汽车专业英语(幻灯片)Chapter 3 Engine(2.5).ppt

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 camshaft),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-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.As the camshaft rotates,the lobe,or high spot of the cam,pushes against parts connected to the stem of the valve.This action forces 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 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 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）,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 clearance: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 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.,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要预留一些间隙使气门得以完全关闭。这就是说，气门传动机构运动要与气门有一个充分远的距离，使得气门在气门弹簧作用下紧闭气门座。可是如果间隙过大，会引起轻微的金属敲打声。,So that the valves can close fully some clearance is needed in the operating mechanism.This means that the operating mechanism must be able to move sufficiently far enough away from the valve to allow the valves to be fully closed against its seat by the valve spring.However,if the clearance is set too great this will cause a light metallic tapping noise.,Valve timing: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 stoke overlap for a short period of time.This is called valve overlap.Valve timing and valve overlap vary on different engines.,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，这称为气门重叠。不同的发动机，其配气相位和气门重叠是不一样的。,Valve timing:Opening the intake valve before TDC and closing it after BDC increases the fill of air-fuel mixture in the cylinder.Opening the intake valve early helps overcome the static inertia of the air-fuel mixture at the beginning of the intake stroke,while leaving the intake valve open after BDC takes advantage of the kinetic inertia of the moving air-fuel mixture.This increases volumetric efficiency.,在上止点前打开进气门和在下止点后关闭进气门可增加气缸内可燃混合气的进气量。提前打开进气门有助于克服静态的惯性，同时在下止点后开着进气门可充分利用可燃混合气运动时的惯性，这可增加容积效率。,Cam design and control dynamic:The entire valve-train assembly can be viewed as a spring/mass system in which the conversion from stored to free energy causes forced vibration.Valve-train assemblies with overhead camshafts can be represented with sufficient accuracy by a 1-mass system(consisting of the moving mass,the valve-train assembly stiffness and corresponding damping).,整个气门机构可看成一个弹簧-质量系统，其储存的能量转化为自由能量时会引起受迫振动。带有顶置凸轮轴的气门机构可非常精确地用单质量系统来表示(由运动质量、气门机构的刚度和相应的阻尼组成)。,Camshaft drive mechanism:Each cam must revolve once during the four-stroke cycle to open a valve.A cycle,remember,corresponds with two revolutions of the crankshaft.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.,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。在一个循环里曲轴是转动两圈的。因此，凸轮轴正好以曲轴转速的一半旋转，这是由2:1的传动比来实现的。连接凸轮轴的齿轮齿数是连接曲轴的齿轮齿数的两倍。,Electronic valve control system:,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 control strategy.,电控气门系统代替机械式的凸轮轴，用执行器控制每个气门独立的进、排气正时。EVC通过每个气门上的独立执行器控制进气门和排气门的开启、关闭时间以及升程量。由机械式驱动气门到独立控制执行器的气门改变，极大的增加了发动机控制策略的灵活性。,VTEC=Variable Valve Timing and Valve Lift Electronic Control System可变气门配气相位和气门升程电子控制系统,EVC=Electronic Valve Control System电子式气阀控制系统,VTC=Variable Timing Control 可变正时控制,i-VTEC=VTEC+VTC,VVT-i=Variable Valve Timing and Lift with intelligence 智能可变配气正时系统,VTEC=Variable Valve Timing and Valve Lift Electronic Control System 可变气门配气相位和气门升程电子控制系统,