Scroll type compressor with improved rotation preventing means

A scroll type compressor includes a stationary scroll element, a movable scroll element orbiting about a given axis and cooperating with the stationary scroll element for compressing a fluid in a compression chamber defined between the two scroll elements, and a rotation preventing unit for preventing rotation of the movable scroll element about its own axis. The rotation preventing unit has at least a plurality of pairs of scroll side pins mounted on the movable scroll element and housing side pins mounted on a housing of the compressor. When the compression chamber has a reduced volume of 10 through 22% of an initial volume thereof immediately after completion of sucking of the fluid, at least two of the plurality of scroll side pins are arranged to be symmetrical with one another with respect to a line L.sub.2 which passes through a rotating center O.sub.R of the movable scroll element and is perpendicular to a different line L.sub.1 which passes through the rotating center O.sub.R of the movable scroll element and an orbiting center O.sub.S of the movable scroll element. The two scroll side pins are also arranged on a leading side to the cooperating housing side pins, respectively, in a direction corresponding to a direction of rotation of the movable scroll element about the rotating center O.sub.R.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a scroll type compressor adapted 
to being incorporated in a climate control system or an air-conditioning 
system, and more particularly, relates to a rotation preventing means 
accommodated in a scroll type compressor to prevent a movable scroll 
element from being rotated about its own axis during the operation of the 
compressor. 
2. Description of the Related Art 
Generally, a scroll type compressor includes a stationary scroll element 
having a fixed base plate and a spiral or wrap element fixed to an end 
face of the fixed base plate, and a movable scroll element having a base 
plate and a movable spiral or wrap element fixed to an end face of the 
base plate. The stationary and movable scroll elements are housed in a 
housing and engage one another so that the spiral elements of the 
stationary and movable scroll elements are mutually engaged with one 
another to define compression chambers in the shape of pockets moving from 
an outer portion of the stationary and movable scroll elements toward the 
center of both elements. Namely, when the movable scroll element orbits 
about the center of the stationary scroll element, the pocket-like 
compression chambers are gradually shifted from the outer portion of the 
engaged spiral elements of both stationary and movable scroll elements to 
the center of both elements so as to compress a fluid which is, typically, 
a refrigerant gas. 
The above-mentioned scroll type compressor is conventionally provided with 
a rotation preventing means for preventing the movable scroll element from 
being rotated about its own axis and to permit it to perform an orbiting 
motion about the center of the stationary scroll element. A typical 
rotation preventing means is disclosed in Japanese Unexamined Patent 
Application Publication (Kokai) No. 62-199983, which includes a plurality 
of pin and ring assemblies, each being provided with a first pin fixedly 
attached to the base plate of the movable scroll element, a different 
second pin fixedly attached to an inner wall of the housing confronting 
the base plate of the movable scroll element, and a ring element fitted 
around outer ends of the first and second pins. Thus, when the movable 
scroll element orbits around the central axis of the stationary scroll 
element, the first pins of the pin and ring assemblies attached to the 
movable scroll element turn around the second pins attached to the 
stationary scroll element under the control of the ring element. Thus, the 
movable scroll element is prevented from being rotated about its own axis, 
and is permitted to orbit about the center of the stationary scroll 
element. 
When the compressor operates so as to compress the fluid, e.g., a 
refrigerant gas, a reaction force acts on the movable scroll element. A 
part of the reaction force applies a moment to the movable element acting 
to rotate it about its own axis. Therefore, the first and second pins of 
the rotation preventing means mounted on the movable scroll element and 
the housing receive a reaction force as a load from the movable scroll 
element which is proportional to the extent of the moment acting on the 
movable scroll element. Therefore, for instance, the load might be 
concentrically applied to one of the pairs of pin and ring assemblies of 
the rotation preventing means to thereby cause a breakage of the pin and 
ring assembly. However, if the diameters of the pins of the rotation 
preventing means are increased so as to increase a mechanical strength 
thereof, the entire size of the scroll type compressor becomes large. 
