GB2305477A

GB2305477A - Master cylinder

Info

Publication number: GB2305477A
Application number: GB9518615A
Authority: GB
Inventors: Jacques Loche
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1995-09-12
Filing date: 1995-09-12
Publication date: 1997-04-09
Anticipated expiration: 2015-09-12
Also published as: GB9518615D0; GB2305477B

Abstract

A master cylinder 10 comprises a housing 12 which is closed at one end 16; a piston 38 reciprocally movable relative to the housing to alter fluid pressure in a pressure chamber 42; a push rod 24 connected with the piston for manual operation of the master cylinder; a wall 28 positioned adjacent the closed end of the housing; and actuation means for moving the wall relative to the housing and the piston towards the piston to increase fluid pressure in the pressure chamber for example for traction control, cruise control, and will start. The wall may be moved by a hydraulic actuator 66 or by a screw (104, Fig.3) driven by an electric motor (102).

Description

MASTER CYLINDER The present invention relates to a master cylinder for the braking system of a motor vehicle.

A known hydraulic braking system in a motor vehicle includes a master cylinder comprising a tubular housing which is closed at one end. Slidably positioned within the housing is a pair of pistons which, with the housing, define a pair of pressure chambers. Movement of the pistons towards the closed end of the housing pressurises the fluid in the pressure chambers to cause the operation of the brakes.

Under normal operation, the movement of the pistons is caused by the vehicle driver pressing the brake pedal.

In motor vehicles which have traction control, cruise control, etc., the pistons may additionally be moved by an electronically control system which causes the exertion of fluid pressure behind the piston furthest from the closed end of the housing. This has the same effect as when the vehicle operator presses the brake pedal, and causes operation of the brakes. Examples of this known arrangement are described in WO-A-9422699 and GB-A-2224796.

It is an object of the present invention to provide an improvement to this known arrangement.

A master cylinder in accordance with the present invention comprises a housing which is substantially cylindrical and closed at one end; a piston reciprocally movable relative to the housing to alter fluid pressure in a pressure chamber located between the piston and the closed end of the housing; a push rod connected with the piston for manual operation of the master cylinder; a wall positioned within the housing adjacent the closed end of the housing and reciprocally movable relative to the housing, the pressure chamber being located between the wall and the piston; and actuation means for moving the wall relative to the housing and the piston towards the piston to increase fluid pressure in the pressure chamber.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a master cylinder in accordance with the present invention; Figure 2 is a cross-sectional view of a second embodiment of master cylinder in accordance with the present invention; and Figure 3 is a cross-sectional view of a third embodiment of master cylinder in accordance with the present invention.

Referring to Figure 1, the master cylinder 10 comprises a housing 12 having a cylindrical bore 14 with a longitudinal axis A. The bore 14 is closed at one end 16 of the housing 12 by an end fitting 18. The bore 14 is open at the other end 20 of the housing 12.

The housing 12 is secured at the other end 20 to a wall 22 of a brake booster housing or to the firewall (not shown) of a motor vehicle. A push rod 24 extends through the open end 20 of the housing 12 into the bore 14. The push rod 24 is movable along the axis A on manual operation of the brakes by the vehicle operator in the usual manner. A tubular sleeve 26 is positioned inside the bore 14 and makes a close sliding fit therewith such that the sleeve can reciprocally move along the axis A relative to the housing 12. The sleeve 26 is closed by an end wall 28 adjacent the closed end 16 of the housing 12. The sleeve 26 is biased towards the closed end 16 of the housing 12 by a spring 30. Projections 32 on the end fitting 18 engage the end wall 28 of the sleeve 26 in the normal or at rest position of the sleeve to define a fluid chamber 34 between the end fitting and the end wall.

The sleeve 26 defines a bore 36 which is coaxial with the bore 14 of the housing 12 on axis A.

Positioned within the bore 36 of the sleeve 26 is a pair of pistons 38,40. The pistons 38,40 make a sealing sliding fit with the bore 36 of the sleeve 26 and are capable of reciprocal movement along the axis A relative to the sleeve 26 and the housing 12. The primary piston 38 is connected with the push rod 24. A primary high pressure chamber 42 is defined within the bore 36 between the primary piston 38 and the secondary piston 40. A secondary high pressure chamber 44 is defined within the bore 36 between the secondary piston 40 and the end wall 28 of the sleeve 26. The primary piston 38 is shaped to define a primary low pressure chamber 46 between its ends with the bore 36. The secondary piston 40 is shaped to define a secondary low pressure chamber 48 between its ends with the bore 36.

