JP2657930B2 - Control method of all-electric power steering - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling an all-electric power steering, and more particularly to a method for correcting a mechanical loss in power steering.

[Conventional technology]

Conventional motor-assisted power steering generates a very large mechanical loss due to motor friction, reduction gear efficiency (pinion-rack efficiency, rack pad friction in the case of pinion assist), and the desired assist force can be obtained. There was no problem.

Also, in order for the force from the tire side to be transmitted to the steering wheel, it is necessary to always overcome the above loss, so that the road surface reaction force is difficult to be transmitted to the steering wheel, and the steering feeling is deteriorated.

[Problems to be solved by the invention]

Conventionally, there has been a method of canceling the friction of the motor and a control of cutting and returning the handle, but it has not compensated for the loss of the gear mechanical part.

The present invention has been made in view of such a point,
An object of the present invention is to provide a control method of an all-electric power steering that can correct a mechanical loss in the power steering.

[Means for solving the problem]

In order to achieve such an object, the present invention obtains an instruction value of an assist motor drive current from a detected steering wheel torque value, and stops the motor at a motor end voltage VM ′ corresponding to the obtained instruction value of the assist motor drive current. From the motor end voltage at the time and the motor drive current, and compares the obtained motor end voltage VM ′ with the motor end voltage VM read at the time of detection of the steering wheel torque value, and when VM> VM ′, The rotation direction of the motor is determined to be the same as the direction of the indicated value, and VM <
In the case of VM ′, it is determined that the rotation direction of the motor is not the same as the direction of the indicated value, and if it is determined that the direction is the same, the first predetermined correction value is added to the indicated value to obtain a new indicated value. ,
When it is determined that the directions are not the same, a second predetermined correction value different from the first predetermined correction value is subtracted from the specified value to obtain a new specified value of the assist motor drive current.

[Action]

In the control method of the all-electric power steering according to the present invention, whether or not the rotation direction of the motor is the same as the direction of the rotation instruction is detected by the motor end voltage, and a different instruction value is set depending on whether or not the rotation direction is the same. It is something to do.

〔Example〕

FIG. 2 is a circuit diagram showing an assist motor drive control circuit for explaining an embodiment of a control method of an all-electric power steering according to the present invention. In the figure, 1
Is a torque sensor that outputs a torque signal a, 2 is a filter for removing noise of the torque signal a, 3 is a vehicle speed sensor that outputs a vehicle speed signal b, and 4 is a CP that controls the entire circuit.
U and 4a are A / D converters of the CPU 4, 5 is a D / A converter, 6 is a comparator, 7 and 8 are AND circuits, 9 to 12 are driving units, 13 is power switch means such as a relay, 14 to 14 17 is a transistor connected to the drive units 9 to 12, 18 is an assist motor, 19 and 20 are resistors for detecting a motor current, 21 is a current detector, 22 and 23 are analog switches, 24 is a buffer, and BT is a battery. It is.

Next, the general operation of the circuit shown in FIG. 2 will be described.
The torque signal a is input to the A / D converter 4a of the CPU 4, and the vehicle speed signal b is directly input to the CPU 4. The CPU 4 outputs a drive current value c as a command value from the signals a and b to the D / A converter 5, and outputs a right signal d and a left signal e for determining the rotation of the motor. The analog drive current value output from the A / D converter 5 is compared with the motor current value from the current detector 21 by the comparator 6, and if the drive current value is larger than the motor current value, the AND circuits 7, 8 "1" is output, and if it is small, "0" is output.
Is output. Here, the CPU 4 outputs the right signal d of “1” and “0”.
If the drive current value is larger than the motor current value, the AND circuit 7 outputs “1”.
Is output, and the drive section 9 drives the transistor 14. Further, the drive unit 12 directly inputs the right signal d from the CPU 4 and drives the transistor 17. Therefore, a current flows from left to right through the motor 18, and the motor 18 rotates rightward.
When the drive current value is smaller than the motor current value, or when both the right signal d and the left signal e are “0”, none of the transistors is driven.

In the case of clockwise rotation, the analog switch 22 is turned on, and the voltage at the left end of the motor 18 is supplied to the CPU 4 via the buffer 24.
Is input to The voltage at the right end of the motor 18 is substantially close to the body potential of the vehicle body, and therefore, the voltage at the left end of the motor 18 is substantially the motor end voltage. In the case of the left rotation, the analog switch 23 is turned on, and the same operation is performed.

Next, an embodiment of the present invention will be described with reference to FIGS. In FIG. 1, first, a steering wheel torque value is detected by the torque sensor 1 (step 31). Next, CPU4
Calculates an instruction value of the drive current corresponding to the steering wheel torque value (step 32). This is obtained from a characteristic curve S as shown in FIG. 3A stored in the memory of the CPU 4. In FIG. 3 (a), the horizontal axis indicates the left and right steering wheel torques, and the vertical axis indicates the motor instruction value (the instruction value of the drive current).

Next, the CPU 4 reads the motor-side voltage value via the analog switches 22 and 23 and the buffer 24 (step 3).
3) By comparing the read motor end voltage value with the motor end voltage corresponding to the indicated value, it is determined whether or not the rotation direction of the motor 18 is the same as the indicated direction (step 34). CPU4
Stores a graph of motor end voltage VM vs. indicated value as shown in FIG. 3 (b) in a memory, and determines whether or not the read motor end voltage VM is larger than VM ′ = instruction value × k. I do. The motor end voltage VM 'indicates characteristics when the rotation is zero, and when VM>VM', it indicates that the motor 18 is rotating in the same direction as the designated direction (hereinafter referred to as "forward rotation"). If VM <VM ′, it indicates that the motor 18 is rotating in a direction opposite to the designated direction (hereinafter referred to as “reverse rotation”). The fact that the motor 18 is rotating in the opposite direction means that the motor 18 is being rotated by an external force such as a tire.

