test drive question

[bpratt]

Do you know if the engine will run continuously to provide engine braking as you descend a mountain if you start with a fully charged battery?

I don't know the answer to that question for sure. But I believe if the battery is fully charged and you are going down a steep hill, the engine doesn't actually run but the motor generator that is connected to the engine will turn it over to bleed off the power from the driving motor to provide braking. Even though the engine is turning, it is using no gas.

 

[insightman]

I don't know the answer to that question for sure. But I believe if the battery is fully charged and you are going down a steep hill, the engine doesn't actually run but the motor generator that is connected to the engine will turn it over to bleed off the power from the driving motor to provide braking. Even though the engine is turning, it is using no gas.

Yes, that's what previous iterations of Honda's i-MMD 2-motor hybrid system have always done. However, if using the starter motor/generator to spin the unfueled engine works to bleed off the energy generated by the traction motor functioning as a generator, then why, oh why, does the engine ever need to start up shortly after setting out from the garage with a fully charged battery?

I need someone to do the Clarity-down-the-mountain test to see if the engine starts up and burns fuel all the way down. That would be a reproducible event that Honda could be tasked to explain. The Honda engineers' who wrote the paper describing the i-MMD system in the 2014 Accord Hybrid repeatedly emphasize how the system is designed to reduce fuel consumption.

Also, if the engine doesn't start up coming down the mountain, does spinning the unfueled engine light up the engine icon?

 

[bfd]

It's never really a fully charged battery if Honda did it right (just like the battery will never go to zero charge). So part of the bleed off may have to do with keeping the battery charge level within some preset parameter because there should be some capacity for a limited charge even if the gauge says full…

On the Tesla, we can set the range of "full charge". Typically we have it at 80%, but there are times when traveling that we'll set it at 100%.

 

[insightman]

Ok, I'll amend my test specification to "descending from the top of a mountain with the battery as fully charged as the onboard charger is designed to permit."

Does the engine start and use fuel all the way down or does the starter motor/generator spin the unfueled engine to burn off the energy that would otherwise exceed the state-of-charge Honda allows the battery to acquire? Does the engine icon illuminate if the starter motor/generator is spinning the unfueled engine? What do the moving electron bars on the animated diagram show? Do they show battery power going to the engine?

If only there was an EVSE-equipped mountain near Ann Arbor I could answer the questions on this ever-growing list for myself.