Braking control device of vehicle

Abstract

To provide a braking control device of a vehicle that can execute starting-assist control of suppressing a vehicle from moving backward on an uphill road, which can improve hill-climbing performance.SOLUTION: A braking control device comprises an actuator that can individually adjust braking torque applied to a plurality of wheels, and a controller that holds the braking torque so as to prevent a vehicle from moving backward on an uphill road through the actuator and then executes starting-assist control of gradually reducing the braking torque. The controller can execute traction control by which the braking torque is increased in a slip wheel in which an acceleration slip of the wheel becomes larger than a predetermined slip to reduce the acceleration slip. Further, the controller determines a final control amount Qt on the basis of a first control amount Qa of the braking torque relating to the starting-assist control and a second control amount Qb of the braking torque relating to the traction control, and controls the braking torque on the basis of the final control amount Qt.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Patent Document 1 describes that in order to prevent a vehicle from having difficulty starting on packed snow uphill roads, "when traction control is started in step S1 (TCS intervention), the rear wheel climb rate, i.e., the rate of increase in the wheel rotation speed, becomes greater than threshold A in step S2, the clutch is released N times or more in step S3, and the hill climbing impossibility determination is established (ON) in step S4, the traction control unit either temporarily prohibits traction control, increases the target slip amount in steps, or gradually increases the target slip amount." Here, the device in Patent Document 1 solves the problem of a vehicle in which the clutch is released when the engine rotation speed decreases, and traction control is prohibited above a certain vehicle speed.

[0003] Meanwhile, vehicles (especially four-wheel drive vehicles) are required to be able to run on rough roads. The applicant has developed a vehicle braking control device as described in Patent Document 2. The device includes a braking force holding process for holding the braking force on the right and left driving wheels to keep the vehicle stopped, and a braking force reduction process for reducing the braking force on the right and left driving wheels when the vehicle starts moving due to an increase in the driving force output from the power source, and a braking force correction unit 83 for slowing down the reduction rate of the braking force on the driving wheel on which the acceleration slip has occurred, when an acceleration slip occurs on one of the right and left driving wheels during the braking force reduction process, compared to the reduction rate of the braking force on the driving wheel on which the acceleration slip has occurred. It is desired that the device improves the hill climbing performance during the start assist control. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-142262 A [Patent Document 2] Patent Publication No. 2021-098449 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above problems, an object of the present invention is to provide a vehicle braking control device capable of executing start assist control for suppressing the vehicle rolling back on an uphill road, which can improve the hill climbing performance. [Means for solving the problem]

[0006] The vehicle braking control device (SC) according to the present invention includes an actuator (HU) capable of individually adjusting a braking torque (Tb) for a plurality of wheels (WH), and a controller (ECU) for executing a start assist control for gradually reducing the braking torque (Tb) after maintaining the braking torque (Tb) via the actuator (HU) so that the vehicle does not roll back on an uphill road. The controller (ECU) can execute a traction control for reducing the acceleration slip (Sw) by increasing the braking torque (Tb) for slipping wheels (WHs) whose acceleration slip (Sw) of the wheels (WH) is greater than a predetermined slip (sx). Furthermore, the controller (ECU) determines a final control amount (Qt) based on a first control amount (Qa) of the braking torque (Tb) related to the start assist control and a second control amount (Qb) of the braking torque (Tb) related to the traction control, and controls the braking torque (Tb) based on the final control amount (Qt). For example, the controller (ECU) determines the final control amount (Qt) by adding the second control amount (Qb) to the first control amount (Qa). Alternatively, the controller (ECU) determines the larger of the first control amount (Qa) and the second control amount (Qb) as the final control amount (Qt). With the above configuration, the acceleration slip Sw of the slipping wheel WHs in which excessive acceleration slip Sw is occurring is suppressed by increasing the braking torque Tb. This improves the hill climbing performance in the start assist control.

[0007] In the vehicle braking control device (SC) according to the present invention, when the vehicle is stopped at the time (t3) when the slipping wheel (WHs) occurs, the controller (ECU) holds the braking torque (Tb) at the gripping wheels (WHg) that do not fall under the slipping wheels (WHs). When the vehicle is moving forward at the time (t3) when the slipping wheel (WHs) occurs, the controller (ECU) sets the braking torque (Tb) at the gripping wheels (WHg) that do not fall under the slipping wheels (WHs) to zero. When the vehicle is moving backward at the time (t3) when the slipping wheel (WHs) occurs, the controller (ECU) increases the braking torque (Tb) at the gripping wheels (WHg) that do not fall under the slipping wheels (WHs). According to the above configuration, the braking torque Tb of the gripping wheels WHg is also appropriately adjusted. This further improves the hill-climbing performance in the start assist control. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a vehicle equipped with a vehicle braking control device SC according to the present invention. [Diagram 2] 2 is a schematic diagram for explaining a configuration example of a braking control device SC. FIG. [Diagram 3] FIG. 4 is a flow diagram for explaining the processing of the start assistance control (particularly, the slipping wheel WHs). [Figure 4] FIG. 11 is a flow chart for explaining the processing of the start assistance control (particularly, the grip wheel WHg). [Diagram 5] FIG. 4 is a time series diagram for explaining the operation of the start assistance control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Symbols of components> In the following explanation, components, signals, values, etc. with the same symbol, such as "CW", have the same function. The subscripts "f" and "r" at the end of various symbols related to wheels are generic symbols that indicate whether the element is related to the front or rear wheels. Specifically, "f" indicates an element related to the front wheels, and "r" indicates an element related to the rear wheels. For example, a wheel cylinder CW is written as a front wheel cylinder CWf and a rear wheel cylinder CWr. Furthermore, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its generic name.