Each high pressure chamber 42,44 has a fluid outlet 50,52 respectively for pressurised fluid to reach the brakes (not shown) of the motor vehicle. A spring 54 is positioned in the primary high pressure chamber 42 to bias the primary piston 38 and the secondary piston 40 away from one another. A spring 56 is positioned in the secondary high pressure chamber 44 to bias the secondary piston 40 away from the end wall 28 of the sleeve 26. A tubular insert 58 (through which the push rod 24 extends) positioned at the open end 20 of the bore 14 in the housing 12 acts as a stop for the primary piston 38 to limit the movement of the primary piston away from the end wall 28 of the sleeve 26.

Fluid inlet ports 59,60 in the sleeve 26 allow hydraulic fluid to flow from a fluid reservoir (not shown) to the primary and secondary low pressure chambers 46,48 respectively. Dilation ports 62,64 in the sleeve 26 allow hydraulic fluid to flow between the primary and secondary high pressure chambers 42,44 respectively and the fluid reservoir.

The fluid chamber 34 is connected to a hydraulic actuator 66 which is capable of providing a controlled fluid pressure. The hydraulic actuator 66 (which can be an electrically operated pump or an electrically driven piston) is controlled by a central processing unit (CPU) 68 which monitors various vehicle parameters and actuates the hydraulic actuator to provide pressurised fluid in the fluid chamber 34 dependent on the monitored signals.

Examples of such hydraulic actuators 66 are known to those skilled in the art for use in vehicles having ABS (an anti-slip braking system), and will not be described in detail.

On depression of the vehicle brake pedal (not shown) by the vehicle operator, the master cylinder 10 acts like a normal known dual master cylinder. The push rod 24 moves towards the closed end 16 of the housing 12 to cause the primary and secondary pistons 38,40 to similarly move relative to the housing 12 and the sleeve 26. This relative movement closes the dilation ports 62, 64 and causes an increase in the fluid pressure in the fluid in the primary and secondary high pressure chambers 42,44 to actuate the vehicle brakes (not shown). Release of the brake pedal allows the reverse movement of the primary and secondary pistons 38,40 and the push rod 24 relative to the housing 12 and the sleeve 26 to release the brakes.

In this respect, the master cylinder 10 acts in substantially the same manner as known dual master cylinders.

If the CPU 68 monitors the need for brake actuation, for example, for traction control, cruise control, hill start, etc. purposes, the CPU actuates the hydraulic actuator 66 to increase fluid pressure in the fluid chamber 34. This increase in fluid pressure causes the sleeve 26 to move in an axial direction against the bias of the spring 30 in a direction away from the closed end 16 of the housing 12. During this movement of the sleeve 26 relative to the housing 12, the primary piston 38 engages the tubular insert 58 so that the primary piston 38 remains substantially stationary relative to the housing 12 and the sleeve moves relative to the primary piston. This relative movement closes the dilation ports 62, 64 and increases the fluid pressure in the primary and secondary high pressure chambers 42,44 to actuate the vehicle brakes.

The fluid pressure in the fluid pressure 34 is controlled by the CPU 68 dependent on the monitored vehicle parameters, thereby controlling the amount of relative movement between the sleeve 26 and the housing 12 and between the sleeve and the primary piston 38, and, therefore, the amount of fluid pressure applied to the brakes. On reverse actuation of the hydraulic actuator 66, the fluid pressure in the fluid chamber 34 decreases to allow the sleeve 26 to return to its normal or at-rest position in engagement with the end fitting 18 due to the bias of spring 30 to release the vehicle brakes.

The second embodiment of master cylinder 10' shown in Figure 2 is similar to the first embodiment shown in Figure 1, and like parts have been given the same reference number. In this second embodiment, the dilation port 64 is omitted and replaced by a centre port compensation valve 70 in the secondary piston 40, the operation of which is well known to those skilled in the art. The tubular insert is also omitted and is replaced by an annular end fitting 72 which is secured in the bore 36 in the sleeve 26 at the open end 74 thereof by a clip 75 and which makes a sealing sliding fit with the push rod 24. An example of a suitable end fitting 72 is described in GB-A-2256687. The annular end fitting 72 defines with the primary piston 38 and the bore 36, the primary low pressure chamber 46. The annular end fitting 72 also acts as a stop for the primary piston 38.The fluid chamber 34 is positioned in a closed bore 76 in the end fitting 18, and a sleeve actuating piston 78 is positioned in the closed bore.

The piston 78 is biased by a spring 80 into engagement with the end wall 28 of the sleeve 26. Any increase in fluid pressure in the fluid chamber 34 causes the piston 78 to act on the end wall 28 of the sleeve 26 to move the sleeve in an axial direction relative to the housing 12 and the primary piston 38 to increase the fluid pressure in the primary and secondary high pressure chambers 42,44, in a similar manner to that described above in respect of the first embodiment of master cylinder 10.

