JPH0111576Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brake booster, and more particularly to a so-called low-travel brake booster that includes a plurality of diaphragm pistons within a closed shell.

Generally, this type of brake booster has two diaphragm pistons disposed coaxially in the longitudinal direction within a sealed shell in which opposing ends of a front shell and a rear shell are hermetically fitted. The diaphragm pistons are operatively connected to each other so as to be movable relative to each other in the axial direction, and each of the outer peripheral bead portions of the diaphragm in each of the diaphragm pistons is hermetically locked to the inner peripheral surface of the hermetic shell, so that the inside of the hermetic shell is sealed. A switching valve mechanism is formed between the two constant pressure chambers to which negative pressure is applied and the two constant pressure chambers via the respective diaphragm pistons, and is assembled to the rear diaphragm piston to selectively connect the constant pressure chambers and the atmosphere. It is divided into communicating variable pressure chambers, and due to the pressure difference between the variable pressure chamber and each of the constant pressure chambers, the front diaphragm piston is moved axially forward, and the rear diaphragm piston is moved forward in the axial direction. The piston is configured to move rearward in the axial direction.

By the way, in this type of brake booster, both the front and rear shells constituting the closed shell are formed into cylindrical shapes with approximately the same diameter, as seen in, for example, U.S. Patent No. 3,143,929, and the outer circumference of each diaphragm is The bead portion is hermetically secured to the inner circumferential surface of one or both of the shells. Therefore, it is necessary to provide a plurality of annular recesses on the inner circumferential surface of one or both of the front and rear shells for locking the outer peripheral bead of each diaphragm, and the required number of annular recesses must be provided. In order to ensure this, the cylindrical portion of at least one of both shells must have a predetermined length. However, the cylindrical parts of both shells constitute the maximum diameter part of the sealed shell, and for this reason, this type of brake booster has a diaphragm piston on the front side that produces an assisting force, and a diaphragm piston on the rear side that does not produce an assisting force. The diameter of the diaphragm piston on the side is set to be approximately the same diameter, making the piston larger than required for its function, and occupying a large space in the limited engine room.

The present invention was devised to solve this problem, and its main purpose is to form the rear shell into a special shape and provide a plurality of annular recesses in which the outer peripheral bead of each diaphragm is engaged. By providing this type of brake booster, the axial length of the maximum diameter portion of the hermetic shell can be shortened, and this type of brake booster can be miniaturized.

In order to achieve this object, the present invention provides a brake booster of this type in which the rear shell is expanded toward the open end side of the front shell so that the peripheral edge of the open end reaches the peripheral edge of the open end of the front shell. An annular recess is formed in a conical shape to be fitted inside, and an annular recess in which each of the outer peripheral bead portions of each diaphragm is locked is provided at a radially intermediate portion between the peripheral edge of the opening end of the shell and the inner surface thereof, The structure is characterized by the fact that each of the outer peripheral bead portions of each diaphragm is hermetically locked in each of these annular recesses. Therefore, in the present invention, it is not necessary to provide all the annular recesses necessary for locking the outer peripheral bead portions of each diaphragm on the inner circumferential surfaces of the cylindrical portions of both shells that form the maximum diameter portion of the sealing shell. Therefore, the axial length of at least one of the cylindrical portions of both shells can be made shorter than before. As a result, the axial length of the maximum diameter part of the hermetic shell can be shortened without affecting the required assisting force in any way, making it possible to downsize this type of brake booster and making it easier to install it in the engine room. The occupied space can be reduced.

Hereinafter, the present invention will be explained based on the drawings. FIG. 1 shows an embodiment of a low-travel type brake booster according to the present invention. The closed shell 10 of this type of brake booster includes a front shell 1
1 and a rear shell 12 are hermetically fitted at their opposing ends, and a pair of diaphragm pistons 20 and 30 are disposed inside the shell, respectively, and the rear diaphragm piston 20 has a A switching valve mechanism 40 is assembled.

The rear diaphragm piston 20 has a cylindrical first
Piston body 21 and first piston body 21
A cylindrical second piston body 22 with a bottom is airtightly and slidably fitted onto the front end of the second piston body 22, and a diaphragm 24 is integrally fixed with the piston plate 23 onto the rear end of the second piston body 22. The first piston body 21 has a rear shell 12.
It is supported airtightly and slidably in the axial direction approximately at the center of the shaft. This rear diaphragm piston 20
, a plurality of claws 23a provided on the piston plate 23 are latched onto a protrusion 21a provided on the first piston body, and the protrusion 21a and the second
A predetermined gap is formed between the flange portions 22a of the piston bodies 22, and both piston bodies 2
A predetermined relative sliding movement in the axial direction is allowed between 1 and 22. Further, the diaphragm 24 extends along the front side surface of the piston plate 23 to the outer periphery, and its outer peripheral bead portion 24a is hermetically locked in a second annular recess 12e of the rear shell 12, which will be described later. Thereby, the diaphragm 24 forms a first constant pressure chamber R1 on its rear side, and forms a variable pressure chamber R2 on its front side together with a diaphragm 34 of a front diaphragm piston 30, which will be described later. 1st constant pressure chamber R
1 is connected to the engine intake manifold A to which negative pressure is applied from the engine.
Communication holes 21 provided in both piston bodies 21 and 22
It communicates with the variable pressure chamber R2 through b, 21c, and 22b. Such communication is provided by a switching valve mechanism 40, which will be described later.
Interrupted by In addition, the first piston body 2
1 is biased rearward by a coil spring 25 whose one end is locked to a retainer 13 provided on the rear shell 12, and comes into contact with the stopper portion 12a of the rear shell 12, and further rearward sliding is restricted. There is. Further, the front end of the first piston body 21 and the second
A rubber reaction disk 26 is interposed between the bottoms of the piston body 22.

