JP3597609B2 - Electric power steering device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device for reducing the driver's steering force by directly applying the driving force of an electric motor to a manual steering system.
[0002]
[Prior art]
An electric power steering system in which an electric motor is provided in a manual steering system that converts a steering angle given to a steering wheel into a steering angle of a wheel, and a driving force of the electric motor is added to the manual steering system to reduce a driver's steering force. Devices are known. As shown in FIG. 1, the electric power steering apparatus includes a pinion 4 connected to a steering shaft 2 integrally connected to a steering wheel 1 via a connection shaft 3 having universal joints 3a and 3b. Manual steering comprising a rack and pinion mechanism comprising a rack shaft 8 having both ends connected to knuckle arms 7 of left and right front wheels 6 via tie rods 5 while being able to engage and reciprocate in the vehicle width direction. Force generating means 9, an electric motor 10 arranged coaxially with the rack shaft 8 to generate an auxiliary steering force for reducing the steering force by the manual steering force generating means 9, and manual steering acting on the pinion 4. a torque detector 11 for detecting a force T _P, a steering angle detecting means 12 for detecting the rotation angle θ of the steering wheel 1, the detection value T _P A control unit 13 for controlling the output of the electric motor 10 based on θ.
[0003]
Control means 13, as shown in FIG. 2, the output target value generating means 14 for setting the output torque to be generated in the electric motor 10, and outputs the electric motor based on the output target value I _T to thereby generated 10 the consists motor driving means 15 for controlling driving, so as to control the assist steering force to be generated by the electric motor 10 based on the output T _P of the steering force detecting means 11.
[0004]
In the conventional power steering apparatus described above, when steering on a road surface having a low friction coefficient μ such as a snowy road, the road surface reaction force is not sufficiently transmitted to the driver due to slip between the road surface and the wheels, and the vehicle turns. There was a problem that it was difficult to give an appropriate steering angle to the curvature of the circle. To cope with such a problem, a steering force control device that changes the steering assist force in accordance with the slip ratio of the drive wheels is disclosed in Japanese Patent Application Laid-Open No. 3-112777.
[0005]
[Problems to be solved by the invention]
However, the technique proposed in the above publication merely reduces the steering assist force at the time of slipping, and thus impairs the self-aligning torque, that is, the force for returning the steered wheels to straight traveling.
[0006]
[Means for Solving the Problems]
In order to solve such a problem, it is possible to appropriately adjust an auxiliary steering force according to a slip state of a wheel without impairing a self-aligning torque and to provide a deterrence force against excessive steering by a driver. Therefore, in the present invention, a manual steering system for manually giving a steering angle to a steered wheel of a vehicle, a steering force detecting means for detecting a steering force of the manual steering system, and a manual steering system are added. In an electric power steering device having an electric motor that generates auxiliary power and a control unit that controls the output of the electric motor based on a detection value of the steering force detection unit, a lateral acceleration detection unit that detects a lateral acceleration of the vehicle, or provided with a slip ratio detecting means for detecting a yawing angular velocity detecting means and the wheel slip ratio detecting the yawing angular velocity of the vehicle, lateral acceleration detection means or Yoi, Multiplication means for multiplying the signal corresponding to the detected value of the grayed angular velocity detection signal and the slip ratio detecting means corresponding to the detected value of the unit, the lateral acceleration detecting means or multiplying the signal corresponding to the detected value of the yaw angular velocity detecting means, The control means is provided with a subtraction means for subtracting the signal of the means, and the motor is controlled based on the output of the subtraction means.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail based on specific embodiments shown in the accompanying drawings.
[0008]
FIG. 3 shows a block diagram of basic electric power steering control to which the present invention is applied . For example, the output T _P from the torque detector 11 provided between in the steering shaft 2 and the pinion 4 in FIG. 1 is input to the output target value generating means 14 to generate a basic output target value signal I _1. This is the same as the conventional control system. In contrast, the steering angle detecting means 12 provided on the steering shaft 2, by correcting the output target value I ₁ based on appropriate consideration the signal output from below the slip ratio detecting means 19, the wheels The driving force of the electric motor 10 is controlled so as to give the driver an appropriate steering reaction force according to the slip ratio of the motor.
[0009]
When the output θ of the steering angle detecting means 12 is inputted to the steering reaction force setting unit 17, the steering reaction force signal I _RC is output obtained by searching a preset map in the steering reaction force setting means 17 . On the other hand, the outputs ω _FR , ω _FL , ω _RR , ω _{RL of} the wheel rotational angular velocity detecting means 18 provided for each of the four wheels are input to the slip rate detecting means 19, and based on this, the slip is calculated by the method described later. The rate S is calculated. When the slip ratio S is input to the damping coefficient setting means 20, a damping coefficient signal k obtained by searching a map set in the damping coefficient setting means 20 is output. These steering reaction force signal I _RC and attenuation coefficient signal k is multiplied by the multiplier 21 is output as a correction signal I _2.
[0010]
The correction signal I ₂ is subtracted by the subtractor 22 from the basic output target value signal I ₁ is input to the motor driving unit 15 as a target value I _T anew motor output, used as a control command value for the motor 10.
[0011]
Here, the slip ratio S of the wheel is represented by an average wheel rotational angular velocity ω _F = (ω _FR + ω _FL ) / 2 on the driving wheel side.
And the average wheel rotational angular velocity ω _R = (ω _RR + ω _RL ) / 2 on the driven wheel side
And from
_{S = (ω F -ω R)} / ω F
It is required as follows.
[0012]
When braking the vehicle in a range where the wheels do not lock, the slip ratio may be estimated based on the change in the wheel peripheral speed at that time. The steering angle detecting means 11 not only directly obtains the rotation angle of the steering wheel 1 with a rotation angle detector such as a rotary encoder, but also converts the detected value of the linear stroke of the rack shaft 8 into a rotation angle. You may ask.
[0013]
Next, the operation of the above embodiment will be described. Since the friction coefficient μ is high road slip ratio S is small, the output I ₂ output θ is large becomes even multiplier 21 of the steering angle detecting means 12 is not increased, the target value I _T of the motor output is mainly steered is determined only by the output value T _P of the force detection means 11. And in the friction coefficient μ is low road, so subtracts the output I ₂ of the multiplier 21 becomes large because the slip ratio S is large from the basic output target value signal I _1, the target value of the motor power during the cut of the steering wheel 1 I _T decreases, it is possible to provide a deterrent to excessive steering of the driver. Also when returning the steering wheel 1 in the friction coefficient μ is low road surface, the output T _P of the steering force detecting means 11 becomes zero, the output of the subtracter 22 becomes a negative value, the motor 10 is rather the steering wheel 1 , And a high self-aligning torque can be obtained.
[0014]
4 and 5 show block diagrams of electric power steering control according to the present invention. This means that, instead of the output θ of the steering angle detecting means 12 shown in FIG. 3, the lateral acceleration value obtained by the lateral acceleration detecting means 23 (see FIG. 4) or the yawing angular velocity value obtained by the yawing angular velocity detecting means 24 The driving force of the electric motor 10 is controlled in the same manner as described above (see FIG. 5).
[0015]
【The invention's effect】
As described above, according to the present invention, in the electric power steering device, by adjusting the steering assist force in accordance with the driving conditions, it is possible to apply an appropriate steering reaction force to the steering wheel, so that Warning and prevent excessive steering. Particularly, by adopting the above configuration, the correction value I ₂ from the basic output target value I ₁ which becomes zero in the state without addition of steering torque to the steering wheel is subtracted, the torque in the return direction, i.e. the self-aligning torque You don't have to hurt.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a steering device to which the present invention is applied.
FIG. 2 is a basic control flow chart of an auxiliary steering force generating motor.
FIG. 3 is a schematic flow chart until a motor output target value is output in consideration of a steering angle and a wheel angular velocity.
FIG. 4 is a schematic flow chart until a motor output target value is output in consideration of a steering angle and a lateral acceleration.
FIG. 5 is a schematic flow chart until a motor output target value is output in consideration of a steering angle and a yawing angular velocity.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 steering wheel 2 steering shaft 3 connecting shaft 4 pinion 5 tie rod 6 front wheel 7 knuckle arm 8 rack shaft 9 manual steering force generating means 10 electric motor 11 steering force detecting means 12 steering angle detecting means 13 control means 14 output target value generating means 15 electric motor Driving means 17 Steering reaction force setting means 18 Wheel rotation angular velocity detecting means 19 Slip rate detecting means 20 Damping coefficient setting means 21 Multiplier 22 Subtractor 23 Lateral acceleration detector 24 Yawing angular velocity detector

