汽车专业英语(幻灯片)Chapter 3 Engine(2.5).ppt
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1、Review 1:Whats the main function of the Valve System?,Open and close the valves at just the right time.2)Remove as much of the burned gases as is possible and increases volumetric efficiency.,2.5:valve system,Review 2:How many types of the Valve Train?,OHC(overhead camshaft)DHOC(dual overhead camsha
2、ft),Push-rod,Review 3:How many types of the Camshaft Drive Mechanism?,Gear Drive Chain Drive Belt Drive,Rocker-arm(摇臂),Camshaft,Tappet(Cam follower)(挺柱/挺杆),Push-rod,Valve clearances,Valve Spring,Valve stem,Valve seat(气门座),Valve head,Piston,Rocker-shaft,adjuster,Valve operation:The cam is an egg-shap
3、ed piece of metal on a shaft that rotates in coordination with the crankshaft.The metal shaft,called the camshaft,typically has individual cams for each valve in the engine.As the camshaft rotates,the lobe,or high spot of the cam,pushes against parts connected to the stem of the valve.This action fo
4、rces the valve to move downward.This action could open an inlet valve for an intake stroke,or open an exhaust valve for an exhaust stroke.,凸轮是一个蛋形的金属块,它安装在同曲轴协调运转的一根金属轴上,该轴称为凸轮轴,其上有同发动机每一个气门对应的凸轮。当凸轮轴旋转时,凸轮的最高点,也就是凸圆,推动连接气门杆的部件,使得气门向下运动,在进气冲程打开进气门,在排气冲程打开排气门。,Valve operation:In this arrangement,the
5、cam lobes push against round metal cylinders called cam follower.As the lobe of the cam comes up under the cam follower,it pushes the cam follower upward(away from the camshaft).The cam follower rides against a push rod,which pushes against a rocker arm.The rocker arm pivots on a shaft through its c
6、enter.As one side of the rocker arm moves up,the other side moves down,just like a seesaw.The downward-moving side of the rocker arm pushes on the valve stem to open the valve.(p27),在这种方案中,凸轮凸圆推动圆形的金属筒,也就是挺柱。凸轮凸圆运动到挺柱下方时,推动挺柱远离凸轮轴向上运动。挺柱带着推杆,推杆推动摇臂,摇臂绕摇臂轴的中心转动。摇臂的一端升起,另一端就落下,这类似于跷跷板。摇臂向下运动的一端推动气门杆打开
7、气门。,Because a push-rod valve train has additional parts,it is more difficult to run at high speeds.Push-rod engines typically run at slower speeds and,consequently,produce less horse-power than overhead camshaft designs of equal size.由于推杆气门传动有附件,很难高速运行推杆气门传动的发动机运转速度慢,因此与同样尺寸的顶置凸轮轴发动机相比,其马力要小,Valve c
8、learance:When the engine runs in compression stroke and power stroke,the valves must close tightly on their seats to produce a gas-tight seal and thus prevent the gases escaping from the combustion chamber.If the valves do not close fully the engine will not develop full power.Also the valve heads w
9、ill be liable to be burnt by the passing hot gases,and there is the likelihood of the piston crown touching an open valve,which can seriously damage the engine.,当发动机在压缩冲程和作功冲程工作时,气门必须紧贴在气门座上,形成良好的气密性以防止燃烧室漏气。如果气门关闭不严,发动机就不能发挥出全部的功率。而且气门头部容易被经过的高温气体烧蚀,活塞顶部也可能会碰到气门使发动机严重损坏。,Valve clearance:,所以在气门传动机构中
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