MPG with C/Control on

[Dieselman]

Surely that recalls the last speed set?

I thought it was press up (increase / down (decrease) to the pressure point for 1mph and beyond pressure point for 5mph?

The first pull is to recall, subsequent ones add 1mph.

 

[rf065]

No reason at all why using the limiter should give better mpg.

Doing a constant 70 uses the same amount of energy whether you control the fuel input yourself or let electronics do it for you.

The limiter will ensure your speed does not creep up inadvertently.
Quite often I start a long journey at 70mph & end up doing 80 or 90mph.
In those circumstances using it should give better mpg.

There is a technique where after reaching your cruising speed, you relax the pressure on the accelerator and the car will maintain that speed without slowing down but using less fuel, cruise control cannot do this. There are more extreme techniques used by "Hypermilers" (http://www.motherjones.com/news/feature/2007/01/king_of_the_hypermilers.html)
to eke out the most mpg possible. Cruise control is like a computer, it only does what it is programmed to do, and that is to keep a constant speed, it does not care how much fuel it uses to do that & any driver with a bit of knowledge and practice can better it.


Russ

 

[Dryce]

Cruise control is like a computer, it only does what it is programmed to do, and that is to keep a constant speed, it does not care how much fuel it uses to do that & any driver with a bit of knowledge and practice can better it.

The CC system in principle 'knows' more about what is going on in your engine than your right foot does.

Furthermore don't assume that the position of said right foot bears any direct relationship to the actual fuel being fed to the engine. On modern cars it's just giving an electrical input to the car's computer which then does its own thing

 

[flango]

The CC system in principle 'knows' more about what is going on in your engine than your right foot does.

Furthermore don't assume that the position of said right foot bears any direct relationship to the actual fuel being fed to the engine. On modern cars it's just giving an electrical input to the car's computer which then does its own thing

I doubt that very much as it is just another input into the computer and has no direct link to engine function or outputs all it does is tell the computer please maintain x mph the computer then does the rest.

On modern cars the accelarator might just be giving out a signal on drive by wire systems but that signal is proportional to the force on the pedal hence harder the pedal is pushed the faster the car will go, (see my earlier post on sprintboosters and this). The cars computers or ECU will never do their own thing they will operate within defined limits depending upon what signals they are receiving and will work on pre defined engine maps for a particular scenario

A good driver will listen to the car and get to know what sounds right and more importantly will recognise small changes in that sound to realise something is wrong. Lets not forget the human brain is a far more powerful processor of information than any computer you will find on a car.

 

[Dryce]

A good driver will listen to the car and get to know what sounds right and more importantly will recognise small changes in that sound to realise something is wrong. Lets not forget the human brain is a far more powerful processor of information than any computer you will find on a car.

At a macro level your ear can do a reasonable job. But things have changed.

Back in the old days your ear used to tell you if the car was say pinking. You don't hear cars pinking or knocking these these days because there's that little black box adjusting things behind the scenes.

There are multiple fast loop feedback systems that deal with things way before the feedback system that involves the driver gets a chance to respond.

 

[flango]

At a macro level your ear can do a reasonable job. But things have changed.

Back in the old days your ear used to tell you if the car was say pinking. You don't hear cars pinking or knocking these these days because there's that little black box adjusting things behind the scenes.

There are multiple fast loop feedback systems that deal with things way before the feedback system that involves the driver gets a chance to respond.

What about when the little black boxes screw up? I have seen no end of cars brought in pinking and knocking as a result of failed ecu components, if you are not listening then presumably you drive on unaware creating yet further damage and destruction?

You might want to consider the earlier post " You are in control of the car not the other way around" Driver intervention can save serious engine damage when the computer fails, therefore driver response in this scenario is critical as the little black box wont sort it out

 

[rf065]

The CC system in principle 'knows' more about what is going on in your engine than your right foot does.

Furthermore don't assume that the position of said right foot bears any direct relationship to the actual fuel being fed to the engine. On modern cars it's just giving an electrical input to the car's computer which then does its own thing

I'm afraid you could not be more wrong with both of those statements.
I've searched the net for a more technical explanation as some people seem to think CC was invented as an aid to increase fuel consumption, the best explanation I can find is the following...............

"As somewhat of an expert in automotive engineering (i hold an MSc in it) i can say that the use of cruise control does effect your MPG but in a negative way.

