Negative pressure type booster

In a negative pressure type booster, an atmospheric valve seat is formed on an annular disk of an input member, which disk extends radially outward. The annular disk and an annular diaphragm located frontward of the annular disk and mounted to the input member define an annular atmospheric chamber. The atmospheric chamber communicates with the atmosphere via an air hole formed in the annular disk. The diaphragm is supported from the front by a power piston. The diaphragm is a flexible member. Inner and outer circumferential portions of the flexible member are formed into respective rolling portions for allowing frontward/rearward movement of the input member by means of curviform deformation. An atmospheric control valve portion, which is seated on and separated from the atmospheric valve seat, and a vacuum control valve portion, which is seated on and separated from a vacuum valve seat formed on the power piston, are axially separated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a negative pressure type booster for use in, for example, a vehicular brake system.

2. Description of the Related Art

A negative pressure type booster of the above-mentioned type is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 08-310379. The disclosed negative pressure type booster includes a housing; a movable wall mounted in the housing in a frontward/rearward movable condition and dividing the interior of the housing into a constant-pressure chamber and a variable-pressure chamber; a power piston connected to the movable wall in a frontward/rearward movable condition; an input member provided in the power piston in a frontward/rearward movable condition relative to the power piston and receiving an external operation force applied thereto in a frontward direction; an output member for outputting, to an external device, a thrust force generated frontward by the power piston; a control valve mounted in the power piston and comprising an atmospheric control valve portion and a vacuum control valve portion, the atmospheric control valve portion facing frontward, toward an atmospheric valve seat provided on the input member, and adapted to establish/shut off communication between the variable-pressure chamber and the atmosphere in cooperation with the atmospheric valve seat, and the vacuum control valve portion facing frontward, toward a vacuum valve seat provided on the power piston, and adapted to establish/shut off communication between the variable-pressure chamber and the constant-pressure chamber in cooperation with the vacuum valve seat; first biasing means for biasing the control valve frontward toward the atmospheric valve seat and the vacuum valve seat; second biasing means for biasing the input member rearward; and a stopper for limiting the quantity of movement of the input member relative to the power piston effected by biasing force of the second biasing means. Notably, when the negative pressure type booster is applied to, for example, a vehicular brake system, the term “rearward” refers to the side toward a brake pedal or the side toward the vehicular rear, and the term “frontward” refers to the side toward a brake master cylinder or the side toward the vehicular front.

In the negative pressure type booster disclosed in above-mentioned Japanese Patent Application Laid-Open (kokal) No. 08-310379, the input member includes a plunger that is mounted to the power piston in a frontward/rearward movable condition, and an input rod connected to the plunger. The atmospheric valve seat is formed at a rear end portion of the plunger. In such a configuration, when the atmospheric valve seat and the atmospheric control valve portion are in contact with each other to thereby shut off communication between the variable-pressure chamber and the atmosphere, a differential pressure between a vacuum in the variable-pressure chamber and the atmospheric pressure is exerted on the area of an atmospheric valve as measured with the effective diameter of the atmospheric valve (pressure reception area). A differential-pressure-induced force pushes the input member frontward. In an ordinary state (in a non-operational state; hereinafter the same applies), in order to maintain contact between the atmospheric valve seat and the atmospheric control valve portion, the biasing force of the second biasing means must be set greater than the differential-pressure-induced force.

In a negative pressure type booster of the above-mentioned type, in an ordinary state where the atmospheric valve seat is in contact with the atmospheric control valve portion, and the vacuum control valve portion is separated from the vacuum valve seat, a vacuum in the variable-pressure chamber may vary due to, for example, a variation in pressure of a vacuum source. Thus, the biasing force of the second biasing member is determined so as to cope with a potential high vacuum associated with the vacuum variation in the variable-pressure chamber. As a result, in an ordinary state, if a vacuum in the variable-pressure chamber becomes low, an operation force required to separate the atmospheric valve seat from the atmospheric control valve portion; i.e., startup load, will increase, giving an operator (a vehicle driver) a sensation of unusual operation. This problem arises eminently in the case where the effective diameter of the atmospheric valve is increased in order to obtain high operational response, as in the case of the above-mentioned negative pressure type booster disclosed in the above-described patent publication.

SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the above-mentioned problem, and an object of the invention is to provide a negative pressure type booster having a mechanism for reducing a differential-pressure-induced force (a working force induced by a differential pressure between a vacuum in a variable-pressure chamber and the atmospheric pressure) exerted on an input member having an atmospheric valve seat, whereby even when, in an ordinary state, a vacuum in the variable-pressure chamber varies, a variation in operation force can be reduced.

To achieve the above object, the present invention provides a negative pressure type booster comprising a housing; a movable wall mounted in the housing to be movable frontward and rearward, the movable wall dividing the interior of the housing into a constant-pressure chamber and a variable-pressure chamber; a power piston connected to the movable wall and being movable frontward and rearward; an input member provided in the power piston to be movable frontward and rearward relative to the power piston, the input member receiving an external operation force applied thereto in a frontward direction; an output member for outputting, to an external device, a frontward thrust force generated by the power piston; a control valve mounted in the power piston and comprising an atmospheric control valve portion and a vacuum control valve portion, the atmospheric control valve portion facing frontward, toward an atmospheric valve seat provided on the input member, and adapted to establish and shut off communication between the variable-pressure chamber and the atmosphere in cooperation with the atmospheric valve seat, and the vacuum control valve portion facing frontward, toward a vacuum valve seat provided on the power piston, and adapted to establish and shut off communication between the variable-pressure chamber and the constant-pressure chamber in cooperation with the vacuum valve seat; first biasing means for biasing the control valve frontward toward the atmospheric valve seat and the vacuum valve seat; second biasing means for biasing the input member rearward; and a stopper for limiting a quantity of movement of the input member relative to the power piston effected by biasing force of the second biasing means. In the negative pressure type booster of the present invention, the atmospheric valve seat is formed on an annular portion of the input member extending radially outward; the annular portion and an annular diaphragm located frontward of the annular portion and mounted to the input member define an annular atmospheric chamber; the atmospheric chamber communicates with the atmosphere via an air hole formed in the annular portion or in the input member; and the diaphragm is supported from the front by the power piston.

In the negative pressure type booster of the present invention, the area of a portion of the input member having the atmospheric valve seat which receives a differential pressure (a differential pressure between a vacuum in the variable-pressure chamber and the atmospheric pressure) can be equal to a differential area obtained by subtracting the cross-sectional area of the annular atmospheric chamber from the area of the atmospheric valve as measured with the effective diameter of the atmospheric valve; in other words, the area which receives the differential pressure can be reduced by the cross-sectional area of the annular atmospheric chamber. Accordingly, a differential-pressure-induced force (a working force induced by the differential pressure between a vacuum in the variable-pressure chamber and the atmospheric pressure) that is exerted on the input member having the atmospheric valve seat can be reduced. Even when, in an ordinary state, a vacuum in the variable-pressure chamber varies, a variation in operation force associated with separation of the atmospheric valve seat from the atmospheric control valve portion; i.e., a variation in startup force, can be reduced to such a level as not to give an operator (a vehicle driver) a sensation of unusual operation.

Preferably, the diaphragm is a flexible member (e.g., a rubber diaphragm), and an inner or outer circumferential portion of the flexible member assumes a rolling structure for allowing frontward/rearward movement of the input member by means of curviform deformation. In this case, in operation of the input member, the inner or outer circumferential portion of the flexible member undergoes curviform deformation to thereby allow frontward/rearward movement of the input member. Thus, the input member to which the flexible member is mounted can be operated smoothly.

