GB2068067A

GB2068067A - Pneumatic servo booster

Info

Publication number: GB2068067A
Application number: GB8101006A
Authority: GB
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1980-01-21
Filing date: 1981-01-14
Publication date: 1981-08-05
Also published as: DE3101795A1; AU6628881A; DE3101795C2; AU542928B2; GB2068067B

Abstract

A pneumatic servo booster including a shell housing consisting of front and rear shells 2, 3, a valve body 12 slidably extending through an opening formed in the rear shell, a flexible diaphragm 4 connected to the valve body and to the inner circumference of the shell housing to divide the interior of the housing into front and rear chambers, a valve mechanism 10 incorporated in the valve body for controlling the pressure difference between the two chambers, and at least one reinforcing rod 28 extending between front and rear shells and through the two chambers. The valve mechanism comprises a plunger 13 slidably received in the valve body and connected to an input rod 18, a valve seat 12c formed on the valve body, another valve seat formed on the plunger, and a poppet valve 11 cooperating with the valve seats. A return movment restricting member 35 is slidably mounted on the reinforcing rod and restricts the return movement of the plunger thereby establishing the rearmost position of the plunger. <IMAGE>

Description

SPECIFICATION Pneumatic servo booster This invention relates to pneumatic servo boosters and, particularly to pneumatic servo boosters of the kind including a shell housing consisting of front and rear shells, a valve body slidably extending through an opening formed in the rear shell, a flexible diaphragm connected to the valve body and partitioning the interior of the shell housing into two chambers, a valve mechanism incorporated in the valve body for controlling the pressure difference between the two chambers, and at least one reinforcing rod extending between the front and rear shells and through the interior of the shell housing.

Conventionally, the valve mechanism comprises a poppet valve, a valve seat formed on the valve body, and another valve seat formed on a plunger which is connected to an input rod and is slidably mounted on the valve body. When the poppet valve is spaced from the valve seat of the valve body and is seated on the valve seat of the plunger, the two chambers in the shell housing are communicated with one another and are maintained at a first referential pressure such as a vacuum pressure. When the poppet valve engages with the valve seat of the valve body and separates from the valve seat of the plunger the communication between the two chambers is intercepted and a second referential pressure such as the atomospheric pressure is introduced into such as the rear chamber, thereby generating a pressure difference between the two chambers.It will be noted that one of the chambers such as the front chamber is permanently maintained at the first referential pressure.

The reinforcing rod is effective in increasing the mechanical strength of the shell housing and, is particularly advantageous when the rear end of the servo booster is secured to a body of the vehicle, and a member of a hydraulic braking system of the vehicle such as a master cylinder is connected to the front end of the servo booster and is supported thereby in a canti-lever style.

In the non-actuated condition of the conventional servo boosters of the kind aforementioned, the valve body returns to its rearmost position due to a return spring and the plunger also retracts to its rearmost position which is defined by a stop provided on the valve body. At that condition, a clearance is formed between the valve seat of the valve body and the poppet valve.The clearance defines the maximum lift of the poppet valve with respect to the valve seat of the valve body in the return stroke of the servo booster, thus, in the view-point of the responsiveness of the servo booster, it is preferable to increase the clearance, however, in actuating the servo booster, the pressure difference between the two chambers does not generate until the clearance has been taken up and the poppet valve separates from the valve seat of the plunger, therefore, the clearance deterioarates the pedal feeling.

An object of the present invention is to solve the problems aforementioned and to provide a pneumatic servo booster having an improved responsiveness both in the actuating and return strokes.

The pneumatic servo booster according to the invention is characterized by a return movement restricting member which cooperates with the reinforcing rod to restrict the return movement of the plunger when the plunger returns to its return position.

Preferably, the return movement restricting member is slidably mounted on the reinforcing rod, and engages with a shoulder formed on the rear end portion of the rod and with the plunger when the plunger returns to its return position.

The foregoing and other objects and advantages of the invention will become apparent from the following description with reference to the attached drawings.

In the drawings: Figure 1 is a longitudinal sectional view of a prior art pneumatic servo booster, with the lower half thereof being of a vertical cross-section and the upper half thereof being of a horizontal crosssection; Figure 2 is a longitudinal sectional view similar to Figure 1 but showing a first embodiment of the present invention; Figures 3 - 5 are sectional views showing the essential portion of the servo booster of Figure 2 showing the relationship between the plunger, the return movement restricting member and the valve body in respective stages of the actuation; Figure 6 is a perspective view of the return movement restricting member and the plunger of the servo booster of Figure 2; Figures 7-9 are explanatory views showing passages formed in the servo booster.

