Application status and development trend of sensors in automobile

With the development of electronic technology, the degree of automobile electronization is increasing. The traditional mechanical system has been difficult to solve some problems related to the functional requirements of automobile, so it will gradually be replaced by electronic control system. As the key component of the automobile electronic control system, the sensor directly affects the performance of the system. At present, there are about dozens to hundreds of sensors on ordinary cars, and more on luxury cars. These sensors are mainly distributed in engine control system, chassis control system and body control system.

1. Sensor for engine control

There are many kinds of sensors for engine, including temperature sensor, pressure sensor, rotation sensor, flow sensor, position sensor, concentration sensor, knock sensor, etc. This kind of sensor is the core of the whole vehicle sensor. It can improve the engine power, reduce the fuel consumption, reduce the exhaust gas, reflect the fault, etc. because it works in the engine vibration, gasoline vapor, sludge, water bloom and other harsh environment, its technical index of the adverse environment resistance is higher than the general sensor. There are many requirements for their performance indicators, the most important of which is the measurement accuracy and reliability, otherwise the errors caused by sensor detection will eventually lead to engine control system failure or failure.

Knock sensor

The knock sensor detects the knock or combustion noise of the engine under various working conditions to avoid the abnormal operation of the engine.

(1) temperature sensor: it mainly detects the engine temperature, suction 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 injection nozzle needle valve, so as to ensure the best mixture for the engine and achieve the exhaust purification effect. The temperature sensors used in practice are mainly wire wound resistance type, thermistor type and thermocouple type. Wire wound resistance temperature sensor has high accuracy, but poor response characteristics; thermal sensor has high sensitivity, good response characteristics, but poor linearity, and low applicable temperature; thermocouple sensor has high accuracy and wide temperature measurement range, but needs to consider amplifier and cold end treatment.

(2) pressure sensor: it mainly detects the negative pressure of cylinder, so as to control the ignition and fuel injection; detects the atmospheric pressure, so as to control the time-space fuel ratio of climbing; detects the internal pressure of cylinder, so as to control the ignition advance angle; detects the exhaust gas recirculation flow, engine oil pressure, brake oil pressure, tire air pressure, etc., and responds to the relevant amount. At present, there are several kinds of pressure sensors used in vehicles, including capacitor type, piezoresistive type, differential transformer type (LVDT), surface elastic wave type (SAW). Capacitor type sensor has the characteristics of high input energy, good dynamic response, good environmental adaptability, etc.; piezoresistive type is greatly affected by temperature, need to set another temperature compensation circuit, but suitable for mass production; LVDT type has large output, easy to digital output, but poor vibration resistance; saw type has small volume, light weight, low power consumption, strong reliability, high sensitivity, high resolution, digital It is a kind of ideal sensor.

(3) rotation sensor: it is mainly used to detect crankshaft angle, engine revolution, throttle opening, vehicle speed, etc., so as to control ignition advance angle, fuel quantity and injection time, etc. the products mainly include generator type, magnetoresistance type, Hall effect type, optical type, vibration type, etc.

(4) oxygen sensor: detect the hollow fuel ratio of exhaust gas, send negative feedback signal to the oil supply system to correct the injection pulse, adjust the air fuel ratio to the theoretical value, so as to achieve the ideal exhaust purification effect, commonly used are zirconia and titanium oxide sensors.

(5) flow sensor: measure the intake air volume and fuel flow to control the air-fuel ratio. There are mainly air flow sensor and fuel flow sensor. The air flow sensor detects the amount of air entering to control the injection quantity of the electronic injector, so as to obtain a more accurate air-fuel ratio. The practical products are mainly Kalman vortex, vane and hot wire. Kalman type has no moving parts, which is sensitive and has high accuracy; hot wire type is easy to be affected by the pulsation of suction gas and is easy to break; fuel flow sensor is used to detect the fuel flow rate to calculate the fuel consumption of automobile, and the products mainly include water truck type and ball cycle type.

(6) knock sensor: it detects the vibration of the engine and adjusts the ignition time according to the detected knock signal. The main products are magnetostrictive and piezoelectric.

