GB2053395A - Servo booster for a vehicle braking system - Google Patents

Abstract

The invention is concerned with the problem of providing a fluid connection between a valve chamber of a servo booster and the variable pressure rear housing chamber (3) defined behind the movable wall (2, 11), when the movable wall is sealed at its radially inner periphery to a stationary sleeve or force transmitting tube (5). The piston (11) of the movable wall is provided with a through-passage (37) which opens at its rear end (37b) to the rear chamber (3) and its front end (37a) is connected by a rubber tube (36) to a passage (35) in the valve casing (17) leading to the valve chamber. <IMAGE>

Description

SPECIFICATION Servo booster for a vehicle braking system This invention relates to a servo booster for a vehicle braking system.

In our G.B. Patent Application No. 7940338 (2036901 A) we have disclosed a servo booster in which the movable wall of the booster is sealed to the rear housing wall by a seal means located radially outwards from the valve casing of the booster, and a valve chamber in the valve casing is connected to the rear chamber of the booster by a U-shaped passage which extends through an arm which integrally connects an annular piston of the movable wall to the valve casing, the passage terminating in a port located in the piston radially outwards of the seal means and opening to the rear chamber.

It is difficult to provide such a U-shaped passage in the integral assembly. In one of the constructions previously described it was necessary to close the passage with a blanking plate, and in another construction a ball was used as a plug.

According to the present invention a servo booster for a vehicle braking system comprises a booster housing, a movable wall dividing the interior of the housing into two chambers and comprising an annular piston which is sealed at its radially inner extremity directly or indirectly to the rear housing wall by a seal means located radially outwards from a valve casing connected to the piston by a force transmitting member, a valve member in the valve casing being connected to the rear chamber of the booster by a passage which extends rearwardly through the piston and which terminates at its rear end in a first port located radially outwards of the seal and opening to the rear chamber, and at its front end in a second port which is connected by an independently formed tube to a passage in the valve casing leading to the valve chamber.

Although the force transmitting member may be formed integrally with the piston and valve casing it is preferably an independently formed member, conveniently in the form of an annular hub which houses a valve reaction disc, and a depending radially outwardly directed flange which abuts a forwardly facing surface on the piston, the hub being secured to the valve casing.

Preferably the second port is located in the forwardly facing surface, and the arrangement is such that one end of the tube is retained in position around the second port by the force transmitting member.

The force transmitting member is preferably retained in abutting relationship with the forwardly facing surface of the piston by a return spring for the movable wall.

The hub of the force transmitting member is preferably sealed to the valve casing by an annular seal which is conveniently formed integrally with the tube.

In Patent Specification G.B. No. 2031 086A is disclosed a servo booster which incorporates a tubular reinforcing member which extends through the movable wall of the booster for transmitting braking reaction forces in use, substantially to relieve the booster housing of such forces and thereby enable the use of a lightweight housing.

The present invention is particularly suitable for use with such a tubular reinforcing member, the tubular reinforcing member being provided with a series of circumferentially spaced, axially extending slots, the tube is arranged to extend through one of the slots, and the force transmitting member comprises a plurality of spokes which extend through respective slots.

A servo booster in accordance with the 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 the booster; and Figure 2 is a fragmentary view also in axial section but taken in a different plane to Figure 1.

The booster illustrated in the drawings has a housing 1 formed by two lightweight plastics mouldings 1 a, 1 b which snap fit together at their peripheries and hoid between them the outer edge of a rolling diaphragm 2 of a movable wall which divides the housing interior into two chambers 3, 4. The diaphragm 2 is annular and its inner edge seals against the outside of a tubular reinforcing member 5, which extends coaxially between the two housing shells 1 a, 1 b, in order to effect a seal between the movable wall and the rear housing wall. The member 5 has a flange 6 which is rigidly secured to the rear housing shell 1 a by fasteners 7. The fasteners project rearwardly from the housing and are screw-threaded for securing the booster to the vehicle bulkhead.The forward end of the member 5 surrounds an annular boss of the housing shell 1 b and has an outwardly directed lip engaged by a collar 8 fixed to the housing shell 1 b by fasteners 9 of the same form as fasteners 7, and which fasteners 9 are used to secure a master cylinder to the booster to be actuated directly by an axial output member 10 of the booster. The reinforcing member 5 serves to transmit forces between the opposite end of the booster housing and since the housing shells are not required to transmit these forces they can be constructed as comparatively thin plastics mouldings enabling a reduction in weight of the booster.

