US3275225A

US3275225A - Fluid compressor

Info

Publication number: US3275225A
Application number: US357561A
Authority: US
Inventors: Forrest O E Schultz
Original assignee: Midland Ross Corp
Current assignee: MIDBRAKE Corp
Priority date: 1964-04-06
Filing date: 1964-04-06
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27
Also published as: GB1030458A; DE1503579B2; DE1503579A1; DE1503579C3

Description

Sept. 27, 1966 F. o. E. SCHULTZ 3,

FLUID COMPRESSOR Filed April 6, 1964 2 Sheets-Sheet 1 2 I INVENTOR.

P01212275 T [7.5. 501m TZ.

BY WW .9? QQWM (1 AT: Y5.

p 27, 1966 F. o. E. SCHULTZ 3,275,225

FLUID COMPRESSOR Filed April 6, 1964 2 Sheets-Sheet 2 OUTLINE OF AcTw/L 07012.

OUTLINE OF INVENTOR. .FUHHEST [7.5. 501% T2.

United States Patent 3,275,225 FLUID COMPRESSOR Forrest O. E. Schultz, Owosso, Mich., assignor to Midland-Ross Corporation, Cleveland, Ohio, a corporation of Ohio Filed Apr. 6, 1964, Ser. No. 357,561 8 Claims. (Cl. 230-141) This invention relates to improved apparatus for compressing fluids and particularly compressible fluids such as air. More particularly, the invention relates to an improved compressor of the lobed-rotor type, frequently called a Roots blower or compressor after an early patentee of the configuration (Reissue Patent 2,369 of October 2, 1866).

A typical lobed-rotor compressor comprises two rotating elements or rotors which are caused to rotate in opposite directions about spaced parallel axes in an appropriately contoured chamber. Each rotor is provided with a number of spaced apart outwardly extending lobes,

usually two, and an equal number of recesses alternately spaced between the lobes. In current practice the alternate lobes and recesses usually comprise arcs of circles of equal diameter.

In such an arrangement, the rotation of the rotors is so synchronized, as by timing gears, and the spacing between the rotor axes is so maintained, that some predetermined clearance is continually maintained between the rotors as the lobe of one rotor and the recess of the other rotate into and out of register with one another. The purpose of this clearance is, of course, to prevent wear which would arise if the rotors Were permitted to rub against one another. However, the clearance so provided between the rotors inherently constitutes a path for compressed fluid to escape back from the high pressure side of the compressor to the low pressure side of the compressor with consequent loss of volumetric efficiency of the compressor. Defined as slip, this leakage is a constant for any given compressor at a given pressure and is independent of compressor speed. Hence, compressor volumetric efficiency for a lobed-rotor compressor decreases substantially as the compressor speed is reduced from the maximum or rated speed. This characteristic of lobed-rotor compressors has generally limited their commercial utility to substantially constant speed (constant output volume) applications.

In accordance with the present invention, however, there is provided a lobed-rotor compressor having rotors of a novel configuration which is advantageous in minimizing compressor slip and which imparts commercial utility to the compressor for applications requiring Wide variation in compressor speed. A particular application for such a compressor is in providing compressed air for the ManAirOx (manifold air oxidation) automotive exhaust purification system which is being developed pursuant to the anti-smog campaigns of Los Angeles and other communities. Typical requirements for a compressor for such an application are that it be able to provide 230 cubic feet per minute (standard conditions) of air at 0-10 p.s.i.g. pressure over an operating speed range of 1000-10,000 revolutions per minute. Prior to the present invention no I known lobed-rotor compressors were able to satisfactorily meet these requirements.

For a further understanding of the invention, attention is directed tothe following portion of the specification, the drawing, and the appended claims.

In the drawing:

FIG. 1 is an elevational sectional view of a compressor embodying the present invention;

FIG. 2 is a sectional view taken on line 22 of FIG. 1; FIG. 3 is an outline view of a rotor showing the geometrical configuration of its periphery.

"ice

FIGS. 4 and 5 are outline views showing the clearance between rotors, and between each rotor and the wall of the surrounding chamber, for various positions of rotors of the configuration shown at FIG. 3.

As shown at FIGS. 1 and 2, the preferred embodiment of the present invention comprises a cast housing 11 peripherally enclosed by a wall 12 and having an internal wall 13 oriented generally transversely of peripheral wall and intermediate the ends thereof. Peripheral wall 12 and internall wall 13 are effective to form adjacent chambers 14 and 15 each of which is open at the end opposite from the other chamber. Open-ended chambers 14 and 15 are normally closed by

end closure plates

16 and 17 respectively, which are secured to casting 11 by bolts 18 threaded into tapped holes 19 in casting 11.

