US2733854A - chang - Google Patents

Description

Feb. 7, 1956 s, s, CHANG 2,733,854

CONE TYPE COMPRESSOR Filed March 22, 1952 2 Sheets-Sheet l IN V TOR.

SHELaaN-S L. 4N6,

Feb. 7, 1956 s. s. CHANG CONE TYPE COMPRESSOR 2 Sheets-Sheet 2 Filed March 22, 1952 United States Patent CONE TYPE COMPRESSOR Sheldon S. L. Chang, Springfield, Ohio, assignor to Robbins & Myers, Inc., Springfield, Ohio, a corporation of Ohio Application March 22', 1952, Serial No. 278,029

4 Claims. (Cl.'230--148) This invention relates to. cone-type pumps. In the copending applicationof Byram and Chang, Serial No; 159,078, filediApril'29,= 1950, now Patent'No. 2,590,751, dated-March 25, 1952, thereis. a generaLdisclosure of pumps having relatively flat disc-like pumping elements wherein the pumping elements are provided with spiral threads, and wherein one of 'the elements has one thread more than the other element.

In my copending application,.Serial No. 159,077, also filed April 29, 1950, now PatentNo, 2,590,435, dated March 25, 1952, there is a more detailed disclosure offlat rotary pumps. In the last. mentioned application there were disclosed pumps other. than fiat types having: cone shaped or bowl. shaped or flare: shaped .purnpingelements.

The principal. object of thepresent invention is to provide a compressor of the cone type as referred to in said copending application by aparticular arrangement-ofthe pumping surfaces so that the pumpingupocket becomes progressively smaller in size to produce a compressing action.

A lathe having a complex tool movement for producing the elements of the compressor hereindisclosedis disclosed and claimed in my copending application, Serial No. 278,030, filed March 22,1952.

It is another object of the invention to provide an efficient and. economical compressor for mechanical refrigeration installations and the like.

In studying up the background. for. an understanding of the present invention reference is madeto the Moineau Reissue Patent No. 21,374, original No. 2,085,115. The idea of a conical compressor wassuggested in that patent but no disclosure was made as to the requirement ofthe particular surfaces involved, or how those requirements might be met.

It is another object of the present'invention to provide for a compressor. having'conical pumpingelements which may be made on a mass production basis; It is still another object of the invention to provide such elements whichwould not have tobe'selectively fitted since variations in shrinkage in casting may be automatically compensated.

These and other objectsof the invention which will be pointed out in greater detail hereinafter, or which will be apparent to one skilled in the art upon reading these. specifications, I accomplish by that certain construction andiarrang'e'ment of parts of which I shall now disclose certain'exemplary embodiments.

Reference is made to the drawings forming a part hereof in which:

Figures laand 1b are diagrams useful in understanding the principlesof" the present invention; and

Figures 2, 3, 4 and 5am longitudinal cross sectional views of a number of' modifications of compressors according to the present invention.

A pump according to the Moineau patent above mentioned has pumping pockets which have a constant volume throughout their travel: In-order to operate as= a 2,733,854 Patented Feb. 7, 1956 pockets must shrink in size as they pass through the device in' order to compress the fluid trapped therein as they carry it from the low pressure end to the high pressure endL Furthermore, thesepockets mustremain totally sealed atall timesexcept at the inlet and at the outlet.

The proper or desirable-ratio of compression depends upon the physical properties-of the refrigerant, as well as on the requirementsof the particular application. For example, for a compressor used in a room cooler unit with Freon 12 as a refrigerant, the ratio-ofcompression should be in the neighborhood of 3.

Because all refrigerants at the compressor stage are in a gaseous state they are much more likely to leak than liquids, such as water and oil. In order to prevent excessive leakage at working pressures very close-tolerants on the stator and rotor dimensions must be maintained. It is axiomatic that precision work and low cost are generally not compatible.

The present compressor provides a solution to the two I main difiiculties as stated above.

compressor efiiciently and quietly these progressing 1 In the terminology used in connection with pumps accordingto the various Moineau patents, the pitch, eccentricity and rotor diameter of the compressor according to the present invention-decrease continuously from the inlet to the outlet so asto decrease the volume of the pumping pockets. How the pockets are caused to remain sealed while they are continuously decreased in size will appear as this description proceeds.

