Air Flow Sensor
The function of the air flow sensor is to convert the amount of air inhaled into the engine into an electrical signal and provide it to the electronic control unit (ECU). It is the main basis for determining the basic fuel injection volume.
Vane type: The vane-type air flow sensor belongs to the volumetric flow type. This sensor has a simple structure and low cost. However, since its moving vane occupies a large area of the intake duct, it reduces the fluidity of the intake system and increases the intake resistance. Therefore, it is now less used.
Karman vortex type: The Karman vortex-type air flow sensor belongs to the volumetric flow type and is widely used in Toyota and Mitsubishi vehicles. This sensor has the characteristics of small size, lightweight, no wear, simple intake duct, small intake resistance, high detection accuracy, and fast response. However, it has a high cost and is mostly used in high-end cars.
Hotwire type: The hot wire-type air flow sensor belongs to the mass flow type. It can directly detect the mass flow of intake air and does not need to correct the intake temperature and atmospheric pressure. Since this sensor has no moving parts, it has small intake resistance and good response characteristics and can correctly detect the air intake volume during sudden deceleration. Therefore, it is widely used.
Hot film type: The hot film-type air flow sensor belongs to the mass flow type. It was developed by General Motors of the United States and is widely used in vehicles produced by General Motors and Isuzu of Japan. The working principle of this sensor is the same as that of the hot wire sensor. Only the hot wire of the heating element is changed to a hot film (composed of heating metal platinum fixed on a thin resin film). This structure can make the heating element not directly bear the resistance generated by airflow, thereby increasing the strength and improving the reliability at work.
Engine Temperature Sensor
The function of the engine temperature sensor is to convert the temperature change of gas or liquid into an electrical signal and provide it to the ECU.
Water temperature sensor: Installed on the cylinder block, it is used to detect the temperature information of the engine cooling water convert this information into an electrical signal, and provide it to the engine electronic control unit (ECU).
Intake air temperature sensor: In the L-type EFI system, the engine intake air temperature sensor is installed on the airflow sensor. In the D-type EFI system, it is installed in the air filter housing or the surge tank to provide the engine electronic control unit (ECU) with the engine intake air temperature information.
Fuel temperature sensor: Used in the diesel engine electronic control distribution pump fuel injection system to provide the engine electronic control unit (ECU) with fuel temperature information for precise control of fuel injection volume.
Position and Speed Sensors
Throttle position sensor, crankshaft position sensor, vehicle speed sensor, and accelerator pedal position sensor are used to provide various position information for the ECU.
Throttle position sensor: The throttle position sensor is installed on the throttle body and can simultaneously convert information such as throttle opening, idle speed, and high load into electrical signals and provide them to the ECU. There are two types of throttle position sensors: linear output type and switch output type. In comparison, the latter has poorer detection performance but a simple structure and low price. Some EFI systems install both types of throttle position sensors. The switch output type sensor is used to detect the engine idle and full load states, while the linear output type sensor is used to detect the opening degree of the entire throttle.
Crankshaft position sensor: Used to provide the ECU with engine crankshaft angle position signal, piston stroke position signal, and engine speed signal. There are three types: magnetoelectric type, photoelectric type, and Hall type. The first two are usually installed in the distributor and rotate with the distributor. The latter is installed at the front end of the crankshaft. Since the magnetoelectric sensor and the Hall sensor have strong anti-interference ability and good recognition ability at high speeds, they are widely used.
Vehicle speed sensor: Installed on the transmission output shaft or main reducer to provide the electronic control unit (ECU) with the vehicle speed signal. The structure and principle of this sensor are very similar to those of the crankshaft position sensor.
Accelerator pedal (throttle pedal) position sensor: Usually used on direct injection engines to provide the ECU with information on load size, load range, acceleration, and deceleration. The ECU determines the fuel injection volume in the engine combustion stratified zone (there are two combustion forms of direct injection engines: stratified combustion and homogeneous combustion) according to this information.
Exhaust Purification Sensors
Exhaust purification sensors are used to convert relevant information in the exhaust into electrical signals and provide them to the ECU.
