Refrigeration unit for land transportation and operation control method of refrigeration unit for land transportation

Abstract

 An operation control method of a refrigeration unit for land transportation in which a plurality of evaporator units are parallelly connected into a refrigerant circuit (10) for circulating a refrigerant by a compressor (11) driven by a dedicated drive source, and a plurality of different transport temperatures can be respectively created for a plurality of freezing sections which are distributedly arranged with the plurality of evaporator units, comprising: employing throttle mechanisms whose opening degrees are adjustable, as well as providing a low pressure sensor (18) which detects the evaporating pressure of the refrigerant from the evaporator units, for the refrigerant circuit (10); and performing a priority control for lower setpoint temperature which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, when a plurality of operation requests have been made for a plurality of the evaporator units, during a various temperature cooling operation having different setpoint temperatures for the respective freezing sections.

Description

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

[0001] The present invention relates to a refrigeration unit for land transportation to be applied to a loading chamber of a truck, and an operation control method of such a refrigeration unit for land transportation.

[0002] This application is based on Japanese Patent Application No. 2007-337112, the content of which is incorporated herein by reference.

2. DESCRIPTION OF RELATED ART

[0003] Refrigeration units for land transportation to be installed in loading chambers (vans) of trucks for cooling the inside can be classified into: a direct driven type which uses the output from the vehicle engine to drive the compressor for compressing a refrigerant; and a sub engine type comprising a dedicated drive source (such as an engine or an electric motor).

[0004] In addition, there is another type of refrigeration unit for land transportation, a multi-type in which a plurality of (usually, two or three) evaporator units are connected to one compressor so that different transport temperatures can be respectively created for a plurality of compartments.

[0005] In such a multi-type refrigeration unit for land transportation, temperature differential type automatic expansion valves (hereunder, thermal expansion valves) have been widely used as throttle mechanisms. In addition, when it comes to a multi-type, a conventional refrigeration unit for land transportation has a structure in which a plurality of evaporator units with thermal expansion valves are parallelly connected to one compressor. The distribution of the refrigerant for respective evaporator units depends on the operations of these thermal expansion valves.

[0006] Therefore, in a simultaneous operation system which simultaneously operates all evaporator units receiving the operation request, if the setpoint temperatures are largely different for respective compartments, the endothermic amount of the evaporator unit installed in a compartment having a higher setpoint temperature becomes dominant, and it becomes difficult to save the necessary capacity for evaporator unit(s) having lower setpoint temperature(s). Accordingly, a solution for this problem is required, and a switching operation system comprising one operating evaporator unit which sequentially switches the unit to be operated, has been publicly known.

[0007] Besides, another air conditioner for vehicle, called a dual air conditioner, has been known, in which: a pair of evaporators are parallelly connected into a refrigerant circuit which receives a refrigerant supplied from a compressor that is driven by the vehicle engine; and electromagnetic valves and thermal expansion valves are arranged on the refrigerant inlet sides of both evaporators (for example, refer to Japanese Unexamined Patent Application, Publication No. 2001-322423).

[0008] Further, a refrigerating system has also been known which is applicable to a plurality of low temperature showcases having different chamber cooling temperatures, so that effective energy-saving operation can be achieved (for example, refer to Japanese Unexamined Patent Application, Publication No. 2005-315495).

[0009] Incidentally, such a multi-type refrigeration unit for land transportation features a very wide range of the requested setpoint temperature, such as about -30°C to +30°C. That is to say, a refrigeration unit for transportation is used for a wide range of setpoint temperature, including for frozen foods to be transported at a cooled temperature of about -30°C, for chilled foods to be transported at a retained temperature of about -1°C to 5°C, and for products to be transported at a retained chamber temperature of about 30°C. In the case of a general air conditioner, the setpoint temperature range is about 20°C to 30°C.

[0010] As described above, since the setpoint temperature range of refrigeration units for land transportation is wide over low temperatures, evaporators are to be inevitably used in frosted conditions. Accordingly, the design and operation control have to be done in consideration of frosting. In particular, in the case of the multi-type, the presence/absence of frost and the amount of frost vary depending on each compartment. Therefore, it is necessary to minimize the influence of defrosting against the temperature.

[0011] In addition, the loading chamber of the multi-type often employs a movable partition panel which can change the partition position according to the load volume, and a flap-type partition panel toward the ceiling for use without the partition. Therefore, the airtightness with such a partition panel becomes insufficient, and thus the heat insulation property is lowered to thereby increase the temperature interference between compartments having different setpoint temperatures.

[0012] Moreover, in such a refrigeration unit for land transportation, the door of the loading chamber has to be opened/closed during delivery, and therefore the temperature of the inside air frequently and rapidly changes. That is to say, in the case of a refrigeration unit for land transportation, it means that the required cooling capacity is frequently and rapidly changed due to the opening/closing operation of the door. Accordingly, the anticipated situation is that, even after the temperature has been converged at the setpoint temperature for each compartment, the inside temperature frequently diverges from the setpoint temperature due to the opening/closing operation of the door, or the like. The capacity distribution control capable of manipulating such a situation is desired.

[0013] In addition, in the case of a refrigeration unit for land transportation, the refrigeration load largely varies depending on the cargo. That is to say, the heat load without a cargo is approximately in proportion to the inner volume of the chamber; whereas, if a cargo is placed therein, the heat load is largely influenced by the thermal capacity and the self heat of the cargo (for example, heat of respiration from vegetables). The influence of the thermal capacity of the cargo can be avoided by a recommended precooling treatment before loading the cargo.

[0014] Further, in the case of a refrigeration unit for land transportation, the condenser air volume is changed by the travelling speed of the vehicle, and thus the operational status is momentarily changed. Accordingly, when the outside air temperature is high, the traveling wind improves the balance of the refrigerating cycle; whereas, when the outside air temperature is low, the differential pressure between high and low pressures can not be achieved due to overcooling, and a risk may occur in which a necessary amount of the refrigerant for circulation can not be saved.

[0015] As described above, the multi-type refrigeration unit for land transportation has a specific problem in that when the setpoint temperatures are largely different for respective freezing sections, the endothermic amount of the evaporator having a higher setpoint temperature becomes dominant; that is to say, a large amount of the refrigerant is evaporated at the higher setpoint temperature side, and it becomes difficult for the refrigerant to flow into the low temperature side, as a result of which the necessary capacity can be hardly saved for the lower setpoint temperature side. However, the switching system which controls the operation while sequentially switching the evaporator unit to be operated, has a problem of cost increment, since larger evaporator units have to be selected in consideration of the operation factor for its on/off control. Further, since the temperature fluctuates due to the on/off operation, highly accurate temperature control is difficult.

BRIEF SUMMARY OF THE INVENTION

[0016] From such situations, there is a demand for: a refrigeration unit for land transportation which enables inexpensive, user-friendly, and highly accurate temperature control without causing the occurrence of insufficient capacity in a freezing section having lower setpoint temperature, even if the setpoint temperatures are largely different between freezing sections; and an operation control method thereof.

[0017] The present invention takes the abovementioned situations into consideration with an object of providing: a refrigeration unit for land transportation which enables inexpensive, user-friendly, and highly accurate temperature control while reducing the risk of cooling failure in a freezing section having lower setpoint temperature; and an operation control method thereof.

