JP7703863B2 - Vehicle brake control device - Google Patents

Description

This disclosure relates to a vehicle braking control device.

Patent Document 1 describes how, with the objective of "executing brake pressure control for a longer period of time," "the M/C pressure generated by the auxiliary pressure source 100 is set to the maximum value of the W/C pressure for each wheel FL to RR. This makes it possible to avoid generating M/C pressure more than necessary. Furthermore, when generating W/C pressure for each wheel FL to RR, there is no need to reduce the high M/C pressure to use it as the W/C pressure, so the amount of brake fluid discharged to the reservoirs 20 and 40 through the pressure reduction control valves 21, 22, 41, and 42 can be reduced. This makes it possible to reduce the frequency of operation of the motor 60, suppresses temperature increases in the motor 60, and allows brake pressure control to be performed for a longer period of time."

In Patent Document 1, a target hydraulic pressure (also called "required hydraulic pressure") is calculated for each wheel cylinder, and an auxiliary pressure source (also called "pressure source") is controlled based on the maximum value of the multiple target hydraulic pressures. That is, the hydraulic pressure of the wheel cylinder corresponding to the maximum value (called "selected braking hydraulic pressure Pwx") is adjusted by the pressure source. Then, in the wheel cylinders other than the one corresponding to the maximum value, the braking hydraulic pressure (called "non-selected braking hydraulic pressure Pwz") is adjusted by reducing it from the output hydraulic pressure of the pressure source (called "supply hydraulic pressure Pm") by controlling the pressure boost valve (also called "inlet valve") and the pressure reducing valve (also called "outlet valve").

As described above, the non-selected brake fluid pressure Pwz is adjusted by reducing it from the supply fluid pressure Pm of the pressurized source, and this adjustment is achieved by discharging the brake fluid BF into the reservoir RC through control of the inlet and outlet valves. At this time, the amount of brake fluid BF changes in the fluid paths (brake piping, flow paths in the fluid unit, hoses, etc.) of the brake control device SC. This change in fluid amount may cause fluctuations in the supply fluid pressure Pm. It is desirable for the vehicle brake control device SC to be able to adjust the selected brake fluid pressure Pwx by suppressing fluctuations (pressure fluctuations) in the fluid pressure (supply fluid pressure) Pm output by the pressurized source.

JP 2015-193344 A

The object of the present invention is to provide a vehicle brake control device that can suppress fluctuations in hydraulic pressure in wheel cylinders caused by fluctuations in hydraulic pressure supplied from a pressure source.

The brake control device according to the present invention adjusts the hydraulic pressure (Pw) of a plurality of wheel cylinders (CW) of a vehicle individually, and includes a pressure source (YA) that increases the hydraulic pressure (Pw) of the plurality of wheel cylinders (CW), a communication passage (HS) that connects the pressure source (YA) and the plurality of wheel cylinders (CW), an inlet valve (UI) provided in the communication passage (HS), a pressure reduction passage (HG) that connects the communication passage (HS) between the plurality of wheel cylinders (CW) and the inlet valve (UI) to a reservoir (RC), an outlet valve (VO) provided in the pressure reduction passage (HG), and a hydraulic pressure sensor (PB) that detects the hydraulic pressure output by the pressure source (YA) as a supply hydraulic pressure (Pm). ) and a controller (ECU) that "calculates a plurality of target hydraulic pressures (Pt) required for the plurality of wheel cylinders (CW), determines the maximum value of the plurality of target hydraulic pressures (Pt) as a maximum target hydraulic pressure (Ptx), adjusts the hydraulic pressure (Pwx) of a selected wheel cylinder (CWx) corresponding to the maximum target hydraulic pressure (Ptx) among the plurality of wheel cylinders (CW) by the pressurizing source (YA), and adjusts the hydraulic pressure (Pwz) of a non-selected wheel cylinder (CWz) that does not correspond to the selected wheel cylinder (CWx) among the plurality of wheel cylinders (CW) by the inlet valve (UIz) and the outlet valve (VOz)." The controller (ECU) controls the selected inlet valve (UIx) among the inlet valves (UI) corresponding to the selected wheel cylinder (CWx) based on the deviation (hP) between the maximum target hydraulic pressure (Ptx) and the supply hydraulic pressure (Pm).

The brake control device according to the present invention further includes a pressure regulating valve (UB) provided in the communication path (HS) between the pressurizing source (YA) and the inlet valve (UI). The controller (ECU) controls a selective pressure regulating valve (UBx) corresponding to the selected wheel cylinder (CWx) among the pressure regulating valves (UB) based on the deviation (hP). When the supply hydraulic pressure (Pm) is smaller than the maximum target hydraulic pressure (Ptx), the controller (ECU) energizes the selective pressure regulating valve (UBx) and does not energize the selective inlet valve (UIx). When the supply hydraulic pressure (Pm) is larger than the maximum target hydraulic pressure (Ptx), the controller (ECU) energizes the selective inlet valve (UIx) and does not energize the selective pressure regulating valve (UBx).

According to the above configuration, the opening amounts Li and Lb of the inlet valve UI and pressure regulating valve UB are adjusted based on the hydraulic pressure deviation hP, thereby suppressing fluctuations in the supply hydraulic pressure Pm and transmitting it to the selected wheel cylinder CWx. This reduces fluctuations in the hydraulic pressure Pwx in the selected wheel cylinder CWx.

1 is a configuration diagram for explaining an entire vehicle JV equipped with a braking control device SC. FIG. 2 is a schematic diagram for explaining a configuration example of a first unit YA. 13 is a schematic diagram for explaining a configuration example of a second unit YB. FIG. FIG. 11 is a flow chart for explaining a method of adjusting a brake fluid pressure Pw during off-road control. 4 is a schematic diagram for explaining an inlet valve UI and a pressure regulating valve UB. FIG. FIG. 4 is a block diagram for explaining fluctuation suppression control. FIG. 4 is a time series diagram for explaining the operation of the fluctuation suppression control.

The following describes an embodiment of a vehicle braking control device SC according to the present invention with reference to the drawings.

<Symbols of components>
In the following description, components, signals, values, etc. that are given the same symbol, such as "CW", have the same function. The subscripts "f" and "r" added to the end of various symbols related to wheels are generic symbols that indicate whether the element is related to the front wheels or the rear wheels. Specifically, "f" indicates an element related to the front wheels, and "r" indicates an element related to the rear wheels. For example, a wheel cylinder CW is written as a front wheel cylinder CWf and a rear wheel cylinder CWr. Furthermore, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its generic name.

<Vehicle JV equipped with brake control device SC>
With reference to the configuration diagram of Fig. 1, the entire vehicle JV equipped with the brake control device SC according to the present invention will be described. The vehicle JV is equipped with an acceleration operation member AP, a braking operation member BP, a steering operation member SH, and various sensors (BA, etc.). The acceleration operation member (e.g., accelerator pedal) AP is a member operated by the driver to accelerate the vehicle JV and control the speed of the vehicle JV (vehicle body speed Vx). The braking operation member (e.g., brake pedal) BP is a member operated by the driver to decelerate the vehicle. The steering operation member (e.g., steering wheel) SH is a member operated by the driver to turn the vehicle JV.

The vehicle JV is provided with various sensors as listed below. Detection signals (Ba, etc.) of these sensors are input to a braking controller ECU (also simply referred to as a "brake controller"), which will be described later.
- An acceleration operation amount sensor AA that detects the operation amount (acceleration operation amount) Aa of the acceleration operation member AP, a braking operation amount sensor BA that detects the operation amount (braking operation amount) Ba of the braking operation member BP, and a steering operation amount sensor SA that detects the operation amount (steering operation amount, for example, steering angle) Sa of the steering operation member SH.
A wheel speed sensor VW detects the rotation speed (wheel speed) Vw of the wheels WH.
In the vehicle JV (particularly the vehicle body), there are a yaw rate sensor YR that detects a yaw rate Yr, a longitudinal acceleration sensor GX that detects a longitudinal acceleration Gx, and a lateral acceleration sensor GY that detects a lateral acceleration Gy.

In addition, various switches are provided, such as a switch XD for downhill assist control and a switch XC for crawl control, to issue commands for various automatic braking controls, which will be described later. These switches XD and XC are operated by the driver. An operation signal Xd (a downhill assist control signal) from the switch XD and an operation signal Xc (a crawl control signal) from the switch XC are input to the brake controller ECU.

The vehicle JV is equipped with a brake system SX and a brake control device SC. The brake control device SC uses a so-called front and rear type (also called "type II") brake system as two systems.

The brake device SX is supplied with a brake fluid pressure Pw generated by the brake control device SC. The brake device SX generates a braking force Fb on the wheel WH according to the brake fluid pressure Pw. The brake device SX includes a rotating member (e.g., a brake disc) KT and a brake caliper CP. The rotating member KT is fixed to the wheel WH of the vehicle, and the brake caliper CP is provided so as to sandwich the rotating member KT. The brake caliper CP is provided with a wheel cylinder CW. The brake control device SC supplies the wheel cylinder CW with brake fluid BF adjusted to the brake fluid pressure Pw. The brake fluid pressure Pw presses a friction member (e.g., a brake pad) MS against the rotating member KT. The rotating member KT and the wheel WH are fixed so as to rotate together, and the frictional force generated at this time generates a braking torque Tb (resulting in a braking force Fb) on the wheel WH.

The brake control device SC adjusts the actual brake fluid pressure Pw according to the operation amount Ba of the brake operating member BP, and supplies the brake fluid pressure Pw to the brake device SX (particularly the wheel cylinder CW) via the front and rear wheel connection paths HSf and HSr. The brake control device SC is composed of a master cylinder CM, a fluid unit HU, and a brake controller ECU. The fluid unit HU is composed of two units (first and second units) YA and YB. The components of the brake control device SC (solenoid valves, electric motors, etc. included in the first and second units YA and YB) are controlled by the controller ECU. The controller ECU is composed of a microprocessor MP that performs signal processing, and a drive circuit DD that drives the solenoid valves and the electric motor. The controller ECU for braking, the motor controller ECP described later, and the power transmission controller ECT are each connected to the communication bus BS. Therefore, information (detected values, calculated values) is shared between these controllers via the communication bus BS. For example, the brake controller ECU calculates the vehicle speed Vx based on the wheel speed Vw. The vehicle speed Vx is transmitted to another controller through the communication bus BS. The controller ECU receives the acceleration operation amount Aa, the braking operation amount Ba, the steering operation amount Sa, the yaw rate Yr, the longitudinal acceleration Gx, the lateral acceleration Gy, the wheel speed Vw, the operation signal Xc (for crawl control), the operation signal Xd (for downhill assist control), and the like. Based on these signals, the brake controller ECU controls the fluid unit HU. The brake control device SC will be described in detail later.

The vehicle JV is equipped with a prime mover control device GC and a power transmission device TS. The vehicle JV is a four-wheel drive vehicle in which all four wheels WH are drive wheels (wheels to which the drive torque Td is transmitted and which generate the drive force Fd).

