Abstract:
A temperature control system having an increased heating performance. The system includes a compressor adapted to compress a fluid, a heat exchanger coupled to the compressor such that compressed fluid moves from the compressor to the heat exchanger, and a pressure regulating valve positioned between the compressor and the heat exchanger such that compressed fluid from the compressor moves through the valve before reaching the heat exchanger. The pressure-regulating valve is designed to stay in a closed position until the pressure of the fluid from the compressor reaches a desired value. By virtue of this design, the pressure of the fluid in increased, thus resulting in an increased in the temperature of the fluid. Upon reaching the desired pressure, the valve opens to allow the highly-pressurized fluid to flow to the heat exchanger.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to transport temperature control systems and, more particularly, to transport temperature control systems having heating and cooling cycles which utilize hot compressor discharge gas. 
     BACKGROUND OF THE INVENTION 
     Transportation temperature control systems typically can operate in either a cooling mode or a heating mode to provide the necessary conditions for a cargo container, such as a truck or trailer box section. Examples of such systems can be found in U.S. Pat. No. 4,419,866 to Howland; U.S. Pat. No. 4,748,818 to Satterness et al.; U.S. Pat. No. 4,912,933 to Renken; U.S. Pat. No. 5,056,324 to Haley; and U.S. Pat. No. 5,669,223 to Haley et al., all of which are incorporated herein by reference. Such systems switch between the cooling and heating modes of operation by way of a mode selector switch. In the cooling mode or cycle, hot compressor discharge gas is fed in series to a condenser, a receiver, a heat exchanger, an expansion valve, an evaporator, an accumulator and back to the compressor. In the heating mode or cycle, the mode selector diverts the hot compressor discharge gas to an evaporator defrost pan heater, the evaporator, the heat exchanger, the accumulator, and back to the compressor. The heating cycle is commonly used to defrost the evaporator. As generally known, in cold environments, such as during the winter months in cold climate areas, it is usually necessary for transportation temperature control systems to generate a certain amount of heat to keep the contents, typically food items or liquid drinks, contained within the truck or trailer box from freezing. Thus, the heating cycle can also be used to warm-up the truck or trailer box. 
     SUMMARY OF THE INVENTION 
     It is generally desirable to maximize the heating or defrosting capacity of the heating cycle in order to enhance the operation of a transport temperature control system. It has been observed that known transport temperature control systems sometimes fail to generate sufficient heat to ensure higher operating temperatures within a truck or trailer box when the box is subjected to a cold environment. It has also been observed that known transport temperature control systems sometimes lack enough heating capacity during a heating cycle to properly defrost the evaporator, which results in defrost timeouts because the evaporator does not reach a specified termination temperature during a specified time period. Thus, there is a need for a new and improved transport temperature control system having an increased heating capacity and a method of providing the same. In addition, there is a need to enhance the heating capacity of transport temperature control systems without significantly increasing the costs associated with such systems and without significantly increasing the overall size and weight of such systems so as not to adversely affect the operating efficiency of such systems. 
     The present invention provides a temperature control system having an increased heating performance. In one embodiment, the system includes a compressor adapted to compress a fluid, a heat exchanger coupled to the compressor such that compressed fluid moves from the compressor to the heat exchanger, and a pressure regulating valve positioned between the compressor and the heat exchanger such that compressed fluid from the compressor moves through the valve before reaching the heat exchanger. The pressure-regulating valve is designed to stay in a closed position until the pressure of the fluid from the compressor reaches a desired value. By virtue of this design, the pressure of the fluid is increased, thus resulting in an increase in the temperature of the fluid. Upon reaching the desired pressure, the valve opens to allow the highly-pressurized fluid to flow to the heat exchanger. 
     In one embodiment, the pressure-regulating valve includes a pressurized volume having a pressure charge sufficient to offset the compressor discharge pressure so as to close the pressure-regulating valve until such time as the desired compressor discharge pressure is reached. For example, the pressurized volume can be contained by a pressurized dome. In a preferred embodiment, the pressure regulating valve includes an upper plunger communicating with the pressurized volume, a lower plunger communicating with the pressurized fluid, and an actuating member (e.g., an actuating pin) coupling the upper plunger to the lower plunger. 
     The above-described system can be used in connection with a transport temperature control system that is capable of providing both heating and cooling. Such systems typically include an expansion valve fluidly coupled to the heat exchanger, a condenser fluidly coupled to the expansion valve, and a valve assembly (e.g., a three-way valve) fluidly coupled between the compressor and the pressure-regulating valve. The valve assembly can selectively direct pressurized fluid coming from the compressor to either the condenser (corresponding with the cooling mode) or the pressure regulating valve (corresponding with the heating mode). In the cooling mode, the heat exchanger acts as an evaporator. 
     The present invention is particularly suitable for increasing the heating performance of an existing temperature control system. To do this, the pressure-regulating valve is sold as a kit with a desired pressure charge. The valve is then installed in fluid communication between the valve assembly and the heat exchanger. 
    
    
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings in which like numerals are used to designate like features. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a transport temperature control system embodying the present invention, the system being in cooling mode. 
