JPH07329807A - Steering control device for vehicle - Google Patents

Abstract

PURPOSE:To secure proper initial responsiveness in a steering control device for vehicle even when a steering angle deviation between a target steering angle value and an actual steering angle value is little. CONSTITUTION:A target steering angle value of a dirigible road wheel being a control object is determined by a target steering angle determining means, an actual steering value of the dirigible road wheel is measured by measuring means 61, 62, and a steering angle deviation between the actual steering angle value and the target steering angle value is calculated by a steering angle deviation calculating means 24. In accordance with a duty determined by a duty determining means 31 in compliance with this steering angle deviation, a steering angle control means 12 is driven to control a steering angle of the dirigible road wheel. In this case, when the steering angle deviation is not more than a specified value, an increasing ratio of the duty in relation to the steering angle deviation is determined larger in comparison to the case where the deviation exceeds the specified value, and even when the deviation is little, the steering angle control means is controlled with a large duty.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering control device, and more particularly to a front wheel steering device for correcting the steering angle of the front wheels of a four-wheel vehicle and a rear wheel steering device for adjusting the steering angle of the rear wheels. Related to a simple steering control device.

[0002]

2. Description of the Related Art Conventionally, there are known front wheel steering devices for correcting the steering angles of front wheels of four-wheeled vehicles and rear wheel steering devices for adjusting the steering angles of rear wheels. For example, JP-A-2-200573
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a method of controlling a pulse to an electric motor according to a target steering angle of a secondary steering wheel, an actual steering angle of a secondary steering wheel, and a vehicle speed when steering a secondary steering wheel to a target steering angle according to a steering angle of a primary steering wheel. A four-wheel steering control device is disclosed which changes the duty ratio of a current to control steering of a sub-steering wheel. And
As a result, in the high vehicle speed range, the steered wheels are reliably steered to the target steering angle, and in the low vehicle speed range, vibrations are prevented from occurring in the steered wheels, and the steered wheels are stably steered. It is described that it can be done. Specifically, as shown in FIG. 6 of the publication, the duty ratio increases as the deviation between the target steering angle of the rear wheels and the actual steering angle increases, and this relationship is changed depending on the vehicle speed. ing.

[0003]

However, in the four-wheel steering control device described in the above publication, when the deviation between the target steering angle and the actual steering angle is small, the duty ratio (simply called the duty) is small, so that the motor, etc. The current that drives the actuator is reduced. For this reason, it becomes difficult to start the actuator with a large static friction force and the initial responsiveness deteriorates, so that the range of actuator selection is narrowed or the actuator needs to be improved separately.

Therefore, it is an object of the present invention to ensure an appropriate initial response in a vehicle steering control device even when the steering angle deviation between the target steering angle value and the actual steering angle value is small. .

[0005]

In order to achieve the above object, in the present invention, a target rudder angle setting means for setting a target rudder angle value of a steered wheel to be controlled, and an actual rudder angle value of the steered wheel. Measuring means, a steering angle deviation calculating means for calculating a steering angle deviation between the actual steering angle value and the target steering angle value, a duty setting means for setting a duty according to the steering angle deviation, A steering control device for a vehicle, comprising: a steering angle control means for controlling a steering angle of the steered wheels in accordance with an output of a setting means, wherein the duty setting means is configured to set a predetermined value when the steering angle deviation is a predetermined value or less. The duty increase rate with respect to the steering angle deviation is set to a large value as compared with the case of exceeding.

[0006]

In the vehicle steering control device having the above structure, the target steering angle setting means sets the target steering angle value of the steered wheel to be controlled, and the measuring means sets the actual steering angle value of the steered wheel. To be measured. Then, the steering angle deviation calculating means calculates the steering angle deviation between the actual steering angle value and the target steering angle value. The duty is set by the duty setting means in accordance with the steering angle deviation, and the steering angle control means is driven in accordance with the duty to control the steering angle of the steered wheels. Here, in the duty setting means, when the steering angle deviation is less than or equal to a predetermined value, the duty increase rate with respect to the steering angle deviation is set to be larger than when the steering angle deviation exceeds the predetermined value. However, the steering angle control means is controlled with a large duty. Therefore, for example, even when an actuator having a large static friction force is used, the initial driving force can be secured.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the steering control device of the present invention will be described below with reference to the drawings. The present embodiment relates to a rear wheel steering control device that steers rear wheels in response to steering of front wheels of a vehicle. FIG. 2 shows an overall configuration of a vehicle equipped with a steering control device. The front wheels 13 and 14 are steered by a front wheel steering mechanism 10 in accordance with a turning operation of a steering wheel 19. The front wheel steering mechanism 10 includes, for example, a front wheel steering angle sensor 17 of a potentiometer for detecting the steering angle amounts of the front wheels 13 and 14.
Is provided, and the measurement data is supplied to the electronic control unit 20.

