Vehicle braking control system

Abstract

To provide a braking control device of a vehicle constituted of two braking units, which is configured so that liquid pressure is suppressed from varying when a lower braking unit applies pressure.SOLUTION: A braking control device of a vehicle comprises: an upper braking unit (SA) that applies pressure to supply pressure (Pm) by making a pressure-adjusting valve (UA) squeeze circulation flow (KN) ejected by a fluid pump (QA) that is driven with an electric motor (MA); and a lower braking unit (SB), arranged among the upper braking unit (SA) and wheel cylinders (CW), which applies pressure to the supply pressure (Pm) and outputs wheel pressure (Pw) to the wheel cylinders (CW). The upper braking unit (SA) makes a rotation speed (Na) of the electric motor (MA) lower when the lower braking unit (SB) applies pressure to the wheel pressure (Pw) in comparison with when the lower braking unit (SB) does not apply pressure to the wheel pressure (Pw).SELECTED DRAWING: Figure 2

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 liquid volume of the wheel brake based on the target hydraulic pressure, and also determines the actual liquid 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 liquid volume and the actual liquid 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 parts: an upper fluid unit and a lower fluid unit. In the upper fluid unit, the braking fluid discharged by the fluid pump driven by an electric motor is adjusted to a regulated hydraulic pressure (also referred to as "servo pressure"). Then, the input hydraulic pressure (also referred to as "supply pressure") adjusted by the servo pressure is transmitted as wheel pressure to the wheel cylinder via the lower fluid unit. When the wheel pressure increases in the lower fluid unit, hydraulic pressure fluctuations may occur. The braking control device is required to address these hydraulic pressure fluctuations.

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 suppress hydraulic pressure fluctuations when pressurization is performed in the lower braking unit. [Means for solving the problem]

[0006] The vehicle braking control device (SC) according to the present invention comprises an upper braking unit (SA) that pressurizes the supply pressure (Pm) by throttling the circulating flow (KN) discharged by a fluid pump (QA) driven by an electric motor (MA) with 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), pressurizes the supply pressure (Pm), and outputs wheel pressure (Pw) to the wheel cylinder (CW). When the lower braking unit (SB) pressurizes the wheel pressure (Pw), the upper braking unit (SA) reduces the rotational speed (Na) of the electric motor (MA) compared to when the lower braking unit (SB) does not pressurize the wheel pressure (Pw).

[0007] The vehicle braking control device (SC) according to the present invention includes an upper braking unit (SA) that pressurizes the supply pressure (Pm) by throttling the circulating flow (KN) discharged by a fluid pump (QA) driven by an electric motor (MA) with a pressure regulating valve (UA) according to the braking request amount (Bs), and a lower braking unit (SB) that is positioned between the upper braking unit (SA) and the wheel cylinder (CW), pressurizes the supply pressure (Pm), and outputs wheel pressure (Pw) to the wheel cylinder (CW). The upper braking unit (SA) calculates a target pressure (Pt) based on the braking request amount (Bs), and if the lower braking unit (SB) does not pressurize the wheel pressure (Pw), it controls the rotational speed (Na) of the electric motor (MA) based on the instruction flow rate (Qs) calculated from the target pressure (Pt) and the compensation flow rate (Qh) calculated from the supply pressure (Pm). On the other hand, when the lower braking unit (SB) pressurizes the wheel pressure (Pw), the upper braking unit (SA) controls the rotational speed (Na) of the electric motor (MA) based solely on the compensating flow rate (Qh).

[0008] According to the above configuration, when pressurization is performed in the lower braking unit SB, the flow rate change in the upper braking unit SA is suppressed, and therefore the hydraulic pressure fluctuation in the upper braking unit SA is suppressed. [Brief explanation of the drawing]

[0009] [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 control of the pressure regulating valve UA. [Figure 5] This is a block diagram illustrating a first control example of the upper electric motor MA. [Figure 6] This is a time-series diagram illustrating a second control example of the upper electric motor MA. [Modes for carrying out the invention]

[0010] <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.

[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 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."

[0012] 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.

[0013] <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.

[0014] 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.

[0015] The vehicle JV is equipped with a parking brake device PK. The parking brake device PK is composed of a parking switch BB, a parking brake controller EP, and an electric actuator (not shown). The parking switch BB is a switch operated by the driver. A parking signal Bb is output from the parking switch BB and input to the parking brake controller EP (also referred to as the "parking controller"). When the vehicle JV is stopped (i.e., when the vehicle body speed Vx is "0"), the parking controller EP applies the parking brake in the on state of the parking signal Bb and releases the parking brake in the off state of the parking signal Bb. Here, the operation and release of the parking brake are performed by an electric actuator provided on the rear wheels. The vehicle body speed Vx is input to the parking controller EP to determine the stopped state of the vehicle JV.

[0016] The parking signal Bb is also input to the braking control device SC (particularly, the lower controller EB). When the vehicle JV is running (for example, when the vehicle body speed Vx is equal to or higher than a predetermined vehicle speed vx) and the parking signal Bb is turned on, the electric actuator is not operated, and the braking control device SC increases the wheel pressure Pw to a preset predetermined pressure pw (constant). The control for pressurizing the wheel pressure Pw based on the parking signal Bb during vehicle running is called "dynamic braking control".

