WO2010012288A1

WO2010012288A1 - Clutch actuator

Info

Publication number: WO2010012288A1
Application number: PCT/EP2008/006248
Authority: WO
Inventors: Kjell Arne Drag; Stefan Beeger
Original assignee: Kongsberg Automotive As
Priority date: 2008-07-29
Filing date: 2008-07-29
Publication date: 2010-02-04

Abstract

The present invention refers to a clutch actuator for usage in a clutch system of a vehicle comprising a first actuator unit (1A, 1B), a second actuator unit (5) and a driving component, wherein the first actuator unit and the second actuator unit (5) are spaced apart from each other, wherein the first actuator unit is movable relative to the second actuator unit (5), such that the distance between the first actuator unit and the second actuator unit (5) is variable, wherein said movement is driven by the driving component. The invention is characterised in that the driving component comprises a flexible, inflatable body (7A,7B) located between the first actuator unit and the second actuator unit (5), such that the distance between the first actuator unit and the second actuator unit (5) increases when the flexible, inflatable body is inflated.

Description

Clutch actuator

The present invention refers to a clutch actuator for usage in a clutch system of a vehicle comprising a first actuator unit, a second actuator unit and a driving component, wherein the first actuator unit and the second actuator unit are spaced apart from each other, wherein the first actuator unit is movable relative to the second actuator unit, such that the distance between the first actuator unit and the second actuator unit is variable, wherein said relative movement of the first actuator unit is driven by the driving component.

Known actuators for vehicle clutches comprise as the driving component a metal cylinder controlling the distance between two parallel clutch plates which may transfer rotational force when they have frictional contact. Typically, a piston is arranged to move axially within the cylinder. The piston is attached to push an actuator rod that is arranged to act on the release lever or release bearing of the clutch to be actuated. The clutch is often actuated by introduction of fluid in a cylinder chamber at one side of the piston, creating a fluid pressure and causing the piston to move. A piston arrangement for actuating a vehicle clutch is in most known vehicle clutches a suitable solution since the clutch plates need to fulfil a fine-controlled one-dimensional movement without tilting or other transverse force components.

A clutch actuator according to the preamble of claim 1 is described in EP 0 185 176 Bl. More specifically, EP 0 185 176 Bl describes a so-called twin-clutch, double clutch or dual clutch transmission (DCT) with essentially two separate concentric clutches for odd and even gears, respectively. The outer clutch drives the odd numbered gears, while the inner clutch drives the even numbered gears. An advantage of such DCTs is that shifts can be accomplished without interrupting power, by applying the engine's torque to one clutch just as the engine's torque is being disconnected from the other clutch. Since synchronisers can be used in such a way that an odd gear select command can be transferred while driving the car in an even gear, and vice versa, DCTs may be more quickly than single-clutch AMTs (automated-manual" transmissions). Also, with a DCT, shifts can be made more smoothly than with a single-clutch AMT, making a DCT more suitable for street- driving .

However, the driving component of the two concentric clutches described in EP 0 185 176 Bl are two pneumatically controlled pistons in cylinders arranged to actuate movable annular sleeves which act as actuator units. A disadvantage of a pis- ton arrangement in a metal cylinder is that such an arrangement is very space consuming since the metal cylinder must be large enough to include the piston's stroke length. Known solutions of this kind are also expensive as they include a large number of mechanical parts, and many parts are made of metal which adds to the costs and to the weight of the clutch system.

Moreover, the piston within a cylinder having sliding contact with the inner wall of the cylinder creates a friction between the piston and the cylinder causing wear. Additionally, the piston must be equipped with sliding sealing lips which presents a potential risk for leakage.

It is therefore the object of the present invention to provide an improved clutch actuator which overcomes the disadvantages of the solutions known in the prior art. The clutch actuator needs to be compact, inexpensive, durable and easy to control. This object is solved by the inventive gear shift system according to the features of claim 1. Preferred embodiments of the invention are subject of the dependent claims.

