Scroll machine with relieved flank surface

A scroll compressor is disclosed in which either or both of the spiral wraps of the scroll members are reduced in thickness (i.e., cut away) adjacent to the inlet port defining the starting point the vanes would theoretically sealingly engage one another to initiate compression. Additionally, either or both of the spiral wraps of the scroll members may be reduced in thickness (i.e. cut away) adjacent to the discharge port where the vanes separate and the compression chambers defined thereby communicate with the discharge port. Provision of a smooth transition at the points of engagement cooperates to reduce noise and wear during operation of the compressor.

This invention relates to scroll-type machines and more particularly to a 
scroll wrap configuration which reduces scroll wrap noise and wear during 
operation of the machine. 
Scroll machines generally comprise mated first and second scroll members 
each having an end plate on which is provided an upstanding spiral wrap 
interleaved with the wrap on the other scroll member; the wraps engaging 
each other at substantially line contacts so as to define traveling 
pockets of varying volume as one scroll member is caused to orbit relative 
to the other. The machine may be a pump, compressor or expander. 
Some scroll machines have been found to have undesirable noise in 
operation. In trying to identify the noise it has been found during 
manufacture, machining forces can cause the outer free end of one or both 
of the spiral wraps to be deflected slightly radially outwardly. After 
machining, the free end springs back to its original position thus 
presenting a slightly misaligned projection which can cause undesirable 
engagement between the respective scroll wraps during relative orbital 
movement. Alternatively, when scroll wraps are machined into a solid 
surface with no free end on the wrap, tool deflection, rather than wrap 
deflection, can occur which has the same end result. This engaging contact 
not only can result in a banging noise but can contribute to wear of the 
scroll assembly, and possibly places additional loads on the crankshaft. 
Even if there is no distortion of the wrap end it is believed that this 
may be a relatively noisy area in the machine. Noise also can result from 
the sudden dynamic change in conditions at the point where the inner ends 
of the scroll wraps first communicate with the discharge port and/or 
separate from one another during operation. 
The primary object of this invention therefore resides in the provision of 
a scroll-type machine which overcomes the aforementioned noise and wear 
problems in a simple and inexpensive manner which does not result in any 
significant loss of efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Although the principles of the present invention may be applied to many 
different types of scroll-type machines, the discussion herein relates to 
a hermetic scroll-type machine including a pair of interfitting spiral 
vanes of equal shape (involutes of a circle) with one being non-orbiting 
and the other being orbitally driven by a crankshaft, which machine has 
specific utility in the compression of refrigerant for air conditioning 
and refrigeration. A machine of the present type is disclosed in 
assignee's pending application, Ser. No. 899,003, filed Aug. 22, 1986, now 
Pat. No. 4,767,293, entitled Scroll-Type Machine, the disclosure of which 
is expressly incorporated herein by reference. 
An exemplary embodiment of a scroll compressor 10 according to the present 
invention comprises a scroll assembly 12 for compressing gases, a motor 
(not shown), a vertically disposed crankshaft including at one end thereof 
a crank pin 14 for drivingly interconnecting the scroll assembly to the 
motor via a drive bushing 15, a compressor body 16, and a shell 18 
enclosing all of the above elements. The scroll assembly 12 includes an 
orbiting scroll member 20 including a scroll end plate 22 and a scroll 
wrap 24 of desired flank profile (e.g. an involute of a circle) upstanding 
thereform, and a non-orbiting scroll member 26 including a scroll end 
plate 28 and a scroll wrap 30 of similar flank profile upstanding 
therefrom, compressor body 16 supporting orbiting end plate 22 via the 
usual thrust surface 31. The scroll assembly also includes a central 
discharge port 32 in non-orbiting end plate 28, a similarly shaped fluid 
transfer recess 33 in orbiting scroll end plate 22 and a suction inlet 
port area 34. 
