Note: Descriptions are shown in the official language in which they were submitted.
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SCROLL TYPE FLUID DISPLACEMENT APPARATUS
WITH IMPROVED ANTI-WEAR DEV~C~
BACKGROUND OF THE INVENTION
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This invention relates to a scroll type fluid displacement
apparatus, and more particularly, to an improved anti-wear device for
the scrolls used in a scroll type fluid compressor.
Scroll type fluid displacement apparatus are well known in the
prior Mrt. For example, U.S. Patent No. 801,182 issued to Creux
discloses the basic construction of a scroll type fluid displacement
app~ratus including two scrolls each having a circular end plate and a
spiroidal or involute spiral element. The scrolls are maintained at an
angular and radial offset so that both spiral elements interfit to form
a plurality of line contacts between their curved surfaces to thereby
seal off and define at least one pair of fluid pockets. The relative
orbital motion of the two scrolls shifts the line cont~cts along the spi-
ral curved surfaces and, as a result, the volume of the fluid pockets
increases or decreases, dependent on the direction of the orbital
motion. Thus, a scroll type fluid displacement apparatus may be used
to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type,
scroll type compressors have certain advantages, such as fewer parts
and continuous compression of fluid. However, one of the problems
with scroll type compressors is ineffective sealing of the fluid pockets.
Axial and radial sealing of the fluid pockets must b0 maintained in a
scroll type compressor in order to flchieve efficient operat;on~ The
fluid pockets are defined by line contacts between the interfitting spi-
ral elements and the axial contacts between the axial end surface of
one spiral element and the inner end surface of the facing end plate.
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Various techniques have been used in the prior art
to solve the axial sealing problem. In U.S. Patent No.
3,334,635, a seal alement is mounted on khe axial end
surface of each spiral element and urged toward the end
surface of the facing end plate by an urging device to
effectuate suf~icient axial sealing between the axial
end surface of the spiral element and the end surface of
the facing end plate. But, in the above '635 patent,
because the seal element is urged toward the end surface
of the facing end plate by an urging device, over a
period of time, abrasions occur between the seal
elements and the end plate of the scroll, especially
when lightweight alloys such as aluminum alloys are used
as the scroll material. When the end plate wears due to
abrasion, the seal elements also are damaged, and the
axial contact between the end surface of the spiral
element and the inner end surface of the end plate
becomes imperfect, which reduces compressor efficiency.
One solution to the above disadvantages involves
providiny an anti-wear device for the scrolls which
includes an anti-wear plate disposed on an end surface
of the end plate of at least one of the scrolls. The
anti-wear plate faces the axial end surface of the
spiral element of the other scroll to prevent wear and
maintain axial sealing.
As reference now will be made to the drawings
these first will be briefly described as follows:
Figure 1 i5 a vertical sectional view of an earlier
version of a scroll type fluid compressor.
Figure 2 is a vertical sectional view of a scroll
type fluid compressor in accordance with an embodiment
of this invention.
Figure 3(a) is a front view of the fixed scroll
used in Figure 2 and Figure 3(b) is a vertical sectional
view of the fixed scroll in Figure 3(a).
Figure 4(a) is a front view of a fixed scroll with
an involute plate and Figure 4(b~ is -a vertical
sectional view of the fixed scroll in Figure ~(a).
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As shown in Figure 1, which is a vertical
cross~sectional view of an earlier version of a scroll
type fluid compressor, anti-wear plates 41' are disposed
on an axial end surface of each end plate 271', 281'.
Shims 1~3' are provided to establish a predetermined
axial clearance between the axial end surface of each
spiral element and the opposing anti-wear plate. Shims
113' are disposed between front end plate 11' and
cup-shaped casing 12'. Even though the shim thickness
is properly selected in the initial state, the axial
clearance between the axial end surface of each seal
element and the opposing anti-wear plate may change due
to bending of e.ach end plate in response ko pressure
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changes. Also, once the thrust race and thrust balls of the rotation
prevention/thrust bearing device settle due to a continuous compression
gas load, the tight seal between the axial end surfuce of the seal ele-
ment and the opposing snti-wear plate may be lost. Addition~lly, the
spiral element, in particular, the central portion of the spiral element,
expands in response to thermal changes in the compressed fluid causing
further loss of sealing.
Though solutions exist for loss of axial sealing due to bending of
the end plate and settling in the ball coupling type rotation
prevention/thrust bearing device, no acceptable solution exists Ior
changes in the axial length of the spiral element due to thermal
changes. Thus, despite the existence of solutions to the other prob-
lems mentioned above, effective axial sealing between the seal element
and the anti-wear plate can be easily lost.
