Vehicle braking control device

Abstract

To provide a braking control device of a vehicle, which can improve responsiveness to increase of wheel pressure.SOLUTION: A braking control device comprises: a pressure-adjusting unit that adjusts wheel pressure Pw of a wheel cylinder by servo pressure generated by an electric motor as a power source; an electromagnetic valve provided in a transmission path of liquid pressure ranging from the servo pressure to the wheel pressure Pw; and a controller that controls the pressure-adjusting unit. The controller calculates pressure drop Pd in the electromagnetic valve on the basis of indicated pressure Ps calculated from a requested braking amount and the wheel pressure Pw. Further the controller determines target pressure Pt in which the pressure drop Pd is added to the indicated pressure Ps, and controls the pressure-adjusting unit on the basis of the target pressure Pt.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Patent Document 1 describes a hydraulic control unit that incorporates the concept of flow control to achieve both control accuracy and responsiveness in hydraulic control of wheel brakes. In Patent Document 1, a controller determines a target hydraulic volume for the wheel brakes based on a target hydraulic pressure, and determines an actual hydraulic volume for the wheel brakes based on hydraulic pressure detected by a brake hydraulic pressure detection means. A target flow volume for the wheel brakes is then determined based on the target hydraulic volume and the actual hydraulic volume, and operation of the hydraulic control unit is controlled based on the target flow volume.

[0003] The applicant has developed a brake control device as described in Patent Document 2. The device in Patent Document 2 is composed of two components: an upper and a lower fluid unit. In the upper fluid unit, brake fluid discharged by a fluid pump is adjusted to a regulated fluid pressure (also called "servo pressure"). The servo pressure is then transmitted to the wheel cylinder as wheel pressure via the lower fluid unit. The lower fluid unit includes multiple solenoid valves to independently control wheel pressure for anti-lock brake control, anti-skid control, etc. When servo pressure is transmitted from the upper fluid unit as wheel pressure, the solenoid valves can act as resistance, delaying the increase in wheel pressure. To address this issue, brake control devices are desired that have improved wheel pressure increase responsiveness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-296704 [Patent Document 2] Japanese Patent Application Publication No. 2019-059294 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a vehicle brake control device that can improve the response to an increase in wheel pressure. [Means for solving the problem]

[0006] The vehicle braking control device (SC) of the present invention comprises a "pressure regulating unit (CA) that adjusts the wheel pressure (Pw) of the wheel cylinder (CW) using a servo pressure (Pu) generated using an electric motor (MA) as a power source," an "electromagnetic valve (e.g., an inlet valve VI) provided in a hydraulic pressure transmission path (HS) from the servo pressure (Pu) to the wheel pressure (Pw)," and a "controller (EA) that controls the pressure regulating unit (CA)."

[0007] In the vehicle brake control device (SC) according to the present invention, the controller (EA) calculates a pressure loss (Pd) at the solenoid valve (e.g., inlet valve VI) based on a command pressure (Ps) calculated from a braking demand (Bs) and the wheel pressure (Pw), determines a target pressure (Pt = Ps + Pd) by adding the pressure loss (Pd) to the command pressure (Ps), and controls the pressure regulating unit (CA) based on the target pressure (Pt). For example, the controller (EA) calculates a predicted flow rate (Qy) passing through the solenoid valve (VI) based on a deviation (hRs) between a command fluid volume (Rs) calculated from the command pressure (Ps) and an actual fluid volume (Rw) calculated from the wheel pressure (Pw), and calculates the pressure loss (Pd) based on the predicted flow rate (Qy). With the above configuration, the target pressure Pt is determined taking into account the pressure loss Pd at the solenoid valve, thereby improving the responsiveness to an increase in wheel pressure Pw. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram for explaining the overall configuration of a vehicle JV equipped with a braking control device SC according to the present invention. [Figure 2] 3 is a schematic diagram for explaining an example of the configuration of an upper braking unit SA. FIG. [Figure 3] 3 is a schematic diagram for explaining a configuration example of a lower braking unit SB. FIG. [Figure 4] FIG. 4 is a flowchart illustrating an example of a pressure regulation control process. [Figure 5] FIG. 4 is a block diagram for explaining the calculation of a target pressure Pt. [Figure 6] FIG. 4 is a block diagram for explaining drive control of a pressure regulating valve UA. [Figure 7] FIG. 2 is a block diagram for explaining the drive control of the electric motor MA. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Symbols for components, etc., and suffixes at the end of the symbols> In the following description, components, calculation processes, signals, characteristics, and values ​​with the same symbols, such as "CW," have the same function. The suffixes "f" and "r" at the end of the symbols 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 a "front wheel cylinder CWf" and a "rear wheel cylinder CWr." Furthermore, the suffixes "f" and "r" at the end of the symbol can be omitted. When the suffixes "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.

[0010] In the fluid path from the master cylinder CM to the wheel cylinder CW, the side closer to the master cylinder CM (the side farther from the wheel cylinder CW) is referred to as the "upper" side, and the side closer to the wheel cylinder CW (the side farther from the master cylinder CM) is referred to as the "lower" side. In addition, in the circulating flows KN, KL of the brake fluid BF, the side closer to the discharge ports of the fluid pumps QA, QB (the side farther from the suction ports) is referred to as the "upstream side," and the side closer to the suction ports of the fluid pumps QA, QB (the side farther from the discharge ports) is referred to as the "downstream side."

[0011] The upper actuator YA (also referred to as the "upper fluid unit") of the upper braking unit SA, the lower actuator YB (also referred to as the "lower fluid unit") of the lower braking unit SB, and the wheel cylinder CW are connected by a fluid path (communication path HS). Furthermore, the upper and lower actuators YA and YB are connected to various components (UA, etc.) by fluid paths. Here, the "fluid path" is a path for moving the brake fluid BF, and corresponds to piping, flow paths within the actuator, hoses, etc. In the following description, the communication path HS, reflux path HK, return path HL, reservoir path HR, input path HN, servo path HV, pressure reduction path HG, etc. are fluid paths.

[0012] <Vehicle JV equipped with braking control device SC> The overall configuration of a vehicle JV equipped with a braking control device SC according to the present invention will be described with reference to the schematic diagram of FIG. 1. The vehicle JV is equipped with a driving assistance device DS that automatically decelerates and stops the vehicle (referred to as "automatic braking control") via the braking control device SC, either in place of or assisting the driver. The driving assistance device DS is composed of a distance sensor OB and a control unit ED for the driving assistance device (also referred to as a "driving assistance controller"). The distance sensor OB detects a distance Ob (relative distance) between the host vehicle JV and an object (such as another vehicle, a fixed object, a person, a bicycle, a stop line, a sign, a traffic light, etc.) ahead of the host vehicle JV, and inputs the detected distance Ob to the driving assistance controller ED. The driving assistance controller ED calculates a required deceleration Gs for automatically stopping the vehicle JV based on the relative distance Ob. The required deceleration Gs is a target value for the vehicle deceleration for executing the automatic braking control. The required deceleration Gs is output to a communication bus BS.

[0013] A vehicle JV is equipped with front and rear wheel braking devices SXf, SXr (=SX). The braking device SX is composed of a brake caliper CP, a friction member MS (e.g., brake pad), and a rotating member KT (e.g., brake disc). The brake caliper CP is provided with a wheel cylinder CW. The hydraulic pressure Pw (referred to as "wheel pressure") in the wheel cylinder CW presses the friction member MS against the rotating member KT fixed to each wheel WH. This generates a frictional braking force Fm on the wheel WH. The "frictional braking force Fm" is the braking force generated by the wheel pressure Pw.

[0014] The vehicle JV is equipped with a brake operating member BP and a steering operating member SH. The brake operating member BP (e.g., a brake pedal) is a member that the driver operates to decelerate the vehicle JV. The steering operating member SH (e.g., a steering wheel) is a member that the driver operates to turn the vehicle JV.