A vehicle speed sensor 9 for detecting the speed of the vehicle
Is provided and its output is supplied to the electronic control unit 20. As the vehicle speed sensor 9, a pair of sensors may be used to detect the vehicle speed in two systems, and the average value or the maximum value thereof may be output as the vehicle speed.
With this configuration, the sensor abnormality can be easily detected.

A rear wheel steering mechanism 18 is connected to the rear wheels 15 and 16 and steered according to the rotation of the motor 12.
In this embodiment, the motor 12 is a three-phase brushless motor,
A relative steering angle sensor 61 that detects the rotation angle of the motor 12 is provided at the axial end portion. As the relative steering angle sensor 61, a magnetic pole sensor that outputs a magnetic pole signal according to a change in the magnetic pole of the motor 12 is used, or a general rotary encoder is used, but the output signal represents a relative steering angle value. It will be. In this embodiment, two sets of magnetic pole sensors are provided, and the steering control can be continued even if one of them fails. Further, as shown in FIGS. 2 and 3, an absolute steering angle sensor 62 of a potentiometer for detecting the steering angle amounts of the rear wheels 15 and 16 is provided. Thus, the relative steering angle sensor 61 and the absolute steering angle sensor 62 constitute a rear wheel steering angle sensor 60 (FIG. 5), which detects the actual steering angles of the rear wheels 15 and 16.

As shown in FIG. 3, the rear wheel steering mechanism 18 of this embodiment has a cover 52 fixed to a housing 51. The cover 52 is integrated with the motor housing 53 of the motor 12 and the relative steering angle sensor 61. Is provided.
As is clear from FIG. 4, a rack shaft 55 is provided at right angles to the traveling direction of the vehicle, and both ends of the rack shaft 55 are connected to knuckle arms of rear wheels via ball joints 58. A tube 59 is fitted to the right end of the housing 51 in FIG.
Even in the case where 5 is provided, the tube 57 can be replaced without changing the housing 51. A rack 56 is formed on the rack shaft 55, and the rack 56 is configured to mesh with a pinion 57 extending in the front-rear direction of the vehicle.

As shown in FIG. 4, a pinion 12p is provided at the tip of a motor shaft 12s of the motor 12, and a gear 12g meshes with the pinion 12p to form a hypoid gear. This hypoid gear is the motor 12
The rotation of the motor shaft 12s is transmitted as the rotation of the gear 12g, but when the rotational force is applied to the gear 12g from the rack shaft 55 side, the reverse efficiency is set to zero so that the motor shaft 12s of the motor 12 does not rotate. Has been done. In the rear wheel steering mechanism 18 of the present embodiment having such a configuration, the static friction force described above is relatively small, but a large static friction force may occur depending on the design and assembly.

The motor 12 is constructed so as to be controlled by a signal from the electronic control unit 20. That is, the electronic control unit 20 is supplied with outputs of the vehicle speed sensor 9, the front wheel steering angle sensor 17, the rear wheel steering angle sensor 60 including the relative steering angle sensor 61, and the absolute steering angle sensor 62,
The rotation amount of the motor 12 is set according to these outputs,
A control signal is supplied to the motor 12.

FIG. 5 shows the structure of the electronic control unit 20. The electronic control unit 20 has a battery 41 mounted on the vehicle.
Are connected. That is, the battery 41 is connected to the motor driver 44 via the fuse and the power supply terminal IP1, and is also connected to the motor driver 44 and the constant voltage regulator 43 via the fuse, the ignition switch 42, and the power supply terminal IP2. The constant voltage regulator 43 outputs a constant voltage Vcc.

