MPG with C/Control on

[hawk20]

That has got to be the most dangerous use of cc, .

What has? I said I use it to maintain chosen speed in speed limit areas if little traffic -what's wrong with that. If need to slow down for any reason, I have brakes! Means you don't need to keep checking speedo so can concentrate on looking at the road, pedestrians, possible problems etc. Good safety feature.

Limiter can be used instead in speed limit areas with similar benefits IMO. Some prefer one; some the other. I use both from time to time and find both useful.

 

[Dryce]

WIf need to slow down for any reason, I have brakes!

You can also cover the brake pedal with your right foot so no delay in getting it over from the accelerator.

 

[teknow]

I have an A160 Auto.

I too notice that cruise uses more juice. I think it depends how you use it though.

Here is an example.

I have to brake down from 80 to 60. I then re-engage cruise.

My A-class decides to accelerate gradually to just below 70. It then kicks down and gives it "full beans" to 80!

If I were driving, I would have made sure it didn't kick down.

Also, going down to Plymouth on M5 there are some decent hills and it constantly kicks down too.

However, cruise is ace so why worry about petrol?!?!?

 

[Number_Cruncher]

>>My A-class decides to accelerate gradually to just below 70. It then kicks down and gives it "full beans" to 80!

This is a quirk, resulting from the combination of the control law in the cruise control computer, and the way that an automatic gearbox takes an input from throttle position to determine gear change points.

The control law is (most likely) a so-called P+I type. This means that part of the throttle motion demanded by the controller is proportional (P) to the speed error, and part of the throttle motion is some multiple of the integral (I) of the speed error.

So during the aceleration from 60 to 80, although the proportional part of the controller action is decreasing as the speed increases, and the error decreases, the integral action is still increasing throughout the duration. It seems that in this case, the strength of the integrator action is sufficient to apply enough throttle to force a kickdown.

 

[teknow]

>>My A-class decides to accelerate gradually to just below 70. It then kicks down and gives it "full beans" to 80!

This is a quirk, resulting from the combination of the control law in the cruise control computer, and the way that an automatic gearbox takes an input from throttle position to determine gear change points.

The control law is (most likely) a so-called P+I type. This means that part of the throttle motion demanded by the controller is proportional (P) to the speed error, and part of the throttle motion is some multiple of the integral (I) of the speed error.

So during the aceleration from 60 to 80, although the proportional part of the controller action is decreasing as the speed increases, and the error decreases, the integral action is still increasing throughout the duration. It seems that in this case, the strength of the integrator action is sufficient to apply enough throttle to force a kickdown.

CRIKEY!

I always thought it was preprogrammed because in this scenario, you are most likely on a motorway and Mercedes anticipate that getting back to the original speed quickly is safer.

 

[st4]

Psssst .... you have a W211. The only thing you actually control directly is the steering. The accelerator and brakes are bother computer controlled.

I control the inputs to them though

This is a real agree to disagree thread, I just think I drive my car better when my feet use the pedals, and as a result I get better MPG as a I constantly adjust my speed to fit the road conditions.

Take the M8 thru to edinburgh from Glasgow on Friday night, I didn't use CC, I got 40mpg + and it gave me something to do as I was all comfy in my 211.

 

[coupe deville]

Watched a repeat of a topgear prog this afternoon on 'Dave' where JC was driving from London to Edinburgh and back in an Audi A8 4 litre TD on 1 tank of fuel. He checked fuel consumption with CC on and it showed 32mpg. With CC off it showed 38mpg. Admittedly he was driving in a style to get to Edinburgh and back on 1 tankfull but its still a big difference.

 

[Dryce]

Watched a repeat of a topgear prog this afternoon on 'Dave' where JC was driving from London to Edinburgh and back in an Audi A8 4 litre TD on 1 tank of fuel. He checked fuel consumption with CC on and it showed 32mpg. With CC off it showed 38mpg. Admittedly he was driving in a style to get to Edinburgh and back on 1 tankfull but its still a big difference.

You honestly expect CC to get 32 vs 38 for the driver?

We wouldn't even be having this thread if it was that open and shut - on either side!

 

[BTB 500]

Just as an aside, while looking at the story about the couple that have just set an MPG record in the USA I see Shell recommend using CC to aid economy

8. Use cruise control on major roads and in free-flowing traffic

http://www.shell.us/home/content/us...oad/fuels/fuelstretch/fuelstretch_052908.html

 

[st4]

Just as an aside, while looking at the story about the couple that have just set an MPG record in the USA I see Shell recommend using CC to aid economy
http://www.shell.us/home/content/us...oad/fuels/fuelstretch/fuelstretch_052908.html

Shell would say that, so you use more and fill up more often.

