Method and condenser dryer for drying clothes

Abstract: The invention relates to a method and an apparatus for drying clothes, in which the temperature of the drying air is pre-set in accordance with the type of clothes to be handled. The method is characterized in that, during a drying cycle, also the rotating speed of the drum is variable within ranges that are pre-set in accordance with the type of clothes being handled in a manner that is proportional to the amount of water that is removed from the clothes, ie. inversely proportional to the desired drying degree.

Description: The present invention refers to a method and a condenser-type tumble-apparatus for drying clothes, in particular for home use. A clothes drying machine of the traditional type comprises, inside a substantially parallelepiped outer casing, a drum adapted to be kept rotating by an electric motor at a speed of approx. 50 rpm, as well as, further to a blower, a closed-loop circuit for the circulation of the drying air, in which there are arranged both heating means and means for the condensation of the moisture being removed in the form of steam from the clothes that are kept tumbling in the rotating drum. The cooling air for the condenser is taken in from the surrounding ambient by means of a second blower and is then exhausted downstream of the condenser. A first serious drawback of traditional clothes drying machines lies in the practical impossibility for them to ensure drying of woollen clothes without damaging them to some extent. The way in which the clothes are caused to impinge against the inner surface of the drum during the rotation thereof, cause the woollen fibres to undergo felting, ie. to become matted together. A second drawback lies in the fact that the sole variable in the drying cycles offered by such machines is the duration of the process, although it may be associated to the desired degree of dryness to be obtained. The result is that the performance capabilities of currently existing machines are not satisfactory for all users under all circumstances. A further, and certainly not less serious drawback of prior-art machines lies in the fact that, at the present state of the art, only models that are provided with a heat pump, which is a delicate, complex, bulky and definitely expensive piece of equipment, have energy usage records that allow them to fall within the range of values belonging to the class A according to the European Union energy rating and labelling scheme. As it can readily be appreciated, however, the altogether not widespread diffusion of such models on the marketplace only marginally contributes to an overall reduction in energy usage, which on the other hand is the actual and sole reason why the above cited energy labelling scheme has been introduced for home appliances. The patent application EP-A-0 933 465 has recently suggested the option of replacing the rotating drum with a chamber in which a so-called fluidised bed is created through the forced outflow of hot drying air, through a plurality of ports, from the bottom of the chamber. The velocity of this air counterbalances the weight of the clothes being handled, which therefore remain suspended, ie. floating throughout the duration of the drying cycles, without impinging against the walls of the chamber. Even though no practical experiments have been carried out to verify such a concept, it can be readily appreciated that a reliable thermo-fluid-dynamic control of the air is a quite difficult and problematic matter, particularly if the progressive reduction in the weight of the clothes and the unpredictable variability of fibres and fabrics are considered. US Patent No. 5,704,136 discloses a method of controlling the drying operation of a washing machine that comprises substantially three drying steps. During these steps, i.e. during the drying cycle, the revolution speed of the motor is gradually increased without stops. Japanese Patent Application No. JP 07 289793 discloses a dryer in which a microcomputer controls the electrification of heaters and decreases impulsively the rotation speed of a turning drum when the drying target ratio reaches pre-set values. It would therefore be desirable, and is actually a first purpose of the present invention, to provide a method for drying clothes, which is free of all such above-cited drawbacks. A further purpose of the present invention is to provide an associated apparatus for drying clothes, which is capable of offering users performance records that were simply unthinkable of up to now. The characteristics recited in the appended claims enable these and further aims to be reached. Anyway, features and advantages of the present invention can be more readily understood from the description that is given below of a preferred, although not sole embodiment by way of non-limiting example with reference to the accompanying drawing, in which: Figure 1 is a partially see-through view of a clothes drying machine according to the present invention; Figure 2 is a diagrammatical view, in the form of a Cartesian chart, of the pattern followed by the rotation speed of the drum during a drying cycle for three different types of fabrics (woollens, cottons, synthetic fibres); Figure 3 is a diagrammatical view, in the form of a Cartesian chart, of the pattern followed by the temperature, the amount of moisture removed and the rotation speed of the drum during a drying cycle of cotton clothes. With reference to Figure 1, a clothes drying machine comprises a substantially parallelepiped outer casing 1, part of which are among other things a control panel with the various control, setting and indicating members 2 of the machine, a front loading door 3 and a front socle carrying a pair of apertures 4 and 5 in a side-by-side arrangement. The metal rotating drum 10, which is housed in said outer casing 1, comprises in turn: a substantially cylindrical skirt or wrapping 11 with the traditional agitator means 18; a rear flange 12 with a plurality of perforations 13 that may be clustered into a relatively compact circular crown close to the skirt 11; a solid disk 16, sustained by means of some spacers 17 by the rear flange 12 and having a slightly smaller diameter than the skirt 11, in such a way as to leave an annular gap, whose function will be described in greater detail further on; a front flange, in the middle of which there is provided a large circular aperture. This aperture is adapted to be shut by the protruding inner door 6, which is also provided with a plurality of perforations 7 and sustains in the lower portion thereof a lint filter 8 arranged at the inlet of a first shaped conduit 9 situated in the zone comprised between the base of the outer casing 1 and the skirt 11 of the drum 10. Inside said conduit 9 there is housed a cross-flow condenser 20, to which there is associated a vessel (not shown) for collecting the condensed steam. By means of a drive belt 15 engaging an appropriate groove or race provided in the skirt 11, the drum 10 is driven so as to rotate about a sensibly horizontal axis by a first electric motor 21 which is supported by the base of the outer casing 1 and on to the shaft of which there is shrink-fitted, further to the pulley for the belt 15, the fan wheel of a first blower 22. The speed of rotation of the drum 10 and the blower 22 is variable in a stepless, ie. continuous manner, eg. From approx. 