US2595829A

US2595829A - Axial flow fan and compressor

Info

Publication number: US2595829A
Application number: US717235A
Authority: US
Inventors: George A Dean
Original assignee: Benson Manufacturing Co
Current assignee: Benson Manufacturing Co
Priority date: 1946-12-19
Filing date: 1946-12-19
Publication date: 1952-05-06
Anticipated expiration: 1969-05-06

Description

May 6 1952 G. A. DEAN 2,595,829

AXIAL FLOW FAN AND COMPRESSOR Filed D60. 19, 1946 /6 .la /2 /A/' @i jr/m Patented May 6, 1952 AXIAL FLOW FAN AND COMPRESSOR George A. Dean, Radburn, N. J., assignor to Benson Manufacturing Company, Kansas City, Mo.,

a corporation of Missouri YAppiication December 19, 1946, Serial No. 717,235

7 Claims. l

This invention relates in general to axial flow fans and compressors and is concerned more particularly with the mounting of the blades in such devices.

It is well known that aircraft engine performance may be improved very considerably by the use of cooling fans, with a resultant improvement in the rate of climb, ceiling, top speed at high altitudes, useful load and cruising economy. In such fans the blade mountings assume great importance because it is exceedingly difficult or even impossible to prevent vibration of the blades notwithstanding the fact that care is taken to properly balance the fan.

A similar problem exists in connection with axial iiow compressors, for instance those currently employed in conjunction with the gas turbines used for propelling aircraft. These compressers have radial impeller blades which inevitably tend to vibrate individually at high rotational speeds, and accordingly the blade mounting requires special consideration.

It is an object of the invention to provide a fiuid impeller, and more particularly an axial iiow fan or compresser, of exceedingly simple and eco-- nomic construction which is light in weight yet very rugged.

Another object is to provide an improved blade mounting arrangement having facilities for dampening or absorbing vibration of the blade.

Still another object is to provide a blade construction which will uniformly distribute stresses imposed upon the vibration dampening member.

A further object is to provide a blade mounting wherein the blades may be inserted or removed for replacement Witho-ut the aid of tools.

Another object is to provide improved facilities for balancing the fan or impeller.

According to one feature of the invention the blades are pivotally mounted in individual sockets in the hub, which sockets include a resilient material for dampening the blade vibrations.

According to another feature of the invention the moment produced by the pitch or lift of the blades tending to rotate the blades in one direction in their respective sockets is balanced by a moment produced by centrifugal action thereby to equalize the stress imposed on the dampening member.

Other objects and features will appear in the course of the follo-wing description.

In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith, and in which like reference numerals are employed to indicate like parts of the various views,

Fig. l is a fragmentary elevational view of the front of a fan embodying the invention,

Fig. 2 is a developed View showing a portion of the same fan in side elevation,

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2 in the direction of the arrows,

Fig. 4 is a sectional view taken along the line Il--ll of Fig. 2 in the direction of the arrows, and

Fig. 5 is a sectional View of a blade showing a modified construction.

Fig. 6 is an enlarged sectional view of a modified blade showing in detail the offset of the blade stem with respect to a hub radius through the pivotal axis of the blade.

Referring more particularly tothe drawings, the fan illustrated therein comprises an annular hub Ill having a series of vanes or blades i l extending radially outward therefrom. The hub preferably is formed of a light weight magnesium alloy and it has an internal iiange or web i2 which makes it generally T-shaped in radial cross section. A series of apertures I3 are provided in this flange to facilitate bolting or otherwise fastening the hub to its supporting and driving member (not shown). The mechanism for rotating the fan forms no part of the present invention, but it will be understood that in most cases the hub will be attached to the propeller shaft just forward of the engine so that it is driven at propeller speed.

The individual blades preferably are moulded o-f synthetic resin, but wood, light weight metal or other suitable material obviously might be substituted. As shown in Fig. 3, each blade has a semi-cylindrical root portion I4 which is positioned in a conforming socket or recess l5 in the hub. These recesses are machined diagonally in `the outer periphery of the hub (see Fig. 2) so that they give the blades a predetermined pitch. Under the root of each blade is a resilient cushion or vibration dampening member Iii. This urges the blade outwardly so that the convex surface of the blade root bears snugly against the concave surface of the recess l5; however, member iii will yield suiciently to permit the blade to pivot slightly in the socket. A filler band Il of resilient material is provided around the blade just above the root thereof to form a surface which is flush with the outer periphery of the hub. For convenience it is preferred to bond the latter band directly to the blade, for instance by cement.

