HYDRAULIC APPARATUS

The invention relates to hydraulic apparatus and is particularly, but not exclusively, concerned with hydraulic apparatus for operating a friction clutch in a vehicle.

Space is normally at a premium in the engine compartment of a motor vehicle and it is highly desirable, where possible, to keep the size of components to a minimum so as to take up as little space as possible.

Hitherto, it has been common to provide a master cylinder, say for operating a clutch of the vehicle, with a reservoir which is either in the form of a body built in to the master cylinder and which extends transversely therefrom over a substantial distance or is in the form of a remotely located container connected to the master cylinder by a conduit. In the former case, it is necessary to provide sufficient room around the master cylinder to accommodate the transversely extending reservoir. In the latter case, it is necessary to provide sufficient room to locate the remote reservoir.

In GB-A-559,891 a reservoir is formed within a piston ^' of a master cylinder and whilst the arrangement is reasonably compact the capacity of the reservoir is somewhat restricted.

In EF-A-0142290 a reservoir is formed in an elongate extension of a master cylinder. Whilst such an arrangement provides a radially compact arrangement the master cylinder is lengthened considerably which can be a problem where space is at a premium.

An object of the present invention is to provide an improved form of hydraulic apparatus having a built in reservoir which will reduce the foregoing problem.

According to one aspect of the invention there is provided hydraulic piston movable in the cyli'nder a pressure chamber in the cylinder which is placed under pressure by movement of the piston in one direction in the cylinder, and a reservoir in an axially extending bore in the piston for supplying the pressure chamber with hydraulic fluid, characterised in that the reservoir is formed partly in said axially extending bore in the piston and partly in the cylinder into which the axially

extending bore opens.

In that way, not only is the use of a body which projects transversely from the cylinder for a substantial distance avoided, but the reservoir extends into both the piston and the cylinder giving optimum capacity with minimal axial length.

Capacity can be increased further by making full use of the piston length so that the bore is elongated and extends through a part of or a part associated with the piston which, in use, projects out of the cylinder. Conveniently, operating force may be applied to said part of the piston by means such as a clutch pedal.

The pressure chamber may be annular so as to extend around a part of the piston in which the axially extending bore is formed.

Preferably, the reservoir extends around the axis of the cylinder, e.g., coaxial therewith.

Preferably, the pressure chamber is defined between an outer wall of the cylinder and an inner wall of the cylinder coaxial with the outer wall. The inner wall may define a bore in which the part of

the piston housing the axially extending bore therein is slidable. The piston may include an annular portion which is slidable between the coaxial inner and outer walls of the cylinder.

A flexible diaphragm preferably extends into the reservoir and may be of the extendable bellows type. The diaphragm may extend axially of the reservoir. The diaphragm preferably separates fluid in the reservoir from ambient air which may communicate with an air space to one side of the diaphragm via means such as a vent. Preferably part of the diaphragm may extend into the bore of the piston. In such a case, that part of the diaphragm which extends into the bore of the piston may be of small cross-section than the remaining part of the diaphragm.

The invention also includes hydraulic apparatus including a piston movable in a cylinder, a pressure chamber in the cylinder which is placed under pressure by movement of the piston in one direction in the cylinder, and a reservoir for supplying the pressure chamber with hydraulic fluid, substantially the whole of said reservoir being arranged adjacent the axis of said cylinder with a flexible diaphragm extending therein to

separate fluid from ambient air. Preferably, the piston and/or the cylinder is formed with a passage to enable fluid to pass from the reservoir to the pressure chamber. The passage may comprise a groove and may extend axially of the cylinder. Preferably, the passage is opened by the piston when the piston approaches a rest position.

The piston may be movable from a rest position by an external force such as a clutch pedal and movable in the opposite direction by bias means such as a spring.

Stop means may be provided for defining the rest position for the piston. The stop means may be carried by part of the piston and may be in the form of a ring-like member located, say, in a peripheral groove on said part of the piston. The ring-like member may snap fit on the piston, e.g., in the groove. The ring-like member may include sprags to effect such snap fitting. Sprags may be conveniently formed by punching or stamping the material of the ^* stop means.

