JP2643701B2 - Vehicle rear-wheel in-phase steering control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to steering of front wheels,
The present invention relates to a rear-wheel in-phase steering control method for a vehicle in which a rear wheel is steered in phase with a front wheel.

[0002]

2. Description of the Related Art According to this kind of rear-wheel in-phase steering control method, basically when a vehicle is turning, a rear wheel steering amount corresponding to a front wheel steering amount or a vehicle speed is obtained, and the rear wheel steering amount is calculated. Based on this, the rear wheels are steered in phase with the front wheels. In this way, when the rear wheels are steered in phase, the posture of the vehicle at the time of turning, that is, the running stability thereof, can be increased.

[0003] In other words, when the rear wheels are steered together with the front wheels, the grip force of the tires increases, thereby increasing the running stability of the vehicle.

[0004]

However, the conventional rear-wheel in-phase steering control method assumes that the vehicle is traveling on a flat road surface having a large road surface friction coefficient (road surface μ). Therefore, the rear wheel steering amount is simply obtained from the front wheel steering amount and the vehicle speed. Therefore, in a situation where the vehicle is traveling on a so-called low μ road having a small road μ, the slip amount of the rear wheels increases even if the rear wheels are steered in phase with the front wheels when turning. As a result, the amount of wheel steering thereafter becomes insufficient, and the turning performance is reduced.

[0005] On the other hand, even in a situation where the vehicle goes uphill or downhill, the amount of rear wheel steering may not be appropriate during turning due to the movement of the vehicle load before and after. In other words, when turning while descending a slope, the rear wheel load of the vehicle decreases, and the grip force of the rear wheels decreases, causing the vehicle to swing as a result. Apparently, it tends to oversteer.

On the other hand, when turning while climbing a hill,
Conversely, since the rear wheel load increases, the grip force of the tires of the rear wheels increases more than necessary, so that the rear portion of the vehicle is easily bent, and the turning of the vehicle has an apparent understeer tendency. Therefore, the running road surface is low μ
Even on a road, or when the vehicle goes uphill or downhill, the turning response becomes unstable, and
The instability of the response becomes large especially on a low μ road and on a downhill.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is that even when the vehicle is traveling on a low μ road or a sloping road, it is suitable for the traveling state of the vehicle when turning. It is another object of the present invention to provide a rear wheel in-phase steering control method that can secure a high running stability and obtain a stable turning response by calculating a rear wheel steering amount.

[0008]

According to the method of controlling the rear wheel in-phase steering of a vehicle according to the present invention, a reference steering amount of a rear wheel corresponding to a front wheel steering amount is obtained at the time of turning of the vehicle, and at least a road surface friction coefficient of a running road surface is obtained. the fuzzy inference and from the slope of the road surface
Correction amount is determined, and the correction operation determined in accordance with the correction amount is determined.
A corrected steering amount is obtained according to a steering coefficient and the front wheel steering amount,
The rear wheels are steered in the same phase as the front wheels based on the rear wheel steering amount obtained by adding the corrected steering amount to the reference steering amount.

[0009]

According to the above-described method of controlling the rear-wheel in-phase steering of the vehicle, when the vehicle is turning, the reference steering amount corresponding to the front-wheel steering is calculated based on the running condition of the vehicle, that is, the road surface friction coefficient and the gradient of the road surface according to fuzzy inference. Add the required corrected steering amount,
The rear wheel steering amount is calculated, and the rear wheel is steered in the same phase as the front wheel based on the rear wheel steering amount.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, four-wheel steering (4 W
S) The system is shown schematically. The 4WS system includes tandem oil pumps 2 and 3 driven by an engine 1 of a vehicle.
Both 3 are connected to an oil reservoir 4.

One oil pump 2 is connected to a power steering device 6 via an oil supply line 5. Specifically, the oil supply line 5 is connected to a pair of pressure chambers 9 and 10 of the front wheel power cylinder 8 via a steering control valve (not shown) built in the gear box 7 of the power steering device 6. Have been. Both ends of the piston rod in the front wheel power cylinder 8 are connected to the left and right front wheels FW, however, only one front wheel FW is shown in the figure.

