JPH1178836A - Driving force control device for four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the other wheels from being unnecessarily braked when the velocity of some of the wheels is reduced, and sufficiently improve a rough road ability and a turning characteristic of the vehicle while the differential revolution of each wheel is properly inhibited. SOLUTION: This control device calculates (S20) the body velocity Vb of the center of gravity of the vehicle according to the wheel velocity Vwi of each wheel, and calculates (S40) the basic wheel velocity Vbi of each wheel according to the body velocity Vb, then calculates (S50) the slip amount SLi of each wheel as the difference between the actual wheel velocity Vwi and the basic wheel velocity Vbi. When the slip amount SLi is positive (S60), the control basic amount A Vwi of each wheel is calculated (S70) according to the slip amount SLi, and the control targeted amount ΔVt is calculated (S80) according to the vehicle velocity V and the lateral acceleration Gy, also the targeted control amount BPi of each wheel is calculated (S90) according to the difference between the control basic amount ΔVwi and the control targeted amount ΔVt, then the brake pressure of each wheel is controlled (S100, S110) according to the targeted control amount BPi.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle, and more particularly, to a driving force control device for a four-wheel drive vehicle.

[0002]

2. Description of the Related Art One of the driving force control devices for a four-wheel drive vehicle is disclosed in, for example, Japanese Patent Application No. Hei.
As described in US Pat. No. 23,695 and drawings, a drive configured to calculate a wheel speed difference between front and rear or left and right wheels and to apply a braking force to a wheel having a drive slip based on the wheel speed difference. Force controllers have already been proposed.

According to such a driving force control device, a wheel having a driving slip is automatically braked and its wheel speed is reduced to an appropriate value, so that a wheel speed difference between front and rear or left and right wheels becomes excessive. And the actual driving force of each wheel can be increased without providing a dedicated differential limiting mechanism such as a differential lock mechanism.

[0004]

However, in the driving force control device as described above, if the wheel speed of any one of the wheels decreases for some reason, it is determined that the other wheels are in the driving slip state. Therefore, there is a problem that the vehicle is decelerated due to unnecessary braking of other wheels.

Further, it is necessary to prevent unnecessary drive slip control from being performed due to a difference in wheel speed between the inner and outer wheels during turning of the vehicle. Therefore, a small differential target value between the left and right wheels is set. Therefore, there is a problem that it is impossible to sufficiently improve running performance on a rough road (stack escape performance) and turning performance at the time of turning.

The present invention relates to a driving force control apparatus for a four-wheel drive vehicle configured to control the braking force of the wheels based on the wheel speed difference between the front and rear or left and right wheels to suppress the differential rotation of each wheel. SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and a main object of the present invention is to obtain a magnitude of a drive slip of each wheel based on a vehicle speed at a reference position of the vehicle and a wheel speed of each wheel. At the same time, by braking the wheels based on the difference in the magnitude of the drive slip between the wheels, it is possible to prevent unnecessary braking of the other wheels when the wheel speed of any of the wheels decreases, and The objective of the present invention is to sufficiently improve the vehicle's ability to travel on rough roads and the turning performance while favorably suppressing the differential rotation of the vehicle.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a structure according to claim 1, namely, means for detecting the actual wheel speed of each wheel, and the vehicle speed at a reference position of the vehicle. Means for estimating the actual wheel speed of each wheel at the reference position, and means for estimating the actual wheel speed of each wheel at the reference position. This is achieved by a four-wheel drive vehicle driving force control device having means for calculating the magnitude of the driving slip and means for calculating the braking target amount for each wheel based on the difference in the magnitude of the driving slip between the wheels. You.

According to the configuration of the first aspect, the vehicle speed at the reference position of the vehicle is estimated as the reference wheel speed, and the actual wheel speed of each wheel at the reference position is estimated. The magnitude of the drive slip of each wheel is calculated based on the actual wheel speed of each wheel and the reference wheel speed, and the braking target amount of each wheel is calculated based on the difference in the magnitude of the drive slip between the wheels. Even if the wheel speed of one of the wheels decreases due to some factor, it is not determined that the other wheels are in the drive slip state, and therefore, the wheels are not unnecessarily braked.

Further, since the difference in wheel speed between the inner and outer wheels required for turning of the vehicle is reflected in the reference wheel speed, the differential target value between the left and right wheels can be set to be small. It is possible to sufficiently improve the vehicle's ability to travel on rough roads and turn performance while preventing unnecessary drive slip control from being performed due to the speed difference.

