JP4042570B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device configured to assist steering by transmitting a driving force of an electric motor to a steering mechanism.
[0002]
[Prior art]
Conventionally, an electric power steering device that assists steering by transmitting torque generated by an electric motor to a steering mechanism of a vehicle has been used. The electric motor is driven and controlled based on a target current value determined in accordance with a steering torque applied to the steering wheel and a vehicle speed.
Along with the acceleration and deceleration of the vehicle, the shared load on the front shaft side where the steering mechanism is arranged changes. That is, when the vehicle is accelerated, the front axle load is reduced by 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. Therefore, the steering force becomes light especially during sudden acceleration, and conversely, the steering force becomes heavy during sudden deceleration, so that the steering feeling changes according to the acceleration / deceleration of the vehicle.
[0003]
Therefore, it has been proposed to correct the target drive value for driving the electric motor in accordance with the acceleration of the vehicle (Patent Document 1 below).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-142442
[Problems to be solved by the invention]
However, for example, when calculating the acceleration of the vehicle using the output signal of the vehicle speed sensor, if the vehicle speed sensor fails or a failure occurs in the transmission path of the output signal of the vehicle speed sensor, such vehicle speed Due to the failure of the sensor system, the absolute value of acceleration obtained by calculation becomes extremely large. When the target drive value is corrected based on the acceleration having such a large absolute value, unnecessary 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 device is provided with fail-safe control for detecting or detecting the failure of the vehicle speed sensor system and limiting or stopping the drive of the electric motor. During the period until the process is performed, unnecessary correction of the target drive value is performed, which causes a feeling of strangeness in steering.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric power steering device capable of giving an appropriate steering assist force to a steering mechanism in accordance with vehicle acceleration while preventing an undesired correction of a target drive value. That is.
[0007]
[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 transmitting a driving force of an electric motor (M) to a steering mechanism (3), which detects a steering state. Steering state detection means (5) for outputting a steering state detection signal, and target driving value setting means (21) for setting the target driving value of the electric motor based on the steering state detected by the steering state detecting means. And an acceleration detection means (24) for detecting the acceleration of the vehicle on which the electric power steering device is mounted, and a target drive value set by the target drive value setting means in accordance with the acceleration detected by the acceleration detection means. Acceleration adaptive correction means (25, 26) for correcting the electric motor, and the electric motor is driven based on the target drive value corrected by the acceleration adaptive correction means. Correction restriction means (25) for restricting correction of the target drive value by the acceleration adaptive correction means when the absolute value of the acceleration detected by the motor drive means (27, 30) and the acceleration detection means is not less than a predetermined value. And an electric power steering device.
[0008]
In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
According to the present invention, since the target drive value of the electric motor is corrected according to the acceleration of the vehicle (mainly the longitudinal acceleration), 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 a predetermined value, the correction of the target drive value according to the vehicle acceleration is limited. Therefore, when the acceleration detection unit cannot accurately detect the vehicle acceleration, It is possible to suppress undesired correction on the value. As a result, even when a failure occurs in the detection of the acceleration of the vehicle by the acceleration detecting means, a sense of steering discomfort does not occur, and a good steering feeling can be obtained.
[0009]
The steering state detecting means may be a torque sensor that detects a steering torque applied to an operation member (for example, a steering wheel) for steering operation.
The target drive value setting means preferably sets the target drive value based not only on the steering state but also on the vehicle speed.
Further, the acceleration detection means may calculate the acceleration of the vehicle based on the vehicle speed detected by the vehicle speed detection means, or directly detect the longitudinal acceleration of the vehicle by an acceleration sensor. Alternatively, vehicle longitudinal acceleration information 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]
Further, 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 in which the acceleration gain with respect to the acceleration of the vehicle is determined.
The acceleration gain map defines an acceleration gain of 1 or less if the acceleration is positive (ie, when accelerating), and defines an acceleration gain of 1 or more if the acceleration is a negative value (ie, when decelerating). 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 the acceleration gain map is set so that the gain becomes smaller as the acceleration increases, a better steering feeling can be realized.
