JPH04349069A - Motor control device of four-wheel steering car - Google Patents

Abstract

PURPOSE:To keep well the responsivity and convergence characteristic by sensing the road surface load equivalent, setting the damping constant smaller with a greater equivalent, thereupon controlling the motor current, and thereby eliminating influence of the varying road surface load at the time of cornering. CONSTITUTION:A motor control device as per invention includes a road surface load equivalent sensing means (c) to sense the road surface load equivalent for the car wheel steered by a motor (a) and a damping constant setting means (d) to set the damping constant smaller with a greater road surface load. This is further equipped with a steering angle follow-up value change speed calculating means (e) to sense the steering angle follow-up value change speed of the car wheel steered by the motor (a) and a motor current calculating means (f) to calculate the motor current on the basis of the damping constant and the steering angle follow-up value change speed, and the motor current determined by this means (f) is impressed on the motor (a) with the aid of a motor driving means (g).

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has a motor steering mechanism that uses an electric motor as an actuator for the rear wheel or front and rear wheels, and the electric motor controls the steering angle of the rear wheel or front and rear wheels when the steering wheel is operated. The present invention relates to a motor control device for a four-wheel steering vehicle.

0002

2. Description of the Related Art Conventionally, as a four-wheel steering vehicle having a steering mechanism on the rear wheels using an electric motor as an actuator, there has been known, for example, the one described in Japanese Patent Application Laid-Open No. 61-46766. As a four-wheel steering vehicle having a steering mechanism in the front and rear wheels using a steering mechanism as an actuator, for example, the one described in Japanese Patent Application Laid-open No. 89171/1983 is known.

[0003] The former conventional source describes that when the steering wheel is operated, a target value of the steering angle of the front and rear wheels is determined according to the amount of steering wheel operation, and the steering angle of the front and rear wheels is controlled by an electric motor to obtain this target value of the steering angle. The latter conventional source states that when the front wheels are steered by steering wheel operation, a target value of the rear wheel steering angle is determined according to the front wheel steering angle, and the steering angle of the front and rear wheels is controlled by an electric motor to obtain this target value of the rear wheel steering angle. The content to be controlled is shown.

In a motor steering mechanism using an electric motor as an actuator as described above, the motor is controlled by the motor control formula shown below. IM = L・θε−m・d(θM)+Kp I
M: Motor current
L: proportionality constant
θε: Deviation between target value and follow-up value
m: damping constant
d(θM): Motor rotation angular velocity
Kp: Friction correction constant

[0005]

However, in such a motor control device for a four-wheel steering vehicle, since the damping constant m is given by a fixed value in the above motor control equation, the step response characteristics and When looking at the frequency response characteristics, the characteristics are greatly affected by the magnitude of the road surface load.

That is, looking at the step response characteristics when the damping constant m is set based on a medium road load, as shown in FIG. 14, when the target steering angle value is given in steps, the road load The larger the damping constant m, the lower the response, and if the damping constant m is a fixed value, the value is too large and the response becomes dull. Furthermore, the smaller the road surface load, the higher the responsiveness, and if the damping constant m is a fixed value, the value is too small and overshoot occurs.

Furthermore, looking at the frequency response characteristics, as shown in FIG. 15, especially in the high frequency range where the steering angle changes rapidly when the road surface load is small, a peak due to resonance appears in the gain characteristics, and a peak in the phase characteristics appears. A sudden phase drop appears.

The present invention has been made with attention to the above-mentioned problem, and is a motor control device for a four-wheel steering vehicle having a motor steering mechanism using an electric motor as an actuator for the rear wheels or front and rear wheels. The objective is to maintain optimal responsiveness and convergence without being affected by changes in road load.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the motor control device for a four-wheel steering vehicle of the present invention detects a road load equivalent value, and sets a damping constant to a smaller value as the road load equivalent value increases. This was used as a means to control the motor current.

That is, as shown in the diagram corresponding to the claims in FIG. 1, a steering mechanism is provided that has a motor steering mechanism b on the rear wheel or front and rear wheels using an electric motor a as an actuator, and steers the rear wheel or front and rear wheels when the steering wheel is operated. In a four-wheel steering vehicle in which the angle is controlled by an electric motor, a road surface load equivalent value detection means c detects a road surface load equivalent value of the wheels steered by the electric motor a, and the damping constant is set to be smaller as the road surface load is larger. a damping constant setting means d for setting a value to a value; and a steering angle following value change speed calculating means e for detecting a change speed of a steering angle follow-up value of the wheels steered by the electric motor a.
, a motor current calculation means f for calculating a motor current based on at least the damping constant and the steering angle follow-up value change rate, and a motor for applying the motor current obtained by the motor current calculation means f to the electric motor a. Drive means g
It is characterized by having the following.