[0010]

According to a preferred aspect of the present invention, in the above-described structure of the first aspect, the reference position of the vehicle is the position of each wheel, and the vehicle speed at the reference position is determined. The means for estimating the reference wheel speed estimates the vehicle speed at a specific position of the vehicle based on the actual wheel speed of each wheel, and calculates the vehicle speed at each wheel position based on the vehicle speed at the specific position. It is configured to estimate by calculation (preferred mode 1).

According to another preferred embodiment of the present invention, in the above-mentioned preferred embodiment 1, the specific position of the vehicle is set at the center of gravity of the vehicle (preferred embodiment 2). .

According to another preferred embodiment of the present invention, in the above-mentioned configuration of the first aspect, the difference in the magnitude of the drive slip between the respective wheels is determined by the magnitude of the magnitude of the drive slip between the left and right wheels. It is configured to be a linear sum of the difference and the difference between the average value of the drive slip magnitudes of the left and right front wheels and the average value of the drive slip magnitudes of the left and right rear wheels (preferred embodiment 3).

[0013]

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

FIG. 1 is a schematic diagram showing one embodiment of a driving force control apparatus for a four-wheel drive vehicle according to the present invention.

In FIG. 1, reference numeral 10 denotes an engine. The driving force of the engine 10 is transmitted to an output shaft 16 via a torque converter 12 and a transmission 14, and the driving force of the output shaft 16 is a center differential 1.
The power is transmitted to the front wheel propeller shaft 20 and the rear wheel propeller shaft 22 by 8. As is well known, the output of the engine 10 is controlled in accordance with the depression amount of an accelerator pedal (not shown in FIG. 1) operated by the driver.

The driving force of the front wheel propeller shaft 20 is transmitted to the left front wheel axle 26L and the right front wheel axle 26R by the front wheel differential 24.
8FL and 28FR are rotationally driven. Similarly, the driving force of the rear wheel propeller shaft 22 is the rear wheel differential 30
To the left rear wheel axle 32L and the right rear wheel axle 32R, whereby the left and right rear wheels 34RL and 34RR are rotationally driven.

The braking force of the left and right front wheels 28FL, 28FR and the left and right rear wheels 34RL, 34RR is controlled by a hydraulic circuit 38 of a braking device 36.
Corresponding wheel cylinders 40FL, 40FR, 40
It is controlled by controlling the braking pressure of RL and 40RR. Although not shown in the drawing, the hydraulic circuit 38 includes a reservoir, an oil pump, various valve devices, and the like, and the braking pressure of each wheel cylinder is normally driven in response to the driver's depression operation of the brake pedal 42. It is controlled by a master cylinder 44 and, if necessary, by an electric control unit 44 as will be described in detail later.

The electric control unit 44 includes a wheel speed sensor 4
Signals indicating the wheel speeds Vfr, Vfl, Vrr, Vrl of the left and right front wheels and left and right rear wheels from 6fr, 46fl, 46rr, 46rl, a signal indicating the yaw rate γ of the vehicle from the yaw rate sensor 48,
A signal indicating the longitudinal acceleration Gx and a lateral acceleration Gy of the vehicle from the longitudinal acceleration sensor 50 and the lateral acceleration sensor 52, a signal indicating the vehicle speed V from the vehicle speed sensor 54, and a signal indicating the steering angle θ from the steering angle sensor 56 are input. It has become. The yaw rate sensor 48, the lateral acceleration sensor 52
The steering angle sensor 56 detects lateral acceleration and the like with the left turning direction of the vehicle as positive, and the longitudinal acceleration sensor 50 detects longitudinal acceleration with the acceleration direction of the vehicle as positive.

As will be described later in detail, the electric controller 44 calculates the vehicle speed Vb at the center of gravity of the vehicle based on the wheel speed Vwi (i = fr, fl, rr, rl) of each wheel, and calculates the vehicle speed. Based on Vb, the reference wheel speed Vbi of each wheel is calculated as the vehicle speed at the position of each wheel, and the slip amount SLi of each wheel is calculated as the difference between the actual wheel speed Vwi and the reference wheel speed Vbi. The control reference amount ΔVwi for each wheel is calculated based on the slip amount SLi, the control target amount ΔVt is calculated based on the vehicle speed V and the lateral acceleration Gy, and the target value for each wheel is calculated based on the difference between the control reference amount ΔVwi and the control target amount ΔVt. The control amount BPi is calculated, the duty ratio DRi of the pressure increase / decrease control valve of each wheel is calculated based on the target control amount BPi, and the pressure increase / decrease control valve of each wheel is controlled based on the duty ratio DRi to reduce the braking pressure of each wheel. Control to a value corresponding to the target control amount BPi, More suppress unwanted differential rotation of each wheel.

