Patent ID: 12227155

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring to the drawings, there will be described in detail a brake device1for a vehicle according to one embodiment of the present disclosure. It is to be understood that the present disclosure is not limited to the details of following embodiment but may be embodied with various changes and modifications based on the knowledge of those skilled in the art.

A. Configuration of Brake Device

Referring to a hydraulic circuit diagram ofFIG.1, there will be described a configuration of the brake device1according to one embodiment of the present disclosure. The brake device1is configured to apply a braking force to each of four wheels, i.e., front right and left wheels and rear right and left wheels. As apparent fromFIG.1, the brake device1includes wheel brake devices90FL,90FR,90RL,90RR respectively provided for a front left wheel, a front right wheel, a rear left wheel, and a rear right wheel. (Hereinafter, the brake devices90FL,90FR,90RL,90RR will be each referred to as “wheel brake device90” where appropriate.)

As illustrated inFIG.2, the wheel brake device90has an ordinary configuration. For instance, the wheel brake device90includes a disc rotor91that rotates with the corresponding wheel and a brake caliper92supported by a carrier that rotatably holds the wheel. The brake caliper92includes brake pads93, a wheel cylinder94to which a fluid is supplied, and an actuator96. The actuator96includes a piston95. The actuator96is configured to move the piston95by a pressure of the fluid supplied to the wheel cylinder94so as to press the brake pad93against the disc rotor91. The piston95moves in accordance with a pressure in a hydraulic-pressure chamber94aformed in the wheel cylinder94. The hydraulic-pressure chamber94ais defined by the piston95and the wheel cylinder94. To the hydraulic-pressure chamber94a, the fluid is supplied from the second system14.FIG.2illustrates a configuration of the wheel brake device90RR,90RL provided for the rear wheel. The wheel brake device90RR,90RL is provided with an electric parking brake11, which will be later described.

The brake device1includes a first system12and a second system14. In terms of a flow of the fluid supplied to the wheel brake devices90, the first system12may be referred to as an upstream system, and the second system14may be referred to as a downstream system. As later described, the fluid supplied from the first system12is supplied to the wheel cylinders94via the second system14. The brake device1includes a brake pedal16, which is one example of a brake operating member.

The first system12includes: a reservoir20in which the fluid is stored at atmospheric pressure; a first pump device22for pumping up the fluid in the reservoir20; a master cylinder28to which the brake pedal16is coupled; a regulator30, which is a pressure regulating device; and an electromagnetic pressure-increasing linear valve SLA and an electromagnetic pressure-reducing linear valve SLR. The first pump device22includes a pump22aof a plunger type and a pump motor22bconfigured to drive the pump22a. The pump motor22bis an electric motor.

The master cylinder28includes a housing28aand three pistons disposed in the housing28a, i.e., an input piston28b, a first master piston28c, and a second master piston28d. An inter-piston chamber R1is defined between the input piston28band the first master piston28cin the housing28a. A first master chamber R2is defined between the first master piston28cand the second master piston28din the housing28a. A second master chamber R3is defined in front of the second master piston28din the housing28a(on the left side inFIG.1). An annular servo chamber R4is defined at the rear of a flange28eof the first master piston28cin the housing28a(on the right side inFIG.1). An annular reaction-force chamber R5is defined in front of the flange28ein the housing28a. The input piston28bis coupled to the brake pedal16via a rod32.

The connection state of the reservoir20and the first master chamber R2is switched from a communicating state to an isolated state when the first master piston28cmoves forward from its initial position by a predetermined amount. Likewise, the connection state of the reservoir20and the second master chamber R3is switched from a communicating state to an isolated state when the second master piston28dmoves forward from its initial position by a predetermined amount. These configurations are provided by through-holes, etc., formed in the first master piston28cand the second master piston28d.

There is formed, in the first system12, an inter-chamber communication passage34for establishing communication between the inter-piston chamber R1and the reaction-force chamber R5. In the inter-chamber communication passage34, an inter-chamber communication valve SGH is disposed. The inter-chamber communication valve SGH is a normally-closed electromagnetic open/close valve. The normally-closed valve is in a closed state when not energized and in an open state when energized. There is formed, in the first system12, a reaction-force-chamber release passage36for establishing communication between: the reservoir20; and a portion of the inter-chamber communication passage34located between the inter-chamber communication valve SGH and the reaction-force chamber R5. In the reaction-force-chamber release passage36, a two-chamber shut-off valve SSA is disposed. The two-chamber shut-off valve SSA is a normally-open electromagnetic open/close valve. The normally-open valve is in an open state when not energized and in a closed state when energized. A stroke simulator38is connected to a portion of the inter-chamber communication passage34located between the inter-chamber communication valve SGH and the reaction-force chamber R5. The stroke simulator38permits a depressing operation of the brake pedal16while applying an operation reaction force to the brake pedal16.

In a normal operation, the inter-chamber communication valve SGH and the two-chamber shut-off valve SSA are energized so that the inter-chamber communication valve SGH is placed in the open state and the two-chamber shut-off valve SSA is placed in the closed state. That is, the inter-piston chamber R1and the reaction-force chamber R5are closed while communicating with each other. A pressure receiving area of the first master piston28cwith respect to the inter-piston chamber R1is equal to a pressure receiving area of the flange28eof the first master piston28cwith respect to the reaction-force chamber R5. Thus, in the state in which the inter-chamber communication valve SGH and the two-chamber shut-off valve SSA are energized, the first master piston28cdoes not move forward even when the fluid in the inter-piston chamber R1is pressurized by the operation of the brake pedal16. When the fluid is supplied to the servo chamber R4in this state, the first master piston28cmoves forward by a force corresponding to a servo pressure that is the pressure of the fluid, and the second master piston28dmoves forward by the forward movement of the first master piston28c. The forward movements of the first master piston28cand the second master piston28dcause the fluid in the first master chamber R2and the second master chamber R3to be pressurized to a master pressure that corresponds to the servo pressure, so that the pressurized fluid is supplied to the second system14via master fluid passages40f,40r(hereinafter each referred to as “master fluid passage40” where appropriate).

In a case where an electric failure is occurring, the inter-chamber communication valve SGH and the two-chamber shut-off valve SSA are not energized, so that the reaction-force chamber R5is released while the inter-piston chamber R1is kept closed. In this state, the first master piston28cand the second master piston28dmove forward by an operation force applied to the brake pedal16by a vehicle driver, without depending on the servo pressure, and the fluid having the master pressure corresponding to the operation force by the vehicle driver is supplied to the second system14.

The regulator30is a pressure regulating device including a spool valve mechanism. In short, the regulator30includes: a casing30a; and a piston30band a spool30cdisposed in the casing30a. The piston30band the spool30care urged toward the front side (toward the left side inFIG.1) by respective springs. In the casing30a, a first pilot chamber R6is defined between the piston30band the spool30c, and a second pilot chamber R7is defined in front of the piston30b. It is noted that the second pilot chamber R7constitutes part of the master fluid passage40fdescribed above.

A low-pressure port P1, a high-pressure port P2, and a regulated-pressure port P3are formed in the casing30a. The low-pressure port P1is connected to the reservoir20, the high-pressure port P2is connected to the first pump device22, and the regulated-pressure port P3is connected to the servo chamber R4of the master cylinder28, via respective fluid passages.FIG.1illustrates a state in which the pressure is not introduced into the first pilot chamber R6. In this state, the spool30cis located at its front end position, the low-pressure port P1and the regulated-pressure port P3are held in communication with each other, and the high-pressure port P2and the regulated-pressure port P3are isolated from each other. Here, the pressure of the fluid in the first pilot chamber R6is referred to as a first pilot pressure. When the fluid having a relatively high first pilot pressure is supplied to the first pilot chamber R6, the spool30cmoves backward, the low-pressure port P1and the regulated-pressure port P3are isolated from each other, and the high-pressure port P2and the regulated-pressure port P3are brought into communication with each other. In short, the regulator30supplies the fluid whose pressure level corresponds to the first pilot pressure from the regulated-pressure port P3to the servo chamber R4of the master cylinder28. In other words, the regulator30has a function of regulating the servo pressure to a pressure level corresponding to the first pilot pressure.