Preferably, the control valve is configured such that the atmospheric control valve portion and the vacuum control valve portion are arranged axially apart from each other. In this case, the effective diameter of the atmospheric valve, which is composed of the atmospheric valve seat and the atmospheric control valve portion, can be increased without restriction by the vacuum control valve portion of the control valve. Thus, an air path can have a sufficiently large cross-sectional area, thereby enhancing operational response of the negative pressure type booster.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will next be described in detail with reference to the drawings.FIGS. 1 and 2show a negative pressure type booster according to an embodiment of the present invention. The negative pressure type booster includes a movable wall20and a power piston30, which are mounted to a housing10, as well as an input member40, an output member50, a key member60, and a control valve70, which are mounted in the power piston30.

As shown inFIG. 1, the housing10includes a front shell11and a rear shell12. The movable wall20divides the interior of the housing10into a constant-pressure chamber R1and a variable-pressure chamber R2. The constant-pressure chamber R1communicates with a vacuum source (e.g., an unillustrated intake manifold of an engine) at all times via a vacuum introduction pipe13. Communication is established/shut off between the variable-pressure chamber R2and the constant-pressure chamber R1and between the variable-pressure chamber R2and the atmosphere. The housing10is fixedly attached to a vehicular body (not shown), by means of threaded rear end portions of a plurality of tie rods14(FIG. 1shows only a single tie rod14). The tie rods14extend airtightly through the housing10and the movable wall20. Notably, a brake master cylinder MC is fixedly connected to threaded front end portions of the tie rods14.

The movable wall20includes a metal plate21and a rubber diaphragm22and is disposed in a frontward/rearward movable condition relative to the housing10. The diaphragm22is airtightly sandwiched, at its bead portion formed at its outer peripheral edge, between the front shell11and a peripheral bend edge portion of the rear shell12. The diaphragm22, together with the plate21, is airtightly and fixedly fitted, at its bead portion formed at its inner peripheral edge, into a circumferential groove formed on the outer surface of a front flange portion of the power piston30.

A rear end portion MC1aof a cylinder body MC1of the brake master cylinder MC shown inFIG. 1airtightly extends through a central cylinder portion of the front shell11and projects into the constant-pressure chamber R1. The rear surface of a flange portion MC1bof the cylinder body MC1abuts the front surface of the front shell11. A piston MC2of the brake master cylinder MC projects rearward into the constant-pressure chamber R1from the cylinder body MC1and is pushed frontward by means of the front end of the output member50.

The power piston30is a hollow piston connected to the movable wall20. A cylindrical portion of the power piston30is connected to the rear shell12airtightly and in a frontward/rearward movable condition. A spring31disposed between the power piston30and the front shell11of the housing10biases the power piston30rearward. As shown inFIG. 2, an axial hole extends through the power piston30. The axial hole includes, in the direction from the front end surface to the rear end surface of the power piston30, a reaction chamber hole30a; a stepped plunger receptive-hole30bhaving a diameter smaller than that of the reaction chamber hole30a; a support-member-and-control-valve receptive-hole30chaving a diameter greater than that of the plunger receptive-hole30b; and a filter receptive-hole30d. An annular groove30eis formed on the power piston30integrally with the reaction chamber hole30aand coaxially with the plunger receptive-hole30b.

The power piston30has a radially extending key member insertion hole30fin association with the plunger receptive-hole30c. Also, the power piston30has a communication hole30gthrough which the constant-pressure chamber R1and the support-member-and-control-valve receptive-hole30ccan communicate with each other. An annular vacuum valve seat30his formed at a rear end portion of the communication hole30g. A vacuum control valve portion70aof the control valve70can be seated on the vacuum valve seat30h.

The input member40is provided in the power piston30in a frontward/rearward movable condition relative to the power piston30and receives an external operation force. The input member40includes a plunger41and an input rod42. The plunger41is accommodated in the plunger receptive-hole30band in the support-member-and-control-valve receptive-hole30cand is axially (frontward/rearward) movable in relation to the power piston30. The quantity of movement of the plunger41is limited by a key member60mounted to the power piston30. The input rod42is articularly joined, at its spherical end portion42a, to the plunger41and is connected, at its rear end portion42b, to a brake pedal BP.

