GB2312723A

GB2312723A - Friction clutch actuator having a slipping clutch

Info

Publication number: GB2312723A
Application number: GB9708898A
Authority: GB
Inventors: Jens Dorfschmid
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1996-05-02
Filing date: 1997-05-02
Publication date: 1997-11-05
Also published as: ES2140299A1; FR2748305A1; ES2140299B1; GB9708898D0

Description

2312723 ACTUATING DRIVE FOR A FRICTION CLUTCH The invention relates to an

actuating drive for operation of a friction clutch, comprising a drive having an output shaft, reduction gearing having an input member driven by the drive and an output member operatively connected to the friction clutch and provided with stops, and a slipping clutch provided between the output shaft of the drive and the input member of the reduction gearing, the clutch having at least one friction surface urged by a spring means into frictional engagement with at least one opposing friction surface, relative movement of the friction surface and opposing friction surface taking place when a predetermined torque acting on the slipping clutch is exceeded. The drive may be operated by an electronic control means.

An actuating drive of the kind set forth is already known from DE-A-43 36 445. The end of the output shaft is mounted in the gearbox input shaft and has external splines for non-rotational connection with a number of friction plates which are mounted on it to slide axially. Between these friction plates there are friction plates which are axially slidably connected through external splines to internal splines of a receiver formed as a hollow shaft on the end of the gearbox input shaft adjacent the drive. The friction plates are in frictional engagement through the spring force of a plate spring which abuts against a projection provided on the end of the receiver to form a slipping clutch. The receiver is rigidly connected to the input shaft of the reduction gearing which is mounted by its end remote from the receiver.

A drawback of this slipping clutch is that the torque is transmitted through the splines of the friction plates, so that these are heavily loaded and it may be necessary to provide reinforcement of the friction linings of 2 the plates in the region of the splines. The gearbox input shaft can be driven in each direction by the drive. On an alteration of the direction of movement the contact surfaces of the splines change. This will tend to cause impacts leading to heavy loading of the splines, and a high degree of wear. To prevent the impacts and the wear or keep them to a minimum, the clearance between the inter-engaging splines must be as small as possible. To achieve a small clearance between the splines the manufacturing tolerances must be kept to a minimum, resulting in high manufacturing costs.

Furthermore, the friction plates wear during operation of the slipping clutch, so that the axial thickness of the friction plates decreases. This reduced axial thickness is compensated for by the corresponding depression of the plate spring. However, this causes a displacement of the operating range of the plate spring so that the pressure force generated by the plate spring alters. Alteration of the spring characteristic in the operating range of the slipping clutch leads to an unwanted alteration in the operating behaviour of the clutch. If the slipping clutch is tuned initially for optimum matching with the actuating drive, displacement in the operating range of the plate spring introduces slip at a lower torque, so slip occurs prematurely.

It is the aim of the invention to develop a slipping clutch of an actuating drive so that the manufacturing costs of the clutch are reduced by a particularly simple construction and so that the clutch has a long working life with satisfactory operation.

According to a first aspect of the present invention, in an actuating drive for operation of a friction clutch of the kind set forth the friction surface is connected to the opposing friction surface through at least one 3 detent element at least partly received in a recess in at least one of the friction surfaces, the or each detent element acting to prevent relative movement of the friction surfaces until the predetermined torque is exceeded, and on relative movement of the friction surfaces the or each detent element moves out of the or each recess to increase the axial distance between the friction surfaces against the force of the spring means.

As the friction surface is connected to the opposing friction surface through the detent elements, this overcomes the problems of wear on the connection. The mounting of the detent elements in recesses in the friction surfaces ensures that when the slipping torque lies below the predetermined slipping torque relative movement of friction surface with respect to opposing friction surface is prevented. If, as a result of faulty control of the drive, the output member of the reduction gearing cannot move, e.g. on collapse of a component present in the transmission path between the actuating drive and the friction clutch, the torque applied from the drive at least partially engages the slipping clutch. When the slipping torque is exceeded there is a relative movement of the friction surface and opposing friction surface. The detent elements also move out of the recesses at least at one side, causing an increase in the axial distance between the friction surfaces against the action of the spring means. In this way the torque acting on the slipping clutch is at least partially converted into potential energy of the spring means.

Furthermore, a part of the applied torque is converted into friction energy at the points of contact of the detent elements with one of the friction surfaces, as a consequence of the relative movement. The contact between the detent elements and the friction surfaces is maintained by the force of the spring means.

