JP2017171107A - Brake control device and brake control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brake control device and a brake control method which can suppress an unstable behavior at the initial stage of μ change.SOLUTION: The brake control device comprises: a braking force control unit HU which makes a braking force generation portion W/C provided to each wheel of a vehicle to generate braking force; a μ change determination portion which determines a μ change in which road surface μ of one wheel of left and right wheels at a front side in an advancing direction of the vehicle changes from high μ to low μ, with respect to a split μ road surface having road surfaces μ different from each other between the left and right wheels; and a braking force control portion that controls the braking force control unit so that braking force of wheels at the rear side in the advancing direction of the vehicle is restricted, when the μ change is determined in a state where braking force is generated in respective wheels FL-RR.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a brake control device and a brake control method.

  When the vehicle enters the split μ road surface, one road surface μ of the left and right wheels changes from high μ to low μ (μ change). In a conventional brake control device, when a μ change occurs during sudden braking of the vehicle, the wheel cylinder hydraulic pressure of the wheels on the high μ road is lowered so that the difference in braking force between the left and right wheels is within an allowable range. An example of a technique related to the above description is disclosed in Patent Document 1.

JP 2013-071658

In the above-described prior art, there is a need to suppress the unstable behavior at the initial stage of the μ change in which the left and right wheels are changed only on the front wheel side and the rear wheel side is not changed.
An object of the present invention is to provide a brake control device and a brake control method capable of suppressing unstable behavior at the beginning of μ change.

  The brake control device according to the embodiment of the present invention limits the braking force of the rear wheel in the traveling direction of the vehicle when it is determined that the μ change occurs while the braking force is generated in each wheel.

  Therefore, the unstable behavior at the beginning of μ change can be suppressed.

FIG. 3 is a hydraulic circuit diagram of the hydraulic unit HU according to the first embodiment. It is a block diagram of the brake control apparatus of Embodiment 1. FIG. 3 is a control block diagram of a braking force limiting process according to the first embodiment. It is a flowchart which shows the flow of the ABS control processing of Embodiment 1. 3 is a flowchart illustrating a flow of μ change determination processing according to the first embodiment. It is the setting map of the determination time according to the estimated vehicle body speed. 3 is a flowchart illustrating a flow of a braking force limiting process according to the first embodiment. It is a setting map of the 1st gain according to behavior change. It is a setting map of the 2nd gain according to presumed vehicle speed. It is explanatory drawing of μ change in a split μ road surface. It is a time chart which shows the operation | movement at the time of split micro road surface approach in the conventional brake control apparatus. 6 is a time chart showing an operation when entering a split μ road surface when the behavior change at the initial stage of the μ change is small in the first embodiment. 6 is a time chart showing an operation when entering a split μ road surface when the behavior change at the initial stage of μ change is large in the first embodiment. 5 is a time chart showing an operation when entering a split μ road surface when a μ change is predicted in the first embodiment.

Embodiment 1
FIG. 1 is a hydraulic circuit diagram of the hydraulic unit HU of the first embodiment, and FIG. 2 is a configuration diagram of the brake control device of the first embodiment.
The brake control device according to the first embodiment is applied to, for example, an engine vehicle. The brake control device according to the first embodiment includes a brake pedal BP, a master cylinder M / C, a wheel cylinder (braking force generation unit) W / C, a hydraulic unit (braking force control unit) HU, and an electronic control unit (control unit) ECU. Have
The brake pedal BP is connected to the master cylinder M / C via the input rod IR. The brake booster BB uses the intake negative pressure generated by the engine to boost the brake operating force. The master cylinder M / C replenishes brake fluid from the reservoir tank RSV and generates a master cylinder fluid pressure according to the operation of the brake pedal BP. The hydraulic unit HU connects the master cylinder M / C and each wheel cylinder W / C. Each wheel cylinder W / C is provided on each wheel (left front wheel FL, right front wheel FR, left rear wheel RL, right rear wheel RR) of the vehicle, and generates a braking force corresponding to the brake fluid. The electronic control unit ECU controls the hydraulic unit HU based on input information such as the operation amount of the brake pedal BP so that the wheel cylinder hydraulic pressure of each wheel cylinder W / C becomes a desired hydraulic pressure.

[Hydraulic unit]
The hydraulic unit HU has two systems (P system and S system) of brake piping. The brake piping is, for example, an X piping format. Hereinafter, in order to distinguish between a part corresponding to the P system and a part corresponding to the S system, the suffixes P and S are added to the end of each code. If the part corresponding to the P system and the part corresponding to the S system are not distinguished, the subscripts P and S are omitted. Also, when distinguishing the part corresponding to the left front wheel FL, the part corresponding to the right front wheel FR, the part corresponding to the left rear wheel RL, and the part corresponding to the right rear wheel RR, the subscript FL at the end of each symbol , FR, RL, RR are attached. If the part corresponding to the left front wheel FL, the part corresponding to the right front wheel FR, the part corresponding to the left rear wheel RL, and the part corresponding to the right rear wheel RR are not distinguished, the subscripts FL, FR, RL, and RR are omitted. . The P system is connected to the wheel cylinder W / C (FL) of the left front wheel FL and the wheel cylinder W / C (RR) of the right rear wheel RR. The S system is connected to the wheel cylinder W / C (RL) of the left rear wheel RL and the wheel cylinder W / C (FR) of the right front wheel FR. The P system and the S system have oil pumps (pumps) PP and PS. The oil pumps PP and PS are driven by one motor M. The motor M is a rotary electric motor. Oil pumps PP and PS are plunger pumps.

