WO2007136367A1

WO2007136367A1 - Low friction ball separator for propeller blade ball bearings

Info

Publication number: WO2007136367A1
Application number: PCT/US2006/019437
Authority: WO
Inventors: Paul A. Carvalho; Aaron T. Nardi; Robert W. Pruden; Noah M. Toth
Original assignee: Hamilton Sundstrand
Priority date: 2006-05-18
Filing date: 2006-05-18
Publication date: 2007-11-29
Also published as: GB0815240D0; GB2448649B; GB2448649A; DE112006003836T5

Abstract

A ball separator is utilized to mount and insert a plurality of ball bearings into mating grooves in a propeller hub and propeller blade. The ball separator has a link portion connecting a plurality of pockets. The pockets support spaced ones of said ball bearings. The pockets have a surface that includes at least two distinct surface portions. A central surface portion closely matches an outer periphery of the ball bearing, while a second portion formed around the first portion is spaced by a slightly greater amount. The second portion is not in contact with the ball bearing, and thus friction is reduced and clearance is provided for circulation of oil. On the other hand, the second portion does provide support to hold the ball bearing within the ball separator when the ball separator is being inserted or removed into the grooves. In addition, a material is developed for forming the ball separator with the material minimizing stick-slip problems. The material is a Nylon 6/6 filled by PTFE and a fluorinated lubricating oil to a total combined additive level of between 6 and 12% by weight.

Description

LOW FRICTION BALL SEPARATOR FOR PROPELLER BLADE BALL BEARINGS

BACKGROUND OF THE INVENTION This application relates to an improved ball separator for mounting ball bearing within hub grooves in a propeller hub that mounts a propeller blade. The pockets within the ball separator are formed on at least two radii, such that one surface is in contact with the ball bearings, and another surface_. is closely spaced from the ball bearings. Propeller hubs include a plurality of openings which each receive a propeller blade. A typical way of mounting a blade within the hub is the use of a row of ball bearings mounted into mating grooves in the hub and the blade. Typically, an opening in the hub allows the passage of the ball bearings into the mating grooves. The blade is then locked in place with some form of lock or support ring. One type of such assembly known in the art utilizes a length of ball separator material, sometimes called a necklace, to separate and mount a plurality of ball bearings. The ball bearings can then be inserted into the groove through the opening in the hub, and as a row with the length of the ball separator. The ball separator includes links connecting adjacent ball separator pockets. The balls sit between these pockets. The ball separators in the prior art have had pockets that closely match the ball bearing's outer surface across the entire portion of the ball separator.

One problem experienced with this structure, is that when the ball separator length is mounted into the groove and through the opening, it is bent into a reverse curve. In early ball separators, the balls would sometimes fall out in this orientation. Thus, current ball separators have pockets of a shape that closely matches the shape of a ball over a relatively large angular range.

This raises some undesirable results. First, the friction between the ball separators and the ball is relatively high since it is over such a large area. Also, since the pockets closely match the outer periphery of the ball bearing, it is difficult for lubricating oil to reach the area between the ball bearings and the ball separator pockets. The material utilized to make the prior art ball separators has some undesirable characteristics. The prior art was formed of a Nylon 616 with 0.5 - 6.5% Molybdenum

Disulfide. This additive and material combination may have resulted in some undesirable stick-slip occurrence. One example of the prior art material is available under the trade name Nylatron GS .

SUMMARY QF THE INVENTION

In a disclosed embodiment of this invention, the pockets within a ball separator are formed to have at least two surfaces. A first, more central surface is closely matched to the outer periphery of the ball bearing, and provides guidance and support for the ball bearing. A second surface, which, in a disclosed embodiment, surrounds the first surface, is spaced slightly from the ball bearing. This second surface will prevent the ball bearing from falling outwardly of the ball separator or necklace when it is moved into the grooves (i.e., in the reverse curvature orientation). Still, the spaced surface will not provide the high friction experienced in the prior art, and will further provide clearance for circulation of lubricating oil.

