GB2376275A

GB2376275A - Clutch and gear actuator

Info

Publication number: GB2376275A
Application number: GB0114079A
Authority: GB
Inventors: John Vivian Comfort; David Anthony Harries; Bernhard Boll
Original assignee: LuK Lamellen und Kupplungsbau Beteiligungs KG; LuK Lamellen und Kupplungsbau GmbH
Current assignee: Schaeffler Buehl Verwaltungs GmbH; LuK Lamellen und Kupplungsbau GmbH
Priority date: 2001-06-09
Filing date: 2001-06-09
Publication date: 2002-12-11
Also published as: GB0114079D0

Abstract

An electric actuator for vehicle clutch or gear selector comprises electric motor 14 having output shaft 12 with double pinion 10 rotatably and eccentrically mounted thereon. The double pinion has first and second sets of teeth, the number of teeth (M) in one set 18 being greater than that of the other 16 and the first set of teeth 16 meshing with fixed internal gear 20 and the second set meshing with internal gear 24 of output member 22 mounted for rotation coaxially of the motor output shaft. The number of teeth on the internal gears being the number of teeth the first and second sets of pinion teeth N. M respectively plus 2 e k teeth, e being the eccentricity of rotation of the double pinion and k is a constant inversely proportional to the pitch of the teeth. Output member operates ball screw, rack or shift drum.

Description

CLUTCH AND GEAR ACTUATORS

The present invention relates to clutch and gear actuators and in particular electric motor actuators for control of a clutch or a gear selector mechanism of an automated transmission systems for a motor vehicle.

Electric motor actuators which are used to control the clutches and gear shifter mechanisms of automated transmission systems typically utilize a worm and worm gear drive mechanism to provide a high ratio reduction, for example as disclosed in GB2325036, GB2313885 and GB2309761 the disclosure of which explicit reference is made and whose content is expressly incorporated in the disclosure content of the present application, in order to convert the high speed, relatively low torque drive of the electric motor into a slow speed relatively high torque required to actuate a clutch or gear shifter mechanism. Typically the drive ratios of such mechanisms are of the order of 50 : 1 to 60 : 1.

The worm gear drives utilized hitherto have the disadvantage that they are relatively large and present serious difficulties with regard to the packaging constraints encountered in automated transmission systems for motor vehicles.

The present invention utilizes a high ratio drive of concentric construction to overcome the disadvantages of the worm drive used hitherto.

In accordance with one aspect of the present invention an electric motor actuator for control of a clutch or gear selector mechanism of a motor vehicle ; includes an electric motor, an output shaft of the electric motor, and a drive mechanism comprising a double pinion mounted eccentrically on the output shaft of the electric motor and rotatable relative thereto, the double pinion having first and second sets of teeth, the number of teeth in

one set being greater than the number of teeth in the other set, the first set of teeth meshing with the teeth of a fixed internal gear, the second set of teeth meshing with the teeth of an internal gear mounted for rotation with an output member which is mounted for rotation coaxially of

the output shaft of the electric motor, the number of teeth on the fixed IIIL. PL internal gear and the internal gear on the output member being equal to the number of teeth on the first and second sets of teeth of the double pinion, respectively, plus 2sk teeth where"s"is the eccentricity of rotation of the double pinion and"k"is a constant inversely proportional to the pitch of the teeth.

With the drive mechanism described above;

the drive ratio i = N (M + n) n (N-M) where M = the number of teeth in the first set of teeth of the double pinion ; N = the number of teeth in the first set of teeth of the double pinion ; and n = 2sk.

The values of M, N and n must consequently be selected to provide the required drive ratio which will typically be from 50: 1 to 60: 1.

The drive used in the present invention is particularly advantageous for use with shift drums for example as disclosed in GB2308874 and GB2311829 the disclosures of which explicit reference is made and whose content is expressly incorporated in the disclosure content of the present application, in which the electric motor and drive mechanism may be mounted coaxially within the shift drum. The drive mechanism

described above may alternatively be used with linear actuators, for example ball and screw actuators or rack and pinion mechanisms.

A further advantage of the present invention is that the actuators may be made self locking with minimal increase in the internal friction of the drive mechanism.

The invention is now described by way of example only, with reference to the accompany drawings, in which: Figure 1 illustrates diagramatically a drive mechanism utilized in clutch or gear actuators according to the present invention; Figure 2 shows in sectional side elevation a shift drum actuator in accordance with the present invention; Figure 3 shows in sectional side elevation a ball and screw actuator in accordance with the present invention; Figure 4 shows in sectional side elevation a rack and pinion actuator in accordance with the present invention; and Figure 5 shows in sectional side elevation an alternative form of shift drum actuator in accordance with the present invention.

