Variable flank relief for scroll wraps

A scroll compressor having a non-uniform generating radius for its scroll wraps is formed to have a flank relief which is greatest at locations having the highest generating radius. In scroll compressors having non-uniform generating radii, there is an increased likelihood of contact at the areas having the highest generating radius. Thus, flank relief is provided at the areas having the higher generating radii. In addition, the flank relief is preferably proportional to the generating radius. Further at areas having a generating radius below a predetermined minimum, no flank relief is necessary.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement in flank relief to correct for 
rotational misalignment on non-constant generating radius scroll 
compressor wraps. 
Scroll compressors are becoming widely utilized in refrigerant compression 
applications. As known, scroll compressors include two scroll members each 
having base and a generally spiral wrap extending from the base. The two 
spiral wraps interfit to define a plurality of compression chambers. One 
of the scroll members is driven to orbit relative to the other. In one 
type scroll compressor, both members orbit and this invention also extends 
to this type compressor. As the two scroll members orbit relative to each 
other, the size of the chambers between the scroll wraps are decreased to 
compress an entrapped fluid. 
Traditionally, scroll compressors have had their spiral wraps formed as 
involutes of a circle. These spiral wraps have a constant generating 
radius, and thus expand ever increasingly from a common center. These 
traditional scroll wraps have typically also had constant thicknesses for 
the wraps. Much of the early design of scroll compressors relied on a 
model of an idealized scroll wherein the two scroll wraps were perfect 
involutes, and were both perfectly centered about a common center. 
However, manufacturing tolerances and variations often result in 
imperfections, especially near the beginning and ending points of the 
scroll wraps. These imperfections cause one of the scroll wraps to contact 
the other scroll wrap prior to the remainder of the scroll wrap coming 
into contact. That is, due to imperfections in the manufacturing process, 
there has sometimes been inadvertent contact. This has resulted in 
undesirable noise. 
The prior art has attempted to address this problem by forming a relief in 
the flanks of the scroll compressors at either the beginning and/or ending 
points of the wraps. This causes these regions which formally contacted 
prior to the remainder of the scroll wrap coming into contact, to instead 
contact at about the same time or even after the remainder of the scroll 
wrap comes into contact. This process reduced or eliminated the 
inadvertent contact and correspondingly reduced undesirable noise. 
For the traditional scroll wraps which are based on involutes of a circle 
and which have a constant pitch, or spacing, between successive wraps, 
rotational misalignment of the two scrolls does not usually cause 
difficulty with inadvertent contact and any associated undesirable noise. 
Because successive wraps have equal spacing, i.e., constant pitch, any 
relative rotation of the wraps causes an equal error to be introduced at 
each contact point between the wraps and thus the relative contact between 
wraps is unchanged. Normally, the only problem associated with relative 
rotation between the wraps is loss of performance as the induced error in 
contact points causes one set of points to open up to form clearances 
through which compressed vapor can leak. 
More recently, scroll compressor designers have achieved increased 
operational benefits by scroll wraps which are not formed on an involute 
of a circle. 
As examples, hybrid scroll wraps and high order scroll wraps are often 
utilized in modern scroll compressors. In these scroll compressors, there 
is not a constant generating radius along the entire wrap. Some of the 
scroll wraps are formed of several segments each formed on a circular arc. 
The segments are connected together to form an entire wrap. However, 
across the wrap the generating radius changes. Further, other types of 
scroll wraps have varying generating radiuses, and varying profiles. 
When rotational misalignment occurs with non-uniform generating radius 
scroll compressors, the initial contact point during rotational 
misalignment moves. It is no longer necessarily at the beginning or end of 
the wrap. It may also move instantaneously from one portion of the wrap to 
another during operation, thus causing a series of inadvertent contacts. 
This multiplies the potential for undesirable noise. Thus, the above 
discussed solution is not applicable to scroll compressors having a 
non-uniform generating radius. 
SUMMARY OF THE INVENTION 
In the disclosed embodiment of this invention, a scroll compressor is 
provided wherein the flank wraps are relieved based upon the generating 
radius at the location on the wrap. Applicant has recognized that 
undesirable contact is most likely to occur at areas with a higher 
generating radius. Thus, the greater the generating radius, the more 
relief that is provided. If the generating radius is below a minimum, then 
no flank relief may be necessary. The designer might rely upon the 
assumption that the contact which will occur will occur at the higher 
generating radius locations where relief is used. It is beneficial to 
minimize the amount of relief, as the relief does reduce the capacity of 
the compressor. 