Thus, in order to prevent breakage of the rotation preventing means and to 
simultaneously reduce the size of the body of the compressor, the rotation 
preventing means provided with the plurality of pin and ring assemblies 
must be arranged so that a substantially identical load is applied to 
respective pin and ring assemblies of the rotation preventing means. 
At this stage, according to an experiment conducted by the present 
inventors, the moment applied to the movable scroll element and causing 
the rotation of the movable scroll element about its own axis changes to 
have a single peak value i.e., the maximum value thereof during one 
complete rotation of a drive or crank shaft of the compressor, as shown in 
the graph of FIG. 6. For example, when a scroll type compressor was 
operated under a condition such that a suction and a discharge pressures 
of the fluid of the compressor were set as 4.0 kgf/cm.sup.2 and 30 
kgf/cm.sup.2, respectively, the maximum value of the moment causing the 
rotation of the movable scroll element about its own axis occurred when 
the volume of each of the plurality of compression chambers is reduced to 
16% of the initial volume thereof presented immediately after the suction 
of the fluid. Namely, the maximum value of the moment occurs when the 
volumetric ratio of each of the compression chambers reaches 16%. 
Therefore, the present inventors further conducted experiments to detect 
how the moment causing a rotation of the movable scroll element changes 
depending upon a change in the suction and discharge pressures of the 
compressor, and detected that in general, the maximum value of the moment 
occurs when the volumetric ratio of the compressor is between 10 through 
22%. 
When the moment changes to the maximum value thereof, the load applied to 
the rotation preventing means also becomes the maximum. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a scroll type 
compressor provided with a rotation preventing means for a movable scroll 
element, which includes a plurality of pin and ring assemblies, each 
having a pair of pins mounted on a compressor housing and the scroll 
element, respectively, and a ring therein, and which further includes an 
arrangement wherein a substantially identical load is evenly applied to 
each pair of pins of the plurality of pin and ring assemblies. 
In accordance with an aspect of the present invention, there is provided a 
scroll type compressor for compressing a fluid which comprises: 
a housing unit for forming an outer framework of the compressor and 
provided with an inlet port for introducing the fluid before compression 
into the compressor and an outlet for delivering the fluid after 
compression; 
a shaft rotatably supported in the housing unit and having an inner portion 
thereof forming a drive part of the compressor; 
a stationary scroll element provided with a stationary end plate secured to 
the housing unit for forming a sealed cavity between the housing unit and 
the stationary end plate, and a stationary spiral member formed on one end 
of the end plate and arranged in the sealed cavity; 
a movable scroll element provided with a movable end plate having an inner 
end face facing the sealed cavity and an outer end face opposite to the 
inner end face on which a flange portion operatively connected to the 
drive part of the shaft, and a movable spiral member formed on the inner 
end face of the movable end plate, the movable spiral member being movably 
engaged with the stationary spiral member and defining a compression 
chamber between the stationary and movable scroll elements which has an 
initial volume reducible to compress the fluid; and 
a rotation preventing unit for preventing rotation of the movable scroll 
element about its own axis and permitting the movable scroll element to 
implement an orbital motion about a given axis in response to rotation of 
the shaft, the rotation preventing unit including: 
a plurality of scroll side pins mounted in the outer end face of the 
movable end plate so as to project from the outer end face, and having a 
cylindrical face thereof, respectively; 
a plurality of housing side pins mounted in the housing unit so as to 
project toward the plurality of scroll side pins and having a cylindrical 
face thereof, respectively, the plurality of housing pins and the scroll 
side pins forming a plurality of pairs of cooperative scroll and housing 
side pins; and 
a plurality of ring elements, each of the ring elements being arranged to 
be engaged with each of the plurality of pairs of cooperative scroll and 
housing side pins in such a manner that an inner wall of the ring element 
is in contact with the cooperative scroll and housing side pins to thereby 
prevent rotation of the movable scroll element. 
