JP2004074983A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform inertia compensation control while inhibiting the impact of disturbance due to the reverse input from a road surface. <P>SOLUTION: A base inertia compensation current value is found based on a motor rotation angular acceleration. A deviation ε between the absolute value of operation angular velocity of a steering wheel 1 and the absolute value of steering angular velocity of a steering mechanism 3 is found, and an inertia compensation gain is found based on the deviation ε. By multiplying the inertial compensation gain by the base inertia compensation current value, a correction value for the inertia compensation control is found. By adding the correction value to a base target current value defined based on a steering torque T and a vehicle velocity V, a target current value for the control of an electric motor M is found. Since the sign of the deviation ε is different between when the steering wheel 1 is operated and when the disturbance from the road surface is input, the impact of the disturbance can be eliminated by appropriately setting the inertial compensation gain corresponding to the deviation ε. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering apparatus that transmits a driving force of an electric motor to a steering mechanism to assist steering.
[0002]
[Prior art]
2. Description of the Related Art An electric power steering apparatus that assists steering by mechanically transmitting a driving force of an electric motor to a steering mechanism has been conventionally used. The electric motor is controlled based on a target current value set according to the steering torque applied to the steering wheel, whereby a steering assist force corresponding to the steering torque is given to the steering mechanism.
[0003]
Since the inertia of the steering mechanism itself and the inertia of an electric motor mechanically coupled to the steering mechanism become a load during steering, inertia compensation control for reducing the steering load due to these inertia may be adopted. Specifically, the rotational angular acceleration of the electric motor is obtained, and inertia compensation control is achieved by adding an inertial compensation current corresponding to the rotational angular acceleration to the target current value.
[0004]
[Problems to be solved by the invention]
However, since the inertia compensation control is a control for increasing the steering assist force in the direction of acceleration of the rotation of the electric motor, disturbance due to reverse input from the road surface is promoted, which causes the vehicle to wobble. There are cases.
Therefore, an object of the present invention is to provide an electric power steering device capable of favorably performing steering assist while suppressing the influence of disturbance due to reverse input from a road surface.
[0005]
Means for Solving the Problems and Effects of the Invention
According to a first aspect of the present invention, a driving force generated by an electric motor (M) controlled according to an operation of an operation member (1) is transmitted to a steering mechanism (3) to perform steering. An assisted electric power steering device, comprising: an operation amount detection means (5) for detecting an operation amount of the operation member; and a target drive value of the electric motor based on the operation amount detected by the operation amount detection means. Basic target drive value setting means (11) for setting a basic target drive value as a basic value, operation angular velocity detection means (21) for detecting the operation angular velocity of the operation member, and steering angular velocity on the steering mechanism side. A steering angular velocity detecting means (22); and the base angular velocity detected by the operating angular velocity detecting means and a steering angular velocity detected by the steering angular velocity detecting means. Correction means (12) for correcting the basic target drive value set by the target drive value setting means to determine a target drive value for controlling the electric motor, and the correction means (12) based on the target drive value determined by the correction means. An electric power steering apparatus, comprising: a motor driving means (15) for driving an electric motor. 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.
[0006]
According to the present invention, the operation angular velocity and the steering angular velocity are detected, and the basic target drive value is corrected according to the deviation to obtain the target drive value. Since the above-mentioned deviation takes different values when the driver operates the operating member and when the disturbance is input from the road surface, the basic target drive value is excluded from the influence of the disturbance input from the road surface. Corrections can be made. That is, for example, since the correction for inertia compensation can be performed only when the driver operates the operating member, the influence of disturbance input from the road surface can be suppressed, and a good steering feeling can be realized.
[0007]
It is preferable that the correction means corrects the basic target drive value based on a deviation between the absolute value of the operation angular velocity and the absolute value of the steering angular velocity.