[0018] In order to achieve the above object, the present invention provides the following solutions.

[0019] A first aspect of the present invention is an operation control method of a refrigeration unit for land transportation in which a plurality of evaporator units are parallelly connected into a refrigerant circuit for circulating a refrigerant by a compressor driven by a dedicated drive source, and a plurality of different transport temperatures can be respectively created for a plurality of freezing sections which are distributedly arranged with the plurality of evaporator units, comprising: employing throttle mechanisms whose opening degrees are adjustable, as well as providing a low pressure sensor which detects the evaporating pressure of the refrigerant from the evaporator units, for the refrigerant circuit; and performing a priority control for lower setpoint temperature which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, when a plurality of operation requests have been made for a plurality of the evaporator units, during a various temperature cooling operation having different setpoint temperatures for the respective freezing sections.

[0020] According to the first aspect mentioned above, for the refrigerant circuit are employed the throttle mechanisms whose opening degrees are adjustable, and is provided a low pressure sensor which detects the evaporating pressure of the refrigerant from the evaporator units; and a priority control for lower setpoint temperature is performed, which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, when a plurality of operation requests have been made for a plurality of the evaporator units, during a various temperature cooling operation having different setpoint temperatures for the respective freezing sections. Therefore, upon execution of the cooling operation having different setpoint temperatures, the freezing capacity for the higher setpoint temperature side can be suppressed so as to save the freezing capacity for the lower setpoint temperature side by the operation control which preferentially distributes the refrigerant to the lower setpoint temperature side.

[0021] In the above control method, the priority control for lower setpoint temperature is preferably selected in a case where the following conditions are all satisfied: a condition where a difference in the setpoint temperature (Tset) between respective freezing sections is greater than a predetermined value (α); a condition where an inside temperature (Tair) of the lower setpoint temperature side is lower than the setpoint temperature (Tset) of the higher setpoint temperature side; and a condition where the rate of change in the inside temperature (ΔTair) of the lower setpoint temperature side is smaller than a predetermined value (β). In this case, the difference in the setpoint temperature (Tset) between respective freezing sections may be the absolute value of the temperature difference (ΔTset).

[0022] In such a control method, it can be determined that the refrigerant distribution amount to the lower setpoint temperature side is small and the freezing capacity thereof is insufficient, in the situation that: the difference in the setpoint temperature between respective freezing sections is large; the inside temperature of the lower setpoint temperature side is lower than the setpoint temperature of the higher setpoint temperature side; and the rate of change in the inside temperature of the lower setpoint temperature side is smaller than a predetermined value. Accordingly, by selecting the priority control for lower setpoint temperature which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, the refrigerant shortage can be solved and the freezing capacity can be retained.

[0023] In the first aspect mentioned above, preferably, the opening degree of the throttle mechanism of the evaporator unit having lower setpoint temperature is controlled by controlling the superheat degree at the outlet of the evaporator, and the opening degree of the throttle mechanism of the evaporator unit having higher setpoint temperature is controlled so as not to exceed a maximum evaporating pressure, in the priority control for lower setpoint temperature.

[0024] In addition, in the first aspect mentioned above, a superheat degree at an outlet of the evaporators may be controlled with reference to values detected by the low pressure sensor and an evaporator outlet refrigerant thermometer, in the priority control for lower setpoint temperature.

[0025] Moreover, in the first aspect mentioned above, during a cooling operation having approximately same setpoint temperatures for freezing sections, a priority control for total freezing capacity is preferably performed in which respective evaporator units individually control their superheat degrees.

[0026] A second aspect of the present invention is a refrigeration unit for land transportation in which a plurality of evaporator units are parallelly connected into a refrigerant circuit for circulating a refrigerant by a compressor driven by a dedicated drive source, and a plurality of different transport temperatures can be respectively created for a plurality of freezing sections which are distributedly arranged with the plurality of evaporator units, comprising: throttle mechanisms whose opening degrees are adjustable, and which are provided in the refrigerant circuit; a low pressure sensor which detects the evaporating pressure of the refrigerant from the evaporator units: and a controller which performs a priority control for lower setpoint temperature by the above operation control method, during a various temperature cooling operation having different setpoint temperatures for the respective freezing sections.

[0027] According to such a refrigeration unit for land transportation, there are provided the throttle mechanisms whose opening degrees are adjustable, and which are provided in the refrigerant circuit; the low pressure sensor which detects the evaporating pressure of the refrigerant from the evaporator units: and the controller which performs a priority control for lower setpoint temperature by the above operation control method, during a various temperature cooling operation having different setpoint temperatures for respective freezing sections. Therefore, during a various temperature cooling operation having different setpoint temperatures for respective freezing sections, a priority control for lower setpoint temperature is performed, in which the opening degrees of the throttle mechanisms are narrowed to perform the operation to achieve an evaporating pressure which can provide the freezing capacity necessary for the lower setpoint temperature side. By so doing, the operation control which preferentially distributes the refrigerant to the lower setpoint temperature side can be achieved while suppressing the freezing capacity on the higher setpoint temperature side.

[0028] According to the present invention mentioned above, in a multi-type refrigeration unit for land transportation and an control method of such a refrigeration unit for land transportation, inexpensive, user-friendly, and highly accurate temperature control becomes possible without causing the occurrence of insufficient capacity in a freezing section having lower setpoint temperature, even if the setpoint temperatures are largely different between freezing sections.

[0029] Accordingly, the capacity control can be achieved preferentially for the lower setpoint temperature side having greater temperature difference from the outside air and larger intrusive heat. Therefore, the risk caused by insufficient cooling capacity can be greatly reduced, and the time to reach the setpoint temperature of the lower setpoint temperature side can be shortened.

[0030] Further, different temperature transportation having extremely different setpoint temperatures becomes possible, which thereby provides an effect of improving the user-friendliness.

[0031] In addition, since the cooling capacity for each freezing section can be controlled, highly accurate temperature control becomes possible.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0032] 

FIG. 1 is a system diagram showing an example of the configuration of a refrigerant circuit, as one embodiment of the refrigeration unit for land transportation according to the present invention.

FIG. 2 shows an example of the arrangement of the refrigeration unit for land transportation installed in a loading chamber of a truck.

FIG. 3 is a flowchart showing an example of the selective operation control for executing the refrigerant distribution control that has been selected from "Refrigerant distribution control I" and "Refrigerant distribution control II" according to the situation, in the refrigeration unit for land transportation of the present invention.

FIG. 4 is a flowchart showing an example of the operation control of the "Refrigerant distribution control I".

FIG. 5A is a flowchart showing an example of the operation control of the "Refrigerant distribution control II".

FIG. 5B is a flowchart showing an example of the operation control of the "Refrigerant distribution control II".

FIG. 6 shows the inflow and outflow of heat in simulation.

FIG. 7A shows the simulation results during pull-down operation, under conventional control.

FIG. 7B shows the simulation results during pull-down operation, under selective control of the present invention.

FIG. 8A shows the simulation results while the door was opened/closed for unloading, under conventional control.

