being operated to disengage it. Thanks to the nearness of the ball nut17 to the plunger 19, the operation to disengage the clutch can be performed quickly by moving theball nut 17 only a small distance. ln this position, the motor is stopped and the brake 10 activated tohold the transmission means 13 in the position shown in the Figure.

Fig. 6 discloses a second operation position where the clutch actuator 1 is operated to disengage theclutch. The motor 3 now delivers a torque to the transmission means 13 and the ball screw 15 isrotated so that the ball nut 17 moves linearly in the distal direction and abuts the plunger 19. ln this position, the brake 10 is not active and the ball nut 17 pushes against the plunger 19 with aforce that must be larger than the clutch force in order to move the plunger 19 in the distal direction.

Fig. 7 shows a third operational position, where the ball nut 17 has continued the movement in thedistal direction and pushed the plunger 19 and push rod that together form the clutch operatingmechanism 49 to the position where the clutch is disengaged.

The clutch actuator 1 is held in the third operating position until the clutch is again to be engaged.The motor 3 then ceases to act on the transmission means 13 to hold the ball nut 17 in position, andonce the force with which the ball nut 17 presses against the plunger becomes smaller than theclutch force, the clutch operating mechanism 49 is able to push the ball nut 17 in the proximaldirection and thereby cause a rotation of the ball screw 15 in the other direction. The brake 10 canbe activated to brake this rotation and allow the ball nut 17 to reach the first operation position in acontrolled manner, and thanks to the dimensioning of the brake 10 where the maximum brake forceis smaller than the clutch force, the brake 10 is not able to completely prevent the movement of theball nut 17. Thanks to the use of the brake 10 rather than using the motor 3 for driving the ball nut 17to the first operational position, energy can be saved and the torque from the ball screw 15 duringthe movement of the ball nut 17 in the proximal direction is transformed into heat at the brake 10rather than in the motor 3. This is advantageous in reducing the wear on the motor 3 and therebyprolonging its life.

The brake 10 can be activated by a control unit (not shown) that serves to control the operation ofthe clutch actuator 1 but can also be activated automatically by a linear force or a torque in thebackward direction, said force or torque acting on the clutch actuator 1 by the clutch operatingmechanism 49. lt may also be activated by a torque in the backward direction at the reduction gear.The brake 10 would then be activated each time the clutch actuator 1 is operated to engage theclutch and serves to decrease the velocity of the transmission means 13 in the backward direction.

The backward direction is defined as the direction of rotation that generates a linear movement ofthe transmission means in the proximal direction, i.e. away from the clutch operating mechanism 49.

The clutch actuator 1 according to the present invention is also especially advantageous in the eventof a loss of power of the motor 3, since the interaction between the clutch operating mechanism 49,the transmission means 13 and the brake 10 allow for a failsafe operation of the clutch actuator 1.This is achieved by the actuator performing a controlled proximal movement of the ball nut 17, themovement being driven by the return force generated by the clutch operating mechanism 49 andbeing slowed by the brake 10 (which is too weak to totally resist this force but which is strongenough to prevent a dangerously rapid movement of the ball nut which would result in an abrupt re-engagement of the clutch) so that the clutch is engaged and the vehicle can be driven to a secureplace for maintenance or repair after an actuator power loss or motor failure has occurred.

The relationship between the clutch force, motor torque and pitch of the ball screw are given byTorsion = clutch force * pitch/Zrt, which determines the torque given by the clutch force acting on the transmission means; and therelationship between the movement of the ball nut, the clutch force and the friction is given by Torsionu = clutch force * urwhere u is the friction factor and r is the median contact radius on the brake disk.

Also provided are software for controlling the normal and failsafe operation of the clutch actuator 1.The software can be stored and executed by a control unit with storage means, such as are generallyknown in the art. Furthermore, the software is able to detect and control the position of thetransmission means in order to operate the clutch actuator. The invention also comprises a vehiclehaving a clutch actuator as defined above, wherein the vehicle comprises a clutch with a clutchoperating mechanism that is able to act on the transmission means with a clutch force, said clutchforce being smaller than the force for generating a linear movement. Preferably, the clutch force islarger than the maximum braking force, so that the benefits and advantages described above areachieved.

