JP2913850B2 - Motor control device for four-wheel steering vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a motor steering mechanism using an electric motor as an actuator at the rear wheels or front and rear wheels, and controls the steering angle of the rear wheels or front and rear wheels when the steering wheel is operated by the electric motor. 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 using an electric motor as an actuator at a rear wheel, for example, one disclosed in Japanese Patent Application Laid-Open No. 61-46766 is known. As a four-wheel steering vehicle having a steering mechanism having front and rear wheels as actuators, for example, one described in Japanese Patent Application Laid-Open No. 61-89171 is known.

[0003] In the former conventional source, a steering angle target value of the front and rear wheels is determined according to a steering wheel operation amount at the time of steering operation, and the steering angle of the front and rear wheels is controlled by an electric motor in order to obtain the steering angle target value. In the latter conventional source, the rear wheel steering angle target value is determined according to the front wheel steering angle when steering the front wheel by operating the steering wheel, and the steering angle of the front and rear wheels is adjusted by an electric motor to obtain the rear wheel steering angle target value. The contents to be controlled are shown.

In a motor steering mechanism using an electric motor as an actuator as described above, motor control is performed by the following motor control formula. IM = LＬθε−md ・ (θM) + Kp IM: Motor current L: Proportional 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, the damping constant m is given by a fixed value in the above-mentioned motor control formula, so that the step response characteristic and the When looking at the frequency response characteristics, the characteristics are greatly affected by the magnitude of the road surface load.

[0006] In other words, 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 steering angle target value is given in steps, as shown in FIG. The larger the value is, the lower the response is, and the damping constant m with a fixed value is too large and the response becomes dull. In addition, the smaller the road surface load, the higher the responsiveness, and the damping constant m with a fixed value is too small to cause overshoot.

As shown in FIG. 15, the frequency response characteristic shows a peak due to resonance in the gain characteristic and a phase characteristic in the high frequency region where the steering angle change speed is high especially when the road surface load is small. Sudden phase drop appears.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In a motor control device of a four-wheel steering vehicle having a motor steering mechanism using an electric motor as an actuator on rear wheels or front and rear wheels, the present invention relates to It is an object to maintain optimal responsiveness and convergence without being affected by a change in road surface load.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, a motor control device for a four-wheel steering vehicle according to 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. In this way, the motor current is controlled.

That is, as shown in the claim correspondence diagram of FIG. 1, a motor steering mechanism b having an electric motor a as an actuator is provided on a rear wheel or front and rear wheels, and a steering wheel for steering the rear wheel or front and rear wheels when operating a steering wheel. The angle is controlled by an electric motor by the following motor control formula IM = LＬθθ−m ・ d (θM) + Kp IM: Motor current L: Proportional constant θε: Deviation between target value and follow-up value m: Damping constant d (θM): Motor rotational angular velocity Kp: in a four-wheel steering vehicle controlled using a friction correction constant , a road load equivalent value detecting means c for detecting a road load equivalent value of a wheel steered by the electric motor a; A damping constant setting means d for setting the damping constant m to a smaller value as the value is larger; a steering angle following value changing speed of a wheel steered by the electric motor a (= motor rotation angular speed d (θM)) And the steering angle tracking value change rate calculating means e for detecting, and said damping constant m and the steering angle tracking value change rate d (.theta.M)
A motor current calculating means f for calculating a motor current IM based on the motor control equation; and a motor driving means g for applying the motor current obtained by the motor current calculating means f to the electric motor a. It is characterized by being.

[0011]

When the vehicle is turning with a large road load, the damping constant setting means d sets the road load equivalent value detecting means c.
Damping constant increases as the road surface load detected by
m is set to a small value, and the electric motor a is controlled based on the motor control formula using the damping constant m and the steering angle following value change speed d (θM) . Therefore, a large during cornering at road load, while the damping force of the motor steering mechanism b is increased by the road load, total by both by reducing the damping force applied by the motor <br/> over motor control formula The damping force becomes optimal, and shows high response and convergence characteristics even in the step response and the frequency response.

[0012] when turning with a small road load, the damping constant setting means d, damping constant m by road load detected by the road load equivalent value detecting means c is small is set to a large value, the damping constant m
The electric motor a is controlled on the basis of the motor control formula using the steering angle follow-up value change speed d (θM) . Therefore, small during a turn running of the road surface load, while the damping force of the motor steering mechanism b is reduced by the road surface load, total damping force by both by increasing the damping force applied by the motor control equation optimal And high characteristics in response and convergence in step response and frequency response.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

The configuration will be described.

