Vehicle braking control device

Abstract

To provide a vehicle brake control device capable of curbing fluctuation in fluid pressure of a wheel cylinder due to the fluctuation of supply fluid pressure from a pressure source.SOLUTION: A brake control device comprises: a pressure source which increases a fluid pressure of a wheel cylinder; a communication passage which connects the pressure source and the wheel cylinder; an inlet valve installed on the communication passage; a fluid pressure sensor which detects the fluid pressure output from the pressure source as a supply fluid pressure; and a controller which calculates a plurality of target fluid pressures required for the wheel cylinder, determines the largest target fluid pressure among the plurality of target fluid pressures as a maximum target fluid pressure, causes the pressure source to adjust the fluid pressure of the selected wheel cylinder corresponding to the maximum target fluid pressure, and causes the inlet valve and an outlet valve to adjust the fluid pressure of the unselected wheel cylinder not corresponding to the selected wheel cylinder. The controller controls the selected inlet valve corresponding to the selected wheel cylinder on the basis of a difference between the maximum target fluid pressure and the supply fluid pressure.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes that, for the purpose of "executing brake pressure control for a longer time", "the M / C pressure generated by the auxiliary pressure source 100 is set to the maximum value of the W / C pressures of each wheel FL to RR. As a result, it is not necessary to generate an M / C pressure more than necessary. And when generating the W / C pressures of each wheel FL to RR, since it is not necessary to reduce the high-pressure M / C pressure to use it as the W / C pressure, the amount of brake fluid discharged to the reservoirs 20 and 40 through each pressure reducing control valve 21, 22, 41, 42 can be reduced. Therefore, it is possible to reduce the operating frequency of the motor 60, suppress the temperature rise of the motor 60, and perform brake pressure control for a long time."

[0003] In Patent Document 1, a target hydraulic pressure (also referred to as "required hydraulic pressure") is calculated for each wheel cylinder, and an auxiliary pressure source (simply also referred to as "pressure source") is controlled based on the maximum value among the plurality of target hydraulic pressures. That is, the hydraulic pressure of the wheel cylinder corresponding to the maximum value (referred to as "selected braking hydraulic pressure Pwx") is adjusted by the pressure source. And for wheel cylinders other than the wheel cylinder corresponding to the maximum value, the braking hydraulic pressure (referred to as "non-selected braking hydraulic pressure Pwz") is adjusted by reducing it from the output hydraulic pressure of the pressure source (referred to as "supply hydraulic pressure Pm") by controlling a pressure increasing valve (also referred to as "inlet valve") and a pressure reducing valve (also referred to as "outlet valve").

[0004] As described above, the non-selective braking hydraulic pressure Pwz is adjusted by being decreased from the supply hydraulic pressure Pm of the pressure source. This pressure adjustment is achieved by discharging the braking fluid BF to the reservoir RC by controlling the inlet valve and the outlet valve. At this time, a change in the amount of the braking fluid BF occurs in the fluid passages (braking pipes, fluid passages in the fluid unit, hoses, etc.) of the braking control device SC. Then, due to this change in the amount of the fluid, fluctuations in the supply hydraulic pressure Pm may occur. In the braking control device SC of a vehicle, it is desired that fluctuations (pressure fluctuations) in the hydraulic pressure (supply hydraulic pressure) Pm output from the pressure source are suppressed so that the selective braking hydraulic pressure Pwx can be adjusted.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a braking control device for a vehicle that can suppress fluctuations in the hydraulic pressure of a wheel cylinder caused by fluctuations in the supply hydraulic pressure from a pressure source.

Means for Solving the Problems

[0007] The braking control device according to the present invention individually adjusts the hydraulic pressure (Pw) of a plurality of wheel cylinders (CW) of a vehicle, and includes a pressurizing source (YA) for increasing the hydraulic pressure (Pw) of the plurality of wheel cylinders (CW), a communication path (HS) connecting the pressurizing source (YA) and the plurality of wheel cylinders (CW), an inlet valve (UI) provided in the communication path (HS), a decompression path (HG) connecting the communication path (HS) between the plurality of wheel cylinders (CW) and the inlet valve (UI) to a reservoir (RC), an outlet valve (VO) provided in the decompression path (HG), a hydraulic pressure sensor (PB) for detecting the hydraulic pressure output by the pressurizing source (YA) as a supply hydraulic pressure (Pm), and "a controller (ECU) that calculates a plurality of target hydraulic pressures (Pt) required for the plurality of wheel cylinders (CW), determines the maximum value among the plurality of target hydraulic pressures (Pt) as a maximum target hydraulic pressure (Ptx), adjusts the hydraulic pressure (Pwx) of a selected wheel cylinder (CWx) corresponding to the maximum target hydraulic pressure (Ptx) among the plurality of wheel cylinders (CW) by the pressurizing source (YA), and adjusts the hydraulic pressure (Pwz) of a non-selected wheel cylinder (CWz) that does not correspond to the selected wheel cylinder (CWx) among the plurality of wheel cylinders (CW) by the inlet valve (UIz) and the outlet valve (VOz)". And the controller (ECU) controls a selected inlet valve (UIx) corresponding to the selected wheel cylinder (CWx) among the inlet valves (UI) based on a deviation (hP) between the maximum target hydraulic pressure (Ptx) and the supply hydraulic pressure (Pm).

[0008] Furthermore, the braking control device according to the present invention includes a pressure regulating valve (UB) provided in the communication path (HS) between the pressurizing source (YA) and the inlet valve (UI). Then, based on the deviation (hP), the controller (ECU) controls the selected pressure regulating valve (UBx) corresponding to the selected wheel cylinder (CWx) among the pressure regulating valves (UB). When the supply hydraulic pressure (Pm) is smaller than the maximum target hydraulic pressure (Ptx), the controller (ECU) energizes the selected pressure regulating valve (UBx) and does not energize the selected inlet valve (UIx). When the supply hydraulic pressure (Pm) is larger than the maximum target hydraulic pressure (Ptx), the controller (ECU) energizes the selected inlet valve (UIx) and does not energize the selected pressure regulating valve (UBx).

[0009] According to the above configuration, fluctuations in the supply hydraulic pressure Pm are suppressed and transmitted to the selected wheel cylinder CWx by adjusting the opening amounts Li and Lb of the inlet valve UI and the pressure regulating valve UB based on the hydraulic pressure deviation hP. Therefore, fluctuations in the hydraulic pressure Pwx of the selected wheel cylinder CWx can be reduced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0011] Hereinafter, an embodiment of a braking control device SC for a vehicle according to the present invention will be described with reference to the drawings.

[0012] <Symbols of components, etc.> In the following description, components such as members, signals, values, etc. denoted by the same symbol, such as "CW", have the same function. The subscripts "f" and "r" attached to the ends of various symbols related to the wheels are collective symbols indicating whether the element is related to the front wheels or the rear wheels. Specifically, "f" indicates an element related to the front wheels, and "r" indicates an element related to the rear wheels. For example, in the wheel cylinder CW, it is expressed as the front wheel cylinder CWf and the rear wheel cylinder CWr. Furthermore, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its general term.

[0013] <Vehicle JV equipped with braking control device SC> Referring to the configuration diagram of FIG. 1, the entire vehicle JV equipped with the braking control device SC according to the present invention will be described. The vehicle JV is provided with an acceleration operation member AP, a braking operation member BP, a steering operation member SH, and various sensors (BA, etc.). The acceleration operation member (for example, an accelerator pedal) AP is a member that the driver operates to accelerate the vehicle JV and control the speed (vehicle body speed Vx) of the vehicle JV. The braking operation member (for example, a brake pedal) BP is a member that the driver operates to decelerate the vehicle. The steering operation member (for example, a steering wheel) SH is a member that the driver operates to turn the vehicle JV.

[0014] The vehicle JV is provided with various sensors listed below. The detection signals (Ba, etc.) of these sensors are input to a controller ECU for braking (also simply referred to as the "braking controller") described later. · An acceleration operation amount sensor AA that detects the operation amount (acceleration operation amount) Aa of the acceleration operation member AP, a braking operation amount sensor BA that detects the operation amount (braking operation amount) Ba of the braking operation member BP, and a steering operation amount sensor SA that detects the operation amount (steering operation amount, for example, steering angle) Sa of the steering operation member SH. · A wheel speed sensor VW that detects the rotational speed (wheel speed) Vw of the wheel WH. · In the vehicle JV (particularly, the vehicle body), a yaw rate sensor YR that detects the yaw rate Yr, a longitudinal acceleration sensor GX that detects the longitudinal acceleration Gx, and a lateral acceleration sensor GY that detects the lateral acceleration Gy.

[0015] In addition, various switches such as a switch XD for downhill assist control and a switch XC for crawl control are provided to give instructions for various automatic braking controls described later. These switches XD and XC are operated by the driver. Then, an operation signal Xd (a signal for downhill assist control) from the switch XD and an operation signal Xc (a signal for crawl control) from the switch XC are input to the brake controller ECU.

[0016] The vehicle JV is equipped with a braking device SX and a brake control device SC. In the brake control device SC, a so-called front-rear type (also referred to as "Type II") is adopted as the two braking systems.

[0017] The braking device SX is supplied with a braking fluid pressure Pw generated by the brake control device SC. Then, by the braking device SX, a braking force Fb is generated on the wheel WH according to the braking fluid pressure Pw. The braking device SX includes a rotating member (for example, a brake disk) KT and a brake caliper CP. The rotating member KT is fixed to the wheel WH of the vehicle, and the brake caliper CP is provided so as to sandwich the rotating member KT. A wheel cylinder CW is provided in the brake caliper CP. The wheel cylinder CW is supplied with a braking fluid BF adjusted to the braking fluid pressure Pw from the brake control device SC. By the braking fluid pressure Pw, a friction member (for example, a brake pad) MS is pressed against the rotating member KT. Since the rotating member KT and the wheel WH are fixed to rotate integrally, a braking torque Tb (as a result, a braking force Fb) is generated on the wheel WH by the frictional force generated at this time.

[0018] The braking control device SC adjusts the actual braking hydraulic pressure Pw according to the operation amount Ba of the braking operation member BP, and supplies the braking hydraulic pressure Pw to the braking device SX (particularly, the wheel cylinder CW) via the front and rear wheel connecting paths HSf and HSr. The braking control device SC is composed of a master cylinder CM, a fluid unit HU, and a braking controller ECU. And the fluid unit HU is composed of two units (the first and second units) YA and YB. The components of the braking control device SC (such as solenoid valves and electric motors included in the first and second units YA and YB) are controlled by the controller ECU. The controller ECU is composed of a microprocessor MP that performs signal processing and a drive circuit DD that drives solenoid valves and electric motors. Each of the braking controller ECU, the prime mover controller ECP described later, and the power transmission controller ECT is connected to the communication bus BS. Therefore, information (detection values, calculation values) is shared among these controllers via the communication bus BS. For example, in the braking controller ECU, the vehicle body speed Vx is calculated based on the wheel speed Vw. The vehicle body speed Vx is transmitted to other controllers through the communication bus BS. The acceleration operation amount Aa, the braking operation amount Ba, the steering operation amount Sa, the yaw rate Yr, the longitudinal acceleration Gx, the lateral acceleration Gy, the wheel speed Vw, the operation signal Xc (for crawl control), the operation signal Xd (for downhill assist control), etc. are input to the controller ECU. Based on these signals, the fluid unit HU is controlled by the braking controller ECU. The details of the braking control device SC will be described later.

[0019] The vehicle JV is equipped with a prime mover control device GC and a power transmission device TS. The vehicle JV is a four-wheel drive vehicle in which all four wheels WH are drive wheels (wheels to which the drive torque Td is transmitted to generate the driving force Fd).