  The hydraulic unit HU has a housing HSG. Inside the housing HSG, a plurality of liquid paths (liquid path 1 and the like) and an oil pump P are provided. A motor M is fixed to the housing HSG. The liquid path 1 connects the master cylinder M / C and each wheel cylinder W / C. The liquid path 1S branches to the liquid paths 1RL and 1FR. The liquid path 1RL is connected to the wheel cylinder W / C (RL), and the liquid path 1FR is connected to the wheel cylinder W / C (FR). The liquid path 1P branches to the liquid paths 1FL and 1RR. The liquid path 1FL is connected to the wheel cylinder W / C (FL), and the liquid path 1RR is connected to the wheel cylinder W / C (RR). On the liquid path 1, a gate-out valve (hereinafter referred to as G / V-OUT) 2, which is a normally open solenoid valve, is provided. A master cylinder fluid pressure sensor 3 for detecting the master cylinder fluid pressure is provided at a position closer to the master cylinder than G / V-OUT2P of the fluid path 1P of the P system. On the liquid path 1, a liquid path 4 is provided in parallel with G / V-OUT2. A check valve 5 is provided on the liquid path 4. The check valve 5 allows the flow of brake fluid from the master cylinder M / C to the wheel cylinder W / C and prohibits the flow in the opposite direction. On the liquid passages 1FL, 1FR, 1RR, 1RL, solenoid-in valves (hereinafter referred to as Sol / V-IN) 6 which are normally open solenoid valves corresponding to the respective wheel cylinders W / C are provided. On the liquid path 1, a liquid path 7 is provided in parallel with the Sol / V-IN 6. A check valve 8 is provided on the liquid path 7. The check valve 8 allows the brake fluid to flow in the direction from the wheel cylinder W / C toward the master cylinder M / C, and prohibits the flow in the opposite direction.

The liquid path 9 connects the discharge side of the oil pump P and a position downstream of G / V-OUT2 of the liquid path 1. A discharge valve 10 is provided on the liquid path 9. The discharge valve 10 allows the flow of brake fluid in the direction from the oil pump P toward the fluid path 9, and prohibits the flow in the opposite direction. The liquid path 11 and the liquid path 12 connect the position on the master cylinder side with respect to G / V-OUT2 of the liquid path 1 and the suction side of the oil pump P. A suction valve 17 is provided in the liquid path 12. A pressure regulating reservoir 13 is provided between the liquid path 11 and the liquid path 12. The liquid path 14 is connected to the pressure regulating reservoir 13. The liquid path 14S branches into the liquid paths 14RL and 14FR. The liquid path 14RL is connected to a position between the Sol / V-IN 6RL of the liquid path 1RL and the wheel cylinder W / C (RL). The liquid path 14FR is connected to a position between the Sol / V-IN6FR of the liquid path 1FR and the wheel cylinder W / C (FR). The liquid path 14P branches to the liquid paths 14FL and 14RR. The liquid path 14FL is connected to a position between the Sol / V-IN6FL of the liquid path 1FL and the wheel cylinder W / C (FL). The liquid path 14RR is connected to a position between the Sol / V-IN 6RR of the liquid path 1RR and the wheel cylinder W / C (RR). On the liquid path 14, a solenoid-out valve (hereinafter referred to as Sol / V-OUT) 15 which is a normally closed solenoid valve is provided.
The pressure regulating reservoir 13 includes a reservoir piston 13a, a reservoir spring 13b, and a check valve 16. The reservoir piston 13a is provided so as to be able to stroke up and down in the reservoir. The reservoir piston 13a descends as the amount of brake fluid flowing into the reservoir increases and rises as the amount of brake fluid decreases. The reservoir spring 13b biases the reservoir piston 13a in the upward direction. The check valve 16 includes a ball valve 16a and a valve seat 16b. The ball valve 16a is provided integrally with the reservoir piston 13a and moves up and down according to the stroke of the reservoir piston 13a. The ball valve 16a is urged in the downward direction by a valve spring (not shown). The elastic force of the valve spring is set to be weaker than the elastic force of the reservoir spring 13b. The valve seat 16b contacts the ball valve 16a when the ball valve 16a is lowered.

[Electronic control unit ECU]
The electronic control unit ECU is connected to a master cylinder hydraulic pressure sensor 3, a wheel speed sensor 21, a negative pressure sensor 22, a CAN communication line 23, a battery 24, and a vehicle behavior stability control switch 25. The electronic control unit ECU has a yaw rate sensor 26 and a lateral acceleration sensor 27. The wheel speed sensor 21 is provided in each wheel FL to RR, and detects the wheel speed of the corresponding wheel. The negative pressure sensor 22 detects the negative pressure of the brake booster BB. The CAN communication line 23 is connected to an external ECU (external world recognition device) 28. The external ECU 28 recognizes the road surface condition in the traveling direction of the vehicle using an in-vehicle camera or the like. The battery 24 supplies power to the electronic control unit ECU while the ignition switch 29 is on. The vehicle behavior stability control switch 25 is a switch for the driver to switch operation / non-operation of vehicle dynamics control (hereinafter referred to as VDC control). The yaw rate sensor 26 detects the yaw rate of the vehicle. The lateral acceleration sensor 27 detects the lateral acceleration of the vehicle.
The electronic control unit ECU is based on input information from each sensor 3, 21, 22, 26, 27 and CAN communication line 23, G / V-OUT2 solenoid 30, Sol / V-IN6 solenoid 31, Sol / V -The solenoid 32 and the motor M of OUT15 are driven. Thereby, each brake control such as an anti-skid brake system (hereinafter referred to as ABS control) and VDC control can be realized. ABS control suppresses continuation of locking by repeatedly reducing, maintaining, and increasing the wheel cylinder hydraulic pressure when the wheel is locked during the driver's braking operation. In VDC control, when the vehicle's steering characteristics become oversteer or understeer during turning, the wheel cylinder hydraulic pressure of the specified wheel is increased by the brake fluid pressurized by the oil pump P, and the yaw moment is reduced in a direction that weakens oversteer and understeer. generate.

