FIELD OF INVENTION:

This invention relates to a vacuum booster of a brake system using vacuum assisted hydraulic brake system for LCV, SUV and all cars.

PRIOR ART:

Vacuum brake boosters are employed in order to boost the brake force exerted by the driver at the brake pedal. Various types of vacuum boosters are known. Generally speaking, vacuum boosters include a housing having an interior divided into a constant pressure chamber and a variable pressure chamber by a movable wall. The movable wall is connected in a unitary manner to a power piston, and the constant pressure chamber is always ih communication with an intake manifold of the engine so that negative pressure is introduced into the constant pressure chamber. The power piston includes a vacuum valve for establishing or interrupting communication between the constant pressure chamber and the variable pressure chamber, and an air valve for establishing or interrupting communication between the variable pressure chamber and the- atmosphere. The power piston is connected to a master cylinder via a reaction disc and an output rod. In the vacuum booster constructed in the foregoing manner, a booster actuator for automatically actuating the vacuum booster is provided to perform the automatic pressure control.

The vacuum brake booster consists of at least two chambers exhibiting a difference in pressure. These chambers are the working chamber and the vacuum chamber, which are integrated into the brake system- in such a fashion that the working chamber is connected to the atmosphere. The vacuum chamber is bled by means of a vacuum supply. Both chambers are separated by a diaphragm. The vacuum furnished by the internal combustion engine or a vacuum pump boosts the pedal force that is to be applied by the driver.

l In conventional vacuum booster when brake applies typicall the control piston pushes the reaction disc and the disc absorbs the control piston as it is an elastic material. There will be some differential pressures also on the reaction disc by way of the reaction pressure from master cylinder spring and from the return spring inside the chamber. Thus the reaction disc works only as a rubber seal to create softness in the pedal.

In conventional power boosters, an air valve assembly is opened upon depression of the brake pedal by the operator to admit atmospheric air to at least a variable pressure chamber of the power booster housing. This creates a pressure differential across a diaphragm separating the variable pressure chamber from a constant pressure chamber of the housing. The diaphragm is coupled to the power piston and transmits a force resulting from the pressure differential to the power piston and, ultimately, to the master cylinder. During normal brake application rates, the air valve assembly operates as described and the resilient reaction disc provides a reaction or feedback force to the operator through the air valve assembly to the brake pedal.

In conventional vacuum booster when brake applies the variable pressure chamber and constant pressure chambers will be closed and separated from each other and the balance air in the constant pressure chamber should be cleared by pump only and it will take more time.

OBJECT OF INVENTION

The present invention generally relates to power boosters for brake systems, such as those used in automobiles, for intensifying the input force between a brake pedal and a master cylinder and to achieve an improved method of braking.

The another object of the invention is to employ a relatively hard material for the reaction disc. Trie another object of the invention is to assist the vacuum pump set in a diaphragm type vacuum booster.

The another object of the invention is to have a reaction disc which does not compress into the control piston of control valve and play additional role beyond absorption of braking force and reaction force as done in conventional booster.

DESCRIPTION OF INVENTION

One aspect of the present invention relates to a vacuum brake booster and a method of improved operation of a vacuum brake booster of a vehicle brake system.

This invention is an improvement over other related patents available in prior art. The various aspects of the invention are illustrated in detail by way of the embodiments and are described making reference to the Figures wherever applicable.

In the subject of vacuum brake booster, the words 'rear chamber', 'variable pressure chamber', 'apply chamber', 'working chamber' are used interchangeably to mean the same chamber. Similarly front chamber, constant pressure chamber, vacuum chamber are refer to the same chamber of a vacuum brake booster.

The invention is illustrated with respect to Fig. 1- 3

a. Cross section of Vacuum Brake Booster

b. Displaced reaction disc/valve as envisaged in invention

c. Reaction disc as in Conventional Vacuum Booster

Part Numbers marked in Fig. (1-3)

