2011 Stop/Start function for saving fuel consumption

[e92zero]

Hi Guys,

I have this thought in my head for a while and was wondering if anyone else have more knowledge about this.

Clarification: I have no problem with the fuel consumption on this car (flame suit on)!

So BMW went on and implemented a stop/start function in our beloved V8 to save fuel consumption (3%?!?) which only helps if you drive in the city a lot. For those of us that drives on freeway pretty much exclusively, this doesn't help fuel consumtion at all. I know our car will cut fuel supply if the car is in gear and you let off the throttle. So cutting fuel supply and not firing the spark is nothing new for engines.

From an engineering standpoint, why didn't BMW incorporate cylinder shut off also for light throttle cruising? Let's say the current engine firing order for 2 cycles is 1-5-4-8-7-2-6-3-1-5-4-8-7-2-6-3

change it to 1- -4- -7- -6- -5- -8- -2- -3 basically skip firing a cyclinder for every other group (12, 34, 56, 78).

Given that we have a V8. This would work better than the other system on the market where they just shut off 1 bank of the cylinders that can potentially cause uneven wear on their engine in the long run. Since our engine spins pretty high at around 3k @ 70 mph, the missing pulses in the cycle should also be hardly noticeable.

This on the other hand should improve our highway rating by 100% which should easily get us out of the gas guzzler tax and help to pass any fleet/epa consumption standard in 2012 or the future ==> They can keep our beloved V8 na engine around for longer instead of going turbo.

The other thread just show people can easily accomplish 20+mpg on the freeway and I hardly imagine we will need all the power all the time on the freeway. If we do, we can turn it off like the stop/start function. Imagine getting 40+ mpg on the freeway.

I know our M3/V8 is nearing the end of it's life/cycle () so this is a moot point. I just wondered why BMW didn't do it from an engineering standpoint when they decide to put in the stop/start function to save fuel consumption.

Another Clarification: I have no problem with the fuel consumption on this car!

Cheers

[Seattle S65B40]

Originally Posted by e92zero

Hi Guys,

I have this thought in my head for a while and was wondering if anyone else have more knowledge about this.

Clarification: I have no problem with the fuel consumption on this car (fame suit on)!

So BMW went on and implemented a stop/start function in our beloved V8 to save fuel consumption (3%?!?) which only helps if you drive in the city a lot. For those of us that drives on freeway pretty much exclusively, this doesn't help fuel consumtion at all. I know our car will cut fuel supply if the car is in gear and you let off the throttle. So cutting fuel supply and not firing the spark is nothing new for engines.

From an engineering standpoint, why didn't BMW incorporate cylinder shut off also for light throttle cruising? Let's say the current engine firing order for 2 cycles is 1-5-4-8-7-2-6-3-1-5-4-8-7-2-6-3

change it to 1- -4- -7- -6- -5- -8- -2- -3 basically skip firing a cyclinder for every other group (12, 34, 56, 78).

Given that we have a V8. This would work better than the other system on the market where they just shut off 1 bank of the cyclinders and causing uneven wear on their engine in the long run. Since our engine spins pretty high at around 3k @ 70 mph, the missing pulses in the cycle should hardly be noticeable.

This on the other hand should improve our highway rating by 100% which should easily get us out of the gas gluzzer tax and help to pass any fleet/epa consumption standard in 2012 or the future ==> They can keep our beloved V8 na engine around for longer instead of going turbo.

The other thread just show people can easily accomplish 20+mpg on the freeway and I hardly imagine we will need all the power all the time on the freeway. If we do, we can turn it off like the stop/start function. Imagine getting 40+ mpg on the freeway.

I know our M3/V8 is nearing the end of it's life/cycle () so this is a moot point. I just wondered why BMW didn't do it from an engineering standpoint when they decide to put in the stop/start function to save fuel consumption.

Another Clarification: I have no problem with the fuel consumption on this car!

Cheers

Interesting write up. Thanks. I don't have enough engineering know-how to chime in on this, but I will say that Start/Stop is dumbtarted on this car. I also heard it sounds like you're stalling every time you come to a light.

[Krozi]

Interesting write up for sure. Changing the firing cycle after every cycle would ensure even wear on engine components. Basically if one cylinder doesnt fire on the first cycle, have it fire on the next cycle and keep switching around.

This idea I actually like. The stupid and pointless stop and go feature is just a marketing gimmick to "fit in" with other car manufacturers. That's why I hate it so much.
Having a system that yields legitimate MPG gains would be very good on the highway.

