Thanks. This is an area I have had questions about.

It is easy but pricey. IMHO, it is a good investment but my one Ebay CD for my wife's Echo turned out to be not worthy.

Bob Wilson

 

The HSH-II requires "The ATF Cooler", which means it produced a lot of heat and some energy is converted to the heat.
I believe Prius eCVT is more efficient because it does not require separate cooling.
http://techinfo.toyota.com/ site is only $10/day subscription fee.

Ken@Japan

 

Adding to Ken's note, there is a wealth of information about the Prius transaxle performance in this report:
http://www.ornl.gov/~webworks/cppr/y2001/rpt/121813.pdf

The mechanical energy loss as a function of ICE speed ranges from 150-1,100 watts. However, the vehicle typically holds speed on level ground at the low end of this scale, under 500W. The motor-generators are running ~95% efficiency.

I have the earlier model Prius and it takes almost 20 minutes to reach a stable transaxle oil temperature during the summer. Even then, it is only 50F warmer than ambient. One reason for lower cold weather performance is the difficulty of getting the transaxle oil to an optimum viscosity when it is cold.

Bob Wilson

 

Thanks for the info Ken & Bob.

I was a little concerned about getting it from a third party or just ordering it from my dealership. I may just give this site a try and see what type of literature I can get. As a brief side note: We got helpful cooperation from Honda and that netted us a very good library of materials ranging from paper & electronic documentation to videos.

On the matter of which is most efficient:
I usually avoid getting into discussions of which system is better because until we have lab performance/assessment metrics it is merely a matter of technical or brand zealotry.
I have to admit that I am fascinated by the techology in my new Prius but I have no less admiration for the endless enginuity in Honda's engineering. So forgive me for not tagging along on a direct comparision of the two hybrid offerings.

For the time being I am fortunate and grateful to ride on both crests of today's hybrid offerings. I am sure most would agree: Despite the challenges, it is a good time to live in.


Cheers;


MSantos

 

You are welcome!
This is one of the reasons I've been a long time advocate of MPG vs MPH graphs. It was my first and longest running Prius performance effort and critical to evaluate the effectiveness of vehicle and driving changes:

http://hiwaay.net/~bzwilson/prius/

Good luck!
Bob Wilson

 

Hahaha very nice Ken - I don't pretend to know more, I'm just exploring this idea - so far it's been quite the discussion. The lossiness of the belt-CVT is the #1 killer for the idea so far, and not something I'd previously considered.

I'd like to do a theoretical calculation on what adding that belt-CVT would do to energy recapture as well. Elsewhere on this forum the best energy recapture you can get out of the Prius is about 70%, so:
Prius: 70% * 95% * 97% = 64%
That being, max regen * electric motor efficiency * PSD efficiency. The PSD technically is involved twice here, once on the way in and once on the way out, but the 70% data takes the way in into account already, so 64% is roughly what's delivered back to the wheels.

Prius + belt CVT: 70% * 90% * 95% * 97% * 90% = 52%
The 2 additional 90%'s are the belt efficiency getting calculated in - 52% isn't bad but it's still a hit that reduces the use of energy recapture/electric accel. A relatively big reduction in usefulness, I'd say.

Towing I'm saying that theoretically you could have the mechanical CVT continue to engage even when the car is off (the same way many other parts of the Prius engage when off to protect it) so that towing with front wheels down was safe.

Gliding at high speeds The use of a high-speed Glide may be dubious on level ground (though I'd still prefer to have it), but I frequently drive down the 405 into the LA valley where 85mph is the norm and the downhill is consistently somewhat steep. Gliding here would be perfect - there is air resistance, but it's just enough to maintain my speed at no fuel cost. Currently I have to burn fuel during this time instead, enough to idle the engine, or perhaps a little more.

"The Winner" I didn't want to turn this into a discussion of which is better, the Civic or the Prius, I just wanted to explore what would happen if you put one of Honda's best ideas into the Prius. So far I've found the discussion really interesting - maybe other readers have too. I think so far "religious posts" have been avoided, which is great to see.

This is indeed a discussion with more academic than real benefit, but I enjoy the learning.

