VEHICLE BRAKING DEVICE AND FAILURE DETERMINATION METHOD THEREFOR

A vehicle braking device includes a braking actuator, a hydraulic pressure generation device, a hydraulic pressure sensor, and an electronic control unit. The electronic control unit is configured to execute an upstream pressure maintaining process of controlling the hydraulic pressure generation device to increase and maintain the upstream hydraulic pressure, a downstream pressurization process of controlling the braking actuator such that hydraulic fluid is supplied to the wheel cylinder through the hydraulic pressure flow path in a state in which the upstream hydraulic pressure is maintained, and a failure determination process of determining that a failure has occurred in the braking actuator in a case where the upstream hydraulic pressure is not decreased to be equal to or lower than a determination threshold value as the downstream pressurization process is executed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-045818 filed on Mar. 22, 2022, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a vehicle braking device and a failure determination method therefor.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2010-042744 (JP 2010-042744 A) discloses a vehicle braking device. The vehicle braking device includes a hydraulic actuator. The hydraulic actuator appropriately adjusts a hydraulic pressure of brake fluid supplied from a power hydraulic pressure source or a master cylinder unit and sends the adjusted hydraulic pressure to a wheel cylinder. In the vehicle braking device, a plurality of hydraulic pressure sensors provided in hydraulic pressure pipes for supplying the hydraulic pressure to the wheel cylinder are used to detect an abnormality in the hydraulic actuator. Specifically, the abnormality detection is executed based on a relative relationship between output values of the hydraulic pressure sensors.

SUMMARY

As described above, in the abnormality detection of the hydraulic actuator (braking actuator) in the vehicle braking device disclosed in JP 2010-042744 A, the relative relationship between the output values of the hydraulic pressure sensors provided in the hydraulic pressure pipes for supplying the hydraulic pressure to the wheel cylinder is needed. Such a configuration leads to an increase in a cost of the vehicle braking device.

The present disclosure has been made in view of the problems described above, and is to enable to make a failure determination for a braking actuator that controls a hydraulic pressure in a wheel cylinder by using an upstream hydraulic pressure supplied to the braking actuator.

A first aspect of the present disclosure relates to a vehicle braking device includes a braking actuator, a hydraulic pressure generation device, a hydraulic pressure sensor, and an electronic control unit. The braking actuator is configured to control a hydraulic pressure in a wheel cylinder. The hydraulic pressure generation device is connected to the braking actuator through a hydraulic pressure flow path and is configured to execute increasing and maintaining an upstream hydraulic pressure supplied to the braking actuator through the hydraulic pressure flow path. The hydraulic pressure sensor is configured to detect the upstream hydraulic pressure. The electronic control unit is configured to execute an upstream pressure maintaining process of controlling the hydraulic pressure generation device to increase and maintain the upstream hydraulic pressure. The electronic control unit is configured to execute a downstream pressurization process of controlling the braking actuator such that hydraulic fluid is supplied to the wheel cylinder through the hydraulic pressure flow path in a state in which the upstream hydraulic pressure is maintained. The electronic control unit is configured to execute a failure determination process of determining that a failure has occurred in the braking actuator in a case where the upstream hydraulic pressure is not decreased to be equal to or lower than a determination threshold value as the downstream pressurization process is executed.

A second aspect of the present disclosure relates to a failure determination method for a vehicle braking device is a method of determining the presence or absence of a failure of a vehicle braking device including a braking actuator configured to control a hydraulic pressure in a wheel cylinder, a hydraulic pressure generation device connected to the braking actuator through a hydraulic pressure flow path and configured to execute increasing and maintaining an upstream hydraulic pressure supplied to the braking actuator through the hydraulic pressure flow path, and a hydraulic pressure sensor configured to detect the upstream hydraulic pressure. The failure determination method includes an upstream pressure maintaining process of controlling the hydraulic pressure generation device to increase and maintain the upstream hydraulic pressure. The failure determination method includes a downstream pressurization process of controlling the braking actuator such that hydraulic fluid is supplied to the wheel cylinder through the hydraulic pressure flow path in a state in which the upstream hydraulic pressure is maintained. The failure determination method includes a failure determination process of determining that a failure has occurred in the braking actuator in a case where the upstream hydraulic pressure is not decreased to be equal to or lower than a determination threshold value as the downstream pressurization process is executed.