Generally speaking, precision work pieces cannot be madeby mass production methods, such as molding and casting; The reason for this is that the work piece shrinks while it coolsand solidifies. The percent of shrinkage depends upon the material and on the'operating temperature and is difficult to control.

If the operating temperature is uniform on all parts of the work piece however, audit the work piece is allowed to cool off uniformly and slowly it would shrink uniformly in all dimensions accordingto physical laws. Of course for difierent operating temperatures and materials the amount of shrinkage would be different, but it would alwaysbe uniform in all dimensions percentagewise for: any given work piece.- Thus, for example, a true sphere would always remain spherical, a'true' cylinder would always remaincylindrical, and a true cone would always remain a. true cone.

If a cylinder is to be fitted. into a cylindrical shell within afraction of a thousandth. of an inch, and both members are to be produced by moldingand' casting, avery difiicult' production problem would be faced- The. diameters of the cylinder and shell would botlrvary over a range of a few thousandths of an inch. Either of the tolerants must be relaxed or the costs of selective fitting and rejectilon wouldbe prohibitive. The situation isentirely different in fitting a cone to a cone-type shell. The apex angle of the cone is not. changed fora three dimensional shrinkage. The' differencein the amount of shrinkage between the two members can be compensated for by a displacement in an axial direction.

Of course, the cone type compressor is more complicated than a simple cone-because of the threads and the stator and rotor surfaces. However, if the variations. in eccentricity, pitch and rotor diameter follow agiven set of rules, the difference in the amount of shrinkage between the two members can be perfectly compensated for by an axial displacement and anangular displacement. This is possible only for a compressor. It cannot be done'for a pump according to'myaforesaid co pending applications; This point will be proven hereinafter mathematically.

The ability to compensate for shrinkage makes it possible to make a compressoraccording to the present invention on' a mass production basis. Careful machinery work would be done in connection with precision dies and molds, and the stators and rotors both may be produced by casting and molding; No selective fitting is required since variations in shrinkage can be automatically compensated as above pointed out.

Returning for a moment to the pump according to the Moineau patent mentioned above, or according to any of the pumps according to the various Moineau patents, when the rotor of such a pump rotates its axis is forced to revolve about the stator axis in the opposite sense at the same speed. Similarly when the rotor of a compressor according to the present invention rotates, its axis is forced to nutate about the stator axis in the opposite sense at the same speed. The rotor axis and the stator axis meet at a fixed point. The mechanical construction of the pump should be such that no restraint is placed on the relative motion between the rotor and stator. Just as the pump according to the Moineau patent has a connecting rod, so either a connecting rod or universal joint is needed. for a compressor according to the present invention. If a universal joint is used it must be at the fixed point where the two axes meet.

Referring now more particularly to Figures la and 1b, if we take a cross section of the rotor surface at a given distance from the fixed point, we would find that the cross sectionis represented by a circle with its center displaced at a fixed angle 6 from the axis of the rotor. When the rotor rotates three motions occur simultaneously.

1. There is a rotation of the circle about its own center.

2. A rotation of the center of the circle about the rotor axis in the same sense as the direction of rotation of the rotor.

3. There is rotation of the rotor axis about the stator axis in the opposite sense to the rotor rotation resulting from the forcednutational movement.

The first motion mentioned above is immaterial insofar as the action of the compressor is concerned. The rotation of the circle about its center does not change the position of the circle since its position is completely determined by the position of its center. The second type of motion mentioned above results in a movement of the center of the circle and the position of the center of the circle relative to the axis of the. rotor may be expressed as:

In Equation 1, l is the distance from the fixed point to the circle, w is the angular velocity of the rotor. A is an angle representing an increment in which the circle is displaced. Since these generating circles of the rotor are displaced in continuously varying directions to form a thread, the angle A is a function of w. Its expression as a function of w determines the natures of the machine as to whether it is a pump or a compressor.

Equation 1 is in complex vector notation. 6] represents the magnitude of the displacement of the center of the circle, and wt-l-A represents its angle.

