Indirect Cooling Refrigerator With Freezing and Storage Chambers and a Forced Air Circulating Path

The present invention relates to a refrigerator with a freezing chamber and, more particularly, to a refrigerator with a freezing chamber capable of preventing the temperature in the freezing chamber from rising by a simple structure when frost adhered to an evaporator is removed.

As a system for cooling a freezing chamber in a refrigerator with a freezing chamber and a storage chamber, a direct cooling type in which an evaporator is arranged directly in a freezing chamber, and so-called an indirect cooling type employing a cooling air forced convection system in which a cooling chamber having an air circulating path containing an evaporator is provided adjacent to a freezing chamber and the air in the freezing chamber is circulated by a convection fan through the air circulating path are known. Since the indirect cooling system employs the cooling air forced convention system, it has an advantage that the air in the freezing chamber can be uniformly cooled in a short time. Even in this indirect cooling system, frost on the surface of an evaporator provided in the air circulating path should be frequently removed.

A defrosting of the surface of an evaporator is in general executed by heating the evaporator by a defrosting heater. However, in a conventional refrigerator with a freezing chamber of indirect cooling type, an air convection occurs between the freezing chamber and the air circulating path at the defrosting time, resulting in a rise in the temperature of the freezing chamber. This arises a problem that foodstuffs cannot be contained in the freezing chamber at the defrosting time.

In order to eliminate such drawbacks, it has been proposed to provide a damper which opens and closes the air circulating path in the path to drive the damper plate to the closed position, i.e., to the position for closing the air circulating path at the defrosting time, thereby preventing the air convection between the freezing chamber and the circulating path so as to prevent the freezing chamber from rising at its temperature at the defrosting time.

However, since the damper plate is opened and closed by a solenoid in the conventional refrigerator with a freezing chamber having the above-described damper plate, a damper drive mechanism is large in size and expensive, thereby disadvantageously causing an expensive refrigerator.

Accordingly, it is an object of the present invention to provide a refrigerator with a freezing chamber capable of simplifying a damper plate drive mechanism, reducing in size, facilitating the control of a defrosting, and decreasing an electric power necessary for defrosting.

According to the present invention, there is provided a refrigerator with a freezing chamber which comprises a freezing chamber; a storage chamber; a partition wall provided between the freezing chamber and the storage chamber; and a cooling chamber for forming a forced air circulating path of an air inlet provided adjacent to the freezing chamber for intaking air in the freezing chamber, an inlet air path for passing the intaken air, an evaporator for cooling the intaken air and having a defrosting heater, a cooled air path for passing the cooled air, an air outlet for exhausting the cooled air to the freezing chamber, and a convection fan for circulating the air. This forced air circulating path includes a damper plate for opening and closing the circulating path, damper plate supporting means for supporting the damper plate in the opened or closed state, and damper plate drive means for driving the damper plate to the opened position at the cooling time of the freezing chamber and to the closed position when frost adhered to the surface of the evaporator is removed by means of a shape memory alloy member.

The shape memory alloy member displaces from a first status to a second status when the member is heated to its status changing temperature or higher, and displaces from the second status to the first status when the member is cooled to the status changing temperature or lower. Therefore, this shape memory alloy member can be displaced from the first status to the second status by heating the member by means of an electric heater to control the damper plate to the closed position and to control the damper plate to the opened position by changing the alloy member from the second status to the first status by cooling the member by means of the evaporator. Since the shape memory alloy member and the electric heater are simply associated in this manner so as to control the opening and closing of the damper plate, the damper drive mechanism can be remarkably reduced in size as compared with that using a solenoid, and the inexpensive refrigerator with a freezing chamber can be produced. Further, energy of the electric heater used for controlling the damper plate can be also used for the defrosting energy, and part of the heat energy used for the defrosting can be used for the damper plate control energy.