The electronic control unit 20 has a microprocessor 45 which is a control means, and the microprocessor 45 is operated by a constant voltage Vcc. The detection signals of the vehicle speed sensor 9, the front wheel steering angle sensor 17 and the rear wheel steering angle sensor 60 are input to the microprocessor 45 via the interface 46. The terminals of each phase of the motor 12 are connected to the motor driver 44 of the electronic control unit 20. Electric power is supplied to the motor driver 44 from power supply terminals IP1 and IP2. Then, the control signal is output from the microprocessor 45 to the motor driver 44.

In the microprocessor 45, FIG.
The target rudder angle is set according to the control block diagram shown in (1), and the servo control of the motor 12 is performed. First, in the target value setting unit 21, for example, the target steering angle value θa of the rear wheels 15 and 16 is set according to the steering angles of the front wheels 13 and 14 and the vehicle speed. Specifically, the target steering angle value θa is calculated based on the product of the coefficient set by the target value setting unit 21 according to the output of the front wheel steering angle sensor 17 and the coefficient set by the output of the vehicle speed sensor 9. Is set.

For example, when the vehicle is stopped, the rear wheels 1
5 and 16 are inversely proportional to the steering angles of the front wheels 13 and 14, and the front wheel 1
Target steering angle value θ so that steering is performed in the opposite direction to 3 and 14
a is set, which reduces the turning radius of the vehicle. Further, when the vehicle is traveling at high speed, the target steering angle value θa is set to be proportional to the steering angle of the front wheels 13 and 14, and the rear wheels 15 and 16 are steered in the same direction as the front wheels 13 and 14, Good maneuvering stability when turning.

The target steering angle value θa set as described above
Is differentiated by the differentiator 22, and the differential gain setting unit 23 obtains the differential gain Gθa from the differential value Dθa according to a predetermined characteristic. That is, when the absolute value of the differential value Dθa is less than or equal to a predetermined value (for example, 0.12 deg), the differential gain Gθa is set to 0, and when the absolute value of the differential value Dθa is at least a predetermined value (for example, 0.48 deg). The differential gain Gθa is set to a predetermined value (for example, 4). Therefore,
As shown in FIG. 8, when the absolute value of the differential value Dθa is within the range of 0.12 to 0.48 deg, the differential gain G
θa has a value of 0 to 4.

On the other hand, the rotation angle θm of the motor 12 is detected by the relative steering angle sensor 61, is output as the actual steering angle value θr via the steering angle conversion unit 33, and is supplied to the subtraction unit 24. The output of the relative steering angle sensor 61 is a relative steering angle value as described above and does not represent the actual steering angle value, but is corrected by the steering angle conversion unit 33 based on the output of the absolute steering angle sensor 62. Therefore, the actual steering angle value θr is output from the steering angle conversion unit 33.

In the subtracting unit 24, the actual steering angle value θr is subtracted from the target steering angle value θa to obtain the steering angle deviation Δθa. This steering angle deviation Δθa is processed as follows via the steering angle deviation dead zone applying unit 25.

As shown in FIG. 6, the steering angle deviation dead zone applying section 25 processes the output steering angle deviation value θd as 0 when the absolute value of the steering angle deviation Δθa is equal to or smaller than a predetermined value α. Thus, the control is configured to stop when the value of the steering angle deviation Δθa is small. The steering angle deviation value θd obtained in this way is used in the differentiating section 26 and the proportional section 28.
Sent to. The proportional portion 28 multiplies the steering angle deviation value θd by a predetermined proportional gain to obtain a proportional term Ps. Further, the differentiator 26 differentiates the steering angle deviation value θd to obtain the steering angle deviation differential value Dθd.

This steering angle deviation differential value Dθd is multiplied by the differential gain Gθa set by the differential gain setting unit 23 as described above in the multiplication unit 27 to obtain the differential term Ds. Then, the proportional term Ps and the differential term Ds are added by the adder 29 to obtain the steering angle control amount, that is, the steering angle value θc.

The steering angle value θc is limited by the steering angle deviation limiter 30. In the steering angle deviation limiter 30, for example, as shown in FIG. 9, the control amount Oc is set in proportion to the steering angle value θc, and the control amount Oc is equal to or more than a predetermined upper limit value (for example, 1.5 deg) or a predetermined lower limit. Value (eg -1.
5 deg) or less. This control amount Oc is the duty D in the deviation-duty converter 31.
It is converted into y and supplied to the pulse width modulation (PWM) unit 32. In the pulse width modulator 32, the duty D
A pulse signal Pw corresponding to y is formed and output to the motor driver 44.

