Why does the ICE rev up for no reason?

[insightman]

My head is swimming from taking in all this engineering, but I have seen all the power flows with the gear icon illuminated. I’ve seen power go to and from the battery with a slight pause between. And any downhill that triggers regen seems to turn off Engine Drive Mode and then it comes back on after a longer pause.

Engine Drive mode is so tenuous! It doesn't take much of an uphill or downhill to blip out of that mode. However, when you ease off the accelerator in Engine Drive mode, don't you see regen occurring? I'll have to force myself to press the HV button next time I'm on the expressway to confirm it for myself.

 

[ClarityBill]

Engine Drive mode is so tenuous! It doesn't take much of an uphill or downhill to blip out of that mode. However, when you ease off the accelerator in Engine Drive mode, don't you see regen occurring? I'll have to force myself to press the HV button next time I'm on the expressway to confirm it for myself.

I think Engine Drive mode has a ~2 mile EV band width. If you can get in the middle of the band, Engine Drive mode will stay on.

'Band width' means the engine will shut off if the EV Range gets 1 mile above the set point, and the engine will rev up if the EV range gets 1 mile below the set point.

The ICE in engine Drive mode provides about 3/16 of the power gauge, and the battery has to regen or discharge to make up the difference on the driving power requirements. When the regen or discharge takes the battery out of the target range, the gear disappears.

The battery cannot accept any power from the ICE when the driving power gauge goes into regen range.

 

[MNSteve]

I think Engine Drive mode has a ~2 mile EV band width. If you can get in the middle of the band, Engine Drive mode will stay on.

'Band width' means the engine will shut off if the EV Range gets 1 mile above the set point, and the engine will rev up if the EV range gets 1 mile below the set point.

Interesting theory, and would explain why engine drive mode is so elusive for me. Do you think that this "set point" is based on what the EV range was when you went into HV?

 

[JCA]

I was under the impression that Engine Drive mode was taking ICE and sending directly to the wheels (through the various clutches, eCVT tranny, etc.,) and therefore not charging or discharging the battery as @ken_wells had asked. If this in incorrect, then I stand corrected.

There really isn't a mechanical "CVT" or any sort of physically variable transmission in the Clarity -- what Honda refers to as "e-CVT" for marketing purposes is just the fact that the engine generates electricity through the generator/starter motor, and that as much electricity as needed is sent to the traction motor or to the battery.

There's a single fixed-ratio clutch that directly connects the engine to the wheels additionally -- this is really more for opportunistic efficiency at a specific range of speed and load (kind of like "overdrive" in older automatic transmission cars was a specific mechanical linkup used in cruising scenarios). Even when that clutch is engaged, the engine is still also driving the generator/starter motor (there's no way to disconnect that), which can be feeding electricity to the battery or indirectly to the traction motor, which is why you can see all of the power flows at the same time on the energy display.

 

[RickSE]

I was under the impression that Engine Drive mode was taking ICE and sending directly to the wheels (through the various clutches, eCVT tranny, etc.,) and therefore not charging or discharging the battery as @ken_wells had asked. If this in incorrect, then I stand corrected.

I have seen engine drive mode with my battery being charged at the same time. It tends to happen on a flat or slightly downward stretch of highway when I’m going between 50 and 65 mph.

 

[ClarityBill]

Interesting theory, and would explain why engine drive mode is so elusive for me. Do you think that this "set point" is based on what the EV range was when you went into HV?

Yes, I think the "set point' is based on the EV range when you went into HV.

If I get out of the 'band width' I switch out of HV, and back in. This gives a new 'set point', and the gear will come back.