Fig. 47.—One form of governor used on motor cars.
A sketch of a neat governor, with regulating attachment, is given in Fig. 47. The governor shaft is driven from the engine. As the balls, B B, increase their velocity, they fly away from the shaft and move the arms, A A, and a sliding tube, C, towards the right. This rocks the lever R, and allows the valves in the inlet pipe to close and reduce the supply of air and gas. A wedge, W, which can be raised or lowered by lever L, intervenes between the end of R and the valve stem. If this lever be lifted to its highest position, the governing commences at a lower speed, as the valve then has but a short distance to travel before closing completely. For high speeds the driver depresses L, forces the wedge down, and so minimizes the effect of the governor.
THE CLUTCH.
The engine shaft has on its rear end the fly-wheel, which has a broad and heavy rim, turned to a conical shape inside. Close to this, revolving loosely on the shaft, is the clutch plate, a heavy disc with a broad edge so shaped as to fit the inside of a fly-wheel. It is generally faced with leather. A very strong spring presses the plate into the fly-wheel, and the resulting friction is sufficient to prevent any slip. Projections on the rear of the clutch engage with the gear-box shaft. The driver throws out the clutch by depressing a lever with his foot. Some clutches dispense with the leather lining. These are termed metal to metal clutches.
THE GEAR-BOX.
We now come to a very interesting detail of the motor car, the gear-box. The steam-engine has its speed increased by admitting more steam to the cylinders. But an explosion engine must be run at a high speed to develop its full power, and when heavier work has to be done on a hill it becomes necessary to alter the speed ratio of engine to driving-wheels. Our illustration (Fig. 48) gives a section of a gear-box, which will serve as a typical example. It provides three forward speeds and one reverse. To understand how it works, we must study the illustration carefully. Pinion 1 is mounted on a hollow shaft turned by the clutch. Into the hollow shaft projects the end of another shaft carrying pinions 6 and 4. Pinion 6 slides up and down this shaft, which is square at this point, but round inside the loose pinion 4. Pinions 2 and 3 are keyed to a square secondary shaft, and are respectively always in gear with 1 and 4; but 5 can be slid backwards and forwards so as to engage or disengage with 6. In the illustration no gear is "in." If the engine is working, 1 revolves 2, 2 turns 3, and 3 revolves 4 idly on its shaft.
Fig. 48.—The gear-box of a motor car.