Reduction gearbox

When the reduction in the rotational speed of the shaft between the prime mover and the driven machine is needed, gear reduces are used.  This change in speed produces corresponding increases in torque on the output shaft of the reducer, permitting relatively small, cheap high speed motors to drive machines requiring substantially higher power and Slower of speed.

Functions

The leverage of the engine over the driving shaft is increased by gear reducers

The engine and can turn more rapidly and generate more power to carry the load more effectively from rest by making use of the gear ratios

The gear box enables the engine to be disengaged from the driving shaft and idle when while the vehicle is stationary

A reverse gear is provided by the gear box that allows the engine to continue to run in the same direction

Types of gears utilised by reduction gear boxes

Spur gears

When spur gears are used, to engage the counter shaft drive gear, the gear must be changed.  If the gears are to be changed quietly, double declutching is usually required.  The disadvantage with spur gears is that gear changing is difficult because only two or three teeth are engaged and the gear been changed as fairly heavy.

Helical toothed gears

These gears are used in synchronised gear boxes.  The gears on the main shaft and the gears of the counter shaft drive gear always remain engaged.  The gears on the main shaft have small straight teeth that correspond with those of the synchronised unit.

This results in less wear on the teeth because all the teeth engage simultaneously instead of only two or three as in sliding gears.  Helical teeth also provide a much quieter drive and because more teeth are engaged, the gears are stronger.  The disadvantage of helical teeth is that they cause a lateral pressure.

Double helical toothed gears

The teeth of double helical toothed gears are cut in two opposing angles around the gear.  This eliminates the lateral pressure and ensures quiet driving.

construction

When arranging a gear train the following must be taken into account:

The space occupied by the gearing

The pitch of the teeth

The total speed reduction required and the largest speed reduction that can be allowed in one step

Speed reducers combine rigidity and strength and are manufactured from case-hardened steel, accurately generated and ground. Shafts are located on dual-purpose bearings of ample capacity. In either direction and at all speeds, there must be a positive lubrication.

worm-gear reduction unit

The worm wheel is driven by a high tensile steel worm and, to provide a smooth reduction, can be coupled directly to the motor shaft.

This type of reduction, when driven by a single start worm, has a ratio of around 40:1.