Scroll type fluid machine with prevention of stress concentration

A scroll type fluid machine comprising a pair of mutually engaged scroll members each including a side plate and a spiral lap uprightly disposed on an inside surface of the side plate; when the scroll members are relatively resolved in solar motion relationship, a fluid volume in sealed chambers defined by the pair of engaged scroll members being varied, so that a pressure of the fluid in the sealed chambers is thereby varied in order to discharge a gas therefrom, characterized by constituting so that stress may not concentrate at stress concentration portions of the scroll members, i.e., at corners of inner end base portions of the laps and the inside surfaces of the side plates in an eddy center section of the scroll members; and a method for forming the scroll members which permit improving productivity, characterized by forming, at the stress concentration portion of each scroll member, a round having a relatively large curvature radius which is enough to provide it with fatigue strength, and then finishing a relatively small round by means of a cutter for finish working.

BACKGROUND OF THE INVENTION 
(i) Field of the Invention 
The present invention relates to a scroll type fluid machine which can be 
employed as a compressor, an expanding machine, an electric motor or the 
like, and to a method for molding scroll members used in the fluid 
machine. 
(ii) Description of the Prior Art 
FIGS. 19 and 20 (which is a sectional view taken along the line XX--XX in 
FIG. 19) of accompanying drawings show one embodiment of a scroll body in 
a conventional scroll type compressor. A pair of scroll bodies 01, 02 are 
engaged with each other, with their laps 01a, 02a deviating from each 
other in phase as much as an angle of 180.degree., and with tip ends 01c, 
02c of the laps 01a, 02a closely contacting with inside surfaces 01d, 02d 
of side plates 01b, 02b. In consequence, when both the scroll bodies are 
revolved relatively, fluid volumes in sealed chambers 03, 04 defined by 
the pair of engaged scroll bodies 01, 02 will be reduced gradually while 
they are moved toward their center, in order to compress a gas in the 
chambers 03, 04 and to then discharge it through a discharge opening 05 at 
the central position of the machine. 
Techniques for manufacturing this type of scroll members 01, 02 can be 
classified into two methods. One of them comprises separately preparing 
the side plates and the laps, and then combining both to each other. 
Another method comprises simultaneously and integrally preparing the side 
plates and the laps. In the case of the former method, the technique of 
fixing the laps to the side plates is less reliable and a working accuracy 
is also insufficient, and thus the side plates and the laps, after their 
fixation, must be finally finished on all of their surfaces which will be 
in contact with the partner scroll. For this reason, the method in which 
the scroll members 01, 02 are integrally and simultagenously formed has 
heretofore been employed. 
However, the conventional integral type of fluid machine takes the system 
that the gas in the sealed chambers 03, 04 is airtightly retained, 
therefore as shown enlargedly in FIG. 21, angular portions at the corner 
of base portions of the laps 01a, 02a and inside surfaces 01d, 02d of the 
side plates 01b, 02b cannot be rounded and have right angles. As a result, 
stress will concentrate at these angular corner portions, and the base 
portions of the laps 01a, 02a will be poor in strength, depending upon a 
height of the laps 01a, 02a and compressive conditions. Further, a 
repeated application of an engaging force between the laps 01a, 02a and/or 
a pressure of the gas in the sealed chambers 03, 04 will lead to the 
occurrence of cracks and breakage troubles. It can thus be appreciated 
that the conventional integral method possesses no satisfactory 
reliability. 
The pressure of the gas in the sealed chambers 03, 04 becomes higher as the 
sealed chambers 03, 04 approach the center of the spiral laps, and it is 
to be noted that the siffness of the spiral laps 01a, 02a is smaller at 
their inner end portions, i.e., at their central portions than at other 
portions thereof. In most cases, accordingly, cracks and breakage troubles 
have appeared at a base of an inner end portion (at an end in the center 
of a spiral eddy) of each lap 01a or 02a, as shown by an arrow in FIG. 23. 
If an attempt is made to round the angular portions A.sub.2 at the corners 
of the bases of the laps 01a, 02a and the inside surfaces 01d, 02d of the 
side plates 01b, 02b on condition that the gas in the sealed chambers 03, 
04 is airtightly retained, a constitution in FIG. 22 can be conceived. 
