JP2643700B2 - 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] The rear wheel steering amount is determined according to the front wheel steering amount and the vehicle speed as described above. For example, in a situation where the vehicle is traveling on a slippery low μ road, the above-described condition is applied. The road surface friction coefficient, that is, the road surface μ, is added to the reference steering amount.
It is preferable to correct the rear wheel steering amount by adding the corrected steering amount determined in accordance with the following formula, and to steer the rear wheels based on the corrected rear wheel steering amount. In other words, in a situation where the road surface μ is small, the tire grip force can be further increased by the amount by which the rear wheel steering amount is increased by the correction at the time of turning of the vehicle, thereby improving the running stability of the vehicle. It can be secured high.

[0004]

However, when the rear wheel steering amount is immediately increased by the correction during turning in the above-described driving situation, the vehicle moves laterally more than the turning motion. Difficult for the vehicle to turn,
This gives the impression that the turning performance of the vehicle is poor.

For this reason, even when the vehicle is traveling on a low μ road, it has been difficult to add a sufficient correction steering amount to the reference steering amount. The present invention has been made on the basis of the above-described circumstances, and an object thereof is to add a sufficient correction steering amount to a reference steering amount of a rear wheel according to a running condition of a vehicle when the vehicle turns. It is another object of the present invention to provide a method for controlling the rear-wheel in-phase steering of a vehicle, which can secure the turning performance of the vehicle.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a reference steering amount of a rear wheel according to a front wheel steering is obtained when a vehicle turns.
A method in which a corrected steering amount of a rear wheel according to a traveling state of a vehicle is obtained, and the rear wheel is steered in the same phase as a front wheel based on a rear wheel steering amount obtained by adding the reference steering amount and the corrected steering amount. In the rear wheel in-phase steering control method of the present invention,
When determining the rear-wheel steering amount, have a predetermined delay to the reference steering amount
The corrected steering amount is added.

[0007]

According to the above-described method of controlling the rear-wheel in-phase steering of the vehicle, when the vehicle turns, in the initial stage of the turn, the reference steering amount is obtained as it is as the rear wheel steering amount. In-phase steering of the rear wheels is performed based on the steering amount. Then, after this, the corrected steering amount with a predetermined delay is added to the reference steering amount according to the traveling state of the vehicle, so that the rear wheels are steered in phase based on the corrected rear wheel steering amount. Will be.

[0008]

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 pipe 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 similarly to the front wheel power cylinder 8, and the oil supply pipe 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 composed of 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 electrical 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 pipes 16 and 17, and returns the other pressure chamber to the return pipe via the other of the oil supply pipes 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, There is a rear wheel steering angle sensor 30 for detecting the actual rear wheel steering amount δA of the rear wheel RW.

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, in the case of this embodiment, the ECU 24 includes a detection circuit for detecting the road surface μ of the traveling road surface of the vehicle. 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. The road surface μ is detected from the pressure values detected by the pressure sensors 26 and 27.

That is, although a 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. The calculation procedure will be described below. First,
As described above, the steering wheel angle θH, the vehicle speed V, and the road surface μ
Is detected, the vehicle speed V is supplied to a block 31, where a reference in-phase steering coefficient KB is calculated. Here, the vehicle speed V can of course be determined based on the sensor signal from the vehicle speed sensor 28 described above, but also based on the sensor signal from the wheel speed sensor 29.
The vehicle speed V can be calculated.

In obtaining the reference in-phase steering coefficient KB based on the vehicle speed V in block 31, 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 31
B is then supplied to block 32, which
The reference in-phase steering amount δRB of the rear wheel RW is calculated and obtained. That is, the block 32 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 32 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 33. Vehicle speed V
Is also supplied to a block 34, which is further supplied with a road surface μ. In block 34, the in-phase corrected steering coefficient KC is calculated based on the vehicle speed V and the road surface μ. Specifically, the in-phase corrected steering coefficient KC can be obtained from the graph of FIG.