In a preferred embodiment, the apparatus is in the form of a master cylinder and the pressure chamber is connected to a slave cylinder, the slave

cylinder including a chamber defined between inner and outer walls of a cylinder for receiving fluid from the master cylinder, a piston movable in the cylinder for driving an operating member of the slave cylinder, and bias means which is arranged normally to provide an axial bias to the output member in the direction in which operating force is applied to the operating member by the piston.

According to a further aspect of the invention there is provided hydraulic apparatus including a cylinder, a piston movable in the cylinder, an operating member forming part of or being associated with the piston and bias means which is arranged normally to provide an axial bias to the operating member, characterised in that the cylinder defines an annular chamber for fluid defined between inner and outer walls of the cylinder, the piston being annular and slidable in said chamber and the axial bias is applied either in he direction in which operating force is applied to the operating member by the piston or in a direction opposite to the direction in which operating force is applied by the operating member to the piston.

The bias means preferably acts against the piston and may react against part of the cylinder. The part of the cylinder against which the bias means reacts is preferably part of said inner wall of the cylinder.

The inner wall may be defined by a tubular extension. Part of the piston or an operating member associated therewith preferably passes axially through said tubular extension. The tubular extension preferably passes axially through part of the piston and may slidably support the piston. An abutment member may be interposed between the tubular extension and the bias means. The abutment member may be sleeve like including a location portion which locates inside the tubular extension. Where the abutment member is sleeve like, it may include a support portion, said support portion and bias means being positioned one within the other to support one end of the bias means. Where the location and the support portions are provided, they may be separated by a shoulder which abuts the said tubular extension.

The piston may be conveniently of substantially U- • shaped cross-section.

One end of the piston, may be formed with a surface against which a complementary surface of the output member or a member in abutment therewith can slide to enable the output member to tilt during operation of the slave cylinder.

The said surface of the piston may be concave and the surface of the output member convex. The interengaging surfaces of the piston and push rod or the member associated therewith may be adjacent an end of the operating member remote from an opposite end which projects axially out of the cylinder.

The apparatus may be in the form of a master or slave cylinder. In the former case, the master cylinder may include means for enabling the annular chamber to communicate with a reservoir of hydraulic fluid when the piston occupies a rest position in the cylinder. In the former case the cylinder may include means for enabling the annular chamber to communicate with a master cylinder.

Apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:-

Fig l.is a cross-sec ion through a master cylinder and slave cylinder arrangement for operating a friction clutch of a vehicle. The cross-section through each cylinder being divided into upper and lower halves showing working and rest positions of the pistons of the cylinders.

Fig.2 is an end elevation of the piston of the slave cylinder looking in the direction of arrow III in Fig.1 , and

Fig.3 is a cross-section through an alternative form of master cylinder in accordance with the invention.

The master cylinder 10 comprises a cylinder 11 having a closure 12 secured within its right-hand end as viewed in Fig.1. The closure 12 is formed with a vent 13 and is integral with a mounting member 14 which pivotally locates on a ball-like mounting 15 in ball and socket manner. The cylinder is formed with an outlet port 16 which opens into a socket 17 defined by an annular radial projections 18. A sealing ring 20 is located in a groove 21 at the bottom of the socket 17.

The cylinαer houses a piston 19 which includes a part 119 extending out of the left-hand end of the- cylinder 11 and sealingly engages a seal 20. The piston has a relatively larger diameter right-hand end which supports a seal 22 sealingly engaging the internal surface of the cylinder 11. An annular stop member 23 engages a shoulder 24 on the piston and serves to locate one end of a compression spring 25 the other end of which engages a ring¬ like member 26 which abuts a shoulder ^' 27 on the cylinder 11. The spring 25 normally biases the piston 19 into the position shown in the upper half of the master cylinder cross-section known herein as the rest position.

The rest position is dictated by stop member 28 carried by the piston 19. The stop member 28 comprises an annular ring of metal which is punched to define one or more inwardly projecting sprags 29. The or each sprag snaps resiliently into a groove 30 formed in the piston. The stop member 28 has a right-hand annular end surface 32 which, in the rest position of the piston, abuts the left- hand end of the cylinder 11.