As illustrated in figure 1, a double pinion 10 is mounted on the output shaft 12 of an electric motor 14. The double pinion 10 is mounted rotatably on the shaft 12 eccentrically thereof, the axis of rotation of the pinion 10 being offset from the axis of rotation of the shaft by the eccentricity E.

The double pinion 10 defines a primary pinion 1 6 having N teeth and a secondary pinion 18 having M teeth. The primary pinion 16 meshes with an internal gear ring 20 mounted in fixed relationship coaxially of the electric motor 14. The internal gear ring 20 has N + n teeth, where n = 2ek, where"k"is a constant depending on the pitch of the teeth.

An output member 22 is mounted for rotation coaxially of the output shaft 10 of the electric motor 14. The secondary pinion 18 meshes with an internal gear 24 on the output member 22, the internal gear 24 having M + n teeth.

The drive ratio i for the gear mechanism described above;

The values of M, N and n are selected to provide and appropriate gear ratio which is preferably of the order of 40: 1 to 60: 1, for example as illustrated in table 1 below.

Table 1

Number of Teeth Drive ratio i M N n 22 20 5 -54.O* 24 22 5 -63. 8 * 29 35 3 62. 2 23 29 3 41. 9 18 22 3 38. 5 18 22 2 55. 0 * negative value signifies rotation of output member in opposite direction to motor shaft.

The drive mechanism described above also has the advantage that friction in the drive mechanism will prevent loads applied to the output member from reversing the drive, so that the drive mechanism may be self locking. This is particularly advantageous with clutch actuators where the actuator must, for example, hold members of the clutch apart while the clutch is disengaged, against the spring load urging the members into engagement.

According to a preferred embodiment as described in detail below, an eccentric is mounted on the output shaft of the electric motor 14, the double pinion 12 being mounted on the eccentric by means of a sliding bearing. With this construction:

the minimum coefficient of friction for se ! f tocking p. = sv (N-R) R (N + s) where R = the radius of the eccentric.

From the above it follows that the smaller the eccentricity the smaller the friction required for self locking. Moreover for clutch and gear actuators a small eccentricity is required in order to provide the drive ratios required.

Figure 2 illustrates a gear shift drum assembly utilizing the drive mechanism described above. The electric motor 14 is mounted on a cylindrical housing 30, the motor 14 being secured to an internal flange 32 located adjacent one end 34 of the housing 30. An external flange 35 at the other end of housing 30, is adapted to be secured to, for example, a gear box housing. The fixed internal gear ring 20 is provided at end 34 of housing 30.

An eccentric 36 is mounted on the output shaft 12 of the electric motor 14, the double pinion 10 being rotatably mounted on the eccentric 36 by means of a rolling bearing 38. The primary pinion 16 of double pinion 10

meshes with the internal gear ring 20, so that upon rotation of shaft 12, the double pinion 10 will roll around the internal gear ring 20.

A shift drum 40 is rotatably mounted on the outer diameter of the cyiindricai housing 3û by means of ro ! ! ! ng bearings 42. The end of the shift drum 40 remote from flange 36 of housing 30 is closed, the closed end of the shift drum 40 being rotatably mounted on the output shaft 12 of electric motor 14, by rolling bearing 44. The internal gear ring 24 is provided on the shift drum 40 adjacent the closed end there of, the internal gear ring 24 meshing with the secondary pinion 18 of the double pinion 10.

When the electric motor 14 drives shaft 12, so that the double pinion 10 rolls around the internal gear 20, engagement of the secondary pinion 18 with the internal gear 24 will cause the shift drum 40 to rotate, the drive ratio typically being of the order of 40: 1 to 60 : 1.

The linear drive illustrated in figure 3 may typically be used to control movement of a piston of an hydraulic master cylinder of the type disclosed in GB2325036, GB231 3885 and GB2309761, which in turn will supply hydraulic pressure to a clutch slave cylinder to control engagement and disengagement of a clutch. Alternatively linear actuators of this type may be used to control engagement and disengagement of a clutch, or selection of a gear ratio, via a suitable mechanical linkage mechanism or cable drive.

In the linear actuator illustrated in figure 3, the double pinion 10 is rotatably mounted on an eccentric 36 mounted on the output shaft 12 of the electric motor 14, in similar manner to that described with reference to figure 3. The pinion 10 is however mounted on the eccentric 36 by means of a sliding bearing, in order to provide sufficient friction in the

drive to prevent wind back of the linear actuator when a load is applied thereto.

