Indeed, some of us have turned many engines by hand, but doing it to this one is almost eerily easy. No joke.

That continues to be very true. As an informal confirmation of that: with the cold weather we're having ,the gas engine on our Prius starts right away and runs most of the time producing very low FE. From the rather premature results I am seeing, I am beginning to suspect that the HCH-2 may end-up with a slight edge in FE primarily in city driving. Both cars are plugged in the same garage. But under more normal scenarios, the Prius can tap into its efficiency right from the start by keeping the gas engine out of the picture (except when we consider the engine's own weight, of course).

While the optimizations in its design and operation do not alter the basic Otto cycle characteristics they do try to set it appart from the typical Otto crowd. As they claim in the link, Honda views the enhancements to its gas powerplant as important as the enhacements on the electric side of the equation.
In the end, I suspect that the IMA system was never supposed to be any more than what "IMA" stands for. And true to that is that the HCH-2 without the electric motor is almost useless and even frustrating for any normal human being to deal with. We are not just talking about lacking low end torque. We're talking about insufficient (even mediocre) performance at almost any RPM without that electric motor - expecially when factoring in the car's own curb weight.

In all fairness to the HCH-2, only after driving the vehicle for a good while did I realize that the IMA system claims its FE advantage under very different operating circumstances than that of a Prius.

That is why I avoid getting into the "One is better than the other" exchange because in the end they are still too close to call - all despite the HSD being a design with greater current and future potential.

I definitely agree, that is a very important missing chart. I'm going to see if I can find one: it is easier and faster than having to create it. If I can't find a good one I might as well start logging the OBD data on the HCH-II.


Cheers;

MSantos

 

Hummm. Good point. However, depending on the state of charge , the EV-only operation on the HCH-II is much shorter in duration that what we can get out of the Prius. However short it may be, it is also more critical in its role of maximize FE. Managing the SoC on either car continues to be the perenial requirement for attaining maximum FE.

On the HCH-2, the heat due to friction alone is very low. So low in fact that extremely long glides in cold weather may cause the idle stop to be missed when arriving to a red light. Besides, all HCH-2 have 0W20 oil in addition to all the friction reducing features built into its design (as shown in the video link). Other fluids, including the CVT's ATF fluid are also specially blended by Honda for this reason too.
Heck, even the CVT belt (and many other "friction" parts) were designed and manufactured by Honda "inhouse" in a maddening attempt to reduce unnecessary friction. Many folks have stated, and I will agree, the darn powertrain is an endless showcase of "low friction engineering".

Cheers;

MSantos

 

Hi,

I do enjoy chatting with you about this. Just a couple of comments to share.

It looks like roller cam followers instead of the traditional sliding followers. This would reduce valve friction.



Some of us in Prius_Technical_Stuff are looking at an ICE thermostat hack. But you have block heaters in both?

This is one common characteristic of both architectures, providing peak power from the motor-battery.

Do you have an ICE torque or HP value? This would be great.

Bob Wilson

 

Yes, I do have block heaters on both. I always get them installed at the time of purchase.

One thing I've noticed (again, informally): The HCH2 gas engine is faster to get up to the ideal temperature but it also cools down alot quicker. The Prius's gas engine takes a little longer to arrive to the ideal temps but once it gets there it seems to sustain it longer. This leads me to believe that in cold weather and shorter urban driving distances the HCH-2 may have a tiny FE edge. I guess, I'll know for sure at the end of the winter season.

At the moment I use my PDA to observe and log the OBD stream. The software however only has an "Accelleration timer" feature and a "Calculated load value %" among the other regular sensor readings. I was looking into different software (like Auterra's) that actually calculates and plots a power/torque curve in addition to other very useful features.

Cheers;

MSantos

 

In response to the PDF about varying Hybrid systems (including GM's), the most interesting part of those slides was the other hybrid systems - all dual-planetary gear systems, which are certainly more lossy than the HSD, yet do gain one clear advantage: high-speed Glide. GM's model needlessly involves a clutch and shifter which helps explain why their solution is ineffective and late. However, it would let you Glide freely with both the electric and gas motor at 0rpm, which would be a nice feature while avoiding the losses of a CVT belt. Interesting design if you remove the clutch and shifter.

The Honda approach, not shown in the slides, is arguably simpler by not involving a planetary gear, and I wonder what MPG would be available if their belt CVT were replaced with a less lossy (even simpler?) mechanical CVT.

Specific to the Prius, there's a lot of good data about THS-I, which I can only infer to THS-II. In particular I appreciated the real efficiency curve of the Prius gas engine. It was also interesting to see the "SoC strategy" discussion where Toyota considered several operational modes and how to keep SoC stable for each; it explains why sometimes the SoC seems brilliantly stable and sometimes it veers off considerably - in the latter my driving fell outside expected driving patterns.

 

The Honda CVT solution does involve a planetary gear with carrier (as well as a sun gear) which is located on the input shaft of the CVT. The planetary gear set accommodates the reverse brake and forward clutch.

Cheers;

MSantos