JPH0357568Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a brake booster that uses fluid pressure to boost the operating force for a brake device.

[Prior art]

Generally, a brake booster includes a power piston that is disposed inside a housing and uses its diaphragm to divide the inside of the housing into a constant pressure chamber and a variable pressure chamber, and a large diameter portion of a stepped hole provided in the piston body of the power piston. a rod-shaped output member whose rear end is fitted so as to be movable in the axial direction through an elastic reaction member and protrudes from the front part of the housing in an airtight and slidable manner; a plunger that is fitted and inserted so as to be movable in the axial direction and faces the reaction member; and a front end of the plunger that is engaged with the rear end of the plunger to protrude the rear of the housing and move forward between the two chambers. It is equipped with a rod-shaped input member that operates a valve that controls the differential pressure of the valve.

In this type of brake booster, the reaction force from the output member during operation is distributed to the plunger and the piston body of the power piston via the reaction member, which reduces the pressure receiving area ratio of the plunger to the reaction member. Then, the input is transmitted to the output member with a boost according to the ratio of the input side pressure receiving area to the output side pressure receiving area.

[Problem that the invention attempts to solve]

By the way, in general, when operating a brake device, when the pressing force on the brake pedal is small, a good brake feeling is that the braking force increases in a quadratic curve as the pressing force on the brake pedal increases, as shown in Figure 4. You can say that. Furthermore, for example, in the friction material of a disc brake, there is a tendency for the friction coefficient to decrease as the disc brake oil pressure increases, although there are differences in degree, and this tendency has an adverse effect on the above-mentioned quadratic curve relationship.

In order to obtain such a quadratic relationship, it is possible to construct a brake booster in which the boost ratio increases when the brake pedal depression force reaches a predetermined value in a small range, but such a brake booster has not yet been proposed. It has not been. The present invention provides such a brake booster.

[Means for solving problems]

In the brake booster of the above-mentioned type, the present invention is such that, when moving forward, the space between the inner periphery of the small diameter part of the stepped hole and the outer periphery of the plunger engages with an outward flange provided on the plunger, and moves further forward. has an inward flange portion that restricts movement of the plunger, and moves integrally with the plunger, and when moving rearward, engages with a stepped portion of an annular recess formed on the inner periphery of the small diameter portion to move further rearward. A compression method for assembling a sleeve whose movement is restricted and moving integrally with the piston body, and urging the sleeve between the sleeve and the plunger to elastically engage the outward flange of the plunger. A spring is inserted.

[Functions and effects of the idea]

In the brake booster of the present invention, if the value per unit area of the reaction force during operation is smaller than the value per unit area of the set load of the compression spring, the pressure receiving surface on the input member side for the reaction force is the plunger. It is the sum of the end faces of the sleeve. Furthermore, when the force applied to the brake pedal is increased so that the former value becomes greater than the latter value, the compression spring is bent, and the sleeve moves back and engages a predetermined part of the piston body of the power piston, that is, the stepped part of the annular recess. The plunger is integrated with the main body, and the pressure receiving surface on the input member side is only the end surface of the plunger.

Therefore, according to the brake booster, when the depression force on the brake pedal reaches a predetermined value, the pressure receiving area on the input member side decreases, and the boost ratio increases in accordance with this decrease. Therefore, by setting the set load of the compression spring to a predetermined value, a brake booster can be obtained in which the boost ratio increases when the brake pedal depression force reaches a predetermined value in a small range.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings. FIG. 1 shows an example in which the present invention is implemented in a tandem type brake booster. In this brake booster, a housing 10 is composed of a pair of front and rear shells 11, 12 and an intermediate plate 13, and the interior thereof is divided into front and rear chambers by the intermediate plate 13, and a power piston 20 is concentrically arranged in the housing 10. It is located in

The power piston 20 includes a stepped cylindrical main body 21 with a first diaphragm 22 at the tip and a second diaphragm 23 in the middle thereof.The piston main body 21 has a rear shell 12 and an intermediate plate 13. It is penetrated airtightly and slidably. The first diaphragm 22 is located in the front chamber of the housing 10, and its outer peripheral edge is connected to the front shell 11.
and the intermediate plate 13 to move the front chamber into the first
It is divided into a constant pressure chamber R1 and a first variable chamber R2. The second diaphragm 23 is located in the rear chamber of the housing 10, and its outer peripheral edge is held between the inner peripheral edge of the rear end of the rear shell 12, and the rear chamber is divided into a second constant pressure chamber R3 and a second variable pressure chamber R4. There is a stepped cylindrical shape 24 in the hub inner hole 21a of the piston body 21.
are fitted. The piston main body 21 and the stepped cylinder body 24 include a first communication passage 25a that communicates both constant pressure chambers R1 and R3, a second communication passage 25b that communicates both variable pressure chambers R2 and R4, and both communication passages 25.
A third communication path 25c is provided that allows communication between a and 25b. Note that the first constant pressure chamber R1 is connected to an intake manifold of an engine (not shown), and a predetermined negative pressure is applied thereto. Also, the first
A compression spring 26 for return is interposed in the constant pressure chamber R1.