In the first system12, a second pilot pressure (equal to the master pressure), which is the pressure of the fluid in the second pilot chamber R7, is slightly lower than the first pilot pressure. Thus, the piston30bdoes not operate in the normal condition. However, in a situation in which the first pilot pressure is not introduced due to an electric failure or the like, for instance, the fluid having the servo pressure whose pressure level corresponds to the second pilot pressure is supplied from the regulator30to the master cylinder28until the pressure of the fluid supplied from the first pump device22becomes low to a certain extent.

The pressure-increasing linear valve SLA and the pressure-reducing linear valve SLR are disposed in series in a fluid passage that connects the first pump device22and the reservoir20. The pressure-increasing linear valve SLA and the pressure-reducing linear valve SLR regulate the pressure of the fluid therebetween, namely, the valves SLA, SLR regulate the first pilot pressure. The pressure-increasing linear valve SLA is a normally-closed linear valve and regulates a difference between the pressure of the fluid on the upstream side thereof and the pressure of the fluid on the downstream side thereof, i.e., a pressure difference, depending on the energizing current supplied thereto. Specifically, the pressure-increasing linear valve SLA regulates the pressure difference such that the pressure difference is decreased with an increase in the energizing current supplied thereto. The pressure-reducing linear valve SLR is a normally-open linear valve and regulates a difference between the pressure of the fluid on the upstream side thereof and the pressure of the fluid on the downstream side thereof, i.e., a pressure difference, depending on the energizing current supplied thereto. Specifically, the pressure-reducing linear valve SLR regulates the pressure difference such that the pressure difference is increased with an increase in the energizing current supplied thereto. Though not described in detail, the first pilot pressure introduced into the regulator30is controlled by controlling the energizing current supplied to each of the pressure-increasing linear valve SLA and the pressure-reducing linear valve SLR.

The second system14is constituted by two systems corresponding to the two master fluid passages40f,40r, i.e., a front-wheel system50fand a rear-wheel system50r. (Hereinafter, the front-wheel system50fand the rear-wheel system50rwill be each referred to as “system50” where appropriate.) The second system14includes electromagnetic pressure-regulating linear valves SMF, SMR, pressure holding valves SFLH, SFRH, SRLH, SRRH, and pressure reducing valves SFLR, SFRR, SRLR, SRRR. Hereinafter, the pressure-regulating linear valves SMF, SMR will be each referred to as “pressure-regulating linear valve SM”, the pressure holding valves SFLH, SFRH, SRLH, SRRH will be each referred to as “pressure holding valve SH”, and the pressure reducing valves SFLR, SFRR, SRLR, SRRR will be each referred to as “pressure reducing valve SR” where appropriate.

In each of the front-wheel system50fand the rear-wheel system50r, the master fluid passage40branches into two to-wheel supply passages52L,52R (hereinafter each referred to as “to-wheel supply passage52” where appropriate) for supplying the fluid to the right and left wheel brake devices90, respectively. The pressure-regulating linear valve SM is disposed upstream of the branch point. The pressure holding valve SH is disposed in each to-wheel supply passage52. The pressure reducing valve SR is disposed in a pressure reduction passage56, which connects a reservoir54and a portion of each to-wheel supply passage52located between the pressure holding valve SH and the wheel brake device90.

Though not described in detail, a second pump device58is provided in each of the front-wheel system50fand the rear-wheel system50r. The second pump device58includes a pump58a. A pump motor58bfor driving the pumps58aof the respective pump devices58is provided. In the present embodiment, the pump motor58bis provided in common to both the front-wheel system50fand the rear-wheel system50r. The pump motor58bmay be provided for each second pump device58. The second pump device58is configured to pump up the fluid from the reservoir54and supply the fluid to a portion of the to-wheel supply passage52located upstream of the pressure holding valve SH via a check valve60. A portion of the master fluid passage40located upstream of the pressure-regulating linear valve SM is connected to the reservoir54via an inflow permission valve62, which permits the fluid to flow into the reservoir54in a state in which the amount of the fluid in the reservoir54is less than a set amount.

Each pressure holding valve SH is a normally-open electromagnetic open/close valve, and each pressure reducing valve SR is a normally-closed electromagnetic open/close valve. None of the pressure holding valves SH and the pressure reducing valves SR are energized in the normal condition. The pressure holding valves SH and the pressure reducing valves SR are energized when a wheel pressure, which is a hydraulic pressure in the wheel cylinder94of each wheel brake device90, is released in a case where the brake device1executes an antilock (ABS) operation, a traction control (TRC) operation, a vehicle stability control (VSC) operation, etc.

Each pressure-regulating linear valve SM is a normally-open electromagnetic linear valve. The pressure-regulating linear valve SM regulates a pressure difference, namely, a difference between the master pressure and the wheel pressure, depending on the energizing current supplied thereto. Specifically, the pressure-regulating linear valve SM regulates the pressure difference so as to be increased with an increase in the energizing current. By controlling the supply current to the pressure-regulating linear valves SM while driving the second pump devices58, the fluid, whose pressure is regulated in accordance with the supply current so as to be higher than the master pressure, is supplied to each wheel brake device90. Thus, the brake device1is configured such that the fluid is supplied from the first system12to the second system14. Further, in a case where the master pressure is defined as a first hydraulic pressure and the wheel pressure is defined as a second hydraulic pressure, the second system14is configured to be capable of supplying, to each wheel brake device90, the fluid having the second hydraulic pressure higher than the first hydraulic pressure that is the pressure of the fluid supplied from the first system12.

The first system12includes a first brake ECU (electronic control unit)70as a controller for controlling the first system12, and the second system14includes a second brake ECU (electronic control unit)72as a controller for controlling the second system14. The first brake ECU70controls operations of the pump motor22bof the first pump device22, the pressure-increasing linear valve SLA, the pressure-reducing linear valve SLR, the inter-chamber communication valve SGH, the two-chamber shut-off valve SSA, for instance. The first brake ECU70includes a computer and drivers (drive circuits) for the pump motor22b, the pressure-increasing linear valve SLA, the pressure-reducing linear valve SLR, the inter-chamber communication valve SGH, and the two-chamber shut-off valve SSA, etc.

The second brake ECU72controls operations of the pump motor58bfor the second pump devices58, the pressure-regulating linear valves SM, the pressure holding valves SH, and the pressure reducing valves SR, etc., of the respective front-wheel system50fand rear-wheel system50r. The second brake ECU72includes a computer and drivers (drive circuits) for the pump motor58b, the pressure-regulating linear valves SM, the pressure holding valves SH, the pressure reducing valves SR, etc. The first brake ECU70and the second brake ECU72transmit and receive information to and from each other via a CAN (controllable area network or car area network), not illustrated, to respectively control the first system12and the second system14.

B. Control of Brake Device

In the normal operation, namely, in a situation in which no failure occurs in the brake device1, the first system12and the second system14are controlled respectively by the first brake ECU70and the second brake ECU72independently of each other. Hereinafter, the control of the first system12and the control of the second system14will be described in this order.

i) Control of First System

In the first system12, there is mainly executed a control of the master pressure. The control of the master pressure is executed by controlling the electric current supplied to each of the pressure-increasing linear valve SLA and the pressure-reducing linear valve SLR based on a pedal stroke that is an operation amount (depression amount) of the brake pedal16. The first brake ECU70determines, based on the pedal stroke, a target braking force (that will also be referred to as a necessary braking force or a required braking force). In the case of automated driving, the target braking force is determined by other ECU and is transmitted to the first brake ECU70and the second brake ECU72, for instance.

The brake device1redundantly includes two pedal stroke sensors102a,102beach for detecting the pedal stroke. The pedal stroke detected by the pedal stroke sensor102ais utilized in the control of the master pressure while the pedal stroke detected by the pedal stroke sensor102bis utilized in the control of the hydraulic pressure in the wheel cylinder94(hereinafter referred to as “wheel pressure” where appropriate) that will be later described.

The first brake ECU70determines a target servo pressure based on the target braking force. The target servo pressure is determined also based on a contribution ratio of the first system12in the braking force. In the brake device1, the braking force can be controlled solely by the first system12, solely by the second system14, or cooperatively by the first system12and the second system14. Briefly, the braking force can be controlled by controlling the pressure of the fluid supplied from the first system12, namely, by controlling the master pressure, while keeping the pressure-regulating linear valves SM of the second system14in the open state. Further, even if the master pressure is kept at atmospheric pressure, the braking force can be controlled by controlling the energizing current to the pressure-regulating linear valves SM while driving the second pump devices58of the second system14. Moreover, the braking force can be controlled as follows. The energizing current to the pressure-regulating linear valves SM is controlled while driving the second pump devices58, so as to control the pressure difference between the wheel pressure and the master pressure in a state in which the pressure level of the master pressure is made lower than that of the target braking force.

