Braking control device for vehicles

Abstract

This braking control device for vehicles comprises: a control cylinder into which a control piston is inserted and which generates a servo pressure by moving the control piston with an electric motor; a servo pressure sensor which detects the servo pressure; and a controller which controls the electric motor on the basis of the servo pressure. The braking control device adjusts a wheel pressure of a wheel cylinder according to the servo pressure. The controller acquires a discharge liquid amount from the control cylinder, calculates an estimated liquid amount on the basis of the servo pressure and a conversion map, and controls the electric motor on the basis of a deviation between the discharge liquid amount and the estimated liquid amount. For example, the controller calculates a target pressure on the basis of a braking request amount, calculates a standard liquid amount on the basis of the target pressure and the conversion map, and controls a rotation angle of the electric motor on the basis of the standard liquid amount and the deviation.

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 1 having a motor-driven cylinder 13, wheel cylinders 2b and 3b, a stroke sensor 11a that detects a brake pedal operation amount Ps, a target value setting circuit 33 that sets a target stroke St of the motor-driven cylinder 13 in accordance with the brake pedal operation amount Ps, and a hydraulic pressure compensation circuit 38 that corrects the target stroke St in a direction that reduces a deviation that occurs between a brake hydraulic pressure reference value Bo corresponding to the brake pedal operation amount Ps and an actual brake hydraulic pressure B, so that the braking force can be changed in accordance with the brake pedal operation amount when the load fluid loss characteristic changes, thereby making the driver aware of the change in the load fluid loss characteristic. The vehicle brake device 1 further includes a stroke limiting circuit 51 that suppresses a compensation value ΔB by the hydraulic pressure compensation circuit 38 based on the brake pedal operation amount Ps.

[0003] In the device disclosed in Patent Document 1, a target value setting circuit 33 uses a map or the like to determine the target stroke St of the motor-driven cylinder 13 corresponding to the corrected brake fluid pressure Bt. The conversion map from hydraulic pressure to the electric cylinder stroke (i.e., the amount of brake fluid discharged from the electric cylinder) represents the relationship between the hydraulic pressure in the wheel cylinder and the amount of brake fluid (working fluid) supplied to the wheel cylinder. This relationship is called the "hydraulic pressure-fluid volume characteristic." The hydraulic pressure-fluid volume characteristic is basically determined by the stiffness of the brake caliper, friction members, etc., but it also contains errors due to variations, aging, etc. These errors are caused by the presence or absence of gas in the device, wear of the friction members, etc.

[0004] International Publication No. 2012 / 086162

[0005] In view of the above problems, an object of the present invention is to provide a vehicle brake control device that adjusts hydraulic pressure using an electric motor, in which errors in a conversion map that represents hydraulic pressure-liquid volume characteristics can be compensated for.

[0006] The vehicle brake control device (SA) according to the present invention includes a control cylinder (CC) into which a control piston (NC) is inserted and which generates a servo pressure (Pa) by moving the control piston (NC) using an electric motor (MA), a servo pressure sensor (PA) that detects the servo pressure (Pa), and a controller (EA) that controls the electric motor (MA) based on the servo pressure (Pa), and adjusts a wheel pressure (Pw) of a wheel cylinder (CW) using the servo pressure (Pa). The controller (EA) acquires a fluid discharge amount (Ej) from the control cylinder (CC), calculates an estimated fluid amount (Ee) based on the servo pressure (Pa) and a conversion map (Zef, Zer, Zek), and controls the electric motor (MA) based on a deviation (hE) between the fluid discharge amount (Ej) and the estimated fluid amount (Ee).

[0007] In the vehicle brake control device (SA) according to the present invention, the controller (EA) calculates a target pressure (Pt) based on a braking demand (Bs), calculates a standard fluid volume (Es) based on the target pressure (Pt) and the conversion map (Zef, Zer, Zek), and controls the rotation angle (Ka) of the electric motor (MA) based on the standard fluid volume (Es) and the deviation (hE). The controller (EA) also sets the relationship between the volume of brake fluid flowing into the wheel cylinder (CW) and the wheel pressure (Pw) as the conversion map (Zef, Zer, Zek).

[0008] Although the conversion maps Zef, Zer, and Zek representing the hydraulic pressure-fluid volume characteristics contain errors, the above configuration can appropriately compensate for these errors. As a result, the volume of brake fluid BF discharged from the control cylinder CC is adjusted to be just enough relative to the target pressure Pt, improving the accuracy of pressure regulation by the control cylinder CC (i.e., the electric cylinder DN) driven by the electric motor MA.