It will be noted that the piston 19 is annular so as to define an elongated internal bore 33

extending through part 119 and terminating at a blind left-hand end 34. The bore 33 opens at its right hand end into the cylinder 11. The closure member 12 has a peripheral groove 35 therein in which is located a bead-like end section 36 of a bellows diaphragm 37 which sealingly engages the groove and the adjacent internal surface of a portion 11a of cylinder 11. The bellows diaphragm includes a first section 38 which fits closely within the portion 11a and a relatively smaller diameter second section 39 which fits within the bore 33 of the piston 19. The bellows diaphragm 37 has a closed left-hand end 40. The vent 13 communicates between the interior of the diaphragm 37 and the ambient air.

It will be noted that the portion 11a is formed with a number of axial grooves 42 one of which 42a extends axially along the cylinder 11 and terminates immediately in front of the seal 22 when the piston 19 occupies its rest position. It will also be noted that recesses 33a in the piston 19 provide clearances C between the bore 33 in the piston and the outer periphery of the second section 39 of the bellows diaphragm.

The part 119 of the piston 19 passes sealingly through a seal 41 on the cylinder 11 and is formed with a ball and socket connection 43 for a member 44 such as a clutch pedal. A bellows seal 31 is arranged between the cylinder 11 and stop member 28.

The master cylinder 10 is connected to the slave cylinder (indicated generally at 45) by means of a flexible conduit 46. The conduit 46 has one end section 47 positioned within the socket 17 and retained therein by a sleeve-like fitting 48. An identical retaining arrangement is provided for the conduit 46 at the slave cylinder end.

The slave cylinder 45 comprises a cylinder 45a having an outer cylinder wall 54 formed with a port 56 and having its right-hand end closed by means of a snap-fit cover 57. The cylinder has a coaxially extending tube 58 integral there with which terminates at an end surface 59 substantially mid¬ way along the cylinder. The slave cylinder 54 has a support section 60 by means of which the slave cylinder can be mounted on a member 62 and retained thereon by a snap ring 63.

An annular piston 64 is slidable on the tube 58 and has a radial flange 65 at its left-hand end in abutment with a four point seal 65a which sealingly engages the inner periphery of the cylinder outer wall 54 and the outer periphery of the inner wall 58. As shown in Fig.3, the piston 58 is generally cylindrical and has a plurality coaxially extending ribs 66. The right-hand end of the piston 64 is formed with a concave spherical surface 67 which slidably engages a convex spherical surface 68 at the right-hand end of an operating rod 69. The right-hand end of the piston is formed with an inwardly extending flange 70 which engages one end of a compression spring 72. The opposite end of the spring 72 engages an annular shoulder 73 of an abutment member 74. The abutment member 74 has a cylindrical location section 75 which locates inside the tube 58 and a support section 76 which extends into and supports the spring 72. The spring normally applies a bias to the piston 64 so as to urge the surfaces 67, 68 together.

The operating rod 69 projects out of the left-hand end of the slave cylinder and engages a bellows seal 77. The extreme left-hand end of the operating rod, in the embodiment shown, is secured by means of a locking member 79 to fingers 80 of a

diaphragm spring of a friction clutch. The fingers 80 normally occupy the position indicated at A so as normally to position the piston in the position shown in the upper half of the slave cylinder cross-section. In that way, the spring 72 applies a bias to the pushrod in the direction in which the piston, in use, applies an operating load to the pushrod to release the clutch. Therefore, any axial play which would otherwise exist between the operating rod 69 and the clutch spring fingers 80 is taken up.

In use, the master cylinder 10, slave cylinder 45 and conduit 46 are filled with hydraulic fluid bled of air through a port 90.

