EP1475474A1

EP1475474A1 - Household clothes drying machine with improved fan arrangement

Info

Publication number: EP1475474A1
Application number: EP04009650A
Authority: EP
Inventors: Ugo Favret; Silvano Cimetta; Flavio Noviello
Original assignee: Electrolux Home Products Corp NV
Current assignee: Electrolux Home Products Corp NV
Priority date: 2003-05-09
Filing date: 2004-04-23
Publication date: 2004-11-10
Anticipated expiration: 2024-04-23
Also published as: EP1475474B1; ES2283895T3; SI1475474T1; DE602004005098D1; ATE356244T1; ITPN20030015U1; DE602004005098T2

Abstract

Clothes drying machine comprising a drum (1) for holding the clothes to be dried, a first fan (5) adapted to blow a first flow of drying air through said drum, a condenser (3) through which said flow of drying air is caused to pass, a cooling air conduit (4) conveying a second flow of fresh air through said condenser, said second flow of air being blown by a second fan (6) associated to said cooling air conduit, a motor (7) that is adapted to selectively rotate in a main direction and in a secondary direction opposite thereto, and to jointly drive said first and said second fan (5,6). The latter comprises a plurality of first planar vanes (9) that appear like being arranged on a surface of a cylinder, radially with respect to the axis (X) of said cylinder, said axis constituting also the axis of rotation of said second fan (6), and a plurality of second vanes (10) that are inclined relative to the axis of the fan, so as to bring about a flow urging the air contained in said second fan outwards when this fan rotates according to said secondary mode. During the initial stage of the drying process, said motor rotates solely according to said secondary mode.