[0020] The prime mover control device GC is composed of a prime mover PG and a controller ECP for the prime mover that controls it (simply referred to as the "prime mover controller" as well). The prime mover PG is a general term for devices that convert various energies existing in nature into mechanical work (mechanical energy). Taking the case where an internal combustion engine (gasoline engine) is adopted as the prime mover PG as an example for explanation. The prime mover PG generates power (driving torque Td) for driving four wheels WH. The prime mover PG is controlled by a prime mover controller (engine controller) ECP, and its output is adjusted. Specifically, the prime mover PG includes a throttle device TH, a fuel injection device FI, and an engine speed sensor NE. The throttle opening Th is controlled by the throttle device TH, and the fuel injection amount Fi is controlled by the fuel injection device FI, respectively. And based on the engine speed Ne detected by the speed sensor NE, at least one of the throttle opening Th and the fuel injection amount Fi is controlled by the prime mover controller ECP. As a result, the output of the prime mover PG is adjusted.

[0021] The output (rotational power) of the prime mover control device GC (especially the prime mover PG) is input to the power transmission device TS. And the output of the prime mover PG is transmitted to the four wheels WH via the power transmission device TS, and a driving force Fd is generated at each of the wheels WH. The power transmission device TS includes a power transmission mechanism TD and a controller ECT for power transmission that controls it (simply referred to as the "power transmission controller" as well). The power transmission mechanism TD is composed of a main transmission MH, a sub-transmission FH, a front-wheel differential mechanism DF, a center differential mechanism DC, and a rear-wheel differential mechanism DR. The main transmission MH is an automatic transmission that shifts gears according to the running state of the vehicle. The output of the prime mover PG is input to the sub-transmission FH via the main transmission MH. The sub-transmission FH enables switching between a high-speed gear and a low-speed gear for four-wheel drive.

[0022] The output from the auxiliary transmission FH is input to the respective differential mechanisms DF (front-wheel differential gear), DC (center differential gear), and DR (rear-wheel differential gear). The front-wheel drive torque Tdf is transmitted to the left and right front wheels WHf via the front-wheel differential mechanism DF and the front-wheel drive shaft. Also, the rear-wheel drive torque Tdr is transmitted to the left and right rear wheels WHr via the center differential mechanism DC, the rear-wheel differential mechanism DR, and the rear-wheel drive shaft. Since the power generated by the prime mover PG is transmitted to the front wheels WHf and the rear wheels WHr via the differential mechanisms DF, DC, and DR, a rotational speed difference (i.e., differential) between the respective wheels WH is allowed. Each component (such as MH) of the power transmission mechanism TD is controlled by the power transmission controller ECT. Specifically, the main transmission MH, the auxiliary transmission FH, and the differential mechanisms DF, DC, and DR are each controlled by the power transmission controller ECT.

[0023] <Off-road control> In the vehicle JV, off-road control is executed. "Off-road control" is to maintain the vehicle body speed Vx at a low speed on an unpaved road (also referred to as "off-road") or the like. Here, off-road control is a general term for "downhill assist control" and "crawl control". Since downhill assist control and crawl control are well-known, they will be briefly described below.

[0024] "Downhill Assist Control" is also called "Hill Descent Control". On a downhill road, it adjusts the braking force Fb so that the vehicle body speed Vx is maintained at or below a predetermined vehicle speed vd without the driver operating the braking operation member BP. Downhill Assist Control is instructed by an operation signal Xd (Downhill Assist Control signal) from the Downhill Assist Control switch XD operated by the driver. When the operation signal Xd indicates an on state, Downhill Assist Control is executed, but it is not executed when the operation signal Xd is in an off state. In addition to instructing the necessity of executing Downhill Assist Control by the switch XD, the set speed vd by Downhill Assist Control is also instructed. That is, the operation signal Xd includes information on the target value (set speed) vd of the vehicle body speed Vx of the vehicle JV. In Downhill Assist Control, the braking fluid pressure Pw of each wheel WH is individually adjusted so that wheel lock and skidding of the wheels WH are suppressed and the vehicle body speed Vx coincides with and is maintained at a predetermined low speed (set speed) vd.

[0025] "Crawl Control" is an advanced version of the above Downhill Assist Control. In Crawl Control, the braking control device SC and the prime mover control device GC control the braking force Fb and the driving force Fd so that the vehicle body speed Vx is maintained at a predetermined set vehicle speed vc without operating the acceleration operation member (accelerator pedal) AP and the braking operation member (brake pedal) BP. That is, Crawl Control operates not only on a downhill slope but also on an uphill slope.

[0026] Specifically, the crawl control is instructed by an operation signal Xc (a switch signal for crawl control) from a crawl control switch XC operated by the driver. When the operation signal (switch signal) Xc indicates an on state, the crawl control is executed, but when the operation signal Xc is in an off state, it is not executed. In addition to instructing the necessity of executing the crawl control by the switch XC, the set speed vc by the crawl control is also instructed. That is, the operation signal Xc includes information on the target value (set speed) vc of the vehicle body speed Vx of the vehicle JV. In the crawl control, the output of the prime mover PG is adjusted and the brake hydraulic pressure Pw of each wheel WH is individually adjusted so that the locking and skidding of the wheels WH are suppressed and the vehicle body speed Vx matches and is maintained at a predetermined constant low speed (set speed) vc. On sandy, dirt, rocky, muddy roads, etc., delicate operations of the acceleration operation member AP and the brake operation member BP are required, but the crawl control suitably assists driving in such situations.

[0027] As described above, by the off-road control (for example, downhill assist control, crawl control), skidding of the wheels WH is avoided, so the stability of the vehicle JV is ensured, and it becomes possible to drive while maintaining the vehicle body speed Vx constant (extremely low speeds vd, vc). At this time, since operations of the acceleration operation member AP and the brake operation member BP by the driver are not required, the driver can concentrate on operating the steering operation member SH. That is, the off-road control improves the drivability on rough terrain and the like.

[0028] <First Unit YA> Referring to the schematic diagram of FIG. 2, a configuration example of the first unit YA included in the fluid unit HU will be described. The first unit YA is a pressurizing source for increasing the hydraulic pressure (braking hydraulic pressure) Pw of the four wheel cylinders CW. In the example, the first unit YA is integrated with the master cylinder CM. And a front-rear type braking system is adopted. The first unit YA is composed of an apply unit AU including the master cylinder CM and a pressurizing unit KU. The apply unit AU and the pressurizing unit KU are controlled by the brake controller ECU. Specifically, the controller ECU receives the braking operation amount Ba (at least one of the simulator hydraulic pressure Ps, operation displacement Sp, and operation force Fp), wheel speed Vw, accumulator hydraulic pressure Pc, servo hydraulic pressure Pu, and supply hydraulic pressure Pm. Based on these signals, drive signals Vn for the input valve VN, Vr for the release valve VR, Uz for the pressure increasing valve UZ, Ug for the pressure reducing valve UG, and Ma for the accumulator electric motor MA are calculated. Then, according to the drive signals "Vn, Vr, Uz, Ug, Ma", the solenoid valves "VN, VR, UZ, UG" constituting the first unit YA and the accumulator electric motor MA are controlled (driven).

[0029] As described later, the fluid unit HU, wheel cylinder CW, etc. are connected by a communication path HS, input path HN, pressure reducing path HG, and return path HK. These are fluid paths through which the brake fluid BF moves. Examples of the fluid paths (HS, etc.) include fluid pipes, flow paths inside the fluid unit HU, hoses, etc.

[0030] ≪Apply Unit AU≫ The apply unit AU is composed of a master reservoir RV, master cylinder CM, first and second master pistons NP, NS, first and second master springs DP, DS, input cylinder CN, input piston NN, input spring DN, input valve VN, release valve VR, stroke simulator SS, and simulator hydraulic pressure sensor PS.

[0031] The master reservoir (also referred to as the "atmospheric pressure reservoir") RV is a tank for the working liquid, and the brake fluid BF is stored therein. The master reservoir RV is connected to the master cylinder CM (particularly, the front wheel and rear wheel master chambers Rmf, Rmr).

[0032] The master cylinder CM is a cylinder member having a bottom. Inside the master cylinder CM, first and second master pistons NP, NS are inserted, and the inside thereof is sealed by a seal member SL and divided into front wheel and rear wheel master chambers Rmf, Rmr. The master cylinder CM is of the so-called tandem type. In the front wheel and rear wheel master chambers Rmf, Rmr, first and second master springs DP, DS are provided. By the first and second springs DP, DS, the first and second master pistons NP, NS are pressed in the retreat direction Hb (the direction in which the volume of the master chamber Rm increases, opposite to the forward direction Ha). The front wheel and rear wheel master chambers Rmf, Rmr (= Rm) are finally connected to the front wheel and rear wheel wheel cylinders CWf, CWr (= CW) via the front wheel and rear wheel communication paths HSf, HSr (= HS) and the second unit YB, respectively. When the first and second master pistons NP, NS are moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases), the brake fluid BF of the hydraulic pressure Pm (referred to as the "supply hydraulic pressure" and being the "front wheel and rear wheel supply hydraulic pressures Pmf, Pmr") is supplied from the first unit YA (particularly, the master cylinder CM) to the second unit YB. Here, the front wheel supply hydraulic pressure Pmf and the rear wheel supply hydraulic pressure Pmr are equal.

[0033] The first master piston NP is provided with a flange portion. By this flange portion, the inside of the master cylinder CM is further partitioned into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru is arranged to face the front wheel master chamber Rmf with the first master piston NP interposed therebetween. Also, the rear chamber Ro is sandwiched between the front wheel master chamber Rmf and the servo chamber Ru and is arranged therebetween. The servo chamber Ru and the rear chamber Ro are also sealed by the seal member SL in the same manner as above.

[0034] The input cylinder CN is fixed to the master cylinder CM. Inside the input cylinder CN, an input piston NN is inserted and sealed by a seal member SL, forming an input chamber Rn. The input piston NN is mechanically connected to the braking operation member BP via a clevis (U-shaped link). A flange is provided on the input piston NN. An input spring DN is provided between this flange and the mounting surface of the input cylinder CN with respect to the master cylinder CM. By the input spring DN, the input piston NN is pressed in the retraction direction Hb.

[0035] The application unit AU is provided with an input chamber Rn, a servo chamber Ru, a rear chamber Ro, and hydraulic chambers of the front and rear wheel master chambers Rmf, Rmr. Here, the "hydraulic chamber" is a chamber filled with brake fluid BF and sealed by a seal member SL. The volume of each hydraulic chamber is changed by the movement of the input piston NN, the first and second master pistons NP, NS. In the arrangement of the hydraulic chambers, along the central axis Jm of the master cylinder CM, in order from the side closer to the braking operation member BP, there are the input chamber Rn, the servo chamber Ru, the rear chamber Ro, the front wheel master chamber Rmf, and the rear wheel master chamber Rmr.

[0036] The input chamber Rn and the rear chamber Ro are connected via an input passage HN. An input valve VN is provided in the input passage HN. The input passage HN is connected to the master reservoir RV via an open valve VR between the rear chamber Ro and the input valve VN. The input valve VN and the open valve VR are two-position solenoid valves (also referred to as "on-off valves") having an open position (connected state) and a closed position (blocked state). A normally closed solenoid valve is adopted as the input valve VN. A normally open solenoid valve is adopted as the open valve VR. The input valve VN and the open valve VR are driven (controlled) by drive signals Vn, Vr from the brake controller ECU.

