JPH09242575A - Behavior control device for four-wheel drive vehicle - Google Patents

Abstract

(57) Abstract: In a four-wheel drive vehicle in which the differential of the rear wheels is a torque proportional differential device, unnecessary reduction of engine output is prevented and the vehicle is prevented from entering a spin state. To do. SOLUTION: The wheel speeds of the left and right front wheels and the yaw rate of the vehicle are detected (step 10), and a reference wheel speed difference ΔVwy between the left and right front wheels is calculated based on the yaw rate of the vehicle (step 20). The actual wheel speed difference ΔVwa of the front wheels is calculated (step 30). The magnitude of deviation between the reference wheel speed difference ΔVwy and the actual wheel speed difference ΔVwa ΔVwd
iff is calculated (step 40), and the deviation magnitude ΔVwdif
The output of the engine is controlled so that the output reduction amount of the engine increases as f increases, and the spin moment is reduced (steps 50 to 130).

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As one of engine output control devices for four-wheel drive vehicles, as disclosed in, for example, Japanese Patent Laid-Open No. 6-323172, wheel acceleration slip is detected, and wheel acceleration slip is detected. BACKGROUND ART Engine output control devices, which are sometimes configured to reduce engine output to reduce wheel drive torque, are known in the art.

According to such an engine output control device, the driving torque of the wheels is prevented from becoming excessive by controlling the output of the engine according to the acceleration slip of the wheels during acceleration of the vehicle. The wheels are prevented from idling even when the condition of the road surface changes suddenly or the vehicle starts on a road surface having a low friction coefficient.

[0004]

As is well known, in a four-wheel drive vehicle, the driving force of the engine is distributed to the front wheels and the rear wheels by the center differential, and the driving force for the front wheels is distributed to the left and right by the differential of the front wheels. The driving force for the rear wheels is distributed to the front wheels, and the driving force for the rear wheels is distributed to the left and right rear wheels by the differential of the rear wheels.

In particular, in a four-wheel drive vehicle in which the rear wheel differential is a torque proportional type differential device also called a Tosen differential, when all the four wheels are in a slip state at the time of turning acceleration of the vehicle, a ground load is applied. Only the front wheel on the outside of high turning recovers the grip first, and the rear wheels on the left and right maintain the same slip state due to the existence of the torque proportional differential, so that only the cornering force of the front wheel on the outside of turning becomes large and the vehicle has a large spin. A moment may act, and as a result, the behavior of the vehicle may suddenly become unstable.

Further, in order to solve the above-mentioned problem in the four-wheel drive vehicle in which the differential of the rear wheels is a torque proportional differential device, it is considered to reduce the output of the engine when the vehicle accelerates with turning. However, if all four wheels are not in the slipping state, the acceleration of the vehicle will be limited and the driver will feel dissatisfied, although there is no fear of spin generation due to the above reasons. .

The present invention has been made in view of the above-mentioned problems in a four-wheel drive vehicle in which the differential of the rear wheels is a torque proportional type differential device, and the main problem of the present invention is the left and right front wheels. By determining the difference between the acceleration slip states, the engine output is prevented from being unnecessarily reduced during turning acceleration of the vehicle and the vehicle is prevented from entering the spin state.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned main problem is that the behavior control device for a four-wheel drive vehicle according to the present invention, that is, the rear wheel differential is a torque proportional differential device. Then, the means for detecting the wheel speeds of the left and right front wheels, the means for detecting the yaw rate of the vehicle, and the reference wheel speed difference ΔVwy of the left and right front wheels based on the yaw rate of the vehicle.
And a means for calculating the actual wheel speed difference ΔVwa between the left and right front wheels from the detected wheel speeds of the left and right front wheels, the reference wheel speed difference ΔVwy and the actual wheel speed difference ΔV.
Behavior control device for four-wheel drive vehicle having means for calculating the magnitude ΔVwdiff of the deviation from wa and means for controlling the output of the engine so that the greater the magnitude of the deviation ΔVwdiff is, the greater the amount of output reduction of the engine is Achieved by

