At highway speeds the CVT seems to rev the engine much higher to maintain speed on cruise control than when driving up the same hill manually. EG some hills I can drive up at 70mph at 3k RPM with, say, X bars of assist; letting the CC do it will see the engine turning 3800-4000 RPM with maybe X-2 bars. Why not keep the engine turning slower with greater throttle openings and / or more electric assist? Thought that was generally more efficient.

Thanks for your insight. oops, no pun...

 

Hi,

That is the biggest "issue" I have with my HCH! Drives me up the wall. I suspect that what the cruise control is trying to do is maintain the SOC of the batteries. That is - it doesn't want to use all the batteries because it doesn't know when the hill will be over and it will have a chance to regen. them again.

Not sure if that is the real reason - but I think it makes sense. I would be glad to hear any other opinions too...

Eric

 

I am also trying to understand the control strategy for the HCH. To me it seems that it has a few, contrary goals:

a) want to keep revs as low as possible, to be able to keep full throttle and get highest efficency
b) wants to avoid changing gear ratio too often or too quickly
c) wants to assist ICE using the IMA, when high power is needed
d) wants to keep charge level between 4 and 8 bars
e) ...and many more, just listed the most important ones

So what happens when you go uphill using the cruise, is that often the hill is not a perfect linear grade, but has areas which are steeper, or less step. When in a steep part, revs and assist will go up, but then in a less steep part, the revs will be kept high and only IMA will be reduced. If the hill gets steeper again, IMA will go on full again. (This is to avoid changing gear ratios.) When you reach the top, revs will slowly reduce, sometimes even so slow so you get into regen.

When you don't use cruise, especially on a hill you know well, you will keep the pedal steady, and avoid the high revs. I think if you would control the pedal in the same way as the cruise does (well, the pedal is not moving, but you get the picture), you would get about the same behavior?

Why would the HCH want to avoid changing gear ratio? I can think of three reasons, one is to save the actuators and mechanics, the second that ignition/fuel parameters are tuned better in steady state, so efficience improves, the third is purely cosmetical, that a steady, high rev is less annoying than revs going up and down. (There's a fourth also, that it shifts cam lobs somewhere in the rev range, and it doesn't want to do that too often either, for efficency and wear reasons.)

I also suspect that it tries to avoid a rev range around 3000-3800 rpm, for some reason. I get a feeling that it goes to full IMA up to 3000, then gives up and switches to 3800 with no IMA.

Comments?