JPH092220A - Vehicle braking force distribution control method - Google Patents

Abstract

(57) [Summary] [Purpose] Left and right front wheel brakes and left and right front wheel brakes and left and right wheels based on the results of comparison of the value obtained by subtracting the wheel speed of the front wheel from the wheel speed of the rear wheel and the speed difference target value on the left side and the right side, respectively. In the braking force distribution control method for a vehicle in which at least the left and right rear wheel brakes of the rear wheel brakes are individually adjusted to control the front-rear braking force distribution on the left side and the right side, respectively, the steering characteristics during turning braking are While improving, control the front-rear braking force distribution. [Structure] At the time of turning the vehicle, at least the target wheel speed difference value on the turning inner wheel side is changed so as to be larger than that when the vehicle goes straight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to left and right front wheel brakes based on the results of comparing a value obtained by subtracting the wheel speed of a front wheel from a wheel speed of a rear wheel and a wheel speed difference target value on the left side and the right side, respectively. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking force distribution control method for a vehicle, in which at least the left and right rear wheel brakes of the left and right rear wheel brakes are individually adjusted to control the front and rear braking force distributions on the left and right sides, respectively.

[0002]

2. Description of the Related Art Conventionally, there is a technique for achieving an ideal braking force distribution by performing front and rear braking force distribution control so as to eliminate the front and rear wheel speed difference.
It is already known from the publication No. 26584.

[0003]

However, the above-mentioned prior art does not consider the influence on the steering stability due to the brake operation at the time of turning of the vehicle, and the steering characteristic intended by the occupant is controlled by the front and rear braking force distribution control. May not be obtained.

The present invention has been made in view of the above circumstances, and provides a vehicle braking force distribution control method capable of controlling front-rear braking force distribution while improving steering characteristics during turning braking. The purpose is to

[0005]

In order to achieve the above object, the invention according to claim 1 sets a value obtained by subtracting a wheel speed of a front wheel from a wheel speed of a rear wheel and a wheel speed difference target value on the left and right sides. On the basis of the results of comparison with each, at least the left, right front wheel brake and left, right rear wheel brake,
In a vehicle brake force distribution control method in which the brake fluid pressure of the right rear wheel brake is individually adjusted to control the front-rear brake force distribution on the left side and the right side, respectively, when the vehicle is turning, a target wheel speed difference value at least on the turning inner wheel side is set to the vehicle. The feature is that it is changed to be larger than that when going straight.

According to the second aspect of the present invention, in addition to the configuration of the first aspect of the invention, at least the wheel speed difference target value on the turning inner wheel side is made large in accordance with the increase in the vehicle body speed. To set.

According to the third aspect of the present invention, in addition to the configuration of the first aspect of the invention, at least the wheel speed difference target value on the turning inner wheel side is increased by the amount of change in the yaw rate of the vehicle body per unit time. It is set to be large according to.

According to the invention of claim 4, in addition to the configuration of the invention of claim 3, the yaw rate of the vehicle body is calculated based on the speed difference between the left and right driven wheels.

[0009]

According to the structure of the first aspect of the present invention, when the vehicle is turning, at least the turning inner wheel side, which has a small load, responds to the fact that the wheel speed difference target value becomes larger at least on the turning inner wheel side than when the vehicle goes straight. It is possible to reduce the braking force distribution ratio of the rear wheels in order to secure the lateral force of the rear wheels while avoiding the loss of the braking force as a whole, so that the yaw rate changes suddenly according to the braking operation during turning. It can be avoided.

According to the configuration of the invention described in claim 2,
The yaw rate tends to change suddenly with the braking operation during high-speed turning based on the front / rear braking force distribution control, but at least the wheel speed difference target value on the inside wheel turning side becomes large as the vehicle speed increases. By doing so, it becomes possible to avoid a sudden change in the yaw rate.

According to the third aspect of the present invention, at least the wheel speed difference target value on the turning inner wheel side is changed according to the amount of change in the yaw rate, and a sudden change in the yaw rate is suppressed to stabilize the vehicle behavior. It becomes possible to control the braking force in each direction.

