Vehicle braking control system

Abstract

To provide a braking control device of a vehicle constituted of two braking units, which can improve anti-lock brake control.SOLUTION: A braking control device of a vehicle comprises: an upper braking unit that outputs supply pressure (Pm) by making a pressure-adjusting valve squeeze circulation flow ejected by a fluid pump that is driven with an electric motor; and a lower braking unit, arranged among the upper braking unit and wheel cylinders, which adjusts the supply pressure (Pm) and outputs wheel pressure to the wheel cylinder. The upper braking unit makes a rotation speed of the electric motor higher when the lower braking unit executes anti-lock brake control.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

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

[0003] By the way, the applicant has developed a braking control device as described in Patent Document 2. The device of Patent Document 2 is composed of two upper and lower braking units. In the upper braking unit, the braking fluid discharged by the fluid pump driven by the electric motor is adjusted to the regulated hydraulic pressure (also referred to as "servo pressure"). Then, the input hydraulic pressure (also referred to as "supply pressure") adjusted by the regulated hydraulic pressure is transmitted as wheel pressure to the wheel cylinder via the lower braking unit. The anti-lock brake control is executed in the lower braking unit, but a situation may occur where its performance is insufficient. The braking control device is required to address this.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present invention is to provide a vehicle braking control device composed of two braking units that can improve the performance of anti-lock brake control. [Means for solving the problem]

[0006] The vehicle braking control device (SC) according to the present invention comprises: an upper braking unit (SA) that outputs a supply pressure (Pm) by throttling the circulating flow (KN) discharged by a fluid pump (QA) driven by an electric motor (MA) using a pressure regulating valve (UA); and a lower braking unit (SB) that is positioned between the upper braking unit (SA) and a wheel cylinder (CW) and adjusts the supply pressure (Pm) to output wheel pressure (Pw) to the wheel cylinder (CW). The upper braking unit (SA) increases the rotational speed (Na) of the electric motor (MA) when the lower braking unit (SB) performs anti-lock brake control. With the above configuration, when anti-lock brake control is performed in the lower braking unit SB, the amount of brake fluid supplied from the upper braking unit SA to the lower braking unit SB is increased, thereby improving the performance of the anti-lock brake control.

[0007] In the vehicle braking control device (SC) according to the present invention, the upper braking unit (SA) determines the amount of increase (Nz) of the rotational speed (Na) based on the increasing gradient (kP) of the wheel pressure (Pw) in the anti-lock brake control. With the above configuration, the rotational speed Na of the electric motor MA is increased only to the extent necessary for performing the anti-lock brake control. This improves the performance of the anti-lock brake control and reduces the power consumption of the electric motor MA of the upper braking unit SA. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram illustrating the overall configuration of a vehicle joint venture (JV) equipped with the braking control device SC according to the present invention. [Figure 2] This is a schematic diagram illustrating an example configuration of the upper braking unit SA. [Figure 3] This is a schematic diagram illustrating an example configuration of the lower braking unit SB. [Figure 4] This is a block diagram illustrating the drive control of the pressure regulating valve UA. [Figure 5] This is a block diagram illustrating the drive control of the upper electric motor MA. [Modes for carrying out the invention]

[0009] <Symbols for constituent components, etc., and subscripts at the end of the symbols> In the following explanation, components, calculation processes, signals, characteristics, and values ​​that are denoted by the same symbol, such as "CW," represent the same function. The subscripts "f" and "r" at the end of the symbols related to each wheel are general symbols indicating whether they relate to the front or rear wheel system. For example, a wheel cylinder CW provided on each wheel is written as "front wheel cylinder CWf" and "rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" at the end of the symbols may be omitted. When the subscripts "f" and "r" are omitted, each symbol represents a general term. For example, "CW" is a general term for the 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 further from the wheel cylinder CW) is referred to as the "upper part," and the side closer to the wheel cylinder CW (the side further from the master cylinder CM) is referred to as the "lower part." Furthermore, in the circulating flows KN and KL of the brake fluid BF, the side closer to the discharge section of the fluid pumps QA and QB (the side further from the suction section) is referred to as the "upstream side," and the side closer to the suction section of the fluid pumps QA and QB (the side further from the discharge section) is referred to as the "downstream side."

[0011] The upper actuator YA (also called the "upper fluid unit") of the upper braking unit SA, the lower actuator YB (also called the "lower fluid unit") of the lower braking unit SB, and the wheel cylinder CW are connected by a fluid passage (connecting passage HS). Furthermore, various components (UA, etc.) are connected by fluid passages in the upper and lower actuators YA and YB. Here, the "fluid passage" is a path for moving the braking fluid BF, and includes piping, flow paths within actuators, hoses, etc. In the following explanation, the connecting passage HS, return passage HK, return passage HL, reservoir passage HR, input passage HN, servo passage HV, pressure reducing passage HG, etc., are fluid passages.

[0012] <Vehicle joint venture equipped with a braking control system (SC)> Referring to the schematic diagram in Figure 1, the overall configuration of a vehicle JV equipped with the braking control device SC according to the present invention will be described. The vehicle JV is equipped with a driver assistance device DS so as to perform control ("automatic braking control") that automatically decelerates and stops the vehicle via the braking control device SC, either on behalf of the driver or assisting the driver. The driver assistance device DS consists of a distance sensor OB and a control unit ED for the driver assistance device (also called a "driver assistance controller"). The distance sensor OB detects the distance Ob (relative distance) between the vehicle JV and an object (other vehicle, fixed object, person, bicycle, stop line, sign, signal, etc.) in front of the vehicle JV, and inputs this distance to the driver assistance controller ED. Based on the relative distance Ob, the driver assistance controller ED calculates the required deceleration Gs for automatically stopping the vehicle JV. The required deceleration Gs is the target value of the vehicle deceleration degree for executing automatic braking control. The required deceleration Gs is output to the communication bus BS.