In the control by the first system12, a relatively large braking force, which requires a relatively large amount of the fluid to be supplied to each wheel brake device90, is attained at earlier timing than in the control by the second system14. In the control by the second system14, the braking force rises more quickly and the followability in a region in which the braking force is relatively small is better than in the control by the first system12. Here, the good followability means that an actual braking force is less likely to be delayed with respect to the braking force to be required. In view of the difference in the characteristics between the first system12and the second system14, the brake device1may be configured such that contribution by the second system14is increased when the target braking force is relatively small while contribution by the first system12is increased when the target braking force is relatively large, for instance.

Based on the target servo pressure, the first brake ECU70determines the target first pilot pressure as a target of the first pilot pressure. Based on the target first pilot pressure, the first brake ECU70causes the first pump device22to be operated and determines the supply current to the pressure-increasing linear valve SLA and the supply current to the pressure-reducing linear valve SLR. The first brake ECU70supplies the determined supply currents (the energizing currents) to the corresponding electromagnetic valves. Thus, the fluid having the master pressure is supplied from the first system12to the second system14.

The first system12includes a servo pressure sensor104for detecting an actual servo pressure. For instance, the target first pilot pressure may be determined according to a feedback control law based on a deviation of the actual servo pressure with respect to the target servo pressure. The first system12includes a reaction force pressure sensor106for detecting the pressure of the fluid in the stroke simulator38as a reaction force pressure. The target braking force may be determined based on the reaction force pressure, namely, based on a brake operation force applied to the brake pedal16by the vehicle driver.

ii) Control of Second Brake System

The control of the second system14is for controlling the wheel pressure to a value corresponding to the target braking force. The control of the wheel pressure is executed for the front-wheel system50fand the rear-wheel system50rindependently of each other. Because the control executed for the front-wheel system50fand the control executed for the rear-wheel system50rare identical, the controls will be explained focusing on one control.

Like the first brake ECU70, the second brake ECU72determines the target braking force. The determination of the target braking force may be performed by one of the first brake ECU70and the second brake ECU72, and the other of the ECUs70,72may perform the determination based on information sent from the one of the ECUs70,72via the CAN.

The second brake ECU72determines the target wheel pressure based on the target braking force. The second brake ECU72executes various controls based on a difference between the actual master pressure detected by a pressure sensor108and the target wheel pressure, i.e., a pressure difference ΔP. When the actual master pressure is less than the target wheel pressure, the second brake ECU72causes the second pump device58to be driven and determines the energizing current supplied to the pressure-regulating linear valve SM based on the pressure difference ΔP. The second brake ECU72supplies the determined energizing current to the pressure-regulating linear valve SM. When the pressure difference ΔP is 0, the second brake ECU72stops operating the second pump device58and determines the energizing current to be 0.

The second system14includes pressure sensors110each provided for a corresponding one of the front-wheel system50fand the rear-wheel system50rfor detecting an actual wheel pressure. The energizing current supplied to the pressure-regulating linear valve SM may be determined according to a feedback control law based on a deviation of the actual wheel pressure with respect to the target wheel pressure. As in the control of the master pressure in the first system12, the target braking force may be determined based on the reaction force pressure. It is noted that the wheel pressure may be estimated based on a control status.

The first brake ECU70and the second brake ECU72communicate with each other, so that the two ECUs70,72operate in a coordinated fashion or in conjunction with each other. It can be said that one controller8for controlling the brake device1is constituted by the first brake ECU70and the second brake ECU72, as illustrated inFIG.3. The controller8includes one or more processors and one or more memory. Hereinafter, the first brake ECU70and the second brake ECU72will be collectively referred to as the controller8where appropriate. As described above, the brake device1includes the first system12and the second system14as one example of the fluid supply portion that supplies the fluid to the wheel cylinder94of each brake device90utilizing the fluid in the reservoir20. The brake device1is configured to apply the braking force to each wheel by pressing the brake pads93against the disc rotor91in accordance with the wheel pressure.

The brake device1according to the present embodiment is an on-demand hydraulic brake device not including an accumulator (high-pressure source). Thus, the fluid level in the reservoir20, i.e., a remaining amount of the fluid in the reservoir20, varies in conjunction with the wheel pressure, i.e., the amount of the fluid supplied to the wheel cylinders94. Roughly speaking, the amount of the fluid supplied to each wheel cylinder94increases and the fluid level in the reservoir20is reduced with an increase in the wheel pressure. In other words, it can be said that the fluid level in the reservoir20is lowered by a control of increasing the braking force, i.e., a control of moving the piston95forward and that the fluid level in the reservoir20is raised by a control of decreasing the braking force, i.e., a control of moving the piston95backward.

C. Electric Parking Brake

An electric parking brake11is provided for each of the wheel brake devices90RR,90RL of the rear wheels. As illustrated inFIG.2, the electric parking brake11is configured to convert a rotary motion of the output shaft of the electric motor11ainto a linear motion of a linearly movable member11cby a motion converting mechanism11band to cause the linearly movable member11cto press the piston95to thereby move the piston95. The electric motor11ais controlled by the controller8, for instance. The motion converting mechanism11bis constituted by a plurality of gears. The motion converting mechanism11bfunctions as a speed reducing mechanism and converts the rotary motion of the output shaft into the linear motion of the linearly movable member11c.

When the electric parking brake11is activated by an operation of the vehicle driver, for instance, the electric motor11ais operated to cause the linearly movable member11cto press the piston95, so that the brake pads93are pressed against the disc rotor91by the piston95to generate the braking force. The electric parking brake11is provided with a known lock mechanism for prohibiting the movement of the linearly movable member11c. In the state in which the braking force is generated by the movement of the linearly movable member11c, the lock mechanism locks the linearly movable member11c. Thus, the state in which the braking force is generated is maintained without the electric motor11abeing powered. In the locked state of the electric parking brake11, the braking force is being applied to the wheel.

The electric parking brake11is normally activated by a vehicle driver's manipulation of a switch or the like in a state in which the vehicle is at standstill and the braking force is being generated by depression of the brake pedal16. Accordingly, the brake pads93are further pressed against the disc rotor91by the linearly movable member11cand the piston95from the state of pressing the disc rotor91. That is, the activation of the electric parking brake11causes the piston95to move forward, so that the volume of the hydraulic-pressure chamber94aof the wheel cylinder94is increased.

When the electric parking brake11is turned off, the piston95moves backward to a predetermined position. In this state, the piston95is movable forward and backward in accordance with the pressure in the hydraulic-pressure chamber94a. At an initial position of the piston95, the linearly movable member11cand the piston95do not contact each other, and the piston95is movable forward and backward. The initial position of the piston95is, for instance, a position of the piston95in a state in which the brake operation has never been performed and the wheel pressure is equal to atmospheric pressure. In the description of the present specification, the direction in which the piston95moves toward the disc rotor91(i.e., the direction in which the hydraulic-pressure chamber94ais enlarged) is defined as a forward direction, and the direction in which the piston95moves away from the disc rotor91(i.e., the direction in which the hydraulic-pressure chamber94ais narrowed) is defined as a backward direction. A clamping force of the electric parking brake11is a force by which the brake pads93clamp the disc rotor91. The clamping force increases as the piston95moves forward, namely, the clamping force increases with an increase in a control current of the electric motor11a, for instance.

D. Fluid-Leakage Detection

The brake device1monitors the fluid level in the reservoir20and monitors whether the fluid leakage is occurring. The brake device1includes a fluid level sensor20aand the controller8. As illustrated inFIG.3, the controller8includes a wear-amount estimating portion81, a heat-generation-amount estimating portion82, a reduction-amount estimating portion83, a fluid-leakage determining portion84, a work-amount estimating portion85, and a replacement-timing determining portion86. Functions of the portions81-85are effectuated by the controller8. In this respect, the brake device1may include another ECU having the functions of the portions81-85, which is an electronic control unit including one or more processors like other ECUs. The embodiment will be described hereinafter assuming that automated driving or automatic brake is mainly performed. For instance, a description as to a work amount of the second system14, etc., will be made on the precondition that the reservoir20and the second system14(as one example of the fluid supply portion) are held in communication with each other, namely, the master pistons28c,28dare not moved forward.