Movement of the blades longitudinally in their respective supporting slots or sockets is prevented by means of retaining strips I8 positioned in channels or grooves I9- which are machined in opposite sides of the hub. The retaining strips are stamped in the form of arcuate segments from a sheet of phenol ber or other relatively thin flexible material and are inserted in the retaining groove at 20 where the marginal walls of the groove are cut away to provide an entrance. It will be seen that the blades are positioned between the two retaining strips, each blade being separated from the strips, however, by spacing members 2| and 22 positioned adjacent opposite ends of the blade root. The individual spacing members 22 preferably are molded of phenolic material, and each has a contour conforming with the socket recesses I5 so that it may be inserted in the end thereof; also provided on each spacing member 22 is a grooved flange 23 which conforms with the outer marginal wall of the upper groove I9 when the spacer is in place. Spacers 2| are wafers of resilient material and may, if desired, be bonded either to the ends of the blade root or to the spacing members 22.

A series of holes 24 are drilled diagonally (see Fig. 2) through the hub to reduce the weight thereof. During the balancing of the fan, one or more of these holes may be reamed to remove metal or. alternatively, small cork plugs may be inserted in one or more of the holes to achieve balance.

The fan may be assembled without the use of tools by first sliding the blades II and the dampening members I6 into their respective slots, then inserting spacing members 2l and-22 and finally sliding the segmental retaining strips I8 into place over the spacing members. In performing the latter operation it will be understood that one end of each retaining strip is inserted through the entrance 20 as illustrated in the case of strip I8', the strip then being fed into groove or channel I9 through this opening and advanced until it abuts the end of the preceding strip. After the last retaining strip has been thus inserted, the groove therefore being filled around its entire circumference, all of the strips are advanced slightly so that an intermediate portion of one strip spans the entrance opening 20. If balancing plugs are to be inserted in any of the holes 24, this will be done, of course, before the strips I8 are put in place, the latter strips then serving also to hold such plugs.

In order to remove a blade the above procedure is reversed. That is, the strips I8 are moved in groove I9 until the end of one strip is disposed under opening 2D; the end of this strip then is lifted through the opening so that the strip may be withdrawn from the groove. The remaining strips then are moved to expose the root of any desired blade, permitting removal of the spacers 22 associated with that blade and the withdrawal of the blade itself from its supporting socket.

When the fan is in operation any tendency of an individual blade to vibrate manifests itself as a slight rocking or pivoting of the blade about the axis C of its root portion. The dampening member resists such rocking and tends to maintain the blade erect but at the same time is sufciently resilient to absorb the vibration which occurs. It will be noted from Fig. 2 that the ends of the blade roots are oblique to the axis C, and that resilient spacers 2| serve to prevent binding which might otherwise occur between the blade roots and the adjacent spacers 22 as the blade pivots.

Due to the pitch or lift of the blades each has a force L acting upon it during rotation of the fan as is indicated in Fig. 3. Thiswill tend to put the left-hand edge of the dampening member I6 under compression. Each blade also is subjected to a centrifugal force during rotation and if the blade is constructed as shown by solid lines in Fig. 3, this force will act through the root pivot axis C and be directed radially outward toward the tip of the blade; if, however, the blade is formed so that the center line of its extending portion is offset slightly with respect to a hub radius R through the axis C of the root portion (see Fig. 6 and dotted lines in Fig. 3), the centrifugal force F, acting along said center line, will tend to rotate the blade clockwise about C, and hence put the right-hand edge of the dampening member IB under compression. In other words, by proper displacement of the blade from center it is possible to create a moment which will balance the moment created by the lift L, whereby the stresses in the dampening member will be substantially equalized.

A modied form of the blade root is shown in Fig. 5. In this, the dampening member and the resilient filler band around the neck of the blade are formed as a single piece 25. The fundamental action is similar to that explained above, but because the Whole centrifugal force acting on the blade during rotation of the fan is borne by the dampening member 25, it is preferred to employ this construction only in the case of relatively slow moving fans. It will be understood that the blade I I, may be displaced with respect to the root pivot axis C to equalize the stresses on member 25 in the same fashion as discussed above.

For convenience of description the foregoing explanation of the invention has dealt particularly with the construction of a fan for cooling an aircraft engine. It should be understood, however, that this is merely exemplary, and that the same form of blade mounting may be employed for axial flow compressers or other fluid impelling devices. In a compresser, the fluid engaging portion of the blade ordinarily would be concavo-convex when viewed from the same angle as Fig. 2, but the configuration of this uidengaging portion of the blade forms no part of the present invention.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinbefore set forth together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and sub-combinations of utility may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

Having thus described my invention, i claim:

l. A fan or fluid impeller, comprising a hub, a plurality of blades pivotally supported on said hub, the axis about which each blade pivots relative the hub being oblique to the axis of rotation of the hub, the mass of each blade being un balanced with respect to a radial plane through said oblique axis whereby the centrifugal force acting on the blade due to rotation of the fan produces a moment tending to turn the blade about its oblique axis.