[0011]
In the acceleration gain map, it is preferable that the acceleration gain is set to “1” regardless of the acceleration value for acceleration in a predetermined range (dead zone) near zero. Thus, by providing a so-called dead zone, it is possible to prevent the vehicle from being erroneously recognized as being accelerated or decelerated and to prevent the target drive value from being subjected to unnecessary correction.
Furthermore, the acceleration adaptive correction means may determine the acceleration gain according to an acceleration gain map that is determined so that the 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 value. Thereby, when the absolute value of the acceleration is equal to or greater than the predetermined threshold value, the target drive value is not corrected, 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 where the absolute value of acceleration is equal to or greater than the predetermined threshold in the acceleration gain map corresponds to the correction limiting unit (in this case, correction prohibiting unit).
[0012]
The acceleration gain map is preferably set so that the acceleration gain approaches 1 as the absolute value of the acceleration increases when the absolute value of the acceleration is greater than or equal to a predetermined threshold value. As a result, the correction of the target drive value in the region where the absolute value of the acceleration exceeds a predetermined threshold value is limited. That is, a portion of the acceleration gain map that is equal to or greater than the predetermined threshold corresponds to the correction limiting unit.
[0013]
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 showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. The steering torque applied to the steering wheel 1 as the operation member is mechanically transmitted to the steering mechanism 3 via the 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 coupled to the steering wheel 1 side and an output shaft 2B coupled to the steering mechanism 3 side. The input shaft 2A and the output shaft 2B are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the steering torque, and the direction and amount of the twist are detected by the torque sensor 5.
[0015]
For example, the torque sensor 5 is configured by 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 rotational direction. The output signal of the torque sensor 5 is input to the controller 10 (ECU: electronic control unit).
The controller 10 is further input with an output signal of a vehicle speed sensor 7 that detects the vehicle speed of the vehicle on which the electric power steering device is mounted.
[0016]
The controller 10 determines a target current value of the electric motor M in accordance with the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 7, and a steering assist force corresponding to the steering torque or the like is given to the steering mechanism 3. The electric motor M is controlled to be driven.
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 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 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 taken in, 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 determine that there is an abnormality. In response to this, there is provided a fail-safe control unit 23 that performs a fail-safe process for guiding the target current value to zero to limit or stop the driving of the electric motor M. Further, the microcomputer 20 sets an acceleration calculation unit 24 that calculates the acceleration (front-rear direction acceleration) of the vehicle based on the output signal of the vehicle speed sensor 7 and an acceleration gain corresponding to the acceleration obtained by the acceleration calculation unit 24. An acceleration gain setting unit 25 that performs the acceleration adaptive correction on the target current value by multiplying the acceleration gain set by the acceleration gain setting unit 25 by the target current value set by the target current value setting unit 21 26 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 given to the motor driver 30, whereby the electric motor M is supplied with power.
[0018]
FIG. 2 is a diagram for explaining the function of the target current value setting unit 21, and shows the relationship (assist characteristic) of the target current value with respect to the steering torque. For the steering torque, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The target current value is a positive value when a steering assist force for rightward steering is to be generated from the electric motor M, and is a negative value when a steering assist force for leftward steering is to be generated from the electric motor M. The value of
[0019]
The target current value takes a positive value for a positive value of the steering torque and takes a negative value for a negative value of the steering torque. When the steering torque is a minute value in the range (dead zone) of -T1 to T1, the target current value is set to zero. Further, the absolute value of the target current value is set to be smaller as the vehicle speed detected by the vehicle speed sensor 7 is higher. As a result, a large steering assist force can be generated during low-speed traveling, and the steering assist force can be reduced during high-speed traveling.
[0020]
FIG. 3 is a diagram for explaining the function 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 characteristics of acceleration gain with respect to vehicle acceleration, and is stored in advance in a memory in the microcomputer 20.
