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 system and a method to regulate a target brake pressure to hold a vehicle during a parking brake failure.

Background of the invention

[0002] All Vehicles are equipped with Parking Brakes. The purpose of Parking Brakes is to hold the vehicle in the same geographical position for a very long time. A parking brake usually controls the rear brakes and it is a separate device from the vehicle’s regular hydraulic brakes. They are completely mechanical and use only cables and levers to operate. When a parking brake lever is pulled (or when a parking brake pedal is pushed), the cables are tightened, which in turn will pull a lever that compress the brake shoes against the brake drum that in turn prevents the motion of the vehicle.
[0003] The state of the art now has electronic parking brake (EPB), also known as an electric parking brake or electric park brake which are electronically controlled parking brake, whereby the driver activates the holding mechanism with a button and the brake pads are electrically applied to the rear wheels. This is accomplished by an electronic control unit (ECU) and an actuator mechanism.
[0004] There are many possible failures that can occur to the Parking Brakes such as situations when cable is cut off, lever is broken, Brakes are stuck at open position (no Brakes Applied) or when rakes are stuck at closed position (brakes Applied always) etc. In case of failure of parking brakes, the holding force is not available to hold the vehicle.
[0005] There is a need to provide a secondary backup functionality in vehicles equipped with EPB during a parking brake failure. The same can be done through ESP hydraulic system. When the vehicle goes to a standstill position, sufficient braking pressure can be retained in the brake circuits.
[0006] The hydraulic braking system (of the ESP) includes all the components required to transfer the hydraulic pressure from brake pedals to the brake calipers/drums. A typical brake circuit in the hydraulic braking system comprises of a master cylinder, brake lines, brake hoses and brake calipers. The brake circuits comprise valves that are electrically operated to control the pressure in the brake lines.

[0007] Typically, a hydraulic braking system has two Umschaltventil valves (USV) (one for each brake circuit). The Brake pressure is retained in all the four wheels by continuously actuating (by supplying constant holding current) both USV valves to closed position. USV valves tend to overheat if the holding current is supplied continuously for a long time (~10 minutes). Due to this limitation ESP cannot hold the vehicle for a long time. Hence, after some time(~10 minutes), ESP transfers the Braking control to the Electronic Parking Brakes(EPB).

[0008] The USV valves are not 100% leak proof for longtime holding. The Brake pressure built in all the four wheels tend to leak gradually, leading to less sufficient holding pressure, which in turn may lead to vehicle roll.
[0009] The solution to the above problem is being achieved by retaining an equivalent brake pressure required to hold the vehicle in only one, or two or three wheels by alternating the brake pressure between at least two brake circuits at regular intervals.

[0010] This allows each one of the USV valves to cool down while the other is being actuated to provide a holding pressure to the vehicle. In this manner, leakage in holding pressure is prevented and the time period up to which vehicle hold functionality is provided can be extended.
[0011] Brief description of the accompanying drawings
An embodiment of the invention is described with reference to the following accompanying drawings:
[0012] Figure 1 depicts a system to regulate a target brake pressure to hold a vehicle during a parking brake failure.
[0013] Figure 2 depicts a flowchart for a method to regulate a target brake pressure to hold a vehicle during a parking brake failure.
Detailed description of the drawings:

[0014] The present disclosure provides a system and a method to regulate a target brake pressure to hold a vehicle during a parking brake failure.
[0015] The disclosed method and system provide a vehicle equipped with the EPB, a sufficient braking pressure, to hold the vehicle in the event of a parking brake failure.
[0016] Once a EPB failure is detected in the vehicle, a ‘vehicle hold’ function is enabled by the driver (or automatically). In case the vehicle reaches or is already in standstill and the driver has applied some brake pressure, the applied brake pressure will be held by the ‘vehicle hold’ function. In this way, the vehicle will remain in a standstill for up to a pre-defined time even upon the failure of electronic parking brake.
[0017] If the driver wants to drive away while ‘vehicle hold’ phase is active, the brake pressure will be released as soon as the system detects the driver´s intention to drive off. The driver´s intention to move off is detected by the engine torque reaching a level which is sufficient to move the vehicle in the required direction. The driver may also manually deactivate the vehicle hold function through an interface.