In the first embodiment, a braking force limiting process for limiting the braking force of a predetermined wheel is performed during ABS control with the aim of suppressing unstable behavior during traveling on a split μ road surface. The split μ road surface is a road surface in which the road surface μ differs greatly between the left and right wheels. A road surface having a uniform road surface and a high road surface μ with respect to the split μ road surface is referred to as a uniform high μ road surface.
FIG. 3 is a control block diagram of the braking force limiting process according to the first embodiment. The electronic control unit ECU includes a large slip front wheel acceleration calculation unit (large slip front wheel acceleration detection unit) 40, a front wheel estimated W / C hydraulic pressure calculation unit 41, a front wheel left / right W / C hydraulic pressure difference calculation unit (front wheel left / right A braking force difference calculation unit) 42, a yaw rate change amount calculation unit (turning state change amount detection unit) 43, a μ change determination unit 44, and a braking force control unit 45 are provided as programs. Hereinafter, the braking force limiting process when the vehicle moves forward will be described. The braking force limiting process when the vehicle is moving backward is obtained by replacing the front and rear wheels in the following description.
The slip large-side front wheel acceleration calculation unit 40 differentiates the wheel speed of a wheel having a large slip amount (= the wheel on the low μ road (the wheel on the low μ side)) of the front wheels FL and FR, and the slip large-side front wheel. Calculate acceleration. The slip amount is a value obtained by subtracting the vehicle body speed from the estimated vehicle body speed. The estimated vehicle body speed is, for example, the highest wheel speed of each wheel FL to RR.
The front wheel estimated W / C hydraulic pressure calculation unit 41 calculates the estimated wheel cylinder hydraulic pressure of the front wheels FL and FR, respectively. The estimated wheel cylinder hydraulic pressure is obtained from the master cylinder hydraulic pressure and the operating states of Sol / V-IN6 and Sol / V-OUT15.
The front wheel left / right W / C hydraulic pressure difference calculation unit 42 calculates the absolute value of the difference between the estimated wheel cylinder hydraulic pressure of the left front wheel FL and the estimated wheel cylinder hydraulic pressure of the right front wheel FR as the front wheel left / right wheel cylinder hydraulic pressure difference.
The yaw rate change amount calculation unit 43 calculates the yaw rate change amount by differentiating the yaw rate.

The μ change determination unit 44 reads the slip large front wheel speed, the slip large front wheel acceleration, the front wheel right / left wheel cylinder hydraulic pressure difference, the vehicle body speed, and the yaw rate change amount. Based on the read information, the μ change determination unit 44 determines whether or not a μ change has occurred on one of the left and right front wheels FL and FR as it enters the split μ road surface, and whether or not a μ change will occur in the near future. Determine. In other words, the μ change determination unit 44 has a μ change detection and prediction function. μ change means that the road surface μ of one of the left and right wheels is switched from high μ to low μ. In the near future, it will be several seconds, for example.
When the driver depresses the brake pedal BP and the μ change determination unit 44 determines that one of the left and right front wheels FL, FR is a μ change, the braking force control unit 45 includes the rear wheels RL, RR. A braking force restriction control is performed to control the hydraulic unit HU so as to preferentially limit the braking force of the wheel on the high μ road (the wheel on the high μ side). In principle, the braking force control unit 45 continues the braking force limiting process for a predetermined time. When the left and right rear wheels RL and RR are locked during the braking force limiting process, the braking force control unit 45 determines the wheel cylinder hydraulic pressure of the wheel by the wheel speed feedback control as in general ABS control. Control according to μ.
The braking force control unit 45 performs an ABS split braking process after the braking force limiting process. The ABS split braking process is a well-known control that limits the wheel cylinder hydraulic pressure difference to a predetermined value or less while suppressing wheel lock by wheel speed feedback control. Note that the braking force control unit 45 performs the ABS normal process when it is not determined to be the μ change. The normal ABS processing is a general ABS control.

[ABS control processing]
FIG. 4 is a flowchart illustrating the flow of the ABS control process according to the first embodiment.
In step S1, the μ change determination unit 44 performs μ change determination processing. Step S1 is a μ change determination step. Details of the μ change determination process will be described later.
In step S2, the braking force control unit 45 determines whether or not there is a μ change of one of the left and right front wheels FL and FR. If YES, the process proceeds to step S3. If NO, the process proceeds to step S4.
In step S3, the braking force control unit 45 performs a braking force limiting process. Step S3 is a rear wheel braking force limiting step. Details of the braking force limiting process will be described later.
In step S4, the braking force control unit 45 performs ABS normal processing.
In step S5, the braking force control unit 45 performs an ABS split braking process. The ABS split braking process continues until the traveling road is switched from the split μ road surface to the uniform high μ road surface.

[Μ change judgment processing]
FIG. 5 is a flowchart illustrating the flow of the μ change determination process according to the first embodiment.
In step S11, it is determined whether one μ change of the left and right front wheels FL and FR is predicted in the near future from the road surface condition in the traveling direction of the vehicle. If YES, the process proceeds to step S17. If NO, the process proceeds to step S12. For example, when the presence of a split μ road surface can be confirmed in front of the vehicle traveling path from the road surface condition, it can be predicted that there will be a μ change in the near future.
In step S12, it is determined whether the slip large-side front wheel acceleration is equal to or less than a predetermined value. If YES, the process proceeds to step S13. If NO, the process proceeds to step S18. The predetermined value is an acceleration at which it can be determined that the slip is caused by a sudden decrease in the road surface μ.
In step S13, it is determined whether or not the slip large-side front wheel speed is equal to or less than a predetermined value. If YES, the process proceeds to step S14. If NO, the process proceeds to step S18. The predetermined value is a speed at which the wheel cylinder hydraulic pressure is reduced by the AS normal process.
In step S14, the front wheel left and right wheel cylinder hydraulic pressure differential is integrated to calculate a front wheel left and right wheel cylinder hydraulic pressure differential integrated value.
In step S15, it is determined whether or not the front wheel left and right wheel cylinder hydraulic pressure difference integral value is greater than or equal to a predetermined value. If YES, the process proceeds to step S16. If NO, the process proceeds to step S18. The predetermined value is a value by which it can be determined that the split μ road continues, and this value corresponds to the μ change determination time. Here, the determination time is shortened as the vehicle body speed increases as shown in FIG. That is, the predetermined value is set to a smaller value as the vehicle body speed is higher.
In step S16, it is determined whether the yaw rate change amount is a predetermined value or more. If YES, the process proceeds to step S17. If NO, the process proceeds to step S18. The predetermined value is the minimum value of the yaw rate change amount predicted that the vehicle behavior becomes unstable.
In step S17, it is determined that there is a μ change. If the previous step is step S11, the μ change is predicted, and if the previous step is step S16, the μ change is detected.
In step S18, it is determined that there is no μ change.

