WO2004065827A1

WO2004065827A1 - Seals

Info

Publication number: WO2004065827A1
Application number: PCT/GB2004/000128
Authority: WO
Inventors: Frederick Leger; Adrian Charles Buckmaster; Anthony Mark Sheerin
Original assignee: Automotive Products France S.A.
Priority date: 2003-01-23
Filing date: 2004-01-14
Publication date: 2004-08-05
Also published as: GB0301511D0

Abstract

An annular seal (39) for use in a hydraulic cylinder in which a piston (12) moves along a bore (13) in a cylinder body defining a hydraulic working chamber (16) ahead of the piston, the seal having a forward lip portion (40) exposed to the hydraulic pressure in the working chamber which seals the working chamber against egress of fluid from the working chamber around the piston, and a rearward lobe portion (41) which has a rear face which seats against a support surface (12a) on the piston or body, the lobe portion sealing against the ingress of air or other contaminants around the piston into the working chamber. In the unpressurised condition, in the vicinity of the lobe portion the rear face (42) of the seal (39) slopes (9) away from the support face (12a) towards the working chamber (16) so that when the seal is pressurised the rear face is not forced past the support surface into the clearance (x) between the piston (12) and bore (13). The seal (39, 52) may be of the twin lip and lobe type used to seal an annular piston to inner and outer walls of an annular bore or to seal a cylindrical piston within a cylindrical bore or of the single lip and lobe type (52, 58, 59) in which the seal is held captive in the walls of an annular or cylindrical bore to seal against a moving annular or cylindrical piston or is held in a recess in a moving piston for sealing with a mating bore.

Description

SEALS

This invention relates to seals and in particular to annular seals used to seal a sliding piston in a bore of a hydraulic cylinder.

In a hydraulic cylinder, it is imperative for the effective operation of the cylinder that adequate sealing be provided between the piston and the bore of the cylinder. This sealing is necessary in order to ensure that pressurised fluid does not leak past the piston in one direction, that air does not leak past the piston in the opposite direction, and that contaminants are kept out of the sealing interface to maintain an effective air and pressure fluid seal between the piston and the bore of the cylinder.

British patent No 2229790-B discloses an annular seal for use in a hydraulic cylinder in which a piston moves along a bore in a cylinder body defining a hydraulic working chamber ahead of the piston, the seal having a forward lip portion exposed to the hydraulic pressure in the working chamber which seals the working chamber against egress of fluid from the working chamber around the piston, and a rearward lobe portion which has a rear face which seats against a support surface on the piston or body, the lobe portion sealing against the ingress of air or other contaminants around the piston into the working chamber. Such a seal is hereinafter referred to as of the kind described

Whilst annular seals of the kind described operate satisfactorily they can experience problems, particularly when level of clearance between the piston and bore is relatively large (to reduce manufacturing costs)^ due to the working chamber pressure extruding the lobe portion past the support surface into the clearance between the piston and bore. This in turn can result eventually, due to the oscillations of the piston in the bore, in part of the lobe portion being cut-off and the seal lobe fragments contaminating the sealing interface of the bore leading to leakage from the working chamber. Whilst this problem can be overcome by the fitting of an anti-extrusion ring behind the seal between the seal and the support surface, this introduces further cost into the design. It is an object of the present invention to provide a seal which at least mitigates the above problem of seal extrusion.

Thus in accordance with the present invention there is provided an annular seal of the kind described in which, in the unpressurised condition, in the vicinity of the lobe portion the rear face of the seal slopes away from the support face towards the working chamber so that when the seal is pressurised the rear face is not forced past the support surface into the clearance between the piston and bore.

The seal may be of the twin lip and lobe type used to seal an annular piston to inner and outer walls of an annular bore or to seal a cylindrical piston within a cylindrical bore. Alternatively, the seal may be of the single lip and lobe type in which the seal is held captive in the walls of an annular or cylindrical bore to seal against a moving annular or cylindrical piston or may be held in a recess in a moving piston for sealing with a mating bore.