The effective ends of wraps 24 and 30 are disposed on diametrically opposed 
axes "x" and "y", respectively, with the end of wrap 24 indicated at 36 
and the end of wrap 30 at 38 (this wrap is continued outwardly and 
circumferentially to define a suction passage but this continued portion 
does not act as a wrap because it never engages the orbiting wrap). The 
inner end of non-orbiting wrap 30 is indicated at 40 and the inner end of 
orbiting wrap 24 is indicated at 42. 
In accordance with this invention it has been discovered that the benefits 
sought can be obtained if the outer surface of each wrap is relieved in 
the area thereof where it would otherwise be engaged by the outer end of 
the other wrap. As shown, orbiting wrap 24 has a portion of its radially 
outwardly facing surface adjacent its radially outer free end 36 cut away 
or relieved to define a modified offset surface 50 staring at point "A" at 
the free end of the wrap and extending approximately 180.degree. to 
190.degree. to a point "B" (just past axis "y") and then a ramp surface 52 
tapering at a constant rate radially outwardly (approximately 20.degree.) 
from point "B" to a point "C" whereupon the wrap surface assumes its 
normal involute shape. Phantom line "D" (FIG. 4) represents the outer 
flank surface of orbiting wrap 24 without being relieved in accordance 
with the present invention. 
Similarly, non-orbiting wrap 30 has a modified offset surface 60 extending 
approximately 8.degree. to 9.degree. between points "E" and "F" and a ramp 
surface 62 tapering at a constant rate radially outwardly approximately 
20.degree. to 21.degree. from point "F" to a point "G", the latter 
representing the point where wrap 30 is back to its original profile and 
thickness. Phantom line "H" (FIG. 3) represents the outer involute flank 
surface of nonorbiting wrap 30 without being relieved in accordance with 
this invention. 
Modified surfaces 50 and 60 are easily formed by merely offsetting the 
wrap-machining cutter very slightly radially inwardly (e.g. 0.04 mm in a 
scroll having an orbiting wrap roughly 85 mm in overall outside diameter) 
to generate an offset surface parallel to the normal involute surface. 
Thus based upon the above exemplary dimensions, it can be determined that 
the ramp has a circumferential length equal to about 370 times the radial 
depth of the relieved surface. Leakage is minimal because the offset is so 
small and because this is a relatively low pressure zone in the machine. 
It has been learned that additional benefits can be obtained by also 
relieving the wraps near the inner ends thereof. Thus, orbiting wrap 24 
has a portion of its radially inwardly facing flank surface adjacent its 
radially inner free end 42 cut away or relieved to reduce wrap thickness. 
The removed portion defines a modified surface 64 which tapers at constant 
rate radially outwardly from a point "J" to a point "K". Similarly, 
non-orbiting wrap 30 has a portion of its radially inwardly facing flank 
surface adjacent its radially inner free end 40 cut away to reduce wrap 
thickness, the removed portion defining a modified surface 66 which tapers 
at constant rate radially outwardly from a point "L" to a point "M". 
Points "J" and "L" are located at a point disposed on the wrap flank 
surfaces slightly radially outwardly of the point of normal separation of 
the wraps, preferably at the point that discharge port 32 and recess 33 
are opened. The configuration of the discharge port 32 (and corresponding 
recess 33) is disclosed in detail in assignee's application, Ser. No. 
123,927, entitled Scroll Machine Center Port filed of even date in the 
name of Gary J. Anderson, now abandoned, the disclosure of which is 
expressly incorporated herein by reference. Points "K" and "M" are located 
slightly radially inwardly of the normal separation point of wraps if they 
had true involute flank surface. The resulting ramps, which are shown in 
greatly exaggerated form, smooth the transition from loading to unloading 
of the wrap ends. Leakage is not a problem in the ramped area because the 
discharge port is already opened. 
Modifying the flank surfaces in the manner described has been found to 
reduce noise and wear, and it is believed that it will also allow the 
manufacturing process to be less precise and/or faster, and thus less 
expensive. 
While it will be apparent that the preferred embodiments of the invention 
disclosed are well calculated to provide the advantages above stated, it 
will be appreciated that the invention is susceptible to modification, 
variation and change without departing from the proper scope or fair 
meaning of the subjoined claims.