Braking control device for vehicle

Abstract

This braking control device is applied to a vehicle having front wheels equipped with a regeneration device. The braking control device comprises: a control cylinder that generates a basic pressure by using an electric motor as a power source; a solenoid valve that adjusts the basic pressure to an adjustment pressure; and a controller that controls the electric motor and the solenoid valve. The braking control device controls the front wheel pressure of a front wheel cylinder by means of the adjustment pressure and controls the rear wheel pressure of a rear wheel cylinder by means of the basic pressure. The controller: calculates fluid volumes to be supplied to the front wheel cylinder and the rear wheel cylinder as front-wheel and rear-wheel nominal fluid volumes, on the basis of a front-wheel target pressure and a rear-wheel target pressure which are target values for the front wheel pressure and the rear wheel pressure, respectively; controls the electric motor on the basis of the front-wheel and the rear-wheel nominal fluid volumes; and controls the solenoid valve on the basis of the front-wheel target pressure and the rear-wheel target pressure.

Description

Vehicle braking control device

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

[0002] Patent Document 1 describes a vehicle brake device that, when controlling the brake fluid pressure generated by an electric hydraulic pressure generating means by feedback of the rotation angle of an electric motor, includes an electric hydraulic pressure generating means (23) that generates brake fluid pressure by operating an electric motor (32) and an electric motor control means (U) that controls the operation of the electric motor (32), in order to maintain a constant relationship between the rotation angle and the generated brake fluid pressure, and the electric motor control means (U) calculates a target rotation angle of the electric motor (32) for causing the electric hydraulic pressure generating means (23) to generate brake fluid pressure corresponding to the amount of brake operation by the driver, and performs feedback control so that the actual rotation angle of the electric motor (32) coincides with the target rotation angle, and the electric motor control means (U) includes a correction means (M5) that corrects the target rotation angle of the electric motor (32) based on the actual brake fluid pressure generated by the electric hydraulic pressure generating means (23).

[0003] Specifically, in the device described in Patent Document 1, the stroke of the brake pedal 12 detected by the stroke sensor Sb is converted into a brake fluid pressure (target brake fluid pressure) to be generated in the slave cylinder 23 (also referred to as the "control cylinder"). The target brake fluid pressure is converted into a rotation angle (target rotation angle) of an electric motor 32 (also referred to as the "electric motor") of the slave cylinder 23. The electric motor is then controlled based on the target rotation angle.

[0004] The applicant has developed a braking control device as described in Patent Document 2. The braking control device includes an electric cylinder 51 that discharges brake fluid from an output port 516 at a hydraulic pressure corresponding to the drive of an electric motor 513, a master cylinder 31 configured such that brake fluid flows out of the master chamber Rm as a result of movement of a master piston 43 in response to an increase in hydraulic pressure in the servo chamber Rs, and brake fluid flows into the master chamber Rm as a result of movement of the master piston 43 in response to a decrease in hydraulic pressure in the servo chamber Rs, a first flow path 331 connecting the master chamber Rm to the wheel cylinder 11 for the front wheels, a sixth flow path 58 that connects the output port 516 to the wheel cylinder 11 for the rear wheels, a fifth flow path 55 that connects the sixth flow path 58 to the servo chamber Rs, and a differential pressure adjustment valve 551 that is provided in the fifth flow path 55 and adjusts the differential pressure between the first hydraulic pressure, which is the hydraulic pressure in the sixth flow path 58, and the second hydraulic pressure, which is the hydraulic pressure in the servo chamber Rs. In such a device, it is necessary to control not only the electric motor but also the differential pressure adjusting valve (solenoid valve).

[0005] Japanese Patent Application No. 2022-197101

[0006] In view of the above problems, an object of the present invention is to provide a vehicle braking control device that adjusts the hydraulic pressure in the wheel cylinders of the front and rear wheels individually, and that can appropriately control the electric motor and the solenoid valve.

[0007] The vehicle braking control device (SA) of the present invention is applied to a vehicle equipped with a regenerative device (KG) on the front wheels (WHf), and is equipped with a control cylinder (CC) that generates a base pressure (Pa) using an electric motor (MA) as a power source, an solenoid valve (UC) that adjusts the base pressure (Pa) to an adjustment pressure (Pb), and a controller (EA) that controls the electric motor (MA) and the solenoid valve (UC), and controls the front wheel pressure (Pwf) of the front wheel cylinder (CWf) using the adjustment pressure (Pb), and controls the rear wheel pressure (Pwr) of the rear wheel cylinder (CWr) using the base pressure (Pa).

[0008] In the vehicle braking control device (SA) of the present invention, the controller (EA) calculates the amount of fluid to be supplied to the front and rear wheel cylinders (CWf, CWr) as front and rear wheel standard fluid amounts (Esf, Esr) based on front and rear wheel target pressures (Ptf, Ptr), which are target values ​​for the front and rear wheel pressures (Pwf, Pwr), controls the electric motor (MA) based on the front and rear wheel standard fluid amounts (Esf, Esr), and controls the solenoid valves (UC) based on the front and rear wheel target pressures (Ptf, Ptr).

[0009] In the vehicle brake control device (SA) according to the present invention, the controller (EA) acquires the fluid discharge amount (Ej) from the control cylinder (CC), calculates an estimated fluid amount (Ee) based on the base pressure (Pa) and the regulated pressure (Pb), and controls the rotation angle (Ka) of the electric motor (MA) based on the deviation (hE) between the fluid discharge amount (Ej) and the estimated fluid amount (Ee). The controller (EA) also calculates a target differential pressure (St) based on the front and rear wheel target pressures (Ptf, Ptr), and controls the valve current (Ic) supplied to the solenoid valve (UC) based on the target differential pressure (St).

[0010] The hydraulic pressure Pw generated in the wheel cylinder CW is determined according to the amount of hydraulic fluid supplied to the wheel cylinder CW. Therefore, the brake control device SA controls the rotation angle Ka of the electric motor MA based on the relationship between hydraulic pressure and hydraulic fluid volume (i.e., hydraulic pressure-hydraulic volume characteristics). This allows the amount of hydraulic fluid required to achieve the base pressure Pa to be discharged from the electric cylinder DN (particularly the control cylinder CC). Furthermore, the differential pressure Sa between the hydraulic pressure Pa on the side closer to the electric cylinder DN and the hydraulic pressure Pb on the side farther from the electric cylinder DN is determined according to the valve current Ic supplied to the pressure regulating valve UC. Therefore, the pressure regulating valve UC operates based on the target differential pressure St. According to the above configuration, the brake control device SA, which individually adjusts the hydraulic pressures in the wheel cylinders of the front and rear wheels using dual pressure regulation, appropriately controls the electric motor MA and the pressure regulating valve UC. As a result, the base pressure Pa and the regulated pressure Pb can be accurately adjusted in the dual pressure regulation.

[0011] Fig. 1 is a schematic diagram for explaining a first embodiment of a vehicle brake control device SA; Fig. 2 is a flow chart for explaining the process of pressure regulation control; Fig. 3 is a block diagram for explaining drive control of an electric cylinder DN; Fig. 4 is a block diagram for explaining drive control of a pressure regulating valve UC; Fig. 5 is a schematic diagram for explaining a second embodiment of a vehicle brake control device SA;

[0012] <Symbols of components, etc., and subscripts at the end of symbols> In the following description, components, arithmetic processes, signals, characteristics, and values ​​with the same symbol, such as "CW," have the same function. The subscripts "f" and "r" at the end of the symbol for each wheel are generic symbols that indicate whether the symbol relates to the front or rear wheel system. For example, a wheel cylinder CW provided on each wheel is written as "front wheel cylinder CWf, rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" at the end of a symbol can be omitted. When the subscripts "f" and "r" are omitted, each symbol represents a generic term. For example, "CW" is a generic term for wheel cylinders provided on the front and rear wheels of a vehicle. Furthermore, the generic term "CW" can also be written as "CW (= CWf, CWr)."

[0013] The brake control device SA, hydraulic pressure correction device SZ, and wheel cylinder CW are connected by a fluid path (communication path HS). Furthermore, in the brake control device SA and hydraulic pressure correction device SZ, various components (CC, UC, etc.) are connected by fluid paths. Here, the "fluid path" is a path for moving brake fluid BF, and corresponds to piping, flow paths in the actuator, hoses, etc. In the following explanation, the communication path HS, reservoir path HR, input path HN, servo path HU, supply path HH, etc. are fluid paths.

[0014] <First Embodiment of Brake Control Device SA> A first embodiment of a brake control device SA for a vehicle will be described with reference to the schematic diagram of Fig. 1. The brake control device SA is applied to, for example, a hybrid vehicle equipped with an electric motor for driving, or an electric vehicle.

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

[0016] The vehicle is equipped with a regenerative device KG. The regenerative device KG is composed of a generator GN for energy regeneration (also referred to as an "electric motor / generator" or "regenerative generator"), a control unit EG for the regenerative device KG (also referred to as a "regenerative controller"), and a regenerative storage battery (not shown). The regenerative generator GN also serves as an electric motor for driving. During regenerative braking, the electric motor / generator GN operates as a generator, and the generated electric power is stored in the regenerative storage battery via the regenerative controller EG. At this time, a regenerative braking force Fg acts on the wheels. That is, the regenerative device KG can generate the regenerative braking force Fg. For example, the regenerative device KG is provided on the front wheels WHf. Therefore, the regenerative braking force Fg is generated on the front wheels WHf. The regenerative device KG (particularly, the regenerative controller EG) is connected to the communication bus BS.

[0017] The vehicle is equipped with a driving assistance device KJ. The driving assistance device KJ performs automatic speed control. The driving assistance device KJ is composed of an object detection sensor SJ and a driving assistance controller EJ (also simply referred to as a "driving assistance controller"). The object detection sensor SJ detects a distance Sj (referred to as a "relative distance," or, if the object is a preceding vehicle, as an "inter-vehicle distance") to an object ahead of the vehicle (including a preceding vehicle traveling ahead of the vehicle). For example, a radar sensor, a millimeter-wave sensor, an image sensor, or the like may be used as the object detection sensor SJ. The driving assistance controller EJ calculates a target acceleration Gs of the vehicle (a target value of the vehicle's body acceleration in the longitudinal direction) based on the detection result Sj (relative distance) of the object detection sensor SJ. The driving assistance device KJ (particularly, the driving assistance controller EJ) is connected to a communication bus BS. The target acceleration Gs is transmitted to a braking control device SA via the communication bus BS. The braking control device SA adjusts the braking forces Fg and Fe in accordance with the target acceleration Gs, thereby controlling the vehicle speed Vx (vehicle speed).

