Vehicle braking control device

Abstract

To provide a braking control device that increases brake fluid pressure with an electric motor as a power source, and which surely maintains a vehicle stopping state even when the electric motor is stopped.SOLUTION: A braking control device comprises an actuator HU and a controller ECU. The actuator HU composed of a fluid pump QA driven by an electric motor MA, and a pressure regulating valve UA regulating brake fluid BF discharged by the fluid pump QA to servo fluid pressure Pa, regulates brake fluid pressure Pw of a wheel cylinder CW by the servo fluid pressure Pa. The controller ECU controls the servo fluid pressure Pa via the actuator HU on the basis of an operation quantity Ba of a braking operation member BP. Furthermore, the controller ECU closes the pressure regulating valve UA after increasing the servo fluid pressure Pa by predetermined fluid pressure Pk when a vehicle JV is stopped, and stops driving of the electric motor MA.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] The applicant is developing a braking control device as described in Patent Document 1 for the purpose of "preventing the occurrence of control hunting due to unnecessary motor restart during motor stop control for stopping the pump motor". Specifically, the braking control device includes a master cylinder, a wheel cylinder, a VDC brake hydraulic actuator, and a differential pressure brake control unit. The differential pressure brake control unit includes a motor stop control unit that stops the VDC motor when a stop condition is satisfied (step S5 → step S7), and a motor restart control unit that waits for a restart determination of the VDC motor while an operation holding duration condition is not satisfied, that is, while the braking operation holding duration for continuing the braking operation holding state during motor stop control exceeds a predetermined time X required for the wheel cylinder pressure to drop to a predetermined pressure due to liquid leakage from the differential pressure valve (step S8).

[0003] In the braking control device described in Patent Document 1, when the electric motor is stopped and the braking pedal holding duration exceeds a predetermined time and the vehicle starts to move slightly, the electric motor is redriven and the hydraulic pressure of the wheel cylinder (also referred to as "braking hydraulic pressure") is increased. For example, when the vehicle is stopped on a slope, even if the braking hydraulic pressure decreases slightly, the vehicle may move significantly. From the perspective of the driver's discomfort, it is desirable to avoid the vehicle moving inadvertently. Therefore, a braking control device for a vehicle that can surely maintain a stopped state even on a slope is desired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a braking control device for a vehicle that increases braking hydraulic pressure using an electric motor as a power source, which can surely maintain a stopped state even when the electric motor is stopped.

Means for Solving the Problems

[0006] The braking control device for a vehicle according to the present invention includes "a fluid pump (QA) driven by an electric motor (MA), and a pressure regulating valve (UA) that adjusts the braking fluid (BF) discharged by the fluid pump (QA) to servo hydraulic pressure (Pa), and an actuator (HU) that adjusts the braking hydraulic pressure (Pw) of the wheel cylinder (CW) of the vehicle (JV) by the servo hydraulic pressure (Pa)", and "a controller (ECU) that controls the servo hydraulic pressure (Pa) via the actuator (HU) based on the operation amount (Ba) of the braking operation member (BP) of the vehicle (JV)".

[0007] In the braking control device for a vehicle according to the present invention, when the vehicle (JV) stops, the controller (ECU) increases the servo hydraulic pressure (Pa) by a predetermined hydraulic pressure (Pk), then closes the pressure regulating valve (UA), and stops driving the electric motor (MA). According to this configuration, in maintaining the stop of the vehicle JV, there is a margin of the predetermined hydraulic pressure Pk, so that the stopped state can be surely maintained even when the driving of the electric motor MA is stopped.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of a braking control device SC for a vehicle according to the present invention will be described with reference to the drawings.

[0010] <Symbols of Components, etc.> In the following description, components such as members, signals, values, etc. denoted by the same symbol, such as "CW", have the same function. The subscripts "f" and "r" attached to the ends of various symbols related to wheels are inclusive symbols indicating whether the element is related to the front wheels or the rear wheels. Specifically, "f" indicates an element related to the front wheels, and "r" indicates an element related to the rear wheels. For example, in the wheel cylinder CW, it is expressed as "front wheel wheel cylinder CWf, rear wheel wheel cylinder CWr". Further, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its general name.

[0011] <Embodiment of the Braking Control Device SC> With reference to the schematic diagram of FIG. 1, an embodiment of the braking control device SC will be described. The vehicle JV is provided with a braking operation member BP, a braking device SX, various sensors (VW, etc.), and a braking control device SC.

[0012] The vehicle JV is provided with a braking operation member BP. The braking operation member (for example, a brake pedal) BP is a member that the driver operates to decelerate the vehicle. According to the operation amount Ba of the braking operation member BP, the braking control device SC generates a braking hydraulic pressure Pw in the wheel cylinder CW.

[0013] For each wheel WH of vehicle JV, a braking device SX is provided to generate a braking force Fx on the wheel WH according to the braking hydraulic pressure Pw. The braking device SX is composed of a rotating member (for example, a brake disk) KT and a brake caliper CP. The rotating member KT is fixed to the wheel WH, and the brake caliper CP is provided so as to sandwich the rotating member KT. A wheel cylinder CW is provided in the brake caliper CP. Braking fluid BF adjusted to the braking hydraulic pressure Pw is supplied as the braking hydraulic pressure Pw from the braking control device SC to the wheel cylinder CW. By the braking hydraulic pressure Pw, a friction member (for example, a brake pad) is pressed against the rotating member KT. Since the rotating member KT and the wheel WH are fixed to rotate integrally, a braking force Fx is generated on the wheel WH by the frictional force generated at this time.

[0014] Vehicle JV includes various sensors such as a braking operation amount sensor BA, a steering angle sensor SA, a wheel speed sensor VW, a yaw rate sensor YR, a longitudinal acceleration sensor GX, and a lateral acceleration sensor GY.

[0015] A braking operation amount sensor BA is provided to detect the operation amount Ba of a braking operation member (brake pedal) BP. Specifically, as the braking operation amount sensor BA, at least one of an input hydraulic pressure sensor PN that detects the hydraulic pressure Pn (referred to as "input hydraulic pressure") in an input chamber Rn (described later), an operation displacement sensor SP that detects the operation displacement Sp of the braking operation member BP, and an operation force sensor FP that detects the operation force Fp of the braking operation member BP is adopted. That is, by the operation amount sensor BA, at least one of the input hydraulic pressure Pn, the braking operation displacement Sp, and the braking operation force Fp is detected as the braking operation amount Ba.

[0016] A steering amount sensor SA (not shown) is provided to detect an operation amount Sa of a steering operation member (e.g., a steering wheel) (not shown). The steering operation amount Sa is a displacement from a steering neutral position "Sa = 0" corresponding to straight running of the vehicle. Each wheel WH of the vehicle JV is provided with a wheel speed sensor VW that detects a wheel speed Vw which is the rotational speed of the wheel WH. Further, the vehicle JV is provided with a yaw rate sensor YR (not shown) that detects an actual yaw rate (yaw angular velocity) Yr of the vehicle body, a longitudinal acceleration sensor GX that detects an acceleration in the longitudinal direction of the vehicle body (longitudinal acceleration) Gx, and a lateral acceleration sensor GY (not shown) that detects an acceleration in the lateral direction of the vehicle body (lateral acceleration).

[0017] The vehicle JV is provided with a brake control device SC to supply a brake fluid BF pressurized to a brake device SX (particularly, a wheel cylinder CW). Specifically, the brake control device SC electrically generates and adjusts a brake fluid pressure Pw according to an operation amount Ba of a brake operation member BP. Then, the brake fluid pressure Pw is supplied to the wheel cylinder CW. The brake control device SC is composed of a fluid unit HU (also referred to as an "actuator") including a master cylinder CM, and a controller ECU (simply referred to as a "controller") for the brake control device SC.

[0018] ≪Fluid Unit HU≫ The fluid unit HU electrically generates a brake fluid pressure Pw using an electric motor MA as a power source. Then, the brake fluid pressure Pw is supplied to the wheel cylinder CW via front and rear wheel connecting paths HSf, HSr. For example, in the brake control device SC, a so-called front-rear type (also referred to as "Type II") is adopted as two brake systems. Hereinafter, a configuration example of the fluid unit HU will be described in detail. The fluid unit HU is composed of an apply unit AU (including a master cylinder CM) and a pressurizing unit KU. Note that the fluid unit HU and the wheel cylinder CW are connected by a connecting path HS, an input path HN, a reservoir path HR, a reflux path HK, and a servo path HV. These are fluid paths through which the brake fluid BF moves, and correspond to fluid pipes, fluid paths in the fluid unit HU, hoses, etc.