In the case of forward rotation, the process proceeds to step 35, where the indicated value × A ×
The calculation of ΔF (steps 35 and 36) is performed, and this value (first predetermined correction value) is added to the instruction value of step 32 (step 37). This means that, when y = mx + n, x and x are designated values and y is the drive current. This will be described with reference to FIG. In FIG. 3C, a characteristic line S1 shown by a dotted line shows an ideal case without mechanical loss, and a solid characteristic line S2 shows an actual characteristic (characteristic without correction). For the drive current I1, the characteristic line
The mechanical output indicated by S2 is P1. This output P1 is smaller than the value P2 on the ideal characteristic line S1, which means that the assist is insufficient. In order to obtain the output P2 on the characteristic line S2, the drive current value must be I2. Correcting the current I1 to I2 is performed in steps 35 to 37 or step 38.
This is the operation at ~ 40. In other words, the characteristic line
S2 is an ideal characteristic line S1. The portion of the characteristic line S2 in the first quadrant of the graph of FIG. 3 (c) indicated by an upward arrow indicates a case where the motor 18 is rotating forward, and the portion indicated by a downward arrow indicates a case where the motor 18 is rotating reversely. . In the case of the reverse rotation, an output of the value P3 is obtained by the drive current I1, and since this value is larger than the ideal value P2, the drive current is reduced to I3 so that the output value becomes P2. This means that the mechanical losses that make it difficult for external forces to be transmitted to the steering wheel are cancelled. In this manner, the characteristics of the ideal characteristic line S1 can be obtained in the forward rotation and the reverse rotation, and a sufficiently large assist force can be obtained, and the steering feeling can be improved.

In the reverse rotation operation shown in steps 38 to 40, the second predetermined correction value obtained in steps 38 and 39 is subtracted from the instruction value. This is clear from the description of FIG. 3 (c).

Next, the instruction values obtained in steps 35 to 37 or steps 38 to 40 are output, and the motor 18 is driven (step 4
1).

In the above embodiment, the case where the characteristic line S2 is matched with the characteristic line S1 has been described. However, it is preferable that the characteristic of S3 be left with some hysteresis for stability of the steering system. In addition, the correction amount may be reduced at high speed or at low speed in consideration of the steering feeling preference. In this case, the characteristic line is, for example, a dashed line S3 and a solid line in FIG.
What is necessary is just to change according to speed within the range of S2.

〔The invention's effect〕

As described above, according to the present invention, the instruction value of the assist motor driving current is obtained from the detected steering wheel torque value, and the motor terminal voltage VM ′ corresponding to the obtained instruction value of the assist motor driving current is determined by the motor terminal voltage when the motor is stopped. It is obtained from the relationship between the voltage and the motor drive current, and the obtained motor end voltage VM ′
Is compared with the motor end voltage VM read when the steering wheel torque value is detected. If VM> VM ′, the rotation direction of the motor is determined to be the same as the direction of the indicated value, and if VM <VM ′, Determines that the rotation direction of the motor is not the same as the direction of the indicated value, and if it is determined to be the same direction, adds a first predetermined correction value to the indicated value to obtain a new indicated value. If it is determined, the second predetermined correction value different from the first predetermined correction value is subtracted from the instruction value to obtain a new instruction value of the assist drive current, so that the mechanical loss in power steering can be sufficiently reduced. Since the correction can be made and the road surface reaction force can be easily transmitted to the steering operator, a sufficient assisting force can be obtained as compared with the related art, and the steering feeling can be improved.

[Brief description of the drawings]

FIGS. 1 and 2 are diagrams and a flow chart of an assist motor drive control circuit for explaining an embodiment of another control method of an all-electric power steering according to the present invention.
The figure is a graph showing various maps stored in the memory in the CPU. 1 torque sensor, 2 filter, 3 vehicle speed sensor, 4 CPU, 4a A / D converter, 5 D / A converter,
6 ... Comparator, 7,8 ... And circuit, 9-12 ... Drive unit, 13 ... Power switch means such as relay, 14-17 ...
Transistor, 18… Assist motor, 19,20… Resistance, 21… Current detector, 22,23 …… Analog switch, 2
4 ... buffer, BT ... battery.

Claims (1)

(57) [Claims] 1. An assist motor drive current instruction value is obtained from a detected steering wheel torque value, and a motor end voltage VM 'corresponding to the obtained assist motor drive current instruction value is calculated based on the motor end voltage when the motor is stopped and the motor drive voltage. The obtained motor end voltage VM 'is compared with the obtained motor end voltage VM read at the time of detection of the steering wheel torque value, and when VM>VM', the rotation direction of the motor is designated. Direction is determined to be the same as the value direction, and if VM <VM ', the rotation direction of the motor is determined to be not the same direction as the direction of the indicated value, and if it is determined to be the same direction, the first predetermined correction is performed. The value is added to the indicated value to obtain a new indicated value, and when it is determined that the directions are not the same, a second predetermined correction value different from the first predetermined correction value is subtracted from the indicated value to obtain a new indicated value. Assist motor drive current All electric power steering control method characterized by the 示値.