Scroll member for use in a positive displacement device, and a method for manufacturing the same

A scroll member comprising a metallic end plate having a spiroidal groove on one side thereof, and a through-hole communicating with the groove, and a resin wrap joined to the groove of the end plate so as to protrude from the surface of the end plate. The wrap being formed by injection molding, and the through-hole and the groove being filled with part of the wrap.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a scroll member used in a positive 
displacement device, such as a compressor, pump or expander, and a method 
for manufacturing the scroll member. 
2. Description of the Related Art 
In a positive displacement device, e.g., a scroll compressor, processes of 
suction, compression, and discharge can be executed simultaneously in a 
plurality of chambers. Accordingly, driving torque fluctuates only 
slightly, the level of noise or vibration during operation if low, and the 
compression efficiency is improved. Thus, the scroll compressor may be 
utilized for gas compression in the cooling system of refrigerators or 
freezers, and in the air-conditioning system of air conditioners, etc. 
In the scroll compressor, a scroll compressing unit is disposed in an 
airtight housing, and gas is introduced into the unit to be compressed and 
discharged thereby. The scroll compressing unit comprises a pair of scroll 
members in lubricative contact with each other; a stationary scroll member 
fixed to the housing and a orbiting scroll member orbiting relatively to 
the stationary member. Each scroll member has a substantially circular end 
plate and a spiroidal wrap planted in one side of the end plate. Usually, 
the spiroidal configuration of the wrap is either an involute curve or a 
continuous curve determined by a plurality of circular arcs (that is 
series semi-circle curve), so that the respective wrap-side faces of the 
two scroll members are in contact with each other simultaneously at a 
plurality of contact areas when the scroll members are joined together. 
The respective wraps of the two scroll members have the same height so 
that the end faces of the wraps abut against the end plates opposite 
thereto. Thus, when the scroll members are combined together, a plurality 
of crescent-shaped compression chambers are defined by the wraps and the 
end plates. 
When the scroll compressor is operated, the orbiting scroll member orbits 
relatively to the stationer scroll member, so that the sliding-contact 
portions between the side faces of the wraps move successively from the 
peripheral edge portion toward the central portion. As a result, the 
crescent-shaped compression chambers are reduced in capacity, so that the 
gas in the chambers is compressed. The compressed gas is discharged from 
the housing through a discharge port in the center of the end plate. 
The end plate and the wrap are made from forgings or die castings, by 
machining the forgings or die castings by means of an NC cutting machine 
into products having predetermined sizes. This method of manufacturing the 
end plate and the wrap requires great cost, and cannot be employed to 
manufacture the end plate and the wrap in large quantities. This is why 
the use of this method has been limited to the manufacture of the end 
plates and the wraps for use in large-capacity compressors. 
To manufacture the end plate of the scroll member at low cost, the end 
plate can be made of steel or aluminum, and a spiroidal groove can be cut 
in one surface of the end plate. In this case, the wrap is fitted in the 
spiroidal groove, thereby forming the scroll member. However, this method 
has a problem. The wraps of both scroll members must be in oil-sealed 
contact, and the end of either wrap must also be in oil-sealed contact 
with the end plate. For example, the gap between the contacting sides of 
the wraps must be reduced to 10 .mu.m or less, in order that the gas 
leakage from the compression chamber is minimized and, hence, the 
compressor has a sufficient compression efficiency. Therefore, the 
allowable tolerance of either scroll member must be 5 .mu.m or less, and 
the components of either scroll member must be scraped with an extremely 
high precision. 
However, in above-mentioned method for manufacturing, it is hard to form 
the groove in the end plate with high accuracy, so that a desired working 
accuracy cannot be obtained. It is also difficult to fit the wrap 
accurately into the groove, so that the gap between the adjacent turns of 
the wrap is prone to errors. Accordingly, the mounting accuracy for the 
wrap becomes so low that the compressed gas is liable to leak from 
chambers, thus failing to enjoy high compressibility. In such scroll 
member of the wrap-fit type, moreover, the formation of the groove in the 
end plate requires much labor, thereby entailing increase in manufacturing 
cost. 