Note that the electric control device 44 is actually, for example, C
It may be constituted by one microcomputer including a PU, a ROM, a RAM, and an input / output device and a drive circuit.
The electric control device 44 may be a part of a behavior control device that stabilizes the behavior of the vehicle by controlling, for example, the braking / driving force of each wheel.

Next, the main routine of the driving force control of each wheel in the embodiment will be described with reference to the flowchart shown in FIG. The control according to the flowchart shown in FIG. 2 is started by closing an ignition switch (not shown). For example, the right front wheel, the left front wheel,
It is repeatedly executed at predetermined time intervals in the order of the right rear wheel and the left rear wheel.

First, in step 10, the wheel speed Vwi of each wheel detected by the wheel speed sensors 46fr to 46rl.
Is read, and in step 20, the vehicle speed Vb at the center of gravity as a specific position of the vehicle is calculated based on the wheel speeds Vwi and the like in accordance with the flowchart shown in FIG.

In step 30, the deviation Gy between the lateral acceleration Gy and the product Vb.γ of the vehicle speed Vb and the yaw rate γ is calculated.
The deviation of the lateral acceleration, ie, the side slip acceleration Vyd of the vehicle is calculated as −Vb · γ, and the side slip speed Vy of the vehicle body is calculated by integrating the deviation Vyd of the lateral acceleration. Ratio Vy / Vb
Is calculated as the slip angle β of the vehicle body at the center of gravity of the vehicle.

In step 40, the steering angle δ of the front wheels is calculated according to the following equation 1 using Nsg as the steering gear ratio, and Lf is the distance between the center of gravity and the axle of the front wheels.
T is the tread of the vehicle, and the reference wheel speed Vbi (i = fr, fl, r
r, rl) are calculated.

[0025]

Δ = θ / Nsg

## EQU2 ## Vbfr = Vb.cos (δ-β) -γ (T / 2)
cosδ + γ · sinδ · Lf Vbfl = Vb · cos (δ−β) + γ (T / 2) cosδ +
γ · sin δ · Lf Vbrr = Vb · cosβ + γ · T / 2 Vbrl = Vb · cosβ−γ · T / 2

In step 50, the slip amount SLi (i = fr, fl, rr, rl) of each wheel is calculated as the deviation between the actual wheel speed Vwi of each wheel and the reference wheel speed Vbi according to the following equation (3). In step 60, the slip amount SL of each wheel
It is determined whether or not i is positive. If a negative determination is made, the process returns to step 10, and if an affirmative determination is made, the process proceeds to step 70.

## EQU3 ## SLi = Vwi-Vbi

In step 70, the control reference amount ΔVwi (i = f) for each wheel is set in accordance with the flowchart shown in FIG.
r, fl, rr, rl) are calculated, and in step 80, the control target amount ΔVt is obtained from the map corresponding to the graph shown in FIG. 5 based on the vehicle speed V and the absolute value of the lateral acceleration Gy of the vehicle.
Is calculated. The vehicle speed V may be replaced with the vehicle speed Vb.

In step 90, the control target amount BPi (i = fr, fl, rr, rl) of each wheel is calculated in accordance with the following equation 4 as Ka is a positive constant smaller than 1 and close to 1. In step 100, based on the control target amount BPi, the duty ratio DRi (i = fr, fl, rr, r) of the pressure increasing / decreasing control valve of each wheel is obtained from the map corresponding to the graph shown in FIG.
l) is calculated, and in step 100, the pressure increasing / decreasing control valve of each wheel is opened and closed based on the duty ratio DRi so that the braking force of each wheel is controlled to a value corresponding to the control target amount BPi. .

BPi = Ka (ΔVwi−ΔVt)

In step 100, when the duty ratio DRi is positive, the braking pressure of the corresponding wheel is increased, and when the duty ratio DRi is negative, the braking pressure of the corresponding wheel is reduced, and the duty ratio DRi becomes 0. In the case of, the braking pressure of the corresponding wheel is held.

