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 invention relates to a brake by wire systems and more specifically to enable a brake-by-wire functionality in the event of failure of a sensor of the brake-by-wire system.

[0002] Background of the invention

[0003] A brake-by-wire system includes a brake assembly, a pedal assembly, a pedal feel simulator unit and an actuator assembly or a pressure unit. The actuator assembly/pressure unit consists of a plunger piston system which is connected to a high dynamic motor using a planetary gear. A controller receives braking signals from the pedal assembly and outputs a command signal to the actuator. The actuator drives the motor and plunger which push the brake fluid to the brakes.
[0004] Thus, the driver requested pressure (pressure applied on the brake pedal) is boosted (amplified) in the brake by-wire mode. The pedal is coupled to the pedal feel simulator through a valve when in By-wire mode. The pedal feel simulator provides a comfortable pedal feel to the driver. Due to reasons such as sensor failure or leakage in the brake circuits or the master cylinder, the brake-by-wire functionality of the vehicle is disabled, in such a scenario the vehicle runs in the backup mode where the driver directly pushes the fluid to the brakes. Therefore, in the backup mode, no boosting of driver pressure occurs.
[0005] In the brake by-wire-system, when driver presses the brake, the driver requested pressure is calculated using master cylinder sensor and input rod sensor. The calculated pressure is sent to pressure controller for the actuation. The controller calculates the required volume flow (motor speed) to realize the target pressure and actuates the motor accordingly. The ratio of driver applied pressure from master cylinder sensor and the system actuated pressure decides the boost ratio (in comparison with conventional vacuum booster). In case of the sensor failures (either master cylinder sensor or input rod sensor), the state of the art is to switch to mechanical backup state, where driver directly pushes the brake fluid to the brakes.
[0006] Even if one of the sensor is working, the detection of latent failures in the system is not possible. If in such a scenario the brake by wire functionality is continued relying on the sensors still functioning, there is a risk of actuation of too little brake pressure than the actual brake pressure requested by the driver.
[0007] The prior art US2014028084 AA discloses a motor vehicle brake system operable in a brake-by-wire and fallback modes. The system includes a brake pedal, a master cylinder, a reservoir, a travel simulator , an electrically controllable pressure source , isolation valves pumps and a low-pressure accumulator, an inlet valve and an outlet valve for each wheel brake , valves connected to the pumps (, and a control and regulation unit. A valve arrangement establishes for each brake circuit a connection from the pressure chamber of the master cylinder to the modulator admission pressure line and disconnects the connection when unenergized, the valve arrangement preventing the pressure source from being subjected to pressure from the pressure chambers.
[0008] The present disclosure proposes a controller to enable a brake-by-wire functionality in the event of failure of a sensor and a method thereof. In the present disclosure, during the sensors’ failure the system will neither stay in complete “by wire mode” nor will go to complete “mechanical backup”, rather system will go to another state called “one circuit mode”. The driver request will be calculated from available sensors (either master cylinder sensor or input rod sensor) depending on the failure. By using the driver requested pressure the system will boost only one brake circuit (through the by wire mode) , and the other circuit will always be coupled to the driver and mechanical braking functionality will be provided.

Brief description of the accompanying drawings
[0009] Preferred exemplary embodiments of the present invention will hereinafter be described in conjunction with the appended drawings:

[0010] Figure 1 depicts a brake by wire system comprising a controller to enable a brake-by-wire functionality during a fault in at least one sensor , according to an embodiment of the present disclosure.
[0011] Figure 2 depicts a flowchart of the method to enable a brake-by-wire functionality during a fault in at least one sensor of a brake-by-wire system, according to an embodiment of the present disclosure.

Detailed description of the drawings

[0012] 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.

[0013] The advantages of the present invention will be apparent with this detailed description, wherein, the best method known to the applicant to implement the invention has also been described. It is however to be noted that numerous alternate embodiments of the present invention are possible and the disclosure of one of them is not to be construed as limiting the others.

[0014] The disclosure further provides examples for the working of the present disclosure and the best method known to the applicant to perform the said disclosure. The working of the present disclosure as described below is to be taken just as an example and should not impart any limitation.

