Vehicle brake system

Provided is a vehicle brake system capable of reducing a sense of discomfort felt by a driver, even if a transmission is shifted when a braking force holding function for keeping a vehicle stationary is in operation. A vehicle brake system includes a control system capable of determining whether an automatic transmission is set in a driving mode or in a non-driving mode, and is capable of operating the braking force holding function for keeping the vehicle stationary by holding a braking force generated through a brake pedal operation. Further, the control system operates the braking force holding function when a vehicle speed becomes lower than a predetermined threshold value by the braking force generated through the brake pedal operation, and if the control system determines that the automatic transmission is set in a non-driving mode, the control unit increases the braking force and holds the braking force.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under Title 35, United States Code, 119 (a)-(d) of Japanese Patent Application No. 2013-108181 filed on May 22, 2013 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a vehicle brake system.

BACKGROUND ART

A vehicle brake device (vehicle brake system) which has a hydraulic holding function is, for example, disclosed in Patent Document 1. When a driver generates a braking force to a vehicle by operating a brake operation unit (brake pedal or the like), even if the driver releases the brake operation unit when the vehicle is stopped and in a stationary state, the hydraulic holding function keeps the vehicle stationary by holding the braking force.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

If the vehicle brake device described in Patent Document 1 is included in a vehicle equipped with an automatic transmission as a transmission, when the automatic transmission is shifted to a drive mode from a neutral mode while the hydraulic holding function is in operation, a creep force is applied to the vehicle.

Therefore, when the hydraulic holding function is in operation as a braking force holding function and the vehicle is kept stationary, if the automatic transmission is shifted to the drive mode from the neutral mode, the driver feels a sense of discomfort because the vehicle starts moving for a moment. Therefore, an object of the present invention is to provide a vehicle brake system capable of reducing the sense of discomfort felt by the driver, even if the transmission is shifted when the braking force holding function for keeping the vehicle stationary is in operation.

Solution to Problem

In order to solve the above problem, a vehicle brake system according to the present invention includes a control unit capable of determining whether a transmission is set in a driving mode, in which a power outputted by a power unit of a vehicle is transmitted to driving wheels, or in a non-driving mode other than the driving mode, and a booster unit for increasing a braking force generated when a brake operation unit is operated, and the vehicle brake system is configured to be able to operate a braking force holding function for holding the braking force which is generated by operating the brake operation unit. Further, the vehicle brake system is characterized in that the control unit operates the braking force holding function when the braking force is applied and a speed of the vehicle becomes lower than a predetermined speed threshold value, and when the control unit operates the braking force holding function and determines that the transmission is set in the non-driving mode, the control unit increases the braking force, which is generated by operating the brake operation unit, by the booster unit and holds the braking force.

According to the present invention, when the control unit operates the braking force holding function for keeping the vehicle stationary by holding the braking force generated by operating the brake operation unit, if the transmission is set in the non-driving mode (the neutral mode or the like), the vehicle brake system can increase the braking force and hold it. If the transmission is an automatic transmission, when the transmission is shifted to the driving mode (the drive mode or the like), a creep force is applied to the vehicle, and if the braking force is small when the braking force holding function is in operation, the vehicle starts moving by the creep force in some cases. In a state where the transmission is set in the non-driving mode, when the braking force holding function is in operation, the vehicle brake system increases the braking force and holds it. Hereby, the vehicle is prevented from starting moving due to the creep force, and thus a sense of discomfort felt by the driver can be reduced.

Further, the vehicle brake system according to the present invention is characterized in that when the control unit operates the braking force holding function and determines that the transmission is set in the non-driving mode, if the braking force generated by operating the brake operation unit is smaller than a predetermined defined braking force, the control unit increases the braking force by the booster unit up to the defined braking force and holds the braking force.

According to the present invention, if the transmission is set in the non-driving mode when the braking force holding function is in operation, the braking force is increased to the defined braking force by the booster unit only when the braking force generated by operating the brake operation unit is smaller than the predetermined defined braking force set in advance. Therefore, the driving of the booster unit becomes limited, and thus it is possible to suppress energy consumption due to the driving of the booster unit.

Further, a vehicle brake system according to the present invention is characterized in that the vehicle brake system includes a control unit capable of determining whether a transmission is set in the driving mode, in which a power outputted by a power unit of a vehicle is transmitted to driving wheels, or in the non-driving mode other than the driving mode, and is configured to be able to operate a braking force holding function for holding a braking force which is generated by operating a brake operation unit. Furthermore, the vehicle brake system is characterized in that when the braking force is applied and a speed of the vehicle becomes lower than a predetermined speed threshold value, if the control unit determines that the transmission is set in the non-driving mode, the control unit operates the braking force holding function when the braking force is more than or equal to a predetermined defined braking force.

According to the present invention, if the control unit determines that the transmission is in the non-driving mode when it determines that the vehicle is stopped, the control unit operates the braking force holding function when the braking force generated by operating the brake operation unit is more than or equal to the predetermined defined braking force. Therefore, the vehicle brake system keeps the braking force of sufficient magnitude to prevent the vehicle from starting moving due to the creep force, and thus operates the braking force holding function. Hereby, even if the transmission is shifted to the driving mode, the vehicle is prevented from starting moving due to the creep force, and thus the sense of discomfort felt by the driver can be reduced.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a vehicle brake system capable of reducing a sense of discomfort felt by a driver even if the transmission is shifted when the braking force holding function for keeping the vehicle stationary is in operation.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment according to the present invention will be described in detail with reference to the accompanying drawings.FIG. 1is a block diagram of a vehicle according to the first embodiment, andFIG. 2is a schematic block diagram of a vehicle brake system according to the first embodiment.

A vehicle brake system10according to the first embodiment is included in a vehicle1which is configured as shown inFIG. 1. The vehicle1is configured to travel by transmitting a power outputted through a power unit such as an internal combustion engine (an engine2) to drive wheels (for example, a right front wheel WFR and a left front wheel WFL), and includes an automatic transmission3as a transmission between the driving wheels and the engine2. Further, the vehicle1includes the vehicle brake system10for applying a braking force to each of wheels (the right front wheel WFR, the left front wheel WFL, a left rear wheel WRL, a right rear wheel WRR) by being controlled by a control unit150. Then, the control unit150of the first embodiment is configured to be inputted a signal indicating a mode of the automatic transmission3selected by an unillustrated selector lever or the like. Incidentally, the vehicle1may include driving wheels of the left rear wheel WRL and the right rear wheel WRR, or include driving wheels of all.

The automatic transmission3of the first embodiment can be set in a driving mode (a drive mode, a reverse mode, or the like), in which the power outputted by the engine2is transmitted to the driving wheels (the right front wheel WFR, the left front wheel WFL), or in a non-driving mode (a neutral mode, a parking mode, or the like) other than the drive modes. Further, the control unit150is configured to be capable of determining, by the signal indicating the mode, whether the automatic transmission3is set in the driving mode or is set in the non-driving mode.

As shown inFIG. 2, the vehicle brake system10of the first embodiment is configured to include a hydraulic pressure generator (an input device)14, a pedal stroke sensor St, a motor cylinder device16, and a vehicle behavior stabilizing device18(hereinafter, referred to as a VSA (Vehicle Stability Assist) device18, VSA; registered trademark). When a brake operation unit such as a brake pedal12is operated by a driver, the input device14generates a hydraulic pressure (brake hydraulic pressure) in accordance with an input of the operation, to a brake fluid which is a hydraulic fluid. The pedal stroke sensor St detects an operation amount (a stroke) when the brake pedal12is operated to be depressed. The motor cylinder device16controls a slave hydraulic pressure as the brake hydraulic pressure. The VSA device18assists stabilization of a vehicle behavior.

These input device14, motor cylinder device16, and VSA device18are, for example, connected with one another through conduit paths (hydraulic paths) made of pipe materials such as a hose or a tube, while the input device14and the motor cylinder device16are electrically connected with each other through an unillustrated harness, as the by-wire brake system.

