Washer-dryer apparatus

Abstract: A washer-dryer apparatus is offered in which the evaporation rate is high from the beginning of the pre-heat drying cycle and the spin-drying rate remain high and hence the pre-heat drying rate is high. That is, in a washer-dryer apparatus which performs the pre-heat drying cycle and normal drying cycle, feed water control means is provided for controlling the water supply to a water-cooled heat exchanger, by which the water supply is started, for example, a certain elapsed time after the start of the pre-heat drying cycle to keep the evaporation rate and the spin-drying rate high, providing increased pre-heat drying rate.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a washer-dryer apparatus that has a pre-heat drying function of performing the final spin-drying cycle of washing while providing hot air to the interior of a rapidly spinning rotatable drum. Description of the Prior Art Referring first to Fig. 1, a conventional drum washer-dryer will be described. The drum washer-dryer has a washing drum 105 supported by suspension means 103 in a washer outer housing 101, a spin-dryer (a rotatable drum) 107 mounted in the washing drum 105 in a manner to be rotatable on the horizontal axis X thereof, a fan 102 for creating an air flow or stream to be fed into the spin-dryer 107, and a heat exchanger (dehumidifier) 109 for dehumidifying the air stream provided by the fan 102. The drum washer-dryer is further equipped with a heater 111 for heating the air dehumidified by the dehumidifier 109, a drive motor 104 for driving the spin-dryer 107, a pulley 106 fixedly secured to the tip end portion of the rotary shaft 104a of the motor 104, a pulley 108 affixed to the rotary shaft 107a of the spin-dryer 107, a belt 110 spanned or stretched between the pulleys 106 and 108, a feed valve 112 for feeding water to the washing drum 105, and a feed valve 113 for feeding water to the heat exchanger 109. With the drum washer-dryer of the above construction, a user opens an access door 115, then puts the laundry into the spin-dryer 107 together with a detergent, and turns ON a washing start key (not shown). Then, a microcomputer detects the turning-ON of the start key and controls the feed valve 112 to feed water into the washing drum 105. Upon completion of the feeding of water, the microcomputer controls the drive motor 104 to rotate at a predetermined rotational speed. As the drive motor 104 is thus driven, its turning force is transmitted by the belt 110 to the spin-dryer 107 via the pulleys 106 and 108. As a result, the spin-dryer 107 is driven corresponding to the rotation of the drive motor 104 to create running water in the spin-dryer 107, thereby doing laundry. Thereafter, the microcomputer controls the respective parts of the washer-dryer to perform draining (draining of waste water), water feeding, rinsing, draining and spin-drying cycles in a predetermined sequential order. The spin-drying cycle of such a washer-dryer is composed of pre-heat drying and normal drying. The pre-heat cycle will be described first. When the spin-drying cycle is reached, the microcomputer turns ON the fan 102, the heat exchanger 109 and the heater 111 to drive them and, at the same time, drives the motor 104 to rapidly spin it (at such a rotational speed that centrifugal force exerted on the wet laundry is equal to or greater than the gravity acting thereon). In consequence, an air stream is provided by the fan 102, then dehumidified by the heat exchanger 109 and heated by the heater 111, and the warm air is provided via an air duct 118 to the interior of the rapidly spinning spin-dryer 107 (as indicated by arrows W). The warm air thus blown into the spin-dryer 107 is fed back to the fan 102 via perforations 116 and warm air outlets 105a of the spin-dryer 107, thereafter being dehumidified, heated and fed into the spin-dryer 107 again. In this way, the drying air circulates through the drum washer-dryer. Thus, the garments or the laundry is gradually dried by spin-drying of the rapidly spinning spin-dryer 107 and by evaporation with the hot air blown into the washing drum 105 from the heater 111 and the fan 102. The moisture-laden air is dehumidified by the heat exchanger 109 and the resulting water is discharged to the outside. Having performed the pre-heat drying for a predetermined period of time, the microcomputer switches the spin-dryer 107 to a low-speed rotation (at such a rotational speed that centrifugal force exerted on the wet laundry is smaller than the gravity acting thereon) for normal drying. Incidentally, the drying rate by pre-heating is the sum of the spin-drying rate by the rapidly spinning of the spin-dryer 107 and the evaporation rate by the hot air provided by the heater 111 and the fan 102. Here, the drying rate is defined as the water content that comes out of the laundry per unit time. Next, a description will be given of variations in the spin-drying rate and the evaporation rate with the lapse of time. The evaporation rate Wv during pre-heat drying can be given by the following equation: Wv = hDrA(Xw - Xo) where hD is the heat transfer rate of the laundry, r the air density, A the surface of the laundry, Xo the absolute humidity of air and Xw the specific humidity at saturation at the surface temperature of the laundry. Fig. 2 is a graph showing variations in the evaporation rate and the spin-drying rate with time during pre-heat drying. During the early stages of pre-heat drying, the absolute humidity at saturation Xw is low because of low garment or laundry temperature, and