Figure 10 is a sectional view taken along line X-X in Figure 9; Figure ii is a longitudinal sectional view similar to Figure 2, but showing a second embodiment of the invention; Figures 12 - 14 are views similar to Figures 3 - 5, respectively; Figure 15 is a perspective view similar to Figure 6, and Figure 16 is a partial sectional view showing a modified form of resilient member of Figure 12.

Figure 1 illustrates a typical prior art pneumatic servo booster which comprises a shell housing 1 consisting of front and rear shells 2 and 3, a flexible diaphragm 4 dividing the interior of the housing into two chambers A and B, a power piston 5 secured to the diaphragm 4. A poppet valve mechanism 10 connects or disconnects the communication between the two chambers A and B and the communication between the chamber B and the atmosphere.

It will be noted that the chamber A is permanently connected with a source of vacuum pressure such as an intake manifold of an engine of a vehicle. The poppet valve mechanism 10 comprises a poppet valve 11, an annular valve seat 12formed on a valve body 12, and an annular valve seat 13b formed on a plunger 13. The valve body 12 slidably extends through the rear shell 3 and has a large diameter portion 1 2a on the inner end thereof, to which the inner periphery 4a of the diaphragm 4 is connected.

The plunger 13 is slidably fitted in the valve body 12 and is secured to an input rod 18. The relative axial movement of the plunger 13 with respect to the valve body 12 is restricted by the radially inner end 5a of the power piston 5 which is loosely fitted in an annular groove 13a formed in the outercircumfer- ence of the plunger 13. It will be noted that the power piston 5 has a non-circular opening to define the inner end 5a. An annular seal 14 is interposed between the rear shell 13 and a small diameter portion 12b of the valve body 12 so as to sealingly and slidably support the valve body 12. The small diameter portion 12b of the valve body 12 has a bore 15 therein, and a spring retainer 16 is fitted in the bore 15 and is retained by a shoulder 15a formed in the bore 15.The spring retainer 16 supports one end 1 1b of the poppet valve 11 and sealingly urges the one end against the bore 15. The other end 1 1a of the poppet valve 11 cooperates with the valve seats 1 2c and 13b. The input rod 18 is rearwardly biassed by a coil spring 19 which is supported on the spring retainer 16.

In the non-actuated condition of the servo booster shown in the drawing, the rearward movement of the plunger 13 is restricted by the inner end 5a of the power piston 5 and a clearance 6 is formed between the poppet valve 11 and the valve seat 12c of the valve body 12, while, the poppet valve 11 engages with the valve seat 13b of the plunger 13. The chamber B is connected with the chamber A through an axial passage 20 formed in the large diameter portion 12a of the valve body 12, an annular space 21 formed in the valve body 12, and a radial passage 22 formed in the valve body 12.

In actuating the servo booster, the input rod 18 is displaced leftward as viewed in the drawing, the poppet valve 11 engages with the valve seat 1 2c after taking up the clearance 6 thereby disconnecting the communication between the chambers A and B.

Thereafter, the poppet valve 11 separates from the valve seat 13b of the plunger 13so that the chamber B is connected with the atmosphere through the radial passage 22, the annular space 21, a space formed in the bore 15 of the valve body 12 and around the input rod 18, an air cleaner, and an opening formed in the rear end of the small diameter portion 1 2b of the valve body. A pressure difference generates between the chambers A and B, and the power piston 5 and the diaphragm 4 together with the valve body 12 displace leftward. An output force is transmitted through an output rod 26 to such as a piston of a master cyliner (not shown) of a hydraulic braking system of the vehicle.There is provided a reaction disc 25 to transmit the output force from the power piston 5 to the output rod 26 and also to transmit a reaction force to the input rod 18 through the plunger 13.

It will be understood that the responsiveness of the servo booster in the actuating stroke is mainly determined by the maximum lift or the clearance between the valve seat 13b of the plunger 13 and the poppet valve it in the actuating stroke, and the responsiveness in the return stroke is mainly determined by the maximum lift or the clearance between the valve seat 12c of the valve body and the poppet valve 11 in the return stroke. In the prior art servo booster shown in the drawing, the maximum clearance between the valve seat 1 2c and the poppet valve 12 is equal to the clearance 6 in the nonactuated condition. However, the clearance 6 consti- tutes an ineffective stroke in the actuating stroke thereby deteriorating the pedal feeling.

