Automatic gearbox and regular use of neutral

itsmeagain

Ditzy_Mitzy said:

neilmcl said:

itsmeagain said:

neilmcl said:

Advocado said:

itsmeagain said:

neilmcl said:

BOWFER said:

Advocado said:

basill said:

Not just DSG, Volvo 8 speed non dsg autos coast in eco mode.   Must be something to save.    Emissions if not actual fuel possibly 🙂

If Volvo of all manufacturers have their cars coast, it can't be as dangerous as people on here seem to think.

I think the 'danger' part of it is being grossly exaggerated by some on here, I'm not joining in on that.
My electric car has very little to zero braking effect in D.
I have to select B mode to get any.
I wouldn't call it dangerous at all, it's just people getting all preachy.

Not at all.

Just think for a minute, your coasting downhill in a near 3 tonne vehicle do you really think your stopping distance is going to be the same as a vehicle that's in gear. It certainly won't be and every cm you can save in an emergency stop is critical. Nothing preachy about, it's just a simple fact.

Can you please explain why you think that a modern auto vehicle, auto selecting the highest gear and only changing down each time the revs get low (offering very low engine braking), would stop significantly earlier, than the same vehicle in Neutral. Bear in mind that modern braking systems are perfectly capable of locking the wheels and delivering near perfect cadence braking whether in gear or not?

Also bear in mind that the brakes are relatively 'cold' having not needed them to maintain speed down the hill.

Please explain the technical reason for this fact without saying that it's a well known fact.

I've already asked @neilmcl to explain his theories, but he goes uncharacteristically quiet.

Don't make things up, I've answered every single reply you've put to me up to this post. And yes, I've gone quiet now but that's because my Dad's gone into hospital so my attention is elsewhere.

I'll leave this thread now as I've got other things to deal with but you asked for second opinions, and I gave mine, I'm more than happy for you to ignore, dispute them, that's what the forum is all about after all.

Good luck with your Dad!

I thought you said (copy/paste) "Just think for a minute, your coasting downhill in a near 3 tonne vehicle do you really think your stopping distance is going to be the same as a vehicle that's in gear. It certainly won't be and every cm you can save in an emergency stop is critical. Nothing preachy about, it's just a simple fact"

Now that's very 'preachy' because without explanation it's a leap of faith.
If "it's just a simple fact", can you "simply" explain it please? I genuinely don't understand the logic.
I'm not sure from your last post if you've changed your mind, now claiming it's 'opinion' where earlier it was fact?
Please clarify, is this a fact that you can explain or an opinion that you can't?

Thanks for the concern regarding my Dad.

Can I ask you a question, in a manual do you not agree that it takes more effort to stop car if you brake with the clutch depressed than it is if you brake whilst in gear, then use the clutch at the last minute? The point I was making that it should be obvious that emergency braking, downhill whilst in neutral will take far more effort than if the speed is already being kept in check (for want of a better phrase) by the correct gear.

Also, to address @BOWFER's point regarding EVs, don't most EVs perform a certain amount of regenerative braking anyway, even if not explicitly set. I'm genuinely asking, as I don't know.

The answer to the point about a manual, petrol driven car, to keep things as simple as possible, is that there might be a slight advantage to being in gear during the initial phase of an emergency stop, but it's probably too minor to make any difference in the real world.  
What I don't know, because I'm not a scientist, is how small the advantage is.  The engine braking effect comes from the engine's desire to work as an air pump.  When the throttle is closed, manifold vacuum increases (I've read up on it), which means that it's more difficult for the piston on the induction stroke to draw in air.  That causes the piston to descend more slowly, with them all doing it crankshaft speed is reduced.  
Now: with a manual gearbox, the road wheels are directly connected to the crankshaft via the gearbox and clutch.  That means applying a retarding force to the wheels will, eventually, apply a retarding force to the engine itself.  Applying the brakes, therefore, reduces engine revolutions.
The point, then, is that applying a strong retarding force to the wheels will also apply a strong retarding force to the engine.  If said force causes the engine to slow more quickly than it otherwise would with a closed throttle and no brakes applied, engine braking in other words, then presumably it won't be drawing on the manifold vacuum in the same way.  Ergo, under emergency stop conditions, I suspect there is a crossover point at which the effects of the mechanical brakes overwhelm the engine's ability to work as an additional brake.  Where is that point?  I don't know...

Excellent. You should have had an attempt at my previous quiz question. You are trying to explain what is known as pumping or throttle losses only, however there's also the mechanical friction losses that are proportional to engine speed that contribute to engine braking.

