GB2104989A

GB2104989A - Pneumatic servo booster

Info

Publication number: GB2104989A
Application number: GB08217655A
Authority: GB
Inventors: Hiromi Ando; Toshio Takayama
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1981-06-20
Filing date: 1982-06-18
Publication date: 1983-03-16
Also published as: JPS57204257U; DE3222929A1; GB2104989B; FR2508115A1

Abstract

A clearance ( delta ) is formed between the reaction disc (17) and the output shaft (12) in the unactuated condition of a pneumatic servo booster including a casing (1), a power piston (2) partitioning the interior of the casing into front and rear chambers, a reaction disc (17) formed of a deformable material and received in the power piston, an output shaft (12) located frontward of the reaction disc and receiving the output force of the servo booster from the power piston and through the reaction disc, an input shaft (7,8) located rearward of the reaction disc and receiving the reaction force of the output shaft through the reaction disc, and a valve mechanism (3b, 8a, 9) incorporated in the power piston and operated by the input shaft to generate a pressure difference between the front and rear chambers. <IMAGE>

Description

SPECIFICATION Pneumatic servo booster This invention relates to a pneumatic servo booster, for example, for use in a braking system of a vehicle and, particularly to a servo booster of the kind including a casing, a power piston partitioning the interior of the casing into front and rear chambers, an output shaft located in the front chamber and receiving the output of the servo booster from the power piston, a valve mechanism incorporated in the power piston, an input shaft extending through the rear end of the servo booster and adapted to actuate the valve mechanism for establishing a pressure difference between front and rear chambers, and a reaction disc formed of a deformable material and received in the power piston with one surface thereof engaging with the output shaft for transmitting the output force thereto and the other surface of the reaction disc engaging with the power piston and with the forward end of the input shaft.

In a servo booster of the kind aforementioned, the boosting ratio or the ratio between the output force and the input force is determined by the ratio between the pressure receiving area of the output shaft against the reaction disc and the pressure receiving area of the input shaft against the reaction disc. Usually, the reaction disc is received in a recess formed in the front surface of the power piston, with the front surface of the reaction disc engaging with the rear end of the output shaft and the rear surface of the reaction disc engaging with the bottom of the recess and facing the front end of the input shaft. In the unactuated condition of the servo booster, the front end of the input shaft is spaced from the rear surface of the reaction disc.The spacing between the front end of the input shaft (usually, the front end of a plunger which is integrally connected to the input shaft and is slidably disposed in the power piston) is effective to improve the pedal feeling and to obtain so-called "step-up" characteristics.

However, there is a problem in the prior art servo booster aforementioned in that a part of the rear end portion of the reaction disc bulges towards the input shaft to fill the spacing therebetween each time the brakes are applied and, accordingly, the reaction disc tends to age in relatively short period.

According to the invention, a pneumatic servo booster includes a casing, a power piston partitioning the interior of the casing into front and rear chambers, a reaction disc formed of a deformable material and received in the power piston, an output shaft located forwardly of the reaction disc and receiving the output force of the servo booster from the power piston and through the reaction disc, an input shaft located rearwardly of the reaction disc so as to receive the reaction force of the output shaft through the reaction disc, and a valve mechanism incorporated in the power piston and adapted to be operated by the input shaft to establish a pressure difference between the front and rear chambers, a clearance being formed between the reaction disc and the output shaft in the front and rearward directions and in the unactuated condition of the servo booster.

Preferably, another deformable member being deformable more easily than the reaction disc is interposed between the power piston and the output shaft so as to maintain the space or the clearance between the output shaft and the reaction disc in the unactuated condition of the servo booster.

When the output force does not exceed a predetermined level, the output force is solely transmitted through the other deformable member from the power piston to the output shaft, and no reaction force is transmitted to the input shaft.

Accordingly, it is possible to obtain a desired step-up characteristics and to minimize the deterioration of the reaction disc. Further, the invention can easily be applied to existing prior art servo boosters.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal sectional view of a pneumatic servo booster according to one embodiment of the invention; Fig. 2 is a graph showing the characteristic of the servo booster of Fig. 1, and Fig. 3 is a partial sectional view showing a detail of another embodiment of the invention.