In the master cylinder, the hydraulic fluid occupies a chamber 82 (constituting the aforesaid pressure chamber) between the seals 22 and 41, the bore 33 in the piston and the spaces between the outer periphery of the bellows diaphragm 37 and the adjacent surfaces of the piston 19 and the of the cylinder 11. In that way, the bore 33 and the space around the second section 39 of the bellows diaphragm within bore 33 and the space around the first section 38 of the bellows diaphragm within the cylinder 11 and the extension 11a together form

a reservoir 83 for the hydraulic fluid which can pass from the reservoir to the chamber 82 through the groove 42 as described below. As the reservoir is defined by both the cylinder 11 and the piston 10 it can have considerable capacity without an appreciate increase in axial or radial dimension of the master cylinder.

In the slave cylinder 45, hydraulic fluid occupies an annular chamber 84 between the seal 65a, the cylinder wall 54 and the tube 58 defining the inner cylinder wall.

When an axial force is applied to the piston 19 of the master cylinder by the member 44, the piston moves towards the position shown in the lower half of the master cylinder cross-section. The seal 22 immediately closes the groove 42a so that fluid from the reservoir 83 cannot pass between the chamber 82 and the reservoir. Movement of the piston 19 to the left expels fluid from chamber 82, through the conduit 46 and into the chamber 84 of the slave cylinder 45 thereby urging the piston 64 towards the position shown in the lower half of the slave cylinder cross-section. Such movement of the piston 64 urges the operating rod 69 to the right thereby applying a force to the fingers 80 of the

diaphragm spring ^* to release the clutch.

When the force applied by the member 44 is relieved, the load applied to the operating member 69 by the fingers 80 urges the piston 64 of the master cylinder back towards its position shown in the upper half of the slave cylinder cross-section and fluid is expelled from chamber 84 into chamber 82. The incoming fluid and the load applied by spring 25 urges the piston 19 back towards its rest position until the stop 28 engages the end surface of the cylinder 11. At that position the seal 22 uncovers the left-hand end of the groove 42 to allow fluid to communicate between the reservoir 83 and the chamber 82, e.g., as clutch wear occurs.

It will be noted from the cross-section through the master cylinder, that the bellows diaphragm 37 extends and contracts during operation of the master cylinder, air being drawn in and expelled through the vent 13 during such movement of the diaphragm. It will also be noted that the stop member 23 engages the ring-like member 26 to limit the travel of the piston 19 to the left.

The clearance C permit fluid within the bore 33 to pass between the second and smaller section 39 of

the bellows diaphragm 37 and the piston.

As shown in Fig.1, the portion 11a (which extends rightwards from a position adjacent the right-hand end of the piston in the rest position) is integral with the cylinder 11 although* it could be a . separate secured thereto.

The master cylinder arrangement described above is particularly advantageous as the reservoir is coaxial with axis X of the cylinder does not require the provision of a large radially projecting container as is common place with prior art devices. With the reservoir being arranged adjacent the axis of the cylinder 11 the master cylinder 10 is particularly compact and ideal for use where there is very little space available in the vehicle.

The slave cylinder described above is also particularly advantageous not only in the provision of the spring 72 for taking up any free play but also in the way in which the interengaging curved surfaces will permit tilting of the operating member 69 relative to the cylinder 54 when in use. Also, the slave cylinder arrangement places the seal 65a well away from the left hand end of the

slave cylinder and, therefore, at substantially the maximum distance from contaminants such as dirt and water should the later succeed in entering the cylinder. The piston is supported by the outer periphery of tube 58 which engages the inner periphery of the piston.

If desired, the slave cylinder 45 can be modified so as to take the form of a master cylinder. In that case, the port 56 will comprise an outlet port for fluid when the piston 64 is moved to the left by applying an axial force to the operating member 69 by means, say, a clutch pedal. Also, the cylinder 54 will be formed with a port 90 (shown in broken lines) in communication with a reservoir (not shown) and which will be closed by the seal 65a at the onset of piston movement. The cylinder 54 will also be provided with a further port 91 (broken lines) for communication with the reservoir and through which fluid will be drawn during movement of the piston 64 to the left. Where the cylinder 45 takes the form of a master cylinder, the spring 72 will apply a bias to the piston 64 in a direction opposite to the direction in which load is applied to the piston by the operating member 69. Preferably, a sealing ring (not shown) will be located between the snap-fit cover 57 and the

cylinder 45a to seal against .ingress of foreign matter and escape of fluid. Also the bellows seal 7.7 and remaining space around operating member 69 within piston 64 may be filled with hydraulic fluid.

Fig.3 illustrates an alternative form of the master cylinder to that shown in Fig.1. In Fig.3 the piston, cylinder, diaphragm and other parts which correspond to parts shown in Fig.1 carry the same reference numerals followed by a dash. The master cylinder 10' comprises a cylinder 11' having an outer cylindrical wall 100 formed with a port 16' at its left hand end. The cylinder has a coaxially extending tube 103 therein which terminates at an end surface 104 part way along the cylinder. The tube 103 defines an inner wall and the outer an inner walls 100, 103 together define an annular pressure chamber 82' therebetween. The tube 103 has a bore 103a.

A piston 19' includes an annular portion 19a slidable between the inner and outer walls through the chamber 82' and has a seal 22' at its left hand end. The piston includes a coaxial tubular part 119' which passes coaxially through bore 103a and projects out of the cylinder. A suitable seal (not

shown) may be provided between the tube 103 and a part 119' of the piston 19'. The left hand end of the part 119' extends out of the cylinder and is formed with a ball and socket connection 43-' for a member 44' as in Fig.1. A return spring 25* may be located between the piston 19' and the end face 104 or may be arranged in an alternative position to apply a return bias to the piston 19'.

The right hand end of the cylinder 11* includes the closure member 12' as in Fig=1 which is suitably retained axially in position by, e.g., a screw 110. As in Fig.1, the closure 12' has a peripheral groove 35' in which is located a bead-like end section 36' of a bellows diaphragm 37' which sealingly engages the groove and the adjacent internal surface of the cylinder 11'. As in Fig.1, the bellows diaphragm includes a first section 38' which lies within the cylinder 11' and a relatively smaller diameter second section 39' which fits within a bore 33' of the piston 19'. The closure 12 is formed with a vent 13' and is integral with a ball mounting member 14' which pivotally locates on a ball-like mounting 15* in ball socket manner.

In use, the master cylinder 10', associated slave cylinder and interconnecting conduit are filled

with ny rauiic fluid bled of air. In the master cylinder 10', the hydraulic fluid occupies chamber 82' in front of the piston 19' and the spaces between the outer periphery of the bellows diaphragm 37' and the adjacent surfaces of the piston 19' and the cylinder 11'. In that way, the bore 33', the space around he second section 39' of the bellows diaphragm 37' within the bore 33' and the space around the first section 38' of the bellows diaphragm within the cylinder 11' together form a reservoir 83' for the hydraulic fluid which can pass from the reservoir to the chamber 82' through a groove 42'.

When an axial force is applied to the piston 19' by the member 44', the piston moves to the left and the seal 22' immediately closes the groove 112 so that fluid from the reservoir 83' cannot pass between the chamber 82' and the reservoir. Movement of the piston 19' to the left expels fluid from the chamber 82' through the port 16' to the slave cylinder. As in the lower half of Fig.1, the bellows diaphragm 37' expands axially during such movement of the piston, air being drawn in through vent 13'. When the force applied by the member 44* is relieved, the piston moves back towards the position shown in Fig.3 until the seal 22' uncovers

tiie left hand end of the groove 42' to allow fluid to communicate between the reservoir 83' and the chamber 82', e.g., as clutch wear occurs. A suitable stop (not shown in Fig.3) may be provided for limiting the movement of piston 19' towards the right.

The master cylinder 10 is also advantageous in that the cylinder 11 may be formed from plastics with no bosses formed on the cylinder 11 over the working stroke of seal 22, the radial projection 18 being disposed to the left of the seal 22 when the piston occupies its full travel position shown in the lower half of the master cylinder cross-section. The slave cylinder of Fig.1 and master cylinder of Fig.3 may also be formed from plastics.

The master cylinder 10, slave cylinder 45 and conduit 46 may be pre-filled with hydraulic fluid as an assembly.