GB2058260A - A pneumatic servo booster - Google Patents

Abstract

A pneumatic servo booster of the kind including a housing, a valve body 5 incorporating a valve mechanism and slidably mounted in the housing, a piston plate 23 and a flexible diaphragm connected to the valve body for dividing the interior of the housing into two chambers 3 and 4, and a bayonet type connection between the valve body 5 and the piston plate 23. The bayonet type connection comprises a non-circular central opening 24 formed in the piston plate, a correspondingly shaped non-circular flange portion 20 formed on the valve body, a lug portion 25 integrally formed on the piston plate and projecting therefrom in the direction of the axis of the servo booster, and a retaining portion 21a formed in the outer circumferential portion of the valve body 5 for fittingly receiving the lug portion 25 to restrict the relative rotation between the piston plate and the valve body, thereby retaining the bayonet type connection at the connected condition. <IMAGE>

Description

SPECIFICATION A pneumatic servo booster This invention relates to a pneumatic servo booster and, particularly to pneumatic servo boosters of the kind including a housing, a valve body incorporating a valve mechanism and slidably mounted in the housing, a piston plate and a flexible diaphragm connected to the valve body to divide the interior of the housing into two chambers, and a bayonet type connection provided between the piston plate and the valve body.

A pneumatic servo booster of the aforementioned kind is widely used in an hydraulic braking system of an automobile. The servo booster utilizes vacuum pressure in an intake manifold of an engine or pressurized air supplied from a compressor. The valve mechanism controls the communication between the two chambers and between one of the chambers and the atmospheric air or a source of pressurized air. A differential pressure generated between the two chambers is transmitted to an output rod through the piston plate.

Various proposals have been made with respect to the connection between the piston plate and the valve body. A bayonet type connection, as disclosed in US patent specification 3981227, is simple in construction, can save the number of parts, thereby reducing manufacturing and assembling costs. Typically, the bayonet type connection comprises a non-circular shaped opening formed in the central portion of the piston plate, a correspondingly shaped non-circular shaft or head portion formed on the valve body, a radial shoulder defined on one end of the shaft or head portion, and a rotation preventing member.In assembling the piston plate with the valve body, the non-circular shaft or head portion of the valve body has been passed through the non-circular opening of the piston plate at a specific angular positional relationship between the piston plate and the valve body, thereafter, the piston plate is rotated relative to the valve body by a predetermined angle so that the radial shoulder engage with one side surface of the piston plate, and the rotation preventing member is installed to restrict the relative rotation between the piston plate and the valve body. Thus, the valve body and the piston plate are reliably connected in a simple manner.However, the rotation control member has usually been formed of a plate like member separate from the piston plate and mounted in its position afterwards of the aforesaid passing through and rotating process, thus, the mounting process has been troublesome and time consuming.

An object of the present invention is to provide a pneumatic servo booster eiiminating the shortcoming of the prior art device.

According to the present invention there is provided a pneumatic servo booster comprising a housing, a valve body incorporating a valve mechanism and slidably mounted in the housing, a piston plate and a flexible diaphragm secured to the valve body to divide the interior of the housing into two chambers, and a bayonet type connection provided between the piston plate and the valve body, the bayonet type connection comprising a non-circular central opening formed in the piston plate for passing therethrough a correspondingly shaped non-circular flange portion formed on the outer circumference of the valve body at a specific relative angular positional relationship between the piston plate and the valve body, a pawl portion integrally provided on the piston plate and a retaining portion formed in the valve body for fitting engagement with the pawl portion of the piston plate when the non-circular flange portion of the valve body has been passed through the non-circular opening of the piston plate and the valve body has been rotated relative to the piston plate, thereby restricting the rotation of the valve body relative to the piston plate.

Preferably, the pawl portion projects from one side surface of the piston plate and is received in a recess formed in a large diameter flange portion which is provided on the valve body at a location adjacent to the non-circular flange portion.

The present invention will now be described further, by way of example only, with reference to the accompanying drawings, exemplifying a preferred embodiment of the invention, in which: Fig. 1 is a longitudinal sectional view of a pneumatic servo booster according to the invention; Fig. 2 is a side view of the valve body incorporated in the servo booster of Fig. 1, in looking in the leftward direction in Fig. 1, and Fig. 3 is a partial side view of the piston plate to show the non-circular opening.

The pneumatic servo booster shown in the drawings comprises a shell housing 1 formed of a front shell 1 A and a rear shell 1 B, a flexible diaphragm 2 dividing the interior of the shell housing 1 into front and rear chambers 3 and 4, and a valve body 5 slidably and sealingly mounted in the rear shell 1 B.