More specifically, the correcting means sets a basic inertia compensation drive value for compensating, for example, a basic inertia compensation drive value for compensating for inertia of the electric motor and the steering mechanism in accordance with, for example, a rotational angular acceleration of the electric motor. Means (26) and an inertia compensation gain setting for setting an inertia compensation gain to be multiplied by the basic inertia compensation drive value in accordance with a deviation (| operation angular velocity |-| steering angular velocity |) of the operation angular velocity absolute value from the steering angular velocity absolute value. Means (24), multiplication means (27) for obtaining an inertia compensation drive value by multiplying the basic inertia compensation drive value by the inertia compensation gain set by the inertia compensation gain setting means, and the multiplication means obtained by the multiplication means. Adding means (28) for adding the inertia compensation drive value to the basic target drive value.
[0008]
In this case, the inertia compensation gain when the deviation is a positive value takes a first value (G1), when the deviation is a negative value (especially, when the negative threshold epsilon _th following values) Is preferably set to a second value (G2; G2 <G1). Further, for example, the inertia compensation gain takes the first value if the deviation is greater than a predetermined threshold (ε _th, preferably a negative value), and takes the first value if the deviation is smaller than the threshold. It is preferable that the setting is made so as to switch between the first value and the second value near the threshold value so as to take the value of 2. In this case, in order to prevent a sudden change in the inertia compensation gain near the threshold, the inertia compensation gain changes between a first value and a second value at a predetermined gradient with respect to the deviation. It is preferable to do so.
[0009]
When the driver operates the operating member, the absolute value of the operating angular velocity becomes larger than the absolute value of the steering angular velocity, and when there is a disturbance input from the road surface, the absolute value of the steering angular velocity becomes larger than the absolute value of the operating angular velocity. Become. Therefore, by setting the inertia compensation gain as described above, good inertia compensation control can be realized while suppressing or eliminating the influence of disturbance input from the road surface.
It is preferable that a torsion bar (4) elastically twisted and deformed in accordance with torque applied to the operation member or disturbance torque from a road surface is interposed between the operation member and the steering mechanism. The operating angular velocity detecting means detects the operating angular velocity of the operating member on the operating member side of the torsion bar, and the steering angular velocity detecting means detects the steering angular velocity of the steering mechanism on the steering mechanism side of the torsion bar. It is preferable to detect.
[0010]
The steering angular velocity detecting means may detect a back electromotive force of the electric motor and determine a steering angular velocity based on the detected back electromotive force.
Further, a pair of steering angle sensors (6, 7) are provided with the torsion bar interposed therebetween, and the operation angular velocity is obtained based on the output of the steering angle sensor on the operation member side, and based on the output of the steering angle sensor on the steering mechanism side. Alternatively, the steering angular velocity may be obtained by using
The configuration can be simplified by using a sensor (a so-called angle torque sensor) capable of detecting a torque (an example of an operation amount) acting on the operation member and a steering angle on the operation member side and a steering angle on the steering mechanism side. Can be.
[0011]
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 transmitted to a steering mechanism 3 via a steering shaft 2. A driving force generated from the electric motor M is mechanically transmitted to the steering mechanism 3 as a steering assist force via a gear mechanism or by a direct drive method.
[0012]
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 according to the steering torque T, and the direction and amount of the twist are detected by a torque sensor 5. The output signal of the torque sensor 5 is input to the controller 10 (ECU).
[0013]
The controller 10 includes, in addition to the output signal of the torque sensor 5, an operation angle sensor 6 for detecting an operation angle θh as a rotation angle of the steering wheel 1, and a steering angle sensor for detecting a steering angle θp of the steering mechanism 3 side. 7 and a vehicle speed sensor 8 for detecting a vehicle speed V of a vehicle equipped with the electric power steering device. The operation angle sensor 6 detects the rotation angle of the input shaft 2A as the operation angle θh, and the steering angle sensor 7 detects the rotation angle of the output shaft 2B (the pinion when the steering mechanism 3 has a rack-and-pinion mechanism). Is detected as the steering angle θp.
