JP2022169246A - vehicle braking controller - Google Patents

Abstract

To provide a braking control device of a vehicle that can execute turning support control by which a turning radius of the vehicle is reduced, which can achieve both durability and reduction in size and weight.SOLUTION: A braking control device executes turning support control by which a turning radius of a vehicle is reduced by applying braking torque to a turning inner wheel of the vehicle. The braking control device comprises: a first unit that increases liquid pressure of a wheel cylinder and applies braking torque; a second unit that applies braking torque independently from the first unit; and a controller that controls the first unit and the second unit. The controller makes only the first unit apply braking torque when starting the turning support control, and performs specific determination of whether an operation situation of the first unit is severe or not after starting the turning support control, and when affirming the specific determination, makes the second unit apply braking torque.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to a vehicle braking control device.

In Patent Document 1, in order to turn the vehicle with a smaller turning radius regardless of the conditions of the vehicle and the road surface, "When a request for turning support control occurs while the vehicle is traveling at extremely low speeds, the A first rotational moment M1 generated in the vehicle with the rear wheel on the inner side of the turn as a fulcrum when the wheel speed of the wheel is assumed to be zero, and when the wheel speed of the front wheel on the inner side of the turn is assumed to be zero. A second rotational moment M2 generated in the vehicle with the front wheel on the inner side of the turn as a fulcrum is calculated, and if the magnitude |M1| of the first rotational moment is greater than or equal to the magnitude |M2| When determined, the target wheel speed of the rear wheel on the inner side of the turn is set to zero, and when it is determined that the magnitude of the first rotational moment |M1| is less than the magnitude of the second rotational moment |M2| Execute turning support control that sets the target wheel speed of the inside front wheel to zero.

In Patent Document 1, the target wheel speed of the front wheel or rear wheel on the inner side of the turn is set to zero to reduce the turning radius of the vehicle, and the wheel is locked. By the way, in a braking control device that utilizes the pressure of brake fluid (hydraulic pressure), a relatively high hydraulic pressure is required to cope with wheel lock. The durability of the braking control device must be determined assuming a situation in which high hydraulic pressure continues to act for a long period of time. In a brake control device, there is a trade-off between the robustness of the device and the size/weight. Therefore, there is a demand for a brake control device that can achieve a reduction in size and weight while ensuring durability.

JP 2020-090155

SUMMARY OF THE INVENTION It is an object of the present invention to provide a braking control device for a vehicle capable of executing turning support control for reducing the turning radius of the vehicle, which can achieve both durability and reduction in size and weight of the device.

A braking control device according to the present invention performs turning support control for reducing a turning radius of the vehicle by applying a braking torque (Tqu) to a turning inner wheel (WHu) of the vehicle. A first unit (YA) that increases the hydraulic pressure of the cylinder (CW) to apply the braking torque (Tqu), and a second unit (YA) that applies the braking torque (Tqu) separately from the first unit (YA). A unit (YB), and a controller (ECU) that controls the first unit (YA) and the second unit (YB).

In the braking control device according to the present invention, the controller (ECU) applies the braking torque (Tqu) only by the first unit (YA) when starting the turning support control, and the turning support control is started. After the start, a specific determination is made as to whether or not the operating state of the first unit (YA) is severe, and if the specific determination (S230) is affirmative, the braking torque (Tqu ). Specifically, the controller (ECU) reduces the first component (Ta) of the braking torque (Tqu) by the first unit (YA) from the time (u6) when the specific determination (S230) is affirmative. , increases the second component (Tb) of the braking torque (Tqu) by the second unit (YB).

The braking control device SC comprises two different units, first and second units YA, YB. Then, when the load condition of the first unit YA becomes severe (that is, when the specific determination is affirmative), the load is shared by the second unit YB. Therefore, in the braking control device SC capable of executing the turning support control for reducing the turning radius of the vehicle, both durability and reduction in size and weight can be favorably achieved.

1 is a configuration diagram for explaining a vehicle JV equipped with a braking control device SC; FIG. FIG. 4 is a schematic diagram for explaining a first configuration example of the first unit YA; FIG. 4 is a schematic diagram for explaining a configuration example of a second unit YB; FIG. 5 is a flow chart for explaining turning support control; FIG. 4 is a time series diagram for explaining an example of operation of turning support control; FIG. 4 is a flow chart for explaining sharing control; It is a time-series diagram for demonstrating the operation example of sharing control. FIG. 11 is a schematic diagram for explaining a second configuration example of the first unit YA;

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

<Symbols of constituent elements, etc.>
In the following description, constituent elements such as members, signals, values, etc. denoted by the same reference numerals such as "CW" have the same function. The suffixes "f" and "r" attached to the end of various symbols related to wheels are generic symbols indicating whether the elements relate 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, the wheel cylinders CW are denoted as front wheel cylinder CWf and rear wheel cylinder CWr. Additionally, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its generic name.

<Vehicle JV equipped with braking control device SC>
An overall vehicle JV equipped with a braking control device SC according to the present invention will be described with reference to the configuration diagram of FIG. The vehicle JV is equipped with an acceleration operation member AP, a braking operation member BP, a steering operation member SH, and various sensors (BA, etc.). An acceleration operation member (for example, an accelerator pedal) AP is a member operated by the driver to accelerate the vehicle JV and control the speed of the vehicle JV (vehicle speed Vx). A braking operation member (for example, a brake pedal) BP is a member operated by the driver to decelerate the vehicle JV. A steering operation member (for example, a steering wheel) SH is a member operated by the driver to turn the vehicle JV.

The vehicle JV is equipped with various sensors listed below. Detection signals (Ba, etc.) of these sensors are input to a controller ECU for braking (also referred to simply as a "braking controller"), which will be 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 member A steering operation amount sensor SA for detecting an operation amount (steering operation amount, for example, a steering angle) Sa of the SH.
- A wheel speed sensor VW for detecting the rotational speed (wheel speed) Vw of the wheel WH.
- A yaw rate sensor YR for detecting a yaw rate Yr, a longitudinal acceleration sensor GX for detecting a longitudinal acceleration Gx, and a lateral acceleration sensor GY for detecting a lateral acceleration Gy in a vehicle JV (in particular, a vehicle body).

In addition, various switches such as a switch XC for crawling control and a switch XA for turning support control are provided. These switches XC, XA are operated by the driver. An operation signal Xc (crawl control signal) from the crawl control switch XC and an operation signal Xa (turning support control signal) from the turning support control switch XA are input to the braking controller ECU.

The vehicle JV is equipped with a braking device SX and a braking control device SC. The braking control device SC employs a so-called front-rear type (also referred to as "II type") as the two braking systems.

A braking fluid pressure Pw generated by a braking control device SC is supplied to the braking device SX. A braking torque Tq is applied to the wheels WH by the braking device SX in accordance with the braking fluid pressure Pw to generate a braking force Fx. The braking device SX includes a rotating member (for example, brake disc) KT and a brake caliper CP. The rotary member KT is fixed to the wheel WH of the vehicle, and a brake caliper CP is provided so as to sandwich the rotary member KT. A wheel cylinder CW is provided in the brake caliper CP. A braking fluid BF adjusted to a braking fluid pressure Pw is supplied to the wheel cylinder CW from the braking control device SC. The braking fluid pressure Pw presses the friction member (for example, brake pad) MS against the rotating member KT. Since the rotating member KT and the wheels WH are fixed so as to rotate integrally, the frictional force generated at this time generates braking torque Tq (resulting in braking force Fx) in the wheels WH.