The steering control valve is switched by operating the steering wheel 11, and selects the flow direction of oil to be supplied to the front wheel power cylinder 8 according to the steering direction of the steering wheel 11, and selects one of the pressure chambers. Oil can be supplied. From the gear box 7, the return line 1
The return line 12 has one end connected to the steering control valve and the other end connected to the oil reservoir 4 described above.

On the other hand, the oil pump 3 is connected to a rear wheel hydraulic control valve 14 via an oil supply line 13. The rear wheel hydraulic control valve 14 is a 4-port, 3-position electromagnetic direction switching valve as shown in the figure, and the oil supply line 13 is connected to its input port I. The return port R of the rear wheel hydraulic control valve 14 is connected to the oil reservoir 4 via a return line 15, and the pair of output ports O 1 and O 2 are connected to oil supply lines 16 and 17.
And is connected to the rear wheel power cylinder 18 via the

That is, the rear wheel power cylinder 18 has a pair of pressure chambers 19 and 20 like the front wheel power cylinder 8, and the oil supply line 1 is connected to these pressure chambers 19 and 20.
6 and 17 are respectively connected. Rear wheel power cylinder 1
Both ends of the piston rod 8 are connected to the left and right rear wheels RW, respectively, and a center spring 21 is housed in the rear wheel power cylinder 18. When the rear wheel power cylinder 18 is not operated, the center spring 21 urges the piston rod to a neutral position to maintain the rear wheel RW in a straight running state.

Further, the oil supply line 13 and the return line 15 are connected to each other by a bypass line 22. In the bypass line 22, a hydraulic switching valve 23 formed by an electromagnetic on-off valve is provided. It is interposed. The rear wheel hydraulic pressure control valve 14 and the hydraulic pressure switching valve 23 are provided by an electronic control unit (EC
U) The switching operation is performed in response to a command signal from the ECU 24. Therefore, the solenoids of the rear wheel hydraulic control valve 14 and the hydraulic switching valve 23 are electrically connected to the ECU 24, respectively.

Unless an electric abnormality is detected by the ECU 24 or the power is not turned off, the solenoid of the hydraulic switching valve 23 is always excited by the ECU 24, whereby the hydraulic switching valve 23 is closed. In state. On the other hand, when one solenoid of the rear wheel hydraulic control valve 14 is excited by the ECU 24, the rear wheel hydraulic control valve 14 is switched from the illustrated neutral position to one switching position. Therefore, for the first time at this time, the rear wheel hydraulic control valve 1
4 supplies oil to one pressure chamber of the rear wheel power cylinder 18 through one of the oil supply lines 16 and 17, and returns the other pressure chamber to the return pipe via the other of the oil supply lines 16 and 17. By being connected to the road 15, the rear wheel power cylinder 18 is operated on one side, and as a result, the rear wheel RW is steered by a predetermined rear wheel steering amount.

Here, the rear wheel RW is steered in phase with respect to the front wheel FW, and the amount of rear wheel steering is determined by the ECU 24 in accordance with the steering of the front wheel FW and the running condition of the vehicle. Has become. Therefore, various sensors are electrically connected to the ECU 24. These sensors include a handlebar angle sensor 25 for detecting the handlebar angle θH of the handlebar, the pressure in the pressure chambers 9 and 10 of the front wheel power cylinder 8, and the like. , A vehicle speed sensor 28 for detecting a vehicle speed from rotation of an output shaft of a transmission (not shown) in the engine 1, a wheel speed sensor 29 for detecting a wheel speed of a front wheel FW, A rear wheel steering angle sensor 30 for detecting the actual rear wheel steering amount δA of the rear wheel RW, a road surface gradient sensor 31 for detecting a gradient of a running road surface, a lateral G sensor 32 for detecting a lateral acceleration (lateral G) acting on the vehicle, and the like. There is.

As the rear wheel steering angle sensor 30, for example, a stroke sensor for detecting a stroke of a piston rod in the rear wheel power cylinder 18 can be used. The steering amount ΔA can be obtained. Further, since it is difficult to actually detect the gradient of the traveling road surface with respect to the road surface gradient sensor 31, by using an inclinometer for detecting the inclination of the vehicle body as the road surface gradient sensor 31, the inclination from the inclinometer can be reduced. The road surface gradient can be detected based on the sensor signal.