     FIG. 2 is another schematic of the transport temperature control system of FIG. 1, the system being in heating mode. 
     FIG. 3 is a cross-sectional view of a pressure-regulating valve of the transport temperature control system of FIGS. 1 and 2. 
     FIG. 4 is a perspective view of the pressure-regulating valve of FIG.  3 . 
     FIG. 5 is an exploded view of the pressure-regulating valve of FIG.  4 . 
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 illustrate a transport temperature control system  100  embodying the present invention. It should be understood that the present invention is capable of use in other transport temperature control systems, and the illustrated transport temperature control system  100  is merely shown and described as an example of one such system. 
     Referring to FIG. 1, the temperature control system  100  is mounted on a suitable surface of a truck or trailer, such as wall  10 . The system  100  includes a closed refrigerant circuit  14  that includes a refrigerant compressor  18  driven by a prime mover, such as an internal combustion engine (not shown). The compressor  18  is connected to a heat/cool mode selecting three-way valve  22  via a hot gas line  26 . It should be understood that the function of the three-way valve  22 , which has cooling and heating outlet ports  30  and  34 , respectively, may be provided by separate valves, if desired. A high-pressure cutout  38  is placed within the hot gas line  26 . If the discharge pressure of the compressor  18  exceeds a specified value, the high-pressure cutout  38  will inform the controller (not shown) to shut down the compressor  18 . A temperature sensor  42  is positioned on the compressor  18 . If the temperature of the compressor  18  exceeds a specified value, the sensor  42  will inform the controller to shut down the compressor  18 . A sump sight glass  46  is provided on the compressor  18  for viewing the level of the oil in the compressor  18 . 
     FIG. 1 illustrates the cooling cycle of the temperature control system  100 . The cooling port  30  of the three-way valve  22  connects the compressor  18  in the cooling cycle  50 . The cooling cycle  50  includes a condenser coil  54  having an inlet end  58  and an outlet end  62  that is connected to an inlet side  66  of a receiver tank  70 , which includes a service valve  74 . A thermal bulb  78 , liquid injection valve  82  and liquid injection line  86  cooperate with the outlet end  62  of the condenser coil  54  to inject liquid into the compressor  18  if the compressor  18  is too hot. A filter dryer  90  is located downstream from the receiver tank  70 . A one-way check valve  94  is placed in the fluid line or conduit  98  to prevent back flow of the fluid into the receiver tank  70 . A dual section heat exchanger  102  is located downstream from the check valve  94 . 
     High-pressure liquid refrigerant passes through a first section of the heat exchanger  102  and continues on to an expansion valve  106 . The expansion valve  106  is controlled by an expansion valve thermal bulb  110  and an equalizer line  114 . The outlet of the expansion valve  106  is connected to a distributor  118 , which distributes refrigerant to inlets on the inlet end  120  of an evaporator coil  122 . The evaporator coil  122  is disposed within the box of the truck or trailer. The outlet end  124  of evaporator coil  122  is connected to the inlet end  126  of a closed accumulator tank  128  by line  130  and by way of the remaining or second section of the heat exchanger  102 . Gaseous refrigerant in accumulator tank  128  is directed from the outlet end  132  thereof to the suction port of compressor  18  via a suction line  134 , a suction service valve  136  and throttling valve  138 . A purge valve  142  is placed between the check valve  94  and the accumulator  126 . During the cooling mode, the valve  142  is closed so that the refrigerant travels to the heat exchanger  102  rather than directly to the accumulator  126 . The function of the valve  142  will be further explained below in connection with the heating cycle. 
     The three-way valve  22  is operated by a pilot solenoid valve  146 , which is in a conduit  150  extending between the compressor  18  and the three-way valve  22 . When the pilot solenoid valve  146  is closed, the three-way valve  22  is spring biased to its cooling position to direct hot, high-pressure refrigerant gas from compressor  18  to condenser coil  54 . Arrows  152  illustrate the flow of refrigerant from the compressor  18 , through the cooling cycle  50 , and back again to the compressor  18 . 
     When the pilot solenoid valve  146  is open, the three-way valve  22  is operated to its heating position. FIG. 2 illustrates a heating cycle  154 . Arrows  156  illustrate the flow of refrigerant from the compressor  18 , through the heating cycle  154 , and back to the compressor  18 . When the evaporator coil  122  requires defrosting, and also when a heating mode is required to hold the thermostat set point of the load being conditioned, the pilot solenoid valve  146  is opened after a predetermined time delay, as will be further explained below. Opening three-way valve  22  to its heating position blocks refrigerant from flowing out of the outlet port  30  and directs it to the outlet port  34 . Thus, the heating position of the three-way valve  22  diverts the hot, high-pressure gas from compressor  18  away from the cooling cycle  50  and into the heating cycle  154 . 
