高职高专汽车专业英语.ppt

1、书名：汽车专业英语 ISBN： 978-7-111-42342-3 作者：卢晓春 出版社：机械工业出版社 本书配有电子课件,Task 1 The Operation Cycle of an Engine,Paragraph,At present, the most automobile uses an internal combustion engine in the world. What is an internal combustion engine? How does the internal combustion engine work? Engine Construction,Fo

2、ur strokes The most common engine is the four-stroke piston engineThese four strokes are intake stroke, compression stroke，power stroke and exhaust stroke.,Intake Stroke The intake stroke of a four-stroke engine begins with the piston at top dead center(TDC)The starter causes the crankshaft to rotat

3、e in a clockwise direction（Fig. 2-3） The crankshaft，through the connecting rod，forces the piston to move downwardThis downward movement of the piston creates a vacuum，a difference in pressure，in the space above the pistonThe engine manufacturer times the intake valve action so that it opens automati

4、cally at or slightly before the piston starts downTherefore, a mixture of gasoline and air，pushed by the atmospheric pressure outside the engine, rushes through the intake manifold and into the engine cylinderAt the same time, the exhaust valve remains closed during this downward stroke of the pisto

5、n. This valve closure prevents the entering airfuel charge from escaping through the exhaust port. After the piston reaches the bottom of its first stroke, the cylinder is practically full of an airfuel chargeThe drawing of an airfuel charge into the cylinder in this manner，during the downward movem

6、ent of the piston，constitutes the intake stroke of the piston,Compression Stroke After the piston reaches bottom dead center(BDC)，it moves upward again as the starter continues to turn the crankshaft in a clockwise directionAs the piston is beginning to move upward，the intake valve closes，and the ex

7、haust valve remains closedSince both valves are closed，the piston compresses the airfuel mixture in the small space between the top of the piston and the cylinder headAs the piston reaches TDC again during its upward travel，the compression stroke of the piston is overThe airfuel charge is now under

8、compression so that it will produce a great deal of power when the spark plug ignites it,Power Stroke Just as or slightly before the piston reaches TDC on the compression stroke with the airfuel mixture fully compressed，a timed electrical spark appears at the spark plugThis spark ignites the compres

9、sed airfuel mixtureThe burning mixture begins to expand；the pressure in the combustion chamber above the piston immediately increasesThis results in a high pressure applied to the top of the pistonNow，both valves remain closed during the power strokeThis assures that the total force of the expanding

10、 gas applies itself to the head of the pistonThis tremendous force pushes the piston downward on the power stroke，causing the connecting rod to rotate the crankshaft. In other words，the force resulting from the expansion of the burning airfuel mixture is turning the crankshaft,Exhaust Stroke Near th

11、e end of the downward movement of the piston on the power stroke，the camshaft opens the exhaust valve，but the intake valve remains closedAlthough much of the gas pressure has expended itself driving the piston downward，some pressure still remains when the exhaust valve opensThis remaining pressurize

12、d gas flows comparatively freely from the cylinder through the passage (port) opened by the exhaust valve. Then，as the piston again moves up in the cylinder，it drives any remaining gases out of the cylinder past the open exhaust valveAs the piston travels through the TDC position and starts downward

13、 again in the cylinder，a new operating cycle beginsThe four strokes are continuously repeated in every cylinder as long as the engine remains running,Words & expressions vehicle：交通工具，车辆 charge：充气，装料 engine：发动机， 引擎， draw：吸引，吸人 stroke：冲程，行程 constitute：组成，构成 piston：活塞 ignite：点火，点燃 crankshaft：曲轴 spark：火

14、花 intake：入口，进口，吸入 combustion：燃烧 clockwise：顺时针方向 port：通道，港口，端口 gasoline：汽油 internal combustion engine：内燃机 manifold：进、排气歧管 intakestroke：进气行程 remain：保持，逗留，剩余 compression stroke： 压缩行程 airfuel mixture： 空气燃油混合物(可燃混合气 exhaust stroke：排气行程 power stroke：作功行程 connecting rod ：连杆 top dead center(TDC) ：上止点 atmosp

15、heric pressure ：大气压力 intake valve：进气门 bottom dead center(BDC)：下止点 exhaust valve：排气门 spark plug：火花塞,Task 2 Connecting Rod and Crankshaft,Paragraph,Connecting rod and crankshaft Connecting rod and crankshaft is very important framework of the engine, which converts the heat energy of fuel into mechani

16、cal energy for moving the vehicleHow does it is achieve? Piston The engine manufacturer fits a piston into each cylinder of the engineThe piston is a movable part or plug that receives the pressure from the burning airfuel mixture and converts this pressure into reciprocating(up-and-down)motion. Man