The braking control device SC adjusts the actual braking fluid pressure Pw according to the operation amount Ba of the braking operation member BP, and controls the braking device SX (in particular, the wheel cylinder CW ) is supplied with the braking fluid pressure Pw. The braking control device SC is composed of a master cylinder CM, a fluid unit HU, and a braking controller ECU. The fluid unit HU is composed of two units (first and second units) YA and YB. Components of the braking control device SC (electromagnetic valves, electric motors, etc. included in the first and second units YA, 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 the solenoid valve and the electric motor. A controller ECU for braking, a controller ECP for a prime mover (described later), and a controller ECT for power transmission (described later) are each connected to a communication bus BS. Therefore, information (detected values, calculated values) is shared between these controllers via the communication bus BS. For example, the brake controller ECU calculates the vehicle body speed Vx based on the wheel speed Vw. The vehicle body speed Vx is transmitted to other controllers through the communication bus BS. The braking controller ECU includes an acceleration operation amount Aa, a braking operation amount Ba, a steering operation amount Sa, a yaw rate Yr, a longitudinal acceleration Gx, a lateral acceleration Gy, a wheel speed Vw, an operation signal Xc (for crawling control), an operation signal Xa (turning for support control), etc. are input. Based on these signals, the brake controller ECU controls the hydraulic unit HU. The details of the braking control device SC will be described later.

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 drive torque Td is transmitted to generate drive force Fd).

The prime mover control device GC is composed of a prime mover PG and a prime mover controller ECP (simply referred to as "prime mover controller") for controlling the prime mover PG. The prime mover PG is a general term for devices that convert various types of energy existing in nature into mechanical work (dynamic energy). A case where an internal combustion engine (gasoline engine) is employed as the prime mover PG will be described as an example. The prime mover PG generates power (driving torque Td) for driving the four wheels WH. The prime mover PG is controlled by a prime mover controller (engine controller) ECP to adjust its output. 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. At least one of the throttle opening Th and the fuel injection amount Fi is controlled by the prime mover controller ECP based on the engine speed Ne detected by the speed sensor NE. As a result, the output of the prime mover PG is adjusted.

The output (rotational power) of the prime mover control device GC (in particular, the prime mover PG) is input to the power transmission device TS. Then, the output of the prime mover PG is transmitted to the four wheels WH via the power transmission device TS, and the driving force Fd is generated by each of the wheels WH. The power transmission device TS includes a power transmission mechanism TD and a power transmission controller ECT (simply referred to as a "power transmission controller") for controlling the power transmission mechanism TD. The power transmission mechanism TD is composed of a main transmission MH, an auxiliary transmission FH, a front wheel differential mechanism DF, a central 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 auxiliary 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.

The output from the auxiliary transmission FH is input to each differential mechanism DF (front wheel differential gear), DC (central 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 central differential mechanism DC, the rear wheel differential mechanism DR, and the rear wheel drive shafts. 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 (that is, a differential) between the wheels WH is allowed. be. Each component (such as MH) of the power transmission mechanism TD is controlled by a power transmission controller ECT. Specifically, the power transmission controller ECT controls each of the main transmission MH, the auxiliary transmission FH, and the differential mechanisms DF, DC, and DR.

<First Configuration Example of First Unit YA>
A first configuration example of the first unit YA included in the fluid unit HU will be described with reference to the schematic diagram of FIG. The first unit YA is a pressurization source for increasing the hydraulic pressure (brake hydraulic pressure) Pw of the four wheel cylinders CW. In the example, the first unit YA is integrated with the master cylinder CM. A front/rear brake piping system is adopted. The first unit YA is composed of an apply unit AU including a master cylinder CM and a pressure unit KU. The apply unit AU and pressurization unit KU are controlled by the braking controller ECU. Specifically, the controller ECU has a braking operation amount Ba (at least one of simulator hydraulic pressure Ps, operation displacement Sp, and operation force Fp), wheel speed Vw, accumulator hydraulic pressure Pc, servo hydraulic pressure Pu, supply fluid Based on these signals, the drive signal Vn for the input valve VN, the drive signal Vr for the release valve VR, the drive signal Uz for the pressure increasing valve UZ, the drive signal Ug for the pressure reducing valve UG, and the drive signal Ug for the pressure accumulating electric motor MA are generated. A drive signal Ma is 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 electric motor MA for pressure accumulation are controlled (driven). ) is done.

As will be described later, the fluid unit HU, wheel cylinder CW, etc. are connected by a communication path HS, an input path HN, a pressure reduction path HG, a return path HK, and a servo path HV. These are the fluid paths through which the damping fluid BF is moved. Fluid pipes, flow paths in the fluid unit HU, hoses, etc. correspond to the fluid paths (HS, etc.).

≪Apply unit AU≫
The apply unit AU includes a master reservoir RV, a master cylinder CM, first and second master pistons NP and NS, first and second master springs DP and DS, an input cylinder CN, an input piston NN, an input spring DN, and an input valve VN. , open valve VR, stroke simulator SS, and simulator fluid pressure sensor PS.

The master reservoir (also called "atmospheric pressure reservoir") RV is a tank for the hydraulic fluid, in which the brake fluid BF is stored. The master reservoir RV is connected to the master cylinder CM (in particular, the front wheel and rear wheel master chambers Rmf and Rmr).

The master cylinder CM is a cylinder member having a bottom. First and second master pistons NP and NS are inserted into the interior of the master cylinder CM, the interior of which is sealed by a seal member SL and divided into front wheel and rear wheel master chambers Rmf and Rmr. The master cylinder CM is of a so-called tandem type. The front and rear wheel master chambers Rmf and Rmr (=Rm) are connected via the front and rear wheel communication paths HSf and HSr (=HS) and the second unit YB, and finally the front and rear wheel cylinders CWf. , CWr (=CW), respectively. When the first and second master pistons NP and NS are moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases), the first unit YA (especially the master cylinder CM) moves toward the second unit YB. , hydraulic pressure Pm (referred to as "supplied hydraulic pressure", which is "front and rear wheel supply hydraulic pressures Pmf, Pmr"). Here, the front wheel supply hydraulic pressure Pmf and the rear wheel supply hydraulic pressure Pmr are equal.

A flange portion (flange) Tp is provided on the first master piston NP. The interior of the master cylinder CM is further partitioned into a servo chamber Ru and a rear chamber Ro by the flange Tp. The servo chamber Ru is arranged to face the front wheel master chamber Rmf across the first master piston NP. Further, the rear chamber Ro is sandwiched between the front wheel master chamber Rmf and the servo chamber Ru and arranged therebetween. The servo chamber Ru and the rear chamber Ro are also sealed by the seal member SL in the same manner as described above.

Input cylinder CN is fixed to master cylinder CM. An input piston NN is inserted inside the input cylinder CN and sealed by a seal member SL to form an input chamber Rn. The input piston NN is mechanically connected to the brake operating member BP via a clevis (U-shaped link).

The apply unit AU is provided with an input chamber Rn, a servo chamber Ru, a rear chamber Ro, and hydraulic chambers of front wheel and rear wheel master chambers Rmf and Rmr. Here, the "hydraulic chamber" is a chamber filled with the damping fluid BF and sealed by the seal member SL. The volume of each hydraulic chamber is changed by movement of the input piston NN, first and second master pistons NP, NS.

The input chamber Rn and the rear chamber Ro are connected via an input path HN. An input valve VN is provided in the input path HN. The input path HN is connected to the master reservoir RV via a release valve VR between the rear chamber Ro and the input valve VN. The input valve VN and the release valve VR are two-position solenoid valves (also called "on/off valves") having an open position (communication state) and a closed position (blockage state). A normally closed solenoid valve is employed as the input valve VN. A normally open solenoid valve is employed as the open valve VR. The input valve VN and open valve VR are driven (controlled) by drive signals Vn and Vr from the braking controller ECU.