4 This slipping clutch is particularly economical to manufacture because it has few, easily produced components. Further, the influence of temperature on the behaviour of the clutch is extremely small as the clutch operates by mechanical engagement of the detent elements in the recesses.

To activate the slipping clutch this mechanical interengagement has first to be overcome against the action of the spring force. As the excessive torque applied from the drive is partially converted into potential energy and not only into friction energy with resulting generation of heat, the wear which arises as a result of friction is minimised. Added to this is the fact that friction co-efficients are strongly dependent on temperature. In this slipping clutch the size of the engaging friction surfaces is substantially reduced because of the detent elements. The heat generated at the friction surfaces of the detent elements can be removed by the air between the detent elements. The dependence on temperature is therefore greatly reduced in the slipping clutch and can be virtually neglected.

Preferably both the friction surface and the opposite friction surface have recesses in which the detent elements are received. The detent elements may be balls. The assembly of the slipping clutch is then particularly simple. The detent elements are inserted in the recesses in one friction surface and the opposing friction surface is laid on the detent elements so that the recesses in this friction surface come to engage the detent elements. The spring means is then fitted.

Alternatively, one of the friction surfaces has projections comprising the detent elements, received in recesses in the other friction surface. Accordingly, one of the friction surfaces can be formed integrally with the detent elements, so that the number of components required is further reduced. Assembly is particularly simple as the detent elements no longer have to be inserted. The manufacturing costs are further reduced by the omission of this working step. The projections are preferably formed in the opposing friction surface, which may then be produced as an injection-moulded component using a hard plastics material.

The spring means is preferably a plate spring, but may comprise one or more helical springs.

In order to achieve a constant slipping torque over the entire working life of the slipping clutch the spring characteristic of a plate spring should remain constant over the operating depression and compression range. It is also desirable for the slipping torque to remain constant on wear of the friction surfaces, and consequently reduced axial thickness of the friction parts in the rest condition. Slipping clutches whose operation is based on engagement between friction surfaces have their axial thickness reduced over their working life due to wear, and it is particularly important that alteration of the axial thickness is compensated, to achieve unaltered behaviour. Compensation by the provision of a plate spring having a particular spring characteristic has been found to be particularly simple.

According to a second aspect of the present invention, in an actuating drive for operation of a friction clutch of the kind set forth, the spring means comprises a plate spring with at least one notch having a radial component.

Such a plate spring with notches having a radial component has, after depression compensating for the reduced axial thickness of the friction parts, a substantially constant spring characteristic over its compression range during operation of the slipping clutch.

6 Preferably, the or each notch having a radial component is arranged at the inner radius of the plate spring.

For either aspect of the invention, the construction of the slipping clutch can be simplified if one of the friction surfaces forms a part of a housing of the clutch. Preferably the opposing friction surface forms part of the housing. The friction surface is preferably integral with the housing. Advantageously the clutch housing is of cylindrical shape, one end of the cylinder being closed and forming one of the friction surfaces.

The number of components of the clutch is kept to a minimum. The clutch housing is preferably made in one piece, which reduces manufacturing costs. The other friction surface is installed in the housing and is urged by the spring means against the base of the housing forming the friction surface. The assembly of the clutch is particularly simple by appropriate choice of the shape of housing.

In one embodiment the plate spring is operatively connected at its radially outer rim to an axially movable member having a friction surface.

The connection may be through an intermediate disc, to protect the friction surface if necessary.

Alternatively the plate spring has its radially outer rim abutting a projection provided on the clutch housing. A locating ring engaging in a recess in the clutch housing may comprise the projection. An intermediate disc is then not required.

One friction surface is preferably connected directly to the output shaft of the drive and is driven through it from the drive. The other friction surface is provided on a friction lining urged by the spring means 7 against one friction surface, the friction lining being axially movable.

This ensures that on wear of the friction lining its position is automatically adjusted by the spring force acting on it, so that a constant spring force is achieved.

If the actuating drive is mounted in a vehicle, where numerous vibrations are generated by the engine and transmitted to adjacent components it is necessary for the individual components to be mounted properly. Vibrations are also transmitted to the gearbox input shaft of the reduction gearing. To minimise radial movements of the input shaft it is preferred to mount it at one end. It is then difficult for it to move as a result of the vibrations transmitted to it.