According to the present disclosure, the failure determination for the braking actuator can be made by using the hydraulic pressure sensor that detects the upstream hydraulic pressure supplied to the braking actuator. That is, the failure determination for the braking actuator can be made without including the hydraulic pressure sensors that directly detect individual wheel cylinder pressures.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present disclosure will be described with reference to the accompanying drawings. Note that, in a case where the number, a quantity, an amount, a range, and the like of each element are described in the following embodiment, the technical idea according to the present disclosure is not limited to the described numerical values except for a case of being particularly pointed out or a case of being clearly specified in principle by the described numerical values.

1. Configuration of Vehicle Braking Device

FIG.1is a diagram showing a configuration of a vehicle braking device10according to an embodiment. The vehicle braking device10shown inFIG.1is mounted on a vehicle and brakes the vehicle. The vehicle braking device10includes a hydraulic pressure generation device12, a braking actuator14, a braking mechanism16, and an electronic control unit (ECU)18.

The braking mechanism16is, for example, a disc type, and is provided individually for each of wheels1FL,1FR,1RL,1RR of the vehicle. The braking mechanism16includes wheel cylinders16FL,16FR,16RL,16RR corresponding to the wheels1FL,1FR,1RL,1RR, respectively.

The hydraulic pressure generation device12includes a master cylinder20and is configured to generate a hydraulic pressure in response to an operation of a brake pedal2as a braking operation member. In addition, the hydraulic pressure generation device12also includes a servo pressure generation device22that can generate the hydraulic pressure without depending on the operation of the brake pedal2. The braking actuator14receives the supply of the hydraulic pressure from the hydraulic pressure generation device12.

The hydraulic pressure generation device12and the braking actuator14are controlled by the ECU18. By actuating the hydraulic pressure generation device12by the ECU18, the hydraulic pressures (wheel cylinder pressures Pwc) of hydraulic fluid in all the wheel cylinders16FL,16FR,16RL,16RR can be collectively controlled. In addition, the braking actuator14is configured to individually control the wheel cylinder pressures Pwc of the wheel cylinders16FL,16FR,16RL,16RR by controlling the hydraulic pressure supplied from the hydraulic pressure generation device12.

The ECU18controls actuations of the hydraulic pressure generation device12and the braking actuator14. Specifically, the ECU18includes a processor, a storage device, and an input/output interface. The input/output interface takes in sensor signals from sensors (hydraulic pressure sensors70,74, upstream hydraulic pressure sensors100,102, and the like described below) attached to the vehicle, and outputs operation signals to the hydraulic pressure generation device12and the braking actuator14. The processor executes various processes related to control of the hydraulic pressure generation device12and the braking actuator14. The storage device stores various programs and various data (including maps) used for the process by the processor. The process by the ECU18is realized by the processor reading out the program from the storage device and executing the read out program.

Note that a plurality of ECUs18may be provided. For example, the ECU18may include an ECU that controls the actuation of the hydraulic pressure generation device12and an ECU that controls the actuation of the braking actuator14. More specifically, the hydraulic pressure generation device12and the braking actuator14may be configured as separate units. For example, the hydraulic pressure generation device12is configured as one unit with the ECU that controls the actuation of the hydraulic pressure generation device12, and the braking actuator14may be configured as another unit with the ECU that controls the actuation of the braking actuator14.

1-1. Hydraulic Pressure Generation Device

As described above, the hydraulic pressure generation device12includes the master cylinder20and the servo pressure generation device22. The master cylinder is connected to the braking actuator14through hydraulic pressure flow paths24,26. Note that, in the description of the master cylinder20, as shown inFIG.1, a left side of a paper surface is referred to as a front side, and a right side of the paper surface is referred to as a rear side.