A stroke simulator (simply referred to as “simulator”) SS is connected to the rear chamber Ro. The simulator SS generates an operating force Fp for the brake operating member BP. A piston and an elastic body (for example, a compression spring) are provided inside the simulator SS. When the brake fluid BF flows into the simulator SS, the piston is pushed by the brake fluid BF. Since a force is applied to the piston by the elastic body in a direction to prevent the inflow of the brake fluid BF, an operating force Fp is generated for the brake operating member BP. In other words, the operating characteristics of the brake operating member BP (the relationship between the operating displacement Sp and the operating force Fp) are formed by the simulator SS.

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 is also the hydraulic pressure of the input chamber Rn and the rear chamber Ro). The simulator hydraulic pressure sensor PS is one of the braking operation amount sensors BA described above. The simulator hydraulic pressure Ps is input to the braking controller ECU as a braking operation amount Ba.

In addition to the simulator hydraulic pressure sensor PS, the first unit YA includes, as a braking operation amount sensor BA, an operation displacement sensor SP for detecting an operation displacement Sp of the braking operation member BP and/or an operation force of the braking operation member BP. An operating force sensor FP is provided to detect Fp. That is, at least one of the simulator hydraulic pressure sensor PS, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP is employed as the braking operation amount sensor BA. 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.

≪Pressurization unit KU≫
A supply hydraulic pressure Pm is generated and regulated by the pressure unit KU. The pressurization unit KU includes a pressure accumulation fluid pump QA, a pressure accumulation electric motor MA, an accumulator AC, an accumulator hydraulic pressure sensor PC, a pressure cylinder CK, a pressure piston NK, a pressure increasing valve UZ, a pressure reducing valve UG, and a servo hydraulic pressure. It is composed of a sensor PU.

The pressurizing unit KU is provided with a fluid pump QA for pressure accumulation so as to accumulate pressure in the accumulator AC. The pressure accumulating fluid pump QA is driven by the pressure accumulating electric motor MA and pumps up the brake fluid BF from the master reservoir RV. 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 to the accumulator hydraulic pressure Pc. An accumulator hydraulic pressure sensor PC is provided to detect the accumulator hydraulic pressure Pc. The braking controller ECU controls the electric motor MA for pressure accumulation so that the accumulator hydraulic pressure Pc is maintained within a predetermined range.

The pressurizing unit KU is provided with a pressurizing cylinder CK for adjusting the accumulator hydraulic pressure Pc from the accumulator AC and supplying it to the servo chamber Ru. A pressure piston NK is inserted into the pressure cylinder CK. The pressurizing piston NK partitions the inside of the pressurizing cylinder CK into three hydraulic pressure chambers Rp (pilot chamber), Rv (annular chamber), and Rk (pressurization chamber) sealed with a seal member SL. ing. 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 opposite side of the pressurizing piston NK from the pressurizing chamber Rk in the pressurizing 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.

An annular concave portion (constricted portion) is provided on the outer peripheral portion of the pressurizing piston NK. An annular chamber Rv is formed by this annular recess and the inner peripheral portion of the pressurizing cylinder CK. Further, a valve body Vv (for example, a spool valve) is formed on the outer peripheral portion of the pressurizing piston NK. The valve element Vv is supplied with the braking fluid BF pressurized to the accumulator hydraulic pressure Pc from the accumulator AC. The accumulator hydraulic pressure Pc is adjusted by the valve body Vv and introduced 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".

Specifically, when the pressurizing 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. Then, the accumulator AC is passed through the valve body Vv of the pressurizing 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 pressure in the annular chamber Rv and the pressurizing chamber Rk) match. brake fluid BF is supplied from . That is, the high 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 braking controller ECU. The controller ECU adjusts the pilot hydraulic pressure Pp based on the servo hydraulic pressure Pu, and finally controls the servo hydraulic pressure Pu to match the target value. Since the pressure chamber Rk and the servo chamber Ru are connected by a fluid path, the brake fluid BF adjusted to the servo hydraulic pressure Pu is supplied from the pressure unit KU to the servo chamber Ru.

<Second unit YB>
A configuration example of the second unit YB included in the fluid unit HU will be described with reference to the schematic diagram of FIG. The second unit YB has a power source (driving source) different from that of the first unit YA. For example, the second unit YB is provided between the first unit YA and the wheel cylinder CW in the communication path HS (fluid path for moving the brake fluid BF). The braking control device SC can adjust (increase, maintain, or decrease) the supply hydraulic pressure Pm by means of 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 performs antilock brake control (control to suppress locking of the wheels WH), traction control (control to suppress idle rotation of the wheels WH), and vehicle stability control (to suppress excessive understeer and oversteer). control). The second unit YB is composed of a supply fluid pressure sensor PM, a pressure regulating valve UB, a reflux fluid pump QB, a reflux electric motor MB, a pressure regulating reservoir RC, an inlet valve UI, and an outlet valve VO.

Like the first unit YA, the second unit YB is also controlled by the braking controller ECU. Specifically, based on the above-described various signals (Ba, etc.), the controller ECU outputs a drive signal Ub for the pressure regulating valve UB, a drive signal Ui for the inlet valve UI, a drive signal Vo for the outlet valve VO, and a drive signal for the return electric motor MB. A signal Mb is computed. Then, according to these drive signals (Ub, etc.), the electromagnetic valves "UB, UI, VO" and the return electric motor MB, which constitute the second unit YB, are controlled (driven).

Front and rear wheel pressure regulating valves UBf and UBr (=UB) are provided in front and rear wheel communication paths HSf and HSr (=HS). The pressure regulating valve UB (solenoid valve) is a normally open linear valve (also called "differential pressure valve" or "proportional valve"). The upper portion of the pressure regulating valve UB (portion of the connecting passage HS on the side closer to the first unit YA) and the lower portion of the pressure regulating valve UB (the portion of the connecting passage HS on the side closer to the wheel cylinder CW) form the front and rear wheel return passages. They are connected by HKf and HKr (=HK). The return path HK is provided with front and rear wheel return fluid pumps QBf and QBr (=QB) and front and rear wheel pressure regulating reservoirs RCf and RCr (=RC). The return fluid pump QB is driven by a return electric motor MB. A supply hydraulic pressure sensor PM is provided above the pressure regulating valve UB so as to detect the actual hydraulic pressure (supply hydraulic pressure) Pm supplied by the first unit YA.

When the electric motor MB is driven to rotate, the fluid pump QB sucks the braking fluid BF from the upper portion of the pressure regulating valve UB and discharges the braking fluid BF to the lower portion of the pressure regulating valve UB. As a result, the communication path HS and the return path HK are the return KN of the brake fluid BF (that is, the front wheel and rear wheel return KNf, KNr) containing the pressure regulating reservoir RC, and the flow of the circulating brake fluid BF. ) occurs. When the return KN of the brake fluid BF is throttled by the pressure regulating valve UB, the orifice effect causes the fluid pressure Pq at the bottom of the pressure regulating valve UB (referred to as “adjusted fluid pressure”) to change to the fluid pressure Pm at the top of the pressure regulating valve UB (supply fluid pressure). In other words, the second unit YB adjusts the hydraulic pressure difference mQ (also referred to as “differential pressure”) between the supply hydraulic pressure Pm and the adjustment hydraulic pressure Pq. In the second unit YB, the reflux electric motor MB, the reflux fluid pump QB, and the pressure regulating valve UB are referred to as a "pressurization source KB." The second unit YB (particularly the pressure source KB) has a power source separate from the first unit YA (particularly the pressure unit KU).

