RE: What is a 'coasting' function? PH Explains

[2Btoo]

Didn't the Trabant have a 'freewheel' feature that achieved exactly this; if the road speed was greater than the engine speed then the engine drive was disconnected. I seem to remember it was achieved with a sprag clutch in the drivechain.

And who would have thought that we are currently looking to such mechanisms as 'advanced' when Trabant got there 50 years ago!

[sjwb]

I loved the freewheel on my 96. Foot off the throttle and it would continue unabated like a tea clipper under full sail. Had very good brakes though.
The nicest, but unintended touch, was the ability to change gear without the clutch. Just lift the throttle and shift the lovely column lever. Happy days.

[mrbarnett]

Mammasaid said:

Max_Torque said:

Mammasaid said:

Brakes to slow, gears to go.

You do know it's cheaper to replace brake pads than gearboxes??

All completely irrelevant in 2018.

1) No modern car will "loose control" if you lift off the accelerator (under conditions where it wouldn't also have loose control if you braked, and as most people dont' left foot brake, you always have to lift off first.......

But still can cause driven wheels to lose traction in wet/greasy conditions in a manual gearbox which is what I was driving at. It's what ABS was invented for, stamp on the brakes and the driver can steer out of trouble (that's the idea anyway). However changing down and releasing the clutch rapidly can cause the loss of traction and sometimes no amount of electronic intervention can overcome this.

Which is why I'll either blip the throttle on downchange to match (or approximately match) engine speed with transmission speed, or wait until the revs are sufficiently low enough to now impress enough drag from the engine on the transmission. I do something similar in my automatic, only it matches the revs for me. If I leave the car in auto, it'll do it itself.

Mechanical sympathy comes in many forms.

[Mr2Mike]

Mammasaid said:

You do know it's cheaper to replace brake pads than gearboxes??

The classic response when the subject of engine braking is brought up. How many gearboxes have had to be replaced solely due to people using normal amounts of engine braking? I suspect it will be somewhere around zero.

[otolith]

Mr2Mike said:

Mammasaid said:

You do know it's cheaper to replace brake pads than gearboxes??

The classic response when the subject of engine braking is brought up. How many gearboxes have had to be replaced solely due to people using normal amounts of engine braking? I suspect it will be somewhere around zero.

Slowing down by lifting off in advance will reduce the wear on everything. Slowing down by banging it down through the gears will cause wear, to the clutch if nothing else, especially if done by someone not good at rev matching.

[Olivergt]

So essentially, the gearbox/engine is automating exactly what any decent Hypermiler would be doing to improve fuel efficiency. The only difference is that a human can read the road ahead a lot better than the computers in the car and make better decisions on when to coast etc.

[Lucas Ayde]

I've got a 'coast' function on my car when in 'Eco' mode and during normal driving it seems to make very little difference indeed to overall fuel economy - but does make the car massively more annoying to drive as when engaged, it feels like the accelerator is linked to the throttle by a rubber band.

If you apply the brakes at all - even the merest dab - it does at least disengage the coast until you have re-applied the accelerator, so you can still use the engine braking effect coming up to a junction or going down a hill.

I get best economy on the open road by using the adaptive cruise in conjunction with the 'Eco' mode but I do notice that it doesn't make use of coasting - the gains are coming from the more gentle acceleration and whatever other ECU tricks are employed.