Further, according to the structure of the invention described in claim 4, the device for directly detecting the yaw rate becomes unnecessary, and the slip of the turning inner wheel increases the speed difference between the left and right driven wheels, thereby increasing the calculated yaw rate. As a result, it becomes possible to detect the unstable state of the vehicle with higher sensitivity.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a front-wheel drive vehicle will be described below with reference to the drawings.

1 to 6 show an embodiment of the present invention, FIG. 1 is a hydraulic circuit diagram of a brake device, FIG. 2 is a diagram showing a structure of a brake pressure adjusting means, and FIG. 3 is a braking force. A flow chart showing a distribution control procedure, FIG.
A flow chart showing a correction coefficient calculation procedure in steps,
FIG. 5 is a flowchart showing a control amount calculation procedure in the eleventh step of FIG. 3, and FIG. 6 is a diagram showing an example of controlling the front wheel braking force by vehicle deceleration.

First, in FIG. 1, a brake pedal 3 is interlocked and connected to a tandem type master cylinder M having first and second output ports 1 and 2, and the master cylinder is operated in response to a depression operation of the brake pedal 3. Independent brake fluid pressures are output from the first and second output ports 1 and 2 of M. Thus the first output port 1 and the first brake hydraulic system 5 having a braking pressure regulating means 4 _1
1 is connected, the right front wheel W _FR in the mounted right front wheel brake B _FR and the left rear wheels W _RL in the mounted left rear wheel brake B _RL is connected to the first brake hydraulic system 5 _1. Also in the second output port 2, the second brake hydraulic system 5 ₂ is connected, the left front wheel W _FL left front wheel brake is mounted on the B _FL and the right rear wheel W _RR having a braking pressure regulating means 4 ₂ loaded right rear wheel brake B _RR is connected to the second brake hydraulic system 5 _2. Thus, each brake B _FL ,
B _FR , B _RL , and B _RR exert a braking force according to the applied brake fluid pressure, and are, for example, disc brakes.

Left and right front wheels W_FL, W_FRThe rotation speed of
Left and right front wheel rotation speed sensor S_FL, S_FRRespectively detected by
Left, right rear wheel W_RL, W_RRRotation speed of left and right rear wheels
Speed sensor S_RL, S_RRRespectively. these
Rotation speed sensor S_FL, S_FR, S _RL, S_RRDetected value is electronic
Input to the control unit 6, the electronic control unit 6
Rolling speed sensor S_FL, S_FR, S_RL, S_RRBased on the detected value of
Brake pressure adjusting means 4 ₁, 4_TwoControls the operation of.

In FIG. 2, the first brake hydraulic system 5₁
Brake pressure adjusting means 4₁Is the master cylinder M
The brake fluid pressure output from the first output port 1 of the
Wheel brake B_FRSupply valve 7 that can act on_FAnd the first
The brake fluid pressure output from output port 1 is adjusted to the left rear wheel
B_RLSupply valve 7 that can act on_RAnd the reservoir 8
And right front wheel brake B_FRBrake fluid pressure to the reservoir 8
Releasable electromagnetic release valve 9_FAnd the left rear wheel brake B_RLNobu
Electromagnetic release valve 9 capable of releasing rake hydraulic pressure to the reservoir 8
_RAnd the hydraulic fluid pumped from the reservoir 8 to the first output port.
And a hydraulic pump 10 that can be returned to the
It is an anti-lock brake control device. Thus electromagnetic supply
Valve 7_F, 7_RIs the first output port 1 and each car when demagnetized
Wheel brake B _FR, B_RLThe state of communicating between the
1 output port 1 to each wheel brake B _FR, B_RLBlur to
-Wheel brakes are blocked but each wheel brake B_FR, B_RLOr
Allows the flow of brake fluid from the 1st output port 1 side to
It is possible to switch between the state and the electromagnetic release valve 9_F, 9_RDisappears
Each wheel brake B when magnetized_FR, B_RLAnd between the reservoirs 8
Brake B of each wheel when it is shut off and when it is excited_FR, B_RLYou
It is possible to switch between and the state in which the reservoirs 8 communicate with each other.