[0009] It is a schematic diagram for explaining a first embodiment of the brake control device SA of the vehicle. It is a flow diagram for explaining the process of pressure regulation control. It is a block diagram for explaining the drive control of the electric cylinder DN. It is a schematic diagram for explaining a second embodiment of the brake control device SA of the vehicle.

[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, etc.) are connected by fluid paths. Here, a "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.

[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 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 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).

[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 servo pressure Pa 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 servo pressure Pa to a hydraulic pressure correction device SZ. The hydraulic pressure correction device SZ adjusts the supply pressure Pm and the servo 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 servo pressure Pa. The hydraulic pressure generating unit PU is also referred to as an "electric cylinder DN." The electric cylinder DN includes an 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 the servo 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). The linear power of a linearly moving member (described later) 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 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.

[0025] 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.

[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 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.

[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 servo pressure Pa. In other words, the electric cylinder DN uses the electric motor MA as a power source to output the servo 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. The hydraulic pressure generating unit PU is provided with a servo pressure sensor PA to detect a servo pressure Pa (hydraulic pressure generated by the electric cylinder DN).

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

[0032] When an increase in servo pressure Pa is required, the rotational power of the electric motor MA is increased. This rotational power is transmitted to the conversion mechanism GH via the reducer GS and output as linear power of the linearly moving member. Then, the control piston NC is pressed by the linearly moving 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 servo pressure Pa (internal pressure of the control chamber Rc) increases from "0 (atmospheric pressure)." Brake fluid BF pressurized to the servo pressure Pa is output (pumped) from the control chamber Rc of the control cylinder CC.

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

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

[0035] A servo pressure Pa is supplied to the servo chamber Ru from the hydraulic pressure generating unit PU (electric cylinder DN). The servo pressure Pa causes the apply unit AP to output a supply pressure Pm. Here, the "supply pressure Pm" is the internal pressure of the master chamber Rm, and is also referred to as the "master pressure." When "Pa = 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 in communication with the master reservoir RV. Therefore, the master pressure Pm is "0 (atmospheric pressure)."

[0036] Brake fluid BF is stored inside the master reservoir RV (also called the "atmospheric pressure reservoir"). When the servo pressure Pa 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, "Pa = Pm."

[0037] [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.

[0038] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to a brake operating member BP (brake pedal) so as to move in conjunction with the movement of the brake operating member BP. 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 servo pressure Pa, thereby realizing regenerative cooperative control.

[0039] 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.

[0040] When power is not supplied to the first and second control valves VA and VB, the first control valve VA is closed and the second control valve VB is open. 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.

[0041] When power is supplied to the first and second control valves VA and VB, the first control valve VA is opened and the second control valve VB is closed. This allows the master piston NM to be displaced separately from the brake operating member BP. 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.

[0042] <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.).

[0043] 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 servo pressure Pa (detection value of the servo pressure sensor PA), and the motor rotation angle Ka (detection value of the rotation angle sensor KA). 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.

[0044] 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 (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. In addition, 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.

[0045] The braking controller EA calculates drive signals Va and Vb for the first and second control valves VA and VB, and a drive signal Ma for the electric motor MA. The switching elements are then driven in response to the various drive signals (Ma, etc.). Specifically, in controlling the solenoid valves, power is supplied to the first and second control valves VA 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 signal Ma is determined based on a pressure regulation control algorithm, and the electric motor MA is controlled based on the drive signal Ma.

[0046] <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 servo pressure Pa is supplied directly from a 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 servo 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.

[0047] 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 servo pressure Pa is transmitted as the supply pressure Pm via the master piston NM. Therefore, the supply pressure Pm corresponds to the servo pressure Pa, and the supply pressure sensor PM corresponds to the servo pressure sensor PA. In other words, the supply pressure Pm is an example of the servo pressure Pa, and the supply pressure sensor PM is an example of the servo pressure sensor PA.

[0048] 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 servo pressure Pa is transmitted to the front wheel cylinder CWf as the front wheel pressure Pwf via the supply pressure Pm, and is also transmitted directly to the rear wheel cylinder CWr as the rear wheel pressure Pwr. In other words, "Pa = Pm = Pwf" is established in the front wheel braking system, and "Pa = Pwr" is established in the rear wheel braking system.

[0049] 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.