Fig. 8a and 8b disclose an alternative embodiment of the brake of the actuator according to theinvention. Most of the components are identical to the preferred embodiment described above, butinstead of the wrap spring brake the brake comprises a helical spring 56 mounted around the ballscrew 15 of the transmission means and covered by a sleeve 57. The helical spring 56 acts as a one-way brake and provides a braking torque when the transmission means rotate in the backwardsdirection, i.e. towards engaging the clutch, in a similar way as the preferred embodiment describedabove and also delivers a braking torque in a failsafe mode. The braking torque is achieved throughan unraveling of the helical spring 56 that arises when the ball screw 15 is rotated in the oppositedirection from the motor output 5 and thereby amplifies the motor torque when used as a brake. lt is to be noted that the alternative embodiment is in many ways similar to the other embodimentsdescribed herein and that features of the different embodiments may be combined with each otherwithin the scope of the claims.

Fig. 9 discloses the normal operation of the clutch actuator 1 where in a first step 101 thetransmission means 13 are moved from the installation position to the third operation position viathe first and second operation positions to disengage the clutch. ln a second step 102, the ball nut 17is held in position by the motor 3 delivering a torque that is transformed to a force equal to theclutch force so that the ball nut 17 is held stably against the plunger 19 of the clutch operatingmechanism 49. ln a third step 103 the motor 3 stops and the brake 10 is activated so that the ball nut17 is pushed in a proximal direction at a controlled speed. ln a fourth step 104 the ball nut 17 hasreached the first operation position and is held stably.

Fig. 10 discloses the failsafe operation of the clutch actuator 1, where in a first failsafe step 201 apower loss at the motor 3 is detected. lf the clutch actuator 1 is currently operated to disengage theclutch, a power loss will immediately result in the clutch force pushing the transmission means 13 inthe proximal direction so that the ball nut 17 is rotated around the ball screw 15 in the backwardsdirection.

The purpose of the failsafe operation is to slow the speed of the transmission means so that the clutch can be engaged through a controlled operation without the risk of damage or wear to the motor. This is achieved by engaging the brake and short circuiting the motor so that the speed oftransmission means of the clutch actuator is reduced. ln a second failsafe step 202, it may also be determined whether a decrease of velocity of thetransmission means 13 is actually necessary to prevent damage to the clutch actuator or heatgeneration at the motor 3. lf it is determined that the velocity should decrease, the velocity isdecreased in a third failsafe step 203 by short circuiting to ground and thereby activate the braketorque available in the motor. Since the maximum brake force is not sufficient to completely halt themovement of the transmission means 13, this will result in a decrease of velocity and in a heatgeneration at the brake 10 rather than in the motor 3. ln a fifth failsafe step 205, it is determinedwhether the transmission means 13 have reached the first operation position where the ball nut 17 isno longer in contact with the plunger 19. lf not, the second failsafe step 202 is repeated as above.

When it is determined in the fifth failsafe step 205 that the first operation position has been reached,the failsafe operation is finished in a sixth failsafe step 206. lf in the second failsafe step 202 it is determined that the velocity does not have to be decreased, theoperation is continued in a fourth failsafe step 204 where a predetermined time interval is allowed topass without an activation of the brake 10. After that interval has passed, the operation is moved tothe fifth failsafe step as described above.

To further explain the relationship between the torque supplied by the motor 3 and the position ofthe transmission means 13, Fig. 11 is provided and discloses the motor torque required to move thetransmission means to act on the clutch operating mechanism to disengage the clutch. Also shown isthe motor torque required in the other direction to engage the clutch, and it is to be noted thatconsiderably less motor torque is required in the proximal direction, i.e. to engage the clutch. ln theevent of a power loss, the motor is thus used as a generator to power the electronics and allow it tocontrol the speed of engagement.

The scope of the present disclosure is defined by the following claims rather than by the detaileddescription of the embodiment. lt shall be understood that all modifications and embodimentsconceived from the meaning and scope of the claims and their equivalents are included in the scopeof the present disclosure.