[0018] In such a braking pressure regulating means 4 _1,
The right front wheel brake B _FR and the left rear wheel brake B are controlled by controlling the electromagnetic supply valves 7 _F and 7 _R and the electromagnetic release valves 9 _F and 9 _R.
The anti-lock brake control of _RL can be executed, and the braking force distribution of the right front wheel brake B _FR and the left rear wheel brake B _RL can be adjusted.

[0019] Also braking pressure regulating means 4 ₂ in the second brake hydraulic system 5 _2, the braking pressure adjusting means 4 ₁ are configured similarly to the anti-lock of the left front wheel brake B _FL and the right rear wheel brake B _RR The brake control can be executed and the braking force distribution of the left front wheel brake B _FL and the right rear wheel brake B _RR can be adjusted.

[0020] In the electronic control unit 6, FIG. 3, which control operation in accordance with the procedure shown in FIGS. 4 and 5 is executed, first, in the first step S1 of FIG. 3, the front wheel rotation speed omega _F and after The wheel rotation speed ω _R is calculated, and in the second step S2, whether the correction coefficient k is calculated by the correction coefficient calculation means 14 ₁ and 14 ₂ and whether the front-rear braking force distribution control based on the wheel speed difference is to be performed or not. A control decision is made.

Calculation of the correction coefficient k in the second step S2
And control decisions are executed according to the procedure of FIG.
Yes, the procedure of FIG. 4 will be described below. First step M
In 1, it is determined whether or not the vehicle is running at a constant speed, and the constant speed running is performed.
Only in the row state, the process proceeds to the next second step M2. This
Here, the determination in the first step M1 is performed by, for example, the third step described later.
It is determined in step M3 that the number of times of integration has reached the specified value.
Until the rotation speed ω _F, Ω_RIs the prescribed volatility
It is done depending on whether it is within
This eliminates the effect of slip caused by acceleration and deceleration
In order to obtain the true radius of the tire as accurately as possible
It is. Therefore, in the low speed range where errors due to sharp turns are likely to occur,
Excludes high-speed areas where drive wheel slippage due to driving force increases
It may be judged by the vehicle speed to remove
If there is a rudder angle sensor and the rudder angle is large,
It may be possible to judge by the steering angle so that
Depending on the engine throttle opening and fuel injection amount,
Eliminates large driving force when driving force can be calculated
You may make it.

In the second step M2, the front wheel rotation speed ω _F
And the ratio k _O (= ω _F / ω _R ) of the rear wheel rotation speed ω _R and the integrated value k _S (= k _S + k _O ) are calculated. Thus, the initial value of the integrated value k _S is "0".

In the third step M3, it is determined whether or not the number of times of integration has reached a specified value, for example, 200 times. Therefore, the measurement error of the rotation speed increases as the vehicle speed increases,
It is desirable that the specified value be set larger as the vehicle speed increases. When it is determined in the third step M3 that the specified value has not been reached, the process returns to the first step M1, and when it is determined that the specified value has been reached, the integrated value K _S is divided by the number of integrations in the fourth step M4. As a result, the correction coefficient k as the average rotation speed ratio at the specified number of times of integration is obtained.

[0024] In the fifth step M5, a correction coefficient k _n-1 previously obtained, whether the absolute value of the difference between the correction coefficient k _n obtained in this study are less than a specified value is determined, the absolute If the value is less than the prescribed value, the confirmation flag is set in the sixth step M6 as the confirmation of the correction coefficient k, and if the absolute value is equal to or greater than the prescribed value, the correction coefficient k is determined.
Is not determined, the determination flag is reset in the seventh step M7. That is, it is determined whether or not the fluctuation range of the correction coefficient k is equal to or larger than the specified value, and when the fluctuation range is equal to or larger than the specified value, the correction coefficient k is determined to be undetermined and the confirmation flag is reset.

Further, in the eighth step M8, the integrated value k _S
Is set to "0" and the number of times of integration is set to "0". When it is determined in the first step M1 that the vehicle is not traveling at a constant speed, the process proceeds from the first step M1 to the eighth step M8.