[0015] The vehicle JV is equipped with various sensors (BA, etc.) listed below. Detection signals (Ba, etc.) from these sensors are input to controllers EA and EB and used for various controls. - A braking operation amount sensor BA is provided which detects the operation amount Ba (referred to as the "braking operation amount") of the brake operating member BP. For example, an operation displacement sensor SP which detects the operation displacement Sp of the brake operating member BP is provided as the braking operation amount sensor BA. In addition, a simulator pressure sensor PZ is employed which detects the hydraulic pressure Pz (referred to as the "simulator pressure") of the stroke simulator SS. In the brake control device SC, the braking operation amount Ba is a general term for a signal which represents the driver's braking intention, and the braking operation amount sensor BA is a general term for a sensor which detects the braking operation amount Ba. The braking operation amount Ba is input to the upper controller EA. - Wheel speed sensors VW are provided to detect the rotational speed (wheel speed) Vw of the wheels WH. The wheel speed Vw is input to the lower controller EB. The lower controller EB then calculates the vehicle speed Vx based on the wheel speed Vw. Furthermore, the lower controller EB executes antilock brake control to prevent the wheels WH from locking and traction control to prevent the drive wheels WH from spinning based on the wheel speed Vw and the vehicle speed Vx. A steering operation amount sensor SK is provided to detect the operation amount Sk (steering operation amount, for example, steering angle) of the steering operation member SH. A yaw rate sensor YR to detect the yaw rate Yr, a longitudinal acceleration sensor GX to detect the longitudinal acceleration Gx, and a lateral acceleration sensor GY to detect the lateral acceleration Gy are provided for the vehicle JV (particularly the vehicle body). These sensor signals are input to the lower controller EB. The lower controller EB then executes electronic stability control (ESC) to suppress oversteer and understeer and stabilize the yawing behavior of the vehicle JV.

[0016] The vehicle JV is equipped with a brake control device SC. The brake control device SC employs two brake systems, a front and rear type (also called "type II"), and the actual wheel pressure Pw is adjusted by the brake control device SC.

[0017] The brake control device SC is composed of two brake units SA and SB. The upper brake unit SA is composed of an upper actuator YA (upper fluid unit) and an upper controller EA (upper control unit). The upper actuator YA is controlled by the upper controller EA. The lower brake unit SB is disposed between the upper brake unit SA and the wheel cylinder CW. The lower brake unit SB is composed of a lower actuator YB (lower fluid unit) and a lower controller EB (lower control unit). The lower actuator YB is controlled by the lower controller EB.

[0018] The upper braking unit SA (particularly, the upper controller EA), the lower braking unit SB (particularly, the lower controller EB), and the driving assistance device DS (particularly, the driving assistance controller ED) are connected to a communication bus BS. The "communication bus BS" has a network structure in which multiple controllers (control units) hang from communication lines. Signals are transmitted between the multiple controllers (EA, EB, ED, etc.) via the communication bus BS. In other words, the multiple 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.

[0019] <Upper braking unit SA> An example of the configuration of the upper braking unit SA of the braking control device SC will be described with reference to the schematic diagram of Figure 2. The upper braking unit SA generates a supply pressure Pm in response to operation of the brake operating member BP (brake pedal). The supply pressure Pm is ultimately supplied to the wheel cylinder CW via a communication path HS (fluid path) and a lower braking unit SB. The upper braking unit SA is composed of an upper actuator YA and an upper controller EA.

[0020] <Upper actuator YA> The upper actuator YA is composed of an apply unit AP, a pressure adjustment unit CA, and an input unit NR.

[0021] [Apply Unit AP] In response to the operation of the brake operating member BP, a supply pressure Pm is output from the apply unit AP, which is composed of a tandem master cylinder CM and primary and secondary master pistons NM and NS.

[0022] A tandem master cylinder CM houses primary and secondary master pistons NM and NS. The interior of the master cylinder CM is divided into four hydraulic chambers Rmf, Rmr, Ru, and Ro by the two master pistons NM and NS. The front and rear master chambers Rmf and Rmr (= Rm) are divided by the bottom of one side of the master cylinder CM and the master pistons NM and NS. The interior of the master cylinder CM is further divided into a servo chamber Ru and a reaction chamber Ro by the flange Tu of the master piston NM. The master chamber Rm and the servo chamber Ru are positioned opposite each other across the flange Tu. These hydraulic chambers Rmf, Rmr, Ru, and Ro are sealed by a seal member SL. Therefore, when the master pistons NM and NS move, frictional force is generated between the seal member SL and its sliding surface. The pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are made equal.

[0023] When braking is not in progress, the master pistons NM and NS are in their most retracted positions (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is connected to the master reservoir RV. Brake fluid BF is stored inside the master reservoir RV (also called the "atmospheric pressure reservoir"). When the brake operating member BP is operated, the master pistons NM and NS are moved forward in the Ha direction (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 pistons NM and NS are further moved forward in the Ha direction, the front and rear wheel supply pressures Pmf and Pmr (= Pm) increase 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. Because the supply pressure Pm is the hydraulic pressure in the master chamber Rm, it is also called the "master pressure."

[0024] [Pressure Regulating Unit CA] A servo pressure Pu is supplied to the servo chamber Ru of the apply unit AP by a pressure adjustment unit CA, which is composed of an upper electric motor MA, an upper fluid pump QA, and a pressure adjustment valve UA.

[0025] An upper electric motor MA (also simply referred to as "electric motor") drives an upper fluid pump QA (also simply referred to as "fluid pump"). In the fluid pump QA, the suction port and discharge port are connected by a return passage HK (fluid path). The suction port of the fluid pump QA is also connected to a master reservoir RV via a reservoir path HR. A check valve is provided at the discharge port of the fluid pump QA.

[0026] A normally open pressure regulating valve UA is provided in the return path HK. The pressure regulating valve UA is a linear solenoid valve whose opening amount is continuously controlled based on the energization state (e.g., supply current Ia). The pressure regulating valve UA adjusts the hydraulic pressure difference (differential pressure) between its upstream and downstream sides, and is therefore also called a "differential pressure valve."

[0027] When the electric motor MA is driven and brake fluid BF is discharged from the fluid pump QA, a circulating flow KN (indicated by the dashed arrow) of brake fluid BF is generated in the return path HK. When the pressure regulating valve UA is fully open (when not energized, since the pressure regulating valve UA is normally open), the fluid pressure Pu (called "servo pressure") between the discharge port of the fluid pump QA and the pressure regulating valve UA in the return path HK is "0" (atmospheric pressure). When the amount of current Ia (supply current) to the pressure regulating valve UA is increased, the pressure regulating valve UA throttles the circulating flow KN (the flow of brake fluid BF circulating in the return path HK). In other words, the pressure regulating valve UA narrows the flow path of the return path HK, thereby exerting an orifice effect. As a result, the fluid pressure Pu upstream of the pressure regulating valve UA increases from "0." That is, in the circulating flow KN, a hydraulic pressure difference (differential pressure) is generated between the hydraulic pressure Pu (servo pressure) on the upstream side and the hydraulic pressure (atmospheric pressure) on the downstream side of the pressure regulating valve UA. The differential pressure is adjusted by the current Ia supplied to the pressure regulating valve UA.

[0028] The return path HK is connected to the servo chamber Ru via a servo path HV (fluid path) at a location between the discharge portion of the fluid pump QA (more specifically, the downstream portion of the check valve) and the pressure regulating valve UA. Therefore, the servo pressure Pu is introduced (supplied) to the servo chamber Ru. As the servo pressure Pu increases, the master pistons NM and NS are pressed forward Ha, and the hydraulic pressures Pmf and Pmr (front and rear wheel supply pressures) in the front and rear wheel master chambers Rmf and Rmr increase.

[0029] The front and rear wheel master chambers Rmf and Rmr (=Rm) are connected to the front and rear wheel communication passages HSf and HSR (=HS). The front and rear wheel communication passages HSf and HSR are connected to the front and rear wheel cylinders CWf and CWr (=CW) via the lower brake unit SB (particularly, the lower actuator YB). Therefore, the front and rear wheel supply pressures Pmf and Pmr are supplied from the upper brake unit SA to the front and rear wheel cylinders CWf and CWr. Here, the front wheel supply pressure Pmf and the rear wheel supply pressure Pmr are equal (i.e., "Pmf = Pmr").

[0030] [Input unit NR] The input unit NR operates the brake operating member BP to realize regenerative cooperative control, but creates a state in which wheel pressure Pw is not generated. "Regenerative cooperative control" coordinates the friction braking force Fm (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to motor / generator) so that the kinetic energy of the vehicle JV can be efficiently recovered as electrical energy by the motor / generator (not shown) during braking. The input unit NR is composed of an input cylinder CN, an input piston NN, an intake valve VA, an open valve VB, a stroke simulator SS, and a simulator hydraulic pressure sensor PZ.

[0031] 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 the brake operating member BP (brake pedal) via a clevis (U-shaped link) so that it moves in conjunction with the brake operating member BP. There is a gap Ks (also called "separation displacement") between the end face of the input piston NN and the end face of the primary piston NM. Regenerative cooperative control is achieved by adjusting the separation distance Ks using the servo pressure Pu.

[0032] The input chamber Rn of the input unit NR is connected to the reaction chamber Ro of the apply unit AP via an input path HN (fluid path). A normally closed inlet valve VA is provided in the input path HN. The input path HN is connected to the master reservoir RV via a reservoir path HR between the inlet valve VA and the reaction chamber Ro. A normally open release valve VB is provided in the reservoir path HR. The inlet valve VA and the release valve VB are on-off solenoid valves. A stroke simulator SS (also simply referred to as "simulator") is connected to the input path HN between the inlet valve VA and the reaction chamber Ro.