Claims

1. Clutch actuator for a vehicle, comprising - a motor (3) for generating a motor torque - transmission means (13) for transforming said motor torque into a force for generating amovement able to act on a clutch operating mechanism, anda brake (10) able to generate a braking force for braking said transmission means (13),characterized in the maximum braking force able to be generated by said brake (10) isless than the maximum force for generating a movement.

2. Clutch actuator according to claim 1, characterized in that the transmission means (13) are able toreceive a clutch force from the clutch operating mechanism, said clutch force being smaller than theforce for generating a movement.

3. Clutch actuator according to claim 2, characterized in that the clutch force is larger than themaximum braking force.

4. Clutch actuator according to any of claims 1-3, characterized in that said transmission means (13)comprise a ball screw arranged to receive said motor torque and a ball nut mounted on said ballscrew, and that said movement able to act on a clutch operating mechanism is a linear movement.

5. Clutch actuator according to any of claims 1-3, characterized in that said transmission means (13)comprise a lead screw.

6. Clutch actuator according to any of claims 1-5, characterized in that the brake (10) is a one-waybrake (10) able to brake (10) the transmission means (13) in a proximal direction away from saidclutch operating mechanism.

7. Clutch actuator according to any of claims 1-6, characterized in that the brake (10) is arranged tobrake (10) the transmission means (13) in a proximal direction only.

8. Clutch actuator according to any previous claim, characterized in that the brake (10) is a wrapspring brake (10).

9. Clutch actuator according to any previous claim, characterized in that the brake (10) (10) isarranged to be activated by a linear force in the proximal direction acting on the transmission means(13).

10. Clutch actuator according to any previous claims, characterized in that the brake (10) (10) isarranged to be activated by a torque that rotates the transmission means (13) in a backwardsdirection to generate a linear movement in the proximal direction.

11. Clutch actuator according to any previous claims, characterized in that the brake (10) (10) isarranged to be activated by a torque in a backwards direction at the reduction gear (9).

12. Vehicle comprising a clutch actuator having a motor (3) for generating a motor torque,transmission means (13) for transforming said motor torque into a force for generating a movementable to act on a clutch operating mechanism, and a brake (10) able to generate a braking force forbraking said transmission means (13), wherein the maximum braking force able to be generated by 8 said brake (10) is less than the maximum force for generating a movement, characterized in saidvehicle further comprising a clutch having a clutch operating mechanism that is able to act on thetransmission means (13) with a clutch force, said clutch force being smaller than the force forgenerating a movement.

13. Vehicle according to claim 12, characterized in that the clutch force is larger than the maximumbraking force.

14. Method for failsafe operation of a clutch actuator, characterized in the method comprising thesteps of - detecting a power loss at a motor (3) arranged to operate the clutch actuator- engaging a brake (10) and short circuiting the motor (3) so that the speed of transmissionmeans (13) of the clutch actuator is reduced.

15. Method according to claim 14, characterized in the method further comprising the steps of - determining if a decrease of velocity of a transmission means (13) for performing amovement is necessary and activating the brake (10) if so, - determining if the transmission means (13) have reached a first operation position, andrepeating the step of determining if a decrease of velocity is necessary until said firstoperation position has been reached.

16. Method according to claim 14 or 15, characterized in that the brake (10) is activated by a rotationof the transmission means (13) in a backwards direction.

17. Method according to any of claims 14-16, characterized in that the velocity of the transmissionmeans (13) is also decreased by short circuiting the motor (3).

18. Software for performing the steps of a method for failsafe operation of a clutch actuator, saidmethod characterized by comprising the steps of - detecting a power loss at a motor (3) arranged to operate the clutch actuator - determining if a decrease of velocity of a transmission means (13) for performing amovement is necessary and activating a brake (10) if so, - determining if the transmission means (13) have reached a first operation position, andrepeating the step of determining if a decrease of velocity is necessary until said firstoperation position has been reached.

19. Computer storage means arranged to store and execute software for performing the steps of amethod for failsafe operation of a clutch actuator, said method characterized by comprising thesteps of - detecting a power loss at a motor (3) arranged to operate the clutch actuator - determining if a decrease of velocity of a transmission means (13) for performing amovement is necessary and activating a brake (10) if so, - determining if the transmission means (13) have reached a first operation position, andrepeating the step of determining if a decrease of velocity is necessary until said firstoperation position has been reached.