closed loop fuel trim 汽车闭关控制与燃油矫正.pdf

Closed Loop Systems A system that controls its output by monitoring its output is said to be a closed loop system. An example of a closed loop system is the vehicles charging system. The voltage regulator adjusts the voltage output of the alternator by monitoring alternator voltage output. If voltage is too low, the voltage regulator will increase alternator output. Without the voltage regulator, alternator output could not be adjusted to match the electrical loads. Many systems are closed loop systems. Some other examples are: cruise control, ignition system knock control, idle speed control, and closed loop air/fuel ratio correction control. When the ECM corrects the air/fuel ratio based on the oxygen or air/fuel ratio sensor, the system is said to be in closed loop. Open Loop Systems An open loop system does not monitor its output and make adjustments based on its output. The temperature control in a vehicle not equipped with automatic air conditioning serves as an example. Closed Loop Fuel Control The ECM needs to monitor the exhaust stream and adjust the air/fuel ratio so that the catalytic converter will operate at peak efficiency, reducing regulated emission gases. Measuring the amount of oxygen remaining after combustion is a means to indicate the air/fuel ratio. A richer mixture will consume more oxygen during combustion than a leaner mixture. The oxygen sensor or air/fuel ratio sensor measures the amount of oxygen remaining after combustion in the exhaust stream. From this information, the ECM will control the injection duration to achieve the desired, ideal air/fuel ratio of 14.7: 1. This is necessary so the catalytic converter will operate at peak efficiency. Note: The engine operation often requires different air/fuel ratios for starting, maximum power, and maximum fuel economy. The 14.7:1 ratio is for catalytic converter efficiency. FUEL SYSTEMS #3 - CLOSED LOOP / FUEL TRIM