The compressed air flow meter is focused on processing information about the incoming quantity of masses into the internal combustion engine cylinders. Devices are common on electronically controlled gasoline and diesel engines. These devices are divided into several types, which we consider below.
Modifications with butterfly valves
A 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 rotates at a certain angle under the flow of air, overcoming the action of a spiral spring.
This creates an insignificant loss of pressure. To avoid fluctuations in the pressure damper, including at idle, a damping compartment is also included in the design, which also has a damper. It has a similar work surface. The capacity of the damper chamber and the gap between the working elements are selected in such a way that the pressure barrier monitors the rapid conversion of air flow during injection. The mechanical movement of the pressure head is transformed into a change in electrical voltage using a potentiometer, then transferred to the control unit, providing an accurate dosage of fuel.
Operation of the potentiometer and associated parts
In the above type of flowmeter for compressed air, the battery voltage is supplied to the resistor through the main relay of the node. The ballast element reduces the rate to 5.0-10.0 volts. The resulting voltage is fed to the contacts of the control unit and the end at the output of the rheostat of the potentiometer. The second output end is connected to the mass. The pulses of the potentiometer are removed from the motor through the sensor connectors to the controller contact.
The geometric features of the internal operation of the flowmeter provide a logical correlation between the air flow and the position of the damper. This makes it possible to calculate the optimal composition of the mixture at low loads. The potentiometer is mounted in a sealed enclosure, consists of a ceramic base, contacts and resistors. The resistance of the last elements has a constant value, does not depend on temperature differences in the motor block.
Features
To exclude the influence of battery voltage on the signal generated by the potentiometer of an industrial compressed air flow meter, the electronics takes into account the difference between the input and output indicators.
In parallel with the electrical circuit, an intake air temperature indicator (resistor with a negative thermal coefficient) is connected. Its resistance decreases with increasing temperature parameter. The pulses from the sensor transform the output signal, depending on the temperature of the incoming air flows. For the passage of air at idle, a bypass channel under the shutter is used.
Heated Thread Option
The advantages of this type of compressed air flow meter are 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 amount of incoming air. Variants with heated filament and film function identically. The conductor located in the air stream is heated by electric current, cooled under the air surrounding it.
- Temperature sensor; 2. ring with wire; 3. rheostat.
Principle of operation of a compressed air flow meter with a filament
The thread under the influence of electric current heats up, the temperature is maintained stably. If the element starts to cool, the current restores the indicator to the desired value. The change in current force is read by the control unit and is assigned to the measured parameters, allowing to determine the flow rate of intake air. The built-in sensor is designed to eliminate distortion of the final results.
The incoming air stream encompasses a heated conductor integrated in the meter. The electronic control system monitors a constant temperature indicator of the conductor in relation to a similar parameter of the incoming air. As the flow volume increases, the thread will cool. 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 engine speed of the crankshaft. The controller also receives information about the temperature of the refrigerant and the incoming air flows. Analyzing the information of the incoming signals, the unit gives out pulses of the fuel injection period to the nozzles.
Film sensor
Another type of compressed air flow meter is an analogue with a film hot-wire anemometer. Here, the measuring nozzle is built into the mass analog, which can have different sizes, depending on the nominal air flow of the engine. An element is installed behind the air filter on the inlet channel.
The incoming air stream enters the collector, enveloping the sensitive indicator, which also includes a computing circuit. Further, air 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 computer using special pins.
1. Measuring circuit; 2. aperture; 3. pressure chamber; 4. measuring part; 5. ceramic backing.
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.
- In this case, a sharp decrease in temperature is observed on each part of the heating zone.
- The heating of the diaphragm is registered by a pair of independent resistors installed before and after the heating element.
- If there is no air supply at the inlet, the temperature on each side is the same.
- After the flow begins to flow around the sensitive sensor, the temperature parameter distribution along the diaphragm changes.
The heat is dissipated in the air, which causes the mass flow rate around the sensitive element of the indicator. In this case, the purpose of the compressed air flow meter determines the temperature difference so 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.
Rise Flowmeter
This device, in contrast to the analogues considered above, serves to measure the average flow rate and volume not of air masses, but of various electrically conductive liquids. The devices are available in several versions, however, they have a similar device and operating principle based on electromagnetic action. These devices can be produced in a single version or with a remote unit. The output part operates on a current or pulse-frequency indicator. The main scope of application is pipelines DN 10-DN 200 mm, the relative error is 0.2-2.0%. Compared to mechanical sensors, Rise electromagnetic flowmeters offer several 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.