JPH02120179A - Control method for electric power steering - Google Patents

Abstract

PURPOSE:To make assist control performable at the safety side irrespective of any trouble in a torque sensor by controlling a driving current of an electric motor according to a low level torque value among torque values or output of plural numbers of torque sensors detecting steering torque. CONSTITUTION:A torque value T in use on assist control is determined on the basis of respective torque values T1, T2 being detected by two torque sensors 5, 6 but at time of this determination, first the second torque value T2 is compared with a minimum torque value Tmin and a maximum torque value Tmax in a normal range, and then the absolute value of a difference between both these torque values T1 and T2 is compared with a maximum error DELTAT of both torque values. When it is so judged that there is no trouble from these compared results, the absolute values of both torque values T1, T2 are compared, and the low level torque value is determined as the torque value T. Then, a steering assist value is operated from this determined torque value T and a car speed V by a car speed sensor 21, thereby driving and controlling an electric motor 8.

Description

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

[Conventional technology]

Conventionally, various electric power steering devices have been proposed that detect the steering torque of a steering system, control the drive current of an electric motor according to the detected steering torque, and assist the steering torque. Among these, there is one in which a plurality of torque sensors are provided to specifically detect steering torque, and when the steering torque values detected by these sensors are substantially different, the steering force is not assisted by the electric motor ( Utility Model Application No. 62-152880).

In the case of this power steering device, the detection signal of one of the torque sensors is used to assist control fn of the steering torque.
While doing so, the signal levels of both torque sensors are compared, and when the difference in level exceeds a certain value, it is determined that the torque sensor has failed and the assist control is stopped. Therefore, it is possible to have a fail-safe function in the event of a torque sensor failure, and there is an advantage that safe driving is ensured without any hindrance to driving even in the event of a failure of the torque sensor.

[Problem to be solved by the invention]

However, in the case of the power steering device described above, when one torque sensor fails and the difference in signal level between both torque sensors exceeds a certain value, if the time required to determine the failure is long, the steering torque will be reduced during that time. There is a problem in that the assist control is executed and a shock is generated in the steering system.

On the other hand, if the failure determination time is shortened, the above-mentioned shock can be eliminated, but there is a problem in that when noise etc. temporarily enters one of the torque sensors, it is incorrectly determined to be a failure, and steering torque assist control stops. There is.

Therefore, an object of the present invention is to provide an electric power steering system that can always perform assist control on the safe side even if the torque sensor fails in any way, and that can prevent erroneous determination of failure due to noise, etc. The object of the present invention is to provide a method for controlling a device.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a plurality of torque sensors for detecting steering torque, and generates a drive current of an electric motor according to a low-level torque value among the torque values detected by these torque sensors. It is characterized by controlling.

[Effect]

For example, if one torque sensor fails with a higher signal level, the assist control is executed using the detection signal of the other torque sensor with a lower signal level. Furthermore, if one of the torque sensors has a failure in which the signal level is lower, the assist control is executed using the detection signal of the failed torque sensor. In other words, no matter how the torque sensor malfunctions, assist control can always be performed on the safe side.

Furthermore, as described above, when the torque sensor fails, assist control is always performed to the safe side, so the failure determination time can be lengthened. Therefore, erroneous determination of failure due to noise or the like can be prevented.

[Embodiment] FIG. 1 shows a schematic configuration of an electric power steering device according to the present invention.

A steering shaft 2 is fixed to the handle 1, and a pinion shaft 3 is connected to the tip of the shaft 2. A pinion 3a formed at the tip of the pinion shaft 3 meshes with a rack 4 that is slidably guided in the rotational and axial directions. Binion shaft 3 above
Two torque sensors 5.6 are attached around the pinion shaft 3 to independently detect the steering torque acting on the pinion shaft 3. A pinion 7 for assisting the steering torque is also engaged with the rack 4, and this pinion 7 is driven by an electric motor 8. Note that a speed reduction mechanism 9 for torque amplification is provided between the pinion 7 and the electric motor 8.

Both ends of the rack 4 are connected to steering knuckles 16.17 that support left and right front wheels 1415 via a pole joint 1011 and tie rods 12.13.

The controller 20 is composed of a microcomputer, and receives the detection signals from the torque sensors 5 and 6 and the vehicle speed signal from the vehicle speed sensor 21, and controls the drive current of the electric motor 8 based on these input signals as shown in FIG. , assists with steering force.

