US2771240A - Automatic dynamic balancer - Google Patents

Description

Nov. 20, 1956 P. J. GURIN 2,771,240

AUTOMATIC DYNAMIC BALANCE-R Filed Aug. 27, 1952 2 Sheets-Sheet l 4 Tram/yrs Nov. 20, 1956 i, J, GURlN 2,771,240

AUTOMATIC DYNAMIC BALANCER Filed Aug. 27, 1952 2 Sheets-Sheet 2 United States Patent 2,771,240 AUTOMATIC DYNAMIC BALANCER Peter J. Gurin, Ardmore, Pa. Application August 27, 1952, Serial No. 306,745 1 Claim. (Cl. 230134) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to dynamic balancing of rotating bodies and particularly to the automatic balancing of high speed rotating blade assemblies such as employed in gas turbine power plants.

In the high rotating speeds of turbine blade assemblies and the like any irregularities or nonuniformity in the distribution of the mass about the axis of rotation, no matter how minute, will produce disturbing forces which in turn will cause vibrations. It is difiicult in the manufacture of multi-blade assemblies to bring the axis of rotation into accurate coincidence with the central axis of inertia of the assembly. Therefore, in the case of high speed multi-blade assemblies, it becomes necessary to accurately balance the assembly in order to remove the vibrations and establish quiet running.

An important object of the invention is to provide an automatically balanced high speed blade assembly for use in gas turbines and the like which is self operable during actual use of the blade assembly to correct for any unbalance that might exist.

Another important object of the invention is to provide improved means for balancing multi-blade assemblies of the character described which assumes the form of one or more circular raceways concentric with the axis of rotation and each containing one or more spherical members or balls which are freely movable throughout the circular path of the raceway.

A further important object of the invention is to provide a novel arrangement for automatically balancing bladed assemblies while the same are in use and in such a manner as to strengthen the mounting of the blades and to increase the efficiency by reducing tip loss.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference 'to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a cross sectional view through an axial-flow air compressor and showing one of the blade assemblies with the automatic balancing provision of this invention;

Fig. 2 is a diametrical sectional view of the blade assembly of Fig. 1 taken along line 2-2 thereof;

Fig. 3 is a cross sectional view through an axial-flow air compressor and showing a modified form of the invention embodied in one of the blade assemblies thereof;

Fig. 4 is a diametrical sectional view of the blade assembly of Fig. 3 taken along line 44 thereof;

Fig. 5 is a side elevation of an axial-fiow air compressor partially broken away in section and showing a further modification of the invention applied thereto;

Fig. 6 is a cross sectional view of the compressor of Fig. 5 taken along line 66 thereof; and

Fig. 7 is an end view of the compressor of Fig. 5.

The invention is illustrated herein as embodied in high 2,771,240 Patented-Nov. 20, 1956 ice speed blade assemblies such as employed in axial-flow compressors of aircraft gas turbines. Such blade assemblies are subjected to high centrifugal forces and to air impact at high velocities and provisions are usually made to reduce or minimize the results of such forces as much as possible. Under high speed operating conditions, any irregularity or non-uniformity of the mass distribution with respect to the axis of rotation will be magnified and set up condition-s which may damage the blade assemblies or possibly cause irreparable damage to the gas turbine.

The present invention provides automatic means which is sensitive to any unbalance in the rotating blade assembly and which is self operable to shift weights to The hub or disc 12 is intern-ally shaped to provide an annular cavity or conduit 16 extending around the axis of the rotation of the blade assembly. The conduit fiorms a raceway of uniform cross section whose center of curvature coincides with the axis of rotation of the blade assembly. Enclosed within the raceway are a plurality of weights in the form of spherical members :or balls 18 which are of the same size and capable of freely moving through the raceway.

In the operation {of the blade assembly, so far described,

if the assembly is accurately balanced, the balls will 1 assume positions in the raceway equidistant from one an other. However, if there is an unbalance present, resulting in a displacement of the axis'of rotation and the axis of inertia, forces will be produced urging the balls toward one side of the assembly and closer together than their equidistant spaced relationship. Such an unbalanced condition causes the production of the tengential force exerted on each ball and urging it toward the lighter side of the blade assembly. The balls are required to move in this direction by the fixed path prescribed by the groove or chamber 16. Fig. 1 illustrates an unbal anced condition wherein the balls 18 have displaced themselves toward the lighter side of the rotating blade assembly to bring the assembly into balance.

Figs. 3 and 4 illustrated a modification of the invention wherein the balancing system is provided on the periphery of the blades rather than adjacent totheir roots as in the preceding figures. The blades, hub and shaft, are designated by the same reference characters. The outer ends of the blades 10 are connected together by the ringshaped sleeve 20 extending completely around the blade assembly as shown in Fig. 3.