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

In the motor control device for a four-wheel steering vehicle according to the first embodiment, as shown in FIG. 2, steering of the front wheels 1 and 2 is performed by a steering handle 3 and a mechanical link type steering mechanism 4. This includes, for example, a steering gear, a pitman arm, a relay rod, side rods 5, 6, knuckle arms 7, 8, and the like.

The steering of the rear wheels 9, 10 is performed by an electric steering device 11 (corresponding to a motor steering mechanism).
Done 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 in which the rack 12 is inserted has a reduction mechanism 18 and a motor 19 (electric motor). ) And a fail-safe solenoid 20. The motor 19 and the fail-safe solenoid 2
0 is driven and controlled by a controller 26 which 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 detecting means), and the like.

FIG. 3 is a cross-sectional view showing a specific configuration of the electric steering apparatus 11, in which a rack tube 17 in which the 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 reduction mechanism 18 includes a motor pinion 32 connected to a motor shaft of the motor 19, and a motor pinion 32.
And a rack pinion 35 fixed to the ring gear 33 and meshing with the rack gear 12a. Therefore, the motor 19
Rotates, the motor pinion 32 → the 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 between the rotating rack pinion 35 and the rack gear 12a to steer the rear wheels 9, 10. The amount of steering of the rear wheels 9, 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 the encoder 24 for detecting the rotation angle is connected to the rack pinion 35 via a coupler 36.

The fail-safe solenoid 20 includes:
The lock pin 20a is provided so as to be able to advance and retreat, and when the electronic control system or the like fails, the lock shaft 20a is fitted into a lock groove 12b formed in the rack shaft 12 so that the rack shaft 12 and the rear wheels 9, 10 can be moved. It is fixed at a position to maintain the neutral steering angle position.

The operation will be described.

First, in a motor steering mechanism using an electric motor as an actuator, motor control is performed by the following motor control formula. IM = L ・ θε−md ・ (θM) + Kp (1) IM: motor current L: proportional constant θε: deviation between target value and follow-up value m: damping constant d (θM): motor rotation angular velocity 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 model to which a spring load simulating the road surface load can be replaced as shown in FIG. In this motor steering mechanism model, the static characteristic of the motor current value IM with respect to the motor torque shows a proportional characteristic as shown in FIG. Here, since the motor torque can be replaced with the deviation between the target value and the following value from the relationship that the road load increases in proportion to the rear wheel steering angle, the motor torque becomes as shown in the characteristic of FIG. If so, the following equation can be obtained.

IM = L · θε + Kp (2) In addition, the dynamic characteristic that determines the response of the rear wheel steering angle to the drive command to the motor has a damping property in a motor steering mechanism having a better response than a hydraulic steering mechanism or the like. Should be considered. Therefore, the attenuation term {-m · d (θM)} is
By adding to the equation (2), the motor control equation shown in the equation (1) can be obtained. Note that the damping force is in a relationship proportional to the change speed of the steering angle following value.
As described above, the motor rotation angular velocity may be used, or the stroke velocity may be used.

FIG. 7 is a flowchart showing the flow of the motor control operation performed by the controller 26.
Each step will be described.

In step 70, input signals are read from the sensors 21 to 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 a steering angle target value calculating means). ). Note that the rear wheel steering angle target value θR * is determined by, for example, a method described in Japanese Patent Application Laid-Open No. 1-2202579 or the like in order to obtain optimum turning performance.

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

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

In step 74, the motor rotation angular velocity d (θM) is calculated based on the motor rotation angle θM detected by the encoder 24 in the current processing and the stored motor rotation angle θMM detected in the processing several times before. (Corresponding to a steering angle following value changing speed calculating means).

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

In step 76, the motor current IM is calculated by the above equation (1) (corresponding to motor current calculation means). Note that the proportionality constant L and the friction correction constant Kp are given by fixed values set in advance.

In step 77, the motor current IM obtained in step 76 is output to the motor 19 (corresponding to motor driving means).

Next, a turning operation of a four-wheel steering vehicle equipped with the first embodiment on a road surface having a different load will be described.

(A) Turning with a large road load When turning with a large road load, in step 75, the larger the road load F detected by the load cell 25, the smaller the damping constant m is set. 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 rotation angular velocity d (θM).

Therefore, when the vehicle is turning with a large road load, the damping force of the electric steering device 11 increases due to the road load. On the other hand, by reducing the damping force given by the motor current control equation (1), the total The damping force becomes optimum, and as shown in FIG. 9, the response is fast and the convergence is good in the step response characteristics.
As shown by 0, an optimal first-order lag characteristic is shown in the gain characteristic and the phase characteristic of the frequency response characteristic.

