Читать книгу Farm Machinery and Equipment - Harris Pearson Smith - Страница 18

The method of transmitting power from its source to the point of use is one of the greatest problems of the farm-equipment designer. The problem is relatively simple when a tractor is used to operate a threshing machine. The size and speed of the pulleys on the two units are approximately the same. The tractor pulley is lined up with the thresher pulley, and a flat belt is fitted over them and tightened by backing the tractor. The power is ready to be transmitted from the tractor to the thresher. But the problem is multiplied many times in the case of a self-propelled combine, where the source of power is an engine mounted on the machine. Power must be transmitted to a slow-revolving reel and to a high-speed fan. Rotating movement must be changed into back-and-forth movement for the knife on the cutter bar and to an oscillating or shaking movement for the straw rack and grain pan. All this is done by means of pulleys and belts, sprocket wheels and chain, gears, and shafts. The operation is made possible by having good bearings to support the shafts and parts. The various parts of the machine are held together by different kinds of bolts and screws. Therefore, it is well to learn something about all these units to have an appreciation of their use in the design and construction of farm equipment.