JP2003081102A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device to prevent vibration of a steering wheel when an assist gain is high. SOLUTION: An inertia compensation current applied on a drive current is decreased as an assist gain is increased.

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 device that assists a steering force with an electric motor.

[0002]

2. Description of the Related Art FIG. 3 shows a schematic configuration of a conventional electric power steering apparatus. Further, FIG. 4 shows an example of a drive control procedure of the electric motor. The electric power steering apparatus detects a torque sensor 2 that detects a steering torque applied to a steered wheel, a vehicle speed sensor 7 that detects a vehicle speed, a drive circuit 4 that drives an electric motor 5, and a motor current of the electric motor 5. CPU to which an electric current detection circuit 6 that operates and an angular acceleration detection circuit 26 that detects the angular acceleration of the electric motor 5 are connected
1 for controlling the drive of the electric motor 5 based on the steering torque and the vehicle speed, the motor current and the angular acceleration. The torque sensor 2 and the vehicle speed sensor 7 have interfaces 3 and 8 respectively.
Is connected to the CPU 1 via. The steering torque is detected based on the twist angle of a connecting shaft (torsion bar) that connects the input shaft connected to the steered wheels and the output shaft connected to the steering mechanism.

The CPU 1 operates as an A / D conversion means 11 and A / D converts the detection signal of the torque sensor 2. Since the input shaft and the output shaft are connected by a torsion bar, a delay in rotation may occur between the two shafts, which may cause vibration. Therefore, phase compensation is performed to compensate for the rotation delay. The CPU 1 operates as the phase compensating means 12 to perform phase compensation of the A / D converted steering torque (S10). The CPU 1 operates as the vehicle speed calculation means 9,
The vehicle speed is obtained from the detection signal of the vehicle speed sensor 7 (S12).

The memory of the CPU 1 stores a table 13 in which the relationship between the steering torque and the vehicle speed and the drive current (target current) of the electric motor 5 is set. Table 13
The horizontal axis of is the steering torque (T), and the vertical axis is the target current (I). The CPU 1 reads the target current corresponding to the steering torque and the vehicle speed, which have been phase-compensated (S14).

The CPU 1 operates as the A / D conversion means 24 and A / D converts the detection signal of the angular acceleration detection circuit 26. The CPU 1 operates as the multiplying unit 22, and multiplies the current corresponding to the angular acceleration of the electric motor 5 by the gain G to obtain the inertia compensation current (S20). The CPU 1 sets the value of the gain G according to the vehicle speed. The CPU 1 uses the adding means 14
And adds the inertia compensation current to the read target current (S22).

The CPU 1 operates as A / D conversion means 19 and A / D converts the detection signal of the current detection circuit 6. CP
U1 operates as the subtraction means 15 and obtains the difference between the motor current and the target current to which the inertia compensation current is added (hereinafter referred to as the corrected target current) (S24). The CPU 1 operates as the PI calculation means 16 and performs PI calculation on the obtained difference (S2
6) Determine the voltage (target voltage) to be applied to the electric motor 5.

FIG. 5 shows the processing procedure of the PI calculation by the CPU 1.
Shown in. After obtaining the difference ΔI _n ΔI _n = I _M −I _S between the target current I _M and the motor current I _S (S1), the integral element I _n I _n = ΔI _n × K _I (K _I : constant) is calculated. Yes (S2).

Next, the calculated difference ΔI _n and the previously calculated difference ΔI _n
After calculating the difference _{ΔP n ΔP n = ΔI n -ΔI} n-1 and _n-1 (S3), a proportional element _{P n P n = ΔP n ×} K P (K P: constant) is calculated (S4) .

[0009] Then, the target voltage V to be applied to the electric motor _{5 M V M = {(V} 0 + I n + P n) + V 0} / 2 (V 0:
After calculating the previous target voltage) (S5), V ₀ and ΔI _n-1 are set to V _M and Δ
It is updated to I _n (S6).

The CPU 1 operates as the PWM means 17,
The duty ratio of the PWM signal is determined so that the voltage applied to the electric motor 5 becomes the calculated target voltage V _M. C
PU1 (PWM means 17) outputs P according to the target voltage V _M.
The WM signal and the signal indicating the rotation direction of the electric motor 5 are set to 4
The electric current is supplied to the drive circuit 4 which forms an H-type bridge with one switch transistor (S28) to drive the electric motor 5.

[0011]

The electric power steering apparatus has a high rate of change of the drive current with respect to the steering torque (hereinafter referred to as assist gain) at the time of stop and low speed running. However, when the assist gain is high, phase compensation is performed. Of the steering wheel is apt to occur and the vibration of the steering wheel is likely to occur, which often gives the driver an unpleasant feeling. By reducing the assist gain, the above-mentioned vibration of the steering wheel can be suppressed, but since the correction drive is reduced, the steering assist force is reduced,
The handle becomes heavy.

