Vehicle braking control device

Abstract

To provide a braking control device constituted of two braking units, in which a lower braking unit that executes side-slip prevention control is used in common.SOLUTION: A braking control device comprises: an upper braking unit that electrically outputs supply pressure (Pm) in accordance with a requested braking (Bs); and a lower braking unit, arranged among the upper braking unit and a plurality of wheel cylinders, which adjusts the supply pressure (Pm) for each of the plurality of wheel cylinders and outputs wheel pressure. The upper braking unit increases the supply pressure (Pm) up to requested pressure (Pe) which is necessary to execute side-slip prevention control, when the lower braking unit executes the side-slip prevention control.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent Document 1 describes a method for improving the initial response of brake fluid pressure generation in a control (called "anti-slip control") that stabilizes vehicle behavior by controlling the yaw moment of the vehicle. "A yaw moment control device is disposed in a fluid path between a slave cylinder, which generates brake fluid pressure using a first electric motor driven in response to the driver's brake pedal depression, and the wheel cylinders, and the slave cylinder is temporarily activated when the yaw moment control starts to operate." The device in Patent Document 1 is composed of two brake units: a unit (called the "upper braking unit") powered by a first electric motor (also called the "upper electric motor") and a unit (called the "lower braking unit") powered by a second electric motor (also called the "lower electric motor"). In the device in Patent Document 1, both the upper and lower braking units increase the hydraulic pressure in the wheel cylinders (called "wheel pressure") at the start of anti-slip control, thereby improving the response of the wheel pressure increase.

[0003] In anti-skid control, the braking force, yaw moment, and other factors required to stabilize vehicle behavior depend on the vehicle's specifications. Therefore, the output of the lower braking unit that executes anti-skid control must be set for each vehicle. In a brake control device, it is desirable for the lower braking unit to be standardized across various vehicles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-227023 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 is configured with two brake units, in which the lower brake unit that executes anti-skid control can be made common. [Means for solving the problem]

[0006] A vehicle brake control device (SC) according to the present invention includes an upper brake unit (SA) that electrically outputs a supply pressure (Pm) in accordance with a braking demand (Bs), and a lower brake unit (SB) that is disposed between the upper brake unit (SA) and a plurality of wheel cylinders (CW) and that individually adjusts the supply pressure (Pm) for each of the plurality of wheel cylinders (CW) to output a wheel pressure (Pw). When the lower brake unit (SB) executes anti-skid control, the upper brake unit (SA) increases the supply pressure (Pm) to a demand pressure (Pe) required for executing the anti-skid control. Here, the demand pressure (Pe) is determined based on the maximum value (Max[Po]) of the required pressures (Po) required for each of the plurality of wheel cylinders (CW).

[0007] According to the above configuration, the hydraulic pressure Pe (required pressure) required for anti-skid control is supplied by the upper brake unit SA. Therefore, in the lower brake unit SB, it is only necessary to individually adjust the hydraulic pressure Pm (supplied pressure) supplied from the upper brake unit SA at each wheel cylinder CW. Because the lower brake unit SB does not require high-pressure and high-response output, the lower brake unit SB can be used for vehicles with different specifications, and standardization is achieved.

[0008] In the vehicle brake control device (SC) according to the present invention, when the upper brake unit (SA) cannot increase the supply pressure (Pm) to the required pressure (Pe), the lower brake unit (SB) increases the wheel pressure (Pw) by the amount of the deviation (hP) between the supply pressure (Pm) and the required pressure (Pe). With the above configuration, even if a drop in output occurs in the upper brake unit SA, the required pressure Pe is achieved, so the performance of the anti-skid control is ensured. [Brief explanation of the drawings]

[0009] [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 block diagram for explaining pressure regulation control in an upper braking unit SA. [Figure 5] FIG. 10 is a flow chart for explaining complementary control in the lower braking unit SB. DETAILED DESCRIPTION OF THE INVENTION

[0010] <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.

[0011] 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."

[0012] 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.

[0013] <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.

[0014] 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.

[0015] 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.

[0016] 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 speeds Vw (wheel speeds) of the wheels WH. The wheel speeds Vw are input to the lower controller EB. The lower controller EB then calculates the vehicle speed Vx based on the wheel speeds 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 speeds 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] <Upper braking unit SA> An example of the configuration of the upper braking unit SA will be described with reference to the schematic diagram of Fig. 2. The upper braking unit SA generates a supply pressure Pm in response to operation of a 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.

