Pulse 'n' Glide style of driving

[Wideboy]

Originally Posted by Milky Bar Kid

That's what my boss told me!!

Gav...how the hell would we be able to prove someone was coasting???

no idea, i was always told i'd be booked for it

i still do it

Originally Posted by Tommy H

+1 - Top gear fuel challenge a few years ago said you actually use less fuel leaving it in gear and engine braking at lights than either coasting or using the brake.

Although, they do talk some carp so could have been having us on.

Agree when wanting to slow down at lights etc, leave it in gear and coast up to them, but when going downhill if you leave it in gear of course you will use more fuel cos of the gears slowing you down, so neutral and when you get to a speed you think slow enough blip of the throttle into gear and away again, simples.

[Nobbylad]

Originally Posted by Wideboy

no idea, i was always told i'd be booked for it

i still do it

lol...that could be used in so many responses

What if the car's automatic It's a while since I had a manual car. I don't like 'driving' in neutral as the brake servo don't work.

[yorkie_chris]

Originally Posted by Milky Bar Kid

That's what my boss told me!!

Gav...how the hell would we be able to prove someone was coasting???

Same way you manage to prove a couple mph over the limit is dangerous driving

Originally Posted by Ed

What if the car's automatic It's a while since I had a manual car. I don't like 'driving' in neutral as the brake servo don't work.

That could probably be disabled but I'm not sure what else you could do other than general eco mileage driving style. Or not buying an auto because they're naturally thirsty.

[punyXpress]

Originally Posted by Bluepete

I am lead to believe that with many modern engines, when the road speed is above the engine speed, the injectors turn off.

In other words, on downhills, just take your foot off the gas, leave the engine engaged and the fuel stops flowing. This gives higher mpg than coasting as the engine needs fuel to idle whilst coasting.

Pete

But wouldn't you get engine braking?

[embee]

A few issues here (as usual )

As far as I was aware, the Prius is a CVT and I didn't think it had a clutch you could "dip" (I'm pretty sure the one I tried was a 2 pedal jobbie), may be wrong.

Yes, FI engines have "overrun fuel cut-off" above a certain RPM (around 1500rpm typically) so on overrun don't use fuel, but the engine braking means you slow down and then have to use fuel again. If you truly coast, yes the engine is idling, but the car will run as far as the kinetic energy will take it and if it's more than a couple of percent downhill gradient it'll keep on going, aerodynamic drag permitting. Coasting sensibly will give better fuel economy than overrun in gear. Out of interest, a typical car engine will use around 0.2L/hr per litre swept volume at idle.

On those economy run competitions they are strictly not allowed to squirt and coast.

Brake systems do work with the engine idling, as long as it doesn't actually stall. Not quite sure how ABS systems are designed to work if the engine stalls, I would have thought as long as the ignition is on it'll still work, it's electric. Even vac servo systems will usually give you one or 2 brake applications after the engine stops before you lose all assistance.

Once upon a time some Saabs did indeed have freewheels when they had 2-stroke engines as long periods of overrun starved them of oil. See Wiki

I'm a bit surprised with modern control systems that there isn't a freewheel system in use, it could be done on a part open throttle (trailing) so if you took your foot right off it would re-engage engine braking, but under the right conditions you could gain the benefit of freewheeling.

[DarrenSV650S]

I'm so glad my car doesn't have a mpg gauge. I think if it did I'd put a sticker over it

Just thrash it, you'll get there quicker!

embee - I haven't got or driven a Prius but there are videos of "zany" Americans on utube explaining it....

You talk about flywheels to extend that coasting range an extra few hundred meters which is a cool idea

Idea 1 ....How about "frictionless electro magnetic super conducting wheel bearings" on on four wheels ? Roll all the way down the M1 !

Idea 2 ...Electic motor wrapped / mounted on the drive shaft with push & squirt button on the steering wheel for when your coasting again to extend the range linked to a 24 volt battery that is triggle charge by the engine. Or a capictor type battery with like a green power gauge. After five minutes of driving the green leds indicate full. Then on the next roll/coast you press on the button to sustain the coast.

Fiat and I think the new sporty/eco Honda CR are doing electric engine wrapped around the drive shaft type thing.

As I said 3 hours drives is a long time to think about these types of crazy ideas.

[embee]

OK, just watched a clip. They are using the hybrid function that stops the petrol engine on trailing throttle but doesn't apply regenerative (electric) braking until you take your foot off the throttle altogether (see the note in my earlier post about potential for freewheel on trailing throttle).

In his Prius the engine only shuts down if you do it below about 40mph, above this it remains idling, presumably purely for driveability reasons, so benefits are less.

It's worth noting that they were saying the method gives useful mpg gains below 30mph average compared to steady speed driving, he was accelerating up to 37mph and coasting down to about 20mph. Not sure that would be much fun on the open road and would seriosly pi$$ other road users off in traffic. He said above 30mph the gains were insignificant.

It reminds me of when I was in the Alps in my Yaris, which has a quite accurate mpg readout. I drove about 30mls up 2000m or so into the mountains and stopped at a cafe, getting about 35mpg I think. I then drove back, about 20mls on overrun without touching the throttle, and got 999mpg (as high as it would read).