[0033] When power is not supplied to the inlet valve VA and the release valve VB, the inlet valve VA is closed and the release valve VB is open. Closing the inlet valve VA seals the input chamber Rn, creating a fluid lock. This allows the master pistons NM and NS to displace integrally with the brake operating member BP. Opening the release valve VB connects the simulator SS to the master reservoir RV. When power is supplied to the inlet valve VA and the release valve VB, the inlet valve VA is opened and the release valve VB is closed. This allows the master pistons NM and NS to displace independently of the brake operating member BP. Since the input chamber Rn is connected to the stroke simulator SS, the operating force Fp of the brake operating member BP is generated by the simulator SS. A simulator pressure sensor PZ is provided in the input line HN between the inlet valve VA and the reaction force chamber Ro to detect the hydraulic pressure Pz (simulator pressure) in the simulator SS. The simulator pressure Pz is also the internal pressure of the input chamber Rn, and is therefore also a state quantity that represents the operating force Fp of the brake operating member BP.

[0034] The state in which the master pistons NM, NS and the brake operating member BP are displaced separately (when the solenoid valves VA, VB are energized) is called the "first mode (or by-wire mode)." In the first mode, the brake control device SC functions as a brake-by-wire type device (i.e., a device that can generate a frictional braking force Fm independently of the driver's braking operation). Therefore, in the first mode, the wheel pressure Pw is generated independently of the operation of the brake operating member BP. On the other hand, the state in which the master pistons NM, NS and the brake operating member BP are displaced together (when the solenoid valves VA, VB are not energized) is called the "second mode (or manual mode)." In the second mode, the wheel pressure Pw is linked to the driver's braking operation. The input unit NR selects one of the operation modes, the first mode (by-wire mode) or the second mode (manual mode), depending on whether or not power is supplied to the introduction valve VA and the release valve VB.

[0035] <Upper controller EA> The upper actuator YA is controlled by the upper controller EA. The upper controller EA is composed of a microprocessor MP and a drive circuit DR. The upper 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 (EB, ED, etc.).

[0036] A braking operation amount Ba is input to the upper controller EA. The braking operation amount Ba is a collective term for a state quantity that represents the operation amount of the brake operating member BP. As the braking operation amount Ba, a detection signal Sp (operation displacement) of the operation displacement sensor SP and a detection signal Pz (simulator pressure) of the simulator pressure sensor PZ are directly input from the braking operation amount sensor BA to the upper controller EA. In addition, a supply pressure Pm, a wheel pressure Pw, a required deceleration Gs, etc. are input to the upper controller EA via a communication bus BS. The "supply pressure Pm" is the output pressure of the upper actuator YA. The supply pressure Pm is detected by a supply pressure sensor PM provided in the lower actuator YB and transmitted from the lower controller EB. The wheel pressure Pw is detected by a wheel pressure sensor PW provided in the lower actuator YB and transmitted from the lower controller EB. Alternatively, the wheel pressure Pw may be estimated by the upper controller EA. The required deceleration Gs is a target value for automatic braking control, calculated by the driving assistance controller ED, and transmitted from the driving assistance controller ED.

[0037] The upper controller EA (particularly the microprocessor MP) is programmed with a pressure regulation control algorithm. "Pressure regulation control" is a control for adjusting the supply pressure Pm (ultimately the wheel pressure Pw). The pressure regulation control is executed based on the braking operation amount Ba (operation displacement Sp, simulator pressure Pz), the required deceleration Gs, and the supply pressure Pm. Here, the braking operation amount Ba and the required deceleration Gs are collectively referred to as the "braking request amount Bs." The braking request amount Bs is an input signal for instructing (requesting) the generation of the supply pressure Pm (and consequently the wheel pressure Pw to be generated by the brake control device SC).

[0038] Based on the pressure control algorithm, the drive circuit DR drives the electric motor MA that constitutes the upper actuator YA, and various solenoid valves (such as UA). The drive circuit DR is configured with an H-bridge circuit using switching elements (for example, MOS-FETs) to drive the electric motor MA. Also, the drive circuit DR is equipped with switching elements to drive various solenoid valves (such as UA). In addition, the drive circuit DR includes a motor current sensor (not shown) that detects the supply current Im (referred to as "motor current") to the electric motor MA, and a pressure regulating valve current sensor (not shown) that detects the supply current Ia (referred to as "pressure regulating valve current") to the pressure regulating valve UA. Note that the electric motor MA is provided with a rotation angle sensor (not shown) that detects the rotation angle Ka (referred to as "motor rotation angle") of its rotor (rotor). And based on the motor rotation angle Ka, the motor rotation speed Na is calculated.

[0039] The upper controller EA calculates a target current It (target value) corresponding to the supply current Ia (actual value) based on the braking demand amount Bs (such as Ba, Gs, etc.) of the vehicle. In the control of the pressure regulating valve UA, the supply current Ia (pressure regulating valve current) is controlled to approach and match the target current It. Also, the upper controller EA calculates a target rotation speed Nt (target value) corresponding to the motor rotation speed Na (actual value) based on the braking demand amount Bs. In the control of the electric motor MA, the motor current Im is controlled so that the actual rotation speed Na approaches and matches the target rotation speed Nt. Specifically, if "Nt>Na", the motor current Im is increased so that the motor rotation speed Na increases, and if "Nt<Na", the motor current Im is decreased so that the motor rotation speed Na decreases. Based on these control algorithms, drive signals Ma for controlling the electric motor MA, and drive signals Ua, Va, Vb for controlling various solenoid valves UA, VA, VB are calculated. And according to the drive signals (such as Ma), the switching elements of the drive circuit DR are driven, and the electric motor MA, and the solenoid valves UA, VA, VB are controlled.

[0040] <Lower braking unit SB> An example of the configuration of the lower braking unit SB of the braking control device SC will be described with reference to the schematic diagram in Fig. 3. The lower braking unit SB is a general-purpose unit (device) for performing antilock brake control, traction control, anti-skid control, etc. In antilock brake control, traction control, anti-skid control, etc., the wheel pressure Pw of each wheel cylinder CW is adjusted independently, so these are also collectively referred to as "independent control for each wheel."

[0041] The lower braking unit SB is supplied with front and rear wheel supply pressures Pmf and Pmr (=Pm) from the upper braking unit SA. The front and rear wheel supply pressures Pmf and Pmr are then adjusted (increased or decreased) by the lower braking unit SB, and are ultimately output as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) for the front and rear wheel cylinders CWf and CWr. The lower braking unit SB is composed of a lower actuator YB and a lower controller EB.

[0042] <Lower Actuator YB> The lower actuator YB is provided in the communication passage HS between the upper actuator YA and the wheel cylinder CW and includes a supply pressure sensor PM, a wheel pressure sensor PW, a control valve UB, a lower fluid pump QB, a lower electric motor MB, a pressure regulating reservoir RB, an inlet valve VI, and an outlet valve VO.

[0043] Front and rear wheel control valves UBf and UBr (=UB) are provided in the front and rear wheel communication passages HSf and HSR (=HS). The control valves UB are normally open linear solenoid valves (differential pressure valves) like the pressure regulating valve UA. The control valves UB allow the wheel pressure Pw to be increased from the supply pressure Pm individually for the front and rear wheel systems.

[0044] Front and rear wheel supply pressure sensors PMf, PMr (=PM) are provided to detect actual hydraulic pressures Pmf, Pmr (front and rear wheel supply pressures) supplied from the upper actuator YA (particularly, front and rear wheel master chambers Rmf, Rmr). The supply pressure sensor PM is also referred to as a "master pressure sensor" and is built into the lower actuator YB. Signals of the front and rear wheel supply pressures Pmf, Pmr (=Pm) are input directly to the lower controller EB and output to the communication bus BS. Note that, since the front wheel supply pressure Pmf and the rear wheel supply pressure Pmr are substantially the same, either one of the front and rear wheel supply pressure sensors PMf, PMr may be omitted. For example, in a configuration in which the rear wheel supply pressure sensor PMr is omitted, only the front wheel supply pressure Pmf is detected by the front wheel supply pressure sensor PMf.

[0045] Wheel pressure sensors PW are provided to detect wheel pressure Pw, which is the actual hydraulic pressure in each wheel cylinder CW. The wheel pressure Pw is output from the lower actuator YB. The wheel pressure sensors PW are built into the lower actuator YB. A signal of the wheel pressure Pw is directly input to the lower controller EB and output to the communication bus BS. When anti-lock brake control or the like is not being executed, the supply pressure Pm and the wheel pressure Pw are statically equal. For this reason, at least one wheel pressure sensor PW may be provided in the lower actuator YB, and the remaining ones may be omitted. Alternatively, all wheel pressure sensors PW may be omitted. In this configuration, the wheel pressure Pw used for pressure regulation control is the supply pressure Pm or an estimated value calculated from the target pressure Pt.

