GB2278167A

GB2278167A - Brake booster

Info

Publication number: GB2278167A
Application number: GB9414475A
Authority: GB
Inventors: Makoto Watanabe
Original assignee: Jidosha Kiki Co Ltd
Current assignee: Jidosha Kiki Co Ltd
Priority date: 1991-07-19
Filing date: 1992-07-07
Publication date: 1994-11-23
Anticipated expiration: 2012-07-07
Also published as: GB9414475D0; GB2278167B

Abstract

A brake booster provided with a function to serve as an automatic brake is disclosed. A bellows 217 disposed within a shell 202 has a rear bead 217b which is held against the inner surface of a front opening of a valve body 207 of the brake booster by means of a retainer 239 which is held in place in the valve body by a valve body return spring 240. The arrangement thereby effectively prevents failure of the hermetic sealing of the bellows in the region of the rear bead. When a valve mechanism in the valve body is not operated, the space A' will communicate with a variable pressure chamber B, and, upon switching of a solenoid valve (43, Fig. 1), air will be introduced into space A' and chamber B to effect automatic braking. <IMAGE>

Description

BRAKE BOOSTER The invention relates to a brake booster, and more particularly, to an improvement of a brake booster provided with a function to serve as an automatic brake.

Known in the art, as disclosed in United States Patent No. 4,966,248, for example, is a brake booster able to serve as an automatic brake and comprising a power piston between valve body, constant and variable pressure chambers within a shell of the booster communication able to establish between the constant and the variable pressure chambers through a valve mechanism and a variable pressure passage, and bellows disposed within the constant pressure chamber and having a rear opening connected to the constant pressure passage and a front end connected to the shell. The interior of the bellow may be connected to a negative pressure source or it may be connected to atmosphere and in the latter case the effect is to actuate the brake booster without depressing a brake pedal.

Another brake booster provided with a function to serve as an automatic brake is also disclosed in United States Patent No. 4,667,471.

In the brake booster disclosed in US 4,966,248, the rear end of the bellows is connected to a constant pressure passage takes place as follows: an annular groove is formed around the outer periphery of a valve body on which the power piston slides, rearward of a location where a front end of the constant pressure passage opens thereinto, and the rear end of the bellows is fitted into the annular groove by utilizing its own resilience, thereby maintaining a hermetic seal in this region.

However, when atmospheric pressure is introduced into the bellows to cause the brake booster to function as an automatic brake, the entire bellows will tend to expand radially outward, whereupon the rear end of the bellows in the annular groove in the valve body will be urged in both the axial direction and radially outward. Accordingly, there is a risk of causing failure of the hermetic seal or leakage from the region where the rear end of the bellows is connected atmospheric pressure is introduced into the bellows.

In one aspect the present invention relates to a brake booster comprising a valve body slidably disposed within a shell, a power piston connected to the valve body, constant and variable pressure chambers formed on opposite sides of the power piston, a valve mechanism disposed in the valve body for switching a fluid circuit, a passage formed in the valve body having a front end which opens into a front end face of the valve body for providing communication between the constant and variable pressure chambers through the valve mechanism which switches a fluid circuit and for providing a communication between the constant and variable pressure chambers through the valve mechanism, bellows disposed within the constant pressure chamber having a rear opening connected to said passage in the valve body and a front end connected to the shell, and an internal space within the bellows being arranged to be connected to a suction or a pressure source. A spring is provided between the shell and the valve body for urging the valve body rearward. The rear end of the bellows is formed as an increased thickness bead which is fitted into an opening formed in the valve body providing the front end of said passage. Under this condition, said bellows bead is disposed in abutment against the inner peripheral surface of said opening by means of a locking step formed on the front end of the retainer to prevent the bead from being disengaged in the forward direction. In addition, the rear end of the retainer is interposed. between the spring and the valve body and thus is secured to the valve body.

It will be appreciated that if the rear end of the bellows tends to be stressed both axially and radially upon introducing the atmospheric pressure into the internal space within the bellows, because the rear end of the bellows is located within the annular recess formed in the power piston and is held in place by securing means, the rear end is restrained against being displaced in either the radially outward direction or the axial direction, thus preventing a failure of the hermetic seal in the region where the rear end of the bellows is connected.

