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.
[Illustration: J. I. Case Friction Clutch.]
The friction clutch shown in illustration is constructed as follows:
The friction pulley is constructed with a friction ring upon its arms,
the outer ring acting as a guard or protection, the friction ring being
turned accurately to receive the wooden shoes attached to the driving
arm; these wooden friction shoes are fitted to the outer surface of the
ring as well as the inner, all being connected to one set of levers;
so when force is applied to engage the friction to start the engine
there is no tendency or danger of bursting the rim, as the pressure
is equal on both sides of it. The pulley is keyed to the crank shaft,
while the driving arm, with driving pinion secured firmly to it, runs
loosely upon the shaft. Upon the hub of driving arm is placed a sliding
sleeve with lever attached, which connects with toggle levers beneath
the sliding pieces which contain the wooden friction shoes, the whole
being operated by the sliding strap from footboard of engine near by
the reverse lever. This makes a strong and convenient arrangement for
transmitting power.
Many other styles of clutches are made by engine builders, adapted to
their particular style of engines, a common way being to have the shoes
tighten against the inner rim of the fly-wheel. This is not deemed as
good an arrangement, for the reason that the pressure or strain is all
outward against the rim, though their being used extensively indicates
good results.
When operating a friction clutch, always draw or push the lever over
gradually. By doing this the engine will start slowly and easily, while
if the lever is jammed over suddenly, the engine will start with a
jerk, which is liable to damage the traction gear. The latter should
never be done unless absolutely necessary to get the engine out of bad
places on the road.