Superheat control for optimum capacity under power limitation and using a suction modulation valve

#The field of the present invention relates to control systems for transport refrigeration systems. More -specifically, the present invention is directed towards maximizing the system's refrigerating capacity when the system is limited in power capability by adjusting the expansion valve superheat setting.

#A transport refrigeration system used to control enclosed areas, such as the box used on trucks, trailers, containers, or similar intermodal units, functions by absorbing heat from the enclosed area and releasing heat outside of the box into the environment. One problem with the mounting environmental and economic demands placed upon the designers of such systems is that increasing functional demands are placed upon the system while, at the same time, the limitations on the power supply for the system are likewise increasing.

#Existing transport refrigeration systems teach the ability to enhance hot gas heating and hot gas defrosting cycles of a transport refrigeration system, while reducing dependency upon the amount of heat absorbed into the accumulator tank of the system.

#FIG. 1 shows a schematic of the transport refrigeration system of the present invention;

#FIG. 2 shows a block schematic of a first preferred embodiment of a controller of the present invention; and

#FIG. 2a shows a block schematic of a second preferred embodiment of a controller of the present invention.

#The invention that is the subject of the present application is one of a series of applications dealing with transport refrigeration system design and control, the other copending applications including: "Voltage Control Using Engine Speed" (U.S. patent application Ser. No. 09/277,507); "Economy Mode For Transport Refrigeration Units" (U.S. Pat. No. 6,044,651); "Compressor Operating Envelope Management" (U.S. patent application Ser. No. 09/277,473); "High Engine Coolant Temperature Control" (U.S. patent application Ser. No. 09/277,472); "Generator Power Management" (U.S. patent application Ser. No. 09/277,509); and "Electronic Expansion Valve Control Without Pressure Sensor Reading" (U.S. patent application Ser. No. 09/277,333) all of which are assigned to the assignees of the present invention and which are hereby incorporated herein by reference. These inventions are most preferably designed for use in transportation refrigeration systems of the type described in copending applications entitled: "Transport Refrigeration Unit With Non-Synchronous Generator Power System;" Electrically Powered Trailer Refrigeration Unit With Integrally Mounted Diesel Driven Permanent Magnet Generator;" and "Transport Refrigeration Unit With Synchronous Generator Power System." each of which were invented by Robert Chopko. Kenneth Barrett, and James Wilson, and each of which were likewise assigned to the assignees of the present invention. The teachings and disclosures of these applications are likewise incorporated herein by reference.

#FIG. 1 illustrates a schematic representation of the transport refrigeration system 100 of the present invention. The refrigerant (which, in its most preferred embodiment is R404A) is used to cool the box air (i.e., the air within the container or trailer or truck) of the refrigeration transport system 100. is first compressed by a compressor 116, which is driven by a motor 118, which is most preferably an integrated electric drive motor driven by a synchronous generator 120 operating at low speed (most preferably 45 Hz) or high speed (most preferably 65 Hz). Another preferred embodiment of the present invention, however, provides for motor 118 to be a diesel engine, most preferably a four cylinder, 2200 cc displacement diesel engine which preferably operates at a high speed (about 1950 RPM) or at low speed (about 1350 RPM). The motor or engine 118 most preferably drives a 6 cylinder compressor 116 having a displacement of 600 cc, the compressor 116 further having two unloaders, each for selectively unloading a pair of cylinders under selective operating conditions.

#In the condenser, the (preferably vapor state) refrigerant is compressed to a higher temperature and pressure. The refrigerant then moves to the air-cooled condenser 114, which includes a plurality of condenser coil fins and tubes 122, which receiver air, typically blown by a condenser fan (not shown). By removing latent heat through this step, the refrigerant condenses to a high pressure/high temperature liquid and flow to a receiver 132 that provides storage for excess liquid refrigerant during low temperature operation. From the receiver 132, the refrigerant flows through subcooler unit 140, then to a filter-drier 124 which keeps the refrigerant clean and dry, and then to a heat exchanger 142, which increases the refrigerant subcooling.