JPH05238409A - Electric power steering device - Google Patents

Abstract

(57) [Abstract] [Purpose] To enhance the steering feeling during high-acceleration steering and the convergence when the steering wheel is released, and to facilitate steering wheel operation during emergency avoidance. [Structure] Assist motor 6, torque sensor 21,
A steering acceleration sensor 45 that detects a steering acceleration of a steering system in an electric power steering apparatus that includes a vehicle speed sensor 22 and a control unit 100 that controls driving of a motor 6 based on outputs of the sensors 21 and 22. The steering wheel upper inertia compensating unit 30 that calculates upper inertia compensation for compensating the upper inertial force of the steering wheel 1 based on the steering acceleration detected by the steering acceleration sensor 45 and the output of the torque sensor 21, and the steering acceleration sensor 45 detects the upper inertia compensation unit 30. And a motor inertia compensation unit 40 that calculates a motor inertia compensation value that compensates the inertia of the motor 6 based on the steering acceleration, and the control unit 100 controls the motor 6 based on the outputs of the compensation units 30 and 40. Correct the control value that controls the drive.

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. Further, the inertia of the motor is compensated by positive feedback of the motor acceleration (see, for example, Japanese Patent Laid-Open No. 3-178870).

[0004]

However, in such a conventional electric power steering apparatus,
Since the inertia compensation of the motor is performed only by the positive feedback of the motor acceleration, the gain of the positive feedback cannot be increased due to the oscillation, and the sufficient compensation effect cannot be obtained. Therefore, there is a problem that the steering feeling is deteriorated during high acceleration steering.

Further, there is a problem that the convergence property is not sufficiently obtained when the steering wheel is released during high speed traveling, and the convergence time is long. Furthermore, the steering wheel operability during high-speed traveling is poor, so steering wheel operation during emergency avoidance is not easy,
I couldn't improve my safety anymore.

Therefore, the present invention can improve the steering feeling during high-acceleration steering and the convergence when the steering wheel is released during high-speed traveling, and facilitate the steering operation during emergency avoidance to further enhance safety. It is an object of the present invention to provide an electric power steering device that can be used.

[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,
A steering acceleration of the steering system in 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. And an upper inertia compensation for calculating an upper inertia compensation value for compensating the upper inertia force of the steering wheel based on the steering acceleration detected by the steering acceleration detection means and the output of the steering torque detection means. Value calculation means and motor inertia compensation value calculation means for calculating a motor inertia compensation value for compensating the motor inertia based on the steering acceleration detected by the steering acceleration detection means, and the control means includes upper inertia compensation A control value for controlling the drive of the motor is corrected based on the outputs of the value calculation means and the motor inertia compensation value calculation means. The features.

[0008]

In the present invention, the upper inertia compensation value at the steering wheel is calculated from the detected steering acceleration and the output of the steering torque detecting means and added to the command value of the assist motor. This compensates for the upper inertial force of the steering wheel. Further, a motor inertia compensation value is calculated from the steering acceleration detected by the steering acceleration detecting means and added to the command value of the assist motor. Thereby, the inertia of the assist motor is compensated.

Therefore, the inertia of the upper part of the steering wheel and the motor is sufficiently compensated, and the steering feeling similar to that at the time of low acceleration steering is maintained even at the time of high acceleration steering, and the deterioration of the steering feeling such as a feeling of deadness is prevented. Convergence increases when the steering wheel is released while driving at high speed. In addition, the steering wheel operation during emergency avoidance becomes easy, and safety is further improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 5 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 21 (see FIG.
Steering torque (return torque) is detected by
The vehicle speed sensor 22 (see FIG. 1) detects the vehicle speed. 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 unit 20 includes a detection torque V of a torque sensor (steering torque detection means) 21.
_T and the vehicle speed V _S detected by the vehicle speed sensor (vehicle speed detecting means) 22 are given. The assist torque value instruction function unit 23 in the assist command unit 20 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 24 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 25. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 25 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 26, and the differential value of the detected torque V _T is added to the output of the multiplication calculator 25 by the phase compensator 26.
The output (reference current command value) of the assist command unit 20 is supplied to the current control unit 60.

