新编汽车专业英语第3版黄汽驰电子课件Unit2PassageA.pptxVIP

Unit Two　Engine Construction;Passage A Crank Mechanism and Its Main Components;The block group contains the following main components (see Fig. 2-2):;Cylinder head is bolted to the top of the cylinder block with a gasket in between sealing the block and forming the combustion chambers with the cylinders． Cylinder head holds camshafts, valves, spark plugs and injectors． Oil panis at the bottom of the cylinder block． It is a container for storage of engine oil．;Piston and connecting-rod group has some main components as follows ( see Fig.2-3):;Pistonis a cylindrical shaped hollow part made of aluminum alloy． It can be divided into three parts: crown, ring groove and skirt (see Fig.2-4). Its reciprocating movements in the cylinder transform the energy of the expanding gases into mechanical energy．;Piston rings are inserted in the ring grooves on the top of the piston． Most pistons have three rings: the top two are compression rings and the lower ring is an oil ring． They function as sealing between the piston and cylinder wall, lubricating, heat transferring and piston supporting in the cylinder．;Connecting rod connects the piston to the crankshaft． It has a small end and a big end． The small end attaches to the piston with the piston pin and the big end connects to the crank pin of the crankshaft．;Crankshaft and flywheel group includes the following components (see Fig. 2-5):;Crankshaftis one of the most important parts in the engine． It is held in the crankcase in the cylinder block and converts the reciprocating motion of the pistons into a rotary motion for the drive wheels． In a 4-cylinder engine, the crankshaft usually has three main journals and four crank pins attached to the big ends of the connecting rods． Every crankshaft has counter weights whose purpose is to balance the weight of the connecting rods． Its front end is used to drive the valve train, water pump and cooling fan, and its rear end is used to install the flywheel．;Flywheel is a