In a typical heat transfer system such as a motor vehicle air conditioning system, a refrigerant which serves as the working medium is cycled through an engine drive driven compressor, a condenser, a receiver, an expansion device and an evaporator in that order. The refrigerant is compressed while in a vapor state by the compressor and delivered to the condenser where it rejects heat and condenses to a liquid which then flows to the receiver. The receiver condenses any remaining refrigerant vapor as well as acts as a reservoir of refrigerant for the system and is also commonly provided with a desiccant to trap any water that may have entered the system. The condensed refrigerant from the receiver is then reduced in pressure by the expansion device and flows to the evaporator where it absorbs heat and changes phase from liquid back to vapor. The low pressure vapor then flows back to the compressor to repeat the cycle. In a heat pump system using these components but with an electric motor driven compressor and providing both cooled and heated air such as in an electrically powered passenger vehicle or living space, the flow is reversed with respect to the condenser and evaporator in a heat mode so that the refrigerant now absorbs heat in the former and rejects heat in the latter and the expansion device and receiver must be plumbed accordingly. Moreover, an additional expansion device may be needed to meet the different heat transfer demands depending on what mode the system is in; i.e. cooling or heating. The expansion device is normally separate from the receiver and the necessary plumbing including added valves becomes quite extensive in making the required alternative connections between the condenser, evaporator, receiver and expansion device(s).
In both types of systems, the expansion device plays a very important role in that it controls the refrigerant flow and thereby the amount of cooling and/or heating that can be achieved. Fixed opening expansion devices such as orifices or capillary tubes are used to minimize costs in certain applications but are not preferred where heat transfer efficiency and response to varying heat transfer demands takes priority. Far more desirable are expansion valves that provide a strategic variable flow rate in accordance with variable operating conditions to maximize the heat transfer efficiency of the system and provide cooling or heating according to demand.
There are various types of expansion valves including the pressure controlled diaphragm type utilizing a control pressure that changes with a critical temperature in the system such as at the outlet of the evaporator. In this type valve, the control pressure operates on a diaphragm to adjust the expansion valve opening to provide increased or decreased refrigerant flow to meet a current demand as reflected by this control pressure. Other types of expansion valves include those which are controlled by a solenoid that may be of either the on-off type that opens and closes the valve with a controlled pulse to regulate the flow or of the proportional type that is controlled by varying the power thereto to adjust the degree of valve opening to produce the desired flow. Another type expansion valve employs a stepping motor that operates like the proportional solenoid to provide controlled flow with a variable size valve opening. The most accurate control of flow is provided by the above solenoid and stepping motor controlled types but they typically lack in versatility in meeting the requirements of both a one-way flow and a two-way or reverse flow refrigerant system.
In addition, the conventional expansion valve is typically separate from the receiver and is not readily adapted for incorporation therewith where two-directional flow is required. Moreover, both the conventional expansion valves and receivers do not readily lend themselves to a simplified plumbing arrangement with respect to the system and each other where they are installed together as an assembly and are required to operate with reverse flow or flow in just one direction.