JPH11310121A - Vehicular braking control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive understeer by restricting braking force automatically applied to a turning outside wheel when judged as required to start brake assist control when judged as turning time by judging whether or not a vehicle turns. SOLUTION: An initialized microcomputer MCP reads in respective detecting signals of wheel speed sensors WS1 to WS4, a fluid pressure sensor PS (master cylinder fluid pressure Pmc), lateral acceleration sensor Gy, a front wheel steering angle sensor and a yaw rate sensor. Next, a wheel speed of respective wheels is arithmetically operated, an estimated car body speed is determined, and is normalized to reduce an error by a difference between inner/outer wheels at vehicle turning time to arithmetically operate a longitudinal directional car body deceleration in a vehicular gravity center position. A control mode of an antiskid control is set, and a starget slip rate is set so as to control braking force to respective wheels by a brake fluid pressure controller BC by fluid pressure servo control to thereby prevent excessive understeer when starting brake assist control at vehicle turning time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to assist a driver in operating a brake pedal by automatically increasing a braking force when the brake pedal is depressed at a rapid speed or when the brake pedal is depressed deeply. The present invention relates to a vehicle brake control device having a brake assist control function.

[0002]

2. Description of the Related Art During traveling of a vehicle, for example, during emergency braking, a brake pedal is depressed at a rapid speed. However, the pedaling force is insufficient or it is difficult to maintain the pedaling force, so that an appropriate braking force may not be obtained. In light of this, recently,
It has been proposed to add a brake assist control function,
Already installed in some commercial vehicles. This brake assist control automatically increases the braking force when the brake pedal is depressed at a rapid speed to assist the driver in operating the brake pedal. Generally, the boosting function of the vacuum booster is used. Control is being done.

Here, for the purpose of completely or partially saving the vacuum booster, there is a technology for performing brake assist control using a pump for anti-skid control or traction control (Japanese Patent Laid-Open No. 8-230634). Are known. Specifically, this is a wheel cylinder, a master cylinder, a main hydraulic pressure path connecting the master cylinder to the wheel cylinder, a first on-off valve for opening and closing the main hydraulic pressure path, and a first on-off valve. A hydraulic pump that connects the discharge side between the hydraulic cylinder and the wheel cylinder and discharges brake fluid that has been pressurized to the wheel cylinder, an auxiliary hydraulic path that connects the suction side of the hydraulic pump to the master cylinder, and an auxiliary hydraulic path And a second on-off valve for opening and closing the valve.

Further, a pressure sensor for detecting the output hydraulic pressure of the master cylinder is provided, and when the master cylinder hydraulic pressure is equal to or higher than a predetermined hydraulic pressure and the increasing rate of the master cylinder hydraulic pressure exceeds a predetermined ratio, a hydraulic pump is provided. In addition, the first and second opening / closing valves are controlled, and as shown in FIG. 8 of the publication, brake assist control is performed such that the wheel cylinder hydraulic pressure is higher than the master cylinder hydraulic pressure by a predetermined raising pressure.

[0005]

However, in this case, no measure is taken when the brake assist control is started during turning of the vehicle. Therefore, when the brake assist control is started during turning of the vehicle, the braking force of all the wheels sharply increases, and the cornering force of all the wheels (particularly, the turning outer wheel having a large wheel load) sharply decreases. As a result, the vehicle may have an excessive tendency to understeer.

Therefore, an object of the present invention is to prevent excessive understeer when brake assist control is started during turning of a vehicle.

[0007]

According to a first aspect of the present invention, there is provided a brake control apparatus for a vehicle, comprising: a brake operation detecting means for detecting an operation amount or an operation speed of a brake pedal; Start determining means for determining whether or not to start the brake assist control based on the detection result of the operation detecting means; and automatically controlling the braking force on all wheels of the vehicle when the start determining means determines that the brake assist control needs to be started. And a control means for performing a brake assist control by giving the vehicle turning control. The turning control means for determining whether or not the vehicle is turning, the control means comprising: If the start determination means determines that the brake assist control needs to be started during the middle determination, the braking force automatically applied to the turning outer wheel is limited. Are those that form.

According to the first aspect of the present invention, when it is determined that the brake assist control needs to be started during turning of the vehicle, the braking force to be automatically applied to the turning outer wheel is limited. When the control is started, the cornering force of the turning outer wheel having a large wheel load can be prevented from sharply decreasing, and as a result, excessive understeer can be prevented.

According to the first aspect of the present invention, as set forth in the second aspect of the present invention, a wheel speed detecting means for detecting a rotational speed of each wheel of the vehicle, and each of the wheels according to a detection result of the wheel speed detecting means. Real slip rate calculating means for calculating an actual slip rate; and actual deceleration detecting means for detecting an actual deceleration of the vehicle, wherein the control means determines a target deceleration of the vehicle based on a detection result of the brake operation detecting means. Target deceleration setting means for setting, a deviation calculating means for calculating a deviation between the actual deceleration of the vehicle and the target deceleration, and a target slip rate setting means for setting a target slip rate for each wheel according to the deviation. ,
A target slip ratio correcting unit that corrects the target slip ratio of the turning outer wheel to a small value when the start determining unit determines that the brake assist control needs to be started while the turning determining unit determines that the vehicle is turning; and It is preferable that a braking force is automatically applied to all wheels of the vehicle in accordance with a comparison result between the actual slip rate of each wheel and the target slip rate or the corrected target slip rate.

