Brake control device for a vehicle

Abstract

The present application relates to a brake control device of a vehicle. The brake control device is provided with: a control cylinder that generates a servo pressure by movement of a control piston driven by a motor; a solenoid valve of a normally open type that is provided on a hydraulic pressure transmission path from the control cylinder to a wheel cylinder; and a controller that controls the motor and the solenoid valve. The brake control device adjusts a wheel cylinder pressure of the wheel cylinder by the servo pressure. In a case where a temperature correlation value related to a temperature of a structural member involved with the motor exceeds a threshold value, the controller closes the solenoid valve and reduces the servo pressure to a lower limit pressure set based on a maximum rated value at which continuous power supply to the structural member is possible. Further, when a differential pressure between the wheel cylinder pressure and the lower limit pressure is small, the controller reduces a valve current supplied for closing the solenoid valve compared to when the differential pressure is large.

Description

Technical Field

[0001] This 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 hydraulic brake fluid corresponding to the drive of an electric motor from an output port; a master cylinder configured to allow brake fluid to flow out of the master chamber by moving a master piston that increases with the hydraulic pressure in the servo chamber, and to allow brake fluid to flow into the master chamber by moving a master piston that decreases with the hydraulic pressure in the servo chamber; a first flow path connecting the master chamber to a front wheel cylinder; a sixth flow path connecting the output port to a rear wheel cylinder; a fifth flow path connecting the sixth flow path to the servo chamber; and a differential pressure regulating valve provided in the fifth flow path, which adjusts the 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, in such braking control devices, the electric motor and its drive circuit may generate heat. For example, in the electric power steering mechanism described in Patent Document 2, a holding valve (also called a "solenoid valve") is included to control the connection between the wheel cylinder that generates braking force on the wheel and the master cylinder. When braking is continuously applied and the pressure rise in the wheel cylinder continues, the holding valve is closed and the power supply to the electric motor is reduced. In such a device, the power consumption of the solenoid valve needs to be considered.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2024-82901

[0005] Patent Document 2: Japanese Patent Application Publication No. 2009-040122 Summary of the Invention

[0006] In view of the above-mentioned problems, the object of the present invention is to provide a braking control device for a vehicle that suppresses the heating of structural components involved in the electric motor by using a solenoid valve to maintain wheel cylinder pressure, and is able to suppress the power consumption of the solenoid valve.

[0007] The vehicle braking control device (SC) of the present invention includes: an electric cylinder (DN) that generates servo pressure (Pa) by moving a control piston (NC) driven by an electric motor (MA); a normally open solenoid valve (UZ) disposed in the hydraulic transmission path (HS) from the electric cylinder (DN) to the wheel cylinder (CW); and a controller (EE, etc.) that controls the electric motor (MA) and the solenoid valve (UZ), wherein the vehicle braking control device adjusts the wheel cylinder pressure (Pw) of the wheel cylinder (CW) by the servo pressure (Pa).

[0008] In the vehicle braking control device (SC) of the present invention, when the temperature-related value (Xm) associated with the temperature of the structural components (MA, DR, etc.) involved in 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 rated value that allows continuous energization of the structural components (MA, DR, etc.). Furthermore, when comparing the differential pressure (sPx) between the wheel cylinder pressure (Pw) and the lower limit pressure (px), the controller (EE, etc.) reduces the valve current (Iz) supplied for closing the solenoid valve (UZ) compared to when comparing the differential pressure (sPx).

[0009] The valve current Iz required to close the pressure regulating valve UZ is determined by the differential pressure between the cylinder pressure Pw and the servo pressure Pa. According to the above structure, since the decrease in the servo pressure Pa is limited to the lower limit pressure px, this differential pressure can be suppressed to a certain extent. Therefore, due to the reduction in valve current Iz, the power consumption of the pressure regulating valve UZ is suppressed.

[0010] In the vehicle braking control device (SC) of the present invention, the solenoid valve (UZ) includes a front wheel solenoid valve (UZf) disposed relative to the front wheel cylinder (CWf) of the wheel cylinders (CW), and a rear wheel solenoid valve (UZr) disposed relative to the rear wheel cylinder (CWr) of the wheel cylinders (CW). When the servo pressure (Pa) is reduced, the controller (EE, etc.) closes the front wheel solenoid valve (UZf) and keeps the rear wheel solenoid valve (UZr) open. According to this structure, since it is not necessary to supply power to the rear wheel pressure regulating valve UZr, power consumption is correspondingly reduced. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating a first embodiment of a vehicle's braking control device SC (particularly the upper unit SA).

[0012] Figure 2 This is a schematic diagram illustrating the structure of the lower unit SZ of the braking control device SC.

[0013] Figure 3 It is a flowchart used to illustrate the process of voltage regulation control, which includes specific processing.

[0014] Figure 4 It is a time series graph used to illustrate the actions of a specific process.

[0015] Figure 5 This is a schematic diagram used to explain the second embodiment of the upper unit SA.

[0016] Figure 6 This is a flowchart illustrating the process of selecting a pressure regulating valve to be closed when performing a specific process in the third embodiment of the braking control device SC.

[0017] Figure 7 (a) to (c) are time series graphs used to illustrate the actions of a specific process in the third embodiment of the braking control device SC. Detailed Implementation

[0018] <Symbols for structural components, etc., and the subscript at the end of the symbol>

[0019] In the following description, structural components, processing operations, signals, characteristics, and values ​​bearing the same symbols such as "CW" have the same function. The subscripts "f" and "r" appended to the symbols related to each wheel indicate which system in the front or rear wheels they pertain to. For example, in the context of wheel cylinders CW installed in each wheel, it is expressed as "front wheel cylinder CWf, rear wheel cylinder CWr". Furthermore, the subscripts "f" and "r" at the end of the symbols are sometimes omitted. When the subscripts "f" and "r" are omitted, each symbol represents its collective name. For example, "CW" is the collective name for the wheel cylinders installed in the front and rear wheels of a vehicle. Additionally, "CW" as a collective name is also expressed as "CW (=CWf, CWr)".

[0020] In the brake control unit SC, the upper unit SA, the lower unit SZ, and the wheel cylinder CW are connected via a fluid path (connecting path HS). Furthermore, various components (CC, etc.) within the upper unit SA and the lower unit SZ are connected via fluid paths. Here, a "fluid path" is the path used to move the brake fluid BF, including piping, flow paths within the actuator, hoses, etc. In the following description, the connecting path HS, reservoir path HR, input path HN, servo path HU, and replenishment path HH are fluid paths.

[0021] In the hydraulic transmission path (fluid path HU, HS, etc.) related to the servo pressure Pa, the side closer to the hydraulic generating unit PU (i.e., the side farther from the wheel cylinder CW) is called the "upper part". Conversely, the side farther from the hydraulic generating unit PU (i.e., the side closer to the wheel cylinder CW) is called the "lower part".

[0022] <First Embodiment of Braking Control Device SC>

[0023] Reference Figure 1 The schematic diagram illustrates a first embodiment of a vehicle's braking control device SC (particularly the upper unit SA). The braking control device SC consists of an upper unit SA and a lower unit SZ. For example, the braking control device SC is suitable for hybrid vehicles or electric vehicles equipped with a driving electric motor.

[0024] The front and rear wheels WHf and WHr (=WH) of the vehicle are equipped with braking devices SX (=SXf, SXr). The braking device SX consists of a brake caliper, friction components (e.g., brake pads), and a rotating component KT (e.g., brake disc). A wheel cylinder CW is located within the brake caliper (not shown). Through hydraulic pressure Pw within the wheel cylinder CW (referred to as "wheel cylinder pressure"), the friction components (not shown) are pressed against the rotating component KT fixed to each wheel WH, applying a braking torque Tb to the wheel. As a result, a frictional braking force Fe (also called "hydraulic braking force") is generated on the wheel WH. Therefore, the braking device SX can be described as "a device that generates frictional braking force Fe through wheel cylinder pressure Pw" or "a device that converts wheel cylinder pressure Pw into frictional braking force Fe."

[0025] The vehicle is equipped with a brake operating component BP and various sensors (SP, etc.). The brake operating component BP (e.g., the brake pedal) is an operating component used by the driver to decelerate the vehicle. The vehicle is equipped with an operating displacement sensor SP that detects the operating displacement Sp of the brake operating component BP. The operating displacement Sp is one of the state quantities (state variables) representing the operating amount of the brake operating component BP. In the in-line control type brake control device SC, it is a signal representing the driver's braking intention (i.e., brake indication). In addition to the operating displacement sensor SP, the hydraulic pressure Pn (referred to as "input pressure") of the input chamber Rn (described later) is also used as another state quantity representing the braking operation amount. The input pressure Pn is detected by the input pressure sensor PN. The operating displacement Sp, input pressure Pn, etc., are collectively referred to as "brake operation amount Ba". Furthermore, the operating displacement sensor SP and the input pressure sensor PN that detect the operating displacement Sp and input pressure Pn (i.e., brake operation amount Ba) are collectively referred to as "brake operation amount sensor BA".

[0026] The vehicle is equipped with various sensors for braking control, such as anti-lock braking and sideslip prevention (i.e., individual control of the wheel cylinder pressure Pw of each wheel). Specifically, each wheel WH is equipped with a wheel speed sensor VW that detects its rotational speed Vw (referred to as "wheel speed"). In addition, it is equipped with: a steering input sensor that detects the steering input Sw (e.g., steering angle) of steering operation components (e.g., steering wheel); a yaw rate sensor that detects the vehicle's yaw rate Yr; a front and rear acceleration sensor that detects the vehicle's front and rear acceleration Gx (also referred to as "deceleration"); and a lateral acceleration sensor that detects the vehicle's lateral acceleration Gy (none of which are shown in the figure).