17、ufacturers make most engine pistons from aluminum, which is less than half the weight of iron. Iron pistons were common in early automotive engines.,Piston Rings Some operating clearance must exist between the piston and the cylinder wall；however，some form of seal is necessary between the piston and

18、 the cylinder wall to prevent blowbyConsequently，piston rings are used to provide the necessary seal to eliminate blowby and to control oil consumption. Automotive pistons have two kinds of rings：compression and oil controlThe compression rings primarily seal against the loss of airfuel mixture as t

19、he piston compresses it and also the combustion pressure as the mixture burnsWhile the function of the oil control ring is to prevent excessive amounts of oil from working up into the combustion chamber,Connecting Rods As mentioned earlier，the piston moves up and down in the cylinder，in a reciprocat

20、ing motionIn order to rotate the drive wheels，a connecting rod and crankshaft must change reciprocating motion to rotaryThe connecting rod itself attaches at one end to the piston and on the other end to the crankpin section of the crankshaft,Crankshaft The crankshaft is the main rotating member，or

21、shaft，of the engineIts function，along with the connecting rod，is to change the reciprocating motion of the piston to rotaryIn addition，the crankshaft is responsible for driving the camshaft through timing gears, plus operating the accessories via a system of belts and pulleysLastly，the crankshaft Ca

22、rries the total torque-turning or twisting effort and delivers it to the flywheelFrom the flywheel the torque then passes either to the friction clutch assembly or to the torque converter Designed into the one-piece crankshaft are areas for main bearing journals，crankpins，counterweights，flywheel fla

23、nge，and driving hub,Flywheel The flywheel is a comparatively heavy wheel，bolted to the flange on the rear end of the crankshaftIts function is to keep the engine running smoothly between power strokesIts inertia tends to keep the flywheel rotating at a constant speedThe flywheel also has several oth

24、er functionsFor example，the flywheel has gear teeth around its outer circumferenceThese teeth mesh with teeth located on the starting motor drive pinion in order to crank the engine overIn addition, the rear surface of the flywheel serves as the driving member of the clutch assembly,Words 圆周 piston

25、ring 活塞环 bearing cap 轴承盖 compression ring 气环 thrust washer 推力垫片 oil control ring 油环 main bearing 主轴承 connecting rod 连杆 connecting rod cap 连杆盖 connecting rod bearing 连杆轴承,Task 3Valve Gear,Valve gear When the engine is running, the valve opened and closed frequently, that controls fuel entry and exhau

26、st emissions. Valve Modem engines have cylinder heads that contain valvesThese valves open and close ports to allow or stop the flow of gases into or from the combustion chamberEach cylinder requires at least two：an intake and exhaust,Camshaft The camshaft is another rotating shaft within the engine

27、；it serves usually three functionsFirst，the camshaft has a series of cams that can change rotary motion to straight-line motion which cause the intake and exhaust valves to openThe camshaft will have one cam for each valve，or，in most engines，two cams per cylinderSecond , the camshaft has an eccentri

28、c，or special cam ，designed to operate the fuel pumpFinally，the camshaft has a gear that drives the oil pump and ignition distributor Lifter (Tappet) A lifter is a cylindrical part within an engine that rests on a cam of the camshaftAs the camshaft rotates ，the cam raises the lifter，and the lifter in

29、 turn opens a valveThe lifter may be in direct contact with the tip of the valve stem ，or it may bear against a push rod that functions along with a rocker-arm assembly to open a valve,Push Rods and Rocker Arms Along with the camshaft，valves，valve seats，and valve springs，some valve trains have sever

30、al other componentsthe push rods and rocker armsThe push rod is a metal rod that fits between the lifter and the rocker arm. Its function is to transmit cam lobe lift from the camshaft to the rocker arm assemblyThe rocker arm is nothing more than a precision-designed leverIts function is to convert

31、the upward motion of a push rod into downward motion that compresses the spring and opens the valve Valve Timing Duration is the length of time a valve is openThe measurement of this open period is not in units of time because the actual time a valve remains open varies with engine speed Therefore，t

32、his measurement is in degrees of crankshaft rotation ， which does not change with speed To lengthen the time and to accelerate the air/fuel mixture flow into the cylinders, both the intake and exhaust valves must be open at the same time for a short periodThe overlap is provided in order to take adv

33、antage of the inertial forces in the escaping exhaust gases. These gases create strong suction as they rush out of the combustion chamber,Timing Gears The manufacturer machines a cam lobe into a given shape that produces a given amount of alve-open duration and overlap. Furthermore，meshing the timin

