Test methodology
Hardware-in-the-loop (HiL) explained: real hardware, simulated world
Key facts
- HiL tests a real component against a simulated environment that computes along in real time.
- The load motor of the bench applies exactly the torques to the real component that the simulation model demands.
- The biggest benefit: reproducible corner cases and automated regression tests, long before a field test would be possible.
The principle: one component real, the rest simulated
In a hardware-in-the-loop test the specimen is real, but its environment is a computational model. An e-bike drive, for example, runs physically on the bench while rider, route, gradient and driving resistances are simulated in real time. In every cycle, the model computes which load torque the simulated world would currently produce, and the bench's load motor applies exactly this torque to the real shaft. To the specimen it feels like a real mountain ride, just reproducible down to the detail.
Why HiL beats the field test
A field test answers the question “does it work today, on this route, with this rider?”. A HiL test answers “does it work under defined conditions, repeatable at any time?”. Corner cases that are dangerous or hardly producible outdoors (blocking loads, extreme load changes, misbehaviour of other components) can be run safely and as often as desired on the bench. And because every test run starts identically, software revisions become comparable: after every change the same test suite runs automatically, the basis for regression testing along the V-model.
MiL, SiL, HiL: how they differ
Three stages coexist in development: model-in-the-loop (everything simulated, including the specimen as a model), software-in-the-loop (the real control software runs against a model, but without real hardware) and hardware-in-the-loop (real hardware on the bench against the simulated remaining world). The later the stage, the more realistic and the more expensive the individual test. The art lies in finding errors as early as possible and using HiL for what only becomes visible with real hardware: friction, thermal behaviour, tolerances, control behaviour.
And at ENGtron?
The ENGtron drivetrain test bench is HiL-capable: real-time simulation at 1 ms cycle time, DAkkS-calibrated torque measurement and automated regression tests for motors, gearboxes, robotic actuators and e-bike shifting systems.
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