Negative pressure boosting device

In a negative pressure boosting device of the present invention, upon depression of a pedal at a normal speed, an input shaft 11 and a valve plunger 10 move forward to close a vacuum valve 15 and open an atmospheric valve 16 and a power piston 5, a valve body 4, and an output shaft 24 move forward. In the initial stage of operation, hooks 27c and 31a are not engaged with each other so that a cylindrical member 27 does not move forward, thereby shortening the stroke of the input shaft 11 as compared to a conventional one. Upon rapid depression of the pedal, a press face 10a presses a pressed face 27e so as to deform an engaging arm portion 27b, thereby disengaging the hooks 27c and 31a from each other. The cylindrical member 27 is moved backward by a spring 30 to push a vacuum valve portion 12b so that the atmospheric valve portion 12a is spaced apart from the atmospheric valve seat 14 more rapidly than that of the service braking, thereby increasing the jumping amount and thus rapidly intensifying the output.

BACKGROUND OF THE INVENTION

The present invention relates to a negative pressure boosting device used as a brake booster or the like and, more particularly, to a negative pressure boosting device capable of shortening the stroke of an input shaft thereof in the initial stage of its normal operation and capable of providing larger output in the event of emergency braking operation as compared to the normal operation.

Conventionally, a negative pressure boosting device utilizing negative pressure is used as a brake booster in an automobile such as a passenger car. Upon depression of the brake pedal for normal braking operation, an input shaft is moved forward to move a valve plunger, connecting the input shaft, forward. Accordingly, a valve element of a control valve arranged in the valve body is seated on a vacuum valve seat similarly formed in the valve body so as to close a vacuum valve, while an atmospheric valve seat formed in the valve plunger is spaced apart from the valve element of the control valve so as to open an atmospheric valve. Accordingly, a variable pressure chamber into which a negative pressure is introduced in the inoperative state is isolated from a constant pressure chamber into which the negative pressure is always introduced. At the same time, the variable pressure chamber is in communication with the atmosphere. Therefore, the atmosphere is introduced into the variable pressure chamber through the open atmospheric valve, resulting in a pressure difference between the variable pressure chamber and the constant pressure chamber. Because of the pressure difference, the power piston is moved forward so that the valve body and an output shaft are moved forward. In this manner, the negative pressure boosting device boosts the input (i.e. pedaling force) of the input shaft in accordance with a predetermined servo ratio to output. The output of the negative pressure boosting device moves a piston of a master cylinder, whereby the master cylinder produces a master cylinder pressure. With this master cylinder pressure, wheel cylinders are actuated, thereby operating the service braking.

Generally, the negative pressure boosting device has a jumping (JP) characteristic. That is, as shown inFIG. 6, no reaction is transmitted from the output shaft to the input shaft when the input is small, while reaction is transmitted to the input shaft via a reaction mechanism to substantially generate a predetermined output when the input is somewhat large.

As the brake pedal is released so that the input shaft is moved backward, the atmospheric valve seat abuts on the valve element of the control valve to close the atmospheric valve and, at the same time, the valve element is spaced apart from the vacuum valve seat to open the vacuum valve, whereby the variable chamber is isolated from the atmosphere and is in communication with the constant pressure chamber. Then, the atmosphere introduced in the variable pressure chamber is discharged to a negative pressure source through the open vacuum valve and the constant pressure chamber so that the negative pressure is introduced into the variable pressure chamber, thereby canceling the pressure difference between the variable pressure chamber and the constant pressure chamber. As a result of this, the power piston is moved backward so that the valve body and output shaft are moved backward to their inoperative positions, whereby the output of the negative pressure boosting device dies out. Therefore, the piston of the master cylinder is moved backward to its inoperative position so that the master cylinder pressure dies out, thereby canceling the service braking.

By the way, in a brake system including the master cylinder and the wheel cylinders, a predetermined amount of brake fluid should be supplied from the master cylinder to the wheel cylinders until the wheel cylinders actually generate braking force after the master cylinder is actuated to start the supply of brake fluid to the wheel cylinders. The travel of the piston of the master cylinder until the wheel cylinders actually generate braking force is called loss stroke. For the loss stroke, the piston of the master cylinder must have longer stroke. This makes the output shaft and the input shaft of the negative pressure boosting device longer and, as a result, makes the pedal stroke longer.

Accordingly, Japanese Patent Unexamined Publication No. H05-193486 discloses a negative pressure boosting device which can shorten the stroke of an input shaft of the negative pressure boosting device, i.e. shorten the pedal stroke, even with such a loss stroke in the brake system.

The negative pressure boosting device disclosed in the publication is provided with a sleeve having a valve seat of a vacuum valve (hereinafter, referred to as “vacuum valve seat”) at a rear portion thereof and slidably fitted to the inner periphery of the valve body. The sleeve is always urged by a spring in a direction of opening the vacuum valve. When the negative pressure boosting device is not operated, the rearmost position of the sleeve is defined by a key member restricting the backward movement of the valve body. As the input shaft is moved forward by the depression of a brake pedal, the vacuum valve is closed and an atmospheric valve is opened in the same manner as mentioned above so that the atmosphere is introduced into a variable chamber to move a power piston, the valve body, and an output shaft forward. Accordingly, the negative pressure boosting device outputs.