End closure plates

16 and 17 are also shown as being of cast construction and each is shown as being provided with fins 21 on the exterior thereof for the dissipation of heat. The exterior of wall 12 is also provided with fins 21 for dissipating heat.

Disposed within chamber 15 are a pair of

lobed rotors

22 and 23 which are identical, except for the possibility of normal minor variations in the manufacture of otherwise identical elements.

Rotors

22 and 23 are attached to spaced apart

parallel shafts

24 and 25, respectively, by means of

pins

26 and 27. Shaft 25 is journaled in spaced apart

bearings

28 and 29, located in chamber 14, and has a portion extending outwardly from chamber 14 through closure plate 16 for connection to motive means (not shown). Shaft 24 is also journaled in spaced apart bearings located in chamber 14, viz

bearings

31 and 32, and attached thereto is a gear 33 disposed

intermediate bearings

31 and 32. Gear 33 meshes with a similar gear 34 attached to shaft 25

intermediate bearings

28 and 29. Thus, rotation of shaft 25 by means externally of the compressor will result in rotation in opposite directions rotated in a clockwise direction, with resulting counterclockwise rotation of shaft 24 and rotor 22, where will be a compressing effect exerted by the rotors on fluid entering chamber 15 through internally threaded connection 35 which will cause the fluid to exit from chamber 15 at higher pressure through outlet connection 36.

As shown at FIG. 3, the geometrical configuration of each of

rotors

22 and 23 comprises a plurality (shown as two) of lobes having the configuration of an epicycloid, and an equal number of recesses spaced between successive lobes and having the configuration of a hypocycloid. The dotted outline is the outline of a true alternating epicycloid-hypocycloid rotor configuration which is generated about a base circle of diameter B by a point on the circumference of a rolling circle of diameter A which alternately rolls for one revolution along the outside of the base circle and thence for one revolution along the inside of the base circle. In generating such a configuration the diameter of the rolling circle bears the following relationship to the diameter of the base circle: A=B/2N, where N is the number of desired lobes in the resulting configuration. Thus, to generate the outline of a double-lobed rotor, the relationship between the diameter of the rolling circle and the diameter of the base circle is determined by the formula A=B/4.

If a blower were constructed having a pair of identical rotors of the configuration of alternating epicycloids and hypocycloids according to the formula A=B/2N and were disposed on parallel axes separated by a distance B, the diameter of the base circle, there would, in theory,

be line contact between the rotors throughout their rotation with neither clearance nor interference at any point of their rotation. In practice, of course, it is not desired to design for any contact between the rotors because the rubbing action of rotor on rotor would generate excessive heat at operating speeds of the order of up to 10,000 r.p.m., with resulting excessive wear, and because inevitable manufacturing deviations from the precise standard could lead to interference between the rotors which would impair the operability of the blower.

Accordingly, it is necessary to depart from the rotor that required in view of the relative difiiculty involved in manufacturing to an optimum clearance, because excessive clearance results in increased slip and reduced volumetric efficiency. The points of necessary clearance between blower parts, listed in order of increasing importance from the standpoint of difiiculty in manufacturing to an optimum clearance, are as follows:

(1) Between that point of each epicycloid lobe, which is radially most remote from the axis of rotation of the rotor, and the inner surface of wall 12 of the blower.

(In this regard it is noted that the configuration of the inner surface of wall 12 is that of the outline of intersecting circles of a diameter, D, which bears the relationship to the base circle: D=B+B/N, with each of the intersecting circles drawn about centers at the axes of

rotor shafts

24 and 25 which, in turn, are separated by a distance equal to the diameter of base circle of each rotor.) This point of clearance is the least critical because it is affected by the manufacturing precision of only one rotor, the part whose dimensions are most difficult to hold, rather than both rotors.

(2) Between the two rotors when they are oriented at right angles to one another, as shown at FIG. 4: This point of clearance is more critical because it is affected by the manufacturing precision of both rotors and by the axial spacing between the rotor shafts.

(3) Between the two rotors when they are oriented parallel to one another: In addition to the fact that this point of clearance is affected by the manufacturing precision of both rotors and by the spacing of the rot-or shafts,

it is also affected by the angilar orientation of both rotors which, in turn, is affected by such factors as backlash in the driving gears and torsional deflection in the rotor shafts.