Further, there are provided two reinforcing rods 28 which extend respectively between the front and rear shells 2 and 3 and through the chambers A and B. In the embodiment, the rods 28 pierce through large diameter flange portion 1 2a of the valve body, the power piston 5 and an opening of the flexible diaphragm 4. A bellows-like seal member surrounds the rod 28 so as to intercept the communication between the chambers A and B and aiong the circumference of the rod 28.

The present invention relates to improvements in prior art pneumatic servo booster as shown in Figure 1 wherein the clearance 6 between the poppet valve and the valve seat of the valve body in the nonactuated condition of the servo booster is decreased as small as possible thereby improving the pedal feeling, and the clearance in the return stroke of the servo booster is increased as large as possible thereby improving the responsiveness.

Figures 2 - 7 illustrate a pneumatic servo booster according to the invention and, since the construction of which is generally similar to the servo booster of Figure 1, the same numerals have been applied to corresponding parts and detailed descriptions therefor are omitted.

According to the invention, a return movement restricting member 35 is provided to restrict the return movement of the plunger 13 with respect to the housing 1. The return movement restriction member 35 is, as shown in Figure 6, a generally rectangular rigid plate member having a bore 36 in one end portion, a bore 37 in the mid portion, and a slot 38 in the other end portion. The restricting member 35 is loosely received in a radially extending groove 41 of the large diameter portion 12a of the valve body 12, with the bore 36 loosely receiving therethrough one of the reinforcing rods 28, and the slot 38 receiving the small diameter portion of the plunger 13 which is defined by the annular groove 13a.The bore 37 acts to loosely receive the there- - through one of tightening screws 40 which secure the power piston 5 and a disc holder 39 with the large diameter portion 12a of the valve body 12. The restricting member 35 can move in the groove 41 in the direction of the axis of the servo booster. The reinforcing rod 28 engaging with the bore 36 of the restricting member 35 has a shoulder 28c on the rear end portion, so that when the valve body 12 retracts to its rearmost position as shown in Figure 2, the restricting member 35 engages with the shoulder 28c and with the power piston 5 thereby restricting the rearward movement of the valve body 12. At that condition, the input rod 18 and the plunger 13 also move rearward due to the spring 19, and the rearward movement is restricted by the restricting member 35 which engages with the wall 13d of the annular groove 13a of the plunger 13. A small clearance 6, is formed between the poppet valve 11 and the valve seat 13b of the plunger 13. The clearance 1 is preferably as small as possible, however, it is essential that the poppet valve 11 is tightly engaging with the valve seat 1 2c of the valve body 12. Since the return or retracting movement of the plunger 13 is restricted by the restricting member 35, the radially inner end 5a of the power piston 5 does not engage with the annular groove 13a of the plunger 13.

The space 21 defined by the valve seat 12c of the valve body 12, the valve seat 13b of the plunger 13 and the poppet valve 11 is communicated with the chamber B through a passage 42 formed in the valve body 12 and the groove 41 and, also with the atmosphere through the clearance 61, the interior of the poppet valve 11 and an opening formed in the rear end of the valve body 12. Thus, in the normal non-actuated condition of the servo booster, the valve body 12 slightly displaces frontward from the position shown in Figure 2 to take up the clearance 6,. Such condition is shown in Figure 3.

It will be noted that the servo booster takes the condition of Figure 2 only when the booster has been newly assembled, and when the chamber A is connected to a source of vacuum pressure the valve body 2 moves leftward so that the poppet valve 11 firstly engages with the valve seat 13b of the plunger 13 and, secondly, separates from the valve seat 12c of the valve body 12 thereby exhausting the air in the chamber B to the source of vacuum pressure through the chamber A. Thereafter, the valve body 12 returns to the condition of Figure 3.

At the normal non-actuated condition of Figure 3, the poppet valve 11 engages with the valve seats 1 2c and 13b so that the chamber B is isolated both from the chamber A and the atmosphere. When a brake pedal (not shown) of the vehicle is depressed the plunger 13 moves leftward thereby the valve seat 1 3b of the plunger 13 instantly separates from the poppet valve 11 to introduce the atmospheric air into the chamber B. A differential pressure generates between the chambers B and A and the servo booster actuates. There is not any ineffective movement of the input rod 18 thus improving the pedal feeling. Such condition is shown in Figure 4.

