【正文】 Such belts are made of synthetic rubber and reinforced with internal steel or fiberglass strands. The belts have teeth, or slotted spaces to engage and drive teeth on gear wheels. A belt typically is used on engines with overheadcam valve trains. （ 2） Chain drive On some engines, a metal chain is used to connect the crankshaft and camshaft gears. Most pushrod engines and some OHC engines have. （ 3） Gearlchains drive The camshaft and crankshaft gears can be connected directly, or meshed. This type of operating linkage monly is used on older sixcylinder, inline engines. A camshaft driven by a chain or belt turns in the same direction as the crankshaft. But a camshaft driven directly by the crankshaft gear turns in the opposite direction. Timing belts are used because they cost less than chains and operate more quietly. A typical timing belt is made of neoprene (synthetic rubber) reinforced with fiberglass. 。 + 17176。 ATDC. Thus, for a period of 34176。. But like the inlet valve, the exhaust valve needs time to reach the fullopen position, It also needs time to reach the fullclosed position. So the exhaust valve opens before BDC and closes after TDC. Valve Overlap The intake opens at 17176。 revolution, or 180176。 they enclose, or encase, the crankshaft. The oil pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine. The oil drains off and runs down into the pan. Thus, there is constant circulation of oil between the pan and the working parts of the engine. Inlet Valve Timing If the inlet valve opened at TDC of the intake stroke and closed at BDC of that stroke, it would have a duration of 180176。s mechanical energy into electrical energy and recharges the battery. Engine Block The engine block is the basic frame of the engine. All other engine parts either fit inside it or fasten to it. It holds the cylinders, water jackets, and oil engine block also holds the crankshaft, which fastens to the bottom of the block. The camshaft also fits inside the block, except on overheadcam engines (OHC). In most cars, this block is made of gray iron, or an alloy (mixture) of gray iron and other metals, such as nickel or chromium. Engine blocks are castings. Some engine blocks, especially those in smaller cars, are made of cast aluminum. This metal is much lighter than iron. However, iron wears better than aluminum. Therefore, the cylinders in most aluminum engines are lined with iron or steel sleeves. These sleeves are called cylinder sleeves. Some engine blocks are made entirely of aluminum. Cylinder Head The cylinder head fastens to the top of the block, just as a roof fits over a house. The underside forms the bustion chamber with the top of the piston. The most mon cylinder head types are the hemi, wedge, and three of these terms refer to the shape of the engine39。s not normal deformation of the cylinder and piston damage the normal clearance, resulting in the deterioration process. Therefore, how to reduce the gasoline engine heat load, it is to enhance its overall performance an important research topic. Engine The engine acts as the power unit. The internal bustion engine is most mon: this obtains its power by burning a liquid fuel inside the engine cylinder. There are two types of engine :gasoline(also called a sparkignition engine) and diesel(also called a pressionignition engine).Both engines are called heat engines。 Diesel easy evaporation in winter when cold starting problems. Because of these features, previously used in diesel engines, medium radial truck. The new development : small highspeed diesel engine emission standards has been achieved in Euc22 rope III. Traditionally, due to relatively heavy diesel engine or gasoline engine power as indicators (low speed), noise, vibration higher. Smoke and carbon particles (PM) emissions is fairly serious, very little has been favored by car. But with the advances in technology in recent years Diesel, especially small highspeed diesel engine is a new development of a number of advanced technologies, Fo