Diferent Types Types o Gear Box, their Applications & Utilization A gearbox consists of a means of transmitting mechanical torque between two shafts with structural support between them. Normally it is contained within a casing which would provide the structural support and also have containment and safety functions. Most gearboxes are designed for speed reduction though some may be suitable for speed increasing duties. Some types are not suitable for reverse driving and the system may require the prevention of 'over-running'. Shafts are usually provided with a means of accepting and delivering torque in the form of a eyway or splines suitable for connecting to a coupling or to another unit. Shafts will have a limited protrusion from the casing.
Figure 3 !ypical "eatures of a #earbox $asing
"igure % shows typical features of a gearbox $AS&N# which performs several functions •
structural support of the shaft bearings and hence the gear loadings(
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transfer of torque reaction to supporting structure or further drive element(
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containment of lubricant and exclusion of foreign matter(
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provision of safety and noise barrier(
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dissipation of heat generated by friction(
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unitisation of assembly) thus aiding testing) installation) and maintenance(
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enhancement of visual qualities(
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"ollowing shows the shaft orientations available for the gearbox types covered in this #uide.
*A+A,,, SA"!S S*0+ ,&$A, *&$3$,&$
*+*N/&$0,A+ SA"!S 45, 26+M S*&+6&/
S12/ SA"!S $+6SS/ ,&$A,
1. Spur
Spur gearboxes contain spur gears which have teeth cut parallel to the shaft axis and are only suitable for parallel shaft applications. However they facilitate the arrangement of a sliding gear ratio change. Input and output shafts may be arranged on the same side of the casing or opposite sides. For concentric input and output shafts an internal 'layshaft' is needed.
2. Helical
Helical gearboxes have many characteristics which are identical to spur boxes but as a result of tooth form their performance is enhanced in terms of power speed ratio and peripheral speed. !heir mechanical e"ciency is marginally inferior due to a greater sliding contact at the gear tooth faces but this is rarely a problem. !hey are not suitable for a sliding gear change.
#. $picyclic
$picyclic gearboxes are a versatile arrangement of spur or helical gears in which the input and output shafts are concentric and either shaft or the casing may be constrained to be the stationary element the tor%ue being transmitted between the other two. !he three main elements are thus a 'sun' gear a 'ring' gear and a number of 'planet' gears meshing with both. &ide ranges of speed ratio are obtainable from a given set of elements and very large reductions result from compounding stages. !hey tend to have high powerweight and powerbul( ratios and are available for a wide range of powers.
). *evel
*evel gearboxes are used for drives where shafts are not parallel but whose axes intersect. !he most common intersection angle is +,- but other angles are possible. right angle drive with a 1/1 speed ratio is sometimes called a 'mitre' box.
0. &orm
&orm gearboxes allow high ratios of speed reduction within a single stage coupled with nonparallel nonintersecting shafts. everse drive is not normally permissible and under some circumstances positive loc(ing of reverse drive results.
3. Spiroid
Spiroid gearboxes perform a similar function to worm boxes but the gears have characteristics which combine those of the bevel and worm gears. High powers and speed ratios are possible and mechanical e"ciencies higher than worm boxes for e%uivalent ratios.
Harmonic drives consist of a gearbox which allows two gears with a large number of teeth to rotate such that a third element rotates according to the difference between the numbers of teeth on the gears.
!orque capacity is high in relation to bul and weight) speed ratios range between 789 and :;89 and mechanical efficiency between <8= and >;=. 4aclash is very small and can be totally eliminated with special units.