Claims (2)

A manual steering system for manually applying a steering angle to the steered wheels of the vehicle, steering force detection means for detecting a steering force of the manual steering system, an electric motor for generating auxiliary power to be added to the manual steering system, Control means for controlling the output of the electric motor based on the detection value of the steering force detection means,
Along with lateral acceleration detecting means for detecting the lateral acceleration of the vehicle and slip rate detecting means for detecting the slip rate of the wheels,
Multiplying means for multiplying a signal corresponding to a detected value of the lateral acceleration detecting means and a signal corresponding to a detected value of the slip ratio detecting means,
Subtraction means for subtracting the signal of the multiplication means from a signal corresponding to the detection value of the steering force detection means,
An electric power steering apparatus for controlling the electric motor based on an output of the subtraction means. A manual steering system for manually applying a steering angle to the steered wheels of the vehicle, steering force detection means for detecting a steering force of the manual steering system, an electric motor for generating auxiliary power to be added to the manual steering system, Control means for controlling the output of the electric motor based on the detection value of the steering force detection means,
A yaw angular velocity detecting means for detecting a yaw angular velocity of the vehicle and a slip rate detecting means for detecting a wheel slip rate;
Multiplying means for multiplying a signal corresponding to a detected value of the yawing angular velocity detecting means by a signal corresponding to a detected value of the slip ratio detecting means,
Subtraction means for subtracting the signal of the multiplication means from a signal corresponding to the detection value of the steering force detection means,
An electric power steering apparatus for controlling the electric motor based on an output of the subtraction means.

Images