JP3328042B2 - Control device for electric power steering system for vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device mounted on a vehicle, and more particularly to a control device for controlling the direction and magnitude of an assist torque generated by the device.

[0002]

2. Description of the Related Art In an electric power steering apparatus, a steering torque generated by a driver turning a steering wheel is detected by a steering torque detecting means, and a current corresponding to the detected torque is applied to an electric motor. Since the electric motor that is rotationally driven by this application is engaged with the mechanism of the steering device, the electric motor generates necessary assist torque and performs steering. Generally, any of a manual steering device, a hydraulic power steering device, and an electric power steering device has a self-aligning function. That is, in the process of returning to the straight running state after turning, if the driver turns the force to rotate the steering wheel to zero (so-called released state), the wheels automatically return to the neutral position direction. The torque that tends to return to the neutral position direction increases as the vehicle speed increases. At this time, in the electric power steering apparatus, if the wheels are first turned to the right, for example, the wheels move toward the neutral position, that is, to the left by the self-aligning function. Since the force by which the driver turns the steering wheel is zero, the steering torque should be originally zero. Therefore, the value detected by the steering torque detecting means also becomes 0, the electric motor is not energized, does not generate assist power, and rotates leftward while meshing with the mechanism of the steering device. Of course, the steering wheel also turns to the left.

[0003]

However, in the conventional electric power steering system, the return of the steering wheel after turning at low vehicle speed is poor due to the inertia of the rotor of the electric motor and the like, and the astringency at high vehicle speed is low. There was a problem that was bad. That is, in the process of returning to the straight running state after the driver turns the steering wheel and turns at low vehicle speed, the return is poor compared to the manual steering device and the hydraulic power steering device (FIGS. 7A, a2 and 7B2). 7 (a) a1, (b) b1), in severe cases, the driver has to turn the steering wheel in the straight traveling direction again. Also, in the process of returning to straight after turning at a high vehicle speed (particularly in the process of returning in a released state), the self-aligning function causes the wheels to return to the neutral position in an excessively strong direction, and passes through the neutral position in the opposite direction. The vehicle turns (FIG. 8 (c) a1). When the vehicle is steered in the opposite direction, the self-aligning function attempts to return to the neutral position again, eventually meandering (FIG. 8A), and deteriorating convergence. The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a control device for an electric power steering device for a vehicle that can improve the return of a steering wheel at a low vehicle speed and improve convergence at a high vehicle speed. The purpose is to provide.

[0004]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a vehicle speed detecting means, a steering torque detecting means for detecting a steering torque generated by a driver turning a steering wheel, Motor speed detection means for detecting the rotation speed of the electric motor; motor acceleration detection means for detecting the rotation acceleration of the electric motor; motor rotation direction and steering torque based on a signal from the motor speed detection means and a signal from the steering torque detection means. Determining means for determining whether or not the directions are the same direction; and determining the assist torque according to the vehicle speed and the steering torque if the determination is the same direction, and determining the vehicle speed and the electric motor rotation speed if the determination is different. Alternatively, at low vehicle speeds, the assist torque in the same direction as the motor rotation direction is used according to the rotational acceleration, and at high vehicle speeds, the assist torque in the direction opposite to the motor rotation direction is used. And assist torque determining means for constant,
And a driving means for applying a current corresponding to the determined assist torque to the electric motor to drive the electric motor to rotate.

[0005]