1. Vacuum Brake Booster

2. Housing

3. Constant pressure chamber

4. Variable pressure chamber

5. Movable Wall

6. Intake manifold 7. ¹ Vacuum Valve

8. air valve

9. Reaction disc

10. out put rod

11. Diaphragm

12. control piston

13. return spring

14. control valve

15. input member/push rod

16. valve plunger

17. valve operating rod

18. control valve spring

19. hub

20. reaction valve

21. elastomeric reaction disc

22. output piston head

23. central cylindrical portion

It is the physics of vacuum that is exploited usefully in the invention which is an improvement of a typical conventional vacuum / diaphragm type booster used for braking in a vehicle. In such a system the vacuum pump has the duty to pull air out of vacuum chamber void of any or most air or gas molecules. The physics of vacuum is that molecules in the air do not like areas of low pressure and rush to immediately escape to high pressure areas. In short, the air removal rate is the measure of vacuum pump capacity. In the invention, there is an attempt to use this principle advantageously. During the progressive depression of brake pedal, the vacuum chamber is in vacuum and variable pressure chamber rises towards atmospheric pressure. It is the vacuum pump which solely sucks the air from vacuum chamber in any known prior art systems. In this invention, the vacuum pump work load is reduced by momentarily connecting the two chambers whereby balance air in vacuum chamber escapes into variable pressure chamber and leaving vacuum chamber in vacuum. The reaction disc/valve in the invention system is utilized intelligently to connect the chambers momentarily for this purpose. The reaction disc/valve along with control piston is displaced momentarily by the reaction force of master cylinder to connect the two chambers momentarily during progressive brake application.

According to the embodiments of the vacuum booster of the present invention, backward (second) direction corresponds to the brake pedal side relative to the vacuum booster or the rear side of the vehicle and the forward (first) direction corresponds to the master cylinder side relative to the vacuum booster or the fore side of the vehicle.

The braking system of an automotive vehicle is generally provided with a brake operating member such as a brake pedal which is operatively connected to the master cylinder through a vacuum booster. The master cylinder is a mechanism for pressurizing a fluid in the pressuring chamber to generate the same level of hydraulic pressure corresponding to a brake operating force which acts on the brake pedal.

The vacuum booster as conventionally known are vacuum suspended diaphragm. This means that when the brakes are released and engine is running, vacuum is present on both sides of the diaphragm when the pedal is pressed atmospheric pressure is admitted to the rear of the diaphragm to develop booster force.

A typical vacuum booster includes a housing defining a control volume in which a movable diaphragm separates the control volume into an apply chamber and a vacuum chamber. A power piston extends through and engages the diaphragm and has an axial bore containing a valve assembly that controls a diaphragm pressure differential across the diaphragm. The power piston drives an output rod in the forward direction. The output rod has a rearward portion exposed to pressure within the vacuum chamber and a forward face exposed to atmospheric pressure. When the pressure within vacuum chamber is less than atmospheric, a piston pressure differential across the power piston provides a return force in the rearward direction to the power piston. Brake power boosters generally utilize fluid pressure, or differentials thereof, to provide a power assist in applying force to the master cylinder of the brake system. Upon application of an input force on the brake pedal, an input member such as a pushrod activates the power booster. The power booster intensifies the force by a calibrated amount and transfers the force to a power piston which then moves the master cylinder to apply the brakes at each wheel. Power boosters also include a mechanism for transferring the feel of the brake operation back from the master cylinder through the power booster to the brake pedal. This allows the vehicle operator to feel whether they are applying more or less force with their foot. A typical mechanism includes a reaction body and a reaction disc each carried within the power piston. When the brakes are applied, a reaction force is transmitted back through the power piston and reaction disc. The reaction disc is resilient so that it may be compressed and partially extruded through the annular reaction body thereby transferring a portion of the total output force back to the brake pedal.

In one embodiment, the vacuum booster has a hollow housing and includes a power piston means equipped with a diaphragm disposed within the housing so as to partition the internal enclosed space of the housing into a constant pressure chamber on the side of master cylinder and a variable pressure chamber on the side of the brake pedal. The constant pressure chamber is always in communication with a vacuum pressure source which typically may be in the form of an intake pipe of an engine of the vehicle. The variable pressure chamber is selectively communicating with the constant pressure chamber and the atmosphere through a control valve means.

In one embodiment, typically a power piston is associated with a valve plunger disposed on the side of the brake pedal and a master cylinder piston rod on the side of master cylinder.

Typically a valve operating rod is coaxially connected at one end thereof to the valve plunger such that the valve operating rod is movable with the valve plunger and at the other end to the brake pedal so that brake pedal is connected to the valve plunger through the valve operating rod. The mutually connected valve plunger and valve operating rod co-operate to function as an input rod of the vacuum booster. Such a conventional booster piston rod is associated with the pressuring piston of master cylinder and transmits the output of the vacuum booster to the master cylinder and thereby functions as an output rod of the vacuum booster.

In any conventional system, the power piston accommodates a reaction disc/valve such that the power piston and valve plunger contact the reaction disc in one of the opposite axial directions of the vacuum booster, while the booster piston rod contacts the reaction disc in the other axial direction.

The valve mechanism is operably associated with the constant pressure chamber, the variable pressure chamber and the ambient atmosphere.

The valve mechanism is operated accordingly to a relative axial position of the valve operating rod and the power piston and includes a control valve, an air valve, a vacuum valve and a control valve spring.