Thus, the correction coefficient k is obtained and the control judgment is executed by the subroutine of FIG. 4, but this is executed on the left side and the right side respectively, and the correction coefficient k for each of the left and right sides. _L and k _R are required.

Referring again to FIG. 3, calculation of the correction coefficient k and
In the third step S3 after the end of the control judgment
Wheel W_FL, W_FR, W_RL, W_RRThe wheel speed of is calculated. You
That is, the left front wheel speed V_WFL, Front right wheel speed V_WFR, Left rear wheel speed
Degree V_WRLAnd right rear wheel speed V _WRRBut each wheel W_FL,
W_FR, W_RL, W_RRThe rotation speed of_FL, Ω_FR, Ω_RL, Ω_RR
And the tire radius is r
Is calculated.

V _WFL = r × ω _FL V _WFR = r × ω _FR V _WRL = r × ω _RL V _WRR = r × ω _RR Both rear wheel speeds V among the wheel speeds thus obtained
_{The WRL} and V _WRR are used as they are, but the correction coefficients k _L and V _L are used for the left and right front wheel speeds V _WFL and V _WFR .
The following correction by K _R is performed.

V _WFL = V _WFL / k _L V _WFR = V _WFR / k _R By the way, the above-mentioned processing of the second and third steps S2 and S3 is similarly executed between the left and right wheels. Yes, which gives accurate wheel speeds for all four wheels.

In the fourth step S4, front and rear wheel speed differences ΔV _L and ΔV _R are calculated on the left and right sides, respectively, based on the following equations.

ΔV _L = V _WRL −V _WFL ΔV _R = V _WRR −V _{WFR In} the fifth step S5, the yaw rate γ is calculated according to the following formula based on the wheel speeds of the driven wheels, that is, the left and right rear wheels.

Γ = (V _WRR −V _WRL ) / (tread) Further, in a sixth step S6, the wheel speed difference target value ΔV _O when the vehicle goes straight is calculated according to the following equation.

ΔV _O = λV _V -d where V _V is the vehicle body speed, and the left and right rear wheel speeds V
_{It is} obtained by performing filtering processing on the average value of _WRL and V _WRR , and λ and d are constant values. If the wheel speed difference target value ΔV _O becomes large, braking force distribution control is performed to increase the wheel speed on the rear wheel side, that is, to increase the braking force on the front wheel side.

In the seventh step S7, it is determined whether the amount of change (dγ / dt) of the yaw rate γ per unit time is positive or negative. Depending on the determination result, the process proceeds to the eighth step S8 or the ninth step S9 to turn. The target wheel speed difference value ΔV _O on the inner wheel side in this state is corrected. When it is determined that the change amount (dγ / dt) of the yaw rate γ per unit time is positive, it is determined that the vehicle is turning left, and the eighth step S is performed.
8, the left wheel speed difference target value Δ, which is the inner wheel side of turning, is set.
If V _OL is corrected as (ΔV _O + ε · V _V ) and it is determined that the change amount (dγ / dt) of the yaw rate γ per unit time is negative, it is determined that the vehicle is turning right and the ninth step Proceeding to S9, the right wheel speed difference target value ΔV _OR, which is the inner wheel side of the turn, is corrected as (ΔV _O + ε · V _V ).

In the eighth and ninth steps S8 and S9, ε is a value obtained from map data using the vehicle body speed V _V and | dγ / dt | as parameters, and the vehicle body speed V _V and | dγ / dt | In a region where is relatively small, ε is “0”, and ε increases as the vehicle speed V _V and | dγ / dt | increase.

