GB2169974A

GB2169974A - Hydraulic booster

Info

Publication number: GB2169974A
Application number: GB08525386A
Authority: GB
Inventors: Kenji Shirai
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1985-01-22
Filing date: 1985-10-15
Publication date: 1986-07-23
Also published as: FR2576368A1; DE3538317A1; GB8525386D0; JPS61169362A; GB2169974B; FR2576368B1

Abstract

A hydraulic booster for automotive vehicles brakes (or clutches) includes a booster body 2 with a booster chamber 10 connected via a check valve 12 to a jumping hydraulic pressure circuit 36, and a pressure chamber 13 connected to a booster hydraulic pressure circuit 34. A control piston 19 is interposed between a power piston 3 and a spool piston 25 formed with a center bore 26 and radial port 27. The jumping hydraulic pressure circuit 36, booster hydraulic pressure circuit 34 and a return circuit 41 are all connected to a reservoir 30 as shown. The jumping pressure in booster chamber 10 acts on the rear end face of power piston 3 even if no force is applied to input rod 9 - when force is applied spool piston 25 moves forwardly to close a port 20 in control piston 19 to prevent flow from chamber 10 to a reserve chamber 17. Jumping pressure in chamber 10 rises - check valve 12 closes - during further movement of spool piston 25 ports 22,21,27 are brought into communication so that pressure in circuit 34 is introduced into booster chamber 10. <IMAGE>

Description

SPECIFICATION Hydraulic booster This invention relates to hydraulic booster for automotive vehicles, and more particularly it is concerned with a hydraulic booster for automotive vehicles wherein a booster chamber is defined between a rear end face of a power piston slidably fitted in a booster body and having an output rod and a rear wall of the booster body, and wherein an axial center bore of a spool piston movably fitted in the power piston is brought into and out of communication with the booster chamber and a pressure chamber for the power piston via a portformed in the power piston.

As is well known, an automotive vehicle is equipped with a braking system to ensure the safety of travel. In recent years, the output power of automotive vehicles has greatly increased and the load they can carry has also increased in weight. In addition, the performance of an automotive vehicle running at high speed has also shown a marked improvement.

As a result, the use of hydraulic brakes relying on a master cylinder of the type in which a force applied to a brake pedal is directly exerted on wheel brakes has become unsatisfactory in providing a braking force of desired magnitude. Thus, the present tendency is to use a vacuum booster or hydraulic booster provided with means for providing booster effect.

Braking systems incorporating therein a booster each comprises a hydraulic circuit which is a closed system. Thus, the braking systems of this type are standardized in parts and simple in construction, so that they can be produced on a mass production basis. They seldom develop mechanical and electrical failures, and maintenance and inspection can be performed with ease. Because of these advantages, vacuum boosters are widely in use. Advances have also been made in the progress of the art of hydraulic boosters. For example, a hydraulic booster disclosed in Japanese Utility Model Unexamined Publication No. 161561/82 is of a type which comprises a power piston and a spool piston located in the power piston and is capable of improving the maneuverbility of the vehicle by manipulating the brakes in a manner to absorb the shock applied through the master cylinder.

Although advances have been made considerably in the art of hydraulically boosting a braking pressure, there are still problems that should be solved to provide a satisfactory braking system provided with hydraulic boosters.

One of the problems raised with regard to the hydraulic booster is that the hydraulic booster is lower than the vacuum booster in the stabilization of a force applied to the brake pedal when the brake is applied.

More specifically, Figure 4 shows a diagram in which the abscissa represents the force F (kg) applied to the brake pedal and the ordinate indicates the braking pressure P (kg/cm2). The vacuum booster has a characteristic such that, as indicated by a curve C, a jumping action P' takes place as soon as the force P is applied to the brake pedal. This shows that the braking pressure P applied by the master cylinder to the wheel brakes is in proportion to the force F, thereby enabling the driver who depresses the brake pedal with the force F to get a feeling of stability.

Meanwhile, the hydraulic booster has a characteristic such that, as indicated by a curve C', a jumping action P' does not take place when the force F is applied to the brake pedal, with a result that the driver is forced to exert himself in depressing the brake pedal in initial stages of brake application.