Typically the angle of slope of the rear face is of the order of 40 degrees.

Since the rear sloping face is a non-sealing face it may be arranged to locate mould separation ridges on this face to minimise their effect.

The invention also provides a hydraulic actuator fitted with an annular seal as described above.

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

Figure 1 is an axial section through a known type of hydraulic clutch actuator;

Figure 2 shows on a larger scale details of the seal used in the actuator of Figure 1; Figure 3 shown on an even larger scale how the seal of Figure 2 may be distorted under pressure when there is a significant gap between the piston and the bore;

Figure 4 shows a cross-section of a seal in accordance with the invention in an unpressurised condition;

Figure 5 shows the seal of Figure 4 fitted in an actuator of the form shown in Figure 1;

Figure 6 shows diagrammatically the three part mould used to mould the seal of Figure 4;

Figure 7 shows an alternative cylindrical form of actuator filled with a seal in accordance with the present invention, and

Figures 8 and 9 show the seal of the present invention applied to a single lip and lobe configuration.

Figure 1 shows a typical hydraulic clutch operating cylinder 10 employing an annular seal 11 of the kind described. The cylinder comprises an annular piston 12 which is slideable in an annular cylinder bore 13 defined between inner and outer cylinder walls 14 and 15 respectively. The cylinder is extended to its maximum length (shown in figure 1) by pressurising working chamber 16 by the introduction of pressurised fluid via fluid connection 17.

Piston 12 acts on a release bearing support member 19 which carries a clutch release bearing 20 whose outer race 21 has a flange 22 which engages associated clutch release fingers 23. Release bearing support 19 has an outer cover portion 24 which includes circumferentially spaced claws 25 which are snapped over a circumferentially extending flange 26 formed on outer cylinder wall 15. The interaction between claws 25 and flange 26 limits the maximum extension of the hydraulic cylinder. A compression spring 27 acts between the release bearing support member 19 and a metal cup member 28 received within the inner wall 14 of the cylinder. Thus described the hydraulic actuator is a conventional so-called concentric slave cylinder for use in the operation of a vehicle clutch. The clutch is disengaged by pressurising working chamber 16 to displace piston 12 to the left as viewed in figure 1 thus also pushing the clutch fingers 23 to the left to disengage the clutch. The clutch is re-engaged by releasing the pressure in working chamber 16 to allow the piston and the clutch fingers 23 to move to the right as viewed in figure 1.

The form of the conventional annular seal 11 is shown on a larger scale in Figure 2. The seal has a forward portion with a pair of lips 30 which slide up and down the inner and outer walls 14 and 15 of annular cylinder bore 13 sealing the bore against egress of fluid under pressure from the working chamber 16. The seal also has a rearward portion which includes a pair of sealing lobes 31 which again slide up and down inner and outer walls 14 and 15 of the annular cylinder bore 13 and whose primary function is to prevent the ingress of air and contaminants into the working chamber 16 from the left of the seal as viewed in figures 1 and 2. The seal has a rear face 32 which is supported from a support surface 12a of the piston 12.

When the fluid in chamber 16 is pressurised the annular seal 11 is displaced to the left as viewed in figures 1 and 2 and the sealing lobes 31 tend to be forced or extruded into the small clearance 'x' between the bore 13 and the piston 12 as shown on a further enlarged scale in figure 3. In figure 3 the extruded portions of the lobes 31 are indicated at 31a.

As will be appreciated, this tendency to form the extruded portions 31 a of the lobes 31 combined with the sliding movement of piston 12 relative to bore 13 eventually leads to these extruded portions being severed from the main body of the seal with these severed seal portions 31a forming contaminants which may enter the working chamber 16 and which generally detract from the good sealing of the sliding contact between the seal 11 and the bore 13 resulting in leakage and possibly seal failure.

