A defrosting method of a refrigerating circuit used for a refrigerator car

Abstract: A frost formed at a cooling unit (13) is effectively defrosted by two steps of defrosting. First step (41-47) mainly defrosts a frost formed at an outer surface of an evaporator (131) by means of directly leading discharged gas to the evaporator. Second step (48-57) mainly defrosts a frost formed at the cooling unit (13) except the evaporator (131) by means of making air in a refrigerating container pass through the heated evaporator (131).

Description: This invention relates to a refrigerating circuit used for a refrigerator car, and more particularly, to a defrosting method of the refrigerating circuit used for a refrigerator car. With reference to Figure 1, refrigerating circuit 10 generally used for a refrigerator car is schematically shown. Refrigerating circuit 10 includes compressor 11, condenser 12 and cooling unit 13 disposed within a refrigerating container (not shown). Compressor 11 is provided with electromagnetic clutch 111 intermittently transfering the dynamic power from an engine (not shown) of an automobile to compressor 11. Cooling unit 13 comprises evaporator 131, evaporator motor fan 132, a casing disposing evaporator 131 therewithin (not shown). Conduits 14, 15, 16 connect compressor 11 and condenser 12, condenser 12 and evaporator 131, evaporator 131 and compressor 11, respectively. Condenser 12 condenses refrigerant gas discharged from compressor 11. Condenser motor fan 121 is disposed near condenser 12 and makes outside air of the automobile pass through condenser 12. Expansion valve 17 is disposed between condenser 12 and evaporator 131 through conduit 15 and expands condensed refrigerant flowing from condenser 12. Evaporator motor fan 132 is disposed near evaporator 131 and makes air in the refrigerating container (not shown) pass through evaporator 131. Bypass conduit 18 connect conduit 14 and a portion of conduit 15 located between expansion valve 17 and evaporator 131. Solenoid valve 19 located in bypass conduit 18 selectively bypasses the refrigerant gas discharged from compressor 11 to evaporator 131. Defrosting the frost formed at cooling unit 13 is carried out as following. When a refrigeration control apparatus (not shown) including a defrosting control system receives a signal for defrosting the frost formed at cooling unit 13, refrigerant gas discharged from compressor 11 is bypassed to evaporator 131 by operation of solenoid valve 19. Bypassing discharged refrigerant gas to evaporator 131 is continued until a predetermined time elapses. When the predetermined time has elapsed, refrigerant gas flows into condenser 12 by operation of solenoid valve 19. Accordingly, defrosting the frost formed at cooling unit 13 is terminated and refrigeration of the refrigerating container begins again. Furthermore, in another type of defrosting control system, defrosting the frost formed at cooling unit 13 is terminate when the temperature of the outer surface of evaporator reaches a predetermined value. However, in above-mentioned prior art systems, the frost formed at the evaporator, the motor fan, the casing and the drain pipe is defrosted at a time by only leading discharged refrigerant gas into the evaporator so that the time of leading discharged refrigerant gas into the evaporator is long. Accordingly, a remarkable rise of the temperature in the refrigerating container causing an inferior cooling down characteristic in the refrigerating container occurs. Furthermore, durability of the compressor is reduced by compressing the discharged refrigerant gas for a long time. It is the object of this invention to provide an improved defrosting method of a refrigerating circuit which is used for a refrigerator car. This defrosting method improves the cooling down characteristic in the refrigerating container and prevents the reduction of compressor durability. A refrigerating circuit used for a refrigerator car includes a compressor, a condenser, an expansion valve, a cooling unit and a valve member. The condenser condenses refrigerant gas discharged from the compressor. The expansion valve expands condensed refrigerant flowing from the condenser. The cooling unit comprises an evaporator and a fan, and is disposed within a refrigerating container. The valve member selectively switches the course of a flow of the discharged refrigerant gas in order to directly lead the discharged refrigerant gas to the evaporator. A fan of the cooling unit causes air to pass through the evaporator. The method of defrosting the frost formed at the cooling unit according to the invention comprises a first and a second step as indicated in claims 1 and 3. In the first step, the frost formed at the outer surface of the evaporator is defrosted by directly leading the discharged refrigerant gas to the evaporator. In the second step, the frost formed at the cooling unit except the evaporator is defrosted by means of