JP2001010475A - Vehicle motion control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effect smooth control by appropriately applying braking forces to rear wheels even if the friction coefficient of a road surface varies during understeer restraining control. SOLUTION: When an excessive understeer occurs while a vehicle is turning, a braking force control means BR applies braking forces to at least rear wheels RR, RL to effect control for restraining the understeer. When a friction coefficient estimated by a friction coefficient estimating means FE is greater than a predetermined reference value, braking forces are applied to the rear wheels RR, RL on both sides, and when the friction coefficient estimated is not greater than the reference value, the braking force is applied only to the rear wheel located inward of a turn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motion control device for a vehicle, and more particularly, to applying a braking force to each wheel during vehicle motion including turning of the vehicle, regardless of whether a brake pedal is operated. The present invention relates to a vehicle motion control device for stabilizing the motion state of a vehicle.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a means for directly controlling a turning moment by controlling a left and right difference of a braking force as a means for controlling a motion characteristic of a vehicle, in particular, a turning characteristic. For example, in Japanese Patent Application Laid-Open No. 9-164932,
When it is determined that the vehicle is excessively oversteering while turning, the braking force is applied to each wheel of the vehicle so as to generate an outward moment with respect to the vehicle, the oversteer suppression control is performed, and the vehicle is excessively steered while turning. A motion control device is disclosed which applies a braking force to each wheel of a vehicle so as to generate an inward moment on the vehicle when it is determined that the vehicle is understeer, and performs understeer suppression control. This publication proposes, in particular, performing correction control so that the braking force applied to each wheel increases or decreases in accordance with the estimated change rate of the road surface friction coefficient.

Japanese Patent Application Laid-Open No. 9-109852 relates to a conventional behavior control device described in Japanese Patent Application Laid-Open No. 6-24304. When the braking force is controlled by the drift-out suppression control so that the slip ratio of the turning outer wheel and the inner wheel becomes the same, the lateral force of the turning inner wheel decreases excessively, and especially the drift-out condition occurs. It is an object of the present invention to prevent the braking force of the turning inner rear wheel from becoming excessive in the latter half of the drift-out suppression control because there is a possibility that a spin state is likely to occur in the latter half of the drift-out suppression control toward convergence. . In the same publication, in a vehicle behavior control device that suppresses drift-out by controlling braking force of a rear wheel, a braking force of a turning inner wheel is controlled by a braking force of an outer turning wheel after a point in time during the drift-out suppression control. It has been proposed to make it smaller than the power. In particular,
After a lapse of a predetermined time from the time when the drift-out state amount starts to decrease, the slip ratio of the rear wheel on the inside of the turn is reduced.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 9-109.
In the device described in Japanese Patent Application Laid-Open No. 852/852,
No correspondence is taken according to changes in the road surface friction coefficient as described in JP-A-164932. Therefore, when the road surface friction coefficient is low, stability may be impaired if braking force is applied to both wheels behind the vehicle for the purpose of drift-out suppression control. JP-A-9-10
According to the device described in Japanese Patent No. 9852, the slip ratio of the rear inner wheel is controlled to be small after a predetermined time has elapsed from the time when the drift-out state amount has started to decrease, but the road surface friction coefficient is not necessarily limited. Does not correspond to a change in

Accordingly, the present invention provides a vehicle motion control apparatus for applying a braking force to the rear wheels of a vehicle during understeer suppression control, whereby the braking force is appropriately applied to the rear wheels even when the road surface friction coefficient changes. It is another object of the present invention to smoothly perform understeer suppression control.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, a braking force is applied to each of a front wheel and a rear wheel of a vehicle according to at least an operation of a brake pedal. Controlling the braking force applying means based on the determination result of the vehicle motion state determining means for determining stability during vehicle motion including turning of the vehicle, and controlling the braking force applying means. A braking control means for controlling a vehicle so as to suppress understeer by applying a braking force to at least rear wheels of the vehicle when it is determined that the vehicle is excessively understeered during turning. , A friction coefficient estimating means for estimating a friction coefficient of a traveling road surface of the vehicle, wherein the braking force control means has an estimated friction coefficient of the friction coefficient estimating means larger than a predetermined reference value. In some cases, braking force is applied to the rear wheels on both sides of the vehicle, and when the estimated friction coefficient of the friction coefficient estimating means is equal to or less than a predetermined reference value, braking force is applied only to the rear wheels inside the turning of the vehicle. It is configured so that

Further, according to a second aspect of the present invention, a wheel speed detecting means for detecting a wheel speed of each of the wheels, and a slip ratio of each of the wheels is calculated based on at least the wheel speed detected by the wheel speed detecting means. And a target slip ratio setting unit configured to set a target slip ratio for each of the wheels based on a determination result of the vehicle motion state determination unit. Based on the deviation between the target slip rate set by the slip rate setting means and the slip rate calculated by the slip rate calculation means,
In addition to controlling the braking force applied to each wheel, when controlling the braking force on the rear wheels of the vehicle, when the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the rear wheel on the outside of the turn, the estimated friction is determined. The braking force applied to the rear wheel outside the turning is controlled based on the value obtained by reducing the target slip ratio in accordance with the decrease in the coefficient, and the estimated friction coefficient of the friction coefficient estimating means is adjusted for the rear wheel outside the turning. When the value is smaller than the reference value for the rear wheel on the inside of the turn set to be smaller than the reference value, the target slip ratio for the rear wheel on the inside of the turn set by the target slip ratio setting means decreases in accordance with the decrease in the estimated friction coefficient. It is preferable that the braking force applied to the rear inner wheel is controlled based on the set value.