[0021] <Upper actuator YA> The upper actuator YA is composed of an apply unit AP, a pressure adjustment unit CA, and an input unit NR.

[0022] [Apply Unit AP] In response to 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.

[0023] Primary and secondary master pistons NM and NS are inserted into the tandem master cylinder CM. 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 wheel 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 portion Tu of the master piston NM. The master chamber Rm and the servo chamber Ru are arranged opposite each other with the flange portion Tu in between. These hydraulic chambers Rmf, Rmr, Ru, and Ro are sealed by a seal member SL. The pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are made equal.

[0024] 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."

[0025] [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.

[0026] 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.

[0027] 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."

[0028] 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 and also referred to as the "upper circulating flow") 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 hydraulic pressure Pu (referred to as the "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 hydraulic 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.

[0029] 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.

[0030] 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").

[0031] [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.

[0032] 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 master piston NM. Regenerative cooperative control is achieved by adjusting the separation distance Ks using the servo pressure Pu.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] <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.).

[0037] The upper controller EA receives a braking operation amount Ba. The braking operation amount Ba is a general term for a state quantity that represents the operation amount of the brake operating member BP. As the braking operation amount Ba, the detection signal Sp (operation displacement) of the operation displacement sensor SP and the 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, the upper controller EA receives a supply pressure Pm, a required deceleration Gs, etc. 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 required deceleration Gs is a required value for automatic braking control, calculated by the driving assistance controller ED, and transmitted from the driving assistance controller ED.

[0038] An algorithm for pressure regulation control is programmed in the upper controller EA (particularly the microprocessor MP). "Pressure regulation control" is 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), required deceleration Gs, supply pressure Pm, etc. Here, the braking operation amount Ba and required deceleration Gs are collectively referred to as "requested braking amount Bs." The requested braking amount Bs is an input signal for instructing (requesting) the generation of supply pressure Pm (and consequently, wheel pressure Pw to be generated by the brake control device SC).

[0039] 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). In the drive circuit DR, an H-bridge circuit is constituted by switching elements (for example, MOS-FETs) to drive the electric motor MA. Also, the drive circuit DR is provided 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 a rotation angle sensor (not shown) that detects the rotation angle Ka (referred to as "motor rotation angle") of the rotor of the electric motor MA is provided. And based on the motor rotation angle Ka, the motor rotation speed Na is calculated.

[0040] In the upper controller EA, based on the braking demand amount Bs (such as Ba, Gs) of the vehicle, a target current It (target value) corresponding to the pressure regulating valve current Ia (actual value) is calculated. And in the control of the pressure regulating valve UA, the pressure regulating valve current Ia is controlled to approach and match the target current It. Also, in the upper controller EA, based on the braking demand amount Bs, a target rotation speed Nt (target value) corresponding to the motor rotation speed Na (actual value) is calculated. And 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.

[0041] <Lower braking unit SB> An example of the configuration of the lower braking unit SB of the brake 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 traction control and anti-skid control, the wheel pressure Pw of each wheel cylinder CW is automatically increased independently of the operation of the brake operating member BP.

[0042] 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.

[0043] <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 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.

[0044] 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.

[0045] 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.

[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, which includes 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 (also referred to as the "lower circulating flow"), 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 anti-lock brake control, traction 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 body speed Vx based on the wheel speed Vw. The lower controller EB executes electronic stability control (ESC) to appropriately maintain the steering characteristics of the vehicle JV (i.e., suppress understeer and oversteer) and improve the directional stability of the vehicle JV.

[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 in upper braking unit SA> The pressure regulation control in the upper braking unit SA will be described with reference to the block diagram in Figure 4. In the pressure regulation control, the supply pressure Pm (=Pw), which is the output pressure of the upper braking unit SA, is regulated. In detail, a target pressure Pt is determined, and the pressure regulating valve UA regulates the servo pressure Pu based on this target pressure Pt, thereby ultimately adjusting the supply pressure Pm.

[0054] The pressure regulation control is composed of a required pressure calculation block PO, a demand pressure calculation block PE, a command pressure calculation block PS, a target pressure calculation block PT, 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. For example, the processing of the required pressure calculation block PO and the demand pressure calculation block PE is executed by the lower controller EB, and the other processing (PS, PT, etc.) is executed by the upper controller EA.

