Refrigeration – Refrigeration producer – With lubricant handling means
Reexamination Certificate
1999-07-08
2001-06-26
Tapolcal, William E. (Department: 3744)
Refrigeration
Refrigeration producer
With lubricant handling means
Reexamination Certificate
active
06250099
ABSTRACT:
BACKGROUND
The present invention relates to a supercritical refrigerating cycle that utilizes carbon dioxide as a coolant.
An example of a refrigerating cycle utilizing carbon dioxide (CO
2
) as a coolant, which is disclosed in Japanese Examined Patent Publication No. H 7-18602, comprises a compressor, a radiator, a counter-flow heat exchanger, a means for expansion, an evaporator, an accumulator and the like.
In this structure, coolant is compressed by the compressor to be a vapor-phase coolant with a high pressure, and then it is cooled at the radiator to reduce its enthalpy. During this process, since the high-pressure vapor-phase coolant is at a temperature equal to or higher than a supercritical temperature (in a supercritical range) of the coolant, it is not condensed and does not become a liquid phase state at the radiator. In this point, the refrigerating cycle is different from prior refrigerating cycles employing Freon. Then, the high pressure coolant with the reduced enthalpy travels through the expansion valve so that its pressure is reduced down to a vapor-liquid mix range, and thus, the liquid-phase component is increased for the first time in the coolant in this stage. Subsequently, the liquid-phase component in the coolant absorbs heat of a medium traveling through the evaporator to be evaporated and then it is taken into the compressor.
In the refrigerating cycle described above, the counter-flow heat exchanger achieves heat exchange between the low temperature vapor-phase coolant taken into the compressor and the high-pressure vapor-phase coolant after passing through the radiator, and since the low pressure vapor-phase coolant is heated and at the same time the high-pressure vapor-phase coolant is cooled at the counter-flow heat exchanger, the efficiency of the refrigerating cycle is improved.
However, as it is a known fact that there is an optimal heat exchanging capacity in a refrigerating cycle employing a counter-flow heat exchanger depending upon the environment in which it is operated or the operating state. It is another known fact that if the environment or the operating state changes, the optimal heat exchanging capacity also changes, and therefore the optimal heat exchanging capacity must be adjusted in order to achieve improved efficiency under varying conditions. However, if the optimal heat exchanging capacity is changed, a problem arises such that the degree of superheat of the coolant in an intake side of the compressor becomes excessive, resulting in a high discharge temperature.
The temperature of the air entering the radiator changes constantly (due to changes in the external air temperature, during idling or high speed operation and the like). Furthermore, the force to drive the compressor is derived from the running engine so that the rotating state of the compressor changes in conformance to the running state. As such, when a refrigerating cycle as described above is employed in an air conditioning system for vehicles, problems arise because the environment or the operating state changes frequently.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a refrigerating cycle that utilizes carbon dioxide as a coolant to achieve an improvement in the efficiency of the refrigerating cycle and to respond quickly and precisely to changes in the environment or the operating state.
In order to achieve the object described above, the refrigerating cycle according to the present invention, which comprises, at least, a compressor for compressing a vapor-phase coolant to a supercritical range, a radiator for radiating heat from the vapor-phase coolant in the supercritical range discharged from the compressor, a means for expansion for lowering pressure of the vapor-phase coolant in the supercritical range after passing through the radiator down to a vapor-liquid two-phase range and an evaporator for evaporating a liquid-phase component in the coolant with pressure reduced by the means for expansion, characterized in that the means for expansion is constituted of a first means for expansion and a second means for expansion, that a means for vapor-liquid separation is provided between the first means for expansion and the second means for expansion to separate the coolant with pressure reduced to the vapor-liquid two-phase range by the first means for expansion into a vapor-phase coolant to be returned to the compressor and a liquid-phase coolant to be delivered to the second means for expansion, and that a means for oil separation is provided on an upstream side of the second means for expansion to separate oil from the coolant and return the separated oil to the compressor.
Thus, according to the present invention, because the first and second means for expansion are provided and the means for vapor-liquid separation is provided between the first and second means for expansion, the pressure of the high-pressure vapor-phase coolant compressed by the compressor and cooled by the radiator is reduced to an intermediate pressure and the vapor-liquid two-phase range by the first means for expansion, the coolant with a vapor-liquid mix substance is separated into a vapor-phase coolant and a liquid-phase coolant by the means for vapor-liquid separation, only the liquid-phase coolant is expanded by the second means for expansion and the vapor-phase coolant is taken into the intake side of the compressor while maintaining the intermediate pressure, so that unnecessary energy for compressing the vapor-phase coolant may be controlled to achieve an improvement in the cycle efficiency.
In addition, because the means for oil separation is provided on the upstream side of the second means for expansion to separate the oil component from the liquid-phase coolant traveling to the second means for expansion and the evaporator, any reduction in the heat exchanging capability attributable to oil adhering in coolant passages in the evaporator can be prevented. Furthermore, since the separated oil at a low temperature is directly returned to the drive portion of the compressor, the efficiency of the compressor may be improved.
Moreover, in the present invention, it is preferred that a threephase phase separator integrating the means for oil separation and the means for vapor-liquid separation is provided between the first means for expansion and the second means for expansion. Thus, the structure of the refrigerating cycle may be simplified.
In addition, in the present invention, it is desirable that the means for oil separation is provided on the upstream side of the first means for expansion. Thus, the first means for expansion c an reduce the pressure of only the pure coolant from which oil is separated to assure a reduction in the pressure of the coolant to the vapor-liquid mix range with a high degree of reliability.
Alternatively, in the present invention, it is preferred that a three-phase separator integrating the means for oil separation, the means for vapor-liquid separation and a first means for expansion communicating between the means for oil separation and the means for vapor-liquid separation is provided between the radiator and the second means for expansion. Thus, the structure of the refrigerating cycle may be simplified.
In addition, in the present invention, it is desirable that the means for oil separation is provided on the upstream side of the radiator. Since carbon dioxide utilized as the coolant remains in the vapor phase state until it reaches the first means for expansion, oil solubility to the coolant is low, so that the oil adheres to the passage walls in the radiator and it causes reduction in the heat exchanging capability, as a result, it is desirable that the means for oil separation is provided on the upstream side of the radiator.
Furthermore, in the present invention, it is desirable that the first means for expansion is an orifice tube and the s econd means for expansion is an automatic expansion valve which is controlled so as to maintain a degree of superheat thereof constantly. Alternatively, the fi
Furuya Shunichi
Kanai Hiroshi
Tapolcal William E.
Wenderoth , Lind & Ponack, L.L.P.
Zexel Corporation
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