FIG. 1 is a longitudinal sectional view showing a refrigerator with a freezing chamber according to a first embodiment of the present invention;

FIGS. 2A, 2B are sectional views of the forced air circulating path in FIG. 1, FIG. 2C is a sectional view of a camper plate drive mechanism;

FIG. 3 is a longitudinal sectional view of a refrigerator with a freezing chamber according to a second embodiment of the present invention;

FIGS. 4A, 4B are partial sectional views of the forced air circulating path in FIG. 3;

FIG. 5 is a block diagram of an example of a defrosting controller used for the refrigerator with a freezing chamber of the present invention;

FIG. 6 is a view showing an example of temperature control characteristics of the shape memory alloy in FIG. 3;

FIG. 7 is a partial sectional view of the cooled air circulating path for describing a third embodiment of the present invention;

FIG. 8 is a view showing part of a longitudinal section of a refrigerator with a freezing chamber illustrating a fourth embodiment of the present invention;

FIGS. 9A, 9B are sectional views showing part of the forced air circulating path in FIG. 8;

FIG. 10 is a view showing part of a longitudinal section of a refrigerator with a freezing chamber illustrating a fifth embodiment of the present invention;

FIGS. 11A, 11B are sectional views showing part of the forced air circulating path in FIG. 10; and

FIG. 12 is a view showing a modified example of FIG. 11B.

In FIG. 1 showing a first embodiment of a refrigerator with a freezing chamber of the present invention, a housing 1 of the refrigerator has a top wall 2, a bottom wall 3, a first rear wall 4, a second rear wall 5, a partition wall 6, side walls, and openable doors 7, 8. Thermal insulators 9 are respectively filled in these walls. A freezing chamber 10 is formed in the upper inner space of the housing 1, and a storage chamber 11 is formed in the lower inner space of the housing 1. A cooling chamber 13 is provided adjacent to the freezing chamber 10. The cooling chamber 13 is formed of partition members 13a, 13b provided in the freezing chamber 10, the first rear wall 4 and the partition wall 6. An evaporator 14 is provided between the partition wall 6 and the partition member 13b. A convection fan 16 is provided to produce forced convection in the space formed between the partition member 13b, the partition wall 6 and the first rear wall 4. A first cooled air path 16 and a second cooled air path 17 which communicate with the cooling chamber 13 are provided in the right side of the evaporator 14 of the drawing. The first cooled air path 16 is formed between the partition member 13b and the first rear wall 4. The second cooled air path 17 is formed between the side of the partition wall 6 and the second rear wall 5. An intaken air path 18 is provided at the left side of the evaporator 14 of the drawing, and a first air intake hole 19 and a second air intake hole 20 which communicate with the path 18 are provided. A defrosting heater 21 for removing frost adhered to the evaporator 14, i.e., energized only at the defrosting time is provided at the evaporator 14. A damper plate 22 for opening and closing the first air intake hole 19, a drive mechanism 23 for the damper plate 22, and a rod 24 for connecting the damper plate drive mechanism 23 to the damper plate 22 are provided in the intaken air path 18. Reference numeral 27 designates a condenser which constructs a refrigerative cycle system (not shown) of the refrigerator shown, and numeral 28 is a compressor which similarly constructs the refrigerative cycle system.

The damper plate 22 and the drive mechanism 23 for the damper plate 22 will now be described in detail with reference to FIGS. 2A to 2C. A projecting portion 31 is provided at the end of the first air intake hole 19 of the partition member 13b and a projecting portion 31 is provided at the portion opposed to the projecting portion 30 of the partition wall 6a. The damper plate 22 is provided to rotate around a stationary shaft 32 as a center, to close the first air intake hole 19 in the vicinity of the projecting portions 30, 31 or to open the air intake hole 19 separate from the projecting portions 30, 31. A rod 24 for driving the damper plate 22 is connected between the damper plate 22 and the damper drive mechanism 23. FIG. 2A shows the case that the damper plate 22 opens the air intake hole 19, FIG. 2B shows the case that the damper plate 22 closes the air intake hole 19, and FIG. 2C shows the internal structure of the damper drive mechanism 23. This damper drive mechanism 23 has a metal double cylinder 34 formed of inner and outer cylinder members, a damper drive heater 36 insulated and wound between the outer and inner cylinder members and a spring-shaped shape memory alloy member 38 secured at one end to the bottom of the inner cylinder member and at the other to one end of the rod 24 extending toward the evaporator 14. The right end of the double cylinder 34 of the drawing is formed in a flange shape, and the flange portion is thermally contacted with the evaporator 14. When this spring-shaped shape memory alloy member 38 is heated to a temperature exceeding the status changing temperature of the shape memory alloy member 38 by means of a damper drive heater 36, the shape memory alloy member 38 extends axially of the coil in length stored in advance at the status changing temperature, and closes the first air intake hole 19, as shown in FIG. 2B. When the shape memory alloy member 38 is cooled to the status changing temperature or lower, the shape memory alloy member 38 contracts axially of the coil, and the damper plate 22 opens the first air intake hole 19 as shown in FIG. 2A.