According to the present invention the driving component comprises a flexible, inflatable body located between the first actuator unit and the second actuator unit, such that the distance between the first actuator unit and the second actuator unit increases when the flexible, inflatable body is inflated. Preferably, the flexible, inflatable body is a rubber bellow.

A flexible, inflatable body is a very compact solution as the gap between the first actuator unit and the second actuator unit is used as the pressurised volume which is always needed in a pneumatically or hydraulically actuated or assisted clutch. The flexible material of the inflatable body, such as rubber, is inexpensive, durable and relatively light. There is no need for numerous mechanical components and no sliding sealing lips are needed which could be subject to wear causing a risk of leakage. The flexible, inflatable body can be moulded by injection in such a way that the expansion properties are easy to control by the appropriate applied fluid pressure .

It is advantageous if the flexible, inflatable body has essentially the form of a flexible tube with a first end section sealed air-tightly to the first actuator unit and a second end section sealed air-tightly to the second actuator unit. Thereby, the flexible, inflatable body may be inflatable through a bore in the first or second actuator unit. The first actuator unit may comprise at least one actuator plate arranged parallel to the second actuator unit and each having a supporting ring of a rigid material, preferably metal or reinforced plastic material, attached to it. The rigid supporting rings may be integrally sealed to the flexible, inflatable body during their injection moulding production process. The rigid supporting rings may be fixed to the respective actuator plates by an air-tight sealing contact, for instance by means of a lever press to create a tight fit attachment. In this configuration the flexible, inflatable body acts as an expansion bellows.

Preferably, the flexible, inflatable body has a ribbed inner surface, wherein the inner ribs run essentially along the in- ner periphery. The inner ribs have the advantage that they allow a bulging deformation radially inwards while preventing a bulging deformation radially outwards.

It is particularly preferred that the flexible, inflatable body has a middle section between the first end section and the second end section, wherein the middle section has a smaller diameter than the end sections. It is to be understood that this shape of the flexible, inflatable body refers to the initial state, i.e. the shape after its moulding. Each section may comprise one rib each, i.e. the middle section and the end sections each comprise an inner rib, such that neighbouring ribs are spaced apart when the flexible, inflatable body is deflated and contact each other when the flexible, inflatable body is inflated to its maximum.

In a preferred embodiment of the invention the clutch actuator comprises at least two flexible, inflatable bodies which are essentially arranged in parallel to each other in an annular arrangement, such that the flexible, inflatable bodies are an- nularly distributed around a central axis A. This annular arrangement of a plurality of bellows provides a very compact system configuration. At least two, but preferably all, of the flexible, inflatable bodies may be synchronised in their inflation and deflation operations. This is preferably achieved by a common connection to a fluid pressure supply which is controlled by a common valve.

In order to actuate DCTs it may be advantageous if the clutch actuator comprises two groups of flexible, inflatable bodies, wherein the flexible, inflatable bodies of the same group are synchronised among each other in their inflation and deflation operations, respectively, and wherein flexible, inflatable bodies of alternating groups are annularly distributed around the axis A. It may be furthermore advantageous if the flexible, inflatable bodies of one group have a larger initial volume than the flexible, inflatable bodies of the other group. In such a configuration the two clutches may be actuated with different fluid pressures, powers or actuation lengths. This may be especially advantageous if the there is less initial fluid pressure available or desirable for switching into the first gear before the start of driving than switching to higher gears during driving. It will be appreciated that a larger flexible, inflatable body needs less fluid pressure than a small one to effect the same actuating force. As the necessary stroke length is typically the same for all gears, the larger volume of one group of flexible, inflatable bodies is preferably realised by a larger cross-sectional area of the circular actuator plates which represents a movable chamber wall of the pressurised volume in the rubber bellow. The switching of higher gears during driving may be possible or desirable at higher pressures such that the small flexible, inflatable bodies may be advantageous for switching to even gears in order to save space consumption. The arrangement of flexible, inflatable bodies of alternating groups guarantees a uniform annular distribution in order to avoid tilting effects or any transversal force components. To achieve this it is further preferred that the flexible, inflatable bodies of one group are synchronised among each other in their inflation and deflation operations. Further to actuate DCTs, it is advantageous if the second actuator unit is fixed in position relative to the vehicle and the clutch actuator comprises another first actuator unit, such that there is an outer first actuator unit and an inner first actuator unit which are independently of each other movable with respect to the second actuator unit. The first group of flexible, inflatable bodies may then be arranged between the outer first actuator unit and the second actuator unit and the second group of flexible, inflatable bodies may be arranged between the inner first actuator unit and the second actuator unit. Each flexible, inflatable body may then be inflatable through a bore in the static second actuator unit.