According to a third aspect of the present invention, when the braking force is controlled by the braking force control means, the estimated friction coefficient of the friction coefficient estimating means is smaller than a front wheel reference value. In some cases, the braking force applied to the front outside wheel of the vehicle on the outside of the turn is controlled based on a value obtained by reducing the target slip ratio for the front wheel on the outside of the turn set by the target slip ratio setting means in accordance with the decrease in the estimated friction coefficient. It is good to be constituted as follows.

The vehicle speed of the vehicle may be estimated based on the wheel speed detected by the wheel speed detecting means, and the slip ratio may be calculated based on the estimated vehicle speed and the detected wheel speed. Further, the friction coefficient estimating means may be configured to detect a lateral acceleration and a longitudinal acceleration of the vehicle and calculate a friction coefficient based on the detection results.

[0010]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a motion control device according to the present invention, in which a braking force is applied to front wheels FR, FL and rear wheels RR, RL of a vehicle according to at least an operation of a brake pedal BP. A power application means BF; a vehicle movement state determination means VC for determining stability during vehicle movement including turning of the vehicle; and a braking force application means B based on the determination result of the vehicle movement state determination means VC.
A braking force control means BR for controlling the vehicle wheel F to control understeer by applying a braking force to at least rear wheels RR and RL of the vehicle when it is determined that the vehicle is excessively understeering during turning. Is provided with friction coefficient estimating means FE for estimating the friction coefficient of the traveling road surface. And
When the estimated friction coefficient of the friction coefficient estimating means FE is larger than a predetermined reference value, the braking force control means BR applies braking force to the rear wheels RR and RL on both sides, and the friction coefficient estimating means F
When the estimated friction coefficient of E is equal to or smaller than a predetermined reference value, the braking force is applied only to the rear wheel inside the turning.

In this embodiment, wheel speed detecting means WD for detecting the wheel speed of each wheel, slip rate calculating means AS for calculating a slip rate of each wheel based on at least the detected wheel speed, and vehicle motion state determination A target slip ratio setting means DS for setting a target slip ratio for each wheel based on the determination result of the means VC is provided. The braking force control means BR controls the braking force to be applied to each wheel based on the difference between the target slip rate set by the target slip rate setting means DS and the slip rate calculated by the slip rate calculation means AS. In the braking force control for the wheels RR and RL, when the estimated friction coefficient of the friction coefficient estimating means FE is smaller than the reference value for the rear wheel on the outside of the turning, the target slip ratio is reduced according to the decrease of the estimated friction coefficient. The braking force applied to the rear wheel on the outside of the turn is controlled based on the reference value, and the estimated friction coefficient of the friction coefficient estimating means FE is smaller than the reference value for the rear wheel on the inside of the turn set to be smaller than the reference value for the rear wheel on the outside of the turn. , The target slip ratio for the rear wheel on the inside of the turn set by the target slip ratio setting means DS is assigned to the rear wheel on the inside of the turn based on the value reduced in accordance with the decrease in the estimated friction coefficient. It is configured to control the braking force.

Further, the braking force control means BR performs a friction coefficient estimating means FE when controlling the braking force on the front wheels on the outside of the turn.
When the estimated friction coefficient is smaller than the front wheel reference value, the target slip ratio for the front wheel outside the turning set by the target slip ratio setting means DS is reduced based on the value obtained by decreasing the estimated friction coefficient in accordance with the decrease in the estimated friction coefficient. It is configured to control the braking force applied to the front wheels.

FIG. 2 shows an overall structure of a vehicle including the motion control device. An engine EG is an internal combustion engine provided with a throttle control device TH and a fuel injection device FI. In the throttle control device TH, an accelerator pedal AP is used. The main throttle opening of the main throttle valve MT is controlled in accordance with the operation of. In addition, according to the output of the electronic control unit ECU, the sub-throttle valve ST of the throttle control unit TH is driven to control the sub-throttle opening, and the fuel injection device FI is driven to control the fuel injection amount. It is configured. The engine EG of the present embodiment includes a shift control device GS and a differential gear DF.
Are connected to the wheels RL and RR at the rear of the vehicle via
A so-called rear-wheel drive system is configured. As for the braking system, wheel cylinders Wfl, Wfr, Wrl, Wrr are mounted on wheels FL, FR, RL, RR, respectively.
A brake fluid pressure control device BC is connected to these wheel cylinders Wfl and the like. The wheel FL indicates the front left wheel when viewed from the driver's seat, and hereinafter the wheel FR indicates the front right wheel.
The wheel RL indicates a rear left wheel, and the wheel RR indicates a rear right wheel. In the present embodiment, a so-called X pipe is configured.

