Braking control device for vehicle

Abstract

This braking control device is applied to a vehicle provided with a regenerative device on a front wheel. The braking control device is provided with a control cylinder that generates a basic pressure with an electric motor serving as a power source, an electromagnetic valve that adjusts the basic pressure to an adjusted pressure, and a controller that controls the electric motor and the electromagnetic valve. The device controls a front wheel pressure at the adjusted pressure and controls a rear wheel pressure at the basic pressure. The controller executes either: one-system pressure adjustment in which a total braking force corresponding to a required braking amount is reached by making the adjusted pressure equal to the basic pressure; or two-system pressure adjustment in which the adjusted pressure is made lower than the basic pressure so that the total braking force is reached in a state in which distribution of the total braking force to the front and rear is kept at prescribed values. A first instructed pressure for controlling the adjusted pressure in the one-system pressure adjustment and a second instructed pressure for controlling the adjusted pressure in the two-system pressure adjustment are computed, and either the one-system pressure adjustment or the two-system pressure adjustment is selected on the basis of a comparison between the first instructed pressure and the second instructed pressure.

Description

Vehicle braking control device

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

[0002] Patent Literature 1 describes a braking control device for a vehicle equipped with an energy regeneration device that can achieve both vehicle stability during braking and a sufficient amount of regenerated energy. Specifically, the braking control device is applied to a vehicle equipped with a regenerative generator on the front wheels and includes an actuator that applies front wheel torque and rear wheel torque, and a controller that adjusts the front wheel torque and rear wheel torque separately. If the regenerative braking force Fg generated by the regenerative generator has not reached a maximum regenerative force Fx, which is the maximum value that can be generated, the controller sets the front wheel torque and rear wheel torque to zero. On the other hand, if the regenerative braking force Fg has reached the maximum regenerative force Fx, the controller increases the rear wheel torque from zero before increasing the front wheel torque from zero. Furthermore, when the regenerative braking force reaches the maximum regenerative force, the controller calculates a rear wheel reference force based on a required braking force corresponding to the amount of braking operation of the vehicle and the front / rear ratio of the braking force acting on the vehicle, calculates a complementary braking force based on the required braking force and the maximum regenerative force, and when the complementary braking force is equal to or less than the rear wheel reference force, maintains the front wheel torque at zero and increases the rear wheel torque based on the complementary braking force, and when the complementary braking force is greater than the rear wheel reference force, increases the front wheel torque based on the complementary braking force and the rear wheel reference force and increases the rear wheel torque based on the rear wheel reference force. The pressure regulation control described in Patent Document 1 is also called "two-system pressure regulation."

[0003] 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 provided in the fifth flow path 55 to adjust 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 the device of Patent Document 2, there is a limitation in the relationship between the first hydraulic pressure and the second hydraulic pressure. Even in such a braking control device equipped with an electric cylinder, it is desired to implement the above-mentioned two-system pressure regulation.

[0004] Japanese Patent Application No. 2022-197101

[0005] In view of the above problems, an object of the present invention is to provide a brake control device for a vehicle equipped with an electric cylinder that can perform dual-system pressure regulation.

[0006] 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 generates the base pressure (Pa) and the adjustment pressure (Pb) based on the required braking amount (Bs) of the vehicle, controls the hydraulic pressure (Pwf) of the front wheel cylinder (CWf) using the adjustment pressure (Pb), and controls the hydraulic pressure (Pwr) of the rear wheel cylinder (CWr) using the base pressure (Pa).

[0007] In the vehicle braking control device (SA) of the present invention, when the regenerative device (KG) generates a regenerative braking force (Fg), the controller (EA) can perform one of single-system pressure regulation, in which the regulated pressure (Pb) is made equal to the base pressure (Pa) to achieve a total braking force (Fu) corresponding to the required braking amount (Bs), and dual-system pressure regulation, in which the regulated pressure (Pb) is made smaller than the base pressure (Pa) to achieve the total braking force (Fu) while maintaining the front / rear distribution of the total braking force (Fu) at a predetermined value (hf), and the controller (EA) calculates a first command pressure (P1sb) for controlling the regulated pressure (Pb) in the single-system pressure regulation and a second command pressure (P2sb) for controlling the regulated pressure (Pb) in the dual-system pressure regulation, and determines whether to select the single-system pressure regulation or the dual-system pressure regulation based on a comparison between the first command pressure (P1sb) and the second command pressure (P2sb). Specifically, the controller (EA) selects the single-system pressure regulation when the second command pressure (P2sb) is equal to or greater than the first command pressure (P1sb), and selects the dual-system pressure regulation when the second command pressure (P2sb) is less than the first command pressure (P1sb).

