The Danfoss Motor states that the motor sensor control system is the heart of the entire automotive sensor. It has many types, temperature sensors, pressure sensors, position and speed sensors, flow sensors, oxygen sensors and knock sensors. These sensors provide motor operating conditions information to the motor's electronic control unit (ECU) for ECU control of motor operating conditions to improve motor power, reduce fuel consumption, reduce exhaust emissions, and detect faults.
Because the motor is working at high temperatures (motor 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 harsh environments such as steam, salt spray, corrosion and sludge pollution, the sensors of the motor control system must be able to withstand high temperatures and have a technical index in harsh environments that is 1-2 orders of magnitude higher than that of general industrial sensors, where * The key is measurement accuracy and reliability. Otherwise, the measurement error caused by the sensor will eventually cause the motor control system to malfunction or cause malfunctions.
Temperature Sensor
The temperature sensor is mainly used to detect motor temperature, intake gas temperature, cooling water temperature, fuel temperature, and temperature inside the catalyst.
Temperature sensors are wired, resistive, thermistor and thermocouple. 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 ~ 120 ° C, accuracy 2.0%), metal or semiconductor film air temperature sensor (-40 ° C ~ 150 ° C, accuracy 2.0%, 5%, response time 20ms).
The motor coolant temperature sensor is used to detect the temperature of the motor coolant and convert the temperature signal into an electrical signal that is sent to the motor control module (ECU) as the primary correction signal for gasoline injection, ignition timing, idle speed, and exhaust emissions control.
Intake air temperature sensor (IAT)
The intake air temperature sensor is used to detect the intake air temperature, and converts the intake air temperature signal into an electric signal and sends it to the motor control module (ECU) as a correction signal for gasoline injection and ignition timing.
The exhaust gas temperature sensor is used to detect the temperature of the recirculated exhaust gas to reflect the flow rate of the exhaust gas recirculation.
If the motor temperature sensor fails, there will be difficulties in the cold start of the car at a very low temperature, poor running characteristics during the warm-up phase, increased fuel consumption, and increased exhaust emissions.
Pressure Sensor
The pressure sensor is mainly used to detect cylinder negative pressure, atmospheric pressure, turbo motor 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, and a temperature compensation circuit is required, but it is suitable for mass production; the LVDT type pressure sensor has a large output, is easy to digital output, but has poor anti-interference;
SAW pressure sensor has the characteristics of small size, light weight, low power consumption, high reliability, high sensitivity, high resolution, digital output, etc. It is used for pressure detection of automobile suction valve and can work stably at high temperature. It is An ideal sensor.
The function of the intake manifold pressure sensor (MAP) is to detect the vacuum degree of the intake manifold and convert the pressure signal into an electronic signal for delivery to the motor control computer, which is the main reference signal for controlling the injection pulse width and ignition timing. There are two types of semiconductor varistor and capacitive intake manifold pressure sensors.
If the intake manifold pressure sensor fails, the motor will start difficult, the performance will be abnormal, the acceleration will be worse, the idle speed will be unstable, the fuel consumption will be large, the acceleration will be unstable, and the tempering, firing, fuel consumption, deflagration and other faults will occur during acceleration.
The oil pressure sensor is used to detect the motor oil pressure and send an alarm signal when the pressure is insufficient. When the oil pressure is not enough, the oil lamp on the instrument panel will light up. There are generally two, one on the main oil passage and one on the cylinder head.
Flow Sensors
Flow sensors are primarily used for the measurement of motor air flow and fuel flow. The function of the air flow sensor is to convert the amount of air sucked into the motor cylinder per unit time into an electric signal and send it to the motor control module (ECU), which is one of the basic signals for determining the fuel injection amount and the ignition timing, and is used for determining the motor control system. Combustion conditions, control air-fuel ratio, start-up, ignition, etc.
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 to be temperature compensated;
The Karman vortex air flowmeter has no moving parts, which is sensitive and accurate, and requires temperature compensation.