2. A fan or uid impeller, comprising a hub having around its periphery a series of undercut recesses each forming an enlarged pocket spaced inwardly from the peripheral surface of the hub and opening onto said surface through a restricted throat, a plurality of blades each having an enlarged root disposed in one of said pockets with the stem of the blade extending outwardly through the throat, the root and pocket being shaped to provide matching convex and concave surfaces respectively forming a bearing for limited pivotal movement of the blade relative the hub, the edges of the throat at its narrowest point being-spaced laterally from said stem to permit lateral shifting of said stem upon such pivotal movement, and resilient, compressible material in said throat opening lling the space between the stem of the blade and the edges of said opening.

3. A fan or fluid impeller comprising a hub having around its periphery a series of undercut recesses each forming an enlarged pocket spaced inwardly from the peripheral surface of the hub and opening onto said surface through a restricted throat, a plurality of blades each having an integral enlarged root disposed in one of said pockets with the stem of the blade extending outwardly through said throat opening, said pocket having a concave segmento-cylindrical face bisected by said throat opening, said integral blade root having a convex segmento-cylindrical face bisected by the blade stem, the bottom of said pocket being spaced below the bottom of the blade root, a resilient compressible member between said bottoms urging the blade outwardly whereby said convex face of the blade root is maintained in engagement with the concave face of said pocket, said convex and concave faces being coaxial, of substantially equal radius and forming a bearing for limited pivotal movement of said blade about their common axis, the edges of said throat at its narrowest point being spaced laterally from the blade stem to permit lateral shifting of said stem upon such pivotal movement, and resilient compressible material in said throat opening filling the space between the stem of the blade and the edges of said opening.

4. A fan or fluid impeller, comprising a hub having around its periphery a series of undercut recesses each forming an enlarged pocket spaced inwardly from the peripheral surface of the hub and opening onto said surface through a restricted throat, a plurality of blades each having an enlarged root disposed in one of said pockets with the stem of the blade extending outwardly through the throat, the root and pocket being shaped to provide matching convex and concave surfaces respectively forming a bearing for limited pivotal movement of the blade relative the hub about an axis within the recess, the mass of each blade being unbalanced with respect to a, radial plane through said axis whereby the centrifugal force acting on the blade due to rotation of the fan produces a movement tending to turn the blade about its axis, and the edges of the throat at its narrowest point being spaced laterally from said stem to permit lateral shifting of the stem upon pivotal movement.

5. A fan or fluid impeller, comprising a hub having around its periphery a series of undercut recesses each forming an enlarged pocket spaced inwardly from the peripheral surface of the hub and opening onto said surface through a restricted throat, the center line of each recess being oblique to the hubs axis of rotation; a plurality of blades each having an enlarged root disposed in one of said sockets with the stem of the blade extending outwardly through the throat, the root and pocket being shaped to provide matching convex and concave surfaces respectively forming a bearing for limited pivotal movement of the blade about an axis substantially parallel to the center line of the recess and the ends of the root being slanted to parallel the respective ends of the recess, the edges of the throat at its narrowest point being spaced laterally from said stem to permit lateral shifting of the stem upon pivotal movement of the root, blade retaining members covering opposite ends of each recess, and a resilient pad between each blade retaining member and the adjacent end of the blade root.

6. A fan or fluid impeller comprising a hub having around its periphery a series of undercut recesses each forming an enlarged pocket spaced inwardly from the peripheral surface of the hub and opening onto said surface through a restricted throat, a plurality of blades each having an integral enlarged root disposed in one of said pockets with the stem of the blade extending outwardly through said throat opening, the edges of the throat being spaced laterally from the blade stem, said pocket having a concave segmentocylindrical face bisected by said throat opening, said integral blade root having a convex segmento-cylindrical face bisected by the blade stem, the bottom of said pocket being spaced below the bottom of the blade root, a resilient compressible member between said bottoms urging said blade outwardly whereby said convex face of the blade root is maintained in engagement with the concave face of said pocket, said convex and concave faces being co-axial of substantially equal radius and forming a bearing for limited pivotal movement of said blade about their common axis and said resilient compressible member being so constructed and arranged as to yieldably resist said pivotal movement in either direction.

7. A device as in claim 6 wherein the axis of said concave and convex bearing surfaces is oblique to the axis of rotation of said hub.

GEORGE A. DEAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 784,431 Rambal Mar. 7, 1905 995,367 Patitz June is, 1911 1,891,948 Rice Dec. 27, 1932 2,125,948 Ocker Aug. 9, 1938 2,317,338 Rydmark Apr. 20, 1943 2,473,899 Murphy June 21, 1949 FOREIGN PATENTS Number Country Date 7,139 Sweden Sept. 5, 1896