US3602615A

US3602615A - Actuator with improved tooth profile

Info

Publication number: US3602615A
Application number: US13544A
Authority: US
Inventors: Louis R Erwin
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1970-02-24
Filing date: 1970-02-24
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31
Also published as: DE2108762B2; GB1340018A; CA919456A; DE2108762C3; DE2108762A1

Abstract

An actuator of a type which includes a stationary member having a plurality of gear tooth cavities arranged in an approximately circular formation about an axis, an output gear arranged in a coaxial relation with the stationary member axis, a free floating ring gear having a pitch center of internal teeth which is spaced a predetermined distance from said axis, the ring gear having its internal teeth arranged in an engaged driving relation with the output gear and having a plurality of external teeth corresponding in number to the number of cavities in the stationary member wherein the ring gear teeth and the gear tooth cavities in the stationary member are of arcuate shape to thereby provide the actuator with rotation constraint of the ring gear such that uniform rotation of the ring gear internal teeth pitch circle center about the output gear center will result in uniform rotation of the output gear. A form of the actuator is also disclosed in which the arcuate teeth are on the stationary member and the gear tooth cavities are in the ring gear.

Description

United States Patent [72] Inventor Louis R. Erwin Livonia, Mich. [21] Appl. No. 13,544 [22] Filed Feb. 24, 1970 [45] Patented Aug. 31, 1971 [73] Assignee The Bendix Corporation [54] ACTUATOR WITH IMPROVED TOOTH PROFILE 6 Claims, 5 Drawing Figs.

[52] US. Cl 418/61, 74/804 [51] Int. CL F01c 1/02 [50] FieldoiSearch 418/61; 74/804 [56] References Cited UNITED STATES PATENTS 457,295 8/1891 Tilden 418/61 3,217,566 11/1965 Sanson 74/804 3,391,608 7/1968 Huber 418/61 X 3,443,378 5/1969 Monroe et a]. 418/61 X 3,490,383 l/l970 Parrett 418/61 6/ 1970 Boyadjiefi et al 418/61 Primary Examiner-Carlton R. Croyle Assistant ExaminerWilbur J. Goodlin Attorneys-Olsen & Stephenson, William F. Thornton and Flame, Hartz, Smith and Thompson ABSTRACT: An actuator of a type which includes a stationar'y member having a plurality of gear tooth cavities arrangedin an approximately circular formation about an axis, an output gear arranged in a coaxial relation with the stationary member axis, a free floating ring gear having a pitch center of internal teeth which is spaced a predetermined distance from said axis, the ring gear having its internal teeth arranged in an engaged driving relation with the output gear and having a plurality of external teeth corresponding in number to the number of cavities in the stationary member wherein the ring gear teeth and the gear tooth cavities in the stationary member are of arcuate shape to thereby provide the actuator with rotation constraint of the ring gear such that uniform rotation of the ring gear internal teeth pitch circle center about the output gear center will result in uniform rotation of the output gear. A form of the actuator is also disclosed in which the arcuate teeth are on the stationary member and the gear tooth cavities are in the ring gear.

PATENTEU M531 l97l SHEET 1 UF 2 INVENTOR LOUIS R. ERWIN BY w) M ATTORNEYS PATENTED A0931 IS?! SHEET 2 0F 2 ENTOR LOUIS R.

ATTORNEYS ACTUATOR WITH IMPROVED'TOOTH CROSS .RE'FERENCE 'TO COBENDING APPLICATIONS The actuator of this invention is an improvement-on the actuators shown in copending application .Ser. No. 667,459 filed Sept. 13, 1967 and application Ser. No. 678,951 filed -ct."3"0, 1967, now Pat. No. 3,516,765 owned by the assignee of this application.

SUMMARY OF THE INVENTION This invention relates generally to .an actuator of the general type described in the aforementioned copending patent applications in which a free floating eccentric ring gear is moved in an orbital path by a rotating force so that it coacts with a stationary member and an output member to drive the output member. in particular, this invention relates to an actuator of this type in which there is a 1:1 gear ratio relationship between the stationary member and the ring gear. When the ring gear external teeth are of the conventional involute shape in this general type of actuator, ratios other than 1:1 can be designed with resulting well defined contact ratios. Contact ratio is the ratio of the arc of action to the circular pitch. The are of action is the arc of the pitch circle through which a tooth travels from the time it first makes contact with a mating tooth until contact with the mating tooth is discontinued. In the 1:1 ratio case, the contact ratio computed by the involute formulas becomes undefined and it can be shown that motion of the ring gear center about the output gear center without ring gear rotation is not accompanied by continuous contact with the stationary member. Since contact with the stationary member is required to provide a reaction point for the ring gear, motion in the 1:1 ratio case cannot be simple circular motion of the ring gear center about the output gear center but must necessarily involve ring gear rotational movement. This rotational movement is undesirable as it causes nonuniform output gear torque and speed, even if the torque on the ring is completely uniform. Also, due to the very complex ring gear motion, tooth loads and contact point sliding velocities are very difficult to compute, which leads to difiiculty with design for adequate wear. This invention constrains ring gearrotation about the internal teeth pitch circle center while allowing that center to move around the output gear center,