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

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

[0015] The vehicle JV is equipped with various sensors (BA, etc.) listed below. The detection signals (Ba, etc.) from these sensors are input to controllers EA and EB and used for various control purposes. - A braking amount sensor BA is provided to detect the operating amount Ba ("braking amount") of the braking operating member BP. For example, as the braking amount sensor BA, an operating displacement sensor SP is provided to detect the operating displacement Sp of the braking operating member BP. In addition, a simulator pressure sensor PZ is used to detect the hydraulic pressure Pz ("simulator pressure") of the stroke simulator SS. In the braking control device SC, the braking amount Ba is a general term for signals representing the driver's intention to brake, and the braking amount sensor BA is a general term for sensors that detect the braking amount Ba. The braking amount Ba is input to the upper controller EA. - A wheel speed sensor VW for detecting the rotational speed Vw (wheel speed) of the wheel WH is provided. The wheel speed Vw is input to the lower controller EB. Then, the lower controller EB calculates the vehicle body speed Vx based on the wheel speed Vw. Further, the lower controller EB performs antilock brake control to prevent the wheel WH from locking and traction control to prevent the drive wheel WH from slipping, based on the wheel speed Vw and the vehicle body speed Vx. - A steering operation amount sensor SK for detecting the operation amount Sk (steering operation amount, for example, steering angle) of the steering operation member SH is provided. For the vehicle JV (particularly, the vehicle body), a yaw rate sensor YR for detecting the yaw rate Yr, a longitudinal acceleration sensor GX for detecting the longitudinal acceleration Gx, and a lateral acceleration sensor GY for detecting the lateral acceleration Gy are provided. These sensor signals are input to the lower controller EB. Then, the lower controller EB performs skid prevention control (ESC: Electronic Stability Control) to suppress oversteer and understeer and stabilize the yawing behavior of the vehicle JV.

[0016] The vehicle JV is equipped with a braking control device SC. In the braking control device SC, a front-rear type (also referred to as "Type II") is adopted as the two braking systems. The actual wheel pressure Pw is adjusted by the braking control device SC.

[0017] The braking control device SC is composed of two braking units SA and SB. The upper braking 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. A lower braking unit SB is arranged between the upper braking unit SA and the wheel cylinder CW. The lower braking 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 the communication bus BS. The "communication bus BS" has a network structure in which a plurality of controllers (control units) are suspended from a communication line. Signal transmission is performed among the plurality of controllers (EA, EB, ED, etc.) via the communication bus BS. That is, the plurality of controllers can transmit signals (detection values, calculation values, control flags, etc.) to the communication bus BS and can receive signals from the communication bus BS.

[0019] <Upper braking unit SA> Referring to the schematic diagram of FIG. 2, a configuration example of the upper braking unit SA will be described. The upper braking unit SA generates a supply pressure Pm in response to an operation of the braking operation member BP (brake pedal). The supply pressure Pm is finally supplied to the wheel cylinder CW via the connection path HS (fluid path) and the 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 regulating unit CA, and an input unit NR.

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

[0022] The tandem-type master cylinder CM contains 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 wheel master chambers Rmf and Rmr (=Rm) are separated by one side of the bottom of the master cylinder CM and by the master pistons NM and NS. Furthermore, the interior of the master cylinder CM is 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 with the flange Tu in between. These hydraulic chambers Rmf, Rmr, Ru, and Ro are sealed by a sealing member SL. The pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are equal.

[0023] When not braking, the master pistons NM and NS are in their most retracted position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is in communication with the master reservoir RV. Brake fluid BF is stored inside the master reservoir RV (also called the "atmospheric pressure reservoir"). When the braking operating member BP is operated, the master pistons NM and NS are moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases). This movement disconnects the communication between the master chamber Rm and the master reservoir RV. When the master pistons NM and NS are moved further in the forward direction Ha, the front and rear wheel supply pressures Pmf and Pmr (=Pm) increase from "0 (atmospheric pressure)". As a result, the brake fluid BF, pressurized to supply pressure Pm, is output (pressurized) from the master chamber Rm of the master cylinder CM. Since the supply pressure Pm is the hydraulic pressure of the master chamber Rm, it is also called the "master pressure".

[0024] [Pressure Regulating Unit CA] The pressure regulating unit CA supplies servo pressure Pu to the servo chamber Ru of the apply unit AP. The pressure regulating unit CA consists of an upper electric motor MA, an upper fluid pump QA, and a pressure regulating valve UA.

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

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

[0027] When the electric motor MA is driven and breech fluid BF is discharged from the fluid pump QA, a circulating flow KN (indicated by the dashed arrow) of breech fluid BF is generated in the return channel HK. When the pressure regulating valve UA is fully open (since the pressure regulating valve UA is normally open, this is when it is not energized), the hydraulic pressure Pu (referred to as "servo pressure") between the discharge section of the fluid pump QA and the pressure regulating valve UA in the return channel HK is "0 (atmospheric pressure)". When the amount of current Ia (supply current) supplied to the pressure regulating valve UA is increased, the circulating flow KN (the flow of breech fluid BF circulating in the return channel HK) is restricted by the pressure regulating valve UA. In other words, the flow path of the return channel HK is narrowed by the pressure regulating valve UA, and the orifice effect of the pressure regulating valve UA is exerted. As a result, the hydraulic pressure Pu upstream of the pressure regulating valve UA increases from "0". In other words, in a circulating flow KN, a pressure difference (differential pressure) is generated between the upstream hydraulic pressure Pu (servo pressure) and the downstream hydraulic pressure (atmospheric pressure) with respect to the pressure regulating valve UA. This differential pressure is regulated by the current Ia supplied to the pressure regulating valve UA.

[0028] The return channel HK is connected to the servo chamber Ru via the servo channel HV (fluid channel) at the point between the discharge section of the fluid pump QA (specifically, the downstream section of the check valve) and the pressure regulating valve UA. Thus, the servo pressure Pu is introduced (supplied) to the servo chamber Ru. An increase in the servo pressure Pu pushes the master pistons NM and NS in the forward direction Ha, and increases the hydraulic pressures Pmf and Pmr (front and rear wheel supply pressures) in the front and rear wheel master chambers Rmf and Rmr, respectively.

