US3620655A

US3620655A - Balanced rotor machine

Info

Publication number: US3620655A
Application number: US44737A
Authority: US
Inventors: Bo Olof Roland Arnegard
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1969-06-18
Filing date: 1970-06-09
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: BE752107A; GB1321483A; JPS503202B1; DE2029831A1; FR2046853B1; FR2046853A1; SE336190B; DE2029831C3

Abstract

Rotary piston machines have a casing with two intersecting cylindrical bores in which a main rotor and a gate rotor are mounted for rotation. Each rotor has a hub and one tooth extending from the hub. The main rotor tooth has a concave flank and a convex flank and the gate rotor tooth has a concave and a second flank. The main rotor has an opening in the concave flank and a cavity extending from said opening into the rotor, and the gate rotor has an opening in the second flank and a cavity extending from said opening into the rotor. The cavities are formed so that each rotor is statically and dynamically balanced.

Description

United States Patent 72] Inventor B0 0101 Roland Arnegard Skarholmen, Sweden [21] Appl. No. 44,737 [22] Filed June 9, 1970 [45] Patented Nov. 16, 1971 [73] Assignee Atlas Copco Aktiebolag Nacka, Sweden [32] Priority June 18, 1969 [33] Sweden [31] 8635/69 [54] BALANCED ROTOR MACHINE 6 Claims, 7 Drawing Figs.

[52] 11.8. CI 418/151, 418/ 191 [51] Int. Cl ..F01c 21/00, FOle 1/20 [50] Field oi'Search 418/191, 205, 206, 151

[56] References Cited UNITED STATES PATENTS 449,148 3/1891 Weston 418/151 X 685,775 11/1901 Lindsay 418/191 X 1,704,938 3/1929 Gardes 418/191 1,846,692 2/1932 Schmidt 418/206 2,097,037 10/1937 Northey 418/206 2,690,869 10/1954 Brown 418/151 X 3,050,011 8/1962 Karl et a1... 418/206 3,535,060 10/1970 Brown 418/191 X FOREIGN PATENTS 836,465 10/1938 France 418/191 341,324 1/1931 Great Britain 418/206 Primary Examiner-Carlton R. Croyle Assistant Examiner-Wilbur J. Goodlin Attorney-Munson & Fiddler ABSTRACT: Rotary piston machines have a casing with two intersecting cylindrical bores in which a main rotor and a gate rotor are mounted for rotationv Each rotor has a hub and one tooth extending from the hub. The main rotor tooth has a concave flank and a convex flank and the gate rotor tooth has a concave and a second flank. The main rotor has an opening in the concave flank and a cavity extending from said opening into the rotor, and the gate rotor has an opening in the second flank and a cavity extending from said opening into the rotor. The cavities are formed so that each rotor is statically and dynamically balanced.

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' BALANCED ROTOR MACHINE This invention relates to balanced rotary piston machines having a main rotor and gate rotor provided each per se with a hub having a portion with substantially constant radius and with a tooth, said tooth on the main rotor having a concave flank and a convex flank, said convex flank merging into said hub portion of the main rotor, said tooth on the gate rotor having at least a concave flank and a second flank merging into the hub portion of the gate rotor, said hub on the main rotor having a recess adjacent said concave flank of the main rotor tooth for the passage of the gate rotor tooth, said hub on the gate rotor having a recess adjacent said concave flank of the gate rotor tooth for the passage of the main rotor tooth, and said machine having a casing with intersecting cylindrical bores, one for each rotor, and end walls formed with axial inlet and outlet ports for an elastic working fluid, said rotors being mounted for rotation in said casing for positive displacement and change of volume of quantities of working fluid moving through the machine at each working cycle, and said machine having means for synchronizing the rotation of the rotors. One object of this invention is to provide a balanced rotary piston machine which is easy to balance and easy to manufacture and which may be manufactured at low cost. Another object of this invention is to provide a balanced rotary piston machine which has high capacity in relation to the external dimensions of the machine and particularly of the machine casing. A still further object of the invention is to provide a balanced rotary piston machine of the type described in which the inlet and outlet ports are as large as possible. A further object of the invention is to provide a balanced rotary piston machine of the type described in which the velocity of the working medium in the machine and in the inand outlet ports is low. A still further object of the invention is to provide a rotary piston machine with one tooth on each rotor and which is balanced statically as well as dynamically.