The air valve co-operates with control valve to selectively connect and disconnect the variable pressure chamber to and from atmosphere.

The air valve is disposed such that the air valve is moveable with the valve plunger. The control valve is attached to the valve operating rod such that the control valve is biased so as to be seated on the air valve under a biasing force of the control valve spring fixed to the valve operating rod.

The vacuum valve cooperates with the control valve to selectively connect and disconnect the variable pressure chamber to and from the constant pressure chamber.

The vacuum valve is disposed such that the vacuum valve is moveable with the power piston.

In non-operating state of the vacuum booster, the control valve is seated on the air valve and at the same time spaced apart from the vacuum valve, so that the variable pressure chamber is disconnected from the atmosphere and is connected with the constant pressure chamber.

In this non-operating state, the pressure in the variable pressure chamber is equal to that in constant pressure vacuum chamber, namely, is a negative or sub- atmospheric pressure (lower than the atmospheric pressure)

In operating state, the valve operating rod is moved towards the power piston and control valve is eventually seated on the vacuum valve, so that the variable pressure chamber is disconnected from the constant pressure chamber. When the valve operating rod is further moved towards the power piston, the air valve is spaced apart from the control valve, so that the variable pressure chamber is brought into communication with the atmosphere. In this operating state, the pressure in the variable pressure chamber is gradually raised towards atmospheric pressure, causing a differential pressure difference between the pressures in the two chambers so that the power piston is moved towards the constant pressure chamber, thereby the brake operating force acting on the brake pedal boosted by the vacuum booster and boosted force is transmitted to the master cylinder.

The pressure difference of the constant and variable pressure chamber will NOT increase after the pressure in the variable pressure chamber has been raised to the atmospheric pressure, even if the brake pedal is depressed further with an increased force. Since the difference between the two chambers is now a 'fixed differential' i.e. the variable pressure chamber is at atmospheric pressure and the constant pressure chamber is in vacuum. Thus the vacuum booster has a boosting limit, at which the vacuum booster then becomes inoperable to perform its boosting function. The further displacement of the plunger depends only on the force applied to the input rod.

The boosting limit point depends upon the difference between the pressure in the constant pressure chamber namely the negative pressure in the intake pipe of the vehicle engine and the atmospheric pressure. If the negative pressure in the intake pipe varies, the boosting limit point correspondingly varies. In a typical brake booster with a reaction disc, the input pushrod and vacuum valve plunger bear on typical rubber disc. The reaction disc is located in the power piston and compresses under the force of the pedal. Its ability to compress lets it absorb reaction force back from the master cylinder when the brakes are applied. As the disc compresses and feeds back reaction force to the pedal push rod, it also modulates the action of vacuum and air control valves to adjust pressure on the diaphragm. The harder the brake pedal is pressed the more the disc compresses and the greater the feed back feel applied to the pedal.

In a known braking system a fact that the boosting limit of vacuum booster is reached is detected when pressure in variable-pressure chamber has been raised to the atmospheric pressure.

But in this invention relating to an improved vacuum brake booster technology, when brake applies the air inside the front constant pressure chamber is released through hub and control valve. In conventional vacuum booster an input push rod, control valve, hub, diaphragm, control piston, reaction disc and an output push rod is been used as movable components. In ABD vacuum booster an input push rod, control valve, hub, diaphragm, control piston, reaction valve, elastomeric reaction disc (may or may not be used) and an output push rod is been used as movable components. This technology will be used in both single and double diaphragm vacuum boosters.

In non operational position of the vacuum booster, the variable pressure chamber and constant pressure chamber are interconnected. When brake applies the control piston closes the interconnection and the input push rod pushes forward the control piston. Further, the control piston pushes the reaction valve forward and thus a clearance space will be created between the hub base and reaction valve. In this position a passage will be created through the hub and control piston which opens to rear variable pressure chamber. The balance air inside the constant pressure chamber will be released through this passage created by way of the said reaction valve most preferably a metallic reaction valve into the rear variable pressure chamber. This helps a sudden release of pressured air from the constant pressure chamber instead of merely depending on the vacuum pump for sucking out the air from the constant pressure vacuum chamber. Thus the constant pressure chamber becomes completely in vacuum more speedily and without straining the vacuum pump unduly. An elastomeric reaction disc may or may not been used between the output piston head and the reaction valve to reduce the friction.

When brake pedal released, opens the passage and allows the communication between the two chambers.