[0027] The vehicle is equipped with a brake control unit SC. The brake control unit SC uses a so-called front and rear type (also known as "Type II") braking system as a two-system braking system. The brake control unit SC adjusts the wheel cylinder pressure Pw of each wheel cylinder CW.

[0028] The braking control unit SC consists of two braking units SA and SZ. The upper unit SA consists 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 consists 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 and YZ are also referred to as "upper and lower fluid units." Furthermore, the upper and lower controllers EA and EZ are also referred to as "upper and lower control units."

[0029] The upper unit SA (especially the upper controller EA) and the lower unit SZ (especially the lower controller EZ) are connected to the communication bus BS. Signals are transmitted between multiple controllers (EA, EZ, etc.) via the communication bus BS. That is, multiple controllers can send signals (detected values, calculated values, control flags, etc.) to the communication bus BS and can receive signals from the communication bus BS.

[0030] <Structure of the upper unit SA>

[0031] The structure of the upper unit SA in the first embodiment will be described. The upper unit SA generates a servo pressure Pa based on the operation of the brake operating component BP (brake pedal). Then, the servo pressure Pa is used to output supply pressures Ps (=Psf, Psr) from the upper unit SA to the lower unit SZ. Specifically, in the system related to the front wheel cylinder CWf, the main pressure Pm is output as the front wheel supply pressure Psf. 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, ultimately supplying the front and rear wheel cylinder pressures Pwf and Pwr (=Pw) ​​to the front and rear wheel cylinders CWf and CWr (=CW). The upper unit SA consists of an upper actuator YA and an upper controller EA.

[0032] <<Upper Actuator YA>>

[0033] The upper actuator YA (upper fluid unit) consists of a hydraulic generation unit PU, a pressure application unit AP, and an input unit NR.

[0034] [Hydraulic generation unit PU]

[0035] The hydraulic generating unit PU uses an electric motor MA as its power source to generate servo pressure Pa. The hydraulic generating unit PU is also called "electric cylinder DN". The electric cylinder DN includes an 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.

[0036] The electric motor MA is the power source (pressure source) used to generate servo pressure Pa. "Power" is the energy required to move the movable parts (GS, GH, NC, etc.) in the electric cylinder DN. For example, power is defined as the 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 obtained by multiplying the shaft torque of the electric motor MA by the rotational speed of the electric motor MA (specifically, the motor shaft). Additionally, the linear power of the linear motion component (described later) is obtained by multiplying the thrust (force acting in the direction of the central axis) of the linear motion component by the linear velocity (velocity along the central axis).

[0037] The motor MA is a three-phase brushless motor. A rotation angle sensor KA and a motor temperature sensor TM are installed in the motor MA. The rotation angle sensor KA detects the position Ka (rotation angle) of the motor shaft. Additionally, the motor temperature sensor TM detects the temperature Tm of the motor MA (e.g., the motor coil).

[0038] Power is supplied to the motor coils from the upper controller EA (specifically the 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 the rotation angle sensor KA. Then, in the upper controller EA, the switching elements of the drive circuit DR (also called the "inverter circuit") are driven based on the motor rotation angle Ka, switching the three-phase motor current Im (the total current flowing through the U, V, and W phases) of the motor. The rotational power of the motor MA is output from the motor MA to the reducer GS.

[0039] The first rotational power output from the motor MA is reduced in speed by a speed reducer GS. Specifically, the input shaft of the speed reducer GS is fixed to the motor shaft. Furthermore, the output shaft of the speed reducer GS is fixed to the rotating component of the conversion mechanism GH. In the speed reducer GS, the speed input from the motor MA decreases, and the torque input from the motor MA increases. Then, the reduced rotational power (also called the "second rotational power") is output from the speed reducer GS to the conversion mechanism GH.

[0040] The conversion mechanism GH consists of a rotating component that performs rotary motion and a linear motion component that performs linear motion. In the conversion mechanism GH, the rotary power output from the reducer GS is input to the rotating component. Then, the second rotary power input to the rotating component is converted into the linear power of the linear motion component. The conversion mechanism GH is also called a "rotation-linear motion conversion mechanism". An anti-rotation component is engaged on the linear motion component. As a result, the rotational motion of the linear motion component is stopped, and therefore the linear motion component moves along the rotation axis of the rotating component.

[0041] Linear power is transmitted to the control piston NC via the linear motion component 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 the control chamber Rc (hydraulic chamber). Specifically, the outer circumferential surface of the control piston NC and the inner circumferential surface of the control cylinder CC are sealed by two sealing components SL. Thus, the control chamber Rc becomes hydraulically sealed. The hydraulic pressure of the control cylinder CC (i.e., the control chamber Rc) is a servo pressure Pa. That is to say, in the electric cylinder DN, the electric motor MA is the power source, and the output servo pressure Pa is [not specified].

[0042] The control cylinder CC is connected to the servo chamber Ru (described later) of the pressure application unit AP via the servo circuit HU (fluid circuit). Additionally, the control cylinder CC is connected to the rear wheel cylinder CWr via the rear wheel connection circuit HSr (fluid circuit) through the lower unit SZ. A servo pressure sensor PA is installed in the hydraulic generation unit PU to detect the servo pressure Pa (the hydraulic pressure generated by the electric cylinder DN).

[0043] Figure 1 The diagram shows the state where the electric cylinder DN is not generating servo pressure Pa. A through-hole is provided between the two sealing components SL of the control cylinder CC. Additionally, a through-hole is provided in the control piston NC. A supply path HH (fluid path) connected to the main 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 main 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 called the "initial position". In the initial position, the control piston NC displaces to its maximum extent in its backward direction Hb, and the volume of the control chamber Rc is at its maximum.

[0044] When an increase in servo pressure Pa is required, the rotational power of the electric motor MA is increased. This rotational power is transmitted to the conversion mechanism GH via the reducer GS, serving as the linear power output of the linear motion component. Then, the linear motion component presses the control piston NC, thereby moving the control piston NC in the forward direction Ha (the direction in which the volume of the control chamber Rc decreases). This movement first disconnects the connection between the control chamber Rc and the main reservoir RV. As the control piston NC moves further in the forward direction Ha, the servo pressure Pa (the internal pressure of the control chamber Rc) increases from "0 (atmospheric pressure)". The brake fluid BF, pressurized to the servo pressure Pa, is output (pumped) from the control chamber Rc of the control cylinder CC.

[0045] When maintaining the servo pressure Pa is necessary, the rotation of the motor MA stops. The movement of the control piston NC stops, and the servo pressure Pa remains constant. When reducing the servo pressure Pa is necessary, the rotational force of the motor MA is reduced. Due to the effect of the servo pressure Pa, the motor MA rotates in the reverse direction, thus the control piston NC moves in the backward direction Hb (the direction in which the volume of the control chamber Rc increases). The brake fluid BF returns to the control chamber Rc, thus reducing the servo pressure Pa.

[0046] [Pressure Application Unit AP]

[0047] The pressure unit AP consists of a single-unit main cylinder CM and a main piston NM. The main piston NM is inserted into the single-unit main cylinder CM. The interior of the main cylinder CM is divided into three hydraulic chambers Rm, Ru, and Rs by the main piston NM. The main chamber Rm is formed by the main cylinder CM and the main piston NM. Furthermore, the interior of the main cylinder CM is divided into a servo chamber Ru and a reaction chamber Rs by the flange Tu of the main piston NM. Here, the pressure-bearing area rm of the main chamber Rm is equal to the pressure-bearing area ru of the servo chamber Ru.

[0048] Servo pressure Pa is supplied from the hydraulic generating unit PU (electric cylinder DN) to the servo chamber Ru. Through the servo pressure Pa, the main pressure Pm is output from the pressure applying unit AP as the front wheel supply pressure Psf. Here, "main pressure Pm" is the internal pressure of the main chamber Rm. When "Pa=0" (e.g., during non-braking), the master piston NM is in its final retracted position (i.e., the position where the main chamber Rm has the largest volume). In this state, the main chamber Rm of the master cylinder CM is connected to the main reservoir RV. Therefore, the main pressure Pm is "0 (atmospheric pressure)".

[0049] Brake fluid BF is stored inside the main reservoir RV (also known as the "atmospheric reservoir"). When the servo pressure Pa increases 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 disconnects the connection between the master chamber Rm and the main reservoir RV. Then, as the master piston NM moves further in the forward direction Da, the main pressure Pm increases from "0 (atmospheric pressure)". Thus, the brake fluid BF, pressurized to the main pressure Pm, is pumped from the master cylinder CM through the master chamber Rm towards the lower unit SZ. Furthermore, since "rm=ru", if the sliding resistance of the sealing component SL is ignored, then "Pa=Pm".

[0050] [Input Unit NR]

[0051] Regenerative coordinated control is achieved through the input unit NR. "Regenerative coordinated control" refers to coordinating the friction braking force Fe (braking force generated by the wheel cylinder pressure Pw) with the regenerative braking force Fg (braking force generated by the regenerative device) to efficiently recover the vehicle's kinetic energy as electrical energy during braking. In regenerative coordinated control, a state may occur where the braking actuation component BP is activated but the wheel cylinder pressure Pw is not generated. The input unit NR consists of the input cylinder CN, input piston NN, first control valve VA, second control valve VB, stroke simulator SS, and input pressure sensor PN.

[0052] Input cylinder CN is fixed to master cylinder CM. Input piston NN is inserted into input cylinder CN. Input piston NN is mechanically connected to brake operating component BP so as to coordinate with the movement of brake operating component BP (brake pedal). There is a gap Ln (also called "separation distance") between the end face of input piston NN and the end face of master piston NM. The separation distance Ln is adjusted by servo pressure Pa to achieve regenerative coordinated control.

