The invention relates to a master cylinder assembly and is particularly but not exclusively concerned with a master cylinder assembly for use in a vehicle.

Master cylinders are in wide use in the motor vehicle industry wherein they serve in conjunction with an associated slave cylinder to control various systems of the motor vehicle. For example, the clutches of manual transmission vehicles and the vehicle brakes are often actuated by respective cylinders receiving pressure fluid from associated master cylinders actuated by a clutch or brake pedal of the vehicle. In both cases the master cylinder is directly and manually actuated by the vehicle operator by suitable actuation of the associated control pedal of the vehicle. Whereas manual actuation of a master cylinder is effective to produce the desired resultant action at the associated slave cylinder, there are situations where it is desirable to provide power operation of the master cylinder.

In EP-A-0223 358 there is described a motor driven actuator for use in a hydraulic circuit of an anti- lock braking system of a vehicle. The actuator includes an assembly comprising a motor and a cylinder, the motor being arranged to effect axial

movement of a piston in the cylinder through a drive transmission. The motor is arranged alongside the cylinder and whilst the length of the assembly is reduced as a result of mounting the motor in that way, the width of the assembly is increased which can be disadvantageous.

An object of the present invention is to provide an improved and more compact master cylinder assembly which is particularly suitable for use in engaging and disengaging a clutch of a manual transmission vehicle.

According to the invention there is provided a master cylinder assembly comprising a hydraulic actuator cylinder, a piston arranged in the cylinder and dividing the cylinder into primary and secondary chambers which, in use, are occupied by hydraulic fluid, a motor for effecting relative movement between the piston and cylinder through a drive transmission at least a part of which drive transmission is arranged within the secondary chamber.

The positioning of at least part of the drive transmission within the secondary chamber provides a particularly compact assembly. The arrangement

according to the invention is also particularly advantageous over that described in EP-A-0223 358 as the transmission part (or parts) in the secondary chamber will, in use, be immersed in the hydraulic fluid which will provide continuous lubrication for the immersed part or parts.

Preferably the drive transmission includes a member which sealing extends through a secondary chamber seal for inhibiting escape of hydraulic fluid from the secondary chamber.

The member may be an intermediate member between the piston and a drive output shaft of the motor. The intermediate member may transmit drive to another transmission part through a pin, spline, key or the like. The intermediate member may be held drivably fast with the drive output shaft by means of a further pin, spline, key or the like.

The transmission may be rotatably mounted within a journal bearing carried by the cylinder within the secondary chamber.

Preferably, the motor, which may be an electrically powered motor, has its drive output shaft coaxial with the piston. Such an arrangement leads to

further a compact form of actuator.

The cylinder may include an elongate housing with the motor mounted on one end of the housing.

The relative movement is preferably effected by means of a ballscrew which comprises the aforesaid part of the transmission arranged in the secondary chamber.

An anti-rotation means may be provided to prevent relative rotation between the piston and the cylinder during operation of the motor. Conveniently, the anti-rotation means may extend between the piston and cylinder and may include a pin and slot arrangement where, e.g., the pin travels along ^' a slot extending in the direction of relative movement between the piston and cylinder.

Preferably a sensor is provided to sense said relative movement between the piston and cylinder. The sensor, e.g., a potentiometer, may be arranged to sense the position of a.projection associated with the piston. Where the aforesaid anti-rotation means is provided, the projection can conveniently form part of the anti-rotation means. For example where the anti-rotation means includes a pin, the pin may also serve to operate the sensor. The sensor may

include an arm, movement of which rotates an operative element of the sensor, which arm is co- operable with said projection. By using a pin as mentioned above, the pin may simply locate in a slot in the arm so that movement of the pin in a direction axially of the piston and cylinder causes the arm to rotate.

A master cylinder assembly in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

Fig.1 is a longitudinal cross-section through a motor and master cylinder for use in a clutch release system of a motor vehicle, and

Fig.2 is a plan view of the master cylinder of Fig.1 with the motor removed.