(B) When turning with a small road load When turning with a small road load, in step 75, the road load F detected by the load cell 25 is set to a small value and the damping constant m is set to a large value. 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 the vehicle is turning with a small road load, the damping force of the electric steering device 11 is reduced by the road load. On the other hand, by increasing the damping force given by the motor current control equation (1), the total The damping force is optimal, and as shown in FIG. 9, the step response characteristic shows good convergence without overshoot. As shown in FIG. 10, the frequency response characteristic has the optimal gain characteristic and phase characteristic. Shows first-order lag characteristics.

The effect will be described.

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

(2) Since the road load is directly detected by the load cell 25, when the road load changes, the change condition is immediately detected, and the optimum damping constant m is set with good response. Can be.

Next, a second embodiment will be described.

The apparatus of the second embodiment uses the load cell 25 for directly measuring the road load as the road load equivalent value detecting means, whereas the apparatus of the first embodiment is proportional to the road load. Deviation θε (rear wheel steering angle target value θR *
(Absolute value obtained by subtracting the rear wheel steering angle follow-up value θR from the above) is regarded as a road load equivalent value. Since the configuration is the same as that of the first embodiment shown in FIGS. 2 and 3, the description is omitted.

The operation will be described.

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

Accordingly, for example, when considering the step response characteristics, as shown in FIG. 13, the deviation θε between the rear wheel steering angle target value θR * and the rear wheel steering angle follow-up value θR is large, and A In the region, quick response is obtained by setting the damping constant m small. In a region where the deviation θε between the rear wheel steering angle target value θR * and the rear wheel steering angle following value θR is small and convergence is required, the rear wheel steering angle following value θR does not overshoot and the rear wheel steering angle target value θR does not overshoot. In order to converge to the value θR *, the damping constant m is set small.

As described above, in the apparatus of the second embodiment, since the deviation .theta..epsilon. Is a value equivalent to a road load, the load cell 25 and the like for detecting the road load are not mounted. The device can maintain optimal responsiveness and convergence without being affected by changes in road surface load.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and even if there are changes and additions without departing from the gist of the invention, the invention is included in the invention. It is.

For example, in the embodiment, the application example in which the motor steering mechanism is adopted only for the rear wheel is shown, but the motor steering mechanism may be adopted for the front and rear wheels.

[0049]

In the present invention, as has been described above, according to the present invention, have a motor steering mechanism for an actuator of the electric motor to the rear wheel or the front and rear wheels, the motor-controlled
In the motor control device of the four-wheel steering vehicle that controls the motor current , the road load equivalent value is detected, and as the road load equivalent value increases, the damping constant is set to a smaller value to control the motor current. An effect is obtained that optimal responsiveness and convergence can be maintained without being affected by changes in road surface load during turning.

[Brief description of the 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 cross-sectional view showing a specific configuration of the electric steering device of the first embodiment.

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

FIG. 5 is a characteristic diagram of a motor current value with respect to a motor torque in the electric steering apparatus.

FIG. 6 is a characteristic diagram of a motor current value with respect to a deviation between a target value and a following value in the electric steering apparatus.

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

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

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

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

FIG. 11 is a flowchart illustrating a flow of a motor control operation performed by the controller of the first embodiment apparatus.

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

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

FIG. 14 is a diagram illustrating a follow-up value response characteristic when the road load is large and a follow-up value response characteristic when the road load is small when a step-like target value is given with a fixed damping constant.

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

[Explanation of symbols]

 a electric motor b motor steering mechanism c road surface load equivalent value detecting means d damping constant setting means e steering angle following value changing speed calculating means f motor current calculating means g motor driving means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI B62D 121: 00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04 B62D 6/00

Claims (1)

(57) [Claims] 1. A motor steering mechanism having an electric motor as an actuator at a rear wheel or a front and rear wheel, and a steering angle for steering the rear wheel or the front and rear wheels at the time of operating a steering wheel is controlled by an electric motor by the following motor control type IM = L. · θε-m · d (θM ) + Kp IM: motor current L: proportional constant Shitaipushiron: deviation between the target value and the following value m: damping constant d (.theta.M): motor rotational angular velocity Kp: controlled using a friction correction constant In a four-wheel steering vehicle, a road load equivalent value detecting unit that detects a road load equivalent value of a wheel steered by the electric motor, and a damping constant setting unit that sets a damping constant m to a smaller value as the road load increases. When the the steering angle tracking value change rate calculating means for detecting a steering angle tracking value changing speed of the wheel that is steered by an electric motor (= motor rotation angular speed d (.theta.M)), the Damping Grayed constant m and the steering angle tracking value change rate d and (.theta.M)
A motor current calculating means for calculating a motor current IM based on the motor control formula , and a motor driving means for applying the motor current obtained by the motor current calculating means to the electric motor. A motor control device for a four-wheel steering vehicle.