Washing machine with drying function

Abstract

A washing machine with a drying function includes a water tub, a rotating tub mounted in the water tub so as to be rotatable, a driver rotating the rotating tub, a circulation passage defined so as to communicate with the water tub, a warm-air supply unit circularly supplying warm air through the circulation passage into the water tub and the rotating tub, a water-supply unit supplying water into the water tub, a control unit controlling the driver, the warm-air supply unit and the water-supply unit thereby to be capable of controlling wash, rinse, dehydration and drying steps, and a preheating unit executing a preheating operation in which warm air is supplied into the water tub and the rotating tub during rotation of the rotating tub before the wash step is executed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-12671, filed on Jan. 20, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine having a drying function and provided with a warm-air generator.

2. Description of the Related Art

A drum washing machine with a drying function can provide effective washing action while reserving a relatively smaller amount of water in a lower interior of a water tub or drum, for example. Accordingly, the aforesaid drum washing machine can achieve water saving. Furthermore, laundry is vertically moved in a drum when the drum is rotated. When warm air is supplied into the drum, the entire laundry can efficiently be dried while being agitated. The above-described type drum washing machine with the drying function has recently been diffused rapidly.

On the other hand, in order that a sufficient cleaning performance may be achieved from a small amount of wash water, some types of the foregoing drum washing machines have recently been designed so that wash water is warmed to accelerate activation of enzyme contained in a detergent. A method of warming wash water includes heating wash water by a sheathed heater disposed on a bottom of a wash tub, and introducing, into a drum, warm air produced by a warm-air supplier comprising a fan and a heater so that wash water is heated. JP-A-2-277494 discloses the construction of a drum washing machine of the aforesaid type, for example.

However, in the aforesaid method using the sheathed heater, on one hand, the sheathed heater disposed in the water needs to be provided with a safety arrangement against electric leakage. On the other hand, in the method using the warm-air supplier, both wash water and warm air are fluid and accordingly, thermal conduction from warm air to wash water has a low efficiency, whereupon it takes a lot of time to warm overall wash water in the drum.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a washing machine with a drying function, in which wash water can be heated by a simple construction efficiently.

The present invention provides a washing machine with a drying function, comprising a water tub, a rotating tub provided in the water tub so as to be rotatable, a driver rotating the rotating tub, a circulation passage defined so as to communicate with the water tub, a warm-air supply unit circularly supplying warm air through the circulation passage into the water tub and the rotating tub, a water-supply unit supplying water into the water tub, a control unit controlling the driver, the warm-air supply unit and the water-supply unit thereby to be capable of controlling wash, rinse, dehydration and drying steps, and a preheating unit executing a preheating operation in which warm air is supplied into the water tub and the rotating tub during rotation of the rotating tub before the wash step is executed.

The preheating operation is carried out before the wash step is carried out and when no water is reserved in the water tub. Accordingly, warm air is supplied into the water tub and the rotating tub so that heat is directly applied to laundry, the water tub and the rotating tub. Water reserved in the water tub in the wash tub subsequently to the preheating is warmed by making use of heat stored in the laundry, water tub and rotating tub by the preheating. Consequently, heat can be conducted from the warm air to water in the water tub more efficiently as compared with the construction that water in the water tub is directly heated by warm air.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become clear upon reviewing the following description of the embodiment with reference to the accompanying drawings, in which:

FIG. 1 is a schematic front view of a drum washing machine with a drying function in accordance with a first embodiment of the present invention;

FIG. 2 is a schematic block diagram showing an electrical arrangement of the washing machine;

FIG. 3 is a flowchart showing a washing operation;

FIGS. 4A to 4C illustrate water levels in a water tub and motion of laundry in a preheating, preliminary washing and main washing respectively;

FIG. 5 is a graph showing the relationship between an amount of laundry and a water temperature, a temperature in a water tub and a target laundry temperature;

FIG. 6 is a view similar to FIG. 1, showing a second embodiment of the invention;

FIG. 7 is a view similar to FIG. 4A; and

FIG. 8 is a graph showing the relationship between an amount of laundry, and a temperature in a water tub and a target laundry temperature in a modified form of the first embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the present invention will be described with reference to FIGS. 1 to 5. Referring to FIG. 1, a washing machine with a drying function includes a generally cylindrical water tub 1 and a generally cylindrical rotating tub or drum 2 mounted in the water tub. The water tub 1 is elastically supported by elastic supporting units (not shown). The water tub 1 is substantially non-porous and accordingly enables to reserve water. The drum 2 serves as a washing tub, dehydrating tub and drying tub and has a number of through-holes 2a formed through a circumferential wall thereof. The drum 2 further has a plurality of baffles (not shown).

