US3743987A

US3743987A - Spline for rotary actuator

Info

Publication number: US3743987A
Application number: US00286010A
Authority: US
Inventors: B Yost
Original assignee: Ledex Inc
Current assignee: LUCAS LEDEX Inc
Priority date: 1972-09-05
Filing date: 1972-09-05
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03

Abstract

An improved spline for drivingly connecting the armature of a rotary solenoid actuator to an output shaft driven by the armature comprises needle bearings lodged between confronting flutes of the armature and the driven shaft. The flutes have flat angularly disposed longitudinal walls so as to make line contact with the needle bearings.

Description

United States Patent [1 1 Yost July 3, 1973 [54] SPLINE FOR ROTARY ACTUATOR 3,136,930 6/1964 Straub 335/228 3,320,822 5/1967 Tatom 335/228 X [75] Inventor: Dam", Ohm 3,308,410 3/1967 Biser 335/223 73 A L d I Da ton,Oho sslgnee e ex nc y 1 Primary Examiner-George Harris [22] Fil d; S t, 5, 1972 Attorney-H. Talman Dybvig An improved spline for drivingly connecting the arma- [52] US. Cl. 335/228, 74/89 ture of a rotary solenoid actuator to an output shaft [51] Int. Cl. H0 7/08 d i en by the armature comprises needle bearings [58] Field Of Search 335/228, 272; lodged between confronting flutes of the armature and 3 39 the driven shaft. The flutes have flat angularly disposed longitudinal walls so as to make line contact with the [56] References Cited needle bearings.

UNITED STATES PATENTS 11/1960 Leland et al 74/88 9 Claims, 5 Drawing Figures Bum July 3, 1913 3,743,987

JlE-I 1 SPLINE FOR ROTARY ACTUATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This application relates to rotary solenoid actuators of the type in which an armature is drawn helically toward an electromagnet and, more particularly, to a spline connection between the armature and a shaft driven thereby, the spline connection representing a helical to purely rotary motion converter enabling a driven shaft to derive rotary torque from the armature while not moving axially with the armature.

2. Description of the Prior Art Prior art examples of solenoid devices which enable a helically advancing armature to transmit only its rotational movement to the driven shaft appear in United States Pat. Nos. 2,959,969, 3,320,822 and 3,308,410.

SUMMARY OF THE INVENTION Helical to rotary motion converters known in the prior art have been found wanting in compactness and design simplicity. With the present invention the desired compactness and simplicity is obtained by providing a bore through the solenoid armature in which the driven shaft is received, providing confronting flutes in the interior wall in the bore through the armature and the exterior wall of the shaft, and keying or splining the shaft to the armature by means of elongated needle bearings which allow the armature to move axially on the shaft with a minimum of friction.

DESCRIPTION OF THE DRAWING In the drawing FIG. I is a perspective view of a rotary solenoid actuator embodying the present invention.

FIG. 2 is a side elevation view of the actuator.

FIG. 3 is a fragmentary section view taken substantially along the line 3-3 of FIG. 1.

FIG. 4 is a section view taken substantially along the line 4-4 of FIG. 2.

FIG. 5 is an enlarged, partly fragmented section view taken along the line 5-5 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The rotary solenoid actuator illustrated in the drawing comprises an electromagnet assembly housed in a generally cylindrical ferromagnetic casing 10. As best appears in FIG. 5 the electromagnet assembly comprises a ferromagnetic base plate 12 press fitted into the casing and having an integral upstanding generally cylindrical core member 14. The core member 14 is smaller in diameter than the interior of the casing 10 and the annular space between the casing 10 and the core member 14 is occupied by a solenoid coil 16 having terminal connections 17a and 17b which pass through suitable apertures in the casing 10.

Fitted within a central aperture through the core member 14 is a sleeve bearing 30 journalling a shaft 28. Encircling the shaft 28 is a ferromagnetic armature 18, the armature being attracted to the core member 14 upon energization of the coil 16.

The armature 18 has a cylindrical head 19 which is of a reduced diameter sized to enter an annular plate 20. The head 19 is peened as shown at 21 to fixedly lock the plate to the armature 18. The surface of the plate 20 which confronts the casing 10 has three inclined arcuate recesses 22 stamped into the face thereof. The stamping of the recesses into one face of the plate 20 produces buldges 22a in the opposite face of the plate 20. It can be noted that the recesses 22 are spaced equally about the axis of the shaft 28.

Similarly disposed recesses 25 are stamped into an annular flange 26 integral with and directed inwardly from the casing 10. As shown in FIG. 3, the recesses in the flange 26 are oppositely inclined with respect to the recesses in the plate 20 so that one recess has its deepest end at a clockwise extreme and the other recess has its deepest end at a counterclockwise extreme. Ball elements 24 are interposed between the

recesses

22 and 25, there being one ball element between each pair of confronting recesses.

