JPS61202973A - Motor power steering device - Google Patents

Abstract

PURPOSE:To prevent hunting from occurring by providing a steering torque control system having hysteresis characteristics in a power steering reinforcing the steering force with a motor controlled via a detection signal of steering torque. CONSTITUTION:The said device amplifies a steering force signal from a torque detector 1 with an amplifier 2 then feeds it to the left and right turn detection circuits 3, 4, a motor drive circuit 5, and an absolute value circuit 6 respectively. When a steering wheel is detected to be operated to the left turn, for example, a selector switch 7 is transferred to the left turn, an the output current of the motor drive circuit 5 is fed to a motor 8. An output signal in response to the steering force from the absolute value circuit 6 is applied to a clutch control circuit 9 to control a clutch 10 provided between the motor 8 and a steering mechanism. In this case, an additional circuit 11 made by connecting a non-linear circuit 12 and a hysteresis circuit 13 in series is provided between the absolute value circuit 6 and clutch control circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric power steering device, that is, a device that uses an electric motor to assist in steering force.

(Prior art) An electric power steering device detects the steering force applied to the steering wheel by detecting the amount of twist of the steering shaft, and rotates the electric motor in forward or reverse direction depending on the presence or absence of the detection signal.
The torque generated by the electric motor is transmitted to the steering mechanism via a clutch controlled by the detection signal, thereby assisting the steering force, and FIG. 6 shows the control system of the prior art. be. The detection signal representing the steering force detected by the torque detector 1 is amplified by an amplifier 2 and then sent in parallel to a left rotation detection circuit 3, a right rotation detection circuit 4, a motor drive circuit 5, and an absolute value circuit 6. Supplied. When the steering wheel is being rotated counterclockwise, the counterclockwise rotation detection circuit 3 generates an output, switches the motor rotation selector switch 7 to counterclockwise rotation, and supplies direct current as the output of the motor drive circuit 5 to the motor 8. death,
Rotate it to the left. On the other hand, the absolute value circuit 6 outputs an output signal having a magnitude corresponding to the steering force, regardless of the steering direction, and supplies it to the clutch control circuit 9. The clutch control circuit 9 controls a clutch 10 inserted between the motor 8 and the steering mechanism, reduces the torque generated by the motor 8 to an amount necessary for assisting the steering force, and then transmits the torque to the steering mechanism.

(Problems to be Solved by the Invention) FIG. 7 shows the responsiveness of the steering assist force (assist amount) of the conventional electric power steering device. As the output of the torque detector 1 increases, the assist amount also increases, and the increase in steering force is reduced. As a result, the detected torque amount is at time t.

Although the smell exceeds its peak and begins to decrease, the amount of assist continues to increase because the mechanical system of the electric power steering device cannot respond immediately due to inertia.

Therefore, the assist amount becomes excessive (F,), and the detected torque amount is drastically reduced, and the assist amount is not reduced until time t2. The assist amount F2 after this reduction is an appropriate value F. Since it becomes too small due to further inertia, the detected torque amount is increased again and the above operation is repeated. In other words, hunting occurs.

An object of the present invention is to prevent the occurrence of hunting in an electric power steering device and to obtain assist characteristics similar to those of a hydraulic power steering device.

(Means for solving the problem) For the above purpose, the present invention inserts a hysteresis circuit into a circuit that controls the amount of assist, and adjusts the detected torque amount and
It is characterized by providing a hysteresis characteristic between the amount of assist controlled thereby.

(Function) The hysteresis characteristic is such that a larger output signal, that is, a larger torque amount is obtained for the same input signal level when the detected torque amount, which is the input signal, is decreasing than when it is increasing. Even if the amount of assist exceeds an appropriate value and the detected torque amount begins to decrease, the amount of assist does not decrease sharply. As a result, overshooting does not occur and therefore no hunting occurs.

(Example) FIG. 1 is a system diagram of an embodiment of the present invention.

In this figure, the components other than the additional circuit 11 surrounded by a dotted line are the same as the conventional electric power steering device shown in FIG. The additional circuit 11 has a nonlinear circuit 12 and a hysteresis circuit 13 connected in series, and is inserted between the absolute value circuit 6 and the clutch control circuit 9.

FIG. 2 shows an example of the nonlinear circuit 12. Since the amplifier 12α does not produce an output until there is an input at a certain level determined by the reference voltage "rgf", only the amplifier 12b operates while the input signal, that is, the detected torque amount is small, and the amplification rate AV determined by this, An amplified output signal is produced.When the input signal exceeds said certain level,
Amplifier 12α also becomes operational, and its output is
Since the width is increased by b, it is a two-step width increase, and the width increase rate AV is
The width will be increased at an increase rate AV2 that is even greater than the above. Therefore, the amplification characteristic of this nonlinear circuit 12 is
It becomes a broken line as shown in the figure.

The reason why the additional circuit 11 includes the nonlinear circuit 12 is as follows. That is, in a situation where the steering wheel is slightly rotated and a small amount of detected torque is output, assisting the steering force is either unnecessary or even harmful.

Therefore, it is necessary to provide a dead zone for this. The reason for this is that the low output region up to the above-mentioned corner point provides this. Up to this point, even if the detected torque amount increases, almost no output is generated, so no power steering operation occurs.