The hot wire air flow meter has high measurement accuracy and does not require temperature compensation, but is susceptible to gas pulsation and is easy to break;
The hot film air flow meter and the hot wire air flow meter have the same measurement principle, but have a small volume, are suitable for mass production, and have 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%.
If the air flow sensor fails, there will be difficulty in starting the motor, performance is abnormal, idle speed is unstable, tempering, shooting, acceleration, fuel consumption, deflagration, etc. during acceleration.
The fuel flow sensor is used to detect the 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 <10ms.
Position and speed sensor
The position and speed sensors are mainly used to detect crank angle, motor 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, accuracy is 0.5. Hereinafter, the bending angle is measured to be 0.1.
The crankshaft position sensor is one of the main sensors in the motor centralized control system. It is an indispensable signal source for confirming the crank angle position and motor speed. The motor control module (ECU) uses this signal to control the fuel injection amount and injection timing. Ignition time (ignition advance angle), ignition coil charge closing angle, idle speed and operation of 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, there will be failures such as motor failure, poor acceleration, unstable idle speed, and intermittent flameout.
The camshaft position sensor is used to detect the rotational position of the camshaft. The motor control module (ECU) uses this signal to determine the cylinder sequence of the motor to control the fuel injection sequence and the ignition sequence. When the camshaft position sensor fails, the motor output power. Will decrease.
The throttle opening sensor is used to detect the opening of the throttle and the speed of the switch, and convert the signal into a voltage signal to the control computer of the motor as a control of the injection pulse width, ignition timing, idle speed, and exhaust emissions. The main correction signal is also an auxiliary signal for the air flow sensor or the intake manifold pressure sensor.
The throttle position sensor is a variable resistor, and most throttle position sensors include a sliding contact arm associated with the throttle shaft that slides around the resistive material provided on the shaft of the movable contact.
The analog throttle position sensor is a three-wire sensor. One of the wires is powered by the 5V voltage from the computer power supply to the sensor resistance material, and the other wire is connected to the other end of the resistor material to provide (negative) grounding to the sensor. The third wire is connected to the movable contact of the sensor to provide a signal output to the (ECU) computer. The voltage at each point on the resistive material is detected by the movable contact and is proportional to the throttle angle.
The switch type throttle position sensor is composed of two switch contacts forming a rotary switch, and a normally closed contact constitutes an idle switch. When the throttle is in the idle position, it is in a closed state, and the idle control input terminal of the motor control computer is grounded. After the grounding, the motor control computer receives this signal, then the motor can enter the idle closed-loop control, or the motor can be stopped when the motor is in the (downward) state, and the other normally open contact throttle opening reaches the full load state. , the motor control computer's full load input signal grounding ground. After the motor control computer receives this signal, the motor can be put into full load enrichment control state.
The throttle is a very important sensor because the computer uses its signals to calculate motor load, ignition time, exhaust gas recirculation control, and idle speed control. A bad throttle body position sensor can cause problems such as acceleration lag and idle speed instability, as well as driving performance problems and failure of emission tests.
If the throttle sensor fails; the motor is difficult to start, the idle speed is unstable, the motor performance is poor, the flame is easy to extinguish, and there is a bump when the load changes during deceleration.
Oxygen Sensor
Sensor structure and principle Once the air-fuel ratio of the motor deviates from the theoretical air-fuel ratio, the purification ability of the three-way catalyst for CO, HC and NOx will drop sharply. Therefore, in order to achieve a good exhaust gas purification performance of the motor equipped with the three-way catalytic converter, the air-fuel ratio of the mixture must be controlled within a 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 on the motor using the three-way catalytic converter. Oxygen sensors currently used in automobiles are available in both zirconia and titania.