[0010] <Vehicles equipped with braking control system SC> With reference to the schematic diagram of Fig. 1, the entirety of a vehicle equipped with a braking control device SC will be described. The vehicle is equipped with an acceleration operation member AP, a braking operation member BP, a steering operation member (not shown), and various sensors (BA, etc.). The acceleration operation member AP (e.g., an accelerator pedal) is a member that the driver operates to accelerate the vehicle and control the vehicle's traveling speed Vx. The braking operation member BP (e.g., a brake pedal) is a member that the driver operates to decelerate the vehicle. The steering operation member (e.g., a steering wheel) is a member that the driver operates to turn the vehicle.

[0011] The vehicle is equipped with various sensors, as listed below. Detection signals (Ba, etc.) from these sensors are input to a braking controller ECU (also simply referred to as a "braking controller"), which will be described later. -Acceleration operation amount sensor AA that detects the operation amount Aa (acceleration operation amount) of the acceleration operation member AP. For example, the acceleration operation amount sensor AA is attached to the acceleration operation member AP and detects the operation displacement of the acceleration operation member AP as the acceleration operation amount Aa. - A brake operation amount sensor BA that detects an operation amount Ba (braking operation amount) of the brake operating member BP. For example, the brake operation amount sensor BA is attached to the brake operating member BP and detects the operation displacement of the brake operating member BP as the braking operation amount Ba. Alternatively, a master pressure Pm detected by a master pressure sensor PM (described later) may be used as the braking operation amount Ba. - A steering operation amount sensor SA that detects an operation amount Sa (steering operation amount) of a steering operation member. For example, the steering operation amount sensor SA is attached to the steering operation member and detects the operation displacement (steering angle) of the steering operation member as the operation amount Sa. - Wheel speed sensor VW that detects the rotation speed Vw (also called "wheel speed") of the wheels WH. The wheel speed sensor VW is provided on each wheel WH. The braking control device SC calculates the vehicle running speed Vx based on the wheel speed Vw. The running speed Vx is also called "vehicle speed" so as to be distinguished from the wheel speed Vw. In the vehicle (particularly the vehicle body), 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.

[0012] The vehicle is equipped with a master cylinder CM, a brake control device SC, and a brake device SX. The vehicle employs a so-called front and rear type (also called "type II") brake system as the two-system brake system. The master cylinder CM, the brake control device SC, and the brake device SX are connected by the front wheel and rear wheel connection paths HSf and HSR.

[0013] A tandem type master cylinder CM is used. The interior of the master cylinder CM is divided into two hydraulic chambers by two master pistons. The two hydraulic chambers are also called the "front and rear master chambers." The master pistons are moved in conjunction with the brake operating member BP. As a result, the front and rear master Pmf and Pmr (=Pm) are output from the master cylinder CM (particularly the front and rear master chambers) to the brake control device SC.

[0014] The brake control device SC adjusts (increases or decreases) the master pressure Pm and supplies it to the brake device SX (particularly, the wheel cylinder CW) as the wheel pressure Pw. The brake control device SC will be described in detail later.

[0015] The braking device SX applies a braking torque Tb to the wheel WH according to the wheel pressure Pw in the wheel cylinder CW. As a result, a braking force Fb is generated in the wheel WH. Specifically, the braking device SX includes a rotating member KT (e.g., a brake disc) 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. The brake caliper CP is provided with a wheel cylinder CW. The brake control device SC supplies the wheel cylinder CW with braking fluid BF adjusted to the wheel pressure Pw. The wheel pressure Pw presses a friction member MS (e.g., a brake pad) against the rotating member KT. Since the rotating member KT and the wheel WH are fixed so as to rotate integrally, the frictional force generated at this time generates a braking torque Tb (as a result, a braking force Fb) in the wheel WH. Therefore, the wheel pressure Pw corresponds to the braking torque Tb.

[0016] The vehicle is equipped with a prime mover control device SG and a power transmission device ST. The vehicle is a four-wheel drive vehicle in which all four wheels WH are drive wheels. A drive torque is applied to the drive wheels WH by the prime mover control device SG. As a result, a drive force is generated in the drive wheels WH.

[0017] The prime mover control device SG is composed of a prime mover PG and a prime mover controller ECP (also simply referred to as a "prime mover controller") that controls the prime mover PG. An example will be described in which an internal combustion engine (gasoline engine) is used as the prime mover PG. The prime mover PG generates power (i.e., driving torque) for driving four wheels WH. The prime mover PG is controlled by the prime mover controller ECP, and its output is adjusted. In detail, the prime mover PG includes a throttle device, a fuel injection device, and an engine speed sensor. The throttle opening is controlled by the throttle device, and the fuel injection amount is controlled by the fuel injection device. Then, at least one of the throttle opening and the fuel injection amount is controlled by the prime mover controller ECP based on the engine speed detected by the speed sensor. As a result, the output of the prime mover PG is adjusted.

[0018] The prime mover PG may be an electric motor for driving the vehicle. That is, the brake control device SC is applicable not only to internal combustion engine vehicles, but also to hybrid vehicles, electric vehicles, and the like.

[0019] The output (rotational power) of the prime mover control device SG (particularly, the prime mover PG) is input to the power transmission device ST. The output (power) of the prime mover PG is then transmitted as driving torque to the four wheels WH via the power transmission device ST. As a result, driving force is generated in each of the wheels WH. The power transmission device ST is composed of a power transmission mechanism and a power transmission controller ECT (also simply referred to as a "power transmission controller") that controls the same. The power transmission mechanism includes a transmission (not shown), a front wheel differential mechanism FD, a center differential mechanism CD, and a rear wheel differential mechanism RD. Here, the power transmission mechanism is controlled by the power transmission controller ECT.