In step 21 of the vehicle speed Vbi calculation routine shown in FIG. 3, Ku is used as a coefficient for adjusting the unit and the speed at the wheel position at the yaw rate and the center of gravity of the vehicle are calculated according to the following equation (5). The speed difference Vyr from the speed at the time is calculated.

Vyr = γ · (T / 2) · Ku · π / 180

In step 22, using W as the weight of the vehicle, H as the height of the center of gravity of the vehicle, and L as the wheel base, the load movement amount ΔWgx of each wheel by the longitudinal acceleration Gx is calculated according to the following equation (6).

ΔWgx = Gx · W · H / L / 2

In step 23, the load movement amounts .DELTA.Wgyf and .DELTA.Wgyr of the front wheel and the rear wheel due to the lateral acceleration Gy are calculated in accordance with the following equation 7 using Gpf and Gpr as the roll rigidity distribution on the front wheel side and the rear wheel side, respectively.

ΔWgyf = (Gy · W · H / T) · Gpf ΔWgyr = (Gy · W · H / T) · Gpr

In step 24, g is the gravitational acceleration, K is the tire stiffness, and Rt is the tire radius. The dynamic correction coefficient Kdi (i = fr, fl, rr, rl) are calculated.

Kdfr = 1 + ｛− ΔWgx + ΔWgyf｝ · g / K / Rt Kdfl = 1 + ｛− ΔWgx−ΔWgyf｝ · g / K / RtKdrr = 1 + ｛ΔWgx + ΔWgyf｝ · g / K / RtKdrl = 1 + ｛W ΔWgyf｝ · g / K / Rt

In step 25, the longitudinal velocity V of the vehicle at the center of gravity of the vehicle for each wheel according to the following equation (9)
ri (i = fr, fl, rr, rl) is calculated.

Vrfr = Kdfr.Vwfr.cos.delta.-Vyr Vrfl = Kdfl.Vwfl.cos.delta. + Vyr Vrrr = Kdrr.Vwrr-Vyr Vrrl = Kdrl.Vwrl + Vyr.

In step 26, it is determined whether or not the longitudinal acceleration Gx of the vehicle is positive, that is, whether or not the vehicle is accelerating. If an affirmative determination is made, the process proceeds to step 27. In this case, the minimum value of the front-rear speeds Vri of the vehicle body is selected as the front-rear speed Vws, and if a negative determination is made, the maximum value of the front-rear speeds Vri of the vehicle body is selected in step 28 as the front-rear speed Vws.

In step 29, Vbf is set to the vehicle speed obtained in step 29 one cycle before, and α
The vehicle speed Vb is calculated according to the following equation 10 with 1 and α2 being positive constants. In the following Expression 10, MED means that an intermediate value of three numerical values in parentheses is selected.

Vb = MED [Vms, Vbf + α1, Vbf−α2]

The control reference amount ΔV for each wheel shown in FIG.
In step 71 of the wi calculation routine, the lateral acceleration G
Based on y, a coefficient Kcfr is calculated from a map corresponding to the graph shown in FIG. 7, and a coefficient Kcfl is calculated from a map corresponding to the graph shown in FIG. Based on the absolute value of the lateral acceleration Gy, the coefficient Kb is obtained from a map corresponding to the graph shown in FIG.
Is calculated. The coefficient Kb is set to 0 when the deceleration slip of any one wheel is excessive.

In step 73, the average slip amount SLaf of the left and right front wheels is calculated according to the following equation (11).

## EQU11 ## SLaf = ｛(Vwfr + Vwfl)-(Vbfr +
Vbfl)｝ / 2

In step 74, the average slip amount SLa of the left and right rear wheels is calculated according to the following equation (12).

Slar = １２ (Vwrr + Vwrl) − (Vbrr +
Vbrl)｝ / 2

In step 75, the control reference amount ΔVwi (i = fr, fl, rr, rl) of each wheel is calculated according to the following equation (13).

ΔVwfr = SLfr−Kcfr · SLfl + Kb ·
(SLaf−SLar) ΔVwfl = SLfl−Kcfl · SLfr + Kb · (SLaf−
(SLar) ΔVwrr = SLrr−SLrl + Kb (SLar−SLaf) ΔVwrl = SLrl−SLrr + Kb (SLar−SLaf)

In the above equation (13), when SLi <0, SLi is set to 0, when SLaf-Slar <0, SLaf-Slar is set to 0, and SLa-SLaf <
When it is 0, Slar-SLaf is set to 0.

