Sensors for engine control systems:
Sensors for engine control systems are at the heart of the entire automotive sensor, including temperature sensors, pressure sensors, position and speed sensors, flow sensors, gas concentration sensors, and knock sensors. These sensors provide engine operating status information to the engine's electronic control unit (ECU) for precise control of engine operating conditions to improve engine power, reduce fuel consumption, reduce exhaust emissions, and detect faults.
Due to the high temperature of the engine (engine surface temperature up to 150 ° C, exhaust manifold up to 650 ° C), vibration (acceleration 30 g), impact (acceleration 50 g), humidity (100% RH, -40 ° C -120 ° C) and In the harsh environment of steam, salt spray, corrosion and sludge pollution, the technical specifications of the engine control system for harsh environments are 1-2 orders of magnitude higher than those of general industrial sensors, the most critical of which is measurement accuracy and reliability. Otherwise, the measurement error caused by the sensor will eventually cause the engine control system to malfunction or malfunction.
Temperature sensor
Temperature sensors are mainly used to detect engine temperature, suction gas temperature, cooling water temperature, fuel temperature, and catalytic temperature. There are three main types of temperature sensors: wirewound resistance, thermistor type and thermocouple type. The three types of sensors have their own characteristics, and their applications are slightly different. The wirewound resistance type temperature sensor has high precision, but the response characteristics are poor; the thermistor type temperature sensor has high sensitivity and good response characteristics, but the linearity is poor, and the temperature is low; the thermocouple resistance type temperature sensor has high precision and the measurement temperature. The range is wide, but it needs to be used with the amplifier and cold junction processing.
The products that have been put into practical use are thermistor type temperature sensors (general type -50 ° C ~ 130 ° C, accuracy 1.5%, response time 10 ms; high temperature type 600 ° C ~ 1000 ° C, accuracy 5%, response time 10 ms), ferrite type Temperature sensor (ON/OFF type, -40 ° C to 120 ° C, accuracy 2.0%), metal or semiconductor film air temperature sensor (-40 ° C ~ 150 ° C, accuracy 2.0%, 5%, response time 20 ms).
2. Pressure sensor
The pressure sensor is mainly used to detect cylinder negative pressure, atmospheric pressure, turbo engine boost ratio, cylinder internal pressure, oil pressure and the like. The suction negative pressure sensor is mainly used for suction pressure, negative pressure and oil pressure detection. Automotive pressure sensors are widely used in capacitive, piezoresistive, differential transformer (LVDT) and surface elastic wave (SAW) applications.
Capacitive pressure sensor is mainly used for detecting negative pressure, hydraulic pressure and air pressure. The measuring range is 20~100kPa. It has the characteristics of high input energy, good dynamic response and good environmental adaptability. The piezoresistive pressure sensor is greatly affected by temperature. Another temperature compensation circuit is provided, but it is suitable for mass production; LVDT type pressure sensor has large output and is easy to digital output, but has poor anti-interference; SAW type pressure sensor has small volume, light weight, low power consumption and high reliability. High sensitivity, high resolution, digital output, etc. It is used for pressure detection of automotive suction valves and can work stably at high temperatures. It is an ideal sensor.
3. Flow sensor
Flow sensors are primarily used for the measurement of engine air flow and fuel flow. The measurement of air flow is used by the engine control system to determine combustion conditions, control air/fuel ratio, starting, ignition, and the like. The air flow sensor has four types: rotary vane type (vane type), Karman scroll type, hot line type, and hot film type. The rotary vane type (vane type) air flow meter has a simple structure, low measurement accuracy, and the measured air flow rate needs temperature compensation; the Karman scroll type air flow meter has no moving parts, reflects sensitivity, high precision, and also needs Temperature compensation; hot wire air flow meter with high measurement accuracy, no temperature compensation, but susceptible to gas pulsation, easy to break the wire; hot film air flow meter and hot wire air flow meter measurement principle is the same, but the volume is small, suitable Mass production, low cost. The main technical indicators of the air flow sensor are: working range 0.11 ~ 103 cubic meters / min, working temperature -40 ° C ~ 120 ° C, accuracy ≤ 1%.
The fuel flow sensor is used to detect fuel flow. It mainly has a water wheel type and a recirculating ball type. Its dynamic range is 0-60kg/h, the working temperature is -40°C-120°C, the accuracy is ±1%, and the response time is less than 10ms.
4. Position and speed sensor
The position and speed sensors are mainly used to detect crank angle, engine speed, throttle opening, and vehicle speed. At present, the position and speed sensors used in automobiles mainly include alternator type, magnetoresistive type, Hall effect type, reed switch type, optical type, semiconductor magnetic transistor type, etc., and the measurement range is 0°-360°, and the accuracy is ±0.5. Below °, the bending angle is measured to ±0.1.
There are many kinds of speed sensors, such as rotating the sensitive wheel, also rotating the sensitive power transmission shaft, and rotating the sensitive differential driven shaft. 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 needed. The speed measurement range is 0.5-250km/h, the repetition accuracy is 0.1%, and the distance measurement error is better than 0.3%.
