US3158039A

US3158039A - Dynamic balancing system for rotating structures

Info

Publication number: US3158039A
Application number: US174160A
Authority: US
Inventors: Favrot Paul
Original assignee: LANDIS GENDRON SA
Current assignee: LANDIS GENDRON SA
Priority date: 1961-02-28
Filing date: 1962-02-19
Publication date: 1964-11-24
Anticipated expiration: 1981-11-24
Also published as: DE1698523B1; GB951704A; CH377554A; FR1290875A; NL275196A

Description

center shifts in United States Patent O pany ,of France lFiled Feb. 19, 1962Ser. No. 174,id Claims priority, application France Feb. 2S, i961 vS Claims. (Cl. i4-575) This invention relates to .systems for dynamically balancing rotating mechanical members, a problem that arises in connection with any type of high-speed rotary machinery. Taking as an .example the case of a highspeed revolving grinding wheel in a grinding or rectifying machine, the center of gravity of the wheel is liable to shift slightly off-center with time because of irregularities in wear coupled with minor non-unformities in the density of vthe wheel material, and/or in the distribution of moisture in the pores of the wheel. At the high `:angular speeds involved, even very small offthe center of gravity can result in the of large centrifugal forces liable to cause development heavy rea breakdown of the grinding wheel or other volving part concerned.

It has already been proposed to provide automatic dynamic rebalancing systems comprising essentially an annular recess filled with oil, for instance having the shape of a tore, formed in a member carried by a shaft and concentric to said shaft, this recess being divided by separation means in a certain number of chambers (usually 3 arcuate chambers extending each along 60, while said separation means extend each along the same arcuate distance). ln each of said chambers a movable mass is located, said mass being free to be displaceable along the wall of the chamber in which it is located, the chambers communicating with each other by passages extending through said separation means. The 3 passages above are connected respectively to 3 ducts provided in the shaft and opening radially in the oil lm of the bearing, each of the pressure receiving openings being at 120 in respect to any one of the other openings. The pressure differentials created in the oil film of the bearing by an unbalance are transmitted to the corresponding chamber, so that the movable masses are supposed to move 'in respect to each other so as to compensate the unbalancing effect.

Unfortunately, the experience has proved that systems of the type above are not able to ensure the proper feeding of oil with the clearance. provided in usual oil bearings due to the unsuliicient output of oil supplied by the oil ilrn of the bearing, said output being unsufiicient for rapidly acting on the compensating masses in order to displace them according to the pressure variations. To increase said output it would have been necessary to increase considerably the pressure differentials acting on the pressure receiving openings of the ducts mentioned above and located at 120 in respect to each other (which would actually mean the increase of the value of the compensating signal). This result could only be obtained .by an increase of the section of the clearance which would not be compatible with a proper operation of the rotating system. In addition, the low output mentioned above may induce to reduce the volume of the chambers (which could not be extended beyond 60), so that the limited displacement of the balancing masses did not permit to compensate the balancing forces when these forces became high enough to be objectionable.

It is an object of this invention to provide an improved automatic dynamic re-balancing system for rotating mechanical members, which will have better performance characteristics than similar systems heretofore Patented Nov. 24, 1964 ICC available; objects are to increase the response rate of such systems and -to ensure a 4more uniformly effective balancing action throughout the rotation of lthe rotary member.

In fulfilling these objects of the invention, there is provided in a dynamic balancing system of the type above defined, a plurality of circumferentially spaced recesses formed in the periphery of the rotating shaft within its bearing said recesses being equal in number to the plurality of movable elements, passage means connecting each of said recesses with a corresponding one of .the balancing chambers, and means for supplying fluid .under pressure to veach recess and, consequently, to the corresponding 'interconnected balancing chamber. So, a body of iiuid under pressure is interposed between said shaft and bearing, in the zone including said recesses, said body supporting at least partially said shaft in the manner rknown in liuid type bearings.

In other terms, a bearing of the uid type combined with a balancing system permits to solve the diiiicult problem of feeding the annular recess practically, because it permits `both to vary in the desired manner the output vof the iiuid and the `value of the pressure differentials supplying the compensating signal, this type of bearing being unaffected when mechanical clearances are relatively high, which again is due to the fact that the shaft is completely floating in the iluid under pressure without .ever contacting ,the stationary mechanical parts.