2. Sensor for chassis control

The sensors for chassis control refer to the sensors distributed in transmission control system, suspension control system, power steering system and anti lock braking system. They have different functions in different systems, but the working principle is the same as the sensors in the engine. There are mainly the following types of sensors.

(1) sensors for transmission control: mainly including speed sensor, acceleration sensor, engine load sensor, engine speed sensor, clutch sensor, water temperature sensor, oil temperature sensor, etc. The information obtained by these sensors is processed so that the electronic control device can control the shift point and the torque converter to lock, so as to achieve the maximum power and fuel economy.

(2) sensors for suspension system control: mainly including speed sensor, throttle valve opening sensor, acceleration sensor, body height sensor, steering wheel angle sensor, etc. According to the information detected by these sensors, the system can automatically adjust the height of the vehicle, restrain the change of vehicle posture, and realize the control of vehicle comfort, handling stability and driving stability.

(3) sensors for power steering system: mainly including speed sensors, engine speed sensors, torque sensors, etc., which can be used to make the power steering electronic control system realize light steering control, improve response characteristics, reduce engine loss, increase output power, save fuel, etc.

(4) the anti lock brake sensor mainly uses the wheel angle speed sensor to detect the wheel speed, control the brake oil pressure and improve the brake performance when the slip rate of each wheel is 20%, so as to ensure the vehicle handling and stability.

3. Sensor for body control

The main purpose of using this kind of sensor is to improve the safety, reliability and comfort of the car. The technical requirements of its resistance to harsh environment are not as strict as those of sensors for engine and chassis. The general industrial sensors can be applied with a little improvement. It is mainly used in a variety of temperature sensors, air volume sensors, sunshine sensors, etc. in the automatic air conditioning system, speed sensors in the brake door lock system, acceleration sensors in the air bag system, light sensors in the brightness automatic control, ultrasonic sensors in the dead angle alarm system, image sensors, etc.

4. Research and development trend of vehicle sensors

Because of the importance of sensors in the electronic control system, in a sense, the competition of advanced vehicles is the competition of sensors. Countries all over the world attach great importance to their theoretical research, application of new materials and product development. Diamond has good heat resistance and high thermal stability. The surface of diamond begins to carbonize only when the temperature is above 1200 ℃ in vacuum and 600 ℃ in the atmosphere. With this feature, a thermal sensor suitable for high temperature can be made. The temperature can be monitored and controlled from normal temperature to 600 ℃, and it can be used in the harsh environment with high temperature and corrosive gas. The performance is stable It has a long service life and can be used for high temperature measurement in engine. In addition, the deformation rate of diamond is very high at high temperature. The vibration sensor and acceleration sensor can be made by using this characteristic. It can be used as a pressure sensor with high temperature, corrosion resistance and high sensitivity, which can be used for vibration detection, engine and cylinder pressure measurement.

Optical fiber sensor has been paid more and more attention because of its strong anti-interference, high sensitivity, light weight, small volume, suitable for telemetry and so on. At present, many mature products have come out, such as optical fiber torque sensor, temperature, vibration, pressure, flow and other sensors.

At the same time, with the development of microelectronics and micromachining technology, sensors are developing towards miniaturization, multifunction and intelligence. Micromachining technology is used to encapsulate micromechanical sensor, signal conditioner and data processing device on a chip. Because of its small size, low price, easy integration and other characteristics, it can improve the system test accuracy. For example, the micro pressure sensor and the micro temperature sensor are integrated together, and the pressure and temperature are measured at the same time, then the temperature effect in the pressure measurement can be eliminated by the on-chip calculation. At present, many micro sensors are available, such as pressure sensors, accelerometers, silicon accelerometers for anti-collision, etc. It is said that the micro pressure sensor embedded in the car tire can maintain proper inflation, avoid over inflation or under inflation, thus saving 10% fuel. The multi-functional characteristic enables the sensor to detect two or more characteristic parameters at the same time. Because of the special computer, the intelligent sensor has the characteristics of intelligence.

In addition, sensor response time, output and computer interface are also important research topics. With the development of electronic technology, the technology of vehicle sensor will be improved.

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