[0029] The front and rear wheel master chambers Rmf and Rmr (=Rm) are connected to the front and rear wheel connecting passages HSf and HSr (=HS). The front and rear wheel connecting passages HSf and HSr are connected to the front and rear wheel cylinders CWf and CWr (=CW) via the lower braking unit SB (particularly the lower actuator YB). Therefore, the front and rear wheel supply pressures Pmf and Pmr are supplied from the upper braking 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 braking control member BP to achieve regenerative cooperative control, but creates a state in which no wheel pressure Pw is generated. "Regenerative cooperative control" is a system that, during braking, makes the kinetic energy of the vehicle JV efficiently recovered as electrical energy by the motor / generator (not shown) by coordinating the friction braking force Fm (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to the motor / generator). The input unit NR consists of an input cylinder CN, an input piston NN, an introduction valve VA, an opening 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. The input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to the braking pedal BP via a clevis (U-shaped link) so as to be linked to the braking pedal 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 braking coordinated control is achieved by adjusting the separation distance Ks with 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 the input path HN (fluid path). The input path HN is equipped with a normally closed inlet valve VA. Between the inlet valve VA and the reaction chamber Ro, the input path HN is connected to the master reservoir RV via the reservoir path HR. The reservoir path HR is equipped with a normally open valve VB. The inlet valve VA and the open valve VB are on / off type solenoid valves. Between the inlet valve VA and the reaction chamber Ro, the stroke simulator SS (also simply called the "simulator") is connected to the input path HN.

[0033] If 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 opened. Closing the inlet valve VA seals the input chamber Rn and locks the fluid. As a result, the master pistons NM and NS are displaced together with the braking operating member BP. Also, opening the release valve VB connects the simulator SS to the master reservoir RV. If 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. As a result, the master pistons NM and NS can be displaced separately from the braking operating member BP. In this case, the input chamber Rn is connected to the stroke simulator SS, so the operating force Fp of the braking operating member BP is generated by the simulator SS. A simulator pressure sensor PZ is provided in the input path HN between the inlet valve VA and the reaction force chamber Ro to detect the fluid pressure Pz (simulator pressure) in the simulator SS. Furthermore, since the simulator pressure Pz is also the internal pressure of the input chamber Rn, it is also a state variable that represents the operating force Fp of the braking operating member BP.

[0034] The state in which the master pistons NM and NS and the braking operating member BP are displaced separately (when the solenoid valves VA and VB are energized) is referred to as "Mode 1 (or By-Wire Mode)". In Mode 1, the braking control device SC functions as a brake-by-wire type device (i.e., a device in which friction braking force Fm can be generated independently of the driver's braking operation). Therefore, in Mode 1, the wheel pressure Pw is generated independently of the operation of the braking operating member BP. On the other hand, the state in which the master pistons NM and NS and the braking operating member BP are displaced together (when the solenoid valves VA and VB are not energized) is referred to as "Mode 2 (or Manual Mode)". In Mode 2, the wheel pressure Pw is linked to the driver's braking operation. The input unit NR selects one of the two operating modes, Mode 1 (By-Wire Mode) or Mode 2 (Manual Mode), depending on whether or not power is supplied to the intake 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 consists of a microprocessor MP and a drive circuit DR. The upper controller EA is connected to the communication bus BS so that it can share signals (detected values, calculated values, control flags, etc.) with other controllers (EB, ED, etc.).

[0036] The upper controller EA receives the braking operation amount Ba as input. The braking operation amount Ba is a general term for the state quantity that represents the amount of operation of the braking operation member BP. The detection signal Sp (operational displacement) from the operation displacement sensor SP and the detection signal Pz (simulator pressure) from the simulator pressure sensor PZ are directly input to the upper controller EA as the braking operation amount Ba from the braking operation amount sensor BA. In addition, the upper controller EA receives the supply pressure Pm, requested deceleration Gs, etc. via the communication bus BS. The "supply pressure Pm" is the output pressure of the upper actuator YA. The supply pressure Pm is detected by the supply pressure sensor PM located on the lower actuator YB and transmitted from the lower controller EB. The requested deceleration Gs is the requested value for automatic braking control, calculated by the driver support controller ED and transmitted from the driver support controller ED.

[0037] The upper controller EA (specifically the microprocessor MP) is programmed with a pressure regulation control algorithm. Pressure regulation control is the control for adjusting the supply pressure Pm (ultimately the wheel pressure Pw). Pressure regulation control is performed based on the braking operation amount Ba (operating displacement Sp, simulator pressure Pz), the requested deceleration Gs, the supply pressure Pm, etc. Here, the braking operation amount Ba and the requested deceleration Gs are collectively referred to as the "braking request amount Bs". The braking request amount Bs is an input signal to instruct (request) the generation of the supply pressure Pm (and consequently, the wheel pressure Pw that should be generated by the braking 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 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) for detecting the rotation angle Ka (referred to as "motor rotation angle") of the rotor of the electric motor MA is provided. Based on the motor rotation angle Ka, the motor rotation speed Na is calculated.

[0039] 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. 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. 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 actual rotation speed Na increases, and if "Nt < Na", the motor current Im is decreased so that the actual 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. Then, 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> Referring to the schematic diagram in Figure 3, an example configuration of the lower braking unit SB of the braking control device SC will be described. The lower braking unit SB is a general-purpose unit (device) for performing anti-lock brake control, traction control, anti-skid control, etc.

[0041] The lower braking unit SB receives front and rear wheel supply pressures Pmf and Pmr (=Pm) from the upper braking unit SA. The lower braking unit SB then adjusts (increases or decreases) the front and rear wheel supply pressures Pmf and Pmr, and finally outputs them 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 consists of the lower actuator YB and the lower controller EB.

[0042] ≪Lower Actuator YB≫ The lower actuator YB is located in the connecting passage HS between the upper actuator YA and the wheel cylinder CW. The lower actuator YB consists of 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.

[0043] Front and rear wheel control valves UBf and UBr (=UB) are installed in the front and rear wheel connecting passages HSf and HSr (=HS). Control valve UB is a normally open linear solenoid valve (differential pressure valve), similar to the pressure regulating valve UA. Control valve UB allows the wheel pressure Pw to be increased individually in the front and rear wheel systems from the supply pressure Pm.