Therefore, it is desirable to incorporate some modification to the configuration of a true rotor which will result in a satisfactory clearance between the rotors when they are oriented parallel to one another; a lesser, but nonetheless still satisfactory clearance between the rotors when they are oriented at right angles to one another; and a minimal, but still satisfactory clearance between the radially most remote point of each lobe and the inner surface of the blower wall. This relative priority of clearances can be met by constructing a rotor with alternating epicycloid lobes and hypocycloid recesses where the epicycloid lobe is generated by a point on the circumference of a rolling circle whose diameter is less than that determined by the formula B/2N by a predetermined amount,

' C, and where the hypocycloid recesses are generated by a rolling circle whose diameter is greater than that determined by the formula B/2N by the same predetermined amount, C. This is shown at FIG. 3 where the partial outline of an actual rotor following the modified configuration is shown for the epicycloid lobe on the right and the hypocycloid lobe at the top.

As shown at FIGS. 4 and 5, a blower with rotors having the outline of the actual rotor of FIG. 3, will incorporate a design clearance of C between the radially most remote point of the epicycloid lobe and the internal surface of the surrounding blower wall. As shown at FIG. 4, V the rotors will have a design clearance equal to 2C when they are disposed at right angles to one another. And as shown at FIG. 5, the rotors will have a design clearance equal to 1rC when they are disposed parallel to one another. This increasing order of magnitude of design clearances matches nicely with the increasing order of difliculty in manufacturing to a design clearance and is the only known rotor design formula which does so.

As an example, presented for the purpose of further illustrating and disclosing the invention, it has been found that a blower with double-lobed rotors constructed in accordance with the present invention, wherein the diameter B of the base circle of each rotor was one and onehalf inches, and wherein the difference C by which the diameter of the rolling circle for each epicycloid lobe was less than that determined by the formula was of the order of 0.001 inch, while the difference by which the diameter of the rolling circle for each hypocycloid recess exceeds that determined by the formula A=B/2N by the same amount, was capable of operating within the specifications established by a number of automobile manufacturers in regard to ManAirOx exhaust purification systems.

In view of known manufacturing techniques for accurately geometrically describing a member whose extent can be expressed by an algebraic formula, there will be a number of manufacturing techniques obvious to a skilled artisan for manufacturing rotors according to the foregoing configuration. As an example, it has been found that such rotors can be quite accurately manufactured in quantity lots from sintered metal powders in accurately constructed dies. In the construction of the die the outline of the rotor curve is developed in plywood at about times actual size by means of a jig borer which operates accurately through a coordinate arrangement to both plot the points of the curve outline and to drill the holes. The plywood model is smoothed out and then reduced through one or more stages by means of a pantograph to make a very accurate template to be used by the die maker.

The best mode known to me to carry out this invention has been described above in terms .sufliciently full, clear, concise, and exact as to enable any person skilled in the art to make and use the same. It is to be understood, however, that it is contemplated that other modes of practicing the invention can be made by a skilled artisan without departing from the scope of the invention which is defined only by the appended claims.

I claim:

1. In fluid compressor apparatus comprising, in combination: wall means defining a compressor chamber having an inlet for fluid to be compressed and an outlet for compressed fluid; a pair of rotatable lobed rotors disposed within the chamber on spaced axes; and means for rotating the rotors in unison in opposite directions;

and characterized in that each rotor comprises a plurality of lobes of substantially epicycloidal configuration and an equal number of recesses of substantially hypocycloidal configuration alternated between successive lobes, wherein each epicycloidal lobe is generated by a point on the circumference of a rolling circle of a diameter not greater than A rolling on a portion of the exterior of a base circle of a diameter B and wherein each hypocycloidal recess is generated by a rolling circle of a diameter not less than A rolling on an inside adjacent portion of the same base circle, in which A is determined by the formula A=B/2N where N is equal to the number of lobes; and further characterized in that the spacing between rotor axes is equal to B. I

2. Apparatus according to claim 1 wherein the wall means defining the compressor chamber comprises a wall circumscribing the rotors characterized in that the inner surface of the wall generally follows the outline of interthe formula D=B+B/N, and in that the intersecting circles are generated about centers at the axes of the rotors.

3. Apparatus according to claim 1 wherein each epicycloidal lobe is generated by a rolling circle of a diameter AC having its dimension decreased by the value of the clearance factor C and each hypocycloidal recess is generated by a rolling circle of a diameter A-l-C having its dimension increased by the value of the clearance factor C, where C is not materially in excess of 0.001 B.

4. Apparatus according to claim 3 wherein the wall means defining the compressor chamber comprises a wall circumscribing the rotors characterized in that the inner surface of the wall generally follows the outline of intersecting circles of a diameter D which is determined by the formular D=B+B/N, and in that the intersecting circles are generated about centers at the axes of the rotors.