 

[BTB 500]

Shell would say that, so you use more and fill up more often.

So all the other tips on that website are wrong as well?

 

[glojo]

Just as an aside, while looking at the story about the couple that have just set an MPG record in the USA I see Shell recommend using CC to aid economy
http://www.shell.us/home/content/us...oad/fuels/fuelstretch/fuelstretch_052908.html

That speaks volumes,
Far be it for me to gossip but when my cousin regularly drives from Florida to Washington DC. They swap drivers with the car blatting along the freeway and yup.... It is in cruise control.

regards
John

 

[st4]

So all the other tips on that website are wrong as well?

Maybe not some of the more obvious ones like check your tyres are in order, just taking economical driving tips from one of the words largest oil companies seems a bit odd, call me a cyncic all you like.

However I've heard what car mention CC as an aide to economical driving. I find that to be bad advice in my experience.

 

[BTB 500]

just taking economical driving tips from one of the words largest oil companies seems a bit odd, call me a cyncic all you like.

OK, you're a cynic.

Why do you think Shell have sponsored a 'mileage marathon' event for the last 30 years?

http://en.wikipedia.org/wiki/Eco-Marathon

Pretty sure I read that some of the UK gas / electricty companies were actually giving 'rewards' to customers who lowered their consumption.

 

[rf065]

Just as an aside, while looking at the story about the couple that have just set an MPG record in the USA I see Shell recommend using CC to aid economy
http://www.shell.us/home/content/us...oad/fuels/fuelstretch/fuelstretch_052908.html

The actual advice in full says, "Use cruise control on major roads and in free-flowing traffic: Maintaining a constant speed can improve gasoline mileage."

It is maintaining a constant speed that improves MPG, not CC per se.
CC is only increasing your MPG is you are incapable of concentrating on your speed, many of us can do that by ourselves and increase MPG even further than CC can.

Russ

 

[Diesel Benz]

It is maintaining a constant speed that improves MPG, not CC per se.
CC is only increasing your MPG is you are incapable of concentrating on your speed, many of us can do that by ourselves and increase MPG even further than CC can.

That sounds interesting. CC increases MPG and the driver adds on top. How did the car move before the two improvements?

 

[rf065]

That sounds interesting. CC increases MPG and the driver adds on top. How did the car move before the two improvements?

Now I remember why I've ignored this thread for so long.

Russ

 

[st4]

OK, you're a cynic.

Why do you think Shell have sponsored a 'mileage marathon' event for the last 30 years?

Be seen to be green - certainly over the last decade anyway there has been a major shift towards discussing so called green behaviours. Its called PR. Politicians are at it, its now un PC to talk about benefiting motorists. Not one party has mentioned major road building and making things better for the British motorist. However plenty has been said about the environment. It was in the Times BTW and this isn't one of my rants, just an observation.

 

[hawk20]

Just as an aside, while looking at the story about the couple that have just set an MPG record in the USA I see Shell recommend using CC to aid economy
http://www.shell.us/home/content/us...oad/fuels/fuelstretch/fuelstretch_052908.html

Great posting but I doubt if you'll convince them. None so blind as those who cannot see. Humans are notoriously bad at concentrating for long periods, while electronics can do it forever. All those who think they are great drivers will, of course, say they can keep a constant speed for mile after mile, but if one measured them scientifically over a long period, we would find the they vary their speed much more than they imagine. That is human nature. Cruise keeps the speed constant; that is its nature.

But this is becoming like kids playing tis, tin't; tis tisn't. Has even one person altered their position?

 

[glojo]

All those who think they are great drivers will, of course, say they can keep a constant speed for mile after mile, but if one measured them scientifically over a long period, we would find the they vary their speed much more than they imagine. That is human nature. Cruise keeps the speed constant; that is its nature.

Totally agree with that but it is really a laboratory situation. I would love to know where we could maintain an EXACT speed anywhere in Devon during the height of the day for 'mile after mile'

There is none so blind as those that cannot see and the USA has hundreds of miles of freeway where cruise control is a great way of making the drive more relaxed just like you have rightly said BUT................... Surely you must agree that it then becomes tempting to allow the concentration levels to lower.. Yes we are all perfect drivers, yes we all have our feet hovering over brakes, accelerators, clutches, heads or even ears. The truth however is there are a huge number of accidents where drivers loose concentration and nod off.

I cannot think of anything more boring than piloting a large airliner at night. I have been in the cockpit and seen pilots doing crosswords, playing games, or a dozen other occupations all to try and keep awake. Disconnect the automatic gadgets and make them concentrate would possibly keep them more alert as opposed to just sitting, looking out a window, but I suppose there is none so blind as those that refuse to see

John