Automatic gearbox and regular use of neutral

itsmeagain

ontheroad1970 said:

itsmeagain said:

ontheroad1970 said:

I don't see how locking the wheels is a desirable thing at all, what with ABS and all.

Just to clarify, no one said that it was desirable to lock-up the wheels. I was saying that "modern braking systems are perfectly capable of locking the wheels". I.e, modern brakes are more than capable of achieving maximum braking, without the additional support of engine braking to do so.

The question... why would additional 'in gear' engine braking make the car stop quicker than using a modern braking system alone? I.e, "with ABS and all"

You think it will be safer with switched off engines?  You seem to be all for them.  So all electrics disengaged, an extra step to take to react to an unpredictable incident, or a predictable incident with an inattentive driver.  Of course those that want to lessen the safety protections are always 100% safe and attentive with eyes all over their heads so they never miss a thing.  

Back in the real world, all drivers get inattentive from time to time, some more than others.  Id rather that other drivers weren't turning their ignition off, with less power being supplied to the bakes through servo systems etc.  

The reference to locking brakes being desirable was inferred by your comment try comprehending what you write.

It will not be safer with automated switched off engines (stop on the move), but it will not be less safe. I do not propose that drivers switch off/on the engine themselves during coasting.

The electrics would not be switched off during an automated coasting engine stop. As mentioned earlier, the full benefits of such systems will not be seen until beltless engines. There are already engines will electric brake pumps, PAS, AC, ISG's etc without the need for the engine to turn to power what were traditionally ancillary belted items. Whether the driver is attentive or not makes no difference to what automated system is used. Cars are becoming safer and safer with these automated systems.

As you say, you inferred something from what I wrote. Try comprehending what you read rather than being so presumptuous.

Again... what is the benefit of 'in-gear' engine braking in the case of emergency braking when the brakes alone are more than capable of locking the wheels. For clarity - this should not be misinterpreted as me claiming that it's desirable to lock up the wheels! However... it will emerge in later posts that ABS does cycle between locking/partially locking the wheels and unlocking them...

BOWFER

Ditzy_Mitzy said:

Herzlos said:

itsmeagain said:

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?

Presumably said modern auto would start changing down gear quickly when the brakes are pressed hard and the vehicle speed reduces, thus increasing the effect of engine braking? Even if it's only a slight effect in higher gears, more braking is better than none in an emergency situation?

Plus there's no guarantee that the brakes are actually cold, if the driver has been riding them all the way down the hill to try and maintain a steady speed.

It depends what type of auto it is.  If conventional and changing down, it will need to unlatch the torque convertor.  In such a state the engine braking effect will be negligible as there is no solid link between the engine and the wheels.  Automated manual is anyone's guess, and will depend on whether the car lets the clutch in between down changes.  I'd assume not, as it may want to avoid damaging anything.  

DSG changes down for you as you brake hard, in D or S mode.

BOWFER

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?

Mark_in_Kent

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.

fred990

Out of idle curiosity as a manual gearbox driver, do modern autos (either dsg or tc's) change down sequentially or just block change? Can't imagine them going through each gear in turn? 

BOWFER

fred990 said:

Out of idle curiosity as a manual gearbox driver, do modern autos (either dsg or tc's) change down sequentially or just block change? Can't imagine them going through each gear in turn? 

DSG changes down in turn.

Advocado

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?  

Ditzy_Mitzy

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?

Electric cars can simulate engine braking if they so wish, but are not obliged to.  The issue you refer to is actually much older, as traditional diesel engines don't give any braking effect either.  
The bottom line is that engine braking probably doesn't offer any appreciable benefit in an emergency stop.  The only benefits of coming down the gearbox, as used to be taught, is that engine braking is available as a backup in the event of brake failure.  A neighbour used to have a Beetle with no brakes that I went in once or twice.  Slowing down was achieved by changing down and, when speed was sufficiently reduced, applying the handbrake!  

prowla

neilmcl said:

Advocado said:

I have a 2019 VW with an auto gearbox.  When I take my foot off the accelerator, there is quite heavy engine braking - going down a steep hill and it will still lose speed.

But popping it into neutral and it'll coast for what feels like forever.  And by doing so regularly, my mpg improves massively - around 45 mpg instead of 33-36mpg.

But does this do any harm to the gearbox?  I'm assuming not because, in this world of computers, I'm guessing it wouldn't let me do anything that would cause any damage, but wanted a second opinon.

It's called engine braking and it's exactly what you should be doing to control your speed. Coasting like this is not recommended and means your not fully in control, and I'd especially wouldn't recommend it with a DSG gearbox as you could damage the mechatronic.

I've never understood why coasting means you're not fully in control.

Mark_in_Kent

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

I expect you do have a fuel injector as they became commonplace in about 1995.
To be honest, I don't know all the factors involved in your situation such as; how you measured it, different fuels, what period of time, number of times measured, external facts such as temperature, your engine, is the fuel injector working etc. 
The improved fuel economy sounds great by the way, I just wouldn't coast myself as I don't think it's safe to do so. Disclosure: I have passed my Advanced Driving test.