On a side gear engine the power is transmitted from a small pinion on the main shaft to an intermediate gear, from this gear to the differential gear on cross shaft which is placed under the cylindrical part of the boiler against the fire box. To this shaft are keyed two small pinions at each end, which mesh in large spur gears fastened securely to the traction wheels.
On a rear gear engine the power is transmitted from the small pinion on crank shaft to large spur gear attached to one end of cross shaft, which crosses the boiler at the rear end. To the other end of this shaft is attached a small pinion that meshes in the large differential gear which is attached to traction wheel and main axle.
DIFFERENTIAL GEAR.
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.
FRICTION CLUTCH.
This attachment on a traction engine is almost indispensable as it allows the engineer to give the whole power of the engine instantly to the traction gear in getting the engine out of bad places, or to move the engine backward or forward with so little apparent effort as to be almost imperceptible, while the engine may be running at full speed; also for tightening the main drive belt when attached to machinery without stopping the engine.