Thus, according to the illustrated embodiment, in step 20, the wheel speeds Vwi (i = fr, fl, rr,
rl), the vehicle speed Vb at the center of gravity of the vehicle is calculated, and in step 30, the slip angle β of the vehicle is calculated. In step 40, the vehicle speed at each wheel position is calculated based on the vehicle speed Vb. The reference wheel speed Vbi of each wheel is calculated. In step 50, the slip amount SLi of each wheel is calculated as the difference between the actual wheel speed Vwi and the reference wheel speed Vbi.

When the slip amount SLi is positive, the control reference amount ΔVwi for each wheel is calculated in step 70 based on the slip amount SLi, and in step 80 the control target amount ΔVt is calculated based on the vehicle speed V and the lateral acceleration Gy. In step 90, the target control amount BPi of each wheel is calculated based on the difference between the control reference amount ΔVwi and the control target amount ΔVt. In step 100, the pressure increase / decrease control of each wheel is performed based on the target control amount BPi. The duty ratio DRi of the valve is calculated, and in step 110, the pressure increase / decrease control valve of each wheel is controlled based on the duty ratio DRi, so that the braking pressure of each wheel is controlled to a value corresponding to the target control amount BPi. .

For example, if no excessive drive slip has occurred on any of the wheels, the slip amount SLi of each wheel becomes 0 or a very small value, and the program proceeds to step 60.
In step 90, the target control amount BPi of each wheel calculated in step 90 becomes 0 or a very small value, and the braking force control for suppressing the differential rotation is not executed.

On the other hand, if an excessive drive slip occurs on any of the wheels, the slip amount SLi of the relevant wheel becomes a relatively large positive value, and an affirmative determination is made in step 60, and steps 70 to 110 are performed. Is performed, excessive drive slip can be reduced, and differential rotation can be reliably suppressed.

In particular, even if an excessive drive slip occurs on any of the wheels during turning of the vehicle, the reference wheel speed Vbi of each wheel calculated in step 40 is calculated based on the vehicle speed Vb, Since the wheel speed difference corresponding to the difference in the turning radius of the wheels is reflected, it is possible to avoid the deterioration of the turning performance and poor road running performance of the vehicle due to the braking force control for suppressing the differential rotation, Further, the dead zone (-BPo to BPo) of the map shown in FIG. 6 for calculating the duty ratio DRi in step 100 can be reduced to improve the differential rotation suppression performance during normal running of the vehicle. .

Further, even if the wheel speed of any one of the wheels is reduced and an excessive deceleration slip is generated in the wheel, a negative determination is made in step 60 for the wheel to prevent the differential rotation. No braking force control is performed, and for the other wheels, in the calculation of the control reference amount ΔVwi in step 70, the slip amount SLi of the relevant wheel is set to 0.
And the coefficient Kb is set to 0, the control reference amount .DELTA.Vwi of the other wheels is prevented from being calculated to an excessive value, so that unnecessary braking force control is performed for the other wheels. Can be prevented.

In particular, according to the illustrated embodiment, the target control amount ΔVt calculated from the map shown in FIG. 5 is set to increase as the vehicle speed increases and to decrease as the lateral acceleration increases. The coefficients Kcfr and Kcfl calculated from the maps shown in FIG. 7 and FIG. 8 are set so as to decrease as the corresponding lateral acceleration in the vehicle lateral direction increases, so that these target control amounts and coefficients correspond to the vehicle speed and the lateral acceleration. Regardless, the turning performance of the vehicle can be improved without deteriorating the differential rotation suppressing performance as compared with the case where the rotation speed is constant.

Further, for example, when the vehicle is traveling at a low speed and a large steering angle, the rolling resistance of the front wheels becomes large and the wheel speed of the front wheels becomes small. Therefore, each value calculated using the detected value Vwi of the wheel speed sensor is used. Although the reliability of the reference wheel speed Vbi of the wheels decreases, according to the illustrated embodiment, the coefficient Kb calculated from the map shown in FIG. 9 is set to decrease as the absolute value of the steering angle θ increases. Therefore, in a situation where the reliability of the reference wheel speed Vbi of each wheel is low as described above,
It is possible to reduce a possibility that the braking force control for suppressing the unnecessary differential rotation due to the inaccuracy of the reference wheel speed Vbi is performed.

Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to the above-described embodiments, and various other embodiments may be included within the scope of the present invention. It will be clear to those skilled in the art that is possible.

