The present invention relates to a machine of the rotary screw type for a gaseous medium having a compression sec¬ tion and an expansion section driving the compression sec¬ tion. In a compressor a gaseous medium is compressed to a higher pressure which consumes power. In an expander a gaseous medium is expanded which generates power. It is thus possible to drive a compressor by use of an expander. An example of this is disclosed in DE-PS 1 811 284 showing a rotary screw compressor driven by a rotary screw expan¬ der. A similar example is disclosed in an article in the magazine "Gluckaus" 9/1960, pages 576 and 577.

According to known technique in this field, as exempli¬ fied by the above cited references, the compressor and the expander are made as separate units, each one having its own separate working space with inlet and outlet ports and being connected only by the common driving shafts . Such a construction of an expander-driven compressor therefore will be relatively complicated. The object of the present invention is to make an expander-driverf compressor, which is more simple in its construction than known machines in this field.

This object is according to the invention attained in that a machine of the introductionally defined kind has the features specified in the characterizing portion of claim 1 of the present application.

A machine according to the invention has the advantages of being very compact and simple in its construction and requiring a minimum of ports for the supply and discharge of the working medium since a common intermediate pressure port can be used for both the medium being compressed and the medium being expanded. It is therefore particularly suitable to be used where low weight and small dimensions are aspired, e.g. in applications in aeroplans .

The invention will be further explained by the following detailed description of preferred embodiments of the invention and with reference to the accompanying drawings. Figure 1 is a side view of a machine according to a first embodiment of the invention.

Figure 2 is an enlarged section along line II-II in figure 1.

Figure 3 is a simplified side view of the male rotor of the machine in figure 1. Figure 4 is a diagram illustrating the working process of the machine in figures 1 to 3.

Figure 5 is a top view of a machine according to a second embodiment of the invention, the upper half of the casing being removed. Figures 6 and 7 are sections taken along lines VI-VI and VII-VII, respectively, of figure 5.

Figure 8 is a simplified side view of the male rotor of the machine in figure 5.

Figure 9 is a diagram illustrating the working process of the machine in figures 5 to 8.

Figures 10 and 11 are simplified side views of the male rotor in machines according to further embodiments of the inventio .

Figures 12 and 13 are diagrams illustrating the working process of the machines in figures 10 and 11, respectively. Figure 1 is a side view of a machine according to a first embodiment of the invention. The casing, composed of two end walls 4 and 6 and a barrel wall 2 extending there¬ between, defines a working space in which two rotors cooperate. Outside the end walls 4 and 6, there are bearing housings 26 and 28. The machine has a first inlet channel 8 for pressurized air, a second inlet channel 10 for vacuum and a common outlet channel 12 leading to atmospheric pressure. As can be seen in figure 2 the working space formed by the casing has the shape of two intersecting cylinders and contains a male rotor 14 and a female rotor 16. The male

rotor 14 has four helically extending lobes 18 and inter¬ mediate grooves 22 and the female rotor 16 has six lobes 20 and intermediate grooves 24. The rotors intermesh through the lobes 18, 20 and grooves 24, 22 forming working chambers between the rotors and the walls 2, 4, 6 of the casing. The working chambers travel axially along the machine as the rotors rotate, thereby changing their volumes. The volume of each working chamber starts rom zero at one end of the machine and rises continuously up to a maximum, from which it then decreases down to zero again at the other end of the machine. These volume changes are used for expansion and compression of air by providing ports for supply and withdrawal of air of different pressures at the relevant locations of this cycle. How these ports are located relative to the expanding and decreasing working chambers can best be understood from figure 3, schematically showing the male rotor 14 in a side view. The tips of the lobes form sealing lines S with the barrel wall and between two sealing lines a chamber C is formed. The chamber register with a similar chamber formed by the lobes of the female rotor and together they constitute a working chamber of chevronlike shape. For the purpose of understanding the working process it is sufficient to regard only the part of the working chamber which can be seen in the figure. At operation each working chamber C passes five phases during its complete working cycle; A first filling phase, an expansion phase, a second filling phase, a compression phase and a discharge phase. At the upper left end of the machine as viewed in figure 3 pressurized air of a pressure P2 above atmospheric pressure is supplied from the high pressure inlet channel 8 through a high pressure inlet port 30 to a working chamber, in which the volume is rising from zero to a comparatively small value V<| , when communication with the high pressure inlet port 30 is cut off by the trailing sealing line of the working chamber. This constitutes the first filling phase.

As the working chamber then travels further to the right in the figure its volume increases further causing a de¬ crease in the pressure. This expansion phase continues until the leading sealing line of the working chamber reaches the low pressure inlet port 32. At this moment the volume of the working chamber has increased to V2, large enough for creating a vacuum of a pressure p- _j in the work¬ ing chamber.

When the leading sealing line of the working chamber has reached the low pressure inlet port 32 the working chamber starts to communicate with the low pressure inlet channel 10 in which the pressure is at the same vacuum level. p- _| to which the pressure in the working chamber has been ^" ex¬ panded. When the working chamber is in communication with the low pressure inlet channel 10 its volume will increase still further, but the pressure will remain constant at the pressure level of the low pressure inlet channel 10, since air is sucked therefrom into the working chamber. This second filling phase ends when the working chamber has travelled so far to the right that communication with the low pressure inlet port 32 is cut off by the trailing sealing line.

The working chamber now has its maximum volume V3 and the compression phase starts in that the volume of the working chamber starts to decrease. The compression con¬ tinues until the leading sealing line reaches the outlet port 34. The outlet port 34 is located such that the pressure in the working chamber has been raised to atmospheric pressure P _Q when the working chamber comes into communication therewith. The volume at this moment has decreased to V4.

The air of atmospheric pressure is then discharged to the surrounding atmosphere through the outlet port 34 during the discharge phase of the working cycle as the volume of the working chamber decreases from V to zero.

As is apparent from the above description of the working cycle the machine includes an expansion section and a compression section. The expansion section is constituted by those working chambers that communicate with the high pressure inlet port and those working chambers in which the air expands before the chambers are brought into communica¬ tion with the low pressure inlet port 32. The compression section is constituted by the rest of the working cham¬ bers. The locations of the ports and the dimensions of the machine are such that the work generated in the expansion section equals the work required for driving the compres¬ sion section.

The working cycle is in figure 4 illustrated by ^' a pV-diagram, indicatiing the five phases thereof. I is the first filling phase from V = 0; p = P2 to V = Vi; P = P2

II is the expansion phase from V = v-j ; p = P2 to V = V2; p = Pi

III is the second filling phase from V = 2; P = P-j to V = V3; p = p<|

IV is the compression phase from V = V ₃ ; p = i to V = V4; p = PQ

V is the discharge phase from V = V4; p = PO to V = O; p = Q Figure 5 illustrates a second embodiment of the inven¬ tion and is a top view thereof, where the upper part of the casing is left out. In this embodiment each of the two rotors 114 and 116 is divided into two parts of different shape, thereby forming an expansion section and a compres- sion section. The male rotor 114 thus is composed of an expansion part 114a and a compression part 114b and the female rotor 116 of an expansion part 116a and a compres¬ sion part 116b. The pitch angle α _ma , αf _a of the spiral on each expansion part 114a and 116a is smaller than the pitch angle α^, α^ of the spiral on each corresponding compres¬ sion part 114b and 116b. And the axial pitch S _ma , Sf _a of each expansion part 114a and 116a is smaller than the axial pitch Sm _b and Sffc of each corresponding compression part 114b and 116b. Furthermore the direction of the spirals on

the two parts of each rotor are opposed relative to each other. The diameter of the female rotor 116 is the same for its two parts 116a and 116b, whereas the male rotor compression part 114b has a larger diameter than the male rotor expansion part 114a. The shape of the rotors in planes perpendicular to the rotor axes can be seen in figures 6 and 7 showing transverse sections through the expansion section and the compression section, respective¬ ly. Both parts of the male rotor 114 have three lobes 118a, 118b with intermediate grooves 122a, 122b but differ in shape. Both parts of the female rotor 116 have five lobes 120a, 120b with intermediate grooves 124a, 124b and differ in shape.

A high pressure inlet port is provided at the left end as viewed in figure 5 of the expansion section for the supply of pressurized air, and a low pressure inlet port is provided at the right end of the compression section for the supply of air at vacuum level. Where the two sections meet there is a common outlet port leading to atmospheric pressure. None of these ports can be seen in figure 5, but are shown in the schematic figure 8.

Figure 8 schematically illustrates how the machine operates and shows the male rotor 114 in a simplified side view. At the upper left end, as seen in the figure, of the expansion section air of a pressure P2 above atmospheric pressure is supplied from a high pressure inlet channel 108 through a high pressure inlet port 130 into the expansion section of the working space, where the expansion part 114a of the male rotor and the related cooperating part of the female rotor (not shown) expand the air to atmospheric pressure P _Q . The air of atmospheric pressure leaves the machine through a common outlet port 134 to an outlet channel 112. At the upper right part of the compression section air of a pressure p-| below atmospheric pressure is supplied to the compression section of the working space from a low pressure inlet channel 110 through a low pressure inlet port 132. The air is compressed to

atmospheric pressure by the compression part 114b of the male rotor and the related cooperating part of the female rotor. The compressed air of atmospheric pressure leaves the machine through the common outlet port 134 together with the air from the expansion section.

There is no partition wall between the two sections where the expansion parts and the compression parts of the rotors meet. Due to the fact that the ports are so located that the pressurized air is expanded to the same pressure as the pressure to which the vacuum is compressed, i.e. atmospheric pressure, there is no need for separating the ■ ^■ two sections by such a partition wall.

The working process is illustrated in a pV-diagram in figure 9. The upper part of the diagram represents the expansion and the lower part the compression.

A machine according to the invention, as exemplified by the two embodiments thereof described above, offers a simple and reliable way of producing and maintaining a certain vacuum level using pressurized air as the only driving source, and having one single working space for both the driving and the working. In particular the embodiment shown in figures 1 to 4 entails considerable advantages, since one single pair of uniform rotors simultaneously acts as an expander and a compressor and thus requires no special measures for matching these two to each other, which otherwise would be necessary. In addition the manufacture of the rotors will be simple, as, due to their uniform shape, only one cutting process is required for each rotor. As earlier mentioned the small dimensions and light weight which can be attained with a machine according to the invention makes it particularly suitable for installa¬ tions in an aeroplan for producing vacuum, e.g. for use in its vacuum toilet system. The embodiments of the machine described above can be modified for use in other applications. By connecting the low pressure port to a channel of atmospheric pressure it

can be used in situations when pressurized air is available but there is a requirement of pressurized air of lower pressure. The waste of energy which occurs when simply throttling the pressurized air to the required level there- by is avoided, since the energy of the expansion of the high pressure air to the required level is made use of for compressing atmospheric air to this pressure level.

Still further modi ications of the machine are schemati¬ cally illustrated in figures 10 and 11, showing applica- tions where the machine is used for amplifying pressure. In figure 10 pressurized air of pressure P2 is supplied from., the intermediate pressure channel 212 to the machine and expands therein to atmospheric pressure p- _| . A part of the expanded air is discharged through the low pressure port 232 connected to a channel 210 of atmospheric pressure. After the working chamber is cut off from communication with the low pressure port 232 the remaining air of atmos¬ pheric pressure is compressed to a pressure 3 exceeding the inlet pressure P2 and leaves the machine through the high pressure outlet port 230.

Figure 11 shows a machine which is modified in co - parence with the one shown in figure 10 in that there is provided a second intermediate pressure inlet port 336. Through this port air of the same pressure P2 as the air in the common intermediate pressure inlet port 334 is supplied to a working chamber after communication between the working chamber and the low pressure outlet port 332 is cut off. The compression thus starts from a higher pressure level than in the embodiment of figure 10. Figures 12 and 13 illustrate in pV-diagrams the working process of the machines of figures 10 and 11, respectively.

As illustrated by the different embodiments of the machine described above its advantages can be made use of in many different applications for converting pressures to desired levels. Thus, it can be used as a vacuum producer or as a pressure amplifier or for reducing pressure in such a way that the amount of air at the reduced pressure level is larger than the amount of supplied high pressure air.