The motor 14 is secured to a concentric housing 50 which defines the fixed internal gear ring 20 which meshes with the primary pinion 16 of double pinion 10. An annular output member 22 is rotatably mounted to the housing 50 and output shaft 12 of motor 14 by means of rolling bearings 52, 54. The output member 50 defines the internal gear ring 24 which meshes with the secondary pinion 18.

The end 56 of output member 22 remote from motor 14 defines the internal threaded portion of a ball screw actuator 58. An outer threaded portion 60 of the ball screw actuator 58 is mounted coaxially of the inner portion 56, with a series of balls 62 located therebetween, in the thread formation defined by the inner and outer portions 56, 60. The outer portion 60 of the ball screw actuator 58 has a plunger formation 64 which extends through an end wall 66 of housing 50, the plunger formation 64 being moveable axially of the housing 50 but constrained from rotation relative thereto. The plunger formation 64, which may be connected directly or indirectly to the piston of an hydraulic master cylinder, will thereby be moved axially by rotation of the output member 22, when driven by the electric motor 14.

A compensating spring 68 acts between the output member 22 and outer portion 60 of the ball screw actuator 58, urging the outer portion 60 towards the end wall 66 of housing 50. The compensating spring 68 will thereby oppose the load applied by the clutch spring. Typically, the compensating spring 68 will be arranged to be under compression when the clutch is fully engaged and the ball screw actuator 58 is at a limit of its movement away from the closed end of housing 50. The load applied by compensating spring 68 will thereby assist the electric motor 14 as the ball screw actuator 58 is driven to disengage the clutch. In this manner a

smaller electric motor 14 may be used, than would be required if a compensating spring 68 were not present.

Figure 4 illustrates a rack and pinion drive actuator, similar to the actuator iiiustrated in figure 3, in vvhich the ûütpüt member 22 defines a pinion 70 which engages a rack 72 which extends transversely of the housing 50.

In the embodiment illustrated in Figure 5, a shift drum 80 is mounted coaxially of an electric motor 82, the shift drum 80 extending axially from the motor flange 84 so that the drive mechanism 86 is located between the electric motor 82 and the shift drum 80.

The shift drum 80 comprises a tubular member 90 with a track 92 formed from sheet material secured to the external diameter of the tubular member 90 adjacent one end thereof. The other end 94 of the tubular member 90 is of enlarged diameter, a radiused shoulder portion 96 being provided between the body 98 of the tubular member 90 and the enlarged diameter end 94. An internal gear ring 100 is a press fit within the enlarged diameter end 94 of tubular member 90, the internal gear ring 100 being fixed rotationally and axially with respect to tubular member 90.

A tubular housing member 102 is adapted to be bolted to the motor flange 84. The tubular housing member 102 has a body portion 104, the internal diameter of which is greater than the external diameter of the enlarged diameter end 94 of tubular member 90. An external flange formation 106 is provided at one end of housing member 102 and is adapted to be bolted to the motor flange 84. The other end 108 of housing member 102 is of reduced diameter having an internal diameter less than the external diameter of the enlarged end 94 of tubular member 90 but greater than the external diameter of the body portion 98 of

tubular member 90. The reduced diameter end 108 of housing member 102 defines a radiused shoulder 110.

The tubular member 90 is assembled coaxially of the housing member 102 with the larger diameter end 94 located within the housing 102 and the body portion 98 and track 92 extending out of the smaller diameter end 108 of the housing member 102. The radiused shoulders 96 of the tubular member 90 and 108 of the housing member 102 define the inner and outer races of a ball bearing 112 which rotationally locate the tubular member 90 radially, and axially away from the flange formation 106 end of housing member 102.

An internal gear ring 114 is a press fit within the housing member 102 so that it is fixed axially and rotationally thereof. The adjacent external diameter and radial face of internal gear ring 100 and internal diameter and radial face of internal gear ring 114, form the internal and external races 116, 118 for a further ball bearing 120 which locates the tubular member radially and axially towards from the flange formation 106 end of housing member 102.

A double pinion 122 is mounted for rotation on an eccentric 123 provided on the output shaft 124 of the electric motor 82, by means of a sliding bearing 126. The pinions 128 and 130 defining the double pinion 122 are adapted to engage internal gear rings 100 and 144, respectively, when the housing member 102 is bolted to the motor flange 104 by means of flange formation 106.

The pinions 1 28 and 130 of the double pinion 122 have different numbers of teeth and the internal gear rings 100 and 114 have a corresponding number of teeth respectively, as discussed above, in order to provide the required drive ratio.

