JP2004217085A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of giving proper steering auxiliary power in correspondence with acceleration of a vehicle to a steering mechanism while preventing undesired correction of a target driving value. <P>SOLUTION: A target electric current value setting part 21 sets a target electric current value in accordance with car velocity and steering torque. An acceleration gain setting part 25 sets acceleration gain in correspondence with acceleration of the vehicle and a correction part 26 corrects the target electric current value by multiplying the target electric current value by the acceleration gain. The electric motor M is controlled in accordance with the target electric current value after this correction. The acceleration gain setting part 25 specifies the acceleration gain in accordance with an acceleration gain map specified to limit correction of the target driving value at the time when the acceleration absolute value exceeds a specified value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device configured to transmit driving force of an electric motor to a steering mechanism to assist steering.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering device that assists steering by transmitting a torque generated by an electric motor to a steering mechanism of a vehicle has been used. The drive of the electric motor is controlled based on a target current value determined according to the steering torque applied to the steering wheel and the vehicle speed.
As the vehicle accelerates and decelerates, the shared load on the front shaft on which the steering mechanism is disposed changes. That is, when the vehicle accelerates, the load on the front shaft decreases due to the load movement from the front wheel side to the rear wheel side. On the other hand, when the vehicle decelerates, the load moves from the rear wheel side to the front wheel side, and the front axle load increases. For this reason, the steering force is reduced particularly at the time of rapid acceleration, and the steering force is increased at the time of sudden deceleration, so that the steering feeling changes according to the acceleration and deceleration of the vehicle.
[0003]
Therefore, it has been proposed to correct a target drive value for driving an electric motor in accordance with the acceleration of a vehicle (Japanese Patent Application Laid-Open No. H11-163873).
[0004]
[Patent Document 1]
JP 2000-142442 A
[Problems to be solved by the invention]
However, for example, when the acceleration of the vehicle is calculated using the output signal of the vehicle speed sensor, if the vehicle speed sensor fails or a failure such as a disconnection occurs in the transmission path of the output signal of the vehicle speed sensor, the vehicle speed becomes such. Due to the failure of the sensor system, the absolute value of the acceleration obtained by the calculation becomes extremely large. When the target drive value is corrected based on the acceleration having such a large absolute value, useless correction is performed on the target drive value, and as a result, the steering feeling is significantly deteriorated.
[0006]
Of course, the electric power steering system is provided with fail-safe control that detects a failure of the vehicle speed sensor system and limits or stops the driving of the electric motor. However, after the failure determination of the vehicle speed sensor system is performed, fail-safe control is performed. Unnecessary corrections to the target drive value are performed during the period until the processing is performed, thereby causing a feeling of steering discomfort.
Therefore, an object of the present invention is to provide an electric power steering apparatus that can provide an appropriate steering assist force to a steering mechanism according to the acceleration of a vehicle while preventing an undesired correction of a target drive value. That is.
[0007]
Means for Solving the Problems and Effects of the Invention
According to an embodiment of the present invention, there is provided an electric power steering apparatus for transmitting a driving force of an electric motor (M) to a steering mechanism (3) to assist in steering, and detects a steering state. A steering state detection means (5) for outputting a steering state detection signal, and a target drive value setting means (21) for setting a target drive value of the electric motor based on the steering state detected by the steering state detection means. Acceleration detection means (24) for detecting the acceleration of a vehicle on which the electric power steering device is mounted; and a target drive value set by the target drive value setting means according to the acceleration detected by the acceleration detection means. An acceleration adaptive correction means (25, 26) for correcting the electric motor based on the target drive value corrected by the acceleration adaptive correction means. Motor drive means (27, 30) and correction limiting means (25) for limiting the correction of the target drive value by the acceleration adaptive correction means when the absolute value of the acceleration detected by the acceleration detection means is equal to or greater than a predetermined value. And an electric power steering device.
[0008]
It should be noted that the alphanumeric characters in parentheses indicate corresponding components and the like in embodiments described later. Hereinafter, the same applies in this section.
According to the present invention, the target drive value of the electric motor is corrected according to the acceleration of the vehicle (mainly, the longitudinal acceleration), so that a good steering feeling can be obtained regardless of the acceleration of the vehicle. When the absolute value of the acceleration is equal to or greater than the predetermined value, the correction of the target drive value according to the vehicle acceleration is limited. Therefore, when the acceleration detection means cannot accurately detect the acceleration of the vehicle, the target drive value is corrected. Undesired correction to the value can be suppressed. As a result, even when a problem occurs in the detection of the acceleration of the vehicle by the acceleration detection means, a feeling of strange steering does not occur, so that a good steering feeling can be obtained.