The prime mover control device GC is composed of a prime mover PG and a prime mover controller ECP (also simply called a "prime mover controller") that controls it. The prime mover PG is a general term for a device that converts various types of energy that exist in the natural world into mechanical work (dynamic energy). An example will be described in which an internal combustion engine (gasoline engine) is used as the prime mover PG. The prime mover PG generates power (driving torque Td) for driving the four wheels WH. The prime mover PG is controlled by a prime mover controller (engine controller) ECP, and its output is adjusted. In detail, the prime mover PG includes a throttle device TH, a fuel injection device FI, and an engine speed sensor NE. The throttle opening Th is controlled by the throttle device TH, and the fuel injection amount Fi is controlled by the fuel injection device FI. Based on the engine speed Ne detected by the speed sensor NE, at least one of the throttle opening Th and the fuel injection amount Fi is controlled by the prime mover controller ECP. As a result, the output of the prime mover PG is adjusted.

The output (rotational power) of the prime mover control device GC (particularly the prime mover PG) is input to the power transmission device TS. The output of the prime mover PG is then transmitted to the four wheels WH via the power transmission device TS, and a driving force Fd is generated at each of the wheels WH. The power transmission device TS includes a power transmission mechanism TD and a power transmission controller ECT (also simply called the "power transmission controller") that controls it. The power transmission mechanism TD is composed of a main transmission MH, an auxiliary transmission FH, a front wheel differential mechanism DF, a central differential mechanism DC, and a rear wheel differential mechanism DR. The main transmission MH is an automatic transmission that changes gears according to the running state of the vehicle. The output of the prime mover PG is input to the auxiliary transmission FH via the main transmission MH. The auxiliary transmission FH enables switching between high-speed and low-speed gears for four-wheel drive.

The output from the auxiliary transmission FH is input to each of the differential mechanisms DF (front wheel differential gear), DC (center differential gear), and DR (rear wheel differential gear). The front wheel drive torque Tdf is transmitted to the left and right front wheels WHf via the front wheel differential mechanism DF and the front wheel drive shaft. The rear wheel drive torque Tdr is transmitted to the left and right rear wheels WHr via the center differential mechanism DC, the rear wheel differential mechanism DR, and the rear wheel drive shaft. Since the power generated by the prime mover PG is transmitted to the front wheels WHf and the rear wheels WHr via the differential mechanisms DF, DC, and DR, a rotational speed difference (i.e., differential) between each wheel WH is allowed. Each component of the power transmission mechanism TD (MH, etc.) is controlled by the power transmission controller ECT. Specifically, the main transmission MH, the auxiliary transmission FH, and the differential mechanisms DF, DC, and DR are each controlled by the power transmission controller ECT.

<Off-road control>
Off-road control is executed in the vehicle JV. "Off-road control" is to maintain the vehicle speed Vx at a low speed on unpaved roads (also called "off-road") and the like. Here, off-road control is a general term for "downhill assist control" and "crawl control." Downhill assist control and crawl control are well known, so they will be briefly described below.

"Downhill assist control", also known as "hill descent control", adjusts the braking force Fb so that the vehicle speed Vx is maintained at or below a predetermined vehicle speed vd on a downhill road, even if the driver does not operate the brake operating member BP. Downhill assist control is commanded by an operation signal Xd (downhill assist control signal) from a downhill assist control switch XD operated by the driver. When the operation signal Xd indicates an on state, downhill assist control is executed, but when the operation signal Xd is in an off state, it is not executed. In addition to commanding whether or not downhill assist control needs to be executed, the switch XD also commands the set speed vd for downhill assist control. That is, the operation signal Xd contains information on the target value (set speed) vd of the vehicle speed Vx of the vehicle JV. In downhill assist control, wheel lock and skidding of the wheels WH are suppressed, and the brake fluid pressure Pw of each wheel WH is adjusted individually so that the vehicle speed Vx matches and is maintained at a preset constant low speed (set speed) vd.

"Crawl control" is a further evolution of the downhill assist control described above. In crawl control, the braking force Fb and driving force Fd are controlled by the brake control device SC and prime mover control device GC so that the vehicle speed Vx is maintained at a predetermined set vehicle speed vc, even if the acceleration operating member (accelerator pedal) AP and the braking operating member (brake pedal) BP are not operated. In other words, crawl control is activated not only on downhill slopes, but also on uphill slopes.

Specifically, crawl control is instructed by an operation signal Xc (switch signal for crawl control) from a crawl control switch XC operated by the driver. When the operation signal (switch signal) Xc indicates an on state, crawl control is executed, but when the operation signal Xc is in an off state, crawl control is not executed. The switch XC also instructs whether or not to execute crawl control, and also instructs the set speed vc for crawl control. That is, the operation signal Xc contains information on the target value (set speed) vc of the vehicle body speed Vx of the vehicle JV. In crawl control, the locking and skidding of the wheels WH are suppressed, and the output of the prime mover PG is adjusted and the brake fluid pressure Pw of each wheel WH is individually adjusted so that the vehicle body speed Vx coincides with and is maintained at a preset constant low speed (set speed) vc. On sand, dirt, rocky roads, muddy roads, etc., delicate operation of the acceleration operation member AP and the braking operation member BP is required, but crawl control effectively assists driving in such conditions.

As explained above, off-road control (e.g., downhill assist control, crawl control) prevents the wheels WH from skidding, ensuring the stability of the vehicle JV and enabling the vehicle to travel with the vehicle speed Vx maintained constant (very low speeds vd, vc). At this time, the driver is not required to operate the acceleration operating member AP or the braking operating member BP, so the driver can concentrate on operating the steering operating member SH. In other words, off-road control improves the vehicle's ability to traverse rough terrain, etc.

<First unit YA>
An example of the configuration of the first unit YA included in the fluid unit HU will be described with reference to the schematic diagram of FIG. 2. The first unit YA is a pressure source for increasing the hydraulic pressure (braking hydraulic pressure) Pw of the four wheel cylinders CW. In this example, the first unit YA is integrated with the master cylinder CM. A front and rear brake system is adopted. The first unit YA is composed of an apply unit AU including the master cylinder CM, and a pressurizing unit KU. The apply unit AU and the pressurizing unit KU are controlled by a brake controller ECU. In detail, the controller ECU receives the braking operation amount Ba (at least one of the simulator hydraulic pressure Ps, the operation displacement Sp, and the operation force Fp), the wheel speed Vw, the accumulator hydraulic pressure Pc, the servo hydraulic pressure Pu, and the supply hydraulic pressure Pm, and calculates a drive signal Vn for the input valve VN, a drive signal Vr for the open valve VR, a drive signal Uz for the boost valve UZ, a drive signal Ug for the pressure reducing valve UG, and a drive signal Ma for the pressure accumulating electric motor MA based on these signals.Then, in response to the drive signals "Vn, Vr, Uz, Ug, Ma", the solenoid valves "VN, VR, UZ, UG" constituting the first unit YA and the pressure accumulating electric motor MA are controlled (driven).

As described below, the fluid unit HU, wheel cylinder CW, etc. are connected by the communication path HS, input path HN, pressure reduction path HG, and return path HK. These are fluid paths through which the brake fluid BF moves. Fluid paths (HS, etc.) include fluid piping, flow paths within the fluid unit HU, hoses, etc.

<<Apply Unit AU>>
The apply unit AU is composed of a master reservoir RV, a master cylinder CM, first and second master pistons NP, NS, first and second master springs DP, DS, an input cylinder CN, an input piston NN, an input spring DN, an input valve VN, an open valve VR, a stroke simulator SS, and a simulator hydraulic pressure sensor PS.

The master reservoir (also called the "atmospheric pressure reservoir") RV is a tank for hydraulic fluid, and brake fluid BF is stored inside it. The master reservoir RV is connected to the master cylinder CM (particularly the front and rear wheel master chambers Rmf and Rmr).

The master cylinder CM is a cylinder member having a bottom. First and second master pistons NP, NS are inserted inside the master cylinder CM, and the interior is sealed by a seal member SL to separate the front and rear wheel master chambers Rmf, Rmr. The master cylinder CM is of the so-called tandem type. First and second master springs DP, DS are provided in the front and rear wheel master chambers Rmf, Rmr. The first and second springs DP, DS press the first and second master pistons NP, NS in the backward direction Hb (the direction in which the volume of the master chamber Rm increases, the opposite direction to the forward direction Ha). The front and rear wheel master chambers Rmf, Rmr (=Rm) are ultimately connected to the front and rear wheel cylinders CWf, CWr (=CW), respectively, via the front and rear wheel connection passages HSf, HSr (=HS) and the second unit YB. When the first and second master pistons NP, NS are moved forward Ha (in the direction in which the volume of the master chamber Rm decreases), brake fluid BF of hydraulic pressure Pm (referred to as "supplied hydraulic pressure" and "front and rear wheel supplied hydraulic pressure Pmf, Pmr") is supplied from the first unit YA (particularly the master cylinder CM) to the second unit YB. Here, the front wheel supplied hydraulic pressure Pmf and the rear wheel supplied hydraulic pressure Pmr are equal.

The first master piston NP is provided with a flange. This flange further divides the interior of the master cylinder CM into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru is disposed opposite the front wheel master chamber Rmf across the first master piston NP. The rear chamber Ro is sandwiched between the front wheel master chamber Rmf and the servo chamber Ru, and is disposed between them. The servo chamber Ru and the rear chamber Ro are also sealed by the seal member SL, as described above.

The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted inside the input cylinder CN and sealed with a seal member SL to form an input chamber Rn. The input piston NN is mechanically connected to the brake operating member BP via a clevis (U-shaped link). A flange is provided on the input piston NN. An input spring DN is provided between this flange and the mounting surface of the input cylinder CN relative to the master cylinder CM. The input spring DN presses the input piston NN in the backward direction Hb.

The apply unit AU is provided with hydraulic chambers: input chamber Rn, servo chamber Ru, rear chamber Ro, and front and rear master chambers Rmf and Rmr. Here, the "hydraulic chambers" are chambers filled with brake fluid BF and sealed by a seal member SL. The volume of each hydraulic chamber is changed by the movement of the input piston NN and the first and second master pistons NP and NS. The hydraulic chambers are arranged along the central axis Jm of the master cylinder CM in the following order from the side closest to the brake operating member BP: input chamber Rn, servo chamber Ru, rear chamber Ro, front master chamber Rmf, and rear master chamber Rmr.

The input chamber Rn and the rear chamber Ro are connected via an input path HN. An input valve VN is provided in the input path HN. The input path HN is connected to the master reservoir RV between the rear chamber Ro and the input valve VN via an open valve VR. The input valve VN and the open valve VR are two-position solenoid valves (also called "on-off valves") that have an open position (connected state) and a closed position (blocked state). A normally closed solenoid valve is used as the input valve VN. A normally open solenoid valve is used as the open valve VR. The input valve VN and the open valve VR are driven (controlled) by drive signals Vn and Vr from the brake controller ECU.

A stroke simulator (also simply referred to as "simulator") SS is connected to the rear chamber Ro. The simulator SS generates an operating force Fp for the brake operating member BP. A piston and an elastic body (e.g., a compression spring) are provided inside the simulator SS. When brake fluid BF flows into the simulator SS, the piston is pushed by the brake fluid BF. A force is applied to the piston by the elastic body in a direction that prevents the inflow of brake fluid BF, so that an operating force Fp for the brake operating member BP is generated. In other words, the operating characteristic of the brake operating member BP (the relationship between the operating displacement Sp and the operating force Fp) is formed by the simulator SS.