Further features and advantages of the invention will become apparent from the following description with reference to the attached drawings, in which: Fig. 1 is a longitudinal section of a brake booster having a constant pressure chamber containing a bellows for automatic brake operation; Fig. 2 is a fragmentary view, to an enlarged scale, of a part of Fig. 1; and Fig. 3 is a fragmentary view in longitudinal section of an embodiment of the present invention as applied to the brake booster of Fig. 1.

Fig. 1 shows a brake booster of the tandem type including a shell 1, which is defined by connecting a front shell 2 and a rear shell 3 together. The interior of the shell 1 is divided by a centerplate 4 into a forwardly located, front chamber 5 and a rearwardly located rear chamber 6.

Axial portions of the centerplate 4 and the rear shell 3 are formed with through-openings, through which a valve body -7 in the form of a stepped cylinder slidably extends1 with seal members 8 maintaining a hermetic seal between the respective openings and the valve body 7.

A front and a rear power piston 9, 10 are disposed in the front and the rear chamber 5, 6, respectively. The inner periphery of each power piston 9 or 10 is connected to the outer periphery of the valve body 7, and a front and a rear diaphragm 11, 12 are applied to the back surfaces of the respective power pistons 9. 10. Each diaphragm 11, 12 includes a bead lla, 12a extending around its inner periphery, which is also connected to the outer periphery of the valve body 7. The front diaphragm 11 also includes a bead llb which extends around the outer periphery thereof, and which is axially held sandwiched between an annular wall 2a of the front shell 2 and an opposing wall 4a of the centerplate 4.In this manner, the front diaphragm 11 partitions the interior of the front chamber 5 into a forwardly located, constant pressure chamber A and a rearwardly located1 variable pressure chamber B. Also, the rear diaphragm 12 includes a bead 12b extending around the outer periphery thereof, which is held sandwiched by portions of the front and the rear shell 2, 3 where they are connected together. The rear diaphragm 12 also partitions the interior of the rear chamber 6 into a forwardly located.

constant pressure chamber C and a rearwardly located.

variable pressure chamber D.

A valve-mechanism 16, which is constructed in a manner well known in the art, is disposed within the valve body 7. Neglecting for te moment the provision of bellows, to be described later, the valve mechanism 16 is capable of functioning to switch a fluid circuit between the two constant pressure chambers A, C and two variable pressure chambers B, D. Specifically, the valve mechanism 16 comprises an annular first valve seat 18 formed on the valve body 7, an annular second valve seat 20 formed on the right end of a valve plunger 19 which is slidable within the valve body 7, at a location radially inward of the first valve seat 18, and a valve element 12 which is adapted to be seated upon either seat 18 or 20 from the right, as viewed in Fig. 1, under the resilience of a spring 21.

A space located radially outward of a first seal defined by the engagement of the valve element 22 with the first valve seat 18 communicates with the constant pressure chamber A through an axially extending, first constant pressure passage 23 which is formed in the valve body 7, assuming that bellows 17 is not provided. A negative pressure from a suitable source of negative pressure is adapted to be introduced into the constant pressure chamber A through a first negative pressure introducing piping 24 connected to the front shell 2, with a check valve 25 disposed between the source and the piping 24 to allow a fluid flow only in a direction from the source toward the constant pressure chamber A.The constant pressure chamber A is maintained in communication with the constant pressure chamber C defined within the rear chamber through a second constant pressure passage 26 which is defined radially outside the bead llb of the front diaphragm 11. Accordingly, a negative pressure is normally introduced into the both constant pressure chambers A and C.

On the other hand, a space located radially inward of the first seal defined try the engagement between the valve element 22 and the first valve seat 18 and radially outward of an annular second seal defined by the engagement of the valve element 22 with the second valve seat 20, or a space located intermediate the both annular seals communicates with the variable pressure chamber D through a radially extending first variable pressure passage 27 which is formed in the valve body 7, and thence communicates with the variable pressure chamber B through an axially extending second variable pressure passage 28 which is also formed in the valve body 7.

Finally, a space located radially inward of the inner or second annular seal defined by the engagement of the valve element 22 with the second valve seat 20 communicates with the atmosphere through a pressure passage 29 formed in the valve body 7 and a filter 30 disposed therein.