Oxygen sensor: There are two major types of oxygen sensors: zirconia type and titanium oxide type. Installed on the exhaust pipe, it is used to feed back the actual air-fuel ratio signal to the ECU and converge the actual air-fuel ratio within a narrow range near the theoretical value to form a closed-loop control. In comparison, the titanium oxide oxygen sensor has the characteristics of simple structure, small size, low cost, etc. However, its resistance changes greatly with temperature changes. Therefore, when used at high temperatures, certain temperature compensation measures are usually taken.
Exhaust gas recirculation displacement sensor: Mainly used to provide the electronic control system with the opening information of the exhaust gas recirculation control valve to facilitate the corresponding control of the operation of the exhaust gas treatment system.
Differential pressure sensor: Installed downstream of the particulate trap, it is used to provide the electronic control system with the differential pressure information of the particulate trap to facilitate the timely high-temperature burning of the particulates in the particulate trap and prevent the exhaust back pressure from rising.
NOx sensor: Used to provide the electronic control system with the concentration information of NOx in the exhaust gas after-treatment system to facilitate the corresponding control of the operation of the post-treatment SCR system.
Exhaust temperature sensor: Usually installed near the three-way catalytic converter and used to detect its working temperature convert this signal into an electrical signal and provide it to the electronic control system.
EGR temperature sensor: Usually installed downstream of the EGR valve and used to detect the temperature of the EGR convert this signal into an electrical signal and provide it to the electronic control system.
Automatic Air Conditioning System Sensors
In addition to temperature sensors, the automatic air conditioning system also uses some other sensors.
In-car temperature sensor: Usually installed on the lower side of the instrument panel. It is a thermistor temperature sensor with negative temperature coefficient characteristics and is used to provide the in-car temperature signal to the air conditioning electronic control unit (ECU).
Outside environment temperature sensor: It is also a thermistor temperature sensor with negative temperature coefficient characteristics. Usually installed on the lower side of the front bumper of the vehicle, it is used to provide the outside temperature signal of the vehicle compartment to the air conditioning electronic control unit (ECU).
Evaporator temperature sensor: Usually installed on the evaporator housing and used to detect the temperature change inside the refrigeration device and provide the detected signal to the air conditioning electronic control unit (ECU).
Sunlight radiation sensor: A photodiode sensor is usually installed under the front windshield of the car. It is used to convert the degree of sunlight radiation into an electrical signal and provide it to the air conditioning electronic control unit (ECU).
Coolant flow sensor: Usually installed between the receiver drier and the expansion valve and used to detect the flow of refrigerant convert this change into an electrical signal and provide it to the air conditioning electronic control unit (ECU).
Compressor lock sensor: A magnetoelectric sensor is usually installed inside the compressor and used to detect the speed of the compressor convert this change into an electrical signal and provide it to the air conditioning electronic control unit (ECU).
Smoke concentration sensor: Used to detect the smoke level in the vehicle compartment and convert this change into an electrical signal and provide it to the air conditioning electronic control unit (ECU). The ECU will automatically turn on or off the air exchanger according to this information to keep the air in the vehicle compartment fresh.
Humidity sensor: Used to detect the anti-fogging of the vehicle windshield and the humidity in the vehicle compartment and convert this change into an electrical signal and provide it to the air conditioning electronic control unit (ECU).
Liquid Level Sensor
The structural forms of liquid-level sensors mainly include float type, reed switch type, thermosensitive switch type, variable resistance type, electrode type (for measuring storage batteries), and many others.
Fuel level sensor: Used to detect the amount of fuel storage and convert this change into an electrical signal and provide it to the relevant electronic control system or fuel gauge. The relevant system will display whether the fuel volume is lower than the set value.
Coolant level sensor: Used to detect the amount of coolant storage and convert this change into an electrical signal and provide it to the relevant electronic control system or water level display system. The relevant system will display whether the coolant volume is lower than the set value.
Brake fluid level sensor: Used to detect the amount of brake fluid storage and convert this change into an electrical signal and provide it to the relevant electronic control system or brake fluid level display system. The relevant system will display whether the brake fluid volume is lower than the set value.
Battery level sensor: Used to detect the amount of electrolyte storage in the battery and convert this change into an electrical signal and provide it to the relevant electronic control system or alarm circuit. The relevant system will display whether the electrolyte volume is lower than the set value.
Oil Pressure Sensor
The function of the oil pressure sensor is to convert the change in oil pressure into an electrical signal and provide it to the ECU.