Wheel speed sensors WS1 to WS4 are arranged on the wheels FL, FR, RL, RR, and are connected to the electronic control unit ECU. The rotation speed of each wheel, that is, the number of pulses proportional to the wheel speed, is measured. Is input to the electronic control unit ECU. Further, the brake switch BS which is turned on when the brake pedal BP is depressed, the steering angle θ of the wheels FL and FR in front of the vehicle.
The front wheel steering angle sensor SSf for detecting f, the lateral acceleration sensor YG for detecting the lateral acceleration of the vehicle, and the changing speed of the vehicle rotation angle (yaw angle) around a vertical axis passing through the center of gravity of the vehicle, that is, the yaw angular speed (yaw rate) is detected. A yaw rate sensor YS or the like is connected to the electronic control unit ECU.

The electronic control unit ECU of the present embodiment has a configuration shown in FIG.
As shown in FIG. 1, a microcomputer CMP comprising a processing unit CPU, a memory ROM, a RAM, an input port IPT, an output port OPT, and the like, which are interconnected via a bus, is provided. The wheel speed sensor WS
1 to WS4, brake switch BS, front wheel steering angle sensor SSf, yaw rate sensor YS, lateral acceleration sensor YG, etc.
It is configured to be input from the PT to the processing unit CPU. Further, control signals are output from the output port OPT to the throttle control device TH and the brake fluid pressure control device BC via the drive circuit ACT.

In the microcomputer CMP,
The memory ROM stores programs to be used for various processes including the flowcharts shown in FIGS. 3 to 5, the processing unit CPU executes the programs while an ignition switch (not shown) is closed, and the memory RAM stores 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.

In this embodiment constructed as described above, a series of processes such as braking steering control and anti-skid control are performed by the electronic control unit ECU, and when an ignition switch (not shown) is closed. The execution of the program corresponding to the flowcharts of FIG. 3 to FIG. 5 starts. FIG. 3 shows the entire control operation of the vehicle. First, in step 101, the microcomputer CMP is initialized and various calculated values are cleared. Next, step 102
, The detection signals of the wheel speed sensors WS1 to WS4 are read, the detection signal of the front wheel steering angle sensor SSf (steering angle θf), the detected yaw rate γa of the yaw rate sensor YS, and the detected acceleration of the lateral acceleration sensor YG (ie, Acceleration, which is represented by Gya).

Next, the routine proceeds to step 103, where the wheel speeds Vw ** of each wheel (** represents each wheel FR etc.) are calculated, and these are differentiated to obtain the wheel acceleration DVw ** of each wheel. Can be Subsequently, in step 104, the maximum value of the wheel speed Vw ** of each wheel is calculated as the estimated vehicle speed Vso at the position of the center of gravity of the vehicle (Vso = MAX (Vw **)). Further, an estimated vehicle speed Vso ** is obtained for each wheel based on the wheel speed Vw ** of each wheel, and if necessary, normalization is performed to reduce an error based on a difference between the inner and outer wheels when the vehicle turns. . Further, the estimated vehicle speed Vso is differentiated, and an estimated vehicle acceleration (including an estimated vehicle deceleration having the opposite sign) DVso at the position of the vehicle center of gravity is calculated.

Next, at step 105, the wheel speed V of each wheel obtained at steps 102 and 103 is calculated.
Based on w ** and the estimated vehicle speed Vso ** (or the normalized estimated vehicle speed), the actual slip ratio Sa ** of each wheel is Sa ** =
(Vso **-Vw **) / Vso **. next,
In step 106, based on the estimated vehicle body acceleration DVso at the position of the center of gravity of the vehicle and the actual lateral acceleration Gya of the detection signal of the lateral acceleration sensor YG, the road surface friction coefficient μ is approximately (DVso ² +
Gya ² ) calculated as ^1/2 . Alternatively, based on the peak value of the longitudinal acceleration and the peak value of the lateral acceleration within a predetermined time, the calculation can be performed using the same approximate expression as described above. Further, as means for detecting the road surface friction coefficient, various means such as a sensor for directly detecting the road surface friction coefficient can be used.

Subsequently, at step 108, the vehicle body slip angular velocity Dβ is calculated, and the vehicle body slip angle β is calculated. The vehicle body slip angle β represents the slip of the vehicle body with respect to the traveling direction of the vehicle as an angle, and can be calculated and estimated as follows. That is, the vehicle body side slip angular velocity Dβ is a differential value dβ / dt of the vehicle body side slip angle β,
In step 107, it can be obtained as Dβ = Gya / Vso−γa, which is integrated in step 108 and β = ∫
The vehicle body slip angle β can be obtained as (Gya / Vso−γa) dt.

Then, the routine proceeds to step 109, where a braking steering control mode is set, and a target slip ratio to be used for braking steering control is set as will be described later. The braking force on each wheel is controlled. This braking steering control is superimposed on control in all control modes described later.
Thereafter, the process proceeds to step 110, where it is determined whether or not the anti-skid control start condition is satisfied. If the start condition is satisfied and it is determined that the anti-skid control is to be started at the time of braking steering, the initial specifying control is immediately terminated and step 111 is performed. Is set to a control mode for performing both braking steering control and anti-skid control.