In the initial stage of the operation of the negative pressure boosting device, until the key member abuts on a stopper formed in the valve body and starts to move forward together with the valve body, the sleeve is held at its initial position by the spring and the vacuum valve and the atmospheric valve are held to balance with each other so that only the valve body moves relative to the input shaft. Therefore, the stroke of the valve body or the output shaft should be longer than the stroke of the input shaft. In other words, the device disclosed in the publication has a shorter stroke of the input shaft, i.e. a shorter pedal stroke, compared to the conventional negative pressure boosting device for the same stroke of the output shaft.

On the other hand, in a brake system, there is a case, such as for emergency braking, that it is necessary to produce desired large braking force more rapidly than that of the service braking operation immediately after the depression of the brake pedal. Therefore, it has been traditionally desirable to employ a brake assist (hereinafter, referred to as “BA”) control system in a brake system. By employing the BA control system, large braking force can be rapidly produced even with small pedaling force. For improving the brake boosting control, it is preferable to not only shorten the pedal stroke as described above but also perform the BA control.

To shorten the stroke of the input shaft in the initial stage of the service braking operation and to perform the BA control in the event of the emergency braking operation, there is an idea of modifying the negative pressure boosting device disclosed in the aforesaid publication to be capable of outputting desired large braking force more rapidly than that of the service braking, for example, in the event of emergency braking.

However, it is difficult to output desired large braking force more rapidly than that of the service braking operation, in the event of emergency braking, that is, it is difficult to exhibit the BA control in the negative pressure boosting device because the output must be the same for the same input applied to the input shaft even in the event of emergency braking operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a negative pressure boosting device capable of performing improved boosting control, with shortening the stroke of an input member or an input shaft and, in addition, producing desired large output more rapidly than that of service braking, with small input in the event of emergency braking operation.

To achieve the above-mentioned object, a negative pressure boosting device of the present invention is a negative pressure boosting device of which an output member is actuated to produce an output by the introduction of atmosphere during operation of an input member and is characterized by comprising: an input stroke shortening means for shortening the stroke of said input member relative to the stroke of said output member in the initial stage of operation; and a rapid output intensifying means for intensifying said output more rapidly than that of the normal operation when said input member is operated more rapidly than that for the normal operation.

Further, a negative pressure boosting device of the present invention comprises at least: a valve body which is arranged to freely move forward and backward relative to a space defined by a shell and airtightly and slidably penetrates said shell; a power piston which is connected to said valve body and divides said space into a contact pressure chamber in which negative pressure is introduced and a variable pressure chamber in which atmosphere is introduced during operation; a valve plunger which is movably arranged in said valve body; an input shaft which is connected to said valve plunger and is arranged in said valve body to allow the forward and backward movement of said input shaft relative to said valve body; an output shaft which moves together with said valve body by the operation of said power piston to produce an output; a vacuum valve which is arranged in said valve body and is controlled by the forward and backward movement of said valve plunger to impede or allow the communication between said constant pressure chamber and said variable pressure camber; and an atmospheric valve which is arranged in said valve body and is controlled by the forward and backward movement of said valve plunger to impede or allow the communication between said variable pressure camber and the atmosphere, and is characterized by comprising: an input stroke shortening means for shortening the stroke of said input shaft relative to the stroke of said output shaft in the initial stage of operation; and a rapid output intensifying means for intensifying said output more rapidly than that of the normal operation when said input shaft is operated more rapidly than that for the normal operation.

The present invention is further characterized in that said vacuum valve comprises a vacuum valve member which is arranged in said valve body and a vacuum valve seat which is arranged movably relative to said valve body and on which said vacuum valve member can be seated, and that said input stroke shortening means moves said valve body relative to said vacuum valve seat in the initial stage of operation and then moves said vacuum valve seat together with said valve body after said valve body is moved a predetermined distance relative to said vacuum valve seat.

The present invention is furthermore characterized in that said rapid output intensifying means is actuated when said input shaft is operated more rapidly than that for the normal operation and rapidly opens said atmospheric valve to increase the jumping amount so as to obtain an output larger than that of the normal operation.

The present invention is still characterized in that said atmospheric valve comprises an atmospheric valve member which is arranged in said valve body and an atmospheric valve seat which is provided on said valve plunger and on which said atmospheric valve member is seated, and that said rapid output intensifying means is actuated when said input shaft is operated more rapidly than that for the normal operation and moves said vacuum valve, said atmospheric valve member, and said atmospheric valve seat backward relative to said valve body more largely than that of the normal operation.

The present invention is still further characterized in that said vacuum valve comprises a vacuum valve member which is arranged in said valve body and a vacuum valve seat which is arranged movably relative to said valve body and on which said vacuum valve member can be seated; said atmospheric valve comprises an atmospheric valve member which is arranged in said valve body and an atmospheric valve seat which is provided on said valve plunger and on which said atmospheric valve member is seated; said vacuum valve member and said atmospheric valve member are movable together with each other; a cylindrical member having said vacuum valve seat on one end thereof is disposed airtightly and slidably relative to said valve body; said input stroke shortening means comprises a valve body-side engaging portion provided on said valve body and a cylindrical member-side engaging portion provided on said cylindrical member which is set to have a predetermined distance from said valve body-side engaging portion when the negative pressure booster is not operated, wherein said valve body-side engaging portion and said cylindrical member-side engaging portion are not engaged with each other in the initial stage of operation, while said valve body-side engaging portion and said cylindrical member-side engaging portion are engaged with each other after said valve body moves relative to said cylindrical member to cancel said predetermined distance therebetween, thereby moving said cylindrical member together with said valve body; and said rapid output intensifying means moves said atmospheric valve member and said atmospheric valve seat backward more largely than that of the normal operation by that said cylindrical member pushes said vacuum valve member when said input shaft is operated more rapidly than that for the normal operation.

