WO2001061195A1

WO2001061195A1 - Rotary positive-displacement compressor with conical rotors

Info

Publication number: WO2001061195A1
Application number: PCT/EP2001/001681
Authority: WO
Inventors: Giovanni Mimmi; Paolo Pennacchi
Original assignee: Universita' Degli Studi Di Pavia
Priority date: 2000-02-15
Filing date: 2001-02-15
Publication date: 2001-08-23
Also published as: IT1316638B1; AU2001240621A1; ITMI20000257A0; ITMI20000257A1

Abstract

Rotary positive-displacement compressor (1) to compress fluids, comprising a box (2) containing two rotors (3, 3', 4, 4') defining an essentially conical surface with an aperture angle at the apex (α, β) of less than 180 °, with an essentially linear area of reciprocal contact (10). The axes of rotation (X, Y) of the rotors form between them an angle (δ) greater than zero and are coaxial with their respective drive shafts (5, 6) that connect them to motors. The box (2) is provided with one or more inlet (A) and outlet (S) ports for the fluid. The surface of each rotor has a grove (11) in the form of a screw thread with a conjugated form that extends in a spiral and concentrically in relation to the axis (X, Y) of the rotor. The axes of the rotors are coplanar or skewed, defining two variants of implementation of the compressor.

Description

ROTARY POSITIVE-DISPLACEMENT COMPRESSOR WITH CONICAL

ROTORS

Field of the invention

The present invention refers to a rotary machine of the compressor type, used to compress fluids, in particular compressible fluids such as air or other gases. State of the art

It is known that rotary compressors are distinguished from reciprocating compressors in that they do not have any internal parts in reciprocating movement and thus certain troublesome inertial forces produced by reciprocating movements of these parts are eliminated. There are rotary compressors of the positive- displacement type with different forms of implementation that can be grouped into various categories: rotary positive-displacement compressors with sliding vanes, with rotating paddle wheels, with endless screws.

In addition to rotary positive-displacement compressors, there are also centrifugal ones of the fluid-mechanical type which act on the fluid to be treated by means of rotary blading, but without creating closed volumes of fluid inside the actual compressor. The fluid treated in this manner remains in a volume that communicates openly both with the tank on the delivery side and the tank on the suction side, thus forming a continuous and constant flow. The head that can be obtained with this type of compressor is generally limited.

Instead, as regards rotary positive-displacement compressors with sliding vanes, their drawback is that scraping occurs between the vanes, the rotors and the external machine casing, with consequent wear, overheating of the compressor and low efficiency.

In the case of rotary positive-displacement screw compressors or with cylindrical rotors, the fluid is treated in closed volumes that are conveyed from the suction area towards the delivery area of the machine without any substantial reduction in the volume of the fluid during this passage towards delivery. This creates a sudden difference in pressure between the two areas of the compressor, as the fluid is simply moved towards the delivery area without being reduced in volume and instead comes suddenly into direct communication with a high pressure area. This situation causes impacts, noise and vibrations. Summary of the invention

Consequently, it is an object of the present invention to overcome the problems discussed above of known compressors.

A primary object of this invention is to provide a highly efficient and reliable compressor, running silently and with low friction between moving parts. Another object of the present invention is to provide a compressor able to operate continually and regularly without any sudden changes in pressure and thus improve the operating conditions by reducing sound emissions and vibrations. A further aim of the present invention is to provide a compressor that compresses treated fluids with a gradual and linear increase in the pressure value between the suction and delivery area.

These aims are achieved by a rotary positive-displacement compressor having the features of claim 1. Thanks to these features, the fluid compression operation is performed continually, the efficiency of the compressor increases substantially and, moreover, noise and vibrations generated during operation are reduced. Brief description of the Figures

Further characteristics and advantages of the invention shall become more apparent in the light of the detailed description of preferred, non exclusive, embodiments of a rotary positive-displacement compressor with conical rotors, illustrated by way of non limitative examples with the aid of the enclosed drawings in which:

Fig. 1 represents a sectional view of a first embodiment of the compressor according to the invention wherein the rotors have coplanar axes; Fig. 2 represents a sectional view of a second embodiment of the compressor according to the invention wherein the rotors have skewed axes; Fig. 3 represents a schematic sectional view of a third form of implementation of the rotors according to the invention wherein the conical rotors have non- rectilinear cone generatrices;