That is, when the steering force of the steering wheel 1 increases at low speeds, the drive current also increases rapidly and the assist steering force also increases. Therefore, it becomes easier to operate the steering wheel during low-speed cornering or when parking the vehicle. On the other hand, at high speeds, the drive current increases as the steering force of the steering wheel l increases, but the slope of the increase is lower than at low speeds. Therefore, the driver can feel the steering wheel's response when driving at high speed, and driving stability can be ensured.

Next, control of the electric power steering device according to the present invention will be explained.

FIG. 2 shows the main routine. First, step 30 is performed to determine the torque value "T" used for assist control from the detection signals obtained from the two torque sensors 5 and 6.
), then step 31) to determine the vehicle speed “v°” detected by the vehicle speed sensor 21, and step 32) to calculate the steering assist amount, which is the assist steering force, from these torque value “T” and vehicle speed “■”. , and finally, an assist signal corresponding to this amount of steering assist is sent to the electric motor 8.
Step 33), and repeat this operation thereafter.

FIG. 3 shows details of the routine for determining the torque value "T" in step 30. That is, the first torque value "T1" is input from the first torque sensor 5 (step 40), and then the second torque value "T" is input from the second torque sensor 6 (step 41).Next, In order to determine the abnormality of the torque sensor 5.6, the second torque value T2 is set to the minimum torque value Ta17 and the maximum torque value T*s in the normal range.
Compare x with step 42), and further Ml) compare the absolute value of the difference between the first straight line T1 and the second straight line T2 with the maximum error ΔT between both torque values (step 43).

If both the conditions in steps 42 and 43 are satisfied, it is determined that there is no abnormality in the torque sensor 5.6, and the fail counter Fe is set to 1t=0 (step 44), and then the first torque value T is set. Both absolute values of the second torque value T2 are compared (step 45). IT.

If ≦IT2 l, the first torque value T is at a low level;
is determined as the torque value T (step 46), and conversely, IT
, l>lTz l, the low level second torque value T2 is determined as the torque value T, step 47), and the process returns.

If any of the conditions in steps 42 and 43 are not satisfied, it is determined that there is an abnormality in the torque sensor 5.6,
Add 1 to the fail counters Fc, L (step 48), and compare the added fail counter Fc++L with the fail judgment delay constant C (step 49). In other words, the abnormality in the torque sensors 5 and 6 is a primary noise. Determine whether the problem is caused by a problem or a malfunction. Fe
, , <C, it is determined that it is noise, and the control from step 45 onwards is executed. Conversely, if F cfit≧C, it is determined that one of the torque sensors 5, 6 has failed, and the assist control is stopped (step 50).

In the above control, for example, if an abnormality occurs in the direction where the signal level of one torque sensor is higher, even if it is not determined that there is a failure in step 49, the other torque sensor with the lower signal level is The detected signal is determined as the torque value T.

If an abnormality occurs in the lower signal level of one torque sensor, even if it is not determined that there is a failure in step 49, the detection signal of the other torque sensor with the lower signal level is detected in steps 45 to 47. The detection signal of the failed torque sensor is determined as the torque value T. Therefore, even if the torque sensors 5 and 6 fail in any manner, assist control can always be performed on the safe side.

In addition, since assist control is always performed to the safe side when the torque sensor 5.6 fails, there is no need to quickly perform failure determination, and the failure determination delay constant C, which is the failure determination time, is eliminated.
can be set to a larger value than before. Therefore, erroneous determination of failure due to noise or the like can be prevented.

Note that in the control shown in FIG. 3, the assist control is stopped when it is determined that one of the torque sensors is in failure (step 50), but the assist control may be continued. That is, in the present invention, since assist control is always performed using a low-level torque signal, safety can be ensured even if control continues even if one torque sensor is out of order.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the drive current of the electric motor is controlled according to the low-level torque value among the torque values detected by the plurality of torque sensors. Regardless of the manner in which the failure occurs, assist control can always be performed on the safe side, and the failure determination time can be extended, so that erroneous determination of failure due to noise or the like can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a schematic structural diagram of the electric power steering device according to the present invention, Fig. 2 is a flowchart of the main routine of assist control, Fig. 3 is a flowchart of the torque value determination routine, and Fig. 4 is a steering wheel steering force. FIG. 3 is a diagram showing the relationship between motor drive current and motor drive current. l...Handle, 2...Steering shaft, 5
゜6...Torque sensor, 8...Electric motor, 20.
··controller.

Claims (1)

[Claims] In an electric power steering device that detects the steering torque of a steering system and controls the drive current of an electric motor according to the detected steering torque to assist the steering torque, a plurality of sensors for detecting the steering torque are used. A method for controlling an electric power steering device, comprising: providing a torque sensor; and controlling a drive current of an electric motor according to a low-level torque value among the torque values detected by the torque sensors.