JP3865529B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device that assists a steering operation by using a rotational force of a motor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering device that assists steering by generating a steering assist force according to a steering torque input by a steering operation from a motor and applying the steering assist force generated from the motor to a steering mechanism is known. Yes.
[0003]
In many of such electric power steering devices, a motor current target value corresponding to the magnitude of the steering torque input to the steering mechanism is set according to an assist characteristic line created in advance. The motor current target value is a current value to be supplied to the motor. By controlling the motor drive circuit so that the motor current target value and the current value that actually flows through the motor coincide with each other, the motor current target value corresponds to the steering torque. A steering assist force can be generated from the motor.
[0004]
As shown in FIG. 5, a steering torque range (dead zone) in which steering assistance is not performed is set in advance in the assist characteristic line referred to in this motor control. If the steering torque input to the steering mechanism is within the dead zone, the power supply to the motor is stopped and steering assistance is not performed. As a result, the vehicle can be prevented from wobbling due to undesired steering assistance when the vehicle is traveling straight ahead, and the steering stability can be improved.
[0005]
[Problems to be solved by the invention]
However, when the left and right steering is repeated such that the steering torque repeatedly fluctuates near the boundary of the dead zone, the motor is frequently turned on and off, resulting in motor start noise and motor torque ripple. There was a risk of frequent vibration.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric power steering device that solves the above technical problem and can suppress the occurrence of vibrations caused by motor start noise and motor torque ripple.
[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 apparatus that drives a motor based on a motor current target value and transmits the driving force of the motor to a steering mechanism to assist steering. Steering torque detection means for detecting steering torque input to the steering mechanism, current target value setting means for setting a motor current target value based on the steering torque detected by the steering torque detection means, and the motor Means for calculating a motor rotation speed based on a pulse signal input from a motor rotation angle sensor for detecting the rotation angle of the motor, and a determination means for determining whether the steering mode of the steering mechanism satisfies a predetermined condition; , if it is determined to satisfy the predetermined condition by the determination means, by the said current target value setting means Look including a dead zone width changing means for changing the width of the dead band range of the steering torque motor current target value is set to zero, the predetermined condition, the steering direction is switched, and, beyond a torque neutral point And the rotation speed of the motor is equal to or greater than a predetermined reference value, and the dead zone changing means is determined when the determination means determines that the predetermined condition is satisfied. An electric power steering apparatus characterized by changing the width of the dead zone to be narrow .
[0008]
According to the present invention, when the manner of steering by the driver of the vehicle satisfies a predetermined condition, the dead band width at which the motor current target value for the steering torque is set to zero is changed. As a result, for example, when sudden steering in the left-right direction in which the steering torque repeatedly fluctuates in the vicinity of the boundary of the dead zone, the width of the dead zone is changed to be narrower than before, thereby turning the motor on / off. Can be prevented from being repeated. As a result, generation of motor start noise and generation of vibration due to motor torque ripple can be suppressed.
[0009]
Further, the steering direction is switched, the torque neutral point is not exceeded, and it is determined whether or not the condition that the motor rotational speed is equal to or higher than a predetermined reference value is satisfied. It is possible to satisfactorily determine whether or not the sudden steering in the left-right direction is performed such that the torque repeats the fluctuation near the boundary of the dead zone.
Incidentally, the electric power steering apparatus, as set forth in claim 2, when the width of the dead zone Ru is modified by the dead zone width changing means, the assist characteristic curve showing the relationship between the steering torque and the motor current target value Further, it may further include means for changing to a bend line having at least one bend point in a region below a predetermined motor current target value so that the width of the dead zone becomes narrow .
[0010]
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 together with a cross-sectional structure of a steering mechanism. The steering mechanism 1 is coupled to a rack 11 arranged along the vehicle width direction, a pinion shaft 12 having a pinion portion meshing with the rack 11 in a gear box 17 at a tip, and both ends of the rack 11 to be rotatable. The tie rod 13 is provided, and a knuckle arm 14 is rotatably coupled to the tip of the tie rod 13.