     The heating cycle  154  includes a hot gas line or conduit  158 , an evaporator defrost pan heater  162 , the distributor  11   8 , the evaporator coil  122 , the second section of the heat exchanger  102  and the accumulator  128 . The expansion valve  106  is bypassed during the heating mode. If the heating mode  154  is initiated by a defrost cycle, an evaporator fan (not shown) is not operated or, if the fan remains operative, an air damper  166  is closed to prevent warm air from being delivered through the opening  170  into the box of the truck or trailer. If it is desirable to hold a thermostat set point temperature, the evaporator fan may be operated to draw air up through opening  174  and blow the air across the evaporator coil  122  and out the opening  170 . The air damper  166  remains open during this operation. 
     The heating cycle  154  further includes a pressure regulating valve  178  positioned within the line  158  downstream from the three-way valve  22 . A preferred pressure regulating DPR8 valve  178  available from Alco Controls, a division of Emerson Electric, of St. Louis, Mo. is illustrated in FIG.  3 . However, other pressure regulating valves may be used to accomplish the features of the present invention. The main function of the pressure regulating valve  178  is to cause the discharge pressure of the compressor  18  to increase, thereby increasing the temperature of the discharge gas or vapor so as to provide an increased heating capacity for the system  100 . 
     As shown in FIG. 3, the valve  178  includes a dome  182 , a charging port  186 , a diaphragm  190 , an upper plunger  194 , a keeper  198  and locator spring assembly  202 , a valve body  206 , an actuator pin  210 , a spring  214 , a lower plunger  218 , a coupling  222 , an inlet  226 , an outlet  230 , and a pressure regulating inlet  234 . A first portion of the line  158  (FIG. 2) extending from the three-way valve  22  communicates with the inlet  226 , and the outlet  230  communicates with a second portion of the line  158  that feeds into the evaporator defrost pan heater  162 . Although not clearly shown in FIGS. 1 and 2, the pressure regulating inlet  234  is in flow communication with the compressor  18  via line  238  (FIGS. 4 and 5) which communicates with line  158  via coupling  242  (FIGS.  4  and  5 ). 
     The dome  182  of the valve  178  is given a predetermined pressure charge via the charging port  186 . In a preferred embodiment, the dome  182  is charged at 70 degrees ambient temperature to 325 psig with nitrogen. If the pressure in the dome  182  is greater than the pressure of the discharge gas from the compressor  18 , the valve  178  will be closed because the pressure in the dome  182  pushes the diaphragm  190 , the upper plunger  194 , the actuator pin  210 , and the lower plunger  218  in a downward direction (with reference to FIG.  3 ), such that the lower plunger  218  closes the inlet  226 . When the valve  178  is closed, discharge gas from the compressor flows into the inlet  226  and through the line  238 . The gas entering the inlet  226  cannot flow any farther until the inlet  226  is opened. The gas flowing through line  238  exits into pocket  246 . The upper plunger  194  prevents the gas from flowing out of the pocket  246 . As the discharge gas of the compressor is continually pushed against the valve  178 , the discharge pressure of the compressor  18  will increase. As the discharge pressure increases, the temperature of the discharge gas increases. Once the pressure of the gas flowing into the pocket  246  exceeds the pressure in the dome  182 , the gas in the pocket  246  will push the upper plunger  194 , the diaphragm  190 , and therefore the actuator pin  210  and lower plunger  218 , in an upward direction (with reference to FIG.  3 ), thereby opening the inlet  226  to allow the hot gas to flow through the valve  178  and out of the outlet  230  to continue on through the heating cycle  154 . 
     The increased temperature of the gas leaving the compressor  18  improves the heating capacity of the system  100 . The valve  178  may be operated in various manners, but the valve  178  is preferably adapted to open when a predetermined pressure is reached. This pressure is determined based on the size of the compressor and other considerations so as not to damage the system  100  during operation. In a preferred system, the valve  178  is adapted to open when the compressor discharge pressure is around 400 psia. According to the principles of the present invention, an increase in heating capacity is positively correlated to an increase in the discharge pressure of the compressor  18 . 
     In order to maximize the heating capacity of the system  100 , it is desirable to recover the refrigerant that is found in the condenser  54  and receiver tank  70  during the cooling mode  50  before changing to the heating mode  154 . Before the three-way valve  22  is opened to the heating mode  154 , the purge valve  142  is opened so that gas pushes the refrigerant out of the condenser  54  and tank  70 , through the line  98 , past the opened purge valve  142  and into the accumulator  128 . The purge valve  142  may be any suitable valve, but a TherMax valve available from the assignee of this application is well suited for use with the present invention. Preferably, the purge valve  142  is opened for at least two minutes prior to the opening of the three-way valve  22  for the heating cycle  154 . 
     Variations and modifications of the foregoing are within the scope of the present invention. It should be noted that other solutions to increase the heating capacity of a transport temperature control system have been discovered. One solution is to use engine water to heat the accumulator tank, thereby increasing its effectiveness as an evaporator to increase system heating capacity. However, it was determined that this alone may not be sufficient to boost heating performance an appropriate amount. Another solution is to combine a lower charged discharge pressure-regulating valve with a system which uses engine water to heat the accumulator tank. Although this was determined to provide acceptable results, the additional valves and electronics needed to control this system deemed this solution less satisfactory than the preferred high discharge pressure regulator described above. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
     Various features of the invention are set forth in the following claims.