[0055] The required pressure calculation block PO calculates the required pressure Po corresponding to the wheel pressure Pw of each wheel cylinder CW based on the wheel speed Vw, steering operation amount Sk, yaw rate Yr, lateral acceleration Gy, etc. The "required pressure Po" is a target value for each wheel cylinder CW required to execute anti-skid control. "Anti-skid control" is also called "vehicle behavior stabilization control." In anti-skid control, unstable behavior of the vehicle JV (i.e., oversteer, understeer) is stabilized by applying braking force to each wheel WH (ultimately, applying a yaw moment).

[0056] The required pressure calculation block PO calculates the degree (level) of stability of the vehicle JV based on the vehicle body speed Vx, steering operation amount Sk, yaw rate Yr, and lateral acceleration Gy. Specifically, the required pressure calculation block PO performs the following calculations. First, the vehicle body speed Vx is calculated based on the wheel speed Vw. Then, a target behavior (e.g., a target yaw rate and a target slip angle) is calculated based on the vehicle body speed Vx and the steering operation amount Sk. Furthermore, an actual behavior (e.g., an actual yaw rate and an actual slip angle) corresponding to the target behavior is calculated based on the yaw rate Yr, lateral acceleration Gy, etc. The steering characteristics (degree of understeer / oversteer) of the vehicle JV are identified based on a comparison result between the target behavior and the actual behavior (e.g., the difference between the target behavior and the actual behavior). The required pressure Po corresponding to each wheel pressure Pw is determined so that the steering characteristics are optimized (i.e., the vehicle behavior is stabilized). In anti-skid control, for example, four required pressures Po are calculated. Then, each wheel pressure Pw is controlled to approach and match each required pressure Po. This applies a yaw moment to the vehicle JV, suppresses understeer and oversteer, and stabilizes the yawing behavior of the vehicle JV.

[0057] The required pressure Pe is calculated in the required pressure calculation block PE based on the required pressure Po. The "required pressure Pe" is a target value required for executing anti-skid control. Specifically, the largest of the multiple required pressures Po is determined as the required pressure Pe (i.e., "Pe = MAX(Po)"). Alternatively, the required pressure Pe may be determined by adding a predetermined pressure pe to the largest of the multiple required pressures Po (i.e., "Pe = MAX(Po) + pe"). Here, the "predetermined pressure pe" is a predetermined value (constant) that is set in advance. In either case, the required pressure Pe is determined based on the maximum value of the required pressure Po. The required pressure Pe is transmitted from the lower controller EB to the communication bus BS and received by the upper controller EA.

[0058] The command pressure calculation block PS calculates a command pressure Ps based on the braking demand Bs. The "braking demand Bs" is a collective term for the braking operation amount Ba and the required deceleration Gs, and is an input for instructing the generation of the supply pressure Pm (i.e., the wheel pressure Pw to be generated by the brake control device SC). The braking demand 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 braking demand Bs. 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 to increase as the braking demand Bs increases, according to a preset calculation map Zps.

[0059] In the target pressure calculation block PT, the target pressure Pt is calculated based on the indicated pressure Ps and the required pressure Pe. The "target pressure Pt" is the final target value corresponding to the supply pressure Pm (as a result, the wheel pressure Pw). Specifically, the larger value between the indicated pressure Ps and the required pressure Pe is determined as the target pressure Pt (that is, "Pt = MAX(Ps, Pe)"). Therefore, when "Ps > Pe" and the indicated pressure Ps is adopted as the target pressure Pt, the target pressure Pt is the target value corresponding to the wheel pressure Pw to be achieved according to the braking demand amount Bs. Also, when "Ps < Pe" and the required pressure Pe is adopted as the target pressure Pt, the target pressure Pt is the target value corresponding to the wheel pressure Pw required for the anti-skid control.

[0060] In the indicated current calculation block IS, the indicated current Is is calculated based on the target pressure Pt and a preset calculation map Zis. The "indicated current Is" is the target value corresponding to the supply current Ia of the pressure regulating valve UA required to achieve the target pressure Pt. The indicated current Is is determined to increase according to the increase of the target pressure Pt according to the calculation map Zis. The indicated current calculation block IS corresponds to the feedforward control based on the target pressure Pt.

[0061] In the hydraulic pressure deviation calculation block PH, the deviation hP between the target pressure Pt and the supply pressure Pm (referred to as "hydraulic pressure deviation") is calculated. Specifically, the supply pressure Pm is subtracted from the target pressure Pt to determine the hydraulic pressure deviation hP (that is, "hP = Pt - Pm").