Thus, the driver is unable to have a feeding of stability when he or she applies the brake.

The use of the hydraulic booster has, therefore, suffered the disadvantage that to apply the force F of high magnitude in initial stages of brake application to produce a braking pressure commensurate with the force F while avoiding overbraking immediately after the application of the force F requires highly developed techniques on the part of the driver in applying the brake. Stated differently, whether or not the hydraulic booster works satisfactorily in achieving the desired effects depends on the skills of the individual driver. When the driver is a novice or when the automotive vehicle is fresh from the production line, the hydraulic booster suffers the disadvantage that the brake might be applied with a sudden burst, not smoothly.

Because of this disadvantage, the hydraulic booster offering the advantages noted hereinabove has been prevented from achieving the desired effects.

This invention has been developed for the purpose of solving the aforesaid problem of the prior art with regard to a force applied by the driver to the brake pedal in initial stages of brake application. Accordingly, the invention has as its principal object the provision of a hydraulic booster for automotive vehicles which enables, while a force is being applied to the brake pedal as the driver feels the need to apply the brake to the automotive vehicle, a force of substantially the same magnitude to be applied from start to finish to allow a braking pressure proportional to the applied force to be applied to the wheel brakes, to permit the brake to be applied to the automotive vehicle smoothly and steadily whereby the hydraulic booster according to the invention can contribute to the advances of the art in the field of the braking systems for automotive vehicles.

Another object is to provide a hydraulic booster for automotive vehicles comprising a pressure reducing valve mounted in the jumping hydraulic pressure circuit.

Still another object is to provide a hydraulic booster for automotive vehicles wherein the jumping hydraulic pressure circuit is connected in parallel with the booster hydraulic pressure circuit to the hydraulic pump.

Still another object is to provide a hydraulic booster for automotive vehicles wherein the control piston is formed with a port connected to the return circuit and located in a position in which it can be opened and closed by the spool piston.

A further object is to provide a hydraulic booster for automotive vehicles wherein the control piston is formed with a port adapted to be brought into and out of communication with a port of the power piston communicating with a pressure chamber and a port and an axial center bore of the spool piston.

To accomplish the aforesaid objects, the invention provides a hydraulic booster wherein a jumping hydraulic pressure of a predetermined level is applied by a hydraulic pump from a reservoir through the jumping hydraulic pressure circuit to a booster chamber defined between a rear end face of the power piston slidably fitted in a booster body which is disposed behind, and connected to, a master cylinder for wheel brakes of the automotive vehicle. When no force is applied by the driver to the brake pedal to depress same, the jumping hydraulic pressure is returned via the return circuit through a port of the control piston to the reservoir from the booster chamber.When the driver feels the need to apply the brake and applies a force to the brake pedal, the spool piston moves forwardly through the control piston fitted in an axial center bore of the power piston to block the port of the control piston to breakethe return circuit, with a resultthatthe jumping hydraulic pressure in the booster chamber rises and performs a jumping action. As a result, the power piston is moved forwardly and the ports of the power piston, control piston and spool piston and the axial center bore of the spool piston are brought into communication with each other, so that a booster pressure intoduced into the pressure chamberforthe power piston from the reservoir through the booster hydraulic pressure circuit is led to the booster chamber.Thus, a braking pressure proportional to the force applied to the brake pedal is produced and transmitted via the master cylinder to the wheel brakes.

The hydraulic booster according to the invention which is basically suitable for use with braking systems for automotive vehicles enables a boosted braking pressure to be produced which is proportional to the force applied by the drive to depress the brake pedal from the time the brake pedal is depressed to the time the brake is applied to the vehicle completely. Thus, the driver has the feeling of stable and smooth brake application when a force is applied to the brake pedal to depress same.

This is conducive to increased safety in driving automotive vehicles because the hydraulic booster according to the invention allows a force to be smoothly applied to the brake pedal at all times regardless of whether the driver is a skilled one or the driver is familiar with the vehicle because the driver has a pleasant feeling whenever he or she applied the brake.

