Pitch Change Bearing System

The present invention relates to a bearing assembly, and more particularly to a pitch change bearing assembly for a helicopter hub.

In a helicopter hub assembly, it is necessary to interconnect the yoke to the hub. Such an interconnection is accomplished utilizing a pitch change bearing assembly to accommodate pitch change motions, blade shear reaction, and cocking motions between the non-feathering portion of the hub, the yoke, and the feathering portion of the hub, the grip. A critical factor in the design of pitch change bearing assemblies is the size of the assembly. If large pitch ranges are required to be accommodated, large bearings are required to handle the shear forces which result in increased size requirements of the yoke and grip. It is therefore desirable that the pitch change bearing assembly have a relatively small envelope to minimize the size of the yoke and grip.

A need has thus arisen for a pitch change bearing assembly for a helicopter hub, to provide pitch change motions, blade shear reactions and cocking motions in a minimum space envelope.

In accordance with the present invention, a pitch change bearing assembly for a helicopter hub having a yoke and a grip is provided. The bearing assembly includes a shaft having first and second ends. A first radial elastomeric bearing is disposed on the first end of the shaft. A second radial elastomeric bearing is disposed on the second end of the shaft. The first and second radial elastomeric bearings are disposed parallel to one another. A third radial elastomeric bearing is disposed on the shaft between and spaced apart from the first and second radial elastomeric bearings and is parallel to the first and second radial elastomeric bearings. Structure is provided for attaching the third radial elastomeric bearing to the grip. Structure is further provided for attaching the first and second radial elastomeric bearings to the yoke.

For a more complete understanding of the present invention and for further advantages thereof, reference is now made to the following Description of the Preferred Embodiments taken in conjunction with the accompanying Drawings in which:

FIG. 1 is an exploded perspective view of a portion of a helicopter hub illustrating the present pitch change bearing assembly; and

FIG. 2 is a cross-sectional view of the present pitch change bearing assembly shown in FIG. 1.

Referring to FIG. 1, an exploded perspective view of a portion of a helicopter hub is illustrated, and is generally identified by the numeral 10. The hub 10 includes a grip 12 and a yoke 14. The present pitch change bearing assembly is disposed between grip 12 and yoke 14, and is identified by the numeral 18. Pitch change bearing assembly 18 comprises an inboard assembly for interconnecting the inboard portion of yoke 14 to grip 12. The present pitch change bearing assembly 18 provides pitch change motions, blade shear reactions, and cocking motions in a minimal space envelope shown as an aperture 20 within yoke 14.

Pitch change bearing assembly 18 includes a shaft 24 on which are mounted a plurality of elastomeric bearing elements to be subsequently described with respect to FIG. 2. Shaft 24 is disposed between an upper housing member 28 and a lower housing member 30. Upper housing member 28 includes a mounting plate 34 for mating with an upper portion 12a of grip 12. Upper housing member 28 is attached to upper portion 12a of grip 12 using bolts 38. Lower housing member 30 includes a mounting plate 42 for mating with a lower portion 12b of grip 12, and is attached to lower portion 12b utilizing bolts 44.

Further disposed circumferentially around shaft 24 is an upper bearing retainer 48 which mates with a lower bearing retainer 50. Upper bearing retainer 48 and lower bearing retainer 50 are disposed within aperture 20 of yoke 14 within a recess 54. Upper bearing retainer 48 and lower bearing retainer 50 once positioned within aperture 20 are interconnected utilizing bolts 56. Aperture 20 may have a diameter of, for example, four inches.

Referring simultaneously to FIGS. 1 and 2, wherein like numerals are utilized for like and corresponding components identified with respect to FIG. 1, shaft 24 includes ends 24a and 24b. Mounted concentrically around end 24a of shaft 24 is a radial elastomeric bearing element 60. Radial elastomeric bearing element 60 engages upper bearing retainer 48 and lower bearing retainer 50. Disposed concentric on shaft 24 and at end 24b of shaft 24 is a second radial elastomeric bearing element 62 which is disposed parallel to radial elastomeric bearing element 60. Radial elastomeric bearing element 62 also engages upper bearing retainer 48 and lower bearing retainer 50.

Centrally disposed on shaft 24 and spaced apart from radial elastomeric bearing elements 60 and 62 is a third radial elastomeric bearing element 66. Radial elastomeric bearing elements 60, 62 and 66 are all disposed parallel to and rectilinear with respect to each other. Disposed concentrically around radial elastomeric bearing element 66 is a spherical elastomeric bearing element 68 which engages upper housing member 28 and lower housing member 30. Elastomeric bearing elements 60, 62, 66 and 68 are composed of a rubber component with distributed metallic transition shims as is well known to those skilled in the art.

In operation of the present pitch change bearing assembly 18, pitch change motions and blade shear reactions are shared between radial elastomeric bearing elements 60, 62 and 66 and spherical elastomeric bearing element 68. Radial elastomeric bearing elements 60, 62, and 66 and spherical elastomeric bearing element 68 share the torsional forces imparted by grip 12 and therefore make it possible to reduce the size of the envelope of the pitch change bearing assembly 18. Torsional forces on pitch change bearing assembly are illustrated by arrow 70. Cocking motion illustrated by arrow 72 is accommodated primarily by spherical elastomeric bearing element 68. Radial elastomeric bearing elements 60 and 62 translate torsional motion and a small amount of axial motion illustrated by arrow 74 between grip 12 and yoke 14. Radial elastomeric bearing elements 60 and 62 react to large radial forces indicated by arrows 76 and are soft in the torsional direction and axial direction. Spherical elastomeric bearing element 68 is soft in the cocking direction and soft in the torsional direction while being stiff in the radial plane. Radial elastomeric bearing element 66 is soft in the axial direction while both spherical elastomeric bearing element 68 and radial elastomeric bearing element 66 are stiff in the radial direction. Rotational motion of grip 12 is transferred to shaft 24 through spherical elastomeric bearing element 68 and radial elastomeric bearing element 66.

Therefore, it can be seen that the present invention provides for a pitch change bearing assembly having a relatively small envelope for accommodating pitch change motions, blade shear reactions and cocking motions between a helicopter hub grip and yoke.

Whereas the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art and it is intended to encompass such changes and modifications as fall within the scope of the appended claims.