Regen from braking (using the motors to brake instead of the disk brakes) is better than engine regen, but no regen is better yet. That is, it is better not to need to slow down at all, but if you must decelerate, then regen braking allows recharging of the battery that does not need to be done less efficiently by the engine.

To put it another way, for any battery charge that is used, a slightly greater charge is needed to recharge the battery. The recharge can come from braking or directly from the ICE. Braking is the result of decelerating from a prior acceleration. Acceleration can come from the ICE, or the battery (or from going down a hill which required prior climbing the hill, etc.). It is less efficient to accelerate the car in order to recharge the battery by braking, than it is for the ICE to just charge the battery. However, acceleration has the advantage of getting you somewhere (the purpose of the vehicle!). The point is, all recharging comes from the ICE one way or another. If you must brake, then regen just makes the whole acceleration-deceleration cycle more efficient. It's less efficient than ICE direct battery charging, as measured in WH of charge/gallon of gas, but is more efficient in MPG because it includes going somewhere!

Regen from the ICE is less efficient, but allows the total vehicle efficiency to improve over a non-hybrid, in most cases. This is mostly true because it allows equivalent performance with a more efficient engine, and allows the engine to operate more efficiently most of the time.

Let me know if this is not adequately confusing!

-- Alan

 

Well the confusing factor is more than adequate. Thanks for finally clearing up what braking is. I never would have thought!
Seriously, your long explanation is a bit circular. How do you accelerate the car to charge the battery by braking? I always thought you accelerate to go faster, and the charging cycle happens in the background as the battery demand required, as long as the ICE was on, and it would start the ICE if needed. Acceleration was not needed to charge the car just the ICE running.
The bottom line questions are, what makes the little cars appear, can you effect them (or are they just informational), and do you want to see more or less little cars (or 1/2 cars) on the display for best mileage?

 

Deceleration is done mostly with the "brakes" which are mostly done with the motor/generators (MG1 & MG2). This is all that is counted for computing the regen car symbols on the consumption display. Regen means re-generation of current, where ICE charging is just generation (not re-generation). So, deceleration is where regen power comes from.

All deceleration can only come from prior acceleration. You can't slow down if you did speed up first! To go from, say, 45 MPH to a stop, you have to get up to 45 MPH first, and that requires acceleration. Acceleration comes from one of three sources: gasoline (ICE), battery, or external forces, like being pushed. Ignoring the external forces, which there usually is none, then all acceleration comes from the ICE or the battery. All battery power comes from prior charging of the battery, which can only come from regen, or from gasoline (ICE), which really means it all comes from gas, since regen was prior deceleration which came from prior acceleration. Not really circular, as it always gets to the gasoline, one way or another.

When the battery is low, the computer will tap the ICE to charge it, unless regen is available. The battery goes low because the motors assist in acceleration (or for AC or other electrical loads within the car, most of which are small compared to accelerating the car).

The regen symbols means that some energy was saved (by braking) for use later, resulting in less gasoline needed later. However, that saved energy is a small part of the energy that was used earlier to get to the speed (or up the hill, etc.) that got you to the point where you could regen some of it back. In any non-hybrid, all of the prior acceleration is spent energy, and none of it can be recaptured (regen) for reuse later.

To put it another way, less energy is used to hold a constant speed (getting 50+ MPG at over 50 MPH is easy on flat and level road at a constant speed), then is used to slow down and then accelerate back to the original speed (it is hard to accelerate to 50 MPH at more than 20 MPG). In a non-hybrid, all of the braking energy used to slow down is completely wasted, where a hybrid can capture some of the braking energy (regen) to reduce the amount of gasoline needed to speed back up later (with the electric motors assisting the acceleration).

-- Alan

PS Further obfuscation available on request.

 

No thanks, you've done enough obfuscation for me...

 

As a rough analogy, it's a bit like saying the most efficient way to use a light bulb is never to turn it on. The most efficient way to drive is never needing to slow down. In practice though, you always need to do some of both. Stomping on the brakes all the time is like using 60W bulbs, whereas gentle and light braking is like using a 13W CFL. Same general outcome, but less energy wasted.

 

I totally understand that it is energy 101.
But that still does explain the relationship of the cute little cars to mileage or breaking habits.
The simple question from the first post was:
"nicst47
Explain the pic of the little car =50wh regenerated?
I have been trying to figure out exactly what does it mean when I have a symbol of 1/2 a car, an entire car, or sometimes a car and a half on the mpg screen."

Maybe I'm a bit thick, but my question was simply do you want more or less little cars (generated power), can you effect this power generation, or does it even matter.

 

Ah, well, if you're going to press me for an actual useful answer... I don't usually give those...

But here goes...

In my opinion, as you suggested, it doesn't matter. The number of little cars means absolutely nothing, at least by itself. You can achieve a low and high # of cars both by being efficient and inefficient.

Here's another analogy (I love them, they are fun).

It's like measuring fuel efficiency by counting the number of times signal indicator is used. Using your signal indicator less often might be more efficient because the need to slow down, turn, and accelerate is less. But needing to turn more might allow taking better, faster, more efficient routes to destination. In other words, the single piece of data by itself, useless.

Have fun with them, play around and see how they make a difference. I think that is really what they are for.

 

The more cars and half cars on the screen, the more energy you recovered during braking, and the more the better, so long as you don't do any extra acceleration just to get your car symbols on the screen.

So long as you are well above 5 MPH, and not braking so hard as to need the ABS, and so long as your battery is not completely charged, then your braking will be with regen. Within these limits, the faster you decelerate from, and the longer you keep decelerating, the more cars and half-cars you will get. Going down a long steep grade with the brakes on all the way will get you a bunch of them. Just going down a long hill with no accelerator or brake pedal (coasting) with get you a few, as "coasting" on the HSD is equivalent to light braking-regen so as to simulate the slowing you would get in a non-hybrid car from engine compression.

-- Alan

 

Thanks to both Droid 13 and Alan,
OK that's what I thought. It's a bit like the wonderfully animated NAV screen that shows you if the car is running on battery or ICE or both. Interesting to look at but mostly useless information that you really can't effect too much.
Now that that is cleared up what the heck is a "Veracitorian Muser"?

 

All of the previous logic holds true, but here is the layman's look at it:

a) If you can minimize your braking, the better your fuel economy.
E.g. timing a light so you never have to come to a stop = better fuel economy than if you raced to the light, stopped, and then accelerated after it turned green.

This holds true for any car. That is the main point being made above.

However, there are sutations where you really must brake. E.g. a stop sign, and you obey traffic laws.
then:

b) If you have to apply the brakes, then a gradual application of them allows more regeneration to occur. This is better, in most cases, since you are usually minimizing the need for the ICE to run purely to charge the batteries.

So, bottom line is 'Given that someone applies good FE driving techniques such as trying to minimize braking when possible', then generally the more 'regen cars' shown, the better.

All that being said, if your traction battery is at full charge, the 'regen' power from braking gets lost. No clue whether it would show a 'regen car' in that case.