IL44462A - Rotor and gear assembly for rotary mechanisms - Google Patents

Abstract

An improved rotor and gear assembly for rotary mechanisms of the trochoidal type, in which a rotor having a central bore is mounted for rotation on a shaft, with a bearing between the rotor bore and the journal portion of the shaft. An internally toothed ring gear is secured to a side face of the rotor for engagement with a stationary spur gear to maintain phasing between the rotor and its trochoidal housing during the planetary and rotary motion of the rotor within the housing. The ring gear is mounted on the rotor in such a manner as to maintain concentricity therewith while permitting differences in thermal expansion between the materials of the rotor and the gear, and without imposing stress on the mounting means or the bearing without causing distortion in the gear or the rotor.

Description

nay rmonm ιιβή nan o Eotor and gear aesembly for rotary mechanisms OUTBOARD MARINE CORPORATION/.

C. 42638 ROTOR AND CHAR ASSEMBLY TOR ROTARY MECHANISMS Abstract : An improved rotor and gear assembly for rotary mechanisms of , ; the trochoidal type, in which a rotor having a central bore is :: mounted for rotation on a shaft, with a bearing between the rotor bore and the journal portion of the shaft. An internally toothed ring gear is secured to a side face of the rotor for engagement .with a stationary spur gear to maiirtain phasing between the rotor and its trochoidal housing during the planetary and rotary motion of the rotor within the housing, 'flic ring gear is mounted on the ■rotor in such a manner as to maintain concentricity therewith while permitting differences in thermal expansion between the materials of the rotor and the gear, and without imposing stress on the mount ;ing means or the bearing and without causing distortion in the gear or the rotor. !j ' Background This invention relates to rotary mechanisms of the trochoidal ': type for pumps, compressors, internal combustion engines, and fluid motors, and more particularly to a rotor and gear assembly for such :; mechanisms .

In such mechanisms of the prior art the bearing on the- shaft journal has sometimes been a barrel extension of the ring gear, as in U. S. Patent No. 3,111,261. In that patent- the ring gear was ■ -. 'i ■] radially splined to the rotor to prevent relative rotation between i| the two parts and still allow differences in thermal growth. The : gear was retained axially by a ringnut at the opposite end of the earing sleeve. Since thermal growth of the rotor would free the bearing .sleeve from the rotor bore with possible excess clearance therebetween, the sleeve was surrounded by a second bearing sleeve with a severe shrink fit in the. rotor, so that clearances developing would be divided between the shaft journal and the adjacent inner bearing, and between the inner bearing and the outer bearing. Such an arrangement requires a good deal o A generally similar arrangement is disclosed in Patent NO. 3,230,789 wherein a single bearing is used, having splines extending radially tlicrcfrom with the rotor cast onto the outer circumference of the bearing sleeve and engaging the splines. The ring gear is bolted to the splines of the bearing. Although this construction may be somewhat cheaper than the previous one, it is nevertheless an expensive item, requiring that the radially extending splines be highly finished before casting the rotor metal on them, since slippage arising from differential expansion must be along tli c spline surfaces. Further, the attachment of the gear by firm bolting to the splines of the bearing restricts thermal growth of the bearing.

No. 3,383,936 is a further example of expensive splining between the rotor and the gear to prevent rotation of the gear in respect jto the rotor, while allowing radial differential expansion. device shown therein also contains firm axial attachments been the gear and rotor so that axial expansion imposes a strain the parts. ' ί In Patent No. 3,400,604 the gear is restrained from rotation relative to the roto by dowel pins having a tight fi in both parts, and It is stated that, radial growth of the ~ rotor will be transferred to the gear by the equally spaced dowels and thus maintain concentricity. This assumptio has been found to be incorrect, however, since the gear, being of more rigid material than th rotor and having a lower coefficient of thermal expansion, restricts rotor growth,and causes distortions therei and strain on the dowel pins. i; . The present- Invention provides a rptery mechanism, a rotor and gear assembly comprising in combination a rotor having a rotational axis and parallel sides transverse to the axis and having a bore therethrough coaxial therewith, a ring gear born at one side of the rotor coaxial with the. bore, at least three means at selected radial locations for securing the gear against rotation relative to the rotor, each of the securing means Including an aperture and associated means extending therein permitting differential movement between the rotor and gear along a radius passing through its own location but preventing differential movement in the circumferential direction and thus maintaining concentricity of the rotor and gear.

It is therefore an object of the invention to provide a rotor and ring gear assembly for trochoidal rotary mechanisms allowing differential thermal growth of the parts without strain or distortion.

It is another object to provide such an assembly wherein the gear maintains concentricity with the rotor.