The plunger41can abut, at its front end, a reaction member80accommodated in the reaction chamber hole30aof the power piston30. An annular disk43is integrally mounted to the rear end of the plunger41. An annular atmospheric valve seat43ais formed on the rear surface of an outer circumferential portion of the disk43. The atmospheric valve seat43ais seated on an atmospheric control valve portion70bof the control valve70in such a manner as to be able to be separated from the atmospheric control valve portion70b. The reaction member80is a reaction rubber disk. While being accommodated in a cylindrical portion51aof a rear member51of the output member50, the reaction member80abuts the reaction force reception surface of the power piston30and can abut the front surface of the plunger41.

The output member50includes the rear member51and an output rod52(seeFIG. 1). The rear member51, together with the reaction member80, is mounted in the reaction chamber hole30aof the power piston30and is fitted into the annular groove30e, in an axially movable condition. The output rod52is united to a front end portion of the rear member51. The front end of the output rod52abuts an engagement portion of the piston MC2of the brake master cylinder MC in such a manner as to be able to push the piston MC2.

The key member60is a stopper for limiting the axial movement of the plunger41relative to the power piston30and for limiting the rearward movement of the power piston30relative to the housing10. The key member60is inserted into the radially extending key member insertion hole30fformed in the power piston30. The axially measured thickness of the key member60is smaller than the axially measured dimension of the key member insertion hole30f, so that the key member60can move axially by a predetermined quantity relative to the power piston30.

The key member60can abut the rear shell12at the rear surface of its opposite end portions projecting radially outward from the power piston30. The rearward movement limit position of the power piston30relative to the housing10is where, as shown inFIG. 2, the front wall of the key member insertion hole30fis in contact with the front surface of the key member60while the rear surface of opposite end portions of the key member60is in contact with the rear shell12. The key member60can abut, at its central portion, front and rear walls41aand41b, respectively, of an annular groove formed at an axially central portion of the plunger41. The rearward movement limit position of the plunger41relative to the power piston30is where the front wall41aof the annular groove is in contact with the front surface of the key member60while the rear surface of the key member60is in contact with the rear wall of the key member insertion hole30f. The frontward movement limit position of the plunger41relative to the power piston30is where the rear wall41bof the annular groove is in contact with the rear surface of the key member60while the front surface of the key member60is in contact with the front wall of the key member insertion hole30f.

The control valve70includes an annular movable portion70A having the vacuum control valve portion70aand the atmospheric control valve portion70b; an annular stationary portion70B fitted fixedly and airtightly to a stepped portion formed on the wall of the support-member-and-control-valve receptive-hole30cof the power piston30; and a cylindrical bellows portion70C connecting the annular movable portion70A and the annular stationary portion70B. The annular movable portion70A is biased frontward by a spring71interposed between the annular movable portion70A and the input rod42and is axially movable. While a spring72interposed between the annular stationary portion70B and the input rod42applies frontward force to the annular stationary portion70B, the annular stationary portion70B is fixedly attached to the power piston30.

The vacuum control valve portion70acan be seated on and separated from the annular vacuum valve seat30hformed on the power piston30. When the vacuum control valve portion70ais seated on the vacuum valve seat30h, communication is shut off between the constant-pressure chamber R1and the variable-pressure chamber R2. When the vacuum control valve portion70ais separated from the vacuum valve seat30h, communication is established between the constant-pressure chamber R1and the variable-pressure chamber R2. The atmospheric control valve portion70bcan be seated on and separated from the annular atmospheric valve seat43aformed on the annular disk43. When the atmospheric control valve portion70bis seated on the atmospheric valve seat43a, communication is shut off between the variable-pressure chamber R2and the atmosphere. When the atmospheric control valve portion70bis separated from the atmospheric valve seat43a, communication is established between the variable-pressure chamber R2and the atmosphere.