[0019] [Application Unit AU] The application unit AU is composed of a master reservoir RV, a master cylinder CM, a master piston NM, a master spring DM, an input cylinder CN, an input piston NN, an input spring DN, an input valve VN, a release valve VR, a stroke simulator SS, and an input hydraulic pressure sensor PN. The application unit AU is provided with various hydraulic chambers including an input chamber Rn, a servo chamber Ru, a rear chamber Ro, and a master chamber Rm. Here, the "hydraulic chamber" is a chamber filled with the brake fluid BF and sealed by a seal member SL. Note that the volume of each hydraulic chamber is changed by the movement of the input piston NN and the master piston NM.

[0020] The master reservoir (also referred to as the "atmospheric pressure reservoir") RV is a tank for the working liquid, and the brake fluid BF is stored therein. The master reservoir RV is connected to the master cylinder CM (particularly, the master chamber Rm).

[0021] The master cylinder CM is a cylinder member having a bottom. Inside the master cylinder CM, a master piston NM is inserted, and its interior is sealed by a seal member SL to form a master chamber Rm. The master cylinder CM is of the so-called single type. The master chamber Rm is finally connected to the front wheel wheel cylinder CWf via the front wheel connection path HSf and the hydraulic modulator MJ. When the master piston NM is moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases), the brake fluid BF with a hydraulic pressure Pm (referred to as the "supply hydraulic pressure") is supplied from the fluid unit HU (particularly, the master cylinder CM) to the hydraulic modulator MJ (finally, the front wheel wheel cylinder CWf).

[0022] The master piston NM is provided with a flange part (flange) Tp. By this flange part Tp, the interior of the master cylinder CM is further partitioned into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru is arranged to face the master chamber Rm with the master piston NM interposed therebetween. Further, the rear chamber Ro is sandwiched between the master chamber Rm and the servo chamber Ru and is disposed therebetween. The servo chamber Ru and the rear chamber Ro are also sealed by a seal member SL in the same manner as described above.

[0023] For example, the pressure receiving area of the flange part Tp (that is, the pressure receiving area of the servo chamber Ru) ru is set to be equal to the pressure receiving area of the master piston NM (that is, the pressure receiving area of the master chamber Rm) rm. In this case, the hydraulic pressure Pa (described later) introduced into the servo chamber Ru and the supply hydraulic pressure Pm are the same in the steady state (that is, since "ru = rm", "Pa = Pm").

[0024] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the interior of the input cylinder CN and is sealed by a seal member SL, thereby forming an input chamber Rn. The input piston NN is mechanically connected to the braking operation member BP via a clevis (U-shaped link). The input piston NN is provided with a flange part (flange) Tn. An input spring DN is provided between the mounting surface of the input cylinder CN to the master cylinder CM and the flange part Tn of the input piston NN. The input spring DN presses the flange part Tn against the bottom of the input cylinder CN along the central axis of the master cylinder CM.

[0025] When not braking, inside the input cylinder CN, the master piston NM (especially, the end face Mp) and the input piston NN (especially, the end face Mn) have a gap Ks (also referred to as the "separation distance"). When not braking, the pistons NM and NN are in the position in the most rearward direction Hb (referred to as the "initial position" of each piston). The gap Ks in this situation is referred to as the "predetermined distance ks (also referred to as the 'initial gap')". In the input chamber Rn, since the master piston NM and the input piston NN are separated by the separation distance Ks, a situation is created where, despite the braking operation member BP being operated, the braking hydraulic pressure Pw is not generated. That is, the execution of the regenerative cooperative control is enabled by the separation distance Ks. Note that the separation distance Ks is controlled (adjusted) by the servo hydraulic pressure Pa (described later).

[0026] The input chamber Rn and the rear chamber Ro are connected via the input passage HN. And an input valve VN is provided in the input passage HN. The input passage HN is connected to the master reservoir RV between the rear chamber Ro and the input valve VN via the open valve VR and the reservoir passage. The input valve VN and the open valve VR are two-position solenoid valves (also referred to as "on-off valves") having an open position (communicating state) and a closed position (blocking state). A normally closed solenoid valve is adopted as the input valve VN. Also, a normally open solenoid valve is adopted as the open valve VR.

[0027] A stroke simulator (simply also referred to as the "simulator") SS is connected to the rear chamber Ro. The operation force Fp of the braking operation member BP is generated by the simulator SS. Inside the simulator SS, a piston and an elastic body (for example, a compression spring) are provided. When the braking fluid BF flows into the simulator SS, the piston is pushed by the braking fluid BF. Since a force is applied to the piston in the direction to block the inflow of the braking fluid BF by the elastic body, the operation force Fp of the braking operation member BP is generated. That is, the operation characteristics (the relationship between the operation displacement Sp and the operation force Fp) of the braking operation member BP are formed by the simulator SS.

[0028] An input hydraulic pressure sensor PN is provided to detect the hydraulic pressure Pn (referred to as "input hydraulic pressure") in the input chamber Rn. The input hydraulic pressure Pn is also the hydraulic pressure of the simulator SS and the rear chamber Ro. The input hydraulic pressure sensor PN is one of the above-described braking operation amount sensors BA, and the input hydraulic pressure Pn is input to the brake controller ECU as the braking operation amount Ba.

[0029] In addition to the input hydraulic pressure sensor PN, the fluid unit HU is provided with an operation displacement sensor SP that detects the operation displacement Sp of the braking operation member BP and / or an operation force sensor FP that detects the operation force Fp of the braking operation member BP as the braking operation amount sensor BA. That is, as the braking operation amount sensor BA, at least one of the input hydraulic pressure sensor PN, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP is adopted. Therefore, the braking operation amount Ba is at least one of the input hydraulic pressure Pn, the operation displacement Sp, and the operation force Fp.

[0030] [Pressurizing Unit KU] The pressurizing unit KU is composed of an electric motor MA, a fluid pump QA, a pressure regulating valve UA, a supply hydraulic pressure sensor PM, and a servo hydraulic pressure sensor PA. In the pressurizing unit KU, the pressure of the braking fluid BF discharged by the fluid pump QA driven by the electric motor MA is adjusted by the pressure regulating valve UA. Here, the hydraulic pressure adjusted by the pressure regulating valve UA is referred to as "servo hydraulic pressure Pa". The servo hydraulic pressure Pa is supplied to the apply unit AU (particularly, the servo chamber Ru) and the rear wheel cylinder CWr, and finally, the front wheel and rear wheel braking hydraulic pressures Pwf, Pwr (= Pw) are generated.

[0031] A combination of "one electric motor MA" and "one fluid pump QA driven by the electric motor MA" constitutes an electric pump. The electric motor MA is a power source for generating and adjusting the hydraulic pressure Pw (braking hydraulic pressure) of the wheel cylinder CW during braking. The electric motor MA is provided with a rotation angle sensor KA for detecting the rotation angle Ka of the electric motor MA (particularly, the rotor).

[0032] In the fluid pump QA, the suction part Qs and the discharge part Qt are connected via a reflux path HK. Also, the suction part Qs of the fluid pump QA is connected to the master reservoir RV via a reservoir path HR. When the electric motor MA is driven and the fluid pump QA is rotated, the brake fluid BF circulates in the reflux path HK. Also, when the amount of the brake fluid BF is insufficient in the reflux path HK, the application unit AU, the wheel cylinder CW, etc., the brake fluid BF is sucked from the master reservoir RV via the reservoir path HR. Note that a check valve GA is provided in the reflux path HK (particularly, the discharge part Qt of the fluid pump QA) so that the fluid pump QA is not reversed.

[0033] A pressure regulating valve UA is provided in the reflux path HK so as to adjust the pressure Pa (servo hydraulic pressure) of the brake fluid BF discharged by the fluid pump QA. The pressure regulating valve UA is a linear solenoid valve (also referred to as a "proportional valve" or a "differential pressure valve") in which the valve opening amount (lift amount) is continuously controlled according to its energized state (for example, supply current). A normally open solenoid valve is adopted as the pressure regulating valve UA.