[0053] The input chamber Rn of the input unit NR is connected to the reaction chamber Rs of the pressure unit AP via the input path HN (fluid path). A normally closed first control valve VA is installed in the input path HN. The input path HN is connected to the main reservoir RV via the reservoir path HR (fluid path) between the first control valve VA and the reaction chamber Rs. A normally open second control valve VB is installed in the reservoir path HR. The first and second control valves VA and VB are on / off type solenoid valves. A stroke simulator SS is connected to the input path HN between the first control valve VA and the reaction chamber Rs.

[0054] When no power is 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. Because the first control valve VA is closed, the input chamber Rn is sealed, forming a hydraulic lock. As a result, the main piston NM and the braking operating component BP move together. Furthermore, because the second control valve VB is open, the stroke simulator SS and the reaction chamber Rs are connected to the main reservoir RV.

[0055] When power is supplied to the first and second control valves VA and VB, the first control valve VA opens and the second control valve VB closes. This allows the main piston NM to move separately from the brake operating component BP. At this time, since the input chamber Rn is connected to the stroke simulator SS, the operating force of the brake operating component BP is generated by the stroke simulator SS. An input pressure sensor PN is installed on the input path HN between the input chamber Rn and the first control valve VA to detect the input pressure Pn. Furthermore, the input pressure Pn is also the hydraulic pressure within the stroke simulator SS.

[0056] <<Upper Controller EA>>

[0057] The upper actuator YA is controlled by the upper controller EA (upper control unit). The upper controller EA consists of a microprocessor MP and a drive circuit DR. The upper controller EA is connected to the communication bus BS so that signals (detected values, calculated values, control flags, etc.) can be shared with other controllers (EZ, etc.).

[0058] Various signals, such as operating displacement Sp (detected by operating displacement sensor SP), input pressure Pn (detected by input pressure sensor PN), servo pressure Pa (detected by servo pressure sensor PA), and motor rotation angle Ka (detected by rotation angle sensor KA), are directly input to the upper controller EA. Furthermore, various signals, such as main pressure Pm (supply pressure) and vehicle speed Vx, are input to the upper controller EA via the communication bus BS. Additionally, the upper controller EA outputs a specific processing execution flag FL (described later) to the communication bus BS. Moreover, in the lower controller EZ, the pressure regulating valve UZ is controlled based on the execution flag FL obtained from the communication bus BS.

[0059] The upper controller EA (especially the microprocessor MP) is programmed with a voltage regulation control algorithm. "Voltage regulation control" is used to regulate the wheel cylinder pressure Pw (=Pwf, Pwr). Voltage regulation control is executed based on the various signals mentioned above (Sp, Pa, etc.). Based on the voltage regulation control algorithm, the drive circuit DR drives the motor MA and various solenoid valves (VA, etc.). In the drive circuit DR, an inverter circuit is constructed using switching elements (e.g., MOS-FETs) to drive the motor MA. Additionally, the drive circuit DR includes switching elements to drive various solenoid valves. Furthermore, the drive circuit DR is equipped with a motor current sensor IM that detects the supply current Im (motor current) to the 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-FETs, etc.) in the inverter circuit as the circuit temperature Td.

[0060] In the upper controller EA, the drive signals Va and Vb for the first and second control valves VA and VB, and the drive signal Ma for the motor MA, are calculated. Then, the aforementioned switching elements are driven according to the various drive signals (Ma, etc.). Specifically, in the control of the solenoid valves, power is supplied to the first and second control valves VA and VB based on the drive signals Va and Vb. As a result, the first control valve VA opens, and the second control valve VB closes. Furthermore, the drive signal Ma is determined based on a voltage regulation control algorithm, and the motor MA is controlled based on the drive signal Ma.

[0061] <Lower Unit SZ>

[0062] Reference Figure 2The diagram below illustrates the structure of the lower unit SZ. The lower unit SZ is a general-purpose unit used for performing anti-lock braking control, traction control, and sideslip prevention control. The main 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"). Then, in the lower unit SZ, the front and rear wheel supply pressures Psf and Psr (=Ps) are adjusted (increased or decreased) and output as the hydraulic pressures Pwf and Pwr (front and rear wheel cylinder pressures) for the front and rear wheel cylinders CWf and CWr. The lower unit SZ consists of a lower actuator YZ and a lower controller EZ.

[0063] <<Lower Actuator YZ>>

[0064] The lower actuator YZ (lower fluid unit) is located on the connecting path HS between the upper actuator YA and the wheel cylinder CW. The lower actuator YZ consists of a pressure regulating valve UZ, a supply pressure sensor PS, a fluid pump QZ, a motor MZ, a pressure regulating reservoir RZ, an inlet valve VI, and an outlet valve VO.

[0065] Pressure regulating valves UZ (=UZf, UZr) are installed on the connecting path HS (=HSf, HSR). Pressure regulating valve UZ is a normally open linear solenoid valve. Through the front and rear wheel pressure regulating valves UZf and UZr (equivalent to "solenoid valves"), the front and rear wheel cylinder pressures Pwf and Pwr can be increased from the supply pressures Psf and Psr of the front and rear wheels, respectively. In the lower unit SZ, the front and rear wheel cylinder pressures Pwf and Pwr can be adjusted independently through the front and rear wheel pressure regulating valves UZf and UZr.

[0066] A bypass circuit (fluid path) is provided in the connecting path HS (=HSf, HSR) to connect the upper and lower parts of the pressure regulating valve UZ (=UZf, UZr). Furthermore, an upper check valve GU (=GUf, GUr) is provided in the bypass circuit. 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 (equivalent to a "check valve") is configured to bypass the pressure regulating valve UZ, allowing hydraulic transmission from the electric cylinder DN (specifically the control cylinder CC) to the wheel cylinder CW, but blocking hydraulic transmission from the wheel cylinder CW toward the electric cylinder DN.

[0067] A front wheel and rear wheel supply pressure sensors PSf and PSr (=PS) are installed on the upper part of the pressure regulating valve UZ (near the connecting path HS on the side of the upper actuator YA) to detect the front wheel and rear wheel supply pressures Psf and Psr (=Ps). The supply pressure Ps (=Psf and Psr) detected by the supply pressure sensors PS (=PSf and PSr) is input to the lower controller EZ. Here, the rear wheel supply pressure sensor PSr can be omitted.

[0068] The upper and lower parts of the pressure regulating valve UZ (=UZf, UZr) are connected via the return oil circuit HZ (=HZf, HZr). A fluid pump QZ (=QZf, QZr) and a pressure regulating reservoir RZ (=RZf, RZr) are installed in the return oil circuit HZ (fluid circuit). The fluid pump QZ is driven by an electric motor MZ. The electric motor MZ is the power source for increasing the supply pressure Ps (=Psf, Psr). Since the electric motor MZ and the fluid pump QZ are contained in the lower unit SZ, they are also referred to as the "lower electric motor MZ" and the "lower fluid pump QZ".

[0069] When the motor MZ is driven, brake fluid BF is drawn from the upper part of the pressure regulating valve UZ by the fluid pump QZ and discharged to the lower part of the pressure regulating valve UZ. This creates a circulating flow KZ of brake fluid BF, including the pressure regulating reservoir RZ, in the connecting circuit HS and the return circuit HZ (indicated by the dashed arrow). When the flow path of the connecting circuit HS is narrowed by the pressure regulating valve UZ, and the circulating flow KZ of brake fluid BF is throttled, the hydraulic pressure Pp (also called the "adjusting pressure") at the lower part of the pressure regulating valve UZ increases from the hydraulic pressure Ps (supply pressure) at the upper part of the pressure regulating valve UZ, utilizing the orifice effect. In the relationship between the supply pressure Ps and the adjusting pressure Pp, the adjusting pressure Pp is greater than or equal to the supply pressure Ps (i.e., "Pp ≥ Ps"). In other words, the adjusting pressure Pp can be increased from the supply pressure Ps.

[0070] Inside the lower actuator YZ, the front wheel and rear wheel connecting paths HSf and HSR each branch into two, connecting to the front wheel and rear wheel cylinders CWf and CWr, respectively. Each wheel cylinder CW is equipped with a normally open inlet valve VI and a normally closed outlet valve VO, allowing for individual adjustment of the cylinder pressure Pw. Specifically, the inlet valve VI is located on the branched connecting path HS (i.e., the side of the connecting path HS closest to the wheel cylinder CW relative to the branch). The connecting path HS, below the inlet valve VI (the part of the connecting path HS closest to the wheel cylinder CW), connects to the pressure regulating reservoir RZ via a pressure reducing path HG (fluid path). Furthermore, the outlet valve VO is located on the pressure reducing path HG. Both the inlet valve VI and the outlet valve VO are on / off type solenoid valves.

[0071] A fluid path bypassing the inlet valve VI (VIf, VIr) is provided in the connecting passage HS (=HSf, HSR), and a lower check valve GV (=GVf, GVr) is configured on this fluid path. The flow direction of the lower check valve GV is opposite to that of the upper check valve GU. That is, the lower check valve GV allows flow from the wheel cylinder CW, but prevents flow toward the wheel cylinder CW.

[0072] The wheel cylinder pressure Pw can be individually adjusted for each wheel cylinder CW via the inlet valve VI and the outlet valve VO. When neither the inlet valve VI nor the outlet valve VO is powered and is inactive, the inlet valve VI is open and the outlet valve VO is closed. In this state, the wheel cylinder pressure Pw equals the adjustment pressure Pp. To decrease the wheel cylinder pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. The inflow of brake fluid BF into the wheel cylinder CW is stopped, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RZ, thus decreasing the wheel cylinder pressure Pw. To increase the wheel cylinder pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. The outflow of brake fluid BF into the pressure regulating reservoir RZ is stopped, and the adjustment pressure Pp from the pressure regulating valve UZ is supplied to the wheel cylinder CW, thus increasing the wheel cylinder pressure Pw. However, the increase is limited to the adjustment pressure Pp. To maintain the wheel cylinder pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Because the wheel cylinder CW is fluidly sealed, the wheel cylinder pressure Pw remains constant.

