There are many types of sensors used in cars, with a wide range of applications. The following introduces the applications of sensors in automotive engine control, safety systems, vehicle monitoring, and self diagnosis.

The electronic control of engines has always been considered one of the main application areas of MEMS technology in automobiles. The sensors used in the engine control system are the core of the entire automotive sensor system, with many types including temperature sensors, pressure sensors, position and speed sensors, flow sensors, gas concentration sensors, and knock sensors. These sensors provide the electronic control unit of the engine with information on the working condition of the engine, allowing the electronic control unit to accurately control the working condition of the engine, in order to improve its power performance, reduce fuel consumption, decrease exhaust emissions, and perform fault detection. 

1. Temperature sensor

Automotive temperature sensors are mainly used to detect engine temperature, intake gas temperature, cooling water temperature, fuel temperature, and catalytic temperature. There are three main types of temperature sensors: thermistor type, wire wound resistor type, and thermocouple resistor type. These three types of sensors each have their own characteristics and slightly different application scenarios. Thermistor temperature sensors have high sensitivity and good response characteristics, but poor linearity and low temperature adaptability. Among them, the universal temperature measurement range is -50 ℃ to 30 ℃, with an accuracy of 1.5% and a response time of 10 ms; High temperature type is between 600 ℃ and 1000 ℃, with an accuracy of 5% and a response time of 10ms; The wire wound resistance temperature sensor has high accuracy, but poor response characteristics; Thermocouple resistance temperature sensors have high accuracy and a wide temperature measurement range, but they need to be used in conjunction with amplifiers and cold junction processing. Other practical products include ferrite temperature sensors (temperature measurement range of -40 ℃ to 120 ℃, accuracy of 2.0%), metal or semiconductor film air temperature sensors (temperature measurement range of -40 ℃ to 150 ℃, accuracy of 2.0%, 5%, response time of about 20 ms), etc.

2. Pressure sensor

Pressure sensors are the most commonly used sensors in automobiles, mainly used to detect airbag storage pressure, transmission system fluid pressure, fuel injection pressure, engine oil pressure, intake pipe pressure, air filtration system fluid pressure, etc. At present, the main companies dedicated to the development and production of pressure sensors for automobiles include Motorola and Deke Electronic Instruments, Lucas Novasensor， Hi Stat，NipponDenzo， Siemens, Texas Instruments, etc.

The commonly used automotive pressure sensors include capacitive, piezoresistive, differential transformer, and surface acoustic wave sensors. Capacitive pressure sensors are mainly used to detect negative pressure, hydraulic pressure, and air pressure, with a measurement range of 20kPa to 100kPa. They are characterized by high input energy, good dynamic response characteristics, and good environmental adaptability; The performance of piezoresistive pressure sensors is greatly affected by temperature and requires an additional temperature compensation circuit, but it is suitable for large-scale production; The differential transformer pressure sensor has a large output and is easy to output digitally, but has poor anti-interference performance; Surface acoustic wave pressure sensors have the characteristics of small size, light weight, low power consumption, high reliability, high sensitivity, high resolution, and digital output. They are used for pressure detection of automotive intake valves and can work stably at high temperatures.

The intelligent tire pressure sensor KP500 developed by Infineon, a German company, integrates pressure and temperature sensing modules internally. It does not require the addition of acceleration sensors in the sensor module and can automatically start up and perform self inspection when the car is started. It can measure pressure, temperature, and voltage, etc. All functions are integrated on a 0.8 μ m bipolar complementary metal oxide semiconductor (BiCMOS) using surface micro machining technology. The electrically erasable programmable read-only memory in each sensor module stores a unique 32-bit chip identification code. The chip identification code can be read out by a synchronous serial interface and can be used to identify the position of various tire pressure sensors. When receiving data, the first step is to check the chip identification code. If it is found that the chip identification code does not match, the received data frame will be discarded.