[0037] A stroke simulator (also simply referred to as the "simulator") SS is connected to the rear chamber Ro. The simulator SS generates the operating force Fp of the braking operation member BP. Inside the simulator SS, a piston and an elastic body (for example, a compression spring) are provided. When the braking fluid BF flows into the simulator SS, the piston is pushed by the braking fluid BF. Since a force is applied to the piston in a direction to prevent the inflow of the braking fluid BF by the elastic body, the operating force Fp of the braking operation member BP is generated. That is, the operating characteristics (the relationship between the operating displacement Sp and the operating force Fp) of the braking operation member BP are formed by the simulator SS.

[0038] A simulator hydraulic pressure sensor PS is provided to detect the hydraulic pressure Ps of the simulator SS (which is the simulator hydraulic pressure and also the hydraulic pressure of the input chamber Rn and the rear chamber Ro). The simulator hydraulic pressure sensor PS is one of the above-mentioned braking operation amount sensors BA. The simulator hydraulic pressure Ps is input to the braking controller ECU as the braking operation amount Ba.

[0039] In the first unit YA, in addition to the simulator hydraulic pressure sensor PS, as the braking operation amount sensor BA, an operation displacement sensor SP for detecting the operation displacement Sp of the braking operation member BP and / or an operation force sensor FP for detecting the operation force Fp of the braking operation member BP are provided. That is, as the braking operation amount sensor BA, at least one of the simulator hydraulic pressure sensor PS, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP is adopted. Therefore, the braking operation amount Ba is at least one of the simulator hydraulic pressure Ps, the operation displacement Sp, and the operation force Fp.

[0040] ≪Pressurizing Unit KU≫ The pressurizing unit KU generates and adjusts the supply hydraulic pressure Pm. The pressurizing unit KU is composed of a fluid pump QA for pressure accumulation, an electric motor MA for pressure accumulation, an accumulator AC, an accumulator hydraulic pressure sensor PC, a pressurizing cylinder CK, a pressurizing piston NK, a pressure increasing valve UZ, a pressure reducing valve UG, and a servo hydraulic pressure sensor PU.

[0041] The pressure unit KU is provided with a fluid pump QA for pressure accumulation so as to accumulate the accumulator AC. The pressure accumulation fluid pump QA is driven by an electric motor MA for pressure accumulation and pumps up the brake fluid BF from the master reservoir RV. Then, the brake fluid BF discharged from the fluid pump QA is stored in the accumulator AC. The accumulator AC stores the brake fluid BF pressurized up to the accumulator hydraulic pressure Pc. An accumulator hydraulic pressure sensor PC is provided to detect the accumulator hydraulic pressure Pc.

[0042] The electric motor MA for pressure accumulation is controlled by the brake controller ECU so that the accumulator hydraulic pressure Pc is maintained within a predetermined range. Specifically, when the accumulator hydraulic pressure Pc is less than the lower limit value pl, the electric motor MA is driven at a predetermined rotational speed. Also, when the accumulator hydraulic pressure Pc is greater than or equal to the upper limit value pu, the electric motor MA is stopped. Here, the lower limit value pl and the upper limit value pu are preset predetermined values (constants) and are in the relationship of "pl < pu". By controlling the electric motor MA, the accumulator hydraulic pressure Pc is maintained within the range from the lower limit value pl to the upper limit value pu.

[0043] The pressure unit KU is provided with a pressure cylinder CK to adjust the accumulator hydraulic pressure Pc from the accumulator AC and supply it to the servo chamber Ru. A pressure piston NK is inserted into the pressure cylinder CK. By the pressure piston NK, the inside of the pressure cylinder CK is partitioned into three hydraulic pressure chambers, i.e., a pilot chamber Rp, an annular chamber Rv, and a pressure chamber Rk, which are sealed by a seal member SL. The pilot chamber Rp and the pressure chamber Rk are arranged so as to sandwich the pressure piston NK. That is, the pilot chamber Rp is located on the side opposite to the pressure chamber Rk with respect to the pressure piston NK in the pressure cylinder CK. The pilot chamber Rp is supplied with a pilot hydraulic pressure Pp adjusted by a pressure increasing valve UZ and a pressure reducing valve UG, which will be described later.

[0044] An annular recess (constriction) is provided on the outer peripheral portion of the pressure piston NK. An annular chamber Rv is formed by this annular recess and the inner peripheral portion of the pressure cylinder CK. Further, a valve body Vv (for example, a spool valve) is formed on the outer peripheral portion of the pressure piston NK. And a brake fluid BF pressurized to the accumulator hydraulic pressure Pc from the accumulator AC is supplied to this valve body Vv. The valve body Vv regulates the accumulator hydraulic pressure Pc and introduces it into the annular chamber Rv. The annular chamber Rv communicates with the pressure chamber Rk through a through hole provided in the pressure piston NK. Therefore, the hydraulic pressure in the annular chamber Rv and the hydraulic pressure in the pressure chamber Rk are the same. This hydraulic pressure is referred to as "servo hydraulic pressure Pu".

[0045] Specifically, when the pressure piston NK is moved by the hydraulic pressure (pilot hydraulic pressure) Pp in the pilot chamber Rp, the opening amount of the valve body Vv changes. And the brake fluid BF is supplied from the accumulator AC through the valve body Vv of the pressure piston NK so that the pilot hydraulic pressure Pp (the hydraulic pressure in the pilot chamber Rp) and the servo hydraulic pressure Pu (the hydraulic pressures in the annular chamber Rv and the pressure chamber Rk) match. That is, the high-pressure accumulator hydraulic pressure Pc is throttled by the valve body Vv and adjusted to the servo hydraulic pressure Pu. A servo hydraulic pressure sensor PU is provided to detect the actual servo hydraulic pressure Pu. The detected servo hydraulic pressure Pu is input to the brake controller ECU. The controller ECU adjusts the pilot hydraulic pressure Pp based on the servo hydraulic pressure Pu, and finally controls so that the servo hydraulic pressure Pu matches the target value. Since the pressure chamber Rk and the servo chamber Ru are connected by a fluid passage, the brake fluid BF adjusted to the servo hydraulic pressure Pu is supplied from the pressure unit KU to the servo chamber Ru.

[0046] ≪Operation of the First Unit YA≫ When not braking (i.e., when the braking operation member BP is not being operated), the pistons "NN, NP, NS" are pressed by the springs "DN, DP, DS" and are returned to their initial positions (the positions where they have moved the most in the backward direction Hb). In this state, the front-wheel and rear-wheel master chambers Rmf, Rmr and the master reservoir RV are in communication, and the front-wheel and rear-wheel supply hydraulic pressures Pmf, Pmr are "0 (atmospheric pressure)". Also, at the initial positions of the respective pistons, there is a gap between the input piston NN and the first master piston NP. Similarly, when not braking, the pressure increasing valve UZ is closed and the pressure reducing valve UG is open, so the pilot chamber Rp and the master reservoir RV are in communication, and the pilot hydraulic pressure Pp is "0 (atmospheric pressure)". And the pressurizing piston NK is pressed against the bottom of the pressurizing cylinder CK by the compression spring DK, and the valve body Vv (spool valve) is closed. Since the pressurizing chamber Rk and the master reservoir RV are in communication, the servo hydraulic pressure Pu is also "0". Further, when not braking, the input valve VN and the release valve VR are open, and the rear chamber Ro and the input chamber Rn are in communication with the master reservoir RV, so the internal pressures Po, Pn of these are also "0". That is, when not braking, it is in the state of "Pmf = Pmr = Pp = Pu = Po = Pn = 0".

[0047] During braking (i.e., when the braking operation member BP is operated), the input valve VN is opened and the release valve VR is closed. That is, the input chamber Rn and the rear chamber Ro are in a communicating state, and the communicating state between the rear chamber Ro and the master reservoir RV is blocked and made non-communicating. As the operation amount Ba of the braking operation member BP increases, the input piston NN moves in the forward direction Ha, and the braking fluid BF is discharged from the input chamber Rn. Since this braking fluid BF is absorbed by the stroke simulator SS, the hydraulic pressure Pn (input hydraulic pressure) of the input chamber Rn and the hydraulic pressure Po (rear hydraulic pressure) of the rear chamber Ro are increased, and an operating force Fp is generated on the braking operation member BP. At this time, the pressure increasing valve UZ and the pressure reducing valve UG are controlled according to the braking operation amount Ba (at least one of the simulator hydraulic pressure Ps, the operation displacement Sp, and the operation force Fp), and the hydraulic pressure Pp (pilot hydraulic pressure) of the pilot chamber Rp is increased. In response to the increase in the pilot hydraulic pressure Pp, the valve body Vv is opened, and the hydraulic pressure Pu (servo hydraulic pressure) of the annular chamber Rv and the pressurizing chamber Rk is increased. Since this servo hydraulic pressure Pu is supplied to the servo chamber Ru, the first master piston NP is pressed in the forward direction Ha and moves in the forward direction Ha. As the first master piston NP moves in the forward direction Ha, the front-wheel and rear-wheel supply hydraulic pressures Pmf, Pmr (= Pm) are increased. Then, the braking fluid BF adjusted to the supply hydraulic pressure Pm by the first unit YA is supplied to the second unit YB, and finally the braking hydraulic pressure Pw of the wheel cylinder CW is increased.

[0048] Since the braking control device SC is a so-called brake-by-wire type, when the vehicle is an electric vehicle (for example, an electric car or a hybrid car), regenerative cooperative control is executed. Since there is a gap between the input piston NN and the first master piston NP, by controlling the servo hydraulic pressure Pu, the relative positional relationship between the input piston NN and the first and second master pistons NP, NS can be arbitrarily adjusted within the range of this gap. For example, when only the braking force by regenerative braking is required, "Pu = 0" is set, and the supply hydraulic pressures Pm from the front-wheel and rear-wheel master chambers Rmf, Rmr remain "0". The braking force due to the friction between the rotating member KT and the friction member is not generated, and the braking force Fb is generated only by the regenerative braking force of the driving electric motor functioning as a generator.

[0049] <Second unit YB> Referring to the schematic diagram of FIG. 3, a configuration example of the second unit YB included in the fluid unit HU will be described. The second unit YB is provided between the first unit YA and the wheel cylinder CW in the communication path HS (a fluid path for moving the brake fluid BF). The brake control device SC can adjust (increase, hold, decrease) the supply hydraulic pressure Pm by the second unit YB. That is, the hydraulic pressure Pw of the wheel cylinder CW is finally adjusted by the second unit YB. For example, the second unit YB is used for anti-lock brake control (control to suppress locking of the wheel WH), traction control (control to suppress spinning of the wheel WH), and vehicle stability control (control to suppress excessive understeer and oversteer). The second unit YB is composed of a supply hydraulic pressure sensor PM, a pressure regulating valve UB, a fluid pump QB for reflux, an electric motor MB for reflux, a pressure regulating reservoir RC, an inlet valve UI, and an outlet valve VO.

[0050] Similar to the first unit YA, the second unit YB is also controlled by the brake controller ECU. Specifically, in the controller ECU, drive signals Ub of the pressure regulating valve UB, Ui of the inlet valve UI, Vo of the outlet valve VO, and Mb of the electric motor MB for reflux are calculated based on the above-described various signals (Ba, etc.). Then, according to these drive signals (Ub, etc.), the solenoid valves "UB, UI, VO" constituting the second unit YB and the electric motor MB for reflux are controlled (driven).

[0051] The front wheel, rear wheel pressure regulating valves UBf, UBr (= UB) are provided in the front wheel, rear wheel connecting paths HSf, HSr (= HS). The pressure regulating valve UB (solenoid valve) is a normally open linear valve (also referred to as a "differential pressure valve" or "proportional valve"). The upper part of the pressure regulating valve UB (the part of the connecting path HS close to the first unit YA) and the lower part of the pressure regulating valve UB (the part of the connecting path HS close to the wheel cylinder CW) are connected by the front wheel, rear wheel return paths HKf, HKr (= HK). The return path HK is provided with the front wheel, rear wheel return fluid pumps QBf, QBr (= QB), and the front wheel, rear wheel pressure regulating reservoirs RCf, RCr (= RC). The return fluid pump QB is driven by the return electric motor MB. A supply fluid pressure sensor PM is provided at the upper part of the pressure regulating valve UB to detect the actual hydraulic pressure (supply hydraulic pressure) Pm supplied by the first unit YA.