To help understand pumping loss, imagine a syringe with the open end completely chopped off. You can imagine that pulling the plunger down to pull in air would take little effort, you'd let it go and the plunger would stay where you left it.
Now imagine that the syringe has a fine needle (simulated closed throttle), you pull the plunger and it creates a partial vacuum in the syringe that you have to pull against, you let the plunger go and it returns half way back up the syringe to relieve the vacuum. This is similar to 'pumping loss' where crankshaft energy is robbed to pull the piston down when the pressure in the crankcase (below the piston) is much higher than the pressure above, and wants to return back up against the direction that the crank is pulling it. There air will reach sonic velocity and have losses around the throttle. I know that there's some technical errors here - if you're an expert in fluid dynamics - no need to pick me up on it - i'm trying to make it easy!

You were right to qualify your statement as being for petrols. Having said the above, diesels usually have little pumping loss because they are substantially unthrottled and have lots of EGR that ensures that the manifold runs close to atmospheric pressure during low load conditions!

However, the OP explained that the vehicle was slowing down 'in gear', so he was taking it out of gear. To go down the hill in gear, he would have needed to open the throttle slightly else it would have decelerated (not being able to cover the brake in anticipation of an emergency). If an emergency occurred he only has to press the brake. If he'd have been in gear with his foot on the throttle, he'd have to swap from accelerator to brake before braking.

born_again

Advocado said:

I haven’t driven a manual for many years, but aren’t you supposed to depress the clutch and brake when emergency braking?

No. You depress the clutch just before you stop to stop the car stalling. Just as you would in normal driving.

born_again

Advocado said:

Mark_in_Kent said:

Coasting in neutral was better for fuel efficiency in the pre-fuel injector days.

itsmeagain, I think your question in that form is hard to answer. If you broke it down:

What is the benefit of 'in-gear' engine braking -, easy... fuel is shut off, less wear/heat on brakes, more control as the engine is assisting slowing, not having to change into gear in an emergency situation aka another thing to think about, can more easily drive out of the problem e.g. puncture at speed or skid, engine torque will slow car if hit by another car/ driver issue,  etc  

If you have to make an emergency stop, simply use the brakes. Hopefully, everyone agrees.

 BTW you would fail the advanced driving test if you selected neutral to travel downhill.

So considering my fuel economy is improved as a result of coasting, my 2019 VW must be pre-fuel injector?  

Improved in what way?
While just descending a hill?
Average mpg on a trip that includes a downhill?
Per tankful of fuel?

Keep_pedalling

BOWFER said:

Keep_pedalling said:

BOWFER said:

All this fuss about engine braking, yet no-one has commented on me twice pointing out electric vehicles don't offer any as standard.
So those who think engine braking makes a difference during emergency braking are what, just burying their heads in the sand?

Even in D mode EVs use regen on breaking. Lightly hitting the breaks on my ID3 slows the car down using the motor alone, the actual breaks only kick in under heavier breaking where both are used.

Yes, but it's 'engine braking effect' that's being discussed here.
If you lift off the throttle in your ID3 going down a hill, will the car effectively freewheel or slow down?
In the Leaf's standard D mode, the car will more or less freewheel and even speed up if the hill is steep enough.
I'd have to select B to get any slowing down (engine braking) effect
Note this is only coming off the throttle, not applying the brake pedal.
I will select B in winter if going down a snowy hill to help me 'hold back' without touching the brake pedal.

My point was in an EV, if I have to hit the brakes in an emergency I will instantly get breaking from regen and the brakes. In a van coasting in neutral there will be no engine  breaking in an emergency stop as there will be no time to engage drive.

itsmeagain

Keep_pedalling said:

BOWFER said:

Keep_pedalling said:

BOWFER said:

All this fuss about engine braking, yet no-one has commented on me twice pointing out electric vehicles don't offer any as standard.
So those who think engine braking makes a difference during emergency braking are what, just burying their heads in the sand?

Even in D mode EVs use regen on breaking. Lightly hitting the breaks on my ID3 slows the car down using the motor alone, the actual breaks only kick in under heavier breaking where both are used.

Yes, but it's 'engine braking effect' that's being discussed here.
If you lift off the throttle in your ID3 going down a hill, will the car effectively freewheel or slow down?
In the Leaf's standard D mode, the car will more or less freewheel and even speed up if the hill is steep enough.
I'd have to select B to get any slowing down (engine braking) effect
Note this is only coming off the throttle, not applying the brake pedal.
I will select B in winter if going down a snowy hill to help me 'hold back' without touching the brake pedal.

