Discharge system for rotary rolling piston compressor

Discharge system for rotary rolling piston compressor of the type that comprises a cylinder housing a rolling annular piston and a sliding vane which defines a suction and discharge volumes in the space between the piston and the cylinder and the inner faces of main and sub bearing plates, one of the plates having a discharge valve in communication with the discharge volume and being provided with a suction orifice. A gas outlet means communicates with the interior of the cylinder and has at least two gas intake positions one arranged in the extreme final region of the discharge volume and the other arranged radially set back and angularly advanced relative to the first.

BACKGROUND OF THE INVENTION 
The present invention relates to a rotary rolling piston compressor, and 
more specifically to a new implementation for the discharge system of this 
type of compressor. 
The dimensioning of the discharge system components of a rotary rolling 
piston compressor, which are the discharge orifice, the discharge valve, 
the valve reinforcement and the bumper is crucial to the compressor's 
satisfactory performance. 
Among the variables that influence this dimensioning is the discharge 
orifice diameter. A large diameter has the advantage of more rapidly 
discharging the gas compressed in the interior of the cylinder, therefore, 
reducing the loss by over compression, related to the readiness of the 
cylinder emptying at every discharge cycle. However, a discharge orifice 
of a large diameter increases the compressor dead volume. This impairs the 
compressor volumetric efficiency by the gas backflow at high pressure to 
the suction volume and it may reduce the suction fill up operation. Also 
the energy efficiency is decreased, also by the gas that flows from the 
dead volume back to the suction volume since this increases the 
compression work at every new cycle. 
Another disadvantage of using a large diameter at the discharge orifice is 
due to the geometrical fact that the larger is the orifice the earlier the 
compressor compression cycle will finish, i.e., at a rotation angle some 
degrees earlier. This reduces the compression cycle and at the same time 
it also increases another dead volume which is formed between the cylinder 
and the rolling piston walls and the vane wall at the end of the 
compression, giving rise to the same disadvantages already said to be the 
case of the dead volume created in the discharge orifice. Besides that, a 
larger discharge orifice diameter increases the compressor noise level. 
This is described in the technical literature on the subject. 
One method commonly used to reduce the above mentioned problems, especially 
in large capacity compressors, is the utilization of two discharge 
orifices and respective valves, each one placed at each end of the cover 
of the compressor set. This solution has the disadvantages of needing the 
placement of two discharge valves with all their assembly procedures and 
the machining of two valve seats, as well as requiring the provision of 
two muffler chambers. Furthermore, an increase of the compressor noise 
level is almost certain to happen. 
Another known solution uses a discharge system with cylindrical valve (see 
Brazilian patent PI 860 3449). In this solution, the discharge area is 
enlarged with the placement of several holes lying across the cylinder 
internal wall. Although this solution is effective in relation to the 
efficiency of the gas discharge, obviously it is difficult to execute due 
to the transverse machining of the holes. 
BRIEF DESCRIPTION OF THE INVENTION 
The object of the present invention is to provide a discharge system for a 
rotary rolling piston compressor which is able to eliminate the 
deficiencies mentioned above of the presently known systems. 
The discharge system of the present invention is used in a rotary rolling 
piston compressor of the type that includes a cylinder housing a rolling 
annular piston and a sliding vane. The vane defines the discharge and 
suction volumes, or chambers, in the space between the piston and the 
cylinder. The discharge and suction chambers are also defined by the 
surfaces of main and sub bearings, one being on each side of the cylinder. 
The bearing or sub bearing is provided with a discharge valve in 
communication with the cylinder discharge volume through a gas outlet 
mean. A bearing or sub bearing is provided with a suction orifice. The 
opening and the closing of both the gas outlet means and the suction 
orifice is caused by the angular position of the adjacent annular face of 
the rolling piston. 
According to the invention, the gas outlet means communicates with the 
interior of the cylinder discharge volume and has at least two spaced 
apart gas intake or inlet positions. The inlet positions have an angular 
alignment relative to the discharge volume. 
In a preferred embodiment, there are two inlets for the gas discharge 
means. The second inlet position is arranged adjacent to the sliding vane 
and to the external cylindrical surface of the discharge volume. The first 
inlet position is arranged radially set back relative to the second and 
angularly advanced in relation to it, considering the direction of piston 
rotation. The alignment, the separation and the dimensioning of the said 
gas intake positions are made so that the closing of the second position 
begins upon the end of the closing of the first position; the reopening of 
the first position begins only after the beginning of the reopening of the 
second position; and the reopening of the first position is completed only 
upon the end of the reopening of the second position. 
In one embodiment of the invention the gas outlet means is provided in the 
form of a single orifice arranged through one of the bearing plates. One 
end of the single orifice, which is turned to the discharge volume of the 
cylinder, defines the gas discharge orifice second inlet position and the 
first gas discharge orifice inlet position is defined by an end of a 
recess made on the internal face of the respective bearing plate, 
according to the said angular alignment to the compressed discharge 
volume. The other end at the orifice communicates with the extremity of 
the gas discharge orifice which defines the first gas intake position. 
The discharge system operates in the following manner: While the rolling 
piston is completing its compression cycle, the discharge begins (at about 
240.degree.). At this point, both inlets of the gas discharge orifices are 
open. As the piston continues rotation, its annular face closes the first 
orifice inlet until the end of the cycle and the completed discharge. With 
this arrangement, a considerable improvement on the discharge system 
operation is achieved. 
The first inlet position of the gas discharge orifice will only act in the 
initial part of the discharge when a greater volume of gas needs to be 
discharged. Gradually, the rolling piston annular face will be closing the 
inlet thus making possible a smooth discharge. 
Another important fact is that the first inlet of the gas discharge orifice 
is placed slightly away from the cylinder wall. This makes possible the 
delay of its reopening. Therefore, the dead volume backflow contained in 
the first inlet position only occurs at the time that the second inlet 
position is also reopening, after the rolling piston passage. The 
expression "reopening" means to reestablish the fluid communication among 
the dead volume of gas contained in the gas outlet mean and the cylinder 
suction chamber. This occurs after the passage of the annular face of the 
rolling piston over the internal extremity of the gas outlet means. While 
the annular face of the rolling piston is passing through the positions of 
the inlets to the gas discharge orifices, the fluid communication (or 
backflow) will be cut. After the passage of the rolling piston the fluid 
communication is reestablished. 
This delay on the reopening makes possible a better filling of the suction 
volume, without problems of gas backflow by the suction orifice. 
Therefore, care should be taken so that the shock wave caused by the 
release of dead volume of gas compressed in the gas outlet means does not 
have enough time to achieve the suction hole before its closing, that is 
why their reopening are delayed at maximum. 
Also, the fact of the rolling piston itself closing the first inlet 
position of the gas discharge means makes possible that all gas inlet 
positions are actuated by the same valve without problems of gas backflow 
already discharged in the shell back to the cylinder. 
Another benefit of this solution is that it keeps away the problems of 
increase of noise level resultant of the use of a diameter of a too large 
orifice in order to improve the readiness of the discharge of the 
cylinder. 
As constructive benefits, the invention uses the same valve stop, 
fastening, seat and single muffler chamber to both discharge orifices and 
also, the simplicity of the required machining, can be mentioned.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1 the compressor under discussion includes a shell 1 to 
which suction 1a and discharge 1b tubes are fixedly mounted and in whose 
interior a compressor set and an electric motor are conventionally 
mounted. 
The compressor set includes a cylinder 2, a main bearing 3 and a sub 
bearing 4. The main bearing 3 and sub bearing 4 plates are fixedly mounted 
to opposite walls of the cylinder 2, serving as the bearings for a 
crankshaft 5 of an electric motor which drives an eccentrically mounted 
rolling piston 6 in the interior of the cylinder 2. The electric motor has 
a coiled stator 9 and a rotor 10 to which the crankshaft 5 is mounted. 
The compressor set also has a vane 7 (illustrated in FIGS. 2, 5a and 5f) 
axially biased by a spring 8 (FIG. 2) to slide in the interior of a radial 
slot of the wall of cylinder 2 with one end riding against the surface of 
the rolling piston 6. The sliding vane 7 defines on one side or face with 
the cylinder and the volume between the faces of the bearing and sub 
bearing a suction chamber. On the other side of the vane a discharge 
volume is formed. 
As illustrated in FIGS. 2, 3, 4a and 4b, the sub bearing 4 has an elongated 
recess 11 formed on its exterior face. A suction orifice 15 is also formed 
through the sub-bearing. In the elongated recess 11 there is located a 
laminar spring leaf type discharge valve 13 and a stop 14, the end of each 
being mounted to the sub bearing by a rivet 12. 
The recess in the sub bearing plate 4 forms the gas outlet means from the 
interior of the cylinder 2 and, more specifically, from the discharge 
volume defined between the rolling piston 6 and the cylinder 2. 
In the configuration illustrated in FIGS. 3, 4a, 4b, 5a and 5e the gas 
outlet includes two discharge orifices 20a and 20b separated from each 
other and located near one end of the elongated recess 11. The orifices 
20a and 20b define two distinct gas inlet positions for gas discharge 
arranged on the part of the internal face of the sub bearing 4 which 
communicates with the cylinder 2 discharge volume. 
As shown in FIG. 4a the ends of the orifices 20a and 20b on the extended 
face of the sub bearing have respective distinct surrounding seats 23a and 
23b for the valve 13. In FIG. 4b these orifices 20a and 20b are surrounded 
by a single seat 24. The orifices 20a, 20b are normally closed by the 
spring loaded valve 13 which rests on the seats 23a, 23b. In operation, 
the valve 13 is opened by the internal pressure in the cylinder discharge 
chamber. As the piston 6 rotates past an opening 20a or 20b it closes that 
opening and prevents gas from entering to open the valve 13. 
As best seen in FIGS. 5a to 5e, the inlet of the second discharge orifice 
20b is located adjacent to the external cylindrical face of the discharge 
volume and closer to the vane 7. The suction volume chamber is on the 
other side of the vane. The inlet of the second orifice 20b position is in 
the extreme final region of the cylinder discharge volume, i.e., in the 
place commonly used to the placement of the discharge orifice of any 
rotary rolling piston compressor. 
The first discharge orifice 20a inlet is located at a point angularly 
advanced relative to the rotation of the piston 6 and radially set back 
relative to the second discharge orifice 20b. The radial set back and the 
angular advance of the first orifice 20a in relation to the second one 20b 
is selected so that the reopening of the first orifice 20a, after the 
passage of the piston 6, only takes place after the reopening of the 
second discharge orifice 20b (see FIG. 5e). 
With this arrangement, both discharge orifices 20a and 20b are arranged on 
an angular alignment to the cylinder discharge volume with the 
dimensioning of the diameter of the orifices 20a and 20b realized in a way 
to allow a smooth and efficient discharge of the compressed gas in the 
discharge volume, with a minimum of dead volume. 
The discharge valve arrangement also causes the closing of the second 
discharge orifice 20b to start only upon the end of the closing of the 
first discharge orifice 20a (see FIG. 5c) by the action of the annular of 
the rolling piston 6, thereby allowing a progressive and smooth discharge 
of the compressed gas. The duct area of the gas outlet is then 
progressively reduced from a maximum value, corresponding to the beginning 
of the discharge when there is a greater volume of compressed gas in the 
cylinder, to a null value or of discharge closing, as while the volume of 
compressed gas to be discharged is getting reduced. 
The discharge orifices 20a and 20b are positioned so that the reopening of 
the first orifice 20a only gets completed upon the end of the reopening of 
the second orifice 20b (See FIG. 5e) meaning that the dead volume release 
of the first orifice 20a only takes place after the closing of the suction 
orifice 15 by the rolling piston 6, it being understood that the second 
orifice 20b is conventionally projected to reopen only after the closing 
of the suction orifices. 
FIG. 5f illustrates a variation of the gas outlet mean that is defined by a 
single discharge opening 21 with the shape of an elongated slot having one 
end placed at the extreme final region of the cylinder 2 discharge volume. 
This slot communicates with the elongated recess 11 of the external face 
of the sub bearing plate 4, under the discharge valve 13. 
As seen, the discharge opening 21 is arranged according to the same 
alignment applied to the orifices 20a and 20b of the first embodiment, in 
a way to maintain the first end 21a in a position radially set back and 
angularly advanced relative to the other end 21b of the discharge opening 
21. 
Regarding the first embodiment it is also possible to provide more than two 
gas discharge orifices according to the same angular alignment to the 
cylinder 2 arranged in the described way with relation to both discharge 
orifices of FIGS. 3, 4, 4a and 5e. 
It is also possible to have an association of the two embodiments, in a way 
to have, for example, two or more orifices with the internal extreme of 
that more angularly advanced connected to an elongated internal recess of 
the bearing plate in which the discharge valve is placed, this internal 
recess being responsible for the definition of the first position of gas 
intake. 
While only two configurations for the discharge system have been shown, it 
should be understood that alterations can be done without digressing from 
the inventive conception defined in the claims.