Rotary compressor

A cylindrical rotor journalled in a housing has an even number of vanes slidable in slots in the rotor and adapted to sealingly engage the inside wall surface of the housing to form working chambers between the rotor, said wall surface and the vanes, the rotor being provided with recesses adapted to cooperate with outlet parts in the end walls of the housing to form outlet passages for compressed gas. Piston means are located radially inside each of these recesses and connected to a diametrically opposed vane, each piston means being movable into the corresponding recess by said vane so as to fill up the recess and thereby force the gas therein out through the corresponding outlet port.

The present invention relates to a rotary compressor of the vane type 
comprising a housing provided with inlet ports for a gas to be compressed, 
a cylindrical rotor rotatably journalled in the housing, and an even 
number of vanes slidable in slots in the rotor and adapted to sealingly 
engage the inside wall surface of the housing in order to form working 
chambers between said rotor, said wall surface and said vanes, the rotor 
being provided with recesses adapted to cooperate with outlet ports in the 
end walls of the housing to form outlet passages for compressed gas. 
The recesses of the rotor constitute a portion of the so-called dead space 
of the compressor, which means the portion of a working chamber remaining 
after the exhaust phase. The amount of compressed gas present in this dead 
space is not discharged through the outlet port but will instead expand 
during the subsequent suction phase. The energy developed during the 
expansion cannot usually be utilized but will more or less be lost, which 
affects the efficiency of the compressor. The dead space also contributes 
to reducing the built-in volume ratio, which means the ratio between the 
largest volume of a working chamber after completion of the suction phase, 
and the smallest volume of the working chamber prior to the exhaustion. It 
is therefore desirable to minimize the volume of the dead space as far as 
possible without causing other negative effects on the efficiency, such as 
an increased pressure drop during the exhaustion of the compressed gas. 
A compressor made in accordance with the present invention has a 
considerably improved efficiency due to eliminating the disadvantageous 
effect of the dead space substantially completely, and at the same time 
other negative effects are avoided. This has been achieved by a rotary 
compressor of the aforementioned kind which, according to the invention, 
is generally characterized by piston means provided radially inside each 
of the recesses in the rotor and connected to the diametrically opposite 
vanes, each of said piston means being movable into the respective recess 
in order to fill up the same successively and thereby force the gas in the 
recess out through the corresponding outlet port.

The vane compressor shown in FIG. 1 comprises a housing 1, the interior of 
which is confined by two plane, parallel end walls 2 and 3 and a 
cylindrical circumferential wall 4 having an approximately elliptical 
cross-sectional outline. A circular cylindrical rotor 5 is journalled in 
the housing 1 and divides the interior thereof into two identical working 
chambers 6 and 7. Each working chamber has inlet ports 8 and outlet ports 
9 provided in the end walls 2 and 3. 
The rotor 5 is connected to a driving shaft 10 and is provided with vanes 
11 which are slidable in radial slots in the rotor and sealingly engaged 
with the walls of the working chambers 6 and 7. In addition, the rotor has 
recesses 13 at both ends which are adapted to cooperate with the outlet 
ports 9 in the end walls to form outlet passages for compressed gas. 
Radially inside each of the recesses 13 is a piston means 14 which is 
connected to the diametrically opposite vane and is thus slidable together 
therewith. In this embodiment, the piston means are made integral with the 
respective vanes. 
During rotation of the rotor 5 in the direction of the arrow in FIG. 1, the 
gas sucked in through the inlets 8 into the working chamber in front of 
each vane is compressed until the recesses 13 of the rotor reach the 
outlet ports 9, and then the gas begins to flow out through these ports. 
During the discharge period in which the recesses 13 pass along the outlet 
ports, the vanes are slid radially inwardly in the rotor, whereby the 
piston means 14 will be displaced into the recesses. Since the 
cross-section of the piston means corresponds to that of the recesses, the 
latter will be filled up completely so that the gas therein will be forced 
out through the outlet ports 9. The disadvantage of the dead spaces formed 
by the recesses of the rotor in conventionally designed vane compressors 
is thus eliminated substantially completely. 
As appears from FIG. 1, the outlet ports 9 are formed so that the width 
thereof decreases in the direction of rotation of the rotor, the side of 
the ports facing the center having a contour which corresponds to the path 
of movement of the piston means 14. In spite of the decreasing width of 
the outlet ports, the discharge flow velocity and consequently also the 
pressure drop across the outlet are still kept at an acceptable level, 
since the amount of gas discharged per unit of time decreases 
correspondingly. 
In the embodiments according to FIGS. 3 and 4, the design of the compressor 
housing is the same as that described above, but the rotor is provided 
with four vanes 21. The compressor housing has been omitted in FIG. 4. The 
rotor is provided at each of its ends with recesses 23, and in each of 
these recesses is a displaceable piston means 24 which is connected by 
means of a rod 25 to the diametrically opposite vane. In principle, the 
operation of this embodiment of the compressor is the same as that 
described with reference to FIGS. 1 and 2. Thus, during the exhaust phase 
the amount of gas present in the recesses 23 is displaced by the piston 
means 24 and forced out through the outlet ports in the end walls of the 
compressor housing.