Inside the second unit YB, the front and rear wheel communication paths HSf and HSr are each branched into two and connected to the front and rear wheel cylinders CWf and CWr. An inlet valve UI and an outlet valve VO are provided for each wheel cylinder CW. The inlet valve UI (solenoid valve) is a normally open linear valve like the pressure regulating valve UB. However, the opening directions of the pressure regulating valve UB and the inlet valve UI are different. Specifically, since the pressure regulating valve UB opens in response to the flow of the brake fluid BF from the wheel cylinder CW to the master cylinder CM, the regulating hydraulic pressure Pq is equal to or higher than the supply hydraulic pressure Pm in the pressure regulation by the pressure regulating valve UB. (ie, “Pq≧Pm”). On the other hand, since the inlet valve UI opens in response to the flow from the master cylinder CM to the wheel cylinder CW, the braking hydraulic pressure Pw is equal to or lower than the regulated hydraulic pressure Pq in the pressure regulation by the inlet valve UI (that is, "Pq ≧Pw').

The inlet valve UI is provided in the branched communication path HS (that is, the side closer to the wheel cylinder CW with respect to the branched portion of the communication path HS). The communication path HS is connected to the pressure regulating reservoir RC via the pressure reduction path HG at the lower portion of the inlet valve UI (the portion of the communication path HS on the side closer to the wheel cylinder CW). An outlet valve VO, which is a normally closed on/off valve, is arranged in the pressure reducing passage HG.

Inlet valve UI and outlet valve VO are individually controlled so that brake fluid pressure Pw is adjusted separately for each wheel cylinder CW. In order to reduce the brake fluid pressure Pw, the inlet valve UI is closed and the outlet valve VO is opened. Since the inflow of the brake fluid BF into the wheel cylinder CW is blocked and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RC, the brake fluid pressure Pw is reduced. In order to increase the brake fluid pressure Pw, the inlet valve UI is opened and the outlet valve VO is closed. Since the braking fluid BF is prevented from flowing out to the pressure regulating reservoir RC, and the regulating fluid pressure Pq from the pressure regulating valve UB is supplied to the wheel cylinder CW, the braking fluid pressure Pw is increased. In order to maintain the braking fluid pressure Pw, both the inlet valve UI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the brake fluid pressure Pw is maintained constant.

<Turn support control>
Turning support control will be described. The "turning support control" reduces the turning radius of the vehicle JV by applying a braking torque Tqu to the wheel WHu on the inner side of the turn. For example, turning support control is performed on the premise that crawl control is being performed. Here, the "crawl control" is to keep the vehicle speed Vx constant at a low speed on an unpaved road (also called "off-road") or the like.

≪Crawl control≫
First, crawl control will be described. Crawl control is performed by the braking control device SC and the prime mover control device GC even if the acceleration operation member (accelerator pedal) AP and the braking operation member (brake pedal) BP are not operated. The force Fd is controlled to maintain the vehicle body speed Vx at a predetermined set vehicle speed vc. Crawl control is instructed by an operation signal Xc (switch signal for crawl control) from a crawl control switch XC operated by the driver. Crawl control is executed when the operation signal (switch signal) Xc indicates an ON state, but is not executed when the operation signal Xc is in an OFF state. Further, the switch XC instructs whether or not the crawl control is to be executed, and also instructs the set speed vc by the crawl control. 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, side slip of the vehicle JV is suppressed, and the vehicle body speed Vx is maintained at a predetermined constant low speed (set speed) vc. In order to realize this function, the output of the prime mover PG is adjusted, and the braking hydraulic pressure Pw of each wheel WH is individually adjusted. On sandy ground, dirt roads, rocky roads, muddy roads, etc., delicate operations of the acceleration operation member AP and the braking operation member BP are required. However, the crawl control allows the driver to concentrate on the operation of the steering operation member SH, and also improves the running performance on rough terrain and the like.

A process for adjusting the braking fluid pressure Pw in crawl control will be described. In crawl control, target hydraulic pressure Pt for each wheel cylinder CW is calculated based on deviation hV between actual vehicle body speed Vx and set speed vc (target value of vehicle body speed Vx in crawl control). That is, in crawl control, the braking hydraulic pressure Pw is individually adjusted for each wheel cylinder CW. Specifically, a deviation hV between the vehicle body speed Vx and the set speed vc is calculated (that is, "hV=Vx-vc"). Based on the speed deviation hV, a target total braking force Fvt, which is a target value of the braking force acting on the entire vehicle JV (sum of the braking forces of the four wheels), is calculated. Furthermore, the distribution ratio Hw for 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) Fxt of the braking force Fx for each wheel WH (that is, "Fxt=Fvt·Hw"). Ultimately, the target braking force Fxt is converted into the dimension of the hydraulic pressure in each wheel cylinder CW based on the specifications of the braking device SX, the braking control device SC, etc., and the target hydraulic pressure corresponding to the braking hydraulic pressure Pw Pt is calculated. For example, the distribution ratio Hw can be set to "0.25" so as to be uniform among the four wheels WH. Alternatively, the distribution ratio Hwf for the front wheels WHf may be set to be larger than the distribution ratio Hwr for the rear wheels WHr.

The maximum value among the four target hydraulic pressures Pt is determined as the maximum target hydraulic pressure Ptx. The first unit YA is controlled based on the maximum target hydraulic pressure Ptx. Specifically, the actual hydraulic pressure Pwx (referred to as "selected braking hydraulic pressure") for the wheel cylinder (referred to as "selected wheel cylinder CWx") corresponding to the maximum target hydraulic pressure Ptx approaches and coincides with the maximum target hydraulic pressure Ptx. The first unit YA (in particular, the pressurizing unit KU) is controlled so as to do so. At this time, the inlet valve UIx (referred to as "selected inlet valve") and the outlet valve VOx (referred to as "selected outlet valve") corresponding to the selected wheel cylinder CWx are de-energized. Therefore, the selected braking hydraulic pressure Pwx matches the supply hydraulic pressure Pm.

Actual hydraulic pressures (referred to as "non-selected braking hydraulic pressure Pwz") of the remaining three wheel cylinders (referred to as "non-selected wheel cylinders CWz") that do not correspond to the selected wheel cylinder CWx among the four wheel cylinders CW is controlled by a non-selected inlet valve UIz and a non-selected outlet valve VOz. Here, the “non-selected inlet valve UIz” are the remaining three inlet valves that do not correspond to the selected inlet valve UIx among the four inlet valves UI. "Non-selected outlet valves VOz" are the remaining three outlet valves that are not selected outlet valves VOx among the four outlet valves VO.

Specifically, one of the three control modes of "decrease mode", "increase mode", and "hold mode" is selected for adjusting the non-selected braking hydraulic pressure Pwz. In the decrease mode, when the non-selected braking hydraulic pressure Pwz needs to be decreased, 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 portion of the unselected inlet valve UIz (on the side closer to the first unit YA), but the unselected inlet valve UIz is closed. supply is blocked. 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 fluid pressure Pwz is reduced.

In the increase mode, when the unselected braking hydraulic pressure Pwz needs to be increased, the unselected outlet valve VOz is closed and the unselected inlet valve UIz is opened. Closing the unselected outlet valve VOz prevents the braking fluid BF from flowing out to the pressure regulation reservoir RC. Since the supplied hydraulic pressure Pm is supplied to the unselected wheel cylinder CWz through the unselected inlet valve UIz, the braking hydraulic pressure Pwz is increased. Since the adjustment of the non-selected braking hydraulic pressure Pwz is based on the supply hydraulic pressure Pm (=Pwx) generated by the first unit YA, the upper limit of the non-selected braking hydraulic pressure Pwz is the selected braking hydraulic pressure Pwx (ie, “Pwz≦Pwx”).

In the holding mode, both the non-selected inlet valve UIz and the non-selected outlet valve VOz are closed when it is necessary to hold the non-selected braking hydraulic pressure Pwz. Since the non-selected wheel cylinders CWz are fluidly sealed, the non-selected braking hydraulic pressure Pwz is maintained constant. Note that the hold mode may be omitted in the adjustment of the non-selected braking hydraulic pressure Pwz. In this case, the braking fluid pressure Pwz of the non-selected wheel cylinder CWz is adjusted by repeating the decrease mode and the increase mode.