There are provided passages 6, 7 and 8 in the valve body 5 to communicate the front and rear chambers 3 and 4 with one another, and a valve member 10 connected to an input rod 9 is slidably disposed in a small diameter bore 5a of the valve body 5. A poppet valve 12 having a generally tubular configuration and formed of resilient material normally engages with an annular valve seat 1 Oa formed on the outer end of the valve member 10 to separate the chamber 4 from the atmosphere. A coil spring 11 acts on the poppet valve 12. The poppet valve 12 is adapted to engage with an annular valve seat 1 Ob which is formed on a radial shoulder defined on the outer end of the small diameter bore portion Sb in the valve body 5.When the poppet valve 12 seats on the valve seat 1 Oa and is separated from the valve seat 1 or, the rear chamber 4 is communicated with the front chamber 3 which is connected to a source of vacuum pressure such as an intake manifold of an engine and the chambers 3 and 4 are separated from the atmosphere. When poppet valve 12 engages with the valve seat lOb the communication between the chambers 3 and 4 is disconnected and, when the poppet valve 12 is separated from the valve seat 1 Oa, the chamber 4 is communicated with the atmospheric air which passes through an opening formed in the outer or the right end of the valve body 5, an air filter 14 and an annular space defined between the input rod 9 and the poppet valve 12.

The inner end of the small diameter bore 5a of the valve body 5 is connected with an annular recess 16 which is formed in the inner end of the valve body 5. A reaction disc 17 and the inner end portion 1 8a of an output rod 18 are received in the recess 16, and the outer or the front end 1 8h of the output rod 1 8 sealingly passes through the front shell 1 A to project outside of the pneumatic servo booster. A return spring 19 extends between the front shell 1 A and the valve body 5. A dust boot 15 is provided between the outer or the right end of the valve body 5 and the rear shell 1 B.

On the inner end of the valve body 5, there is provided a large diameter flange 21. A noncircular shaped flange 20 is also formed on the outer periphery of the valve body 5 to define an annular groove 22 between the large diameter flange 21.

A piston plate 23 having a non-circular central opening 24 is bonded to the diaphragm 2 and, the piston plate 23 is connected to the valve body 5 through a bayonet type connection consisting of the non-circular opening 24 in the piston plate 23 and the non-circular flange 20. The non-circular opening 24 is adapted to snugly pass therethrough the non-circular flange 20 of the valve body 2 at a specific angular positional relationship between the valve body 5 and the piston plate 23. It will be noted that the piston plate 23, the diaphragm 2, and the valve body 5 cooperate to divide the interior of the housing 1 into chambers 3 and 4. The inner circumference 2a of the diaphragm 2 is fittingly engaging with the outer circumference of the valve body 5.

In the embodiment, the non-circular opening 24 in the piston plate 23 and the non-circular flange 20 of the valve body 5 have, as shown in Figs. 3 and 2, generally rectangular configuration with each of the corner portions such as 24a being rounded by a circumcircle. Preferably, the sides of the rectangle define an inscribed circle as shown in Fig. 2. The non-circular flange 20 defines a radial shoulder which constitutes a portion of the annular groove 22.

The bayonet type connection between the valve body S and the piston plate 23 consisting of the non-circular opening 24 in the piston plate 23 and the non-circular flange 20 of the valve body 5 can be brought into the connected condition by passing through the opening 24 the non-circular flange 20 at a specific angular relationship and by rotating the piston plate 23 in the annular groove 22 by a predetermined angle, preferably about 45 in this case, so that the radial shoulder defined by the non-circular flange 20 engages with a side surface of the piston plate 23, thereby preventing the relative displacement therebetween in the axial direction. Incidentally, shown at 26 in Fig. 1 is retaining plate having a bifurcated end 26a. The plate 26 is inserted into the valve body 5 and restrict the movement of the valve member 10.

The general construction of the pneumatic servo booster and the bayonet type connection between the piston plate and the valve body described as above is known to public, however, in the prior art servo booster the bayonet type connection has been retained in the connected condition by a rotation control member having a complicated construction.