Description

The present invention refers to an improved kind of clothes drying machine, preferably of the type for use in households, which is particularly quiet, i.e. low-noise in operation.
Although reference to a regular, autonomous clothes drying machine will be made throughout the following description, it shall be appreciated that what is set forth below may similarly be applied to and, therefore, be suitable for combined clothes washing and drying machines.
Clothes drying machines are largely known in the art to generally operate according to different principles and modes, including the condenser mode, i.e. the operation based on the condensation of the moisture contained in a stream of drying air that is first blown through the drum, where it removes moisture from the clothes contained therein, and flows eventually out of the same drum and into the condenser, and the exhaust mode, in which said flow of moisture-laden hot air is exhausted as such outside the machine.
These machines are largely known to be substantially implemented by installing a ventilation system, i.e. usually a blower formed by a fan and an electric motor associated thereto, and a heating arrangement, which draw air from the outside and, via an appropriate conduit arrangement, heat up such air and blow it into and through the drum holding the clothes to be dried.
Within the above-mentioned conduit there is installed a heating element which, when appropriately energized, heats up the air that flows over it as blown by said blower, so that air is let into the drum which is sufficiently hot to cause the moisture contained in the clothes to evaporate.
Therefore, upon having been so blown into the drum, the hot air causes the moisture contained in the clothes to evaporate and becomes almost saturated, or even fully saturated, with this evaporated moisture. The resulting hot, moisture-laden air is then forced further by said blower to create a continuous flow that is conveyed into and through an appropriate condensation arrangement, which is usually formed by a heat-exchanger that is flown through - along the so-called "hot path" - by said stream of hot moisture-laden air and - along the so-called "cold path" - by a substantially continuous stream of air taken in from the surrounding ambient and exhausted again into the same surrounding ambient upon having so flown across said heat exchanger.
Usually, even this flow of air along the "cold path" of the heat exchanger is brought about and kept up by a blower formed by a fan driven by a respective electric motor.
These clothes drying machines are rather simple, cost-effective and reliably operating appliances. However, they are also generally known to share a major drawback in that they generate a lot of noise when operating, owing to the stream of air that is blown at considerably high flow rates into and through the intake and exhaust conduits.
The practical result is that limitations usually arise in the use of these machines in certain periods or certain places, and this actually makes the utilization thereof quite less interesting to the average users.
The most direct, immediate technical solution that is considered for implementation in view of providing the required circulation of said two distinct flows of air is the one relying on the use of respective fans mounted in the corresponding conduits and driven by respective, independently controlled motors.
Such solution, however, has a drawback - and certainly a heavily weighing one in a product intended for a mass consumer market - in that it implies an additional and certainly not negligible cost due to the provision of two distinct motors along with the respective connection and control arrangements. In addition, the provision of a second motor requires a space that is usually not available inside the machine, unless other functions or performance capabilities of the same machine are given up, i.e. sacrificed correspondingly.
In view of eliminating these drawbacks, it is a known practice to connect both said fans to a single electric motor and, from the disclosure in the Italian patent application No. PN92A000016 filed by this same Applicant, the practice is also known to cause said motor to selectively rotate in the two opposite directions of rotation.
Such function is required by the fact that, if the drum is driven to always rotate in the same direction, and if also the hot air stream is caused to always flow in the same direction, the clothes to be dried in the drum tend to eventually entangle and roll up into a ball, thereby heavily affecting the final drying results in terms of both speed and quality.
Therefore, in order to prevent such problem from occurring, said single drive motor is controlled to alternately rotate in the two opposite directions of rotation, in which there are defined a main direction of rotation, wherein the vanes or blades are arranged so as to provide a maximum of flow rate and ventilation efficiency, and an opposite direction of rotation, which is also referred to as the reverse direction of rotation.
It has however been found that the noise generated by the fan in the cooling air conduit during the main operating mode is rather high, amounting for instance to about 67 dB, while however sustaining a flow rate of approx. 200 m³/hr, whereas the same noise lowers, for instance down to approx. 63 dB, during the reverse operating mode, when a lower flow rate of approx. 80 m³/hr is anyway sustained (the above-noted values are merely indicative).
