How much does Hybrid really contribute to mileage?

Yup, it's really hard to separate the "hybrid" benefits from a "normal" car because it's a complete system, not an add-on.

According to Toyota improvements in fuel economy were from:
1. Aerodynamics.
2. Engine shut-off when not needed.
3. Energy recovery from regeneration.
4. Efficiency gain from the "Atkinson cycle" (it's not really a -true- Atkinson engine).
5. Efficiency gain in the HSD vs a "more normal" transmission.
6. Weight trimming on whole car (al. hood etc).
7. Efficiency gain in the engine, from matching it to the requirements of the HSD.

Not in order of importance. I've got a pie chart for the GII but haven't seen one yet for the GIII.

 

Would you please post it for the rest of us to see ? Or alternatively post a link where it might be found? Thanks!

 

An excellent list, I would add:

• low rolling resistance tires (all Prius)
• electric powered, steering, brakes and A/C instead of vampire on the engine

Added with the ZVW30 (2010) Prius:

• 1.8L engine turns slower than 1.5L at high power
• cooled exhaust at high power to avoid fuel enrichment
• exhaust heat recovery for faster warm-up
• dry-sump transaxle for lower rolling resistance
• lower drag, valve train
• higher voltage MG1/MG2 reduce (I**2)*R losses
• muffler valve opens at high power for reduced back pressure
• electric water pump to reduce pumping losses

The following SAE papers cover a lot of the Prius features:

• "Development of Electric Motors for the TOYOTA Hybrid Vehicle "PRIUS" - describes the NHW10, the first Prius
• SAE 2000-01-C042 - "Development of the Hybrid Vehicle and its Future Expectation" - describes the NHW11
• SAE 2004-01-0064 - "Development of New-Generation Hybrid System THS II - "Drastic Improvement of Power Performance and Fuel Economy" describes the NHW20
• SAE 2009-01-1061 - "Development of New 1.8-Liter Engine for Hybrid Vehicles" - describes ZVW30 engine
• SAE 2009-01-0726 - "Development of New Hybrid Transmission for Compact-Class Vehicles" - describes ZVW30 transaxle
• "New car features" - part of the Toyota technical documentation series

Bob Wilson

 

Here's the pie chart from Toyota for the GII.

 

Hi kgali,

They call it Hybrid Synergy Drive, because it really is a synergy between the high efficiency engine (with poor low end torque) and the electric drive system. Take one out of the equation, and the car just cannot work as a modern vehicle on the whole.

 

In the city, I think quite a bit

The HSD allows the ICE to shut off. There is always overhead when the ICE runs. On my commute (70% of my driving), the engine is off over half the time. The batteries (and HSD) allow that to happen: I can be comfortable (AC on in DC in the summer), I can control the car PS/PB. On a conventional car, those items run off the ICE. The A/C in particular is a significant current drain, and could not be powered by a conventional battery.

The net effect for me is probably 40 - 50% increase in efficiency on my commute.

 

In the city, I think quite a bit

The HSD allows the ICE to shut off. There is always overhead when the ICE runs. On my commute (70% of my driving), the engine is off over half the time. The batteries (and HSD) allow that to happen: I can be comfortable (AC on in DC in the summer), I can control the car PS/PB. On a conventional car, those items run off the ICE. The A/C in particular is a significant current drain, and could not be powered by a conventional battery.

The net effect for me is probably 40 - 50% increase in efficiency on my commute.

My previous ride, a Subaru Forester, which was about the same size (but adds AWD), got 18 MPG on my commute. The Prius: 50+ (60 MPG to work, 50 home according to the trip computer).

 

Divide by 2, give or take 10%. It's roughly 50/50 for normal driving--not the pulse-glide stuff.

That means the ICE component is getting about 25mpg.

 

Sorry, but it's more complex than that. Your statement would be true if you got the battery charge either from all regeneration or by charging it at home, but you didn't. Quite a bit came from the ICE, How much? I don't know.

 

On the highway, the hybrid part of the prius really don't contribute much at all. It is the efficient engine, aerodynamic shape, cvt to keep the engine efficient, low rolling resistance tires, efficient electrically driven accessories that do the bulk of the work.

In the city the hybrid contributes a great deal. The big savings come in regenerative braking, engine off at stops and in slow moving traffic. The hsd also keeps the engine in a more efficient power band. I would guess it would be in the low 30s without the hybrid portions. The camry hybrid goes has 33mpg city versus 21mpg city for the non-hybrid model.

 

You do realize, of course, that with a Prius the CVT *is* the hybrid system. I understand the point you are trying to make, but it doesn't directly apply to HSD.