My point was in an EV, if I have to hit the brakes in an emergency I will instantly get breaking from regen and the brakes. In a van coasting in neutral there will be no engine  breaking in an emergency stop as there will be no time to engage drive.

Agreed, assuming that full regen was active instantly (which must have some delay even if it is too quick for you to perceive). But... what would be the disadvantage caused by the Van being in neutral and not having the engine 'breaking' (as you call it) in this scenario? Bear in mind that the missing engine braking is insignificant compared to the main wheel brakes?

BOWFER

Keep_pedalling said:

BOWFER said:

Keep_pedalling said:

BOWFER said:

All this fuss about engine braking, yet no-one has commented on me twice pointing out electric vehicles don't offer any as standard.
So those who think engine braking makes a difference during emergency braking are what, just burying their heads in the sand?

Even in D mode EVs use regen on breaking. Lightly hitting the breaks on my ID3 slows the car down using the motor alone, the actual breaks only kick in under heavier breaking where both are used.

Yes, but it's 'engine braking effect' that's being discussed here.
If you lift off the throttle in your ID3 going down a hill, will the car effectively freewheel or slow down?
In the Leaf's standard D mode, the car will more or less freewheel and even speed up if the hill is steep enough.
I'd have to select B to get any slowing down (engine braking) effect
Note this is only coming off the throttle, not applying the brake pedal.
I will select B in winter if going down a snowy hill to help me 'hold back' without touching the brake pedal.

My point was in an EV, if I have to hit the brakes in an emergency I will instantly get breaking from regen and the brakes. In a van coasting in neutral there will be no engine  breaking in an emergency stop as there will be no time to engage drive.

No you won't get *braking* from regen and the brakes.
That's what I've been saying all along, the default setting in many EVs is that there's little to no regen braking in 'D' mode.
You come off the throttle, the car effectively coasts - same an ICE car in neutral.
In an emergency you'd be going to straight to brakes.

Jenni_D

But when you press the brake pedal an EV (generally) also uses regen braking to a) assist in braking and b) pass charge back to the battery - yes? That's what @Keep_pedalling clearly alluded to, as they didn't mention coasting at all in the sentence where they mentioned "hitting the brakes".  

BOWFER

Jenni_D said:

But when you press the brake pedal an EV (generally) also uses regen braking to a) assist in braking and b) pass charge back to the battery - yes? That's what @Keep_pedalling clearly alluded to, as they didn't mention coasting at all in the sentence where they mentioned "hitting the brakes".  

In an emergency braking scenario, forget all bout regen braking.
That only applies to very light braking, if you hit the brake pedal it's going straight to the good-old-fashioned (and by god, car brakes are old fashioned...) hydraulic jobs.

itsmeagain

BOWFER said:

Jenni_D said:

But when you press the brake pedal an EV (generally) also uses regen braking to a) assist in braking and b) pass charge back to the battery - yes? That's what @Keep_pedalling clearly alluded to, as they didn't mention coasting at all in the sentence where they mentioned "hitting the brakes".  

In an emergency braking scenario, forget all bout regen braking.
That only applies to very light braking, if you hit the brake pedal it's going straight to the good-old-fashioned (and by god, car brakes are old fashioned...) hydraulic jobs.

I was once the passenger/calibrator in a well known EV, where on the track I typed in a parameter value that gave maximum generator charging. The tyres screeched, my laptop went flying and I was never foolish enough to try it again! The driver was less than impressed and still doesn't see the funny side!

BOWFER

itsmeagain said:

BOWFER said:

Jenni_D said:

But when you press the brake pedal an EV (generally) also uses regen braking to a) assist in braking and b) pass charge back to the battery - yes? That's what @Keep_pedalling clearly alluded to, as they didn't mention coasting at all in the sentence where they mentioned "hitting the brakes".  

In an emergency braking scenario, forget all bout regen braking.
That only applies to very light braking, if you hit the brake pedal it's going straight to the good-old-fashioned (and by god, car brakes are old fashioned...) hydraulic jobs.

I was once the passenger/calibrator in a well known EV, where on the track I typed in a parameter value that gave maximum generator charging. The tyres screeched, my laptop went flying and I was never foolish enough to try it again! The driver was less than impressed and still doesn't see the funny side!

I don't doubt the capability is there, but they clearly ramp it back to protect the general public from themselves.
Having said that, some adjustment on my Leaf would be nice, rather than the set amount 'B' offers.