What is the sensor of the engine electronic control system?
The function of the air flow meter is to accurately measure the intake air under all operating conditions of the engine, so as to better manage the engine and reduce exhaust emissions.
First, basic function and installation location
Both hot film and hot wire air flow meters are thermal flow meters. Part of the airflow flowing through the sensor unit in the intake pipe is measured through a measuring channel in the air flowmeter housing. The measured temperature value is analyzed in the electronic analysis device, and the air flow meter transmits a voltage corresponding to the air quality to the engine electronic control unit. Only with this voltage signal can the fuel injection time and the actual torque of the engine be calculated.
When the air flow sensor fails, the engine will calculate the air quality through a characteristic curve (throttle angle and engine speed), and the engine will experience abnormal power at this time.
The air flow meter is generally installed behind the air filter and in front of the throttle body; it can also be installed on the air filter or on the throttle body.
Second, structural principle and detection
1. Hot wire air flow meter
1. Basic structure
The heating body of the hot-wire air flow sensor is platinum wire, and there are two structural forms: hot-wire mainstream and hot-wire bypass.
The structure of the hot-wire mainstream air flow sensor is shown in the figure below. There is a heated platinum wire in the air flow meter that is exposed to the intake air flow. By applying a specified current to the platinum wire, the ECM can heat it to a specified temperature. The intake air flow can cool the platinum heating wire and the internal thermistor, thereby changing their resistance value. To maintain a stable current value, the ECM changes the voltage applied to the platinum wire and the internal thermistor. The voltage value is proportional to the air flow through the sensor, and the ECM uses this value to calculate the intake air volume.
The platinum heating wire and the temperature sensor form a bridge circuit, and by controlling the transistor, the pressure difference between A and B is kept equal to maintain a predetermined temperature.
2. Typical circuit connection
Toyota Camry 1ZR-FE, 2ZR-FE, and 5AR-FE engines use hot-wire air flow meters. The circuit connection of the 5AR-FE engine air flow meters is shown in the figure below.
The sensor 3# is the 12V power supply provided by the No. 1 relay, and the sensors 4# and 5# are the signal output terminals, which are respectively connected to the 92# and 91# of the E26 terminal of the engine control unit.
3. Single detection of air flow sensor
Remove the air flow sensor assembly, and visually check whether there is any foreign matter on the platinum hot wire (heater) of the mass air flow meter sub-assembly. If there are foreign objects, replace the sensor assembly.
Check the resistance of the intake air temperature sensor built into the air flow sensor. 1# of the plug E14 is the signal output terminal of the intake air temperature sensor, and 2# is the ground terminal.
2. Hot film air flow meter
1. Basic principles
The working principle of the hot-film air flow sensor is similar to that of the hot-wire air flow sensor. The difference is: the hot-film type does not use platinum wire as the hot wire, but the hot-wire resistance, compensation resistor and bridge resistance are made by thick film technology. Constructed on the same ceramic substrate. This structure makes the heating element not directly bear the force generated by the air flow, increases the strength of the heating element, and improves the reliability of the air flow meter. The error is small, the cost is low, the resistance value is high, and the current consumption is small. , It can be small and light. The signal output voltage varies linearly between 0 and 5v. However, the responsiveness of the hot film heating element is slightly poor.
The 2016 Toyota Camry Hybrid 6AR-FSE engine uses a new silicon chip thermal mode air flow sensor (HMF6), and the sensor’s internal digital processing circuit makes the sensor output more accurate.
The air flow sensor has a built-in intake air temperature sensor. The intake air flow passes through the temperature sensor (before the heater), the heater, and the temperature sensor (after the heater) of the silicon chip sensor in the bypass pipe. Since the temperature of the intake air increases when it contacts the heater, the temperature of the intake air when it flows through the temperature sensor (behind the heater) is higher than the temperature when it flows through the temperature sensor (before the heater). According to the rate of intake air flowing through the silicon chip sensor, the temperature difference of the intake air at each temperature sensor is different. The temperature sensor bridge circuit detects the temperature difference, and the control circuit converts it into a pulse signal and outputs it to the ECM. When the temperature detected by the temperature sensor (before the heater) is higher than the temperature detected by the temperature sensor (after the heater), it is determined that the intake air is returning.
Sensor internal circuit
Sensor and ECU connection circuit diagram
2. Single sensor detection
Disconnect the ignition switch and remove the sensor. Visually check whether there is any foreign matter on the temperature sensor (thermistor) of the air flow sensor. Replace the sensor if there is a foreign object; check the resistance between 2# and 3# of the sensor E78 with a multimeter (intake air temperature sensor), the detection should comply with the following figure, if not, replace the sensor.
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