汽車專業(yè)英語課件3chapter2.42.5

1、復習o 提問（教師說發(fā)動機漢語部件名稱，同學回答英文名稱）o 用英語說明內燃機分類方式和類別o what are four strokes in a four-stroke-cycle engine?學習內容學習內容本次課學習內容、目標和重點難點本次課學習內容、目標和重點難點學習目標學習目標難點重點難點重點2.4 pistons, connecting rods and 2.4 pistons, connecting rods and crankshaftcrankshaft2.5 valve system2.5 valve system1.1.掌握曲柄連桿機構主要組成、零件英文名掌握曲柄連桿

2、機構主要組成、零件英文名稱；稱；2.2.了解了解vvtvvt系統(tǒng)的主要功能系統(tǒng)的主要功能1.1.重點為記憶曲柄連桿機構主要組成、零件重點為記憶曲柄連桿機構主要組成、零件英文專業(yè)術語英文專業(yè)術語2.2.難點需要記憶的生詞偏多難點需要記憶的生詞偏多3.3.漢譯準確表達也是難點漢譯準確表達也是難點chapter 2 internal combustion engine2.4 pistons, connecting rods and crankshaft bearingjournalthrowattachreciprocatingbri:nlrouttrisiprkeitin.軸承軸承n.軸頸軸頸n.

3、& v.投擲，扔；投擲，扔；n.投擲距離，偏心投擲距離，偏心距離，擺幅；（距離，擺幅；（pl.）曲柄）曲柄v.附著，連接，固定（附著，連接，固定（to）a.往復的往復的2.4.1 new words and phrases 2.4.1 piston and connecting rodthe piston must move down through the cylinder to produce a vacuum to draw a fuel charge into the cylinder. it then travels up in the cylinder and compre

4、sses the mixture. when the mixture is fired, the pressure of the expanding gas is transmitted to the top of the piston. this drives the piston back down through the cylinder with great force, transmitting the energy of the expanding gas to the crankshaft. the piston then travels up through the cylin

5、der and exhausts the burned fuel charge.pistons are usually made of aluminum. often, aluminum pistons are tin-plated to allow proper break-in when the engine is started. aluminum pistons can be forged, but they are more commonly cast. cast iron is a good material for pistons used in a slow-speed eng

6、ine. it has excellent wear characteristics and will provide good performance. chapter 2 internal combustion engine2.4 pistons, connecting rods and crankshaft 2.4.2 textfig.2-5 pistons, connecting rods and crankshaft as the name implies, connecting rods are used to connect pistons to the crankshaft (

7、fig.2-5). the upper end of the rod has a hole through it for the piston pin. the bottom of the large end of the connecting rod (fig.2-6) must be removed so the rod can be installed on the crankshaft journal. the section that is removed is called the connecting rod cap. connecting rods are normally m

8、ade of alloy steel. they are drop-forged to shape and then machined.fig.2-6 connecting rodchapter 2 internal combustion engine2.4 pistons, connecting rods and crankshaft 2.4.2 crankshaft the engine crankshaft (fig.2-7) provides a constant turning force to the wheels. it has throws to which connectin

9、g rods are attached, and its function is to change the reciprocating motion of the piston to a rotary motion to drive the wheels. crankshafts are made of alloy steel or cast iron. the crankshaft is held in position by a series of main bearings. the maximum number of main bearings for a crankshaft is

10、 one more than the number of cylinders. it may have fewer main bearings than cylinders.chapter 2 internal combustion engine2.4 pistons, connecting rods and crankshaft most engines use precision insert bearings that are constructed like the connecting rod bearings, but are somewhat larger. in additio

11、n to supporting the crankshaft, one of the main bearings must control the forward and backward movement.fig.2-7 crankshaft chapter 2 internal combustion engine2.5 valve system lifterclearanceliftklirnsn.挺桿挺桿n.間隙間隙2.5.1 new words and phrases the camshaft must turn at one-half crankshaft speed. the ca

12、mshaft is linked with crankshaft by one of three ways: belt drive, chain drive and gear drive. the main components of the valve system are: camshaft. it is used to open and close the valves. generally only one camshaft is used in most engines. newer engines are increasingly equipped with two or more

13、 camshafts (figure 2-8). valves. each engine cylinder ordinarily has two valves. however, modern engines often use four valves per cylinder (two intake valves and two exhaust valves). in order to prevent burning, the valve must give off heat to the valve seat and to the valve guide. the valve must m

14、ake good contact with the seat and must run with minimum clearance in the guide.chapter 2 internal combustion engine2.5 valve system 2.5.2 text valve lifters. mechanical valve lifters were used in older engines. most valve trains that contain mechanical lifters have some provision for adjusting clea

15、rance. hydraulic valve lifters perform the same job as mechanical lifters. however, hydraulic lifters are self-adjusting, operate with no lifter-to-rocker arm clearance, and uses engine oil under pressure to operate. hydraulic lifters are quiet in operation.chapter 2 internal combustion engine2.5 va

16、lve system fig.2-8 dual overhead camshaft（dohc）補充：three types of camshaft drive凸輪軸三種傳動方式：凸輪軸三種傳動方式：belt drive 帶傳動帶傳動gear drive 齒輪傳動齒輪傳動chain drive 鏈傳動鏈傳動 variable valve timing system eliminates the compromise of conventional valve timing with the introduction of vvt. by continuously varying intake v

17、alve timing (up to 60 crank angle degrees), toyota optimizes low- to mid-speed torque, improves fuel economy and lowers emissions without having a negative impact on idle. in essence, the system controls valve overlap, which means it can eliminate it completely for a glass smooth idle, or maximize i

18、t to boost volumetric efficiency and reduce pumping lossesthis translates into power, economy and cleaner running at all engine speeds. 補充： continuously variable valve timing （cvvt） the heart of the system is the intake cam pulley, which consists of an inner and outer section. the inner portion is fixed to the camshaft and nests inside the belt-driven outer pulley via helical spline gears. an electronically controlled hydraulic piston moves the pulley halves relati