Torque sensor

Details Torque sensor Torque sensor

1999-01-14

2002-05-14

Fuller, Benjamin R. (Department: 2855)

Measuring and testing

Dynamometers

Responsive to torque

C073S862080, C073S862000, C073S001090

Reexamination Certificate

active

06386052

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a torque sensor for non-contact-detecting steering torque generated in a rotating shaft of a steering wheel of a vehicle, and more particularly to a torque sensor of a type, which has impedance which is changed in accordance with the generated steering torque, which is capable of easily correcting deviation in the voltage in a neutral state which is caused from a dimensional error, an assembling error or an output error of an electronic element and which is arranged to be operated in a manner different from that during the detection so as to detect breakdown of the elements. Further, the present invention also relates to a torque sensor incorporating a bridge circuit including a pair of coils having impedances which are changed in opposite directions in accordance with generated torque and a pair of electric resistors so as to detect the torque in accordance with transient voltage generated in the connection portion between the coils of the bridge circuit and the electric resistors and structured such that an abnormality of short circuit of the pair of the coils is detected.
The present application is based on Japanese Patent Applications No. Hei. 9-190121 and Hei. 10-292765, which are incorporated herein by reference.
2. Description of the Related Art
An electric power steering apparatus for assisting a steering apparatus for an automobile or a vehicle uses rotational force of a motor. The rotational force of the motor for the assistance is, through reduction gears, transmitted to a steering shaft or a rack shaft by a transmission mechanism including gears or a belt. The structure of a usual electric power steering apparatus will now be described with reference to
FIG. 15. A
shaft
2
of a steering wheel
1
is connected to tie rods
6
of wheels, which must be steered, through a reduction gear
3
A, universal joints
4
a
and
4
b
and a pinion-and-rack mechanism
5
. The shaft
2
is provided with a torque sensor
100
for detecting the steering torque of the steering wheel
1
. A motor
20
for enhancing the steering force of the steering wheel
1
is connected to the shaft
2
through a clutch
21
and a reduction gear
3
A. A control unit
200
for controlling the power steering apparatus is supplied with electric power from a battery
14
through an ignition key
11
. The control unit
200
calculates assist-steering instruction value I for-the assist instruction in accordance with steering torque T detected by the torque sensor
100
and vehicle speed V detected by a vehicle-speed sensor
12
. In accordance with the calculated assist-steering instruction value I, the control unit
200
controls an electric current which must be supplied to the motor
20
. The clutch
21
is controlled by the control unit
200
so as to be turned on or off. In usual operation state, the clutch
21
is turned on (connected). If the control unit
200
determines that the steering apparatus is out of order, or if power supply from the battery
14
is interrupted by the ignition key
11
, the clutch
21
is turned off (disconnected).
The control unit
200
comprises a CPU. A general function of a program which is executed in the CPU is as shown in FIG.
16
. Steering torque T detected and input by the torque sensor
100
is supplied to a phase compensator
201
so that the phase of the steering torque T is compensated in order to improve the stability of the steering system. Steering torque TA having the compensated phase is supplied to an assist-steering instruction value calculator
202
. Also vehicle speed V detected by the vehicle-speed sensor
12
is supplied to the assist-steering instruction value calculator
202
. In accordance with the supplied steering torque TA and the vehicle speed V, the assist-steering instruction value calculator
202
determines assist-steering instruction value I which is a required control value of an electric current which is supplied to the motor
20
. The assist-steering instruction value calculator
202
is provided with a memory
203
. In the memory
203
, the assist-steering instruction value I corresponding to the steering torque is stored such that the vehicle speed V serves as a parameter which must be used in an operation for calculating the assist-steering instruction value I which is performed by the assist-steering instruction value calculator
202
. The assist-steering instruction value I is supplied to a subtractor
200
A and a differentiation compensator
204
of a feed-forward system in order to raise the response speed. Deviation (I−i) in the subtractor
200
A is supplied to a proportional compensator
205
. An obtained proportional output is supplied to an adder
200
B and an integrator
206
in order to improve the characteristic of a feedback system. Also outputs of the differentiation compensator
204
and the integrator
206
are supplied to the adder
200
B so as to be added to each other. Current control value E, which is a result of addition performed by the adder
200
B, is, as a motor rotating signal, supplied to a motor rotating circuit
207
. Motor current value i is detected by a motor-current detection circuit
208
so that motor current value i is fed back to the subtractor
200
A.
The torque sensor
100
of the above-mentioned power steering apparatus may be, for example, a torque sensor disclosed in Japanese Patent Publication No. Sho. 63-45528. In this torque sensor, two cylindrical bodies are fitted coaxially in such a manner as to rotate relatively in response to a torque generated at a shaft, wherein a long groove and teeth are alternately formed in an axial direction on the outer cylindrical surface of the inner cylindrical body while a cut is formed on the outer cylindrical body in such a manner that the overlap amount may vary according to the relative rotation between the cylindrical bodies and wherein a coil is provided so as to cover the outer cylindrical body. The torque generated on the shaft can be detected through measurement of the impedance of the coil since the impedance of the coil varies when the overlapping amount of the groove and the cut is varied by changing relative rotation position of the two cylindrical bodies.
It is certain that the above-described torque sensor is able to detect the torque generated at the shaft in response to the variation in the coil impedance. In the above-described torque sensor, however, an oscillator for oscillation of accurate sine-wave alternating current is needed for a highly accurate torque sensor since the coil is driven by a high-frequency alternating current. This causes a problem of high production costs since a large number of electronic parts which respectively require a high accuracy are needed. Another problem is that since the coil is driven by a sine-wave alternating current whereas the coil is actually driven with application of offset voltages to unify the actual direction of the current (single-side supply power drive), the structure is uneconomical with an extremely large current consumption and the large current consumption results with a large amount of heat generation.
The torque sensor encounters deviation of output voltage from a predetermined neutral voltage for a controller when input torque is zero owning to assembling error of a sensor element, such as a shaft or tolerance of en electronic part in a signal processing system. Therefore, the output voltage must always be adjusted. The adjustment of the voltage is, however, performed by adjusting the position in the torque sensor portion. Thus, a complicated operation must be performed. Since the adjustment accuracy depends on the reliability of the fixing method, movement of a fixed element causes a risk of self-steer to occur. Also A/D reference voltage for determining a predetermined voltage for the controller has tolerance. Therefore, even if the neutral voltage for the torque sensor is accurately set to a predetermined level, there is apprehension that the controller erroneously recognizes the shi

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