JP2785398B2 - Electric power steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device that assists a steering force by a rotation output of a motor.

Conventional technology and its problems In conventional electric power steering systems,
The steering assist (auxiliary) motor is controlled based on the steering torque detection value and the vehicle speed detection value to generate a steering assist torque. In such an electric power steering system, a braking circuit is provided to brake the assist motor in the vicinity of the neutral position of the steering wheel because the release stability at a high vehicle speed is insufficient due to the inertia force of the assist motor. The device is considered (for example, the actual opening 61-1)
No. 69675). However, in this device, since the braking steering angle range in which the braking is to be applied is determined, the braking circuit is turned on / off at the boundary of the braking steering angle range, and the assist / assist control is performed.
There is a problem that the output torque of the motor changes rapidly. For this reason, the release speed changes suddenly, and unnaturalness is felt.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device capable of achieving a natural feeling release operation.

The present invention is directed to an electric power system that generates a steering command based on a detected steering torque, a detected vehicle speed, and the like, and controls a steering assist motor that generates a steering assist torque based on the assist command. In a steering device, a means for detecting a steering angle, a means for detecting a steering angular velocity, a means for calculating a viscosity compensation value according to a detected steering angular velocity, and a constant that decreases as the absolute value of the steering angle increases according to the detected steering angle Means for generating a viscosity command value by multiplying the calculated viscosity compensation value by the constant, and a means for correcting the assist command based on the viscosity command value. Features.

Preferably, a means for detecting a released state based on the detected steering torque and the detected steering angular velocity is further provided, and the viscosity command output control section outputs a viscosity command value created only when the released state is detected.

According to the present invention, the viscosity command value increases as the absolute value of the steering angle decreases. Therefore, it is possible to prevent the steering wheel from becoming unstable near the neutral position by releasing the hand by viscous braking. In addition, at the beginning of the braking effect, the steering angle is relatively large, so the braking force is small at this time. As the vehicle approaches the neutral position, a large braking force can be obtained, so that the convergence to the neutral position becomes natural.

Further, by outputting the viscosity command value only when the release is detected, it is possible to prevent a decrease in the return speed due to unnecessary braking other than the release.

FIG. 1 is a block diagram functionally showing an entire embodiment of an electric power steering apparatus according to the present invention.
FIG. 2 is a configuration diagram showing an example of a steering mechanical system to which the power steering device is applied.

First, the power steering mechanical system shown in FIG. 2 will be described.

The rotational force of the steering wheel 71 is transmitted to a steering gear 72 including a pinion gear via a handle shaft, further transmitted to a rack shaft 74 by the pinion gear, and the wheel 75 is turned via a knuckle arm or the like. The torque of a steering assist (auxiliary) motor (DC motor) 10 controlled and driven by the control device 11 is transmitted to the rack shaft 74 by meshing the steering gear 73 including a pinion gear with the rack shaft 74, and The steering by 71 will be assisted. The handle 71 and the rotating shaft of the motor 10 are mechanically connected by gears 72, 73 and a rack shaft 74. The steering torque (torsional torque) is detected by the steering torque sensor 21, and the vehicle speed is detected by the vehicle speed sensor 22, and the control device 11 controls the motor 10 based on the detected torque, vehicle speed, and the like as described later. The operating power of the control device 11 and the motor 10 is supplied from a battery 12 mounted on the vehicle.

The control device 11 includes a current detector, a driving circuit for driving the motor 10, a computer (CPU, for example, a microprocessor) for controlling the entire control of the motor 10, a memory, and an interface circuit between the computer and the above input and output devices. And so on. In FIG. 1, various functions of the computer built in the control device 11 can be positioned as a block diagram, together with blocks showing other input / output devices and various circuits.

In Figure 1, the assist command section 20 is given and the detected vehicle speed V _S of the detected torque V _T and the vehicle speed sensor 22 of the torque sensor 21. Assist torque instruction function section 23 in the assist command section 20 outputs a command value representing the assist torque to be generated by the motor 10 in accordance with the detected torque V _T.
The multiplication constant function unit 24 generates a constant according to the detected vehicle speed V _S , and this constant is used by the multiplication operation unit 25 to calculate the above assist
Multiplied by the torque command value. As a result, the assist torque value output from the multiplication unit 25 (or the motor current command value), as shown in FIG. 3, the value determined by the detected torque V _T and the detected vehicle speed V _S. Figure 3, in accordance with the steering torque V _T, approximately proportional motor current flows (assist torque is generated) in this respect to the steering torque V _T of a range, a constant that exceeds the above range motor current flows (assist torque is generated) manner, and, according to the vehicle speed V _S, to reduce the motor current (assist torque) when the vehicle speed V _S is high, the motor current when the vehicle speed V _S is slow ( To increase the assist torque)
This indicates that an assist command for controlling the motor 10 is generated. Detected torque V _T is given to the phase compensator 26, by which the differential value of the detected torque V _T by the phase compensator 26 is added to the output of the multiplication unit 25, and finally the output of the assist command section 20 (Reference current command value).

After adding a command value of a viscosity command unit described later to this reference current command value, the current control unit 40 sets a target current command value.
Given to. The current control unit 40 may be entirely configured by a hardware circuit, or may be partially configured by a computer.
It can also be realized by software.