[0011]
The knuckle arm 14 is rotatably provided around the kingpin 15, and a steering wheel 16 is attached to the knuckle arm 14. A base end portion of the pinion shaft 12 is coupled to a steering shaft via a universal joint, and a steering wheel (not shown) is fixed to one end of the steering shaft, for example. With this configuration, when the steering wheel is rotated, the rack 11 is displaced in the longitudinal direction thereof, the knuckle arm 14 is rotated around the kingpin 15, and the direction of the steering wheel 16 is changed.
[0012]
The electric power steering apparatus 2 has a three-phase brushless motor M provided in association with the middle part of the rack 11. The motor M includes a case 21 fixed to the vehicle. In the case 21, a rotor 22 is disposed so as to surround the rack 11, and a stator 23 is disposed so as to surround the rotor 22. .
[0013]
A ball nut 31 is connected to one end of the rotor 22. The ball nut 31 is screwed into a screw shaft portion 32 formed in the middle of the rack 11 via a plurality of balls, whereby a ball screw mechanism 30 is formed. Further, bearings 33 and 34 are interposed between the ball nut 31 and the case 21 of the motor M, and a bearing 35 is interposed between the case 21 and the vicinity of the other end of the rotor 22. ing.
[0014]
With this configuration, when the motor M is energized and torque is applied to the rotor 22, the applied torque is transmitted to the ball nut 31 connected to the rotor 22. The torque transmitted to the ball nut 31 is converted into a driving force in the vehicle width direction of the rack 11 by the ball screw mechanism 30. Thus, the force generated from the motor M is applied to the steering mechanism 1.
[0015]
The magnitude of the steering assist force is adjusted by controlling the drive current of the motor M. The drive current of the motor M is controlled by the controller 40 via the motor driver 50. The controller 40 includes a vehicle speed sensor 61 for detecting the vehicle speed, a torque sensor 62 for detecting the steering torque, a motor rotation angle sensor 63 for detecting the rotation angle of the motor M, and the magnitude of the current flowing through the motor M. An output signal of the motor current detection circuit 70 for detecting the length is inputted. The controller 40 sets a motor current target value to be supplied to the motor M based on each output signal, and controls the motor driver 50 based on the motor current target value.
[0016]
The vehicle speed sensor 61 is realized, for example, by a wheel speed sensor that is provided in association with a wheel and outputs a pulse signal at a cycle corresponding to the rotation speed of the wheel. In this case, the vehicle speed that is the speed of the vehicle can be obtained by measuring the period or frequency of the pulse signal.
The torque sensor 62 divides the pinion shaft 12 into an input shaft on the steering wheel side and an output shaft on the rack 11 side, connects the input shaft and the output shaft with a torsion bar, and twists the torsion bar. This is realized by a configuration for detecting the quantity. That is, since the torque applied to the steering wheel and the torsion amount of the torsion bar correspond one-to-one, the steering torque can be detected by detecting the torsion amount with an appropriate detection mechanism such as a potentiometer.
[0017]
The motor rotation angle sensor 63 is composed of a rotary encoder or the like, and is provided in association with the rotor 22. Based on the pulse signal output from the rotary encoder, the rotational position of the rotor 22, that is, the rotational angle of the motor M can be detected.
FIG. 2 is a diagram showing an assist characteristic line for setting the motor current target value D according to the steering torque T. As shown in FIG. The controller 40 sets a motor current target value D corresponding to the steering torque T detected by the torque sensor 62 in accordance with the assist characteristic line shown in FIG. In FIG. 2, a negative sign (−) is assigned to the steering torque T when steered in the left direction, and a positive sign (+) is imparted to the steering torque T when steered in the right direction. It will be attached.
[0018]
The assist characteristic line is provided with a dead zone where the motor current target value D with respect to the steering torque T is zero. That is, when the absolute value of the steering torque T detected by the torque sensor 62 is equal to or smaller than the absolute values of the predetermined threshold values + T1 and −T1, and the relationship of the inequality −T1 ≦ T ≦ + T1 is satisfied, the motor The current target value D is set to zero, and the motor M is not driven.
