JPH0325075A - Motor-driven power steering - Google Patents

Abstract

PURPOSE:To improve safety and reliability in the running of an automobile by constructing the title device in such a way as to judge the failure of torque sensors from the logical product of the output signals of a torque direction nonconformity detecting means and a dead zone detecting means. CONSTITUTION:The torsion torque of a steering handle is detected at two torque sensors 1, 2. The direction of each torsion torque is discriminated by discriminating means 5a, 5b from the detection signals of these torque sensors 1, 2, and the nonconformity of torque directions is discriminated at a torque direction nonconformity detecting means 5c.. A dead zone detecting means 5d further detects that the detection signal of one torque sensor 1 is outside the fixed range. The failure of the torque sensors 1, 2 is discriminated by the logical product of the output signals of these torque direction nonconformity detecting means 5c and dead zone detecting means 5d, thus performing protective action.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an electric power steering device that uses an electric motor to reduce the steering force of a steering wheel of an automobile, and in particular, to detect a failure of a torque sensor. This invention relates to an electric power steering device that improves safety by using a torque sensor. (Prior technology) An electric power steering device detects the steering force of the steering wheel using a torque sensor, and adjusts the current of the electric motor according to the torque detection signal. The torque sensor is controlled so as to reduce the steering force by generating assist torque.Therefore, since failure of the torque sensor has a fatal effect, various protection methods have been proposed.

(Problem to be solved by the invention) In particular, if a torque detection signal is output with a polarity opposite to the direction of steering torque due to an abnormality in the torque sensor, assist torque is applied in a direction contrary to the driver's intention, which can be dangerous. The object of the present invention is to detect and take protective action against torque sensor failure, which is the most dangerous failure mode.

[Structure of the invention]

(aII! Means and operation for solving the problem) In order to achieve the above object, the present invention includes a torque sensor that detects the torsional torque of the steering wheel, and adjusts the current of the electric motor according to the torque detection signal to generate assist torque. As shown in Figure 1, an electric power steering device that controls a steering wheel uses two torque sensors that detect the torsional torque of the steering wheel, and determines the direction of the torsional torque from the detection signals of these two torque sensors and determines the torque direction. A torque direction mismatch detection means for determining a mismatch between the torque direction mismatch detection means and a dead zone detection means for detecting that the detection signal of one of the torque sensors is outside a certain range is provided. This is an electric power steering device that enables protective operation by determining failure of the torque sensor from the AND of output signals.

(Example) An embodiment of the invention is shown in FIG.

In FIG. 2, l is a torque sensor (not shown) that detects the torsional torque of the handle and is used for assist torque control;
2 is a torque sensor that detects the twisting torque of the steering wheel and is used to detect failures, similar to the torque sensor 1; 3 is a control unit that adjusts the current of the motor 4 in accordance with the detection signal of the torque sensor 1; The control section 3 includes an A/D conversion means 3a for converting an analog torque detection signal Ti into a digital torque detection signal Ti, a current reference determining means 3b for determining a current base increase according to this signal T1X. a current control means 3c for controlling the current I of the motor 4 according to the IT style standard construction; It is composed of current detection means 3d.

Reference numeral 5A denotes a torque direction mismatch detecting means for determining a mismatch in torque direction from the detection signals of torque sensors 1 and 2. Comparators 5a and 5b determine the direction of torsional torque from the signals of torque sensors 1 and 2; Detecting exclusive OR (Exclusive○R) circuit 5
c. Consists of an adjustment resistor 5f for setting the detection level. Further, in this embodiment, the dead zone detection means 5d is
It is configured to detect that the torsional torque is outside a certain range using a digital torque detection signal TIX.

In the above embodiment, the detection characteristics of the torque sensor 1.2 are as shown in characteristic A in FIG. 3, where the output voltage is v0 when the steering wheel twisting torque is zero, increases when the torque is positive, and decreases when the torque is negative 1. .

The detection characteristic of the torque sensor is manufactured with the above-mentioned characteristic A as the target, but due to variations during mass production, changes in ambient temperature, changes over time, etc., an error of ∆V with respect to characteristic A occurs as in characteristics B and C.

The dead fF detecting means 5d sets the range of the output voltage of the torque sensor 1 in the range v0±2ΔV as a dead zone, and outputs a signal DE having a logical value of "1" when the output voltage is other than that range.

The detection level of the adjustment resistor 5f is set to the above v0,
The comparators 5a and 5b are this ■. and torque sensor 1,
The direction of the torsional torque is determined by comparing the two output voltages.

That is, if the output voltage of the torque sensor is greater than V0, it is determined to be a positive torque and a logical value "l" is output; if it is smaller than v0, it is determined to be a negative torque and a logical value {1 0 j#
Outputs . ? The alternative OR circuit 5c is a comparator 5a
, 5b do not match, it is determined that the torque direction does not match, and a signal CS of logic value #IIT is output. When both the signals DE and CS become at 1 u, the AND circuit 5e outputs a torque sensor failure signal FD, stops the operation of the current control means 3c, and reduces the current of the motor 4 to zero, thereby reducing the assist torque to zero. Perform fail-safe operation. In this case, when the detection characteristic of torque sensor 1 is characteristic A in Fig. 3, the torsional torque range of ±τ2 is excluded as a dead zone, so even if the detection characteristic of torque sensor 2 has an error in the range of characteristics B and C, it will cause an error. It will never be detected. Also, the detection characteristic of torque sensor 1 is characteristic B or characteristic C.
When , the torsional torque is 1τ, 〜τ■ or −τ■〜τ,
This range is excluded as insensitive, and even if the detection characteristic of the torque sensor 2 has an error of ΔV in the opposite direction, it will not be erroneously detected.

According to this embodiment, the function of the dead zone detection means can be implemented by a microcomputer, and the number of hardware components is reduced, further improving reliability and economical efficiency.

〔Effect of the invention〕

According to the present invention, it is possible to perform a protective operation by detecting an abnormality in the detection signal of the torque sensor, especially when the torque detection signal is generated in the direction opposite to the direction of the twisting torque of the steering wheel. In addition, it is possible to provide an electric power steering device that is simple in structure and easy to adjust, and is economical and suitable for mass production.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an electric power steering device of the present invention, FIG. 2 is a diagram of an embodiment of the present invention, and FIG. 3 is a detection characteristic diagram of a torque sensor. 1... Torque sensor 3... Control section 3a...A
/D conversion means 3b...Current reference determining means 3c...
Current control means 3d... Current detection means 4... Motor 5... Torque sensor failure detection means 5a, 5b.
...Torque direction determining means (comparator) 5c...Discrepancy detecting means 5d...Dead zone detecting means 5e...AND circuit (exclusive OR circuit) 5f...Adjusting resistor

Claims (1)

[Claims] Equipped with a torque sensor that detects the twisting torque of the handle.
In an electric power steering device that controls the assist torque by adjusting the current of the electric motor according to the torque detection signal, two torque sensors detect the torsional torque of the steering wheel, and each torsion is detected from the detection signals of these two torque sensors. The torque direction mismatch detection means includes a torque direction mismatch detection means for determining the direction of torque and a mismatch in the torque direction, and a dead zone detection means for detecting that the detection signal of one of the torque sensors is outside a certain range. An electric power steering device characterized in that a failure of a torque sensor is determined from a logical product of an output signal of the dead zone detection means and an output signal of the dead zone detection means.