In one embodiment, the relief is proportional to the generating radius, at 
least for areas where the generating radius is over a predetermined 
minimum. 
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.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
A scroll compressor 15 is illustrated in FIG. 1A. As shown, an orbiting 
scroll member 16 has a wrap which interfits with the wrap of a 
non-orbiting scroll member 18. As known, the orbiting scroll is driven to 
orbit relative to the nonorbiting scroll. 
A portion of a scroll compressor wrap 20 from one of scrolls 16, 18 is 
illustrated in FIG. 1B. Wrap 20 is an example of a current production 
wrap. it must be understood that this invention extends to any scroll 
compressor having a non-uniform generating radius, and not just wrap 20. 
As shown, scroll wrap 20 has areas A-F and A.sup.1 -F.sup.1 having 
different generating radii. The generating radii of same portions are 
relatively small as shown in FIG. 2. Thus, no flank relief may be 
necessary at those areas. The generating radii at other portions is 
greater. For that reason, flank relief may be necessary at those areas. It 
is the portions such as A and E with higher generating radii which are 
likely to contact the opposed scroll wrap if rotational misalignment 
occurs. Thus, by forming the reliefs over portions such as A and E the 
present invention will reduce undesirable contact and the operational 
noise. 
FIG. 2 shows the generating radius R.sub.g for the scroll compressor of 
FIG. 1B. As shown, the generating radius increases upwardly over area A 
and then drops. From the end of area A, the generating radius is constant 
through area B. From the end of area B the generating radius decreases 
through area C. A constant relatively low generating radius area occurs 
over area D. The generating radius increases over area E, and from area E 
the generating radius again decreases to a constant low generating radius 
over area F. Through area F the generating radius is low and constant. As 
can be appreciated from FIG. 1B, there is an inner wrap and an outer wrap, 
and there are areas A.sup.1 -F.sup.1 and A-F on the respective sides. The 
areas differ in their extent on the inner and outer wraps. 
FIG. 3 shows the possible relief for the scroll compressor along the points 
illustrated in FIG. 2. As can be seen, through area A, as the radius 
increases and decreases, the relief is respectively higher and lower. Over 
areas B relief is constant. Over part of area C the relief decreases 
downwardly to zero. By the end of area C and all of area D the generating 
radius is relatively small. At a point Z in area C, the generating radius 
drops below a predetermined value L. See FIG. 2. When the generating 
radius drops below L, no relief is necessary. Thus, no relief is necessary 
over the end of area C and all of area D. Area E has the relief since the 
generating radius increases again. Notably, at the beginning of both areas 
A and at or near the end of E, the generating radius may be below L, and 
thus no relief may be used at those areas. Area F has a generating radius 
below predetermined minimum L. The designer may determine no flank relief 
is necessary. 
In summary, in the main feature of this invention, the placement and 
magnitude of a relief on a scroll flank wrap is dictated by the generating 
radius at each individual points on the wrap. 
FIGS. 4A and 4B show the flank relief 26 and 28, in dotted line, on one 
flank in the areas A.sup.1 and E.sup.1. Areas A.sup.1 -F.sup.1 as 
illustrated have a generating radius similar to that shown in FIG. 2. As 
should be understood from FIG. 3, area 26 may extend downwardly through 
area B.sup.1 , and a portion of area C.sup.1 . The size of the flank 
relief is greatly exaggerated. In fact, the actual flank relief is very 
small, and would not be visible in this figure. 
In forming the scroll members according to the present invention, the 
initial design of the wraps is considered. A flank relief is then 
developed based upon the generating radius of the wrap design. The actual 
relief is very small, and is exaggerated in FIG. 4A and 4B. The wrap can 
be cut initially to the final desired profile, including the relief. 
Further, while one scroll member is shown in these figures, it should be 
understood that both scroll members 16 and 18 could have the relief. 
Although a preferred embodiment of this invention has been disclosed, a 
worker of ordinary skill in the 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.