If you want a hybrid car with power look at the Accord or perhaps the Camry.

 

Then again if the hill is fairly short the Prius may be just fine. A test drive would tell you what you need to know...

 

Thanks for the quick reply...It's what I figured..but, and excuse my possibly dumb question ..so the prius would run exclusively on battery driving up this hill??? i thought the car was smart enough to switch power sources when it needed to.

 

Hi Brad,

The Prius' computer decides the best combination of power (from battery and from the internal combustion engine (ICE)) to be delivered to optimize the fuel efficiency. So, in the case of driving up the hill, there is a high power demand. In such a case, the power would probably be supplied by BOTH the ICE and the batteries.

So, in simple terms .. if the ICE can deliver about 74 HP, and the batteries provide 30 HP, your car drives like a 104 HP car .. (I know, I should be talking in terms of torque rather than in HP, for the technically inclined .. but I am simplifying this concept so as to make it easier to understand..)

Regards,

 

Exactly, so the car may climb the hill just fine on 104 HP but if the hill is long enough to drain the battery you will be climbing on the engine alone and stuck with only 74 HP (which is not a lot). My Civic is similar. It does fine at medium speeds (40-60) on all most hills but at higher speeds like 70mph it has trouble keeping speed with some of the longer uphills.

One time I let the pack drain too far before downshifting and ended up crawling up a hill at 40 mph the the gas pedal floored. Note that this only happened once, I plan ahead for that hill now and make sure that the battery has a good charge before attempting the hill.

Once again, a test drive will tell you one way or another...

 

Hi,

What is really smart is something that was pointed out to me over in PriusChat. It seems "heretical" mode is the key that allows a Prius to drive around with the throttle plate open 99% of the time.

What happens is MG1 uses some power from MG2 to 'lug' the Prius engine down. The engine opens the throttle plate larger and larger to meet the energy load but MG1 forces the ICE to run slower and slower BUT not so slow as to stall it out. It is a type of 'load managed engine power control.' The effect is to eliminate normal pumping losses caused by a partially closed throttle plate.

This goes a long way to explaining the unusually high specific fuel consumption at low power demands.

Bob Wilson

 

That would have to be a MONSTER hill! When I started driving the Prius I kept tabs on the energy monitor to see what the power flow was like while hill climbing. I've since added a tachometer to get a rough idea of how much of the engine's power it is producing at any given time. So far I have not encountered a hill that required battery power to maintain 60-65mph. Instead the engine winds out past 3,000RPM and keeps battery power in reserve to absorb quick changes in load. The one exception is the case where prior use of regenerative braking has brought the battery above the nominal 60%, in which case it does send power to the wheels until that "extra" charge is dissipated.

 

Hi Bob,
Thank you for your great explanation!

One question...
How much percent have you seen about the heretical mode comparing the normal mode on a flat highway, say 60 mph?
Was it 100% heretical mode? Or, a few % and mostly on normal mode?

Ken@Japan

 

Hi Ken,
You are very welcome. Your earlier comment about my power sketch woke me up to the possibilities and I began to understand what the Graham scanner was telling me. The Toyota SAE paper brought everything together.

This is an area that begs investigation, especially in urban driving. Right now, my best indicator is MG2_Nm and I only recently began recording it. I'll see if I can post copies of the data in Prius_Technical_Stuff files area.

BTW, the Toyota paper reported changes in the ICE performance curves from "energy re-circulation" that showed a modification from the normal ICE curve downward and to the right. Their cumulative graph and my specific fuel consumption graph share similar shapes. The only difference is their specific fuel consumption areas don't extend as far into the low-rpm region as some of the high-efficiency data points. It remains a puzzle.

It looks like an optimum strategy should maximize ICE operation in open throttle plate mode. One area I'm wondering about is the throttle plate position versus degree of 'heretical' mode. Hobbit has a vacuum gauge, another throttle plate position indicator. However, it may be possible to use either the mass-flow versus ICE rpm or injector MS versus ICE rpm to detect partial and open throttle plate operation.

Bob Wilson

 

Perhaps I should not have spoke for the Prius, although I'm nearly sure I've read about folks in hilly/mountainous running their Prius packs dry.

Help other Prius owners! Ever run your pack dry?