5. In fluid compressor apparatus comprising, in combination: wall means defining a compressor chamber having an inlet for fluid to be compressed and an outlet for compressed fluid; a pair of rotatable lobed rotors disposed within the chamber on spaced axes; and means for rotating the rotors in unison in opposite directions; and characterized in that each rotor comprises a pair of lobes of substantially epicycloidal configuration and a pair of recesses of substantially hypocycloidal configuration alternated between successive lobes, wherein each epicycloidal lobe is generated by a point on the circumference of a rolling circle of a diameter not greater than A rolling on a portion of the exterior of a base circle of a diameter B and wherein each hypocycloidal recess is generated by a rolling circle of a diameter not less than A rolling on an inside adjacent portion of the same base circle, in which A is determined by the formula A=B/2N where N is equal to the number of lobes; and further characterized in that the spacing between rotor axes is equal to B.

6. Apparatus according to claim 5 wherein the wall means defining the compressor chamber comprises a wall circumscribing the rotors characterized in that the inner surface of the wall generally follows the outline of intersecting circles of a diameter D which is determined by the formula D=1.5B, and in that the intersecting circles are generated about centers at the axes of the rotors.

7. Apparatus according to claim 6 wherein each epicycloidal lobe is generated by a rolling circle of a diameter A-C having its dimension increased by the value of the clearance factor C and each hypocycloidal recess is generated by a rolling circle of a diameter A+C having its dimension increased by the value of the clearance factor C, where C is not materially in excess of 0.001 B.

8. Apparatus according to claim 7 wherein the wall means defining the compressor chamber comprises a wall circumscribing the rotors characterized in that the inner surface of the wall generally follows the outline of intersecting circles of a diameter D which is determined by the formula D=1.5B, and in that the intersecting circles are generated about centers at the axes of the rotors.

References Cited by the Examiner UNITED STATES PATENTS 166,295 8/1875 Palmer et al. 230-141 2,547,392 3/1951 Hill et al. 103-126 2,666,336 1/1954 Hill et al. 103-126 2,965,039 12/1960 Morita 103-126 2,988,065 6/1961 Wankel et al. 103-126 2,994,277 8/1961 Merritt 103-126 3,089,638 5/1963 Rose 230-141 3,105,634 10/1963 Hubrich 230-141 3,106,166 10/1963 Tomasko et al 103-126 MARK NEWMAN, Primary Examiner.

WILBUR I. GOODLIN, Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION September 27, 1966 Patent N00 3,275,225

Forrest O. E. Schultz It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 10, for "internall" read internal line 40, for "where" read there column 3, line 12, for "clearance" read clearances column 6, line 10, for "increased" read decreased --o Signed and sealed this 22nd day of August 19670 (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents

Claims

1. IN FLUID COMPRESSOR APPARATUS COMPRISING, IN COMBINATION: WALL MEANS DEFINING A COMPRESSOR CHAMBER HAVING AN INLET FOR FLUID TO BE COMPRESSED AND AN OUTLET FOR COMPRESSED FLUID; A PAIR OF ROTATABLE LOAD ROTORS DISPOSED WITHIN THE CHAMBER ON SPACED AXES, AND MEANS FOR ROTATING THE ROTORS IN UNISON IN OPPOSITE DIRECTIONS; AND CHARACTERIZED IN THAT EACH ROTOR COMPRISES A PLURALITY OF LOBES OF SUBSTANTIALLY EPICYCLOIDAL CONFIGURATION AND AN EQUAL NUMBER OF RECESSES OF SUBSTANTIALLY HYPOCYCLOIDAL CONFIGURATION ALTERNATED BETWEEN SUCCESSIVE LOBES, WHEREIN EACH EPICYCLOIDAL LOBE IS GENERATED BY A POINT ON THE CIRCUMFERENCE OF A ROLLING CIRCLE OF A DIAMETER NOT GREATER THAN A ROLLING ON A PORTION OF THE EXTERIOR OF A BASE CIRCLE OF A DIAMETER B AND WHEREIN EACH HYPOCYCLOIDAL RECESS IS GENERATED BY A ROLLING CIRCLE OF A DIAMETER NOT LESS THAN A ROLLINGGON AN INSIDE ADJACENT PORTION OF THE SAME BASE CIRCLE, IN WHICH A IS DETERMINED BY THE FORMULA A=B/2N WHERE N IS EQUAL TO THE NUMBER OF LOBES; AND FURTHER CHARACTERIZED IN THAT THE SPACING BETWEEN ROTOR AXES IS EQUAL TO B.