In the following a preferred embodiment of the invention is discussed in further detail with reference to the accompanying figures .

Fig. 1 shows a perspective view of a preferred embodiment of an inventive dual-clutch actuator.

Fig. 2 shows a rear view of a preferred embodiment of an inventive dual-clutch actuator.

Fig. 3 shows a side view of a preferred embodiment of an inventive dual-clutch actuator.

Fig. 4 shows a front view of a preferred embodiment of an inventive dual-clutch actuator.

Fig. 5 to 7 show longitudinal cut views of a preferred embodiment of an inventive dual-clutch actuator in different actuation states. Fig. 8 to 10 show detailed longitudinal cut views of a preferred embodiment of an inventive clutch actuator in different actuation states.

Fig. 11 shows a detailed perspective view of a preferred embodiment of an inventive dual-clutch actuator.

The dual-clutch actuator shown in Figure 1 comprises an outer first actuator unit IA and an inner first actuator unit IB. The two first actuator units IA, IB have each the shape of nested sleeves with three circular actuator plates 3A, 3B extending radially with an azimuthal angular distance of 120°. The actuator plates 3B of the inner first actuator unit IB are arranged such that they are 60° azimuthally rotated relative to the actuator plates 3A of the outer first actuator unit IA. Thereby, the first actuator unit 1 has an outer shape of a six-leaved blossom with a central axis A. The two first actuator units IA, IB are independently of each other movable along the central axis A.

The clutch actuator also comprises a second actuator unit 5 which is spaced apart from the first actuator unit 1 along the central axis A. The surface of the second actuator unit 5 facing towards the first actuator unit 1 is parallel to the ac- tuator plates 3A, 3B and extends perpendicular to the central axis A. The radial outer shape of the second actuator unit 5 corresponds to the six-leaved blossom shape of the first actuator unit 1. In contrast to the first actuator unit 1 the second actuator unit 5 is fixed with respect to the vehicle frame (not shown) and formed in one piece.

In the gap between the first actuator unit 1 and the second actuator unit 5 the clutch actuator comprises six flexible, inflatable bodies 7A, 7B in form of rubber bellows. They are arranged in parallel to each other in an annular arrangement corresponding to the six-leaved blossom shape, i.e. they are annularly distributed with an azimuthal angular distance of 60° to each other around the central axis A. The flexible, inflatable bodies 7A, 7B have essentially the form of a flexible tube with a first end section 9 sealed air-tightly to the first actuator unit 1 and a second end section 11 sealed air- tightly to the second actuator unit 5 which is better visible in Figures 3 and 5 to 10. In order to guide the movement of the first actuator unit 1 along the central axis A the two first actuator units IA, IB in form of nested sleeves are arranged on a fixed central rigid tube or rod 13. In order to prevent a rotation around the central axis A one or more of the actuator plates 3A, 3B may be framed by shells 15A, 15B fixed to the second actuator unit 5. Also visible in Figure 1 are connectors 17A, 17B for position sensor systems which are adapted to sense the distance between the actuator plate 3A and/or 3B, respectively, and the second actuator unit 5.

