FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION An Improved brake system for vehicles
APPLICANTS
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Mr. Deepak R R, Mr. Anshuman Gupta, Mr.Bisen Badal,
all Indian nationals
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

FIFLD OF INVENTION:
This invention relates to a brake system of an automobile and more particularly it relates to hydraulic brake system with vacuum booster.
BACKGROUND OF INVENTION:
All automobiles are provided with brake system to reduce risk of any mishap. Hydraulic brake system is one of the commonly used brake systems in cars, Utility vehicles(UV) and Light Commercial Vehicle (LCV)s. Hydraulic brake circuit mainly consist of a brake pedal, vacuum booster, tandem master cylinder, fluid reservoir, disc/ drum brakes & bundy tubes. The force applied by the driver gets amplified and acts on the disc/ drum to stop the vehicle. Many vehicles have been reported with poor brake feel.due to poor co-relation/ relationship between the pedal effort applied, pedal travel, deceleration level achieved and stopping distance. Brake feel also depend upon the time lag between the force applied on brake pedal and the response of braking system. Hence "brake feel" can be improved by reducing the response time of the brake system.
Apart from modifications/ analysis done on disc/ drum brakes, brake pedal etc, the analysis of the brake booster has always being done considering the vacuum pump side of the diaphragm with modifications being suggested for the same like increasing the vacuum pump size or adding a vacuum reservoir. WO9605091 teaches pneumatic brake booster for motor vehicle which is able to dispense with a pressure reservoir for a brake booster that works with pneumatic overpressure and is actuated by means of a brake, pedal, which consists of first chamber on the brake pedal side of a movable wall which divides the booster housing into two chambers having a continuous connection with a compressed-air source and that when actuated, a control valve controlling the pneumatic pressure differential acting on the movable wall establishing a connection to the atmosphere for the second chamber on the side of the movable wall facing away from the brake pedal.

The drawbacks associated with above said prior art is that in this case specially designed booster is required and it cannot be easily accommodated on the existing normal boosters.
OBJECTS OF THE INVENTION:
> The main object of this invention is to provide a brake system having improved response time to enhance the "brake feel" of the automobile.
> Another object of this invention is to provide a brake system with an increased knee point position so as to increase the range of operation of booster and tandem master cylinder.
> Yet another object of this invention is to provide a brake system which is simple in construction and cost effective.
BRIEF DESCRIPTION OF INVENTION;
According to present invention a brake system for a vehicle comprising a pedal assembly, a vacuum booster assembly for activating braking of said vehicle and connected to said pedal assembly, a pressure source for generating compressed air and communicating with said vacuum booster through a control valve operated by a solenoid, an electrical switch provided which is activated by said pedal assembly, a pressure switch connected to said pressure source, said electrical switch and said pressure switch electrically connected to said solenoid.
"When the brake pedal is pressed, the feedback is sensed by the brake boost control module & simultaneously brake booster gets actuated through mechanical linkages. Brake boost control module directs the compressed air from compressed air source into the brake booster.
The differential pressure in the brake booster has increased because of compressed air fed to it instead of air at atmospheric pressure which enhances the braking assistance.

In case of any failure/ leakage in pressurized air circuit, brake boost control module shall set system to open to atmospheric pressure wherein it would act as a normal brake booster.
This invention finally aims at reducing the response time of the brake circuit and thereby reducing the stopping distance and improving the "brake feel" of an automobile.
DETAILED DESCRIPTION OF INVENTION:
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same,
Figure 1 shows the layout of brake system in accordance with the invention Figure 2 shows the close view of the valve body with circular disc and pushrod Figure 3 shows comparison between conventional & modified vacuum booster with TMC in relation to TMC pressure generation with time.
Figure 4 shows comparison between conventional & modified vacuum booster with TMC in relation to automobile stopping distance with time for same pedal effort.
Now referring to figures 1 and 2 improved brake system comprises of a brake pedal (1) with brake light switch (2). circular disc with holes (5) fitted at the end of valve body assembly (6) of vacuum booster (7), flexible hose (22) is connected to the said circular disc with holes (5). End of said flexible hose (22) is communicating to a intercooler (17) connected to a turbocharger (14) through a control valve (21). A non-return valve (20) is provided on the communication line (22) for arresting the flow back into the intercooler. An air reservoir (19) provided to supply pressurized air to the vacuum booster through the control valve (21) and it is also connected to the intercooler for charging, The control valve (21) operated by a solenoid controlled by the brake light switch and a pressure switch (18).