[0044] Front and rear wheel supply pressure sensors PMf and PMr (=PM) are provided to detect the actual hydraulic pressures Pmf and Pmr (front and rear wheel supply pressures) supplied from the upper actuator YA (particularly the front and rear wheel master chambers Rmf and Rmr). The supply pressure sensor PM is also called the "master pressure sensor" and is built into the lower actuator YB. The signals for the front and rear wheel supply pressures Pmf and Pmr (=Pm) are directly input to the lower controller EB and output to the communication bus BS. Since the front wheel supply pressure Pmf and the rear wheel supply pressure Pmr are essentially the same, either the front or rear wheel supply pressure sensors PMf or PMr may be omitted. For example, in a configuration where 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] The upper part of the front and rear wheel control valves UBf and UBr (the part of the communication passage HS closer to the upper actuator YA) and the lower part of the front and rear wheel control valves UBf and UBr (the part of the communication passage HS closer to the wheel cylinder CW) are connected by the front and rear wheel return passages HLf and HLr. The front and rear wheel return passages HLf and HLr are equipped with the front and rear lower fluid pumps QBf and QBr (=QB) and the front and rear pressure regulating reservoirs RBf and RBr (=RB). The lower fluid pump QB is driven by the lower electric motor MB.

[0046] When the lower electric motor MB (also simply called the "electric motor") is driven, the lower fluid pump QB (also simply called the "fluid pump") draws the brake fluid BF from the top of the control valve UB and discharges it from the bottom of the control valve UB. This generates a circulating flow KL of brake fluid BF in the connecting passage HS and the return passage HL, including the fluid pump QB, the control valve UB, and the pressure regulating reservoir RB (i.e., the front and rear wheel circulating flows KLf and KLr, indicated by the dashed arrows). When the flow path of the connecting passage HS is narrowed by the control valve UB, and the circulating flow KL of brake fluid BF is restricted, the orifice effect causes the fluid pressure Pq ("regulating pressure") at the bottom of the control valve UB to increase from the fluid pressure Pm (supply pressure) at the top of the control valve UB. In other words, in the circulating flow KL, the hydraulic pressure difference (differential pressure) between the downstream hydraulic pressure Pm (supply pressure) and the upstream hydraulic pressure Pq (regulating pressure) is regulated by the control valve UB. Regarding the relationship between the supply pressure Pm and the regulating pressure Pq, the regulating pressure Pq is greater than or equal to the supply pressure Pm (i.e., "Pq ≥ Pm"). As explained above, the mechanism for generating the regulating pressure Pq in the lower actuator YB is the same as the mechanism for generating the servo pressure Pu in the upper actuator YA.

[0047] Inside the lower actuator YB, the front and rear wheel connecting passages HSf and HSr are each branched into two, and connected to the front and rear wheel cylinders CWf and CWr, respectively. To allow individual adjustment of each wheel pressure Pw, a normally open inlet valve VI and a normally closed outlet valve VO are provided for each wheel cylinder CW. Specifically, the inlet valve VI is located in the branched connecting passage HS (i.e., on the side of the connecting passage HS closer to the wheel cylinder CW). The connecting passage HS is connected to the pressure regulating reservoir RB via a pressure reducing passage HG (fluid passage) at the lower part of the inlet valve VI (the part of the connecting passage HS closer to the wheel cylinder CW). The outlet valve VO is located in the pressure reducing passage HG. On / off type solenoid valves are used as the inlet valve VI and the outlet valve VO. 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 enables the execution of anti-lock braking control, traction control, and anti-skid control, among other functions.

[0048] ≪Lower Controller EB≫ The lower actuator YB is controlled by the lower controller EB. The lower controller EB, like the upper controller EA, consists of a microprocessor MP and a drive circuit DR. Since the lower controller EB is connected to the communication bus BS, the upper controller EA and the lower controller EB can share signals via the communication bus BS.

[0049] The lower controller EB (particularly the microprocessor MP) receives inputs of wheel speed Vw, steering input Sk, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy. The lower controller EB performs anti-lock brake control, traction control, and anti-skid control. Specifically, the lower controller EB drives the lower electric motor MB and various solenoid valves (UB, etc.) that constitute the lower actuator YB so that these controls can be performed. The drive circuit DR of the lower controller EB is configured with an H-bridge circuit using switching elements (e.g., MOS-FETs) to drive the lower electric motor MB. The drive circuit DR is also equipped with switching elements to drive various solenoid valves (UB, etc.). Based on the control algorithm programmed into the microprocessor MP, the drive signal Ub for the control valve UB, the drive signal Vi for the inlet valve VI, the drive signal Vo for the outlet valve VO, and the drive signal Mb for the lower electric motor MB are calculated. Then, based on the drive signal (Ub, etc.), the drive circuit DR controls the lower electric motor MB and the solenoid valves UB, VI, and VO.

[0050] In the lower controller EB, the vehicle speed Vx is calculated based on the wheel speed Vw. When anti-lock brake control (also called "ABS control") is performed, the deceleration slip (the difference between the vehicle speed Vx and the wheel speed Vw), which represents the degree of slip of each wheel WH, is calculated based on the vehicle speed Vx and the wheel speed Vw. If the deceleration slip exceeds a control threshold (a predetermined value set in advance), the wheel pressure Pw is adjusted to prevent wheel lock. In other words, the lower controller EB controls the inlet valve VI and the outlet valve VO to individually decrease, increase, and maintain the wheel pressure Pw for each wheel cylinder CW.

[0051] If power is not supplied to the inlet valve VI and the outlet valve VO, and their operation is stopped, the inlet valve VI is opened and the outlet valve VO is closed. In this state, the wheel pressure Pw is equal to the regulated pressure Pq. When ABS control is performed, the wheel pressure Pw is independently adjusted for each wheel cylinder CW by driving 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. The inflow of brake fluid BF into the wheel cylinder CW is prevented, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RB, so the wheel pressure Pw is decreased. To increase the wheel pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. The outflow of brake fluid BF to the pressure regulating reservoir RB is prevented, and the regulated pressure Pq from the pressure regulating valve UB is supplied to the wheel cylinder CW, so the wheel pressure Pw is increased. Here, the upper limit of the increase in wheel pressure Pw is the regulating pressure Pq. In order to maintain the wheel pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidically sealed, the wheel pressure Pw is maintained at a constant level.