The master cylinder20has a cylinder body28. An inside of the cylinder body28is partitioned into a front chamber and a rear chamber by a partition wall30having an annular shape. A first master piston32and a second master piston34are disposed in the front chamber. An input piston36having a rear end portion coupled to the brake pedal2is disposed in the rear chamber. The first master piston32and the second master piston34each move forward to pressurize the hydraulic fluid and supply the pressurized hydraulic fluid to the braking actuator14through hydraulic pressure flow paths24,26. The input piston36moves forward by a brake operation force applied to the brake pedal2.

The first master piston32penetrates the partition wall30and protrudes into the rear chamber. An inter-piston chamber38is formed between the first master piston32and the input piston36. In addition, the first master piston32also has a flange portion40formed to face the partition wall30on a side of the front chamber. A servo chamber42having an annular shape is formed between the flange portion40and the partition wall30. The hydraulic fluid of which the pressure is adjusted by the servo pressure generation device22is introduced into the servo chamber42.

On the other hand, on a front side of the flange portion40, a facing chamber44having an annular shape and facing the servo chamber42with the flange portion40therebetween is formed. The inter-piston chamber38and the facing chamber44are connected by the hydraulic pressure flow path46. An electromagnetic valve48is disposed in the hydraulic pressure flow path46. In addition, the hydraulic pressure flow path46is connected to a first end of the hydraulic pressure flow path50between the facing chamber44and the electromagnetic valve48. A second end side of the hydraulic pressure flow path50is branched into two branches, one of which is connected to a regulator62and the other of which is connected to a reaction force generation device51including a stroke simulator. The electromagnetic valve54is disposed in the hydraulic pressure flow path50after being branched to a side of the regulator62.

The servo pressure generation device22includes a power hydraulic pressure source56, a pressure increase valve58, a pressure decrease valve60, and the regulator62of a mechanical type. The power hydraulic pressure source56generates a high hydraulic pressure independently of a brake operation of a driver by supplying power. The pressure increase valve58is a normally closed type linear electromagnetic valve. The pressure decrease valve60is a normally open type linear electromagnetic valve.

The power hydraulic pressure source56includes an electric motor64, a pump66for servo, an accumulator68, and the hydraulic pressure sensor70that detects the hydraulic pressure in the accumulator68(accumulator pressure Pa). The pump66is driven by the electric motor64to pump up the hydraulic fluid from an atmospheric pressure reservoir52and pressurize the hydraulic fluid. The accumulator68stores the hydraulic fluid pressurized by the pump66. The ECU18controls the actuation of the pump66by controlling the electric motor64such that the accumulator pressure detected by the hydraulic pressure sensor70falls within a set range. The high-pressure hydraulic fluid in the accumulator68is supplied to the regulator62. The regulator62adjusts the pressure of the supplied hydraulic fluid and supplies the adjusted hydraulic fluid to the master cylinder20.

An operation mode of the vehicle braking device10controlled by the ECU18include a linear mode. In the linear mode, the inter-piston chamber38and the facing chamber44are communicated with each other by opening the electromagnetic valve48. In addition, by closing the electromagnetic valve54, the communication between the facing chamber44and the atmospheric pressure reservoir52through the regulator62is cut off. By controlling opening degrees of the pressure increase valve58and the pressure decrease valve60in the control state, a servo pressure Psv that is the hydraulic pressure in the servo chamber42in the master cylinder20is controlled. The servo pressure Psv is detected by the hydraulic pressure sensor74disposed in the hydraulic pressure flow path72connecting the regulator62and the servo chamber42to each other.

The rear chamber inside the cylinder body28includes a first master chamber76and a second master chamber78. The first master chamber76is formed by being partitioned by the cylinder body28, the first master piston32, and the second master piston34. The second master chamber78is adjacent to the first master chamber76through the second master piston34and is formed by being partitioned by the cylinder body28and the second master piston34.

