The gearing on a traction engine must be so designed as to allow one
of the ground or traction wheels to run faster than the other, when
turning engine either to right or left on the road. To accomplish
this, the Differential Gear is made use of, and answers all purposes
admirably.
The Differential Gear on many styles of engines is attached to the
cross shaft, while on others it is secured to the main axle, and, as
generally constructed, consists of one large spur gear, having three or
four bevel pinions placed in it at equal distances apart and from the
center of main gear. These pinions revolve loosely on pins secured to
the gear, and the spur gear runs loosely on the cross shaft or axle.
At each side of the spur gear are placed bevel gears, meshing into the
bevel pinions, one of which is keyed fast to the shaft or axle, while
the other is firmly bolted to small pinion that drives the traction
wheel, or to hub of the traction wheel, which also runs loosely on its
axle.
This device allows one drive wheel to remain idle while the opposite
wheel may revolve as fast as is required to make the turn.
Differential Gears should be kept well greased with solid oil or axle
grease to prevent the cogs from being cut and wearing away rapidly.