The fluid level sensor20ameasures a value of a level of the fluid in the reservoir20. The fluid level sensor20ais a known level sensor (level meter) of a capacitance type, an ultrasonic type, or the like. The fluid level sensor20ameasures the value of the fluid level all the time utilizing an output value that changes proportionately with the change in the fluid level in the reservoir20such as a current value, a voltage value, or a capacitance. The fluid level sensor20ais configured such that the output value linearly changes with respect to the change in the fluid level. For instance, the capacitance level sensor is capable of detecting the fluid level by measuring the capacitance based on a correlation between the fluid level and the capacitance. In this instance, the level sensor is constructed such that the fluid surface is located between two electrodes, for instance. The fluid level sensor20ais constituted such that the output value changes with respect to the change in the fluid level per unit level, for instance. Unlike the level switch, the level sensor is typically capable of detecting the fluid level value each time when the fluid level changes or every unit time. The level switch can detect that the fluid level is lower than a constant value but cannot measure the fluid level value. Any known level sensors are employable as the fluid level sensor20a, and a detailed description of the configuration of the fluid level sensor20ais dispensed with. The fluid level sensor20atransmits regularly, e.g., at a short cycle, the detection result to the controller8, for instance. It can be said that the fluid level sensor20alinearly changes the output with respect to the change in the fluid level. It can be further said that the fluid level sensor20adetects the fluid level linearly, e.g., continuously.

Estimation of Wear Amount

The wear-amount estimating portion81estimates a wear amount of the brake pads93based on a result of measurement by the fluid level sensor20a. Based on the measurement result by the fluid level sensor20a, the wear-amount estimating portion81records the fluid level at every predetermined timing continuously from a brand-new state of the vehicle or replaced timing of the brake pads93. The predetermined timing is set to timing immediately after the electric parking brake11is turned off in a state in which ignition (key switch) is turned on. For instance, the predetermined timing is set to timing when the braking force is being generated by the hydraulic pressure, namely, timing before the brake pedal16is released in a state in which the electric parking brake11is turned off and the ignition is turned on.

The fluid level detected at the predetermined timing is the fluid level when the brake pads93are being pressed against the disc rotor91, namely, when the braking force is being generated, in a state in which the ignition is turned on and the magnitude of the clamping force of the electric parking brake11is not relevant to the fluid level. That is, the state in which the fluid level is detected in the present embodiment is a state in which the piston95has moved forward by the wheel pressure. It can be said that the predetermined timing is timing at which a predetermined braking force is being generated only by the wheel pressure before the vehicle starts after the turning on of the ignition.

The wear-amount estimating portion81records information on the fluid level at the predetermined timing and calculates a difference between: a present fluid level in present measurement; and an initial fluid level in initial measurement and at normal temperature (e.g., the fluid level when the brake pads93are brand-new and at normal temperature). That is, the wear-amount estimating portion81calculates an amount of change in the fluid level from the initial measurement (hereinafter referred to as “aging-dependent fluid-level change amount” where appropriate). The record of the fluid level at the initial measurement is reset when the brake pads93are replaced, for instance.

The wear-amount estimating portion81receives information on a heat generation amount of the brake pads93(that will be later described) from the heat-generation-amount estimating portion82and estimates the wear amount of the brake pads93based on the aging-dependent fluid-level change amount and the heat generation amount. The amount of the forward movement of the piston95for generating the braking force increases with an increase in the wear amount of the brake pads93. That is, the volume of the hydraulic-pressure chamber94ain the state in which the braking force is being generated increases with an increase in the wear amount of the brake pads93, and the fluid amount supplied from the reservoir via the fluid circuit is accordingly increased. When not considering the heat generation amount, the fluid level at the predetermined timing is reduced with an increase in the wear amount of the brake pads93. Thus, there exists a positive correlation between the aging-dependent fluid-level change amount and the wear amount of the brake pads93. As illustrated inFIG.4, the fluid-leakage determining portion84stores in advance a first map representing a relationship between the aging-dependent fluid-level change amount (i.e., the reduction amount) and the wear amount.

When considering the heat generation amount, as the heat generation amount of the brake pads93increases, the brake pads93expand and the forward movement amount of the piston95for generating the braking force becomes small. That is, the volume of the hydraulic-pressure chamber94ain the state in which the braking force is being generated decreases with an increase in the heat generation amount of the brake pads93, and the fluid amount to be required accordingly becomes small. Based on the findings, the wear-amount estimating portion81calculates the wear amount of the brake pads93based on a product of a value obtained by subtracting the heat generation amount (i.e., the expansion amount) from the aging-dependent fluid-level change amount and a constant (coefficient), e.g., the wear amount=(the aging-dependent fluid-level change amount−the heat generation amount)×the constant.

The wear-amount estimating portion81calculates the wear amount based on information on the latest heat generation amount received from the heat-generation-amount estimating portion82, for instance. In a case where a predetermined length of time or more has elapsed from the time of estimation (calculation) of the latest heat generation amount, for instance, the wear-amount estimating portion81calculates the wear amount by setting the heat generation amount to 0.

Estimation of Heat Generation Amount

The heat-generation-amount estimating portion82estimates the heat generation amount of the brake pads93based on the measurement result by the fluid level sensor20a. Each time when one brake operation is completed, the heat-generation-amount estimating portion82calculates the heat generation amount based on a difference between the fluid level immediately before the start of the brake operation and the fluid level immediately after the completion of the brake operation. This difference will be hereinafter referred to as “brake-operation-dependent fluid-level change amount” where appropriate. In the case of manual driving, the one brake operation is a process executed from when the brake pedal16is depressed to when the brake pedal16returns to the initial position. In the case of automated driving, the one brake operation is a process executed from when the braking force is generated by the wheel pressure to when the braking force becomes equal to 0.

The heat-generation-amount estimating portion82keeps recording the measurement result of the fluid level sensor20a. When one brake operation is completed, the heat-generation-amount estimating portion82subtracts the fluid level immediately before the start of the brake operation from the fluid level immediately after the completion of the brake operation. The heat-generation-amount estimating portion82calculates the heat generation amount of the brake pads93based on a product of a value obtained by the subtraction (i.e., the brake-operation-dependent fluid-level change amount) and a constant (coefficient), e.g., the heat generation amount=the brake-operation-dependent fluid-level change amount×the constant. There exists a relationship, e.g., a positive correlation, between the heat generation amount and the expansion amount. Thus, the expansion amount can be estimated from the heat generation amount.

When the brake pads93generate heat and expand due to the brake operation, the contact of the brake pads93and the disc rotor91is not cancelled after expansion at a position of the piston95where the brake pads93and the disc rotor91are not in contact before expansion. In this case, the piston95is pushed backward further from the initial position. That is, the expansion of the brake pads93causes the volume of the hydraulic-pressure chamber94ato be decreased and causes the fluid level in the reservoir20to be increased.

Thus, there exists a positive correlation between the brake-operation-dependent fluid-level change amount (i.e., the increase amount) and the heat generation amount of the brake pads93. As illustrated inFIG.5, the fluid-leakage determining portion84stores in advance a second map representing the relationship between the brake-operation-dependent fluid-level change amount and the heat generation amount. Based on the findings, the heat-generation-amount estimating portion82estimates the heat generation amount of the brake pads93. The heat-generation-amount estimating portion82transmits information on the heat generation amount to the wear-amount estimating portion81and the fluid-leakage determining portion84each time when the heat generation amount is estimated or as needed.

The heat-generation-amount estimating portion82records the heat generation amount for every estimation and calculates an integrated value of the heat generation amount, i.e., a total heat generation amount. The integrated value is a total value of the heat generation amounts, for instance. The heat generation amount in initial recording results from the brake operation initially performed in a brand-new state of the vehicle or the brake operation initially performed after replacement of the brake pads93. The integrated value is stored as a total thermal load of the brake pads93.