The sleeve may be of the cross section shown in Fig. 4 having a flat outer periphery 22 and side walls 24-24 which extend parallel to one another and radially of the assembly for a short distance before rounding inwardly to complete the inner side of the sleeve. Positioned within the sleeve 20 is a conduit or tube 26 of circular cross section throughout its length and forming an endless loop whose center of curvature coincides with the axis of rotation of the blade assembly. Carried within the tube 26 is a plurality of balls 28 which are free to roll therein throughout its circular extent. The balls are preferably just sufiiciently undersize the cross section of the tube as to roll freely the-rethrough play.

As previously described in the embodiment of the invention, an unbalance in the rotating blade assembly will cause the production of tangential forces urging the without noticeable lateral 3 balls to the lighter side of the assembly. They may dispose themselves as shown in Fig. 3 in a relatively close relationship on one side of the axis of rotation to bring the blade assembly in balanced relationship.

In addition to serving this purpose the sleeve and its internal bal-l carrying tube 26 also serve to strengthen blades 10 against vibration and to prevent tip loss." The outer ends of the blades may be arcuately recessed to seat the sleeve 26 and thereby form a stiffening ring or rim for the assembly.

In Figs. 5, 6 and 7 there is shown a modified form of arrangement for balancing a high speed rotating unit having a considerable axial dimension, such as several or all of the stages of a multi-stage axial-flow compressor of an aircraft gas turbine. The modified arrangement employs a plurality of weight-guiding tracks or tubes extending longitudinally to the compressor and gene-rally but not exactly parallel to the axis of rotation. These tracks or tubes are closed at their opposite ends and contain one or more freely movable weighted elements :or balls similar to those previously described.

Referring in more detail to Figs. 5, 6, and 7, the multistage compressor comprises a plurality of sets of blade assemblies, each identified by thesimilar characters previously applied. The blade assemblies are mounted on a common shaft 14 and each includes a disk or hub 12 and a plurality of circularly spaced apart blades 10. Enclosing the blade assemblies is a housing of comparatively small radial dimension but extending substantially the length of the compressor unit. The housing includes an outer wall and an inner wall 32, coaxially related and concentrically positioned with respect to the axis of the shaft 14. The two walls 30 and 32 are radially spaced apart from one another as is evident in the several figures and may be closed at their opposite ends by an end wall 34.

Within the clearance formed between the walls 30 and 32 there is provided a plurality of tubes designated by the reference character 36. Instead of extending circularly around the axis of rotation as in the previous embodiments of the invention, the tubes 36 extend longitudinally 'of the compressor unit and generally parallel to the axis of rotation. The tubes are arranged in angular relationship to one another, as shown in Fig. 5, the angularity therebetween being such that the tubes form a uniform pattern around the axis of rotation. The tubes extend substantially the full length of the housing formed by the walls 30 and 32 and each assumes a slight curvature, as shown in Figs. 6 and 7, having its axis coinciding with that of the blade assembly. Carried within each tube 36 is one or more freely movable weights or balls 38.

The tubes 36 are so arranged that their mid-sections are equally circularly spaced apart from one another completely around blade assembly. The diverging relation of the tubes to one another is such that each tube cooperates with its neighboring tube on one side to form a V having its apex at one end of the housing and cooperates with its neighboring tube on the other side to form a V having its apex at the other end of the housing. It is noted that the tubes are slightly arcuate from end to the other end thereof, and all are equidistant from the axis of notation.

In the operationwof the modification shown in Figs. 5, 6, and 7, any unbalanced condition present in the rotating assembly will cause the balls 38 to shift along their respective tubes toward. one or theother end of the compressor unit. Some will shift further than others along their tubes and thereby distribute their weight more on one side of the axis of rotation than the other side.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

In combination with a multistage axial-flow gas turbine compressor having a plurality of sets of coaxially related blade assemblies, a housing enclosing the blade assemblies and being secured to the tips of the blades for joint rotation. therewith, said housing having an inner wall and an outer wall concentrically related and slightly spaced about from one another to form an annularly shaped clearance the-rebetween, a plurality of tubes positioned in the clearance formed by the walls of the housing and each extending generally longitudinally of the compressor, sa'idtubes at the same angle to one another and being so arranged that each tube cooperates with its neighbor on one side to form a V having its apex at one end of the housing and cooperates with its neighbor on the other side to form a V having its apex at the other end of the housing, said tubes being further arranged that at their mid-points they are equally circularly spaced around the axis of rotation of the compressor, and a ball in each tube and capable of rolling freely to assume positions therein during the rotation of the compressor acting to bring same into dynamic balance.

References Cited in the file of this patent UNITED STATES PATENTS 414,642 Herrick Nov. 5, 1889 1,183,745 Ledyard May 16, 1916 1,209,730 Leblanc Dec. 26, 1916 1,856,820 Robinson May 3, 1932 2,155,052 Byland Apr. 18, 1939 2,313,024 Salomon Mar. 2, 1943 2,349,187 Meyer May 16, 1944

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