Since the reference wheel speed difference ΔVwy between the left and right front wheels in the above configuration is calculated based on the yaw rate of the vehicle, it is calculated as the wheel speed difference in a situation where the left and right front wheels are not in acceleration slip. Further, when none of the left and right front wheels is in acceleration slippage or when the left and right front wheels are in the same degree of acceleration slippage, the actual wheel speed difference ΔVwa between the left and right front wheels
Is the same as the reference wheel speed difference ΔVwy, but if only the front wheels on the outside of the turn recover grip from the state where the left and right front wheels are slipping, the magnitude of the actual wheel speed difference ΔVwa becomes larger than the reference wheel speed difference ΔVwy. Therefore, the reference wheel speed difference Δ
Magnitude of deviation between Vwy and actual wheel speed difference ΔVwa ΔVwdiff
Thus, it is possible to determine whether or not only the front wheel on the outside of the turn has recovered the grip, and it is possible to estimate the difference between the grip states of the left and right front wheels.

According to the above-mentioned structure of claim 1, the magnitude Δ of the deviation between the reference wheel speed difference ΔVwy and the actual wheel speed difference ΔVwa.
The output of the engine is controlled so that the output reduction amount of the engine increases as Vwdiff increases, in other words, the difference between the grip states of the left and right front wheels increases. When the grip is restored, the spin moment acting on the vehicle is reduced, which prevents the behavior of the vehicle from suddenly becoming unstable.

According to the present invention, in order to effectively achieve the above object, in the structure of claim 1, the output reduction amount of the engine is reduced when the vehicle is substantially in a straight traveling state. It is configured to have means (configuration of claim 2).

As described above, only the front wheel on the outside of the turning recovers the grip and a large spin moment acts on the vehicle when the vehicle accelerates while turning, so that the vehicle is substantially in a straight traveling state and is in a spin state. It is preferable not to reduce the output of the engine unnecessarily when there is no risk of becoming.

According to the second aspect of the present invention, when the vehicle is substantially traveling straight ahead, the engine output reduction amount is reduced, so that it is possible to prevent the engine output from being unnecessarily greatly reduced. This prevents the driver from feeling unsatisfactory that the vehicle cannot be sufficiently accelerated when the vehicle accelerates straight ahead.

[0014]

According to one preferred embodiment of the present invention, in the above-mentioned constitution of claim 1 or 2,
It is configured to have a means for estimating the friction coefficient of the road surface and a means for decreasing the output reduction amount of the engine as the friction coefficient of the road surface is higher when the estimated value of the friction coefficient of the road surface is a predetermined value or more.

According to another preferred aspect of the present invention, in the above-mentioned structure of claim 1 or 2, when the vehicle speed is equal to or higher than a predetermined value, a means for reducing the output reduction amount of the engine as the vehicle speed becomes higher. Is configured to have.

[0016]

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 configuration diagram showing one embodiment of a behavior control device 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.
8 is transmitted to the front wheel propeller shaft 20 and the rear wheel propeller shaft 22.

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, whereby the left and right front wheels 2 are transmitted.
8FL and 28FR are rotationally driven. Similarly, the driving force of the rear wheel propeller shaft 22 is the rear wheel differential 30.
Is transmitted 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 front wheel differential 24 is a free differential, while the rear wheel differential 30 is a torque proportional differential device.

The output of the engine 10 is controlled by a main throttle 36 and a sub-throttle 38, which are controlled by the driver according to the amount of depression of an accelerator pedal, which is not shown in FIG. The sub throttle 38 is controlled by an engine control device 40 via an actuator 42.

The engine control device 40 receives a signal indicating the engine speed Ne from the rotation speed sensor 44 of the engine 10 and signals indicating various other engine control parameters, and also the throttle opening sensor 46.
Further, a signal indicating the opening φm of the main throttle 36 is input. The engine control unit 40 calculates the target torque Treq of the engine based on the engine speed Ne and other parameters, and calculates the target opening φst of the sub-throttle 38 based on the target torque Treq. In particular, the behavior control unit 50 controls the sub-throttle control. When the command signal is input, the calculated target opening is replaced with the input target opening φst, and a control signal is output to the actuator 42 so that the opening of the sub-throttle 38 becomes the target opening φst. The output of is increased or decreased.

