Abstract
A novel approach to optimizing control accuracy of pitch angle of the blades of an airplane propeller or wind turbine rotor by using laminated rubber (elastomeric) bearings in place of rolling element bearings so that the former's smooth torque vs. deflection characteristics minimally influence the balance of passive control torques upon the pitch axis due to calibrated springs and forces resulting from rotation speed and/or aerodynamic drag.
Claims
1. A system for control of the angle about the pitch axis of airfoil blades, comprising at least one variable pitch airfoil blade having a blade root and receiving aerodynamic torque about said pitch axis, a hub rotating about a central axis and having blade-retaining means, at least one thrust-receiving elastomeric bearing for each said airfoil blade, a source of torque about said pitch axis upon each said blade derived from torsional spring action, a source of torque about said pitch axis upon each said blade derived from centrifugal force resulting from the speed of said rotation, and said at least one elastomeric bearing is interposed between each said blade root and said retaining means to receive thrust imposed by said blade and to transfer it to said retaining means of said hub while yielding in pitch angle to the net torque imposed by a calibrated combination of said aerodynamic torque and said torsional spring torque and said torque derived from centrifugal force.
2. Claim 2 wherein said system is realized by a constant-speed aircraft propeller.
3. Claim 2 wherein said system is realized by a variable-pitch wind turbine rotor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1 and 3 are typical torque vs. deflection curves for rolling-element and elastomeric bearings, respectively.
[0014] FIG. 2 represents the basic construction and function of an elastomeric thrust bearing.
[0015] FIG. 4 shows the hub of a rotor blade using an elastomeric thrust bearing encircling the spindle and interposed between two radial bearings.
[0016] FIG. 5 shows the hub of a rotor blade using an elastomeric thrust bearing encircling the spindle and emplaced outboard of two radial bearings.
[0017] FIG. 6 shows the hub of a 3-bladed rotor using elastomeric conical bearings encircling each blade spindle and replacing one of two radial bearings.
[0018] FIG. 7 shows the hub of a rotor blade using a small elastomeric thrust bearing enclosed within an end-nut structure extended beyond the spindle and outboard of two radial bearings.
[0019] FIG. 8 shows the hub of a rotor blade using a small elastomeric thrust bearing within a hollow spindle and interposed between two radial bearing
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIGS. 1 and 3 are typical torque vs. deflection curves for rolling-element and elastomeric bearings, respectively. FIG. 1 illustrates the instantaneous change in friction torque experienced by a rolling-element thrust bearing under high load conditions. FIG. 3 instead shows the smooth incremental change in torque experienced by an elastomeric bearing under the same conditions.
[0021] FIG. 2 represents the basic construction and function of an elastomeric thrust bearing 1. Laminated rubber or elastomeric bearings comprise a stack of many thin alternate layers of metal 2 (white) and rubber 3 (black) bonded together to form a solid mass. It may have a central aperture as shown. The bearing yields to partial rotation, which depends upon incremental movements between each of the metal layers via sideways shearing action within the intervening rubber layers. The illustration depicts the partial rotation of the top of the bearing, showing movement of a line that is vertical when drawn upon the bearing at rest. The line remains vertical on the metal layers, but shifts along with the rubber layers; so oscillation about the axis results in a distribution of action between the individual rubber layers. As this occurs, a spring-like proportional opposing force or torque develops, resulting from the rubber shear stress, but frictional resistance is negligible. Obviously, angular motion is limited by the stretch of the rubber in the layers, and continuous rotation is not possible.
[0022] At the same time, this stack of laminations can sustain very high normal forces between its top and bottom surfaces, such as 10,000 psi or more (depicted by the black arrow acting downwards upon the stack and resisted by the surface upon which it rests). But compression is very slight, because the rubber layers are too thin to squeeze out from between the metal layers (as thin as 0.002″, but relatively few are shown, being thicker for clarity).
[0023] The laminations are flat in the illustrated cross-section, but their shape may instead may be truncated conical (as in a lampshade), hemispherical or wrapped into a cylindrical arc. So a laminated bearing can resist thrust, radial, or combined normal forces, depending upon the configuration of its laminate surfaces, while permitting limited lateral or angular movement between its opposed outer loading members.
[0024] FIG. 4 shows a cross-section of the hub 4 of a rotor blade using an elastomeric thrust bearing 1 encircling the spindle 5 and interposed between two radial bearings 6 within a housing 7. The spindle is retained against thrust within the housing by an end nut 8 and the internal ring locknut 9.
[0025] The pitch angular freedom of motion is shown by arrows 10, and the thrust load transmitted between the spindle 5 and the housing 7 is indicated by the heavy arrows pulling apart along the pitch axis 11, while the well-understood means of application of control torques about the pitch axis are not shown (this applies to all the following drawings as well).
[0026] FIG. 5 shows the hub 4 of a rotor blade using an elastomeric thrust bearing 1 encircling the spindle 5 and emplaced outboard of two radial bearings.6. The spindle is retained against thrust within the housing 7 by an end nut 8.
[0027] FIG. 6 shows the central hub 4 and one blade with integral spindle 5 of a 3-bladed propeller, rotatable about an axis perpendicular to the paper, seen as the point 19. It employs elastomeric conical bearings 1, each of which and an associated radial bearing 6 are split into halves (unseen) allowing them to encircle the spindle 5. Another elastomeric thrust bearing 12, small and disk-like, is indicated to be pushed against the end of spindle 5 by a Bellville spring 13 in order to maintain positive pressure upon the conical thrust bearing at all times to keep it properly positioned when at rest while permitting free angular movement.
[0028] FIG. 7 shows the hub 4 with a rotor blade spindle 5 supported within a housing 7 by two radial bearings 6. The spindle is capped by a cylindrical structure 8 that serves as an end-nut on the spindle and extends axially to an end-cap 14 that internally supports a small elastomeric thrust bearing 1. Housing 7 has two diametrically-opposed slots 15 and cylindrical structure 8 has two diametrically-opposed windows 16 that together permit beam 17 to pass transversely through them. Beam 17 serves to transfer the thrust load from the housing 7 through but not touching the windows 16 and impinging upon the thrust bearing 1 through a loading pad 18. The windows 16 are wide enough circumferentially to permit spindle 5 to rotate through the desired range of pitch angles relative to housing 7.
[0029] FIG. 8 shows the hub 4 of a rotor blade with a hollow spindle 5 supported by two radial bearings 6 within housing 7. A small elastomeric thrust bearing 1 is positioned against the internal face of spindle end 14 between the radial bearings. Housing 7 has two diametrically-opposed slots 15 and hollow spindle 5 has diametrically opposed windows 16 that together permit beam 17 (seen end-on) to pass transversely through them (similar to FIG. 7). Beam 17 serves to transfer the thrust load from the housing 7 through but not touching the windows 16 and impinging upon the thrust bearing 1 through a loading pad 18. The windows 16 are wide enough circumferentially to permit spindle 5 to rotate through the desired range of pitch angles relative to housing 7.
[0030] FIGS. 7 and 8 illustrate just two of other possible configurations of structure, using a single beam to transfer thrust from the housing to the small elastomeric bearing. All such configurations would make possible the minimization of the bearing torque introduced into the balance of torques upon the pitch axis, thereby minimizing the effect of any variation of rubber properties upon the calibration of the overall spring effects.
[0031] It will be understood that the embodiments described above are merely exemplary and that persons skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention as defined in the appended claims.
