Types Gear

1 types

1.1 external vs internal gears
1.2 spur
1.3 helical

1.3.1 skew gears


1.4 double helical
1.5 bevel
1.6 spiral bevels
1.7 hypoid
1.8 crown
1.9 worm
1.10 non-circular
1.11 rack , pinion
1.12 epicyclic

1.12.1 sun , planet


1.13 harmonic gear
1.14 cage gear
1.15 magnetic gear

types
external vs internal gears

internal gear

an external gear 1 teeth formed on outer surface of cylinder or cone. conversely, internal gear 1 teeth formed on inner surface of cylinder or cone. bevel gears, internal gear 1 pitch angle exceeding 90 degrees. internal gears not cause output shaft direction reversal.

spur

spur gear

spur gears or straight-cut gears simplest type of gear. consist of cylinder or disk teeth projecting radially. though teeth not straight-sided (but of special form achieve constant drive ratio, involute less commonly cycloidal), edge of each tooth straight , aligned parallel axis of rotation. these gears mesh correctly if fitted parallel shafts. no axial thrust created tooth loads. spur gears excellent @ moderate speeds tend noisy @ high speeds.

helical

an external contact helical gear in action



helical gears

top: parallel configuration

bottom: crossed configuration

helical or dry fixed gears offer refinement on spur gears. leading edges of teeth not parallel axis of rotation, set @ angle. since gear curved, angling makes tooth shape segment of helix. helical gears can meshed in parallel or crossed orientations. former refers when shafts parallel each other; common orientation. in latter, shafts non-parallel, , in configuration gears known skew gears .

the angled teeth engage more gradually spur gear teeth, causing them run more smoothly , quietly. parallel helical gears, each pair of teeth first make contact @ single point @ 1 side of gear wheel; moving curve of contact grows gradually across tooth face maximum, recedes until teeth break contact @ single point on opposite side. in spur gears, teeth meet @ line contact across entire width, causing stress , noise. spur gears make characteristic whine @ high speeds. reason spur gears used in low-speed applications , in situations noise control not problem, , helical gears used in high-speed applications, large power transmission, or noise abatement important. speed considered high when pitch line velocity exceeds 25 m/s.

a disadvantage of helical gears resultant thrust along axis of gear, must accommodated appropriate thrust bearings, , greater degree of sliding friction between meshing teeth, addressed additives in lubricant.

skew gears

for crossed or skew configuration, gears must have same pressure angle , normal pitch; however, helix angle , handedness can different. relationship between 2 shafts defined helix angle(s) of 2 shafts , handedness, defined:

e
=

β

1


+

β

2




{\displaystyle e=\beta _{1}+\beta _{2}}

gears of same handedness,




e
=

β

1


−

β

2




{\displaystyle e=\beta _{1}-\beta _{2}}

gears of opposite handedness,

where



β


{\displaystyle \beta }

helix angle gear. crossed configuration less mechanically sound because there point contact between gears, whereas in parallel configuration there line contact.

quite commonly, helical gears used helix angle of 1 having negative of helix angle of other; such pair might referred having right-handed helix , left-handed helix of equal angles. 2 equal opposite angles add zero: angle between shafts zero—that is, shafts parallel. sum or difference (as described in equations above) not zero, shafts crossed. shafts crossed @ right angles, helix angles of same hand because must add 90 degrees. (this case gears in illustration above: mesh correctly in crossed configuration: parallel configuration, 1 of helix angles should reversed. gears illustrated cannot mesh shafts parallel.)

