JP2004149069A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a torque-free feeling from being given to a driver while turning an operating means such as a steering wheel. <P>SOLUTION: When a steering angular speed calculated by a steering angular speed calculating part 22 and a motor angular acceleration calculated by a motor angular acceleration calculating part 23 have mutually reverse marks, a basic correction value in accordance with the motor angular acceleration is set by a basic correction current value setting part 241. A vehicle speed gain in accordance with vehicle speed is set by a vehicle speed gain setting part 242. The basic correction current value calculated by the basic correction current value setting part 241 and the vehicle speed gain calculated by the vehicle speed gain setting part 242 are multiplied by a multiplying part 243. An electric motor M is controlled regarding a value derived by adding a multiplication value (the correction current value) to a basic target current value as a target current value. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device that assists steering by giving a torque generated from an electric motor to a steering mechanism of a vehicle.
[0002]
[Prior art]
BACKGROUND ART Conventionally, an electric power steering device that assists steering by transmitting a driving force of an electric motor to a steering mechanism has been used (for example, see Patent Documents 1 and 2). 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 assisting force corresponding to the steering torque is given to the steering mechanism.
[0003]
The target current value is set according to a predetermined assist characteristic. The assist characteristic defines the relationship between the steering torque and the target current value, and can be approximated by cubic curves 81 and 82 as shown in FIG. The cubic curve 81 approximately represents the assist characteristic during low-speed traveling, and the cubic curve 82 approximately represents the assist characteristic during high-speed traveling. As for the steering torque, 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 a steering assist force in the right direction is to be generated from the electric motor, and a negative value when a steering assist force in the left direction is to be generated from the electric motor. You.
[0004]
When a steering torque in the right direction is applied to the steering wheel, the electric motor should generate a steering assist force in the right direction. Therefore, for a positive value of the steering torque, the target current value is a positive value. Should be taken. On the other hand, when the steering torque in the left direction is applied to the steering wheel, the electric motor should generate the steering assist force in the left direction. Therefore, for a negative value of the steering torque, the target current value is negative. Should be taken. That is, the target current value should take the value of the same sign as the steering torque.
[0005]
However, in the cubic curve 81, the steering torque and the target current value have opposite signs when the steering torque is in the range of -T1 to + T1, and in the cubic curve 82, the steering torque is in the range of -T2 to + T2. The torque and the target current value have different signs. Therefore, the assist characteristic at the time of low-speed running is determined such that the steering torque is in a range of −T1 to + T1 as a torque dead zone, and the target current value is zero for the steering torque within this torque dead zone. Further, the assist characteristics at the time of high-speed running are set such that the target current value becomes zero with respect to the steering torque within the torque dead zone in a range where the steering torque is -T2 to + T2.
[0006]
[Patent Document 1]
Japanese Patent No. 2936211 [Patent Document 2]
JP 2000-289639 A
[Problems to be solved by the invention]
According to the assist characteristics approximated by the cubic curves 81 and 82, when the steering wheel is quickly turned to one side during low-speed running, the steering assist is started immediately after the start of the turning, and the steering torque is reduced. With the increase, the steering assist force (target current value) sharply increases. On the other hand, if the steering wheel is quickly turned to one side during high-speed driving, the steering assist force gradually increases for a while after the steering torque leaves the torque dead zone, but when the steering torque increases to some extent, As the steering torque increases, the steering assist force sharply increases. As a result, the steering wheel suddenly becomes lighter, giving the driver a feeling of torque loss (a feeling of steering discomfort) to the driver.
[0008]
Accordingly, an object of the present invention is to provide an electric power steering device which can prevent a driver from feeling torque loss during turning of an operating means such as a steering wheel, thereby improving a steering feeling. .