The above problem of seal extrusion into the clearance 'x' between the piston 12 and the bore 13 is solved in accordance with the present invention by the use of an annular seal 39 having the configuration shown in figures 4 and 5. Figure 4 shows the seal cross-section in an unpressurised condition prior to fitting into an actuator of the form shown in figure 1 and figure 5 shows the seal when fitted in its operational position ahead of piston 12. As can be seen from figures 4 and 5 the seal 39 in accordance with the present invention has a pair of sealing lips 40 and a pair of sealing lobes 41 whose functions are the same as the lips 30 and 31 previously described with reference to seal 11. The rear seal face 42 in the vicinity of the lobes 41 slopes away from the support surface 12a of the piston towards the working chamber 16 at an acute angle θ which is typically of the order of 40 degrees and the contact point P2 of the lobes 41 and bore 13 is further away from support surface 12a that the contact point PI (see figure 2) of the previous seal 11. By relieving the rear face 42 of the seal 39 in the manner described above when the seal is pressurised by the fluid in working chamber 16 it tends to adopt the dotted line configuration shown in figure 5 and indicated at 42a in which the rear face 42a of the seal no longer extends beyond the support face 12a of the piston and is not extruded into the clearance 'x' between the piston 12 and the bore 13. The present invention thus overcomes the problem of seal extrusion without the added cost of the use of an anti-extrusion ring behind the seal.

The seal 39 can be moulded in a three part mould (see figure 6) with the mould having three mould portions X, Y and Z. Mould portions X and Y and X and Z separate at sharp corners 43 and 44 of the seal to avoid problems of ridges formed in the seal due to moulding flash. The separation of mould portions Z and Y is arranged to occur along the outer angled portion 42 of the rear face so that the moulding flash ridge 42b which is formed at this mould portion separation has no effect on the operation of the seal as it is on a non sealing surface of the seal. Alternatively the separation between mould portions Z and Y may be in the plane of the lower surface of the seal as viewed in figure 6.

Although the invention has been described above in relation to an annular concentric slave cylinder it is equally applicable, as shown in figure 7, to a conventional cylindrical type actuator in which a cylindrical piston 50 slides up and down within a cylindrical bore 51 and the annular seal 52 seals the contact between the piston and the cylindrical bore. Again in this application the cut-away rear face of the seal of the present invention prevents extrusion of the seal into the clearance x between the piston 50 and the bore 51. Also the invention is applicable to single lip and lobe seals, as shown for example in figures 8 and 9, in which stationary seals 58 and 59 housed in grooves 57 and 56 respectively each having a single lip 60 and lobe 61 which seal against an annular piston 62 which in turn operates release bearing 20 via bearing support 19 as described above. As will be appreciated seals 58 and 59 are in effect half of the twin lip and lobe seal 39 described above.

The present invention thus provides a seal construction which mitigates the problem of seal lobe extrusion discussed above.

Claims

1. An annular seal of the kind described in which, in the unpressurised condition, in the vicinity of the lobe portion the rear face of the seal slopes away from the support face towards the working chamber so that when the seal is pressurised the rear face is not forced past the support surface into the clearance between the piston and bore.

2. A seal according to claim 1 of the twin lip and lobe type used to seal an annular piston to inner and outer walls of an annular bore or to seal a cylindrical piston within a cylindrical bore.

3. A seal according to claim 1 of the single lip and lobe type in which the seal is held captive in the walls of an annular or cylindrical bore to seal against a moving annular or cylindrical piston or is held in a recess in a moving piston for sealing with a mating bore.

4. A seal according to any one of claims 1 to 3 in which the angle of slope of the rear face is of the order of 40 degrees.

5. A seal according to any one of claims 1 to 4 produced by moulding in which mould separation lines are located on the rear sloping face of the seal to minimise their effect on sealing.

6. A hydraulic actuator fitted with an annular seal in accordance with any one of claims l to 5.

7. An annular seal of the kind described constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1, 4, 5 and 6 or Figure 7 or Figures 8 and 9 of the accompanying drawings.