TECHNICAL FIELD 
     The present invention relates to a clothes dryer, and more particularly, to a clothes dryer of exhaust type including a vapor compression cycle system. The clothes dryer improves drying efficiency by drying laundry by supplying heat to an introduced air from a heat exchange cycle system. 
     BACKGROUND ART 
     Clothes dryers are mainly used to dry clothes by removing moisture from clothes that have just been washed. 
     The clothes dryers can be classified into an exhaust type and a condensation type according to a processing method of moist air generated while drying laundry. The former type employs a method of exhausting moist air from a dryer, while the latter employs a method of removing moisture by condensing moist air exhausted from a dryer and circulating the moisture-removed air again in the dryer. 
     Typically, in the exhaust type dryer, an air intake duct and an air exhaust duct are connected to a rotatable drum disposed inside a cabinet, the air intake duct having a heater disposed therein. 
     As air outside the dryer is introduced into the air intake duct by driving a fan, the air is heated to a high temperature by a heater. The heating temperature reaches up to about 100° C. This high temperature air is introduced into a drying drum in the dryer, thus drying laundry in the drum. In the drying procedure, the high temperature air gets to contain the moisture included in the laundry, and high humidity air is discharged through the air exhaust duct. Although such a conventional clothes dryer that delivers heat to an introduced air by using a heater has a merit that the overall drying time is shortened by the heater&#39;s rapid heating of air and it can be manufactured to have a large capacity, it has a drawback that the energy consumption is large because an introduced air is heated by the heater. Especially, there is a great probability that damages may occur depending on the material of laundry in the drying procedure since the laundry is dried with air of high temperature of 100° C. or higher. 
     Meanwhile, the condensation type clothes dryer has a merit that it can be manufactured in a built-in type since it requires no air exhaust duct for discharging air out of the clothes dryer, while it has a drawback that it requires a long drying time and is difficult to be manufactured to have a large capacity although its energy efficiency is higher than the exhaust type. Under this background, there is a demand for a clothes dryer that provides a high energy efficiency and is so improved that it may not cause a damage to laundry. 
     Meanwhile, in areas with a high humidity, for example, near seashores or areas with a long rain season, there is a problem in that the drying efficiency is relatively lower when the clothes dryer is used. This is because a large amount of moisture is contained in the air used to dry laundry. It requires a lot of time to dry laundry since the air containing a large amount of moisture is introduced into the drying drum with the moisture not being removed enough even if the air is increased in temperature by the heater, resultantly increasing the energy consumption required to complete the drying. Subsequently, there is a demand for a clothes dryer for supplying air to a drying drum with moisture removed enough from an introduced air. 
     DISCLOSURE OF THE INVENTION 
     Therefore, an object of the present invention is to provide a clothes dryer which improves energy efficiency and has little possibility of causing a damage to laundry due to a high temperature air in a drying procedure. 
     Another object of the present invention is to provide a clothes dryer which can introduce air to a drying drum with moisture removed enough from the introduced air. 
     Still another object of the present invention is to provide a clothes dryer which is compact with improved space utilization. 
     To achieve the above objects, according to a first aspect of the present invention, there is provided a clothes dryer, comprising: a cabinet; a drying container rotationally mounted in the cabinet; a driving portion for supplying a torque to the drying container; a first air path connected to one side of the drying container; a second air path connected to the other side of the drying container and connected to outside of the cabinet; and first and second heat exchange portions for exchanging heat with air introduced into the first air path. 
     Preferably, the first air path and the second air path are located below the drying container, and the first heat exchange portion is located in front of the second heat exchange portion on the first air path. 
     The cabinet is provided at the front face with an opening for putting laundry in and out of the drying container. 
     A fan for creating an air flow is disposed at least one of the first and second air paths. Preferably, the fan receives a torque from the driving portion. 
     According to a second aspect of the present invention, there is provided comprising: a cabinet; a drying container rotationally mounted in the cabinet; a driving portion for supplying a torque to the drying container; a first air path connected to one side of the drying container; a second air path connected to the other side of the drying container and connected to outside of the cabinet; and first and second heat exchange portions for exchanging heat with air introduced into the first air path, wherein the second air path has a damper for opening and closing the paths disposed thereon. 
     A temperature sensor or humidity sensor is disposed in front of the damper on the second air path. The damper is controlled in at least two states including an opened state and a closed state according to a predetermined value of a signal sensed by the temperature sensor or humidity sensor. 
     According to a second aspect of the present invention, there is provided comprising: a cabinet; a drying container rotationally mounted in the cabinet; a driving portion for supplying a torque to the drying container; a first air path connected to one side of the drying container; a second air path connected to the other side of the drying container and connected to outside of the cabinet; and first and second heat exchange portions for exchanging heat with air introduced into the first air path, wherein an auxiliary air inlet is formed on the first air path. 