[0034] When the electric motor MA is operating, a circulation flow KN of the brake fluid BF (the flow of the fluid returns to the original flow again, simply also referred to as "reflux") as shown by the dashed arrow is generated in the reflux path HK. The servo hydraulic pressure Pa (the pressure between the discharge part Qt of the fluid pump QA and the pressure regulating valve UA) is adjusted by restricting the reflux KN by the pressure regulating valve UA (the so-called orifice effect). Note that since the pressure regulating valve UA is of the normally open type, it is in the fully open state when not energized, and the servo hydraulic pressure Pa is "0".

[0035] The return passage HK is connected to the servo chamber Ru via the servo passage HV between the check valve GA and the pressure regulating valve UA. Therefore, the servo hydraulic pressure Pa is supplied to the servo chamber Ru. In a configuration where the pressure receiving area ru of the servo chamber Ru is equal to the pressure receiving area rm of the master chamber Rm, when the servo hydraulic pressure Pa is supplied to the servo chamber Ru, a supply hydraulic pressure Pm that is the same pressure as the servo hydraulic pressure Pa is output from the master chamber Rm (that is, "Pm = Pa"). Furthermore, even in a configuration where the pressure receiving areas ru and rm are different, since their relationship (for example, the ratio of the pressure receiving areas) is known, the supply hydraulic pressure Pm and the servo hydraulic pressure Pa can be mutually converted.

[0036] The master chamber Rm of the master cylinder CM is connected to the front wheel wheel cylinder CWf via the front wheel connection passage HSf and the hydraulic modulator MJ. The hydraulic modulator MJ is for independently and individually adjusting the hydraulic pressure Pw of each wheel cylinder CW in anti-lock brake control, vehicle stability control, etc. The front wheel connection passage HSf branches into two within the hydraulic modulator MJ. The branched front wheel connection passages HSf are connected to each of the front wheel wheel cylinders CWf. A supply hydraulic pressure sensor PM is provided in the front wheel connection passage HSf so as to detect the hydraulic pressure Pm of the brake fluid BF supplied from the master chamber Rm. For example, the supply hydraulic pressure sensor PM is included within the hydraulic modulator MJ. Here, when the hydraulic modulator MJ is not operating, the supply hydraulic pressure Pm is equal to the hydraulic pressure (front wheel brake hydraulic pressure) Pwf within the front wheel wheel cylinder CWf.

[0037] In the adjustment of the front-wheel braking hydraulic pressure Pwf (for example, pressurization), the servo hydraulic pressure Pa is transmitted via the master cylinder CM in the order of "Ru →Rm → CWf". On the other hand, the adjustment of the rear-wheel braking hydraulic pressure Pwr (for example, pressurization) is performed by directly supplying the servo hydraulic pressure Pa to the rear-wheel wheel cylinder CWr. Specifically, the rear-wheel communication path HSr is connected to the reflux path HK between the check valve GA and the pressure regulating valve UA. Further, the rear-wheel communication path HSr is branched into two within the hydraulic modulator MJ and connected to each of the rear-wheel wheel cylinders CWr. A servo hydraulic pressure sensor PA is provided in the rear-wheel communication path HSr to detect the servo hydraulic pressure Pa. When the apply unit AU is configured with "ru = rm", although there is a time lag between the servo hydraulic pressure Pa and the supply hydraulic pressure Pm, they are substantially (steadily) equal, so one of the servo hydraulic pressure sensor PA and the supply hydraulic pressure sensor PM may be omitted. Similarly to the above, when the hydraulic modulator MJ is not operating, the servo hydraulic pressure Pa is equal to the hydraulic pressure (rear-wheel braking hydraulic pressure) Pwr in the rear-wheel wheel cylinder CWr.

[0038] ≪Controller ECU≫ The braking control device SC is provided with a controller ECU to control the above-mentioned fluid unit HU. Signals such as the braking operation amount Ba, the supply hydraulic pressure Pm, the servo hydraulic pressure Pa, the wheel speed Vw, and the longitudinal acceleration Gx are input to the controller ECU. Then, based on these signals, the solenoid valves, electric motors, etc. that make up the fluid unit HU are controlled by the controller ECU. The controller ECU is composed of a "microprocessor MP that performs signal processing" and a "drive circuit DD that drives solenoid valves and electric motors". Note that the controller ECU is connected to other controllers via a communication bus BS so that it can share information (detection values, calculation values, etc.) with other systems.

[0039] In the controller ECU, the vehicle body speed Vx of the vehicle JV is calculated based on the wheel speed Vw. Also, in the controller ECU, an antilock brake control for suppressing the lock of the wheel WH is executed based on the wheel speed Vw and the vehicle body speed Vx. Further, in the controller ECU, vehicle stability control for maintaining the stability of the vehicle JV (that is, suppressing excessive understeer / oversteer behavior) is executed based on the steering operation amount Sa, yaw rate Yr, longitudinal acceleration Gx, lateral acceleration Gy, etc.

[0040] ≪Drive of the fluid unit HU by the controller ECU≫ A signal of the braking operation amount Ba is input to the controller ECU. Here, the braking operation amount Ba is a signal indicating the degree (magnitude) of the operation of the braking operation member BP. For example, at least one of the input hydraulic pressure Pn, operation displacement Sp, and operation force Fp is adopted as the braking operation amount Ba. Signals (Pa, etc.) from various sensors (PA, etc.) provided in the fluid unit HU are input to the controller ECU. Based on these signals and the control algorithm programmed in the microprocessor MP provided in the controller ECU, drive signals Vn of the input valve VN, Vr of the release valve VR, Ua of the pressure regulating valve UA, and Ma of the electric motor MA are calculated. Electric power is supplied to the controller ECU from the storage battery BU. Based on this power supply, the solenoid valves "VN, VR, UA" and the electric motor MA constituting the fluid unit HU are controlled (driven) according to the drive signals "Vn, Vr, Ua, Ma".

[0041] Specifically, the controller ECU is provided with a drive circuit DD for driving solenoid valves "VN, VR, UA" and electric motor MA. The drive circuit DD is supplied with power from the auxiliary battery BU. In the drive circuit DD, a bridge circuit is formed by switching elements (power semiconductor devices such as MOS-FETs and IGBTs) to drive the electric motor MA. Based on the motor drive signal Ma, the energization state of each switching element is controlled, and the output of the electric motor MA is controlled. Also, in the drive circuit DD, based on the drive signals "Vn, Vr, Ua", the energization states (i.e., excitation states) of the solenoid valves "VN, VR, UA" are controlled to drive them.

[0042] During braking when the braking operation member BP is operated, the input valve VN is opened and the release valve VR is closed. Therefore, in conjunction with the movement of the braking operation member BP, the braking fluid BF discharged from the input chamber Rn is moved to the simulator SS. Thereby, the operating force Fp of the braking operation member BP is formed. Also, during braking, the electric motor MA and the pressure regulating valve UA are driven. The braking fluid BF discharged from the fluid pump QA is throttled by the pressure regulating valve UA, thereby adjusting the servo hydraulic pressure Pa. The servo hydraulic pressure Pa is transmitted from the servo chamber Ru to the master chamber Rm via the master piston NM and is supplied as the supply hydraulic pressure Pm to the front wheel cylinder CWf. On the other hand, the servo hydraulic pressure Pa is directly supplied to the rear wheel cylinder CWr.

[0043] <Processing of Pressure Regulation Control> Referring to the flowchart of FIG. 2, an example of the processing of pressure regulation control in the braking control device SC will be described. "Pressure regulation control" is to generate and adjust the servo hydraulic pressure Pa electrically using the electric motor MA as a power source, thereby adjusting the hydraulic pressures Pwf and Pwr (front and rear wheel braking hydraulic pressures) of the front and rear wheel cylinders CWf and CWr respectively. The algorithm of the pressure regulation control is programmed in the microprocessor MP in the controller ECU.

[0044] In the following description, in the braking control device SC described with reference to FIG. 1, a configuration of "ru = rm" is assumed. Therefore, the servo hydraulic pressure Pa and the supply hydraulic pressure Pm are equal (strictly equal in the steady state).

[0045] In step S110, various signals including the braking operation amount Ba, the supply hydraulic pressure Pm, the servo hydraulic pressure Pa, the wheel speed Vw, the longitudinal and lateral acceleration Gx, etc. are read. Here, the braking operation amount Ba (a general term for the operation state amount of the braking operation member BP) is detected by the braking operation amount sensor BA. The supply hydraulic pressure Pm is detected by the supply hydraulic pressure sensor PM. The servo hydraulic pressure Pa is detected by the servo hydraulic pressure sensor PA. The wheel speed Vw is detected by the wheel speed sensor VW. The longitudinal and lateral acceleration Gx is detected by the longitudinal and lateral acceleration sensor GX.