Among these, the hydraulic paths will be described. With reference to a connection point A1 (slightly below center) inFIG. 2, one connection port20aof the input device14and the connection point A1 are connected through a first piping tube22a, and an outlet port24aof the motor cylinder device16and the connection point A1 are connected through a second piping tube22b, and further, an inlet port26aof the VSA device18and the connection point A1 are connected through a third piping tube22c.

With reference to another connection point A2 inFIG. 2, the other connection port20bof the input device14and the connection point A2 are connected through a fourth piping tube22d, and another outlet port24bof the motor cylinder device16and the connection point A2 are connected through a fifth piping tube22e, and further, another inlet port26bof the VSA device18and the connection point A2 are connected through a sixth piping tube22f.

The VSA device18is provided with a plurality of outlet ports28ato28d. A first outlet port28ais connected to a wheel cylinder32FR of a disc brake mechanism30aprovided on a front right wheel WFR through a seventh piping tube22g. A second outlet port28bis connected to a wheel cylinder32RL of a disc brake mechanism30bprovided on a rear left wheel WRL through an eighth piping tube22h. A third outlet port28cis connected to a wheel cylinder32RR of a disc brake mechanism30cprovided on a rear right wheel WRR through a ninth piping tube22i. A fourth outlet port28dis connected to a wheel cylinder32FL of a disc brake mechanism30dprovided on a front left wheel WFL through a tenth piping tube22j.

In this case, a brake fluid is supplied to each of the wheel cylinders32FR,32RL,32RR, and32FL of the disc brake mechanisms30ato30dthrough the piping tubes22gto22jconnected to each of the outlet ports28ato28d. Each of the wheel cylinders32FR,32RL,32RR, and32FL is actuated upon an increase of the brake hydraulic pressure in each of the wheel cylinders32FR,32RL,32RR, and32FL, and a friction force against the corresponding wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL) is increased, and thus the braking force is applied to the corresponding wheels.

Further, each of the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL includes wheel speed sensors35a,35b,35c,35dfor detecting wheel speeds, respectively, and a measurement signal generated by measuring the wheel speed of each of the wheels by each of the wheel speed sensors35a,35b,35c,35dis inputted into the control unit150.

The input device14includes a tandem-type master cylinder34capable of generating the hydraulic pressure in the brake fluid in accordance with the operation of the brake pedal12by the driver, and a reservoir (first reservoir36) attached to the master cylinder34. In a cylinder tube38of the master cylinder34, two pistons (a secondary piston40a, a primary piston40b), which are spaced by a predetermined distance from each other in an axial direction of the cylinder tube38, are disposed slidably. The secondary piston40ais disposed in close proximity to the brake pedal12, and connected to the brake pedal12via a push rod42. Further, the primary piston40bis disposed further from the brake pedal12than the secondary piston40a.

Further, a pair of cap seals44Pa,44Pb which exhibits a ring shape and is in sliding contact with an outer periphery of the primary piston40b, and a pair of cap seals44Sa,44Sb which exhibits a ring shape and is in sliding contact with an outer periphery of the secondary piston40a, are attached to an inner wall of the cylinder tube38. Furthermore, one spring member50ais provided between the secondary piston40aand the primary piston40b, and the other spring member50bis provided between the primary piston40band a side end portion38aon a closed end side of the cylinder tube38.

Further, a guide rod48bis extended in a sliding direction of the primary piston40bfrom the side end portion38aof the cylinder tube38, and the primary piston40bslides while being guided by the guide rod48b. Furthermore, a guide rod48ais extended in a sliding direction of the secondary piston40afrom an end portion of the secondary piston40aside of the primary piston40b, and the secondary piston40aslides while being guided by the guide rod48a. Then, the secondary piston40aand the primary piston40bare arranged in series while being connected by the guide rod48a. The guide rods48a,48bwill be described later in detail.

Further, the cylinder tube38of the master cylinder34is provided with two supply ports (a secondary supply port46a, a first supply port46b), two relief ports (a secondary relief port52a, a first relief port52b), and two outlet ports54a,54b. In this case, the second supply port46a, the first supply port46b, and the secondary relief port52a, the first relief port52bare provided so as to join together to be in communication with an unillustrated reservoir chamber in the first reservoir36, respectively. Furthermore, the pair of cap seals44Sa,44Sb slidably contacting with the outer periphery of the secondary piston40ais disposed sandwiching the second relief port52ain the sliding direction of the secondary piston40a. Further, the pair of cap seals44Pa,44Pb slidably contacting with the outer periphery of the primary piston40bis disposed sandwiching the first relief port52bin the sliding direction of the primary piston40b.

Further, a second pressure chamber56aand first pressure chamber56b, which generate a hydraulic pressure in accordance with a depression force applied to the brake pedal12by the driver, are provided in the cylinder tube38of the master cylinder34. The second pressure chamber56ais provided to be in communication with the connection port20avia a second hydraulic path58a, and the first pressure chamber56bis provided to be in communication with the other connection port20bvia a first hydraulic path58b. The second pressure chamber56aand the first pressure chamber56bare sealed liquid-tightly therebetween with the pair of cup seals44Sa,44Sb. Further, the brake pedal12side of the second pressure chamber56ais sealed liquid-tightly with the pair of cup seals44Pa,44Pb.

The first pressure chamber56bis configured to generate a hydraulic pressure in accordance with a displacement of the primary piston40b, and second pressure chamber56ais configured to generate a hydraulic pressure in accordance with a displacement of the secondary piston40a. Further, the secondary piston40ais connected to the brake pedal12via the push rod42, and is displaced in the cylinder tube38in accordance with the operation of the brake pedal12. Furthermore, the primary piston40bis displaced by a hydraulic pressure generated in the second pressure chamber56aby the displacement of the secondary piston40a. In other words, the primary piston40bis displaced in response to the secondary piston40a.

Between the master cylinder34and the connection port20a, a pressure sensor Pm is provided on the upstream side of the second hydraulic path58a, while a second shut-off valve60amade of a normally open type solenoid valve is provided on the downstream side of the second hydraulic path58a. The pressure sensor Pm is adapted to measure the hydraulic pressure on the upstream side closer to the master cylinder34than the second shut-off valve60aon the second hydraulic path58a.

Between the master cylinder34and the other connection port20b, a first shut-off valve60bmade of a normally open type solenoid valve is provided on the upstream side of the first hydraulic path58b, while a pressure sensor Pp is provided on the downstream side of the first hydraulic path58b. The pressure sensor Pp is adapted to measure the hydraulic pressure on the downstream side closer to the wheel cylinders32FR,32RL,32RR, and32FL than the first shut-off valve60bon the first hydraulic path58b.

The term “normally open” of the first shut-off valve60band the second shut-off valve60ameans that a normal position (a valving element position when not energized) of the valve is in a state of an open position (normally open). Note that, inFIG. 2, the first shut-off valve60band the second shut-off valve60arespectively shows a closed valve state in which a solenoid is energized to actuate an unillustrated valving element.

On the first hydraulic path58bbetween the master cylinder34and the first shut-off valve60b, a branch hydraulic path58cbifurcated from the second hydraulic path58bis provided, and a third shut-off valve62made of a normally closed type solenoid valve and a stroke simulator64are connected in series to the branch hydraulic path58c. The term “normally closed” of the third shut-off valve62means that a normal position (a valving element position when not energized) of the valve is in a state of a closed position (normally closed). Note that, inFIG. 2, the third shut-off valve62shows an open valve state in which a solenoid is energized to actuate an unillustrated valving element.

The stroke simulator64is a device which makes the driver feel as if the braking force is generated in accordance with the depression force by generating a reaction force and a stroke for a depression operation of the brake pedal12at the time of by-wire control, and is disposed on the master cylinder34side from the first shut-off valve60bon the first hydraulic path58b. The stroke simulator64is provided with a hydraulic chamber65which is in communication with the branch hydraulic path58c, and is provided so as to be capable of absorbing the brake fluid which is derived from the first pressure chamber56bof the master cylinder34via the hydraulic chamber65.