In addition, the present invention is characterized in that said valve body is provided with the other vacuum valve seat of said vacuum valve, wherein said vacuum valve member is seated on said the other vacuum valve seat at the beginning of operation in which the control for shortening the stroke of said input shaft is performed by said input stroke shortening means, and said vacuum valve member is seated on the vacuum valve seat provided on said cylindrical member during and after the operation in which the control for shortening the stroke of said input shaft is performed by said input stroke shortening means.

According to the negative pressure boosting device of the present invention having the aforementioned structure, the stroke of the input member can be shortened in the initial stage of the operation relative to the stroke of the output member by the input stroke shortening means and, in addition, the output can be intensified more rapidly than that of the normal operation when the input member is operated more rapidly than that for the normal operation by the rapid output intensifying means.

Further, according to the negative pressure boosting device of the present invention, the stroke of the input shaft can be effectively shortened in the initial stage of the operation relative to the stroke of the output shaft by the input stroke shortening means and, in addition, the output can be intensified more rapidly than that of the normal operation when the input shaft is operated more rapidly than that for the normal operation by the rapid-output intensifying means.

Therefore, the negative pressure boosting device of the present invention can perform improved boosting control.

By employing the negative pressure boosting device of the present invention as a brake booster, even if a brake system has a loss stroke as mentioned above, the loss stroke can be effectively cancelled with shortening the pedal stroke of a brake pedal in the initial stage of braking operation. In addition, in the event of emergency braking, the braking force can be intensified more rapidly than that of the service braking, thereby rapidly and effectively performing the emergency braking.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a sectional view showing an embodiment of a negative pressure boosting device according to the present invention in its inoperative state,FIG. 2is an enlarged sectional view showing a portion including a vacuum valve and an atmospheric valve in the negative pressure boosting device shown inFIG. 1,FIG. 3is a sectional view partially showing the operative state of a cylindrical member in the negative pressure boosting device shown inFIG. 1, andFIGS. 4(a)–4(c) are illustrations for explaining the operation of hooks in the negative pressure boosting device shown inFIG. 1, whereinFIG. 4(a) is a sectional view partially showing the inoperative state where the hooks are not engaged with each other,FIG. 4(b) is a sectional view partially showing a state on the way of operation, andFIG. 4(c) is a sectional view partially showing the state where the hooks are engaged with each other. In the following description, the terms such as “front or fore” and “rear or back” refer to the left and the right, respectively, in the drawings.

It should be noted that component parts in a negative pressure boosting device of this embodiment, similar or corresponding to the parts of the conventional negative pressure boosting device, will be briefly explained. InFIG. 1, numeral1designates the negative pressure boosting device;2designates a front shell;3designates a rear shell;4designates a valve body;5designates a power piston which is composed of a power piston member6attached to the valve body4and a diaphragm7disposed between the valve body4and the shells2,3;8designates a constant pressure chamber which is formed in a space inside the shells2,3and defined by the power piston5and in which negative pressure is always introduced;9designates a variable chamber which is formed in the space inside the shells2,3and defined by the power piston5and in which atmosphere is introduced when the negative pressure boosting device is operated;10designates a valve plunger;11designates an input shaft (corresponding to the input member of the present invention) which is connected to a brake pedal (not shown) and controls the operation of the valve plunger10;12designates a valve element disposed in the valve body4;13designates an annular vacuum valve seat formed in the valve body4;14designates an annular atmospheric valve seat formed in the valve plunger10;15designates a vacuum valve which is composed of the valve element12and the vacuum valve seat13(corresponding to the other vacuum valve seat of the present invention);16designates an atmospheric valve which is composed of the valve element12and the atmospheric valve seat14;17designates a control valve which is composed of the vacuum valve15and the atmospheric valve16and selectively controls the connection of the variable pressure chamber9between the constant pressure chamber8and the atmosphere;18designates a valve spring which always urges the valve element12in a direction seating the valve element12on the vacuum valve seat13;19designates an atmosphere introducing passage;20designates a vacuum passage;21designates a key member which is inserted into a key way4aformed in the valve body4to restrict the movement of the valve plunger10relative to the valve body4to a predetermined amount defined according to the axial width of the key way4aand to define the rearmost positions of the valve body4and the valve plunger10;22designates a spacing member;23designates a reaction disk;24designates an output shaft (corresponding to the output member of the present invention); and25designates a return spring; and26designates a negative pressure introducing passage connected to a negative pressure source (not shown).

Similarly to the conventional negative pressure boosting device, the output shaft24penetrates the front shell2in such a manner as to allow the output shaft24to move relative to the front shell2. At the portion where the output shaft24penetrates the front shell2, the contact pressure chamber8is airtightly sealed from the atmosphere by a suitable sealing means (not shown). In addition, the valve body4penetrates the rear shell3in such a manner as to allow the valve shaft4to move relative to the rear shell3. At the portion where the valve body4penetrates the rear shell3, the variable pressure chamber9is airtightly sealed from the atmosphere by a cup seal (shown without numeral).