A further object is to provide such a rotor and gear assembl I having a bearing for the shaft journal, wherein the bearing is not •'subject to constriction in the radial or axial directions by ■reason of the gear mounting. i- f. Still another object is to provide such an assembly wherein I the material of the rotor body and the material of the ring gear have different coefficients of. thermal expansion. ij It is a further object to provide a rotor and ring gear ii ; assembly wherein the rotor body is formed of a relatively lighter weight metal . Γ Other objects and advantages will become apparent on reading lithe following specification in connection with the accompanying drawings . ϋ i!thercfore also with the axis of the shaft eccentric portion 26. ! :|As shown, gear 28 is recessed wholly within the hollow interior of !jthc rotor, but may in some cases be positioned within aperture 21 jjwith its axially outer face flush with the outer face of side wall " 14 , or the gear may even have some portion projecting slightly beyond the rotor side wall to run against the end wall of the .housing.

! In operation of the rotary mechanism the rotor ma become ; considerably heated. This is particularly true when the mechanism : is an internal combustion engine, but also occurs with pumps used I; f or pumping hot fluids, with compressors when the gas is heated by lithe effect of compression, and with fluid motors which are driven ;by hot fluids. The material of the rotor is therefore subject to thermal expansion during operation, followed by contraction on ; subsequent cooling. Such rotors arc frequently formed of aluminum lor one of its alloys in order to save weight and in order that the ;; weight of the rotor shall exert less bearing friction and so con-. suinc less power, whether the power is being generated in an engine |;0 applied to a pump or other mechanism. The gear, although it i-docs not transmit toi-quc, is nevertheless subject to ordinary !j frictional wear, and to intermittent cyclical loading as the rotor ;' ; moves transversely across bearing clearances owing to the sinusoidal ;| loading of the rotary mechanism. The gear is therefore formed of i; o suitable gear steel. p This diversity of materials results in the gear and the rotor jjhavin different coefficients of thermal expansion, especially in tithe case of a light weight rotor, since in a general way aluminum |i i! and its alloys have about double the thermal expansion of steel, ii 'Rotors arc sometimes formed of nodular cast iron, and though this and gear should be made of materials having identical t ermal response, the problem of differential expansion would still exist, since the rotor metal is directly exposed to the source of heat, and the interface between the two parts acts as a substantial impediment to heat transfcv. < It is important for efficient operation of the rotary mechanism that the rotor and its attached pear should maintain their concentricity, during the initial period of warm- up, during steady operation, and during- cooling after shutdown. It has been assumed in the prior art that, where the gear was mounted by firm bolting or located by tightly fitting dowels in both parts, or otherwise firmly piloted, the expansion of the rotor hub would be transmitted •by the mounting means and compel the gear to expand an equal amount This has been found not to be the case. Tight dowels have resulted in constraint of the hub on the gear side so that it could not expand so much as the free side, with the result that the bore became tapered and the bearing likewise,, with consequent bearing failures. The same defect occurred when the rotor had a flange against which the inner diameter of the gear t ng seated. hcn firm bolting was used, if the bolts were torqucd tightly enough to preclude relative transverse movement between the gear and the rotor, the same problem could occur again, and there was no provision for differential axial expansion, again with resultant deformation. ' : The present invention overcomes these limitations by providing means for attaching the gear to the rotor in such a manner that both the gear and the rotor nrc frco to expand radially and axially s and at shutdown. These conditions will be maintained whether the gear and the rotor have identical coefficients of thermal expansion ;or whether they are different, without regard to whichever part lias the greater thermal response. ! I The plane face 29 of the rotor hub 17 has extending axially therefrom a plurality of cylindrical dowels or pins 31 projecting from the hub face no more than the 'thickness of the gear 28. The pins may be equiangularly spaced as shown, or may have some other orientation. There must be at least three such pins 31 and ordinarily that is the preferred number, although in some instances thcro may be more. Pins 31 have a tight fit in the rotor hub, such that they will not become loose when the parts arc subjected to the greatest degree of thermal expansion anticipated. Λ convenient way of securing firm seating of the pins is by an interference fit j! In radial directions, however, apertures 32 are elongated ; sufficiently to allow relative radial movement between the pins !and the slots, which permits thermal expansion and contraction without change in the concentricity of the parts. The amount of ^elongation of apertures 32 is much exaggerated in the drawings for i clarity of illustration, but in practice it need not be great. The actual amount of elongation of slots 32 will be chosen in accordance with a given design, with reference to the coefficients of thermal expansion of the rotor metal and the gear metal, the maximum temperature which may be reached at the surface of the rotor, ! the thermal gradient between the surface