Fig. 207.
The relation of motion between b and c is in this case constant (2 to 1), but this relation may be made variable by a construction such as shown in [Fig. 207], in which the wheel b is carried in a gear-wheel h, which rides upon the shaft d. Suppose now that h remains stationary while a revolves, then motion will be transmitted through b to c, and this motion will be constant and in proportion to the relative diameters of a and c. But suppose by means of an independent pinion the wheel h be rotated upon its axis, then increased motion will be imparted to c, and the amount of the increase will be determined by the speed of rotation of h, which may be made variable by means of cone pulleys or other suitable mechanical devices.
Fig. 208.
[Fig. 208] represents an arrangement of gearing used upon steam fire-engines and traction engines to enable them to turn easily in a short radius, as in turning corners in narrow streets. The object is to enable the driving wheel on either side of the engine to increase or diminish its rotation to suit the conditions caused by the leading or front pair of steering wheels.
In the figures a is a plate wheel having the lugs l, by means of which it may be rotated by a chain. a is a working fit on the shaft s, and carries three pinions e pivoted upon their axes p. f is a bevel-gear, a working fit on s, while c is a similar gear fast to s. The pinions b, d are to drive gears on the wheels of the engine, the wheels being a working fit on the axle. Let it now be noted that if s be rotated, c and f will rotate in opposite directions and a will remain stationary. But if a be rotated, then all the gears will rotate with it, but e will not rotate upon p unless there be an unequal resistance to the motion of pinions d and b. So soon, however, as there exists an inequality of resistance between d and b then pinions e operate. For example, let b have more resistance than d, and b will rotate more slowly, causing pinion e to rotate and move c faster than is due to the motion of the chain wheel a, thus causing the wheel on one side of the engine to retard and the other to increase its motion, and thus enable the engine to turn easily. From its action this arrangement is termed the equalizing gear.
In [Figs. 209] to [214] are shown what are known as mangle-wheels from their having been first used in clothes mangling machines.
