Scroll type compressor with elongated discharge port

An improved scroll type compressor having enlarged fixed and orbiting spiral element tips with parallel flat faces is disclosed. A discharge port for discharging compressed fluids is positioned in the fixed end plate. The discharge port is shaped to provide an opening that is effectively elongated adjacent the flat face of the fixed spiral element. In one preferred embodiment, the discharge port has a pair of elongated sides that extend in parallel with the flat face of the fixed spiral element. Another preferred embodiment the discharge port includes a plurality of holes arranged such that a common tangent to the perimeter of the holes is substantially parallel to the flat face of the fixed spiral element. A tapered surface may also be provided in the flat face of the enlarged tip of the orbiting spiral element to improve communication between the compression chamber and the discharge port.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a scroll type compressor provided with a 
fixed scroll and an orbiting scroll. More particularly, it relates to an 
improved scroll tip and discharge port arrangement. 
2. Description of the Related Art 
Japanese Unexamined Patent Publication No. 59-218380 discloses a compressor 
as shown in FIGS. 13 to 15. This compressor has a fixed scroll 91 fixed in 
a housing 90 and an orbiting scroll 92. The orbiting scroll 92 is 
supported revolvable around the axis of the fixed scroll 91 in the housing 
90. 
The fixed scroll 91 comprises a fixed end plate 911 and a fixed spiral 
element 912 formed integrally with the bottom surface of the fixed end 
plate 911. The fixed spiral element 912 has its inner and outer walls 
formed along involute curves. Likewise, the orbiting scroll 92 comprises 
an orbiting end plate 921 and an orbiting spiral element 922 formed 
integrally with the top surface of the orbiting end plate 921. The 
orbiting spiral element 922 also has its inner and outer walls formed 
along involute curves. The fixed spiral element 912 and the orbiting 
spiral element 922 slide against each other. 
In this compressor, a drive shaft 95 rotates by the interaction of a stator 
93 and a rotor 94 mounted on the drive shaft 95. As the drive shaft 95 
rotates, the orbiting scroll 92 revolves around the axis of the fixed 
scroll 91 by the work of an eccentric pin 95a slightly eccentric to the 
drive shaft 95 and a rotation preventing device 96. In accordance with 
this revolution, a plurality of compression chambers 97 to be formed in a 
sealed state between the fixed scroll 91 and the orbiting scroll 92 move 
toward the center of the fixed scroll 91 while sequentially reducing their 
volumes. 
A discharge port 98 is provided in the center of the fixed end plate 911. 
As shown in FIGS. 13 and 14, the fully compressed gas in a compression 
chamber 971 is discharged through the discharge port 98 into a discharge 
chamber 99. As the orbiting scroll 92 revolves, the fluid in the next 
compression chamber 972 (which follows the compression chamber 971) is 
sequentially discharged from the discharge port 98. 
As shown in FIGS. 14 and 15, a tapered surface 922b is cut in a tip portion 
922a in the center of the orbiting spiral element 922. This tapered 
surface 922b and the inner wall of a center tip portion 912a of the fixed 
spiral element 912 constitute a passage that permits communication between 
the compression chamber 971 in the final compression stage and the 
discharge port 98. The existence of this passage reduces the discharge 
resistance at the time the gas in the compression chamber 971 is 
discharged through the discharge port 98 into the discharge chamber 99. 
In the conventional compressor, the end portions of the fixed spiral 
element 912 and orbiting spiral element 922 slide against the end plates 
of the mating scrolls while being pressed together in order to form sealed 
compression chambers. Both tip portions 912a and 922a receive the pressure 
of the gas in the most compressed state at the final compression state. 
Those tip portions 912a and 922a should therefore have a sufficient 
strength. 
The formation of the tapered surface 922b at the end position of the tip 
portion 922a however decreases the strength of the tip portion 922a 
significantly. The tip portion 922a may therefore be damaged by the 
sliding action against the tip portion 912a and the high pressure. Because 
of these drawbacks, it is very difficult to use this type of tip design in 
a scroll type compressors for vehicles, which is required to operate under 
the conditions of fast rotation and high compression. 