In view of improving this situation, experiments have been run on a type of cooling fan, whose vanes are oriented in an "inverted" manner as compared with traditional-type vanes. This term of "inverted" vanes, or blades, is intended to mean that the vanes are curved in an arc-like manner, but, instead of featuring the concavity thereof oriented towards the direction that is tangential to the movement of the same vane, they are arranged at an angle of 180° with respect to the axis that extends therethrough and is parallel to the axis of rotation of the fan, so that it is actually the convexity thereof that is oriented towards the direction that is tangential to the movement of the same vane.
It has however been found that such design variant, while on the one side bringing about an actual reduction in the noise generated during the main operating mode, so that it lowers from about 67 dB to about 64 dB, causes on the other side the noise generated during the reverse operating mode to undesirably increase, e.g. from typically 64 dB to approx. 70 dB.
In practice, the different noise generation pattern of the two kinds of vanes is best illustrated by the two graphs appearing in the attached Figures 1 and 2, in which the first graph shows the noise generation pattern of the vanes according to the prior art, whereas the second graph illustrates the corresponding noise generation pattern of the above-mentioned "inverted" vanes.
It clearly appears that the higher level of noise (70 dB9 generated during the reverse operating mode by the "inverted" vanes only and solely occurs exactly during the short periods in which the machine operates in the reverse mode. However, albeit fully acceptable under the applicable standard regulations, this noise may anyway prove rather disturbing and irritating to regular users.
In order to make such noise less unacceptable, the possibility of course exists for the machine to be so designed and fitted as to allow the time in which the motor has to operate in said reverse mode - in view of preventing the clothes from getting entangled or rolling up into a ball - to be reduced to a minimum with respect to the time in which said motor is on the contrary allowed to operate in the main mode.
However, even in this case the noise generated by the fan in the cooling air conduit is quite frequently felt as being excessive for the actual sensitivity of the average user.
Moreover, during the initial phase of the drying cycle the need arises for both the clothes to be dried and the drying air to be heated up to steady-state temperature, so that condensation would turn out as being quite reduced in its extent and, as a result, would make a cooling down of the drying air straightaway useless - if not even detrimental or, anyway, disadvantageous.
On the other hand, during the following phases of the drying process, i.e. when the air is already heated up to process temperature, it has been found that - for an adequate condensation effect to be attained - there is no need for the condenser to be flown through by any sustained stream of fresh air, even a reduced flow rate of such cooling air being in fact sufficient to this purpose under the circumstances (in some extreme cases there may even be no need at all for any stream of cooling air to be provided, actually).
In this connection, a look should in fact be taken at Figure 3, which shows a graph illustrating both the flow rate P of condensed moisture and the temperature T of the air leaving the drum versus the time elapsed from the beginning of the drying process.
In this Figure, it can be readily noticed that, in the initial phase to of the drying process, the flow rate Po is at a maximum even if, in the same period of time, the temperature is still far away from the quite high values it is due to reach during the final phases of the drying cycle.
Those skilled in the art will therefore readily appreciate that the function itself of the cooling air fan during the initial phases of the drying process could practically be simply omitted or, anyway, reduced to a minimum, without putting any penalty on the overall drying performance of the machine, while on the other hand certainly achieving a significant reduction in the total time required to complete the drying cycle, as well as a reduction in energy usage owing to a smaller power input required by said cooling air fan.
It would therefore be desirable to provide a cooling air fan which is capable, at least during the reverse operating mode, to force the air into the related circuit at a significantly reduced flow rate, and for a shorter period of time, to the purpose of reducing both energy usage, without of course affecting condensation performance to any extent, and the overall time required to complete the drying cycle on the whole.
According to the present invention, this aim is reached, along with further ones that will be apparent from the following description, 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 4 is a general symbolical, schematic view of a clothes drying machine provided with a condenser arrangement and two fans rigidly connected with each other, according to the present invention;
Figure 5 and Figure 6 are perspective front and rear views, respectively, of a fan for circulating cooling air in the condenser of a clothes drying machine according to the present invention;
Figure 7 and Figure 8 are a front and a median cross-sectional view, respectively, of the same cooling air fan;
Figure 9 and Figure 10 are a rear and a side view, respectively, of the same cooling air fan;
Figure 11 is a diagrammatical view showing, in a single graph, two distinct curves concerning the temperature pattern of the drying air for an alternating mode of operation of a cooling fan since the beginning of the drying cycle according to prior art (curve A) and for a just secondary mode of operation of the same fan during the initial phase of the drying cycle (curve B), respectively;
Figures 12 and 12A are schematical views of the flow directions of the cooling air during the secondary phase for both a prior-art fan (Figure 12) and a fan according to the present invention (Figure 12A), respectively.

