Textiles: fluid treating apparatus – Machines – Tumbling
Reexamination Certificate
2000-05-18
2002-11-05
Stinson, Frankie L. (Department: 1746)
Textiles: fluid treating apparatus
Machines
Tumbling
C068S024000
Reexamination Certificate
active
06474114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to drum type washing machines, and more particularly to such a drum type washing machine including an electric motor directly rotating a rotating tub.
2. Description of the Prior Art
FIG. 14
illustrates one of conventional drum type washing machines. The shown drum type washing machine comprises an outer cabinet
1
and a water tub
2
elastically supported by a plurality of suspension mechanisms
3
in the cabinet. A drum-shaped rotating tub
4
is provided for rotation in the water tub
2
. A bearing housing
6
is mounted on a rear wall of the water housing
2
. The rotating tub
4
has a shaft
5
extending rearward from a rear thereof. The shaft
5
is supported on bearings
7
and
8
held in the bearing housing
6
. The shaft
5
has a rear end to which a driven pulley
9
is mounted. A motor support
10
is mounted on a lower portion of the water tub
2
. An electric motor
11
is supported by the motor support
10
. The motor
11
includes a rotational shaft
12
on which a driving pulley
13
is mounted. A transmission belt
14
extends between the driving and driven pulleys
13
and
9
.
In the above-described construction, torque developed by the motor
11
is transmitted via the shaft
12
, driving pulley
13
, belt
14
and driven pulley
9
to the shaft
5
so that the rotating tub
4
is rotated. However, a belt transmission mechanism including the driving and driven pulleys
13
and
9
and the belt
14
complicates the construction of the washing machine and accordingly increases the manufacturing cost. Furthermore, each of the pulleys
13
and
9
and the belt
14
produces oscillation or vibration in the transmission of motor torque. In particular, high-speed rotation of the motor
11
causes the belt
14
to slip, thereby swinging the belt. This increases the vibration produced by the belt transmission mechanism such that a loud noise is produced.
To solve the above-described problem, the prior art has provided a drum type washing machine as shown in FIG.
15
. The drum type washing machine shown in
FIG. 15
comprises a water tub
2
and an electric motor
21
provided on a rear wall of the water tub
2
. More specifically, a mounting member
24
is fixed on the rear wall of the water tub
2
so as to cover a bearing housing
6
. The motor
21
includes a stator
23
fixed to the mounting member
24
. The motor
21
also includes a rotor
22
connected to a rear end of a shaft
5
of the rotating tub. Japanese Patent Application Publication No. 9-182369 (1997) also discloses a drum type washing machine having the same construction as described above.
Torque developed by the motor
21
is directly transmitted to the shaft
5
and accordingly to the rotating tub
4
without a belt transmission mechanism in the aforesaid drum type washing machine. As a result, the construction of the driving mechanism for the rotating tub
4
is simplified and the manufacturing cost can be reduced accordingly. Furthermore, the vibration and noise can be reduced since no belt transmission mechanism is required.
Generally speaking, when a center of a stator and a center of rotation of a rotor of an electric motor are displaced relative to each other, an air gap defined between the stator and rotor is varied depending upon a rotation angle. This reduces the accuracy of the motor and produces vibration and noise. Accordingly, the center of the stator and the center of rotation of the rotor need to agree with each other with the greatest circumspection. The motor
11
as an end product is mounted on the lower portion of the water tub
2
in the conventional drum type washing machine. Accordingly, the center of the stator and the center of rotation of the rotor need not be aligned with each other regarding the motor
11
.
On the other hand, the motor
21
includes a combination of the stator
23
fixed to the mounting member
24
and the rotor
22
fixed to the rear end of the shaft
5
. More specifically, the center of the stator
23
and the center of rotation of the rotor
22
need to be aligned with each other. Thus, the motor
21
needs to be mounted with the greater circumspection in the aforesaid direct-drive drum type washing machine than in the aforesaid drum type washing machine with the belt transmission mechanism. Further, laundry sometimes tends to be one-sided during a dehydrating operation regarding the aforesaid drum type washing machine with the belt transmission mechanism. When the laundry becomes one-sided, the magnitude of centrifugal force acting on a portion of the rotating tub
5
differs from the magnitude of centrifugal force acting on the other portion of the rotating tub. For example, when laundry in the rotating tub
4
is one-sided at an area A shown by the two-dot chain line in
FIG. 14
, a large centrifugal force F
1
is applied to the area A, the bearings
7
and
8
in the bearing housing
6
are subjected to loads F
2
and F
3
respectively.
Since bellows connect an opening side of the water tub to the outer cabinet in each of the aforesaid drum type washing machine, a supporting structure for the water tub tends to become more rigid than the one of an automatic washing machine of the vertical axis type. When a part of the rotating tub is subjected to a large centrifugal force F
1
during the dehydrating operation, the loads F
2
and F
3
acting on the respective bearings
7
and
8
are increased such that the bearing housing
6
and parts around the bearing housing would be deformed. In the drum type washing machine shown in
FIG. 14
, the motor
11
is not almost affected by the loads F
2
and F
3
both acting on the bearing housing
6
since the motor is mounted on the lower portion of the water tub
2
. More specifically, the motor
11
is subjected to no large force other than the tension F
4
of the belt
14
.
On the other hand, the stator
23
is fixed on the mounting member
24
surrounding the bearing housing
6
in the drum type washing machine shown in FIG.
15
. Accordingly, the stator
23
is easy to be affected by the loads F
2
and F
3
. The positional relation between the rotor
22
and the stator
23
changes when the bearing housing
6
and the mounting member
24
are deformed by the loads F
2
and F
3
. As a result, the center of the stator
23
and the center of rotation of the rotor
22
are displaced relative to each other.
Furthermore, in the drum type washing machines, a washing/dehydrating capacity and a rotational speed in the dehydrating operation differ from one type to another. In the case of a drum type washing machine having a large washing/dehydrating capacity, the size of the rotating tub
4
is increased and a larger amount of laundry is accommodated in the rotating tub. Thus, the washing machine of the large capacity type requires a larger drive torque than that of the small capacity type. Further, the washing machine with a high rotational speed for the dehydrating operation requires a higher durability of the shaft
5
than that with a low rotational speed for the dehydrating operation. Accordingly, the diameter of the shaft
5
tends to be increased.
In view of the above-described problem, the construction of the connection between the shaft
5
and the driven pulley
9
or between the shaft
5
and the rotor
22
needs to be changed according to the washing capacity, the dehydrating capacity or the rotational speed in the dehydrating operation. The construction of the connection between the shaft
5
and the driven pulley
9
is changed in the following manner. The driven pulley
9
is die-cast from aluminum and accordingly, the construction can easily be changed by cutting a portion of the driven pulley
9
connected to the shaft
5
. On the other hand, when the shaft
5
and the rotor
22
are cut so that the construction of the connection between them is changed, there is a possibility that the center of the stator
23
and the center of rotation of the rotor
22
may be displaced relative to each other. As a result,
Ito Masumi
Yamazaki Fumitaka
Pillsbury & Winthrop LLP
Stinson Frankie L.
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