[0014]
When the driver applies torque to the steering wheel 1 to twist the torsion bar 4, the operation angle θh changes prior to the steering angle θp, and when there is a disturbance input from the road surface via the steering mechanism 3, the steering angle θp fluctuates prior to the operation angle θh. If the sign of the deviation ε (= | dθh / dt | − | dθp / dt |) of the absolute value of the operation angular velocity | dθh / dt | with respect to the absolute value of the steering angular velocity | dθp / dt | Can be determined that the steering wheel 1 is operated, and if the sign of the deviation ε is negative, it can be determined that the torsion bar 4 is twisted due to disturbance input from the road surface.
[0015]
The controller 10 supplies a drive current corresponding to the steering torque T detected by the torque sensor 5 and the vehicle speed V detected by the vehicle speed sensor 8 to the electric motor M, and the steering assist force corresponding to the steering torque T and the vehicle speed V is applied to the steering. The drive of the electric motor M is controlled so as to be given to the mechanism 3.
The controller 10 includes a basic target current value setting unit 11 that sets a basic target current value according to the steering torque T and the vehicle speed V by a program process performed by a microcomputer provided therein, and the basic target current value setting unit 11. By performing a correction for inertia compensation control on the basic target current value set by the control unit, each function of the correction unit 12 for setting an appropriate target current value is realized. The motor driver 15 is controlled based on the target current value set by the correction unit 12, and an appropriate drive current is supplied from the motor driver 15 to the electric motor M.
[0016]
The correction unit 12 performs time differentiation of the operation angle θh detected by the operation angle sensor 6 to obtain an operation angular velocity dθh / dt, and performs time differentiation of the steering angle θp detected by the steering angle sensor 7 to perform steering. A steering angular velocity calculator 22 for calculating the angular velocity dθp / dt, and a deviation ε (= | dθh / dt | − | dθp / dt |) of the absolute value | dθh / dt | of the operation angular velocity with respect to the absolute value | dθp / dt | of the steering angular velocity ), And an inertia compensation gain setting unit 24 that sets the inertia compensation gain G based on the deviation ε. The correction unit 12 further detects a back electromotive force of the electric motor M, and estimates a rotation angular acceleration of the electric motor M from the back electromotive force, and a motor rotation angular acceleration calculation unit 25. And a basic inertia compensation current value calculation unit 26 for calculating a basic inertia compensation current value which is a basic value of the inertia compensation current value based on the motor rotation angular acceleration obtained by the above. The correction unit 12 also multiplies the basic inertia compensation current value calculated by the basic inertia compensation current value calculation unit 26 by the inertia compensation gain G set by the inertia compensation gain setting unit 24 to obtain an inertia compensation current value. 27, and an adding unit 28 for adding the inertia compensation current value output from the multiplying unit 27 to the basic target current value set by the basic target current value setting unit 11. By the addition in the adding section 28, a target current value corrected for inertia compensation is obtained, and the motor driver 15 is controlled based on the target current value.
[0017]
FIG. 2 is a diagram for explaining the operation of the basic target current value setting unit 11, and shows the relationship between the steering torque T and the basic target current value. As the steering torque T, 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. Further, the basic target current value is a positive value when the electric motor M is to generate a steering assist force for rightward steering, and when the electric motor M is to generate a steering assist force for leftward steering. Negative value.
[0018]
The basic 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 minute value in the range of -T1 to T1 (for example, T1 = 0.4 Nm) (torque dead zone), the basic target current value is set to zero. The absolute value of the basic target current value is set to be smaller as the vehicle speed V detected by the vehicle speed sensor 8 is higher. 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.