consequently, the evaporation rate is low and the input (hot air) by the heater 111 is spent mainly in heating the garments. As the garment temperature rises and consequently the absolute humidity Xw increases with the lapse of time, the evaporation rate also increases accordingly (see the evaporation rate in Fig. 2). In the beginning stage of pre-heat drying, water soaking in the garment surface or the like is removed first but water trapped by capillary action near fabric fibers remains unremoved; hence, the spin-drying rate drops with time (see the spin-drying rate in Fig. 2). Immediately after the start of pre-heat drying, however, the prior art example begins to feed a certain amount of water to the heat exchanger to cool and dehumidify the air circulating through the drum washer-dryer as described previously--this gives rise to such problems as mentioned below. A first problem concerns the evaporation rate. It is desirable to raise the absolute humidity at saturation Xw in the garment surface as soon as possible in the early stages of pre-heat drying. To meet this requirement, it is preferable that the amount of heat exchanged be small. Directly after the start of pre-heat drying, even if the circulating air (indicated by the arrows in Fig. 1) is cooled by the heater exchanger 109, sensible heat forms a particularly large proportion of the overall amount of heat that is removed from the circulating air; hence, the heat exchange is useless right after the start of pre-heat drying. When heating of the garment proceeds and the above-mentioned absolute humidity Xw rises, however, the evaporation rate increases by cooling and dehumidifying the circulating air with the heat exchanger 109 to thereby lower the absolute humidity Xo of the air. A second problem concerns the spin-drying rate. The higher the circulating air temperature is, the higher the water temperature in the garment and the lower the viscosity and surface tension of the water. That is, the less the circulating air is cooled by the heat exchanger 109, the higher the spin-drying rate increases. For this reason, the spin-drying rate is low due to a decrease in the circulating air temperature caused by useless heat exchange in early stages of pre-heat drying. EP-A2-0 716 178 discloses a washer-dryer apparatus according to the preamble of claim 1. DE-OS 1 585 945 discloses a dryer apparatus which is operated such that at the stand of a drying cycle at first a heater is turned on, and then, when a considerable evaporation of water from the laundry occurs, the cooling water for a dehumidifyer is turned on. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a washer-dryer apparatus that produces reduction in the pre-heat drying time. To attain the above objective, the washer-dryer apparatus according to the present invention has the features which are recited in claim 1. Preferred embodiments of the invention are recited in the dependent claims. According to an aspect of the present invention, the feed water control means controls the volume of cooling water that is fed to the water-cooled heat exchanger. This prevents the cooling water from dashing into the heat exchanger from the beginning of the pre-heat drying cycle; thus, the amount of heat exchanged is kept down and the absolute humidity at saturation Xw in the garment surface rises, causing an increase in the evaporation rate. Furthermore, since cooling of the circulating air by the heat exchange decreases, the spin-drying rate increases. According to another aspect of the present invention, the feed water control means is means for starting water supply a certain elapsed time after the start of the pre-heat drying cycle. According to another aspect of the present invention, the feed water control means has detecting means for determining the timing for starting the water supply after the elapse of the certain time. That is, upon detecting the elapse of the certain time after the beginning of the pre-heat drying cycle, the water supply to the water-cooled heat exchanger is started. According to another aspect of the present invention, the feed water control means is means for increasing the feed rate with time after the beginning of the pre-heat drying cycle. That is, as shown in Figs. 6(A) and (B), the feed rate increases with time after starting the pre-heat drying cycle. Such feed rate control suppresses the heat exchange in early stages of the pre-heat drying cycle, and hence it prompts faster heating of the laundry. Moreover, as the evaporation rate increases with time, the circulating air is cooled and dehumidified with higher efficiency. According to another aspect of the present invention, the feed water control means controls the feed rate according to the feed water temperature after the start of the pre-heat drying cycle. According to another aspect of the present invention, the feed water control means has water temperature detect means. The feed water control means detects the feed water temperature by the water temperature detect means and controls the feed rate according to the detected water temperature. That is, the feed water control means controls the feed rate for the heat exchanger according to the temperature of the air circulating through the washer-dryer apparatus. According to still another aspect of the present invention, circulating air temperature detect means is used to detect the circulating air temperature. The feed water control means controls the feed rate for the heat exchanger according to the circulating air temperature detected by the detect means. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal-sectional view of a conventional drum washer-dryer apparatus; Fig. 2 is a graph showing the relationships of the spin-drying and the evaporation rate to elapsed time in the conventional drum washer-dryer apparatus; Fig. 3 is a longitudinal-sectional view of a washer-dryer apparatus according to a first embodiment of the present invention; Fig. 4 does not form part of the invention; Fig. 5 is a longitudinal-sectional view of a washer-dryer apparatus according to a second embodiment of the present invention; Fig. 6(A) is a graph showing a gradual increase in the feed rate for the water-cooled heat exchanger soon after the start of the pre-heat drying cycle in a third embodiment of the present invention; Fig. 6(B) is a graph similarly showing a gradual increase in the feed rate a certain elapsed time after the start of the pre-heat drying cycle; and Fig. 7 is a graph showing the relationships of the spin-drying and the evaporation rate to the elapse of time. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereinafter be described with reference to its embodiments illustrated in the accompanying drawings. In Fig. 3 there is illustrated a longitudinal-section view of a first embodiment of the drum washer-dryer apparatus of the present invention. The drum washer-dryer of this embodiment has a washing drum 105 supported by suspension means 103 in a washer outer housing 101, a spin-dryer (a rotatable drum) 107 mounted in the washing drum 105 in a manner to be rotatable on the horizontal axis X thereof, a fan 102 for creating an air stream to be fed into the spin-dryer 107, and a heat exchanger (dehumidifier) 109 for dehumidifying the air stream provided by the fan 102. The drum washer-dryer is further equipped with a heater 111 for heating the air dehumidified by the dehumidifier 109, a drive motor 104 for driving the spin-dryer 107, a pulley 106 fixedly secured to the tip end portion of the rotary shaft 104a of the motor 104, a pulley 108 affixed to the rotary shaft 107a of the spin-dryer 107, a belt 110 spanned or stretched between the pulleys 106 and 108, a feed valve 112 for feeding water to the washing drum 105, a feed valve 113 for feeding water to the heat exchanger 109 and a microcomputer 120 for controlling the respective parts of the washer-dryer. With the drum washer-dryer of the above construction, a user opens an access door 115, then puts the laundry into the spin-dryer 107 together with a detergent, and turns ON a washing start key (not shown). Then, the microcomputer 120 detects the turning-ON of the start key and controls the feed valve 112 to feed water into the washing drum 105. Upon completion of the feeding of water, the microcomputer 120 controls the drive motor 104 to rotate at a predetermined rotational speed. As the drive motor 104 is thus driven, its turning force is transmitted by the belt 110 to the spin-dryer 107 via the pulleys 106 and 108. As a result, the spin-dryer 107 is driven with the rotation of the drive motor 104 to create running water in the spin-dryer 107, thereby doing laundry. Thereafter, the microcomputer 120 controls the respective parts of the washer-dryer to perform draining (draining of waste water), water feeding, rinsing, draining and spin-drying cycles in a predetermined sequential order. When the spin-drying cycle is reached, the microcomputer 120 performs pre-heat drying. In the first place, the microcomputer 120 turns ON the fan 102, the heat exchanger 109 and the heater 111 to drive them and, at the same time, drives the motor 104 to rapidly spin it (at such a rotational speed that centrifugal force exerted on the wet laundry is equal to or greater than the gravity acting thereon). In consequence, an air stream is provided by the fan 102, then dehumidified by the heat exchanger 109 and heated by the heater 111, and the warm air is provided via an air duct 118 to the interior of the rapidly spinning spin-dryer 107 (as indicated by arrows W). The warm air thus blown into the spin-dryer 107 is fed back to the fan 102 via perforations 116 and warm air outlets 105a of the spin-dryer 107, thereafter being dehumidified, heated and fed into the spin-dryer 107 again. In this way, the drying air circulates through the drum washer-dryer. Thus, the garments or the laundry is gradually dried by spin-drying of the rapidly spinning spin-dryer 107 and by evaporation with the hot air blown into the washing drum 105 from the heater 111 and the fan 102. The moisture-laden air is dehumidified by the heat exchanger 109 and the resulting water is discharged to the outside. Having performed the pre-heat drying for a predetermined period of time, the microcomputer 120 switches the spin-dryer 107 to a low-speed rotation (at such a rotational speed that centrifugal force exerted on the wet laundry is smaller than the gravity acting thereon) for normal drying. The present invention features control of the feed valve for the heat exchanger during the pre-heat drying cycle. That is, the microcomputer 120 controls the feed valve during the pre-heat drying cycle for the most efficient heating and drying of the laundry. This embodiment is adapted to provide increased drying rate by starting the water supply after the elapse of a certain period of time. The following points are important in the early stages of pre-heat drying as referred to previously with reference to the prior art example. That is, faster heating of the laundry is desirable in the early stages of pre-heat drying and the evaporation rate increases as the pre-heat