In consideration of these circumstances, an improved forming technique has 
been developed. In this method, a wrap and an end plate are formed 
integrally, instead of being formed separately. Disclosed in Japanese 
Patent Disclosure No. 59-135309 is an integral forming method in which a 
scroll member is integrally formed by injection molding of synthetic resin 
using metallic mold. According to this method, a wrap and an end plate are 
formed integrally, so that the scroll member can be manufactured quickly. 
Since the scroll member has a complicated configuration, and is usually 
designed so that the wrap is thinner than the end plate, so the individual 
parts of the member are subject to differences in contraction rate during 
a process of solidification. Thus, the scroll member is warped, and the 
desired working accuracy cannot be obtained. 
Disclosed in Japanese Utility Model Disclosure No. 60-8493, moreover, is a 
scroll member of a type such that a spiroidal core, which protrudes from 
one side of an end plate, is coated with resin by injection molding. 
In the scroll member of this type, however, the resin is injected through a 
passage on the mold side, so that its finally solidifying portion is 
situated on the end-face (or top) side of a wrap. Due to differences in 
contraction rate, therefore, the core cannot be coated as required, so 
that the shape of the wrap, especially of its end face, is lowered in 
accuracy. Since an injection hole and a vent hole of a mold opens 
corresponding to the wrap end face burrs are formed on the end face, when 
these burrs are removed by scraping the precision of the wrap the end 
face, is impaired. 
In general, the wrap end face is liable to wear when it slides on the other 
end plate. In order to prevent the gas from being by-passed, it is to be 
desired that no gap should exist between the contact portions of the wrap 
end face and the end plate. I the scroll member, furthermore, the working 
accuracy of wraps is so low that the wraps and the end plates wear much by 
unbalance sliding. Thus, the scroll member is lowered in life performance. 
SUMMARY OF THE INVENTION 
The present invention has been contrived in consideration of these 
circumstances, and has an object to provide a high-performance scroll 
member having high-accuracy wraps and capable of high-efficiency 
compression. 
Another object of the invention is to provide a method for manufacturing a 
scroll member, capable of forming a high-accuracy wrap easily and quickly. 
A scroll member according to the present invention comprises a metallic end 
plate having a spiroidal groove on one side thereof, and a through-hole 
communicating with the groove, and a resin wrap joined to the groove of 
the end plate so as to protrude from the surface of the end plate, the 
wrap being formed by molding and the through-hole and the groove being 
filled with part of the wrap. 
A method for manufacturing a scroll member according to the present 
invention comprises forming a spiroidal groove on one side of an end 
plate, setting the end plate in mold means for defining the shape of a 
wrap, and injecting resin into the groove from the end-plate side, thereby 
molding the wrap. 
Preferably, in this case, the end plate is formed with a passage connecting 
the groove and the opposite side to the grooved surface thereof, so that 
the resin is injected into the groove through the passage. Preferably, 
moreover, a passage for deflation is provided separately from the 
connecting passage. 
The cross-sectional shape of the groove may be square, trapezoid or the 
other. Preferably, in this case, the width of the bottom portion of the 
groove is greater than that of its opening portion. 
Preferably, furthermore, the wrap is formed of a resin which is 
particularly high in strength, lubricity, wear resistance, heat 
resistance, and durability. More specifically, the wrap is preferably 
formed of a super-engineering plastic such as liquid-crystal polymer resin 
(LCP resin). 
The end plate, which is in sliding contact with the wrap, is preferably 
made of an alloy which essentially consists of iron, brass, or aluminum, 
and is strong, and slides well on the wrap when lubricated with oil. If a 
deep groove is needed, the end plate is preferably formed by pasting a 
plurality of sheets, each having a recess and a projection, together. 
Alternatively, moreover, the end plate may be formed by injection molding 
of resin, without using metal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Various embodiments of the present invention will now be described in 
detail with reference to the accompanying drawings. 
As shown in FIG. 1 and 12, scroll compressing unit 10 according to a first 
embodiment, which is composed of a combination of stationary scroll member 
12 and orbiting scroll member 14, is disposed in the heremetically housing 
sealed 100, having a discharge part 110 and a suction port 105, of a 
scroll compressor so that the axis of unit 10 is directed vertically. 