In a case where the servo pressure Psv is increased by controlling the pressure increase valve58and the pressure decrease valve60, both the first master piston32and the second master piston34move toward the front side. As a result, the communication between the atmospheric pressure reservoir52and each of the master chambers76,78is released, and the hydraulic pressure (master cylinder pressure Pmc) in each of the master chambers76,78is increased. On the other hand, in a case where the servo pressure Psv is decreased by controlling the pressure increase valve58and the pressure decrease valve60, both the first master piston32and the second master piston34move toward the rear side. As a result, the master cylinder pressure Pmc in each of the master chambers76,78is decreased.

As described above, with the servo pressure generation device22, the master cylinder pressure Pmc in each of the master chambers76,78can be controlled by controlling the pressure increase valve58and the pressure decrease valve60to control the servo pressure Psv. Moreover, the master cylinder pressures Pmc in the master chambers76,78are supplied to the braking actuator14through the hydraulic pressure flow paths24,26, respectively. Therefore, the master cylinder pressure Pmc corresponds to an example of an “upstream hydraulic pressure” according to the present disclosure.

More specifically, the master cylinder20is configured such that the master cylinder pressures Pmc in all the master chambers76,78controlled as described above are substantially equal. Therefore, the master cylinder pressures Pmc (upstream hydraulic pressure) supplied to first and second control systems80,90described below of the braking actuator14through the hydraulic pressure flow paths24,26, respectively, are also substantially equal.

Moreover, with the hydraulic pressure generation device12, the master cylinder pressure Pmc (upstream hydraulic pressure) increased by increasing the servo pressure Psv as described above can be maintained. Specifically, the ECU18closes (more specifically, fully closes) the pressure decrease valve60of the servo pressure generation device22in a state in which the upstream hydraulic pressure is increased (that is, in a state in which the hydraulic fluid in the hydraulic pressure generation device12is pressurized). As a result, the hydraulic fluid can be contained in the inside of each of the master chambers76,78and the inside of each of the hydraulic pressure flow paths24,26and the braking actuator14positioned on a downstream side thereof. That is, the master cylinder pressure Pmc (upstream hydraulic pressure) is maintained.

The braking actuator14includes the first control system80and the second control system90. The first control system80receives the supply of the master cylinder pressure Pmc from the first master chamber76through the hydraulic pressure flow path24, and controls the wheel cylinder pressures Pwc of the wheel cylinders16FR,16FL corresponding to the right and left front wheels1FR,1FL. On the other hand, the second control system90receives the supply of the master cylinder pressure Pmc from the second master chamber78through the hydraulic pressure flow path26, and controls the wheel cylinder pressures Pwc of the wheel cylinders16RR,16RL corresponding to the right and left rear wheels1RR,1RL.

The first control system80includes pressure increase valves81FL,81FR, pressure decrease valves82FL,82FR, a reservoir83, a pump84, and an electromagnetic valve85. The pressure increase valves81FL,81FR are normally open type electromagnetic valves. The pressure decrease valves82FL,82FR are normally closed type electromagnetic valves. The braking actuator14includes an electric motor79that drives the pump84. In the configuration example shown inFIG.1, the electric motor79is shared between the first control system80and the second control system90, and also drives a pump94of the second control system90. Instead of such an example, the electric motors that drive the pumps84,94may be provided separately. The electromagnetic valve85is a normally open type.

The first control system80includes a hydraulic pressure flow path86having a first end connected to the hydraulic pressure flow path24from the master cylinder20. The hydraulic pressure flow path86is branched as branch flow paths86FL,86FR on the way. The branch flow paths86FL,86FR are connected to the wheel cylinders16FL,16FR, respectively. Therefore, the master cylinder pressure Pmc from the master cylinder20is transmitted to each of the wheel cylinders16FL,16FR through the hydraulic pressure flow path86. The pressure increase valves81FL,81FR are disposed in the branch flow paths86FL,86FR, respectively.