The use of the hydraulic booster according to the invention eliminates the need to resort to the techniques which require skills of depressing the brake pedal hard in initial stages of brake application and then lessening the force applied to the brake pedal after the driver has become acquanted with the characteristic behavior of the particular automo tive vehicle. Thus, the risk that an unnecessarily large load might be applied to the brake pedal in initial stages of brake application and cause the brake to be applied with a sudden burst, not smoothly, can be avoided.

The feature of the invention that the jumping hydraulic pressure circuit is connected in parallel with the booster hydraulic pressure circuit enables the jumping hydraulic pressure circuit to be connected to the booster chamber defined between the rear end force of the power piston mounted in the booster body and the rear wall of the booster body and adapted to have a booster pressure applied thereto, thereby simplifying the construction of the hydraulic booster.

The provision of the control piston between the power piston and the spool piston enables the control piston to selectively connect the booster hydraulic pressure circuit orthe jumping hydraulic pressure circuit to the booster chamber, thereby allowing the spool piston moving back and forth together with an input rod as a unit to move smoothly with no more resistance offered to its movement than the resistance offered by its sliding contact with the power piston. This at least enables a substantially constant force to be applied to the power piston when the brake pedal is depressed.

In the drawings: Figure 1 is a vertical sectional view of the hydraulic booster comprising one embodiment of the invention, showing hydraulic circuits connecting various parts of the hydraulic booster together; Figures 2 and 3 are sectionai views of the hydraulic booster shown in Figure 1, shown when the brake is applied; Figure 4 is a diagram showing the relation between the force applied to the brake pedal to depress same and the braking pressure established in a hydraulic booster of the prior art; Firgure 5 is a diagram showing the relation between the input rod of the power piston and the resistance offered to the spool piston; and Figure 6 is a diagram showing the relation between the jumping pressure and the braking pressure established in the hydraulic booster shown in Figure 1 according to the invention.

A preferred embodiment of the invention will now be described by referring to the accompanying drawings.

Referring to Figure 1,the reference numeral 1 generally designates the hydraulic booster according to the invention for an automotive vehicle comprising a booster body 2 which is connected to, and disposed rearwardly of, a well-known master cylinder, not shown, which is connected to front and rear wheel brakes. A power piston 3 is mounted inside the booster body 2 through seal rings 4for sliding movement, and a return spring 7 is mounted between an end stopper 5 and a cap 6 in a forward section of the booster body 2. An output rod 8 extends out of the cap 6 to be connected to the master cylinder, and an input rod 9 of a push rod connected to the brake pedal on the floor near the driver's seat, not shown, is connected to a rear wall of the booster body 2.

A booster chamber 10 is defined between a rear end face of the power piston 3 and the rear wall of the booster body 2 and connected to a jumping hydraulic pressure inlet portion 12 provided with a ball valve 11 serving as a check valve, The power piston 3 is narrowed in a central portion thereof to define a pressure chamber 13 between the narrowed central portion of the power piston 3 and a side wall of the booster body 2 which is maintained in communication with a booster pressure inlet portion 14 of the booster body 2 located within the range of the stroke of the power piston 3.

The power piston 3 is formed in the interior thereof with an axial center bore 15 and in a forward end portion thereof with a port 16 which is connected to a return port 18 of the booster body 2 via a reserver chamber 17 interposed between the power piston 3 and the end stopper 5. A control piston 19 is slidably fitted in the axial center bore 15 of the power piston 3, and a port 20 formed in a forward end portion of the control piston 19 is adapted to be brought into and out of communication with the port 16 of the power piston 3.

The control piston 19 is formed in a central portion thereof with a radial port 21 which is maintained at all times in communication with a radial port 22 located substantially in a central portion of the power piston 3.

The control piston 19 is formed at a rear end thereof with an end face which is configured to allow an inwardly extending hook flange 23 at a front end of the power piston 3 to be brought into and out of contact therewith, and a spring 24 is mounted between the end face of the control piston 3 and a forward end of the input rod 9.