[0020] The front wheel drive torque (and thus the front wheel drive force) is transmitted to the left and right front wheels WHf via the front wheel differential mechanism FD and the front wheel drive shaft. The rear wheel drive torque (and thus the rear wheel drive force) is transmitted to the left and right rear wheels WHr via the central differential mechanism CD, the rear wheel differential mechanism RD and the rear wheel drive shaft. Because the power generated by the prime mover PG is transmitted to the front and rear wheels WHf and WHr via the differential mechanisms DF, CD and RD, a difference in rotational speed (i.e., differential) between the wheels WH is permitted.

[0021] <Brake control device SC> The brake control device SC will be described with reference to the schematic diagram of FIG. 2. The brake control device SC is provided between the master cylinder CM and the wheel cylinder CW. The master pressure Pm is adjusted (increased, maintained, decreased) by the brake control device SC. The brake control device SC is used for anti-lock brake control (control for suppressing locking of the wheels WH), traction control (control for suppressing slippage of the wheels WH), and anti-skid control (control for suppressing excessive understeer and oversteer, so-called ESC). The brake control device SC is composed of a fluid unit HU and a brake controller ECU.

[0022] <Fluid unit HU> The fluid unit HU (corresponding to an "actuator") is composed of a master pressure sensor PM, a pressure regulating valve UA, a fluid pump HP, an electric motor MT, a pressure regulating reservoir RC, an inlet valve VI, and an outlet valve VO.

[0023] Front and rear wheel pressure regulating valves UAf, UAr (=UA) are provided in the front and rear wheel communication passages HSf, HSR (=HS). The pressure regulating valve UA is a normally open linear solenoid valve (differential pressure valve). The pressure regulating valve UA can increase the wheel pressure Pw from the master pressure Pm individually in the front and rear wheel systems.

[0024] The front and rear wheel master pressure sensors PMf, PMr (=PM) are provided above the front and rear wheel pressure regulating valves UAf, UAr (at the portion of the communication passage HS closer to the master cylinder CM) to detect the actual hydraulic pressures Pmf, Pmr (front and rear wheel master pressures) supplied from the master cylinder CM (particularly the front and rear wheel master chambers Rmf, Rmr). The master pressure sensor PM is built into the fluid unit HU. Signals of the front and rear wheel master pressures Pmf, Pmr (=Pm) are input to the brake controller ECU. Note that since the front wheel master pressure Pmf and the rear wheel master pressure Pmr are substantially the same, either one of the front and rear wheel master pressure sensors PMf, PMr may be omitted. For example, the rear wheel master pressure sensor PMr is omitted, and only the front wheel master pressure Pmf is detected by the front wheel master pressure sensor PMf.

[0025] The front and rear wheel return paths HKf, HKr (=HK) connect the upper portions of the front and rear wheel pressure regulating valves UAf, UAr (portions of the communication paths HS closer to the master cylinder CM) to the lower portions of the front and rear wheel pressure regulating valves UAf, UAr (portions of the communication paths HS closer to the wheel cylinders CW). The front and rear wheel return paths HKf, HKr are provided with front and rear wheel fluid pumps HPf, HPr (=HP) and front and rear wheel pressure regulating reservoirs RCf, RCr (=RC). The fluid pumps HP are driven by an electric motor MT.

[0026] When the electric motor MT is driven, the fluid pump HP sucks brake fluid BF from the top of the pressure regulating valve UA and discharges it to the bottom of the pressure regulating valve UA. As a result, a circulation flow KN of brake fluid BF (i.e., front and rear wheel circulation flows KNf and KNr, indicated by dashed arrows) is generated in the communication path HS and the return path HK, including the fluid pump HP and the pressure regulating reservoir RC. When the pressure regulating valve UA narrows the flow path of the communication path HS and throttles the circulation flow KN of brake fluid BF, the orifice effect created by this causes the hydraulic pressure Pp (referred to as "regulation pressure") at the bottom of the pressure regulating valve UA to increase from the hydraulic pressure Pm (master pressure) at the top of the pressure regulating valve UA. In other words, in the circulation flow KN, a hydraulic pressure difference sP (also called "differential pressure") between the downstream hydraulic pressure Pm (master pressure) and the upstream hydraulic pressure Pp (adjustment pressure) is generated by the pressure regulating valve UA (i.e., "Pp = Pm + sP"). Note that in terms of the magnitude relationship between the master pressure Pm and the adjustment pressure Pp, the adjustment pressure Pp is equal to or greater than the master pressure Pm (i.e., "Pp ≧ Pm").

[0027] Inside the fluid unit HU, the front and rear wheel communication passages HSf, HSR are each branched into two and connected to the front and rear wheel cylinders CWf, CWr. A normally open inlet valve VI and a normally closed outlet valve VO are provided for each wheel cylinder CW so that each wheel pressure Pw can be adjusted individually. Specifically, the inlet valve VI is provided in the branched communication passage HS (i.e., on the side closer to the wheel cylinder CW with respect to the branching part of the communication passage HS). The communication passage HS is connected to the pressure regulating reservoir RC via a pressure reducing passage HG at a lower part of the inlet valve VI (the part of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO is provided in the pressure reducing passage HG. An on-off type solenoid valve is used as the inlet valve VI and the outlet valve VO.

[0028] In the fluid unit HU, the wheel pressure Pw is independently adjusted for each wheel cylinder CW by the inlet valve VI and the outlet valve VO. To reduce the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. The inflow of brake fluid BF into the wheel cylinder CW is blocked, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RC, so that the wheel pressure Pw is reduced. To increase the wheel pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. The outflow of brake fluid BF to the pressure regulating reservoir RC is blocked, and the regulated pressure Pp from the pressure regulating valve UA is supplied to the wheel cylinder CW, so that the wheel pressure Pw is increased. However, the upper limit of the increase in the wheel pressure Pw is the regulated pressure Pp. To maintain the wheel pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the wheel pressure Pw is maintained constant.

