Refrigeration – Automatic control – Humidity sensor
Reexamination Certificate
1999-08-20
2001-02-20
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Humidity sensor
C062S176600, C062S228500, C062S229000, C062S133000, C236S04400R, C165S230000
Reexamination Certificate
active
06189325
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an air conditioning system for the passenger compartment of a motor vehicle, and more particularly to an air conditioning system which can provide both heating and cooling for the passenger compartment; and to a method of operating such an air conditioning system.
BACKGROUND OF THE INVENTION
Air conditioning systems for the passenger compartments of motor vehicles are well known. Such systems include arrangements for the flow of air across the internal surface of the windscreen of the motor vehicle. In general, these systems comprise an inside heat exchanger (located within the passenger compartment) and an outside heat exchanger (located outside the passenger compartment). A pair of fluid passages connect the heat exchangers to allow the circulation of fluid through the heat exchangers. An expansion device is positioned in one of the fluid passages. A compressor and accumulator/dryer is positioned in the other fluid passage. When fluid is pumped by the compressor through the outside heat exchanger, the expansion device, the inside heat exchanger and the accumulator/dryer in succession, air passing through the inside heat exchanger is cooled as the air flows into the passenger compartment across the windscreen. When fluid is pumped in the reverse direction through the inside heat exchanger, the expansion device, the outside heat exchanger and the accumulator/dryer in succession, air passing through the inside heat exchanger is heated as the air flows into the passenger compartment across the windscreen. A reversing valve can be positioned in the other fluid passage to provide the required flow direction for the fluid.
During the cooling cycle, the air passing through the inside heat exchanger may be de-humidified, leading to a build-up of condensation on the inside heat exchanger. During a subsequent heating cycle, the condensation may be evaporated, increasing the risk of internal fogging of the windscreen. This potential problem may be avoided either by limiting the time of the heating cycle, or by using a second inside heat exchanger during the heating cycle (with the first inside heat exchanger only being used during a cooling cycle). Both of these potential solutions have limitations.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the above mentioned problem.
An air conditioning system in accordance with the present invention for a passenger compartment of a motor vehicle having a windscreen comprises a first heat exchanger positionable outside the passenger compartment; a second heat exchanger positionable inside the passenger compartment; a first fluid passage between the first and second heat exchangers; a second fluid passage between the first and second heat exchangers; an expansion device positioned in the first fluid passage; an electronically controlled variable stroke compressor for pumping fluid into the second fluid passage and either in a first direction sequentially through the first heat exchanger, the expansion device, and the second heat exchanger, or in a second direction sequentially through the second heat exchanger, the expansion device, and the first heat exchanger; reverse flow means in the second fluid passage for controlling the direction of the flow of fluid; first sensing means providing a first output signal indicative of the dewpoint temperature of the air leaving the second heat exchanger; second sensing means providing a second output signal indicative of the temperature of the windscreen; and control means electrically connected to the first and second sensing means and to the compressor for receiving the first and second output signals, for determining a dewpoint temperature for the air leaving the second heat exchanger dependent on the first output signal, for determining the windscreen temperature from the second output signal, for comparing the determined dewpoint temperature to the determined windscreen temperature, and for controlling the stroke of the compressor to maintain the dewpoint temperature at or below the windscreen temperature during fluid flow in the second direction.
Because of the use of an electronically controlled variable stroke compressor, the present invention allows more precise control of the pumping capacity of the compressor when the air conditioning system is heating the passenger compartment. The present invention provides an air conditioning system which operates dependent on sensed conditions to reduce the risk of internal fogging of the windscreen without the need for limiting the time of operation of the heating cycle and without the need for another heat exchanger inside the passenger compartment.
REFERENCES:
patent: 4783970 (1988-11-01), Takahashi
patent: 4852363 (1989-08-01), Kampf et al.
patent: 4896589 (1990-01-01), Takahashi
patent: 4917293 (1990-04-01), Fedter et al.
patent: 4920755 (1990-05-01), Tadahiro
O'Brien John F.
Pittion Laurent
Delphi Technologies Inc.
Griffin Patrick M.
Tanner Harry B.
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