75 to approx. 50 rpm, and this, in a preferred embodiment of the present invention, is obtained through the use of a brushless synchronous motor as the first electric motor 21. The intake side of said first blower 22 is situated at the end of said first shaped conduit 9, and therefore downstream of the steam condenser 20, while the delivery side of the same blower 22 is situated at the inlet of a second shaped conduit 23 that extends upwards in the rear zone of the outer casing and is connected, through appropriate sealing means (not shown), to the perforations 13 of the rear flange 12 of the rotating drum 10. Inside said second shaped conduit 23 there is housed a per se well-known electric heating unit 24. Owing to the construction that has been described above, the conduit 9 with the lint filter 8 and the steam condenser 20, the interior of the rotating drum 10, and the conduit 23 with the heating unit 24 constitute the closed-loop circuit of the drying air which, as compared with traditional clothes drying machines, offers the feature according to which the forced air flow inside the drum 10 is diverted towards the skirt 11, through the afore mentioned annular gap existing between the latter and the periphery of the disk 16, as this is indicated by the arrows in Figure 1. The base of the outer casing supports also a second electric motor 25, which is preferably also of the brushless synchronous type, and which, for the reasons that will be explained further on, is supplied via a thermistor-type element (not shown). The motor 25 drives a second blower 26 having its intake side connected with the aperture 4 in the socle of the outer casing and its delivery side connected with the steam condenser 20, obviously in a direction which is perpendicular to that of the conduit 9. On the opposite side with respect to the one that is connected with the intake side of the second blower 26, the condenser 20 is connected to the aperture 5 in the socle of the outer casing. Owing to this construction as described just above, the cooling air is therefore taken in from the ambient in which the clothes drying machine is installed through the aperture 4 by means of the blower 26 and, upon causing the steam carried by the hot drying air to condense in the condenser 20, it is exhausted back into the same ambient through the aperture 5. The clothes drying method according to the present invention is based on two peculiarities, the first one of which lies in the already mentioned variability of the rotating speed of both the drum 10 and the drying air blower 23 thanks to the first electric motor 21, while the second one lies in the fact that the processor means of the apparatus are adapted to automatically select the drying parameters that are most appropriate to each type of fabrics and amount of clothes being handled. In a preferred embodiment, all what a user is required to do is in fact to solely select, through the control means 2 located on the control panel 1, the type of fabrics of which the clothes to be dried are made (eg. wool, synthetic fibres, cotton, etc.), the weight and/or the desired degree of dryness of the clothes (eg. bone dry for storage in a wardrobe, moist for further ironing, and the like) and the desired time for the drying cycle to come to an end. The values of the various parameters of the drying process, such as the rotating speed of the drum 10 and the first blower 22, the power input rate of the heating unit 25 and/or the temperature of the air when entering the drum 10, the starting time and the duration of the drying cycle are set and controlled by said processor means with the associated sensors. Figure 2 illustrates the basic feature of the present invention, which lies in the progressively decreasing pattern followed by the rotating speed (n) of the motor 21 speed versus time (t), or again the pattern followed by the rotating speed of the drum 10 and the flow rate of the drying air delivered by the first blower 22, during a drying cycle. The speed (n) is higher in the case of woollen clothes (curve I), lower in the case of cotton clothes (curve II) and the lowest in the case of synthetic-fibre clothes (curve III). Therefore, according to a further feature of the present invention. The high rotating speed in the case of woollen clothes actually causes them to remain pressed, albeit gently, against the skirt 11 of the drum 10, so that they are no longer tossed about repeatedly as it occurs in traditional machines and the fibres are practically preventing from becoming matted together, ie. from felting. Furthermore, the diversion of the air flow brought about by the disk 16 contributes to a more even drying of the clothes, since short-circuits are avoided between the inlet and the outlet of the drying air inside the drum 10. Figure 3 in turn illustrates, by way of exemplification, the pattern followed by the temperature (°C) of the drying air (curve A), the amount (kg) of water removed from the clothes (curve B) and, again, the rotating speed (n) of the drum 10 and the first blower 22 (curve C) versus time (t), ie. during a drying cycle, in the case of cotton clothes. As it can be noticed, according to the main feature of the present invention, the rotating speed (n) is proportional to the amount (kg) of water removed, ie. inversely proportional to the desired degree of dryness to be reached. Thanks to the present invention, therefore, the possibility is given to obtain following results, which are on the contrary absolutely unobtainable in the clothes drying machines currently available on the market: a) the possibility of drying woollen clothes; b) the utilization of low-price power supplied at reduced rates during night hours for drying the clothes (except for woollens) by letting the drum 10 rotate at a reduced and constant speed (so that noise emissions are definitely low), preferably in combination with a reduced power input of the heating unit 25; c) thanks to the thermistor-type element provided in the power supply line to the second motor 25, possibility for the second blower 26 to be only started, in view of ensuring forced cooling of the drying air in the condenser 20, upon the temperature of the drying air reaching steady-state values (corresponding to the peak of curve A in Figure 3), ie. only after such an air is actually capable of removing moisture from the clothes. This of course enables significant results to be obtained in terms of energy saving effects.