[0052] When the electric motor MB is rotationally driven, the fluid pump QB sucks the braking fluid BF from the upper part of the pressure regulating valve UB and discharges the braking fluid BF to the lower part of the pressure regulating valve UB. As a result, a return KN of the braking fluid BF (that is, the front wheel, rear wheel return KNf, KNr, which is the flow of the circulating braking fluid BF) including the pressure regulating reservoir RC is generated in the connecting path HS and the return path HK. When the return KN of the braking fluid BF is restricted by the pressure regulating valve UB, the hydraulic pressure Pq (referred to as the "adjusted hydraulic pressure") at the lower part of the pressure regulating valve UB is increased from the hydraulic pressure Pm (supply hydraulic pressure) at the upper part of the pressure regulating valve UB due to the orifice effect. That is, it is possible for the second unit YB to increase the front wheel, rear wheel braking hydraulic pressures Pwf, Pwr (= Pw) from the supply hydraulic pressure Pm. In the second unit YB, the return electric motor MB, the return fluid pump QB, and the pressure regulating valve UB are referred to as a "pressure source KB".

[0053] Inside the second unit YB, the front-wheel and rear-wheel connection paths HSf and HSr are each branched into two and connected to the front-wheel and rear-wheel wheel cylinders CWf and CWr, respectively. And for each wheel cylinder CW, an inlet valve UI and an outlet valve VO are provided. The inlet valve UI (electromagnetic valve) is a normally open linear valve, similar to the pressure regulating valve UB. However, the pressure regulating valve UB and the inlet valve UI open in different directions. Specifically, since the pressure regulating valve UB opens corresponding to the flow of the brake fluid BF from the wheel cylinder CW to the master cylinder CM, in the pressure regulation by the pressure regulating valve UB, the regulated hydraulic pressure Pq is equal to or higher than the supply hydraulic pressure Pm (i.e., "Pq≧Pm"). On the other hand, since the inlet valve UI opens corresponding to the flow from the master cylinder CM to the wheel cylinder CW, in the pressure regulation by the inlet valve UI, the brake hydraulic pressure Pw is equal to or lower than the regulated hydraulic pressure Pq (i.e., "Pq≧Pw").

[0054] The inlet valve UI is provided in the branched connection path HS (i.e., the side closer to the wheel cylinder CW with respect to the branch portion of the connection path HS). The connection path HS is connected to the pressure regulating reservoir RC via a pressure reducing path HG at the lower part of the inlet valve UI (the portion of the connection path HS closer to the wheel cylinder CW). And in the pressure reducing path HG, an outlet valve VO, which is a normally closed on-off valve, is arranged.

[0055] The inlet valve UI and the outlet valve VO are individually controlled so that the braking hydraulic pressure Pw is adjusted separately for each wheel cylinder CW. To decrease the braking hydraulic pressure Pw, the inlet valve UI is closed and the outlet valve VO is opened. The inflow of the braking fluid BF into the wheel cylinder CW is blocked and the braking fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RC, so the braking hydraulic pressure Pw is decreased. To increase the braking hydraulic pressure Pw, the inlet valve UI is opened and the outlet valve VO is closed. The outflow of the braking fluid BF to the pressure regulating reservoir RC is blocked and the regulated hydraulic pressure Pq from the pressure regulating valve UB is supplied to the wheel cylinder CW, so the braking hydraulic pressure Pw is increased. To hold the braking hydraulic pressure Pw, both the inlet valve UI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the braking hydraulic pressure Pw is maintained constant.

[0056] <Adjustment of Braking Hydraulic Pressure Pw in Off-Road Control> Referring to the flowchart of FIG. 4, the adjustment process of the braking hydraulic pressure Pw in off-road control will be described. As described above, off-road control is a general term for downhill assist control and crawl control. Hereinafter, the process will be described taking crawl control as an example. Note that for downhill assist control, replacing "Xc" with "Xd" and "vc" with "vd" respectively corresponds to the description of the control.

[0057] In step S110, various signals including the operation signal Xc for crawl control, the wheel speed Vw, the vehicle body speed Vx, the servo hydraulic pressure Pu, the supply hydraulic pressure Pm, etc. are read. Here, the vehicle body speed Vx is calculated by the brake controller ECU based on the wheel speed Vw and a known method. Further, the operation signal Xc includes a signal related to the necessity of executing crawl control and information on the set speed vc of crawl control.

[0058] In step S120, based on an operation signal (switch signal) Xc or the like, it is determined whether "crawl control (i.e., off-road control) is activated or not (presence or absence of an activation request)". If the activation of crawl control is requested by the switch signal Xc, step S120 is affirmed and the process proceeds to step S130. On the other hand, if step S120 is negated, the process returns to step S110.

[0059] In step S130, based on the deviation hV between the actual vehicle body speed Vx and the set speed vc (the target value of the vehicle body speed Vx in crawl control), the target hydraulic pressure Pt of each wheel cylinder CW is calculated. That is, in crawl control, the braking hydraulic pressure Pw is adjusted individually for each wheel cylinder CW. Specifically, the deviation hV between the vehicle body speed Vx and the set speed vc is calculated (i.e., "hV = Vx - vc"). Here, the set speed vc is the target value of the vehicle body speed Vx in crawl control. Based on the speed deviation hV, the target total braking force Fvt, which is the target value of the braking force acting on the entire vehicle (the sum of the braking forces of the four wheels), is calculated. Further, the distribution ratio Hw of each wheel WH is determined, and the target total braking force Fvt is multiplied by the ratio Hw to determine the target value (target braking force) Fbt of the braking force Fb of each wheel WH (i.e., "Fbt = Fvt·Hw"). Finally, based on the specifications of the braking device SX, the braking control device SC, etc., the target braking force Fbt is converted into the dimension of the hydraulic pressure in each wheel cylinder CW, and the target hydraulic pressure Pt corresponding to the braking hydraulic pressure Pw is calculated. For example, the distribution ratio Hw can be set to "0.25" so as to be uniform among the four wheels WH. Also, the distribution ratio Hwf of the front wheels WHf may be set to be larger than the distribution ratio Hwr of the rear wheels WHr.

[0060] In addition, at least one of the following five corrections is considered in the calculation of the target braking force Fbt of each wheel WH. And the final target hydraulic pressure Pt is determined according to the corrected target braking force Fbt. (Correction 1): Adjust so that the distribution ratio of the braking force to the front wheels WHf increases as the set speed vc decreases. (Correction 2): When the set speed vc is set in a low speed area (low speed region), a lower limit value fbl (referred to as "lower limit braking force") is set for the braking force Fb. And at least the lower limit braking force fbl is generated for each wheel WH. (Correction 3): When the vehicle body speed Vx exceeds the set speed vc, the lower limit braking force fbl is set, and at least the lower limit braking force fbl is generated for each wheel WH. (Correction 4): When the driving force Fd is greater than a predetermined value, the lower limit braking force fbl is set, and at least the lower limit braking force fbl is generated for each wheel WH. (Correction 5): When the vehicle stops during control, a limit is imposed on the decrease in the braking force for a predetermined time after the stop.

[0061] In step S140, the selected wheel cylinder CWx and the non - selected wheel cylinder CWz are determined. The "selected wheel cylinder CWx" is the wheel cylinder CW corresponding to the maximum value Ptx (also referred to as "maximum target hydraulic pressure") among the plurality of target hydraulic pressures Pt. Also, the "non - selected wheel cylinder CWz" is a wheel cylinder CW other than the selected wheel cylinder CWx among the wheel cylinders CW. That is, one of the four wheel cylinders CW provided for the wheels WH of the vehicle JV is the selected wheel cylinder CWx, and the remaining three are non - selected wheel cylinders CWz.

[0062] In the following description, among those related to the wheel cylinder CW, it is indicated that the subscript "x" corresponds to the selected wheel cylinder CWx, and the subscript "z" corresponds to the non-selected wheel cylinder CWz, respectively. Therefore, among the four actual braking hydraulic pressures Pw, the actual hydraulic pressure of the selected wheel cylinder CWx is referred to as the "selected braking hydraulic pressure Pwx", and the actual hydraulic pressure of the non-selected wheel cylinder CWz is referred to as the "non-selected braking hydraulic pressure Pwz", respectively. Also, among the four target hydraulic pressures Pt, the one corresponding to the non-selected wheel cylinder CWz is referred to as the "non-selected target hydraulic pressure Ptz". Note that since the maximum target hydraulic pressure Ptx (the target hydraulic pressure corresponding to the selected wheel cylinder) is the maximum value of the target hydraulic pressure Pt, the magnitude relationship between the non-selected target hydraulic pressure Ptz (as a result, the actual non-selected braking hydraulic pressure Pwz) and the maximum target hydraulic pressure Ptx (as a result, the actual selected braking hydraulic pressure Pwx) is "Ptz ≦ Ptx, Pwz ≦ Pwx".

[0063] For the components provided corresponding to each of the four wheel cylinders CW, the elements corresponding to the selected wheel cylinder CWx are given the subscript "x", and the elements corresponding to the non-selected wheel cylinder CWz (that is, the elements not corresponding to the selected wheel cylinder CWx) are given the subscript "z". For example, among the four inlet valves UI and the outlet valve VO, each component corresponding to the selected wheel cylinder CWx is referred to as the "selected inlet valve UIx" and the "selected outlet valve VOx". On the other hand, among the four inlet valves UI and the outlet valve VO, each component corresponding to the non-selected wheel cylinder CWz is referred to as the "non-selected inlet valve UIz" and the "non-selected outlet valve VOz".

[0064] Furthermore, in the braking control device SC, two systems of braking fluid passages are adopted. Components of the system including the selective wheel cylinder CWx are suffixed with "x", and components of the system not including the selective wheel cylinder CWx are suffixed with "z". For example, among the two communication passages HS, the pressure regulating valve UB, the pressure regulating reservoir RC, and the fluid pump QB, each component belonging to the system including the selective wheel cylinder CWx is referred to as "selective communication passage HSx", "selective pressure regulating valve UBx", "selective pressure regulating reservoir RCx", and "selective fluid pump QBx". On the other hand, among the two communication passages HS, the pressure regulating valve UB, the pressure regulating reservoir RC, and the fluid pump QB, each component belonging to the system not including the selective wheel cylinder CWx is referred to as "non-selective communication passage HSz", "non-selective pressure regulating valve UBz", "non-selective pressure regulating reservoir RCz", and "non-selective fluid pump QBz".

[0065] In step S150, based on the maximum target hydraulic pressure Ptx (the maximum value among the four target hydraulic pressures Pt), the selective braking hydraulic pressure Pwx (the actual hydraulic pressure of the selective wheel cylinder CWx) is adjusted. The selective braking hydraulic pressure Pwx is achieved by controlling the first unit YA. That is, the pressurizing unit KU of the first unit YA is controlled (driven) so that the actual selective braking hydraulic pressure Pwx matches the maximum target hydraulic pressure Ptx. Specifically, the target value Pv of the servo hydraulic pressure Pu corresponding to the maximum target hydraulic pressure Ptx (also referred to as the "target servo hydraulic pressure") is calculated, and the pressure increasing valve UZ and the pressure reducing valve UG are controlled (so-called hydraulic feedback control) so that the actual servo hydraulic pressure Pu (the detected value of the servo hydraulic pressure sensor PU) matches the target servo hydraulic pressure Pv (the target value). In the selective wheel cylinder CWx, the inlet valve UI and the outlet valve VO are in a non-energized state, and they are in a fully open state (i.e., the valve opening amount is maximum). Therefore, the selective braking hydraulic pressure Pwx matches the supply hydraulic pressure Pm.