[0008] According to the above configuration, dual-system pressure regulation can be performed in the brake control device SA using an electric cylinder that has limitations on the adjustment of the regulated pressure Pb, thereby achieving both energy regeneration and vehicle stability.

[0009] It is a schematic diagram for explaining a first embodiment of the vehicle brake control device SA. It is a flow diagram for explaining the processing of pressure regulation control. It is a characteristic diagram for explaining the operation of pressure regulation control. It is a schematic diagram for explaining a second embodiment of the vehicle brake control device SA.

[0010] <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)."

[0011] 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, etc. are fluid paths.

[0012] <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.

[0013] 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."

[0014] 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.

[0015] 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's traveling speed Vx (vehicle speed).

[0016] 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."

[0017] A vehicle is equipped with various sensors for braking control (i.e., individual control of 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).

[0018] 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.

[0019] 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.

[0020] <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.

[0021] <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.

[0022] [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.

[0023] 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).

[0024] 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 rotation angle Ka) is detected by the rotation angle sensor KA. Then, three-phase motor currents Im (a collective term for currents flowing through the U, V, and W phases) corresponding to the U, V, and W phases are switched based on the rotation angle Ka of the motor shaft.

[0025] Specifically, a signal representing the rotation angle Ka detected by the rotation angle sensor KA is input to the braking 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. Rotational power is then output from the electric motor MA to the reducer GS.

[0026] 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.

[0027] 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 rotational power output from the reducer GS is input to the rotating member. The second 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.

[0028] 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.

[0029] 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.

[0030] The control cylinder CC is connected to a servo chamber Ru (described later) of the apply unit AP via a servo path HU (fluid path). The control cylinder CC is also connected to a rear wheel cylinder CWr via a rear wheel communication path HSr (fluid path) and a hydraulic pressure correcting device SZ. A base pressure sensor PA is provided in the hydraulic pressure generating unit PU to detect a base pressure Pa.

[0031] 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 line HH, which is 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 line 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.

[0032] 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.

[0033] 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.

[0034] 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. The pressure regulating valve UC is also called a "differential pressure valve" because it regulates the hydraulic pressure difference (differential pressure). The pressure regulating valve UC regulates the base pressure Pa output from the electric cylinder DN to an adjustment pressure Pb.

[0035] 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). In the hydraulic pressure generating unit PU, an adjustment pressure sensor PB is provided between the pressure regulating valve UC and the servo chamber Ru to detect the adjustment pressure Pb.

[0036] 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.

[0037] [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.

[0038] A regulated pressure Pb is supplied to the servo chamber Ru from the hydraulic pressure generating unit PU. The regulated pressure Pb causes the apply unit AP to output a supply pressure Pm. When Pb = 0 (e.g., when braking is not in progress), the master piston NM is in its most retracted position (i.e., the position where the volume of the master chamber Rm is at its maximum). In this state, the master chamber Rm of the master cylinder CM is in communication with the master reservoir RV. Brake fluid BF is stored inside the master reservoir RV (also referred to as the "atmospheric pressure reservoir"). When the regulated 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 is further moved in the forward direction Da, the supply pressure Pm (the internal pressure of the master chamber Rm, also referred to as "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, "Pb = Pm."

[0039] [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 regenerative generator GN) 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 of 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.

[0044] <Brake Controller EA> The brake controller EA controls the brake actuator YA. The brake controller EA is composed of a microprocessor MP and a drive circuit DR. The brake 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, etc.).

[0045] The brake controller EA directly receives various signals, such as the operation displacement Sp (detected value of the operation displacement sensor SP), input pressure Pn (detected value of the input pressure sensor PN), base pressure Pa (detected value of the base pressure sensor PA), regulated pressure Pb (detected value of the regulated pressure sensor PB), and motor rotation angle Ka (detected value of the rotation angle sensor KA). Furthermore, the controller EA also receives various signals, such as the supply pressure Pm, standard regenerative braking force Fz, vehicle running speed Vx (also referred to as "vehicle speed"), and 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.

[0046] 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 H-bridge circuit (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.

[0047] 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.

[0048] <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 to the front and rear wheel cylinders CWf and CWr as front and rear wheel pressures Pwf and Pwr.

[0049] 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.

[0050] 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, and the base pressure Pa is transmitted directly to the rear wheel cylinder CWr as the rear wheel pressure Pwr. Therefore, in the front wheel braking system, "Pb = Pm = Pwf" holds, and in the rear wheel braking system, "Pa = Pwr" holds.

[0051] 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.

