With the development of electronic technology, the degree of automotive electronics continues to increase, and traditional mechanical systems have been difficult to solve certain problems related to automotive functional requirements, and will therefore be gradually replaced by electronic control systems. Sensors, as key components of automotive electronic control systems, have a direct impact on system performance. At present, there are dozens to hundreds of sensors on ordinary cars, and more on luxury cars. These sensors are mainly distributed in engine control systems, chassis control systems and body control systems.
1 Sensor for engine control
There are many types of sensors for engines, including temperature sensors, pressure sensors, rotation sensors, flow sensors, position sensors, concentration sensors, knock sensors, etc. This type of sensor is the core of the entire vehicle sensor. Using them can improve engine power, reduce fuel consumption, reduce exhaust gas, reflect faults, etc., because they work in harsh environments such as engine vibration, gasoline vapor, sludge, water spray, etc. The technical indicators of resistance to harsh environments are higher than ordinary sensors. There are many requirements for their performance indicators, the most critical of which is measurement accuracy and reliability, otherwise the errors caused by sensor detection will eventually cause the engine control system to fail or cause malfunctions.
The knock sensor detects knock or combustion noise under various operating conditions of the engine to avoid engine malfunction.
(1) Temperature sensor: It mainly detects the engine temperature, intake gas temperature, cooling water temperature, fuel temperature, catalytic temperature, etc., and converts them into electrical signals, so as to control the opening time and duration of the needle valve of the injector to ensure supply to the engine Optimum mixture and achieve exhaust purification effect. The temperature sensors used in practical applications are mainly wire wound resistance type, thermistor type and thermocouple type. Wire-wound resistance temperature sensors have high accuracy but poor response characteristics; thermal sensors have high sensitivity and good response characteristics, but have poor linearity and low applicable temperature; thermocouple sensors have high accuracy and a wide temperature range. But need to consider amplifier and cold junction processing issues.
(2) Pressure sensor: mainly detects the negative pressure of the cylinder to control ignition and fuel injection; detects the atmospheric pressure to control the air-fuel ratio during climbing; detects the internal pressure of the cylinder to control the ignition advance angle; detects the exhaust gas recirculation flow, engine oil pressure, Brake oil pressure, tire air pressure, etc., and respond to related quantities. There are currently several types of automotive pressure sensors. Capacitive, piezoresistive, differential transformer (LVDT), and surface acoustic wave (SAW) are more commonly used. Capacitive sensors have the characteristics of high input energy, good dynamic response, and good environmental adaptability; piezoresistive type is greatly affected by temperature, and a temperature compensation circuit is required, but it is suitable for mass production; LVDT type has large output and is easy to digital output , But the vibration resistance is poor; SAW type has the characteristics of small size, light weight, low power consumption, strong reliability, high sensitivity, high resolution, digital output, etc., is an ideal sensor.
(3) Rotation sensor: It is mainly used to detect crank angle, engine revolution, damper opening, vehicle speed, etc., so as to control ignition advance angle, fuel dosing and injection time, etc. The products are mainly generator type, magnetoresistive type, Huo Seoul effect type, optical type, vibration type and so on.
(4) Oxygen sensor: Detect the air-fuel ratio in the exhaust gas and send a negative feedback signal to the fuel supply system to correct the fuel injection pulse and adjust the air-fuel ratio to the theoretical value to achieve the ideal exhaust purification effect. Commonly used are zirconia and Titanium oxide sensor.
(5) Flow sensor: Measure air intake and fuel flow to control air-fuel ratio. There are mainly air flow sensors and fuel flow sensors. The air flow sensor detects the amount of incoming air to control the amount of fuel injected by the electronic injector to obtain a more accurate air-fuel ratio. The actual products used are Kalman vortex, vane, and hot wire. Kalman type has no moving parts, sensitive response and high accuracy; hot-wire type is susceptible to the pulsation of inhaled gas and is easy to break the wire; fuel flow sensor is used to detect the fuel flow rate to calculate the fuel consumption of the car. The main products are waterwheels Type, ball circulation type.
(6) Knock sensor: Detects the vibration of the engine and adjusts the ignition timing appropriately according to the detected knock signal. The main products are magnetostrictive and piezoelectric.