In disclosed embodiments of this invention, the pocket has two surfaces, with the more closely matched surface being on a radii of .6915", and the more spaced surface being at a radii of .7115". That is, the amount of clearance is on the order of .02". The relatively small additional clearance provides benefits in reducing friction and improving oil circulation. Of course, other clearances would still come within the scope of this invention. The clearance is preferably sufficient to provide the benefit mentioned above, while still small enough that it can provide the ball retention feature. Also, in a disclosed embodiment, a material developed for use in this application provides benefits. In particular, the material is a Nylon 6/6 filled by PTFE and a fluorinated lubricating oil.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial view of a propeller hub and blade. Figure 2 shows an assembly step in mounting the blade within the hub. Figure 3 shows another view of the assembly step. Figure 4 is a view of a ball separator according to the present invention.

Figure 5 is a view of one portion of the ball separator of the present invention. Figure 6 is a side view of one portion of the ball separator of the present invention.

Figure 7 is a view of the entire ball separator of the present invention. Figure 8 shows another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A propeller mount system 20 is illustrated in Figure 1. As known, a hub 22 has an opening 23 to receive a blade 24. As known, the hub 22 will actually rotate about an axis generally perpendicular to a central axis of the blade 24. A plurality of the blades 24 are mounted to the hub 22, and spaced circumferentially about the axis of rotation A. It should be understood the axis of rotation A is actually spaced further from the blade 24 than is illustrated. It is included in Figure 1 simply for orientation.

A support ring 25 locks the blade 24 to the hub 22. As shown, grooves 26 and 30 in the hub 22 mate with grooves 28 and 32 in the blade 24, and receive ball bearings 34. The ball bearings 34 support and lock the blade 24 within the blade 22.

As shown in Figure 2, openings 38 within the hub 22 allow the ball bearings to be moved as an assembled row 40 into the grooves 30-32 and 26-28. The balls 34 include a ball separator 42 that mounts all of the balls as a single element, sometimes called a necklace.

As shown in Figure 3, when the necklace 40 is moved into the opening 38, it sometimes must bend into a reverse curve orientation. This orientation could cause the balls 34 to leave the separator 42, unless the separator had supported surfaces which extend over a relatively large angle. As mentioned in the prior art, this relatively large support surface resulted in undesirably high friction. Figure 4 shows a portion of the inventive ball separator 42 and necklace 40.

As shown, a connecting link 43 connects pockets 44. The balls 34 are mounted between the pockets 44. It is these pockets 44 that have to extend over a relatively great angular range to prevent the balls from leaving the ball separator 42 when in the reverse angle orientation.

Figure 5 shows two pockets 44 receiving a ball 34. As shown, a first surface 46 is closely in contact with the outer surface of the ball 34. A second surface 48 is spaced by a slightly smaller distance from the ball 34. This greater distance is small, and on the order of .02" in one embodiment. In the above-mentioned embodiment, the diameter of the ball bearing is

.6875". The diameter of the first surface of the pocket is .6915" and the diameter of the loose-fitting second surface of the pocket is .7115". Thus, the step between the two surfaces is .02" as mentioned above. The second surface diameter is approximately 3.5% larger than the ball bearing. There is a maximum limit to how much larger the second surface can be relative to the ball bearing, while still providing the retention function. The exact dimension will vary with the geometry of the hub, the size of the ball, etc. In general, it is believed that the second surface of the pocket should not be at a diameter that is more than 10% larger than the diameter of the ball bearing. The greater spacing of the surface 48 provides clearance that allows lubricating oil to reach the surfaces of the ball 34 and the pockets 44. Further, by spacing surface 48 further from the ball 34, the amount of friction between the ball 34 and the pockets 44 is decreased. On the other hand, the angular range of the entire surface for preventing the ball from leaving the separator 42 when in a reverse orientation is still provided.

Figure 6 show a connecting link 43, and an interior surface of a portion 44. As shown, a closely spaced portion 46 may be generally circular, and at a central portion of the pocket 44 while the surface 48 is formed around this portion 46.

Figure 7 shows the entire ball separator 42. Two ends 100 will typically abut when the entire ball separator 42 is mounted within a propeller hub. The present invention preferably utilizes a plastic to form the ball separator.