[0052] <Pressure Regulation Control Processing> An example of the pressure regulation control processing will be described with reference to the flowchart of FIG. 2 . In pressure regulation control, regenerative cooperative control between the regenerative device KG and the brake control device SA is executed. Furthermore, regenerative cooperative control includes single-path pressure regulation and dual-path pressure regulation. In single-path pressure regulation, the base pressure Pa and the regulated pressure Pb are made equal to achieve a total braking force Fu corresponding to the required braking amount Bs. In single-path pressure regulation, the base pressure Pa and the regulated pressure Pb are collectively adjusted, and therefore this is also referred to as "collectively adjusted pressure." In contrast, in dual-path pressure regulation, the regulated pressure Pb is made smaller than the base pressure Pa, and therefore a 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 dual-path pressure regulation, the base pressure Pa and the regulated pressure Pb are collectively adjusted, and therefore this is also referred to as "individual adjusted pressure." In regenerative cooperative control, one of single-system pressure regulation and dual-system pressure regulation is selected and executed to accommodate the limitations caused by the configuration of the braking control device SA described above (i.e., the inability to reduce the regulated pressure Pb by the pressure regulating valve UC alone).

[0053] <<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).

[0054] <Various Hydraulic Pressures> The various hydraulic pressures are divided into hydraulic pressures in single-system pressure regulation and hydraulic pressures in dual-system pressure regulation. Hydraulic pressures related to single-system pressure regulation have the word "first" added to their names. Hydraulic pressures related to dual-system pressure regulation have the word "second" added to their names. The various hydraulic pressures in the explanation of pressure regulation control are as follows: - "First command basal pressure P1sa" corresponds to the target value for controlling the basal pressure Pa (actual value) in single-system pressure regulation. - "Second command basal pressure P2sa" is the target value for controlling the basal pressure Pa (actual value) in dual-system pressure regulation. - "First command regulated pressure P1sb" corresponds to the target value for controlling the regulated pressure Pb (actual value) in single-system pressure regulation. - "Second command regulated pressure P2sb" corresponds to the target value for controlling the regulated pressure Pb (actual value) in dual-system pressure regulation.

[0055] In pressure regulation control, either single-system pressure regulation or dual-system pressure regulation is ultimately performed. - "Basal pressure Pa" is the actual value of the final output of the electric cylinder DN (i.e., the internal pressure of the control chamber Rc). That is, the basal pressure Pa is the discharge pressure of the electric cylinder DN regardless of whether single-system pressure regulation or dual-system pressure regulation is used. The basal pressure Pa is detected (acquired) by the basal pressure sensor PA. - "Target basal pressure Pta" corresponds to a target value for controlling the basal pressure Pa (actual value). One of the first command basal pressure P1sa and the second command basal pressure P2sa is used as the target basal pressure Pta. - "Adjusted pressure Pb" is the actual value of the final hydraulic pressure obtained by adjusting the basal pressure Pa by the pressure regulator valve UC. That is, the adjusted pressure Pb is the hydraulic pressure adjusted by the pressure regulator valve UC regardless of whether single-system pressure regulation or dual-system pressure regulation is used. The regulated pressure Pb is detected (acquired) by the regulated pressure sensor PB. Alternatively, the regulated pressure Pb may be detected (acquired) by the supply pressure sensor PM. Therefore, the supply pressure Pm corresponds to one of the regulated pressures Pb, and the supply pressure sensor PM corresponds to one of the regulated pressure sensors PB. The "target regulated pressure Ptb" corresponds to a target value for controlling the regulated pressure Pb (actual value). One of the first command regulated pressure P1sb and the second command regulated pressure P2sb is used as the target basal pressure Pta.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] In step S130, a first command base pressure P1sa and a first command adjustment pressure P1sb (corresponding to the "first command pressure") for performing single-system pressure adjustment are calculated based on the target total braking force Fv and the standard regenerative braking force Fz. In single-system pressure adjustment, the base pressure Pa and the adjustment pressure Pb are made equal, so the first command base pressure P1sa and the first command adjustment pressure P1sb are equal (i.e., "P1sa = P1sb"). In step S130, first, a sum Fnt (also referred to as the "target sum") of the target regenerative braking force Fh and the target frictional braking force Fn is calculated. Here, the "target sum Fnt" is the sum of the front wheel target frictional braking force Fnf and the rear wheel target frictional braking force Fnr (i.e., "Fnt = Fnf + Fnr"). In single-system pressure adjustment, the command pressures P1sa and P1sb are determined for the following two cases:

[0060] 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 sum Fnt (target sum) of the target frictional braking forces Fn is set to 0. That is, when Fv≦Fz, it is determined that Fh=Fv, Fnt=0.

[0061] Case (2): When the target total braking force Fv is greater than the standard regenerative braking force Fz, the target regenerative braking force Fh is set equal to the standard regenerative braking force Fz, and the target sum Fnt 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 Fv > Fz, Fh = Fz, Fnt = Fv - Fh = Fv - Fz are determined.