Further, in the case of this embodiment, the ECU 24
A detection circuit for detecting the road surface μ of the traveling road surface of the vehicle is included. Various methods are conceivable for the detection of the road surface μ, but the detection circuit of this embodiment uses the steering wheel angle θH detected by the steering wheel angle sensor 25, the vehicle speed V detected by the vehicle speed sensor 28, and the front wheel power cylinder 8. Pressure sensor 26,
The road surface μ is detected from the pressure value detected at 27.

That is, although the detailed description is omitted here, the principle of detecting the road surface μ is as follows.
7, the front wheel power cylinder 8
Second, that the operating pressure is proportional to the cornering force of the front wheel FW, third, that the cornering force is proportional to the product of the side slip angle of the front wheel FW and the road surface μ, Is based on the fact that the side slip angle is expressed using the vehicle speed V, the steering wheel angle θH, and the road surface μ.

Next, referring to FIG. 2, there is shown in a block diagram a calculation procedure of the rear wheel steering amount δR in the ECU 24, and the calculation procedure will be described below. First,
As described above, the steering wheel angle θH, vehicle speed V, road surface μ,
When the road surface gradient α and the lateral G are respectively detected, the vehicle speed V is supplied to a block 33 where the reference in-phase steering coefficient KB is calculated. Here, the vehicle speed V can be determined based on the sensor signal from the vehicle speed sensor 28 described above, but the vehicle speed V can also be calculated based on the sensor signal from the wheel speed sensor 29. .

In obtaining the reference in-phase steering coefficient KB based on the vehicle speed V in block 33, the reference in-phase steering coefficient KB can be specifically calculated from the graph of FIG. In the graph of FIG. 3, the reference in-phase steering coefficient KB with respect to the vehicle speed V is obtained in advance, and as shown in this graph,
The reference in-phase steering coefficient KB is such that the vehicle speed V is V0 (for example, 60 km /
h) When the vehicle speed V increases, it has a characteristic that it increases to some extent sharply as the vehicle speed V increases, and thereafter converges to its maximum value.

The reference in-phase steering coefficient K obtained in block 33
B is then supplied to block 34, which
The reference in-phase steering amount δRB of the rear wheel RW is calculated and obtained. That is, the block 34 includes the reference in-phase steering coefficient K
In addition to B, the steering wheel angle θH is also supplied, and the reference in-phase steering amount δRB of the rear wheel RW is determined by the reference in-phase steering coefficient KB
And the steering angle θH, that is, calculated by the following equation.

ΔRB = KB · θH Accordingly, the reference in-phase steering amount δRB obtained in block 34 is
When the vehicle speed V becomes equal to or higher than V0, it increases with the turning of the steering wheel 11. Thereafter, the reference in-phase steering amount δRB is supplied to the adding unit 35. Vehicle speed V
Is also supplied to the block 36, and the block 36 is also supplied with the correction amount X from the block 37. Therefore, in block 36, the in-phase corrected steering coefficient KC is calculated based on the vehicle speed V and the correction amount X. Specifically, the in-phase corrected steering coefficient KC is obtained from the graph of FIG. Can be.

That is, as shown in FIG. 4, when the correction amount X takes a positive value, the in-phase corrected steering coefficient KC is calculated from the time when the vehicle speed V reaches a certain vehicle speed. It has a characteristic of drawing a substantially triangular shape that gradually increases with rising and then gradually decreases. Further, this characteristic differs depending on the magnitude of the correction amount X. As the correction amount X increases, the triangular shape of the characteristic increases. That is, the correction amounts X1, X2, X3, X4 shown in FIG.
Is expressed, for example, by the following equation.

X1>X2>X3>X4> 0 Here, the values V1, V2, V3, V4 of the vehicle speed V at which the in-phase corrected steering coefficient KC starts to increase are smaller as the correction amount X is larger. However, when the vehicle speed V has reached V6 or more, the in-phase corrected steering coefficient KC is 0 regardless of the magnitude of the correction amount X.

Further, when the correction amount X takes a negative value, for example, in the case of the characteristic indicated by X5, the characteristic of the inverted triangle shape is different from the characteristic of the triangular shape in which the correction amount X takes a positive value. It has become. Therefore, when the correction amount X is a negative value, the in-phase corrected steering coefficient KC also takes a negative value. In FIG. 4, the vehicle speeds V1, V2, V3, V4, V5, V6
Are 20 km / h, 30 km / h, 40 km / h, 50 km / h, 6
It is 0 km / h and 100 km / h.