[0066] In step S160, based on the target hydraulic pressure Ptz of the non-selected wheel cylinder CWz, the non-selected braking hydraulic pressure Pwz (the actual hydraulic pressure of the non-selected wheel cylinder CWz) is adjusted. The non-selected braking hydraulic pressure Pwz is achieved by controlling the inlet valve UIz (referred to as the "non-selected inlet valve") and the outlet valve Voz (referred to as the "non-selected outlet valve") in the second unit YB. That is, the non-selected inlet valve UIz and the non-selected outlet valve Voz are controlled (driven) so that the actual non-selected braking hydraulic pressure Pwz matches the non-selected target hydraulic pressure Ptz of the non-selected wheel cylinder CWz. In the adjustment of the non-selected braking hydraulic pressure Pwz, the first unit YA is used as the pressure source. Therefore, in the second unit YB, hydraulic pressure adjustment is performed based on the supply hydraulic pressure Pm from the first unit YA.

[0067] Specifically, for the adjustment of the non-selected braking hydraulic pressure Pwz, one of the three control modes, namely the "decrease mode", the "increase mode", and the "hold mode", is selected. In the decrease mode, when it is necessary to decrease the non-selected braking hydraulic pressure Pwz, the non-selected inlet valve UIz is closed and the non-selected outlet valve Voz is opened. The supply hydraulic pressure Pm corresponding to the maximum target hydraulic pressure Ptx is supplied to the upper part of the non-selected inlet valve UIz (the side close to the first unit YA), but since the non-selected inlet valve UIz is closed, this supply is blocked. Then, since the non-selected outlet valve Voz is opened, the braking fluid BF in the non-selected wheel cylinder CWz flows out to the pressure regulating reservoir RC, and the non-selected braking hydraulic pressure Pwz is decreased.

[0068] In the increasing mode, when an increase in the non-selective braking hydraulic pressure Pwz is required, the non-selective outlet valve Voz is closed and the non-selective inlet valve Uiz is opened. By closing the non-selective outlet valve Voz, the outflow of the braking fluid BF to the pressure regulating reservoir RC is blocked. Then, since the supply hydraulic pressure Pm is supplied to the non-selective wheel cylinder CWz through the non-selective inlet valve Uiz, the braking hydraulic pressure Pwz is increased. Note that in the adjustment of the non-selective braking hydraulic pressure Pwz, since the supply hydraulic pressure Pm (= Pwx) generated by the first unit YA is used as a basis, the upper limit of the non-selective braking hydraulic pressure Pwz is the selective braking hydraulic pressure Pwx (i.e., "Pwz ≦ Pwx").

[0069] In the holding mode, when it is necessary to hold the non-selective braking hydraulic pressure Pwz, both the non-selective inlet valve Uiz and the non-selective outlet valve Voz are closed. Since the non-selective wheel cylinder CWz is fluid-tightly sealed, the non-selective braking hydraulic pressure Pwz is maintained constant. Note that in the adjustment of the non-selective braking hydraulic pressure Pwz, the holding mode may be omitted. In this case, the braking hydraulic pressure Pwz of the non-selective wheel cylinder CWz is adjusted by repeating the decreasing mode and the increasing mode.

[0070] In step S170, the electric motor MB for reflux is driven. In the adjustment of the non-selective braking hydraulic pressure Pwz (particularly in the decreasing mode), the pressure is reduced by flowing the braking fluid BF out to the pressure regulating reservoir RC. However, the reflux electric motor MB rotates the reflux fluid pump QB so as to return the braking fluid BF accumulated in the pressure regulating reservoir RC to the communication path HS between the pressure regulating valve UB and the inlet valve UI.

[0071] In step S170, the driving / stopping of the electric motor MB may be performed based on the amount of the braking fluid BF in the pressure regulating reservoir RC (referred to as the "reservoir fluid amount Ec") so as to suppress the heat generation of the electric motor MB. Specifically, when the reservoir fluid amount Ec is less than a predetermined fluid amount ex, the electric motor MB is stopped. And when the reservoir fluid amount Ec is equal to or more than the predetermined fluid amount ex, the electric motor MB is energized and the fluid pump QB is driven. Here, the predetermined fluid amount ex is a preset predetermined value (constant). Note that the reservoir fluid amount Ec is estimated based on the driving state (e.g., valve opening time) of the outlet valve VOz, the driving state of the electric motor MB, and the like.

[0072] <Structure of inlet valve UI and pressure regulating valve UB, etc.> Referring to FIGS. 5(a) and 5(b), the inlet valve UI and the pressure regulating valve UB will be described. The inlet valve UI and the pressure regulating valve UB are normally open linear valves (solenoid valves) and are controlled by the braking controller ECU.

[0073] ≪Structure of inlet valve UI≫ First, referring to the schematic diagram of FIG. 5(a), the structure of the inlet valve UI will be described. In the inlet valve UI, as the energization amount Ii (e.g., current value) increases, the valve opening amount (lift amount) Li decreases. The inlet valve UI is composed of a solenoid SD, a valve body VT, a guide member GD, a holding member HJ, and a spring member SB.

[0074] The solenoid SD is composed of a fixed coil CL and a plunger (movable iron core) PL. The fixed coil CL is fixed to the housing of the inlet valve UI (for example, the guide member GD). A valve body VT is fixed to the plunger PL. The tip Vt of the valve body VT is formed (machined) into a spherical shape. In the inlet valve UI, the gap (i.e., the valve opening amount) Li between the spherical tip Vt and the valve seat Vz formed (machined) into a conical shape on the holding member HJ described later is linearly controlled according to the energization amount (current value) to the fixed coil CL. In this linear control, when a current is passed through the fixed coil CL, the force Ca (a downward thrust in the figure, referred to as "attractive force") that pulls the plunger PL into the fixed coil CL is utilized.

[0075] The guide member GD is provided with two holes having different diameters. The hole with the smaller diameter of the two holes is called the "guide hole Ag", and the hole with the larger diameter is called the "sealing hole Af". The valve body VT is inserted into the guide hole Ag of the guide member GD so as to be smoothly movable along its central axis Jv. In the guide member GD, the sealing hole Af located on the side opposite to the side of the plunger PL is sealed by the holding member HJ. Specifically, the holding member HJ is press-fitted into the cylindrical inner peripheral portion of the sealing hole Af.

[0076] A valve chamber Rz is formed by the inner peripheral portion of the sealing hole Af of the guide member GD, the end face of the holding member HJ, and the valve body VT. In the holding member HJ, a conical valve seat Vz is formed on the end face on the side of the valve chamber Rz. Here, the conical surface of the valve seat Vz faces the wheel cylinder CW in the communication path HS. An inflow hole Ai is provided at the center of the valve seat Vz. The braking fluid BF adjusted to the regulated hydraulic pressure Pq by the pressure regulating valve UB is supplied to the inflow hole Ai. The inflow hole Ai is connected to the fluid pump QB for reflux via a reflux path HK. A check valve is provided in the holding member HJ so that the braking fluid BF can move from the side of the valve chamber Rz to the side of the fluid pump QB for reflux.

[0077] Between the holding member HJ and the valve body VT, a spring member SB (for example, a compression coil spring) is provided so as to press the valve body VT toward the plunger PL side. By the spring member SB, the valve body VT is pushed toward the plunger PL side with an elastic force Cs (an upward thrust force in the figure). Here, the plunger PL, the valve body VT (tip portion Vt), the spring member SB, the valve seat Vz, and the inflow hole Ai are coaxially arranged on the central axis Jv. Therefore, the attractive force Ca and the elastic force Cs oppose each other on the central axis Jv.

[0078] An outflow hole Ao is provided in the inner peripheral portion of the sealing hole Af that forms the valve chamber Rz. The outflow hole Ao is connected to the wheel cylinder CW via the communication path HS. From the outflow hole Ao, the braking fluid BF adjusted to the braking hydraulic pressure Pw by the inlet valve UI (that is, the gap Li between the tip portion Vt and the valve seat Vz) is supplied to the wheel cylinder CW. In the communication path HS, between the outflow hole Ao and the wheel cylinder CW, it is connected to the reflux fluid pump QB via the pressure reducing path HG and the outlet valve VO. In the pressure reducing path HG, a pressure regulating reservoir RC is connected between the outlet valve VO and the reflux fluid pump QB.

[0079] When the energization to the fixed coil CL is stopped (that is, in the state of "Ii = 0"), the attractive force Ca is not generated, and the valve body VT is pressed toward the solenoid SD (plunger PL, fixed coil CL) side by the elastic force Cs. Therefore, the tip portion Vt of the valve body VT is separated from the valve seat Vz. That is, the inlet valve UI is fully open.

[0080] When the fixed coil CL is energized, an attractive force Ca is generated. Due to this attractive force Ca, the tip Vt of the valve body VT is pressed in the direction of the valve seat Vz, and the inlet valve UI tends to close. At this time, in addition to the elastic force Cs, a force Cb (an upward thrust in Fig. 5(a), referred to as "fluid force") with which the braking fluid BF tries to flow from the pressure regulating valve UB to the wheel cylinder CW side acts on the valve body VT. In the inlet valve UI, in a state where the resultant force Cg of the fluid force Cb and the elastic force Cs is balanced with the attractive force Ca, the difference wQ (differential pressure) between the hydraulic pressure (regulated hydraulic pressure) Pq on the pressure regulating valve UB side and the hydraulic pressure (braking hydraulic pressure) Pw on the wheel cylinder CW side is determined. In other words, the relationship between the energization amount Ii to the inlet valve UI and the hydraulic pressure difference wQ (=Pq - Pw) is uniquely determined.

[0081] ≪Structure of the pressure regulating valve UB≫ Next, with reference to Fig. 5(a), the structure of the pressure regulating valve UB will be described. In Fig. 5(a), the symbols described in [ ] correspond to the description of the pressure regulating valve UB. Similar to the inlet valve UI, in the pressure regulating valve UB as well, as the energization amount Ib (for example, current value) increases, the valve opening amount Lb (the gap between the valve seat Vz and the tip Vt of the valve body in the pressure regulating valve UB) decreases. The structure of the pressure regulating valve UB is basically the same as that of the inlet valve UI. The difference between the pressure regulating valve UB and the inlet valve UI lies in the connection method in the fluid path. This difference will be briefly described below.

[0082] The inlet hole Ai of the inlet valve UI is connected to the pressure regulating valve UB, while the inlet hole Ai of the pressure regulating valve UB is connected to the inlet valve UI. Therefore, the inlet hole Ai of the inlet valve UI and the inlet hole Ai of the pressure regulating valve UB are connected via the communication path HS. The outlet hole Ao of the inlet valve UI is connected to the wheel cylinder CW, while the inlet hole Ai of the pressure regulating valve UB is connected to the master cylinder CM. Therefore, in the pressure regulating valve UB, in a state where the suction force Ca and the resultant force Cg (= Cb + Cs) are balanced, the difference mQ (differential pressure) between the hydraulic pressure (regulated hydraulic pressure) Pq on the side of the inlet valve UI and the hydraulic pressure (supply hydraulic pressure) Pm on the side of the master cylinder CM is determined. In other words, the relationship between the energization amount Ib to the pressure regulating valve UB and the hydraulic pressure difference mQ (= Pq - Pm) is uniquely determined. Note that the valve seat conical surface Vz of the inlet valve UI faces the direction of the wheel cylinder CW, while the valve seat conical surface Vz of the pressure regulating valve UB faces the direction of the master cylinder CM. From this, the magnitude relationship among the supply hydraulic pressure Pm, the regulated hydraulic pressure Pq, and the braking hydraulic pressure Pw is determined.