[0062] Next, command pressures P1sa and P1sb are calculated based on the target sum Fnt. Specifically, the command pressures P1sa and P1sb are determined based on the specifications of the brake device SX (=SXf, SXr) so that the target sum Fnt is satisfied under the condition "P1sa = P1sb." That is, in the case (1) where "Fv ≦ Fz," the command pressures P1sa and P1sb are determined to be "0." In contrast, in the case (2) where "Fv > Fz," the command pressures P1sa and P1sb are determined so that "P1sa = P1sb" is satisfied and the sum Fnt (target sum) of the target frictional braking forces Fn is equal to the value "Fv - Fh." Here, the "specifications of the brake device SX" include the pressure-receiving area of ​​the wheel cylinder CW, the effective braking radius of the rotating member KT, the friction coefficient of the friction material, and the effective radius of the wheel WH.

[0063] In step S140, a second command base pressure P2sa and a second command adjustment pressure P2sb (corresponding to the "second command pressure") for performing dual-system pressure adjustment are calculated based on the target total braking force Fv and the standard regenerative braking force Fz. In dual-system pressure adjustment, the base pressure Pa and the adjustment pressure Pb are adjusted separately, so the second command base pressure P2sa and the second command adjustment pressure P2sb are different. In particular, because the adjustment pressure Pb is adjusted downward from the base pressure Pa, the second command adjustment pressure P2sb is smaller than the second command base pressure P2sa (i.e., "P2sa > P2sb"). In dual-system pressure adjustment, the command pressures P2sa and P2sb are determined for the following three cases:

[0064] Case (3): 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.

[0065] Case (4): 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."

[0066] 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)".

[0067] Case (5): 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 multiplying the value obtained by subtracting the distribution ratio hf from "1" 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.

[0068] Next, a second command base pressure P2sa is calculated based on the rear wheel target frictional braking force Fnr. That is, the rear wheel target frictional braking force Fnr is converted into the second command base pressure P2sa based on the specifications of the rear wheel brake device SXr. Similarly, a second command adjustment pressure P2sb is calculated based on the front wheel target frictional braking force Fnf. The front wheel target frictional braking force Fnf is converted into the second command adjustment pressure P2sb based on the specifications of the front wheel brake device SXf. As above, the specifications 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. Note that, since the adjustment pressure Pb is transmitted to the front wheel cylinder CWf via the master cylinder CM and the master piston NM, the calculation of the second command adjustment pressure P2sb can take into account the sliding resistance of the seal member SL.

[0069] In the dual-system pressure regulation, when Fv≦Fz (3), the second command base pressure P2sa and the second command adjustment pressure P2sb are both maintained at 0 so that the regenerative device KG recovers the maximum amount of energy. When Fz<Fv≦(Fz / hf) (4), the second command base pressure P2sa (resulting in the rear wheel pressure Pwr) is increased from 0 while the second command adjustment pressure P2sb (resulting in the front wheel pressure Pwf) is maintained at 0 so that the front-rear distribution of the total braking force Fu quickly reaches the predetermined ratio hf. When Fv>(Fz / hf) (5), the second command base pressure P2sa and the second command adjustment pressure P2sb are both increased while P2sa>P2sb so that the front-rear distribution of the total braking force Fu is maintained at the predetermined ratio hf.

[0070] In step S150, it is determined whether the second command adjusting pressure P2sb is smaller than the first command adjusting pressure P1sb. If the second command adjusting pressure P2sb is less than the first command adjusting pressure P1sb and the determination in step S150 is affirmative, dual-system pressure regulation is selected and the process proceeds to step S160. If the second command adjusting pressure P2sb is equal to or greater than the first command adjusting pressure P1sb and the determination in step S150 is negative, single-system pressure regulation is selected and the process proceeds to step S170.

[0071] In step S160, dual-system pressure regulation (individual pressure regulation) is performed. In dual-system pressure regulation, the basal pressure Pa and the regulated pressure Pb are individually regulated by the electric cylinder DN and the pressure regulation valve UC. Specifically, the second command basal pressure P2sa is adopted as the final target value Pta (target basal pressure) for controlling the basal pressure Pa. Furthermore, the second command regulated pressure P2sb is adopted as the final target value Ptb (target regulated pressure) for controlling the regulated pressure Pb. That is, in step S160, it is determined that "Pta = P2sa, Ptb = P2sb."

[0072] In step S170, one-system pressure regulation (collectively regulated pressure) is performed. In dual-system pressure regulation, the basal pressure Pa and the regulated pressure Pb are regulated together by only the electric cylinder DN. Specifically, the first command basal pressure P1sa is adopted as the final target value Pta (target basal pressure) for controlling the basal pressure Pa. Furthermore, the first command regulated pressure P1sb is adopted as the final target value Ptb (target regulated pressure) for controlling the regulated pressure Pb. That is, in step S170, "Pta = Ptb = P1sa = P1sb" is determined.