That is, as shown in FIG. 4, the in-phase corrected steering coefficient KC is determined by increasing the vehicle speed V from the time when the vehicle speed V reaches a certain vehicle speed when the road surface μ takes a positive value. , The characteristics gradually draw, and thereafter gradually decrease, so as to draw a substantially triangular shape. Further, this characteristic differs depending on the size of the road surface μ, and as the road surface μ becomes smaller, the triangular shape of the characteristic becomes larger.
That is, the relationship among the road surfaces μ1, μ2, μ3, and μ4 shown in FIG.

Μ1 <μ2 <μ3 <μ4 <1 Here, the values V1, V2, V3, and V4 of the vehicle speed V at which the in-phase corrected steering coefficient KC starts to increase are smaller as the road surface μ is smaller. When the vehicle speed V has reached V6 or more, the in-phase corrected steering coefficient KC is 0 regardless of the size of the road surface μ. On a high μ road where the road surface μ is 1, the in-phase correction steering coefficient KC is 0.

Further, FIG. 4 also shows the characteristics in the case where the road surface μ takes a value of 1 or more, μ5. This characteristic is different from the triangular shape characteristic in which the road surface μ takes a value of 1 or less. , An inverted triangular shape. Therefore, when the road surface μ has a value of 1 or more, the in-phase correction steering coefficient KC takes a negative value. V1, V2, V3, V4, V5 and V6 are:
For example, 20km / h, 30km / h, 40km / h, 50km / h, 60
km / h and 100 km / h.

When the in-phase corrected steering coefficient KC is obtained in block 34, the in-phase corrected steering coefficient KC is supplied to the next block 35, where the in-phase corrected steering amount δRC is calculated. That is, similarly to the case of the block 32 described above, the steering wheel angle θH is also supplied to the block 35, 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 manner is supplied to the adding section 33, and is added to the reference in-phase steering amount δRB in the adding section 33, so that The wheel steering amount δR will be calculated.
Are not directly connected to the adder 33, and a block 36 is interposed between them. This block 36
Is a first-order lag element as shown.
In the case of this embodiment, the time constant T of the first-order lag element is supplied from the block 37. In this block 37, the time constant T is determined based on the vehicle speed V and the road surface μ.

More specifically, in block 37, the time constant T is calculated from the graph shown in FIG. FIG.
As is clear from the graph, when the road surface μ takes a value of 1 or less 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
When the vehicle speed V deviates from a predetermined speed range, the vehicle speed V8 (for example, 80 k
m / h), the time constant T decreases. When the road surface μ takes a value of 1 or more, the time constant T is unconditionally set to 0.

Incidentally, regarding the graphs of FIGS. 3 to 5,
These are mapped in a nonvolatile memory (not shown) in the EUC 24 and stored in advance, and the reference in-phase steering coefficient KB, the in-phase correction steering coefficient KC, and the time constant T
May be read out. According to the above-described calculation procedure of the rear wheel steering amount δR, when the vehicle speed V is equal to or higher than V1, the reference in-phase steering coefficient KB rises as is clear from FIG. When the vehicle turns, the reference in-phase steering amount δRB of the rear wheel RW is calculated.

On the other hand, when the vehicle is turning as described above, in a running condition where the road surface μ takes a small value, as is apparent from the graph of FIG.
And a positive value corresponding to the vehicle speed V at that time, the in-phase corrected steering amount δRC is calculated based on the KC and the steering wheel angle θH, and the in-phase corrected steering amount δRC and the reference in-phase steering are calculated. The amount δRB and the amount δRB are summed up by the adder 33 to obtain the rear wheel steering amount δR.

When the rear wheel steering amount δR is calculated in this manner, the ECU 24 determines based on the sensor signal from the rear wheel steering angle sensor 30 that the actual rear wheel steering amount δRA matches the rear wheel steering amount δR. Next, 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. Here, 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 33, but is passed to the adding unit 33 after passing through the first-order lag element of the block 36. Supplied, the in-phase corrected steering amount δRC is
The predetermined delay time is added to the reference in-phase steering amount ΔRB.