[0011]

[Operation] When turning with a large road load, the damping constant setting means d uses the road load equivalent value detection means c.
The damping constant is set to a smaller value as the road surface load detected is larger, and the electric motor a is controlled based on this damping constant and the steering angle follow-up value change rate. Therefore, when turning with a large road load,
While the damping force of motor steering mechanism b increases due to road surface load, by reducing the damping force applied by the motor current control system, the total damping force from both becomes optimal, and responsiveness is also achieved in step response and frequency response. and exhibits high convergence characteristics.

When turning with a small road load, the damping constant is set to a large value by the damping constant setting means d because the road load detected by the road load equivalent value detecting means c is small, and this damping constant and the steering The electric motor a is controlled based on the rate of change of the angular follow-up value. Therefore, when turning with a small road load, the damping force of motor steering mechanism b decreases due to the road load, but by increasing the damping force given by the motor current control system, the total damping force from both can be optimized. It exhibits high responsiveness and convergence in step response and frequency response.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

The configuration will be explained.

FIG. 2 is an overall system diagram showing a motor control device for a four-wheel steering vehicle to which the device of the first embodiment of the present invention is applied.

In the motor control system for a four-wheel steering vehicle according to the first embodiment, as shown in FIG. 2, the front wheels 1 and 2 are steered by a steering handle 3 and a mechanically linked steering mechanism 4. This includes, for example, steering gear, pitman arm, relay rod, side rod 5,
6, knuckle arms 7, 8, etc.

[0017] The steering of the rear wheels 9 and 10 is performed by an electric steering device 11 (corresponding to a motor steering mechanism).
It is carried out by The rear wheels 9 and 10 are connected by a rack shaft 12, side rods 13 and 14, and knuckle arms 15 and 16, and a rack tube 17 into which the rack 12 is inserted has a deceleration mechanism 18 and a motor 19 (an electric motor ) and a fail-safe solenoid 20 are provided, and this motor 19 and fail-safe solenoid 2
0 is driven and controlled by a controller 26 that inputs signals from a vehicle speed sensor 21, a front wheel steering angle sensor 22, a stroke sensor 23, an encoder 24, a load cell 25 (corresponding to road surface load equivalent value detection means), and the like.

FIG. 3 is a sectional view showing a specific configuration of the electric steering device 11, in which a rack tube 17 into which a rack 12 is inserted is fixed to the vehicle body via a bracket. Side rods 13 and 14 are connected to both ends of the rack 12 via ball joints 30 and 31. The speed reduction mechanism 18 includes a motor pinion 32 connected to the motor shaft of the motor 19, and a motor pinion 32 connected to the motor shaft of the motor 19.
It is composed of a ring gear 33 that meshes with the rack gear 12a, and a rack pinion 35 that is fixed to the ring gear 33 and meshes with the rack gear 12a. Therefore, motor 19
When rotates, motor pinion 32 → ring gear 33 →
The rotation is transmitted to the rack pinion 35, and the rack shaft 12 is moved in the axial direction by the meshing of the rotating rack pinion 35 and the rack gear 12a, and the rear wheels 9 and 10 are steered. The amount of steering of the rear wheels 9 and 10 is proportional to the amount of movement of the rack shaft 12, that is, the amount of rotation of the motor 19.

A sensor shaft 24a of an encoder 24 for detecting the rotation angle of the rack and pinion 35 is connected via a coupler 36.

The fail-safe solenoid 20 includes:
A lock pin 20a is provided to be movable back and forth, and in the event of a failure in the electronic control system, etc., by fitting the lock pin 20a into a lock groove 12b formed in the rack shaft 12, the rack shaft 12 can be fixed to the rear wheels 9, 10. It is fixed at a position that maintains the neutral steering angle position.

[0021] The action will be explained.

First, in a motor steering mechanism using an electric motor as an actuator, the motor is controlled by the motor control formula shown below. IM = L・θε−m・d(θM)+Kp

...(1) IM: Motor current
L: proportionality constant
θε: Deviation between target value and follow-up value m: Damping constant
d(θM): Motor rotational angular speed Kp: Friction correction constant In other words, when the road load increases in proportion to the rear wheel steering angle in the motor steering mechanism, a spring load that simulates the road load is added as shown in Fig. 4. It can be replaced with the model. In this motor steering mechanism model, motor current value IM for motor torque
The static characteristic of shows a proportional characteristic as shown in FIG. Here, the motor torque can be replaced with the deviation between the target value and the follow-up value due to the relationship in which the road load increases in proportion to the rear wheel steering angle. If you think about it, you can get the following formula.