[0017] The vehicle JV is equipped with a braking operation member BP and a steering operation member SH. The braking operation member BP (for example, a brake pedal) is a member operated by the driver to decelerate the vehicle JV. The steering operation member SH (for example, a steering wheel) is a member operated by the driver to turn the vehicle JV.

[0018] The vehicle JV is equipped with various sensors (BA, etc.) listed below. The detection signals (Ba, etc.) of these sensors are input to the upper and lower braking units SA, SB (particularly, the controllers EA, EB) and used for various controls. - 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. In the upper braking unit SA, control related to the service brake (service brake) ("service brake control") is executed based on the braking amount Ba, and a supply pressure Pm (resulting in wheel pressure Pw) is generated. A wheel speed sensor VW is provided to detect the rotational speed Vw (wheel speed) of the wheel WH. The wheel speed Vw is input to the lower controller EB. The lower controller EB then calculates the vehicle speed Vx based on the wheel speed Vw. Furthermore, the lower controller EB performs anti-lock brake control to prevent the wheel WH from locking, based on the wheel speed Vw and the vehicle speed Vx.

[0019] A steering operation amount sensor SK is provided to detect the amount of operation Sk (steering operation amount, for example, steering angle) of the steering operation member SH. In addition, for the vehicle JV (especially the vehicle body), a yaw rate sensor YR is provided to detect the yaw rate Yr, a longitudinal acceleration sensor GX is provided to detect the longitudinal acceleration Gx, and a lateral acceleration sensor GY is provided to detect the lateral acceleration Gy. These sensor signals are input to the lower controller EB. The lower controller EB then performs Electronic Stability Control (ESC) to suppress oversteer and understeer and stabilize the yaw behavior of the vehicle JV. - Brake assist control (so-called BA control) is executed based on the operation speed dB which is the amount of change over time of the braking operation amount Ba. When the driver quickly operates the braking operation member BP (that is, when the operation speed dB is equal to or higher than a predetermined speed db set in advance), the generation of the wheel pressure Pw is assisted by the brake assist control so that the wheel pressure Pw becomes larger than the wheel pressure Pw corresponding to the operation amount Ba of the braking operation member BP. For example, as the operation speed dB, the operation change amount dS which is the time differential value of the operation displacement Sp is adopted.

[0020] 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.

[0021] 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.

[0022] The upper braking unit SA (especially the upper controller EA), the lower braking unit SB (especially the lower controller EB), the driver assistance device DS (especially the driver assistance controller ED), and the parking brake device PK (especially the parking controller EP) are connected to the communication bus BS. The "communication bus BS" has a network structure in which multiple controllers (control units) are connected to a communication line. Signal transmission between multiple controllers (EA, EB, ED, EP, etc.) is carried out via the communication bus BS. In other words, multiple controllers can send signals (detected values, calculated values, control flags, etc.) to the communication bus BS and can also receive signals from the communication bus BS.

[0023] <Upper braking unit SA> Referring to the schematic diagram in Figure 2, an example of the configuration of the upper braking unit SA will be described. The upper braking unit SA generates a supply pressure Pm in response to the operation of the braking operating member BP (brake pedal). The supply pressure Pm is ultimately supplied to the wheel cylinder CW via the connecting passage HS (fluid passage) and the lower braking unit SB. The upper braking unit SA consists of an upper actuator YA and an upper controller EA.

[0024] ≪Upper Actuator YA≫ The upper actuator YA consists of an apply unit AP, a pressure regulating unit CA, and an input unit NR.

[0025] [Apply Unit AP] In response to the operation of the braking operating member BP, the apply unit AP outputs a supply pressure Pm. The apply unit AP consists of a tandem-type master cylinder CM and primary and secondary master pistons NM and NS.

[0026] 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.

[0027] 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".

[0028] [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.

[0029] 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.

[0030] 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".

[0031] 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.

[0032] 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.

[0033] 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").

[0034] [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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] ≪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, EP, etc.).

[0040] The upper controller EA receives the braking operation amount Ba as input. The braking operation amount Ba is a general term for state variables that represent 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, 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 provided 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.

[0041] 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).

[0042] Based on the pressure regulation 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 the "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 the "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 the "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.

[0043] In the upper controller EA, based on the braking demand amount Bs (such as Ba, Gs, etc.) 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 of the vehicle, 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 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. 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.

[0044] <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 at least one of the following: automatic braking control, anti-lock brake control, anti-skid control, brake assist control, etc. Since it is necessary to increase the wheel pressure Pw from the supply pressure Pm to perform these controls, the lower braking unit SB is equipped with a pressurization function.

[0045] 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.

[0046] ≪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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 supply pressure Pm (or regulating pressure Pq) for each wheel.

[0052] ≪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.

[0053] The lower controller EB (specifically the microprocessor MP) receives inputs of wheel speed Vw, steering input Sk, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy. Based on the wheel speed Vw, the lower controller EB calculates the vehicle speed Vx. The vehicle speed Vx is transmitted to the communication bus BS for use by other devices (DS, PK, etc.).

[0054] The lower controller EB performs anti-lock brake control, anti-skid control, and other functions. 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 signals (Ub, etc.), the drive circuit DR controls the lower electric motor MB and the solenoid valves UB, VI, and VO.

