JPH0339861B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control device for an electric power steering device for an automobile.

Prior Art In automobiles, in order to reduce the need for steering wheel operations when turning the steering wheel, a torque sensor is provided to detect the steering torque during the steering operation, and this converts the steering torque into an electrical quantity. An electric power steering device has already been developed that variably controls the output of the electric device in response to changes in the steering torque and performs power assist in accordance with the steering torque (see, for example, Japanese Patent Publication No. 41246/1983).

Problems to be Solved by the Invention The electric power steering device as described above has various problems as described below.

(1) Return of the steering wheel after steering becomes difficult due to the inertia of the electric motor, the friction of the motor speed reducer, etc.

(2) Due to phase delays in signal transmission in the electric circuit, a time delay occurs between when the torsional torque sensor detects the steering torque and when the electric motor generates power assist. In such a case, the steering system becomes vulnerable to disturbances and self-excited vibrations are likely to occur during stationary steering.

Furthermore, since the electric motor provides power assist to the steering mechanism via the reducer, the response of the steering wheel may deteriorate due to the inertia of the electric motor and the friction of the reducer, giving the driver a strange feeling when steering. I have something to give.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can overcome the various drawbacks of the conventional devices as described above.

Means for Solving the Problems The present invention provides a torsional torque sensor that detects the torsional torque of a steering shaft and generates a torsional torque signal in an electric power steering device that performs power assist for steering using the output of an electric motor. an assist direction motor current instruction section that issues an assist direction motor current command value based on a sum signal of the torsion torque signal and the signal of a phase compensation section that issues a signal proportional to the differential value of the torsion torque signal of the torsion torque sensor; and a return direction motor current instruction section that issues a predetermined return direction motor current command value in the direction of returning to the straight traveling direction according to the steering angle, and the assist direction motor current instruction value of the assist direction motor current instruction section and the return direction motor current instruction section are provided. The present invention is characterized in that a control circuit is provided that adds the return direction motor current command value of the motor current instruction section and controls the current value supplied to the electric motor based on the added value.

Function The present invention operates as follows by employing the above configuration.

The control circuit is driven by an addition signal of a return direction motor current command value having a predetermined magnitude in the direction of returning to the straight direction according to the steering angle and an assist direction motor current command value based on the torsional torque signal of the steering shaft. Therefore, when the torsional torque of the steering shaft is zero or close to zero, the return direction motor current command value causes the electric motor to output in the direction of returning to the straight traveling direction, thereby canceling out the resistance to the movement of the steering wheel in the return direction. Moreover, by adding a signal proportional to the differential value of the torsional torque signal to the torsional torque signal of the steering shaft, a sudden change in the torsional torque signal can be detected and the responsiveness of the steering system can be improved.

Embodiments The present invention will be described in detail with reference to embodiments shown in the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, in which reference numeral 1 includes a steering angle sensor 11 that detects the steering wheel angle, and a return torque value indicating function unit 12 that issues a return direction motor current command value based on the steering angle sensor 11. In the return direction motor current instruction section, the return torque value instruction function section 12 continuously changes within a range of a certain steering angle |θ°|
|θ°| or more, the configuration is such that a constant return direction motor current command value iθ is generated in the direction of returning to the straight traveling direction.

Reference numeral 2 denotes an assist direction motor current instruction section which includes a torsional torque sensor 21 that detects the torsional torque of the steering shaft, and an output torque value instruction function section 22 that issues an assist direction motor current command value based on the torsional torque sensor 21.

Reference numeral 3 denotes a phase compensator that differentiates the torsional torque signal of the torsional torque sensor 21 and extracts a sudden change in the torsional torque signal, and the output signal from the phase compensator 3 is added to the torsional torque signal of the torsional torque sensor 21. It is configured so that

4 is a positive/negative discrimination section 41, an electric motor drive section 42,
A control circuit for a conventional electric power steering device consisting of an absolute value conversion section 43, a duty control section 44, and an armature current detection section 45. The output of the control circuit 4 drives the electric motor 5 and provides power assist to the steering mechanism 6. give.

That is, when the added signal obtained by adding the signals from the return direction motor current instruction section 1 and the assist direction motor current instruction section 2 is input to the control circuit 4, the polarity of the signal is determined by the positive/negative discrimination section 41 and the electric The rotation direction of the electric motor is determined by the motor drive section 42, and the absolute value of the signal is taken by the absolute value conversion section 43, and the duty control section 44
The absolute value of the signal is compared with the output of the armature current detection section 45, and the duty ratio is determined so that the motor current matches the command value (absolute value of the above signal), and the electric motor drive section 42 is controlled. It's summery.