A spool piston 25 formed with an axial center bore 26 is fitted in the interior of the control piston 19 for axial sliding movement relative to the control piston 19, and a radial port 27 is formed in a central portion of the spool piston 25 to bring the axial center bore 26 into and out of communication with the radial port 21 of the control piston 19. A port 28 is formed art a rear end of the spool piston 25 and adapted to be brought into and out of communication with the booster chamber 10.

The numeral 29 designates hydraulic circuits connected to the hydraulic booster body 2 of the aforesaid construction in a closed circuit system. The hydraulic circuits 29 comprise a booster hydraulic pressure circuit 34 connecting a reservoir 30 to the booster pressure inlet portion 14 and mounting a hydraulic pump 32 driven by a motor 31 and a check valve 33, and a jumping hydraulic pressure circuit 36 connected in parallel with the booster hydraulic pressure circuit 34 and mounting a throttle 35 and a pressure reducing valve 37 communicating with the reservoir 30 and connected in series with the circuit 34, to connect the reservoir 30 to the jumping hydraulic pressure inlet portion 12.A relief valve 38 is mounted between the reservoir 30 and the booster hydraulic pressure circuit 34, and an accumulator 39 and a pressure switch 40 are connected to the booster hydraulic pressure circuit 34 in parallel with the relief valve 38. A return circuit 41 connects the return port 18 to the reservoir 30.

Operation of the hydraulic booster of the aforesaid construction will be described. When the automotive vehicle travels and no brake is applied thereto by the driver, the hydraulic pump 32 delivers a hydraulic fluid of a predetermined pressure level from the reservoir 30 to the booster hydraulic pressure circuit 34 and the jumping hydraulic pressure circuit 36 branching from the booster hydraulic pressure circuit 34 and connected in parallel therewith.

The hydraulic fluid delivered to the booster hydraulic pressure circuit 34 is introduced as a booster hydraulic pressure into the pressure chamber 13, because no force is applied to the brake pedal and the input rod 9 does not push the spool piston 25, so that the port 27 of the spool piston 25 is out of index with the port 21 of the control piston 19 and no communication is maintained between the ports 21 and 27. This actuates the relief valve 38 to cause the hydraulic fluid delivered by the hydraulic pump 32 to flow in circulation to the reservoir 30 via the check valve 33 and relief valve 38, without applying pressure to the power piston.

Meanwhile, the hydraulic fluid delivered to the jumping hydraulic pressure circuit 36 has its pressure reduced to a predetermined level subsequently to be described by the pressure reducing valve 37 before being introduced through the jumping hydraulic pressure inlet portion 12 into the booster chamber 10 by opening the check valve 11,to thereby apply the jumping pressure of the aforesaid low level at all times.

Since the spool piston 25 is not pressed by the input rod 9 as described hereinabove, a forward end portion of the spool piston 25 does not close the port 20 of the control piston 19, so that the booster chamber 10 is communicated via the axial center bore 26 of the booster piston 25 and the forward port 16 of the power piston 3 with the reserver chamber 17 and return port 18. As a result, the hydraulic fluid delivered from the reservoir 30 to the jumping hydraulic pressure circuit 36 flows in circulation from the booster chamber 10 to the reservoir 30 via the port 28, bore 26, port 20, reserver chamber 17 and return port 18.

It will be understood that the jumping pressure in the booster chamber 10 acts on the rear end face of the power piston 3 even if no force is applied to the brake pedal.

Figure 5 shows a diagram in which the abscissa represents the hydraulic pressure P' (in kg/cm2) in the booster chamber 10 and the ordinate indicates the load (in kg). Itwill be seen that the output characteristic of the power piston 3 indicated by a straight line C1 is such that a pressure P1 (jumping pressure) applied to the power piston 3 produces a force slightly lower than the sum of the reaction of the input rod 9, the load applied by the spring 24 and the resistance C3 offered to the sliding movement, as indicated by the diagram.

Assume that the driver feels the need to apply the brake to the automotive vehicle and depresses the brake pedal, not shown. This causes the input rod 9 serving as a push rod to move forwardly as shown in Figure 2, to cause the spool piston 25 to move forwardly against the biasing force of the spring 24.