FIG. 8B shows the simulation results while the door was opened/closed for unloading, under selective control of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereunder is a description of one embodiment of a refrigeration unit for land transportation, and an operation control method of such a unit for land transportation according to the present invention, with reference to drawings.

[0034] FIG. 1 is a system diagram showing an example of the configuration of a refrigerant circuit of the refrigeration unit for land transportation. FIG. 2 shows an example of the arrangement of the refrigeration unit for land transportation installed in a loading chamber of a truck.

[0035] The refrigeration unit for land transportation shown in FIG. 1 and FIG. 2 is installed in a loading chamber (van) mounted on a loading platform of a vehicle such as a truck, is capable of cooling a plurality of partitioned freezing sections at different temperatures inside the loading chamber, and thus is called a multi-type.

[0036] As shown in FIG. 2, on the loading platform of the truck 1 is mounted a loading chamber 2 which forms a cooling space. The inside of this loading chamber 2 is provided with a partition wall 3 to be thereby divided into two freezing sections consisting of a first loading chamber 2A and a second loading chamber 2B.

[0037] The refrigeration unit for land transportation comprises, for example: a condensing unit 4 installed underneath the loading platform of the truck 1, or the like; and a couple of evaporator units 5A and 5B installed for respective freezing sections. In the illustrated example, the evaporator unit 5A is installed on an appropriate upper part in the first loading chamber 2A, and the evaporator unit 5B is installed on an appropriate upper part in the second loading chamber 2B.

[0038] As shown in FIG. 2, the aforementioned refrigeration unit for land transportation comprises a refrigerant circuit 10 capable of cooling the first loading chamber 2A and the second loading chamber 2B at different temperatures. This refrigerant circuit 10 is configured to cool the freezing sections in the loading chamber 2 at desired temperatures, by means of circulation of a refrigerant which is sent out from a compressor 11 and passes through heat exchangers and the like while repeating state changes within a closed circuit.

[0039] The refrigerant circuit 10 forms a closed circuit for circulating the refrigerant, through connection between the compressor 11, a condenser 12, a first electronic expansion valve 13A, and a first evaporator 14A, via a refrigerant pipe 15.

[0040] In addition, this refrigerant circuit 10 is provided with a refrigerant branch pipe 16 which is branched from a downstream side of the condenser 12, is connected to a downstream side of the first evaporator 14A, and is arranged in parallel with the refrigerant pipe 15 provided with the first electronic expansion valve 13A and a first evaporator 14A. This refrigerant branch pipe 16 is provided with the second electronic expansion valve 13B and a second evaporator 14B. That is to say, the second electronic expansion valve 13B and the second evaporator 14B are arranged in parallel with the first electronic expansion valve 13A and the first evaporator 14A.

[0041] Moreover, a first thermistor 17A is a thermometer which is provided in a vicinity of the outlet of the first evaporator 14A, to detect the temperature of the refrigerant at the outlet. A second thermistor 17B is a thermometer which is provided in a vicinity of the outlet of the second evaporator 14B, to detect the temperature of the refrigerant at the outlet. That is to say, the first thermistor 17A and the second thermistor 17B serve as evaporator outlet refrigerant thermometers which can detect the superheat degrees of the refrigerant at the outlets of the evaporators.

[0042] Further, a low pressure sensor 18 is a pressure sensor which is provided at a downstream side of the first evaporator 14A and the second evaporator 14B to measure the evaporating pressure from both evaporators.

[0043] The compressor 11 comprises a dedicated drive source (such as an engine or an electric motor) independent of the vehicle engine. Such a refrigeration unit for land transportation is called a sub engine type. Unlike a direct driven type which uses the output from the vehicle engine, such a sub engine type refrigeration unit for land transportation has an advantage in which the operation of the compressor 11 affecting the cooling capacity is not influenced by the vehicle engine the rotation frequency of which is frequently changed according to the running state of the vehicle.

[0044] The condenser 12 is a heat exchanger (radiator) which condenses the refrigerant by exchanging the high temperature and high pressure gaseous refrigerant supplied from the compressor 11 with the outside air.

[0045] The first electronic expansion valve 13A is a throttle mechanism provided at an upstream side of the first evaporator 14A, and has a function of lowering the pressure and the temperature of the refrigerant by rapidly and adiabatically expanding the high temperature and high pressure refrigerant that has been condensed (liquefied) through the condenser 12. The electronic expansion valve used herein is a throttle mechanism whose opening degree is adjustable.

[0046] In addition, the second electronic expansion valve 13B is a throttle mechanism provided at an upstream side of the second evaporator 14B, and has the same function as that of the first electronic expansion valve 13A.

[0047] The first evaporator 14A is a heat exchanger (heat absorber) which is provided in the freezing section of the first loading chamber 2A, and evaporates the refrigerant by exchanging the liquid refrigerant with the air inside the loading chamber. That is to say, it has a function of cooling the air inside the first loading chamber 2A by drawing the evaporation heat when the refrigerant is being evaporated.

[0048] In addition, the second evaporator 14B is a heat exchanger provided in the freezing section of the second loading chamber 2B, and has the same function as that of the second evaporator 14A.

[0049] The first evaporator 14A and the second evaporator 14B respectively comprise a fun (not shown) for circulating the air in the first loading chamber 2A and the second loading chamber 2B.

[0050] The first thermistor 17A is a thermometer which detects the temperature of the refrigerant at the outlet of the first evaporator 14A. In the same manner, the second thermistor 17B is a thermometer which detects the temperature of the refrigerant at the outlet of the second evaporator 14B.

[0051] The low pressure sensor 18 is a pressure sensor which detects the pressure of the low pressure refrigerant circulating through the refrigerant circuit 10. That is to say, the low pressure sensor 18 is a pressure sensor which detects the pressure of the gaseous refrigerant to be sucked and compressed by the compressor 11.

[0052] In thus configured refrigerant circuit 10, the compressor 11, the condenser 12, and a controller (not shown) serve as the main components of the condensing unit 4. Moreover, the first electronic expansion valve 13A, the first evaporator 14A, the first thermistor 17A, and the like serve as the main components of the evaporator unit 5A. The second electronic expansion valve 13B, the second evaporator 14B, the second thermistor 17B, and the like serve as the main components of the evaporator unit 5B.

[0053] In addition, the controller in the condensing unit 4 executes the operation control of the compressor 11, the opening degree control of the first electronic expansion valve 13A and the second electronic expansion valve 13B, and the like, according to predetermined control flows, since various operating conditions such as the setpoint temperature set by the user, the temperatures detected by the first thermistor 17A and the second thermistor 17B, and the value detected by the low pressure sensor 18 are input therein.

[0054] Hereunder is a description of the operation control in the controller which selectively switches the refrigerant distribution control according to the situation; that is to say, the selective operation control for selecting an optimum refrigerant distribution control according to the situation, between "Refrigerant distribution control I" in which respective evaporator units individually control the superheat degrees, and "Refrigerant distribution control II" which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, with reference to the flowcharts of FIG. 3 to FIG. 5B.