Before explaining the operating conditions of the device of the present invention, a general control mode of the electric power steering device will be explained.

In principle, conventional electric power steering devices use a torsional torque sensor 21 that detects the torsional torque of the steering shaft and generates _{a torsional torque signal V T as} shown in FIG. By inputting the command value i of the output torque value instruction function unit 22 which issues the assist direction motor current command value i to the electric motor as shown in FIG. I'm going.

That is, when the steering wheel is slightly turned during steering, when the torsional torque signal V _T reaches V _R1 or V _L1 in Fig. 2, the signal V _R1 or V _L1
This determines whether the steering wheel is operated to the right or left, and determines the direction of the current that should be passed through the electric motor. Further, when the handle is rotated and the torsional torque signal V _T reaches the level of V _R2 or V _L2 , the control circuit starts operating according to that signal, and from then on, the control circuit operates as shown in Fig. 3 according to the torsional torque signal. The electric motor is designed to provide power assist to the electric motor according to the torsional torque of the steering shaft.

In the present invention, as shown in FIG. 1, an assist direction motor is constructed of a conventional steering shaft torsional torque sensor 21 and an output torque value instruction function section 22 that issues an assist direction motor current command value i based on the torsional torque signal V _T thereof. In addition to the current instruction section 2, a phase compensation section 3 that emits a signal proportional to the differential value of the torsional torque signal of the torsional torque sensor 21;
The above-mentioned torsional torque sensor includes a steering angle sensor 11 that detects the steering wheel angle of a steering wheel, and a return direction motor current instruction section 1 that includes a return torque value instruction function section 12 that issues a return direction motor current command value iθ based on the signal thereof. The assist direction motor current command value of the assist direction motor current command section 2 which issues the assist direction motor current command value based on the addition signal of the torsional torque signal of 21 and the signal of the phase compensation section 3, and the return direction motor current command section. The present invention is characterized in that it is provided with a control circuit 4 that controls the current value supplied to the electric motor by adding a value to the return direction motor current command value of No. 1.

That is, as shown in FIG. 4, the return direction motor current indicator 1 changes continuously in the range below a certain angle |θ゜|, and remains constant in the direction of returning to the straight traveling direction above |θ゜| It is configured to generate a value return direction motor current command value iθ.

For example, when the steering wheel is turned to the right, if the return direction motor current command value iθ due to this steering angle is added to the assist direction motor current command value i in Fig. 3, this addition causes the assist direction motor current command value i to gradually move downward. When the steering angle exceeds θ°, the assist direction motor current command value i changes as shown in Figure 5.
A signal that has been translated downward by iθ is obtained.

Based on this output signal, the control circuit 4 rotates the electric motor 5 with a current control characteristic that is obtained by shifting the conventional current control characteristic shown by the solid line downward in parallel by an amount corresponding to iθ as shown by the dotted line in FIG. It performs control and provides power assist to the steering mechanism 6.

As described above, when steering with power assist by the electric motor 5 is completed and the operating force of the steering wheel is reduced when returning to straight running, the assist direction motor current command value becomes zero. At that time, the steering angle is naturally greater than θ°, so the control characteristics of the control circuit 4 are in a state where the steering wheel is translated downward by an amount corresponding to iθ, as shown by the dotted line in FIG. When the torque is zero or close to zero, an output in the left-turn direction represented by iθ is generated, and the electric motor 5 rotates in the handle return direction. The rotational torque of the electric motor 5 cancels the resistance to the return movement of the steering wheel due to the inertia of the electric motor, the friction of the reducer, etc., so the steering mechanism 6 can be operated accurately by the caster effect on the wheel side. Return to the straight direction.

When the steering mechanism approaches the straight-ahead position and the steering angle enters the range within θ°, the return direction motor current command value gradually approaches zero as shown in Figure 4, so the control characteristics of the control circuit 4 are as shown in Figure 5. From the state shown by the dotted line, it gradually moves upward in parallel, and the output iθ in the left-hand direction also gradually decreases, and the return torque of the electric motor 5 becomes zero in the vicinity of the straight-ahead position, returning to the straight-ahead position. By the way, the control characteristics of the control circuit 4 return to the same state as the conventional one, as shown by the solid line in FIG.