[0073] In step S180, the electric motor MA and the pressure regulating valve UC are controlled based on the target base pressure Pta and the target adjustment pressure Ptb. Specifically, in the braking system for the rear wheel cylinder CWr, when regenerative cooperative control is executed, the electric cylinder DN (particularly the electric motor MA) is driven so that the base pressure Pa (the value detected by the base pressure sensor PA) approaches and matches the target base pressure Pta, regardless of whether single-system pressure regulation or dual-system pressure regulation is being used.

[0074] On the other hand, in the brake system for the front wheel cylinder CWf, in regenerative cooperative control with single-path pressure regulation, no current is supplied to the pressure regulator valve UC. That is, the pressure regulator valve UC is fully open, and the regulated pressure Pb is equal to the base pressure Pa. In contrast, in regenerative cooperative control with dual-path pressure regulation, the pressure regulator valve UC is driven so that the differential pressure sPj (also referred to as the "actual differential pressure") between the base pressure Pa and the regulated pressure Pb approaches and matches the differential pressure sPt (also referred to as the "target differential pressure") between the target base pressure Pta and the target regulated pressure Ptb. Specifically, the target current It to the pressure regulator valve UC is determined based on the target differential pressure sPt (= Pta - Ptb). The target current It is then corrected so that the actual differential pressure sPj (= Pa - Pb) becomes "0." As a result, the pressure regulating valve UC is controlled so that the regulated pressure Pb (the value detected by the regulated pressure sensor PB and / or the supply pressure sensor PM) approaches and coincides with the target regulated pressure Ptb.

[0075] The amount of regeneration by the generator GN (resulting in the regenerative braking force Fg) is limited by the ratings of the power transistors (e.g., IGBTs) constituting the regeneration controller EG and the charge acceptance of the battery. For example, the generator GN is controlled so that the amount of regeneration is a predetermined power (electrical energy per unit time). When the power (power) is constant, the regenerative braking torque by the generator GN (resulting in the regenerative braking force Fg) is inversely proportional to the rotational speed Ng of the generator GN (i.e., the vehicle speed Vx). Furthermore, as the rotational speed Ng of the generator GN decreases, the amount of regeneration decreases, and the regenerative braking force Fg decreases. Therefore, as the vehicle's traveling speed Vx decreases, the standard regenerative braking force Fz temporarily increases and is then limited to the upper limit value fz. Then, just before the vehicle stops, the standard regenerative braking force Fz decreases as the vehicle speed Vx decreases.

[0076] As described above, the brake control device SA has a limit on the relationship between the base pressure Pa and the regulated pressure Pb. Specifically, the brake control device SA can increase the regulated pressure Pb up to the base pressure Pa (i.e., the upper limit of the regulated pressure Pb is the base pressure Pa). However, once the regulated pressure Pb increases, it cannot decrease unless the base pressure Pa decreases. In other words, the pressure regulating valve UC can prevent the regulated pressure Pb from increasing, but cannot decrease the regulated pressure Pb. This is because, in the configuration of the brake control device SA, the servo chamber Ru is not connected to a low-pressure portion such as the master reservoir RV.

[0077] Taking these factors into consideration, the brake control device SA determines whether to perform single-path pressure regulation or dual-path pressure regulation based on a comparison between the first command regulating pressure P1sb and the second command regulating pressure P2sb. When the second command regulating pressure P2sb is less than the first command regulating pressure P1sb (i.e., when P1sb > P2sb), there is room for an increase in the regulating pressure Pb, and therefore dual-path pressure regulation is selected. On the other hand, when the second command regulating pressure P2sb is equal to or greater than the first command regulating pressure P1sb (i.e., when P1sb ≦ P2sb), it is necessary to decrease the regulating pressure Pb, and therefore single-path pressure regulation is selected. As a result, the brake control device SA regenerates sufficient energy using the regenerating device KG, and, if possible, performs dual-path control, thereby ensuring the running stability of the vehicle.

[0078] <Operation of Pressure Regulation Control> The operation, action, and effect of the pressure regulation control will be described with reference to the characteristic diagram of FIG. 3 . FIG. 3(a) shows the characteristic of the standard regenerative braking force Fz in the regenerative device KG. The standard regenerative braking force Fz is the limit value of the regenerative braking force Fg that can be generated, and transitions along a characteristic Zfz. Specifically, the standard regenerative braking force Fz increases as the rotational speed Ng (i.e., the vehicle speed Vx) of the generator GN decreases until the rotational speed Ng reaches a first predetermined speed no. Then, within the range of the rotational speed Ng from the first predetermined speed no to a second predetermined speed np, the standard regenerative braking force Fz is limited to an upper limit value fz. When the rotational speed Ng becomes smaller than the second predetermined speed np, the standard regenerative braking force Fz decreases as the rotational speed Ng decreases.