In the return stroke of the servo booster shown in Figure 5, the restricting member 35 is displaced rearward due to the return movement of the plunger 13, and the maximum lift 62 of the poppet valve 11 from the valve seat 1 2c is substantially defined by the depth of the groove 41 of the valve body 12 minus the thickness of the restricting member 35.

Therefore, it is possible to increase the responsiveness of the servo booster in the return stroke as desired. It will be noted that the maximum lift or the clearance 62 can be determined as desired irrespective to the ineffective stroke of the prior art servo booster in the actuating stroke.

Figures 7 - 10 show various arrangements of the passage 42 connecting the space 21 with the chamber B through the groove 41. In Figure 7, two axially extending passages 42 are formed in the valve body 12 and are partially defined by the outer circumference of the plunger 13. In Figure 8, passages 42' are defined by axially extending grooves formed in the plunger 13. In Figures 9 and 10, an arcuate passage 42" is formed in the valve body 12 separately from the bore receiving slidablytherein the plunger 13.

The embodiment shown in Figures 11 - 15 is generally similar to the embodiment shown in Figures 2 - 7 and corresponding numerals have been applied to corresponding parts, thus, detailed description therefor is omitted.

As shown in Figures 11 and 12 which correspond respectively with Figures 2 and 3, the rearward movement of the restricting member is stopped by a resilient sleeve 45. The sleeve 45 is fitted on the rear end portion of the reinforcing rod 28, and is preferably formed of such as rubber or synthetic resin. In the return stroke of the servo booster, the restricting member 35 engages with the resilient sleeve 45 thereby stopping the return movement of the piunger 13 and the input rod 18. The input rod and the plunger smoothly return to the non-actuated condition, and the generation of noises can be suppressed.

The operation of the servo booster of Figures 11 15 is otherwise similar to the embodiment of Figures 2-7.

Figure 16 shows a modified form wherein a resilient ring 46 is fitted on the reinforcing rod 28 and, when the restricting member 35 returns to the rearmost position, the ring 46 is clamped between the restricting member 35 and a shoulder 28d provided on the rear end portion of the reinforcing rod 28. The ring 46 is preferably formed of rubber or synthetic resin but, alternatively, the ring 46 may be substituted by one or more wave washers.

In the embodiments, two reinforcing rods 28 are provided in the vertical central plane, but the reinforcing rods may be arranged in the horizontal central plane. Further, three or more reinforcing rods may be provided as desired. The restricting member 35 may slidably be mounted on either one of the reinforcing rods.

As described heretofore, according to the invention, a return movement restricting member is axially movably mounted on a reinforcing rod and in the valve body to restrict the return movement of the plunger when the plunger returns to its rearmost position. Whereby the poppet valve can engage with the valve seat of the valve body and with the valve seat of the plunger in the normal non-actuated condition of the servo booster, thus improving the pedal feeling in actuating the servo booster and also improving the responsiveness in the return stroke.

Although the description has been made with respect to so-called vacuum servo booster, it will be understood that the invention may be applied to any types of pneumatic servo boosters.

Claims

1. A pneumatic servo booster including a shell housing consisting of front and rear shells, a valve body slidably extending through an opening formed in the rear shell, a flexible diaphragm connected to the valve body and partitioning the interior of the shell housing into two chambers, a valve mechanism incorporated in the valve body and including a poppet valve and two valve seats formed respectively on the valve body and a plunger which is connected with an input rod and is slidably fitted in the valve body, said valve mechanism communicates said two chambers when the poppet valve is spaced from the valve seat of the valve body and is seated on the valve seat of the plunger, and at least one reinforcing rod extending between the front and rear shells and through the interior of the shell housing, characterized in that a return movement restricting member is provided in connection with said rod to restrict the return movement of said plunger when the plunger returns to its return position.

2. A pneumatic servo booster according to Claim 1 wherein the return movement restricting member is slidably mounted on said rod, and engages with a shoulder formed on the rear end portion of said rod and with said plunger when the valve body returns to its return position.

3. A pneumatic servo booster according to Claim 2 wherein the return movement restricting member engages with said shoulder interposing therebetween a resilient member.

4. A pneumatic servo booster according to Claim 1 wherein the radially inner end of said return movement restricting member is received in an annular groove formed in said plunger.

5. A pneumatic servo booster according to Claim 1 wherein said return movement restricting member loosely extends through a radial opening formed in said valve body, and said opening acts as a part of the passage connecting said two chambers.

6. A pneumatic servo booster substantially as herein described with reference to, and as shown in, Figures 2to 10 or Figures 11 to 15 or Figure 16 ofthe accompanying drawings.