Defined between the front end face of the spacing member22and the rear end face of the reaction disk23, facing to the front end face of the spacing member22, is a cylindrical space S1having a predetermined clearance L in the axial direction.

Description will now be made as regard to characterizing portions of the negative pressure boosting device1of this embodiment which are different from the conventional negative pressure boosting device.

As shown inFIG. 2, in the negative pressure boosting device1of this embodiment, the valve element12comprises an atmospheric valve portion12a(corresponding to the atmospheric valve member of the present invention) which can be seated on the atmospheric valve seat14and a vacuum valve portion12b(corresponding to the vacuum valve member of the present invention) which can be seated on the vacuum valve seat13. The atmospheric valve portion12aand the vacuum valve portion12bare connected to each other by a connecting member12cso that these valve portions move together.

A cylindrical member27is slidably fitted in the axial inner bore of the valve body4airtightly by a seal member such as an O-ring. As shown inFIG. 3as an enlarged partial illustration, the cylindrical member27has a cylindrical sliding portion27aand an engaging arm portion27bwhich extends forward from the cylindrical sliding portion27aand is elastically bendable. The engaging arm portion27bis in a form of a cantilever having elastic bendability of which the proximal end is the sliding portion27aand has a hook27c(corresponding to the cylindrical member-side engaging portion) formed at the free end thereof. The engaging arm portion27bhas a projection27dformed between the cylindrical sliding portion27aand the hook27c. The rear surface of the projection27dis formed in a tapered surface inclined backward toward the outside and is a pressed face27e. The cylindrical member27further has a stopper portion27f(shown inFIG. 2) which is formed in the inner periphery thereof and is capable of abutting with the key member21. At the rear end of the cylindrical member27, a vacuum valve seat27gon which the vacuum valve portion12bof the valve element12can be seated is formed. In the negative pressure boosting device1of this embodiment, the vacuum valve seat27gcooperates with the vacuum valve seat13to compose the vacuum valve15(hereinafter, the vacuum valve seat13formed in the valve body4is called the first vacuum valve seat13and the vacuum valve seat27gformed in the cylindrical member27is called the second vacuum valve seat27g).

A spring30is compressed and disposed between a retainer29attached to the valve body4and the cylindrical sliding portion27aof the cylindrical member27. The cylindrical member27is always urged backward by the spring force of the spring30.

As shown inFIG. 2, at the front end of the valve body4, the guide31is fixed to the valve body4. The guide31slidably guides the spacing member22and the hook27cof the engaging arm portion27b. As shown inFIG. 4(a) as an enlarged illustration, the guide31is provided with a hook31a(corresponding to the valve body-side engaging portion of the present invention) formed on the outer periphery of a rear end portion of the guide31. The hook31acan engage the hook27cof the engaging arm portion in the axial direction. When the negative pressure boosting device1is not operated, as shown inFIG. 4(a), a predetermined distance A is set between a contact face31a1of the hook31aand a contact face27c1of the hook27cso that the hooks27cand31aare set not to engage each other in the axial direction.

The front end face of the guide31is formed in a tapered face31bhaving a truncated cone shape. The tapered face31bis inclined backward toward the inner periphery of the guide31. Because of the tapered face31b, an annular space S2is formed between the tapered face31band a rear end face of the reaction disk23facing to the tapered face31bwhen the negative pressure boosting device1is not operated.

As shown inFIG. 2, the valve plunger10is provided with a press face10acomprising a tapered face, having a truncated cone shape, and inclined backward toward the outer periphery. The press face10ais formed to confront the press face27eof the cylindrical member27in the axial direction. According to the forward movement of the valve plunger10relative to the cylindrical member27, the press face10aof the valve plunger10comes in contact with the pressed face27eof the cylindrical member27to press the pressed face27e.

Since the press face10aand the pressed face27eare formed in tapered surfaces as mentioned above, the wedge effect is created when the pressed face27eis pressed by the press face10a. Because of this wedge effect, the engaging arm portion27bis elastically deformed outwardly (downwardly in the drawing) because of the elastic bendability as shown inFIG. 3. The deformation of the engaging arm portion27bcancels the axial engagement between the hook27cof the engaging arm portion and the hook31aof the guide31. As the axial engagement between the hooks27band31ais cancelled, the cylindrical member27moves backward relative to the valve body4by the spring force of the spring30so that the second vacuum valve seat27gcomes in contact with the vacuum valve portion12bof the valve element12to push the vacuum valve portion12band the atmospheric valve portion12abackward.

In the state where the axial distance A is set between the hooks27cand31a, the second vacuum valve seat27gof the cylindrical member27is located ahead of the first vacuum valve seat13by a predetermined distance B. In this embodiment, the predetermined distance B is set to be smaller than the predetermined distance A (B<A). In the state where the distance A between the hooks27cand31ais extinct so that the hooks27cand31aare engaged with each other, because of B<A, the second vacuum valve seat27gof the cylindrical member27projects backward relative to the first vacuum valve seat13to push both the vacuum valve portion12band the atmospheric valve portion12abackward.

Assuming that the negative pressure boosting device1of this embodiment is adopted to a brake system, the operation of the device will now be described.

