Regeneration in EV mode? Fuel economy in HV mode?

Regenerative braking is a benefit of having a battery and electric motors.

 

A smaller, more efficient engine would do better than the 1.8 liter used in the new Gen III as far as mileage is concerned, but mileage isn't the only consideration. The 1.8 was selected because it is a new design used in several other Toyota cars, not because 1.8 liter engines get better mileage than 1.5 liter ones. A very large number of tweaks contribute to the overall improved mileage of the Gen III.

You are absolutely correct that all cars get better mileage when driven at ideal constant speeds. The ideal speed for any given design will vary by engine, transmission, ambient conditions, and aerodynamics. Regardless of the details, the important point is that it is relatively easy to keep a car moving on the flat at a moderate speed.

Everything deviating from this ideal will hurt mileage. Braking, accelerating, and hill climbing are all evil from the standpoint of mileage. They are necessary evils in the real world, since all real driving requires them to some degree. Likewise acceleration and hill climbing hurt mileage by requiring automotive designers to include larger engines. Even when driving at the ideal speed we are paying for the potential need to accelerate or hill climb. This too is a necessary evil, although many cars contain engines that can only be called excessive for real world driving.

The hybrid design of the Prius allows us to minimize the effect of these mileage killing necessary evils. We get to use a smaller, more efficient engine than that used in comparable cars. We also get to use regenerative braking to help recapture otherwise wasted energy.

Minimizing mileage killing evils is a good thing. It's an even better thing if they can be avoided entirely. That's the entire point about it being better to avoid braking if you can. Regenerative braking is better than friction braking. No braking is better than regenerative braking. It's a very simple point.

No one is suggesting that you drive without braking. That's impossible. No one is suggesting that you always drive your car at the ideal speed. That's not possible either. Both provide the theoretical maximum mileage under ideal conditions. As we move further away from these ideals, we also move further away from the best possible mileage. It's not a condemnation of anyones driving, it's simply a physical fact.

Tom

 

Part of my post was teasing in your POV. I should have added smileys. This interweb stuff is so confusing.

I'm not sure where this idea of a smaller engine is necessarily more efficient comes from. There are three things that makes the 1.8L Gen III engine more efficient than the 1.5L Gen II. One is that it is more powerful per revolution, so that it can spin slower and reduce friction losses. Anouther is it keeps its efficiency thorough a larger power range, which is partially that it is more powerful. Given the architecture of the engine increased volume was the path Toyota chose. The additonal power allowed toyota to use anouther fuel saving technology EGR, which might have reduced horsepower too much if they stuck with the 1.5. Other choices could have been DI and/or turbo or supercharging. The 1.5 could have used EGR, but it would have increased acceleration time and reduced efficiency at highway speeds versus the higher horsepower replacement. Toyota has stated they plan to use the 1.5 powerplant in other hybrids.

 

IMO, the Prius get better mpg in city driving because you are generally driving slower, driving in EV with the ICE off and doing a fair bit of coasting/gliding up to stops with the ICE shut off and no idling at stops. Conventional cars don't get better mpg in city driving because their engines are always running at at least idle speed, especially at low demand, such as 35-45 mph. And they idle at stops. And they idle when coasting to a stop.

3PriusMike

 

I think kstat's point was that the most efficient driving avoids unnecessary deceleration and avoids unnecessary braking. Through anticipatory driving he'll can avoid most braking so get little benefit from regeneration, with the primary benefit being on downhill stretches where he is forced to brake to avoid acceleration.

I expect that Toyota's figures will be based on "normal" driving that includes avoidable braking.

 

Wrong. A Larger displacement engine with more horsepower ensures greater fuel efficiency. That's because the engine can output more torque at lower RPM, so when you are cruising on the highway, your RPM is lower. This was in all the reviews for the 2010 prius. More HP= More MPG. If Toyota used the 1.5 engine in this prius, we would have the same mileage as the Gen II.

Thats why the Gen III has better mileage than the Gen II. Its because of the higher horsepower. The 1.8liter Engine does get better mileage than the 1.5liter engine. Look at the cruising RPMs of both engines at 75mph. While us Gen III owners are getting 48mpg, Gen IIs get 44mpg.

Otherwise, everything else between the Gen II/Gen III is similar. The coefficient of drag is within 0.01, same battery used, same tire size....i got a whole list of these.