The six flexible, inflatable bodies 7A, 7B have two different sizes. Those three inflatable bodies 7A connected to the outer first actuator unit IA have a larger volume than those three inflatable bodies 7B connected to the inner first actuator unit IB, i.e. the cross-sectional area of the circular actuator plates 3A which represents a chamber wall of the pressur- ised volume in the rubber bellow 7A is larger than the respective cross-sectional area of the circular actuator plates 3B. The larger inflatable bodies 7A and the smaller inflatable bodies 7A are annularly distributed around the axis A in an alternating manner.

A pneumatic system for inflation and deflation of the rubber bellows 7A, 7B is only partly visible in Figure 1. Figure 2 shows this more clearly in a rear view of the second actuator unit 5. The three portions of the second actuator unit 5 adapted to be connected to the three respective larger inflat- able bodies 7A are connected by a common channel 19A having an angled V-shape in a plane B-B perpendicular to the central axis A. The common channel 19A has a knee 21A in the vicinity of the centre of one of the three portions of the second ac- tuator unit 5 adapted to be connected to the three respective larger inflatable bodies 7A. Two legs 23A, 25A extend from the knee 2 IA towards the centre of the other two of the three portions of the second actuator unit 5 adapted to be connected to the three respective larger inflatable bodies 7A. The two end openings of the legs 23A, 25A are plugged in operation. Connected to one leg 23A of the common channel 19A is a control valve 27A acting as a common inlet and outlet valve in order to synchronise the three larger rubber bellows 7A in their inflation and deflation operations.

Essentially in a mirror symmetric configuration the three portions of the second actuator unit 5 adapted to be connected to the three respective smaller inflatable bodies 7B are connected by a common channel 19B having an angled Λ-shape in a plane C-C perpendicular to the central axis A. The plane C-C runs parallel to plane B-B with a small distance such that the channels 19A and 19B do not interfere (see Figure 3) . The common channel 19B has a knee 21B essentially ' opposite to the knee 21A of channel 19A with respect to the central axis A. Two legs 23B, 25B extend from the knee 21B towards the centre of the other two of the three portions of the second actuator unit 5 adapted to be connected to the three respective smaller inflatable bodies 7B. The two end openings of the legs 23B, 25B are plugged in operation. In analogy to the channel 19A, there is a control valve 27B acting as a common inlet and outlet valve connected to one leg 23B of the common channel 19B in order to synchronise the three smaller rubber bellows 7B in their inflation and deflation operations. There is also a rotation stop 29 present which prevents the clutch actuator from rotating with respect to other parts of the vehicle. The side view of Figure 3 shows even more clearly the control valves 27A, 27B and the common channels 19A, 19B. The volume difference between the larger rubber bellows 7A and the smaller rubber bellows 7B becomes apparent. The shape of both types of rubber bellows 7A, 7B is essentially the same. They have the form of a flexible tube with a first end section 9 sealed air-tightly to the first actuator unit 1 and a second end section 11 sealed air-tightly to the second actuator unit 5. The rubber bellows 7A, 7B are air-tightly attached to the actuator units 1 and 5, respectively, by means of rigid supporting rings 31, preferably made of metal or reinforced plastic material. The rigid supporting rings 31 are integrally sealed to the flexible, inflatable bodies 7A, 7B during an in- jection moulding production process of the flexible, inflatable bodies 7A, 7B. The flexible, inflatable bodies 7A, 7B are then fixed to the respective actuator plates via the rigid supporting rings 31 with an air-tight sealing contact. It is also visible in Figure 3 that the flexible, inflatable bodies 7A, 7B have a middle section 33 between the first end section 9 and the second end section 11, wherein the middle section has 33 a smaller diameter than the end sections 9, 11. Therefore, the flexible, inflatable bodies 7A, 7B have essentially a concave shape tapering from the end sections 9, 11 towards the middle section 33.

