汽车专业英语电子课件Unit4

1、Unit 4Fuel Supply SystemText AText A Introduction of Fuel Supply SystemThe function of the fuel supply system is to store and supply fuel to the cylinder chamber where it can be mixed with air, vaporized and burned to produce energy. Fuel injection has become the primary fuel delivery system used in

2、 automotive engines, and having almost completely replaced carburetors in the late 1980s. A fuel-injected engine often produces more power than an equivalent carbureted engine. Fig.4.1 shows the basic structure of fuel-injected engine.Text B Principle and Construction Principle and ConstructionThe f

3、uel, which can be either gasoline or diesel is stored in a fuel tank. A fuel pump draws the fuel from the tank through fuel lines and delivers it through a fuel filter to fuel injector, then delivered to the cylinder chamber for combustion. If anyone of the parts in the system break down the engine

4、will not run.Text B Principle and Construction Principle and ConstructionFuel Tank Tank location and design are always a compromise with available space. Most automobiles have a single tank located in the rear of the vehicle. In the tank there is a sending unit which tells the gas gauge how much gas

5、 is in the tank. Fuel tanks today have internal baffles to prevent the fuel from splashing back and forth. All tanks have a fuel filler pipe, a fuel outlet line to the engine and a vent system. All fuel tanks must be vented. Before 1970, fuel tanks were vented to the atmosphere, emitting hydrocarbon

6、 emissions. Since 1970 all tanks are vented through a charcoal canister, into the engine to be burned before being released to the atmosphere.Text B Principle and Construction Principle and ConstructionFuel PumpTwo types of fuel pumps are used in automobiles: mechanical and electric. All fuel inject

7、ed cars today use electric fuel pumps, while most carbureted cars use mechanical fuel pumps. Many cars today, locate the fuel pump inside the fuel tank. Mechanical pumps operate on pressures of 46 psi (pounds per square inch), while electric pumps can operate on pressures of 3040 psi. Current is sup

8、plied to the pump immediately when the key is turned. This allows for constant pressure on the system for immediate starting. Electric fuel pumps look identical, so be careful when replacing a fuel pump that the proper one is used. Fuel pumps are rated by pressure and volume. When checking fuel pump

9、 operation, both specifications must be checked and met.Text B Principle and Construction Principle and ConstructionFuel FilterThe fuel filter is the key to a properly functioning fuel delivery system. Most cars use two filters. One inside the gas tank and the other one in a line to the fuel injecto

10、rs or carburetor. Unless some severe and unusual condition occurs to cause a large amount of dirt to enter the gas tank, it is only necessary to replace the filter in the line.Text B Principle and Construction Principle and ConstructionFuel InjectorIn EFI-equipped engines fuel injection is done with

11、 injectors, which are small on/off valves controlled by an electronic signal. Fig.4.2 shows the animated cut of a typical fuel injector.Text B Principle and Construction Principle and ConstructionText C EFI EFIWith the advent of electronic fuel injection (EFI), the diesel and gasoline hardware has b

12、ecome similar. In some designs the engine management system also controls the transmission. EFI mainly consist of injectors, fuel pump, fuel pressure regulator, ECM, crank/cam position sensor, hall effect sensor, MAF sensor(sometimes this is inferred with a MAP sensor) and oxygen sensor. Sensors monitor the engines operation and environmental conditions and transmit the data to the engine management system to determine how much fuel should be pumped to the fue