[0018] This ‘vehicle hold’ function operates through the hydraulic braking system of the Electronic Stability Program (ESP). The hydraulic braking system includes all the components required to transfer the hydraulic pressure from brake pedals to the brake calipers/drums. A typical brake circuit in the hydraulic braking system comprises of a master cylinder, brake lines, brake hoses and brake calipers. The brake circuits comprise valves that are electrically operated to control the pressure in the brake lines. The brake circuits comprise solenoid valves that are electrically operated to control (release) pressure in the brake lines of the hydraulic braking system.

[0019] 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.
[0020] Figure 1 depicts a system to regulate a target brake pressure to hold a vehicle during a parking brake failure. The system (20) comprises a hydraulic braking system (1). The hydraulic braking system comprises at least two brake circuits (2a, 2b) to transmit a target brake pressure (the pressure to hold the vehicle in a standstill position) to at least one wheel of the vehicle.
[0021] In an example, one of the at least two brake circuits (2a and 2b) may have plurality of brake lines (2a1, 2a2, 2b1, 2b2) and plurality of valves (3, 3a, 3b) to supply a target brake pressure (the pressure required to hold the vehicle) to at least one of the wheel 10a 10b 10c 10d. The brake lines 2a1 2a1, 2a2, 2b1 and 2b2 may respectively transmit a brake pressure to the wheels 10a, 10b, 10c, and 10d of the vehicle.
[0022] In an example, (10 a) may be Front Left wheel, (10b) may be Rear Right wheel, (10c) may be Front Right wheel and (10d) may be Rear Left wheel.
[0023] The depicted brake circuits are only examples and the same can have multiple configurations. Any of the embodiments in the present disclosure is not to be construed as limiting the scope of this disclosure.
[0024] In an example, the two depicted brake circuits are mutually independent, each of which supplies diagonally opposing brakes to the wheels. Operation of the brake system can be carried out using a brake pedal (4) that uses a master cylinder (5) to apply hydraulic pressure independently to both brake circuits (2a, 2b). The system may comprise plurality of devices to measure the occurring pressure (such as a pressure sensor (9) ).

[0025] The system may further comprise pumps (6a, 6b) associated with the respective brake circuits, which are driven by a common electric motor (7) which can be activated by a controller (8) in order to supply additional fluid pressure. In addition, the controller also controls the position of the illustrated solenoid valves (3, 3a, 3b). The plurality of solenoid valves (3, 3a, 3b) operated by the controller (8) adjust the braking pressure for each individual brake. The valves (3a)and (3b) are the Umschaltventil valves (USV) (reversing valves) for respective brake circuits (2a, 2b). The controller (8) is in communication with the hydraulic braking system (1).

[0026] The controller (8) maybe an engine control unit (ECU) present either inside or outside the hydraulic braking system (1). In another embodiment the controller may be a part of the ESP (electronic stability program) known in the art. The controller may have an inbuilt processing power and an associated memory. The controller(8) regulates the target brake pressure to hold vehicle during a parking brake failure. The controller is adapted to control the transmission of target brake pressure in at least one brake circuit (2a, 2b) of the HBS by controlling the opening and closing of at least one valve(3, 3a, 3b) of the HBS. The disclosed controller (8) detects an event of failure of parking brake and measures the target brake pressure to hold the vehicle in the event of failure of parking brake. The controller is further adapted to alternate the transmission of the target brake pressure to the at least one brake circuit (2a, 2b) after the predefined time. The at least one brake circuit comprises a first brake circuit (2a) and a second brake circuit (2b) such that, the transmission of target brake pressure is alternated between the first and the second brake circuit.

[0027] The controller alternates and distributes the target brake pressure in at least one brake line(2a1,2a2, 2b1,2b2) of the at least one brake circuit (2a, 2b).
[0028] The at least one brake line (2a1, 2a2, 2b1, 2b2) comprises a first brake line (2a1, 2b1) and a second brake line (2a2, 2b2) such that, a sum of a first brake pressure transmitted in the first brake line and a second brake pressure transmitted in the second brake line is equal to the target brake pressure to hold the vehicle.
[0029] The controller alternates and distributes the transmission of the target brake pressure to the at least one brake circuit comprising the at least one brake line by controlling the opening and closing of the at least one valve of the HBS.