The behavior control device 50 includes a yaw rate sensor 5
2, the signal indicating the yaw rate γ of the vehicle, the wheel speed sensors 54fl and 54fr indicating the left and right front wheel speeds Vfl and Vfr, the vehicle speed sensor 56 indicating the vehicle speed V, the longitudinal acceleration sensor 58 and the lateral acceleration sensor 60, respectively. Signals indicating longitudinal acceleration Gx and lateral acceleration Gy of the vehicle are input. The lateral acceleration sensor 60, the yaw rate sensor 52 and the like detect lateral acceleration and the like with the left turning direction of the vehicle being positive, and the longitudinal acceleration sensor 58 detects longitudinal acceleration with the acceleration direction of the vehicle being positive.

As will be described in detail later, the behavior control device 5
0 calculates the reference wheel speed difference ΔVwy between the left and right front wheels based on the yaw rate γ of the vehicle, calculates the actual wheel speed difference ΔVwa between the left and right front wheels from the detected wheel speed of the left and right front wheels, and calculates the reference wheel speed difference ΔVwy and the actual wheel speed. Magnitude of deviation from difference ΔVwa ΔV
wdiff is calculated, the target opening φst of the sub-throttle 38 is calculated so that the output reduction amount of the engine 10 increases as the deviation ΔVwdiff increases, and the sub-throttle control command signal corresponding to the target opening φst is controlled by the engine. Device 4
0 is output.

The engine control device 40 and the behavior control device 50 may actually be composed of a microcomputer including a CPU, a ROM, a RAM, an input / output device, and a drive circuit.

Next, the main routine of the vehicle behavior control in the embodiment will be described with reference to the flow chart shown in FIG. The control according to the flowchart shown in FIG. 2 is started by closing an ignition switch (not shown) and is repeatedly executed at predetermined time intervals.

First, in step 10, a signal or the like indicating the yaw rate γ of the vehicle detected by the yaw rate sensor 52 is read, and in step 20, Tr is the tread of the vehicle and the left and right front wheels are calculated according to the following equation 1. The reference wheel speed difference ΔVwy is calculated.

[Formula 1] ΔVwy = Tr × γ

In step 30, the actual wheel speed difference ΔVwa between the left and right front wheels is calculated according to the following equation 2 based on the wheel speed Vfl of the left front wheel and the wheel speed Vfr of the right front wheel, and in step 40 the following number is calculated. Reference wheel speed difference Δ
Magnitude of deviation between Vwy and actual wheel speed difference ΔVwa ΔVwdiff
Is calculated.

[0028]

[Formula 2] ΔVwy = Vfr−Vfl

[Formula 3] ΔVwdiff = | ΔVwy−ΔVwa |

In step 50, the correction coefficient Kv is calculated from the map corresponding to the graph shown in FIG. 4 based on the vehicle speed V detected by the vehicle speed sensor 56, and in step 60, the yaw rate γ of the vehicle is calculated. Based on the map corresponding to the graph shown in FIG. 5, the correction coefficient Ky is calculated, and in step 70, the correction coefficient Ky is calculated according to the flowchart shown in FIG. The correction coefficient Kr is calculated from the map corresponding to the graph shown.

In step 80, the corrected reference wheel speed difference ΔVwy and the actual wheel speed difference ΔVwa are calculated according to the following equation 4.
The magnitude δVwdiff of the deviation from is calculated and step 90
In this case, the engine output torque reduction amount Tdwn is calculated from the map corresponding to the graph shown in FIG. 7, and in step 100, the engine output Tall is calculated from the map corresponding to the graph shown in FIG. Is calculated.

(4) δwdiff = ΔVwdiff × Kv × Ky × Kr

In step 110, the target torque Treq of the engine is calculated according to the following equation 5, and in step 120 the target torque Treq is calculated based on the target torque Treq and the engine speed Ne input from the engine control unit 40.
The target opening φst of the sub-throttle is calculated from the map corresponding to the graph shown in FIG. 3, and in step 130, the control command signal for controlling the opening of the sub-throttle 38 to the target opening φst is the engine control device. It is output to 40.

## EQU5 ## Treq = (100-Tdwn) * Tall

Next, referring to the flow chart shown in FIG. 3, the estimated value μ of the friction coefficient of the road surface in the illustrated embodiment
The calculation routine of g will be described. The control according to the flowchart shown in FIG. 3 is executed by interruption every predetermined time.

At step 210, signals indicating the longitudinal acceleration Gx and lateral acceleration Gy of the vehicle detected by the longitudinal acceleration sensor 58 and the lateral acceleration sensor 60, respectively, are read, and at step 220, road friction. The horizontal acceleration Gxy of the vehicle for calculating the estimated value μg of the coefficient is calculated according to the following equation 6.