The present invention has been made in view of the above circumstances, and the inertia compensation current is changed so that the phase compensation functions by providing the changing means for changing the inertia compensation current as the assist gain increases. An object of the present invention is to provide an electric power steering device capable of preventing vibration of a steering wheel.

Further, according to the present invention, the inertia compensation current is set by multiplying the current corresponding to the rotational inertia of the electric motor by the gain G, and the changing means is provided for changing the gain G as the assist gain increases. Accordingly, it is an object of the present invention to provide an electric power steering device capable of changing the gain G so that the phase compensation functions and preventing the vibration of the steering wheel.

Further, according to the present invention, by providing a table in which the correspondence between the assist gain and the gain G of the inertia compensation current is set, the gain G corresponding to the assist gain is obtained so that the phase compensation functions. An object of the present invention is to provide an electric power steering device that can change the inertia compensation current and prevent the steering wheel from vibrating.

Further, according to the present invention, the current corresponding to the angular acceleration of the electric motor is used as the current corresponding to the inertia of the rotation of the electric motor, so that the inertia of the rotation is compensated and the drag feeling during steering is improved. It is an object of the present invention to provide an electric power steering device capable of performing the above.

[0016]

An electric power steering apparatus according to a first aspect of the present invention includes a means for setting a drive current of an electric motor for steering assistance according to a torque applied to a steered wheel, and a rotation of the electric motor. And a means for setting an inertia compensation current according to the inertia of the electric power steering apparatus for driving the electric motor with a correction drive current obtained by adding the inertia compensation current to the drive current. Is provided with a changing unit that changes the inertia compensation current so that the correction drive current decreases as the rate of change increases.

In this electric power steering system, the changing means changes the setting of the inertia compensation current so that the correction driving current decreases as the rate of change (assist gain) of the driving current with respect to the steering torque increases. Here, the correction driving current to be reduced is an absolute value, and the absolute value of the inertia compensation current having the same sign as the correction driving current is decreased to reduce the absolute value of the correction driving current. Hereinafter, a case where the correction drive current and the inertia compensation current are positive will be described. The resonance frequency formed by the inertia of rotation of the handle and the electric motor and the rigidity of the torsion bar is approximately proportional to the square root of the spring constant and approximately inversely proportional to the square root of the moment of inertia. Therefore, when the inertia decreases, the resonance frequency becomes high, and the phase compensation may not function. When the assist gain is high, the phase compensation function deteriorates and steering wheel vibration easily occurs.However, the phase compensation is performed by changing the inertia compensation current by the changing means to increase the apparent inertia and lower the resonance frequency. It can be made to function and prevent vibration of the handle.

An electric power steering apparatus according to a second aspect of the present invention is the electric power steering apparatus according to the first aspect, wherein the means for setting the inertia compensation current sets the inertia compensation current by multiplying the current according to the inertia of rotation of the electric motor by a gain. Is configured to
The changing means is configured to change the gain to change the inertia compensation current.

Since this electric power steering apparatus sets the inertia compensation current by multiplying the current according to the inertia of the rotation of the electric motor by the gain, the changing means changes the gain to change the inertia compensation current. be able to. When the assist gain is high, the inertia compensation current can be reduced to make the phase compensation function, and the vibration of the steering wheel can be prevented.

An electric power steering apparatus according to a third aspect of the invention is the electric power steering apparatus according to the second aspect of the invention, in which the rate of change is obtained from a table in which the correspondence relationship between the rate of change and the set value of the gain is set, and the torque and the drive current. And a means for obtaining a set value corresponding to the obtained change rate based on the correspondence relationship, wherein the changing means is arranged to change the gain to the obtained set value. .

In this electric power steering apparatus, the gain setting value is obtained by the setting value obtaining means on the basis of the change rate obtained by the change rate obtaining means and the correspondence relationship in the table. The changing unit changes the gain that is multiplied by the current according to the rotational inertia of the electric motor to the obtained set value. By changing the gain, it is possible to change the inertia compensating current when the assist gain is high so as to function the phase compensation and prevent the vibration of the steering wheel.

An electric power steering apparatus according to a fourth aspect of the present invention is the electric power steering apparatus according to the second or third aspect, wherein the current according to the inertia is a current according to the angular acceleration of the electric motor.