With reference to Figure 4, in a clothes drying machine according to a preferred embodiment of the present invention there is provided a drum 1 adapted to hold the clothes to be dried, to which there is associated a conduit 2 for the drying air to be circulated therethrough; this conduit extends to also pass through a condenser arrangement 3 that is adapted to condense the moisture contained in the air circulating therethrough, said condenser being flown through by a stream of "cold" air, i.e. air that is taken in from the surrounding ambient and sent to said condenser 3 via a corresponding conduit 4.
Both conduits 2 and 4 contain respective fans 5 and 6 thereinside to bring about the respective streams of drying and cooling air; furthermore, the shafts of said two fans 5 and 6 are connected in a generally known manner, even via appropriate kinematical links, to a single drive motor 7, so that the rotation of this motor will cause said to fans to correspondingly rotate in a synchronous manner, wherein said motor 7 is controlled by suitable control means (not shown) that are adapted to cause it to selectively rotate in the two possible directions of rotation, and this obviously enables said two fans to be in turn caused to rotate in a selective, but anyway mutually consistent manner (wherein by "mutually consistent" is meant that, when a first fan rotates in a definite direction, the second fan unchangingly rotates in a single and same direction of its own; and when the direction of rotation of said first fan is reversed, the second fan will change its own direction of rotation, too).
Said cooling air fan is usually enclosed in a casing generally known as "scroll", whose shape is such as to enable the air being blown by said fan to be effectively used and directed into the conduit leading to the condenser under as small as possible an efficiency loss.
In the traditional mode of operation, the motor driving the fan can also be used, via suitable motion transmission means, to rotatably drive also the clothes-holding drum and it is actually a common practice, in this connection, to let this motor be operated for short periods of time in the normal, or main, direction of rotation, said periods being alternated with other short periods of time, in which it rotates in the reverse, or secondary, direction.
The proposed solution according to the present invention is essentially based on the observation that, according to the prior art, the condenser cooling fan is usually of the so-called "tangential" type, i.e. it is made in the shape of a hollow geometrical cylinder , in which the side cylindrical surface is traversed by a multiplicity of vanes 9, which are variously curved, i.e. concave or convex, with respect to the tangent being projected in the direction of rotation; as already stated hereinbefore, the simple curvature of the vanes brings about an excessive noise generation, which is however modified when switching over from the main mode of operation to the reverse or secondary one, thereby creating the possibility of reducing the average amplitude of the noise through a shorter duration of the period of reverse operation. In fact, from the illustration in Figure 2 it can be readily inferred that, if the period of reverse operation is shortened, at a level of noise of 70 dB, and all other conditions remaining unaltered the average amplitude of the same noise is certainly reduced.
Under the circumstances, it has therefore been assumed - and later even verified experimentally - that by providing the vanes on the cylindrical outline of the fan 6 in the form of simple planar vanes 9, as shown for instance in Figures 5 through to 10 (these vanes project radially with respect to the axis X of the same fan, but with a related radial dimension D that is rather limited with respect to the radius of said hollow cylinder, so that said planar vanes 9 turn out as being arranged on the borders of said cylinder and are not substantially present thereinside), the result is a considerably lower noise generation, typically of approx. 64.5 to 65 dB.
However, the noise reduction that can be obtained in this way is still quite limited in its extent and, furthermore, it must be recognized that said cooling air fan keeps being driven, i.e. operating, even when this is certainly not necessary, and might therefore be safely omitted, i.e. during the initial phases of the drying cycle when the drying air is still too cold, so that any further cooling down of the condenser would do nothing else but bring about a poorer condensation performance.
In order to improve this certainly non-ideal situation, the fan 6, according to the present invention, has been provided, further to said first vanes 9 arranged radially with respect to the axis of the cylinder that is substantially defined by them, with an additional plurality of second vanes 10, wherein these are arranged between said axis X of said hollow geometrical cylinder and the related outside cylindrical surface or, more precisely, between the intersection point 0 of said axis X with one of the two bases of said cylinder, and that portion 11 of the outside surface of said geometrical cylinder which lies adjacent to said base, indicated symbolically at 12, as this is most clearly illustrated in Figures 5 to 10.
Said second vanes 10 are themselves arranged radially, in the sense that they project in a fan-like wise from said central point 0, from which they diverge.
In the above-mentioned Figures, said second vanes 10 are represented in the form of curved surfaces (they are fluted surfaces, i.e. a particular case of curved surfaces), whose front or rear projection, however, looks as a corresponding plurality of similar triangles having a vertex at said point 0, as exemplified in Figures 7 and 8. In this illustration said vanes are represented in the form of curved triangular surfaces that are substantially inclined with respect to the plane containing said base 12.
It will of course be appreciated that said second vanes 10 may take other forms, e.g. they may be petal-shaped or be given the shape of screw blades, wherein they must in all cases feature an overall geometrical configuration such that, when the fan 9 rotates in a given direction, said second vanes will taken in air axially from the outside ambient, through the section of the cylinder that is indicated symbolically at 13 and lies on the opposite side with respect to said base 12; in other words, in this direction of rotation said second vanes take in the outside air axially and cause it to flow into the geometrical cylinder, so that this air will eventually be more easily taken in and pushed by said first vanes 9 tangentially thereto.
If the direction of rotation changes, then it can be readily verified - as it is also easy to guess, on the other hand - that the effect of said second vanes 10 is to drive back the air from the interior of the cylinder towards the outside, however again in the axial direction and through said second base 13. In this way, a kind of air screen is created, which is formed by said air being blown outwards as represented schematically by the arrow F in Figure 12A (and as this can be most effectively and clearly understood by comparing the flows/arrows indicated in the two Figures 12 and 12A), and which prevents air form being regularly delivered into the fan and, from here, on to the respective first vanes thereof, with the ultimate result that the amount of air that is blown tangentially by said first vanes is considerably smaller than the amount of air that is on the contrary blown when the fan rotates in the opposite direction.
More than that, it has also been observed that, when the fan rotates in the direction of rotation producing the least flow, also the noise generated by the same fan is kept down to levels quite close to those typical of the fan rotating in its main direction of rotation.
Therefore, if said second fan is used as the cooling air fan 6 and is mounted so that, during the secondary operating mode, it generates not only the least air flow, but also the least noise, and if the duration of said secondary operation periods is at the same time shortened, then the targeted aim is fully reached, since no need actually arises for the condenser to be cooled down during the initial phases of the drying process, when condensation is in fact still limited owing to the drying air temperature not having reached any adequately high value yet, whereas the slight loss in condensation efficiency incurred as the drying process progresses can be readily compensated for by said shortened duration of the secondary operation periods, so that the overall ultimate result is not affected at all.
If the above considerations are applied to the extreme, it may be even concluded that it would be possible, and even advantageous, for the rotation of the cooling fan in its main operating mode to be fully suppressed during the initial period of the drying process, and for said cooling fan to be allowed to only rotate in its secondary operating mode, thereby obtaining the twofold result of a satisfactorily low noise generation and a shorter drying time on the whole, without any penalty being put on condensation efficiency. This kind of operation can be readily implemented by anyone skilled in the art using largely known means, which shall therefore not be described or illustrated here any further.
It is only upon conclusion of the above-mentioned initial phase of the drying process that the cooling air fan is allowed to alternately rotate in the two opposite directions of rotation, according to programme sequences that are already known as such in the art and designed so as to enable an effective condensation process to take place during the main operating mode of the cooling air fan, whereas the secondary operating mode thereof is selected so as to be as short as possible and is anyway allowed to be carried out to the sole purpose of disentangling clothes that may in the meantime have rolled up into a ball.
To the sole purpose of serving as a symbolical illustration, Figure 11 shows two distinct graphs indicating the temperature pattern of the drying air with a cooling fan of a prior-art kind alternately rotating in both directions, i.e. operating alternately in both its main and secondary modes since the beginning (curve A), and with a cooling fan according to the present invention rotating only in its secondary direction of rotation, i.e. operating in its sole secondary operating mode during the initial phase of the drying process (curve B), respectively.
It clearly appears that, in the second case, the air temperature rises in a much quicker manner and this fact - far from being a drawback - is an advantage, actually, since it contributes to shortening the overall drying time and reducing the noise, without putting any significant penalty on the efficiency of the condensation process.
The function itself of the cooling air fan shall therefore be capable of being controlled selectively both through appropriate commands that may be imparted via external control means and on the basis of other parameters, such as for instance time, temperature or the like.
Anyway, the actual criteria which the control of the operation of said fan is to be based upon, as well as a quantification of the related functions and the implementation of the related control circuits are fully within the capabilities of those skilled in the art who, based on routine experiments, are in fact able to identify and implement corresponding optimum solutions.