An operation of the refrigerator shown in FIG. 1 will now be described. The energization of the defrosting heater 21 and the damper drive heater 36 and the driving of the convection fan 15 are controlled by a defrosting control circuit (not shown). When the defrosting control circuit receives a defrosting command signal, the control circuit controls to stop supplying refrigerant to the evaporator 14 during a predetermined period from the thus receiving time point, stop rotating the convection fan 15 and energize tbe defrosting heater 21 and the damper drive heater 36. The control circuit controls to supply the refrigerant to the evaporator 14 except the above predetermined period, rotate the fan 15 and stop the energization of the heater 21 and the heater 36.

The operation of the refrigerator in FIG. 1 of the case that the defrosting command signal is not applied to the defrosting control circuit will be as below. The refrigerant is supplied to the evaporator 14, the fan 15 is rotated, and the heaters 21 and 36 are cut off. In this case, since the spring-shaped memory alloy member 38 is cooled to the status changing temperature or lower, the memory alloy member 38 is contracted, and the damper plate 22 opens the first air intake hole 19, as shown in FIG. 2. Thus, a forced air circulating path which has the fan 15, the first cooled air path 16, the first cooled air exhaust hole 25, the freezing chamber 10, the first air intake hole 19, the intaken air path 18 and the evaporator 14 is formed. Since the air in the freezing chamber 10 is, therefore, cooled by the evaporator 14 while passing through the cooling chamber 13, the interior of the freezing chamber 10 is consequently cooled. When the freezing chamber 10 is thus completely cooled, the forced air circulating path which has the route of the evaporator 14, the fan 15, the second cooled air path 17, the storage chamber 11, the second air intake hole 20, the intaken air path 18 and the evaporator 14 is simultaneously formed. Therefore, the air in the storage chamber 11 is circulated through this route. Since the air in the storage chamber 11 is cooled while passing in the cooling chamber 13 in this manner, the storage chamber 11 is also cooled. As described above, an ordinary cooling operation is carried out in the refrigerator with a freezing chamber except the defrosting period. The compressor 28 is operated ON or OFF repeatedly during this ordinary cooling operation. The temperatures in the freezing chamber 10 and storage chamber 11 can be controlled by the known control system. In other words, the temperatures in the freezing chamber 10 and storage chamber 11 can be controlled by means of the control of the distribution of the flow rate of the air flowing in the freezing chamber and storage chamber and the ON and OFF of the compressor 28.

Frost is adhered to the surface of the evaporator 14 while the above-described cooling operation in the refrigerator is conducted. This frost can be removed as follows: A defrosting command signal is applied to a defrosting control circuit (not shown). The control circuit controls to stop supplying refrigerant to the evaporator 14 during a predetermined period from the reception of the defrosting command signal, stop the rotation of the fan 15 and energize the defrosting heater 21 and the damper drive heater 36. When the damper drive heater 36 is energized, the shape memory alloy member 38 is heated to the status changing temperature or higher. Therefore, the spring-shaped shape memory alloy member 38 will extend. Thus, as shown in FIG. 2B, the first air intake hole 19 is closed by the damper plate 22. On the other hand, the air of the evaporator 14 and hence the air in the cooling chamber 13 is raised at the temperature by the energization of the defrosting heater 21. Therefore, the frost adhered to the surface of the evaporator 14 is removed. Water droplets produced as a result of the removal of the frost from the evaporator 14 is exhausted externally of the refrigerator by known means per se. Since the first air intake hole 19 is closed by the damper plate 22, air convection occurring through the cooling chamber 13, i.e., the first cooled air exhaust hole 16a, the freezing chamber 10 and the first air intake hole 19 does not take place. Consequently, even if the temperature of the air in the cooling chamber 13 rises, the temperature of the air in the freezing chamber 10 does not rise. This means that the quality of foodstuffs contained in the refrigerator does not decrease even if the defrosting of the evaporator 14 is carried out while the foodstuffs are stored in the freezing chamber 10.