 

The Hybrid Synergy Drive / Toyota Synergy Drive is radically different from ordinary vehicles so it takes a while to understand how it really works. Even with a mini-scanner, I'm learning new things all the time. You might consider joining some of the more technical Prius groups that have archived SAE and other papers. But let me share some 'new ways of thinking:'

1. MG1 balances ICE torque - in an ordinary mechanical transmission, the ICE asserts a counter torque via the housing to the gears. In the Toyota system, the counter torque is against MG1. Lugging the engine is all but impossible because MG1 responds instantly to the ICE. Think 'electric spring' and this also helps dealing with the ICE power pulses. Best of all, the eCVT allows significant amounts of power to be drawn at low rpm without stressing the engine.
2. Auto-shutdown - at speeds below 42 mph, the ICE periodically shuts down and the battery and MG2 maintain speed. At slower speeds, the ratio of ICE on-time decreases relative to MG2 maintained EV speed. When the ICE runs, it is not only powering the wheels but also charging the battery to sustain the next EV mode. The average between the ICE on-time and EV-time is the effective MPG.
3. Atkinson Cycle - the compression stroke is 8:1 and the expansion stroke 13:1. This results in a very efficient engine over a broad power range. I don't see a significant fall-off in engine efficiency until 3,500 rpm. Other engines typically are turning 1,500-2,000 rpm faster to generate more power.

The IMA has looks like an engine torque range extender. A traditional Otto cycle has, even with variable valve timing, a somewhat narrow, optimum power range and in small displacement engines, problems generating low-speed torque. But adding a motor significantly improves the low-end torque. Unfortunately, it burdens EV mode with ICE mechanical drag even with the valves held open.

The mechanical CVT has a power-pulse challenge. On one side is about 20 lbs of pistons, rods and crankshaft trying to generate power pulses and on the other, 2,000+ lbs of inertial mass. This puts a heck of a stress on the mechanical parts.

Bob Wilson

 

Sorry Bob, but if I may say: amist the VERY good points there are some inaccuracies.

For instance:

- First, it is not a traditional Otto cycle engine. There are too many design features that will rather qualify it as a very unsual (hence not traditional) ICE. According to many Honda engineers it represents the most efficient design they've ever produced. Coming from Honda that is that is something I take seriously because they are not only the largest ICE producers in the world but they also produce some of the best ICE powerplants. (of course some folks will disagree on the last one)
- During EV, the valves are held "closed" to minimize pumping losses. Yes, it is true that the crankshaft turns and still offers significant mechanical resistance on the already small motor. However, Honda's engineers did attempt to mitigate those losses and ended up producing a very low friction powerplant. I am still amazed at how easy it is to turn that crankshaft when the cam lobes are in the disconnected state (VCM on).

Now, can EV-mode on the HCH-2 ever amount to much more than a coast extender at any speed above 7 mph? Definitely not! Strictly from a superficial perspective this system can easily be dismissed as a waste, but I think we can do better than that.

Perhaps the following link will help just a little.

Cheers;

MSantos

 

Is it possible that Honda's design, while somewhat inefficient in turning the gas motor during EV operation, may allow EV to run longer for other reasons? For example that the gas motor can still move oil through and heat it due to the friction of still turning over. Just an interesting observation - the Prius hits a wall with these issues at times, while its electric-only efficiency is obviously very good.

 

Actually the reference you provided had the engine characteristic curves I was interested in seeing.

I've turned other engines by hand by removing the spark plugs. In contrast, the Prius stops the engine at speeds below 42 mph, no ICE drag at all.

EV mode is pretty much the key to Prius efficiency below 42 mph. Above 42 mph, the motor assists as needed for peak power demands. However, there are two modes of high-speed 'coasting' that are under investigation.

It was helpful when I found this chart at the end:


As Honda points out, the low-end torque is enhanced by the motor. Otherwise, the redish colored engine curves look like a traditional Otto cycle performance curves. The only chart missing is specific hp, the rate of fuel burn per hp.

This is what I'm seeing for my Prius where "fuel ms_sec" is proportional to fuel burned:

Do we have similar specific fuel consumption data for the Honda ICE?

Bob Wilson