Figure 4 illustrates the six-leaved blossom shape of the clutch actuator in a front view of the first actuator unit 1. Moreover, the nested sleeves of the two first actuator units IA, IB are visible with three circular actuator plates 3A, 3B each extending radially with an azimuthal angular distance of 120° and being actuated by the respective three large and three small rubber bellows 7A, 7B. In order to demonstrate the operation of the clutch actuator Figures 5 to 7 show longitudinal cut views of the clutch actuator in different actuation states. In Figure 5 both groups of rubber bellows types 7A and 7B are in an initial deflated state. This is the initial state in which both clutch plates (not shown) , assuming a normally closed clutch, have fric- tional contact with their respective counter-parts in order to transfer rotational force. In case of a normally open clutch, the clutch plates have no frictional contact with their re- spective counter-parts in the initial deflated state of the clutch actuator as shown in Figure 5. Assuming a normally closed clutch, the frictional contact is typically provided by the resilient force of a corresponding clutch spring (not shown) and the force to open the clutch may be provided by the hydraulic or pneumatic force from the clutch actuator. Con- trarily, in case of a normally open clutch, the clutch spring is used to urge the clutch plates away from their respective counter-parts and the hydraulic or pneumatic force from the clutch actuator urges the clutch plates into frictional con- tact with their respective counter-parts. In both cases the pressure force from the clutch actuator works against the resilient force of the clutch spring. Therefore, the first actuator unit 1 is urged by the resilient force of one or two clutch springs into the initial position shown_^ in Figure 5.

In the following Figure 6 a state of the clutch actuator is shown in which typically the first gear is inserted in order to start driving. Depending on whether it is a normally closed or open clutch this is achieved in a different way. Assuming a normally closed clutch the clutch plates for both the first and the second gear have contact in the initial state in which driving is impossible. The gear shift action to start driving is then the opening of the clutch plate for the second gear such that force from the engine is transferred to the gear box via the first gear only. Other way round, a normally open clutch needs a closing action of the clutch plate for the first gear such that force from the engine is transferred to the gear box via the first gear.

In Figure 6 the large rubber bellows 7A are inflated and shown in a state of maximal expansion, whereas the small rubber bellows 7B are still deflated. Three axial bores 35A in the second actuator unit 5 connect the respective three inner volumes of the large rubber bellows 7A with the common channel 19A, such that the inflation of fluid can be conducted in a syn- chronised way via the common channel 19A which is controlled by the control valve 27A. Analogously, three further axial bores 35B in the second actuator unit 5 connect the respective three inner volumes of the small rubber bellows 7B with the common channel 19B, such that the inflation of fluid can be conducted in a synchronised way via the common channel 19B which is controlled by the control valve 27B.

The fluid pressure in the large rubber bellows 7A urges the outer first actuator unit IA to move away from the second ac- tuator unit 5 such that the distance between them increases. Since the two first actuator units IA, IB are independently movable the inner first actuator unit IB may remain in its initial position. As the outer first actuator unit IA corresponds to the outer sleeve of the nested sleeves, the clutch plate contact for an even gear may be released (given a normally closed clutch) . Given a normally open clutch, the clutch plate for an odd gear may be brought into contact. It will be appreciated that the fluid pressure in the rubber bellows 7A must be large enough to overcome the resilient force of a clutch spring in order to effect the desired clutch release action.

It may be advantageous if the large rubber bellows 7A are used to actuate the insertion of the first gear to start driving as there may be less initial fluid pressure available or desir- able before the start of driving than actuating higher gear shifts during driving. It will be appreciated that the larger rubber bellows 7A need less fluid pressure than the small rubber bellows 7B to effect the same actuating force. Preferably, this is achieved as shown in the figures by a larger cross- sectional area of the circular actuator plates 3A which represents a chamber wall of the pressurised volume in the rubber bellow 7A. The switching of the follow-up gears during driving may be conducted with higher pressure such that the small rub- ber bellows 7B is advantageous for switching to even gears in order to save space consumption.

