GB2032552A

GB2032552A - Vacuum brake boosters

Info

Publication number: GB2032552A
Application number: GB7933451A
Authority: GB
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1978-09-28
Filing date: 1979-09-27
Publication date: 1980-05-08
Also published as: GB2032552B; AU5097579A; JPS5548580U; ES484534A1; ZA795014B

Abstract

A vacuum servomotor has a deformable reaction disc (10) for transmitting an output force from the power piston (3) to an output shaft (12) and also transmitting a reaction force from the output shaft to the input shaft (6). The reaction disc (10) is received in a recess (3e) formed in the front surface of the power piston, and the rear end of the output shaft is slidingly received in the recess and is connected inseparably to the reaction disc with a projection-and-recess connection (12a, 10a) formed therebetween. <IMAGE>

Description

SPECIFICATION Pneumatic force multiplying device This invention relates to pneumatic force multiplying devices, such as vacuum servomotors of the like, which are particularly adapted for use in a hydraulic braking system of a vehicle.

Conventional vacuum servomotors comprise a housing, a power piston slidingly mounted in the housing and cooperating with a flexible diaphragrr to divide the interior of the housing into front and rear chambers, a valve mechanism incorporated in the power piston, an input shaft for actuating the valve mechanism, thereby generating a differentia pressure across the power piston, an output shaft projecting out of the housing through the forward end thereof, and a reaction mechanism for transmitting a reaction force to the input shaft.

One prior art reaction mechanism comprises a resilient reaction disc disposed in a recess formed in the front surface of the power piston with the rear end of the output rod being slidingly received in the recess. The reaction disc acts to transmit the output force from the power piston to the output shaft and also to transmit the reaction force to the input shaft.

However, in pneumatic force multiplying devices having the construction aforementioned, the power piston is usually formed of a hard synthetic resin and the output shaft of a metal, thus, the sliding resistance therebetween is very small such that the output shaft sometimes slips out of the power piston in transporting the device or in assembling the device with a vehicle.

For preventing the output shaft from slipping out of the pneumatic force multiplying device there has been provided an additional retaining member on the power piston or between the power piston and the output shaft. However, such countermeasure is objectionable since the number of parts will be increased, thus complicating the construction, increasing the costs and necessitating additional labour in assembly operations, etc.

An object of the present invention is to provide a force multiplying device obviating the usage of any additional retaining members for the output shaft.

According to the invention, the deformable reaction disc is received in a recess formed in the front surface of the power piston in a tight-fit condition, and the rear end of the output shaft is slidably received in the recess and is connected inseparably to the reaction disc with a projectionand-recess connection formed therebetween.

Since the sliding resistance between the power piston and the reaction disc which is formed of a material deformable under pressure is very large, the slipping out of the output shaft can reliably be prevented by the reaction disc.

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 force multiplying device according to the invention; Fig. 2 is a larger scale view showing a portion of Fig. 1, of significance to Dbe present invention; and Fig. 3 is a detail sectional view showing the significant portion of another embodiment of the present invention.

The pneumatic force multiplying device illustrated in Fig. 1 is a vacuum servomotor having a generally conventional construction and comprises a housing 1 defined by a front shell 1 A and a rear shell 1 B, and the interior of the housing 1 is divided into two, front and rear chambers 4 and 5 by a flexible diaphragm 2 and a power piston 3 which is attached to the diaphragm 2.

The power piston 3 sealingly passes through the rear shell 1 B to extend outside of the housing 1 and is slidable with respect to the rear shell 1 B in the left- and right-ward directions as viewed in the drawing (which are hereinafter referred as frontand rear-ward directions respectively). The front chamber 4 is normally connected with a source of vacuum pressure such as an intake manifold of an engine (not shown).

An input rod 6 and a plunger 7 constitute an input shaft. The rear end of the input rod 6 is connected to a brake pedal or the like (not shown), and the spherically shaped front end of the input rod 6 is rockingly and inseparably connected to the plunger 7, thus, the input rod 6 and the plunger 7 integrally move forwards in applying the brake.

Valve seats 3b and 7a are formed respectively on the rear ends of a cylinder portion 3a of the power piston 3 and the plunger 7 to cooperate with a poppet valve 9 which is biassed forwards with respect to the input rod 6 by means of a coil spring 8. In the unactuated condition of the device as shown in Fig. 1, the poppet valve 9 engages with the valve seat 7a and is spaced from the valve seat 3b, whereby the front chamber 4 is communicated with the rear chamber 5 through passages 3c and 3d, but the two chambers 4 and 5 are isolated from the atmospheric air. It will be noted that a space in the power piston 3 rearwards of the poppet valve 9 is communicated permanently with the atmospheric air.

There is provided a cylindrically shaped recess 3e in the front surface of the power piston 3. The recess 3e is coaxial with the cylinder portion 3a and connected therewith through a reduced diameter coaxial opening 3f which slidably receives therein a reduced diameter end portion 7b of the plunger 7. A reaction disc 10, formed of a material deformable under pressure such as rubber or the like, is received in the recess 3e, and the rear end of an output shaft 1 2 is slidingly received in the recess 3e. The output shaft 1 2 passes sealingiy and slidingly through the front shell 1 A to project outside of the housing 1 and is connected with a brake-applying member, such as a piston of a master cylinder (not shown).

The input rod 6 is biassed rearward or rightward in the drawing by a spring 11, and the power piston 6 is biassed in the same direction by a return spring 13. The rearward movement of the input shaft 6, 7 is prevented by a stop 14.