Yes staying at a constant speed is a good way to increase your MPG and cruise control would be fine if every road in the world was flat and level, however it is not and resistance from different road surfaces, weather and all sorts of other things causes problems.

The reason for this is that most cruise control systems work by operating your throttle control for you in order to stay at a regular speed, as your speed drops the cruise control opens up the throttle incrementally until the speed is brought back to its correct state. The problem is that because cruise control doesn't know about hills or different conditions it will start to 'feather' the throttle. This is to say keep coming on and off it in order to balance your speed. You might not feel it while driving but it is doing it.

This can seriously effect the fuel efficiency of your engine as it needs a constant and smooth throttle operation in order to work its best. Ultimately only humans at this point and provide this."

Russ

 

[Dryce]

What about when the little black boxes screw up? I have seen no end of cars brought in pinking and knocking as a result of failed ecu components, if you are not listening then presumably you drive on unaware creating yet further damage and destruction?
[/qoute]

But that's remedial behaviour by the driver. Not normal driving.

If you hear a bang or see an orange light appear then you should respond appriopriately.

And these days you're more likely to see the orange light come on rather than hear a problem when it comes to combustion processes.

You might want to consider the earlier post " You are in control of the car not the other way around" Driver intervention can save serious engine damage when the computer fails, therefore driver response in this scenario is critical as the little black box wont sort it out

This scenario is doesn't have much to do with cruise control.

There has been a change in the way mechanical things are controlled - whether it be a printer, CD player, or a car engine system. It used to be that things were precision machined and calibrated. You selected a control position and the actuators would move appropriately. There might be some feed back somewhere.

Modern systems are based on feedback systems. Your CD player positions its laser using positional feedback and some crappy non-precision plastic mechanical components to hold things in roughly the right position. (Some of the early CD players were beautifully machined - and then by around 87/88 they went all plastic). Your car deals with timing and fuel injection using feedback. You don't set an exact actuator position or open a valve a set amount - you roughly set it and then twiddle it a bit and see what happens and if you don't like it you twiddle it a bit more. And if you really don't like what happens you record an error and set the engine check light - and if you really really don't like what's going on you limp or shutdown.

Chances are the engine check light comes on well before the driver notices
a problem.

 

[wemorgan]

This can seriously effect the fuel efficiency of your engine as it needs a constant and smooth throttle operation in order to work its best. Ultimately only humans at this point and provide this."

I don't have a strong view one way or the other whether CC improves MPG. But as someone who does use CC on the motorways I often find cars overtaking me, then slowing down, I overtake, then they accelerate again and all of this on a flat straight quiet stretch of road.

So I am sure there are many non users of CC who do correctly maintain and adjust their speed correctly that benefits MPG, but from my experience there are still plenty of drivers out there not paying attention and randomly adjusting their speed which surely cannot improve MPG.

 

[flango]

What about when the little black boxes screw up? I have seen no end of cars brought in pinking and knocking as a result of failed ecu components, if you are not listening then presumably you drive on unaware creating yet further damage and destruction?
[/qoute]

But that's remedial behaviour by the driver. Not normal driving.

If you hear a bang or see an orange light appear then you should respond appriopriately.

And these days you're more likely to see the orange light come on rather than hear a problem when it comes to combustion processes.



This scenario is doesn't have much to do with cruise control.

There has been a change in the way mechanical things are controlled - whether it be a printer, CD player, or a car engine system. It used to be that things were precision machined and calibrated. You selected a control position and the actuators would move appropriately. There might be some feed back somewhere.

Modern systems are based on feedback systems. Your CD player positions its laser using positional feedback and some crappy non-precision plastic mechanical components to hold things in roughly the right position. (Some of the early CD players were beautifully machined - and then by around 87/88 they went all plastic). Your car deals with timing and fuel injection using feedback. You don't set an exact actuator position or open a valve a set amount - you roughly set it and then twiddle it a bit and see what happens and if you don't like it you twiddle it a bit more. And if you really don't like what happens you record an error and set the engine check light - and if you really really don't like what's going on you limp or shutdown.

Chances are the engine check light comes on well before the driver notices
a problem.

Sorry but you a relying on computers again a bit OTT this but many mercs dont even bring on the check light when they have a fault, my 230 clk recently had a failed lamda sensor did it bring on a check light NO, did I notice something was wrong YES

Peoples reliance on computers never ceases to amze me, its like school kids now that can't do maths without a calculator beggers belief!!

