GB2058977A

GB2058977A - Servo booster

Info

Publication number: GB2058977A
Application number: GB8026920A
Authority: GB
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1979-08-20
Filing date: 1980-08-19
Publication date: 1981-04-15
Also published as: FR2463869A1; AU6149880A; JPS5631950U; DE3031296A1

Abstract

The booster is of the kind including a piston plate (3) cooperating with a resilient diaphragm (4) for receiving a differential pressure produced across two chambers (A, B) which are defined in a housing, a generally cylindrical valve body (2) having therein a valve mechanism controlling the pressure in at least one of the two chambers, a head portion (2a) of a non-circular configuration formed on the valve body, a reduced diameter neck portion (2b) formed adjacent to the head portion to define therebetween a generally radial shoulder, an opening (3a) of a non-circular configuration formed in the piston plate for passing therethrough the head portion at a predetermined angular positional relationship. The valve body and the piston plate are connected by passing the head portion through the opening and rotating the piston plate around the neck portion so that the piston plate engages with the radial shoulder with the diaphragm being clamped between the piston plate and the valve body. A radial projection (3b) on the piston plate and a corresponding recess (2d) on the radial shoulder of the valve body engage when the piston plate has been rotated on the neck, and the resiliency of the diaphragm is utilized to maintain the engagement. <IMAGE>

Description

SPECIFICATION Servo booster This invention relates to servo boosters and, more particularly, to an improvement in a mechanism for connecting a valve body and a piston plate of a pneumatic servo booster which constitute the power piston of the servo booster.

In a conventional vacuum servo booster which is well-known as one kind of the pneumatic servo booster, a power piston is constituted by a generally cylindrical valve body disposed at the central portion of the servo booster, and a piston plate which is disposed around the periphery of the valve body and which is adapted to receive a differential pressure produced between two chambers which are defined in a housing and are partitioned by a resilient diaphragm. In such case, the piston plate and the valve body are usually connected by bolts which also act to clamp the inner periphery of the diaphragm between the piston plate and the valve body, and the connecting mechanism comprises a plurality of threaded holes formed in the valve body, holes formed in the piston plate, and bolts inserted from the side of the piston plate.

However, an air passage is provided in the valve body and, thus it is necessary to arrange the threaded holes radially outside of the air passage which inevitably increases the outer diameter of the valve body. Further, in attaining the desired tightening force in such a screw-thread connection, the threaded holes are required to have a substantial depth thus increasing the thickness of the valve body.

Further, there are problems in strength with respect to the tightening stress produced around the threaded holes and with respect to thermal stress, particularly when the valve body is formed of a synthetic resin material.

In order to solve the problems aforementioned there has been proposed a vacuum booster wherein an opening of a non-circular configuration is formed in the piston plate and a correspondingly shaped head portion of a non-circular configuration is formed in the valve body, which are engageable with one another at a predetermined angular positional relationship therebetween, and a reduced diameter neck portion is formed adjacent to the non-circular head portion of the valve body to define a generally radial shoulder between the head portion and the neck portion. The piston plate is secured to the valve body by passing the head portion through the opening at the predetermined angular relationship and by rotating the piston plate around the reduced diameter neck portion through a predetermined angle so that the inner circumference of the piston plate engages with the radial shoulder.The inner circumference of the diaphragm is clamped between the piston plate and a radial flange formed on the valve body and adjacent to the reduced diameter neck portion.

Various proposals have been made for preventing the relative rotation between the piston plate and the valve body but the construction of the rotation preventing mechanism is complicated and the function is not reliable.

An object of the present invention is to prevent the aforesaid shortcomings by providing a projection on either of the piston plate and the radial shoulder and a correspondingly shaped recess in the other of the piston plate and the radial shoulder such that the projection and the recess engage with one another when the piston plate is rotated around the reduced diameter neck portion. The engagement between the projection and the recess is maintained by the resiliency of the diaphragm.

The present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a vacuum servo booster according to the invention; Figure 2 is an enlarged end view of a portion of the vacuum servo booster of Fig. 1; Figure 3 is an enlarged longitudinal sectional view taken along line Ill-Ill in Fig. 2; and Figure 4 is a partial sectional view taken along line IV-IV in Fig. 3.

