MPG with C/Control on

[flango]

can't believe we are still debating this one!!!!!!

 

[st4]

can't believe we are still debating this one!!!!!!

There is nothing to debate, CC is a PITA.

 

[Diesel Benz]

Interestingly, you haven't offered a shred of evidence to support your theory, yet you rubbish the statements of someone with a MSc in Automotive Engineering? That's my last word on the subject as it going nowhere.
Russ

I'm hesitating to comment when you stated this was your last comment on this thread. Please feel free to respond as I don't want to count on you not coming back.

I'd like to say that I have a higher grade on physics but I'm still not asking members to count on my view or knowledge but I've provided them physical facts that everyone can use to conclude themselves.

The evidence you provided in an earlier post had no theory supporting the views. The statement as I understood was just that the engine runs with least fuel if it is throttled smoothly. I can only refer to MB documentation, I cannot copy the info here but since the modern CC is implemented by the ECU, there is no better info available to run the engine properly taking into account fuel consumption. If you want to keep constant speed, the modern cruise makes it with the least fuel consumption.

I'll attach an example MB engine efficiency plot, try to imagine the average for the different driving styles over the plot!

I'm not going to put my helmet on (I'm counting on the fact that there is at least the English Channel between us ).

 

[hawk20]

Interestingly, you haven't offered a shred of evidence to support your theory, yet you rubbish the statements of someone with a MSc in Automotive Engineering? That's my last word on the subject as it going nowhere.

Russ

Actually, if you read carefully what I said, I do offer a shred of evidence.

 

[Dieselman]

Looks like it's going to be windy down South.

 

[oldcro]

Surely if the very small amount of fuel used by engaging cruise control and or using the aircon is such an issue then consider a change of car to a more economical one.

 

[st4]

Surely if the very small amount of fuel used by engaging cruise control and or using the aircon is such an issue then consider a change of car to a more economical one.

You're actually right, I don't like CC as I don't like it, not because of 1-2mpg which wallet wise I won't really see. So there we have it, if you're finding the consumption the overiding factor in to "engage or not to engage" your car isn't the car for you.

 

[glojo]

I stopped posting on this thread because those that believed it was more economical to drive using cruise control were simply not listening to the sound reasons being put forward that disagreed with their reasoning.

However on our local TV we have just listened to a driving expert who competed in the recent 400 mile Green marathon thingie. He laughed when asked about cruise control and stated that this aid will brake if a car exceeds the set speed whereas the human being will see that there is no need for this. The most important issue regarding economical driving is.....

'Forward observation and anticipation'.

His words not mine

I can put my hand on my heart and honestly say that I never primed this expert. All he is saying all blatant common sense which any competent driver will accept.

I fear that some folks are being blinded by theoretical numbers and not looking at the real picture.

Forget setting the cruise control at 70mph, put it at 60mph.

If the car goes down a gradient then it will brake to keep its speed at the required level. The human brain however will survey the situation and might say there is no need to brake I will lift off the throttle. Now common sense tells me that lifting off the throttle will cut the fuel supply to a level that is negligible, but cruise control has braked our vehicle and kept the throttle at the required speed. if the car gains momentum then once more the brakes will be applied and this will keep going until the road conditions alter. The sensible driver wins every time.

Here is an extract of some tips for economical driving.

[FONT=Arial, Helvetica, sans-serif]Smarter Driving Tips[/FONT]

• [FONT=Arial, Helvetica, sans-serif]The challenge is to first measure your MPG – either by checking your car’s on-board computer or the manufacturer’s manual – and see if you can improve upon it by:[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Changing up through the gears at between 2,000 and 2,500 rpm[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Ease your speed. Driving at 70mph uses around 15 per cent more fuel than at 50mph[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Anticipate to avoid unnecessary acceleration and braking[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Use air conditioning sparingly as it greatly increases fuel consumption[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Switch off the engine whenever safe to do so[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Check tyre pressures regularly[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Remove unnecessary weight from your car[/FONT]
  • [FONT=Arial, Helvetica, sans-serif]Reduce aerodynamic drag whenever possible, e.g. by removing roof racks when not in use.[/FONT]

These are not my tips and are extracted from the marathon site, but note one ill informed member of this forum suggested that it was economical to use 'brisk' acceleration to quickly get to the desired speed.