When a predetermined period of time is elapsed upon reception of the defrosting command signal by the defrosting control circuit so that the defrosting operation has completed, the control circuit controls to restart supplying the refrigerant to the evaporator 14, rotate again the fan 15 and restop energizing the defrosting heater 21 and the damper drive haater 36. As a result, the evaporator 14 and the shape memory alloy member 38 are respectively cooled again. When the shape memory alloy member 38 is cooled to the status changing temperature or lower, the spring-shaped shape memory alloy member 38 contracts axially. Thus, the first air intake hole 19 is again opened by the damper plate 22, as shown in FIG. 2A, and the cooling operation of the refrigerator restarts. In this case, the shape memory alloy has in general hysteresis characteristic of the temperature that the extending status changing temperature and the contracting status changing temperature are different. The spring-shaped shape memory alloy member 38 can control the damper plate 22 so as to maintain the damper plate 22 in the closed state while the evaporator 14 is not sufficiently cooled and to open the damper plate 22 after the evaporator 14 is sufficiently cooled. Thus, the air stored in the cooling chamber 13 and maintained at high temperature can be prevented from being introduced into the freezing chamber 10 when the cooling operation of the refrigerator is restarted.

Since the damper drive mechanism 23 is composed in a simple combination of the shape memory alloy member 38 and the heater 36 in the embodiment shown in FIG. 1, the damper drive mechanism can be reduced in size and inexpensively produced. As the heater (damper drive heater) 36 for heating the shape memory alloy member may be composed as part of the defrosting heater 21, the defrosting electric lower can be reduced.

A second embodiment of the present invention will now be described with reference to FIG. 3. In FIG. 3, a housing 1 of the refrigerator has a top wall 2, a bottom wall 3, a first rear wall 4, a second rear wall 5, a partition wall 6, a sub-partition wall 6a, side walls, and openable doors 7, 8. Thermal insulators 9 are respectively filled in these walls. The inner space of the housing 1 is divided into a freezing chamber 10, a storage chamber 11 and a cooling chamber 13. The freezing chamber 10 is surrounded by the top wall 2, the partition wall 6, the sub-partition wall 6a, the door 7 and the side walls, the cooling chamber 13 is surrounded by the sub-partition wall 6a, the first rear wall 4, and part of the side alls, and the storage chamber 11 is surrounded by the partition wall 6, the bottom wall 3, the second rear wall 5, the door 8 and the side walls. A first evaporator 14 is provided in the cooling chamber 13, and a second evaporator 40 is provided in the upper space of the storage chamber 11. A compressor 28 is arranged in the lower space of the refrigerator housing 1 to contact external air. Reference numeral 27 designates, a condenser. The first evaporator 14, the second evaporator 40, the condenser 27 and a compressor 28 are connected in series with each other to construct a refrigerative cycle system. The refrigerative cycle system is controlled by an operation controller (not shown). More particularly, the operation controller controls the ON and OFF of the compressor 28, and controls so that the temperatures in the freezing chamber and storage chamber 11 become a set temperature.

A structure in the cooling chamber 13 will now be described in detail. An intaken air path 18 is formed in the lower part of the first evaporator of the drawing. An air intake hole 19 is opened between the intaken air path 18 and the freezing chamber 10, and the air is intaken in a direction as designated by an arrow in FIG. 3. A cooled air path 16 is formed in the upper part of the first evaporator 14 of the drawing. A damper plate 22 and a damper drive mechanism 41 are provided in the cooled air path 16. A fan 15 is provided in the cooled air path 16, and this fan 16 exhausts the cooled air through the cooled air exhaust hole 16a in a direction as designated by an arrow in FIG. 3.