[0029] When the normally open inlet valve VI and the normally closed outlet valve VO are not energized and are deactivated, the inlet valve VI is opened and the outlet valve VO is closed. In this state, the wheel pressure Pw is equal to the regulated pressure Pp (i.e., "Pp=Pw").

[0030] <Brake controller ECU> The hydraulic unit HU is controlled by the brake controller ECU. The brake controller ECU is composed of a microprocessor MP and a drive circuit DR. The brake controller ECU can share signals with other controllers (ECP, ECT, etc.) via a communication bus BS.

[0031] The wheel speed Vw, the steering amount Sa, the yaw rate Yr, the longitudinal acceleration Gx, and the lateral acceleration Gy are input to the brake controller ECU (particularly the microprocessor MP). The brake controller ECU calculates the vehicle running speed Vx (vehicle body speed) based on the wheel speed Vw.

[0032] In the braking controller ECU, the drive circuit DR is controlled according to a control algorithm programmed in the microprocessor MP. Specifically, the drive circuit DR drives the electric motor MT and various solenoid valves (UA, etc.) constituting the fluid unit HU. In the drive circuit DR, an H-bridge circuit is configured with switching elements (e.g., MOS-FET) to drive the electric motor MT. The drive circuit DR is also provided with switching elements to drive the various solenoid valves (UA, etc.). Based on the control algorithm of the microprocessor MP, a drive signal Mt for the electric motor MT, a drive signal Ua for the pressure regulating valve UA, a drive signal Vi for the inlet valve VI, and a drive signal Vo for the outlet valve VO are calculated. Then, the drive circuit DR controls the supply current to the electric motor MT and the solenoid valves UA, VI, and VO based on the drive signals (Mt, Ua, etc.). Specifically, the drive circuit DR is provided with a motor current sensor (not shown) that detects a supply current Im (actual value, referred to as "motor current") to the electric motor MT, and a valve current sensor (not shown) that detects a supply current Ia (actual value, referred to as "pressure regulating valve current") to the pressure regulating valve UA. The motor current Im and the valve current Ia are adjusted according to the motor drive signal Mt and the valve drive signal Ua.

[0033] <Start assist control processing (especially slipping wheels WHs)> "Start assist control" is a control that suppresses the vehicle from rolling back when starting on an uphill road. Start assist control is also called "slope start assist control" or "hill start assist control." Specifically, in start assist control, when the operation of the braking operation member BP (brake pedal) is switched to the operation of the acceleration operation member AP (accelerator pedal) (so-called switching of the operation pedal) during starting after the vehicle has stopped on an uphill road (also called an "uphill road"), the wheel pressure Pw is maintained for a predetermined time ta (for example, 1 to 2 seconds). This allows the vehicle to start smoothly without rolling back.

[0034] The process for slipping wheels WHs in the start assist control will be described with reference to the flow diagram of FIG. 3. Here, "slipping wheels WHs" are driving wheels whose acceleration slip Sw becomes excessive during execution of the start assist control. Note that a wheel whose acceleration slip Sw falls within an appropriate range during execution of the start assist control is called a "grip wheel WHg." In detail, whether a wheel is a slipping wheel WHs or a gripping wheel WHg is determined according to the relationship between the traction control threshold value sx and the acceleration slip Sw. That is, a wheel whose acceleration slip Sw is less than the threshold value sx is a gripping wheel WHg, and a wheel whose acceleration slip Sw is equal to or greater than the threshold value sx is a slipping wheel WHs.

[0035] In step S110, various signals are read. Specifically, the wheel speed Vw (detected value of the wheel speed sensor VW), the acceleration operation amount Aa (detected value of the acceleration operation amount sensor AA), the braking operation amount Ba (detected value of the braking operation amount sensor BA), the longitudinal acceleration Gx (detected value of the longitudinal acceleration sensor GX), etc. are read. Then, in step S110, the vehicle body speed Vx is calculated based on the wheel speed Vw. For example, the vehicle body speed Vx is determined based on the slowest wheel speed Vw. Furthermore, in step S110, the gradient θ of the uphill road (also called the "uphill gradient") is calculated based on the longitudinal acceleration Gx. Specifically, the uphill gradient θ is determined based on the gravity component detected as the longitudinal acceleration Gx.

[0036] In step S120, a control amount Qa (also referred to as a "first control amount") of the start assist control is calculated. For example, the first control amount Qa is determined in the dimension of hydraulic pressure so as to correspond to the wheel pressure Pw. First, in step S120, it is determined whether or not the permission conditions related to the start assist control are satisfied. The execution of the start assist control is permitted when the vehicle is stopped on an uphill road. Specifically, "the vehicle is stopped on an uphill road" is determined based on "the upward gradient θ is equal to or greater than a predetermined gradient kx, and the vehicle speed Vx is zero (0)". Here, the predetermined gradient kx is a predetermined value (constant) that has been set in advance. Once the permission conditions for the start assist control are satisfied, the execution is permitted until the control is terminated.

[0037] Furthermore, in step S120, the start assistance control is started at the time when the state in which the brake operating member BP is operated is switched to the state in which the acceleration operating member AP is operated (i.e., at the corresponding calculation period). Specifically, when the braking operation amount Ba becomes "0" and the acceleration operation amount Aa becomes greater than "0", the execution of the start assistance control is started and the calculation of the first control amount Qa is started. Specifically, as shown in the blowout portion XQA, the first control amount Qa is calculated based on a preset calculation map Zqa with the passage of time T. In the calculation map Zqa, first, the first control amount Qa at the control start time (i.e., the time "T=0") is set as an initial value qo. Then, the first control amount Qa is maintained at the initial value qo until the time T reaches a predetermined time ta. Thereafter, the first control amount Qa is decreased at a predetermined gradient gk (amount of decrease per unit time). The start assistance control is terminated at time tb when the first control amount Qa becomes 0. Here, the predetermined time ta and the predetermined gradient gk are predetermined values ​​(constants) that are set in advance.