[0009]
Note that the steering state detection means may be a torque sensor that detects a steering torque applied to an operation member (for example, a steering wheel) for steering operation.
Further, it is preferable that the target drive value setting means sets the target drive value based on not only the steering state but also the vehicle speed of the vehicle.
Further, the acceleration detecting means may calculate the acceleration of the vehicle based on the vehicle speed detected by the vehicle speed detecting means, or may directly detect the longitudinal acceleration of the vehicle using an acceleration sensor. Alternatively, the information on the longitudinal acceleration of the vehicle may be obtained based on the output of a vehicle height sensor that detects the vehicle height of the front wheel portion or the rear wheel portion of the vehicle.
[0010]
Furthermore, the acceleration adaptive correction means may correct the target drive value by multiplying the target drive value by an acceleration gain. In this case, the acceleration adaptive correction means may determine the acceleration gain based on an acceleration gain map that determines the acceleration gain for the vehicle acceleration.
The acceleration gain map defines an acceleration gain of 1 or less when the acceleration is positive (ie, during acceleration), and defines an acceleration gain of 1 or more when the acceleration is a negative value (ie, during deceleration). Is preferred. As a result, the steering assist force can be reduced during acceleration and the steering assist force can be increased during deceleration, so that a substantially constant steering feeling can be realized regardless of the acceleration of the vehicle. Further, if an acceleration gain map is set such that the gain is determined to be smaller as the acceleration is larger, a better steering feeling can be realized.
[0011]
Further, it is preferable that the acceleration gain map sets the acceleration gain to “1” regardless of the acceleration value for the acceleration in a predetermined range (dead zone) near zero. By providing a dead zone in this manner, it is possible to prevent the vehicle from being erroneously recognized as accelerating or decelerating, and prevent unnecessary correction to the target drive value.
Further, the acceleration adaptive correction means may determine the acceleration gain in accordance with an acceleration gain map determined so that correction of the target drive value is limited when the absolute value of the acceleration is equal to or greater than a predetermined value. More specifically, the acceleration gain map preferably fixes the acceleration gain to “1” regardless of the acceleration when the absolute value of the acceleration of the vehicle is equal to or greater than a predetermined threshold. Accordingly, when the absolute value of the acceleration is equal to or larger than the predetermined threshold value, the correction to the target drive value is not performed, and as a result, the correction of the target drive value by the acceleration adaptive correction means is prohibited. That is, in this case, a region in the acceleration gain map where the absolute value of the acceleration is equal to or larger than the predetermined threshold value corresponds to the correction restricting unit (in this case, the correction prohibiting unit).
[0012]
Further, it is preferable that the acceleration gain map is set such that, when the absolute value of the acceleration is equal to or larger than a predetermined threshold value, the acceleration gain approaches “1” as the absolute value of the acceleration increases. This limits the correction of the target drive value in a region where the absolute value of the acceleration exceeds a predetermined threshold. That is, a portion of the acceleration gain map that is equal to or larger than the predetermined threshold value corresponds to the correction limiting unit.
[0013]
BEST MODE FOR CARRYING OUT 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 showing an electric configuration of an electric power steering apparatus according to one embodiment of the present invention. A steering torque applied to a steering wheel 1 as an operation member is mechanically transmitted to a steering mechanism 3 via a steering shaft 2. A steering assist force is transmitted from the electric motor M to the steering mechanism 3.
[0014]
The steering shaft 2 is divided into an input shaft 2A connected to the steering wheel 1 and an output shaft 2B connected to the steering mechanism 3. The input shaft 2A and the output shaft 2B are connected to a torsion bar 4. Are connected to each other. The torsion bar 4 generates a twist in accordance with the steering torque, and the direction and amount of the twist are detected by a torque sensor 5.
[0015]
The torque sensor 5 is, for example, a magnetic sensor that detects a magnetic resistance that changes in accordance with a change in the positional relationship between the input shaft 2A and the output shaft 2B in the rotation direction. The output signal of the torque sensor 5 is input to a controller 10 (ECU: electronic control unit).
Further, an output signal of a vehicle speed sensor 7 for detecting a vehicle speed of a vehicle equipped with the electric power steering device is input to the controller 10.