When it is determined in step 110 that the anti-skid control start condition is not satisfied, the process proceeds to step 112, where it is determined whether the front-rear braking force distribution control start condition is satisfied. When it is determined that the braking force distribution control is started, the routine proceeds to step 113, where a control mode for performing both the braking steering control and the longitudinal braking force distribution control is set. Is satisfied or not. If it is determined that the traction control is started during the brake steering control, the control mode is set to perform both the brake steering control and the traction control in step 115, and if neither control is determined to be started during the brake steering control, In step 116, it is determined whether the brake steering control start condition is satisfied.

If it is determined in step 116 that the braking steering control has been started, the routine proceeds to step 117, where a control mode in which only the braking steering control is performed is set. Then, after performing the hydraulic servo control in step 118 based on these control modes, the process returns to step 102. In the front / rear braking force distribution control mode, the distribution of the braking force applied to the rear wheels to the braking force applied to the front wheels is controlled so as to maintain stability of the vehicle during braking of the vehicle. Step 116
If it is determined that the conditions for starting the braking steering control are not satisfied in step, the solenoids of all the solenoid valves are turned off in step 119, and the process returns to step. It should be noted that, based on steps 111, 113, 115, and 117, the sub-throttle opening of the throttle control device TH is adjusted as necessary according to the vehicle motion state, the output of the engine EG is reduced, and the driving force is limited. .

FIG. 4 shows the specific processing contents of the braking steering control in step 109 of FIG. 3. The braking steering control includes oversteer suppression control and understeer suppression control. And / or a target slip ratio corresponding to the understeer suppression control is set. First, in steps 201 and 202, the start and end of the oversteer suppression control and the understeer suppression control are determined.

The start / end determination of the oversteer suppression control performed in step 201 is performed based on whether or not the vehicle is in a control region (a region outside a pair of parallel dashed lines) shown in FIG. That is, if the vehicle enters the control region according to the values of the vehicle body slip angle β and the vehicle body slip angular velocity Dβ at the time of the determination, the oversteer suppression control is started, and if the vehicle leaves the control region, the oversteer suppression control is ended. Control is performed as indicated by the arrow curve. In addition, the braking force of each wheel is controlled so that the control amount increases from the boundary indicated by the dashed line in FIG. 8 to the outside of the control region.

On the other hand, the start / end determination of the understeer suppression control performed in step 202 is performed based on whether or not the vehicle is in a control area indicated by oblique lines in FIG. That is,
At the time of determination, the actual lateral acceleration G with respect to the target lateral acceleration Gyt
In response to the change of ya, if the vehicle deviates from the ideal state shown by the dashed line and enters the control region, understeer suppression control is started,
When the vehicle exits the control region, the understeer suppression control is terminated, and the control is performed as indicated by the arrow curve in FIG.

Subsequently, it is determined in step 203 whether or not the oversteer suppression control is being controlled, and if not, it is determined in step 204 whether or not the understeer suppression control is being controlled. If not, the process returns to the main routine. When it is determined in step 204 that the vehicle is understeer suppression control, the process proceeds to step 205, and the target slip ratio of each wheel is set for understeer suppression control described later. If it is determined in step 203 that the vehicle is in the oversteer suppression control, the process proceeds to step 206 to determine whether or not the vehicle is understeer suppression control. Is set for If it is determined in step 206 that the understeer suppression control is being performed, the oversteer suppression control and the understeer suppression control are performed simultaneously, and in step 208, a target slip ratio for simultaneous control is set.

The target slip ratio of each wheel when understeer suppression control is performed in step 205 is as follows:
It is a value obtained by multiplying the standard target slip ratio by a correction coefficient. That is, the target slip ratio of the front wheel on the outside of the turn is a value (Kfo · Stuf) obtained by multiplying the standard target slip ratio Stufo by the correction coefficient Kfo.
o) is set. Then, the target slip rate of the rear wheel on the outside of the turn is set to a value (Kro · Struro) obtained by multiplying the standard target slip rate Sturo by the correction coefficient Kro, and the target slip rate of the rear wheel on the inside of the turn is set to the standard target slip rate Sturi. It is set to a value (Kri · Sturi) multiplied by the correction coefficient Kri. As for the sign of the slip ratio (S) shown here, "t" represents "target" and is compared with "a" representing "actual measurement" described later.
“u” represents “understeer suppression control”, “r” represents “rear wheel”, “o” represents “outside”, and “i” represents “inside”. The correction coefficients Kfo, Kro, and Kri will be described later with reference to FIGS.