~ urthermore, it should be noted that, in scroll type fluid com-
pressors, the interfitting spiral elements extend through se~reral temper-
ature zones. These different temperature æones are created because
there are a plurality of pairs of sealed off fluid pockets between the
interfitting spiral elements, each of which has a different temperature
and pressure. Because temperature and pressure at the central fluid
pocket are the greatest, the central portion of each spiral element
usually is the highest temperature and pressure area. Therefore, in
order to achieve effective axial sealing in the central portion of the
spiral elements, changes in axial clearance due to thermal changes
must be minimized. However, to solve this thermal problem in the
central portion of the spiral elements, if the initial axial clearance
between the seal element and the anti-wear plate is set to a
minimum, the central portions of the spiral elements strongly contact
the opposing anti-wear plate resulting in abnormal wearing of the spiral
elements and excessive force acting on the base portion of each spiral
element.
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S~MMARY OF THE INVENTION
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It is an object of an aspect of this invention to provide
a scroll type fluid displacement apparatus which achieves suf-
ficient axial sealing despite thermal changes in the spiral
elements.
It is an object of an aspect of this invention to pro-
vide a scroll type fluid displaceMent apparatus which
prevents abnormal wear of and damage to the scrolls.
It is an object of an aspect of this invention to realize
the above objects with a simple construction which can be
simply manufactured at low cost.
A scroll type fluid displacement apparatus according to
an embodiment of this invention includes a pair of scrolls,
each comprising an end plate and a spiral wrap extending
from one side surface of the end plate. The spiral wraps
interfit at an angular and radial offset to make a plurality
of line contacts to define at least one pair of sealed off
fluid pockets. A driving mechanism is operatively connected
to one of the scrolls to effect the orbital motion of the one
scroll relative to the other scroll while simultaneously
preventing rota-tion of the one scroll. At least one involute
plate is disposed between an axial end surface of one spiral
element and the inner end surface of theopposing end plate.
The involute plate covers only the area of the surface of the
end plate of the scroll where the spiral wrap makes axial
contact during the orbital motion of the one scroll to
thereby prevent excessive wear and abrasibn. An indentation
or depressed portion is formed on the end surface of the
end plate on which the involute plate is disposed. This inden-
tation or depressed portion is located near the central
portion of the end plate to define an axial air gap between
the involute plate and the central portion of the end
surface of the end plate to permit thermal expansion in the
central portion without loss of axial sealing caused by wear
and abrasion.
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Various aspects of the invention are as follows:
In a scroll type fluid displacement compressor
including a pair of scrolls each having a circular end
plate and a spiral wrap extending from an axial end
surface of said circular end plate, said pair of scrolls
being maintained at an angular and radial offset so that
said spiral wraps interEit to form a pluralit~ of line
contacts between their spiral curved surfaces to thereby
seal off and define at least one pair of fluid pockets,
a driving mechanism operative:Ly connected to one of said
scrolls to effect relative orbital motion with respect
to the other of said scrolls to thereby change the
volume of the fluid pockets, and an involute plate
disposed on an axial en~ surface of the circular end
plate of both said scrolls to cover the area on which
contact is made by an axial end surface of the opposing
spiral wrap, the improvement comprising a depressed
portion formed at the entire center high pressure
portion only of said end plates of both said scrolls to
increase volumetric efficiency by compensating for
thermal expansion, said depressed portion and said
involute plate defining an axial air gap between an
inner end surface of said involute plate and a bottom
surface of said depressed portion on both said scrolls.
In a scroll type fluid displacement compressor
including a housing having a fluid inlet port and fluid
outlet port, a fixed scroll fixedly disposed within
said housing and having a circular end plate from which
a first spiral wrap extends, an orbiting scroll having a
circular end plate from which a second spiral wrap
extends, said first and second spiral wraps interfitting
at an angular and radial offset to form a plurality of
line contacts to define at least one pair of sealed off
fluid pockets, a driving mechanism operatively connected
to said orb.iting scroll to effect the orbital motion of
said orbiting scroll and a rotation preventing means for
preventing the rotating motion of said orbiting scroll
during the orbital motion of said orbiting scroll to
thereby change the volume of the fluid pockets, the
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improvement comprising an involute plate disposed on
both of said end plates of said fixed and orbiting
scrolls to cover the area on which contact is made by an
axial end surface of the opposing spiral wrap, and a
depressed portion formed at the entire center high
pressure portion only of said end plates of both said
scrolls to increase volumetric efficiency by
compen~ating for thermal expansion, said depressed
portion and said involute plate defining an axial air
gap between an inner end surface of said involute plate
and the opposing surface of said end plate on both said
scrolls.