In the tenth step S10, the vehicle speed V _V
The vehicle body deceleration G is calculated based on the above, and thereafter, in the eleventh step S11, the control amounts of the brake pressure adjusting means 4 ₁ and 4 ₂ are calculated. Here, the processing of the eleventh step S11 is executed according to the procedure shown in FIG. 5, and in the first step N1 of FIG. 5, it is judged whether or not the confirmation flag is set, and the confirmation flag is set. The second step N2, Δ
It is determined whether or not V _R > ΔV _OR and ΔV _L > ΔV _OL . Therefore, ΔV _R > ΔV _OR , ΔV _L ≧ ΔV _OL indicate that the rear wheel speed V _WR is too fast. At this time, the rear wheel braking force is increased in the third step N3. The controlled variable is defined. In addition, ΔV _R <ΔV _OR ,
When ΔV _L <ΔV _OL is determined in the second step N2, the rear wheel speed V _WR is too slow, and in this case, the rear wheel braking force is reduced in the fourth step N4. The control amount is defined in.

On the other hand, when it is determined that the confirmation flag is not set, in the fifth step N5,
The control amount is determined so that the rear wheel braking force changes according to the vehicle body deceleration G as shown in FIG. Here, the line L _{1 in} FIG. 6 shows an example in which the rear wheel braking force is kept constant after the vehicle body deceleration G reaches a constant value, and the line L ₂ corresponds to the vehicle body deceleration G. This is an example in which the rear wheel braking force is changed stepwise.

Next, the operation of this embodiment will be described.
And the front wheel rotation speed ω_FAnd rear wheel rotation speed ω_RRatio k_O
The difference between the actual wheel diameter and the set wheel diameter based on
A correction coefficient k corresponding to is calculated and the front and rear wheel speeds V
_WFL, V_WFR; V_WRL, V_WRRFront wheel speed V_WFL,
V_WFRIs corrected by the correction coefficient k, and the rear wheel speed V_WRL, V
_WRRAnd the corrected front wheel speed V_WFL, V_WFRBased on
Brake pressure adjusting means 4₁, 4 _TwoIs calculated.
Therefore, when the tire radius changes,
Appropriate braking force distribution control considering changes in
Can be.

Moreover, the correction coefficient k depends on the running conditions of the vehicle.
When the correction coefficient k changes significantly due to a drive wheel slip on a slope or the like, the control amount calculation based on the comparison result of the front and rear wheel speeds is prohibited. Unnecessary braking force distribution control due to short-term changes in tire radius of motion can be eliminated.

Further, when the braking force distribution control based on the comparison of the wheel speeds is prohibited, the control amount is calculated so as to obtain the brake fluid pressure ratio depending on the vehicle body deceleration G, so the front and rear wheel speeds are calculated. Even if the braking force distribution based on the comparison result is prohibited, the braking force distribution control can be performed to some extent.

Further, when braking while the vehicle is turning
Is the left and right wheel speed difference target value ΔV_OL, ΔV_ORAre mutually
Set differently. That is, while turning left
Wheel speed difference target value ΔV on the left side, which is the inner ring side_OLIs (ΔV_O
+ Ε · V_V) Is corrected as
Difference target value ΔV_ORIs the vehicle speed V_VIs a value determined by
During turning, the target wheel speed difference Δ on the right side, which is the inner wheel side of turning
V_ORIs (ΔV_O+ Ε · V _V) Is corrected as
Left wheel speed difference target value ΔV_OLIs the vehicle speed V_VDetermined by
Value. This allows the turning inner wheel with the smaller load to
The braking force distribution of the rear side wheels is reduced and the tire lateral force is increased.
In addition to being large, there is a difference in left and right braking force
The yaw moment generated by the
The yaw rate may suddenly change due to the rear brake force distribution control.
Is suppressed.

Moreover, the left and right wheel speed difference target values ΔV _OL ,
ΔV _OR becomes large as the difference between the wheel speed difference target values ΔV _OL and ΔV _OR increases with an increase in the vehicle body speed V _{V and} an increase in the amount of change | dγ / dt | per unit time of the yaw rate. It is possible to effectively suppress a sudden change in the yaw rate during high-speed traveling and during a steep steering where the yaw rate is likely to change suddenly.

Further, since the yaw rate is calculated based on the speed difference between the left and right driven wheels, that is, the left and right rear wheels, an expensive device for directly detecting the yaw rate is unnecessary. The slip of the turning inner wheel causes a large speed difference between the left and right driven wheels, and as a result, the calculated yaw rate becomes large. Therefore, by calculating the yaw rate based on the speed difference between the left and right driven wheels, that is, the left and right rear wheels, The unstable state of can be detected with higher sensitivity.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the present invention described in the claims. It is possible.