In the deviation-duty converter 31, the duty Dy is set based on the deviation-duty characteristic shown by the solid line in FIG. 9, for example. That is, depending on the control amount Oc corresponding to the steering angle deviation, when the steering angle deviation is less than or equal to the predetermined value Kc, the duty D is greater than that when the steering angle deviation exceeds the predetermined value Kc.
The increase rate of y is set to be large. The predetermined value Kc is set to a value that can cancel the static friction force generated when the actuator including the motor 12 starts driving. This allows the motor 12 to be operated with a small steering angle deviation.
Even when is activated against the static friction force, a predetermined drive current can be obtained for the motor 12, and the desired drive force can be secured. Thus, the actuator including the motor 12 has a proper initial response.

The deviation-duty characteristic used in the deviation-duty converter 31 may be set as shown by the two-dot chain line in FIG. According to this characteristic, when even a slight steering angle deviation occurs (that is, the predetermined value Kc is set to the minimum), the predetermined duty value Kd is immediately set, and thereafter the inclination is the same as that of the conventional example (shown by the broken line). To increase.

Thus, the motor 12 is servo-controlled by the motor driver 44 in accordance with the pulse signal Pw supplied thereto to be rotationally driven. An integral term may be added to the PD control. Further, since the rotation angle θm of the motor 12 changes depending on the fluctuation of the power supply voltage, the battery voltage may be measured and the pulse signal Pw may be corrected according to the battery voltage.

[0026]

Since the present invention is constructed as described above, it has the following effects. That is, in the present invention, the steering angle control means controls the steering angle with respect to the steered wheels to be controlled, and the steering angle control amount is calculated by calculating the steering angle deviation between the actual steering angle value and the target steering angle value. In the duty setting means, when the steering angle deviation is less than or equal to the predetermined value, the duty ratio with respect to the steering angle deviation is set to be larger than that when the steering angle deviation exceeds the predetermined value. Even when it is small, the steering angle control means can be controlled with a large duty to ensure the desired driving force. Therefore, appropriate initial responsiveness can be obtained even when the static friction force is large.

[Brief description of drawings]

FIG. 1 is a control block diagram relating to servo control of a motor according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a vehicle steering control device according to an embodiment of the present invention.

FIG. 3 is a front view of a rear wheel steering mechanism according to an embodiment of the present invention.

FIG. 4 is a partial cross-sectional view of a rear wheel steering mechanism according to an embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of an electronic control unit used in an embodiment of the present invention.

FIG. 6 is a graph showing the input / output characteristics of the steering angle deviation dead zone applying unit in the embodiment of the present invention.

FIG. 7 is a graph showing the input / output characteristics of the steering angle deviation limiter in one embodiment of the present invention.

FIG. 8 is a graph showing the input / output characteristics of the differential gain setting section in the embodiment of the present invention.

FIG. 9 is a graph showing the input / output characteristics of the deviation-duty converter in one embodiment of the present invention.

[Explanation of symbols]

 9 Vehicle speed sensor 11 Rear wheel steering angle sensor 12 Motor (electric motor) 17 Front wheel steering angle sensor 20 Electronic control unit 22 Differentiating part 23 Differential gain setting part 24 Subtracting part 25 Steering angle deviation dead zone applying part 26 Differentiating part 27 Multiplying part 28 Proportional Part 29 Addition part 30 Steering angle deviation limiter 31 Deviation-duty conversion part 32 Pulse width modulation part 33 Steering angle conversion part 43 Constant voltage regulator 44 Motor driver 45 Microprocessor 46 Interface 60 Rear wheel steering angle sensor 61 Relative steering angle sensor 62 Absolute Rudder angle sensor

Claims (1)

[Claims] 1. A target rudder angle setting means for setting a target rudder angle value of a steering wheel to be controlled, a measuring means for measuring an actual rudder angle value of the steered wheel, the actual rudder angle value and the target rudder angle. Steering angle deviation calculating means for calculating a steering angle deviation of a value, duty setting means for setting a duty according to the steering angle deviation, and a rudder for controlling the steering angle of the steered wheels according to the output of the duty setting means. In the vehicle steering control device including the angle control means, the duty setting means, when the steering angle deviation is equal to or less than a predetermined value, exceeds the predetermined value, and an increase rate of the duty with respect to the steering angle deviation. Is set to a large value, a steering control device for a vehicle.