The spring71is biasing means for biasing the movable portion70A of the control valve70frontward toward the atmospheric valve seat43aand the vacuum valve seat30hand for biasing the input member40rearward. The spring72is biasing means for biasing the input member40rearward such that, in an ordinary state, the atmospheric valve seat43ais in contact with (abuts) the atmospheric control valve portion70b, and the vacuum control valve portion70ais separated from the vacuum valve seat30h. Biasing forces of the springs71and72are determined on the basis of a differential-pressure-induced force that in turn is determined on the basis of the effective diameter of the bellows portion70C of the control valve70or the effective diameter (seal diameter) of an atmospheric valve that is composed of the atmospheric valve seat43aand the atmospheric control valve portion70b. Notably, the effective diameter of the bellows portion70C is set substantially equal to the effective diameter (seal diameter) of the atmospheric valve.

Filters91and92are disposed in the filter receptive-hole30dof the power piston30and between the input rod42and the power piston30. The air can flow into the filters91and92through a ventilation hole93aformed in a boot93, which is adapted to externally protect the cylindrical body of the power piston30. The boot93is fixedly fitted, at its front end portion, to a tubular rear-end portion of the rear shell12of the housing10and is fixedly fitted, at its rear end portion, to an axially intermediate portion of the input rod42.

In the present embodiment, an annular diaphragm44is mounted to the plunger41and located frontward of the annular disk43, which is mounted to the plunger41. The annular diaphragm44and the annular disk43define an annular atmospheric chamber R3on the forward side of the annular disk43. The diaphragm44is formed of a flexible material such as rubber and is airtightly connected, at its bead portion formed at its inner circumferential edge, to the plunger41. The diaphragm44is airtightly press-fitted, at its outer circumferential edge portion, to a cylindrical portion43bformed at an outer circumferential portion of the annular disk43. A metal ring45is bonded to the exterior of the outer circumferential edge portion of the diaphragm44.

The annular atmospheric chamber R3, which is defined by the diaphragm44and the annular disk43, communicates with the atmosphere via an air hole43c(this air hole may be formed in the plunger41or in an engagement portion between the plunger41and the annular disk43). The diaphragm44has rolling portions44aand44bformed at inner and outer circumferential portions, respectively. An end portion of a tubular support member46abuts the diaphragm44at the front surface of a portion extending between the rolling portions44aand44b. The rolling portions44aand44bproject frontward and allow frontward/rearward movement of the plunger41by means of curviform deformation. The effective diameter of the rolling portion44b, which is formed at an outer circumferential portion of the diaphragm44, is set substantially equal to the effective diameter (seal diameter) of the atmospheric valve, which is composed of the atmospheric valve seat43aand the atmospheric control valve portion70b.

The tubular support member46is fixedly fitted, at its front end portion, to a boss portion30iof the power piston30and supports the diaphragm44from the front. In a state where differential pressure is generated between the variable-pressure chamber R2and the atmospheric chamber R3; i.e., in a state where the atmospheric valve seat43ais in contact with (abuts) the atmospheric control valve portion70b, and the vacuum control valve portion70ais separated from the vacuum valve seat30h, a differential-pressure-induced force exerted on the diaphragm44is supported by the power piston30via the tubular support member46.

In the thus-configured negative pressure type booster of the present embodiment, during braking, the input member40moves frontward relative to the power piston30and against biasing forces of the springs71and72. Thus, the atmospheric valve seat43ais separated from the atmospheric control valve portion70b, and the vacuum control valve portion70acomes into contact with (abuts) the vacuum valve seat30h. Also, the front end surface of the plunger41abuts the reaction member80, and an ordinary braking operation is performed.

In the negative pressure type booster of the present embodiment, the annular diaphragm44is mounted to the input member40and located frontward of the annular disk43; and the annular diaphragm44and the annular disk43define the annular atmospheric chamber R3. The annular atmospheric chamber R3communicates with the atmosphere via the air hole43cformed in the annular disk43. A portion of the diaphragm44extending between the rolling portions44aand44bis supported from the front by the power piston30via the tubular support member46.

