Abstract:
A system and method for controlling the climate within a storage container including at least two cargo areas. The system includes one compressor, one condenser, and two evaporators. Each of the evaporators includes a crankcase pressure regulator, a gas valve and a liquid valve. The crankcase pressure regulators provide a common pressure between each of the evaporators and the compressor regardless of the pressure at the evaporator. A control system selectively actuates the gas and liquid valves according to a predefined control mode to obtain and maintain a desired temperature.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a climate control system for controlling simultaneous cooling and heating functions in separate compartments with one compressor and one condenser. 
     Delivery trucks and trailers transporting temperature sensitive cargo include specially designed climate control systems. Typically, climate control systems such as refrigeration systems include a motor driving a compressor mounted outside of a cargo area. Refrigerant flows from the compressor through a condenser outside the cargo area, and to at least one remotely located evaporator unit. The refrigerant flows through an evaporator coil in the cargo area and back to the compressor. Cooling fans mounted as part of the evaporator blow air across the evaporator coils such that the air is cooled and expelled into the cargo area. 
     One type of climate control system is a direct drive unit where the compressor is driven by the engine of the motor vehicle during travel and when standing for brief periods. A standby compressor operates when it is not practical to run the motor vehicle engine. A simple system includes only one compartment maintained at a single temperature. However, cargo compartments having more than one temperature-controlled compartment are being increasingly put into service. Cargo trucks with two cargo areas capable of maintaining separate temperatures increases the efficiency of the delivery truck and has become increasingly in demand as home delivery service of fresh and frozen foods has gained increased popularity. 
     A direct drive system including one compressor and one condenser is not practical for applications requiring heating or defrost in one compartment and cooling in another compartment. This is so because the heating function requires the use of coolant at high-pressure, where the cooling function requires the use of coolant at low-pressure. Both high-pressure and low pressure cannot co-exist in the same common compressor suction line. 
     For this reason it is desirable to design a system and method to concurrently heat one compartment and cool another with a single compressor and condenser. 
     SUMMARY OF THE INVENTION 
     An embodiment of a climate control system for a container truck of this invention includes a compressor, a condenser and at least two evaporator assemblies, capable of heating in one compartment and cooling in another. 
     The primary motive engine of the motor vehicle drives the compressor during most operating periods, and a standby compressor is provided for use during periods when it is not practical to operate the engine of the motor vehicle. The evaporator assemblies are mounted within separate compartments of the container and are both supplied coolant from the common condenser. The system includes a liquid line communicating coolant in a liquid state from the condenser to each of the evaporators and a hot gas bypass circuit that communicates hot gas from the compressor to each of the evaporators. Hot gas from the bypass circuit provides for heating of the specific compartment and for defrost of each of the evaporators. Coolant flow from the condenser is controlled by a liquid solenoid valve and from the bypass circuit by a hot gas solenoid valve. 
     Coolant exiting each of the evaporators is routed through a common circuit to the compressor. The common line is held at a predetermined coolant pressure, regardless of the coolant pressure at each of the evaporators by way of two individual crankcase pressure regulators. Each of the evaporators includes a crankcase pressure regulator such that coolant pressure within the evaporator does not vary the pressure within the common coolant line back to the compressor. The system of the subject invention is capable of cooling in one compartment with one evaporator and heating in another compartment with the other evaporator. This is accomplished by the use of the separate crankcase regulators for each evaporator. With separate crankcase regulators, beating and cooling with a common compressor is possible because the pressure in the common suction line can not be at two different pressures. 
     In operation, a controller controls each of the solenoid valves of the system to obtain the desired temperature. The controller selectively opens or closes either the liquid or the hot gas valve to obtain a desired temperature. The controller of this invention includes an automatic mode and a priority mode that governs how the various valves are actuated to obtain the desired compartment temperature. 
