Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2000-04-14
2001-11-20
Walberg, Teresa (Department: 3742)
Refrigeration
Automatic control
Refrigeration producer
Reexamination Certificate
active
06318100
ABSTRACT:
I. FIELD OF THE INVENTION
The field of the present invention relates to control systems for transport refrigeration systems. More specifically, the present invention is directed towards managing refrigerant in a transport refrigeration system with one or more electronic control valves, including the electronic expansion valve (EXV), the electronic hot gas valve (ESV), and/or the electronic suction modulation valve (EMV).
II. DESCRIPTION OF THE PRIOR ART
A transport refrigeration system used to control enclosed areas, such as the insulated 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. Current transport refrigeration systems use mechanical valves to control refrigerant flow, pressure and temperature based upon various desired operating modes. Such control valves offer only a crude control of these operating parameters, while requiring unnecessary complexity in the tubing needed to manage the refrigerant.
Transport refrigeration systems currently employ a variety of controls to manage the operating parameters of a transport refrigeration system. As can be shown by U.S. Pat. Nos. 5,626,027 and 5,577,390, both assigned to the assignee of the present invention, compressors can be operated in a multi-stage mode or in single stage modes depending upon operating temperature. Such references further discuss generally the use of suction modulation for capacity control. However, the inventors believe that currently available prior art commercial designs, including those sold by assignee, do not offer a simplified transport refrigeration system tubing utilizing an integrated electronic refrigerant control.
The applicants have found that, in order to optimize management of a transport refrigeration system while simplifying the tubing system used, it is desirable to improve capacity and control power demand by combining a number of control features, including: 1) controlling refrigerant flow rate (i.e., through superheat control) with an electronic expansion valve; 2) controlling superheat to closer tolerances than currently used in commercial transport systems; 3) using an electronic expansion valve and/or electronic suction modulation valve to limit flow rate in cooling operating mode; and 4) using an electronic hot gas valve to limit flow rate during heating and defrost mode. The present invention thus allows for the elimination of certain previously desirable hardware and/or control features, including the liquid solenoid valve, a high pressure compressor discharge valve, defrost termination switches, mechanical suction throttling devices, compressor unloaders, and accumulator tanks.
III. SUMMARY OF THE INVENTION
The control process and system of the present invention calls for the integrated electronic management of a transport refrigeration system using the combined controls of a electronic exchange valve (EXV), electronic hot gas valve (ESV) and electronic suction modulation valve (EMV). The use of such valves as called for in the present invention preferably calls for the elimination or change of certain hardware and the implementation of certain controller protocols, preferably through the use of a microprocessor controller.
Specifically, the present invention calls for replacing the mechanical expansion valve (TXV) of a transport refrigeration system with an EXV. The TXV equalizer line and temperature sensing bulb used on existing transport refrigeration units would likewise be replaced with an evaporator pressure transducer (EPT) and an evaporator temperature sensor (EVAP).
The present invention further calls for the elimination of a liquid solenoid valve (SV
2
) through the use of an EXV and/or EMV to control superheat and power demand. The use of the EMV for purposes of power control in the present invention might also allows for the elimination of compressor unloaders. The present invention also preferably replaces the compressor high pressure switch (HP
2
) with a discharge pressure transducer (DPT or CDP). The ESV similarly allows for elimination of certain existing transport refrigeration unit hardware, such as hot gas solenoids (SV
3
, SV
4
) or three way valves. Finally, the present invention calls for using certain existing sensors on transport refrigeration systems (including the ambient temperature sensor (AAT or ATS), return air sensor (RAS or RAT) supply air sensor (SAS), compressor discharge temperature sensor (CDT) and water temperature sensor (WTS)) in conjunction with the EXV, ESV and EMV in order to control power consumption, refrigerant control rate and temperature.
The control process and system of the present invention uses an evaporator coil temperature sensor (EVAP), an evaporator pressure transducer (EPT), a discharge pressure transducer (DPT or CDP), and an ambient temperature sensor (AAT or ATS). In a further alternative preferred embodiment, the present invention could further include additional sensors to such as an engine water temperature sensor (WTS) and/or a compressor discharge temperature sensor (CDT) to control the shutdown of the transport refrigeration unit.
In essence, the transport refrigeration unit microprocessor (MICRO) uses inputs from the sensors referenced above to control the EXV, ESV and EMV. Specifically, the MICRO reads the EVAP and EPT inputs and calculates or approximates the actual evaporator coil superheat level within the system. The MICRO then compares this calculated superheat level and compares it with a desired superheat level which is stored within memory. The MICRO then generates control signals to close or open the EXV based upon differences between the calculated and desired superheat settings. The various desired superheat levels, in turn, will be set or determined by the MICRO depending upon which mode the transport refrigeration unit is in.
In its “base” setting, the controller monitors and calculates the superheat so as to minimize the level of superheating (short of flood back of liquid refrigerant into the compressor) and thus maximizing the capacity of transport refrigeration system. During pull-down (i.e., the mode in which transport refrigeration units are trying to reduce the temperature of the conditioned space), power is limited. Thus, by controlling the discharge pressure through the adjustment of the EXV, the system can limit compressor discharge pressure such that the maximum power limit is not exceeded. Similarly, in an alternative control system using the EMV of the present invention can similarly control discharge pressure.
In another variant from the base setting, when the operation of the system has caused the temperature of the engine coolant to approach its safety limit, the controller will cause an additional superheat offset to be added to the base level. This system adjustment will effectively reduce the engine load and avoid a high coolant temperature shutdown.
In yet another variant from the base setting, the control features of the present invention (specifically, the use of superheat offset) can be used to optimize partial load operation. The use of such a superheat offset reduces capacity and, more importantly, reduces unit fuel consumption.
Also, the addition of the EMV and ESV allows better effective power control in all operating modes of the transport refrigeration unit. In heating mode, the EMV will modulate to control power in a manner similar to the EXV power control in cooling mode. In addition, the EMV allows for accurate power control in the cooling mode without reducing the evaporator coil temperature, thus allowing humidity control via the EMV rather than the compressor unloaders, thus eliminating the unloaders and similar power control devices.
One example of the EMV control in a preferred embodiment of the present invention occurs upon reaching the maximum allowable evaporator superheat. In such an instance, the EMV will further modulate the refrigerant flow rate instead of the EXV or unloaders, thus providing a more effective control.
Finall
Brendel Thomas Edward
Lane L. Thomas
Morse Douglas Herbert
Reason John Robert
Rusert Mead Robert
Carrier Corporation
Niro Scavone Haller & Niro
Robinson Daniel
Walberg Teresa
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