According to the invention, the reaction disc 10 is tightly fitted in the recess 3e of the power piston 3, and the rear end of the output shaft 12 is connected inseparably to the reaction disc with a projection and recess connection formed therebetween. In the embodiment of Figs. 1 and 2, there are formed a frontward facing shoulder 3g on the step in the diameter between the recess 3e and the opening 3ffor preventing rearward movement of the reaction disc 1 0, and a rearward facing shoulder 3h in the annular wall of the recess 3e which is defined by an annular and tapered recess 3jfor preventing frontward movement of the reaction disc 10.Further, an annular projection 1 2a is formed in the rear end portion of the output shaft 1 2 and is received in a correspondingly shaped annular recess 1 Oa formed in the front end of the reaction disc 1 0.

The annular projection 1 2a is shaped such that the diameter thereof gradually increases in the rearward direction, and the recess 1 Oa correspondingly has a tapered shape such that the inner diameter thereof gradually increases in the rearward direction. The annular projection 1 2a and the annular recess 1 Oa cooperate to constitute a projection-and-recess connection.

The force multiplying action of the vacuum servomotor having the construction vacuum servomotors and, therefore, description will hereinafter be made briefly. Firstly, a forward thrust is applied on the input rod 6 by depressing the brake pedal, the communication between the rear and front chambers 4 and 5 is intercepted and, thereafter, the atmospheric air is introduced into the rear chamber 5, whereby, a differential pressure is generated between the rear and front chambers 4 and 5, and the diaphragm 2 and the power piston 3 move forward thus starting the force multiplying action. The multiplied force or the thrust acting on the power piston 3 is transmitted through the reaction disc 10 to the output shaft 12.While, a reaction force corresponding to the output force acting on the output shaft 12 is transmitted to the input shaft through the reaction disc 10 which is compressed between the power piston 3 and the output shaft 1 2 and deforms such that a portion of the disc 10 enters the opening 3e to abut with the plunger 7 so as to transmit the reaction force.

In transporting the force multiplying the device or in assembling the device, the output shaft 1 2 sometimes receives a force in the forward direction under the effect of vibrations or the like; the reaction disc 1 2 also receives a force in the same direction since, according to the invention, the output shaft 1 2 is inseparably connected with the reaction disc 1 0. However, the sliding resistance between the reaction disc 10 and the power piston 3 is so large that the reaction disc 10 will not slip out of the recess 3e thereby preventing the output shaft 1 2 from slipping out of the power piston 3.In the embodiment of Figs. 1 and 2, the projection-and-recess engagement between the output shaft 12 and the reaction disc 10 comprises inclined or tapered, surfaces as shown in the drawings; thus, when the force in the forward direction is applied on the output shaft 1 2 the reaction disc 10 receives a force expanding the outer diameter thereof thus increasing the sliding resistance. It will be noted that the step 3h in the diameter of the recess 3e may be omitted.

Fig. 3 illustrates a modified form of the invention wherein a reduced diameter portion and an annular groove or recess 1 2b contiguous to the reduced diameter portion are formed in the rear end portion of the output shaft 12, and which are snugly received in a correspondingly shaped annular recess formed in the front surface of the reaction disc 1 0. In the embodiment, the recess 1 2b is formed in the output shaft 12, and a correspondingly shaped annular projection is formed on the inner circumference of the reaction disc 10 to constitute the inseparable projection and-recess connection.

In the embodiment shown in Fig. 1 , the front chamber 4 is a vacuum chamber and the rear chamber is an atmospheric pressure chamber, however, the present invention may be applied to any types of pneumatic force multiplying devices such as an atmospheric pressure-compressed air type or a vacuum pressure-compressed air type.

The projection-and-recess connection according to the invention may include screw-threaded connection or the like. As described heretofore, the slipping out of the output shaft 12 can, according to the invention, reliably be prevented by utilizing the reaction disc itself, thus, it is possible to omit any additional retaining members orthe like and to simplify the construction, thus reducing the costs in the manufacturing and assembling process. Further, the output shaft is firstly connected with the reaction disc and, thereafter, they are inserted into the recess in the power piston, thus, the reaction disc can easily be assembled with the power piston.

Claims

1. A pneumatic force multiplying device including a housing, a power piston slidingly mounted in the housing, a flexible diaphragm cooperating with the power piston to divide the interior of the housing into front and rear chambers, a valve mechanism incorporated in the power piston, an input shaft for actuating the valve mechanism to generate a differential pressure between said chambers, and a reaction disc for transmitting a forward thrust from the power piston to an output shaft and transmitting a reaction force from the output shaft to the input shaft, the reaction disc being received in a recess formed in the front surface of the power piston, and the rear end of the output shaft being slidably received in the recess and connected inseparably to the reaction disc with a projection-and-recess connection formed therebetween.

2. A pneumatic force multiplying device as claimed in claim 1 wherein the recess is a cylindrical bore formed in the power piston, and the reaction disc is tightiy fitted in the bore.

3. A pneumatic force multiplying device as claimed in claim 1 or 2 wherein a reduced diameter end portion and an annular groove contiguous to the reduced diameter end portion are formed at the rear end of the output shaft, and a correspondingly shaped recess is formed in the reaction disc to engage therewith.

4. A pneumatic force multiplying device as claimed in claim 1 or 2 wherein an annular projection is formed on the rear end of the output shaft, the shape of the projection being such that its outer diameter gradually increases in the rearward direction, and the reaction disc has a recess in the front surface thereof for snugly receiving the annular projection therein.

5. A pneumatic force multiplying device constructed substantiaily as herein described with reference to and as illustrated in the drawings.