Fig. 43. Neutral Position.
The transmission gearing is, therefore, the most satisfactory solution of the problem, because changing the engine speed destroys its effectiveness, and we shall, therefore, consider some of the types for that purpose.
There are two distinct systems of transmission, namely: The Positive, and the Frictional. Of the positive system we have the planetary and the sliding gear types. The sliding gear type has two methods of control, one known as the progressive, and the other the selective.
Characteristics of Transmission.—The progressive, selective and planetary types, are entirely different from the frictional system, for the reason that they effect the changes by step movements, the speeds being produced at certain ratios, whereas the frictional method has indefinite and infinite ratios.
Fig. 44. Intermediate.
The following diagrams will clearly bring out the distinctive features of each. Fig. 42 shows a shaft A, which derives power from the engine, having in line with it a shaft B, which connects with the driven shaft. The shaft B is squared, but it has a round end C, which is socketed axially within the head of the shaft A.
The Progressive.—The head D has a small pinion E, and on its side is provided with projecting teeth F. The loosely-revolving squared shaft B has thereon a pair of spur gear G H, separated from each other a trifle more than the width of each gear, and they are united by an intermediate hub so they turn in unison.
Fig. 45. High.