[0083] ≪Magnitude Relationship among Supply Hydraulic Pressure Pm, Regulated Hydraulic Pressure Pq, and Braking Hydraulic Pressure Pw≫ With reference to the schematic diagram (partial hydraulic circuit diagram) of FIG. 5(b), the magnitude relationship (i.e., the range in which hydraulic pressure can occur) among the supply hydraulic pressure Pm, the regulated hydraulic pressure Pq, and the braking hydraulic pressure Pw will be described. As described above, the master cylinder CM and the wheel cylinder CW of the first unit YA are connected via the communication path HS. In the communication path HS, the inlet valve UI and the pressure regulating valve UB are arranged in order from the closest to the wheel cylinder CW. That is, an inlet valve UI is provided in the communication path HS between the master cylinder CM and the wheel cylinder CW. And a pressure regulating valve UB is provided in the communication path HS between the master cylinder CM and the inlet valve UI.

[0084] The magnitude relationship among the supply hydraulic pressure Pm, the adjustment hydraulic pressure Pq, and the braking hydraulic pressure Pw depends on the direction in which the suction force Ca acts on the inlet valve UI and the pressure regulating valve UB. Specifically, in the inlet valve UI, the valve seat surface Vz (conical surface) faces the direction of the wheel cylinder CW in the communication path HS. And due to the suction force Ca of the inlet valve UI, the tip Vt of the valve body is pressed against the valve seat Vz. That is, the suction force Ca of the inlet valve UI is generated in a direction that opposes the flow force Cb corresponding to the flow of the braking fluid BF from the master cylinder CM side to the wheel cylinder CW side. Therefore, in the state where the inlet valve UI is energized, the hydraulic pressure Pq (adjustment hydraulic pressure between the pressure regulating valve UB and the inlet valve UI) on the master cylinder CM side with respect to the inlet valve UI is always equal to or higher than the hydraulic pressure (braking hydraulic pressure) Pw on the wheel cylinder CW side with respect to the inlet valve UI (that is, "Pq≧Pw"). In other words, the braking hydraulic pressure Pw can be adjusted within the range of being equal to or lower than the adjustment hydraulic pressure Pq by the inlet valve UI. Note that since the inlet valve UI is of the normally open type, when "Ii = 0", the inlet valve UI is fully opened. That is, in the state of "Ii = 0", the opening amount Li of the inlet valve UI becomes maximum and "Pw = Pq".

[0085] In the pressure regulating valve UB, the valve seat surface Vz (conical surface) faces the master cylinder CM in the communication path HS. In the pressure regulating valve UB, since it is opposite to the inlet valve UI in the direction of the valve seat Vz, the suction force Ca of the pressure regulating valve UB is generated in a direction that opposes the fluid force Cb corresponding to the flow of the braking fluid BF from the wheel cylinder CW side to the master cylinder CM side. Therefore, in the state where the pressure regulating valve UB is energized, the hydraulic pressure Pq on the wheel cylinder CW side with respect to the pressure regulating valve UB (the regulated hydraulic pressure between the pressure regulating valve UB and the inlet valve UI) is always equal to or higher than the hydraulic pressure (supply hydraulic pressure) Pm on the master cylinder CM side with respect to the pressure regulating valve UB (i.e., "Pq≧Pm"). In other words, the regulated hydraulic pressure Pq can be adjusted within a range equal to or higher than the supply hydraulic pressure Pm by the pressure regulating valve UB. Note that the pressure regulating valve UB is also of the normally open type like the inlet valve UI, so the pressure regulating valve UB is fully opened by "Ib = 0". That is, in the state of "Ib = 0", the opening amount Lb of the pressure regulating valve UB becomes maximum and "Pw = Pq".

[0086] <Processing of Fluctuation Suppression Control> With reference to the block diagram of FIG. 6, the arithmetic processing of the fluctuation suppression control will be described. "Fluctuation suppression control" is to suppress the fluctuation of the selected braking hydraulic pressure Pwx in the selected wheel cylinder CWx. The algorithm of the fluctuation suppression control is programmed in the microprocessor MP of the brake controller ECU. The following description regarding the fluctuation suppression control targets the selected wheel cylinder CWx (the wheel cylinder CW corresponding to the maximum target hydraulic pressure Ptx). Therefore, unless otherwise specified, "CW" represents "CWx", "Pw" represents "Pwx", "Pq" represents "Pqx", "UI" represents "UIx", "UB" represents "UBx", "Iit" represents "Iitx", "Ii" represents "Iix", "Ibt" represents "Ibtx", "Ib" represents "Ibx", "II" represents "IIx", and "IB" represents "IBx", respectively.

[0087] First, the reasons for the fluctuations in the selected braking hydraulic pressure Pwx will be explained. As described above, the hydraulic pressure Pwx of the selected wheel cylinder CWx is increased and decreased by the first unit YA (specifically, the pressurizing unit KU). Specifically, the supply hydraulic pressure Pm generated by the first unit YA is supplied to the selected wheel cylinder CWx as the selected braking hydraulic pressure Pwx. On the other hand, the hydraulic pressure Pwz of the non-selected wheel cylinder CWz is adjusted by the non-selected inlet valve UIz and the non-selected outlet valve VOz. When the non-selected braking hydraulic pressure Pwz is controlled, fluctuations in the amount (liquid amount) of the braking fluid BF occur in the fluid path (such as HS). Specifically, when an increase in the non-selected braking hydraulic pressure Pwz is required, the non-selected inlet valve UIz is opened, and the braking fluid BF is moved to the non-selected wheel cylinder CWz. When it is necessary to maintain the non-selected braking hydraulic pressure Pwz, both the non-selected inlet valve UIz and the non-selected outlet valve VOz are closed, so the braking fluid BF is not consumed in the non-selected wheel cylinder CWz. When a decrease in the non-selected braking hydraulic pressure Pwz is required, the non-selected inlet valve UIz is closed and the non-selected outlet valve VOz is opened, so the braking fluid BF is moved from the non-selected wheel cylinder CWz to the pressure regulating reservoir RC. Further, when the amount (reservoir liquid amount) Ec of the braking fluid BF in the pressure regulating reservoir RC increases, the electric motor MB is driven, and the braking fluid BF is returned by the fluid pump QB between the pressure regulating valve UB and the inlet valve UI. Thus, in the communication path HSx related to the selected wheel cylinder CWx, in addition to adjusting the supply hydraulic pressure Pm (= Pwx), a change in the liquid amount of the braking fluid BF occurs as a disturbance. Due to this change in the liquid amount, fluctuations occur in the supply hydraulic pressure Pm (and as a result, the selected braking hydraulic pressure Pwx). The fluctuation suppression control is to suppress the hydraulic pressure fluctuations in the selected braking hydraulic pressure Pwx.

[0088] The fluctuation suppression control is composed of a hydraulic pressure deviation calculation block HP, a target energization amount calculation block IIT related to the inlet valve UI, a target energization amount calculation block IBT related to the pressure regulating valve UB, and an energization amount feedback control block IFB.

[0089] In the hydraulic pressure deviation calculation block HP, the deviation hP between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx is calculated. Specifically, the hydraulic pressure deviation hP is a state quantity (state variable) determined by subtracting the maximum target hydraulic pressure Ptx from the supply hydraulic pressure Pm (the detected value of the supply hydraulic pressure sensor PM) (that is, "hP = Pm - Ptx"). When the hydraulic pressure deviation hP has a positive sign (that is, when the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx), the hydraulic pressure deviation hP is input to the target energization amount calculation block IIT related to the inlet valve UI. Conversely, when the hydraulic pressure deviation hP has a negative sign (that is, when the supply hydraulic pressure Pm is less than the maximum target hydraulic pressure Ptx), the hydraulic pressure deviation hP is input to the target energization amount calculation block IBT related to the pressure regulating valve UB.

[0090] In the target energization amount calculation block IIT related to the inlet valve UI (also referred to as the "first target energization amount calculation block"), based on the magnitude (absolute value) |hP| of the hydraulic pressure deviation hP, the target energization amount Iit of the inlet valve UI (also referred to as the "first target energization amount") is calculated. The first target energization amount Iit is the target value corresponding to the actual energization amount Ii (also referred to as the "first energization amount") for the inlet valve UI to adjust the braking hydraulic pressure Pw to decrease from the regulated hydraulic pressure Pq and make the actual selected braking hydraulic pressure Pwx approach the maximum target hydraulic pressure Ptx. Specifically, in the first target energization amount calculation block IIT related to the inlet valve UI, the IP characteristic of the inlet valve UI (a known characteristic representing the relationship between the energization amount Ii and the hydraulic pressure difference wQ) is preset as the calculation map Zii. Then, according to the calculation map Zii, the greater the magnitude |hP| of the hydraulic pressure deviation hP, the greater the target energization amount Iit is calculated. In other words, the target energization amount Iit is the target value for generating a hydraulic pressure difference wQ (the difference between the regulated hydraulic pressure Pq and the braking hydraulic pressure Pw) corresponding to the hydraulic pressure deviation hP to compensate for the excess of the selected braking hydraulic pressure Pwx over the maximum target hydraulic pressure Ptx. Note that in the first target energization amount calculation block IIT related to the inlet valve UI, since the pressure regulating valve UB cannot decrease the regulated hydraulic pressure Pq from the supply hydraulic pressure Pm, the target energization amount Ibt related to the pressure regulating valve UB is determined to be "0 (non-energized)".

[0091] In the target energization amount calculation block IBT (also referred to as the "second target energization amount calculation block") related to the pressure regulating valve UB, based on the magnitude (absolute value) |hP| of the hydraulic pressure deviation hP, the target energization amount Ibt (also referred to as the "second target energization amount") of the pressure regulating valve UB is calculated. The second target energization amount Ibt is the target value corresponding to the actual energization amount Ib (also referred to as the "second energization amount") for the pressure regulating valve UB to increase the regulated hydraulic pressure Pq from the supply hydraulic pressure Pm and bring the actual selective braking hydraulic pressure Pwx closer to the maximum target hydraulic pressure Ptx. Specifically, in the second target energization amount calculation block IBT, the IP characteristic (a known characteristic representing the relationship between the energization amount Ib and the hydraulic pressure difference mQ) of the pressure regulating valve UB is preset as the calculation map Zib. And according to the calculation map Zib, the larger the magnitude |hP| of the hydraulic pressure deviation hP, the larger the target energization amount Ibt is calculated. In other words, the target energization amount Ibt is the target value for generating a hydraulic pressure difference mQ (the difference between the regulated hydraulic pressure Pq and the supply hydraulic pressure Pm) corresponding to the hydraulic pressure deviation hP so as to compensate for the shortage of the selective braking hydraulic pressure Pwx with respect to the maximum target hydraulic pressure Ptx. Note that in the second target energization amount calculation block IBT related to the pressure regulating valve UB, since the inlet valve UI cannot increase the regulated hydraulic pressure Pq, the target energization amount Iit related to the inlet valve UI is determined to be "0 (non-energized)".

[0092] In the energization amount feedback control block IFB, based on the first and second target energization amounts Ibt, Iit, energization amount feedback control is executed, and power is supplied to the inlet valve UI and the pressure regulating valve UB. The drive circuit DD is provided with first and second energization amount sensors (for example, current sensors) II, IB to detect the actual first and second energization amounts Ii, Ib of the inlet valve UI and the pressure regulating valve UB. And when power is supplied to the inlet valve UI and the pressure regulating valve UB, in the energization amount feedback control block IFB of the drive circuit DD, energization amount feedback control is executed so that the actual first and second energization amounts Ii, Ib (the detected values of the first and second energization amount sensors II, IB) match the first and second target energization amounts Iit, Ibt.