Similarly the third motion mentioned above introduces a displacement of the rotor axis about the stator axis. At a distance l,.it may be expressed as:

r2=e e (2) Hence the relative motionof the center of the circle with respect to the center of the stator may be expressed as:

Equation 3 shows that the combined motion of the two circular motions of Equations 1 and 2 is a linear simple harmonic oscillation along the direction Since the distance I was chosen arbitrarily, this derivation will hold true for all cross sections of the rotor. Thus, with the combined motion of a forward rotation of the rotor, and a backward nutation of the rotor axis, all the circular cross sections of the rotor oscillate back and forth along various linear paths. As the angle appears both as a space angle and a time phase angle, and as A is a function of l and consequently varies with l, the path of oscillation is along a continuously varying direction, and the oscillation has a continuously varying phase angle as the distance 1 changes from one end to the other.

correspondingly, the cross section of the stator at a distance I from the fixed point consists of two semicircles of the same diameter as the rotor diameter D, and a connecting cylindrical portion with an arc length 4d. D is a function of l. The longitudinal direction of the cross section is in the same direction as. the rotor oscillation,

wt+ g-=2tt7r and on the other side Each compressor or pump stage corresponds to one stator pitch (AA=21|-) or two rotor pitches (AA=41r). As wt increases with time the boundaries of the pumping pockets move in the direction of decreasing A.

The foregoing description will fit either a pump or a compressor. It demonstrates how a pumping pocket, varying in size, can be kept sealed at all times by the lines generated by the points a and b of Figure lb, and the sections for which wt+A=2mr or (2nl l )1r. For the cone type compressor of the present invention two additional requirements are that the rotor diameter D should be proportional to the distance I, and that the angle A should be proportional to the logarithm of I. In other words:

D=k1l (4) A=k2 loge l (5) When these equations are satisfied it can be shown that a three dimensional uniform shrinkage can be compensated perfectly and does'not introduce error. For a three dimensional shrinkage all the linear dimensions are multiplied by a constant C, where C 1. The angles are in no way changed.

Let A, e, l and D represent the angles and dimensions after the rotor has shrunk uniformly. We have:

From Equation 4, 9 can be written as:

greases f -5 FiomEquation 8; 6 can-be written as:

%=-k,io 1'40, log.

It will; be clear that the constant angular dilference ka loge C' can be compensatedifor' by a" rotation. of: the rotor "in that amount. Equation 11 thenb'ecomes:

Comparing Equations wand 12 withEquations- 4 and 5,. Wev may see thatv the rotor surface remains exactly thesame after shrinkage asbefore. The uniform shrinkage of: the stator canxbe considered asa uniform expansion: of the. rotor in. the same ratio. The same deductions'above: prove that the surfaces remain matched. In. this case, however, C -1.

Equations4 and automatically specify the elements fora compressor. The threads are closer together at smaller values. of l. The rotor diameter D and the eccentricity'el are also smaller for smaller values of l. For'aconstant'volume pumpthe threads should be farther apart at smaller valuesof' 1. Consequently Equation 5 cannot besatisfiedfor a pump. After shrinkage a similar equation to can be derivedfor a cone. type pump, but the difference in angle due to thedifference between I. and-l would not be .constant asset forth in Equation 11. Though the general shape remains unaltered the threads would no. longer match after shrinkage. Thus, it can beseen thatthe advantage of? the-cone. type compressor pointed out above is not shared by the; cone type pump. The theoretical volume and compression ratio of the pump may be calculated as, follows:

From Figure 1b itis readily verified that the area of the section 1 between the stator and rotor is:

where 0'=toi+% The volume of the pocket from 0:0 to 0 =21r is:

where l2 and l; are valuesoflfor 6 equal to 0 and21r respectively. From Equation 5 it is readily shown that Equations 18 and 19" giverthevolumeofla single pumpingpocket. As the pocket travels. from the suction end to the pressure end, the volume decreases at the rate of 11 Let lsand, lplfiPfCSGllt thevalue of cat the suc- In each revolution two pockets of fluid are carried into the compressor at the suction end. Hence the theoretical displacement per minute is:

renew RPM' "3' k, 36) 6 231 In this equation. 6 is in radians, ls is ininches, and M is in. gallons per minute.