[0038] In step S130, a control amount Qb (also referred to as a "second control amount") of the traction control is calculated for each wheel WH. The second control amount Qb is determined as the same physical amount (e.g., hydraulic pressure) as the first control amount Qa. In traction control, first, a predetermined speed vk (e.g., a constant) is added to the vehicle speed Vx to determine a reference speed Vk of the driving wheels. In addition, an average speed Vh, which is the average value of the left and right wheel speeds Vw of the driving wheels, is calculated. Then, an acceleration slip Sw is calculated based on the reference speed Vk and the average speed Vh. Specifically, the reference speed Vk is subtracted from the average speed Vh to determine the acceleration slip Sw (i.e., "Sw=Vh-Vk").

[0039] Next, in step S130, the second control amount Qb is calculated based on the acceleration slip Sw. Specifically, as shown in the blowout section XQB, the second control amount Qb is calculated based on the acceleration slip Sw and a preset calculation map Zqb. In the calculation map Zqb, when the acceleration slip Sw is less than a predetermined slip sx, the second control amount Qb is determined to be "0". In other words, the predetermined slip sx is a condition for starting execution of traction control and is a threshold value. When the acceleration slip Sw is equal to or greater than the predetermined slip sx, the second control amount Qb is determined to be larger according to the calculation map Zqb as the acceleration slip Sw increases. The second control amount Qb is provided with an upper limit value qm. Here, the predetermined slip sx and the upper limit value qm are predetermined values ​​(constants) that are set in advance.

[0040] In calculating the second control amount Qb, the wheel acceleration dV (i.e., the increase in the wheel speed Vw per unit time) may be taken into consideration. Specifically, the second control amount Qb is determined so as to increase as the wheel acceleration dV increases. Furthermore, the second control amount Qb may be calculated based on the time integral value of the acceleration slip Sw.

[0041] In step S140, a final control amount Qt is calculated for each wheel WH based on the first control amount Qa and the second control amount Qb. The final control amount Qt is a result of adjusting the control amount Qa (first control amount) related to the start assist control and the control amount Qb (second control amount) related to the traction control. In other words, the final control amount Qt suppresses excessive acceleration slip Sw of the slipping wheels WHs, while the start assist control is executed satisfactorily. Specifically, in step S140, the second control amount Qb is added to the first control amount Qa to determine the final control amount Qt (i.e., "Qt=Qa+Qb"). Note that for a wheel whose acceleration slip Sw is less than a predetermined slip sx (i.e., a grip wheel WHg), "Qb=0" is satisfied, and therefore the first control amount Qa is determined as the final control amount Qt.

[0042] In step S140, the larger of the first control amount Qa and the second control amount Qb may be determined as the final control amount Qt (i.e., "Qt = MAX (Qa, Qb)"). The first control amount Qa is decreased as time T passes. On the other hand, the second control amount Qb is increased as the acceleration slip Sw increases. In the slipping wheels WHs where the acceleration slip Sw becomes excessive, the second control amount Qb is dominant over the first control amount Qa, so the larger of the first control amount Qa and the second control amount Qb is adopted as the final control amount Qt. Regardless of the calculation method, the increase in the acceleration slip Sw is appropriately suppressed.

[0043] In step S150, the hydraulic unit HU is driven based on the final control amount Qt. Here, the final control amount Qt is a target value corresponding to the wheel pressure Pw (actual value). When the start assist control is executed, "Pm=0". Therefore, based on the larger final control amount Qt (also called "specific control amount Qto") of the left and right wheels, the regulated pressure Pp is increased by the pressure regulating valve UA, etc. Specifically, based on the specific control amount Qto, the current It (also called "target current") to be supplied to the pressure regulating valve UA is determined. Then, the drive signal Ua is determined so that the valve current Ia (actual value, detected value) approaches and coincides with the target current It (target value). As a result, the regulated pressure Pp is supplied as the wheel pressure Pw to the wheel WH corresponding to the specific control amount Qto.

[0044] On the other hand, in the wheel WH corresponding to the smaller final control amount Qt (also referred to as the "dependent control amount Qtj") of the left and right wheels, the wheel pressure Pw is reduced from the regulated pressure Pp by the inlet valve VI and the outlet valve VO. That is, the drive signal Vi of the inlet valve VI and the drive signal Vo of the outlet valve VO are determined based on the dependent control amount Qtj. As a result, the regulated pressure Pp is reduced in the wheel WH corresponding to the dependent control amount Qtj and is supplied as the wheel pressure Pw. As described above, in the braking control device SC, hydraulic pressure adjustment is performed in each wheel cylinder CW so that the wheel pressure Pw (actual value) approaches and matches the final control amount Qt (target value).

[0045] In the braking control device SC, when acceleration slip Sw occurs during execution of the start assist control, the final control amount Qt is determined to suppress the acceleration slip Sw. Then, the wheel pressure Pw is increased to reduce the acceleration slip Sw of the slipping wheel WHs. As a result, sufficient driving force is generated, and the hill-climbing performance is improved during the start assist control.

[0046] In detail, in the slipping wheel WHs, the acceleration slip Sw is suppressed by increasing the wheel pressure Pw. As a result, the driving force of the slipping wheel WHs is increased. In addition, when one of the left and right drive wheels connected via a differential device spins, power is not transmitted to the other drive wheel. By suppressing the acceleration slip Pw of the slipping wheel WHs, the power of the prime mover PG is transmitted to the gripping wheel WHg located on the opposite side of the differential device, and the driving force of the gripping wheel WHg is increased.