making air in the refrigerating container pass through the evaporator. Figure 1 is a schematic block diagram of a refrigerating circuit generally used for a refrigerant car. Figure 2 is a schematic block diagram of a refrigerating circuit used for a refrigerant car in accordance with one embodiment of this invention. Figure 3 is a schematic circuit diagram of a refrigerating control apparatus of a refrigerating circuit in accordance with one embodiment of this invention. Figure 4 is a flow chart of a defrosting method of a refrigerating circuit in accordance with one embodiment of this invention. With reference to Figure 2, refrigerating circuit 100 used for a refrigerator car is schematically shown. In the drawing same numerals are used to denote the corresponding elements shown in Figure 1. Refrigerating circuit 100 includes pressure switch 22 and first and second thermal sensors 23 and 24. Pressure switch 22 is connected to conduit 16 as well as super heat switch 21. First and second thermal sensors 23 and 24 sense temperature of a fin of evaporator 131 and temperature of leaving air from evaporator 131 respectively. Refrigerating circuit 100 further includes third thermal sensor 25 shown in Figure 3. Third thermal sensor 25 senses temperature of air in the refrigerating container. With reference to Figure 3, a schematic circuit diagram of refrigerating control apparatus 30 of a refrigerating circuit in accordance with one embodiment of this invention is shown. Refrigerating control apparatus 30 comprises micro computer 31 connecting to first, second and third thermal sensors 23, 24 and 25, high pressure switch 20, super heat switch 21 and pressure switch 22 those which send an input signal to micro computer 31. First, second, third and fourth solenoid switches 32, 33, 34 and 35 are connected to micro computer 31. Accessory switch 36, first and second fuses 37 and 38 connect micro computer 31 and battery 39 in parallel. Each terminal end of electromagnetic clutch 111 and evaporated motor fan 132 connect to a wire provided with first fuse 37 through first and third solenoid switches 32 and 34 respetively. Each terminal end of solenoid valve 19 and condenser motor fan 121 connect to a wire provided with second fuse 38 through second and fourth solenoid switches 33 and 35 respectively. Micro computer 31 earthes to a body of the automobile through wire 301. In operation, when first solenoid switch 32 is turned on by receiving a turning-on signal from micro computer 31, electromagnetic clutch 111 begins its operation to drive compressor 11. When second solenoid switch 33 is turned on by receiving a turning-on signal from micro computer 31, solenoid valve 19 is opened to bypass discharged refrigerant gas to evaporator 131. When third solenoid switch 34 is turned on by receiving a turning-on signal from micro computer 31, evaporator motor fan 132 begins its operation to make air in the refrigerating container pass through evaporator 131. When fourth solenoid switch 35 is turned on by receiving a turning-on signal from micro computer 31, condenser motor fan 121 begins its operation to make outside air of the automobile pass through condenser 12. On the other hand, when first solenoid switch 32 is turned off by receiving a turning-off signal from micro computer 31, electromagnetic clutch 111 terminates its operation in order to terminate the operation of compressor 11. When second solenoid switch 33 is turned off by receiving a turning-off signal from micro computer 31, solenoid valve 19 is closed to lead discharged refrigerant gas to condenser 12 only. When third solenoid switch 34 is turned off by receiving a turning-off signal from micro computer 31, evaporator motor fan 132 terminates its operation. When fourth solenoid switch 35 is turned off by receiving a turning-off signal from micro computer 31, condenser motor fan 121 terminates its operation. Furthermore, when the pressure of an outlet portion of evaporator 131 exceeds 18kg/cm², pressure switch 22 sensing the pressure of the outlet portion of evaporator 131 is turned off. Accordingly, turning-on signal of pressure switch send to micro computer 31 is vanished. With reference to Figure 4, a flow chart of a defrosting method of a refrigerating circuit in accordance with one embodiment of this invention is shown. Defrosting control method includes following steps. When micro computer 31 receives the defrosting signal in an auto defrosting mode or a manual defrosting mode at start step 41, a hot gas defrosting i.e. , mainly defrosting a frost formed at an outer surface of evaporator 131 by means of directly leading the discharged refrigerant gas to evaporator 131, at step 42 is begun by turning on solenoid switches 32, 33 and 35 and turning off solenoid switch 34. Step 43 judges whether the hot gas defrosting has lasted 15 minutes. If the hot gas defrosting has lasted 15 minutes, step 43 proceeds to step 46. While the hot gas defrosting has not