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l. V `I. t * * 8 Spiral-bevel ' geor teeth hevo ovo'lopping OCtlon %A Cmiibc is a term sometimes opplicd skew gears. They are stronger end run to any method of transmitting motion more smoothly and quietly than spiral- from one shaft to another. It includes bevel gears, which in turn run much pulleys and belts, sprockets and chains, more smoothly and quietly than skew rocker arms and links, and toothed bevels. Hypoid gears were first used wheels or gears. Many problems ro- by the automotive industry in 1925. lating to Iho different methods of mo Their operating qualities, together with tion transmission are similar, but each the fact that their pinion offset permits ir -*.M has its separate and distinct field of usefulness. Here we will deal with the design of lower automobile bodies, have proved such an advantage that fe toothed gearing only. today the majority of American automo Gears may be classified with refer biles have adopted them. Other uses ence to' the elements of their teeth, and aiso the relative position of their axes are in steel and paper mills, and on locomotives and printing presses. In i: -l or shafts, as: Fig. I--Spur gears con nect parallel shafts and have straight teeth. Fig. 2--Bevel gears connect shafts whose axes meet if they are pro longed and have straight teeth. Fig. 3 9 This skow-beveJ geor design hot skew teeth In both the oeor and the pinion f A Hypofd gear hoi curved teeth; pin. Wion axis is offset below thot of geor | A Zero! geor is o curved-tooth bevel I m design with a zero spiral ongle another design of this gear, Fig. -11, the pinion shaft crosses the gear face to permit placing bearing at pinion. Zero! geors, Fig. 12. are a curvedtooth bevel design with zero-degree m, I --Worm geara connect shafts that are spiral ongle. They combine the local not parallel. Their axes do not meet, and they have aenewlike teeth. Fig. 4 --Spiral gears connect shafts that are Apply Right Gear to the Job to Get Longer Service ised tooth contact of spirol-bcvel gears with the low thrust toads of straightbevel gears, Their tooth arrangement either parallel or at an anglo, but their produces smooth, quiet operation even axes do not meet and their teeth are under extremely high loads. For these helical. reasons zerol gears are replacing Under the heading of spur gears, the internal gear and pinion. Fig. S, should be considered, ft is the opposite of an external gear and its teeth point toward its center. Because of this condition, for the same tooth ratio the length of the line of tooth action is greater. Also, the teeth come into and go out of con tact with less slippage. An internal gear has several advan tages when properly applied, such as in drives for truck and tractor rear axles. With its mating pinion, it operates on a closer center distance than an ex-, ternal gear of the same size and forms its own gear guard, ft has more teeth in contact with its pinion than a cor responding-size external gear. All these advantages give longer IIfe and greater strength. Internal geors also have heli cal teeth. Racks that also fall into the spur- John K Rewall, application engineer, Philadelphia Gear Worici, compares characteristics of gears common in industrial appli cations. One gear may run smoother and at higher speed, trans mit greater load, suit application better than another design gear category ore straight pieces with teeth that mesh with spur gears, Theo retically. if a straight rack were ex tended until it reached around the earth, it would actually be a spur-gear. Rocks.may also be cue helical and her ringbone. Gears, other than straight-tooth spur for connecting parallel shafts, are heli cal, Fig. 6, and herringbone spur gears, Fig. 7. They meet demands for smooth, silent operation not attainable with straight-tooth spur gears. Helical ad herringbone gears of proper desip oh* promote long gear life and high operat ing efficiency. These so-called qusktf gears have teeth that extend hohcsUf across their faco. This obliquity keep the teeth of each meshing pair ia en gagement, until one or more of the Idlowing pairs ore well engaged, web eliminates sudden load transfer, 1P*^ or shock on the teeth. As o result of the overlapping e"d| of tpir&l-bevel-gear teeth, Fig. 8, load tninferred from tooth to tooth with| cu shocks or sudden changes-In tooth fitssare. With straight-tooth gears, .tnoiferring load from tooth to tooth suto noise and vibration, especially jr Mieetble at high speeds. Because of larger number of teeth in contact, the consequently greater area over *fcich the lead is spread, curved-tooth' finl-bevel gears transmit greater luds then straight bevels. Fig. 2, of same size. Spiral-bevel gears can hsoimit power between shafts at prte^Uy any anglo and speed. They are Specially desirable where smooth, ^dtt gears are required end for large ru** at high speeds where pinion site ***1 be kept as small as possible. Their ^adnaous pitch-line contact makes it FtscUcsble to obtain good performance ^ a srasller number of teeth In pinion than is possiblo with straight bevels. Spiral-bevel gears run on either bait or taper-roller bearings to provide for thrust and radial loads. Their efficiency compares favorably with ac curately generated etraigbt-tooih bevels. Skew-bevel geors are another variety of bevel gearing, in which the tooth arrangement departs from the usual radial plan of straight-line teeth. The axes of the gears are not in a common plane. There ore two designs of theseunorthodox gear drives. In one the pinion has ordinary straight teeth, like Fig. 2, and the gear has oblique teeth, which are the most commonly used. The other hos skew teeth in both pinion and gear, Fig. 9. Hypold gears. Fig. 10, hove curved teeth liko the spirel-bcvcl design, but have the pinion axis offset above or below the center of the gear axis like straight-bevel gears in many applica tions where thrust limitations prevent use of spiral-bevel designs. Like straight-bevel gears, terol gears have no Inward axial thrust. With zerodegree spiral angle, thrust loads are the same os for equivalent straight-bevel gears; therefore, terol gears can be sub stituted for straight-bevel gears, with out changing thrust bearings. Like other bevel gears, they are designed with long and short addendum tooth proportions for smooth, quiet operation, and with large fillet radii (or maximum strength. The worm ond gear Is not a new mechanism; the spiral screw was studied by Archimedes (2B7-212 BC), It hes been during the lest 40 years, . however, that complex engineering and research work has brought it to its present high state of efficiency and use- r Aft `fv 74 13441 POWER ,0WEg junc 1948 |)4$) 74 Jki