[0018] A vehicle is equipped with a brake operating member BP and various sensors (such as SP). The brake operating member BP (e.g., a brake pedal) is an operating member used by the driver to decelerate the vehicle. The vehicle is provided with an operation displacement sensor SP that detects an operation displacement Sp of the brake operating member BP. The operation displacement Sp is one of the state quantities (state variables) that indicate the operation amount of the brake operating member BP, and in a brake-by-wire type brake control device SA, it is a signal that indicates the driver's intention to brake (i.e., a braking command). In addition to the operation displacement sensor SP, a hydraulic pressure Pn (referred to as "input pressure") in an input chamber Rn (described later) is used as another state quantity that indicates the braking operation amount. The input pressure Pn is detected by an input pressure sensor PN. The operation displacement Sp, input pressure Pn, etc. are collectively referred to as the "braking operation amount Ba." The operation displacement sensor SP and the input pressure sensor PN that detect the operation displacement Sp and the input pressure Pn (i.e., the braking operation amount Ba) are referred to as a "braking operation amount sensor BA."

[0019] A vehicle is equipped with various sensors for braking control (i.e., individual control of each wheel pressure Pw), such as antilock brake control and anti-skid control. Specifically, each wheel WH is equipped with a wheel speed sensor VW for detecting its rotational speed Vw (referred to as "wheel speed"). Also equipped are a steering amount sensor for detecting the steering amount Sw (e.g., operation angle) of a steering operation member (e.g., a steering wheel), a yaw rate sensor for detecting the yaw rate Yr of the vehicle, a longitudinal acceleration sensor for detecting the longitudinal acceleration Gx (also referred to as "deceleration") of the vehicle, and a lateral acceleration sensor for detecting the lateral acceleration Gy of the vehicle (all not shown).

[0020] The vehicle is equipped with a brake control device SA. The brake control device SA employs a so-called front and rear type (also called "type II") dual brake system. The brake control device SA adjusts the wheel pressure Pw of each wheel cylinder CW.

[0021] The brake control device SA (particularly, the brake controller EA) and the hydraulic pressure correction device SZ (particularly, the correction controller EZ) are connected to a communication bus BS. The communication bus BS allows signals to be transmitted between the controllers (EA, EZ, EG, EJ, etc.). That is, the controllers can transmit signals (detected values, calculated values, control flags, etc.) to the communication bus BS and can also receive signals from the communication bus BS.

[0022] <Configuration of Brake Control Device SA> The configuration of the brake control device SA according to the first embodiment will be described. The brake control device SA generates a base pressure Pa and an adjustment pressure Pb in response to operation of the brake operating member BP (brake pedal). The brake control device SA then outputs a supply pressure Pm and a base pressure Pa to a hydraulic pressure correction device SZ. The hydraulic pressure correction device SZ adjusts the supply pressure Pm and the base pressure Pa, and ultimately supplies front and rear wheel pressures Pwf and Pwr to the front and rear wheel cylinders CWf and CWr. The brake control device SA is made up of a brake actuator YA and a brake controller EA.

[0023] <Brake Actuator YA> The brake actuator YA is composed of a hydraulic pressure generating unit PU, an apply unit AP, and an input unit NR.

[0024] [Hydraulic Pressure Generating Unit PU] The hydraulic pressure generating unit PU uses an electric motor MA as a power source to generate a base pressure Pa and an adjustment pressure Pb. The hydraulic pressure generating unit PU is composed of an electric cylinder DN and a pressure regulating valve UC. Here, the electric cylinder DN includes the electric motor MA, a rotation angle sensor KA, a reducer GS, a conversion mechanism GH, a control cylinder CC, and a control piston NC.

[0025] The electric motor MA is a power source (pressurizing source) for generating a base pressure Pa (hydraulic pressure generated by the electric cylinder DN). "Power" refers to the energy required to move the movable members (GS, GH, NC, etc.) in the electric cylinder DN. For example, power is defined as a physical quantity, namely, energy per unit time (also called "power"). Rotational power (also called "first rotational power") is output from the electric motor MA. The rotational power of the electric motor MA is calculated by multiplying the shaft torque of the electric motor MA by the rotational speed of the electric motor MA (particularly, the motor shaft). Note that the linear power of a linearly moving member (described below) is calculated by multiplying the thrust of the linearly moving member (a force acting in the direction of the central axis) by the linear speed of the linearly moving member (speed in the direction along the central axis).

[0026] A three-phase brushless motor is employed as the electric motor MA. The electric motor MA includes a motor coil, a motor shaft, and a rotation angle sensor KA. The motor coil is fixed to a motor housing. Power is supplied to the motor coil from a controller EA (particularly, a drive circuit DR). The motor shaft is rotatably supported relative to the motor housing. A permanent magnet is fixed to the outer periphery of the motor shaft. In the three-phase brushless motor MA, the magnetic pole position of the permanent magnet (i.e., the motor rotation angle Ka) is detected by a rotation angle sensor KA (also equivalent to a "liquid level sensor"). Then, three-phase motor current Im (a collective term for currents flowing through the U, V, and W phases) corresponding to the U, V, and W phases is switched based on the rotation angle Ka of the motor shaft.

[0027] Specifically, a signal of the rotation angle Ka (which also corresponds to the "ejection liquid volume Ej (described later)") detected by the rotation angle sensor KA is transmitted to the controller EA (particularly the microprocessor MP). The controller EA drives the switching elements of the drive circuit DR (also called the "inverter circuit") in accordance with the rotation angle Ka. This switches the motor current Im flowing through the motor coil, driving the electric motor MA. Then, a first rotational power is output from the electric motor MA to the reducer GS.

[0028] The reducer GS reduces the speed of the first rotational power output from the electric motor MA. Specifically, the input shaft of the reducer GS is fixed to the motor shaft. Also, the output shaft of the reducer GS is fixed to the rotating member of the conversion mechanism GH. The reducer GS reduces the speed input from the electric motor MA and increases the torque input from the electric motor MA. The reduced rotational power (also referred to as "second rotational power") is then output from the reducer GS to the conversion mechanism GH.

[0029] The conversion mechanism GH is composed of a rotating member that performs rotational motion and a linearly moving member that performs linear motion. In the conversion mechanism GH, the second rotational power output from the reducer GS is input to the rotating member. The rotational power input to the rotating member is then converted into linear power for the linearly moving member. The conversion mechanism GH is also called a "rotation-linear conversion mechanism." A rotation stopper member is engaged with the linearly moving member. This prevents the rotational motion of the linearly moving member, so that the linearly moving member moves along the rotation axis of the rotating member.

[0030] For example, a "ball screw" is employed as the conversion mechanism GH. Specifically, in the ball screw mechanism, a rotating member, which is a shaft member, is fixed to the output shaft of the reducer GS. The rotating member is inserted into a linearly moving member having a cylindrical shape. A ball screw groove is formed on the outer peripheral surface of the rotating member. Similarly, a ball screw groove is also formed on the inner peripheral surface of the linearly moving member. A plurality of balls (steel balls) are fitted into the ball screw groove.

[0031] A linear motion member of the conversion mechanism GH transmits linear power to the control piston NC. The control piston NC is inserted into the control cylinder CC. A control chamber Rc (hydraulic pressure chamber) is formed inside the control cylinder CC by the control piston NC. More specifically, the outer peripheral surface of the control piston NC and the inner peripheral surface of the control cylinder CC are sealed by two seal members SL. This makes the control chamber Rc liquid-tight. The hydraulic pressure in the control cylinder CC (i.e., the control chamber Rc) is the "base pressure Pa." In other words, the electric cylinder DN uses the electric motor MA as a power source to output the base pressure Pa.

[0032] The control cylinder CC is connected to a servo chamber Ru (described later) of the apply unit AP via a servo path HU (fluid path). The control cylinder CC is also connected to a rear wheel cylinder CWr via a rear wheel communication path HSr (fluid path) and a hydraulic pressure correcting device SZ. The hydraulic pressure generating unit PU is provided with a base pressure sensor PA to detect a base pressure Pa (hydraulic pressure generated by the electric cylinder DN).

[0033] FIG. 1 illustrates a state in which the electric cylinder DN does not generate a base pressure Pa. The control cylinder CC has a through-hole between two seal members SL. The control piston NC also has a through-hole. A supply path HH (fluid path) connected to a master reservoir RV is connected to the through-hole of the control cylinder CC. In the illustrated state, the control chamber Rc is connected to the master reservoir RV via the through-hole and the supply path HH, and the base pressure Pa is "0 (atmospheric pressure)." The position of the control piston NC in this state is referred to as the "initial position." In the initial position, the control piston NC is displaced to its maximum in the backward direction Hb, and the volume of the control chamber Rc is maximized.

[0034] When an increase in the base pressure Pa is required, the rotational power of the electric motor MA is increased. This rotational power is transmitted to the conversion mechanism GH via the reducer GS and output as linear power of the linearly-acting member. Then, the control piston NC is pressed by the linearly-acting member, causing the control piston NC to move forward in the direction Ha (a direction in which the volume of the control chamber Rc decreases). This movement first blocks communication between the control chamber Rc and the master reservoir RV. When the control piston NC is further moved forward in the direction Ha, the base pressure Pa (internal pressure of the control chamber Rc) is increased from "0 (atmospheric pressure)." Brake fluid BF pressurized to the base pressure Pa is output (pumped) from the control chamber Rc of the control cylinder CC.

[0035] When it is necessary to maintain the base pressure Pa, the rotation of the electric motor MA is stopped. The movement of the control piston NC is stopped, and the base pressure Pa is maintained constant. When it is necessary to decrease the base pressure Pa, the rotational power of the electric motor MA is reduced. The base pressure Pa causes the electric motor MA to rotate in the reverse direction, so that the control piston NC moves in the backward direction Hb (the direction in which the volume of the control chamber Rc increases). At this time, the brake fluid BF is returned toward the control chamber Rc, and the base pressure Pa is decreased.

[0036] A pressure regulating valve UC (corresponding to a "solenoid valve") is provided in the servo path HU (a fluid path connecting the control chamber Rc and the servo chamber Ru). The pressure regulating valve UC is a normally open linear solenoid valve whose valve opening amount (lift amount) is continuously controlled according to the supplied current Ic (referred to as the "valve current"). The pressure regulating valve UC is also called a "differential pressure valve" because it adjusts the hydraulic pressure difference (differential pressure). The pressure regulating valve UC adjusts the base pressure Pa output from the electric cylinder DN to an adjustment pressure Pb.