According to this configuration, if it is determined that the brake assist control needs to be started during the turning of the vehicle, the target slip ratio of the turning outer wheel is corrected to a small value. In addition, the braking force automatically applied to the turning outer wheel can be limited, and as a result, excessive understeer can be prevented.

According to a second aspect of the present invention, as set forth in the third aspect of the present invention, the target slip ratio correction means calculates the target slip ratio correction amount of the turning outer front wheel by the target slip ratio correction amount of the turning outer rear wheel. It is preferable to make it larger than the above.

According to this configuration, the correction amount of the target slip ratio of the front wheel on the outside of the turning is made larger than the correction amount of the target slip ratio of the rear wheel on the outside of the turning, so that the correction is automatically applied to the front outside wheel of the turning with the largest wheel load. The braking force to be applied can be limited more than the turning outer rear wheel that is smaller than the turning outer front wheel load. As a result, excessive understeer can be prevented more reliably.

According to a second aspect of the present invention, as set forth in the fourth aspect of the present invention, the target slip ratio correction means is configured to set a correction amount of a target slip ratio of a turning outer wheel in accordance with a turning state. ,preferable.

According to this configuration, since the correction amount of the target slip ratio of the turning outer wheel is set according to the turning state, the braking force of the turning outer wheel can be appropriately controlled according to the turning state.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a braking control device according to the present invention, wherein an engine EG includes a throttle control device TH.
In the internal combustion engine provided with the fuel injection device FI, the throttle control device TH controls the main throttle opening of the main throttle valve MT according to the operation of the accelerator pedal AP. Further, the sub-throttle valve ST of the throttle control device TH is driven to control the sub-throttle opening in accordance with the output of the electronic control unit ECU, and the fuel injection device FI is driven to control the fuel injection amount. It is configured. The engine EG of the present embodiment is connected to wheels FL and FR in front of the vehicle via a shift control device GS and a differential gear DF, and is configured as a so-called front wheel drive system. It is not limited.

Next, regarding the braking system, the wheels FL, F
Wheel cylinders Wfl, Wf for R, RL, RR, respectively
r, Wrl, Wrr are mounted, and a brake fluid pressure control device PC is connected to these wheel cylinders Wfl and the like. The wheels RL and RR indicate driven wheels. The brake fluid pressure control device PC is configured as shown in FIG. 2, which will be described later.

The wheels FL, FR, RL, RR are provided with wheel speed sensors WS1 to WS4, which are connected to the electronic control unit ECU, and which control the rotational speed of each wheel, that is, the number of pulses proportional to the wheel speed. Is input to the electronic control unit ECU. A hydraulic pressure sensor PS for detecting an output brake hydraulic pressure (hereinafter, referred to as master cylinder hydraulic pressure) Pmc of the master cylinder MC is connected to the electronic control unit ECU, and a signal representing the master cylinder hydraulic pressure Pmc is transmitted to the electronic control unit ECU. It is configured to be inputted to. Further, a brake switch BS which is turned on when the brake pedal BP is depressed, a front wheel steering angle sensor (not shown) for detecting the steering angle θf of the wheels FL and FR in front of the vehicle, and a lateral sensor for detecting the lateral acceleration Gya of the vehicle. An acceleration sensor Gy, a yaw rate sensor (not shown) for detecting the vehicle yaw rate γ, and the like are connected to the electronic control unit ECU.

The electronic control unit ECU of the present embodiment comprises processing units CP connected to each other via a bus.
A microcomputer MCP including a U, a memory ROM, a RAM, an input port IPT, an output port OPT, and the like is provided. Output signals from the wheel speed sensors WSl to WS4, the hydraulic pressure sensor PS, the brake switch BS, the front wheel steering angle sensor, the yaw rate sensor, the lateral acceleration sensor, and the like are input to the processing unit CPU from the input port IPT via the amplifier circuit AMP. It is configured to: Further, a control signal is output from the output port OPT to the throttle control device TH and the brake fluid pressure control device PC via the drive circuit ACT.

In the microcomputer MCP,
The memory ROM stores programs for various processes including the flowcharts shown in FIGS. 3 to 9, the processing unit CPU executes the programs while an ignition switch (not shown) is closed, and the memory RAM executes the programs. Temporarily stores the variable data required for the execution of For each control such as throttle control,
Alternatively, a plurality of microcomputers may be configured by appropriately combining related controls, and the microcomputers may be electrically connected to each other.