[0052] In the lower braking unit SB, the reduction of wheel pressure Pw under ABS control is achieved by moving brake fluid BF from the wheel cylinder CW to the pressure regulating reservoir RB. Since the volume of the pressure regulating reservoir RB is finite, the electric motor MB is driven when ABS control is performed to prevent it from becoming full. When the electric motor MB is driven, the fluid pump QB pumps the brake fluid BF that has flowed into the pressure regulating reservoir RB out of the reservoir RB and returns it to the top of the inlet valve VI. This allows the wheel pressure Pw to be continuously reduced.

[0053] <Drive control of pressure regulating valve UA> Referring to the block diagram in Figure 4, an example of the drive control process for the pressure regulating valve UA will be described. This process is performed by the upper controller EA. The servo pressure Pu is adjusted by the pressure regulating valve UA, and ultimately the supply pressure Pm (=Pw) ​​is adjusted. The drive control of the pressure regulating valve UA consists of a target pressure calculation block PT, an instruction current calculation block IS, a hydraulic pressure deviation calculation block PH, a compensation current calculation block IH, and a current feedback control block IF.

[0054] In the target pressure calculation block PT, the target pressure Pt is calculated based on the braking request amount Bs. The "braking request amount Bs" is a collective term for the braking operation amount Ba and the requested deceleration Gs, and is an input for instructing the generation of supply pressure Pm (i.e., the wheel pressure Pw that should be generated by the braking control device SC). The braking request amount Bs is calculated based on the braking operation amount Ba and the requested deceleration Gs. For example, the braking operation amount Ba and the requested deceleration Gs are compared in the dimension of vehicle deceleration, and the larger of the two is determined as the braking request amount Bs. The "target pressure Pt" is a target value corresponding to the supply pressure Pm. The target pressure Pt is calculated to increase as the braking request amount Bs increases, according to the pre-set calculation map Zpt. In other words, the target pressure Pt is determined to increase as the braking request amount Bs increases.

[0055] In the instruction current calculation block IS, the instruction current Is is calculated based on the target pressure Pt and a preset calculation map Zis. The instruction 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. According to the calculation map Zis, the instruction current Is is determined to increase as the target pressure Pt increases. The instruction current calculation block IS corresponds to feedforward control based on the target pressure Pt.

[0056] The hydraulic pressure deviation calculation block PH calculates the deviation hP (referred to as the "hydraulic pressure deviation") between the target pressure Pt and the supply pressure Pm. Specifically, the supply pressure Pm is subtracted from the target pressure Pt to determine the hydraulic pressure deviation hP (i.e., "hP = Pt - Pm").

[0057] In the compensation current calculation block IH, the compensation current Ih is calculated based on the hydraulic pressure deviation hP and a preset calculation map Zih. The indicator current Is is calculated in accordance with 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 (reduce) this error. The compensation current Ih is determined to increase as the hydraulic pressure deviation hP increases, according to the calculation map Zih. Specifically, if the target pressure Pt is greater than the supply pressure Pm and the hydraulic pressure deviation hP is positive, a positive compensation current Ih is determined so that the indicator current Is increases. On the other hand, if the target pressure Pt is less than the supply pressure Pm and the hydraulic pressure deviation hP is negative, a negative compensation current Ih is determined so that the indicator current Is decreases. Here, a dead zone is provided in the calculation map Zih. Furthermore, the compensation current calculation block IH corresponds to feedback control based on the supply pressure Pm.

[0058] A compensation current Ih is added to the instruction current Is to calculate the target current It (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 instruction current Is, which is a feedforward term, and the compensation current Ih, which is a feedback term. Therefore, the drive control of the pressure regulating valve UA consists of feedforward control (processing of the instruction current calculation block IS) and feedback control (processing of the compensation current calculation block IH) in the hydraulic system.

[0059] 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.

[0060] <Drive Control of Electric Motor MA> Before describing an example of controlling the electric motor MA, we will explain the flow rate of the brake fluid BF required for the execution of anti-lock braking control (ABS control). In ABS control, when a tendency for wheel lock (i.e., an increase in deceleration slip) appears in the wheel cylinder CW corresponding to the wheel WH, a pressure reduction is performed to suppress this tendency to lock. The decrease in wheel pressure Pw is achieved by moving the brake fluid BF from the wheel cylinder CW to the pressure regulating reservoir RB through the outlet valve VO. Then, when the deceleration slip (the difference between the vehicle speed Vx and the wheel speed Vw) is decreasing, the pressure is increased in this wheel cylinder CW to restore the braking force that had been reduced. The increase in wheel pressure Pw is achieved by moving the brake fluid BF from the top of the inlet valve VI to the wheel cylinder CW. At this time, the brake fluid BF is supplied to the wheel cylinder CW by being returned from the pressure regulating reservoir RB to the top of the inlet valve VI by the lower fluid pump QB driven by the lower electric motor MB. In addition, brake fluid BF is also supplied to the wheel cylinder CW from the upper braking unit SA. Therefore, if the amount of brake fluid BF supplied from the upper braking unit SA (for example, the amount of fluid per unit time) is insufficient, the amount of brake fluid may be insufficient when the lower braking unit SB performs ABS control. If a fluid shortage occurs, a situation may arise where the rate of increase of wheel pressure Pw (the amount of increase of wheel pressure Pw per unit time, also called the "pressure increase gradient") cannot be obtained sufficiently.

[0061] [First control example related to motor rotation speed Na] In the braking control device SC, when ABS control is not performed, the upper electric motor MA is driven at a preset constant rotational speed na. Then, to avoid the aforementioned fluid shortage, when the lower braking unit SB performs ABS control, the rotational speed Na (motor speed) of the electric motor MA is increased in the upper braking unit SA. Here, the amount of increase Nz in motor speed Na is preset to a predetermined rotational speed nx (constant) to correspond to the fluid volume required for ABS control.