[0037] Specifically, the pressure regulating valve UC is composed of a valve body, a valve seat, and a solenoid. The solenoid's plunger is fixed to the valve body. When current Ic is supplied to the solenoid's coil, the plunger is attracted to the coil, generating thrust. This thrust pushes the valve body toward the valve seat. This prevents brake fluid BF from flowing from the control cylinder CC toward the servo chamber Ru. As a result, the pressure regulating valve UC blocks the base pressure Pa, allowing the pressure regulating valve UC to adjust the adjustment pressure Pb to be smaller than the base pressure Pa. When current Ic is not supplied to the pressure regulating valve UC, the pressure regulating valve UC is fully open, so the base pressure Pa and the adjustment pressure Pb are equal (i.e., when Ic = 0, Pa = Pb). The hydraulic pressure generating unit PU is provided with an adjustment pressure sensor PB between the pressure regulating valve UC and the servo chamber Ru to detect the adjustment pressure Pb.

[0038] The brake control device SA has limitations on the adjustment of the regulated pressure Pb. As described above, the pressure regulating valve UC prevents the inflow of brake fluid BF pressurized to the base pressure Pa, thereby making the regulated pressure Pb smaller than the base pressure Pa. However, the pressure regulating valve UC cannot reduce the regulated pressure Pb by itself. In other words, in order to reduce the regulated pressure Pb, the base pressure Pa must be reduced.

[0039] [Apply Unit AP] The apply unit AP is composed of a single-type master cylinder CM and a master piston NM. The master piston NM is inserted into the single-type master cylinder CM. The interior of the master cylinder CM is divided into three hydraulic chambers Rm, Ru, and Rs by the master piston NM. The master chamber Rm is formed by the master cylinder CM and the master piston NM. Furthermore, the interior of the master cylinder CM is divided into a servo chamber Ru and a reaction chamber Rs by a flange portion Tu of the master piston NM. Here, the pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are set equal to each other.

[0040] The servo chamber Ru is supplied with an adjustment pressure Pb from the hydraulic pressure generating unit PU. The adjustment pressure Pb causes the apply unit AP to output a supply pressure Pm (corresponding to the "adjustment pressure Pb"). Here, the "supply pressure Pm" is the internal pressure of the master chamber Rm, and is also referred to as the "master pressure." When "Pb = 0" (for example, when not braking), the master piston NM is in its most retracted position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is connected to the master reservoir RV. Therefore, the master pressure Pm is "0 (atmospheric pressure)."

[0041] Brake fluid BF is stored inside the master reservoir RV (also referred to as the "atmospheric pressure reservoir"). When the adjustment pressure Pb increases from "0," the master piston NM moves in the forward direction Da (the direction in which the volume of the master chamber Rm decreases). This movement blocks communication between the master chamber Rm and the master reservoir RV. When the master piston NM then moves further in the forward direction Da, the supply pressure Pm (master pressure) increases from "0 (atmospheric pressure)." As a result, brake fluid BF pressurized to the supply pressure Pm is output (pressurized and fed) from the master chamber Rm of the master cylinder CM toward the hydraulic pressure correction device SZ. Note that since "rm = ru," if the sliding resistance of the seal member SL is ignored, then "Pb = Pm."

[0042] [Input Unit NR] The input unit NR realizes regenerative cooperative control. "Regenerative cooperative control" cooperates the friction braking force Fe (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to the regenerative device KG) so that the kinetic energy of the vehicle can be efficiently recovered as electrical energy during braking. In regenerative cooperative control, the brake operating member BP is operated, but a state is created in which the wheel pressure Pw is not generated. The input unit NR is composed of an input cylinder CN, an input piston NN, a first control valve VA, a second control valve VB, a stroke simulator SS, and an input pressure sensor PN.

[0043] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to a brake operating member BP (brake pedal) so as to move in conjunction with the movement of the brake operating member BP. A gap Ln (also referred to as the "separation distance") is defined between the end face of the input piston NN and the end face of the master piston NM. The separation distance Ln is adjusted by the adjustment pressure Pb, thereby realizing regenerative cooperative control.

[0044] The input chamber Rn of the input unit NR is connected to the reaction force chamber Rs of the apply unit AP via an input path HN (fluid path). A normally closed first control valve VA is provided in the input path HN. The input path HN is connected to a master reservoir RV via a reservoir path HR (fluid path) between the first control valve VA and the reaction force chamber Rs. A normally open second control valve VB is provided in the reservoir path HR. On-off solenoid valves are used for the first and second control valves VA and VB. A stroke simulator SS is connected to the input path HN between the first control valve VA and the reaction force chamber Rs.

[0045] When power is not supplied to the first and second control valves VA and VB, the first control valve VA is closed and the second control valve VB is open. Closing the first control valve VA seals the input chamber Rn, creating a fluid lock. This causes the master piston NM to displace integrally with the brake operating member BP. Opening the second control valve VB also connects the stroke simulator SS and the reaction chamber Rs to the master reservoir RV.

[0046] When power is supplied to the first and second control valves VA and VB, the first control valve VA is opened and the second control valve VB is closed. This allows the master piston NM to be displaced separately from the brake operating member BP. Since the input chamber Rn is connected to the stroke simulator SS, the operating force for the brake operating member BP is generated by the stroke simulator SS. An input pressure sensor PN is provided in the input line HN between the input chamber Rn and the first control valve VA to detect the input pressure Pn. The input pressure Pn is also the hydraulic pressure within the stroke simulator SS.

[0047] <Brake Controller EA> The brake actuator YA is controlled by the brake controller EA. The brake controller EA is composed of a microprocessor MP and a drive circuit DR. The controller EA is connected to a communication bus BS so that signals (detected values, calculated values, control flags, etc.) can be shared with other controllers (EZ, EG, EJ, etc.).

[0048] The brake controller EA directly receives various signals such as the operation displacement Sp (detection value of the operation displacement sensor SP), the input pressure Pn (detection value of the input pressure sensor PN), the base pressure Pa (detection value of the base pressure sensor PA), and the motor rotation angle Ka (detection value of the rotation angle sensor KA). Furthermore, the controller EA receives various signals such as the supply pressure Pm, the standard regenerative braking force Fz, the vehicle speed Vx, and the target acceleration Gs from the communication bus BS. The brake controller EA also outputs a target regenerative braking force Fh (target value of the regenerative braking force Fg) to the communication bus BS. The regenerative controller EG controls the regenerative braking force Fg (actual value) based on the target regenerative braking force Fh (target value) acquired from the communication bus BS.

[0049] The brake controller EA (particularly the microprocessor MP) is programmed with a pressure regulation control algorithm. "Pressure regulation control" is control for adjusting the wheel pressure Pw (=Pwf, Pwr) and includes regenerative cooperative control. Pressure regulation control is performed based on the various signals (Sp, Pa, etc.) described above. Based on the pressure regulation control algorithm, the drive circuit DR drives the electric motor MA and various solenoid valves (UC, VA, etc.). The drive circuit DR includes an inverter circuit configured with switching elements (e.g., MOS-FETs) to drive the electric motor MA. The drive circuit DR also includes switching elements to drive the various solenoid valves. Additionally, the drive circuit DR includes a motor current sensor (not shown) that detects the current Im (motor current) supplied to the electric motor MA. The electric motor MA is provided with a rotation angle sensor KA to detect the position Ka (rotation angle) of the motor shaft.

[0050] The braking controller EA calculates drive signals Va and Vb for the first and second control valves VA and VB, a drive signal Uc for the pressure regulating valve UC, and a drive signal Ma for the electric motor MA. The switching elements are then driven in response to the various drive signals (Uc, Ma, etc.). Specifically, in controlling the solenoid valves, power is supplied to the first and second control valves VA and VB based on the drive signals Va and Vb. This opens the first control valve VA and closes the second control valve VB. Additionally, the drive signals Uc and Ma are determined based on a pressure regulation control algorithm. The pressure regulating valve UC is then controlled based on the drive signal Uc, and the electric motor MA is controlled based on the drive signal Ma.

[0051] <Hydraulic Pressure Modification Device SZ> A hydraulic pressure modification device SZ is provided between the brake control device SA and the wheel cylinders CW. The hydraulic pressure modification device SZ performs antilock brake control, traction control, anti-skid control, etc. In the brake system for the front wheels WHf (i.e., the front wheel connecting line HSf), a supply pressure Pm is supplied from the master cylinder CM to the hydraulic pressure modification device SZ. On the other hand, in the brake system for the rear wheels WHr (i.e., the rear wheel connecting line HSr), a base pressure Pa is supplied directly from the hydraulic pressure generating unit PU to the hydraulic pressure modification device SZ. The hydraulic pressure modification device SZ adjusts (increases or decreases) the supply pressure Pm and the base pressure Pa, and outputs them as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) for the front and rear wheel cylinders CWf and CWr.

[0052] The hydraulic pressure correction device SZ is composed of a correction actuator YZ and a correction controller EZ. The configuration of the correction actuator YZ is well known, so a description thereof will be omitted. The correction actuator YZ is provided with a supply pressure sensor PM to detect the supply pressure Pm. The adjustment pressure Pb is transmitted as the supply pressure Pm via the master piston NM. Therefore, the supply pressure Pm corresponds to the adjustment pressure Pb, and the supply pressure sensor PM corresponds to the adjustment pressure sensor PB. In other words, the supply pressure Pm is an example of the adjustment pressure Pb, and the supply pressure sensor PM is an example of the adjustment pressure sensor PB.

[0053] When the regenerative braking cooperative control is executed, the operation of the correction actuator YZ is stopped. Therefore, during the execution of the regenerative braking cooperative control, the adjustment pressure Pb is transmitted to the front wheel cylinder CWf as the front wheel pressure Pwf via the supply pressure Pm, while the base pressure Pa is transmitted directly to the rear wheel cylinder CWr as the rear wheel pressure Pwr. In other words, in the front wheel braking system, "Pb = Pm = Pwf" holds, and in the rear wheel braking system, "Pa = Pwr" holds.

[0054] The correction controller EZ is connected to the brake controller EA via a communication bus BS. The wheel speed Vw detected by the wheel speed sensor VW and the supply pressure Pm detected by the supply pressure sensor PM are input to the correction controller EZ. The correction controller EZ then calculates the vehicle traveling speed Vx (body speed) based on the wheel speed Vw. The body speed Vx and the supply pressure Pm are transmitted to the brake controller EA via the communication bus BS.

[0055] <Pressure Regulation Control Processing> An example of the pressure regulation control processing will be described with reference to the flow chart of Figure 2. In pressure regulation control, regenerative cooperative control is performed between the regenerative device KG and the brake control device SA. In regenerative cooperative control, the adjustment pressure Pb is made smaller than the base pressure Pa, so that the total braking force Fu corresponding to the required braking amount Bs is achieved while the front / rear distribution of the total braking force Fu is maintained at a predetermined value hf. In this control, the front wheel pressure Pwf and the rear wheel pressure Pwr are adjusted separately, so this control is also called "two-system pressure regulation."