Stationary scroll member 12 is fixed to the housing, and orbiting scroll 
member 14 is in contact with the lower portion of member 12. Boss 25 is 
formed on the rear face of member 14. An orbiting drive mechanism is 
coupled to boss 25 by means of a crank shaft (not shown). 
End plates 16 and 22 of scroll members 12 and 14 are each in the form of a 
substantially circular metal plate. Spiroidal grooves 17 and 23 are formed 
on the one-side faces of members 12 and 14, respectively. Spiroidal wraps 
18 and 24 are planted in grooves 17 and 23, respectively, so as to 
protrude from the respective one-side faces of end plates 16 and 22 at 
right angles thereto. Wraps 18 and 24 are obtained by forming a 
super-engineering plastic (resin particularly high in strength, lubricity, 
wear resistance, heat resistance, and durability), such as liquid-crystal 
polymer resin, by injection molding. In this case, the width of grooves 17 
and 23 is substantially equal to that of wraps 18 and 24. 
The cross-sectional shape of the grooves can be varied. As shown in FIG. 5, 
for example, groove 38 of end plate 37 may be formed by two steps of 
pressing work so that its bottom portion is wider than its opening. The 
junction of the wrap and the end plate can be further strengthened by 
shaping groove 38 like this. 
Wraps 18 and 24 have substantially the same shape, and are designed so that 
the respective end faces of wraps 18 and 24 abut against end plates 22 and 
16, respectively, when scroll members 12 and 14 are joined together with 
their wrap-side faces opposed to each other. The respective side faces of 
wraps 18 and 24 are in contact with each other at a plurality of 
positions. Thus, crescent-shaped compression chambers are defined between 
end plates 16 and 22 and wraps 1B and 24. A hole 19 is bored through the 
center of stationary scroll member 12 so that compressed gas is discharged 
to the outside through hole 19. 
Referring now to FIGS. 3 and 4, a method for manufacturing the scroll 
member will be described. 
A disk with a diameter of about 75 mm is cut out from a steel sheet with a 
thickness of about 6 mm, and holes for injection and deflation are bored 
through proper portions of the disk. Groove 17 (23), having the shape of 
an involute curve or a series semi-circle curve, is formed in one-side 
surface of the disk by die forging (step 1). 
A mold release agent is applied to groove 33 of metallic mold half 32 (step 
2). The mold release agent need not be applied, when the inner surface of 
groove 33 is sufficiently smooth, or when the resin injected is of such 
type that can easily released from the mold when solidified. 
End plate 16 (22) molded in step 1 is fitted into mold half 32 so that its 
groove 17 (23) is in alignment with groove 33 of mold half 32. Then, the 
other mold half 34 is put on end plate 16 (22) so that the holes 39, 40 
for injection and deflation of the end plates are in alignment with 
injection hole 35 and vent hole 36 of mold half 34, respectively. Mold 32 
and 34 are bound together by means of restriction means to prevent 
disengagement (step 3). 
Mold 32 and 34 are preheated to a predetermined temperature (step 4). 
A gate of an injection-molding machine is connected to injection hole 35, 
and molten LCP resin liquid-crystal polymer resin) is injected into 
grooves 17 (23) and 33 (step 5). 
After the resin is solidified, mold 32 and 34 are unbound, end plate 16 
(22) is taken out from mold 32 and 34, and burrs are removed from holes 35 
and 36 (step 6). 
The end face of the wrap is finish-ground to improve its evenness (step 7). 
Thus, scroll member 12 (14), as shown in FIG. 2, is completed such that 
the thickness, height, and space (gap) of wrap 18 (24) are 3 mm, 10 mm, 
and 8 mm, respectively. 
According to the first embodiment described above, the resin is injected 
from the groove side of the end plate, so that its finally solidifying 
portion is situated at the root portion of the wrap. Practically, 
therefore, the shape of the wrap is not influenced by local contraction. 
Thus, the scroll member can be finished with high accuracy, so that the 
duty of the grinding work afterward can be lightened. Since no fins are 
produced on the end face of the wrap, the accuracy of the wrap can be 
prevented from being lowered by deburring. The special resin for use as 
the wrap material is highly lubricant against metal. Therefore, the 
friction loss of the wraps by their sliding action can be made smaller 
than when the wrap are made of metal. 
