When the car engine is running, each system will be in different working states, such as water temperature, oil temperature, intake pressure, throttle position, etc. The car computer cannot read this information directly and must be converted into electrical signals that the computer can recognize. The car sensor performs such a task. It converts the light, electricity, temperature, pressure, time and other information in the car into electrical signals, and then inputs them into the on-board computer system. Then, the program pre-stored in the computer performs calculations and analysis to determine the running state of the car.
The engine sensor control system is the core of the entire car sensor. It includes many types, such as temperature sensors, pressure sensors, position and speed sensors, flow sensors, oxygen sensors and knock sensors. These sensors provide information about the engine's working conditions to the engine's electronic control unit (ECU), so that the ECU can accurately calculate and control the engine's working conditions to improve the engine's power, reduce fuel consumption, reduce exhaust emissions and perform fault detection.
Since the engine works at high temperature (engine surface temperature can reach 150℃, exhaust manifold can reach 650℃), vibration (acceleration 30g), impact (acceleration 50g), humidity (100%RH, -40℃-120℃) and steam, salt spray, corrosion and sludge pollution and other harsh environments, the sensors of the engine control system must be able to withstand high temperatures and have a technical index 1-2 orders of magnitude higher than general industrial sensors in harsh environments, among which the most critical is measurement accuracy and reliability. Otherwise, the measurement error caused by the sensor will eventually make it difficult for the engine control system to work properly or cause failure factors.
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Temperature Sensor
Temperature sensors are mainly used to detect engine temperature, intake gas temperature, cooling water temperature, fuel temperature, and temperature inside the catalyst.
Temperature sensors are mainly of three types: wirewound resistor, thermistor, and thermocouple resistor. Each type of sensor has its own characteristics and slightly different application scenarios.
Wirewound resistor temperature sensors have high accuracy but poor response characteristics; thermistor temperature sensors have high sensitivity and good response characteristics, but poor linearity and low adaptability to temperature; thermocouple temperature sensors have high accuracy and a wide measurement temperature range, but need to be used with amplifiers and cold end processing.
The practical products include thermistor temperature sensor (general type -50℃~130℃, accuracy 1.5%, response time 10ms; high temperature type 600℃~1000℃, accuracy 5%, response time 10ms), ferrite temperature sensor (ON/OFF type, -40℃~120℃, accuracy 2.0%), metal or semiconductor film air temperature sensor (-40℃~150℃, accuracy 2.0%, 5%, response time 20ms), etc.
The engine coolant temperature sensor is used to detect the temperature of the engine coolant and convert the temperature signal into an electrical signal to transmit it to the engine control module (ECU) as the main correction signal for gasoline injection, ignition timing, idle speed and exhaust emission control,e.g. MG ZS, LDV T60, GWM JOLION.
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Oil Pressure Sensor
Oil pressure sensors are mainly used to detect cylinder negative pressure, atmospheric pressure, turbocharger boost ratio, cylinder pressure, oil pressure, etc.
Intake negative pressure sensors are mainly used to detect intake pressure, negative pressure, and oil pressure. The most commonly used pressure sensors for automobiles are capacitive, piezoresistive, differential transformer (LVDT), and surface elastic wave (SAW).
Capacitive pressure sensors are mainly used to detect negative pressure, hydraulic pressure, and air pressure. The measurement range is 20~100kPa. They have the characteristics of high input energy, good dynamic response characteristics, and good environmental adaptability, e.g. in MG ZS, LDV T60, GWM JOLION, CHERY TIGGO7/ TIGGO8.
The piezoresistive pressure sensor is greatly affected by temperature and requires a separate temperature compensation circuit, but is suitable for mass production; the LVDT pressure sensor has a large output and is easy to digitally output, but has poor anti-interference;
The SAW pressure sensor has the characteristics of small size, light weight, low power consumption, high reliability, high sensitivity, high resolution, and digital output. It is used for automobile intake valve pressure detection and can work stably at high temperatures. It is an ideal sensor.
The function of the intake manifold pressure sensor (MAP) is to detect the vacuum degree of the intake manifold and convert the pressure signal into an electronic signal to transmit it to the engine control computer. It is the main reference signal for controlling the injection pulse width and ignition timing. It is divided into semiconductor piezoresistance and capacitive intake manifold pressure sensors.
If the intake manifold pressure sensor fails, the engine will have difficulty starting, abnormal performance, poor acceleration, unstable idling, high fuel consumption, unstable acceleration, backfire and backfire during acceleration, high fuel consumption, explosion and other fault phenomena
The oil pressure sensor is used to detect the engine oil pressure and send out an alarm signal when the pressure is insufficient. When the oil pressure is insufficient, the oil light on the dashboard will light up. There are usually two, one on the main oil channel and one on the cylinder head.
3.Air Flow Sensors
The flow sensor is mainly used to measure the engine air flow and fuel flow. The function of the air flow sensor is to convert the amount of air sucked into the engine cylinder per unit time into an electrical signal and send it to the engine control module (ECU). It is one of the basic signals that determine the injection amount and ignition timing. It is used by the engine control system to determine the combustion conditions, control the air-fuel ratio, start, ignition, etc, in cars like CHANGAN EADO, GEELY COOLRAY.
There are four types of air flow sensors: rotary vane type (blade type), Karman vortex type, hot wire type, and hot film type.
The rotary vane type (vane type) air flow meter has a simple structure and low measurement accuracy. The measured air flow needs to be temperature compensated;
The Karman vortex type air flow meter has no moving parts, is sensitive, has high accuracy, and also needs temperature compensation;
The hot wire type air flow meter has high measurement accuracy and does not require temperature compensation, but is easily affected by gas pulsation and is prone to wire breakage;
The hot film type air flow meter has the same measurement principle as the hot wire type air flow meter, but has a small volume, is suitable for mass production, and has low cost.
The main technical indicators of the air flow sensor are: working range 0.11~103 cubic meters/min, working temperature -40℃~120℃, accuracy ≤1%.
If the air flow sensor fails, the engine will be difficult to start, performance will be abnormal, idling will be unstable, backfire and backfire during acceleration, fuel consumption will be high, and explosion will occur.
Fuel flow sensors are used to detect fuel flow, mainly water wheel type and circulating ball type, with a dynamic range of 0~60kg/h, operating temperature of -40℃~120℃, accuracy of 1%, and response time of <10ms.
Edited by Asiautos Auto Part