Thus, when a force is applied to the brake pedal, the spool piston 25 moves forwardly together with the input rod 9 substantially immediately after the application of the force to the brake pedal, and the forward end portion of the spool piston 25 immediately closes the port 20 formed in the forward end portion of the control piston 19 as shown in Figure 2, with the result that the jumping pressure in the booster chamber 10 is prevented from flowing through the port 28, the axial center bore 26 of the spool piston 25, the port 20 of the control piston 19 and the reserver chamber 17 to the return port 18.

Thus the jumping pressure in the booster chamber 10 immediately rises to a higher level and causes the power piston 3 to move forwardly.

As the jumping pressure in the booster chamber 10 tends to rise above the predetermined level,the check valve 11 is brought to a closed position to avoid a rise in jumping pressure.

The control piston 19 is constructed such that its rear end has a cross-sectional area Da which is smaller than the cross-sectional area D2 of a shoulder at the forward end portion thereof in the vicinity of the power piston 3. Thus, the jumping pressure acting on the forward end portion of the control piston 19 via the port 28 and the axial center bore 26 of the spool piston 25 is high in level as a total pressure, so that the control piston 19 remains stationary until the hook flange 23 of the power piston 3 move forwardly and move the control piston 19 forwardly against the biasing force of the spring 24. This makes the jumping pressure in the booster chamber 10 rise suddenly to thereby move the power piston 3 forwardly, as described hereinabove.

When the jumping action referred to hereinabove makes the driver feel the need to further apply the brake, the driver further depresses the brake pedal (in this case a constant pressure is applied to the power piston 3 with or without the driver being aware of it), so that the input rod 9 continuously moves forwardly at a constant velocity. After this process is performed, the spool piston 25 also moves forwardly at the constant velocity.

Thus, even if the jumping pressure in the booster chamber 10 is applied to the power piston 3, the spool piston 25 continues to move forwardly until the port 27 of the spool piston 27 is brought into index with the port 21 of the control piston 19 as shown in Figure 3.

When the posts 27 and 21 are brought into index with each other as shown in Figure 3, the jumping pressure moves the power piston 3 forwardly and the hook flange 23 at the rear end of the power piston 3 moves the control piston 19 together with the power piston 3, so that the port 22 of the power piston 3 is indexed with the port 21 ofthe control piston 19. This brings the ports 22, 21 and 27 into communication with each other. As a result, the pressure chamber 13 defined between the power piston 3 and the booster body 2 is brought into communication with the axial center bore 26 of the spool piston 25, so that the hydraulic pressure in the booster hydraulic pressure circuit 34 is introduced into the booster chamber 10 via the pressure chamber 13, ports 22, 21 and 28 and the axial center bore 26 of the spool chamber 25.This allows the hydraulic pressure supplied by the hydraulic pump 32 from the reservoir 30 to be boosted and applied to the power piston 3, causing the power piston 3 to move forwardly. This causes the output rod 8 of the power piston 3 to apply the braking pressure to the wheel brakes via the master cylinder.

As noted hereinabove, the booster pressure is higher than the jumping pressure, so that the booster pressure in the booster chamber 10 moves the check valve 11 to a closed position to avoid the high booster pressure being applied to the jumping hydraulic pressure circuit 36.

As the booster pressure rises, the control piston 19 is further moved forwardly by the hook flange 23 at the rear end of the power piston 3 which also moves forwardly, so that the two pistons 3 and 19 move forwardly relative to the spool piston 25. This brings the port 27 of the spool piston 25 out of index with the port 21 of the control piston 19, with a result that the booster pressure being introduced into the pressure chamber 13 via the booster hydraulic pressure inlet portion 14 is prevented from being introduced into the booster chamber 10.Also, the port 20 in the forward end portion of the control piston 19 is still blocked because it is disposed rearwardly of the rear end of the spool piston 25, so that the booster pressure in the booster chamber 10 is prevented by the blocked port 20 from being introduced into the outlet port 18 from the reserver chamber 17 via the port 28 and the axial center bore 26 of the spool piston 25. This keeps the booster pressure in the booster chamber 10 balanced.