     Preferably, the auxiliary air inlet is formed between the first heat exchange portion and the second heat exchange portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a perspective view showing the outer appearance of a clothes dryer; 
         FIG. 2  is a perspective view showing the inside of a clothes dryer according to one embodiment of the present invention; 
         FIG. 3  is a perspective view showing the inside of a clothes dryer according to one embodiment of the present invention; 
         FIG. 4  is a plan view showing parts disposed on the bottom of the clothes dryer of  FIG. 2 ; 
         FIG. 5  is a schematic view showing a refrigerant flow and an air flow in the clothes dryer according to the present invention; 
         FIG. 6  is a perspective view showing some parts of the inside of the clothes dryer according to the present invention; 
         FIG. 7  is a plan view showing an air flow introduced into the clothes dryer; 
         FIG. 8  is a schematic view showing some parts of the clothes dryer provided with a damper; and 
         FIG. 9  is a graph showing a rate of change in temperature (or humidity) in the drying container. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
     While the invention has been described in connection with preferred embodiments, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     First, referring to  FIG. 1 , one example of a clothes dryer  10  according to the present invention is illustrated. A cabinet  12  provided with an entrance  14  in the front face is hollow inside, with a drying container rotationally mounted therein. 
       FIGS. 2 and 3  illustrates an inner structure of the clothes dryer in more detail. 
     The drying container  16  is a cylindrical-shaped structure, and disposed so as to rotate around an axis substantially parallel to the bottom of the cabinet  12 . 
     The drying container  16  is made rotatable by receiving a torque from a driving portion  18 , e.g., a motor, disposed on a lower side thereof, preferably, on the bottom of the cabinet  12 . Typically, as a torque transmission means, a belt engaged by being extended from a driving shaft of the driving portion  18  to the outer peripheral surface of the drying container  16  is suitable. As described later, the driving portion is also able to transmit a torque to a fan  40  disposed inside the cabinet  12  and creating an air flow. 
       FIG. 4  illustrates various elements disposed on the bottom of the cabinet of the clothes dryer. As illustrated in  FIGS. 2 to 4 , a first air channel  20  through which intake air flows is connected to at one side of the drying container  16 , and a second air path  22  through which exhaust air from the drying container flows is connected to the other side thereof. It does not matter if the entrance of the first air path  20  is not exposed out of the cabinet  12 , but it is preferable that the outlet of the second air path  22  is exposed out of the cabinet  12 . the shapes of the first air path  20  and second air path  22  are not specifically restricted, but the direction or position of each part of the paths may be changed so as to be suitable to the space in the cabinet. 
     A first heat exchange portion  30  and a second heat exchange portion  32  are disposed in the first air path  20 . The heat exchange portions  30  and  32  remove moisture by removing heat from the air flowing into the first air path  20 , and increases the temperature of the air by applying heat. Thus, the air passing through the first air path  20  enters the drying container  16  in a dried and temperature-increased state. 
     It is preferable that the first heat exchange portion  30  and the second heat exchange portion  32  form a thermodynamic cycle. For this, the cabinet  12  further includes a compressor  34  and an expansion device  36  are preferably disposed in the lower side of the drying container or lower than the drying container. The first heat exchange portion  30  and the second heat exchange portion  32  are connected by a pipe  38  to form one closed loop. Such a cycle is a kind of “vapor compression cycle”, and serves as a heat pump with respect to air flowing through the first air channel  30 . 
       FIG. 5  schematically illustrates a refrigerant flow and an air flow in the aforementioned cycle. A proper refrigerant flows in the pipe  38  for connecting each of the elements of the cycle. As for the direction thereof, the refrigerant proceeds to the first heat exchange portion  30  from the second heat exchange portion  32  through the expansion device  36 , and then proceeds to the second heat exchange portion  32  from the first heat exchange portion  30  through the compressor  34 . This flow direction of the refrigerant is indicated by a dotted arrow. 
     The air flowing into the first air path  20  passes through the two heat exchange portions  30  and  32  and enters the drying container  16 , and then is exhausted via the second air path  22 . This flow direction is indicated by a dotted arrow. 
     It is preferable that the air entering the first air path  20  enters the drying container in a dried state after it is increased in temperature by firstly having its moisture removed in the first heat exchange portion  30  and then receiving heat from the second heat exchange portion  32 . Therefore, it is preferable that an evaporator for absorbing heat from a flowing air is used is used as the first heat exchange portion  30 , a condenser for supplying heat to a flowing air is used as the second heat exchange portion  32 , and the first heat exchange portion is disposed more forward than the second heat exchange portion is. 