In Figure 7 a state of the clutch actuator is shown in which typically a second, fourth or sixth gear is inserted. Figure 7 shows an inflated state of the small rubber bellows 7B, whereas the large rubber bellows 7A are deflated. The fluid pressure in the small rubber bellows 7B urges the inner first actuator unit IB to move away from the second actuator unit 5 such that the distance between them increases. As the inner first actuator unit IB corresponds to the inner sleeve of the nested sleeves, the clutch plate contact for an odd numbered gear may be released (given a normally closed clutch) . Given a normally open clutch, the clutch plate for an even gear may be brought into contact. Again, it will be appreciated that the fluid pressure in the rubber bellows 7B must be large enough to overcome the resilient force of a clutch spring in order to effect the desired clutch release action. Although not explicitly shown, it is further appreciated that the two clutches may operate completely independent of each other, i.e. both groups of rubber bellows 7A and 7B may also be inflated simultaneously in order to effect a simultaneous clutch release action. It is however preferred to switch gears very quickly by inflating one group of rubber bellows 7A, 7B while the other 7B, 7A is deflated simultaneously, and vice versa. Fig. 8 to 10 show one rubber bellows 7 in more detail by longitudinal cut views at different actuation states. Since the two types of rubber bellows 7A, 7B only differ in size, but have essentially the same shape and composition, the rubber bellows 7 depicted in Figures 8 to 10 may be of either type. The rubber bellows 7 has the form of a flexible tube with a first end section 9 sealed air-tightly to the first actuator unit 1 and a second end section 11 sealed air-tightly to the second actuator unit 5. The rubber bellows 7 are air-tightly attached to the actuator units 1 and 5, respectively, by means of rigid supporting rings 31, preferably made of metal or reinforced plastic material. The rigid supporting rings 31 are integrally sealed to the flexible, inflatable body 7 during its injection moulding production process. The flexible, in- flatable body is fixed to the first and second actuator units 1, 5 via the rigid supporting rings 31 with an air-tight sealing contact. It is also visible in Figure 8 that the rubber bellows 7 has a middle section 33 between the first end section 9 and the second end section 11, wherein the middle sec- tion 33 has a smaller diameter than the end sections 9, 11. Therefore, the rubber bellows 7 has essentially a concave shape tapering from the end sections 9, 11 towards the middle section 33.

The rubber bellows 7 comprises a ribbed inner surface, wherein the inner ribs 37 run essentially along the inner periphery. More specifically, the middle section 33 and the end sections 9, 11 of the rubber bellows 7 each comprise an inner rib 37, such that neighbouring ribs 37 are spaced apart when the rub- ber bellows 7 is deflated as shown in Figure 8 and contact each other when the rubber bellows 7 is inflated to its maximum as shown in Figure 10. An intermediate state between a fully deflated and a fully inflated state is shown in Figure 9. The inner ribs 37 and the gaps 39 between them act as a hinge closing the gaps 39 between the rips 37 when the rubber bellows 7 is inflated and expands. Upon inflation and an increased fluid pressure inside the rubber bellows 7 the middle section 33 increases its diameter until it almost reaches the diameter of the end sections 9, 11. When the rubber bellows 7 is inflated to its maximum, as shown in Figure 10, the inner ribs 37 contact each other such that the gap 39 between them vanished. This prevents the middle section 33 from bulging further outward. It will be appreciated that there may be any suitable number of inner ribs 37 in order to achieve the de~ sired result. In this completely inflated state the rubber bellows 7 is stretched to its maximal length along the axis D parallel to the central axis A, wherein the first and the second actuator units 1, 5 have the maximal distance to each other .

The compactness of the inventive design becomes apparent on Fig. 11 showing a detailed perspective view of a rubber bellows 7 sandwiched between the first and the second actuator unit 1, 5. The second actuator unit 5 shows further three threaded holes 41 which do not extend into the inner volume. The threaded holes 41 are adapted to receive mounting screws in order to attach the second actuator unit 5 to other parts.