[0055] The selective operation control to be described herein relates to an operation control method of a refrigeration unit for land transportation in which the evaporator units 5A and 5B are parallelly connected into the refrigerant circuit 10 for circulating the refrigerant by a compressor 11 driven by a dedicated drive source, and different transport temperatures can be respectively created for freezing sections (first loading chamber 2A and second loading chamber 2B) which are distributedly arranged with two evaporator units 5A and 5B, comprising: employing the electronic expansion valves 13A and 13B whose opening degrees are adjustable, as well as providing the low pressure sensor 18 which detects the evaporating pressure of the refrigerant from the evaporator units 5A and 5B, for the refrigerant circuit 10.

[0056] In addition, the operation control also performs a priority control for lower setpoint temperature, in which, during a various temperature cooling operation having different setpoint temperatures for the first loading chamber 2A and the second loading chamber 2B, that is to say, a various temperature cooling operation for respectively creating different transport temperatures for freezing sections, the opening degrees of the first electronic expansion valve 13A and the second electronic expansion valve 13B are narrowed to perform the operation to achieve an evaporating pressure which can provide the freezing capacity necessary for the freezing section having lower setpoint temperature.

[0057] FIG. 3 is a flowchart showing an example of the selective operation control for selecting an optimum control system according to the situation, between two preset refrigerant distribution controls: "Refrigerant distribution control I" and "Refrigerant distribution control II".

[0058] In addition, FIG. 4 is a flowchart showing an example of the operation control of the "Refrigerant distribution control I". FIG. 5A and FIG. 5B are flowcharts showing an example of the operation control of the "Refrigerant distribution control II".

[0059] In the selective control of FIG. 3, firstly, the control is initiated by the "Start" in Step S1. Then, the flow goes to the next Step S2 to determine whether or not "Control mode is set". That is to say, in this Step S2, it is determined whether either one of the control modes has been already set or not, between: "Refrigerant distribution control I" in which two evaporator units 5A and 5B individually control the superheat degrees, and "Refrigerant distribution control II" which preferentially distributes the refrigerant to the lower setpoint temperature side.

[0060] In the determination of Step S2, if it is determined that "Control mode is set" is NO since any control mode has not been set yet, then the flow goes to the Step M1 that will be described later, to execute the "Refrigerant distribution control I". That is to say, the "Refrigerant distribution control I" is meant to be selected in the initial setting of the selective control.

[0061] However, by the determination of Step S2, if it is determined that "Control mode is set" is YES, then the flow goes to the next Step S3 to determine whether or not "Thermo-ON request is made" in the evaporator units 5A and 5B.

[0062] In Step S3, if it is determined that "Thermo-ON request is made" is YES since the thermo-ON request has been made for at least either one of the evaporator units 5A and 5B, then the flow goes to the next Step S4 to determine whether or not "A plurality of thermo-ON requests are made". That is to say, if the determination of Step S3 is YES, it is determined whether or not thermo-ON requests have been made for both of the evaporator units 5A and 5B.

[0063] On the other hand, in Step S3, if it is determined that "Thermo-ON request is made" is NO, the flow goes to the next Step S10 to determine whether or not the control mode has been set to the "Refrigerant distribution control II". As a result, if it is determined YES showing that the control mode has been set to the "Refrigerant distribution control II", the flow goes to the Step M1 that will be described later, to thereby switch the control mode to the initial setting of "Refrigerant distribution control I". If it is determined NO showing that the control mode has not been set to the "Refrigerant distribution control II", then it can be determined that no further selective control is needed since the control mode is in the initial setting state.
Accordingly, the flow goes to the "End" in Step S14 to terminate the control.

[0064] In Step S4, if it is determined that "A plurality of thermo-ON requests are made" is YES, the flow goes to the next Step S5 to determine whether or not ΔTset, which means the absolute value (|TsetA - TsetB|) of the setpoint temperature difference between the freezing sections (chamber A and chamber B) installed with the evaporator units 5A and 5B, is greater than a predetermined value α; namely, "|TsetA - TsetB| > α". The term "TsetA" used herein refers to the setpoint temperature for the first loading chamber 2A, while the term "TsetB" refers to the setpoint temperature for the second loading chamber 2B.

[0065] By the determination of Step S5, if it is determined YES showing that the absolute value ΔTset of the temperature difference is greater than the predetermined value α, the flow goes to the next Step S6 to determine whether "TsetA ≤ TsetB" is satisfied or not, that is to say, whether or not the setpoint temperature TsetA is equal to or lower than the setpoint temperature TsetB. In other words, it is determined which freezing section has the lower setpoint temperature, between the first loading chamber 2A and the second loading chamber 2B.

[0066] However, by the determination of Step S5, if it is determined NO showing that the absolute value ΔTset of the temperature difference is equal to or lower than the predetermined value α, then the setpoint temperature difference is small between freezing sections, and therefore the flow goes to the Step M1 that will be described later, to execute the "Refrigerant distribution control I".

[0067] In Step S6, if it is determined YES showing that the setpoint temperature TsetA is equal to or lower than the setpoint temperature TsetB, the flow goes to the next Step S7 to determine whether "TairA < TsetB" is satisfied or not, that is to say, whether or not the inside temperature TairA of the first loading chamber 2A is lower than the setpoint temperature TsetB of the second loading chamber 2B. However, if it is determined NO showing that the setpoint temperature TsetA is higher than the setpoint temperature TsetB, the flow goes to the Step S11 that will be described later to determine whether "TairB < TsetA" is satisfied or not.

[0068] In Step S7, if it is determined YES showing that the inside temperature TairA of the first loading chamber 2A is lower than the setpoint temperature TsetB of the second loading chamber 2B, the flow goes to the next Step S8 to determine whether or not the control mode has been set to the "Refrigerant distribution control II". However, if it is determined NO showing that the inside temperature TairA of the first loading chamber 2A is equal to or higher than the setpoint temperature TsetB of the second loading chamber 2B, the flow goes to the Step M1 that will be described later, to execute the "Refrigerant distribution control I".

[0069] In Step S8, it is determined whether or not the control mode has been set to the "Refrigerant distribution control II". As a result, if it is determined YES showing that the control mode has been set to the "Refrigerant distribution control II", it means that the control mode has been set to the desired control mode and thus it can be determined that no further selective control is needed. Accordingly, the flow goes to the "End" in Step S14 to terminate the control.

[0070] On the other hand, in Step S8, if it is determined NO showing that the control mode has not been set to the "Refrigerant distribution control II", the flow goes to the next Step S9 to determine whether "ΔTairA ≥ β" is satisfied or nor, that is to say, whether or not the rate of change in the inside temperature ΔTairA of the first loading chamber 2A is equal to or greater than a predetermined value β.

[0071] In the determination of Step S9, if it is determined YES showing that the rate of change in the inside temperature ΔTairA of the first loading chamber 2A is equal to or greater than the predetermined value β, it means that the first loading chamber 2A has a sufficient cooling capacity and thus it can be determined that no change from the current operation control is needed. Accordingly, the flow goes to the "End" in Step S14 to terminate the control.

[0072] On the other hand, in the determination of Step S9, if it is determined NO showing that the rate of change in the inside temperature ΔTairA of the first loading chamber 2A, is lower than the predetermined value β, then it can be determined that the cooling capacity is insufficient. Therefore, the flow goes to the next Step M2 to execute the "Refrigerant distribution control II".

