JP3084937B2 - Electric power steering device - Google Patents

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 for assisting a steering force by a rotation output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering devices using motors have been used in place of hydraulic power steering devices, and motors are increasing in the future because of their advantages such as small size and light weight as actuators.

In a conventional power steering apparatus, a torque sensor detects a steering torque of a steering system, a vehicle speed sensor detects a vehicle speed, and controls the driving of a motor connected to the steering system based on the detection results. , Power assist. In general, it is of a vehicle speed sensitive type, and the assist force is controlled in accordance with the input of the torque sensor so as to be light in a low speed range and heavy in a high speed range.

[0004] By the way, in the above-mentioned conventional apparatus, since the torque of the assist motor is reduced by the gear and transmitted to the rack shaft or the like, the inertia moment of the assist motor acts as if it were large. As a result, the convergence at high vehicle speeds deteriorates, and the steering wheel return at low vehicle speeds deteriorates.

Therefore, in order to solve such a problem, an inertia control signal corresponding to the steering angular acceleration is added,
The present applicant has previously proposed a device that suppresses the influence of the inertia moment of the assist motor to reduce the deterioration of convergence at high vehicle speeds and the deterioration of steering wheel return characteristics at low vehicle speeds (for example, See Japanese Unexamined Patent Publication No. 3-178873).

[0006]

However, in such an improved conventional apparatus, it is necessary to provide a rotation angle detector or a rotation angular velocity detector for a motor or a steering wheel. The provision of the power steering device has a problem that the power steering device is expensive.

Therefore, the present invention is to reduce the cost,
It is an object of the present invention to provide an electric power steering device capable of improving both convergence at a high vehicle speed and a return characteristic of a steering wheel at a low vehicle speed.

[0008]

In order to achieve the above object, an electric power steering apparatus according to the present invention is connected to a steering system and generates a steering assist torque.
Steering torque detecting means for detecting a 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. For example,
The inertia compensation means for calculating an inertia compensation value for compensating the inertia of the motor in accordance with the amount of change) of the motor terminal voltage is provided, before
The inertia compensating means is configured to determine the amount of change in the current target value of the motor.
The control means corrects a control value for controlling the driving of the motor based on the inertia compensation value calculated by the inertia compensation means.

[0009]

According to the present invention, the inertia compensation value corresponding to the rotation state of the motor is calculated by the inertia compensation means based on the control information of the motor, that is, typically, the amount of change in the terminal voltage of the motor, and the drive of the assist motor is controlled. Is added to the assist command value. In this case, the amount of change in the motor target
Correction of the inertia compensation value is performed accordingly.

As a result, the influence of the inertia moment of the assist motor is suppressed by the inertia compensation value.

[0011] Therefore, the motor with respect to the inertia compensation value
While reducing the effects of current fluctuations, it is possible to improve the convergence at high vehicle speeds and the steering wheel return characteristics at low vehicle speeds with an inexpensive device without a motor or steering wheel rotation angle detector or rotation angular speed detector. Optimum steering feeling can be obtained.

[0012]

DETAILED 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 a steering gear 2 including a pinion gear via a handle shaft, transmitted to a rack shaft 3 by the pinion gear, and further turned by a knuckle arm or the like. Is done. The rotational force of a steering assist (auxiliary) motor (DC motor) 6 controlled and driven by the control device 5 is transmitted to the rack shaft 3 by meshing the steering gear 7 including a pinion gear with the rack shaft 3, and This will assist steering. The handle 1 and the rotating shaft of 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 described later (FIG. 1)
), The steering torque (return torque) is detected,
The vehicle speed is detected by the vehicle speed sensor 22 (see FIG. 1). Then, the control device 5 controls the motor 6 based on the detected torque, vehicle speed, and the like. The control device 5 and the motor 6 include a battery 8 mounted on the vehicle.
Supplies 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 comprises an interface circuit with the input / output devices.