The reference current command value is added (or subtracted) to the control outputs of the handle upper inertia compensation unit 30 and the motor inertia compensation unit 40, which will be described later, and then given to the current control unit 60 as a target current command value. The current control unit 60 may be entirely configured by a hardware circuit, or a part thereof may be realized by computer software.

The current control unit 60 is a PWM (Pulse) according to an 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 detection unit 66 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 calculation unit 61 are detected.
The deviation from and is calculated. The absolute value of this deviation is obtained by the absolute value converter 64, and the duty ratio of the PWM pulse is determined by the duty generator 65 based on this absolute value.

On the other hand, the polarity (positive or negative) of the above-mentioned deviation is discriminated by the positive / negative discriminating section 62, and the generated duty ratio and the discriminated polarity are given to the motor driving section 63, and the motor driving section 63 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 detected torque V _T of the torque sensor 21 is applied to the differential multiplication unit 51, and the differential detection unit 51 differentiates the detected torque V _T twice. Furthermore, the differential multiplication unit 5
The two-time differential value of the detected torque V _T calculated by 1 is input to the multiplication calculation unit 52, and the multiplication calculation unit 52 calculates the steering angular acceleration d ² θ ₂ / dt ^{2 of the} upper portion of the steering wheel 1 according to the following equation. ..

Here, an equation representing the principle of the torque sensor 21 is shown below. V _T = G (θ ₂ −θ ₁ ), where V _T : detected steering torque G: gain θ ₁ : steering angle of the assist motor θ ₂ : steering angle of the upper part of the steering wheel

The following equation is obtained by differentiating this equation twice. d ² V _T / dt ² = G (d ² θ ₂ / dt ² −d ² θ ₁ / dt ² ) ... The handle from d ² V _T / dt ² and d ² θ ₁ / dt ² in this formula The upper steering angular acceleration d ² θ ₂ / dt ² is obtained. As a result, even if a special sensor is not provided above the steering wheel 1, the steering angular acceleration d ² θ ₂ / d above the steering wheel 1
There is an advantage that t ² is required.

In the following description, the change in the steering angle is represented by using θ to add a dot on the character as usual in the drawings. However, since it is difficult to display the dots in the text of the specification, the steering angle is changed. The change is expressed using dθ / dt, and dot display is not performed. In addition, the steering acceleration θ
Two dots are added on the character by using, but since the dot display is difficult in the text of the specification, the steering acceleration is expressed by d ² θ / dt ² .

On the other hand, reference numeral 45 denotes a steering angular acceleration sensor for detecting the steering angular acceleration d ² θ ₁ / dt ^2.
The output d ² θ ₁ / dt ^{2 of 5} is input to the motor inertia compensation unit 40. The motor inertia compensation section (motor inertia compensation value calculation means) 40 is composed of an inertia compensation value instruction function section 41 and a multiplication calculation section 42. The motor inertia compensator 40 controls the rotor inertia of the motor 6 as if the rotor inertia had become small. The motor inertia compensator 40 eliminates the weight caused by the motor 6 not following the rotation of the steering wheel during a sudden steering operation, and the return speed when the steering wheel is released. Acts to speed up.

The steering angular acceleration d from the steering angular acceleration sensor 45
² θ ₁ / dt ² is given to the inertia compensation value indicator function unit 41,
The command value output from the function unit 41 is multiplied by the multiplication calculation unit 42.
The command value obtained by being multiplied by an appropriate constant is added to the reference current command value of the assist command unit 20.

The steering angular acceleration d ² θ ₂ / dt ^{2 on the} upper portion of the steering wheel calculated by the above-mentioned multiplication calculation unit 52 is added to the steering angular acceleration d ² θ ₁ / dt ² from the steering angular acceleration sensor 45 to obtain the upper portion of the steering wheel. It is input to the inertia compensation unit 30. The steering wheel upper inertia compensation unit (upper inertia compensation value calculation means) 30 is composed of a multiplication calculation unit 32, and the steering angular acceleration d ² of the steering wheel upper portion.
A command value obtained by multiplying the added value of θ ₂ / dt ² and the steering angular acceleration d ² θ ₁ / dt ^{2 by} an appropriate constant in the multiplication calculation unit 32 is added to the reference current command value of the assist command unit 20. To be done.