The scroll type compressor is characterized in that when the compression 
chamber has a reduced volume of 10 through 22% of the initial volume of 
the compression chamber immediately after completion of sucking of the 
fluid before compression, at least two of the plurality of scroll side 
pins (A and B) of the rotation preventing unit are arranged to be 
symmetrical with one another with respect to a line L.sub.2 which passes 
through a rotating center O.sub.R about which the movable scroll element 
rotates and is perpendicular to a different line L.sub.1 which passes 
through the rotating center O.sub.R about which the movable scroll element 
rotates and an orbiting center O.sub.S of the movable scroll element. 
Further, the above-mentioned two of the plurality of scroll side pins are 
arranged on a leading side to the cooperating housing side pins, 
respectively, in a direction corresponding to a direction of rotation of 
the movable scroll element about the rotating center O.sub.R. Thus, when a 
load caused by the maximum moment acting on the movable scroll element 
during the operation of the compressor acts on paired scroll and housing 
side pins of the rotation preventing unit, the load is evenly applied to 
each pair of scroll and housing side pins without occurrence of 
concentration of the load to only one pair of scroll and housing side 
pins. Thus, the rotation preventing unit can be prevented from being 
broken. 
Preferably, the rotation preventing unit comprises an even number of paired 
cooperative scroll side and housing side pins and a corresponding even 
number of ring elements arranged in a region capable of contributing to 
prevention of rotation of the movable scroll element, with respect to the 
line L.sub.1 extending to pass through both the rotating center O.sub.R 
and the orbiting center O.sub.S of the movable scroll element. 
Further, the plurality of scroll side pins of the rotation preventing unit 
are arranged equiangularly on a circle having a center located at the 
rotating center O.sub.R of the movable scroll element, and wherein the 
plurality of housing side pins of the rotation preventing unit are 
arranged equiangularly on a different circle having a center thereof 
located at the orbiting center O.sub.S of the movable scroll element. 
The rotation preventing unit may comprise at the most four pairs of 
cooperative scroll and housing side pins and at the most four ring 
elements engaged with the four pairs of cooperative scroll and housing 
side pins. 
When the compression chamber has a reduced volume at 10 through 22% of said 
initial volume of said compression chamber immediately after completion of 
sucking of the fluid before compression, the two scroll side pins having 
respective centers thereof may be arranged in such a manner that two lines 
passing through the respective centers of the two scroll side pins and the 
rotating center O.sub.R of the movable scroll element and the line L.sub.2 
passing through the rotating center O.sub.R of the movable scroll element 
and being perpendicular to the line L.sub.1 passing through both rotating 
center O.sub.R and orbiting center O.sub.S of the movable scroll element 
define two symmetrical angles with respect to the line L.sub.2, the 
symmetrical angles being substantially +45 degrees and -45 degrees, 
respectively. 
In accordance with another aspect of the present inventions, there is 
provided a scroll type compressor for compressing a fluid which comprises: 
a housing unit for forming an outer framework of the compressor and 
provided with an inlet port for introducing the fluid before compression 
into the compressor and an outlet for delivering the fluid after 
compression; 
a shaft rotatably supported in the housing and having an inner portion 
thereof forming a drive part of the compressor; 
a stationary scroll element including a stationary end plate secured to the 
housing unit for forming a sealed cavity between the housing unit and the 
stationary end plate, and a stationary spiral member formed on one end of 
the end plate and arranged in the sealed cavity; 
a movable scroll element including a movable end plate having an inner end 
face facing the sealed cavity and an outer end face opposite to the inner 
end face on which a flange portion operatively connected to the drive part 
of the shaft, and a movable spiral member formed on the inner end face of 
the movable end plate, the movable spiral member being movably engaged 
with the stationary spiral member and defining a compression chamber 
between the stationary and movable scroll elements which has an initial 
volume reducible to compress the fluid; and 
a rotation preventing unit for preventing rotation of the movable scroll 
element about its own axis and permitting the movable scroll element to 
implement an orbital motion about a given axis in response to rotation of 
the shaft, the rotation preventing unit including: 
a plurality of scroll side pins mounted in the outer end face of the 
movable end plate so as to project from the outer end surface, and having 
a cylindrical face thereof, respectively; and 
a plurality of housing side pins mounted in the housing unit so as to 
project toward the plurality of scroll side pins and having a cylindrical 
surface thereof, respectively, the plurality of housing pins and the 
scroll side pins being arranged in such a manner that the cylindrical 
surfaces of the plurality of scroll side pins and the plurality of housing 
side pins being in constant contact with one another to thereby prevent 
rotation of the movable scroll element during the operation of the 
compressor. 
