JP4189641B2 - Steering force control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a travel control device that improves the stability of vehicle travel, and in particular, a steering reaction generated by a DC motor of an electric power steering device when excessive steering is started during high speed travel or low μ road travel. The present invention relates to a steering force control apparatus that suppresses such steering by force and enhances running stability.
[0002]
[Related background]
In order to improve the running stability of the vehicle, there are travel control devices such as a traction control system that automatically controls the throttle valve according to the slip condition of the wheel and a brake device that automatically activates the brake according to the turning state of the vehicle. Used (see, for example, Patent Documents 1 and 2).
[0003]
It is also known that the power steering device is configured to generate a steering reaction force according to the vehicle behavior. For example, in the vehicle steering apparatus described in Patent Document 3, the steering torque command value includes a steering reaction force component that cancels the vehicle behavior change, thereby improving the straight running stability of the vehicle when a disturbance such as a cross wind acts. Like to do. That is, the one described in Patent Document 3 obtains a target auxiliary steering torque for normal steering assist control based on detection values obtained by a steering angle sensor, a torque sensor, a vehicle speed sensor, a lateral acceleration sensor, and a yaw rate sensor, and a steering angular velocity. Based on the target current value obtained by obtaining the steering reaction force component corresponding to the lateral acceleration, yaw rate and yaw angular acceleration and adding the target steering reaction force, which is the sum of these steering reaction force components, to the target auxiliary steering torque It is comprised so that an electric motor may be driven.
[0004]
[Patent Document 1]
JP-A-3-157255 [Patent Document 2]
JP-A-2-171373 [Patent Document 3]
Japanese Patent Laid-Open No. 6-92252
[Problems to be solved by the invention]
The driver is responsible for driving the vehicle safely, but may not be able to drive safely depending on the road environment and driving skill. For example, a driver with poor driving experience may impair driving stability by performing excessive steering during high-speed driving or low-μ road driving.
[0006]
In this regard, according to the vehicle equipped with the traction control system and the brake device described in Patent Documents 1 and 2, the engine output is reduced so as to recover the running stability when the wheel slips or the turning state becomes unstable. However, this kind of output control and braking control is started after the vehicle has become unstable due to improper driving operation. Therefore, excessive steering during high-speed driving or low-μ road driving It is not something to suppress.
[0007]
Further, the steering device described in Patent Document 3 can prevent a decrease in straight-line stability due to a crosswind or the like, but this also does not prevent excessive steering during high-speed traveling or low-μ road traveling. . Furthermore, Patent Document 3 requires a lateral acceleration sensor and a yaw rate sensor in addition to a rudder angle sensor, a torque sensor, and a vehicle speed sensor that are normally installed in a steering device. In addition, there is a risk that the failure rate in the sensor system will increase. In general, since the steering system is required to have higher reliability than the brake system, it is necessary to reduce the failure rate of the sensor system as much as possible.
[0008]
An object of the present invention is to provide a steering force control device that can suppress excessive steering during high-speed traveling or traveling on a low μ road, and can reduce a failure occurrence rate in a sensor system.
[0009]
[Means for Solving the Problems]
The steering force control device according to the first aspect of the present invention is a target torque setting means for setting a target assist torque of the DC motor of the electric power steering device according to the steering torque and the vehicle speed of the driver, and according to the target assist torque. In addition to the motor drive means that drives the DC motor with the motor voltage , the upper limit value of the motor voltage in the high speed range is such that when the steering angular velocity increases excessively, the output torque of the DC motor becomes negative and a steering reaction force is generated. The motor voltage limiting means for limiting to a small value is provided.
[0010]
According to the first aspect of the present invention, the DC motor of the electric power steering apparatus is driven according to the target assist torque set according to the steering torque and the vehicle speed, as in the conventional electric power steering apparatus. When the steering operation by the driver is performed and the motor rotation speed is increased, the back electromotive force generated in the DC motor is increased, and the motor torque (assist torque) is decreased by that amount. To the motor to compensate for this torque decrease. The applied voltage (motor current) increases to generate assist torque equivalent to the target assist torque. Such assist torque reduces the burden on the driver's steering, but if excessive steering assist is performed during high-speed driving, the running stability of the vehicle is impaired.
[0011]
Even in the conventional electric power steering device, the steering assist is weakened at high speeds, but the voltage applied to the motor can be increased up to the battery voltage without limitation. Therefore, when excessive steering is performed at high speeds, the assist torque is increased. It may occur and running stability may be impaired. In any case, the conventional electric power steering device does not actively suppress excessive steering in a high speed range, and such a compensation action is used to compensate for a decrease in traveling stability caused by excessive steering. It is necessary to use a traveling control device that achieves the above.
[0012]
In this respect, according to the first aspect of the present invention, since the upper limit value of the motor voltage is limited in the high speed range, excessive steering in the high speed range is suppressed in advance, and traveling stability is maintained. That is, as long as the driver's steering is performed within an allowable range, the motor voltage does not exceed the upper limit value even in the high speed range, and thus assist torque is generated. However, excessive steering that exceeds the driving limit of the vehicle, for example, When is started, the DC motor generates a steering reaction force to suppress excessive steering.