The right end of the valve plunger 19 which is slidably disposed within the valve body 7 is connected to an input shaft 34 which is mechanically coupled to a brake pedal, not shown, while its left end is disposed in opposing relationship with the right end face of a reaction disc 36 which is received in a recess 35a formed in one end of a push rod 35. The left end of the rod 35 is mechanically coupled to a piston 37a associated with a master cylinder 37 which extends through an axial opening 2b formed in the front shell 2. A seal member 38 maintains a hermetic seal between the opening 2b and the piston 37a.

A cup-shaped retainer 39 is fitted, from the front side, over the end of the push rod 35 in which the recess 35a is formed and includes a rear end extending radially outward and which is disposed in abutment against a stepped end face 7a of the valve body 7 formed around its inner periphery. A return spring 40 extends between the front shell 2 and this end of the retainer 39 as it abuts against the stepped end face 7a to maintain the valve body 7 in its inoperative position shown. Since the return spring 40 is effective to maintain the rear end of the retainer 39 in abutting relationship against the stepped end face 7a and thus is connected thereto, the withdrawal of the push rod 35 from the valve body 7 is prevented.

Bellows 17, formed of rubber, extends between the wall surface of the front shell 2 and the outer periphery of the valve body 7 at its front end, and defines an internal space A' which communicates with the source of negative pressure through openings formed in a reinforcing plate 41 and the wall of the front shell 2 and through a second negative pressure introducing piping 42 which is mounted on the wall of the front shell 2. In the present embodiment, the piping 42 is not directly connected to the source, but is connected to the first piping 24 at a location downstream of the check valve 25.

A solenoid valve 43 is disposed in the second piping 42 for selectively communicating the second piping 42 with either the atmosphere or the source of negative pressure (namely, the first piping 24). The solenoid valve 43 is controlled by a controller, not shown, to be turned on and off, and in the inoperative condition shown in Fig. 1, the second piping 42 communicates with the source of negative pressure. Accordingly, a negative pressure is introduced into the internal space A' within the bellows 17 through the second piping 42.

By contrast, when the solenoid valve 43 is actuated by the controller, the atmosphere is introduced into the internal space A' within the bellows 17 through the second piping 42. Such atmosphere is also introduced into the both variable pressure chambers B, D through the first constant pressure passage 23, the valve mechanism 16 and the both variable pressure passages 27, 28. Accordingly, in the present embodiment, by actuating the solenoid valve 43 under the inoperative condition of the brake booster shown in Fig. 1, the booster can be operated without depressing a brake pedal. not shown, which is mechanically coupled to the input shaft 34.

Operation In the normal condition of the brake booster, the solenoid valve 43 remains inactive as shown in Fig. 1, and accordingly, the negative pressure is introduced into the internal space A' within the bellows 17 through the second piping 42. The negative pressure is also introduced into the constant pressure chamber A through the first piping 24, and thus the negative pressure is introduced into all the chambers, A, B, C, D and A'.

When a brake pedal, not shown, is depressed under this inoperative condition, the input shaft 34 is driven to the left, whereupon the valve mechanism 16 switches a fluid circuit, introducing the atmosphere into the both variable pressure chambers B and D. This allows an output of a given servo ratio to be derived from the push rod 35 in generally same manner as a conventional brake booster of tandem type.

In distinction to the normal braking operation, when the brake booster described is to be operated as an automatic brake, the solenoid valve 43 may be actuated by the controller under the inoperative condition where the input shaft 34 shown in Fig. 1 is not driven forward.

This allows the atmosphere rather than the negative pressure to be introduced into the internal space A' within the bellows 17, which atmosphere is also introduced into the both variable pressure chambers B and D through the first constant pressure passage 23 and its communicating first and second variable pressure passages 27 and 28.

Accordingly, a pressure differential is developed between the both constant pressure chambers A, C and the both variable pressure chambers B, D, whereby a given output can be derived from the push rod 35 even though the brake pedal has not been depressed.