Oil rail fuel pressure sensor: Usually installed on the oil rail of the diesel engine common rail electronically controlled fuel injection system and used to detect the fuel pressure in the oil rail and convert this change into an electrical signal and provide it to the electronic control unit (ECU).
Fuel tank pressure sensor: Usually installed inside the fuel tank and used to detect the fuel pressure inside the fuel tank and convert this change into an electrical signal and provide it to the relevant electronic control system or alarm circuit.
Oil pressure sensor: Usually installed in the main oil passage of the engine and used to detect the oil pressure and convert this change into an electrical signal and provide it to the relevant electronic control system or alarm circuit.
Transmission oil pressure sensor: Usually installed in the automatic transmission oil pump (or output oil passage) and used to detect the transmission oil pressure and convert this change into an electrical signal and provide it to the relevant electronic control system or alarm circuit.
Sensors for Electronic Suspension and Electronic Steering Systems
Electronic suspension is used to improve vehicle stability, and electronic steering is used to improve steering strength.
Front and rear suspension height sensor: Mainly installed in the electronic suspension system and used to detect the deformation of the front and rear suspensions and convert this change into an electrical signal and provide it to the suspension electronic control unit (ECU).
Vehicle body acceleration sensor: Mainly installed in the electronic suspension system and used to detect the vibration of the vehicle body and convert this change into an electrical signal and provide it to the suspension electronic control unit (ECU), thereby indirectly providing the road condition when the vehicle is running.
Vehicle body displacement sensor: Mainly installed in the electronic suspension system and used to detect the displacement of the vehicle body relative to the axle and convert this change into an electrical signal and provide it to the suspension electronic control unit (ECU) to reflect the ride comfort and height change of the vehicle body.
Steering wheel angle sensor: Mainly installed in the vehicle's electronic steering system and used to detect the steering wheel angle and convert this change into an electrical signal and provide it to the steering electronic control unit (ECU) to calculate the vehicle body tilt degree.
Torque sensor: Mainly installed in the vehicle's electronic steering system and used to detect the steering load torque signal of the steering wheel and convert this change into an electrical signal and provide it to the steering electronic control unit (ECU).
Yaw rate sensor: Used to detect and record the movement of the vehicle around the vertical axis and convert this change into an electrical signal and provide it to the steering electronic control unit (ECU) to judge whether the vehicle is skidding.
Lateral angular velocity sensor: Used to detect the centrifugal force generated when the vehicle turns and convert this change into an electrical signal and provide it to the steering electronic control unit (ECU) to judge whether the vehicle is skidding when passing through a curve.
Sensors for Airbag and Anti-collision Systems
Both airbag and anti-collision systems belong to the vehicle's safety protection systems. The former is used to protect the human body, and the latter is used to protect vehicles and pedestrians.
Collision sensor: Common collision sensors mainly include mechanical collision sensors, magnetic collision sensors, piezoelectric collision sensors, strain gauge collision sensors, piezoresistive collision sensors, and mercury switch collision sensors. The collision sensor is used to detect the signal when the vehicle collides and provide this signal to the airbag ECU.
Safety sensor: Used to detect the severity of the vehicle's impact and provide this signal to the airbag ECU to act as insurance and prevent the airbag from opening by mistake.
Ultrasonic ranging sensor: Usually installed on the rear bumper of the car, it is used to emit ultrasonic waves to the rear of the vehicle. After receiving the reflected ultrasonic waves, it is converted into an electrical signal and provided to the anti-collision control ECU.
Corner sonar (corner radar) sensor: Usually installed on the bumper, it is used to make up for the deficiency of the detection blind area of the ultrasonic sensor. After converting the detected signal, it is provided to the anti-collision control ECU.
Knock sensor: There are several types of knock sensors, mainly including magnetostrictive type, resonant piezoelectric type, and non-resonant piezoelectric type. This type of sensor is usually installed on the engine block and is used to convert the engine vibration signal into an electrical signal and provide it to the engine electronic control unit (ECU) to detect the occurrence time and magnitude of engine knock.
Sensors for Brake, Cruise, and Navigation Systems
Braking belongs to the vehicle's safety protection system, while cruise and navigation belong to the vehicle's comfort system.
Brake pressure switch sensor: Used to detect the pressure of the brake fluid in the brake pipeline and convert the detected signal into an electrical signal and provide it to the electronic control system or alarm control circuit.
