Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1999-08-31
2003-09-23
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
C073S862000, C073S862080
Reexamination Certificate
active
06622576
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a torque sensor for sensing torque acting on an object, and more particularly to a torque sensor suitable for sensing torque that acts between an input shaft connected to a steering wheel of a vehicle and an output shaft connected to a steering mechanism of the vehicle.
2. Description of the Related Art
Conventionally, a torque sensor of the above-described type has been used in a steering mechanism as shown in FIG.
1
.
First, the structure of the conventional steering mechanism will be described with reference to FIG.
1
.
A steering mechanism
10
shown in
FIG. 1
comprises a hollow shaft
11
connected to a steering wheel (not shown) of a vehicle. A lower portion of the shaft
11
passes through and is supported by an upper portion
12
a
of a housing
12
. Another shaft
13
is inserted into a lower portion
12
b
of the housing
12
. A pinion
14
is provided on a lower portion of the shaft
13
, and the pinion
14
is in meshing-engagement with a rack R. An unillustrated motor is provided and drivingly connected to the rack R in order to assist the driver's steering operation.
A torsion bar
15
is accommodated inside the shaft
11
. The upper end of the torsion bar
15
is connected to the shaft
11
by means of a pin
16
, and the lower end of the torsion bar
15
is in spline-engagement with the shaft
13
.
Therefore, when a torque is applied to the shaft
11
upon operation of the steering wheel, the torsion bar
15
is twisted, so that a relative displacement is produced between the shaft
11
and the shaft
13
.
Within the housing
12
, a sensor ring
17
formed of a magnetic material is provided on the shaft
11
, and a sensor ring
18
formed of a magnetic material is provided on the shaft
13
. Further, a torque sensing coil
19
is provided inside the housing
12
such that the torque sensing coil
19
surrounds the sensor rings
17
and
18
with a predetermined gap formed therebetween. When a relative displacement is produced between the shafts
11
and
13
, the amount of overlap between the sensor rings
17
and
18
changes, resulting in a change in the inductance of the torque sensing coil
19
. Thus, a signal corresponding to the sensed torque is obtained from the torque sensing coil
19
. The torque sensing coil
19
is connected to an interface circuit (hereinafter referred to as an “I/F circuit”)
80
disposed at the right end of the housing
12
in FIG.
1
. The I/F circuit
80
is connected to a microcomputer (not shown) provided in the vehicle.
Next, operation of the I/F circuit
80
will be described with reference to FIG.
2
.
DC current supplied from a DC power source
81
is supplied to a regulator circuit
83
via a filter circuit
82
, which eliminates unnecessary harmonic components from the DC current. The regulator circuit
83
receives the DC current output from the filter circuit
82
and generates a reference voltage. An oscillator circuit
84
generates a sinusoidal signal on the basis of the reference voltage output from the regulator circuit
83
. The sinusoidal signal is applied to the torque sensing coil
19
.
As a result, a sinusoidal voltage corresponding to the inductance of the torque sensing coil
19
is generated between the opposite ends of the torque sensing coil
19
. The AC component is extracted from the sinusoidal voltage by a DC cut circuit
85
and is detected by a detection circuit
86
, so that a DC voltage proportional to the amplitude of the extracted AC component is output from the detection circuit
86
. The DC voltage is then input to an addition circuit
87
.
The sinusoidal voltage generated between the opposite ends of the torque sensing coil
19
is input to a temperature compensation circuit
88
, which outputs a temperature drift signal that indicates variation in the inductance of the torque sensing coil
19
caused by temperature. The temperature drift signal is input to the addition circuit
87
.
The addition circuit
87
calculates a difference between the signal output from the detection circuit
86
and the temperature drift signal output from the temperature compensation circuit
88
and cancels out the temperature drift component to thereby output a torque component signal, which is output to a scaling circuit
89
. The scaling circuit
89
amplifies the torque component signal at a preset gain to thereby scale up the torque component signal. The scaled-up torque component signal is amplified by an output amplifier circuit
90
. Subsequently, after being amplified by the amplifier circuit
90
, the torque component signal is output to an A/C conversion circuit
91
as a torque signal, so that the torque signal is converted to a digital signal, which is output to a microcomputer provided in the vehicle.
On the basis of the magnitudes of input digital signals, the microcomputer calculates an amount of assist to be applied to the steering mechanism and outputs to the motor a drive signal corresponding to the calculated amount of assist. Thus, the steering mechanism is assisted through rotation of the motor.
However, the above-described conventional torque sensor requires a large number of circuits, such as a circuit for applying a sinusoidal signal to the torque sensing coil
19
and a circuit for sensing the inductance of the torque sensing coil
19
as torque, which makes it difficult to enhance the reliability of the torque sensor.
Further, in the conventional torque sensor, since the torque signal output from the output amplifier circuit
90
is an analog signal, torque cannot be detected unless the voltage applied to the circuits is prevented from becoming lower than the operation voltage of the microcomputer even when a voltage drop occurs.
Therefore, in addition to a power source for the microcomputer, there must be provided a DC power source
81
which supplies the oscillation circuit
84
with a voltage (e.g., 8V) higher than the operating voltage (e.g., 5V) of the microcomputer.
As described above, the conventional torque sensor is complicated in terms of circuit configuration and requires a plurality of power sources, which makes it difficult to improve reliability and reduce manufacturing costs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a torque sensor which can simplify the configuration of a circuit for sensing torque and which decreases the number of power sources to thereby improve reliability and reduce production costs.
In order to achieve the above object, the present invention provides a torque sensor which is provided with a coil whose inductance changes in accordance with variation in torque acting on an object and which detects the torque on the basis of the inductance of the coil, the torque sensor comprising: a first oscillation circuit for detecting the inductance of the coil and for oscillating a signal having a period corresponding to the detected inductance; a period detection section for detecting the period of the signal generated by the first oscillation circuit; and a torque detection section for detecting the torque on the basis of the period detected by the period detection section.
This structure eliminates necessity for provision of an oscillation circuit for applying a sinusoidal signal to the coil. Further, since the signal oscillated by the first oscillation circuit can be input directly to a microcomputer for direct measurement, digital processing becomes simple, and an A/D conversion circuit or a like circuit becomes unnecessary. Further, since torque can be sensed regardless of variation in supplied voltage, a single power source can be used commonly for torque sensing and for the microcomputer. Accordingly, no additional power source is required.
As described above, the circuit configuration can be simplified and the number of power sources can be reduced, as compared to conventional torque sensors. Therefore, the reliability of the torque sensor is improved, and the production cost of the torque sensor is reduced. Further, since the
Asano Takatsugu
Nagashima Ichiro
Nakano Jiro
Oue Hisashi
Tsukamoto Takeshi
Allen Andre
Lefkowitz Edward
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyoda Koki Kabushiki Kaisha
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