[0062] 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.

[0063] 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.

[0064] 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 current is executed. Therefore, in the drive control of the pressure regulating valve UA, in addition to the feedback control related to hydraulic pressure, feedback control related to current is provided.

[0065] The braking control device SC is equipped with two braking units SA and SB. One is the upper braking unit SA. The upper braking unit SA electrically outputs the supply pressure Pm according to the braking required amount Bs (for example, the braking operation amount Ba, the required deceleration Gs). Specifically, the upper braking unit SA can output the supply pressure Pm independently of the operation of the braking operation member BP by the driver, using the electric motor MA as a power source. The other is the lower braking unit SB. The lower braking unit SB is provided between the upper braking unit SA and the plurality of wheel cylinders CW. The lower braking unit SB can individually adjust (increase, decrease) the supply pressure Pm for each of the plurality of wheel cylinders CW and output the wheel pressure Pw. Specifically, the lower braking unit SB is equipped with an electric motor MB, a fluid pump QB, and a plurality of solenoid valves (VI, VO, etc.). And in the lower braking unit SB, by controlling the electric motor MB and the plurality of solenoid valves, the wheel pressure Pw can be adjusted for each wheel cylinder CW.

[0066] In the brake control device SC, when the lower brake unit SB executes anti-skid control, the upper brake unit SA increases the supply pressure Pm to the required pressure Pe required to execute anti-skid control. In other words, the required pressure Pe required to execute anti-skid control is supplied to the lower brake unit SB from the upper brake unit SA as the supply pressure Pm. More specifically, when the required pressure Pe required to execute anti-skid control is greater than the command pressure Ps calculated from the braking operation amount Ba, a deviation hP between the supply pressure Pm and the required pressure Pe is calculated based on the required pressure Pe (=Pt), and the supply pressure Pm is electrically controlled so that the deviation hP becomes "0." As a typical example, when the brake operating member BP is not operated and automatic braking control is not being executed (i.e., when the braking operation amount Bs is "0"), the supply pressure Pm is controlled to approach and match the required pressure Pe. The command pressure Ps is determined to increase as the braking operation amount Ba increases.

[0067] The required pressure Pe is determined based on the required pressure Po corresponding to each wheel pressure Pw. Specifically, in anti-skid control, the required pressure Po (target value) required for each wheel cylinder CW is calculated based on the yaw rate Yr, etc., to suppress unstable behavior of the vehicle JV (i.e., oversteer / understeer). The required pressure Pe is calculated based on the maximum value (Max[Po]) of these multiple required pressures Po. For example, the maximum value of the required pressure Po itself is determined as the required pressure Pe. Alternatively, a predetermined pressure pe may be added to the maximum value of the required pressure Po to determine the required pressure Pe. In either case, the required pressure Pe is calculated based on the maximum value of the required pressure Po.

[0068] The lower brake unit SB is equipped with a control valve UB that increases the supply pressure Pm by throttling the lower circulation flow KL discharged by the lower fluid pump QB, which is driven by the lower electric motor MB. However, if the required pressure Pe is achieved by the supply pressure Pm from the upper brake unit SA, it is not necessary for the lower brake unit SB to increase the supply pressure Pm. In such a case, no power is supplied to the control valve UB, and the control valve UB is maintained in a fully open state. Note that the electric motor MB is driven during execution of anti-skid control to discharge the brake fluid BF from the pressure regulating reservoir RB.

[0069] In anti-skid control, braking force is generated individually for each wheel WH by individually controlling each wheel pressure Pw. This applies a yaw moment to the vehicle and further decelerates the vehicle, improving directional stability. The magnitude of the yaw moment and braking force required to stabilize the vehicle depends on the vehicle's specifications (vehicle weight, yaw moment of inertia, center of gravity height, etc.). Specifically, a vehicle with a larger yaw moment of inertia (a quantity representing the degree of inertia with respect to rotational motion in the yaw direction) requires a larger yaw moment (e.g., difference in braking force between the left and right wheels). Furthermore, a vehicle with a larger weight and / or center of gravity height requires a larger braking force. Therefore, the greater the vehicle weight, yaw moment of inertia, center of gravity height, etc., the greater the required pressure Pe and the more responsive it is required. For this reason, in a system in which the wheel pressure required for anti-skid control is generated by a lower braking unit, the rated output of the lower braking unit must be set for each vehicle model based on the vehicle specifications (yaw moment of inertia, vehicle weight, center of gravity position, etc.).