[0050] <Pressure Regulation Control Processing> An example of the pressure regulation control processing will be described with reference to the flowchart of Figure 2. In the pressure regulation control, regenerative cooperative control is executed between the regenerative device KG and the brake control device SA. In the regenerative cooperative control, the regenerative braking force Fg and the friction braking force Fe are adjusted to work together, and a total braking force Fu corresponding to the required braking amount Bs is achieved.

[0051] <<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).

[0052] <<Various Hydraulic Pressures>> The various hydraulic pressures in the explanation of pressure regulation control are as follows: - "Servo pressure Pa" is the output of the electric cylinder DN (i.e., the internal pressure of the control chamber Rc). The servo pressure Pa is detected (acquired) by the servo pressure sensor PA. - "Target pressure Pt" corresponds to a target value for controlling the servo pressure Pa (actual value).

[0053] 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 feedback control of hydraulic pressure, 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 target pressure Pt is determined to correspond to the wheel pressure Pw. The wheel pressure Pw (actual value) is then determined from the servo pressure Pa (the value detected by the servo pressure sensor PA) after being compensated for the hydraulic pressure equivalent to the above resistances.

[0054] 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.

[0055] 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), the target acceleration Gs, the servo pressure Pa, and the standard regenerative braking force Fz. The braking operation amount Ba and the target acceleration Gs are collectively referred to as the "braking demand amount Bs." The braking demand amount Bs is a state quantity that represents a braking demand for the vehicle. The servo pressure Pa is acquired by at least one of the servo pressure sensor PA 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.

[0056] 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).

[0057] In step S130, a target pressure Pt is calculated based on the target total braking force Fv and the standard regenerative braking force Fz so that regenerative cooperative control is performed. The "target pressure Pt" is a target value for the wheel pressure Pw, and is a target value for controlling the servo pressure Pa. 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"). The target pressure Pt is then determined for the following two cases:

[0058] 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.

[0059] 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.

[0060] Next, a target pressure Pt is calculated based on the target sum Fnt. Specifically, the target pressure Pt is determined based on the specifications of the brake device SX (= SXf, SXr) so that the target sum Fnt is satisfied. That is, in the case (1) where "Fv≦Fz," the target pressure Pt is determined to be "0." In contrast, in the case (2) where "Fv>Fz," the target pressure Pt is determined so that 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 (brake disc), the friction coefficient of the friction member (brake pad), and the effective radius of the wheel WH.

[0061] In step S140, the electric motor MA is controlled based on the target pressure Pt. Specifically, first, the wheel pressure Pw is calculated from the servo pressure Pa, taking into account resistance in the hydraulic pressure transmission path (such as the sliding resistance of the seal member SL). Here, the servo pressure Pa is acquired by at least one of the servo pressure sensor PA and the supply pressure sensor PM. Then, the servo pressure Pa is controlled by driving the electric cylinder DN (particularly the electric motor MA) so that the wheel pressure Pw (calculated actual value) approaches and matches the target pressure Pt (target value).

[0062] <Drive Control of Electric Cylinder DN> Details of the drive control of the electric cylinder DN (i.e., the processing of 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 target pressure Pt, servo pressure Pa, and 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.

[0063] The wheel pressure calculation block PW calculates the wheel pressure Pw based on the servo pressure Pa. As described above, the target pressure Pt is determined so as to correspond to the wheel pressure Pw. Therefore, the wheel pressure Pw is determined from the servo pressure Pa based on the resistance in the hydraulic pressure transmission path.

[0064] The hydraulic pressure to hydraulic volume conversion block ZE converts (converts) hydraulic pressure to hydraulic 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. The hydraulic volume conversion block ZE has front and rear wheel conversion maps Zef and Zer (corresponding to "conversion maps"). 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.

[0065] 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.

[0066] 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 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.

[0067] Specifically, the standard fluid volume calculation block ES calculates a front wheel standard fluid volume Esf based on the target pressure Pt 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 target pressure Pt. Similarly, the standard fluid volume calculation block ES calculates a rear wheel standard fluid volume Esr based on the target pressure Pt 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 target pressure Pt. 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.

[0068] The estimated fluid volume calculation block EE calculates an estimated fluid volume Ee based on the wheel pressure Pw 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 cylinder CWf and the rear wheel cylinder CWr to generate the wheel pressure Pw. Specifically, the front wheel estimated fluid volume Eef is calculated based on the wheel pressure Pw 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 Pw 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 volume of fluid that is estimated to have flowed from the control cylinder CC to the wheel cylinder CW. Note that since the wheel pressure Pw is derived from the servo pressure Pa, it can be said that "the estimated fluid volume Ee is calculated based on the servo pressure Pa and the front and rear wheel conversion maps Zef and Zer."

