GB2339256A

GB2339256A - A concentric actuator with a flexible member inside working chamber

Info

Publication number: GB2339256A
Application number: GB9814807A
Authority: GB
Inventors: Roland Collemare; Laurent Compain
Original assignee: Automotive Products France SA
Current assignee: Automotive Products France SA
Priority date: 1998-07-08
Filing date: 1998-07-08
Publication date: 2000-01-19
Anticipated expiration: 2018-07-08
Also published as: GB9814807D0; GB2339256B

Description

2339256 A2600 ACTUATORS This invention relates to actuators, and in

particular to so-called concentric actuators in which a piston slides between concentric inner and outer working chamber walls.

There is a long-standing requirement to provide an efficient but cheap form of concentric I I actuator particularly for use as a slave cylinder for the operation of a vehicle clutch.

Thus according to the invention there is provided a concentric type actuator comprising a working chamber defined by inner and outer concentric housing walls within which a piston member slides to operate an associated function, the actuator being characterised in that within the working chamber is located a flexible actuating member which when internally pressurised expands within the working chamber to displace the piston.

The above actuator removes the need for a sliding seal between the piston and chamber walls. Also the need for manufacturing accuracy in the production of the chamber walls and piston is reduced enabling these components to be made by cost effective moulding or stamping processes.

The flexible actuatincr member may comprise a hollow coiled member which is wound within 0 the working chamber.

The coiled actuating member is preferably formed from an extruded tube which may be, for example, rubber (EPDM) or a flexible metallic material such as bronze beryllium.

An end of the coiled actuating member may be closed by welding or by pinching the end of the tube between two parts of the actuator.

An inlet into the coiled actuating member may be formed by trapping an open end of the coil I C> between an outer housing part and an inner housing part containing a fluid inlet opening.

2 Where necessary the size of the actuating chamber can be increased (to provide for extra clutch wear) by increasing the length of the coiled actuating member.

The flexible actuating member may alternatively comprise an annular diaphragm which lines the working chamber. The diaphragm may be of pleated form.

I In a preferred arrangement the diaphragm terminates in two concentric edge beads which are held captive in the actuator housing, The diaphragm may include wall portions which overlap and are held spaced apart by bracing means. The bracing means may comprise a ring (typically of C-section) which contacts the overlapping portions.

Preferably the inlet into the working chamber is through an aperture in the bracing means.

One bead of the diaphragm may be trapped between overlapping portions of the actuator housing and the other bead may be held in a recess in the actuator housing by the bracing means.

The actuator of the present invention is particularly suitable for use as a clutch actuator and the pre-load of the piston onto an associated clutch release bearing can be provided by the unpressurised flexible actuating member.

The flexible actuating member may be at its normal size when unpressurised and may be arranged to expand when pressurised. Alternatively the flexible actuating member may be compressed when unpressurised and may assume substantially its normal size when pressurised.

3 Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figures I and 2 show axial sections through the actuator which utilises a coiled actuating member in the clutch engaged and clutch dis-engaged conditions respectively; Figures 3 and 4 show an alternative arrangement of coiled actuating member-, Figures 5 and 6 show alternative arrangements for closing off the end of the coiled actuating member-, Figure 7 shows a cross-section of a typical coiled actuating member- Figures 8 and 9 show sectional perspective views of an actuator which utilises a diaphragm type actuating member in the clutch engaged and disengaged conditions respectively, and Figure 10 shows part of figure 10 on an enlarged scale.

Referring to figures I and 2 a concentric slave cylinder for the operation of the vehicle clutch comprises an injection moulded housing 10 having outer and inner concentric walls I I and 12 between which an annular plastics piston 13 is slideable thus defining a working chamber 14. Within working chamber 14 is disposed a flexible coiled actuating member 15 having its open end 15a connected with an inlet port 16. The inlet port connection is provided by trapping the end 15a of the coiled member between an outer portion 16 of the housing 10 and an inner component 17 which contains an inlet opening 18. The component 18 is externally threaded at 19 to receive a pipe fitting (not shown' for the introduction of fluid into the coiled flexible actuating member ftom an associated master cylinder.

The piston 13 acts on a clutch release bearing 20 via a plastics outer sleeve member 21 which slides on the outer wall I I of housing 10. A coil spring 2.3 acts between an inner sheet metal sleeve 22 supported on inner wall 111 and sleeve 21 to provide the normal pre-load on the 4 release bearing 20.

As shown in figures I and 2, the coiled flexible actuating member 15 is compressed when in the clutch engaged condition and when pressurised by the inlet port 16 assumes its normal size and in doing so displaces piston 13 to the right, as viewed in figure 2, thus moving the associated clutch actuating lever 24 in the direction of arrow X.

If desired the bearing pre-load could be provided by the compressed flexible member 15 and coil spring 23 could be dispensed with.

Figures 3 and 4 show diagrammatically an alternative coiled flexible member arrangement in which the coiled flexible member 25 assumes its normal size when in the clutch disengaged condition and when pressurised to disengage the clutch expands beyond its normal size to the condition shown at 25a in figure 4. If desired, as shown in figure 4, an additional piston member 26 may be provided between the coiled flexible actuating member 25 and the piston 13 in order to avoid direct contact between these members.