[0056] <<Various Braking Forces>> The various braking forces in the explanation of pressure adjustment control are as follows: - "Total braking force Fu" is the actual braking force acting on the entire vehicle. The target value corresponding to the total braking force Fu is "target total braking force Fv". - "Frictional braking force Fe (hydraulic braking force)" is the braking force actually generated by the wheel pressure Pw. The target value corresponding to the frictional braking force Fe is "target frictional braking force Fn". - "Regenerative braking force Fg" is the braking force actually generated by the regenerative device KG. The target value corresponding to the regenerative braking force Fg is "target regenerative braking force Fh". The target regenerative braking force Fh is calculated by the brake control device SA (particularly, the brake controller EA) and transmitted to the regenerative device KG (particularly, the regenerative controller EG) via the communication bus BS. In the regenerative device KG, the regenerative controller EG controls the generator GN so that the actual regenerative braking force Fg approaches and coincides with the target regenerative braking force Fh. The "standard regenerative braking force Fz" is the maximum value (limit value) of the regenerative braking force Fg that the regenerative device KG can generate. Therefore, the regenerative device KG can generate a regenerative braking force Fg in the range from "Fg = 0" to the standard regenerative braking force Fz. The standard regenerative braking force Fz is calculated by the regenerative device KG (particularly, the regenerative controller EG) and transmitted to the brake control device SA (particularly, the brake controller EA) via the communication bus BS. The standard regenerative braking force Fz can be limited depending on the vehicle's driving conditions (e.g., the friction coefficient of the road).

[0057] <Various Hydraulic Pressures> The various hydraulic pressures in the explanation of pressure regulation control are as follows. - "Base pressure Pa" is the output of the electric cylinder DN (i.e., the internal pressure of the control chamber Rc). The base pressure Pa is detected (acquired) by the base pressure sensor PA. - "Adjusted pressure Pb" is the hydraulic pressure obtained by adjusting the base pressure Pa using the pressure regulating valve UC. The adjusted pressure Pb is detected (acquired) by the adjusted pressure sensor PB. Alternatively, the adjusted pressure Pb may be detected (acquired) by the supply pressure sensor PM. Therefore, the supply pressure Pm corresponds to one of the adjusted pressures Pb, and the supply pressure sensor PM corresponds to one of the adjusted pressure sensors PB. - "Rear wheel target pressure Ptr" corresponds to a target value for controlling the base pressure Pa (actual value). Furthermore, "front wheel target pressure Ptf" corresponds to a target value for controlling the adjusted pressure Pb. This is based on the fact that the rear wheel pressure Pwr is adjusted by the base pressure Pa, and the front wheel pressure Pwf is adjusted by the adjustment pressure Pb.

[0058] The hydraulic pressure transmission in the brake control device SA involves various resistances, such as pipe friction resistance in the fluid path, resistance due to the solenoid valve orifice, and sliding resistance of the seal member SL. In hydraulic pressure feedback control, the actual value is controlled to match the target value. However, taking these resistances into consideration, it is desirable to compare the actual value with the target value at the same location. In the following explanation, this comparison is performed at the wheel cylinder CW. That is, the rear wheel target pressure Ptr is determined to correspond to the rear wheel pressure Pwr. The rear wheel pressure Pwr (actual value) is determined from the base pressure Pa (detected value by the base pressure sensor PA) after compensation for the hydraulic pressure equivalent to the resistance. Similarly, the front wheel target pressure Ptf is determined to correspond to the front wheel pressure Pwf. The front wheel pressure Pwf (actual value) is determined from the adjustment pressure Pb (detected value by the adjustment pressure sensor PB) after compensation for the hydraulic pressure equivalent to the resistance.

[0059] In pressure regulation control, first, power is supplied to the first and second control valves VA, VB. The normally closed first control valve VA is opened, and the normally open second control valve VB is closed. This allows the master piston NM and the brake operating member BP to be displaced separately, so that the front and rear wheel pressures Pwf, Pwr can be adjusted independently of the operation of the brake operating member BP. At this time, the operating force of the brake operating member BP is generated by the stroke simulator SS.

[0060] In step S110, various signals are read in the brake controller EA. The brake controller EA acquires the braking operation amount Ba (collectively referring to Sp and Pn), target acceleration Gs, base pressure Pa, regulated pressure Pb, and standard regenerative braking force Fz. The braking operation amount Ba and target acceleration Gs are collectively referred to as the "braking demand amount Bs." The braking demand amount Bs is a state quantity representing a braking demand for the vehicle. The base pressure Pa is acquired by the base pressure sensor PA. The regulated pressure Pb is acquired by at least one of the regulated pressure sensor PB and the supply pressure sensor PM. The standard regenerative braking force Fz is determined by the regenerative device KG (particularly the regenerative controller EG) and is received by the brake controller EA via the communication bus BS.

[0061] In step S120, a target total braking force Fv (a target value of the total braking force Fu acting on the entire vehicle) is calculated based on the braking demand Bs and the calculation map Zfv. According to the calculation map Zfv, the target total braking force Fv is calculated to be "0" when the braking demand Bs is less than a predetermined amount bo. When the braking demand Bs is equal to or greater than the predetermined amount bo, the target total braking force Fv is calculated to increase from "0" as the braking demand Bs increases. Here, the "predetermined amount bo" is a predetermined value (constant) that is set in advance (see the target total braking force calculation block FV).

[0062] In step S130, the rear wheel target pressure Ptr and front wheel target pressure Ptf for performing dual-system pressure regulation are calculated based on the target total braking force Fv and the standard regenerative braking force Fz. In dual-system pressure regulation, the base pressure Pa and the adjustment pressure Pb are adjusted separately. Specifically, the adjustment pressure Pb is adjusted to decrease from the base pressure Pa. Therefore, the front wheel target pressure Ptf is smaller than the rear wheel target pressure Ptr (i.e., "Ptr<Ptf"). In dual-system pressure regulation, the front and rear wheel target pressures Ptf and Ptr are determined for the following three cases:

[0063] Case (1): When the target total braking force Fv is equal to or less than the standard regenerative braking force Fz, the target regenerative braking force Fh is set equal to the target total braking force Fv, and the front and rear wheel target friction braking forces Fnf, Fnr are set to 0. That is, when Fv≦Fz, it is determined that Fh=Fv, Fnf=Fnr=0.

[0064] Case (2): When the target total braking force Fv is greater than the standard regenerative braking force Fz and is equal to or less than the value "Fz / hf" obtained by dividing the standard regenerative braking force Fz by the distribution ratio hf, the target regenerative braking force Fh is set equal to the target total braking force Fv. Then, the front wheel target frictional braking force Fnf is set to "0," and the rear wheel target frictional braking force Fnr is set to a value obtained by subtracting the target regenerative braking force Fh (= Fz) from the target total braking force Fv. That is, when "Fz<Fv≦(Fz / hf)," the following are determined: Fh=Fz, Fnf=0, Fnr=Fv-Fh=Fv-Fz."

[0065] Here, the "allocation ratio hf" is the ratio of the front wheel target braking force (i.e., the sum of the target regenerative braking force Fh and the front wheel target frictional braking force Fnf) to the target total braking force Fv (resulting in the total braking force Fu). The allocation ratio hf (also called the "front wheel ratio") is set in advance as a predetermined value (constant) based on the vehicle specifications (center of gravity position, wheelbase, etc.). The allocation ratio hf is equal to the ratio of the front wheel frictional braking force Fef to the total braking force Fu when the regenerative braking force Fg is not acting and the front wheel pressure Pwf and the rear wheel pressure Pwr are equal. In other words, when "Fg = 0, Pwf = Pwr", then "hf = Fef / Fu = Fef / (Fef + Fer)".

[0066] Case (3): When the target total braking force Fv is greater than the value "Fz / hf" obtained by dividing the standard regenerative braking force Fz by the distribution ratio hf, the target regenerative braking force Fh is set equal to the target total braking force Fv. The front wheel target frictional braking force Fnf is calculated by subtracting the target regenerative braking force Fh from the value "hf·Fv" obtained by multiplying the target total braking force Fv by the front wheel ratio hf. The rear wheel target frictional braking force Fnr is calculated by subtracting the distribution ratio hf from "1" and multiplying the result by the target total braking force Fv. That is, when "Fv > (Fz / hf)," the following are determined: Fh = Fz, Fnf = hf·Fv - Fh, Fnr = (1 - hf)·Fv.

[0067] Next, a rear wheel target pressure Ptr is calculated based on the rear wheel target friction braking force Fnr. That is, the rear wheel target friction braking force Fnr is converted into the rear wheel target pressure Ptr based on the specifications of the rear wheel braking device SXr. Similarly, a front wheel target pressure Ptf is calculated based on the front wheel target friction braking force Fnf. That is, the front wheel target friction braking force Fnf is converted into the front wheel target pressure Ptf based on the specifications of the front wheel braking device SXf. The specifications of the braking device SX (= SXf, SXr) include the pressure-receiving area of ​​the wheel cylinder CW, the effective braking radius of the rotating member KT (brake disc), the friction coefficient of the friction member (brake pad), the effective radius of the wheel WH (tire), etc.

[0068] In the case (1) where Fv≦Fz, the front and rear wheel target pressures Ptf and Ptr are both maintained at 0 so that the regenerative device KG recovers the maximum amount of energy. In the case (2) where Fz<Fv≦(Fz / hf), the front wheel target pressure Ptf (resulting in the front wheel pressure Pwf) is maintained at 0, and the rear wheel target pressure Ptr (resulting in the rear wheel pressure Pwr) is increased from 0 so that the front-rear distribution of the total braking force Fu quickly reaches the predetermined ratio hf. Furthermore, in the case (3) where Fv>(Fz / hf), the front and rear wheel target pressures Ptf and Ptr are both increased in the state where Ptr>Ptf so that the front-rear distribution of the total braking force Fu is maintained at the predetermined ratio hf.

[0069] In step S140, the electric motor MA and the pressure regulating valve UC are controlled based on the rear wheel target pressure Ptr and the front wheel target pressure Ptf. Specifically, when regenerative cooperative control is performed, the electric cylinder DN (particularly the electric motor MA) controls the base pressure Pa so that the rear wheel pressure Pwr approaches and matches the rear wheel target pressure Ptr. The pressure regulating valve UC also controls the differential pressure Sa (also referred to as the "actual differential pressure") between the base pressure Pa and the regulated pressure Pb so that the front wheel pressure Pwf approaches and matches the front wheel target pressure Ptf. Specifically, the valve current Ic is adjusted so that the target differential pressure St calculated from the front and rear wheel target pressures Ptf and Ptr approaches and matches the actual differential pressure Sa calculated from the base pressure Pa and the regulated pressure Pb. Here, the base pressure Pa is acquired by the base pressure sensor PA. The regulated pressure Pb is obtained by at least one of the regulated pressure sensor PB and the supply pressure sensor PM.