[0079] Assume a situation in which the required braking amount Bs is gradually increased from "0" and then maintained constant. The braking force distribution diagram (relationship between front wheel braking force Fxf and rear wheel braking force Fxr) in FIG. 3(b) corresponds to the characteristic diagram in FIG. 3(a). In FIGS. 3(a) and 3(b), the state (operating point) at each time point is shown in square brackets [ ]. Note that the characteristic Cho (also referred to as the "reference characteristic") in FIG. 3(b) is the relationship between the front wheel braking force Fxf and the rear wheel braking force Fxr in the state in which "Fg = 0" and "Pwf = Pwr", and represents "hf = Fxf / (Fxf + Fxr)."

[0080] At time t0, braking begins. At the beginning of braking, "P1sb>P2sb" is satisfied, and dual-system pressure regulation is performed. At time t0, "Fg = 0" and "Fxf = Fxr = 0" are true. Until time t1, there is a margin in the standard regenerative braking force Fz relative to the target total braking force Fv, so dual-system pressure regulation in case (3) is performed. As a result, the target total braking force Fv is achieved by the regenerative braking force Fg alone, and the front and rear wheel friction braking forces Fef and Fer are "0." Therefore, the operating point on the braking force distribution diagram shifts from the origin O along the X-axis.

[0081] At time t1, the target total braking force Fv reaches the standard regenerative braking force Fz (value fo). After time t1, dual-system pressure adjustment in case (4) is performed. As a result, the operating point increases along the Y-axis from point (A) toward point (B) on the reference characteristic Cho. That is, due to dual-system pressure adjustment, the front / rear distribution of the total braking force Fu quickly reaches the predetermined ratio hf. When the front / rear distribution of the total braking force Fu reaches the reference characteristic Cho, dual-system pressure adjustment in case (5) is performed. As a result, the front and rear wheel braking forces Fxf and Fxr are increased while the front / rear distribution of the total braking force Fu is maintained at the predetermined ratio hf. That is, the operating point transitions from point (B) to point (C) along the reference characteristic Cho.

[0082] At time t2, an increase in the standard regenerative braking force Fz due to a decrease in vehicle speed Vx makes it necessary to decrease the second command adjusting pressure P2sb. However, there is a limit to the relationship between the base pressure Pa and the adjusting pressure Pb. Therefore, the pressure adjustment control is switched from dual-system pressure adjustment to single-system pressure adjustment, and single-system pressure adjustment in case (2) is performed. The operating point deviates from the reference characteristic Cho and transitions from point (C) to point (D) along the constant acceleration line.

[0083] At time t3, the standard regenerative braking force Fz reaches its upper limit value fz. At this time, the required braking amount Bs is maintained at a constant value, and the regenerative braking force Fg is constant at the upper limit value fz, so the operating point remains at point (D). At time t4, the standard regenerative braking force Fz (and consequently the regenerative braking force Fg) is reduced due to a decrease in vehicle speed Vx. At time t4, a so-called replacement operation between the regenerative braking force Fg and the frictional braking force Fe is initiated. In the replacement operation, the decrease in the regenerative braking force Fg is compensated for by an increase in the frictional braking force Fe. The operating point transitions from point (D) toward point (C). Thereafter, the vehicle stops, and "Fg = 0" is reached, so the operating point transitions to point (C) on the reference characteristic Cho.

[0084] When the amount of regenerative energy is limited to a certain extent, such as in the initial stage of braking (i.e., when P1sb>P2sb), dual-system pressure regulation is selected as the pressure regulation control. This ensures the amount of regenerative energy and maintains an appropriate front / rear distribution of the total braking force Fu, thereby improving the running stability of the vehicle.

[0085] When the amount of regenerative energy increases as the vehicle's traveling speed Vx (vehicle speed) decreases (i.e., when "P1sb≦P2sb"), the pressure regulation control is switched from dual-system pressure regulation to single-system pressure regulation. This allows the vehicle's kinetic energy to be fully recovered as electrical energy. Note that with single-system pressure regulation, the front / rear distribution of the total braking force Fu is determined spontaneously as a result of changes in the regenerative braking force Fg. However, since the vehicle speed Vx has already decreased in this situation, driving stability is not a high priority.