A brushless DC motor 3 of the outer rotor type (serving as a driver) is mounted on a left side of the water tub 1, for example. The motor 3 has a rotational shaft 3a horizontally extending through a hole (not shown) of the water tub 1 to be connected to a central left side of the drum 2. Thus, the drum 2 is rotated with a rotor (not shown) of the motor 3. A support shaft 2b coaxial with the rotational shaft 3a protrudes from a side of the drum 2 opposed to the motor 3 and is rotatably supported on the corresponding side of the water tub 1. The drum 2 is thus rotated about a substantially horizontal axis.

The water tub 1 has a peripheral wall including an upper part formed with an access opening (not shown) through which laundry is put into and taken out of the drum 2. The drum 2 has an opening (not shown) corresponding to the access opening. The drum 2 is controlled so as normally to stop with the opening being located at an upper part of the drum so that laundry can be put into and taken out of the drum 2 through the upper part of the drum.

A circulation passage 4 with a duct structure is defined on the right of the water tub 1. The water tub 1 has a warm-air outlet 1a formed through a lower right portion thereof. The circulation passage 4 has one end connected to the warm-air outlet 1a. The water tub 1 also has warm-air inlets 1b formed through a potion of the water tub 1 around the support shaft 2b mounted on the right side of the water tub. The drum 2 also has openings 2c formed through a portion of the drum 2 around the support shaft 2b so that the openings correspond to the warm-air inlets 1b respectively. The circulation passage 4 has the other end connected to the warm-air inlet 1b.

A water-cooled heat exchanger 5 is provided in the middle of the circulation passage 4. A water pouring unit 6 is provided in an upper portion of the heat exchanger 5 for pouring water into an interior of the heat exchanger. A blowing fan unit 7 and a heater unit 8 are provided in an upper interior of the circulation passage 4 located over the heat exchanger 5. When the blowing fan unit 7 and the heater unit 8 are driven, air in the circulation passage 4 is heated so that warm air is produced. The warm air is caused to flow in a direction of arrow A in FIG. 1 by the blowing action of the blowing fan unit 7 to be supplied through the warm-air inlets 1b and openings 1c into the water tub 1 and the drum 2. The warm air supplied into the drum 2 flows through the holes 2a into the water tub 1, returning through the warm-air outlets 1a into the circulation passage 4. The warm air is then caused to flow upward through the heat exchanger 5. Thus the warm air is circulated repeatedly. The blowing fan unit 7 and heater unit 8 serve as warm-air supply unit in the embodiment.

A drain hole 9 is formed in the bottom of the water tub 1. A drain hose 10 is connected via a drain valve 11 to the drain hole 9. An overflow port 12 is formed in the right side of the water tub 1 so as to be located below the warm-air inlet 1b. An overflow hose 13 is connected to the overflow port 12. The overflow hose 13 is further connected to the drain hose 10 downstream with respect to the drain valve 11.

A temperature sensor 14 is mounted on a portion of the right side inner face of the water tub 1 located just over the overflow port 12. The temperature sensor 14 comprises a thermistor and detects a temperature in the water tub 1. Another temperature sensor 15 is provided in the lower interior of the heat exchanger 5. The temperature sensor 15 also comprises a thermistor and detects a temperature of water supplied from the water pouring unit 6. The temperature sensor 14 serves as a laundry temperature sensor, whereas the temperature sensor 15 serves an ambient temperature sensor.

FIG. 2 shows an electrical arrangement of the washing machine. A control device 20 comprises a microcomputer and serves as a control unit for controlling an overall operation of the washing machine and a preheating unit. Connected to the control device 20 are a switch input section 21, a water level sensor 22, a rotation sensor 23 and the aforesaid temperature sensors 14 and 15. The switch input section 21 delivers a detection signal (operation signal) according to an amount of operation of an operation switch (not shown). The water level sensor 22 delivers a detection signal according to a water level in the water tub 1. The rotation sensor 23 delivers a detection signal according to a rotational speed of the motor 3.

The motor 3 is connected via an inverter circuit 24 to the control device 20. A water-supply valve 26 (a water-supply unit), a heater element 27, a fan motor 28, the drain valve 11 are connected via a drive circuit 25 to the control device 20. The water-supply valve 26 switches a water supply path between a water-supply path extending from a tap (not shown) of the water service to the water pouring unit 6 and a water-supply path extending from the tap to the water tub 1. The heater element 27 constitutes the heater unit 8, and the fan motor 28 constitutes the blowing fan unit 7. The control device 20 controls the motor 3, water-supply valve 26, heater element 27, fan motor 28 and drain valve 11 based on a control program previously stored therein.