[0009]
Means for Solving the Problems and Effects of the Invention
According to the first aspect of the present invention, an electric motor (M) is controlled in accordance with an operation of an operation means (1), and a torque generated from the electric motor is supplied to a steering mechanism (3). An electric power steering apparatus for assisting steering by operating a basic control signal generating means (21) for generating a basic control signal according to a steering torque applied to the operating means, and an operation for detecting an operating speed of the operating means. Speed detecting means (4, 22); motor angular acceleration detecting means (6, 23) for detecting a motor angular acceleration which is a rotational angular acceleration of the electric motor; and motor angular acceleration detected by the motor angular acceleration detecting means. The motor angular velocity of the electric motor that is generating torque for assisting steering in the direction of the operation speed detected by the operation speed detection means decreases based on Motor angular velocity decrease determining means (24, S3, S4, S5, S6) for judging whether or not the motor angular velocity is decreased when the motor angular velocity decrease determining means determines that the motor angular velocity is decreasing. An electric power steering apparatus comprising: a correction unit (24, 25) for correcting the basic control signal generated by the basic control signal generation unit in accordance with the motor angular acceleration detected by the unit.
[0010]
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 above configuration, when the motor angular speed of the electric motor that is generating torque for assisting steering in the direction of the operation speed is decreasing, the motor angular acceleration is detected based on the motor angular acceleration detected by the motor angular acceleration detection unit. The basic control signal generated by the basic control signal generating means is corrected.
[0011]
It is conceivable that in the case of a sharp turn steering from the dead zone, the loss of the steering torque occurs when the torque generated from the electric motor (steering assist force) increases and the steering torque applied to the operation means decreases. . The degree of decrease in the steering torque at that time is greater as the degree of change in the motor angular velocity is greater.
Therefore, if the basic control signal is reduced and corrected in accordance with the magnitude of the motor angular acceleration, a sudden increase in the steering assist force during the turning of the operating means can be suppressed. It is possible to prevent a sense of missing torque. Therefore, an excellent steering feeling can be realized when the operating means is turned (turned back).
[0012]
According to a second aspect of the present invention, the basic control signal generating means sets a basic target current value of the electric motor according to the steering torque applied to the operating means, and sets the set basic target current value. When the basic control signal is generated, the correction means for reducing and correcting the basic control signal in accordance with the magnitude of the motor angular acceleration determines that the motor angular velocity is reduced by the motor angular velocity reduction determining means. Correction current value setting means (241) for setting a correction current value according to the magnitude of the motor angular acceleration detected by the motor angular acceleration detection means, and a correction set by the correction current value setting means. Means (25) for reducing and correcting the basic target current value represented by the basic control signal generated by the basic control signal generation means based on the current value. It may be.
[0013]
According to a third aspect of the present invention, the electric power steering device further includes a vehicle speed detecting means (5) for detecting a vehicle speed, and wherein the correcting means is configured such that the vehicle speed detected by the vehicle speed detecting means is equal to or higher than a predetermined vehicle speed. When the motor angular velocity reduction determining means determines that the motor angular velocity is decreasing, the basic control signal generating means generates the basic control signal generated in accordance with the motor angular acceleration detected by the motor angular acceleration detecting means. 3. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus corrects a control signal.
[0014]
According to this configuration, it is possible to correct the basic control signal only when the vehicle speed is equal to or higher than the predetermined vehicle speed, and to suppress a sudden increase in the steering assist force during the turning of the operating means.
[0015]
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 a configuration of an electric power steering apparatus according to one embodiment of the present invention. In this electric power steering device, the electronic control unit 2 controls the driving of the electric motor M based on the operation of the steering wheel 1, thereby providing the steering mechanism 3 with the torque generated from the electric motor M to achieve steering assist. It is configured to
[0016]
The steering mechanism 3 includes a steering shaft 31 connected to the steering wheel 1, a pinion gear 32 provided at the tip of the steering shaft 31, and a rack bar 33 provided to be able to linearly move in the width direction of the vehicle. When the steering wheel 1 is operated, the steering shaft 31 rotates, and with this rotation, the pinion gear 32 rotates. The rotation of the pinion gear 32 causes the rack bar 33 to linearly move in the width direction of the vehicle (the longitudinal direction of the rack bar 33). The linear motion of the rack bar 33 is converted into a steering force of the front left and right wheels for steering by a tie rod or a knuckle arm (not shown). The torque generated by the electric motor M is input to the rack bar 33 via the speed reducer 34, for example.