<<Processing of turning support control>>
Next, the turning support control processing will be described with reference to the flowchart of FIG. The turning support control is commanded by the signal Xa of the control switch XA. The turn assist control algorithm is programmed into the microprocessor MP of the brake controller ECU. Note that the steering operation amount Sa is a state quantity (variable) having positive and negative signs in order to express the turning direction of the vehicle. .

In step S110, turning support control switch signal Xa, crawl control execution flag FC, turning support control execution flag FS, steering operation amount Sa (for example, steering angle), wheel speed Vw, supply fluid pressure Pm, servo fluid Various signals including the pressure Pu are read. The switch signal Xa indicates the necessity or non-necessity of the turning support control transmitted from the turning support control switch XA. Support control is not required. The execution flag FC is a control flag that indicates the execution state of the crawl control, where "FC=1" indicates execution, and "FC=0" indicates non-execution. Similarly, the execution flag FS is a control flag that indicates the execution state of the turning support control. "FS=1" indicates that it is being executed, and "FS=0" indicates that it is not being executed. The wheel speed Vw is based on the detected value of the wheel speed sensor VW, the supplied hydraulic pressure Pm is based on the detected value of the supplied hydraulic pressure sensor PM, and the servo hydraulic pressure Pu is based on the detected value of the servo hydraulic pressure PU. calculated respectively.

In step S120, "whether or not turning support control is being executed" is determined based on the execution flag FS for turning support control. If the execution flag FS is "0 (non-execution state)", step S120 is negative, and the process proceeds to step S130. On the other hand, when the execution flag FS is "1 (executing state)", step S120 is affirmative, and the process proceeds to step S140.

In step S130, it is determined whether or not turning support control is started (start determination) based on the turning support control switch signal Xa and the steering operation amount Sa (absolute value). If at least one of "the switch signal Xa is in an off state" and "the steering operation amount Sa is less than the predetermined starting amount sx" is satisfied, step S130 is denied and the process returns to step S110. On the other hand, if "the switch signal Xa is in an ON state" and "the steering operation amount Sa is equal to or greater than the predetermined starting amount sx", step S130 is affirmative, and the process proceeds to step S150. Here, the predetermined start amount sx is a control start threshold corresponding to the steering operation amount Sa, and is a preset predetermined value (positive constant).

In step S140, it is determined whether or not the turning support control is terminated (termination determination) based on the switch signal Xa and the steering operation amount Sa (absolute value). If at least one of "the switch signal Xa is in an off state" and "the steering operation amount Sa is less than the predetermined termination amount sz" is satisfied, step S140 is affirmative, and the process proceeds to step S160. On the other hand, if "the switch signal Xa is in an ON state" and "the steering operation amount Sa is equal to or greater than the predetermined end amount sz", step S140 is denied, and the process proceeds to step S150. Here, the predetermined termination amount sz is a control termination threshold value corresponding to the steering operation amount Sa, and is a preset predetermined value (positive constant). As for the magnitude relationship between the predetermined starting amount sx and the predetermined ending amount sz, the predetermined ending amount sz is smaller than the predetermined starting amount sx.

In step S150, a braking torque Tqu (referred to as "turning inner braking torque") is applied to the turning inner wheel WHu so as to reduce the turning radius of the vehicle JV. Specifically, the target hydraulic pressure Ptu (referred to as the “turning inner target hydraulic pressure”) of the wheel cylinder CWu (referred to as the “turning inner wheel cylinder”) provided for the turning inner wheel WHu is set to the preset pressure increase gradient ka incremented by (predetermined constant). Accordingly, the actual hydraulic pressure Pwu of the turning inner wheel cylinder CWu (referred to as "turning inner braking hydraulic pressure") is increased. When the turn inner wheel WHu is locked, the turn inner target hydraulic pressure Ptu is kept constant, and the turn inner brake hydraulic pressure Pwu is held. In other words, the hydraulic pressures Ptu (target value) and Pwu (actual value) of the turning inner wheel cylinder CWu are increased until the turning inner wheel WHu is locked, and are maintained at constant values after locking. When the rear wheel WHur on the inner side of the turn is selected as the inner wheel WHu of the turn, the effect of reducing the turning radius is high. Pwur (actual value) is increased.

At step S160, the turning support control is terminated. Turning inner braking torque Tqu applied to reduce the turning radius of vehicle JV is reduced. It should be noted that when the turning inner braking torque Tqu (that is, turning inner braking hydraulic pressure Pwu) is reduced, the gradient of the decrease is limited and is gradually reduced so that the vehicle behavior does not suddenly change.

<Operation of turning support control>
An operation example of turning support control will be described with reference to the time series diagram of FIG. In this example, it is assumed that the steering operation member SH (steering wheel) is operated in the left turning direction when the crawl control is being executed and the switch signal Xa for turning support control is in the ON state. ing. Further, in the turning support control, the braking torque Tqur is applied by increasing the braking fluid pressure Pwur to the turning inner rear wheel WHur (that is, the left rear wheel with respect to the traveling direction of the vehicle JV), which has a high control effect. It is Here, since the actual braking hydraulic pressure Pwur is controlled to match the target hydraulic pressure Ptur, the target value Ptur and the actual value Pwur overlap in the diagram.

Until time t0, the operating member SH is held in the straight-ahead direction, and the steering operation amount Sa is "0 (neutral position)". At time t0, the operating member SH begins to be operated leftward, and the steering operation amount Sa is increased from "0". Since the vehicle body speed Vx is maintained at the set speed vc (target speed for crawl control set by switch XC) by crawl control, the wheel speed Vwur of the left rear wheel remains constant at the set speed vc until time t0. is. Here, the left rear wheel corresponds to the turning inner rear wheel WHur because the vehicle JV turns to the left and turning support control is started. The turning inner rear wheel WHur is also simply referred to as the "inner rear wheel". Further, the wheel speed Vwur of the inner rear wheel WHur is the wheel speed corresponding to the turning inner rear wheel after turning support control is started, and is also simply referred to as the "inner rear wheel speed".

At time t1, the steering operation amount Sa reaches the start predetermined amount sx, the condition of step S130 is satisfied, and the turning support control is started. The target hydraulic pressure Ptur for the left rear wheel is increased at the pressure increase gradient ka. Accordingly, the brake hydraulic pressure Pwur for the left rear wheel is increased at the pressure increase gradient ka. Here, the braking hydraulic pressure Pwur of the inner rear wheel WHur is the braking hydraulic pressure corresponding to the turning inner rear wheel after turning support control is started, and is also simply referred to as the "inner rear wheel hydraulic pressure". Further, the pressure increase gradient ka is a preset predetermined value (constant). At time t1, the execution flag FS for turning support control is switched from "0 (non-operating)" to "1 (operating)".

After time t1, the inner rear wheel speed Vwur decreases as the inner rear wheel hydraulic pressure Pwur increases. At time t2, the inner rear wheel WHur is locked, and the inner rear wheel speed Vwur becomes "0". Since the inner rear wheel hydraulic pressure Pwur does not need to be increased any more, it is maintained at the value pa from time t2. At time t2, the duration Tk of the locked state of the inner rear wheel WHur (referred to as "lock duration") is calculated.