In the example of FIG. 3, the acceleration gain is determined so as to monotonously decrease as the acceleration increases according to the acceleration value between the lower limit threshold value −TH and the upper limit threshold value + TH (where TH> 0). It has been. A constant acceleration gain “1” is set for accelerations lower than the lower threshold −TH and accelerations higher than the upper threshold 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 correct 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. Thereby, 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 (rapid deceleration region) A1 corresponding to a case where the vehicle is decelerating rapidly. In this sudden deceleration region A1, the acceleration gain is determined to decrease monotonously (linearly in the example of FIG. 3) from a predetermined upper limit value UL (> 1) to “1”. 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 so as to decrease monotonously (linearly in the example of FIG. 3) from “1” to a predetermined lower limit value LL (<1).
[0022]
By determining the acceleration gain based on such an acceleration gain map and multiplying this acceleration gain by the target current value, an almost constant steering burden can be applied regardless of the change in the front axle load accompanying acceleration or deceleration of the vehicle. This can be realized and a good steering feeling can be obtained. In particular, since the change in steering force during sudden acceleration and sudden deceleration can be reduced, safety during steering for emergency avoidance can be improved, and steering feeling can be improved.
[0023]
Further, when the absolute value of the acceleration is equal to or greater than the threshold value TH, the acceleration gain is fixed to “1” and the correction of the target current value according to the acceleration is prohibited. When the acceleration calculated by the acceleration calculation unit 24 becomes an extremely large abnormal value, correction of the target current value based on such an abnormal value can be prevented, and the uncomfortable feeling of steering can be prevented.
Abnormality of the vehicle speed sensor system is determined by the abnormality determination unit 22, and failsafe control is performed by the failsafe control unit 23 based on the determination result, but a certain time is required until the determination processing by the abnormality determination unit 22 is finalized. Furthermore, the fail-safe process by the fail-safe control unit 23 also requires a certain time. 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 occurs. Such a situation can be reliably avoided by determining the acceleration gain according to the acceleration gain map shown in FIG.
[0024]
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the example of FIG. 3, the acceleration gain map is defined as a polygonal line that combines line segments. However, as shown in FIG. 4, the acceleration gains in the sudden deceleration region A1 and the sudden acceleration region A2 are determined according to a curve. It may be.
In the acceleration gain maps shown in FIGS. 3 and 4, the acceleration gain is fixed to “1” in the region below the lower threshold −TH and the region above the upper threshold TH. 3 and FIG. 4, as indicated by a two-dot chain line, a second upper limit threshold TH1 (> TH) larger than the upper limit threshold TH and a second lower limit threshold smaller than the lower limit threshold −TH. Each value -TH1 is determined, and in the region between the upper threshold value TH and the second upper threshold value TH1, the acceleration gain is set so as to approach “1” from the lower limit value LL as the acceleration increases. It may be determined. Similarly, in the 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 embodiment, the target current value is used as the target drive value for controlling the electric motor M. However, the assist torque target value, which is the target voltage value or the target value of the steering assist force, is used as the target drive value. It may be used.
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 showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the function 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]
DESCRIPTION OF SYMBOLS 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 part 22 Abnormality judgment part 23 Fail safe control part 24 Acceleration calculating part 25 Acceleration gain setting part 26 Correction part 27 Control signal generator 30 Motor driver TH, TH1 Upper threshold value -TH, -TH1 Lower threshold value A1 Rapid deceleration region A2 Rapid acceleration region DZ Dead zone UL Upper limit value LL Lower limit value M Electric motor

Claims (1)

An electric power steering device for assisting steering by transmitting a driving force of an electric motor to a steering mechanism,
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 detecting means for detecting the acceleration of the vehicle on which the electric power steering device is mounted;
Acceleration adaptive correction means for correcting the target drive value set by the target drive value setting means in accordance with 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 acceleration detected by the acceleration detection unit is equal to or greater than a predetermined value.

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