英语翻译VALVE gearIn an internal combustion engine,the valve gea

英语翻译
VALVE gearIn an internal combustion engine,the valve gear provides timely admission of the fresh charge into the cylinders and exhaust of spent gases from them.For this purpose the valves at definite moments open and close the intake and exhaust ports in the cylinder head,through which the cylinders communicate with the intake and exhaust manifold.The valve gear is composed of timing gears,a camshaft,tappets,push rods,rockers,valves,valve seats,spring with fasteners and valve guides.The timing gears in most engines are housed in a special case fitted at the front end of the engine .These are necessary to transmit rotation from the crankshaft to the camshaft,fuel injection pump shaft ,and to oil pump and other mechanisms.The gears are made of steel and use helical teeth to reduce noise.Camshaft's function is to open the engine valves positively and timely,in a definite sequence,and to control their closing against the return action action of the valve springs.The shaft is made integral with its cams and bearing journals.Each cam controls a single valve,either intake or exhaust.In some autombile engines,the camshaft is made integral with fuel pump eccentric wheel and oil pump drive gear.The camshaft bearings are lubricated with oil supplied under pressure from the main gallery in the cylinder block.The tappets serve to transmit the force from the camshaft to the push rods.The tappets are small cylindrical bores receiving the push rods.They are made of cast iron or steel and located in the guides ,which may be made integral with cylinder block or removable as in the engine.When the engines operate,the tappets continuously rotate about their axes for uniform wear.The rotaion is ensured by a convex surface of their bottoms and a slanted surface of the cams.The push rods transmit the force from the tappets to the rocker.They usually have small convex balls inserted on each of their ends.These convex balls fit into the tappet and rocker arm to allow proper movement.Overhead camshafts do not need the push rod.