The above-described scroll type compressor is characterized in that when 
the compression chamber has a reduced volume of 10 through 22% of the 
initial volume of the compression chamber immediately after completion of 
sucking of the fluid before compression, at least two of the plurality of 
scroll side pins of the rotation preventing unit are arranged to be 
symmetrical with one another with respect to a line L.sub.2 which passes 
through a rotating center O.sub.R about which the movable scroll element 
rotates and is perpendicular to a different line L.sub.1 which passes 
through the rotating center O.sub.R about which the movable scroll element 
rotates and an orbiting center O.sub.S of the movable scroll element. 
The housing side pins cooperative with the two scroll side pins are 
arranged on a leading side to the two scroll side pins, respectively, in a 
direction corresponding to a direction of rotation of the movable scroll 
element about the rotating center O.sub.R. Thus, when a load caused by the 
maximum moment acting on the movable scroll element during the operation 
of the compressor acts on paired scroll and housing side pins of the 
rotation preventing unit, the load is evenly applied to each pair of 
scroll and housing side pins without occurrence of concentration of the 
load to only one pair of scroll and housing side pins. Thus, the rotation 
preventing unit can be prevented from being broken.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(First Embodiment) 
FIG. 1 illustrates a general construction of a scroll type fluid compressor 
1 including a stationary scroll element and a movable scroll element. The 
compressor 1 has a front housing 2 having a central portion thereof in 
which an anti-friction bearing 4 is mounted to rotatably support a crank 
or drive shaft 3. The crank shaft 3 has a small diameter portion extending 
outwardly toward a central opening of the front housing 2, a large 
diameter portion 3a concentric and integral with the small diameter 
portion, and fitted in the inner race of the bearing 4, and a drive key 5a 
integral with the large diameter portion 3a and arranged to be eccentric 
with the central axis of the large diameter portion 3a of the crank shaft 
3. A movable scroll element 6 having a spiral member 6a spirally extending 
around a given axis is mounted in an axially inner end portion of the 
front housing 2. The movable scroll element 6 also has a movable end plate 
6b having an inner end face located far from the drive key 5a and the 
opposite outer end face located close to the large diameter portion 5a. 
The spiral member 6a is integrally secured to the inner end face of the 
end plate 6b. The movable scroll element 6 further has a boss portion 6c 
secured to a central portion of the outer end face of the end plate 6b. 
The boss portion 6c of the movable scroll element 6 has a bearing 7 
mounted in a central bore portion formed therein, and having a bush 8 
forming an inner race thereof. The bush 8 has a key way 8a in which the 
drive key 5a of the crank shaft 3 is securely keyed. The key way 8a and 
the drive key 5a have substantially rectangular cross-sections, as best 
shown in FIG. 2. At this stage, in the cross section of the key way 8a and 
the drive key 5a, as shown in FIG. 2, the longitudinal length of the 
rectangular shaped key way 8a of the bush 8 is larger than that of the 
rectangularly shaped drive key 5a of the crank shaft 3. Thus, the drive 
key 5a is slidably movable in the key way 8a of the bush 8 in a direction 
corresponding to the longitudinal direction of the key way 8a. 