[0015] The brake-by-wire system includes a brake assembly (coupled with the base brakes of front and rear wheels of the vehicle), a pedal assembly coupled with a pedal feel simulator, and a pressure unit comprising an actuator and a motor to provide a target brake pressure. The actuator consists of a plunger piston system which is connected to the high dynamic motor using planetary gear. The controller receives braking signals from the pedal assembly and outputs a command signal to the actuator. The actuator drives the motor and plunger which push the brake fluid to the brakes. The brake assembly is connected to the pressure unit in a brake by-wire mode. In the brake by wire mode, the driver requested pressure is boosted.

[0016] The pedal is coupled to the pedal feel simulator through a simulator separation valve when the vehicle is in the brake by-wire mode to provide a comfortable pedal feel to the driver.
[0017] Due to reasons such as sensor failures, where an input brake pressure requested by the driver cannot be measured, the vehicle goes into a backup mode wherein, the brake is applied mechanically through hydraulic means as in conventional braking systems. The mechanical braking/backup mode includes a hydraulic connection between pedal interface to the brakes, where the driver directly pushes the fluid to the brakes, therefore no boosting of driver pressure possible in the backup mode.
[0018] The brake assembly comprises a tandem master cylinder connected with a first brake circuit and a second brake circuit and a first and second circuit separation valves (CSV 1 and CSV2, respectively). When the vehicle is in by wire mode, these CSVs isolate the pedal assembly from the base brakes (braking the wheels). In the backup mode the CSVs are opened to provide a direct communication between the pedal assembly and the brakes.
[0019] The pressure unit is connected to the first and second brake circuit through the first and second plunger separation valve (PSV1 and PSV2). The PSVs are in normal position (PSVs opened) that provides hydraulic communication between pressure unit to the brakes when in the by wire mode and the PSVs are closed when the system is in backup mode (mechanical braking) to isolate the pressure unit from brakes when during the mechanical backup mode.
[0020] In a brake by wire system, when a driver presses the brake, the driver requested pressure is calculated using a master cylinder pressure sensor and input rod sensor , the calculated target pressure is sent to pressure unit for the actuation. The controller calculates the required volume flow (and motor speed) to realize the target pressure and actuate the motor accordingly. The ratio of driver applied pressure from master cylinder pressure sensor and the system actuated pressure decides a boost ratio.
[0021] In case of the sensor failures including either master cylinder sensor or input rod sensor, as per the state of the art requirement, the driver directly pushes the brake fluid to the brakes. Therefore, no boosting of driver pressure is possible in this mode. The reasons to switch to this mechanical back up is an underlying safety concern. For instance, in an example, in case of master cylinder pressure sensor failure, the system cannot depend completely on the input rod sensor because a second failure of a simulator separation valve or a leakage in the pedal feel simulator will result in a calculation error and actuation of too less brake pressure than driver originally intended. This means, the performance in this situation is worser than the driver would have got in mechanical back up.
[0022] In another example, in case of input rod sensor failure, the system cannot depend completely on master cylinder pressure sensor because a second failure of leakage in tandem master cylinder results the pressure drop in master cylinder pressure sensor. It is not possible to distinguish this pressure drop as driver release or leakage. This means in case if the real leakage occurs, the system will reduce the brake pressure and the performance in this situation would be worse than what the driver would have got in mechanical back up.
[0023] In order to solve the problem aforementioned, in the present invention during the sensors failure, the proposed brake by wire system will neither stay in “by wire mode” nor go to “mechanical backup”, rather the brake by wire system will go to another herein referred to as the “one circuit mode”. The driver request will be calculated from available sensors (either master cylinder sensor or input rod sensor) depending on the failure. By using the driver requested pressure the system will boost only one and the other will be coupled to the driver.
[0024] Referring to Figure 1, disclosed is a brake by wire system (10) comprising a controller(1) to enable a brake-by-wire functionality during a fault in at least one sensor (2,3, 4a, 4b), according to an embodiment of the present disclosure.
[0025] Disclosed is a controller (1) to enable a brake-by-wire functionality during a fault in at least one sensor (2,3, 4a, 4b) of a brake-by-wire system(10) of a vehicle. The controller may have an input/output interface, and associated memory to store a software logic. The controller may be a general electronic control unit for automobiles the applications of which are widely known in the art. The controller may further include a diagnostic unit for detection of any fault in the sensors associated with the brake by wire system of the vehicle. Said brake by wire system comprises a first brake circuit (5) with a first circuit separation valve (CSV1) (5a) and a second brake circuit (6) with a second circuit separation valve (CSV2) (6a).
[0026] From Figure 1, in an example, the at least one sensor (2) is an input rod sensor to monitor how much the brake pedal is applied by the driver and the at least one sensor (3) is a master cylinder pressure sensor to monitor the pressure in a tandem master cylinder (7). The tandem master cylinder may have two chambers 7a and 7b, connected to the first and second brake circuits. The first and second brake circuits (5, 6) are connected to the tandem master cylinder (as shown in Fig 1) through the respective first and second CSV (5a, 6a). A test separation valve (TSV) may separate the TMC from a brake fluid reservoir (15).
[0027] A pressure unit (8) comprising an actuator (8b) and a motor (8a) provides a target brake pressure. The actuator consists of a plunger piston system which in connected to the high dynamic motor using planetary gear. The pressure unit (8) further comprises a plunger supply pressure sensor (4a), the Motor current sensor (8d) and the motor position sensor (8c).. The pressure unit is connected to the first and second brake circuits (5,6) with the respective first and second plunger separation valves (PSV) (5b, 6b). When the system is in brake by wire mode (as explained above), the PSVs (5b, 6b) are kept open and the CSVs (5a,6a) are closed.

