Motor-car principles; the gasoline automobile

by Roger B. Whitman

When the car is moving, sliding the gears without first withdrawing the clutch will bring together two gears that are revolving at different speeds, and as it is necessary for them to be rotating equally in order that they may mesh, either the speed of the car must be changed to bring the speed of the gear on the square shaft to that of the countershaft gear, or the speed of the engine must be changed to bring the countershaft gear to the speed of the gear on the square shaft. If the change is from a low to a higher speed, the countershaft will be moving much faster than the square shaft, and their gears being brought into contact will result in the slowing of one and speeding up of the other until the speeds are the same, but in so doing the ends of the teeth will grind against each other, resulting in the wear of the chisel-pointed ends, if not in the breaking of the teeth. Withdrawing the clutch obviates this difficulty, for it frees the countershaft, permitting its gear to take the speed of the square-shaft gear without wear or damage, and when the change is made, the slow engagement of the clutch brings the speed of both to that required by the crank shaft.

CHAPTER IX
TRANSMISSION—(Continued)

While the planetary type of change-speed mechanism, which is in extensive use for runabouts and light commercial wagons, also employs gears, their arrangement is along different lines. The first three diagrams in Fig. 35 serve to illustrate the principle.

Fig. 35.—Planetary Type.

The gear A in these diagrams is attached directly to the crank shaft, and in mesh with it are four other gears (B) of the same size. Surrounding them is an internal gear (C), this being a ring with teeth cut on its inner face, the four gears meshing with it. The shafts, or studs, on which the four gears revolve are supported by a metal ring (D), which maintains the gears at equal distances from each other. The first diagram shows the mechanism in the reverse position, for driving the car backward, the car being driven by the internal gear. To have the internal gear revolve in the direction opposite to that of the crank shaft, as is necessary, the ring supporting the four gears is held stationary, with the result that as the crank-shaft gear revolves the four gears are revolved on their studs. As these gears are in mesh with the internal gear, that is revolved, and moves in the same direction as the four gears and in the opposite direction to the crank shaft.

For the low-speed forward, the ring is released and the internal gear held stationary, the car now being driven by the ring instead of by the internal gear. If the four gears were free from the internal gear, they and their ring would revolve with the crank-shaft gear without rotating on their studs, but being in mesh with the internal gear, they roll around it as a wheel rolls along the ground, rotating on their studs. A simple experiment that will illustrate this motion is to crook the forefinger around a napkin ring or similar object, placing a pencil between it and the finger, and revolving the ring with the other hand. The finger being stationary, the pencil, which is revolved in the opposite direction to the ring, will roll along it. In this the napkin ring represents the crank-shaft gear, the pencil one of the four gears, and the finger the internal gear. As the four gears roll around, the ring moves also, for it is carried by the studs on which the four gears revolve. If each of the four gears has fifty teeth, and the internal gear two hundred teeth, each gear must make four revolutions in order to roll around the internal gear to the point where it started. The crank-shaft gear also having fifty teeth, it revolves at the same speed, and as four revolutions of the four gears are necessary in order that they may roll completely around the internal gear, the crank-shaft gear will make four revolutions in the same time. The ring moves with the four gears, and revolves once around the crank shaft in the same time. As the car moves according to the rotation of this ring, it will go at one quarter the speed that it would make if the wheels were directly connected with the crank shaft instead of with the ring.

For the high speed, the internal gear and the ring are locked to the crank shaft so that all revolve together, the wheels being driven by either the ring or the internal gear.

In these diagrams the drive of the wheels is supposed to be shifted from the internal gear to the ring, which is not a practical arrangement, and the planetary change-speed mechanism as applied to an automobile is shown in the lower diagram in Fig. 35.

In this there are two sets of crank-shaft gears, gears and rings, and internal gears, one set being for the reverse and the other for low and high speeds. Between the two crank-shaft gears is a loose sleeve, one end of which forms the internal gear for the reverse, and the other end the ring supporting the studs on which revolve the four gears for the low speed. The sprocket for the chain drive to the rear axle is carried on this sleeve. Two more loose sleeves are on the shaft, one forming the ring on which revolve the four gears for the reverse, and being extended to form a brake drum outside of the internal gear, and the other carrying the internal gear for the low-speed combination, its outside face serving as a brake drum.