Estimation of Fluid-Level Reduction Amount Arising from Braking

The reduction-amount estimating portion (corresponding to “WC reduction-amount estimating portion” and “EPB reduction-amount estimating portion”)83estimates an amount of reduction in the fluid level arising from an increase in the braking force. The reduction-amount estimating portion83estimates the reduction amount of the fluid level based on a generation status of the braking force, specifically, based on the wheel pressure or the clamping force of the electric parking brake11. As illustrated inFIGS.6and7, the reduction-amount estimating portion83stores: a third map representing a relationship between the wheel pressure and the change amount of the fluid level (i.e., the reduction amount); and a fourth map representing a relationship between the clamping force of the electric parking brake11and the change amount of the fluid level (i.e., the reduction amount).

The reduction-amount estimating portion83estimates a change amount “c1” of the fluid level arising from the hydraulic-pressure control based on information on the wheel pressure (i.e., the detection value by the pressure sensor110) and the third map. The reduction-amount estimating portion83further estimates a change amount “c2” of the fluid level arising from the operation of the electric parking brake11based on the clamping force and the fourth map. The clamping force of the electric parking brake11is adjusted, for instance, by inclination of the road surface when the vehicle is at standstill. The controller8recognizes the clamping force (e.g., the rotational position of the electric motor11a), and the fluid-leakage determining portion84can obtain present clamping force information. The reduction-amount estimating portion83transmits information on the fluid-level change amounts c1, c2 to the fluid-leakage determining portion84.

Fluid-Leakage Determination

The fluid-leakage determining portion84determines the presence or absence of the fluid leakage based on the measurement result by the fluid level sensor20a, the wear amount estimated by the wear-amount estimating portion81, the heat generation amount estimated by the heat-generation-amount estimating portion82, and the reduction amount estimated by the reduction-amount estimating portion83(corresponding to “WC reduction amount” and “EPB reduction amount”).

The fluid-leakage determining portion84stores the fluid level in the brake operation performed immediately after replacement of the brake pads93and at normal temperature, namely, the fluid level when the electric parking brake11is not operating. The value of the recorded fluid level is the same as the value of the initial fluid level utilized in calculation by the wear-amount estimating portion81and will be hereinafter referred to as “initial fluid level” where appropriate.

The fluid-leakage determining portion84executes a fluid-leakage determination program at a short cycle. Each time when executing the program, the fluid-leakage determining portion84calculates a difference between the present fluid level and the initial fluid level (hereinafter referred to as “present fluid-level change amount” where appropriate). The fluid-leakage determining portion84compares the present fluid-level change amount ΔL to a fluid leakage threshold Th. When the present fluid-level change amount ΔL is greater than the fluid leakage threshold Th, the fluid-leakage determining portion84determines that the fluid leakage is occurring and gives the vehicle driver a warning by a display or a voice message, for instance.

The fluid-leakage determining portion84determines the fluid leakage threshold Th based on the wear amount estimated by the wear-amount estimating portion81, the heat generation amount estimated by the heat-generation-amount estimating portion82, and the reduction amount estimated by the reduction-amount estimating portion83. The fluid-leakage determining portion84estimates a change amount “a” of the fluid level arising from the wear of the brake pads93based on the pre-stored relationship between the wear amount of the brake pads93and the change amount of the fluid level (i.e., the first map ofFIG.4) and the information on the latest wear amount estimated by the wear-amount estimating portion81.

The fluid-leakage determining portion84estimates a change amount “b” of the fluid level arising from the heat generation of the brake pads93based on the pre-stored relationship between the heat generation amount of the brake pads93and the change amount of the fluid level (i.e., the second map ofFIG.5) and the information on the latest heat generation amount estimated by the heat-generation-amount estimating portion82. In a case where a predetermined length of time has elapsed from the time of calculation of the latest heat generation amount, the fluid-leakage determining portion84may set the heat generation amount to 0.

The fluid-leakage determining portion84obtains, from various portions, information on the fluid-level change amount “a” based on the wear amount, the fluid-level change amount “b” based on the heat generation amount (the expansion amount), the fluid-level change amount (the WC reduction amount) “c1” based on the wheel pressure, and the fluid-level change amount (the EPB reduction amount) “c2” based on the clamping force. The fluid-leakage determining portion84determines the fluid leakage threshold Th based on a constant X and the fluid-level change amounts a, b, c1, c2. The constant X is set from the viewpoint of preventing erroneous detection. The fluid leakage threshold Th is determined according to the following expression, for instance. Though the fluid-level change amounts c1, c2 need not necessarily be utilized, the accuracy in determination of the fluid leakage is enhanced through the use of the fluid-level change amounts c1, c2.
Th=X−a+b−(c1+c2)

The fluid-level change amount “a” arises from the wear of the brake pads93. The fluid-level change amount “a” is an amount of change in the direction of decrease of the fluid level. In a state in which the fluid level is reduced due to the wear, a margin of the remaining amount of the fluid in the reservoir20with respect to the decrease in the fluid level that arises from the hydraulic-pressure control (the pressure-increase control) of the systems12,14is smaller, as compared with that in a state in which the brake pads93are not worn. That is, in the state in which the fluid level is decreased due to the wear of the brake pads93, the reservoir20is relatively likely to become empty. It is thus preferable to issue a warning at early timing when there is a possibility of the fluid leakage. In the automated driving vehicle, in particular, the fluid-leakage detection based on the reaction force value at the time of depression of the brake pedal16is not performed, and there is a possibility that the accuracy of the fluid-leakage detection is lowered. It is thus desirable to detect the fluid-leakage at early timing. The fluid-leakage determining portion84decreases the fluid leakage threshold Th by subtracting the fluid-level change amount “a” from the constant X in calculating the fluid leakage threshold Th. This is for allowing determination of the presence of the fluid leakage to be made at a stage where the present fluid-level change amount is relatively small in a state in which the brake pads93are worn.

The fluid-level change amount “b” arises from the heat generation amount (i.e., the expansion amount) of the brake pads93. The fluid-level change amount “b” is an amount of change in the direction of increase of the fluid level. In a state in which the fluid level is increased due to the expansion of the brake pads93, the margin of the remaining amount of the fluid in the reservoir20with respect to the decrease in the fluid level that arises from the hydraulic-pressure control (the pressure-increase control) of the systems12,14is larger, as compared with that in a state in which the brake pads93are not expanded. That is, in the state in which the fluid level is increased due to the expansion of the brake pads93, the reservoir20is relatively not likely to become empty. Thus, the fluid-leakage determining portion84increases the fluid leakage threshold Th by adding the fluid-level change amount “b” to the constant X in calculating the fluid leakage threshold Th.

The fluid-level change amount “c1” arises from the pressure-increase control executed by the first system12and/or the second system14. The fluid-level change amount “c1” is an amount of change in the direction of decrease of the fluid level. As described above with respect to the fluid-level change amount “a”, the fluid-leakage determining portion84decreases the fluid leakage threshold Th by subtracting the fluid-level change amount “c1” from the constant X in calculating the fluid leakage threshold Th for enabling the fluid leakage to be detected at early timing.

The fluid-level change amount “c2” arises from the operation of the electric parking brake11from its released state to its locked state. The fluid-level change amount “c2” is an amount of change in the direction of decrease of the fluid level. As described above with respect to the fluid-level change amount “a”, the fluid-leakage determining portion84deceases the fluid leakage threshold Th by subtracting the fluid-level change amount “c2” from the constant X in calculating the fluid leakage threshold Th for enabling the fluid leakage to be detected at early timing. In this way, the fluid-leakage determining portion84determines the presence or absence of the fluid leakage based on the above expression. Each of the maps described above is created based on results of a fluid-level change test conducted in advance. The occurrence of the fluid leakage may be determined when the fluid level is reduced in a state in which the wheel pressure is constant such as during execution of a wheel-pressure holding control in which the wheel pressure is held.

Summary of Fluid-Leakage Determination

The brake device1includes the first system12and the second system14functioning as the fluid supply portion and configured to supply the fluid to the wheel cylinder94of each wheel brake device90utilizing the fluid in the reservoir20. The brake device1is configured such that the piston95presses the brake pads93against the disc rotor91in accordance with the wheel pressure, so as to apply the braking force to the wheel. The brake device1includes the fluid level sensor20aconfigured to measure the value of the fluid level in the reservoir20, the wear-amount estimating portion81configured to estimate the wear amount of the brake pads93based on the result of measurement by the fluid level sensor20a, the heat-generation-amount estimating portion82configured to estimate the heat generation amount of the brake pads93based on the result of measurement by the fluid level sensor20a, and the fluid-leakage determining portion84configured to determine whether the fluid leakage is occurring based on the change amount of the fluid level, the wear amount, and the heat generation amount.