[0016]
The controller 10 determines a target current value of the electric motor M according to the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 7, and applies a steering assist force corresponding to the steering torque to the steering mechanism 3. Drive control of the electric motor M so that
The controller 10 includes a microcomputer 20 and a motor driver 30 that drives the electric motor M based on a control signal from the microcomputer 20.
[0017]
The microcomputer 20 substantially has a plurality of function processing units realized by executing the program processing. Specifically, the microcomputer 20 includes a target current value setting unit 21 that sets a target current value of the electric motor M based on the outputs of the torque sensor 5 and the vehicle speed sensor 7, and each of the torque sensor 5 and the vehicle speed sensor 7. The output signal is fetched, and the abnormality determination unit 22 that determines whether there is an abnormality in the torque sensor 5 or its signal transmission path or the vehicle speed sensor 7 or its signal transmission path, and the abnormality determination unit 22 determines that there is an abnormality. In response to this, a fail-safe control unit 23 that executes a fail-safe process for guiding the target current value to zero to limit or stop driving of the electric motor M is provided. Further, the microcomputer 20 sets an acceleration calculator 24 for calculating the acceleration of the vehicle (longitudinal acceleration) based on the output signal of the vehicle speed sensor 7 and an acceleration gain corresponding to the acceleration calculated by the acceleration calculator 24. An acceleration gain setting unit 25 that performs an acceleration adaptive correction on the target current value by multiplying the target current value set by the target current value setting unit 21 by the acceleration gain set by the acceleration gain setting unit 25 And a control signal generation unit 27 that generates a motor control signal (for example, a PWM (Pulse Width Modulation) control signal) based on the target current value corrected by the correction unit 26. The control signal generated by the control signal generation unit 27 is supplied to the motor driver 30, whereby power is supplied to the electric motor M.
[0018]
FIG. 2 is a diagram for explaining the operation of the target current value setting unit 21, and shows a relationship (assist characteristic) between the steering torque and the target current value. As the steering torque, for example, the torque for steering in the right direction has a positive value, and the torque for steering in the left direction has a negative value. The target current value is a positive value when the electric motor M is to generate a steering assist force for rightward steering, and is negative when the electric motor M is to generate a steering assist force for leftward steering. Value.
[0019]
The target current value has a positive value for a positive value of the steering torque, and has a negative value for a negative value of the steering torque. When the steering torque is a small value in the range (dead zone) of -T1 to T1, the target current value is set to zero. The absolute value of the target current value is set to decrease as the vehicle speed detected by the vehicle speed sensor 7 increases. As a result, a large steering assist force can be generated during low-speed running, and the steering assist force can be reduced during high-speed running.
[0020]
FIG. 3 is a diagram for explaining the operation of the acceleration gain setting unit 25, and shows an example of an acceleration gain map referred to when setting the acceleration gain. The acceleration gain map is a map (table) that defines the characteristics of the acceleration gain with respect to the acceleration of the vehicle, and is stored in a memory in the microcomputer 20 in advance.
In the example of FIG. 3, the acceleration gain is determined so as to monotonously decrease as the acceleration increases in accordance with an acceleration value between a lower threshold value −TH and an upper threshold value + TH (where TH> 0). Have been. A constant acceleration gain “1” is set for the acceleration equal to or less than the lower threshold value −TH and the acceleration equal to or greater than the upper threshold value TH. That is, when the absolute value of the acceleration of the vehicle is equal to or greater than the threshold value TH, the acceleration gain is fixed to “1”, and the correction unit 26 does not perform correction on the target current value. That is, the correction of the target current value based on the acceleration is prohibited.
[0021]
On the other hand, when the acceleration of the vehicle takes a value within a predetermined dead zone DZ near zero, the acceleration gain is fixed to “1” regardless of the acceleration value. As a result, the target current value based on the acceleration is not corrected for the acceleration value in the dead zone DZ. As a result, it is possible to prevent the target current value from being unnecessarily corrected due to the obtained acceleration error.
A region between the lower threshold value -TH and the dead zone DZ is a region (sudden deceleration region) A1 corresponding to a case where the vehicle is rapidly decelerating. In the rapid deceleration region A1, the acceleration gain is determined to decrease monotonically (in the example of FIG. 3, linearly) from a predetermined upper limit value UL (> 1) to “1”. Further, an acceleration region between the dead zone DZ and the upper threshold TH is a region (rapid acceleration region) A2 corresponding to a case where the vehicle is rapidly accelerating. In the rapid acceleration region A2, the acceleration gain is determined to decrease monotonically (linearly in the example of FIG. 3) from “1” to a predetermined lower limit LL (<1).
