JPH04287754A - Braking force control device - Google Patents

Abstract

PURPOSE:To improve the turning performance at the time of braking by correctly judging the behavior of a vehicle body at the time of turning and correctly changing the target slip ratio of each wheel. CONSTITUTION:In the braking slip control, the target yaw rate gammad is calculated (S10) from the estimated vehicle speed Ve (S2, 4-6) and the steering angle theta(S9), the actual yaw rate gammaa (S3) is subtracted from the target yaw rate gammad to calculate the yaw rate deviation DELTAgamma, the yaw rate deviation DELTAgamma is multiplied by the actual yaw rate gammaa to calcuate the turning characteristic value C (S11), and target slip ratios Sd-fl, Sd-fr, Sd-rl, Sd-rr of individual wheels are determined in response to the turning characteristic value C (S12, S14).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the braking force of a vehicle, and more particularly to a technique for controlling the braking force in order to improve the turning performance of a vehicle.

0002

2. Description of the Related Art When braking is performed while a vehicle is turning, the slip rate of the wheels increases and the collin ring force decreases, which may result in oversteer or understeer. Measures to suppress this tendency are measures to improve turning performance, and are disclosed in Japanese Patent Application Laid-Open Nos. 60-248466 and 1-17805.
This is already known from Publication No. 9 and the like.

The method described in Japanese Patent Application Laid-open No. 60-248466 utilizes the fact that the cornering force of a wheel changes depending on the slip ratio of the wheel, and it is possible to determine whether the actual turning characteristics tend to understeer or oversteer. When the turning characteristic value, which indicates both whether the vehicle is in the current state and the strength of that tendency, exceeds a set value, a braking force difference is applied between the front wheel brakes and the rear wheel brakes to suppress the understeer tendency or oversteer tendency. A front-rear braking force distribution control means is provided. If there is a tendency to oversteer, the braking force on the front wheels is increased to increase the slip ratio and reduce the cornering force of the front wheels, and conversely, the braking force of the rear wheels is decreased to increase the cornering force. If there is a tendency for understeer, the braking force on the rear wheels is increased and the braking force on the front wheels is decreased, thereby returning the vehicle to neutral steering.

On the other hand, the system described in Japanese Patent Application Laid-Open No. 1-178059 generates a yaw moment in the vehicle body due to the difference in braking force between the right rear wheel and the left rear wheel, thereby suppressing the tendency to understeer or oversteer. There is a braking force left/right distribution control means that creates a braking force difference between the right rear wheel brake and the left rear wheel brake to generate the above-mentioned yaw moment when the lateral acceleration of the vehicle body exceeds a set lateral acceleration. It will be done.

[0005]

[Problem to be solved by the invention] The above-mentioned Japanese Patent Application Laid-Open No. 60-24
The braking force control device described in Publication No. 8466 obtains a turning characteristic value by subtracting the absolute value of the target yaw rate from the absolute value of the actual yaw rate, regardless of whether the turning direction of the vehicle is left or right. If the turning characteristic value is positive, it is determined that the larger its absolute value is, the stronger the tendency to oversteer is. On the other hand, if the turning characteristic value is negative, it is determined that the larger the absolute value is, the stronger the tendency to understeer is to be shown. In other words,
Using the premise that the sign (direction) of the actual yaw rate and the target yaw rate always match, regardless of whether the vehicle is turning to the left or right, if the turning characteristic value is positive, it indicates an oversteer tendency or a negative turning characteristic value. If so, it is determined that the vehicle exhibits an understeer tendency.

However, the signs of the actual yaw rate and the target yaw rate do not always match; for example, in order to perform a quick lane change while the vehicle is moving straight, or to perform drifting while the vehicle is turning, the signs of the actual yaw rate and the target yaw rate are not always the same. If a so-called countersteering operation is performed in which the front wheels, which are the steered wheels, are steered in the opposite direction, the signs of the actual yaw rate and the target yaw rate will no longer match. Because the above-mentioned braking force control device obtains the turning characteristic value by subtracting the absolute value of the target yaw rate from the absolute value of the actual yaw rate, regardless of whether or not it is in a countersteer state, the actual turning characteristic may not be determined correctly. There was a problem. This will be explained in detail below.

[0007] In braking force front and rear distribution control, when an understeer tendency occurs, whether turning left or right, the front wheels are on the side where the braking force is decreasing and the rear wheels are on the side where the braking force is increasing; on the other hand, when there is a tendency to oversteer, If this occurs or the vehicle enters a countersteer state, the rear wheels should be on the side where the braking force is reduced and the front wheels should be on the side where the braking force is increased. However, the braking force control device obtains the turning characteristic value by subtracting the absolute value of the target yaw rate from the absolute value of the actual yaw rate. , if an oversteer tendency occurs, it becomes positive, and the direction of the actual turning characteristics can be determined correctly, but
When in a countersteer state, the turning characteristic value is not necessarily positive as in the case of oversteer tendency, but may be positive or negative depending on the magnitude relationship between the absolute value of the actual yaw rate and the absolute value of the target yaw rate. Therefore, the direction of the actual turning characteristics cannot be determined correctly. Furthermore, since this braking force control device obtains the absolute value of the turning characteristic value regardless of whether the direction of the actual yaw rate and the direction of the target yaw rate are the same or different, the strength of the actual turning characteristic cannot be determined correctly. .

[0008] Even when performing braking force left/right distribution control using the turning characteristic values obtained in this way, for the same reason as in braking force front/rear distribution control, the direction of the actual turning characteristic is and strength cannot be determined correctly.