(Inoperative State of the Negative Pressure Boosting Device)

In the negative pressure boosting device, negative pressure is always introduced into the constant pressure chamber8through the negative pressure introducing passage25. In the inoperative state of the negative pressure boosting device1as shown inFIG. 1andFIG. 2, the key member21abuts on the rear shell3and is therefore located at the rearmost position. By the key member21, the valve body4and the valve plunger6are located at their rearmost positions and the power piston5, the input shaft11, and the output shaft24are also located at their rearmost positions. In this inoperative state, the atmospheric valve portion12aof the valve element12is seated on the atmospheric valve seat14and the vacuum valve portion12bof the valve element12is spaced apart from the first vacuum valve seat13and the second vacuum valve seat27g. Therefore, the variable pressure chamber9is isolated from the atmosphere and is in communication with the constant pressure chamber8so that the negative pressure is introduced into the variable pressure chamber9. This means that there is substantially no pressure difference between the variable pressure chamber9and the constant pressure chamber8.

The stopper portion27fof the cylindrical member27abuts on the key member21to restrict the backward movement of the cylindrical member27, thereby defining the initial position of the cylindrical member27relative to the valve body4. In this state, there is the axial space A between the hooks27cand31aso that the hooks27cand31aare not engaged with each other and the second vacuum valve seat27gis located ahead of the first vacuum valve seat13by the predetermined distance B. The press face10aof the valve plunger10is positioned behind the pressed face27eof the projection27dof the engaging arm portion27bby a predetermined distance to confront the pressed face27ein the axial direction.

As the brake pedal is depressed at a normal speed for service braking operation, the input shaft11moves forward so that the valve plunger10moves forward. Therefore, the vacuum valve portion12bof the valve element12is seated on the first vacuum valve seat13and, at the same time, the atmospheric vacuum valve seat14is spaced apart from the atmospheric valve portion12aof the valve element12, thereby closing the vacuum valve15and opening the atmospheric valve16. That is, the variable pressure chamber9is isolated from the constant pressure chamber8and is in communication with the atmosphere. The atmosphere is therefore introduced into the variable pressure chamber9through the atmosphere introducing passage19and the open atmospheric valve16. As a result, a pressure difference is created between the variable pressure chamber9and the constant pressure chamber8so as to move the power piston5forward and further move the output shaft24forward via the valve body4, thereby moving the piston of the master cylinder (not shown) forward.

In the initial stage of operation of the negative pressure boosting device1, the hooks27cand31aare not engaged with each other in the axial direction and the cylindrical member27is held at its initial position even when the valve body4moves forward because of the spring force of the spring30and the contact between the stopper portion27fand the key member21. Accordingly, the valve body4and the output shaft24move forward relative to the cylindrical member27. Then, as shown inFIG. 4(b), the hook31aof the guide31comes closer to the hook27cof the cylindrical member to shorten the distance between the engaging faces27c1and31a1which was the space A at the initiation. Accordingly, in the initial stage of the operation of the negative pressure boosting device1, the stroke of the valve body4and the stroke of the output shaft24are longer than the stroke of the input shaft11. In other words, in the initial stage of the operation of the negative pressure boosting device1, the stroke of the input shaft11is shortened as compared to the conventional negative pressure boosting device for the same stroke of the output shaft24. As a result, the pedal stroke is also shortened. In a portion of the brake system between the master cylinder and the wheel cylinders, the loss stroke as mentioned above can be effectively absorbed by shorter stroke of the input shaft11(i.e. shorter pedal stroke).

By the forward movement of the valve body4relative to the cylindrical member27by a predetermined distance (that is, the valve body4moves relative to the second vacuum valve seat27gby the predetermined distance), the distance between the engaging surfaces27c1,31a1is extinct so that the hooks27c,31aare engaged with each other as shown inFIG. 4(c). After that, the cylindrical member27moves together with the valve body4. In this manner, the operation of shortening the stroke of the input shaft11is accomplished. As mentioned above, the hooks27c,31acompose the input stroke shortening means of the present invention.

Since the relation B<A is set, in the state where the hooks27cand31aare engaged with each other, the second vacuum valve seat27gprojects backward relative to the first vacuum valve seat13. The vacuum valve portion12band the atmospheric valve portion12aare both pushed backward. The amount C moved by pushing is obtained by:
C=A−B
In this case, the distance A is the total stroke of the cylindrical member27during the stroke shortening operation as shown inFIG. 2. The words inFIG. 2will be expressed. Either of the movable vacuum valve and the movable valve is the cylindrical member27and the step length of the movable vacuum valve is the aforementioned distance B.

On the other hand, since the atmospheric valve portion12ais pushed backward, the space is created between the atmospheric valve portion12aand the atmospheric valve seat14, that is, the atmospheric valve16is opened in the same manner as the conventional negative pressure boosting device.

The forward movement of the valve plunger10moves the spacing member22forward. At this point, however, the spacing member22does not come in contact with the reaction disk23yet so that the reaction force is not transmitted from the output shaft24to the brake pedal via the reaction disk23, the spacing member22, valve plunger10, and the input shaft11. As the input shaft11further moves forward, the power piston5further moves forward, thereby further moving the pistion of the master cylinder forward through the valve body4and the output shaft24.

As the loss stroke is extinct, the negative pressure boosting device1substantially produces an output. By this output, the master cylinder produces a master cylinder pressure. By this master cylinder pressure, the wheel cylinders are actuated to produce braking force.

At this point, brake reaction force exerted on the output shaft24from the master cylinder makes the reaction disk23to swell backward, whereby the spacing member22abuts on the reaction disk23. Accordingly, the reaction force starts to be transmitted from the output shaft24to the brake pedal through the reaction disk23, the spacing member22, the valve plunger10, and the input shaft11. That is, the negative pressure boosting device1produces an output corresponding to the input and exhibits the jumping characteristic in the service braking operation as shown inFIG. 6.