[0055] The lower controller EB controls the inlet valve VI and outlet valve VO to individually decrease, increase, and maintain the wheel pressure Pw for each wheel cylinder CW. If power is not supplied to the inlet valve VI and 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 regulating 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 outlet valve VO. To decrease the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. This prevents the inflow of brake fluid BF into the wheel cylinder CW, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RB, thus decreasing the wheel pressure Pw. 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 regulating pressure Pq from the pressure regulating valve UB is 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 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.

[0056] The lower controller EB transmits an operation flag FB to the upper controller EA via the communication bus BS, indicating whether or not pressurization is being performed in the lower braking unit SB (i.e., whether or not power is being supplied to the control valve UB). The "operation flag FB" is a control flag, and a value of "0" indicates that "pressurization is not being performed in the lower braking unit SB (i.e., power supply to the control valve UB is stopped and the control valve UB is fully open)," while a value of "1" indicates that "pressurization is being performed in the lower braking unit SB (i.e., power is being supplied to the control valve UB and the circulating flow KL is being throttled by the control valve UB)."

[0057] <Drive control of pressure regulating valve UA> Referring to the block diagram in Figure 4, an example of controlling the pressure regulating valve UA will be described. This process is performed by the upper controller EA. The pressure regulating valve UA adjusts the servo pressure Pu, and ultimately adjusts the supply pressure Pm (=Pw). The drive control of the pressure regulating valve UA 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.

[0058] 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 general term for the requested values ​​to the upper braking unit SA, 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 supply pressure Pm is requested based on at least one of the braking operation amount Ba and the requested deceleration Gs. In this case, the braking request amount Bs is calculated based on the braking operation amount Ba and the requested deceleration Gs. Specifically, 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. Then, the target pressure Pt is calculated based on the braking request amount Bs. The "target pressure Pt" is the target value corresponding to the supply pressure Pm. The target pressure Pt is calculated according to a preset calculation map Zpt such that the target pressure Pt increases as the braking request amount Bs increases.

[0059] 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.

[0060] 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").

[0061] 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.

[0062] 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.

[0063] In the current feedback control block IF, based on the target current It (target value) and the supply current Ia (actual value), the 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.

[0064] <First Control Example of Electric Motor MA> Referring to the block diagram of FIG. 5, the first control example of the upper electric motor MA will be described. In the first control example, the electric motor MA is controlled based on flow rate control. The drive control of the electric motor MA is executed by the upper controller EA. The control of the electric motor MA is composed of 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 rotation speed calculation block NT, and a rotation speed feedback control block NF.

[0065] In the liquid volume conversion block PR, based on the target pressure Pt and the supply pressure Pm, the target liquid volume Rt and the actual liquid volume Rj are calculated. In the liquid volume conversion block PR, based on a preset calculation map Zpr, the target pressure Pt is converted into the target liquid volume Rt, and the supply pressure Pm is converted into the actual liquid volume Rj. Here, the "target liquid volume Rt" is the liquid volume required to achieve the target pressure Pt (the volume of the braking fluid BF to be moved to the wheel cylinder CW). Also, the "actual liquid volume Rj" is the liquid volume that has already flowed into the wheel cylinder CW to generate the supply pressure Pm (as a result, the wheel pressure Pw).

[0066] 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.

[0067] In the QS flow rate calculation block, the indicated flow rate Qs is calculated based on the target fluid volume Rt. Specifically, the target fluid volume Rt is differentiated with respect to time to determine the indicated flow rate Qs (i.e., "Qs = d(Rt) / dt"). The indicated flow rate Qs is the flow rate required to achieve the target pressure Pt and corresponds to the feedforward term in flow control. Therefore, the QS flow rate calculation block corresponds to feedforward control in flow control.

[0068] 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 Qh is the flow rate required for the supply pressure Pm to match the target pressure Pt, and corresponds to the feedback term in flow control. Therefore, the compensation flow rate calculation block QH corresponds to the feedback control in flow control.

[0069] In the target flow rate calculation block QT, the target flow rate Qt is calculated based on the indicative flow rate Qs and the compensation flow rate Qh. The "target flow rate Qt" is the final target value to achieve the target pressure Pt. Specifically, the indicative flow rate Qs and the compensation flow rate Qh are added together to determine the target flow rate Qt (i.e., "Qt = Qs + Qh").

[0070] In the target rotation speed calculation block NT, the target rotation speed Nt is calculated based on the target flow rate Qt. The "target rotation speed Nt" is a target value corresponding to the rotation speed Na (actual value) of the electric motor MA. Specifically, based on the discharge amount of the fluid pump QA (the volume of the braking fluid BF discharged per rotation), the target rotation speed Nt is determined to increase as the target flow rate Qt increases. Furthermore, the minimum flow rate of the pressure regulating valve UA and the minimum rotation speed of the electric motor MA are taken into account for the target rotation speed Nt. The "minimum flow rate" is the minimum required flow rate for the pressure regulating valve UA to regulate the servo pressure Pu and is preset. Also, the "minimum rotation speed" is the minimum value of the rotation speed at which the electric motor MA can continue to rotate stably. Considering these factors, a lower limit rotation speed nt (a preset value) is set for the target rotation speed Nt. Therefore, when the target rotation speed Nt calculated based on the target flow rate Qt is greater than or equal to the lower limit rotation speed nt, the limitation by the lower limit rotation speed nt is not imposed, and the calculated target rotation speed Nt is used as it is. On the other hand, when the target rotation speed Nt calculated based on the target flow rate Qt is less than the lower limit rotation speed nt, the target rotation speed Nt is determined to be the lower limit rotation speed nt (i.e., "Nt = nt").