 

[flango]

I'm afraid you could not be more wrong with both of those statements.
I've searched the net for a more technical explanation as some people seem to think CC was invented as an aid to increase fuel consumption, the best explanation I can find is the following...............

"As somewhat of an expert in automotive engineering (i hold an MSc in it) i can say that the use of cruise control does effect your MPG but in a negative way.

Yes staying at a constant speed is a good way to increase your MPG and cruise control would be fine if every road in the world was flat and level, however it is not and resistance from different road surfaces, weather and all sorts of other things causes problems.

The reason for this is that most cruise control systems work by operating your throttle control for you in order to stay at a regular speed, as your speed drops the cruise control opens up the throttle incrementally until the speed is brought back to its correct state. The problem is that because cruise control doesn't know about hills or different conditions it will start to 'feather' the throttle. This is to say keep coming on and off it in order to balance your speed. You might not feel it while driving but it is doing it.

This can seriously effect the fuel efficiency of your engine as it needs a constant and smooth throttle operation in order to work its best. Ultimately only humans at this point and provide this."

Russ

This is the definitive answer from someone obviously well qualified in the subject and without wanting to sound like a "trekkie" you cannot change the laws of physics which apply here, hence CC has a negative Impact on Fuel economy. Nuff said.

 

[Dieselman]

I don't have a strong view one way or the other whether CC improves MPG. But as someone who does use CC on the motorways I often find cars overtaking me, then slowing down, I overtake, then they accelerate again and all of this on a flat straight quiet stretch of road.

So I am sure there are many non users of CC who do correctly maintain and adjust their speed correctly that benefits MPG, but from my experience there are still plenty of drivers out there not paying attention and randomly adjusting their speed which surely cannot improve MPG.

Probably because it's incredibly hard to maintain a set speed. I doubt posters on here that say they do, actually do in reality.
I notice this trait all the time when 'on cruise'.

I think CC does use more fuel but not because of fine control deviations as they will have little bearing due to momentum being conserved, but because the CC will attempt o accelerate up hills and decelerate down them. A driver would allow a slight rolling off of speed whilst going uphill and increase momentum whilst going down, as that wouldn't take much additional fuel but would carry a benefit further on.
It also tends to accelerate back to a set speed more quickly, so hold a lower gear longer than an economical driver would.


I love CC and use it all the time.

 

[Dryce]

I'm afraid you could not be more wrong with both of those statements.

OK then I own up.

I have never designed an engine control and monitoring system. I have no idea what a 51 or C196 is. And I've never been near large diesel plant, military diesel engines, turbines, industrial plant of any kind, or anything remotely electrical or hydraulic.

It was all a dream.

I apologise. My imagination runs away with me all the time.

Just don't ask me what colour the boathouse at Hereford is.

 

[Dieselman]

Peoples reliance on computers never ceases to amze me, its like school kids now that can't do maths without a calculator beggers belief!!

Or spell without spell checkers....

 

[Dryce]

Peoples reliance on computers never ceases to amze me,

Clearly cars are a lot worse than they used to be in the seventies. All these evil little microsprocessors getting in the way.

However. As regards fault recording and display there is a difficult balance between having an check or warning light on almost continually because of lots of deviations from spec or silently recording faults.

 

[flango]

Or spell without spell checkers....

Damn computers again!!!! duff wireless keyboard, you never had this with Typewriters! ( Not living in the dark ages honest) but must get around to buying a new keyboard

 

[flango]

Clearly cars are a lot worse than they used to be in the seventies. All these evil little microsprocessors getting in the way.

However. As regards fault recording and display there is a difficult balance between having an check or warning light on almost continually because of lots of deviations from spec or silently recording faults.

Cars are obviously better now as technology has moved on but my point was don't rely on the computer / microchip as sooner or later it will screw up, maybe without warning?

 

[Dryce]

So I am sure there are many non users of CC who do correctly maintain and adjust their speed correctly that benefits MPG, but from my experience there are still plenty of drivers out there not paying attention and randomly adjusting their speed which surely cannot improve MPG.

Those who lose against CC will be the ones who allow their speed to consistently rise. Drag will get them.

Those who drop off their speed might well see an apparent gain over CC because in reality their average speed may be lower than they realise.

 

[BTB 500]

Just don't ask me what colour the boathouse at Hereford is.

Good film

 

[wemorgan]

Good film

Sure is.......to tentatively return back to topic.....the S8 looked like it was driven with the CC set at 100mph around those mountain roads