T;he bellows 17 includes a front end of an increased thickness to provide a front bead 17a and also a rear end of an increased thickness to provide a rear bead 17b. The front bead 17a is held in abutment against the wall surface of the front shell 2 by being urged by an inner peripheral portion of a support member 44 disposed within the constant pressure chamber A, which is effective to maintain a hermetic seal and to prevent a displacement of the front bead 17a. Outer peripheral portion of the support member 44 is disposed in overlapping relationship with the bead llb extending around the outer periphery of the front diaphragm 11 and is held sandwiched between an annular wall 2a of the front shell 2 and an opposing wall 4a of the centerplate 4.The support member 44 is formed with a plurality of through-openings at selected positions to allow the negative pressure from the first piping 24 to be introduced into the constant pressure chamber A.

As shown to an enlarged scale in Fig. 2, the rear bead 17b of the bellows 17.is initially fitted around the outer periphery of the valve body 7 from the front side thereof, and is then held in abutment against the inner peripheral edge of the front power piston 9, such abutment being maintained by an annular retainer 45 which is snapped in place around the outer periphery of the valve- body 7 from the front side to thereby prevent the disengagement of the bead 17b.

The inner peripheral edge of the power piston 9 is formed with a tubular portion 9a which extends axially forward and also with an annular recess 9b which continues from the tubular portion 9a and located radially outward thereof. When mounting the front power piston 9 on the valve body 7, the tubular portion 9a is fitted over the outer periphery of the valve body from the rear side until the tip of the tubular portion 9a abuts against a positioning step 7b formed on the outer periphery of the valve body 7.When so positioned, the inner peripheral surface of the tubular portion 9a is effective to maintain in place the bead ila extending around the inner periphery of the front diaphragm 11 and which is fitted in an annular groove 7c formed in the valve body 7 at a location adjacent to the positioning step 7b, thereby connecting the front power piston 9 and the front diaphragm 11 to the outer periphery of the valve body 7.

The rear bead 17b of the bellows 17 is fitted into the annular recess 9b formed in the front power piston 9 and is held in abutment against it, and under this condition. the retainer 45 is snapped around the outer periphery of the valve body 7 to bear against the rear bead 17b, thereby preventing the disengagement thereof.

T.he rear bead 17b is formed with a plurality of forwardly extending projections 17c which are spaced apart circumferentially for abutment against the retainer 45.

Additionally, the outer periphery of the valve body 7 is formed with a locking step 7d at a location forward of the positioning step 7b, and the locking step 7d is engaged by the inner edge of the retainer 45, thus preventing the disengagement of the retainer 45 from the outer periphery of the valve body 7.

It will be seen that the retainer 45 comprises a radial portion 45a for abutment against the projections 17c on the rear bead 17b, a plurality of slanted claws 45b continuing radially inward from the radial portion 45a, and a forwardmost engaging portion 45c which is formed by folding outwardly the inner edge of the claws 45b at an obtuse angle, the engaging portion 45c engaging the locking step 7d on the valve body 7 to prevent the retainer 45 from being disengaged from the outer periphery of the valve body 7.

With the described construction, when the atmosphere is introduced into the internal space A' within the bellows 17, the entire bellows 17 will be expanded, whereby the front bead 17a and the rear bead 17b of the bellows 17 will be pulled both radially and axially. However, the front bead 17a is held in place by the support member 44 while the rear bead 17b is held by the combination of the annular recess 9b in the front power piston 9 and the retainer 45, whereby any displacement of the rear bead 17b, and accordingly, a consequent failure of the hermetic seal is prevented.

The provision of the plurality of projections 17c on the rear bead 17b for abutment against the retainer 45 is effective to prevent a failure of the hermetic seal as a result of any one or more of the projections 17c being damaged as by the abutment by the retainer 45 as the rear bead 17b is repeatedly pulled in the axial direction.

It is to be noted that a juncture between the engaging portion 45c, which is in effect the inner peripheral edge of the retainer 45, and the claws 45b is folded in a manner to provide a smooth curved surface in order to prevent any portion of the retainer 45 from ablating or damaging the outer periphery of the valve body 7 as a result of its sliding contact with such outer periphery when the retainer 45 is snapped in place around the valve body 7.

The engagement of the engaging portion 45c of the retainer 45 with the locking step 7d on the valve body 7 is effective to prevent the disengagement of the retainer 45 from the outer periphery of the valve body 7 in an advantageous manner.

