JPH05155347A - Rear wheel in-phase steering control method of vehicle - Google Patents

Abstract

PURPOSE:To secure the running stability of a vehicle by adding a correction according to the running condition to the rear wheel steering amount while securing the turning round property of the vehicle, when the rear wheels are steered in a phase identical to that of the front wheels in a turning operation of the vehicle. CONSTITUTION:In a rear wheel in-phase steering control method of a vehicle, an in-phase correction steering amount of the rear wheels deltaRC according to the vehicle running condition, such as the road surface mu, is found, while a standard in-phase steering amount of the rear wheels deltaRB according to the front wheel steering is found in a turning operation of the vehicle. And by adding the in-phase correction steering amount deltaRC to the in-phase standard steering amount deltaRB while giving a specific delay to the deltaRB, the real wheel steering amount deltaR is to be found.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art According to this type of rear wheel in-phase steering control method, basically, when the vehicle is turning, the steering amount of the front wheels and the steering amount of the rear wheels corresponding to the vehicle speed are obtained, and the steering amount of the rear wheels 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 enhanced.

By the way, 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 reference steering amount is the friction coefficient of the road surface, that is, the road surface μ
It is preferable to correct the rear wheel steering amount by adding the correction steering amount determined according to the above, and to steer the rear wheels based on the corrected rear wheel steering amount. That is, when the road surface μ is small, the grip force of the tire can be further increased by the amount by which the rear wheel steering amount is increased due to the correction when the vehicle is turning, thereby improving the running stability of the vehicle. It will be possible to secure a high price.

[0004]

However, in the above-mentioned traveling condition, when the rear wheel steering amount is immediately increased by the correction during turning, the vehicle has a larger lateral movement than the turning motion. Is difficult for the person to bend, that is,
It gives the impression that the vehicle has poor turning ability.

Therefore, even when the vehicle is traveling on a low μ road, it is difficult to add a sufficient correction steering amount to the reference steering amount. The present invention has been made based on the above-mentioned circumstances, and an object thereof is to add a sufficient correction steering amount to the reference steering amount of the rear wheels when the vehicle turns, depending on the traveling condition of the vehicle. (EN) It is possible to provide a rear-wheel in-phase steering control method for a vehicle, which is capable of ensuring the turning performance of the vehicle.

[0006]

According to the present invention, while the vehicle is turning, the reference steering amount of the rear wheels is obtained according to the steering of the front wheels.
A method in which the corrected steering amount of the rear wheels is obtained according to the running condition of the vehicle, and the rear wheels are steered in phase with the front wheels based on the 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 calculating the rear wheel steering amount, the reference steering amount is delayed by a predetermined amount and the corrected steering amount is added.

[0007]

According to the above-described rear wheel in-phase steering control method of the vehicle, when the vehicle turns, the reference steering amount is obtained as it is as the rear wheel steering amount at the beginning of the turning, and the rear wheel steering amount, that is, the reference steering amount. In-phase steering of the rear wheels is performed based on the steering amount. Then, after that, the corrected steering amount according to the traveling state of the vehicle is added to the reference steering amount with a predetermined delay, so that the rear wheels are steered in phase based on the corrected rear wheel steering amount. Become.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, four-wheel steering of a vehicle (4W
S) The system is shown schematically. The 4WS system includes tandem oil pumps 2 and 3 driven by a vehicle engine 1.
Both 3 are connected to the 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, respectively. Has been done. 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 and operated by the operation of the steering wheel 11, and selects the flow direction of the oil to be supplied to the front wheel power cylinder 8 in accordance with the steering direction of the steering wheel 11 to select one of the pressure chambers. It is possible to supply oil to. Also, from the gear box 7, the return line 1
2 extends, and one end of the return line 12 is connected to the steering control valve and the other end is 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 composed of a 4-port 3-position electromagnetic direction switching valve as shown in the drawing, and the oil supply pipe line 13 is connected to the input port I thereof. 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 O1 and O2 are connected to the oil supply lines 16 and 17.
It is connected to the rear wheel power cylinder 18 via.

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 pipe line 1 is provided in 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, and a center spring 21 is housed in the rear wheel power cylinder 18. The center spring 21 biases the piston rod to the neutral position when the rear wheel power cylinder 18 is not operated, and maintains the straight traveling state of the rear wheel RW.

Further, the oil supply line 13 and the return line 15 described above are connected to each other by a bypass line 22. In the bypass line 22, a hydraulic pressure switching valve 23, which is an electromagnetic on-off valve, is connected. It has been inserted. The rear wheel hydraulic pressure control valve 14 and the hydraulic pressure switching valve 23 are electronic control units (EC
U) 24 receives the command signal from the U) 24, and the switching operation is performed. Therefore, the solenoids of the rear wheel hydraulic pressure control valve 14 and the hydraulic pressure 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 off, the solenoid of the hydraulic pressure switching valve 23 is constantly excited by the ECU 24, and the hydraulic pressure switching valve 23 is closed. Is in a 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, at this time, for the first 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 the other pressure chamber returns 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 to one side, and as a result, the rear wheel RW is steered by a predetermined rear wheel steering amount.

