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
[0001] The present disclosure relates to a brake booster and more specifically to a system to control a pressure in a brake boosting system of a vehicle.

Background of the invention
[0002] Brake boosters allow for a reduction in the pedal force that the driver must apply in order to achieve a desired braking effect. The vacuum brake boosters stand out by virtue of their low weight and optimized braking power.

[0003] A brake booster has two chambers, which are separated by a moving membrane (Diaphragm). To amplify the driver's pedal force, a pressure difference is created between both chambers of the brake booster. To do this, the brake booster is evacuated in a non-activated state. When the driver actuates the brake pedal, ambient air flows into the rear chamber, creating higher pressure in front of the membrane (Diaphragm). Such a pressure difference is created between both of the chambers that the diaphragm plate presses in the direction of the tandem master cylinder and thus supports the force of the driver's foot.

[0004] In vehicle brake boosting systems, maximum brake boost assistance is obtained when the rear chamber of brake booster reaches a maximum atmospheric pressure (also known as the knee point) above which large pedal effort is needed. Currently this can be controlled by air valve and plunger travel distance.

[0005] In higher altitudes such as hill stations, due to reduced atmospheric pressure for the same calibrated position of air valve at sea level, the knee point bit (maximum atmospheric pressure) comes earlier compared to sea level. Thus altitudes require larger brake pedal force compared to sea level.

[0006] The prior art IN02937DE2013 A method involves determining change in position indication of a brake request device i.e. brake pedal (3). Pressure in chambers (7, 8) of a brake booster (2) is determined dependent on the determined change in position. A vacuum pump (11) is checked depending on the printing specification. Position change is calculated as the difference between a current detection cycle in a determined position of the brake pedal and a previous sensing cycle detected during position indication of the brake pedal. the vacuum pump is activated, when the pressure determined as an absolute pressure though the pressure information, exceeds a predetermined pressure threshold value, or when the pressure determined as a relative pressure through the pressure information, in particular as vacuum, drops below a predetermined pressure threshold value.

[0007] In the present invention, instead of using ambient pressure sensor for close looping the control for knee point, it is modelled such that based on deceleration of vehicle upon braking in different conditions, a learning model is implemented such that it predicts ambient pressure and adapts boost pressure set point accordingly.

[0008] Brief description of the accompanying drawings:
An embodiment of the invention is described with reference to the following accompanying drawings:

[0009] Figure 1 depicts a controller to control a pressure in a brake boosting system of a vehicle.

Detailed description of the drawings:

[0010] The present invention will now be described by way of example, with reference to accompanying drawings. Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In predetermined instances, details which are not necessary for an understanding of the present invention, or which render other details difficult to perceive may have been omitted.
[0011] Figure 1 depicts a controller (15) to control a brake boosting system of a vehicle. The brake boosting system (1) comprises a brake booster (2) comprising a vacuum chamber (7) having a vacuum pressure (p) and a pressure chamber (8) having an atmospheric pressure (P). Said vacuum chamber and said pressure chamber are separated by a membrane 9.
[0012] The brake booster (2) is coupled to a brake pedal (3) as a braking demand unit. The brake pedal (3) is connected to a piston rod (4), which passes through the brake booster (2) and is connected to a piston (5) of a hydraulic brake cylinder (6). The brake cylinder (6) is connected hydraulically to the hydraulic brake system of the vehicle, and is used for transmitting a braking force in the corresponding brake devices (not shown) on the wheels of the vehicle.

[0013] The brake booster (2) has the vacuum chamber (7) and the pressure chamber (8), through which the piston rod (4) is guided. The vacuum chamber (7) and the pressure chamber (8) are separated from each other in a pressure tight manner by the flexibly movable membrane (9). The membrane (9) is firmly connected to the piston rod (4), so that the movement of the membrane (9) is transmitted to the piston rod (4). In the vacuum chamber (7), a return spring (10) is provided, which is tensioned between a housing of the brake booster (2) and the piston rod (4) such that during the release (non-operating state) of the brake pedal (3), this moves back with a restoring force into a starting position.

[0014] Upon actuation of the brake pedal (3), the piston rod (4) moves in the direction against the brake cylinder (6), wherein the return spring (10) is tensioned.

[0015] The vacuum chamber (7) is connected to an electrical or other controllable vacuum pump (11), so that a vacuum can be generated during operation of the vacuum pump (11) in the vacuum chamber (7). In the shown starting position of the non-actuated brake pedal (3), same pressure is present in the vacuum chamber (7) and in the pressure chamber (8).