[0086] As described above, the brake control device SA using the electric cylinder DN has limitations on the adjustment of the adjustment pressure Pb, but it appropriately selects between single-path pressure regulation and dual-path pressure regulation based on the required braking amount Bs (resulting in the total braking force Fu) and the operating state of the regenerative device KG. In other words, even a brake control device SA that employs the electric cylinder DN can perform dual-path pressure regulation. As a result, the brake control device SA can ensure both the amount of energy regeneration and the improvement of vehicle stability.

[0087] <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. 4. In the second embodiment, similarly to the first embodiment, single-system pressure regulation and dual-system pressure regulation can be selectively performed.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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 due to the thrust of the solenoid. This allows the pressure regulating valve UC to adjust the regulated pressure Pb (i.e., front wheel pressure Pwf) to be smaller than the base pressure Pa (i.e., rear wheel pressure Pwr). 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 regulated pressure Pb, which is reduced from the base pressure Pa by the pressure regulating valve UC, is transmitted to the front wheel cylinder CWf as the front wheel pressure Pwf. Meanwhile, the base pressure Pa is transmitted to the rear wheel cylinder CWr as the 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 for a reduction in the regulated pressure Pb.

[0093] 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 reduced to the regulated pressure Pb by the pressure regulating valve UC. At this time, the regulated pressure Pb can be increased up to the base pressure Pa, but a reduction in the regulated pressure Pb requires a reduction in the base pressure Pa. Therefore, in the second embodiment, whether to execute single-path pressure regulation or dual-path pressure regulation is determined based on a comparison between the first command regulated pressure P1sb and the second command regulated pressure P2sb. When the second command regulated pressure P2sb is less than the first command regulated pressure P1sb, there is room for an increase in the regulated pressure Pb, and therefore dual-path pressure regulation is selected. On the other hand, when the second command regulated pressure P2sb is equal to or greater than the first command regulated pressure P1sb, single-path pressure regulation is selected. In the second embodiment, the same effects as in the first embodiment (execution of dual-path pressure regulation, ensuring an amount of energy regeneration, improving vehicle stability, etc.) are achieved.

[0094] <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.

[0095] 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.

[0096] The hydraulic pressure transmission in the brake control device SC 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, the actual value and the target value must be compared at the same location. In the above-described embodiment, the base pressure Pa (the value detected by the base pressure sensor PA) is controlled to approach and match the target base pressure Pta. Furthermore, the adjustment pressure Pb (the value detected by the adjustment pressure sensor PB and / or the supply pressure sensor PM) is controlled to approach and match the target adjustment pressure Ptb. That is, the location where the target value and the actual value are compared (also referred to as the "comparison location") is the location where the servo pressure sensor PA or the like is installed. 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 wheel cylinder CW is used as the comparison portion, and the target basal pressure Pta and target adjusted pressure Ptb are determined to correspond to the wheel pressure Pw (actual value), and the wheel pressure Pw is estimated from the basal pressure Pa and adjusted pressure Pb after compensating for the hydraulic pressure component due to the resistance. In pressure adjustment control, regardless of the location of the comparison portion between the target value and the actual value, the first and second command basal pressures P1sa and P2sa are target values ​​for controlling the basal pressure Pa (actual value), and the first and second command adjusted pressures P1sb and P2sb are target values ​​for controlling the adjusted pressure Pb (actual value).

[0097] 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 Pta, Ptb, etc. are calculated based on the braking demand amount Bs via state quantities related to the force from the longitudinal force acting on the vehicle to the deceleration of the vehicle.

[0098] 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.

[0099] 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.

[0100] 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 the base pressure Pa and the adjusted pressure Pb based on the required braking amount Bs of the vehicle, controls the hydraulic pressure Pwf in the front wheel cylinders CWf using the adjusted pressure Pb, and controls the hydraulic pressure Pwr in the rear wheel cylinders CWr using the base pressure Pa.

[0101] 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.

[0102] In the brake control device SA, the controller EA can perform either single-path pressure regulation or dual-path pressure regulation when the regenerative device KG generates a regenerative braking force Fg (i.e., when regenerative cooperative control is being performed). Here, single-path pressure regulation achieves a total braking force Fu corresponding to the required braking amount Bs by making the regulated pressure Pb equal to the base pressure Pa. Meanwhile, dual-path pressure regulation achieves the total braking force Fu while maintaining the front-rear distribution of the total braking force Fu at a predetermined value hf (a preset distribution ratio) by making the regulated pressure Pb smaller than the base pressure Pa. The controller EA calculates a first command regulated pressure P1sb (first command pressure) for controlling the regulated pressure Pb in the single-path pressure regulation and a second command regulated pressure P2sb (second command pressure) for controlling the regulated pressure Pb in the dual-path pressure regulation. Then, based on a comparison between the first command regulated pressure P1sb and the second command regulated pressure P2sb, the controller EA determines whether to select single-path pressure regulation or dual-path pressure regulation.