[0093] The pressure regulating valve UB is supplied with the supply hydraulic pressure Pm, and the pressure regulating valve UB can adjust the regulated hydraulic pressure Pq within a range equal to or higher than the supply hydraulic pressure Pm. Also, the inlet valve UI is supplied with the regulated hydraulic pressure Pq, and the inlet valve UI can adjust the braking hydraulic pressure Pw within a range equal to or lower than the regulated hydraulic pressure Pq. When the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx, an increase in the supply hydraulic pressure Pm is unnecessary. Therefore, power is not supplied to the pressure regulating valve UB, and the pressure regulating valve UB is fully opened to achieve the state of "Pm = Pq". Then, by the inlet valve UI, the selective braking hydraulic pressure Pwx is decreased from the supply hydraulic pressure Pm (= Pq) so as to match the maximum target hydraulic pressure Ptx. At the supply hydraulic pressure Pm, the surplus hydraulic pressure component with respect to the maximum target hydraulic pressure Ptx (i.e., the hydraulic pressure deviation hP with a positive sign) is compensated, and the compensated hydraulic pressure is supplied to the selective wheel cylinder CWx as the selective braking hydraulic pressure Pwx.

[0094] When the supply hydraulic pressure Pm is less than the maximum target hydraulic pressure Ptx, a decrease in the supply hydraulic pressure Pm is unnecessary. Therefore, power is not supplied to the inlet valve UI, and the inlet valve UI is fully opened to achieve the state of "Pq = Pw". Then, by the pressure regulating valve UB, the braking hydraulic pressure Pw (= Pq) is increased from the supply hydraulic pressure Pm so as to match the maximum target hydraulic pressure Ptx. At the supply hydraulic pressure Pm, the deficit hydraulic pressure component with respect to the maximum target hydraulic pressure Ptx (i.e., the hydraulic pressure deviation hP with a negative sign) is compensated, and the compensated hydraulic pressure is supplied to the selective wheel cylinder CWx as the selective braking hydraulic pressure Pwx.

[0095] As described above, in the fluctuation suppression control, the fluctuation of the supply hydraulic pressure Pm is not suppressed. However, when the supply hydraulic pressure Pm is transmitted to the selective wheel cylinder CWx as the selective braking hydraulic pressure Pwx, by adjusting the opening amounts Li and Lb of the inlet valve UI and the pressure regulating valve UB based on the hydraulic pressure deviation hP (i.e., adjusting the actual first and second energization amounts Ii and Ib to the inlet valve UI and the pressure regulating valve UB), the excess or deficiency with respect to the maximum target hydraulic pressure Ptx is compensated. Therefore, the hydraulic pressure fluctuation of the selective braking hydraulic pressure Pwx is reduced. As a result, in the selective wheel cylinder CWx, the influence of the fluctuation of the supply hydraulic pressure Pm is reduced, so the control accuracy of the selective braking hydraulic pressure Pwx is improved, and the performance of the off-road control is enhanced.

[0096] <Operation of Fluctuation Suppression Control> With reference to the time-series diagram of FIG. 7 (a diagram showing changes in state variables accompanying the transition of time T), the operation of the fluctuation suppression control will be described. The upper part of FIG. 7 shows the maximum target hydraulic pressure Ptx (indicated by a one-dot chain line), the supply hydraulic pressure Pm (indicated by a solid line), and the selected braking hydraulic pressure Pwx (indicated by a broken line).

[0097] Immediately before time t1, the supply hydraulic pressure Pm substantially coincides with the maximum target hydraulic pressure Ptx. Thereafter, due to fluctuations in the supply hydraulic pressure Pm, the supply hydraulic pressure Pm becomes greater than the maximum target hydraulic pressure Ptx, and a deviation hP (= Pm - Ptx) between the supply hydraulic pressure Pm and the maximum target hydraulic pressure Ptx begins to occur. At time t1, when the hydraulic pressure deviation hP exceeds the dead zone of the fluctuation suppression control (a region for suppressing control hunting, a predetermined control threshold value), the fluctuation of the supply hydraulic pressure Pm is suppressed by the selected inlet valve UIx. Specifically, since the supply hydraulic pressure Pm is greater than the maximum target hydraulic pressure Ptx and the hydraulic pressure deviation hP has a positive sign, the selected pressure regulating valve UBx is not energized, and the selected inlet valve UIx is driven in accordance with the first target energization amount Iit calculated based on the hydraulic pressure deviation hP. Here, the selected pressure regulating valve UBx is one of the two pressure regulating valves UB and is provided in the communication path HSx including the selected wheel cylinder CWx. The selected inlet valve UIx is one of the four inlet valves UI and corresponds to the selected wheel cylinder CWx. Since the supply hydraulic pressure Pm is decreased and adjusted by the selected inlet valve UIx, the selected braking hydraulic pressure Pwx is controlled to approach and coincide with the maximum target hydraulic pressure Ptx. At time t2, since the hydraulic pressure deviation hP becomes less than the control threshold value and enters the dead zone, the driving of the energized selected inlet valve UIx is stopped.

[0098] After time point t3, due to the fluctuation of the supply liquid pressure Pm, the supply liquid pressure Pm becomes smaller than the maximum target liquid pressure Ptx, and a deviation hP (= Pm - Ptx) between the supply liquid pressure Pm and the maximum target liquid pressure Ptx begins to occur. At time point t3, when the liquid pressure deviation hP exceeds the dead zone of the fluctuation suppression control, then the fluctuation of the supply liquid pressure Pm is suppressed by the selection pressure regulating valve UBx. Specifically, since the supply liquid pressure Pm is smaller than the maximum target liquid pressure Ptx and the liquid pressure deviation hP has a negative sign, the selection inlet valve UIx is not energized, and the selection pressure regulating valve UBx is driven according to the second target energization amount Ibt calculated based on the liquid pressure deviation hP. Thereby, since the supply liquid pressure Pm is increased and adjusted by the selection pressure regulating valve UBx, the selection braking liquid pressure Pwx is controlled to approach and match the maximum target liquid pressure Ptx. At time point t4, since the liquid pressure deviation hP enters the above dead zone, the drive of the selection pressure regulating valve UBx is stopped.

[0099] After time point t4, when "Pm > Ptx" and the liquid pressure deviation hP exceeds the dead zone (predetermined threshold), the selection inlet valve UIx is activated (energized), and the selection pressure regulating valve UBx is deactivated (de-energized), whereby the supply liquid pressure Pm is decreased and adjusted, and the fluctuation of the selection braking liquid pressure Pwx is suppressed (see time points t5 to t6). On the other hand, when "Pm < Ptx" and the liquid pressure deviation hP exceeds the dead zone (predetermined threshold), the selection pressure regulating valve UBx is activated (energized), and the selection inlet valve UIx is deactivated (de-energized), whereby the supply liquid pressure Pm is increased and adjusted, and the fluctuation of the selection braking liquid pressure Pwx is suppressed (see time points t7 to t8).

[0100] In the communication path HS from the master cylinder CM to the wheel cylinder CW, hydraulic pressure fluctuations (particularly, fluctuations in the supply hydraulic pressure Pm) occur due to changes in the amount of the braking fluid BF consumed by the non-selective wheel cylinder CWz. In the fluctuation suppression control, based on the hydraulic pressure deviation hP, the supply hydraulic pressure Pm is increased by the selective pressure regulating valve UBx, and the supply hydraulic pressure Pm is decreased by the selective inlet valve UIx. The fluctuations in the supply hydraulic pressure Pm are not directly transmitted to the selective wheel cylinder CWx, but are attenuated by the selective inlet valve UIx and the selective pressure regulating valve UBx and then transmitted to the selective wheel cylinder CWx. As a result, the selective braking hydraulic pressure Pwx approaches the maximum target hydraulic pressure Ptx and is adjusted to match it. The braking hydraulic pressure Pwx of the selective wheel cylinder CWx is basically adjusted (increased or decreased) by the first unit YA (i.e., the supply hydraulic pressure Pm), and is further adjusted by the selective inlet valve UIx and the selective pressure regulating valve UBx according to the fluctuation suppression control. Due to the improvement in the pressure regulating accuracy in the selective wheel cylinder CWx by the fluctuation suppression control, the performance improvement of the off-road control can be achieved.

[0101] In the braking control device SC, as described in step S170, the driving / stopping of the electric motor MB is performed based on the reservoir hydraulic pressure Ec. The fluctuations in the supply hydraulic pressure Pm are caused by changes in the liquid volume of the braking fluid BF, and such changes are likely to occur at the start / stop of the driving of the electric motor MB (i.e., the fluid pump QB). Therefore, although the stopping of the electric motor MB is necessary for suppressing the heat generation of the electric motor MB, it becomes a factor of hydraulic pressure fluctuations, and thus it should not be performed frequently under normal circumstances (when the fluctuation suppression control is not applied). However, since the application of the fluctuation suppression control can suppress the fluctuations in the supply hydraulic pressure Pm, the stopping of the electric motor MB can be actively performed. That is, the fluctuation suppression control also has the effect of leading to the suppression of the heat generation of the electric motor MB.

[0102] <Other Embodiments> Hereinafter, other embodiments of the braking control device SC will be described. Also in other embodiments, the same effects as described above (i.e., suppression of fluctuations in the hydraulic pressure Pw of the wheel cylinder CW caused by fluctuations in the supply hydraulic pressure Pm from the first unit YA which is a pressurizing source) are achieved.

[0103] ≪Adoption of Electric Cylinder Type Pressure Source≫ In the above-described embodiment, as the first unit YA (pressure source), the accumulator hydraulic pressure Pc stored in the accumulator AC was used. Instead of this, the braking hydraulic pressure Pw may be increased by directly driving a piston inserted into a cylinder by an electric motor. That is, a so-called electric cylinder type may be adopted as the first unit YA. Since the configuration of the electric cylinder type is known, for example, in "WO2012 / 046703" and the like, the configuration will be briefly described below. The first unit YA of the electric cylinder type is composed of a pressure regulating cylinder, a pressure regulating piston, a linear motion conversion mechanism, and an electric motor.

[0104] Separate from the master cylinder CM, a pressure regulating cylinder (also referred to as a "slave cylinder") is provided. The pressure regulating cylinder has the same configuration as the master cylinder CM and is, for example, a tandem type cylinder. Two pressure regulating pistons are inserted into the pressure regulating cylinder via an elastic body (compression spring). One of the two pressure regulating pistons is connected to the electric motor via a linear motion conversion mechanism (for example, a screw mechanism). Here, the linear motion conversion mechanism converts the rotational power of the electric motor into the linear power (thrust) of the pressure regulating piston.

[0105] The pressure regulating piston is driven by an electric motor. Specifically, when the electric motor rotates, its power is converted into the linear power of the pressure regulating piston by a linear motion conversion mechanism. Inside the pressure regulating cylinder, it is partitioned into two pressure regulating chambers by two pressure regulating pistons and a seal member. The two pressure regulating chambers are connected to the wheel cylinder CW via a communication path HS and a second unit YB. Therefore, when the electric motor is driven, the volume of the pressure regulating chamber decreases, so the braking fluid BF is pumped from the pressure regulating chamber to the wheel cylinder CW at the supply hydraulic pressure Pm. That is, in the electric cylinder type first unit YA, the supply hydraulic pressure Pm is directly controlled (regulated) by adjusting the output of the electric motor without using the solenoid valves UZ and UG. In this configuration, the hydraulic pressure Pwx of the selected wheel cylinder CWx is controlled by the electric motor. And the hydraulic pressure Pwz of the non - selected wheel cylinder CWz is adjusted by the non - selected inlet valve UIz and the non - selected outlet valve VOz.