The stroke simulator64includes a first return spring66ahaving a high spring constant, a second return spring66bhaving a low spring constant, which are arranged in series with each other, and a simulator piston68which is urged by the first and second return springs66a,66b. Further, the stroke simulator64is provided such that an operation feeling for the brake pedal12is equivalent to the operation feeling when depressing a conventional master cylinder34by setting an increasing gradient of the pedal reaction force to be low in the former period of depression of the brake pedal12, and by setting the pedal reaction force to be high in the latter period of depression of the brake pedal12. In other words, the stroke simulator64is configured to generate the reaction force in accordance with the hydraulic pressure of the brake fluid derived from the first pressure chamber56b, and apply the reaction force to the brake pedal12via the master cylinder34.

The hydraulic paths are roughly divided into a second hydraulic system70awhich connects the second pressure chamber56aof the master cylinder34to the plurality of wheel cylinders32FR,32RL, and a first hydraulic system70bwhich connects the first pressure chamber56bof the master cylinder34to the plurality of wheel cylinders32RR,32FL.

The second hydraulic system70ais composed of the second hydraulic path58awhich connects the outlet port54aof the master cylinder34(cylinder tube38) in the input device14to the connection port20a, the piping tubes22a,22bwhich connect the connection port20aof the input device14to the outlet port24aof the motor cylinder device16, the piping tube22b,22cwhich connect the outlet port24aof the motor cylinder device16to the inlet port26aof the VSA device18, and the piping tubes22g,22hwhich connect the outlet ports28a,28bof the VSA device18to the wheel cylinders32FR,32RL, respectively.

The first hydraulic system70bhas the first hydraulic path58bwhich connects the outlet port54bof the master cylinder34(cylinder tube38) in the input device14to the other connection port20b, the piping tubes22d,22ewhich connect the other connection port20bof the input device14to the outlet port24bof the motor cylinder device16, the piping tube22e,22fwhich connect the outlet port24bof the motor cylinder device16to the inlet port26bof the VSA device18, and the piping tubes22i,22jwhich connect the outlet ports28c,28dof the VSA device18to the wheel cylinders32RR,32FL, respectively.

The motor cylinder device16has a motor (an electric motor72), an actuator mechanism74, and a cylinder mechanism76which is urged by the actuator mechanism74.

The actuator mechanism74is provided on an output shaft72bside of the electric motor72, and has a gear mechanism (deceleration mechanism)78and a ball screw structure80. The gear mechanism78transmits a rotational driving force of the electric motor72by meshing a plurality of gears, and the ball screw structure80includes balls80band a ball screw shaft80awhich moves back and forth in the axial direction by being transmitted the rotational driving force via the gear mechanism78. In the first embodiment, the ball screw structure80is housed in a mechanism housing portion173aof an actuator housing172together with the gear mechanism78.

The cylinder mechanism76has a substantially cylindrical cylinder body82and a second reservoir84attached to the cylinder body82. The second reservoir84is connected to the first reservoir36attached to the master cylinder34of the input device14via a piping tube86, and is provided such that the brake fluid stored in the first reservoir36is supplied to the second reservoir84via the piping tube86. Note that, the piping tube86may be provided with a tank which stores the brake fluid. The open end portion of the cylinder body82having a substantially cylindrical shape is fitted into the actuator housing172composed of a housing body172F and a housing cover172R, and thus the cylinder body82and the actuator housing172are connected with each other, to construct the motor cylinder device16.

In the cylinder body82, a second slave piston88aand a first slave piston88b, which are separated by a predetermined distance in an axial direction of the cylinder body82, are arranged slidably. The second slave piston88ais disposed in close proximity to the ball screw structure80side, to come into contact with one end portion of the ball screw shaft80a, and is displaced integrally with the ball screw shaft80ain a direction of an arrow X1 or X2. Further, the first slave piston88bis disposed further from the ball screw structure80side than the second slave piston88a.

The electric motor72according to the first embodiment is configured to be covered with a motor casing72awhich is formed separately from the cylinder body82, and is disposed such that the output shaft72bis substantially in parallel with the sliding direction (axial direction) of the second slave piston88aand first slave piston88b. Further, it is configured such that the rotational driving of the output shaft72bis transmitted to the ball screw structure80via the gear mechanism78.

The gear mechanism78is, for example, composed of three gears, which are a first gear78a, a third gear78c, and a second gear78b. The first gear is attached to the output shaft72bof the electric motor72, and the third gear78crotates the balls80b, which make the ball screw shaft80amove back and forth in the axial direction, around the axis of the ball screw shaft80a, and further the second gear78btransmits a rotation of the first gear78ato the third gear78c. Furthermore, the third gear78crotates around the axis of the ball screw shaft80a.

By the structure described above, the actuator mechanism74according to the first embodiment converts the rotational driving force of the output shaft72bof the electric motor72into a reciprocating driving force (linear driving force) of the ball screw shaft80a.

On the outer peripheral surface of the first slave piston88b, via annular step portions, each of a pair of slave cup seals90a,90bis mounted. Between the pair of slave cup seals90a,90b, a first back chamber94b, which is in communication with a reservoir port92bto be described later, is formed. Note that, between the second slave piston88aand the first slave piston88b, a second return spring96ais provided, and between the side end portion of the cylinder body82and the first slave piston88b, a first return spring96bis provided.

An annular guide piston90c, which liquid-tightly seals a gap between the mechanism housing portion173aand the outer peripheral surface of the second slave piston88a, and guides the second slave piston88amovably in the axial direction, is provided behind the second slave piston88aso as to close the cylinder body82as a seal member. A gap between the second slave piston88aand the guide piston90cis preferably configured to be liquid-tight by mounting an unillustrated slave cup seal on the inner peripheral surface of the guide piston90cinto which the second slave piston88apenetrates. Further, on the outer peripheral surface of the front portion of the second slave piston88a, a slave cup seal90bis mounted via an annular step portion. With this configuration, the brake fluid filled in the cylinder body82is sealed in the cylinder body82by the guide piston90c, and does not flow into the side of the actuator housing172. Note that, between the guide piston90cand the slave cup seal90b, a second back chamber94a, which is in communication with a reservoir port92ato be described later, is formed.

In the cylinder body82of the cylinder mechanism76, two reservoir ports92a,92band two outlet ports24a,24bare provided. In this case, the reservoir port92a(92b) is provided so as to be in communication with an unillustrated reservoir chamber in the second reservoir84.

Further, in the cylinder body82, the second hydraulic chamber98aand the first hydraulic chamber98bare provided. The second hydraulic chamber98acontrols a brake hydraulic pressure which is outputted from the outlet port24ato the wheel cylinders32FR,32RL side, and the first hydraulic chamber98bcontrols a brake hydraulic pressure which is outputted from the other outlet port24bto the wheel cylinders32RR,32FL side.

With this configuration, the second back chamber94a, the first back chamber94b, the second hydraulic chamber98a, and the first hydraulic chamber98b, in which the brake fluid is sealed, are sealing portions of the brake fluid in the cylinder body82, and are partitioned liquid-tightly (hermetically) from the mechanism housing portion173aof the actuator housing172by the guide piston90cwhich functions as a seal member. Note that, a method of attaching the guide piston90cto the cylinder body82is not limited thereto, and for example, it may be configured to be attached by an unillustrated circlip.

Between the second slave piston88aand the first slave piston88b, a regulation unit100for regulating maximum strokes (maximum displacement distances) and minimum strokes (minimum displacement distances) of the second slave piston88aand the first slave piston88bis provided. Further, on the first slave piston88b, a stopper pin102for regulating a sliding range of the first slave piston88bto prevent over-return to the second slave piston88aside is provided. With this configuration, when one system fails, a failure in the other system is prevented, particularly during backup time when braking by the master cylinder34.

The VSA device18is composed of known components, and has a second brake system110afor controlling the second hydraulic system70aconnected to the disc brake mechanisms30a,30b(the wheel cylinders32FR,32RL) of the front right wheel WFR and the rear left wheel WRL, and a first brake system110bfor controlling the first hydraulic system70bconnected to the disc brake mechanisms30c,30d(the wheel cylinders32RR,32FL) of the rear right wheel WRR and the front left wheel WFL. Here, the second brake system110amay be a hydraulic system connected to the disc brake mechanisms provided on the front left wheel WFL and the front right wheel WFR, and the first brake system110bmay be a hydraulic system connected to the disc brake mechanisms provided on the rear right wheel WRR and the rear left wheel WRL. Further, the second brake system110amay be a hydraulic system connected to the disc brake mechanisms provided on the front right wheel WFR and the rear right wheel WRR on one side of the vehicle body, and the first brake system110bmay be a hydraulic system connected to the disc brake mechanisms provided on the front left wheel WFL and the rear left wheel WRL on the other side of the vehicle body.