Moreover, as in FIG. 22, if it is contemplated to round the angular portion 
at the base corner A.sub.2 of the lap 01a of the scroll members 01 and the 
inside surface 01b of the side plate 01b, the respective laps 01a, 02a of 
the pair of scroll members 01, 02 must also be rounded on their tip 
portions B.sub.2 in order to prevent the angular portion A.sub.2 from 
contacting with the tip portion of the lap 02a of the partner scroll 
member 02. 
In short, it is necessary to round off, in the same shape, the angular 
portions A.sub.2 at the corners of the laps 01a, 02a and the side plates 
01b, 02b of both the scroll members 01, 02 as well as the tip portions 
B.sub.2 of the corresponding laps 01a, 02a. 
In order to obtain such a structure, an extremely intricate working will be 
required and costs of the mechanical working will increase noticeably. For 
this reason, such a constitution can be designed only on a desk, but has 
not been put into practice. 
SUMMARY OF THE INVENTION 
The present invention has now been achieved in view of the above-mentioned 
situations. 
An object of the present invention is to provide a scroll type fluid 
machine and a method for forming scroll members used therein, and 
according to the present invention, it can be accomplished to protect, 
from cracks and breakage troubles, angular portions at the corners of 
inner end base portions of laps and inside surfaces of side plates in the 
eddy center of spiral scroll members. 
For the achievement of the above-mentioned object, the present invention 
comprises the following gists: 
(I) A scroll type fluid machine comprising a pair of mutually engaged 
scroll members each including a side plate and a spiral lap uprightly 
disposed on an inside surface of the side plate; when the scroll members 
are relatively revolved, in solar motion relationship, fluid volumes in 
sealed chambers defined by the pair of engaged scroll members being 
varied, so that a pressure of the fluid in the sealed chambers is thereby 
varied in order to discharge a gas therefrom, characterized by: 
(i) constituting so that stress may not concentrate at corners of inner end 
base portions of the laps of the scroll members and the inside surfaces of 
the side plates, and 
(ii) the scroll members which are prepared by blowing, on rounds each 
having a curvature radius .rho. at the corners of the inner end base 
portions of the laps and the inside surfaces of the side plates of the 
scroll members, solid grains each having a smaller diameter than the 
above-mentioned curvature radius .rho., and mechanically finishing 
portions of the laps and the side plates other than the portions on which 
the solid grains have been blown. 
(II) A method for forming scroll members used in a scroll type fluid 
machine comprising a pair of engaged scroll members each including a side 
plate and a spiral lap uprightly disposed on an inside surface of the side 
plate; when the scroll members are relatively revolved in solar motion 
relationship, fluid volumes in sealed chambers defined by the pair of 
engaged scroll members being varied, so that a pressure of the fluid in 
the sealed chambers is thereby varied in order to discharge a gas 
therefrom, the method being characterized by roughly working each corner 
of an inner end base portion of the lap and the inside surface of the side 
plate of the scroll member so as to form a complete round having a 
relatively large curvature radius which is enough to provide the lap with 
fatigue strength, by the use of a cutter, and finishing, at each corner 
portion, a round having a relatively small curvature radius which does not 
contact with a tip end portion of the lap of the partner scroll member, by 
the use of a cutter. 
The fluid machine according to the present invention has the 
above-mentioned constitution, and effects in the following paragraphs (I) 
(i) and (ii) as well as (II) can be obtained: 
(I) (i) Since the fluid machine is constructed so that stress may not 
concentrate at each corner of the inside end base portion of the lap and 
the inside surface of the side plate of the scroll member, the occurrence 
of cracks and breakage troubles can be prevented at the corner. In this 
case, both the scrolls are engaged with each other at the same positions 
thereof as in the conventional one, and thus the performance is at a level 
similar to that of the conventional one. 
