Regeneration in EV mode? Fuel economy in HV mode?

Any regen is less efficient than simply conserving the momentum. Braking will never increase mpg or (edit: reduce) wh/m, even when a portion of the energy goes back in the pack.

Braking is sometimes helpful to avoid hitting things.

 

It's a bummer to read that the new batteries will only recharge from a cord, and not during operation. Around where I live, we have very long hills that would be more then enough to recharge all of the batteries.

From home it's about 20-25 miles up and over the pass where about half of the ride would be electric, then downhill which would refill the batteries, then to the soccer fields or other locations which are 20 miles or more from the bottom of the hill - again depleting the battery, then back and up the hill (on gas) then downhill again to recharge, then another 15 miles or more home on battery.

Since our 2010 gets close to 50MPG now up and down all of the hills, being able to do 60+ miles of an 120+ mile trip all on battery would be impressive (no gas going down the hills!).

Maybe the regen generates power too fast to charge the battery pack safely, or it was just too hard to do. Without the regen - it would be really nice to have about twice the electric range to make this a decision point for me over a pure EV. As is - likely to go with the EV.

 

No really? i never used the brake before to avoid hitting things. i just swerved out of the way. Your cynical and useless post amuses me.

this is the real world. you will lose momentum. where have you been? the reason hybrids are efficient is because they have regenerative braking. And i really dont feel like explaining why. Real cars need real braking. But you're right, lets just all use traditional brakes instead because regen is inefficient. psh lol. Whats the point of conserving momentum when you need to bring your car to a stop? id rather have that excess energy converted into electrical power instead of heat.

 

Hes not talking about using the friction brakes. Hes talking in terms of a pure mpg standpoint.

It is always better to glide when possible.

Regenerative braking is not the only reason why hybrids are efficient. It's the aerodynamics, its the engine type, and the fact that the engine turns off at speed!

Even better then the above is driving technique: Don't accelerate needlessly such that your forced to use any type of braking (regenerative or friction). Of course, there are always unavoidable braking incidents, and of course, regenerative braking is better then friction braking.

 

Regen braking is a neat but overall minor reason why hybrids are efficient. The more regen you do, the lower your mpg. I concur regen beats friction, and I concur that we all use our brakes. Prius efficiency comes largely from the ability to use a smallish ICE and a smallish MG in concert to propel the car at acceptable rates. I would guess, based on the near absence of regen cars in my display that it contributes less than .5 mpg to my results on a typical tank. Clearly that varies with terrain.

What I try to stamp out is the recurring notion among newbies that they can brake their way to high mpg. There exists a preconceived idea that Prius mpg comes from accelerating from the pack very slowly and then braking to recharge. The truth favors normal acceleration combined with conservation of momentum, just as it does with non-hybrids.

 

Hybrid efficiency comes from: Regenerative Braking & The Use of the Atkinson (vs Otto) Cycle in the ICEs. Without regenerative braking, the ICE would have to recharge the HV batteries more often. So Regen braking does contribute WAY MORE than 0.5mpg improvement.

Take into account the Lexus Hybrids, which have more horsepower than their all-gas counterparts, but still get better mileage. This is not because the engine is smaller and weaker...

 

Not for me. I never stated what it did for you or others. The real point is, the more regen "benefit" you get, the less you have succeeded in anticipating the conditions ahead for maximum mpg. I'm not saying you should try for the best mpg or that conditions even permit DWB (driving without brakes) to its full potential most of the time.

Your view is counter to all I have seen here and to my own experience. You can also check out the Prius II article by xcel at cleanmpg.com. He walks the walk on conservation of momentum and his results are exhibit 1. When you beat his mpg, then we should talk about your magic brake pedal.

 

So, the ICE propelled the car, and rather than allow the car to glide, you saved energy by a 50% efficient round trip from kinetic to chemical and back to kinetic? Clearly this 50% efficient conversion/reconversion cannot beat simply gliding. The ICE charges the battery from excess power during pulses, sufficient to run my typical 12V load. Thus, my SoC rarely changes from 6 bars. I rarely regen in significant amounts.

On the freeway, I regen upon exit every 2 to 5 hours when I need to take a off ramp. Surely that is not adding WAY MORE than .5 mpg to my 60 mpg segment?

In town, I brake in emergencies and when I have reached too fast a speed (traffic dictates, poor estimate on my part). I assure you that for me, this is not much regen. With a warm car, mpg runs in the 70s.

 

I think you are confused about the point most people are making. The biggest savings in gasoline for a hybrid are in the city. The biggest sources of the savings are regen, and the ability to use electric power instead of the engine at low power levels when the engine is least efficient. When I descend a hill and hit a stop sign, I don't really have much of a choice but to hit the brakes. Driving in city traffic, going 4mph to manage the lights will cause a dangerous situation of people jamming around me.