[Braking force limit processing]
FIG. 7 is a flowchart showing the flow of the braking force limiting process according to the first embodiment.
In step S31, it is determined whether a μ change is detected. If YES, the process proceeds to step S32. If NO (when a μ change is predicted), the process proceeds to S34.
In step S32, it is determined whether the behavior change is large. If YES, the process proceeds to step S33, and if NO, the process proceeds to step S34. The behavior change is, for example, the yaw rate change amount at the time of detecting the μ change, and when the yaw rate change amount is equal to or larger than a preset yaw rate change amount threshold, it is determined that the behavior change is large. The predetermined value is a yaw rate change amount that the vehicle behavior is expected to be unstable only by limiting the braking force of the rear wheels on the high μ side, and is a value larger than the predetermined value of S16. Step S32 is a behavior change determination step.
In step S33, the braking force of the front and rear wheels on the high μ side is simultaneously limited. The braking force limit amount of the front wheels FL and FR and the rear wheels RL and RR is variable in accordance with the behavior change (yaw rate change amount) and the vehicle body speed. The braking force limit amount is obtained by multiplying a predetermined reference value by the first gain corresponding to the behavior change and the second gain corresponding to the vehicle body speed. FIG. 8 is a setting map of the first gain according to the behavior change. The first gain is set to a larger value as the behavior change (yaw rate change amount) is larger. An upper limit and a lower limit are provided for the first gain. FIG. 9 is a second gain setting map corresponding to the vehicle body speed. The second gain is set to a larger value as the vehicle body speed is higher. A lower limit is provided for the second gain. The process of step S33 continues for a certain time.
In step S34, the braking force of the rear wheel on the high μ side is limited. The braking force limit amount is set in accordance with the braking force limit amount setting method in S33. When the immediately preceding step is S31, the reference value of the braking force limit amount is made smaller than the reference value of S33, and the first gain is set to the minimum value. The process of step S34 continues for a certain time.
In step S35, it is determined whether the unstable behavior continues. If YES, the process proceeds to step S36, and if NO, this control is terminated. For example, if the behavior change (yaw rate change amount) is equal to or greater than the predetermined value of S32, it is determined that the unstable behavior is continuing.
In step S36, the braking force of the front wheel on the high μ side is limited. The braking force limit amount is set in accordance with the braking force limit amount setting method in S33. Step S36 is a front wheel braking force limiting step.

[Unstable behavior when running on a split μ road]
FIG. 10 is an explanatory diagram of μ change on the split μ road surface. The split μ road surface is a high μ road surface on the right side in the traveling direction of the vehicle and a low μ road surface on the left side. At the vehicle position A, only the left front wheel is on the low μ road, and the other wheels (right front wheel, left rear wheel, right rear wheel) are on the high μ road. At vehicle position B, the left front wheel and the left rear wheel are on a low μ road, and the right front wheel and the right rear wheel are on a high μ road.
When a vehicle that has started sudden braking on a uniform high μ road surface enters the split μ road surface, first, a μ change occurs on the left front wheel. The road surface μ of the left front wheel changes from high μ to low μ due to μ change. Since the wheel cylinder hydraulic pressure of the left front wheel is near the lock hydraulic pressure, the left front wheel on the low μ road is locked. ABS control reduces the wheel cylinder hydraulic pressure on the left front wheel. At this time, since the wheel cylinder hydraulic pressure of the right front wheel is near the lock hydraulic pressure, the wheel cylinder hydraulic pressure difference between the left and right front wheels becomes large. As a result, a braking force difference is generated between the left and right front wheels, and a yaw moment is generated clockwise around the center of gravity of the vehicle (clockwise in FIG. 10).
Subsequently, a μ change occurs in the left rear wheel. With the μ change, the road surface μ of the left rear wheel changes from high μ to low μ. Since the wheel cylinder hydraulic pressure of the left rear wheel is close to the lock hydraulic pressure, the left rear wheel on the low μ road is locked. ABS control reduces the hydraulic pressure of the wheel cylinder on the left rear wheel. At this time, since the wheel cylinder hydraulic pressure of the right rear wheel is near the lock hydraulic pressure, the wheel cylinder hydraulic pressure difference between the left and right rear wheels becomes large. As a result, a braking force difference is generated between the left and right rear wheels, and a yaw moment in the clockwise direction at the center of gravity of the vehicle is promoted.

In response to the above problem, in the conventional brake control device, when it is determined that one of the left and right wheels has changed by μ during braking of the vehicle, the wheel on the high μ side is adjusted so that the difference in braking force between the left and right wheels is within an allowable range. The wheel cylinder hydraulic pressure is reduced.
FIG. 11 is a time chart showing the operation at the time of entering the split μ road surface in the conventional brake control device. As a premise, the wheel cylinder hydraulic pressure of each wheel is close to the lock hydraulic pressure because the driver depresses the brake pedal strongly. The split μ road surface is the same as in FIG.
At time t1, the wheel speed of the left front wheel decreases with the μ change of the left front wheel. When the left front wheel locks slightly after time t1, the wheel cylinder hydraulic pressure of the left front wheel decreases due to the intervention of ABS control.
At time t2, the wheel cylinder hydraulic pressure of the right front wheel is reduced so that the wheel cylinder hydraulic pressure difference between the left and right front wheels becomes an allowable differential pressure corresponding to the road surface μ by the determination of the μ change of the left front wheel.
At time t3, the wheel speed of the left rear wheel decreases with the μ change of the left rear wheel. When the left rear wheel locks, the wheel cylinder hydraulic pressure of the left rear wheel decreases due to the intervention of ABS control. The wheel cylinder hydraulic pressure of the left rear wheel is reduced so that the wheel cylinder hydraulic pressure difference between the left and right rear wheels becomes an allowable differential pressure at the same time or slightly after the decrease of the wheel cylinder hydraulic pressure of the left rear wheel.

