192 clutches and power-stop control – Clutches – Automatic
Reexamination Certificate
2002-05-14
2004-08-03
Rodriguez, Saul (Department: 3681)
192 clutches and power-stop control
Clutches
Automatic
C192S044000, C192S045000, C192S084100
Reexamination Certificate
active
06769524
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an electromagnetic clutch which couples and uncouples two rotary shafts under an electromagnetic force. It also relates to a rotation transmission device provided with such an electromagnetic clutch for carrying out change over of transmission and shutoff of a driving force in a drive line of various machines and vehicles.
An electromagnetic clutch is used as a device for connecting and disconnecting power in a power transmission line to selectively change over transmission and shutoff of power in various machines and vehicles, such as front and rear wheels of a 4WD car.
FIGS. 9-12
show a conventional rotation transmission device provided with an electromagnetic clutch.
The device has an inner member (inner ring)
1
coupled through a serration
38
to an input shaft
7
so as to rotate together, and has an outer member (outer ring)
2
rotatably mounted concentrically around the inner member
1
. A plurality of cam surfaces
9
are formed on the inner member
1
, while a cylindrical surface
10
is formed on the outer member
2
to define an annular space between these surfaces. A retainer
5
is provided in the annular space, and rollers
6
performing as engaging elements are retained in a plurality of pockets
8
formed in the retainer
5
to mount the rollers in the annular space. A switch spring
11
is engaged between the retainer
5
and the inner member
1
to bias the retainer
5
to a neutral position where the rollers
6
do not engage the cylindrical surface
10
or the cam surfaces
9
.
By changing the phase of the retainer
5
, the rollers
6
will engage and disengage between the inner member
1
and the outer member
2
. This arrangement forms a clutch.
The electromagnetic clutch portion comprises a rotor
15
having a
-shaped section and fixed to a cylindrical rotor support
17
formed of a nonmagnetic material, and comprises an armature
13
provided at one end of the retainer
5
so as to be axially movable but relatively nonrotatable. The rotor is and armature
13
are arranged with a suitable gap kept therebetween by a separating spring
18
. An electromagnetic coil
16
for pressing the rotor
15
and the armature
13
against each other by a magnetic force is nonrotatably arranged in the rotor
15
through a field core
3
fixed to the housing
4
. By turning on and off a current to the electromagnetic coil
16
, the rollers
6
are engaged and disengaged between the inner member
1
and the outer member
2
.
When a current to the electromagnetic coil
16
is off, the rollers
6
are biased by the switch spring
11
through the retainer
5
to their neutral position on the cam surfaces
9
formed on the inner member
1
, so that the inner member
1
and the outer member
2
can idle.
When it is desired to engage the inner member
1
with the outer member
2
, a current is supplied to the electromagnetic coil
16
. The armature
13
coupled to the retainer
5
is attracted by magnetic force toward and pressed against the rotor
15
.
Frictional torque due to pressing acts between the retainer
5
and the outer member
2
through the armature
13
and the rotor
15
. When the inner member
1
and the outer member
2
rotate relative to each other, the frictional torque overcomes the torque of the switch spring
11
, so that the retainer
5
and the rollers
6
as the engaging elements rotate with the outer member
2
. As a result, the rollers
6
as the engaging elements move from the neutral positions on the cam surfaces to wedge-engagement positions where the inner member
1
and the outer member
2
are engaged together and driven.
The rotor
15
of such an electromagnetic clutch comprises cylindrical portions
15
a
and
15
b
formed on the inner-diameter and outer-diameter sides, respectively, and a disk portion
15
c
that opposes the armature
13
(FIG.
12
).
The field core
3
for mounting the electromagnetic coil
16
comprises cylindrical portions
3
a
and
3
b
formed on its inner-diameter and outer-diameter sides, respectively, and an end face portion
3
c
through which it is fixed to the housing
4
.
A lead wire
20
for supplying a current to the electromagnetic coil
16
is led out of the field core
3
through the end face portion
3
c
of the field core
3
out of the housing
4
.
As described above, since an electromagnetic clutch is engaged by the attraction force produced by the electromagnetic coil
16
, if the attraction force is weak, the armature
13
and the rotor
15
may be kept separate from each other, so that the clutch may not be engaged.
Thus, it is desired to ensure engagement of the clutch by increasing the magnetic attraction force of the electromagnetic coil
16
as much as possible, thereby improving reliability of operation.
But in many applications, the space for installing the electromagnetic clutch portion in the housing
4
is limited, so that the ability to increase the size of the electromagnetic coil
16
is limited.
Thus, a first object of this invention is to increase the magnetic attraction force of the electromagnetic coil as much as possible in a limited installation space, thereby improving reliability of operation.
FIG. 13
shows another conventional rotation transmission device.
In this prior art device, the housing
4
and the outer member
2
are supported through a bearing
33
, and entry of foreign matter into the rotation transmission device is prevented by sealing devices
50
,
51
provided at both ends of the housing
4
.
As the sealing device
50
, which is provided on the open side of the housing, a combination of a sealing plate such as a slinger and a sealing lip is used. The sealing device
50
is pressed into the end face of the housing
4
on its open side.
Thus, if during operation the housing
4
and the outer member
2
are displaced relative to each other in the axial direction due to rattling, and the sealing plate of the sealing device
50
protrudes outside through the opening of the housing
4
, the sealing properties may deteriorate.
Under use conditions where there are many flying stones, if the sealing device
50
is located at the end face of the housing
4
on its open side, a flying stone may hit, for example the sealing plate of the sealing device
50
, thus deforming it and deteriorating the sealing property.
Also, in this rotation transmission device, a bearing
33
, which supports the outer member
2
and the housing
4
, is provided on the outer peripheral side of the portion forming the clutch. The bearing
33
comprises an inner ring
33
a
, an outer ring
33
b
and a plurality of rolling elements
33
c
. When the clutch engages, the rollers
6
engage the outer member
2
and the inner member
1
, so that the outer diameter of the outer member
2
, which forms the clutch, increases. This increases the load acting between the inner ring
33
a
and the rolling elements
33
c
of the bearing
33
, so that if the interference between the outer ring
2
and the bearing
33
is large, the bearing
33
may be damaged.
Also, in conventional rotation transmission devices, grease is sealed by providing sealing members
33
d
on both sides of the inner ring
33
a
and the outer ring
33
b
of the bearing
33
. However, separately carrying out lubrication of the bearing
33
and lubrication of the clutch portion causes costs to increase.
Thus, a second object of this invention is to prevent deterioration of sealing, damage to the bearing and cost increase in the rotation transmission device.
SUMMARY OF THE INVENTION
According to this invention, in order to solve the first object, the dimensions of the field core are optimized to increase the magnetic attraction force of the electromagnetic coil as much as possible.
Heretofore, the field core
3
was formed by press molding, and as shown in the enlarged view of
FIG. 12
, the thickness A of the cylindrical portion
3
a
on the inner-diameter side of the field core
3
had the same thickness as the thickness B of the cylindrical portion
3
b
on the outer-diameter side. Th
Nagano Yoshitaka
Sato Koji
Yasui Makoto
NTN Corporation
Rodriguez Saul
Wenderoth , Lind & Ponack, L.L.P.
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