[e92zero]

hahah, yah, i heard those also. Going forward, every companies will look for way to save fuel consumption, no way around it. But imho, I think cyclinder shut off on the freeway crusing is safer/less intrusive than killing the engine at a light for various reasons.

Cheers.

[BimmerM]

I remember reading about this years ago when GM implemented the exact thing mentioned above on some of their engines. It's nothing new. Perhaps BMW has their reasons.

More info if curious: http://en.wikipedia.org/wiki/Displacement_on_demand

[RandyB]

I'm happy to have missed out on this little gem. I'm not sure how I will ever avoid it with a next-gen car though. What a joke on a car like this - thank goodness it can be turned off in the US at least.

[e92zero]

^ I am glad I missed it also. I got the 2011.00 one.

BimmerM. I remember reading up on the GM version a while back also but that implementation is a bit more complicated with system to deactivate the valves and it's a pre-set group of cylinders that's always deactivated. I don't think deactivating a set group of cylinders is a good design since it will cause uneven wear in the engine in the long run. I might be wrong on this.

What I am thinking is pretty much half way of our existing complete fuel cut off (in gear lift off throttle coasting). It's more or less in the line of skipping a firing beat for each cylinder but in the end all cylinders are still working to even out the load on the engine components. Should only require a change in the software programming? Or maybe I am over simplying the implementation. BMW probably has a good reason that we are not aware of. Just fun discussion/speculation for us outsiders.

Cheers.

[SamS]

Originally Posted by RandyB

I'm happy to have missed out on this little gem. I'm not sure how I will ever avoid it with a next-gen car though. What a joke on a car like this - thank goodness it can be turned off in the US at least.

It's not that big of a deal... you actually have to turn it on, i.e. it is off by default in the US.

[pmccut]

Originally Posted by SamS

It's not that big of a deal... you actually have to turn it on, i.e. it is off by default in the US.

I must be one of the few that likes the feature. It seems to do a nice job when I'm driving around downtown stopped at a light 75% of the journey.

+ If you replaced your stock exhaust it's a nice sound when the engine fires back up

[-=Hot|Ice=-]

Calling RadiationJoe...

[Kurohouou]

It really isn't bad at all. Its never on by default, so if you never want to worry about it. Just do what every other M3 driver does. Turn the car on and drive. Unless you manually turn it on you don't have it... Still I like having the option at least as I drive through a few long lights on my way to work. About 1/3 of my trip is sitting at stop lights.

[piloto]

I don't know if when tested on the European fuel consumption cycle (as well as C02 emission during the same test), the cylinder shutoff will have a bigger affect than total engine shutdown at a stop. I think the cylinder deactivation is a better solution for actual use, but I suspect BMW's decision is more based on meeting regulatory standards, especially the European standard, where idling is included in both the urban and extra-urban (highway) cycles.

Below is an excerpt of what the Euro standard is (taken from http://www.fuelsaver.govt.nz/explain.html)

"The European test method
There are two parts to the European fuel consumption test, an urban and an extra-urban cycle. The cars tested have to be run-in; that means they must have been driven for at least 3,000 km before testing.

Urban cycle
The urban test cycle is carried out in a laboratory at an ambient temperature of 20°C to 30°C on a rolling road from a cold start; ie, the engine has not run for several hours. The cycle consists of a series of accelerations, steady-speed driving, decelerating and idling. The maximum speed is 50 km/h, the average speed is 19 km/h and the distance covered is four km. The urban cycle is repeated four times.

Extra-urban cycle
This cycle is conducted immediately after the urban cycle, and consists of about half steady-speed driving and the rest accelerations, decelerations and some idling. The maximum speed is 120 km/h, average speed is 63 km/h and the distance covered is seven km.

Combined fuel consumption figure
The results of the urban and extra-urban cycles are combined and presented as the final figure. This is arrived at by averaging the two parts of the test and weighting them by the distances covered in each part.

[kmarei]

Originally Posted by e92zero

Hi Guys,

I have this thought in my head for a while and was wondering if anyone else have more knowledge about this.

Clarification: I have no problem with the fuel consumption on this car (flame suit on)!

So BMW went on and implemented a stop/start function in our beloved V8 to save fuel consumption (3%?!?) which only helps if you drive in the city a lot. For those of us that drives on freeway pretty much exclusively, this doesn't help fuel consumtion at all. I know our car will cut fuel supply if the car is in gear and you let off the throttle. So cutting fuel supply and not firing the spark is nothing new for engines.