The operation rod 31, which is an output member, has a rod portion 31a with a predetermined length and a plunger portion 31 with a large diameter.
b, as shown in Figures 1 and 2,
The plunger portion 31b is slidably inserted into the large-diameter inner hole 24a of the stepped cylindrical shape 24 via a disk-shaped reaction rubber 32. In this state, the operation rod 31 protrudes airtightly and slidably from the center of the front shell 11 and is connected to a piston of a master cylinder (not shown). Also,
A small-diameter plunger 33 is fitted into the small-diameter inner hole 24b of the stepped cylinder 24 so as to be slidable in the axial direction by a predetermined amount, and the head of a push rod 34 serving as an input member is fitted into the rear end thereof. There is. This push rod 34 passes through an air filter 35 fitted into the rear inner hole 21c of the piston body 21 and projects rearward. Note that the rear part of the piston body 21 and the push rod 34 are covered with a dust boot 36.

The valve mechanism 40 includes a rubber cylindrical valve body 42 fitted into a retainer 41 that is fitted and fixed in the rear inner hole 21c of the piston body 21, and a push rod 34.
A compression spring 43 is interposed between the valve body 42 and the valve body 42. This compression spring 43 is connected to the valve body 42.
The first valve seat 44a is always biased forward and the valve body 42 is provided at the rear end of the plunger 33, or the second valve seat 44b is provided at the open end of the third communication passage 25c of the piston body 21. seated. A compression spring 37 for returning the push rod 34 is interposed between the push rod 34 and the retainer 41.

In this brake booster, the push rod 34 moves forward in response to depression of a brake pedal (not shown), and when the push rod 34 is not operated, the valve body 42 of the valve mechanism 40 is in the first position.
It is seated on the valve seat 44a, communicates the second variable pressure chamber R4 with the third communication passage 25c, and blocks communication of the second variable pressure chamber R4 with the atmosphere. Therefore, both constant pressure chambers R1, R3 and both variable pressure chambers R2, R4 are communicated and maintained at the same negative pressure, and the brake booster is in a non-operating state. When the brake pedal (not shown) is depressed in this state, the push rod 34 moves forward, causing the plunger 33 integrated therewith to slide forward. During this time, the valve body 42 is expanded by the action of the compression spring 43 and is seated on the second valve seat 44b, cutting off communication between the second variable pressure chamber R4 and the third communication passage 25c, and opening the second variable pressure chamber R4 to the atmosphere. communicate.

As a result, the atmosphere is applied to both variable pressure chambers R2 and R4, and a pressure difference is generated between both constant pressure chambers R1 and R3, and the power piston 20 slides forward due to this pressure difference. As a result, the operation rod 31 moves forward and slides the piston of a master cylinder (not shown), generating high hydraulic pressure in the master cylinder and operating the brake device. The power piston 20 stops when the input from the push rod 34 side and the reaction force from the operation rod 31 side are balanced.

Accordingly, in this embodiment, as particularly shown in an enlarged manner in FIG. spring 3
9 is assembled.

The sleeve 38 consists of a cylindrical portion 38a and an inward flange portion 38b provided at the rear end, and the sleeve 38
It is fitted onto the small diameter portion 33a of No. 3 via a compression spring 39 so as to be slidable in the axial direction. The compression spring 39 urges the sleeve 38 forward, causing the inward flange portion 38b of the sleeve 38 to move toward the plunger 33.
The outer flange portion 33b is engaged with the outer flange portion 33b provided at the tip of the outer flange portion 33b. This restricts the sleeve 38 from sliding further forward. On the other hand, an annular recess 24 is provided at the front end of the small diameter inner hole 24b of the stepped cylinder 24.
c is formed, and the sleeve 38 is fitted into this annular recess 24c so as to be slidable in the axial direction. This sleeve 38 engages with the stepped portion of the annular recess 24c via the plunger 33 by the action of the compression spring 37 for returning the push rod 34 when it is not activated, and further rearward sliding is restricted. ing. Note that in this state, the plunger 3
The circular end face of the outward flange portion 33b of No. 3 and the annular end face of the sleeve 38 are substantially on the same plane, and a minute gap is maintained between these end faces and the end face of the reaction rubber 32.