Further, in the conventional compressor, the compressed gas in the 
compression chamber 971 is discharged to the discharge port 98, passing 
through an opening enclosed by the circular inner wall of the discharge 
chamber 98 and the curved inner wall or the tip portion 922a of the 
orbiting spiral element 922. As the orbiting scroll 92 revolves, the tip 
portion 922a of the orbiting spiral element 922 gradually reduces the 
cross-sectional area of the passage between the discharge port 98 and the 
compression chamber 971. 
Immediately before completion of the gas discharging, the cross-sectional 
area of the passage between the discharge port 98 and the compression 
chamber 971 decreases rapidly. Even if the tapered surface 922b is 
provided at the tip portion 922a, the discharge resistance will not be 
reduced sufficiently immediately before completion of the gas discharging 
when such reduction is needed most. 
Furthermore, to optimize compression efficiency, it is desirable that the 
following compression chamber 972 does not communicate with the discharge 
port simultaneously with the compression chamber 971. This is because the 
compressed gases exiting compression chamber 971 would expand into the 
following chamber. The re-expansion reduces the compression efficiency. 
SUMMARY OF THE INVENTION 
Accordingly, it is a primary objective of the present invention to provide 
a compressor which can ensure sufficient strength for the center tip 
portions of fixed and orbiting scrolls, and can effectively decrease the 
discharge resistance of a compressed fluid while maintaining an effective 
compression efficiency. 
To achieve the foregoing and other objects and in accordance with the 
purpose of the present invention, an improved scroll type compressor is 
provided. The compressor includes a fixed scroll having a fixed end plate 
and a fixed spiral element. The fixed spiral element includes a thick 
fixed tip portion having a flat face on an inner wall side. An orbiting 
scroll including an orbiting end plate and an orbiting spiral element is 
mounted for orbital revolving movement relative to the fixed scroll. The 
orbiting spiral element includes a thick orbital tip portion having a flat 
face on an inner wall side that faces the flat face of the fixed spiral 
element. The orbiting spiral elements are interleaved such that the flat 
faces of the fixed and orbital tip portions are periodically positioned 
adjacent each other during revolution of the orbiting scroll. The 
interleaved spiral elements define at least one airtight compression 
chamber between the fixed scroll and the orbiting scroll. A discharge port 
for discharging fluids from the compression chamber is positioned in the 
fixed end plate. The discharge port is shaped to provide an opening that 
is effectively elongated adjacent the flat face of the fixed spiral 
element. 
In one preferred embodiment, the discharge port has a pair of elongated 
sides that extend in parallel with the flat face of the fixed spiral 
element. Another preferred embodiment the discharge port includes a 
plurality of holes arranged such that a common tangent to the perimeter of 
the holes is substantially parallel to the flat face of the fixed spiral 
element. 
A tapered surface or bevel is provided contiguous with the flat face of the 
orbiting spiral element on the thick tip portion of the orbiting spiral 
element to improve communication between the compression chamber and the 
discharge port.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
A first embodiment of the present invention will now be described referring 
to FIGS. 1 through 7. As shown in FIG. 1, a scroll type compressor has a 
pair of housings 1 and 9 which are to be connected together. In the 
housing 1, a fixed scroll 2 is fixed and a orbiting scroll 3 is provided. 
The fixed scroll 2 includes a disk-shaped fixed end plate 12, and a fixed 
spiral element 13 formed integrally with the orbiting scroll side of that 
end plate 12. Likewise, the orbiting scroll 3 includes a disk-shaped 
orbiting end plate 14, and an orbiting spiral element 15 formed integrally 
with the fixed scroll side of that end plate 14. As both spiral elements 
13 and 15 slide against each other, a plurality of compression chambers 5 
are formed between the scrolls 2 and 3. 
In the housings 1 and 9, a drive shaft 4 is supported via a radial bearing 
4a. An eccentric pin 10 eccentric to the axis of the drive shaft 4 is 
provided at the end portion of the drive shaft 4. A counter weight 11 is 
secured to the proximal end side of the eccentric pin 10. A bushing 7 is 
fitted on the free end of the eccentric pin 10. The orbiting scroll 3 is 
supported on the bushing 7 via a bearing 7a. 