Since the second brake system110aand the first brake system110bhave the same structures with each other, those corresponding to each other in the second brake system110aand in the first brake system110bare given the same reference numerals, while descriptions will be focused on the second brake system110a, and descriptions of the first brake system110bwill be appended in parentheses.

The second brake system110a(the first brake system110b) has common conduit paths (a first common hydraulic path112and a second common hydraulic path114), which are common to the wheel cylinders32FR,32RL (32RR,32FL). Among these, the first common hydraulic path112is a supply path for supplying the brake hydraulic pressure to the wheel cylinders32FR,32RL (32RR,32FL). The VSA device18includes a regulator valve116, a first check valve118, a first inlet valve120, a second check valve122, a second inlet valve124, and a third check valve126. The regulator valve116is made of a normally open type solenoid valve disposed between an inlet port26a(26b) and the first common hydraulic path112. The first check valve118is disposed in parallel with the regulator valve116, and allows the brake fluid to flow from the inlet port26a(26b) side to the side of the first common hydraulic path112(prevents the brake fluid from flowing to the inlet port26a(26b) side from the side of the first common hydraulic path112). The first inlet valve120is made of a normally open type solenoid valve disposed between the first common hydraulic path112and the first outlet port28a(fourth outlet port28d). The second check valve122is disposed in parallel with the first inlet valve120, and allows the brake fluid to flow from the first outlet port28a(fourth outlet port28d) side to the side of the first common hydraulic path112(prevents the brake fluid from flowing to the first outlet port28a(fourth outlet port28d) side from the side of the first common hydraulic path112). The second inlet valve124is made of a normally open type solenoid valve disposed between the first common hydraulic path112and the second outlet port28b(third outlet port28c). The third check valve126is disposed in parallel with the second inlet valve124, and allows the brake fluid to flow from the second outlet port28b(third outlet port28c) side to the side of the first common hydraulic path112(prevents the brake fluid from flowing to the second outlet port28b(third outlet port28c) side from the side of the first common hydraulic path112).

Note that, the VSA device18of the first embodiment is provided with a pressure sensor P1 for measuring the brake hydraulic pressure in the first common hydraulic path112, and a measurement signal measured by the pressure sensor P1 is inputted into the control unit150.

The first inlet valve120and the second inlet valve124are opening/closing means for opening and closing the conduit path (first common hydraulic path112) through which the brake hydraulic pressure is supplied to the wheel cylinders32FR,32RL,32RR,32FL. When the first inlet valve120is closed, supply of the brake hydraulic pressure from the first common hydraulic path112to the wheel cylinders32FR,32RL is shut off. Further, when the second inlet valve124is closed, supply of the brake hydraulic pressure from the first common hydraulic path112to the wheel cylinders32RR,32FL is shut off.

Further, the VSA18includes a first outlet valve128, a second outlet valve130, a reservoir132, a fourth check valve134, a pump136, an intake valve138, a discharge valve140, a motor M, and a suction valve142. The first outlet valve128is made of a normally closed type solenoid valve disposed between the first outlet port28a(fourth outlet port28d) and the second common hydraulic path114. The second outlet valve130is made of a normally closed type solenoid valve disposed between the second outlet port28b(third outlet port28c) and the second common hydraulic path114. The reservoir132is connected to the second common hydraulic path114. The fourth check valve134is disposed between the first common hydraulic path112and the second common hydraulic path114, and allows the brake fluid to flow from the second common hydraulic path114side to the first common hydraulic path112side (prevents the brake fluid from flowing to the second common hydraulic path114side from the first common hydraulic path112side). The pump136is disposed between the fourth check valve134and the first common hydraulic path112, and supplies the brake fluid to the first common hydraulic path112side from the second common hydraulic path114side. The intake valve138and the discharge valve140are disposed respectively before and after the pump136driven by the motor M. The suction valve142is made of a normally closed type solenoid valve disposed between the second common hydraulic path114and the inlet port26a(26b).

Note that, in the second brake system110a, on a conduit path (hydraulic path) in close proximity to the inlet port26a, a pressure sensor Ph for measuring the brake hydraulic pressure which is outputted from the output port24aof the motor cylinder device16and controlled through the second hydraulic chamber98aof the motor cylinder device16, is provided. Measurement signals measured by the respective pressure sensors Pm, Pp, and Ph are inputted into the control unit150. Further, the VSA device18is capable of performing ABS (Antilock Brake System) control, in addition to VSA control. Furthermore, in place of the VSA device18, an ABS device equipped with only ABS function may be configured to be connected. The vehicle brake system10according to the first embodiment is basically configured as described above, and the operation and effect will be described in the following.

In a normal state where the vehicle brake system10works properly, the first shutoff valve60band the second shutoff valve60amade of normally open type solenoid valves are in the closed valve state by energization, and the third shutoff valve62made of a normally closed type solenoid valve is in the open valve state by energization. Therefore, since the second hydraulic system70aand the first hydraulic system70bare shut off by the second shutoff valve60aand the first shutoff valve60b, the hydraulic pressure generated by the master cylinder34of the input device14is not transmitted to the wheel cylinders32FR,32RL,32RR,32FL of the disc brake mechanisms30ato30d.

In this case, the hydraulic pressure generated in the first pressure chamber56bof the master cylinder34is transmitted to the hydraulic chamber65of the stroke simulator64via the branch hydraulic path58cand the third shutoff valve62in the open valve state. By the hydraulic pressure supplied to the hydraulic chamber65, the simulator piston68is displaced against the spring force of the first and second return springs66a,66b, and thus a stroke of the brake pedal12is allowed while a pseudo-pedal reaction force is generated and applied to the brake pedal12. As a consequence, a brake feeling which is not uncomfortable for the driver is obtained.

In such a system state, upon detecting the depression of the brake pedal12by the driver, the control unit150determines the braking and drives the electric motor72of the motor cylinder device16to urge the actuator mechanism74, and displaces the second slave piston88aand the first slave piston88btoward the direction of the arrow X1 inFIG. 2, against the spring forces of the second return spring96aand the first return spring96b. By the displacement of the second slave piston88aand the first slave piston88b, the brake hydraulic pressure in the second hydraulic chamber98aand the brake hydraulic pressure in the first hydraulic chamber98bare pressurized so as to be balanced with each other, and thus an intended brake hydraulic pressure is generated.

Specifically, the control unit150calculates a depression operation amount (hereinafter, appropriately referred to as “brake operation amount”) of the brake pedal12in accordance with a measured value of the pedal stroke sensor St, and sets a brake hydraulic pressure which is a target in consideration of a regenerative braking force Pmot on the basis of the brake operation amount, and then generates the brake hydraulic pressure which is set, in the motor cylinder device16.

The control unit150of the first embodiment is, for example, composed of a micro computer constituted by a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and peripheral devices, neither of which is shown. Then, the control unit150is configured to perform by the CPU a program stored in the ROM in advance, and control the vehicle brake system10. Further, an electrical signal in the first embodiment is, for example, a control signal for controlling the electric motor72, or power to drive the electric motor72.

Further, an operation amount measurement unit for measuring the depression operation amount (brake operation amount) of the brake pedal12is not limited to the stroke sensor St, but may be a sensor capable of measuring the depression operation amount of the brake pedal12. It may be, for example, configured that the hydraulic pressure measured by the pressure sensor Pm as the operation amount measurement unit is converted to the depression operation amount of the brake pedal12, or the depression operation amount (brake operation amount) of the brake pedal12is measured by an unillustrated depression force sensor.