[0073] Incidentally, in the above Step S6, if it is determined NO showing that the setpoint temperature TsetA of the first loading chamber 2A is equal to or higher than the setpoint temperature TsetB of the second loading chamber 2B, the flow goes to the next Step S11 to determine whether "TairB < TsetA" is satisfied or not, that is to say, whether or not the inside temperature TairB of the second loading chamber 2B is lower than the setpoint temperature TsetA of the first loading chamber 2A. As a result, if it is determined YES showing that the inside temperature TairB of the second loading chamber 2B is lower than the setpoint temperature TsetA of the first loading chamber 2A, the flow goes to the next Step S12 to determine whether or not the control mode has been set to the "Refrigerant distribution control II".

[0074] In Step S12, it is determined whether or not the control mode has been set to the "Refrigerant distribution control II". As a result, if it is determined YES showing that the control mode has been set to the "Refrigerant distribution control II", it means that the control mode has been set to the desired control mode and thus it can be determined that no further selective control is needed. Accordingly, the flow goes to the "End" in Step S14 to terminate the control.

[0075] On the other hand, in Step S12, if it is determined NO showing that the control mode has not been set to the "Refrigerant distribution control II", the flow goes to the next Step S13 determine whether "ΔTairB ≥ β" is satisfied or nor, that is to say, whether or not the rate of change in the inside temperature ΔTairB of the second loading chamber 2B, is equal to or greater than a predetermined value β.

[0076] In the determination of Step S13, if it is determined YES showing that the rate of change in the inside temperature ΔTairB of the second loading chamber 2B is equal to or greater than the predetermined value β, it means that the second loading chamber 2B has a sufficient cooling capacity and thus it can be determined that no change from the current operation control is needed. Accordingly, the flow goes to the "End" in Step S14 to terminate the control.

[0077] On the other hand, in the determination of Step S13, if it is determined NO showing that the rate of change in the inside temperature ΔTairB of the second loading chamber 2B is lower than the predetermined value β, then it can be determined that the cooling capacity is insufficient. Therefore, the flow goes to the next Step M2 to execute the "Refrigerant distribution control II".

[0078] Next is a description of the "Refrigerant distribution control I" of the Step M1 mentioned above, with reference to the flowchart of FIG. 4. The control flow described hereinbelow exclusively shows parts related to the opening degree control of electronic expansion valves.

[0079] In this control, firstly the opening degree control as for the expansion valve of the first loading chamber 2A is executed from Step S21 to S29, followed by execution of the same opening degree control as for the expansion valve of the first loading chamber 2B. In the flowcharts of FIG. 4, FIG. 5A, and FIG. 5B, the first loading chamber 2A is denoted by chamber A and the second loading chamber 2B is denoted by chamber B.

[0080] Regarding the opening degree control of the expansion valve of the first loading chamber 2A, in the first Step S21, it is determined whether or not "Chamber A cooling thermo is ON". As a result, if it is determined YES showing that the first loading chamber 2A is in the thermo-ON state, the flow goes to the next Step S22 to determine whether or not "Chamber A expansion valve is fully closed". If it is determined NO, the flow goes to the next Step S27 to determine whether or not "Chamber A expansion valve is fully closed".

[0081] By the determination of Step S22, if it is determined NO showing that the first electronic expansion valve 13A of the first loading chamber 2A is opened and not in the fully closed state, the flow goes to the next Step S23 to execute the "Calculation of chamber A evaporator outlet superheat degree". After such a calculation of the superheat degree at the outlet of the first evaporator 14A, the flow goes to the next Step S24 to execute the "Calculation of chamber A expansion valve opening degree". Thus calculated arithmetic setpoint opening degree of the first electronic expansion valve 13A means an opening degree which sets the superheat degree at the outlet of the first evaporator 14A to be within a predetermined control range (for example, the superheat degree would be about 3°C to 7°C).

[0082] After the arithmetic setpoint opening degree of the first electronic expansion valve 13A has been calculated in Step S24, the flow goes to the next Step S25 to determine whether or not "Change of chamber A expansion valve opening degree" should be made. That is to say, it is determined whether or not the opening degree needs to be changed from the current opening degree, upon comparison between the current opening degree of the first electronic expansion valve 13A and the arithmetic setpoint opening degree calculated in Step S24.

[0083] By the determination of Step S25, if it is determined YES showing that the opening degree of the first electronic expansion valve 13A needs to be changed, the flow goes to the next Step S26 to execute the "Change of chamber A expansion valve opening degree". That is to say, the opening degree of the first electronic expansion valve 13A is changed from the current opening degree to the arithmetic setpoint opening degree. However, if it is determined NO showing that the opening degree of the first electronic expansion valve 13A does not need to be changed, the flow goes to the opening degree control of the expansion valve of second loading chamber 2B that will be described later.

[0084] On the other hand, by the determination of Step S22, if it is determined YES showing that the first electronic expansion valve 13A of the first loading chamber 2A is in the fully closed state, the flow goes to the next Step S29 to execute the "Setting of chamber A expansion valve initial opening degree". Then, the flow goes to the opening degree control of the chamber B expansion valve that will be described later.

[0085] As a result of determination of the abovementioned Step S27 regarding whether or not "Chamber A expansion valve is fully closed", if it is determined NO showing that the first electronic expansion valve 13A is not fully closed, the flow goes to the next Step S28 to execute the operation of "Full closure of chamber A expansion valve". Accordingly, the first electronic expansion valve 13A is brought into the fully closed state, including the case where the determination is "Fully closed" in the Step S27, and the flow goes to the opening degree control of the chamber B expansion valve that will be described later.

[0086] Subsequently, the opening degree control of the expansion valve of the second loading chamber 2B is executed. This opening degree control of the expansion valve is substantially the same as that of the abovementioned opening degree control of the expansion valve from Step S21 to Step S29, and the control can be executed by replacing the first loading chamber 2A (chamber A) with the second loading chamber 2B (chamber B) in each control step.

[0087] By the execution of the "Refrigerant distribution control I" of Step M1 in this manner, the superheat degrees can be respectively and independently controlled by individual evaporator units 5A and 5B.

[0088] Next is a description of the "Refrigerant distribution control II" of the Step M2, with reference to the flowcharts of FIG. 5A and FIG. 5B. This control is to intensively control the opening degrees of the electronic expansion valve (first electronic expansion valve 13A and the second electronic expansion valve 13B) of the evaporator units 5A and 5B, to achieve an evaporating temperature which can provide a sufficient freezing capacity for the freezing section having lower inside temperature. That is to say, the "Refrigerant distribution control II" is a control in which the opening degrees of the first electronic expansion valve 13A and the second electronic expansion valve 13B are intentionally narrowed to perform the operation to achieve an evaporating pressure which can provide the freezing capacity necessary for the unit having lower setpoint temperature between two evaporator units 5A and 5B, upon execution of cooling operation having different setpoint temperatures.

[0089] In other words, the "Refrigerant distribution control II" is a priority control for lower setpoint temperature which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, when a plurality of operation requests have been made for a plurality of evaporator units, during a various temperature cooling operation having different setpoint temperatures for respective freezing sections, in a refrigerant circuit for which electronic expansion valves being throttle mechanisms whose opening degrees are adjustable, are employed, and a low pressure sensor which detects the evaporating pressure of the refrigerant from the evaporator units, is provided.