Here, there is a lag in timing between the left front wheel μ change and the left rear wheel μ change. Then, at the beginning of the μ change (section t1 to t3) in which the left front wheel has changed μ and the left rear wheel has not changed, the rear wheel is on a high μ road. For this reason, the wheel cylinder hydraulic pressure of the rear wheel is in the vicinity of the lock hydraulic pressure. In other words, at the beginning of the μ change, most of the force that can be generated by the rear tire is used for the tire longitudinal force (braking force). As a result, when the vehicle turns due to the difference in braking force between the left and right front wheels, the tire lateral force of the rear wheels cannot be sufficiently secured. If the tire lateral force of the rear wheels is insufficient during turning, the vehicle steer characteristic becomes oversteer, and the vehicle behavior becomes unstable.
Therefore, in order to suppress the unstable behavior at the beginning of the μ change, the yaw moment generated at the beginning of the μ change must be reduced. In order to realize this, it is necessary to shorten the μ change determination time and to reduce the wheel cylinder hydraulic pressure of the wheel on the high μ side of the left and right front wheels earlier. However, if the μ change determination time is shortened, misjudgment caused by noise such as road surface disturbances (for example, pebbles, falling objects on the road such as branches and wooden pieces, manholes) increases. That is, the noise resistance in the μ change determination is lowered. Here, considering the load movement in the vehicle front-rear direction during braking, a decrease in the braking force of the front wheels has a great influence on the deceleration fluctuation of the vehicle. For this reason, erroneous determination of μ change leads to an extension of the braking distance. Therefore, in the conventional brake control device, it is difficult to shorten the μ change determination time, and thus the unstable behavior at the initial stage of the μ change is not sufficiently suppressed. In addition, although the prior art which determines the left and right wheel cylinder hydraulic pressure by select low at the time of μ change determination is also known, the same problem as described above occurs.

[Suppression of unstable behavior at the beginning of μ change]
In contrast, in the braking force limiting process of the first embodiment, when one μ change of the left and right front wheels FL and FR is determined, the left and right front wheels FL and FR control the rear wheel on the same side as the high μ wheel. Limit power.
(When initial behavior change is small)
FIG. 12 is a time chart showing an operation at the time of approaching the split μ road surface when the behavior change at the initial stage of μ change is small in the first embodiment. The premise is the same as in FIG.
At time t1, the wheel speed of the left front wheel FL decreases with the μ change of the left front wheel FL. When the left front wheel FL locks slightly after time t1, the wheel cylinder hydraulic pressure of the left front wheel FL is reduced by the ABS normal processing.
At time t2, the routine shifts from the ABS normal processing to the braking force limiting processing by determining that the left front wheel FL is μ change (detection of μ change). In the case of FIG. 12, since the initial behavior change is small (the yaw rate change amount is smaller than the yaw rate change amount threshold value), the wheel cylinder hydraulic pressure of the right rear wheel RR is reduced. By reducing the tire longitudinal force (braking force) of the right rear wheel RR, the tire lateral force of the right rear wheel RR can be sufficiently ensured when the vehicle turns due to the braking force difference between the left and right front wheels FL and FR. As a result, the steering characteristic of the vehicle becomes understeer, so that unstable behavior at the beginning of the μ change can be suppressed. Further, since the braking force of the right rear wheel RR is smaller than the braking force of the left rear wheel RL, a difference in braking force between the left and right rear wheels RL and RR occurs. The yaw moment generated by this braking force difference acts in a direction to cancel the yaw moment generated by the braking force difference between the left and right front wheels FL and FR. Thereby, the behavior change in the initial stage of μ change can be suppressed. In addition, a decrease in the braking force of the right rear wheel RR has a small effect on the vehicle deceleration fluctuation. For this reason, it is possible to suppress the extension of the braking distance accompanying the erroneous determination of the μ change. As a result, the μ change determination time can be shortened and the response of the braking force limitation of the right rear wheel RR can be improved as compared with the prior art that reduces the braking force of the front wheels.

At time t3, the wheel speed of the left rear wheel RL decreases with the μ change of the left rear wheel RL. When the left rear wheel RL is locked, the wheel cylinder hydraulic pressure of the left rear wheel RL is reduced.
At time t4, since the yaw rate does not converge even after the braking force of the right rear wheel RL is limited, it is determined that the unstable behavior continues, and the wheel cylinder hydraulic pressure of the right front wheel FR is reduced (the front wheel wheel cylinder hydraulic pressure is reduced). solid line). Unstable behavior can be suppressed by reducing the difference in braking force between the left and right front wheels FL and FR. Further, by reducing the wheel cylinder hydraulic pressure of the right rear wheel RR after reducing the wheel cylinder hydraulic pressure of the right rear wheel RR, it is possible to gain a determination time from the occurrence of the μ change until the wheel cylinder hydraulic pressure of the front wheel is reduced. Thereby, the influence on the deceleration fluctuation | variation of the vehicle accompanying the misjudgment of μ change can be suppressed.
When it is determined that the yaw rate converges at time t4 and the unstable behavior does not continue, the wheel cylinder hydraulic pressure of the right front wheel FR is not reduced (the one-dot chain line of the front wheel wheel cylinder hydraulic pressure). When the unstable behavior is solved only by limiting the braking force of the right rear wheel RL, it is possible to suppress the extension of the braking distance by not limiting the braking force of the unnecessary front wheel (right front wheel FR).

(When initial behavior change is large)
FIG. 13 is a time chart showing an operation when entering the split μ road surface when the behavior change at the initial stage of the μ change is large in the first embodiment. The premise is the same as in FIG.
The time t1 is the same as the time t1 in FIG.
At time t2, the shift from the ABS normal processing to the braking force limiting processing is performed by determining that the left front wheel FL is μ change (detection of μ change). In the case of FIG. 13, since the initial behavior change is large (the yaw rate change amount is larger than the yaw rate change amount threshold value), the wheel cylinder hydraulic pressures of the right front wheel FR and the right rear wheel RR are simultaneously reduced. When the initial behavior change is large, the unstable behavior cannot be suppressed only by limiting the braking force of the right rear wheel RR. Unstable behavior can be suppressed by restricting the braking force of the right front wheel FR in addition to the right rear wheel RR.
At time t3, the wheel speed of the left rear wheel RL decreases with the μ change of the left rear wheel RL. When the left rear wheel RL is locked, the wheel cylinder hydraulic pressure of the left rear wheel RL is reduced.