At any steady speed a non-hybrid car could be built that would easily beat the Prius mileage. The key would be using the smallest possible efficient engine directly coupled to the drive wheels. The down side, of course, is that it would be undrivable in real world conditions.

Tom

 

You're making a comparison between a subcompact and a midsize car. I assume you are comparing the Prius EPA rating (50MPG) with a very conservative and gentle Civic driving (EPA rating is at 29MPG...). Some are reporting 55-60MPG with their Prius. According to the EPA individual estimates, the 2007 Civic gets 35-40MPG at best.

You need to chose what to compare: 29 to 50, or 35/40/40-47 to 55-60 MPG...

I've just made a search on fueleconomy.gov. No car sold in the US achieves 50MPG exception made of the Prius. The nexts to best are the Civic Hybrid, at only 42MPG and the Insight at 41MPG. No other car gets more than 40MPG combined. At higher than 35MPG, you only add a Smart ForTwo.

 

Correct, the excellent FE at highway speed is due to the Atkinson engine run at its most efficient speed (made possible by the virtual "CVT"). But this would not be possible without being part of the Synergy Drive.



i.e. the poor power of the Atkinson engine would give intolerable accelerations without the motor help (in fact it would accelerate at all as the engine would stall without a torque converter) and a real CVT would be less efficient than the Prius Power Split Device.

 

This question is very interesting and with out any actual scientific or even reasonable study I would guess the original comparison to a 1.8 liter small car is about as good as it gets.

 

If you consider that the 1.8L of the Prius is an Atkinson-cycle engine (not Otto-cycle like almost everything else on the road), you should rather consider it to be something like a 1.4-1.5L. Atkinson-cycle engines have a better efficiency, while giving up power in exchange.

See : Atkinson Meets Otto: Why the Prius is So Efficient - Newsroom : Our Point of View Post / Toyota

 

I would guess that the regenerative braking effect is significant but not huge. My friend just got a Ford Focus and gets close to 40 mpg on the highway. I get about 42 mpg with my 2001 Prius (if I check my mpg the old fashioned way I find the Prius computer is about 5% too optimistic). It doesn't seem like the mpg advantage is that big a deal anymore.

 

I wonder why the other companies don't have a large difference between hybrid and non hybrid models. The Malibu Hybrid, the Vue Hybrid, Saturn's car, um... the tahoe.. They all have such a tiny little amount of difference. I'm not even all that satisfied with the camry hybrid. Is it just due to them keeping the larger engine size, AND adding the electric?

The only slightly larger vehicle I'm impressed with hybrid-wise is the escape. It's not bad.

 

Mazda will be shipping a miller cycle (similar to toyota's atkinson) 1.3L engine with cvt on the 2011 mazda 2 in japan. They claim its 20% more efficient than an otto engine hooked to an automatic transmission.

I'm sure toyota could produce a similar power train scaled up for the prius. The engine and cvt would need to be redesigned, but toyota definitely has the engineering to do this. The prius would drop a great deal of weight and production cost. You could get slightly slower acceleration and similar highway milage. Note the camry hybrid only gets 10% better mpg on the highway than the regular Camry. To scale the 74hp mazda engine to 110hp for the prius would make it 1.9Liters.

 

The GM hybrids all serve to discredit the idea that hybrids work, they simplely stop when idling, no real regen, no real assist of the engine HP, no electric only mode, no real effect on gas mileage. GM Hybrids are to hybrids what GM diesels were to Diesels, an attempt to set the idea back 20 years.
[ame=http://en.wikipedia.org/wiki/Oldsmobile_Diesel_V6_engine]Oldsmobile Diesel V6 engine - Wikipedia, the free encyclopedia[/ame]
[ame=http://en.wikipedia.org/wiki/Mild_hybrid]Mild hybrid - Wikipedia, the free encyclopedia[/ame]

Hybrids from other vendors that are shoehorned into existing cars (Escape, Fusion, Camry, Highlander, Civic, etc.) do very well compared to GM hybrids, but not as well as scratch built designs. (Insight, Prius)

 

I'm guessing that since you've had your Prius only 5 weeks, you aren't really comparing apples to apples yet.

Instead, you are likely comparing the Civic in good weather to a Prius in winter weather. And you are comparing a well broken-in Civic with a mature driving style to an un-broken-in Prius for which you are still early on the learning curve. I don't think the same driving style can bring out the best of both models.

For evidence to back up my supposition, look at the EPA Fuel Economy Side-by-Side Comparison. Your Civic often far exceeds the best user estimate posted there, but your Prius is far short of the best, much closer to average.

I'd like to see what you are achieving on the Prius in late spring, and again at the end of next summer. I doubt that it will be a mere 54.