[0046] In step S120, the vehicle body speed Vx is calculated based on the wheel speed Vw and a known method. Also, the vehicle body speed Vx may be obtained from another controller through the communication bus BS.

[0047] In step S130, a required hydraulic pressure Ps (variable) is calculated. The required hydraulic pressure Ps is a target value corresponding to the servo hydraulic pressure Pa (actual value) for decelerating the vehicle JV requested by the driver. The required hydraulic pressure Ps is determined based on the braking operation amount Ba (variable) and the calculation map Zps as shown in block X130. Specifically, according to the calculation map Zps, when the braking operation amount Ba is within the range from "0" to the play amount bo, the required hydraulic pressure Ps is calculated to be "0". And when the braking operation amount Ba is equal to or greater than the play amount bo, the required hydraulic pressure Ps is calculated to increase from "zero" as the braking operation amount Ba increases. That is, when "Ba ≧ bo", it is determined that the greater the braking operation amount Ba, the greater the required hydraulic pressure Ps. Here, the play amount bo is a predetermined value (constant) set in advance and corresponds to the play in the braking operation member BP.

[0048] ]In step S140, based on the vehicle body speed Vx, it is determined whether the vehicle JV is in a stopped state (referred to as "stop determination"). If the vehicle body speed Vx is greater than "0" and the vehicle JV is still decelerating, the stop determination is negative, and the process proceeds to step S150. If the vehicle body speed Vx is "0" and the vehicle JV is stopped, the stop determination is positive, and the process proceeds to step S160.

[0049] In step S150, deceleration control is executed. "Deceleration control" decelerates the vehicle JV according to the braking operation amount Ba. Specifically, in deceleration control, the required hydraulic pressure Ps required by the braking operation amount Ba is calculated as the target hydraulic pressure Pt (i.e., "Pt = Ps"). Here, the target hydraulic pressure Pt is the final target value of the hydraulic pressure to be achieved by the braking control device SC. Therefore, the required hydraulic pressure Ps can be said to be an intermediate target value for calculating the target hydraulic pressure Pt.

[0050] In the deceleration control of step S150, the fluid unit HU is controlled so that the servo hydraulic pressure Pa (actual value) approaches and matches the target hydraulic pressure Pt (target value). Since the pressure receiving area ru of the servo chamber Ru is the same as the pressure receiving area rm of the master chamber Rm, the supply hydraulic pressure Pm equal to the servo hydraulic pressure Pa is supplied from the master chamber Rm to the front wheel wheel cylinder CWf. Also, the servo hydraulic pressure Pa is directly supplied to the rear wheel wheel cylinder CWr.

[0051] In step S150, when the braking operation member BP is operated (for example, when the condition "Pt > 0" is satisfied), the electric motor MA is driven. In driving the electric motor MA, a target rotational speed Nt is determined. The target rotational speed Nt is determined based on the target hydraulic pressure Pt. For example, the greater the time change amount dP of the target hydraulic pressure Pt (that is, the time differential value of the target hydraulic pressure Pt), the greater the target rotational speed Nt is calculated to be. Then, rotational speed feedback control is executed based on the target rotational speed Nt and the actual rotational speed Ns. Here, the actual rotational speed Ns is calculated based on the detection value (rotation angle) Ka of the rotation angle sensor KA provided in the electric motor MA. Alternatively, a rotational speed sensor NS for detecting the motor rotational speed (rotational speed) Ns may be provided.

[0052] In the rotational speed feedback control of the electric motor MA, a deviation hN between the target rotational speed Nt and the actual rotational speed Ns is calculated (that is, "hN = Nt - Ns"). Then, the energization amount (current value) Im to the electric motor MA (for example, the duty ratio Dm in the PWM control (pulse width modulation control) of the electric motor) is adjusted so that the rotational speed deviation hN approaches and matches "0". Specifically, when the rotational speed deviation hN is greater than a predetermined rotational speed hn, the current value Im of the electric motor MA is increased, and the electric motor MA is accelerated. On the other hand, when the rotational speed deviation hN is less than the predetermined rotational speed "-hn", the current value Im of the electric motor MA is decreased, and the electric motor MA is decelerated. Here, the predetermined rotational speed hn is the dead zone of the control and is a predetermined value (a constant with a positive sign) set in advance. Note that the target rotational speed Nt may be determined as a predetermined rotational speed nt (constant) set in advance, rather than being calculated as a function of the target hydraulic pressure Pt.

[0053] In response to the driving of the electric motor MA, the fluid pump QA rotates, and the brake fluid BF is discharged from the fluid pump QA. Then, a reflux KN of the brake fluid BF occurs in the reflux passage HK. The pressure regulating valve UA is driven, and by restricting this reflux KN, the servo hydraulic pressure Pa (and as a result, the supply hydraulic pressure Pm and the brake hydraulic pressure Pw) is adjusted. Specifically, based on the target hydraulic pressure Pt and the arithmetic map Zit, a target value It (referred to as the "target energization amount") of the energization amount (for example, the current value) to the pressure regulating valve UA is calculated. The arithmetic map Zit is a characteristic (the so-called IP characteristic) representing the relationship between the current value of the pressure regulating valve UA and the servo hydraulic pressure Pa, and is preset. Since the pressure regulating valve UA is a normally open linear solenoid valve, in the arithmetic map Zit, the larger the target hydraulic pressure Pt, the larger the target energization amount It is calculated to be.

[0054] Furthermore, the target energization amount It may be adjusted by hydraulic feedback control so that the actual servo hydraulic pressure Pa (the detected value of the servo hydraulic pressure sensor PA) approaches and matches the target hydraulic pressure Pt. In the hydraulic feedback control, based on the target hydraulic pressure Pt and the servo hydraulic pressure Pa, the deviation hP is calculated (that is, "hP = Pt - Pa"). Then, the target energization amount It is adjusted so that the hydraulic deviation hP approaches and matches "0". Specifically, when the hydraulic deviation hP is greater than a predetermined hydraulic pressure hp, the target energization amount It (and as a result, the actual energization amount Ia) of the pressure regulating valve UA is increased, and the valve opening amount of the pressure regulating valve UA is decreased. On the other hand, when the hydraulic deviation hP is less than the predetermined hydraulic pressure "-hp", the energization amounts It and Ia of the pressure regulating valve UA are decreased, and the valve opening amount of the pressure regulating valve UA is increased. Here, the predetermined hydraulic pressure hp is the dead zone of the control and is a preset predetermined value (a positive constant).

[0055] In the drive control of the pressure regulating valve UA, energization feedback control is executed so that the actual energization amount Ia approaches and matches the target energization amount It. Here, the actual energization amount Ia (for example, the current value) is detected by an energization amount sensor IA (not shown) (for example, a current sensor) provided in the drive circuit DD. In the energization feedback control of the pressure regulating valve UA, the deviation hI is calculated based on the target energization amount It and the actual energization amount Ia (that is, "hI = It - Ia"). Then, the duty ratio Da in the PWM control (pulse width modulation control) of the pressure regulating valve UA is adjusted so that the energization deviation hI approaches and matches "0". Specifically, when the energization deviation hI is greater than a predetermined hydraulic pressure hi, the duty ratio Da (and as a result, the actual energization amount Ia) is increased, and the energization amount Ia is increased. On the other hand, when the energization deviation hI is less than the predetermined hydraulic pressure "-hi", the duty ratio Da is decreased, and the energization amount Ia is decreased. Here, the predetermined hydraulic pressure hi is the dead zone of the control and is a preset predetermined value (a constant with a positive sign).

[0056] In step S160, stop control is executed. "Stop control" is to maintain the stopped state of the vehicle JV. Although details will be described later, in stop control, the servo hydraulic pressure Pa (and as a result, the supply hydraulic pressure Pm and the brake hydraulic pressure Pw) is raised by a predetermined hydraulic pressure Pk, then the pressure regulating valve UA is closed, and the drive of the electric motor MA is stopped.