This shows a brake fluid pressure control device BC.
In response to the operation of the brake pedal BP, the master cylinder MC is boosted via the vacuum booster VB, and the brake fluid in the master reservoir LRS is pressurized and the wheels F
The master cylinder pressure is output to the hydraulic system on the R, RL and wheel FL, RR side. The master cylinder MC is a tandem type master cylinder, and two pressure chambers are connected to respective brake hydraulic systems. That is, the first pressure chamber MCa is connected to the brake fluid pressure system on the wheels FR and RL, and the second pressure chamber MCb is connected to the wheels FL and R.
It is connected to the brake hydraulic system on the R side.

In the brake hydraulic system for the wheels FR and RL, the first pressure chamber MCa is connected to the wheel cylinders Wfr and Wrl via a main hydraulic passage MF and branch hydraulic passages MFr and MFl, respectively. I have. In the main hydraulic path MF,
A normally opened two-port two-position first electromagnetic on-off valve SC1 (functioning as a so-called cutoff valve, hereinafter simply referred to as on-off valve SC1) is provided. Further, the first pressure chamber MCa is connected to a check valve C described later via an auxiliary hydraulic pressure path MFc.
V5 and CV6. The aforementioned hydraulic pressure sensor PS is connected to the auxiliary hydraulic pressure passage MFc, and detects the master cylinder hydraulic pressure Pmc. As a sensor for detecting the operation state of the brake pedal BP, a stroke sensor for detecting the stroke of the brake pedal BP may be used instead of the hydraulic pressure sensor PS.

The branch hydraulic pressure paths MFr and MFl are provided with normally open two-port two-position solenoid valves PC1 and PC2 (hereinafter simply referred to as valve PC1 and PC2). Further, check valves CV1 and CV2 are arranged in parallel with these, respectively. The check valves CV1 and CV2 allow only the flow of the brake fluid in the direction of the master cylinder MC, and the brake fluid in the wheel cylinders Wfr and Wrl passes through the check valves CV1 and CV2 and the on-off valve SC1. The master cylinder MC is returned to the master cylinder reservoir LRS. Therefore, when the brake pedal BP is released, the wheel cylinder Wf
The fluid pressure in r and Wrl can quickly follow the fluid pressure drop on the master cylinder MC side. Further, the wheel cylinder Wfr,
Discharge-side branch hydraulic pressure passages RFr, R connected to Wrl
Fl, normally closed 2-port 2-position solenoid on-off valve PC
5, PC6 (hereinafter simply referred to as on-off valves PC5, PC6)
Is disposed, and the discharge hydraulic pressure line RF where the branch hydraulic pressure lines RFr and RFl join is connected to the auxiliary reservoir RS1.

The auxiliary reservoir RS1 has a check valve CV6,
The suction side of the hydraulic pump HP1 is connected via CV5,
The discharge side is connected to the upstream side of the on-off valves PC1 and PC2 via the check valve CV7 and the hydraulic path MFp. The hydraulic pump HP1 is driven by a single electric motor M together with the hydraulic pump HP2, introduces brake fluid from the suction side, increases the pressure to a predetermined pressure, and outputs it from the discharge side. The auxiliary reservoir RS1 is connected to the master reservoir LR of the master cylinder MC.
It is provided independently of S, and can be called an accumulator, and has a piston and a spring, and is configured to be able to store a predetermined volume of brake fluid.

The master cylinder MC is provided with an auxiliary hydraulic passage MFc.
Is connected between the check valve CV5 and the check valve CV6 on the suction side of the hydraulic pump HP1. Check valve CV5
Is for blocking the flow of the brake fluid to the auxiliary reservoir RS1 and allowing the flow in the reverse direction. The check valves CV6 and CV7 regulate the flow of the brake fluid discharged through the hydraulic pump HP1 in a certain direction, and are usually integrally formed in the hydraulic pump HP1. Thus, the on-off valve SI1 shuts off communication between the master cylinder MC and the suction side of the hydraulic pump HP1 at the normal closed position shown in FIG. 2, and opens and closes the master cylinder MC and the hydraulic pump H at the open position.
It is switched so that the suction side of P1 communicates.

A relief valve RV1 and a check valve AV1 are arranged in parallel with the on-off valve SC1. The relief valve RV1 is connected from the master cylinder MC to the on-off valves PC1, P
Restrict the flow of brake fluid in the C2 direction,
1, when the brake fluid pressure on the PC2 side becomes higher than the master cylinder fluid pressure by a predetermined pressure or more, the master cylinder M
The brake fluid allows the flow of the brake fluid in the direction C (a so-called relative pressure relief valve), which can prevent the brake fluid discharged from the hydraulic pump HP1 from exceeding a predetermined pressure. The check valve AV1 permits the flow of the brake fluid in the direction of the wheel cylinders Wfr and Wrl, and prohibits the flow in the reverse direction. Due to the presence of the check valve AV1, the on-off valve S
Even when C1 is in the closed position, when the brake pedal BP is depressed, the brake fluid pressure in the wheel cylinders Wfr and Wrl is increased. A damper DP1 is provided on the discharge side of the hydraulic pump HP1, and a proportioning valve PV is provided in a hydraulic path leading to the wheel cylinder Wrl on the rear wheel side.
1 is interposed.

