GB2122705A

GB2122705A - Pneumatic servo booster

Info

Publication number: GB2122705A
Application number: GB08307721A
Authority: GB
Inventors: Mitsuhiro Endou
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1982-04-20
Filing date: 1983-03-21
Publication date: 1984-01-18
Also published as: GB8307721D0; JPS58158748U

Abstract

An annular bead 49 having a thick thickness is formed integrally on the diaphragm 4 for controlling the deflecting movement of the second wall portion of a pneumatic servo booster including a cylindrical casing 2, a power piston having a large diameter portion 5 disposed in the casing and a small diameter value housing portion 9 slidingly and sealingly extending through one end of the casing, and a flexible diphragm 4 cooperating with the large diameter portion of the power piston for partitioning the interior of the casing into two chambers A, B. The diagraphm has a first annular wall portion extending generally along one side surface of the large diameter portion 5 of the power piston with the radially inner circumferential end 8 thereof being secured annular wall portion 10 extending from the outer circumferential end of the first wall portion to the inner circumference of the casing and being secured thereto. <IMAGE>

Description

SPECIFICATION Pneumatic servo booster This invention relates to a pneumatic servo booster for use in such as a hydraulic brake system of an automotive vehicle and, particularly to a pneumatic servo booster of the kind including a cylindrical casing, a power piston having a large diameter portion disposed in the casing and a small diameter portion slidingly and sealingly extending through one end of the casing, and a flexible diaphragm cooperating with the large diameter portion of the power piston for partitioning the interior of the casing into two chambers.One of the chambers remote from the small diameter portion of the power piston is usually defined as a low pressure chamber and is permanently communicated with a source of low pressure such as an intake manifold of an engine of the vehicle, and the other chamber which encircles a portion of the small diameter portion of the power piston is defined as a high pressure chamber and a source of high pressure such as atmospheric air or a compressor. A valve mechanism is usually incorporated in the power piston.

Usually, the outer circumferential portion of the flexible diaphragm is fixedly connected to the inner circumference of the casing and at least a part of the inner circumferential portion of the diaphragm extends along one side surface of the large diameter portion of the power piston with the inner circumferential end being fixedly connected to the power piston.

The pneumatic servo booster of aforesaid kind operates generally satisfactorily, however, there is a shortcoming such that when the power piston is displaced in the casing without introducing the differential pressure between the high and low pressure chambers, the pressure in the low pressure chamber will become higher than the pressure in the high pressure chamber whereby the diaphragm is pressed in the direction opposite to normal operating condition of the servo booster, and the diaphragm would sometimes usually be distorted which will cause discrepancies such as damages in the diaphragm, irregular movement of the power piston and the like.Such displacement of the power piston without introducing the differential pressure is performed in such as the assembling line of the automotive vehicle for effecting air bleeding operation of a master cylinder which is rigidiy connected to the servo booster.

The present invention aims to overcome aforesaid shortcomings and the pneumatic servo booster according to the invention comprises a cylindrical casing, a power piston having a large diameter portion disposed in the casing and a small diameter portion slidingly and sealingly extending through one end of the casing, and a flexible diaphragm cooperating with the large diameter portion of the power piston for partitioning the interior of the casing into two chambers, wherein the diaphragm has a first annular wall portion extending generally along one side surface of the large diameter portion of the power piston with the radially inner circumferential end thereof being secured to the power piston, and a second annular wall portion extending from the outer circumferential end of the first wall portion to the inner circumference of the casing and being secured thereto, and an annular bead having a thick thickness is formed integrally on the diaphragm for controlling the deflecting movement of the diaphragm in the condition different from the normal operating condition of the servo booster.

The invention will hereinafter be explained in detail with reference to accompanying drawings exemplifying a preferred embodiment of the invention wherein: Fig. 1 is a longitudinal sectional view of a pneumatic servo booster according to the invention; and Fig. 2 is an explanatory partial view showing an unusually distorted diaphragm according to a prior art servo booster.

In Fig. 1 , the pneumatic servo booster according to the invention is defined generally at reference numeral 1 and includes a cylindrical casing formed of a front shell 2 and a rear shell 3, and the interior of the casing is partitioned into two chambers or high and low pressure chambers B and A by a flexible diaphragm 4 formed of a resilient material such as an annular rubber sheet and a power piston 5 which is secured to the diaphragm 4. The communication and the interception between the low and high > ressure chambers A and B are controlled by a poppet valve mechanism 6.The outer peripheral portion of the diaphragm 4 is clamped sealingly between shells 2 and 3 and the inner circumferential portion is formed as an annular flange 8 which is clamped sealingly between the power piston and a generally cylindrical valve body 9. The valve body 9 is secured to the power piston 5 to constitute a power piston assembly. The diaphragm 4 further has a generally U-shaped rolling portion 10 near to the outer circumferential portion.