[0071] In the rotation speed feedback control block NF, based on the target rotation speed Nt (target value) and the motor rotation speed Na (actual value), a drive signal Ma is calculated so that the motor rotation speed Na approaches and matches the target rotation speed Nt. Here, the motor rotation speed Na is calculated based on the detection value Ka (rotation angle) of the rotation angle sensor KA provided in the electric motor MA. Specifically, the motor rotation angle Ka is differentiated with respect to time to determine the motor rotation speed Na. In the rotation speed feedback control block NF, if "Nt > Na", the drive signal Ma is determined so that the actual rotation speed Na increases. On the other hand, if "Nt < Na", the drive signal Ma is determined so that the actual rotation speed Na decreases. That is, in the rotation speed feedback control block NF, feedback control related to the motor rotation speed is executed.

[0072] <Pressure source in the braking control device SC> The braking control device SC is equipped with two pressurizing sources (power sources for increasing wheel pressure Pw): the upper braking unit SA and the lower braking unit SB. When the wheel pressure Pw is pressurized by the upper braking unit SA, the upper electric motor MA is driven, causing the braking fluid BF to be discharged from the upper fluid pump QA, and a circulating flow KN of the braking fluid BF (also called the "upper circulating flow") is generated in the return channel HK. Then, based on the target pressure Pt calculated from the braking requirement Bs, the target current It (pressure regulating valve target current) for the pressure regulating valve UA is calculated, and control is performed so that the actual supply current Ia (pressure regulating valve current) flowing to the pressure regulating valve UA approaches and matches the target current It. Here, the supply current Ia is detected by the pressure regulating valve current sensor IA provided in the drive circuit DR of the upper controller EA. By supplying power to the pressure regulating valve UA, the upper circulating flow KN is throttled, which pressurizes the supply pressure Pm, and as a result, the wheel pressure Pw is pressurized.

[0073] Similarly, when the lower braking unit SB pressurizes the wheel pressure Pw, the lower electric motor MB is driven, causing the brake fluid BF to be discharged from the lower fluid pump QB, and a circulating flow KL of the brake fluid BF (also called the "lower circulating flow") is generated in the connecting passage HS and the return passage HL. Then, based on the braking requirement Bs, the target differential pressure St is calculated. The "target differential pressure St" is a target value corresponding to the fluid pressure difference (actual value) between the supply pressure Pm and the regulating pressure Pq. Based on the target differential pressure St, the target current Iu (control valve target current) for the control valve UB is calculated, and control is performed so that the actual supply current Ib (control valve current) flowing through the control valve UB approaches and matches the target current Iu. Here, the supply current Ib is detected by a control valve current sensor (not shown) provided in the drive circuit DR of the lower controller EB. By supplying power to the control valve UB, the lower circulating flow KL is throttled, and the wheel pressure Pw (=Pq) is increased from the supply pressure Pm.

[0074] The braking control unit SC performs various control functions. The upper and lower braking units SA and SB are used as pressure sources for each control function. This document summarizes the control functions in the braking control unit SC that require pressure, and the pressure sources for those functions. - Service brake control (i.e., functions related to the service brake) is performed by pressurization in the upper braking unit SA. In service brake control, the braking operation amount Ba is adopted as the braking request amount Bs. Then, based on the target pressure Pt calculated from the braking request amount Bs (=Ba), the supply pressure Pm is increased to match the target pressure Pt. Here, the target pressure Pt is determined to be larger the larger the braking operation amount Ba is. In service brake control, pressurization is not performed by the lower braking unit SB, so the supply pressure Pm is output to the wheel cylinder CW as the wheel pressure Pw. - Dynamic brake control is performed by pressurization in the lower braking unit SB, taking into account the redundancy of the braking control device SC. In dynamic brake control, the braking request amount Bs is calculated based on the fact that the signal Bb (parking signal) from the parking switch BB is switched from the off state to the on state while the vehicle is in motion (i.e., when the vehicle speed Vx is greater than "0"). Then, according to the braking request amount Bs of the dynamic brake control, the wheel pressure Pw is pressurized to a predetermined pressure pw. Here, the predetermined pressure pw is a predetermined value (constant) that is set in advance.

[0075] - Brake assist control is performed by pressurizing either the upper braking unit SA or the lower braking unit SB. In brake assist control, the braking requirement Bs is calculated based on the operating speed dB (the rate of change over time of the braking operation amount Ba, for example, the rate of change over time of the operating displacement Sp). Based on the braking requirement Bs of brake assist control, the target pressure Pt calculated in the service brake control is increased. In other words, in brake assist control, the wheel pressure Pw is increased compared to the case of service brake control. - Automatic braking control is performed by pressurizing either the upper braking unit SA or the lower braking unit SB. In automatic braking control, the braking requirement Bs is calculated based on the required deceleration Gs. The wheel pressure Pw is applied based on the target pressure Pt calculated from the braking requirement Bs. Here, the target pressure Pt is determined to increase as the required deceleration Gs increases. - Anti-skid control (especially the initial pressure for this control) is performed by pressurizing either the upper braking unit SA or the lower braking unit SB. In anti-skid control, the braking requirement Bs is calculated based on the yaw rate Yr. Specifically, the braking requirement Bs is determined based on the deviation between the target behavior calculated from the steering input Sk and the actual behavior calculated from the yaw rate Yr. Then, in accordance with the braking requirement Bs of the anti-skid control, the wheel pressure Pw is increased to suppress oversteer and understeer and stabilize the vehicle behavior. Individual adjustment of the wheel pressure Pw in anti-skid control is performed in the lower braking unit SB (especially the inlet valve VI and the outlet valve VO).