[0046] The front and rear wheel return paths HLf, HLr (=HL) connect the upper portions of the front and rear wheel control valves UBf, UBr (the portion of the communication path HS closer to the upper actuator YA) with the lower portions of the front and rear wheel control valves UBf, UBr (the portion of the communication path HS closer to the wheel cylinder CW). The front and rear wheel return paths HLf, HLr are provided with front and rear wheel lower fluid pumps QBf, QBr (=QB) and front and rear wheel pressure regulating reservoirs RBf, RBr (=RB). The lower fluid pump QB is driven by a lower electric motor MB.

[0047] When the lower electric motor MB (also simply referred to as the "electric motor") is driven, the lower fluid pump QB (also simply referred to as the "fluid pump") sucks brake fluid BF from the top of the control valve UB and discharges it from the bottom of the control valve UB. As a result, a circulating flow KL of brake fluid BF (i.e., front and rear wheel circulating flows KLf and KLr, indicated by dashed arrows) is generated in the communication path HS and the return path HL, encompassing the fluid pump QB, the control valve UB, and the pressure regulating reservoir RB. When the control valve UB narrows the flow path of the communication path HS and throttles the circulating flow KL of brake fluid BF, the orifice effect created increases the hydraulic pressure Pq (referred to as the "regulating pressure") below the control valve UB from the hydraulic pressure Pm (supply pressure) above the control valve UB. In other words, in the circulation flow KL, the hydraulic pressure difference (differential pressure) between the hydraulic pressure Pm (supply pressure) on the downstream side and the hydraulic pressure Pq (adjustment pressure) on the upstream side is adjusted by the control valve UB. Note that the magnitude relationship between the supply pressure Pm and the adjustment pressure Pq is such that the adjustment pressure Pq is equal to or greater than the supply pressure Pm (i.e., "Pq≧Pm"). As explained above, the mechanism by which the adjustment pressure Pq is generated in the lower actuator YB is the same as the mechanism by which the servo pressure Pu is generated in the upper actuator YA.

[0048] Inside the lower actuator YB, the front and rear wheel communication passages HSf and HSR are each branched into two, which are connected to the front and rear wheel cylinders CWf and CWr. A normally-open inlet valve VI and a normally-closed outlet valve VO are provided for each wheel cylinder CW so that each wheel pressure Pw can be individually adjusted. Specifically, the inlet valve VI is provided in the branched communication passage HS (i.e., on the side of the communication passage HS closer to the wheel cylinder CW). The communication passage HS is connected to the pressure regulating reservoir RB via a pressure reduction passage HG (fluid passage) below the inlet valve VI (the portion of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO is provided in the pressure reduction passage HG. The inlet valve VI and the outlet valve VO are on-off solenoid valves. The inlet valve VI and the outlet valve VO allow the wheel pressure Pw to be individually reduced from the regulated pressure Pq (or supply pressure Pm) at each wheel. This allows independent control of each wheel (antilock brake control, anti-skid control, etc.) to be performed.

[0049] When the inlet valve VI and the outlet valve VO are not energized and are deactivated, the inlet valve VI is open and the outlet valve VO is closed. In this state, the wheel pressure Pw is equal to the regulated pressure Pq. The wheel pressure Pw is independently adjusted for each wheel cylinder CW by operating the inlet valve VI and the outlet valve VO. To decrease the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. This prevents brake fluid BF from flowing into the wheel cylinder CW and causes the brake fluid BF in the wheel cylinder CW to flow into the pressure regulating reservoir RB, thereby decreasing the wheel pressure Pw. To increase the wheel pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. This prevents brake fluid BF from flowing into the pressure regulating reservoir RB and causes the regulated pressure Pq from the pressure regulating valve UB to be supplied to the wheel cylinder CW, thereby increasing the wheel pressure Pw. Here, the upper limit of the increase in wheel pressure Pw is the regulated pressure Pq. To maintain the wheel pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the wheel pressure Pw is maintained constant.

[0050] <Lower controller EB> The lower actuator YB is controlled by the lower controller EB. Like the upper controller EA, the lower controller EB is composed of a microprocessor MP and a drive circuit DR. The lower controller EB is connected to a communication bus BS, so that the upper controller EA and the lower controller EB can share signals via the communication bus BS.

[0051] The wheel speed Vw, steering operation amount Sk, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy are input to the lower controller EB (particularly, the microprocessor MP). The lower controller EB calculates the vehicle speed Vx based on the wheel speed Vw. The lower controller EB executes independent control of each wheel. Specifically, as the independent control of each wheel, antilock brake control (ABS control) that suppresses locking of the wheels WH, traction control that suppresses spin of the drive wheels, and electronic stability control (ESC) that suppresses understeer and oversteer to improve the directional stability of the vehicle are executed.

[0052] The lower controller EB drives the lower electric motor MB that constitutes the lower actuator YB and various solenoid valves (UB, etc.). The drive circuit DR of the lower controller EB configures an H-bridge circuit using switching elements (e.g., MOS-FET) to drive the lower electric motor MB. The drive circuit DR also includes switching elements to drive the various solenoid valves (UB, etc.). Based on a control algorithm programmed in the microprocessor MP, a drive signal Ub for the control valve UB, a drive signal Vi for the inlet valve VI, a drive signal Vo for the outlet valve VO, and a drive signal Mb for the lower electric motor MB are calculated. Then, based on the drive signals (Ub, etc.), the drive circuit DR controls the lower electric motor MB and the solenoid valves UB, VI, and VO.

[0053] <Pressure regulation control processing> The pressure regulation control process will be described with reference to the flow chart in Figure 4. Pressure regulation control is the control of the supply pressure Pm (and consequently the wheel pressure Pw) based on the vehicle braking demand Bs (Ba, Gs, etc.). The pressure regulation control algorithm is programmed in the microprocessor MP of the upper controller EA.

[0054] In describing the example process, the following assumptions are made: In pressure regulation control, the lower actuator YB is not driven, and only the upper actuator YA is driven. Therefore, the wheel pressure Pw is regulated only by the upper actuator YA, so the wheel pressure Pw and the supply pressure Pm statically (steadily) match (i.e., "Pm = Pw"). However, dynamically, pressure loss Pd occurs in the control valve UB in the lower actuator YB and in the inlet valve VI, so the wheel pressure Pw is smaller than the supply pressure Pm (i.e., "Pm > Pw"). In the upper actuator YA, the pressure-receiving area rm (also called the "master area") of the master chamber Rm and the pressure-receiving area ru (also called the "servo area") of the servo chamber Ru are set equal. Therefore, "rm = ru", and in a static state, "Pm = Pu" (where the frictional resistance of the seal member SL is ignored). The supply pressure sensor PM is built into the lower actuator YB. The upper controller EA acquires the supply pressure Pm from the lower controller EB via the communication bus BS. In the lower actuator YB, the rear wheel supply pressure sensor PMr is omitted, and only the front wheel supply pressure sensor PMf is provided as the supply pressure sensor PM. Therefore, only the front wheel supply pressure Pmf is used as the signal of the supply pressure Pm.

[0055] In step S110, the upper controller EA supplies power to the inlet valve VA and the release valve VB. This opens the normally closed inlet valve VA and closes the normally open release valve VB, and a first mode is selected in which the master pistons NM, NS and the brake operating member BP can be displaced separately. In the first mode, the supply pressure Pm (i.e., the wheel pressure Pw) is adjusted independently of the operation of the brake operating member BP. At this time, the operating force Fp of the brake operating member BP is generated by the stroke simulator SS.

[0056] In step S120, various signals (Ba, etc.) are read. The braking operation amount Ba (Sp, Pz, etc.) is detected based on the braking operation amount BA (SP, PZ, etc.) and input to the upper controller EA. The required deceleration Gs is acquired from the driving assistance controller ED via the communication bus BS. The supply pressure Pm and the wheel pressure Pw are acquired from the lower controller EB via the communication bus BS.

[0057] In step S130, a required braking amount Bs is calculated based on the braking operation amount Ba and the required deceleration Gs. For example, the braking operation amount Ba and the required deceleration Gs are compared in terms of vehicle deceleration, and the larger of them is determined as the required braking amount Bs. The required braking amount Bs is an instruction value for the supply pressure Pm (=Pw) ​​required by the brake control device SC.