[0016] Upon actuation of the brake pedal (3) by means of a valve actuating element (12), an intermediate chamber valve (13) between the vacuum chamber (7) and the pressure chamber (8), in particular in the membrane (9), is closed, while the valve actuating element (12) is moved by the actuation of the brake pedal (3), for example, in the direction of the membrane (9). At the same time, an outer valve (14) is opened by the movement of the valve actuating element (12), so that ambient air may flow into the pressure chamber (8). Thereby, a pressure difference is caused by the membrane (9). The action of pressure difference exerts a force on the piston rod (4) in the direction of the brake cylinder (6). This force supports the force exerted by the driver on the brake pedal (3). During the release of the brake pedal (3), the intermediate chamber valve (13) located between the vacuum chamber (7) and the pressure chamber (8) is opened, so that the air present in the pressure chamber (8) flows into the vacuum chamber (7). Simultaneously, the outer valve (14) is closed, so that a pressure compensation takes place between the vacuum chamber (7) and the pressure chamber (8).

[0017] The brake pedal (3) is further connected to a position sensor (16) in order to provide information about the position of the brake pedal (3). The controller (15) is provided for operating the brake boosting system (1), which receives the information of the position of the brake pedal (3) from the position sensor (16), and the vacuum pump (11) is activated or deactivated to keep the sufficient vacuum pressure in the air chambers (7, 8).

[0018] Both during the actuation and during the release of the brake pedal (3), the pressure in the vacuum chamber (7) is increased by the movement of the piston rod (4) and the valve function of the brake booster (2). Upon actuation of the brake pedal (3), the membrane (9) is moved in the direction of the vacuum chamber (7) by the movement of the piston rod (4), so that its volume is reduced, and thereby increases the pressure present therein. When the brake pedal (3) is released, the piston rod 4 moves back due to the spring action of the return spring (10), wherein the intermediate chamber valve (13) is opened, and air from the pressure chamber (8), which is under a higher pressure, in particular ambient pressure, flows in the vacuum chamber (7) through the intermediate chamber valve (13).

[0019] The controller controls the brake boosting system to provide a sufficient pressure difference between the vacuum chamber (7) and the pressure chamber (8). The vacuum pump (11) is used to ensure that there is always a sufficient vacuum in the vacuum chamber (7) of the brake booster (2).

[0020] According to an aspect of the present invention, the controller may be a vehicle control unit in communication with different electric control units (including the braking control unit) within the vehicle.

[0021] As known in the art, brake booster assists till maximum atmospheric pressure, above which large pedal force is required. The controller controls the vacuum pressure for boosting based on a boost pressure set point. However, even if the vehicle is traversing in high altitude region, the boost pressure set point calibrated in the controller is according to sea level atmospheric pressure. This results in setpoint deviation between altitude and sea level conditions which results in reduction of knee point. Thus a large brake pedal force is needed at higher altitudes.
[0022] To solve the aforementioned problem, said controller is adapted to provide the vacuum pressure based on an actual ambient pressure of an actual surrounding of the vehicle, and an actual deceleration time taken by the vehicle when the braking force is applied to the brake pedal.
[0023] To achieve the same, different vacuum pressure values are modelled based on different ambient pressure conditions. All change in values of different initial velocities at different braking forces applied are recorded experimentally at a sea level condition. Different deceleration times are mapped to corresponding velocities and the corresponding applied braking force. These mapped values are compared with actual deceleration time in different ambient pressures. That is, for a vehicle at a sea level, moving at an X Kmph of initial velocity, when a braking force of Y Newton is applied on the brake pedal of the vehicle, a T unit of deceleration time is obtained. For the same vehicle at an ambient pressure in a surrounding other than the sea level (such as when a vehicle is at an altitude), a deceleration time of Z unit may be taken by the vehicle when the said vehicle moves at X Kmph and Y Newton of brake force is applied to it. Thus, deviations in deceleration times at different velocities and different brake pressures are recorded . Thus deviations in the deceleration time are mapped at different ambient pressure conditions. The deviations mapped out in different ambient pressure conditions are modelled. Based on a comparing the actual values (when the vehicle is operating in an actual surrounding) with the modelled values, the controller determines the vacuum pressure to be provided in of brake booster.
[0024] Therefore, the controller(15) determines the actual ambient pressure by comparing the actual deceleration time taken by a vehicle when the braking force is applied in an actual surrounding of the vehicle, with a known deceleration time taken by the vehicle when the braking force is applied at a known ambient pressure of a known surrounding of the vehicle. The vacuum pressure is determined based on the actual ambient pressure obtained by said comparison.