 

The reason why the gen 3 has a higher mpg then the gen 2 is not SOLELY based on ANY one factor.

The power split device on the gen 3 has been redesigned and made more powerful and lighter. I think it also has an "overdrive" gear connecting the engine to the planet gear system in the psd purely for use on the highways to further reduce rpms.

Electric water pumps eliminates the parasitic engine load that a belt would have added.

And are you all forgetting about when the prius turns OFF the engine in city driving?
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A larger displacement engine does not ENSURE greater fuel efficiency. Going by your logic, they might as well have put a 500hp v12 4.0 liter engine in the prius and gotten 1000 mpg right?

Anyway, the type of engine is based on what loads they optimize for. Every engine has its own optimal load. It just so happens that 1.8 is more more optimally sized for different loads. Toyota could have wanted to optimize the engine for more highway driving - which necessitated a bigger engine.

Guys, instead of quibbling about what is the definitive upgrade that's responsible for the most efficiency gains, just ACCEPT that its a combination of A TON of differences in the implementation in the redesign of the prius! ~1k patents were issued for this generation of prius alone.
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now back to the topic:

Exactly what wh/mile are you expecting? Keep in mind that the car isn't constantly using power while driving. Remember the laws of physics? An object in motion tends to stay in motion.

This means, the only watts the car is using is to accelerate and to overcome rolling resistance (and wind resistance). After it has accelerated to your driving speed, it uses VERY LITTLE ENERGY to keep moving! (except when traveling at high speeds, where wind resistance takes a huge amount of energy to overcome).

 

I give up. You haven't a clue. Please listen to the moderator's request and get this thread back on track.

Tom

 

Yes let's get this back on track. Given that the PHV has the same milage, engine, and motors, but more weight and both larger battery power and capacity, I assume the battery must have something to do with the increased relative efficiency.

It is possible that having a larger battery capacity allow toyota to run the engine in a more efficient power and store that extra power, but given ken's graphs, the gen III is already fairly efficient here.

So someone posted that peak power is 40kw in the phv, versus 27kw in the standard prius, do we know what peak charging is from the regen brakes and battery. I am also curious about the charging efficiency of the new battery versus the standard Nimh.

The psd and mg1 and mg2 were reduced in weight by 66lbs, but the car itself is more heavy. The power increased though which allows it to accellerate faster in ev mode in the phv, and generate more power in mg1 in standard hybrid mode. The psd implements a ratio of motor rpm to wheel rpm through mg1, so this overdrive is really mg1 pushing the engine instead of resisting and generating energy. It was the same on the Gen II. The lower rpms are because the engine can generate the needed power at a lower rpm (result of replacing the engine with a more powerful one) resulting in less frictional losses from the engine.

Electric accessories reduce parasitic losses, which is great and the big one is electric ac which came before. This power must come either plugging in, which is the great advantage of the phv, regenrant braking, or generation of excess power by the mg. This last bit is helped to do more efficiently by a engine that is efficient at higher power levels.

Well why make all those small cylinders, it is easier to get a more efficient engine with bigger volumes cylinder as this increases volume to area. There are weight, and price, and volume penalties to more horsepower. If you want to go with an old 500hp design you should look at the porsche 918 phev. It has a 3.4L V8 and uses DI and other tricks to be efficient. The battery size is probably similar to the phv and provides 16 miles of electric range. The cars are about the same weight, and porsche claims higher mpg numbers but who knows how they are testing as the car isn't in production yet. The price is kind of the problem here though, its probably 20x more expensive than the phv prius. If you made an atkinson valved 2L aluminum DI Turbo engine you could probably get it to be lighter more powerful and efficient than the 1.8.

It appears from choices they picked it for cost and efficiency. They let the car get heavier and wanted it to be faster and more efficient. They could have used the old engine and had it be slower and less efficient on the tests. Or they could have made a new turbo, di, engine that would have improved both. The prius improved with little changes.

Well the thread was about regen on the phv, and some really strange ideas have come up to why this is not important. IF its not important just ignore the thread, don't baffle us with some lame excuses.

200-250wh/mile seem to be the range of hybrids with a lot of strangeness based of use of HVAC systems in different climates. One key is it takes more than that power to get up to speed, so to minimize power consumption it helps a great deal to recover that kinetic energy in braking. One advantage phev's have over their BEV breathren is in cold conditions the engine can more efficiently warm the cabin and batteries than the batteries themselves.