[0070] <Drive Control of Electric Cylinder DN> Details of the drive control of the electric cylinder DN in step S140 will be described with reference to the block diagram of Figure 3. The electric cylinder DN (especially the electric motor MA) is controlled based on the front wheel target pressure Ptf, the rear wheel target pressure Ptr, the base pressure Pa, the adjustment pressure Pb, and the motor rotation angle Ka. The drive control of the electric motor MA is configured by a wheel pressure calculation block PW, a hydraulic pressure / liquid volume conversion block ZE, a discharged fluid volume calculation block EJ, a reference value calculation block KS, a correction value calculation block KH, a target rotation angle calculation block KT, and a rotation angle feedback control block KF.

[0071] The wheel pressure calculation block PW calculates the rear wheel pressure Pwr based on the base pressure Pa. The front wheel pressure Pwf is calculated based on the regulated pressure Pb. As described above, the target pressure Pt is determined to correspond to the wheel pressure Pw. Therefore, the rear wheel pressure Pwr is calculated from the base pressure Pa, and the front wheel pressure Pwf is calculated from the regulated pressure Pb, based on the resistance in the hydraulic pressure transmission path. Note that the transmission paths of the base pressure Pa and the regulated pressure Pb are different for the front wheel pressure Pwf and the rear wheel pressure Pwr, and this is taken into account in resistance compensation. Specifically, the regulated pressure Pb is transmitted to the front wheel cylinder CWf via the master cylinder CM and the master piston NM, so the sliding resistance of the seal member SL is taken into account in the calculation of the front wheel pressure Pwf. However, because the base pressure Pa is supplied directly to the rear wheel cylinder CWr, it is not necessary to consider the sliding resistance of the seal member SL.

[0072] The hydraulic pressure to fluid volume conversion block ZE converts (converts) hydraulic pressure to fluid volume. "Hydraulic pressure" refers to the pressure in the wheel cylinder CW, and "fluid volume" refers to the volume of brake fluid BF in the wheel cylinder CW. Front and rear wheel conversion maps Zef and Zer (corresponding to "conversion maps") are set in the hydraulic pressure to fluid volume conversion block ZE. The conversion maps Zef and Zer represent the relationship between the hydraulic pressure Pw generated in the wheel cylinder CW and the volume of brake fluid BF in the wheel cylinder CW (also referred to as "hydraulic pressure-fluid volume characteristics"). The front and rear wheel conversion maps Zef and Zer are determined in advance through experiments, analysis, etc., and are stored in the controller EA.

[0073] In the hydraulic pressure-fluid volume characteristic (nonlinear characteristic of wheel pressure Pw), when the wheel pressure Pw is low, a larger amount of fluid is required to generate the wheel pressure Pw compared to when the wheel pressure Pw is high. Conversely, when the wheel pressure Pw is high, a smaller amount of fluid can be used to generate the wheel pressure Pw compared to when the wheel pressure Pw is low. In other words, in the hydraulic pressure-fluid volume characteristic, the fluid volume increases in an "upward convex" manner as the wheel pressure Pw increases. The nonlinearity of the hydraulic pressure-fluid volume characteristic is based on the fact that the stiffness characteristics (for example, stiffness of the brake caliper, friction members, etc.) of the brake device SX (= SXf, SXr) are nonlinear. Because the stiffness characteristics of the front wheel brake device SXf and the rear wheel brake device SXr are different, the front wheel and rear wheel conversion maps Zef and Zer are set separately.

[0074] The hydraulic pressure / fluid volume conversion block ZE includes a reference fluid volume calculation block ES and an estimated fluid volume calculation block EE. The reference fluid volume calculation block ES calculates a reference fluid volume Es based on the target pressure Pt (=Ptf, Ptr) and the front and rear wheel conversion maps Zef and Zer. The "reference fluid volume Es" is the amount (volume) of brake fluid BF that should flow into the front wheel cylinder CWf and the rear wheel cylinder CWr to achieve the target pressure Pt. In other words, the reference fluid volume Es is the target value for the amount of fluid that should be supplied from the control cylinder CC to the wheel cylinder CW.

[0075] Specifically, the standard fluid volume calculation block ES calculates a front wheel standard fluid volume Esf based on the front wheel target pressure Ptf and the front wheel conversion map Zef. The "front wheel standard fluid volume Esf" is the amount of fluid (the volume of brake fluid BF) that should flow into the front wheel cylinder CWf to achieve the front wheel target pressure Ptf. Similarly, the standard fluid volume calculation block ES calculates a rear wheel standard fluid volume Esr based on the rear wheel target pressure Ptr and the rear wheel conversion map Zer. The "rear wheel standard fluid volume Esr" is the amount of fluid that should flow into the rear wheel cylinder CWr to achieve the rear wheel target pressure Ptr. The front wheel standard fluid volume Esf and the rear wheel standard fluid volume Esr are then added together to determine the standard fluid volume Es (i.e., "Es = Esf + Esr"). In other words, the standard fluid volume Es is the sum of the front wheel standard fluid volume Esf and the rear wheel standard fluid volume Esr.

[0076] The estimated fluid volume calculation block EE calculates an estimated fluid volume Ee based on the "front wheel pressure Pwf calculated from the adjusted pressure Pb," the "rear wheel pressure Pwr calculated from the base pressure Pa," and the "front and rear wheel conversion maps Zef and Zer." The "estimated fluid volume Ee" is the amount (volume) of brake fluid BF that should have already been supplied to the front wheel cylinders CWf and the rear wheel cylinders CWr to generate the wheel pressure Pw (= Pwf, Pwr). Specifically, the front wheel estimated fluid volume Eef is calculated based on the front wheel pressure Pwf and the front wheel conversion map Zef (i.e., the hydraulic pressure-fluid volume characteristics of the front wheel cylinder CWf). Similarly, the rear wheel estimated fluid volume Eer is calculated based on the rear wheel pressure Pwr and the rear wheel conversion map Zer (i.e., the hydraulic pressure-fluid volume characteristics of the rear wheel cylinder CWr). The front wheel estimated fluid volume Eef and the rear wheel estimated fluid volume Eer are then added together to determine the estimated fluid volume Ee (i.e., "Ee = Eef + Eer"). In other words, the estimated fluid volume Ee is the sum of the front wheel estimated fluid volume Eef and the rear wheel estimated fluid volume Eer, and is the amount of fluid estimated to have flowed from the control cylinder CC into the front and rear wheel cylinders CWf and CWr. Note that the front and rear wheel pressures Pwf and Pwr are derived from the base pressure Pa and the regulated pressure Pb, so it can be said that "the estimated fluid volume calculation block EE calculates the estimated fluid volume Ee based on the base pressure Pa, the regulated pressure Pb, and the conversion maps Zef and Zer."

[0077] The fluid discharge volume calculation block EJ calculates the fluid discharge volume Ej based on the motor rotation angle Ka (actual value). The "fluid discharge volume Ej" is the amount (volume) of brake fluid BF actually discharged (discharged) from the electric cylinder DN (i.e., the control cylinder CC). The fluid discharge volume calculation block EJ converts the rotation angle Ka into the fluid discharge volume Ej based on the specifications of the electric cylinder DN. The specifications of the electric cylinder DN include the reduction ratio of the reducer GS, the lead of the conversion mechanism GH (the displacement of the linearly acting member per one rotation of the rotating member), the pressure-receiving area of ​​the control piston NC, etc.

[0078] The fluid discharge volume calculation block EJ may use the piston stroke Sn to obtain the fluid discharge volume Ej (the volume of fluid delivered from the control cylinder CC). Specifically, the electric cylinder DN is provided with a stroke sensor SN that obtains the displacement (piston stroke) of the control piston NC. The fluid discharge volume Ej is determined based on the piston stroke Sn and the pressure-receiving area of ​​the control piston NC. The rotation angle sensor KA and the stroke sensor SN are used to determine the fluid discharge volume Ej from the control cylinder CC, and are therefore collectively referred to as "fluid volume sensors." In other words, the fluid discharge volume calculation block EJ determines the fluid discharge volume Ej based on the detection results of the fluid volume sensors KA and SN.

[0079] The reference value calculation block KS determines a reference value Ks based on the standard fluid volume Es (= Esf + Esr). The "reference value Ks" is a state variable (variable) for determining a target value for controlling the electric motor MA. Specifically, the reference value Ks is a state variable obtained by converting the standard fluid volume Es into a dimension (i.e., a physical quantity) ranging from the standard fluid volume Es to the rotation angle of the electric motor MA. For example, the dimension (physical quantity) of the reference value Ks may be any one of the dimensions of the fluid volume, the displacement of the control piston NC, and the rotation angle of the electric motor MA. The specifications of the components of the electric cylinder DN are known. The reference value calculation block KS converts the standard fluid volume Es into the reference value Ks based on the specifications of the electric cylinder DN (e.g., the reduction ratio of the reducer GS, the lead of the conversion mechanism GH, the pressure-receiving area of ​​the control piston NC, etc.). Therefore, the reference value Ks is determined to be larger as the standard fluid volume Es increases.

[0080] The correction value calculation block KH calculates a correction value Kh based on the estimated fluid volume Ee and the discharge fluid volume Ej. The front and rear wheel conversion maps Zef and Zer are preset, but they contain errors due to variations, aging, and the like. These errors are caused by the presence or absence of gas inside the braking device SX, wear of friction members, and the like. The "correction value Kh" is a state quantity (variable) for compensating for these errors. The correction value calculation block KH calculates the deviation hE (fluid volume deviation) between the estimated fluid volume Ee and the discharge fluid volume Ej. For example, the estimated fluid volume Ee is subtracted from the discharge fluid volume Ej to determine the fluid volume deviation hE (i.e., "hE = Ej - Ee"). The fluid volume deviation hE is then converted into the same dimension (physical quantity) as the reference value Ks based on the specifications of the components of the electric cylinder DN, and the correction value Kh is determined. Therefore, the larger the liquid volume deviation hE, the larger the correction value Kh is determined to be, and the smaller the liquid volume deviation hE, the smaller the correction value Kh is determined to be.

[0081] The target rotation angle Kt is calculated in the target rotation angle calculation block KT based on the reference value Ks and the correction value Kh. The "target rotation angle Kt" is the final target value for controlling the rotation angle Ka of the electric motor MA. For example, the reference value Ks and the correction value Kh are added together to determine the command value Ku (i.e., "Ku = Ks + Kh"). The "command value Ku" corresponds to an intermediate target value for determining the target rotation angle Kt. Here, the physical quantity (dimension) of the command value Ku is the same as the physical quantities of the reference value Ks and the correction value Kh.

