Device for measuring torque with high accuracy

Details Device for measuring torque with high accuracy Device for measuring torque with high accuracy

2002-09-25

2004-03-30

Lefkowitz, Edward (Department: 2855)

Measuring and testing

Dynamometers

Responsive to torque

C073S862331

Reexamination Certificate

active

06711970

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle steering apparatus, particularly to a device for measuring torque with high accuracy for use as a vehicle steering apparatus in which resolvers are used as a turning angle detector.
2. Description of the Related Art
In general, moving or stopped vehicle wheels (in contact with a road surface) turn to a certain orientation once the steering wheel of the vehicle is turned by a driver. However, since there is a friction force acting between the wheels and the road surface, it is impossible for the wheels to turn to exactly the same angle as the steering wheel because of a transmission loss involved in a motive force transmitting process.
In order to solve the above problem, it is necessary to measure and then compensate for a difference between the turning angle of the steering wheel and that of the vehicle wheels. Traditionally, what has been in actual use is a torque sensor since it can provide such a desired function. Namely, the torque sensor can be used to measure a deviation between the turning angle of the steering wheel and that of the vehicle wheels. Meanwhile, a driving means provided independently of the torque sensor is used to rotate the vehicle wheels in response to an extent of the measured deviation In this way, it is possible to always steer the vehicle in a correct direction as directed by the driver.
FIG. 5
is a perspective view showing an external appearance of a torque sensor used in a conventional vehicle steering apparatus having the aforementioned functions.
FIG. 6
is a partially enlarged explanatory view showing a part of the torque sensor shown in FIG.
5
. As shown in the drawings, the conventional torque sensor comprises an input shaft
72
whose one end is combined with a steering wheel
71
, an output shaft
74
whose one end is connected to the vehicle wheels, and a torsion bar
73
which is deformed to a certain extent corresponding to an actual steering operation. Further, three detection rings
66
to
68
are provided between the input shaft
72
and the output shaft
74
. In fact, these detection rings
66
to
68
are all made of a magnetic material and arranged with spaces between one another at a predetermined interval between the input shaft
72
and the output shaft
74
. Specifically, the first detection ring
66
is combined with the external surface of the input shaft
72
closer than any other detection rings to the steering wheel
71
, and is rotatable at exactly the same angle with the steering wheel
71
. The second detection ring
67
is combined with the outer peripheral surface of the central portion of the torsion bar
73
. The third detection ring
68
is combined with the external surface of one end of the output shaft
74
, which is the end connected to the vehicle wheels and is rotatable at substantially the same angle with the vehicle wheels.
Further, one end face of the first detection ring
66
(which is in fact an end face facing the second detection ring
67
), is formed into a tooth section. Similarly, an end face of the second detection ring
67
and an end face of the third detection ring
68
(the two end faces are facing each other) are also each formed with tooth sections. Moreover, a coil (first coil)
61
is wound around an interval between the first and second detection rings
66
and
67
, while another coil (second coil)
70
is wound around an interval between the second and third detection rings
67
and
68
. Specifically, both of the coils
61
and
70
are all connected to a processing unit
69
.
Next, the description will be given to explain an operation of the conventional torque sensor constructed in the above-described manner, which is for use as a vehicle steering apparatus in a vehicle. Namely, once a driver turns the steering wheel
71
, the input shaft
72
, the output shaft
74
and the torsion bar
73
are rotated. At this time, one end of the torsion bar
73
(which is connected to the steering wheel
71
) is twisted larger and thus rotate more than the other end of the torsion bar
73
which is connected to the vehicle wheels. In other words, when the steering wheel
71
is turned (revolved), a friction force acting between the vehicle wheels and the road surface brings the following results. The rotation angle of the first detection ring
66
is larger than the rotation angle of the second detection ring
67
, while the rotation angle of the second detection ring
67
is larger than the rotation angle of the third detection ring
68
.
In this way, although there is almost no change in the mutually facing area between the tooth section of the first detection ring
66
and the second detection ring
67
, there is a change in the mutually facing area between the tooth section of the second detection ring
67
and the tooth section of the third detection ring
68
. For this reason, there is a change in an external magnetic flux between the second detection ring
67
and the third detection ring
68
, thus causing a change in the magnetic flux passing through the second coil
70
. Here, the inductances of the first and second coils
61
and
70
are set at exactly the same value. Accordingly, with the rotation of the steering wheel
71
, although there is not, any change in the magnetic flux passing through the first coil
61
, there is a change in the magnetic flux passing though the second coil
70
. In this way, by measuring a change in an induced electromotive force of the second coil
70
with respect to an induced electromotive force of the first coil
61
, it is possible to measure a rotational deviation between the steering wheel
71
and the vehicle wheels.
On the other hand, there has long been known another device called a resolver which comprises a rotary transformer as shown in FIG.
7
. In fact, such a resolver includes a rotary shaft
50
, a rotor
54
mounted on the rotary shaft
50
, a resolver excitation winding
58
wound around the rotor, an inner core
56
, and a transformer output winding
60
wound around the inner core
56
. Actually, all these elements are rotatably mounted by means of bearings
51
A and
51
B located within a casing
52
. Further, the casing
52
also encloses a stator
53
, a resolver output winding
57
wound around the stator
53
, an outer core
55
, and a transformer excitation winding
59
wound around the outer core
55
.
An excitation voltage applied to the transformer excitation winding
59
is induced in the transformer output winding
60
, by virtue of an action of the rotary transformer formed by the outer core
55
and the inner core
56
. The voltage induced in the transformer output winding
60
is then applied to the resolver excitation winding
58
. In this way, X and Y components of the rotation angle are correspondingly outputted to the resolver output winding
57
with the rotation of the rotary shaft
50
, respectively.
As described above, the conventional torque sensor shown in
FIGS. 5 and 6
has three detection rings and two coils, forming a mutually facing area between the tooth section of the first and second detection rings
66
and
67
, and another mutually facing area between the tooth sections of the second and third detection rings
67
and
68
. In fact, there is a relative change in each of the above two mutually facing areas, and such a relative change causes a change in an induced electromotive force, so that it is possible to measure a difference between the induced electromotive forces of the first and second coils
61
and
70
.
However, although the input shaft
72
, the output shaft
74
and the torsion bar
73
are rotated once the steering wheel
71
is turned, at this time, one end of the torsion bar
73
connected to the steering wheel
71
is twisted larger and thus rotate more than the other end of the torsion bar
73
connected to the vehicle wheels. Accordingly, there is only a reduced change in a mutually facing area between the tooth sections of the second and third detection rings
67
and
68
. As a res

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