[0030] In an example , in order to regulate the transmission of target brake pressure during the EPB failure, the controller may receive the following inputs:
• A Parking Brake Request (either from the driver or automatically upon detection of EPB failure inside the vehicle)

• A Parking Brake Failure Status (to know if there is any failure in the Parking Brakes due to which holding force cannot be extended)

• Target brake pressure at vehicle Level to hold the vehicle at standstill (the same can be estimated by the pressure applied by the user on the brake pedal to hold the vehicle still. The same further considers the mass of the vehicle and the gradient at which it is parked)
• Battery State (to know if there is enough energy left in the Battery to perform the Hydraulic Backup. To perform the Hydraulic Backup the pump and valves must be operated at regular intervals. It is possible only if there is sufficient energy left in the battery)
• Vehicle velocity (To know if the vehicle is in standstill. The proposed function shall be activated only when the vehicle is in standstill)
• Holding time: The time to provide the vehicle hold functionality may be calculated dynamically using a mathematical model that is based on the inputs of target brake pressure to hold the Vehicle at Standstill and the Battery state. .

[0031] In an example, whenever the driver requests the activation of the vehicle hold feature during the parking brake failure through a human machine interface (HMI) (optionally, the vehicle automatically switches to enable the vehicle hold function), the controller in communication with said hydraulic braking system is adapted to measure a target brake pressure to hold the vehicle. The controller (8) regulates said target brake pressure for at least one wheel of said vehicle through at least two brake circuits (2a, 2b) of said hydraulic braking system. The controller(8) alternates the transmission of target brake pressure to at least one wheel (10, 10b, 10c , 10d) of said vehicle after a pre-defined time interval. The pre-defined time may be the ‘holding time’ being inputted in the controller as explained above.

[0032] The controller (8) regulates the target brake pressure through selectively operating at least one of said brake circuit (2a, 2b) of the hydraulic braking system. The target brake pressure to be applied to hold the vehicle to at least one wheel of the vehicle may be measured based on the mass of the vehicle, the gradient (geographical position) based on which it is parked on or based on the force required to hold the vehicle when the EPB was functioning or based on the brake pressure applied by the driver to hold the vehicle in a standstill position at a pre-defined inclination).
[0033] As the required target brake pressure (to hold the vehicle in a standstill position) is alternated between the two brake circuits (2a, 2b), only one USV valve (3a) is actuated at a time while the other (3b) gets a cooling time before the next actuation.
[0034] In an example, the controller may further estimate time for which the holding pressure through can be provided by ESP. The same can be made known to the user by displaying it in the vehicle’s cabin dashboard or through a Mobile application or both.
[0035] The working of the system will now be further described in this disclosure by way of an example. Any arbitrary physical values (including values of time limits and target brake pressures) are assumed for explanatory purposes only and are not limited by such assumptions.

[0036] In an example, assuming that 45 bars of pressure is required in two wheels(10a, 10b) connected by brake circuit (2a) to hold the vehicle in standstill position and further assuming that USV (3a) is responsible for retaining pressure in Front Left/Rear Right wheels (10a, 10b) and USV (3b) is responsible for retaining pressure in Front Right (10c) and Rear Left wheels (10d) , the brake pressure is alternated between the two circuits (2a, 2b) at every 30 minutes (time limit of 30 minute is assumed and not to be construed as limiting ).
[0037] During the first 30 minutes, holding current corresponding to 45 bars of pressure is supplied only to USV(3a) (in the brake circuit 2a, )by the controller while USV (3b) (in the brake circuit 2b) is not actuated(allowed to cool down). Therefore, the front Left wheel (10a) & Rear Right wheel(10b) hold 45 bars of pressure. During the next 30 minutes, Holding current corresponding to 45 bars of pressure is supplied only to USV (3b) while USV (3a) is not actuated(allowed to cool down). The Front Right wheel (10b) & Rear Left wheel (10d) hold 45 bars of pressure. Thus, each USV gets a cooling time before the next actuation that prevents the USVs from overheating. Each Brake circuit is refreshed with the required holding pressure at constant frequency. This prevents the leakage in holding pressure & prevents the vehicle from rolling back. Further, the target brake pressure may be divided or distributed within the brake lines (2a1, 2a2, 2b1, 2b2). In an example, to provide 45bars of brake pressure in 2a, any combination of two brake pressures may be distributed between brake lines 2a1 and 2a2).