Brake light switch sensor: Used to detect the on-off status of the brake light circuit and convert the detected signal into an electrical signal and provide it to the electronic control system or relevant control circuit.
Distance sensor: Used to detect obstacles in front and behind the car and the distance between the car and other vehicles, and convert the detected signal into an electrical signal and provide it to the anti-collision electronic control system or relevant control circuit.
Compass sensor: Used to detect the geomagnetic field and convert the detected signal into an electrical signal and provide it to the navigation electronic control system or relevant control circuit for judging the driving direction.
Gyroscope sensor: Used to detect the driving direction of the car and convert the detected signal into an electrical signal and provide it to the navigation electronic control system or relevant control circuit for automatic data recording.
Pressure and Speed Sensors
Pressure sensors mainly include semiconductor piezoresistive type, capacitive type, variable inductance type driven by diaphragm box, and surface acoustic wave type. The first two are more widely used. They have the characteristics of small size, high precision, low cost, good response performance, strong versatility, and wide detection range.
Intake manifold absolute pressure sensor: Used in D-type EFI systems. Different from the airflow sensor, the intake manifold absolute pressure sensor adopts an indirect measurement method, that is, according to the engine load change, the relative value of the absolute pressure in the intake manifold is measured, and then the engine intake air volume is calculated.
Boost pressure sensor: Usually installed on turbocharged engines and used to detect the working condition of the turbocharger. After converting the change into an electrical signal, it is provided to the electronic control unit (ECU) for the ECU to control the fuel injection pulse and the pressure of the supercharger.
Cylinder combustion pressure sensor: There are two types of cylinder combustion pressure sensors: one is a direct type sensor with the side of the combustion chamber as the pressure surface, abbreviated as PDS; the other is a washer-shaped pressure sensor fastened to the spark plug, abbreviated as PGS. The former can realize linear detection of combustion chamber pressure. The latter has good assemblability and is suitable for higher-precision knock control, misfire detection, etc. The cylinder combustion pressure sensor is used to provide the ECU with the cylinder combustion pressure signal. The control system can obtain a lot of information from the combustion pressure sensor to control the engine promptly, such as judging the optimal ignition time and valve timing.
Tire pressure detection sensor: The tire pressure detection sensor uses the temperature difference compensation and correction method. It can generate a series of electronic signals according to the changes in tire pressure, tire temperature, and battery voltage and provide them to the ECU to measure the tire pressure promptly. Its working pressure can reach up to 1380 kPa, the working temperature is -40~125°C and the accuracy rate is not less than 1%.
Wheel speed sensor: Used to detect the wheel speed and provide this signal to the ABS ECU. After processing, the vehicle speed signal parameters are obtained. The wheel speed sensor is usually installed on the wheel, reducer, or transmission. Generally, the signal is obtained by using the electromagnetic induction or photoelectric induction principle. The installation quantity depends on the system layout and control method.
Deceleration sensor: The commonly used deceleration sensors mainly include differential voltage deceleration sensors and switch deceleration sensors. The former detects the deceleration signal by the movement of the sliding part when the vehicle decelerates, and the latter senses the deceleration magnitude by the movement position of the inertial part when the vehicle decelerates. The deceleration sensor is also called a G sensor. It is used to detect wheel acceleration or braking deceleration and is used as an auxiliary signal for threshold control and to detect and control the braking process on roads with a low adhesion coefficient.
Other Sensors
Oil quality sensor: The oil quality sensor uses ceramic capacitors to detect the stability of the oil medium to ensure timely oil change, reduce engine wear, and prolong its service life.
Electric seat sensor: Usually installed around the lower part of the seat and used to provide the seat electronic control system with signals of seat front-back and up-down positions to automatically adjust the seat position and has a memory function. Generally, it is composed of four sensors, including a sliding position sensor, a front vertical position sensor, a rear vertical position sensor, and an inclination position sensor.
Headlight high-low beam control sensor: Used when the car meets at night to sense the light intensity of the oncoming vehicle and convert this change into an electrical signal and provide it to the headlight electronic control system to timely transform the lights and prevent glare.
Fingerprint sensor: Mainly applied in the vehicle's safety anti-theft system and used to identify the legal driver. The error rate of detection is less than 0.01%. 
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