The poppet valve mechanism 6 is received in the valve body 9 and comprises a resilient poppet valve 11 and a plunger 12. The plunger 12 is slidably received in a small diameter portion of an axial bore in the valve body 9, and relatively axial displacement of the plunger 12 with respect to the valve body 9 is limited by a restricting member 1 5 which is fitted in an annular groove 14 in the plunger 12. The valve body 9 is siidably and sealingly supported on a radially inner circumference 16 of the rear shell 3 through a seal member 17 and is displaceable relative to the shells 2 and 3 in the direction of the axis of the servo booster.The valve body 9 includes a large diameter inner end portion 1 3 and a generally tubular small diameter portion 1 8. The bore receiving the plunger 12 in the valve body 9 is counterbored at two steps toward the small diameter end or the right end as viewed in Fig. 1 to form an intermediate diameter bore portion and a large diameter bore portion 19. A spring retainer 21 is retained at a shoulder 20 defined between the intermediate and large diameter bore portions to retain one end 22 of the poppet valve 11 sealingly against the intermediate diameter bore portion. The other end 23 of the poppet valve 11 is urged leftward in the drawing by a coil spring 24 which acts between the end 23 of the poppet valve and the spring retainer 21.The end 23 of the poppet valve 11 is adapted to engage with an annular valve seat 25 formed on the right or rear end of the plunger 12 and also with a concentric annular valve seat 26 formed on the valve body 9 at the diametral step between the intermediate diameter bore portion and the bore receiving the plunger 12. The plunger 12 is connected to an input rod 27 with a ball end 28 of the input rod 27 being forcibly fitted in a recess 29 formed in the rear or the right end of the plunger 12. The input rod 27 extends through the bore portions of the valve body 9 to the outside and the rear end thereof is adapted to be connected with such as a brake pedal. The input rod 27 is biased rearwards or in the rightward direction in the drawing by a spring 30 which also is retained on the spring retainer 21.

As a result, in the normal inactuated condition of the servo booster, the input rod 27 and the plunger 1 2 are pushed rightward in the drawing and the control member 15 received in the annular groove 14 in the plunger 12 abuts with a shoulder 32 of a rod 31 which extends between front and rear shells 2 and 3.

An axial opening 33 is provided in the valve body 9 to communicate the chamber A with the intermediate diameter portion of the valve body, and radial passage 34 (shown at broken lines in Fig. 1) is also provided in the valve body to communicate the chamber B with the bore portion receiving the plunger 12, so that when the poppet valve 11 is separated from the valve seat 26, the chambers A and B are communicated through openings 33 and 34. When the poppet valve 11 is separated from the valve seat 25 on the plunger 12, the chamber B communicates with atmospheric air through the passage 34, an opening formed in the end portion 23 of the poppet valve 11, and opening formed in the spring retainer 21, and an air filter provided in the large diameter bore portion 19 of the valve body 9.

The rod 31 extends between the front and rear shells 2 and 3 with a head portion 35 thereof firmly abutting with the inner wall of the rear shell 3 and mounting thereon a reinforcing plate 36.

The reinforcing plate 36 supports and retains the seal member 1 7 on the inner circumference thereof. The rod 31 extends loosely through openings which are respectively formed in the large diameter portion 13 of the valve body 9, the power piston 5 and a disc plate 37 which is secured to the front surface of the piston plate 5.

The tip end of the rod 31 extends through an open 39 in the front shell 2, and the rod 31 is secured to the front shell 2 by nuts 40 and 41. It will be understood that there are provided two or more rods are provided in the servo booster in angularly spaced relationship. The opening formed in the power piston assembly and the nut 40 retain respectively axially opposite ends of a flexible and extendible tubular member 42 which surrounds the rod 31 between the power piston assembly and the inner wall of the front shell 2 so as to prevent communication between chambers A and B around the outer circumference of the rod 31. A plurality of studs 43 (only one is shown in Fig. 1) are secured to the reinforcing plate 36 to extend rearwards from the rear shell 3. The studs 43 are utilized to mount the servo booster on such as a body of the vehicle.

A vacuum pressure introducing pipe 44 is secured to the front shell 2, and the pipe 44 is adapted to be connected to a source of vacuum pressure such as an intake manifold of an engine of the vehicle (not shown) through a check valve 45.

An output rod 46 is mounted on the disc plate 37 and receives the output force from the power piston assembly through a resilient reaction disc 47, and the output rod 46 sealingly and slidingly extends through a central opening in the front shell 2 to transmit the output force to such as a master cylinder of hydraulic braking system of the vehicle. The master cylinder (not shown) is preferably mounted on the front shell 2 by means of screw-threaded tip end portions 50 of the rods 31. A return spring 48 is interposed between the front shell 2 and the disc plate 37.

According to the invention, there is provided an annular bead 49 on the diaphragm 4 at a location near to the outer circumference of the power piston 5. The bead 49 has a thick thickness as compared with the remaining portion of the diaphragm 4.

The pneumatic servo booster having aforesaid construction operates as follows. In the normal inactuated conditions shown in Fig. 1, the chamber A is communicated with the source of vacuum pressure, the plunger 12 and the input rod 27 take the rearmost positions with the control member 1 5 engaging with the shoulder 32 of the rod 31, the end portion 23 of the poppet valve 11 engages with the valve seat 25 and 26 on the plunger 12 and the valve body 9 thereby isolating the chamber B both from the chamber A and the atmosphere, and the pressure in the chamber B is slightly higher than the pressure in the chamber A.