On the other hand, in the brake fluid pressure system on the wheels FL and RR, similarly, a normally open 2-port 2-position solenoid valve SC2 (first opening / closing valve) including a reservoir RS2, a damper DP2, and a proportioning valve PV2. Valve), normally closed 2-port 2-position solenoid valve SI2 (second on-off valve), normally-open 2-port 2-position solenoid valve PC3, PC
4. Normally closed 2-port 2-position solenoid valve PC7, PC
8, check valves CV3, CV4, CV8 to CV10, a relief valve RV2, and a check valve AV2. The hydraulic pump HP2 is driven by the electric motor M to
Driven with P1.

The above-mentioned electric motor M, on-off valves SC1, SC
2, SI1, SI2 and on-off valves PC1 to PC8 are
Drive control is performed by the above-described electronic control unit ECU, and various controls such as brake assist control, anti-skid control, braking steering control (oversteer suppression control or understeer suppression control), front-rear braking force distribution control, and traction control, which will be described later, are performed. .

In the present embodiment configured as described above, a series of processes such as braking steering control, brake assist control, anti-skid control, and the like are performed by the electronic control unit ECU, and an ignition switch (not shown) is opened. Then, the execution of the program corresponding to the flowcharts of FIGS. 3 to 9 starts.

FIG. 3 shows the operation of the braking control. First, at step 101, the microcomputer MCP is initialized and various calculated values are cleared. Then step 1
At 02, the detection signals of the wheel speed sensors WS1 to WS4 are read, and the detection signal of the hydraulic pressure sensor PS (master cylinder hydraulic pressure Pmc) is read. Also,
The detection signal of the lateral acceleration sensor Gy (that is, the actual lateral acceleration Gy)
a), a detection signal (steering angle θf) of the front wheel steering angle sensor and a detection signal (actual yaw rate γ) of the yaw rate sensor are read.

Subsequently, the routine proceeds to step 103, where the master cylinder pressure Pmc is differentiated, and the master cylinder pressure Pmc is differentiated.
Is differentiated to obtain a master cylinder hydraulic pressure change rate DPmc. Then, in step 104, the wheel speed Vw ** (** represents each wheel) of each wheel is calculated, and the wheel speed Vw ** of each wheel is differentiated to obtain the wheel acceleration DVw ** of each wheel. Is calculated. Next, at step 105, the estimated vehicle speed Vso ** at the position of the center of gravity of the vehicle is calculated based on the wheel speed Vw ** of each wheel, and the estimated vehicle speed Vso ** at each wheel position is obtained. Furthermore, if necessary, normalization is performed on each wheel position vehicle speed Vso ** in order to reduce an error based on a difference between the inner and outer wheels when the vehicle turns. Further, the vehicle body deceleration (hereinafter referred to as vehicle body deceleration) DVso in the front-rear direction at the position of the center of gravity of the vehicle is calculated by differentiating the vehicle speed Vso at the position of the center of gravity.
(Note that, here, the vehicle body deceleration is used for convenience of description, but if the sign is reversed, it becomes the vehicle body acceleration.)

Next, at step 106, the wheel speed Vw * of each wheel obtained at steps 103 and 104 described above.
* And the estimated vehicle speed Vso ** at each wheel position (or the normalized estimated vehicle speed at each wheel position), the actual slip ratio Sa ** of each wheel is Sa ** = (Vso ** − Vw). **) / Vso **
Is required. Next, at step 107, based on the vehicle body deceleration DVso at the position of the center of gravity and the actual lateral acceleration Gya, the road surface friction coefficient μ is approximately μ = (DVso2 + Gya).
2) Estimated as 1/2. The road surface friction coefficient μ ** at each wheel position may be calculated based on the road surface friction coefficient μ and the estimated value of the wheel cylinder hydraulic pressure Pw ** of each wheel.

Subsequently, brake assist control is performed in step 108, which will be described later. Then, the process proceeds to a step 109, wherein various control modes such as anti-skid control are set, and a target slip ratio to be provided for the various control modes is set. Next, by the hydraulic servo control in step 110, the brake hydraulic pressure control device PC is controlled to control the braking force on each wheel. In particular, in the brake assist control, the electric motor M and the on-off valve SC
1, SC2, SI1, SI2 are drive-controlled.

Next, referring to FIG. 4, step 10 in FIG.
8 will be described in detail.

First, at step 201, it is determined whether or not the brake assist control flag FL is the flag F1 or the flag F2.
Here, the flag F1 indicates that the start specifying control is being performed, and the flag F2 indicates that this control is being performed. At step 202, it is determined whether or not the BA control start condition is satisfied. If so, the process proceeds to step 203, where the control flag FL is set to the start specific control in-progress flag F1. Here, the condition for starting the brake assist control is determined by the detected hydraulic pressure Pm of the hydraulic pressure sensor PS.
c is greater than or equal to a predetermined value, and the detected fluid pressure change rate D
Pmc is equal to or higher than a predetermined ratio.