[0090] In this control, in the first Step S41, it is determined whether "TsetA < TsetB" is satisfied or not. That is to say, upon comparison between the setpoint temperature TsetA of the first loading chamber 2A and the setpoint temperature TsetB of the second loading chamber 2B, if it is determined YES showing that the setpoint temperature TsetA of the first loading chamber 2A is lower than the setpoint temperature TsetB of the second loading chamber 2B, the flow goes to the next Step S42. If it is determined NO showing that the setpoint temperature TsetA of the first loading chamber 2A is equal to or higher than the setpoint temperature TsetB of the second loading chamber 2B, the flow goes to Step S61 that will be described later.

[0091] The Step S42 is to determine whether or not the "Refrigerant distribution control I" has been performed last time. If the last refrigerant distribution control is the "Refrigerant distribution control I", it is determined YES and the flow goes to Step S71.

[0092] In Step S71, the "Setting of chamber A expansion valve initial opening degree /setting of chamber B expansion valve minimum opening degree" is executed. Then, the flow goes to the "End" in the final Step S56 to terminate the control.

[0093] On the other hand, if it is determined NO in the abovementioned Step S42, the flow goes to the next Step S43 to execute the "Calculation of maximum low pressure PLmax". This calculation is to calculate the allowable maximum low pressure PLmax for the low pressure of the compressor 11 (the pressure of the refrigerant at the suction side).

[0094] After the calculation of the maximum low pressure PLmax in Step S43, the flow goes to the next Step S45 to execute the "Calculation of chamber A evaporator outlet superheat degree". Once the superheat degree at the outlet of the first evaporator 14A has been obtained by this calculation, the flow goes to the next Step S46 to execute the "Calculation of chamber A expansion valve opening degree". Thus calculated arithmetic setpoint opening degree of the first electronic expansion valve 13A means an opening degree which sets the superheat degree at the outlet of the first evaporator 14A to be within a predetermined control range.

[0095] After the arithmetic setpoint opening degree of the first electronic expansion valve 13A has been calculated in this manner, the flow goes to the next Step S47 to determine whether or not the "Change of chamber A expansion valve opening degree" should be made. That is to say, it is determined whether or not the opening degree needs to be changed from the current opening degree, upon comparison between the current opening degree of the first electronic expansion valve 13A and the arithmetic setpoint opening degree calculated in Step S46.

[0096] By the determination of Step S47, if it is determined YES showing that the opening degree of the first electronic expansion valve 13A needs to be changed, the flow goes to the next Step S48 to execute the "Change of chamber A expansion valve opening degree". That is to say, the opening degree of the first electronic expansion valve 13A is changed from the current opening degree to the arithmetic setpoint opening degree. However, if it is determined NO showing that the opening degree of the first electronic expansion valve 13A does not need to be changed, the flow goes to the next Step S49 by bypassing Step S48. Even if the "Change of chamber A expansion valve opening degree" has been executed in Step S48, the flow also goes to the next Step S49 thereafter.

[0097] In Step S49, it is determined whether or not "Chamber A evaporator outlet superheat degree is within a suitable range". That is to say, it is determined whether or not the actual outlet superheat degree obtained from the temperature of the refrigerant at the outlet that has been detected by the first thermistor 17A, that is to say, the superheat degree of the refrigerant at the outlet of the first evaporator 14A, is within a predetermined suitable range.

[0098] As a result, if it is determined YES showing that the superheat degree from the first evaporator 14A is within the suitable range, the flow goes to the next Step S50 to determine whether or not the condition of "PL(n) < PLmax" is satisfied. However, if it is determined NO showing that the superheat degree from the first evaporator 14A is out of the suitable range, it can be determined that the refrigerant distribution adjustment to the chamber A evaporator, to which the refrigerant is supposed to be preferentially distributed, is not completed. Therefore, the flow goes to the Step S56 to terminate the control without executing the control of the chamber B expansion valve.

[0099] In Step S50, the maximum low pressure PLmax calculated in Step S43 is compared with the detected low pressure PL(n) which is the value detected by the low pressure sensor 18. As a result, if it is determined YES showing that the detected low pressure PL(n) is smaller than the maximum low pressure PLmax, it is possible to increase the current low pressure and therefore the flow goes to the next Step S51 to execute the control of the "Chamber B expansion valve opening degree + Y". That is to say, the control which adds Y to the opening degree of the second electronic expansion valve 13B of the second loading chamber 2B having a higher setpoint temperature, is executed, and then the flow goes to the "End" in the final Step S56 to terminate the control.

[0100] On the other hand, if it is determined NO showing that the detected low pressure PL(n) is equal to or greater than the maximum low pressure PLmax, the current low pressure exceeds the upper limit, and therefore the flow goes to the next Step S52 to execute the calculation of the opening degree by "Chamber B expansion valve opening degree - γ". That is to say, the calculation which subtracts a predetermined value γ from the current opening degree of the second electronic expansion valve 13B is executed (reduced opening degree), and then the flow goes to the next Step S53 to determine whether the "Chamber B expansion valve opening degree (reduced opening degree) < minimum opening degree" is satisfied or not. This determination is to determine whether or not any change can be made to further reduce the current opening degree, upon comparison between the reduced opening degree of the second electronic expansion valve 13B calculated in Step S52 and the allowable minimum opening degree.

[0101] In the determination of Step S53, if it is determined YES showing that the reduced opening degree is lower than the minimum opening degree, the opening degree of the electronic expansion valve 13B can not be reduced any further, and thus the flow goes to the next Step S54 to control to achieve the "Chamber B expansion valve opening degree = minimum opening degree". That is to say, the second expansion valve 13B is set to the minimum opening degree, and then the flow goes to the "End" in the final Step S56 to terminate the control.

[0102] On the other hand, in the determination of Step S53, if it is determined NO showing that the reduced opening degree is equal to or greater than the minimum opening degree, the flow goes to the next Step S55 to execute the control of the "Chamber B expansion valve opening degree - γ". That is to say, since it is possible to narrow the opening degree of the second expansion valve 13B, the opening degree is narrowed by γ to achieve the reduced opening degree calculated in Step S52. Then, the flow goes to the "End" in the final Step S56 to terminate the control.

[0103] Incidentally, in the above Step S41, if it is determined NO since the setpoint temperature TsetA of the chamber A is equal to or higher than the setpoint temperature TsetB of the chamber B, that is to say, if the setpoint temperature of the chamber B is lower than that of the chamber A, the flow goes to Step S61 to determine whether or not the "Refrigerant distribution control I" has been performed last time. This determination is the same as that of Step S42. If the last refrigerant distribution control is the "Refrigerant distribution control I", it is determined YES and the flow goes to Step S71. In Step S71, the "Setting of chamber A expansion valve initial opening degree / setting of chamber B expansion valve minimum opening degree" is executed. Then, the flow goes to the "End" in the final Step S56 to terminate the control.