As described above, the correction amount X is calculated in the block 37.
In this block 37,
The road surface μ, the road surface gradient α, and the lateral G are supplied, respectively, and the Zrock 37 can calculate the correction amount X from the road surface μ, the road surface gradient α, and the lateral G by fuzzy inference. That is, referring to FIG. 5, the correction values xi for each rule of fuzzy inference are shown, and the membership functions corresponding to the road surface μ, the road surface gradient α, and the lateral G under the rule are shown. Each rule is defined as follows.

Rule 1: The road surface μ is high, the road surface is downhill, and the lateral G is low. Rule 2: The road surface μ is high, the road surface is downhill, and the lateral G is high. Rule 3: The road surface μ is high, the road surface is flat, and the lateral G is low. Rule 4: The road surface μ is high, the road surface is flat, and the lateral G is high. Rule 5: The road surface μ is high, the road surface is uphill, and the lateral G is low.

Rule 6: The road surface μ is high, the road surface is uphill, and the lateral G is high. Rule 7: The road surface μ is low and the road surface is downhill. Rule 8: The road surface μ is low and the road surface is flat. Rule 9: The road surface μ is low and the road surface has an upward slope. In FIG. 5, α (+) indicates the uphill side, and α (−) indicates the downhill side. In addition, the membership functions for the horizontal G are not specified in the rules 7, 8, and 9. Therefore, the values of the membership functions for the horizontal G in the rules 7, 8, and 9 are defined as the horizontal G. Regardless of the size of
It becomes 1. In other words, when the traveling road surface is a low μ road, the turning performance of the vehicle is inevitably deteriorated.
There is no need to consider the value of the lateral G.

Accordingly, when the road surface μ, the road surface gradient α and the lateral G are supplied to the block 37, the value of the membership function for each rule, that is, the contribution wi is calculated based on these values, and the correction amount is calculated. X is calculated from the weighted average of the correction value xi for each rule and its contribution wi, that is, the following equation. X = Σxi · wi / (Σwi) In the above equation, i represents the number of each rule.

Here, as the contribution wi in each rule, the minimum value among the values of the membership functions in the rule is adopted. Specifically, as shown in FIG. 6, the road surface μ is 1.0 and the road surface gradient α is 0.3%
, And the value of each membership function in Rule 1 is 1.0, 0.3, 0.
If it is 8, the contribution w1 of rule 1 is 0.3. Similarly, in rule 2, the values of the membership functions are 1.0, 0.3, and 0.2, so that the contribution w2 of rule 2 is 0.2.

Therefore, by calculating the contribution wi in each rule as described above, the correction amount X
Can be calculated. Block 36 as described above
When the in-phase corrected steering coefficient KC is obtained from the graph of FIG. 4 based on the vehicle speed V and the correction amount X, the in-phase corrected steering coefficient KC is then supplied to the block 38.
The in-phase corrected steering amount ΔRC is calculated. That is, as in the case of the above-described block 34, the steering wheel angle θH is also supplied to the block 38, and the in-phase corrected steering amount δRC is calculated by multiplying the in-phase corrected steering coefficient KC by the steering wheel angle θH, that is, Is calculated.

ΔRC = KC · θH The in-phase corrected steering amount δRC calculated in this way is supplied to the adding section 35, and added to the reference in-phase steering amount δRB in the adding section 35, so that The wheel steering amount δR will be calculated, however,
Is not directly connected to the adder 35, and a block 39 is interposed between them. This block 39
Is a first-order low-pass filter, ie, a first-order lag element.
In the case of this embodiment, the time constant T of the first-order lag element is supplied from the block 40. In this block 40, the time constant T is determined based on the vehicle speed V and the correction amount X.

Specifically, in the block 40, the time constant T is calculated from the graph shown in FIG. As is clear from the graph of FIG. 7, when the correction amount X takes a positive value and the vehicle speed V is within a predetermined speed range from V7 (for example, 30 km / h), the time constant T takes a predetermined value. And the vehicle speed V
Is out of the predetermined speed range, and the vehicle speed V8 (for example, 80 km / h)
, The time constant T decreases. When the correction amount X takes a negative value, the time constant T is unconditionally set to zero.