The damper plate 22 and the drive mechanism 41 for the damper plate 22 will be described in more detail with reference to FIGS. 4A, 4B. The damper plate and the damper drive mechanism supporting member 42 having a projecting portion 42a is fixedly secured to the inner surface of the first rear wall 4 in the cooling chamber 13. A damper supporting member 43 having a projecting portion 43a is fixedly secured to the inner surface of of the sub-partition wall 6a to the supporting member 42. The damper plate 22 is rotatable around a shaft 22a provided at one end of the damper plate 22 as a center. The damper drive mechanism 41 includes a heating plate 45, a heater 46 and a temperature sensor 47. The one end of the heating plate 45 is fixed to the supporting plate 42, and the heater 46 and the sensor 47 are provided on the lower surface of the extended part of the drawing. One end of a slender shape memory alloy member 44 is secured fixedly to the upper surface of the heating plate 45, aid the other end of the shape memory alloy member 44 is coupled through a member 48 to the lower surface of the damper plate 22. When the shape memory alloy member 44 is held at the status changing temperature or lower, the stationary end portion and the free end portion of the alloy member 44 form a predetermined angle as shown in FIG. 4A, the damper plate 22 is lifted by the free end portion of the member 44, and the damper plate 22 is disposed at the opened position. When the shape memory alloy member 44 is heated to the status changing temperature or higher through the heating plate 45 by means of the heater 46, the alloy member 44 displaces, as shown in FIG. 4B, so that the stationary end portion and the free end portion become a rectilinear line. Therefore, the damper plate 22 interrupts the communication between the cooling chamber 13 and the freezing chamber 10 in a manner supported by the damper plate 22 and the projecting portions 42a, 43a.

An example of a defrosting controller will now be described with reference to FIG. 5. The defrosting controller 50 as an integrating counter 52 for integrating a time period in which the motor 51 of a compressor 28 is being energized and outputting a logical "1" when the counter 52, for example, counts 8 hours, a switching circuit 53 for closing ON when receiving the signal of this logical "1" and continuing this ON state for a predetermined time period, for example, for 40 min., a temperature control circuit 54 of the shape memory alloy 44, receiving an output of the temperature sensor 47 and an output of the switching circuit 53 for controlling the energization of the heater 46 in response to the output of the sensor 47, a delay circuit 55, receiving the output (logical "1") of the integrating counter 52 for delaying the signal "1" by a predetermined period, for example, 5 min. to produce an output, a switching circuit 56 for turning ON by the output "1" of the delay circuit 55 for energizing the defrosting heater 21 of the first evaporator 14, and a timer 57 receiving the output signal "1" of the delay circuit 55 for producing a reset output after a predetermined period, for example, 30 min. to reset the integrating counter 52 by the reset output. The output "1" of the counter 52 is applied to the operation controller (not shown) of the refrigerator as a stop signal of the cooling operation control. The temperature control circuit 54 controls the ON and OFF of the input to the heater 47 so that the temperature of the shape memory alloy member 44 is maintained slightly higher than the temperature of the status changing temperature in response to the output of the temperature sensor 47.

An operation of the second embodiment of the refrigerator with a freezing chamber will now be described with reference to FIGS. 3, 4A, 4B, 5, 6. While the logical "1" is not dispatched from the integrating counter 52, the refrigerator is operated in cooling. At this time, the damper plate 22 is maintained in opened state as shown in FIG. 4A, and the fan 15 is continuously operated. In other words, the temperatures of the freezing chamber 10 and the storage chamber 11 are maintained to the set value by the ON and OFF control of the compressor motor 51. When the integrated value of the operating period of the motor 51 becomes, for example, 8 hours, the integrating counter 52 outputs a logical "1". As a result, the cooling operation of the refrigerator is stopped, and the supply of refrigerant to the evaporators 14, 40 and the operation of the fan 15 are stopped. When the counter 52 outputs the logical "1", the switching circuit 53 closes ON to flow a current to the heater 46. Consequently, the shape memory alloy member 44 is abruptly heated during the time period t.sub.1 indicated by (T0-T1) in FIG. 6. When the shape memory alloy member 44 is then heated to the status changing temperature TM of the alloy memory 44 at the time point T1, the alloy member 44 displaces rectilinearly as shown in FIG. 4B, with the result that the damper plate 22 takes its closed position. The temperature sensors 47 detects the temperature of the alloy member 44, and controls the alloy member 46 with the result through the temperature control circuit 54 to maintain the alloy member 44 at a temperature slightly higher than the temperature of the status changing temperature of the member 44. Therefore, the alloy member 44 can be maintained in a rectilinear state as shown in FIG. 4B. Consequently, the freezing chamber 10 and the cooling chamber 13 are maintained in cut-off state. In this case, the alloy member 44 and the damper plate 22 are not heated to the temperature higher than required as shown by a broken line 58 in FIG. 6. The defrosting control circuit 54 will now be described in more detail. When the set time (e.g., 5 min.) (T0-T1) of the delay circuit 55 is elapsed, the switching circuit 56 closes ON to energize the defrosting heater 21. The damper plate 22 is already disposed at the closed state (in FIG. 4B) at the time point T1 when the switching circuit 54 is closed ON. The defrosting heater 21 is energized at the time period (T1-T2) (e.g., 30 min.). The evaporator 14 and hence the temperature in the cooling chamber 13 is raised at its temperature during the time period, and the frost on the surface of the evaporator 14 is externally exhausted as water droplets. Since the hot air in the cooling chamber 13 does not flow into the freezing chamber 10 due to the closed state of the damper plate 22, the quality of foodstuffs is not deteriorated even if the defrosting is executed while the foodstuffs are contained in the freezing chamber 10 in the same manner as in the first embodiment shown in FIG. 1.