FIG. 1 is a block diagram showing various functions of a computer built in the control device 5 in other blocks.
It is drawn with blocks showing output devices and various circuits. In this figure, an assist command unit 20 includes a detection torque V of a torque sensor (steering torque detection unit) 21.
_T and the detected vehicle speed V _S of the vehicle speed sensor (vehicle speed detecting means) 22 are given. Assist torque value indicator function unit 23 in the assist command section 20 outputs a command value representing an assist torque to be generated by the motor 6 in accordance with the detected torque V _T.

Further, the multiplication constant function section 24 calculates the detected vehicle speed V _S
, And the constant is multiplied by the above-mentioned assist torque command value in the multiplication operation unit 25. 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.

[0018] Figure 3, according to 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 This indicates that an assist command for controlling the motor 6 is generated so as to increase the torque).

The detected torque _VT is also given to the phase compensator 26. In the phase compensator 26, the detected torque V _T
Is calculated, and a signal obtained by multiplying the differential value by a constant corresponding to the vehicle speed V _S generated in the differential multiplication constant function section 27 is output. Then, the output of the phase compensation unit 26 is added to the output of the multiplication operation unit 25, so that the assist command unit 2
An output of 0 (reference current command value) is supplied to the current control unit 40.

A command value for inertia compensation, which will be described later, is added to the reference current command value, which is then provided to the current control unit 40 as a target current command value. The current control unit 40 may be entirely configured by a hardware circuit, or a part of the current control unit 40 may be realized by computer software.

The current control unit 40 is, for example, a PWM (Pulse Pulse) according to an H-bridge driving method including four switching elements.
The drive control of the motor 6 is performed by a chopper operation using a (Width Modulation) pulse, and the PWM pulse is determined so that the current target value and the current detection value im match.

For example, in the case of the current feedback P (proportional) control, the armature current of the motor 6 is detected by the armature current detector 46, and the current target value and the current supplied by the voltage manipulated variable calculator 41 are calculated. The deviation from the detection value im is calculated. The absolute value of this deviation is obtained by the absolute value converter 44, and the duty generator 45
The duty ratio of the WM pulse is determined.

The polarity (positive or negative) of the deviation is determined by the positive / negative determining unit 42, and the generated duty ratio and the determined polarity are given to the motor driving unit 43,
Drives the motor 6 by controlling on / off of four switching elements wired in an H-bridge type based on these values.

The above shows the case of current feedback P (proportional) control, but there are other feedback control methods such as PI (proportional / integral) control and PID (proportional / integral / derivative) control. . The current control unit 4
A current control method of estimating a disturbance with respect to 0 and feed-forwarding the disturbance may be used.

On the other hand, the control value of the motor driving section 43 is input to the inertia compensating section 30,
(Corresponding to inertia compensation means) includes a motor voltage detection unit 31, a change amount calculation unit 32, an inertia compensation value indicating function unit 33, a multiplication operation unit 34, and a vehicle speed operation constant function unit 35.

The motor voltage detecting section 31 includes a motor driving section 43
The motor terminal voltage Vm based on the control value from
The change amount calculator 32 calculates the change amount [dV of the motor terminal voltage Vm.
m / dt] = Vm (n) -Vm (n-1).
Vm (n) is the motor terminal voltage Vm at a certain sampling time, and Vm (n-1) is the motor terminal voltage Vm at the sampling time one time earlier than that.

In the following description, the variation [dVm / dt] of the motor terminal voltage Vm is represented by adding one dot to Vm in the drawing. On the other hand, in the specification text, Vm
This display is not performed because it is difficult to add and represent a dot on the.