The vacuum servo booster shown in Fig. 1 comprises a housing 1 consisting of a front shell 1 a and a rear shell 1 b forming a closed container, a valve body 2 slidably supported in the housing 1 and having therein a valve mechanism controlling the differential pressure across two chambers A and B defined in the housing 1, a piston plate 3, and a diaphragm 4 dividing the interior of the housing 1 into the two chambers A and B and receiving the differential pressure in cooperation with the piston plate 3.

On the inner or the left end of the valve body 2 as viewed in Fig. 1, there is formed a head portion 2a having a non-circular configuration such as shown in Fig. 2; and an opening 3a having a non-circular configuration corresponding to the head portion 2a is formed at the central portion of the piston plate 3. The opening 3a can receive therethrough the head portion 2a at a predetermined angular positional relationship. The head portion 2a and the opening 3a may have any suitable configuration other than a circle, but preferably, there is defined an inscribed circle of a suitable diameter therein.

A neck portion 2b is formed adjacent to the head portion 2a. The diameter of the neck portion 2b is such that the piston plate 3 can rotate around the neck portion 2b when the head portion 2a has been passed through the opening 3a, and preferably, the neck portion 2b is defined by the inscribed circle in the head portion 2a for good mechanical strength.

Further, an annular flange 2c is formed adjacent to the neck portion 2b of the valve body 2 such that the inner peripheral portion 4a of the diaphragm 4 can be clamped between the annular flange 2e of the valve body 2 and the piston plate 3.

Thus, in assembling a power piston according to the present invention, the inner peripheral portion 4a of the diaphragm 4 is firstly located on the annular flange 2c of the valve body 2, then the piston plate 3 is fitted on the valve body 2 with the opening 3a of the piston plate 3 and the head portion 2a of the valve body 2 being aligned at a predetermined angular positional relationship and tha piston plate 3 is pushed in the direction of the axis of the valve body 2 against the resiliency of the inner peripheral portion 4a of the diaphragm 4 and, after passing through the head portion 2a of the valve body 2, the piston plate 4 is rotated through a predetermined angle (in the embodiment, a suitable angle less than 90 , preferably 45 ) with respect to the valve body 2 and around the neck portion 2b of the valve body 2, whereby the inner peripheral portion of the opening 3a of the piston plate 3 engages with and is retained by a generally radial shoulder 2e defined between the head portion 2a and the neck portion 2b of the valve body 2. The valve body 2, the piston plate 3 and the diaphragm 4 are tightly connected due to the resiliency of the diaphragm in the direction of the thickness thereof, thereby constituting the power piston.

Thereafter, the outer peripheral portion 4b of the diaphragm 4 is clamped between the shells 1 a and 1 b. Shown at 5 in Figs. 1 and 3 is a ring embedded in an annular groove of the diaphragm 4 so as to prevent the material of the inner peripheral portion 4a of the diaphragm 4 from escaping in the radially outward direction when compressing the inner peripheral portion 4a in the thicknesswise direction, whereby a predetermined interference can be assured.

For preventing the relative rotation between the piston plate 3 and the valve body 2 thereby retaining the power piston in the assembled condition, a recess 2d is formed in the shoulder 2e of the valve body 2 and a projection 3b is formed on the piston plate 3 according to the invention. The projection 3b projects generally towards the axis of the power piston and, in the embodiment, engages with the recess 2when the piston plate 3 is rotated through 45 , thereby preventing the relative rotation between the piston plate 3 and the valve body 2. The engagement between the projection 3b and the recess 2d is retained by the resiliency of the diaphragm 4.

In the embodiment, only one projection 3b and one recess 2d are formed between the piston plate 3 and the valve body 2, and the configuration thereof is a generally radially extending ridge or groove like shape; however, it is possible to provide any suitable number of mutually engaging projections and recesses having any desired configuration.

Further, the projection may be provided on the shoulder 2e with the recess being formed in the piston plate.