[0069] 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.

[0070] 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, a stroke sensor SN is provided in the electric cylinder DN to obtain 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The correction value Kh is a state variable for making the wheel pressure Pw coincide with the target pressure Pt. 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 volume Ee is determined from the wheel pressure Pw (actual value)" and "when the hydraulic volume is optimized, the hydraulic pressure is also optimized." In the brake control device SA, the servo pressure Pa is controlled by feedback control based on the correction value Kh so that the wheel pressure Pw approaches and coincides with the target pressure Pt.

[0075] 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.

[0076] 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.

[0077] <<Modification>> In the above-described embodiment, the standard fluid volume calculation block ES and the estimated fluid volume calculation block EE are provided with separate calculation maps, the front wheel conversion map Zef and the rear wheel conversion map Zer, for converting hydraulic pressure to hydraulic volume. The front wheel standard fluid volume Esf and the rear wheel standard fluid volume Esr are calculated separately, and the front wheel estimated fluid volume Eef and the rear wheel estimated fluid volume Eer are determined separately. Alternatively, a conversion map Zek (also referred to as an "integrated conversion map") that integrates the front and rear wheel conversion maps Zef and Zer may be used as the calculation map for converting hydraulic pressure to hydraulic volume (see the characteristics indicated by the dashed line). The integrated conversion map Zek also defines the relationship between hydraulic pressure and hydraulic volume. In a configuration in which the integrated conversion map Zek is used, the reference value Ks is determined based on the target pressure Pt and the standard fluid volume Es calculated from the integrated conversion map Zek. Similarly, the correction value Kh is determined based on the servo pressure Pa (i.e., the wheel pressure Pw) and the estimated fluid volume Ee calculated from the integrated conversion map Zek. Note that the integrated conversion map Zek is also determined in advance through experiments, analysis, etc., just like the front and rear wheel conversion maps Zef and Zer.

[0078] <<Function and Effect>> 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.

[0079] The brake control device SA determines a target rotation angle Kt based on a standard fluid volume Es calculated from the target pressure Pt. 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 target pressure Pt.

[0080] The conversion maps Zef, Zer, and Zek, 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 friction members, etc. Specifically, when gas is present, a larger volume 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 volume of fluid is required to achieve the same hydraulic pressure compared to when the wear is small.

[0081] The brake control device SA determines a correction value Kh to compensate for errors in the conversion maps Zef, Zer, and Zek. The correction value Kh is determined based on the estimated fluid volume Ee (the volume of fluid estimated to have flowed into the wheel cylinder CW) calculated from the servo pressure Pa and the fluid volume Ej (the fluid volume discharged) actually discharged from the control cylinder CC. Here, the fluid volume Ej is obtained by a fluid volume sensor (KA, SN, etc.). The same conversion maps Zef, Zer, and Zek 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 fluid volume Ej, represents errors contained in the conversion maps Zef, Zer, and Zek. The reference value Ks is corrected by the correction value Kh to determine the target rotation angle Kt, thereby correcting the effects of the errors.

[0082] 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, Zer, and Zek are shifted in a manner that reduces the true value along the vertical axis (the hydraulic pressure axis). In other words, the conversion maps Zef, Zer, and Zek determine fluid volumes that are smaller than the true value at the same hydraulic pressure. Therefore, the 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 discharge fluid amount Ej is smaller than the estimated fluid amount Ee (i.e., when Ej < Ee, hE < 0), the conversion maps Zef, Zer, and Zek are offset from the true value so as to be enlarged in the direction of the vertical axis (hydraulic pressure axis). In other words, the conversion maps Zef, Zer, and Zek determine a fluid amount greater than the true value at the same hydraulic pressure. Therefore, the target rotation angle Kt is corrected to be smaller by a correction value Kh calculated from the fluid amount deviation hE. The correction value Kh is determined to be larger, including the positive and negative signs, as the fluid amount deviation hE increases. Through correction based on the fluid amount deviation hE, the amount Ej (discharge fluid 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 pressure Pt. As a result, the electric cylinder DN adjusts the servo pressure Pa with high precision so that the wheel pressure Pw coincides with the target pressure Pt.

[0083] <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, the electric motor MA of the electric cylinder DN is controlled by the same method as in the first embodiment.

[0084] In the first embodiment, the servo pressure Pa 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).

[0085] 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.