(ii) Each round having a curvature radius .rho. is present at each corner 
of the inside end base portion of the lap and the inside surface of the 
side plate and is provided with compressive residual stress by blowing 
solid grains thereon, and fatigue strength at the rounded portion is 
heightened about 65% more than that of the conventional one, together with 
the increse in its surface hardness. Therefore, the fluid machine of the 
present invention can prevent cracks and breakage troubles from occurring 
at the corners of the inside end base portions of the laps. Further, since 
the portions where the scroll members are engaged with each other are 
mechanically finished in the same way as in the conventional one, it can 
be avoided that a fluid in the sealed chambers leaks out therefrom. 
Accordingly, the performance of the fluid machine does not deteriorate. 
(II) At a stress concentration position in each scroll member, i.e., at the 
corner of the base of the lap and the inside surface of the side plate, 
the relatively large round can be roughly formed which is sufficient to 
ensure the lap with fatigue strength, and finishing another round can be 
accomplished in a simple manner of cutting each corner portion of the lap 
by the use of a finishing cutter after the rough working. Therefore, the 
number of the working hours is not increased and the productivity can be 
improved. 
Further, after the rough working, the above-mentioned round can be formed 
at each corner portion, and this round has the relatively small curvature 
radius which does not contact with the tip end portion of the lap of the 
partner scroll member. Therefore, the scroll type fluid machine of the 
present invention can prevent the fluid from leaking out through the 
sealed chambers. In consequence, it can be avoided that its performance 
deteriorates.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
EMBODIMENT 1 
The first embodiment of the present invention will be described in detail 
in reference to FIGS. 1 and 2. 
Referring to FIGS. 1 and 2, numeral 11 is a scroll member, and numeral 11a 
is a spiral lap which is prepared integrally on an inside surface 11d of a 
side plate 11b by means of casting, forging or injection molding. Contact 
surfaces extending outwardly from points a and b may be finally finished 
in a mechanical manner, and in this connection, the above-mentioned 
contact surfaces are the portions where the laps 11a of a pair of scroll 
members are engaged with each other. On the contary, a leading nose 
section extending between the points a and b at an inner end portion (an 
end portion at an eddy center of the spiral lap) of the lap 11a is not 
finished mechanically, and a round at the corner of the base of the lap 
11a and the inside surface 11d of the side plate 11b, i.e., a round 
already formed on a scroll stock is left as it is there. 
In this way, the round R having a radius .rho. is formed only at the corner 
of the inner end portion of the lap 11a and the inside surface 11d of the 
side plate llb. 
As a result, it can be avoided that stress concentrates at the corner of 
the inner end portion of the lap 11a and the inside surface 11d of the 
side plate 11b, and the occurrence of the cracks and breakage troubles can 
be prevented at this corner. 
As described above, the position where the round R having the radius .rho. 
is formed is only the inner end portion of the lap, and it is thus 
unnecessary to form the rounds on base portions A.sub.2 and tip portions 
B.sub.2 of the laps as exhibited in FIG. 22. Therefore, the 
above-mentioned object of the present invention can be accomplished by an 
extremely simple manufacturing method. 
The aforesaid points a and b of the inner end portion (the end portion at 
the eddy center of the spiral lap) may be positioned arbitrarily within 
"involute curve-effective limit points which depend upon a parameter 
.beta." which is suggested in, for example, Japanese Patent Application 
No. 111658/1984 (U.S. Ser. No. 738,049 filed May 24, 1985). 
This theory will be described by quoting from this Japanese patent 
application, and FIG. 25 attached hereto is quoted from FIG. 1 of the 
aforesaid Japanese application. 
Referring to FIG. 25, there is shown a stationary spiral element 701, and 
reference numerals 711 and 712 are an outer curve and an inner curve, 
respectively. 
It is seen that the outer curve 711 is an involute curve having a starting 
point A and that a base circle of a radius b, a curvilinear section E-F of 
the inner curve 712 is of an involute curve having an angular shift of 
(.pi.-.lambda./b) with respect to the outer curve 711. It is also seen 
that a curvilinear section E-I is of an arc having the same radius Rc as 
the radius of an end milling cutter, and that a section I-G is an arc 
having a center O.sub.3 and a radius R.sub.7. There is shown a connection 
curve 713 which is of an arc having a radius r and which joints smoothly 
the outer curve 711 and the inner curve 712. 