[0019]
The controller 40 is steered rightward or leftward by the driver, and when the absolute value of the steering torque T input at this time exceeds the absolute value of the threshold values + T1, -T1, the linear function L , M, the motor current target value D is set to a larger value as the absolute value of the steering torque T is larger. Further, when the absolute value of the steering torque T exceeds the predetermined upper limit values + T2 and −T2, the controller 40 sets the motor current target value D to a constant value D1.
[0020]
Further, the controller 40 changes the above-described assist characteristic line as shown by a two-dot chain line in FIG. 2 when the manner of the steering operation by the driver of the vehicle satisfies a predetermined condition. That is, the width of the dead zone is changed to a value αW obtained by multiplying the initial value W by a coefficient α (0 ≦ α <1), and the primary functions L and M are accordingly changed to the origin direction along the coordinate axis of the steering torque T. Translate to. As a result, when the absolute value of the steering torque T exceeds the absolute value of the changed threshold value + αT1, −αT1 obtained by multiplying the threshold value + T1, −T1 by the coefficient α, after the parallel movement indicated by the two-dot chain line In accordance with the linear functions L and M, the motor current target value D is set to a larger value as the absolute value of the steering torque T is larger. When the absolute value of the steering torque T exceeds the changed upper limit value + αT2, −αT2 obtained by multiplying the upper limit value + T2, −T2 by the coefficient α, the motor current target value D is set to a constant value D1.
[0021]
FIG. 3 is a flowchart for explaining the operation of the controller 40 regarding the change of the assist characteristic line. The operation shown in this flowchart is started in response to the steering operation performed by the driver.
When the steering operation by the driver is performed, the controller 40 refers to the output of the torque sensor 62 and checks whether or not the steering direction by the steering operation has been switched (step S1). If the steering direction is not switched (NO in step S1), the coefficient α for changing the dead zone width is set to 1 (step S5), and the assist characteristic line is not changed. Then, the controller 40 sets a motor current target value according to the unchanged assist characteristic line (shown by a solid line in FIG. 2), and controls the driving of the motor M based on the motor current target value (step S6).
[0022]
On the other hand, if the steering direction has been switched (YES in step S1), it is next determined whether or not steering has been performed that exceeds the torque neutral point (step S2). That is, the controller 40 determines whether or not the steering torque T detected by the torque sensor has been switched from −T to + T or from + T to −T. When steering is performed so as to exceed the torque neutral point (YES in step S2), the controller 40 sets the coefficient α to 1 (step S5) and does not change the assist characteristic line. Then, the driving of the motor M is controlled according to the unchanged assist characteristic line (step S6).
[0023]
If steering that exceeds the torque neutral point is not performed (NO in step S2), the controller 40 calculates the motor rotation speed N based on the pulse signal input from the motor rotation angle sensor 63, and It is determined whether or not the calculated motor rotation speed N is equal to or greater than a reference value B appropriately determined for each type of vehicle by performing an experiment in advance (step S3). In other words, it is determined whether the steering speed by the driver is high or low. When the motor rotation speed N is less than the reference value B and the steering speed is relatively low, the controller 40 sets the coefficient α to 1 (step S5) and follows the unchanged assist characteristic line. The drive of the motor M is controlled (step S6).
[0024]
If the motor rotation speed N calculated based on the pulse signal from the motor rotation angle sensor 63 is equal to or higher than the reference value B and the steering speed is relatively high, the controller 40 calculates the coefficient α based on the motor rotation speed N. (0 ≦ α <1) is set (step S4), and the dead zone width of the assist characteristic line is changed to αW. Further, the linear functions L and M are translated in accordance with the changed dead band width αW. For example, the coefficient α is determined by a function f (N) of the motor rotation speed N. Specifically, the coefficient α may be set by multiplying the motor rotational speed N by a constant a. In this case, f (N) = aN. Thereby, the change of the assist characteristic line is achieved, and the controller 40 controls the drive of the motor M according to the changed assist characteristic line (step S6).
[0025]
In this embodiment, step S1 corresponds to the function of direction switching determination means, and step S3 corresponds to the function of steering speed determination means.