     A plurality of heat exchange pins are generally mounted at the heat exchange portions  30  and  32  in order to increase a heat transfer area on the pipe through which refrigerant passes. A flowing air firstly delivers heat to the evaporator to remove its moisture while evaporating the refrigerant, and then receives heat from the condenser to be increased to a temperature higher than about 50° C., preferably, 50 to 75° C. 
     Preferably, each of the elements constituting the above cycle, that is, the first heat exchange portion  30 , the second heat exchange portion  32 , the compressor  34 , the expansion device, and the pipe  38  connecting them are all disposed inside the cabinet  12 , especially, below the drying container  16 . For this, it is appropriate that at least some parts of the first air path, where the first heat exchange portion  30  and the second heat exchange portion  32  are disposed, are disposed below the drying container  16 , and at least some parts of the second air path  22  are disposed below the drying container  16  too. 
     By this arrangement, there is no need to increase the volume of the cabinet, thus the inner space can be utilized efficiently, resultantly making the clothes dryer compact. If the aforementioned elements are exposed out of the clothes dryer or the volume of the cabinet is increased, the installation area of the clothes dryer in a building becomes larger, thereby decreasing the spatial utilization. 
       FIG. 6  illustrates some parts of the clothes dryer according to the present invention. As illustrated therein, a belt  42  is wound around the outer peripheral surface of the drying container  16 , and the belt  42  is connected to a rotary shaft  18   a  of the driving portion  18  and transfers a torque to the drying container  16 . The driving portion  18  is also connected to a fan  40  disposed on the second air path  22  to drive the fan. Thus, the driving portion  18  can rotate the drying container  16  and the fan  40  simultaneously. As above, the drying container  16  and the fan  40  are driven at a time only by the one driving portion  18 , so that the space utilization in the cabinet can be increased and no additional apparatus is required, which is advantageous. Although, in  FIG. 6 , the fan  40  is disposed in the second air path  22  near the drying container  16 , it may also be disposed on the first air path only if it can be supplied with a torque from the driving portion  18 . 
     Meanwhile, a filter ( 21  of  FIG. 3 ) is disposed on the first air path  20  before the first heat exchange portion is disposed, so that it may remove contaminants, such as dusts, contained in an introduced air in advance. 
     A drying process of the clothes dryer of the present invention having this construction will be described below. 
     When the fan  40  is driven by the rotation of the driving portion  18 , a suction force is generated to introduce external air to the entrance of the first air path  20 . As the introduced air passes through the first heat exchange portion  30 , the moisture contained in the air is removed through a first heat exchange. The air changed to a low temperature and low humidity while passing through the first heat exchange portion  32  undergoes a secondary heat exchange while passing the second heat exchange portion  32  of a high temperature. The air changed to a high temperature and low humidity continuously passes through the inside of the first air path  20  and reaches to one side of the drying container  16 . 
     The air having passed through the second heat exchange  32  maintains a temperature of about 50 to 75° C. The high temperature air maintaining this degree of temperature can smoothly perform drying without damaging laundry in the drying container  16 . 
     The high temperature and low humidity introduced into the drying container  16  delivers heat while in contact with laundry containing moisture, and receives moisture from laundry and comes out of the drying container in the form of a high humidity air. The high humidity air flown out of the drying container is exhausted out of the cabinet  12  through the second air path  22 . 
     In the clothes dryer according to the present invention, a heat generating system using a vapor compression cycle exhibits heating performance two or three times larger as compared to a heater type, under the assumption that the same power is used. Thus, power consumption can be reduced. 
     Further, the temperature of air introduced into the drying container is lower as compared to drying using a heater type, which causes less damage of laundry. 
     Besides, the first heat exchange portion of the heat generating system removes moisture from the air introduced into the first air path, thus dries laundry with low humidity air. Therefore, the drying efficiency is improved. Especially, the clothes dryer of this invention is effective to dry clothes in humid areas. 
     If the clothes dryer is used in dry areas, no moisture removal process accompanied by a heat exchange in the first heat exchange portion would be required. Further, since the temperature of air becomes lower in the moisture removal process, the efficiency of the overall system may be degraded. Thus, there is a need to make the second heat exchange portion and the air directly contact with each other without undergoing the heat exchange in the first heat exchange portion. 
       FIG. 7  illustrates a clothes dryer of a modified structure according to another embodiment of the present invention. Air is introduced into a filter  21  disposed at the entrance side of the first air path  20 . Further, an auxiliary air inlet  50  is formed at a side of the first air path. The auxiliary air inlet  50  may be exposed out of the cabinet  12  as shown in the drawing, or may not be exposed. The auxiliary air inlet  50  is preferably formed at a side of the first air path between the first heat exchange portion  30  and the second heat exchange portion  32 . A filter  51  for removing dusts contained in external air may be disposed on the auxiliary air inlet  50 . 