The balanced rotary piston machine according to the invention is substantially characterized by a first cavity which extends from an opening in the concave flank of the main rotor tooth into the tooth and the main rotor hub so far that the main rotor is statically and dynamically balanced with respect to the rotation axis of the main rotor, and by a second cavity which extends from an opening in the second flank of the gate rotor tooth into the tooth and the gate rotor hub so far that the gaterotor is statically and dynamically balanced with respect to the rotation axis of the gate rotor.

The invention is also characterized by one or more of the features set forth in the appended claims. The rotary piston machine according to the invention is primarily intended to operate as a compressor but may also be carried out so as to operate as a motor. In the accompanying drawings one embodiment of a balanced rotary piston machine according to the invention carried out as a compressor is illustrated by way of example together with a modification.

FIG. 1 is an end view of a rotary piston compressor according to the invention with one tooth on each rotor.

FIG. 2 is a cross section of the compressor in which, however, the rotors are illustrated in end view.

FIG. 3 is a longitudinal axial section on a plane through the rotor axes on line III-III in FIG. 1.

FIG. 4 is an end view of the cooperating main and gate rotors of the machine in FIGS. l-3.

FIGS. 5 and 6 are detail views on a reduced scale somewhat diagrammatic illustrating the rotors and contours of the cylinder bores, as viewed from one end of the rotors in the moment when compression starts and the moment when discharge starts, respectively.

FIG. 7 is a view similar to FIG. 4 with the two rotors in a position where the tooth tips of the rotors have just met, said rotors being somewhat modified with regard to the rotors illustrated in FIG. 2 and 4-6.

The rotary piston machine illustrated in FIGS. 17 is a single-stage tooth compressor provided with a main rotor and a gate rotor each per se provided with one tooth. The machine is provided with a casing which consists of a central compressor housing I provided with two end walls 2, 3 which are bolted to the central compressor housing 1 by means of bolts 4. The housing 1 is provided with two cylindrical intersecting

bores

5, 6 with parallel axes which bores intersect to a certain degree. The

bores

5,6 and end walls 2, 3 form working chambers for a main rotor 7 and a gate rotor 8 which rotors are provided and secured on

parallel shafts

9 and 10, respectively, which are mounted for rotation in bearings in the end walls 2, 3 and synchronized by means of a toothed gear transmission 12 and sealed towards the working chambers in the housing 1 by sealing rings 13. The housing 1 is provided with an inlet conduit portion 14 and an outlet conduit portion 15 which two portions end up in

planes

16 and 17 which are perpendicular one to the other and parallel with the rotor axis. A passage 18 from the conduit portion 14 leads through the end walls 2 and 3 and the housing 1 to inlet ports for the working chamber of the machine which inlet port consists of a radial inlet port portion 19 and two axial inlet port portions 20 one in each end wall. The outlet conduit portion 15 is through an outlet passage 21 in the housing 1 and the end walls 2, 3 connected to two axial outlet ports 22 one in each end wall. The housing 1 is air cooled and the end walls 2, 3 are liquid cooled and are for this purpose provided with liquid cooling fluid passages 23 and passages 2 for draining cooling fluid from the transmission housing 34.

The main rotor 7 has a hub with a hub portion 25 with constant radius which in the illustrated embodiment extends through an angle of 225 of the periphery of the main rotor hub. The main rotor hub, furthermore, carries a tooth 26 which has a leading convex flank which is formed by a flat portion 27 which connects the hub portion 25 with constant radius with a preferably circularly arcuate portion 28 which extends to the tip 29 of the tooth. The trailing flank of the main rotor tooth 30 is concave and disposed immediately adjacent a recess 31 which is formed in the hub and extends to and merges into the hub portion 25.

The main rotor 7 has a cavity 32 which extends into the main rotor from an opening 33 in the trailing concave flank 30 of the main rotor tooth, said opening extending over the main part of said flank. The cavity 32 is shaped in such a manner that the main rotor is dynamically and naturally also statically balanced.