For example, an example in which an antilock brake control device is used as the brake pressure adjusting means has been shown, but a brake pressure adjusting means capable of adjusting only the hydraulic pressure of the rear wheel brakes may be used. Further, in the above embodiment, the brake device for the X pipe has been described, but the present invention can be applied to all brake devices of the pipe type.

[0046]

As described above, according to the first aspect of the present invention, at the time of turning the vehicle, the target value of the wheel speed difference at least on the turning inner wheel side is changed to be larger than that when the vehicle goes straight, so that the load is small. It is possible to increase the lateral force while avoiding the loss of the braking force by reducing the braking force distribution ratio of the rear wheels on the turning inner wheel side, which causes a sudden change in the yaw rate according to the braking operation at the time of turning. It is possible to perform the front-rear braking force distribution control while avoiding this.

According to the second aspect of the present invention, at least the wheel speed difference target value on the turning inner wheel side is set so as to become large in accordance with the increase in the vehicle speed, so that the yaw rate is likely to change suddenly at high speed. It is possible to effectively suppress a sudden change in the yaw rate.

According to the third aspect of the present invention, at least the wheel speed difference target value on the turning inner wheel side is set so as to increase in accordance with the increase in the amount of change in the yaw rate of the vehicle body per unit time. It becomes possible to perform the braking force control in the direction of stabilizing the vehicle behavior by suppressing the sudden change of the yaw rate.

Further, according to the invention described in claim 4, since the yaw rate of the vehicle body is calculated based on the speed difference between the left and right driven wheels, an expensive device for directly detecting the yaw rate is unnecessary and the vehicle is unstable. The state can be detected with higher sensitivity.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a brake device.

FIG. 2 is a diagram showing a configuration of a brake pressure adjusting unit.

FIG. 3 is a flowchart showing a braking force distribution control procedure.

4 is a flowchart showing a correction coefficient calculation procedure in a second step of FIG.

FIG. 5 is a flowchart showing a control amount calculation procedure in the eleventh step of FIG.

FIG. 6 is a diagram showing an example of controlling front wheel braking force by vehicle deceleration.

[Explanation of symbols]

B _FL・ ・ ・ Left front wheel brake B _FR・ ・ ・ Right front wheel brake B _RL・ ・ ・ Left rear wheel brake B _RR・ ・ ・ Right rear wheel brake W _FL・ ・ ・ Left front wheel W _FR・ ・ ・ Right front wheel W _RL・ ・ ・ Left rear wheel W _RR・ ・ ・ Right rear wheel

Claims (4)

[Claims] 1. A result obtained by comparing a value obtained by subtracting a wheel speed of a front wheel (W _FL , W _FR ) from a wheel speed of a rear wheel (W _RL , W _RR ) and a wheel speed difference target value on the left side and the right side, respectively. Based on this, the brake fluid pressures of at least the left and right rear wheel brakes (B _RL , B _RR ) of the left and right front wheel brakes (B _FL , B _FR ) and the left and right rear wheel brakes (B _RL , B _RR ) are individually determined. In the braking force distribution control method of the vehicle that adjusts to the left and right to control the front-rear braking force distribution respectively, at the time of turning the vehicle, change the target wheel speed difference value at least on the turning inner wheel side to be larger than that when the vehicle goes straight. A braking force distribution control method for a vehicle, comprising: 2. The braking force distribution control method for a vehicle according to claim 1, wherein the wheel speed difference target value at least on the turning inner wheel side is set so as to become large in accordance with an increase in the vehicle body speed. 3. The wheel speed difference target value at least on the turning inner wheel side is set so as to become large in accordance with an increase in the amount of change in the yaw rate of the vehicle body per unit time. Vehicle braking force distribution control method. 4. The braking force distribution control method for a vehicle according to claim 3, wherein the yaw rate of the vehicle body is calculated based on the speed difference between the left and right driven wheels.