A simulator hydraulic pressure sensor PS is provided to detect the hydraulic pressure Ps of the simulator SS (simulator hydraulic pressure, which is also the hydraulic pressure in the input chamber Rn and the rear chamber Ro). The simulator hydraulic pressure sensor PS is one of the braking operation amount sensors BA described above. The simulator hydraulic pressure Ps is input to the braking controller ECU as the braking operation amount Ba.

In addition to the simulator hydraulic pressure sensor PS, the first unit YA is provided with a braking operation amount sensor BA, which includes an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP, and/or an operation force sensor FP that detects the operation force Fp of the brake operating member BP. In other words, at least one of the simulator hydraulic pressure sensor PS, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP is used as the braking operation amount sensor BA. Therefore, the braking operation amount Ba is at least one of the simulator hydraulic pressure Ps, the operation displacement Sp, and the operation force Fp.

<Pressure unit KU>
The pressurizing unit KU generates and adjusts the supply hydraulic pressure Pm. The pressurizing unit KU is composed of an accumulator fluid pump QA, an accumulator electric motor MA, an accumulator AC, an accumulator hydraulic pressure sensor PC, a pressurizing cylinder CK, a pressurizing piston NK, a pressure booster valve UZ, a pressure reducing valve UG, and a servo hydraulic pressure sensor PU.

The pressurizing unit KU is provided with a pressure-accumulating fluid pump QA to accumulate pressure in the accumulator AC. The pressure-accumulating fluid pump QA is driven by a pressure-accumulating electric motor MA, and pumps up brake fluid BF from the master reservoir RV. The brake fluid BF discharged from the fluid pump QA is then accumulated in the accumulator AC. The accumulator AC stores brake fluid BF pressurized to the accumulator pressure Pc. An accumulator pressure sensor PC is provided to detect the accumulator pressure Pc.

The brake controller ECU controls the electric motor MA for accumulating pressure so that the accumulator hydraulic pressure Pc is maintained within a predetermined range. Specifically, when the accumulator hydraulic pressure Pc is less than the lower limit value pl, the electric motor MA is driven at a predetermined rotation speed. When the accumulator hydraulic pressure Pc is equal to or greater than the upper limit value pu, the electric motor MA is stopped. Here, the lower limit value pl and the upper limit value pu are preset values (constants) and have the relationship "pl < pu." By controlling the electric motor MA, the accumulator hydraulic pressure Pc is maintained in the range from the lower limit value pl to the upper limit value pu.

The pressurizing unit KU is provided with a pressurizing cylinder CK to adjust the accumulator hydraulic pressure Pc from the accumulator AC and supply it to the servo chamber Ru. A pressurizing piston NK is inserted into the pressurizing cylinder CK. The pressurizing piston NK divides the inside of the pressurizing cylinder CK into three hydraulic chambers Rp (pilot chamber), Rv (annular chamber), and Rk (pressurizing chamber), which are sealed with a seal member SL. The pilot chamber Rp and the pressurizing chamber Rk are arranged to sandwich the pressurizing piston NK. In other words, the pilot chamber Rp is located on the opposite side of the pressurizing chamber Rk with respect to the pressurizing piston NK in the pressurizing cylinder CK. The pilot hydraulic pressure Pp adjusted by the booster valve UZ and the pressure reducing valve UG, which will be described later, is supplied to the pilot chamber Rp.

The outer periphery of the pressurizing piston NK is provided with an annular recess (constricted portion). This annular recess and the inner periphery of the pressurizing cylinder CK form an annular chamber Rv. Furthermore, a valve body Vv (e.g., a spool valve) is formed on the outer periphery of the pressurizing piston NK. Brake fluid BF pressurized to accumulator hydraulic pressure Pc is supplied from the accumulator AC to this valve body Vv. The accumulator hydraulic pressure Pc is adjusted by the valve body Vv and introduced into the annular chamber Rv. The annular chamber Rv is connected to the pressurizing chamber Rk via a through hole provided in the pressurizing piston NK. Therefore, the hydraulic pressure in the annular chamber Rv and the hydraulic pressure in the pressurizing chamber Rk are the same. This hydraulic pressure is called the "servo hydraulic pressure Pu".

Specifically, when the pressurizing piston NK is moved by the hydraulic pressure (pilot hydraulic pressure) Pp in the pilot chamber Rp, the opening amount of the valve body Vv changes. Then, brake fluid BF is supplied from the accumulator AC through the valve body Vv of the pressurizing piston NK so that the pilot hydraulic pressure Pp (hydraulic pressure in the pilot chamber Rp) and the servo hydraulic pressure Pu (hydraulic pressure in the annular chamber Rv and pressurizing chamber Rk) match. In other words, the high-pressure accumulator hydraulic pressure Pc is throttled by the valve body Vv and adjusted to the servo hydraulic pressure Pu. A servo hydraulic pressure sensor PU is provided to detect the actual servo hydraulic pressure Pu. The detected servo hydraulic pressure Pu is input to the brake controller ECU. The controller ECU adjusts the pilot hydraulic pressure Pp based on the servo hydraulic pressure Pu, and ultimately controls the servo hydraulic pressure Pu to match the target value. The pressure chamber Rk and the servo chamber Ru are connected by a fluid path, so that braking fluid BF adjusted to the servo hydraulic pressure Pu is supplied from the pressure unit KU to the servo chamber Ru.

<<Operation of the first unit YA>>
When braking is not being applied (i.e., when the brake operating member BP is not being operated), the pistons "NN, NP, NS" are pressed by the springs "DN, DP, DS" and returned to their initial positions (the positions where they are moved furthest in the backward direction Hb). In this state, the front and rear wheel master chambers Rmf, Rmr are in communication with the master reservoir RV, and the front and rear wheel supply hydraulic pressures Pmf, Pmr are "0 (atmospheric pressure)". In addition, at the initial positions of the pistons, there is a gap between the input piston NN and the first master piston NP. Similarly, when braking is not being applied, the boost valve UZ is closed and the pressure reducing valve UG is open, so that the pilot chamber Rp is in communication with the master reservoir RV, and the pilot hydraulic pressure Pp is "0 (atmospheric pressure)". The pressurizing piston NK is pressed against the bottom of the pressurizing cylinder CK by the compression spring DK, and the valve body Vv (spool valve) is closed. Since the pressurizing chamber Rk and the master reservoir RV are in communication with each other, the servo hydraulic pressure Pu is also 0. Furthermore, when braking is not being applied, the input valve VN and the release valve VR are open, and the rear chamber Ro and the input chamber Rn are in communication with the master reservoir RV, so the internal pressures Po and Pn are also 0. In other words, when braking is not being applied, the state is "Pmf = Pmr = Pp = Pu = Po = Pn = 0".

During braking (i.e., when the brake operating member BP is operated), the input valve VN is open and the release valve VR is closed. That is, the input chamber Rn and the rear chamber Ro are in communication with each other, and the communication between the rear chamber Ro and the master reservoir RV is cut off and they are in a non-communicating state. As the operation amount Ba of the brake operating member BP increases, the input piston NN is moved in the forward direction Ha and brake fluid BF is discharged from the input chamber Rn. This brake fluid BF is absorbed by the stroke simulator SS, so that the hydraulic pressure Pn (input hydraulic pressure) in the input chamber Rn and the hydraulic pressure Po (rear hydraulic pressure) in the rear chamber Ro are increased, and an operating force Fp is generated in the brake operating member BP. At this time, the boost valve UZ and the pressure reducing valve UG are controlled according to the braking operation amount Ba (at least one of the simulator hydraulic pressure Ps, the operation displacement Sp, and the operation force Fp), and the hydraulic pressure Pp (pilot hydraulic pressure) in the pilot chamber Rp is increased. In response to the increase in the pilot hydraulic pressure Pp, the valve body Vv is opened, and the hydraulic pressure Pu (servo hydraulic pressure) in the annular chamber Rv and the pressurizing chamber Rk is increased. Since this servo hydraulic pressure Pu is supplied to the servo chamber Ru, the first master piston NP is pressed in the forward direction Ha and moves in the forward direction Ha. As the first master piston NP moves in the forward direction Ha, the front and rear wheel supply hydraulic pressures Pmf and Pmr (=Pm) are increased. Then, the brake fluid BF adjusted to the supply hydraulic pressure Pm by the first unit YA is supplied to the second unit YB, and finally the brake hydraulic pressure Pw in the wheel cylinder CW is increased.

The brake control device SC is of the so-called brake-by-wire type, so that when the vehicle is an electric vehicle (e.g., an electric car, a hybrid car), regenerative cooperative control is executed. Since there is a gap between the input piston NN and the first master piston NP, the relative positional relationship between the input piston NN and the first and second master pistons NP, NS can be adjusted as desired within the range of this gap by controlling the servo hydraulic pressure Pu. For example, when only braking force from regenerative braking is required, "Pu = 0" is set, and the supply hydraulic pressure Pm from the front and rear wheel master chambers Rmf, Rmr is left at "0". No braking force is generated by friction between the rotating member KT and the friction member, and the braking force Fb is generated only by the regenerative braking force of the drive electric motor that functions as a generator.

<Second unit YB>
A configuration example of the second unit YB included in the fluid unit HU will be described with reference to the schematic diagram of FIG. 3. The second unit YB is provided between the first unit YA and the wheel cylinder CW in the communication path HS (a fluid path for moving the brake fluid BF). The brake control device SC can adjust (increase, hold, decrease) the supply fluid pressure Pm by the second unit YB. That is, the second unit YB finally adjusts the fluid pressure Pw of the wheel cylinder CW. For example, the second unit YB is used for antilock brake control (control for suppressing locking of the wheels WH), traction control (control for suppressing slippage of the wheels WH), and vehicle stability control (control for suppressing excessive understeer and oversteer). The second unit YB is composed of a supply fluid pressure sensor PM, a pressure regulating valve UB, a return fluid pump QB, a return electric motor MB, a pressure regulating reservoir RC, an inlet valve UI, and an outlet valve VO.

Like the first unit YA, the second unit YB is also controlled by the brake controller ECU. In detail, the controller ECU calculates the drive signal Ub of the pressure regulating valve UB, the drive signal Ui of the inlet valve UI, the drive signal Vo of the outlet valve VO, and the drive signal Mb of the recirculation electric motor MB based on the various signals (Ba, etc.) described above. Then, in response to these drive signals (Ub, etc.), the solenoid valves "UB, UI, VO" constituting the second unit YB and the recirculation electric motor MB are controlled (driven).