     The climate control system of this invention efficiently manages the actuation of the various valves to control thermostatically different temperatures in different compartments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
     FIG. 1 is a schematic drawing of the subject climate control system; 
     FIG. 2 is a flow chart of system operation in automatic mode for cooling in one compartment and heating in the other compartment; 
     FIG. 3 is another flow chart of system operation in automatic mode for heating in both compartments; 
     FIG. 4, is another flow chart of system operation in automatic mode for cooling in both compartments; 
     FIG. 5, is a flow chart of system operation in priority mode for cooling in both compartments; and 
     FIG. 6, is a flow chart of system operation in priority for heating in both compartments. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A climate control system for a container moved by a motor vehicle  10  is shown in FIG.  1  and includes a compressor  12 , a condenser  19  and at least two evaporator assemblies  15 , 16 . The primary motive engine  18  of the motor vehicle  10  drives the compressor  12  during most operating periods, and a standby compressor  14  is provided for use during periods when it is not practical to operate the engine  18  of the motor vehicle  10 . 
     The evaporator assemblies  15 , 16  are mounted within first and second compartments  20 , 22  and are both supplied coolant from the common condenser  19 . The system includes a liquid line  24  communicating coolant in a liquid state from the condenser  19  to each of the evaporators  15 , 16 . Each of the evaporators  15 , 16  includes a liquid valve  26 , 28  selectively actuated to allow coolant to each of the evaporators  15 , 16 . Expansion valves  30 , 32  are disposed between the liquid valves  26 , 28  and evaporator coils  66 , 68 . The expansion valves  30 , 32  and the liquid valves can by of any type known to one skilled in the art. 
     A hot gas bypass circuit  34  communicates hot gas from the compressor  12  to each of the evaporators  15 , 16 . Hot gas from the bypass circuit  34  provides for heating of the specific compartment  20 , 22  and for defrost of each of the evaporator coils  66 , 68 . Hot gas solenoid valves  36 ,  38  are disposed to selectively open and close hot gas from entering respective evaporators  15 , 16 . 
     Coolant exiting each of the evaporators  15 , 16  is routed through a common circuit  40  to the compressor  12 . The common circuit  40  is held at a predetermined coolant pressure, regardless of coolant pressures at each of the evaporators  15 , 16  by way of crankcase pressure regulators  42 , 44 . The crankcase pressure regulators  42 , 44  for each of the evaporators  15 , 16  controls coolant pressure in the common coolant circuit  40  regardless of coolant pressure within each evaporator  15 , 16 . 
     The addition of the crankcase pressure regulator  42 , 44  for each evaporator  15 , 16  allows for thermostatically different temperatures in each of the compartments  20 , 22  while using a common compressor  12 , and condenser  19 . In this system, coolant from the compressor  12  cools to a liquid form under pressure in the condenser  19  and is routed to the evaporators  15 , 16 . The liquid coolant proceeds through the expansion valves  30 , 32  to the evaporator coils  66 , 68  where the coolant expands. The coolant exits the evaporator coils  66 , 68  at a low pressure and proceeds back to the compressor  12 . The low pressure from the evaporator coils  66 , 68  maybe of two different low-pressure levels even in cooling—cooling mode. 
     For heating within one of the compartments  20 ,  22 , coolant in the hot gas form bypasses the condenser  19  and proceeds directly to the evaporator coils  66 , 68 . During heating, the liquid control valve  26 , 28  for the heated compartment  20 , 22  is closed and the hot gas solenoid  36 , 38  is opened. The system of the subject invention is capable of cooling in one of the compartment  20 , 22  with one of the evaporators  15 , 16  and heating in the other compartment  20 , 22 . This is only accomplished because of the use of a separate crankcase regulators  42 , 44  for each evaporator  15 , 16 . Without separate crankcase regulators  42 , 44 , heating and cooling with a common compressor is not possible because the pressure in the common circuit  40  would not be compatible with the different pressure at the other evaporator  15 , 16 . In other words, the common circuit  40  is set to a specific pressure below the lowest pressure possible at the evaporators  15 , 16  such that there exists at all times a sufficient pressure drop to ensure proper and efficient coolant flow. The lowest pressure possible is when the compartment is being heated and the hot gas solenoid valve for that compartment is actuated to allow low-pressure hot gas to the evaporator. 