It should be noted that, as shown in FIG. 2, the key way 8a of the bush 8 
and the drive key 5a of the crank shaft 3 are arranged in such a manner 
that the common center line of the key way 8a and the drive key 5a is 
turned by an angle "w" from an axis along which an eccentricity 
".epsilon." occurs between the bush 8 and the large diameter portion 3a of 
the drive shaft 3. The above-mentioned turning of the center line of the 
key way 8a and the drive key 5a is given in a direction opposite to the 
direction "OB" in which the movable scroll element 6 performs an orbital 
motion. The drive key 5a, the bush 8, and the key way 8a form a crank 
portion 5 for causing the orbital motion of the movable scroll element 6 
with respect to a later-described stationary scroll element. 
The scroll type compressor 1 further includes a stationary scroll element 9 
provided with a spiral member 9a, and a stationary end plate 9b. The 
stationary scroll element 6 is secured to the inner end of the front 
housing 2 by means of screw bolts (not shown in FIG. 1) so as to define an 
inner cavity 10 in which the movable scroll element 6 performs the orbital 
motion with respect to the stationary scroll element 9 about an axis of 
rotation of the crank shaft 3. 
The stationary end plate 9b of the stationary scroll element 9 is centrally 
provided with a discharge port 11 for discharging a compressed fluid from 
compression chambers defined by the movable and stationary spiral members 
6a and 9a. 
The discharge port 11 is in communication with a large cavity defined by 
the end of the stationary scroll element 9 and a rear housing 12. The 
large cavity is provided so as to act as a muffling chamber for muffling 
the pulsations in the discharged fluid, and accordingly, it is referred to 
as a muffling chamber 13. 
A check valve 14 made of spring steel plate is arranged in the muffling 
chamber 13 so as to open and close the discharge port 11 on the side 
adjacent to the muffling chamber 13. The check valve 14 prevents the 
discharged fluid from reversely flowing from the muffling chamber 13 into 
the compression chambers. As clearly shown in FIG. 1, the check valve 14 
is attached to an end face of the stationary end plate 9b, facing the 
muffling chamber 13. The check valve 14 is backed up by a valve support 15 
acting so as to limit the opening movement of the check valve 14. 
The movable spiral members 6a of the movable scroll element 6 and the 
stationary spiral member 9a of the stationary scroll element 9 are 
provided with sealing grooves formed in the frontmost ends thereof in 
which a tip sealing element 16 is fitted so as to hermetically seal the 
compression chambers defined between both movable and stationary scroll 
elements 6 and 9. The tip sealing element 16 is made of synthetic resin 
material, typically, polytetrafluoroethylene. 
The outer end face of the end plate 6b of the movable scroll element 6 is 
provided with a plurality of circular bores 18 formed therein at an outer 
portion of the element 6 for receiving press-fitted cylindrical pins 19 
which will be hereinafter referred to as scroll side pins. In the 
described embodiment, four circular holes 18 are arranged so as to receive 
the four cylindrical scroll side pins 19, as shown in FIG. 3. 
On the other hand, the end of the front housing 2 facing the end plate 6b 
of the movable scroll element 6 is provided with a plurality of circular 
holes 20 at positions disposed to be not in alignment with but close to 
the holes 18 of the movable scroll element 6. Thus, in the described 
embodiment, four circular holes 20 for receiving cylindrical pins 21 
press-fitted therein. The cylindrical pins 21 will be hereinafter referred 
to as housing side pins. It should be noted that one of the scroll side 
pins 19 and one of the housing side pins 21, which are disposed to be 
close to each other, form a pair of rotation preventing pins of the 
rotation preventing means. Namely, in the described embodiment of FIG. 3, 
four pairs of rotation preventing pins are arranged equiangularly in the 
outer portion of the movable end plate 6b and the end face of the front 
housing 2. The scroll side pins 19 and the housing side pins 21 are made 
of wear-resistant and mechanically strong metallic material, for example, 
a high-carbon chromium bearing steel. The pair of scroll side and housing 
side pins 19 and 21 are engaged with a ring element 22 so that the former 
pins 19 and 21 are enclosed by the latter ring element 22. The ring 
element 22 is made of a wear-resistant and mechanically strong metallic 
material similar to the material of the scroll side and housing side pins 
19 and 21, e.g., a high-carbon chromium bearing steel. 