Claims

1. A clutch actuator for usage in a clutch system of a vehicle comprising a first actuator unit (1), a second actua- tor unit (5) and a driving component, wherein the first actuator unit (1) and the second actuator unit (5) are spaced apart from each other, wherein the first actuator unit (1) is movable relative to the second actuator unit (5), such that the distance between the first actuator unit (1) and the second actuator unit (5) is variable, wherein said relative movement of the first actuator unit is driven by the driving component, characterised in that the driving component comprises a flexible, inflatable body (7) located between the first actuator unit (1) and the second actuator unit (5), such that the distance between the first actuator unit (1) and the second actuator unit (5) increases when the flexible, inflatable body (7) is inflated.

2. A clutch actuator according to claim 1, wherein the flexible, inflatable body (7) is a rubber bellow.

3. A clutch actuator according to claim 1 or 2, wherein the flexible, inflatable body (7) has essentially the form of a flexible tube with a first end section (9) sealed air- tightly to the first actuator unit (1) and a second end section (11) sealed air-tightly to the" second actuator unit (5) .

4. A clutch actuator according to any of the preceding claims, wherein the flexible, inflatable body (7) has a ribbed inner surface, wherein the inner ribs (37) run essentially along the inner periphery.

5. A clutch actuator according to claim 3 or 4 , wherein the flexible, inflatable body (7) has a middle section (33) between the first end section (9) and the second end section (11), wherein the middle section (33) has a smaller diameter than the end sections (9, 11).

6. A clutch actuator according to claim 5, wherein the middle section (33) and the end sections (9, 11) -each comprise an inner rib (37), such that neighbouring ribs (41) are spaced apart when the flexible, inflatable body (7) is deflated and contact each other when the flexible, inflatable body (7) is inflated to its maximum.

7. A clutch actuator according to any one of the claims 3 to 6, wherein the flexible, inflatable body (7) is inflatable through a bore (35) in the first or second actuator unit (1, 5).

8. A clutch actuator according to any of the preceding claims, wherein the first actuator unit ..(1) comprises at least one actuator plate (3) arranged parallel to the second actuator unit (5) .

9. A clutch actuator according to any of the preceding claims, wherein the clutch actuator comprises at least two flexible, inflatable bodies (7) which are essentially arranged in parallel to each other in an annular arrangement, such that the flexible, inflatable bodies (7) are annularly distributed around a central axis (A) .

10. A clutch actuator according to claim 9, wherein at least two of the flexible, inflatable bodies (7) are synchronised in their inflation and deflation operations.

11. A clutch actuator according to claim 9 or 10, wherein the clutch actuator comprises two groups of flexible, inflatable bodies (7A, 7B), wherein the flexible, inflatable bodies (7A, 7B) of the same group are synchronised among each other in their inflation and deflation operations, respectively, and wherein flexible, inflatable bodies (7A, 7B) of alternating groups are annularly distributed around the axis A.

12. A clutch actuator according to claim 11, wherein the flexible, inflatable bodies (7A) of one group have a larger initial volume than the flexible, inflatable bodies (7B) of the other group.

13. A clutch actuator according to any of the- claims 10 to 12, wherein the flexible, inflatable bodies (7A, 7B) are synchronised in their inflation and deflation operations by a common channel (19A, 19B) to a fluid pressure supply.

14. A clutch actuator according to any of the claims 11 to 13, wherein the second actuator unit (5) is fixed in position relative to the vehicle and the clutch actuator comprises another first actuator unit, such that there is an outer first actuator unit (IA) and an inner first actuator unit (IB) which are independently of each other movable with respect to the second actuator unit (5) , wherein the first group of flexible, inflatable bodies (7A). is arranged between the outer first actuator unit (IA) and the second actuator unit (5) and the second group of flexible, in- flatable bodies (7B) is arranged between the inner first actuator unit (IB) and the second actuator unit (5) .

15. A clutch actuator according to any of the claims 3 to 14, wherein each flexible, inflatable body (7A, 7B) is inflat- able through a bore (35A, 35B) in the second actuator unit (5) .