The compressed air flow meter is focused on processing information about the amount of mass entering the internal combustion engine cylinders. The devices are common on gasoline and diesel engines with electronic control. These devices are divided into several types, which we will consider below.
Modifications with butterfly valves
The compressed air flow meter of this configuration is located between the throttle body and the air cleaner. The principle of operation of the device is based on the resistance of the medium. The device measures the force applied to the damper, which, under the air flow, rotates at a certain angle, overcoming the action of a helical spring.
This creates an insignificant loss of pressure. To avoid fluctuations of the pressure damper, including at idle, a damping compartment is included in the design, in which there is also a damper. It has the same work surface. The capacity of the damper chamber and the gap between the working elements are selected in such a way that the pressure baffle monitors the rapid transformation of the flowair during injection. The mechanical movement of the pressure wall is transformed into a change in electrical voltage using a potentiometer, then transmitted to the control unit, ensuring accurate fuel dosage.
Operation of the potentiometer and related parts
In the above type of compressed air flow meter, battery voltage is applied to the resistor through the main relay of the assembly. The ballast element reduces the indicator to 5.0-10.0 volts. The resulting voltage is supplied to the contacts of the control unit and the end at the output of the potentiometer rheostat. The second output end is connected to ground. Potentiometer pulses are taken from the motor through the sensor connectors to the controller pin.
The flow meter's internal working geometry provides a logical correlation between airflow and damper position. This makes it possible to calculate the optimal composition of the mixture at low loads. The potentiometer is mounted in a sealed case, consists of a ceramic base, contacts and resistors. The resistance of the last elements has a constant value, does not depend on temperature changes in the motor unit.
Features
In order to eliminate the effect of the battery voltage on the signal produced by the potentiometer of an industrial compressed air flow meter, the electronics takes into account the difference between the incoming and outgoing value.
The intake air temperature indicator (NTC resistor) is connected in parallel with the electrical circuit. Hisresistance decreases with increasing temperature. Pulses from the sensor transform the output signal, depending on the temperature of the incoming air streams. For the passage of air at idle, a bypass channel under the damper is used.
Heated filament option
The advantage of this type of compressed air flow meters is the absence of mechanically active elements, which increases the working life of the unit. In fact, this device is a thermal load sensor of the power unit. It is mounted between the air filter and the throttle valve, determining the volume of incoming air. The heated filament and film versions function identically. The conductor, which is in the air stream, is heated by electric current, cooled under the air flowing over it.
Temperature sensor; 2. ring with wire; 3. rheostat
The principle of operation of a compressed air flow meter with a filament
The thread is heated under the influence of electric current, the temperature is maintained stably. If the element begins to cool down, the current restores the indicator to the required value. The change in current strength is read by the control unit and is included in the measured parameters, which make it possible to determine the intake air flow. The built-in sensor is designed to eliminate distortion of the final results.
The incoming air flow covers the heated conductor built into the meter. The electronic control system monitors a constant valuetemperature of the conductor in relation to a similar parameter of the incoming air. As the flow volume increases, the filament will cool down. As a result, the amount of current required to maintain a stable conductor temperature is considered a measure of the mass of air entering the engine compartment. The current is transformed into voltage pulses processed by the control unit as an input characteristic, along with the rotational speed of the “engine” crankshaft. The controller also receives information about the temperature of the refrigerant and the incoming air flows. Analyzing the information of incoming signals, the unit generates pulses of the fuel injection period to the injectors.
Film sensor
Another type of compressed air flow meter is an analogue with a hot-film anemometer. Here the metering pipe is built into the mass analogue, which can have different sizes, depending on the nominal air consumption of the engine. The element is installed behind the air filter on the inlet.
The incoming air flow enters the collector, enveloping a sensitive indicator, which also includes a computing circuit. The air then passes through the bypass compartment behind the sensor element. The sensitivity of the device can be improved by improving the design of the bypass channel with the ability to determine the reverse currents of the air mass. The indicator is connected to the ECU using special pins.
1. Measuring chain; 2. diaphragm; 3. pressure chamber; 4.measuring part; 5. ceramic substrate.
How does a mass flow meter work?
The principle of operation of the device in question consists of the following steps:
- The mechanical microscopic diaphragm is heated by a central resistor.
- At the same time, there is a sharp drop in temperature in every part of the heating zone.
- Diaphragm heating is detected by a pair of independent resistors installed before and after the heating element.
- If there is no air supply to the intake, the temperature on each side is the same.
- After the beginning of the flow around the sensitive sensor, the distribution of the temperature parameter across the diaphragm changes.
Heat is dissipated in the air, causing mass flow around the indicator's sensing element. At the same time, the purpose of the compressed air flow meter determines the temperature difference in such a way that the measure of the total flow rate does not depend on the absolute temperature. As a result, the device in question registers the amount and direction of the incoming air.
Flow meter "Rise"
This device, unlike the analogs discussed above, is used to measure the average flow rate and volume of various electrically conductive liquids, not air masses. The devices are available in several modifications, but they have a similar device and principle of operation based on electromagnetic action. These devices can be produced in a single version or withpull-out block. The output part operates on a current or frequency-pulse indicator. The main scope of application is pipelines Du 10-Du 200 mm, the relative error is 0.2-2.0%. Compared to mechanical sensors, Vzlet electromagnetic flowmeters have a number of advantages. The main one is the absence of pressure leaks in the controlled area, which makes it possible to reduce energy consumption. In addition, they are more resistant to aggressive and other problematic environments.
