附 录SensorsPerformance of any control system is，first of all，related to the accuracy with which information about the operating variables or parameters is relayed to the controlling process. The sensors used to monitor the variables do so by converting the variables physical quantities into related electrical signals. Common measures in automobiles are flow，temperature，position，position/speed，knock and oxygen concentration.Air Flow SensorMass Air Flow sensors convert the amount of air drawn into the engine into a voltage signal. The ECM needs to know intake air volume to calculate engine load. This is necessary to determine how much fuel to inject， when to ignite the cylinder， and when to shift the transmission. The air flow sensor is located directly in the intake air stream，between the air cleaner and body where it can measure incoming air.Mass Air Flow Sensor: Hot Wire TypeThe primary components of the MAF sensor are a thermistor，a platinum hot wire， and an electronic control circuit.The thermistor measures the temperature of incoming air. The hot wire is maintained at a constant temperature in relation to the thermistor by the electronic control circuit. An increase in air flow will cause the hot wire to lose heat faster and the electronic control circuitry will compensate by sending more current through the wire. The electronic control circuit simultaneously measures the current flow and puts out a voltage signal (VG) in proportion to current flow.Vane Air Flow MeterThe vane air flow meter provides the ECM with an accurate measure of the load placed on the engine. The ECM uses it to calculate basic injection duration and basic ignition advance angle.Temperature sensorThe ECM needs to adjust a variety of system based on temperature. It is critical for proper operation of these systems that the engine reaching operating temperature and temperature is accurately signed to the ECM. Temperature sensor measure Engine Coolant Temperature (ECT)，Intake Air Temperature (IAT)， and Exhaust Recirculation Gases (EGR)，etc.Engine Coolant Temperature (ECT) SensorThe ECT responds to change in Engine Coolant Temperature. By measuring engine coolant temperature，the ECT knows the average temperature of the engine. The ECT is usually located in a coolant passage just before the thermostat.Intake Air Temperature (IAT) SensorThe IAT detects the temperature of the incoming air stream. On vehicles equipped with a MAP sensor，the IAT is part of the MAP sensor. The IAT is used for detecting ambient temperature on a cold start and intake air temperature as the engine heats up the incoming air.Exhaust Gas Recirculation Temperature (EGR) SensorThe EGR Temperature Sensor is located in the EGR passage and measures the temperature of the exhaust gases. When the EGR vavle opens， temperature increases. Form the increase in temperature，the ECM knows the EGR vavle is open and that exhaust gases are flowing.ECT， IAT， &EGR Temperature Sensor OperationThough these sensors are measuring different things，they all operate in the same way. From the voltage signal of the temperature sensor，the ECM knows the temperature. As the temperature of the sensor heats up，the voltage signal decreases. The decrease in the voltage signal is caused by the decrease in resistance. The change in resistant causes the voltage signal to drop. From the voltage signal，the ECM can determine the temperature of the coolant，intake air，or exhaust gas temperature.Position SensorIn many applications，the ECM needs to know the position of mechanical components. The throttle position sensor (TPS) indicates position of the throttle vavle. Accelerator pedal position sensor indicates position of the accelerator pedal. Exhaust gas (EGR) vavle position sensor indicate position of the EGR vavle，these sensors operate the same way.Throttle position sensorThe TPS is mounted on the throttle body and converts the throttle vavle angle into an electronic signal. As the throttle opens， the signal voltage increases. The ECM uses throttle vavle position information to know:Engine mode: idle， part throttle， wide open throttle.Switch off AC and emission controls at Wide Open Throttle (WOT).Air-fuel ratio correction.Fuel cut control.EGR Vavle Position SensorThe EGR vavle position sensor is mounted on the EGR vavle and detects the height of the EGR vavle. The ECM uses this signal to control EGR vavle height. The EGR vavle position sensor converts the movement and position of the EGR vavle into an electrical signal. Operation is identical to the TPS except that the signal arm is moved by the EGR vavle.Position /Speed SensorPosition/Speed sensors provide information to the ECM about the position of a component，the speed of a component，and the change in speed of a component. The following sensors provide this data:Camshaft position sensor (also called G sensor).Crankshaft position sensor (also called NE sensor).Vehicle speed sensor.T