2 Sensors for chassis control
Chassis control sensors refer to the sensors distributed in the transmission control system, suspension control system, power steering system, and anti-lock brake system. They have different functions in different systems, but the working principle is the same as the sensors in the engine. There are several types of sensors.
(1) Transmission control sensors: There are mainly vehicle speed sensors, acceleration sensors, engine load sensors, engine speed sensors, clutch sensors, water temperature sensors, and oil temperature sensors. The information obtained by the detection of these sensors is processed to make the electronic control device control the shift point and lock the torque converter to achieve maximum power and maximum fuel economy.
(2) Sensors for suspension system control: There are mainly speed sensors, throttle opening sensors, acceleration sensors, body height sensors, steering wheel angle sensors, and so on. The system automatically adjusts the vehicle height based on the information detected by these sensors, suppresses changes in vehicle posture, etc., and achieves control of vehicle comfort, steering stability, and driving stability.
(3) Sensors for power steering systems: There are mainly vehicle speed sensors, engine speed sensors, torque sensors, etc., which use these sensors to make the power steering electronic control system to achieve light steering, improve response characteristics, reduce engine losses, increase output power, Save fuel, etc.
(4) The anti-lock brake sensor mainly uses the wheel angular speed sensor to detect the wheel speed, control the brake oil pressure when the slip rate of each wheel is 20%, improve the braking performance, and ensure vehicle maneuverability and stability.
Sensor for body control
The main purpose of using such sensors is to improve the safety, reliability, and comfort of automobiles. The technical requirements for resistance to harsh environments are not as strict as those for engines and chassis sensors. General industrial sensors can be applied with a little improvement. There are mainly various temperature sensors, air volume sensors, sunlight sensors, etc. used in automatic air-conditioning systems, vehicle speed sensors in brake door lock systems, acceleration sensors in airbag systems, automatic brightness control light sensors, and dead angle alarm systems. Ultrasonic sensors, image sensors, etc.
4 Research and Development Trends of Automotive Sensors
Because of the importance of sensors in electronic control systems, in a sense, the competition of advanced cars is the competition of sensors. Countries around the world attach great importance to their theoretical research, new material applications, and product development. Diamond has good heat resistance and high thermal stability. Carbonization only begins to occur on the surface above 1 200 ° C in a vacuum, and carbonization begins to occur above 600 ° C in the atmosphere. Using this feature, a thermal sensor suitable for high temperatures is produced. Temperature monitoring and control from normal temperature to 600 ℃, and suitable for use in harsh environments with high temperature and corrosive gas, stable performance, long service life, can be used for high temperature measurement in the engine. In addition, diamond has a high deformation rate at high temperatures. Using this feature, vibration sensors and acceleration sensors used in high temperature environments can be manufactured. Combined with other materials, the diaphragm can be used as a high-temperature, corrosion-resistant, high-sensitivity pressure sensor for vibration detection and measurement of engine and cylinder pressure.
Optical fiber sensors are receiving widespread attention due to their strong anti-interference, high sensitivity, light weight, small size, and suitable for telemetry. At present, many mature products have come out, such as optical fiber torque sensors, and sensors such as temperature, vibration, pressure, and flow.
While developing and using new materials, due to the development of microelectronic technology and micromachining technology, sensors are developing in the direction of miniaturization, multifunction, and intelligence. Miniaturized sensors use micro-machining technology to integrate micron-level sensitive components, signal conditioners, and data processing devices on a single chip. Due to its small size, cheap price, and easy integration, it can improve system test accuracy. For example, by integrating a miniature pressure sensor and a miniature temperature sensor, and measuring the pressure and temperature at the same time, the in-chip operation can be used to eliminate the pressure measurement. Temperature effect. At present, many miniature sensors are available, such as pressure sensors, accelerometers, and silicon accelerometers for collision prevention. It is said that embedding a miniature pressure sensor in a car tire can maintain proper inflation and avoid over or under inflation, which can save 10% of fuel. Versatile features enable the sensor to detect two or more characteristic parameters simultaneously. The smart sensor is intelligent because it has a dedicated computer.
In addition, issues such as sensor response time, output and computer interface are also important research topics. With the development of electronic technology, the technology of automotive sensors is bound to improve.