[0073] <<Lower Controller EZ>>

[0074] The lower actuator YZ is controlled by the lower controller EZ (lower control unit). Like the upper controller EA, the lower controller EZ consists of a microprocessor MP and a drive circuit DR. The lower controller EZ is connected to the communication bus BS. Therefore, the upper controller EA and the lower controller EZ can share signals via the communication bus BS.

[0075] The lower controller EZ (specifically the microprocessor MP) is input with sensor signals such as supply pressure Ps, wheel speed Vw, steering input Sw, yaw rate Yr, front-to-rear acceleration Gx, and lateral acceleration Gy. Furthermore, the lower controller EZ calculates the vehicle's travel speed Vx (also known as "vehicle speed") based on the wheel speed Vw. The lower controller EZ also executes anti-lock braking control (ABS control) to prevent wheel lock-up, traction control to prevent wheel spin, and sideslip prevention control (ESC) to improve vehicle directional stability by suppressing understeer / oversteer.

[0076] The lower controller EZ, based on a control algorithm programmed in the microprocessor MP, drives the motor MZ, which constitutes the lower actuator YZ, and various solenoid valves (UZ, etc.) via the drive circuit DR. In the drive circuit DR of the lower controller EZ, an H-bridge circuit is constructed using switching elements (e.g., MOS-FETs) to drive the motor MZ. Additionally, the drive circuit DR is equipped with switching elements to drive various solenoid valves (UZ, etc.). Furthermore, the drive circuit DR includes a motor current sensor (not shown) that detects the supply current Im to the 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 for the motor MZ, the drive signal Uz for the pressure regulating valve UZ, the drive signal Vi for the inlet valve VI, and the drive signal Vo for the outlet valve VO are calculated. Then, based on the drive signals (Uz, etc.), the drive circuit DR controls the motor MZ and the solenoid valves UZ, VI, and VO.

[0077] <Processing of Voltage Regulation Control>

[0078] Reference Figure 3 The flowchart illustrates an example of voltage regulation control. In voltage regulation control, each step is executed per operation cycle. Furthermore, voltage regulation control includes specific processing to suppress temperature rise in components involved in the electric motor MA. Specifically, steps S130 to S230 correspond to this specific processing. This specific processing is permitted when the vehicle is stationary. That is, when the vehicle speed Vx (vehicle speed) is "0", the specific processing can be performed. Conversely, when the vehicle speed Vx is greater than "0", the specific processing is prohibited.

[0079] Specific processes are executed by the upper unit SA and the lower unit SZ. Specifically, the control processes related to the motor MA are executed by the upper controller EA. The upper controller EA drives the motor MA in the upper actuator YA. On the other hand, the control processes related to the pressure regulating valve UZ are executed by the lower controller EZ. The lower controller EZ drives only the pressure regulating valve UZ in the lower actuator YZ. In other words, in this specific process, the driving of the lower motor MZ, the inlet valve VI, and the outlet valve VO is stopped. The on / off indication of the pressure regulating valve UZ is transmitted from the upper controller EA to the lower controller EZ via the execution flag FL.

[0080] In pressure regulation control, power is first supplied to the first and second control valves VA and VB. The normally closed first control valve VA opens, and the normally open second control valve VB closes. This allows the main piston NM and the brake operating component BP to move separately, thus the front and rear wheel cylinder pressures Pwf and Pwr can be adjusted independently of the operation of the brake operating component BP. At this time, the operating force of the brake operating component BP is generated by the stroke simulator SS.

[0081] In step S110, the upper controller EA reads various signals. The signals for braking operation quantity Ba (a collective term for Sp and Pn), servo pressure Pa, and vehicle speed Vx are input to the upper controller EA. Braking operation quantity Ba is acquired by the operation quantity sensor BA. Servo pressure Pa is acquired by the servo pressure sensor PA. Vehicle speed Vx is calculated in the lower controller EZ based on wheel speed Vw and acquired by the upper controller EA via the communication bus BS.

[0082] In step S120, the indicated pressure Pd is calculated based on the braking operation amount Ba and the calculation mapping Zpd. The "indicated pressure Pd" is the target value of the wheel cylinder pressure Pw requested by the driver. In pressure regulation control, the wheel cylinder pressure Pw is adjusted via the servo pressure Pa, but the servo pressure Pa (actual value) is ultimately adjusted via the target pressure Pt (described later). Therefore, the indicated pressure Pd corresponds to an intermediate target value in pressure regulation control. Specifically, according to the calculation mapping Zpd, when the braking operation amount Ba is less than a predetermined amount bo, the indicated pressure Pd is calculated as "0". Moreover, when the braking operation amount Ba is greater than or equal to the predetermined amount bo, the indicated pressure Pd is calculated to increase from "0" as the braking operation amount Ba increases. Here, the predetermined amount bo corresponds to the free travel of the braking operation component BP, etc., and is preset as a predetermined value (constant) (refer to the indicated pressure calculation block PD above).

[0083] In step S130, it is determined whether a "specific process is being executed." The "specific process" is a control process used to suppress overheating of structural components involved in the motor MA. Here, "structural components involved in the motor MA" include the motor MA itself, the drive circuit DR (especially switching elements) that drives the motor MA, wires, etc. If the specific process is not being executed, step S130 is denied, and the process proceeds to step S140. If the specific process is already being executed, step S130 is affirmed, and the process proceeds to step S150.

[0084] In step S140, it is determined whether to "start a specific process". This determination process is called "start determination". The specific process is determined to start if the following conditions are met: Additionally, the vehicle being stationary is a prerequisite for performing the specific process (i.e., a condition permitting the specific process).

[0085] [Starting Conditions]

[0086] The temperature-related value Xm, which is related to the temperature of the structural components (MA, DR, etc.) involved in the motor MA, exceeds the start threshold xm. Here, the "temperature-related value Xm" is equivalent to at least one of the temperature Tm of the motor MA (e.g., the motor coil) and the temperature Td of the drive circuit DR (e.g., the switching element). Alternatively, the time integral value of the motor current Im can also be used as the temperature-related value Xm. Furthermore, the start threshold xm is a predetermined value (constant) set in advance.

[0087] If the temperature correlation value Xm does not reach the start threshold xm, step S140 is denied, and the process proceeds to step S180. Conversely, if the temperature correlation value Xm is greater than the start threshold xm, step S140 is affirmed, and the process proceeds to step S160. At this time, the execution flag FL switches from "0" to "1". The "execution flag FL" is a control flag indicating the execution state of a specific process. Here, "FL=0" indicates that the specific process has not been executed, and "FL=1" indicates that the specific process has been executed. Additionally, the execution flag FL is also a control flag used to instruct the lower controller EZ to close the pressure regulating valve UZ.

[0088] In step S150, it is determined whether to "end a specific process". This determination process is called "end determination". The specific process is determined to end if the following conditions are met.

[0089] [End Condition]

[0090] The indicated pressure Pd, calculated based on the braking operation amount Ba, becomes less than the maintained wheel cylinder pressure Pw. Here, the wheel cylinder pressure Pw is an estimate based on the servo pressure Pa. Furthermore, when estimating the wheel cylinder pressure Pw, the decrease in wheel cylinder pressure Pw due to leakage from the pressure regulating valve UZ can be ignored or considered. Ignoring leakage, the wheel cylinder pressure Pw is estimated as the servo pressure Pa at the moment the pressure regulating valve UZ closes (at the start of a specific process) or when the servo pressure Pa is repressurized and reaches the indicated pressure Pd. Considering leakage, the wheel cylinder pressure Pw is estimated based on the elapsed time from the moment the pressure regulating valve UZ closes or the moment the servo pressure Pa repressurizes. In either case, the wheel cylinder pressure Pw is determined based on the servo pressure Pa.

[0091] If the termination condition is not met, step S150 is rejected, and the process proceeds to step S160. At this time, specific processing continues, and the execution flag FL remains "1". If the termination condition is met, step S150 is affirmed, and the process proceeds to step S230. At this time, the execution flag FL switches from "1 (executed)" to "0 (not executed)".

[0092] In step S160, a target current It is calculated to close the pressure regulating valve UZ. 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, the hydraulic pressure difference sPx (also called "specific differential pressure") between the indicated pressure Pd and the lower limit pressure px (described later) is calculated (i.e., "sPx = Pd - px"). At this time, since the cylinder pressure Pw increases to the indicated pressure Pd through the servo pressure Pa, the specific differential pressure sPx is also the hydraulic pressure difference between the cylinder pressure Pw (= Pa) and the lower limit pressure px (i.e., "sPx = Pw - px").

[0093] In step S160, the valve-closing current Ih is calculated based on a specific differential pressure 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 in order to counteract the specific differential pressure sPx. Specifically, the valve-closing current Ih is determined according to a pre-set calculation mapping Zih; the larger the specific differential pressure sPx, the larger the valve-closing current Ih (refer to the valve-closing current calculation block IH). Furthermore, in step S160, a margin current ic is added to the valve-closing current Ih to determine the target current It (i.e., "It = Ih + ic"), in order to more reliably close the pressure regulating valve UZ. Here, the "target current It" is the target value of the supply current Iz (valve current) to the pressure regulating valve UZ for closing the pressure regulating valve UZ in a specific process. Additionally, the "margin current ic" is a pre-set predetermined value (constant) that increases the valve-closing current Ih to ensure that the target current It has a margin. The target current It (target value) is determined based on the valve closing current Ih. The larger the specific differential pressure sPx, the larger the target current It.