According to one form of this invention, the teeth on the ting gear, and the corresponding tooth cavities formed in the stationary member, are formed with arcuate surfaces which provide for a continuous contact of a gear tooth on the ring gear with the adjacent wall of the stationary member and for a smooth transfer of contact with the stationary member from one ring gear tooth to the next. Each tooth on the ring gear which meshes with the stationary member is shaped so that it has a terminal end, a base line, and a pair of side surfaces extending from the base line to the terminal end, with each of the side surfaces being of a generally arcuate shape. When one of the ring gear teeth is positioned symmetrically within a tooth cavity in the stationary member, the cavity sidewalls which are also arcuate, are shaped so that the spacing between each cavity sidewall and the adjacent'tooth sidewall'progres-' sively decreases in a direction toward the tooth end. The axis of revolution for each arcuate tooth sidewall is positioned between the tooth baseline and the tooth'end and is spaced from the baseline a distance corresponding substantially to the spacing between the center of the pitch circle of the internal teeth of the ring gear and the axis of the output gear. The axis of revolution of each tooth cavity sidewall is located substantially on the tooth base line when the tooth is positioned symmetrically within the cavity.

This particular tooth construction provides for continuous contact of a tooth with a cavity sidewall when the ring gear is in a positions to make that tooth the working tooth. When the ring gear has orbited to a position in which the next successive tooth is the working tooth, there is a smooth transfer of contact from the first working tooth to the second since the teeth fcanlbe designed to maintain contact for an arc of ring gear inthe working-arcs of the individual teeth so that the second tooth actually starts its working are (effective contact are) before the first working tooth loses contact. This results in a smooth transfer of contact from each tooth to the next tooth.

The result is a regular motion of the output gear with simply defined contactpoint loads and sliding velocities relative to ring gear center velocity and the torque bei n'g 'carried. This allows systematic design for desired life. In another form of the invention, the same desirable results are obtained by forming the arcuate teeth :on the stationary member and forming the cavities therefore in the ring gear.

Further objects, features and advantages of this invention will become apparent from a consideration of the following description, the appended claims, and the accompanying drawings in which:

FIG. 1 is :a sectional view of an actuator constructed according to this invention;

FIG. 2 is a sectional view of the actuator shown in FIG. 1 as seen from substantially the line 2-2 in F IG. 1;

FIG. 3 isa diagrammatic illustration of one of the gear teeth in the actuator shown in FIG. 2 and shaped according to this invention;

FIG. 4 is a sectional view, like FIG. 2, of a modified form of the actuator of this invention; and

FIG. 5 is a diagrammatic view, like FIG. 3 of one of the gear teeth in the actuator shown in FIG. 4 and shaped according to this invention.

With reference to the drawing, the actuator of this invention, indicated generally at 10, is shown in FIGS. 1 and 2 as including a housing or stationary member 12 formed with a plurality of gear tooth cavities 14 arranged in an approximately circular formation about an axis 16. An output gear 18, illustrated as being attached to an output shaft 20 rotatably supported on the member 12, has teeth 22 arranged on a pitch circle 19. The gear 18 is mounted on the stationary member 12 so that it is in a coaxial relation with the axis 16. A free floating ring gear 24 has a plurality of external teeth 26 corresponding in number to the number of tooth cavities 14 and a plurality of internal teeth 28 arranged on a pitch circle 21. The teeth 28 mesh with the output gear teeth 22. By free floating is meant that the ring gear 24 is free of any support in the actuator 10 other than for its engagement with the stationary member 12 and the output gear 18. The ring gear teeth 26 always have at least one engagement point with the stationary member 12 and theteeth 28 always have at least one engagement point with the output gear teeth 22. The ring gear 24 is configured so that it has a center point 30 (which is the center of the pitch circle of teeth 28) which is spaced at all times from the axis 16 by a distance e. (The geometric center is also the center of mass if the ring gearis completely symmetrical, but this is not an essential feature.)