[0025] The controller (15) provides the vacuum pressure so determined by controlling the vacuum pump (11) in connection with the vacuum chamber of the brake boosting system (1). It is to be understood that based on the mapped values the controller can also determine an altitude of the actual surrounding on the vehicle based on the actual ambient pressure.

[0026] For a cohesive understanding, referring again to Figure 1, the same depicts the controller(15) to control a pressure in a brake boosting system(1) of the vehicle, said brake boosting system comprising the brake booster(2) comprising the vacuum chamber(7) having the vacuum pressure (p) and the pressure chamber(8) having the atmospheric pressure (P), said vacuum chamber and said pressure chamber separated by the membrane (9).Characterized in that, said controller(15) adapted to provide the vacuum pressure based on the actual ambient pressure of the actual surrounding of the vehicle, and the actual deceleration time taken by the vehicle when the braking force is applied to the brake pedal (3).

[0027] The actual ambient pressure is determined by comparing the actual deceleration time taken by the vehicle when the braking force is applied in the actual surrounding of the vehicle, with the known deceleration time taken by the vehicle when the braking force is applied at the known ambient pressure of the known surrounding of the vehicle.
[0028] The vacuum pressure is determined based on the actual ambient pressure obtained by said comparison. The controller provides the vacuum pressure by controlling the vacuum pump(11) in connection with the vacuum chamber of the brake boosting system (1). The controller determines an altitude of the actual surrounding on the vehicle based on the actual ambient pressure.
[0029] Plurality of known deceleration times corresponding to plurality of the braking forces are mapped against plurality of known ambient pressures. The controller (15) calculates a deviation between the actual deceleration time taken when the braking force is applied and the known deceleration time taken when the braking force is applied at the known ambient pressure.
[0030] The controller calculates the actual ambient pressure of the surrounding of the vehicle based on said deviation.

[0031] Therefore, according to the present invention, if the vehicle is traversing in high altitude region instead of the boost pressure set point calibrated according to sea level atmospheric pressure, the brake boosting will adapt to the ambient pressure conditions and suitable vacuum pressure will be provided to have a boosting effect similar to the effect at sea level. This allows for efficient brake boosting performance at high altitudes.
, Claims:We Claim:
1. A controller(15) to control a pressure in a brake boosting system(1) of a vehicle, said brake boosting system comprising:

-a brake booster(2) comprising a vacuum chamber(7) having a vacuum pressure (p) and a pressure chamber(8) having an atmospheric pressure (P), said vacuum chamber and said pressure chamber separated by a membrane (9),

characterized in that,

said controller(15) adapted to provide the vacuum pressure based on:
- an actual ambient pressure of an actual surrounding of the vehicle, and
- an actual deceleration time taken by the vehicle when a braking force is applied to the brake pedal (3).

2. The controller (15) as claimed in Claim 1, wherein, the actual ambient pressure is determined by comparing –
the actual deceleration time taken by a vehicle when the braking force is applied in the actual surrounding of the vehicle, with

a known deceleration time taken by the vehicle when the braking force is applied at a known ambient pressure of a known surrounding of the vehicle.

3. The controller(15) as claimed in Claim 2, wherein, the vacuum pressure is determined based on the actual ambient pressure obtained by said comparison.

4. The controller (15) as claimed in Claim 1, wherein, the controller provides the vacuum pressure by controlling a vacuum pump(11) in connection with the vacuum chamber of the brake boosting system.

5. The controller (15) as claimed in Claim 2, wherein, the controller determines an altitude of the actual surrounding on the vehicle based on the actual ambient pressure.

6. The controller (15) as claimed in Claim 2 , wherein, plurality of known deceleration times corresponding to plurality of the braking forces are mapped against plurality of known ambient pressures.

7. The controller (15) as Claimed in Claim 2, wherein, the controller calculates a deviation between the actual deceleration time taken when the braking force is applied and the known deceleration time taken when the braking force is applied at the known ambient pressure.

8. The controller (15) as claimed in Claim7, wherein, the controller calculates the actual ambient pressure of the surrounding of the vehicle based on said deviation.

9. The controller (15) as claimed in Claim 1, wherein, the controller is a vehicle control unit of the vehicle.