[0094] In step S170, it is determined whether a "pressurization process for the servo pressure Pa" is needed. In a specific process (particularly a depressurization process), in order to suppress the temperature rise of the components involved in the motor MA, the servo pressure Pa is reduced while the wheel cylinder CW is in a fluid-locked state by closing the pressure regulating valve UZ. However, even when the pressure regulating valve UZ is closed, brake fluid BF leakage occurs at that point. When the pressure regulating valve UZ is just closed, the wheel cylinder pressure Pw is maintained at the indicated pressure Pd, but it gradually decreases over time. In the "pressurization process," the target pressure Pt is increased again to compensate for the decrease in wheel cylinder pressure Pw due to brake fluid BF leakage (resulting in an increase in the servo pressure Pa).

[0095] In step S170, if at least one of the following conditions is met: "the decompression time Tk (described later) has not reached the first predetermined time tx" or "the holding time Tj (described later) has lasted for the second predetermined time tz", step S170 is denied, and the process proceeds to step S190. Conversely, if "the decompression time Tk is greater than or equal to the first predetermined time tx" and "the holding time Tj is less than the second predetermined time tz", step S170 is affirmed, and the process proceeds to step S210. Here, the first predetermined time tx is a threshold corresponding to the decompression time Tk, and is a pre-set predetermined value (constant). Similarly, the second predetermined time tz is a threshold corresponding to the holding time Tj, and is a pre-set predetermined value (constant).

[0096] In steps S180, S190, S210, and S230, a target pressure Pt corresponding to various processes is determined based on the indicated pressure Pd. The indicated pressure Pd is the target value of the servo pressure Pa (which results in the wheel cylinder pressure Pw) indicated by the driver, but in certain processes, the servo pressure Pa is reduced from the indicated pressure Pd to suppress heat generation. The "target pressure Pt" is the final target value corresponding to the servo pressure Pa used to indicate the 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 (especially the electric motor MA) to bring it close to and match the target pressure Pt.

[0097] In step S180, normal pressure regulation control is performed (i.e., pressure regulation control without performing a specific process). This control process is called "normal process". In normal process, the indicated pressure Pd is determined to be the target pressure Pt (i.e., "Pt=Pd"). Additionally, in normal process, the lower actuator YZ stops operating. Therefore, no power is supplied to the pressure regulating valve UZ, and the normally open type pressure regulating valve UZ is fully open.

[0098] Steps S190 to S230 are specific processing steps. These specific processing steps include depressurization, pressurization, and termination. Furthermore, in these specific processing steps, the relationship between the indicated pressure Pd and the target pressure Pt is such that the target pressure Pt is below the indicated pressure Pd (i.e., "Pt ≤ Pd").

[0099] In step S190, a pressure reduction process is performed within a specific process. In this pressure reduction process, the load on the motor MA is reduced to suppress heat generation in the structural components involved in the motor MA. Specifically, in step S190, based on the indicated pressure Pd and the calculation map Zpg, the target pressure Pt (the target value used to control the servo pressure Pa) is determined as a pressure reduction gradient dg decreasing from the indicated pressure Pd to the lower limit pressure px. For example, in the calculation map Zpg, the target pressure Pt is calculated as time T elapses from the moment when step S140 is first confirmed (the corresponding calculation cycle, the moment when the execution flag FL switches from "0" to "1") (i.e., "T=0"). Here, the pressure reduction gradient dg (the amount of hydraulic pressure reduction per unit time) is a predetermined value (constant). Additionally, the lower limit pressure px is a predetermined value (constant) (refer to the target pressure calculation block PT).

[0100] The lower limit pressure px is set based on the rating of the structural components involved in the motor MA that can continuously energize (also known as the "continuous rating"). For example, the maximum value of the motor current Im that can continuously flow through the motor MA is the continuous rating. In this case, the continuous rating is also called the "current capacity". The lower limit pressure px is determined as the hydraulic pressure equivalent to the continuous rating (current capacity) of the structural components of the motor MA. In detail, the lower limit pressure px is determined based on the continuous rating of the component with the most severe thermal load among the structural components involved in the motor MA. As an example, the lower limit pressure px is set corresponding to the continuous rating of the switching element (MOS-FET, etc.) that switches the three-phase motor current Im.

[0101] During the pressure reduction process, the heating of the structural components involved in the motor MA is suppressed because the supply current Im to the motor MA is reduced. During the pressure reduction process, the pressure regulating valve UZ remains closed, and the wheel cylinder pressure Pw of the wheel cylinder CW is sealed (so-called liquid-locked state). Therefore, even if the servo pressure Pa decreases due to the reduction in motor current Im, the wheel cylinder pressure Pw remains approximately constant.

[0102] In step S200, the decompression time Tk is calculated. "Decompression time Tk" is the elapsed time associated with the decompression process. For example, the decompression time Tk is determined as the elapsed time from the moment the target pressure Pt (which results in the servo pressure Pa) begins to decrease (the corresponding operation cycle). The decompression time Tk is used for the determination in step S170.

[0103] In step S210, a pressure boosting process is performed within a specific process. In this process, to ensure the wheel cylinder pressure Pw matches the indicated pressure Pd, the servo pressure Pa, which has been reduced to the lower limit pressure px, is increased back to the indicated pressure Pd. Specifically, in step S210, based on the indicated pressure Pd and the computational mapping Zpz, the target pressure Pt is determined to increase from the lower limit pressure px to the indicated pressure Pd with a pressure boosting gradient dz. Here, the pressure boosting gradient dz (the increase in hydraulic pressure per unit time) is a pre-set predetermined value (constant). During the pressure boosting process, the pressure regulating valve UZ remains 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 cylinder pressure Pw increases via the check valve GU. Thus, the wheel cylinder pressure Pw increases reliably without decreasing.

[0104] In step S220, the holding time Tj is calculated. "Holding time Tj" is the elapsed time related to the pressurization process. For example, the holding time Tj is determined as the elapsed time from the moment when the target pressure Pt (which results in the servo pressure Pa) matches the indicated pressure Pd (the corresponding operation cycle). The holding time Tj is used for the determination in step S170.

[0105] In step S230, the termination process in the specific process is executed. The termination process is executed when the brake operation component BP is returned and the indicated pressure Pd becomes less than the wheel cylinder pressure Pw. In the termination process, the wheel cylinder pressure Pw is reduced by gradually opening the pressure regulating valve UZ. Then, after the wheel cylinder pressure Pw matches the servo pressure Pa, the servo pressure Pa (= Pw) is reduced by the electric cylinder DN.

[0106] <Specific processing actions>

[0107] Reference Figure 4 The time-series graphs (graphs showing the changes of various state quantities over time T) illustrate the actions of a specific process. The graphs envision a situation where, after the vehicle stops, the operating quantity Ba of the braking operation component BP increases, and then the temperature-related value Xm exceeds the initial threshold xm. Furthermore, since the valve current Iz is controlled to match the target current It, their graphs overlap. Similarly, since the servo pressure Pa is controlled to match the target pressure Pt, their graphs overlap. Additionally, in this specific process, the pressure regulating valve UZ is actuated, but the actuation of other structural components of the lower actuator YZ (MZ, VI, VO, etc.) is stopped.

[0108] Before time t0, through the normal processing of the braking operation amount Ba based on the value ba, a servo pressure Pa (=Pw) ​​with the value pa is generated, and the vehicle decelerates. At time t0, the vehicle stops. At time t0, the condition "Vx=0" is met, and the specific process is set to the permitted state. Specifically, at time t0, the permission flag FK switches from "0" to "1". Here, the "permission flag FK" is a control flag indicating whether a specific process is permitted or prohibited. In the permission flag FK, "0" indicates prohibition, and "1" indicates permission.

[0109] At time t1, the braking operation amount Ba increases from value ba. Consequently, the indicated pressure Pd increases from value pa. As the indicated pressure Pd increases, the temperature correlation value Xm gradually increases. At time t2, the braking operation amount Ba remains at value bb, and the indicated pressure Pd remains at value pb.

[0110] At time t3, the temperature correlation value Xm exceeds the start threshold xm (a pre-set constant). The temperature correlation value Xm is determined based on at least one of the following: the temperature Tm (motor temperature) of the motor MA, the temperature Td (circuit temperature) of the drive circuit DR, and the motor current Im (especially its time integral value). At time t3, the determination in step S140 is satisfied, and the pressure reduction process related to the specific process begins. At time t3, the target current It is calculated to reliably close the pressure regulating valve UZ. Specifically, the target current It is determined as the value ix by adding a margin current ic to the valve closing current Ih. The valve current Iz corresponding to the target current It is supplied to the pressure regulating valve UZ, thereby closing the pressure regulating valve UZ. In addition, the valve closing current Ih is determined based on a specific differential pressure sPx (the difference between the wheel cylinder pressure Pw and the lower limit pressure px), and the larger the specific differential pressure sPx, the larger the valve closing current Ih. Therefore, the valve current Iz used to close the pressure regulating valve UZ is smaller when the specific differential pressure sPx between the cylinder pressure Pw and the lower limit pressure px is smaller than when the specific differential pressure sPx is larger.

[0111] Starting at time t3, according to the computational mapping Zpg, the target pressure Pt decreases with the decompression gradient dg as time T progresses. Furthermore, at time t3, the decompression time Tk is calculated.

[0112] After time t3, because the wheel cylinder CW is sealed by the pressure regulating valve UZ, the wheel cylinder pressure Pw hardly decreases even if the servo pressure Pa decreases. However, the wheel cylinder pressure Pw will decrease slightly due to leakage at the pressure regulating valve UZ. At time t4, according to the calculation mapping Zpg, the target pressure Pt remains at the lower limit pressure px. From time t4 onwards, the state of "Pt=px" is maintained.