[0057] <Processing of Stop Control> With reference to the flowchart of FIG. 3, an example of the processing of the stop control in step S160 will be described. As described above, in stop control, the drive of unnecessary components such as the electric motor MA is stopped to achieve power saving. Further, in stop control, the servo hydraulic pressure Pa is increased with respect to the required hydraulic pressure Ps corresponding to the braking operation amount Ba so that the electric motor MA is not frequently redriven due to leakage of the brake fluid BF in the pressure regulating valve UA or the vehicle JV does not start moving on a road gradient. Note that, as in the case of FIG. 2, in the brake control device SC, the pressure receiving area ru of the servo chamber Ru and the pressure receiving area rm of the master chamber Rm are made equal, so the relationship "Pa = Pm" holds.

[0058] In step S210, a boosting process is executed. "Boosting" means that the servo hydraulic pressure Pa (= Pm = Pw) is increased by a predetermined hydraulic pressure Pk. Here, the predetermined hydraulic pressure Pk is also referred to as the "boosting hydraulic pressure". Specifically, in the boosting process in the parking control, the predetermined hydraulic pressure Pk is further added to the required hydraulic pressure Ps required by the braking operation amount Ba, and the target hydraulic pressure Pt, which is the final target value, is calculated (that is, "Pt = Ps + Pk"). Then, in step S210, based on the boosted target hydraulic pressure Pt, the above-described rotational speed feedback control, hydraulic pressure feedback control, and energization amount feedback control are applied, and the electric motor MA and the pressure regulating valve UA are controlled. Thereby, the fluid unit HU is driven (controlled) so that the servo hydraulic pressure Pa approaches and matches the target hydraulic pressure Pt.

[0059] For example, the predetermined hydraulic pressure Pk (boosting hydraulic pressure) is determined as a preset predetermined value (constant). Further, the predetermined hydraulic pressure Pk may be calculated based on the road surface gradient Kv. Specifically, as shown in block X210, according to the calculation map Zpk, the larger the road surface gradient Kv, the larger the predetermined hydraulic pressure Pk is determined. The road surface gradient Kv is the inclination of the road with respect to the front-rear direction (travel direction) of the vehicle JV when the vehicle JV stops (for example, the inclination of an uphill road or a downhill road). The road surface gradient Kv is calculated based on the detected value (front-rear acceleration) Gx of the front-rear acceleration sensor GX. Further, the road surface gradient Kv may be obtained from the map information via the communication bus BS or the like. In the calculation map Zpk, a lower limit value pk and an upper limit value pj are provided for the calculated predetermined hydraulic pressure Pk. Here, the lower limit value pk and the upper limit value pj are preset predetermined values (constants).

[0060] Furthermore, the predetermined hydraulic pressure Pk may be determined to gradually decrease as the braking operation member BP is returned toward "0 (initial position corresponding to the non-braking state)". Here, a lower limit value pk is provided for the predetermined hydraulic pressure Pk. Specifically, the predetermined hydraulic pressure Pk is determined when the vehicle JV stops (at the time of stopping). And when the braking operation amount Ba is constant, the predetermined hydraulic pressure Pk at the time of stopping is maintained. Thereafter, as the braking operation amount Ba decreases, the predetermined hydraulic pressure Pk sequentially decreases. However, since the lower limit value pk is provided for the predetermined hydraulic pressure Pk, even when the stop control ends, the target hydraulic pressure Pt is at least greater than the required hydraulic pressure Ps by the amount of the lower limit value pk.

[0061] In step S220, based on the motor drive signal Ma, the pressure regulating valve drive signal Ua, etc., it is determined whether "the operating state of the fluid unit HU is in the holding state or not (referred to as 'holding determination')". Here, the "holding state" is a state in which the pressure regulating valve UA is closed and the electric motor MA is stopped so as to maintain the servo hydraulic pressure Pa constant (that is, the rotational speed Ns is in the state of "0"). When the fluid unit HU is not in the holding state and step S220 is negated, the process proceeds to step S230. On the other hand, when the fluid unit HU is in the holding state and step S220 is affirmed, the process proceeds to step S240.

[0062] In step S230, based on the braking operation amount Ba, the target hydraulic pressure Pt, and the servo hydraulic pressure Pa, it is determined whether or not the "holding state is started (referred to as 'start determination')". The start determination of the holding state is affirmed when "the braking operation amount Ba is constant" and "the servo hydraulic pressure Pa matches the target hydraulic pressure Pt" are satisfied. For example, "the braking operation amount Ba is constant" is affirmed when the state where the operation speed dB (the amount of change in time of the braking operation amount Ba) is less than the predetermined speed db continues for the first predetermined time tb. Also, "the servo hydraulic pressure Pa matches the target hydraulic pressure Pt" is affirmed when the state where the deviation hP between the target hydraulic pressure Pt and the servo hydraulic pressure Pa is less than the predetermined deviation hx continues for the second predetermined time th. Here, the predetermined speed db, the predetermined deviation hx, and the first and second predetermined times tb and th are predetermined values (constants) set in advance. If step S230 is negated, the process is returned to step S110. On the other hand, if step S230 is affirmed, the process proceeds to step S260. Note that if step S230 is negated because although the braking operation amount Ba is constant, the servo hydraulic pressure Pa has not yet reached the target hydraulic pressure Pt, in subsequent arithmetic processing (particularly step S220), the servo hydraulic pressure Pa is increased so that the servo hydraulic pressure Pa matches the target hydraulic pressure Pt.

[0063] In step S240, based on the braking operation amount Ba, the target hydraulic pressure Pt, and the servo hydraulic pressure Pa, it is determined whether or not the holding state is released (ended) (referred to as "end determination"). The end determination of the holding state is affirmed when at least one of "the braking operation amount Ba has changed" and "the servo hydraulic pressure Pa and the target hydraulic pressure Pt no longer match" is satisfied. For example, "the braking operation amount Ba has changed" is affirmed when the braking operation member BP is further operated and the braking operation amount Ba is increased, or when the braking operation member BP is returned and the braking operation amount Ba is decreased. Also, "the servo hydraulic pressure Pa and the target hydraulic pressure Pt no longer match" is affirmed, for example, when the servo hydraulic pressure Pa decreases due to a leak in the pressure regulating valve UA. If step S240 is negated, the process proceeds to step S260. On the other hand, if step S240 is affirmed, the process proceeds to step S250.

[0064] In step S250, based on the braking operation amount Ba, the target hydraulic pressure Pt, and the servo hydraulic pressure Pa, it is determined whether or not a decrease in the servo hydraulic pressure Pa is necessary (referred to as "pressure reduction determination"). When the braking operation amount Ba is decreased and a decrease in the servo hydraulic pressure Pa is necessary (i.e., when a pressure reduction instruction is given), step S250 is affirmed and the process proceeds to step S270. On the other hand, when an increase in the servo hydraulic pressure Pa is necessary (i.e., when a pressure reduction instruction is not given), step S250 is negated and the process proceeds to step S280.

[0065] In step S260, with the power consumption of the brake control device SC reduced, the electric motor MA is stopped and the pressure regulating valve UA is closed so that the servo hydraulic pressure Pa is maintained constant. That is, in step S260, the above holding state is achieved. When the holding state starts or continues, in step S260, for example, the duty ratio Dm in the PWM control of the electric motor MA is set to "0". That is, no voltage is applied to the electric motor MA, and the motor current Im is set to "0". The electric motor MA stops being driven, and the rotation of the electric motor MA stops (i.e., "Ns = 0" is achieved). Also, the actual energization amount Ia of the pressure regulating valve UA is increased so that the pressure regulating valve UA is surely closed. As a result, in the reflux path HK, the braking fluid BF is sealed between the check valve GA and the pressure regulating valve UA. By closing the pressure regulating valve UA, the servo hydraulic pressure Pa is held at a constant value (i.e., the hydraulic pressure value immediately before the pressure regulating valve UA is closed).

[0066] In step S270, with the driving of the electric motor MA stopped, the actual energization amount Ia (and as a result, the opening amount of the pressure regulating valve UA) of the pressure regulating valve UA is adjusted so that the servo hydraulic pressure Pa is decreased. When a pressure reduction of the servo hydraulic pressure Pa is instructed from the holding state, in step S270, while the state of "Ns = 0" is maintained, the target energization amount It (and as a result, the actual energization amount Ia) is decreased according to the target hydraulic pressure Pt. The pressure regulating valve UA that was closed is opened, and its opening amount is adjusted (increased) based on the target hydraulic pressure Pt. As a result, the servo hydraulic pressure Pa is decreased in response to the pressure reduction instruction.