[0019]
FIG. 3 is a diagram showing an example of setting the basic inertia compensation current value by the basic inertia compensation current value calculation unit 26. The rotational angular acceleration of the electric motor M is positive in the right steering direction and negative in the left steering direction. The basic inertia compensation current value is maintained at zero within a predetermined dead zone in which the rotational angular acceleration of the electric motor M is near zero. Outside the dead zone, the basic inertia compensation current value is set so as to increase monotonically as the rotational angular acceleration of the electric motor M increases. That is, as the absolute value of the rotational angular acceleration of the electric motor M increases, the steering load caused by the inertia of the electric motor M and the steering mechanism 3 increases, so that the absolute value of the basic inertia compensation current value increases. Further, the basic inertia compensation current value is set so that its sign is the same as the sign of the motor rotation angular acceleration. As a result, the basic target current value is corrected so as to increase the steering assist force in the direction of the motor rotational angular acceleration.
[0020]
Note that the basic inertia compensation current value calculation unit 26 can be configured using a memory that stores a table corresponding to the characteristics as shown in FIG. 3, or an operation according to a function that realizes the characteristics as shown in FIG. Can be realized by causing a microcomputer to execute.
FIG. 4 is a diagram illustrating an example of setting the inertia compensation gain by the inertia compensation gain setting unit 24. The inertia compensation gain G is set in a range of 0 ≦ G ≦ 1 according to the above-mentioned deviation ε. In this embodiment, around a predetermined threshold value ε _th (in this embodiment, ε _th <0), the inertia compensation gain G includes a first value G1 (= 1) and a second value G2 (0 ≦ G2 <1) is gradually switched at a certain gradient. That is, in a range where the deviation ε is larger than the threshold ε _th + Δε (Δε> 0), the inertia compensation gain G takes a large value G1, and in a range where the deviation ε is smaller than the threshold ε _th −Δε, the inertia compensation gain G becomes Take a small value G2.
[0021]
As described above, when the deviation ε is a positive value, it is considered that the driver is operating the steering wheel 1, and when the deviation ε is a negative value, it is considered that a disturbance input from the road surface has occurred. Therefore, by setting the inertia compensation gain G as described above, when the driver operates the steering wheel 1, the contribution of the inertia compensation current value to the target current value increases. On the other hand, when a disturbance is input from the road surface, the contribution of the inertia compensation current value to the target current value decreases. In this manner, good inertia compensation control can be realized while eliminating the influence of disturbance input from the road surface.
[0022]
Further, in this embodiment, the inertia compensation gain G in smaller ranges than deviation epsilon is the threshold epsilon _th since takes a large value G2 than zero, the reverse input from the road surface is transmitted slightly to the steering wheel 1. Thereby, the driver can feel information such as road surface condition by vibration of the steering wheel 1 or the like.
In the greater range than the deviation epsilon threshold epsilon _th, but deviation epsilon is the inertia compensation gain G be negative there is a taking a large value G1, the absolute value of the deviation epsilon is a small range , Is a small disturbance range, no problem. Of course, in the range where the absolute value of the deviation ε is small, even if the deviation ε is a positive value, the inertia compensation is not so important. Therefore, the inertia compensation gain is determined according to the characteristic shown by the two-dot chain line in FIG. You may do so.
[0023]
The inertia compensation gain setting unit 24 can be configured using a memory that stores a table corresponding to the characteristic as shown in FIG. 4, or a function G = f (ε) realizing the characteristic as shown in FIG. Can be realized by causing a microcomputer to execute the operation according to the following.
As mentioned above, although one Embodiment of this invention was described, this invention can be implemented in another form. For example, in the above embodiment, the torque sensor 5 is provided in addition to the operation angle sensor 6 and the steering angle sensor 7, but the operation angle θh detected by the operation angle sensor 6 and the steering angle detected by the steering angle sensor 7 are provided. Since the difference from θp corresponds to the amount of twist and the direction of the torsion bar 4, for example, a subtraction unit (which may be realized by a program process) for finding the difference between the operation angle θh and the steering angle θp inside the controller 10. ) May be provided, and the output of the subtraction unit may be used as information corresponding to the steering torque T. Accordingly, the cost can be reduced by eliminating the torque sensor 5. For example, by using the configuration shown in Japanese Patent Application Laid-Open No. 2000-352502 (for example, FIG. 3 of the publication), the operation angle θh, the steering angle θp, and the steering torque T can be determined by one sensor (so-called angle torque sensor). Can be detected.
