"Automatic" engine braking

Here we go again!

 

So you've still not managed to reach the condition you're being contrary about - when the car can no longer produce drag by regeneration due to full battery, so must either produce engine drag or nothing. So you did not manage to produce a relevant result.

If you've never managed to fill your battery you have no relevant first-hand knowledge to agree with or contradict the observations of those who have experienced full batteries.

I don't understand why you can't grasp the logic here.

 

Well, if you value facts over ego, you need to clean up your post. It has erroneous assertions and assumptions. Surely you know that the overnight charge does not charge the traction battery to 100% SOC. In your post you are making the presumption that you can hear engine braking, even on an engine design with variable valve timing and with CVT in the place of a normal transmission.

A good way to set your path forward is to abandon the attempt to override everyone else. After all, there were errors in the posts of all the other threads you set up to argue about your pet peeve.

.... Or is this the AI posting again?

 

He's using the common tool of the conspiracy theory. He challenges you to prove him wrong, but when you present him with proof he declares you a liar or mistaken. How does he know that you are wrong? Easy, he disagrees with you.

 

In the hope of increasing knowledge, rather than ignoring it, do we have data on how 'full' 100% is? Not in the sense of SoC, but in terms of how much regen power is available, compared to lower SoC? Is it set at a level where you still have normal regen, or is it already diminished? I've never spotted it diminished from the dash display, but that's not very conclusive.

I believe this should be clearly visible in Techstream etc, so maybe there's already been G4 observations.

One more observation - the Predictive EV Drive that the USA doesn't have is keen to shed charge initially, before starting its auto switching to HV mode. (So if your journey starts on a motorway it won't switch to HV immediately if at 100%, but use EV down to 80 or 90%) That could be about increasing regen ability, or it could just be about battery life.

 

This BC trip must be the one Paul referred to in post #56 of his earlier thread on the same topic (a good thread to review for any newcomer wondering about this one).

For clarity, when Paul refers to "the claim of automatic engine braking", he specifically means the claim that the car's ability to spin the engine in fuel-cut mode to resist forward motion is not exclusively used when B is selected, but can also be observed when D is selected and the traction battery is too full to accept more regen.

Drivers who have already observed that happening, many capturing it on OBD-II instruments, may be puzzled at so much attention to the question whether it happens or not. But then, Paul has a Prime, with its much larger battery, so the "battery too full to accept more regen" condition is much less often reached in everyday driving.

Paul conducted an earlier test, in less-demanding terrain, and reported it in post #53 of that earlier thread. In advance of that test, he had been advised (posts #38, #39, and #50) of ways to conduct that test that would give it the best verifiability and credibility, in case he found himself reporting a result at odds with what others have experienced and often captured on instruments.

He used none of that advice in that earlier test, choosing instead to report with no quantitative data,

An alert reader will spot (credit where credit is due, KMO did spot) that Paul's report itself says regen braking continued all the way down, which is a dead giveaway that the necessary "battery too full to accept regen" condition never was reached, and therefore the claim Paul meant to test did not get tested.

That led to the anticipation around Paul's planned BC trip, in which he would "have a good opportunity for a do-over, and may be able to do it over with more attention to the reproducibility and credibility of his work."

Which brings us to this thread, in which he has made that trip, again without observing any of the earlier advice on how to conduct an effective test, relying not on instruments but on "windows down, audio system off, and I surely would have heard".

From this test, Paul reports again having "experienced 'braking' of a sort, but it wasn't engine braking, it was regenerative braking", and so reveals that in this test, also, the necessary condition of "battery too full to accept regen" was never reached, and the claim Paul wanted to test was not tested.

This is worth drilling into just a little further. If the car is on a steep downgrade, speed being held by regen braking, and then the battery becomes too full to accept more regen, at that moment, without any change by the driver, something different must start happening.

Regen braking at that moment will cease. If the car applies no other source of rolling resistance instead (such as engine braking), then the car's speed must begin to substantially pick up as soon as the resistance from regen ceases.

That second alternative is a claim Paul has, in fact, made, in an even earlier thread:

Paul may be convinced that's what happens when the battery can accept no more regen, and others may be convinced that engine braking is what happens then, but one thing that cannot happen then is that the car just keeps going down the hill the way it was while regen was happening.

Paul's test here has not reported that he noticed engine braking, and also has not reported that regen ceased and the car's speed then began taking off. Those are two alternative claims about what could happen when the battery's regen capacity is filled, but because that capacity didn't get filled, neither of those claims got tested.