In this case, the valve body4moves relative to the valve plunger10and the spacing member22so that the clearance L between the reaction disk23and the spacing member22is enlarged. Since a space S2is ensured by the tapered face31bof the guide31, the reaction disk23easily swells into the space S2SO as to absorb the enlarged clearance L. Accordingly, the jumping characteristic of the negative pressure boosting device of this embodiment is nearly equal to the jumping characteristic of the conventional negative pressure boosting device. The stroke of the input shaft11is shortened without significantly changing the jumping characteristic, thereby providing the same brake feeling as the conventional negative pressure boosting device.

As the output of the negative pressure boosting device1becomes equal to a predetermined value which is a value obtained by amplifying the input of the input shaft11according to a servo ratio, the atmospheric valve portion12ais seated on the atmospheric valve seat14to close the atmospheric valve16(the vacuum valve15is already closed since the vacuum valve portion12bis seated on the second vacuum valve seat27g), that is, the negative pressure boosting device1becomes in a balanced state in the middle load region. As a result, the wheel cylinders produce relatively large braking force i.e. amplified pedaling force. The service braking is operated with this braking force.

As the brake pedal is released in order to cancel the service braking from the state in which the atmospheric valve16and the vacuum valve15of the negative pressure boosting device1are both closed as shown inFIG. 3, the input shaft11and the valve plunger10are both intended to move backward. Since air (atmosphere) is introduced into the variable chamber9, however, the valve body4and the cylindrical member27do not immediately move backward. Therefore, the atmospheric valve seat14of the valve plunger10presses the atmospheric valve portion12aof the valve element12backward so that the vacuum valve portion12bis spaced apart from the second vacuum valve seat27gto open the vacuum valve15. Then, the variable pressure chamber9becomes in communication with the constant pressure chamber8via the open vacuum valve15and the vacuum passage20. The air in the variable pressure chamber9is discharged to the vacuum source through the open vacuum valve15, the vacuum passage20, the constant pressure chamber8, and the negative pressure introducing passage26.

Therefore, the inner pressure of the variable pressure chamber9is lowered to reduce the pressure difference between the variable pressure chamber9and the constant pressure chamber8. Accordingly, the power piston5, the valve body4, and the output shaft24move backward because of the spring force of the return spring25. According to the backward movement of the valve body4, the piston of the master cylinder and the output shaft24are also moved backward by the spring force of the return spring of the piston of the master cylinder, thereby initiating cancellation of the service braking.

As the key member21comes in contact with the rear shell3as shown inFIG. 2, the key member21is stopped from further moving backward. However, the valve body4, the cylindrical member27, the valve plunger10, and the input shaft11further move backward. First, the stopper portion27fof the cylindrical member27comes in contact with the key member21as shown inFIG. 2and is therefore stopped from further moving backward. Since the valve body4, the valve plunger10, and the input shaft11further move backward, however, the cylindrical member27move forward relative to the valve body4. Accordingly, the second vacuum valve seat27gis positioned ahead of the first vacuum valve seat13.

The valve plunger10comes in contact with the key member21as shown inFIG. 2and is therefore stopped from further moving backward. Further, the front end4a1of the key way4aof the valve body4comes in contact with the key member21as shown inFIG. 2so that the valve body4is stopped from further moving backward. In this manner, the master cylinder is returned in its inoperative state so that the master cylinder pressure dies out. At the same time, the wheel cylinders are returned in their inoperative states so that the braking force dies out, thereby canceling the service braking.

As the brake pedal is depressed at a speed larger than the normal speed in order to conduct the emergency braking, the BA control is performed. That is, by the rapid depression of the brake pedal, the input shaft11and the valve plunger10move forward relative to the valve body4, the cylindrical member27, and the guide31by an amount larger than that in case of the service braking. Therefore, similarly to the service braking, the vacuum valve portion12bis seated on the first vacuum valve seat13to close the vacuum valve15and the atmospheric valve seat14is spaced apart from the atmospheric valve portion12ato open the atmospheric valve16. Accordingly, the valve body4and the output shaft24move forward so as to cancel the aforesaid loss stroke, similarly to the service braking. At this point, since the cylindrical member27does not move forward, the valve body4moves forward relative to the cylindrical member27so that hook31aof the guide engages the hook27cof the engaging arm portion in the axial direction. After that, because of this engagement, the cylindrical member27and the valve body4move together.

Since the valve plunger10largely moves forward, the press face10acomes into contact with the pressed face27eof the engaging arm portion27bto press the pressed face27eforward. Then, since the press face10aand the pressed face27eare formed in tapered surfaces, the engaging arm portion27bis elastically deformed outwardly by wedge effect created between the press face10aand the pressed face27eas shown inFIG. 3as mentioned above. The deformation of the engaging arm portion27bcancels the engagement between the hook27cand the hook31a. As the engagement between the hooks27band31ais cancelled, the cylindrical member27is moved backward largely relative to the valve body4by the spring force of the spring30. At this point, the rear end face of the key member21abuts on the rear end4a2of the key way4aof the valve body4so that the key member21is prevented from moving backward relative to the valve body4. As the stopper portion27fof the cylindrical member27comes in contact with the key member21, the cylindrical member27is stopped from moving relative to the valve body4and is thus prevented from further moving backward. In this state, the projection27dof the engaging arm portion27bis held in contact with the press face10aof the valve plunger10or the outer peripheral surface of the valve plunger10as an extending portion of the press face10aso that the hook27cis held in such a position not to engage the hook31a.