[0038] It is also to be understood that the target brake pressure may also be applied through both the brake circuits(2a, 2b) through unequal brake pressure transmitted in individual brake lines (2a1, 2a2,2b1,2b2) such that the sum of all brake pressures through the brake lines is equal to target brake pressure. In such a situation, the brake pressure across all brake lines (any of 2a1, 2a2, 2b1, 2b2) may be alternated in addition to alternating the brake pressure in the individual brake circuits. Thus to provide 45 bars of target brake pressure, 20 bars of pressure may be transmitted in 2a1 and 25 bars of brake pressure may be transmitted in 2a2. Or in another example, to provide 45 bars of target brake pressure, 10 bars of pressure may be transmitted in 2a1 and 10 bars of brake pressure may be transmitted in 2a2 which adds up to 20 bars being transmitted in the brake circuit 2a1. The rest of the 25 bars maybe transmitted through the brake lines (2b1 and 2b2) of brake circuit 2b. After 30 minutes, the target brake pressure transmitted in the first and second brake circuits is alternated wherein, 10 bars of pressure may be transmitted in 2b1 and 10 bars of brake pressure may be transmitted in 2b2 which adds up to 20 bars being transmitted in the brake circuit 2b. The rest of the 25 bars maybe transmitted through the brake lines (2a1 and 2a2) of brake circuit 2a.

[0039] It is to be further understood, numerous combinations possible to transmit the target brake pressure across the wheels to hold the vehicle and the ones listed in this disclosure are not exhaustive and not to be construed as limiting the scope in any manner.

[0040] Referring to figure 2, the same depicts a flowchart for a method method to regulate a target brake pressure to hold a vehicle during a parking brake failure. The method (100) is implemented by the system (20) including the controller (8) in communication with the hydraulic braking system (HBS) (1) as explained and described in Figure 1 above.
[0041] The method (100) comprises the first step (101) of controlling, by the controller, the transmission of target brake pressure in at least one brake circuit of the HBS by controlling the opening and closing of at least one valve of the HBS;
[0042] The second method step (102) includes detecting, by the controller, an event of failure of parking brake and the third step (103) of measuring, by the controller, the target brake pressure to hold the vehicle in the event of failure of parking brake. The characterizing steps of method (104) include alternating, by the controller, the transmission of the target brake pressure to the at least one brake circuit after a predefined time, said at least one brake circuit comprising any one of a first brake circuit and a second brake circuit such that the transmission of target pressure is alternated between the first and the second brake circuit. The target pressure based on a target brake pressure applied by a user on a brake pedal of the vehicle before releasing the said brake pedal. The further step (104a) includes alternating and distributing by the controller, the target pressure in at least one brake line of the at least one brake circuit, said at least one brake line comprising a first brake line and a second brake line such that, a sum of a first target brake pressure transmitted in the first brake line and a second target brake pressure transmitted in the second brake line is equal to the target brake pressure to hold the vehicle.

[0043] Alternation and distribution by the controller of the transmission of the target brake pressure to the at least one brake circuit comprising the at least one brake line is done by the controller by controlling the opening and closing of the at least one valve of the HBS.

[0044] Alternation and distribution by the controller of the target pressure in the first and second brake line in the first brake circuit, and a second brake line and a third brake line in the second brake circuit is such that, a sum of a target brake pressure transmitted in the first, second , third and fourth brake line is equal to the target brake pressure to hold the vehicle.
[0045] In an example, assuming that 45 bars of pressure is required in two wheels(10a, 10b) connected by brake circuit (2a) to hold the vehicle in standstill position and further assuming that USV (3a) is responsible for retaining pressure in Front Left/Rear Right wheels (10a, 10b) and USV (3b) is responsible for retaining pressure in Front Right (10c) and Rear Left wheels (10d) , the brake pressure is alternated between the two circuits (2a, 2b) at every 10 minutes (time limit of 10 minute is assumed and not to be construed as limiting ).
[0046] During the first 10 minutes, holding current corresponding to 45 bars of pressure is supplied only to USV(3a) (in the brake circuit 2a, )by the controller while USV (3b) (in the brake circuit 2b) is not actuated(allowed to cool down). Therefore, the front Left wheel (10a) & Rear Right wheel(10b) hold 45 bars of pressure. During the next 10 minutes, Holding current corresponding to 45 bars of pressure is supplied only to USV (3b) while USV (3a) is not actuated(allowed to cool down). The Front Right wheel (10b) & Rear Left wheel (10d) hold 45 bars of pressure. Thus, each USV gets a cooling time before the next actuation that prevents the USVs from overheating. Each Brake circuit is refreshed with the required holding pressure at constant frequency. This prevents the leakage in holding pressure & prevents the vehicle from rolling back.
[0047] The disclosure advantageously prevents any leakage in pressure to hold the vehicle standstill upon failure of parking brake in a vehicle equipped with EPB and extends the time period up to the vehicle hold functionality can be provided. This extended time period can provide the function of EPB in the vehicle during an EPB failure.
, Claims:WE CLAIM:

1. A controller (8) to regulate a target brake pressure to hold a vehicle during a parking brake failure, said controller in communication with a hydraulic braking system (HBS) (1),
said controller (8) adapted to:
- control the transmission of target brake pressure in at least one brake circuit (2a, 2b) of the HBS by controlling the opening and closing of at least one valve (3,3a,3b) of the HBS;
- detect an event of failure of parking brake;
- measure the target brake pressure to hold the vehicle in the event of failure of parking brake,
characterized in that, said controller further adapted to:
- alternate the transmission of the target brake pressure to the at least one brake circuit(2a, 2b) after a predefined time, said at least one brake circuit comprises a first brake circuit(2a) and a second brake circuit (2b) such that, the transmission of target brake pressure is alternated between the first and the second brake circuit (2a,2b).

2. The controller(8) as claimed in Claim 1, wherein, the controller measures the target bake pressure based on a target brake pressure applied by a user on a brake pedal(4) of the vehicle before releasing the said brake pedal(4).

3. The controller(8) as claimed in Claim 1, wherein, the controller alternates and distributes the target brake pressure in at least one brake line(2a1, 2a2,2b1,2b2) of the at least one brake circuit.

4. The controller as claimed in Claim 3, wherein, said at least one brake line comprises a first brake line (2a1) and a second brake line(2a2) such that, a sum of a first target brake pressure transmitted in the first brake line and a second target brake pressure transmitted in the second brake line is equal to the target brake pressure to hold the vehicle.

5. The controller (8) as claimed in Claim 1, wherein, the controller alternates and distributes the transmission of the target brake pressure to the at least one brake circuit(2a, 2b) comprising the at least one brake line (2a1, 2a1, 2b1, 2b2) by controlling the opening and closing of the at least one valve of the HBS.

6. A method(100) to regulate a target brake pressure to hold a vehicle during a parking brake failure in the vehicle by a controller, said controller is in communication with a hydraulic braking system (HBS),
the method comprises the steps of:
- controlling, by the controller, the transmission of target brake pressure in at least one brake circuit of the HBS by controlling the opening and closing of at least one valve of the HBS (101);
- detecting, by the controller, an event of failure of parking brake (102) ;
- - measuring, by the controller, the target brake pressure to hold the vehicle in the event of failure of parking brake (103);
characterized in that, method further comprises the steps of:
- alternating, by the controller, the transmission of the target brake pressure to the at least one brake circuit after a predefined time, said at least one brake circuit comprising any one of a first brake circuit and a second brake circuit such that the transmission of target pressure is alternated between the first and the second brake circuit (104).

7. The method (100) as claimed in Claim 5, wherein, measuring by the controller, the target pressure based on a target brake pressure applied by a user on a brake pedal of the vehicle before releasing the said brake pedal.

8. The method as claimed in Claim 5, wherein, alternating and distributing by the controller, the target pressure in at least one brake line of the at least one brake circuit, said at least one brake line comprising a first brake line and a second brake line such that, a sum of a first target brake pressure transmitted in the first brake line and a second target brake pressure transmitted in the second brake line is equal to the target brake pressure to hold the vehicle (104a).

9. The method (100) as claimed in Claim 5, wherein, alternating and distributing by the controller, the transmission of the target brake pressure to the at least one brake circuit comprising the at least one brake line by controlling the opening and closing of the at least one valve of the HBS.

10. The method (100) as claimed in Claim 5, wherein, alternating and distributing by the controller, the target pressure in -

-the first and second brake line in the first brake circuit, and
-a second brake line and a third brake line in the second brake circuit,
such that, a sum of a target brake pressure transmitted in the first, second , third and fourth brake line is equal to the target brake pressure to hold the vehicle.