汽车专业英语Chapter3Engine (2).ppt

汽汽车专业英英语Chapter3EngineChapter 3 Valve and Gasoline Fuel System 3/7/20232Automotive Engineering EnglishQu.2:How many types of Valve Train?(气门传动气门传动)OHC(Overhead Camshaft)顶置凸轮轴顶置凸轮轴Push-rodChapter 3 Valve and Gasoline Fuel System 3/7/20233Automotive Engineering EnglishQu.3:How many types of Camshaft Drive Mechanism?Belt Drive Gear DriveChain DriveChapter 3 Valve and Gasoline Fuel System 3/7/20234Automotive Engineering EnglishRocker-arm（摇臂）（摇臂）CamshaftTappet(Cam follower)（挺柱）（挺柱）Push-rodValve clearancesValve SpringValve stemValve seat（insert）（气门座）（气门座）Valve headPistonRocker-shaftChapter 3 Valve and Gasoline Fuel System 3/7/20235Automotive Engineering EnglishThe cam is an egg-shaped 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.（p26）凸轮是一个凸轮是一个蛋形的金属块蛋形的金属块，它安装在同曲轴，它安装在同曲轴协调运转的一根轴上，该轴称为凸轮轴，其上协调运转的一根轴上，该轴称为凸轮轴，其上通通常常有单独的凸轮与发动机每一个气门对应。有单独的凸轮与发动机每一个气门对应。1)Valve operationChapter 3 Valve and Gasoline Fuel System 3/7/20236Automotive Engineering English In this arrangement,the 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).在这种布置方案中，在这种布置方案中，凸轮凸圆凸轮凸圆推动圆形的金属筒，推动圆形的金属筒，也就是也就是凸轮挺杆（挺柱）凸轮挺杆（挺柱）。凸轮凸圆运动到挺杆下方。凸轮凸圆运动到挺杆下方时，推动挺杆远离凸轮轴向上运动。时，推动挺杆远离凸轮轴向上运动。Chapter 3 Valve and Gasoline Fuel System 3/7/20237Automotive Engineering English挺柱带着推动摇臂的推杆，摇臂挺柱带着推动摇臂的推杆，摇臂绕绕摇臂轴的中心转动。摇臂轴的中心转动。摇臂的一端升起，另一端就落下，这类似于摇臂的一端升起，另一端就落下，这类似于跷跷板跷跷板。摇臂向下运动的一端推动气门杆打开气门。摇臂向下运动的一端推动气门杆打开气门。The cam follower rides against a push rod,which pushes against a rocker arm.The rocker arm pivots on a shaft through its center.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）Chapter 3 Valve and Gasoline Fuel System 3/7/20238Automotive Engineering English 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.当发动机在压缩冲程和做功冲程工作时，气门必须紧贴在当发动机在压缩冲程和做功冲程工作时，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。气门座上，形成良好的气密性以防止燃烧室漏气。2)Valve clearance 气门间隙气门间隙Chapter 3 Valve and Gasoline Fuel System 3/7/20239Automotive Engineering English如果气门关闭不严，发动机就不能发挥出全如果气门关闭不严，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部的功率。而且气门头部容易被经过的高温气体烧蚀，气体烧蚀，活塞顶部活塞顶部也可能会碰到气门使发也可能会碰到气门使发动机严重损坏。动机严重损坏。2)Valve clearance 气门间隙气门间隙 If the valves do not close fully the engine will not develop full power.Also the valve heads will 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.（p28）Chapter 3 Valve and Gasoline Fuel System 3/7/202310Automotive Engineering English It is apparent from this description that the exhaust valve stays open for a short period of time during which the intake valve is also open.In other words,the end of the exhaust stroke and the beginning of the intake stroke overlap for a short period of time.This is called valve overlap.Valve timing and valve overlap vary on different engines.（p28）由上显而易见由上显而易见，排气门在进气门打开的一小段时间内也打开着。换，排气门在进气门打开的一小段时间内也打开着。换句话说，排气冲程终了和进气冲程初期有一小段时间的重叠，这称句话说，排气冲程终了和进气冲程初期有一小段时间的重叠，这称为为气门重叠气门重叠。不同的发动机，其。不同的发动机，其配气正时配气正时和气门重叠是不一样的。和气门重叠是不一样的。3)Valve timing 配气正时配气正时/配气相位配气相位Chapter 3 Valve and Gasoline Fuel System 3/7/202311Automotive Engineering English Each cam must revolve once during the four-stroke cycle to open a valve.A cycle,remember,corresponds with two revolutions of the crankshaft.在一个四冲程的循环里，每个凸轮转在一个四冲程的循环里，每个凸轮转动一次来打开一个气门。在一个循环里曲动一次来打开一个气门。在一个循环里曲轴是转动两圈的。因此，凸轮轴必须以曲轴是转动两圈的。因此，凸轮轴必须以曲轴转速的一半旋转，这是由轴转速的一半旋转，这是由2:12:1的传动比来的传动比来实现的。连接凸轮轴的齿轮齿数是连接曲实现的。连接凸轮轴的齿轮齿数是连接曲轴的齿轮齿数的轴的齿轮齿数的2 2倍倍。5)Camshaft drive mechanism Therefore,the camshaft must revolve at exactly half the speed of the crankshaft.This is accomplished with a 2:1 gear ratio.A gear connected to the camshaft has twice the number of teeth as a gear connected to the crankshaft.（p29）Chapter 3 Valve and Gasoline Fuel System 3/7/202312Automotive Engineering English An electronic valve control system replaces the mechanical camshaft,controlling each valve with actuators for independent valve timing.The EVC system controls the opening and closing time and lift amount of each intake and exhaust valve with independent actuators on each valve.Changing from a mechanical driven valve into independently controlled actuator valve provides a huge amount of flexibility in engine strategy.（p30）电控气门控制系统电控气门控制系统(EVC)(EVC)代替了机械式的凸轮轴，用执行代替了机械式的凸轮轴，用执行器控制每个气门独立的进、排气正时。器控制每个气门独立的进、排气正时。EVCEVC通过每个气门上的通过每个气门上的独立执行器独立执行器控制进气门和排气门的开启、关闭时间以及控制进气门和排气门的开启、关闭时间以及升程升程量量。由机械式驱动气门到独立控制执行器气门的转变，极大。由机械式驱动气门到独立控制执行器气门的转变，极大的增加了发动机控制策略的灵活性。的增加了发动机控制策略的灵活性。6)Electronic valve control system(EVC)电控气门控制系统电控气门控制系统Chapter 3 Valve and Gasoline Fuel System 3/7/202313Automotive Engineering EnglishVTC=Variable Timing Control 可变配气正时控制可变配气正时控制 i-VTEC=VTEC+VTCVVT-i=Variable Valve Timing-intelligent 智能可变配气正时系统智能可变配气正时系统VTEC=Variable Valve Timing and Lift Electronic Control System 可变气门正时和升程电子控制系统可变气门正时和升程电子控制系统 谢谢大家！结结 语语