[0047] In normal traction control (i.e., traction control when start assist control is not being executed), the output of the prime mover PG is reduced to suppress acceleration slip Sw. However, in traction control when start assist control is being executed, the vehicle must move forward on an uphill road, so the output of the prime mover PG is not suppressed. That is, in traction control when start assist control is being executed, power corresponding to the operation amount Aa of the acceleration operating member AP is output from the prime mover PG. In other words, in traction control, when start assist control is not being executed, the power of the prime mover PG is reduced from the power based on the acceleration operation amount Aa, but when start assist control is being executed, the power is not reduced.

[0048] <Start assist control processing (especially grip wheels WHg)> Referring to the flowchart of FIG. 4, the processing of the grip wheel WHg in the start assist control will be described. In the start assist control, in the slip wheel WHs, "Sw ≧ sx" is satisfied and the traction control is executed. On the other hand, in the grip wheel WHg, "Sw < sx", and the traction control is not executed. Note that in the grip wheel WHg, since the acceleration slip Sw is small, the capacity for increasing the driving force is large.

[0049] In step S210, various signals are read. Specifically, the acceleration slip Sw at each wheel WH, the vehicle body speed Vx, etc. are read. In step S220, based on the acceleration slip Sw at each wheel WH, it is determined whether or not "a slip wheel WHs is generated". If all the wheels WH are grip wheels WHg and the generation of the slip wheel WHs is denied, step S220 is denied and the process returns to step S210. On the other hand, if at least one of the wheels WH is a slip wheel WHs, step S220 is affirmed and the process proceeds to step S230.

[0050] In step S230, based on the vehicle body speed Vx, it is determined whether or not "the vehicle is stopped". If the vehicle is stopped, step S230 is affirmed and the process proceeds to step S250. On the other hand, if the vehicle is not stopped (i.e., when the vehicle is moving forward or backward), step S230 is denied and the process proceeds to step S240.

[0051] In step S240, based on the vehicle body speed Vx, it is determined whether or not "the vehicle is moving forward". If the vehicle is moving forward, step S240 is affirmed and the process proceeds to step S260. On the other hand, if the vehicle is not moving forward (i.e., when the vehicle is moving backward), step S240 is denied and the process proceeds to step S270.

[0052] In step S250, the first control amount Qa is adjusted when the vehicle is stopped. In step S250, the first control amount Qa for the gripping wheels WHg is maintained (i.e., it is neither increased nor decreased). The fact that the vehicle is stopped despite the occurrence of slipping wheels WHs means that the driving force acting on the vehicle is insufficient. In this state, if the first control amount Qa for the gripping wheels WHg is gradually decreased, there is a possibility that the vehicle will roll back. For this reason, the first control amount Qa is maintained for the gripping wheels WHg to prevent the vehicle from rolling back.

[0053] In step S260, the first control amount Qa is adjusted when the vehicle is moving forward. In step S260, the first control amount Qa for the gripping wheels WHg is set to "0". When the vehicle is already moving forward, the driving force acting on the vehicle is sufficient, and the probability that the vehicle will move backward due to an uphill road is extremely low. Therefore, "Qa = 0" is determined for the gripping wheels WHg. This improves the acceleration of the vehicle.

[0054] In step S270, the first control amount Qa is adjusted when the vehicle is moving backward. In step S270, the first control amount Qa for the gripping wheels WHg is increased. The fact that the vehicle is moving backward despite the occurrence of slipping wheels WHs means that the slipping wheels WHs are spinning or the like. For this reason, the first control amount Qa for the gripping wheels WHg is increased so that the vehicle does not move backward.

[0055] In step S280, for the grip wheel WHg for which traction control is not being executed, the final control amount Qt is determined to be equal to the first control amount Qa. That is, for the grip wheel WHg, "Qb=0" is calculated, so "Qt=Qa". Then, in step S290, the hydraulic unit HU (actuator) is driven. Note that the process of step S290 is the same as the process of step S150, and the hydraulic unit HU is controlled in the grip wheel WHg so that the wheel pressure Pw is equal to the final control amount Qt.

[0056] <Start assist control operation> The operation of the start assist control will be described with reference to the time series diagram of Figure 5. The start assist control is a control that suppresses the vehicle from rolling back when starting on an uphill road (uphill). Therefore, the start assist control is executed on the condition that the vehicle is stopped on an uphill road. Note that the wheel pressure Pw (actual value) is controlled to match the final control amount Qt (target value), so they overlap on the diagram.

[0057] At time t0, the driver is operating the brake operating member BP, and a wheel pressure Pw of value qo is generated. At time t1, the driver's operation is switched from the brake operating member BP to the acceleration operating member AP. As a result, at time t1, the execution of start assist control is started. Specifically, even if the operation of the brake operating member BP is ended, the final control amount Qt (as a result, the wheel pressure Pw) is maintained at the initial value qo for a predetermined time ta according to the calculation map Zqa. Since the operation of the acceleration operating member AP is started at time t1, the acceleration operating amount Aa is gradually increased. Accordingly, the output of the prime mover PG is increased.

[0058] At time t2, the time T from the start of execution of the launch assistance control reaches a predetermined time ta. Accordingly, the final control amount Qt (and thus the wheel pressure Pw) decreases from the initial value qo at a predetermined gradient gk. Due to the decrease in the wheel pressure Pw and the increase in the drive torque by the prime mover PG, the acceleration slip Sw increases at the wheels WH.