[0067] In step S280, the driving of the electric motor MA is restarted and the actual energization amount Ia (and as a result, the opening amount of the pressure regulating valve UA) of the pressure regulating valve UA is adjusted so that the servo hydraulic pressure Pa is increased. When an increase in the servo hydraulic pressure Pa is instructed from the holding state, in step S280, the electric motor MA (particularly, the actual rotation speed Ns) is controlled according to the increased target hydraulic pressure Pt, and then the target energization amount It (and as a result, the actual energization amount Ia) is increased according to the target hydraulic pressure Pt. The pressure regulating valve UA that was closed is opened, and its opening amount is adjusted based on the target hydraulic pressure Pt. As a result, the servo hydraulic pressure Pa is increased in response to the pressure increase instruction.

[0068] The above has described the stop control in the pressure regulation control. The stop control starts when the vehicle JV stops and the stopped state is determined, and continues even when the vehicle JV starts to move. The stop control ends when the condition that the braking operation amount Ba is less than or equal to a predetermined amount bx is satisfied. Here, the predetermined amount bx is a threshold value corresponding to the braking operation amount Ba, and is a predetermined value (constant) near "0" set in advance. For example, the predetermined amount bx can be set to "0". In this case, after the vehicle JV starts to move, the stop control continues to be executed until the braking operation member BP is completely returned to the initial position "0", and the servo hydraulic pressure Pa (and as a result, the braking hydraulic pressure Pw) is increased. Then, when the braking operation is completely finished and the braking operation amount Ba is returned to "0", the stop control ends, and the predetermined hydraulic pressure Pk is stepwise decreased to "0". In other words, during the execution of the stop control, even if the vehicle JV is moving, the servo hydraulic pressure Pa continues to be increased by a predetermined hydraulic pressure Pk (at least by the lower limit value pk) with respect to the required hydraulic pressure Ps.

[0069] In the stop control, first, the servo hydraulic pressure Pa (and as a result, the braking hydraulic pressure Pw) is increased by a predetermined hydraulic pressure Pk with respect to the required hydraulic pressure Ps calculated based on the braking operation amount Ba. Then, the pressure regulating valve UA is closed and the drive of the electric motor MA is stopped. That is, a margin of a predetermined hydraulic pressure Pk due to the increase is expected, and the closing of the pressure regulating valve UA and the stopping of the electric motor MA are executed. Therefore, even if there is some hydraulic leakage in the pressure regulating valve UA or the like, the stopped state of the vehicle JV can be surely maintained.

[0070] The increase in the predetermined hydraulic pressure Pk due to the parking control continues even after the vehicle JV starts moving and ends when the braking operation amount Ba becomes equal to or less than the predetermined amount bx. If the increase ends immediately when the vehicle JV starts moving (i.e., when it is no longer in the parked state), discontinuity may occur in the movement of the vehicle JV (e.g., vehicle body acceleration), and the driver may feel discomfort. To avoid such a situation, the increase in the predetermined hydraulic pressure Pk ends when "Ba ≤ bx" is satisfied. In this way, by continuing the increase in the servo hydraulic pressure Pa, the above discontinuity is avoided when the vehicle JV starts, and smooth and good starting characteristics can be ensured.

[0071] <Operation of the pressure control> With reference to the time-series diagram of FIG. 4 (a transition diagram of various state quantities with respect to the passage of time T), an operation example of the parking control (particularly, the processes of steps S260 and S270) will be described. In the example, a situation is assumed in which the vehicle JV traveling at a constant speed vo is decelerated and then stopped. Here, the road surface at the time when the vehicle JV stops is a downhill road with a downward slope. Also, in the end condition of the parking control, the predetermined amount bx (a threshold value related to the braking operation amount Ba) is set to "0".

[0072] As described above, in the braking control device SC, since "ru = rm", "Pa = Pm". Further, when the electric motor MA is driven, the target rotational speed Nt is calculated to be a predetermined rotational speed nt set in advance. Therefore, by setting the motor drive signal Ma to "0", the stop of the electric motor MA (i.e., "Nt = 0" and the off state of the electric motor MA) is instructed, and by setting the drive signal Ma to "1", the drive of the electric motor MA (i.e., "Nt = nt" and the on state of the electric motor MA) is instructed.

[0073] In the line diagram, from time point u0 (the start time of the braking operation) to time point u3 (the stop determination time point) corresponds to the deceleration control in step S150, and from time point u3 to time point u8 (the end time of the braking operation) corresponds to the stop control in step S160. Since the servo hydraulic pressure Pa is controlled to match the target hydraulic pressure Pt, the servo hydraulic pressure Pa and the target hydraulic pressure Pt overlap. Also, since the actual energization amount Ia is controlled to match the target energization amount It, the actual energization amount Ia and the target energization amount It overlap.

[0074] Until time point u0, no braking operation is performed, and the vehicle JV is traveling at a constant speed of "Vx = vo". Therefore, until time point u0, the target energization amount It (and as a result, the actual energization amount Ia) is "0 (non-energized)", the pressure regulating valve UA is fully open, the drive signal Ma is "0", and the rotational motion of the electric motor MA is stopped.

[0075] At time point u0, the operation of the braking operation member BP is started, and the braking operation amount Ba is increased from "0 (initial position)". Then, at time point u1, the braking operation amount Ba is held at the value ba. From time point u0, according to the arithmetic map Zps, the required hydraulic pressure Ps is sequentially increased from "0". Then, from time point u1, corresponding to "Ba = ba", the required hydraulic pressure Ps is maintained at the value pa. Since the vehicle JV has not yet stopped, the deceleration control in step S150 is executed. Therefore, the final target value (target hydraulic pressure) Pt is calculated to be equal to the required hydraulic pressure Ps. That is, the target hydraulic pressure Pt is determined based on "Pt = Ps". By the deceleration control, at time point u0, the deceleration of the vehicle JV is started, and from time point u1, corresponding to "Pa = pa", the vehicle body deceleration is constant and the vehicle body speed Vx is decreased.

[0076] In the pressure regulation control in deceleration control, the fluid unit HU (particularly, the pressurizing unit KU) is controlled so that the servo hydraulic pressure Pa approaches and matches the target hydraulic pressure Pt. Specifically, at the time point u0 when the operation of the braking operation member BP is started, "Ma = 1 (on state)" is instructed, and the rotational drive of the electric motor MA is started. Along with the on-operation of the electric motor MA, the braking fluid BF is discharged from the fluid pump QA, and a circulating flow KN of the braking fluid BF is generated in the reflux path HK. According to the target hydraulic pressure Pt, the target energization amount It of the pressure regulating valve UA is determined. Then, the actual energization amount Ia is controlled to approach and match the target energization amount It. By adjusting the actual energization amount Ia, the valve opening amount of the pressure regulating valve UA is determined, and the servo hydraulic pressure Pa is adjusted by the orifice effect when the circulating flow KN of the braking fluid BF is throttled by the pressure regulating valve UA. Thereby, the servo hydraulic pressure Pa is adjusted to match the target hydraulic pressure Pt (= Ps).

[0077] At the time point u2, the vehicle body speed Vx becomes "0", and the vehicle JV stops. Immediately after the time point u2 (i.e., the time point u3), the stop determination in step S140 is affirmed, and the stop state (i.e., the state of "Vx = 0") is identified. Along with this, the state flag FT is switched from "0" to "1". Here, the state flag FT is a control flag indicating the stop state, where "1" indicates the stop state and "0" indicates the traveling state (a traveling state where the vehicle JV is moving, not the stop state).

[0078] At the time point u3, the pressure regulation control is switched from deceleration control (the process of step S150) to stop control (the process of step S160). In other words, at the time point u3, the deceleration control is terminated, and the stop control is started. Thereby, from the time point u3, the final target value (target hydraulic pressure) Pt is calculated by adding the predetermined hydraulic pressure Pk to the required hydraulic pressure Ps (an intermediate target value). That is, the target hydraulic pressure Pt is determined based on "Pt = Ps + Pk". In the case of stop control, compared with the case of deceleration control, even with the same braking operation amount Ba, a servo hydraulic pressure Pa that is higher by the predetermined hydraulic pressure Pk is required.

[0079] Also in parking control, the servo hydraulic pressure Pa (and as a result, the braking hydraulic pressure Pw) is adjusted to approach and match the target hydraulic pressure Pt by the same method as the deceleration control (driving the electric motor MA and adjusting the actual energization amount Ia of the pressure regulating valve UA). The target energization amount It is increased by only the predetermined energization amount Ik corresponding to the predetermined hydraulic pressure Pk. As a result, the actual energization amount Ia, which was the value ia, is increased to the value ib.