[0070] In the brake control system SC, the required pressure Pe required for anti-skid control is generated by the upper brake unit SA. The upper brake unit SA also responds to sudden operation of the brake operating member BP. Since the upper brake unit SA can generate high wheel pressure Pw with high response, the rated output of the upper brake unit SA is sufficient for anti-skid control. In the brake control system SC, the required pressure Pe is supplied from the upper brake unit SA as supply pressure Pm, so the lower brake unit SB only needs to individually adjust the supply pressure Pm based on each required pressure Po, and there is no need to further increase the differential pressure between the supply pressure Pm and the wheel pressure Pw. In other words, adjusting the wheel pressure Pw in the lower brake unit SB is sufficient by maintaining the hydraulic pressure, reducing the supply pressure Pm, and increasing it to the supply pressure Pm.

[0071] In the brake control device SC, the lower brake unit SB is not required to have a large output (high-response and high-pressure output) during anti-skid control. Therefore, the ratings of the lower brake unit SB (output of the lower electric motor MB, discharge volume of the lower fluid pump QB, etc.) can be set regardless of the vehicle specifications. Therefore, in the brake control device SC, the common lower brake unit SB can be applied to vehicles with a large vehicle weight, yaw moment of inertia, etc. (i.e., large vehicles). In other words, the lower brake unit SB that performs anti-skid control can be commonized for various vehicles. The pressurizing function of the lower brake unit SB is used for complementary control, which will be described next.

[0072] <Complementary control by lower braking unit SB> The complementary control in the lower brake unit SB will be described with reference to the flow chart of FIG. 5. In the brake control device SC, the wheel pressure Pw can be increased not only by the upper brake unit SA but also by the lower brake unit SB during anti-skid control. The "complementary control" is a control in which, when the upper brake unit SA is unable to generate a sufficient supply pressure Pm during anti-skid control (i.e., when a drop in output occurs in the upper brake unit SA and the target pressure Pt cannot be achieved), the lower brake unit SB compensates for the shortage. The complementary control process is executed by the upper and lower brake units SA and SB (particularly the upper and lower controllers EA and EB). Note that the following description assumes a situation in which the command pressure Ps is smaller than the required pressure Pe and the required pressure Pe is calculated as the target pressure Pt (i.e., when "Pt = Pe").

[0073] In step S110, various signals are read in the upper and lower controllers EA and EB. Specifically, the supply pressure Pm, the required pressure Pe, the power supply voltage Vm, the motor temperature Tm, etc. are acquired. The supply pressure Pm is detected by the supply pressure sensor PM and acquired by the lower controller EB. The supply pressure Pm is also acquired by the upper controller EA via the communication bus BS. The required pressure Pe is calculated by the lower controller EB and acquired by the upper controller EA via the communication bus BS. The power supply voltage Vm is the supply voltage to the upper electric motor MA, and is detected by a voltage sensor (not shown) provided in the drive circuit DR of the upper controller EA and acquired by the upper controller EA. The motor temperature Tm is the temperature related to the upper electric motor MA. Specifically, the motor temperature Tm corresponds to the temperature of the electric motor MA itself, the temperature of the drive circuit DR that drives the electric motor MA, etc. The motor temperature Tm is detected by a temperature sensor (not shown) provided in the electric motor MA and a temperature sensor (not shown) provided in the drive circuit DR, and is acquired by the upper controller EA. The power supply voltage Vm and the motor temperature Tm are acquired by the lower controller EB via the communication bus BS.

[0074] In step S120, various state quantities such as the hydraulic pressure deviation hP are calculated by the upper and lower controllers EA and EB. The hydraulic pressure deviation hP is a state quantity representing the shortage of the supply pressure Pm with respect to the target pressure Pt. The hydraulic pressure deviation hP is determined by subtracting the supply pressure Pm from the target pressure Pt in the same manner as the processing of the aforementioned hydraulic pressure deviation calculation block PH (that is, hP = Pt - Pm). Since "Pt = Pe", it is "hP = Pe - Pm".