I will quote from this site:

Anticipate road conditions and drive smoothly, avoid sharp acceleration and heavy braking. This saves fuel and reduces accident rates.

This is tip 2 on the home page of this event.

Now if anyone can improve the claimed economy figures by 30% and do this by continually engaging cruise control then I want to sit in their car and witness it because it is to put it crudely.............. tosh. If you want to drive economically then you will never beat the human brain. Folks wanted facts well log onto the site and see how the latest Chevrolet faired:

a Chevrolet Corvette Z06 with a manufacturer’s combined mpg of 19.2, managed to achieve 30.96mpg, an improvement of 61.26 per cent, despite its massive seven-litre engine. Driver and navigator Richard Hammond and Carla McAlpine proved that even so-called ‘gas guzzler’ sports cars can be driven more economically.

This CVhevrolet was driving on he perscribed route which was NOT flat clinical labority type conditions. They went up hill down dale and through our towjns and cities. a 61% improvement is not to be laughed at or dismissd. We wanted facts, we wanted figures, but I bet those that still think it more economical to use cruise control will still say black is white.

Many posts ago I suggested the following:

Anyone that is really interested in improving their driving skills should consider taking an advanced driving course. It will make you a better driver, a safer driver and by improving your observation skills, it will also save you fuel.

This was also suggested on the TV interview and this expert has been retained by a large national company to give lessons to their many drivers.

Regards
John the cheeky

 

[Dieter]

Hi,

I don't care one iota whether c.control is more efficient than one's right foot or not...but I will take umbrage with the words of the above so-called expert (not John).

'Normal' cruise control (not adaptive) only controls engine speed, NOT the brakes.

My practical experience is that even when I reduce speed (using cruise control) the system appears to rely on engine braking...not brake breaking...so no fuel supplied (hence mpg on trip can/will/does increase dependent on total miles travelled). It also changes down through the gears...so I'm afraid this so-called expert is blowing hot air.

If, as I and others have said, fuel consumption is the be all and all raison d'etre for driving...buy a more economical car or go by bus.


Cheers,

 

[st4]

Thanks John, proves what I already know and do Funny you mention the MPG marathon as me and a pal were discussing doing it next year.

You didn't make this big enough so just to spell it out once more

'Forward observation and anticipation'.

 

[glojo]

Hi,

I don't care one iota whether c.control is more efficient than one's right foot or not...but I will take umbrage with the words of the above so-called expert (not John).

'Normal' cruise control (not adaptive) only controls engine speed, NOT the brakes.

My practical experience is that even when I reduce speed (using cruise control) the system appears to rely on engine braking...not brake breaking...so no fuel supplied (hence mpg on trip can/will/does increase dependent on total miles travelled). It also changes down through the gears...so I'm afraid this so-called expert is blowing hot air.

If, as I and others have said, fuel consumption is the be all and all raison d'etre for driving...buy a more economical car or go by bus.


Cheers,

Hi Dieter,
I have no idea of how the system works but this is an extract from the 211 manual

Cruise control

Cruise control maintains a constant road speed for you. It brakes automatically in order to avoid exceeding the set speed. On long and steep downhill gradients, especially if the vehicle is laden or towing a trailer, you must shift to a lower gear in good time or select shift range 1, 2 or 3 in vehicles with automatic transmission*. By doing so you will make use of the braking effect of the engine, which relieves the load on the brake system and prevents the brakes from overheating and wearing too quickly.

We use Cruise control on long journeys and really like it so I have no issues either way, but I wonder how much engine braking there is at 60mph in the highest gear when going down hill?

Regards
John

 

[Dieselman]

On cars with SBC the brakes can be applied to steady the speed but with regular braking systems this isn't used.
I think the term braking refers to engine braking, which CC will do, whereas a driver would allow the speed to build so as to make use of the additional free momentum after the incline had finished.

 

[Number_Cruncher]

>>to make use of the additional free momentum

Where do get this free momentum from - I want some!

 

[glojo]

On cars with SBC the brakes can be applied to steady the speed but with regular braking systems this isn't used.
I think the term braking refers to engine braking, which CC will do, whereas a driver would allow the speed to build so as to make use of the additional free momentum after the incline had finished.

I think we could twist the wording to mean what your saying but they specifically mention engine braking when using lower gears.