[0076] As explained above, in service brake control, pressure is applied by the upper braking unit SA, and in dynamic brake control, pressure is applied by the lower braking unit SB. Furthermore, in brake assist control, automatic braking control, and anti-skid control, pressure is applied by either the upper braking unit SA or the lower braking unit SB. As an example, in the braking control device SC, service brake control, automatic braking control, and anti-skid control are performed using the upper braking unit SA as the pressure source, while brake assist control and dynamic brake control are performed using the lower braking unit SB as the pressure source.

[0077] <Liquid pressure fluctuations during pressurization transitions> In the braking control device SC, there are situations where pressurization is being carried out by one of the upper or lower braking units SA or SB, while pressurization is being initiated by the other of the upper or lower braking units SA or SB. Pressurization by only one of the upper or lower braking units SA or SB is called "single pressurization," and pressurization by both of the upper and lower braking units SA or SB is called "joint pressurization." In other words, the above situation is a transition from single pressurization by the upper braking unit SA or the lower braking unit SB to joint pressurization by the upper and lower braking units SA and SB. Such a state transition is called a "pressurization transition." When a pressurization transition occurs, a change in hydraulic pressure may occur in the servo pressure Pu (resulting in supply pressure Pm and wheel pressure Pw).

[0078] The reason for the hydraulic pressure fluctuation during pressurization transitions is explained below. When pressurization is performed by the upper braking unit SA, the brake fluid BF is moved from the upper braking unit SA to the wheel cylinder CW via the lower braking unit SB, thereby increasing the wheel pressure Pw. Due to the pressurization by the lower braking unit SB, the flow rate passing through the pressure regulating valve UA changes, causing the servo pressure Pu to change. In detail, when pressurization is performed by the lower braking unit SB, the wheel pressure Pw increases from the supply pressure Pm, so the wheel pressure Pw becomes higher than the supply pressure Pm. In other words, when pressurization is not performed by the lower braking unit SB (also called "lower braking unit SB is unpressurized"), the brake fluid BF is moved from the upper braking unit SA to the wheel cylinder CW, but when pressurization is performed by the lower braking unit SB (also called "lower braking unit SB is pressurized"), the brake fluid BF is no longer moved from the upper braking unit SA to the wheel cylinder CW. In the two cases described above (the unpressurized / pressurized state of the lower braking unit SB), assuming that the electric motor MA is driven at the same rotational speed, the flow rate of the upper circulating flow KN will be higher when the lower braking unit SB is pressurized compared to when it is unpressurized. Therefore, when the lower braking unit SB transitions from the unpressurized state to the pressurized state, the servo pressure Pu (and consequently the supply pressure Pm and wheel pressure Pw) increases along with the increase in the flow rate of the upper circulating flow KN. The servo pressure Pu will eventually converge through the control of the pressure regulating valve UA based on the supply pressure Pm (i.e., hydraulic feedback control). However, transiently, the increase in servo pressure Pu and the hydraulic feedback control to suppress it cause the hydraulic pressure (Pu, Pm, Pq, Pw, etc.) to become oscillating.

[0079] <Suppression of hydraulic pressure fluctuations> Referring again to the block diagram in Figure 5, the control of the upper electric motor MA to suppress hydraulic pressure fluctuations during pressurization transitions (i.e., state transitions from individual pressurization to joint pressurization) will be explained. The operation flag FB transmitted from the lower controller EB via the communication bus BS is received by the upper controller EA. The operation flag FB is a control flag that indicates whether or not pressurization is active in the lower braking unit SB. Specifically, "FB=0" indicates that the lower braking unit SB is not pressurized (i.e., the control valve UB is not powered), and "FB=1" indicates that the lower braking unit SB is pressurized (i.e., the control valve UB is powered).

[0080] The operation flag FB is input to the target rotational speed calculation block NT. If "FB=0" and no pressurization is performed by the lower braking unit SB, the target rotational speed Nt is calculated based on the method described above. That is, the target rotational speed Nt is determined to be larger as the target flow rate Qt increases. On the other hand, if "FB=1" and pressurization is performed by the lower braking unit SB, the target rotational speed Nt is calculated to be smaller than when pressurization is not performed by the lower braking unit SB. For example, the target rotational speed Nt is determined to be a predetermined rotational speed nx. Here, "predetermined rotational speed nx" is a predetermined value (constant) set in advance. For example, the predetermined rotational speed nx may be determined to be equal to the lower limit rotational speed nt. Here, the lower limit rotational speed nt is the minimum rotational speed required for the pressure regulating valve UA to adjust the servo pressure Pu and for the electric motor MA to rotate stably, and is set in advance as a constant.