drying proceeds. After certain elapsed time, the evaporation rate will increase in the case where the circulating air is cooled and dehumidified. Accordingly, the average drying rate can be increased by starting the water supply to the heat exchanger 109 a predetermined period of time after the initiation of the pre-heat drying cycle instead of starting the water supply at the beginning of the pre-heat drying cycle. Next, a second embodiment of the invention will be described. This embodiment is equipped with detect means for determining the water supply start timing. The optimum water supply start timing varies with the cooling power of the heat exchanger 109. It is the cooling water temperature that has an influence on the cooling power after the delivery of the washer-dryer apparatus to the user. That is, since tap water is usually employed as the cooling water for the water-cooled heat exchanger, the feed water temperature (the cooling water temperature) undergoes seasonal changes or temporal changes in a day. With a view to providing increased pre-heat drying power of the washer-dryer of the first embodiment, cooling water temperature detect means is used to determine the water supply timing according to the cooling water temperature. Fig. 5 is a longitudinal-sectional view of the washer-dryer apparatus of this embodiment, wherein a temperature sensor 1 is placed in a feed water conduit to the heat exchanger 109. In this embodiment, in the case of performing the pre-heat drying cycle after the washing and rinsing cycle, the feed water temperature during the final rinsing cycle is measured using the temperature sensor 1. An alternative is to feed the cooling water to the heat exchanger for a short time and measure its temperature prior to the start of the pre-heat drying operation. Thus, the feed water temperature is already known at the start of the pre-heat drying cycle and the cooling power of the heat exchange 109 can be predicted. Then, the water supply to the heat exchanger 109 is started at the timing that maximizes the average drying rate, determined by the relationships of the premeasured feed water temperature and the water supply stating time to the spin-drying and the evaporation rate. Next, a third embodiment of the invention will be described. This embodiment is intended to increase the feed rate with time. As referred to previously, the following points are important at the beginning stage of pre-heat drying. That is, faster heating of the laundry is desirable in the early stages of pre-heat drying and the evaporation rate increases as the pre-heat drying proceeds. After certain elapsed time, the evaporation rate will increase in the case where the circulating air is cooled and dehumidified. Accordingly, the importance of the flow rate of the cooing water increases with time. When a feed valve 113b for the heat exchanger 109 is capable of controlling the flow rate by the microcomputer 120 in a washer-dryer apparatus of the Fig. 5 construction, the feed rate is increased with time immediately after the start of the pre-heat drying cycle or after a certain elapsed time, thereby increasing the cooling power of the heat exchanger 109 with the lapse of time (see Figs. 6(A) and (B)). The feed water rate may also be changed by raising the rate of increase with time. Thus, it is possible to increase the average drying rate by running with relative low cooling power while heating of the laundry is important in the early stages of the pre-heat drying cycle and by increasing the cooling power as the importance of dehumidification increases. Next, a fourth embodiment of the present invention will be described, which is intended to control the flow rate of the feed water according to its temperature. The spin-drying rate is affected by the temperature of the circulating air (indicted by the arrows) and the evaporation rate by the temperature and humidity of the circulating air. The temperature and humidity of the circulating air change with the cooling power of the water-cooled heat exchanger 109, and the higher the cooling power, the less the temperature and humidity of the circulating air increases. As a result, the spin-drying rate and the evaporation rate vary with the magnitude of the cooling power of the water-cooled heat exchanger 109 (Fig. 7 shows the case of starting the water supply right after the start of the pre-heat drying cycle). In other words, there exists cooling power with which the drying rate becomes maximum, and an optimum value fit for the actual apparatus is obtainable. In practice, however, since tap water is used as the cooling water for the water-cooled heat exchanger 109, the feed water temperature changes with seasons or time periods of use. In other words, since the cooling power varies when the feed rate is held constant, it is impossible to adjust the cooling power to the premeasured optimum value. This embodiment is to control the feed rate according to the feed water temperature to adjust the cooling power of the heat exchanger to the preset optimum value, thereby improving the pre-heat drying function. Referring to Fig. 5, this embodiment will be described, which has a feed valve 113b capable of controlling the flow rate therethrough by the microcomputer 120 and a temperature sensor 1 for measuring the temperature of the feed water to the heat exchanger 109. After the start of the pre-heat drying cycle, the feed valve 113a is opened to permit the passage therethrough of the feed water in a given quantity. In this instance, no particular limitation is imposed on the