The backward movement of the cylindrical member27brings the second vacuum valve seat27ginto contact with the vacuum valve portion12bof the valve element12and pushes the vacuum valve portion12band the atmospheric valve portion12abackward. Assuming the amount moved by pushing as D, the total stroke E of the cylindrical member27relative to the valve body4is obtained by:
E=A+D

Since the vacuum valve portion12bis pushed backward, the vacuum valve portion12bis spaced apart from the first vacuum valve seat13. However, the second vacuum valve seat27gstill abuts on the vacuum valve portion12bso that the vacuum valve15is still closed. Since the atmospheric valve portion12ais pushed backward, the atmospheric valve portion12ais spaced apart from the atmospheric valve seat14more rapidly than that of the service braking so as to open the atmospheric valve16, whereby the atmosphere is introduced into the variable pressure chamber. Therefore, the valve body4moves forward, the atmospheric valve portion12ais seated on the atmospheric valve seat14to close the atmospheric valve16again. The negative pressure boosting device1becomes in a balanced state in the middle load region in which, as for the control valve17, the vacuum valve15and the atmospheric valve16are both closed.

In the BA control operation, the balanced position of the vacuum valve15and the atmospheric valve16is shifted backward compared to the normal operation, thereby creating a clearance L larger than that in case of normal operation between the spacing member22and the reaction disk23. This clearance L functions as a clearance for increasing the jumping amount (JP amount) of the negative pressure boosting device1.

Therefore, as shown inFIG. 6, the jumping amount (JP amount) of the negative pressure boosting device1is increased as compared to the normal operation so that the negative pressure boosting device1rapidly produces an output larger than that in case of service braking, thereby rapidly and effectively conducting the emergency braking.

The rapid output intensifying means of the present invention is composed of sliding portion27a, the engaging arm portion27b, the hooks27cand31a, the pressed face27eof the projection27d, the press face10aof the valve plunger10, and the spring30.

As the brake pedal is released in order to cancel the emergency braking, the input shaft11and the valve plunger10move backward in the same manner as the aforementioned service braking. Since the air (atmosphere) is introduced into the variable pressure chamber9, however, the valve body4and the cylindrical member27do not immediately move backward. Therefore, the atmospheric valve seat14of the valve plunger10presses the atmospheric valve portion12aof the valve element12backward so that the vacuum valve portion12bis spaced apart from the second vacuum valve seat27gto open the vacuum valve15. Then, the variable pressure chamber9becomes in communication with the constant pressure chamber8via the open vacuum valve15and the vacuum passage20. The air in the variable pressure chamber9is discharged to the vacuum source through the open vacuum valve15, the vacuum passage20, the constant pressure chamber8, and the negative pressure introducing passage26.

The pressing force of the press face10aof the valve plunger10relative to the pressed face27eof the engaging arm portion27bis reduced so that the deformation of the engaging arm portion27bis reduced because of its elasticity.

On the other hand, the inner pressure of the variable pressure chamber9is lowered to reduce the pressure difference between the variable pressure chamber9and the constant pressure chamber8. Accordingly, the power piston5, the valve body4, and the output shaft24move backward because of the spring force of the return spring25. According to the backward movement of the valve body4, the piston of the master cylinder and the output shaft24are also moved backward by the spring force of the return spring of the piston of the master cylinder, thereby initiating cancellation of the emergency braking.

As the key member21comes in contact with the rear shell3as shown inFIG. 2, the key member21is stopped from further moving backward. In addition, since the stopper portion27fabuts on the key member21, the cylindrical member27is stopped from further moving backward. However, the valve body4, the valve plunger10, and the input shaft11further move backward so that the cylindrical member27moves forward relative to the valve body4. Accordingly, the second vacuum valve seat27gis positioned ahead of the first vacuum valve seat13. In addition, the press face10ais spaced apart from the pressed face27e, that is, does not press the pressed face27enow. At the same time, the hook31amoves backward relative to the hook27cso as to cancel the radial overlapping between the hook31aand the hook27cso that the engaging arm portion27returns to its initial state because of its elasticity.

Then the valve plunger10comes in contact with the key member21as shown inFIG. 2and is thus prevented from further moving backward. In addition, the front end4a1of the key way4aof the valve body4comes in contact with the key member21as shown inFIG. 2, so that the valve body4is thus prevented from further moving backward. In this manner, the negative pressure boosting device1becomes in the initial inoperative state as shown inFIG. 1andFIG. 2. Therefore, the master cylinder becomes in its inoperative state so that the master cylinder pressure dies out. At the same time, the wheel cylinders become in their inoperative states so that the braking force dies out, thereby canceling the emergency braking.

By employing the negative pressure boosting device1of this embodiment in a brake system, a large stroke of the output shaft24can be obtained while the stroke of the input shaft11is shortened. Therefore, the loss stroke in a portion of the brake system between the master cylinder and the wheel cylinders can be effectively cancelled with a small pedal stroke in the initial stage of the braking operation.

In the event of emergency braking, the output of the negative pressure boosting device can be rapidly intensified by rapidly opening the atmospheric valve16to increase the jumping amount. The BA control is therefore performed, thereby rapidly and effectively operating the emergency braking.