[0022]
An acceleration gain is determined based on such an acceleration gain map, and by multiplying the acceleration gain by a target current value, an almost constant steering load can be obtained regardless of a change in the front shaft shared load accompanying the acceleration or deceleration of the vehicle. It can be realized and a good steering feeling can be obtained. In particular, since the change in the steering force at the time of sudden acceleration and sudden deceleration can be reduced, the safety at the time of steering for emergency avoidance can be improved, and the steering feeling can be improved.
[0023]
Further, when the absolute value of the acceleration is equal to or larger than the threshold value TH, the acceleration gain is fixed at "1" and the correction of the target current value according to the acceleration is prohibited. In the case where the acceleration calculated by the acceleration calculation unit 24 has an extremely large abnormal value, it is possible to prevent the correction of the target current value based on such an abnormal value, and it is possible to prevent the occurrence of steering discomfort.
The abnormality of the vehicle speed sensor system is determined by the abnormality determination unit 22, and fail-safe control is performed by the fail-safe control unit 23 based on the determination result. Further, a certain time is also required for the fail-safe processing by the fail-safe control unit 23. During this time, if the target current value is corrected based on the abnormal value obtained by the acceleration calculation unit 24, a feeling of steering discomfort will occur. Such a situation can be reliably avoided by determining the acceleration gain according to the acceleration gain map shown in FIG.
[0024]
As described above, one embodiment of the present invention has been described, but the present invention can be embodied in other forms. For example, in the example of FIG. 3, the acceleration gain map is defined as a polygonal line obtained by connecting the line segments. However, as illustrated in FIG. It may be.
In the acceleration gain maps shown in FIGS. 3 and 4, the acceleration gain is fixed to “1” in a region equal to or lower than the lower threshold value −TH and in a region equal to or higher than the upper threshold value TH. 3 and FIG. 4, as indicated by a two-dot chain line, a second upper threshold TH1 (> TH) larger than the upper threshold TH, and a second lower threshold smaller than the lower threshold −TH. Value -TH1, and the acceleration gain is set so as to approach "1" from the lower limit value LL with an increase in acceleration in a region between the upper threshold value TH and the second upper threshold value TH1. May be determined. Similarly, in a region between the lower limit threshold value -TH and the second lower limit threshold value -TH1, the acceleration value decreases from the upper limit value UL to "1" as the acceleration decreases (the absolute value of the acceleration increases). The acceleration gain may be determined as described above.
[0025]
In the above-described embodiment, the target current value is used as the target drive value for controlling the electric motor M. However, the target torque value that is the target value of the target voltage value or the target value of the steering assist force is used as the target drive value. May be used.
In addition, various design changes can be made within the scope of the matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an electric configuration of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining an operation of a target current value setting unit, and shows a relationship (assist characteristic) of a target current value with respect to a steering torque.
FIG. 3 is a diagram illustrating an example of an acceleration gain map.
FIG. 4 is a diagram showing another example of an acceleration gain map.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 steering wheel 2 steering shaft 3 steering mechanism 4 torsion bar 5 torque sensor 7 vehicle speed sensor 10 controller 20 microcomputer 21 target current value setting unit 22 abnormality determination unit 23 failsafe control unit 24 acceleration calculation unit 25 acceleration gain setting unit 26 correction unit 27 Control signal generator 30 Motor driver TH, TH1 Upper threshold value -TH, -TH1 Lower threshold value A1 Sudden deceleration region A2 Sudden acceleration region DZ Dead zone UL Upper limit value LL Lower limit value M Electric motor

Claims (1)

An electric power steering device that transmits a driving force of an electric motor to a steering mechanism to assist in steering,
Steering state detection means for detecting a steering state and outputting a steering state detection signal;
Target drive value setting means for setting a target drive value of the electric motor based on the steering state detected by the steering state detection means;
Acceleration detection means for detecting the acceleration of a vehicle equipped with the electric power steering device;
Acceleration adaptive correction means for correcting the target drive value set by the target drive value setting means according to the acceleration detected by the acceleration detection means,
Motor drive means for driving the electric motor based on the target drive value corrected by the acceleration adaptive correction means,
An electric power steering apparatus, comprising: a correction limiting unit that limits correction of a target drive value by the acceleration adaptive correction unit when an absolute value of the acceleration detected by the acceleration detection unit is equal to or greater than a predetermined value.

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