[0058] In step S140, a command pressure Ps is calculated based on the braking demand Bs and a preset calculation map Zps. The "command pressure Ps" is a target value corresponding to the supply pressure Pm, and is an intermediate target value for calculating the target pressure Pt, which is the final target value. The command pressure Ps is calculated in accordance with the calculation map Zps so as to increase as the braking demand Bs increases.

[0059] In step S150, a target pressure Pt is calculated based on the command pressure Ps. The "target pressure Pt" is a final target value corresponding to the supply pressure Pm (and consequently, the wheel pressure Pw). In pressure regulation control, when the servo pressure Pu from the upper brake unit SA is transmitted as the wheel pressure Pw to the wheel cylinder CW via the lower brake unit SB, the movement of brake fluid BF from the upper brake unit SA to the wheel cylinder CW (i.e., the flow of brake fluid BF) occurs. At this time, no power is supplied to the normally open solenoid valves UB and VI provided in the lower actuator YB, and these valves are open. There is a limit to the opening amount of the solenoid valves UB and VI. Even when the solenoid valves UB and VI are fully open, the flow path of the brake fluid BF (i.e., the communication path HS) is narrowed, making it difficult for the brake fluid BF to flow. In other words, the solenoid valves UB and VI act as resistance, resulting in energy loss. As a result, the hydraulic pressure is lower below the solenoid valves UB and VI (i.e., on the wheel cylinder CW side) than above (i.e., on the upper brake unit SA side). This drop in hydraulic pressure is referred to as "pressure loss Pd." In other words, the pressure loss Pd occurs due to energy loss when the brake fluid BF passes through the solenoid valves UB and VI. In step S150, the pressure loss Pd is estimated for the command pressure Ps, and a target pressure Pt is calculated. Specifically, the sum of the command pressure Ps and the pressure loss Pd is determined as the target pressure Pt (i.e., "Pt = Ps + Pd"). The method for calculating the pressure loss Pd will be described later.

[0060] In step S160, the upper controller EA controls the upper actuator YA (particularly, the pressure adjustment unit CA) so that the supply pressure Pm (actual value) approaches and coincides with the target pressure Pt (target value). Specifically, the upper electric motor MA is driven, and the upper fluid pump QA discharges brake fluid BF. This generates a circulation flow KN (also referred to as an "upper circulation flow") of brake fluid BF in the return path HK. Then, the pressure adjustment valve UA is driven, and the circulation flow KN is throttled, thereby generating a servo pressure Pu. When the upper actuator YA is driven, the pressure adjustment valve UA is controlled by feedback control based on the supply pressure Pm so that the supply pressure Pm approaches the target pressure Pt. Note that, since the drive of the lower actuator YB is stopped, the wheel pressure Pw coincides with the supply pressure Pm.

[0061] <Calculation process of target pressure Pt> The calculation process of the target pressure Pt (particularly the process of step S150) will be described with reference to the block diagram of FIG. 5. As described above, when the wheel pressure Pw increases, the brake fluid BF flows from the upper actuator YA toward the wheel cylinder CW. At this time, the flow path is narrowed by the solenoid valves UB and VI that constitute the lower actuator YB, making it difficult for the brake fluid BF to flow. Because the solenoid valves UB and VI act as resistance, the wheel pressure Pw decreases from the supply pressure Pm. In this way, a pressure loss Pd occurs in the lower actuator YB, but the target pressure Pt is a target value that takes into account the influence of this pressure loss Pd. The calculation process of the target pressure Pt is composed of a fluid volume conversion block PR, an instruction volume deviation calculation block RSH, a predicted flow rate calculation block QY, and a pressure loss calculation block PD.

[0062] The fluid volume conversion block PR calculates the command fluid volume Rs and the actual fluid volume Rw based on the command pressure Ps, the wheel pressure Pw, and a preset calculation map Zpr. Here, the command pressure Ps is an intermediate target value calculated based on the braking demand Bs for the vehicle. Specifically, the command pressure Ps is determined to increase as the braking demand Bs increases. The wheel pressure Pw is a value detected by the wheel pressure sensor PW. Alternatively, the wheel pressure Pw may be an estimated value. The wheel pressure Pw depends on the amount (volume, also simply referred to as "fluid volume") of brake fluid BF flowing into the wheel cylinder CW. The relationship between the inflow amount (fluid volume) of brake fluid BF and the wheel pressure Pw is based on the rigidity of the braking device SX (e.g., the rigidity of the brake caliper CP, the brake pad MS, etc.).

[0063] The fluid volume conversion block PR has a preset calculation map Zpr representing the relationship between fluid volume and hydraulic pressure. The fluid volume conversion block PR converts the command pressure Ps into a command fluid volume Rs and the wheel pressure Pw into an actual fluid volume Rw according to the calculation map Zpr. The command fluid volume Rs is the volume of fluid required to achieve the command pressure Ps. The actual fluid volume Rw is the volume of fluid that has already flowed into the wheel cylinder CW to generate the wheel pressure Pw (actual or estimated). Therefore, the command fluid volume Rs is the target value of the fluid volume calculated based on the command pressure Ps, and the actual fluid volume Rw is the actual value of the fluid volume calculated based on the wheel pressure Pw.

[0064] The command amount deviation calculation block RSH calculates the deviation hRs (referred to as the "command amount deviation") between the command amount Rs and the actual amount Rw. Specifically, the command amount deviation hRs is determined by subtracting the actual amount Rw from the command amount Rs (i.e., "hRs = Rs - Rw"). The "command amount deviation hRs" is the target value for the amount of fluid that should flow into the wheel cylinder CW in the future in order to achieve the command pressure Ps.

[0065] The predicted flow rate calculation block QY calculates a predicted flow rate Qy based on the instruction amount deviation hRs. The "predicted flow rate Qy" is a value that predicts the flow rate (amount of fluid passing per unit time) of brake fluid BF passing through the solenoid valves UB and VI. Specifically, the predicted flow rate calculation block QY differentiates the instruction amount deviation hRs with respect to time to determine the predicted flow rate Qy (predicted value) (i.e., "Qy = d(hRs) / dt").

[0066] The pressure loss calculation block PD calculates the pressure loss Pd occurring in the solenoid valves UB and VI based on the predicted flow rate Qy. Specifically, the solenoid valves UB and VI are considered as a composite orifice. Then, using the flow coefficient C and orifice area A of the composite orifice, the pressure loss Pd is determined by the following formula (1). Pd={Qy / (C·A)}^2 …Equation (1) According to equation (1), the pressure loss Pd is calculated to increase as the predicted flow rate Qy increases.

[0067] The target pressure Pt is calculated based on the command pressure Ps and the pressure loss Pd. Specifically, the target pressure Pt is determined by adding the pressure loss Pd to the command pressure Ps to compensate for the effect of the pressure loss Pd (i.e., "Pt = Ps + Pd"). Note that the flow coefficient C varies depending on the viscosity of the brake fluid BF, so a flow coefficient C corresponding to the temperature Tb of the brake fluid BF may be used in calculating the pressure loss Pd. Specifically, the lower the temperature Tb of the brake fluid BF, the lower the viscosity, so the lower the pressure loss Pd is determined to be, so the lower the temperature Tb. Here, the temperature Tb is detected by a fluid temperature sensor (not shown). Alternatively, it may be estimated based on the detected value of an outside air temperature sensor (not shown).

[0068] The calculation process for the target pressure Pt is summarized below. The flow rate Qy (predicted flow rate) of brake fluid BF passing through the control valve UB and the inlet valve VI is calculated based on the command pressure Ps calculated based on the braking demand Bs and the actual wheel pressure Pw. This is because, when the solenoid valves UB and VI are considered as orifices, the opening area A is known, and therefore the pressure loss Pd can be calculated based on the predicted flow rate Qy. The pressure loss Pd is determined to increase as the predicted flow rate Qy increases (more specifically, in proportion to the square of the predicted flow rate Qy). The target pressure Pt is calculated by adding the predicted pressure loss Pd to the command pressure Ps. In other words, the target pressure Pt includes a hydraulic pressure Pd equivalent to the pressure loss. This suppresses the response delay of the wheel pressure Pw (i.e., a delay in pressure increase) when the braking demand Bs increases suddenly (i.e., when the predicted flow rate Qy is large).

[0069] The pressure loss Pd becomes an issue when the hydraulic pressures (Pu, Pm, Pw, etc.) increase as the braking demand Bs increases (referred to as "pressure increase"). Therefore, calculation of the target pressure Pt based on the pressure loss Pd should be performed only when the hydraulic pressures are increased. For example, when the braking demand Bs is maintained constant and the hydraulic pressures (Pu, Pm, Pw, etc.) are constant (referred to as "steady state"), the command pressure Ps and the wheel pressure Pw are equal, and the predicted flow rate Qy is "0." Therefore, no pressure loss Pd occurs, and "Pd = 0" is determined. On the other hand, when the braking demand Bs is decreased and the hydraulic pressures (Pu, Pm, Pw, etc.) decrease (referred to as "pressure decrease"), the command pressure Ps is smaller than the wheel pressure Pw, and therefore the pressure loss Pd is calculated to be a negative value, but is determined as "Pd = 0."