Front and rear wheel pressure regulating valves UBf, UBr (= UB) are provided in the front and rear wheel connection passages HSf, HSr (= HS). The pressure regulating valve UB (solenoid valve) is a normally open linear valve (also called a "differential pressure valve" or "proportional valve"). The upper part of the pressure regulating valve UB (the part of the connection passage HS closer to the first unit YA) and the lower part of the pressure regulating valve UB (the part of the connection passage HS closer to the wheel cylinder CW) are connected by the front and rear wheel return passages HKf, HKr (= HK). The return passage HK is provided with front and rear wheel return fluid pumps QBf, QBr (= QB) and front and rear wheel pressure regulating reservoirs RCf, RCr (= RC). The return fluid pump QB is driven by a return electric motor MB. A supply fluid pressure sensor PM is provided above the pressure regulator valve UB to detect the actual fluid pressure (supply fluid pressure) Pm supplied by the first unit YA.

When the electric motor MB is driven to rotate, the fluid pump QB sucks in brake fluid BF from the top of the pressure regulating valve UB and discharges brake fluid BF to the bottom of the pressure regulating valve UB. As a result, a return flow KN of brake fluid BF (i.e., front and rear wheel return flows KNf and KNr, which are a circulating flow of brake fluid BF) is generated in the communication path HS and the return path HK, including the pressure regulating reservoir RC. When the return flow KN of brake fluid BF is throttled by the pressure regulating valve UB, the orifice effect increases the hydraulic pressure Pq (referred to as the "adjusted hydraulic pressure") at the bottom of the pressure regulating valve UB from the hydraulic pressure Pm (supply hydraulic pressure) at the top of the pressure regulating valve UB. In other words, the second unit YB can increase the front and rear wheel brake hydraulic pressures Pwf and Pwr (=Pw) from the supply hydraulic pressure Pm. In the second unit YB, the reflux electric motor MB, the reflux fluid pump QB, and the pressure regulator valve UB are referred to as the "pressure source KB."

Inside the second unit YB, the front and rear wheel communication passages HSf and HSr are each branched into two and connected to the front and rear wheel cylinders CWf and CWr. An inlet valve UI and an outlet valve VO are provided for each wheel cylinder CW. The inlet valve UI (solenoid valve) is a normally open linear valve, like the pressure regulating valve UB. However, the pressure regulating valve UB and the inlet valve UI open in different directions. In detail, the pressure regulating valve UB opens in response to the flow of brake fluid BF from the wheel cylinder CW to the master cylinder CM, so that in the pressure regulation by the pressure regulating valve UB, the regulated fluid pressure Pq is equal to or greater than the supply fluid pressure Pm (i.e., "Pq ≧ Pm"). On the other hand, the inlet valve UI opens in response to the flow from the master cylinder CM to the wheel cylinder CW, so that in the pressure regulation by the inlet valve UI, the brake fluid pressure Pw is equal to or less than the regulated fluid pressure Pq (i.e., "Pq ≧ Pw").

The inlet valve UI is provided in the branched communication passage HS (i.e., the side closer to the wheel cylinder CW than the branch of the communication passage HS). The communication passage HS is connected to the pressure regulating reservoir RC via a pressure reduction passage HG at the lower part of the inlet valve UI (the part of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO, which is a normally closed on/off valve, is disposed in the pressure reduction passage HG.

The inlet valve UI and outlet valve VO are individually controlled so that the brake fluid pressure Pw is adjusted separately for each wheel cylinder CW. To reduce the brake fluid pressure Pw, the inlet valve UI is closed and the outlet valve VO is opened. The inflow of brake fluid BF into the wheel cylinder CW is prevented, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RC, so that the brake fluid pressure Pw is reduced. To increase the brake fluid pressure Pw, the inlet valve UI is opened and the outlet valve VO is closed. The outflow of brake fluid BF to the pressure regulating reservoir RC is prevented, and the adjusted hydraulic pressure Pq from the pressure regulating valve UB is supplied to the wheel cylinder CW, so that the brake fluid pressure Pw is increased. To maintain the brake fluid pressure Pw, both the inlet valve UI and the outlet valve VO are closed. The wheel cylinder CW is fluidly sealed, so the braking fluid pressure Pw is maintained constant.

<Adjustment of Brake Fluid Pressure Pw in Off-Road Control>
The adjustment process of the brake fluid pressure Pw in the off-road control will be described with reference to the flow diagram of Figure 4. As described above, the off-road control is a general term for the downhill assist control and the crawl control, but the process will be described below using the crawl control as an example. Note that the explanation of the downhill assist control corresponds to the explanation of the control with "Xc" replaced with "Xd" and "vc" replaced with "vd".

In step S110, various signals including the operation signal Xc for crawl control, wheel speed Vw, vehicle speed Vx, servo hydraulic pressure Pu, supply hydraulic pressure Pm, etc. are read. Here, the vehicle speed Vx is calculated by the brake controller ECU based on the wheel speed Vw and a known method. In addition, the operation signal Xc includes a signal related to whether or not crawl control is to be performed, and information on the set speed vc for crawl control.

In step S120, it is determined whether crawl control (i.e., off-road control) is activated (whether or not there is an activation request) based on the operation signal (switch signal) Xc, etc. If the switch signal Xc requests activation of crawl control, step S120 is judged as positive, and the process proceeds to step S130. On the other hand, if step S120 is judged as negative, the process returns to step S110.

In step S130, the target hydraulic pressure Pt of each wheel cylinder CW is calculated based on the deviation hV between the actual vehicle speed Vx and the set speed vc (the target value of the vehicle speed Vx in crawl control). That is, in crawl control, the brake hydraulic pressure Pw is adjusted individually for each wheel cylinder CW. In detail, the deviation hV between the vehicle speed Vx and the set speed vc is calculated (i.e., "hV = Vx - vc"). Here, the set speed vc is the target value of the vehicle speed Vx in crawl control. Based on the speed deviation hV, the target total braking force Fvt, which is the target value of the braking force acting on the entire vehicle (the sum of the braking forces of the four wheels), is calculated. Furthermore, the distribution ratio Hw of each wheel WH is determined, and the target total braking force Fvt is multiplied by the ratio Hw to determine the target value (target braking force) Fbt of the braking force Fb of each wheel WH (i.e., "Fbt = Fvt Hw"). Finally, the target braking force Fbt is converted into the dimension of hydraulic pressure in each wheel cylinder CW based on the specifications of the brake device SX, the brake control device SC, etc., and the target hydraulic pressure Pt corresponding to the brake hydraulic pressure Pw is calculated. For example, the distribution ratio Hw can be set to "0.25" so that it is uniform among the four wheels WH. Also, the distribution ratio Hwf of the front wheels WHf may be set to be greater than the distribution ratio Hwr of the rear wheels WHr.

In addition, at least one of the following five corrections is taken into consideration in calculating the target braking force Fbt of each wheel WH. Then, the final target hydraulic pressure Pt is determined according to the corrected target braking force Fbt.
(Correction 1): The smaller the set speed vc, the greater the distribution ratio of the braking force to the front wheels WHf.
(Correction 2): When the set speed vc is set in a small range (low speed range), a lower limit value fbl (referred to as the "lower limit braking force") is set for the braking force Fb. Then, at least the lower limit braking force fbl is generated on each wheel WH.
(Correction 3): When the vehicle speed Vx exceeds the set speed vc, a lower limit braking force fbl is set, and at least the lower limit braking force fbl is generated on each wheel WH.
(Correction 4): When the driving force Fd is greater than a predetermined value, a lower limit braking force fbl is set, and at least the lower limit braking force fbl is generated on each wheel WH.
(Correction 5): If the vehicle stops during control, the reduction in braking force is limited for a predetermined time after the vehicle stops.

In step S140, the selected wheel cylinder CWx and the non-selected wheel cylinder CWz are determined. The "selected wheel cylinder CWx" is the wheel cylinder CW that corresponds to the maximum value Ptx (also called the "maximum target hydraulic pressure") among the multiple target hydraulic pressures Pt. The "non-selected wheel cylinder CWz" is the wheel cylinder CW other than the selected wheel cylinder CWx among the wheel cylinders CW. In other words, one of the four wheel cylinders CW provided on the wheels WH of the vehicle JV is the selected wheel cylinder CWx, and the remaining three are the non-selected wheel cylinders CWz.

In the following description, the subscript "x" indicates that the wheel cylinder CW corresponds to the selected wheel cylinder CWx, and the subscript "z" indicates that the wheel cylinder CW corresponds to the non-selected wheel cylinder CWz. Therefore, among the four actual brake fluid pressures Pw, the actual brake fluid pressure of the selected wheel cylinder CWx is referred to as the "selected brake fluid pressure Pwx," and the actual brake fluid pressure of the non-selected wheel cylinder CWz is referred to as the "non-selected brake fluid pressure Pwz." Furthermore, among the four target brake fluid pressures Pt, the one that corresponds to the non-selected wheel cylinder CWz is referred to as the "non-selected target brake fluid pressure Ptz." In addition, since the maximum target hydraulic pressure Ptx (the target hydraulic pressure corresponding to the selected wheel cylinder) is the maximum value of the target hydraulic pressure Pt, the magnitude relationship between the non-selected target hydraulic pressure Ptz (resulting in the actual non-selected braking hydraulic pressure Pwz) and the maximum target hydraulic pressure Ptx (resulting in the actual selected braking hydraulic pressure Pwx) is "Ptz ≦ Ptx, Pwz ≦ Pwx".

Among the components provided corresponding to each of the four wheel cylinders CW, the suffix "x" is given to the components corresponding to the selected wheel cylinder CWx, and the suffix "z" is given to the components corresponding to the non-selected wheel cylinder CWz (i.e., the components not corresponding to the selected wheel cylinder CWx). For example, among the four inlet valves UI and outlet valve VO, the components corresponding to the selected wheel cylinder CWx are referred to as the "selected inlet valve UIx" and the "selected outlet valve VOx". On the other hand, among the four inlet valves UI and outlet valve VO, the components corresponding to the non-selected wheel cylinder CWz are referred to as the "non-selected inlet valve UIz" and the "non-selected outlet valve VOz".

Furthermore, the brake control device SC employs two brake fluid paths, with the suffix "x" attached to the components of the path that includes the selected wheel cylinder CWx, and the suffix "z" attached to the components of the path that does not include the selected wheel cylinder CWx. For example, among the two communication paths HS, the pressure regulating valve UB, the pressure regulating reservoir RC, and the fluid pump QB, the components that belong to the path that includes the selected wheel cylinder CWx are referred to as the "selected communication path HSx," the "selected pressure regulating valve UBx," the "selected pressure regulating reservoir RCx," and the "selected fluid pump QBx." On the other hand, among the two communication paths HS, the pressure regulating valve UB, the pressure regulating reservoir RC, and the fluid pump QB, the components that belong to the path that does not include the selected wheel cylinder CWx are referred to as the "non-selected communication path HSz," the "non-selected pressure regulating valve UBz," the "non-selected pressure regulating reservoir RCz," and the "non-selected fluid pump QBz."