Claims

Clothes drying machine, or combined clothes washing and drying machine, comprising a drum (1) for holding the clothes to be dried, a first fan (5) adapted to blow a first flow of drying air through said drum, a condenser (3) through which said flow of drying air is caused to pass, a cooling air conduit (4) conveying a second flow of fresh air through said condenser (3), said second flow of air being brought about by a second fan (6) associated to said cooling air conduit (4), a motor (7) that is adapted to selectively rotate in a main direction and in a secondary direction opposite thereto, and to jointly drive said first and said second fan (5, 6), characterized in that said second fan comprises a plurality of first planar vanes (9) that appear like being arranged on a surface of a cylinder, radially with respect to the axis (X) of said cylinder, said axis constituting also the axis of rotation of said second fan (6).
Clothes drying machine, or combined clothes washing and drying machine, according to the preamble of claim 1, characterized in that said second fan (6) also comprises a plurality of second vanes (10) that are provided on a base (12) of said cylinder, fanning out from the centre (0) of said base, said second vanes (6) being inclined relative to said base (12) so as to bring about a flow of air directed from said base (12) outwards via the interior of said cylinder, when said second fan (6) rotates according to said secondary mode.
Clothes drying machine, or combined clothes washing and drying machine, according to claim 1 or 2, characterized in that said second vanes (10) are so shaped as to feature a triangular projection on a plane extending parallel to said base (12).
Machine according to any of the preceding claims, characterized in that it is provided with means adapted to enable said motor (7) to rotate according to said main operating mode and said secondary operating mode in a selectively pre-definable manner.
Machine according to claim 4, characterized in that, during the initial stage of the drying process, said motor rotates solely according to said secondary mode.