[0075] In step S130, it is determined whether "the upper braking unit SA can generate the target pressure Pt or not". This determination is referred to as "feasibility determination". The feasibility determination is executed based on at least one of the hydraulic pressure deviation hP, the power supply voltage Vm, and the motor temperature Tm. Specifically, it is determined based on at least one of the methods listed below. (1) The feasibility determination is made by determining whether "the hydraulic pressure deviation hP is less than the predetermined pressure hp or not". The predetermined pressure hp is a predetermined value (constant) set in advance. When "hP < hp", it is determined that "the generation of the target pressure Pt is possible (referred to as the "possible state")", and the feasibility determination is affirmed. On the other hand, when "hP ≥ hp", it is determined that "the generation of the target pressure Pt is impossible (referred to as the "impossible state")", and the feasibility determination is negated. (2) The feasibility determination is made by determining whether "the power supply voltage Vm is greater than or equal to the predetermined voltage vm or not". The predetermined voltage vm is a predetermined value (constant) set in advance. When "Vm ≥ vm", the possible state is determined, and when "Vm < vm", the impossible state is determined. This is based on the fact that when the power supply voltage Vm is low, the output of the electric motor MA decreases. (3) The feasibility determination is made by determining whether "the motor temperature Tm is less than the predetermined temperature td or not". The predetermined temperature tm is a predetermined value (constant) set in advance. When "Tm < tm", the possible state is determined, and when "Tm ≥ tm", the impossible state is determined. This is based on the fact that when the motor temperature Tm is high, the output of the electric motor MA decreases.

[0076] If the determination is affirmative, normal control is executed in steps S140 and S150. Here, "normal control" is the pressure regulation control described with reference to Fig. 4, in which the target pressure Pt (=Pe) is achieved only by the upper brake unit SA. Therefore, in the lower brake unit SB, the lower electric motor MB, the inlet valve VI, and the outlet valve VO are energized and driven, but the control valve UB is not energized and its drive is stopped.

[0077] In step S140, the upper controller EA drives the upper actuator YA. Specifically, the upper electric motor MA is driven to generate the upper circulation flow KN in the return path HK. Then, the pressure regulating valve UA is driven based on the method described above, and the supply pressure Pm is controlled to approach and match the target pressure Pt (=Pe).

[0078] In step S150, the lower controller EB drives the lower actuator YB. Specifically, the lower electric motor MB is driven, and the lower fluid pump QB returns the brake fluid BF that has flowed into the pressure regulating reservoir RB to the top of the inlet valve VI. This is because the wheel pressure Pw is reduced during anti-skid control by moving the brake fluid BF from the wheel cylinder CW to the pressure regulating reservoir RB, but the volume of the pressure regulating reservoir RB is finite. The fluid pump QB pumps the brake fluid BF out of the pressure regulating reservoir RB so that the wheel pressure Pw can continue to decrease.

[0079] Furthermore, in step S150, in the anti-skid control, each wheel pressure Pw is individually adjusted to control the yaw moment acting on the vehicle body. The wheel pressure Pw is individually adjusted by operating the inlet valve VI and the outlet valve VO, as described above, using the supply pressure Pm as the base pressure. Therefore, the adjustable range of the wheel pressure Pw is equal to or less than the supply pressure Pm. Note that in normal control, the base pressure Pe (required pressure) for the anti-skid control is supplied by the upper braking unit SA, so power supply to the control valve UB is stopped and it is not driven. Since the electric motor MB is driven, the circulating flow KL is generated by the fluid pump QB. However, since the control valve UB is fully open, the hydraulic pressure Pq (adjusted pressure) below the control valve UB (upstream side of the fluid pump QB) remains the same as the pressure Pm (supply pressure) above the control valve UB (downstream side of the fluid pump QB) (i.e., "Pm = Pq").

[0080] If the determination is negative, complementary control is executed in steps S160 and S170. Complementary control is a control in which, when the supply pressure Pm is insufficient relative to the target pressure Pt (i.e., the required pressure Pe), the lower brake unit SB compensates for the shortage. In step S160, as in step S140, the upper controller EA drives the upper actuator YA. In step S170, the lower controller EB drives the lower actuator YB based on the hydraulic pressure deviation hP. The hydraulic pressure deviation hP is the difference between the target pressure Pt (target value) and the supply pressure Pm (actual value), and is therefore a state quantity that represents the shortage of the supply pressure Pm relative to the required pressure Pe. Therefore, in the lower brake unit SB, the supply current Ib to the control valve UB is controlled based on the hydraulic pressure deviation hP. During execution of the anti-skid control, the electric motor MB is driven and the hydraulic pump QB generates the lower circulation flow KL. Therefore, when the opening amount of the control valve UB is reduced by the supply current Ib, the flow path of the communication path HS is narrowed, and a pressure difference is generated, causing the adjustment pressure Pq to increase from the supply pressure Pm.