[0082] The correction value Kh is a state variable for making the rear wheel pressure Pwr coincide with the rear wheel target pressure Ptr. In other words, the correction of the reference value Ks based on the correction value Kh corresponds to feedback control of the amount of brake fluid BF. The correction using the correction value Kh also functions as feedback control of the hydraulic pressure. This is based on the fact that "the estimated hydraulic pressure Ee is determined from the hydraulic pressures Pwf and Pwr (actual values)" and "when the hydraulic pressure is optimized, the hydraulic pressure is also optimized." In the brake control device SA, feedback control based on the correction value Kh controls the rear wheel pressure Pwr to approach and coincide with the rear wheel target pressure Ptr.

[0083] The target rotation angle calculation block KT calculates the target rotation angle Kt based on the command value Ku. Specifically, the command value Ku is converted into the dimension (physical quantity) of the motor rotation angle Ka using the specifications of the components of the electric cylinder DN (e.g., the reduction ratio of the reducer GS, the lead of the conversion mechanism GH, etc.), and the target rotation angle Kt is determined. When determining the target rotation angle Kt, the responsiveness of the electric motor MA can be taken into consideration. For example, a response model of the electric motor MA may impose a limit on the response speed (i.e., the amount of change per unit time) of the target rotation angle Kt. This is based on the fact that even if a step-like change in the target rotation angle Kt is calculated, the electric motor MA cannot keep up with it. In any case, the target rotation angle calculation block KT determines the target rotation angle Kt, which is the final target value, based on the reference value Ks and the correction value Kh.

[0084] The rotational angle feedback control block KF controls the electric motor MA based on the target rotational angle Kt and the actual motor rotational angle Ka. Specifically, a drive signal Ma for the electric motor MA is determined so that the motor rotational angle Ka (actual value) acquired by the rotational angle sensor KA approaches and matches the target rotational angle Kt (target value) (i.e., so that the deviation hK between the target value Kt and the actual value Ka approaches "0"). The drive circuit DR (inverter circuit) then adjusts the current Im (motor current) supplied to the electric motor MA based on the motor drive signal Ma. In other words, the rotational angle feedback control block KF executes what is known as rotational angle feedback control.

[0085] In the brake control device SA, the rotation angle Ka of the electric motor MA is converted into the displacement of the control piston NC by the conversion mechanism GH. A fluid volume (the volume of brake fluid BF) corresponding to the displacement of the control piston NC is discharged from the control cylinder CC to the wheel cylinder CW. The wheel pressure Pw is determined by the amount of fluid flowing into the wheel cylinder CW according to the hydraulic pressure-fluid volume characteristic of the wheel cylinder CW. The hydraulic pressure-fluid volume characteristic is also called the "fluid consumption volume characteristic" because it is the amount of fluid consumed in the wheel cylinder CW to generate the wheel pressure Pw.

[0086] The brake control device SA determines a target rotation angle Kt based on a rear wheel standard fluid volume Esr calculated from the rear wheel target pressure Ptr and a front wheel standard fluid volume Esf calculated from the front wheel target pressure Ptf. The electric motor MA is then controlled so that the actual rotation angle Ka coincides with the target rotation angle Kt. As a result, an appropriate amount of brake fluid BF is discharged from the electric cylinder DN (particularly the control cylinder CC) to achieve the base pressure Pa.

[0087] The front and rear wheel conversion maps Zef and Zer, which are stored in advance in the brake controller EA (particularly the microprocessor MP) as hydraulic pressure-liquid volume characteristics (liquid consumption volume characteristics), include errors due to the presence of gas (air, etc.) in the device, wear of the friction members, etc. Specifically, when gas is present, a larger amount of fluid is required to achieve the same hydraulic pressure compared to when no gas is present. Also, when the friction members are heavily worn, a smaller amount of fluid is required to achieve the same hydraulic pressure compared to when the wear is small.

[0088] The brake control device SA determines a correction value Kh to compensate for errors in the conversion maps Zef and Zer. The correction value Kh is determined based on the estimated rear wheel fluid volume Eer (the amount of fluid estimated to have flowed into the rear wheel cylinder CWr) calculated from the base pressure Pa, the estimated front wheel fluid volume Eef (the amount of fluid estimated to have flowed into the front wheel cylinder CWf) calculated from the adjustment pressure Pb, and the fluid volume Ej (the amount of fluid discharged) actually discharged from the control cylinder CC. The discharge fluid volume Ej is obtained by the fluid volume sensors KA and SN. The same conversion maps Zef and Zer used to calculate the standard fluid volume Es are used to calculate the estimated fluid volume Ee. Therefore, the correction value Kh, which is based on the deviation hE between the estimated fluid volume Ee and the discharge fluid volume Ej, represents the error contained in the conversion maps Zef and Zer. The reference value Ks is corrected by the correction value Kh to determine the target rotation angle Kt, thereby correcting the influence of the error.

[0089] The fluid volume deviation hE is determined by subtracting the estimated fluid volume Ee from the discharged fluid volume Ej (i.e., "hE = Ej - Ee"). When the discharged fluid volume Ej is greater than the estimated fluid volume Ee (i.e., "Ej > Ee, hE > 0"), the conversion maps Zef and Zer are shifted in a manner that reduces the fluid volume along the vertical axis (hydraulic pressure axis) relative to the true value. In other words, in the conversion maps Zef and Zer, the fluid volume is determined to be smaller than the true value at the same fluid pressure. Therefore, a correction value Kh calculated from the fluid volume deviation hE is added to the reference value Ks calculated from the standard fluid volume Es, thereby correcting the target rotation angle Kt to be larger. On the other hand, when the discharged fluid volume Ej is smaller than the estimated fluid volume Ee (i.e., "Ej < Ee, hE < 0"), the conversion maps Zef, Zer, and Zek are shifted in a manner that expands the fluid volume along the vertical axis (hydraulic pressure axis) relative to the true value. In other words, in the conversion maps Zef and Zer, the fluid volume is determined to be larger than the true value at the same hydraulic pressure. Therefore, the target rotation angle Kt is corrected to be smaller by the correction value Kh calculated from the fluid volume deviation hE. The correction value Kh is determined to be larger as the fluid volume deviation hE is larger, including the positive and negative signs. By correcting based on the fluid volume deviation hE, the amount Ej (fluid discharge amount) of brake fluid BF discharged from the electric cylinder DN (particularly the control cylinder CC) is adjusted to be just enough relative to the target pressures Ptf and Ptr. As a result, the electric cylinder DN can accurately adjust the rear wheel pressure Pwr to match the rear wheel target pressure Ptr.

[0090] <Drive Control of Pressure Regulator Valve UC> The drive control of the pressure regulator valve UC in step S140 will be described in detail with reference to the block diagram of Figure 4. The pressure regulator valve UC is controlled based on the front wheel target pressure Ptf, the rear wheel target pressure Ptr, the base pressure Pa, and the regulated pressure Pb. The drive control of the pressure regulator valve UC is configured by a target differential pressure calculation block ST, a command current calculation block IS, an actual differential pressure calculation block SA, a differential pressure deviation calculation block HS, a compensation current calculation block IH, a target valve current calculation block IT, and a current feedback control block IF.

[0091] A target differential pressure calculation block ST calculates a target differential pressure St based on the rear wheel target pressure Ptr and the front wheel target pressure Ptf. The "target differential pressure St" is a target value of the hydraulic force difference (differential pressure) generated by the pressure regulator valve UC. Specifically, the target differential pressure St is determined by subtracting the front wheel target pressure Ptf from the rear wheel target pressure Ptr, taking the above resistance into consideration.

[0092] A command current calculation block IS calculates a command current Is based on the target differential pressure St and a preset calculation map Zis. The "command current Is" is a target value corresponding to the valve current Ic (actual value) supplied to the pressure regulating valve UC. The command current Is is determined in accordance with the calculation map Zis so that it increases as the target differential pressure St increases.

[0093] The actual differential pressure calculation block SA calculates the actual differential pressure Sa based on the basal pressure Pa and the regulated pressure Pb. The "actual differential pressure Sa" is the hydraulic force difference (actual differential pressure) actually occurring at the pressure regulating valve UC. Specifically, the actual differential pressure Sa is determined by subtracting the regulated pressure Pb from the basal pressure Pa (i.e., "Sa = Pa - Pb"). Here, the basal pressure Pa is detected by the basal pressure sensor PA. The regulated pressure Pb is detected by at least one of the regulated pressure sensor PB and the supply pressure sensor PM.

[0094] A differential pressure deviation calculation block HS calculates a differential pressure deviation hS based on the target differential pressure St and the actual differential pressure Sa. The "differential pressure deviation hS" is the deviation between the target differential pressure St and the actual differential pressure Sa, and corresponds to an error in the control of the pressure regulating valve UC. When a valve current Ic equal to the command current Is is supplied to the pressure regulating valve UC, the actual differential pressure Sa should essentially match the target differential pressure St. However, in reality, an error hS occurs. Specifically, the differential pressure deviation hS is determined by subtracting the actual differential pressure Sa from the target differential pressure St (i.e., "hS = St - Sa").

[0095] A compensation current calculation block IH calculates a compensation current Ih based on the differential pressure deviation hS and a preset calculation map Zih. The "compensation current Ih" is used to compensate for the error hS and make the actual differential pressure Sa equal to the target differential pressure St. The compensation current Ih is determined in accordance with the calculation map Zih so that it increases as the differential pressure deviation hS increases. Note that a dead band is provided in the calculation map Zih.

[0096] A target valve current calculation block IT calculates a target valve current It based on the command current Is and the compensation current Ih. The "target valve current It" is the final target value of the valve current Ic supplied to the pressure regulating valve UC. Specifically, the target valve current It is determined by adding the compensation current Ih to the command current Is (i.e., "It = Is + Ih"). The target valve current calculation block IT determines the target valve current It using the compensation current Ih so that the actual differential pressure Sa approaches and matches the target differential pressure St.

[0097] For example, if the target differential pressure St is greater than the actual differential pressure Sa, the actual differential pressure Sa is insufficient. In the differential pressure deviation calculation block HS, the differential pressure deviation hS is determined as a positive value, and the compensation current Ih is determined as a positive value according to the calculation map Zih. In the target valve current calculation block IT, the target valve current It is increased from the command current Is by the compensation current Ih, so the insufficient actual differential pressure Sa is increased to match the target differential pressure St. Conversely, if the target differential pressure St is smaller than the actual differential pressure Sa, the actual differential pressure Sa is in excess, and the differential pressure deviation hS is determined as a negative value. As a result, the compensation current Ih is also determined as a negative value, and the target valve current It is reduced from the command current Is. As a result, the excessive actual differential pressure Sa is reduced to match the target differential pressure St. In other words, the compensation current Ih brings the differential pressure deviation hS (error) closer to "0" and matches.