From time t3, the steering operation member SH is held, and the steering operation amount Sa is maintained at the value sa. At time t4, lock continuation time Tk reaches predetermined time tk. The predetermined time tk is a preset predetermined value (constant). At time t4, the hydraulic pressures Ptur (target value) and Pwur (actual value) of the turning inner rear wheel WHur are decreased so that the locked state of the inner rear wheel WHur is temporarily released. The reduction of the inner rear wheel hydraulic pressure Pwur is to prevent the wheel (tire) from having a flat spot (appearance of a flat deformed portion on a part of the tread surface of the tire). Specifically, when the condition “Tk≧tk” is satisfied, the inner rear wheel hydraulic pressure Pwur is decreased from the value pa by the value pd at the decompression gradient kb (predetermined constant). As a result, the inner rear wheel speed Vwur is increased from "0" to the value vb (see time t5).

When at least one of "the inner rear wheel hydraulic pressures Ptur and Pwur are decreased by a predetermined hydraulic pressure pd" and "the inner rear wheel speed Vwur is increased by a predetermined speed vb" is satisfied. At t5, the inner rear wheel hydraulic pressures Ptur and Pwur are again increased at the pressure increase gradient kc. Here, the predetermined hydraulic pressure pd, the predetermined speed vb, and the pressure increase gradient kc are preset predetermined values (constants). Then, at time t6, when the turning inside rear wheel WHur is locked again, the inside rear wheel hydraulic pressures Ptur and Pwur are held. At the same time, counting of lock duration time Tk is started. After time t6, the operation (locking operation and unlocking operation) from time t2 to time t6 is alternately repeated by maintaining, decreasing, and increasing the turning inner rear wheel hydraulic pressures Ptur and Pwur. That is, the first lock operation is performed from time t2 to time t4, then the lock is released, and the second lock operation is performed from time t6 to time t7, after which the lock is released. is released, and the third lock operation is started from time t9.

<Shared control>
The sharing control will be described with reference to the flowchart of FIG. In the "sharing control", not only the first unit YA but also the second unit YB share the pressure source for applying the braking torque Tqu to the turning inner wheel WHu.

In the turning support control, the turning inner brake hydraulic pressure Pwu is increased until at least the rear wheels of the turning inner wheels are locked so as to decrease the turning radius of the vehicle JV. At this time, the wheel cylinder CW provided for the wheel to be locked corresponds to the selected wheel cylinder CWx, and the hydraulic pressure Pwx thereof is adjusted by the first unit YA. In other words, the first unit YA is required to output a high hydraulic pressure for locking the turning inner wheel WHu. Since the turning support control is sometimes operated on a winding off-road with continuous curves, the operation time may be long. Therefore, in order to alleviate the load on the first unit YA, a control (that is, sharing control) is adopted in which the second unit YB also shares the turning support control.

At step S210, various signals including the servo hydraulic pressure Pu, the supply hydraulic pressure Pm, the adjustment hydraulic pressure Pq, the braking hydraulic pressure Pw, and the control activation flag FS for turning support control are read. The servo hydraulic pressure Pu is calculated based on the detected value of the servo hydraulic pressure sensor PU, and the supply hydraulic pressure Pm is calculated based on the detected value of the supply hydraulic pressure sensor PM. The regulating hydraulic pressure Pq is calculated based on the supply hydraulic pressure Pm and the driving state of the pressure regulating valve UB. An adjustment hydraulic pressure sensor PQ may be provided to detect the adjustment hydraulic pressure Pq. Also, the brake fluid pressure Pw is calculated based on the driving states of the pressure regulating valve UB, the inlet valve UI, and the outlet valve VO. A brake fluid pressure sensor PW may be provided to detect the brake fluid pressure Pw.

In step S220, "whether or not turning support control is being executed" is determined based on the execution flag FS for turning support control. If the execution flag FS is "0 (non-execution)", step S220 is denied and the process returns to step S210. On the other hand, when the execution flag FS is "1 (executing)", step S220 is affirmative, and the process proceeds to step S230.

At step S230, it is determined whether or not the operating condition of the first unit YA is severe. This determination is referred to as "specific determination", and the determination condition is referred to as "specific condition". Therefore, in step S230, it is determined whether or not the specific condition is satisfied. Examples of specific conditions are listed below.

Specific condition (1): "whether or not a first predetermined time tj has passed since the locked state of the turning inner wheel WHu (for example, the inner rear wheel WHur) was first generated (referred to as the 'initial locking time point'). ” will be determined accordingly. Therefore, step S230 is satisfied when the first predetermined time tj has passed since the time of the initial locking. Here, the first predetermined time tj is a preset predetermined value (constant).

Specific condition (2): Determined according to "whether or not the second predetermined time ti has passed since the time point when the turning support control was started (referred to as the 'control start time point')". Therefore, step S230 is satisfied when the second predetermined time ti has passed since the start of control. Here, the second predetermined time ti is a preset predetermined value (constant).

Specific condition (3): "A third predetermined time tx from the point in time when the braking torque Tqu of the turning inner wheel WHu (for example, the inner rear wheel WHur) reaches or exceeds a predetermined torque tq for the first time (referred to as the 'high load occurrence time point'). has elapsed or not". Therefore, step S230 is satisfied when the third predetermined time tx has passed since the high load occurred. Here, each of the predetermined torque tq and the third predetermined time tx is a preset predetermined value (constant). Since the turning inner braking torque Tqu corresponds to the turning inner braking hydraulic pressure Pwu, the specific condition (3) is "the hydraulic pressure Ptu (target value) of the turning inner wheel WHu (for example, the inner rear wheel WHur), Pwu (Actual value) may be determined according to whether or not a third predetermined time tx has elapsed since the time when the (actual value) became equal to or greater than the predetermined hydraulic pressure px for the first time (that is, the time when the high load occurred). Here, the predetermined hydraulic pressure px is a predetermined value (constant) set in advance and a value corresponding to the predetermined torque tq.

If step S230 is negative, the process proceeds to step S240. On the other hand, when step S230 is affirmative, the process proceeds to step S250.

In step S240, the braking torque Tqu is applied to the turning inner wheel WHu only by the first unit YA. If step S230 is negative, it means that the load on the first unit YA is not so large. Therefore, similarly to crawl control, the turning inner braking torque Tqu (for example, the inner braking hydraulic pressure Pwu) is increased only by the first unit YA. Note that, at the start of the turning support control, the turning inner braking torque Tqu is applied only by the first unit YA.

In step S250, the component Ta (referred to as "first component") of the turning inner braking torque Tqu due to the first unit YA is reduced. If step S230 is affirmative, it means that the load on the first unit YA is large. Therefore, the first component Ta due to the first unit YA is reduced. For example, the first component Ta is reduced by reducing the supply hydraulic pressure Pm generated by the first unit YA.

In step S260, the component Tb (referred to as the "second component") of the turning inner braking torque Tqu due to the second unit YB is increased so as to compensate for the decrease in the first component Ta. For example, the second component Tb is increased by the second unit YB from the supplied hydraulic pressure Pm to the adjusted hydraulic pressure Pq (that is, the hydraulic pressure difference mQ is increased). Here, since the increase in the second component Tb complements the decrease in the first component Ta, the absolute value of the first component Ta and the absolute value of the second component Tb are equal. Accordingly, the hydraulic pressure difference mQ is increased by the amount corresponding to the decrease in the supplied hydraulic pressure Pm, so that the relationship "Ta+Tb=0" is maintained.

The turning support control requires a large turning inner braking torque Tqu to lock the turning inner wheel WHu. If the durability of the braking control device is determined so that this braking torque Tqu can be generated only by the first unit YA over a long period of time, the size and weight of the braking control device (especially the first unit YA) is enlarged. In the braking control device SC, when the load condition of the first unit YA becomes severe, the load of the first unit YA is shared by the second unit YB to reduce the load of the first unit YA. Here, the second unit YB has a power source different from that of the first unit YA, and can apply the turning inner braking torque Tqu. There is a trade-off relationship between durability (sturdiness) and reduction in size and weight. can be compatible.