In the case where poor steering of the steering wheel after turning is a problem during low-speed running and when the astringency after turning is a problem during high-speed running, both wheels are provided by the self-aligning mechanism of the steering device. Is trying to return to the neutral direction. In this case, the driver has almost released the steering wheel. Therefore, the steering torque should be originally zero. However, since the steering wheel tends to stop at the original position due to the mass of the steering wheel, a small steering torque is generated in the turning direction opposite to the returning direction of the steering wheel. At this time, since the electric motor is engaged with the mechanism of the steering device, it rotates in the return direction. Therefore, if the direction of the steering torque is different from the direction of the motor rotation, it means that the steering wheel is poorly returned at the time of low vehicle speed running or the convergence after turning is poor at the time of high vehicle speed running. Therefore, at low vehicle speeds, steering wheel return can be improved by generating assist torque in the same direction as the motor rotation direction. At a high vehicle speed, by generating assist torque in the direction opposite to the motor rotation direction, meandering can be prevented and convergence can be improved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a control block diagram of a control device that controls an electric motor in the electric power steering device for a vehicle according to the present embodiment. The portion within the dotted line in the figure is the portion that has existed conventionally. In the figure, a steering torque detecting means 1 detects a steering torque generated by a driver turning a steering wheel. That is, for example, a torsion bar that is easily twisted is provided in the middle of the steering rod, and when the driver turns the steering wheel, the torsion bar is twisted, and the upper and lower portions sandwiching the torsion bar relatively rotate. The steering torque can be detected by detecting the rotation angle. The vehicle speed detecting means 3 detects a vehicle speed. The assist torque determining means 51, 52, 53 determines an assist torque to be generated by the electric motor 7. As will be described in detail later, the first assist torque determination unit 51
Determines the assist torque according to the vehicle speed and the steering torque. The second assist torque determining means 52 determines the assist torque according to the vehicle speed and the motor rotation speed. The third assist torque determination 53 determines an assist torque according to the vehicle speed and the motor rotational acceleration.

The electric motor current value determining means 9 determines a current value to be applied to the electric motor 7 based on the determined assist torque. Current motor driving means 1
1 actually applies the determined current value to the electric motor. The electric motor current detecting means 13 detects a current value actually applied to the electric motor, and increases or decreases a command signal to the electric motor driving means 11 so that the determined electric motor current value matches. . The motor speed detecting means 15 detects the rotation speed of the electric motor 7. The motor acceleration detecting means 17 detects the rotational acceleration by processing the detection signal from the motor speed detecting means by a differentiating circuit. These rotational speeds and rotational accelerations are detected not only in magnitude but also in direction. Judgment means 1
9 determines whether or not the motor rotation direction obtained by the signal from the motor speed detecting means 15 and the direction of the steering torque given by the signal from the steering torque detecting means 1 are the same. Based on the result of this determination, it is selected which of the assist torque determination means 51, 52, and 53 to operate.

[0008] The first assist torque determining means 51 determines the assist torque T1 based on the graph of FIG.
The torque T1 determined in FIG. 4 is substantially the same as that used in the conventional electric power steering device. That is, as the steering torque gradually increases from 0, the assist torque T1 sharply rises and increases, and when the steering torque exceeds a certain value, the assist torque becomes constant. This assist torque T1 decreases as the vehicle speed increases. Second assist torque determining means 52
Determines the assist torque T2 from the graph of FIG. FIG. 5 shows that the determined assist torque T2 increases as the motor rotation speed increases. Further, the vehicle speed is divided into a low speed region and a high speed region around the vicinity of 40 km, and a positive torque is determined in a low speed region, and a negative torque is determined in a high speed region. The sign of + means that the torque is in the same direction as the motor rotation direction. -Means that the torque is opposite to the motor rotation direction.
The third assist torque determining means 53 determines the assist torque T3 based on FIG. FIG. 6 means that the assist torque T3 determined as the motor rotational acceleration increases increases. Then, the vehicle speed is divided into a low speed region and a high speed region as in FIG. 5, and a constant value of torque is obtained in the low speed region regardless of the vehicle speed. In the high-speed range, the torque value increases in proportion to the vehicle speed.

FIG. 2 is a control flowchart showing the control of FIG. That is, if the determination means 19 (FIG. 1) determines that the motor rotation direction and the direction of the steering torque are the same (S1), the target assist torque Tas is only the assist torque T1 similar to the conventional one (S2). ). If it is determined that the directions are different (S1), the target assist torque Tas is the sum of the assist torques T1, T2, and T3 (S1).
3). In FIG. 3, the rotation of the electric motor accompanying the return of the steering wheel during low-speed running will be described. As described above, the electric power steering device also has a self-aligning function like other manual steering devices and hydraulic power steering devices, for example, after turning to the right,
If the force for rotating the steering wheel of the driver is reduced to zero, the wheels automatically try to return to the neutral position, that is, to the left (FIG. 3).
(A)). At this time, since the electric motor 7 remains engaged with the mechanism of the steering device, it similarly rotates rightward (FIG. 3B). The rotation speed at this time is 0 in the initial steering state, suddenly increases when returning to the neutral position, and returns to 0 when returning to the neutral position. The rotation acceleration at this time is + (acceleration) in the first half of rotation.
In the latter half, it is-(deceleration) ((c) in the figure). And since the graph of (c) changes smoothly,
Two rounded peaks having different directions are formed.

