JPH05155352A - Electromotive power steering device - Google Patents

Abstract

PURPOSE:To reduce a handle restoring time and any overshoot at the same time. when a handle holding is released. CONSTITUTION:The electromotive power steering device is composed by providing a motor 6 connected to a steering system and generating a steering assist torque, a torque sensor 11 to detect the steering torque of the steering system, a car speed sensor 12 to detect the car speed, and a control means 100 to control the drive of the motor 6 depending on the outputs of the torque sensor 11 and the car speed sensor 12. In this case, a motor data inferring means 32 to infer the rotation angle and the angular velocity of the motor 6, a restoration force control means 60 to apply a negative feedback to the steering assist torque according to the rotation angle of the motor 6, and a motor viscosity control means 40 to convert the negative feedback gain of the motor angular velocity according to the car speed are provided, and the control means 100 corrects a control value to control the drive of the motor 6 depending on the outputs of the restoration force control means 60 and the motor viscosity control means 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus suitable for use in a vehicle, and more particularly to a power steering apparatus which assists a steering force with a rotational output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering systems using a motor instead of a hydraulic type have been used as a vehicle power steering device, and the motor has an increasing tendency in the future due to advantages such as small size and light weight as an actuator.

In the conventional power steering system, the torque sensor detects the steering torque of the steering system, the vehicle speed sensor detects the vehicle speed, and the drive of the motor connected to the steering system is controlled based on the detection results. , Power assist is done. Generally, it is a vehicle speed sensitive type, and the assist force is controlled according to the torque sensor input so that it is light in the low speed range and heavy in the high speed range.

[0004]

However, in the conventional electric power steering apparatus which does not have the means for detecting the rotation angle of the motor, the restoring force corresponding to the rotation angle of the motor cannot be applied. When the steering wheel is released, at low speeds, the steering wheel return time becomes long and at the same time the steering wheel cannot return to the neutral point. On the other hand, at high speeds, there was a problem that vibration overshoot was large and settling time was long, which particularly hinders safety.

Further, although steering of the steering wheel is in a low frequency range of 10 and several KHz or less, if there is no negative feedback for giving the above restoring force, the control system cannot be designed in the low frequency range, so that a desired control characteristic is obtained. There was a problem that the design that could be achieved was difficult. Further, when the above-mentioned negative feedback is given, there is a drawback that the return time and the overshoot cannot be shortened at the same time if the negative feedback gain of the motor speed is constant.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electric power steering system which can shorten the steering wheel return time and overshoot at the same time when the vehicle is released.

[0007]

To achieve the above object, an electric power steering apparatus according to the present invention comprises a motor connected to a steering system for generating a steering assist torque,
Steering torque detecting means for detecting the steering torque of the steering system,
An electric power steering apparatus comprising: vehicle speed detecting means for detecting a vehicle speed; and control means for controlling driving of the motor based on outputs of the steering torque detecting means and the vehicle speed detecting means. The motor information estimating means for estimating the angular velocity, the restoring force control means for giving a negative feedback to the steering assist torque according to the rotation angle of the motor, and the motor viscosity controlling means for changing the negative feedback gain of the motor angular velocity according to the vehicle speed. And the control means is
A control value for controlling the drive of the motor is corrected based on the outputs of the restoring force control means and the motor viscosity control means.

Further, preferably, the motor information estimating means estimates the rotation angle and angular velocity of the motor from the current, voltage or induced voltage of the motor, and the restoring force control means obtains a negative feedback gain of the motor angular velocity at low speed. It is preferable to lower the value and increase the negative feedback gain of the motor angular velocity at high speed.

[0009]

According to the present invention, the rotation angle and the angular velocity of the motor are estimated, the steering assist torque is negatively fed back according to the rotation angle of the motor, and the negative feedback gain of the motor angular velocity is changed according to the vehicle speed. For example, at low speed, the negative feedback gain of the motor angular velocity is low, and at high speed, the negative feedback gain of the motor angular velocity is high. Therefore, the steering wheel return time and the overshoot at the time of release can be shortened at the same time.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 6 are views showing an embodiment of an electric power steering apparatus according to the present invention. FIG. 1 is a block diagram functionally showing the entire apparatus. 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. In FIG. 2, the rotational force of the steering wheel 1 is transmitted to the steering gear 2 including the pinion gear via the handle shaft, is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through the knuckle arm and the like. To be done. Further, the rotational force of the steering assist (auxiliary) motor (DC motor) 6 controlled and controlled by the control device 5 is transmitted to the rack shaft 3 by the meshing of the steering shaft 7 including the pinion gear and the rack shaft 3, and the steering wheel 1 is used. It will assist steering. The rotating shafts of the handle 1 and the motor 6 are mechanically connected by gears 2 and 7 and a rack shaft 3.

