Roller cam assembly

#Early prime movers or power sources such as the mill stream water wheel; and, later the steam engine, created a need for transferring power from one place to another through torque transfer. An early example of torque transfer was the belt and pulley assembly, frequently utilized in machine shops to drive various machines.

#The early prime movers generated low revolutions per minute (rpm) and mechanically simple torque transfer mechanisms were capable of creating very little power. In portable machines, chains and sprockets are often used to transfer power. The most common example of this form of torque transfer is the ordinary bicycle. The bicycle sprocket and chain are a roller cam assembly; and the relative motion between the roller in the chain and the sprocket is that of an involute. It is the shape of the sprocket that enables the power to be transferred smoothly.

#With the need to transfer torque between adjacent parallel and perpendicular shafts, something else had to be devised. In fact, the old water wheels that were used to grind grain employed wooden pegs as gear teeth to transfer torque; but, as rpm and torque increased, it was observed that a fluctuation in speeds occurred, creating destructive forces. This fluctuation resulted from the variations during rotation of the effective radii between the meshing of the pegged wheels.

#FIG. 1 is an elevated axial view of a curtate epitrochoidal cam and roller ring assembly wherein the axis of the cam is within or inside the pitch circle of the roller ring.

#FIG. 2 is the same view as FIG. 1, in partial section, showing a one-half pitch clockwise displacement from FIG. 1.

#FIG. 3 is an elevated side view of FIG. 1 after rotating the roller cam assembly 90° in the horizontal plane.

#An understanding of the disclosed roller cam assembly can be best appreciated by referring to the drawing. This disclosure describes four different types of trochoid cam profiles that can interact efficiently with appropriately matched roller ring assemblies. These cam profiles can be described either mathematically or mechanically. This document will do both. The cams can be located internal to the circumference of the roller ring assembly (see FIGS. 1 & 7). Or they can be located externally to the circumference of the roller ring assembly (see FIGS. 4 & 8). Additionally, the cam can also surround the roller ring as in FIGS. 9-12. When the cam is internal or external to the roller ring assembly, but not surrounding the roller ring assembly, it is an epitrochoid cam. In this disclosure, the cams and roller rings move the same as with the gears. The cam shape controls the relative motion between them so as to generate the same output as gears. Herein are described two types of epitrochoidal cams namely, curtate (FIG. 1) and prolate (FIG. 4). Similarly, we will describe two types of roller ring-surrounding cams namely, curtate hypotrochoidal (see FIGS. 10 & 12) and prolate hypotrochoidal (see FIGS. 9 & 11). Furthermore, the trochoidal cam and roller ring arrangement lends itself to use in epicyclic transmissions as depicted in FIGS. 11 & 12.

#FIG. 1 shows an axial view of a curtate epitrochoidal cam and roller ring assembly 10 wherein the input shaft 28 and the output shaft 14 are offset and project into and out of the plane of the page. In this figure, “A” represents the input torque on the roller ring 24 as delivered by the roller ring input shaft 28. This clockwise torque “A” will drive the curtate epitrochoid cam 12 in a clockwise direction resulting in a reduced output torque “B” which is transferred to the output shaft 14. Because there are more roller elements 26 on the input roller ring than teeth on the cam 12, this configuration represents an overdrive transmission in which a 0.67 turn on the input shaft 28 results in 1.0 turn of the output shaft 14. The pitch circle of the cam 12 and roller ring 24 are represented by the circles labeled 21 & 31 respectively. The pitch circles contact and turn on each other without slipping at the 12 o'clock position. The pitch of the cam 12 and the roller ring 24 is represented by the value of “X” where the indicated radii cross the pitch circle 21 of the cam 12. Reference 27 is intended to indicate that the rollers can consist essentially of a sleeve with a bushing for high loading or any of a variety of commercially available cantilevered rollers with internal roller bearings for lower load applications and reduced frictional losses. These designs do not exclude the use of rollers with end supports. In this disclosure, end supports are not included in the drawing to simplify the figures and the visualizations of the designs.

#Upon closer inspection of FIG. 1, the range of roller pin 26 interactions with the cam 12 is apparent. The cam position 22 depicts the initial contact or driving interaction between the roller pin 26 and the cam tooth 30. Similarly, the cam position 20 shows the final contact region between the cam tooth 30 and the roller pin 26. The interaction between the roller pin and a curtate epitrochoid cam is fairly complex and will be explained in detail by referring to FIG. 8b. Briefly, the interacting roller pin makes several transitions from driving 22 to holding 17 to a neutral or nodal position 18 back to a driving position 19 and to a final holding interaction in position 20. Such intricate interactions are not obvious upon a casual scanning of the figures.