[0028] Further, The pedal (11) is coupled to the pedal feel simulator unit(16) through a simulator separation valve (SSV) (9a) when in By-wire mode. The pedal feel simulator (9) provides a comfortable pedal feel to the driver. The same is coupled with a simulator pressure sensor (4b). When the system is in mechanical mode (mechanical braking), the CSVs (5a, 6a) are opened and the PSVs (5b, 6b) and SSV (9) are closed. A person skilled in the art would appreciate that the brake by wire system also comprises the valves (12a, 12b, 12c, 12d) as the inlet valves and valves (13a, 13b,13c,13d) as the outlet valves for the base brakes (14a, 14b,14c,14d) of the vehicle. The same are not being described in detail for the sake of brevity.
[0029] Said controller is adapted to control the said first and second CSV (5a, 6a), and said at least one sensor (2,3,4a-b) comprising a healthy sensor and a unhealthy sensor. Said controller is configured to receive an input brake pressure request from the healthy sensor when the fault is detected in the unhealthy sensor. The controller enables a brake-by-wire functionality in the first brake circuit (5) and enables a mechanical braking functionality in the second brake circuit (6).
[0030] A person skilled in the art will appreciate that the brake-by-wire systems as known in the art comprise multiple valves and sensors which are controlled by the controller to enable a braking functionality.
[0031] A person skilled in the art would further appreciate that the aforementioned unhealthy/healthy sensors can in an example any one of the master cylinder pressure sensor (3) and the input rod sensor (2), that is, either one of the two can be unhealthy (faulty) so as to receive the input brake pressure request from the healthy (not faulty) sensor. The fault can occur in any of the two and the same is not be construed as limiting the scope of the invention.
[0032] The controller receives said input brake pressure request which is detected by the healthy sensor and based on the said input brake pressure request, the controller enables the mechanical braking functionality in the first brake circuit by signaling the actuator to actuate the opening of the first circuit separation valve and closing of the PSV (5b) and the controller enables the brake-by-wire functionality in the second brake circuit by signaling the actuator to actuate the closing of the second circuit separation valve and opening the second PSV (6b).
[0033] In an example, when a fault occurs in the at least one sensor (2,3), instead of switching completely to mechanical braking, the controller enables brake by wire functionality in the at least one circuit (5,6) and a mechanical braking functionality in the other brake circuit (5,6). The said event can be term as a ‘one circuit mode where the brake by wire functionality is being provided in a single circuit of the brake by wire system.
[0034] In an example, assuming that the sensor (2) is detected by the controller to be an unhealthy sensor (for instance, the input rod sensor (2) has a fault), the controller will enable the brake by wire functionality in the second circuit (6) and a mechanical braking functionality in the first circuit (5). In order to enable the brake by wire functionality in the second circuit (6), an input brake pressure request can be measured by the second sensor (the master cylinder pressure sensor (3)) being the healthy sensor. In an example, the pedal feel simulator (including the simulator pressure sensor (4b)) and the plunger supply pressure sensor(4c) can further be relied to calculate the input brake pressure request, provided there is no fault detected in the Pedal feel simulator or the Simulator separation valve and further no leakage in the tandem master cylinder. The simulator separation valve will be opened (provided there is no fault in the pedal feel simulator or the SSV (9) or no leakage in the tandem master cylinder). If a fault in the pedal feel simulator/SSV or a leakage in tandem master cylinder is known, the SSV (9) may remain closed. Based on the input brake pressure request, the controller can signal the motor and actuators in the pressure unit to provide a target brake pressure by providing the appropriate power to move the piston in a chamber of the tandem master cylinder. Further, the CSV (6a) will be closed. The first PSV (5b) will be open and the simulator separation valve(9a) will also be opened (provided there is no fault is the pedal feel simulator or the SSV or no leakage in the tandem master cylinder). If a fault in the pedal feel simulator unit (16) is known, the SSV (9) may remain closed. A mechanical braking in the first brake circuit (5)can be provided by the controller, by closing the opening CSV (5a) and closing the first PSV (5b). Therefore, the driver applied pressure is directly connected to the base brakes (14a-14d) of the vehicle. A person skilled in the art would appreciate that the controller is also adopted to control the inlet/outlet valves (12a-12d)/(13a-13d)the same can be opened or closed depending on the brake circuit(5,6) to which they are connected to in order to provide the required brake pressure to the wheels. The aforementioned example thus can advantageously provide the brake by wire functionality safely, in spite of a possible leakage in the tandem master cylinder.