[0081] In the target rotational speed calculation block NT, the target rotational speed Nt is calculated such that when the lower braking unit SB is pressurized, the target rotational speed Nt is smaller than when the lower braking unit SB is not pressurized. As a result, the rotational speed Na of the electric motor MA is smaller when the lower braking unit SB is pressurized compared to when the lower braking unit SB is not pressurized. This suppresses changes (especially increases) in the flow rate in the upper braking unit SA during the state transition from individual pressurization to joint pressurization. Consequently, a sharp increase in servo pressure Pu is avoided, and thus hydraulic pressure fluctuations are suppressed.

[0082] The operation flag FB is input to the target flow rate calculation block QT, and the target flow rate Qt may be adjusted based on whether or not pressurization is performed by the lower braking unit SB. Specifically, if "FB=0" and pressurization is not performed by the lower braking unit SB, the target flow rate Qt is calculated in the manner described above. Specifically, the target flow rate Qt is calculated by adding the indicative flow rate Qs calculated from the target pressure Pt and the compensation flow rate Qh calculated from the supply pressure Pm. Then, based on the discharge rate of the fluid pump QA, the target flow rate Qt is converted to the target rotational speed Nt. In other words, if the wheel pressure Pw is not pressurized by the lower braking unit SB, the rotational speed Na of the electric motor MA is controlled based on the indicative flow rate Qs and the compensation flow rate Qh. On the other hand, if "FB=1" and pressurization is performed by the lower braking unit SB, the indicative flow rate Qs is calculated to be "0". In other words, when the wheel pressure Pw is pressurized by the lower braking unit SB, the target flow rate Qt is calculated based solely on the compensating flow rate Qh, and therefore the rotational speed Na of the electric motor MA is controlled based solely on the compensating flow rate Qh.

[0083] In the initial stages of braking (i.e., the stage when wheel pressure Pw begins to be generated), the amount of brake fluid BF consumed by the braking device SX (CP, MS, etc.) (referred to as "consumption amount") is large. In rotational speed control of an electric motor MA based on flow rate, in the initial stages of braking, the amount of change of braking requirement Bs over time is large, so the instructed flow rate Qs is calculated to be large. When pressurization is performed by the upper braking unit SA alone, the motor rotational speed Na increases rapidly due to the component of the instructed flow rate Qs in the target flow rate Qt. As a result, a large amount of brake fluid BF is moved to the wheel cylinder CW, improving the pressure increase responsiveness of the wheel pressure Pw in the initial stages of braking. On the other hand, when pressurization is performed by the lower braking unit SB, a certain amount of brake fluid BF has already been moved to the wheel cylinder CW by the lower braking unit SB, so there is no need to supply a large amount of brake fluid BF to the wheel cylinder CW. For this reason, even at the start of pressurization by the upper braking unit SA (i.e., the pressurization transition time), "Qs=0" is determined, and the target flow rate Qt is calculated to be small. As a result, the target rotational speed Nt is reduced, and the motor rotational speed Na is reduced. This suppresses the increase in flow rate in the upper braking unit SA during pressurization transitions. Since a sudden increase in servo pressure Pu is avoided, fluctuations in hydraulic pressure (i.e., supply pressure Pm, wheel pressure Pw) are suppressed.

[0084] Even when pressurization by the upper braking unit SA begins first, followed by pressurization by the lower braking unit SB, the indicative flow rate Qs is set to "0" at the time of pressurization by the lower braking unit SB (i.e., the pressurization transition point), and the target flow rate Qt is determined. Similarly, the increase in flow rate in the upper braking unit SA is suppressed. This prevents a sudden increase in servo pressure Pu and suppresses hydraulic pressure fluctuations.

[0085] <Second control example of electric motor MA> Referring to the time-series diagram in Figure 6 (a diagram showing the transition of state variables over time T), a second control example of the upper electric motor MA will be explained. In the control of the electric motor MA, in the first control example, the target rotational speed Nt was determined based on the flow rate required to pressurize the wheel pressure Pw (i.e., the indicative flow rate Qs and the compensating flow rate Qh). Instead, in the second control example, the target rotational speed Nt is determined by a preset pattern. Note that the actual rotational speed Na is controlled to match the target rotational speed Nt, so in the figure, the target rotational speed Nt and the actual rotational speed Na overlap.

[0086] Referring to Figure 6(a), the case where the upper braking unit SA pressurizes the engine while the lower braking unit SB is not pressurizing it (i.e., the case of pressurization by the upper braking unit SA alone) will be explained. In this case, as time T elapses, the target rotational speed Nt is calculated as shown by characteristic Xa (shown by the dashed line). At time t0, when pressurization by the upper braking unit SA alone begins, the target rotational speed Nt rapidly increases to the starting rotational speed na. The "starting rotational speed na" is a predetermined value (constant) set in advance. At the start of braking, the amount of fluid consumed by the braking device SX (the amount of fluid consumed due to the rigidity of the brake caliper CP, friction member MS, etc.) is large, so the target rotational speed Nt is determined to be a relatively large value so that a large amount of brake fluid BF is supplied.

[0087] At time t1, the target rotational speed Nt is reduced toward the steady-state rotational speed nb. The "steady-state rotational speed nb" is a predetermined value (constant) and is smaller than the starting rotational speed na. After a predetermined time tx (a predetermined constant) has elapsed since the start of the electric motor MA (i.e., time t0), the target rotational speed Nt is reduced so that the motor rotational speed Na decreases. This is based on the fact that as the wheel pressure Pw increases to a certain extent, the amount of fluid consumed by the braking system SX decreases, and therefore the amount of braking fluid BF required becomes less.