For example, in the illustrated embodiment, the specific position of the vehicle for calculating the vehicle speed Vb is the center of gravity of the vehicle, but the specific position may be set to a position other than the center of gravity of the vehicle. The reference position of the vehicle for calculating the reference wheel speed is the position of each wheel. The reference position is set, for example, at the center of gravity of the vehicle, and the magnitude of the drive slip of each wheel is determined by the position of each wheel at the center of gravity. The calculation may be performed based on the actual wheel speed and the reference wheel speed (body speed at the center of gravity).

In the illustrated embodiment, the magnitude of the driving slip is determined by the actual wheel speed Vwi of each wheel and the reference wheel speed Vwi.
Although the slip amount SLi is calculated as the deviation from bi, the magnitude of the drive slip may be calculated as a slip ratio (Vwi-Vbi) / Vbi based on the reference wheel speed.

In the illustrated embodiment, the vehicle speed Vb is calculated based on the minimum or maximum value of the vehicle speed Vri for each wheel according to the sign of the longitudinal acceleration Gx of the vehicle. However, the weight may be calculated as the average value of the vehicle speed Vri for each wheel, and the weight of each wheel which is increased or decreased according to the running condition of the vehicle is represented by the following equation (14).
May be calculated as a weighted average of the vehicle speeds Vri of the respective wheels according to

Vb = (Wfr · Vrfr + Wfl · Vrfl + Wrr)
・ Vrrr + Wrl ・ Vrrl) / (Wfr + Wfl + Wrr + Wr)
l)

[0054]

As is apparent from the above description, according to the present invention, even if the wheel speed of one of the wheels decreases due to some factor, it is determined that the other wheels are in the drive slip state. Since there is no wheel, unnecessary braking of the wheels can be reliably avoided, and the difference in wheel speed between the inner and outer turning wheels required when turning the vehicle is reflected in the reference wheel speed. The differential target value of the vehicle can be set small, so that unnecessary drive slip control due to the wheel speed difference between the inner and outer turning wheels is prevented from being performed, and the vehicle's ability to travel on rough roads and turning performance is improved. It can be improved sufficiently.

The magnitude of the drive slip of each wheel is calculated based on the actual wheel speed of each wheel and the reference wheel speed based on the vehicle speed, and the braking target amount of each wheel is calculated based on the magnitude of the drive slip. In this case, if the vehicle speed is estimated to be low for some reason, braking force is applied to all four wheels, so that braking energy is wasted and the vehicle is unnecessarily decelerated. , Since the braking target amount of each wheel is calculated based on the difference in drive slip between the wheels,
The problem described above can be reliably avoided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a driving force control device for a four-wheel drive vehicle according to the present invention.

FIG. 2 is a general flowchart showing a main routine of driving force control in the embodiment.

FIG. 3 is a flowchart illustrating a vehicle speed Vb calculation routine according to the embodiment.

FIG. 4 is a flowchart showing a control reference amount ΔVwi calculation routine for each wheel in the embodiment.

FIG. 5 is a graph showing a relationship between absolute values of a vehicle speed V and a lateral acceleration Gy and a control target amount ΔVt.

FIG. 6 is a graph showing a relationship between a control target amount BPi of each wheel and a duty ratio DRi of each wheel.

FIG. 7 is a graph showing a relationship between a lateral acceleration Gy and a coefficient Kcfr.

FIG. 8 is a graph showing a relationship between a lateral acceleration Gy and a coefficient Kcfl.

FIG. 9 is a graph showing a relationship between an absolute value of a steering angle θ and a coefficient Kb.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Engine 18 ... Center differential 24 ... Front wheel differential 30 ... Rear wheel differential 36 ... Braking device 38 ... Hydraulic circuit 40 ... Electric control device 46fr-46rl ... Wheel speed sensor 48 ... Yaw rate sensor 50 ... Front-back acceleration sensor 52 ... Lateral acceleration Sensor 54: Vehicle speed sensor 56: Steering angle sensor

Claims (1)

[Claims] Means for detecting the actual wheel speed of each wheel, means for estimating the vehicle speed at a reference position of the vehicle as a reference wheel speed, and estimating the actual wheel speed of each wheel at the reference position. Means for calculating the magnitude of the drive slip of each wheel based on the actual wheel speed and the reference wheel speed of each wheel at the reference position, and calculating the difference in the magnitude of the drive slip between the wheels. Means for calculating a braking target amount for each wheel based on the driving force of the four-wheel drive vehicle.