In one embodiment, Nylon 6/6 (polyiminoadipoyl-iminohexamethylene) filled by

PTFE (polytetrafluoroethylene) and a fluorinated lubricating oil, such as perfluoropolyether oils or Fluoroguard®, to a total combined additive level of 6-12% by weight was used. Of course, other materials can be utilized.

The particular material is found to have valuable benefits in this application. The previously used materials provided good friction properties, but have had some stick-slip problems. The present invention, utilizing a Nylon 6/6 material filled by PTFE and a fluorinated lubricating oil provides a material with minimal stick-slip problems, while still retaining the preferred Nylon 6/6 base polymer. Thus, the present invention provides a product that has a good compressive strength, flexibility and creep resistance, while still minimizing the cost. In general, it would be desirable to utilize more PTFE, however these materials are quite expensive.

Another embodiment is illustrated in Figure 8. Here, a ball separator pocket 150 is illustrated having a loose surface 152 and a closer-fitting surface 154. The closer-fitting surface 154 can be made entirely of a PTFE insert, while the remainder of the pocket can be formed of Nylon 6/6.

Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

CLAIMSWe claim:

1. A propeller comprising: a propeller hub having at least one opening, and a blade received within said at least one opening; said hub having at least one groove, and said blade having at least one groove mating with said groove of said hub, and a plurality of ball bearings mounted within said mating grooves of said hub and said blade, a ball separator mounting said plurality of ball bearings, said ball separator having connecting links and a plurality of pockets mounted between adjacent ones of said ball bearings, said pockets having a surface for supporting said ball bearings, said surface having at least two areas spaced from a center point of an associated one of said ball bearings by different distances, with a first portion being spaced to be in close contact with said ball bearing, and a second portion spaced further from said center point.

2. The propeller as set forth in claim 1, wherein said pockets are formed of a Nylon 6/6 polymer filled by PTFE, and a fluorinated lubricating oil.

3. The propeller as set forth in claim 2, wherein the total combined additive level is between 6 - 12% by weight.

4. The propeller as set forth in claim 1, wherein said second portion being formed around said first portion.

5. The propeller as set forth in claim 1, wherein said first portion and said second portion are generally circular.

6. The propeller as set forth in claim 1, wherein said ball bearings have a diameter, and said second portion being spaced from said center point by a diameter, with the diameter of said second portion being no more than 110% of the diameter of said ball bearing.

7. The propeller as set forth in claim 1, wherein said first portion is formed of a distinct material than said second portion.

8. A necklace for use in a propeller hub and blade mount system comprising: a ball separator mounting a plurality of ball bearings, said ball separator having connecting links and a plurality of pockets mounted between adjacent ones of said ball bearings, said pockets having a surface for supporting said ball bearings, said surface having at least two areas spaced from a center point of an associated one of said ball bearings by different distances, with a first portion being spaced to be in close contact with said ball bearing, and a second portion spaced further from said center point.

9. The necklace as set forth in claim 1, wherein said pockets are formed of a Nylon 6/6 polymer filled by PTFE, and a fluorinated lubricating oil.

10. The necklace as set forth in claim 2, wherein the total combined additive level is between 6 - 12% by weight.

11. The necklace as set forth in claim 8, wherein said second portion being formed around said first portion.

12. The necklace as set forth in claim 8, wherein said first portion is generally circular, and said second portion is generally circular.

13. The necklace as set forth in claim 8, wherein said ball bearings have a diameter, and said second portion being spaced from said center point by a diameter, with the diameter of said second portion being no more than 110% of the diameter of said ball bearing.

14. The propeller as set forth in claim 8, wherein said first portion is formed of a distinct material than said second portion.

15. A necklace for use in a propeller hub and blade mount system comprising: a ball separator mounting a plurality of ball bearings, said ball separator having connecting links and a plurality of pockets mounted between adjacent ones of said ball bearings, said pockets having a surface for supporting said ball bearings; and said ball separator having at least a portion formed of Nylon 616 filled by PTFE, and a fluorinated lubricating oil, with a total combined additive level of 6 - 12% by weight.