外文翻譯---發(fā)動(dòng)機(jī)零件及其工作原理模具設(shè)計(jì)與制造-模具設(shè)計(jì)(存儲(chǔ)版)
【正文】 f today!ˉ s automobiles use sparkignitedfourstroke reciprocating gasoline engines. A reciprocating gasoline engine has a round piston in a cylinder, a connecting rod, and a crankshaft. The principle of its operation is simple. The piston moves up in the cylinder, pressing a mixture of air and fuel in front of it. Compressing the air and fuel makes it very flammable. When the piston reaches the top of its travel, the airfuel mixture is the piston is pushed down in the cylinder by the expanding gases, it pushes on the rod, forcing the crankshaft to rotate. Power is taken from the rotation of the crankshaft to propel the car. As the crankshaft turns, the piston is returned to the top of the cylinder to repeat the cycle again. The continuing upanddown motion of the piston is why the engine is called a reciprocating engine. The burning mixture is sealed into the cylinder on the top end by a cylinder head and a head gasket (). The cylinder head hasintake and exhaust ports. The intake port allows the flow of the airfuel mixture into the cylinder. The exhaust port allows the escape of the exhaust gases after the mixture has been burned. Each port is sealed by a valve that is opened by a lobe on the camshaft and closed by a spring (). The piston is sealed to the cylinder with piston rings that slide against the cylinder wall as the piston moves up and down. FourStroke Cycle The fourstroke cycle is described here using a single cylinder engine (). Automobile engines actually have multiple cylinders. The movement of the piston from the top of its travel to the bottom of its travel is called a stroke. Each cycle required to burnthe airfuelmixture has four strokes. Hence the name, fourstroke cycle. 共 9 頁 第 5 頁 The Valve Is Operated by a Lobe The FourStroke Cycle During the intake stroke, the piston is pulled down by the turning crankshaft, creating a vacuum above it. Because the intake valve is open while the piston is moving down, the airfuel mixture is drawn into the cylinder through the intake valve port. The mixture is supplied to the cylinder by the fuel system. Gasoline is especially bustible when one part of it is atomized with about 15 parts of air. Atomization makes the mixture like fog. The piston moves back up in the cylinder on the pression stroke, pressing the airfuel, making it far more bustible. As the piston approaches the top of its travel, a spark plug ignites the mixture. During the power stroke the burning fuel expands rapidly, forcing the piston to move back down in the cylinder. The exhaust valve opens as the piston approaches the bottom of its is so that burning gases can escape before the piston begins to move upward in the cylinder once again. 共 9 頁 第 6 頁 During the exhaust stroke the piston moves back up, forcing any remaining e
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