[0017]
In connection with the steering shaft 31, an angle torque sensor 4 for detecting a steering angle of the steering wheel 1 and a steering torque input to the steering wheel 1 is provided. Specifically, the steering shaft 31 has a configuration in which an input shaft 31A connected to the steering wheel 1 and an output shaft 31B connected to a rack bar 33 via a pinion gear 32 are connected by a torsion bar 35, The angle torque sensor 4 detects the rotation angles of the input shaft 31A and the output shaft 31B, and outputs a signal corresponding to the detected rotation angle of the input shaft 31A as a steering angle detection signal. A signal corresponding to a value obtained by multiplying the rotation angle difference with the output shaft 31B by the elastic constant of the torsion bar 35 is output as a steering torque detection signal. Output signals (a steering angle detection signal and a steering torque detection signal) of the angle torque sensor 4 are provided to the electronic control unit 2.
[0018]
The electronic control unit 2 is further provided with an output signal of a vehicle speed sensor 5 for detecting a vehicle speed and an output signal of a motor angle sensor 6 for detecting a rotation angle (motor angle) of a rotor of the electric motor M. I have. The motor angle sensor 6 can be composed of, for example, a resolver that outputs a signal corresponding to the rotational position of the rotor.
The motor angle is zero when the steering angle of the steering wheel is zero (when the vehicle is traveling straight), and takes a positive value when the steering wheel is steered to the right. When the wheel is steered to the left, a negative value is assumed.
[0019]
FIG. 2 is a block diagram for explaining the configuration of the electronic control unit 2. The electronic control unit 2 includes a microcomputer, and sets a basic target current value according to a steering torque detected by the angle torque sensor 4 and a vehicle speed detected by the vehicle speed sensor 5 by a program process executed by the microcomputer. A basic target current value setting unit 21, a steering angular velocity calculating unit 22 that calculates a steering angular velocity by differentiating the steering angle detected by the angle torque sensor 4 with time, and a second-order time differentiation of the motor angle detected by the motor angle sensor 6. The steering angle is calculated based on the motor angular acceleration calculating section 23 that calculates the motor angular acceleration by the steering angular velocity calculating section 22, the motor angular acceleration calculated by the motor angular acceleration calculating section 23, and the vehicle speed detected by the vehicle speed sensor 5. Prevents the feeling of torque loss when turning the wheel 1 A correction current value calculation unit 24 for calculating a correction current value for performing the correction, a basic target current value set by the basic target current value setting unit 21 and a correction current value calculated by the correction current value calculation unit 24 are added. The functions of an adding unit 25 that generates a target current value of the electric motor M and a PWM signal generating unit 26 that generates a PWM signal corresponding to the target current value generated by the adding unit 25 are realized.
[0020]
The correction current value calculation unit 24 includes a basic correction current value setting unit 241 that sets a basic correction current value based on the steering angular velocity calculated by the steering angular velocity calculation unit 22 and the motor angular acceleration calculated by the motor angular acceleration calculation unit 23. A vehicle speed gain setting unit 242 for setting a vehicle speed gain according to the vehicle speed detected by the vehicle speed sensor 5, a basic correction current value set by the basic correction current value setting unit 241 and a vehicle speed gain set by the vehicle speed gain setting unit 242. And a multiplication unit 243 that generates a correction current value by multiplying.
[0021]
The electronic control unit 2 further includes a motor driver 27 for supplying power to the electric motor M. The motor driver 27 is configured by a bridge circuit of a power element, and the on / off of the power element is controlled by the PWM signal generated by the PWM signal generation unit 26, so that the on / off of the power element is controlled. The drive voltage is supplied to the electric motor M.