[0088] Next, we will explain the case where the upper braking unit SA applies pressure while the lower braking unit SB is applying pressure (i.e., joint pressure). When a pressure transition occurs, the target rotational speed Nt is calculated as shown in characteristic Xb (shown by the solid line). At time t0, pressure is applied by the upper braking unit SA. In other words, before time t0, the system is in a state of sole pressure application by the lower braking unit SB, but at time t0, it transitions to a state of joint pressure application by both the upper and lower braking units SA and SB. At time t0, when the pressure transition begins, the target rotational speed Nt is increased to a predetermined rotational speed nx. The predetermined rotational speed nx is a predetermined value (constant) set in advance and is smaller than the starting rotational speed na. For example, the predetermined rotational speed nx can be determined to be equal to the lower limit rotational speed nt mentioned above.

[0089] In the second control example, when the upper braking unit SA is pressurized independently, the target rotational speed Nt of the electric motor MA is calculated from a pattern set by a predetermined time tx, a starting rotational speed na, and a steady-state rotational speed nb. When a pressurization transition occurs, the target rotational speed Nt is determined to a predetermined rotational speed nx such that it is smaller than the target rotational speed Nt (i.e., the starting rotational speed na) when the upper braking unit SA is pressurized independently. Therefore, the motor rotational speed Na during the pressurization transition is made smaller than the motor rotational speed Na when the upper braking unit SA is pressurized independently. By suppressing the increase in flow rate in the upper braking unit SA, a sudden increase in servo pressure Pu is avoided, and thus fluctuations in supply pressure Pm and wheel pressure Pw are suppressed.

[0090] In the above example, the switching from the starting rotational speed na to the steady rotational speed nb during the independent pressurization of the upper braking unit SA was performed based on the elapsed time from the start of braking. Alternatively, the required speed dR, which is the time change of the braking requirement Bs, may be calculated, and the switching may be performed based on the magnitude of the required speed dR. Specifically, if the required speed dR is greater than or equal to a predetermined speed dr, the target rotational speed Nt is determined to be the starting rotational speed na, and if the required speed dR is less than the predetermined speed dr, the target rotational speed Nt is determined to be the steady rotational speed nb. Here, "predetermined speed dr" is a predetermined value (constant) set in advance. This is based on the fact that a larger required speed dR necessitates a higher flow rate of the braking fluid BF.

[0091] Next, referring to Figure 6(b), we will explain the case where the upper braking unit SA has already applied pressure, and the lower braking unit SB then applies pressure. In this case, the target rotational speed Nt is calculated as shown by characteristic Xc (shown as a solid line). Up to time t2, since the upper braking unit SA is the only one applying pressure, the target rotational speed Nt is determined to be the steady-state rotational speed nb. As a result, the motor rotational speed Na is maintained at a constant speed of the steady-state rotational speed nb. At time t2, when the upper braking unit SA starts applying pressure, the target rotational speed Nt is reduced to a predetermined rotational speed nx. Similarly, by reducing the motor rotational speed Na, changes in flow rate in the upper braking unit SA are avoided, and thus hydraulic pressure fluctuations are suppressed.

[0092] <Other Embodiments> Other embodiments will be described below. In other embodiments, the same effects as described above (such as suppression of hydraulic pressure fluctuations when pressurized in the lower braking unit SB) are achieved.

[0093] In the above-described embodiment, in controlling the rotational speed 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, 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 of the electric motor MA. In this configuration, when transitioning from individual pressurization to joint pressurization, the motor current Im is reduced by a predetermined current im (a preset constant), and the motor rotational speed Na is reduced.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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").

[0098] <Summary of Embodiments> This document summarizes the embodiment of the braking control device SC. The braking control device SC is equipped with two braking units SA and SB as pressurization sources for the wheel pressure Pw. In the upper braking unit SA, the supply pressure Pm is pressurized by throttling the circulating flow KN discharged by the fluid pump QA, which is driven by the electric motor MA, with the pressure regulating valve UA. The supply pressure Pm is ultimately output to the wheel cylinder CW, and the wheel pressure Pw is pressurized by the supply pressure Pm. The lower braking unit SB is positioned between the upper braking unit SA and the wheel cylinder CW. The supply pressure Pm is pressurized by the lower braking unit SB and output to the wheel cylinder CW as the wheel pressure Pw. In the braking control device SC, if pressurization is not performed by the lower braking unit SB, the supply pressure Pm pressurized by the upper braking unit SA is supplied to the wheel cylinder CW as the wheel pressure Pw. Conversely, if no pressurization is performed by the upper braking unit SA, the supply pressure Pm is "0 (atmospheric pressure)," and therefore the wheel pressure Pw is pressurized from "0" by the lower braking unit SB.

[0099] In the upper braking unit SA, when the lower braking unit SB pressurizes the wheel pressure Pw (i.e., when a hydraulic pressure difference occurs between the supply pressure Pm and the adjustment pressure Pq), the rotational speed Na of the electric motor MA is controlled to be lower compared to when the lower braking unit SB does not pressurize the wheel pressure Pw (when no hydraulic pressure difference occurs between the supply pressure Pm and the adjustment pressure Pq). In other words, the motor rotational speed Na when the lower braking unit SB pressurizes the wheel pressure Pw is smaller than the motor rotational speed Na when the lower braking unit SB does not pressurize the wheel pressure Pw.

