Description
(1) air flow meter
"a" 4-way black connector
Supplier: BOSCH
Role
Role of the air flowmeter
- To measure the quantity of air admitted into the engine
- To measure the temperature of the air admitted
Function
Inlet air flow
(1) air flow meter
"A" clean air
"B" air containing impurities
"b" clean air measuring channel
"c" main air outlet
"d" detection cell
"e" clean air measuring channel outlet
"f" main air inlet
The body of the sensor has a bypass duct to ensure that the signal is not disturbed by any impurities contained in the air or by corrosion
The main flow of air enters the body of the sensor at "f" and the impurities contained in the admitted air, being heavier than the clean air, are evacuated via the principal outlet "c"
The flow of air traverses the measuring channel and acts on a detection cell "d" that has a thin heated membrane
The hot film membrane is maintained at a constant temperature (approximately 120° higher than the temperature of the air at the inlet) by a heating resistor
The flow of air that passes through the measuring channel tends to draw heat from the membrane and consequently, to maintain this latter at a constant temperature, a certain current must pass through the resistor
This current proportional to the flow of air is measured by the integral electronic stage which delivers a variable frequency signal that is a function of the flow of air at the inlet
Intake air temperature
(1) air flow meter
"g" air temperature sensor
The inlet air temperature sensor is a negative temperature coefficient (NTC) sensor
The NTC (Negative Temperature Coefficient) resistance value changes in relation to the change in the temperature
- When the temperature increases, the resistance value decreases
- When the temperature decreases, the resistance value increases
The value of the CTN (negative temperature coefficient) resistance is processed by the electronic stage of the air flowmeter
The electronic stage of the air flowmeter delivers an open cycle ratio output signal (RCO)
Electrical features
| designation | minimal value | maximal value |
|---|---|---|
| operating temperature | -40 °C | 120 °C |
| operating temperature (for a maximum duration of 3 minutes) | - | 130 °C |
| supply voltage | 7,5 V | 17 V |
| supply current | 0,06A | 0,1A |
| frequency of the signal for the flow of air at the inlet | 1,5 kHz | 12 kHz |
| error in measuring the flow of air at the inlet | 2% | 5% |
Inlet air flow
The frequency of the output signal varies as a function of the flow of air measured
"F" nominal frequency (Hz)
"G" air flow (Kg/h)
| air flow | nominal frequency |
|---|---|
| 10 Kg/h | 2012 Hz |
| 40 Kg/h | 2507 Hz |
| 105 Kg/h | 3204 Hz |
| 220 Kg/h | 4308 Hz |
| 480 Kg/h | 7759 Hz |
| 620 Kg/h | 11130 Hz |
Intake air temperature
"H" nominal resistance (ohms)
"J" air temperature (°C)
| nominal resistance | air temperature |
|---|---|
| 40000 ohms | -40 °C |
| 30000 ohms | -34 °C |
| 20000 ohms | -25 °C |
| 10000 ohms | -12 °C |
| 5000 ohms | 4 °C |
| 4000 ohms | 8 °C |
| 3000 ohms | 14 °C |
| 2000 ohms | 23 °C |
| 1000 ohms | 40 °C |
| 652 ohms | 60 °C |
| 0 ohms | 130 °C |
Connector
| number of channels | allocation of channels of connector |
|---|---|
| 1 | supply voltage (12V) |
| 2 | earth |
| 3 | air temperature signal |
| 4 | air flow signal |
Programming/initialisation
Programming is necessary if the part is removed/refitted