3d animation of helical gears (parallel axis)
3d animation of helical gears (crossed axis)

double helical

herringbone gears

double helical gears , herringbone gears similar, difference herringbone gears not have groove in middle double helical gears do. double helical gears overcome problem of axial thrust presented single helical gears using 2 sets of teeth set in v shape. double helical gear can thought of 2 mirrored helical gears joined together. arrangement cancels out net axial thrust, since each half of gear thrusts in opposite direction, resulting in net axial force of zero. arrangement can remove need thrust bearings. however, double helical gears more difficult manufacture due more complicated shape.

for both possible rotational directions, there exist 2 possible arrangements oppositely-oriented helical gears or gear faces. 1 arrangement stable, , other unstable. in stable orientation, helical gear faces oriented each axial force directed toward center of gear. in unstable orientation, both axial forces directed away center of gear. in both arrangements, total (or net) axial force on each gear 0 when gears aligned correctly. if gears become misaligned in axial direction, unstable arrangement generates net force may lead disassembly of gear train, while stable arrangement generates net corrective force. if direction of rotation reversed, direction of axial thrusts reversed, stable configuration becomes unstable, , conversely.

stable double helical gears can directly interchanged spur gears without need different bearings.

bevel


bevel gear

a bevel gear shaped right circular cone of tip cut off. when 2 bevel gears mesh, imaginary vertices must occupy same point. shaft axes intersect @ point, forming arbitrary non-straight angle between shafts. angle between shafts can except 0 or 180 degrees. bevel gears equal numbers of teeth , shaft axes @ 90 degrees called miter gears.

spiral bevels

spiral bevel gears

spiral bevel gears can manufactured gleason types (circular arc non-constant tooth depth), oerlikon , curvex types (circular arc constant tooth depth), klingelnberg cyclo-palloid (epicycloid constant tooth depth) or klingelnberg palloid. spiral bevel gears have same advantages , disadvantages relative straight-cut cousins helical gears spur gears. straight bevel gears used @ speeds below 5 m/s (1000 ft/min), or, small gears, 1000 r.p.m.

note: cylindrical gear tooth profile corresponds involute, bevel gear tooth profile octoid. traditional bevel gear generators (like gleason, klingelnberg, heidenreich & harbeck, wmw modul) manufacture bevel gears octoidal tooth profile. important: 5-axis milled bevel gear sets important choose same calculation / layout conventional manufacturing method. simplified calculated bevel gears on basis of equivalent cylindrical gear in normal section involute tooth form show deviant tooth form reduced tooth strength 10-28% without offset , 45% offset [diss. hünecke, tu dresden]. furthermore, involute bevel gear sets cause more noise.

hypoid

hypoid gear

hypoid gears resemble spiral bevel gears except shaft axes not intersect. pitch surfaces appear conical but, compensate offset shaft, in fact hyperboloids of revolution. hypoid gears designed operate shafts @ 90 degrees. depending on side shaft offset to, relative angling of teeth, contact between hypoid gear teeth may smoother , more gradual spiral bevel gear teeth, have sliding action along meshing teeth rotates , therefore require of viscous types of gear oil avoid being extruded mating tooth faces, oil designated hp (for hypoid) followed number denoting viscosity. also, pinion can designed fewer teeth spiral bevel pinion, result gear ratios of 60:1 , higher feasible using single set of hypoid gears. style of gear common in motor vehicle drive trains, in concert differential. whereas regular (nonhypoid) ring-and-pinion gear set suitable many applications, not ideal vehicle drive trains because generates more noise , vibration hypoid does. bringing hypoid gears market mass-production applications engineering improvement of 1920s.

crown

crown gear

crown gears or contrate gears particular form of bevel gear teeth project @ right angles plane of wheel; in orientation teeth resemble points on crown. crown gear can mesh accurately bevel gear, although crown gears seen meshing spur gears. crown gear meshed escapement such found in mechanical clocks.

worm

worm gear



4-start worm , wheel

worms resemble screws. worm meshed worm wheel, looks similar spur gear.

worm-and-gear sets simple , compact way achieve high torque, low speed gear ratio. example, helical gears limited gear ratios of less 10:1 while worm-and-gear sets vary 10:1 500:1. disadvantage potential considerable sliding action, leading low efficiency.