[0062] In the first control example, the upper electric motor MA is driven at a constant rotational speed na before the start of ABS control, and at the start of ABS control (corresponding calculation cycle), the rotational speed is increased from the constant rotational speed na by a predetermined rotational speed nx. For example, information that "ABS control has been performed" is transmitted by the execution flag FA being sent from the lower braking unit SB to the upper braking unit SA via the communication bus BS. The "execution flag FA" is a control flag that indicates whether or not ABS control is being performed in the lower braking unit SB. In the execution flag FA, "0" indicates that ABS control is not being performed, and "1" indicates that ABS control is being performed. In the upper braking unit SA, at the moment the execution flag FA switches from "0" to "1" (the start of ABS control), a predetermined rotational speed nx is added to the target rotational speed Nt of the electric motor MA. Then, the actual motor rotational speed Na is increased by the target rotational speed Nt, which has been increased by the predetermined rotational speed nx. In other words, as a result of controlling "Nt=na+nx", "Na=na+nx" is achieved.

[0063] In the braking control device SC, when ABS control is performed in the lower braking unit, the rotational speed Na of the electric motor MA increases, which increases the amount of brake fluid BF supplied from the upper braking unit SA to the lower braking unit SB (flow rate, which is the amount of fluid per unit time). As a result, the lower braking unit SB has sufficient fluid to perform ABS control. Consequently, a sufficient increase in wheel pressure Pw is ensured in the ABS control, improving its performance.

[0064] [Second control example related to motor rotation speed Na] In ABS control, the wheel pressure Pw is adjusted individually for each wheel cylinder CW, so the amount of brake fluid BF required by the lower braking unit SB depends on the control mode of each wheel cylinder CW. Here, "control mode" includes a pressure-boosting mode that increases the wheel pressure Pw, a holding mode that maintains the wheel pressure Pw at a constant level, and a pressure-reducing mode that decreases the wheel pressure Pw. In the pressure-boosting mode, the movement of brake fluid BF to the wheel cylinder CW is required. However, in the holding mode or pressure-reducing mode, the inlet valve VI is closed, and the movement of brake fluid BF to the wheel cylinder CW is unnecessary. In other words, in ABS control, the amount of brake fluid required by the lower braking unit SB changes moment by moment. Note that the holding mode may be omitted in the control modes. In this configuration of ABS control, either the pressure-boosting mode or the pressure-reducing mode is selected.

[0065] Referring to the block diagram in Figure 5, a second control example of the upper electric motor MA corresponding to the above flow rate change will be described. The second control example of electric motor MA consists of a required pressure calculation block PO, a gradient calculation block KP, a requested flow rate calculation block QE, a liquid volume conversion block PR, a liquid volume deviation calculation block RH, a commanded flow rate calculation block QS, a compensation flow rate calculation block QH, a target flow rate calculation block QT, a target rotational speed calculation block NT, and a rotational speed feedback control block NF. For example, the processing of the required pressure calculation block PO, the gradient calculation block KP, and the requested flow rate calculation block QE is performed by the lower controller EB, while other processing (PR, RH, etc.) is performed by the upper controller EA.

[0066] In the required pressure calculation block PO, the required pressure Po corresponding to the wheel pressure Pw of each wheel cylinder CW is calculated based on the wheel speed Vw. The "required pressure Po" is the target value for each wheel cylinder CW required for the execution of ABS control (anti-lock braking control). By adjusting the wheel pressure Pw based on the required pressure Po, locking of each wheel WH is individually avoided.

[0067] In the required pressure calculation block PO, the vehicle speed Vx is first calculated based on the wheel speed Vw. Then, in ABS control, the slip state of the wheels WH is calculated based on the comparison result between the vehicle speed Vx and the wheel speed Vw of each wheel WH. For example, the deceleration slip, which is the difference between the wheel speed Vw of each wheel WH and the vehicle speed Vx, is determined as the slip state. Then, the required pressure Po is determined for each wheel so that locking of each wheel WH is suppressed.

[0068] In the gradient calculation block KP, the increasing gradient kP (also called the "target increasing gradient") is calculated based on the required pressure Po. Specifically, the required pressure Po in each wheel cylinder CW is differentiated with respect to time, and the respective increasing gradient (the amount of increase in the required pressure Po per unit time) is determined as the increasing gradient kP. Therefore, the "increasing gradient kP" is the target value corresponding to the actual increasing gradient (the amount of increase per unit time) of the wheel pressure Pw. Note that if the required pressure Po is maintained at a constant value, or if the required pressure Po is decreased, the increasing gradient kP is determined to be "0".

[0069] In the requested flow rate calculation block QE, the requested flow rate Qe is calculated based on the increasing gradient kP (target increasing gradient) corresponding to each wheel cylinder CW. The "required flow rate Qe" is the flow rate of brake fluid BF required to perform ABS control. The requested flow rate Qe is determined based on the sum ΣkP (total value) of the increasing gradient kP for each wheel cylinder CW. Specifically, in the requested flow rate calculation block QE, each increasing gradient kP is added together to calculate the total value ΣkP. Then, according to the pre-set calculation map Zqe, the requested flow rate Qe is determined such that it increases as the total value ΣkP increases. The requested flow rate Qe is transmitted from the lower controller EB to the communication bus BS and received by the upper controller EA.

[0070] In the fluid volume conversion block PR, the target fluid volume Rt and the actual fluid volume Rj are calculated based on the target pressure Pt and the supply pressure Pm. In the fluid volume conversion block PR, the target pressure Pt is converted to the target fluid volume Rt and the supply pressure Pm is converted to the actual fluid volume Rj based on the pre-set calculation map Zpr. Here, "target fluid volume Rt" is the amount of fluid required to achieve the target pressure Pt (the volume of brake fluid BF that should be moved to the wheel cylinder CW). Also, "actual fluid volume Rj" is the amount of fluid that has already flowed into the wheel cylinder CW in order to generate the supply pressure Pm (and consequently, the wheel pressure Pw).

[0071] In the liquid volume deviation calculation block RH, the deviation hR (referred to as the "liquid volume deviation") between the target liquid volume Rt and the actual liquid volume Rj is calculated. Specifically, the actual liquid volume Rj is subtracted from the target liquid volume Rt to determine the liquid volume deviation hR (i.e., "hR = Rt - Rj"). The "liquid volume deviation hR" is the target value of the liquid volume that should flow into the wheel cylinder CW in order to achieve the target pressure Pt.