The timer circuit 57 applies a reset signal to the integrating counter 52 to reset the counter 52 at the time point T2 in which the set time limit (e.g., 30 min.) of the timer 57 is elapsed from the starting time point T1 of the energization of the defrosting heater 21. Therefore, the heat 21 is deenergized at the time point T2, and the operation controller of the refrigerator switches the refrigerator to the cooling operation. In the defrosting control circuit shown in FIG. 5, in turn on period of the switching circuit 53 is set to 40 min, the delay time of the delay circuit 55 is set to 5 min, and the time limit of the timer circuit 57 is set to 30 min. Thus, the damper plate 22 is returned to the opened position shown in FIG. 4A at the time point T3 after the timer period t.sub.3 (e.g., 5 min.) between the time points T2 and T3 shown in FIG. 6 is elapsed. This time point T3 is substantially the restarting time point of the cooling operation of the freezing chamber 10. In this invention, the t.sub.3 between the time points T2 and T3 is called "closure extension period of the damper plate 22".

In a refrigerator having a defrosting control circuit shown in FIG. 5, the shape memory alloy 44 can be rapidly heated to drive the damper plate 22 to take a closed position with the heater having a large capacity. The heating period of the heater 46 is a period t.sub.1 which is immediately before the time T.sub.1 in which the energization of the defrosting heater 21 starts. The temperature of the memory alloy member 44 is controlled to be slightly higher than the status changing temperature of the member 44 after the time point T1. Thus, the period of time to be taken for closing the damper plate is shorten and the freezing chamber 10 is not affected by the large power for controlling the damper plate.

FIG. 7 shows a third embodiment of the present invention. In the second embodiment (FIG. 3), a bidirectional shape memory alloy member 44 is employed as the drive mechanism 41 of the damper plate 22. In FIG. 7, a unidirectional shape memory alloy member 62 is, on the other hand, used to construct a drive mechanism for the damper plate. Tn FIG. 7, a supporting plate 60 is fixedly secured to the inner wall of a first rear wall 4, and a supporting plate 61 is fixedly secured to the inner wall of a sub-partition wall 6a. Projections 60a, 60b are formed on the supporting plate 60, and projections 61a, 61b are formed on the supporting plate 61. Fulcra 22b, 22c are formed at the damper plate 22 rotating at a shaft 22a as a rotating center. A spring-shaped shape memory alloy 62 is coupled between the fulcrum 22b of the damper plate 22 and the projection 61b of the supporting plate 61, and a bias spring 63 is coupled between the fulcrum 22c of the damper plate 22 and the projection 60a of the supporting plate 60. A heating plate 45 is fixedly secured at one end thereof to the lower portion of the projection 61b and extended at the other end along the spring-shaped shape memory alloy member 62. A heater 46 for heating the alloy member 62 and a temperature sensor 47 for detecting the temperature of the alloy member 62 are provided at the heating plate 45. When the alloy member 62 is maintained at the status changing temperature or lower, the alloy member 62 is in the stable to be extended, with the result that the damper plate 22 is disposed at the opened position as shown in FIG. 7 by the operation of the bias spring 63. However, when the alloy member 62 is heated to the status changing temperature the alloy member 62 is contracted. Therefore, the damper plate 22 is driven to the closed position, supported by the projections 60b and 61a, thereby cutting off the communication between the cooling chamber 13 and the cooled air path 56. Thus, the heater 46 can be controlled corresponding to the defrosting controller 50 which has the switching circuit 53 and the temperature control circuit 54 in FIG. 5. Further, the energization of the heater 46 may be controlled by using the defrosting controller which operates by the output of a defrosting thickness detector.