     By forming the auxiliary air inlet  50 , the first air path  20  has two air inlets. The air supplied to the drying container  16  via the first air path contains the air passing through the first heat exchange portion  30  and the air directly passing though the heat exchange portion  32  without passing through the first heat exchange portion. The air introduced via the auxiliary air inlet  50  and only passing through the second heat exchange portion  32  has no heat loss caused by heat exchange with the first heat exchange portion  30 , thus it can be introduced into the drying container  16  in a relatively high temperature state. 
     As above, by varying the air inlets of the first air path, the air supplied to the drying container can obtain a dual effect of heat loss reduction and moisture removal. Further, the overall efficiency of the vapor compression cycle system can be improved. 
     Hereinafter, a clothes dryer according to a second aspect of the present invention will be described. 
     An exhaust type dryer injects high temperature air to one side of a drying container, and discharges humid air to the other side thereof. Such a process is always the same from an initial stage of drying until an end stage of drying. If high temperature air stays in the drying container for a while and then is directly discharged out of the drying drum, this is not efficient in terms of energy utilization. That is, energy consumption is increased in the overall drying process. 
     In the present invention, the energy efficiency is increased by controlling an air flow such that the time during which air stays in the drying container may differ depending on a drying procedure. In a preferred embodiment, a damper for opening and closing the paths is disposed on the second air path through which air is discharged to thus control an air flow. 
       FIG. 8  schematically illustrates some parts of the clothes dryer with a damper disposed thereto. 
     A damper  60  is disposed near the drying container  16  on the second air path  22 . 
     A sensor  63  for sensing a temperature or humidity of air discharged from the drying container  16  is disposed in front of the damper  60 . The damper  60  is controlled according to a temperature or humidity sensed by the sensor  62 , thereby adjusting the flow of air passing through the second air path  22 . 
     A method of controlling the opening and closing of the damper can be selected variously according to a dried state of laundry or a state of the air discharged from the drying container. 
     Referring to  FIG. 9 , a rate of change per time in temperature (A) or humidity (B) of air discharged from the drying container is shown. A degree of opening and closing the damper may be changed based on a saturation point Ps at which an increase rate of temperature sensed by the sensor becomes lower or a decrease rate of humidity becomes slow. 
     For example, it is possible to control the damper to be closed if a measured temperature of an air outlet portion of the drying container is less than a predetermined temperature (i.e., 60° C.) or control the damper to be opened if it is greater than the predetermined temperature. Besides, it is also possible to close the damper until a measured humidity of air discharged from the air outlet portion of the drying container reaches a predetermined value and open the damper if it exceeds the predetermined value. 
     By this method, the damper is closed in an initial stage of drying to increase the time during which a high temperature air stays in the drying container, and the damper is opened in an intermediate or end stage of drying to increase a discharge amount of air. Therefore, there is a lot of time for which high temperature air is contacted with laundry in the initial stage of drying, thus even a small air flow can be efficiently utilized for drying. Further, in the intermediate or end stage of drying, the energy consumption can be reduced by decreasing an air heating degree rather than by increasing an air flow amount. 
     Meanwhile, if the damper is fully opened for a long time, the pressure in the drying container may be excessively increased or a large load may be applied to the fan for creating an air flow. To prevent this, the step of partially opening the damper may be included. 
     That is, a multistage damper control method may be used in which the damper is fully opened if a measured pressure in the drying container reaches a predetermined pressure or if a temperature or humidity reaches a predetermined value after the damper is slightly opened in advance when the temperature or humidity reaches a given value before the air outlet in the drying container reaches the predetermined temperature or humidity. 
     As described above, the present invention can properly control a humidity and temperature of air introduced to the drying container by including first and second heat exchange portions serving as heat pumps. 
     Furthermore, if the vapor compression cycle system is disposed below the drying container as in the present invention, the internal structure of the dryer is utilized as its, and thus there is no need for volume increase. That is, the space required to dispose the system gets smaller as compared to the case where the system is disposed at a side or rear of the cabinet. 
     Besides, the present invention can control an air path resistance by changing the degree of opening and closing the damper disposed between the drying container and the air path. When the air path resistance is increased, the time for which high temperature air stays in the drying drum can be lengthened, thereby removing a lot of moisture from laundry. Consequently, the energy consumption of the dryer can be reduced.
A clothes dryer is provided. In the dryer, air flowing into a drying container is provided with heat from heat pump. The clothes dryer comprises a cabinet, a drying container rotationally mounted in the cabinet, a motor providing the container with rotational force, a first air path connected to a side of the container, a second air path connected to another side of the container and to the outside of the cabinet, and a first heat exchanging member and a second heat exchanging member in the first air path. A damper may be additionally included in the second air path.