lasted 15 minutes, step 43 proceeds to step 44. Step 44 judges whether pressure switch 22 turns off. If pressure switch 22 turns off, step 44 proceeds to step 46. While pressure switch 22 does not turn off, step 44 proceeds to step 45. Step 45 compares Tf i.e. , temperature of a fin of evaporator 131, with 15°C as the predetermined value. If Tf is equal or higher than 15°C, step 45 proceeds to step 46. While Tf if lower than 15°C, step 45 flows back to step 42. At step 46, a first draining i.e. , mainly draining the condensed water at the outer surface of evaporator 131, is begun by turning off solenoid switches 32, 33 and 34 and still turning on solenoid switch 35. With respect to step 44 and step 45, step 44 more effictively prevents the overload operation of compressor 11 due to compressing excessively high temperature refrigerant gas than step 45. Because, the pressure in conduit 16 usually reaches 18kg/cm² faster than the temperatures of the fin of evaporator 131 reaches 15°C. Accordingly, compressor 11 is turned off earlier by step 44 than by step 45 on the safe side. Furthermore, above mentioned relation between step 44 and step 45 can more effectively prevent over-load operation of compressor 11 in the high speed rotation of compressor 11. Step 47 judges whether the first draining has lasted 4 minutes. If the first draining has lasted 4 minutes, step 47 proceeds to step 48. While the first draining has not lasted 4 minutes, step 47 flows back to step 46. Step 48 compares Tf with 15°C. If Tf is equal or higher than 15°C, step 48 proceeds to step 49. While Tf is lower than 15°C, step 48 proceeds to step 53. At step 49, an air passing through i.e. , mainly defrosting a frost formed at cooling unit 13 except evaporator 131 by means of making air in the refrigerating container pass through said evaporator, is begun by turning off solenoid switches 32 and 33 and turning on solenoid switches 34 and 35. Step 50 judges whether the air pressing through has lasted 30 seconds. If the air passing through has lasted 30 seconds, step 50 proceeds to step 51. While the air passing through has not lasted 30 seconds, step 50 flows back to step 49. At step 53, an air passing through with hot gas defrosting, i.e. , mainly defrosting a frost formed at cooling unit 13 except evaporator 131 by means of making air in the refrigerating container pass through evaporator 131 and directly leading the discharged refrigerant gas to evaporator 131, is begun by turning on all solenoid switches 32, 33, 34 and 35. Step 54 compares Tf with 15°C. If Tf is equal or higher than 15°C, step 54 proceeds to step 51. While Tf is lower than 15°C, step 54 proceeds to step 55. Step 55 judges whether the air passing through with hot gas defrosting has lasted 30 seconds. If the air passing through with hot gas defrosting has lasted 30 seconds, step 55 proceeds to step 51. While the air passing through with hot gas defrosting has not lasted 30 seconds, step 55 proceeds to step 56. Step 56 judges whether pressure switch 22 turns off. If pressure switch 22 turns off, step 56 proceeds to step 51. While pressure switch 22 does not turn off, step 56 flows back to step 53. At step 51, a second draining i.e. , mainly draining the condensed water at the cooling unit 13 except evaporator 131, is begun by turning off solenoid switches 32, 33 and 34 and turning on solenoid switch 35. Step 52 judges whether the second draining is elapsed 4 minutes. If the second draining has not lasted 4 minutes, step 52 flows back to step 51. While the second draining has lasted 4 minutes, step 52 proceeds to end step 57. Accordingly, whole procedure is terminated. Furthermore, the auto defrosting mode includes two types of defrosting. One is a defrosting in cyclic and another is a defrosting with a frost detector. The defrosting in cyclic type begins to defrost on the condition that 2 hours more are elapsed after accessory switch 36 turning on or after all steps of defrosting a frost formed at cooling unit 13 being terminated, and Tf is lower than a set temperature of air in the refrigerating container Tc added 5°C. On the other hand , on the condition that 10 minutes more are elapsed after accessory switch 36 turning on or after all steps of defrosting a frost formed at cooling until 13 being terminated, Tf is lower than 0°C, and To i.e. , temperature of leaving air from evaporator 131 is lower than temperature of air in the refrigerating container by 7K, the defrosting with a frost detector type begins to defrost independently of above-mentioned conditions of the defrosting in cycle type. When the manual defrosting mode is switched to the auto defrosting mode, defrosting a frost formed at cooling unit 13 is automatically begun by above-mentioned conditions being satisfied. In this manual defrosting mode, micro computer 31 neglects a defrosting signal generated by turning on a defrosting switch (not shown) during defrosting a frost formed at cooling unit 13 .