On the other hand, when the oversteer suppression control is performed in step 207, the target slip ratio of each wheel is set such that the front wheel on the outer side of the turn is set to Stefo and the rear wheel on the inner side of the turn is set to Steri. The latter target slip ratio Steri is set to 0 in the present embodiment. Where "e"
Represents “oversteer suppression control”. The target slip ratio of each wheel in step 208 is set to Stefo for the front wheel on the outside of the turn, but Kro is set for the rear wheel on the outside of the turn.
-Set to Sturo, the rear wheels inside the turn are set to Kri and Sturi, respectively. That is, when the oversteer suppression control and the understeer suppression control are performed at the same time, the front wheels on the outside of the turn are set in the same manner as the target slip ratio of the oversteer suppression control, and the rear wheels are all set in the same manner as the target slip ratio of the understeer suppression control. Is set. In any case, the front wheels on the inside of the turn (that is, the driven wheels in the rear-wheel drive vehicle) are not controlled because the estimated vehicle speed is calculated.

To set the target slip ratio for oversteer suppression control in step 207, the vehicle body slip angle β and the vehicle body slip angular speed Dβ are used. In setting the standard target slip ratio in the understeer suppression control, the target lateral acceleration is set. The difference between Gyt and the actual lateral acceleration Gya is used. For example, the target slip ratio Stefo of the front wheel on the outside of the turn provided for the oversteer suppression control is Stefo = K1 · β
+ K2 · Dβ, and the target slip ratio Steri of the rear wheel inside the turning is set to “0”. Here, K1, K2
Is a constant, which is set to a value for controlling the pressing direction (direction in which the braking force is increased).

On the other hand, the standard target slip ratio provided for the understeer suppression control includes a target lateral acceleration Gyt and an actual lateral acceleration Gyt.
It is set as follows based on the deviation ΔGy of ya. That is, the standard target slip ratio Stufo for the front wheel on the outside of the turn.
Is set to K3 ・ ΔGy, and the constant K3 is set to a value for controlling the pressurizing direction (or the depressurizing direction). Similarly, the standard target slip ratio Sturo for the rear wheel on the outside of the turn is
Is set to K4 ・ ΔGy, and the constant K4 is set to a value for controlling the pressing direction. Then, the standard target slip ratio Sturi for the rear wheel on the inside of the turn is set to K5 · ΔGy, and the constant K5 is set to a value for controlling the pressing direction.

Here, the correction coefficients Kro, Kri, and K used for the understeer suppression control in steps 205 and 208.
fo is set as shown in FIGS. First, as shown by a solid line in FIG. 6, the correction coefficient Kro for the rear wheel outside the turning is such that the road surface friction coefficient μ estimated in step 106 is larger than a reference value Kμo for the rear wheel outside the turning (for example, 0.5). , The correction coefficient Kro is set to 1, and the standard target slip ratio Sturo is used as it is as the target slip ratio. When the road surface friction coefficient μ is smaller than the turning-side rear wheel reference value Kμo, the correction coefficient Kro decreases in accordance with the decrease in the road surface friction coefficient μ, and the rear wheel reference value Kμr (for example, 0.3
) Is set to be 0. That is, when the road surface friction coefficient μ is smaller than the rear wheel reference value Kμr, the braking force is not applied to the rear wheel outside the turning, and the braking force is applied only to the rear wheel inside the turning.

On the other hand, the correction coefficient Kri for the rear wheel on the inside of the turn is, as shown by the broken line in FIG. 6, the road surface friction coefficient μ is larger than the reference value Kμi (for example, 0.2) for the rear wheel on the inside of the turn. In some cases, the correction coefficient Kri is set to 1, and the standard target slip ratio Sturi is used as it is. When the road surface friction coefficient μ is smaller than the rear wheel reference value Kμi on the inside of the turn, the correction coefficient Kri decreases according to the decrease of the road surface friction coefficient μ, and the road surface friction coefficient μ becomes zero and the correction coefficient Kri becomes zero. Is set to When the road surface friction coefficient μ becomes smaller than the rear wheel reference value Kμr, the target slip ratio for the rear wheel on the outside of the turn during the understeer suppression control is set to 0, and the target slip ratio for only the rear wheel on the inside of the turn is set. The braking force control according to Kri · Sturi is performed, and the target slip ratio Kri · S
turi is set to a value that decreases as the road surface friction coefficient μ decreases.

As shown in FIG. 7, the correction coefficient Kfo used for the understeer suppression control of the front wheel on the outside of the turn is 1 when the road surface friction coefficient μ is larger than the front wheel reference value Kμf (for example, 0.3). And the standard target slip ratio Stu
fo and Stufi are used as they are. When the road surface friction coefficient μ is smaller than the front wheel reference value Kμf, the road surface friction coefficient μ
The correction coefficient Kfo decreases in accordance with the decrease of the reference value, and is set to, for example, 0 at the same value (for example, 0.2) as the rear wheel reference value Kμi on the inside of the turn.

FIG. 5 shows the processing of the hydraulic servo control performed in step 118 of FIG. 3. The slip ratio servo control of the wheel cylinder hydraulic pressure is performed for each wheel. First, steps 205, 207 or 20 described above are performed.
The target slip ratio St ** set in step 8 is used in step 30.
1, and these are read as they are as the target slip rates St ** of the respective wheels.