The inertia compensation value indicating function unit 33 determines the output of the inertia compensation value indicating function unit as shown in FIG. 4 according to the motor terminal voltage change amount [dVm / dt]. On the other hand, the vehicle speed calculation constant function unit 35 calculates a vehicle speed calculation constant as shown in FIG. 5 according to the vehicle speed V _S , and outputs it to the multiplication calculation unit 34. The multiplication operation unit 34 determines the output of the inertia compensation unit 30 by multiplying the output of the inertia compensation value indicating function unit by the vehicle speed operation constant. The output of the inertia compensation unit 30 is added to the output of the assist command unit 20 (reference current command value), and is supplied to the current control unit 40 as a current target value.

Here, the inertia compensating unit 30 controls the motor 6 as if the rotor inertia became small. The inertia compensating unit 30 eliminates the weight caused by the motor 6 not following the rotation of the steering wheel at the time of a sharp steering. An inertia compensation value for controlling so as to increase the return speed when the hand is released is added to the output of the assist command unit 20. The assist command unit 20 and the current control unit 40 are
Is configured.

Next, the operation of the present apparatus will be described. First, the steering torque V _T of the steering system is detected by the torque sensor 21, the vehicle speed V _S is detected by the vehicle speed sensor 22, the drive of the motor 6 connected to the steering system on the basis of these detection results is controlled Then, power assist is performed. In this control, common vehicle speed-sensitive control, i.e., lightly in the low-speed range, the assist force is controlled in accordance with the steering torque V _T so heavy in high speed range.

On the other hand, in the inertia compensating section 30, the motor terminal voltage Vm is detected by the motor voltage detecting section 31, and the amount of change [dVm / dt] is calculated and output to the inertia compensation value indicating function section as shown in FIG. Is calculated, and a vehicle speed calculation constant as shown in FIG. 5 is calculated by the vehicle speed calculation constant function unit 35 in accordance with the vehicle speed V _S , and the vehicle speed calculation constant is multiplied by the output of the inertia compensation value indicating function unit to provide an assist command. Part 2
0 is added to the output.

Since the motor terminal voltage Vm is control information relating to the so-called "GD ² " which is the inertia of the rotor of the motor 6, it becomes data capable of compensating the inertia of the motor 6. Therefore, the influence of the inertia moment of the motor 6 is effectively suppressed by adding the output of the inertia compensation value indicating function section corrected according to the vehicle speed V _S to the output of the assist command section 20. That is, the convergence at high vehicle speeds and the steering wheel return characteristics at low vehicle speeds can be improved,
An optimal steering feeling can be obtained.

In particular, since the output of the inertia compensation value indicating function section is corrected in accordance with the vehicle speed V _S , the convergence at high vehicle speed,
The responsiveness can be further improved, and the steering wheel return characteristics can be made moderate without excessive inertia compensation at a low vehicle speed.

In this case, in this embodiment, the ON / OFF state of the motor 6 is set.
The motor terminal voltage Vm is detected by the inertia compensating unit 30 from the control value of the motor driving unit 43 performing the off control, and this can be realized only by a simple hardware circuit.
Therefore, there is no need to provide a rotation angle detector for detecting the rotation angle of the motor 6 or the steering wheel (the steering wheel 1) or a rotation angular speed detector for detecting the rotation angular speed, and the above control can be performed with an inexpensive device. The effect is obtained.

Next, another embodiment of the present invention will be described. This embodiment uses the amount of change in the motor current target value as the control information of the motor 6. FIG. 6 is a block diagram functionally showing the entire power steering apparatus according to another embodiment. In the description of FIG. 6, the same components as those in FIG. 1 described above are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 6, reference numeral 50 denotes an inertia compensating unit (corresponding to inertial compensating means). The inertial compensating unit 50 includes a motor voltage detecting unit 31, a change amount calculating unit 32, and an inertial compensation value indicating function unit 3.
3, a change amount calculation unit 51, a correction value calculation unit 52, and a correction unit 53.

The change amount calculating section 51 calculates the current target value Id based on the current target value Id output from the assist command section 20.
[DId / dt] = Id (n) −Id (n−
1) is calculated. Id (n) is a current target value at a certain sampling time, and Id (n-1) is a current target value at a sampling time one time before that.