The brake hydraulic pressure in the second hydraulic chamber98aand the first hydraulic chamber98bof the motor cylinder device16is transmitted to the wheel cylinders32FR,32RL,32RR,32FL of the disc brake mechanisms30ato30dvia the first and second inlet valves120,124in the open valve state of the VSA device18, and an intended brake force is applied to each of the wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL) by the operations of the wheel cylinders32FR,32RL,32RR,32FL.

In other words, in the vehicle brake system10according to the first embodiment, in a normal state where the motor cylinder device16which functions as a power hydraulic pressure source, the control unit150which performs by-wire control, and the like, are operational, the brake system of so-called brake-by-wire type is active. The brake system of brake-by-wire type actuates the disc brake mechanisms30ato30dby the hydraulic pressure generated by the motor cylinder device16, in a state where the communication between the master cylinder34for generating the hydraulic pressure via the brake pedal12depressed by the driver and the disc brake mechanisms30ato30d(wheel cylinders32FR,32RL,32RR,32FL) for braking each of the wheels is shut off by the second shutoff valve60aand the first shutoff valve60b.

On the other hand, in an abnormal state where the motor cylinder device16and the like are inoperative, the brake system of so-called conventional hydraulic type is active. The conventional brake system actuates the disc brake mechanisms30ato30d(wheel cylinders32FR,32RL,32RR,32FL) by transmitting the hydraulic pressure generated by the master cylinder device34to the disc brake mechanisms30ato30d(wheel cylinders32FR,32RL,32RR,32FL) as the brake hydraulic pressure, while the second shutoff valve60aand the first shutoff valve60bare respectively in the open valve states and the third shutoff valve62is in the closed valve state.

In the vehicle brake system10configured as described above, when the driver operates to depress the brake pedal12, the brake hydraulic pressure generated in the motor cylinder16is supplied to the wheel cylinders32FR,32RL,32RR,32FL of the respective wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL) via the VSA device18. Then, by the brake hydraulic pressure supplied to the wheel cylinders32FR,32RL,32RR,32FL, a caliper pressure is generated in each of the disc brake mechanisms30a,30b,30c,30d, and the braking force is applied to the respective wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL). The vehicle1(seeFIG. 1) stops and becomes in a stationary state by the braking force being applied to the respective wheels.

Further, when the pump136of the VSA device18is driven to supply the brake fluid to the first common hydraulic path112side from the second common hydraulic path114side, the brake hydraulic pressure in the first common hydraulic path112is boosted, and the brake hydraulic pressure supplied to the wheel cylinders32FR,32RL,32RR,32FL is boosted. And thereby the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30dis increased, and braking force applied to the vehicle1is increased. Therefore, in the first embodiment, the pump136functions as a booster unit for increasing the braking force applied to the vehicle1.

Further, when the braking force is applied to the vehicle1by the depression operation of the brake pedal12and the vehicle speed of the vehicle1is lower than a predetermined speed threshold value set in advance, the control unit150of the first embodiment determines that the vehicle1is stationary, and operates a braking force holding function (brake hold function) by controlling the vehicle brake system10. Note that, the predetermined speed threshold value for the control unit150to determine that the vehicle1is stationary is preferably set as appropriate.

FIGS. 3A to 3Dare diagrams showing states where a brake hold function is in operation in the first embodiment. Incidentally, the vertical axis inFIG. 3Aindicates the vehicle speed, and the vertical axis inFIG. 3Bindicates the caliper pressure, and further the horizontal axes inFIGS. 3A,3B indicate the time. Further,FIG. 3Cshows a time course of an operating state (ON, OFF) of the brake hold function, andFIG. 3Dshows a time course of the mode (drive mode, neutral mode) of the automatic transmission.

The brake hold function which operates in the vehicle brake system10(seeFIG. 2) of the first embodiment is a function of maintaining a state in which the brake hydraulic pressure is supplied to the wheel cylinders32FR,32RL,32RR,32FL (seeFIG. 2) of the respective wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL), when the vehicle speed of the vehicle1(seeFIG. 1) is lower than the predetermined speed threshold value set in advance. By the brake hold function being operated, for example, when the driver releases his/her foot from the brake pedal12(seeFIG. 2) and the brake pedal12is released, the state in which the braking force is applied to the respective wheels is maintained and a start of movement of the vehicle1is suppressed.

As shown inFIG. 3A, when the driver operates to depress the brake pedal12(seeFIG. 2) at the time t1, the control unit150(seeFIG. 2) generates an initial brake hydraulic pressure through the motor cylinder16(seeFIG. 2) and supplies the initial brake hydraulic pressure to the wheel cylinders32FR,32RL,32RR,32FL. Hereby, the caliper pressure is applied to operate the disc brake mechanisms30a,30b,30c,30dof the respective wheels as shown inFIG. 3B, and the vehicle speed of the vehicle1(seeFIG. 1) is reduced as shown inFIG. 3A.

When the vehicle speed of the vehicle1(seeFIG. 1), which is calculated on the basis of the wheel speeds of the respective wheels measured by the wheel speed sensors35a,35b,35c,35d(seeFIG. 2), becomes lower than the predetermined speed threshold value at the time t2, the control unit150(seeFIG. 2) of the first embodiment determines that the vehicle1(seeFIG. 1) is stationary, and operates the brake hold function (turns on the brake hold function) as shown inFIG. 3C. Specifically, when the control unit150determines that the vehicle1is stationary at the time t2, it closes the normally open type regulator valve116(seeFIG. 2) included in the VSA device18(seeFIG. 2). Hereby, the brake hydraulic pressure generated in the motor cylinder device16(seeFIG. 2) is sealed in the VSA device18(the first common hydraulic path112, the second common hydraulic path114), and the state in which the brake hydraulic pressure is supplied to the wheel cylinders32FR,32RL,32RR,32FL (seeFIG. 2) is maintained. Then, the vehicle1is maintained in the stationary state by operating the brake hold function.

In the first embodiment, the state in which supply of the brake hydraulic pressure to the wheel cylinders32FR,32RL,32RR,32FL (seeFIG. 2) is maintained is achieved by closing the regulator valve116(seeFIG. 2), and the caliper pressure is thereby maintained in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) of the respective wheels. This condition is referred to as a state (an ON state) in which the brake hold mechanism operates.

When an unillustrated accelerator pedal is operated to be depressed by the driver, the control unit150(seeFIG. 2) determines that a condition for stopping the brake hold function is established, and opens the regulator valve116(seeFIG. 2). The brake hydraulic pressure sealed in the VSA device18(the first common hydraulic path112, the second common hydraulic path114) is released from the VSA device18via the inlet port26a(seeFIG. 2), and supply of the brake hydraulic pressure to the wheel cylinders32FR,32RL,32RR,32FL (seeFIG. 2) is stopped, and thus the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) of the respective wheels is eliminated. In the first embodiment, the state in which supply of the brake hydraulic pressure to the wheel cylinders32FR,32RL,32RR,32FL is stopped, and the caliper pressure in the disc brake mechanisms30a,30b,30c,30dof the respective wheels is reduced, is referred to as a state (an OFF state) in which the brake hold mechanism is stopped.

In this manner, when the vehicle1(seeFIG. 1) is stationary, the control unit150(seeFIG. 2) of the first embodiment closes the regulator valve116(seeFIG. 2) of the VSA device18, and operates (turns on) the brake hold function. Further, the control unit150may be configured to operate an unillustrated electric parking brake to apply the braking force to the vehicle1and switch the brake hold function to the electric parking brake when a predetermined time elapses after closing of the regulator valve116. At this time, the predetermined time until the control unit150operates the electric parking brake after closing the regulator valve116is set in advance. The predetermined time is, for example, set to a time until the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30dof the respective wheels is reduced after the brake fluid leaks from the closed regulator valve116, that is, a time capable of holding the caliper pressure by the regulator valve116.

Further, as shown inFIG. 1, the vehicle1according to the first embodiment includes the automatic transmission3as the transmission. When the automatic transmission3is set in the driving mode such as the drive mode (forward drive mode) and the reverse mode (rearward drive mode), a creep force is applied to the vehicle1. Therefore, when the vehicle1is stopped in a state where the automatic transmission3is set in the drive mode, the braking force applied to the respective wheels (the right front wheel WFR, the left front wheel WFL, a left rear wheel WRL, a right rear wheel WRR) can suppress a forward movement of the vehicle1due to the creep force.