The steering wheel upper part inertia compensation unit 30 controls the inertia of the steering wheel upper part as if it appears to be small (that is, compensates for the upper part inertial force of the steering wheel 1) and accelerates the return speed when the steering wheel is released. And acts to increase astringency.

Although the steering angular acceleration sensor 45 detects the steering angular acceleration d ² θ ₁ / dt ² , the steering angular acceleration sensor 45 is, for example, a tachogenerator, an encoder or the like and differentiates or integrates their outputs. It can also be realized by a circuit. Further, instead of the steering angular acceleration sensor 45, an observer for estimating the steering angular acceleration may be provided.

This observer estimates the steering angular acceleration (rotational acceleration of the motor 6) based on the voltage applied to the motor 6 and the armature current, or based on the command current value to the motor 6 and the measured armature current. To do. The assist command section 20 and the current control section 60 constitute the control means 100.

Next, the operation of this apparatus will be described. First, the torque sensor 21 detects the steering torque V _T of the steering system, the vehicle speed sensor 22 detects the vehicle speed V _{S, and the} drive of the motor 6 connected to the steering system is controlled based on these detection results. , Power assist is performed. In this control, general vehicle speed-sensitive control, that is, the assist force is controlled according to the steering torque V _T so that it is light in the low speed range and heavy in the high speed range.

On the other hand, the steering torque V _T of the steering system is inputted torque twice differential value d ² V _T / dt ² is calculated differentiating unit 51, the torque twice differential value d ² V _T / dt ² From the multiplication calculation unit 52, the steering angle acceleration d ² θ ₂ above the steering wheel
/ Dt ² is calculated, added to the steering angular acceleration d ² θ ₁ / dt ² from the steering angular acceleration sensor 45, and input to the steering wheel upper inertia compensation unit 30. The steering wheel upper inertia compensation unit 30 creates a command value by multiplying the addition value of the steering wheel angular acceleration d ² θ ₂ / dt ² of the steering wheel upper part and the steering angular acceleration d ² θ ₁ / dt ^{2 by} an appropriate constant to generate an assist command. It is added to the reference current command value of the unit 20.

As a result, the reference current command value of the assist command section 20 is corrected, that is, the upper inertial force of the steering wheel 1 is compensated and the inertial force of the upper portion of the steering wheel is controlled as if it were apparently small. Therefore, the return speed is increased when the handle is released, and the convergence can be improved.

On the other hand, the steering angular acceleration d ² θ ₁ / dt ² from the steering angular acceleration sensor 45 is given to the motor inertia compensation 40,
The motor inertia compensation unit 40 creates a command value for compensating the inertia of the motor 6 and adds it to the reference current command value of the assist command unit 20. As a result, the reference current command value of the assist command unit 20 is corrected, that is, the rotor inertia of the motor 6 is controlled as if the rotor inertia was reduced, and the motor 6 does not follow the rotation of the steering wheel 1 at the time of sudden steering. Is eliminated.

Therefore, as described above, the inertia compensation of the upper part of the handle and the motor is sufficiently performed,
The steering feeling similar to that at the time of low acceleration steering can be maintained at the time of high acceleration steering, the deterioration of the steering feeling such as a feeling of stuffiness can be prevented, and the return and convergence when the steering wheel is released during high speed traveling can be enhanced.

More specifically, the steering assist torque Tm of the conventional steering assist motor is determined by the following equation. Tm = HS ... where H: gain due to vehicle speed S: conventional detected steering torque

On the other hand, in the case of the present embodiment, means for detecting the steering angular acceleration d ² θ ₁ / dt ² of the steering assist motor 6 (that is, the steering angular acceleration sensor 45) is provided, and the torque sensor 21 is further provided. The steering angular acceleration d ² θ ₂ / dt ² at the upper part of the steering wheel is obtained by using an equation obtained by differentiating the above-mentioned equation representing the principle of the above, and the steering assist torque Tmnew is newly determined by the following equation. There is. Tmnew = H ₃ · V _T + H ₂ · (d ² θ ₂ / dt ² ) + H ₁ · (d ² θ ₁ / dt ² ) ...

The steering assist torque T
In order to determine mnew, the model shown in FIG. 4 is assumed in this embodiment. That is, when the model shown in FIG. 4 is assumed for the upper part of the steering wheel and the steering assist motor 6, the equation shown below is established for the torque T during steering.