The differential pressure between chambers B and A counteracts the force of the return spring 48.

In applying brakes, the input rod 27 is pushed leftward by depressing the brake pedal. The plunger 12 is displaced leftward with the valve seat 25 on the plunger 12 separating from the poppet valve 11 while maintaining the engagement with the valve seat 26. The atmospheric air enters into the chamber B. As a result, the power piston receives a differential pressure between chambers B and A and the differential pressure force acting on the power piston is transmitted to the output rod 46 through the reaction disc 47. The reaction disc 47 also transmits a reaction force to the input rod 27 through the plunger 12. The valve body 9 moves leftward until the poppet valve 11 engages again with the valve seat 25 on the plunger. At that condition, the chamber B is isolated both from the chamber A and the atmosphere and the servo booster takes an equilibrium condition.The control member 1 5 displaces leftward along the rod 31 in response to the displacement of the valve body 9.

When the force applied on the brake pedal is released, the input rod 27 and the plunger 12 are pushed rightward relative to the valve body 9 by the spring 30, thus, the poppet valve 11 is separated from the valve seat 26 on the valve body 9, whereby the chamber B is communicated with the chamber A through openings 34 and 33, and the pressure in the chamber B decreases and approaches the pressure in the chamber A. The power piston assembly moves rightward by the force of the return spring 48. The control member 15 abuts with the shoulder 32 of the rod 31 and stops the rightward or return movement of the plunger 12 and the input rod 27 with respect to the rear shell 3. Finally the rightward movement of the valve body 9 stops with the valve seat vai 9R the valve body 9 engaging with the poppet valve 11.The servo booster takes the inactuated condition as shown in the drawing.

The pneumatic servo booster having aforesaid general construction operates satisfactorily in normal operating conditions as heretofore described. However, when the servo booster is incorporated in a hydraulic braking system of an automotive vehicle, the input rod would sometimes be displaced without introducing the vacuum pressure in the chamber A, such as when it is required to bleed air from the master cylinder in the assembling process of the hydraulic system or in the maintenance or repair work of the hydraulic system.When the input rod 27 is moved leftward without introducing the vacuum pressure in the chamber A, the pressure in the chamber A will sometimes become higher than the pressure in the chamber B so that the disphragm 4 is pressed toward the chamber B with the air in the chamber A acting on the diaphragm 4 generally in the direction of arrow C which tends to separate the diaphragm 4 from the power piston 5.

According to the invention, the annular bead 49 is integrally provided on a portion near to the outer circumference of the power piston 5, the deformation of the diaphragm 4 can effectively controlled. In prior art servo booster, when the pressure condition between the chambers A and B is inversed, the diaphragm 4 has sometimes been excessively deformed such as shown in Fig. 2 and clamped between the power piston and the rear shell 3. It will be understood that the diaphragm is deformed into a wave shaped configuration extending both in the radial and circumferential directions although Fig. 2 shows only the wave shaped deformation extending in the radial direction, and that the annular bead 49 having a thick thickness can effectively prevent the radially inward deformation thereby preventing wave shaped deformation.In the embodiment, a generally U-shaped rolling portion 10 is provided on the diaphragm 4 and the annular bead 49 is located radially inward of the rolling portion 10. It is defective to provide an annular bead or a thick thickness annular portion radially outward of the rolling wall portion 10 since the fabricating process is complicated and such annular bead may sometimes be clamped on the inner wall of the casing.

In the embodiment, the annular bead 49 has a generally semi-circular cross-section, but the configuration of the annular bead is not limited to the embodiment. Further, in the embodiment, the pneumatic servo booster operates between vacuum pressure and atmospheric pressure, but the invention is applicable to other types of pneumatic servo boosters. Further, the power piston assembly according to the embodiment is constituted of valve body 9, the plate-like power piston 5 and a disc plate 37, however, the invention can similar be applied to other types of servo booster.

Claims

1. A pneumatic servo booster comprising a cylindrical casing, a power piston having a large diameter portion disposed in the casing and a small diameter portion slidingly and sealingly extending through one end of the casing, and a flexible diaphragm cooperating with the large diameter portion of the power piston for partitioning the interior of the casing into two chambers, said diaphragm having a first annular wall portion extending generally along one side surface of the large diameter portion of the power piston with the radially inner circumferential end thereof being secured to the power piston, and a second annular wall portion extending from the outer circumferential end of the first wall portion to the inner circumference of the casing and being secured thereto, wherein an annular bead having a thick thickness is formed integrally on said diaphragm for controlling the deflecting movement of the second wall portion.

2. A pneumatic servo booster as in Claim 1 wherein said annular bead is formed near to the outer circumference of the first wall portion.

3. A pneumatic servo booster as in Claim 1 wherein said annular bead is formed on the second wall portion.

4. A pneumatic servo booster substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 of the accompanying drawing.