Inductor devices – With outer casing or housing – Potted type
Reexamination Certificate
2001-06-29
2003-03-25
Mai, Anh (Department: 2832)
Inductor devices
With outer casing or housing
Potted type
C336S090000, C336S092000
Reexamination Certificate
active
06538546
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic core for a non-contact displacement sensor, and more concretely to a magnetic core for a non-contact torque sensor using a green compact made of an insulated soft magnetic powder being cheap and having a relatively high specific resistance value or so-called powder magnetic core as a skeleton of a coil receiving member constituting the magnetic core and effectively improving mechanical characteristics, which have caused trouble in the use of the green compact, and particularly useful for an electrically operated power steering apparatus for an automobile.
2. Description of Related Art
The power steering apparatus is an apparatus for assisting a steering effort of the automobile. Although a hydraulic power steering apparatus was mainstream in the past, so-called electrically operated power steering apparatus assisting the steering effort by an electric motor is recently and widely developed.
The electrically operated power steering apparatus has various advantages that a controllability is excellent as compared with that of the hydraulic power steering apparatus, and mechanical portions are simple, and a fuel consumption is good, and power is supplied to the electric motor only in case of necessity and the like.
In the system of the electrically operated power steering apparatus, a direction and a quantity of power when operating a handle (a steering wheel) are detected by a torque sensor and a current of the electric motor assisting the steering effort is controlled by a control unit in accordance with the detected value.
In
FIG. 7
is shown a main part of a representative non-contact torque sensor constituting the electrically operated power steering apparatus.
The torque sensor
101
is mainly comprised of an input shaft
102
connected to a handle (not shown), an output shaft
103
connected to a side of the steering wheel, a torsion bar
104
connecting the shaft
102
to the shaft
103
, first and second detecting rings
105
and
106
arranged on an outer peripheral side of the torsion bar
104
at sides of the input shaft
102
and the output shaft
103
and opposite to each other, and a magnetic core
108
comprising a detecting coil
107
for detecting a relative displacement of the first detecting ring
105
displaced in accordance with a displacement of the torsion bar
104
when a torque is applied to the input shaft
102
with respect to the second detecting ring
106
as a change of an inductance at a non-contact state.
And also, the magnetic core
108
is mainly comprised of the detecting coil
107
wound around a coil bobbin, a toroidal coil receiving member
109
having a space for receiving the detecting coil
107
therein, forming a closed space S together with the detecting coil
107
received therein and retaining the detecting coil
107
in a position separated away at a constant distance from outer circumferential surfaces of the detecting rings
105
and
106
, and lead wires
110
connected at their one ends to the detecting coil
107
and led out at the other ends outward from the coil receiving member
109
.
In the conventional magnetic core
108
, as shown in
FIG. 8
, the coil receiving member
109
comprises a coil receiving case
111
receiving the detecting coil
107
and a cap
112
press fitted into an opening of the case
111
. Each of the coil receiving case
111
and the cap
112
is made of a soft magnetic sintered body formed by compression shaping powder of an electromagnetic stainless steel system or an iron-based soft magnetic material into a green compact and further sintering the green compact. And also, the detecting coil
107
is generally fixed to the inner surface of the coil receiving member
109
with an adhesive
113
.
However, since the soft magnetic sintered body is low in the specific resistance value as compared with ferrite, sendust alloy or the like and bad in the detecting sensitivity, if a frequency of a driving power is set to a high value for improving the detecting sensitivity, an eddy current loss becomes large and an inductance lowers, and hence the detecting sensitivity is rather degraded and it is difficult to conduct the detection in a higher accuracy.
On the other hand, as the ferrite and sendust alloy have excellent magnetic properties, they enable the detection in a higher accuracy, but are expensive, so that the application of them to the coil receiving member is unfavorable from a viewpoint of the cost. In addition, the ferrite has a drawback that the temperature change of the inductance is large.
Moreover, the coil receiving member having a relatively high specific resistance value and being cheap is known to be constructed with a green compact made of insulated soft magnetic powder.
The coil receiving member constituted with such a green compact is known to have a good detecting sensitivity because the eddy current loss is small in case of applying a high frequency current. Since the green compact is not subjected to a sintering, however, the coil receiving member is weak in the strength and has particularly a fear of easily breaking when a shock is applied thereto, so that the manufacture is difficult in the conventional press-fitting structure. Furthermore, the applications are critical, and it is said that the application to the electrically operated power steering is difficult in the existing technique.
In the conventional magnetic core (FIG.
8
), the detecting coil
107
, more concretely, the coil bobbin
114
wound with the detecting coil is merely fixed to the inner surface of the coil receiving member
109
through the adhesive, so that there is assumed a case that the fixing of the coil bobbin
114
to the inner surface of the coil receiving member
109
becomes insufficient. In this case, it is assumed that a strong impact force is applied to the coil receiving member
109
by the coil bobbin
114
to thereby break the coil receiving member
109
.
Moreover, nothing is filled in the closed space S formed after the detecting coil
107
is received in the coil receiving member
109
, so that there is a possibility of disturbing the wound state of the detecting coil
107
, which is in danger of giving a largely bad influence upon the magnetic properties.
Therefore, when the coil receiving member is made of the above green compact, it is required to surely fix the detecting coil
107
to the coil receiving member
109
and to take means for maintaining the wound state of the detecting coil.
And also, a usual displacement sensor is arranged in a housing made of an aluminum alloy or the like in internally contact therewith in order to avoid an influence by an electromagnetic wave from exterior. However, when the coil receiving member not provided on its outer surface with an insulating coating internally contacts with the housing, the eddy current generates in the housing and there is caused a problem of lowering the sensitivity of the detecting coil. In addition, when the housing is made of the aluminum alloy, it is apt to easily cause a phenomenon of biting onto the coil receiving member by a difference of thermal expansion coefficient between the housing and the coil receiving member, especially by a large thermal shrinkage of the housing at a low temperature, and there may be a case that the magnetic core is distorted by such a phenomenon to cause a deviation in the inductance.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a magnetic core for a non-contact torque sensor using a green compact made of an insulated soft magnetic powder being cheap and having a relatively high specific resistance value as a skeleton of a coil receiving member constituting the magnetic core and effectively improving mechanical characteristics, which have caused trouble in the use of the green compact, and particularly useful for an electrically operated power steering apparatus for an automobile.
According to the invention, there is the provision of in a magnetic core for a non-contact displa
Moriyama Masakazu
Nagano Hidenobu
Nakatani Norio
Nakaura Shunsuke
Sanada Takahiro
Mai Anh
Tokyo Sintered Metal Company Limited
Young & Thompson
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