[Equation 6] Gxy = (Gx ² + Gy ² ) ^1/2

In step 230, the horizontal acceleration Gxy
Is greater than or equal to the estimated value μg (n-1) of the friction coefficient of the road surface one cycle before, and when a positive determination is made, the coefficient K is set to 1 in step 240, When a negative determination is made, the coefficient K is set to 0.01 in step 250. In step 260, the estimated value μg of the friction coefficient of the road surface is calculated according to the following equation 7.

(7) μg = (1−K) * μg (n-1) + K * Gxy

In the illustrated embodiment, the friction coefficient of the road surface is calculated as the root sum of squares of Gx and Gy, but it may be estimated by the absolute value of the lateral acceleration Gy of the vehicle. , And the lateral acceleration components Gyfy at the front wheel position and the rear wheel position generated by yawing of the vehicle,
Gyry is calculated and these components and lateral acceleration G of the vehicle are calculated.
The lateral acceleration components Gyf and Gyr at the front wheel position and the rear wheel position are calculated as the sum of y, the larger value of Gyf and Gyr is calculated as the lateral acceleration Gys, and the square sum square root of Gx and Gys is calculated. Good.

Thus, according to the illustrated embodiment, the vehicle is turning without the left and right front wheels accelerating and slipping, or the vehicle is turning with the left and right front wheels accelerating and slipping to the same extent. Then, the reference wheel speed difference ΔV
wy and the actual wheel speed difference ΔVwa are substantially the same value,
Since the magnitude of these deviations ΔVwdiff becomes substantially 0, the output torque reduction amount Tdwn of the engine 10 calculated in step 90 becomes 0, and therefore the engine output is not reduced in this case, It is controlled substantially according to the amount of depression of the accelerator pedal by the driver, and the driver does not feel unsatisfactory that the vehicle cannot be sufficiently accelerated.

On the other hand, when only the front wheels on the outside of the turn recover the grip from the state where the left and right front wheels and the left and right rear wheels are in acceleration slip, the actual wheel speed difference ΔVwa becomes the reference wheel speed difference ΔVwa.
It becomes a value different from Vwy, and the magnitude δVwdiff of the corrected wheel speed difference calculated in step 80 is δ.
The engine output torque reduction amount Tdwn
Also becomes a positive value, and in this case, the driving force of each wheel, in particular, the driving force of the front wheel on the outside of the turning that restores grip is reduced, so that the spin moment imparted to the vehicle is reduced. The risk of the vehicle spinning is reduced.

In particular, according to the illustrated embodiment, the correction coefficient Ky based on the yaw rate γ is 0 or when the magnitude of the yaw rate γ is substantially 0, in other words, when the vehicle is in a substantially straight traveling state. The output torque reduction amount Tdwn of the engine 10 is also reduced by setting the value smaller than 1 and reducing the magnitude δVwdiff of the deviation of the corrected wheel speed difference, so that the vehicle may be in a spin state. When not present, the driver is prevented from feeling unsatisfactory that the vehicle cannot be sufficiently accelerated due to the unnecessarily reduced output of the engine.

Further, the acceleration slip of the wheels occurs remarkably when the friction coefficient of the road surface is low, and there is a risk of spin generation due to the fact that only the front wheels on the outside of the turn recover grip from the state where the four wheels are in acceleration slip. This decreases as the coefficient of friction of the road surface increases, thus reducing the need to reduce the output of the engine.

According to the illustrated embodiment, the correction coefficient Kr based on the estimated value μg of the friction coefficient of the road surface is the estimated value of the friction coefficient of the road surface when the estimated value μg of the friction coefficient of the road surface is equal to or larger than the predetermined value μgo. Since the higher the value is, the smaller the value becomes, the smaller the value becomes. Therefore, when the friction coefficient of the road surface is high and the possibility that the vehicle is in the spin state is low, the output of the engine is unnecessarily reduced. It also prevents the feeling of dissatisfaction that the vehicle cannot be accelerated sufficiently.

Further, the acceleration slip of the wheels occurs remarkably when the vehicle speed is in a low speed range such as when the vehicle starts, and only the front wheel outside the turning recovers the grip from the state where the four wheels are in the acceleration slip. The risk of spin generation due to this becomes smaller as the vehicle speed becomes higher, and therefore the necessity of reducing the engine output is also reduced.