In step S150, the selected brake fluid pressure Pwx (the actual hydraulic pressure of the selected wheel cylinder CWx) is adjusted based on the maximum target hydraulic pressure Ptx (the maximum value of the four target hydraulic pressures Pt). The selected brake fluid pressure Pwx is achieved by controlling the first unit YA. That is, the pressurizing unit KU of the first unit YA is controlled (driven) so that the actual selected brake fluid pressure Pwx coincides with the maximum target hydraulic pressure Ptx. In detail, a target value Pv (also called "target servo hydraulic pressure") of the servo fluid pressure Pu corresponding to the maximum target hydraulic pressure Ptx is calculated, and the pressure increase valve UZ and the pressure reduction valve UG are controlled (so-called hydraulic feedback control) so that the actual servo fluid pressure Pu (detection value of the servo fluid pressure sensor PU) coincides with the target servo fluid pressure Pv (target value). In the selected wheel cylinder CWx, the inlet valve UI and the outlet valve VO are de-energized and are fully open (i.e., at their maximum opening). Therefore, the selected brake fluid pressure Pwx is equal to the supply fluid pressure Pm.

In step S160, the non-selected brake fluid pressure Pwz (the actual hydraulic pressure of the non-selected wheel cylinder CWz) is adjusted based on the target hydraulic pressure Ptz of the non-selected wheel cylinder CWz. The non-selected brake fluid pressure Pwz is achieved by controlling the inlet valve UIz (referred to as the "non-selected inlet valve") and the outlet valve VOz (referred to as the "non-selected outlet valve") in the second unit YB. In other words, the non-selected inlet valve UIz and the non-selected outlet valve VOz are controlled (driven) so that the actual non-selected brake fluid pressure Pwz coincides with the non-selected target hydraulic pressure Ptz of the non-selected wheel cylinder CWz. In addition, in the adjustment of the non-selected brake fluid pressure Pwz, the first unit YA is used as the pressure source. Therefore, in the second unit YB, hydraulic pressure adjustment is performed based on the supply hydraulic pressure Pm from the first unit YA.

In detail, one of three control modes, "decrease mode", "increase mode" and "hold mode", is selected for adjusting the non-selected brake fluid pressure Pwz. In the decrease mode, when it is necessary to decrease the non-selected brake fluid pressure Pwz, the non-selected inlet valve UIz is closed and the non-selected outlet valve VOz is opened. The upper part of the non-selected inlet valve UIz (the side closer to the first unit YA) is supplied with the supply fluid pressure Pm corresponding to the maximum target fluid pressure Ptx, but since the non-selected inlet valve UIz is closed, this supply is prevented. Then, since the non-selected outlet valve VOz is opened, the brake fluid BF in the non-selected wheel cylinder CWz flows out to the pressure regulating reservoir RC, and the non-selected brake fluid pressure Pwz is decreased.

In the increase mode, when it is necessary to increase the non-selected brake fluid pressure Pwz, the non-selected outlet valve VOz is closed and the non-selected inlet valve UIz is opened. Closing the non-selected outlet valve VOz prevents the brake fluid BF from flowing out to the pressure regulating reservoir RC. Then, the supply fluid pressure Pm is supplied to the non-selected wheel cylinder CWz through the non-selected inlet valve UIz, so the brake fluid pressure Pwz is increased. Note that the adjustment of the non-selected brake fluid pressure Pwz is based on the supply fluid pressure Pm (=Pwx) generated by the first unit YA, so the upper limit of the non-selected brake fluid pressure Pwz is the selected brake fluid pressure Pwx (i.e., "Pwz≦Pwx").

In the hold mode, when it is necessary to hold the non-selected brake fluid pressure Pwz, both the non-selected inlet valve UIz and the non-selected outlet valve VOz are closed. Since the non-selected wheel cylinder CWz is fluidically sealed, the non-selected brake fluid pressure Pwz is maintained constant. Note that the hold mode may be omitted when adjusting the non-selected brake fluid pressure Pwz. In this case, the decrease mode and the increase mode are alternately performed to adjust the brake fluid pressure Pwz of the non-selected wheel cylinder CWz.

In step S170, the return electric motor MB is driven. When adjusting the non-selected brake fluid pressure Pwz (particularly in the decrease mode), the brake fluid BF is reduced in pressure by flowing out to the pressure regulating reservoir RC, but the return fluid pump QB is rotated by the return electric motor MB to return the brake fluid BF accumulated in the pressure regulating reservoir RC to the communication path HS between the pressure regulating valve UB and the inlet valve UI.

In step S170, the electric motor MB may be driven/stopped based on the amount of brake fluid BF in the pressure regulating reservoir RC (referred to as the "reservoir fluid amount Ec") to suppress heat generation from the electric motor MB. Specifically, when the reservoir fluid amount Ec is less than a predetermined fluid amount ex, the electric motor MB is stopped. When the reservoir fluid amount Ec is equal to or greater than the predetermined fluid amount ex, the electric motor MB is energized and the fluid pump QB is driven. Here, the predetermined fluid amount ex is a preset value (constant). The reservoir fluid amount Ec is estimated based on the drive state of the outlet valve VOz (e.g., the valve opening time), the drive state of the electric motor MB, etc.

<Structures of the inlet valve UI and the pressure regulating valve UB>
5A and 5B, the inlet valve UI and the pressure regulating valve UB will be described. The inlet valve UI and the pressure regulating valve UB are normally open linear valves (solenoid valves) and are controlled by the brake controller ECU.

<Structure of inlet valve UI>
First, the structure of the inlet valve UI will be described with reference to the schematic diagram of Fig. 5(a). In the inlet valve UI, the valve opening amount (lift amount) Li decreases as the amount of current Ii (e.g., current value) increases. The inlet valve UI is composed of a solenoid SD, a valve body VT, a guide member GD, a holding member HJ, and a spring member SB.

The solenoid SD is composed of a fixed coil CL and a plunger (movable iron core) PL. The fixed coil CL is fixed to the housing (e.g., guide member GD) of the inlet valve UI. A valve body VT is fixed to the plunger PL. The tip Vt of the valve body VT is formed (machined) into a spherical shape. In the inlet valve UI, the gap (i.e., the valve opening amount) Li between the spherical tip Vt and the valve seat Vz, which is formed (machined) into a conical shape on the holding member HJ described below, is linearly controlled according to the amount of electricity (current value) passed through the fixed coil CL. This linear control utilizes the force Ca (downward thrust in the figure, called "suction force") that draws the plunger PL into the fixed coil CL when current is passed through the fixed coil CL.

The guide member GD has two holes with different diameters. The smaller of the two holes is called the "guide hole Ag" and the larger of the two holes is called the "sealing hole Af". The valve body VT is inserted into the guide hole Ag of the guide member GD so that it can move smoothly along its central axis Jv. In the guide member GD, the sealing hole Af, which is located on the side opposite the plunger PL, is sealed by a retaining member HJ. Specifically, the retaining member HJ is pressed into the cylindrical inner periphery of the sealing hole Af.

The valve chamber Rz is formed by the inner periphery of the sealing hole Af of the guide member GD, the end face of the holding member HJ, and the valve body VT. A conical valve seat Vz is formed on the end face of the holding member HJ on the side of the valve chamber Rz. Here, the conical surface of the valve seat Vz faces the wheel cylinder CW in the communication passage HS. An inlet hole Ai is provided in the center of the valve seat Vz. Brake fluid BF adjusted to the regulated hydraulic pressure Pq by the pressure regulating valve UB is supplied to the inlet hole Ai. The inlet hole Ai is connected to the return fluid pump QB via the return passage HK. A check valve is provided on the holding member HJ from the valve chamber Rz side to the return fluid pump QB side so that the brake fluid BF can move.

A spring member SB (e.g., a compression coil spring) is provided between the retaining member HJ and the valve body VT to press the valve body VT toward the plunger PL. The spring member SB presses the valve body VT toward the plunger PL with an elastic force Cs (upward thrust in the figure). Here, the plunger PL, valve body VT (tip Vt), spring member SB, valve seat Vz, and inlet hole Ai are arranged coaxially on the central axis Jv. Therefore, the suction force Ca and the elastic force Cs oppose each other on the central axis Jv.

An outflow hole Ao is provided on the inner periphery of the sealing hole Af that forms the valve chamber Rz. The outflow hole Ao is connected to the wheel cylinder CW via a communication passage HS. Brake fluid BF adjusted to the brake fluid pressure Pw by the inlet valve UI (i.e., the tip Vt and the gap Li between the valve seat Vz) is supplied from the outflow hole Ao to the wheel cylinder CW. In the communication passage HS, the space between the outflow hole Ao and the wheel cylinder CW is connected to the return fluid pump QB via the pressure reduction passage HG and the outlet valve VO. In the pressure reduction passage HG, a pressure adjustment reservoir RC is connected between the outlet valve VO and the return fluid pump QB.

When the power supply to the fixed coil CL is stopped (i.e., when Ii = 0), the suction force Ca is not generated and the valve body VT is pressed toward the solenoid SD (plunger PL, fixed coil CL) by the elastic force Cs. Therefore, the tip Vt of the valve body VT is separated from the valve seat Vz. In other words, the inlet valve UI is completely open.

When the fixed coil CL is energized, an attractive force Ca is generated. This attractive force Ca presses the tip Vt of the valve body VT toward the valve seat Vz, and the inlet valve UI is about to close. At this time, in addition to the elastic force Cs, the valve body VT is subjected to a force Cb (an upward thrust in FIG. 5A, called the "fluid force") that causes the brake fluid BF to flow from the pressure regulating valve UB to the wheel cylinder CW. In the inlet valve UI, the difference wQ (differential pressure) between the hydraulic pressure (adjusted hydraulic pressure) Pq on the pressure regulating valve UB side and the hydraulic pressure (braking hydraulic pressure) Pw on the wheel cylinder CW side is determined when the combined force Cg of the fluid force Cb and the elastic force Cs and the attractive force Ca are in balance. In other words, the relationship between the amount of electricity Ii to the inlet valve UI and the hydraulic pressure difference wQ (= Pq - Pw) is uniquely determined.

<Structure of pressure adjusting valve UB>
Next, the structure of the pressure regulating valve UB will be described with reference to Fig. 5(a). In Fig. 5(a), the symbols in [ ] correspond to the description of the pressure regulating valve UB. As with the inlet valve UI, in the pressure regulating valve UB, the valve opening amount Lb (the gap between the valve seat Vz and the valve body tip portion Vt in the pressure regulating valve UB) decreases as the amount of current Ib (e.g., the current value) increases. The structure of the pressure regulating valve UB is basically the same as that of the inlet valve UI. The difference between the pressure regulating valve UB and the inlet valve UI is the method of connection in the fluid path. This difference will be briefly described below.

The inlet port Ai of the inlet valve UI is connected to the pressure regulating valve UB, while the inlet port Ai of the pressure regulating valve UB is connected to the inlet valve UI. Therefore, the inlet port Ai of the inlet valve UI and the inlet port Ai of the pressure regulating valve UB are connected via the communication path HS. The outlet port Ao of the inlet valve UI is connected to the wheel cylinder CW, while the inlet port Ai of the pressure regulating valve UB is connected to the master cylinder CM. Therefore, in the pressure regulating valve UB, when the suction force Ca and the resultant force Cg (= Cb + Cs) are in balance, the difference mQ (differential pressure) between the hydraulic pressure (adjusted hydraulic pressure) Pq on the inlet valve UI side and the hydraulic pressure (supplied hydraulic pressure) Pm on the master cylinder CM side is determined. In other words, the relationship between the amount of current Ib to the pressure regulating valve UB and the hydraulic pressure difference mQ (= Pq - Pm) is uniquely determined. The conical valve seat surface Vz of the inlet valve UI faces the wheel cylinder CW, while the conical valve seat surface Vz of the pressure regulating valve UB faces the master cylinder CM. This determines the magnitude relationship between the supply hydraulic pressure Pm, the adjustment hydraulic pressure Pq, and the braking hydraulic pressure Pw.