Referring to FIG. 7, description will be made on the improvement of the return of the steering wheel at the time of running at a low vehicle speed. FIG. 7A shows an actual traveling locus of a vehicle. FIG. 7B shows the steering angle of the steering wheel corresponding to FIG. 7A. Return of the handle of the manual steering device or hydraulic power steering device (Fig. 7
Compared with b2) of FIG. 7B, the return of the steering wheel is even worse in the conventional electric power steering device (b in FIG. 7B).
1). For example, as shown in FIG.
(A) After a4), the steering wheel is turned rightward (FIG. 7).
(A) a5) When the driver turns the steering wheel to zero force when the direction of the vehicle changes by 90 degrees and releases the steering wheel, if the steering wheel is returned at an ideal speed, a dotted line in the figure is used. Then, the trajectory of the vehicle is obtained in a direction at 90 degrees to the initial trajectory. However, in the conventional manual steering device or hydraulic power steering device, the return of the steering wheel is poor, so that the distance l2 required for the return is increased, and the steering is turned deeper than 90 degrees (FIG. 7A).
A2). If the return of the steering wheel is still worse and the return is not sufficient, the vehicle keeps turning and deviates greatly from the ideal trajectory (a1 in FIG. 7A).

[0011] The following (1), (2), and (3) can be considered as the reasons why the steering wheel return in the conventional electric power steering apparatus during traveling at a low vehicle speed is poor. (1) That is, in the electric power steering device, the rotor of the electric motor 7, which is the driving source, meshes with the mechanism of the steering device at a gear ratio of several tens to one, and will return to the neutral position by the self-aligning function. Can not return quickly. (2) Further, the return is poor due to fiction of gears and the like used in the mechanism of the steering device. (3) In addition, the handle tends to rotate in the return direction together with the wheels and the like by the self-aligning mechanism, but the inertia of trying to stop at the original position due to the mass of the handle itself acts. A small steering torque in the direction remains. The steering torque is detected by the steering torque detecting means, and a current for rotating the electric motor in the turning direction is applied, so that the steering wheel returns further worse (FIGS. 7 (a) a1, (b) b1). Therefore, the return of the handle of the conventional manual steering device or hydraulic power steering device is slightly better (FIGS. 7 (a) a2, (b) b2).

However, according to this embodiment, as described above, the assist torque is generated in the same direction as the motor rotation direction, that is, the return direction. That is, in the low speed range, the plus torque in FIGS. 5 and 6, that is, the torque in the same direction as the motor rotation direction is determined as the assist torques T2 and T3. Therefore, as shown in FIG. 4, the torque in the direction opposite to the motor rotation direction determined by the steering torque is sufficiently canceled. That is, since the steering torque generated in the turning direction due to the inertia due to the mass of the steering wheel itself is generally small, the assist torque T1 generated based on the steering torque is also small. On the other hand, by setting the assist torques T2 and T3 in the low speed range in FIGS. 5 and 6 to be sufficiently large, the assist torque Tas in the same direction as the motor rotation direction can be determined and generated. Therefore, the steering angle of the wheel quickly returns to the neutral position (FIG. 7).
(B) b3), the distance l3 required for return also becomes smaller, and the trajectory of the vehicle approaches the ideal dashed trajectory (FIG.
3). When the vehicle is running at a low vehicle speed, the assist torque T3 is constant regardless of the vehicle speed in a low vehicle speed range as shown in FIG. I have.

