US20080256790A1

US20080256790A1 - Rod end assembly

Info

Publication number: US20080256790A1
Application number: US11/788,117
Authority: US
Inventors: John Cowles; Arthur Gay; Jay Phoenix
Original assignee: Roller Bearing Company of America Inc
Current assignee: Roller Bearing Company of America Inc
Priority date: 2007-04-18
Filing date: 2007-04-18
Publication date: 2008-10-23

Abstract

A rod end assembly includes a rod having a shank thereon, the shank comprising an intermediate journal portion and a threaded end portion. There are one or more roller bearings mounted on the journal portion of the shank. The bearings each have an inner ring and an outer ring, and include an endmost bearing. A nut is mounted on the threaded portion of the shank to engage the endmost bearing. There is a rod end body secured to the rod end. The rod end body has a mounting portion that is configured to rest on the roller bearings and to engage the outer ring of the endmost bearing. In addition, the rod end body has a coupling portion for connecting to another device.

Description

FIELD OF THE INVENTION

This invention relates to rod end assemblies, and in particular, to a rod end assembly that includes a bearing mounted onto one end of a rod.

BACKGROUND

A rod end assembly is mounted on the end of a rod to facilitate connecting the rod to another device. An illustrative use for a rod end assembly is on a ball screw assembly, which is a device for translating rotational motion of a first member to linear motion in a second member. A typical ball screw assembly comprises two members: one member comprises a threaded rod having a spiral raceway for ball rollers in a nut, and the other member is a nut that encircles the rod and encloses the ball rollers. A rod end assembly on the end of the threaded rod is useful for connecting the rod to a device that will drive the ball screw assembly by rotating the rod, or that will be moved by the ball screw assembly in response to rotation of the nut. Prior art rod end assemblies have inefficient designs that require excessive numbers of parts; that entail inefficient assembly procedures; that have low moment load carrying capability and that have limited useful life.
It is a general object of this invention to provide an apparatus that improves upon, or overcomes the problems and drawbacks of, prior art rod end assemblies.

SUMMARY OF THE INVENTION

The present invention resides in one aspect in a rod end assembly comprising a rod having a rod end with a shank thereon. The shank comprises an intermediate journal portion and a threaded end portion. There are one or more roller bearings mounted on the shank, including an endmost bearing. Each bearing comprises an inner ring and an outer ring. A bearing retainer nut is mounted on the threaded end portion of the shank and engages the inner ring of the endmost bearing. There is a rod end body secured to the rod end. The rod end body comprises a mounting portion that is configured to rest on the roller bearings. The mounting portion comprises an internal shoulder to engage the outer ring of the endmost bearing. In addition, the rod end body has a coupling portion for connecting to another device.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a ball screw assembly for use with a rod end assembly as described herein;

FIG. 2 is a schematic cross-sectional view of a rod end assembly on the rod of the ball screw assembly of FIG. 1;

FIG. 3 is an elevation view of the rod end assembly of FIG. 2, taken along line A-A; and

FIG. 4 is an exploded view of the rod end assembly of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

