Claims:We Claim:

1. A vacuum check valve (103) to prevent leak of vacuum in a vacuum brake booster (102), said valve comprising :
- 3 chambers (204, 206, 208)
- a first port (210) connecting chamber 204 to a vacuum source of an engine
- a second port (212) connecting chamber (208) to a vacuum chamber (102b) of said vacuum booster (102)
- a first membrane (200) disposed between chamber (204) and chamber (206)
- a second membrane (202) disposed between chamber (206) and (208)
- said first membrane (200) and said second membrane (202) being in open position when the engine is in running condition, thereby allowing vacuum to enter in chambers (204, 206, 208)
- said first membrane (200) and said second membrane (202) being in closed position when engine stops running, thereby trapping vacuum in chambers (204, 206, 208 and 102b)

2. A vacuum check valve (103) wherein said membranes are made of resilient material
3. A vacuum check valve (103) wherein said membranes allow flow of fluid in only one direction
4. A vacuum brake booster (102) for a braking system, said valve vacuum booster comprising:
- A first chamber 102a
- A second chamber 102b, said first chamber and second chamber separated by a valve
- A membrane 105 separating said first and second chambers 102a, 102b
- A push rod 114 coupled to said membrane 105
- A vacuum check valve (103) said check valve (103) comprising
- 3 chambers (204, 206, 208)
- a first port (210) connecting chamber 204 to a vacuum source of an
engine
- a second port (212) connecting chamber (208) to a chamber (102b) of
said vacuum booster (102)
- a first membrane (200) disposed between chamber (204) and chamber
(206)
- a second membrane (202) disposed between chamber (206) and (208)
- said first membrane (200) and said second membrane (202) being in
open position when the engine is in running condition, thereby
allowing vacuum to enter in chambers (204, 206, 208)
- said first membrane (200) and said second membrane (202) being in
closed position when engine stops running, thereby trapping vacuum
in chambers (204, 206, and 208 and 102b)

, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[001] This invention relates to the field of brake vacuum boosters for vehicles. The invention in particular relates to a valve to prevent leakage of vacuum or entry of atmospheric pressure in a vacuum brake booster.

Background of the invention

[002] Now days, the vehicles use vacuum booster for braking the vehicle. The vacuum booster is used to reduce the manual force required for press the brake pedal to brake the vehicle. The Vacuum brake boosters make use of vacuum generated by the engine to amplify the force applied by foot on the brake pedal. Thus with little force applied at the brake pedal, the force is amplified by the brake booster and larger force is transferred to the pistons to generate appropriate hydraulic force.

The vacuum booster needs vacuum in one chamber to generate the force. This vacuum is generated when the engine is running. When the engine is switched off, the vacuum in the chamber slowly starts leaking to the atmosphere.

[003] Some prior arts try to reduce the leakage of the vacuum by modifying the diaphragm or mounting of the diaphragm. One prior art KR19980060726U discloses a brake booster, the diaphragm has a plurality of mounting holes in the circumferential direction with constant annular spacing. The mounting holes are through formed.

The prior art US2009071147A discloses a control system and a method to detect leakage of vacuum in a brake booster. The system includes an engine evaluation module that detects an engine off condition. A pressure evaluation module, during the engine off condition, monitors hydraulic brake line pressure, detects a change in brake booster pressure, and determines a brake booster vacuum decay rate based on the change in brake booster pressure. A fault reporting module detects a brake booster system fault based on the brake line pressure and the brake booster vacuum decay rate.

Brief description of the accompanying drawing

[004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[005] Fig. 1 illustrates a braking system for a vehicle
Fig. 2 and 3 illustrate a valve with double diaphragm.

Detailed description of the embodiments

[006] FIG. 1 illustrates a typical braking system 100 for a vehicle. The braking system may be a completely mechanical and hydraulic system or a combination of mechanical, hydraulic and electronics system. The braking system 100 typically comprises a vacuum brake booster 102, a tandem master cylinder 104, a brake oil reservoir 106, a hydraulic circuit 108, a brake caliper 110, a brake pedal 112 and a brake push rod 114. The brake pedal 112 is mechanically coupled to the brake push rod 114. The brake booster 102 comprises of two chambers 102a and 102b with a membrane 105 separating the two chambers. The chamber 102a is referred as working chamber and chamber 102b is referred as vacuum chamber. The membrane 105 is made of elastomeric material. The push rod comprises 114 comprises 3 parts, 114a, 114b and 114c. A spring 116 maintains the push rod at a predefined position when there is no force on the brake pedal. The hydraulic circuit 108 is coupled to a brake caliper 110. The brake caliper applies force on the brake disc 111 to reduce the speed of the vehicle whenever brake pedal is pressed by the user. The vacuum chamber 102b is connected to a vacuum source through a vacuum check valve 103.

[007] There is a first valve connecting the working chamber 102a to the atmosphere whenever brake pedal is pressed. There is a second valve connecting the working chamber 102a to the vacuum chamber 102b. The first and second valves are not shown in fig. 1.

[008] In this document the terms “vacuum brake booster”, “brake booster”, “vacuum booster”, “booster” are used interchangeably.

The working of the brake system is explained below.

[009] Assume that the vehicle is moving at a certain speed and there is no force applied on the brake pedal. In this scenario, the first valve is closed thereby cutting the atmospheric air entering into the chamber 102a.The second valve is open connecting both the chambers. Both the chambers are filled with vacuum and are under equilibrium position. The membrane 105 is also under equilibrium position.