The aforementioned copending applications show how a force vector can be caused to shift in angle as point 30 moves about point 16. Assume that this force vector can be so positioned that a component will keep teeth 28 and teeth 22, in tight mesh so that center distance e is essentially constant, as it will be for tightly meshed involute profile teeth. Then only that component of the force vector which is at right angles to a line from point 16 to the point 17 where the pitch circle 19 of teeth 28 touches the pitch circle 21 of teeth 22 will be effective in causing torque to be imposed on member 18. This force vector is hereinafter called F If member 16 is stationary, a reaction force will be generated equal but opposite in direction to the initial force F The torque required to hold the member 18 stationary will be force F times R0, where R0 represents the distance between

points

16 and 17, and this will be the available output torque on the output member 18. Further discussion of the force vector will not be attempted here, since the means of developing the force vector are not shown except to note that under the assumption of tight meshing of

members

18 and 24 and the geometry of the teeth 26 and cavities 14, the only possible motion of point 30 is along a circle of radius e"about point 16. Since there are more teeth 28 than teeth 22, a complete rotation of point 30 counterclockwise about point 16 results in a partial clockwise rotation of member 18 about point 16. The ratio of rotations of point 30 about point 16 to rotations of member 18 about point 16 is the number of teeth 22 divided by the number of teeth 28 less the number of teeth 22. This is the same as Role.

The improvement in the actuator of this invention is in the shape of the ring gear teeth 26 and the cavities 14 in which the teeth 26 are located. The shapes of a tooth 26 and a cavity 14 are illustrated in FIG. 3 wherein the tooth 26 is shown in a position located symmetrically within the cavity 14 and with point 30 directly above axis 16. As shown in FIG. 3, the tooth 26 has a terminal end 32, an imaginery base line 34 perpendicular to a radius 35 from point 30 and

side surfaces

36 and 38. Since the shapes of the

side surfaces

36 and 38 are substantially identical, being only rightand left-hand versions of each other, but not necessarily symmetrically located relative to the radius 35 to which the base. line 34 is perpendicular, only the surface 36 is described in detail hereinafter.

The major portion 40 of the surface 36, extending from the tooth end 32 to a point 42 adjacent the base line 34 is arcuate in shape having an axis 44 of revolution spaced from the base line 34 a distance e"corresponding to the eccentricity e"of the ring gear 24 relative to the axis 16. The surface portion 40 is located on a radius R having its center at the axis of revolution 44. A portion 46 of the surface 36, extending from the point 42 to the base line 34 and equal in length to the distance e, can be substantially straight. This portion 46 of the tooth is noncontacting and therefore can be any shape which will clear the corner 68 of the cavity 14 as each point on the tooth surface moves along the arc of a.circle of radius e whose center is directly below the subject point.

The tooth surface 38 is similarly shaped having an axis 48 of revolution spaced from the axis 44 a distance which determines the width of the tooth 26. Design considerations in each particular instance will determine the desired width of the tooth 26 and do not form a part of the present invention. It is to be understood, therefore, that the tooth can be of any desired width and can also be of any desired length, the tooth end 32 being also located a distance from the base line 34 determined by design considerations in each instance.

The cavity 14 has sidewalls 50 and 52 which are also arcuate in shape, and since they are rightand left-hand versions of each other, only the shape of the surface 50 will be described in detail. The surface 50 has an axis 54 of revolution located on the base line 34 and spaced from the axis 44 a distance equal to the eccentricity of the ring gear 24 relative to the output gear axis 16. Similarly, the surface 52 has an axis 56 of revolution located on the base line 34. As shown in FIG. 3, the surface 50 is tangent to

imaginary circles

58, 60 and 62 each of which has a radius e. The centers of the

circles

58, 60 and 62 are determined by locating imaginary radii which intersect the tooth surface 36 and are perpendicular to the base line 34. The contact angle, namely the angle of rotation of the ring gear center 30 about the axis 16 during which each tooth 26 is in engagement with the stationary member 12 is indicated at A in FIG. 3 for counterclockwise orbiting movement of the ring gear 24 and at B in FIG. 3 for clockwise orbiting movement of the ring gear 24 relative to the axis 16. Since the tooth surfaces 36 and 38 are rightand left-hand versions of each other, the angles A and B are equal. Thus, for counterclockwise orbiting movement of the ring gear 24, contactof the tooth 26 with the cavity surface 50 will commence at point 66 on the surface 50 and continues as the ring gear center 30 moves counterclockwise about the axis 16 until point 42 on tooth 26 engages the point 68 on the surface 50. At such time, or sooner, the next tooth 26, moving in a counterclockwise direction about the ring gear 24 will contact the next surface 50 in the counterclockwise adjacent cavity 14 in the stationary member 12. Thus, well defined tooth contact is obtained which is geometrically consistent with the desired motion restraint. During motion from the position shown until initial contact at point 66, theload bearing contact would be on the tooth next clockwise from theone shown.