The arrangement of the ball elements 24 and the

recesses

22 and 25 is such that when the plate 20 is rotated in the clockwise direction as viewed in FIG. I the ball elements 24 roll to the shallow ends of the confronting recesses, and the separation between the armature 18 and the core member 14 approaches a maximum separation. When the plate 20 is rotated oppositely in a counterclockwise direction, the ball elements 24 roll to the deep ends of their respective recesses and the armature 18 makes its closest approach to the core member 14.

The shaft 28 is given a clockwise bias as it appears in FIG. 1 by means of a return spring 46 caged within a circular array of lugs 48 struck outwardly from a caging plate 51 affixed to base plate 12 by any suitable means such as spot welding. The return spring 46 is a spiral spring having its innermost end seated in a suitably located slot, not shown, in the shaft 28 and having a tongue 47 struck outwardly from its outermost convolution for booking engagement to any one of the lugs 48. By proper selection of the lug 48 engaged by the tongue 47 a bias normally sufficient to hold the ball elements 24 in the shallow ends of the

recesses

22 and 25 can be preselected.

As best appears in FIG. 5 the armature 18 is received within the center of the annular flange 26 with a slight clearance. Upon energization of the coil 16 a flux path exists through the core piece 14, across its base plate 12 upwardly through the casing 10, across the flange 26, then across the relatively small clearance separating the flange 26 from the armature 18. The armature l8 seeks to close this flux path by moving axially toward the core piece 14.

It can thus be seen that upon energization of the coil 16 the armature 18 will be attracted toward the pole piece 14 so that the ball elements 24 are compressed between the

recesses

22 and 25 and thereby induced roll to the deeper ends of such recesses. The armature is thus induced to rotate helically toward the pole piece 14 and against the bias of the spring 46. The ball elements acting in the

recesses

22 and 25 can be said, accordingly, to comprise an axial to helical motion conversion means. The primary purpose of the present invention is to so couple the armature 18 to the shaft 28 that only the rotary component of this helical motion is transmitted to the shaft 28.

As appears in FIG. 5 the shaft 28 has a diametrically enlarged collar portion 32 which is larger than the diameter of the shaft, either at its uppermost or lowermost end, and especially regions adjacent thereto. Flutes or indentations 38 which are V-shaped in cross section are milled or broached longitudinally along the length of the collar portion 32, there being four such flutes at equiangular intervals around the axis of the shaft 28. The enlargement of the collar portion 32 compared to the diameter of the shaft 28 at other portions along its length is to accomodate and thereby simplify the milling of the flutes 38.

As best appears in FIG. 4 the armature 18 has an aperture 34 sized to loosely receive the collar portion 32. Four equiangularly spaced V-shaped flutes or indentations 36 are milled or broached into the interior wall of the armature and throughout the axial length of the armature. Needle bearings 4th, which are preferrably a hardened steel, are sized to enter between confronting

flutes

36 and 38 in such fashion that when four needle bearings 40 are inserted, each individually between confronting pairs of

flutes

36 and 38 in the manner shown in FIG. 4, the armature 1% is aligned coaxially with the shaft 28. The bearings 40 have a circumferential interflt with the

flutes

36 and 38 which prevents relative rotation between the armature and the shaft, but are not axially confined by the flutes.

Those skilled in the art will recognize that the circumferential interfit can be achieved with only two diametrically disposed needle bearings or could be achieved with three or more needle bearings disposed at equiangulai positions. However, since it is normally an easier matter to mill or broach diametrically opposite sides of a work piece, and since the tolerance to which the

flutes

36 and 38 must be formed can be reduced by increasing the number of flutes, the preferred embodiment employs four needle bearings 40 and accomodating flutes as shown in FIG. 4. The needle bearings are retained axially adjacent the armature 18 by means of an annular spacer 42 surrounding the shaft 28 in the air gap between the armature and the core piece 14 and a cooperating annular spacer 44 located above the armature 18. The spacer 44 is confined by a split spring ring 54 seated in an annular groove 55 located in the collar portion 32 of the shaft 28.

in the preferred practice of this invention the axial length of the needle bearings 4th is only slightly less than the axial space available between the

spacers

42 and 44. This assures that the armature 18 will receive substantially full bearing support from the needle bearings 4th, not only in its uppermost position as shown in FIG. but also in its lowermost position after the armature 18 has advanced downwardly toward the pole piece K4. With such construction the primary sliding motion occurring during operation of the solenoid is a sliding motion of the armature 18 on the needle bearings M which remain relatively stationary. Since the needle bearings make only line contact with the side walls of the flutes 36 in the armature, sliding friction is nominal and the likelihood of seizure between any of the bearings and its confining flutes 36 is virtually nonexistant.