[0113] Due to leakage at the pressure regulating valve UZ, the wheel cylinder pressure Pw begins to decrease from the indicated pressure Pd. At time t5, the decompression time Tk reaches the first predetermined time tx. At time t5, the determination in step S170 is satisfied, and the pressurization process associated with the specific process begins. At this time, the decompression time Tk is reset to "0". Starting from time t5, according to the calculation mapping Zpz, the target pressure Pt increases with a pressurization gradient dz as time T elapses. After time t5, the pressure regulating valve UZ also remains closed. However, when the target pressure Pt (which results in the servo pressure Pa) becomes greater than the wheel cylinder pressure Pw, the servo pressure Pa is supplied to the wheel cylinder CW through the check valve GU.

[0114] At time t6, the target pressure Pt reaches the indicated pressure Pd. At time t6, the holding time Tj is calculated. From time t6, the state of "Pt=Pd" is maintained. At time t7, the holding time Tj reaches the second predetermined time tz. Therefore, the determination in step S170 is negated, and the decompression process related to the specific process is restarted. 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 computational mapping Zpg. Similarly, at time t7, the decompression time Tk, which has been reset to "0", is calculated.

[0115] At time t8, the brake operation component BP begins its return operation, and the brake operation amount Ba, maintained at value bb, begins to decrease. As the brake operation amount Ba decreases, the indicated pressure Pd decreases. At time t9, the indicated pressure Pd becomes less than the wheel cylinder pressure Pw (estimated value), and the termination condition is met. At time t9, the previously closed pressure regulating valve UZ begins to open. Specifically, at time t9, the target current It decreases by the amount of the margin current ic, making the target current It equal to the valve closing current Ih. Then, after time t9, the target current It is determined based on the hydraulic pressure difference sPt between the indicated pressure Pd and the target pressure Pt, and the calculated mapping Zih. Consequently, the valve current Iz gradually decreases, and the pressure regulating valve UZ opens to achieve the hydraulic pressure difference sPt. As a result, the wheel cylinder pressure Pw decreases along the indicated pressure Pd.

[0116] At time t10, the indicated pressure Pd (resulting in the wheel cylinder pressure Pw) reaches the target pressure Pt (resulting in the servo pressure Pa) to be maintained constant. At time t10, power supply to the pressure regulating valve UZ is stopped, and the pressure regulating valve UZ is fully open. Furthermore, starting from time t10, the target pressure Pt is determined to be equal to the indicated pressure Pd. Therefore, after time t10, as the indicated pressure Pd decreases, the wheel cylinder pressure Pw (= Pa) decreases.

[0117] <<The Role and Effects of Specific Treatments>>

[0118] The valve current Iz required to close the pressure regulating valve UZ depends on the pressure difference between the high-pressure side hydraulic pressure (i.e., wheel cylinder pressure Pw) and the low-pressure side hydraulic pressure (i.e., servo pressure Pa) of 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, in a specific process, if the servo pressure Pa drops to "0 (atmospheric pressure)," the pressure difference between the wheel cylinder pressure Pw and the servo pressure Pa becomes larger, requiring a larger valve current Iz. However, in the brake control device SC, since the servo pressure Pa only drops to the lower limit pressure px, the difference sPx (specific differential pressure) between the wheel cylinder pressure Pw and the lower limit pressure px can be suppressed to a certain extent. Thus, the valve current Iz can be suppressed to the necessary minimum, thereby achieving power saving of the pressure regulating valve UZ in a specific process.

[0119] Furthermore, the lower limit pressure px is preset to a predetermined value based on the continuous rated value that allows the structural components (MA, DR, etc.) of the motor MA to be continuously energized. Even if the motor MA is driven at the continuous rated value, the temperature that balances heat generation and heat dissipation / cooling 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.

[0120] The pressure regulating valve UZ includes a front wheel pressure regulating valve UZf located relative to the front wheel cylinder CWf in the wheel cylinder CW, and a rear wheel pressure regulating valve UZr located relative to the rear wheel cylinder CWr in the wheel cylinder CW. In the brake control device SC, when a specific process is performed, a valve current Iz is supplied to close the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr. As a result, the front wheel cylinder pressure Pwf and the rear wheel cylinder pressure Pwr are maintained. As a result, the power consumption associated with the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr is reduced. In addition, since the braking force is maintained even when the servo pressure Pa decreases, the parking state can be reliably maintained even when a specific process is performed.

[0121] The pressure regulating valve UZ (solenoid valve) consists of a valve core driven by a solenoid and a valve seat that the valve core can contact. The pressure regulating valve UZ adjusts the hydraulic pressure Pp through the gap between the valve seat and the valve core. In certain operations, the valve seat and valve core are in close contact, and the pressure regulating valve UZ is closed. However, even in this state, a small gap exists between the valve seat and valve core, which may lead to leakage of brake fluid BF. The degree of fluid leakage when the pressure regulating valve UZ is closed depends on the pressure difference between the high-pressure side hydraulic pressure (i.e., wheel cylinder pressure Pw) and the low-pressure side hydraulic pressure (i.e., servo pressure Pa) of the pressure regulating valve UZ. For example, in a certain operation, if the servo pressure Pa (= Ps) drops to "0 (atmospheres)," the pressure difference between the wheel cylinder pressure Pw and the servo pressure Pa increases, and leakage at the pressure regulating valve UZ becomes significant. However, in the brake control unit SC, since the servo pressure Pa only drops to the lower limit pressure px, the decrease in wheel cylinder pressure Pw due to fluid leakage is suppressed.

[0122] Furthermore, in the specific processing of the brake control device SC, in addition to the pressure reduction processing, a pressure boosting processing is also provided. Through the pressure boosting processing, the reduced wheel cylinder pressure Pw is increased to the indicated pressure Pd. That is, the pressure boosting processing can compensate for the drop in wheel cylinder pressure Pw caused by fluid leakage at the pressure regulating valve UZ.

[0123] Furthermore, in the brake control unit SC, the increase in wheel cylinder pressure Pw during the boosting process is achieved via a check valve GU. That is, even during boosting, the pressure regulating valve UZ remains closed. The wheel cylinder pressure Pw will not decrease due to the opening of the pressure regulating valve UZ, thus reliably increasing the wheel cylinder pressure Pw. Additionally, the check valve GU is configured to bypass the pressure regulating valve UZ, allowing pressure transmission from the electric cylinder DN (particularly the control cylinder CC) towards the wheel cylinder CW, but preventing pressure transmission from the wheel cylinder CW towards the electric cylinder DN.

[0124] <Modifications of the First Embodiment>

[0125] A variation of the first embodiment will be described.

[0126] In the above embodiment, a single-unit cylinder is used as the master cylinder CM, with the main pressure Pm transmitted to the front wheel cylinder CWf and the servo pressure Pa transmitted to the rear wheel cylinder CWr. Alternatively, a series-type cylinder can be used as the master cylinder CM. In this structure, the master cylinder CM forms two hydraulic chambers, namely the front wheel and rear wheel main chambers Rmf and Rmr. Then, the servo pressure Pa supplied to the servo chamber Ru generates the main pressures Pmf and Pmr of the front and rear wheels, which are then transmitted to the front and rear wheel cylinders CWf and CWr, respectively.

[0127] In the above embodiment, in the pressure unit AP, the pressure-bearing area rm (main area) of the main chamber Rm and the pressure-bearing area ru (servo area) of the servo chamber Ru are set to be equal. Here, the main area rm and the servo area ru may also be unequal. In structures where the main area rm and the servo area ru are different, the conversion calculation between the main pressure Pm (=Psf) and the servo pressure Pa can be performed based on the area ratio of the servo area ru to the main area rm (i.e., based on the conversion of "Pm·rm=Pa·ru").

[0128] In the aforementioned specific process, the front wheel cylinder pressure Pwf and the rear wheel cylinder pressure Pwr are controlled in the same way. Specifically, when the specific process begins, both the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr are closed, and then the servo pressure Pa is adjusted by the electric cylinder DN. Alternatively, the front wheel pressure regulating valve UZf can be closed, but the rear wheel pressure regulating valve UZr can remain open. The pressure regulating valves UZ include: a front wheel pressure regulating valve UZf (equivalent to a "front wheel solenoid valve") positioned relative to the front wheel cylinder CWf, and a rear wheel pressure regulating valve UZr (equivalent to a "rear wheel solenoid valve") positioned relative to the rear wheel cylinder CWr; however, during the execution of the specific process, the front wheel pressure regulating valve UZf is closed, but the rear wheel pressure regulating valve UZr remains open. In this configuration, the front wheel cylinder CWf is sealed by closing the front wheel pressure regulating valve UZf, and the front wheel cylinder pressure Pwf remains approximately constant (see reference). Figure 4 The change of "Pw"), but the rear wheel cylinder pressure Pwr increases or decreases in conjunction with the servo pressure Pa (refer to Figure 4 (The change in "Pa"). In a specific process, since the rear wheel pressure regulating valve UZr remains de-energized, power consumption is reduced accordingly. In addition, in terms of braking force generation, the contribution of the front wheel cylinder pressure Pwf is much greater than that of the rear wheel cylinder pressure Pwr, so maintaining the front wheel cylinder pressure Pwf can sufficiently maintain the stopping state.

[0129] Furthermore, in certain procedures, the rear wheel pressure regulating valve UZr can be closed, but the front wheel pressure regulating valve UZf remains open. In this configuration, the rear wheel cylinder CWr is sealed by the closure of the rear wheel pressure regulating valve UZr, thus maintaining the rear wheel cylinder pressure Pwr at a substantially constant level (see reference). Figure 4 The evolution of "Pw"). On the other hand, the front wheel cylinder pressure Pwf increases or decreases in conjunction with the servo pressure Pa (refer to...). Figure 4 (The change of "Pa"). In a specific process, since the front wheel pressure regulating valve UZf remains unenergized, power consumption is reduced accordingly.