The basic component of the zirconia oxygen sensor is a special ceramic body, that is, a zirconia solid electrolyte, which is made of a tubular body (zirconium tube) and fixed in a fixing sleeve with mounting threads. The surface of the zirconium tube is equipped with a gas permeable platinum electrode, and is provided with a protective tube and a wire joint. The inner surface of the zirconium tube is connected to the atmosphere, the outer surface is connected with the exhaust gas, and a protective sleeve is further mounted on the outer surface, and the sleeve is provided with a venting groove. The ceramic body of the zirconium tube is porous, allowing oxygen to permeate into the solid electrolyte. At a higher temperature (above 300 ° C), oxygen is ionized. If the oxygen concentration measured in the ceramic body (atmosphere) (exhaust gas) is different, A voltage drop is generated on the surface of the two platinum electrodes, and the side having a high oxygen content is at a high potential. When the mixed gas is diluted, the exhaust gas contains more oxygen, and the difference in concentration between the two sides is small, and only a small voltage is generated; on the contrary, when the mixed gas is rich, a high voltage is generated. According to the measured voltage value, the oxygen content of the outer surface of the oxygen sensor can be measured, and the oxygen content in the exhaust gas of the motor mainly depends on the air-fuel ratio of the mixed gas. Therefore, the ECU analyzes the combustion state of the gasoline according to the electric signal input by the oxygen sensor, so as to timely Correct the fuel injection so that the air-fuel ratio is in an ideal condition, that is, λ = 1, so this sensor is also called a lambda sensor.
Oxygen sensors generally have four types of lead wires: single wire, double wire, three wire, and four wire. The single wire is a zirconia type oxygen sensor; the double wire is a titanium oxide type oxygen sensor; and the three wires and four wires are zirconia type oxygen sensors.
The difference between the three lines and the four lines: the heater negative pole of the three-wire oxygen sensor and the signal output negative pole share one line, and the heater negative pole and the signal negative pole of the four-wire oxygen sensor each use one line.
Knock sensor
The knock sensor refers to an abnormal phenomenon of spontaneous combustion generated by the final mixture in the combustion chamber. Since the knocking generates high-intensity pressure waves to hit the combustion chamber, not only a sharp metal sound can be heard. It also has a large impact on the components of the motor. Premature ignition time is the main cause of knocking. In order to make the motor run at * high power. * It is good to advance the ignition time to the limit of the motor just to the extent of knocking, so a knock sensor must be added to the ignition system.
The knock sensor is used to detect whether knocking occurs during combustion of the motor, and the knock signal is sent to the motor control computer as an important reference signal for correcting the ignition advance angle.
There are two common knock sensors, one is a magnetostrictive knock sensor, and the other is a piezoelectric knock sensor.
A common knock sensor is primarily piezoelectric, which is mounted on the cylinder of the motor, which utilizes the piezoelectric effect of crystal or ceramic polycrystals. It is also possible to use a piezoresistive effect of doped silicon or the like. Piezoelectric elements/weights, wires, etc. are mounted in the outer casing of the sensor. The principle is that when the vibration of the cylinder block of the motor is transmitted to the sensor casing, a relative movement occurs between the casing and the weight. The piezoelectric element and the weight which are sandwiched in the middle are changed in compression, and the voltage signal of the output is changed, and the control unit can only detect the voltage formed by the 7KHZ vibration. The knock intensity is judged based on the magnitude of this voltage. The ignition time is accordingly delayed to avoid knocking.
The shape and structure of the magnetostrictive knock sensor have a magnet, a ferromagnetic core excited by a magnet, and a coil around the core. The working principle is: when the cylinder block of the motor vibrates, the sensor resonates with the motor at about 7 kHz, and the magnetic permeability of the ferromagnetic material core changes, so that the magnetic flux density of the * magnet through the core also changes, thereby An induced electromotive force is generated in the winding around the core, and this electrical signal is input to the ECU.
The knock sensor has two types: non-resonant type and resonant type pressure. It is generally installed between 2 and 3 cylinders, or one of the 1 and 2 cylinders, and the middle of the 3 and 4 cylinders. The connection line of a general knock sensor is wrapped with a shielded wire.
When the knock sensor fails, the motor will deflagrate, the ignition timing is out of alignment, the fuel consumption is high, the power is reduced, and the motor is rough.