In addition, the first control system80also includes a hydraulic pressure flow path87. The hydraulic pressure flow path87connects each of the branch flow path86FL between the pressure increase valve81FL and the wheel cylinder16FL and the branch flow path86FR between the pressure increase valve81FR and the wheel cylinder16FR to each of the reservoir83and an inlet of the pump84. The pressure decrease valves82FL,82FR are disposed in the hydraulic pressure flow path87at locations at which the hydraulic pressures in the branch flow paths86FL,86FR can be decreased. An outlet of the pump84is connected to the hydraulic pressure flow path86through the hydraulic pressure flow path88on an upstream side of the pressure increase valves81FL,81FR (close side to the master cylinder20).

The electromagnetic valve85is disposed in the hydraulic pressure flow path86on the upstream side of the pressure increase valves81FL,81FR. In an open state, the electromagnetic valve85allows a communication state between a side of the master cylinder20and a side of the wheel cylinder16FL. In the communication state, the master cylinder pressure Pmc and the wheel cylinder pressure Pwc are substantially equal. In addition, in a closed state, the electromagnetic valve85cuts off the communication.

The reservoir83is connected to the hydraulic pressure flow path86on an upstream side of the electromagnetic valve85through the hydraulic pressure flow path89. The reservoir83is configured as follows. That is, when the pump84is not actuated, the reservoir83cuts off the communication between the hydraulic pressure flow path89and the hydraulic pressure flow paths87,88. On the other hand, when the pump84is actuated, a piston83ain the reservoir83is operated to ensure the communication. As a result, the hydraulic fluid is supplied from the hydraulic pressure flow path24to the hydraulic pressure flow path88through the hydraulic pressure flow path89and the hydraulic pressure flow path87.

The second control system90includes pressure increase valves91RL,91RR, pressure decrease valves92RL,92RR, a reservoir93, the pump94, an electromagnetic valve95, a hydraulic pressure flow path96(including branch flow paths96RL,96RR), hydraulic pressure flow paths97,98,99. Since such a configuration of the second control system90is the same as the configuration of the first control system80, the detailed description thereof will be omitted.

With the braking actuator14configured as described above, for execution of various braking controls, such as vehicle stability control (VSC) and anti-lock brake control (ABS control), the wheel cylinder pressures Pwc of all the wheel cylinders16FL,16FR,16RL,16RR can be controlled individually.

In addition, with the braking actuator14, the electric motor79is driven to actuate the pumps84,94in a state in which opening degrees of the electromagnetic valves85,95are made smaller than in a fully open state, so that the hydraulic fluid inside the braking actuator14can be pressurized by the braking actuator14alone.

1-3. Upstream Hydraulic Pressure Sensor

The vehicle braking device10includes upstream hydraulic pressure sensors100,102.

The upstream hydraulic pressure sensor100detects the upstream hydraulic pressure (master cylinder pressure Pmc) supplied from the first master chamber76to the first control system80of the braking actuator14. As an example, the upstream hydraulic pressure sensor100is attached to the hydraulic pressure flow path24. Instead of such an example, the upstream hydraulic pressure sensor100may be attached to the hydraulic pressure flow path86on the upstream side of the electromagnetic valve85, or may be attached to the cylinder body28to directly detect the master cylinder pressure Pmc in the first master chamber76.

Similarly, the upstream hydraulic pressure sensor102detects the upstream hydraulic pressure supplied from the second master chamber78to the second control system90of the braking actuator14. As an example, the upstream hydraulic pressure sensor102is attached to the hydraulic pressure flow path26. Instead of such an example, the upstream hydraulic pressure sensor102may be attached to the hydraulic pressure flow path96on the upstream side of the electromagnetic valve95, or may be attached to the cylinder body28to directly detect the master cylinder pressure Pmc in the second master chamber78.