A point B is a boundary point existing between the outer curve 711 and a 
connection curve 713, where these curves may share an identical tangential 
line. It is seen that it is of an involute curve in the area outside of 
the point B (on the point C's side), while it becomes an arc in the area 
inside of the point B (on the point G's side). 
The point A is the starting point of the outer curve 711, the point C is an 
arbitrary point existing in the area sufficiently outside of the outer 
curve 711, and the point F is an arbitrary point existing in the area 
sufficiently outside of the inner curve 712. The point G is a point of 
intersection between the arc having a radius R.sub.7 in the inner curve 
712 and the connection curve 713, and this point may be on an arbitary 
position on an arc having a radius r in the range D-B. 
Also, it is notable that this dimensional relationship may hold good in the 
case of the revolving spiral element. 
Now, the radii R.sub.7 and r may be given with the following equations; 
that is 
EQU R.sub.7 =.lambda.+b.beta.+d 
EQU r=b.beta.+d 
where 
.lambda. is the radius of revolutionary motion; 
b is the radius of a base circle; 
##EQU1## 
.beta. is a parameter, which represents a marginal range for the choice of 
an involute curve. 
It is seen that a straight line passing the origin O and defined at the 
angle of .beta. with respect to the X-axis and the straight line EO.sub.2 
and the extension of the straight line BO.sub.1 intersect orthogonally 
with each other, and that the straight line segments EO.sub.2 and BO.sub.1 
are in parallel with each other. 
According to the configuration of the spiral element mentioned above, it is 
noted that when installed in position, the point F on the involute curve 
at an arbitrary point sufficiently outside of the inner curve of the 
stationary spiral element 701 will come to contact with the corresponding 
point on the involute section of the outer curve on the part of the 
revolving spiral element (not shown), which point of contact will shift 
gradually radially inwardly as the revolving spiral element moves in 
revolution. And the point of contact is shifting to the point E on the 
inner curve 712 of the stationary spiral element 701, contacting with the 
corresponding point on the outer curve of the revolving spiral element 
(the same point as the point B on the part of the stationary spiral 
element). As the revolutionary motion of the spiral element continues 
still further, it is seen that the both elements are now caused to be 
moved with a gap of .DELTA.C defined between the curvilinear section E-D-G 
of the curve 602 and the section E-I-G of the curve 712. 
Therefore, it is notable that the contact engagement between the both 
spiral elements at the central leading ends thereof will continue till it 
reaches the point E (in contact with the point B on the complementary 
spiral element), therefore a small gap of .DELTA.C existing between the 
two in mutual engagement. 
That is to say, in the section between the involute curve-effective limit 
points E and B which are dependent upon the parameter .beta., constitution 
is made so that a small clearance may be present between the spiral 
members. 
The points a and b (in FIG. 1) in each scroll member according to the 
present invention are arranged at suitable positions within the 
above-mentioned points E and B, and the portions which extend outside the 
points a and b (on the side of the involute curve) of the scroll member 
have the same right angle corners A.sub.1 as in FIG. 21. This constitution 
permits accomplishing a proper engagement of both the spiral members and 
providing a good performance, and since both the spiral members are not in 
contact with each other between the points a and b, the suitable rounds 
can be formed at bases of the laps. Further, the portions where both the 
scrolls engage with each other are finished by the same final working as 
in the conventional one, and thus the performace is also the same as in 
the conventional one. 
Needless to say, the corner portions of scroll stocks can be rounded by a 
mechanical working, as exhibited in FIGS. 1 and 2. 
EMBODIMENT 2 
Next, Embodiment 2 of the present invention will be described. 
In Embodiment 1 just described, the round R having the shape of the recess, 
which has been formed at the corner of an inner end base portion of the 
lap 11a and the inside surface 11d of the side plate 11b of the scroll 
stock, may be left as it is there. 
Alternatively, instead of leaving the recess-shaped round which has been 
formed on the stock, the corner portion may be rounded in the form of the 
recess by mechanically working the stock. 