As the driver further applies a force to the brake pedal, the input rod 8 further moves forwardly. This causes the spool piston 25 to move forwardly, with a result that the port 27 is brought into index with the port 21 of the control piston 19 to allow the booster pressure in the pressure chamber 13 to be introduced into the booster chamber 10 again via the axial center bore 26 of the booster piston 25. This increases the force with which the power piston 3 is moved forwardly, so that a boosted braking pressure is transmitted and applied to the wheel brakes via the master cylinder.

The process described hereinabove is repeated automatically to enable the brake to be applied with a braking pressure which is boosted as designed.

As the driver releases the force being applied to the brake pedal by recognizing the fact that the application of the brake is no longer necessary, the brake pedal is restored to its original position by a return piston, not shown, and the input rod 9 moves rearwardly together with the brake pedal. The power piston 3 is moved rearwardly by the biasing force of the return spring 7, together with the control piston 19. This causes the spool piston 25 to move rearwardly, so that the port 20 in the forward end portion of the control piston 19 is opened. Since the spool piston 25 is secured to the forward end of the input rod 9, the spool piston 25 moves as a unit with the input rod 9, thereby instantly opening or closing the port 20. The booster pressure in the booster chamber 10 risen to a high pressure level is allowed to return, as the port 20 is opened, to the reservoir 30 via the port 28, axial center bore 26, port 20, port 16, reserver chamber 17, return port 18 and return circuit 41. As a result, the pressure in the booster chamber 10 drops to the initial level.

Figure 6 shows in a diagram the relation between the jumping pressure and the braking pressure established as the driver applies a force to the brake pedal. In the diagram, the abscissa represents the force F (kg) and the ordinate indicates the load P (kg/cm2). Immediately after the brake pedal is depressed, a jumping pressure P1 is applied to the booster chamber 10 to allow a braking pressure C4 that is boosted to act immediately in proportion to the force applied to the brake pedal. Thus, the driver need not exert himself in depressing the brake pedal because he or she does not have the feeling of the brake pedal being heavy as has hitherto been the case with the hydraulic boosters of the prior art. The driver is enabled to apply the brake smoothly with a pleasant feeling while depressing the brake pedal, so that the brake can be applied smoothly, not in a sudden burst.

While the invention has been shown and described by referring to a preferred embodiment thereof, it is to be understood that the invention is not limited to the specific form of the embodiment, and that it can have application not only in brakes but also in clutches.

Claims

1. A hydraulic booster for automotive vehicles comprising: a booster body; a power piston slidably fitted in said booster body; an output rod connected to a front end of said power piston; a booster chamber defined between an end face of said power piston and a rear wall of said booster body; and a spool piston slidably fitted in said power piston, said spool piston being formed with an axial center bore and a radial port adapted to be brought into and out of communication with said booster chamber and a pressure chamber for the power piston via a port formed in the power piston; wherein the improvement comprises: a jumping hydraulic pressure circuit connected at one end to a reservoir for a hydraulic fluid and at an opposite end to said booster chamber via a check valve; a booster hydraulic pressure circuit connected at one end to said reservoir and at an opposite end to said pressure chamber; a control piston interposed between said power piston and spool piston; and a return circuit connected to said reservoir and adapted to be connected to and disconnected from said control piston.

2. A hydraulic booster for automotive vehicles as claimed in claim 1, wherein said jumping hydraulic pressure circuit mounts a pressure reducing valve therein.

3. A hydraulic booster for automotive vehicles as claimed in claim 1,wherein said jumping hydraulic pressure circuit and booster hydraulic pressure circuit are connected in parallel with each other and to a hydraulic pump.

4. A hydraulic booster for automotive vehicles as claimed in claim 1, wherein said control piston is connected to said return circuit via a port, said port being formed in a position in which it is opened and closed by said spool piston.

5. A hydraulic booster for automotive vehicles as claimed in claim 1,wherein said control piston is formed with another port adapted to be brought into index with the port of said power piston communicated with said pressure chamber and the radial port and axial center bore of said spool piston.

6. A hydraulic booster for automotive vehicles, the booster being substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.