In contrast, when the automatic transmission3(seeFIG. 1) is set in the neutral mode (non-driving mode), the creep force is not applied to the vehicle1(seeFIG. 1). Therefore, when the automatic transmission3is set in the neutral mode, the vehicle1is stopped to be in the stationary state by the braking force smaller than that in a case where the automatic transmission3is set in the drive mode. For example, when the vehicle1is stopped in a state where the automatic transmission3is set in the neutral mode, and the brake hold function operates at the time t2, if the creep force is applied to the vehicle1by shifting the automatic transmission3into the drive mode at the time t3 after the time t2 as shown inFIG. 3D, the vehicle speed is increased by the creep force and the vehicle1starts moving as indicated by an one-dot chain line inFIG. 3Ain some cases.

When the brake hold function operates, the control unit150(seeFIG. 1) of the first embodiment calculates the vehicle speed of the vehicle1(seeFIG. 1) on the basis of the wheel speeds detected by the wheel speed sensors35a,35b,35c,35d(seeFIG. 2). When the control unit150determines that the vehicle speed of the vehicle1is larger than a predetermined value at the time t4 shown inFIG. 3A, it controls the VSA18(seeFIG. 2) so that the caliper pressure is increased. Specifically, the control unit150determines that the vehicle1has started moving when the vehicle speed of the vehicle1is larger than the predetermined value, and it drives the pump136(seeFIG. 2) of the VSA device18to supply the brake fluid to the first common hydraulic path112(seeFIG. 2) side from the second common hydraulic path114(FIG. 2) side, and increases the brake hydraulic pressure in the first common hydraulic path112at the time t4. As a result, the brake hydraulic pressure supplied to the wheel cylinders32FR,32RL,32RR,32FL (seeFIG. 2) of the respective wheels (the front right wheel WFR, the rear left wheel WRL, the rear right wheel WRR, and the front left wheel WFL) is increased. Then, the caliper pressure in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) is increased from the time t4 as indicated by an one-dot chain line inFIG. 3B, and the braking force applied to the respective wheels is increased, and thus the vehicle1is stopped again to be in the stationary state.

In other words, if the automatic transmission3(seeFIG. 3) is shifted to the drive mode from the neutral mode after the time t2 when the brake hold function operates, the vehicle1(seeFIG. 1) starts moving for a moment and is stopped, and thereby the driver feels a sense of discomfort. Therefore, the vehicle brake system10(seeFIG. 1) of the first embodiment is configured to reduce the sense of discomfort felt by the driver, when the mode of the automatic transmission3is shifted during operation of the brake hold function.

When the control unit150(seeFIG. 1) of the first embodiment determines that the vehicle1(seeFIG. 1) is stationary at the time t2, and operates the brake hold function (that is, when closing the regulator valve116of the VSA device18), it obtains the mode of the automatic transmission3(seeFIG. 1). When the mode of the automatic transmission3is the neutral mode (non-driving mode), the control unit150drives the pump136(seeFIG. 2) at the time t2′ after the regulator valve116(seeFIG. 2) of the VSA device18is closed. Hereby, the brake fluid is supplied to the first common hydraulic path112(seeFIG. 2) from the second common hydraulic path114(seeFIG. 2), and the brake hydraulic pressure in the first common hydraulic path112is increased. When the brake hydraulic pressure in the first common hydraulic path112is increased, the caliper pressure of the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) is increased as indicated by a solid line inFIG. 3B, and the braking force applied to the vehicle1is increased.

Note that, if the regulator valve116(seeFIG. 2) is configured to include a sensor (not shown) for detecting a valve opening degree, the control unit150(seeFIG. 2) can detect that the regulator valve116is closed at the time t2′, thereby driving the pump136(seeFIG. 2). Further, the control unit150may be configured not to detect the opening of the regulator valve116, but to drive the pump136at the time t2 when it determines that the vehicle1(seeFIG. 1) is stationary.

At this time, if the initial caliper pressure generated in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) is lower than a predetermined pressure PHIGHindicated inFIG. 3B, the control unit150(seeFIG. 2) drives the pump136(seeFIG. 2) to increase the initial caliper pressure. The control unit then stops the pump136when the caliper pressure is increased to the predetermined pressure PHIGH, which may also be referred to herein as an enhanced pressure level.

Note that, the control unit150shown inFIG. 2may be configured to determine whether or not the caliper pressure is increased to the predetermined pressure PHIGHon the basis of the brake hydraulic pressure in the first common hydraulic path112, the brake hydraulic pressure being calculated on the basis of the measurement signal inputted from the pressure sensor P1 included in the VSA device18. For example, if a map showing a relationship between the caliper pressure and the brake hydraulic pressure in the first common hydraulic path112is set in advance and is stored in an unillustrated storage unit of the control unit150, the control unit150can calculate the caliper pressure on the basis of the brake hydraulic pressure in the first common hydraulic path112with reference to the map. The control unit150stops the pump136when it determines that the caliper pressure calculated in this manner is increased to the predetermined pressure PHIGH. As a result, the braking force applied to the vehicle1(seeFIG. 1) is increased.

Further, the caliper pressure (predetermined pressure PHIGH) when the control unit150stops the pump136may be a pressure through which a braking force (defined braking force in the first embodiment), that is capable of stopping the vehicle1(seeFIG. 1) against the creep force generated when the automatic transmission3is set in the drive mode, is applied to the respective wheels. Such a predetermined pressure PHIGHis preferably set in advance by experimental measurement or the like. In other words, according to the vehicle brake system10of the first embodiment, if the automatic transmission3is in the neutral mode when the brake hold function operates, the braking force applied to the vehicle1is increased up to and held at the defined braking force, when the braking force applied to the vehicle1is smaller than the defined braking force (the braking force applied to the vehicle1when the caliper pressure is the predetermined pressure PHIGH) set in advance.

Note that, when the control unit150operates the brake hold function, if the automatic transmission3(seeFIG. 1) is in the neutral mode, the control unit150may be configured to increase the braking force by driving the pump136(seeFIG. 2) without determining whether or not the braking force applied to the vehicle1(seeFIG. 1) is smaller than the defined braking force, that is, without determining whether or not the caliper pressure is lower than the predetermined pressure PHIGH. For example, as indicated by a two-dot chain line inFIG. 3B, the control unit150may be configured to increase the caliper pressure (the braking force) by driving the pump136even if the caliper pressure is higher than the predetermined pressure PHIGHat the time t2 when the control unit150operates the brake hold function. In this case, as indicated by the two-dot chain line inFIG. 3B, the control unit150may be, for example, configured to stop the pump136when the caliper pressure is increased by a predetermined differential pressure ΔP. Such a predetermined differential pressure ΔP may be, for example, a differential pressure for increasing the braking force so as to suppress the start of movement of the vehicle1due to the creep force generated when the automatic transmission3is shifted to the drive mode from the neutral mode. Note that, if the caliper pressure exceeds the maximum value of the caliper pressure when the caliper pressure is increased by the differential pressure ΔP, the control unit150may be configured to increase the caliper pressure to the maximum value.

In this manner, according to the vehicle brake system10of the first embodiment, if the automatic transmission3(seeFIG. 1) is set in the neutral mode (non-driving mode) when the vehicle1(seeFIG. 1) is stationary and the brake hold function operates, the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) is increased to the predetermined pressure PHIGH. When the caliper pressure is increased to the predetermined pressure PHIGH, the braking force applied to the vehicle1is increased, to suppress the forward movement of the vehicle1due to the creep force generated when the automatic transmission3is set in the drive mode. Therefore, even if the automatic transmission3is shifted to the drive mode from the neutral mode during operation of the brake hold function, the vehicle1does not start moving.

As a result, when the automatic transmission3(seeFIG. 1) is shifted to the drive mode from the neutral mode during operation of the brake hold function, the vehicle1(seeFIG. 1) is suppressed from starting moving for a moment, and the sense of discomfort felt by the driver is reduced.