From an engineering standpoint, why didn't BMW incorporate cylinder shut off also for light throttle cruising? Let's say the current engine firing order for 2 cycles is 1-5-4-8-7-2-6-3-1-5-4-8-7-2-6-3

change it to 1- -4- -7- -6- -5- -8- -2- -3 basically skip firing a cyclinder for every other group (12, 34, 56, 78).

Given that we have a V8. This would work better than the other system on the market where they just shut off 1 bank of the cylinders that can potentially cause uneven wear on their engine in the long run. Since our engine spins pretty high at around 3k @ 70 mph, the missing pulses in the cycle should also be hardly noticeable.

This on the other hand should improve our highway rating by 100% which should easily get us out of the gas guzzler tax and help to pass any fleet/epa consumption standard in 2012 or the future ==> They can keep our beloved V8 na engine around for longer instead of going turbo.

The other thread just show people can easily accomplish 20+mpg on the freeway and I hardly imagine we will need all the power all the time on the freeway. If we do, we can turn it off like the stop/start function. Imagine getting 40+ mpg on the freeway.

I know our M3/V8 is nearing the end of it's life/cycle () so this is a moot point. I just wondered why BMW didn't do it from an engineering standpoint when they decide to put in the stop/start function to save fuel consumption.

Another Clarification: I have no problem with the fuel consumption on this car!

Cheers

so why do you have a problem with the fuel consumption on this car?

[e92zero]

^That was to protect myself from people jumping in saying if you worry about fuel consumption, you shouldn't get the m3, etc.

Just wondered if BMW went the route to implement a system that cut down on fuel consumption, why not this.

Piloto: Thanks for the insight on the EU test cycle.

[goldminer]

Originally Posted by e92zero

Hi Guys,

I have this thought in my head for a while and was wondering if anyone else have more knowledge about this.

Clarification: I have no problem with the fuel consumption on this car (flame suit on)!

So BMW went on and implemented a stop/start function in our beloved V8 to save fuel consumption (3%?!?) which only helps if you drive in the city a lot. For those of us that drives on freeway pretty much exclusively, this doesn't help fuel consumtion at all. I know our car will cut fuel supply if the car is in gear and you let off the throttle. So cutting fuel supply and not firing the spark is nothing new for engines.

From an engineering standpoint, why didn't BMW incorporate cylinder shut off also for light throttle cruising? Let's say the current engine firing order for 2 cycles is 1-5-4-8-7-2-6-3-1-5-4-8-7-2-6-3

change it to 1- -4- -7- -6- -5- -8- -2- -3 basically skip firing a cyclinder for every other group (12, 34, 56, 78).

Given that we have a V8. This would work better than the other system on the market where they just shut off 1 bank of the cylinders that can potentially cause uneven wear on their engine in the long run. Since our engine spins pretty high at around 3k @ 70 mph, the missing pulses in the cycle should also be hardly noticeable.

This on the other hand should improve our highway rating by 100% which should easily get us out of the gas guzzler tax and help to pass any fleet/epa consumption standard in 2012 or the future ==> They can keep our beloved V8 na engine around for longer instead of going turbo.

The other thread just show people can easily accomplish 20+mpg on the freeway and I hardly imagine we will need all the power all the time on the freeway. If we do, we can turn it off like the stop/start function. Imagine getting 40+ mpg on the freeway.

I know our M3/V8 is nearing the end of it's life/cycle () so this is a moot point. I just wondered why BMW didn't do it from an engineering standpoint when they decide to put in the stop/start function to save fuel consumption.

Another Clarification: I have no problem with the fuel consumption on this car!

Cheers

I'm not sure that this will work. On most engines that have cylinder deactivation they don't just stop delivering fuel and spark. They disable the valves on that bank as well, keeping them closed. This causes the compressed air in the cylinders to act like a spring thereby significantly lessening the amount of energy required to spin the engine against dead cylinders. I don't think you could alternate, every 2 rpm, the cylinders which have their valves deactivated let alone the complexity of doing this to 2 sides of the engine, not just one.

Also, I wonder if the BMW has enough low-rpm torque to do it. Cylinder deactivation is usually done on large, low-reving American V8s.

[e92zero]

^I see, thanks for the insight. I didn't think too much about the spring effect of keeping the valve close, the pumping lost, and the low end torque of our engine. I just thought if they can cut all fuel and spark to the entire engine during coasting, why not give us half of that. hehehe, my silly thoughts.

Cheers.