Automotive secondary loop air conditioning system

Details Automotive secondary loop air conditioning system Automotive secondary loop air conditioning system

2000-10-03

2001-05-15

McDermott, Corrine (Department: 3744)

Refrigeration

With vehicle feature

Occupant-type vehicle

C062S434000

Reexamination Certificate

active

06230508

ABSTRACT:

TECHNICAL FIELD
This invention relates to automotive air conditioning systems in general, and specifically to a secondary loop system that provides an improved performance.
BACKGROUND OF THE INVENTION
Typical automotive air conditioning systems use the familiar refrigerant cycle system of compressor, condenser, expansion valve and evaporator, through which pressurized refrigerant is continually pumped while the compressor is active. An inherent drawback of the typical system is that it is either on or off. That is, there is no thermal storage or reservoir capacity in such a system that can take over temporarily to maintain passenger comfort when the compressor is turned off for a short time, or which can be activated initially to provide cooling capacity when the system has been shut down for a relatively longer time.
A secondary loop system provides the potential for a reservoir of cooling capacity. In such a system, the conventional refrigerant loop is not used to directly cool the air that is blown into the passenger space. Instead, an intermediate, two fluid heat exchanger, typically known as a chiller, cools a secondary, non pressurized liquid by heat exchange with the cold refrigerant. The cooled secondary liquid is then pumped in a second circuit to one or more air to liquid heat exchangers, over which cooled air is blown into the passenger space. With the non pressurized liquid in the secondary loop, it is feasible to provide a large volume reservoir of “cold”, from which cold liquid can continue to be pumped, even when the primary, refrigerant circuit and its compressor is shut down. Such a reservoir is not possible with just a refrigerant loop.
A potential drawback of the secondary loop system is the response of the reservoir after a long period of system shut down, or “soak” as it is sometimes called. Then, the large reservoir of “cold” becomes a large reservoir of “hot” instead, feeding the secondary loop with hot liquid until the whole system can be cooled down. Under those circumstances, the reservoir can actually lengthen the response time and delay passenger comfort.
SUMMARY OF THE INVENTION
The invention provides an improved secondary loop system that maintains the ability of the system to bridge temporary, shorter shut downs of the refrigerant loop, but which avoids the lag problem inherent in a long shut down.
In the embodiment disclosed, a basically conventional primary refrigerant loop provides expanded and “cold” refrigerant, but not directly to an evaporator within the vehicle interior, but rather to one half of a so called “chiller.” Within the chiller, an unpressurized, warm secondary liquid is cooled by the cold refrigerant, and pumped through a secondary loop to a liquid to air heat exchanger within the vehicle passenger space. The interior, non pressurized heat exchanger provides cooled air to the passenger space. Within the secondary, pumped liquid loop, a large liquid reservoir is interposed. The reservoir liquid becomes chilled as the system operates and, if the primary, refrigerant loop is temporarily shut down for some reason, can continue to provide cold liquid (and cooled air) to the passenger space.
The reservoir also has novel features that avoid the lag time problem inherent in long periods of shut downs. The reservoir contains a means to temporarily by pass the greatest portion of the reservoir volume when the liquid in the reservoir has become too warm to meet passenger comfort demands. The reservoir is provided with either a smaller volume portion, or a complete by pass, which is initially engaged, so that the entire reservoir volume need not be cooled down at the start. The secondary loop and secondary, interior heat exchanger will reach comfort temperature more quickly than they would if the entire reservoir volume had to be cooled down as well. When a suitable cold temperature is achieved in the by passed secondary loop, the larger portion of reservoir volume is brought on line gradually, so as to not impact passenger comfort, until it, too, has been cooled down to the same degree. Now, the entire volume of the reservoir is sufficiently cooled to provide a “cold reserve.”


REFERENCES:
patent: 3675441 (1972-07-01), Perez
patent: 4227376 (1980-10-01), Ishizaki
patent: 5005386 (1991-04-01), MacCracken et al.
patent: 5904052 (1999-05-01), Inoue et al.
patent: 5910157 (1999-06-01), Noda

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