34、g gears or installing the chain onto the sprockets at a specific place will time the valves to open and close at the proper moment in the engines cycle,Words & expressions Function 功能，作用Component 部分，部件，零件，元件 Cam 凸轮 Lever 杆，杠杆 Eccentric 偏心轮 Duration 持续时间 Gear 齿轮，传动装置Suction 吸入，吸引 1ifter 挺杆 Mesh 啮合，相啮

35、合 Assembly 安装，装配，部件，装置，组合体 push rod 气门推杆 cam lobe 凸轮凸起部，凸轮工作部分 valve spring 气门弹簧 valve timing 气门正时 rocker arm 气门摇臂 Sprocket 链轮齿,Task 4Engine Lubricating System,Engine Lubricating System Lubrication Principles Reducing friction to minimize wear and loss of power is the primary job a lubrications syst

36、em must perform. Residual oil on engine parte also provides lubrication for engine start-up. The engine oil forms a seal among the pistons, rings and cylinders. It also helps to cool engine parts. Without the cleaning action of the lubricating system, carbon and varnish build-up would be excessive.

37、The engine oil also absorbs the shock and dampens the noise of moving parts. How successful the lubrication system is in performing all these functions depends on a number of factors and conditions. There must be an adequate supply of good-quality lubricant delivered to all moving engine parts under

38、 sufficient pressure to provide hydrodynamic lubrication of rotating parts and oil adhesion to surface subject to sliding friction.,Parts of the Pressure-Lubrication System Oil pan The oil pan bolts under the engine block, where it seals off the bottom of engine. Shaped like trough, this sheet-metal

39、 pan serves as the reservoir for about 5 quarts of oil. As oil flows from the engine, it drains downward into the oil pan. The oil pump sucks oil from the lowest part of the oil pan-the oil sump. Many oil pans have baffles, which are thin metal partition. These baffles keep the oil in the sump when

40、the car corners heard of brakes suddenly. A drain plug at the bottom of the sump allows oil to be drained from the engine. The oil-pan gasket fits between the oil pand and the bottom of the engine block.,In most time, the oil circulates in the engine, and then returns to the pan. It stays in the pan

41、 until drawn back into the engine by the oil pump. During operation, the sump usually holds 2 to 3 quarts of oil. The rest of the oil moves through the passageways of the lubrication system. With the engine off, the pan holds about four quarts of oil. The fifth quart is in the oil filter. Because a

42、pool of oil always rests in the sump, the type of lubrication system is called a wet-sump oiling system. A dry-sump oil system is used in many racing engines. This system has a separate storage tank for the oil. A second oil pump draws oil from the oil pan as soon as the oil drains from the engine.

43、As a result, a dry-sump system can circulate more oil through the engine than a wet-sump system.,Oil Pump In most cars, the oil pump is in the crankcase above the sump. It draws oil through a tube that extends downward into the sump. This tube, called the oil-pump pickup tube, has a filter screen ov

44、er its bottom end. Ten screen keeps large pieces of sludge and dirt from being drawn into the pump. The tube may be hinged on the pump end so that it can move up and down as the oil level changes in the sump. Thus, the pump always always draws oil from the top of the sump, not from the bottom where

45、the dirt and sludge tend to settle. Modern cars have two common types of oil pumps-the gear-type and rotor- type.,Oil Filters A modern engine uses a full-flow filtering system. In this system, the output of the oil pump flows through the oil filter before moving through the engine. In other words, t

46、he oil is filtered and cleaned before each trip through the engine. When an engine rens at 3,000 rpm, its entire five quarts of oil pass through the filter at least once every minute. Thus the oil filter ensures that only clean oil enters the engine.,Modern engine use replaceable oil filters. When d

47、irty, such a screw-on filter is replaced with a new one. Inside the steel outer casing of the unit, a special pater acts as a filter. Folded and tightly packed, this paper has just the right porosity. These tiny holes in the paper allow oil to pass through, but filter out dirt and sludge. The paper

48、is treated to protect it from acid or water in the oil. Normally, oil enters the oil filter from the outside. Oil enters the filter around the outer edge of the base. The oil flows through the paper to the center of the container. It thenflows out to the engine. Most filters also have a pressure-rel

49、ief valve, or bypass valve. Such a valve allows oil to flow to the engine with out going through the filter. This is necessary when the filter becomes too clogged for oil to pass through. Thus, a plugged filter allows dirty oil to circulate through the engine. To prevent this, the oil and oil filter

50、 should be changed regularly.,Engine Lubrication An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact. The heat generated due to the tremendous amounts of friction would melt the metals, leading to the destruction of the engine. To prevent this, all moving parts ride on a thin film of oil that is pumped between all the moving parts of the engine. Once between the moving parts, the oil serves two purposes. One purpose is to lubricate the be