Subsequently, from step 203 to step 20
Proceeding to 4, the start specific control calculation is performed. That is, the duty Dis of the on-off valve SI * provided for the start specifying control and the execution time Ts of the start specifying control are set. In particular,
The duty Dis of the opening / closing valve SI * is selected from a map (not shown) according to the master cylinder hydraulic pressure Pmc and the change rate DPmc of the master cylinder hydraulic pressure at the time when the control start is required. The duty Dis of the on-off valve SI * is set to be larger as the master cylinder fluid pressure Pmc is higher, and the duty Dis of the on-off valve SI * is set to be larger as the master cylinder fluid pressure change rate (increase rate) DPmc is larger. Further, the execution time Ts of the start specifying control is determined by setting the target brake fluid amount Vc to be supplied to the wheel cylinder WC to the hydraulic pump H in consideration of the duty Dis of the on-off valve SI * and the like.
The time (P) divided by the discharge amount Vp per unit time of P and the fixed time Tc (for example, 1 sec) are set to the smaller time.

Then, the process proceeds to a step 205, wherein it is determined whether or not the vehicle is turning. Specifically, it is determined whether the lateral acceleration Gya of the vehicle detected by the lateral acceleration sensor Gy is equal to or greater than a predetermined value. When the lateral acceleration sensor Gy is not used, the lateral acceleration Gya is calculated as Gya = k (VwRR-Vw
RL) (VwRR + VwRL) / 2Tr. Here, Tr is the dread of the vehicle, and k is a coefficient for converting the unit. If it is not determined in step 205 that the vehicle is turning, the process proceeds to step 206, where the duty of the opening / closing valve SI * for start specification control is set to the value selected in step 204, and the duty of the opening / closing valve SC * is 100%. Is set to Next, at step 207, it is determined whether or not the execution time Ts has elapsed since the start of the brake assist control.
Return to the main routine of step 3. If it has passed, step 2
After the control flag FL is set to F2 at 08,
Returning to the main routine of FIG.

On the other hand, if it is determined in step 205 that the vehicle is turning, the process proceeds to step 209, where the duty of the opening / closing valve SI * for specifying start is set to the value selected in step 204, and the opening / closing valve SC * is set. Duty is 100
Set to%. Next, in step 210, the vehicle deceleration Δg corresponding to the predetermined hydraulic pressure for brake assist control is added to the vehicle deceleration Gm corresponding to the master cylinder hydraulic pressure Pmc, and the target deceleration G * of the vehicle is set. Is done. That is, the target deceleration G * according to the operation amount of the brake pedal BP is set. Then, step 21
In step 1, the difference between the target deceleration G * of the vehicle and the vehicle deceleration DVso at the position of the center of gravity used as the actual deceleration is calculated. Then, the process proceeds to a step 212, wherein the control flag FL
Is determined to be F1, but if it is not F1, the routine proceeds to step 213, where a brake assist control amount calculation described later is performed. Here, since the control flag FL is F1, the process jumps from step 213 to step 214, where a brake assist braking force distribution control amount calculation described later is performed, and the target slip ratio Sb ** of each wheel is set.

On the other hand, if it is determined in step 201 that the control flag FL is the start-specific control-in-progress flag F1 or the main control-in-progress flag F2, the flow advances to step 215 to determine whether or not the brake assist control end condition is satisfied (ie, the control (Necessity of termination) is determined. Here, the brake switch BS is turned off, the vehicle body speed Vso at the center of gravity position is equal to or lower than a predetermined speed, and the master cylinder hydraulic pressure Pmc is set to a predetermined lower limit Pa (for example, 1MP).
a) When any one of the following conditions is satisfied, it is determined that control termination is necessary. If it is determined in step 215 that the termination condition is not satisfied, the process proceeds to step 216, where it is determined whether the control flag FL is F1. If so, the processing of steps 206 to 208 is executed again. If it is determined in step 216 that the control flag FL is not F1, the process proceeds to step 212 after steps 210 and 211 described above are executed. In step 212, it is determined whether or not the control flag FL is F1. Here, since the control flag FL is the main control flag F2, the process proceeds to step 213, where the deceleration deviation ΔG is used as the control deviation to determine the brake assist control amount. An operation is performed. That is, FIG.
Opening / closing valve SI based on the deceleration deviation ΔG using the graph of FIG.
*, SC * duty (ratio of energization time) is set. Specifically, on the pressure increasing side (the deceleration deviation ΔG is positive),
The duty Di of the on-off valve SI * is set so as to be proportional to the deceleration deviation.
c is a constant value in the vicinity of 100%, which is a substantially closed position.
Here, when the deceleration deviation 0 <ΔG <Gk, the on-off valve S
The duty Di of I * is set to 0%, and the on-off valve SI * is closed. On the other hand, on the pressure reducing side (the deceleration deviation ΔG is negative), the duty Dc of the on-off valve SC * is set to be proportional to the deceleration deviation, and the duty Di of the on-off valve SI * is set to a constant value near 0%. And is set to a substantially closed position.
Further, a predetermined limit is imposed on the duty Di of the on-off valve SI *. That is, even if the deceleration deviation ΔG is large, the duty Di of the on-off valve SI * is set to the predetermined upper limit Du.
It is set so as not to exceed p. This is because an excessive amount of brake fluid is supplied from the master cylinder MC to the hydraulic pump HP
As a result, the sinking of the brake pedal BP and the fluctuation of the output signal of the hydraulic pressure sensor PS can be suppressed as much as possible. Then, step 2
The program proceeds to 14, and after a brake assist braking force distribution control amount calculation described later is performed, the process returns to the main routine of FIG.