[0081] As shown in the supply current calculation block XB, the supply current Ib (referred to as the "control valve current") to the control valve UB is calculated based on the hydraulic pressure deviation hP (the target value of the differential pressure by the control valve UB) (see the balloon). Specifically, the supply current Ib is controlled based on a preset calculation map Zib so that it increases as the hydraulic pressure deviation hP increases. Therefore, by supplying power to the control valve UB, the regulated pressure Pq is increased from the supply pressure Pm by the hydraulic pressure deviation hP. In other words, if the upper brake unit SA cannot achieve the supply pressure Pe, the shortage is made up by the lower brake unit SB. Note that even in the complementary control, the individual control of each wheel pressure Pw is performed by the inlet valve VI and the outlet valve VO provided below the control valve UB.

[0082] When the required pressure Pe is realized by the upper brake unit SA (i.e., when the supply pressure Pm reaches the required pressure Pe), the control valve UB in the lower brake unit SB is not supplied with power and is maintained in a fully open state. On the other hand, when the supply pressure Pm is insufficient for the required pressure Pe, the control valve UB is supplied with power and the circulation flow KL is throttled, so that the shortage of the supply pressure Pm relative to the required pressure Pe (i.e., the hydraulic pressure "Pe-Pm") is compensated for by the lower brake unit SB. This complementary control reduces the output of the upper brake unit SA (particularly the upper electric motor MA and the pressure regulating valve UA), so that the required pressure Pe is achieved even when the upper brake unit SA cannot achieve it. As a result, the performance of the anti-skid control is ensured, and the stability of the vehicle JV is reliably maintained.

[0083] <Other embodiments> Other embodiments will be described below. The other embodiments also provide the same effects as those described above (such as the common use of the lower braking unit SB).

[0084] In the above-described embodiment, the required pressure Pe is calculated by the lower brake unit SB and transmitted to the upper brake unit SA. Alternatively, the required pressure Pe may be calculated by the upper brake unit SA. Since signals such as the wheel speed Vw and the yaw rate Yr are input to the lower brake unit SB, the determination of the start / end of anti-skid control and the calculation of each required pressure Po corresponding to each wheel pressure Pw are performed by the lower brake unit SB. However, since the upper and lower brake units SA and SB share signals via the communication bus BS, the required pressure Pe can be calculated by the upper brake unit SA. Therefore, the required pressure Pe is calculated by either the upper or lower brake unit SA or SB based on the required pressure Po.

[0085] 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.

[0086] 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).

[0087] 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.

[0088] 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").

[0089] <Summary of the embodiment> An embodiment of the brake control device SC will be summarized below. The brake control device SC includes an upper brake unit SA that electrically outputs a supply pressure Pm in accordance with a braking demand Bs, and a lower brake unit SB that is disposed between the upper brake unit SA and a plurality of wheel cylinders CW and that individually adjusts the supply pressure Pm for each of the plurality of wheel cylinders CW to output a wheel pressure Pw. In the lower brake unit SB, the supply pressure Pm is individually increased or decreased for each wheel cylinder CW, thereby enabling individual adjustment of the wheel pressure Pw.

[0090] When anti-skid control is performed by the lower brake unit SB, the required pressure Pe required to perform the anti-skid control is supplied from the upper brake unit SA. That is, the supply pressure Pm output from the upper brake unit SA is increased until it reaches the required pressure Pe. For example, when the required braking amount Bs is "0" and anti-skid control is not being performed, the operation of both the upper and lower brake units SA and SB is stopped, and wheel pressure Pw is not generated. In this state, when anti-skid control is performed by the lower brake unit SB, not only is the lower brake unit SB operated, but the upper brake unit SA is also operated to supply the required pressure Pe. Here, anti-skid control is a control that automatically and individually adjusts (i.e., increases and decreases) the wheel pressure Pw to control the yaw moment acting on the vehicle JV, suppress oversteer and understeer, and optimize steering characteristics.

[0091] The required pressure Pe is determined based on the maximum value Max[Po] of the required pressures Po required for each of the plurality of wheel cylinders CW. For example, the lower braking unit SB calculates the required pressure Po for each of the plurality of wheel cylinders CW based on the wheel speed Vw, steering operation amount Sk, yaw rate Yr, lateral acceleration Gy, etc. Then, the required pressure Pe is determined based on the maximum value of the plurality of required pressures Po.