(When predicting μ change)
FIG. 14 is a time chart showing the operation when entering the split μ road surface when the μ change is predicted in the first embodiment. The premise is the same as in FIG.
At time t1, the shift from the ABS normal processing to the braking force limiting processing is performed due to the determination of the μ change of the left front wheel FL (μ change prediction), and the right rear wheel RR on the high μ side of the left and right rear wheels RL, RR is changed. Reduce wheel cylinder hydraulic pressure. Since the wheel cylinder depressurization amount is smaller than the wheel cylinder depressurization amount at the time of the μ change detection shown in FIGS. 12 and 13, there is no influence on the vehicle deceleration fluctuation.
At time t2, the wheel speed of the left front wheel FL decreases with the μ change of the left front wheel FL. When the left front wheel FL locks slightly after time t2, the wheel cylinder hydraulic pressure of the left front wheel FL is reduced. At this time, since the braking force of the right rear wheel RR is already limited, compared to the case where the braking force limitation of the right rear wheel RR is started after detecting the μ change, the braking force difference between the left and right front wheels FL, FR The generated yaw moment can be suppressed. Thereby, the behavior change in the initial stage of μ change can be suppressed.
Since time t3 and after is the same as time t3 and after in FIG. 12, description thereof is omitted.

The effects of Embodiment 1 are listed below.
The electronic control unit ECU determines the μ change when the μ change determination unit 44 determines the μ change of one of the left and right front wheels FL, FR, and when the braking force is generated in each wheel FL to RR. Includes a braking force control unit 45 that controls the hydraulic unit HU so as to limit the braking force of the rear wheels. Thereby, since the steer characteristic of the vehicle in the early stage of μ change can be made understeer, the unstable behavior in the early stage of μ change can be suppressed. In addition, since the influence on the vehicle deceleration fluctuation can be reduced as compared with the case where the braking force of the front wheels is limited, the extension of the braking distance can be suppressed.
The μ change determination unit 44 determines μ change based on the behavior of a wheel with a large slip amount (the wheel on the low μ side) of the left and right front wheels FL, FR. By looking at the actual behavior of the left and right front wheels FL and FR, μ changes can be detected accurately.
The braking force control unit 45 restricts the braking force of the left and right rear wheels (high μ side rear wheel) of the left and right front wheels FL and FR on the same side as the high μ side wheel. As a result, the yaw moment generated by the difference in braking force between the left and right front wheels FL and FR can be reduced, so that the behavior change at the initial stage of the μ change can be suppressed.
When the yaw rate change amount is smaller than a preset yaw rate change amount threshold, the braking force control unit 45 controls the hydraulic pressure unit HU so as to limit the braking force of the rear wheels. When the behavior change accompanying the μ change is smaller than the threshold value, the behavior change can be suppressed only by limiting the braking force of the rear wheels. Therefore, in this case, by not performing unnecessary braking force restriction on the front wheels, it is possible to reduce the influence on the vehicle deceleration fluctuation, and thus it is possible to suppress the extension of the braking behavior.

The braking force control unit 45 continues the unstable behavior of the vehicle after limiting the braking force of the left and right rear wheels (high μ side rear wheel) of the left and right front wheels FL and FR on the same left and right side. If so, the hydraulic unit HU is controlled so as to limit the braking force of the wheel on the high μ side of the left and right front wheels FL, FR. When the unstable behavior cannot be suppressed only by the braking force limitation of the rear wheels, the unstable behavior can be suppressed because the braking force difference between the left and right front wheels FL and FR can be reduced by limiting the braking force of the front wheels. In addition, since the determination time from the occurrence of the μ change until the braking force of the front wheels is limited can be gained, the influence on the deceleration change of the vehicle due to the erroneous determination of the μ change can be suppressed.
When the yaw rate change amount is larger than a preset yaw rate change amount threshold value, the braking force control unit 45 controls the wheel on the high μ side of the left and right front wheels FL and FR and the rear wheel on the same side as the wheel. The hydraulic unit HU is controlled so as to limit the power. When the behavior change accompanying μ change is larger than the threshold value, the behavior change cannot be suppressed only by limiting the braking force of the rear wheels. Therefore, in this case, the unstable behavior can be suppressed by restricting the braking force on the front and rear wheels from the beginning.
The μ change determination unit 44 includes a slip large-side front wheel acceleration calculation unit 40 that detects acceleration of a wheel having a large slip amount among the left and right front wheels FL and FR, and a right and left wheel cylinder hydraulic pressure difference between the left and right front wheels FL and FR (left and right braking force). The μ change is determined based on signals from the front wheel left / right W / C hydraulic pressure difference calculation unit 42 that calculates the difference) and the yaw rate change amount calculation unit 43 that calculates the yaw rate change amount. When the ground contact surfaces of the left and right front wheels FL, FR change from a uniform high μ road surface to a split μ road surface, first, the acceleration of the wheel on the low μ road becomes a negative value, and the slip amount increases. When the slip amount increases, ABS control (ABS normal processing) intervenes and a wheel cylinder hydraulic pressure difference between the left and right front wheels FL and FR occurs. The integral value of the wheel cylinder hydraulic pressure difference increases as the split μ road surface continues. Next, a yaw moment is generated around the center of gravity of the vehicle due to the difference in braking force between the left and right front wheels FL and FR, and the behavior changes in the vehicle. At this time, the approach to the split μ road surface can be determined from the acceleration of the wheel. Also, the intervention of ABS control can be determined from the difference in hydraulic pressure between the left and right wheel cylinders. Furthermore, a change in vehicle behavior can be predicted from the amount of yaw rate change. Therefore, the μ change is determined based on the signals from the slip large side front wheel acceleration calculation unit 40, the front wheel left / right W / C hydraulic pressure difference calculation unit 42, and the yaw rate change calculation unit 43, so that the μ change initial stage can be accurately and quickly determined. Can be determined.