If it is determined in step 215 that the conditions for terminating the brake assist control are satisfied, step 217 is executed.
The control flag FL is set to the end specifying control in-progress flag F3. Next, in step 218, an end specifying control operation is executed. That is, the change rate of the master cylinder fluid pressure (decrease rate) DPmc at the time when the control end is required.
, The duty Dce of the on-off valve SC * provided for the end specifying control is set. That is, DPmc ≦ DPmc1
(For example, 100 kgf / cm ² / sec), Dce is Dce
2 (for example, 85%), DPmc1 <DPmc ≦ DPm
In the case of c2 (for example, 150 kgf / cm ² / sec), Dce is changed to Dce1 (for example, 20%) smaller than Dce2,
When Pmc2 <DPmc, Dce is set to 0%. That is, the duty Dce of the on-off valve SC *
In order to reflect the driver's intention, the value is increased when the decrease rate of the master cylinder hydraulic pressure is large. Further, the execution time Te of the end specifying control is a predetermined time (for example, 0.2 sec).
Is set to

Then, the process proceeds to a step 219, wherein the duty of the on-off valve SC * for the end specifying control is set to the value selected in the step 218, and the duty of the on-off valve SI * is set to 0%. Next, at step 220, the execution time Te after the brake assist control ends.
Is determined, and if not, the process returns to the main routine of FIG.
After the control flag FL is set to F0,
Return to the main routine.

On the other hand, if it is determined in step 202 that the BA control start condition is not satisfied (that is, the end specifying control is being performed or not controlled), the process proceeds to step 222, where the control flag FL determines whether the end specifying control flag F3 has been set. It is determined whether the answer is NO, and if so, after steps 219 to 221 are executed again, the process returns to the main routine of FIG. Step 2
If it is determined in step 22 that the control flag FL is not F3, it means non-control, and the process returns to the main routine in FIG.

As described above, if the vehicle is turning when it is determined that the brake assist control needs to be started, step 214 is executed.
Of the brake assist braking force distribution control amount is executed.

Referring to FIG. 5, the calculation of the brake assist braking force distribution control amount in step 214 will be described.

First, at step 401, it is determined whether or not the estimated vehicle body deceleration DVso is equal to or greater than a predetermined value. If it is determined that the estimated vehicle deceleration DVso is less than the predetermined value, the process proceeds to step 403, where it is determined whether the vehicle is turning. If it is determined that the vehicle is turning, the process proceeds to step 402. If it is determined that the vehicle is not turning, the process proceeds to step 406. After the target slip ratio Sb ** is set to 0, the process returns to the subroutine of FIG.

In step 402, the target slip ratio Sb ** of each wheel is set according to the vehicle deceleration deviation ΔG. That is, the target slip ratio Sb ** of each wheel is set to be larger as the vehicle deceleration deviation ΔG is larger. Further, in order to ensure vehicle stability, the target slip ratio SbR * of the rear wheels is set smaller than the target slip ratio SbF * of the front wheels.

After the processing of step 402, step 404
The correction amount ΔSb ** of the target slip ratio Sb ** set in step 402 is set according to the lateral acceleration Gy of the vehicle. That is, when the vehicle lateral acceleration Gy is equal to or more than a positive predetermined value (that is, when the vehicle is turning left), the vehicle lateral acceleration Gy
The correction amount ΔSb * R of the right front and rear wheels that are the turning outer wheels is set to a positive value, and the correction amount ΔSb * L of the left front and rear wheels that are the turning inner wheels is set to 0 in accordance with the absolute value of You. Here, the correction amount ΔSbRR for the right front wheel is the correction amount ΔSbRR for the right rear wheel.
Set to greater than Further, when the vehicle lateral acceleration Gy is equal to or less than a negative predetermined value (that is, when the vehicle is turning right), the correction amount of the front left and right wheels that are the turning outer wheels is determined according to the magnitude of the absolute value of the vehicle lateral acceleration Gy. ΔSb * L is set to a positive value, and the correction amount ΔSb * R for the front right and left wheels, which are the turning inside wheels, is set to 0. Here, the correction amount ΔSbFL for the left front wheel is set to be larger than the correction amount ΔSbRL for the left rear wheel. When the vehicle lateral acceleration Gy is equal to or more than the negative predetermined value and less than the positive predetermined value (when the vehicle is not turning), the correction amount ΔS for all wheels is used.
b ** is set to 0. Then, the process proceeds to a step 405, wherein the target slip ratios Sb ** of all the wheels are set to MAX (0, Sb
**-ΔSb **), and returns to the subroutine of FIG. Here, MAX (A, B) means the larger of A and B. Therefore, the target slip ratio of the turning outer wheel is set smaller than the target slip ratio of the turning inner wheel.