On the other hand, a steering torque sensor 11 (see FIG.
Steering torque (return torque) is detected by
The vehicle speed is detected by the vehicle speed sensor 12 (see FIG. 1). Then, the motor 6 is controlled by the control device 5 based on the detected torque, the vehicle speed, and the like. The control device 5 and the motor 6 have a battery 8 mounted on the vehicle.
Is supplied with its operating power.

The control device 5 includes detectors such as a current detector and a voltage detector, a drive circuit for driving the motor 6, a computer (CPU, for example, a microprocessor) for controlling the overall control of the motor 6, a memory, and a computer. It is composed of an interface circuit with the input / output device.

Next, FIG. 1 is a block diagram showing various functions of a computer incorporated in the control device 5 for other input / output.
It is drawn together with blocks showing output devices and various circuits. In this figure, the assist command section 10 includes a torque V detected by a torque sensor (steering torque detecting means) 11.
_T and the vehicle speed V _S detected by the vehicle speed sensor (vehicle speed detecting means) 12 are given. The assist torque value instruction function unit 13 in the assist command unit 10 outputs a command value representing the assist torque to be generated by the motor 6 according to the detected torque V _T.

Further, the multiplication constant function unit 14 detects the detected vehicle speed V _S
A constant is generated according to the above, and this constant is multiplied by the above-mentioned assist torque command value in the multiplication calculator 15. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 15 becomes a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG.

[0016] Figure 3 is based on the steering torque V _T, which substantially proportional to the motor current (assist torque is generated) flows against the steering torque V _T of a range, when it exceeds the above range, as constant motor current flows (the assist torque is generated), also according to the vehicle speed V _S, the motor current (assist when when the vehicle speed V _S is high to reduce the motor current (assist torque), the vehicle speed V _S is low It indicates that an assist command for controlling the motor 6 is generated so that the torque is increased.

The detected torque V _T is also given to the phase compensator 16, and the phase compensator 16 adds the differential value of the detected torque V _T to the output of the multiplication calculator 15,
The output (reference current command value) of the assist command unit 10 is supplied to the current control unit 20. The reference current command value is added (or subtracted) with a command value for angular position, velocity and acceleration control (which may be at least one), which will be described later, and then given to the current control unit 20 as a target current command value. .. The current control unit 20 may be entirely configured by a hardware circuit, or a part thereof may be implemented by computer software.

The current control unit 20 is a PWM (Pulse) that follows the H-bridge drive method including, for example, four switching elements.
The motor 6 is driven and controlled by a chopper operation using a (Width Modulation) pulse, and current feedback control is performed. That is, the armature current detector 26 detects the armature current ia of the motor 6, and the target current command value and the detected current ia given by the current deviation calculator 21.
The deviation from and is calculated. The absolute value of the deviation is obtained by the absolute value converter 24, and the duty generator 25 determines the duty ratio of the PWM pulse based on the absolute value.

On the other hand, the polarity (positive or negative) of the deviation is discriminated by the positive / negative discriminating section 22, and the generated duty ratio and the discriminated polarity are given to the motor driving section 23, and the motor driving section 23 determines these values. Based on the above, the four switching elements wired in the H bridge type are controlled to be turned on / off to drive the motor 6.

The applied voltage v of the motor 6 is the applied voltage detector 3
The applied voltage v detected by 1 and the armature current ia described above are given to the steering angle data estimation means (motor information estimation means) 32. This rudder angle data estimation means 3
Reference numeral 2 is an observer for estimating the rotation speed dθ / dt of the motor 6 from the given motor voltage v and the motor current ia. The rotation speed dθ / dt of the motor 6 represents the steering angular speed, which corresponds to the steering amount.

In the following description, a change in the steering angle is represented by adding a dot on the character by using θ as usual in the drawings. However, since the dot display is difficult in the text of the specification, the steering angle is changed. The change dθ / dt will be appropriately represented as Sθ. In addition, a mountain-shaped symbol is added to the upper side of the estimated value in the drawing. On the other hand, in the text of the specification, it is difficult to add a mountain-shaped symbol to the upper side of the estimated value, and therefore this display is omitted.

An example of the functional configuration of the steering angle data estimating means 32 is shown in FIG. 4, and the rotation speed dθ of the motor 6 is calculated from the input motor voltage v and the motor current ia by the parameters of the arithmetic units 301 to 308. / Dt is estimated. The block diagram of FIG. 4 realizes the operation of the following formula 1. In FIG. 4, 1 / s represents an integral element.