`continutnls around the circumference thereof so `las to permit fully 4uninhibited flow of fluid and transmission of pressure variations yaround the raceway for producing the compensatory shifting displacements of the movable elements along their arcuate path.

According to the invention, vabutments are provided inside the annular recess to positively limit the displacement .of each compensating mass so that no separation means are necessary and a continuous annular recess takes place of the known arcuate chambers of a reduced length. It is also an object to provide an improved .construction o'f the movable balancing elements, which will ensure their smooth, free-floating, self-lubricated displacement along the continuous annular raceway in sealing engagement with the walls thereof, while rendering the manufacture of such elements simple and inexpensive.

It is still another object of the invention to supply iiuid under pressure in parallel to each sustentation recess and corresponding balancing chamber.

The above and further objects and advantages of the invention as well as the novel features thereof will appear from the description to follow, in which an exemplary embodiment yof the improved dynamic balancing system is disclosed for purposes of illustration but not of limitation with reference to the accompanying diagrammatic drawings, wherein:

FIG. l is a view of the improved apparatus in axial section;

FIGS. 2 and 3 are cross sectional views respectively on the planes designated Il--ll Aand Ill- III in FIG. l.

As shown an annular member 1 shown as a cylindrical member is secured on a shaft 2 for rotation therewith. Shaft 2 is rotatably mounted within a bore in a smooth bea-ring member 3 by way of a fluid bearing later described. The shaft is here shown as being horizontal and the annular part 1 is mounted on an end of the shaft by way of a rigid assembly generally designated 4 and providing a housing within it Vfor the active portion of a dynamic balancing or compensating system presently described. The assembly 4 comprises a pair of parallel spaced iianges 5 and 6 and a spacer ring 7 positioned between said flanges adjacent the radially outer surfaces thereof, said fianges and ring being suitably secured by means not shown within the central bore of annular member 1. The assembly 4 is held in firm engagement against a shoulder il provided on shaft 2 by means such as a retainer nut 9 screwed on a threaded end part of the shaft.

There is thus defined within the assembly 4, internally of flanges 5 and 6 and ring 7 a continuous annular space of rectangular cross section. Disposed in this annular space or raceway are three movable reaction elements, preferably in the form of generally

cylindrical rollers

11, 12, 13. The rollers are so dimensioned that they are freely displaceable along arcuate paths within the raceway while being at all times retained in positions such that their axes are parallel to the axis of the shaft 2. For this purpose the diameter of each roller is just slightly smaller, e.g. by an amount of the order of 0.02 mm., than the difference in radius between ring 7 and shaft 2, and the length of each roller is just slightly smaller, say

by about the same amount of 0.02 mm., than the axial spacing between the inner faces of flanges 5 and 6.

The three

rollers

11, 12, 13 define, in the continuous raceway, three compensating or

balancing chambers

17, 18, 19. As will be apparent later the volumes of the three chambers are variable with the relative positions of the three rollers round the raceway. However, means such as

stops

51, 52, 53 projecting from the inner periphery of ring 7 at 120 degree spacings therearound, are provided for positively limiting the arcuate displacements of the three rollers to arcs such that the positions of the three chambers cannot wander unrestrainedly around the circumference of the shaft for reasons that will later appear. To promote smooth frictionless displacement of the rollers along their arcuate paths, the opposite end faces of each roller are interconnected by a number of axial passages, herein shown as a central passage 57 and four passages 58 spaced around the circumference of the roller and connecting at their opposite ends with annular grooves 59 formed in the roller end faces.

Formed in the peripheral surface of shaft 2 within the axial extent of bearing sleeve 3 are three arcuate sustentation recesses 21, 22, 23 (see FIG. 3) which are of equal arcuate extent and are separated by equal arcuate distances. In operation fluid under pressure is maintained in the three recesses through means presentlydescribed. Fluid flowing out of the recesses is collected by three longitudinal grooves 31, 32, 33 formed in the periphery of shaft 2 intermediate the recesses as shown in FIG. 3, said grooves connecting at their opposite ends with a pair of circumferential channels 35 and 36 formed in the shaft beyond the ends of the recesses (see FIG. 1). The channels 3S, 36 communicate with registering channels 37, 3S formed in the inner periphery of sleeve 3 from which the fluid is returned to a sump or exhaust.