Forces are transmitted from the diaphragm 2 to the output member 10 by a piston 1 which is a moulded plastics component, and by an independently formed metal transmitting member 12. The member 12 has an annular rim 13 which is held by a snap fit with integral projections 14 of the piston 11. A return spring 1 5 of the booster acts between the collar 8 and the rim 13 of member 1 2 and urges the piston 11 and diaphragm 2 to the position illustrated in an unactuated condition of the booster.The transmitting member 12 includes an annular hub 1 6 which is fitted into the forward end of a tubular casing 1 7 enclosing the booster valve system, a rib extending about the hub being received in a groove in casing 17 to lock the member 12 and casing 17 together. Hub 16 is connected to the rim 13 by spokes 18, these spokes passing through respective longitudinal slots 1 9 provided in the reinforcing member 5 and extending rearwardly from the front end almost to the flange 6.

The hub 1 6 has a stepped internal bore with the larger and smaller diameter portions separated by a forwardly facing annular shoulder. The rear end of the output member 10 is received in the larger diameter portion of the hub 16 and a rubber reaction disc 20 is interposed between the output member and the internal shoulder. Slidable in the smaller diameter bore portion of the hub is a valve piston 21 whose rear end slides within a part of the tubular casing 1 7 having a reduced interior diameter. A first annular valve seat 23 is formed on the rear face of valve piston 21 and a second annular valve seat 24 is formed on a rearwardly facing internal shoulder of the casing 17. The valve seats 23, 24 co-operate with a common annular valve member 25 in a manner which is explained in more detail below.

Valve member 25 has a reinforcing washer 26 and has an integral skirt with a thickened edge held in sealing engagement with the interior of casing 1 7 by a ring 27 which abuts a narrow shoulder of casing 17. An actuating rod 28 extends axially through the rear end of casing 17 and has a ball at its forward end fixed in a socket in the valve piston 21. Two radial abutments are provided on the rod 28 and a first spring 29 acts between the forward abutment and the washer 26 to bias the valve member into co-operation with the valve seats 23, 24, while a second spring 22 acts between a washer 30 in engagement with the rear abutment and the ring 27 for holding the ring 27 against its supporting shoulder and providing a return force for the actuating rod.The washer 30 serves to support and protect against damage a filter element 31 inserted between the actuating rod and casing 1 7. The tubular casing 1 7 is axially slidable in the booster housing and is sealed to the shell 1 a by a rubber boot 32.

The valve system controls communication of the rear chamber 3 with the front chamber 4 and ambient atmosphere. A passageway 33 formed through the wall of the casing 17, a seal 34 sealing the front face of casing 17 to the transmitting member 12, and the member 12 itself, opens at one end into the chamber 4 and at the other end into the casing at a position radially outside the valve seat 24.

As may be seen in Figure 2, a passage 35 opens into the casing 1 7 inwardly of seat 24 and a rubber tube 36 formed integrally with the seal 34 connects the passage opening at the casing periphery with a hole in the flange 13 of transmitting member 12. A bead 36' at one end of the tube 36 seals against the piston 11 around a port 37a at the front end of a passage 37 extending rearwardly through the piston. The bead 36' is held in sealing engagement with the piston 11 by the rim 1 3 under the force of spring 1 5. The diaphragm 2 has an aperture which surrounds a further port 37b at the rear end of the passage 37, and a sleeve 38 is inserted through the aperture and into the port 37b to ensure a tight seal between the diaphragm 2 and piston 11.It will be noted that the port 37b is located radially outwards of the rolling diaphragm portion 2a.

The tube 36 preferably extends through the same slot 1 9 as does one of the spokes 1 8, the circumferential width of that slot being made sufficiently large to provide clearance, and the axially extending portion of the tube 36 is provided on one side with a pair of webs, not shown, which grip the radially inner and outer surface of the corresponding spoke 18 to retain the tube 36 in position.