The graphs and the membership functions shown in FIGS. 3 to 5 and 7 are mapped in a non-volatile memory (not shown) in the EUC 24 and stored in advance, and the reference in-phase steering coefficient is obtained from these maps. KB, the value of each membership function, the in-phase corrected steering coefficient KC, and the time constant T can be read out. When the rear wheel steering amount δR is calculated as described above, the ECU 24 determines, based on the sensor signal from the rear wheel steering angle sensor 30, such that the actual rear wheel steering amount δRA matches the rear wheel steering amount δR. Thus, the operation of the above-described rear wheel power cylinder 18, that is, the operation of the rear wheel hydraulic control valve 14 is controlled.

According to the above-described calculation procedure of the rear wheel steering amount δR, the correction amount X for determining the in-phase correction steering amount δRC is determined according to fuzzy inference. A driving situation in which the traveling road surface is low and the traveling road surface is downgraded or flat conforms to the rules 7 or 8 among the above-mentioned rules, and the correction amount X is mainly obtained from the rules 7 and 8. Become. here,
The correction values x7 and x8 of the rules 7 and 8 are set to be larger than the correction values of the other rules. In this case, the calculated correction amount X has a large positive value.

When the correction amount X has a large positive value, the in-phase corrected steering coefficient KC also has a large value, as is clear from the graph of FIG. 4, and the in-phase corrected steering amount δRC increases, and the rear wheel steering amount increases. ΔR is largely corrected in the increasing direction.
Therefore, in a situation where the road surface μ is low and slippery, the rear wheel steering amount ΔR is greatly increased and corrected when turning, so that the grip force of the tire is increased and the running stability can be secured. In addition, in the case of a low μ road and a down slope,
Although the vehicle load moves to the front wheels and the turning of the vehicle tends to oversteer, this oversteering tendency is canceled by increasing the rear wheel steering amount ΔR.

On the other hand, in a situation where the running road surface is a low μ road and has an uphill slope, rule 9 is satisfied, and in this case also, the increase correction of the rear wheel steering amount δR is performed. However, since the correction value x9 in the rule 9 is smaller than the correction values x7 and x8 in the rules 7 and 8, the ratio of the increase correction of the rear wheel steering amount δR here is the low μ
It is smaller than on a road and downhill. In the case of such an upward gradient, it is preferable to reduce the rear wheel steering amount ΔR to eliminate the apparent understeer tendency, but if the road surface is a low μ road and it is easy to slip, Also in this case, it is more preferable to increase the rear wheel steering amount δR by increasing the gripping force of the rear wheel RW to some extent.

In this regard, when the traveling road surface is a high μ road and the road surface is an upward slope, the rules 5 and 6 are satisfied, but the correction values x5 and x6 of these rules 5 and 6 are respectively. Since this is a negative value, the in-phase corrected steering coefficient KC, that is, the in-phase corrected steering amount ΔRC also becomes a negative value, and the rear wheel steering amount ΔR is corrected to decrease. Therefore, in such a situation, the apparent understeer tendency of the vehicle can be eliminated by reducing the rear wheel steering amount ΔR.

Here, in a situation where the above-mentioned rules 5 and 6 are satisfied, further considering the horizontal G, if the horizontal G is in a normal area, the rule 5 is more suitable, On the other hand, when the horizontal G is out of the normal area and becomes larger, the rule 6 is more suitable. This means that Rule 6
In the situation where the vehicle is turning, it means that the vehicle turns sharply. In this case, the rear wheel steering amount δR is corrected to be much smaller than in the case of rule 5,
The running stability of the vehicle can be ensured.

If the traveling road surface is a high-μ road and a flat road, the rules 3 and 4 are satisfied. Even in the case of the rules 3 and 4, the horizontal G represents a normal area. In situations where the value deviates and takes a large value and the vehicle turns sharply, Rule 4 is more suitable, and in this case also,
The rear wheel steering amount ΔR is slightly reduced and corrected. Rule 3
Therefore, the correction value x3 of Rule 3 is 0.0, so that the correction of the rear wheel steering amount δR is not substantially performed.

Further, if the traveling road surface is a high μ road and has a downward slope, the rules 1 and 2 are satisfied. In this case, the rear wheel steering amount δR is corrected to increase and the apparent oversteer tendency is eliminated. Is done. However, even in this case, if the lateral G is out of the normal region and takes a large value, and the vehicle shows a sharp turn, the rule 2
Therefore, the ratio of the increase correction of the rear wheel steering amount δR is reduced as compared with the rule 1.

