I know it has something to do with the regenerative brakes but why only rev the engine some of the time and not all of the time?
https://youtu.be/yW2lEXiNv6k?si=co5TDcu5gKnL0fDB watch this clip from 0:17 to 0:38 to get a feel of the bus in forwards motion
https://youtu.be/Uc5VOVxcenU?si=7KT5H1lNXXGjgHJJ skip to 1:24 to experience the phenomenon that I’m talking about. Why rev when braking? But only sometimes
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Sounds like the batteries are full from regen so the diesel is revving up for more engine braking.
Honda’s hybrids do something similar. Especially when going through long descents in elevation, when the batteries are full, the motor-alternator on the IC engine will spin up the engine to dissipate the electrical braking.
Hybrid or not, many heavy modern vehicles with automatic transmissions will use automatic engine braking to help slow the vehicle. The revving isn’t directly related to regenerative braking. Incorporating both automatic engine braking and regenerative braking would explain why it doesn’t rev every time the brakes are pressed. The CPU is looking at battery level, vehicle speed and brake pressure and determining second by second what the optimal mix of regen, friction and engine braking should be applied.
I found some papers here:
https://web.archive.org/web/20180131221248/http://www.hybridrive.com/series-e.php
https://web.archive.org/web/20180909093817/http://www.hybridrive.com/pdf/bus/PCS.pdf
https://web.archive.org/web/20190318181247/http://hybridrive.com/pdf/bus/DDTM-100.pdf
https://web.archive.org/web/20180909090812/http://www.hybridrive.com/pdf/bus/MTS.pdf
Since it can’t engine brake obvious the answer to “what diesel doin?” is power demand but for what? One thought was is the bus had a separate electric retarder for long descents or needs to run the compressor when activating air brakes.