Brake pedal (1) transfers motion to vacuum booster (7) through a clevis pin (3) via push rod (4). Said push rod (4) slides through the circular disc (5) and actuates the valves present in the valve body assembly (6) thereby allowing air to move axially inside the booster. Intercooler (17) gets the compressed air from turbocharger (14) which consisting of a turbine (15) and compressor (16).
The vacuum booster (7) in vehicles is used to give the required assist or boost during braking. It works on the principle of differential pressure. A diaphragm (8) separates the two chambers inside the vacuum booster (7). The push rod side of the vacuum booster (7) has a provision for air inlet and the other side is connected to the tandem master cylinder (12). When the engine is running, the vacuum pump (11) helps in maintaining equal level of vacuum on both sides of the diaphragm (8). Vacuum booster (7) is connected to vacuum pump (11) through a vacuum hose (10) and a non return valve (9). When the brake pedal (1) is applied, the push rod (4) of the vacuum booster (7) moves in through the sealing ring (23) of the circular disc (5) meant for sealing of the air leakage between the circular disc (5) and push rod (4) (refer figure 2). This movement closes the valve between (not shown) the two chambers and allowing atmospheric air to come into the push rod side of the diaphragm (8). This creates a pressure difference between the two chambers due to vacuum at one side and atmospheric pressure at other side and therefore the diaphragm (8) is pushed forward, giving an assist to the brake force applied by the driver. Tandem master cylinder (12), mounted on the Vacuum booster (7) generates hydraulic pressure due to forward movement of diaphragm (8) by means of internal linkage (not shown in figures). This hydraulic pressure gets divided into two hydraulic circuits (13), giving clamping force to brake assembly to stop the automobile.
The compressor (16) of the turbocharger (14) in the vehicle compresses the atmospheric air to a relatively high value which then enters the intercooler (17) where the temperature of the compressed hot air is brought down. In this invention, some amount of air coming out of the intercooler (17) is bled and sent through the

non return valve (20) to the air reservoir (19). Further cooling of compressed air is achieved with the help of fins provided on the outer surface of the air-reservoir (19). A separate compressor or any other source of compressed air can also be used for supplying the compressed air. The movement of the compressed air through the control valve (21) would be either from the reservoir (19) or directly from the intercooler (17) depending on the speed of the engine (not shown). Normally just before braking, the engine would be at high speed, so initially during braking the compressed air would be from Intercooler(17) and then after it would be taken from air reservoir(19). The air reservoir (19) will be having reserve for minimum of 2 brake application after engine (not shown) turned off. The out put side of the control valve is further connected to the circular disc with holes (5) through flexible hose (22). The control valve solenoid is connected in series with the brake light switch (2) on the brake pedal (1) and pressure switch (18). The control valve is operated by the solenoid which in turn activated when the brake pedal is pressed and pressure switch (18) is in connected condition.
The pressure switch (18) will be electrically connected if the pressure in the air reservoir (19) or intercooler is above atmosphere. This is done to minimizing the load on engine by optimally using the compressed air. This also ensure that above atmospheric pressure is supplied to the control valve communicating with the booster. If the pressure source is below atmospheric pressure then the pressure switch disconnected which in turn deactivate the solenoid operating the control valve. The control valve communicates to the atmosphere when the solenoid is not activated. This ensure that the atmospheric pressure or above is supplied to the booster.
Normally when the brake is not applied, the control valve (21) remains in closed condition and prevents entry of compressed air from reservoir (19) to flexible hose (22). When the brake pedal (1) is pressed, the brake light switch (2) gets electrically connected. In order to energize the solenoid to actuate the control valve (21), the brake light switch (2) and pressure switch (18) should be in electrically connected

