JP3935383B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device that assists steering by transmitting torque generated by an electric motor to a steering mechanism.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering device that transmits a driving force generated by an electric motor to a steering mechanism, thereby assisting a driver's steering operation has been used. The electric motor is controlled by an electronic control unit (ECU) for the electric power steering device based on the steering torque applied to the steering wheel, the vehicle speed, and the like.
[0003]
[Problems to be solved by the invention]
When the vehicle is traveling on an uneven road surface such as a gravel road (unpaved road), if the steering wheel enters a small hole or rides on a pebble, reverse input from the road surface (road reaction force) The steering wheel may be directed in a direction not intended by the driver. Such a road surface reaction force is transmitted to the steering wheel via the steering mechanism, so that the steering operability is deteriorated and the driver may feel uncomfortable or the stability of steering may be impaired.
[0004]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric power steering apparatus in which a road surface reaction force input to a steering mechanism is canceled by a steering assist force, thereby improving steering feeling and steering stability.
[0005]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, an invention according to claim 1 is an electric power steering device for assisting steering by applying a torque generated from an electric motor (M) to a steering mechanism (12, 13, 14). Steering torque detecting means (31) for detecting the steering torque applied to the operating member (11) for steering the steering, and the assist to be given to the steering mechanism in accordance with the steering torque detected by the steering torque detecting means Assist torque setting means (212) for determining torque (T), current detection means (211) for detecting the motor current flowing in the electric motor, and the change acceleration of the motor current detected by the current detection means, By multiplying the change acceleration of the motor current by a predetermined coefficient, the road surface reaction force input from the road surface to the steering mechanism is combined. The cancellation torque setting means (214) for determining the road surface reaction force cancellation torque (Ta) for adding the assist torque determined by the assist torque setting means and the addition of the road surface reaction force cancellation torque determined by the cancellation torque setting means An electric power steering apparatus comprising: motor control means (216) for driving and controlling the electric motor based on the value.
[0006]
In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
According to the present invention, while traveling on an uneven road surface such as a gravel road, the road surface reaction force input to the steering mechanism due to the unevenness can be offset by the torque (steering assist force) generated by the electric motor. The road surface reaction force can be prevented from being transmitted to the operation member. Thereby, a steering feeling and a steering stability feeling can be improved.
[0007]
The invention according to claim 2 further includes a filter (213) for removing a component included in a predetermined low frequency range from the motor current detected by the current detecting means, and the canceling torque setting means includes the filter 2. The electric power steering apparatus according to claim 1, wherein a road surface reaction force canceling torque is determined by multiplying a change acceleration of the motor current after passing through a predetermined coefficient.
According to the present invention, the low-frequency component is removed from the motor current detected by the current detection means, so that the road surface reaction force canceling torque is generated based on the change acceleration of the motor current indicating such a low-frequency change. It can be prevented from being set. As a result, when the steering wheel enters a large hole or rides on a large stone, the road surface reaction force is transmitted to the operating member via the steering mechanism, and the fact can be transmitted to the driver.
[0008]
The filter may be a band-pass filter that further removes a noise component from the motor current detected by the current detection means.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. The electric power steering apparatus is configured such that the electronic control unit 21 drives and controls an electric motor M (for example, a brushless motor) based on a steering torque applied from the steering wheel 11 to the steering shaft 12. The steering torque applied to the steering shaft 12 is transmitted to the rack bar 14 via the pinion gear 13 to cause the rack bar 14 to linearly move in the vehicle width direction (longitudinal direction of the rack bar 14). The linear motion of the bar 14 is converted into the steering force of the front left and right wheels for steering by a tie rod or a knuckle arm (not shown). Further, the generated torque of the electric motor M is mechanically transmitted to the rack bar 14 via the speed reducer 15 as a steering assist force.
[0010]
In order to detect the steering torque, a torque sensor 31 is provided in association with the steering shaft 12. Specifically, the steering shaft 12 has a configuration in which an input shaft coupled to the steering wheel 11 side and an output shaft provided with the pinion gear 13 are connected by a torsion bar, and the torque sensor 31 includes the steering wheel 11. The direction and magnitude of the twist generated in the torsion bar when the is operated is detected as the steering torque. A signal representing the steering torque detected by the torque sensor 31 is supplied to an electronic control unit (ECU) 21. The electronic control unit 21 is further provided with a detection signal from a vehicle speed sensor 32 that detects the vehicle speed.
[0011]
The electronic control unit 21 includes a microcomputer and the like. The electronic control unit 21 includes a function processing unit realized by program processing by the microcomputer and a hardware configuration for detecting a motor current supplied to the electric motor M. A current detection unit 211.
The function processing unit realized by the program processing includes an assist torque calculation unit 212 that calculates an assist torque T according to the steering torque detected by the torque sensor 31 and the vehicle speed detected by the vehicle speed sensor 32, and a current detection unit 211. In order to cancel the road surface reaction force input from the road surface based on the band-pass filter processing unit (BPF) 213 that performs a predetermined band-pass filter process on the motor current detected in step 213 and the motor current after the band-pass filter process. The road surface reaction force canceling torque calculating unit 214 for calculating the torque Ta of the vehicle, the added value of the assist torque T calculated by the assist torque calculating unit 212 and the road surface reaction force canceling torque Ta calculated by the road surface reaction force canceling torque calculating unit 214 An addition unit 215 that outputs T + Ta, and an addition value T that is output by the addition unit 215 It sets a target current value corresponding to Ta, contains a current controller 216 for feedback control of the current flowing through the electric motor M based on the target current value thereof set.
[0012]