Various modifications may be made without departing from the invention.

For example while in the above embodiments the double pinion is rotatably mounted in the output shaft of the electric motor on an eccentric, alternatively, the output shaft may be cranked.

Also with regard to the ball screw actuator described with reference to figure 3, the output member of the drive mechanism may define to outer threaded portion of the ball screw rather than the inner portion.

The patent claims submitted with the application are proposed formulations without prejudice to the achievement of further patent protection. The applicant reserves the right to submit claims for further combinations of characteristics, previously only disclosed in the description and/or drawings.

References back used in sub-claims refer to the further development of the subject of the main claim by the characteristics of the respective subclaim ; they are not to be understood as a waiver with regard to achieving independent item protection for the combination of characteristics in the related sub-claims.

Since the subject of the sub-claims can form separate and independent inventions with reference to the prior art on the priority date, the applicant reserves the right to make them the subject of independent claims or of division declarations. Furthermore, they may also contain independent inventions which demonstrate a design which is independent of one of the objects of the preceding sub-claims.

The embodiments are not to be considered a restriction of the invention.

Rather, a wide range of amendments and modifications is possible within the scope of the current disclosure, especially those variations, elements and combinations and/or materials which, for example, the expert can

learn by combining individual ones together with those in the general description and embodiments in addition to characteristics and/or elements or process stages described in the claims and contained in the drawings with the aim of solving a task thus leading to a new object or new process stages or sequences of process stages via combinable characteristics, even where they concern manufacturing, testing and work processes.

Claims

CLAIMS 1. An electric motor actuator for control of a clutch or gear selector mechanism of a motor vehicle including ; an electric motor, an output shaft

of the eiectric motor, and a drive mechanism comprising a doubie pinion T I o mounted eccentrically on the output shaft of the electric motor and rotatable relative thereto, the double pinion having first and second sets of teeth, the number of teeth in one set being greater than the number of teeth in the other set, the first set of teeth meshing with the teeth of a fixed internal gear, the second set of teeth meshing with the teeth of an internal gear mounted for rotation with an output member which is mounted for rotation coaxially of the output shaft of the electric motor, the number of teeth on the fixed internal gear and the internal gear on the output member being equal to the number of teeth on the first and second sets of teeth of the double pinion, respectively, plus 2Ek teeth where"s" is the eccentricity of rotation of the double pinion and"k"is a constant inversely proportional to the pitch of the teeth.
2. An electric motor actuator according to claim 1 in which the drive mechanism has a drive ratio of from 40: 1 to 60: 1.
3. An electric motor actuator according to claim 1 or 2 in which the double pinion is rotatably mounted on an eccentric which is mounted for rotation with the output shaft of the electric motor.
4. An electric motor actuator according to any one of the preceding claims in which the double pinion is rotatably mounted eccentrically of the input shaft by means of a rolling bearing.
5. An electric motor actuator according to any one of the preceding claims in which the actuator is self locking.

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6. An electric motor actuator according to claim 5 in which the double pinion is rotatably mounted eccentrically of the input shaft by means of a sliding bearing.
7. An electric motor actuator according to any one of the preceding claims in which the output member is a shift drum which is adapted to control movement of a gear shift mechanism.
8. An electric motor actuator according to claim 7 in which the electric motor is mounted inside a cylindrical housing, the cylindrical housing defining the fixed internal gear ring, the shift drum being rotatably mounted on the external diameter of the cylindrical housing, the relatively rotatable internal gear ring being provided on an internal diameter of the shift drum.
9. An electric motor actuator according to any one of claims 1 to 6 in which the output member drives a screw actuator.
10. An electric motor actuator according to claim 9 in which the output member drives ball screw actuator, the ball screw actuator comprising an inner and an outer threaded portion with a series of balls located in the thread formation defined therebetween, the output member defining one of the threaded portions of the ball screw actuator, the other threaded portion if the ball screw actuator being moveable axially but constrained rotationally with regard to the output member.
11. An electric motor actuator according to claim 9 or 10 in which a compensating spring is provided between inner and outer threaded portions of the screw actuator.
1 2. An electric motor actuator according to any one of claims 1 to 6 in which the output member drives a rack and pinion mechanism.

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13. An electric motor actuator according to claim 12 in which the output member defines a pinion, said pinion meshing with a rack mounted transversely of the axis of rotation of said pinion.
14. An electric motor actuator substantially as described herein with reference to and as shown in figures 1 to 4 of the accompanying drawings.