In the fluid-leakage determination, the brake device1constructed as described above takes account of the amount of change in the thickness of the brake pads93estimated based on the measured fluid level value, thus enabling accurate fluid-leakage determination. The thickness of the brake pads93becomes small due to the wear and becomes large due to the heat generation. Under the same conditions, the fluid amount in the wheel cylinder94is increased and the fluid level in the reservoir20is reduced when the thickness of the brake pads93becomes small whereas the fluid amount in the wheel cylinder94is decreased and the fluid level in the reservoir20is increased when the thickness of the brake pads93becomes large. By monitoring the change in the fluid level, the condition of the brake pads93can be grasped. The configuration according to the present disclosure enables accurate detection of the fluid leakage owing to the fluid-leakage determination that takes account of the condition of the brake pads93. Unlike the level switch that detects whether the fluid level is less than a predetermined value, the fluid level sensor20ameasures the value of the fluid level such as the output value correlated with the fluid level.

The brake device1further includes the reduction-amount estimating portion83configured to estimate, based on the wheel pressure, the reduction amount of the fluid level arising from the operations of the first system12and the second system14, i.e., the WC reduction amount. Further, the fluid-leakage determining portion84is configured to determine whether the fluid leakage is occurring also based on the reduction amount, i.e., the fluid-level change amount “c1”. This configuration enables the fluid-leakage determination that matches the present generation status of the braking force, namely, the fluid-leakage determination that takes account of the fluid amount utilized in generating the braking force, thus enhancing the accuracy of the fluid-leakage determination.

The brake device1further includes the electric parking brake11configured to move the piston95by the force of the electric motor11a. The reduction-amount estimating portion83estimates, based on the clamping force of the electric parking brake11, the reduction amount of the fluid level arising from the operation of the electric parking brake11, i.e., the EPB reduction amount. Further, the fluid-leakage determining portion84is configured to determine whether the fluid leakage is occurring also based on the reduction amount, i.e., the fluid-level change amount “c2”. This configuration enables the fluid-leakage determination that matches the operating status of the electric parking brake11, thus enhancing the accuracy of the fluid-leakage determination. The brake device1according to the present embodiment enables the fluid-leakage determination that takes account of various changes in the fluid amount when the brake device1is normally operating. Accordingly, the fluid leakage can be detected at early timing, and the warning can be issued at early timing.

E. Replacement-Timing Determination

Estimation of Work Amount

The work-amount estimating portion85estimates a work amount of the pump motor22bof the first pump device22and a work amount of the pump motor58bof the second pump devices58based on the result of measurement by the fluid level sensor20a. The work-amount estimating portion85estimates the work amounts of the pump motors22b,58bbased on: a change amount of the detection value by each pressure sensor110(i.e., the wheel pressure) per unit time; and the corresponding change amount of the fluid level per unit time (hereinafter referred to as “per unit fluid-level change amount” where appropriate). In this respect, the work-amount estimating portion85may utilize a change amount of the target wheel pressure per unit time, in place of the change amount of the detection value by each pressure sensor110per unit time (hereinafter referred to as “pressure change amount” where appropriate).

The work-amount estimating portion85estimates the work amount based on a product obtained by multiplying the pressure change amount by the per unit fluid-level change amount, e.g., the work amount=the pressure change amount×the per unit fluid-level change amount. The work-amount estimating portion85determines the operating states of the pump motor22band the pump motor58bbased on the control status of the controller8. The work-amount estimating portion85estimates the work amount of the pump motor22baccording to the calculation described above in a case where only the pump motor22bis operating. The work-amount estimating portion85estimates the work amount of the pump motor58baccording to the calculation described above in a case where only the pump motor58bis operating.

In a case where both the pump motors22b,58bare operating, the work-amount estimating portion85estimates the work amount of each pump motor22b,58bbased on the contribution ratio and/or the pressure values (i.e., the master pressure and the wheel pressure), for instance. In a case where the pedal stroke influences the fluid level in manual driving, the work-amount estimating portion85may correct the per unit fluid-level change amount based on the detection values by the pedal stroke sensors102a,102b.

The work-amount estimating portion (corresponding to “EPB work-amount estimating portion”)85estimates also a work amount of the electric motor11aof the electric parking brake11. The work-amount estimating portion85estimates the work amount of the electric motor11a(corresponding to “EPB work amount”) based on: the change amount of the wheel pressure per unit time (i.e., the pressure change amount); and the corresponding change amount of the fluid level per unit time (i.e., the per unit fluid-level change amount), in the operation of the electric parking brake11(from its released state to its locked state or vice versa). As described above with respect to the estimation of the work amount of each pump motor22b,58b, the work-amount estimating portion85estimates the work amount of the electric motor11abased on a product of the pressure change amount and the per unit fluid-level change amount, e.g., the work amount=the pressure change amount×the per unit fluid-level change amount. The work amount estimated by the calculation differs depending on different change amounts of the fluid level per unit time.

The work-amount estimating portion85also estimates, for each of the pump motors22b,58band the electric motor11a, a total work amount that is a sum of the work amounts. Each total work amount is reset when a corresponding one of the pump motors22b,58band the electric motor11ais replaced. Each time when the fluid level changes by execution of the control, for instance, the work-amount estimating portion85may calculate the work amount of each of the motors and drive circuits (such as the pumps and electromagnetic valves) for the operation thereof and may calculate the total work amount (that may also be referred to as a load) of each element. In a case where one element performs similar operations (such as in a case where the change amount of the fluid level is the same among the operations), the work-amount estimating portion85may calculate the total work amount by multiplying the number of operations by the work amount. The work-amount estimating portion85may add up the work amounts for the operation of each element and may calculate the load of each element. The total work amount of the electric motor11amay be referred to as a total EPB work amount.

Replacement-Timing Determination

The replacement-timing determining portion (corresponding to “pad replacement-timing determining portion”, “motor replacement-timing determining portion” or “EPB replacement-timing determining portion”)86stores, for each element, a replacement threshold based on results of a durability test conducted in advance. For instance, the replacement-timing determining portion86stores in advance the replacement threshold of each of the pump motors22b,58band the electric motor11aand compares the total work amount of each of the motors22b,58b,11ato the corresponding replacement threshold. When the total work amount exceeds the replacement threshold, the replacement-timing determining portion86notifies the vehicle driver, by a display or a voice massage, that the element in question has reached its end of estimated life. For instance, the replacement-timing determining portion86notifies the vehicle driver that the element in question has reached its replacement timing or the element in question will probably be out of order soon. It can be said that the replacement-timing determining portion86may predict a failure by comparing the total work amount to the replacement threshold.

Summary of Replacement-Timing Determination

The brake device1includes the replacement-timing determining portion86configured to determine timing of replacement of the brake pads93, namely, to determine whether the brake pads93has reached the end of their life, based on at least one of the estimated wear amount and the estimated heat generation amount, namely, based on the estimated wear amount and/or the estimated heat generation amount. This configuration enables the vehicle driver to be notified of the replacement timing of the brake pads93with high accuracy.

The brake device1includes the work-amount estimating portion85configured to estimate, based on the measurement result by the fluid level sensor20aand the wheel pressure, the work amount of the pump motor22bof the first system12, the work amount of the pump motor58bof the second system14, the work amount of the electric motor11a, and the total work amount that is an integrated value of the work amount obtained for each of the pump motor22b, the pump motor58b, and the electric motor11a. The replacement-timing determining portion86is configured to determine timing of replacement of each of the pump motors22b,58band the electric motor11a, namely, to determine whether each of the pump motors22b,58band the electric motor11ahas reached the end of its life, based on the total work amount. This configuration enables the vehicle driver to be notified of the replacement timing of each of the pump motors22b,58band the electric motor11awith high accuracy.