[0080] At time point u4, it is determined that the increase in the servo hydraulic pressure Pa (the servo hydraulic pressure Pa is increased by the predetermined hydraulic pressure Pk) has been completed. At time point u4, step S230 is affirmed and the holding operation is started. As a result, the pressure regulating valve UA is closed and the driving of the electric motor MA is stopped (see step S260). Specifically, the target energization amount It is increased by only the valve closing energization amount Ic so that the pressure regulating valve UA is surely closed. Here, the valve closing energization amount Ic is a preset predetermined value (constant). As a result, the actual energization amount Ia, which was the value ib, is increased to the value ic. Note that the closing of the pressure regulating valve UA may be achieved by increasing the energization amounts It and Ia to the preset predetermined valve closing energization amount ic (constant). When the pressure regulating valve UA is closed, the braking fluid BF is sealed between the check valve GA and the pressure regulating valve UA (also referred to as a "fluid sealing state"), so the servo hydraulic pressure Pa at the time when the pressure regulating valve UA is closed is maintained. Further, at time point u4, the drive signal Ma is switched from "1" to "0" and set to "Im = 0". As a result, the energization of the electric motor MA is stopped and the driving of the electric motor MA is temporarily terminated. In the operation example, the closing of the pressure regulating valve UA and the stopping of the driving of the electric motor MA are performed simultaneously at time point u4, but these operations may be performed with a time difference. That is, one of the closing of the pressure regulating valve UA and the stopping of the electric motor MA may be executed first, and then the other of the closing of the pressure regulating valve UA and the stopping of the electric motor MA may be executed.

[0081] Until time point u5, the braking operation member BP is held and the braking operation amount Ba is maintained constant, so the closing of the pressure regulating valve UA and the stop of the electric motor MA continue. At time point u5, the braking operation member BP begins to be returned by the driver toward the initial position "Ba = 0". At time point u5, since steps S240 and S250 are affirmed, the process switches from the process of step S260 to the process of step S270. At time point u5, the energization amounts It and Ia are decreased by the valve closing energization amount Ic, the pressure regulating valve UA is opened, and it is returned to the state before valve closing.

[0082] After time point u5, as the braking operation amount Ba gradually decreases, the target hydraulic pressure Pt is calculated to gradually decrease. As the target hydraulic pressure Pt decreases, the energization amounts It and Ia are gradually decreased and the opening amount of the pressure regulating valve UA is increased. As a result, the servo hydraulic pressure Pa gradually decreases so as to match the target hydraulic pressure Pt. At this time, the drive stop of the electric motor MA continues (see step S270 above).

[0083] At time point u6, due to the influence of gravity etc. caused by the downhill slope, the vehicle JV starts to move. Immediately after that, at time point u7, the running state of the vehicle JV (i.e., "Vx ≠ 0") is identified and the state flag FT is switched from "1 (stopped state)" to "0 (running state)". However, since the braking operation amount Ba has not been returned to "0 (= bx)", the execution of the stop control (the process of step S160) continues.

[0084] At time point u8 after the vehicle JV has started to move, the braking operation member BP is completely returned to the initial position (non-braking state), and the braking operation amount Ba is set to "0". At time point u8, the stop control (the process of step S160) is terminated and the predetermined hydraulic pressure Pk rapidly decreases to "0". At time point u8, since "Ba = 0", "Ps = 0" (refer to the calculation map Zps). Therefore, at time point u8, the target hydraulic pressure Pt is determined to be "0". The energization amounts It and Ia are set to "0", and the energization to the pressure regulating valve UA is stopped. As a result, the pressure regulating valve UA is fully opened and the servo hydraulic pressure Pa is adjusted to "0".

[0085] The predetermined hydraulic pressure Pk can be calculated to decrease as the braking operation amount Ba decreases. However, the predetermined hydraulic pressure Pk is provided with a preset lower limit value pk (constant). In this case, the target hydraulic pressure Pt transitions as shown by the dashed-dotted line (a). Even in a configuration where the predetermined hydraulic pressure Pk is gradually decreased, immediately before the braking operation ends, the target hydraulic pressure Pt is at least greater than the required hydraulic pressure Ps by the lower limit value pk. Therefore, at the braking end time u8, the target hydraulic pressure Pt rapidly decreases to "0".

[0086] In the process of step S270 described above, even after the vehicle JV starts to run, the stopped state of the electric motor MA is maintained. Instead, when the vehicle JV starts to move, the driving of the electric motor MA may be resumed. An operation example in this case is illustrated by a broken line in the time series diagram of the drive signal Ma. When the state flag FT switches from "1 (stopped state)" to "0 (running state)" at time u7 (that is, when the stopped state is negated), the drive signal Ma is switched from "0 (stop instruction)" to "1 (drive instruction)". Thereby, the driving of the once-stopped electric motor MA is resumed. Since the electric motor MA is driven on the condition that "the vehicle JV is in a running state" and "the braking operation member BP is being operated", the responsiveness related to the start-up of the electric motor MA can be improved.

[0087] By the parking control, the boost of the servo hydraulic pressure Pa (and as a result, the braking hydraulic pressure Pw) is executed, so the parking state of the vehicle JV is surely maintained without being affected by factors such as the road surface gradient. After the boost of the servo hydraulic pressure Pa is performed, the pressure regulating valve UA is closed and the driving of the electric motor MA is stopped. Since a predetermined hydraulic pressure Pk (the boost amount) is expected as a margin for the servo hydraulic pressure Pa required to maintain the parking state, even if the servo hydraulic pressure Pa decreases somewhat due to liquid leakage or the like when the pressure regulating valve UA is closed, the parking state is maintained. Furthermore, since the electric motor MA is stopped with a margin of the predetermined hydraulic pressure Pk, frequent restart of the electric motor MA is avoided.

[0088] Furthermore, the build-up of the servo hydraulic pressure Pa continues until the braking operation amount Ba becomes equal to or less than a predetermined amount bx (for example, until the braking operation is completely finished) even after the vehicle JV has started moving. As a result, the vehicle JV does not start moving suddenly but starts smoothly. That is, it is avoided that the vehicle JV starts with an acceleration greater than intended by the driver.

[0089] <Other Operations of Pressure Control> With reference to the time-series diagram of FIG. 5, another operation example of the pressure control will be described. In the example described with reference to FIG. 4, during the stop, the braking operation member BP was returned to the initial position "0" after being maintained at a constant value (value ba). Another operation example shows a case where the operation amount Ba of the braking operation member BP is increased in the stopped state (see step S280). The assumed situation (stopping on a downhill road, etc.) is the same as the above-described operation example. Also, since the operations up to the time point u4 are the same, the description thereof is omitted.

[0090] At the time point u9, the braking operation amount Ba is increased. At the time point u9, since step S240 is affirmed and step S250 is negated, the process of step S280 is started. As a result, the energization amounts It and Ia are decreased by the valve closing energization amount Ic, and the pressure regulating valve UA is opened (that is, returned to the state before valve closing). Also, at the time point u9, the motor drive signal Ma is switched from "0" to "1", and the re-driving (restart) of the electric motor MA is started. After the time point u9, as the braking operation amount Ba gradually increases, the target hydraulic pressure Pt is calculated to gradually increase. As the target hydraulic pressure Pt increases, the energization amounts It and Ia are gradually increased, and the opening amount of the pressure regulating valve UA is decreased. As a result, the servo hydraulic pressure Pa is gradually increased so as to match the target hydraulic pressure Pt.

[0091] In the pressure control at time point u9, since the stop control is being executed, the target hydraulic pressure Pt has been increased by a predetermined hydraulic pressure Pk from the required hydraulic pressure Ps by the boost process. When the braking operation amount Ba increases during the stop control, the operation amount Ba of the braking operation member BP by the driver is reflected in the pressure control while the boost of the servo hydraulic pressure Pa is being performed. Thereby, the continuity of the pressure control can be ensured.