EMBODIMENT 3 
According to Embodiment 1 given above, as shown in FIG. 24 (the sectional 
view illustrating the engaging condition of both the scrolls in the 
section between the points a and b in FIG. 1), the round portion R is 
brought into contact with the tip end portion of the partner lap (which is 
shown by a onedot chain line in FIG. 24), since the lap has a right angle 
edge and an intact large wall thickness. Therefore, together with the 
formation of the round R at the corner portion, it is necessary to 
decrease the wall thickness of the laps of both the scrolls in compliance 
with the formed R, though a little decline in strength occurs owing to the 
decreased wall thickness. 
In FIG. 24, the lap and the side plate of the partner scroll member 12 are 
represented by reference numerals 12a and 12b, respectively. 
In view of such situations, the rounds R are formed between the points a 
and b in the vicinity of the inner end base portions of the laps of both 
the scrolls, and also on the corresponding tip portions of the laps of 
both the scrolls, the rounds R are left as they are, or beveling is 
carried out so that these tip portions may not contact with the rounds R 
at the base portions of the laps. 
Embodiment 3 of the present invention will be described in detail in 
reference to FIGS. 5 to 7. 
Referring to FIGS. 5 to 7, reference numeral 11 is a scroll body, and 
numerals 11a and 11b are a lap and a side plate, respectively. Rounds R 
having radii of .rho., .rho..sub.1 are formed on the base and the tip of 
the lap only in the region between points a and b at an inner end portion 
of the lap 11a where both the scroll members are not engaged with each 
other. As for the tip of the lap, beveling may be carried out. Sizes of 
the round R and the beveling are suitably decided so that both the scrolls 
may not contact with each other when driven. The partner scroll member is 
constituted similarly. By working in such a way, the laps 11a, 12a are 
engaged in the region between the points a and b in FIG. 5 as shown in a 
sectional view of FIG. 7. In this case, the round R having the radius of 
.rho. is formed at the corner of the lap and the side plate without 
reducing the wall thickness of the inner end portion of the lap at all, 
with the result that the strength of the lap can be improved as much as an 
amount based on the formation of the round R at the corner. Further, the 
portions where both the scroll members are engaged with each other are the 
same as in the conventional one, and thus the performance is also similar 
to that of the conventional one. 
EMBODIMENT 4 
In FIG. 2 regarding Embodiment 1, it is suggested to form the large round R 
at the base of the inner end portion of the lap of the scroll member. Now, 
in order to form the above-mentioned large round R at the base of the 
central lap with the intention of minimizing a remaining fluid volume at 
the end of the discharge process, it is contrived (1) to reduce the wall 
thickness of the lap as much as an amount corresponding to the round R, 
and (2) to bevel the tip of the lap so that it may not contact with the 
round R at the base of the lap. However, the concept (1) will render its 
strength poor and the concept (2) will increase costs disadvatageously 
because of using a cutter having a peculiar shape. 
For these reasons, the wall thickness of the lap is reduced as much as an 
amount corresponding to 1/2 of the original R in order to prevent the 
round R at the inner end base portion of the scroll lap from contacting 
with the partner scroll member. 
Embodiment 4 of the present invention will be described in detail in 
reference to FIGS. 8 and 9. 
Referring to FIGS. 8 and 9, numeral 11 is a scroll body, and numeral 11a is 
a lap of the scroll body 11. At a high stress generation area, i.e., at 
the base of an inner end of the lap 11a, a round R is formed which is the 
same as the round R shown in FIG. 2 regarding Embodiment 1. The wall 
thickness of the lap is decreased as much as an amount corresponding to 
1/2 of the round R. Reference numeral 11b is a side plate of the scroll 
body 11. 
Such a constitution permits minimizing the reduction in the wall thickness 
of the lap and preventing stress from concentrating at the base of the 
lap. 
Since the wall thickness of the lap is reduced by an amount corresponding 
to 1/2 of R with the aim of preventing the round R at the base of the 
inner end portion of the lap from contacting with the partner scroll, the 
decline in the wall thickness of the lap can be minimized, which fact 
permits manufacturing the scroll lap the strength of which is less lost. 
EMBODIMENTS 5 AND 6 
Embodiments 5 and 6 of the present invention will be described in detail in 
reference to drawings. 
