Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Washing machine tank provided with external reinforcing cap on bottom
wall.
The present patent application for industrial invention relates to a
washing machine tank provided with an external reinforcing cap on the
bottom wall.
As it is known, the washing unit of washing machines or dryer/washer
combos comprises a basically cylindrical drum designed to be loaded with
laundry, which rotates inside a tank obtained by moulding plastic materials.
A similar tank is frontally provided with a large opening to load the
laundry, while the bottom wall is provided with a central hole that ends in a
rear cylindrical nozzle, where the shaft protruding from the bottom wall of
the
io drum contained in the tank is exactly inserted, with the interposition of a
bearing support.
In particular, the shaft slightly protrudes outside the tank in order to be
coupled with the electrical motor designed to drive the drum into rotation.
In some cases, the electrical motor is mounted in peripheral position
with respect to the bottom wall of the cylindrical tank; in such a case, a
drive
belt is provided to ensure the joint rotation of the shaft of the electrical
motor
and the shaft of the drum, which are both suitably provided with
corresponding pulleys.
In other cases, the so-called "direct drive" technology is used,
2o according to which the stator of the electrical motor is mounted in the
centre
of the bottom wall of the tank in such a way that the rotor is directly
splined to
the shaft of the drum.
In both cases, however, the bottom wall of the washing machine tank
must be characterised by high structural rigidity in order to withstand
without
damages the high mechanical stress induced by the centrifugal force
generated by the mass of the laundry contained in the rotating drum.
So far, the said rigidity of the bottom wall has been guaranteed by
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means of a network of stiffening ribs provided on the outside of the tank.
When the presence of the said ribs is not sufficient, the bottom wall of
the tank is given an "omega" profile in which some sec#ions of the wall
protrude inwards.
In fact, such a configuration gives the bottom wall of the tank a high
inertia momentum.
A careful examination of the state of the art has identified several
criticai aspects.
In particular, the formation of the external stiffening ribs requires a
large use of moulding material and sophisticated expensive moulds, with very
long moulding time especially due to the need to cool down the ribs.
By considering that the market offers different models of washing
machines in terms of rotation speed of the drums (from 400 to 1,600 rpm.), It
is clear that each model of washing machine must be provided with a tank
with specific mechanical resistance characteristics according to the different
stress imposed by the rotation of the drum.
In view of this, a manufacturer of washing machine tanks must
produce at least five different models of tanks, each of them with different
rigidity and resistance according to the rotation speed of the speeffic
appliance.
~ Moreover, the tanks with bottom wall provided with "omega" profile are
impaired by the fact that they create considerable turbulence in the water
mass contained inside the tank, with consequent high noise level inside the
appiiance, fonnation of foam that requires more rinsing water, and
considerable washing residues in the concave areas of the bottom wall that
are not removed by the rinsing water.
The washing residues originate the so-called "biofiirn", which is
considered detrimental because it favours the proliferation of bacteria and
consequent production of bad odours.
EP 1 528 136 discloses an aggregatc for washing machine
provided with an hollow cylindrical suds container of fibber glass
reinforced polymeric material suitable for containing a drum and a
AMENDED SHEET 23I04I2009
C--ved at the EPO on Dec 01, 200810:00:51. Page 14 of 15
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support structure of cast iron embedded In the bottom wall of the suds
container.
The purpose of the present invention is to find a solution to the
aforementioned problems of the prior technique, in order to reduce
production costs and increase technica!-functiona1 efficiency and versatility
~
2 AMENDED SHEET 23/04/2009
d-,,"'ied at the EPO on Dec 01, 2008 10:00:51. Page 15 of 15
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considerably.
The inventive idea of the present invention consists in a special
composite structure of the bottom wall of a washing machine tank.
More precisely, the tank of the invention is provided with a bottom wall
with smooth surface both internally and externally.
This allows to eliminate the traditional stiffening ribs that protrude
outwards and the raised areas with that protrude inwards, of the type used in
the bottom wall of tanks provided with "omega" profile.