The front diaphragm piston 30 includes a cylindrical piston body 31 with a bottom, an annular reinforcing plate 32 on its outer periphery, and a diaphragm 34 integrally fixed to the piston plate 33. It is fitted onto the outer periphery of the second piston body 22 so as to be slidable in the axial direction and is supported by the second piston body 22 . Further, the diaphragm 34 extends to the outer periphery along the rear side surface of the piston plate 33, and its outer peripheral bead portion 34a is hermetically locked in a first annular recess 12d of the rear shell 12, which will be described later. Thereby, the diaphragm 34 forms a second constant pressure chamber R3 on its front side, and forms a variable pressure chamber R2 together with the diaphragm 24 of the rear diaphragm piston 20 on its rear side. This second constant pressure chamber R3
is connected to the engine intake manifold A, and negative pressure from the engine is applied to it.
Note that an operation rod 35 is fixed to the front end of the piston body 31. The operation rod 35 passes through the substantially central portion of the front shell 11 airtightly and slidably in the axial direction, and its front end is connected to a piston of a master cylinder (not shown). In addition, the piston body 31
has one end locked on the reinforcing plate 14 provided on the front shell 11, is biased rearward by the coil spring 36, comes into contact with the front end of the second piston body 22 of the rear diaphragm piston 20, and is prevented from moving further rearward. Sliding is regulated.

The switching valve mechanism 40 is assembled into the inner hole of the first piston body 21 of the rear diaphragm piston 20, and the valve plunger 41 is fitted into the inner hole of the first piston body 21 of the rear diaphragm piston 20. 42
A retainer 43 that holds the is inserted and fixed.
The valve plunger 41 is connected to a push rod 44 that passes through the dust boot 15 and air filter 16 that cover the rear outer periphery and rear end of the first piston body 21. Cylindrical valve body 42
is urged forward by a coil spring 45 so that its front end abuts against the rear end of the valve plunger 41, and the push rod 44 is urged rearward by a coil spring 46. This push rod 44 moves forward in response to depression of the brake pedal B, and the valve plunger 41 receives a reaction force from the reaction disk 26 during this movement.

In this brake booster, when the push rod 44 is not activated, the first constant pressure chamber R1 and the variable pressure chamber R2 are
are in communication with each other through the communication holes 21b, 21c, and 22b, and all the chambers R1 to R3 are at a predetermined negative pressure, and each diaphragm piston 2
0 and 30 are in the state shown in FIG. 1 due to the urging force of each coil spring 25 and 36. When the brake pedal B is depressed in this state, the push rod 44 is activated and moves forward, and the valve plunger 41 moves forward together with this. During this time, the cylindrical valve body 42 is expanded by the action of the coil spring 45, and the valve seat 2 of the first piston body 21 is expanded.
1d to cut off communication between the first constant pressure chamber R1 and variable pressure chamber R2, and further, the rear end of the valve plunger 41 is separated from the front end of the cylindrical valve body 42, and the variable pressure chamber R
2 to the communication holes 22b, 21c and the air filter 1
6 to the atmosphere. As a result, atmospheric air is applied to the variable pressure chamber R2, and a predetermined pressure difference is generated between the variable pressure chamber R2 and both constant pressure chambers R1 and R3. As a result, the rear diaphragm piston 20 is pressed against the stopper portion 12a of the rear shell 12, and the front diaphragm piston 30 is pressed against the second piston body 22 of the rear diaphragm piston 20.
Slide the upper part forward to move the operation rod 35 forward. As a result, the piston of the master cylinder (not shown) is moved to the operation rod 3.
5 to generate high oil pressure in the master cylinder and brake the vehicle appropriately. During this time, the rear diaphragm piston 20 is in the first constant pressure chamber R.
Since the brake pedal B is always pressed against the stopper part 12a of the rear shell 12 due to the pressure difference between the pressure change chamber R2 and the pressure change chamber R2, the depression stroke of the brake pedal B is a small stroke that moves the valve plunger 41 of the switching valve mechanism 40 by a predetermined amount. nothing.