<<Relationship between the supply hydraulic pressure Pm, the adjusted hydraulic pressure Pq, and the brake hydraulic pressure Pw>>
The magnitude relationship (i.e., the range in which hydraulic pressure can be generated) between the supply hydraulic pressure Pm, the adjusted hydraulic pressure Pq, and the braking hydraulic pressure Pw will be described with reference to the schematic diagram (partial hydraulic circuit diagram) in Fig. 5(b). As described above, the master cylinder CM and the wheel cylinders CW of the first unit YA are connected via the communication passage HS. In the communication passage HS, an inlet valve UI and a pressure regulating valve UB are arranged in order from the wheel cylinder CW. That is, the inlet valve UI is provided in the communication passage HS between the master cylinder CM and the wheel cylinder CW. And, the pressure regulating valve UB is provided in the communication passage HS between the master cylinder CM and the inlet valve UI.

The magnitude relationship between the supply fluid pressure Pm, the regulated fluid pressure Pq, and the brake fluid pressure Pw depends on the direction in which the suction force Ca acts in the inlet valve UI and the pressure regulating valve UB. Specifically, in the inlet valve UI, the valve seat surface Vz (conical surface) faces the wheel cylinder CW in the communication passage HS. The suction force Ca of the inlet valve UI presses the valve body tip Vt against the valve seat Vz. In other words, the suction force Ca of the inlet valve UI is generated in a direction opposed to the fluid force Cb corresponding to the flow of brake fluid BF from the master cylinder CM side to the wheel cylinder CW side. Therefore, when the inlet valve UI is energized, the hydraulic pressure Pq on the master cylinder CM side relative to the inlet valve UI (the adjusted hydraulic pressure between the pressure regulator valve UB and the inlet valve UI) is always equal to or greater than the hydraulic pressure (braking hydraulic pressure) Pw on the wheel cylinder CW side relative to the inlet valve UI (i.e., "Pq ≧ Pw"). In other words, the inlet valve UI can adjust the braking hydraulic pressure Pw within a range equal to or less than the adjusted hydraulic pressure Pq. Since the inlet valve UI is a normally open type, the inlet valve UI is fully opened when "Ii = 0". In other words, when "Ii = 0", the opening amount Li of the inlet valve UI is at its maximum, and "Pw = Pq" is achieved).

In the pressure regulating valve UB, the valve seat surface Vz (conical surface) faces the master cylinder CM in the communication passage HS. In the pressure regulating valve UB, the valve seat Vz faces in the opposite direction to the inlet valve UI, so the suction force Ca of the pressure regulating valve UB is generated in a direction that opposes the fluid force Cb corresponding to the flow of brake fluid BF from the wheel cylinder CW side to the master cylinder CM side. Therefore, when the pressure regulating valve UB is energized, the hydraulic pressure Pq on the wheel cylinder CW side relative to the pressure regulating valve UB (the adjusted hydraulic pressure between the pressure regulating valve UB and the inlet valve UI) is always equal to or greater than the hydraulic pressure (supply hydraulic pressure) Pm on the master cylinder CM side relative to the pressure regulating valve UB (i.e., "Pq ≧ Pm"). In other words, the adjusted hydraulic pressure Pq can be adjusted by the pressure regulating valve UB in a range equal to or greater than the supply hydraulic pressure Pm. In addition, the pressure regulating valve UB is also a normally open type like the inlet valve UI, so when "Ib = 0", the pressure regulating valve UB is fully open. In other words, when "Ib = 0", the opening amount Lb of the pressure regulating valve UB is at its maximum, and "Pw = Pq" is achieved.

<Processing of Fluctuation Suppression Control>
The calculation process of the fluctuation suppression control will be described with reference to the block diagram of FIG. 6. The "fluctuation suppression control" suppresses fluctuations in the selected brake hydraulic pressure Pwx in the selected wheel cylinder CWx. The algorithm of the fluctuation suppression control is programmed in the microprocessor MP of the brake controller ECU. The following description of the fluctuation suppression control targets the selected wheel cylinder CWx (the wheel cylinder CW corresponding to the maximum target hydraulic pressure Ptx). Therefore, unless otherwise specified, "CW" stands for "CWx", "Pw" stands for "Pwx", "Pq" stands for "Pqx", "UI" stands for "UIx", "UB" stands for "UBx", "Iit" stands for "Iitx", "Ii" stands for "Iix", "Ibt" stands for "Ibtx", "Ib" stands for "Ibx", "II" stands for "IIx", and "IB" stands for "IBx".

First, the cause of the fluctuation in the selected brake fluid pressure Pwx will be explained. As described above, the hydraulic pressure Pwx of the selected wheel cylinder CWx is increased or decreased by the first unit YA (particularly, the pressurizing unit KU). Specifically, the supply hydraulic pressure Pm generated by the first unit YA is supplied to the selected wheel cylinder CWx as the selected brake fluid pressure Pwx. On the other hand, the hydraulic pressure Pwz of the non-selected wheel cylinder CWz is adjusted by the non-selected inlet valve UIz and the non-selected outlet valve VOz. When the non-selected brake fluid pressure Pwz is controlled, the amount (fluid volume) of brake fluid BF fluctuates in the fluid path (HS, etc.). Specifically, when it is necessary to increase the non-selected brake fluid pressure Pwz, the non-selected inlet valve UIz is opened and brake fluid BF is moved to the non-selected wheel cylinder CWz. When it is necessary to maintain the non-selected brake fluid pressure Pwz, the non-selected inlet valve UIz and the non-selected outlet valve VOz are both closed, so that the brake fluid BF is not consumed in the non-selected wheel cylinder CWz. When it is necessary to reduce the non-selected brake fluid pressure Pwz, the non-selected inlet valve UIz is closed and the non-selected outlet valve VOz is opened, so that the brake fluid BF is moved from the non-selected wheel cylinder CWz to the pressure regulating reservoir RC. Furthermore, when the amount of brake fluid BF (reservoir fluid amount) Ec in the pressure regulating reservoir RC becomes large, the electric motor MB is driven, and the brake fluid BF is returned between the pressure regulating valve UB and the inlet valve UI by the fluid pump QB. In this way, in the communication passage HSx related to the selected wheel cylinder CWx, a change in the amount of brake fluid BF occurs as a disturbance, in addition to the adjustment of the supply hydraulic pressure Pm (=Pwx). This change in fluid volume causes fluctuations in the supply fluid pressure Pm (and thus the selected braking fluid pressure Pwx). Fluctuation suppression control suppresses fluid pressure fluctuations in the selected braking fluid pressure Pwx.

The fluctuation suppression control is composed of a hydraulic pressure deviation calculation block HP, a target current calculation block IIT for the inlet valve UI, a target current calculation block IBT for the pressure regulating valve UB, and a current feedback control block IFB.

The hydraulic pressure deviation calculation block HP calculates the deviation hP between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx. Specifically, the hydraulic pressure deviation hP is a state quantity (state variable) determined by subtracting the maximum target hydraulic pressure Ptx from the supply hydraulic pressure Pm (the detection value of the supply hydraulic pressure sensor PM) (i.e., "hP = Pm - Ptx"). If the hydraulic pressure deviation hP has a positive sign (i.e., if the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx), the hydraulic pressure deviation hP is input to the target current calculation block IIT related to the inlet valve UI. Conversely, if the hydraulic pressure deviation hP has a negative sign (i.e., if the supply hydraulic pressure Pm is less than the maximum target hydraulic pressure Ptx), the hydraulic pressure deviation hP is input to the target current calculation block IBT related to the pressure regulating valve UB.

In the target current calculation block IIT (also referred to as the "first target current calculation block") for the inlet valve UI, the target current Iit (also referred to as the "first target current") for the inlet valve UI is calculated based on the magnitude (absolute value) |hP| of the hydraulic pressure deviation hP. The first target current Iit is a target value corresponding to the actual current Ii (also referred to as the "first current") for adjusting the brake hydraulic pressure Pw from the adjustment hydraulic pressure Pq by the inlet valve UI to bring the actual selected brake hydraulic pressure Pwx closer to the maximum target hydraulic pressure Ptx. In detail, the IP characteristic (known characteristic representing the relationship between the current Ii and the hydraulic pressure difference wQ) of the inlet valve UI is preset as a calculation map Zii in the first target current calculation block IIT. Then, according to the calculation map Zii, the target current Iit is calculated so that the larger the magnitude |hP| of the hydraulic pressure deviation hP, the larger the target current Iit. In other words, the target current Iit is a target value for generating a hydraulic pressure difference wQ (the difference between the adjusted hydraulic pressure Pq and the braking hydraulic pressure Pw) equivalent to the hydraulic pressure deviation hP to compensate for the excess of the selected braking hydraulic pressure Pwx relative to the maximum target hydraulic pressure Ptx. Note that in the first target current calculation block IIT for the inlet valve UI, the pressure regulating valve UB cannot reduce the adjusted hydraulic pressure Pq from the supply hydraulic pressure Pm, so the target current Ibt for the pressure regulating valve UB is set to "0 (not energized)."

In the target current calculation block IBT (also referred to as the "second target current calculation block") for the pressure regulating valve UB, the target current Ibt (also referred to as the "second target current") of the pressure regulating valve UB is calculated based on the magnitude (absolute value) |hP| of the hydraulic pressure deviation hP. The second target current Ibt is a target value corresponding to the actual current Ib (also referred to as the "second current") for increasing and adjusting the regulated hydraulic pressure Pq from the supply hydraulic pressure Pm by the pressure regulating valve UB to bring the actual selected braking hydraulic pressure Pwx closer to the maximum target hydraulic pressure Ptx. In detail, the second target current calculation block IBT has the IP characteristic of the pressure regulating valve UB (a known characteristic representing the relationship between the current Ib and the hydraulic pressure difference mQ) preset as a calculation map Zib. Then, according to the calculation map Zib, the target current Ibt is calculated to be larger as the magnitude |hP| of the hydraulic pressure deviation hP increases. In other words, the target current Ibt is a target value for generating a hydraulic pressure difference mQ (the difference between the adjusted hydraulic pressure Pq and the supply hydraulic pressure Pm) equivalent to the hydraulic pressure deviation hP to compensate for the shortage of the selected braking hydraulic pressure Pwx relative to the maximum target hydraulic pressure Ptx. In addition, in the second target current calculation block IBT for the pressure regulating valve UB, the inlet valve UI cannot increase the adjusted hydraulic pressure Pq, so the target current Iit for the inlet valve UI is set to "0 (not energized)."