The relation between the constant radius of the hub portion 25 of the main rotor and the maximum radius of the main rotor tooth 26 is in the illustrated embodiment 35 to 60. Preferably, the maximum radius of the main rotor tooth may be 50 to percent larger than the constant radius of the hub portion 25 of the main rotor. The length of the main rotor may preferably be substantially equal to the maximum radius. The invention results in a very favorable utilization of the volume of the compressor casing. Furthennore, a favorable relation between the total sealing line length and the swept volume of the machine is obtained which involves small leakage losses.

The gate rotor 8 has a hub with a hub portion 35 with constant radius which in the illustrated embodiment extends over an angle of 225 of the periphery of the gate rotor and cooperates with the hub portion 25 with constant radius of the main rotor and seals against said portion. However, upon rotation of the rotcirs the peripheral speed of the main rotor hub portion differs from the peripheral speed of the gate rotor hub portion. This difference causes a suitable wear of the rotor surfaces which results in a suitable sealing clearance. The gate rotor has a tooth 36 with a leading concave flank 37 generated by the tip 29 of the tooth 26 of the main rotor during the movement of said tip from the tip 38 of the gate rotor tooth to the root of said tooth. The leading flank of the gate rotor tooth 47 merges at the root of the tooth in a portion 39 which is an envelope to a family of circles generated by the circular areshaped portion 28 of the main rotor tooth on the gate rotor. The envelope portion 39 merges into the hub portion 35 via a portion 40 which is generated by the portion 27 of the main rotor tooth and which consequently an envelope of a family of lines. The gate rotor tooth 36 has a portion 41 at the tooth tip which is shaped as a circular arc and extends from the tip 38 of the tooth and merges into the trailing flank 42 of the gate rotor which is a tangent to the hub portion 35 and may have any suitable shape within certain limits, since it does not have to form a seal with the main rotor. The

tips

38,29 of the tooth may be rounded as obvious from FIG. 7 so that they are not so easily damaged and produce a better seal with the respective cooperating rotor portion. The tip 38 of the gate rotor tooth, the circularly arc-shaped portion 41 and the trailing flank 42 have generated the trailing flank 30 of the main rotor tooth and the recess 31 in the main rotor hub but these portions which extend over an arc of 45 of the rotors do not have to form a seal together.

Since the gate rotor is also asymmetric it has, similarly to the main rotor, been provided with a cavity 43 which extends into the gate rotor from an opening 44 in the trailing flank 42 of the gate rotor tooth. The effective height of the gate rotor tooth is in the illustrated embodiment about one-third of the effective height of the main rotor tooth. By this arrangement and this relation between the heights of the teeth it is possible to carry out the outlet ports so large that the air or gas velocity in these ports stay within reasonable limits and the flow velocities are thereby kept down. Similarly more suitable fluid velocity is obtained in the passages which surround the rotor in the compressor housing.

In order to make this operation of the machine more obvious and clear, the rotors in FIGS. 5 and 6-have been illustrated in the positions which they take when the compression starts as in FIG. 5 and when the discharge starts as in FIG. 6. FIG. 7 which illustrates the modification with rounded rotor tips also illustrates the position of the rotors at the moment when the

tips

29, 38 meet. The distance or gate rotor radius to the sealing line between the tip 29 and the flank 37 should in all positions of the rotors be than the radius to the sealing line between the

convex flank

27, 28 and the hub portion 40, so that the torque of the fluid pressure on the gate rotor tooth is always positive. The direction of rotation of the rotors is illustrated by arrows in FIGS. 1, 2, 5 and 6 and is the same also in FIGS. 4 and 7. FIG. 7 illustrates the rotors in the position they take when the

tip

29 and 38 of the rotor teeth have just arrived into cooperating position where the tooth tip 29 starts to sweep the surface 37 of the tooth 36 in sealing proximity the clearance at the tooth tip 29 in FIG. 7 being somewhat exaggerated. In order to improve the sealing around the rotors, the convex peripheral surfaces of the rotors may preferably be provided with a coating of a material which may be partly worn away, for instance paint. The end surfaces or end walls of the cylinder bores which are directed towards the rotors may also be provided with such surface coating.

The rotor machines described hereinabove should only be considered as examples and may be modified and varied in several different ways within the scope of the following claims.