Claims: Method for drying clothes in a tumble-type drying apparatus, in which the temperature of the drying air is pre-set in accordance with the type of fabrics of which the clothes to be handled are made, and wherein, during a drying cycle, also the revolving speed (n) of the rotating drum is variable within value ranges that are pre-determined in accordance with the type of fabrics characterized in that said revolving speed varies continuously in a manner that is proportional to the amount of water (kg) progressively removed from the clothes during said drying cycle, ie. in a manner that is inversely proportional to the desired degree of dryness to be reached. Drying method according to claim 1, characterized in that , within said pre-set value ranges, the revolving speed of the drum undergoes cyclical variations in both alternate directions of rotation. Apparatus for drying clothes using the method according to the preceding claims, comprising a rotating drum (10) for holding the clothes to be dried, said drum being driven by a first electric motor (21) which is also used to at the same time drive a first blower (22) to ensure a forced flow of drying air in a closed-loop circuit that comprises the rotating drum (10), a lint filter (8), heating means (24) for the drying air, and a steam condenser (20), and comprising also a second blower (26), which is driven by a second motor (25) for moving the air needed for cooling said steam condenser (20) in a circuit provided with apertures (4, 5) communicating with the surrounding ambient, characterized in that it comprises means adapted to vary continuously both the revolving speed of the drum (10) both the flow rate of the drying air delivered by said first blower (22) in a manner that is proportional to the amount of water (kg) progressively removed from the clothes during said drying cycle, ie. in a manner that is inversely proportional to the desired degre of dryness to be reached. Apparatus according to claim 3, characterized in that said first motor (21) for driving the rotating drum (10) and the blower (22) for the drying air, and preferably also said second motor (25) for driving the blower (26) for the cooling air, is a synchronous motor, eg. of the brushless type. Apparatus according to claim 3 or 4, in which the hot drying air is blown into the rotating drum (10) through a plurality of perforations (13) provided in a flange (12) thereof, characterized in that said perforations (13) are preferably clustered into a relatively compact circular crown close to the skirt (11) of the drum (10). Apparatus according to claim 5, characterized in that inside the rotating drum (10) there is provided a solid disk (16), which is sustained through spacer means (17) by said flange (12) provided with said air inlet perforations (13) so as to force said air to flow through the annular gap comprised between the periphery of said disk (16) and the skirt (11) of the drum (10). Apparatus according to any of the preceding claims 3 to 6, characterized in that it comprises programme sequence control means which, in accordance with the selection made by the user via the control members (2) of such variables as the type of fabrics of which the clothes to be dried are made, the weight and/or the desired degree of dryness to be reached and the desired time for the drying cycle to terminate, set and control through associated sensor means the parameters of the drying process such as the revolving speed of said first motor (21), the power input rate of the heating unit (24) and/or the temperature at which the drying air enters the drum (10), the starting time and the duration of the drying cycle. Apparatus according to any of the preceding claims 3 to 7, characterized in that the power supply to the motor (25) driving the blower (26) for the cooling air occurs via thermistor-like means adapted to enable said motor to only start operating after that the temperature at which the drying air enters the rotating drum (10) has reached a steady-state value, in view of reducing the energy usage of the drying cycles.

Inventors: CIMETTA SILVANO, DURAZZANI PIERO, CIMETTA, SILVANO, DURAZZANI, PIERO
Applicants: ELECTROLUX HOME PRODUCTS ITALY, ELECTROLUX HOME PRODUCTS ITALY S.P.A.
Application year: 2000
Main classification: D06F58
IPC codes: D06F58