A master cylinder 9 has a housing 10 formed with first and second bores 12, 13. The housing is formed with a compensation port 14 towards the right-hand end of bore 12 as viewed in Fig.1 and with an outlet bore 15. The bore 15 receives a hose fitting 16 to which one end of a hose 17 is connected. The opposite end of the hose 17 communicates with a slave cylinder

(not shown). The compensation port 14 communicates with a chamber 18 defined between the housing 10 and a mounting 19 bolted to the housing 10. The mounting 19 carries a rotary potentiometer 20 described below and the chamber 18 communicates with a remote reservoir (not shown) via a hose 22. The cylinder housing 10 is formed with a linear slot 23 in a wall thereof which slot extends in the axial direction of bore 13. The right hand end of the cylinder housing 10 supports a journal bearing 24 and is axially fast with an adaptor 25 which locates spigotally in the bore 13.

A piston 26 is slidably mounted in the housing 10 so as to divide the cylinder into a primary chamber 27 and a secondary chamber 28. A primary seal 29 is provided on a cylindrical extension of the piston 26. The piston is normally biased into the position shown by means of a return spring 32 acting between the left hand end of bore 12 and a washer 33 in abutment with the extension 30. The piston 26 has a number of recuperation ports 34 therein and has a hollow cylindrical section 35 which carries a radially extending pin 36. The pin 36 is screwed to the piston and secured in position by a lock nut 37. The pin carries a rotatable roller 38 which is held in position by a nut arrangement 31. The roller 38 can

roll with close working clearance along slot 23 as described below. The cylindrical section 35 threadedly supports a ball holder or ball nut 39 of a ballscrew transmission 40, the latter including a screw 42 having a section 42a formed as a fast helix. The ball holder 39 is locked in position by a grub- screw 41 on the piston 26. The right-hand end of the ball holder 39 abuts an intermediate drive transmission member 43 which is mounted in the bearing 24. The abutment between the ball holder 39 and the intermediate transmission member 43 limits the rightward movement of the piston 26 under the influence of the return spring 32. The intermediate transmission member 43 is rotatably locked to the screw 42 by a diametrical pin 44 which includes a shank portion 45 which extends sealingly through a secondary chamber seal 46 carried by the adaptor 25. The intermediate transmission member 43 is drivably connected by means of a sleeve 47 to a drive output shaft 48 of an electric D.C. motor 49. The sleeve 47 is splined to the intermediate transmission member 43 and has a transverse member 50 which locates in a drive slot 52 in the output shaft 48. The motor 49 has a casing 53 bolted to the adaptor 25.

As mentioned above, a rotary potentiometer 20 is provided. The potentiometer 20 has a spindle 54

which is rotatably fast with a radial arm 55. The arm 55 is formed with a slot 56 (as shown clearly in Fig.2) which receives the upper end of pin 36.

In use, the chambers 18, 27, 28 and all fluid receiving pipes and ports are filled with hydraulic fluid and bled of air. In that way, the components of ballscrew transmission 40 are immersed in the hydraulic fluid along with the journal bearing 24.

On receiving a signal from an external control system, the motor 49 drives its output shaft 48 so as to rotate the screw 42 and advance the piston 26 to the left. The compensation port 14 then becomes sealed off from a primary chamber 27 and hydraulic fluid is forced along the pipe 17 to release the clutch. Rotation of the piston 26 as a result of rotation by the screw 42 is prevented by the pin 36 and roller 38, the latter rolling along slot 23 as the piston moves axially. Such movement of the piston also causes the pin 36 to move the arm 55 of the potentiometer 20 thereby rotating the spindle 54. The potentiometer 20 is wired into a circuit which provides a feedback to the external control system indicating the axial position of the piston. In that way it is possible to effect a finely controlled disengagement/re-engagement of the clutch.

To re-engage the clutch, the piston 26 is allowed to return towards the right under the influence of the clutch spring and return spring 32. Return movement of the piston causes the screw 42 to rotate in the ball holder 39 thereby rotating the motor drive output shaft 48. The motor 49 is left either to free-run to permit continuous axial return movement of the piston or to free-run intermittently through signals received from the external control system to effect a controlled clutch re-engagement.

Alternatively the motor 49 may be driven in a reverse sense so that the piston 26 is moved to the right to permit re-engagement of the clutch.

The master cylinder assembly described is advantageous in that the hydraulic fluid provides a certain amount to lubrication both for the ballscrew transmission 40 and the bearing 24. Moreover the mounting of the motor 49 on one end of the housing 10 with its shaft 48 coaxial with the piston 26 provides a compact assembly which can be positioned in relatively small spaces.

Whilst specific reference has been made to the use of the master cylinder assembly for clutch actuation, it

could be used to actuate slave cylinders of a vehicle braking system.