Means are provided for supplying uid under pressure` in parallel to each of the

balancing chambers

17, 18, 19 and a related one of the shaft recesses 21, 22, 23. As shown, a radial inlet passage 41 formed in the bearing sleeve 3 is adapted to be externally connected with a pressure source of said fluid, e.g. oil. The passage 41 delivers into a circumferential inlet manifold channel 42 formed in the inner surface of sleeve 3. Two or more radial passages 43 formed in shaft 2 connect the circumferential inlet manifold 42 with an axial bore 44 formed through the shaft 2. The outer end of bore 44 is adapted to be sealed with a screw plug as indicated on the left of FIG. 1. Also bored into the shaft around the axial passage 44 are three longitudinal, angularly spaced passages 26. Each of the passages 26 is connected near one end by way of a radial port 46 with the axial passage 44. Further, each passage 26 is connected'by a radial passage 25 with a related point of the continuous annular raceway, the three passages 25 being angularly equispaced and being positioned opposite to the respective stops 51, 52, 53 (see FIG. 2) so as to deliver into each of the three

balancing chambers

17, 13, 19, respectively regardless ofthe positions of the rollers. Moreover, each longitudinal passage 26 connects by another radial passage 27 with the center of a related one of the recesses 21, 22, 23.

interposed in each longitudinal passage 26 between its connection 46 with the central bore 44 and its connection 25 with the raceway is an insert 47 providing a calibrated restricted orifice. Optionally another calibrated insert 30 is shown as inserted into each of the passages 25.

1t will be evident from the description above that pressure fluid from inlet 41 flowing through inlet manifold 42, radial passages 43 and axial bore 44, is thence delivered in parallel, through a restriction such as 47, to each of the three

balancing chambers

17, 18, 19 and the related shaft recesses 21, 22, 23. Effluent fluid from the shaft recesses is returned to the sump via grooves 31, 32, 33, channels 37 and 38 and the outlet shown.

The system operates as follows. Assuming the rotating assembly comprising shaft 2 and the annular part 1 (which be it noted may stand for any complex revolving assembly) is perfectly centered dynamically, i.e. its center of gravity is positioned accurately on the rotational axis of shaft 2, then the thickness of the fluid film between the adjacent surfaces of shaft 2 and bearing sleeve 3 is continually uniform all around the circumference of the shaft throughout each shaft revolution (disregarding for the time being the minor and constant effect of gravity present when the rotational axis is horizontal as here shown). The uid pressure in all three recesses 21, 22, 23 and hence in all three

balancing chambers

17, 13, 19 con nected thereto, is hence continually the same. Because of the equal pressures in

chambers

17, 18, 19, the three

rollers

11, 12, 13 assume equi-angular positions along the raceway as shown'.

Assume now that an unbalance mass is present at some point in the revolving assembly, due to some uncontrollable cause. Such an unbalance mass has here been symbolically indicated as a small additional weight B attached to a point of annular part 1, specifically adjacent the stop 51 marking the center of balancing chamber 17. The unbalance will generate a centrifugal force which throughout each revolution tends to press the recess 21 of the shaft into tight engagement with the inner surface of bearing 3, so that the fluid film thickness is reduced in the corresponding shaft area and the pressure in recess 21 becomes greater while the pressure in the other two recesses Z2, 23 grows correspondingly lower. Similar pressure variations are reflected in the three

balancing chambers

17, 18, 19, respectively connected with the recesses 21, 22, 23, so that the pressure in chamber 17 is increased and that in

chambers

18 and 19 correspondingly decreased. Hence the

rollers

12, 13 defining chamber 17 are urged away from each other along the raceway, increasing the volume of chamber 17 and reducing the volumes of

chambers

18 and 19. This outward motion of

rollers

12, 13 towards roller 11 creates an unbalance reverse from that produced by the mass B, and when the roller displacement has been sufficient to offset the initial unbalance so that the resulting centrifugal force is zero and the shaft is revolving in a centered condition in its bearing, the pressures in the three shaft recesses 21, 22, 23 and hence in the three

chambers

17, 18, 19 are equalized so that the

rollers

12 and 13 remain relatively stationary in their displaced positions. This condition will last so long as the initial unbalance remains unchanged in amount and in phase (or angular position). Should such a change in amount and/ or in phase occur however, a sequence of events generally similar to that described will ensue, and the configuration of the three rollers around the raceway will undergo another shift to meet the changed condition land restore the dynamically zbalanced, lcentered, condition of the shaft.