The pneumatic servo booster illustrated in Fig.

1 comprises a casing 1 consisting of a front shell 1A and a rear shell 1 B, and a power piston 3 constituted by a flexible diaphragm 2, a main body 4, a piston plate 5 and a retaining disc 6.

The outer circumference of the diaphragm 2 is sealingly clamped between the front and rear sheils 1 A and 1 B, and the main body 4 sealingly and slidingly extends through the rear shell 1 B; thus, the power piston 3 partitions the interior of the casing 1 into front and rear chambers A and B.

In the illustrated embodiment, the main body 4 and the retaining disc 6 are formed of a synthetic resin, and are secured together by clamping bolts (only one of which is shown in broken lines). The piston plate is formed of a sheet metal and is bonded to the flexible diaphragm 2.

The front chamber A is connected to a source of vacuum, such as an intake manifold of an engine of an automobile.

An input shaft, constituted by a rod 7 and a plunger 8 connected to the front end (the lefthand end in the drawing) of the rod 7, extends through the rear end of the main body 4. The rear end of the rod 7 is connected to actuating means, such as a brake pedal, and the plunger 8 is slidably fitted in a bore 3a formed in the main body 4. When the brake pedal is depressed, the input shaft moves leftward or in the direction of the output force of the servo booster.

Valve seats 3b and 8a are formed on the rear ends of the bore 3a and the plunger 8 and, in the unactuated condition shown in the drawing, engage respectively with an annular valve poppet 9 formed of a resilient material. A spring 10 acts on the valve poppet 9 in the leftward, and, when the plunger 8 displaces leftward from the position shown in Fig. 1, the valve seat 8a separates from the valve poppet 9.

Further, an annular recess 3e is provided in the front face of the retaining disc 6 of the power piston 3 and opens to the front chamber A. The recess 3e communicates with the bore 3a through a small diameter opening 3f in the retaining disc 6. The recess 3e receives therein a reaction disc 1 7 which is formed of a deformable material, such as rubber. The reaction disc 1 7 abuts with an annular shoulder 39 which is formed between the recess 3e and the opening 3f, so that rearward movement of the reaction disc 1 7 is prevented. The front end portion of the plunger 8 slidingly extends through the opening 3f and abuts the rear surface of the reaction disc 17.

An increase diameter rear end portion 1 2a of an output shaft 12 is slidingly received in the recess 3e and, in the unactuated condition, there is provided a space or clearance a formed between the front surface of the reaction disc 1 7 and the rear surface of the rear end portion 1 2a of the output rod 12.

A cap member 13 is fitted over the front face of the retaining disc 6 and has a central bore through which a reduced diameter portion 1 2b of the output shaft 1 2 freely passes, and the diameter of which is less than that of the rear end portion 1 2a of the output shaft, whereby the rear end portion 1 2a of the output shaft 12 is retained in the recess 3e.

A retaining ring 14 is mounted on the reduced diameter portion 1 2b of the output shaft 12 to support a spring retainer 1 5. A coil spring 1 6 acting as another deformable member extends between the spring retainer 1 5 and the cap member 1 3. The spring 1 6 normally urges the output shaft 12 in the forward direction. The spring force of the spring 1 6 is preferably small so that the spring can easily be deformed as compared with the reaction disc 1 7.

The servo booster further comprises a return spring 11 extending between the front shell 1A and the cap member 1 3 to urge the power piston 3 in the rearward direction, three circumferentially spaced (only one is shown in Fig. 1) reinforcing rods 1 9 extending between front and rear shells 1 A and 1 B, and a restricting plate 1 8 mounted on the plunger 8 to restrict relative movement between the plunger 8 and the main body 4 and to restrict the return position of the input shaft with respect to the casing in the unactuated condition of the servo booster.The main body 4 has therein an axial passage 3c and a radial passage 3d for communicating front and rear chambers A and B when the valve seat 3b is separated from the valve poppet 9 with the valve seat 8a engaging the valve poppet 9. The radial passage 3d also acts to introduce atmospheric air into the rear chamber B when the valve seat 8a is separated from the valve poppet 9 with the valve seat 3b engaging with the valve poppet 9.