Your hyper miler point of you get the best mileage from not going at a speed that you will need to brake is impractical for most of us. That was not the question put forth. For those of us that deal with hills and traffic, having regen braking is one of the key reasons the car can do better than a conventional one. In your situation I would think you could do as well with a diesel as you can tune it to be more efficient than an Atkinson engine.

 

This may be the point that most people are making (perhaps), but it's not true. The biggest mileage gain from a hybrid like the Prius is the ability to use a smaller, more fuel efficient gas engine for real world driving. This gain is most pronounced for what I call "country" driving: cruising along at a steady speed in the mid forties.

Regenerative braking helps, as you point out, especially when forced into stop and go situations. A more skilled driver will benefit less from regeneration than the mindless driver racing up to each stop, although obviously traffic conditions can force anyone into an undesirable driving pattern.

The point ksstathead is trying to make is that braking is something to be avoided, whether regenerative or not. Braking is a necessary evil. We have to do it, but it is undesirable. Regenerative braking makes it less undesirable, but it is still something to be avoided if possible. It's no different than full-throttle acceleration. Sometimes you have to do it to safely merge with traffic or to pass, but from a mileage standpoint it's not something you try to do.

Tom

 

Wrong. The engine size is the same used in the Matrix, Corolla...etc. The engine is exactly the same actually. They just run on different cycles.

Regenerative braking is what give the hybrids their efficiency. That's why the City Mileage is always better than Highway Mileage. In a regular car, all your acceleration energy is lost when you stop at traffic lights. In a hybrid, you get back some of that energy.

 

I would say it is only having to run the ICE for acceleration, versus full time, that makes the difference from Matrix, Corolla to Prius. I beat the EPA with essentially no regen. If I increase my regen, my mpg goes down.

 

We're not all hypermillers here. We don't ignore safety, we drive normally. 95% of us on the forum are "normal" drivers.

 

You and I must have a different definition of truth. Any car will perform better in steady non-accelerated driving. Numerous European diesels can beat the prius in this 40mph type driving, including heavier cars. If your premise was true, the gen II with the smaller engine would do better than the gen III. The gains in tests of hybridized cars consistently show the biggest improvements versus their non-hybrid siblings in city driving. You may notice that many of us on this forum have not changed our driving and moved so that we are going long distances at speeds in the 40s.

Being a bicycle rider and pilot I have great skills at estimating deceleration and lights, unfortunately road conditions often dictate how we must drive. I just think of it as reality, not undesirable. If I'm on a 55mph road with a light I will coast well, and sometimes drivers pass me only to be frustrated that I am 1 car behind without stopping. In most high traffic situations though you shouldn't apply these skills.

Hey with my underpowered engine full-throttle acceleration is desirable. With a bigger battery and a stronger motor I might be able to get by with less than a full throttle. Braking is braking, its not evil. I think I would rather drive my 5 miles on my typical trips, and use the brakes, than spend 2 hours on highway. I definitely get less mpg, but that's ok.

You will definitely get higher mpg if you disconnect your break pedal. You will get a much bigger advantage over a corolla in the city than on your hypermile routes. Add a cvt, DI, and EGR to a car with similar Cda and rolling resistance of the prius and your mileage won't be much of an improvement when your going 40+ and keeping relatively constant speeds.

 

And hopefully the rest of us are safe hypermilers driving legally.

And in Lake Wobegon all the children are above average.

I am not suggesting you hypermile and I certainly want us all to drive safely and respect other traffic. I admit that regen is better than friction, that Atkinsonized is better than Otto, etc. We just differ on which factors account for the greater portion of the miracle that is Prius.

 

The cycle of the engine is neither here nor there. Likewise the size, except for weight and aerodynamics. I should have avoided using the term "smaller".

All that matters is that the hybrid system allows for reasonable driving performance with a more fuel efficient engine. Most cars are very inefficient in the use of their engines, which were selected for performance and not efficiency.

In the case of the Prius, the engine is a small Atkinson Cycle engine. The low-end torque and extra power of MG2 compensates for the lack of torque and relatively low power of the ICE, which otherwise would render the Prius nearly undrivable. The Atkinson Cycle engine is just one way of producing a more efficient prime mover. There are many others.

As for highway verses city mileage, the reason highway mileage is lower is because of aerodynamic drag, which goes up by the square of the speed. This is a simple physical fact, to which all cars are subject. Speed is the enemy of good mileage.

So why do other cars do better at highway speed? They don't. They just do a *lot* worse at low speed. Remember those big engines we were discussing? They are very inefficient when throttled down for low speed driving. That is the fundamental mileage killer at low speed for normal cars.

Obviously regenerative braking also helps. Every little bit helps with the Prius: weight, aerodynamics, Atkinson Cycle ICE, LRR tires, driver information feedback, and regenerative braking. Regenerative braking helps, but it's not the principal factor providing good mileage.

Tom