In the current feedback control block IFB, current feedback control is performed based on the first and second target current amounts Ibt and Iit, and power is supplied to the inlet valve UI and the pressure regulating valve UB. The drive circuit DD is provided with first and second current sensors (e.g., current sensors) II and IB to detect the actual first and second current amounts Ii and Ib of the inlet valve UI and the pressure regulating valve UB. When power is supplied to the inlet valve UI and the pressure regulating valve UB, the current feedback control block IFB of the drive circuit DD performs current feedback control so that the actual first and second current amounts Ii and Ib (detection values of the first and second current sensors II and IB) match the first and second target current amounts Iit and Ibt.

The pressure regulating valve UB is supplied with the supply fluid pressure Pm, which can adjust the adjusted fluid pressure Pq in a range equal to or greater than the supply fluid pressure Pm. The inlet valve UI is also supplied with the adjusted fluid pressure Pq, which can adjust the braking fluid pressure Pw in a range equal to or less than the adjusted fluid pressure Pq. If the supply fluid pressure Pm is greater than the maximum target fluid pressure Ptx, there is no need to increase the supply fluid pressure Pm. For this reason, no power is supplied to the pressure regulating valve UB, which is fully opened and set to a state of "Pm = Pq". The inlet valve UI then reduces the selected braking fluid pressure Pwx from the supply fluid pressure Pm (= Pq) so that it matches the maximum target fluid pressure Ptx. In the supply hydraulic pressure Pm, the excess hydraulic pressure component (i.e., the positive hydraulic pressure deviation hP) relative to the maximum target hydraulic pressure Ptx is compensated, and the compensated hydraulic pressure is supplied to the selected wheel cylinder CWx as the selected braking hydraulic pressure Pwx.

When the supply hydraulic pressure Pm is smaller than the maximum target hydraulic pressure Ptx, there is no need to reduce the supply hydraulic pressure Pm, so no power is supplied to the inlet valve UI, which is fully opened and set to a state of "Pq = Pw". Then, the pressure regulator valve UB increases the brake hydraulic pressure Pw (= Pq) from the supply hydraulic pressure Pm so that it matches the maximum target hydraulic pressure Ptx. In the supply hydraulic pressure Pm, the insufficient hydraulic pressure component (i.e., the hydraulic pressure deviation hP with a negative sign) relative to the maximum target hydraulic pressure Ptx is compensated for, and the compensated hydraulic pressure is supplied to the selected wheel cylinder CWx as the selected brake hydraulic pressure Pwx.

As explained above, the fluctuation suppression control does not suppress fluctuations in the supply hydraulic pressure Pm. However, when the supply hydraulic pressure Pm is transmitted to the selected wheel cylinder CWx as the selected brake hydraulic pressure Pwx, the excess or deficiency relative to the maximum target hydraulic pressure Ptx is compensated for by adjusting the opening amounts Li and Lb of the inlet valve UI and the pressure regulating valve UB based on the hydraulic pressure deviation hP (i.e., adjusting the actual first and second current amounts Ii and Ib to the inlet valve UI and the pressure regulating valve UB), thereby reducing hydraulic pressure fluctuations in the selected brake hydraulic pressure Pwx. As a result, the influence of fluctuations in the supply hydraulic pressure Pm is reduced in the selected wheel cylinder CWx, so the control accuracy of the selected brake hydraulic pressure Pwx is improved and the performance of off-road control is improved.

<Operation of Fluctuation Suppression Control>
The operation of the fluctuation suppression control will be described with reference to the time series diagram of Fig. 7 (a diagram showing changes in state quantities accompanying transitions in time T). The upper part of Fig. 7 shows the maximum target hydraulic pressure Ptx (shown by a dashed line), the supply hydraulic pressure Pm (shown by a solid line), and the selected brake hydraulic pressure Pwx (shown by a dashed line).

Just before time t1, the supply hydraulic pressure Pm is approximately equal to the maximum target hydraulic pressure Ptx. After that, due to fluctuations in the supply hydraulic pressure Pm, the supply hydraulic pressure Pm becomes greater than the maximum target hydraulic pressure Ptx, and a deviation hP (=Pm-Ptx) between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx begins to occur. At time t1, when the hydraulic pressure deviation hP exceeds the dead zone of the fluctuation suppression control (a region for suppressing hunting in the control, a predetermined control threshold), the fluctuation of the supply hydraulic pressure Pm is suppressed by the selective inlet valve UIx. Specifically, since the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx and the hydraulic pressure deviation hP has a positive sign, no current is applied to the selective pressure regulating valve UBx, and the selective inlet valve UIx is driven according to the first target current Iit calculated based on the hydraulic pressure deviation hP. Here, the selective pressure regulating valve UBx is one of the two pressure regulating valves UB that is provided in the communication passage HSx that includes the selected wheel cylinder CWx. The selective inlet valve UIx is one of the four inlet valves UI that corresponds to the selected wheel cylinder CWx. Since the supply hydraulic pressure Pm is reduced and adjusted by the selective inlet valve UIx, the selective braking hydraulic pressure Pwx is controlled to approach and match the maximum target hydraulic pressure Ptx. At time t2, the hydraulic pressure deviation hP falls below the control threshold value and enters the dead zone, so that the drive of the selective inlet valve UIx that was energized is stopped.

After time t3, the supply hydraulic pressure Pm becomes smaller than the maximum target hydraulic pressure Ptx due to the fluctuation of the supply hydraulic pressure Pm, and a deviation hP (=Pm-Ptx) between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx begins to occur. When the hydraulic pressure deviation hP exceeds the dead band of the fluctuation suppression control at time t3, the fluctuation of the supply hydraulic pressure Pm is now suppressed by the selective pressure regulating valve UBx. Specifically, since the supply hydraulic pressure Pm is smaller than the maximum target hydraulic pressure Ptx and the hydraulic pressure deviation hP has a negative sign, no current is applied to the selective inlet valve UIx, and the selective pressure regulating valve UBx is driven according to the second target current Ibt calculated based on the hydraulic pressure deviation hP. As a result, the supply hydraulic pressure Pm is increased and adjusted by the selective pressure regulating valve UBx, so that the selective braking hydraulic pressure Pwx approaches and is controlled to match the maximum target hydraulic pressure Ptx. At time t4, the hydraulic pressure deviation hP enters the dead zone, and the selective pressure regulating valve UBx is deactivated.

After time t4, when "Pm>Ptx" and the hydraulic pressure deviation hP exceeds the dead band (predetermined threshold), the selective inlet valve UIx is operated (energized) and the selective pressure regulating valve UBx is deactivated (de-energized), thereby decreasing the supply hydraulic pressure Pm and suppressing fluctuations in the selected braking hydraulic pressure Pwx (see time t5-t6). On the other hand, when "Pm<Ptx" and the hydraulic pressure deviation hP exceeds the dead band (predetermined threshold), the selective pressure regulating valve UBx is operated (energized) and the selective inlet valve UIx is deactivated (de-energized), thereby increasing the supply hydraulic pressure Pm and suppressing fluctuations in the selected braking hydraulic pressure Pwx (see time t7-t8).

In the communication path HS leading from the master cylinder CM to the wheel cylinder CW, pressure fluctuations (particularly fluctuations in the supply hydraulic pressure Pm) occur due to changes in the amount of brake fluid BF consumed by the non-selected wheel cylinder CWz. In the fluctuation suppression control, the supply hydraulic pressure Pm is increased by the selective pressure regulating valve UBx and decreased by the selective inlet valve UIx based on the hydraulic pressure deviation hP. The fluctuations in the supply hydraulic pressure Pm are not transmitted directly to the selected wheel cylinder CWx, but are attenuated by the selective inlet valve UIx and the selective pressure regulating valve UBx and then transmitted to the selected wheel cylinder CWx. As a result, the selected brake hydraulic pressure Pwx is adjusted to approach and match the maximum target hydraulic pressure Ptx. The brake fluid pressure Pwx of the selected wheel cylinder CWx is basically adjusted (increased or decreased) by the first unit YA (i.e., the supply fluid pressure Pm), but is further adjusted by the selective inlet valve UIx and the selective pressure regulating valve UBx in response to the fluctuation suppression control. The fluctuation suppression control improves the pressure regulation accuracy in the selected wheel cylinder CWx, thereby improving the performance of off-road control.

As explained in step S170, the brake control device SC drives/stops the electric motor MB based on the reservoir hydraulic pressure Ec. Fluctuations in the supply hydraulic pressure Pm are caused by changes in the amount of brake fluid BF, and these changes are likely to occur when the electric motor MB (i.e., the fluid pump QB) starts/stops operation. Therefore, although stopping the electric motor MB is necessary to suppress heat generation in the electric motor MB, stopping the electric motor MB should not usually be performed frequently (when fluctuation suppression control is not applied) because it can cause hydraulic pressure fluctuations. However, by applying the fluctuation suppression control, fluctuations in the supply hydraulic pressure Pm can be suppressed, so the electric motor MB can be stopped proactively. In other words, the fluctuation suppression control also has the effect of suppressing heat generation in the electric motor MB.

<Other embodiments>
Other embodiments of the brake control device SC will be described below. The other embodiments also provide the same effect as described above (i.e., suppression of fluctuations in the hydraulic pressure Pw in the wheel cylinder CW caused by fluctuations in the hydraulic pressure Pm supplied from the first unit YA, which is the pressure source).

<Use of electric cylinder type pressure source>
In the above embodiment, the accumulator hydraulic pressure Pc stored in the accumulator AC is used as the first unit YA (pressurization source). Alternatively, the braking hydraulic pressure Pw may be increased by directly driving a piston inserted in a cylinder by an electric motor. A so-called electric cylinder type may be adopted as the first unit YA. The configuration of the electric cylinder type is publicly known, for example, from "WO2012/046703", and will be briefly described below. The electric cylinder type first unit YA is composed of a pressure regulating cylinder, a pressure regulating piston, a linear motion conversion mechanism, and an electric motor.

A pressure regulating cylinder (also called a "slave cylinder") is provided in addition to the master cylinder CM. The pressure regulating cylinder has the same configuration as the master cylinder CM, and is, for example, a tandem type cylinder. Two pressure regulating pistons are inserted into the pressure regulating cylinder via an elastic body (compression spring). One of the two pressure regulating pistons is connected to an electric motor via a linear motion conversion mechanism (for example, a screw mechanism). Here, the linear motion conversion mechanism converts the rotational power of the electric motor into linear power (thrust) of the pressure regulating piston.

The pressure adjusting piston is driven by the electric motor. In detail, when the electric motor rotates, its power is converted into linear power of the pressure adjusting piston by the linear motion conversion mechanism. The pressure adjusting cylinder is divided into two pressure adjusting chambers by two pressure adjusting pistons and a seal member. The two pressure adjusting chambers are connected to the wheel cylinder CW via the communication path HS and the second unit YB. Therefore, when the electric motor is driven, the volume of the pressure adjusting chamber is reduced, and the brake fluid BF is pumped from the pressure adjusting chamber to the wheel cylinder CW at the supply hydraulic pressure Pm. In other words, in the electric cylinder type first unit YA, the supply hydraulic pressure Pm is directly controlled (adjusted) by adjusting the output of the electric motor without using the solenoid valves UZ and UG. In this configuration, the hydraulic pressure Pwx of the selected wheel cylinder CWx is controlled by the electric motor. The hydraulic pressure Pwz of the non-selected wheel cylinder CWz is adjusted by the non-selected inlet valve UIz and the non-selected outlet valve VOz.