[0104] On the other hand, if it is determined NO in the abovementioned Step S61, the flow goes to the next Step S62 to execute the "Calculation of maximum low pressure PLmax". The calculation of Step S62 is to calculate the allowable maximum low pressure PLmax for the low pressure of the compressor 11 (the pressure of the refrigerant at the suction side), and takes the same process as that of Step S43 mentioned above.

[0105] The following control can be executed likewise of the abovementioned Step S45 to Step S55 in which the opening degree control of the first electronic expansion valve 13A of the first loading chamber 2A has been preferentially performed, before the opening degree control of the second electronic expansion valve 13B of the second loading chamber 2B, by replacing the first loading chamber 2A (chamber A) with the second loading chamber 2B (chamber B) in Step S45 to Step S55, so that the opening degree control of the second electronic expansion valve 13B of the second loading chamber 2B is preferentially performed before the opening degree control of the first electronic expansion valve 13A of the first loading chamber 2A.

[0106] Execution of such a control of the "Refrigerant distribution control II" enables intensive control of the opening degrees of the electronic expansion valves 13A and 13B to achieve an evaporating temperature which can provide a sufficient freezing capacity for the evaporator unit having lower inside temperature, so that the refrigerant can be preferentially distributed to the evaporator unit having lower inside temperature. That is to say, to realize arbitrary control of the refrigerant circulation distribution to the evaporator units 5A and 5B, the unit takes the structure such that the electronic expansion valves 13A and 13B whose opening degrees are adjustable are employed as the throttle mechanisms, and further the low pressure sensor 18 for detecting the evaporating pressure from the evaporators 14A and 14B, is provided, so that, upon execution of a cooling operation having different setpoint temperatures, if performed, the opening degrees of the electronic expansion valves 13A and 13B can be intentionally narrowed to perform the operation to achieve an evaporating pressure which can provide a sufficient freezing capacity for the evaporator unit having lower inside temperature.

[0107] In the above cooling operation having different setpoint temperatures, in the evaporator unit 5A or 5B installed in the freezing section having higher setpoint temperature, the operation is started from the minimum opening degree or equivalent low opening degree as to the corresponding electronic expansion valve 13A or 13B, and the opening degrees of the electronic expansion valves are mutually controlled, so as to achieve an approximately equal balance between the freezing capacity and the heat load estimated from the changes in the inside temperature of each freezing section, and the like.

[0108] At this time, the low temperature sensor detection values detected by the first thermistor 17A and the second thermistor 17B (superheat degrees at the outlets of evaporators) are controlled to achieve the maximum low pressure (low pressure control value) PLmax which is determined so that the evaporator unit 5A or 5B having lower setpoint temperature can retain the freezing capacity.

[0109] Incidentally, hereunder is a description of results of delivery simulations regarding: the abovementioned selective operation control of the present invention which selectively switches between the "Refrigerant distribution control I" and the "Refrigerant distribution control II" according to the situation; and a conventional control which always performs the "Refrigerant distribution control I", with reference to FIG. 6 to FIG. 8.

[0110] In the refrigeration unit for land transportation shown in FIG. 6, the loading chamber 2 is divided into the first loading chamber 2A and the second loading chamber 2B by the partition wall 3. In the following simulation, the first loading chamber 2A is set to a frozen state at the setpoint temperature of -18°C, while the second loading chamber 2B is set to a chilled state at the setpoint temperature of +5°C.

[0111] In the case of the refrigeration unit for land transportation shown in FIG. 6, in the first loading chamber 2A having lower setpoint temperature, the intrusive heat Q1 from the outside and the intrusive heat Q3 from the partition wall 3, serving as the heat load, are cooled down by the freezer endotherm (cooling capacity) Q4 of the first evaporator unit 5A. In addition, in the second loading chamber 2B having higher setpoint temperature, the intrusive heat Q2 from the outside (heat load) is cooled down by the freezer endotherm (cooling capacity) Q5 of the second evaporator unit 5B.

[0112] FIG. 7A and FIG. 7B show the simulation results during pull-down operation in which the rotation frequency of the compressor 11 was set constant: wherein FIG. 7A shows the conventional control; FIG. 7B shows the selective operation control of the present invention; changes in the inside temperature of the chamber A (first loading chamber) 2A are indicated by the solid line; and changes in the inside temperature of the chamber B (second loading chamber) 2B are indicated by the broken line.

[0113] First, according to the simulation results of FIG. 7A in which the cooling operation was performed by continuous "Refrigerant distribution control I" from the beginning; it was shown that, after the initiation of the cooling operation, the inside temperatures of both chambers decreased at an approximately same speed by the simultaneous operation of the evaporator units 5A and 5B, until the second loading chamber 2B having higher setpoint temperature reached +5°C. Thereafter, the inside temperature of the second loading chamber 2B was kept at its setpoint temperature of about +5°C by repetition of the thermo-ON/thermo-OFF operation under a predetermined condition.

[0114] Meanwhile, after the second loading chamber 2B had reached its setpoint temperature to thereby come into the thermo-OFF state, the first loading chamber 2A having lower setpoint temperature showed a large rate of temperature change because the cooling capacity was increased due to the sole operation of the evaporator unit 5A. However, when the second loading chamber 2B came into the thermo-ON state again while the first loading chamber 2A was not cooled down to its setpoint temperature of -18°C, the evaporator units 5A and 5B were subjected to the simultaneous operation. At that time, if the inside temperature of the first loading chamber 2A were lower than the converged temperature upon the simultaneous operation of the "Refrigerant distribution control I", the heat load (Q1 + Q2) might have been greater than the cooling capacity Q4. Accordingly, in such a simultaneous operation, the inside temperature having lower setpoint temperature was not able to be lowered, but resulted to be raised for the excessive amount of heat load. Therefore, the first loading chamber 2A was not able to be cooled down to its desired setpoint temperature of -18°C, or a long time was required until it reached the setpoint temperature.

[0115] On the other hand, in the case of the selective control shown in FIG. 7B, since the "Refrigerant distribution control I" was executed from the beginning of the operation, the inside temperature of the second loading chamber 2B reached its setpoint temperature and the then thermo-ON/thermo-OFF operation was repeated.

[0116] However, in the first loading chamber 2A having lower setpoint temperature, the operation was switched to the "Refrigerant distribution control II" at the time point when the Step S6 condition (TsetA ≤ TsetB) and the Step S9 condition (ΔTairA ≥ β) shown in FIG. 3 had been satisfied. Therefore, the refrigerant was preferentially distributed to increase the cooling capacity, resulting in favorable temperature reduction to the setpoint temperature of -18°C. At that time, the loading chamber 2B was kept at its setpoint temperature of about +5°C by repetition of the thermo-ON/thermo-OFF operation.

[0117] Once the first loading chamber 2A had reached its setpoint temperature in such a manner, the thermo request of the first loading chamber 2A was not present, and therefore the operation was switched to the "Refrigerant distribution control I" by the selective control mentioned above. In the following "Refrigerant distribution control I", the first loading chamber 2A and the second loading chamber 2B were both kept at their setpoint temperatures of about -18°C and +5°C by repetition of the thermo-ON/thermo-OFF operation.

[0118] That is to say, by the selective control of the present invention, during the pull-down operation, the first loading chamber 2A having lower setpoint temperature was able to be quickly cooled down to its setpoint temperature, although the time for operating the second loading chamber 2B having higher setpoint temperature was elongated.