Note that various types of nonlinear circuits 12 other than the one shown in FIG. 2 are well known, and any of them may be used.

In short, it is sufficient to form a dead zone for low input.

The output of the nonlinear circuit 12 is input to a hysteresis circuit 13, which provides a hysteresis characteristic in addition to the above-mentioned insensitivity characteristic to low input. FIG. 4 shows an example of the specific circuit. The hysteresis circuit 13 includes an amplifier 13α,
13b in parallel, and a high input impedance amplifier 13C in series. The output terminal α of the amplifier 13α is connected to the non-grounding side of the peak hold capacitor 16 via the diode 14 in the forward direction, and the output terminal α of the amplifier 13h is connected to the non-grounding side of the capacitor 16 via the diode 15 in the reverse direction. Connected to the ground side. Capacitor 16 is connected to the input terminal of high input impedance amplifier 13C.

The amplification degree AV of the amplifier 135 is larger than the amplification degree AV of the amplifier 13α, as shown in FIG. 5(A), and the levels of their output terminals a and b vary depending on the input level. It changes as shown in graphs α and b. By the way, amplifier 13b
Since a diode in the opposite direction is connected to the output terminal of
The output of the amplifier 13α is held at its peak. Therefore, while the input level is increasing,
The level at terminal C of capacitor 16 rises along graph α and increases as shown by arrow C1 in FIG. 5B. When the input level starts to decrease after rising to P, amplifier 1
The level of the output terminal α of 3α is the level of the terminal C of the capacitor 16.
charging no longer takes place. Further, since the level of the amplifier 13.b#-output terminal S is higher than the level of the terminal C of the capacitor 16, and the diode 19 is connected in the reverse direction, no charging or discharging is performed therefrom. The level of this terminal C is amplified by the high input impedance amplifier 13C and becomes an output signal, but since no charge loss occurs there, the level of the terminal C is kept constant as shown by arrow C2. When the input level decreases to the value indicated by P2, the level of the output terminal S of the amplifier 13b matches the level of the terminal C of the capacitor 16, and since then becomes low, the capacitor 16 is directed to the amplifier 13b via the diode 15. The level of the terminal C follows the level of the terminal S of the amplifier 13b. Therefore, it changes as shown by arrow C3.

In the end, the level of the terminal C of the capacitor 16, that is, the input terminal of the amplifier 13C, is indicated by the arrow CI in FIG. 5B.

This results in a hysteresis characteristic as shown by C2, C, and the output level changes in the same way.

The hysteresis circuit 13 has the following effects on the control characteristics of the electric power steering device. That is,
During a period in which the detected torque amount (input) is increasing, its output increases as shown by arrow C1, and the clutch 10 is controlled via the clutch control circuit 9 to increase the assist amount. When the detected torque amount starts to decrease, the output is held constant as shown by arrow C2, so even if the detected torque amount decreases excessively due to a delay due to inertia in the decrease in the assist amount, the output will be kept constant as shown by arrow C2. , the output is unresponsive and constant. Therefore, the amount of assist does not decrease excessively, and there is no need for re-turning accordingly, so hunting does not occur. When the detected torque amount decreases by a certain amount or more, control is performed to reduce the assist amount for the first time at that stage.

In the above embodiment, the torque generated by the motor 8 is kept constant and the torque is controlled by the clutch 10, but the torque control means may be one that controls the motor 8 itself, such as chopper control. It's okay.

(Effects) As described above, the present invention has a hysteresis characteristic in the assist amount control system, so hunting does not occur during control, and the assist amount is similar to that of a hydraulic type even though it is an electric type. characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a control system of an embodiment of the present invention;
FIG. 2 is a circuit diagram showing an example of a non-linear circuit, FIG. 3 is a graph showing non-linear characteristics, FIG. 4 is a circuit diagram showing an example of a hysteresis circuit, and FIG. 5 is a graph showing hysteresis characteristics. FIG. 6 is a block diagram showing the control system of the prior art, and FIG. 7 is a graph showing the responsiveness of the assist amount in the prior art. DESCRIPTION OF SYMBOLS 1... Torque detection circuit, 8... Motor, 9... Clutch control circuit, 10... Clutch, 13... Hysteresis circuit, 13α, 13b... Amplifier, 14.1
5...Diode, 16...Capacitor. Patent applicant Koyo Seiko Co., Ltd. Koyo Automatic Machine Co., Ltd. Figure 4 Figure 5 P2 P, '-' +IUg Feather

Claims (3)

[Claims] (1) An electric power steering device that energizes an electric motor based on a steering torque detection signal and transmits the generated torque to a steering mechanism while controlling it based on the detection signal to assist steering force. An electric power steering device characterized by having a control system with hysteresis characteristics. (2) The electric power steering device according to claim 1, wherein the torque control means is a clutch controlled by the output of a clutch control circuit. (3) As a means to provide hysteresis characteristics, two amplifiers with different amplification factors that amplify a common input signal, and diodes with different conduction directions connected to their output terminals, respectively, are used. 3. The electric power steering device according to claim 1, further comprising a peak hold capacitor commonly connected to the output terminals of both diodes.