The wear of components is conventionally checked visually by workers, for instance, thus requiring mounting and demounting of components. Further, in a case where the replacement timing is determined or estimated, only the number of times the operation has been performed is usually considered. In other words, the operation performed under different load situations is treated as being performed under the same load situation. Thus, there is a room for improvement in terms of the determination accuracy. In a case where the status of use largely differs among individual vehicles such as the MaaS vehicles, the determination of the replacement timing of the components needs to be made for the individual vehicles. In the present embodiment, the work amount is estimated based on the fluid-level change amount that changes depending upon the operational load, thus enabling the replacement timing of the components to be determined for the individual vehicles. The determination of the replacement timing of the motor (i.e. the estimation of the work amount) includes not only a determination of the replacement timing of the motor body but also a determination of the replacement timing of a motor drive circuit (such as an inverter). In a case where the motor, which is subject to the replacement timing determination, is a brushed motor, the replacement timing of the motor is largely influenced by the replacement timing of the brush. In this case, the replacement timing of the motor determined by the controller8may be referred to as the replacement timing of the motor body. In a case where the subject motor is a brushless motor, the degree of influence of the replacement timing of the motor drive circuit (the inverter) on the replacement timing of the motor is high. In this case, the replacement timing of the motor determined by the controller8may be referred to as the replacement timing of the motor drive circuit.

F. Control Example

Referring toFIG.8, there will be described one example of a fluid-leakage determination program and a replacement-timing determination program executed by the controller8. It is initially determined whether the present fluid-level change amount ΔL, which is a difference between the present fluid level and the initial fluid level, is greater than the fluid leakage threshold Th (S101). In the initial determination, the fluid leakage threshold Th is the constant X (Th=X−a+b−c1−c2). When the present fluid-level change amount ΔL is greater than the fluid leakage threshold Th (S101: Yes), it is determined that the fluid leakage is occurring. In this case, there is executed a process that is to be executed upon occurrence of the fluid leakage, such as outputting the warning (S102).

When the present fluid-level change amount ΔL is not greater than the fluid leakage threshold Th (S101: No), the replacement-timing determination program is executed to calculate or estimate the wear amount of the brake pads93(S103). Based on the calculated wear amount and the first map, the fluid-level change amount “a” is calculated (S104). The heat generation amount of the brake pads93is calculated or estimated (S105). Based on the calculated heat generation amount and the second map, the fluid-level change amount “b” is calculated (S106). Based on the calculated heat generation amount, the total heat generation amount of the brake pads93is calculated (S107).

The work amount of each motor22b,58b,11ais calculated (S108). The fluid-level change amount “c1” is calculated based on the wheel pressure and the third map, and the fluid-level change amount “c2” is calculated based on the clamping force of the electric parking brake11and the fourth map (S109). The total work amount (i.e., the integrated value) of each motor22b,58b,11ais calculated (S110). In this way, the controller8calculates the fluid-level change amounts a, b, c1, c2, the total heat generation amount, and the total work amount of each motor22b,58b,11a. The order of the calculations may be suitably changeable. For instance, the calculations may be carried out simultaneously.

It is subsequently determined whether the wear amount of the brake pads93is greater than a threshold that is set in advance (S111). When the wear amount is greater than the threshold (S111: Yes), the warning as to replacement of the brake pads93is issued to the vehicle driver (S112). When the wear amount is not greater than the threshold (S111: No), it is determined whether the total heat generation amount of the brake pads93, namely, the total thermal load of the brake pads93, is greater than the threshold (S113). When the total thermal load is greater the threshold (S113: Yes), the warning as to replacement of the brake pads93is issued to the vehicle driver (S112).

When the total thermal load is not greater than the threshold (S113: No), it is determined whether the total work amount of each motor22b,58b,11ais greater than a threshold set for each motor22b,58b,11a(S114). When any of the total work amounts is greater than the corresponding threshold (S114: Yes), the warning concerning the corresponding motor22b,58b,11ais issued to the vehicle driver (S115). When all of the total work amounts are not greater than the corresponding thresholds (S114: No), the program ends and returns back to the start of the program. The calculated values a, b, c1, c2 are utilized in next fluid-leakage determination (S101). The controller8repeatedly executes the fluid-leakage determination program and the replacement-timing determination program illustrated inFIG.8at a short cycle.

Examples of Fluid-Level Change and Hydraulic-Pressure Change

Referring toFIG.9, there will be briefly described a change in the wheel pressure and a change in the fluid level in the reservoir20. InFIG.9, the factors responsible for the change in the fluid level are illustrated as follows. A change “z1” is a change that arises from the hydraulic-pressure control, namely, the control load. A change “z2” is a change that arises from the operation of the electric parking brake11, namely, the operational load. A change “z3” is a change that arises from an ABS control, namely, ABS load. A change “z4” is a change that arises from thermal expansion of the brake pads93.

In a time period T1, the brake pedal16is depressed and the ignition is turned on in a state in which the electric parking brake11is locked, so that the wheel pressure is increased and the fluid level is accordingly reduced. Subsequently, when the electric parking brake11is released or turned off and the piston95moves backward, the hydraulic-pressure chamber94ais narrowed, so that the wheel pressure is increased and the fluid level is increased. Subsequently, the brake operation is canceled, the wheel pressure is lowered, and the fluid level is increased. The fluid level at the time when the braking force is 0 is higher than that before the start of the brake operation by an amount that results from releasing of the electric parking brake11.

In a time period T2, the wheel pressure is increased in response to a braking request, so that the fluid level is lowered. Subsequently, the braking request is canceled, the wheel pressure is decreased, and the fluid level is increased. In a time period T3, the wheel pressure is increased and the fluid level is decreased in response to a braking request. Thereafter, the ABS control is executed, and the second system14is operated. In this case, the wheel pressure and the fluid level change in conjunction with each other. The braking request is then canceled, the wheel pressure is decreased, and the fluid level is increased. The fluid level at the time when the braking force is 0 is increased due to the thermal expansion of the brake pads93every time when the brake operation is performed.

In a time period T4, the brake operation for stopping the vehicle is performed. In this case, the wheel pressure is increased, and the fluid level is decreased. After the vehicle stops, the electric parking brake11is turned on, and the piston95moves forward to enlarge the hydraulic-pressure chamber94a, so that the wheel pressure is decreased and the fluid level is decreased. Subsequently, the braking request is canceled, the wheel pressure is decreased, and the fluid level is increased. In a time period T5, reclamping by the electric parking brake11is carried out, so that the fluid level is decreased. This reclamping resets the influence on the clamping force due to the change in the thickness of the brake pads93after having been cooled, and the clamping force is maintained.

The increase in the wheel pressure in the time periods T1-T4 is brought about by the first system12, namely, by the load of the pump motor22b, and the ABS control and an ESC (skid prevention) control are executed by the second system14. The controller8monitors and grasps the operations of the systems12,14. In a case where the second system14(the pump motor58b) is driven while the brake pedal16is being operated, the driving does not cause any change in the fluid level because the reservoir20and the second system14are isolated from each other, but the stroke of the brake pedal16changes. Thus, the controller8can estimate the work amount of the pump motor58bbased on the operating status of the pump motor58band the results of detection by the stroke sensors102a,102b.

The present disclosure may be represented as follows.

(1) A brake device for a vehicle, including a fluid supply portion that supplies a fluid to a wheel cylinder utilizing the fluid in a reservoir, the brake device being configured such that a piston presses brake pads against a disc rotor in accordance with a hydraulic pressure in the wheel cylinder, so as to apply a braking force to a wheel, the brake device including:a fluid level sensor configured to measure a value of a fluid level in the reservoir;a wear-amount estimating portion configured to estimate a wear amount of the brake pads based on a result of measurement by the fluid level sensor;a heat-generation-amount estimating portion configured to estimate a heat generation amount of the brake pads based on the result of measurement by the fluid level sensor; anda fluid-leakage determining portion configured to determine whether a leakage of the fluid is occurring based on i) an amount of change in the fluid level that is based on the result of measurement by the fluid level sensor, ii) the wear amount, and iii) the heat generation amount.

(2) The brake device according to the above form (1), further including a WC reduction-amount estimating portion configured to estimate, based on the hydraulic pressure in the wheel cylinder, a WC reduction amount that is an amount of reduction in the fluid level arising from an operation of the fluid supply portion,wherein the fluid-leakage determining portion is configured to determine whether the leakage of the fluid is occurring also based on the WC reduction amount.

