Yes, it's me again with my 07/56 320d... Tech question(s) related to the 'swingometer' instant fuel consumption gauge:
I'm driving along at a steady speed - say an indicated 70 mph. I ease my foot off the accelerator pedal, and the swingometer shows (logically) an increase in mpg. But there's no fall-off in speed. This implies that by working at it (and by some experimentation) the car can be driven more economically than one might think.
But same, constant speed for less fuel? How? Why? Isn't that defying the laws of physics? Is the swingometer having me on?
|
It's not constant speed. If you can ease off and the car remains at 70, then either you were accelerating at the point you eased off, the gradient of the road has eased, or you will have started to gradually slow.
You don't get nowt for nowt unfortunately.
|
Gordon's right, try and experiment on a level area of road (even an almost invisible incline can affect this) you will find that if you lift your foot off and economy improves, the speed will trail off gradually, alternatively, if speed stays steady then had you not lifted your foot you would have been accelerating.
The trick is figuring out where you can lift your foot off to see economy leap (mine used to jump to infinite mpg when coasting along) but not suffer as a result of the drop off in speed. There's a slope on my way home whereby I can cover about 1/4 mile with my foot off the accelerator and my comuter showing maximum economy. Slowing earlier for junctions etc. all adds to this effect. I think the swingometer style is the best type of economy guage as it's so visible and responds instantly.
|
|
It can depend on gearing, torque and momentum. My mums car has a V6 with a decently high 6th gear so it needs very little gas to keep its speed up whereas my Daihatsu needs alot more adjustment for hills etc. My mums car has a similar gauage to yours, very useful too, if only to point out its barely doing more than 30 mpg at any time and often alot less!
|
It can depend on gearing torque and momentum. My mums car has a V6 with a decently high 6th gear so it needs very little gas to keep its speed up.
Are you sure thats not just an illusion of economy? A large engined car can be tickled along on light throttle making you think its economical. The reality of an actual fuel return can be shocking. I have had large engined cars with instantaneous fuel meters and even driven carefully they arent very good on fuel. Yes, I have squeezed out some half decent mpg's out of a V6 auto, but drive a "regular" car in the same manner and it'd have been very good on fuel.
|
|
|
|
Back in the 1980's Lada made a Car with an instant (no digital) Fuel Consumption gauge - it was a green bar which seemed to be directly connected to the accelerator pedal.
Drive a Yaris a few years ago, where it would give an instant mpg and the effect was largely the same - felt like it was directly connected to pedal.
Point is if these devices update every few metres then similar to the Lada system.
Can you set the frequency of the mpg updates?
Slopes & momentum mean sometimes possible to hold speed with no accelerator as slope balances friction forces.
|
"it was a green bar which seemed to be directly connected to the accelerator pedal"
It measured manifold air pressure - low MAP = high economy.
|
|
|
In most cars nowadays, if you lift your foot of accelerator, fuel supply is cut off and thus fuel economy reading goes up.
More you accelerate, more fuel you'll use.
|
>>More you accelerate, more fuel you'll use. <<
... and the faster you cruise, because of increased wind resistance.
|
An unmentionable place reported this week:
"Nissan has unveiled a world-first piece of technology designed to help drivers improve fuel economy and produce less CO2 from their cars. It's called the ECO Pedal, and what happens is that if you press harder on the accelerator than the system thinks you need to for the driving situation, the pedal exerts upward pressure on your foot by way of suggesting that you might want to back off.
There's a visual equivalent too, in that a steady green light on the instrument panel starts flashing as you approach the limit of acceptable fuel consumption, and then turns amber at the same time as the ECO Pedal begins to argue with your right foot.
According to internal research by Nissan, the ECO Pedal can lead to fuel efficiency improvements of up to 10%, depending on driving conditions. Nissan plans to commercialise the system next year, though there's no word as yet of exactly when it's likely to be introduced on cars sold in the UK."
|
|
Oh great - a wife in the footwell.
|
Tried that once, long time ago, nearly crashed. Well, she wasn't exactly my wife......
;-))))
|
|
I think fuel consumtion is so simple even I can figure it out. The accelerator is a fuel tap, the more you press the more you use.
|
|
|
|
|
