汽车服务工程专业英语课件.ppt

Unit 1 Fundamentals of Automobile,Transmission,Variable Valve Timing,Fuel Injection Systems of Gasoline Engine,Lesson 1,Lesson 2,Lesson 5,Lesson 4,Lesson 3,Lesson 6,Brakes,Structure of Automobile,Basics of Four-stroke Cycle Engine,Lesson 1,Structure of Automobile,The body and frameThe engine or power sourceThe chassis and the electrical equipment,Fig. 1-2 illustrates the body and frame of a typical automobile,The engine is used to power the vehicle. The engine is also called the power source or motor. Most of engines are designed with several supporting technical systems.,the fuel system :mix the air and fuel in the engine.the ignition system :produce an efficient combustion process.the starting and charging system : start the engine and to keep the battery charged during operation.,the lubricating system : keep all engine moving parts lubricated so that friction is reduced internally.the cooling system : keep the engine at the most efficient operating temperature.the air intake system : get air into the engine efficiently and without dirt.,The exhaust system : clean the exhaust gases and to reduce the sound of the exhaust noise.The pollution control system : reduce various emissions from the engine including carbon monoxide, nitrogen oxide(oxides of nitrogen) ,and hydrocarbons.,The chassis consists of the transmission , the running gear and the suspension system. It is shown in Fig.1-3.,The transmission : it is defined as those components that transmit the power from the engine to the wheels.The running gear : consists of the wheels , tires, braking system and steering system.The suspension system : includes such components as the springs, shock absorbers, struts , torsion bars , axles, and connecting linkages.,The electrical equipment mainly comprises the battery ,alternator , lights , instrumentation , electrical devices and electronic control system etc.,Lesson 2,Basics of Four-stroke Cycle Engine,The fundamental parts of the conventional engine are shown in simple diagrammatic form in Fig2-1 which shows a across- section through the cylinder , piston and connecting rod of the engine.,The ideal form consists of a plain cylindrical barrel in which the piston slides, the movement of the piston or “ stroke ” being, in some cases, somewhat longer than the bore, but tending to equality or even less This is known as the stroke : bore ratio.,The usual form of piston for internal combustion engines is an inverted bucket-shape, machined to a close (but free sliding) fit in the cylinder barrel.,The connecting rod transmits the piston load to the crank, causing the latter to turn , thus converting the reciprocating motion of the piston into a rotary motion of the crankshaft The lower end, or“ big end ”, of the connecting rod turns on the crankpin.,In the great majority of internal combustion engines this is of the double-web type, the crankpin, webs and shaft being usually formed from a solid forging . The shaft turns in two or more main bearings ( depending on the number and arrangement of the cylinders ) mounted in the main frame or “crankcase” of the engine.,At one end the crankshaft carries a heavy flywheel, the function of which is to absorb the variations in impulse transmitted to the shaft by the gas and inertia loads and to drive the pistons over the dead points and idle strokes.,The four strokes of the complete cycle are shown at Fig2-2a),b),c) and d).,The four strokes of the cycle are as follows:(a)Induction strokeexhaust valve closed, inlet valve open.(b)Compression strokeboth valves closed.(c)Combustion or working strokeboth valves closed.(d)Exhaust strokeinlet valve closed :exhaust valve open.,Lesson 3,Fuel Injection Systems of Gasoline Engine,Single-point injection(SPI)Multi-point injection (MPI),Aiming the spray at the inlet valve, Fig.3-1 is relatively easy with port injection .,Continuous injectionThis is applicable to both single-and multi-point systems.Timed injection, in which injection takes place over a limited period usually, though not always, once per revolution of the crankshaft.Sequential injection , or phased injection, which, with electronic control, enables the air: fuel ratio to be regulated extremely accurately.,Lesson 4,Variable Valve Timing,Variable valve timing is generally applied in one of two ways: either the point of inlet valve closure is fixed and that of its opening varied, or both are fixed relative to each other but their timing (i.e. , the inlet phase)advanced or retarded simultaneously, generally by rotating the cam relative to the shaft.,By optimizing the valve timing, volumetric efficiency and therefore power and torque can be increased.,Variable phase control(VPC) can be affected in a number of ways. One is to advance and retard the camshaft by means of a sliding muff coupling on a divided shaft, with spiral spines on the driven and straight spines on the drive interfaces, or vice versa. This, however, suffers the disadvantage of high frictional resistance to control operation.,Another method is to install, in the belt or chain drive to the camshaft, a movable idler pulley in combination with a tensioned having a longer than usual stroke.,Movement of the idler pulley towards or away from the drive, Fig4-2,rolls it around the half-speed wheel to advance or retard the timing while, at the same time, the tensioned compensates for the movement.,Variable phase control, Fig.-,implies varying the overlap so that low-speed torque and, with it, specific fuel consumption are improved over most of the speed range. Since the duration of opening remains constant, wide-open throttle power is unaffected.,A combination of lift and timing control (VLTC) , Fig.-4can offer further performance enhancement , but is more costly than VPC.,Lesson 5,Transmission,Transmission Requirements Transmission Arrangement,(1)To provide for disconnecting the engine from the driving wheels.(2)When the engine is running, to enable the connection to the driving wheels to be made smoothly and without shock.(3)To enable the leverage between the engine and driving wheels to be varied.,(4)It must reduce the driveline speed from that of the engine to that of the driving wheels in a ratio of somewhere between about 3:1 andor more , according to the relative size of engine and weight of vehicle.,(5)Turn the drive, if necessary, through 90or perhaps otherwise realign it (6)Enable the driving wheels to rotate at different speeds (7)Provide for relative movement between the engine and driving wheels,This general arrangement of mechanical transmission is shown diagrammatically in Fig.-.,Lesson 6,Brakes,The operation performed in braking is the reverse of that carried out in acceleratingIn the latter the heat energy of the fuel is converted into the kinetic energy of the car, whereas in the former the kinetic energy of the car is converted into heat.,Two distinct demands are made upon the brakes of motor vehiclesFirst, in emergencies they must bring the vehicle to rest in the shortest possible distance, and secondly, they must enable control of the vehicle to be retained when descending long hills.,A driving wheel can be braked in two ways: directly, by means of brakes acting on a drum attached to it; or indirectly, through the transmission by a brake acting on a drum on the main shaft of the gearbox, or on the bevel pinion ,or worm, shaft of the final drive.,Considering manually-operated brakes, the brake pedal or lever may be connected to the actual brake either mechanically, by means of rods or wires, or hydraulically, by means of a fluid in a pipe.,Brakes may be classified into three groups as follows:() friction brakes;() fluid brakes; () electric brakes.,谢谢观看！,