It is found in practice that the `"system described accomplishes a permanent and vcontinual compensation of a dynamic unbalance with very rapid response, a result attributable in part -to the large ow `of fluid and to the high pressure under which the fluid is delivered in a iiuid bearing, as well as to the direct supply of fluid in parallel to each shaft recess and balancing chamber, 'by way of a common restricted orifice 47. This parallel supply of fluid is found to result in substantially improved performance characteristics over what is obtained with a serial supply of iluid through the fluid film of the bearing to the balancing chambers as i-n certain prior systems of the class to which the invention is directed. Moreover, since the bearing recesses 21, 22, 23 are formed in the shaft and hence revolved bodily with the rotating assembly, accurate compensation is had continuously throughout every revolution.

As earlier noted the auxiliary restricted orifices such as 30 shown in the connecting passages 25 may usually be omitted with good results when desired to obtain maximum response speed of the rebalancing system. However, in some cases the insertion of the orifices 30 may be desirable in order to introduce some damping in the response characteristic. This may be especially useful in the case of a substantial gravity force component being present in the system, such as in the horizontal shaft system shown, since such a constant gravity component tends to induce cyclic pressure variations in the balancing chambers as the shaft rotates. Such cyclic pressure variations do not per se tend to produce relative shifting of the balancing rollers, since the mean values of the pressures remain constant. Moreover, normal damping due to the shear of the fluid through the various restricted passages in the fluid flow circuit, including the passages around the rollers, usually suiice to dampen out to a substantial extent the said cyclic variations. However, especially in the case of a lowspeed, heavyweight, horizontally mounted revolving assembly, the use of the optional restricted inserts 30 may prove desirable for further damping out any residual vibrations.

The balancing section of the system including the continuous annular raceway or channel containing the plurality of, preferably three, balancing elements in the form of perforate rollers, in combination with the stop means 51, 52, 53 which positively limit the arcuate displacements of the rollers, as shown and described above, is highly advantageous for several reasons. While being simple and inexpensive to construct and assemble, the continuous annular channel ensures optimal transmission of pressure variations through the body of uid contained therein and hence optimal response to an unbalance; also the available length of displacement of the movable elements is increased for given over-all dimensions. At the same time, the stops positively prevent the straying of the balancing chambers all around the annular channel, which would otherwise result in incorrect operation since each balancing

chamber

17, 18, 19 would then be liable to communicate with the wnong shaft recesses 21, 22, 23; said stops however do not substantially interfere with the continuous character of the annular raceway in regard to the transmission of pressure forces. The cylindrical shape of the

balancing elements

1l, 12, 13 makes them easy to machine to the requisite tolerances and the axial perforations through the elements ensure pressure balance between the opposite ends thereof as well as a self-lubricating effect conducive t-o smooth floating displacement of the rollers around the raceway to effect the desired compensating shifts.

What is claimed is:

1. The combination with a revolving assembly having a shaft rotatable in at least one bearing, of dynamic balancing means for said assembly comprising a plurality of chambers, equi-angularly disposed rat the periphery f of .said .shaft between said shaft and said :bearings ,raceway means .defined :said assembly coaxially ,sur/rounding .said shaft; a plurality of balancing-elements positioned in the raceway for displacement along arcuate paths .therein and defining .a plurality of spaces between said elements, equal in number to said chambers; passage k.means connecting each .chamber with a related space, ,and

means for supplying fluid under pressure to .said passage means, said fluid under pressure supporting at least partially said shaft; whereby a pressure change occurring in any one of said chambers due to dynamic unbalance of the revolving assembly will induce a compensatory shift in the relative position of said elements.

2. The combination with a revolving assembly having a shaft rotatable in a bearing surface, of dynamic balancing means comprising a plurality of equi-angularly disposed chambers recessed in the shaft periphery surrounded by said bearing surface; raceway means defined in said assembly and coaxially surrounding the shaft; a plurality of balancing elements in the raceway displaceable along arcuate paths therein and defining a plurality of spaces between said elements equal in number to said chambers; a passageway connecting each chamber with a related space, fluid supply passage means formed through said bearing surface and other passage means formed through said shaft and communicating with said supply passage means; a plurality of restricted calibrated orifices connecting said other passage means with each of said passageways for supplying pressure fluid in parallel to all pairs of interconnected spaces and chambers; and uid return passage means formed in said bearing surface and communicating with said chambers.