The assist torque calculator 212 calculates an assist torque T according to the steering torque detected by the torque sensor 31 and the vehicle speed detected by the vehicle speed sensor 32 according to a predetermined calculation formula. The calculation formula is determined such that, for example, the value of the assist torque T increases as the steering torque increases or the vehicle speed decreases.
The band-pass filter processing unit 213 performs a predetermined band-pass filter process on the motor current detected by the current detection unit 211, thereby removing noise components from the motor current detected by the current detection unit 211 and steering. The components contained in the frequency range (low frequency range) of the motor current change that appears when the wheel for a car enters a large hole or rides on a large stone are removed. That is, the band-pass filter processing unit 213 passes only the motor current included in the frequency range (for example, 3 to 6 Hz) of the motor current change that appears when the wheel enters a small hole or rides on a pebble. Is given to the road surface reaction force canceling torque calculator 214.
[0013]
The road surface reaction force canceling torque calculation unit 214 obtains a change acceleration d ² i / dt ² of the motor current subjected to the band pass filter process, and a constant K (> 0) to the obtained change acceleration d ² i / dt ^2. Is multiplied by the road surface reaction force canceling torque Ta. Then, the calculated road surface reaction force canceling torque Ta is given to the adding unit 215.
The motor current detected by the current detector 211 changes the steering angle of the wheel when the steering wheel enters a small hole or rides on a pebble while traveling on a rough road such as a gravel road. Accordingly, the motor current flowing through the electric motor M changes. Specifically, when the wheel enters a small hole, the road surface reaction force in the direction of assisting the steering assist force at that time is input to the wheel, and as a result, the motor current flowing through the electric motor M is reduced. The current change acceleration d ² i / dt ² takes a negative value. On the other hand, when the wheel rides on a pebble, the road surface reaction force in the direction opposite to the steering assist force at that time is input to the wheel, and as a result, the motor current flowing through the electric motor M increases, and the motor current change acceleration d ² i / dt ² takes a positive value. Accordingly, the road surface reaction force canceling torque Ta calculated by multiplying the change acceleration d ² i / dt ² of the motor current by a positive constant K is calculated when the wheel enters a small hole or climbs on a pebble. Is set in a direction to cancel the road surface reaction force input to the wheels (steering mechanism).
[0014]
Therefore, a current flowing through the electric motor M is controlled by the current control unit 216 based on the addition value T + Ta of the assist torque T output from the addition unit 215 and the road surface reaction force canceling torque Ta. While traveling on an uneven road surface, the road surface reaction force input to the wheels due to the unevenness can be canceled by the steering assist force generated by the electric motor M, and the road surface reaction force is transmitted to the steering wheel 11. Can be prevented. As a result, the steering feeling and the steering stability can be improved.
[0015]
Further, since the road surface reaction force canceling torque Ta is not set based on a motor current showing a high frequency change like noise, there is no possibility of causing slight vibration of the steering wheel 11 due to noise. Also, it is not set based on the motor current indicating the low frequency change that appears when the wheel enters a large hole or rides on a large stone, so when the wheel enters a large hole or rides on a large stone The road surface reaction force is transmitted to the steering wheel 11 via the wheels, and the fact can be transmitted to the driver.
[0016]
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the addition value T + Ta of the assist torque T calculated by the assist torque calculation unit 212 and the road surface reaction force cancellation torque Ta calculated by the road surface reaction force cancellation torque calculation unit 214 is obtained. Although the target current value corresponding to the value T + Ta is set and the electric motor M is feedback controlled based on the target current value, the target current basic value corresponding to the steering torque is set and the motor current A target current correction value corresponding to the change acceleration d ² i / dt ² is set, and a target current value is set by adding the target current basic value and the target current correction value. Based on this target current value, Further, feedback control of the electric motor M may be performed.
[0017]
Further, the configuration in which the steering wheel 11 is employed as the operation member has been described as an example, but in addition to this, a linearly operated lever, a pedal operated by a foot, or the like may be used as the operation member.
Furthermore, the band-pass filter processing unit 213 performs band-pass filter processing on the motor current detected by the current detection unit 211 and is implemented as software. However, the band-pass filter processing unit 213 includes hardware including resistors and capacitors. A band-pass filter circuit having a wear configuration may be used.
[0018]
In addition, various design changes can be made within the scope of matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Steering shaft 13 Pinion gear 14 Rack bar 21 Electronic control unit 31 Torque sensor 211 Current detection part 212 Assist torque calculation part 213 Band pass filter process part 214 Road surface reaction force cancellation torque calculation part 215 Addition part 216 Current control part M Electric motor

Claims (2)

An electric power steering device for assisting steering by giving a torque generated from an electric motor to a steering mechanism,
Steering torque detection means for detecting a steering torque applied to an operating member for steering the vehicle;
Assist torque setting means for determining assist torque to be applied to the steering mechanism in accordance with the steering torque detected by the steering torque detection means;
Current detecting means for detecting a motor current flowing in the electric motor;
The change acceleration of the motor current detected by the current detection means is obtained and the change acceleration of the motor current is multiplied by a predetermined coefficient, thereby canceling the road reaction force input to the steering mechanism from the road surface. Canceling torque setting means for determining force canceling torque;
Motor control means for drivingly controlling the electric motor based on an added value of the assist torque determined by the assist torque setting means and the road surface reaction force cancellation torque determined by the cancellation torque setting means. Electric power steering device. A filter for removing a component included in a predetermined low frequency range from the motor current detected by the current detection means;
2. The electric power steering according to claim 1, wherein the cancellation torque setting means determines the road surface reaction force cancellation torque by multiplying a change coefficient of the motor current after passing through the filter by a predetermined coefficient. apparatus.

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