The braking force control unit 45 increases the braking force limit amount of the rear wheels as the vehicle behavior change (yaw rate change amount) increases. The larger the behavior change, the higher the possibility of unstable behavior. Therefore, by increasing the braking force limit amount as the behavior change increases, the braking force limit amount can be appropriately set based on the behavior change.
The braking force control unit 45 increases the braking force limit amount of the rear wheel as the vehicle body speed of the vehicle increases. When the left-right braking force difference is the same, the behavior change increases as the vehicle body speed increases. Therefore, by increasing the braking force limit amount as the vehicle body speed increases, an appropriate braking force limit amount can be set based on the height of the vehicle body speed.
The μ change determination unit 44 shortens the μ change determination time (predetermined value in step S15) as the vehicle body speed of the vehicle increases. The higher the vehicle speed, the faster the behavior changes, whereas the driver's response (steering) tends to be delayed, and the unstable behavior increases. Therefore, by making the determination time shorter as the vehicle body speed is higher, an appropriate μ change determination time can be set based on the height of the vehicle body speed.
The μ change determination unit 44 determines the μ change based on the road surface condition in the traveling direction of the vehicle recognized by the external ECU 28. Predicting μ-change and limiting the braking force of the rear wheels in advance before μ-change can suppress unstable behavior at the beginning of μ-change.

[Other Embodiments]
Although the embodiment for carrying out the present invention has been described above, the specific configuration of the present invention is not limited to the configuration of the embodiment, and there are design changes and the like within the scope not departing from the gist of the invention. Are also included in the present invention.
In the first embodiment, the example in which the braking force limit amount of the front and rear wheels is increased as the vehicle behavior change is larger or the vehicle body speed is higher is shown. However, as the vehicle behavior change is larger or the vehicle body speed is higher, the control is increased. The speed limit of power may be increased.

The technical idea that can be grasped from the embodiment described above will be described below.
In one aspect thereof, the brake control device has a braking force control unit that generates a braking force on a braking force generation unit provided on each wheel of the vehicle, and a split μ road surface having a different road surface μ between the left and right wheels. A state in which braking force is generated in each wheel, and a μ change determination unit that determines a μ change in which the road surface μ of one of the left and right wheels of the front wheel in the traveling direction of the vehicle changes from high μ to low μ. A control unit having a braking force control unit that controls the braking force control unit to limit the braking force of the rear wheel in the traveling direction of the vehicle when the μ change is determined .
In a more preferred aspect, in the above aspect, the μ change determination unit determines the μ change based on the behavior of the front wheel in the traveling direction.
In another preferred aspect, in any one of the above aspects, the braking force control unit is configured to limit the braking force of the rear wheel in the traveling direction on the same side as the high μ side wheel among the front wheels in the traveling direction. Control the braking force control unit.
In still another preferred aspect, in any one of the above aspects, the braking force control unit controls the rear wheel in the traveling direction when the behavior change of the vehicle is smaller than a preset behavior change threshold. The braking force control unit is controlled so as to limit power.
In still another preferred aspect, in any one of the above aspects, the braking force control unit, when the unstable behavior of the vehicle continues after limiting the braking force of the rear wheel in the traveling direction, The braking force control unit is controlled so as to limit the braking force of the wheel on the high μ side among the front wheels in the traveling direction.

In still another preferred aspect, in any one of the above aspects, the braking force control unit is configured to increase a high-side wheel in the traveling direction when the vehicle behavior change is greater than a preset behavior change threshold. The braking force control unit is controlled so as to limit the braking force of the wheel on the μ side and the rear wheel in the traveling direction on the same side as the wheel.
In still another preferred aspect, in any one of the above aspects, the μ change determination unit includes a large slip front wheel acceleration detection unit that detects acceleration of a wheel having a large slip amount among the front wheels in the traveling direction; The μ change based on signals from a front wheel left / right braking force difference calculation unit that calculates a left / right braking force difference between the front wheel and a turning state change amount detection unit that detects a change amount of the turning state amount of the vehicle. Determine.
In still another preferred aspect, in any one of the above aspects, the braking force control unit increases the limit amount of the braking force for the rear wheel in the traveling direction or increases the speed limit as the behavior change of the vehicle increases. The braking force control unit is controlled to be higher.
In yet another preferred aspect, in any one of the above aspects, the braking force control unit increases the limit amount of the braking force for the rear wheel in the traveling direction as the vehicle body speed of the vehicle increases, or sets the limit speed. The braking force control unit is controlled to be higher.
In yet another preferred aspect, in any of the above aspects, the μ change determination unit shortens the μ change determination time as the vehicle body speed of the vehicle increases.
According to still another preferred aspect, in any one of the above aspects, the apparatus includes an external recognition device that is provided outside the control unit and recognizes a road surface condition in the traveling direction of the vehicle, and the μ change determination unit includes the road surface The μ change is determined based on the situation.

Further, from another point of view, the brake control device includes a housing in which a fluid path is provided, a braking force generation unit that is provided in each wheel of the vehicle and generates a braking force on the wheel according to the brake fluid pressure, The road surface μ differs between the left and right wheels, and a hydraulic unit that is provided in the housing and includes a pump that generates a brake hydraulic pressure in the braking force generation unit via the liquid path and a motor that drives the pump. The μ change in which the road surface μ of one of the left and right wheels of the front wheel in the traveling direction of the vehicle changes from high μ to low μ with respect to the split μ road surface is determined based on the behavior of the front wheel in the traveling direction of the vehicle. The brake fluid pressure of the braking force generation unit corresponding to the rear wheel in the traveling direction of the vehicle when it is determined that the μ change is in a state where the braking force is generated in each wheel. To reduce the liquid A control unit having a brake fluid pressure control unit for controlling the pressure unit.
Preferably, in the above aspect, the μ change determination unit includes a slip large side front wheel acceleration detection unit that detects acceleration of a wheel having a large slip amount among the traveling direction front wheels, and a control corresponding to the traveling direction front wheel. The μ change is determined based on signals from a front-wheel left-right hydraulic pressure difference calculation unit that calculates an estimated hydraulic pressure difference of the power generation unit, and a turning state change amount detection unit that detects a change amount of the turning state amount of the vehicle. To do.
Furthermore, from another point of view, the brake control method is a brake control method for applying a braking force to each wheel of the vehicle. A μ change determination step for determining a μ change in which the road surface μ of one of the wheels changes from a high μ to a low μ, and the μ change is determined in a state where a braking force is generated in each wheel. In this case, a rear wheel braking force limiting step for limiting the braking force of the rear wheel in the traveling direction of the vehicle is provided.
Preferably, in the above aspect, the μ change determination step determines the μ change based on a behavior of the vehicle.

