Vehicle brake control device

Abstract

To suppress power consumption of a solenoid valve in a vehicle brake control device configured to cause the solenoid valve to maintain wheel pressure so as to suppress heat generation of components related to an electric motor.SOLUTION: A brake control device comprises: a control cylinder that generates servo pressure by movement of a control piston driven by an electric motor; a normally open solenoid valve provided in a liquid pressure transmission path from the control cylinder to a wheel cylinder; and a controller that controls the electric motor and the solenoid valve, where wheel pressure of the wheel cylinder is adjusted by the servo pressure. When a temperature-associated value associated with temperature of a component related to the electric motor exceeds a threshold value, the controller closes the solenoid valve to reduce the servo pressure to a lower limit pressure that is set on the basis of a maximum rating at which the component can be continuously energized. Further, when a differential pressure between the wheel pressure and the lower limit pressure is small, the controller reduces valve current supplied to close the solenoid valve as compared with that of when the differential pressure is large.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a braking control device for a vehicle. [Background technology]

[0002] The applicant has developed a braking control device as described in Patent Document 1. Specifically, the braking control device includes an electric cylinder that discharges brake fluid from an output port at a hydraulic pressure corresponding to the drive of an electric motor, a master cylinder configured such that brake fluid flows out of the master chamber as a result of the movement of the master piston accompanying an increase in hydraulic pressure in the servo chamber, and brake fluid flows into the master chamber as a result of the movement of the master piston accompanying a decrease in hydraulic pressure in the servo chamber, a first flow path connecting the master chamber and a wheel cylinder for the front wheels, a sixth flow path connecting the output port and a wheel cylinder for the rear wheels, a fifth flow path connecting the sixth flow path and the servo chamber, and a differential pressure regulating valve provided in the fifth flow path for regulating a differential pressure between the first hydraulic pressure, which is the hydraulic pressure in the sixth flow path, and the second hydraulic pressure, which is the hydraulic pressure in the servo chamber.

[0003] However, such braking control devices may have the problem of heat generation in the electric motor and its drive circuit, etc. For example, the electric boost mechanism described in Patent Document 2 is provided with a retention valve (also called a "solenoid valve") that controls on / off communication between the wheel cylinder, which generates braking force on the wheels, and the master cylinder, and is described as closing the retention valve and reducing the amount of electricity supplied to the electric motor when the brakes are applied continuously and the pressure in the wheel cylinder continues to rise. In such a device, the power consumption of the solenoid valve needs to be taken into consideration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2024-82901 A [Patent Document 2] JP 2009-040122 A Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above problems, an object of the present invention is to provide a vehicle braking control device that suppresses heat generation in components related to an electric motor by maintaining wheel pressure with a solenoid valve, and that can suppress power consumption of the solenoid valve. [Means for solving the problem]

[0006] The vehicle braking control device (SC) of the present invention comprises an electric cylinder (DN) that generates a servo pressure (Pa) by the movement of a control piston (NC) driven by an electric motor (MA), a normally open solenoid valve (UZ) provided in a hydraulic pressure transmission path (HS) from the electric cylinder (DN) to a wheel cylinder (CW), and a controller (EE, etc.) that controls the electric motor (MA) and the solenoid valve (UZ), and adjusts the wheel pressure (Pw) of the wheel cylinder (CW) by the servo pressure (Pa).

[0007] In the vehicle braking control device (SC) according to the present invention, when a temperature-related value (Xm) related to the temperature of a component (MA, DR, etc.) related to the electric motor (MA) exceeds a threshold value (xm), the controller (EE, etc.) closes the solenoid valve (UZ) and reduces the servo pressure (Pa) to a lower limit pressure (px) set based on the maximum rating at which current can be continuously applied to the component (MA, DR, etc.). When a differential pressure (sPx) between the wheel pressure (Pw) and the lower limit pressure (px) is small, the controller (EE, etc.) reduces the valve current (Iz) supplied to close the solenoid valve (UZ) compared to when the differential pressure (sPx) is large.

[0008] The valve current Iz required to close the pressure regulating valve UZ is determined by the pressure difference between the wheel pressure Pw and the servo pressure Pa. With the above configuration, the decrease in the servo pressure Pa is limited to the lower limit pressure px, so that the pressure difference is kept low to a certain degree. This reduces the valve current Iz, thereby suppressing the power consumption of the pressure regulating valve UZ.

[0009] In the vehicle braking control device (SC) of the present invention, the solenoid valve (UZ) includes a front wheel solenoid valve (UZf) provided for a front wheel cylinder (CWf) of the wheel cylinders (CW), and a rear wheel solenoid valve (UZr) provided for a rear wheel cylinder (CWr) of the wheel cylinders (CW), and when the controller (EE, etc.) reduces the servo pressure (Pa), it closes the front wheel solenoid valve (UZf) and keeps the rear wheel solenoid valve (UZr) open. With the above configuration, it is not necessary to supply power to the rear wheel pressure regulating valve UZr, and power consumption is reduced accordingly. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining a first embodiment of a vehicle braking control device SC (particularly, an upper unit SA). [Diagram 2] 2 is a schematic diagram for explaining a configuration example of a lower unit SZ of a braking control device SC. FIG. [Diagram 3] FIG. 4 is a flow diagram for explaining a process of pressure regulation control including a specific process. [Figure 4] FIG. 11 is a time series diagram for explaining the operation of the specific process. [Diagram 5] 11 is a schematic diagram for explaining a second embodiment of the upper unit SA. FIG. [Figure 6] FIG. 11 is a flow chart for explaining a process for selecting a pressure regulating valve to be closed when a specific process is executed in a third embodiment of the brake control device SC. [Figure 7] 13(a) to 13(c) are time-series diagrams illustrating the operation of a specific process in a third embodiment of the braking control device SC. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Symbols for components, etc. and suffixes at the end of the symbols> In the following description, components, arithmetic processes, signals, characteristics, and values ​​with the same symbol, such as "CW", have the same function. The suffixes "f" and "r" at the end of the symbol for each wheel are generic symbols that indicate whether it is related to the front or rear wheel system. For example, the wheel cylinder CW provided on each wheel is written as "front wheel cylinder CWf, rear wheel cylinder CWr". Furthermore, the suffixes "f" and "r" at the end of the symbol may be omitted. When the suffixes "f" and "r" are omitted, each symbol represents its generic name. For example, "CW" is a generic name for wheel cylinders provided on the front and rear wheels of a vehicle. In addition, "CW" as a generic name can also be written as "CW (= CWf, CWr)".

[0012] In the brake control device SC, the upper unit SA, lower unit SZ, and wheel cylinder CW are connected by a fluid path (communication path HS). Furthermore, in the upper unit SA and lower unit SZ, various components (CC, etc.) are connected by fluid paths. Here, the "fluid path" is a path for moving the brake fluid BF, and corresponds to piping, flow paths in the actuator, hoses, etc. In the following explanation, the communication path HS, reservoir path HR, input path HN, servo path HU, supply path HH, etc. are fluid paths.

[0013] In the hydraulic pressure transmission path (fluid paths HU, HS, etc.) related to the servo pressure Pa, the side closer to the hydraulic pressure generating unit PU (i.e., the side farther from the wheel cylinder CW) is referred to as the "upper" side. In contrast, the side farther from the hydraulic pressure generating unit PU (i.e., the side closer to the wheel cylinder CW) is referred to as the "lower" side.

[0014] <First embodiment of the brake control device SC> A first embodiment of a vehicle braking control device SC (particularly, an upper unit SA) will be described with reference to the schematic diagram of Fig. 1. The braking control device SC is composed of an upper unit SA and a lower unit SZ. For example, the braking control device SC is applied to a hybrid vehicle or an electric vehicle equipped with an electric motor for driving.

[0015] The front and rear wheels WHf, WHr (=WH) of the vehicle are provided with a braking device SX (=SXf, SXr). The braking device SX is composed of a brake caliper, a friction member (e.g., brake pad), and a rotating member KT (e.g., brake disc). The brake caliper (not shown) is provided with a wheel cylinder CW. A hydraulic pressure Pw (called "wheel pressure") in the wheel cylinder CW presses a friction member (not shown) against a rotating member KT fixed to each wheel WH, and a braking torque Tb is applied to the wheel. As a result, a frictional braking force Fe (also called "hydraulic braking force") is generated in the wheel WH. Therefore, the braking device SX can be said to be "a device that generates a frictional braking force Fe by the wheel pressure Pw" or "a device that converts the wheel pressure Pw into a frictional braking force Fe."

[0016] The vehicle is equipped with a brake operating member BP and various sensors (SP, etc.). The brake operating member BP (e.g., a brake pedal) is an operating member for the driver to decelerate the vehicle. The vehicle is provided with an operation displacement sensor SP that detects an operation displacement Sp of the brake operating member BP. The operation displacement Sp is one of state quantities (state variables) that indicate the operation amount of the brake operating member BP, and in a brake-by-wire type brake control device SC, it is a signal that indicates the driver's braking intention (i.e., a braking command). In addition to the operation displacement sensor SP, a hydraulic pressure Pn (referred to as "input pressure") in an input chamber Rn (described later) is adopted as another state quantity that indicates the braking operation amount. The input pressure Pn is detected by an input pressure sensor PN. The operation displacement Sp, the input pressure Pn, etc. are collectively referred to as the "braking operation amount Ba." Further, the operation displacement sensor SP and the input pressure sensor PN which detect the operation displacement Sp and the input pressure Pn (that is, the braking operation amount Ba) are referred to as a "braking operation amount sensor BA."

[0017] A vehicle is provided with various sensors for braking control (i.e., individual control of the wheel pressure Pw of each wheel) such as antilock brake control and skid prevention control. Specifically, each wheel WH is provided with a wheel speed sensor VW that detects its rotation speed Vw (called "wheel speed"). In addition, a steering amount sensor that detects the steering amount Sw (e.g., operation angle) of a steering operation member (e.g., steering wheel), a yaw rate sensor that detects the yaw rate Yr of the vehicle, a longitudinal acceleration sensor that detects the longitudinal acceleration Gx (also called "deceleration") of the vehicle, and a lateral acceleration sensor that detects the lateral acceleration Gy of the vehicle (all not shown).

[0018] The vehicle is equipped with a brake control device SC. The brake control device SC employs a so-called front and rear type (also called "type II") brake system as two systems. The wheel pressure Pw of each wheel cylinder CW is adjusted by the brake control device SC.