In step 404, the correction amount for the front and rear wheels outside the turning is set to a positive value. However, the correction amount for the rear wheels outside the turning may be set to zero.

As shown in FIG. 5, if the vehicle is turning when it is determined that the brake assist control needs to be started, the target slip ratio of the turning outer wheel is corrected to be small according to the turning state. As a result, the braking force automatically applied to the turning outer wheel by the brake assist control is limited (suppressed).

Also, when the vehicle turns during the brake assist control, the target slip ratio of the turning outer wheel is corrected to be small according to the turning state. As a result, the braking force applied to the turning outer wheel by the brake assist control is limited.

As can be seen from FIGS. 4 and 5, when it is determined that the brake assist control is required during the turning of the vehicle, the target slip ratio of each wheel is set in the first calculation cycle, and the control shifts from the start specifying control to the present control. The target slip rate is maintained until the operation is completed.

Next, referring to FIGS. 6 and 7, details of the hydraulic servo control in step 110 of FIG. 3 will be described. Here, the drive control of the on-off valves SI * and SC * and the wheel Slip rate servo control of the cylinder hydraulic pressure is performed.

First, at step 301, it is determined whether or not the braking steering control mode is set, and if so, the routine proceeds to step 302, where the preset target slip ratio Sv ** for braking steering control is set to the target slip ratio of each wheel. If the target slip ratio St ** of each wheel is set to 0, the process proceeds to step 304. In step 304, it is determined whether or not the brake assist braking force distribution control is being performed. If so, in step 305 the target slip ratio St ** for the brake assist braking force distribution control set in step 405 in FIG. After the target slip rate Sb ** is added, the process proceeds to step 306, and otherwise, the process directly proceeds to step 306. Step 30
At 6, the target slip ratio Sd ** for the longitudinal braking force distribution control, the target slip ratio Sr ** for the traction control, and the target slip ratio Ss ** for the anti-skid control are added to the target slip ratio St **. Thus, the target slip ratio St ** is updated. Note that the values of Sb **, Sd **, Sr **, and Ss ** are set to 0 when the corresponding control is not performed.

Then, in step 307, the slip ratio deviation ΔSt ** is calculated for each wheel, and in step 308, the vehicle body acceleration deviation ΔDVso ** is calculated.
Specifically, in step 307, the difference between the target slip rate St ** of each wheel and the actual slip rate Sa ** is calculated to determine a slip rate deviation ΔSt ** (ΔSt ** = St **).
-Sa **). In step 308, the difference between the vehicle deceleration DVso at the position of the center of gravity of the vehicle and the wheel acceleration DVw ** of the wheel to be controlled is calculated, and the vehicle deceleration deviation ΔD
Vso ** is required. At this time, the actual slip ratio Sa ** of each wheel and the vehicle body deceleration deviation ΔDVso ** are calculated differently depending on the control mode such as anti-skid control, traction control, etc., but the description thereof will be omitted.

Then, the routine proceeds to step 309, where the slip ratio deviation ΔSt ** is compared with a predetermined value Ka. If the difference is equal to or larger than the predetermined value Ka, the integrated value of the slip ratio deviation ΔSt ** is updated in step 311. That is, the current slip ratio deviation ΔS
The value obtained by multiplying t ** by the gain GI ** is added to the previous slip ratio deviation integrated value IΔSt **, and the current slip ratio deviation integrated value IΔSt ** is obtained. Slip ratio deviation | ΔSt *
When * | is smaller than the predetermined value Ka, the slip ratio deviation integrated value IΔSt ** is cleared (0) in step 310. Next, in steps 312 to 315, the slip ratio deviation integrated value IΔSt ** is not more than the upper limit Kb and the lower limit K
c is limited to a value greater than or equal to
When the value is lower than the lower limit value Kc, the value is set to Kc, and the process proceeds to step 316.

In step 316, one parameter Y used for brake fluid pressure control in each control mode is set.
** is calculated as Gs ** · (ΔSt ** + IΔSt **). Further, in step 317, another parameter X ** to be provided for the brake fluid pressure control is calculated as Gd ** · ΔDVso **. The gains Gs ** and Gd ** are fixed gains set in advance.

Thereafter, the routine proceeds to step 318, where the hydraulic mode is set for each wheel according to the control map shown in FIG. 9 based on the parameters X ** and Y **. In FIG. 9, each region of a rapid pressure reduction region, a pulse pressure reduction region, a holding region, a pulse pressure increase region, and a rapid pressure increase region is set in advance.
In accordance with the values of the parameters X ** and Y **, it is determined which area the area corresponds to. In the non-control state, the hydraulic mode is not set (the solenoid is off).