It is to be understood that the tooth 26 need not be wide enough to contain the axes of

revolution

44, 48, 54 and 56, as

shown in FIG. 3, but that the. tooth 26 can be narrower if desired and can also terminate in a pointed or in a semicircular end 32 if desired. The number of teeth 26 required on the ring gear 24 is determined by dividing 360 by the contact angle A. By the use of sufficient teeth, a contact overlap which is acceptable can be arbitrarily set. A meaningful contact ratio is defined by the angle of contact per, tooth divided by the minimum contact angle required per tooth to achieve ideal ring gear motion restraint.

It is to be understood that while the actuator 10 is illustrated with all cavities 14 symmetrically placed about the axis 16 of the stationary gear and the teeth 26 symmetrically placed about the center 30 of the pitch circle of teeth 28, this is not a required condition. Each tooth and cavity pair can be designed and spaced independently provided only that adjacent pairs have at least continuity and preferable overlap of their arcs of action when related to the motion of point 30 about axis 16. This can be of considerable practical importance when the means for achieving a torque on the ring gear 24 is developed in a particular application of the invention since a considerable number of slots and/or passages in stationary part 12 might of necessity need to be accommodated.

In the modified form of the actuator of this invention, indicated generally at 10a in FIG. 4, components corresponding to the actuator components described above in the actuator 10 are utilized. Consequently, corresponding numerals are employed to indicate like parts in the actuators l0 and 10a. The actuator 10a differs from the actuator 10 in that in the actuator 10a teeth 70, shaped like the teeth 26 in the actuator 10, are formed on the stationary member 12 and cavities 72 for the teeth 70,, shaped like the cavities 14 in the actuator 10, are formed in the ring gear 24. As shown in FIG. 5, each tooth 70 is shaped like the teeth 26 previously described, the base line 74 of the tooth 70 being tangent to a circle 76 having its center located on the axis 16. Similarly, the cavities 72 are shaped so that the base line 78 for each cavity 72 is tangent to a common circle 80 having its center located at the point 30. It is to be understood that this arrangement of having the base lines tangent to common circles and having the teeth 70 and cavities 72 symmetrical about radii perpendicular the base lines, is not essential. It is only necessary that the radius length to the base line 74 for the tooth 70 from the axis 16 be equal to the radius length plus the eccentricity e" to the mating cavity base line 78 and that the tooth and cavity each have axes corresponding to the

points

54 and 56 in FIG. 3 displaced the same amount and direction from the radius perpendicular to the base line. In operation, the actuator 10a operates like the actuator 10 previously described.

From the above description it is seen, therefore, that this invention provides improved

actuators

10 and 10a by virtue of the geometric configuration of the ring gear teeth 26 and the associated cavities 14 in the stationary member 12 in the actuator l0 and the corresponding stationary member teeth 70 and ring gear cavities 72 in the actuator 1011. This configuration is essentially arcuate having predetermined axes of revolution which determine the precise tooth shape in each instance.

I claim:

1. In an actuator which includes a stationary gear having an axis, an output member arranged in a coaxial relation with said axis and a free floating ring gear having a center which is spaced a predetermined distance from said axis, said ring gear being arranged in an engaged driving relation with said output member, said stationary and ring gears having a plurality of coacting teeth and tooth cavities corresponding in number and arranged in substantially circular formation about said axis and said center respectively, at least some of said teeth being positioned in said cavities whereby said center is movable in an orbital path about said axis and said ring gear is restrained against rotation, the improvement wherein each of said teeth is shaped so that it has an end, a base line and a pair of side surfaces extending from said base line to said end, each of said side surfaces having an arcuate surface portion the axis of revolution of which is located between said base line and said end and is spaced from said base line a distance substantially equal to said predetermined distance.

2. In an actuator having the structure set forth in claim 1 wherein said arcuate portion constitutes the major portion of each of said side surfaces.

3. In an actuator having the structure set forth in claim 2 wherein each of said cavities has sidewalls shaped so that when one of said teeth is positioned symmetrically therein said sidewall is spaced from said tooth at said base line a distance equal to said predetermined distance, said cavity sidewall being curved so that the spacing between said cavity sidewall and the adjacent tooth sidewall progressively decreases in a direction toward said tooth end. 7

4. In an actuator having the structure set forth in claim 3 wherein said cavity sidewall is substantially arcuate having an axis of revolution disposed substantially on said base line.

5. In an actuator having the structure set forth in claim 3 wherein said tooth cavities are formed in said stationary gear and are arranged in a substantially circular formation about said axis.

6. In an actuator having the structure set forth in claim 3 wherein said teeth are formed in said stationary gear and are arranged in a substantially circular formation about said axis.

Claims

3. In an actuator having the structure set forth in claim 2 Wherein each of said cavities has sidewalls shaped so that when one of said teeth is positioned symmetrically therein said sidewall is spaced from said tooth at said base line a distance equal to said predetermined distance, said cavity sidewall being curved so that the spacing between said cavity sidewall and the adjacent tooth sidewall progressively decreases in a direction toward said tooth end.