With these circumstances as a background, the present invention provides a control force control device for controlling the braking force of each wheel so that the actual slip ratio of each wheel provided on the front, rear, left, and right sides of a vehicle body becomes each target slip ratio. This was accomplished with the objective of obtaining a sufficient turning performance improvement effect through braking force front/rear distribution control or braking force left/right distribution control by using parameters that accurately reflect actual turning characteristics.

0010

[Means for Solving the Problem] In order to solve this problem, the braking force control device according to the present invention has the following features: (a) Based on the yaw rate deviation of the actual yaw rate of the vehicle body from the target yaw rate, Left and right wheel target slip rate changing means for changing at least one target slip rate;
(b) It is configured to include at least one of front and rear wheel target slip ratio changing means for changing the target slip ratio of at least one of the front wheels and the rear wheels based on the product of the yaw rate deviation and the actual yaw rate.

Note that both the actual yaw rate and the target yaw rate have different signs depending on the direction in which the vehicle body rotates. Further, the yaw rate deviation may be obtained by subtracting the actual yaw rate from the target yaw rate, or may be obtained by subtracting the target yaw rate from the actual yaw rate.

0012

[Operation] In braking force left/right distribution control, which controls the left/right distribution of braking force by changing the target slip ratio of the left and right wheels, does an understeer tendency occur when the vehicle turns left, or does an oversteer tendency occur when the vehicle turns right? , or when transitioning to countersteer when turning right (hereinafter referred to as the first case), the left wheel is on the target slip rate increasing side (braking force increasing side), and the right wheel is on the target slip rate decreasing side (braking force decreasing side). ), and on the other hand, if there is a tendency to oversteer when turning left, a tendency to understeer when turning right, or a transition to countersteer when turning left (hereinafter referred to as
In the latter case), the right wheel is on the increasing side of the target slip rate, and the left wheel is on the decreasing side. The yaw rate deviation of the actual yaw rate from the target yaw rate has a different sign in the first case and the second case, and the braking force control according to the present invention correctly reflects the direction of the actual turning characteristic as well as its strength. If the target slip ratio of at least one of the left and right wheels is changed in the device based on the yaw rate deviation, braking force left and right distribution control can be achieved as planned regardless of whether the vehicle is in a countersteering state.

On the other hand, in braking force front and rear distribution control, which controls the front and rear distribution of braking force by changing the target slip ratio of the front and rear wheels, whether the vehicle is turning left or right,
When an understeer tendency occurs (hereinafter referred to as the first case), the front wheels are set to the target slip rate decreasing side (cornering force increasing side) and the rear wheels are set to the target slip rate increasing side (cornering force decreasing side), while the oversteer tendency is set to occurs,
Alternatively, when transitioning to the countersteering state (hereinafter referred to as the latter case), the front wheels are set to increase the target slip ratio, and the rear wheels are set to the target slip ratio decrease side. The product of the yaw rate deviation and the actual yaw rate (corresponding to the turning characteristic value in the conventional device) has a different sign in the first and second cases, and it does not only correctly reflect the direction of the actual turning characteristic, but also correct its strength. Therefore, if the target slip ratio of at least one of the front and rear wheels is changed based on the product in the braking force control device according to the present invention, braking force front and rear distribution control can be performed regardless of whether or not the countersteer state is in effect. It will be realized as planned.

By the way, prior to the present invention, the applicant has
In order to accurately determine the actual turning characteristics in front-rear braking force distribution control, we devised a means for changing the target slip ratio of the front and rear wheels, which changes the target slip ratio of the front and rear wheels based on the product of the yaw rate deviation and the sign of the actual yaw rate. . However, when this front and rear wheel target slip rate changing means is adopted, the sign of the actual yaw rate changes regardless of the magnitude of the absolute value of the yaw rate deviation, so the sign of the actual yaw rate changes from positive to negative or vice versa. It has been found that there is a problem in that when the value of the product changes significantly (the sign is reversed) when it changes positively, the target slip ratio, that is, the braking force of the wheels may change somewhat significantly. Therefore, the front and rear wheel target slip rate changing means in the present invention focuses on the fact that the absolute value of the actual yaw rate is sufficiently close to 0 before and after the sign of the actual yaw rate changes, and based on the product of the yaw rate deviation and the actual yaw rate, This is supposed to change the target slip ratio of the front and rear wheels.

[0015]

As is clear from the above explanation, the braking force control device of the present invention uses parameters that accurately reflect the actual turning characteristics, that is, the yaw rate deviation and the product of this and the actual yaw rate to control each wheel. Since the target slip ratio is changed, a sufficient turning performance improvement effect can be obtained by the braking force left/right distribution control or the front/rear distribution control regardless of whether or not the vehicle is in a countersteer state.

Furthermore, when the front and rear wheel target slip ratio changing means of the present invention is employed, the target slip ratio changes smoothly when the sign of the actual yaw rate changes, so that the braking force of each wheel changes smoothly. The effect of smoothness can also be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Several embodiments of the present invention will be described below in detail with reference to the drawings. In FIG. 3, 10 is a master cylinder, which is provided with two independent pressurizing chambers. This master cylinder 10 is connected to a brake pedal 14 as a brake operating member via a booster 12, and generates a brake pressure proportional to the operating force of the brake pedal 14. The brake pressure generated in one pressurizing chamber is transmitted to the main fluid passage 18 via a proportioning/bypass valve (represented by P/B in the figure) 16. The main fluid passage 18 is bifurcated into two branches, each of which is connected to a brake wheel cylinder 26 of the left and right front wheels 22, 24 via an electromagnetic hydraulic pressure control valve (hereinafter simply referred to as a control valve) 20. The brake pressure generated in the other pressure chamber passes through the proportioning/bypass valve 16 to the main fluid passage 3.
0. The main liquid passage 30 also splits into two parts in the middle, and is connected to the wheel cylinders 38 of the brakes of the left and right rear wheels 34, 36 through control valves 32, respectively.