In operation, when the rod 7 is pushed forward by depressing the brake pedal, the plunger 8 moves forward with respect to the power piston 3, and the valve seat 8a on the plunger 8 separates from the valve poppet 9. The atmospheric air is introduced into the rear chamber B, and a pressure difference is generated between the front and rear chambers A and B. The power piston 3 is displaced leftwards; however, in the initial condition, the force acting on the power piston 3 is transmitted to the output shaft 1 2 through the coil spring 16, the spring retainer 1 5 and the retaining ring 14. When the spring 1 6 deflects by the clearance S initially provided between the rear end of the output shaft 2 and the reaction disc 1 7, the rear end of the output shaft 12 abuts the reaction disc 17.

Thereafter, the force acting on the power piston 3 is mainly transmitted to the output shaft 12 through the reaction disc 10, and the reaction force is transmitted to the plunger 8 of the input shaft through the reaction disc 1 7. Thus a desired step up characteristics is obtained between the input force and the output force as shown in Fig.

2.

Fig. 3 shows another embodiment of the invention wherein parts corresponding to the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted. In this embodiment, the cap member 13, the retaining ring 14, the spring retainer 1 5 and the coil spring 1 6 of the first embodiment are substituted by a retainer 20 and a Belleville spring 21. The retainer 20 has a complicated configuration as shown with a first diameter portion being interposed between the inner circumference of the recess 3e and the outer circumference of the increased diameter rear end portion of the output shaft 1 2. The retainer 20 further has an annular flange to receive the spring force of the Belleville spring 21 which is interposed between the annular flange and the power piston 3.The retainer 20 defines an axia! clearance S between the power piston 3, and the clearance a is larger than the clearance b which is defined between the reaction disc 17 and the retainer 20.

In the embodiment shown in Fig. 3, the differential pressure force acting on the power piston 3 is initially transmitted to the output shaft 1 2 through the retainer 20 and the Belleville spring 21. When the Belleville spring 21 deflects by the clearance 8, the reaction disc 1 7 acts to transmit the output force to the output shaft and to transmit the reaction force to the input shaft.

The retainer 20 permits a small misalignment between the output shaft 12 and the power piston 3, thereby preventing sticking between the inner circumference of the recess 3e and the output shaft 12.

It will be understood that the coil spring 16 and the Belleville spring 21 in the illustrated embodiments may be substituted by a resilient body of rubber or the like. Further, it is described that the coil spring 1 6 is easily deformable as compared with the reaction disc 17; however, if desired, the coil spring 16 or the Belleville spring 21 may have a large spring force.

As described heretofore, the reaction disc 1 7 does not project or bulge rearwardly into the reduced diameter opening 3f, thus premature deterioration of the reaction disc is avoided and a long service life is assumed.

Claims

1. A pneumatic servo booster including a casing, a power piston partitioning the interior of the casing into front and rear chambers, a reaction disc formed of a deformable material and received in the power piston, an output shaft located forwardly of the reaction disc and receiving the output force of the servo booster from the power piston and through the reaction disc, an input shaft located rearwardly of the reaction disc so as to receive the reaction force of the output shaft through the reaction disc, and a valve mechanism incorporated in the power piston and adapted to be operated by the input shaft to establish a pressure difference between the front and rear chambers, a clearance being formed between the reaction disc and the output shaft in the front and rearward directions and in the unactuated condition of the servo booster.

2. A pneumatic servo booster according to claim 1, wherein another pressure deformable member, deformable more easily than the reaction disc, is interposed between the power piston and the output shaft, whereby, when the output force is less than a predetermined level the output force is solely transmitted from the power piston to the output shaft through said other deformable member.

3. A pneumatic servo booster constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.