[0019] The braking control device SC is composed of two braking units SA, SZ. The upper unit SA is composed of an upper actuator YA and an upper controller EA. The upper actuator YA is controlled by the upper controller EA. The lower unit SZ is composed of a lower actuator YZ and a lower controller EZ. The lower actuator YZ is controlled by the lower controller EZ. Here, the upper and lower actuators YA, YZ are also referred to as "upper and lower fluid units." Moreover, the upper and lower controllers EA, EZ are also referred to as "upper and lower control units."

[0020] The upper unit SA (particularly, the upper controller EZ) and the lower unit SZ (particularly, the lower controller EZ) are connected to a communication bus BS. Signals are transmitted between the multiple controllers (EA, EZ, etc.) via the communication bus BS. In other words, the multiple controllers can transmit signals (detection values, calculation values, control flags, etc.) to the communication bus BS and can receive signals from the communication bus BS.

[0021] <Upper unit SA configuration> The configuration of the upper unit SA according to the first embodiment will be described. The upper unit SA generates a servo pressure Pa in response to the operation of the brake operating member BP (brake pedal). The servo pressure Pa causes the upper unit SA to output a supply pressure Ps (=Psf, Psr) to the lower unit SZ. Specifically, in the system related to the front wheel cylinder CWf, the master pressure Pm is output as the front wheel supply pressure Psf. In addition, in the system related to the rear wheel cylinder CWr, the servo pressure Pa is output as the rear wheel supply pressure Psr. In the lower unit SZ, the front and rear wheel supply pressures Psf and Psr (=Ps) are adjusted, and finally, the front and rear wheel pressures Pwf and Pwr (=Pw) ​​are supplied to the front and rear wheel cylinders CWf and CWr (=CW). The upper unit SA is composed of an upper actuator YA and an upper controller EA.

[0022] <Upper actuator YA> The upper actuator YA (upper fluid unit) is composed of a hydraulic pressure generating unit PU, an apply unit AP, and an input unit NR.

[0023] [Hydraulic pressure generating unit PU] The hydraulic pressure generating unit PU uses the electric motor MA as a power source to generate a servo pressure Pa. The hydraulic pressure generating unit PU is also called the "electric cylinder DN." The electric cylinder DN includes the electric motor MA, a rotation angle sensor KA, a motor temperature sensor TM, a reducer GS, a conversion mechanism GH, a control cylinder CC, and a control piston NC.

[0024] The electric motor MA is a power source (pressurizing source) for generating the servo pressure Pa. "Power" refers to the energy required to move the movable members (GS, GH, NC, etc.) in the electric cylinder DN. For example, power is defined as a physical quantity, namely, energy per unit time (also called "power"). Rotational power (also called "first rotational power") is output from the electric motor MA. The rotational power of the electric motor MA is the shaft torque of the electric motor MA multiplied by the rotational speed of the electric motor MA (particularly, the motor shaft). The linear power of the linearly moving member (described later) is the thrust of the linearly moving member (force acting in the direction of the central axis) multiplied by the linear speed of the linearly moving member (speed in the direction along the central axis).

[0025] A three-phase brushless motor is adopted as the electric motor MA. The electric motor MA is provided with a rotation angle sensor KA and a motor temperature sensor TM. The rotation angle sensor KA detects the position Ka (rotation angle) of the motor shaft. Furthermore, the motor temperature sensor TM detects the temperature Tm of the electric motor MA (e.g., a motor coil).

[0026] The motor coils are supplied with power from an upper controller EA (particularly, a drive circuit DR). A permanent magnet is fixed to the outer periphery of the motor shaft. In the three-phase brushless motor MA, the magnetic pole position of the permanent magnet (i.e., the motor rotation angle Ka) is detected by a rotation angle sensor KA. Then, in the upper controller EA, the switching elements of the drive circuit DR (also called an "inverter circuit") are driven based on the motor rotation angle Ka, and three-phase motor currents Im (a collective term for the currents flowing through the U, V, and W phases) are switched. The rotational power of the electric motor MA is output from the electric motor MA to the reducer GS.

[0027] The reducer GS reduces the speed of the first rotational power output from the electric motor MA. Specifically, the input shaft of the reducer GS and the motor shaft are fixed. Also, the output shaft of the reducer GS and the rotating member of the conversion mechanism GH are fixed. In the reducer GS, the speed input from the electric motor MA is reduced and the torque input from the electric motor MA is increased. Then, the reduced rotational power (also referred to as "second rotational power") is output from the reducer GS to the conversion mechanism GH.

[0028] The conversion mechanism GH is composed of a rotating member that performs rotational motion and a linear member that performs linear motion. In the conversion mechanism GH, the rotational power output from the reducer GS is input to the rotating member. Then, the second rotational power input to the rotating member is converted into linear power of the linear member. The conversion mechanism GH is also called a "rotation / linear conversion mechanism." A rotation stopper member is engaged with the linear member. This prevents the rotational motion of the linear member, so that the linear member moves along the rotation axis of the rotating member.

[0029] A linear force is transmitted to the control piston NC by the linear motion member of the conversion mechanism GH. The control piston NC is inserted into the control cylinder CC. Inside the control cylinder CC, the control piston NC forms a control chamber Rc (hydraulic pressure chamber). In detail, the outer peripheral surface of the control piston NC and the inner peripheral surface of the control cylinder CC are sealed by two seal members SL. This makes the control chamber Rc liquid-tight. The hydraulic pressure in the control cylinder CC (i.e., the control chamber Rc) is the servo pressure Pa. That is, in the electric cylinder DN, the electric motor MA is used as the power source, and the servo pressure Pa is output.

[0030] The control cylinder CC is connected to a servo chamber Ru (described later) of the apply unit AP via a servo path HU (fluid path). The control cylinder CC is also connected to a rear wheel cylinder CWr via a rear wheel connection path HSR (fluid path) and through a lower unit SZ. A servo pressure sensor PA is provided in the hydraulic pressure generating unit PU to detect the servo pressure Pa (hydraulic pressure generated by the electric cylinder DN).

[0031] FIG. 1 illustrates a state in which the electric cylinder DN does not generate servo pressure Pa. The control cylinder CC has a through hole between two seal members SL. The control piston NC also has a through hole. A supply path HH (fluid path) connected to the master reservoir RV is connected to the through hole of the control cylinder CC. In the illustrated state, the control chamber Rc is connected to the master reservoir RV via the through hole and the supply path HH, and the servo pressure Pa is "0 (atmospheric pressure)". The position of the control piston NC in this state is referred to as the "initial position". In the initial position, the control piston NC is displaced to its maximum in the backward direction Hb, and the volume of the control chamber Rc is maximum.

[0032] When it is necessary to increase the servo pressure Pa, the rotational power of the electric motor MA is increased. The rotational power is transmitted to the conversion mechanism GH via the reducer GS and output as linear power of the linear motion member. Then, the control piston NC is pressed by the linear motion member, so that the control piston NC moves in the forward direction Ha (the direction in which the volume of the control chamber Rc decreases). This movement first blocks communication between the control chamber Rc and the master reservoir RV. When the control piston NC is further moved in the forward direction Ha, the servo pressure Pa (the internal pressure of the control chamber Rc) is increased from "0 (atmospheric pressure)". Brake fluid BF pressurized to the servo pressure Pa is output (pumped) from the control chamber Rc of the control cylinder CC.

[0033] When it is necessary to maintain the servo pressure Pa, the rotation of the electric motor MA is stopped. The movement of the control piston NC is stopped and the servo pressure Pa is maintained constant. When it is necessary to decrease the servo pressure Pa, the rotational power of the electric motor MA is decreased. The servo pressure Pa causes the electric motor MA to rotate in the reverse direction, so that the control piston NC is moved in the backward direction Hb (the direction in which the volume of the control chamber Rc increases). The brake fluid BF is returned toward the control chamber Rc, so the servo pressure Pa is decreased.

[0034] [Apply Unit AP] The apply unit AP is composed of a single-type master cylinder CM and a master piston NM. The master piston NM is inserted into the single-type master cylinder CM. The interior of the master cylinder CM is divided into three hydraulic chambers Rm, Ru, and Rs by the master piston NM. The master chamber Rm is formed by the master cylinder CM and the master piston NM. Furthermore, the interior of the master cylinder CM is divided into a servo chamber Ru and a reaction chamber Rs by a flange portion Tu of the master piston NM. Here, the pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are set to be equal.

[0035] A servo pressure Pa is supplied to the servo chamber Ru from a hydraulic pressure generating unit PU (electric cylinder DN). Due to the servo pressure Pa, the apply unit AP outputs a master pressure Pm as a front wheel supply pressure Psf. Here, the "master pressure Pm" is the internal pressure of the master chamber Rm. When "Pa = 0" (for example, when not braking), the master piston NM is in the most retreated position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is connected to the master reservoir RV. Therefore, the master pressure Pm is "0 (atmospheric pressure)".

[0036] Brake fluid BF is stored inside the master reservoir RV (also called the "atmospheric pressure reservoir"). When the servo pressure Pa is increased from "0", the master piston NM is pressed and moves in the forward direction Da (the direction in which the volume of the master chamber Rm decreases). This movement blocks communication between the master chamber Rm and the master reservoir RV. When the master piston NM further moves in the forward direction Da, the master pressure Pm is increased from "0 (atmospheric pressure)". As a result, brake fluid BF pressurized to the master pressure Pm is output (pressurized) from the master chamber Rm of the master cylinder CM toward the lower unit SZ. Note that since "rm=ru", if the sliding resistance of the seal member SL is ignored, then "Pa=Pm".

[0037] [Input unit NR] The input unit NR realizes regenerative cooperative control. "Regenerative cooperative control" cooperates the frictional braking force Fe (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to the regenerative device) so that the kinetic energy of the vehicle can be efficiently recovered as electrical energy during braking. In regenerative cooperative control, the brake operating member BP is operated, but a state is created in which the wheel pressure Pw is not generated. The input unit NR is composed of an input cylinder CN, an input piston NN, a first control valve VA, a second control valve VB, a stroke simulator SS, and an input pressure sensor PN.

[0038] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to a brake operating member BP (brake pedal) so as to move in conjunction with the movement of the brake operating member BP. There is a gap Ln (also called the "separation distance") between the end face of the input piston NN and the end face of the master piston NM. The separation distance Ln is adjusted by the servo pressure Pa, thereby achieving regenerative cooperative control.