Note that, in the example in which the hydraulic pressure generation device12and the braking actuator14are configured as separate units, the upstream hydraulic pressure sensors100,102may be incorporated in a unit on a side of the braking actuator14, or may be incorporated in a unit on a side of the hydraulic pressure generation device12.

2. Failure Determination for Braking Actuator

For detection of a failure of the braking actuator14, the ECU18sequentially executes an “upstream pressure maintaining process”, a “downstream pressurization process”, and a “failure determination process” described below.

In the upstream pressure maintaining process, the hydraulic pressure generation device12is controlled to increase and maintain the upstream hydraulic pressure (master cylinder pressure Pmc). In the downstream pressurization process, the braking actuator14is controlled such that the hydraulic fluid is supplied to each of the wheel cylinders16FL,16FR,16RL,16RR through the hydraulic pressure flow paths24,26in a state in which the upstream hydraulic pressure is maintained by the upstream pressure maintaining process. More specifically, by maintaining the upstream hydraulic pressure by the upstream pressure maintaining process while increasing the upstream hydraulic pressure, the hydraulic fluid can be well supplied to the braking actuator14from the side of each of the master chambers76,78that are in a sealed state by the control of the braking actuator14in the downstream pressurization process that is subsequently executed. Moreover, in the failure determination process, in a case where the upstream hydraulic pressure is not decreased to be equal to or lower than a determination threshold value THpmc as the downstream pressurization process is executed, a determination is made that the failure has occurred in the braking actuator14.

More specifically, in the failure determination process according to the present embodiment, in a case where the upstream hydraulic pressure is not decreased to be equal to or lower than the determination threshold value THpmc when predetermined time T has elapsed from the start of the downstream pressurization process, a determination is made that the failure has occurred in the braking actuator14.

FIG.2is a flowchart showing a flow of a process related to the failure determination for the braking actuator14according to the embodiment. The process of the flowchart is executed, for example, in a case where a predetermined execution condition related to the failure determination is satisfied while the vehicle is stopped.FIG.3is a time chart showing behavior of the master cylinder pressure Pmc and the wheel cylinder pressure Pwc during the execution of the failure determination for the braking actuator14according to the embodiment.

The processes of steps S100to S104inFIG.2correspond to the upstream pressure maintaining process.

First, in step S100, the ECU18(processor) controls the hydraulic pressure generation device12such that the master cylinder pressure Pmc (upstream hydraulic pressure) is increased to a predetermined value Pmc1. Specifically, the ECU18increases the master cylinder pressure Pmc by controlling the opening degrees of the pressure increase valve58and the pressure decrease valve60provided in the servo pressure generation device22to increase the servo pressure Psv. Note that the ECU18drives the electric motor64to actuate the pump66in a case where it is needed to increase the accumulator pressure Pa to increase the master cylinder pressure Pmc to the predetermined value Pmc1.

Next, in step S102, the ECU18determines whether or not the master cylinder pressure Pmc is increased to the predetermined value Pmc1. As a result, in a case where a determination result is Yes (Pmc>Pmc1), the process proceeds to step S104.

In step S104, the ECU18(fully) closes the pressure decrease valve60of the servo pressure generation device22such that the master cylinder pressure Pmc is maintained at the predetermined value Pmc1. In a case where the pump66is actuated in step S100, the actuation of the pump66is stopped. As a result, a state is obtained in which the master cylinder pressure Pmc (upstream hydraulic pressure) is maintained at the predetermined value Pmc1.

Next, in step S106, the ECU18executes the downstream pressurization process. Specifically, in the downstream pressurization process, the ECU18controls the braking actuator14as follows in the state in which the master cylinder pressure Pmc is maintained at the predetermined value Pmc1as at point in time t1inFIG.3. That is, the ECU18drives the electric motor79to actuate the pumps84,94while controlling the opening degrees of the electromagnetic valves85,95to be smaller than in the fully open state. As a result, a differential pressure can be formed such that each wheel cylinder pressure Pwc is higher than the master cylinder pressure Pmc.