[0023]

[Equation 1]

The parameters of the observer are internal parameters of the motor 6, such as armature resistance R, self-inductance L, torque constant K _T , speed induced voltage constant K _e , viscous resistance coefficient D of the motor shaft, rotor inertia J. Etc. are used to calculate. In this way, the estimated speed dθ / dt obtained from the steering angle data estimation means 32 is differentiated by the differential calculation unit 33, whereby the estimated acceleration d ² θ / d
converted to t ² .

Here, the estimated acceleration is calculated as usual on the drawing.
Two dots are added on top of the character using θ,
Estimated acceleration because it is difficult to display dots in the text of the specification
Degree d 2θ / dt²Will be appropriately expressed as Aθ. Well
In addition, in the drawing, a mountain-shaped symbol is added above the estimated value.
I will decide. On the other hand, in the main text of the specification, the peak is above the estimated value.
Since it is difficult to express by adding the type symbol, this table
No indication is given.

The estimated speed dθ / dt is calculated by calculating the induced voltage of the motor 6 from the detected voltage and the detected current, not by the observer, and dividing this value by the induced voltage constant.
May be estimated and the estimated speed dθ / dt may be integrated to estimate the rotational position (rotation angle) θ of the motor 6.

The estimated speed dθ / dt is the estimated acceleration d ² θ / d to the viscosity command unit 40 which performs negative feedback such as steering angular velocity.
t ² is given to each inertia compensation unit 50 that performs positive feedback of the steering angular acceleration, and is used for controlling the position, speed and acceleration of the motor 6. Any one or two of these controls may be performed, or all of them may be performed. Further, in the configuration of the observer, it is possible to simultaneously estimate the disturbance torque and remove the influence of the disturbance torque on the estimated values of the motor angle and the angular velocity.

The viscosity command section (motor viscosity control means) 40 applies a viscous force to the movement of the steering angle and switches the magnitude of the viscous force according to the vehicle speed. The estimated speed dθ / dt is given to the viscosity compensation value instruction function unit 41, and the viscosity compensation value instruction function unit 41 gives a command value that produces a larger absolute value and reverse torque as the velocity dθ / dt increases. Output. On the other hand, the vehicle speed Vs detected by the vehicle speed sensor 12 is given to a vehicle speed calculation constant function unit 44, and this function unit 44 outputs a larger constant as the vehicle speed Vs is higher. The vehicle speed calculation constant is multiplied by the command value output from the function unit 41 in the multiplication calculation unit 42 via the multiplication calculation unit 45.

This multiplication result is subtracted from the reference current command value output from the assist command unit 10 via the viscosity command output command unit 43. In this way, the output of the viscosity command unit 40 works to reduce the output of the assist command unit 10 to a greater extent as the steering angular velocity dθ / dt increases. Further, the larger the vehicle speed Vs is, the larger the constant becomes so that it is multiplied, and the viscous braking effect becomes greater. This suppresses the instability when returning to the vehicle, which tends to become unstable at higher vehicle speeds, and achieves a good steering feel. Also, at low vehicle speeds, compensation that reduces the viscosity will work, reducing the feeling of stickiness of the steering wheel,
Good handle feeling will be obtained.

The inertia compensator 50 controls the rotor inertia of the motor 6 as if the rotor inertia had decreased. The inertia compensator 50 eliminates the weight generated when the motor 6 does not follow the rotation of the steering wheel at the time of a sudden steering, or when the steering wheel is released. It acts to speed up the return. The estimated steering angular acceleration d ² θ / dt ² is given to the inertia compensation value instruction function unit 51, and the multiplication operation unit 52 multiplies the command value output from this function unit 51 by an appropriate constant to obtain it. The specified command value is added to the reference current command value of the assist command unit 10.

The restoring force compensating section (restoring force control means) 60 basically produces a force for returning the steering angle to the neutral position, that is, restoring force. A command value obtained by multiplying the estimated steering angle position θ by an appropriate constant in the multiplication calculation unit 61 is subtracted from the reference current command value of the assist command unit 10. The assist command section 10 and the current control section 20 constitute the control means 100.

As described above, in this embodiment, the rotation angle θ and the steering angular velocity dθ / dt are estimated by the steering angle data estimating means 32 from the applied voltage v of the motor 6 and the armature current ia, and the rotation angle θ of the motor 6 is calculated. Accordingly, the viscosity command unit 40 negatively feeds back the steering assist torque, and the negative feedback gain of the motor angular velocity is changed according to the vehicle speed.
That is, the negative feedback gain of the motor angular velocity is controlled to be low at low speed, and the negative feedback gain of the motor angular velocity is controlled to be high at high speed.