The operation of the washing machine will now be described. FIG. 3 is a flowchart showing processing for a standard washing/drying operation. Upon start of operation, the drain valve 11 is opened so that a draining operation is carried out (step S1). Consequently, even when water is present in the water tub 1 upon start of the operation, all the water is discharged from the water tub 1. At subsequent step S2, the weight of laundry in the drum 2 is detected. Subsequently, the water-supply valve 26 is switched at step S3 so that the water-supply path leading to the water pouring unit 6 is opened. As a result, the water pouring unit 6 starts a water pouring operation. Since the drain valve 11 is open in this case, water supplied into the heat exchanger 5 is discharged from the drain hole 9 without being reserved. At step S4, the drum 2 is rotated, for example, at 400 rpm. At step S5, the heater element 27 and the fan motor 28 are energized, so that warm air flows through the circulation passage 4 to be supplied into the water tub 1.

The steps S3, S4 and S5 are carried out substantially simultaneously. More specifically, warm air is circulated through the circulation passage 4 supplied with water and the rotating drum 2. Consequently, moisturized warm air is supplied into the drum 2 and the water tub 1 so that heat is applied to laundry in the drum 2 as well as to the drum 2 and the water tub 1. Accordingly, the treatment at steps S3 to S5 constitutes a preheating. Since the drain valve 11 is open in the preheating operation, water is discharged through the drain hole 9 without being reserved. Accordingly, a part of the circulation passage 4 near the warm-air outlet 1a can be prevented from being closed by water, or water can be prevented from entering the drum 2.

A rotational speed of the drum 2 at step S4 is set to about 400 rpm in the embodiment. The reason for this setting is as follows: an experiment conducted by the inventors shows that a centrifugal force starts acting upon laundry and warm air in the drum 2 when a rotational speed of the drum 2 exceeds about 300 rpm and that the centrifugal force moves laundry in the drum uniformly to an inner peripheral surface of the drum 2 as shown in FIG. 4A when the rotational speed of the drum 2 ranges from 400 rpm to 500 rpm (symbol “W” in FIG. 4 designates laundry) Furthermore, warm air flowing into the central interior of the drum 2 is also caused to flow toward the peripheral wall of the drum 2 by the centrifugal force as shown by arrow in FIG. 1B. On the other hand, noise is produced when the rotational speed of the drum 2 exceeds about 400 rpm. In view of the above drawback, the rotational speed of the drum 2 is set so that warm air is blown against the whole laundry uniformly while noise production is restrained.

The above-described preheating finishes when the temperature of laundry in the drum 2 has reached a target temperature. The control device 20 reads the detection signals of the temperature sensors 14 and 15 during the preheating operation. The control device 20 estimates a target temperature of the laundry based on the read detection signal of the temperature sensor 14. Furthermore, the control device 20 is arranged to change the target temperature of laundry according to an amount of laundry and the detection signal of the temperature sensor 15. The relationship among the target temperature of the laundry, the amount of laundry and detection temperatures of temperature sensors 14 and 15 will be described later.

Upon completion of the preheating operation, the control device 20 advances to step S6 to execute a first water-supply. The water-supply valve 26 is switched in the first water-supply so that the water-supply path from the tap to the water tub 1 is opened, whereupon water is supplied into the water tub 1. In this case, water is adapted to be supplied through a detergent case (not shown) into the water tub 1. As a result, detergent contained in the detergent case is supplied into the water tub 1 with the water. The first water supply is carried out until a water level as shown by “L1” in FIG. 4B is reached in the water tub 1. The water level L1 is previously set according to an amount of laundry detected at step S2. The drum 2 is rotated at low speeds (40 rpm, for example) repeatedly alternately in the normal and reverse directions, whereby preliminary washing is carried out. As a result, laundry in the drum 2 is lifted up by baffles and caused to fall down, so that the laundry is tumbled repeatedly thereby to be cleaned.

The water level L1 for the preliminary washing is set to be lower than a water level of normal washing. Accordingly, wash liquid made by dissolution of detergent into water in the water tub 1 has a higher density than usual wash liquid. Furthermore, the temperature of the water supplied into the water tub 1 is increased by heat stored in the laundry, water tub 1 and drum 2 heated by the preliminary washing. Consequently, a high cleaning action can be obtained from the preliminary washing.