[0070] <Drive control of pressure regulating valve UA> An example of the process for controlling the drive of the pressure regulating valve UA (particularly, the process of step S160) will be described with reference to the block diagram of Fig. 6. This process is executed by the upper controller EA. The pressure regulating valve UA adjusts the servo pressure Pu, and ultimately adjusts the supply pressure Pm (=Pw). The drive control of the pressure regulating valve UA is composed of a command current calculation block IS, a hydraulic pressure deviation calculation block PH, a compensation current calculation block IH, and a current feedback control block IF.

[0071] The command current calculation block IS calculates a command current Is based on the target pressure Pt and a preset calculation map Zis. The "command current Is" is a target value corresponding to the supply current Ia (actual value) of the pressure regulating valve UA required to achieve the target pressure Pt. According to the calculation map Zis, the command current Is is determined to increase as the target pressure Pt increases. The command current calculation block IS corresponds to feedforward control based on the target pressure Pt.

[0072] The hydraulic pressure deviation calculation block PH calculates the deviation hP (hydraulic pressure deviation) between the target pressure Pt and the supply pressure Pm. Specifically, the hydraulic pressure deviation hP is determined by subtracting the supply pressure Pm from the target pressure Pt (i.e., "hP = Pt - Pm").

[0073] The compensation current calculation block IH calculates the compensation current Ih based on the hydraulic pressure deviation hP and a preset calculation map Zih. The command current Is is calculated corresponding to the target pressure Pt, but an error may occur between the target pressure Pt and the supply pressure Pm. The "compensation current Ih" is used to compensate for (reduce) this error. The compensation current Ih is determined to increase as the hydraulic pressure deviation hP increases according to the calculation map Zih. More specifically, when the target pressure Pt is greater than the supply pressure Pm and the hydraulic pressure deviation hP has a positive sign, a positive compensation current Ih is determined so that the command current Is increases. On the other hand, when the target pressure Pt is smaller than the supply pressure Pm and the hydraulic pressure deviation hP has a negative sign, a negative compensation current Ih is determined so that the command current Is decreases. Here, a dead band is provided in the calculation map Zih. The compensation current calculation block IH corresponds to feedback control based on the supply pressure Pm.

[0074] The target current It is calculated by adding the compensation current Ih to the command current Is (i.e., "It = Is + Ih"). The "target current It" is the final target value of the current supplied to the pressure regulating valve UA. In other words, the target current It is determined as the sum of the command current Is, which is the feedforward term, and the compensation current Ih, which is the feedback term. Therefore, the drive control of the pressure regulating valve UA is composed of feedforward control (processing of the command current calculation block IS) and feedback control (processing of the compensation current calculation block IH) in terms of hydraulic pressure.

[0075] In the current feedback control block IF, based on the target current It (target value) and the supply current Ia (actual value), a drive signal Ua is calculated so that the supply current Ia approaches and matches the target current It. Here, the supply current Ia is detected by a pressure regulating valve current sensor IA provided in the drive circuit DR. In the current feedback control block IF, if "It > Ia", the drive signal Ua is determined so that the supply current Ia increases. On the other hand, if "It < Ia", the drive signal Ua is determined so that the supply current Ia decreases. That is, in the current feedback control block IF, feedback control related to the current is executed. Therefore, in the drive control of the pressure regulating valve UA, in addition to the feedback control related to the hydraulic pressure, feedback control related to the current is provided.

[0076] <Drive Control of Electric Motor MA> Referring to the block diagram of FIG. 7, a processing example of the drive control of the upper electric motor MA (particularly, the processing of step S160) will be described. This processing is executed by the upper controller EA. The electric motor MA is controlled based on the flow rate of the braking fluid BF so that its power consumption is reduced. The drive control of the electric motor MA is composed of a liquid volume conversion block PR, a target volume deviation calculation block RTH, a commanded flow rate calculation block QS, a compensation flow rate calculation block QH, a target flow rate calculation block QT, a target rotation speed calculation block NT, and a rotation speed feedback control block NF.

[0077] In the liquid volume conversion block PR, based on the target pressure Pt and the wheel pressure Pw, the target liquid volume Rt and the actual liquid volume Rw are calculated. As described with reference to FIG. 5, in the liquid volume conversion block PR, based on a preset calculation map Zpr, the target pressure Pt is converted into the target liquid volume Rt, and the wheel pressure Pw is converted into the actual liquid volume Rw. Here, the target liquid volume Rt is the liquid volume required to achieve the target pressure Pt (the volume of the braking fluid BF to be moved to the wheel cylinder CW). Also, the actual liquid volume Rw is the liquid volume that has already flowed into the wheel cylinder CW to generate the wheel pressure Pw.

[0078] The target amount deviation calculation block RTH calculates the deviation hRt (referred to as the "target amount deviation") between the target fluid amount Rt and the actual fluid amount Rw. Specifically, the target amount deviation hRt is determined by subtracting the actual fluid amount Rw from the target fluid amount Rt (i.e., "hRt = Rt - Rw"). The target fluid amount Rt includes a hydraulic pressure Pd equivalent to the pressure loss. Therefore, the "target amount deviation hRt" is the target value for the amount (volume) of fluid that should flow into the wheel cylinder CW in the future in order to achieve the target pressure Pt that takes into account the pressure loss Pd.

[0079] The command flow rate calculation block QS calculates the command flow rate Qs based on the target fluid volume Rt. Specifically, the target fluid volume Rt is time-differentiated to determine the command flow rate Qs (i.e., "Qs = dRt / dt"). The command flow rate calculation block QS corresponds to feedforward control in flow rate control.

[0080] The compensation flow calculation block QH calculates the compensation flow Qh based on the target amount deviation hRt. Specifically, the target amount deviation hRt is time-differentiated to determine the compensation flow Qh (i.e., "Qh ​​= d(hRt) / dt"). The compensation flow calculation block QH corresponds to feedback control in flow control.

[0081] The target flow rate calculation block QT calculates the target flow rate Qt based on the command flow rate Qs and the compensation flow rate Qh. The "target flow rate Qt" is the final target value of the flow rate required to achieve the target pressure Pt. Specifically, the command flow rate Qs and the compensation flow rate Qh are added together to determine the target flow rate Qt (i.e., "Qt = Qs + Qh"). In other words, the target flow rate Qt is calculated as the sum of the command flow rate Qs, which corresponds to the feedforward term, and the compensation flow rate Qh, which corresponds to the feedback term. In other words, the flow rate control is composed of feedforward control (processing by the command flow rate calculation block QS) and feedback control (processing by the compensation flow rate calculation block QH).

[0082] In the target rotation speed calculation block NT, the target rotation speed Nt of the electric motor MA is calculated based on the target flow rate Qt. The "target rotation speed Nt" is the target value corresponding to the rotation speed Na (actual value) of the electric motor MA. Specifically, based on the discharge amount of the fluid pump QA (the volume of the braking fluid BF discharged per rotation), the target rotation speed Nt is determined to increase as the target flow rate Qt increases. In determining the target rotation speed Nt, the minimum flow rate of the pressure regulating valve UA and the minimum rotation speed of the electric motor MA are taken into consideration. The "minimum flow rate" is the minimum flow rate required for the pressure regulating valve UA to adjust the servo pressure Pu and is preset. Also, the "minimum rotation speed" is the minimum value of the rotation speed at which the electric motor MA can continue to rotate stably. Considering these factors, a lower limit rotation speed nt (a preset predetermined value) is provided for the target rotation speed Nt. Therefore, when the target rotation speed Nt calculated based on the target flow rate Qt is not less than the lower limit rotation speed nt, the limitation by the lower limit rotation speed nt is not imposed, and the calculated target rotation speed Nt is used as it is. On the other hand, when the target rotation speed Nt calculated based on the target flow rate Qt is less than the lower limit rotation speed nt, the target rotation speed Nt is determined to be the lower limit rotation speed nt (i.e., "Nt = nt").