Proportioning/bypass valve 16
When the front system including the main fluid passage 18 is normal, the brake pressure of the rear system including the main fluid passage 30 is reduced proportionally, and when the front system fails, the brake pressure of the master cylinder 1 is reduced.
It has a function of directly transmitting the brake pressure from zero to the wheel cylinders 38 of the left and right rear wheels 34, 36.

As shown in the figure, the control valve 20 is always in an increased pressure state that communicates the wheel cylinder 26 with the master cylinder 10, but when the solenoid 40 is excited with a relatively large current, the wheel cylinder 26 When the solenoid 40 is excited with a relatively small current, the wheel cylinder 26 is cut off from the master cylinder 10 and from the reservoir 42. It changes the state. The control valve 32 is also the solenoid 4
4, the wheel cylinder 38
It switches between an increased pressure state in which it communicates with the master cylinder 10, a reduced pressure state in which it communicates with the reservoir 46, and a held state in which it communicates with neither.

The brake fluid in the reservoir 42 is supplied to the pump 4.
8 and returned to the main liquid passage 18 via the pump passage 50. The rear system similarly includes a pump 54 and a pump passage 56. Those pumps 48, 54
is driven by a motor 58.

The front system also bypasses the control valve 20 from each wheel cylinder 26 to the master cylinder 10.
Each of the recirculation passages 60 is provided with a check valve 62 that prevents the brake fluid from flowing back. The rear system also includes a recirculation passage 66 equipped with a check valve 64.

In the figure, 70 indicates a controller. The controller 70 is mainly a computer, and includes a CPU 72, ROM 74, RAM 76, and a timer 78.
, an input port 80, an output port 82, and a bus 84.

A brake switch 88 is connected to the input port 80.
, wheel speed sensors 90, 92, 94, 96, a steering angle sensor 98, a yaw rate sensor 100, and a longitudinal acceleration sensor 102 are connected. The brake switch 88 detects depression of the brake pedal 14. The wheel speed sensors 90, 92, 94, 96 are connected to the left and right front wheels 22,
24, the wheel speed which is the circumferential speed of each of the left and right rear wheels 34, 36 is detected. The steering angle sensor 98 is attached to the steering device and detects the operating angle of the steering wheel as positive when the steering wheel is operated to the left from the neutral position, and negative when the steering wheel is operated to the right from the neutral position. The yaw rate sensor 100 is attached to the vehicle body and detects a counterclockwise yaw rate as positive and a clockwise yaw rate as negative. A longitudinal acceleration sensor 102 is also attached to the vehicle body, and detects forward longitudinal acceleration as positive and backward longitudinal acceleration as negative. The control valves 20 and 32 and the motor 58 are connected to the output port 82. The ROM 74 stores various programs including a brake slip control program shown in the flowcharts of FIGS. 1 and 2. The CPU 72 controls the control valve 20 by executing the brake slip control program.
, 32, and also controls the pump 4 during braking slip control.
8, 54 from the wheel cylinders 26, 38 by driving the motor 58 to drive the reservoirs 42, 46.
The brake fluid discharged into the cylinder is returned to the master cylinder 10.

The operation of the present vehicle brake system will be explained below. As mentioned above, normally, the control valves 20 and 32 are in a state that allows the master cylinder 10 and the wheel cylinders 26 and 38 to communicate with each other. Therefore, when the brake pedal 14 is depressed, the brake pressure in the master cylinder 10 and the wheel cylinders 26, 38 increases, and the vehicle is braked.

After power is turned on, the controller 70 executes a brake slip control program. First, initial settings are performed in step S1 (hereinafter simply referred to as S1; the same applies to other steps) in FIG. Velocities Vfl, Vfr, Vrl, and Vrr are taken in. In S3, the actual yaw rate γa is taken in and the actual vehicle body slip angle β is estimated. In a linear two-degree-of-freedom region related to vehicle motion (a linear region between vehicle sideslip and yaw), if the actual yaw rate γa is the input signal and the actual vehicle slip angle β is the output signal, then the actual yaw rate γa and the actual vehicle slip angle are A transfer function of (Gbo+Gb1·s)/(1+Tr·s) exists between β and β. However, in the above equation, s is a Laplace operator, and Gbo, Gb1, and Tr are related to the estimated vehicle speed Ve, which will be described later, and are determined according to the Gbo map, Gb1 map, and Tr map stored in the ROM 74. These maps are shown in Figure 4, respectively.
It has the characteristics shown in the graphs of FIGS. 5 and 6. That is, in this step, the actual vehicle body slip angle β corresponding to the actual yaw rate γa and the estimated vehicle body speed Ve is calculated using the transfer function.