If the area determined this time in step 318 is switched from pressure increase to pressure reduction or pressure reduction to pressure increase with respect to the area determined last time, the fall or rise of the brake fluid pressure is made smooth. Since it is necessary, the pressure increase / decrease compensation processing is performed in step 319. For example, when switching from the rapid pressure reduction mode to the pulse pressure increase mode,
Sudden pressure increase control is performed, and the time is determined based on the duration of the immediately previous rapid pressure reduction mode. Then, step 3
At 20, the control mode for each wheel is set in relation to the other wheels. For example, rear row select control is performed, and hydraulic pressure control is performed on the rear wheels RR and RL based on the low-speed wheels.

In step 321, the open / close valves SI * and SC * are set based on the duty Di of the open / close valve SI * and the duty Dc of the open / close valve SC * set in steps 206, 209, 213 and 219 of FIG. Open / close drive (that is, duty drive) and electric motor M
Is also driven. Further, the solenoids of the on-off valves PC1 to PC8 are also driven according to the above-mentioned hydraulic pressure control mode, pressure increase / decrease compensation processing, and each wheel control mode processing, and the braking force of each wheel is controlled.

In the present embodiment, the brake assist control is performed by suctioning and increasing the master cylinder hydraulic pressure by the hydraulic pump and supplying it to the wheel cylinder. However, the present invention is not limited to this. is not. The present invention is also applicable to, for example, a type in which high-pressure brake fluid of an accumulator is supplied to a wheel cylinder, and a type in which a negative-pressure booster is automatically operated to supply master cylinder hydraulic pressure to a wheel cylinder.

[0061]

According to the present invention, when it is determined that the brake assist control needs to be started during the turning of the vehicle, the braking force to be automatically applied to the outer wheels of the turning is limited. Is started, excessive understeer can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment of a braking control device of the present invention.

FIG. 2 is a configuration diagram illustrating an example of a brake fluid pressure control device of FIG. 1;

FIG. 3 is a flowchart showing an entire vehicle braking control according to the embodiment of the present invention.

FIG. 4 is a flowchart showing details of the brake assist control of FIG. 3;

FIG. 5 is a flowchart showing details of a brake assist braking force distribution control amount calculation of FIG. 4;

FIG. 6 is a flowchart showing details of hydraulic servo control in FIG. 3;

FIG. 7 is a flowchart showing details of hydraulic servo control in FIG. 3;

FIG. 8 is a graph showing details of a brake assist control amount calculation of FIG. 4;

FIG. 9 is a graph showing a relationship between a parameter used for brake fluid pressure control and a fluid pressure mode in the embodiment.

[Explanation of symbols]

 FR, FL, RR, RL Wheel Wfr, Wfl, Wrr, Wrl Wheel cylinder BP Brake pedal MC Master cylinder MF Main hydraulic pressure passage SC1, SC2 First open / close valve HP1, HP2 Hydraulic pump MFc Auxiliary hydraulic pressure passage SI1, SI2 Second on-off valve PS Hydraulic pressure sensor (brake operation detecting means) PC1 to PC8 On-off valve ECU Electronic control unit

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoshi Yokoyama 2-1-1 Asahi-cho, Kariya-shi, Aichi Prefecture Aisin Seiki Co., Ltd.

Claims (4)

[Claims] A brake operation detecting means for detecting an operation amount or an operation speed of a brake pedal; a start determining means for determining whether or not to start brake assist control based on a detection result of the brake operation detecting means; A braking means for automatically applying a braking force to all wheels of the vehicle when the means determines that it is necessary to start the brake assist control. When the turn determination means determines that the vehicle is turning, and the start determination means determines that it is necessary to start the brake assist control, the control means includes: A braking control device for a vehicle, wherein a braking force automatically applied to a turning outer wheel is limited. 2. The actual slip ratio calculation device according to claim 1, wherein a wheel speed detection device detects a rotation speed of each wheel of the vehicle, and calculates an actual slip ratio of each wheel according to a detection result of the wheel speed detection device. Means, an actual deceleration detection means for detecting the actual deceleration of the vehicle, the control means, a target deceleration setting means for setting a target deceleration of the vehicle based on the detection result of the brake operation detection means, Deviation calculating means for calculating a deviation between the actual deceleration of the vehicle and the target deceleration, target slip rate setting means for setting a target slip rate for each wheel according to the deviation, If the start determination means determines that the brake assist control needs to be started during the determination, the start determination means has target slip rate correction means for correcting the target slip rate of the turning outer wheel to a small value. Brake control apparatus for a vehicle, characterized in that automatically apply braking force to all the wheels of the vehicle in accordance with the comparison result between the actual slip rate and the target slip ratio or the corrected target slip rate. 3. The vehicle according to claim 2, wherein the target slip ratio correction means makes a correction amount of a target slip ratio of a front wheel outside the turning outside larger than a correction amount of a target slip ratio of a rear wheel outside the turning side. Brake control device. 4. The braking control device for a vehicle according to claim 2, wherein the target slip ratio correction means sets a correction amount of a target slip ratio of a turning outer wheel according to a turning state.