[0100] For the wheel pressure Pw to increase, brake fluid BF must flow into the wheel cylinder CW. The amount of brake fluid BF consumed at this time depends on the rigidity of the braking system SX (CP, MS, etc.). A large amount of brake fluid BF is required to increase the wheel pressure Pw from "0". However, if the wheel pressure Pw has increased to a certain extent, not much brake fluid BF is required. Furthermore, when pressurization is performed by the lower braking unit SB, the wheel pressure Pw is increased from the supply pressure Pm. In other words, since the wheel pressure Pw is greater than the supply pressure Pm, brake fluid BF is not moved from the upper braking unit SA to the wheel cylinder CW. When the lower braking unit SB is pressurized, if the upper braking unit SA attempts to supply the same amount of brake fluid BF as when the lower braking unit SB is unpressurized, an overflow condition occurs in the upper braking unit SA. Therefore, an increase in supply pressure Pm (=Pu) occurs during pressurization transitions. The supply pressure Pm is converged to the target pressure Pt by feedback control, but this process becomes oscillating. In the braking control device SC, if the lower braking unit SB has already pressurized the wheel pressure Pw, the rotational speed Na of the electric motor MA is reduced so that the flow rate in the upper braking unit SA is lower compared to when the lower braking unit SB has not pressurized the wheel pressure Pw. Since the flow rate change in the upper braking unit SA is suppressed, hydraulic pressure fluctuations are reduced.

[0101] In the braking control device SC, the electric motor MA can be driven based on flow rate control. In this control, the rotational speed Na of the electric motor MA is controlled based on the indicative flow rate Qs calculated from the target pressure Pt, and the compensating flow rate Qh calculated from the supply pressure Pm. Here, the indicative flow rate Qs is the flow rate required to achieve the target pressure Pt, and corresponds to the feedforward term in flow rate control. The compensating flow rate Qh is the flow rate required for the supply pressure Pm to match the target pressure Pt, and corresponds to the feedback term in flow rate control. Through flow rate control, the electric motor MA is controlled to ensure the minimum necessary flow rate, thereby suppressing the power consumption of the electric motor MA. The target pressure Pt is calculated based on the braking requirement Bs, and the target pressure Pt increases as the braking requirement Bs increases.

[0102] In the upper braking unit SA, when the lower braking unit SB is not pressurizing the wheel pressure Pw, the rotational speed Na of the electric motor MA is controlled based on the indicative flow rate Qs and the compensating flow rate Qh. Specifically, the motor rotational speed Na is controlled based on the target flow rate Qt, which is the sum of the indicative flow rate Qs and the compensating flow rate Qh. On the other hand, when the lower braking unit SB is pressurizing the wheel pressure Pw, the rotational speed Na of the electric motor MA is controlled based only on the compensating flow rate Qh. Specifically, the motor rotational speed Na is controlled based on the target flow rate Qt, but "Qs=0" is determined and "Qt=Qh" is calculated. With this configuration, the motor rotational speed Na when the lower braking unit SB is pressurizing the wheel pressure Pw is made smaller than the motor rotational speed Na when the lower braking unit SB is not pressurizing the wheel pressure Pw by an amount equivalent to the indicative flow rate Qs. As a result, as described above, the flow rate change in the upper braking unit SA is suppressed, and thus hydraulic pressure fluctuations are reduced. [Explanation of symbols]

[0103] 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, Ps...Indicated pressure, Pt...Target pressure, Pu...Servo pressure, Pm...Supply pressure (PM detected value), Pw...Wheel pressure, Rs...Indicated fluid volume, Rt...Target fluid volume, Rj...Actual fluid volume, hR...Fluid volume deviation, Qs...Indicated flow rate, Qh...Compensated flow rate, Qt...Target flow rate, Nt...Target rotational speed, Na...Actual rotational speed (motor rotational speed), Ka...Rotation angle, Bs...Braking requirement, dB...Required speed (Time change of Bs), Ba...Braking operation amount, Gs...Required deceleration.

Claims

1. An upper braking unit that increases the 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, pressurizes the supply pressure, and outputs wheel pressure to the wheel cylinder. In a braking control device for a vehicle equipped with, The lower braking unit comprises a lower fluid pump and a control valve driven by a lower electric motor, and is configured to increase the supply pressure by restricting the circulating flow of braking fluid generated by the operation of the lower fluid pump with the control valve. A vehicle braking control device wherein the upper braking unit reduces the rotational speed of the electric motor when the lower braking unit pressurizes the wheel pressure, compared to when the lower braking unit does not pressurize the wheel pressure.

2. An upper braking unit that, in accordance with the braking requirement, increases the 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, pressurizes the supply pressure, and outputs wheel pressure to the wheel cylinder. In a braking control device for a vehicle equipped with, The upper braking unit calculates the target pressure based on the braking requirement, If the lower braking unit does not pressurize the wheel pressure, the rotational speed of the electric motor is controlled based on the indicative flow rate calculated from the target pressure and the compensation flow rate calculated from the supply pressure. A vehicle braking control device that controls the rotational speed of the electric motor based solely on the compensation flow rate when the lower braking unit pressurizes the wheel pressure.

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