After that, in S4, the actual wheel speed V of each wheel is
fl, Vfr, Vrl, and Vrr are converted with respect to the center position of the front wheel axle. Specifically, as shown in FIG. 7, if the tread of the vehicle is t and the wheel base is L, the sum of the actual wheel speed Vfl and t・γa/2 is the converted wheel speed V1 of the left front wheel 22, and the actual From wheel speed Vfr to t・γa /
The value obtained by subtracting 2 is the converted wheel speed V2 of the right front wheel 24,
The sum of the actual wheel speed Vrl, t・γa /2 and L・β・γa is the converted wheel speed V3 of the left rear wheel 34, and the actual wheel speed V
rr minus t・γa/2 and L・β・γ
The sum with a is taken as the converted wheel speed V4 of the right rear wheel 36. Those converted wheel speeds V1, V2, V3
and V4 are not affected by the difference in the turning trajectory of each wheel or by the actual vehicle body slip angle β, and if each wheel is not slipping at all, they match each other regardless of the turning state. .

Next, in S5, the longitudinal acceleration Gx is taken in, and in S6, the estimated vehicle speed Ve is calculated. The longitudinal acceleration Gx is 0 or more and the positive upper limit Gu
If it is less than p, the above converted wheel speed V1, V2
, V3 and V4 is estimated to be the vehicle body speed, and when the longitudinal acceleration Gx is smaller than 0 and greater than the negative lower limit Glo, the converted wheel speed V1, V2
, V3 and V4 are estimated to be the vehicle speed, and if the longitudinal acceleration Gx is greater than the upper limit Gup or smaller than the lower limit Glo, the estimated vehicle speed when the longitudinal acceleration Gx becomes this for the first time. Ve (
The longitudinal acceleration Gx is greater than or equal to the lower limit Glo, and the upper limit Gu
It is estimated that the vehicle speed is the sum of the latest estimated vehicle speed Ve (in a state where the vehicle speed was below p) and the integral value of the longitudinal acceleration Gx from that time to the present time.

Thereafter, in S7, the reference wheel speeds Vc-fl, Vc-fr, Vc-rl and Vc-r of each wheel are set.
r (the wheel speed that each wheel assumes when the slip ratio of each wheel is 0 in the current running state (straight running state or turning state)) is determined. Specifically, the value obtained by subtracting t・γa /2 from the estimated vehicle speed Ve is the reference wheel speed Vc-fl of the left front wheel 22, and the estimated vehicle speed Ve and t・γa /
2 is the reference wheel speed Vc-fr of the right front wheel 24, and the value obtained by subtracting the sum of t·γa/2 and L·β·γa from the estimated vehicle speed Ve is the reference wheel speed Vc-fr of the left rear wheel 34.
The reference wheel speed Vc-rr of the right rear wheel 36 is determined by subtracting L.beta..gamma.a from the sum of the estimated vehicle speed Ve and t.gamma.a/2. Subsequently, in S8, the actual slip rates of each wheel Sa-fl, Sa-fr, Sa
-rl and Sa-rr are calculated. Specifically, the reference wheel speeds Vc-fl, Vc-fr, Vc-rl of each wheel
and from Vc-rr to actual wheel speed Vfl, Vfr, Vr
The value obtained by subtracting l, Vrr is the reference wheel speed Vc-fl,
The values divided by Vc-fr, Vc-rl and Vc-rr are the actual slip rates Sa-fl, Sa-fr,
Sa-rl and Sa-rr.

Subsequently, in S9, the actual steering angle θ is taken in, and in S10, the target yaw rate γd is calculated. Assuming that the actual steering angle θ is the input signal and the target yaw rate γd is the output signal, and that they are on a first-order lag system, then γo / (1 + τ・s) exists between the actual steering angle θ and the target yaw rate γd. There is a transfer function. However, in the above equation, s is a Laplace operator, and γo and τ are related to the estimated vehicle speed Ve and are stored in the ROM 74.
Determined according to the o map and the τ map. Each of these maps has characteristics represented by the graphs in FIGS. 8 and 9. That is, in this step,
Using the transfer function, the actual steering angle θ and the estimated vehicle speed Ve
The target yaw rate γd corresponding to this is calculated.

Thereafter, in S11, a yaw rate deviation Δγ is calculated by subtracting the actual yaw rate γa from the target yaw rate γd, and a turning characteristic value C is calculated by multiplying the yaw rate deviation Δγ by the actual yaw rate γa. The sign of the turning characteristic value C does not change depending on whether the turning direction is left or right;
If positive, the larger the absolute value, the stronger the understeer tendency; if negative, the larger the absolute value, the stronger the oversteer tendency. after that,
In S12 to S14, the target slip rate Sd-f of each wheel is
l, Sd-fr, Sd-rl and Sd-rr are determined. Target slip rate of each wheel Sd-fl, Sd-fr,
Sd-rl and Sd-rr are the standard value So and the front and rear wheel target slip rate changes ΔSx-fl, ΔSx-fr, Δ
This is the sum of Sx-rl and ΔSx-rr (hereinafter, they are collectively referred to as ΔSx). Although the standard value So is set to be the same for all four wheels in this embodiment, it can be set to be different depending on, for example, the dynamic characteristics of the vehicle.

Specifically, in S12, the front and rear wheel target slip rate changes ΔSx-fl, ΔSx of each wheel are determined.
-fr, ΔSx-rl and ΔSx-rr are determined in relation to the turning characteristic value C according to the ΔSx map stored in the ROM 74. This map has the characteristics shown in the graph of FIG. As shown by the broken line graph in Fig. 11, there is a relationship between slip ratio and cornering force.
Since the larger the slip ratio, the smaller the cornering force, it is necessary to increase the cornering force of the left and right front wheels 22, 24 while decreasing the cornering force of the left and right rear wheels 34, 36 in order to suppress the tendency to understeer. In this case, the target slip ratios of the left and right front wheels 22, 24 are decreased, while the target slip ratios of the left and right rear wheels 34, 36 are increased, and the oversteer tendency is suppressed or the vehicle body posture after the countersteer operation is reduced. If it is necessary to increase the cornering force of the left and right rear wheels 34, 36 while decreasing the cornering force of the left and right front wheels 22, 24 in order to promote the restoration of the left and right rear wheels 34,
While reducing the target slip rate of 36, the left and right front wheels 22,
This increases the target slip rate of 24.