A fixed ring 22 is secured on a base plate 21, facing the orbiting scroll 
3, with an orbiting ring 23 secured to the back of the orbiting scroll 3. 
A plurality of circular revolution position regulating holes are bored at 
equal intervals in the fixed ring 22 and orbiting ring 23. The position 
regulating holes are arranged in facing pairs and a transmission shoe 24 
is provided between each facing pair of position regulating holes. 
The base plate 21, fixed ring 22, orbiting ring 23 and transmission shoes 
24 constitute a rotation preventing device 8. The action of the rotation 
preventing device 8 allows the orbiting scroll 3 to revolve without 
rotation as the eccentric pin 10 revolves. 
As shown in FIG. 2, the inner and outer walls of the fixed spiral element 
13, excluding the inner wall side of a center tip portion 131 of the fixed 
spiral element 13, are formed along inner and outer involute curves 
I.sub.in and I.sub.out drawn based on a predetermined involute generating 
circle. Further, the inner outline of the fixed spiral element 13 at the 
tip portion 131 is determined along a circular arc S.sub.1 with a radius 
r, a circular arc S.sub.2 with a radius R (R=r+q; wherein q is the radius 
of revolution of the orbiting scroll 3) and a common tangent S.sub.3 to 
these circular arcs S.sub.1 and S.sub.2. 
As shown in FIGS. 2, 3 and 6, therefore, the tip portion 131 of the fixed 
spiral element 13 is made thicker than the tip portion 912a of the 
conventional fixed spiral element 912. A flat face 13a constituting one 
part of the inner wall of the fixed spiral element 13 is formed at that 
part of the tip portion 131 which corresponds to the common tangent 
S.sub.3. 
As shown in FIGS. 2 and 6, an elongated oval or racetrack shaped discharge 
port 16 is formed through the fixed end plate 12. The discharge port 16 
has linear elongated sides 16a and 16b that are substantially parallel to 
the common tangent S.sub.3. The discharge port 16 is provided adjacent to 
the flat face 13a so that one of the elongated sides, 16b, of the 
discharge port 16 adjoins the flat face 13a. Part of the inner wall of the 
discharge port 16 is therefore linked straight to the flat face 13a. 
Since the sides 16a and 16b are somewhat elongated, the discharge port 16 
has nearly the same opening area as the circular discharge port 98 
provided in the conventional compressor having the same size as the 
compressor of this embodiment. 
As shown in FIG. 2, like the inner and outer walls of the fixed spiral 
element 13, those of the orbiting spiral element 15, excluding the inner 
wall side of a center tip portion 151 of the orbiting spiral element 15, 
are formed along the inner and outer involute curves I.sub.in and 
I.sub.out drawn based on a predetermined involute generating circle. 
Further, the inner outline of the orbiting spiral element 15 at the tip 
portion 151 is determined along a circular are F.sub.1 with a radius r, a 
circular arc F.sub.2 with a radius R (R=r+q; wherein q is the radius of 
revolution of the orbiting scroll 3) and a common tangent F.sub.3 to these 
circular arcs F.sub.1 and F.sub.2. 
Therefore, as shown in FIGS. 2, 3 and 7, the tip portion 151 of the 
orbiting spiral element 15 is thicker than the tip portion 922a of the 
conventional orbiting spiral element 922. A flat face 15a constituting one 
part of the inner wall of the orbiting spiral element 15 is formed at the 
part of the tip portion 151 which corresponds to the common tangent 
F.sub.3. 
Since the tip portions 131 and 151 of the fixed spiral element 13 and 
orbiting spiral element 15 are made thicker, they are considerably 
stronger than those of the conventional fixed and orbiting spiral 
elements. 
As the circular arcs S.sub.1 and S.sub.2 on the fixed spiral element side 
contact the circular arcs F.sub.2 and F.sub.1 on the orbiting spiral 
element side, a compression chamber 51 is formed as shown in FIG. 2. As 
the orbiting scroll 3 revolves, the flat face 13a of the fixed spiral 
element 13 periodically comes into close contact with the flat face 15a on 
the orbiting spiral element side as shown in FIG. 5. 
As shown in FIGS. 2, 3 and 7, a tapered or beveled surface 15b is cut in 
the flat face of the tip portion 151 of the orbiting spiral element 15. 
The tapered surface is approximately the same length as the elongated 
sides 16a and 16b of the discharge port 16. The taper in tip portion 151 
forms a narrowed neck therein. However, since the tip portion 151 is 
rather thick, it has a sufficient strength in its neck region. Therefore, 
the formation of the tapered surface 15b does not impair the strength of 
the tip portion 151. 
At the time the opposite flat faces 13a and 15a contact each other, the 
discharge port 16 is almost completely covered with the thick tip portion 
151 as shown in FIG. 5. At this time the tapered surface 15b secures a 
passage between itself and the inner wall of the fixed spiral element 13 
to permit communication of the compression chamber 5 with the discharge 
port 16. 
Meanwhile, when this scroll type compressor is used as a compressor for a 
vehicular air conditioning, the drive shaft 4 is coupled to the driving 
system of the engine of a vehicle through an electromagnetic clutch (not 
shown). When the drive shaft rotates in accordance with the rotation of 
the engine, the rotation of the drive shaft 4 is transmitted via the pin 
10, the bushing 7 and the rotation preventing device 8 to the orbiting 
scroll 3. The orbiting scroll 3 then revolves around the axis of the fixed 
scroll 2. 
In accordance with the revolution of the orbiting scroll 3, the orbiting 
spiral element 15 gradually reduces the volume of the compression chamber 
51 to the final compression stage. The compressed refrigerant gas pushes 
open a discharge valve 6a that is provided outside the discharge port 16. 
The compressed gases are thus discharged into the discharge chamber 6. 
As is apparent from FIG. 2, the flat face 15a of the orbiting spiral 
element 15 becomes almost parallel to the flat face 13a of the fixed 
spiral element 13 and the elongated sides 16a and 16b of the discharge 
port 16 in the compression chamber 51 in the final compression stage. When 
the orbiting scroll 3 revolves further, most of the discharge port 16 is 
covered by the tip portion 151 as shown in FIG. 4. At this time the 
compressed refrigerant gas is discharged into the discharge chamber 6 
through an elongated gap enclosed by the elongated side 16b of the 
discharge port 16 and the flat face 15a of the orbiting spiral element 15. 
According to this embodiment, the gap through which the refrigerant gas 
passes is rather elongated due to the elongated side 16. The is true even 
when the opening area of this gap gradually decreases in accordance with 
the revolution of the orbiting scroll 3. Therefore, the cross-sectional 
area of the communication path between the discharge port 16 and the 
compression chamber 51 is larger than the corresponding communication path 
in conventional circular designs at any point of time before the 
discharging of the compressed gas is completed. 
The tapered surface 15b formed on the orbiting spiral element 15 and the 
inner wall of the fixed spiral element 13 define a passage that permits 
communication between the compression chamber 51 and the discharge port 16 
when the opposing flat faces 13a and 15a come in close contact with each 
other. The presence of this passage can greatly reduce the discharge 
resistance of the compressed gas from the compression chamber 51 to the 
discharge port 16. 
According to this embodiment, after the refrigerant gas in the final 
compression stage is discharged into the discharge chamber 6 smoothly and 
surely, the following compression chamber 52 from the next cycle merges 
with the remnants of compression chamber 51 as the orbiting tip pulls away 
from the fixed tip. However since only a nominal amount of gas remains in 
compression chamber 51 reexpansion of compressed gas is effectively 
minimized or eliminated. 
This action provides a good compression efficiency. It also prevents an 
excessive-pressure load from acting on the tip portions 131 and 151 of the 
fixed and orbiting spiral elements 13 and 15 for a long period of time, 
thus reducing the wear to spiral elements 13 and 15. 
As shown in FIG. 5, when the flat face 13a of the fixed spiral element 13 
closely contacts the flat face 15a of the orbiting spiral element 15, the 
tip portion 151 of the orbiting spiral element 15 almost covers the 
discharge port 16, except that portion which corresponds to the tapered 
surface 15b. The compression chamber 51 in the previous cycle will not 
communicate with the compression chamber 52 in the next cycle via the 
discharge port 16 before the compression chamber 51 in the final 
compression stage completes the gas discharge. 
Second Embodiment 
A description of the second embodiment of the present invention will be 
given below referring to FIGS. 8 through 11, mainly discussing the 
differences from the first embodiment. 
This embodiment differs from the first embodiment in the location of the 
discharge port 16. More specifically, as shown in FIGS. 8, 9 and 11, the 
discharge port 16 bored through the fixed end plate 12 is located slightly 
apart from the flat face 13a of the fixed spiral element 13. Accordingly, 
the flat face 13a is linked to the inner wall of the discharge port 16 via 
a step 12a. 
Like the first embodiment, the discharge port 16 has an elongated oval or 
racetrack shape, and has linear elongated sides 16a and 16b parallel to 
the flat face 13a of the fixed spiral element 13. Since the sides 16a and 
16b are elongated to some extent, the opening area of the discharge port 
16 is secured as in the case of the first embodiment. 
The second embodiment also has a tapered surface 15b cut into the end 
portion of the tip portion 151 of the orbiting spiral element 15. The 
tapered surface extends nearly the same length as the elongated sides 16a 
and 16b of the discharge port 16. It is noted, however, that the size and 
the inclination angle of the tapered surface 15b are determined in such a 
way that a passage for communication between the compression chamber 51 
and discharge port 16 can be secured between the tapered surface 15b and 
the inner wall of the fixed spiral element 13 and the step 12a even when 
both flat faces 13a and 15a come into close contact with each other as 
shown in FIG. 10. 
In the first embodiment, the discharge port 16 is provided adjacent to the 
tip portion 131 of the fixed spiral element 13 so that the inner wall of 
the discharge port 16 is effectively an extension of the flat face 13a of 
the fixed spiral element 13. With this arrangement, the narrowed or neck 
portion of the tip 131 (adjacent the taper) is the weakest portion and is 
most easily damaged. On the other hand, in the second embodiment, the 
discharge port 16 is formed slightly apart from the flat face 13a of the 
fixed spiral element 13 with the step 12a being positioned there between. 
This step 12a improves the strength of the neck portion of the tip 131. 
This improved strength effectively prevents the tip portion 131 from 
breaking at the neck. 
The structures of the other portions of the second embodiment are quite the 
same as those of the first embodiment. The compressor according to the 
second embodiment therefore has all the advantages of the compressor of 
the first embodiment, such as securing the strength of the tip portions 
131 and 151 of both spiral elements, securing the cross-sectional area of 
the passage between the discharge port 16 and compression chamber 51 in 
the final compression stage, the reduction of the discharge resistance and 
the prevention of the reduction in the compression efficiency. 
Although only two embodiments of the present invention have been described 
herein, it should be apparent to those skilled in the art that the present 
invention may be embodied in many other specific forms without departing 
from the spirit or scope of the invention. Particularly, it should be 
understood that this invention may be worked in the form as shown in FIG. 
12. 
In this modification, two short oval discharge holes 17A and 17B are 
provided in the fixed end plate 12 in place of the discharge port 16 
having a single elongated oval as provided in the second embodiment. 
Alternatively, a plurality of substantially circular discharge holes may 
be provided. These discharge holes 17A and 17B are arranged so that a 
common tangent E to the individual circles defining the outlines of the 
discharge holes 17A and 17B is parallel to the flat face 13a of the fixed 
spiral element 13. In this case, the number of the discharge holes may be 
increased, and such a structure may also be applied to the first 
embodiment. The plurality of side by side discharge holes form an 
effectively elongated discharge port. 
The present examples and embodiments are to be considered as illustrative 
and not restrictive and the invention is not to be limited to the details 
given herein, but may be modified within the scope of the appended claims.