Therefore, when the vehicle turns while traveling on the low μ road described above, in the initial stage of the turn, the reference in-phase steering amount δRB becomes the rear wheel steering amount δR as it is, and the rear wheel steering Correction of the amount ΔR by the in-phase correction steering amount ΔRC is still substantially ineffective. 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 starts 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 correction steering amount ΔRC. Therefore, when the vehicle is traveling on a low μ road and after the initial turn, the rear wheel steering amount ΔR is greatly corrected in an increasing direction, so that the tire grip force is further increased and the traveling stability of the vehicle can be improved. .

This is clear from the graph shown in FIG. This graph shows the time change of the steering wheel angle θH and the actual rear wheel steering amount δRA, respectively, and the actual rear wheel steering amount δRA shows the delay time with respect to the turning of the steering wheel 11 as shown by the solid line. Will increase.
The broken line in FIG. 6 shows an example in which the block 36 in FIG. 2 is omitted, and the one-dot chain line shows the reference in-phase steering amount δRB.
Is shown.

Further, in the case of this embodiment, as is clear from the graph of FIG. 4, the smaller the road surface μ, the larger the in-phase corrected steering coefficient KC, that is, the in-phase corrected steering amount δRC, becomes larger. Running stability can be maintained sufficiently high. On the other hand, as is clear from the graph of FIG. 5, in a high-speed region where the vehicle speed V is equal to or higher than V8, the time constant T of the first-order lag element becomes 0. In this case, the calculated in-phase corrected steering amount δRC Is immediately added to the reference in-phase steering amount ΔRB, and the rear wheel steering amount ΔR is obtained. Therefore, when the vehicle is in the high-speed region, the in-phase corrected steering amount δRC quickly works with respect to the rear wheel steering amount δR,
The correction is made with emphasis on the running stability of the vehicle.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in one embodiment,
The in-phase corrected steering amount is determined by the vehicle speed and the road surface μ, however, in addition to the vehicle speed, the in-phase corrected steering amount is determined based on the lateral acceleration acting on the vehicle body, the road surface gradient, etc.
Thereby, it is of course possible to ensure the running stability at the time of turning in various running situations.

[0036]

As described in the foregoing, according to the wheel phase steering control method of a vehicle rear of the present invention, during cornering, with respect to the reference steering amount of the rear wheels, the correction steering amount according to the running condition of the vehicle Add time, rather than because the rear wheel steering amount in addition to the immediate reference steering amount of this correction steering amount, the correction which gave a predetermined delay
Adding steering amount to a reference steering amount, because you are to obtain the rear-wheel steering amount, based on the wheel steering amount after that is determined in this way, if the steering of the rear wheels is controlled in phase, turning In the early stages, while ensuring the turning performance of the vehicle,
In this case, a sufficient correction can be added to the amount of rear wheel steering in accordance with the running condition of the vehicle, and excellent effects such as securing the running stability of the vehicle can be obtained.

[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 in-phase corrected steering coefficients with respect to vehicle speed and road surface μ.

FIG. 5 is a graph showing a time constant of a first-order lag element with respect to a vehicle speed and a road surface μ.

FIG. 6 is a graph showing a time change of a steering wheel angle and an actual rear wheel steering amount.

[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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B62D 137: 00 (72) Inventor Takeshi Takeo 5-33-8 Shiba 5-chome, Minato-ku, Tokyo Mitsubishi Motors (56) References JP-A-62-227866 (JP, A) JP-A-62-116357 (JP, A) JP-A-2-144260 (JP, A) JP-A-60-85067 (JP, A) , A)

Claims (1)

(57) [Claims] When a vehicle is turning, a reference steering amount of a rear wheel according to front wheel steering is determined, and a corrected steering amount of a rear wheel according to a traveling state of the vehicle is determined. In the rear wheel steering control method of a vehicle in which the rear wheels are steered in the same phase as the front wheels based on the rear wheel steering amounts obtained by adding the correction steering amounts, the reference steering amounts have a predetermined delay. A rear wheel in-phase steering control method for obtaining the rear wheel steering amount.