In short, the target slip rate is set to the front wheels 22, 2.
In the front-rear braking force distribution control that changes the braking force between rear wheels 34 and 36, when an understeer tendency occurs (hereinafter referred to as the first case), whether turning left or right, rear wheel 3
4 and 36 are on the increasing side of the target slip rate, and the front wheels 22 and 24 are on the decreasing side.On the other hand, when an oversteer tendency occurs or a countersteering operation is performed (hereinafter referred to as the latter case), the front wheels 22, 24 is on the increasing side of the target slip rate, and the rear wheels 34 and 36 are on the decreasing side of the target slip rate, and the sign of the turning characteristic value C is positive in the first case, negative in the latter case, and , since the absolute value of the turning characteristic value C reflects the gap between the actual yaw rate γa and the target yaw rate γd with relative accuracy, the turning characteristic can be determined without determining whether the actual turning direction of the vehicle is left or right. Immediately from the value C, the front and rear wheels target slip rate change amount ΔSx-fl, Δ
Sx-fr, ΔSx-rl and ΔSx-rr can be determined correctly.

In this embodiment, in order to avoid an excessive increase or decrease in brake pressure, as shown in FIG.
An upper limit value and a lower limit value are provided for -fr, ΔSx-rl, and ΔSx-rr.

Thereafter, in S14, the target slip rates Sd-fl, Sd-fr, Sd-rl and Sd
-rr is the standard value So and the front and rear wheel target slip ratio changes ΔSx-fl, ΔSx-fr, ΔSx-rl, ΔS
x-rr. However, in this step 2
At the time of each execution after the first time, the target slip rate S of each wheel is
d-fl, Sd-fr, Sd-rl and Sd-rr are their previous values and the front and rear wheel target slip rate change amount ΔS of each wheel.
x-fl, ΔSx-fr, ΔSx-rl, ΔSx-rr
is determined as the sum of the current value.

Thereafter, in S15 of FIG. 2, it is determined whether or not the brake switch 88 has detected that the brake pedal 14 has been depressed, that is, whether it is in the ON state. If not, each control is activated in S16. valve 20,
After the demagnetization signal is issued to the solenoids 40 and 44 of 32, the process returns to S2 in FIG. Brake pressure control mode is pressure reduction mode,
Selected from holding mode and pressure increase mode. S1
Steps 7 to 21 are performed in turn for each of the four wheels. In S17, it is determined whether the actual slip rate Sa of one wheel is equal to or higher than the target slip rate Sd, and if so, the pressure reduction mode is selected in S18, and if not, the actual wheel speed of that wheel is selected in S19. Vw
It is determined whether the wheel acceleration Gw, which is the time differential value of , is less than or equal to the set wheel acceleration Gwo. If so, S
Hold mode is selected at 20, otherwise S
At 21, the pressure increase mode is selected. Thereafter, in S22, it is determined whether the control mode selection has been completed for all four wheels, and if so, in S23, a signal is sent to each of the control valves 20, 32 of the four wheels to realize the selected control mode. is served. After that, the process returns to S2 in FIG.

Therefore, in this embodiment, the target slip ratio of the front and rear wheels is changed using the product of the yaw rate deviation and the actual yaw rate, which is a parameter that accurately reflects the actual turning characteristics, so that the vehicle is in a countersteer state. Regardless of whether or not the braking force is distributed in the front and rear directions, a sufficient effect of improving turning performance can be obtained.

Furthermore, in this embodiment, the absolute value of the actual yaw rate is 0 before and after the sign of the actual yaw rate changes.
Focusing on the fact that the target slip rate of the front and rear wheels is changed based on the product of the yaw rate deviation and the actual yaw rate, the change in the target slip rate when the sign of the actual yaw rate changes is the yaw rate deviation Compared to the case where the target slip ratios of the front and rear wheels are changed based on the product of the sign of the actual yaw rate and the sign of the actual yaw rate, the change in the target slip ratio of the front and rear wheels is smoother, and as a result, the effect of smoother changes in the braking force of the front and rear wheels can also be obtained. However, if the change in the target slip ratio when the sign of the actual yaw rate changes is not a big problem,
Alternatively, if the problem can be solved by another method, the target slip ratio of the front and rear wheels may be changed based on the product of the yaw rate deviation and the sign of the actual yaw rate. The effect of being able to correctly determine the characteristics can be obtained.

As is clear from the above description, in this embodiment, the computer performs S2 to S6 and S9 in FIG.
The portion that executes steps 1 to 14 constitutes front and rear wheel target slip ratio changing means.

Although the braking force control device capable of controlling the front and rear distribution of braking force has been described as an embodiment of the present invention, the present invention can also be implemented as a braking force control device capable of controlling the left and right distribution of braking force. It is. Hereinafter, one embodiment of the present invention will be described based on the drawings, and common reference numerals will be used for elements common to the previous embodiments, and explanations using text and drawings will be omitted.