and the position of the ,pins, end the diameter of the circle on which the pins arc located. I; In engines of moderate size, such as about sixty cubic inches per :[ rotor, the relative movement of the pins within their slots will ; bo only a few thousandths of an inch. j The gear is retained axially (best shown in Fig. 4) by axial .detent means comprising a plurality of equiangularly spaced bolts 33 extending through bores in t!ie gear annulus. The bolts 33 each i ave a smooth cylindrical shank portion 34 with a flat shouldered inner end 36 seated against the flat bottom of a bore 37 in the !rotor hub 17, bore 37 having a slightly larger diameter than the i: ;bolt shank so that there is no circumferential contact therewith. i'Coaxial with shank 34 and extending inwardly therefrom the bolt |;hns a threaded continuation 38 of smaller diameter, engaged with la tapped hole 39 in hub 17. The threads of bolt portion 38 and ijholc.39 are in interference engagement, so that when the bolt is !j torqucd down tightly to its shoulder 36 it will not bo loosened by i| thermal expansion. ii The axially outer ends of bolt shanks 34 are positioned co- axially in bores 41 through the gear annulus, which bores are also "slightly larger than the bolt shanks so that there is no contact. Bores 41 have flat-bottomed coaxial countcrbores 42 in the outer gear face, approximately halfway through the thickness of gear 28. The bolts have flat-bottomed heads of smallpr diameter than the jcounterbores and positioned therein, but the length of shanks 34 and the depth of their seating bores 37 arc so proportioned that ,'thc bolthcads do not bear upon the bottoms of countcrbores 42, but jleave a gap 43 of a few thousandths^ of an inch. The dimension of gap 43 is proportioned according to the size of the rotary mechanism, the materials of the rotor and gear, and the" expected maximum temperature, so that with the maximum thermal expansion anticipated the boltheads will not impose any strain on the gear. ' ij It will therefore be seen that gear 28 is axially linked to the rotor hub so that it cannot be parted therefrom. Although the gear appears to be slightly loose o its axial mounting in the cold state, this. is of no . importance , since the amount of clearance under ithc bolthcads is minimal. It has been found that in operation the gear will run cither against the bolthcads or against the rotor hub without play until the temperature reaches a value at which gap 43 >has substantially closed. jj It will also be apparent that the gear can have no circumferential movement relative to the rotor, owing to the bearing of pins 31 against the sides of slots 32. Likewise, there can be no relative movement of the gear transverse to the axis, since such ^transverse movement will always be opposed by at least two of the ipins against the sides of their slots, or by a larger number of ; jpins if the total used is more than three. Differential thermal n any direction is readily possible, but cannot impose any strains or distortions on the gear, the rotor, the mountings, or the bearing, and concentricity cannot be disturbed. I Pigs. S--8 show another embodiment of the same inventive con- ccpt having the same advantages. The rotor here shown is of modified form in order to exemplify the generality of the gear mounting means of the invention and its applicability to the rotors of various rotary mechanisms. Details not necessary to an understanding of the invention have been omitted from the showing. j ;j Uotor 11a is of generally triangular profile with convexly arcuate working faces 12 each having therein a recess 19 as in the previously described embodiment. The main body of the rotor is hollow and comprises a peripheral wall portion 13, parallel side faces 14a and 16a, and a hub portion 17a which is joined to the outer portion 13 by appropriate ribs or webs 18. Hub 17a has a bore 23 therethrough on the rotational axis, with a bearing 24 installed therein. In the assembled rotary mechanism the eccentric portion 26 of a rotatablc shaft 27 will be journalled therein. Λ ring gear 28a is seated against the flat end face of the i; 'rotor hub, coaxial with the rotor body, the bearing, and the eccentric portion 26 of the shaft. The axial ly inner side of gear ;28a is provided with a shouldered extension 46, the outer diameter 'of which is a close fit to tho bore 23 in the hub. The extension 46 i*i positioned within the bore at the installation of the gear, , hich insures coaxiality, and once the gear is mounted the relationship cannot change. If differential thermal expansion occurs,, !!it will always be greater in tho rotor hub than in the gear, so "that the hub will only expand radially away from the gear shoulder without imposing any strain on either part. j split tube can be compressed at installation and / its natural resilience will remain firmly fixed even when the hub undergoes thermal expansion. However, it is to be understood that cither tubular or solid dowels as previously shown may be used in cither embodiment. Although Fig. 5 shows the dowels disposed in three pairs, the invention is not limited to any specific number except that there must be at least three. Further, they need not be cqui angularly spaced in either embodiment, since if it should be convenient to position them otherwise the rotor may be appropriately balanced by other means.

The gear 28a is provided with apertures 32, slotted in Rdi.nl directions and the same in number and spacing as the dowels. The circumferential width of the slots is such as to provide a tight friction fit with the dowel diameter, thus preventing transverse ; and circumferential movement, while allowing sufficient play in radial directions for the anticipated radial thermal movements.