[0086] The front and rear wheel communication passages HSf and HSr (fluid passages connecting the front and rear wheel cylinders CWf and CWr) are connected to the control cylinder CC (particularly, the control chamber Rc) via a communication passage HV (fluid passage). The communication passage HV is also a fluid passage connecting the front and rear wheel communication passages HSf and HSr. A communication valve VC is provided in the communication passage HV.

[0087] 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 servo pressure Pa 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 servo pressure sensor PA may be provided in the hydraulic pressure generating unit PU or in the correction actuator YZ. In a configuration in which the servo pressure sensor PA is provided in the correction actuator YZ, the servo pressure Pa is acquired by the brake controller EA via the communication bus BS.

[0088] In the second embodiment, the same regenerative cooperative control as in the first embodiment is executed, and the same effect (compensation for errors in the conversion map representing the hydraulic pressure-liquid volume characteristics) is achieved.

[0089] <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.

[0090] In the embodiment of the brake control device SA described above, the servo pressure Pa is obtained as a result of detection by the servo pressure sensor PA provided at the discharge portion of the electric cylinder DN. Alternatively, the servo pressure sensor PA may be provided in the hydraulic pressure transmission path from the control cylinder CC to the wheel cylinder CW (see, for example, the supply pressure sensor PM). In either case, the servo pressure Pa used in calculating the estimated hydraulic volume Ee is based on the actual value detected by the servo pressure sensor PA.

[0091] 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.

[0092] In the embodiment of the brake control device SA described above, the target pressure Pt is determined as a target value corresponding to the wheel pressure Pw (actual value). 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 servo pressure sensor PA may be used as the comparison location. In this configuration, the target pressure Pt is determined to correspond to the servo pressure Pa (actual value) after compensating for hydraulic pressure components due to the resistance. In pressure regulation control, regardless of the location where the target value and the actual value are compared, the target pressure Pt is a target value for controlling the servo pressure Pa. Furthermore, the standard hydraulic volume Es is determined based on the target pressure Pt, and the estimated hydraulic volume Ee is determined based on the servo pressure Pa. Furthermore, the actual hydraulic pressure (Pa, Pw, etc.) corresponding to the target pressure Pt is controlled to approach and match the target pressure Pt.

[0093] 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.

[0094] 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 pressure Pt is 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.

[0095] The above-described braking control device SA has been applied to a vehicle in which a regenerative device KG is provided on the front wheels WHf and in which regenerative cooperative control is performed. In a vehicle in which regenerative cooperative control is performed, the regenerative device KG only needs to be provided on at least one of the front wheels WHf and the rear wheels WHr. The braking control device SA can also be applied to a vehicle in which the regenerative device KG is omitted and regenerative cooperative control is not performed. In other words, the braking control device SA can be applied to various vehicles regardless of whether regenerative cooperative control is performed or not.

[0096] 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 conversion between the supply pressure Pm (master pressure) and the servo pressure Pa can be calculated 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 servo pressure sensor PA and the supply pressure Pm is used as the servo pressure Pa, the supply pressure Pm is converted to the servo pressure Pa based on the area ratio.

[0097] Summary of the embodiment The brake control device SA of a vehicle adjusts the wheel pressure Pw of the wheel cylinder CW by the servo pressure Pa. The brake control device SA includes a control cylinder CC, a control piston NC, an electric motor MA, servo pressure sensors (PA, PM, etc.), fluid level sensors (KA, SN, etc.), and a controller EA.

[0098] A control piston NC is inserted into the control cylinder CC. The control cylinder CC generates a servo pressure Pa by moving the control piston NC with the power of the electric motor MA. A servo pressure sensor (PA, PM, etc.) detects and acquires the servo pressure Pa (actual value). A fluid volume sensor (KA, SN, etc.) detects and acquires the actual fluid volume Ej of brake fluid BF delivered from the control cylinder CC. A controller EA calculates a target pressure Pt for controlling the servo pressure Pa based on the vehicle braking demand Bs, and controls the rotation angle (Ka) of the electric motor MA based on the target pressure Pt and the servo pressure Pa.

[0099] The controller EA obtains the volume of brake fluid BF discharged from the control cylinder CC as the discharge fluid amount Ej. Furthermore, an estimated fluid amount Ee estimated to have flowed into the wheel cylinder CW is calculated based on the servo pressure Pa and the conversion maps Zef, Zer, and Zek. The electric motor MA is controlled based on the deviation hE between the estimated fluid amount Ee and the discharge fluid amount Ej. The conversion maps Zef, Zer, and Zek are preset in the controller EA as a relationship between the volume (fluid amount) of brake fluid BF flowing into the wheel cylinder CW and the wheel pressure Pw.