FIG. 3 is a characteristic diagram showing the relationship between the steering torque and the basic 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. 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.
[0022]
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 in the range of -Tn to + Tn (torque dead zone), the basic target current value is set to zero. The width of the torque dead zone is set wider as the vehicle speed increases. For a steering torque outside the torque dead zone, the basic target current increases as the absolute value of the steering torque increases according to a cubic curve in which the basic target current value becomes zero when the steering torque is zero, −Tn and + Tn. The absolute value of the value is set to be large.
[0023]
FIG. 4 is a characteristic diagram illustrating a relationship between a steering angle and a steering torque when the steering wheel 1 is operated left and right. The steering angle is set to zero when the steering wheel 1 is at the steering angle midpoint (neutral position), and takes a negative value in a state where the steering wheel 1 is turned leftward from the steering angle midpoint. Take a positive value with the middle point cut to the right.
From the state where the steering wheel 1 is cut to the left to the steering angle −θ1, the steering wheel is turned to the right, then turned back when the steering angle becomes + θ1, further turned to the left until the steering angle becomes −θ1, and then turned back again. When the operation is performed, the relationship between the steering angle and the steering torque shows a change like a curve LR when the steering wheel 1 is turned from the left side to the right side through the steering angle midpoint, and after turning back on the right side. Ideally shows a change like the curve LL. As shown by the curves LR and LL, if the absolute value of the steering torque monotonically increases with respect to the steering angle until the steering wheel 1 is turned back, the driver feels that the steering wheel 1 is missing torque during the turning of the steering wheel 1. Sensation of sudden lightening).
[0024]
As described with reference to FIG. 3, the basic target current value is set according to a cubic curve with respect to the steering torque outside the torque dead zone. Therefore, if the basic target current value set by the basic target current value setting unit 21 is used as the target current value as it is, especially during high-speed running, the steering angles of the steering wheel 1 immediately before the return of the steering angles -θ2, + θ2 ( θ2: At the moment when the steering torque exceeds the steering angle at which Tn is reached, the generated torque (steering assist force) of the electric motor M suddenly increases, and the driver feels that the torque is missing (the steering wheel 1 suddenly becomes lighter). Sensation). When the steering angle is in the range of + θ2 to + θ1 and -θ2 to -θ1, the absolute value of the steering torque decreases as the absolute value of the steering angle increases, as indicated by the two-dot chain line.
[0025]
Therefore, the correction current value calculation unit 24 uses the basic target current value setting unit 21 so that the relationship between the steering angle and the steering torque is changed from a change like the two-dot chain line to a change like the curves LR and LL. A correction current value for correcting the set basic target current value is calculated.
FIG. 5 is a flowchart for explaining the function of the basic correction current value setting unit 241. First, the basic correction current value setting unit 241 reads the steering angular velocity calculated by the steering angular velocity calculation unit 22 and the motor angular acceleration calculated by the motor angular acceleration calculation unit 23 (Steps S1 and S2). Then, it is determined whether or not the steering angular velocity is a positive value (> 0) (step S3). If the steering angular velocity is a positive value, then the motor angular acceleration is negative (<0). It is determined whether or not there is (step S4). If the steering angular velocity is not a positive value, it is determined whether or not the steering angular velocity is a negative value (<0) (step S5). If the steering angular velocity is a negative value, then the motor angular acceleration is determined. Is a positive value (> 0) (step S6).