[0039] The input chamber Rn of the input unit NR is connected to the reaction chamber Rs of the apply unit AP via an input path HN (fluid path). A normally closed first control valve VA is provided in the input path HN. The input path HN is connected to a master reservoir RV between the first control valve VA and the reaction chamber Rs via a reservoir path HR (fluid path). A normally open second control valve VB is provided in the reservoir path HR. An on-off type solenoid valve is used for the first and second control valves VA and VB. A stroke simulator SS is connected to the input path HN between the first control valve VA and the reaction chamber Rs.

[0040] When power is not supplied to the first and second control valves VA and VB, the first control valve VA is closed and the second control valve VB is open. When the first control valve VA is closed, the input chamber Rn is sealed and fluid-locked. This causes the master piston NM to be displaced integrally with the brake operating member BP. When the second control valve VB is opened, the stroke simulator SS and the reaction chamber Rs are connected to the master reservoir RV.

[0041] When power is supplied to the first and second control valves VA and VB, the first control valve VA is opened and the second control valve VB is closed. This allows the master piston NM to be displaced separately from the brake operating member BP. At this time, the input chamber Rn is connected to the stroke simulator SS, so that the operating force of the brake operating member BP is generated by the stroke simulator SS. An input pressure sensor PN is provided in the input passage HN between the input chamber Rn and the first control valve VA to detect the input pressure Pn. The input pressure Pn is also the hydraulic pressure in the stroke simulator SS.

[0042] <Upper controller EA> The upper actuator YA is controlled by an upper controller EA (upper control unit). The upper controller EA is composed of a microprocessor MP and a drive circuit DR. The upper controller EA is connected to a communication bus BS so that signals (detection values, calculation values, control flags, etc.) can be shared with other controllers (EZ, etc.).

[0043] Various signals such as the operation displacement Sp (detection value of the operation displacement sensor SP), the input pressure Pn (detection value of the input pressure sensor PN), the servo pressure Pa (detection value of the servo pressure sensor PA), and the motor rotation angle Ka (detection value of the rotation angle sensor KA) are directly input to the upper controller EA. Furthermore, various signals such as the master pressure Pm (supply pressure) and the vehicle speed Vx are input to the upper controller EA from the communication bus BS. Also, the upper controller EA outputs an execution flag FL (described later) of a specific process to the communication bus BS. The lower controller EZ controls the pressure regulating valve UZ based on the execution flag FL acquired from the communication bus BS.

[0044] An algorithm for pressure regulation control is programmed in the upper controller EA (particularly, the microprocessor MP). "Pressure regulation control" is a control for adjusting the wheel pressure Pw (=Pwf, Pwr). The pressure regulation control is executed based on the above-mentioned various signals (Sp, Pa, etc.). Based on the pressure regulation control algorithm, the drive circuit DR drives the electric motor MA and various solenoid valves (VA, etc.). In the drive circuit DR, an inverter circuit is configured with switching elements (e.g., MOS-FET) to drive the electric motor MA. The drive circuit DR is also provided with switching elements to drive the various solenoid valves. In addition, the drive circuit DR is provided with a motor current sensor IM that detects the supply current Im (motor current) to the electric motor MA, and a temperature sensor TD that detects the temperature Td (circuit temperature) of the drive circuit DR. For example, the circuit temperature sensor TD detects the temperature of the switching elements (MOS-FET, etc.) of the inverter circuit as the circuit temperature Td.

[0045] In the upper controller EA, drive signals Va, Vb for the first and second control valves VA, VB and a drive signal Ma for the electric motor MA are calculated. Then, the switching elements are driven in response to the various drive signals (Ma, etc.). Specifically, in controlling the solenoid valves, power is supplied to the first and second control valves VA, VB based on the drive signals Va, Vb. As a result, the first control valve VA is opened and the second control valve VB is closed. In addition, the drive signal Ma is determined based on an algorithm for pressure regulation control, and the electric motor MA is controlled based on the drive signal Ma.

[0046] <Lower unit SZ> The configuration of the lower unit SZ will be described with reference to the schematic diagram of FIG. 2. The lower unit SZ is a general-purpose unit for executing anti-lock brake control, traction control, anti-skid control, and the like. The master pressure Pm and servo pressure Pa are input from the upper unit SA to the lower unit SZ as the front and rear wheel supply pressures Psf and Psr (i.e., "Psf=Pm, Psr=Pa"). The front and rear wheel supply pressures Psf and Psr (=Ps) are then adjusted (increased or decreased) by the lower unit SZ, and are output as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) of the front and rear wheel cylinders CWf and CWr. The lower unit SZ is composed of a lower actuator YZ and a lower controller EZ.

[0047] <Lower actuator YZ> The lower actuator YZ (lower fluid unit) is provided between the upper actuator YA and the wheel cylinder CW in the communication passage HS. The lower actuator YZ is composed of a pressure regulating valve UZ, a supply pressure sensor PS, a fluid pump QZ, an electric motor MZ, a pressure regulating reservoir RZ, an inlet valve VI, and an outlet valve VO.

[0048] A pressure regulating valve UZ (=UZf, UZr) is provided in the communication path HS (=HSf, HSR). The pressure regulating valve UZ is a normally open linear solenoid valve. The front and rear wheel pressure regulating valves UZf, UZr (corresponding to "solenoid valve") enable the front and rear wheel pressures Pwf, Pwr to be increased from the front and rear wheel supply pressures Psf, Psr. In the lower unit SZ, the front and rear wheel pressure regulating valves UZf, UZr enable the front and rear wheel pressures Pwf, Pwr to be individually adjusted.

[0049] The communication path HS (= HSf, HSR) is provided with a bypass path (fluid path) that connects the upper and lower parts of the pressure regulating valve UZ (= UZf, UZr). The bypass path is provided with an upper check valve GU (= GUf, GUr). The check valve GU allows flow toward the wheel cylinder CW but blocks flow from the wheel cylinder CW. In other words, the upper check valve GU (corresponding to a "check valve") is disposed to bypass the pressure regulating valve UZ and allows hydraulic pressure transmission from the electric cylinder DN (particularly, the control cylinder CC) to the wheel cylinder CW but blocks hydraulic pressure transmission from the wheel cylinder CW to the electric cylinder DN.

[0050] Front and rear wheel supply pressure sensors PSf, PSr (=PS) are provided above the pressure regulating valve UZ (at the portion of the communication passage HS closer to the upper actuator YA) to detect the front and rear wheel supply pressures Psf, Psr (=Ps). The supply pressure Ps (=Psf, Psr) detected by the supply pressure sensor PS (=PSf, PSr) is input to the lower controller EZ. Here, the rear wheel supply pressure sensor PSr can be omitted.

[0051] The upper and lower parts of the pressure regulating valve UZ (=UZf, UZr) are connected by a return path HZ (=HZf, HZr). A fluid pump QZ (=QZf, QZr) and a pressure regulating reservoir RZ (=RZf, RZr) are provided in the return path HZ (fluid path). The fluid pump QZ is driven by an electric motor MZ. The electric motor MZ is a power source for increasing the supply pressure Ps (=Psf, Psr). The electric motor MZ and the fluid pump QZ are included in the lower unit SZ, and therefore are also referred to as the "lower electric motor MZ" and the "lower fluid pump QZ".

[0052] When the electric motor MZ is driven, the fluid pump QZ sucks the brake fluid BF from the upper part of the pressure regulating valve UZ and discharges it to the lower part of the pressure regulating valve UZ. As a result, a circulating flow KZ (indicated by dashed arrows) of the brake fluid BF, which includes the pressure regulating reservoir RZ, is generated in the communication path HS and the return path HZ. When the flow path of the communication path HS is narrowed by the pressure regulating valve UZ and the circulating flow KZ of the brake fluid BF is throttled, the orifice effect at that time increases the hydraulic pressure Pp (also called the "regulating pressure") at the lower part of the pressure regulating valve UZ from the hydraulic pressure Ps (supply pressure) at the upper part of the pressure regulating valve UZ. In terms of the magnitude relationship between the supply pressure Ps and the regulating pressure Pp, the regulating pressure Pp is equal to or greater than the supply pressure Ps (i.e., "Pp≧Ps"). In other words, the regulating pressure Pp can be increased from the supply pressure Ps.

[0053] Inside the lower actuator YZ, the front and rear wheel communication passages HSf and HSR are each branched into two and connected to the front and rear wheel cylinders CWf and CWr. A normally open inlet valve VI and a normally closed outlet valve VO are provided for each wheel cylinder CW so that each wheel pressure Pw can be adjusted individually. Specifically, the inlet valve VI is provided in the branched communication passage HS (i.e., on the side closer to the wheel cylinder CW with respect to the branching part of the communication passage HS). The communication passage HS is connected to the pressure regulating reservoir RZ via a pressure reducing passage HG (fluid passage) below the inlet valve VI (the part of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO is provided in the pressure reducing passage HG. An on-off type solenoid valve is used as the inlet valve VI and the outlet valve VO.

[0054] The communication passage HS (= HSf, HSR) is provided with a fluid path that bypasses the inlet valve VI (= VIf, VIr), and the lower check valve GV (= GVf, GVr) is disposed in the fluid path. The flow direction of the lower check valve GV is opposite to that of the upper check valve GU. In other words, the lower check valve GV allows flow from the wheel cylinder CW but blocks flow toward the wheel cylinder CW.

[0055] The inlet valve VI and the outlet valve VO can adjust the wheel pressure Pw individually for each wheel cylinder CW. When the inlet valve VI and the outlet valve VO are not energized and are not operating, the inlet valve VI is opened and the outlet valve VO is closed. In this state, the wheel pressure Pw is equal to the regulating pressure Pp. To reduce the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. The inflow of the brake fluid BF into the wheel cylinder CW is prevented and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RZ, so that the wheel pressure Pw is reduced. To increase the wheel pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. The outflow of the brake fluid BF into the pressure regulating reservoir RZ is prevented and the regulating pressure Pp from the pressure regulating valve UZ is supplied to the wheel cylinder CW, so that the wheel pressure Pw is increased. However, the upper limit of the increase is the regulated pressure Pp. To maintain the wheel pressure Pw, the inlet valve VI and the outlet valve VO are both closed. Since the wheel cylinder CW is fluidically sealed, the wheel pressure Pw is maintained constant.

