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Position and speed sensors
Position and speed sensors are mainly used to detect crankshaft angle, engine speed, throttle opening, vehicle speed, etc. At present, the position and speed sensors used in automobiles are mainly AC generator type, magnetic resistance type, Hall effect type, reed switch type, optical type, semiconductor magnetic transistor type, etc., with a measurement range of 0 ~ 360, an accuracy of less than 0.5, and a bending angle of 0.1.
The crankshaft position sensor is one of the most important sensors in the engine centralized control system. It is an indispensable signal source for confirming the crankshaft angle position and engine speed. The engine control module (ECU) uses this signal to control the fuel injection amount, injection timing, ignition time (ignition advance angle), ignition coil charging closing angle, idle speed and the operation of the electric gasoline pump.
According to the principle of signal formation, the crankshaft position sensor (CKP) can be divided into three categories: electromagnetic, photoelectric and Hall effect.
When the crankshaft position sensor fails, the engine will not start, poor acceleration, unstable idle speed, intermittent flameout and other fault phenomena will occur.
The camshaft position sensor is used to detect the angular position of the camshaft. The engine control module (ECU) uses this signal to determine the cylinder sequence of the engine to control the injection sequence and ignition sequence. When the camshaft position sensor fails, the engine's output power will decrease.
2.Oxygen Sensor
Structure and principle of the sensor Once the air-fuel ratio of the engine deviates from the theoretical air-fuel ratio, the purification capacity of the three-way catalyst for CO, HC and NOx will drop sharply. Therefore, in order to achieve the best exhaust purification performance for the engine equipped with a three-way catalytic converter, the air-fuel ratio of the mixture must be controlled within a very narrow range near the theoretical air-fuel ratio.
The oxygen sensor is used to detect the state of the exhaust gas entering the three-way catalytic converter and is an indispensable sensor for engines using the three-way catalytic converter. Currently, there are two types of oxygen sensors used in automobiles: zirconium oxide and titanium oxide.
Oxygen sensors generally have four lead forms: single-wire, double-wire, three-wire and four-wire. Single-wire is a zirconium oxide oxygen sensor; double-wire is a titanium oxide oxygen sensor; three-wire and four-wire are zirconium oxide oxygen sensors.
The difference between three-wire and four-wire: the heater cathode and signal output cathode of the three-wire oxygen sensor share one wire, and the heater cathode and signal cathode of the four-wire oxygen sensor use one wire each.
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Knock sensor
The knock sensor is used to detect whether knock occurs during the combustion process of the engine, and transmit the knock signal to the engine control computer as an important reference signal for correcting the ignition advance angle.
There are two common knock sensors, one is the magnetostrictive knock sensor, and the other is the piezoelectric knock sensor.
Common knock sensors are mainly piezoelectric, which are installed on the cylinder block of the engine. This sensor uses the piezoelectric effect of crystals or ceramic polycrystals. It can also use the piezoelectric resistance effect of doped silicon. The housing of the sensor is equipped with piezoelectric elements/weight blocks and wires. The principle is: when the vibration of the cylinder block of the engine is transmitted to the sensor housing, relative movement occurs between the housing and the weight block. The piezoelectric element and weight block sandwiched in the middle are squeezed and changed, so that the output voltage signal changes, and the control component can only detect the voltage formed by 7KHZ vibration. The knock intensity is judged according to the size of this voltage. Then the ignition time is postponed accordingly to avoid knock.
The appearance and structure of the magnetostrictive knock sensor include a permanent magnet, a strong magnetic core excited by the permanent magnet, and a coil around the core. Its working principle is: when the cylinder block of the engine vibrates, the sensor resonates with the engine at about 7kHz, the magnetic permeability of the strong magnetic material core changes, causing the magnetic flux density of the permanent magnet passing through the core to change, thereby generating an induced electromotive force in the winding around the core, and inputting this electrical signal into the ECU.