From. the standpoint of building an. actual compressor there are many ways" in which the members may be assembled, but for eachassembly two essential conditions must be observed. These are:

1. That the assembly must permitv free nutation of the rotor. axis, and

2. That the pressure. force must be. in. a direction to press the rotor. and stator together instead of pushing them apart. The second condition is necessary for good pressure volume characteristics and for easy starting.

Figures 2, 3 and 4 show three alternative ways of constructing a compressor. In the embodiment of Fig. 2 nutation of the rotor is made possible by means of the universal joint 20 disposed at a position corresponding to the point. 0 of Figure 1a. Inthis figure the rotor is indicated at 21, and a drive shaft at 22. The stator is indicated at 23, and is preferably made of rubber-like material. As illustrated in-Figure 2 the pump casing may be bell shaped as at 24 with a head 25 provided with an inlet port 26; an outlet port is provided. at 27 in the casing 24. The portions 24 and 25 are secured together by means of bolts 28, and a flange 29'- on the stator 23 may serve as a gasket, to provide for fluid tightness.

Att30, Lhave. indicated in broken lines a sleeve. over the stator. This would not be necessary for relatively low pressure applications. However, the fluid' pressure outside the stator presses the stator against the rotor, and if the pressures are relatively high, they may cause too much friction between the. rotor and stator elements, and in such case it may be d'esirable to vulcanize the stator 23 to a metal sleeve 30. In this case the pressure does not apply directly against the rotor. It will be noted that the resiliency of the stator materialat the suctionend will provide suflicient' squeeze against the rotor under pressure by a' slight horizontal movement.

The device of Figure 3 is essentially the same as that of- Figure 2 except that instead of the universal joint structure, I have illustrated the use of a connecting rod 31.

This provides for a more compact assembly as will. be clear. I have also illustrated the drive shaft enteringat the opposite end of the machine merely to indicate the versatility of the construction. It will be seen that the connecting rod 31' is pivotally connected at 32 to the rotor, and that a conical space 33 is provided for the rockingmovement of the connectingrod 31. At its other end the connecting rod' 31 is pivoted at 34 to the drive shaft 35. A packing gland or seal is indicated generally at 36. In this instance the casing member 37 is provided with the outlet port 38, and a casing portion 39 is provided with. the inlet. port 40. Again the stator 41 is oflresilien't. or rubber like material and has the flange 42 which may serve. as a gasket between the two casing portions.

In Figure 4, I have shown an embodiment where the rotor is caused to rotate-concentrically, and where the nutational movement is assumed by the stator. Thus, the rotor 50 is secured toa drive shaft 51 which runs in ball bearings 52. The aperture through which the shaft passes is sealed by. the: seal: 53. Thus, the rotor- 50' rotates axially. The stator 54 is similar. except for the configurationlof'the; threads to thatdisclosed in the Byrarnand Zimmer Patent No. 2,612,845, dated October 7, 1952. The stator 54 is provided with a funnel-like skirt portion at 55, which is provided with the flange 56. The flange 56 again acts as a gasket between the casing portions 57 and 58, with the portion 58 having the outlet port 59, and the portion 57 having the inlet port 60. By virtue of the funnel-like skirt member 55 the stator 54 may move in a nutationalpath and permit the rotor 50 to rotate on its true axis.

In Figure 5, I have shown a double ended construction where the compressors at each end at the same time serve as shaft bearings. Since the compressors are oppositely disposed the thrust is balanced and no thrust bearing is required. The flanges on the two stators serve as gaskets for hermetically sealing the entire motor compressor assembly. The motor armature is indicated at 70 and the seal at 71. The motor and compressor shaft isindicated at 72, and the two'rotors are indicated at 73 and 74. The two stators are shown at 75 and 76 having respectively the flanges 75a and 76a. In this embodiment the casing is a cylindrical element 77 having the heads 73 and 79, each provided respectively with an inlet port at 80 and 81. The outlet ports 83 and 84 are provided in the casing portion 77.

It should be noted that because of the angular movement of the compressors the motor does not run true.

Let L be the stack length of the motor armature and let the pivot points of the two compressors be at the center of the motor, then the maximum value of the eccentricity of the two ends of the armature is:

From the foregoing it will be observed that this particular construction will be limited to short stack motors with a comparatively large air gap. It will be useful for low cost power applications, such as household refrigerators.