As described above, according to this embodiment, the steering speed is relatively high, and the steering torque T does not exceed the torque neutral point, and fluctuates in the vicinity of the threshold values + T1, −T1, which are the boundaries of the dead zone. When the steering operation is repeated, in other words, when sudden steering in the left-right direction is performed such that the steering torque T repeatedly fluctuates near the boundary of the dead band, the dead band width W of the assist characteristic line Is changed to the width αW. As a result, the width of the dead zone is narrowed, so that the motor M is prevented from being repeatedly turned on / off even if the steering torque T is repeatedly steered in the left-right direction so as to repeatedly fluctuate in the vicinity of the dead zone boundary. It is possible to suppress generation of motor start noise and vibration due to motor torque ripple.
[0026]
In the above-described embodiment, the linear functions L and M are translated in accordance with the change of the width W of the dead zone to the width αW. However, as shown in FIG. 4, the linear functions L and M are changed to bent lines P and Q that are bent at points corresponding to a predetermined motor current target value D2 (steering torque + T3, -T3). Also good.
More specifically, the bending lines P and Q both have linear function parts U1 and U2, and the linear function part U2 is a predetermined value + T3, − in the primary functions L and M before the change. This corresponds to the portion corresponding to the steering torque T equal to or greater than the absolute value of T3. On the other hand, the linear function portion U1 is a portion that is referred to when the steering torque T is larger than the absolute value of the changed threshold value + αT1 and −αT1 and smaller than the absolute value of the predetermined value + T3 and −T3. And the inclination is set smaller than that of the linear function portion U2.
[0027]
Thereby, after the assist characteristic line is changed, if the absolute value of the steering torque T is larger than the absolute values of the changed threshold values + αT1 and −αT1, the motor current target value D is a linear function portion U1 having a small inclination. Set according to. If the absolute value of the steering torque T is equal to or greater than the absolute value of the predetermined value + T3, -T3, the motor current target value D is set according to the linear function portion U2 having a large inclination.
[0028]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment. For example, in the above-described embodiment, the linear functions L and M are changed to the bending lines P and Q having the parallel movement or one bending point in accordance with the change of the width W of the dead zone to the width αW. However, it may be changed to a bending line having a plurality of bending points in a region below a predetermined motor current target value.
[0029]
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 apparatus according to an embodiment of the present invention together with a cross-sectional structure of a steering mechanism.
FIG. 2 is a diagram showing an assist characteristic line for setting a motor current target value according to a steering torque.
FIG. 3 is a flowchart for explaining processing for changing an assist characteristic line (dead zone width);
FIG. 4 is a diagram for explaining another embodiment of the present invention.
FIG. 5 is a diagram for explaining conventional motor control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering mechanism 2 Electric power steering apparatus 40 Controller (Current target value setting means, judgment means, dead band width changing means)
50 Motor driver 62 Torque sensor (steering torque detection means)
63 Motor rotation angle sensor (steering speed detection means)
70 Motor current detection circuit M Motor W Dead band width αW Dead band width after change

Claims (2)

In the electric power steering apparatus that drives the motor based on the motor current target value and transmits the driving force of the motor to the steering mechanism to assist the steering.
Steering torque detection means for detecting steering torque input to the steering mechanism;
Current target value setting means for setting a motor current target value based on the steering torque detected by the steering torque detection means;
Means for calculating a motor rotation speed based on a pulse signal input from a motor rotation angle sensor for detecting the rotation angle of the motor;
Determination means for determining whether or not a steering mode of the steering mechanism satisfies a predetermined condition;
When the determination means determines that the predetermined condition is satisfied, the dead band width changes the width of the dead band that is the range of the steering torque in which the motor current target value is set to zero by the current target value setting means. Change means,
The predetermined condition is a condition that the steering direction is switched, the torque neutral point is not exceeded, and the motor rotation speed is equal to or higher than a predetermined reference value.
The dead zone width changing means changes the dead zone width so as to become narrower when it is judged by the judging means that the predetermined condition is satisfied. Upon width of the dead zone Ru is modified by the dead zone width changing means, the assist characteristic curve showing the relationship between the steering torque and the motor current target value, so that the width of the dead band is narrowed, less than a predetermined motor current target value 2. The electric power steering apparatus according to claim 1, further comprising means for changing to a bending line having at least one bending point in the region.

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