[0059] At time t3, a wheel (i.e., slipping wheel WHs) is generated whose acceleration slip Sw is equal to or greater than a predetermined slip sx. The execution of traction control is started for the slipping wheel WHs. In detail, the final control amount Qt is determined by adding the second control amount Qb to the first control amount Qa. Alternatively, the larger of the first control amount Qa and the second control amount Qb is determined as the final control amount Qt. In other words, the final control amount Qt is determined so as to suppress the acceleration slip Sw. The increase in the final control amount Qt increases the wheel pressure Pw in the slipping wheel WHs. This suppresses the slipping wheel WHs from spinning (i.e., wheel spin) and increases the driving force of the slipping wheel WHs. In addition, the driving force of the gripping wheel WHg connected to the slipping wheel WHs is increased via the differential device. In other words, the differential device allows a differential between the left and right wheels, but the increase in the final control amount Qt limits the differential. Therefore, in the braking control device SC, the driving force of the gripping wheels WHg is increased in accordance with the driving force of the slipping wheels WHs.

[0060] At time t3, at least one of the wheels WH has become a slipping wheel WHs, so the determination in step S220 is affirmative, and in the start assist control, the first control amount Qa (resulting in the final control amount Qt) of the gripping wheels WHg is adjusted. For example, as shown in line (A), if the vehicle is stopped at time t3 (the time when the occurrence of a slipping wheel WHs is determined), the final control amount Qt (resulting in the wheel pressure Pw) of the gripping wheels WHg is maintained. In detail, after the final control amount Qt is maintained, it is gradually reduced. This prevents the vehicle from rolling backward, and enables a smooth start. That is, in the start assist control, the hill-climbing performance is improved.

[0061] At time t3, if the vehicle is moving forward, the final control amount Qt (resulting in wheel pressure Pw) at the gripping wheels WHg is immediately set to "0" as shown by line (B). This increases the driving force of the wheels WH, improving the acceleration performance of the vehicle. That is, the climbing performance is improved in the start assist control. At time t3, if the vehicle is moving backward, the final control amount Qt (resulting in wheel pressure Pw) at the gripping wheels WHg is increased as shown by line (C). In detail, the final control amount Qt is increased and then maintained, and then gradually decreased. This prevents the vehicle from moving backward, and achieves a smooth start. That is, the climbing performance is improved in the start assist control.

[0062] The first control amount Qa for the gripping wheels WHg is adjusted based on the state of the vehicle at the time when the slipping wheels WHs occur (i.e., the three cases of stopping, moving forward, and moving backward). The adjustment does not need to be performed in all three cases. That is, the adjustment of the first control amount Qa (resulting in the final control amount Qt) only needs to be performed in at least one of the three cases. For example, if the vehicle is stopped at time t3, the final control amount Qt is maintained, but in other cases (when moving forward or moving backward), the final control amount Qt is gradually decreased at a predetermined gradient gk. Also, if the vehicle is moving forward (stopped or moving backward) at time t3, the final control amount Qt is decreased to "0", but in other cases, the final control amount Qt is gradually decreased at a predetermined gradient gk.

[0063] <Another embodiment of the brake control device SC> Other embodiments of the brake control device SC will now be described. The other embodiments also provide the same effect as above (improvement of hill climbing performance in start assist control).

[0064] In the above embodiment, a disc-type braking device SX is used. Alternatively, a drum-type braking device SX is used. In the drum-type braking device SX, the rotating member KT fixed to the wheel WH is a brake drum, and the friction member is a brake lining attached to a brake shoe.

[0065] In the above embodiment, the control variables Qa, Qb, and Qt (target values) are calculated in terms of the wheel pressure Pw (actual value). In the braking device SX, the braking torque Tb is generated by the wheel pressure Pw, so the control variables Qa, Qb, and Qt (target values) may be calculated in terms of the braking torque Tb as a physical quantity. In either case, the braking control device SC executes control so that the braking torque Tb (actual value) approaches and coincides with the final control variable Qt (target value).

[0066] In the above embodiment, the brake torque Tb is controlled by adjusting the discharge pressure Pp of the fluid pump HP by the pressure regulating valve UA. Alternatively, in the brake control device SC, the brake torque Tb may be controlled by increasing or decreasing the volume of a cylinder into which a piston is inserted, using a piston directly driven by the electric motor MT. Such a brake control device SC is also called an "electric cylinder type" (see, for example, WO2012 / 046703). In the electric cylinder type brake control device SC, the rotational power (torque) of the electric motor MT is converted into linear power (thrust) via a rotation / linear conversion mechanism, thereby moving the piston. This movement of the piston causes brake fluid BF to be pumped from the cylinder, and the wheel pressure Pw (i.e., the brake torque Tb) is adjusted.

[0067] Furthermore, in the brake control device SC, the friction member may be directly pressurized by the electric motor MT without the intervention of the brake fluid BF, thereby generating the brake torque Tb. Such a brake control device SC is also referred to as an "electro-mechanical type" (see, for example, JP 2017-056752 A). In the electro-mechanical type brake control device SC, the rotational power of the electric motor MT is converted into linear power by a rotational-linear conversion mechanism, and the friction member is moved. The friction member is pressed (pressurized) against the rotating member, thereby generating the brake torque Tb.

[0068] In the above embodiment, the brake control device SC is applied to a four-wheel drive vehicle. Alternatively, the brake control device SC may be applied to a two-wheel drive vehicle. In a two-wheel drive vehicle, slipping wheels WHs occur at the driving wheels connected to the prime mover PG. On the other hand, the driven wheels not connected to the prime mover PG are always gripping wheels WHg.

[0069] <Summary of the embodiment> An embodiment of the vehicle braking control device SC will be summarized. The braking control device SC is composed of a fluid unit HU (actuator) and a controller ECU. The fluid unit HU can individually adjust the braking torque Tb for the multiple wheels WH. The controller ECU executes a start assist control, which holds the braking torque Tb and then gradually reduces the braking torque Tb via the fluid unit HU so that the vehicle does not roll back on an uphill road.