5. Gas concentration sensor
The gas concentration sensor is mainly used to detect gas and exhaust emissions in the vehicle body. Among them, the most important is the oxygen sensor, the practical use of zirconia sensor (using temperature -40 ° C ~ 900 ° C, accuracy of 1%), zirconia concentration battery type gas sensor (use temperature 300 ° C ~ 800 ° C), solid An electrolyte type zirconia gas sensor (using a temperature of 0 ° C to 400 ° C with an accuracy of 0.5%) and a titanium dioxide oxygen sensor. Compared with zirconia sensors, titanium dioxide oxygen sensors are characterized by simple structure, light weight, low cost, and strong resistance to lead pollution.
6. Knock sensor
The knock sensor is used to detect the vibration of the engine, by adjusting the ignition advance angle control and avoiding knocking of the engine. Knocking can be detected by three methods: cylinder pressure, engine body vibration, and combustion noise. The knock sensor is magnetostrictive and piezoelectric. The magnetostrictive knock sensor has a temperature range of -40 ° C to 125 ° C and a frequency range of 5 to 10 kHz. The piezoelectric knock sensor has a sensitivity of up to 200 mV/g at a center frequency of 5.417 kHz and an amplitude of 0.1. Good linearity in the range of g ~ 10g.
Chassis control sensor
The chassis control sensor refers to a sensor used in a chassis control system such as a transmission control system, a suspension control system, a power steering system, and an anti-lock brake system. These sensors, although distributed in different systems, work the same way as the corresponding sensors in the engine. Moreover, with the increased integration of automotive electronic control systems and the widespread use of CAN-BUS technology, the same sensor can not only provide signals to the engine control system, but also provide signals to the chassis control system.
The sensors for the automatic transmission system mainly include: a vehicle speed sensor, an accelerator pedal position sensor, an acceleration sensor, a throttle position sensor, an engine speed sensor, a water temperature sensor, and an oil temperature sensor. The sensors for the anti-lock braking system mainly include: wheel speed sensor and vehicle speed sensor; the sensors for the suspension system mainly include: vehicle speed sensor, throttle position sensor, acceleration sensor, vehicle height sensor, steering wheel angle sensor, etc.; The sensors mainly include: vehicle speed sensor, engine speed sensor, torque sensor, oil pressure sensor and so on.
Body control sensor
The body control sensor is mainly used to improve the safety, reliability and comfort of the car. Since the working conditions are not as bad as those of the engine and the chassis, the general industrial sensors can be applied with a slight improvement. There are mainly temperature sensors, humidity sensors, air volume sensors, sunshine sensors, etc. for automatic air conditioning systems; acceleration sensors for use in airbag systems; vehicle speed sensors for door lock control; and light sensors for automatic brightness control; An ultrasonic sensor or a laser sensor used in reversing control; a distance sensor for maintaining a vehicle distance; an image sensor for eliminating a blind spot of a driver, and the like.
Navigation system sensor
With the application of GPS/GIS (Global Positioning System and Geographic Information System) based navigation systems in automobiles, navigation sensors have grown rapidly in recent years. The sensors for the navigation system mainly include: a compass sensor that determines the direction of travel of the car, a gyroscope and a vehicle speed sensor, and a steering wheel angle sensor.
Automotive sensor development trend
Due to the important role of automotive sensors in automotive electronic control systems and the rapidly growing market demand, countries around the world attach great importance to their theoretical research, new material applications and new product development. The future development trend of automotive sensor technology is miniaturization, multi-functionality, integration and intelligence.
Micro-sensors are based on MEMS (Micro-Electro-Mechanical Systems) developed from semiconductor integrated circuit technology. Micro-sensors use micromachining technology to package micro-scale sensitive components, signal processors, and data processing devices on a fast chip. Small size, low price, easy integration, etc., can significantly improve the system test accuracy. The technology is now maturing and can produce a variety of miniature sensors that are sensitive and detect mechanical, magnetic, thermal, chemical and biomass. Due to the advantages of MEMS-based miniature sensors in reducing the cost and improving the performance of automotive electronic systems, they have begun to gradually replace sensors based on traditional electromechanical technology.
Multi-functionality means that one sensor can detect two or more characteristic parameters or chemical parameters, thereby reducing the number of automotive sensors and improving system reliability.
Integration refers to the production of IC sensors using IC manufacturing technology and fine processing technology.
Intelligent means that the sensor is combined with a large-scale integrated circuit, with a CPU, with intelligent functions to reduce the complexity of the ECU, reduce its size, and reduce costs.
In short, with the development of electronic technology and the increasing application of automotive electronic control systems, the demand for automotive sensors will continue to grow at a high speed. Miniaturized, multi-functional, integrated and intelligent sensors will gradually replace traditional sensors and become automobiles. The mainstream of sensors.
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