 

Skipped.

 

it would be helpful to know how much charge the battery had when beginning descent, and how much at the bottom of the hill, and how your speed changed from top to bottom

 

OH THANK GOD we needed another thread about this dumb topic. The dozens of B mode threads we already have aren't enough, we need MORE!!!!

 

If I understand what you're writing, and Gen 5 is different than Gen 4 when in EV mode ( I've read reports that the engine in the Gen 5 Prime starts more often while in EV mode than what's been experienced in Gen 4 ),. than things get even more complicated, since it's not fully known what all the programming thresholds are for engine on in all situations the car can get exposed to.
It's always a question with Gen 4 as well if someone actually finds a new set of programming thresholds that will start the engine. I think it's be rare for someone to find another one for Gen 4 at this point.
Both engine on regen as well as EV mode regen are dynamic, but in pure EV without any engine on trigger(s) regen in B mode is a static hard coded value of regen.
But if the engine starts or the brake pedal is also used while in B mode than regen switches from that static value to its normal dynamic state based on all the parameters at play that make it dynamic.
I'm not sure that explains what I've understood about regen in the Gen 4 and how I believe it works on a consistent basis, but at least I gave it a shot.

I think more confusion comes as a result of Primes new bag of tricks in pure EV mode. that can be near impossible to explain to someone that's never experienced them at least once or as most of us can see from reading this and other threads on the subject.

To get closer to an answer to your question about what regen is limited to,, I've seen regen spike at 80 Amps once for a second or two. I'm sure it can go higher, but I don't know what it's actual hard line is. I've also seen a 100Amp draw in EV mode going up hill on a hwy entrance ramp with the Go Pedal floored, once
and than also only for a second or two.

 

Just to add fuel to the fire, I'm pretty sure the car also uses engine braking during adaptive cruise control. Maybe that's something that's been known here since the gen4 days, but it's new to me as my gen3 only had standard cruise.

I noticed several times over the last two days where the engine would spool up if the car had to decelerate quickly if someone pulled out in front of me.

My general impression is that cruise first tries coasting, then regen braking, then engine braking, and finally friction braking.


SM-S901U ?

 

My gen 3 with only the ordinary cruise control—no adaptive—makes extensive use of engine braking whenever the battery SoC is above 77%, so it would surprise me not at all that the adaptive cruise does so too.

That's different, by the way, from how cruise worked in the gen 1. That was more like cruise control in older cars: it would increase power when you were losing speed, but do nothing special when you were gaining speed. In gen 1 it was handy to combine cruise with B, so it would do a better job holding speed on descents.

In later gens you can't combine cruise with B, because selecting B cancels cruise (a change they might have made to discourage people using B in normal driving). But no functionality was lost, because cruise in the later gens will use regen and/or engine braking if you're gaining speed.

 

Like Chap's 2010, I must confirm that my 2010 and 2012, both of which lacked adaptive cruise control, could also use engine braking during regular cruise control, above a certain battery SoC.

Following up on earlier posts in the other threads, I should add the additional observation that my '24 RAV4 Prime under CC, descending a long steep highway-speed hill (generally described as 7% grade, 2000 vertical feet) on a very hot day, doesn't use full regen capacity all the way down, but does add engine braking into the mix part way down. The CC regen didn't seem to go higher than ~30-40% (by eyeball) of the regen gauge capacity, and engine braking twirled up a bit less than half way down the hill. Foot braking could still push the regen gauge up to max. There is more to this puzzle that I have not figured out, but it does capture vastly more regenerated energy than my Prii ever could.

I haven't (yet) plugged my old ScanGauge into this vehicle, so don't have the added instrumentation. Engine braking was noticed solely by the factory tachometer (found so far only in the optional HUD), not by feel or sound.

My greatest recovered energy (in miles of EV range) have been on slow gravel mountain Forest Service roads, not fast paved highways, on cooler days (don't yet know if that is relevant). 9 net miles on a single pitch descending from a June hike, 13 net miles a week ago. Gross EV-mile upticks across multiple descent pitches (mixed logging roads and highways) on a single drive segment have been as high as 30 miles, though in smaller pieces that get burned off between descent pitches. But since the battery starts full at low elevation, and is mostly depleted during the climbs up to the trailheads, it never gets anywhere near full on the way down. No engine braking on the slow logging roads, but multiple cases of engine braking on the fast highways despite battery not filled.

 

Your test descriptions very clearly betray an extreme lack of attention to, or avoidance of, our described conditions.