The brake control can be improved because it can not only shorten the stroke of the input shaft11but also perform the BA control.

Though the negative pressure boosting device is designed to perform these controls, the number of parts can be reduced and the cost can be reduced because the cylindrical member27employed is common to the control for shortening the stroke of the input shaft11and the BA control. Further, since the mechanical structure composed of the cylindrical member27is employed, these controls can be securely performed with simple structure, thereby improving the reliability and making the device compact.

FIG. 5is a partial enlarged sectional view similar toFIG. 2, showing another embodiment of a negative pressure boosting device according to the present invention in its inoperative state. It should be noted that component parts similar or corresponding to the parts of the aforementioned embodiment are designated with the same reference numerals, thus omitting the detail description of such component parts.

In the aforementioned embodiment, the first vacuum valve seat13is formed in the valve body4and is positioned behind the second vacuum valve seat27gof the cylindrical member27when the negative pressure boosting device1is not operated. However, in a negative pressure boosting device1of this embodiment as shown inFIG. 5, the first valve seat13is not formed in the valve body4and a portion4bof the valve body4corresponding to the first valve seat13of the former embodiment is positioned ahead of the first valve seat13of the former embodiment. That is, the negative pressure boosting device1of this embodiment has only one vacuum valve seat of the vacuum valve15, i.e. the second vacuum valve seat27gformed in the cylindrical member27. The second vacuum valve seat27gprojects backward relative to the portion4b.

The other structure of the negative pressure boosting device1of this embodiment is the same as that of the negative pressure boosting device1of the former embodiment.

Assuming that the negative pressure boosting device1of this embodiment is adopted to a brake system, the operation of the device will now be described.

In the negative pressure boosting device1of the former embodiment, as the input shaft11moves forward for the braking operation, first the vacuum valve portion12bis seated on the first vacuum valve seat13of the valve body4. In the negative pressure boosting device1of this embodiment, however, as the input shaft11moves forward, the vacuum valve portion12bis seated directly on the second vacuum valve seat27gof the cylindrical member27.

The amount C moved by pushing during the shortening of the stroke in the negative pressure boosting device1of this embodiment is obtained by:
C=A
because B=0.

The other actions of the negative pressure boosting device1of this embodiment are substantially the same as those of the former embodiment except actions relating to the first vacuum valve seat13.

In the negative pressure boosting device1of this embodiment, the predetermined distance B as a voidable stroke of the cylindrical member27in the former embodiment does not exist so that the axial length of the negative pressure boosting device1can be shortened for the predetermined distance B.

The other works and effects of the negative pressure boosting device1of this embodiment are also substantially the same as those of the former embodiment.

Though the input stroke shortening means is composed of the hooks27cand31acin the aforementioned embodiments, the present invention is not limited thereto. That is, the input stroke shortening means may be of any construction which can shorten the stroke of the input shaft11at the initial stage of the operation and can be adopted to the negative pressure boosting device. Though the rapid output intensifying means is composed of the engaging arm portion27b, the hook27c, the projection27d, the pressed face27e, the second vacuum valve seat27gas a movable valve seat, the hook31aformed on the guide31, and the spring30, the present invention is not limited thereto. That is, the rapid output intensifying means may be of any structure which can rapidly intensify the output during the emergency braking operation and can be adopted to the negative pressure boosting device.

Though the present invention is adopted to a negative pressure boosting device of a single type having only one power piston5in the aforementioned embodiments, the present invention can be adopted to a negative pressure boosting device of a tandem type having a plurality of power pistons5.

Though the negative pressure boosting device of the present invention is adopted to the brake system in the aforementioned embodiment, the negative pressure boosting device of the present invention can be adopted to other system or device employing a negative pressure boosting device.

As apparent from the above description, according to the negative pressure boosting device of the present invention, the stroke of the input member can be effectively shortened in the initial stage of the operation relative to the stroke of the output member by the input stroke shortening means and, in addition, the output can be intensified more rapidly than that of the normal operation when the input member is operated more rapidly than that for the normal operation by the rapid output intensifying means. Therefore, the negative pressure boosting device of the present invention can perform improved boosting control.

Further, according to the negative pressure boosting device of the present invention, the stroke of the input shaft can be effectively shortened in the initial stage of the operation relative to the stroke of the output shaft by the input stroke shortening means and, in addition, the output can be intensified more rapidly than that of the normal operation when the input shaft is operated more rapidly than that for the normal operation by the rapid output intensifying means. Therefore, the negative pressure boosting device of the present invention can perform improved boosting control.

Though the negative pressure boosting device is designed to perform these controls, the number of parts can be reduced and the cost can be reduced because the cylindrical member employed is common to the control for shortening the stroke of the input shaft and the control for rapidly intensifying the output. Further, since the mechanical structure composed of the cylindrical member is employed, these controls can be securely performed with simple structure, thereby improving the reliability and making the device compact.

By employing the negative pressure boosting device of the present invention as a brake booster, even if a brake system has a loss stroke as mentioned above, the loss stroke can be effectively cancelled with shortening the pedal stroke of a brake pedal in the initial stage of braking operation and, in addition, for the event of emergency braking, the braking force can be intensified more rapidly than that of the service braking, thereby rapidly and effectively performing the emergency braking. The brake control can be improved because it can not only shorten the pedal stroke of the brake pedal but also perform the BA control.