3. Flow sensor

Flow sensors are mainly used for measuring engine air flow and fuel flow. The intake air quantity is one of the basic parameters for calculating fuel injection quantity. The function of an air flow sensor is to sense the magnitude of air flow and convert it into an electrical signal to be transmitted to the electronic control unit of the engine. The measurement of air flow is used in the engine control system to determine combustion conditions, control air-fuel ratio, start, ignition, etc. There are four types of air flow sensors: rotary wing type, Karman vortex type, hot wire type, and hot film type. The main technical specifications of the air flow sensor are: working range of 0.11m3/min to 103m3/min, working temperature of -40 ℃ to 120 ℃, and accuracy>1%. Fuel flow sensors are used to detect fuel flow, mainly including water wheel type and circulating ball type. Their dynamic range is 0-60kg/h, working temperature is -40 ℃ -120 ℃, accuracy is ± 1%, and response time is less than 10ms.

Honeywell's subsidiary micro switch company has produced a micro bridge air flow sensor chip using thermal microfabrication technology. It uses microfabrication technology to create cavities on silicon wafers, with platinum resistors suspended above the cavities. When air flows through the device, heat transfer occurs from below to above in the direction of air flow. Therefore, the lower resistor is cooled and the upper resistor is heated. The air flow rate can be measured by the change in the bridge resistance.

4. Position and speed sensors

The crankshaft position and speed sensor is mainly used to detect engine crankshaft angle, engine speed, throttle opening, vehicle speed, etc., providing reference point signals for ignition timing and injection timing, as well as engine speed signals. At present, the position and speed sensors used in automobiles mainly include AC generator type, reluctance type, Hall effect type, reed switch type, optical type, semiconductor magnetic transistor type, etc. Their measurement range is 0 °~360 °, with an accuracy better than ± 0.5 ° and a bending angle measurement of ± 0.1 °.

There are various types of speed sensors, including those that are sensitive to wheel rotation, those that are sensitive to power transmission shaft rotation, and those that are sensitive to differential driven shaft rotation. When the vehicle speed is higher than 100km/h, the general measurement method has a large error, and a non-contact photoelectric speed sensor is required. The speed measurement range is 0.5km/h to 250km/h, the repeatability is 0.1%, and the distance measurement error is better than 0.3%.

5. Gas concentration sensor

Gas concentration sensors are mainly used to detect gas and exhaust emissions inside the vehicle body. Among them, the most important is the oxygen sensor, which detects the oxygen content in car exhaust, determines the air-fuel ratio based on the oxygen concentration in the exhaust, and sends feedback signals to the microcomputer control device to control the air-fuel ratio to converge to the theoretical value. Commonly used sensors include germanium oxide sensors (operating temperature range of -40 ° C to 900 ° C, accuracy of 1%), chromium oxide concentration battery gas sensors (operating temperature range of 300 ° C to 800 ° C), solid electrolyte chromium oxide gas sensors (operating temperature range of 0 ° C to 400 ° C, accuracy of 0.5%), as well as oxygen dioxide sensors and oxygen dioxide sensors. Compared with germanium oxide sensors, titanium dioxide oxygen sensors have the characteristics of simple structure, lightweight, low cost, and strong resistance to lead pollution. Zirconia micro ion sensor consists of calcium oxide stabilized oxide dislocations, porous platinum thick film working electrode, palladium/oxide thick film parameter electrode, impermeable layer, electrode contact and protective layer. Among them, the stable oxidation of calcium oxide is deposited by reactive sputtering method. Both the working electrode and the reference electrode are made using thick film technology. The output voltage near the ideal A/F point undergoes a sudden change. As the air-fuel ratio increases and the oxygen concentration in the exhaust gas increases, the output voltage of the oxygen sensor decreases; When the air-fuel ratio decreases and the oxygen concentration in the exhaust gas decreases, the output voltage of the oxygen sensor increases. The electronic control unit recognizes this sudden change signal, corrects the fuel injection quantity, and accordingly adjusts the air-fuel ratio to vary around the ideal air-fuel ratio.