I've ridden in a Prius before; although it does have a very smooth transfer from electric to gas, and when "adding" electric power to gas, it still has a slight shudder sometimes.

I've never ridden in in any vehicle equiped with an IMA system, but I do know that it is a very simple, elegant system compared to HSD. Honda rules.

But does Honda, renowned for highly refined engines, have a highly refined IMA system in the HCH II ? Does it shudder comming out of auto-stop, and can you detect when the electric motor is assisting? Is IMA more refined, and less noticable, than the current HSD?

The "shutter" in the Prius is when the ICE turns off. The other transitions are all seamless. The momentary running of the Prius ICE on shut down is due to the use of the "Atkinson cycle" (versus the Otto Cycle) where the intake valves remain open for the first portion of the compression stroke. This pushes some unburnt air/fuel mixture into the intake manifold which keeps the engine running for a moment after the fuel supply is shut off.

Since the "shutter" is not harsh and only occurs once in a while, I wouldn't use it as a reason to choose between a Prius and a Civic. There are other differences you should use in making a decision.

JeffD

Indeed, there are MANY other reasons you should be looking for when deciding between the two cars.

On a side note:
-The Prius engine follows the "Atkinson cycle" which is an outstanding choice for fuel economy and lower rpms.
-The HCH-II is a three mode engine which enables it operate mostly as a Otto cycle engine. So far so good. However, the first mode provides an "Atkinsonised" variation that delivers optimum FE at low rpms. This is often missed by many HCH-II folks including those who often espouse the virtues of the Prius ICE.

All current hybrids provide ever improving transition between power sources but under some circumstances these can remain very noticeable. Look at it as a generational attribute (like a beauty mark) instead of a negative.

Cheers;

MSantos

[qoute]Does it shudder comming out of auto-stop,[/quote]
Yes it does shudder, but my passengers never notice unless I point it out to them. It does not shudder as much as a non-hybrid would as you turn it on.

I have noticed a very low, deep noise when IMA is assisting. As far as detecting it by feeling vibrations, you can't notice at all.
Unlike the Prius, the HCH does not shut off it engine to go into electric-only mode. Instead, it just closes the valves, but keeps the engine rotating. This way, it is not consuming gas, but there is no shudder when going into electric mode.

The only time that I have noticed any choppy driving is at very low speeds (8-12 miles per hour), when the transmission is trying to figure out which gear to shift into.

I couldn't tell you the answer to this. I think it's more of an opinion anyways.

I really think you should test drive a HCH to see what its like and choose which you like better.

msantos said,

"-The Prius engine follows the "Atkinson cycle" which is an outstanding choice for fuel economy and lower rpms.
-The HCH-II is a three mode engine which enables it operate mostly as a Otto cycle engine. So far so good. However, the first mode provides an "Atkinsonised" variation that delivers optimum FE at low rpms. This is often missed by many HCH-II folks including those who often espouse the virtues of the Prius ICE."

The Prius has variable valve timing actually. So I think the Prius engine might be simular to the HCH in that it has "an "Atkinsonised" variation" (I like the way that sounds msanto!) and then other valves for other variations.

Another question...I remember that in the Prius, while it was regenrating/braking, it made a rather loud, very UN-seamless noise. I know that is the noise an electric motor makes while regenerating, but it wasn't a pleasent sound.

Does the HCH II have a much more seamless, less loud (because of the smaller motor?) noise when regenerating?

At first I thought it was pretty smooth, but I must be getting more and more aware of what the car is doing, because I find it rather annoying now (both the shutoff and the restart). It's certainly not as bad as starting a conventional engine (since the electric motor starts it so quickly), but it still shudders the car.

But I still love that it happens. When in a conventional (i.e., non-hybrid) car, it upsets me that the car's just idling away at red lights, wasting gas.

As far as regen, there is a detectable high-pitched whine when you apply the brakes, but if you're like me, you'll rarely be driving in total silence anyway. With the radio on, it's usually not perceptible.

My Prius only makes a low level, high pitched sound when the inverter (not the motor) is handling high current. This is either when it is regenerating or giving the ICE a power boost. The sound is just barely perceptible as has been reported in other hybrids and EVs. If you are hearing an unpleasantly high level sound, something is wrong.

JeffD

I haven't driven or ridden in and HCH2, but I have an HCH1 and have driven a Prius. I would say that the Prius does a bit of a shudder, maybe more of a bump, when the ICE restarts when you get above EV speed. I never noticed it shutting down. Because the ICE restarts on the Prius while you're in motion I think it is a bit more awkward feeling than the IMA system which stops and restarts the ICE just as you're stopping and starting when the car would rock a bit anyway. When the IMA assists it just feels like a boost of power to me.

Seamless IMA? hmm not sure but I'd say comparing the noise to other cars you can hear the change of gears in a automatic transmission more loudly than the switch from electric to gas in the HCH.

Only thing I notice feeling wise is coming to a stop where the AutoStop engages, Car comes to a faily abrupt halt.

If I slow down for a light etc. and it kicks into autostop but the car hasn't quite stopped, then I give it gas again, it will give a bit of a thump when it goes.