FIG. 4is a flowchart showing a procedure in which the control unit operates the brake hold function. With reference toFIG. 4, the procedure in which the control unit150of the first embodiment operates the brake hold function will be described (seeFIGS. 1 to 3D, as appropriate). The control unit150determines whether or not the vehicle1is stationary by the braking force being applied to, on the basis of the wheel speeds measured by the wheel speed sensors35a,35b,35c,35d(Step S1). In Step S1, the control unit150detects that the brake pedal12is operated to be depressed, and calculates the vehicle speed of the vehicle1on the basis of the wheel speeds, and then determines that the vehicle1is stopped (stationary) when the calculated vehicle speed is lower than the predetermined speed threshold value. If the control unit150determines that the vehicle1is stationary by the braking force being applied to (Yes in Step S1), the control unit150operates the brake hold function (Step2). Specifically, the control unit150provides a closing instruction to the regulator valve116of the VSA device18, and closes the regulator valve116. Note that, if the control unit150determines that the vehicle1is not stationary in Step S1(No in Step S1), the control unit150returns the procedure to Step S1.

Further, the control unit150determines whether or not the automatic transmission3is set in the neutral mode (non-driving mode) (Step S3). If the automatic transmission3is set in the neutral mode (Yes in Step S3), the control unit150determines whether or not the caliper pressure is lower than the predetermined pressure PHIGH(Step S4). If the caliper pressure is lower than the predetermined pressure PHIGH(Yes in Step S4), the control unit150drives the pump136of the VSA device18(Step S5). On the other hand, if the caliper pressure is not lower than the predetermined pressure PHIGH(No in Step S4), that is, if the caliper pressure is higher than or equal to the predetermined pressure PHIGH, the control unit150allows the procedure to proceed to Step S8without driving the pump136.

Note that, the control unit150may be configured to drive the pump136in Step S5, after a predetermined time elapses after the control unit150provides the closing instruction to the regulator valve116in Step S2. Hereby, the control unit150can drive the pump136after the regulator valve116is closed. In this case, the predetermined time may be a time required to close the regulator valve116, and is preferably determined in advance by experimental measurement or the like.

The control unit150drives the pump136until the caliper pressure, which is calculated on the basis of the brake hydraulic pressure of the first common hydraulic path112measured by the pressure sensor P1 of the VSA device18, is increased to the predetermined pressure PHIGH(No in Step S6), and when the caliper pressure is higher than or equal to the predetermined pressure PHIGH(Yes in Step S6), the control unit150stops the pump136(Step S7). In other words, the control unit150increases the braking force when the braking force applied to the vehicle1is smaller than the braking force generated by the caliper pressure of the predetermined pressure PHIGH.

And the control unit150waits until the condition for stopping the brake hold function is established (No in Step S8). Note that, the control unit150of the first embodiment determines that the condition for stopping the brake hold function is established, for example, when the unillustrated accelerator pedal is operated to be depressed. When the condition for stopping the brake hold function is established (Yes in Step S8), the control unit150provides an opening instruction to the regulator valve116to open the regulator valve116, and stops the brake hold function (Step S9).

On the other hand, when the control unit150operates the brake hold function (Step S2), if the automatic transmission3is in a mode other than the neutral mode (No in Step S3), for example, if it is in the drive mode, the control unit150allows the procedure to proceed to Step S8without driving the pump136.

As described above, according to the vehicle brake system10(seeFIG. 2) of the first embodiment, when the vehicle1(seeFIG. 1) is stopped to be in a stationary state, the regulator valve116(seeFIG. 2) of the VSA device18is closed and the brake hold function operates. At this time, if the automatic transmission3(seeFIG. 1) is set in the neutral mode (non-driving mode), the control unit150(seeFIG. 2) drives the pump136(seeFIG. 2) of the VSA device18. Hereby, the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) is increased to the predetermined pressure PHIGH, and the braking force applied to the vehicle1is increased. Therefore, even if the automatic transmission3is shifted to the drive mode (driving mode) when the brake hold function operates, the start of movement of the vehicle1due to the creep force generated at that time is suppressed, and the sense of discomfort felt by the driver is reduced.

Note that, if the automatic transmission3(seeFIG. 1) is in the neutral mode (Yes in Step S3inFIG. 4) when the control function150(seeFIG. 2) operates the brake hold function, the control function150may be configured to drive the pump136(seeFIG. 2) (Step S5inFIG. 4) without determining whether or not the caliper pressure is lower than the predetermined pressure PHIGH. In other words, as indicated by a dashed line inFIG. 4, the control unit150may be configured to allow the procedure to proceed to “Step S5” in the case of “Yes in Step S3”. In this case, the control unit150may be configured to stop the pump136(Step S7inFIG. 4) when the caliper pressure is increased by the predetermined differential pressure ΔP in Step S6inFIG. 4.

Second Embodiment

FIGS. 5A to 5Dare diagrams showing a state where a brake hold function is in operation in a second embodiment. Note that, a vertical axis ofFIG. 5Aindicates the vehicle speed, a vertical axis ofFIG. 5Bindicates the caliper pressure, and horizontal axes ofFIGS. 5A,5B indicate the times. Further,FIG. 5Cshows a time course of an operating state (ON, OFF) of the brake hold function, andFIG. 5Dshows a time course of the mode (drive mode, neutral mode) of the automatic transmission.

A vehicle brake system according to the second embodiment of the present invention has the same configuration as that of the vehicle brake system10of the first embodiment shown inFIGS. 1,2. If the automatic transmission3is set in the neutral mode (non-driving mode), even if the control unit150of the second embodiment determines that the vehicle1is stationary after the vehicle speed of the vehicle1(seeFIG. 1) becomes lower than a predetermined speed threshold value, the control unit150does not operate the brake hold function at that time, but operates the brake hold function when the caliper pressure is increased to be more than or equal to the predetermined pressure PHIGHset in advance. In other words, when the control unit150of the second embodiment allows the braking force, which is generated when the caliper pressure is the predetermined pressure PHIGH, to be a predetermined defined braking force, and determines that the vehicle1is stationary, while the braking force of the vehicle1is larger than the defined braking force, the control unit150operates the brake hold function.

Specifically, when the control unit150(seeFIG. 1) of the second embodiment determines that the vehicle1(seeFIG. 1) is stationary in a state where the automatic transmission3(seeFIG. 1) is set in the neutral mode (non-driving mode) at the time t2 as shown inFIG. 5A, if the control unit150determines that the caliper pressure is lower than the predetermined pressure PHIGHat this time, the control unit150does not operate (does not turn on) the brake hold function as shown inFIG. 5C. The predetermined pressure PHIGHof the caliper pressure at this time is a caliper pressure for applying the braking force, which is the defined braking force, to the vehicle1. When the driver further depresses the brake pedal12(seeFIG. 2), and the caliper pressure is increased to the predetermined pressure PHIGHat the time t5 as shown inFIG. 5B, the control unit150determines that the braking force applied to the vehicle1is larger than or equal to the defined braking force, and operates the brake hold function by closing the regulator valve116(seeFIG. 2) of the VSA device18. Note that, the control unit150may be configured to include a warning function or a display function for allowing the driver to recognize that the brake hold function operates, or that the brake hold function stops the operation.

Note that, the caliper pressure (the predetermined pressure PHIGH) when the control unit150(seeFIG. 1) operates the brake hold function is, for example, equivalent to the pressure PHIGHin the first embodiment, and is a caliper pressure through which a braking force (defined braking force in the second embodiment), that is capable of stopping the vehicle1(seeFIG. 1) against the creep force generated when the automatic transmission3(seeFIG. 1) is set in the drive mode, is applied to the respective wheels. Such a predetermined pressure PHIGHis preferably set in advance by experimental measurement or the like.

In this manner, if the automatic transmission3(seeFIG. 1) is set in the neutral mode (non-driving mode), the control unit150(seeFIG. 2) of the vehicle brake system10according to the second embodiment is configured to operates the brake hold function when the vehicle1(seeFIG. 1) is stopped (stationary) and the caliper pressure is higher than or equal to the predetermined pressure PHIGH(that is, when the braking force applied to the vehicle1is larger than or equal to the predetermined defined braking force). Therefore, even if the automatic transmission3is shifted to the drive mode (driving mode) from the neutral mode (non-driving mode) at the time t6 (after the time t5) when the brake hold function operates, and the creep force is applied to the vehicle1, the vehicle1does not start moving forward. As a result, when the automatic transmission3is shifted to the drive mode from the neutral mode during operation of the brake hold function, the vehicle1is suppressed from starting moving for a moment, and the sense of discomfort felt by the driver is reduced.

