I've take the earlier data and used an averaging technique to go from point-to-point per sample to samples with points and the averaged values from earlier and later samples. Not quite a straight-line approximation, it is close enough to make the data more easily understood:
Starting:
The interesting aspects are:
- A - Starting the engine uses MG1 and a slug of power from the traction battery. However, the ~3 second period to make all six samples means in this case, we didn't sample the traction battery power until after the peak MG1 load. This coarse sampling interval means per Nyquist that we need at least seven seconds of steady-state data to even attempt to draw any conclusions.
- B - Shows movement in the parking lot coming to the street. Probably the car was in "N" and the slight spike in battery load comes from the electronic-assisted brake load.
- C - While waiting for traffic to clear, the engine started and put a charge back on the traction battery.
- D - The engine shutoff and the only load is the normal vehicle electrical demand.
- E - During car warm-up, until the catalytic converters get hot enough to work, the car uses EV mode as much as possible. The engine runs but just to heat up the converters.
Acceleration:
The main observations:
- A - To compare MG1 - MG2 efficiency, we need to factor out the traction battery energy and the vehicle overhead load. Then the ratios of MG1 and MG2 can be used for efficiency over the electrical, power path.
- B - Notice that the ratio of mechanical to electrical path load varies significantly. I had once thought it was fixed proportional to the torque ratio but clearly it is not.
Cruse:
Dealing with traffic and overpasses, the data looks pretty noisy but:
- A - This is energy recirculate mode when MG2 acts like a generator and MG1 is a motor adding its power to the ICE and keeping it from spinning faster. The combined power travels over the mechanical path.
- B - Again, the ratio of mechanical and electrical path power is not fixed. This means any fixed assumptions about the electrical path power efficiency and total transaxle efficiency needs to be rethought.
Stopping:
Here we see classical, regenerative braking and sampling and possibly a new, previously undocumented MG1 mode:
- A - In classical regenerative braking, MG2 works as a generator and stuffs energy into the traction battery. However, the traction battery is limited to 20kW so any extra energy has to be handled by the mechanical brakes and/or engine braking.
- B - Here we see a mysterious 4kW with no apparent source. However, close examination of the source data suggests the current sample may have have been missed and/or a brief, no current condition. With a 3 second cycle time for all 6 samples, it is entirely possible a legitimate, no current condition was sampled.
- C - Again, no traction battery power but it is entirely possible that MG1 was just 'all windings tied to ground.' This would turn the motor into one heck of an electronic brake to stop the ICE. But given the heating of MG1, not the best approach. Again, this is probably a sampling issue, not a real operational mode.
Initial testing with a faster polling rate looks to be OK but I haven't recorded any data, yet. Also, converting point-samples into straight-line approximations is the way to go but it is not trivial. I've ordered a GPS receiver that should be here next week. Then I can start a series of benchmarks to accurately measure Prius transaxle energy flows.
Bob Wilson