a worm gear species of helical gear, helix angle large (close 90 degrees) , body long in axial direction. these attributes give screw qualities. distinction between worm , helical gear @ least 1 tooth persists full rotation around helix. if occurs, worm ; if not, helical gear . worm may have few 1 tooth. if tooth persists several turns around helix, worm appears, superficially, have more 1 tooth, 1 in fact sees same tooth reappearing @ intervals along length of worm. usual screw nomenclature applies: one-toothed worm called single thread or single start; worm more 1 tooth called multiple thread or multiple start. helix angle of worm not specified. instead, lead angle, equal 90 degrees minus helix angle, given.

in worm-and-gear set, worm can drive gear. however, if gear attempts drive worm, may or may not succeed. particularly if lead angle small, gear s teeth may lock against worm s teeth, because force component circumferential worm not sufficient overcome friction. in traditional music boxes, however, gear drives worm, has large helix angle. mesh drives speed-limiter vanes mounted on worm shaft.

worm-and-gear sets lock called self locking, can used advantage, instance when desired set position of mechanism turning worm , have mechanism hold position. example machine head found on types of stringed instruments.

if gear in worm-and-gear set ordinary helical gear single point of contact achieved. if medium high power transmission desired, tooth shape of gear modified achieve more intimate contact making both gears partially envelop each other. done making both concave , joining them @ saddle point; called cone-drive or double enveloping .

worm gears can right or left-handed, following long-established practice screw threads.

3d animation of worm-gear set

non-circular

non-circular gears

non-circular gears designed special purposes. while regular gear optimized transmit torque engaged member minimum noise , wear , maximum efficiency, non-circular gear s main objective might ratio variations, axle displacement oscillations , more. common applications include textile machines, potentiometers , continuously variable transmissions.

rack , pinion

a rack toothed bar or rod can thought of sector gear infinitely large radius of curvature. torque can converted linear force meshing rack pinion: pinion turns; rack moves in straight line. such mechanism used in automobiles convert rotation of steering wheel left-to-right motion of tie rod(s). racks feature in theory of gear geometry, where, instance, tooth shape of interchangeable set of gears may specified rack, (infinite radius), , tooth shapes gears of particular actual radii derived that. rack , pinion gear type employed in rack railway.

epicyclic

epicyclic gearing

in epicyclic gearing 1 or more of gear axes moves. examples sun , planet gearing (see below), cycloidal drive, , mechanical differentials.

sun , planet

sun (yellow) , planet (red) gearing

sun , planet gearing method of converting reciprocating motion rotary motion used in steam engines. james watt used on steam engines around patent on crank, provided advantage of increasing flywheel speed watt use lighter flywheel.

in illustration, sun yellow, planet red, reciprocating arm blue, flywheel green , driveshaft gray.

harmonic gear

harmonic gearing

a harmonic gear specialized gearing mechanism used in industrial motion control, robotics , aerospace advantages on traditional gearing systems, including lack of backlash, compactness , high gear ratios.

cage gear

cage gear in pantigo windmill, long island (with driving gearwheel disengaged)

a cage gear, called lantern gear or lantern pinion has cylindrical rods teeth, parallel axle , arranged in circle around it, bars on round bird cage or lantern. assembly held disks @ each end, tooth rods , axle set. cage gears more efficient solid pinions, , dirt can fall through rods rather becoming trapped , increasing wear. can constructed simple tools teeth not formed cutting or milling, rather drilling holes , inserting rods.

sometimes used in clocks, cage gear should driven gearwheel, not used driver. cage gear not favoured conservative clock makers. became popular in turret clocks dirty working conditions commonplace. domestic american clock movements used them.

magnetic gear

all cogs of each gear component of magnetic gears act constant magnet periodic alternation of opposite magnetic poles on mating surfaces. gear components mounted backlash capability similar other mechanical gearings. although cannot exert force traditional gear, such gears work without touching , immune wear, have low noise , can slip without damage making them reliable. can used in configurations not possible gears must physically touching , can operate non-metallic barrier separating driving force load. magnetic coupling can transmit force hermetically sealed enclosure without using radial shaft seal, may leak.