JPH06144272A - Rear wheel steering control device for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To enable rear wheel steering to follow the fast behavior change of a vehicle at the time of high speed travel in a four-wheel steering vehicle provided with rear wheel steering mechanism for steering rear wheels by the rotation of a motor. CONSTITUTION:A microcomputer 35 determines a target steering angle according to the vehicle speed, a yaw rate and a front wheel steering angle and also determines a duty ratio corresponding to the difference between the determined target steering angle and the actual steering angle of lateral rear wheels RW1, RW2 so as to supply a driving circuit 36 with a signal indicating this duty ratio. The driving circuit 36 supplies a motor 21 with a driving current proportional to this duty ratio so that the rotation of the motor 21 is controlled to steer the lateral rear wheels RW1, RW2. When the vehicle speed detected by a vehicle speed sensor 31 is large, the duty ratio is corrected in such a way as to be large compared to the time of the vehicle speed being small, so that the driving current to the motor 21 is made large to make the steering speed of the lateral rear wheels RW1, RW2 fast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a four-wheel steering vehicle having a rear wheel steering mechanism that steers the rear wheels by the rotation of an electric motor. The present invention relates to a rear wheel steering control device for a four-wheel steering vehicle, which controls the rear wheels to a target steering angle by passing a driving current to the electric motor.

[0002]

2. Description of the Related Art Conventionally, as a device of this type, as disclosed in, for example, Japanese Unexamined Patent Publication No. 62-227869.
There is a system in which the rotation speed of an electric motor is controlled to be slower as the vehicle speed increases so that the rear wheels are steered more slowly when traveling at higher speeds.

[0003]

However, although the behavior of the vehicle during running changes faster as the vehicle speed increases, in the above-described conventional device, the rear wheels are steered slowly as the vehicle travels at higher speeds. The rear wheel steering cannot be made to follow the behavior of the vehicle when traveling at high speed. The present invention has been made to solve the above problems, and an object of the present invention is to provide a rear wheel steering control device for a four-wheel steering vehicle that can steer the rear wheels by following changes in the behavior of the vehicle during high-speed traveling. To provide.

[0004]

In order to achieve the above object, the structural features of the present invention include a target rudder angle determining means for deciding a target rudder angle and a rear wheel for detecting an actual rudder angle of a rear wheel. Rear wheel of a four-wheel steering vehicle including steering angle detection means and drive means for causing a drive current according to the difference between the target steering angle and the actual steering angle to flow through an electric motor to steer the rear wheels to the target steering angle In the steering control device,
The vehicle speed detecting means for detecting the vehicle speed and the current control means for controlling the drive current value to be larger when the detected vehicle speed is higher than when the detected vehicle speed is low are provided.

[0005]

According to the present invention constructed as described above, when the vehicle speed detected by the vehicle speed detecting means is high, the current control means compares the drive current value supplied to the electric motor with the low vehicle speed. Since the electric motor is driven at high speed, the rotation speed of the electric motor becomes faster and the steering of the rear wheels becomes faster when the vehicle is running at high speed. The maneuverability of the vehicle is improved. On the other hand, during low-speed traveling where the behavior of the vehicle is slow, steering of the rear wheels is slower than when the vehicle speed is high, that is, the drive current value of the electric motor is controlled to be small, so that it is not necessary to always supply a large current to the electric motor. The power consumption for steering the rear wheels can be reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a front wheel steering mechanism 10 for steering left and right front wheels FW1 and FW2 and a rear wheel steering mechanism for steering left and right rear wheels RW1 and RW2. 1 schematically shows the entire vehicle including a vehicle 20 and an electric control device 30 that electrically controls the rear wheel steering mechanism 20.

The front wheel steering mechanism 10 is provided with a steering handle 11 for steering the left and right front wheels FW1 and FW2 by turning operation.
The handle 11 is fixed to the upper end of the steering shaft 12.
The lower end of the steering shaft 12 meshes with the rack bar 14 in the steering gear box 13. The rack bar 14 is supported in the steering gear box 13 so as to be displaceable in the axial direction, and has tie rods 15a, 15 at both ends.
The left and right front wheels FW1, FW2 are steerably connected via b and knuckle arms 16a, 16b.