Fig. 4 represents details of other variants of the compressor according to the invention wherein the toothing has different profiles;

Fig. 5 represents details of the compressor according to the invention wherein the toothing has different profiles and variable pitch and thickness. Detailed description of the preferred embodiments of the invention

With reference to the Figures, a rotary positive-displacement machine or compressor, indicated globally with reference numeral 1 comprises a sealed box or container 2 with an approximately conical external form. Inside the box 2 there are two conical rotors 3, 4 whose respective axes of rotation X, Y are coplanar and convergent. Said rotors 3, 4 are mounted on their respective motor shafts 5, 6 appropriately supported on the box 2, in a known manner, by means of bearings or bushings. The shaft 6 is driven, in a known manner, by means of motors, not shown in the figures, and in its rotary motion draws the shaft 5 of the other conical rotor 3 in a synchronized manner thanks to cogs 8, 9 which mesh together. The shafts 5, 6 of the rotors 3, 4 can also be rotated by means of motors that are separate and advantageously synchronized with other means of the known type. A variant of the compressor is shown in Figure 2 where each rotor is composed of two cones 3, 3', 4, 4', joined together in correspondence of their narrowest area, to form the median area of each rotor, each of which is of the convergent- divergent type. The widest section, or base of each of the two conical parts is thus located at the extremity of each rotor, i.e. the section of the rotors has a convergent-divergent outline along its axis.

This embodiment makes it possible to balance axial thrusts generated during rotation of the rotors and consequent compression of the fluid. Owing to the particular shape of the rotors, in this variant of the invention the axes are skewed. The box 2 has at least two apertures or ports, for suction A and discharge S respectively, the first located in the area of the maximum diameter of the conical rotors 3, 4 and second in their area of minimum diameter. These ports are connected to ducts that convey the fluid towards the delivery. Said suction A and discharge S ports can be located on the box 2 radially, axially or in a combination of axial and radial, in relation to the rotors 3, 4, as can be seen in figures 1 and 2. Should this be necessary, for example in relation to the quantity of fluid to be treated, more than one of each of the ports A and S may be provided. The respective aperture angle α and β of the pitch cone of each of the rotors is generally greater than 0° and less than 180°, and preferably between 10° and 120°. The angle δ defined by the axes X, Y of the two rotors is equal to α/2 plus β/2. The rotors 3, 4 have an external surface in the form of a conical screw profile that may have even more than one thread start. The sections of the threads of the rotors 3, 4 have a conjugated form to ensure seal of the fluid treated along the directrix 10 of contact of the two rotors.

In accordance with the invention the section of the screw threads, viewed in projection on the plane passing through the axis of the actual rotors, may have different forms as illustrated in Figure 4a, 4b, 4c, in which one of the rotors 4 is represented in detail.

In a further variant, also coming within the scope of the invention and illustrated in Figure 5a, 5b, 5c, the pitch and thickness of the conical screw threads on each of the rotors can be variable. The section of the thread will thus have a variable depth along the entire directrix of the cone, the said depth decreasing in the direction of the smaller section of the rotor at one end, for the variant in Figure 1 , and in the central area, for the variant in Figure 2.

Another embodiment of the invention, not illustrated in the figures, provides that rotors can be implemented with one rotor fitted inside the other, which has a hollow form, similar to internal gear pairs.

In an embodiment of the invention illustrated in Figure 3, the cones may also be produced with generatrices that are not rectilinear, but with various curved forms, such as circular, elliptical, parabolic, etc..

The compressor 1 functions in the following way. Fluids are drawn up through the suction port(s) A and the volumes of compressible fluid enclosed inside the compressor in ducts or closed volumes 11 defined by the threads which, on the one hand with their apices are in sealed contact with the internal surface of the box in the areas 7, and on the other are closed along the common contact line 10, coinciding approximately with the generatrix of the cone. When the rotors rotate, fluid is conveyed along the ducts 11 and the mass of fluid is moved along the generatrices of the conical surfaces of the rotors and, during this movement, the volume is reduced progressively, gradually compressing the fluid. Consequently, in addition to being moved the treated fluid is also compressed with a relevant increase in pressure. The state of the fluid enclosed in the said volumes is thus modified progressively, as it moves from the suction port towards the discharge port s.