A ball screw assembly 10 is shown in FIG. 1. The ball screw assembly 10 comprises a threaded rod 12 on which a ball screw nut 13 is rotatably mounted in a conventional manner. Rod 12 comprises a shank 14 that extends axially from one end of the rod. The shank 14 is configured to receive a rod end assembly as described herein. Shank 14 has an intermediate journal portion 14 a for carrying a bearing assembly and a threaded end portion 14 b for carrying a lock nut. A rod shoulder 14 c is provided adjacent to the journal portion of the shank 14.
An illustrative embodiment of a rod end assembly according to this invention is shown on the shank 14 of the rod 12, in FIG. 2. Rod end assembly 20 comprises a duplex pair of angular contact ball bearings 22, 24 mounted on the intermediate journal portion of the shank 14. The bearings 22, 24 each comprise an inner ring that engages the shank 14, and an outer ring. Optionally, the bearings 22, 24 are thrust bearings disposed in a face-to-face arrangement to each other. The axes of the contact angles of the bearings, indicated in FIG. 2 by axis lines through the ball rollers, converging towards each other as the distance from shank 14 increases. A bearing retainer nut 26 and optional washer 40 are mounted on the threaded end portion 14 b of the shank 14. The bearing retainer nut 26 and washer 40 are configured to laterally engage the inner ring of the endmost bearing on the shank, i.e., the bearing closest to the end of the shank (illustrated as bearing 24). The inner ring of the inner-most bearing (bearing 22) bears laterally against rod shoulder 14 c. An outer retaining nut 34 that has external threads is mounted on rod 12 and may be positioned to laterally engage the outer ring of the inner-most bearing.
Rod end assembly 20 further comprises a rod end body 28 having a mounting portion 30 (FIG. 3) and a coupling portion 32. The mounting portion 30 is configured to encompass the end of the rod, including the shank 14 and the bearings 22, 24, and to rest on the outer rings of the bearings. In addition, the rod end body 28 has an internal shoulder 30 a that is configured to laterally engage the outer ring of the outermost bearing. Mounting portion 30 also has an internally threaded surface that is configured to engage the external threads on outer nut 34.
The coupling portion 32 may be configured in any way suitable to facilitate connecting the rod 12 to another device that drives, or that is driven by, the ball screw assembly. In the illustrated embodiment, the coupling portion 32 of the rod end body 28 comprises a lug with a mounting hole where an optional spherical plain bearing 38 may be mounted.
By screwing the bearing retainer nut 26 onto shank 14 and screwing outer nut 34 into rod end body 28, the bearings 22, 24 can be pre-loaded prior to use.
The rod end body 28 has a grease fitting 36 therein, shown in FIG. 3, to facilitate providing grease to the interior of the rod end assembly 20 once it is mounted on the rod 12.
The ball screw assembly 10 and rod end assembly 20 are designed so that linear actuation of the device attached to the rod end assembly 20 through the spherical bearing 28 can be accomplished in either of two ways: the ball screw nut 13 can be rotated while the ball screw rod 12 is fixed rotationally, or the free end of the ball screw rod 12 can be rotated while the ball screw nut 13 is fixed rotationally. Alternatively, the device can drive the ball screw assembly 10 by rotating the rod 12.
Referring to FIG. 4, the rod end assembly 20 may be assembled by inserting the rod 12 through the outer nut 34. Then, the bearings 22, 24 are mounted on the shank 14 so that the larger cross section outer ring faces are mated together, as shown in FIGS. 2 and 4. An optional washer 40 is placed on the shank over the bearings, the washer 40 being sized to engage only the inner ring of the endmost bearing. Then the bearing retainer nut 26 is screwed down onto the shank to a known preload based on assembly maximum loading. The bearing retainer nut 26 is optionally pre-coated to provide a permanent connection that will not loosen under vibration. Methods of connection include, but are not limited to, the application of thread locking compounds of liquid or solid composition. The rod end body 28 is then slid over the angular contact bearing set and the outer nut 34 is threaded into the rod end body to a torque that is dependent on the expected maximum load applied to the assembly. The outer nut 34 can be locked in place either mechanically or through the use of thread locking compounds of either liquid or solid composition.
Rod end assembly 20 features several advantages over prior art devices. For example, the bearings in the rod end assembly 20 include two angular contact bearings, mounted in a face-to-face orientation, to maximize moment load carrying capability. The intermediate journal portion of the shank preferably provides a slip-fit interface with the duplex pair of bearings in portion 14 a. This interface gives the rod end body 28 a more accurate connection to the ball screw assembly 10, makes the assembly process much easier, and allows much better control of bearing preload which is based on the overall loading the bearings are expected to see in service.
Furthermore, the axial faces of the bearing outer rings are precision ground so that when the bearings are assembled together there is a known gap which applies an optimal, controlled preload to the bearing balls. This controlled preload removes axial play, allows the bearings to function in a high vibration loading situation, and ultimately increases the life of the bearing. The bearing preload is applied with a separate nut and washer that are attached to the threaded end of the ball screw assembly, adjacent to the ground surface supporting the bearings (e.g., nut 26 and washer 40).
In addition, the rod end assembly 20 incorporates a grease fitting to allow greasing of the bearings in service, without disassembling the product. This allows increased maintenance intervals which decreases machine down time due to disassembly, inspection, and lubrication of the bearings.
In an optional embodiment, the spherical plain bearing 38 is staked in place rather than using a large interference fit. This procedure results in an acceptable bearing push out force (the force which, when applied to the bearing while the bearing is mounted in the coupling portion of the rod end body, will cause the bearing to be dislodged from the rod end body) in the while reducing tensile stresses in the region of the rod-end “eye” (or perforation) and the initial break-in torque levels for the spherical bearing.
By changing the bearing type used in the rod-end, the outer diameter of the rod-end was decreased by 13% relative to the comparative device.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. In addition, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
Although the invention has been described with reference to particular embodiments thereof, it will be understood by one of ordinary skill in the art, upon a reading and understanding of the foregoing disclosure, that numerous variations and alterations to the disclosed embodiments will fall within the spirit and scope of this invention and of the appended claims.

Claims

1. A rod end assembly comprising:

a rod comprising a rod end having a shank thereon, the shank comprising an intermediate journal portion and a threaded end portion;

one or more roller bearings mounted on the shank, including an endmost bearing, the one or more roller bearings each comprising an inner ring and an outer ring, and;

a bearing retainer nut that is mounted on the threaded portion of the shank and that engages the inner ring of the endmost bearing;

a rod end body secured to the rod end, the rod end body comprising a mounting portion that is configured to rest on the roller bearings, and comprising an internal shoulder to engage the outer ring of the endmost bearing;

the rod end body further having a coupling portion for connecting to another device.

2. The assembly of claim 1, comprising two angular contact ball bearings on the shank.

3. The assembly of claim 2, wherein the two angular contact ball bearings are in a face-to-face arrangement.

4. The assembly of claim 1, comprising a bearing mounted in the coupling portion.

5. The assembly of claim 1, further comprising an outer nut on the rod, wherein the rod end body is threaded onto the outer nut.

6. The assembly of claim 1, wherein the rod is part of a ball screw assembly, the ball screw assembly further comprising a ball screw nut on the rod.