Upon completion of the preliminary washing, the control device 20 advances to step S8 to execute a second water supply. In the second water supply, water is added into the water tub 1 so that a water level L2 as shown in FIG. 4C is reached in the water tub 1. The water level L2 is previously set according to an amount of laundry detected at step S2 and corresponds to a water level in the normal washing operation. At step S9, the drum 2 is rotated at a low speed (40 rpm, for example) repeatedly alternately in the normal and reverse directions so that a main washing is executed. As a result, laundry in the drum 2 is lifted up by baffles and caused to fall down, so that the laundry is tumbled repeatedly thereby to be cleaned. Since the water level in the main washing is set to the normal water level as described above, a normal cleaning action can be obtained. When the water level in the water tub 1 is reduced below L2 for the reason of absorption of water by laundry or the like, water is supplied into the wash tub 1 for compensation until water level L2 is reached.

The above-described steps S6 through S9 constitute a wash step in the embodiment. Upon completion of the main washing, the drain valve 11 is opened so that water is discharged from the water tub 1 (step S10). Successively, the drum 2 is rotated at high speeds, for example, 800 rpm so that laundry is centrifugally dehydrated (step S1). Subsequently, a rinse step (step S12), dehydration step (step S13) and drying step (step S14) are sequentially executed and thereafter, the washing operation is completed. In the drying step, the heater element 27 and fan motor 28 are energized and the water pouring operation is carried out by the water pouring unit 6 in the same manner as in the preliminary washing. As a result, warm air supplied into the drum 2 absorbs moisture from laundry. The warm air containing moisture is dehumidified by the heat exchanger 5 and heated by the heater unit 8 again. The warm air is returned into the drum 2 so that laundry is dried.

The following describes the relationship among a target laundry temperature, an amount of laundry and temperatures detected by the temperature sensors 14 and 15 in the preheating operation. FIG. 5 shows the relationship among a water temperature detected by the temperature sensor 15, a temperature in the water tub 1 detected by the temperature sensor 15 and a target temperature of laundry, for every amount of laundry. The target temperature of laundry is set in a range from 45° C. to 55° C. according to a water temperature as shown in FIG. 5. The target laundry temperature is thus set in order that a protein component, such as blood, milk or egg, which is one of soil components adherent to laundry may be prevented from being hardened by the preheating operation. Since the protein component is hardened at about 60° C., the target temperature is set so as to be lower than 60° C. so that the protein component can be prevented from being hardened, sticking to a fiber of laundry. Secondly, the target laundry temperature is set in the above-described manner in order that a temperature difference between laundry and water supplied into the water tub 1 in the first water supply may be rendered small for prevention of cloth shrinkage of laundry. A temperature of water supplied into the water tub 1 in the first water supply is substantially equal to a water temperature detected by the temperature sensor 15 in the preliminary washing. Accordingly, a target temperature is set to be low when the water temperature detected by the temperature sensor 15 is low, whereas the target temperature is set to be high when the detected water temperature is high.

Furthermore, the control device 20 estimates a target temperature of laundry from the water-tub interior temperature detected by the temperature sensor 14. The relationship between the water-tub interior temperature and the laundry target temperature was obtained from an experiment conducted by the inventor. Accordingly, when the temperature detected by the temperature sensor 14 has reached the water-tub interior temperature as shown in FIG. 5, the control device 20 determines that the laundry has reached a target temperature, finishing the preliminary heating. A target temperature of laundry is higher by 2° C. to 15° C. than the water-tub interior temperature as shown in FIG. 5. It is considered that warm air flows through the warm-air inlet 1b into the water tub 1 and drum 2 during the preheating and the temperature of warm air is detected by the temperature sensor 14 after heat has been absorbed by laundry, water tub 1 and drum 2. Accordingly, the difference between the laundry temperature and the temperature detected by the temperature sensor 14 tends to be larger as an amount of laundry is large.

According to the foregoing embodiment, the preheating is carried out when no water is reserved in the water tub 1 before execution of the wash step. In the preheating, warm air is supplied into the drum 2 so that laundry, water tub 1 and drum 2 are heated. Water reserved in the water tub 1 is heated in the wash step by making use of heat stored in the laundry, water tub 1 and drum 2 as the result of the preheating. Consequently, heat can be transferred from warm air to the water in the water tub 1 more efficiently as compared with the construction that water in the water tub is directly heated by warm air.

Furthermore, the preheating is carried out making a direct use of the heater unit 8 and blowing fan unit 8 which constitute the drying function of the washing machine. Accordingly, since no new equipment is necessitated for the preheating, the construction of the washing machine can be prevented from complication and the production cost of the washing machine can be prevented from increase.

Water is poured by the water pouring unit 6 in the reheating so that warm air supplied into the water tub 1 is rendered moist. Consequently, laundry can be prevented from being excessively dried in the preheating, whereupon soil can be prevented from becoming difficult to wash off.

