Engine Braking

There's no way it can. It's just basic high school physics.

A moving car has potential kinetic energy, created by the motors of the car. The point of a hybrid or EV is to reclaim as much of that energy as possible, instead of wasting it by braking or from the drag of an engine. In any case slowing down the car requires that the potential kinetic energy of deceleration be dissipated.

No part of the Prius drivetrain is able to make that energy magically disappear. There is a minimum amount of friction in the Prius drivetrain. It was engineered that way to be energy-efficient. When you need to decelerate, you let off the accelerator pedal, and you will see a small amount of regeneration on your instrument panel. This is meant to simulate engine drag on a conventional vehicle, bbcause most of us are familiar with that effect

But if you need to slow down more suddenly, you touch the brake, and regeneration increases but it has a limit, and if you press the brake pedal farther, the friction brakes are activated. Throughout this deceleration, the gas engine is not turning. There is no clutch, therefore it can not slip like a brake pad. No energy can be dissipated through the gas engine. It is stopped. It can't provide any energy dissipation.

I suppose the gas engine could be turned by the drivetrain, and provide some drag, but that would be a bad design. It would be a total waste of energy; when the goal is to recover as much of that energy as possible, to charge the battery and extend the range of the vehicle.

I found out yesterday, by just fooling around, that if you engage the engine brake on a regular decline, the regen gauge shows partial
regenertive braking. I did not know this, and assumed that engine braking only produced hot air to dissipate energy. But it makes good sense not to waste energy if you can put it into the battery.

But the engine brake was designed for when there is no place to put the energy, because the battery is full. When you're coasting down a long, steep hill, there's really no place to put the dissipated energy once the battery is full. I'm not saying it's a common occurence, but it is a potential hazard, and someone could possibly be killed. Once your friction brakes have burned away, it's nice to have the extra option of an engine brake.

But this is not the first time I've gone through all this. I think you should make an effort to understand what I'm trying to say before you react to small snippets taken out of context. I'm always happy to clarify. But constant repitition is not that.

 

What is "potential kinetic energy"?

I think someone failed " basic high school physics".

 

Uncontroversial. It's equally basic high school physics that the friction brakes create no drag when they're not in use, and that regen creates no drag when it's not in use. And yet you seem to understand they both create drag just fine when they are in use. Why is engine braking harder for you?

There is no car where the engine braking effect is achieved by slipping of the clutch. Clutch slipping is only a thing during the moments the clutch is being engaged or released. Engine braking in a conventional car comes from the pumping loss of the engine being turned by the drivetrain, against a closed throttle. A clutch, if any, is fully engaged at that point, and not slipping.

Winner winner chicken dinner! That is exactly what happens. It makes no difference whether the engine is or isn't already turning beforehand. As soon as engine braking begins, the drivetrain is turning it. If it wasn't turning before, now it is.

When the goal is to recover as much energy as possible, that's not the use case for engine braking. But that's not the only goal at all times. As you already understand, when the battery can accept no more energy, that can't be the goal any longer. And if you are descending a long hill with a small battery that will end up full even without all possible energy recovered, then the goal may be to recover some and engine-brake the rest, so that the battery is charged less aggressively. The goal in that case is to extend the life of the vehicle rather than its range.

The car only automatically applies engine braking in the first case, when the battery can accept no more regen. (It actually begins slight engine braking a few % ahead of that point). If you want engine braking applied because you'd prefer a lower charge rate on a long descent, you must indicate that manually by selecting B mode.

We've told you that before, but it's good you found out. The early introduction of a bit of engine braking, plus less regen than would be used for the same slowing rate in D, is what B mode selects.

Naturally, once the battery can accept no more regen at all, you'll find the engine braking completely takes over from regen, just as it does in D.

 

No need for insults.
I think you know what kinetic energy is.
It's potential when it can be used, but has not.

 

ChapmanF
Well, I've reached my limit of trying to be fair and reasonable with you.
I had no choice but to put you on ignore. I am now unable to see any of your posts.

 

I was just trying to stir the pot a little more and see what your reply would be.