In FIGS. 10 and 11, Embodiment 5 is shown. A scroll member 11 which is 
equipped with a spiral lap 11a and a side plate 11b is integrally molded 
by rough working such as forging, casting or injection molding. In this 
case, at an inner end portion of the lap 11a, i.e., at a corner portion of 
the lap 11a and the side plate 11b in a region between points a and b at 
which the lap will begin to contact with the lap of the partner scroll, a 
round R having a curvature radius of .rho. is formed. Afterward, onto the 
round R of the scroll member which is an unfinished stock, a mixture 
including solid grains is blown which is prepared by mixing, with a 
liquid, the solid grains such as steel balls, glass beads or abrasive 
grains each having a curvature radius of .rho. or less. The portions other 
than the above solid grainsblown portion of the lap and the whole of the 
side plate are then finished by means of a mechanical working. The 
treatment of blowing the solid grains may be carried out after the 
mechanical working. 
In Embodiment 6, as shown in FIGS. 12 and 13, a recess may be formed in the 
side plate at the base of the inner end portion of the lap 11a in molding 
the scroll member integrally, whereby a round R.sub.0 having a curvature 
radius .rho. is formed at the corner of the lap 11a and the side plate 
11b. 
According to Embodiment 5, the round having a curvature radius of .rho. is 
present at the corner of the inner end portion of the lap and the side 
plate, and this round is provided with compression residual stress by the 
blow of the solid grains. Further, fatigue strength at the round portion 
is heightened together with the increase in surface hardness. FIG. 14 
shows a ratio of the fatigue strength of the scroll member PS in the 
present embodiment to that of a conventional scroll member CS. The results 
shown therein are obtained under the conditions that a material for the 
scroll members is an aliminum alloy casting, a used test machine is a 
Schenk type plane bending fatigue testing machine, a repeated velocity of 
the test is 1800 cpm, and an ambient temperature is ordinary temperature. 
According to these results, the fatigue strength at the above-mentioned 
round formed in this embodiment is improved about 65% more than that of 
the conventional one, and at the inner end portion of the lap, the 
generation of cracks and breakage troubles is restrained. 
EMBODIMENT 7 
Embodiment 7 of the present invention will be described in detail in 
reference to drawings. 
As shown in FIGS. 17 and 18, a complete round having a relatively large 
curvature radius R.sub.1 which is enough to provide a lap 11a with fatigue 
strength is roughly formed at a corner of at least an inner end base 
portion of the lap 11a and an inside surface 11d of a side plate 11b of a 
scroll member 11 by the use of an end milling cutter. Afterward, as shown 
in FIGS. 15 and 16, a relatively small round having a curvature radius 
R.sub.2 which will not contact with a tip end portion of the lap of the 
partner scroll member is formed, by the end milling cutter, at a corner of 
the base of the lap 11a and the inside surface 11d of the side plate 11b 
within peripheral ranges M and N placed outside points a and b of the lap 
11a of the scroll member 11, and the above-mentioned ranges M and N are 
sections which will begin to contact with the lap of the partner scroll 
member. Further, within a range L between the points a and b, a position 
of the inside surface 11d of the side plate 11b which is placed away from 
a side surface of the lap 11a is mainly cut by the end milling cutter, 
with the aforesaid round having the curvature radius of R.sub.1 left at it 
is. 
These working operations can be accomplished by using the end milling 
cutter for rough working a bit of which has the curvature radius of 
R.sub.1 at its tip, and the end milling cutter for finish working a bit of 
which has the curvature radius of R.sub.2 at its tip. Further, it is 
preferred that the curvature radius R.sub.1 is 10 times or more as much as 
the curvature radius R.sub.2. At corners of the base portions other than 
the stress concentration portion, i.e., the inner end portion of the lap 
11a of the scroll member 11 and the inside surface 11d of the side plate 
11b, a right angle configuration may be formed in a conventional manner, 
or the relatively small round having the curvature radius R.sub.2 may be 
formed directly by means of the end milling cutter so that the aforesaid 
corner portions may not contact with the tip end portion of the lap of the 
partner scroll. If a wear-resistant bottom plate is disposed on the side 
plate of the scroll member, the tip of the bit of the end milling cutter 
for finish working should selectively have such a curvature radius R.sub.2 
as does not interfere with a curvature radius at an end portion of the 
bottom plate.