3. In combination with a revolving assembly including a shaft, a bearing for supporting said shaft with a clearance space therebetween, said shaft having a bearing surface formed with a plurality of circumferentially spaced recesses, means defining in said assembly a continuous annular raceway coaxially surrounding the shaft; a plurality of balancing elements in the raceway displaceable along arcuate paths therein and defining a plurality of spaces between said. elements; the number of said spaces being equal to the number of said recesses, angularly equispaced stop means positioned in said raceway for limiting the arcuate paths of travel of said elements and thereby preserving the relative disposition of said spaces without substantially restricting the flow section of the raceway; a duct connecting each of said spaces with one of said recesses, respectively, and means for conducting iluid under pressure separately to each of said ducts.

4. The combination claimed in claim 3, wherein said ducts include each an axially extending portion formed in said shaft, said portions opening into said raceway at angularly equispaced points substantially radially aligned with said stop means.

5. In combination with a revolving assembly including a shaft, a bearing for supporting said shaft with a clearance space therebetween, said shaft having a bearing surface formed with a plurality of circumferentially spaced recesses, means defining in said assembly a continuous annular raceway coaxially surrounding the shaft; a plurality of cylindrical elements in the raceway positioned with their axes parallel to the shaft axis and displaceable along arcuate paths in the raceway in substantially fluid-sealing freely-displaceable relationship with the walls thereof to define with said walls a plurality of arcuate spaces of variable volume; the number of said spaces being equal to the number of said recesses, angular- 1y equispaced stops in the raceway limiting the arcuate paths of travel of said elements and thereby preserving the relative disposition of the spaces defined between said elements Without substantially restricting the flow section of the raceway; and duct means connecting each of said spaces with one of said recesses, respectively, and

means for conducting7 uid under pressure separately 8. The combination claimed in claim 2, wherein said to each of said duct means. fluid return passage means include passages recessed in 6. The combination claimed in claim 5, wherein said the shaft periphery parallel to the shaft axis and interelements have passages formed therethrough parallel to mediate each pair of adjacent first chambers. the axis of the element and interconnecting the opposite 5 end faces there@ References Cited n the tile of this patent 7. The combination claimed in claim 2, further includ- UNITED STATES PATENTS ing a restricted calibrated orice interposed in the con- 2 659 243 Darrieus Nov 17 1953 nectlon from each of sald passageways to the related 2,778,243 Darrieus Jan. 22. 1957 space in the raceway.

UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent No 3 ,158 ,039 November 24, 1964 Paul Favrot It is hereby certified that error appears in the above numbered p'atent requiring correction and that the said Letters Patent should read as corrected below.

and in the heading to the In the grant, 1ines Z and 12,

for "Landis printed specification, line 5, name of assignee, Gendron S.A." each occurrence Signed and sealed this 20th day of July 1965.

(SEAL) Attest:

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

Claims

1. THE COMBINATION WITH A REVOLVING ASSEMBLY HAVING A SHAFT ROTATABLE IN AT LEAST ONE BEARING, OF DYNAMIC BALANCING MEANS FOR SAID ASSEMBLY COMPRISING A PLURALITY OF CHAMBERS, EQUI-ANGULARLY DISPOSED AT THE PERIPHERY OF SAID SHAFT BETWEEN SAID SHAFT AND SAID BEARING, RACEWAY MEANS DEFINED IN SAID ASSEMBLY COAXIALLY SURROUNDING SAID SHAFT; A PLURALITY OF BALANCING ELEMENTS POSITIONED IN THE RACEWAY FOR DISPLACEMENT ALONG ARCUATE PATHS THEREIN AND DEFINING A PLURALITY OF SPACES BETWEEN SAID ELEMENTS, EQUAL IN NUMBER TO SAID CHAMBERS; PASSAGE MEANS CONNECTING EACH CHAMBER WITH A RELATED SPACE, AND MEANS FOR SUPPLYING FLUID UNDER PRESSURE TO SAID PASSAGE MEANS, SAID FLUID UNDER PRESSURE SUPPORTING AT LEAST PARTIALLY SAID SHAFT; WHEREBY A PRESSURE CHANGE OCCURING IN ANY ONE OF SAID CHAMBERS DUE TO DYNAMIC UNBALANCE OF THE REVOLVING ASSEMBLY WILL INDUCE A COMPENSATORY SHIFT IN THE RELATIVE POSITION OF SAID ELEMENTS.