[0083] In the rotation speed feedback control block NF, based on the target rotation speed Nt (target value) and the actual rotation speed Na (actual value), a drive signal Ma is calculated so that the actual rotation speed Na approaches and matches the target rotation speed Nt. Here, the actual rotation speed Na is calculated based on the detection value Ka (rotation angle) of the rotation angle sensor KA provided in the electric motor MA. Specifically, the motor rotation angle Ka is differentiated with respect to time to determine the motor rotation speed Na. In the rotation speed feedback control block NF, if "Nt > Na", the drive signal Ma is determined so that the actual rotation speed Na increases. On the other hand, if "Nt < Na", the drive signal Ma is determined so that the actual rotation speed Na decreases. That is, in the rotation speed feedback control block NF, feedback control related to the motor rotation speed is executed.

[0084] Although the wheel pressure Pw is detected by the wheel pressure sensor PW, the wheel pressure Pw may also be estimated. In this configuration, the wheel pressure sensor PW is omitted entirely. A method for estimating the wheel pressure Pw will be explained below. In order to estimate the wheel pressure Pw, an estimated fluid volume calculation block RE and a fluid pressure conversion block RP are provided in addition to the above configuration.

[0085] The estimated fluid volume calculation block RE calculates the estimated fluid volume Re based on the target flow rate Qt. Specifically, during the calculation cycle, the previous value Qt[n-1] of the target flow rate Qt is integrated over time to determine the current value Re[n] of the estimated fluid volume Re (i.e., "Re[n]=∫Qt[n-1]·dt"). Here, [ ] represents the calculation cycle, "n-1" represents the previous calculated value, and "n" represents the current calculated value.

[0086] The hydraulic pressure conversion block RP calculates the current value Pw[n] of the wheel pressure Pw based on the current value Re[n] of the estimated hydraulic volume Re. The hydraulic pressure conversion block RP has a preset relationship between hydraulic pressure and hydraulic volume set as a calculation map Zrp. The hydraulic pressure conversion block RP converts the estimated hydraulic volume Re into wheel pressure Pw based on the calculation map Zrp. The calculation maps Zpr and Zrp have an inverse relationship (i.e., an inverse function relationship in which the X-axis and Y-axis are swapped).

[0087] The brake control device SC controls the rotation speed Na of the electric motor MA based on the target flow rate Qt calculated from the target pressure Pt. That is, in controlling the electric motor MA, the necessary and minimum flow rate is determined from the viewpoint of the flow rate of the brake fluid BF, and the electric motor MA is controlled based on that flow rate. As a result, the power consumed by the electric motor MA is reduced.

[0088] The braking control device SC calculates the target flow rate Qt based on the target pressure Pt and the wheel pressure Pw. Then, in each calculation cycle, the current value Pw[n] of the wheel pressure Pw is estimated based on the previous value Qt[n-1] of the target flow rate Qt. This estimation calculation eliminates the need for the wheel pressure sensor PW, simplifying the device.

[0089] <Other embodiments> Other embodiments will be described below, which also provide the same effects as those described above (such as improved response of the wheel pressure Pw).

[0090] In the above-described embodiment, the target flow rate Qt is calculated based on the target pressure Pt and the wheel pressure Pw, and the current value Pw[n] of the wheel pressure Pw is estimated based on the previous value Qt[n-1] of the target flow rate Qt. Alternatively, the actual flow rate Qw corresponding to the target flow rate Qt may be calculated based on the supply pressure Pm, and the current value Pw[n] of the wheel pressure Pw may be estimated based on the previous value Qw[n-1] of the actual flow rate Qw. In this configuration, as in the case where the target flow rate Qt is used, the previous value Qw[n-1] of the actual flow rate Qw calculated from the supply pressure Pm is integrated over time to calculate the current value Re[n] of the estimated fluid volume Re. Then, the current value Pw[n] of the wheel pressure Pw is calculated based on the current value Re[n] of the estimated fluid volume Re.

[0091] In the estimation calculation of the wheel pressure Pw, the servo pressure Pu may be used instead of the supply pressure Pm. In this configuration, a servo pressure sensor is provided to detect the servo pressure Pu (hydraulic pressure in the servo chamber Ru). As described above, the previous value Qw[n-1] of the actual flow rate Qw calculated from the servo pressure Pu is time-integrated to calculate the current value Re[n] of the estimated fluid volume Re. Then, the current value Pw[n] of the wheel pressure Pw is estimated based on the current value Re[n] of the estimated fluid volume Re.

[0092] In the above-described embodiment, the lower braking unit SB (particularly, the lower actuator YB) can increase the supply pressure Pm. Alternatively, the lower actuator YB may be configured to be able to maintain or decrease the supply pressure Pm but unable to increase the supply pressure Pm. In this configuration, the control valve UB is omitted from the configuration shown in FIG. 3. Therefore, the resistance in the lower actuator YB is only the inlet valve VI, and the pressure loss Pd is generated solely by the inlet valve VI. Note that, because anti-lock brake control controls the wheel pressure Pw to be equal to or lower than the supply pressure Pm, the control valve UB is not required for its execution. Furthermore, when an increase in the wheel pressure Pw independent of the operation of the brake operating member BP is required for anti-skid control, traction control, etc., the wheel pressure Pw is increased by the upper braking unit SA (particularly, the pressure adjustment unit CA of the upper actuator YA). Therefore, even in a configuration in which the control valve UB is omitted, the above-described independent wheel control can be performed as well as in a configuration in which the control valve UB is provided.

[0093] In the above-described embodiment, a front-rear type brake system is used as the two-system brake system. Alternatively, a diagonal type (also called "X type") brake system may be used as the two-system brake system. In this configuration, one of the two master chambers Rm is connected to the left front wheel cylinder and the right rear wheel cylinder, and the other of the two master chambers Rm is connected to the right front wheel cylinder and the left rear wheel cylinder.

[0094] In the above-described embodiment, the pressure adjustment unit CA is exemplified as one that adjusts the servo pressure Pu by throttling the circulating flow KN of the brake fluid BF discharged by the fluid pump QA with the pressure adjustment valve UA (a so-called reflux type configuration). Alternatively, the pressure adjustment unit CA may adjust the pressure accumulated in an accumulator with a linear solenoid valve (a so-called accumulator type configuration). Furthermore, the servo pressure Pu may be adjusted by increasing or decreasing the volume inside a cylinder with a piston directly driven by an electric motor (a so-called electric cylinder type configuration). Because the output of the electric motor is proportional to the supply current, it is possible to perform feedforward control based on the target pressure Pt and feedback control based on the supply pressure Pm, similar to the pressure adjustment valve UA.

[0095] In the above-described embodiment, a tandem type master cylinder CM is exemplified. However, a single type master cylinder CM may be employed instead. In this configuration, the secondary master piston NS is omitted. One master chamber Rm is connected to four wheel cylinders CW. In this configuration, the master cylinder CM outputs the same supply pressures Pmf and Pmr (=Pm).

[0096] In a configuration in which a single master cylinder CM is used, the master chamber Rm may be connected to the front wheel cylinder CWf, and the pressure regulating unit CA may be directly connected to the rear wheel cylinder CWr. In this configuration, the master cylinder CM outputs a front wheel supply pressure Pmf to the front wheel cylinder CWf as a front wheel pressure Pwf. Meanwhile, the pressure regulating unit CA outputs a servo pressure Pu to the rear wheel cylinder CWr as a rear wheel supply pressure Pmr.

[0097] In the above-described embodiment, in the apply unit AP, 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 are set equal. The master area rm and the servo area ru do not have to be equal. In a configuration in which the master area rm and the servo area ru are different, the supply pressure Pm and the servo pressure Pu can be converted based on the ratio of the servo area ru to the master area rm (i.e., conversion based on "Pm·rm=Pu·ru").

[0098] <Summary of the embodiment> An embodiment of the brake control device SC will be summarized. The brake control device SC includes a pressure regulating unit CA that adjusts the wheel pressure Pw of the wheel cylinder CW using a servo pressure Pu generated by an electric motor MA as a power source, solenoid valves UB and VI that are provided in a hydraulic pressure transmission path (e.g., a communication path HS) from the servo pressure Pu to the wheel pressure Pw, and a controller EA that controls the pressure regulating unit CA. The solenoid valve VI (inlet valve) is provided to prevent an increase in the wheel pressure Pw for anti-lock brake control. The solenoid valve UB (control valve) is also provided to increase the wheel pressure Pw from the supply pressure Pm for anti-skid control and traction control.

[0099] When the braking demand Bs increases and the hydraulic pressures Pm and Pw increase, the brake fluid BF flows from the upper brake unit SA to the wheel cylinders CW. At this time, the flow path of the brake fluid BF is narrowed by the solenoid valves UB and VI. Therefore, the solenoid valves UB and VI act as a resistance to the flow of the brake fluid BF, causing a pressure loss Pd (a decrease in hydraulic pressure due to energy loss).