In order for the compressor to be efficient, the rotors 3, 4 must ensure perfect contact, sealed, both along the line of contact 10 of the reciprocal directrices and in the area 7 of contact between the apices of each thread and the internal surface of the box 2 and this is implemented with accurate surface machining of the parts. From this description of the compressor according to the invention it is evident that a series of desired advantages are produced, and in particular: the fluid conveyed to the area of the delivery port S has a different pressure than the one in the area of the suction port A and the two areas do not communicate; moreover, the fluid is subjected to gradual compression during movement along the rotors between the two areas and reaches the discharge port S at a higher pressure than when it entered the compressor. Therefore there are no sudden pressure surges, which could cause impacts in the machine, and operation remains more regular and continuous, without backlash and vibrations. This is even more important when operating with high pressure fluids; it is possible to obtain pressure stages of the same value as those obtained with known rotary screw compressors but without the sudden pressure stage at discharge that is typical of the latter; as rotors according to the invention are produced in a single piece there are no radial mobile vanes that scrape against one another and on the casing, with a reduction in relative losses through friction; as the compressor is composed of rotating parts only there are none of the reciprocating movements and inertial forces typical of reciprocating compressors; as the rotors are in a single piece with no parts such as sliding vanes the compressor is more rugged and reliable; unlike rotary positive-displacement compressors with cylindrical screw rotors of the traditional type, there are no surges in pressure that affect the rotors, forces produced by the fluid, which are discharged on the bearings supporting the rotors, generate a load that is more or less constant and without any noteworthy variations, which ensures a longer useful life of the compressor even when it is subjected to high load conditions; in the variant with convergent-divergent rotors the axial forces produced by the fluid on the rotors can be completely balanced.

Claims

CLAIMS 1. Positive-displacement compressor (1) to compress fluids comprising a box (2) containing two rotors (3, 3', 4, 4') coaxial to their respective axes of rotation (X, Y), and placed in such a way to generate an essentially linear reciprocal contact area (10), and comprising motor means to rotate the rotors (3, 3', 4, 4') around said respective axes (X, Y), said box (2) being provided with one or more suction (A) and discharge (S) apertures for the treated fluid, characterised in that the respective surfaces of the two rotors (3, 3', 4, 4'), for at least part of their axial extension, are essentially conical and have an aperture angle at the apex of each rotor (α, β) of less than 180° and that the said axes of rotation (X, Y) of the rotors between them form an angle (δ) greater than zero, or are reciprocally skewed, and in which each of the surfaces of the said rotors has at least one groove (11) extending in a conical spiral and concentrically to their respective axis (X, Y) and in which said at least one groove of the two rotors (3, 3', 4, 4') have a conjugated form.

2. Compressor as claimed in claim 1 , wherein said axes of rotation (X, Y) of the rotors are coplanar.

3. Compressor as claimed in claim 1 , wherein said axes of rotation (X, Y) of the rotors are skewed.

4. Compressor as claimed in one of the claims from 2 to 3, wherein said grooves (11) are in the form of a conical screw thread.

5. Compressor as claimed in claim 4, wherein the profile of the thread has a curvilinear, trapezoidal or triangular section.

6. Compressor as claimed in claim 5, wherein the thread has a variable pitch along the length of the rotor.

7. Compressor as claimed in one or more of the claims from 3 to 6, wherein the said rotors are composed of two portions (3, 3', 4, 4') with a conical form, joined together in their apex area and with a outline allowing the sections of the rotors to extend axially in a convergent-divergent manner.

8. Compressor as claimed in one of the claims from 3 to 6, wherein one of the said rotors is fitted inside the other.

9. Compressor as claimed in claim 1 , wherein the said pitch surface of the rotors is produced by generatrices with a curved form.

10. Compressor as claimed in one or more of the previous claims, wherein the aperture angle at the apex of the rotors is within a range of 10° and 120°.

11. Compressor as claimed in one or more of the previous claims, wherein there are more than one of said fluid suction (A) and discharge (S) apertures positioned in the side area and/or head area of the box (2).