[0035] In another example, assuming that the sensor (3) detected by the controller to be an unhealthy sensor (for instance, the master cylinder pressure sensor(3) has a fault), the controller will enable the brake by wire functionality in the second circuit (6) and a mechanical braking functionality in the first circuit (5). In order to enable the brake by wire functionality in the second circuit (6), an input brake pressure request can be measured by the first sensor (for instance the input rod sensor (2)) being the healthy sensor. In an example, the pedal feel simulator coupled with the simulator pressure sensor (4b) can further be relied to calculate the input brake pressure request, provided there is no fault detected in the Pedal feel simulator unit (16) and further no leakage in the tandem master cylinder. The simulator separation valve will be opened (provided there is no fault is the pedal feel simulator or the SSV or no leakage in the tandem master cylinder). If a fault in the pedal feel simulator/SSV or a leakage in tandem master cylinder is known, the SSV(9) may remain closed. Based on the input brake pressure request, the controller can signal the motor and actuators in the pressure unit to provide a target brake pressure by providing the appropriate power to move the piston in a chamber of the tandem master cylinder. Further, the CSV (6a) will be closed. PSV (6b) will be open and the simulator separation valve will also be opened (provided there is no fault is the pedal feel simulator or the SSV or no leakage in the tandem master cylinder). If a fault in the pedal feel simulator/SSV is known, the SSV may remain closed. A mechanical braking in the first brake circuit (5)can be provided by the controller, by opening the first CSV (5a) and closing the first PSV (5b). Therefore, the driver applied pressure is directly connected to the base brakes (14a-14d) of the vehicle. A person skilled in the art would appreciate that the controller is also adopted to control the inlet/outlet valves (12a-12d)/(13a-13d)the same can be opened or closed depending on the brake circuit(5,6) to which they are connected to provide the brake pressure to the wheels (15). The aforementioned example thus can advantageously provide the brake by wire functionality safely, in spite of a possible leakage in the tandem master cylinder and a fault in the pedal feel simulator or the simulator separation valve.
[0036] Referring to Figure 2, the same depicts a method to enable a brake-by-wire functionality during a fault in at least one sensor of a brake-by-wire system of a vehicle. To implement the method, the Brake by wire system (10) and the controller (1) may be used (as described in Fig 1) may be used. The brake by wire system (10) as described in Figure 1 comprises a first brake circuit {5}with a first circuit separation valve (CSV) {5a} (see Figure 1) and a second brake circuit {6} with a second circuit separation valve (CSV){6a}. A controller is adapted to control the said first and second CSV{5a,6a} and said at least one sensor{2,3}, said at least one sensor comprising any one of a healthy sensor and an unhealthy sensor. The method (100) to enable a brake-by-wire functionality during the fault in said at least one sensor of the brake-by-wire comprises the first step (101) of receiving by the controller an input brake pressure request from the healthy sensor when the fault is detected in the unhealthy sensor. Followed by the step (102) of enabling a brake-by-wire functionality, by the controller, at least one of the first brake circuit and second brake circuit and the step (103) of enabling a mechanical braking functionality, by the controller, at least one of the first brake circuit and second brake circuit. In the method (101) the detection of said input brake pressure is requested by the healthy sensor. In the method (102) enabling the mechanical braking functionality in the second brake circuit is done by the controller, by signaling the actuator to actuate the opening of at least one of the first and second circuit separation valve. Similarly in the method (103) enabling the brake-by-wire functionality in the second brake circuit done by the controller, by signaling the actuator to actuate the closing of at least one of the first and second circuit separation valve.
[0037] The disclosure advantageously provides the brake boost even in case of sensor failures in the brake by wire systems, including any latent failures such as tandem master cylinder leakage(7) and fault in the pedal feel simulator unit (16).
, Claims:
WE CLAIM:
1. A controller (1) to enable a brake-by-wire functionality during a fault in at least one sensor (2,3) of a brake-by-wire system (10) of a vehicle, said brake by wire system comprising:
- a first brake circuit(5) with a first circuit separation valve (CSV) (5a),
-a second brake circuit (6)with a second circuit separation valve (CSV) (6a),
-said controller adapted to control the said first and second CSV (5a, 6a), and said at least one sensor (2,3, 4a, 4b) comprising a healthy sensor (2,3) and a unhealthy sensor (2,3),
characterized in that,
said controller configured to:
-receive an input brake pressure request from the healthy sensor when the fault is detected in the unhealthy sensor ;
-enable a brake-by-wire functionality in any one of the first brake circuit (5) and the second brake circuit (6);and
-enable a mechanical braking functionality in any one of the second brake circuit (6) and the first brake circuit.