IM=L・θε+Kp

(2) In addition, as for the dynamic characteristics that determine the response of the rear wheel steering angle to the drive command to the motor, it is sufficient to consider the damping property in a motor steering mechanism that has better responsiveness than a hydraulic steering mechanism or the like. Therefore, by adding the attenuation term {-m·d(θM)} to the above equation (2), the motor control equation shown in equation (1) can be obtained. Note that the damping force is proportional to the rate of change of the steering angle follow-up value, and the rate of change of the steering angle follow-up value may be the motor rotational angular speed as described above, or the stroke speed.

FIG. 7 is a flow chart showing the flow of motor control operations performed by the controller 26.
Each step will be explained.

In step 70, input signals are read from each sensor 21-25.

In step 71, a rear wheel steering angle target value θR* is calculated based on the vehicle speed V from the vehicle speed sensor 21 and the front wheel steering angle θF from the front wheel steering angle sensor 22 (corresponding to steering angle target value calculation means). ). Note that the rear wheel steering angle target value θR* is determined in order to obtain the optimum turning performance by a method such as that described in, for example, Japanese Patent Laid-Open No. 1-202579.

In step 72, a rear wheel steering angle follow-up value θR is calculated based on the motor rotation angle θM detected by the encoder 24.

In step 73, rear wheel steering angle target value θR*
The deviation θε is calculated from the absolute value obtained by subtracting the rear wheel steering angle follow-up value θR from θR.

In step 74, the motor rotation angular velocity d(θM) is calculated based on the motor rotation angle θM detected by the encoder 24 during the current processing and the stored motor rotation angle θMM detected during the previous processing several times. (corresponds to the steering angle follow-up value change speed calculation means).

In step 75, a damping constant m is set based on the road surface load F detected by the load cell 25 (corresponding to damping constant setting means). Note that the damping constant m for the road surface load F is set to a smaller value as the road surface load F becomes larger, as shown in FIG.

At step 76, the motor current IM is calculated using the above equation (1) (corresponding to motor current calculation means). In addition, the proportionality constant L and the friction correction constant K
p is given by a preset fixed value.

At step 77, the motor current IM determined at step 76 is output to the motor 19 (corresponding to motor drive means).

Next, the turning action on road surfaces with different loads in a four-wheel steering vehicle equipped with the device of the first embodiment will be explained.

(a) When turning with a large road load When turning with a large road load, in step 75, the damping constant m is set to a smaller value as the road load F detected by the load cell 25 becomes larger. The motor 19 is controlled based on the motor current control equation (1) having a damping term obtained by multiplying the damping constant m by the motor rotational angular velocity d(θM).

Therefore, when turning with a large road load, the damping force of the electric steering device 11 increases due to the road load, but by reducing the damping force applied by the motor current control formula (1), the total effect of both is reduced. The damping force is optimal, and as shown in Figure 9, the step response characteristic shows a fast response and good convergence, and as shown in Figure 10, the frequency response characteristic has an optimal gain and phase characteristic. Indicates delay characteristics.

(b) When turning with a small road load When turning with a small road load, in step 75, the damping constant m where the road load F detected by the load cell 25 is small is set to a large value, and this damping The motor 19 is controlled based on the motor current control equation (1) having a damping term obtained by multiplying the constant m by the motor rotational angular velocity d (θM).

Therefore, when turning with a small road load, the damping force of the electric steering device 11 becomes smaller due to the road load, but by increasing the damping force given by the motor current control formula (1), the total effect of both is reduced. The damping force is optimal, and as shown in Figure 9, the step response characteristic shows no overshoot and has good convergence, and as shown in Figure 10, the gain and phase characteristics of the frequency response characteristic are optimal. Shows first-order lag characteristics.

[0038] The effect will be explained.

(1) In a motor control device for a four-wheel steering vehicle having an electric steering device 11 on the rear wheels 9, 10 side, the road surface load F is detected, and the motor current control method (1) increases as the road surface load F increases. Since the device controls the motor current by setting the damping constant m to a small value, it is possible to maintain optimal responsiveness and convergence without being affected by changes in road load during turning.

(2) Since the device directly detects the road surface load using the load cell 25, when the road surface load changes, the changing situation is immediately detected, and the optimal damping constant m can be set with good response. Can be done.

Next, a second embodiment of the apparatus will be explained.

In contrast to the device of the first embodiment, which uses the load cell 25 that directly measures the road surface load as a road surface load equivalent value detection means, the device of the second embodiment uses a load cell 25 that directly measures the road surface load. Deviation θε (rear wheel steering angle target value θR
This is an example in which the absolute value obtained by subtracting the rear wheel steering angle follow-up value θR from * is taken as the road surface load equivalent value. Note that the configuration is the same as that of the first embodiment shown in FIGS. 2 and 3, so a description thereof will be omitted.

