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1、英文资料翻译Emission Control SystemsThe purpose of the emission system is just that it controls the emission and exhaust from a vehicle. The idea is to turn the harmful gases a car manufactures into harmless ones that dont ruin the environment, or persons. Some of problem gases are:1. hydrocarbons（unburne
2、d）.2. Carbon monoxide.3. Carbon dioxide4. Nitrogen oxide.5. Sulfur dioxide.6. Phosphorus.7. Lead and other metal.There are five popular systems used to reduce emissions: the crankcase ventilation system, the evaporative emissions control system, the exhaust gas recirculation system and the catalytic
3、 converter system. In additional to these emissions system, some vehicles incorporate an electronically controlled fuel system, which further reduces emissions.Note: Not all vehicles are equipped with these emission systems.Crankcase ventilation systemSince the early 1960s, all cars have been equipp
4、ed with crankcase ventilation system.When the engine is running, a small portion of the gases which are formed in the combustion chamber leak pas the piston rings and enter the crankcase. Since these gases are under pressure, they tend to escape from the crankcase and enter the atmosphere. if these
5、gases are allowed to remain in the crankcase for any length of time, they contaminate the engine oil and cause sludge to build up in the crankcase. If the gases are allowed to escape to the atmosphere, they pollute the air with unburned hydrocarbons. The job of the crankcase ventilation system is to
6、 recycle thee gases back into the engine combustion chamber where they are re-burned.The crankcase gases are recycled as the engine is running by drawing clean filtered air through the air filter and into the crankcase. As they are passes through the crankcase, it picks up the combustion gases and c
7、arries them out of the crankcase, through the oil separator, through the PCV valve or orifice, and into the induction system. as they enter the intake manifold, they are drawn into the combustion chamber where they are re-burned.The most critical component in the system is the PCV valve that control
8、s the amount of gases that are recycled. At low engine speed increases, the valve opens to admit greater quantities of air to the intake manifold. Some systems do not use a PCV valve. They simply use a restrictor or orifice in the ventilation hose to meter the crankcase gases.If the PCV valve become
9、s blocked or plugged, the gases can not be vented from the crankcase. Since they are under pressure, they ill find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket, it usually creates an oil leak. Besides ca
10、using oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period, promoting the formation of sludge in the engine.Evaporative emission control systemThe evaporative emission control system is designed to prevent fuel tank and carburettor bowl vapours fro
11、m being emitted into the atmosphere. Fuel vapours are absorbed and stored by a fuel vapour charcoal canister. The canister stores them until certain engine conditions are met and the vapours can be purged and burned by the engine.The charcoal canister purge cycle is controlled different ways: either
12、 by a thermostatic vacuum switch, a solenoid or by a timed vacuum source. The thermostatic switch is installed in the coolant passage and prevents canister purge when the engine is below a certain temperature. The solenoid is usually controlled by a computer and is used on feedback fuel systems. The
13、 computer determines when canister purge is appropriate. Depending on the system, this can be engine operating temperature, engine speed, evaporative system pressure or any combination of these. The timed vacuum source uses a manifold vacuum controlled diaphragm o control canister purge. When the en
14、gine is running, full manifold vacuum is applied to the top tube of the purge valve which lifts the valve diaphragm and opens the valve.A vent located in the fuel tank, allows fuel vapours to flow to the charcoal canister. a tank pressure control valve, used on some high altitude applications, preve
15、nts canister purge when the engine is not running. The fuel tank cap does not normally vent to the atmosphere, but is designed to provide both vacuum and pressure relief.Air injection systemIntroducing a controlled amount of air into the exhaust system promotes further oxidation of the gases. This i
16、n turn reduces the amount of carbon monoxide and water, the harmless by-products of combustion. Some system use an air pump, while other use negative exhaust pulses to draw air.The air pump, usually driven by a belt, simply pumps air under a pressure of only a few pounds into each exhaust port. Between the nozzles and the pump is a check valve to keep the hot exhaust gases from flowing back into the pump and hoses thereby destroying them. Most p