[0100] The following describes the location of pressure loss Pd in ​​the hydraulic pressure transmission path from servo pressure Pu to wheel pressure Pw for each of the four illustrated configurations. The explanations show the case where servo pressure Pu and wheel pressure Pw are increased. Therefore, brake fluid BF is moved from the pressure regulating unit CA toward the wheel cylinder CW. (1) In a configuration in which the servo pressure Pu is transmitted via a piston (e.g., NM) and a control valve UB is provided, the servo pressure Pu electrically generated by the pressure adjustment unit CA is transmitted to the wheel cylinder CW in the order of Pu → Pm → [UB] → Pq → [VI] → Pw. Here, [ ] indicates the position of the solenoid valve. A drop in hydraulic pressure (i.e., pressure loss Pd) occurs in the control valve UB and the inlet valve VI. (2) In a configuration in which the servo pressure Pu is transmitted via a piston (e.g., NM) and the control valve UB is omitted, the servo pressure Pu is transmitted to the wheel cylinder CW in the order of Pu → Pm → [VI] → Pw. The hydraulic pressure drop occurs only through the inlet valve VI. (3) In a configuration in which the servo pressure Pu is supplied directly to the wheel cylinder CW without passing through a piston or the like and in which the control valve UB is provided, the servo pressure Pu is transmitted to the wheel cylinder CW in the order of Pu → [UB] → Pq → [VI] → Pw. As in (1) above, a drop in hydraulic pressure occurs in the control valve UB and the inlet valve VI. (4) In a configuration in which the servo pressure Pu is supplied directly to the wheel cylinder CW without passing through a piston or the like and the control valve UB is omitted, the servo pressure Pu is transmitted to the wheel cylinder CW in the order of Pu → [VI] → Pw. As in (2) above, a drop in hydraulic pressure occurs only through the inlet valve VI.

[0101] The controller EA calculates a pressure loss Pd in ​​the solenoid valve (VI, etc.) of the lower actuator YB. Specifically, a command pressure Ps is calculated from the braking demand Bs. The pressure loss Pd is calculated based on the command pressure Ps and the wheel pressure Pw. The target pressure Pt is determined by adding the pressure loss Pd to the command pressure Ps. In other words, the component of the pressure loss Pd is taken into account for the command pressure Ps, and the sum of the command pressure Ps and the pressure loss Pd is determined as the target pressure Pt. The pressure regulating unit CA is controlled based on this target pressure Pt.

[0102] Specifically, the pressure loss Pd is calculated using the following method. First, the command fluid volume Rs (the volume of brake fluid BF that needs to be moved to achieve the command pressure Ps) is calculated from the command pressure Ps. Then, the actual fluid volume Rw (the volume of brake fluid BF that has already been moved to generate the wheel pressure Pw) is calculated from the wheel pressure Pw. The deviation hRs between the command fluid volume Rs and the actual fluid volume Rw (the command volume deviation, which is the volume of brake fluid BF that needs to be moved to increase the wheel pressure Pw to the command pressure Ps) is calculated. Then, the command volume deviation hRs is time-differentiated to determine the predicted flow rate Qy. The predicted flow rate Qy is the amount of brake fluid BF moved per unit time that is required for the wheel pressure Pw to reach the command pressure Ps. The pressure loss Pd is determined based on the predicted flow rate Qy, so that the larger the predicted flow rate Qy, the larger the pressure loss Pd (see equation (1)).

[0103] In the brake control device SC, a solenoid valve (at least an inlet valve VI) is arranged in a hydraulic pressure transmission path (e.g., a connection path HS) from the servo pressure Pu to the wheel pressure Pw to perform anti-lock brake control and the like. The solenoid valves include the control valve UB and the inlet valve VI, and in a configuration in which the control valve UB is omitted, only the inlet valve VI is included. Even in a fully open state, the solenoid valve does not open sufficiently. Therefore, when the flow velocity of the brake fluid BF is relatively high, the solenoid valve acts as a resistance that obstructs the flow of the brake fluid BF, which can result in a pressure loss Pd. In the brake control device SC, the adjustment of the servo pressure Pu output from the pressure adjustment unit CA (i.e., pressure adjustment control) is expected to be affected by the pressure loss Pd. This prevents a delay in the increase of the wheel pressure Pw and improves its pressure increase response.

[0104] For example, in the pressure regulating unit CA, a circulating flow KN discharged by a fluid pump QA driven by an electric motor MA is adjusted to a servo pressure Pu by a pressure regulating valve UA. A controller EA calculates a target current It based on a target pressure Pt, and controls a supply current Ia of the pressure regulating valve UA based on this target current It. Furthermore, the controller EA calculates a target rotation speed Nt based on the target pressure Pt, and controls the actual rotation speed Na of the electric motor MA so that it coincides with this target rotation speed Nt. Because the target rotation speed Nt is determined as a value that is necessary and minimum for pressure regulation control, not only is the response of the wheel pressure Pw improved, but power consumption of the electric motor MA is also reduced.

[0105] The controller EA estimates the wheel pressure Pw based on one of the target pressure Pt, the supply pressure Pm, and the servo pressure Pu. Specifically, at each calculation cycle, the current value Pw[n] of the wheel pressure Pw is estimated based on the previous value Qt[n-1] of the target flow rate Qt calculated from the target pressure Pt. Alternatively, the current value Pw[n] of the wheel pressure Pw is estimated based on the previous value Qw[n-1] of the actual flow rate Qw calculated from the supply pressure Pm or the servo pressure Pu. Estimating the wheel pressure Pw eliminates the need for the wheel pressure sensor PW. As a result, the overall configuration of the device is simplified.

[0106] The pressure loss Pd occurs when a sudden increase in the wheel pressure Pw is required (i.e., when the braking demand Bs increases suddenly), so calculation of the pressure loss Pd (i.e., compensation for the pressure loss) may be limited to when the pressure is increased (i.e., when the braking demand Bs increases). Therefore, when the wheel pressure Pw is maintained or decreased (i.e., when the braking demand Bs is maintained constant or when the braking demand Bs is decreased), calculation of the pressure loss Pd is not performed and the pressure loss Pd is set to "0." In this case, the target pressure Pt is calculated to be equal to the command pressure Ps.

[0107] Furthermore, the calculation of the pressure loss Pd may be restricted to the condition that "the increase in the braking demand amount Bs over time dB must be equal to or greater than a predetermined value db." In other words, when the increase in the braking demand amount Bs per unit time dB is equal to or greater than the predetermined value db, the pressure loss Pd is added to the command pressure Ps to calculate the target pressure Pt. However, when the increase in the time dB is less than the predetermined value db, the pressure loss Pd is set to "0," and the target pressure Pt is determined to be equal to the command pressure Ps. Here, the "predetermined value db" is a preset constant. [Explanation of symbols]

[0108] SC...Brake control device, BP...Brake operating member (brake pedal), CW...Wheel cylinder, SA, SB...Upper and lower braking units, YA, YB...Upper and lower actuators (fluid units), EA, EB...Upper and lower controllers (control units), BS...Communication bus, CM...Master cylinder, CA...Pressure adjustment unit, UA...Pressure adjustment valve, MA, MB...Upper and lower electric motors, QA, QB...Upper and lower fluid pumps, PM...Supply pressure sensor, PW...Wheel pressure sensor, UB...Control valve, VI...Inlet valve, VO...outlet valve, Ps...indicated pressure, Pt...target pressure, Pu...servo pressure, Pm...supply pressure (detected value of PM), Pw...wheel pressure (detected value or estimated value of PW), Pd...pressure loss, Rs...indicated fluid volume, Rt...target fluid volume, Rw...actual fluid volume, Re...estimated fluid volume, hRs...indicated volume deviation, hRt...target volume deviation, Qy...predicted flow rate, Qs...indicated flow rate, Qh...compensated flow rate, Qt...target flow rate, Nt...target rotation speed, Na...actual rotation speed, Ka...rotation angle, Bs...required braking volume, Ba...braking operation volume, Gs...required deceleration.

Claims

1. a pressure adjusting unit that adjusts the wheel pressure of the wheel cylinder by a servo pressure generated by an electric motor as a power source; a solenoid valve provided in a hydraulic pressure transmission path from the servo pressure to the wheel pressure; a controller for controlling the pressure adjustment unit; In a braking control device for a vehicle, The controller calculating a pressure loss in the solenoid valve based on a command pressure calculated from a braking demand amount and the wheel pressure; determining a target pressure by adding the pressure loss to the command pressure; A vehicle braking control device that controls the pressure regulating unit based on the target pressure.

2. 2. The vehicle brake control device according to claim 1, The controller calculates a predicted flow rate passing through the solenoid valve based on the deviation between an indicated fluid volume calculated from the indicated pressure and an actual fluid volume calculated from the wheel pressure, and calculates the pressure loss based on the predicted flow rate.

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