It should be noted that FIG. 3 illustrates the relative positional 
relationship between the four pairs of pin and ring assemblies 19, 21, and 
22, and that of paired pins 19 and 21 and the ring element 22 of each pair 
of pin and ring assembly. Thus, the boss portion 6c of the movable scroll 
element 6, the bearing 7, and the crank portion 5 are omitted for the sake 
of brevity. 
The description of the rotation preventing means for the movable scroll 
element 6 will be provided hereinbelow, with reference to FIGS. 3 and 4. 
The rotation preventing means includes a plurality of pin and ring 
assemblies, i.e., four sets of housing and scroll side pins 19, 21 and 
ring element 22 in the illustrated embodiment. In FIG. 4, one of the four 
pin and ring assemblies is typically shown, in relation to the 
later-described orbiting center "O.sub.S " of the scroll element 6 and the 
rotating center "O.sub.R " of the bearing 7. During the operation of the 
scroll type compressor, a mechanical moment "M" acts on the movable 
element 6 so as to rotate it about the rotating center "O.sub.R " of the 
bearing 7. In the illustrated embodiment, it is assumed that the 
mechanical moment "M" acts in a clockwise direction. The pair of scroll 
and housing side pins 19 and 21 of the rotation preventing means before 
they are acted by the mechanical moment "M" are shown by broken lines in 
FIG. 4. When the mechanical moment "M" on the movable scroll element 6, 
the scroll side pin 19 secured to the scroll element 6 is in turn moved to 
a position shown by a solid line in FIG. 4. Then, if the housing side pin 
21 secured to the inner end of the front housing 2 is similarly moved to a 
position shown by a solid line, the ring element 22 is not locked by both 
pins 19 and 21. Nevertheless, since the housing side pin 21 is fixed, the 
ring element 22 is locked by the pins 19 and 21 and acts so as to prevent 
the rotation of the movable scroll element 6 about its own axis which 
coincides with the rotating center "O.sub.R " of the bearing 7. 
When the rotation preventing means acts so as to prevent rotation of the 
movable scroll element 6, the scroll and housing side pins 19, 20, and the 
ring element 22 take a relative positional relationship therebetween as 
described below. 
Namely, when the volume of each of the compression chambers defined between 
the movable and stationary scroll elements 6 and 9, reaches 10 through 22% 
of the volume taken by each compression chamber immediately after the 
completion of suction of the fluid, at least two of the four scroll side 
pins 19, i.e., the two pins 19 located at positions designated by "A" and 
"B" in FIG. 3 are arranged symmetrically with one another with respect to 
a line "L.sub.2 " which passes the rotating center "O.sub.R " about which 
the movable scroll element 6 is urged to rotate, and is perpendicular to a 
line "L.sub.1 " which passes both the rotating center "O.sub.R " and the 
orbiting center "O.sub.S " of the movable scroll element 6. Thus, angles 
".theta..sub.1 " and ".theta..sub.2 " of the symmetrically arranged two 
pins 19 located at positions "A" and "B", with respect to the line 
"L.sub.2 " can be considered to be the same (".theta..sub.1 
"=".theta..sub.2 "). In the described embodiment having four sets of pin 
and ring element assemblies, the angles ".theta..sub.1 " and 
".theta..sub.2 " of the symmetrically arranged two pins 19 are 45 degrees, 
respectively. 