The detent means for axial retention of the gear comprises a ^plurality of lugs 47 extending radially outwardly from the circum- forenco of the gear; the lugs 47 may be ccplanar with the exposed jfacc of the gear as shown, but arc not necessarily so. Λ like ^plurality of lugs 48 extend radially inwardly from the peripheral ;wall 13 of the rotor body. The axially inward faces of rotor lugs ,48 and the axially outward faces of gear lugs 47 are so positioned that lugs 48 overlap lugs 47 with just sufficient axial clearance j to allow for any anticipated axial expansion, an amount comparable to that allowed in the previously described embodiment. The axial detent means in cither embodiment need not be more than two in ■number if spaced diametrically opposite, but may be any larger number desired. It is usually convenient to have the same number :of axial detents as dowels, spaced intermittently therewith. .i -! Further, although the rotor lugs 48 of this embodiment are shown !as integral parts of the rotor, they may be separate parts bolted :to the rotor or otherwise attached.

' The manner of registering the axial detent means when lugs 48 arc integral with the rotor is shown' in Fig. 8. At assembly of the 'gear and rotor, the gear is set upon the face of the rotor hub with pits barrel extension 40 engaged within the hub bore 23 and lugs 47 'and 48 circumfcrentially out of register by an amount sufficient : to allow axial seating of the gear. The gear is then rotated on the hub to bring gear lugs 47 under rotor lugs 48 in proper cir- cunifcrcntial register. The gear will already have its slotted apertures 32, and if the mating dowel bores in the rotor hub have : already been provided the dowels are then installed. If the hub has not yet been bored for the dowels the operation may be performed through the slotted apertures 32, which provides a conven- • lent method of locating the mating holes in the rotor hub. The ■bearing 24 may bo positioned within rotor bore 23 cither before or ■j after installing the gear, as may be convenient. !j In some cases it may be desirable to have the dowels already seated in the rotor hub before assembling the gear to it. In such ]! a case separable rotor lugs 48 may be used, the gear being axially !jseated with its slotted apertures 32 in engagement with the pro-jj.truding dowels, and tho lugs 48 then attached to the rotor over j; the gear lugs 4 .

■ What is claimed is: 44462/2

Claims (8)

1. In a rotary mechanism, a rotor and gear assembly ^ comprising in combination a rotor having a rotational axis and parallel sides transverse to the axis and having a bore therethrough coaxial therewith, a ring gear borne at one side of the rotor coaxial with the bore, at least three means at selected radial locations for securing the gear against rotation relative to the rotor, each of the securing means including an aperture and associated means extending therein permitting differential movement between the rotor and gear along a radius passing through its own location but preventing differential movement in the circumferential direction and thus maintaining concentricity of the rotor and gear.

2. Th combination recited i Claim 1, wherein each of the securing means comprises a pin projecting in the axial direction from the gear side of the rotor and tightly seated therein, and the gear has an aperture into which the pin extends, the aperture having a lengt in the radial direction greater than the diameter of the pin and having a width providing a close fit with the pin in the circumferential direction.

3. The combination recited in Claim 2, wherein the plurality of securing pins are clrcum erentially spaced around th rotor bore and,radially outside thereof, the gear has an equal number of apertures spaced congruently therewith, and the pins and slots cooperate to prevent relative rotation and to prevent relative movement in directions transverse to the axis and thus maintain concentricity of the rotor and gear. (

4. The combination recited in Claim 3, wherein there are at least three such securing means, and at least two of such securing means cooperate to prevent relative movement between the gear and the rotor in any direction transverse to the axis. I ' ■ ' J ,

5. S. The combination recited in Claim 4, wherein. he rotor bore has a bearing positioned therein coaxial with the gear, and the plurality of gear securing means cooperate to allow differential thermal expansion between the rotor and gear without altering concentricity of the gear and bearing and without imposing strain j !on the parts of the assembly and without restricting thermal growth of the bearing.

6. The combination recited in Claim 5, wherein the gear has a barrel extension positioned within one end of the bearing bore in close fitting relationship therewith to establish concentricity of the gear therewith. j

7. The combination recited in Claim 4, wherein the assembly ■ has axial detent means between the gear and the rotor, the detent ; means being in firm engagement with the rotor and restricting gear movement only in the axial direction without abutment in the transferee ond circumferential directions. |j

8. The combination recited in Claim 7, wherein the gear has • on aperture therethrough for each detent means, and each detent < {■means comprises a bolt member seated in the rotor and havin a i; shank portion extending through the gear aperture without contact i!with the wall thereof, tho shank portion having an enlarged head restricting the gear in the axial direction, there being an axial j: clearance space between, the gear and the bolthcad when the assembly il ls in the cold state allowing thermal expansion in the axial dircc-!: tion without imposing strain o the parts of the assembly. :