Foreword
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The sensors used in automobiles in the 1960s (the application of automotive sensors) ranged from the initial oil pressure sensor, oil quantity sensor and water temperature sensor to the power system (composition of the vehicle transmission system) that helped control the car and maintained a certain amount of air. The scale of automotive sensors has continued to grow and develop, with sensors that control emissions, and today's sensors for anti-lock braking devices and automotive safety airbags. So, what are the types of automotive sensors? Xiaobian made a brief introduction to the types of sensors and their related knowledge by collecting and sorting data.
There are many types of automotive sensors. The sensors that we usually encounter include: temperature sensor (cooling water temperature sensor THW, intake air temperature sensor THA); flow sensor (air flow sensor, fuel flow sensor); intake pressure sensor MAP Throttle position sensor TPS; engine speed sensor; vehicle speed sensor SPD; crank position sensor (ignition timing sensor); oxygen sensor; knock sensor (KNK); air flow sensor;
Let's take a brief look at several commonly used car sensors:
Air flow sensor
The air flow sensor converts the inhaled air into an electrical signal and sends it to the electronic control unit as one of the basic signals for determining the fuel injection. According to different measurement principles, it can be divided into rotary vane air flow sensor Kamen vortex air flow sensor, hot wire air flow sensor VG30E engine and domestic Volvo B230F engine installed in Tianjin Sanfeng passenger car) and hot film air flow sensor Type. The first two are volume flow type, and the latter two are mass flow type. At present, hot-line air flow sensors and hot film air flow sensors are mainly used. In order to form a suitable mixture and achieve an optimum air-fuel ratio, we must accurately control the engine intake air flow. Let us introduce some common air flow sensors.
Oxygen Sensor
When the oxygen content in the exhaust gas is too high, it indicates that the mixture gas is too lean, and the oxygen sensor outputs an electric signal to the ECU, so that it instructs the injector to increase the fuel injection amount; when the oxygen content in the exhaust gas is too low, When the mixture is too rich, the oxygen sensor immediately passes this information to the ECU, which instructs the injector to reduce the amount of fuel injected. The oxygen sensors currently used in automobiles mainly include two types of sensors: a titanium dioxide oxygen sensor and a zirconium dioxide oxygen sensor.
Working principle: The oxygen sensor is installed in the exhaust pipe of the engine to measure the oxygen content in the exhaust gas. It is a battery that generates an electromotive force in accordance with the difference in oxygen concentration between the atmosphere and the exhaust gas. As shown in the figure, platinum is coated on both the inner and outer sides of the ceramic electrolyte to form an electrode. When it is inserted into the exhaust pipe, its outer surface is in contact with the exhaust gas and the inner surface is open to the atmosphere. At temperatures above about 300 degrees, the ceramic electrolyte can become a conductor of oxygen ions. When the mixture is relatively thin, that is, the excess air coefficient α>1, the oxygen content in the exhaust gas is inevitably large, and the difference in oxygen concentration between the inner and outer surfaces of the ceramic electrolyte is small, and only a small voltage is generated; and when the mixed gas is rich, that is, When the excess air coefficient α<1, the oxygen content in the exhaust gas is small, accompanied by a large amount of incomplete combustion products such as CO, hydrocarbons, etc., these components may react with oxygen under the action of the catalyst, consuming exhaust gas. The residual oxygen makes the oxygen concentration on the outer surface of the ceramic electrolyte tend to zero, so that the difference in oxygen concentration inside and outside the electrolyte suddenly increases, and the output voltage of the sensor also suddenly increases, and its value tends to 1V.
Throttle position sensor
(1) Switching throttle position sensor
This throttle position sensor is essentially a transfer switch, also known as a throttle switch. Such throttle position sensors include moving contacts, idle contacts, and full load contacts. The idle state and heavy load state of the engine can be detected by the idle contact and the full load contact. Generally, the moving contact is called a TL contact, the idle contact is called an IDL contact, and the full load contact is called a PSW contact. As can be seen from the structure diagram, under the action of the linkage linked with the throttle, the cam can be rotated, and the movable contact can move along the groove of the cam. This throttle position sensor structure is relatively simple, but its output is discontinuous.
