Electrical resistors – Mechanically variable – Movable contact electrically adjustable over length of...
Reexamination Certificate
2000-12-04
2002-05-28
Enad, Elvin (Department: 2832)
Electrical resistors
Mechanically variable
Movable contact electrically adjustable over length of...
C338S128000, C338S130000
Reexamination Certificate
active
06396386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angle sensor which detects, for example, the steering angle of a steering wheel of an automobile, and, more particularly, to an angle sensor which can detect the angle of rotation of the steering wheel with high precision as a result of preventing rattling caused by backlash between gears or between a gear and a screw shaft inside the angle sensor.
2. Description of the Related Art
FIG. 8
is a plan view showing the internal structure of a conventional angle sensor proposed in U.S. patent application Ser. No. 09-477971 by the inventor of the angle sensor in the application concerned. The conventional angle sensor is used to detect, for example, the steering angle of a steering wheel of an automobile with high precision.
In an angle sensor
1
shown in
FIG. 8
, a rotary member
3
is provided inside a case
2
formed of a synthetic resin material such as plastic. The rotary member
3
is a cylindrically shaped member formed of, for example, a synthetic resin material, and is rotatably supported with respect to the case
2
. The steering wheel of an automobile is inserted into the rotary member
3
, and the rotary member
3
rotates clockwise and counterclockwise along with the steering wheel. A plurality of helical gears
3
a
are formed along the entire outer peripheral surface of the rotary member
3
.
A rotary shaft
9
is rotatably provided inside the case
2
, with the illustrated X dimension being defined as the center axis thereof. A driving gear
8
is secured to the rotary shaft
9
. A plurality of helical gears
8
a
are formed along the entire outer peripheral surface of the driving gear
8
, and engage the helical gears
3
a
of the rotary member
3
. The rotary shaft
9
is formed of a metallic material such as brass or aluminum, and has a spiral thread groove
9
a
formed from the center to one end thereof. A detecting member
4
is provided at the rotary shaft
9
.
The detecting member
4
has a through hole formed therein from one end surface to the other end surface thereof in the direction of movement (that is, in the X dimension). Threads (not shown) which engage the thread groove
9
a
formed in the rotary shaft
9
are formed in the inner peripheral surface defining the through hole. A second magnet
5
B is mounted to the bottom surface of the detecting member
4
by, for example, insert molding. The detecting member
4
is guided in the interior of the case
2
so as to move in a straight line in the X dimension. When the rotary member
3
rotates, the driving gear
8
and the rotary shaft
9
rotate, causing the detecting member
4
and the second magnet
5
B to reciprocate in the X dimension.
A Hall element
6
B is provided at a side opposing the second magnet
5
B, on a fixing member
7
in the case
2
. A magnetized first magnet
5
A is integrally mounted to the outer circumferential surface of the rotary shaft
9
. A second Hall element
6
A is provided on the fixing member
7
so as to oppose the outer circumferential surface of the first magnet
5
A.
When the rotary shaft
9
rotates with the rotation of the rotary member
3
, the first magnet
5
A rotates, causing a sine wave to be output. At the same time, the second magnet
5
B reciprocates in the X dimension, causing values which change linearly through the entire rotational angle range of the steering wheel to be output. By detecting these values, the absolute position of the steering wheel resulting from the angle of rotation (that is, the steering angle) can be detected.
When an attempt is made to detect the angle of rotation (that is, the steering angle) of the steering wheel with high precision using the above-described angle sensor
1
, the problem of rattling due to backlash between the helical gears
3
a
of the rotary member
3
and the helical gears
8
a
of the driving gear
8
arises.
More specifically, in the above-described angle sensor
1
, the rotation of the rotary member
3
is detected, or the detecting member
4
is moved in the X dimension after changing the rotational movement to linear movement. Therefore, when the backlash between the helical gears
3
a
of the rotary member
3
and the helical gears
8
a
of the driving gear
8
is too large, the rattling therebetween causes an error to be produced in the-distance of movement of the detecting member
4
which is moved in the X dimension. Here, when the direction of rotation of the rotary member
3
(or the steering wheel) changes, the driving of the driving gear
8
is reduced in correspondence with the amount of rattling caused by the backlash, causing hysteresis resulting from the direction of rotation to occur, whereby the amount of error is increased.
In the conventional angle sensor
1
, backlash which occurs between the gears is decreased by increasing the degree with which the helical gears
3
a
of the rotary member
3
and the helical gears
8
a
of the driving gear
8
contact each other by biasing, for example, either the rotary member
3
in the Z
2
direction towards the driving gear
8
or the driving gear
8
in the Z
1
direction towards the rotary member
3
.
However, when the degree with which the rotary member
3
and the driving gear
8
contact each other is increased to the extent that rattling does not occur, the biasing force produced between the gears becomes too large, so that rotational torque becomes large, and the rotary shaft
9
gets distorted due to, for example, thermal expansion, making it impossible to smoothly guide the detecting member
4
in the X dimension. In addition, the rotary shaft
9
has a simple beam structure in which both ends thereof are supported, so that, when a biasing force acts, the displacement of the portion corresponding to where the rotary member
3
and the driving gear
8
engage (that is, the center portion) is displaced the greatest, with the displacement becoming smaller towards both ends of the rotary shaft
9
. Therefore, the rate of change of the strength of the magnetic field in the Z dimension with respect to the distance of movement of the second magnet
5
B and the detecting member
4
is no longer linear with respect to the direction of movement. In addition, the distance between the first magnet
5
A and the first Hall element
6
A changes so that a predetermined output can no longer be obtained. Therefore, the distance of movement of the detecting member
4
can no longer be detected precisely, so that the precision with which the angle of rotation (that is, the steering angle) of the rotary member
3
(or the steering wheel) is detected is decreased.
In the above-described conventional angle sensor
1
, the detecting member
4
and the screw shaft
9
a
are constructed so that only the screw shaft
9
a
engages the threads formed in the through hole
4
a
of the detecting hole
4
. Therefore, play (that is, backlash) tends to occur between the threads of the detecting member
4
and the thread grooves of the thread groove
9
a
. The backlash tends to result in rattling of the detecting member
4
in the axial direction (that is, the X dimension), so that a precise distance of movement in accordance with the angle of rotation of the rotary member
3
cannot be obtained by the detecting member
4
. Therefore, the Hall element
6
B can no longer be used to detect with high precision the angle of rotation of a shaft to be detected, such as a steering wheel.
SUMMARY OF THE INVENTION
To overcome the aforementioned conventional problems, it is an object of the present invention to provide an angle sensor which can detect the angle of rotation of a rotary member with high precision as a result of decreasing backlash between a driving gear and a gear of the rotary member.
It is also another object of the present invention to provide an angle sensor in which a detecting member which reciprocates in accordance with the rotation of a screw shaft is advanced with high precision.
To these ends, according to a first aspect of the present invention, there is provided an an
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Enad Elvin
Lee Kyung S.
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