In the case of the above-described embodiment, as is clear from the block diagram of FIG. 2, the calculated in-phase corrected steering amount δRC is not immediately supplied to the adding unit 35,
After passing through the first-order lag element 9, the signal is supplied to the adder 35. Therefore, as is apparent from FIG. 7, the correction amount X takes a positive value, and the vehicle speed V becomes V7 and V8.
In such a situation, the time constant T also takes a predetermined positive value, so that the in-phase corrected steering amount δRC is added to the reference in-phase steering amount δRB with a predetermined delay time. Will be added.

Therefore, in a situation where the correction amount X is a positive value, that is, in a situation where the increase correction of the rear wheel steering amount δR is performed, when the vehicle is turning, the correction is not performed at the beginning of the turn. In other words, the reference in-phase steering amount δRB
R, and the rear-wheel steering amount ΔR is not substantially corrected by the in-phase correction steering amount ΔRC. As a result, in the early stage of turning, since the increase correction for the rear wheel steering amount δR is not effective, the vehicle turns mainly by steering the front wheel FW, so that the turning property of the vehicle can be sufficiently secured, and I do not feel the difficulty of turning.

However, after the vehicle has begun to turn, the calculated in-phase corrected steering amount δRC is more effective than the rear wheel steering amount δR.
Is substantially increased based on the in-phase corrected steering amount ΔRC, and the running stability of the vehicle can be sufficiently ensured as described above. The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in one embodiment, when calculating the correction amount X according to fuzzy inference, a lateral G is added to the road surface μ and the road surface gradient, and from this lateral G,
Although the actual turning condition of the vehicle is also taken into consideration, the handling of the lateral G is not limited to that of the embodiment. That is, the present invention can be implemented without considering the lateral G, and various modes can be considered in the method of considering the lateral G.

[0047]

As described above, according to the method for controlling the rear-wheel in-phase steering of the vehicle according to the present invention, when the corrected steering amount to be added to the reference steering amount of the rear wheel during turning, the road surface friction coefficient and Since the corrected steering amount is determined from the road surface gradient in accordance with fuzzy inference, the corrected steering amount is appropriate in all driving situations, stabilizing the turning response of the vehicle and maintaining the running stability. This is effective in that it is possible to sufficiently secure

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a 4WS system.

FIG. 2 is a block diagram showing a procedure for calculating a rear wheel steering amount.

FIG. 3 is a graph showing a relationship between a vehicle speed and a reference in-phase steering coefficient.

FIG. 4 is a graph showing an in-phase corrected steering coefficient with respect to a vehicle speed and a correction amount X;

FIG. 5 is a map showing a membership function for each rule of fuzzy inference.

FIG. 6 is a diagram for explaining calculation of a degree of contribution obtained from a membership function for each rule.

FIG. 7 is a graph showing a time constant of a first-order lag element with respect to a vehicle speed and a correction amount X;

[Explanation of symbols]

 2, 3 oil pump 8 front wheel power cylinder 11 handle 14 rear wheel hydraulic control valve 18 rear wheel power cylinder 24 ECU 25 handle angle sensor 28 vehicle speed sensor 29 wheel speed sensor 26, 27 pressure sensor 30 rear wheel steering angle sensor 31 road surface gradient sensor 32 Horizontal G sensor

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B62D 113: 00 133: 00 (56) References JP 62-8872 (JP, A) JP JP-A-64-2679 (JP, A) JP-A-62-8871 (JP, A) JP-A-2-144261 (JP, A)

Claims (1)

(57) [Claims] At 1. A vehicle turning, whereas for obtaining a reference steering amount of the rear wheels in accordance with the front-wheel steering amount, by fuzzy inference from the slope of the road surface friction coefficient and road surface at least traveled road complement
A positive steering amount is obtained, and a correction steering member obtained according to the correction amount is obtained.
A corrected steering amount according to the number and the front wheel steering amount,
The corrected steering amount is added to the reference steering amount to obtain a rear wheel steering amount,
A rear wheel in- phase steering control method for a vehicle, wherein the rear wheels are steered in the same phase as the front wheels based on the rear wheel steering amount .