In the brake booster configured in this manner, the reaction force from the operation rod 31 during operation is received by the plunger 33 and the sleeve 38 through the reaction rubber 32 and the stepped portion of the stepped cylinder body 24. It will be done.

Therefore, the area of the end surface of the plunger portion 31b of the operation rod 31 is A, the reaction force from the operation rod 31 is F, and the area of the end surface of the outward flange portion 33b of the plunger 33 is A.
1. Assuming that the area of the end surface of the sleeve 38 is A2 and the set load of the compression spring 39 is f, the relationship between these is as follows. That is, when the value F/A per unit area of the reaction force is less than the value f/A2 per unit area of the set load of the compression spring 39,
Since the compression spring 39 does not bend, the reaction pressure receiving surface on the push rod 34 side is connected to the plunger 33.
and both end surfaces of sleeve 39 (pressure receiving area A1 + A2)
becomes. Therefore, the boost ratio M1 in this case is A/
(A1+A2). Also, if the force on the brake pedal is large and F/A becomes greater than f/A2,
The compression spring 39 is bent and the sleeve 38 is moved back to engage the step of the annular recess 24c in the small diameter inner hole 24b of the stepped cylinder 24, so that the sleeve 38 is integrated with the stepped cylinder 24. Therefore, the reaction force receiving surface on the push rod 34 side is only the end surface of the plunger 33 (pressure receiving area A1), and the boosting ratio in this case is
M2 changes to A/A1. FIG. 3 is a graph showing an example of this result. The figure shows the results when a master cylinder with a cylinder diameter of 22 mm is used, and the first bending point B1 indicates the point at which the gap between the reaction rubber 32, the plunger 33, and the sleeve 38 disappears, and the second turning point B2 shows the result when a master cylinder with a cylinder diameter of 22 mm is used. Deceleration 0.2g
Applies to the neighborhood.

Therefore, according to the brake booster, when the depression force on the brake pedal reaches a predetermined value, the reaction force receiving area on the push rod 34 side decreases, the boost ratio increases, and the braking force increases to the secondary level shown in FIG. The brake feeling increases because it increases in a curve or a value close to this.

In this embodiment, an example in which the present invention is applied to a tandem brake booster is shown, but it goes without saying that the present invention can also be applied to a single brake booster.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a brake booster according to an embodiment of the present invention, Fig. 2 is an enlarged sectional view of main parts of the brake booster, and Fig. 3 shows an example of the relationship between pedal force and reaction force in the brake booster. The graph shown in FIG. 4 is a graph showing the relationship between the pedal force and the braking force when the brake feeling is in good condition. Explanation of symbols, 10...Housing, 20...Power piston, 21...Piston body, 22,2
3... Diaphragm, 31... Operation rod, 32... Reaction rubber, 33... Plunger, 34... Push rod, 38... Sleeve, 39... Compression spring, 40... Valve mechanism.

Claims (1)

[Scope of utility model registration request] A power piston is disposed within a housing and uses its diaphragm to divide the inside of the housing into a constant pressure chamber and a variable pressure chamber, and an elastic reaction member is disposed within a large diameter portion of a stepped hole provided in the piston body of the power piston. a rod-shaped output member whose rear end portion is fitted so as to be movable in the axial direction through the rod-shaped output member and protrudes from the front portion of the housing in an airtight and slidable manner;
a plunger that is fitted into the small diameter portion of the stepped hole so as to be movable in the axial direction and faces the reaction member; and a front end portion of the plunger that is engaged with the rear end portion of the plunger to project the rear portion of the housing and move forward. In the brake booster, the brake booster is provided with a rod-shaped input member that operates a valve for controlling the differential pressure between the two chambers when the plunger moves forward. The plunger has an inward flange portion that engages with an outward flange portion provided on the plunger to restrict further forward movement, and moves integrally with the plunger, and when moving rearward, the inner periphery of the small diameter portion A sleeve is assembled that engages with the stepped portion of the formed annular recess to restrict further rearward movement and moves integrally with the piston body, and the sleeve is attached between the sleeve and the plunger. A brake booster characterized in that a compression spring is interposed to elastically engage the outward flange portion of the plunger.