[0013]
That is, even in the steering force control apparatus according to claim 1, when excessive steering is started in the high speed range, the counter electromotive force of the DC motor increases rapidly and the motor torque decreases rapidly, so that the motor current is greatly increased. However, in the present invention, since the upper limit value of the motor voltage in the high speed range is limited to a small value, not only the generation of the assist torque is prevented, but also the steering motor generates a steering reaction force due to a load on the steering operation. To do. As a result, excessive steering, particularly the steering operation of the steering wheel, is suppressed in the high speed range, and traveling stability is ensured to prevent rollover.
[0014]
Further, as described above, the steering force control apparatus according to claim 1 performs excessive steering using the characteristics of the DC motor (the relationship between the motor torque (motor current) and the motor rotation speed (handle angular velocity)). When it breaks, it generates a steering reaction force, and can be configured simply and inexpensively as compared with a conventional travel control device. Furthermore, the sensor system of the steering force control device can be configured simply and at low cost by a torque sensor, a vehicle speed sensor, and a rudder angle sensor that are normally provided in the electric power steering device, and the failure occurrence rate is low.
[0015]
The invention according to claim 2 is characterized in that the upper limit value of the motor voltage in low μ road running is limited to a small value.
Although the vehicle behavior is likely to be unstable even when steering at a relatively small steering angular velocity on a low μ road, according to the invention described in claim 2, excessive steering during traveling on a low μ road is suppressed in advance. Driving stability during low μ road driving is ensured.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a steering force control apparatus according to an embodiment of the present invention will be described with reference to the drawings.
A vehicle equipped with the steering force control device according to the present embodiment has a vehicle speed sensor (vehicle speed detection means) 11 composed of a wheel speed sensor equipped on each wheel, and a driver's steering torque (steering torque applied to the steering shaft). ) For detecting a steering angle, a steering angle sensor 13 for detecting a steering angle, and a lateral G sensor 14 for detecting a lateral acceleration applied to the vehicle, and a vehicle speed sensor 11 and a torque sensor. And an electric power steering device 15 for generating a steering assist force F corresponding to the vehicle speed V and the steering torque T detected by the vehicle 12.
[0017]
The electric power steering device 15 includes a DC motor 16 connected to a steering mechanism 18 via a reduction gear (not shown), and a control unit 17 that controls the output torque and rotation direction of the motor 16, and the control unit 17 includes: For example, it is configured by a microprocessor or the like and functions as a steering force control device that controls the steering assist force.
[0018]
That is, the control unit 17 includes a target torque setting unit (target torque setting means) 21. The target torque setting unit 21 is a target assist torque according to the steering torque T, the steering direction obtained from the steering torque, and the vehicle speed V. A value (hereinafter referred to as a target torque value) Ttar is set.
FIG. 2 illustrates a map used for setting the target torque value Ttar at a certain vehicle speed. As is apparent from FIG. 2, the target torque value Ttar increases as the steering torque T generated by the steering operation increases, and is positive if the steering torque T is positive (for example, corresponds to a right turn). On the other hand, if the steering torque T is negative, it takes a negative value. That is, the steering assist force corresponding to the target torque value Ttar acts in the same direction as the steering torque T and assists the steering operation.
[0019]
The control unit 17 also flows through the DC motor 16, a positive / negative determining unit 22 that determines whether the target torque value Ttar is positive or negative, a command current setting unit 23 that sets a command current Itar corresponding to the absolute value of the target torque value Ttar. A current detection unit 24 that detects the armature current I via a current sensor (not shown) and a duty ratio setting unit 25 that sets the duty ratio D1 such that the armature current I becomes equal to the command current Itar are provided.
[0020]
Further, the control unit 17 includes a road surface μ detection unit (road surface μ detection means) 26 that detects the friction coefficient μ of the road surface on which the vehicle is currently traveling from the vehicle speed V, the steering angle θ, and the lateral G. The road surface μ detection unit 26 can be configured, for example, like a road surface friction coefficient determination device described in Japanese Patent Application Laid-Open No. 11-194087. The road surface μ detection unit 26 together with the vehicle speed sensor 11, the steering angle sensor 13, and the lateral G sensor 14 Is configured.
[0021]
Further, the control unit 17 is provided with a duty ratio limiting unit 27 that limits the duty ratio D1 input from the duty ratio setting unit 25 to an upper limit value or less obtained from the map illustrated in FIG. As can be seen from FIG. 3, the upper limit value of the duty ratio D1 decreases as the vehicle speed V increases. Further, the upper limit value (indicated by a broken line in FIG. 3) on the low μ road is smaller than the upper limit value (indicated by a solid line in FIG. 3) on the high μ road.
[0022]
The duty ratio D1 set by the duty ratio setting unit 25 is limited to the upper limit value or less by the duty ratio limiting unit 27 and is output to the motor driving unit 28 as the duty ratio D2. That is, the duty ratio D2 is equal to the duty ratio D1 when the duty ratio D1 is smaller than the upper limit value, and is equal to the upper limit value when the duty ratio D1 is larger than the upper limit value.