[0072] In the QS flow rate calculation block, the directed flow rate Qs is calculated based on the target liquid volume Rt. Specifically, the directed flow rate Qs is determined by differentiating the target liquid volume Rt with respect to time (i.e., "Qs = d(Rt) / dt"). The QS flow rate calculation block corresponds to feedforward control in flow control.

[0073] In the compensation flow rate calculation block QH, the compensation flow rate Qh is calculated based on the fluid volume deviation hR. Specifically, the fluid volume deviation hR is differentiated with respect to time to determine the compensation flow rate Qh (i.e., "Qh ​​= d(hR) / dt"). The compensation flow rate calculation block QH corresponds to feedback control in flow rate control.

[0074] In the target flow rate calculation block QT, the target flow rate Qt is calculated based on the requested flow rate Qe, the instructed flow rate Qs, and the compensation flow rate Qh. The "target flow rate Qt" is the final target value that is expected to be the flow rate necessary to achieve the target pressure Pt and to perform ABS control in the lower braking unit SB. Specifically, the requested flow rate Qe, the instructed flow rate Qs, and the compensation flow rate Qh are added together to determine the target flow rate Qt (i.e., "Qt = Qe + Qs + Qh"). In other words, if ABS control is performed in the lower braking unit SB, the target flow rate Qt is determined to be larger by the requested flow rate Qe compared to the case where ABS control is not performed. If ABS control is not performed in the lower braking unit SB, "Qe = 0", so the target flow rate Qt is calculated as the sum of the instructed flow rate Qs and the compensation flow rate Qh.

[0075] In the target rotational speed calculation block NT, the target rotational speed Nt is calculated based on the target flow rate Qt. The "target rotational speed Nt" is a target value corresponding to the rotational speed Na (actual value) of the electric motor MA. Specifically, based on the discharge rate of the fluid pump QA (volume of brake fluid BF discharged per revolution), the target rotational speed Nt is determined such that it increases as the target flow rate Qt increases. The target rotational speed Nt takes into account the minimum flow rate of the pressure regulating valve UA and the minimum rotational speed of the electric motor MA. The "minimum flow rate" is the minimum flow rate required for the pressure regulating valve UA to regulate the servo pressure Pu, and is preset. The "minimum rotational speed" is the minimum rotational speed at which the electric motor MA can continue to rotate stably. Taking these factors into consideration, a lower limit rotational speed nt (a predetermined value preset) is set for the target rotational speed Nt. Therefore, if the target rotational speed Nt calculated based on the target flow rate Qt is greater than or equal to the lower limit rotational speed nt, the restriction by the lower limit rotational speed nt is not applied, and the calculated target rotational speed Nt is used as is. On the other hand, if the target rotational speed Nt calculated based on the target flow rate Qt is less than the lower limit rotational speed nt, the target rotational speed Nt is determined to be the lower limit rotational speed nt (i.e., "Nt = nt").

[0076] In the rotational speed feedback control block NF, based on the target rotational speed Nt (target value) and the motor rotational speed Na (actual value), the drive signal Ma is calculated so that the motor rotational speed Na approaches and matches the target rotational speed Nt. Here, the motor rotational speed Na is calculated based on the detected 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 rotational speed Na. In the rotational speed feedback control block NF, if "Nt > Na", the drive signal Ma is determined so that the actual rotational speed Na increases. On the other hand, if "Nt < Na", the drive signal Ma is determined so that the actual rotational speed Na decreases. That is, in the rotational speed feedback control block NF, feedback control related to the motor rotational speed is executed.

[0077] Summarize the second control example of the motor rotational speed Na. In the braking control device SC, the flow rate (liquid volume per unit time) of the brake fluid BF required for ABS control (antilock brake control) is calculated as the required flow rate Qe. Then, based on the required flow rate Qe, the rotational speed Na of the electric motor MA is controlled. The second control example of the motor rotational speed Na based on the required flow rate Qe is executed as follows. (1) The required pressure Po, which is the target value of the wheel pressure Pw in ABS control, is calculated for each wheel cylinder CW. (2) The required pressure Po of each wheel cylinder CW is differentiated with respect to time to calculate the target increase gradient kP in each wheel cylinder CW. The increase gradient kP is the increase amount of the required pressure Po per unit time when the wheel pressure Pw is increased (i.e., the pressure increase mode). Therefore, when the required pressure Po is maintained constant (i.e., the holding mode) and when the required pressure Po is decreased (i.e., the pressure decrease mode), the increase gradient kP is determined to be "0". (3) The increase gradients kP for each wheel cylinder CW are all added together. Then, based on the total value ΣkP (sum) of the increase gradients kP, the required flow rate Qe is calculated. Specifically, the required flow rate Qe is determined to increase as the total value ΣkP increases. That is, the required flow rate Qe is the necessary and minimum flow rate in the execution of ABS control. (4) Based on the requested flow rate Qe, the motor speed Na is controlled so that the larger the requested flow rate Qe, the greater the motor speed Na. In other words, the increase amount Nz of the motor speed Na is determined based on the increase gradient kP, and the motor speed Na is increased. Note that the requested flow rate Qe is set to "0" when ABS control is not performed and is calculated at the start of ABS control. For this reason, the motor speed Na starts increasing at the start of ABS control (for example, when the execution flag FA input to the target speed calculation block NT switches from "0" to "1").

[0078] As explained above, in the upper braking unit SA, the increase in rotational speed Na of the electric motor MA, Nz, is determined based on the target increase gradient kP for the wheel pressure Pw in ABS control. When ABS control is performed, the increase in motor rotational speed Na, Nz, may be determined to a predetermined rotational speed nx, as in the first control example. However, a certain margin is expected in the predetermined rotational speed nx. Therefore, by being determined based on the required flow rate Qe (i.e., increase gradient kP), the motor rotational speed Na is increased only by the amount necessary for ABS control. Since the increase in motor rotational speed Na is necessary and minimal, the power consumption of the upper electric motor MA is suppressed. In other words, in the second control example, the flow rate of the brake fluid BF in the upper braking unit SA is increased only by the amount necessary for the execution of ABS control in the lower braking unit SB. This ensures the increase gradient (actual value) of the wheel pressure Pw, improves the performance of ABS control, and reduces the power consumption of the electric motor MA.