<Operation of sharing control>
An operation example of sharing control will be described with reference to the time-series diagram of FIG. 7 (transition diagram of various state quantities with respect to time T). The sharing control causes the second unit YB to share the load in order to reduce the load on the first unit YA in applying the braking torque Tqu to the turning inner wheel WHu. Similar to the time-series diagram of FIG. 5, the diagram assumes a situation in the left turning direction, and the inside rear wheel braking hydraulic pressure Pwur (inside A turning inner rear wheel braking torque Tqr is applied by an increase in rear wheel hydraulic pressure. In the operation example, the specific determination is made based on "whether or not the first predetermined time tj has elapsed since the lock state of the rear wheel WHur on the inner side of the turn occurred for the first time (initial lock time)". (see specific condition (1) above). Also, since the actual braking hydraulic pressure Pwur matches the target hydraulic pressure Ptur, the target value Ptur and the actual value Pwur overlap in the diagram.

At time u1, turning support control is started. At the beginning of control, the inner rear wheel hydraulic pressure Pwur (that is, the inner rear wheel braking torque Tqur) is increased only by the first unit YA. Specifically, from time u1, the inner rear wheel target hydraulic pressure Ptur is increased at the pressure increasing gradient ka, and the supply hydraulic pressure Pm is increased at the pressure increasing gradient ka by the first unit YA. At this time, since the second unit YB is not operated, the pressure regulating valve UB is in a non-energized state (that is, in a fully open state), and the hydraulic pressure difference mQ remains "0".

At time u2, the turning inside rear wheel WHur is locked. At time u2, the inner rear wheel target hydraulic pressure Ptur (resultingly, the inner rear wheel braking hydraulic pressure Pwur) is maintained constant at the value pa. Further, at time u2, calculation of the duration Tj (first duration) of the locked state of the inner rear wheel WHur is started. From the time point u2, as described with reference to FIG. 5, the inner rear wheel hydraulic pressures Ptur (target value) and Pwur (actual value) are maintained, decreased, and increased (the processing after time t2 in FIG. 5). ) is repeatedly executed.

At time u6, the first duration Tj reaches the first predetermined time tj (preset constant), and in step S230, the specific condition (that the load condition of the first unit YA has become severe) is satisfied. be. The point in time when step S230 is satisfied for the first time is referred to as the "particular point in time." At a specific time u6, the hydraulic pressure Pm (that is, the first component Ta) supplied by the first unit YA begins to decrease. Then, the hydraulic pressure difference mQ (that is, the second component Tb) by the second unit YB begins to increase so as to compensate for the decrease in the supplied hydraulic pressure Pm. Specifically, after time u6, the supply hydraulic pressure Pm is decreased with a gradient kd, and the hydraulic pressure difference mQ is increased with a gradient ke. Here, the slope of decrease kd and the slope of increase ke are predetermined values (constants) set in advance, and their absolute values are equal (that is, "|kd|=|ke|").

At the time point u7, the supplied hydraulic pressure Pm and the hydraulic pressure difference mQ are kept constant at the value pc and the value pq, respectively. At this time, the relationship is "pa=pc+pq". At time u8, the hydraulic pressure difference mQ is reduced and increased again by the second unit YB so as to avoid a flat spot due to locking of the inside rear wheel WHur of the turn.

Turning support control may be operated for a long time, such as off-road driving with continuous curves. If the first unit YA is configured so as to cope with such a situation, there is a risk that the size of the entire apparatus will increase. In the braking control device SC, two units YA and YB are appropriately used so as to achieve a trade-off relationship between durability and size and weight reduction. Specifically, when the load on the first unit YA is not so severe, the turning support control is executed only by the first unit YA. Then, when the load condition of the first unit YA becomes severe, the load of the first unit YA is reduced, and the load is shared by the second unit YB. As a result, in the braking control device SC capable of executing the turning support control, it is possible to achieve a reduction in size and weight while ensuring durability.

In the operation example, the specific condition (1) is adopted as the specific determination, but the above specific condition (2) may be adopted. In this case, a duration Ti (second duration) from time u1 (control start time) at which turning support control is started is calculated. Then, at a time point (specific time point) u6 when the second duration Ti reaches a second predetermined time ti (preset constant), the supply hydraulic pressure Pm (first component Ta) is reduced and the hydraulic pressure difference mQ (second component Tb) is increased. Further, the specific condition (3) may be adopted for the specific determination. In this case, the duration time Tx (third duration time) from the time point x2 (high load occurrence time point) when the inner rear wheel hydraulic pressures Ptur and Pwur (corresponding to the turning inner braking torque Tqu) for the first time become equal to or higher than the predetermined hydraulic pressure px is calculated. Then, at the time (specific time) u6 when the third duration Tx reaches the third predetermined time tx (preset constant), the supply hydraulic pressure Pm (first component Ta) is reduced, and the hydraulic pressure difference mQ ( The second component Tb) is increased. Even when the specific conditions (2) and (3) are employed, the same effects as in the case of the specific condition (1) are obtained.

<Other embodiments>
Another embodiment of the braking control device SC will be described below. In other embodiments as well, the load on the first unit YA is reduced by the above-described sharing control, so that the above-described effect (that is, achieving both durability and reduction in size and weight of the braking control device SC) can be achieved. Play.

<<Adoption of a reflux type pressure unit KU as the first unit YA and a single type master cylinder CM>>
A second configuration example of the first unit YA will be described with reference to the schematic diagram of FIG. In the first configuration example of the first unit YA, an accumulator type is adopted as the pressure unit KU (pressure source) of the first unit YA, and a tandem type is adopted as the master cylinder CM. . Instead of this, in the second configuration example, a circulation type pressure unit KU and a single type master cylinder CM are employed. As described above, constituent elements such as members, signals, and values denoted by the same symbols have the same function.

In the circulation type pressurization unit KU, in the fluid pump QC driven by the electric motor MC, a suction portion (a portion for sucking the braking fluid BF) and a discharge portion (a portion for discharging the braking fluid BF) form a circulation path HK. is connected. The return path HK is connected to the master reservoir RV, and the fluid pump QC can suck the brake fluid BF from the master reservoir RV. The return path HK is provided with a normally open linear valve UC (a solenoid valve similar to the pressure regulating valve UB of the second unit YB) to regulate the pressure of the brake fluid BF discharged by the fluid pump QC. Here, the hydraulic pressure adjusted by the linear valve UC corresponds to the servo hydraulic pressure Pu in the first configuration example. The return path HK is connected to the servo chamber Ru via the servo path HV between the discharge portion of the fluid pump QC and the linear valve UC. Also, the servo path HV is connected to the rear wheel cylinder CWr via the rear wheel connecting path HSr. Therefore, in the second configuration example, the servo hydraulic pressure Pu is supplied to the servo chamber Ru and the rear wheel cylinder CWr.

The first unit YA can be configured by combining "one of the tandem-type and single-type master cylinders CM" and "one of the accumulator-type and reflux-type pressurizing units KU". That is, "tandem type master cylinder CM + accumulator type pressurization unit KU (illustrated in Fig. 2)", "tandem type master cylinder CM + reflux type pressurization unit KU", "single type master cylinder CM + accumulator type pressurization unit KU". , and “single-type master cylinder CM+recirculating pressure unit KU (illustrated in FIG. 7)” is employed as the first unit YA.

≪Adoption of electric cylinder type as the first unit YA≫
In the first and second configuration examples of the first unit YA, a fluid pump QC driven by an electric motor MC is adopted as the pressurization source KU of the first unit YA. Alternatively, the electric motor may directly drive the piston inserted in the cylinder to increase the braking fluid pressure Pw. A so-called electric cylinder type can be employed as the first unit YA. Since the configuration of the electric cylinder type is known, for example, from WO2012/046703, etc., the configuration will be briefly described below. The electric cylinder type first unit YA is composed of a pressure regulating cylinder, a pressure regulating piston, a direct-acting conversion mechanism, and an electric motor.