Note that, as in the first embodiment, the control unit150(seeFIG. 2) of the second embodiment may be configured to determine whether or not the caliper pressure is increased to the predetermined pressure PHIGH, on the basis of the brake hydraulic pressure in the first common hydraulic path112(seeFIG. 2), which is calculated based on the measurement signal inputted from the pressure sensor P1 (seeFIG. 2) included in the VSA device18.

FIG. 6is a flowchart showing a procedure in which the control unit of the second embodiment operates the brake hold function. With reference toFIG. 6, the procedure in which the control unit150of the second embodiment operates the brake hold function will be described (seeFIGS. 1 to 3D, as appropriate).

The control unit150determines whether or not the vehicle1is stationary by the braking force being applied to, on the basis of the wheel speeds measured by the wheel speed sensors35a,35b,35c,35d(Step S10). In Step S10, the control unit150detects that the brake pedal12is operated to be depressed, and calculates the vehicle speed of the vehicle1on the basis of the wheel speeds, and then determines that the vehicle1is stopped (stationary) by the braking force being applied to, when the calculated vehicle speed is lower than the predetermined speed threshold value. If the control unit150determines that the vehicle1is stationary (Yes in Step S10), the control unit150determines whether or not the automatic transmission3is in the neutral mode (non-driving mode) (Step11). If the control unit150determines that the automatic transmission3is not in the neutral mode (No in Step S11), for example, when it determines that the automatic transmission3is in the drive mode (driving mode), it operates the brake hold function (Step S13). Specifically, the control unit150provides a closing instruction to the regulator valve116of the VSA device18, and closes the regulator valve116. Note that, if the control unit150determines that the vehicle1is not stationary in Step S10(No in Step S10), the control unit150returns the procedure to Step S10.

Further, if the control unit150determines that the automatic transmission3is in the neutral mode in Step S11(Yes in Step S11), the control unit150determines whether or not the caliper pressure is higher than or equal to the predetermined pressure PHIGH(Step S12). That is, in Step S12, the control unit150determines whether or not the braking force of the vehicle1is larger than or equal to the defined braking force. Then, the control unit150waits until the caliper pressure becomes larger than or equal to the predetermined pressure PHIGH(No in Step S12), and when the caliper pressure is larger than or equal to the predetermined pressure PHIGH(Yes in Step S12), the control unit150allow the procedure to proceed to Step S13, and operates the brake hold function.

And the control unit150waits until the condition for stopping the brake hold function is established (No in Step S14). Note that, as in the first embodiment, the control unit150determines that the condition for stopping the brake hold function is established, for example, when the unillustrated accelerator pedal is operated to be depressed. When the condition for stopping the brake hold function is established (Yes in Step S14), the control unit150provides an opening instruction to the regulator valve116to open the regulator valve116, and stops the brake hold function (Step S15).

Note that, in Step S12, when the condition for stopping the brake hold function is established, for example, by the unillustrated accelerator pedal being operated to be depressed before the caliper pressure becomes larger than or equal to the predetermined pressure PHIGH, the control unit150ends the procedure without operating the brake hold function.

As described above, according to the vehicle brake system10(seeFIG. 2) of the second embodiment, when the vehicle1(seeFIG. 1) is stopped to be in a stationary state, if the automatic transmission3(seeFIG. 1) is set in the non-driving mode such as the neutral mode, the regulator valve116(seeFIG. 2) of the VSA device18is closed and the brake hold function operates, when the caliper pressure is larger than or equal to the predetermined pressure PHIGH. When the caliper pressure is larger than or equal to the predetermined pressure PHIGH, even if the creep force is applied to the vehicle1(seeFIG. 1), the vehicle1is kept in the stationary state, and the start of movement of the vehicle1is suppressed. Therefore, even if the automatic transmission3is shifted to the drive mode during operation of the brake hold function, the start of movement of the vehicle1due to the creep force is suppressed, and the sense of discomfort felt by the driver is reduced.

As described above, the vehicle brake system10(seeFIG. 2) of the second embodiment is configured such that the brake hold function operates when the vehicle1(seeFIG. 1) is stationary and the braking force applied to the vehicle1is larger than or equal to the defined braking force, if the automatic transmission3(seeFIG. 1) is set in the non-driving mode such as the neutral mode. With this configuration, when the automatic transmission3is shifted to the driving mode such as the drive mode during the operation of the brake hold function, the start of movement of the vehicle1due to the creep force is suppressed, and the sense of discomfort felt by the driver is reduced.

Further, the vehicle brake system10(seeFIG. 2) of the second embodiment is configured such that the brake hold function operates when the braking force generated by the depression operation of the brake pedal12(seeFIG. 2) is larger than or equal to the defined braking force, and it is not required to increase the braking force during the operation of the brake hold function. Therefore, for example, even if the vehicle brake system10does not include the pump136(seeFIG. 2) which is the booster unit, the brake hold function can be operated so as to suppress the start of movement of the vehicle1(seeFIG. 1) due to the creep force.

Note that, the present invention can be appropriately modified in design without departing from the spirit and scope of the invention. As shown inFIG. 2, the vehicle brake system10of the present embodiment is configured to include an electric brake unit in which the motor cylinder device16driven by the electric motor72generates the braking force, however, it may be, for example, a vehicle brake system including a hydraulic brake unit in which the hydraulic pressure generated in the master cylinder34directly drives the wheel cylinders32FR,32RL,32RR,32FL. Further, the control unit150(seeFIG. 2) of the first embodiment and the second embodiment is configured to calculate the caliper pressure generated in the disc brake mechanisms30a,30b,30c,30d(seeFIG. 2) on the basis of the brake hydraulic pressure in the first common hydraulic path112(seeFIG. 2) of the VSA device18, however, it may be configured such that a pressure sensor for measuring the caliper pressure is included in the disc brake mechanisms30a,30b,30c,30d.

Further, in the second embodiment, the control unit150(seeFIG. 2) may be configured to operate the brake hold function at the time t2 when the control unit150determines that the vehicle1(seeFIG. 1) is stationary.

Further, in the first embodiment and the second embodiment, the vehicle brake system10may be configured to assist a start (so-called hill start) of the vehicle1(seeFIG. 1) which is stationary on a slope (an uphill), or to keep a state in which the braking force is applied to the vehicle1until a driving torque capable of running is generated in the stationary vehicle1, that is, to operate a function (a stop assisting function) for assisting a temporary stop of the vehicle1by holding the braking force with the braking force holding function. Note that, when such a stop assisting function operates, the driver has an intension to stop the vehicle1for a short time, and easily performs a next operation (for example, an operation to allow the vehicle1to be stationary by operating the brake pedal12(seeFIG. 2) to be depressed) quickly if the vehicle1starts moving. On the other hand, in a state where the brake hold function operates for keeping the vehicle1in the stationary state for a long time, when the automatic transmission3(seeFIG. 1) is shifted to the drive mode (driving mode) from the neutral mode (non-driving mode), even if the driver wants to keep the vehicle1in the stationary state, the vehicle1starts moving for a moment and the driver feels the sense of discomfort in some cases. Therefore, as described in the first embodiment or the second embodiment, the vehicle brake system10is preferably configured to operate the brake hold function.

Further, in the first embodiment or the second embodiment, the control unit150(seeFIG. 2) is configured to close the regulator valve116(seeFIG. 2) when operating the brake hold function. However, the control unit150is not limited thereto, but may be configured to close the first inlet valve120(seeFIG. 2) and the second inlet valve124(seeFIG. 2) in place of the regulator valve116. Furthermore, the vehicle brake system10(seeFIG. 1) of the first embodiment and the second embodiment may be not an electric servo brake system, but a brake system including a master power.

REFERENCE SIGNS LIST