According to the invention, a pawl portion 25 is integrally formed on the piston plate 23 by cutting and bending process so that the pawl portion 25 projects toward the large diameter flange 21 of the valve body 5 or in the direction of the axis of the servo booster. A cut-out portion 21 a is formed in the outer circumference of the large diameter flange 21 of the valve body 5 as clearly shown in Fig. 2. The cut-out portion 21a acting as a retaining portion according to the invention and the pawl portion 25 are located such that the pawl portion 25 is received in the cut-out portion 21a when the non-circular flange 20 has been passed through the non-circular opening 24 of the piston plate at a specific angular relationship therebetween and the piston plate is rotated in the annular groove 22 by a predetermined angle.The engagement between the pawl portion 25 and the cut-out portion 21 a effectively prevent the relative rotation between the piston plate and the valve body. It will be noted that in the assembling process aforementioned the pawl portion 25 of the piston plate abuts with the side surface of the flange 21, whereby the piston plate 23 will deflect into a dish-like shape, however, the pawl portion 25 is spaced from the inner circumference of the opening 24, thus the piston plate can resiliently deflect. Further, in the operating condition of the servo booster, the pressure in the chamber 4 is equal to or higher than the pressure in the chamber 3, thus the engagement between the pawl portion 25 and the retaining portion 21a can reliably be maintained.

In the embodiment, the width of the annular groove 22 in the valve body 5 is nearly equal to the thickness of the piston plate 5 which is received therein, but, it is possible to form the inner circumference of the piston plate 23 into a wave-like form so that the piston plate is resiliently received in the groove 22.

The operation of the pneumatic servo booster illustrated in the drawings is similar to the prior art device, and will be explained briefly.

When the input rod 9 is displaced leftward against the force of a spring 13 by depressing a brake pedal (not shown), the poppet valve 1 2 moves leftward together with the valve member 10 to engage with the valve seat 1 Ob, whereby the rear chamber 4 is disconnected from the front chamber 3. The valve member 10 and the input rod 9 further move leftward to separate the poppet valve 12 from the valve seat 1 Oa.

Atmospheric air is introduced into the chamber 4, thereby generating a differential pressure between the chambers 4 and 3. A leftward thrust acts on the valve body 5 and is transmitted to the output rod 1 8 through the reaction disc 1 7. A master cylinder (not shown) is actuated by the output rod 18, and hydraulic pressure generated in the master cylinder is transmitted to wheel brakes.

The reaction force of the output rod 1 8 is transmitted to the valve member 10 according to the resilient deformation of the reaction disc 1 7.

In response to the leftward displacement of the valve body 5, the poppet valve 12 moves leftward together with the valve seat lOb toward the valve seat 1 Oa, whereby the chamber 4 is separated both from the chamber 3 and from the atmospheric air, and the servo booster assumes and equilibrium condition.

When the depressing force applied on the brake pedal is released the servo booster returns to the initial position shown in Fig.1 according to the return spring 1 9.

As described heretofore in detaii, it is possible, according to the invention, to omit the complicated rotation control member in the prior art device, and the bayonet type connection between the valve body and the piston plate is simple in construction, easy in assembling or disassembling operation, and reliable in assuring the operational characteristics. Further, the valve body has a large diameter flange portion abutting with the piston plate, thus, a relatively large portion of the differential pressure force acting across two chambers 3 and 4 is directly received by the valve body and, accordingly, the strength of the piston plate can be reduced.

Claims (5)

1. A pneumatic servo booster comprising a housing, a valve body incorporating a valve mechanism and slidably mounted in the housing, a piston plate and a flexible diaphragm secured to the valve body to divide the interior of the housing into two chambers, and a bayonet type connection provided between the piston plate and the valve body, the bayonet type connection comprising a non-circular central opening formed in the piston plate for passing therethrough a correspondingly shaped non-circular flange portion formed on the outer circumference of the valve body at a specific relative angular positional relationship between the piston plate and the valve body, a pawl portion integrally provided on the piston plate and a retaining portion formed in the valve body for fitting engagement with the pawl portion of the piston plate when the non-circular flange portion of the valve body has been passed through the non-circular opening of the piston plate and the valve body has been rotated relative to the piston plate, thereby restricting the rotation of the valve body relative to the piston plate.

2. A pneumatic servo booster as claimed in claim 1, wherein a large diameter radial flange is provided on the valve body at a location adjacent to the non-circular flange portion, and the retaining portion is a recess formed in the outer circumferential portion of the large diameter flange.

3. A pneumatic servo booster as claimed in claim 2, wherein the pawl portion of the piston plate is a cut-and-bent portion projecting in the direction of the axis of the servo booster.

4. A pneumatic servo booster as claimed in claim 3, wherein the pawl portion of the piston plate is spaced from the inner edge of the noncircular opening of the piston plate in the radially outward direction by a distance which allows a dish shaped deflection of the piston plate when the non-circular flange portion is passed through the non-circular opening of the piston plate with the axially projecting end of the pawl portion abutting with the side surface of the radial flange of the valve body.

5. A pneumatic servo booster constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.