Here, in the drawing, the change amount [dId / dt] of the current target value Id is represented by adding one dot to Id. On the other hand, this display is not performed because it is difficult to add a dot on Id in the specification text.

The correction value calculating section 52 determines a correction value as shown in FIG. 7 according to the variation [dId / dt] of the current target value Id. This correction value is a variation [dI of the current target value Id.
d / dt]. Correction unit 5
Numeral 3 subtracts the correction value from the output of the inertia compensation value indicating function unit 33 to determine the output of the inertia compensation unit 50. Inertial compensation unit 5
The output of 0 is added to the output of the assist command unit 20 (reference current command value) and supplied to the current control unit 40 as a current target value. Others are the same as the above-mentioned embodiment.

In this embodiment, in this embodiment, the output of the inertia compensation value indicating function unit 33 is corrected in accordance with the change amount [dId / dt] of the current target value Id in addition to the same effect as the above embodiment. The motor 6 with respect to the inertia compensation value
Has the effect of reducing the effect of current fluctuations.

Further, since the configuration is such that the target value is used without using the detected value of the motor current, the output of the inertia compensation value indicating function unit 33 can be corrected without the influence of the detection noise. Furthermore, when the current control unit 40 is realized by hardware, there is an effect that a circuit for taking a current value into the CPU is not required, and the device can be realized at low cost.

[0042]

According to the present invention, the inertia compensation value is calculated according to the control information of the motor, and the inertia compensation means further comprises:
The inertia compensation value according to the amount of change in the current target value of the
Since the control value for controlling the driving of the motor is corrected based on the inertia compensation value, the motor power with respect to the inertia compensation value is corrected.
It is not necessary to provide a motor or steering wheel rotational angle detector or rotational angular velocity detector while reducing the effects of flow fluctuations, reducing costs and reducing convergence at high vehicle speeds and steering wheel return characteristics at low vehicle speeds. And an optimum steering feeling can be obtained.

[Brief description of the 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 illustrating an example of a power steering mechanical system according to the embodiment.

FIG. 3 is a diagram showing characteristics of an assist torque according to the embodiment.

FIG. 4 is a diagram illustrating a relationship between a motor terminal voltage change amount and an output of an inertia compensation value indicating function unit according to the embodiment.

FIG. 5 is a diagram showing a relationship between a vehicle speed and a vehicle speed calculation constant according to the embodiment.

FIG. 6 is a functional block diagram of another embodiment of the electric power steering apparatus according to the present invention.

FIG. 7 is a diagram illustrating a relationship between a change amount of a current target value and a correction value according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 6 Motor 20 Assist command part 21 Steering torque sensor (steering torque detecting means) 22 Vehicle speed sensor (vehicle speed detecting means) 30, 50 Inertial compensation part (Inertia compensating means) 31 Motor voltage detecting part 32 Change amount calculating part 33 Inertia Compensation value indicating function unit 34 Multiplication operation unit 35 Vehicle speed operation constant function unit 40 Current control unit 51 Change amount calculation unit 52 Correction value calculation unit 53 Correction unit 100 Control means

Claims (1)

(57) [Claims] 1. A steering assist torque is connected to a steering system.
Motor, a steering torque detecting means for detecting a steering torque of a steering system, a vehicle speed detecting means for detecting a vehicle speed,
Control means for controlling the driving of the motor, based on the control information of the motor, and compensating the inertia of the motor according to the control information of the motor.
Providing an inertia compensation means for calculating an inertia compensation value,The inertia compensating means is configured to calculate a change amount of a current target value of the motor.
The inertia compensation value is corrected according to  The control means controls the inertia calculated by the inertia compensation means.
A control value for controlling the driving of the motor based on the compensation value;
Electric power steering device characterized by correction
Place.