Next, the improvement of the convergence after turning during high-speed running will be described with reference to FIG. The rotor of the conventional electric motor of the electric power steering device has a very large inertia because it meshes with the mechanism of the steering device at a gear ratio of several tens to one. If the driver turns the steering wheel to zero after turning the steering wheel at high vehicle speed, the speed of returning to the neutral position by the self-aligning function becomes large because of the high vehicle speed. Therefore, in combination with the large inertia, the momentum toward the neutral direction increases. For this reason, even if the self-aligning function causes the wheel to return to the neutral position when approaching the neutral position and the force for returning to the neutral position is reduced, the rotor with large inertia continues to rotate, passes the neutral position, and turns the steering wheel in the reverse direction. Will rotate to This rotation produces a steering torque in the opposite direction, and the electric motor attempts to steer in the opposite direction.
Therefore, the vehicle is steered in the opposite direction. After the steering is performed in the reverse direction in this way, the self-aligning function attempts to return to the neutral direction again. For this reason, the steering angles of the wheels are alternately left and right as shown in FIG. 8C a 1, and the vehicle meanders (FIG. 8A). In this way, the handleability at the time of traveling at a high vehicle speed deteriorates, and depending on the characteristics and the vehicle speed of the vehicle, there is a possibility that the vehicle will diverge in the worst case and become a very dangerous state without convergence forever.

However, according to the present embodiment, as described above, as shown in FIG. 5, in the high-speed range of the vehicle speed, the assist torque T2 increases according to the motor rotation speed and the vehicle speed.
At a high vehicle speed, that is, an assist torque T2 in the direction opposite to the motor rotation direction is generated. At this time, the motor rotation speed shown in FIG. 3B is used. Similarly, in the high-speed range in FIG. 6, a plus torque proportional to the motor rotation acceleration is determined. However, as shown in FIG. 3C, when the steering angle approaches the neutral position, the motor rotation acceleration becomes −. Therefore, the determined torque becomes-, and the assist torque T3 in the direction opposite to the motor rotation direction is generated. In this way, the rotor of the electric motor that rotates in the return direction at a high speed with a large inertia is stopped by the positive assist torques T2 and T3 (FIG. 8).
(C) a3), meandering of the vehicle is prevented (FIG. 8 (b)).
That is, in FIG. 3A, as compared with the conventional steering angle locus indicated by a solid line, the assist torque T2 (FIG. 5) using the motor rotation speed of FIG. A rudder angle locus like a dotted line can be obtained. Also, a locus of the steering angle as shown by the dotted line on the lower side of FIG. 3A can be obtained by the assist torque T3 (FIG. 6) using the motor rotational acceleration of FIG. 3C. Further, by determining the assist torque T3 according to the rotational acceleration of the electric motor, the influence of the inertia of the rotor of the electric motor can be reduced. In this way, it is possible to prevent the rotor having a large inertia from moving past the neutral position due to the momentum and rotating the handle in the opposite direction (FIG. 8).
(C) a3) Therefore, convergence can be improved, and meandering of the vehicle can be prevented (FIG. 8B). In FIG. 6, in the high-speed range, the assist torque T3 is large according to the vehicle speed. As a result, as the vehicle speed increases, the steering wheel rotation speed in the process of approaching the neutral position by the self-aligning function decreases, so that the steering wheel can be returned so that the steering wheel rotation speed does not become too slow.

The control of this embodiment will be described with reference to FIG.
Based on the signal from the motor speed detecting means 15 (FIG. 1) and the signal from the steering torque detecting means 1, it is always monitored by the judging means 19 whether the rotation direction of the electric motor 7 is the same as the direction of the steering torque ( S1). While monitoring the same, the same control as in the past is performed, and the assist torque T1 corresponding to the steering torque is changed to the target assist torque Ta.
s is determined (S2). Conversely, if it is determined that the two directions are different, the assist torque T2 and the assist torque T3 are added to the assist torque T1 (S
3). That is, when it is determined that the direction is different, when the wheels try to return to the neutral position direction by the self-aligning function, the steering in the turning direction is caused due to the inertia due to the mass of the released handle. The torque was detected. In other words, there is a possibility that the steering wheel will be released after turning at low vehicle speed and the steering wheel will return poorly, or the return force after steering will be too large after steering at high vehicle speed and the convergence will deteriorate and the vehicle will not be able to return. It is considered that there is a possibility of meandering. Therefore, as described above, T1 is determined according to FIG. 4, T2 is determined according to FIG. 5, and T3 is determined according to FIG. Thus, the above-described target assist torque Tas is determined, and the effect of the present embodiment can be obtained.