The novelty lies in the vacuum booster in one aspect, wherein the brake booster includes a brake master cylinder and a brake pedal comprising a vacuum source and a housing with a cavity therein. A hub means including a central cylindrical portion and a diaphragm is disposed within the said housing. The said central cylindrical portion of said hub means forming a bore and said diaphragm dividing the cavity into variable pressure chamber and a constant pressure chamber. The said hub member having a first passage connected to said constant pressure chamber and separated from a second passage connected to said variable pressure chamber by an annular seat. The said constant chamber being continuously connected to said vacuum source. The said variable pressure chamber being alternatively connected to said constant chamber and to atmospheric pressure. A control valve means is provided having a control piston disposed in said first passage between the said constant pressure chamber and variable pressure chamber for controlling communication therebetween and operably associated with the annular seat. An air valve means is provided which includes a third passage formed between variable pressure chamber and atmosphere and an air valve for controlling communication therebetween. An input push rod is operatively connected to said brake pedal for controlling on-off operation of said control valve means and said air valve means.

An output control means is connected to said hub means for actuating said brake master cylinder in response to movement of brake pedal wherein said output means further comprises a cylindrical control piston rod member slidably disposed in said bore of said cylindrical portion of the hub means and a reaction valve disposed in a home position in said bore of said central cylindrical portion and further disposed between the said output rod and control valve for transmitting force from control valve to the output rod and further said reaction valve engages the control piston of control valve.

The invention is specifically characterized with the improvement of the arrangement comprising of control valve and the reaction valve wherein in a first stage of non- operative "non-contacting" state of control piston with respect to annular seat to allow vacuum present in said constant pressure chamber to be freely communicated to variable pressure chamber and in second state of an operational "contacting" position of control piston to interrupt vacuum communication through said first passage and initiate communication of air from air valve to said variable pressure chamber to create an operational pressure differential across said diaphragm and also thereafter momentarily displace simultaneously the reaction valve towards constant pressure chamber thereby allowing momentarily communication of air from constant pressure chamber into variable pressure chamber through the displaced reaction valve and the hub during the operational contacting position of control valve, and in a third state of an operational 'releasing' position of control piston allowing communication between constant pressure chamber to variable pressure chamber through the said fourth passage until displaced reaction valve returns to home position and thereafter to allow vacuum to balance equally between variable pressure chamber with constant pressure chamber.

The power piston assembly transmits power assisted force from the diaphragm through the power piston and the reaction disc and there through to the master cylinder. The output force applied to the master cylinder results in an equal and opposite opposing force designated as reaction force applied to is transmitted to the driver's foot on the brake pedal.

In another aspect the first chamber is connected to an intake manifold of an engine.

In another aspect the said control valve further comprises a front face disposed at a gap with respect to annular seat disposed in said hub.

The vacuum source of the vacuum booster is an engine intake manifold. The present invention generally provides a power booster for a brake system with a reaction disc having the ability after the pedal brake has pressed and continues to be pressed to create momentarily a passage through the hub and opening the constant pressure chamber into variable chamber thereby allowing air from front constant chamber to be released into rear variable pressure chamber thereby creating a vacuum chamber with best vacuum condition momentarily during a continued application of the brakes. This allows the power booster to maintain a high output force with a reduced input force on the brake pedal. The invention also improves pressure response of the brake system over conventional brake systems as the operator can apply higher forces with a lower input force on the brake pedal. This can lead to shorter vehicle stopping distances. The reaction disc plays a very important role in the operation of the vacuum system as described herein. Hence the shape, configuration and material is of paramount importance.

The operation performed and structure as illustrate has been disclosed for purpose of better understanding of the invention, but the invention is not limited to these embodiments and can be variously modified without departing from the scope of the invention.

The invention essentially discloses a novel method of boosting a brake pedal force with a vacuum type brake booster system which has a movable diaphragm dividing the interior of a housing into a vacuum chamber and a variable pressure chamber and which boosts an input brake pedal force by means of pressure difference between the vacuum chamber and the variable pressure chamber and outputs the boosted force, and wherein a vacuum pump sucks out air from vacuum chamber and system includes a reaction disc/valve comprising the following steps for a braking operation : Receiving a brake pedal force from a driver. Delivering a boosted force to the master cylinder and the method is characterized in releasing a portion of air in the vacuum chamber into the variable pressure chamber during progressive brake operation by momentarily opening a communication between the chambers, thereby reducing the air suction load of the vacuum pump during the braking operation. With the arrangement as known in prior art the reaction disc has a limited but very useful function of transmitting an operating force of the power piston to the booster piston rod and another function of transmitting a reaction force of the booster piston rod to the valve plunger. But in the invention the reaction disc/valve plays a more important role by offloading the vacuum pump load partially.

This technology can be used in both single and double diaphragm vacuum boosters. The reaction disc is also referred to as reaction valve in this subject and thereby reaction disc and reactor valve is the same when mentioned in the specification.

The principles, preferred embodiments and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein is to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.

Various objectives, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings.