[0001] The present invention refers to an improved kind of clothes drying machine, preferably
a tumble dryer of the type intended for use in households, provided with means for
removing moisture from the drying air comprising a conduit, through which there is
conveyed a flow of hot, relatively dry air for entering a rotating drum in which there
have preliminarily been introduced the clothes forming the load to be dried. In the
drum, this flow of hot air moves through and over the clothes to be dried and is eventually
caused to exit the drum to be either let out into the atmosphere, or the ambient,
or re-circulated in a closed-loop circuit, in which said flow of hot and, at this
point, moisture-laden air is dehumidified, heated up again to drying temperature and
blown again into the drum.
[0002] As far as the present invention is concerned, it is of no importance at all for the
clothes dryer to be of a particular kind, i.e. of the first-named kind, or exhaust
type letting out the air directly into the ambient, or the second-named kind provided
with condenser arrangement. In fact, what really matters to the purposes of the present
invention is the presence of a rotating drum holding the load of clothes to be dried,
into which a flow of hot drying air is blown for removing the moisture contained in
the clothes, and from which this air is eventually caused to flow out to be either
exhausted or conveyed to the condensation process for reuse.
[0003] While reference will be made throughout the following description to an autonomous
clothes drying machine, i.e. a machine intended solely for drying clothes, the explanations
and descriptions given below shall be of course be understood as applying equally,
and therefore effectively, to a so-called washer-dryer, i.e. a combination machine
for washing and drying clothes.
[0004] The machines of the kind covered by the present invention are largely known in the
art. They are for instance described, along with detailed argumentations of a technical
nature concerning the advantages and the drawbacks of various design solutions and
embodiments, in the
Italian patent application No. PN2003U000015, relating to a clothes dryer with an improved fan arrangement, as well as in the
European patent application No. 04104117.9 of the same Applicant, to which reference should therefore be made for reasons of
brevity and greater simplicity in this description.
[0005] Anyway, the present invention preferably applies to clothes drying machines that,
further to a condenser for dehumidifying the hot moisture laden air exiting the drum,
are also provided with:
- two distinct fans for the drying air and the condenser cooling air, respectively,
- a single motor adapted to drive said two fans at the same time,
- wherein said motor is adapted to be controlled so as to selectively rotate in the
two opposite directions.
[0006] At any rate, the present invention shall be understood as applying equally well to
condenser-type clothes dryers of a traditional kind, i.e. provided with a normal condenser,
but lacking the other features as mentioned above.
[0007] As all those skilled in the art are well aware of, the process by which the flow
of hot air moving through the drum, and the clothes held therein, removes the moisture
contained in the clothes is mainly due to the fact that the heat supplied by the air
itself heats up the water contained in the clothes, thereby causing it to progressively
evaporate.
[0008] The vapour generated in this way is then immediately taken in by and mixed in the
drying air flowing therethrough, so that it automatically leaves the drum, since said
flow of drying air is practically taken out of the drum continuously.
[0009] However, although quite effective and reliable, this process has a major drawback
in that, even if the heat exchange process taking place between the hot drying air
and the moisture contained in the clothes to be dried is certainly favoured by the
fact that the drum keeps rotating continuously during the drying cycle, thereby increasing
the fraction of drying load that is directly invested by, i.e. directly exposed to
the hot air flowing therethrough, heat conduction between the flow of hot drying air
and the water contained in the clothes to be dried, and due to be removed by said
air, is largely known to be rather limited.
[0010] As a result, in order to enable the whole amount of water present in the clothes
to be caused to evaporate, the need arises for said flow of hot air to be allowed
to circulate through the drum for an extended period of time, so as to make sure that
every single item in the drying load is effectively exposed to and possibly passed
through by said flow of hot air.
[0011] The direct consequence of such constraint is a much longer drying time needed to
achieve the desired results, accompanied by a loss in energy efficiency owing to the
drying machine tending to dissipate outside a certain part of the heat generated thereinside,
and this occurs in a manner that is substantially proportional to the length of the
process time.
[0012] In view of doing away with these drawbacks, known from the patent publication
EP 1 285 987 to LG ELECTRONICS INC. is the practice of providing inside the drum of a clothes
dryer "an extension duct lengthened from the suction duct into the drum, for flowing
the air supplied from the suction duct into the drum, and an exhaust duct connected
to the other side of the drum, for exhausting air which dried clothes to the outside
of the case".
[0013] In this way the possibility is given to improve the drying efficiency to a certain
extent, since such "extension duct" conveys the heated-up air directly into the central
portion of the drum, so as to increase the amount of clothes in the drying load being
directly exposed thereto.
[0014] In addition, although this feature is not mentioned in the above-cited patent publication,
also the surface of said extension duct that is not affected by the plurality of air
holes provided to let out the heated-up air from the interior of the extension duct
and into the drum, is heated up by the drying air; as a result, when the items to
be dried come into contact with this surface, they are heated up by it quite rapidly.
[0015] The resulting direct heating effect is quite appreciable, since heating by direct
conduction between the preferably metal surface of said extension duct and the items
to be dried is generally known to be more efficient than heating by convection, i.e.
the heating effect brought about by the hot air flowing through the drum.
[0016] However, the above-mentioned effect is in this case curtailed to a quite appreciable
extent by the fact that the air-outlet perforations provided all along the extension
duct practically take up a considerable portion of the surface thereof, since they
have to enable a remarkable portion of the hot air flowing through said duct to wholly
and fully escape into the drum.
[0017] As a result, the amount of solid surface materially existing between adjacent perforations
in the extension duct adds up to just a relatively small value, so that the amount
of heat that is exchanged by conduction between the same extension duct and the items
to be dried coming in contact therewith is reduced correspondingly.
[0018] It would therefore be desirable, and it is actually a main object of the present
invention, to provide a clothes drying machine of a general kind, which is particularly
efficient in the use of energy and is at the same time capable of ensuring quicker
operating cycles.
[0019] In addition, this clothes drying machine shall be capable of accommodating such improved
features, without any significant penalty having to be paid in exchange for this as
far as other construction and performance aspects or functions are concerned.
[0020] According to the present invention, these aims, along with further ones that shall
be described further on, are reached in a clothes drying machine incorporating the
features as recited in the appended claims. Anyway, features and advantages of the
present invention will be more readily understood from the description that is given
below by way of nonlimiting example with reference to the accompanying drawings, in
which:
- Figure 1 is a functional schematic view of a clothes dryer according to the prior
art,
- Figure 2 is a functional schematic view of a clothes dryer according to an embodiment
of the present invention;
- Figure 3 is a functional schematic view of a clothes dryer according to a second preferred
embodiment of the invention,
- Figure 4 is an enlargement and a more descriptive view of the embodiment of fig. 3.
With reference to fig. 1, provided in a clothes drying machine according to a prior-art
embodiment there is a drum 1 adapted to hold the clothes to be dried, to which there
is associated a conduit 2 for circulating the flow of drying air. This conduit may
possibly be extended to pass through a condenser arrangement 21, adapted to condense
and, hence, remove the moisture contained in the hot drying air exiting the drum and
flowing therethrough, wherein a flow of "cold" air, i.e. air that is taken in from
the surrounding ambient and sent to the condenser via a respective conduit, is directed
to at the same time flow through the condenser in view of cooling it.
[0021] Thereinside, the conduit 2 contains a respective fan 5 for moving the flow of drying
air, as well as a respective heating element 9 for heating up said drying air.
[0022] Said conduit, upon extending along a flow-path that will be described in greater
detail further on, terminates in a plurality of air-outlet ports 3 opening up directly
inside the drum.
[0023] It should at this point be clearly and explicitly pointed out that this conduit 2
does not solely and strictly consist of a specific physical duct, but rather includes
all material elements that are altogether used and provided to direct the flow of
drying air from the fan 5 up to said outlet ports 3.
[0024] According to the present invention, said conduit is led to extend well into the drum
1 with en extension piece 4 provided thereinside and attached to the rear wall 16
of said drum in a substantially axial arrangement (fig. 2).
[0025] This extension piece 4 appears externally in the shape of a cylinder provided with
an outer wall 10 terminating - on the free side thereof inside the drum - in a closed
wall 11 that is situated at a pre-determined distance D from the rear wall 16 of the
drum from which said extension piece departs.
[0026] Inside said extension piece 4 there is arranged a second cylinder 12, or inner wall,
that is spaced, i.e. separated from the outer surface of said extension piece 4 and
preferably extends coaxially therewith.
[0027] The innermost end portion 14 of said second cylinder 12 is fully open, so that the
hollow interspace or jacket 13 forming between said outer wall 10 and said inner cylinder
12 is capable of joining into the inner space thereof simply via said inner end portion
14 delimiting said inner wall 12.
[0028] In order to prevent the clothes in the drying load from being capable of twisting
up and getting tangled around said extension piece when the drum is driven to rotate
during the drying process, said extension piece 4 is preferably firmly joined with
the rotating body of the drum, so as to rotate jointly therewith. It can be readily
appreciated that the passage of the air from said hollow interspace 13 to the downstream
section of said conduit 2 is ensured by means of a plurality of perforations 17 provided
in said rear wall 16, so as to ensure the required mechanical continuity between the
outermost portion of the rear wall 16 and the innermost portion 16A, on which said
outer wall 10 is applied.
[0029] After having flown through said extension piece 4, the flow of air is then directed
further on by the conduit 2 towards a plurality of further perforations 18, which
are also provided in the rear wall 16 of the drum, so as to definitively lead the
flow of hot air into the drum.
[0030] Basically, therefore:
- said extension piece 4 is firmly joined to the drum 1 with both the outer wall 10
and the second cylinder 12 thereof,
- in the rear wall 16 of the drum there are provided appropriate perforations or ports
17 to enable the flow of hot air to pass both from the conduit 2 into the extension
piece 4 and from this extension piece back again into the portion of conduit 2 located
outside the drum.
[0031] The ways in which all these construction and design variants in the embodiment of
the inventive dryer may be practically implemented are well within the ability of
those skilled in the art, so that they shall not be described in detail any further.
[0032] On the other hand, the way in which an inventive clothes dryer as explained above
operates can at this point be readily appreciated: in fact, the hot air flowing in
from the conduit 2 - instead of being readily and directly blown into the drum and
through the clothes - is caused to first flow through said extension piece 4 by blowing
it either into the inner cylindrical wall 12, leading it through the open end portion
14 thereof and letting it out again through the hollow interspace 13, or the other
way round.
[0033] The hot air flowing back from the extension piece 4 and out through said perforations
17 is led by the final section of the conduit 2 through said outlet perforations 18
to be eventually let into the drum.
[0034] However, while certainly constituting a clear improvement over the prior art, the
above-described solution still has a drawback in that the necessarily limited diameter
of the cylindrical extension piece 4 causes the flow of hot air flowing therethrough
to suffer a pressure drop that can in turn cause the flow rate of the same air to
decrease to such a low value as to practically impair the final performance capabilities
of the machine.
[0035] In order to do away with this drawback, and with particular reference to figures
3 and 4, an advantageously modified embodiment is therefore proposed, which consists
in having the conduit 2 subdivided into two branches operating in parallel in a functional
and not physical sense, i.e. the hot air flowing through said conduit 2 is at a certain
point split up and let into two separate ducts, wherein a first duct is readily directed
into the drum, while the second duct is directed into the extension piece 4, at the
outlet side of which the related air flow is in turn conveyed into the drum.
[0036] A "mixed" kind of operation of the dryer is in this way obtained, which still enables
the advantages provided by the afore-described main embodiment to be derived, however
without having to bear any of the above-noted drawbacks connected therewith.
[0037] This solution can be materially embodied as illustrated in the same figure 4, in
which the second cylinder 12 is attached at the base thereof to the central portion
16A of the rear wall of the drum, whereas the outer wall 10 covers said second cylinder
12 in the way of a cap; the stream of hot air flows through said hollow interspace
13 by passing through - further to said open end portion 14 - also a plurality of
third perforations 20 that are provided to fluidly connect the rear portion of said
outer wall 10 with the interior of the drum 1.
[0038] In addition, for easily imaginable construction-related reasons it has been found
particularly advantageous for the flow of hot air being let into said extension piece
4 to enter it through the interior of said second cylinder 12 and to pass to the drum
through said hollow interspace 13 and said third perforations 20.
[0039] With regard to fig. 5, the substantial advantageous character of the present invention
has been clearly and unequivocally demonstrated experimentally in a number of comparative
tests that, in a normal production-line clothes drying machine used to handle a same
load of similarly wet clothes through a similarly set drying cycle and, therefore,
under fully similar and comparable test conditions, the air temperature when existing
from the drum is varied from curve A2 to curve A1, and condensed water is increased
from curve B2 to curve B 1.
1. Clothes drying or combined washing and drying machine comprising a drum (1) provided
to hold the clothes to be dried, a conduit (2) adapted to circulate a flow of hot
drying air, one or more outlet ports (3) adapted to let the flow of hot drying air
circulating through said conduit (2) into said drum (1), a first fan (5) adapted to
blow a first flow of drying air through said drum and in said conduit (2), a first
heating element (9) provided inside said conduit (2), said conduit (2) for circulating
the drying air being further provided with an extension piece (4) that protrudes from
the rear wall of the drum into the inner volume thereof in a direction coinciding
with the axis of rotation of said drum, characterized in that said extension piece (4) comprises a substantially cylindrical outer wall (10), which
is closed at the innermost end portion (11) thereof inside the drum, and a substantially
cylindrical inner wall or second cylinder (12) that stretches out longitudinally inside
said outer wall (10) and is open at the innermost end portion (14) thereof inside
the drum.
2. Clothes drying or combined washing and drying machine according to claim 1,
characterized in that said innermost end portion (14) of said inner wall (12) is situated at a pre-determined
distance (D) from said outer wall (10), so as to enable a flow of drying air to:
- flow into and through the hollow interspace (13) defined between said outer wall
(10) and said second cylinder (12), and exit through said second cylinder (12),
- or the other way round.
3. Machine according to claim 2, characterized in that said outer wall (10) is firmly joined with the rear wall of said drum.
4. Machine according to claim 2 or 3, characterized in that said second cylinder (12) is firmly joined with the structure of the machine.
5. Machine according to any of the claims 2 to 4, characterized in that a part of the flow of drying air is let into said hollow interspace (13) being defined
between said outer wall (10) and said second cylinder (12), and is finally blown into
said drum through third perforations (20) showed on the rear side of said outer wall
(10).