Further objects, features and other aspects of this
invention will be understood from the following detailed
description of the preferred embodiments of this
invention, referring to the annexed drawings.
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DETAII,ED DESCRIPTION OF THE PRF.FERRED EMBODIMENT
Referring to Figure 2, scroll type refrigerant
compressor l includes compressor housing 10 having a
front end plate 11 mounted on cup-shaped casing 12.
Opening 111 is formed in the center of front end plate
11 for penetration or passage of drive shaft 13.
Annular projection 112 is formed in a rear end surface
of ~ront end plate 11. Annular projection 112 faces
cup-shaped casing 12 and is concentric with opening 111.
An outer peripheral surface of annular projection 112
extends into an inner wall of the opening of cup-shaped
casing 12 so that the opening of cup-shaped casing 12 is
covered by front end plate 11. O-ring 14 .is placed
between the outer peripheral surface of annular
projection 112 and the inner wall of the opening of
cup-shaped casing 12 to seal the mating surfaces of
front end plate 11 and cup-shaped casing 12.
Annular sleeve 15 projects from the front end
surfa~e of front end plate 11 to surround drive shaft
13; annular sleeve 15 defines a shaft seal cavity. In
the embodiment shown in Figure 2, sleeve 15 is formed
separately from front end plate 11. Therefore, sleeve
15 is fixed to the front end surface of front end plate
11 by screws (not shown). O-ring 16 is placed between
the end surface of sleeve 15 and the front end plate 11
and sleeve 15. Alternatively, sleeve 15 may be formed
integral with end plate 11.
.
Drive shaft 13 is rotatably supported by sleeve 15 through
bearing 18 located within the front end of sleeve 15. Drive shaft 13
has disk 19 at its inner end; dislc 19 is rotatably supported by front
end plate 11 through bearing 20 located within opening 111 of front
end plate 11. Shaft seal assembly 21 is coupled to drive shaft 13
within the shaft seal cavity of sleeve 15.
Pulley 22 is rotatably supported by bearing 23 which is curried
on the outer surface of sleeve 15. Electromagnetic coil 24 is fixed
about the outer surface of sleeve 15 by support plate 25 and is
received in an annular CAvity of pulley 22. Armature plate 26 is
el~stically supported on the outer end of drive shaft 13 which extends
from sleeve 15. Pulley 22, m~gnetic coil 24 and armature plate 26
for m a magnetic clutch. In operation, drive shaft 13 is driven by an
external power source, for example the engine of an flutomobile,
through a rotation transmitting device such as the above-explained
magnetic clutch.
A number of elements are located within the inner chamber of
cup-shaped casing 12 including fixed scroll 27, orbiting scroll 28, a
driving mechsnism for orbiting scroll 28 and rotation preventing/thrust
bearing device 35 for orbiting scroll 28. The inner chamber of cup-
shaped c~sing 12 is formed between the inner wall of cup-shaped
casing 12 and the rear end surface of front end plate 11.
Fixed scroll 27 includes circular end plate 271, wrap or spiral
element 272 affixed to or extending from one end surface of end plate
271 and intern~l threaded bosses 273 axially projecting from the other
end surface of end plate 271. An axial end surface of each boss 273
is sealed on the inner end surface of bottom plate portion 121 of
cu~shaped casing 12 and fixed by screws 37 screwed into bosses 273
from the outside of bottom plate portion 121. Thus, fixed scroll 27 is
fixed within the inner chamber of cu~shaped casing 12. Circular end
plate 271 of fixed scroll 27 pflrtitions the inner chamber of cu~shaped
casing 12 into front chamber 29 and rear ch&mber 30~ Seal ring 31 is
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disposed within a circumferential groove of circular end plate 271 to
form a seal between the inner wall of cup-shaped casing 12 and the
outer surface of circular end plate 271. Spiral element 272 of fixed
scroll 27 is located within front chamber 29.
Cup-shaped cnsing 12 is provided with a fluid inlet port 36 and
fluid outlet port 37, which are connected to rear and front chambers
29 and 30, respectively. A hole or discharge port 274 is formed
through circular end plate 271 at a position near the center of spiral
element 272. A reed valve 38 closes discharge port 274.