Referring now to FIG. 6, a second embodiment of the present invention will 
be described. A description of those portions or components which are used 
in common in the first and second embodiments is omitted herein. 
In this second embodiment, end plate 42 is made of resin. End plate 42 has 
been fabricated by injection molding, and a wrap is then formed by 
injecting the resin into groove 43 of the end plate. The width of groove 
43 is made wider than that of groove 33 used to form the wrap. End plate 
42 can be made of a metal, instead of resin. 
According the second embodiment described above, the end plate and the wrap 
are formed separately by injection molding, so that the shapes of the 
individual components to be molded are simple, and each component has a 
uniform thickness. Accordingly, the scroll member is subject to less 
deformation than in the case of integral injection molding. Since 
contraction of the resin can be absorbed the modified groove for the wrap, 
moreover, the wrap can be formed with higher accuracy. Furthermore, that 
part of the end plate corresponding to the location of the groove is 
melted by heat from the molten resin, so that the wrap and the end plate 
can be bonded more firmly to each other. 
Referring now to FIGS. 7 and 10, a third embodiment of the present 
invention will be described. 
A description of those portions or components which are used in common in 
the first to third embodiments is omitted herein. As shown in FIGS. 7 and 
8, end plate 52 of the third embodiment is a composite plate composed of 
four aluminum sheets 54, 55, 56 and 57. End plate 52 has spiroidal groove 
53 and a boss (not shown in FIG. 7) on its front and rear faces, 
respectively. In this case, the width of groove 53 is substantially equal 
to that of a wrap. 
As shown in FIG. 9, spiroidal holes 61a and 61b are formed in sheet 54 and 
55, respectively, by punching so that groove 53 is defined when sheets 54 
and 55 are joined together. Sheets 54 and 55 and support sheet 56 each 
have recess 58 and projection 59 whose depth or height is half the 
thickness of each sheet. Thus, when all the four sheets are joined 
together, their recesses 58 and projections 59 and hole 60 are aligned 
with one another. If they are pressed in this state, sheets 54 to 57 are 
bonded and formed into an integral structure such that recesses 58, 
projections 59, and hole 60 engage one another. In this case, the diameter 
of these cut portions is made smaller enough than that of the wrap lest 
the compressed gas be by-passed via the engaging portions. 
According to the third embodiment described above, even a deep groove can 
be formed accurately for the wrap. 
A conventional composite plate (end plate), which is formed by brazing or 
welding, is subject to distortion by heating. According to the present 
invention, however, the sheets can be pasted together without being 
heated, so that the end plate can be formed without distortion. 
As shown in FIG. 10, spiroidal hole 61a of plate 54 can be narrower than 
spiroidal hole 61b of plate 55, thereby to reduce the opening of groove 
63, and thus changing the shape of groove 63 of end plate 62. In this 
case, the wraps and the end plate can be bonded more firmly to each other. 
Moreover, a scroll member with a complicated shape can be accurately 
manufactured without a substantial distortion. Thus, there may be provided 
a compressor, pump or expander which can be reduced in torque fluctuation 
during operation, and produces less noise and vibration. 
As is shown in FIG. 11, groove 73 of end plate 72 can be narrower than 
groove 33 of mold half 32. 
As has been described above, the wrap can be made of one material selected 
from many, and the end plate can also be made of one selected from many. 
In other words, a variety of combinations of two materials for the wrap 
are the end plate are possible. The wrap and the end plate made of 
different materials, and slide better, one on the other , when lubricated 
with oil than when made of similar materials. Therefore, the wear of the 
wrap and the end plate can be minimized, and the loss of the orbiting 
torque of the scroll member decreases, whereby the scroll member is 
sufficiently reliable. 
According to the present invention, furthermore, the injection molding 
permits the wrap to be formed and bonded to the end plate simultaneously, 
so that a high-accuracy scroll member can be produced easily and quickly. 
Thus, according to the invention, the scroll member can be manufactured at 
lower cost than in the case of the prior art manufacturing method in which 
the wrap is fitted into the groove.