It is to be noted that while the retainer 45 is provided with the engaging portion 45c at its foremost position, such engaging portion 45c may be omitted, thus using only the radial portion 45a and the claws 45b to define the retainer 45. In this instance, the inner peripheral edge of the claws 45c may be chamfered smoothly to prevent the valve body 7 from being damaged.

Fig. 3 shows an embodiment of the present invention illustrating only those features where it differs from the construction of Figs. 1 and 2. In this embodiment, the retainer 45 and the locking step 7d on the valve body 7 shown in Figs. 1 and 2 are eliminated.

Rather than connecting the rear bead 17b of the bellows 17 to the inner peripheral edge of the front power piston 9, the equivalent bellows 217 includes a rear bead 217b which is connected to the inner periphery of valve body 207 at its front end.

Specifically, the inner periphery of the valve bo.dy 207, which defines an opening located at the front end of first constant pressure passage 223, has the rear bead 217b of the bellows 217 fitted therein, which is then held in place by a locking step 239a which is formed at the front end of a retainer 239. The retainer 239 includes a rear end, against which one end of a return spring 240 abuts. The retainer is folded upon itself at this rear end to extend axially forward at a gentle slant, the front extremity of the slanted portion being formed with the locking step 239a. The locking step 239a comprises a radially extending stepped end face, a tubular portion of greater diameter located forwardly of the stepped end face, and another tubular portion of reduced diameter which is located rearward of the stepped end face. The entire locking step 239a is disposed in abutment against the inner periphery of the valve body 207 while retaining the inner end of the rear bend 217b therebetween, thus preventing the rear bead 217b from being disengaged forwardly. In other respects, the arrangement is similar to that shown in Figs. 1 and 2, and corresponding parts are designated by like numerals as used there to which 200 is added.

In use, since the rear bead 217b of the bellows 217 is connected to the inner periphery of the valve body 207, the size of the rear bead 217b which is disposed within the constant pressure chamber A may be reduced, thus allowing the axial dimension of the bellows 217 itself to be reduced.

The described embodiment of the invention is exemplary only and many changes, modifications and substitutions therein will readily occur to those skilled in the art.

Claims

1. A brake booster including a valve body slidably disposed in a shell, a power piston connected to the valve body, constant and variable pressure chambers formed on opposite sides of the power piston, a valve mechanism disposed in the valve body for switching a fluid circuit, a passage formed in the valve body having a front end which opens into a front end face of the valve body for providing communication between the constant and variable pressure chambers through the valve mechanism, a spring extending across the shell and the valve body for urging the valve body rearward, and bellows disposed within the constant pressure chamber having a rear opening connected to said passage in the valve body and a front end connected to the shell, an internal space within the bellows being arranged to be connected to a suction or a pressure source, the rear end of the bellows being formed as an increased thickness bead which is fitted into an opening in the valve body providing the front end of passage, said bellows bead being held in abutment against the inner peripheral surface of said opening by means of a locking step formed on the front end of a retainer to prevent the bead from being disengaged in the forward direction, the rear end of the retainer being interposed between the spring and the valve body to be secured to the valve body.

2. A brake booster according to claim 1 in which the front end of the bellows is also formed as a bead having an increased thickness and is held in abutment against the inner wall of the shell by a support member which is disposed within the constant pressure chamber.

3. A brake booster including a valve body slidably disposed in a shell, a power piston mounted on the valve body between constant and variable pressure chambers within the shell, a valve mechanism disposed in the valve body, a passage formed in the valve body and connected to the valve mechanism having a front end which opens into a front end face of the valve body, the passage for providing communication between the constant and variable pressure chambers through the valve mechanism, a spring extending between the shell and the valve body for urging the valve body rearwards, bellows disposed within the constant pressure chamber having an opening connected to said passage, means for connecting said bellows to a suction or a pressure source, the rear end of the bellows being formed as an increased thickness bead which is inserted into said front end opening of said passage, the bead being held in abutment against the inner peripheral surface of said opening by means of a retainer to prevent the bead from being disengaged in the forward direction, the retainer being secured to the valve body by the spring.

4. A brake booster according to claim 3 wherein the retainer comprises a locking step which bears against the bead to prevent said disengagement.

5. A brake booster constructed and arranged for use and operation substantially as described herein with reference to any of the embodiments illustrated in Fig. 4 of the accompanying drawings.