Some embodiments of the invention are illustrated by way of example in the accompanying drawings, in which:

Figure 1 shows an actuating drive with a slipping clutch; Figure 2 is an enlarged detail of the slipping clutch of Figure 1; Figure 3 shows a further example of a slipping clutch without an intermediate ring; Figure 4 shows a side view of a plate spring provided with notches; Figure 5 is a front elevation of a plate spring provided with notches; Figure 6 shows the characteristics of a spring means; 8 Figure 7 shows a modification of a slipping clutch with detent elements; Figure 8 shows a further modified slipping clutch with a detent element formed as projections integral with the opposing friction surface; Figure 9 shows a front view of a further example of a slipping 10 clutch; Figure 10 is a section through the clutch of Figure 9; Figure 11 is a section through a further slipping clutch; Figure 12 is an isometric view of a further example of a slipping clutch; and Figure 13 is a section through the clutch of Figure 12.

The construction of an actuating dri ve 1 will first be described with reference to Figures 1 and 2. The actuating drive 1 operates a vehicle friction clutch (not shown) automatically. It has a drive 3 acting through a slipping clutch 8 on reduction gearing, which transmits movement through a transmission element 25 to the friction clutch. The drive 3 is in the form of an electric motor 4 with an output shaft 15 which is connected to a friction surface 61 of the slipping clutch 8 so that the shaft 15 and friction surface 61 rotate together. This friction surface 61 is urged by spring means 31 into frictional engagement with an opposing friction surface 63 which is rigidly connected to a gearbox input 9 component 11 of the reduction gearing 9. The input component 11 comprises a gearbox input shaft with teeth 10 which mesh with a gearbox output component 13 in the form of a segmental gearwheel 17. The maximum angular movement of the segmental gearwheel is limited by a stop 19. This stop has an elastomeric covering 21.

The segmental gearwheel 17 is provided with a compensating spring 23. The actuating drive 1 has an associated electronic control means (not shown), to which sensor signals are supplied and which controls the drive 1 in response to the signals received. Preferably, the segmental gearwheel 17 is provided with an incremental transmitter, as described in DE-A-44 33 825.

The operation of the actuating drive 1 is as follows. In order to disengage the friction clutch the electric motor 4 is energised by the electronic control means. As a result the output shaft 15 rotates. The shaft 15 is connected to the slipping clutch 8, by which under normal operating conditions a firm connection to the gearbox input shaft 2 is produced, so that the input shaft 2 also rotates. The segmental gearwheel 17 which meshes with it is therefore driven. At first the segmental gearwheel 17 must be driven by the drive 3 against the force of the compensating spring 23. Soon, after a small angular movement of the gearwheel 17, a dead centre point of the spring 23 is reached. When this point is passed the compensating spring 23 acts to assist the torque applied by the drive 3, so that rapid withdrawal of the friction clutch takes place through the transmission element 25 co-operating with a withdrawal bearing of the friction clutch.

To engage the friction clutch using the actuating drive 1 the drive 3 is energised so that the output shaft 15 rotates in the opposite direction, moving the gearwheel 17 back again. The compensating spring 23 is once again put under stress.

Normally the drive 3 is controlled by the electronic control means in such a way that it is braked shortly before it reaches the stop 19 which is operative for a given direction of movement. The segmental gearwheel 17 approaches the stop 19 but does not actually impact against this stop. This well-regulated operation by the electronic control means is only possible as long as the electronic control means has information on the position of the segmental gearwheel 17 supplied by the signals fed to it. The position of the segmental gearwheel 17 does not have to be monitored continuously. It is sufficient for the signals to supply a starting position and to monitor subsequent changes. Exact monitoring of the position of the segmental gearwheel is possible by the provision of the incremental transmitter associated with the gearwheel.

If the electronic control means is reset, or if the incremental transmitter or the signals (if present) representing the position of the segmental gearwheel fail; and if the friction clutch is just engaged by means of the actuating drive 1, the segmental gearwheel 17 will be driven against the stop 19. As the electronic control means has no information on the position of the segmental gearwheel 17, it cannot brake the gearwheel 17 before it reaches the stop 19 and so the gearwheel 17 hits the stop 19. The driving torque applied by the drive 3 can no longer move the segmental gear wheel 17, which is up against the stop 19, but still acts on the output shaft 15, gearbox input shaft 2 and gear teeth 10, and in particular on the slipping clutch 8 provided between output shaft 15 and gearbox input shaft 2. When a predetermined slipping torque is reached there is relative movement of the friction surface 61 and opposing 11 friction surface 61, to limit the maximum torque which can be transmitted to the gearbox input shaf t 2.