Here, the rear wheels RW are steered in phase with the front wheels FW, and the rear wheel steering amount is determined by the ECU 24 in accordance with the steering of the front wheels FW and the running condition of the vehicle. Is becoming Therefore, various sensors are electrically connected to the ECU 24, and these sensors are connected to the steering wheel angle sensor 25 for detecting the steering wheel angle θH and the pressures in the pressure chambers 9 and 10 of the front wheel power cylinder 8. A pair of pressure sensors 26, 27 for detecting the vehicle speed, a vehicle speed sensor 28 for detecting the vehicle speed from the rotation of an output shaft of a transmission (not shown) in the engine 1, a wheel speed sensor 29 for detecting the wheel speed of the front wheels FW, There is a rear wheel steering angle sensor 30 for detecting the actual rear wheel steering amount δA of the rear wheels RW.

As the rear wheel steering angle sensor 30, for example, a stroke sensor for detecting the stroke of the piston rod in the rear wheel power cylinder 18 can be used. Based on the sensor signal of this stroke sensor, the ECU 24 causes the actual rear wheel to travel. 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. Although various methods are conceivable for detecting the road surface μ, 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 not described in detail here, the principle of detecting the road surface μ is as follows.
The front wheel power cylinder 8 from the deviation of the pressure value detected in 7.
The second is that the working pressure is proportional to the cornering force of the front wheels FW, and the third is that the cornering force is proportional to the product of the sideslip angle of the front wheels FW and the road surface μ. Is based on the fact that the sideslip 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 a block diagram of the 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
When the vehicle speed V is detected, the vehicle speed V is supplied to the block 31, and in this block 31, the reference in-phase steering coefficient KB is calculated. Here, it goes without saying that the vehicle speed V can be obtained 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 determining the reference in-phase steering coefficient KB on the basis of the vehicle speed V in the block 31, specifically, the reference in-phase steering coefficient KB can be 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 /
Above h), it has a characteristic that it rapidly increases to some extent as the vehicle speed V increases, and thereafter converges to its maximum value.

Reference in-phase steering coefficient K obtained in block 31
B is then fed to block 32, which
At, the reference in-phase steering amount δRB of the rear wheels RW is calculated and obtained. That is, the block 32 contains 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 wheels RW is the reference in-phase steering coefficient KB.
And the steering wheel angle θH, that is, it is calculated from the following equation.

ΔRB = KB · θH Therefore, the reference in-phase steering amount δRB obtained in block 32 is
When the vehicle speed V becomes V0 or more, it increases as the steering wheel 11 is cut. After that, the reference in-phase steering amount δRB is supplied to the adding unit 33. Vehicle speed V
Is also supplied to the block 34, and the road surface μ is also supplied to this block 34. 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 increases the vehicle speed V from the time when the vehicle speed V reaches a certain vehicle speed in a situation where the road surface μ has a positive value. The characteristic is that it draws a substantially triangular shape that gradually increases with time and then gradually decreases. Further, this characteristic varies depending on the size of the road surface μ, and the smaller the road surface μ, the larger the triangular shape of the characteristic.
That is, the relationship among the road surfaces μ1, μ2, μ3, μ4 shown in FIG. 4 is expressed by the following equation, for example.

Μ1 <μ2 <μ3 <μ4 <1 Here, the values V1, V2, V3, V4 of the vehicle speed V at which the in-phase correction steering coefficient KC starts to increase become smaller as the road surface μ becomes smaller, but When the vehicle speed V reaches V6 or more, the in-phase correction 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 characteristic when the road surface μ is μ5 which takes a value of 1 or more. This characteristic is different from the triangular shape where the road surface μ takes a value of 1 or less. , Has an inverted triangular shape. Therefore, when the road surface μ is 1 or more, the in-phase correction steering coefficient KC has a negative value. In addition, V1, V2, V3, V4, V5 and V6 are
For example, 20km / h, 30km / h, 40km / h, 50km / h, 60
It is set to km / h and 100 km / h.

When the in-phase corrected steering coefficient KC is obtained in the block 34, the in-phase corrected steering coefficient KC is supplied to the next block 35 to calculate the in-phase corrected steering amount δRC. That is, as in the case of the block 32 described above, the steering wheel angle θH is also supplied to the block 35, and the in-phase correction steering amount δRC is the product of the in-phase correction steering coefficient KC and the steering wheel angle θH, that is, from the following equation. Is calculated.

ΔRC = KCθH The in-phase corrected steering amount δRC calculated in this way is supplied to the adder 33 and added to the reference in-phase steering amount δRB by the adder 33. The wheel steering amount δR will be calculated, however, in the block 35
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, and in this block 37, the time constant T is determined based on the vehicle speed V and the road surface μ.

Specifically, in block 37, the time constant T is calculated from the graph shown in FIG. Figure 5
As is clear from the graph of, when the road surface μ has a value of 1 or less and the vehicle speed V is in a predetermined speed range from V7 (for example, 30 km / h), the time constant T has a predetermined value, and
The vehicle speed V deviates from the predetermined speed range, and the vehicle speed V8 (for example, 80 k
The time constant T decreases as it goes up toward m / h). Further, when the road surface μ has a value of 1 or more, the time constant T is unconditionally 0.