Subsequently, in step 302, the slip ratio deviation ΔSt ** is calculated for each wheel, and in step 303, the vehicle body acceleration deviation ΔDVso ** is calculated.
In step 302, the target slip ratio S of each wheel
The difference between t ** and the actual slip ratio Sa ** is calculated to determine the slip ratio deviation ΔSt ** (ΔSt ** = St ** − Sa *
*). In step 303, the difference between the estimated vehicle acceleration 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 acceleration deviation ΔDV is calculated.
so ** is required. The actual slip ratio S of each wheel at this time
The calculation of a ** and the vehicle body acceleration deviation ΔDVso ** differ depending on the control mode such as anti-skid control, traction control, etc., but the description thereof will be omitted.

Subsequently, the routine proceeds to step 304, where one parameter Y ** used for the brake fluid pressure control in each control mode is calculated as Gs ** · ΔSt **. Where G
s ** is a gain, which is shown in FIG. 10 according to the vehicle side slip angle β.
Is set as shown by the solid line. Step 305
, Another parameter X used for brake fluid pressure control
** is calculated as Gd ** · ΔDVso **. The gain Gd ** at this time is a constant value as shown by a broken line in FIG. Thereafter, the routine proceeds to step 306, where the hydraulic mode is set for each wheel according to the control map shown in FIG. 11 based on the parameters X ** and Y **. In FIG. 11, respective areas of a rapid pressure reduction area, a pulse pressure reduction area, a holding area, a pulse pressure increase area and a rapid pressure increase area are set in advance, and in step 306, according to the values of the parameters X ** and Y **. ,
It is determined which area corresponds. In the non-control state, the hydraulic mode is not set (solenoid off).

When the region determined in step 306 is the pressure increasing mode, the specific hydraulic mode is set in step 307. In addition, when the region determined (at this time) in step 306 is switched from pressure increase to pressure reduction or pressure reduction to pressure increase with respect to the region determined last time, the brake fluid pressure smoothly falls or rises. In step 308, pressure increase / decrease compensation processing is performed. For example, when switching from the rapid pressure reduction mode to the pulse pressure increase mode, rapid pressure increase control is performed, and the time is determined based on the duration of the immediately preceding rapid pressure reduction mode. In accordance with the hydraulic mode, the specific hydraulic mode, and the pressure increasing / decreasing compensation processing, the driving processing of the hydraulic control solenoid is performed in step 309, the solenoid of the brake hydraulic pressure control device BC is driven, and the braking force of each wheel is controlled. Is controlled. The configuration of the brake fluid pressure control device BC will be described later with reference to FIG.

Then, at step 310, a process of driving the hydraulic pump driving motor in the brake hydraulic pressure control device BC is performed. In the above embodiment, the control is performed based on the slip ratio. However, as the control target, in addition to the slip ratio, a target value corresponding to a braking force applied to each wheel, such as a brake fluid pressure of a wheel cylinder of each wheel. Any value may be used.

FIG. 12 shows a braking system including the 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 low pressure reservoir LRS is driven. , And the master cylinder hydraulic pressure is output to two brake hydraulic systems on the wheels FR and RL and on the wheels FL and RR. The master cylinder MC is a tandem type master cylinder having two pressure chambers. One of the pressure chambers is connected to the brake hydraulic system on the wheels FR and RL, and the other pressure chamber is the brake fluid on the wheels FL and RR. It is connected to the pressure system. The output side of the master cylinder MC is provided with a pressure sensor PS for detecting the output hydraulic pressure (master cylinder hydraulic pressure).

In the brake hydraulic system for the wheels FR and RL of this embodiment, one of the pressure chambers is connected to the wheel cylinders Wfr and Wrl via the main hydraulic path MF and the branch hydraulic paths MFr and MFl, respectively. Have been. Main hydraulic path MF
A normally open first on-off valve SC1 (which functions as a so-called cut-off valve, hereinafter simply referred to as on-off valve SC1) is interposed. One of the pressure chambers is an auxiliary hydraulic pressure path MF.
It is connected between check valves CV5 and CV6 described later via c. A normally closed second on-off valve S is provided in the auxiliary hydraulic pressure path MFc.
I1 (hereinafter simply referred to as on-off valve SI1) is interposed. Each of these on-off valves is constituted by a 2-port 2-position electromagnetic on-off valve. The branch hydraulic pressure paths MFr and MFl are normally open two-port two-position solenoid on-off valves PC1 and PC1, respectively.
2 (hereinafter simply referred to as on-off valves PC1 and PC2). In parallel with these, check valves CV1 and CV1, respectively
V2 is interposed.

The check valves CV1 and CV2 allow the flow of the brake fluid in the direction of the master cylinder MC and limit the flow of the brake fluid in the direction of the wheel cylinders Wfr and Wrl. The brake fluid in the wheel cylinders Wfr and Wrl is supplied to the master cylinder MC via the on-off valve SC1 at the first position (the state shown).
Thus, it is configured to be returned to the low pressure reservoir LRS. Thus, when the brake pedal BP is released, the hydraulic pressure in the wheel cylinders Wfr and Wrl can quickly follow the decrease in hydraulic pressure on the master cylinder MC side. Also,
Normally closed two-port two-position solenoid on-off valves PC5 and PC6 (hereinafter simply referred to as on-off valves PC5 and PC6) are respectively connected to discharge-side branch hydraulic pressure paths RFr and RFl that are connected to and connected to the wheel cylinders Wfr and Wrl. And the discharge hydraulic pressure line RF where the branch hydraulic pressure lines RFr and RFl merge is connected to the reservoir R
It is connected to S1.