The rear wheel steering mechanism 20 includes an electric motor 21 such as a brushless motor for steering the rear wheels.
The rotating shaft of the electric motor 21 is the steering gear box 2
The relay rod 23 is supported in the shaft 2 via a speed reduction mechanism so as to be displaceable in the axial direction, and the rod 23 is displaced in the axial direction according to the rotation of the motor. The left and right rear wheels RW1 and RW are provided at both ends of the relay rod 23 via tie rods 24a and 24b and knuckle arms 25a and 25b.
2 are connected, and the left and right rear wheels RW1 and RW2 are steered according to the axial displacement of the relay rod 23.

The electric control unit 30 comprises a vehicle speed sensor 31, a yaw rate sensor 32, a front wheel steering angle sensor 33 and a rear wheel steering angle sensor 34. The vehicle speed sensor 31 detects the vehicle speed V by measuring the rotation of an output shaft of a transmission (not shown) and outputs a detection signal indicating the vehicle speed V. The yaw rate sensor 32 detects the yaw rate γ around the center of gravity of the vehicle body and outputs a detection signal indicating the yaw rate γ. The front wheel steering angle sensor 33 detects the steering angle θf of the left and right front wheels FW1 and FW2 by measuring the rotation angle of the steering shaft 12, and outputs a detection signal representing the steering angle θf. Rear wheel steering angle sensor 34
Detects the steering angle θr of the left and right rear wheels RW1 and RW2 by measuring the rotation angle of the rotary shaft of the electric motor 21, and outputs a detection signal representing the steering angle θr. The yaw rate γ, the front wheel steering angle θf, and the rear wheel steering angle θr are positive in the left rotation direction and negative in the right rotation direction.

These sensors 31 to 34 are connected to the microcomputer 35. The microcomputer 35 includes a CPU, a ROM, a RAM, an I / O, a timer and the like, and executes a program stored in the ROM and corresponding to the flowchart of FIG. A drive circuit 36 is connected to the microcomputer 35.
Is controlled by the microcomputer 35 to flow the drive current from the battery 40 to the electric motor 21 to control the rotation of the electric motor 21. It should be noted that the voltage from the battery 40 is applied to each of the sensors 31 to 34 and the microcomputer 3
5 is also supplied.

Next, the operation of the embodiment configured as described above will be described with reference to the flow chart shown in FIG. When an ignition switch (not shown) is turned on, the microcomputer 35 starts executing the program in step 100 of FIG. 2 and each sensor 3 in step 102.
The detection signals representing the vehicle speed V, the yaw rate γ, the front wheel steering angle θf and the rear wheel steering angle θr are input from 1 to 34, respectively. Next, at step 102, the yaw rate proportional coefficient K1 (see FIG. 3) that changes according to the vehicle speed V is read from the table provided in the ROM.
(See (A)) and the steering angle proportional coefficient K2 (see FIG. 3B) are read out, and in step 106, the target steering angles θr * of the left and right rear wheels RW1 and RW2 are calculated by executing the calculation of the following equation 1.

[0012]

[Equation 1] θr * = K1 · γ + K2 · θf After the calculation of the target steering angle θr *, the deviation Δθ (= θ between the target steering angle θr * and the input rear wheel steering angle θr is calculated in step 108.
r * −θr) is calculated, and this deviation Δθ is calculated in step 110.
Is used to determine the duty ratio D _T for determining the drive current value supplied to the electric motor 21. In determining the duty ratio D _T , the absolute value of the deviation Δθ | Δ
Based on θ |, the table provided in the ROM of the microcomputer 35 and storing the data showing the characteristics of FIG. 4 is referred to, and the duty ratio D corresponding to the same absolute value | Δθ |
_T is derived.