[0024]
In the above embodiment, the rotation angular acceleration of the electric motor M is estimated from the back electromotive force of the electric motor M. However, the steering angle θp detected by the steering angle sensor 7 is second-order time differential (for example, Information corresponding to the rotational angular acceleration of the electric motor M can be obtained by further time-differentiating the output of the angular velocity calculator 22.
Conversely, without providing the steering angle sensor 7, the rotational speed of the electric motor M may be estimated based on the back electromotive force of the electric motor M, and the steering angular speed of the steering mechanism 3 may be obtained based on the estimated rotational speed. it can.
[0025]
Furthermore, since the output characteristics of the electric motor M change with the temperature, the target current value may be corrected according to the temperature of the electric motor M. For example, the temperature TEMP of the electric motor M is detected by a temperature sensor, and the target current value I ₀ is corrected according to the following equation (1) to obtain a corrected target current value I. According to the corrected target current value I, The control of the electric motor M may be performed.
I = I ₀ / {1 + α × (TEMP−TEMP ₀ )} (1)
Here, α (<0) is a temperature correction coefficient (reversible temperature coefficient) of the magnet, and TEMP ₀ represents a reference temperature.
[0026]
Since the generated torque of the electric motor M is proportional to the magnetic flux, and the magnetic flux is proportional to {1 + α × (TEMP−TEMP ₀ )}, the correction according to the above equation (1) makes it possible to reduce the temperature change of the electric motor M. Regardless, excellent steering assist can be realized, and an excellent steering feeling can be realized.
Further, in the above embodiment, the target current value is used as the target drive value for controlling the electric motor M, but the target drive value, which 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.
[0027]
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 electrical configuration of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of a basic target current value setting unit, and shows a relationship between a steering torque and a basic target current value.
FIG. 3 is a diagram showing an example of setting a basic inertia compensation current value by a basic inertia compensation current value calculation unit.
FIG. 4 is a diagram illustrating an example of setting an inertia compensation gain by an inertia compensation gain setting unit.
[Explanation of symbols]
Reference Signs List 1 steering wheel 2 steering shaft 2A input shaft 2B output shaft 3 steering mechanism 4 torsion bar 5 torque sensor 6 operation angle sensor 7 steering angle sensor 8 vehicle speed sensor 10 controller 11 basic target current value setting unit 12 correction unit 15 motor driver 21 operation angular speed Calculation unit 22 Steering angular velocity calculation unit 23 Deviation calculation unit 24 Inertial compensation gain setting unit 25 Motor rotation angular acceleration calculation unit 26 Basic inertia compensation current value calculation unit 27 Multiplication unit 28 Addition unit M Electric motor T Steering torque

Claims (1)

An electric power steering device that transmits a driving force generated by an electric motor controlled according to an operation of an operation member to a steering mechanism to assist in steering,
Operation amount detection means for detecting an operation amount of the operation member,
Basic target drive value setting means for setting a basic target drive value that is a basic value of the target drive value of the electric motor based on the operation amount detected by the operation amount detection means;
Operation angular velocity detection means for detecting an operation angular velocity of the operation member,
Steering angular velocity detecting means for detecting the steering angular velocity on the steering mechanism side,
The electric motor corrects a basic target drive value set by the basic target drive value setting means in accordance with a deviation between the operation angular velocity detected by the operation angular velocity detection means and the steering angular velocity detected by the steering angular velocity detection means. Correction means for determining a target drive value for the control of
An electric power steering apparatus comprising: a motor driving unit that drives the electric motor based on a target driving value determined by the correction unit.

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