RO of the controller 70 in this embodiment
M74 stores a braking slip control program in which the flowchart of FIG. 1 is changed to the flowchart of FIG. 12. In this program, S101 to S11
0 is executed in the same manner as S1 to S10 in FIG.
At 111, the yaw rate deviation Δγ is calculated by subtracting the actual yaw rate γa from the target yaw rate γd. Subsequently, in S112 and 114,
Target slip rate for each wheel Sd-fl, Sd-fr, Sd-
rl and Sd-rr are determined. Target slip rate for each wheel Sd-fl, Sd-fr, Sd-rl, Sd-rr
is the standard value So and the left and right wheel target slip rate change amount Δ of each wheel
Sy-fl, ΔSy-fr, ΔSy-rl, ΔSy-r
r (hereinafter collectively referred to as ΔSy).

[0041] Specifically, in S112,
Left and right wheel target slip rate change ΔSy-fl, ΔSy-f
r, ΔSy-rl and ΔSy-rr are determined in relation to the yaw rate deviation Δγ according to the ΔSy map stored in the ROM 74. This map has the characteristics shown in the graph of FIG. There is a relationship between the slip ratio and the braking force as shown in the solid line graph in Figure 11, and in particular, there is a relationship between the usage range of the slip ratio and the braking force, where the larger the slip ratio is, the greater the braking force is. do. Therefore,
If it is necessary to increase the braking force on the inner wheel of the turn while decreasing the braking force of the outer wheel of the turn in order to suppress the understeer tendency, increase the target slip rate of the inner wheel of the turn while decreasing the target slip rate of the outer wheel of the turn. In addition, in order to suppress the oversteer tendency or to promote recovery of the vehicle body attitude after a countersteer operation, it is necessary to increase the braking force on the outer turning wheel while decreasing the braking force on the inner turning wheel. In some cases, the target slip rate of the outer wheel is increased while the target slip rate of the inner wheel is decreased. The inner turning wheels are the left front wheel 22 and the left rear wheel 34 in the case of a left turn, and the right front wheel 24 and the right rear wheel 36 in the case of a right turn. Further, the turning outer wheels are the right front wheel 24 and the right rear wheel 36 in the case of left turning, and the left front wheel 22 and the left rear wheel 34 in the case of right turning.

In short, the target slip rate is set to the left wheels 22, 3.
4 and the right wheels 24 and 36, if an understeer tendency occurs when turning left, an oversteer tendency occurs when turning right, or a countersteer operation is performed when turning right ( In the case (hereinafter referred to as the first case), the left wheels 22 and 34 are on the side where the target slip ratio increases,
The right wheels 24 and 36 are on the decreasing side, and on the other hand, if an oversteer tendency occurs when turning left, an understeer tendency occurs when turning right, or a countersteer operation is performed when turning left (hereinafter referred to as the latter case). ) has the right wheel 24,3
The sign of the yaw rate deviation Δγ is positive in the first case and negative in the second case, and the sign of the yaw rate deviation Δγ is positive in the first case and negative in the second case. Since the value represents the gap between the actual yaw rate γa and the target yaw rate γd, the yaw rate deviation Δγ can be calculated without determining whether the turning direction of the vehicle is left or right.
Immediately after that, the left and right wheel target slip rate ΔSy−fl, ΔSy
-fr, ΔSy-rl and ΔSy-rr can be determined.

In this embodiment as well, in order to avoid excessive increase and decrease in brake pressure, the left and right wheel target slip ratio changes ΔSy-fl, ΔSy are adjusted as shown in FIG.
-fr, ΔSy-rl, and ΔSy-rr also have upper and lower limits.

Thereafter, in S114 of FIG. 12, the target slip rates Sd-fl, Sd-fr, Sd-rl of each wheel are determined.
and Sd-rr are determined to be the sum of the standard value So and the left and right wheel target slip ratio changes ΔSy-fl, ΔSy-fr, ΔSy-rl, and ΔSy-rr. However, when executing this step each time after the second time, the target slip rates Sd-fl, Sd-fr, Sd-rl and Sd
-rr is its previous value and left and right wheel target slip rate change Δ
Sy-fl, ΔSy-fr, ΔSy-rl and ΔSy
-rr is determined as the sum of the current value. Next, S in Figure 2
Steps 15 and subsequent steps are executed.

Therefore, in this embodiment, the target slip ratio of the left and right wheels is changed using the yaw rate deviation, which is a parameter that accurately reflects the actual turning characteristics, regardless of whether the vehicle is in a countersteer state or not. A sufficient effect of improving turning performance can be obtained by controlling the left and right distribution of braking force.

As is clear from the above description, in this embodiment, the computer's steps S102 to S10 in FIG.
The portion that executes steps 6 and 109 to 114 constitutes left and right wheel target slip ratio changing means.

The present invention can also be implemented as a braking force control device that always performs braking force front/rear distribution control and braking force left/right distribution control simultaneously. Hereinafter, one embodiment thereof will be described based on the drawings.