A pressure regulating cylinder (also called a “slave cylinder”) is provided separately from the master cylinder CM. The pressure regulating cylinder has the same configuration as the master cylinder CM, and is, for example, a tandem cylinder. Two pressure regulating pistons are inserted into the pressure regulating cylinder via elastic bodies (compression springs). One of the two pressure regulating pistons is connected to the electric motor via a rotation/linear conversion mechanism (for example, a screw mechanism). Here, the linear motion conversion mechanism converts the rotary power of the electric motor into the linear power (thrust force) of the pressure regulating piston.

An electric motor drives the pressure regulating piston. Specifically, when the electric motor rotates, its power is converted into linear power for the pressure regulating piston by the direct-acting conversion mechanism. The pressure regulating cylinder 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 the communication path HS and the second unit YB. Accordingly, when the electric motor is driven, the volume of the pressure regulating chamber is reduced, so that the brake fluid BF is force-fed 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 (adjusted) by adjusting the output of the electric motor without using the solenoid valves UZ and UG.

<<Adoption of an electric parking brake device as the second unit YB>>
In the configuration example of the second unit YB described above, one using the brake fluid BF used for vehicle stability control and the like is adopted. Alternatively, an electric parking brake device may be employed as the second unit YB. The configuration of the electric parking brake device is known, for example, from Japanese Patent Application Laid-Open No. 2018-086879, and will be briefly described below.

An electric parking brake device is provided on the rear wheel WHr as a second unit YB. In an electric parking brake device, the rotational power of an electric motor is converted into linear power by a rotation/linear motion conversion mechanism (for example, a screw mechanism). This linear power presses the friction member MS (brake pad) against the rotary member KT (brake disc). Thereby, the braking torque Tqr is applied to the rear wheels WHr.

<Summary of Embodiments of Braking Control Device SC and Operation/Effect>
An embodiment of the braking control device SC will be summarized. Turning support control is executed by the braking control device SC. In the turning support control, braking torque Tqu is applied to the turning inner wheel WHu of the vehicle JV so that the turning radius of the vehicle JV is reduced. The braking control device SC includes "a first unit YA capable of increasing the hydraulic pressure of the wheel cylinder CW and applying the turning inner braking torque Tqu", "a unit other than the first unit YA (in particular, a power A second unit YB, which is a separate source) and capable of applying the turning inner braking torque Tqu, and a controller ECU for controlling the first and second units YA, YB are provided.

In the braking control device SC, when the controller ECU starts the turning support control (that is, at the beginning of the control), the turning inner side braking torque Tqu is applied only by the first unit YA. Then, after the turning support control is started, a specific determination is made as to whether or not the operating state (load state) of the first unit YA is severe. If the specific determination is denied, the turning inner braking torque Tqu is continued to be applied only by the first unit YA. On the other hand, when the specific determination is affirmative (satisfied), the turning inner braking torque Tqu is applied by the second unit YB. Specifically, the controller ECU decreases the first component Ta due to the first unit YA and increases the second component Tb due to the second unit YB in the turning inner braking torque Tqu from the time when the specific determination is affirmed. be done.

The braking control device SC includes two units YA, YB to implement various functions. For example, the first unit YA is used to implement functions such as service braking and crawl control. Also, the second unit YB is used to implement functions such as vehicle stability control and parking brake. Therefore, each of the first and second units YA, YB is provided to implement different functions. Each of the first and second units YA and YB has a different power source (pressure source).

The braking control device SC, which is executed for turning support control, is required to generate braking torque Tq capable of locking the wheels WH for a long period of time. If this demand is to be satisfied with a single unit (that is, the first unit YA), it becomes necessary to increase the size of the apparatus. Therefore, in the braking control device SC, when the load on the first unit YA is not so severe (that is, when the specific determination is not satisfied), the turning support control is executed only by the first unit YA. Then, when the load condition of the first unit YA becomes severe (that is, when the specific determination is satisfied), the load of the first unit YA is reduced, and the load is shared by the second unit YB. . As a result, the demand for durability is satisfied, and at the same time, the size and weight of the braking control device SC can be reduced.

For example, in the braking control device SC, the first duration Tj is calculated from the time when the lock state of the inside wheel WHu of turning is first generated (lock start time). Then, "whether or not the first duration Tj is equal to or longer than the first predetermined time tj" is employed as a specific condition (condition for making a specific determination). Here, the first predetermined time tj is a preset predetermined value (constant). When the first duration Tj reaches the first predetermined time tj (that is, when the first predetermined time tj has passed since the locking start time), the specific condition "Tj≧tj" is satisfied, and the specific determination is made. Since it is affirmative, sharing control is started.

Also, in the braking control device SC, the second duration Ti can be calculated from the time when the turning support control is started (control start time). Then, "whether or not the second duration Ti is equal to or greater than the second predetermined time ti" is employed as the specific condition. Here, the second predetermined time ti is a preset predetermined value (constant). When the second duration Ti reaches the second predetermined time ti (that is, when the second predetermined time ti has passed since the control start time), the specific condition "Ti≧ti" is satisfied, and the specific determination is made. Since it is affirmative, sharing control is started.

Furthermore, in the braking control device SC, the third duration Tx may be calculated from the point in time when the turning inner side braking torque Tqu becomes equal to or greater than the predetermined torque tq for the first time (high load start point). Then, "whether or not the third duration Tx is equal to or longer than the third predetermined time tx" is adopted as the specific condition. Here, the third predetermined time tx and the predetermined torque tq are predetermined values (constants) respectively. When the third duration Tx reaches the third predetermined time tx (that is, when the third predetermined time tx has passed since the start of the high load), the specific condition "Tx≧tx" is satisfied, and the specific determination is affirmed, the sharing control is started.

JV...vehicle, SC...braking control device, SX...braking device, CP...brake caliper, CW...wheel cylinder, KT...rotating member (brake disc), MS...frictional member (brake pad), ECU...braking controller, BS Communication bus XC Crawl control switch XA Rotation support control switch HU Fluid unit YA First unit CM Master cylinder MA Electric motor (for pressure accumulation) KU Pressure unit YB...Second unit, UB... Pressure regulating valve, UI... Inlet valve, VO... Outlet valve, RC... Pressure regulating reservoir, MB... Electric motor (for reflux), QB... Fluid pump (for reflux), PM... Fluid supply pressure Sensors, Pm...Supply hydraulic pressure, Pq...Adjusted hydraulic pressure, Pw...Brake hydraulic pressure (actual hydraulic pressure of CW), Pt...Target hydraulic pressure (target value of Pw), mQ...Hydraulic pressure difference (supply hydraulic pressure Pm and adjustment hydraulic pressure Pq), Tq: braking torque, Vw: wheel speed, Ta: first component (component of braking torque Tq due to first unit YA), Tb: second component (of braking torque Tq component by the second unit YB).

Claims (2)

A braking control device for a vehicle that performs turning support control for reducing a turning radius of the vehicle by applying braking torque to a turning inner wheel of the vehicle,
a first unit that increases the hydraulic pressure of the wheel cylinder of the vehicle to apply the braking torque;
a second unit that applies the braking torque separately from the first unit;
a controller that controls the first unit and the second unit;
with
The controller is
applying the braking torque only by the first unit when starting the turning support control;
After starting the turning support control, a specific determination is made as to whether or not the operating state of the first unit is severe, and if the specific determination is affirmative, the braking torque is applied by the second unit. Braking control device. In the vehicle braking control device according to claim 1,
The controller reduces a first component of the braking torque by the first unit and increases a second component of the braking torque by the second unit from a time when the specific determination is affirmative. .

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