Motor-car principles; the gasoline automobile

by Roger B. Whitman

To obtain the reverse, a brake band is tightened on the drum of the reverse combination, which holds stationary the ring supporting the four gears, giving the result shown on the first diagram of the four gears revolving on their studs, and rotating the internal gear in the direction opposite to that of the crank shaft. The sleeve bearing the sprocket is thus revolved, and the car backs.

For the low speed, the reverse brake band is loosened, and the internal gear of the low-speed combination held stationary by the tightening of the brake band surrounding its drum. The revolution of the crank-shaft gear causes the four gears to revolve on their studs and to roll around the internal gear, revolving the ring and the sleeve bearing the sprocket, which now turns in the direction opposite to that resulting to the application of the reverse, or in the same direction as the crank shaft.

For the high speed, a clutch is engaged that locks the internal gear to the crank shaft, and the four gears then being held between these two are carried around with them, and the sprocket rotates accordingly. When this combination is used, none of the gears are in motion, all revolving with the crank shaft but not on their studs.

The planetary change-speed mechanism gives excellent results for light work, but having only two speeds forward is not adapted to high-powered cars. As the speeds result from the tightening of brake bands on the drums, there is no danger of damaging the gears by mishandling, for the brakes will slip before the teeth will give way. The brakes, which are leather-lined strips of steel, require attention from the wearing of the leather, and the slipping that results from oil working in between them and their drums. No foot clutch is necessary, for the tightening and loosening of the brake bands is controlled by a lever; in some designs, the reverse is applied by means of a foot pedal, and this may be used in braking the car.

Fig. 36.—Individual Clutch and Friction Drive.

The individual-clutch type of change-speed mechanism consists of two shafts, one being an extension of the crank shaft, and the other parallel to it (Fig. 36). On the crank shaft is a sleeve bearing the sprocket and a gear, this sleeve being so arranged that it may revolve loosely, or be locked to the crank shaft and made to revolve with it by a clutch. The crank shaft in addition bears two fixed gears, one being for the low speed and the other for the reverse. On the countershaft is a fixed gear in mesh with the gear carried on the sleeve on the crank shaft, and two loose sleeves bearing gears that are in mesh with the fixed low-speed and reverse gears on the crank shaft. These sleeves are provided with clutches by which they may be locked to the countershaft to revolve with it, or disconnected from it. When the three clutches are disengaged, the crank shaft in revolving carries with it the fixed low-speed and reverse gears, the sleeve bearing the sprocket and gear remaining stationary. The sleeves on the countershaft revolve because their gears are in mesh with the fixed crank-shaft gears, but the countershaft remains stationary. In engaging the low speed, the clutch is thrown in, forcing the countershaft to revolve with the fixed gear, the fixed gear on the countershaft then revolving the gear and driving sprocket carried on the sleeve on the crank shaft. Because of the difference in the size of the gears, the countershaft will revolve at a slower speed than the crank shaft, and the driving sprocket will make but one revolution while the crank shaft makes several. This it is free to do, for the sleeve carrying the sprocket is in no way connected with the crank shaft. For the high speed, the low-speed clutch is withdrawn, and the driving-sprocket clutch engaged, causing the sprocket to revolve with the crank shaft.

The reverse is caused by the introduction of an idler gear between the gears of the crank shaft and countershaft, by which the movement of the latter is reversed.

The application of the friction type of change-speed mechanism to automobiles is recent, and is giving good results for light work. It consists in its simplest form of a heavy disk carried on the engine shaft, on the face of which runs a wheel sliding on a square shaft, so that the two may be in contact at any point from the edge to the center of the disk (Fig. 36). When the wheel is at the center of the disk it is not moved, and the number of speeds at which the square shaft may be driven in relation to that of the disk varies from nothing to the limit, which is obtained when the wheel is in contact with the outer edge of the disk. For the reverse, the wheel is moved across the center of the disk, where it is revolved in the opposite direction.

Another form of friction drive provides two driving disks, the wheel bearing against both, so that its movement is more positive, and there is less chance for slipping.