According to the illustrated embodiment, the correction coefficient Kv based on the vehicle speed V is as follows when the vehicle speed is equal to or higher than the predetermined value Vo.
Since the higher the vehicle speed V is, the smaller the vehicle speed V is gradually set to be. Therefore, when the vehicle speed is high and the possibility that the vehicle is in the spin state is low, the output of the engine is unnecessarily reduced, which causes the driver It also prevents the feeling of dissatisfaction that the vehicle cannot be accelerated sufficiently.

In the above, the present invention has been described in detail with respect to a specific embodiment. However, the present invention is not limited to the above embodiment, and various other embodiments are included within the scope of the present invention. It will be clear to those skilled in the art that is possible.

[0044]

As is apparent from the above description, according to the structure of claim 1 of the present invention, the larger the deviation ΔVwdiff between the reference wheel speed difference ΔVwy and the actual wheel speed difference ΔVwa is, the other words. For example, the engine output is controlled so that the output reduction amount of the engine increases as the difference between the grip states of the left and right front wheels becomes larger. The spin moment that acts on the vehicle can be reduced, which can prevent the vehicle from suddenly entering the spin state.

According to the structure of claim 1, when the left and right front wheels are in the grip state, the deviation magnitude ΔVwdiff
Is substantially 0, the engine output is controlled when the engine output reduction amount is substantially 0, and therefore the driver cannot sufficiently accelerate the vehicle when the vehicle normally turns and accelerates. It is possible to prevent feeling unsatisfied.

In particular, according to the second aspect of the present invention, since the engine output reduction amount is reduced when the vehicle is substantially traveling straight, it is possible to prevent the engine output from being unnecessarily greatly reduced. As a result, it is possible to prevent the driver from feeling unsatisfactory that the vehicle cannot be sufficiently accelerated when the vehicle accelerates straight ahead.

[Brief description of drawings]

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

FIG. 2 is a general flowchart showing a main routine of vehicle behavior control in the embodiment.

FIG. 3 is an estimated value μg of the friction coefficient of the road surface in the embodiment.
3 is a flowchart showing the calculation routine of FIG.

FIG. 4 is a graph showing a relationship between a vehicle speed V and a correction coefficient Kv.

FIG. 5 is a graph showing a relationship between a vehicle yaw rate γ and a correction coefficient Kr.

FIG. 6 is a graph showing a relationship between an estimated value μg of a friction coefficient of a road surface and a correction coefficient Kr.

[FIG. 7] Magnitude of deviation of corrected wheel speed difference δVwdiff
6 is a graph showing a relationship between the engine output torque reduction amount Tdwn.

FIG. 8 is a graph showing the relationship among the main throttle opening φm, the engine speed Ne, and the engine output Tall.

FIG. 9 is a graph showing a relationship between an engine speed Ne, a target torque Treq of the engine, and a sub throttle opening φs.

[Explanation of symbols]

 10 ... Engine 18 ... Center differential 24 ... Front wheel differential 30 ... Rear wheel differential Hydro booster 36 ... Main throttle 38 ... Sub throttle 40 ... Engine control device 50 ... Behavior control device 52 ... Yaw rate sensor 54fl, 54fr ... Wheel speed sensor

Claims (2)

[Claims] 1. A behavior control device for a four-wheel drive vehicle in which a differential of a rear wheel is a torque proportional differential device, means for detecting wheel speeds of left and right front wheels, means for detecting a yaw rate of the vehicle, and Means for calculating a reference wheel speed difference ΔVwy between the left and right front wheels based on the yaw rate of the vehicle; means for calculating an actual wheel speed difference ΔVwa for the left and right front wheels from the detected wheel speeds for the left and right front wheels; and the reference wheel speed difference. The magnitude ΔV of the deviation between ΔVwy and the actual wheel speed difference ΔVwa
Means for calculating wdiff and magnitude of the deviation ΔVwdiff
And a means for controlling the output of the engine so that the output reduction amount of the engine becomes larger as is larger. 2. The behavior control device for a four-wheel drive vehicle according to claim 1, further comprising means for reducing an output reduction amount of the engine when the vehicle is substantially in a straight traveling state. Behavior control device for wheel drive vehicle.