Regarding the graphs of FIGS. 3 to 5,
These are mapped and stored in advance in a nonvolatile memory (not shown) in the EUC 24, and from these maps, the reference in-phase steering coefficient KB, the in-phase correction steering coefficient KC and the time constant T are calculated.
May be read. According to the above-described procedure for calculating the rear wheel steering amount δR, when the vehicle speed V is V1 or more, the reference in-phase steering coefficient KB rises as is apparent from FIG. 3, and in this situation, the steering wheel 11 is turned. When the vehicle turns, the reference in-phase steering amount δRB of the rear wheels RW is calculated.

On the other hand, in a traveling situation in which the road surface μ takes a small value when the vehicle is turning as described above, as is apparent from the graph of FIG. 4, the in-phase correction steering coefficient KC is equal to the road surface μ.
And a positive value corresponding to the vehicle speed V at that time, the in-phase corrected steering amount δRC is calculated based on this KC and the steering wheel angle θH, and this in-phase corrected steering amount δRC and the reference in-phase steering amount. The amount δRB and the amount δRB are added up by the addition unit 33, and the rear wheel steering amount δR is obtained.

When the rear wheel steering amount δR is calculated in this way, the ECU 24 determines that the actual rear wheel steering amount δRA matches the rear wheel steering amount δR based on the sensor signal from the rear wheel steering angle sensor 30. In addition, the operation of the rear wheel power cylinder 18 described above, that is, the rear wheel hydraulic control valve 14 is controlled. Here, as is apparent from the block diagram of FIG. 2, the calculated in-phase corrected steering amount δRC is not immediately supplied to the addition unit 33, but is passed to the addition unit 33 after passing through the first-order lag element of the block 36. Since it is supplied, the in-phase correction steering amount δRC is
With a predetermined delay time, it is added to the reference in-phase steering amount ΔRB.

Therefore, when the vehicle is turned while traveling on the low μ road described above, the reference in-phase steering amount δRB becomes the rear wheel steering amount δR as it is at the initial stage of the turning, and the rear wheel steering is performed. With respect to the amount ΔR, the correction by the in-phase corrected steering amount ΔRC is still substantially ineffective. As a result, at the initial 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 wheels FW, so that sufficient turning performance of the vehicle can be ensured and the driver I don't feel the difficulty of bending.

However, after the vehicle has begun to turn, the calculated in-phase correction steering amount δRC is more effective than the rear wheel steering amount δR, so that the rear wheel steering amount δR is finally obtained.
Is substantially increased based on the in-phase corrected steering amount ΔRC. Therefore, while the vehicle is traveling on a low μ road, after the initial turning, the rear wheel steering amount δR is largely corrected in the direction of increasing, so that the grip force of the tire is further increased and the running stability of the vehicle can be enhanced. ..

This becomes clear from the graph shown in FIG. This graph shows the changes over time of the steering wheel angle θH and the actual rear wheel steering amount δRA. The actual rear wheel steering amount δRA indicates the delay time with respect to the turning of the steering wheel 11 as shown by the solid line. It will be increased.
Note that the broken line in FIG. 6 shows an example in which the block 36 of FIG. 2 is omitted, and the alternate long and short dash line shows the reference in-phase steering amount δRB.
Is shown.

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

The present invention is not limited to the above-described embodiment, and various modifications can be made. 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 obtained based on the lateral acceleration acting on the vehicle body, the road surface gradient, etc.
As a result, it is of course possible to secure traveling stability during turning in various traveling situations.

[0036]

As described above, according to the vehicle rear-wheel in-phase steering control method of the present invention, the corrected steering amount according to the running condition of the vehicle is added to the reference steering amount of the rear wheel during turning. At this time, the corrected steering amount is not immediately added to the reference steering amount to be the rear wheel steering amount, but the corrected steering amount is added to the reference steering amount with a predetermined delay to obtain the rear wheel steering amount. If the steering of the rear wheels is controlled in the same phase based on the rear wheel steering amount thus determined, the turning performance of the vehicle is ensured at the beginning of turning, and after that, According to the traveling situation of No. 1, a sufficient correction can be added to the rear wheel steering amount, and an excellent effect such that traveling stability of the vehicle can be secured at the same time is exhibited.

[Brief description of 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 the relationship between vehicle speed and reference in-phase steering coefficient.

FIG. 4 is a graph showing in-phase corrected steering coefficient 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 change over time 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

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B62D 137: 00 (72) Inventor Takeo Go 33-5-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation

Claims (1)

[Claims] 1. When the vehicle is turning, the reference steering amount of the rear wheels is calculated according to the steering of the front wheels, while the corrected steering amount of the rear wheels is calculated according to the running condition of the vehicle. In the rear wheel steering control method of the vehicle, in which the rear wheels are steered in phase with the front wheels, based on the rear wheel steering amount obtained by adding the corrected steering amount to the reference steering amount with a predetermined delay. In addition, a rear-wheel in-phase steering control method for a vehicle, characterized in that the rear-wheel steering amount is obtained.