[0092] In the brake control device SC, the pressure that serves as the basis for anti-skid control (i.e., the required pressure Pe) is generated by the upper brake unit SA. The rated output of the upper brake unit SA is sufficient for anti-skid control because it is designed to handle sudden braking (braking that generates rapid, high wheel pressure). Because the required pressure Pe is supplied by the upper brake unit SA, the lower brake unit SB (particularly the output of the lower electric motor MB and the discharge volume of the lower fluid pump QB) does not require a significant rated output, even if the vehicle's weight, moment of inertia, etc. are large. In other words, the rating of the lower brake unit SB can be set independently of the vehicle's specifications (weight, moment of inertia, center of gravity height, etc.). This allows for the commonality of the lower brake unit SB that performs anti-skid control.

[0093] In the brake control device SC, if the upper brake unit SA cannot increase the supply pressure Pm to the required pressure Pe, the lower brake unit SB executes complementary control. In complementary control, the wheel pressure Pw is increased by the amount of the deviation hP (hydraulic pressure deviation) between the supply pressure Pm and the required pressure Pe. For example, the lower brake unit SB is equipped with an electric motor MB, a fluid pump QB, and a control valve UB that increases the supply pressure Pm by throttling the circulating flow KL discharged from the fluid pump QB. In complementary control, power is supplied to the electric motor MB, and the circulating flow KL of brake fluid BF is discharged from the fluid pump QB. Then, a supply current Ib determined based on the hydraulic pressure deviation hP is supplied to the control valve UB. As a result, the wheel pressure Pw is increased from the supply pressure Pm by the amount of the hydraulic pressure deviation hP. In other words, if the upper brake unit SA cannot supply the supply pressure Pm corresponding to the required pressure Pe, the hydraulic pressure deviation hP, which is the shortage, is increased in the lower brake unit SB. Because the required pressure Pe is reliably achieved by the complementary control, the performance of the anti-skid control is ensured even if the output of the upper brake unit SA decreases. Note that if the upper brake unit SA can increase the supply pressure Pm to the required pressure Pe, the control valve UB is not energized, but the electric motor MB is. This is because the brake fluid BF that has flowed into the pressure regulating reservoir RB is discharged from the pressure regulating reservoir RB in order to reliably reduce the wheel pressure Pw. [Explanation of symbols]

[0094] SC...brake control device, BP...brake operation 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 regulating unit, UA...pressure regulating valve, MA, MB...upper and lower electric motors, QA, QB...upper and lower fluid pumps, PM...supply pressure sensor, UB...control valve, VI...inlet valve, VO...outlet valve, Po...required pressure, Pe...demand pressure (target value based on Po), Ps...command pressure (target value according to Bs), Pt...target pressure, Pu...servo pressure, Pm...supply pressure (detected value of PM), Pw...wheel pressure, hP...hydraulic pressure deviation (difference between Pt and Pm), Bs...demanded braking amount, Ba...braking operation amount, Gs...demanded deceleration.

Claims

1. an upper braking unit that electrically outputs a supply pressure in accordance with a braking demand; a lower braking unit disposed between the upper braking unit and a plurality of wheel cylinders, the lower braking unit individually adjusting the supply pressure to each of the plurality of wheel cylinders and outputting wheel pressure; In a braking control device for a vehicle, the upper braking unit includes an upper controller and an upper actuator that is controlled by the upper controller to electrically output the supply pressure; the lower braking unit includes a lower controller and a lower actuator that is controlled by the lower controller to individually adjust the wheel pressures of the plurality of wheel cylinders; the upper controller and the lower controller are capable of communicating with each other via a communication bus; When the lower braking unit performs anti-skid control, the lower controller determines a required pressure necessary for executing the anti-skid control based on a maximum value of the required pressures required for each of the plurality of wheel cylinders, and transmits the required pressure to the upper controller via the communication bus; The upper controller calculates the command pressure so that the value increases as the braking request amount increases, determines the larger of the requested pressure and the command pressure received via the communication bus as the target pressure, and operates the upper actuator so that the supply pressure becomes the target pressure.

2. 2. The vehicle brake control device according to claim 1, When the lower braking unit executes anti-skid control, if the upper braking unit cannot increase the supply pressure to the required pressure, The lower controller operates the lower actuator so that the wheel pressure increases by an amount corresponding to a deviation between the supply pressure and the demand pressure.

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