This is an extract from the C-class manual and I don't think they use SBC:

Me thinks someone needs to apologise regarding the braking issues

Cruise control may be unable to maintain the stored speed on uphill gradients. The stored speed is resumed when the gradient evens out. Cruise control maintains the stored speed on downhill gradients by automatically applying the brakes

Just like I suggested earlier, some folks will simply never accept certain things that are clearly correct and I think we have seen more than enough proof now.

Regards
John

 

[Dieselman]

Where do get this free momentum from - I want some!

Try Beachy Head..

 

[Dieter]

Hi,

I also am not mechanically/electronically familiar with exactly how c.control (not adaptive, which obviously uses the brakes) but my subjective feeling is that it does not (tangibly) operate the brakes.

This Wikipedia ( ) link appears to confirm above:

http://en.wikipedia.org/wiki/Cruise_control

Also this article does not mention effect on brakes as none of the 3 components act on the braking system

http://www.mbca.org/pages/tech/MBCA_Troubleshooting_cruise_cont.htm

Just so we agree that we are all singing from the same hymn sheet I agree that "forward observation and anticipation" is the pre-requisite for driving per se.... but there appears to be an innuendo that somehow using cruise control negates this fact....Why? How?

Perhaps I should give up while I am behind

Cheers,

 

[hawk20]

Just shows how wrong experts can be. MB's do not apply the brakes (or most of them don't). So that reason for better economy from humans is completely flawed.

Secondly it is complete nonsense to suggest you cannot use forward thinking and anticipation with cruise. You have to or you would crash. Provided you do that, and you accelerate yourself back to cruising speed (when held up by traffic or whatever) then it is pretty obvious that cruise will give the same economy at a steady speed as a human at the same steady speed.

I stopped posting when it was clear that those who thought cruise did not do as well in MPG as humans were not listening to the opposing arguments.

Interesting from the wikipedia link: -

"Some of those advantages include:

• Its usefulness for long drives across sparsely populated roads. This usually results in better fuel efficiency. "

 

[Diesel Benz]

Just shows how wrong experts can be. MB's do not apply the brakes (or most of them don't).

I was about to comment that this is not right. I remember someone reporting that the face lift W211 would apply brakes when necessary to keep the speed steady on CC. I accepted this view even in the thread and assume the same from Distronic Plus but then I tried to have this confirmed from documents but I did not find anything.

Is it actually that people confuse engine braking with CC from real braking with brakes? Even the W211 before face lift does change to a lower gear if the speed exceeds the CC set value on a downhill road. I have not tested this on strong downhill sections on any of the W211 or W221.

Distronic Plus does use brakes if the radar detects the distance to the one ahead is reducing at a too high speed (where engine braking is not sufficient). But this is a different scenario from what we are talking about here.

Anybody able to refer to some MB documentation confirming this?

 

[Dryce]

I was about to comment that this is not right. I remember someone reporting that the face lift W211 would apply brakes when necessary to keep the speed steady on CC.

I believe the non-facelift W211 will use braking if engine braking is insufficient.

One aspect of CC that isn't mentioned is the controls. MB have it completely right with the single stalk IMHO. The CC systems on Ford, Saab, Vauxhall, Fiat, and Range Rover are fiddlier and less simple - particularly in terms of simply nudging the stalk to disengage and pulling back to resume.

 

[glojo]

Anybody able to refer to some MB documentation confirming this?

The quotes I was using were directly from the Mercedes-Benz handbook and I'm smiling as I am typing because if you use engine braking then you will surely be changing down ......... which means the engine will rev higher for the given speed which will mean that the engine is using more fuel?? I'm enjoying this debate because it seems so simple. Cruise Control is a comfort type feature and NOT an economy one.

Is Wikepedia a better source of information regarding the operation of options for the modern Mercedes or is the relevant owners manual a better choice?

What about someone goes down a gradient at 60mph, sets there Cruise Control for 50 mph and then see what it does? Will it slow the car quicker than if a driver merely lifts their foot off the throttle and let the car do its own thing be that gain momentum or gradually slow?

Remember using engine braking on a modern 5, or even 7 speed box will require downshift or shifts to have any real effect and then the engine will be revving faster which to my understanding will use more fuel than a slower revving engine.

John