Axial travel of the shaft 28 is relative to the core piece M is precluded by the spacer 42, which abuts the shoulder portion 52 in the air gap region, acting in cooperation with a spacer 50 encircling the shaft 28 adjacent the return spring 46. The bottom end of the shaft 28 is swaged to form a shoulder 52 on the shaft 28 which retains the spacer 50.

it can be noted in FIG. 5 that the length of the shaft 28 between the collar portion 32 and the shoulder 52 is occupied entirely by the spacer 42, the core piece 114 and its integral base plate 12, the return spring 46 and its adjacent spacer 50. The return spring 46 is therefore a part of the structure which supports the shaft 28 against axial movement relative to the core piece 114. The security with which the shaft 28 is supported against axial movement is thus dependent upon the ability of the spring 46 to resist collapse in the event the shaft 28 is subjected to axial loading. While the axial loading on the shaft 28 may at first appear nominal because the needle bearings W allow the armature 18 to slide axially on the shaft 28, the axial loads to which the shaft is subjected cannot be entirely ignored. it is true, of course, that when the coil 16 is energized to move the armature l8 downwardly as it appears in FIG. 5,

' and axial loading on the shaft 28 will be small because the armature l8 slides freely on the needle bearings 40. However, when the coil 16 has been deenergized and the spring 46 operates to return the armature by an opposite rotation of the armature 118, the armature 18 is accelerated upwardly as it appears in FIG. 5 and the resultant upward momentum of the armature must be absorbed in part by an impact with the split ring 54. The force of this impact must be ultimately absorbed by an impact of the spacer 50 against the return spring 46. it is found, however, that the upward momentum generated in the armature lb during the return stroke is not great enough to adversely effect the very spring which generated the momentum.

in some applications for the rotary solenoid it is required that the shaft 28 have an extension, not shown, passing centrally through the return spring 46 for engagement with a load device located below the spring 46. in such cases it is found desirable that a second split spring ring, not shown, be engaged to a suitably located annular groove, not shown, in the shaft 28, the second split ring being located between the return spring 46 and the base plate 12. When the second split ring is employed, it cooperates with the spacer 42 to secure the shaft 28 against axial motion relative to the core piece 14, thus allowing elimination of the spacer 50 and the shoulder 52, and extension of the shaft 28 downwardly beyond the return spring 46.

Although a preferred embodiment of the invention has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportions, and the arrangement of parts without departing from the scope of the present invention as more particularly expressed in the following claims.

Having thus described my invention, 1 claim:

1. in a rotary actuator device comprising an electromagnet assembly rotatably supporting a shaft, an armature having a bore receiving said shaft and movable axially along said shaft in response to energization of said electromagnet assembly, axial to helical motion conversion means coacting between said electromagnet assembly and said armature to rotate said armature helically along the axis of said shaft, and helical to rotary motion conversion means coacting between said armature and said shaft to rotate, without axially moving, said shaft, the improvement wherein said helical to rotary motion conversion means comprises a plurality of first indentations in said shaft circumferentially spaced about the axis of said shaft, an equal number of second indentations in the interior wall of said bore, each of said first indentations confronting a second indentation, a plurality of bearing members, there being a one piece bearing member circumferentially interfitting each first indentation and its confronting second indentation, one of the first and second indentations interfitted by each bearing member being an axially extending flute to allow relative axial movement of its interfitting bearing member, and means coacting between said electromagnet assembly and said shaft to support said shaft against axial motion relative to said electromagnet assembly.

2. The rotary actuator device of claim 1 in which the other of the first and second indentations interfitted by each bearing member is also an axially extending flute and said bearing members are needle bearings.

3. The rotary actuator device of claim 2 in which said bore has a generally cylindrical wall and said second indentations are flutes in said wall extending axially throughout the length of said wall.

4. The rotary actuator device of claim 2 in which said flutes are V-shaped in cross section and have line contact with said needle bearings.

5. The rotary actuator device of claim 1 in which said equal number is four.

6. The rotary actuator device of claim 1 in which said shaft has an axially extending collar portion larger in diameter than portions of said shaft adjacent thereto,

and in which said first indentations are flutes axially traversing said collar portion.

7. A spline assembly to nonrotatably couple a shaft with a member movable axially along said shaft, said member having a bore therethrough, said shaft having a radially enlarged collar portion received in said bore, said collar portion having diametrically disposed axially extending flutes traversing the axial length thereof, said bore having diametrically disposed axially extending flutes traversing the length thereof, the flutes of said collar portion confronting the flutes of said bore, and elongated needle bearings interposed between said confronting flutes and circumferentially interfitting said flutes.

8. The spline assembly of claim 7 in which the diametrically disposed flutes in each of said collar portion and said bore comprise two pairs, said flutes in each of said collar portion and said bore disposed at equiangular positions about the axis of said shaft.

9. The spline assembly of claim 7 in which said flutes each have a V-shaped cross section in planes perpendicular to the axis of said shaft.

Claims

5. The rotary actuator device of claim 1 in which said equal number is four.

6. The rotary actuator device of claim 1 in which said shaft has an axially extending collar portion larger in diameter than portions of said shaft adjacent thereto, and in which said first indentations are flutes axially traversing said collar portion.