[0098] The current feedback control block IF determines a drive signal Uc for the pressure regulating valve Uc so that the actual valve current Ic approaches and matches the target valve current It (i.e., so that the deviation hI between the target value It and the actual value Ic approaches "0").The drive circuit DR then supplies power to the pressure regulating valve UC based on the drive signal Uc. That is, the current feedback control block IF executes so-called current feedback control.The valve current Ic is detected by a valve current sensor IC provided in the drive circuit DR.

[0099] The pressure regulating valve UC (linear solenoid valve) adjusts its valve opening amount in accordance with the supplied valve current Ic. By adjusting the valve opening amount, the pressure regulating valve UC controls the hydraulic pressure Pa (base pressure) on the side closer to the electric cylinder DN, the hydraulic pressure Pb (adjusted pressure) on the side farther from the electric cylinder DN, and the hydraulic pressure difference Sa. Therefore, the braking control device SA controls the valve current Ic of the pressure regulating valve UC based on the differential pressure St (target differential pressure) to be generated in the pressure regulating valve UC. Furthermore, the valve current Ic is finely adjusted to reduce an error hS (differential pressure deviation), which is the difference between the actually generated differential pressure Sa (actual differential pressure) and the target differential pressure St. This allows the pressure regulating valve UC to accurately adjust the base pressure Pa generated in the electric cylinder DN to the adjusted pressure Pb.

[0100] Note that when the adjustment pressure Pb is adjusted to match the front wheel target pressure Ptf, the amount of fluid supplied to the front wheel cylinder CWf changes, affecting the base pressure Pa (and consequently the rear wheel pressure Pwr). However, the adjustment of the base pressure Pa takes into account not only the rear wheel target pressure Ptr and the base pressure Pa, but also the front wheel target pressure Ptf and the adjustment pressure Pb. In other words, changes in the base pressure Pa caused by changes in the adjustment pressure Pb are compensated for by a feedback control loop (i.e., a closed loop) via the correction value Kh. Therefore, even if the adjustment pressure Pb changes, the rear wheel pressure Pwr is adjusted to match the rear wheel target pressure Ptr.

[0101] <Second embodiment of brake control device SA> A second embodiment of the brake control device SA for a vehicle will be described with reference to the schematic diagram of Fig. 5. In the second embodiment, the electric motor MA and the pressure regulating valve UC are controlled in the same manner as in the first embodiment.

[0102] In the first embodiment, the adjustment pressure Pb is transmitted as the supply pressure Pm via the master cylinder CM and the master piston NM. That is, the apply unit AP and the hydraulic pressure generating unit PU are arranged in series in the hydraulic pressure transmission path. However, instead of this configuration, the apply unit AP and the hydraulic pressure generating unit PU may be arranged in parallel. In the second embodiment, the apply unit AP (particularly the master cylinder CM) and the hydraulic pressure generating unit PU are each directly connected to the hydraulic pressure correcting device SZ (particularly the correcting actuator YZ).

[0103] Specifically, in the brake control device SA according to the second embodiment, a shutoff valve VM, a simulator valve VS, and a communication valve VC are provided in place of the input unit NR. The shutoff valve VM is a normally open solenoid valve, and the simulator valve VS and the communication valve VC are normally closed solenoid valves. The shutoff valve VM is provided in a front wheel communication passage HSf that connects the master cylinder CM (particularly, the master chamber Rm) and the front wheel cylinders CWf. The stroke simulator SS is connected to the front wheel communication passage HSf between the master cylinder CM and the shutoff valve VM via the simulator valve VS.

[0104] The front-wheel / rear-wheel communication passages HSf, HSr (fluid passages connecting the front-wheel and rear-wheel wheel cylinders CWf, CWr) are connected to the control cylinder CC (particularly, the control chamber Rc) via a communication passage HV (fluid passage). The communication passage HV is also a fluid passage connecting the front-wheel communication passage HSf and the rear-wheel communication passage HSf. A pressure adjusting valve UC and a communication valve VC are provided in the communication passage HV.

[0105] As described above, the pressure regulating valve UC prevents the flow of brake fluid BF from the control cylinder CC toward the front wheel cylinder CWf by the thrust of the solenoid, thereby enabling the pressure regulating valve UC to regulate the adjustment pressure Pb (i.e., the front wheel pressure Pwf) to be smaller than the base pressure Pa (i.e., the rear wheel pressure Pwr).

[0106] That is, the pressure regulating valve UC is provided in the hydraulic pressure transmission path from the control cylinder CC to the front wheel cylinder CWf. The pressure regulating valve UC reduces the base pressure Pa to a regulated pressure Pb, which is transmitted to the front wheel cylinder CWf as a front wheel pressure Pwf. In contrast, the base pressure Pa is transmitted to the rear wheel cylinder CWr as a rear wheel pressure Pwr. Note that the pressure regulating valve UC alone cannot reduce the regulated pressure Pb; a reduction in the base pressure Pa is essential to reduce the regulated pressure Pb.

[0107] During pressure regulation control, power is supplied to the shutoff valve VM, simulator valve VS, and communication valve VC. This closes the shutoff valve VM and opens the simulator valve VS and communication valve VC. The master chamber Rm is disconnected from the front wheel cylinder CWf, and the regulated pressure Pb is supplied to the front wheel cylinder CWf. Since the master chamber Rm is connected to the stroke simulator SS, the operating force of the brake operating member BP (brake pedal) is generated by the stroke simulator SS. The regulated pressure sensor PB may be provided in the hydraulic pressure generating unit PU or in the correction actuator YZ. In a configuration in which the regulated pressure sensor PB is provided in the correction actuator YZ, the regulated pressure Pb is acquired by the brake controller EA via the communication bus BS.

[0108] In the second embodiment, the same regenerative cooperative control as in the first embodiment is executed. Specifically, the base pressure Pa generated by the electric cylinder DN is adjusted to the regulated pressure Pb by the pressure regulating valve UC. In the second embodiment, the same effect as in the first embodiment (appropriate control of the electric motor MA and the pressure regulating valve UC for dual-system pressure regulation) is achieved.

[0109] <Other Embodiments of Brake Control Device SA> Other embodiments of the brake control device SA including the electric cylinder DN will be described. The other embodiments also provide the same effects as those described above.

[0110] In the embodiment of the brake control device SA described above, the base pressure Pa is obtained as a detection result from the base pressure sensor PA provided at the discharge portion of the electric cylinder DN. Alternatively, the base pressure sensor PA may be provided in the hydraulic pressure transmission path from the control cylinder CC to the rear wheel cylinder CWr. In either case, the base pressure Pa used in calculating the estimated hydraulic volume Ee and the actual differential pressure Sa is based on the actual value detected by the base pressure sensor PA.

[0111] Similarly, the adjustment pressure Pb is obtained from the detection result of the adjustment pressure sensor PB provided between the pressure regulator valve UC and the servo chamber Ru. Alternatively, the adjustment pressure sensor PB may be provided in the hydraulic pressure transmission path from the control cylinder CC to the front wheel cylinder CWf (see, for example, the supply pressure sensor PM). In either case, the adjustment pressure Pb used in calculating the estimated hydraulic volume Ee and the actual differential pressure Sa is based on the actual value detected by the adjustment pressure sensor PB.

[0112] In the embodiment of the brake control device SA described above, the discharge fluid volume Ej is obtained from the detection results of at least one of the rotation angle sensor KA and the stroke sensor SN. That is, the discharge fluid volume Ej is calculated based on the displacement Sn of the control piston NC obtained from the motor rotation angle Ka, the piston stroke Sn, etc. Alternatively, a flow rate sensor may be provided to detect the flow rate (fluid volume per unit time) from the control cylinder CC, and the discharge fluid volume Ej may be obtained from the detection value of the flow rate sensor. For example, an ultrasonic type, an electromagnetic type, etc. may be used as the flow rate sensor. In either case, the discharge fluid volume Ej (actual value) is based on the detection result of the fluid volume sensor that detects the discharge volume of brake fluid BF from the electric cylinder DN.

[0113] In the embodiment of the brake control device SA described above, the target pressure Pt (=Ptf, Ptr) is determined as a target value corresponding to the wheel pressure Pw (=Pwf, Pwr). That is, the location where the target value and the actual value are compared (also referred to as the "comparison location") is the wheel cylinder CW. Alternatively, the comparison location may be any location along the hydraulic pressure transmission path from the discharge port of the electric cylinder DN to the wheel cylinder CW. For example, the detection location of the base pressure sensor PA or the adjustment pressure sensor PB may be used as the comparison location. In this configuration, the target pressures Ptf, Ptr are determined to correspond to the base pressure Pa and adjustment pressure Pb, with the hydraulic pressure component due to the resistance compensated for. In pressure regulation control, regardless of where the target value and actual value are compared, the front and rear wheel target pressures Ptf and Ptr are target values ​​for controlling the basal pressure Pa and the regulated pressure Pb, the standard fluid volume Es is determined based on the front and rear wheel target pressures Ptf and Ptr, and the estimated fluid volume Ee is determined based on the basal pressure Pa and the regulated pressure Pb. Furthermore, the target differential pressure St is determined based on the front and rear wheel target pressures Ptf and Ptr, and the actual differential pressure Sa is determined based on the basal pressure Pa and the regulated pressure Pb.

[0114] In the embodiment of the brake control device SA described above, a disc-type brake device SX is used as the brake device SX. Alternatively, a drum-type brake device SX may be used. In a drum-type brake device SX, the rotating member KT fixed to the wheel WH is a brake drum, and the friction member is a brake lining attached to a brake shoe. In a drum-type brake device SX, as in a disc-type brake device SX, the wheel pressure Pw of the wheel cylinder CW presses the brake lining (friction member) against the brake drum (rotating member), generating a frictional braking force Fe.

[0115] In the embodiment of the brake control device SA described above, the target values ​​of various braking forces (Fv, Fz, Fh, Fn, etc.) are calculated in the dimension of the longitudinal force acting on the vehicle (corresponding physical quantity). Alternatively, they may be calculated in the dimension of the acceleration of the vehicle or the torque of the wheels WH. This is based on the fact that state quantities from the longitudinal force to the vehicle acceleration (referred to as "state quantities related to force") are equivalent. Therefore, the target pressures Ptf, Ptr, etc. are calculated based on the braking demand Bs via state quantities related to the force from the longitudinal force acting on the vehicle to the deceleration of the vehicle.