The current control unit 40 is, for example, a PWM (Pulse Width Modul) according to an H-bridge driving method including four switching elements.
ation) Chopper operation using pulse
And performs current feedback control. The armature current of the motor 10 is detected by the armature current detection unit 46, and the deviation between the given target current command value and the detected current is calculated by the current deviation calculation unit 41. The absolute value of this deviation is obtained by the absolute value converter 44, and the duty ratio of the PWM pulse is determined based on this absolute value. On the other hand, the polarity (positive or negative) of the deviation is determined by the positive / negative determining unit 42. The polarity determined as the duty ratio generated by the duty generation unit 45 is given to the motor driving unit 43, and based on these, the motor driving unit 43 controls the four switching elements wired in an H bridge type on and off. Then, the motor 10 is driven.

The viscosity command unit 30 basically has a force for returning the steering angle to the neutral position,
That is, a restoring force is generated. A sensor 34 for detecting the steering angular velocity and a sensor 35 for detecting the steering angle θ are provided. The steering angle speed sensor 34 and the steering angle sensor
35 may be a tachogenerator, an encoder, or the like, or an observer for determining the steering angular velocity may be provided instead of the sensors 34 and 35. This observer is a motor
Based on 10 applied voltages and armature currents or motor
The steering angular velocity (rotational speed of the motor) and the steering angle (rotational angular position of the motor 10) are estimated based on the command current value to the 10 and the measured armature current.

In any case, the steering angular velocity is determined by the viscosity compensation value indicating function unit 31.
Given to. This function part 31 is, as shown in FIG.
The larger the steering angular velocity is, the larger the absolute value is, and outputs a viscosity compensation value that generates a torque in the opposite direction.

On the other hand, the steering angle θ is given to the multiplication constant function unit 36. As shown in FIG. 5, the function section 36 outputs a smaller multiplication constant as the absolute value of the steering angle is larger.
The viscosity compensation value output from 31 is multiplied by the multiplication operation unit 32, and the result is given to the viscosity command output control unit 33.

Further, the detected steering torque _VT and steering angular velocity are given to the release state detection unit 37. The hands-off state detection unit 37, as shown in FIG. 6, the absolute value of the predetermined value T absolute value is less than the predetermined value Th ₁ and the detected steering angular velocity of the detected torque V _T
It determines if it is h ₂ or more and let go state of the steering system, providing a hands-off state detection signal to the viscous command output control unit 33. FIG. 6 shows a change in the torque _VT and the steering angular velocity when the vehicle is released at a high vehicle speed. The hatched portion indicates that the vehicle is released.

The viscosity command output control unit 33 outputs the multiplication result given from the multiplication operation unit 32 as a viscosity command value only when it is determined that the hand is in the released state, and otherwise sets the output value to zero. The output of the output control unit 33 is added (actually subtracted) to the reference current command value output from the assist command unit 20.

In this manner, the output of the viscosity command unit 30 is output only in the hand-released state, and the magnitude thereof increases as the absolute value of the steering angle θ decreases. Therefore, it is possible to prevent the steering wheel from becoming unstable near the neutral position by releasing the hand by viscous braking. In addition, at the beginning of the braking effect, the steering angle is relatively large, so the braking force is small at this time. As the vehicle approaches the neutral position, a large braking force can be obtained, so that the convergence to the neutral position becomes natural.

If necessary, by controlling the rotor inertia of the motor 10 as if it had become smaller, the weight caused by the motor 10 not following the rotation of the steering wheel at the time of sudden steering can be eliminated, and the return speed when releasing the hand can be increased. May be provided, and its output may be added to the output of the assist command unit 20.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an embodiment of the present invention. FIG. 2 is a configuration diagram showing an example of a power steering mechanical system. FIG. 3 is a graph for obtaining a reference current command value based on a steering torque and a vehicle speed. FIG. 4 is a graph showing an example for obtaining a viscosity compensation value according to the steering angular velocity. FIG. 5 is a graph showing an example for obtaining a multiplication constant according to the absolute value of the steering angle. FIG. 6 is a graph showing a time change of the steering angular velocity and the steering torque in a released state at a high vehicle speed. 10: steering assist motor, 20: assist command section, 21: torque sensor, 22: vehicle speed sensor, 30: viscosity command section, 31: viscosity compensation value indicating function section, 32: multiplication operation , 33: Viscosity command output control unit, 34: Rudder angular velocity sensor, 35: Rudder angle sensor, 36: Multiplication constant function unit, 37: Release state detection unit

Claims (2)

(57) [Claims] An electric power steering apparatus for generating an assist command based on a detected steering torque, a detected vehicle speed, and the like, and controlling a steering assist motor that generates a steering assist torque based on the assist command. Means for detecting the steering angle, means for detecting the steering angular velocity, means for calculating the viscosity compensation value according to the detected steering angular velocity, means for generating a constant that becomes smaller as the absolute value of the steering angle increases, according to the detected steering angle, An electric power steering apparatus, comprising: a viscosity command output control unit that creates a viscosity command value by multiplying the calculated viscosity compensation value by the above constant; and a unit that corrects the assist command based on the viscosity command value. 2. The system according to claim 1, further comprising means for detecting a released state based on the detected steering torque and the detected angular velocity, wherein the viscosity command output control section outputs a viscosity command value created only when the released state is detected. Electric power described in 1)
Steering device.