<Application to vehicle stability control, etc.>
In the above embodiment, the fluctuation suppression control is applied to the off-road control. The fluctuation suppression control can be applied not only to the off-road control but also to the control such as the vehicle stability control in which the brake fluid pressure Pw is individually adjusted in the wheel cylinder CW of each wheel WH. The vehicle stability control (also called "side slip prevention control") is a known control that suppresses an unstable state of the vehicle JV (specifically, oversteer behavior, understeer behavior) based on the yaw rate Yr, the lateral acceleration Gy, etc. For example, in the vehicle stability control, when the oversteer behavior is suppressed, the wheel cylinder CW provided on the wheel located on the outside of the turning of the vehicle is determined as the selected wheel cylinder CWx. Then, the brake fluid pressure Pwx of the selected wheel cylinder CWx is adjusted by the first unit YA. On the other hand, the brake fluid pressure Pwz of the non-selected wheel cylinder CWz that does not correspond to the selected wheel cylinder CWx is adjusted by the second unit YB (particularly, the inlet valve UI, the outlet valve VO). In the vehicle stability control, as in the off-road control, the hydraulic pressure Pm supplied from the first unit YA fluctuates, but the fluctuation can be reduced by the above-mentioned fluctuation suppression control (control of the inlet valve UI and the pressure regulating valve UB based on the hydraulic pressure deviation hP), thereby improving the pressure regulation accuracy and the performance of the vehicle stability control.

<Configuration in which pressure regulating valve UB is omitted>
In the above embodiment, the pressure regulating valve UB and the inlet valve UI are provided in the communication passage HS. Here, the pressure regulating valve UB may be omitted. In this configuration, in a situation where "Pm<Ptx", the supply hydraulic pressure Pm cannot be increased, so fluctuations in the supply hydraulic pressure Pm are not suppressed. However, in a situation where "Pm>Ptx", the supply hydraulic pressure Pm is decreased by the inlet valve UI and is supplied to the selected wheel cylinder CWx as the selected brake hydraulic pressure Pwx, so fluctuations in the supply hydraulic pressure Pm can be suppressed. Even in a configuration where the pressure regulating valve UB is omitted, off-road control and vehicle stability control can be executed, so the fluctuation suppression control has its effect.

<Diagonal type fluid path>
In the above embodiment, a front-rear type configuration is adopted as the two brake fluid paths. Alternatively, a diagonal type (also called "X type") brake system can be adopted. In this configuration, one of the two hydraulic chambers formed in the master cylinder CM (or pressure adjusting cylinder) is connected to the right front wheel cylinder and the left rear wheel cylinder, and the other is connected to the left front wheel cylinder and the right rear wheel cylinder.

<Summary and effects of the embodiment of the brake control device SC>
The following is a summary of an embodiment of the brake control device SC. The brake control device SC individually adjusts the hydraulic pressure (brake hydraulic pressure) Pw of the multiple wheel cylinders CW of the vehicle JV. For example, the brake control device SC executes speed control (off-road control) to keep the vehicle speed Vx of the vehicle JV constant at a low speed, and vehicle stability control to suppress the oversteer tendency and understeer tendency of the vehicle JV. The brake control device SC includes a pressurized source YA for increasing the hydraulic pressure Pw of the wheel cylinders CW, a communication passage HS for connecting the pressurized source YA and the wheel cylinders CW, an inlet valve UI provided in the communication passage HS, a pressure reduction passage HG for connecting the communication passage HS between the wheel cylinders CW and the inlet valve UI to a reservoir RC, an outlet valve VO provided in the pressure reduction passage HG, a hydraulic pressure sensor PB for detecting the hydraulic pressure output by the pressurized source YA as a supply hydraulic pressure Pm, and a controller ECU for controlling the pressurized source YA, the inlet valve UI, and the outlet valve VO. The brake control device SC also includes a fluid pump QB driven by an electric motor MB for returning brake fluid BF from the reservoir RC to the communication passage HS between the pressurized source YA and the inlet valve UI.

The controller ECU calculates multiple target hydraulic pressures Pt (target values required for off-road control, vehicle stability control, etc.) required for multiple wheel cylinders CW. Then, it determines the maximum value of the multiple target hydraulic pressures Pt as the maximum target hydraulic pressure Ptx. The controller ECU adjusts the hydraulic pressure Pwx of the selected wheel cylinder CWx corresponding to the maximum target hydraulic pressure Ptx among the multiple wheel cylinders CW using the pressure source YA. On the other hand, it adjusts the hydraulic pressure Pwz of the non-selected wheel cylinder CWz that does not correspond to the selected wheel cylinder CWx among the multiple wheel cylinders CW using the non-selected inlet valve UIz and the non-selected outlet valve VOz.

Furthermore, the controller ECU controls the selective inlet valve UIx corresponding to the selected wheel cylinder CWx among the inlet valves UI based on the deviation hP between the maximum target hydraulic pressure Ptx and the supply hydraulic pressure Pm. Also, in the brake control device SC, a pressure regulating valve UB is provided in the communication passage HS between the pressurizing source YA and the inlet valve UI, and the controller ECU controls the selective pressure regulating valve UBx corresponding to the selected wheel cylinder CWx among the pressure regulating valves UB (the pressure regulating valve provided in the communication passage HSx including the selected wheel cylinder CWx among the two pressure regulating valves UB) based on the deviation hP. In detail, when the supply hydraulic pressure Pm is smaller than the maximum target hydraulic pressure Ptx, the selective pressure regulating valve UBx is energized based on the deviation hP, but the selective inlet valve UIx is not energized. As a result, the excessively low supply hydraulic pressure Pm is increased and adjusted by the selective pressure regulator UBx, and the selected braking hydraulic pressure Pwx approaches the maximum target hydraulic pressure Ptx. Conversely, when the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx, the selective inlet valve UIx is energized based on the deviation hP, but the selective pressure regulator UBx is not energized. As a result, the excessively high supply hydraulic pressure Pm is decreased and adjusted by the selective inlet valve UIx, and the selected braking hydraulic pressure Pwx approaches the maximum target hydraulic pressure Ptx.

In the brake control device SC, the brake fluid pressure Pwx of the selected wheel cylinder CWx corresponding to the maximum target hydraulic pressure Ptx is adjusted by increasing or decreasing the supply hydraulic pressure Pm from the first unit YA, which is the pressure source. On the other hand, the brake fluid pressure Pwz of the non-selected wheel cylinder CWz that does not correspond to the selected wheel cylinder CWx among the wheel cylinders CW is increased or decreased by opening or closing the non-selected inlet valve UIz and the non-selected outlet valve VOz. In the hydraulic pressure adjustment by opening or closing the non-selected inlet valve UIz and the non-selected outlet valve VOz, the brake fluid BF flows out of the communication passage HS and into the communication passage HS, so that the amount (fluid volume) of the brake fluid BF in the communication passage HS changes. Due to this change in the fluid volume, the hydraulic pressure (supply hydraulic pressure) Pm supplied from the first unit YA to the wheel cylinder CW fluctuates. Although the fluctuation suppression control cannot suppress fluctuations in the supply hydraulic pressure Pm itself, the selective pressure regulating valve UBx and the selective inlet valve UIx provided in the fluid path HSx (selective communication path including the selected wheel cylinder CWx) until the supply hydraulic pressure Pm is transmitted as the selected brake hydraulic pressure Pwx suppress fluctuations in the selected brake hydraulic pressure Pwx. In other words, the pressure amplitude of the supply hydraulic pressure Pm is attenuated by the selective pressure regulating valve UBx and the selective inlet valve UIx and transmitted to the selected wheel cylinder CWx. As a result, the pressure regulation accuracy of the selected brake hydraulic pressure Pwx is improved in the selected wheel cylinder CWx, and the performance of the above-mentioned off-road control and vehicle stability control can be improved.

JV...vehicle, SC...brake control device, SX...brake device, CP...brake caliper, CW...wheel cylinder, KT...rotating member (brake disc), MS...friction member (brake pad), ECU...braking controller, HU...fluid unit, YA...first unit (pressure source), CM...master cylinder, YB...second unit, UB...pressure regulating valve, UI...inlet valve, VO...outlet valve, RC...pressure regulating reservoir, MB...electric motor, QB...fluid pump, PM...supply fluid pressure sensor, Pm...supply fluid pressure (detection value of supply fluid pressure sensor PM), Pq...adjusted fluid pressure, Pw...braking fluid pressure, mQ...fluid pressure difference (difference between adjusted fluid pressure Pq and supply fluid pressure Pm), wQ...fluid pressure difference (difference between adjusted fluid pressure Pq and brake fluid pressure Pw), Pt...target hydraulic pressure, Ptx...maximum target hydraulic pressure (maximum value of the target hydraulic pressure Pt), hP...hydraulic pressure deviation (difference between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx), Ii...first current amount (actual current amount of the inlet valve UI), Iit...first target current amount (target value corresponding to the first current amount Ii), Ib...second current amount (actual current amount of the pressure regulating valve UB), Ibt...second target current amount (target value corresponding to the second current amount Ib), CWx...selected wheel cylinder (wheel cylinder among the multiple wheel cylinders that corresponds to the maximum target hydraulic pressure Ptx), CWz...non-selected wheel cylinder (wheel cylinder among the multiple wheel cylinders that does not correspond to the selected wheel cylinder CWx).

Claims (1)

A vehicle brake control device that individually adjusts hydraulic pressures in a plurality of wheel cylinders of a vehicle,
a pressure source for increasing hydraulic pressure in the wheel cylinders;
a communication passage connecting the pressure source and the plurality of wheel cylinders;
an inlet valve provided in the communication passage;
a pressure reducing passage connecting the communication passage between the plurality of wheel cylinders and the inlet valve to a reservoir;
an outlet valve provided in the pressure reduction path;
a hydraulic pressure sensor that detects the hydraulic pressure output from the pressure source as a supply hydraulic pressure;
a pressure regulating valve provided in the communication passage between the pressurized source and the inlet valve;
a controller that calculates a plurality of target hydraulic pressures required for the plurality of wheel cylinders, determines a maximum value of the plurality of target hydraulic pressures as a maximum target hydraulic pressure, adjusts the hydraulic pressure of a selected wheel cylinder among the plurality of wheel cylinders corresponding to the maximum target hydraulic pressure by the pressurizing source, and adjusts the hydraulic pressure of a non-selected wheel cylinder among the plurality of wheel cylinders that does not correspond to the selected wheel cylinder by the inlet valve and the outlet valve,
The controller:
when the supply hydraulic pressure is lower than the maximum target hydraulic pressure, a selective pressure regulating valve among the pressure regulating valves corresponding to the selected wheel cylinder is controlled in a direction to close based on a deviation between the maximum target hydraulic pressure and the supply hydraulic pressure, and a selective inlet valve among the inlet valves corresponding to the selected wheel cylinder is controlled in a direction to open;
When the supplied hydraulic pressure is greater than the maximum target hydraulic pressure, the selective inlet valve is controlled to close based on the deviation, and the selective pressure regulating valve is opened .