Thus, the passageway defined by passage 35, tube 36 passage 37 and sleeve 38 connects the interior of casing 17 with valve chamber 3.

Since tube 36 is located in the front chamber 4 of the booster which is connected permanently to a vacuum source it will not collapse in use.

In the normal unactuated condition of the servo booster the components occupy the positions illustrated, the piston 11 , transmitting member 12 and casing 1 7 (together with the parts enclosed therein) being urged rearwardly to a position in which a thicker pad element 40 of diaphragm 2 abuts against a stop 41 formed on the interior of housing shell 1 a. The actuating rod 28 is biased rearwardly by the spring 22 so that the valve member 25 is engaged by seat 23 and is held off of seat 24. In use, the chamber 4 is connected to a vacuum source, usually the inlet manifold of the engine, and the vacuum pressure is communicated to chamber 3 through the passageway 33 and the passage 34, tube 36 and passage 37. Consequently, there is no pressure difference across the diaphragm and no forces are transmitted to the output member 10.

When the brakes are to be operated the rod 28 is moved forwardly, such as by a pedal actuating mechanism, the valve piston 21 slides forward relative to the hub 16 and casing 17 and the valve member 25 moves with it under the action of spring 29 until it engages the seat 24, which interrupts communication between passageway 33 and passage 34. As the valve piston 21 continues to move forwardly, the seat 23 disengages from valve member 25 and atmospheric air flows in through the rear end of the casing 17 to chamber 3 via filter 31 the passage 35, tube 36 and passage 37. The resulting pressure differential created across the diaphragm causes it to be displaced to the left, as seen in Figure 1, driving the piston member 11 with it. It should be noted here that the diaphragm 2 has two rolling portions 2a, 2b respectively positioned radially inside and outside the piston 11 so that the part of the diaphragm fixed to the piston by the sleeve 38 is not required to move with respect to the piston.

The forward motion of the piston is transmitted to the output member 10 and the casing 17 by the member 12 whose spokes 18 move along the slots 1 9 in the reinforcing tube 5. The output member actuates directly a master cylinder fixed to the front of the booster.

When the actuating force on rod 28 is removed spring 22 moves it and valve piston 21 backwards causing seat 23 to engage valve member 25 and lift it free of seat 24 so that chamber 3 once again communicates with the chamber 4 and the displaced parts are returned to their initial positions by the spring 15.

The above described booster is light in weight, compact and allows a rear end part of the master cylinder to be received within the booster and provide an additional saving of space.

Claims (7)

1. A servo booster for a vehicle braking system comprising a booster housing, a movable wall dividing the interior of the housing into two chambers and comprising an annular piston which is sealed at its radially inner extremity directly or indirectly to the rear housing wall by a seal means located radially outwards from a valve casing connected to the piston by a force transmitting member, a valve chamber in the valve casing being connected to the rear chamber of the booster by a passage which extends rearwardly through the piston and which terminates at its rear end in a first port located radially outwards of the seal and opening to the rear chamber, and at its front end in a second port which is connected by an independently formed tube to a passage in the valve casing leading to the valve chamber.

2. A servo booster as claimed in claim 1 in which the force transmitting member is formed independently of the piston.

3. A servo booster as claimed in claim 2 in which the force transmitting member is retained in abutting relationship with a forwardly facing surface of the piston, the second port being located in the forwardly facing surface, and the arrangement is such that one end of the tube is retained in position around the second port by the force transmitting member.

4. A servo booster as claimed in claim 3 in which the force transmitting member is retained in abutting relationship with the forwardly facing surface of the piston by a return spring for the movable wall.

5. A servo booster as claimed in any of claims 2 to 4 in which the force transmitting member is sealed to the valve casing by an annular seal which is formed integrally with the tube.

6. A servo booster as claimed in any one of the preceding claims comprising a tubular reinforcing member connecting the front and rear walls of the booster housing and provided with a series of circu mferentially spaced, axially extending slots, the tube extending through one of the slots, and the force transmitting member comprising a plurality of spokes which extend through respective slots.

7. A servo booster substantially as described with reference to the accompanying drawings.