A fourth embodiment of the present invention will now be described with reference to FIG. 8. In FIG. 8, a housing 1 of a refrigerator with a freezing chamber has a top wall 2, a first rear wall 4, a second rear wall 5, doors 7, 8, a bottom wall (not shown), side walls, a partition wall 6 in the same manner as the embodiment shown in FIG. 3. The housing 1 also has a freezing chamber 10, a storage chamber 11, a first evaporator 14, a second evaporator in the same manner as the embodiment in FIG. 3. The same reference numerals as in the embodiments shown in FIGS. 3 and 4A, 4B denote the same parts in the fourth embodiment, and the detailed description thereof will be omitted. Only different members will be described in detail. A sub-partition wall 6a has a vertical portion 6a1 and a horizontal portion 6a2, and the horizontal portion 6a2 and the partition wall 6 form an air intake path 18 having an air intake hole 19. The first evaporator 14 is arranged between the lower portion of the vertical portion 6a1 and the first rear wall 4. A supporting plate 65 is secured fixedly to the inner surface of the first rear wall in the upper part of the evaporator 14 of the drawing, and a supporting plate 66 is fixed to the inner surface of the vertical portion 6a1 opposite to the supporting plate 65. Projections 65a, 65b are provided at the supporting plate 54. A projection 66a, is formed at the upper end of the supporting plate 66, and a vessel 67 is fixed to the lower end. This vessel 67 is formed of a thermally conductive material, and formed with vent holes 67a and 67b. The spring-shaped memory alloy member 62 and a damper control heater 46 for selectively heating the member 62 are provided oppositely to the member 62 in the vessel 67. This alloy member 62 is fixed at one end thereof to the vessel 67, and drawn out at the other end from the vent hole 67. This alloy member 62 is contracted at the status changing temperature or higher, and elongated at the status changing temperature or lower by the operation of a bias spring 63. The outer surface of the vessel 67 is thermally contacted, for example, with the cooling fin of the evaporator 14 through a thermally conductive heat conduction plate 68. A shaft 69 which extends horizontally at the position shown in the drawing is fixed in the cooling chamber 13, and the shaft 69 is inserted into the central portion of the damper plate 22 and held rotatably clockwise and counterclockwise. The bias spring 63 is coupled between the projection 65a of the supporting plate 64 and the fulcrum 22c of the damper plate 22, and the other end of the spring-shaped shape memory alloy member 62 is connected to the fulcrum 22b of the damper plate 22. FIG. 9A shows the case that the damper plate 22 is disposed at the opened position, and an arrow designates the direction of the flow of the air of this case. The defrosting heater 21 and the damper control heater 46 of the evaporator 14 are respectively connected to the defrosting control circuits (not shown). FIG. 9B shows the case that the damper plate 22 is disposed at the closed position. In this case, the lower surface of one end of the damper plate 22 is contacted with the upper surface of the projection 66a, the upper surface of the other end of the damper plate 22 is contacted with the lower surface of the projection 65b, and the surface of the damper plate 22 is inclined as shown.

An operation of the embodiment of the refrigerator shown in FIG. 8 will now be described. Since the shape memory alloy member 62 is at the status changing temperature or lower at the ordinary cooling operation time, the member 62 is disposed in the state capable of being extended. Therefore, the damper plate 22 is disposed at the opened position shown in FIG. 9A by the operation of the bias spring 63. When the temperature in the freezing chamber 10 is at the set temperature (set by a thermostat, not shown) or higher, the fan 15 is driven. Consequently, the air in the freezing chamber 10 is circulated in a closed loop of the freezing chamber 10, the intake hole 19, the intaken air path 18, the evaporator 14, the cooled air path 16, the cooled air exhaust hole 16a and the freezing chamber 10. In this manner, the freezing chamber 10 is cooled to a predetermined temperature.

The defrosting control circuit stops rotating of the fan 15 and energizes the defrosting heater 21 and the damper control heater 46 at the defrosting time. Therefore, the temperature in the vessel 67 rises. The shape memory alloy 62 is heated by the heated air in the vessel 67 and the radiation heat from the heater 46. Therefore, the alloy member 62 is heated to the status changing temperature or higher in a short time and contracted. Thus, the damper plate 22 is driven to the closed position shown in FIG. 9B. As a result, the heat energy by the energization of the defrosting heater 21 is stopped from being introduced into the freezing chamber 10.