[0056] <Lower Controller EZ> The lower actuator YZ is controlled by a lower controller EZ (lower control unit). The lower controller EZ, like the upper controller EA, is composed of a microprocessor MP and a drive circuit DR. The lower controller EZ is connected to a communication bus BS. Therefore, the upper controller EA and the lower controller EZ can share signals via the communication bus BS.

[0057] The lower controller EZ (particularly, the microprocessor MP) receives input of sensor signals such as the supply pressure Ps, the wheel speed Vw, the steering amount Sw, the yaw rate Yr, the longitudinal acceleration Gx, and the lateral acceleration Gy. Furthermore, the lower controller EZ calculates the vehicle's traveling speed Vx (also called "vehicle speed") based on the wheel speed Vw. The lower controller EZ executes antilock brake control (so-called ABS control) that suppresses locking of the wheels WH, traction control that suppresses spinning of the drive wheels, and anti-skid control (so-called ESC) that suppresses understeer and oversteer to improve the directional stability of the vehicle.

[0058] The lower controller EZ drives the electric motor MZ constituting the lower actuator YZ and various solenoid valves (UZ, etc.) by the drive circuit DR according to a control algorithm programmed in the microprocessor MP. In the drive circuit DR of the lower controller EZ, an H-bridge circuit is configured with switching elements (e.g., MOS-FET) to drive the electric motor MZ. The drive circuit DR is also provided with switching elements to drive various solenoid valves (UZ, etc.). In addition, the drive circuit DR includes a motor current sensor (not shown) that detects the supply current Im to the electric motor MZ, and a valve current sensor IZ (not shown) that detects the current Iz (also called "valve current") supplied to the pressure regulating valve UZ. Based on the control algorithm, the drive signal Mz of the electric motor MZ, the drive signal Uz of the pressure regulating valve UZ, the drive signal Vi of the inlet valve VI, and the drive signal Vo of the outlet valve VO are calculated. Then, based on the drive signal (Uz, etc.), the electric motor MZ and the solenoid valves UZ, VI, and VO are controlled by the drive circuit DR.

[0059] <Pressure regulation control processing> An example of the voltage regulation control process will be described with reference to the flow chart of FIG. 3. In the voltage regulation control, the process of each step is executed for each calculation cycle. The voltage regulation control includes a specific process for suppressing a temperature rise of components related to the electric motor MA. Specifically, the processes from step S130 to step S230 correspond to the specific process. The specific process is permitted when the vehicle is stopped. That is, when the vehicle travel speed Vx (vehicle speed) is "0", the specific process can be executed. On the other hand, when the vehicle speed Vx is greater than "0", the execution of the specific process is prohibited.

[0060] The specific process is executed by the upper unit SA and the lower unit SZ. That is, the control process related to the electric motor MA is executed by the upper controller EA. The upper actuator YA is driven by the upper controller EA. On the other hand, the control process related to the pressure regulating valve UZ is executed by the lower controller EZ. The lower actuator YZ is driven by the lower controller EZ. That is, in the specific process, the drive of the lower electric motor MZ, the inlet valve VI, and the outlet valve VO is stopped. An instruction to open or close the pressure regulating valve UZ is transmitted from the upper controller EA to the lower controller EZ by the execution flag FL.

[0061] In pressure regulation control, first, power is supplied to the first and second control valves VA, VB. The normally closed first control valve VA is opened, and the normally open second control valve VB is closed. This allows the master piston NM and the brake operating member BP to be displaced separately, so that the front and rear wheel pressures Pwf, Pwr can be adjusted independently of the operation of the brake operating member BP. At this time, the operating force of the brake operating member BP is generated by the stroke simulator SS.

[0062] In step S110, various signals are read in by the upper controller EA. Signals of the braking operation amount Ba (generic term for Sp and Pn), servo pressure Pa, and vehicle speed Vx are input to the upper controller EA. The braking operation amount Ba is acquired by the operation amount sensor BA. The servo pressure Pa is acquired by the servo pressure sensor PA. The vehicle speed Vx is calculated by the lower controller EZ based on the wheel speed Vw, and is acquired by the upper controller EA via the communication bus BS.

[0063] In step S120, a command pressure Pd is calculated based on the braking operation amount Ba and the calculation map Zpd. The "command pressure Pd" is a target value of the wheel pressure Pw requested by the driver. In the pressure regulation control, the wheel pressure Pw is adjusted via the servo pressure Pa, but the servo pressure Pa (actual value) is finally adjusted by the target pressure Pt (described later). Therefore, the command pressure Pd corresponds to an intermediate target value in the pressure regulation control. Specifically, the command pressure Pd is calculated to be "0" according to the calculation map Zpd when the braking operation amount Ba is less than a predetermined amount bo. Then, when the braking operation amount Ba is equal to or greater than the predetermined amount bo, the command pressure Pd is calculated to increase from "0" as the braking operation amount Ba increases. Here, the predetermined amount bo corresponds to the play of the brake operating member BP, etc., and is preset as a predetermined value (constant) (see the command pressure calculation block PD for the above).

[0064] In step S130, it is determined whether "specific processing is being executed." The "specific processing" is a control process for preventing components related to the electric motor MA from overheating. Here, the "components related to the electric motor MA" include the electric motor MA itself, the drive circuit DR (particularly the switching elements) that drive the electric motor MA, the electrical wiring, etc. If the specific processing is not being executed, step S130 is negative, and the process proceeds to step S140. If the specific processing is already being executed, step S130 is positive, and the process proceeds to step S150.

[0065] In step S140, it is determined whether or not to start the specific process. This determination process is called a "start determination." The start of the specific process is determined when the following conditions are satisfied. Note that the vehicle being stopped is a prerequisite for the execution of the specific process (i.e., a permission condition for the specific process).

[0066] [Start condition] The temperature-related value Xm, which is related to the temperature of the components (MA, DR, etc.) related to the electric motor MA, exceeds the start threshold value xm. Here, the "temperature-related value Xm" corresponds to at least one of the temperature Tm of the electric motor MA (e.g., the motor coil) and the temperature Td of the drive circuit DR (e.g., the switching element). The integrated value of the motor current Im over time may also be adopted as the temperature-related value Xm. The start threshold value xm is a predetermined value (constant) that is set in advance.

[0067] If the temperature-related value Xm has not reached the start threshold value xm, step S140 is negative, and the process proceeds to step S180. On the other hand, if the temperature-related value Xm is greater than the start threshold value xm, step S140 is positive, and the process proceeds to step S160. At this time, the execution flag FL is switched from "0" to "1." The "execution flag FL" is a control flag that indicates the execution state of a specific process. Here, "FL=0" indicates that the specific process is not being executed, and "FL=1" indicates that the specific process is being executed. The execution flag FL is also a control flag that instructs the lower controller EZ to close the pressure regulating valve UZ.

[0068] In step S150, it is determined whether the specific process is to be ended. This determination process is called an end determination. The specific process is determined to be ended when the following conditions are satisfied.

[0069] [Ending condition] The command pressure Pd calculated from the braking operation amount Ba becomes smaller than the held wheel pressure Pw. Here, an estimated value based on the servo pressure Pa is used for the wheel pressure Pw. Note that, when estimating the wheel pressure Pw, a decrease in the wheel pressure Pw due to leakage from the pressure regulating valve UZ may or may not be taken into consideration. When the leakage is ignored, the servo pressure Pa at the time when the pressure regulating valve UZ is closed (at the start of the specific processing) or when the servo pressure Pa is re-increased and reaches the command pressure Pd is estimated as the wheel pressure Pw. When the leakage is taken into consideration, the wheel pressure Pw is estimated based on the elapsed time from the time when the pressure regulating valve UZ is closed or the time when the re-increase in the servo pressure Pa is completed. In either case, the wheel pressure Pw is determined based on the servo pressure Pa.

[0070] If the end condition is not satisfied, step S150 is negative and the process proceeds to step S160. At this time, the execution of the specific process continues, and the execution flag FL remains at "1." If the end condition is satisfied, step S150 is positive and the process proceeds to step S230. At this time, the execution flag FL is switched from "1 (execute)" to "0 (not execute)."

[0071] In step S160, a target current It is calculated so that the pressure regulating valve UZ is closed. The "target current It" is a target value corresponding to the valve current Iz (actual value) to be supplied to the pressure regulating valve UZ. For example, in step S160, a hydraulic pressure difference sPx (also referred to as a "specific pressure difference") between the command pressure Pd and the lower limit pressure px (described later) is calculated (i.e., "sPx = Pd - px"). At this time, since the wheel pressure Pw has been increased to the command pressure Pd by the servo pressure Pa, the specific pressure difference sPx is also the hydraulic pressure difference between the wheel pressure Pw (= Pa) and the lower limit pressure px (i.e., "sPx = Pw - px").

[0072] In step S160, the valve closing current Ih is calculated based on the specific pressure difference sPx. The "valve closing current Ih" is a target value corresponding to the minimum supply current Iz required to close the pressure regulating valve UZ against the specific pressure difference sPx. In detail, the valve closing current Ih is determined to be larger as the specific pressure difference sPx increases according to a preset calculation map Zih (see the valve closing current calculation block IH). Furthermore, in step S160, a margin current ic is added to the valve closing current Ih to more reliably close the pressure regulating valve UZ, and the target current It is determined (i.e., "It=Ih+ic"). Here, the "target current It" is a target value of the supply current Iz (valve current) to the pressure regulating valve UZ to close the pressure regulating valve UZ in the specific process, and the "margin current ic" is a preset predetermined value (constant) that increases the valve closing current Ih to allow for a margin in the target current It. The target current It (target value) is determined in accordance with the valve-closing current Ih so as to be larger as the specific differential pressure sPx is larger.

[0073] In step S170, it is determined whether "pressure increase processing of servo pressure Pa is necessary or not." In the specific processing (particularly, pressure reduction processing), in order to suppress a temperature rise of the components related to the electric motor MA, the pressure regulating valve UZ is closed to reduce the servo pressure Pa with the wheel cylinder CW in a fluid-locked state. However, even if the pressure regulating valve UZ is closed, leakage of brake fluid BF occurs there. Initially, when the pressure regulating valve UZ is closed, the wheel pressure Pw is maintained at the command pressure Pd, but gradually decreases as time T passes. In the "pressure increase processing," the target pressure Pt (resulting in the servo pressure Pa) is increased again to compensate for the decrease in wheel pressure Pw caused by leakage of brake fluid BF.