The third embodiment of master cylinder 10" shown in Figure 3 is similar to the first embodiment shown in Figure 1, and like parts have been given the same reference number. In this third embodiment, the outer surface 82 of the sleeve 26 is formed with a number of lands 84 which define areas of reduced diameter between the lands which act as fluid passages between the pressure chambers 42,44,46,48 within the sleeve and ports in the housing 12. For example, port 86 is connectable to a fluid reservoir (not shown) and makes a fluid connection with area 88 which is fluidly connected with inlet port 59 and dilation port 62.

Port 90 is connectable to a fluid reservoir (not shown) and makes a fluid connection with area 92 which is fluidly connected with inlet port 60 and dilation port 64. Port 94 is connectable with the vehicle brakes (not shown) and is fluidly connected with area 96 which is fluidly connected with the fluid outlet 50. Port 98 is connectable with the vehicle brakes (not shown) and is fluidly connected with area 100 which is fluidly connected with the fluid outlet 52.

The actuator means of the master cylinder 10" is provided by an electric motor 102 which replaces the hydraulic actuator of Figure 1, but which is controlled by the CPU 68. The electric motor 102 rotates a screw 104 by way of a gear train 106. The gear train 106 is located in a gear train housing 108 which closes the one end 16 of the bore 14 of the housing 12. As shown, the electric motor 102 is preferably secured to the outer surface of the housing 12. The screw 104 is positioned in the bore 14 of the housing 12 adjacent the end wall 28 of the sleeve 26. A nut 110 is threadably mounted on the screw 104 and is engageable with the end wall 28. If the CPU 68 monitors the need for brake actuation, the CPU actuates the electric motor 102 to rotate the screw 104. This rotation of the screw 104 causes the nut 110 to move in an axial direction towards the end wall 28.The nut 110 engages the end wall 28 to move the sleeve 26 in an axial direction against the bias of the spring 30 in a direction away from the closed end 16 of the housing 12. During this movement of the sleeve 26 relative to the housing 12, the primary piston 38 engages the tubular insert 58 so that the primary piston 38 remains substantially stationary relative to the housing 12 and the sleeve moves relative to the primary piston. This relative movement increases the fluid pressure in the primary and secondary high pressure chambers 42,44 to actuate the vehicle brakes. The amount of rotation of the screw 104 is controlled by the CPU 68 dependent on the monitored vehicle parameters, thereby controlling the amount of relative movement between the sleeve 26 and the housing 12 and between the sleeve and the primary piston 38, and, therefore, the amount of fluid pressure applied to the brakes. On reverse actuation of the electric motor 102, the nut 110 disengages from the end wall 28 to allow the sleeve 26 to return to its normal or at-rest position due to the bias of spring 30 to release the vehicle brakes.

Whilst the present invention has been described above in respect of master cylinders having dual high pressure chambers, it will be appreciated that the present invention is equally applicable to master cylinders having a single high pressure chamber.

Claims

Claims:

1. A master cylinder comprising a housing which is substantially cylindrical and closed at one end; a piston reciprocally movable relative to the housing to alter fluid pressure in a pressure chamber located between the piston and the closed end of the housing; a push rod connected with the piston for manual operation of the master cylinder; a wall positioned within the housing adjacent the closed end of the housing and reciprocally movable relative to the housing, the pressure chamber being located between the wall and the piston; and actuation means for moving the wall relative to the housing and the piston towards the piston to increase fluid pressure in the pressure chamber.

2. A master cylinder as claimed in Claim 1, wherein the wall is an end wall of a sleeve which is substantially cylindrical with an internal bore which is closed at one end by the end wall, the sleeve being reciprocally movable within the housing, and the piston making a sealing sliding fit with the bore in the sleeve, the pressure chamber being located within the bore in the sleeve between the piston and the end wall.

3. A master cylinder as claimed in Claim 1 or Claim 2, wherein the wall is biased towards the closed end of the housing by a spring.

4. A master cylinder as claimed in any one of Claims 1 to 3, wherein the actuation means comprises a hydraulic actuator which a capable of providing fluid at a controlled pressure to a fluid chamber located within the housing between the closed end of the housing and the wall.

5. A master cylinder as claimed in any one of Claims 1 to 3, wherein the actuation means comprises an electrically driven threaded means engageable with the wall to move the wall towards and away from the piston.

6. A master cylinder as claimed in any one of Claims 1 to 5, wherein the operation of the actuation means is controlled by control means which monitors one or more vehicle parameters and controls the operation of the actuation means dependent on the reading from the or each vehicle parameter.

7. A master cylinder substantially as herein described with reference to, and as shown in, Figure 1, or Figure 2, or Figure 3 of the accompanying drawings.