Next, at step 112, referring to the table provided in the ROM of the microcomputer 35 based on the vehicle speed V and storing the data showing the characteristics of FIG. 5,
The coefficient K3 corresponding to the same vehicle speed V is read. After reading the coefficient K3, the duty ratio D _T determined in step 114 is multiplied by the coefficient K3 to correct the duty ratio D _T to the multiplication value K3 · D _T. Then, in step 116, a control signal composed of a signal representing the positive / negative sign sign (Δθ) of the calculated deviation Δθ and a signal representing the corrected duty ratio D _T is output to the drive circuit 36. The drive circuit 36 is
A drive current supplied from the battery 40 and having a magnitude determined by the duty ratio D _T is applied to the electric motor 21 with a positive or negative sign si.
Flow in the direction determined by gn (Δθ). As a result, the electric motor 21 rotates in a direction corresponding to the target steering angle θr *, the rotation is transmitted to the relay rod 23, and the rod 23 is displaced in the axial direction according to the rotation. The axial displacement of the relay rod 23 is transmitted to the left and right rear wheels RW1 and RW2 via the tie rods 24a and 24b and the knuckle arms 25a and 25b, and the rear wheels RW1 and RW2 are steered in the direction of the target steering angle θr *. To be done.

After the processing of step 116, the program is returned to step 102, and the circulation processing of steps 102 to 116 is repeatedly executed to left and right rear wheels RW1, RW.
Steer 2 to the target steering angle θr *. In this case, if the vehicle speed V is low, the coefficient K3 is set to a small value (see FIG. 5), so the duty ratio _DT for controlling the magnitude of the drive current of the electric motor 21 is also small. Therefore, the left and right rear wheels RW
1, When driving at low speed that does not require fast steering of RW2,
Since a small drive current flows through the electric motor 21 and the left and right rear wheels RW1 and RW2 are slowly steered to the target steering angle θr *, it is possible to avoid unnecessary power consumption. On the other hand, when the vehicle speed V increases, the coefficient K3 is set to a large value (see FIG. 5), so the duty ratio D _T that controls the magnitude of the drive current of the electric motor 21 also increases.
Therefore, when driving at high speed, a large drive current flows through the electric motor 21 and the left and right rear wheels RW1 and RW2 are steered quickly.
The steering of W1 and RW2 can be followed.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a vehicle according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a program executed by the microcomputer of FIG.

3A is a change characteristic diagram of a yaw rate proportional coefficient with respect to a vehicle speed, and FIG. 3B is a change characteristic diagram of a steering angle proportional coefficient with respect to a vehicle speed.

FIG. 4 is a change characteristic diagram of a duty ratio with respect to an absolute value of a deviation between a target steering angle and an actual rear wheel steering angle.

FIG. 5 is a change characteristic diagram of a correction coefficient with respect to a vehicle speed for correcting the duty ratio.

[Explanation of symbols]

FW1, FW2 ... front wheels, RW1, RW2 ... rear wheels, 10 ...
Front wheel steering mechanism, 20 ... Rear wheel steering mechanism, 21 ... Electric motor, 30 ... Electric control device, 31 ... Vehicle speed sensor, 32 ... Yaw rate sensor, 33 ... Front wheel steering angle sensor, 34 ... Rear wheel steering angle sensor, 35 ... Micro Computer, 36 ... Driving circuit, 40 ... Battery.

Front Page Continuation (72) Inventor Hideki Katsuraya 2-1-1 Asahi-cho, Kariya City, Aichi Aisin Seiki Co., Ltd.

Claims (1)

[Claims] 1. A target steering angle determining means for determining a target steering angle, which is applied to a four-wheel steering vehicle having a rear wheel steering mechanism for steering a rear wheel by rotation of an electric motor, and an actual steering angle of a rear wheel is detected. Four-wheel steering including a rear-wheel steering angle detecting unit for controlling the rear-wheel steering angle and a driving unit for controlling the rear wheels to the target steering angle by passing a drive current corresponding to the difference between the target steering angle and the actual steering angle to an electric motor. In the rear wheel steering control device for a vehicle, vehicle speed detection means for detecting a vehicle speed and current control means for controlling the drive current value to be larger when the detected vehicle speed is higher than when the detected vehicle speed is low are provided. A rear-wheel steering control device for a four-wheel steering vehicle characterized by: