IE48625B1

IE48625B1 - Screw rotary piston machine

Info

Publication number: IE48625B1
Application number: IE1634/79A
Authority: IE
Original assignee: Klay Edouard; Beyeler Johann
Priority date: 1978-09-20
Filing date: 1979-08-27
Publication date: 1985-03-20
Also published as: JPS5543288A; GB2030227B; YU228779A; GB2030227A; BE878680A; CH635403A5; CA1120447A; IE791634L; IT1123269B; NO150696B; ZA794433B; NL7906453A; ES484284A1; FI792687A; MX149042A; GR66587B; DE2934065A1; DK390679A; IN153024B; DK146861B

Abstract

A meshing-screw compressor, or expander, comprises twin screw-rotors, or "spindles", (1a,b; 2a,b) each rotor having a helical slot (9) in each half thereof whose cross-section decreases toward the rotor center. The sides of the slot (9) are constituted by stepped flats (16) standing perpendicular to the rotor axes. Each rotor may thus be formed by a stack of laminae, or "disks", on a shaft 4 (as indicated in the right-hand half of Fig. 1). Channels 12, 14 for low and high pressure working-fluid may be disposed in the casing 7 as shown.

Description

The invention concerns a screw rotary piston machine for compressing or expanding a medium fed therein, which comprises at least two rotors arranged on parallel axes, said rotors each comprising at least one spiral slot which meshes with a correspondingly shaped spiral projection of the other rotor and which increases or reduces in volume per unit length of the rotor over a part of the length of the latter, and a casing enclosing said rotors and comprising at least one inlet and at least one outlet opening.

In the case of such a machine, it is extremely difficult and laborious to manufacture such rotors with a continuously modified slot cross-section while ensuring the accuracy required. Even relatively insignificant inaccuracies can impair the necessary tightness in sealing the volumes.

This posed the problems of designing a screw rotary piston machine of the kind initially mentioned such that the necessary accuracy could be achieved in a relatively simple manufacturing process.

In accordance with the invention this problem is over20 come in a machine of the kind initially mentioned wherein each said spiral slot is of stepped configuration such that between steps in opposite walls of the slot which lie in a common plane perpendicular to the rotary axis of the rotor, there is in each case defined a space of part circular cross-section, each said space being arranged. - 3 during rotation of said rotors,to be swept by a corresponding portion of the spiral projection of the other rotor, which makes rolling contact with the base of the slot, whereby the medium between the rotors is caused to pass along the spiral slot from the or a said inlet to the or a said outlet whilst being compressed or expanded as the case may be, and each said spiral slot further being so shaped that the first turn thereof adjacent the respective inlet and the last turn thereof adjacent the respective outlet are each of substantially constant cross-section.

The appended drawings show, by way of example, one embodiment of the invention.

Fig. 1 shows a part sectional view of a rotary piston machine in the plane determined by the rotor axes.

Fig. 2 shows a sectional view on line 11-11 of fig. 1.

Fig. 3 shows the cross section of the rotors according to fig. 2, but on a larger scale, and Fig. 4 shows a section view on line 1V-1V of fig. 1.

The screw rotary piston machine according to fig. 1 may be used as a compressor for compressing or as a motor for expanding a gaseous medium fed therein. It features two screw-type twin rotors la, lb; 2a, 2b mounted on parallel shafts, which twin rotors mesh and make rolling contact. Both rotors la, lb and 2a, 2b are provided each with a shaft journal 3 and each with one drive shaft 4. The shaft journals 3 and the drive shafts 4 are set in roller bearings 5 mounted in two identical and opposite bushings 6 of a machine casing 7. The two drive shafts 4 are mutually connected in a rotary manner by identical spur gears 8. The twin rotor halves la,, lb; 2a, - 4 2b each comprise one spiral slot 9 that decreases in width and in radial depth from the outer ends of the rotor toward the middle thereof.

Into each slot 9 of one rotor engages a correspondingly shaped spiral projection 10 of the other rotor so that by means of each slot of the two twin rotor halves la, lb; 2a, 2b the lining of casing 7 and the projection 10 of the cooperating rotor there are defined spaces filled with the gaseous medium and sealed off at the point of rolling contact between the rotors, in the plane determined by the rotor axes.

The outer diameter of the twin rotors la, lb and 2a, 2b decreases conically toward their middle whereas the core diameter increases conically toward the middle. The casing 7 is therefore designed in two parts and provided with longitudinal flanges 11.

If the two twin rotors la, lb and 2a, 2b according to fig. 1 and considered at their upper side are rotated towards each other, then the machine acts as a compressor with the gaseous medium flowing in through inlet channels 12 of the two bushings 6 and compressed toward the middle of the twin rotors la, lb and 2a, 2b where the medium flows into a center groove 13 and through a casing slot 14 through outlet channels 15 out of the machine. As the cross section of the spiral slot 9 decreases from the longitudinal ends of the twin rotors la, lb, 2a, 2b toward their middles, so the individual, sealed-off spaces correspondingly decrease, while pressure and density of the compressed medium are rising. In order to prevent any relative backflow of the medium in the varying cross section of slot 9, the first turn of the slot atthe inlet for the medium and the last turn before the - 5 outlet are provided with a substantially constant slot cross-section. The axial forces brought to bear upon the rotors because of the pressure difference between the medium entering and leaving the machine are compensated at the twin rotors la, lb and 2a, 2b, so that the roller bearings 5 are exposed only to a radial load. With the same direction of rotation, the machine can also be used as a vacuum pump to generate low pressure in channels 12. The rarified medium is then compressed to atmospheric pressure level and it will also leave the machine through channels 15.

If a gaseous medium is fed at super atmospheric pressure into the machine through channels 15, then this medium can expand in the sealed-off spaces whilst passing in the direction toward the channels 12 so that the machine acts as a motor. The twin rotors la, lb, 2a, 2b then rotate, considered from their upper side (fig. 1) away from each other.

The spiral slot 9 is of stepped configuration such that between steps 17 in opposite walls 16 of the slot which lie on a common plane perpendicular to the rotor axis there is in each case defined a space 18 (see Fig. 3) of part circular cross section.

When each rotor has a single spiral slot as shewn in the drawings there is a single space 18 in each plane, which space extends outside over half the circumference of a circle and is limited radially toward the inside by a concentric semi-circle 19. The ends of the semi-circle 19 are connected by symmetrical curves 20 with the ends of the outer circumference 21 and they form corners 22 with the latter.

Where the rotor has a triple slot design, for example, each plane contains three part circular spaces distributed evenly - 6 48623 over the circumference of the circle with each sector-shaped space extending over one sixth of the circumference of the circle.

According to fig. 1, the machine has a circular cross section. Cylinder-shaped holes 23 are used to save material and weight. The two bushings 6 are secured to the casing 7 by tie rods that pass through borings 24.

The machine could be equipped with twin rotors whose outer diameter increases conically toward the middle and whose core diameter decreases toward the middle.

Another advantageous design could be with twin rotors having a constant outer diameter as this would allow for buil ding the machine casing 7 in one part and with cylindershaped borings.

The rotors could also each be formed by a shaft with adjacent ring shaped disks fixedly mounted thereon which disks define the spaces 18. These ring disks must be set off in such a manner that their spaces 18 together form the spiral slot 9. The disks referred to are shown in fig. 1 to the right of the twin rotors.

Fig. 3 shows a diagram of the two rotors la, lb, 2a, 2b, wherein the curves 20 seal off a space 25. In this diagram one corner 22 each of one rotor la, lb rests against one end of the semi-circle 19 of the other rotor 2a, 2b. If the corners 22 move from the upper easing edge 26 to the lower casing edge 27, then they shift on curve 20 first from the outside to the inside toward the ends of the semi-circle 19, while the curved space 25 is forming, and then again from the ends of the semi-circle 19 toward the outside, while the curved space 25 disappears again. However, the - 7 latter is relatively small and remains open toward slot 9 during its formation and during its reduction. The corners 22 of the rotor cross section area (fig. 3) correspond with the edges of the steps 17 (fig. 1) and provide there for a double seal.

The machine features a simple structural design with only fixed and rotary components of a relatively small diameter, thus allowing for very high speeds. This is meant to provide for a low friction seal through lew clearance.

Claims

1. CLAIMS :1. A screw rotary piston machine for compressing or expan ding a medium fed therein, comprising at least two rotors arranged on parallel axes, said rotors each comprising at 5 least one spiral slot which meshes with a correspondingly shaped spiral projection of the other rotor and which increases or reduces in volume per unit length of the rotor over a part of the length of the latter, a casing enclosing said rotors and comprising at least one inlet and at least 10 one outlet opening, each said spiral slot being of stepped configuration such that between steps in opposite walls of the slot which lie in a common plane perpendicular to the rotary axis of the rotor, there is in each case defined a space of part-circular cross-section, and each said space 15 being arranged, during rotation of said rotors, to be swept by a corresponding portion of the spiral projection of the other rotor, which makes rolling contact with the base of the slot, whereby the medium between the rotors is caused to pass along the spiral slot from the or a said inlet to the 20 or a said outlet whilst being compressed or expanded as the case may be, and each said spiral slot further being so shaped that the first turn thereof adjacent the respective inlet and the last turn thereof adjacent the respective outlet are each of substantially constant cross-section. 25

2. A screw rotary piston machine according to Claim 1, wherein each said slot has in the said part thereof of increasing or reducing volume, an axial width and/or a radial depth which correspondingly increases or reduces.

3. A screw rotary piston machine according to Claim 2, 30 wherein the said rotors are of identical shape and have an - 9 outside diameter that decreases conically toward the longitudinal centre and a core diameter that increases toward the longitudinal centre.

4. A screw rotary piston machine according to Claim 2, 5. Wherein the said rotors are of identical shape and have an outside diameter that increases conically toward the longitudinal centre and a core diameter that decreases toward the longitudinal centre.

5. A screw rotary piston machine according to Claim 2, 10 wherein the rotors are of identical shape and have a constant outside diameter.

6. A screw rotary piston machine according to Claim 1, wherein each rotor comprises a shaft onto which are installed non-shift ring discs mounted closely together and each pro15 vided with at least one part-circular recess so that the recesses together form the spiral slot.

7. A screw rotary piston machine substantially as described herein with reference to the accompanying drawings.