Next, the processes of steps S108to S114inFIG.2correspond to the failure determination process.

In a case where the downstream pressurization process is executed as described above, the hydraulic fluid is pressure-fed by the pumps84,94and supplied to each of the wheel cylinders16FL,16FR,16RL,16RR from the side of the master cylinder through the hydraulic pressure flow paths24,26. As a result, in a case where the braking actuator14is normal, the hydraulic fluid inside the braking actuator14is pressurized. That is, as indicated by a solid line in a lower part ofFIG.3, each wheel cylinder pressure Pwc is increased after the elapse of point in time t1.

Moreover, the hydraulic fluid needed to pressurize the braking actuator14is drawn into the braking actuator14from the master cylinder20(hydraulic pressure generation device12) that maintains the pressurized hydraulic fluid. Therefore, in a case where the hydraulic fluid is normally pressurized by the braking actuator14, the master cylinder pressure Pmc is decreased as indicated by a solid line in an upper part ofFIG.3. Therefore, the behavior (increase) of the wheel cylinder pressure Pwc can be grasped in a simulated manner by using the behavior (decrease) of the master cylinder pressure Pmc.

On the other hand, in a case where some kind of failure (for example, a failure of a component of the braking actuator14, such as the pumps84,94or the electromagnetic valves85,95) has occurred in the braking actuator14, for example, as indicated by a dashed line in the lower part ofFIG.3, the wheel cylinder pressure Pwc is solely increased to a value lower than in the normal. Alternatively, depending on an aspect of the failure, the wheel cylinder pressure Pwc may not be substantially increased. Moreover, along with the above, as shown by a dashed line in the upper part ofFIG.3, the master cylinder pressure Pmc on the upstream side is solely decreased to a value higher than in the normal. Alternatively, depending on the aspect of the failure, the master cylinder pressure Pmc may not be substantially decreased.

As described above, the influence of the failure of the braking actuator14on the pressurization of the braking actuator14by the downstream pressurization process executed along with the upstream pressure maintaining process is exerted on the master cylinder pressure Pmc on the upstream side in addition to the wheel cylinder pressure Pwc inside the braking actuator14. Therefore, the upstream hydraulic pressure sensors100,102are used in the failure determination process according to the present embodiment to enable the detection of the failure of the braking actuator14without the detection of each wheel cylinder pressure Pwc.

Here, as indicated by the solid line in the lower part ofFIG.3, the wheel cylinder pressure Pwc is increased with a delay after the start of the downstream pressurization process, and eventually is fixed. Correspondingly, as indicated by the solid line in the upper part ofFIG.3, the master cylinder pressure Pmc is decreased with a delay after the start of the downstream pressurization process, and eventually is fixed. In addition, a virtual determination threshold value curve (chain line) is shown in the lower part ofFIG.3. The virtual determination threshold value curve indicates a change in the wheel cylinder pressure Pwc that occurs at the latest and at least, in consideration of various variation factors in a case where the failure has not occurred in the braking actuator14. The upper part ofFIG.3shows the determination threshold value curve (chain line) specified corresponding to the virtual determination threshold value curve.

From the above, basically, in a case where the master cylinder pressure Pmc is lower than the determination threshold value curve, a determination can be made that the braking actuator14is normal, and in a case where the master cylinder pressure Pmc is not lower than the determination threshold value curve, a determination can be made that the failure has occurred in the braking actuator14. However, as shown in the upper part ofFIG.3, since a decrease amount of the master cylinder pressure Pmc is small immediately after the start of the downstream pressurization process, in a case where the failure determination is made based on the value of the master cylinder pressure Pmc immediately after the start, there is a probability that an erroneous determination is made.

In view of the above points, it is desirable to make the failure determination of the braking actuator14at a timing at which a determination can be made that the master cylinder pressure Pmc has finished decreasing sufficiently after the start of the downstream pressurization process in a case where the braking actuator14is normal. Therefore, in step S108, the ECU18determines whether or not predetermined time T has elapsed from the start of the downstream pressurization process in step S106(point in time t1inFIG.3). Predetermined time T is experimentally acquired in advance and stored in the storage device of the ECU18such that the timing (for example, point in time t2inFIG.3) can be specified.