When the defrosting is finished and the evaporator 14 is restarted, there occurs a difference between the temperature of the air around ths evaporator 14 and the temperature of the air in the vessel 67. Therefore, natural convection occurs through the vent holes 67a, 67b, and cooled air is introduced into the vessel 67. Consequently, the shape memory alloy member 62 is abruptly cooled and extended by the operation of the spring 63. As a result, the damper plate 22 is again driven to the opened position shown in FIG. 9A. When the fan 15 is then driven, the air is circulated as described above, and the interior of the freezing chamber 10 is cooled.

According to the fourth embodiment described above, the heating efficiency of the shape memory alloy member can be improved, and the cooling time of the shape memory alloy member can be shortened.

A fifth embodiment of the present invention will now be described with reference to FIGS. 10, 11A, 11B. The different points of the fifth embodiment in FIG. 10 from the fourth embodiment in FIG. 8 are that the upper surface of the projection 65b of the supporting plate 65 is inclined upwardly, while the upper surface of the projection 65b of a supporting plate 65 is inclined downwardly in FIG. 10; the heat conduction plate 68 is provided in FIG. 8, while the heat conduction plate is not provided in FIG. 10; and a quick cooling evaporator 72 is not provided in FIG. 8, while the quick cooling evaporator 72 is provided in FIG. 10. The same reference numerals as in the embodiments in FIG. 8 denote the same parts in the fifth embodiment in FIG. 10, and the detailed description thereof will be omitted.

In FIG. 11A, the projection 65b of the supporting plate 65 and the projection 66a of the supporting plate 66 respectively operates as stoppers for stopping the counterclockwise rotation of the damper plate 22 of the drawing. In other words, the projection 65b stops the counterclockwise rotation of the damper plate 22 of the drawing at a predetermined position, and the projection 66a stops the counterclockwise rotation at a predetermined position. For example, the stopper 65b frequently rises at part of the plate state as shown in FIG. 9A. When such a stopper exists in the air circulating path, the stream of water produced at the defrosting time is disturbed by the stopper, with the result that smooth drain of water cannot be performed or the water is retained on the stopper. Therefore, when the ordinary cooling operation is started after the defrosting is finished, the water retained on the stopper is frozen, thereby obstructing the smooth operation of the damper plate 22. Or, a problem that a sealability is decreased due to insufficient contact between the projections 65b, 66a and the surface of the damper plate 22 has arisen. The embodiment shown in FIGS. 10. 11A, 11B has eliminated such a problem.

As shown in FIG. 10, the projection 65b is projected inwardly of the cooling chamber 13 with a triangular section shown in FIG. 10, and the upper surface 65b1 and lower surface 65b2 of the triangular section are inclined as shown. In other words, the inclination of the surfaces 65b1 and 65b2 are determined so that the water droplets are naturally flowed down along the surfaces 65b1 and 65b2 by the gravity. The upper surface 66a1 of the projection 66a is gradually inclined toward the inside of the cooling chamber 13. In other words, the surface 66a1 is inclined so that the water droplets can flow down by the gravity without stopping on the surface 66a1. Then, the height of the surface 66a1 is determined to be higher than the height of the surface 65b1. The damper plate 22 is stopped at the closed position by the projections 66a and 65b so as to satisfy the following conditions: The lower surface in the left end of the drawing of the damper plate 22 is contacted with the surface 66a1, and the upper surface of the right end of the drawing is stopped at the damper plate 22 in the state contacted with the surface 65b2. In this case, the damper plate 22 is obviously inclined from the left end to the right end of the drawing. Therefore, the surfaces of the damper plate 22 do not retain deposited water droplets but flow down the droplets by the gravity, and exhaust the water.

This embodiment provides additionally the advantage that water produced at the defrosting is smoothly exhausted, thereby obtaining the smooth operation of the damper plate and the damper plate is effectively sealed. The other advantages of this embodiment are in the same manner as the fourth embodiment shown in FIG. 8.

FIG. 12 show a modified example of FIG. 11B. In FIG. 11B, the first stopping portion 65b is projected toward the cooling chamber 13. In FIG. 12, a first stopping portion 73 is, on the other hand, introduced into the rear wall 4. However, since the surface 73a of the stopping portion 73 contacted with the upper surface of the damper plate 22 is inclined to flow down water droplets, the surface portion 73a is not frozen.