Now, a brief description will be given of the operation and the functions of the vacuum servo booster of Fig. 1 together with a description relating to parts which are not described heretofore. When an input rod 6 which is associated with a brake pedal (not shown) and plunger 7 connected to the input rod 6 are not actuated, the valve body 2 and the piston plate 3 are pressed in the rightward direction as viewed in the drawing by a return spring and are maintained at the position shown in the drawing with the diaphragm 4 abutting the rear shell 1 b.At that position, the chamber A which is normally connected to a source of vacuum such as an intake manifold of an engine communicates with the chamber B through axial and radial passages formed in the valve body 2 and, therefore, the two chambers A and B are at the same pressure and the power piston consisting of the valve body 2, the diaphragm 4 and the piston plate 3 is in its rest position.

When the input rod 6 is pushed leftward by depressing the brake pedal, a valve mechanism incorporated in the valve body 2 firstly interrupts the communication between the chambers A and B and, thereafter, connects the chamber B with atmosphere. The pressure in the chamber B rises toward the atmospheric pressure, whereby a differential pressure is generated between the chambers A and B, and the diaphragm 4, the piston plate 3 and the valve body 2 move together in the leftward direction as viewed in Fig. 1. Thus, the servo motor starts to operate, and the output force is transmitted through the piston plate 3, reaction levers 8, and a fulcrum plate 9 to an output rod 10. A hydraulic pressure is generated in a master cylinder (not shown) which is connected to the output rod 10. The input rod 6 receives the reaction force of the output of the servo motor. The reaction of the force acting of the output rod 10 is transmitted through the fulcrum plate 9 and reaction levers 8 to the plunger 7 which is connected to the input rod 6.

It will be noted that the invention can be applied not only to vacuum servo boosters wherein the differential pressure is generated between a vacuum pressure chamber A and a pressure equal to or less than the atmospheric pressure but also to pressure type servo motors wherein two chambers are at a high pressure and at atmospheric pressure or at a high pressure and a vacuum pressure. Further, the reaction levers 8 and the fulcrum plate 9 may be substituted by a resilient reaction disc for transmitting the output force to the output rod 10 and the reaction force of the plunger 7.

As described hereinbefore, according to the present invention, the piston plate and the valve body can easily and reliably be connected with one another without utilizing any separate rotation preventing members. The relative rotation between the piston plate and the valve body is retained by a projection-andrecess engagement and the resiliency of the inner peripheral portion of the diaphragm is utilized to maintain the projection-and-recess engagement in the engaged condition. In this respect, the ring 5 provided in the diaphragm 4 is effective to maintain the resiliency of the inner peripheral portion of the diaphragm in the axial direction for a long period of usage.

Claims

1. A servo booster including a piston plate cooperating with a resilient diaphragm for receiving a differential pressure produced across two chambers which are defined in a housing, a cylindrical valve body having therein a valve mechanism controlling the pressure in at least one of the two chambers, an opening of non-circular configuration formed through the piston plate, a head portion of non-circular configuration formed on the inner end of said valve body, said opening being adapted to receive therethrough said head portion at a predetermined angular positional relationship therebtween, a reduced diameter neck portion provided adjacent to said head portion, and a generally radial shoulder defined between the reduced diameter neck portion and the head portion of the valve body, said valve body and said piston plate being connected with one another by passing said head portion through said opening in the piston plate and by rotating the piston plate relative to the valve body and around said reduced diameter neck portion, wherein a projection capable of radial extension is formed on either of the piston plate and the radial shoulder and a correspondingly shaped recess is formed in the other of the piston plate and the radial shoulder, said projection and the recess engage with one another when the piston plate is rotated around the reduced diameter neck portion, and the engagement therebetween is maintained by the resiliency of said diaphragm which is clamped between the piston plate and the diaphragm.

2. A servo booster as set forth in claim 1 wherein the diameter of the reduced diameter portion of the valve body is nearly equal to that of an inscribed circle in the non-circular shape of the opening or the head portion.

3. A servo booster as set forth in claim 1 or 2 wherein the inner periphery of the diaphragm is clamped between the piston plate and the valve body, and an annular ring is embedded in the diaphragm to prevent the material of the inner peripheral portion of the diaphragm from escaping in the radially outward direction.

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