[0074] In step S170, if at least one of "the decompression time Tk (described later) has not reached the first predetermined time tx" and "the holding time Tj (described later) continues for the second predetermined time tz" is true, step S170 is negative and the process proceeds to step S190. On the other hand, if "the decompression time Tk is equal to or longer than the first predetermined time tx" and "the holding time Tj is shorter than the second predetermined time tz", step S170 is positive and the process proceeds to step S210. Here, the first predetermined time tx is a threshold value corresponding to the decompression time Tk, and is a preset predetermined value (constant). Similarly, the second predetermined time tz is a threshold value corresponding to the holding time Tj, and is a preset predetermined value (constant).

[0075] In steps S180, S190, S210, and S230, a target pressure Pt is determined according to various processes based on the command pressure Pd. The command pressure Pd is a target value of the servo pressure Pa (resulting in the wheel pressure Pw) commanded by the driver, but in certain processes, the servo pressure Pa may be reduced from the command pressure Pd to suppress heat generation. The "target pressure Pt" is a final target value corresponding to the servo pressure Pa for commanding a reduction in hydraulic pressure. In the above processes, the servo pressure Pa is controlled based on the target pressure Pt. Specifically, the servo pressure Pa is adjusted by the electric cylinder DN (particularly the electric motor MA) so that it approaches and coincides with the target pressure Pt.

[0076] In step S180, normal pressure regulation control (i.e., pressure regulation control when no specific processing is being executed) is executed. This control processing is referred to as "normal processing." In normal processing, the command pressure Pd is determined as the target pressure Pt (i.e., "Pt = Pd"). Note that, in normal processing, the operation of the lower actuator YZ is stopped. Therefore, no power is supplied to the pressure regulation valve UZ, and the normally open pressure regulation valve UZ is in a fully open state.

[0077] Steps S190 to S230 are specific processing. The specific processing includes a pressure reduction process, a pressure increase process, and a termination process. In the specific processing, the magnitude relationship between the command pressure Pd and the target pressure Pt is that the target pressure Pt is equal to or less than the command pressure Pd (i.e., "Pt≦Pd").

[0078] In step S190, a pressure reduction process in the specific process is executed. In the "pressure reduction process", the load of the electric motor MA is reduced so as to suppress heat generation of components related to the electric motor MA. Specifically, in step S190, based on the command pressure Pd and the calculation map Zpg, the target pressure Pt (target value for controlling the servo pressure Pa) is determined so as to decrease from the command pressure Pd to the lower limit pressure px with a pressure reduction gradient dg. For example, in the calculation map Zpg, the point at which step S140 is first made YES (the corresponding calculation cycle, the point at which the execution flag FL is switched from "0" to "1") is set as the starting point (i.e., "T=0"), and the target pressure Pt is calculated according to the passage of time T from that point. Here, the pressure reduction gradient dg (amount of reduction in hydraulic pressure per unit time) is a predetermined value (constant) that has been set in advance. Also, the lower limit pressure px is a predetermined value (constant) that has been set in advance (see the target pressure calculation block PT for the above).

[0079] The lower limit pressure px is set based on the rating (also called "continuous rating") at which a current can be continuously applied to the components of the electric motor MA. For example, the maximum value of the motor current Im that can be continuously passed through the electric motor MA is the continuous rating. In this case, the continuous rating is also called "current capacity." The lower limit pressure px is determined as a hydraulic pressure equivalent to the continuous rating (current capacity) of the components of the electric motor MA. In detail, the lower limit pressure px is determined according to the continuous rating of the most thermally severe component among the components of the electric motor MA. As an example, the lower limit pressure px is set in accordance with the continuous rating of a switching element (such as a MOS-FET) that switches the three-phase motor current Im.

[0080] In the pressure reduction process, the current Im supplied to the electric motor MA is reduced, suppressing heat generation in the components related to the electric motor MA. In the pressure reduction process, the pressure regulating valve UZ is kept closed, and the wheel pressure Pw in the wheel cylinder CW is sealed (so-called fluid lock state). Therefore, even if the servo pressure Pa drops due to a reduction in the motor current Im, the wheel pressure Pw is maintained approximately constant.

[0081] In step S200, a pressure reduction time Tk is calculated. The "pressure reduction time Tk" is the elapsed time related to the pressure reduction process. For example, the pressure reduction time Tk is determined as the elapsed time from the point (corresponding calculation cycle) when the target pressure Pt (resulting in the servo pressure Pa) starts to decrease. The pressure reduction time Tk is used in the judgment of step S170.

[0082] In step S210, a pressure increase process in the specific process is executed. In the pressure increase process, the servo pressure Pa, which has been reduced to the lower limit pressure px, is increased to the command pressure Pd again so that the wheel pressure Pw coincides with the command pressure Pd. Specifically, in step S210, the target pressure Pt is determined to increase from the lower limit pressure px to the command pressure Pd at a pressure increase gradient dz based on the command pressure Pd and the calculation map Zpz. Here, the pressure increase gradient dz (the amount of increase in hydraulic pressure per unit time) is a predetermined value (constant) that is set in advance. Even in the pressure increase process, the pressure regulating valve UZ continues to be closed. Therefore, the brake fluid BF pressurized to the servo pressure Pa flows into the wheel cylinder CW through the check valve GU. In other words, the wheel pressure Pw is increased through the check valve GU. As a result, the wheel pressure Pw is reliably increased without being decreased.

[0083] In step S220, the holding time Tj is calculated. The "holding time Tj" is the elapsed time related to the pressure increase process. For example, the holding time Tj is determined as the elapsed time from the point (corresponding calculation cycle) when the target pressure Pt (as a result, the servo pressure Pa) coincides with the command pressure Pd. The holding time Tj is used in the judgment of step S170.

[0084] In step S230, an end process of the specific process is executed. The end process is executed when the brake operating member BP is returned and the command pressure Pd becomes less than the wheel pressure Pw. In the end process, the pressure regulating valve UZ is gradually opened to reduce the wheel pressure Pw. Then, after the wheel pressure Pw coincides with the servo pressure Pa, the servo pressure Pa (=Pw) ​​is reduced by the electric cylinder DN.

[0085] <Specific processing operation> The operation of the specific process will be described with reference to the time series diagram of FIG. 4 (a diagram showing the transition of each state quantity with the passage of time T). In the diagram, a situation is assumed in which, after the vehicle stops, the operation amount Ba of the brake operating member BP is increased, and then the temperature-related value Xm exceeds the start threshold value xm. Note that the valve current Iz is controlled to match the target current It, so the diagrams overlap. Similarly, the servo pressure Pa is controlled to match the target pressure Pt, so the diagrams overlap. In addition, in the specific process, the pressure regulating valve UZ is driven, but the drive of the other components (MZ, VI, VO, etc.) of the lower actuator YZ is stopped.

[0086] Before time t0, normal processing based on a braking operation amount Ba of value ba generates a servo pressure Pa (=Pw) ​​of value pa, and the vehicle is decelerated. At time t0, the vehicle stops. At time t0, the condition "Vx=0" is satisfied, and the specific processing is permitted. Specifically, at time t0, the permission flag FK is switched from "0" to "1." Here, the "permission flag FK" is a control flag that indicates whether the specific processing is permitted or prohibited. With the permission flag FK, "0" indicates prohibition, and "1" indicates permission.

[0087] At time t1, the braking operation amount Ba is increased from the value ba. This causes the command pressure Pd to be increased from the value pa. As the command pressure Pd increases, the temperature-related value Xm gradually increases. At time t2, the braking operation amount Ba is maintained at the value bb, and the command pressure Pd is maintained at the value pb.

[0088] At time t3, the temperature-related value Xm exceeds the start threshold value xm (a preset predetermined constant). The temperature-related value Xm is determined based on at least one of the temperature Tm (motor temperature) of the electric motor MA, the temperature Td (circuit temperature) of the drive circuit DR, and the motor current Im (particularly, its time integrated value). At time t3, the determination in step S140 is satisfied, and the pressure reduction process related to the specific process is started. At time t3, the target current It is calculated so that the pressure regulating valve UZ is reliably closed. Specifically, the target current It is determined to be a value ix by adding a margin current ic to the valve-closing current Ih. A valve current Iz according to the target current It is supplied to the pressure regulating valve UZ to close the pressure regulating valve UZ. The valve-closing current Ih is determined to be larger as the specific differential pressure sPx (the difference between the wheel pressure Pw and the lower limit pressure px) increases. Therefore, the valve current Iz for closing the pressure regulating valve UZ is set smaller when the specific differential pressure sPx between the wheel pressure Pw and the lower limit pressure px is small than when the specific differential pressure sPx is large.

[0089] From time t3, in accordance with the calculation map Zpg, the target pressure Pt is reduced at a pressure reduction gradient dg with the passage of time T. In addition, at time t3, calculation of the pressure reduction time Tk is started. After time t3, the wheel cylinder CW is sealed by the pressure regulating valve UZ, so even if the servo pressure Pa decreases, the wheel pressure Pw does not decrease at all. However, due to leakage from the pressure regulating valve UZ, the wheel pressure Pw decreases, albeit slightly. At time t4, the target pressure Pt is held at the lower limit pressure px according to the calculation map Zpg. From time t4, the state of "Pt = px" continues.

[0090] Due to leakage at the pressure regulating valve UZ, the wheel pressure Pw decreases from the command pressure Pd. At time t5, the pressure reduction time Tk reaches the first predetermined time tx. At time t5, the judgment at step S170 is satisfied, and the pressure increase process related to the specific process is started. At this time, the pressure reduction time Tk is reset to "0". From time t5, the target pressure Pt is increased at the pressure increase gradient dz as time T passes according to the calculation map Zpz. The pressure regulating valve UZ remains closed even after time t5. However, when the target pressure Pt (resulting in the servo pressure Pa) becomes larger than the wheel pressure Pw, the servo pressure Pa is supplied to the wheel cylinder CW through the check valve GU.

[0091] At time t6, the target pressure Pt reaches the command pressure Pd. At time t6, calculation of the holding time Tj is started. From time t6, the state "Pt=Pd" continues. At time t7, the holding time Tj reaches the second predetermined time tz. As a result, the determination in step S170 is denied, and the pressure reduction process related to the specific process is started again. At this time, the holding time Tj is reset to "0". As described above, from time t7, the target pressure Pt is reduced based on the calculation map Zpg. Similarly, at time t7, calculation of the pressure reduction time Tk, which had been reset to "0", is started.