Claims: A method of defrosting the frost formed at the cooling unit (13) of a refrigerating circuit (100) used for a refrigerator car, the refrigerator circuit (100) including a compressor (11), a condenser (12) condensing refrigerant gas discharged from said compressor (11), an expansion valve (17) expanding condensed refrigerant flowing from said condenser (12), said cooling unit (13) having an evaporator (131) and a fan (132) disposed within a refrigerating container, and a valve member (19) for selectively switching the course of flow of refrigerant gas discharged from said compressor (11) in order to directly lead said discharged refrigerant gas to said evaporator (131), said fan (132) causing the air in said refrigerating container pass through said evaporator (131), the method comprising a first step mainly defrosting the frost formed at the outer surface of said evaporator (131) by means of directly leading said discharged refrigerant gas to said evaporator (131) so as to heat said evaporator (131) characterized by a second step mainly defrosting the frost formed at said cooling unit (13) except at said evaporator (131) by means of causing the air in said refrigerating container pass through said heated evaporator (131) by said fan so as to absorb heat from said heated evaporator, said second step being initiated when said first step is terminated. The method of claim 1, wherein said first step is initiated when a signal of defrosting the frost formed at said cooling unit (13) is generated and being terminated either when a predetermined time of operation of said first step is elapsed or, if this occurs earlier, when the temperature of the outer surface of said evaporator (131) reaches a predetermined value, or when the pressure in an outlet portion of said evaporator (131) reaches a predetermined value, said second step being terminated when a predetermined time of operation of said second step has elapsed. A method of defrosting the frost formed at the cooling unit (13) of a refrigerating circuit (100) used for a refrigerator car, the refrigerating circuit (100) including a compressor (11), a condenser (12) condensing refrigerant gas discharged from said compressor (11), an expansion valve (17) expanding condensed refrigerant flowing from said condenser (12), said cooling unit (13) having an evaporator (131) and a fan (132) disposed within a refrigerating container, and a valve member (19) for selectively switching the course of flow of refrigerant gas discharged from said compressor (11) in order to directly lead said discharged refrigerant gas to said evaporator (131) so as to heat said evaporator (131), said fan (132) causing the air in said refrigerating container pass through said evaporator (131), the method comprising a first step mainly defrosting the frost formed at the outer surface of said evaporator (131) by means of directly leading said discharged refrigerant gas to said evaporator (131) characterized by a second step mainly defrosting the frost formed at said cooling unit (13) except at said evaporator (131) by means of causing the air in said refrigerating container pass through said heated evaporator (131) by said fan so as to absorb heat from said heated evaporator simultaneously with directly leading said discharged refrigerant gas to said evaporator so as to heat said evaporator, said second step being initiated when said first step is terminated. The method of claim 3, wherein said first step is initiated when a signal of defrosting the frost formed at said cooling unit (13) is generated, and being terminated either when a predetermined time of operation of said first step is elapsed or, if this occurs earlier,when the temperature of the outer surface of said evaporator (131) reaches a predetermined value or when the pressure in an outlet portion of said evaporator (131) reaches a predetermined value, said second step being initiated when said first step is terminated, said second step being terminated either when a predetermined time of operation of said second step is elapsed or, if this occurs earlier, when the temperature of the outer surface of said evaporator (131) reaches a predetermined value or when the pressure in an outlet portion of said evaporator (131) reaches a predetermined value. The method of claims 1 or 3, wherin said cooling unit comprises a casing in which said evaporator (131) is disposed, and a pipe member for draining the condensed water in said cooling unit (13) is disposed within the refrigerating container, said second step mainly defrosting the frost formed at said casing, said fan (132) and said pipe member by means of causing the air in said refrigerating container pass through said heated evaporator (131) so as to absorb heat from said heated evaporator. The method of one of claims 1 through 5, characterized in that said fan (132) sucks air through said evaporator (131). The method of one of claims 1 through 6, characterized in that the method is applied to a refrigerating system in which said valve member (19) is a solenoid valve (19).

Inventors: AKIIKE SHIGERU, RIKUKAWA YUUJI, AKIIKE, SHIGERU, RIKUKAWA, YUUJI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1989
Main classification: F25D21
IPC codes: F25D21, F25B47