Toyota Unveils Fuel-saving Technologies for New Prius

I have changed below the values I have added in post #93 to the correct values per the source below (page 6).
My original numbers (73 and 115) were from memory as I couldn't find the source! Sorry for this.


The same source (reporting the press conference held in Japan) reports (page 3) engine compression ratio of 13.1 as compared to 13.0 in Gen 3. Not a big difference that may have resulted from changes in piston surface to enhance burning rate?

Source

 

Side note: The Prius Gen4 "Eco" weights less than 1310 kg (I think
ken1784 mentioned this in one of his postings).

Why is this important?

The Japanese JC08 fuel-economy cycle is performed on a stationary "small chassis dynamometer". You can find a nice schematic picture how the dyno designed for the JC08 cylce works at page page 15 of the regulatory document at
http://www.eccj.or.jp/top_runner/pdf/tr_passenger_vehicles_dec2011.pdf

In the JC08 cycle all cars are classified in IW categories (IW = Equivalent Inertia Weight) . On page 4 of the former mentioned document you can see that a vehicle like the Prius Gen4 "Eco" with a weight of exact 1,310kg has an "equivalend inertia weight" of 1,360kg. A car with a total weight of just 1kg more, like 1311kg, has an "equivalent inertia weight" of 1,470kg.

The fuel-economy test cylce JC08 is performed on a dyno where a flyweel simulates the car inertia weight (the force of accelerating or decelerating the car) on the "stationary dyno". The energy to accelerate a car is direct proportional to its weight. The dyno run with an "equivalent inertia weight" of 1,470kg uses roughly about 8% more energy during acceleration and deceleration compared to a dyno run with an "equivalent inertia weight" of 1,360kg (1470/1360 = 1,08 = 108% = 8% more).

So for a car with the weight of just 1,310kg there is a small advantage over a car with just a few kilos more. It uses less energy to "speed up" and "slow down" on the stationary dyno run, resulting in a slighty better fuel economy number when run on a dyno specified for the JC08 cycle.

This is just a tiny detail, but in my opinion worth mentioning. The goal of a fuel economy of 40km/l (equals to 94 mpg) messured using the JC08 cycle might only be met by the Prius Gen4 "Eco" model.

Best regards,
Pale Fox

 

This was already discussed briefly in another thread, thank you for the detailed explanation and link.
BTW Toyota did that in Gen 3 as well - the L model for Japan weigh also 1310 kg and achieves 23.6 km/l on JC08 while the other models weigh 1350 kg with 30.4 km/l on same cycle.

 

Or the ECO model's improved mpg rating is due in large part to it's lower weight, putting it in a more favourable test category. Seems pretty cynical.

 

it is combination of both, JC08 is stupidly unrealistic, nobody is going to get 95mpg nor they got 80 mpg before... we know its gonna be 10% improvement on more realistic epa cycle, so we already know those numbers.

 

We also know it is going to be ~18% improvement on (unrealistic) NEDC cycle...

 

Like every other car which weighs below the middle weight of its category...

 

This testing varying of testing regimen varying by weight category, it doesn't apply in North America?

 

I -think- when either the GII or GIII is above the "engine stop speed", but the HSD wants to turn the engine to limit MG1 RPMs, it does so with the throttle closed and no fuel injected. This minimizes pumping losses. Yup, some loss is still there, but it's minimized. BUT, in "B", the throttle is opened (with no fuel), to -maximize- pumping losses. At least, that's what I would do if I were the engineer(s).

This has implications for the EGR problems the GIII has. If the engine is running without fuel, any oil that finds its way into the combustion chamber (there is always some) will NOT be burned. Instead it goes out the exhaust port. Some will find its way into the EGR path, partially burning there when the engine gets hot enough, as well as combining with the crud already there. What a surprise the EGR tube gets plugged up! This also implies there is no "problem" to be fixed. It is expected. Some form of design change -might- be possible to reduce this issue. I wonder if the new engine EGR design was changed to reduce this as well as improve the EGR functioning.

 

The EGR issue is actually bugging the hell out of me; I kinda hate inevitable disasters. The latest victim posting, with a bit over 200,000 miles on odometer, finally extracted the component right at the exhaust manifold, draining the coolant in the process, and THEN he can't clean it. It's so fully clogged and baked in, he's electing to replace the component with a salvage part that's in better shape.

Not just another p0401.. PICS! | PriusChat

Cagey Toyota, from the Canadian warranty:


Emission components covered against defect for 36 months 60,000 km or
24 months 40,000 km for performance


EXHAUST GAS RECIRCULAT ION ( EGR ) SYSTEM

• EGR Valve
• EGR Gas Temperature Sensor
• Associated Parts

 

Well there is the '1,000 mile on one tank' club. <grins>

Bob Wilson

 

even better, from Autobild test drive together with Mirai, we know it is going to get 3.1l/100km on NEDC (vs 3.9l for regular model before), as well as be around €30k which is more than before in Europe, but with more equipment standard (again in Europe, for instance Safety Sense P).

 

Despite increased EGR percentage in Gen 4, I think it will be lesser issue than Gen 3(assuming all other things equal). Mainly the reason is, engine is shutting down completely during deceleration in Gen 4 even at higher speeds. So, unlike Gen 3, no exhaust gasses are recirculated back into cylinder when there is no fuel injected(when there is no ignition) because engine is not rotating when decelerating(Except in "B" mode). So lesser of chance of unburnt oil mixed air is sent to EGR valve. Of course usual soot will still be there, but less of this oil residue, reduces chances of choking early.

 

What about the minority of long distance drivers that are putting up to 100,000 miles/year on their Prius'. I've heard of some owners going 300,000 miles in 3 to 5 years without major maintenance issues. Does long distance highway driving not coke up the EGR the way more typical driving could?

 

How much does a new EGR cost? Are there any after market suppliers (China?) making this part?

 

Generally idle control valve is open even when decelerating. Not only that, there is always overlap in valve timing, esp Atkinson cycle. So it is going to suck decent amount of air, at least as much as idle speed, probably more if RPM is more. Only way to reduce pumping losses is to very minimal, completely close both intake and exhaust valves. This can be achieved by Valve control system like BMW Valvetronics (which does not need throttle plate all, only there as fail safe), or Honda cylinder deactivation mechanism, or possibly Toyota CVVLT(Corolla Eco uses this).

Honda Mechanism still needs throttle plate (as it is currently implemented in 2015 vehicles, not sure about 2016), as it is much simpler/cheaper deactivation mechanism(simple pin slide mechanism to lock rocker arm).

 

There's two components, each about $225~250. No's 5 and 6 down the list here:

2010 Toyota Prius Exhaust Gas Recirculation System

 

Well I for one would not be unhappy if the EGR took its feed AFTER the catalytic converter. The reduced 'load' would improve EGR valve life more than enough to pay for the extra pipe.

Bob Wilson

 

Thanks. So if I need to replace all these parts at the 200,000 mile mark, it works out to about 14 cents a gallon of fuel. I don't want to spend $600 and several hours replacing the EGR system, but now every time I fill up I will be thinking about that increased cost of ownership.

That 200,000 mile mark is a guess, it could be sooner.