This electric power steering apparatus multiplies the current corresponding to the angular acceleration of the electric motor by a gain to generate an inertia compensation current. By driving the electric motor with the correction drive current to which the inertia compensation current according to the inertia of rotation is added, the inertia of rotation can be compensated and the drag feeling during steering can be improved. Further, by the above-mentioned changing means, when the assist gain is high, it is possible to change the inertia compensation current to make the phase compensation function and prevent the vibration of the steering wheel.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. FIG. 1 shows a schematic configuration of an electric power steering device of the present invention. The electric power steering apparatus detects a torque sensor 2 that detects a steering torque applied to a steered wheel, a vehicle speed sensor 7 that detects a vehicle speed, a drive circuit 4 that drives an electric motor 5, and a motor current of the electric motor 5. Current detection circuit 6 for
Angular acceleration detection circuit 2 for detecting the angular acceleration of the electric motor 5
6 is connected to the CPU 1, and the drive control of the electric motor 5 is performed based on the steering torque, the vehicle speed, the angular acceleration, and the motor current. The torque sensor 2 and the vehicle speed sensor 7 are connected to the CPU 1 via interfaces 3 and 8, respectively.

The CPU 1 operates as the A / D conversion means 11 and A / D converts the detection signal of the torque sensor 2. CP
U1 operates as the phase compensating means 12 and performs phase compensation of the A / D converted steering torque. The CPU 1 operates as the vehicle speed calculation means 9 and obtains the vehicle speed from the detection signal of the vehicle speed sensor 7. The memory of the CPU 1 stores a table 13 in which the relationship between the steering torque and the vehicle speed and the drive current (target current) of the electric motor 5 is set. The horizontal axis of the table 13 is the steering torque (T), and the vertical axis is the target current (I). The CPU 1 reads out the target current according to the steering torque and the vehicle speed that have been phase-compensated.

The CPU 1 operates as the change rate calculating means 34 to obtain the change rate (assist gain) of the target current with respect to the A / D converted steering torque. The assist gain is
It can be obtained from the detected value and target current value of the steering torque this time and the detected value and target current value of the previous steering torque. The memory of the CPU 1 has an assist gain and a gain G.
A table 30 in which the relationship with is set is stored.
The horizontal axis of the table 30 is the assist gain (D), and the vertical axis is the gain (G). The CPU 1 reads the gain G corresponding to the assist gain.

The correspondence between the steering torque and the target current in the table 13 is set so that the assist gain increases as the steering torque increases. In addition, in the correspondence relationship between the assist gain and the gain G of the table 30,
The gain G is set to decrease as the assist gain increases.

The CPU 1 operates as A / D conversion means 19 and A / D converts the detection signal of the current detection circuit 6. The CPU 1 also operates as the A / D conversion means 24, and A / D converts the detection signal of the angular acceleration detection circuit 26. CPU
1 operates as the multiplication means 32 and reads the gain G
Is multiplied by the current corresponding to the angular acceleration to obtain the inertia compensation current. Further, the CPU 1 operates as the adding means 14 to obtain the sum of the read target current and inertia compensation current. Hereinafter, the target current to which the inertia compensation current is added is called a corrected target current.

The CPU 1 operates as the subtracting means 15,
Find the difference between the corrected target current and the motor current. CPU1
Operates as the PI calculation means 16, performs PI calculation on the obtained difference, and determines the voltage (target voltage) to be given to the electric motor 5. The processing procedure of the PI calculation is the same as the conventional one (FIG. 5).

The CPU 1 operates as the PWM means 17,
The duty ratio of the PWM signal is determined so that the voltage applied to the electric motor 5 becomes the target voltage obtained by the PI calculation. The CPU 1 (PWM means 17) outputs a PWM signal corresponding to the target voltage and a signal indicating the rotation direction of the electric motor 5,
The electric motor 5 is driven by applying it to the drive circuit 4 which has an H-shaped bridge composed of four switch transistors.

The gain G is set so that the inertia compensation current is decreased to increase the apparent inertia and the resonance frequency is decreased to perform the phase compensation as the assist gain increases.

Next, the operation of the electric power steering apparatus according to the present invention will be described. FIG. 2 shows an example of the drive control procedure of the electric motor. Based on the detection signal of the torque sensor 2, the CPU 1 phase-compensates the steering torque (S
10). Further, based on the detection signal of the vehicle speed sensor 7, C
The vehicle speed is calculated by PU1 (S12). The CPU 1 reads the target current corresponding to the steering torque and the vehicle speed with reference to the table 13 (S14).