[0130] Furthermore, in a specific procedure, even with only the rear wheel pressure regulating valve UZr closed (out of the rear wheel pressure regulating valve UZr and the front wheel pressure regulating valve UZf), the electric cylinder DN can still be activated, causing the rear wheel cylinder pressure Pwr to increase compared to the hydraulic pressure at the start of the specific procedure. The phrase "at the start of the specific procedure" here includes not only the initial moment but also the time before and after the initial moment. Therefore, even if the contribution of the rear wheel cylinder pressure Pwr to braking force generation is lower than that of the front wheel cylinder pressure Pwf, it is easier to maintain a stopped state.

[0131] In the specific processing described above (especially the pressurization processing), the calculation of the decompression time Tk begins at the moment when the target pressure Pt (which results in the servo pressure Pa) starts to decrease through the decompression processing (corresponding to the calculation cycle). That is, the starting point for the calculation of the decompression time Tk is the start of decompression. Alternatively, the starting point for the calculation related to the decompression time Tk can also be the moment when the target pressure Pt (which results in the servo pressure Pa) reaches the lower limit pressure px (corresponding to the calculation cycle). In this structure, the decompression time Tk is calculated starting at time t4 (i.e., the end of decompression, which is also the start of the hold period). Then, at time t5, after a first predetermined time tx has elapsed from time t4, the pressurization processing begins.

[0132] <Second Embodiment of Braking Control Device SC>

[0133] Reference Figure 5 A schematic diagram is provided to illustrate a second embodiment of the upper unit SA of the brake control device SC. In the first embodiment, the servo pressure Pa is transmitted as a supply pressure Ps (=Pm) via the master cylinder CM and the master piston NM. In other words, at least in the hydraulic transmission path related to the front wheel cylinder CWf, the pressure application unit AP is configured in series with respect to the hydraulic generation unit PU. Instead of this configuration, in the second embodiment, the pressure application unit AP and the hydraulic generation unit PU are configured in parallel. That is, in the second embodiment, the pressure application unit AP (especially the master cylinder CM) and the hydraulic generation unit PU are directly connected to the lower unit SZ (especially the lower actuator YZ), respectively. In the second embodiment, the same specific processing as in the first embodiment is also performed.

[0134] In the upper unit SA of the second embodiment, a shut-off valve VM, a simulator valve VS, and a connecting valve VC are provided instead of the input unit NR. The shut-off valve VM is a normally open on / off solenoid valve, while the simulator valve VS and the connecting valve VC are normally closed on / off solenoid valves. The shut-off valve VM is located in the front wheel connecting passage HSf, which connects the master cylinder CM (specifically the master chamber Rm) and the front wheel cylinder CWf. The front wheel connecting passage HSf between the master cylinder CM and the shut-off valve VM is connected to the stroke simulator SS via the simulator valve VS.

[0135] The front and rear wheel connecting passages HSf and HSR (fluid passages connecting the front and rear wheel cylinders CWf and CWr) are connected to the control cylinder CC (especially the control chamber Rc) via connecting passage HV (fluid passage). Connecting passage HV is also the fluid passage connecting the front wheel connecting passage HSf and the rear wheel connecting passage HSR. A connecting valve VC is installed in connecting passage HV.

[0136] During pressure regulation control, power is supplied to the shut-off valve VM, simulator valve VS, and connecting valve VC. This closes the shut-off valve VM and opens the simulator valve VS and connecting valve VC. The connection between the main chamber Rm and the front wheel cylinder CWf is severed, and servo pressure Pa is supplied to the front wheel cylinder CWf. Furthermore, since the main chamber Rm is connected to the stroke simulator SS, the operating force of the brake operating component BP (brake pedal) is generated by the stroke simulator SS. Additionally, the servo pressure sensor PA can be located in the hydraulic generation unit PU or in the lower actuator YZ. In the configuration where the servo pressure sensor PA is located in the lower actuator YZ, the servo pressure Pa is obtained from the upper controller EA via the communication bus BS.

[0137] In the second embodiment, the same control as in the first embodiment (including the above-described variations) is performed. Therefore, in the second embodiment, the same effects as in the first embodiment can also be achieved (suppressing the heating of structural components involved in the electric motor MA through specific processing, suppressing the power consumption involved in the pressure regulating valve UZ, compensating for the drop in wheel cylinder pressure Pw due to liquid leakage, etc.).

[0138] <Third Embodiment of Braking Control Device SC>

[0139] Reference Figure 6 and Figure 7 The third embodiment of the braking control device SC will be described.

[0140] The lower actuator YZ has a front wheel system and a rear wheel system. In the lower actuator YZ, the part adjusting the front wheel cylinder CWf corresponds to the "front wheel system," and the part adjusting the rear wheel cylinder CWr corresponds to the "rear wheel system." That is, the front wheel system includes 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 includes 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.

[0141] The controller of either the upper controller EA or the lower controller EZ determines whether an anomaly has occurred in the front wheel system. For example, such a determination is performed by the upper controller EA. The upper controller EA receives the front wheel main pressure Pmf from the lower controller EZ in each predetermined control cycle. Then, when a servo pressure Pa is generated by the action of the electric cylinder DN, the upper controller EA determines whether an anomaly has occurred in the front wheel system by comparing the servo pressure Pa with the front wheel main pressure Pmf.

[0142] Here, if the rate of increase of the servo pressure Pa is significantly different from the rate of increase of the front wheel main pressure Pmf, brake fluid (BF) leakage may have occurred in the front wheel system. Given this situation where brake fluid (BF) leakage occurs in the front wheel system while the servo pressure Pa is maintained, it can be inferred that a deviation will occur between the servo pressure Pa and the front wheel main pressure Pmf.

[0143] Therefore, for example, if at least one of the following two conditions is met, the upper controller EA determines that an abnormality has occurred in the front wheel system. In this case, if neither of the following two conditions is met, the upper controller EA determines that no abnormality has occurred in the front wheel system, that is, the front wheel system is normal.

[0144] • When the servo pressure Pa increases, the difference between the rate of increase of the servo pressure Pa and the rate of increase of the front wheel main pressure Pmf is greater than or equal to a predetermined value.

[0145] • While maintaining the servo pressure Pa, the deviation between the servo pressure Pa and the front wheel main pressure Pmf is above a predetermined value.

[0146] If the upper controller EA determines that there is no abnormality in the front wheel system and performs the aforementioned specific processing, it instructs the lower controller EZ to close the front wheel pressure regulating valve UZf while keeping the rear wheel pressure regulating valve UZr open. When the lower controller EZ receives such an instruction, it suppresses the drop in front wheel cylinder pressure Pwf by closing the front wheel pressure regulating valve UZf, while keeping the rear wheel pressure regulating valve UZr open.

[0147] On the other hand, if the upper controller EA determines that an abnormality has occurred in the front wheel system and performs specific processing, it instructs the lower controller EZ to close the rear wheel pressure regulating valve UZr while keeping the front wheel pressure regulating valve UZf open. When the lower controller EZ receives such an instruction, it suppresses the drop in rear wheel cylinder pressure Pwr by closing the rear wheel pressure regulating valve UZr, while keeping the front wheel pressure regulating valve UZf open.

[0148] <Decision to close the pressure regulating valve when performing specific procedures>

[0149] Reference Figure 6This section describes a series of processes executed by the upper controller EA to determine which of the front wheel pressure regulating valves UZf and UZr should be closed when performing a specific process. This series of processes is repeated according to a predetermined control cycle.

[0150] In step S310, it is determined whether braking force was applied through normal processing. If braking force was applied through normal processing, step S310 is affirmed, and the process proceeds to step S320. On the other hand, if braking force was not applied through normal processing, step S310 is negated. Figure 6 The series of processes shown has temporarily ended.

[0151] In step S320, it is determined whether the aforementioned abnormality has occurred in the front wheel system. If it is determined that an abnormality has occurred in the front wheel system, step S320 is affirmed, and the process proceeds to step S330. On the other hand, if it is determined that no abnormality has occurred in the front wheel system, step S320 is negated, and the process proceeds to step S340.

[0152] In step S330, the selection flag FL1 is set to "1". Selecting the flag FL1 as "1" means that the rear wheel pressure regulating valve UZr is closed when performing a specific process. Then, Figure 6 The series of processes shown has temporarily ended.

[0153] In step S340, the selection flag FL1 is set to "0". Selecting the flag FL1 as "0" means that the front wheel pressure regulating valve UZf is closed when performing a specific process. Then, Figure 6 The series of processes shown has temporarily ended.

[0154] <Specific processing actions>

[0155] Reference Figure 7 In the third embodiment, the specific processing actions will be described focusing on the parts that differ from the specific processing actions in the aforementioned embodiments. Here, the specific processing for a situation where a front wheel system malfunctions will be described.

[0156] The braking operation component BP is activated starting at time t20. Therefore, as follows... Figure 7 As shown in (a) and (b), through normal processing, the servo pressure Pa increases with the increase of the braking operation amount Ba. Therefore, brake fluid BF is supplied to both the front and rear wheel systems.

[0157] At this point, if the front wheel system malfunctions while the rear wheel system remains functioning normally, brake fluid BF is supplied to the rear wheel system, thereby supplying brake fluid BF to the rear wheel cylinder CWr. Thus, as... Figure 7 As shown in (b), the rear wheel cylinder pressure Pwr increases as the servo pressure Pa increases.

[0158] exist Figure 7 In the example shown, at time t21, the braking operation amount Ba is maintained. Therefore, the servo pressure Pa and the rear wheel cylinder pressure Pwr are also maintained. If this state continues, at time t22, the temperature-related value Xm exceeds the start threshold xm, thus initiating the decompression process associated with the specific process.