Next, the viscosity command section 40 and the restoring force compensation section 60
The effect of control by will be described in detail. Typically,
A mechanical model of the steering system is shown in FIG. In FIG. 5, the meaning of each symbol is as follows. K _s : Self-aligning rigidity C _s : Self-aligning viscosity K _t : Torque sensor rigidity C _t : Torque sensor viscosity J ₁ : Handle lower inertia moment J ₂ : Handle upper inertia moment θ ₁ : Handle lower displacement θ ₂ : Handle Upper displacement _Th : Steering torque _Ta : Assist torque

Now, the motor assist torque T_aResilience
-Kθ_iAnd viscous force-C (dθ / dt) Add a torque to be 1.
Eh, Ta = -Kθ_i-C (dθ / dt)₁+ K_f(Θ₂−θ₁), The steering torque T_hTo motor rotation angle θ₁For up to
The transfer function is as shown in the following Expression 2.

[0035]

[Equation 2]

That is, the self-aligning rigidity is increased from K _s to (K + K _s ) by adding the restoring force −Kθ _i , and the self-aligning viscosity is increased by adding the viscous force −C (dθ / dt) _1. It means that it has increased from C _s to (C _s + C). On the other hand, when the steering wheel is released, conventionally, the steering wheel angle at low vehicle speed and at high vehicle speed is as shown by the solid line in FIG. In the case of the present invention, on the other hand, in addition to the restoring force K _s theta ₁ by aligning joined by restoring force K [theta ₁ by restoring force compensation, with restoring force increases, reducing the viscosity coefficient C in the low vehicle speed Therefore, the viscous force (C _s + C) (dθ / dt) becomes small, and as a result, the return time becomes short as shown by the broken line in FIG. 6A, and at the same time the residual steering angle becomes zero.

Further, at high speed, the vibration frequency is increased due to the increase in self-aligning rigidity and the viscosity coefficient C is increased, resulting in FIG.
As shown by the broken line in (b), the convergence time can be shortened and overshoot can be reduced. Therefore, the steering wheel return time and the overshoot at the time of release can be shortened at the same time. Incidentally, for the would force to turn the steering wheel increases relative to the restoring force increases, it can be adjusted by the gain K _f which gives an assist force.

[0038]

According to the present invention, the steering assist torque is negatively fed back according to the rotation angle of the motor, and the negative feedback gain of the motor angular velocity is changed according to the vehicle speed.
The following effects can be obtained. It is possible to shorten the return time when the steering wheel is released in the low vehicle speed range. When releasing the handle in the low vehicle speed range, the handle can be returned to the neutral position. It is possible to shorten the overshoot when the steering wheel is released in the high speed range. It is possible to improve the characteristics in the low frequency range, which is important for the electric power steering control characteristics, and improve the steering feeling.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an embodiment of an electric power steering apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a power steering mechanical system of the same embodiment.

FIG. 3 is a diagram showing characteristics of assist torque in the same example.

FIG. 4 is a functional block diagram showing a configuration of a steering angle data estimating means of the embodiment.

FIG. 5 is a diagram showing a model of a power steering mechanical system of the embodiment.

FIG. 6 is a diagram showing an example of a response of a steering wheel angle when the steering wheel is released according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 6 Motor 11 Steering torque sensor (steering torque detecting means) 12 Vehicle speed sensor (vehicle speed detecting means) 20 Current control section 32 Steering angle data estimating means (motor information estimating means) 40 Viscosity command section (motor viscosity control means) 50 Inertia compensation section 60 Restoring force compensation section (restoring force control means) 100 Control means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 119: 00

Claims (3)

[Claims] 1. A motor connected to a steering system for generating a steering assist torque, a steering torque detecting means for detecting a steering torque of the steering system, a vehicle speed detecting means for detecting a vehicle speed, the steering torque detecting means and the vehicle speed. In an electric power steering apparatus including: a control unit that controls the drive of the motor based on the output of the detection unit; a motor information estimating unit that estimates the rotation angle and the angular velocity of the motor; And a motor viscosity control means for changing the negative feedback gain of the motor angular velocity according to the vehicle speed. The control means is a restoring force control means and a motor viscosity control means. An electric power steering apparatus, wherein a control value for controlling the drive of the motor is corrected based on the output of the electric power steering apparatus. 2. The electric power steering apparatus according to claim 1, wherein the motor information estimating means estimates the rotation angle and angular velocity of the motor from the current, voltage or induced voltage of the motor. 3. The electric power steering apparatus according to claim 1, wherein the restoring force control unit lowers the negative feedback gain of the motor angular velocity at low speeds and increases the negative feedback gain of the motor angular velocity at high speeds. ..