RO of the controller 70 in this embodiment
M74 stores a braking slip control program in which the flowchart of FIG. 1 is changed to the flowchart of FIG. 14. In this program, S201 to S21
1 is executed in the same manner as S1 to S11 in FIG.
At 212, the target slip rate Sd-fl,S of each wheel is determined.
d-fr, Sd-rl and Sd-rr are determined. Target slip rate for each wheel Sd-fl, Sd-fr, Sd-
rl, Sd-rr are the standard value So and the front and rear wheel target slip rate changes ΔSx-fl, ΔSx-fr, ΔSx of each wheel.
-rl, ΔSx-rr and the left and right wheel target slip rate change amount ΔSy-fl, ΔSy-fr, ΔSy-rl, ΔS
It is the sum of y-rr. Specifically, S212
, the front and rear wheel target slip rate change amount ΔSx− of each wheel is
fl, ΔSx-fr, ΔSx-rl and ΔSx-rr
is determined according to the ΔSx map in FIG. 10 in relation to the turning characteristic value C, and the left and right wheel target slip rate change amount Δ
Sy-fl, ΔSy-fr, ΔSy-rl and ΔSy
-rr is related to the yaw rate deviation Δγ, ΔS in FIG.
Determined according to the y map. After that, in S214, the target slip rate Sd-fl, Sd-fr,
Sd-rl and Sd-rr are the standard value So and the front and rear wheel target slip rate changes ΔSx-fl, ΔSx-fr, ΔS
It is determined to be the sum of x-rl and ΔSx-rr and the left and right wheel target slip ratio changes ΔSy-fl, ΔSy-fr, ΔSy-rl, and ΔSy-rr. However, when executing this step each time after the second time, the target slip rates of each wheel Sd-fl, Sd-fr, Sd-rl and Sd-r
r is its previous value and front and rear wheel target slip rate change amount ΔSx
-fl, ΔSx-fr, ΔSx-rl and ΔSx-r
Current value of r and left and right wheel target slip rate change amount ΔSy-fl
, ΔSy-fr, ΔSy-rl, and ΔSy-rr with the current value. Thereafter, the steps after S15 in FIG. 2 are executed.

Therefore, in this embodiment, since the left and right wheel target slip rate change amount and the front and rear wheel target slip rate change amount are determined based on the yaw rate deviation and the product of it and the actual yaw rate, the braking force A sufficient turning performance improvement effect can be obtained by the left-right distribution control and the front-rear distribution control.

As is clear from the above explanation, in this embodiment, steps S202 to 206, 209, 21 in FIG.
The portion that executes steps 0 and 214, the portion that calculates the yaw rate deviation Δγ in S211, and the portion that determines the left and right wheel target slip rate change amount ΔSy in S212 constitute left and right wheel target slip rate changing means. S202 in the diagram
〜206, 209 to 211 and 214, and front and rear wheel target slip rate change amount ΔSx of S212
The portion that determines the front and rear wheel target slip ratios changes means.

The present invention can also be implemented as a braking force control device that always performs braking force left/right distribution control, but performs braking force front/rear distribution control as needed. Hereinafter, one embodiment thereof will be described in detail based on the drawings.

RO of the controller 70 in this embodiment
M74 stores a braking slip control program in which the flowchart of FIG. 1 is changed to the flowchart of FIG. 15. In this program, S301 to S31
1 is executed in the same manner as S1 to S11 in FIG.
312, the front and rear wheel target slip rate change amount Δ of each wheel
Sx-fl, ΔSx-fr, ΔSx-rl, ΔSx-r
r is determined in relation to the turning characteristic value C according to the ΔSx map in FIG.
rr is related to the yaw rate deviation Δγ, ΔSy in FIG.
Determined according to the map. After that, in S313, the absolute value of the yaw rate deviation is the set yaw rate deviation γm
It is determined whether S is less than or equal to ax, and if so, S
314a, the target slip rate Sd-fl of each wheel,
Sd-fr, Sd-rl, and Sd-rr are the standard value So and the left and right wheel target slip rate changes ΔSy-fl, ΔSy-f
r, ΔSy-rl, ΔSy-rr; otherwise, in S314b, the standard value So and the front and rear wheel target slip ratio changes ΔSx-fl, ΔSx-fr
, ΔSx-rl, ΔSx-rr and left and right wheel target slip rate change amount ΔSy-fl, ΔSy-fr, ΔSy-rl, Δ
It is determined to be the sum of Sy-rr. However, when executing S314a each time after the second time, the previous value of the target slip rate Sd-fl, Sd-fr, Sd-rl, Sd-rr of each wheel and the amount of change in the left and right wheel target slip rate ΔSx-fl, ΔS
x-fr, ΔSx-rl, ΔSx-rr, and the target slip ratios Sd-fl, Sd-f for each wheel are determined as the sum of the current values of x-fr, ΔSx-rl, and ΔSx-rr.
Previous values of r, Sd-rl, Sd-rr and front and rear wheel target slip rate changes ΔSy-fl, ΔSy-fr, ΔSy-r
Current value of l, ΔSy-rr and left and right wheel target slip rate change amount ΔSy-fl, ΔSy-fr, ΔSy-rl, ΔSy
-rr is determined as the sum of the current value. After that, S in Figure 2
Steps 15 and subsequent steps are executed.

[0053] Measures to improve turning performance through front-rear braking force distribution control are generally effective when the coefficient of friction of the road surface is high, but are less effective when the friction coefficient of the road surface is low. Therefore, if braking force front and rear distribution control is always performed regardless of the level of the friction coefficient of the road surface, the target slip ratio may be changed unnecessarily. Therefore, in this embodiment, when the absolute value of the yaw rate deviation is less than or equal to the set yaw rate deviation, it is determined that the friction coefficient of the road surface is low, and the braking force front and rear distribution control is omitted, thereby reducing the target slip rate. This prevents drastic changes.

As is clear from the above description, in this embodiment, the computer's steps S302 to S30 in FIG.
6, 309, 310, 313 to 314b, a portion of S311 that calculates the yaw rate deviation Δγ, and a portion of S312 that calculates the left and right wheel target slip rate change amount ΔSy.
The portion that determines the left and right wheel target slip ratio changing means constitutes S302 to 306, 309 to 311, and 3 in the same figure.
The portion that executes steps 13 and 314b and the portion of S312 that determines the front and rear wheel target slip rate change amount ΔSx constitute front and rear wheel target slip rate changing means.