[0070] In the braking control device SC, the controller ECU can execute traction control to reduce the acceleration slip Sw by increasing the braking torque Tb at the slipping wheels WHs where the acceleration slip Sw of the wheels WH becomes larger than a predetermined slip sx. The controller ECU determines a final control amount Qt based on a first control amount Qa of the braking torque Tb related to the start assist control and a second control amount Qb of the braking torque Tb related to the traction control, and controls the braking torque Tb based on the final control amount Qt. For example, the controller ECU determines the final control amount Qt by adding the second control amount Qb to the first control amount Qa. Alternatively, the controller ECU determines the larger of the first control amount Qa and the second control amount Qb as the final control amount Qt.

[0071] In the brake control device SC, even when start assist control is being executed, if the acceleration slip Sw increases, the braking torque Tb is increased. This increases the driving force of the slipping wheels WHs where wheel spin (excessive acceleration slip Sw) is occurring. In addition to the slipping wheels WHs, the driving force of the gripping wheels WHg (wheels with a high ability to generate driving force) connected to the slipping wheels WHs via the differential is increased. Since the increase in braking torque Tb limits the differential motion by the differential, the driving force is increased not only for the slipping wheels WHs but also for the gripping wheels WHg arranged on the opposite side of the differential. As a result, the climbing performance in the start assist control is improved.

[0072] In addition, while the start assist control is being executed, the output of the prime mover PG is prohibited from being reduced by the traction control. That is, when the start assist control is not being executed, the output (power) of the prime mover PG is reduced by the traction control, but while the start assist control is being executed, this is not performed. Since a driving force according to the operation amount Aa of the acceleration operating member AP is generated, the climbing performance as intended by the driver can be achieved.

[0073] If the vehicle is stopped when slipping wheels WHs occur, the controller ECU maintains the braking torque Tb at the gripping wheels WHg that are not slipping wheels WHs. If slipping wheels WHs exist, a situation may arise in which the driving force acting on the vehicle is insufficient. In this situation, if the braking torque Tb is reduced, there is a concern that the vehicle may roll back, but by maintaining the braking torque Tb at the gripping wheels WHg, the vehicle is prevented from rolling back. In other words, the hill-climbing performance is further improved in the start assist control.

[0074] If the vehicle is moving forward when the slipping wheel WHs occurs, the controller ECU sets the braking torque Tb to zero for the gripping wheels WHg that are not slipping wheels WHs. When the vehicle is moving forward, the driving force acting on the vehicle is sufficient. By reducing the braking torque Tb for the gripping wheels WHg to "0", the acceleration of the vehicle is promoted. In other words, the climbing performance is further improved in the start assist control.

[0075] When the vehicle is moving backward at the time when the slipping wheel WHs occurs, the controller ECU increases the braking torque Tb at the gripping wheel WHg that is not a slipping wheel WHs. When the vehicle is moving backward, the driving force acting on the vehicle is insufficient and the braking force is also insufficient. By increasing the braking torque Tb at the gripping wheel WHg, the vehicle is maintained in a stopped state. In other words, the climbing performance is further improved in the start assist control. [Explanation of symbols]

[0076] SC...Brake control device, HU...Fluid unit (actuator), ECU...Controller (brake controller), VW...Wheel speed sensor, GX...Longitudinal acceleration sensor, AP...Acceleration operation member (accelerator pedal), AA...Acceleration operation amount sensor, BP...Brake operation member (brake pedal), BA...Brake operation amount sensor, Aa...Acceleration operation amount, Ba...Brake operation amount, Gx...Longitudinal acceleration, θ...Uphill gradient (gradient of uphill road), Vw...Wheel speed, Vx...Vehicle speed (vehicle running speed), Vk...Reference speed (drive wheels), Sw...Acceleration slip (drive wheels), Tb...Braking torque, Pw...Wheel pressure (equivalent to Tb), Qa...First control amount (control amount of launch assist control), Qb...Second control amount (control amount of traction control), Qt...Final control amount (adjustment result of Qa and Qb), sx...Predetermined slip (threshold value), WH...Wheel, WHs...Slip wheel, WHg...Grip wheel.

Claims

1. an actuator capable of individually adjusting braking torque for a plurality of wheels; a controller that executes a start assist control by holding the braking torque via the actuator and then gradually reducing the braking torque so that the vehicle does not roll back on an uphill road; In a vehicle braking control device comprising: The controller: A traction control can be executed to reduce the acceleration slip by increasing the braking torque of a slipping wheel when the acceleration slip of the wheel becomes larger than a predetermined slip, A vehicle braking control device that determines a final control amount based on a first control amount of the braking torque related to the start assist control and a second control amount of the braking torque related to the traction control, and controls the braking torque based on the final control amount.

2. 2. The vehicle brake control device according to claim 1, A braking control device for a vehicle, wherein the controller determines the final control amount by adding the second control amount to the first control amount.

3. 2. The vehicle brake control device according to claim 1, A braking control device for a vehicle, wherein the controller determines a larger one of the first control amount and the second control amount as the final control amount.

4. The vehicle brake control device according to any one of claims 1 to 3, A vehicle braking control device, wherein the controller maintains the braking torque in a gripping wheel that is not a slipping wheel when the vehicle is stopped at the time when the slipping wheel occurs.

5. The vehicle brake control device according to any one of claims 1 to 3, A vehicle braking control device, wherein the controller sets the braking torque to zero in a gripping wheel that is not a slipping wheel when the vehicle is moving forward at the time when the slipping wheel occurs.

6. The vehicle brake control device according to any one of claims 1 to 3, A vehicle braking control device, wherein the controller increases the braking torque in a gripping wheel that is not a slipping wheel when the vehicle is moving backward at the time when the slipping wheel occurs.

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