[010] When the driver presses the brake pedal to reduce the speed of the vehicle, a force is applied on the brake push rod. The brake push rod moves in the direction of the brake booster. The first valve opens and the second valve closes. The opening of the first valve allows atmospheric air to enter into the chamber 102a. As chamber 102a is at atmospheric pressure and other chamber 102b is filled with vacuum, one side of the membrane 105 experiences atmospheric pressure and the others side of the membrane experiences vacuum. The membrane 105 expands and moves into the chamber 102b, thereby pushing the brake push rod 104c towards the tandem master cylinder with a bigger force. The force applied at the brake pedal is amplified and applied to the brake push rod 104c. The brake push rod 104 pushes the piston in the tandem master cylinder. The force on the pistons in the tandem master cylinder is transferred to the brake oil in the hydraulic circuit 108. Finally the pressure (generated due to force on piston) in the hydraulic circuit causes the calipers 110 to move closer and apply force on the brake disc 111, thereby reducing the speed of the wheels.

[011] When the driver removes the force from the brake pedal, the brake push rod moves towards left (with reference to direction as shown in fig. 1). The first valve closes and the second valve opens. The closing of the first valve cuts off the atmospheric air entering into the chamber 102a. As second valve is open, the chambers 102a and 102b are filled with vacuum. The spring 116 brings the membrane 105 to its original equilibrium position. This results in removal of force on the pistons of the tandem master cylinder resulting in removal of pressure on the calipers and the brake disc.

[012] Vacuum plays an important role in the brake booster based braking systems. Typically the vacuum source is the engine. The engine generates vacuum during the suction stroke and the same is used for brake booster.

[013] The chamber 102b is connected to a vacuum source through the vacuum check valve 103. As long as the engine is running, the vacuum is created and filled in the brake booster chamber 102a and 102b.

[014] When the engine is switched off the engine stops running. There is no generation of vacuum. In the prior arts, the vacuum check valve comprised only one first membrane. This first membrane allows vacuum to flow from vacuum source into the chamber when the engine is running. The function of the first membrane inside the vacuum check valve 103 is to prevent leakage of the atmosphere in to vacuum chamber 102b when the engine is not running. When the engine is not running, as the sealing of the first membrane in the vacuum check valve 103 is not completely perfect, slowly the atmospheric air starts leaking inside vacuum chamber 102b through the sealing of the first membrane. If the engine remains off for a certain time, the entire vacuum leaks into the atmosphere and the chamber 102b is filled with atmospheric air. Under this scenario, on certain vehicles, engine will start only when brake pedal is pressed. When the atmospheric air enters into vacuum chamber 102b because of the leakage in sealing element, when the user tries to start the engine, the brakes will not operate or the user has to apply much higher force on the brake pedal as the vacuum booster is not functional because of non-availability of vacuum in chamber 102b.

[015] The invention proposes a new vacuum check valve 103 to prevent the leakage of the atmospheric air into the vacuum chamber 102b when the engine remains off for a prolonged time.

[016] Shown in fig. 2 is a schematic of the vacuum check valve 103 according to one embodiment of the invention. The vacuum check valve 103 comprises two membranes 200, 202 forming 3 chambers 204, 206. 208. The first port 210 of the vacuum check valve 103 is connected to the vacuum source and the second port 212 is connected to the vacuum booster 102.

[017] The membranes 200, 202 are made of elastomers (resilient materials). The membranes 200, 202 are movably attached to the sealing elements with a pre-tension. When the engine is not running, the pressure on both sides of the membranes 200, 202 is same, hence the pre-tension keeps the membranes 200, 202 attached to the sealing elements i.e. in closed position. When engine is running, because of the suction from the engine, a pressure difference is generated on both sides of the membranes 200, 202. This causes the membranes to overcome the pre-tension and the membranes 200, 202 move away from the sealing element, i.e. to the open position. This allows vacuum in booster chambers 102a and 102b.

[018] When the engine is running, both the membranes 200, 202 are in open position and the vacuum check valve 103 allows the vacuum to flow from vacuum source into the vacuum chamber 102b. When the engine stops running, atmospheric air enters into first port 210. Because of the absence of vacuum sucking from engine, and because of the pre-tension, both the membranes 200, 202 move to closed position. This will seal passage of atmospheric air from first port 210 to second port 212. This results in retaining the vacuum in the vacuum chamber 102b. Whatever vacuum leakage happens from chamber 102b through the first membrane 200 because of the tolerances in the sealing elements, gets trapped in the chamber 206. Now the vacuum has to leak from chamber 206 through the second membrane 200. Because the vacuum leakage is blocked by two membranes 200, 202 in the vacuum check valve 103, it takes much longer time for the vacuum to leak completely through both the membranes 200, 202 compared to the single membrane vacuum check valve of the prior-arts. Leaking of the vacuum is referred to atmospheric air replacing the vacuum in the same enclosure.

[019] Fig. 2 represents the check valve when both membranes 200, 202 are in open position. This is the case when the engine is running. Fig 3 represents the check valve when both membranes 200, 202 are in closed position. This is the case when engine is not running.

[020] According to the invention, the availability of the vacuum is ensured for a longer duration when the engine remains switched off for prolonged duration. This requirement is also to meet safety guidelines for starting the engine after a certain duration of being in off state and brake booster working normally.

[021] Thus the invention proposes a simple vacuum check valve 103 which can retain the vacuum in the brake booster 102 for a prolonged time to meet the safety guideline. Because the vacuum is already available, the brake booster works normally, even before the engine is started. The user can press the brake and start the engine safely.