[0092] At time t8, the brake operating member BP is returned, and the brake operation amount Ba, which has been held at the value bb, starts to decrease. The command pressure Pd is decreased with the decrease in the brake operation amount Ba. At time t9, the command pressure Pd becomes smaller than the wheel pressure Pw (estimated value), and the end condition is established. At time t9, the pressure regulating valve UZ, which has been closed, starts to open. In detail, at time t9, the target current It is decreased by the margin current ic, and the target current It is made equal to the valve closing current Ih. After time t9, the target current It is determined based on the hydraulic pressure difference sPt between the command pressure Pd and the target pressure Pt, and the calculation map Zih. As a result, the valve current Iz is gradually decreased, and the pressure regulating valve UZ is opened so as to achieve the hydraulic pressure difference sPt. As a result, the wheel pressure Pw decreases along with the command pressure Pd.

[0093] At time t10, the command pressure Pd (and thus the wheel pressure Pw) reaches the target pressure Pt (and thus the servo pressure Pa) that had been maintained constant. At time t10, power supply to the pressure regulating valve UZ is stopped, and the pressure regulating valve UZ is fully opened. Furthermore, from time t10 onwards, the target pressure Pt is determined to be equal to the command pressure Pd. As a result, after time t10, the wheel pressure Pw (=Pa) decreases as the command pressure Pd decreases.

[0094] <Actions and Effects of Specific Processing> The valve current Iz required to close the pressure regulating valve UZ depends on the differential pressure between the high pressure side hydraulic pressure (i.e., wheel pressure Pw) and the low pressure side hydraulic pressure (i.e., servo pressure Pa) for the pressure regulating valve UZ. Specifically, the larger the differential pressure, the larger the valve current Iz required to close the pressure regulating valve UZ. For example, when the servo pressure Pa is reduced to "0 (atmospheric pressure)" in the specific process, the differential pressure between the wheel pressure Pw and the servo pressure Pa becomes large, and a large valve current Iz is required. However, in the brake control device SC, the servo pressure Pa is only reduced to the lower limit pressure px, so the difference sPx (specific differential pressure) between the wheel pressure Pw and the lower limit pressure px is kept low to a certain extent. This allows the valve current Iz to be kept to a minimum, thereby saving power in the pressure regulating valve UZ in the specific process.

[0095] The lower limit pressure px is preset as a predetermined value based on the continuous rating at which current can be continuously applied to the components (MA, DR, etc.) of the electric motor MA. Even if the electric motor MA is driven at the continuous rating, the temperature at which heat generation and heat dissipation / cooling are balanced is below the allowable temperature, so even if the servo pressure Pa is maintained at the lower limit pressure px, no thermal problems will occur.

[0096] The pressure regulator valve UZ includes a front wheel pressure regulator valve UZf provided for the front wheel cylinder CWf of the wheel cylinders CW, and a rear wheel pressure regulator valve UZr provided for the rear wheel cylinder CWr of the wheel cylinders CW. When the brake control device SC executes the specific process, a valve current Iz is supplied to the front wheel pressure regulator valve UZf and the rear wheel pressure regulator valve UZr to close them. This maintains the front wheel pressure Pwf and the rear wheel pressure Pwr. This reduces the power consumption related to the front wheel pressure regulator valve UZf and the rear wheel pressure regulator valve UZr. Note that since the braking force is maintained even if the servo pressure Pa is reduced, the vehicle can be reliably maintained in a stopped state even if the specific process is executed.

[0097] The pressure regulating valve UZ (electromagnetic valve) is composed of a valve body driven by a solenoid and a valve seat with which the valve body can come into contact. The pressure regulating valve UZ adjusts the hydraulic pressure Pp by the gap between the valve seat and the valve body. In the specific process, the valve seat and the valve body are brought into close contact with each other, and the pressure regulating valve UZ is closed. However, even in this situation, a small gap exists between the valve seat and the valve body, and leakage of the brake fluid BF may occur. The degree of leakage when the pressure regulating valve UZ is closed depends on the differential pressure between the high pressure side hydraulic pressure (i.e., wheel pressure Pw) and the low pressure side hydraulic pressure (i.e., servo pressure Pa) with respect to the pressure regulating valve UZ. For example, in the specific process, when the servo pressure Pa (=Ps) is reduced to "0 (atmospheric pressure)", the differential pressure between the wheel pressure Pw and the servo pressure Pa becomes large, and leakage at the pressure regulating valve UZ becomes noticeable. However, in the brake control device SC, the servo pressure Pa is only reduced to the lower limit pressure px, so that the reduction in the wheel pressure Pw caused by the fluid leakage is suppressed.

[0098] Furthermore, the specific processing in the brake control device SC includes a pressure increase processing in addition to a pressure reduction processing. The pressure increase processing increases the wheel pressure Pw that has been decreased to the command pressure Pd. That is, the decrease in the wheel pressure Pw caused by the fluid leakage in the pressure regulating valve UZ can be compensated for by the pressure increase processing.

[0099] In addition, in the brake control device SC, the wheel pressure Pw is increased in the pressure increase process via the check valve GU. That is, even when the pressure increase process is being performed, the pressure regulating valve UZ remains closed. Since the wheel pressure Pw does not decrease due to the opening of the pressure regulating valve UZ, the wheel pressure Pw can be reliably increased. The check valve GU is disposed to bypass the pressure regulating valve UZ, and allows the transmission of pressure from the electric cylinder DN (particularly the control cylinder CC) to the wheel cylinder CW, but prevents the transmission of pressure from the wheel cylinder CW to the electric cylinder DN.

[0100] <Modification of the first embodiment> A modification of the first embodiment will be described. In the above-described embodiment, a single type master cylinder CM is used, and the master pressure Pm is transmitted to the front wheel cylinder CWf, and the servo pressure Pa is transmitted to the rear wheel cylinder CWr. Alternatively, a tandem type master cylinder CM may be used. In this configuration, the master cylinder CM has two hydraulic chambers, the front and rear master chambers Rmf and Rmr. Then, the servo pressure Pa supplied to the servo chamber Ru generates the front and rear master pressures Pmf and Pmr, which are transmitted to the front and rear wheel cylinders CWf and CWr.

[0101] In the above-described embodiment, in the apply unit AP, the pressure receiving area rm (master area) of the master chamber Rm and the pressure receiving area ru (servo area) of the servo chamber Ru are set to be equal. Here, the master area rm and the servo area ru do not have to be equal. In a configuration in which the master area rm and the servo area ru are different, it is possible to perform a conversion calculation between the master pressure Pm (=Psf) and the servo pressure Pa based on the area ratio between the servo area ru and the master area rm (i.e., conversion based on "Pm·rm=Pa·ru").

[0102] In the above-mentioned specific processing, the front wheel pressure Pwf and the rear wheel pressure Pwr are controlled in the same manner. In detail, when the specific processing is started, the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr are both closed, and the servo pressure Pa is adjusted by the electric cylinder DN. Alternatively, the front wheel pressure regulating valve UZf may be closed, but the rear wheel pressure regulating valve UZr may not be closed. The pressure regulating valves UZ include the front wheel pressure regulating valve UZf (corresponding to the "front wheel solenoid valve") provided for the front wheel cylinder CWf, and the rear wheel pressure regulating valve UZr (corresponding to the "rear wheel solenoid valve") provided for the rear wheel cylinder CWr, but when the specific processing is executed, the front wheel pressure regulating valve UZf is closed, but the rear wheel pressure regulating valve UZr is left open. In this configuration, the front wheel cylinder CWf is sealed by closing the front wheel pressure regulating valve UZf, and the front wheel pressure Pwf is maintained substantially constant (see the transition of "Pw" in FIG. 4), while the rear wheel pressure Pwr increases or decreases in conjunction with the servo pressure Pa (see the transition of "Pa" in FIG. 4). In the specific processing, the rear wheel pressure regulating valve UZr remains de-energized, thereby reducing power consumption accordingly. Note that, since the contribution of the front wheel pressure Pwf to the generation of braking force is significantly greater than the contribution of the rear wheel pressure Pwr, the stopped state can be adequately maintained by maintaining the front wheel pressure Pwf.

[0103] Also, in the specific processing, the rear wheel pressure regulating valve UZr may be closed, but the front wheel pressure regulating valve UZf may not be closed. In this configuration, the rear wheel cylinder CWr is sealed by closing the rear wheel pressure regulating valve UZr, so the rear wheel pressure Pwr is maintained substantially constant (see the transition of "Pw" in FIG. 4). Meanwhile, the front wheel pressure Pwf increases and decreases in conjunction with the servo pressure Pa (see the transition of "Pa" in FIG. 4). In the specific processing, the front wheel pressure regulating valve UZf remains de-energized, so power consumption is reduced accordingly.

[0104] In addition, in the specific process, when only the rear wheel pressure regulating valve UZr is closed among the rear wheel pressure regulating valve UZr and the front wheel pressure regulating valve UZf, the electric cylinder DN may be operated so that the rear wheel pressure Pwr is increased to a value higher than the hydraulic pressure at the start of the specific process. The "start of the specific process" mentioned here may include not only the start time, but also the time immediately before and the time immediately after the start time. This makes it easier to maintain the stopped state even if the contribution of the rear wheel pressure Pwr to the generation of the braking force is lower than the contribution of the front wheel pressure Pwf.

[0105] In the specific process (particularly the pressure increase process) described above, the calculation of the pressure reduction time Tk is started at the time (corresponding calculation cycle) when the target pressure Pt (resulting in the servo pressure Pa) starts to decrease due to the pressure reduction process. That is, the calculation of the pressure reduction time Tk starts at the time when the pressure reduction starts. Alternatively, the calculation of the pressure reduction time Tk may start at the time (corresponding calculation cycle) when the target pressure Pt (resulting in the servo pressure Pa) reaches the lower limit pressure px. In this configuration, the calculation of the pressure reduction time Tk starts at time t4 (that is, the time when the pressure reduction ends and the time when the holding starts). Then, at time t5 when the first predetermined time tx has elapsed from time t4, the pressure increase process starts.