[0119] FIG. 8A and FIG. 8B show the simulation results in which the door of the chamber A (first loading chamber) was opened/closed in sequence for unloading while the rotation frequency of the compressor 11 was set constant: wherein FIG. 8A shows the conventional control; FIG. 8B shows the selective operation control of the present invention; changes in the inside temperature of the chamber A (first loading chamber) 2A are indicated by the solid line; and changes in the inside temperature of the chamber B (second loading chamber) 2B are indicated by the broken line.

[0120] Firstly, after the door of the first loading chamber 2A had been opened in the state where the first loading chamber 2A and the second loading chamber 2B had been respectively within their ranges of setpoint temperature, and the operation had been performed by the "Refrigerant distribution control I", then the operation of the refrigeration unit for land transportation was halted. That is to say, during the unloading, the operation of the compressor 11 was halted and the refrigeration unit for land transportation was brought into the operation halting state.

[0121] For this reason, the inside temperature of the first loading chamber 2A whose door had been opened, was rapidly raised, and the inside temperature of the second loading chamber 2B whose door was kept closed, was also slowly raised because the operation of the unit had been halted.
Thereafter, after the door of the first loading chamber 2A had been closed due to the completion of unloading, the thermo-ON request was received to restart the operation of the "Refrigerant distribution control I". Regarding the inside temperature after the restart of the operation, the second loading chamber 2B which showed a relatively small temperature rise, was cooled down to its setpoint temperature in a relatively short time, and then was kept at its setpoint temperature of about +5°C by repetition of the thermo-ON/thermo-OFF operation.

[0122] However, in the first loading chamber 2A which showed a large temperature rise, the inside temperature was not lowered to the desired setpoint temperature due to the influence of the insufficient cooling capacity. Then, the next unloading had to be performed in a state where the inside temperature was higher than the setpoint temperature of -18°C. For this reason, after the door of the first loading chamber 2A had been opened, the temperature was raised to be higher than the temperature at the time of the previous unloading. Accordingly, through repetition of the opening/closing operation of the door of the first loading chamber 2A, the inside temperature that was reachable by restarting the cooling operation was prone to gradually rise.

[0123] On the other hand, in the case where the selective control shown in FIG. 8B was executed, after the door of the first loading chamber 2A was closed/opened, the operation was switched to the "Refrigerant distribution control II" at the time point when the Step S6 condition (TsetA ≤ TsetB) and the Step S9 condition (ΔTairA ≥ β) shown in FIG. 3 had been satisfied in the first loading chamber 2A having lower setpoint temperature. Therefore, the refrigerant was preferentially distributed to increase the cooling capacity, allowing the inside temperature to be lowered to its desired setpoint temperature of -18°C before the next opening/closing operation of the door. Accordingly, even if the door of the first loading chamber 2A were repeatedly opened/closed, the gradual increase in the inside temperature reachable by restarting the cooling operation can be prevented, although the time for operating the second loading chamber 2B having higher setpoint temperature was elongated.

[0124] In this manner, inexpensive, user-friendly, and highly accurate temperature control becomes possible without causing the occurrence of insufficient capacity in a freezing section having lower setpoint temperature, even if the setpoint temperatures are largely different between freezing sections. In addition, the capacity control can be achieved preferentially for the lower setpoint temperature side having greater temperature difference from the outside air and larger intrusive heat. Therefore, the risk caused by insufficient cooling capacity can be greatly reduced, and the time to reach the setpoint temperature of the lower setpoint temperature side can be shortened.

[0125] In the above operation, the number of the freezing sections is not limited to two. The operation is also applicable to simultaneous operation of two or more evaporator units installed in two or more freezing sections. Under the condition in which only one evaporator unit is operated among a plurality of evaporator units, the superheat degree at the outlet of the evaporator is controlled by usual means, so as to achieve the maximum capacity by single use thereof.

[0126] The present invention is not to be considered as being limited by the forgoing embodiments, and appropriate modifications can be made without departing from the scope of the present invention.

Claims

1. An operation control method of a refrigeration unit for land transportation in which a plurality of evaporator units (5A, 5B) are parallelly connected into a refrigerant circuit (10) for circulating a refrigerant by a compressor (11) driven by a dedicated drive source, and a plurality of different transport temperatures can be respectively created for a plurality of freezing sections which are distributedly arranged with the plurality of evaporator units, characterized in that it comprises:

employing throttle mechanisms whose opening degrees are adjustable, as well as providing a low pressure sensor (18) which detects the evaporating pressure of the refrigerant from said evaporator units, for said refrigerant circuit (10); and

performing a priority control for lower setpoint temperature which preferentially distributes the refrigerant to an evaporator unit having a lower setpoint temperature, when a plurality of operation requests have been made for a plurality of said evaporator units, during a various temperature cooling operation having different setpoint temperatures for said respective freezing sections.

2. An operation control method of a refrigeration unit for land transportation according to claim 1, characterized in that said priority control for lower setpoint temperature is selected in a case where the following conditions are all satisfied:

a condition where a difference in the setpoint temperature (Tset) between respective freezing sections is greater than a predetermined value (α);

a condition where an inside temperature (Tair) of the lower setpoint temperature side is lower than the setpoint temperature (Tset) of the higher setpoint temperature side; and

a condition where the rate of change in the inside temperature (ΔTair) of the lower setpoint temperature side is smaller than a predetermined value (β).

3. An operation control method of a refrigeration unit for land transportation according to claim 1 or 2, characterized in that an opening degree of the throttle mechanism of the evaporator unit having lower setpoint temperature is controlled by controlling the superheat degree at the outlet of the evaporator, and an opening degree of the throttle mechanism of the evaporator unit having higher setpoint temperature is controlled so as not to exceed a maximum evaporating pressure, in said priority control for lower setpoint temperature.

4. An operation control method of a refrigeration unit for land transportation according to any one of claims 1 to 3, characterized in that a superheat degree at an outlet of the evaporators is controlled with reference to values detected by the low pressure sensor and an evaporator outlet refrigerant thermometer, in said priority control for lower setpoint temperature.

5. An operation control method of a refrigeration unit for land transportation according to any one of claim 1 through claim 4, characterized in that, during a cooling operation having approximately same setpoint temperatures for freezing sections, a priority control for total freezing capacity is performed in which respective evaporator units individually control their superheat degrees.

6. A refrigeration unit for land transportation in which a plurality of evaporator units (5A, 5B) are parallelly connected into a refrigerant circuit (10) for circulating a refrigerant by a compressor (11) driven by a dedicated drive source, and a plurality of different transport temperatures can be respectively created for a plurality of freezing sections which are distributedly arranged with the plurality of evaporator units, characterized in that it comprises:

throttle mechanisms (13A, 13B) whose opening degrees are adjustable, and which are provided in said refrigerant circuit; a low pressure sensor which detects the evaporating pressure of the refrigerant from said evaporator units: and a controller which performs a priority control for lower setpoint temperature by the operation control method according to any one of claim 1 through claim 5, during a various temperature cooling operation having different setpoint temperatures for said respective freezing sections.

Drawing