The CPU 1 obtains the rate of change of the target current with respect to the steering torque (assist gain) (S16), and with reference to the table 30, reads the gain G corresponding to the obtained assist gain (S18). The CPU 1 multiplies the current corresponding to the angular acceleration by the gain G to obtain the inertia compensation current (S
20) and add the obtained inertia compensation current to the target current (S2
2) Find the corrected target current. The CPU 1 obtains a difference between the motor current and the correction target current (S24), performs PI calculation based on the obtained difference (S26), and generates a drive signal. The CPU 1 applies the generated drive signal to the drive circuit 4 (S28) to drive the electric motor 5.

The gain G of the table 30 decreases as the assist gain increases. When the assist gain is high, the inertia compensation current is decreased to increase the apparent inertia, and the resonance frequency is decreased to perform the phase compensation. Make it work.
Since the phase compensation functions, the handle vibration can be prevented.

In the above-described embodiment, the current according to the angular acceleration of the electric motor is used as the current according to the inertia. However, for example, the current according to the angular acceleration of the steering wheel can be used. Alternatively, the rate of change of the target current with respect to the steering torque may be obtained in advance from the table 13 and the correspondence relationship between the steering torque and the differential value (rate of change) may be set to obtain the rate of change corresponding to the steering torque. it can.

[0036]

According to the electric power steering apparatus of the first aspect of the invention, as the rate of change (assist gain) of the drive current with respect to the steering torque increases, the changing means decreases the correction drive current so that the inertia compensation current is reduced. Change the setting. When the assist gain is high, the function of phase compensation deteriorates and steering wheel vibration easily occurs, but the inertia compensation current is decreased by the changing means to increase the apparent inertia to lower the resonance frequency and make the phase compensation function. Vibration of the steering wheel can be prevented.

According to the electric power steering apparatus of the second aspect of the invention, since the current corresponding to the inertia of the rotation of the electric motor is multiplied by the gain to set the inertia compensation current, the changing means changes the gain to change the inertia. The compensation current can be changed. When the assist gain is high, the inertia compensation current can be reduced to make the phase compensation function, and the vibration of the steering wheel can be prevented.

According to the electric power steering apparatus of the third aspect of the present invention, the setting value of the gain of the inertia compensation current is set by the means for obtaining the set value on the basis of the correspondence between the change rate and the set value obtained by the means for obtaining the change rate. Ask for. The changing unit changes the gain that is multiplied by the current according to the rotational inertia of the electric motor to the obtained set value. By changing the gain, it is possible to change the inertia compensating current when the assist gain is high so as to function the phase compensation and prevent the vibration of the steering wheel.

According to the electric power steering apparatus of the fourth aspect of the present invention, the current corresponding to the angular acceleration of the electric motor is multiplied by the gain to generate the inertia compensation current. By driving the electric motor with the correction drive current to which the inertia compensation current according to the inertia of rotation is added, the inertia of rotation can be compensated and the drag feeling during steering can be improved. Further, by the above-mentioned changing means, when the assist gain is high, it is possible to change the inertia compensation current to make the phase compensation function and prevent the vibration of the steering wheel.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an electric power steering device of the present invention.

2 is a flowchart showing an example of a drive control procedure of an electric motor of the electric power steering apparatus shown in FIG.

FIG. 3 is a block diagram showing a configuration example of a conventional electric power steering device.

4 is a flowchart showing an example of a drive control procedure of an electric motor of the electric power steering device shown in FIG.

5 is a PI of the electric power steering apparatus shown in FIG.
It is a flowchart which shows an example of a calculation procedure.

[Explanation of symbols]

1 CPU 2 Torque sensor 5 electric motor 30 tables 26 Angular acceleration detection circuit

Claims (4)

[Claims] 1. A means for setting a drive current of an electric motor for steering assistance according to a torque applied to a steered wheel, and a means for setting an inertia compensation current according to an inertia of rotation of the electric motor. In an electric power steering device that drives the electric motor with a correction drive current obtained by adding the inertia compensation current to the drive current, the correction drive current decreases as the rate of change of the drive current with respect to the torque increases. As described above, the electric power steering apparatus comprising the changing means for changing the inertia compensation current. 2. The means for setting the inertia compensation current is configured to set the inertia compensation current by multiplying a current according to the inertia of rotation of the electric motor by a gain, and the changing means sets the gain compensation current. A change is made so as to change the inertia compensation current.
The electric power steering device described. 3. A table in which a correspondence relationship between the change rate and the set value of the gain is set, a means for obtaining the change rate from the torque and the drive current, and a set value corresponding to the obtained change rate, 3. The electric power steering apparatus according to claim 2, further comprising means for obtaining the gain based on the correspondence relationship, wherein the changing means is configured to change the gain to the obtained set value. 4. The electric power steering apparatus according to claim 2, wherein the current according to the inertia is a current according to angular acceleration of the electric motor.