I claim:

I. A balanced rotor machine having a main rotor and a gate rotor provided each per se with a hub having a hub portion with substantially constant radius and with a tooth, said tooth on the main rotor having a concave flank and a convex flank, said convex flank merging into said hub portion of the main rotor, said tooth on the gate rotor having at least a concave flank and a second flank, said second flank merging into the hub portion of the gate rotor, said hub on the main rotor having a recess adjacent said concave flank of the main rotor tooth for the passage of the gate rotor tooth, said hub on the gate rotor having a recess adjacent said concave flank of the gate rotor tooth for the passage of the main rotor tooth, and said machine having a casing with intersecting cylindrical bores, one for each rotor, and end walls formed with axial inlet and outlet ports for an elastic working fluid, said rotors being mounted for rotation in said bores in said casing for positive displacement and change of volume of quantities of working fluid moving through the machine at each working cycle, and said machine having means for synchronizing the rotation of the rotors, said machine being characterized by a first cavity which extends from an opening in said concave flank of the main rotor tooth into the tooth and the main rotor hub so far that the main rotor is statically and dynamically balanced with respect to the rotation axis of the main rotor, and by a second cavity which extends from an opening in said second flank of the gate rotor tooth into the tooth and the gate rotor hub so far that the gate rotor is statically and dynamically balanced with respect to the rotation axis of the gate rotor.

2. A rotor machine according to claim 1, in which the maximum radius of the main rotor tooth is between 50 and percent larger than the radius of the constant radius hub portion of the main rotor, and in which the opening in the concave flank of the main rotor tooth extends over the main portion of said flank.

3. A rotor machine according to claim 1, in which the difference between the maximum radius of the main rotor tooth and the radius of the main rotor hub portion is larger than the difference between the maximum radius of the gate rotor tooth and the radius of the gate rotor hub portion.

4. A rotor machine according to claim 1, in which the constant radius hub portion of the main rotor extends over an angle of the periphery of the main rotor amounting to a value between and 250 and merges into the convex flank of the main rotor tooth via a flat portion which merges into an arcuate portion extending substantially to the maximum radius of the main rotor tooth.

5. A rotor machine according to claim 1, in which the difference between the maximum radius of the main rotor tooth and the radius of the main rotor hub portion is between two and three times the difference between the maximum gate rotor tooth radius and the radius of the gate rotor hub portion.

6. A rotor machine according to claim 1, in which the rotors consist of a cast shell having an opening and provided with radially inward directed stiffening webs, and in which the opening is disposed in one rotor tooth flank.

Claims

1. A balanced rotor machine having a main rotor and a gate rotor provided each per se with a hub having a hub portion with substantially constant radius and with a tooth, said tooth on the main rotor having a concave flank and a convex flank, said convex flank merging into said hub portion of the main rotor, said tooth on the gate rotor having at least a concave flank and a second flank, said second flank merging into the hub portion of the gate rotor, said hub on the main rotor having a recess adjacent said concave flank of the main rotor tooth for the passage of the gate rotor tooth, said hub on the gate rotor having a recess adjacent said concave flank of the gate rotor tooth for the passage of the main rotor tooth, and said machine having a casing with intersecting cylindrical bores, one for each rotor, and end walls formed with axial inlet and outlet ports for an elastic working fluid, said rotors being mounted for rotation in said bores in said casing for positive displacement and change of volume of quantities of working fluid moving through the machine at each working cycle, and said machine having means for synchronizing the rotation of the rotors, said machine being characterized by a first cavity which extends from an opening in said concave flank of the main rotor tooth into the tooth and the main rotor hub so far that the main rotor is statically and dynamically balanced with respect to the rotation axis of the main rotor, and by a second cavity which extends from an opening in said second flank of the gate rotor tooth into the tooth and the gate rotor hub so far that the gate rotor is statically and dynamically balanced with respect to the rotation axis of the gate rotor.

2. A rotor machine according to claim 1, in which the maximum radius of the main rotor tooth is between 50 and 100 percent larger than the radius of the constant radius hub portion of the main rotor, and in which the opening in the concave flank of the main rotor tooth extends over the main portion of said flank.

4. A rotor machine according to claim 1, in which the constant radius hub portion of the main rotor extends over an angle of the periphery of the main rotor amounting to a value between 180* and 250* and merges into the convex flank of the main rotor tooth via a flat portion which merges into an arcuate portion extending substantially to the maximum radius of the main rotor tooth.