2. The controller (1) as claimed in Claim 1, wherein, said input brake pressure request is detected by the healthy sensor during a fault in the unhealthy sensor.

3. The controller(1) as claimed in Claim 1, wherein, the controller enables the brake by wire functionality based on said input brake pressure request detected by the healthy sensor.

4. The controller as claimed in Claim 1, wherein, the controller (1) enables the mechanical braking functionality in any one of the first brake(5) and the second brake circuit (6) by signaling the actuator to actuate the opening of at least one of the first (5a) and second circuit separation valve (6a).

5. The controller as claimed in Claim 1, wherein, the controller enables the brake-by-wire functionality in any one of the first and second brake circuit by signaling the actuator to actuate the closing of the at least one of the first and second circuit separation valve (5a, 6a).

6. A method (100) to enable a brake-by-wire functionality during a fault in at least one sensor of a brake-by-wire system of a vehicle, said brake by wire system comprising:

-a first brake circuit with a first circuit separation valve (CSV),

-a second brake circuit with a second circuit separation valve (CSV),

-a controller adapted to control the said first and second CSV, and said at least one sensor, said at least one sensor comprising a healthy sensor and an unhealthy sensor;

the method(100) characterized by the steps of,

-receiving by the controller an input brake pressure request from the healthy sensor when the fault is detected in the unhealthy sensor (101);

-enabling a brake-by-wire functionality, by the controller, in any one of the first brake circuit and second brake circuit (102) and;

-enabling a mechanical braking functionality, by the controller, any one of the first brake circuit and second brake circuit (103).

7. The method(100) as claimed in Claim 7, detecting said input brake pressure request by the healthy sensor.

8. The method(100) as claimed in Claim 7, wherein, enabling the mechanical braking functionality in the second brake circuit by the controller, by signaling the actuator to actuate the opening of at least one of the first and second circuit separation valve.

9. The method(100) as claimed in Claim 7, wherein, enabling the brake-by-wire functionality in the second brake circuit by the controller, by signaling the actuator to actuate the closing of at least one of the first and second circuit separation valve.