JPH02164664A - Control method for all-electric power steering - Google Patents

Abstract

PURPOSE:To compensate for mechanical loss by comparing a motor terminal voltage corresponding to a reading of assistant motor driving current to a motor terminal voltage during detection of a handle torque value, and adding and subtracting a correction value in accordance with the decision result: whether the rotational direction of a motor conforms to the direction of the reading or not. CONSTITUTION:When a vehicle is operated, CPU 4 calculates a reading of driving current corresponding to a handle torque value detected by a torque sensor 1 to obtain a motor terminal voltage corresponding to the reading. A motor terminal voltage read out through analog switches 22, 23 and a buffer 24 is compared to the motor terminal voltage corresponding to the above reading to judge whether the rotational direction of a motor 18 is the same as an indicated direction. When the rotational direction is judged to be proper, a specified correction value is added to the reading, and when the rotational direction is judged to be reverse, a specified correction value is subtracted from the reading. The motor 18 is thus driven and controlled by the obtained reading to assist steering force due to a handle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling all-electric power steering, and more particularly to a method for correcting mechanical loss in power steering.

[Conventional technology]

Conventional motor-assisted power steering generates extremely large mechanical losses due to motor friction, reduction gear efficiency (in the case of pinion assist, pinion-to-rank efficiency, rack pad friction), etc., making it impossible to obtain the desired assist force. The problem was that there was no.

Furthermore, in order for the force from the tire side to be transmitted to the steering wheel, it is necessary to always overcome the above-mentioned loss, which makes it difficult for the road reaction force to be transmitted to the steering wheel, resulting in deterioration of the steering feeling.

[Problem to be solved by the invention]

Conventionally, methods to cancel motor friction, handle notches,
Although there was a return control, it did not compensate for the loss of the gear mechanism.

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

[Means to solve the problem]

In order to achieve such an object, the present invention uses a motor terminal voltage corresponding to an instruction value of an assist motor drive current obtained from a detected steering wheel torque value and a motor terminal voltage read at the time of detecting the steering wheel torque value. Compare and detect whether the rotation direction of the motor is the same as the direction of the indicated value,
If they are in the same direction, the first predetermined correction value is added to the instruction value, and if they are not in the same direction, the second predetermined correction value is subtracted from the instruction value to obtain a new instruction value for the assist motor drive current. This is what I did.

[Effect]

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

[Embodiment] FIG. 2 is a circuit diagram showing an assist motor drive control circuit for explaining an embodiment of the all-electric power steering control method 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 from the torque signal a, 3 is a vehicle speed sensor that outputs a vehicle speed signal, 4 is a CPU that controls the entire circuit, 4a is the A/D conversion section of CPU4,
5 is a D/A converter, 6 is a comparator, 7 and 8 are AND circuits,
9 to 12 are drive units, 13 is a power switch means such as a relay, 14 to 17 are transistors connected to the drive units 9 to 12, 18 is an assist motor, 19 and 20 are resistors for detecting motor current, and 21 is a A current detector, 22 and 23 are analog switches, 24 is a buffer, and BT is a battery.

Next, the general operation of the circuit shown in FIG. 2 will be explained. The torque signal a is input to the A/D converter 4a of the CPU 4,
The vehicle speed signal is directly input to the CPU 4. CPU4 is
A drive current value C as a command value is output from the signals a and b to the D/A converter 5, and a right signal d and a left signal e that determine the rotation of the motor are output. The analog drive current value output from the D/A converter 5 is compared with the motor current value from the current detector 21 by a comparator 6, and if the drive current value is larger than the motor current value, an AND circuit 7.8 ``1'' is output for the value, and ``0'' is output if the value is smaller. Here, the CPU
4 outputs a right signal d of "1" and a left signal e of "0", and if the drive current value is larger than the motor current value, the AND circuit 7 outputs the signal rlJ, and the drive Section 9 drives transistor 14 . In addition, the drive unit 12
directly inputs the right signal d from the CPU 4 and drives the transistor 17. Therefore, current flows from left to right in the motor 18, causing the motor 18 to rotate in the right direction. If the drive current value is smaller than the motor current value, or the right signal d,
If the left signals e are both rOJ, neither transistor is driven.

Note that 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 input to the CPU 4 via the buffer 24. The voltage at the right end of the motor 18 is approximately close to the body potential of the vehicle (therefore, the voltage at the left end of the motor 18 is approximately the motor end voltage. In the case of counterclockwise rotation, the analog switch 23 is turned on and the same operation is performed. .

Next, an embodiment of the present invention will be described using FIGS. 1 to 3. In FIG. 1, first, a steering wheel torque value is detected by the torque sensor 1 (step 31). Next, the CPU
4 calculates an instruction value of the drive current corresponding to the above-mentioned handle torque value (step 32), which is obtained from a characteristic curve S as shown in FIG. 3(a) stored in the memory of the CPU 4. In FIG. 3(a), the horizontal axis shows the left and right steering wheel torque, and the vertical axis shows the motor instruction value.

