Fuel-cell systems — cathode air metering ahead of the stack
Mass Air Flow Sensor
Original Bosch HFM7-4.7 ID · −40…+560 kg/h
Air circuit
Overview
One hot-film element in the intake duct measures the mass of the air, not just its volume, so the reading holds when temperature and altitude change. The signal is frequency-coded and covers −40 to +560 kg/h including reverse flow, which means intake pulsation is measured with its direction rather than averaged away. Intake air temperature comes out of the same connector as a second, independent output.
Key features
- Mass flow and intake temperature from one sensor
- Hot-film element — no moving parts in the air path
- Reverse flow measured, not averaged out
- Frequency output, period-coded across the range
- ≤ 18 hPa pressure drop at nominal flow
- Each unit trimmed in its own cylinder housing
Specification
Technical data
Pneumatic and thermal data
| Item | Specification |
|---|---|
| Nominal mass air flow | 480 kg/h |
| Measuring range | −40 … +560 kg/h, reverse flow included |
| Pressure drop at nominal flow | ≤ 18 hPa |
| Accuracy, new part | ± 2 % from 10 to 480 kg/h; ± 3 % at 8 and 560 kg/h |
| Sensor temperature, continuous | −40 … +120 °C, with intake air ≤ 100 °C |
| Sensor temperature, short-term | +120 … +130 °C — max. 3 min, 80 h in total |
| Housing | Size 4.7 cylinder housing, 96 mm overall length |
Electrical data
| Item | Specification |
|---|---|
| Supply voltage | 14 V nominal — operating range 6 … 17 V |
| Current, normal operation | typ. < 0.06 A · max. < 0.1 A |
| Connector | RB 4-pin plug system |
| Mass air flow output | Frequency, period-coded to the flow |
| Intake air temperature output | PWM duty — 38 % at 20 °C, 62 % at 80 °C |
| Power-on time | Signal within ± 3 % of final value after ≤ 0.1 s |
Original Bosch sensor, type HFM7-4.7 ID. Further Bosch documentation is available on request.
Application
Where it is used
Engine intake — petrol and diesel intake air mass
Intake development — air box and duct work on the flow bench
Test benches — reference air flow on dyno and rigs
More in air circuit
Related reading
From the engineering notes
Background on the design decisions behind this component — all articles.
What a fuel cell stack expects from its balance of plant
A stack presents four interfaces — hydrogen, air, coolant and DC bus. Match each one with the right parts and integration gets much simpler.
Mass Air Flow Sensor — product brochure (PDF)
Full specifications, model selection tables and engineering notes. Two pages, English.
Download PDF
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