T = J ₂ · (d ² θ ₂ / dt ² ) + J ₁ · (d ² θ ₁ / dt ² ) + C ₂ · (dθ ₂ / dt) + C ₁ · (dθ ₁ / dt) + Kθ ₁ · ... However, J _2: inertia of the handle upper J _1: steering assist motor inertia C _2: viscosity coefficient of the torque sensor C _1: viscosity coefficient of the tire K: as described above, based on the self aligning torque stiffness this formula The steering assist torque Tmnew is calculated by the equation.

Next, the torque Th that a person steers is expressed by
By subtracting the formula from
It Th = (J₂-H₂) (D²θ₂/ Dt²) + (J₁-H₁) (D²θ₁/ Dt²) + C  2 ・ (dθ₂/ Dt) + C₁・ (Dθ₁/ Dt) + Kθ₁-H₃・ V_T(Θ₂−θ₁) ・ ・ ・ ・ Where θ₂−θ₁> 0, so Kθ₁-H₃・ V_T(Θ₂−θ₁) <Kθ₁..., and the steering torque in the low speed range is the assist torque H.₃・
V_TIs reduced by.

From the above, the apparent inertia of the steering wheel 1 and the motor 6 is reduced. For this reason, the inertial force, which is greatly affected during high-speed steering, is reduced. Further, since the vibration frequency related to the convergence when the handle is released is inversely proportional to the square root of the inertia, the decrease in the inertia increases the vibration frequency and shortens the convergence time.

In this way, the inertia of the steering wheel upper portion and the motor is sufficiently compensated, the apparent steering assist motor 6 and the inertia of the steering wheel upper portion become small, and the resonance frequency becomes high, so that the convergence when the steering wheel is released. It is possible to improve the sex. Further, the steering torque at the time of high-speed steering is reduced, so-called feeling of fatigue can be eliminated, and the steering feeling can be improved. Further, the steering wheel operation during emergency avoidance becomes easy, and the safety can be further improved.

FIG. 5 shows the convergence when the steering wheel is released. Without the compensation of this embodiment, the convergence when the steering wheel is released is poor, and it does not converge even after a long time has passed.
It is apparent that the convergence of the motor 6 is increased only by the inertia compensation, and the convergence of the upper portion of the steering wheel is further improved by performing the inertia compensation of the motor 6 in addition to the inertia compensation of the motor 6.

[0044]

According to the present invention, since the inertia of the steering wheel upper portion and the motor is sufficiently compensated, the apparent steering assist motor and the inertia of the steering wheel upper portion can be reduced, and the steering wheel converges when the steering wheel is released. It is possible to improve the sex. Further, the steering torque at the time of high-speed steering is reduced, and the steering feeling similar to that at the time of low-acceleration steering can be maintained even at the time of high-acceleration steering. it can.
Further, the steering wheel operation during emergency avoidance becomes easy, and the safety can be further improved.

[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 diagram showing a model relating to an upper portion of a handle and a steering assist motor of the same embodiment.

FIG. 5 is a diagram showing the astringency of the same embodiment when the handle is released.

[Explanation of symbols]

1 Steering Handle 6 Motor 20 Assist Command Unit 21 Steering Torque Sensor (Steering Torque Detecting Means) 22 Vehicle Speed Sensor (Vehicle Speed Detecting Means) 30 Handle Upper Inertia Compensation Unit (Upper Inertial Compensation Value Calculation Means) 40 Motor Inertial Compensation Unit (Motor Inertia Compensation) Value calculation means) 100 control means

Claims (1)

[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. An electric power steering apparatus comprising: a control unit that controls the drive of the motor based on the output of the detection unit; a steering acceleration detection unit that detects the steering acceleration of the steering system; and a steering acceleration detection unit that detects the steering acceleration. An upper inertia compensation value calculating means for calculating an upper inertia compensation value for compensating an upper inertia force of the steering wheel based on the output steering acceleration and the output of the steering torque detecting means, and the steering acceleration detected by the steering acceleration detecting means. And a motor inertia compensation value calculating means for calculating a motor inertia compensation value for compensating the motor inertia based on Stage, electric power steering apparatus characterized by correcting the control value for controlling the drive of the motor based on the output of the upper inertia compensation value calculating means and motor inertia compensation value calculating means.