flow rate since this operation is intended mainly for measuring the feed water temperature. After measurement of the water temperature, the feed rate is adjusted in accordance with the measured water temperature so as to set the cooling power of the heat exchanger 109 at the predetermined value. By this, the pre-heat drying cycle can be performed effectively without being affected by changes in the feed water temperature. While this embodiment has been described to begin the water supply immediately after the start of the pre-heat drying cycle, the water supply may also be begun after a certain time elapsed as in the first embodiment. Next, fifth embodiment of the invention will be described. In this embodiment, the same results as those obtainable with the fourth embodiment are obtained through utilization of detection of the circulating air temperature, that is, the flow rate is controlled according to the circulating air temperature. The temperature rising curve of the circulating air changes with the cooling power of the heat exchanger 109; the higher the cooling power, the lower the temperature rising curve. In view of the above, the circulating air temperature at a point after certain elapsed time after the beginning of the pre-heat drying cycle is detected by the temperature sensor 2 in Fig. 5 and the cooling water temperature is estimated from the temperature rising gradient. By controlling the feed rate according to the feed water temperature, the cooling power of the heat exchanger 109 is set at the optimum value, proving enhanced pre-heat drying function. Incidentally, this embodiment is identical with the fourth embodiment except the use of the temperature sensor 2. As described above, according to the present invention, there is provided a washer-dryer apparatus that performs the pre-heat drying cycle and the normal drying cycle and has feed water control means for controlling the water supply to the water-cooled heat exchanger (dehumidifier). By starting the water supply to the heat exchanger a certain elapse time after the beginning of the pre-heat drying cycle, or by increasing the feed rate with the lapse of time after the start of the pre-heat drying cycle, or by adjusting the feed rate according to the feed water temperature after beginning of the pre-heat drying cycle, or adjusting the feed rate according to the temperature of air circulating through the washer-dryer apparatus after the start of the pre-heat drying cycle, the evaporation rate is held high from the beginning of the pre-heat drying cycle and the spin-drying rate is also kept high, so that the pre-heat drying rate is high. It will be apparent that many modifications and variations may be effected without departing from the novel concept of the present invention as recited in the claim 6.

Claims: A washer-dryer apparatus comprising: a washing drum (105), a spin-dryer (107) rotatably mounted in said washing drum (105), blowing means (102) for creating an air stream to be provided to the interior of said spin-dryer (107), a water-cooled heat exchanger (109) for dehumidifying said air stream from said blowing means (102), and feed water control means (120, 113) for controlling the cooling water supply to said water-cooled heat exchanger; wherein in a pre-heat drying cycle for drying laundry after a washing cycle said spin-dryer (107) rapidly spins at such a rotational speed that the centrifugal force exerted on the wet laundry is equal to or greater than the gravity acting thereon; characterized in that , said feed water control means (120, 113) increases in the pre-heat drying cycle the cooling water supply rate with the lapse of time such that a low cooling power, as compared to the cooling power employed for ordinary drying, of said water-cooled heat exchanger (109) is provided in an early stage of said pre-heat drying cycle such that the average drying rate is maximized. A washer-dryer apparatus as claimed in claim 1, wherein said feed water control means (120, 113) starts the water supply after a certain time (t 1 ) has elapsed after the start of said pre-heat drying cycle. A washer-dryer apparatus as claimed in claim 2, wherein said feed water control means (120, 113) has detect means (1) for determining the timing for starting the water supply after the elapse of said certain time. A washer-dryer apparatus as claimed in claim 1, wherein said feed water control means (120, 113b) increases the water supply rate with time after the beginning of said pre-heat drying cycle. A washer-dryer apparatus as claimed in claim 1, wherein said feed water control means (120, 113b, 1) controls the water supply rate according to the temperature of said feed water after the start of said pre-heating cycle. A washer-dryer apparatus as claimed in claim 5, wherein said feed water control means (120, 113b, 1) has water temperature detect means (1) and controls the water supply rate according to the detected water temperature. A washer-dryer apparatus as claimed in claims 1 or 5, wherein said feed water control means (120, 113b, 2) controls the water supply rate according to the temperature of air circulating through said washer-dryer apparatus after the start of said pre-heat drying cycle. A washer-dryer apparatus as claimed in claim 7, further comprising circulating air temperature detect means (2) for detecting said circulating air temperature.

Inventors: ITO MASUMI, KAWABATA SHINICHIRO, ITO, MASUMI, KAWABATA, SHINICHIRO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1997
Main classification: D06F58
IPC codes: D06F58, D06F25, D06F33