(3) The brake device according to the above form (1) or (2), further including:an electric parking brake configured to move the piston by a force of an electric motor; andan EPB reduction-amount estimating portion configured to estimate, based on a clamping force of the electric parking brake, an EPB reduction amount that is an amount of reduction in the fluid level arising from an operation of the electric parking brake,wherein the fluid-leakage determining portion is configured to determine whether the leakage of the fluid is occurring also based on the EPB reduction amount.

(4) The brake device according to any one of the above forms (1)-(3), wherein the fluid-leakage determining portion stores in advance a first map representing a relationship between the wear amount and the amount of change in the fluid level and a second map representing a relationship between the heat generation amount and the amount of change in the fluid level.

(5) The brake device according to any one of the above forms (1)-(4), further comprising a pad replacement-timing determining portion configured to determine timing of replacement of the brake pads based on at least one of the wear amount and the heat generation amount.

(6) The brake device according to any one of the above forms (1)-(5), further including:a work-amount estimating portion configured to estimate a work amount of a pump motor of the fluid supply portion and a total wok amount that is an integrated value of the work amount, based on the result of measurement by the fluid level sensor and the hydraulic pressure in the wheel cylinder; anda motor replacement-timing determining portion configured to determine timing of replacement of the pump motor based on the total work amount.

(7) The brake device according to the above form (6), wherein the work-amount estimating portion is configured to estimate the work amount based on the amount of change in the fluid level per unit time and an amount of change in the hydraulic pressure in the wheel cylinder per unit time.

(8) The brake device according to any one of the above forms (1)-(7), further including:an electric parking brake configured to move the piston by a force of an electric motor;an EPB work-amount estimating portion configured to estimate an EPB work amount that is a work amount of the electric motor and a total EPB work amount that is an integrated value of the EPB work amount, based on the result of measurement by the fluid level sensor and the hydraulic pressure in the wheel cylinder; andan EPB replacement-timing determining portion configured to determine timing of replacement of the electric motor based on the total EPB work amount.

(9) The brake device according to the above form (8), wherein the EPB work-amount estimating portion is configured to estimate the EPB work amount based on the amount of change in the fluid level per unit time and an amount of change in the hydraulic pressure in the wheel cylinder per unit time.

(10) The brake device according to the above form (1),wherein the fluid-leakage determining portion determines that the leakage of the fluid is occurring when a difference between an initial fluid level that is the fluid level initially measured and a present fluid level that is the fluid level presently measured is greater than a fluid leakage threshold, andwherein the fluid-leakage determining portion decreases the fluid leakage threshold based on the wear amount and increases the fluid leakage threshold based on the heat generation amount.

(11) The brake device according to the above form (2),wherein the fluid-leakage determining portion determines that the leakage of the fluid is occurring when a difference between an initial fluid level that is the fluid level initially measured and a present fluid level that is the fluid level presently measured is greater than a fluid leakage threshold, andwherein the fluid-leakage determining portion decreases the fluid leakage threshold based on the wear amount and the WC reduction amount and increases the fluid leakage threshold based on the heat generation amount.

(12) The brake device according to the above form (11), further including:an electric parking brake configured to move the piston by a force of an electric motor; andan EPB reduction-amount estimating portion configured to estimate, based on a clamping force of the electric parking brake, an EPB reduction amount that is an amount of reduction in the fluid level arising from an operation of the electric parking brake,wherein the fluid-leakage determining portion decreases the fluid leakage threshold based on the wear amount, the WC reduction amount, and the EPB reduction amount and increases the fluid leakage threshold based on the heat generation amount.

Modification

The present disclosure is not limited to the details of the embodiment illustrated above. As illustrated inFIG.10, the first system12may include, for instance, an accumulator24, which is a high-pressure source. The accumulator24is disposed between the first pump device22and the pressure-increasing linear valve SLA. Owing to the action of the first pump device22configured to pump up the fluid in the reservoir20, the accumulator24stores the fluid having a high-pressure ranging from a predetermined lower limit pressure to a predetermined upper limit pressure. When the pressure-increasing linear valve SLA is opened, the high-pressure fluid is supplied from the accumulator24to the first pilot chamber R6to move the spool30c, so that the high-pressure port P2and the regulated-pressure port P3are brought into communication with each other. As a result, the high-pressure fluid is supplied from the accumulator24to the servo chamber R4through the ports P2, P3, so that the servo pressure is increased to move the master pistons28c,28dforward. Thus, the master pressure is increased.

A hydraulic pressure in the accumulator24(hereinafter referred to as “accumulator pressure” where appropriate) is detected by a pressure sensor100. Owing to the action of the first pump device22, the fluid is supplied in advance from the reservoir20to the accumulator24, regardless of the presence or absence of a braking request, such that the accumulator pressure is higher than or equal to a predetermined lower limit value. In the first system12equipped with the accumulator24, therefore, timing of decrease of the fluid level in the reservoir20and timing of increase of the wheel pressure differ from each other in some case. The first pump device22stops operating when the accumulator pressure becomes equal to a predetermined value (lower limit value≤predetermined value≤upper limit value). Thus, it is possible to estimate the work amount of the pump motor22bby permitting the controller8to monitor the fluid-level change amount and the operating status of the pump motor22b(and the accumulator pressure, for instance). The reduction-amount estimating portion83can estimate the reduction amount of the fluid level based on the wheel pressure and the accumulator pressure, for instance.

In the system having the accumulator24, the fluid amount pumped up by the pump for the accumulator (i.e., the first pump device22) and the pressure required for pumping up the fluid can be estimated by calculation. In a time period from when the fluid in the accumulator24starts reducing by the brake actuation to when the first pump device22is operated next time, the fluid amount remaining in the accumulator24is unavailable. It is thus difficult to determine which one of the following three factors is responsible for the change in the fluid level in the reservoir20caused at the time of the brake release: (1) The change is caused by the fluid amount returned to the reservoir20from the accumulator24by the brake release; (2) The change is caused by the piston95that has been pushed backward by the thermal expansion of the brake pads93; and (3) The change is caused by the piston95that has moved forward due to the wear of the brake pads93. Due to the factor (2), the fluid level is increased. Due to the factor (3), the fluid level is reduced.

The controller8monitors when the first pump device22is operating. Thus, the fluid in the accumulator24is constant immediately after the first pump device22has pumped up the fluid, namely, immediately after the first pump device22has finished operating such as immediately after the accumulator pressure has become equal to the predetermined value (lower limit value≤predetermined value≤upper limit value). It is accordingly possible to determine which one of the factors (1)-(3) described above is responsible for the change in the fluid level. As for the thermal expansion of the brake pads93, it is considered that the fluid level does not largely change if the number of times braking is performed is small (once or twice, for instance). Thus, the effect of the thermal expansion in this case can be set to be negligible. As for the wear of the brake pads93, braking needs to be performed at a high-pressure for a long length of time for large wear of the brake pads93. In this case, it is considered that the first pump device22operates several times during braking. In this way, a factor determination pattern (conditions) for each event can be preset in the controller8. By comparing the fluid levels between immediately after completion of an n-th time operation of the first pump device22and immediately after completion of an (n+1)-th time operation of the first pump device22or by comparing the fluid levels before and after the operation of the first pump device22, the system according to this modification is capable of performing various calculations (estimations), like the on-demand system of the illustrated embodiment. For instance, each time when the first pump device22finishes operating, the controller8may detect the fluid level and may calculate the change amount of the fluid level.

As for the operation of the electric parking brake11, in a state in which the hydraulic brake by the systems12,14is not operating and the reservoir20and the wheel cylinder94are held in communication with each other, it is possible to detect the change in the fluid level arising from the electric parking brake11without taking account of the influence of the accumulator24. As for the operation of the electric parking brake11when the hydraulic brake by the systems12,14is operating, various calculations can be performed by regarding the change in the fluid level as being caused due to the operation of the electric parking brake11as long as the first pump device22does not operate concurrently with the operation of the electric parking brake11. Even in a case where the first pump device22operates concurrently with the operation of the electric parking brake11, the calculations can be performed with a certain degree of accuracy by measuring and storing, in advance, the rate of change in the fluid level due to the operation of the first pump device22and by regarding a difference between the stored rate of change and the currently calculated rate of change as the change amount of the fluid level due to the operation of the electric parking brake11. InFIG.10, part of the configuration including the second system14is not illustrated.