It will be understood that it is possible to make a metal sleeve air gap motor with the double end construction of Figure 5, but it would be desirable to provide a universal coupling at the pivot point so that the motor can run true. It will be understood that while I have described the invention in considerable detail, numerous modifications may be made without departing from the spirit of the invention, and I therefore do not intend to limit myself otherwise as set forth in the claims which follow.

Having now fully described my invention what I claim as new and desire to secure by Letters Patent, is:

1. A pumping member for a rotary compressor comprising a conical member having a spiral thread, the surface of said member being approximately that generated by a circle about an element of a cone in a plane perpendicular to said element, as said element is moved in increments (A1) around the surface of said cone, accompanied by a continuous change in the position of said circle along said element (1) and a continuous change in the diameter of said circle (D) such that D=k1l and A1=k2 loge l, k1 and kz being constants.

2. A pumping member for a rotary compressor comprising a conical member having a double spiral thread, the surface of said member being approximately that generated by a figure comprising: two semi-circles in planes at a fixed angle to each other connected by a rectangular portion of a cylinder tangent to said planes at the diameters of said semi-circle, such that every point on the periphery of said figure is at an equal distance from a fixed point; when said figure is rotated in increments (A2) about an axis passing through said fixed point and the center of said figure, accompanied by a continuous change 8 length of said portion of a cylinder, such that D=k1R and A log, R

k1 and k2 being constants.

3. A compressor comprising a pair of pumping members, one of said members being fixed, a shaft for driving the other of said members, the other of said members being connected to said shaft by 'a. universal joint, each of said members being conical in shape, one of said members having a spiral thread and having a surface approximately that generated by a circle about an element of a cone in a plane perpendicular to said element, as said element is moved in increments (A1) around the surface of said cone, accompanied by a continuous change in the position of said circle along said element (1) and a continuous change in the diameter of said circle (D) such that D=k1l and A1=k2 log; 1, k1 and k2 being constants; the other of said members having a double spiral thread, and having a surface approximately that generated by a figure comprising: two semi-circles in planes at a fixed angle to each other connected by a rectangular portion of a cylinder tangent to said planes at the diameters of said semi-circles, such that every point on the periphery of said figure is at an equal distance from a fixed point; when said figure is rotated in increments (1h) about an axis passing through said fixed point and the center of said figure, accompanied by a continuous change in the radius of said cylinder (R), and a continuous change in'the diameter of said semicircles (D) and the axial length of said portion of a cylinder, such that D=k1R and log, R

and easing means enclosing said members and having intake and exhaust ports and an entry aperture for said shaft.

4. A compressor having one pair, at least, of conical spirally threaded pumping elements, a casing enclosing said elements, the outer of the elements of said pair being fixed against rotation and dividing said casing into a high pressure and low pressure side, means for rotating the inner of said elements, an inlet port in said casing adjacent the larger ends of said elements, an outlet port in said casing adjacent the smaller ends of said elements, one of said elements being mounted for nutational movement with respect to the others, the inner of said elements having a surface which is approximately that generated by a circle about an element of a cone in a plane perpendicular to said element, as said element is moved in increments (A1) around the surfaceof said cone, accompanied by a continuous change in the position of said circle along said element (l) and a continuous change in the diameter of said circle (D) such that D=k1l and A1=kz log 1, k1 and k2 being constants, and said rotating means including a shaft entering said casing, a shaft extension on said inner element, and a universal joint connection between said shaft and shaft extension at the apex of the generating cone of said inner element.

References Cited in the file of this patent UNITED STATES PATENTS Re.2l,374 Moineau Feb. 27, 1940 (Other references on following page) r 9 UNITED STATES PATENTS Moineau Jan. 21, 1936 Aldridge July 14, 1942 Thompson 5. July 11, 1944 Byram Oct. 10, 1950 Byram Oct. 31, 1950 Byram Nov. 28, 1950 Moineau Mar. 20, 1951 Chang Mar. 25, 1952 10 Lloyd July 15, 1952 Byram et a1 Oct. 7, 1952 FOREIGN FATENTS Sweden Nov. 21, 1935 Australia Apr. 28, 1941 Great Britain Oct. 18, 1935 Great Britain Dec. 8,1942 France Feb. 11, 1935

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