[0023]
The motor drive unit (motor drive means) 28 switches the application direction (polarity) of the applied voltage E to the DC motor 16 according to the sign of the target torque value Trar and duty-controls the battery voltage based on the duty ratio D2. The applied voltage E is variably controlled, whereby the rotational direction of the DC motor 16 and the magnitude of the output torque (steering assist force F) are controlled. Therefore, an average voltage E equal to the product of the battery voltage and the duty ratio D2 (%) is applied to the DC motor 16.
[0024]
FIG. 4 illustrates characteristics of the DC motor 16 (relationship between the applied voltage E, the motor rotation speed N, and the motor torque Tm). The motor torque Tm corresponds to the armature current I flowing through the DC motor 16, and the motor rotation speed N corresponds to the steering wheel angular velocity. As can be seen from FIG. 4, the motor torque Tm decreases as the motor rotation speed N increases, the handle becomes heavier, and when the motor rotation speed N further increases, the motor torque Tm becomes negative. That is, the DC motor 16 generates a steering reaction force. This is because the counter electromotive force generated in the DC motor 16 increases as the motor rotational speed N increases.
[0025]
This steering force control device uses the above characteristics of the DC motor 16 to suppress excessive steering in a high speed range. That is, by limiting the upper limit value of the duty ratio D1 to a smaller value as the vehicle speed V increases, the applied voltage E to the DC motor 16 is gradually reduced from a value E1 corresponding to the battery voltage to E2, E3, for example. Yes. As the motor voltage E decreases, a large steering reaction force is generated when the motor rotation speed N (steering wheel angular velocity) increases, that is, when excessive steering is performed, and the steering wheel becomes heavier, so excessive steering is suppressed. .
[0026]
As can be seen from the above description, the duty ratio limiting unit 27 and the motor driving unit 28 constitute motor voltage limiting means for limiting the upper limit value of the duty ratio D1 in the high speed range to a small value.
FIG. 5 shows the steering operation suppression effect exerted by the steering force control device when the steering wheel is largely turned to the left and right by a solid line, and the broken line in FIG. 5 shows the change in the steering wheel angle when this steering force control device is not equipped. Show. As can be seen from FIG. 5, according to the steering force control device, excessive steering, particularly steering operation, is suppressed.
[0027]
Although the description of the steering force control device according to one embodiment of the present invention has been completed above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the upper limit value of the duty ratio D1 is limited to a small value when traveling on a low μ road. However, in the present invention, it is not essential to change the upper limit value according to the road surface μ. Further, the assist characteristic of the electric power steering apparatus is not limited to that shown in FIG. 2, and the map used for setting the upper limit value of the duty ratio is not limited to that shown in FIG.
[0028]
【The invention's effect】
In the first aspect of the invention, the upper limit value of the motor voltage in the high speed range is limited to a small value, so that excessive steering in the high speed range can be suppressed in advance, and the running stability of the vehicle can be ensured. it can. For example, rollover prevention is achieved. Further, since the present invention uses the characteristics of the DC motor when suppressing excessive steering, the configuration is simple and the cost can be reduced. In addition, since the sensor system can be configured with a sensor that is normally installed in an electric power steering device, it is simple and inexpensive in this respect, and the failure rate in the sensor system can be reduced, and steering control can be performed. The reliability on the top can be increased.
[0029]
In the invention of claim 2, since the upper limit value of the motor voltage on the low μ road is limited to a small value, the running stability during the low μ road running can be ensured.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram showing a steering force control device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a map used for setting a target torque value in a steering force control apparatus.
FIG. 3 is a diagram illustrating a map used for setting an upper limit value of a duty ratio.
FIG. 4 is a diagram illustrating characteristics of a DC motor.
FIG. 5 is a diagram showing a steering operation suppression action of the steering force control device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Vehicle speed sensor 12 Torque sensor 13 Steering angle sensor 14 Lateral G sensor 15 Power steering apparatus 16 DC motor 17 Control unit 21 Target torque setting part 25 Duty ratio setting part 26 Road surface μ detection part 27 Duty ratio restriction part 28 Motor drive part

Claims (2)

Steering torque detection means for detecting steering torque by steering of the driver;
Vehicle speed detection means for detecting the vehicle speed;
Target torque setting means for setting a target assist torque of a DC motor of the electric power steering device according to the steering torque detected by the steering torque detection means and the vehicle speed detected by the vehicle speed detection means;
Motor driving means for driving the DC motor with a motor voltage corresponding to the target assist torque;
Motor voltage limiting means for limiting the upper limit value of the motor voltage in a high speed range to such a small value that the output torque of the DC motor becomes negative and generates a steering reaction force when the steering angular velocity increases excessively. A steering force control device characterized by that. Road surface μ detecting means for detecting the friction coefficient of the road surface on which the vehicle is traveling,
2. The steering force control apparatus according to claim 1, wherein the motor voltage limiting means limits the upper limit value of the motor voltage to a small value when traveling on a low μ road surface.

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