If the electronic control means then recognises the presence of a fault, it either operates in accordance with a control routine which does not require the missing information or the missing information is once again supplied or ascertained.

Various embodiments of the slipping clutch 8 are illustrated in the Figures. The slipping clutch 8 illustrated in Figure 2 has the friction surface 61 formed on a housing 27. The friction surface 63 is formed on a friction lining 29 which is connected to a shaft 14 to rotate with it but to be axially movable relative to the friction surface 61. The friction lining 29 is urged towards the friction surface 61 by the spring means comprising an annular plate spring 33 mounted between two annular discs 65, 67. The disc 67 abuts against a projection 69 on the end of the clutch housing 27 remote from the friction surface 61. The projection 69 is formed by means of a locking ring snapping into a groove 71 in the housing 27 after the introduction of friction lining 29, plate spring 33 and annular discs 65, 67. The radially outer rim of the plate spring 33 acts on the friction lining 29. The plate spring 33 is prevented from being pressed into the friction lining 29 by means of the annular discs 65 arranged between friction lining 61 and plate spring 33. In the case of a hard friction lining 29 or opposing friction surface 63 the annular disc 65 can be omitted.

The slipping clutch 8 of Figure 3 differs from that of Figure 2 in the orientation of the plate spring 33 which has its radially inner rim engaging the disc 65. The connections of the shaft 14 to the friction surfaces 61, 63 are formed by a mechanical connection. Thus, at least 12 one end 73 of the shaft is square and the friction surfaces 61, 63 each have a corresponding square opening 75 for receiving the end 73 of the shaft.

A suitable plate spring 33 for the embodiments of Figures 2 and 3 is shown in side view in Figure 4 and in front elevation in Figure 5. The plate spring 33 has radially extending notches or slots 35 in its radially inner edge 37, which ensure that the spring characteristic and the working range are set to a desired range of operation 77, shown in Figure 6.

The characteristic of such a plate spring 33 is shown in the graph of Figure 6. The operating range 77 of the plate spring 33 at the start of actuation of the drive and the displacement to be expected as a result of a depression of the spring 33 through wear are shown, and it can be seen that the characteristic remains substantially constant in this operating range. The slipping clutch will therefore have a substantially constant slipping torque over its whole working life.

Figure 7 shows a slipping clutch 8 in which the friction surface 63 is provided on the housing 27, and the friction surface 61 on an axially movable member engaged by the inner rim of the plate spring 33. The radially outer rim of the plate spring 33 engages the projection 69. The friction surface 61 is provided with recesses 93. A detent element 91 in the form of a ball 92 is received and engages in a recess. Each ball is also received in a corresponding recess 96 formed in the opposing friction surface 63 on the side facing the friction surface 61. The recesses 96 are deeper than the recesses 93. The balls 91 may be held securely in the opposing friction surface 63, for example by an adhesive. Often the deeper penetration of the detent elements 91 into the recesses 96 in the opposing friction surface 63 is sufficient to retain the detent elements 91 13 in them. The detent elements 91 serve to prevent relative movement of the friction surface 61 and opposing friction surface 63 when the torque applied is below the predetermined slipping torque. When this torque is exceeded, relative movement of the friction surfaces 61, 63 takes place, and the elements 91 move out of the recesses 93 in the friction surface 61.

This increases the axial distance 95 between the friction surfaces 61, 63 against the force in the plate spring 33. The torque applied is therefore partially converted into potential energy of the spring 33, so that not as much energy is converted into heat. This makes the slipping clutch less liable to be affected by temperature and overheating. It can also be arranged that more recesses 93, 96 are formed in the friction surfaces 61, 63 than there are detent elements 91 so that when the torque falls below the predetermined value the clutch 8 returns into its rest condition, whereby the detent elements are once again received on both sides in recesses 91, 96.