Next, the CPU 4 reads the motor end voltage value via the analog switch 22, 23 and the buffer 24 (step 33), compares the read motor end voltage value with the motor end voltage corresponding to the instruction value, Determine whether the rotational direction of the motor 18 is the same as the indicated direction (step 34
). The CPU 4 stores in its memory a graph of the morph end voltage VM versus the instruction value as shown in FIG. . The motor terminal voltage VM" indicates the characteristic when the rotation is zero, and when VM>VMo, it indicates that the motor 18 is rotating in the same direction as the indicated direction (hereinafter referred to as "forward rotation"), and VM <VM" indicates that the motor 18 is rotating in the opposite direction to the indicated direction (hereinafter referred to as "reverse rotation"). If the motor 18 is rotating in the opposite direction, it means that the motor 18 is rotating in the direction opposite to the indicated direction (hereinafter referred to as "reverse rotation"). It means that it is turned by an external force.

In the case of forward rotation, proceed to step 35 and calculate the indicated value x A +
Calculate ΔF (steps 35 and 36) and obtain this value (
(first predetermined correction value) is added to the instruction value in step 32 (step 37), which means determining m and n when y-mx+n (X is the instruction value, y is the drive current). This will be explained using Fig. 3 (C1). In Fig. 3 (C), the dotted characteristic line S1 shows the ideal case with no mechanical loss, and the solid line S2 shows the ideal case. In the case of drive current ■1, which shows the actual characteristics (characteristics without correction), the mechanical output shown by the characteristic line S2 is Pl.This output P1 is smaller than the ideal characteristic, the value P2 at %IS2. , this means that the assist is insufficient.In order to obtain the output P2 in the characteristic MS2, the drive current value is
Must be 2.

Steps 35 to 3 correct the current II to become ■2.
7 or the operations in steps 38-40. In other words, the correction changes the characteristic &1lS2 to the ideal characteristic &iS1
This is what is done. The part indicated by the upward arrow of the characteristic line S2 in the first quadrant of the graph in FIG. 3(C) is when the motor 18 is rotating in the normal direction, and the part indicated by the downward arrow is when the motor 18 is rotating in the reverse direction. .

In case of reverse rotation, drive current! l gives an output of value P3, which is larger than the ideal value P2, so the drive current is reduced to 1.
3 so that the output value becomes P2. This means counteracting mechanical losses that make it difficult for external forces to be transmitted to the handle. In this way, it is possible to have the characteristics of the ideal characteristic line S1 in forward and reverse rotations, to obtain a sufficiently large assisting force, and to improve the steering feeling.

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) above.

Next, the instruction values obtained in steps 35 to 37 or steps 38 to 40 are output, and the motor 18 is driven (step 41).

In the above embodiment, the case where the characteristic line S2 is matched with the characteristic line Sl has been explained, but it is preferable to leave some hysteresis and set the characteristic to 83 in order to stabilize the steering system. Taking into consideration, the correction amount may be reduced at high speed or low speed.
In this case, the characteristic line is, for example, shown in FIG.
What is necessary is to change it according to the speed within the range of solid line S2.

〔Effect of the invention〕

As explained above, the present invention compares the motor terminal voltage corresponding to the instruction value of the assist motor drive current obtained from the detected steering wheel torque value with the motor terminal voltage read at the time of detecting the steering wheel torque value, and It is detected whether the rotation direction is the same direction as the indicated value, and if it is the same direction, a first predetermined correction value is added to the indicated value, and if it is not the same direction, a second predetermined correction value is added from the indicated value. By subtracting the value to obtain the new assist motor drive current instruction value,
Mechanical losses in power steering can be sufficiently compensated for, and road reaction forces can be easily transmitted to the steering person, so it is possible to obtain more sufficient assist force than before, and it also has the effect of improving the steering feeling.

[Brief explanation of the drawing]

1 and 2 are an assist motor drive control circuit diagram and a flowchart for explaining an embodiment of an alternative control method for all-electric power steering according to the present invention;
The figure is a graph showing various maps memorized in the CPtJ. l...torque sensor, 2...filter, 3...vehicle speed sensor, 4...CPU, 4a...A/D conversion unit,
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... Resistor, 21...・Current detector, 22.23...Analog switch, 24...Banpha, BT...Battery patent applicant Jidosha Kiki Co., Ltd.

Claims (1)

[Claims] The motor end voltage corresponding to the indicated value of the assist motor drive current obtained from the detected handle torque value is compared with the motor end voltage read at the time of detecting the handle torque value, and the rotation direction of the motor is determined to match the indicated value. Detecting whether or not the direction is the same as the direction, and if the direction is the same, a first predetermined correction value is added to the indicated value, and if the direction is not the same, a second predetermined correction value is subtracted from the indicated value. A control method for an all-electric power steering system, characterized in that a new command value for an assist motor drive current is set using a new instruction value for an assist motor drive current.