Orbiting scroll 28, which is located in front chamber 29, includes
circular end plate 281 and wrap or spiral element 282 affixed to or
extending from one end surface of circular end plate 281. Spiral ele-
ments 272 and 282 interfit at an angular offset of 180 and at a
predetermined radial offset. Spiral elements 272 and 282 define at
least one pair of sealed off fluid pockets between their interfitting
surfaces. Orbiting scroll 28 is rotatably supported by bushing 33
through bearing 34 placed between the outer peripheral surface of
bushing 33 and the inner surface of annular boss 283 axially projecting
from the end surface of circular end plate 281 of orbiting scroll 28.
Bushing 33 is connected to an inner end of disk 19 at a point radially
offset or eccentric of the axis o~ drive shaft 13.
Rotation preventing/thrust bearing device 35 is disposed around
the outer peripheral surface of boss 282 and placed between the inner
end surface of front end plate 11 and the end surface of circular end
plnte 281 which faces the inner end surface of front end plate 11.
Rotation preventing/thrust bearing device 35 includes fixed ring 351
attached to the inner end surface of front end plate 11, orbiting ring
352 attached to the end surface of circular end plate 281, and a plu-
rality of bearing elements, such as balls 353, placed between the
pockets formed by rings 351 and 352. Rotation of orbiting scroll 28
during orbital motion is prevented by the interaction of balls 353 with
rings 351, 352. The axial thrust load from orbiting scroll 28 also is
supported on front end plate 11 through balls 353.
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In the above arrangement of scroll type refrigerant compressor
1, fluid from the external fluid circuit is introduced into fluid pockets
in the compressor unit through inlet port 36. The fluid pockets com-
prise open sp~ces formed between spiral elements 272 and 282. As
orbiting scroll 282 orbits, the fluid in the fluid pockets moves to the
center of the spiral elements and is compressed. The compressed fluid
from the fluid pockets is discharged into rear chamber 30 from the
fluid pockets through discharge hole 274. The compressed fluid then is
discharged to the external fluid circuit through outlet port 37.
As shown in Figures 2 and 3, spiral elements 272, 282 include
grooves 275, 285 on the axial end surface thereof. Seal element 40 is
disposed in the grooves to provide a senl between the end surface of
each circular end plate 271, 281 and the axial end surface of each
seal element 40. Involute plate 41, which is formed of hard metal,
such as hardened steel, is fitted to the end surface of both circular
end plates 271, 281 to minimize the abrasion and reduce wear of the
scrolls. The central portion of each circular end plate 271, 281 has
an indentation or depressed portion 42 as shown by the dotted area in
Figure 3(a). This depressed portion 42 extends from the center portion
of circular end plate 271 to a position along the spiral curved surface.
Depressed portion 42 could be formed by machine tooling, such as end
milling, and depth "t" is easily defined by the forming process.
When involute plate 41 is fitted on circular end plate 271 to
cover the portion of the end surface on which the axial end surface
of seal element 40 slides during orbital motion of orbiting scroll 28 as
shown in Figure 4(a), an axial air gap is defined between the inner
end surface of involute plate 41 and the bottom surface of depressed
portion 42 as best shown in Figure 4(b). Therefore~ changes in the
axial length of spiral element 282, which are caused by thermal
changes in the central portion of the spiral elements, is absorbed by
deformation of involute plate 41. The deformation of involute plate
41, such as bending deformation, occurs within the axial air gap
defined between the depressed portion and the involute plste. The
depth "t" of depressed portion 42 should correspond to the msximum
expsnsion of the spirsl element in order to absorb chsnges in the axisl
length of the spirsl element. During the operstion of the scroll type
refrigerant compressor, reaction forces caused by the sbove deformstion
which act upon the facing spiral element nre so smsll that the force
trsnsmitted to the bsse portion of the spiral element is reduced.
Also, the sxisl sir gsp between the inner end surfsce of involute plste
~1 and the bottom surf~ce of depressed portion ~2 could be filled by
lubricsting oil because depth "t" hss such a smsll dimension. This
would prevent sny blow-by phenomena from occurring in the sres of
depressed portion ~2.
Finally, it is noted thst, as shown in Figure 2, involute plate 41
csn be disposed on the end surfaces of both end plates 271 snd 281.
In this case, depressed portion 42 is formed on both end plates 271,
281. However, involute plate 41 can be disposed on either of the end
plstes as long as the depressed portion is formed on the end plate on
which the involute pl~te is disposed.
The present invention hss been described in detail in connection
with a preferred embodiment. This embodiment, however, is merely
for example only ~nd the invention is not restricted thereto. It will
be understood by those skilled in the art that other vsristions and
modificstions can be made within the scope of this invention as
defined in the &ppended claims.