After predetermined time T has elapsed in step S108, the process proceeds to step S110. In step S110, the ECU18determines whether or not the master cylinder pressure Pmc is decreased to be equal to or lower than the determination threshold value THpmc. The determination threshold value THpmc is a value on the determination threshold value curve at a point in time when predetermined time T has elapsed (point in time t2inFIG.3), and is acquired in advance and stored in the storage device of the ECU18.

In the example of the vehicle braking device10having the configuration shown inFIG.1, the determination in step S110is made for each of the first and second control systems80,90of the braking actuator14. That is, in step S110, the ECU18determines whether or not the master cylinder pressure Pmc detected by each of the upstream hydraulic pressure sensors100,102is equal to or lower than the determination threshold value THpmc.

Note that, in the example of the vehicle braking device including the hydraulic pressure flow path that can be communicated between the hydraulic pressure flow paths24,26that supply the upstream hydraulic pressure to each of the first and second control systems80,90, and the hydraulic pressure sensor attached to the hydraulic pressure flow path, the failure determination for both the first and second control systems80,90may be made by using the hydraulic pressure sensor (that is, one upstream hydraulic pressure sensor).

In a case where the determination results of both the first and second control systems80,90are Yes (Pmc THpmc) in step S110, the process proceeds to step S112, and the ECU18determines that the braking actuator14is normal.

On the other hand, in a case where the determination result of one or both of the first and second control systems80,90is No (Pmc>THpmc) in step S110, the process proceeds to step S114, and the ECU18determines that the failure has occurred in the braking actuator14.

As described above, with the vehicle braking device10according to the present embodiment, the upstream pressure maintaining process, the downstream pressurization process, and the failure determination process are sequentially executed by cooperatively driving the hydraulic pressure generation device12on the upstream side and the braking actuator14on the downstream side. As a result, the failure determination of the braking actuator14can be made by using each of the upstream hydraulic pressure sensors100,102that detect the master cylinder pressure Pmc (upstream hydraulic pressure) supplied to the braking actuator14(that is, indirectly). With such a method, the failure determination of the braking actuator14can be made without including a plurality of hydraulic pressure sensors that directly detects the individual wheel cylinder pressures Pwc (that is, while suppressing an increase in cost).

More specifically, with the failure determination process according to the present embodiment, in a case where the master cylinder pressure Pmc (upstream hydraulic pressure) is not decreased to be equal to or lower than the determination threshold value THpmc when predetermined time T has elapsed from the start of the downstream pressurization process, a determination is made that the failure has occurred in the braking actuator14. As a result, the failure determination can be made more accurately in consideration of the behavior (seeFIG.3) of the wheel cylinder pressure Pwc and the master cylinder pressure Pmc as the upstream pressure maintaining process and the downstream pressurization process are executed.

4. Another Configuration Example of the Hydraulic Pressure Generation Device

In the hydraulic pressure generation device12having the configuration shown inFIG.1described above, each of the first and second control systems80,90of the braking actuator14receives the supply of the “upstream hydraulic pressure” through the master cylinder20(first and second master chambers76,78). Instead of such an example, in the “braking actuator” according to the present disclosure, one of the first and second control systems may be configured to receive the supply of the upstream hydraulic pressure without going through the master cylinder. Specifically, for example, one of the first and second control systems may be configured to directly receive the supply of the hydraulic fluid pressurized by the power hydraulic pressure source (for example, the power hydraulic pressure source56shown inFIG.1) provided in the hydraulic pressure generation device without going through the master cylinder. In such a configuration, the hydraulic pressure supplied from the power hydraulic pressure source to one of the first and second control systems corresponds to another example of the “upstream hydraulic pressure” according to the present disclosure.