Further, in the state where the driver releases the steering wheel after turning during low-speed running or high-speed running as in this embodiment, the return acceleration to eliminate the adverse effect due to the inertia of the rotor of the electric motor. When the assist torque is determined according to the above, the responsiveness can be improved by detecting the rotational acceleration of the electric motor and setting it as the return acceleration. That is, although it is possible to detect the return acceleration in the upstream portion of the steering device, that is, in the vicinity of the steering wheel, the response can be improved by detecting the acceleration in the downstream portion, that is, the electric motor as in the present embodiment.

[0017]

As described above, according to the control apparatus for an electric power steering device for a vehicle of the present invention, when the return of the steering wheel is likely to be poor at low vehicle speed traveling, the return direction of the steering wheel, that is, the motor rotation. The assist torque is generated in the same direction as the direction to improve the return of the steering wheel.
In addition, when the convergence after turning is likely to be a problem during high-speed running, the wheel attempts to return by the self-aligning function by generating an assist torque in the return direction of the steering wheel, that is, in the direction opposite to the motor rotation direction. It is possible to prevent the momentum from being too strong to pass the neutral position, prevent the vehicle from meandering, and improve high-speed convergence.

[Brief description of the drawings]

FIG. 1 is a control block diagram according to an embodiment of the present invention.

FIG. 2 is a control flowchart according to an embodiment of the present invention.

3A and 3B show rotation of an electric motor in response to a return of a steering wheel during low-speed running in an electric power steering apparatus. FIG. 3A is a diagram showing a temporal change in a steering angle, and FIG.
Is a diagram showing the change over time of the rotation speed of the electric motor,
(C) is a figure which shows the time change of the rotational acceleration of an electric motor.

FIG. 4 is a graph chart for determining an assist torque T1 of FIG. 1 or FIG. 2;

FIG. 5 is a graph chart for determining an assist torque T2 of FIG. 1 or 2;

FIG. 6 is a graph chart for determining an assist torque T3 of FIG. 1 or FIG. 2;

FIGS. 7A and 7B are diagrams for explaining the improvement of the return of the steering wheel at the time of low-speed running according to the present embodiment, in which FIG. 7A is a diagram showing the actual traveling trajectory of the vehicle, and FIG. is there.

FIGS. 8A and 8B are diagrams for explaining the improvement of convergence after turning during high-speed running according to the present embodiment, and FIG. 8A is a diagram showing a running locus of a conventional car, and FIG. It is a figure which shows a running locus, (c) is a figure which shows the return of the steering angle of the steering wheel for expressing the convergence after turning.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering torque detecting means 3 vehicle speed detecting means 7 electric motor 9 electric motor current value determining means 11 electric motor driving means 13 electric motor current detecting means 15 motor speed detecting means 17 motor acceleration detecting means 19 determining means 51 first assist torque detecting Means 52 Second assist torque detecting means 53 Third assist torque detecting means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-164664 (JP, A) JP-A-3-176278 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (1)

(57) [Claims] 1. A vehicle speed detecting means, a steering torque detecting means for detecting a steering torque generated by a driver turning a steering wheel, a motor speed detecting means for detecting a rotation speed of an electric motor, Motor acceleration detecting means for detecting rotational acceleration; determining means for determining whether a motor rotation direction and a steering torque direction are the same direction based on a signal from the motor speed detecting means and a signal from the steering torque detecting means; If the vehicle is in the same direction, the assist torque is determined according to the vehicle speed and the steering torque. If the determination is in a different direction, the assist is performed in the same direction as the motor rotation direction at a low vehicle speed according to the vehicle speed and the electric motor rotation speed or rotational acceleration. An assist torque determining means for determining an assist torque in a direction opposite to the motor rotation direction at a high vehicle speed; A control device for a vehicle electric power steering apparatus and a driving means for driving is applied to the electric motor rotating a current corresponding to the click.