[0106] <Second embodiment of the brake control device SC> A second embodiment of the upper unit SA of the brake control device SC will be described with reference to the schematic diagram of FIG. 5. In the first embodiment, the servo pressure Pa is transmitted as the supply pressure Ps (=Pm) via the master cylinder CM and the master piston NM. In other words, in the hydraulic pressure transmission path related to at least the front wheel cylinder CWf, the apply unit AP is arranged in series with the hydraulic pressure generating unit PU. Instead of this configuration, in the second embodiment, the apply unit AP and the hydraulic pressure generating unit PU are arranged in parallel. That is, in the second embodiment, the apply unit AP (particularly, the master cylinder CM) and the hydraulic pressure generating unit PU are each directly connected to the lower unit SZ (particularly, the lower actuator YZ). In the second embodiment, the same specific processing as in the first embodiment is also executed.

[0107] In the upper unit SA according to the second embodiment, a shutoff valve VM, a simulator valve VS, and a communication valve VC are provided instead of the input unit NR. The shutoff valve VM is a normally open type on-off solenoid valve, and the simulator valve VS and the communication valve VC are normally closed type on-off solenoid valves. The shutoff valve VM is provided in a front wheel communication passage HSf that connects the master cylinder CM (particularly, the master chamber Rm) and the front wheel cylinder CWf. A stroke simulator SS is connected to the front wheel communication passage HSf between the master cylinder CM and the shutoff valve VM via the simulator valve VS.

[0108] The front and rear wheel communication passages HSf and HSR (fluid passages connected to the front and rear wheel cylinders CWf and CWr) are connected to the control cylinder CC (particularly, the control chamber Rc) via a communication passage HV (fluid passage). The communication passage HV is also a fluid passage connecting the front and rear wheel communication passages HSf and HSR. A communication valve VC is provided in the communication passage HV.

[0109] When pressure regulation control is performed, power is supplied to the shutoff valve VM, the simulator valve VS, and the communication valve VC. As a result, the shutoff valve VM is closed, and the simulator valve VS and the communication valve VC are opened. The connection between the master chamber Rm and the front wheel cylinder CWf is cut off, and the servo pressure Pa is supplied to the front wheel cylinder CWf. In addition, since the master chamber Rm is connected to the stroke simulator SS, the operating force of the brake operating member BP (brake pedal) is generated by the stroke simulator SS. The servo pressure sensor PA may be provided in the hydraulic pressure generating unit PU or in the lower actuator YZ. In a configuration in which the servo pressure sensor PA is provided in the lower actuator YZ, the servo pressure Pa is acquired by the upper controller EA via the communication bus BS.

[0110] In the second embodiment, the same control as in the first embodiment (including the above-mentioned modified example) is executed. Therefore, in the second embodiment, the same effects as in the first embodiment (suppression of heat generation of components related to the electric motor MA by the specific process, suppression of power consumption related to the pressure regulating valve UZ, compensation for reduction in the wheel pressure Pw caused by fluid leakage, etc.) are achieved.

[0111] <Third embodiment of the brake control device SC> A third embodiment of the brake control device SC will be described with reference to FIGS. The lower actuator YZ has a front wheel system and a rear wheel system. The part of the lower actuator YZ that adjusts the front wheel cylinder CWf corresponds to the "front wheel system," and the part that adjusts the rear wheel cylinder CWr corresponds to the "rear wheel system." In other words, the front wheel system has a front wheel pressure regulating valve UZf, a fluid pump QZf, a pressure regulating reservoir RZf, an inlet valve VIf, and an outlet valve VOf. The rear wheel system has a rear wheel pressure regulating valve UZr, a fluid pump QZr, a pressure regulating reservoir RZr, an inlet valve VIr, and an outlet valve VOr.

[0112] One of the upper controller EA and the lower controller EZ determines whether or not an abnormality has occurred in the front wheel system. For example, this determination is performed by the upper controller EA. The upper controller EA receives the front wheel master pressure Pmf from the lower controller EZ at every predetermined control cycle. Then, when the servo pressure Pa is generated by the operation of the electric cylinder DN, the upper controller EA compares the servo pressure Pa with the front wheel master pressure Pmf to determine whether or not an abnormality has occurred in the front wheel system.

[0113] If the difference between the rate of increase of the servo pressure Pa and the rate of increase of the front wheel master pressure Pmf is relatively large, there is a possibility that a leakage of brake fluid BF is occurring in the front wheel system. If the servo pressure Pa is maintained in this manner under the condition that a leakage of brake fluid BF is occurring in the front wheel system, it can be inferred that a deviation will occur between the servo pressure Pa and the front wheel master pressure Pmf.

[0114] Therefore, for example, the upper controller EA determines that an abnormality has occurred in the front wheel system when at least one of the following two conditions is satisfied. In this case, the upper controller EA determines that no abnormality has occurred in the front wheel system, that is, determines that the front wheel system is normal, when neither of the following two conditions is satisfied.

[0115] When the servo pressure Pa is increasing, the magnitude of the difference between the rate of increase of the servo pressure Pa and the rate of increase of the front wheel master pressure Pmf is equal to or greater than a predetermined value. When servo pressure Pa is maintained, the deviation between servo pressure Pa and front wheel master pressure Pmf is equal to or greater than a specified value.

[0116] When the upper controller EA executes the above specific process under the condition that it has determined that no abnormality has occurred in the front wheel system, it instructs the lower controller EZ to close the front wheel pressure regulating valve UZf and to keep the rear wheel pressure regulating valve UZr open. When the lower controller EZ receives such an instruction, the lower controller EZ closes the front wheel pressure regulating valve UZf to suppress a decrease in the front wheel pressure Pwf, while keeping the rear wheel pressure regulating valve UZr open.

[0117] On the other hand, when the upper controller EA executes a specific process under a condition in which it has determined that an abnormality has occurred in the front wheel system, it instructs the lower controller EZ to close the rear wheel pressure regulating valve UZr and to keep the front wheel pressure regulating valve UZf open. When the lower controller EZ receives such an instruction, the lower controller EZ closes the rear wheel pressure regulating valve UZr to suppress a decrease in the rear wheel pressure Pwr, while keeping the front wheel pressure regulating valve UZf open.

[0118] <Determination of pressure regulating valve to be closed when specific process is executed> A series of processes executed by the upper controller EA to determine whether to close the front wheel pressure regulating valve UZf or the rear wheel pressure regulating valve UZr when a specific process is executed will be described with reference to Fig. 6. The series of processes is repeatedly executed at a predetermined control period.

[0119] In step S310, it is determined whether or not a braking force is being applied by normal processing. If a braking force is being applied by normal processing, step S310 is judged as YES, and the process proceeds to step S320. On the other hand, if a braking force is not being applied by normal processing, step S310 is judged as NO, and the series of processes shown in FIG. 6 is temporarily terminated.

[0120] In step S320, it is determined whether or not an abnormality such as that described above has occurred in the front wheel system. If it is determined that an abnormality has occurred in the front wheel system, step S320 is judged as YES, and the process proceeds to step S330. On the other hand, if it is determined that an abnormality has not occurred in the front wheel system, step S320 is judged as NO, and the process proceeds to step S340.

[0121] In step S330, the selection flag FL1 is set to "1." The selection flag FL1 being "1" means that the rear wheel pressure regulating valve UZr is closed when the specific process is executed. Then, the series of processes shown in FIG. 6 is temporarily ended.

[0122] In step S340, the selection flag FL1 is set to "0." The selection flag FL1 being "0" means that the front wheel pressure regulating valve UZf is closed when the specific process is executed. Then, the series of processes shown in FIG. 6 is temporarily ended.

[0123] <Specific processing operation> The operation of the identification process in the third embodiment, focusing on the difference from the operation of the identification process in the above embodiments, will be described with reference to Fig. 7. Here, the identification process when an abnormality occurs in the front wheel system will be described.

[0124] Operation of the brake operating member BP begins at time t20. Then, as shown in Figures 7(a) and 7(b), the servo pressure Pa is increased in accordance with an increase in the braking operation amount Ba by normal processing. Then, brake fluid BF is supplied to both the front wheel system and the rear wheel system.

[0125] In this case, if an abnormality occurs in the front wheel system but not in the rear wheel system, brake fluid BF is supplied to the rear wheel system, and brake fluid BF is supplied to the rear wheel cylinder CWr. As a result, the rear wheel pressure Pwr increases in accordance with the increase in servo pressure Pa, as shown in FIG. 7(b).

[0126] 7, the braking operation amount Ba is held at time t21. Therefore, the servo pressure Pa and the rear wheel pressure Pwr are also held. If this state continues, the temperature-related value Xm will exceed the start threshold value xm at time t22, and the pressure reduction process related to the specific process will be started.

[0127] Here, of the front wheel pressure regulator valve UZf and the rear wheel pressure regulator valve UZr, the rear wheel pressure regulator valve UZr is closed, while the front wheel pressure regulator valve UZf is kept open. At time t22, a target current Itr is calculated so that the rear wheel pressure regulator valve UZr is reliably closed. Specifically, as shown in FIG. 7(c), the target current Itr is determined to be a value ix by adding a margin current ic to the valve closing current Ih. A valve current Izr according to the target current Itr is supplied to the rear wheel pressure regulator valve UZr, so that the rear wheel pressure regulator valve UZf is closed. The valve closing current Ih is determined to be larger as the specific differential pressure sPx (the difference between the rear wheel pressure Pwr and the lower limit pressure px) increases. Therefore, when the differential pressure sPx between the rear wheel pressure Pwr and the lower limit pressure px is small, the valve current Izr for closing the rear wheel pressure regulating valve UZr is made smaller than when the specific differential pressure sPx is large. On the other hand, since the target current Itf for the front wheel pressure regulating valve UZf remains at "0", the front wheel pressure regulating valve UZf is maintained in an open state.

[0128] Due to the relationship between the characteristics of the front wheel braking device SXf and the rear wheel braking device SXr, the contribution of the rear wheel pressure Pwr to the generation of braking force is smaller than the contribution of the front wheel pressure Pwf.

[0129] Therefore, in the specific process executed in the third embodiment, the servo pressure Pa is increased at time t22 as shown in Fig. 7(b). Then, following the increase in the servo pressure Pa, the rear wheel pressure Pwr is also increased. As a result, even if the servo pressure Pa is subsequently reduced, the vehicle can be kept stopped by the braking force generated at the rear wheels.