Figure 8 shows a modification of the slipping clutch 8 with detent elements 91. In this clutch 8 of Figure 8 the opposing friction surface 63 is provided not with recesses 96 but with projections 94, forming detent elements. These projections 94 engage in the rest condition in the recesses 93 in the friction surface 61. When slipping occurs, these projections 94 emerge from the recesses 93 as a consequence of the relative movement of the friction surfaces 61, 63. When the slip torque falls below the predetermined value the projections 94 return into the recesses 93, the torque then being insufficient for the projections 94 to move out of the recesses 93 against the engaging force of the plate spring 33. Consequently the slipping clutch 8 returns to the rest condition.

For assembly of Figures 7 and 8 the friction surface 61 simply has to be inserted in the housing 27. Subsequently the plate spring 33 is 14 inserted and is put under stress by fitting a ring 70 into the groove 71 in the housing.

For final assembly of the slipping clutch 8 into the actuating drive 1 of Figure 1 the housing 27 is provided with a profile which is fitted onto the end of the gearbox input shaft 12 provided with a matching profile, to form a mechanical connection. In the same way the output member of the drive is connected to the member carrying the friction surface 61 of the clutch 8 to rotate with it. Without altering the manner of operation of the clipping clutch 8 the housing 27 could equally well be arranged on the side which is adjacent the drive 3.

Figures 9 and 10 show a further construction of a slipping clutch 8. The friction surface 61 and opposing friction surface 63 are held in engagement by spring means comprising helical springs 57. The springs 57 urge the surface 63 axially. Relative angular movement between opposing friction surface 63 and a carrier element 79 on which it is mounted is prevented by axially extending pins 81 which connect the carrier element 79 to the opposing friction surface 63 to be axially slidable but not relatively rotatable.

The slipping clutch 8 illustrated in Figure 11 has, instead of an opposing friction surface 63 formed in one piece, a number of friction pads 83 mounted on pins 81 and urged against the friction surface 61 by means of spiral springs. The friction surface 61 is held axially by a projection 69.

The slipping clutch 8 shown in Figures 12 and 13 comprises a number of friction segments 85 which are urged by spring means comprising leaf springs 87 in a radially outward direction against a is cylindrical friction surface 61. A cylinder 89 carrying the friction surface 61 is rigidly connected to a shaft 14b and the friction segments 85 are rigidly connected to another shaft 14a, through the leaf springs 87.

Claims

16 CLAIMS

1 An actuating drive for operation of a friction clutch of the kind set forth, in which the friction surface is connected to the opposing friction surface through at least one detent element at least partly received in a recess in at least one of the friction surfaces, the or each detent element acting to prevent relative movement of the friction surfaces until the predetermined torque is exceeded, and on relative movement of the friction surfaces the or each detent element moves out of the or each recess to increase the axial distance between the friction surfaces against the force of the spring means.

2. An actuating drive as claimed in claim 1, in which both the friction surface and the opposing friction surface have recesses in which the or each detent element is received.

3. An actuating drive as claimed in claim 2, in which the or each detent element comprises a ball.

4. An actuating drive as claimed in claim 1, in which one of the friction surfaces has projections comprising the detent elements, received in recesses in the other friction surface.

5. An actuating drive as claimed in claim 4, in which the projections are formed in the opposing friction surface.

6. An actuating drive as claimed in any preceding claim, in which the spring means comprises a plate spring.

17

7. An actuating drive as claimed in any of claims 1 to 5, in which the spring means comprises at least one helical spring.

8. An actuating drive for operation of a friction clutch of the kind set forth, in which the spring means comprises a plate spring with at least one notch having a radial component.

9. An actuating drive as claimed in claim 8, in which the or each notch having a radial component is arranged at the inner radius of the 10 plate spring.

10. An actuating drive as claimed in any preceding claim, in which one of the friction surfaces forms a part of a housing of the slipping clutch.

11. An actuating drive as claimed in claim 10, in which the friction surface is integral with the housing.

12. An actuating drive as claimed in claim 10 or claim 11, in which the opposing friction surface forms part of the housing.

13. An actuating drive as claimed in any preceding claim, in which the spring means comprising the plate spring is operatively connected at its radially outer rim to an axially movable member having a friction surface.

14. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figures 1, 2, 4 and 5 of the accompanying drawings.

18

15. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

16. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figure 7 of the accompanying drawings.

17. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figure 8 of the accompanying drawings.

18. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figures 9 and 10 of the accompanying drawings.

19. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figure 11 of the accompanying drawings.

20. An actuating drive for operation of a friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in Figures 12 and 13 of the accompanying drawings.