Figures 5 and 6 show two alternative methods of closing off the other end of coiled flexible actuating member 15. In the arrangement shown in figure 5, the end of the flexible member is folded over and welded together at 15b. In the arrangement shown in figure 6, the end portion l5b of the coiled actuating member is pinched fluid tightly between two components I Oa and I Ob of the housing 10. If an additional piston member 26 is used (as in Figure 4) the other end of coiled actuating member 15 may be closed-off by pinching between piston 13 and piston member 26, As an alternative, the other end of the coiled actuating member 15 can also be moulded in a closed configuration.

As can be seen from figure 6 and in more detail from figure 7 the cross section of the flexible actuating member may be generally rectangular with two parallel sides 15, and 15 " joined by curved sides 151 ". Alternatively, as shown in the other drawings circular or oval sections may be employed.

As will be appreciated the actuator arrangement described above is a particularly simple and cost effective construction which avoids the necessity for close tolerances in the fit between the piston and the cooperating concentric inner and outer chamber walls thus reducing manufacturing costs and involves no moving seals and is therefore less prone to leakage. Also the stroke of the unit can be readily increased by including more coils of the flexible member and the coiled flexible member can be constructed from a wide variety of materials such as rubber (EPDNf) or flexible metallic material such as bronze beryllium.

Figures 8 to 10 show an alternative form of the present invention in which a concentric slave cylinder has a housing 30 having outer and inner concentric walls 31 and 32 between which an annular piston 33 is slideable thus defining a working chamber 34. The working chamber is lined by a flexible annular diaphragm 35 whose edges have beads 36 and 37 respectively. Bead 37 is trapped between portions 3 la and 32a of the outer and inner walls and bead 36 is held in an annular recess 3 8 by a bracing piece 3 9 of generally 'C' shaped cross-section whose limbs 39a and 39b contact overlapping portions 36 and 32b of the diaphragm to hold these apart. A slot 40 is provided in bracing piece 39 to allow free passage of fluid into and out of the interior of the diaphragm 3 5 via inlet connection 4 1.

Figure 8 shows the slave cylinder 30 in the clutch engaged condition in which the diaphragm, which is pleated, is in a semi-collapsed condition and figures 9 and 10 show the cylinder in the clutch disengaged condition in which the piston 33 has been displaced to the left as viewed in figures 9 and 10 to disengage the associated clutch, The diaphragm which lines the working chamber in the arrangement shown in figures 8 to 10 can again be made from rubber or flexible metallic material such as bronze beryllium.

As will be appreciated by lining the working chamber with the diaphragm 3 5 and securely holding the diaphragm in position using the beads 36 and 37 leakage of the working chamber is eliminated and close tolerances in the fit between the piston and the cylinder housing are also avoided.

6 Although the invention has been described above in relation to a slave cylinder it is also equally applicable to master cylinder arrangements.

7 A2600

Claims

I A concentric type actuator comprising a working chamber defined by inner and outer concentric housing walls within which a piston member slides to operate an associated function, the actuator being characterised in that within the working chamber is located a flexible actuating member which when internally pressurised expands within the working chamber to displace the piston.
2. An actuator according to claim 1 in which the flexible actuating member comprises a hollow coiled member which is wound within the working chamber.
3. An actuator according to claim 2 in which the coiled actuating member is formed from an extrude tube of rubber or flexible metallic material
4. An actuator according to any on of claims I to 3 in which an end of the coiled actuator is closed by welding or by pinching the end of the tube between two parts of the actuator housing C,
5. An actuator according to any one of claims I to 4 in which an inlet into the coiled actuator is formed by trapping an open end of the coil between an outer housing part and an inner housing part containing a fluid inlet opening.
6. An actuator according to claim I in which the flexible actuating member comprises an annular diaphragm which lines the working chamber.

1.
7. An actuator according to claim 6 in which the diaphragm is of pleated form.
8. An actuator according to claim 6 or 7 in which the diaphragm terminates in two concentric ed e beads which are held captive in the actuator housing g D 8
9. An actuator according to claim 8 in which the diaphragm has wall portions which overlap and are held apart by bracing means.
10. An actuator according to claim 9 in which the bracing means comprises a ring of generally C-shaped section which contacts the overlapping portions.
11. An actuator according to claim 10 in which the inlet into the working chamber is through an aperture in the bracing means.
12, An actuator according to any one of claims 8 to I I in which one bead of the diaphragm is trapped between overlapping portions of the actuator housing and the other bead is held in a recess in the actuator housing by the bracing means.
13. An actuator according to any one of claims I to 12 for use as a clutch actuator and in which pre-load of the piston onto an associated clutch release bearing is provided by the unpressurised flexible actuating member.
14. An actuator according to any one of claims I to 13 in which the flexible actuating member may be at its normal size when unpressurised and may be arranged to expand when pressurised.
15. An actuator according to any one of claims I to 13 in which the flexible actuating member may be compressed when unpressurised and may assume substantially its normal size when pressurised.
16. A concentric type actuator constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures I to 8 or 9 to I I of the accompanying drawings.