It should be noted that in all of the embodiments described above, the target slip rate Sd of each wheel is a continuous value of the yaw rate deviation Δγ or the turning characteristic value C.
Since the braking force of each wheel is continuously changed according to the change in the braking force, discontinuous changes in the braking force of each wheel are prevented, and the effect of smoothing changes in the behavior of the vehicle body can be obtained. However, it is not essential to continuously change the target slip ratio Sd in this way; for example, it is possible to change the target slip ratio Sd in stages according to the yaw rate deviation Δγ or the turning characteristic value C. be.

Furthermore, in the embodiment described above, the actual yaw rate γa is obtained using the yaw rate sensor 100, and the actual vehicle body slip angle β is estimated using the actual yaw rate γa. The actual vehicle body slip angle β may be obtained using a sensor. By the way, in a linear two-degree-of-freedom region related to vehicle body motion, if the actual steering angle θ is the input signal and the actual yaw rate γa is the output signal, then the actual steering angle θ and the actual yaw rate γa are
Between (Tr ・s+1)・γo / (a・s2 +b・s+
1) If the actual steering angle θ is the input signal and the actual vehicle body slip angle β is the output signal, then between the actual steering angle θ and the actual yaw rate γa, (Gbo+Gb1・s)・γo /(a・s2 +b・
s+1) exists. However, Tr, γ
o, Gbo and Gb1 are values obtained according to the maps of FIGS. 6, 8, 4 and 5, respectively, as described above, and a and b are respectively related to the estimated vehicle speed Ve, and as shown in FIG. 16 and the values obtained according to the maps in FIG. 17. Therefore, yaw rate sensor 1
00 also has a steering angle sensor 9 even if there is no body slip angle sensor.
8, it is possible to estimate both the actual yaw rate γa and the actual vehicle body slip angle β from the actual steering angle θ.

Further, in the embodiment described above, the braking force is made different between the left wheels 22, 34 and the right wheels 24, 36, and the cornering force is made different between the front wheels 22, 24 and the rear wheels 34, 36. In order to vary the target slip ratio Sd of each wheel, the target slip rate Sd of each wheel was variable and the set wheel acceleration Gwo was unchanged, but the set wheel acceleration Gwo can also be made variable.

Furthermore, in the embodiments described above, the target slip ratio Sd of each wheel is achieved by controlling the braking force of the brakes when the vehicle is braked. Target slip rate Sd of each wheel by controlling force
Even if this is achieved, the target slip ratio Sd of each wheel may be achieved by jointly controlling the braking force by the brake and controlling the driving force by the engine or the like. Further, the target slip ratio Sd may be achieved by these methods not only when the vehicle is braking but also when the vehicle is not braking. That is, the braking force of each wheel in the present invention means the force of each wheel to suppress the movement of the vehicle body.

Although several embodiments of the present invention have been described above in detail based on the drawings, these are literally illustrative, and the present invention can be modified with various modifications and improvements based on the knowledge of those skilled in the art. Of course, it is possible to implement the following.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the first half of a brake slip control program in a brake force control device that is an embodiment of the present invention.

FIG. 2 is a flowchart showing the latter half of the brake slip control program.

FIG. 3 is a system diagram of a vehicle brake system including the braking force control device.

FIG. 4 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 5 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 6 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 7 is a diagram for explaining the relationship between actual wheel speed and converted wheel speed.

FIG. 8 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 9 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 10 is a graph showing a map stored in the ROM in FIG. 3;

FIG. 11 is a diagram for explaining the relationship between slip ratio, braking force, and cornering force.

FIG. 12 is a flowchart showing the first half of a brake slip control program in a braking force control device according to another embodiment.

FIG. 13 is a graph showing a map stored in the ROM of the braking force control device.

FIG. 14 is a flowchart showing the first half of a brake slip control program in a braking force control device according to yet another embodiment.

FIG. 15 is a flowchart showing the first half of a brake slip control program in a braking force control device according to yet another embodiment.

FIG. 16 is a graph for explaining a variable a used to estimate an actual yaw rate and an actual vehicle body slip angle from a steering angle.

FIG. 17 is a graph for explaining a variable b used to estimate an actual yaw rate and an actual vehicle body slip angle from a steering angle.

[Explanation of symbols]

10 Master cylinder 20 Solenoid hydraulic control valve 22 Left front wheel 24 Right front wheel 26 Wheel cylinder 32 Electromagnetic hydraulic control valve 34 Left rear wheel 36 Right rear wheel 38 Wheel cylinder 70 Controller 88 Brake switch 98 Steering angle sensor 100 Yaw rate sensor 102 Longitudinal acceleration sensor

Claims (1)

[Claims] 1. A braking force control device that controls the braking force of each wheel so that the actual slip rate of each wheel provided on the front, rear, left, and right sides of a vehicle body becomes each target slip rate, wherein the target yaw rate of the actual yaw rate of the vehicle body is a left and right wheel target slip rate changing means for changing the target slip rate of at least one of the left wheel and the right wheel based on the yaw rate deviation from the front wheel and the rear wheel based on the product of the yaw rate deviation and the actual yaw rate; A braking force control device comprising at least one of front and rear wheel target slip ratio changing means for changing the target slip ratio of at least one of the wheels.