     Each of the evaporators  15 , 16  of the subject invention include at least one fan  46 , 48  for blowing air across the evaporator coils  66 , 68  and into the compartment  20 , 22  to facilitate heating and cooling. The evaporators  15 , 16  also include electric heaters  50 , 52 , 54 , 56  to provide heating with in each compartment  20 , 22  and to defrost each of the evaporators  15 , 16  periodically. 
     In operation, a controller  58  controls the valves  36 , 38 , 26 , and  28  of the system to obtain the desired temperature. The controller  58  selectively opens or closes the valves  36 , 38 , 26 , and  28  based on the desired temperature and operating mode. The controller  58  includes an automatic mode and a priority mode that governs how the valves  36 , 38 , 26  and  28  are actuated to obtain the desired compartment temperature. 
     In the automatic mode the controller  58  operates to open the first hot gas valve  36  or the first liquid valve  26  of the first evaporator  15  depending on the temperature desired within the first compartment  20 . If the temperature of the second compartment  22  is opposite that of the first compartment  20 , then the system in automatic mode will operate sequentially the fans  48 , the road  12 /24 V electric resistance  52  or the standby single phase resistance  56 , the second hot gas valve  38  or the second liquid cooling valve  28  according to a progressive pulse with modulation logic. 
     The Flow chart of FIG. 2 represents the operation of the hot gas valves  36 , 38  and the liquid valves  26 , 28  for thermostatically different temperatures between the first and second compartments  20 , 22 . The first step, indicated at  70 , is to determine a difference between a set temperature (Tsp) and a box or current temperature (Tb). The example illustrated in FIG. 2 is where the first compartment  20  is cooled and the second compartment  22  is heated. The controller begins the cycle by actuating the evaporator fans (EFM1, EFM2) and the first liquid valve  26  (LV1) as indicated at  72 . A predetermined delay time, indicated at  74  by the variable Z expires before another temperature reading is taken and a difference between the desired temperature Tsp and the actual temperature Tb is again determined and a decision made in response to that difference determined at  76 . Note that the temperatures monitored are those of the second compartment  22  that is heated. 
     The first compartment  20  is concurrently being cooled because the evaporator fan  46  and the liquid valve  26  are actuated. Decisions indicted at  78  determined if further delay is initiated or if the controller will move on to actuate the electric heaters (EHR2)  52  or (EHS2)  56  of the second evaporator  16 . As indicated at  80 , the electric heaters  52  or  56  are actuated and remain the only heating means until a specific difference indicated at  82  is obtained. After a difference in temperature reaches a specified difference, the controller  58  actuates the second hot gas valve  38  as indicated at  84 . 
     The second hot gas valve  38  remains on for a specified delay time indicted at  86  and then is cycled to an off position. The second hot gas valve  38  remains off for a specified delay time indicated at  88 . Note that the delay time indicated at  86  and  88  are specified in relation to the number of cycles such that as the number of times the second hot gas valve  38  is cycled changes, the “ON” time indicated at  86  relative to the “OFF” time to change the duration that the second hot gas valve  38  is “ON” as the desired temperature Tsp is approached. 
     The second hot gas valve  38  remains off for a duration indicated at  88  and the on/off cycle continues until the “ON” duration indicated at  86  plus the “OFF” duration indicated at  88  are less than a pre-selected duration as indicated by Z at  89 . Counters indicated at  91  provide for the progressive change in the durations indicated at  88  and  86  that the second hot gas valve  36  is cycled. After reaching a difference in temperature that fulfills the specified conditions indicated at  90 , the cycle is repeated from a point where the second hot gas valve was originally actuated indicated at  92 . 
     FIGS. 3 and 4 are Flow charts representing the order of valve actuation when both compartments  20 , 22  are thermostatically similar such that either heating or cooling is desired for both compartments  20 , 22 . This does not necessarily require that the temperatures in both compartments  20 , 22  are to be the same, only that the desired temperature for both compartments  20 , 22  require either heating or cooling. FIG. 3 represents the order of operation for heating in both compartments  20 , 22 , and FIG. 2 represents the order of operation for cooling in both compartments  20 , 22 . Further, a null condition falls within conditions that would provide for the actuation of the valves  36 , 38 , 26 , and  28 . As appreciated, a null condition refers to a condition were the compartment is allowed to remain at an ambient temperature. 