However, in the brake booster,
A rear shell 12 constituting the closed shell 10 is formed into a conical shape. That is, backward shell 1
2 is formed into a conical shape consisting of a small-diameter cylindrical portion 12b and a tapered portion 12c that gradually expands and extends forward from its front end opening, and the front end opening peripheral edge of the tapered portion 12c is the rear end of the front shell 11. It is formed to have a slightly smaller diameter than the opening periphery. A first annular recess 12d that opens toward the outer circumference is provided at the front end opening periphery of the rear shell 12, and the boundary between the small diameter cylindrical portion 12b and the tapered portion 12c in the rear shell 12 is located on the inner circumference. and a second annular recess 12e that opens toward the front. As shown in FIGS. 1 and 2, the inner ends of three locking pieces 12f fixed to the inner wall of the tapered portion 12c face each of the second annular recesses 12e. In such a rear shell 12, the second annular recess 1
2e, the outer peripheral bead portion 24a of the diaphragm 24 of the rear diaphragm piston 20 shown in FIG. 3 is fitted, and the locking ring 17 shown in FIG. 4 is interposed between each locking piece 12f and the outer peripheral bead portion 24a. As a result, the outer peripheral bead portion 24a is airtightly locked in the second annular recess 12e by the cooperation of each locking piece 12f and the locking ring 17, as shown in FIG.

In addition, in the rear shell 12, the first
The front diaphragm piston 30 is located in the annular recess 12d.
The outer peripheral bead portion 34a of the diaphragm 34 is fitted, and in this state, the front end opening peripheral portion of the rear shell 12 is fitted into the rear end opening peripheral portion of the front shell 11 and secured by caulking.
4a is sandwiched between the first annular recess 12d and the peripheral edge of the rear end opening of the front shell 11, as shown in FIG. 1, and is airtightly locked between them.

Therefore, in the brake booster, there is no need to extend the front shell 11 rearward in order to form a locking portion corresponding to the second annular recess 12e in the front shell 11, and the second annular recess 12e is provided at the radially intermediate portion of the rear shell 12, so the axial length of the maximum diameter part of the sealed shell 10 is shorter than that of conventional brake boosters of this type without reducing the assisting force. It's done. As a result, the annular space of the closed shell 10 on the outer peripheral side of the tapered portion 12c of the rear shell 12 becomes smaller, and the space occupied in the limited engine room also becomes smaller. In addition, in this brake booster, each diaphragm 2 has a simple assembly structure.
The locking portions of the outer peripheral bead portions 24a and 34a of 4 and 34 are ensured to be highly airtight, and the diaphragm pistons 20 and 30 can be assembled to the rear shell 12 to form a subassembly. The adhesion properties can be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the brake booster according to the present invention, FIG. 2 is a perspective view of the rear shell of the device, and FIG. 3 is a perspective view of the diaphragm of the diaphragm piston in the device. Fourth
The figure is a perspective view of a locking ring in the device. Explanation of symbols, 10... Sealing shell, 11... Front shell, 12... Back shell, 12b... Small diameter cylindrical part, 12c... Taper part, 12d, 12e...
Annular recess, 20, 30... diaphragm piston, 21, 22, 31... piston body, 2
4, 34...Diaphragm, 24a, 34a...
Outer peripheral bead portion, 40...Switching valve mechanism, R1, R3
... Constant pressure room, R2... Variable pressure room.

Claims (1)

[Scope of utility model registration request] Two diaphragm pistons are disposed coaxially in the front-rear direction within a sealed shell formed by airtightly fitting opposite ends of a front shell and a rear shell, which are opposed to each other, so that they can be operatively moved relative to each other in the axial direction. and each of the outer peripheral bead portions of the diaphragm in each of these diaphragm pistons is airtightly locked to the inner circumferential surface of the hermetic shell to apply negative pressure inside the hermetic shell. A variable pressure chamber is formed between the constant pressure chamber and the constant pressure chambers via each of the diaphragm pistons, and is divided into a variable pressure chamber that selectively communicates with the constant pressure chamber and the atmosphere by a switching valve mechanism assembled to the rear diaphragm piston. Become,
Due to the pressure difference between the variable pressure chamber and each constant pressure chamber,
In a brake booster configured to move a diaphragm piston on the front side axially forward and move the diaphragm piston on the rear side axially rearward, the rear shell is connected to the open end of the front shell. It is formed into a conical shape that expands to the side and its opening end periphery reaches the opening end periphery of the front shell and is fitted inside the front shell, and the radial direction of the opening end periphery of the front shell and its inner surface. An annular recess into which each of the outer peripheral bead portions of each of the diaphragms is locked is provided in the intermediate portion, and each of the outer peripheral bead portions of each of the diaphragms is airtightly locked in each of these annular recesses. brake booster.