Further, the pins 19 located at the positions "A" and "B" are located on a 
circle having the center thereof positioned at the rotating center O.sub.R 
of movable scroll element 6 and arranged on the leading side with respect 
the respective housing side pins 20 pairing with the two scroll side pins 
19 when viewing in a direction in which the rotation of the movable scroll 
element 6 about its own axis occurs. 
At this stage, the amount of rotation of the movable scroll element 6 about 
its own axis and the positions of the scroll side pins 19 of the rotation 
preventing means can be described in detail with reference to FIG. 4. 
First, the engineering meanings of respective symbols used in the 
description provided hereinbelow will be defined as set forth below. 
M: a mechanical moment acting on the movable scroll element 6 so as to 
rotate the element 6 about its own axis 
d.sub.1 : the diameter of the scroll side pin 19 
d.sub.2 : the diameter of the housing side pin 21 
D: the inner diameter of the ring element 22 
.epsilon.: a radius of an orbital motion of the movable scroll element 6 (a 
distance between the rotating center "O.sub.R " of the movable scroll 
element 6 and the orbiting center "O.sub.S " of the same element 6) 
R: a distance from the center of the scroll side pin 19 to the rotating 
center "O.sub.R " of the movable scroll element 6 
L.sub.1 : a line which passes through both of the rotating center "O.sub.R 
" and the orbiting center O.sub.S of the movable scroll element 6 
L.sub.2 : a line which passes through the rotating center "O.sub.R " of the 
movable scroll element 6 and extends perpendicularly to the line L.sub.1 
.theta..sub.i : an angle (radian) between a line passing through the center 
of any one of scroll side pins 19 and the rotating center "O.sub.R " and 
the line L.sub.2 where the suffix "i" indicates the number of any one of 
the plurality (n) of scroll side pins 19 (0.ltoreq..theta..ltoreq..pi./2) 
d.theta.: an angular amount (radian) of rotation of the movable scroll 
element 6 about its own axis or the axis of rotation of the bearing 7 
F.sub.Pi : a load acting on each of the scroll side pins 19 
F.sub.Mi : a tangential component of the load F.sub.Pi 
S.sub.i : an amount of movement of the scroll side pin 19 upon being acted 
by the load F.sub.Pi 
k: a resistance against a deformation exhibited by each of the scroll side 
pins 19 and the ring element 22 
At this stage, it should be noted that the angle "d.theta." of rotation of 
the movable scroll element 6 about its own axis is sufficiently smaller 
than the distance "R" from the center of the scroll side pin 19 to the 
rotating center "O.sub.R " of the movable scroll element 6. It should 
further be noted that the deformation resistance "k" of the scroll side 
pins 19 and the ring element 22 may be considered to be equivalent to one 
another. It should still further be noted that during the consideration of 
a load applied to each of the pairs of pin and ring assemblies made 
hereinbelow, manufacturing errors of the scroll and housing side pins 19 
and 21, and of the housing side pin 22 may be ignored, and that the paired 
rings 19 and 21 are arranged so as to be in constant contact with the 
inner wall of the associated ring element 22. 
The description of the calculation for obtaining a load F.sub.Pi acting on 
each of the scroll side pins 19 of the rotation preventing means is 
provided below with reference to FIG. 4. 
The amount of movement S.sub.i of the scroll side pin 19 on which a load 
F.sub.Pi acts can be defined by an equation as set forth below. 
EQU S.sub.i =R.times.d.theta..times.cos .theta..sub.i (1) 
The load F.sub.Pi acting on each of the scroll side pins 19 can be obtained 
from the equation (1), and defined by an equation (2) as set forth below. 
EQU F.sub.Pi =k.times.S.sub.i =k.times.R.times.d.theta..times.cos 
.theta..sub.i(2) 
The tangential component of the load F.sub.Pi can be defined by an equation 
(3) as set forth below. 