     The order of actuating valves indicated in the Flow charts of FIGS. 3 and 4, are similar except for the substitution of the specific valve being actuated. As appreciated, for heating, the hot gas valves  36 , and  38  are actuated, and for cooling the liquid valves  26 , 28  are actuated. Operation initiates by determined an initial difference in temperature within the first compartment as indicated at  94  in both FIGS. 3 and 4. The next step, indicated at  96 , begins by actuating the cooling fans  46  and  48  for each of the evaporators  15 , and  16  and either the first hot gas valve  36  or the first liquid valve  26  depending on the desired thermostatic condition. Note that the first liquid valve  26  is represented by LV1 in the flow chart. After the initial conditions are set, the second hot gas valve  38  or second liquid valves  28  are actuated as indicated at  98 . The valve ( 38  or  28 ) remains on for a specified duration indicated at  100  and then is cycled to an off position indicated at  102 . The valve ( 38  or  28 ) remains off for a duration indicated at  104  and the on off cycle continues until the “ON” duration indicated at  100  plus the “OFF” duration indicated at  104  are less than a pre-selected duration as indicated by Z at  106 . 
     Another difference between the set temperature Tsp and the actual temperature Tb is then determined as indicated at  108 . According to the determined difference in temperature indicated at  108 , counters, indicated at  110  are incremented to progressively increase or decrease the delay times indicated at  100  and  104  such that the “ON” time of the valve actuated at  102  is progressively changed until the desired temperature is obtained. 
     The priority mode operates differently from the automatic mode in that when each of the compartments  20 , 22  requires different thermostatic conditions, such as heating in one and cooling in the other, the liquid valve or hot gas valve of a priority evaporator is actuated and the liquid valve or hot gas valve of the other evaporator is simply left off. In this way it is assured that the proper temperature within the priority compartment will be obtained quickly and maintained on a priority status. 
     Referring to the flow charts of FIGS. 5 and 6, when similar thermostatic conditions are required in both compartments  20 , 22  the corresponding valve of the priority compartment is actuated and the corresponding valve of the other evaporator is selectively actuated according to a regressive pulse with modulation logic shown in the flow charts of FIGS. 5 and 6. For illustrative example, the first compartment  20  is designated as the priority compartment. As appreciated, the priority compartment is a selection made according to specific configuration of the climate control system, as understood by one skilled in the art. 
     FIG. 5 is a flow chart indicating the order of operation when cooling is required in both the priority compartment  20  and the second compartment  22 , and FIG. 6 represents operation when heating is required in both compartments  20 , 22 . As appreciated, the hot gas valves  36  and  38  are actuated for heating and the liquid valves  26  and  28  are actuated for cooling. Referring to both FIGS. 5 and 6 the order of operation is initiated by determining a difference in the set temperature Tsp and the actual temperature Tb indicated at  112  in both FIGS. 5 and 6. Initial actuation, as indicated at  114 , of the cooling fans  46  and  48  and the priority compartment valve ( 36  or  26 ). The valve ( 38  or  28 ) for the second compartment is actuated as indicated at  116  for a duration indicated at  118 . 
     The valve ( 38  or  28 ) is then cycled off for the duration indicated at  22 . The total cycle time is then determined at  124  and if less then the predetermined duration identified as “Z” the on/off cycle of the valve is continued. The difference in temperature is determined as indicated at  126  such that if the current difference is less than a previous difference the duration of on/off cycle time is changed as indicated at  132 , otherwise the duration is changed as indicated by  130 . As the temperature difference is decreased, that is it is less than a previous measured temperature difference, the on/off cycle time is reduced, otherwise the on/off cycle time of the second valve ( 38  of  28 ) is increased until the desired temperature Tsp is obtained. In this way, it can be assured that the temperature within the priority compartment  20  is maintained before the temperature in the second compartment  22  is adjusted or accommodated. 
     The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.