In the brake fluid pressure system on the wheels FR and RL, the on-off valves PC1, PC2, PC5 and PC6 constitute a modulator according to the present invention. The branch hydraulic pressure path MF is located upstream of the on-off valves PC1 and PC2.
A hydraulic pump HP1 is interposed in a hydraulic passage MFp that is connected to the pumps r and MFl, and check valves CV5 and CV5 are provided on the suction side thereof.
6 is connected to the reservoir RS1. The discharge side of the hydraulic pump HP1 is connected to the check valve CV7 and the damper D.
They are connected to on-off valves PC1 and PC2 via P1. The hydraulic pump HP1 is driven by one electric motor M together with the hydraulic pump HP2, and is configured to introduce brake fluid from the suction side, increase the pressure to a predetermined pressure, and output the pressure from the discharge side. The reservoir RS1 is provided independently of the low-pressure reservoir LRS of the master cylinder MC, and can also be referred to as an accumulator. The reservoir RS1 includes a piston and a spring, and is configured to store a required amount of brake fluid for various controls. Have been.

The master cylinder MC is connected to a check valve CV5 and a check valve C on the suction side of the hydraulic pump HP1 through a hydraulic passage MFc.
It is connected to V6. The check valve CV5 prevents the flow of the brake fluid to the reservoir RS1, and allows the flow in the reverse direction. Check valves CV6, CV7
Regulates the flow of brake fluid discharged through the hydraulic pump HP1 in a certain direction.
1 are integrally formed. Thus, the on-off valve SI1
Is switched so that communication between the master cylinder MC and the suction side of the hydraulic pump HP1 is interrupted at the normal closed position shown in FIG. 12, and communication between the master cylinder MC and the suction side of the hydraulic pump HP1 is opened at the open position.

Further, in parallel with the on-off valve SC1, the flow of the brake fluid from the master cylinder MC in the direction of the on-off valves PC1, PC2 is restricted, and the brake fluid pressure on the on-off valves PC1, PC2 side becomes the brake fluid on the master cylinder MC side. The relief valve RV1 allows the flow of the brake fluid in the direction of the master cylinder MC when the pressure becomes larger than the pressure difference by a predetermined pressure or more, and allows the flow of the brake fluid in the direction of the wheel cylinders Wfr and Wrl to allow the flow in the opposite direction. A check valve AV1 for inhibiting flow is interposed. When the pressurized brake fluid discharged from the hydraulic pump HP1 becomes larger than the output hydraulic pressure of the master cylinder MC by a predetermined differential pressure or more, the relief valve RV1 supplies the brake fluid to the low-pressure reservoir LRS via the master cylinder MC. The pressure of the discharge brake fluid of the hydraulic pump HP1 is adjusted to a predetermined pressure. Also, the hydraulic pump H
A damper DP1 is disposed on the discharge side of P1, and a proportioning valve PV1 is interposed in a hydraulic path leading to a wheel cylinder Wrl on the rear wheel side.

Similarly, in the brake hydraulic system on the side of the wheels FL and RR, a normally open two-port two-position solenoid valve SC2 and a normally closed two-port, including a reservoir RS2, a damper DP2 and a proportioning valve PV2. 2-position solenoid on-off valve SI2, PC7, PC8, normally open 2 port 2
Position solenoid on-off valves PC3, PC4, check valves CV3, CV
4, CV8 to CV10, a relief valve RV2, and a check valve AV2. The hydraulic pump HP2 is driven by the electric motor M together with the hydraulic pump HP1, and after the electric motor M is started, both the hydraulic pumps HP1 and HP2 are continuously driven.

The on-off valves SC1, SC2, SI1, SI
2 and on-off valves PC1 to PC8 are electronic control units ECU
And various controls including the above-described brake steering control are performed. For example, in order to prevent excessive oversteer, for example, it is necessary to generate a moment countering this. In the brake hydraulic system on the wheels FR and RL, the on-off valve SC1 is controlled during braking steering control.
Is switched to the closed position, the on-off valve SI1 is switched to the open position, the electric motor M is driven, and the hydraulic pump H
The brake fluid is discharged from P1. And on-off valve PC
1, PC2, PC5, and PC6 are appropriately opened and closed by the electronic control unit ECU, and the wheel cylinders Wfr, Wr
1, the pressure of the pulse is increased (slowly increased), reduced or maintained,
The braking force distribution between the front and rear wheels, including the brake fluid pressure systems on the wheels FL and RR, is controlled so as to maintain the course traceability of the vehicle.