[0100] The estimated fluid volume Ee is calculated based on the conversion maps Zef, Zer, and Zek. If the conversion maps Zef, Zer, and Zek are accurate, the estimated fluid volume Ee and the discharge fluid volume Ej will match. If the conversion maps Zef, Zer, and Zek contain errors, the two will not match. In other words, the deviation hE (fluid volume deviation) between the estimated fluid volume Ee and the discharge fluid volume Ej represents the error in the conversion maps Zef, Zer, and Zek. The braking control device SA controls the electric motor MA based on the fluid volume deviation hE to compensate for this error.

[0101] Specifically, the electric motor MA is controlled as follows: A standard fluid volume Es is calculated based on a target pressure Pt calculated from a braking demand Bs and the conversion maps Zef, Zer, and Zek. The standard fluid volume Es is a target value for the fluid volume to flow into the wheel cylinder CW. An estimated fluid volume Ee is calculated based on the servo pressure Pa and the conversion maps Zef, Zer, and Zek. The estimated fluid volume Ee is an estimate of the fluid volume that is estimated to have flowed into the wheel cylinder CW. A reference value Ks calculated from the standard fluid volume Es is then corrected based on a comparison result hE (fluid volume deviation) between the estimated fluid volume Ee (estimated value) and the discharged fluid volume Ej (detected value), and a target rotation angle Kt of the electric motor MA is determined. Furthermore, a supply current Im to the electric motor MA is adjusted so that the motor rotation angle Ka coincides with the target rotation angle Kt. The discharged fluid volume Ej is determined from the detection values ​​of the fluid volume sensors (KA, SN, etc.).

[0102] The conversion maps Zef, Zer, and Zek are pre-stored as predetermined characteristics in the controller EA (particularly, the microprocessor MP). However, the conversion maps Zef, Zer, and Zek contain errors due to gas (air, etc.) present inside the brake device SX, wear of friction members, and the like. The fluid volume deviation hE occurs due to these errors. In the brake control device SA, the target rotation angle Kt of the electric motor MA is corrected based on the fluid volume deviation hE to compensate for the errors in the conversion maps Zef, Zer, and Zek. In other words, in the brake control device SA, the electric motor MA is controlled based on the fluid volume deviation hE.

[0103] Specifically, the fluid volume deviation hE is derived by subtracting the estimated fluid volume Ee from the fluid discharge volume Ej. When the fluid discharge volume Ej is greater than the estimated fluid volume Ee (i.e., when the fluid volume deviation hE has a positive sign), the amount of fluid discharged from the electric cylinder DN is insufficient, and the servo pressure Pa is insufficient. In this situation, the target rotation angle Kt is increased so that the motor rotation angle Ka is increased. On the other hand, when the fluid discharge volume Ej is smaller than the estimated fluid volume Ee (i.e., when the fluid volume deviation hE has a negative sign), the amount of fluid discharged from the electric cylinder DN is excessive, and the servo pressure Pa is excessive. In this situation, the target rotation angle Kt is decreased so that the motor rotation angle Ka is reduced. By adjusting the motor rotation angle Ka using the fluid volume deviation hE, the fluid discharge volume of the electric cylinder DN (particularly the control cylinder CC) is adjusted to be neither too much nor too little with respect to the target pressure Pt. As a result, the accuracy of pressure regulation by the electric cylinder DN is improved.

Claims

1. A vehicle braking control device comprising a control cylinder into which a control piston is inserted and which generates servo pressure by moving the control piston with an electric motor, a servo pressure sensor which detects the servo pressure, and a controller which controls the electric motor based on the servo pressure, and which adjusts the wheel pressure of a wheel cylinder using the servo pressure, wherein the controller obtains the amount of fluid discharged from the control cylinder, calculates an estimated amount of fluid based on the servo pressure and a conversion map, and controls the electric motor based on the deviation between the amount of fluid discharged and the estimated amount of fluid.

2. A vehicle brake control device as described in claim 1, wherein the controller calculates a target pressure based on a braking demand amount, calculates a standard fluid volume based on the target pressure and the conversion map, and controls the rotation angle of the electric motor based on the standard fluid volume and the deviation.

3. A vehicle brake control device as claimed in claim 1 or 2, wherein the controller sets the relationship between the volume of brake fluid flowing into the wheel cylinder and the wheel pressure as the conversion map.

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