[0130] At the subsequent time t23, as in the case of the first embodiment, the servo pressure Pa is reduced to the lower limit pressure px by executing the pressure reducing process related to the specific process. However, it is preferable that the lower limit pressure px when the front wheel pressure regulating valve UZf is not closed is higher than the lower limit pressure px when the front wheel pressure regulating valve UZf is closed. Of course, the lower limit pressure px when the front wheel pressure regulating valve UZf is closed may be the same as the lower limit pressure px when the front wheel pressure regulating valve UZf is closed.

[0131] After time t23, even though the rear wheel pressure regulating valve UZr is closed, the rear wheel pressure Pwr decreases, albeit slightly, due to leakage at the rear wheel pressure regulating valve UZr. Therefore, as in the first embodiment, at the subsequent time t24, the pressure increase process related to the specific process is started. As a result, the servo pressure Pa is increased. In the pressure increase process in the third embodiment, the servo pressure Pa is increased to the servo pressure Pa at time t23. Then, the rear wheel cylinder CWr is supplied with brake fluid BF, so that the rear wheel pressure Pwr is restored. Therefore, at time t25, the pressure decrease process related to the specific process is executed again. In other words, while the braking operation amount Ba is approximately constant, the pressure decrease process and the pressure increase process are periodically repeated.

[0132] Therefore, in the third embodiment, even if only the rear wheel pressure regulating valve UZr out of the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr is closed, the same effects as those of the above embodiments can be obtained.

[0133] When the specific process is executed under the condition that it is determined that no abnormality occurs in the front wheel system, the front wheel pressure regulator valve UZf is closed and the rear wheel pressure regulator valve UZr is opened. The process flow at this time is substantially the same as that in the first embodiment. Therefore, a detailed description will be omitted.

[0134] <Other embodiments> Other embodiments will be described below. The other embodiments also provide the same effects as those described above. In the above embodiment, a disc-type braking device SX is used as the braking device SX. Alternatively, a drum-type braking device SX may be used as the braking device SX. In a drum-type braking device SX, the rotating member KT fixed to the wheel WH is a brake drum, and the friction member is a brake lining attached to a brake shoe. In the drum-type braking device SX, as in the disc-type braking device SX, the wheel pressure Pw of the wheel cylinder CW presses the brake lining (friction member) against the brake drum (rotating member), generating a frictional braking force Fe.

[0135] In the hydraulic pressure transmission in the brake control device SC, various resistances exist, such as the pipe friction resistance of the fluid path (HS, etc.), the resistance as the orifice of the solenoid valve (VI, etc.), the sliding resistance of the seal member SL, etc. In the feedback control related to the hydraulic pressure, the actual value is controlled so as to coincide with the target value, but considering the above resistance, the actual value and the target value need to be compared at the same part. In the above-mentioned embodiment, the target pressure Pt is determined as the target value corresponding to the servo pressure Pa (actual value). That is, the part where the target value and the actual value are compared (also called the "comparison part") is the part where the servo pressure sensor PA is provided. Instead of this, the comparison part may be any part from the discharge part of the electric cylinder DN to the wheel cylinder CW in the path where the hydraulic pressure is transmitted. For example, the wheel cylinder CW is adopted as the comparison part, the target pressure Pt is determined so as to correspond to the wheel pressure Pw (actual value), and the wheel pressure Pw is estimated from the servo pressure Pa with the hydraulic pressure component due to the above resistance compensated for. In a configuration in which the lower part of the pressure regulating valve UZ is used as the comparison part, when the pressure regulating valve UZ is closed in the specific process, the wheel pressure Pw is determined on the assumption that the pressure regulating valve UZ is open. In pressure regulation control, regardless of the location of the comparison part between the target value and the actual value, the target pressure Pt can be said to be a target value for controlling the servo pressure Pa.

[0136] In the above-described embodiment, the pressure regulation control including the specific processing is executed by two controllers EA and EZ. Alternatively, the upper and lower controllers EA and EZ may be integrated to configure one integrated controller EC. Here, the controllers EA, EZ, and EC are referred to as "controller EE." In any case, in the braking control device SC, the electric motor MA and the pressure regulating valve UZ are controlled by the controller EE (i.e., a collective term for the controllers EA, EZ, and EC).

[0137] <Summary of the embodiment> The brake control device SC is provided with a control cylinder CC, a pressure regulating valve UZ, and a controller EE (a collective term for controllers EA, EZ, and EC), and adjusts the wheel pressure Pw of the wheel cylinder CW with servo pressure Pa. The control cylinder CC generates servo pressure Pa by the movement of a control piston NC driven by an electric motor MA. The pressure regulating valve UZ (solenoid valve) is of the normally open type, and is provided in the hydraulic pressure transmission path (HS, etc.) from the control cylinder CC to the wheel cylinder CW. The controller EE controls the electric motor MA and the pressure regulating valve UZ.

[0138] In the brake control device SC, the controller EE executes a specific process to close the pressure regulating valve UZ and reduce the servo pressure Pa when a temperature-related value Xm related to the temperature of a component related to the electric motor MA exceeds a threshold value xm. In the specific process, the servo pressure Pa is reduced to a lower limit pressure px. Here, the lower limit pressure px is set in advance based on the continuous rating of the component of the electric motor MA. In addition, in the specific process, the valve current Iz supplied to close the pressure regulating valve UZ is adjusted based on a differential pressure sPx (specific differential pressure) between the wheel pressure Pw and the lower limit pressure px. Specifically, when the specific differential pressure sPx is small, the valve current Iz is made smaller than when the specific differential pressure sPx is large. By appropriately setting the lower limit pressure px, the valve current Iz to the pressure regulating valve UZ is suppressed to a necessary minimum. As a result, the power consumption of the brake control device SC is reduced.

[0139] The brake control device SC is provided with a front wheel pressure regulator valve UZf associated with the front wheel cylinder CWf and a rear wheel pressure regulator valve UZr associated with the rear wheel cylinder CWr as pressure regulator valves UZ. When a specific process is executed (i.e., when the servo pressure Pa is reduced), the front wheel pressure regulator valve UZf is closed and the rear wheel pressure regulator valve UZr is left open. Since the power consumption of the rear wheel pressure regulator valve UZr becomes "0", the power consumption of the brake control device SC is reduced. Since the front wheel pressure Pwf can generate a greater braking force than the rear wheel pressure Pwr, the vehicle can be reliably maintained stopped even when the specific process is performed using only the front wheel cylinder CWf. [Explanation of symbols]

[0140] SC...Brake control device, BP...Brake operation member (brake pedal), SA, SZ...Upper, lower unit, YA, YZ...Upper, lower actuator, EA, EZ...Upper, lower controller, EC...Integrated controller, EE...Controller (general term for EA, EZ, EC), CW...Wheel cylinder, BS...Communication bus, AP...Apply unit, CM...Master cylinder, NM...Master piston, NR...Input unit, PU...Hydraulic pressure generating unit, DN...Electric cylinder (=PU), MA...Electric motor, DR...Drive circuit (inverter circuit), NC...Control piston, CC...Control cylinder, Rc...Control chamber (hydraulic chamber of CC), VA, VB...1st, 2nd control valve, BA...Brake operation amount sensor (SP, etc.) general term), Ba...braking operation amount (general term for Sp, etc.), Pa...servo pressure (output of DN), PA...servo pressure sensor, Pd...indicated pressure (target value according to Ba), Pt...target pressure (target value for controlling Pa), Pw...wheel pressure, UZ...pressure regulating valve, GU...check valve, SS...stroke simulator, SP...operation displacement sensor, Sp...operation displacement (detected value of SP), Xm...temperature-related value, xm...start threshold for specific processing, px...lower limit pressure, sPx...specific differential pressure (hydraulic pressure difference between Pd, Pw and px), Tk...pressure reduction time (elapsed time related to the decrease in Pa), Tj...holding time (time elapsed from the point at which Pa matches Pd), tx...first specified time (threshold related to Tk), tz...second specified time (threshold related to Tj).

Claims

1. A vehicle brake control device comprising: an electric cylinder that generates a servo pressure by movement of a control piston driven by an electric motor; a normally open solenoid valve provided in a hydraulic pressure transmission path from the electric cylinder to a wheel cylinder; and a controller that controls the electric motor and the solenoid valve, the vehicle brake control device adjusting a wheel pressure of the wheel cylinder by the servo pressure, the controller closes the solenoid valve and reduces the servo pressure to a lower limit pressure set based on a maximum rating at which current can be continuously applied to the component member when a temperature-related value related to a temperature of the component member associated with the electric motor exceeds a threshold value; A vehicle braking control device, wherein the controller reduces a valve current supplied to close the solenoid valve when a pressure difference between the wheel pressure and the lower limit pressure is small, compared to when the pressure difference is large.

2. 2. The vehicle brake control device according to claim 1, the solenoid valves include a front wheel solenoid valve provided for a front wheel cylinder among the wheel cylinders, and a rear wheel solenoid valve provided for a rear wheel cylinder among the wheel cylinders, A vehicle braking control device, wherein the controller closes the front wheel solenoid valves and keeps the rear wheel solenoid valves open when the servo pressure is reduced.

3. 2. The vehicle brake control device according to claim 1, the solenoid valves include a front wheel solenoid valve provided for a front wheel cylinder among the wheel cylinders, and a rear wheel solenoid valve provided for a rear wheel cylinder among the wheel cylinders, A vehicle braking control device, wherein the controller closes the rear wheel solenoid valves and keeps the front wheel solenoid valves open when the servo pressure is reduced and maintained at the lower limit pressure.

4. 3. The vehicle brake control device according to claim 2, Among the hydraulic pressure transmission paths, a system for adjusting the wheel pressure of the front wheel cylinder is a front wheel system, and a system for adjusting the wheel pressure of the rear wheel cylinder is a rear wheel system, the front wheel system includes the front wheel solenoid valve, the rear wheel system includes the rear wheel solenoid valve, The controller: determining whether or not an abnormality has occurred in the front wheel system; when the temperature-related value exceeds the threshold value under a condition in which it is determined that no abnormality has occurred in the front wheel system, the front wheel solenoid valve is closed and the rear wheel solenoid valve is kept open; A vehicle braking control device that closes the rear wheel solenoid valve and keeps the front wheel solenoid valve open when the temperature-related value exceeds the threshold value under a condition in which it is determined that an abnormality has occurred in the front wheel system.

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