[0159] Here, in the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr, the rear wheel pressure regulating valve UZr is closed, while the front wheel pressure regulating valve UZf remains open. At time t22, the target current Itr is calculated to reliably close the rear wheel pressure regulating valve UZr. Specifically, as follows... Figure 7 As shown in (c), a margin current ic is added to the valve-closing current Ih, and the target current Itr is determined to be the value ix. Since the valve current Izr corresponding to the target current Itr is supplied to the rear wheel pressure regulating valve UZr, the rear wheel pressure regulating valve UZf is closed. Furthermore, the valve-closing current Ih is determined based on a specific differential pressure sPx (the difference between the rear wheel cylinder pressure Pwr and the lower limit pressure px), and the larger the specific differential pressure sPx, the larger the valve-closing current Ih. Therefore, the valve current Izr used to close the rear wheel pressure regulating valve UZr is smaller when the differential pressure sPx between the rear wheel cylinder pressure Pwr and the lower limit pressure px is small, compared to 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 "0", the front wheel pressure regulating valve UZf remains open.

[0160] Furthermore, due to the characteristic relationship between the front wheel braking device SXf and the rear wheel braking device SXr, the contribution of the rear wheel cylinder pressure Pwr to the generation of braking force is less than that of the front wheel cylinder pressure Pwf.

[0161] Therefore, in the specific process performed in the third embodiment, such as Figure 7 As shown in (b), at time t22, the servo pressure Pa is increased. Consequently, the rear wheel cylinder pressure Pwr also increases along with the servo pressure Pa. Therefore, even if the servo pressure Pa is subsequently reduced, the vehicle can be kept stationary by the braking force generated by the rear wheels.

[0162] At a subsequent time t23, similar to the case in the first embodiment described above, the servo pressure Pa is reduced to the lower limit pressure px by performing a pressure reduction process related to a 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 not closed can also be the same as the lower limit pressure px when the front wheel pressure regulating valve UZf is closed.

[0163] After time t23, even if the rear wheel pressure regulating valve UZr is closed, the rear wheel cylinder pressure Pwr will decrease slightly due to leakage at the rear wheel pressure regulating valve UZr.

[0164] Therefore, similar to the first embodiment, at time t24, a pressurization process related to a specific process begins. As a result, the servo pressure Pa increases. In the pressurization process of the third embodiment, the servo pressure Pa increases to the servo pressure Pa at time t23. Consequently, since brake fluid BF is supplied to the rear wheel cylinder CWr, the rear wheel cylinder pressure Pwr recovers. Therefore, at time t25, a depressurization process related to the specific process is performed again. That is, during a period when the braking operation amount Ba is approximately constant, the depressurization and pressurization processes are periodically repeated.

[0165] Therefore, in the third embodiment, even if only the rear wheel pressure regulating valve UZr of the front wheel pressure regulating valve UZf and the rear wheel pressure regulating valve UZr is closed, the same effect as the above-described embodiments can be obtained.

[0166] Furthermore, if a specific procedure is performed when it is determined that there is no abnormality in the front wheel system, the front wheel pressure regulating valve UZf is closed, while the rear wheel pressure regulating valve UZr is opened. The procedure in this case is essentially the same as in the first embodiment described above. Therefore, detailed explanation is omitted.

[0167] <Other Implementation Methods>

[0168] Other implementation methods will be described. In other implementation methods, the same effects as described above can be achieved.

[0169] In the above embodiment, a disc brake is used as the braking device SX. Alternatively, a drum brake can also be used as the braking device SX. In the drum brake device SX, the rotating component KT fixed to the wheel WH is the brake drum, and the friction component is the brake pads adhered to the brake shoes. In the drum brake device SX, similarly to the disc brake device SX, the brake pads (friction components) are pressed against the brake drum (rotating component) by the wheel cylinder pressure Pw of the wheel cylinder CW, generating a frictional braking force Fe.

[0170] In the hydraulic transmission of the brake control device SC, there are various resistances, such as the pipe friction resistance of the fluid path (HS, etc.), the resistance of the solenoid valve (VI, etc.) as an orifice, and the sliding resistance of the sealing component SL. In hydraulically related feedback control, the actual value is controlled to match the target value, but considering the aforementioned resistances, the comparison between the actual value and the target value needs to be made at the same location. In the above embodiment, the target pressure Pt is determined as the target value corresponding to the servo pressure Pa (actual value). That is, the location for comparing the target value and the actual value (also called the "comparison location") is the position where the servo pressure sensor PA is installed. Alternatively, the comparison location can also be any location in the hydraulic transmission path from the discharge part of the electric cylinder DN to the wheel cylinder CW. For example, the wheel cylinder CW can be used as the comparison location, and the target pressure Pt is determined to correspond to the wheel cylinder pressure Pw (actual value), which is estimated based on the servo pressure Pa after compensating for the hydraulic components caused by the aforementioned resistances. Furthermore, in a structure that uses the lower part of the pressure regulating valve UZ as the comparison point, if the pressure regulating valve UZ is closed during a specific process, it is assumed that the pressure regulating valve UZ is open to determine the wheel cylinder pressure Pw. In pressure regulation control, regardless of where the comparison point between the target value and the actual value is located, the target pressure Pt can be considered as the target value used to control the servo pressure Pa.

[0171] In the above embodiments, the pressure regulation control, including specific processing, is executed by two controllers EA and EZ. Alternatively, the upper and lower controllers EA and EZ can be integrated to form an integrated controller EC. Here, controllers EA, EZ, and EC are referred to as "controller EE". In either case, in the braking control device SC, the motor MA and the pressure regulating valve UZ are controlled by controller EE (i.e., the collective name of controllers EA, EZ, and EC).

[0172] <Summary of Implementation Methods>

[0173] The brake control unit SC includes a control cylinder CC, a pressure regulating valve UZ, and a controller EE (a collective term for controllers EA, EZ, and EC). The wheel cylinder pressure Pw of wheel cylinder CW is adjusted via a servo pressure Pa. The control cylinder CC generates the servo pressure Pa through the movement of the control piston NC, driven by an electric motor MA. The pressure regulating valve UZ (a solenoid valve) is normally open and is located on the hydraulic 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.

[0174] In the brake control unit SC, when the temperature-related value Xm, which is related to the temperature of the structural components involved in the motor MA, exceeds a threshold xm, the controller EE executes a specific process to close the pressure regulating valve UZ and reduce the servo pressure Pa. In this specific process, the servo pressure Pa is reduced to a lower limit pressure px. Here, the lower limit pressure px is preset based on the continuous ratings of the structural components of the motor MA. Furthermore, in this specific process, the valve current Iz supplied to close the pressure regulating valve UZ is adjusted based on the differential pressure sPx (specific differential pressure) between the wheel cylinder pressure Pw and the lower limit pressure px. Specifically, when the specific differential pressure sPx is small, the valve current Iz is reduced compared to when the specific differential pressure sPx is large. By appropriately setting the lower limit pressure px, the valve current Iz supplied to the pressure regulating valve UZ can be suppressed to the necessary minimum. As a result, the power consumption of the brake control unit SC is reduced.

[0175] The brake control unit SC is equipped with a front wheel pressure regulating valve UZf associated with the front wheel cylinder CWf and a rear wheel pressure regulating valve UZr associated with the rear wheel cylinder CWr, referred to as pressure regulating valve UZ. Furthermore, when performing specific processing (i.e., reducing the servo pressure Pa), the front wheel pressure regulating valve UZf is closed while the rear wheel pressure regulating valve UZr remains open. Since the power consumption of the rear wheel pressure regulating valve UZr becomes "0", power saving of the brake control unit SC is achieved. Additionally, since the front wheel cylinder pressure Pwf can generate greater braking force compared to the rear wheel cylinder pressure Pwr, a stationary state can be reliably maintained even when only specific processing is performed using the front wheel cylinder CWf.

Claims

1. A braking control device for a vehicle, comprising: an electric cylinder that generates servo pressure by moving a control piston driven by an electric motor; a normally open solenoid valve disposed in a hydraulic transmission path from the electric cylinder to a wheel cylinder; and a controller that controls the electric motor and the solenoid valve, wherein the braking control device adjusts the wheel cylinder pressure of the wheel cylinder by the servo pressure, wherein... If the temperature-related value associated with the temperature of the structural components involved in the motor exceeds a threshold, the controller closes the solenoid valve and reduces the servo pressure to a lower limit pressure set based on the maximum rated value that allows continuous energization of the structural components. When the differential pressure between the cylinder pressure and the lower limit pressure is small, the controller reduces the valve current supplied to close the solenoid valve compared to when the differential pressure is large.

2. The vehicle braking control device according to claim 1, wherein, The solenoid valve includes: a front wheel solenoid valve disposed relative to the front wheel cylinder in the wheel cylinder, and a rear wheel solenoid valve disposed relative to the rear wheel cylinder in the wheel cylinder. When the servo pressure is reduced, the controller closes the front wheel solenoid valve while keeping the rear wheel solenoid valve open.

3. The vehicle braking control device according to claim 1, wherein, The solenoid valve includes: a front wheel solenoid valve disposed relative to the front wheel cylinder in the wheel cylinder, and a rear wheel solenoid valve disposed relative to the rear wheel cylinder in the wheel cylinder. When the controller reduces the servo pressure and maintains it at the lower limit pressure, it closes the rear wheel solenoid valve and keeps the front wheel solenoid valve open.

4. The vehicle braking control device according to claim 2, wherein, In the hydraulic transmission path, the system that adjusts the cylinder pressure of the front wheel cylinder is called the front wheel system, and the system that adjusts the cylinder pressure of the rear wheel cylinder is called the rear wheel system. The front wheel system has the front wheel solenoid valve, and the rear wheel system has the rear wheel solenoid valve. The controller is configured as follows: Determine whether the front wheel system is malfunctioning. If the temperature correlation value exceeds the threshold when it is determined that there is no abnormality in the front wheel system, the front wheel solenoid valve is closed, while the rear wheel solenoid valve remains open. If the temperature correlation value exceeds the threshold when it is determined that the front wheel system has malfunctioned, the rear wheel solenoid valve is closed while the front wheel solenoid valve remains open.

Images