Torque detector

Details Torque detector Torque detector

2001-02-23

2003-04-01

Noori, Max (Department: 2855)

Measuring and testing

Dynamometers

Responsive to torque

Reexamination Certificate

active

06539816

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power steering for applying an assist force using an electric motor, and particularly, to a torque detector for detecting steering torque supplied from a steering wheel.
2. Description of Related Art
Torque detectors for a power steering include, for example, the torque detector disclosed in Japanese Patent Laid-open No. 3-74258 by the present applicant.
In the torque detector, as shown in FIG.
12
and
FIG. 13
, an output shaft
2
is rotatably mounted in a gear case
1
and has an end at which a pinion
3
is provided. The pinion
3
is engaged with a rack shaft
4
having both ends linking with wheels (not shown).
The rack shaft
4
is linked with an electric motor (not shown) for applying an assist force.
In the gear case
1
, an input shaft
5
linking with the steering wheel (not shown) is rotatably mounted coaxially with the output shaft
2
. A torsion bar
6
is provided in a hollow portion
5
a
of the input shaft
5
, and has one end secured to the input shaft
5
and the other end secured to the output shaft
2
.
In the detector constructed as above, upon turning the steering wheel (not shown), the torsion bar
6
is twisted in accordance with the input torque of the turned steering wheel, to cause a relative rotation between the input shaft
5
and the output shaft
2
.
A sensor
18
detailed later detects the amount of relative rotation and the direction of the input and output shafts, and a controller (not shown) controls output of the electric motor based on the detected amount and direction.
The electric motor thus controlled by the controller exerts a driving force in accordance with the input torque on the rack shaft
4
to drive the rack shaft
4
for application of an optimum assist force.
Next, the configuration for detecting the input torque will be explained.
A flange
7
is provided on the input shaft
5
. In the flange
7
, three planetary gears
8
are arranged at regular intervals along the circumferential direction with respective pins
9
as shown in FIG.
13
. The planetary gears
8
engage with a sun gear
10
rotatably provided on the outer circumferential face of the input shaft
5
and a rotatable ring gear
11
rotatably mounted in the gear case
1
.
Another flange
12
is provided on the output shaft
2
, and three planetary gears (not shown) are also arranged at regular intervals along the circumferential direction with respective pins. The planetary gears engage with the sun gear
10
and a fixed ring gear
13
secured in the gear case
1
.
In the flange
7
provided on the input shaft
5
, two notches
14
are provided as shown in FIG.
13
. Protrusions
15
are provided in the flange
12
on the output shaft
2
, and respectively inserted into the notches
14
.
A clearance
16
is provided between each notch
14
and the corresponding protrusion
15
to allow the input shaft
5
to rotate relative to the output shaft
2
in the circumferential direction. When the notch
14
and the protrusion
15
make contact with each other, the input shaft
5
and the output shaft
2
integrally rotate. This prevents the torsion bar
6
from becoming extremely twisted and thereby damaged.
A magnetic piece
17
is incorporated in a portion of the outer circumference of the aforementioned rotatable ring gear
11
. The sensor
18
made up of a magnetic resistor element is provided on the inner surface of the gear case
1
facing the magnetic piece
17
.
The magnetic resistor element has a facility in that it varies an electric resistance therein upon reception of external action of magnetic field and detects the resistance variation as a variation of voltage.
The sensor
18
made up of such a magnetic resistor element detects a voltage in accordance with the magnetic flux variation when the magnetic piece
17
is moved by the rotation of the rotatable ring gear
11
. The sensor
18
inputs the detected voltage to the controller (not shown) and the controller controls output of the electric motor. The electric motor exerts the assist force in response to signals from the controller to reduce a steering force to an optimal force.
Next, the operation of the conventional torque detector will be explained.
In the state that a load is transmitted from the wheels (not shown) to the rack shaft
4
, when the steering wheel (not shown) is turned, the turning force is transmitted to the input shaft
5
. However, since the load from the wheels interferes with the rotation of the output shaft
2
, the torsion bar
6
is twisted by the rotation of the input shaft
5
. Thus, the input shaft
5
and the output shaft
2
are relatively rotated within the range of the clearance
16
.
When the input shaft
5
and the output shaft
2
relatively rotate in this way, the rotatable ring gear
11
rotates as follows.
The limitation of the rotation of the output shaft
2
does not allow the planetary gears (not shown) linked with the output shaft
2
to revolve around the sun gear
10
. Additionally, the planetary gears (not shown) cannot rotate due to the engagement with the fixed ring gear
13
. For those reasons, the sun gear
10
engaging with the planetary gears (not shown) is under the condition that its rotation is limited.
Under such condition, when the input shaft
5
rotates in relation to the output shaft
2
, the planetary gears
8
provided in the flange
7
on the input shaft
5
rotate and revolve around the sun gear
10
. Therefore, the rotatable ring gear
11
engaging with the planetary gears
8
rotates slightly.
Upon the rotatable ring gear
11
slightly rotating as explained above, the magnetic piece
17
secured in the ring gear
11
also travels. The sensor
18
detects the amount of travel of the magnetic piece
17
, and the controller (not shown) controls the electric motor in response to the detected signal. In this way, the electric motor applies an optimum assisting force.
Since the sensor
18
and the magnetic piece
17
are out of contact with each other as explained above, there is no significant influence of wear and the like in use of a contact type sensor. This allows the detection of high accurate values.
On the other hand, when the input shaft
5
and the output shaft
2
integrally rotate while the torsion bar
6
is twisted, the rotatable ring gear
11
is adapted to stop rotating. This situation will be detailed below.
When the input shaft
5
and the output shaft
2
integrally rotate, the planetary gears (not shown) provided on the output shaft
2
side rotate and revolve around the sun gear
10
. Therefore, the sun gear
10
engaging with the planetary gears rotates in the same direction as that of the input shaft
5
and output shaft
2
.
The planetary gears
8
provided on the input shaft
5
side revolve in the same direction as that of the input shaft
5
and output shaft
2
, while being rotated by the rotation of the sun gear
10
. That is to say, the planetary gears
8
rotate while revolving around the sun gear
10
.
Such planetary gears
8
travel on the inner face of the rotatable ring gear
11
while engaging therewith due to their rotation. The speed of travel of the planetary gear
8
on the rotatable ring gear
11
is set to be equal to the speed of voluntary revolution of the planetary gear
8
around the sun gear
10
. In other words, the planetary gears
8
travel on the inner face of the rotatable ring gear
11
with simply engaging therewith such that the rotating force of the planetary gears
8
does not act on the rotatable ring gear
11
. Naturally, the rotatable ring gear
11
does not rotate as long as the rotating force of the planetary gears
8
does not act thereon.
The reason for limiting the rotation of the rotatable ring gear
11
as described above is in order to prevent the magnetic piece
17
, provided in the rotatable ring gear
11
, from departing from the position facing the sensor
18
even in the integral rotation of the input shaft
5
and the output shaft
2
.
Specifically, the magnetic piece
17
is provided only i

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