[0043] The action will be explained.

FIG. 11 shows the controller 2 of the second embodiment device.
6 is a flowchart showing the flow of the motor control operation performed in step 6, in which step 73 corresponds to the road surface load equivalent value detection means in the second embodiment device. In step 78, FIG.
2, the larger the deviation θε obtained in step 73, the smaller the damping constant m is set (
(equivalent to damping constant setting means). Furthermore, step 70~
Step 77 is the same as in the case of the apparatus of the first embodiment, so a description thereof will be omitted.

Therefore, when considering step response characteristics, for example, as shown in FIG. In this region, quick response is obtained by setting the damping constant m small. In addition, in a region where the deviation θε between the rear wheel steering angle target value θR* and the rear wheel steering angle tracking value θR is small and convergence is required, the rear wheel steering angle tracking value θR does not overshoot and the rear wheel steering angle is set as the target value. The damping constant m is set small in order to converge to the value θR*.

As explained above, in the second embodiment, the deviation θε is the value equivalent to the road load, so it is advantageous in terms of cost since it does not require the installation of a load cell 25 or the like for detecting the road load. The device makes it possible to maintain optimal responsiveness and convergence without being affected by changes in road surface load.

Although the embodiments have been described above with reference to the drawings, the specific configuration is not limited to the embodiments, and any changes or additions that do not depart from the gist of the present invention are not included in the present invention. It will be done.

For example, in the embodiment, an application example in which the motor steering mechanism is employed only in the rear wheels is shown, but it is also possible to employ the motor steering mechanism in the front and rear wheels.

[0049]

As described above, the present invention provides a motor control device for a four-wheel steering vehicle having a motor steering mechanism using an electric motor as an actuator for the rear wheels or front and rear wheels. The damping constant is set to a smaller value as the road load equivalent value increases, and the motor current is controlled to maintain optimal responsiveness and convergence without being affected by road load changes when turning. The effect of being able to achieve this goal is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to claims showing a motor control device for a four-wheel steering vehicle according to the present invention.

FIG. 2 is an overall system diagram showing a four-wheel steering vehicle to which the motor control device of the first embodiment is applied.

FIG. 3 is a sectional view showing a specific configuration of the electric steering device of the first embodiment.

FIG. 4 is a bench model diagram of the electric steering device.

FIG. 5 is a characteristic diagram of motor current value versus motor torque in the electric steering device.

FIG. 6 is a motor current value characteristic diagram with respect to a deviation between a target value and a follow-up value in an electric steering device.

FIG. 7 is a flowchart showing the flow of motor control operations performed by the controller of the device of the first embodiment.

FIG. 8 is a damping constant setting characteristic diagram with respect to road surface load in the first embodiment device.

FIG. 9 is a step response characteristic diagram of the device of the first embodiment.

FIG. 10 is a frequency response characteristic diagram of the device of the first embodiment.

FIG. 11 is a flowchart showing the flow of motor control operations performed by the controller of the device of the first embodiment.

FIG. 12 is a characteristic diagram of damping constant setting with respect to deviation in the device of the second embodiment.

FIG. 13 is a step response characteristic diagram showing the concept of damping constant setting with respect to deviation in the device of the second embodiment.

FIG. 14 is a diagram of a follow-up value response characteristic when the road surface load is large and a follow-up value response characteristic when the road surface load is small when the damping constant is set to a fixed value and a stepped target value is given.

FIG. 15 is a frequency response characteristic diagram depending on the magnitude of load when the damping constant is set to a fixed value.

[Explanation of symbols]

a Electric motor b Motor steering mechanism c Road surface load equivalent value detection means d Damping constant setting means e Rudder angle follow-up value change speed calculation means f　Motor current calculation means g Motor drive means

Claims (1)

[Claims] 1. A four-wheel steering vehicle having a motor steering mechanism using an electric motor as an actuator on a rear wheel or front and rear wheels, and in which a steering angle for steering the rear wheel or front and rear wheels when a steering wheel is operated is controlled by the electric motor, road surface load equivalent value detection means for detecting a road surface load equivalent value of wheels steered by the electric motor; damping constant setting means for setting a damping constant to a smaller value as the road surface load is larger; a steering angle following value change rate calculation means for detecting a change rate of a steering angle follow-up value of a steered wheel; a motor current calculation means for calculating a motor current based on at least the damping constant and the steering angle follow-up value change rate; A motor control device for a four-wheel steering vehicle, comprising: motor drive means for applying a motor current obtained by the motor current calculation means to the electric motor.