GB2264546A

GB2264546A - A hydraulic servomotor.

Info

Publication number: GB2264546A
Application number: GB9204087A
Authority: GB
Inventors: Maurice John Wimbush
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1992-02-26
Filing date: 1992-02-26
Publication date: 1993-09-01
Anticipated expiration: 2012-02-26
Also published as: GB9204087D0; GB2264546B

Abstract

A hydraulic clutch servo motor (10) having a housing (21) with a slave cylinder (50) formed from a stepped bore (50) with two pistons (52, 54) therein. The smaller piston (52) is connected to a master cylinder (11) and the larger piston (54) acts on the clutch push rod (13) and is connected to a hydraulic pump through valves (23A, 43). The hydraulic pump pressure exerts an auxiliary clutch operating load on the large piston (54) in a controlled manner determined by a pumped fluid flow restrictor (58) which is throttled by movement of the smaller piston (52) towards the larger piston (54) as determined by the master cylinder pressure. <IMAGE>

Description

A HYDRAULIC SERVOMOTOR This invention relates to hydraulic servomotors for use with motor vehicle clutch hydraulic actuation systems.

In particular the servomotor may utilise a pumped fluid supply which already exists on a vehicle for the operation of a power steering system.

Accordingly there is provided a hydraulic servomotor for a clutch hydraulic actuator system, said servo motor having a housing with a slave cylinder therein Eormed from a stepped bore having a pair of in-series different diameter slave pistons arranged therein, the smaller diameter slave piston being operable by a master cylinder generated fluid pressure, and the larger diameter slave cylinder piston being operably connected to a clutch, the two pistons being biased apart but being abutable through reduced diameter end portions and having adjacent opposed annular faces that are connectable to a supply of puniped hydraulic fluid, the pumped fluid supply being constantly open to drain through a flow restriction, said flow restriction being throttled in use by movement of the smaller diameter slave cyl inder piston towards the other larger diameter sl ave piston to cause a bui l d up of fluid pressure acting on the differential areas of the opposed annular faces of the to pistons * to generate an auxiliary load for operation of the clutch.

The invention will he described by way of example and with reference to the accompanying drawings in whi.ch: Fig 1 is a longitudinal section through a first embodiment of the invention and Pig 2 is a graph of hydraulic pressure Vs clutch pedal travel during operation of the servo motor of Fig 1.

Fig 3 is a longitudinal section through a second embodiment of the invention.

The invention relates to clutch hydraulic servo motor having an in-built "spli.tter" valve which can direct the flow of hydraulic fluid in a motor vehicle power steering system for use in operation of a hydraulic clutch control system. The servo motor 10 is connected to a clutch hydraulic master cylinder 11 by a conduit 12. The servomotor 10 operates a clutch (not shown) through an output rod 13.

The servo motor 10 comprises a housing 21 having three parallel bores therein, a first bore 22 housing a preference valve 23, a second bore 30 housing a series of shut off valves 31, 32, 33, and a third bore 50 forming a slave cylinder including two in-seris slave cylinder pistons 52, and 54, the piston 52 being operably connected to the output rod 13, and the piston 54 being operably connected to the master cylinder 11.

The hydraulic power supply enters the housing 21 through an inlet port 26, which in turn is connected to a auxiliary power system, preferably a steering system via an outlet port 27 from the first bore 23.

The inlet port 26 is connected via passageway 34 to one end of the second bore 30, the other end of the bore 30 being connected to drain via outlet 44. The shut-off valves 31, 32, 33, are interconnected by a stem 36 for si.multaneous operation. The valves are biased rightwards (as shown) by a spring 37 acting between said other ond of the bore 30 and a spring end cap 38 which abuts the ball valve 31. The ball valve 31 is biased into a closed condition against a valve seat 41 and the ball valve 32 and 33 are biased into an open condition lifted from their respective valve seats 42 and 43.

The preference valve 23 includes a piston 23a that divides the first bore 22 into a pressure chamber 24 receiving the fluid from the hydraulic power supply pump, and a drain chamber 25 at the reverse side of the piston 23a. The drain chamber 25 is connected to the second bore 30 at a location between the valve seats 41 and 42.

The third bore 50 is a stepped diameter slave cylinder bore having a larger diameter portion 51 housing the slave cylinder outlet piston 52, and a smaller diameter portion 53 which is connected to the clutch master cylinder 11. The smaller diameter portion 53 of the bore 50 houses the spool shaped slave piston 54 having one end face 55 exposed to hydraulic pressure from the master cylinder, and its other end an annular end face 56 exposed to pressure in the annular chamber 63 between the two pistons 54 and 52, and a reduced diameter portion with a frusto-conical valve face 57 thereon that cooperates with a like frusto-conical surface 58 on the adjacent end face of the output piston 52.In an "at-rcs" condition these two surfaces 57, 58 are spaced apart because the two pistons 54 and 52 are biased apart by springs 60, 61, the larger spring 60 acting between the annular end face 56 of piston 54 and the exposed annular end face 66 of the piston 52.

The third bore 50 is connected to the drain via said other end of the second bore 30 through passageway 71 which is located midway along the length of the smaller diameter portion 53 of the bore 50, and opens into the bore 50 between the two seals of the spool piston 54.

The annular chamber 63 between the two piston 52,54 is connected to the second bore 30 by passageway 72 that opens into the second bore between the valve seats 42 and 43.

The piston 54 has a diametrical passageway 74 and an axial. passageway 75 therein that connect the passageway 71 to the frusto-conical end surface 57 of the piston 54.

The valve operates as follows: 1) In an "at-rest" condition hydraulic fluid from the pump circulates through the inlet port 26 into the pressure chamber 24, moving the preference valve piston 23A against the bias of the spring 28, and exits through the outlet port 27.

The spring 28 has a low spring rating and the small back pressure causes fluid to pass through the passageway 34, into the second bore 30, through the valve seat 43 and because the valve 41 is closed, through the passageway 72 and into the annular chamber 63 of the third bore 50. The fluid then passes through the gap between surfaces 57, 58 on the two pistons 54, 52 respectively, through the passageways 75, 74 in the piston 54, through passageway 71 into the said other end of the second bore and to drain via passageway 44.

Fluid will also feed through the valve seat 42 and passageway 35 into the chamber 25 on the reverse side of the preference valve piston 23A.

2) When the clutch pedal is operated the hydraulic pressure Pm acting on the end face 55 of area Al of the piston 54 causes the piston 54 to move axially towards the piston 52, throttling the gap between the surfaces 57, 58. This causes a pressure build up in pressure chamber 24 to a pressure Ps.

The pressure Ps also acts on the reverse side of the preference valve piston 23A so that the spring 28 causes the piston 23A to move rightwards and slightly throttle. the outlet 27 to the steering system and direct a percentage of the pumped fluid supply to the slave cylinder 50.

The pressure Ps will act on the annular end faces 56, 66 of the two pistons 54, and 52 respectively.

If the area of the annular end face 56 is A2 and the area of the larger diameter end face 66 is A3 the PM x Al = Ps A2 with piston 54 held in position dictated by the operation of the clutch pedal. Also if Ps A3 is sufficiently high the piston 52 will move rightwards to operate the clutch.

If a further manual load is applied to tlie clutch pedal the process will repeat itself until the pressure build up within the second and third bores 20,30 is sufficient to operate the clutch (see Fig 2 part A of the graph) The load in the spring 37 which maintains the ball valves 31, 32, 33 in position determines the li.miting pressure for the clutch servo motor.

When the pressure Ps reaches a limiting pressure PL at about 10 bar, the hall valve then moves leftvards to open the valve seat 41, and close the valves 32, 33 and on the valve seats 42, 43 respectively. This cuts the further supply of pressurized fluid to the space between tlie pistons 52 54, opens the drain chamber 25 of preference valve 23 to tank, allowing the spool valve to move leftwards and opening fully the outlet 27 to the steering valve.

The limiting pressure of 10 bar is such that the sum A3 x lOb greatly exceeds loads necessary for operation of the clutch. however the clutch can continue to operate by manually increasing the master cylinder pressure only. Part B of Fig 2.

3) When the clutch is released the pressure Pm will drop, the gap between the surfaces 57,58 will be increased and fluid will flow to tank dropping the pressure in the system.

It is calculated that the servometer will only require some 5% of the steering system pump volume, when fluid is diverted into the servomotor by the preference valve 23.

In the event of a pumped system failure the clutch release load can be applied normally by the piston 54 abutting directly against the piston 52 through the surface 57,58, and in the event of a clutch manual hydraulic failure the power system is isolated from the manual system.

Fig 3 illustrates a general embodiment of the invention in which basically the preference valve and the hall valve are combined as a single unit.

Only these changes will be described.

The preference valve 123 is located in a first bore 122 located coaxially of with an exi.t chamber 130. The first bore 122 is a blind bore separated From the exit chamber 130 by an end wall 120, and the bore 122 and exit chamber 130 are connected hy a coaxial passageway 135.

As before the preference valve 123 divides the first bore 122 into a pressure chamber 124 and a drain chamber 125. The pressure chamber 124 is connected to a fluid supply inlet 126, and to a fluid outlet 127, which is also connected to a power steering valve. The valve 123 has a coaxial stepped through bore 230 therein and a radial bore 172 which interconnects the through-bore 230 with an annular groove 185 in the radially outer surface of the preference valve 123.

The annular groove 185 communicate with a port 186 which opens into the annular chamber 63 between the pistons 52 and 54 in the third bore 50.

The exit chamber 130 is connected by a passageway 171 to the annular space between the seals on the spool slave piston 54 in the third bore 50. The exit chamber has an outlet 44 to tank and the passageway 135 between the exi t chamber 130 and the pressure chamber is closed by a ball valve 131 which is biased into closed position by a spring 37 and end cap 38.

The ball valve 131 is connected by a stem 136 to two other bail valves 132 and 133 located in the stepped bore 230 in the preference valve 123. The two ball valves 132, 133 cooperate with valve seats 142, 143 in the bore 230 so that when the ball valve 131 is closed (as shown) and the valves 132 and 133 are held open by the stem 136 which is a loose fit in the stepped bore 230 to allow for the flow of fl fli (I through said bore 230.

The valve operates in the manner previously described for tlic emi > odiment of Fig 2. The pumped fluid enters the inlet 126 and exits through outlet 127. The back pressure will cause fluid to bleed through the stepped bore 230 into the drain chamber 125 and fluid also enters the third bore via the radial passageway 172, groove 185, and port 186. The fluid will then flow through the gap between the pistons 52, 54 and through the piston 54, into the exit chamber 130 and out to tank via otitlet 44.

When the load is applied to the clutch pedal the sequence of events is as for the emhodiment of Fig 1.

Claims

l. A hydraulic servomotor for a clutch hydraulic actuator system, said servo motor having a housing with a slave cylinder therein formed from a stepped bore having a pair of in-series different diameter slave pistons arranged therein, the smaller diameter slave piston being operable by a master cylinder generated fluid pressure, and the larger diameter slave cylinder piston being operably connected to a clutch, the two pistons being biased apart hut being abutable through reduced diameter end portions and having adjacent opposed annular faces that are connectable to a suppl.y of pumped hydraulic fluid being constantly open to drain through a flow restriction, said flow restriction being throttled in use hy movement of the smaller diameter slave cylinder towards the other larger diameter slave piston to cause a build up of fluid pressure acting on the differential areas of the opposed annular faces of the two pistons, to generate an auxiliary load for operation of the clutch.
2. A Scrvomotor as claimed in Claim 1, wherein the pumped fluid supply is open to drain via a passageway passing through the smaller diameter slave piston, and the flow restriction is constituted by a gap between opposed surfaces on the adjacent end portions of the slave pistons.
3.: A servomotor as claimed in Claim 2 wherein said end faces are frustoconical surfaces.
4. A servomotor as claimed in any one of claims 1 to 3, wherein the supply of pumped hydraulic fluid is connected to the said annular faces in the slave pistons through a first shut-off valve which is biased into an open condition, the shut off valve closing said supply when the fluid pressure exceeds at predetermined value.
5. A servomotor as claimed in claim 4 and further including a preference valve having an inlet connectable to the pumped fluid supply and an outlet connectable to an auxiliary fluid powered system, the preference valve in use acting to throttle the flow of pumped fluid supply to the auxiliary system when said fluid restriction to drain is throttled in response to a master cylinder generated pressure.
6. A servomotor as claimed in claim 5, wherein the preference valve has a piston therein, one face of which is exposed to pumped supply pressure, and the reverse side of which is connected to the pressurized fluid through a second shut-off valve, and, the first shut-off valve is operably connected to the second shut-off valve which is also biased into a open condition to allow the supply of pressurized fluid to the reverse side of the preference valve piston, there being a third shut-off valve which is biased to a closed condition and which is operably connected to the first and second shut off valve so that when said first and second shut off valves close, the third shut off valve opens damping pumped fluid supply directly to drain, and also connecting the reverse side of the preference valve to drain.
7. A servomotor as claimed in claim 6 wherein the first and second shut off valves are arranged concentrically within the preference valve.
8. A hydraulic clutch actuation system including a master cylinder, with conduit connecting the master cylinder to the slave cylinder of a servomotor as claimed in any one of claims 1 to 7.
9. A motor vehicle having a power steering system and including a clutch actuation system as claimed in claim 8, wherein the pumped fluid supply for the power steering system is also utilised for operation of said servomotor.