λ Close Loop Control.ppt

λ Close Loop Control Lambda closed-loop control Of currently available methods, lambda closed-loop control systems incorporating a catalytic converter are the most effective when it comes to cleaning the exhaust gases from spark-ignition engines. None of the available alternatives are capable of reaching anywhere near the same low emissions levels. Λ闭环控制加催化转化器是当前点燃式发动机最有效的减排措施，其它方法都达不到这种方法的低排放水平。 Lambda closed-loop control The 3-way or selective catalytic converter performs particularly well. It is able to reduce the emissions of hydrocarbons, carbon monoxide and nitrous oxides by more than 98%，provided that the engine operates within a very narrow scatter range (1%) centered around the stoichiometric(当量) A/F ratio (λ=1.0). Lambda closed-loop control While consistent maintenance of this restricted tolerance range is necessary under all operating conditions, not even modern injection systems can comply without assistance. 就算是电喷系统开环控制也无法持续的维持空燃比处于一个小范围内。Why？ Lambda closed-loop control The answer is to employ the lambda closed-loop control system which relies on a closed-loop control circuit to consistently maintain the air-fuel mixture entering the engine within the optimal range known as the catalyst window(Figure 1). 必须使用λ闭环控制将混合其空燃比限制在一个最适宜的范围内，此范围称为“催化剂窗口” Lambda closed-loop control Implementing this concept entails monitoring exhaust-gas composition as the basis for making instantaneous corrections in the mixtures fuel content. 要这样做就要持续的监测排气成分，并对混合气成分进行修正。 The monitoring device is the oxygen or lambda sensor. Lambda closed-loop control Because this probe displays a voltage jump when the mixture is precisely stoichiometric(λ=1)，the signal it generates indicates whether the mixture is richer or leaner thanλ=1. 传感器在理论空燃比时会出现电压跳变，故传感器信号可反映混合气是浓还是稀。 Lambda oxygen sensor The oxygen sensor installation It is installed in the exhaust trunk(排气总管), where it monitors the flow of exhaust gases from all cylinders. 氧传感器安装在排气总管上，监测所有缸的排气。 Lambda oxygen sensor Concep