[0048]

The present invention has the following effects because it is configured as described above. That is, in the vehicle motion control device of the present invention, when the estimated friction coefficient of the friction coefficient estimating means is larger than the predetermined reference value, braking force is applied to the rear wheels on both sides, and the estimated friction coefficient is equal to or less than the reference value. In this case, the braking force is applied only to the rear wheels inside the turning, so that the braking force can be appropriately applied to the rear wheels even when the road surface friction coefficient changes during the understeer suppression control. As a result, understeer suppression control can be smoothly performed, and a stable vehicle motion state can be maintained.

In particular, according to the second aspect of the present invention, an inexpensive device can appropriately apply braking force to the rear wheels even when the road surface friction coefficient changes during the understeer suppression control. Understeer suppression control can be performed smoothly.

Further, by adopting a structure in which control for the front wheels is also performed, understeer suppression control can be performed more smoothly.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a motion control device according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an embodiment of a motion control device of the present invention.

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

FIG. 4 is a flowchart illustrating a process of setting a target slip ratio used for braking steering control according to the embodiment of the present invention.

FIG. 5 is a flowchart illustrating a hydraulic servo control process according to an embodiment of the present invention.

FIG. 6 is a graph for setting a correction coefficient of a slip ratio for a rear wheel in one embodiment of the present invention.

FIG. 7 is a graph for setting a correction coefficient of a slip ratio for a front wheel in one embodiment of the present invention.

FIG. 8 is a graph showing an oversteer suppression control start / end determination area according to the embodiment of the present invention.

FIG. 9 is a graph showing a start / end determination area of understeer suppression control according to an embodiment of the present invention.

FIG. 10 is a graph showing a parameter calculation gain used for hydraulic pressure control in one embodiment of the present invention.

FIG. 11 is a graph showing a control map provided to one embodiment of the present invention.

FIG. 12 is a configuration diagram showing a hydraulic system of the vehicle motion control device of the present invention.

[Explanation of symbols]

 BP brake pedal, MC master cylinder M electric motor, HP1, HP2 hydraulic pumps RS1, RS2 reservoirs Wfr, Wfl, Wrr, Wrl Wheel cylinders WS1 to WS4 Wheel speed sensors FR, FL, RR, RL Wheels SC1, SC2, SI1, SI2 on-off valve PC1 to PC8 on-off valve EG engine, ECU electronic control unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D045 BB40 CC01 EE21 FF42 GG10 GG25 GG26 GG27 GG28 3D046 BB21 BB31 BB32 EE01 FF10 HH08 HH21 HH23 HH25 HH26 HH36 HH46 JJ02 JJ06

Claims (3)

[Claims] 1. A braking force applying means for applying a braking force to each of a front wheel and a rear wheel of a vehicle according to at least an operation of a brake pedal, and determining stability during vehicle motion including turning of the vehicle. The vehicle motion state determining means and the braking force applying means are controlled based on a result of the determination by the vehicle motion state determining means. When the vehicle is determined to be excessively understeered during turning, at least the rear wheels of the vehicle are controlled. A vehicle motion control device comprising: a braking force control unit that controls the vehicle so as to suppress understeer by applying power; and a friction coefficient estimating unit that estimates a friction coefficient of a traveling road surface of the vehicle. The control means applies a braking force to the rear wheels on both sides of the vehicle when the estimated friction coefficient of the friction coefficient estimation means is larger than a predetermined reference value,
A motion control device for a vehicle, characterized in that a braking force is applied only to a rear wheel inside a turning of the vehicle when an estimated friction coefficient of the friction coefficient estimating means is equal to or smaller than a predetermined reference value. 2. A wheel speed detecting means for detecting a wheel speed of each wheel, a slip rate calculating means for calculating a slip rate of each wheel based on at least a wheel speed detected by the wheel speed detecting means, and the vehicle Target slip rate setting means for setting a target slip rate for each of the wheels based on the determination result of the motion state determining means, wherein the braking force control means determines the target slip rate set by the target slip rate setting means and the target slip rate. The braking force applied to each of the wheels is controlled based on the deviation of the slip ratio calculated by the slip ratio calculating means, and the estimated friction coefficient of the friction coefficient estimating means is changed to the outside of the turning when controlling the braking force on the rear wheels of the vehicle. When it is smaller than the reference value for the rear wheel, the target slip ratio is reduced and applied to the outer rear wheel based on the value obtained by reducing the target slip ratio in accordance with the decrease in the estimated friction coefficient. When the estimated friction coefficient of the friction coefficient estimating means is smaller than the turning inner rear wheel reference value set to be smaller than the turning outer rear wheel reference value, the target slip ratio is reduced. The braking force applied to the rear inner wheel is controlled based on a value obtained by reducing the target slip ratio for the rear inner wheel set by the setting means in accordance with the decrease in the estimated friction coefficient. The vehicle motion control device according to claim 1, wherein 3. The braking force control means, wherein, when controlling the braking force on the front wheels outside the turning of the vehicle, when the estimated friction coefficient of the friction coefficient estimating means is smaller than a front wheel reference value, the target slip ratio setting means. The braking force applied to the front wheels on the outside of turning of the vehicle is controlled based on the target slip ratio for the front wheels on the outside of the turning set in accordance with the decrease in the estimated friction coefficient. The vehicle motion control device according to claim 2, wherein