In this case the task to give the necessary rigidity and resistance to
io mechanical stress is entrusted to a circular cap designed to be exactly
fitted
against the external side of the bottom wall of the tank.
The plastic moulded cap is preferably provided with a plurality of
spokes, being otherwise defined as cross-piece.
Considering that the spokes of the cap are internally hollow, it appears
evident that, in cooperation with the external side of the flat bottom of the
tank of the invention, the spokes originate a box-shaped structure with
multiple spokes, which is effectively able to guarantee a considerable inertia
momentum both with respect to flexural and torsional stress.
If considered individually, both the smooth bottom wall of the tank and
the cap have modest inertia values due to reduced thickness.
Their stable coupling, however, allows to create the box-shaped
structure effectively provided with mechanical characteristics compatible with
the correct operation of a washing machine.
The advantages of the invention appear evident from this first
description.
First of all, the presence of a perfectly smooth bottom wall ensures
better practical and economic characteristics with reference to moulding, not
only because of the lower complexity of the moulds, but also because of the
lower quantity of plastic material used.
The elimination of the inward protruding sections that are typical of
tanks with "omega" bottom completely prevents the formation of the
undesirable biofilm.
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The presence of the smooth bottom wall of the tank of the invention
generates an excellent distribution of the surface tension that tend to be
created in a totally non-uniform way in the more complicated structures of the
pre-existing tanks, impairing the mechanical characteristics of the same
tanks.
Moreover, the composite structure of the bottom wall of the tank of the
invention ensures practical and economic characteristics also with reference
to the production of different models of tanks for washing machines with
different rotation speeds.
As mentioned earlier, according to the prior technique, each specific
type of washing machine requires a specific tank with specific rigidity and
mechanical resistance properties according to the maximum rotation speed.
Because of the present invention, all different types of washing
machines use the same type of tanks, being provided that the task to
guarantee the correct index of mechanical resistance to the bottom wall of
the tank is entrusted to the cap with multiple spokes.
In view of the above, a manufacturer that makes use of the technology
of the invention will produce a single model of tank, which will be adapted to
each specific model of washing machine by means of a diversified production
of caps (according to the different thickness and profile of the caps).
The need to produce a different range of caps is certainly more
practical and cost-effective compared to the current need to produce a
different range of tanks.
Finally, it must be noted that the favourable weight/performance ratio
determined in the tank of the invention because of the assembly between the
bottom wall of the tank and the cap contributes to optimise the traditional
appendixes provided on the perimeter of washing machine tanks.
Reference is made to the appendixes designed to favour the assembly
in peripheral position of the electrical motor designed to drive the internal
3o drum into rotation, and also to the appendixes used to apply fixing means
used to join the tank to the bearing case of the household appliance during
packaging and transport operations (when the tank, which is usually mounted
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on elastic elements; is subjected to undesired dangerous shocks).
For clarity purposes the description of the invention continues with
reference to the enclosed drawings, which only have an illustrative, not
limiting purpose, whereby:
5 - fig. 1 is an axonometric view of the tank of the invention, without the
reinforcing cap;
- fig. 2 is an axonometric external view of the said cap;
- fig. 3 is an axonometric internal view of the said cap;
- fig. 4 is an axonometric view of the aforementioned components one in front
lo of the other one, without permanent fixing;
- fig. 5 is an axonometric view of the tank in assembled condition;
- fig. 6 is an axonometric exploded view of the tank, in the embodiment
designed to be associated with the corresponding electrical motor according
to the direct drive technology.
is With reference to fig. 1, the tank of the invention (1) is usually
composed of a plastic moulded cylindrical structure and designed to be
frontally closed with a circular flange (not shown in the enclosed figures)
provided with a large opening used to load laundry inside the traditional
rotary
drum (not shown in the enclosed figures) housed in the tank.
20 As mentioned earlier, the peculiarity of the new tank (1) consists in the
presence of a smooth bottom wall (2) without stiffening ribs or inward
projecting areas.
The wall (2) is provided with a central hole (2a) that receives the shaft
of the drum housed in the tank (1).
25 With reference to figs. 2 and 3, the second component of the tank (1)
consists in a sort of circular cap (3) provided with a plurality of internally
hollow spokes (3a) obtained by moulding plastic materials.
In particular, the spokes (3a) protrude from a central cylindrical nozzle
(3b) and are joined at the peripheral ends with the internally hollow annular
3o border (3c) of the cap (3).
As shown in figures 2 and 3, the central nozzle (3b) is considerably
longer than the thickness of the annular perimeter border (3c); because of
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this, the spokes (3a) have a section with decreasing height from the centre to
the peripheral area.
The cyliridrical nozzle (3b) is designed to house a metal bearing
support (SP) that receives exactly the shaft of the drum after passing through
the hole (2a) of the bottom wall (2) of the tank (1); reference is made to
figure
2 that shows the said support (SP) in an exploded view.
The bearing support (SP) is preferably co-moulded with the cap (3).
In any case, the cap (3) is designed to be fixed in external position on
the flat bottom wall (2) of the tank (1), with the concave side facing the
flat
io wall (2).
In order to guarantee the mutual coupling between the two
components, the cap (3) has a basically identical diameter as the bottom wall
(2) of the tank (1) and the central nozzle (3b) of the cap (3) is perfectly
aligned with the hole (2a) obtained in the bottom wall (2).
The cooperation between the cap (3) and the bottom wall (2) of the
tank (1) allows to obtain a box-shaped structure on the back of the tank,
which is composed of a series of radial compartments (V1), each of them is
bordered by one of the spokes (3a) of the cap (3), and an annular
compartment (V2) bordered by the annular border (3c) of the cap (3).
The presence of the box-shaped structure allows the bottom wall (2) to
acquire the necessary resistance to withstand without damages the
mechanical stress transmitted by the rotations of the shaft of the drum full
with wet laundry.
The stable fixing of the cap (3) against the bottom wall (2) of the tank
(1) can be obtained according to different suitable modes, such as gluing,
welding or screwing.
The cap (3) can be also provided on the external side with basically
cylindrical appendixes (4, 5) obtained during the same process and with the
same moulding material used for the cap (3).
The appendixes (4, 5) have a parallel position to the central nozzle
(3b) and are designed to favour the application of the means used to ensure
the stable fixing of the entire tank (1) to the bearing structure of the
washing
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machine during packaging and transportation.
To that end, each appendix (4, 5) is frontally provided with a
corresponding axial hole (4a, 5a) used to screw a corresponding screw.
In particular, in the embodiment of the cap (3) shown in the enclosed
figures, a first opposite pair (4) of appendixes is provided at a higher
height
directly protruding from the annular border (3c), and a second pair (5) of
appendixes is provided at a lower height protruding on the front of
corresponding small hollow arms (5b) that protrude radially from the annular
border (3c).
Finally, a third pair (6) of similar appendixes is provided between the
two appendixes of the second pair (6), protruding on the front of
corresponding small hollow arms (6b), designed to be used to fix the
electrical motor that drives into rotation the shaft of the drum housed inside
the cylindrical nozzle (3b) of the cap (3) by means of a drive belt.
Also the appendixes (6) of the third pair are frontally provided with
axial holes (6a) for suitable fixing screws.
The small radial arms (5a, 6a) are provided with corresponding internal
cavities designed to be exactly covered, when the cap (3) is engaged to the
bottom wall (2) of the tank (1), by corresponding ears (50a, 60a) that
protrude
from the border of the bottom wall (2) of the tank (1) to generate relevant
box-
shaped structures.
In this way, also the small arms (5a, 6a) are advantageously given
high mechanical resistance during operation.
Finally, figure 6 shows the embodiment of the cap (3) designed to
mount the electrical motor according to the direct drive technology.
In such a case, the external surface of the cap (3) is provided with
three fixing holes (3d) for the stator (ST), with a corresponding rotor (RT)
that
rotates outside it splined to the shaft of the drum that partially protrudes
from
the cylindrical nozzle (3b) of the cap (3).