[0026]
When the steering wheel 1 is cut from the left side to the right side through the steering angle midpoint, the steering angular velocity takes a positive value in the steering angle range + θ2 to + θ1, while the basic target current value is set as the target. When the motor control with the current value is performed, the absolute value of the steering torque decreases as shown by a two-dot chain line in FIG. 4, and the motor angular velocity of the electric motor M in the right direction decreases with this. The motor angular acceleration takes a negative value as shown in FIG. Further, when the steering wheel 1 is turned back on the right side and further turned to the left side through the steering angle midpoint, the steering angular velocity takes a negative value in the range of the steering angle −θ2 to −θ1, When the motor control is performed with the basic target current value as the target current value as it is, the absolute value of the steering torque decreases as shown by a two-dot chain line in FIG. 4, and accordingly, the electric motor M moves to the left. Since the motor angular velocity decreases, the motor angular acceleration takes a positive value as shown in FIG. That is, from the state where the steering wheel 1 is cut to the left to the steering angle −θ1, the steering wheel 1 is turned to the right, then turned back when the steering angle becomes + θ1, further turned to the left until the steering angle becomes −θ1, and turned back again. When the steering operation described above is performed, the steering angular velocity and the motor angular acceleration take values opposite to each other in the range of the steering angle + θ2 to + θ1, -θ2 to -θ1.
[0027]
Therefore, when the steering angular velocity and the motor angular acceleration have opposite signs, the basic correction current value setting unit 241 (YES in step S3 → YES in step S4, or NO in step S3 → YES in step S5). → YES in step S6), a basic correction current value corresponding to the motor angular acceleration is set (step S7), and when the steering angular velocity and the motor angular acceleration have the same sign value, or when the steering angular velocity or the motor angular acceleration If at least one is zero, the basic correction current value is set to zero regardless of the value of the motor angular acceleration (step S8).
[0028]
FIG. 7 is a characteristic diagram showing a relationship between the motor angular acceleration and the basic correction current value. The basic correction current value is set to zero when the motor angular acceleration is a small value in the range of -A1 to + A1. This is to prevent the basic correction current value from being erroneously set due to the noise component when the detection signal of the motor angle sensor 6 includes a noise component.
Further, the basic correction current value is set so as to monotonically increase from zero to an upper limit Irmax (in this embodiment, linearly increase) as the motor angular acceleration increases in the range of + A1 to + A2 for the motor angular acceleration. Then, in the range of -A1 to -A2 for the motor angular acceleration, as the motor angular acceleration decreases (as the absolute value of the motor angular acceleration increases), it monotonically decreases from zero to the lower limit Irmin (in this embodiment, Linearly decreasing).
[0029]
When the electric motor M is controlled with the basic target current value as it is as the target current value, the steering wheel 1 is turned to the right from a state where the steering wheel 1 is cut to the steering angle −θ1 to the left, and when the steering angle becomes + θ1. When the steering operation is performed such as turning back, turning leftward until the steering angle becomes −θ1, and turning back again, in the range of steering angles + θ2 to + θ1, −θ2 to −θ1, as shown in FIG. Increases, the absolute value of the motor angular acceleration increases. Therefore, as the absolute value of the motor angular acceleration increases, the absolute value of the basic correction current value is set to a larger value, so that the absolute value of the steering angle in the range of the steering angle + θ2 to + θ1, -θ2 to -θ1. Becomes larger, the absolute value of the target current value can be reduced, and the torque generated from the electric motor M can be reduced.
[0030]
FIG. 8 is a diagram for explaining the function of the vehicle speed gain setting unit 242, and shows the relationship between the vehicle speed and the vehicle speed gain. The vehicle speed gain is set according to the relationship shown in FIG.
In the steering torque-basic target current value characteristic line shown in FIG. 3, as the vehicle speed is higher, the width of the torque dead zone -Tn to + Tn is larger, and the change of the inclination of the tangent at each point on the cubic curve is larger. For this reason, the sense of torque omission (a decrease in the steering torque in the range of the steering angles + θ2 to + θ1, -θ2 to -θ1) that appears when the electric motor M is controlled with the basic target current value as the target current value is as follows. This is more noticeable as the vehicle speed increases. Thus, the vehicle speed gain is set to zero in the range of 0 to V1 for the vehicle speed, and monotonically increases from zero to the upper limit Gmax as the vehicle speed increases in the range of V1 to V2 for the vehicle speed (this embodiment). Is set to increase linearly). Thus, the basic correction current value can be set only when the vehicle speed is higher than V1, and the basic correction current value can be set to a larger value as the vehicle speed increases.