[0079] <Other Embodiments> Other embodiments will be described below. Similar effects (such as improved ABS control performance) will be achieved in these other embodiments as well.

[0080] In the above embodiment, the increasing gradient kP and the requested flow rate Qe were calculated by the lower braking unit SB and transmitted to the upper braking unit SA. Alternatively, the requested flow rate Qe, or "increasing gradient kP and requested flow rate Qe," may be calculated by the upper braking unit SA. Since the lower braking unit SB receives signals such as wheel speed Vw, the determination of the start / end of ABS control and the calculation of each required pressure Po corresponding to each wheel pressure Pw are performed by the lower braking unit SB. However, since signals are shared between the upper and lower braking units SA and SB via the communication bus BS, each calculation is performed as follows: The required pressure Po and increasing gradient kP are calculated by the lower braking unit SB, and the requested flow rate Qe is calculated by the upper braking unit SA. Alternatively, the required pressure Po is calculated by the lower braking unit SB, and the increasing gradient kP and requested flow rate Qe are calculated by the upper braking unit SA. Therefore, the increasing gradient kP is calculated in one of the upper, lower braking units SA or SB, and the required flow rate Qe is also calculated in one of the upper, lower braking units SA or SB.

[0081] In the above-described embodiment, in the control of the electric motor MA, a target rotational speed Nt is calculated, and the actual rotational speed Na is controlled based on this target rotational speed Nt. A correlation exists between the motor rotational speed Na and the current Im supplied to the electric motor MA. Therefore, in the control of the electric motor MA, the rotational speed Na of the electric motor MA may be controlled by adjusting the motor current Im without calculating the target rotational speed Nt. In this configuration, when ABS control is performed, the motor current Im is increased by a predetermined current im (a preset constant), and the motor rotational speed Na is increased.

[0082] In the above-described embodiment, a front-rear type was used as the two braking systems. Alternatively, a diagonal type (also called "X type") may be used as the two braking systems. 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. However, in configurations employing two-system pressure regulation, the braking system is limited to a front-rear type.

[0083] In the above-described embodiment, a tandem type master cylinder CM was exemplified. Alternatively, a single type master cylinder CM may be used. 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 same supply pressures Pmf and Pmr (=Pm) are output from the master cylinder CM.

[0084] In a configuration employing a single-type master cylinder CM, 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 the front wheel supply pressure Pmf to the front wheel cylinder CWf as the front wheel pressure Pwf. On the other hand, the pressure regulating unit CA outputs the servo pressure Pu to the rear wheel cylinder CWr as the rear wheel supply pressure Pmr.

[0085] In the above embodiment, 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 to be equal in the apply unit AP. The master area rm and the servo area ru do not have to be equal. In configurations where the master area rm and the servo area ru are different, the conversion calculation between the supply pressure Pm and the servo pressure Pu can be performed based on the ratio of the servo area ru to the master area rm (i.e., the conversion is based on "Pm·rm=Pu·ru").

[0086] <Summary of Embodiments> The following describes an embodiment of the braking control device SC. 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 a supply pressure Pm according to the braking requirement Bs (e.g., braking operation amount Ba, required deceleration Gs). Specifically, the upper braking unit SA outputs the supply pressure Pm by throttling the circulating flow KN discharged by the fluid pump QA, which is driven by the electric motor MA, with a pressure regulating valve UA. The other is the lower braking unit SB, which is provided between the upper braking unit SA and a plurality of wheel cylinders CW. The lower braking unit SB is a general-purpose unit that performs ABS control, etc. The lower braking unit SB can output wheel pressure Pw by individually adjusting (increasing or decreasing) the supply pressure Pm for each of the plurality of wheel cylinders CW. 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.). In the lower braking unit SB, the wheel pressure Pw is adjusted for each wheel cylinder CW by controlling the electric motor MB and multiple solenoid valves. Based on the wheel speed Vw, the lower braking unit SB performs anti-lock brake control to prevent wheel lock.

[0087] In the braking control device SC, when anti-lock brake control is performed in the lower braking unit SB, the rotational speed Na of the electric motor MA in the upper braking unit SA is increased. The increase in motor rotational speed Na increases the flow rate of the brake fluid BF supplied from the upper braking unit SA to the lower braking unit SB. In the lower braking unit SB, a sufficient amount of brake fluid necessary for ABS control is secured, thus improving its performance. Specifically, a sufficient increase in wheel pressure Pw per unit time (actual increase gradient) in the ABS control's pressure boosting mode is ensured.

[0088] In the upper braking unit SA, the increase in motor speed Na Nz is determined based on the target increase gradient kP related to the wheel pressure Pw in anti-lock brake control. Here, the target increase gradient kP is a target value corresponding to the actual increase gradient of the wheel pressure Pw. The target increase gradient kP is calculated based on the required pressure Po (a target value corresponding to the wheel pressure Pw) required for anti-lock brake control. Because the increase in motor speed Na Nz is determined based on the target increase gradient kP, the increase in motor speed Na is kept to the minimum necessary for the execution of anti-lock brake control. This improves the performance of anti-lock brake control and reduces the power consumption of the electric motor MA. [Explanation of Symbols]

[0089] 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 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 (target value related to Pw in ABS control), kP... Required pressure gradient (time derivative of Po), 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), Qe... Required flow rate (flow rate required for ABS control), Qt... Target flow rate, Na... Motor rotation speed (actual value), Nt... Target rotation speed, Nz... Increase in Na (or Nt), Bs... Braking amount required, Ba... Braking operation amount, Gs... Required deceleration, Vw... Wheel speed, Vx... Vehicle speed, FA... Execution flag.

Claims

[Claim 1] An upper braking unit that outputs supply pressure by restricting the circulating flow discharged by a fluid pump driven by an electric motor using a pressure regulating valve, A lower braking unit is positioned between the upper braking unit and the wheel cylinder, and adjusts the supply pressure to output wheel pressure to the wheel cylinder. In a braking control device for a vehicle equipped with, The upper braking unit increases the rotational speed of the electric motor when the lower braking unit performs anti-lock brake control. The upper braking unit is a vehicle braking control device that determines the amount of increase in rotational speed based on the increasing gradient of the wheel pressure in the anti-lock brake control.

Images