condition. When the brake pedal (1) is advancing for brake application it experience a greater load on the push rod (4) and the push-rod (4) opens a valve in valve assembly (6), allowing compressed air from air reservoir (19), via actuated control valve (21) through the flexible hose (22), to enter the vacuum booster (7) on one side of the diaphragm (8) along with parallely sealing off the vacuum to that side. This increases pressure on diaphragm (8) would push the linkage which in turn pushes the piston in the tandem master cylinder (12). The compressed air entering through the valve assembly (6) flows radially outwards inside the booster chamber in a uniform fashion leading to equal pressure application on the diaphragm (8) area. Due to compressed high pressure air on one side of diaphragm (8) and vacuum on other side, high differential pressure is created and hence push rod (4) operates faster as compared to the earlier system of using air at atmospheric pressure at the pushrod side of vacuum booster (7). This higher differential pressure will lead to obtaining better brake booster characteristics in terms of response time as well as improved brake feel.
As the brake pedal (17) is released, the valve returns to its original position and prevents entry of outside air supply. This restores vacuum to both sides of the diaphragm (8). When the brake pedal (1) reaches to its complete zero position the brake switch (2) on the brake pedal is disconnected and further deactivating the control valve (21) by shifting to its original position. Thus isolating the compressed air between the air reservoir (19) and the flexible hose (22) connecting the valve body (6) of the vacuum booster (7).
In the absence of the air pressure in the air reservoir (19) near or below atmosphere pressure, then the pressure switch (18) will electrically open thereby keeping the control valve (21) in its normal deactivated condition. In this condition the control valve (21) is so designed that it keeps the flexible hose (22) connection open to atmosphere, thereby safeguarding the system by allowing vacuum booster (7) to work normally.

The differentiation in performance is shown between the Conventional system and the Present Invention:
Fig. 3 shows a graph showing position of knee point and reaction time by this
system as compared to conventional system
The graph compares conventional & modified vacuum booster with TMC in
relation to hydraulic pressure generation with time. The reduction of response time
leads to "improved brake feel".
Further, there has been increase in knee point and maximum pressure generation
with the modified vacuum booster with TMC leading to increase in the working
range of TMC.
Fig. 4 shows a graph showing stopping distance of automobile with this system as
compared to conventional system for same pedal efforts
The graph compares conventional and modified vacuum booster with TMC in
relation to automobile stopping distance with time. Reduction in automobile
stopping distance under same testing conditions observed with modified vacuum
booster as per present invention. Since automobile stopping distance is related to
the deceleration level achieved hence, driver will get a feedback of more
« deceleration level generation for same pedal efforts and would perceive
improvement in "brake feel"
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We Claim:
1) A brake system for a vehicle comprising a pedal assembly, a vacuum booster assembly for activating braking of said vehicle and connected to said pedal assembly, a pressure source for generating compressed air and communicating with said vacuum booster through a control valve operated by a solenoid, an electrical switch provided which is activated by said pedal assembly, a pressure switch connected to said pressure source, said electrical switch and said pressure switch electrically connected to said solenoid.
2) The system as claimed in claim 1 wherein said pressure source is an intercooler connected to the engine of said vehicle.
3) The system as claimed in claim 1 wherein said solenoid is activated to control the valve when the electrical switch and pressure switch are in closed condition.
4) The system as claimed in claim 1 wherein said control valve is communicating to the atmosphere when the solenoid is not activated.
5) The system as claimed in claim 1 wherein said control valve is communicating to the pressure source when the solenoid is activated.
6) The system as claimed in claim 3 wherein said pressure switch is closed
when the pressure supplied to the control valve is above a predetermined pressure.
7) The system as claimed in claim 1 wherein a non-return valve provided between said pressure source and said control valve..
8) The system as claimed in claim 1 wherein said pressure source is provided with a reservoir for storing the compressed air and supplying the air when the air pressure form said pressure source is below a predetermined value.

9) A brake system for a vehicle substantially as herein described with reference to accompanying drawings.