When the throttle is fully closed, the voltage is applied to the IDL terminal from the TL terminal and back to the electronic controller. When transmitting signals in such a way, the electronic controller knows that the throttle is now fully closed. When the accelerator pedal is depressed and the throttle is above a certain opening degree, the voltage is transmitted from the TL terminal to the electronic controller through the PSW terminal. The electronic controller understands that the throttle is now open at a certain angle.
(2) Linear throttle position sensor
The linear throttle position sensor is mounted on the throttle and continuously detects the opening of the throttle. It is mainly composed of a potentiometer linked to the throttle valve, an idle contact, and the like. The movable contact of the potentiometer (ie, the throttle opening output contact) slides on the resistive film with the throttle opening, thereby obtaining a linear voltage output proportional to the throttle opening on the contact (TTA terminal). As shown. When the throttle is fully closed, another movable contact associated with the throttle is connected to the IDL contact, and the sensor outputs an idle signal. The linear voltage signal output from the throttle position is A/D converted and sent to the computer.
Pressure Sensor
(1) Capacitive pressure sensor
The capacitive pressure sensor is composed of two moving pieces (elastic metal diaphragm) placed in the cavity, two fixed pieces (metal coating on the upper and lower concave glass of the elastic film), an output terminal and a casing. Two series capacitors are formed between the rotor and the two stators. When the intake pressure acts on the elastic diaphragm, the elastic diaphragm is displaced, which is bound to decrease from one stator to the other, and the distance from the other stator is increased (can be demonstrated by a piece of paper). We can see from the formula that the distance between the two metal electrode plates is one of the important factors affecting the capacitance. When the distance increases, the capacitance decreases, and when the distance decreases, the capacitance increases. This structure, which is caused by an amount of measurement to cause the two sensor elements to be equally and inversely changed, is called a differential structure. If the elastic diaphragm is placed between the side pressure and the atmospheric pressure (the upper cavity of the elastic diaphragm passes through the atmosphere), the gauge pressure is measured; if the elastic diaphragm is placed between the side pressure and the vacuum (the upper part of the elastic diaphragm is empty) The cavity is vacuumed and the absolute pressure is measured.
(2) Differential transformer intake pressure sensor
The differential pressure sensor is an open-circuit mutual inductance inductor sensor. Since it has two secondary coils connected to a differential structure, it is also called a differential transmission.
When the primary coil of the differential transformer is excited by an alternating current source, the secondary coil generates an induced electromotive force. Since the secondary coils are differentially connected, the total output is the difference between the induced electromotive forces of the two coils. When the core is not moving, its total output is zero; when the core moves, the output electromotive force and the core displacement change linearly.
The detection and conversion process of the differential transformer intake pressure sensor is: firstly convert the pressure change into the displacement of the transformer core, and then convert the core displacement into an electrical signal output through the differential transmission. The pressure sensor is mainly composed of a vacuum bellows (corrugated pipe) and a differential transmission. When the air pressure changes, the bellows deforms and drives the core of the differential transformer to move. Due to the displacement of the core, a voltage is generated at the output end of the differential transformer, and the voltage is processed and sent to the input end of the ECU. If the injection time is determined according to the level of the voltage and the injector is operated, the basic fuel injection amount can be determined.
(3) Semiconductor strain gauge intake pressure sensor
Semiconductor pressure intake sensors operate with strain effects.
The so-called strain effect refers to a phenomenon in which the resistance value of a conductor or a semiconductor changes when strain is generated by an external force.
A strain gauge is a chip resistor that operates on the so-called piezoresistive effect principle in which the resistivity of a semiconductor material changes when a certain load is applied in the axial direction.
The intake pressure sensor composed of the resistance strain gauge is mainly composed of a semiconductor strain gauge, a vacuum chamber, a hybrid integrated circuit board and the like. A semiconductor strain gauge is a four-value resistor made by a semiconductor process on a diaphragm and connected as a bridge resistor. The semiconductor resistance bridge strain gauge is placed in a vacuum chamber. Under the action of the intake pressure, the strain gauge is deformed, the resistance value changes, and the bridge loses balance, thereby converting the change of the intake pressure into the output voltage of the resistance bridge. Variety.
to sum up
There are many types of automotive sensors, and different sensor functions require different automotive sensors. This paper mainly introduces the types of automotive sensors used in different parts of the car: air flow sensor, oxygen sensor, throttle position sensor, pressure sensor and so on.
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