In another preferred aspect, in any one of the above aspects, the rear wheel braking force restriction step restricts the braking force of the rear wheel in the traveling direction on the same side as the high μ side wheel among the front wheels in the traveling direction. To do.
According to still another preferred aspect, in any one of the above aspects, the vehicle further includes a behavior change determination step for determining whether or not the vehicle behavior change is larger than a preset behavior change threshold value. In the power limiting step, the braking force is limited when the behavior change of the vehicle is smaller than a preset behavior change threshold.
In still another preferred aspect, in any one of the above aspects, when the unstable behavior of the vehicle continues after the rear wheel braking force limiting step, the high μ side of the traveling direction front wheels A front wheel braking force limiting step for limiting the braking force of the wheels.
In yet another preferred aspect, in any of the above aspects, a behavior change determination step for determining whether or not the behavior change of the vehicle is greater than a preset behavior change threshold; and the behavior change is preset. A front wheel braking force limiting step of limiting the braking force of the wheel on the high μ side among the front wheels in the traveling direction of the vehicle simultaneously with the rear wheel braking force limiting step, Have
In still another preferred aspect, in any of the above aspects, the μ change determination step determines the μ change based on a road surface condition in a traveling direction of the vehicle.

1 liquid channel
40 Slip large side front wheel acceleration calculation unit (slip large side front wheel acceleration detection unit)
42 Front wheel left / right W / C hydraulic pressure difference calculator (front wheel left / right braking force difference calculator)
43 Yaw rate change calculation unit (turning state change detection unit)
44 μ change judgment part
45 Braking force control unit
ECU Electronic control unit (control unit)
HSG housing
HU hydraulic unit (braking force control unit)
M motor
P Oil pump (pump)
W / C wheel cylinder (braking force generator)

Claims (11)

A braking force control unit for generating a braking force in a braking force generator provided on each wheel of the vehicle;
Μ change determination for determining a μ change in which the road surface μ of one of the left and right wheels of the front wheel in the traveling direction of the vehicle changes from high μ to low μ with respect to a split μ road surface in which the road surface μ differs between the left and right wheels And
A braking force that controls the braking force control unit to limit the braking force of the rear wheel in the traveling direction of the vehicle when it is determined that the μ change is in a state where the braking force is generated in each wheel. A control unit;
A control unit having
A brake control device comprising: The brake control device according to claim 1, wherein
The μ change determination unit determines the μ change based on the behavior of the front wheel in the traveling direction. The brake control device according to claim 2,
The braking force control unit controls the braking force control unit so as to limit the braking force of the rear wheel in the traveling direction on the same side as the wheel on the high μ side among the front wheels in the traveling direction. Brake control device. The brake control device according to claim 3,
The braking force control unit controls the braking force control unit to limit the braking force of the rear wheels in the traveling direction when the behavior change of the vehicle is smaller than a preset behavior change threshold. A brake control device. The brake control device according to claim 4, wherein
When the unstable behavior of the vehicle continues after the braking force control unit restricts the braking force of the rear wheel in the traveling direction, the braking force of the wheel on the high μ side among the front wheels in the traveling direction A brake control device that controls the braking force control unit so as to limit the braking force. The brake control device according to claim 3,
When the behavior change of the vehicle is larger than a preset behavior change threshold, the braking force control unit is configured to move a high μ side wheel of the front wheels in the traveling direction and a traveling direction on the same side as the wheels. A brake control device that controls the braking force control unit to limit a braking force of a rear wheel. The brake control device according to claim 2,
The μ change determination unit
A slip large-side front wheel acceleration detecting unit that detects acceleration of a wheel having a large slip amount among the front-side wheels in the traveling direction;
A front wheel left and right braking force difference calculating unit for calculating a left and right braking force difference of the front wheel in the traveling direction;
A turning state change amount detecting unit for detecting a change amount of the turning state amount of the vehicle;
A brake control device that determines the μ change based on a signal from the brake control device. A housing with a liquid path inside;
A braking force generator provided on each wheel of the vehicle, for generating a braking force on the wheel according to the brake fluid pressure;
A pump that is provided in the housing and generates a brake fluid pressure in the braking force generation unit via the fluid path;
A motor for driving the pump;
A hydraulic unit having
Judgment is made based on the behavior of the front wheel in the direction of travel of the vehicle when the road surface μ of one of the left and right wheels changes from high μ to low μ for split μ road surfaces with different road surface μ between the left and right wheels Μ change determination unit to
When the μ change is determined in a state where the braking force is generated in each wheel, the liquid is applied so as to reduce the brake fluid pressure of the braking force generation unit corresponding to the rear wheel in the traveling direction of the vehicle. A brake fluid pressure control unit for controlling the pressure unit;
A control unit having
A brake control device comprising: In a brake control method for applying a braking force to each wheel of a vehicle,
Μ change determination for determining μ change in which road surface μ of one wheel of left and right wheels of the front wheel in the traveling direction of the vehicle changes from high μ to low μ with respect to split μ road surfaces having different road surfaces μ between the left and right wheels Steps,
A rear wheel braking force limiting step for limiting the braking force of the rear wheel in the traveling direction of the vehicle when it is determined that the μ change is in a state where the braking force is generated in each wheel;
A brake control method comprising: The brake control method according to claim 9, wherein
The μ change determination step determines the μ change based on the behavior of the vehicle. The brake control method according to claim 10, wherein
The brake control method according to claim 1, wherein the rear wheel braking force limiting step limits the braking force of the rear wheel in the traveling direction on the same side as the wheel on the high μ side in the front wheel in the traveling direction.

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