[0103] Specifically, the controller EA selects single-system pressure regulation when the second command regulating pressure P2sb is equal to or greater than the first command regulating pressure P1sb, and selects dual-system pressure regulation when the second command regulating pressure P2sb is less than the first command regulating pressure P1sb. In other words, the smaller of the first command regulating pressure P1sb and the second command regulating pressure P2sb is selected, and control corresponding to the selected command regulating pressure is executed between single-system pressure regulation and dual-system pressure regulation.

[0104] In the brake control device SA, a base pressure Pa is output from the electric cylinder DN by the power of the electric motor MA. The base pressure Pa is then reduced and adjusted to an adjustment pressure Pb by the pressure regulating valve UC. The pressure regulating valve UC operates to prevent an increase in the adjustment pressure Pb, thereby creating a state in which the adjustment pressure Pb is less than the base pressure Pa. In the brake control device SA equipped with the electric cylinder DN, the pressure regulating valve UC cannot reduce the adjustment pressure Pb by itself. When the traveling speed Vx (vehicle speed) decreases due to braking, the generateable regenerative braking force Fg (i.e., the standard regenerative braking force Fz) increases. At this time, in order to reduce the adjustment pressure Pb in order to increase the regenerative braking force Fg, it is necessary to reduce the base pressure Pa.

[0105] The brake control device SA switches between single-path pressure regulation and dual-path pressure regulation as appropriate depending on the vehicle conditions (i.e., the degree of increase in the required braking amount Bs and the operating state of the regenerative device KG). Specifically, the brake control device SA selects whether to perform single-path pressure regulation or dual-path pressure regulation based on a comparison between the first command regulating pressure P1sb and the second command regulating pressure P2sb. Dual-path pressure regulation is selected when the second command regulating pressure P2sb is less than the first command regulating pressure P1sb, and single-path pressure regulation is selected when the second command regulating pressure P2sb is equal to or greater than the first command regulating pressure P1sb. This is based on the fact that "P2sb<P1sb" holds when the generation of the regenerative braking force Fg is limited and the regulating pressure Pb can be increased, and "P2sb≧P1sb" holds when the regulating pressure Pb needs to be reduced as the regenerative braking force Fg increases.

[0106] In the brake control device SA, immediately after braking is initiated, the target total braking force Fv (resulting in a total braking force Fu) is gradually increased, and when the traveling speed Vx is relatively high, dual-system pressure regulation is performed. This improves vehicle stability and allows energy regeneration. Thereafter, when the traveling speed Vx decreases due to braking, single-system pressure regulation is performed, thereby allowing sufficient energy regeneration. Note that in single-system pressure regulation, the front / rear distribution of the total braking force Fu is determined as a result of the regenerative braking force Fg. However, when single-system pressure regulation is performed, the traveling speed Vx is decreasing, so energy regeneration takes priority over vehicle stability. In the brake control device SA, single-system pressure regulation and dual-system pressure regulation are appropriately switched depending on the traveling state of the vehicle. In other words, dual-system pressure regulation can be appropriately performed in a brake control device SA using an electric cylinder DN with restrictions on the adjustment of the adjustment pressure Pb. This achieves both energy regeneration and vehicle stability.

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 generates the base pressure and the adjustment pressure based on a required braking amount of the vehicle, controls the hydraulic pressure of the front wheel cylinder by the adjustment pressure, and controls the hydraulic pressure of the rear wheel cylinder by the base pressure, wherein, when the regenerative device generates a regenerative braking force, the controller is capable of performing one of a single-system pressure regulation which makes the adjustment pressure equal to the base pressure to achieve a total braking force corresponding to the required braking amount, and a dual-system pressure regulation which makes the adjustment pressure smaller than the base pressure to achieve the total braking force while maintaining the front / rear distribution of the total braking force at a predetermined value, and calculates a first command pressure for controlling the adjustment pressure in the single-system pressure regulation, and a second command pressure for controlling the adjustment pressure in the dual-system pressure regulation, A braking control device for a vehicle that determines whether to select the single-system pressure regulation or the dual-system pressure regulation based on a comparison between the first command pressure and the second command pressure.

2. A vehicle braking control device as described in claim 1, wherein the controller selects the single-system pressure regulation when the second command pressure is equal to or greater than the first command pressure, and selects the dual-system pressure regulation when the second command pressure is less than the first command pressure.

3. A vehicle brake control device as described in claim 1 or 2, comprising a master chamber and a servo chamber opposed to each other via a master piston, the control cylinder being connected to the servo chamber and the rear wheel cylinder, the master chamber being connected to the front wheel cylinder, and the solenoid valve being disposed between the control cylinder and the servo chamber.

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