Thus, the area of a portion of the annular disk43having the atmospheric valve seat43awhich receives a differential pressure (a differential pressure between a vacuum in the variable-pressure chamber R2and the atmospheric pressure) can be equal to a differential area obtained by subtracting the cross-sectional area of the annular atmospheric chamber R3from the area of the atmospheric valve as measured with the effective diameter of the atmospheric valve; in other words, the area which receives the differential pressure can be reduced by the cross-sectional area of the annular atmospheric chamber R3. Accordingly, a differential-pressure-induced force (a working force induced by the differential pressure between a vacuum in the variable-pressure chamber R2and the atmospheric pressure) that is exerted on the annular disk43having the atmospheric valve seat43acan be reduced. Even when, in an ordinary state (a state in which the atmospheric valve seat43ais in contact with (abuts) the atmospheric control valve portion70b, and the vacuum control valve portion70ais separated from the vacuum valve seat30h), a vacuum in the variable-pressure chamber R2varies, a variation in operation force associated with separation of the atmospheric valve seat43afrom the atmospheric control valve portion70b; i.e., a variation in startup force, can be reduced to such a level as not to give an operator (a vehicle driver) a sensation of unusual operation.

In the negative pressure type booster of the present embodiment, a diaphragm that is located frontward of the annular disk43and defines the annular atmospheric chamber R3in cooperation with the annular disk43is the diaphragm44made of rubber, and inner and outer circumferential portions of the diaphragm44are formed into the rolling portions44aand44b, respectively, for allowing frontward/rearward movement of the input member40by means of curviform deformation. Thus, in a braking operation; i.e., in operation of the input member40, the inner and outer circumferential portions of the diaphragm44undergo curviform deformation to thereby allow frontward/rearward movement of the input member40. Thus, the input member40to which the diaphragm44is mounted can be operated smoothly.

In the negative pressure type booster of the present embodiment, the control valve70is configured such that the atmospheric control valve portion70band the vacuum control valve portion70aare arranged axially apart from each other. Thus, the effective diameter of the atmospheric valve, which is composed of the atmospheric valve seat43aand the atmospheric control valve portion70b, can be increased without restriction by the vacuum control valve portion70aof the control valve70. Thus, an air path can have a sufficiently large cross-sectional area, thereby enhancing operational response of the negative pressure type booster.

FIG. 3shows a negative pressure type booster according to another embodiment of the present invention. In the negative pressure type booster ofFIG. 3, a power piston130includes a large-diameter power piston130A and a small-diameter power piston130B to thereby implement a large-diameter atmospheric valve seat143a. The atmospheric valve seat143ais formed on an annular disk portion143, which is integrally formed on a plunger141. An atmospheric valve that is composed of the atmospheric valve seat143aand an atmospheric control valve portion170bis disposed in the proximity of the variable-pressure chamber R2, to thereby reduce air flow resistance involved in entry of the air into the variable-pressure chamber R2. Thus, the negative pressure type booster of the present embodiment exhibits higher operational response as compared with the previously described embodiment.

The negative pressure type booster ofFIG. 3is substantially identical with that ofFIGS. 1 and 2except that, for example, a vacuum pressure valve seat130his arcuately formed at a rear end portion of a communication hole130gformed in the large-diameter power piston130A; an annular support plate146is affixed to a portion of a diaphragm144extending between rolling portions144aand144band is supported by the power piston130A; a spring171is disposed between a movable portion170A of a control valve170and a stationary portion170B of the control valve170, which is fixedly attached to the small-diameter power piston130B, and biases the movable portion170A frontward; a spring172is disposed between an input rod142and the small-diameter power piston130B and biases the input rod142rearward; and filters191and192are mounted to the input rod142in a unitarily movable condition. Thus, the same or similar structural features are denoted by common reference numerals plus100, and repeated description thereof is omitted.

The above embodiments are described while mentioning a single-type negative pressure type booster. However, the present invention may be embodied in the form of a tandem- or triple-type negative pressure type booster or may be embodied in various other forms without departing from the scope of the invention.