[0092] <Another configuration example of the fluid unit HU> In the above-described fluid unit HU, the servo hydraulic pressure Pa generated by the pressurizing unit KU is transmitted as the front-wheel braking hydraulic pressure Pwf to the front-wheel wheel cylinder CWf via the master cylinder CM in the front-wheel system, and is directly transmitted as the rear-wheel braking hydraulic pressure Pwr to the rear-wheel wheel cylinder CWr in the rear-wheel system. Instead of this, a tandem-type master cylinder CM may be adopted in the fluid unit HU, and the servo hydraulic pressure Pa may be transmitted as the front-wheel and rear-wheel braking hydraulic pressures Pwf and Pwr to the front-wheel and rear-wheel wheel cylinders CWf and CWr via this tandem-type master cylinder CM. Further, a configuration in which the servo hydraulic pressure Pa is transmitted to the wheel cylinder CW via an electromagnetic valve (see, for example, Japanese Patent Application Laid-Open No. 2016-144952) may be adopted. In any case, in the fluid unit HU of the braking control device SC, the fluid pump QA is driven by the electric motor MA, and the braking fluid BF discharged by this fluid pump QA is adjusted to the servo hydraulic pressure Pa by the pressure regulating valve UA. Then, the hydraulic pressure (braking hydraulic pressure) Pw in the wheel cylinder CW is adjusted by the servo hydraulic pressure Pa.

[0093] <Summary of the embodiment of the braking control device SC> The following summarizes an embodiment of the braking control device SC according to the present invention. The braking control device SC is composed of a fluid unit HU (actuator) and a controller ECU. The fluid unit HU is composed of a fluid pump QA driven by an electric motor MA and a pressure regulating valve UA that adjusts the braking fluid BF discharged by the fluid pump QA to the servo hydraulic pressure Pa. Finally, the braking hydraulic pressure Pw of the wheel cylinder CW is adjusted by this servo hydraulic pressure Pa. Further, the servo hydraulic pressure Pa is controlled by the controller ECU via the fluid unit HU based on the operation amount Ba of the braking operation member BP. In the braking control device SC, when the vehicle JV stops (at the stop time), the servo hydraulic pressure Pa is increased by a predetermined hydraulic pressure Pk (boost hydraulic pressure). After that, in the braking control device SC, the pressure regulating valve UA is closed and the driving of the electric motor MA is stopped.

[0094] In the braking control device SC, boosting is executed when the stop state of the vehicle JV is determined (at the stop determination time). As described above, "boosting" means that the servo hydraulic pressure Pa (finally, the braking hydraulic pressure Pw) is increased by a predetermined hydraulic pressure Pk. Specifically, when the vehicle JV is running (that is, when the stop state of the vehicle JV is not determined), the required hydraulic pressure Ps calculated based on the braking operation amount Ba is determined as the target hydraulic pressure Pt (that is, "Pt = Ps"). On the other hand, when the stop state of the vehicle JV is determined, at that determination time, a value obtained by adding the predetermined hydraulic pressure Pk to the required hydraulic pressure Ps is calculated as the target hydraulic pressure Pt (that is, "Pt = Ps + Pk"). That is, at the stop determination time, boosting is performed and the servo hydraulic pressure Pa is increased stepwise by a predetermined hydraulic pressure Pk. By this boosting, it is possible to avoid the vehicle JV starting to move unnecessarily due to factors such as the road surface gradient, and a reliable stop state is ensured.

[0095] In the braking control device SC, after the pressure build-up is completed (that is, after it is confirmed that the actual servo hydraulic pressure Pa has been increased), the pressure regulating valve UA is closed so that the servo hydraulic pressure Pa at that time is maintained. Accordingly, the power supply to the electric motor MA is stopped. Since the braking fluid BF is sealed by the pressure regulating valve UA and the check valve GA, the servo hydraulic pressure Pa is kept constant. In this holding state (that is, "the closed state of the pressure regulating valve UA" and "the stopped state of the electric motor MA"), the servo hydraulic pressure Pa is increased by a predetermined hydraulic pressure Pk from the required hydraulic pressure Ps required by the braking operation amount Ba. In maintaining the stopped state, a margin component of only the predetermined hydraulic pressure Pk is expected with respect to the required hydraulic pressure Ps, so that the stopped state can be surely maintained. Also, since the vehicle JV is prevented from starting to move by the predetermined hydraulic pressure Pk, as long as the braking operation member BP is held, the restart of the electric motor MA is avoided.

[0096] For example, the predetermined hydraulic pressure Pk is determined to be larger as the gradient Kv of the road surface on which the vehicle JV has stopped is larger. Also, it is determined so that the predetermined hydraulic pressure Pk becomes smaller as the operation amount Ba is decreased. Since the predetermined hydraulic pressure Pk (pressure build-up hydraulic pressure) is determined according to the situation, the pressure build-up by the stop control can be appropriately performed.

[0097] In the controller ECU of the braking control device SC, when the braking operation amount Ba decreases in the holding state, the pressure regulating valve UA is opened according to the braking operation amount Ba while the drive of the electric motor MA is stopped. Further, when the braking operation amount Ba decreases, the increase in the servo hydraulic pressure Pa (increase by a predetermined hydraulic pressure Pk) continues even after the vehicle JV starts moving, when the operation amount Ba is greater than a predetermined amount bx (i.e., "Ba > bx"). That is, the increase due to the stop control continues from the time of stop determination until the braking operation amount Ba becomes less than or equal to the predetermined amount bx. Here, the predetermined amount bx is a preset value and can be set to, for example, "0". In the configuration where "bx = 0" is set, the increase continues until immediately before the operation of the braking operation member BP is completely finished, and ends when the braking operation member BP is completely returned to "0". For example, when the road surface gradient Kv is large on a downhill road, when the braking operation amount Ba starts to decrease, the vehicle JV may suddenly start moving with a greater acceleration than intended by the driver. However, since the increase in the servo hydraulic pressure Pa continues even after the start of the vehicle JV's travel (i.e., even if the vehicle JV is not stopped), the vehicle JV can start smoothly.

Explanation of symbols

[0098] JV… Vehicle, SC… Braking control device, BP… Braking operation member, CM… Master cylinder, CW… Wheel cylinder, HU… Fluid unit (actuator), KU… Pressurizing unit, MA… Electric motor, QA… Fluid pump, UA… Pressure regulating valve, SS… Stroke simulator, ECU… Controller, It… Target energization amount, Ia… Actual energization amount, VW… Wheel speed sensor, Vw… Wheel speed (detection value of the wheel speed sensor VW), Vx… Vehicle body speed, BA… Braking operation amount sensor, Ba… Braking operation amount (detection value of the braking operation amount sensor BA), PM… Supply hydraulic pressure sensor, Pm… Supply hydraulic pressure (actual value), PA… Servo hydraulic pressure sensor, Pa… Servo hydraulic pressure (actual value), Ps… Required hydraulic pressure (intermediate target value required by the operation amount Ba), Pt… Target hydraulic pressure (final hydraulic pressure target value), Pk… Predetermined hydraulic pressure (boost hydraulic pressure).

Claims

1. A vehicle braking control device comprising a fluid pump driven by an electric motor, a pressure regulating valve that regulates the braking fluid discharged by the fluid pump to servo hydraulic pressure, and an actuator that regulates the braking hydraulic pressure of a wheel cylinder of a vehicle by the servo hydraulic pressure, and a controller that controls the servo hydraulic pressure via the actuator based on an operation amount of a braking operation member of the vehicle. In the vehicle braking control device, the controller, when the vehicle stops, increases the servo hydraulic pressure by a predetermined hydraulic pressure, then closes the pressure regulating valve, and stops driving of the electric motor, and when the operation amount is increased thereafter, controls the pressure regulating valve and the electric motor so that a state is maintained in which the servo hydraulic pressure is higher than a hydraulic pressure corresponding to the operation amount by the predetermined hydraulic pressure. A vehicle braking control device.

2. A vehicle braking control device comprising a fluid pump driven by an electric motor, a pressure regulating valve that regulates the braking fluid discharged by the fluid pump to servo hydraulic pressure, and an actuator that regulates the braking hydraulic pressure of a wheel cylinder of a vehicle by the servo hydraulic pressure, and a controller that controls the servo hydraulic pressure via the actuator based on an operation amount of a braking operation member of the vehicle. In the vehicle braking control device, the controller, when the vehicle stops, increases the servo hydraulic pressure by a predetermined hydraulic pressure, then closes the pressure regulating valve, and stops driving of the electric motor, and sets the predetermined hydraulic pressure to a larger value as the gradient of the road surface on which the vehicle stops is larger. A vehicle braking control device.

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