[0031]
According to this embodiment, the basic correction current value set by the basic correction current value setting unit 241 is multiplied by the vehicle speed gain set by the vehicle speed gain setting unit 242, and this multiplied value (correction current value) is used as the basic target current. By controlling the electric motor M with the value obtained by adding the value to the target current value, the relationship between the steering angle and the steering torque is changed from the change shown by the two-dot chain line in FIG. 4 to the curves LR and LL. It can be compensated for changes. Therefore, while the steering wheel 1 is being cut, an appropriate response (weight of the steering wheel 1) can be given to the driver, and an excellent steering feeling can be realized.
[0032]
As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various design changes can be made within the scope of the matters described in the claims. It is.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of an electronic control unit.
FIG. 3 is a characteristic diagram illustrating a relationship between a steering torque and a basic target current value.
FIG. 4 is a characteristic diagram showing a relationship between a steering angle and a steering torque when a steering wheel is operated left and right.
FIG. 5 is a flowchart illustrating a function of a basic correction current value setting unit.
FIG. 6 is a characteristic diagram showing a relationship between a steering angle and a motor angular acceleration.
FIG. 7 is a characteristic diagram showing a relationship between a motor angular acceleration and a basic correction current value.
FIG. 8 is a diagram for explaining a function of a vehicle speed gain setting unit, and shows a relationship between a vehicle speed and a vehicle speed gain.
FIG. 9 is a characteristic diagram showing a relationship between a steering torque and a target current value in a conventional electric power steering device.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 steering wheel 2 electronic control unit 3 steering mechanism 4 angle torque sensor 5 vehicle speed sensor 6 motor angle sensor 21 basic target current value setting unit 22 steering angular velocity calculation unit 23 motor angular acceleration calculation unit 24 correction current value calculation unit 25 addition unit 241 basic Correction current value setting unit 242 Vehicle speed gain setting unit 243 Multiplying unit M Electric motor

Claims (3)

An electric power steering device that controls an electric motor in accordance with an operation of an operation unit and applies a generated torque from the electric motor to a steering mechanism to assist steering.
Basic control signal generating means for generating a basic control signal according to the steering torque applied to the operating means,
Operating speed detecting means for detecting the operating speed of the operating means,
Motor angular acceleration detecting means for detecting a motor angular acceleration that is a rotational angular acceleration of the electric motor,
Based on the motor angular acceleration detected by the motor angular acceleration detecting means, the motor angular velocity of the electric motor, which generates torque for assisting steering in the direction of the operating speed detected by the operating speed detecting means, decreases. Motor angular velocity decrease determining means for determining whether or not
When the motor angular velocity decrease determining means determines that the motor angular velocity is decreasing, the basic control signal generated by the basic control signal generating means according to the motor angular acceleration detected by the motor angular acceleration detecting means. An electric power steering apparatus, comprising: a correction unit that corrects a signal. The basic control signal generating means sets a basic target current value of the electric motor according to a steering torque applied to the operating means, and generates a basic control signal representing the set basic target current value. ,
The correction means,
Correction current value setting means for setting a correction current value according to the magnitude of the motor angular acceleration detected by the motor angular acceleration detecting means when the motor angular velocity reduction determining means determines that the motor angular velocity is decreasing; When,
Means for reducing and correcting the basic target current value represented by the basic control signal generated by the basic control signal generation means based on the correction current value set by the correction current value setting means. Item 2. The electric power steering device according to Item 1. The electric power steering device further includes a vehicle speed detection unit that detects a vehicle speed,
When the vehicle speed detected by the vehicle speed detection unit is equal to or higher than a predetermined vehicle speed and the motor angular speed reduction determination unit determines that the motor angular speed is decreasing, the correction unit detects the motor angular acceleration detection unit. 3. The electric power steering apparatus according to claim 1, wherein the basic control signal generated by the basic control signal generating means is corrected in accordance with the motor angular acceleration detected by the electric power steering apparatus.

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