Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1998-09-02
2001-05-29
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S043000, C180S443000, C180S446000, C280S735000, C318S432000
Reexamination Certificate
active
06240349
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improvement of an electric power steering apparatus for steering assistance based on an output of a torque sensor which detects a steering torque. More particularly, the invention relates to detection of malfunction for the torque sensor.
FIG. 1
is a block diagram showing the constitution of an essential part of the conventional electric power steering apparatus. In the electric power steering apparatus, a steering torque signal from a torque sensor
2
provided on a steering shaft (not illustrated) is phase compensated by a phase compensation unit
11
and given to an assist control unit
12
.
Besides, a vehicle speed signal from a vehicle speed sensor
7
is given to the assist control unit
12
. The assist control unit
12
outputs a target current value for assist control (steering assist control) based on the steering torque signal from the phase compensation unit
11
and the vehicle speed signal from the vehicle speed sensor
7
and gives the value to subtracting means
15
.
The subtracting means
15
obtains a deviation between the target current value from the assist control unit
12
and a feed back value of the drive current of the motor
5
detected by the motor current detection circuit
6
, and gives this deviation to the motor drive circuit
16
. The motor drive circuit
16
determines a motor current based on the deviation and gives it to the motor
5
to drive it in rotation.
According to the conventional electric power steering apparatus as described above, when an excessively large input is applied to the torque sensor
2
, the neutral point in order to the measurement may shift. However, when the displacement by the shift is relatively small, there is a problem that the displacement cannot be detected and the apparatus is doing nothing about the condition that the torque sensor
2
has large measuring errors.
As a prior art on the similar problem, there is disclosed in Japanese Patent Publication Unexamined No. H1-178080(1989) “A Fail-safe Device for An Electric Power Steering Apparatus”, wherein the number of times that the input torque is reached into a certain range is counted independently for the right and left side direction, and when the difference of the number between the right and left counts exceeds a certain level, it is judged that a malfunction has occurred. With the apparatus, the malfunction can be detected only when the displacement is large enough.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to settle the problematic points as described above. The object of the present invention is to provide an electric power steering apparatus with which even a small displacement of a neutral point in order to a measurement of a torque sensor can be detected.
The electric power steering apparatus of the present invention for assisting steering based on an output of a torque sensor which detects a steering torque, comprises: cumulating means for cumulating the output for a predetermined period of time; comparing means for comparing an absolute value of the result cumulated by the cumulating means with a predetermined value; and means for detecting a displacement of a detection neutral point of the torque sensor based on the results of comparison by the comparing means.
In this electric power steering apparatus, the cumulating means cumulates the output of the torque sensor for the predetermined period of time. The comparing means compares an absolute value of the cumulated value with the predetermined value, and the means for detecting detects the displacement of the neutral point in order to a measurement of a torque sensor based on the results of comparison.
If the output of the neutral point is “0”, the cumulated output value of the torque sensor should indicate approximately “0” for a long operating time period. Therefore, if the cumulated value is deviated by more than the predetermined value from “0”, then it can be judged that the torque sensor has been failed. Because of this, in case the preset value of the neutral point is “0”, even a small displacement of a neutral point in order to a measurement of a torque sensor can be detected.
Another electric power steering apparatus of the present invention for periodically sampling an output of a torque sensor which detects a steering torque and for assisting steering based on the sampled output, comprises: cumulating means for cumulating the output for a predetermined period of time; counting means for counting number of times cumulated by the cumulating means; calculating means for calculating an average value of the output based on the cumulated value cumulated by the cumulating means and the number of times counted by the counting means; means for calculating a difference between a value to be output by the torque sensor at its neutral point and the average value calculated by the calculating means; comparing means for comparing an absolute value of the difference calculated by the calculating means with a predetermined value; and means for detecting a displacement of a detection neutral point of the torque sensor based on the results of comparison by the comparing means.
In this electric power steering apparatus, the output of the torque sensor is periodically sampled and the sampled outputs are cumulated for the predetermined period of time. The counting means counts the number of times cumulated. The calculating means calculates the average output value of the torque sensor based on the cumulated result and the number of times counted. Further, the means for calculating the difference calculates the difference between the expected output value of the torque sensor at its neutral point and the above average output value. Comparing means compares an absolute value of the calculated difference with the predetermined value, and means for detecting the displacement based on the results of the comparison
The average output value of the torque sensor should show approximately as that at its neutral point for a long operating time period. Therefore, if the average output value for a long predetermined time is deviated by higher than the predetermined value from the neutral point, then it can be judged that the torque sensor has been failed. Because of this, in case that the preset value of the neutral point is not “0”, even a small displacement of a neutral point in order to a measurement of a torque sensor can be detected.
A still further electric power steering apparatus of the invention, further comprises: a vehicle speed sensor for detecting a vehicle speed; and steering angle detecting means for detecting a steering angle, wherein the cumulating means cumulates when the vehicle speed detected by the vehicle speed sensor is higher than a predetermined vehicle speed and the steering angle detected by the steering angle detecting means is within a predetermined range.
In this electric power steering apparatus, the cumulating means cumulates the outputs of the torque sensor when the vehicle speed detected by the vehicle speed sensor is higher than the predetermined vehicle speed and the steering angle detected by the steering angle detecting means is within the predetermined range. Therefore, a small output value of the torque sensor in a condition where the vehicle runs approximately straight becomes the subject of processing, and the detection precision of a small displacement of the neutral point in order to a measurement of the torque sensor can be improved.
Another electric power steering apparatus of the present invention, further comprises: steering angular velocity detecting means for detecting a steering angular velocity, wherein the cumulating means cumulates when the steering angular velocity detected by the steering angular velocity detecting means is lower than a predetermined steering angular velocity
In this electric power steering apparatus, the cumulating means cumulates the outputs of the torque sensor when the steering angular velocity detected by the steering angular velocity detecting means is lowe
Nishimoto Mitsuhiko
Sugimoto Masanori
Beaulieu Yonel
Cuchlinski Jr. William A.
Darby & Darby
Koyo Seiko Co. Ltd.
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