Patent Application
20090035167
This application relates to a scroll compressor wherein the height of the scroll wraps is stepped, and further bypass ports are provided for capacity modulation.
Scroll compressors are known, and are becoming popular in the refrigerant compression industry. In the scroll compressor, a pair of scroll members each has a base with a generally spiral wrap extending from its base. The wraps of the two scroll members interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as the orbital movement occurs, compression chambers defined between the two decrease in volume, such that entrapped refrigerant is compressed.
One feature that is known in scroll compressors is the use of a stepped scroll wrap. In a stepped scroll wrap, more central portions of the scroll wraps have a lower height than the outer portions. A displacement volume at a radially outer portion of the spirals is therefore greater. Since the height of the central portion, which defines a higher pressure space, is reduced, the rigidity of the spiral elements is improved. Further since the volume change ratio in the lower pressure outer area is greater than in the high pressure area, a compression load to crank angle is greater, and hence the torque on a motor is reduced. Further, since the volume in the central compression pocket, which is connected to the discharge chamber, is reduced, a re-expansion volume is reduced to thereby reduce power loss.
Another feature known in scroll compressors is capacity reduction. In one capacity reduction feature, a so-called bypass function is provided which opens ports to communicate a partially compressed refrigerant back to a suction location in the compression cycle. Capacity reduction is provided when lesser capacity is necessary for an associated refrigerant system, such as an air conditioning system.
Capacity reduction through the use of bypass ports have only been provided on scroll compressors having a single height wrap. The capacity reduction has only reduced the capacity of the scroll compressor between 100% of its nominal capacity in a fully loaded configuration and approximately 67% of its capacity. The location of the bypass ports in this prior art have limited the reduction to 33%. It would be desirable to have the ability to further reduce the capacity. However, if one moves the bypass ports further radially inwardly then there is the possibility that the bypass port will communicate with a discharge port of the scroll compressor. This would be undesirable. Moreover, another potential method would be to increase the length of the scroll wraps. However, there are other compromises when this occurs.
In the disclosed embodiment of this invention, a scroll compressor with a stepped wrap is provided with a bypass port. In this manner, much greater reductions in capacity can be achieved. As an example, capacity reduction of approximately 50-60% can be achieved. The use of the stepped wraps ensures that the limitations of the prior art will not occur, as the shorter height central portion will still seal and isolate the bypass ports from the discharge port.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
As shown in this application, outer wrap portions 38 of the orbiting scroll member 26, and 40 of the non-orbiting scroll member 28 have a greater height than more central portions 42 and 44. This structure is generally known in the art, and provides the functions as set forth above. However, what is unique is the inclusion of bypass ports 36 and associated solenoid valves 34 which close off the bypass ports 36 (see
Since the bypass ports are utilized in combination with the stepped wrap configuration, a reduction in capacity of approximately 50-60% can be achieved. Thus, the scroll compressor 20 of this invention has the ability to provide 100% of capacity, or much lower capacity levels, and on the order of 40-50% of normal capacity. Of course, other reductions can be achieved as would be apparent to a scroll compressor designer.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