[0106] ≪Application to Vehicle Stability Control etc.≫ In the above-described embodiment, the fluctuation suppression control is applied to the offload control. The fluctuation suppression control can be applied not only to the offload control but also to control in which the braking hydraulic pressure Pw is individually adjusted at the wheel cylinder CW of each wheel WH such as vehicle stability control. Vehicle stability control (also referred to as "anti-skid control") is a known control for suppressing unstable situations (specifically, oversteer behavior and understeer behavior) of the vehicle JV based on the yaw rate Yr, lateral acceleration Gy, etc. For example, in vehicle stability control, when oversteer behavior is suppressed, the wheel cylinder CW provided on the wheel located on the outer side of the vehicle's turn is determined as the selected wheel cylinder CWx. Then, the braking hydraulic pressure Pwx of the selected wheel cylinder CWx is adjusted by the first unit YA. On the other hand, the braking hydraulic pressure Pwz of the non-selected wheel cylinder CWz that does not correspond to the selected wheel cylinder CWx is adjusted by the second unit YB (specifically, the inlet valve UI and the outlet valve VO). Also in vehicle stability control, similar to the offload control, the hydraulic pressure Pm supplied from the first unit YA fluctuates, but the fluctuation can be reduced by the above-described fluctuation suppression control (control of the inlet valve UI and the pressure regulating valve UB based on the hydraulic pressure deviation hP). As a result, the pressure regulating accuracy can be improved and the performance of the vehicle stability control can be enhanced.

[0107] ≪Configuration in which the pressure regulating valve UB is omitted≫ In the above-described embodiment, the pressure regulating valve UB and the inlet valve UI are provided in the communication path HS. Here, the pressure regulating valve UB may be omitted. In this configuration, in the situation of "Pm < Ptx", since the supply hydraulic pressure Pm cannot be increased and adjusted, the fluctuation of the supply hydraulic pressure Pm is not suppressed. However, in the situation of "Pm > Ptx", the supply hydraulic pressure Pm is decreased and adjusted by the inlet valve UI and supplied to the selected wheel cylinder CWx as the selected braking hydraulic pressure Pwx, so the fluctuation of the supply hydraulic pressure Pm can be suppressed. Even in the configuration in which the pressure regulating valve UB is omitted, since the offload control and the vehicle stability control can be executed, the fluctuation suppression control exhibits its effect.

[0108] ≪Diagonal type fluid path≫ In the above-described embodiment, a front-to-rear configuration was adopted as the two braking fluid passages. Instead of this, a diagonal type (also referred to as "X type") braking system may be adopted. In this configuration, of the two hydraulic chambers formed in the master cylinder CM (or pressure regulating cylinder), one side is connected to the right front wheel cylinder and the left rear wheel cylinder, and the other side is connected to the left front wheel cylinder and the right rear wheel cylinder.

[0109] <Summary of the Embodiment of the Braking Control Device SC and Its Operation and Effects> The embodiments of the braking control device SC are summarized below. The braking control device SC individually adjusts the hydraulic pressure (braking hydraulic pressure) Pw of a plurality of wheel cylinders CW of the vehicle JV. In the braking control device SC, for example, speed control (off-road control) for maintaining the vehicle body speed Vx of the vehicle JV at a constant low speed and vehicle stability control for suppressing the oversteer tendency and understeer tendency of the vehicle JV are executed. The braking control device SC includes a pressurizing source YA for increasing the hydraulic pressure Pw of the plurality of wheel cylinders CW, a communication path HS connecting the pressurizing source YA and the plurality of wheel cylinders CW, an inlet valve UI provided in the communication path HS, a decompression path HG connecting the communication path HS between the plurality of wheel cylinders CW and the inlet valve UI to a reservoir RC, an outlet valve VO provided in the decompression path HG, a hydraulic pressure sensor PB for detecting the hydraulic pressure output by the pressurizing source YA as the supply hydraulic pressure Pm, and a controller ECU for controlling the pressurizing source YA, the inlet valve UI, and the outlet valve VO. Further, the braking control device SC is provided with a fluid pump QB that is driven by an electric motor MB and returns the braking fluid BF in the reservoir RC to the communication path HS between the pressurizing source YA and the inlet valve UI.

[0110] The controller ECU calculates a plurality of target hydraulic pressures Pt (target values required for off-road control, vehicle stability control, etc.) required for a plurality of wheel cylinders CW. Then, the maximum value among the plurality of target hydraulic pressures Pt is determined as the maximum target hydraulic pressure Ptx. The controller ECU adjusts the hydraulic pressure Pwx of the selected wheel cylinder CWx corresponding to the maximum target hydraulic pressure Ptx among the plurality of wheel cylinders CW by means of a pressure source YA. On the other hand, the hydraulic pressure Pwz of the non-selected wheel cylinder CWz that does not correspond to the selected wheel cylinder CWx among the plurality of wheel cylinders CW is adjusted by a non-selected inlet valve UIz and a non-selected outlet valve VOz.

[0111] Furthermore, the controller ECU controls the selected inlet valve UIx corresponding to the selected wheel cylinder CWx among the inlet valves UI based on the deviation hP between the maximum target hydraulic pressure Ptx and the supply hydraulic pressure Pm. Also, a pressure regulating valve UB is provided in a communication path HS between the pressure source YA and the inlet valve UI in the braking control device SC. The controller ECU controls the selected pressure regulating valve UBx (the pressure regulating valve provided in the communication path HSx including the selected wheel cylinder CWx among the two pressure regulating valves UB) corresponding to the selected wheel cylinder CWx among the pressure regulating valves UB based on the deviation hP. Specifically, when the supply hydraulic pressure Pm is smaller than the maximum target hydraulic pressure Ptx, the selected pressure regulating valve UBx is energized based on the deviation hP, but the selected inlet valve UIx is not energized. Thereby, the too small supply hydraulic pressure Pm is increased and adjusted by the selected pressure regulating valve UBx, and the selected braking hydraulic pressure Pwx is brought closer to the maximum target hydraulic pressure Ptx. Conversely, when the supply hydraulic pressure Pm is larger than the maximum target hydraulic pressure Ptx, the selected inlet valve UIx is energized based on the deviation hP, but the selected pressure regulating valve UBx is not energized. Thereby, the too large supply hydraulic pressure Pm is decreased and adjusted by the selected inlet valve UIx, and the selected braking hydraulic pressure Pwx is brought closer to the maximum target hydraulic pressure Ptx.

[0112] In the braking control device SC, the braking hydraulic pressure Pwx of the selected wheel cylinder CWx corresponding to the maximum target hydraulic pressure Ptx is increased, decreased, and adjusted by the supply hydraulic pressure Pm from the first unit YA which is a pressure source. On the other hand, the braking hydraulic pressure Pwz of the non - selected wheel cylinder CWz which does not correspond to the selected wheel cylinder CWx among the wheel cylinders CW is increased and decreased by opening and closing the non - selected inlet valve UIz and the non - selected outlet valve VOz. In the hydraulic pressure adjustment by opening and closing the non - selected inlet valve UIz and the non - selected outlet valve VOz, the outflow of the braking fluid BF from the communication path HS and the inflow of the braking fluid BF into the communication path HS occur, so it is accompanied by a change in the amount (fluid amount) of the braking fluid BF in the communication path HS. Due to this change in the fluid amount, a fluctuation in the hydraulic pressure (supply hydraulic pressure) Pm supplied from the first unit YA to the wheel cylinder CW occurs. In the fluctuation suppression control, although the fluctuation of the supply hydraulic pressure Pm itself cannot be suppressed, the fluctuation of the selected braking hydraulic pressure Pwx is suppressed by the selected pressure regulating valve UBx and the selected inlet valve UIx provided in the fluid path HSx (selected communication path including the selected wheel cylinder CWx) until the supply hydraulic pressure Pm is transmitted as the selected braking hydraulic pressure Pwx. In other words, the pressure amplitude of the supply hydraulic pressure Pm is attenuated by the selected pressure regulating valve UBx and the selected inlet valve UIx and transmitted to the selected wheel cylinder CWx. As a result, in the selected wheel cylinder CWx, the pressure regulating accuracy of the selected braking hydraulic pressure Pwx is improved, so that the performance of the above - mentioned off - road control and vehicle stability control can be improved.

Explanation of Signs

[0113] JV... vehicle, SC... braking control device, SX... braking device, CP... brake caliper, CW... wheel cylinder, KT... rotating member (brake disk), MS... friction member (brake pad), ECU... braking controller, HU... fluid unit, YA... first unit (pressure source), CM... master cylinder, YB... second unit, UB... pressure regulating valve, UI... inlet valve, VO... outlet valve, RC... pressure regulating reservoir, MB... electric motor, QB... fluid pump, PM... supply hydraulic pressure sensor, Pm... supply hydraulic pressure (detection value of supply hydraulic pressure sensor PM), Pq... regulated hydraulic pressure, Pw... braking hydraulic pressure, mQ... hydraulic pressure difference (difference between regulated hydraulic pressure Pq and supply hydraulic pressure Pm), wQ... hydraulic pressure difference (difference between regulated hydraulic pressure Pq and braking hydraulic pressure Pw), Pt... target hydraulic pressure, Ptx... maximum target hydraulic pressure (maximum value of target hydraulic pressure Pt), hP... hydraulic pressure deviation (difference between supply hydraulic pressure Pm and maximum target hydraulic pressure Ptx), Ii... first energization amount (actual energization amount of inlet valve UI), Iit... first target energization amount (target value corresponding to first energization amount Ii), Ib... second energization amount (actual energization amount of pressure regulating valve UB), Ibt... second target energization amount (target value corresponding to second energization amount Ib), CWx... selected wheel cylinder (wheel cylinder corresponding to maximum target hydraulic pressure Ptx among a plurality of wheel cylinders), CWz... non - selected wheel cylinder (wheel cylinder not corresponding to selected wheel cylinder CWx among a plurality of wheel cylinders).

Claims

【Claim 1】 A braking control device for a vehicle that individually adjusts the hydraulic pressure of a plurality of wheel cylinders of the vehicle, a pressurizing source that increases the hydraulic pressure of the plurality of wheel cylinders, a communication path that connects the pressurizing source and the plurality of wheel cylinders, an inlet valve provided in the communication path, a decompression path that connects the communication path between the plurality of wheel cylinders and the inlet valve to a reservoir, an outlet valve provided in the decompression path, a hydraulic pressure sensor that detects the hydraulic pressure output by the pressurizing source as the supply hydraulic pressure, a pressure regulating valve provided in the communication path between the pressurizing source and the inlet valve, calculates a plurality of target hydraulic pressures required for the plurality of wheel cylinders, determines the maximum value among the plurality of target hydraulic pressures as the maximum target hydraulic pressure, adjusts the hydraulic pressure of the selected wheel cylinder corresponding to the maximum target hydraulic pressure among the plurality of wheel cylinders by the pressurizing source, and adjusts the hydraulic pressure of the non-selected wheel cylinders that do not correspond to the selected wheel cylinder among the plurality of wheel cylinders by the inlet valve and the outlet valve, and a controller, the controller, when the supply hydraulic pressure is smaller than the maximum target hydraulic pressure, based on the deviation between the maximum target hydraulic pressure and the supply hydraulic pressure, controls the selected pressure regulating valve corresponding to the selected wheel cylinder among the pressure regulating valves in the closing direction, and opens the selected inlet valve corresponding to the selected wheel cylinder among the inlet valves, when the supply hydraulic pressure is larger than the maximum target hydraulic pressure, based on the deviation, controls the selected inlet valve in the closing direction and opens the selected pressure regulating valve. A braking control device for a vehicle.

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