[0116] In the above-described embodiment of the brake control device SA, the pressure regulating valve UC is provided in the servo path HU or the communication path HV. Alternatively, the pressure regulating valve UC may be provided in the front wheel connecting path HSf. Specifically, the pressure regulating valve UC is disposed in the front wheel connecting path HSf, between the portion to which the base pressure Pa is transmitted and the front wheel cylinder CWf. In either case, the pressure regulating valve UC is provided in the hydraulic pressure transmission path from the control cylinder CC to the front wheel cylinder CWf. The pressure regulating valve UC reduces the base pressure Pa to an adjusted pressure Pb, which is transmitted to the front wheel cylinder CWf as the front wheel pressure Pwf.

[0117] In the first embodiment of the brake control device SA described above, the pressure-receiving area rm (master area) of the master chamber Rm and the pressure-receiving area ru (servo area) of the servo chamber Ru in the apply unit AP are set equal. The master area rm and the servo area ru do not have to be equal. In a configuration in which the master area rm and the servo area ru are different, the supply pressure Pm (master pressure) can be converted to the base pressure Pa based on the area ratio between the servo area ru and the master area rm (i.e., conversion based on "Pm rm = Pa ru"). In a configuration in which the supply pressure sensor PM is used as the adjustment pressure sensor PB and the supply pressure Pm is used as the adjustment pressure Pb, the supply pressure Pm is converted to the adjustment pressure Pb based on the area ratio.

[0118] Summary of the embodiment The brake control device SA is applied to a vehicle equipped with a regenerative device KG on the front wheels WHf. The brake control device SA is composed of a control cylinder CC, a pressure regulating valve UC (solenoid valve), and a brake controller EA. The control cylinder CC generates a base pressure Pa using an electric motor MA as a power source, the pressure regulating valve UC adjusts the base pressure Pa to an adjusted pressure Pb, and the controller EA controls the electric motor MA and the pressure regulating valve UC. The brake control device SA generates a base pressure Pa and an adjusted pressure Pb based on the vehicle's required braking amount Bs, and controls a hydraulic pressure Pwf in the front wheel cylinders CWf using the adjusted pressure Pb, while controlling a hydraulic pressure Pwr in the rear wheel cylinders CWr using the base pressure Pa. The adjusted pressure Pb is smaller than the base pressure Pa.

[0119] For example, the brake control device SA has a master chamber Rm and a servo chamber Ru that face each other via a master piston NM. A control cylinder CC is connected to the servo chamber Ru and the rear wheel cylinder CWr. The master chamber Rm is connected to the front wheel cylinder CWf, and a pressure regulating valve UC is disposed between the control cylinder CC and the servo chamber Ru. With this configuration, the hydraulic pressure Pwf (front wheel pressure) in the front wheel cylinder CWf is controlled by the adjustment pressure Pb, and the hydraulic pressure Pwr (rear wheel pressure) in the rear wheel cylinder CWr is controlled by the base pressure Pa.

[0120] In the brake control system SA, the controller EA calculates a rear wheel standard fluid amount Esr as the amount of fluid to be supplied to the rear wheel cylinder CWr based on a rear wheel target pressure Ptr for controlling the base pressure Pa, and calculates a front wheel standard fluid amount Esf as the amount of fluid to be supplied to the front wheel cylinder CWf based on a front wheel target pressure Ptf for controlling the adjustment pressure Pb.The controller EA then controls the electric motor MA based on the front and rear wheel standard fluid amounts Esf and Esr.At the same time, the controller EA controls the pressure regulating valve UC based on the rear wheel target pressure Ptr and the front wheel target pressure Ptf.

[0121] The wheel pressure Pw is determined by the amount (fluid volume) of brake fluid BF flowing into the wheel cylinder CW. For this reason, the brake control device SA is provided with front and rear wheel conversion maps Zef and Zer. The conversion maps Zef and Zer correspond to a hydraulic pressure-fluid volume characteristic (a nonlinear characteristic in which the fluid volume relative to the hydraulic pressure is "upwardly convex") that represents the relationship between the hydraulic pressure Pw (wheel pressure) generated in the wheel cylinder CW and the fluid volume (volume) of the brake fluid BF supplied to the wheel cylinder CW. Specifically, the conversion maps Zef and Zer define the rate of increase in the standard fluid volumes Esf and Esr in response to an increase in the target pressures Ptf and Ptr, and the rate of increase in the estimated fluid volumes Eef and Eer in response to an increase in the actual hydraulic pressures Pa and Pb.

[0122] The brake control device SA converts hydraulic pressures (Ptf, Ptr, Pa, Pb, etc.) into hydraulic fluid volumes (Esf, Esr, Eef, Eer, etc.) using conversion maps Zef and Zer. That is, a standard hydraulic fluid volume Es (i.e., the sum of the standard hydraulic fluid volumes Esf and Esr) is determined based on the front and rear wheel target pressures Ptf and Ptr and the front and rear wheel conversion maps Zef and Zer. The rotation angle Ka of the electric motor MA is then controlled based on the standard hydraulic fluid volume Es. Since the standard hydraulic fluid volume Es corresponds to the amount of hydraulic fluid that the control cylinder CC must discharge in order to achieve the front and rear wheel target pressures Ptf and Ptr, the required amount of brake fluid BF is discharged from the electric cylinder DN (particularly the control cylinder CC).

[0123] The front and rear wheel conversion maps Zef and Zer are pre-stored as predetermined characteristics in the controller EA (particularly, the microprocessor MP). However, errors occur in the conversion maps Zef and Zer due to gas (e.g., air) present inside the brake device SX, wear of friction members, and other factors. The brake control device SA calculates a correction value Kh to compensate for the errors in the conversion maps Zef and Zer. Specifically, the estimated fluid volume Eef (front wheel estimated fluid volume) supplied to the front wheel cylinder CWf is calculated from the adjustment pressure Pb based on the front wheel conversion map Zef. Furthermore, the estimated fluid volume Eer (rear wheel estimated fluid volume) supplied to the rear wheel cylinder CWr is calculated from the base pressure Pa based on the rear wheel conversion map Zer. Furthermore, the fluid volume Ej (discharge volume) actually discharged from the control cylinder CC is obtained from the detection value of a fluid volume sensor. Here, the basal pressure Pa (actual value) is obtained by a basal pressure sensor (e.g., PA), and the adjusted pressure Pb (actual value) is obtained by an adjusted pressure sensor (e.g., PB, PM). The discharged fluid volume Ej (actual value) is obtained by a fluid volume sensor (e.g., KA, SN). The sum of the front wheel estimated fluid volume Eef and the rear wheel estimated fluid volume Eer is calculated as the estimated fluid volume Ee, and a correction value Kh is calculated based on the deviation hE (fluid volume deviation) between the estimated fluid volume Ee and the discharged fluid volume Ej. Because the correction value Kh is a state quantity obtained by converting the fluid volume deviation hE into the dimension (physical quantity) of the reference value Ks, the correction value Kh is determined to be larger as the fluid volume deviation hE increases.

[0124] As described above, the conversion maps Zef and Zer used to calculate the reference value Ks contain errors, and the correction value Kh represents the errors contained in the conversion maps Zef and Zer. In the brake control device SA, the reference value Ks is corrected by the correction value Kh to determine the target rotation angle Kt. This allows the amount Ej (discharge amount) of brake fluid BF discharged (exhausted) by the electric cylinder DN (particularly the control cylinder CC) to be adjusted so that it is neither too much nor too little with respect to the target pressures Ptf and Ptr. As a result, the accuracy of pressure regulation by the electric cylinder DN is improved.

[0125] The controller EA calculates a target valve current It based on a target differential pressure St calculated from the front and rear wheel target pressures Ptf and Ptr, and controls the valve current Ic (actual value) supplied to the pressure regulator valve UC so that it coincides with the target valve current It (target value). Furthermore, the controller EA calculates an actual differential pressure Sa from the base pressure Pa and the regulated pressure Pb, and determines a deviation hS between the target differential pressure St and the actual differential pressure Sa. The controller EA then adjusts the target valve current It so that the differential pressure deviation hS becomes "0".

[0126] The pressure regulating valve UC adjusts the differential pressure Sa (actual differential pressure) between the hydraulic pressure Pa on the side closer to the electric cylinder DN and the hydraulic pressure Pb on the side farther from the electric cylinder DN, in accordance with the valve current Ic supplied thereto. The brake control device SA controls the valve current Ic of the pressure regulating valve UC based on the target differential pressure St (the differential pressure to be generated by the pressure regulating valve UC). Furthermore, since the adjustment of the actual differential pressure Sa involves an error, the brake control device SA fine-tunes the target valve current It (and consequently the valve current Ic) based on the differential pressure deviation hS (the deviation between the target differential pressure St and the actual differential pressure Sa). This improves the accuracy of pressure regulation by the pressure regulating valve UC.

[0127] When the regulated pressure Pb is adjusted so that the front wheel pressure Paf coincides with the front wheel target pressure Ptf, this affects the base pressure Pa. However, because the base pressure Pa is adjusted according to the correction value Kh, changes in the base pressure Pa caused by changes in the regulated pressure Pb are compensated for each time. In other words, even if the regulated pressure Pb changes, the base pressure Pa is adjusted so that the rear wheel pressure Pwr coincides with the rear wheel target pressure Ptr.

[0128] As described above, in the brake control device SA that individually adjusts the wheel pressures Pwf, Pwr of the front and rear wheel cylinders CWf, CWr by dual pressure regulation, the electric motor MA and the pressure regulating valve UC are appropriately controlled, thereby adjusting the base pressure Pa and the regulating pressure Pb with high precision in the dual pressure regulation. As a result, the amount of energy regeneration is ensured and the running stability of the vehicle is improved.

Claims

1. A vehicle braking control device applied to a vehicle equipped with a regenerative device on the front wheels, comprising a control cylinder which generates a base pressure using an electric motor as a power source, a solenoid valve which adjusts the base pressure to an adjustment pressure, and a controller which controls the electric motor and the solenoid valve, and which controls the front wheel pressure in the front wheel cylinder with the adjustment pressure and the rear wheel pressure in the rear wheel cylinder with the base pressure, wherein the controller calculates the amount of fluid to be supplied to the front and rear wheel wheel cylinders as front and rear standard fluid amounts based on front and rear target pressures which are target values ​​for the front and rear wheel wheel pressures, controls the electric motor based on the front and rear standard fluid amounts, and controls the solenoid valve based on the front and rear target pressures.

2. A vehicle brake control device as described in claim 1, wherein the controller acquires the amount of fluid discharged from the control cylinder, calculates an estimated amount of fluid based on the base pressure and the adjustment pressure, and controls the rotation angle of the electric motor based on the deviation between the amount of fluid discharged and the estimated amount of fluid.

3. A vehicle braking control device as described in claim 1 or 2, wherein the controller calculates a target differential pressure based on the front wheel and rear wheel target pressures, and controls a valve current supplied to the solenoid valve based on the target differential pressure.

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