EQU F.sub.Mi =F.sub.Pi .times.cos .theta..sub.i 
=k.times.R.times.d.theta..times.cos.sup.2 .theta..sub.i (3) 
Further, the mechanical moment M acting on the movable scroll element 6 can 
be defined by an equation (4) below, when a balance between M and F.sub.Mi 
is taken into consideration. 
EQU M=F.sub.M1 .times.R+F.sub.M2 .times.R+ - - - +F.sub.Mn .times.R(4) 
The load F.sub.Pi can be calculated from the above equations (2) through 
(4), and defined as an equation (5) set forth below. 
EQU F.sub.Pi =(M.times.cos .theta..sub.i)/(R.times.(cos.sup.2 .theta..sub.1 
+cos.sup.2 .theta..sub.2 +COS.sup.2 .theta..sub.3 + - - - +cos.sup.2 
.theta..sub.i + - - - +COS.sup.2 .theta..sub.n)) 
At this stage, it should be understood that the calculation of the load 
F.sub.Pi is carried out with respect to only the scroll and housing side 
pins 19 and 21 which work as the rotation preventing means at the moment 
when the calculation is carried out, namely the pins located on the left 
hand side of the line L.sub.1 in FIG. 3. 
From the foregoing description, it will be understood that when two scroll 
side pins 19 are arranged to be symmetrical with one another with respect 
to the line L.sub.2 which passes through the rotating center O.sub.R of 
the movable scroll element 6 and is perpendicular to the line L.sub.1 
which passes through the rotating center O.sub.R and the orbiting center 
O.sub.S of the movable scroll element 6, the load F.sub.Pi cannot be 
concentrated on only a single scroll side pin 19. Namely, if the load 
F.sub.Pi acting on at least two respective scroll side pins 19 located at 
the positions A and B in FIG. 3 are arranged to have an equal value of 
cosine, the load acting on the pin located at the position A and that 
acting on the pin located at the position B can cancel one another, and 
accordingly, the concentration of the load F.sub.Pi on only one of the 
pins 19 does not occur. Further, the load F.sub.Pi acting on any one of 
the two pins 19 can be very small. As a result, if such small load 
condition can be constantly maintained during the operation of the scroll 
type compressor, the size of the compressor itself can be reduced. 
(Second Embodiment) 
In the described first embodiment, the rotation preventing means for the 
movable scroll element 6 includes a plurality of pin and ring assemblies, 
each including a pair of scroll side and housing side pins 19, 21 and a 
ring element 22. However, it should be understood that the present 
invention is equally applicable to a rotation preventing means having no 
ring element. More specifically, a different type of rotation preventing 
means for a scroll type compressor as shown in FIG. 5 includes only a 
plurality of pairs of scroll and housing side pins 19 and 21. At this 
stage, the scroll side pins 19 of the rotation preventing means should be 
arranged so as to be symmetrical with one another with respect to the line 
L.sub.2 which passes through the rotating center "O.sub.R " of the movable 
scroll element 6 and is perpendicular to the line L.sub.1 which passes 
through the rotating center "O.sub.R " and the orbiting center "O.sub.S " 
of the movable scroll element 6. Further, the housing side pins 21 which 
are paired with the scroll side pins 19 located at positions C and D of 
FIG. 5 should be arranged on the leading side to the paired scroll side 
pins 19 in a direction of the rotation of the movable scroll element about 
the center O.sub.R. Thus, rotation of movable scroll element 6 will be 
prevented by scroll side pins 19 labeled C and D contacting housing side 
pins 21. It should be noted that in FIG. 5, the illustration of boss 
portion 6c of the movable scroll element 6, the bearing 7, and the crank 
portion 5 are omitted for the sake of brevity. 
From the foregoing description, it should be understood that in accordance 
with the present invention, the rotation preventing means can avoid 
concentration of a load to any one of the plurality of scroll side pins 
thereof, and thus, the breakage of the rotation preventing means can be 
surely prevented. 
Many variations and modifications will occur to persons skilled in the art 
without departing from the spirits and scope of the invention defined in 
the accompanying claims.