Page:Motors and motor-driving (1902).djvu/235

Rh gear wheels are arranged on their respective shafts at such intervals that when one pair are in gear, the others are out of gear.

In the gear as shown,, the largest wheel on the driving shaft is arranged to engage with , the smallest on the driven shaft, the speed of which is, when these two wheels are in gear, increased; , next in size on the lower shaft, gears with , which is larger in diameter than , so that when these two are engaged, the speed of the top shaft is less than that of the bottom one. Again, when, the smallest of the three on the driving shaft, is in gear with , the largest on the driven one, the speed of the latter is still further reduced. By moving this wheel to the left it just clears wheel  on the upper shaft, and by further movement in this direction is brought into engagement with a third or intermediate wheel, not shown in the drawing, which is in engagement with, and this, by conveying the power through the three wheels, causes  to revolve in the opposite direction to that taken by the other wheels on the top shaft, and thus a reversing action is obtained, and the driving wheels are impelled backwards instead of forwards. This shifting of the gear is effected by sliding the bottom series of gears in either direction as required, bringing the teeth of the two sets of wheels in juxtaposition and pressing the one against the other, till they slide into each other. This is an operation requiring considerable care, as both sets of wheels are revolving at a high rate of speed, one propelled by the motor and the other by the travelling car, and if they were forcibly brought together the teeth would be chipped or even broken off bodily, so that in making the change great care is necessary. The lever must be moved gently, whilst at the same time the foot must be pressed on the lever of the clutch, which is thus disconnected from the motor and the power of propulsion thus removed from the driving shaft whilst the change is being made. When putting a lower gear into operation, as is necessary when climbing a hill, the speed of the car should be allowed to fall to as nearly as possible the calculated speed of