In the above, the magnitude of the return direction motor current command value iθ that should generate the return direction torque when the assist direction motor current command value is zero or close to zero is determined by the return torque value instruction function unit 12. Therefore, by appropriately setting the function of the return torque value indicating function section 12, it is possible to generate a motor torque that exactly cancels the element that resists the steering wheel return force from the wheel side due to the caster effect.

In addition, in the conventional electric power steering device, the torsional torque signal V _T becomes V _R2 as shown in Fig. 2.
When the signal reaches the V _L2 level, the control circuit starts operating according to the signal, so as shown in Figure 3, there is a dead zone on both the left and right sides in which no output voltage is generated between the straight-ahead driving conditions. At the same time, due to delays in signal transmission in the electric circuit, when the steering wheel is operated, the power assist is activated with a delay, giving the driver a strange feeling when steering, and causing vibration when turning the vehicle off. Sometimes.

In order to deal with these problems, in the present invention, a signal proportional to the differential value of the torsional torque signal of the steering shaft is obtained by the phase compensator 3, and an output torque value is specified based on the signal obtained by adding this signal to the torsional torque signal. The control circuit 4 that controls the electric motor 5 is driven by the assist direction motor current command value given by the function section 22.

In the above embodiment, a steering angle sensor that detects the steering angle of the steering wheel was used, but in the case of a rack and pinion type gearbox, it is possible to use the stroke amount of the rack shaft or the rotation angle of the king pin. Of course.

Also, the return direction motor current indicator is at a certain angle |θ゜|
In the above, we have mentioned a device that issues a constant return direction motor current command value in the direction of returning to the straight traveling direction.
It is also possible to use one that issues a return direction motor current command value that increases or decreases as the steering angle increases.

Effects of the Invention The present invention provides an assist direction in which an assist direction motor current command value is issued based on a sum signal of a torsional torque signal of a steering shaft and the signal of a phase compensator which issues a signal proportional to the differential value of the torsional torque signal. The assist direction motor current instruction value of the motor current instruction section and the return direction motor current instruction value of the return direction motor current instruction section that issues a constant value of the return direction motor current instruction value in the direction of returning to the straight traveling direction when the steering angle exceeds a predetermined value angle. The return direction motor current command value is added, and based on the added value, the current control characteristics for the electric motor are shifted in parallel downward when the steering direction is rightward, and upward when steering direction is leftward. This is designed to generate an output that rotates the electric motor in the handle return direction with zero or close to zero torsional torque. Not only can the return characteristics of the rudder of the electric power steering device be significantly improved, but also the range of zero power assist can be reduced under driving conditions where the torsional torque is relatively small relative to the steering angle at high speeds. The larger size eliminates the conventional problem of the steering wheel being too light when driving at high speeds, improves the follow-up of power assist due to delay in signal transmission in the electric circuit, and prevents vibrations during stationary steering. It is possible to eliminate the strange feeling during steering due to the inertia of the electric motor during high-speed driving.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Figs. 2 and 3 show control modes of a conventional electric power steering device, and Fig. 2 is a torsional torque signal characteristic diagram of a steering shaft. FIG. 3 is a characteristic diagram of current control to the electric motor based on the torsional torque signal. 4 and 5 are diagrams showing an example of the control mode of the electric power steering device according to the present invention, in which FIG. 4 is a steering angle signal characteristic diagram, and FIG. 5 is a diagram showing assist direction motor current command value and return direction. FIG. 4 is a characteristic diagram of current control to the electric motor based on a signal added to a motor current command value. DESCRIPTION OF SYMBOLS 1... Return direction motor current instruction section, 11... Rudder angle sensor, 12... Return torque value instruction function section, 2
... Assist direction motor current instruction section, 21 ... Torsional torque sensor, 22 ... Output torque value instruction function section, 3 ... Phase compensation section, 4 ... Control circuit, 5 ...
Electric motor, 6... Steering mechanism.

Claims (1)

[Claims] 1. In an electric power steering device that performs power assist for steering using the output of an electric motor, the torsional torque signal of the torsional torque sensor that detects the torsional torque of the steering shaft and generates the torsional torque signal, and the torsional torque signal of the torsional torque sensor an assist direction motor current instruction section that issues an assist direction motor current command value based on a signal added to the signal of a phase compensation section that issues a signal proportional to the differential value of the torsional torque signal; a return direction motor current instruction section that issues a predetermined return direction motor current command value in the direction, and the assist direction motor current instruction value of the assist direction motor current instruction section and the return direction motor current command of the return direction motor current instruction section are provided. 1. A control device for an electric power steering device, characterized in that a control circuit is provided for adding the current value and controlling the current value supplied to the electric motor based on the added value.