The target temperature of laundry, which is a temperature of laundry in the termination of the preheating, is set to be equal to or lower than 60° C. Consequently, the protein component, which is a soil component of laundry, can be prevented from being hardened. Moreover, the target temperature of laundry is rendered low when the temperature of water is high, whereas the target temperature is rendered high when the water temperature is high. Consequently, since the temperature difference between the laundry heated and the water supplied into the water tub 1 is reduced, the laundry can be prevented from shrinkage or damage.

FIGS. 6 and 7 illustrate a second embodiment of the invention. The following describes only the differences of the second embodiment from the first embodiment. In the second embodiment, identical or similar parts are labeled by the same reference symbols as those in the first embodiment. In the second embodiment, the preheating is executed while a small amount of water is reserved on the bottom of the water tub 1. More specifically, the drain valve 11 is adapted to be closed during the water pouring in the preheating (see step S3 in the flowchart of FIG. 3). Accordingly, water poured into the heat exchanger 5 is reserved in the circulation passage 4 and also flows through the warm-air outlet 1a into the water tub 1 thereby to be reserved in the water tub. The water pouring is carried out until the water reserved in the water tub 1 reaches such a level that the water reserved in the water tub is kept away from contact with the drum 2 and that the water reserved in the water tub does not prevent warm air from passing through the circulation passage 4. The aforesaid water level is designated by symbol “L3” in FIGS. 6 and 7. As the result of the above-described construction, too, moist warm air can be supplied into the water tub 1 in the preheating.

The invention should not be limited to the foregoing embodiments. The embodiments may be modified as follows. For example, the target temperature of laundry in the preheating may be constant irrespective of the temperature of water poured from the water pouring unit 6 when the washing machine is installed in an environment where temperature changes are small throughout the year and changes in the ambient temperature need not be taken into consideration. In this case, for example, as shown in FIG. 8, it is determined that the laundry has reached the target temperature, whereupon the preheating is finished. The determination is based on that the temperature detected by the temperature sensor 14 has reached a previously determined water-tub interior temperature previously set for every amount of laundry. The temperature sensor 15 may be eliminated in the aforesaid arrangement.

The water pouring by the water pouring unit 6 need not be carried out continuously throughout the preheating. The water pouring may be carried out intermittently or for a short period of the preheating. Furthermore, a water pouring time may be controlled according to an amount of laundry or the like. Consequently, warm air can contain moisture.

The water supply (first water supply) before the preliminary wash may be carried out until a normal water level is reached. The water level is reduced in the first washing operation (that is, the preliminary wash) since the dried laundry absorbs water. Then, additional water supply is usually carried out until a set water level is reached in the middle of the washing operation, whereby the lowered water level is returned to the former state. Accordingly, even when the water level for the preliminary wash is set to the normal water level, substantially the same effect can be achieved as the case where the water level is set so as to be lower than the normal water level without execution of additional water supply.

The invention may be applied to a washing machine with drying function, which is provided with a rotating tub rotated about a vertical axis.

The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.

Claims

1. A washing machine with a drying function, comprising:

a water tub;

a rotating tub provided in the water tub so as to be rotatable;

a driver rotating the rotating tub;

a circulation passage defined so as to communicate with the water tub;

a warm-air supply unit circularly supplying warm air through the circulation passage into the water tub and the rotating tub;

a water-supply unit supplying water into the water tub;

a control unit controlling the driver, the warm-air supply unit and the water-supply unit thereby to be capable of controlling wash, rinse, dehydration and drying steps; and

a preheating unit executing a preheating operation in which warm air is supplied into the water tub and the rotating tub during rotation of the rotating tub before the wash step is executed.

2. The washing machine according to claim 1, wherein the preheating unit executes the preheating operation while a small amount of water is reserved in the water tub.

3. The washing machine according to claim 1, further comprising a heat exchanger including a water pouring unit provided midway in the circulation passage for pouring water for dehumidification of air passing through the circulation passage, wherein the preheating unit executes the preheating operation when the water pouring unit has poured water.

4. The washing machine according to claim 1, wherein the wash step includes a main wash and a preliminary wash carried out while water whose amount is smaller than in the main wash is reserved in the wash tub.

5. The washing machine according to claim 1, further comprising a laundry temperature sensor detecting a temperature of laundry in the rotating tub, wherein the preheating unit executes the preheating operation until the temperature of laundry reaches a previously set target temperature.

6. The washing machine according to claim 5, wherein the target temperature is set to 60° or below.

7. The washing machine according to claim 5, further comprising an ambient temperature sensor detecting an ambient temperature, wherein the target temperature is changed according to the ambient temperature.