# Valvetronic: what's the point?



## carve (Nov 3, 2008)

Someone was mentioning the efficiency improvement of valvetronic in another thread. I was thinking about it, and it just doesn't make any sense to me. Maybe someone can set me straight here.

In order to run your gasoline SI engine at less than max torque at a given rpm (without running really lean like diesels do), you MUST reduce the amount of air entering the cylinders. Most engines do this by reducing the pressure by throtteling it down with a butterfly throttle valve. Valvetronic throttles the engine by varying valve lift, down to miniscule amounts. The motor must work just as hard to draw in air against this restriction as it must to draw in air against a throttle valve. That's the whole POINT of a throttle of any kind- to have a pressure drop. If it were any other way and the pressure drop, and therefore pumping losses, were reduced, it would be the equivelent of having the throttle open more than intended.

So, it seems valvetronic must necessarily cause exactly the same pressure drop as a throttle valve. It is a much heavier, more complex, less reliable, and more expensive method of doing this. M engines don't tend to use it, and the N53 got rid of it in favor of having room for direct injection. What's the point of valvetronic?


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## carve (Nov 3, 2008)

I just thought of a good analogy. A throttling system that provides a lower pressure drop is like getting brake pads with a lower coefficient of friction. Friction is their JOB. Now you just need to push the brake pedal harder (close the throttle more) to generate the same amount of friction (pressure drop).


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## gtxragtop (Feb 25, 2008)

carve said:


> Someone was mentioning the efficiency improvement of valvetronic in another thread. I was thinking about it, and it just doesn't make any sense to me. Maybe someone can set me straight here.
> 
> In order to run your gasoline SI engine at less than max torque at a given rpm (without running really lean like diesels do), you MUST reduce the amount of air entering the cylinders. Most engines do this by reducing the pressure by throtteling it down with a butterfly throttle valve. Valvetronic throttles the engine by varying valve lift, down to miniscule amounts. The motor must work just as hard to draw in air against this restriction as it must to draw in air against a throttle valve. That's the whole POINT of a throttle of any kind- to have a pressure drop. If it were any other way and the pressure drop, and therefore pumping losses, were reduced, it would be the equivelent of having the throttle open more than intended.
> 
> So, it seems valvetronic must necessarily cause exactly the same pressure drop as a throttle valve. It is a much heavier, more complex, less reliable, and more expensive method of doing this. M engines don't tend to use it, and the N53 got rid of it in favor of having room for direct injection. What's the point of valvetronic?


Frankly, I doubt the complexity is worth the 5% increase in efficiency. If I had a choice, I would not want it. Something expensive to break. By using lower valve lifts at low RPM and load, the VE (Volumetric efficiency) is higher. http://en.wikipedia.org/wiki/Valvetronic
Interesting read.... http://www.sfsa.org/tutorials/leverarm/index.htm


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## carve (Nov 3, 2008)

From wikipedia....
_
"volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions"_

So, throttling an engine reduces volumetric efficiency intentionally. Valvetronic may help at wide open throttle, but in that scenario it is like any other engine and any of the myriad of variable timing and lift systems out there would do the same even with their butterfly throttle valves. It still doesn't make any sense.


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## TRWham (Aug 21, 2004)

I am not a big fan of Valvetronic, but you are ignoring the impact of duration. By shortening the opening duration, not just relative timing, of the intake valve, Valvetronic reduces pumping losses to zero whenever the valve is closed (when flow is zero, so is pressure drop). In effect, the engine can take a short, but deep breath, rather than a long, shallow one to intake the air it needs to meet the current demand for power.


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## carve (Nov 3, 2008)

TRWham said:


> I am not a big fan of Valvetronic, but you are ignoring the impact of duration. By shortening the opening duration, not just relative timing, of the intake valve, Valvetronic reduces pumping losses to zero whenever the valve is closed (when flow is zero, so is pressure drop). In effect, the engine can take a short, but deep breath, rather than a long, shallow one to intake the air it needs to meet the current demand for power.


That would make sense since once the valve is closed, you basically have an air spring inside the cylinder until the piston goes back up in it's stroke to the point where the valve closed. However, I'm pretty sure valvetronic only varies lift. It does this by varying the leverage ratio between the cam & the valve via a linkage, so cam profile, timing, etc. are all the same- only the lift changes.


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## TRWham (Aug 21, 2004)

No, according to what I have read, including the wiki referenced above, it also controls duration.


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## enc0re (Nov 26, 2006)

The point of Valvetronic is not to be a fancier throttle. It's to control the amount of valve lift.
Low RPM, low lift = efficient, smooth
High RPM, high lift = more power

Lots of sporty NA motors have variable valve lift, e.g.:
Nissan VQ35/VQ37
Toyota 2ZZ-GE


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## carve (Nov 3, 2008)

TRWham said:


> No, according to what I have read, including the wiki referenced above, it also controls duration.


I just re-read it, and some of the links as well. Valvetronic controls lift only via the "lift scaler" link and stepper motor. Do a search for a pic of the linkage and you'll see it can do lift only. It is still generically considered a "VVT" system, but it only controls lift- not timing or duration. _VANOS _controls the timing by advancing the entire camshaft(s) in relation to the crankshaft. It controls ONLY timing and not lift, duration, overlap, or anything else. I suppose Valvetronic lets BMW catch up to some of the other VVT technologies that can vary lift, and even surpass them by a little by offering finer gradations in lift instead of just having increments.

Check out the picture in this thread and you'll see why it can only change lift...

http://www.explorerforum.com/forums/showthread.php?t=150304

So, I guess that solves it. VANOS varies timing by rotating the entire camshaft relative to the crank, and Valvetronic varies lift continualy on top of that. Combined, they offer a continously variable system instead of the incrementally varied system such as VTEC. The advantage of VTEC, however, is that it can also vary duration and opening/closing rates as well as overlap by offering up completely different cam profiles.- something VANOS/Valvetronic can not do since they're always using the same basic cam profile no matter how they manipulate it. VTEC also has a much simpler linkage system and so is much more suitable on high-rpm engines like the NSX and S2000.

Edit- OK...for some reason, VANOS is set up to only offer a couple of big increments crossed over at a particular rpm, much like VTEC. Only a few fixed positions of cam advance were available; high, medium, or off. Only Double VANOS varies continously, and can change exhaust and intake independently, offering a very limited degree of control over overlap on one side of the stroke at the expense of the other side. I don't believe any BMW valve control system can change duration.


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## DSXMachina (Dec 20, 2007)

carve said:


> _I just re-read it, and some of the links as well. Valvetronic controls lift only via the "lift scaler" link and stepper motor. Do a search for a pic of the linkage and you'll see it can do lift only. It is still generically considered a "VVT" system, but it only controls lift- not timing or duration. VANOS controls the timing by advancing the entire camshaft(s) in relation to the crankshaft. I used to think VANOS was like VTEC and varied timing continously and lift in increments, but it only works on timing. I suppose Valvetronic lets BMW catch up to some of the other VVT technologies that can vary lift, and even surpass them by a little by offering finer gradations in lift instead of just having increments.
> 
> Check out the picture in this thread and you'll see why it can only change lift...
> 
> ...


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## carve (Nov 3, 2008)

> I believe you are seriously in error there. Double Vanos changes duration when it changes lift. It can also as you know change timing.


No- it can only change timing. It allows for the intake cam to rotate up to 60 degrees relative to the crank, and the exhaust to rotate up to 25 degrees, and that's all it does. I don't think it can control lift or duration at all, which I also thought it could until today. This actually makes valvetronic make some kind of sense. The reason I started this thread is because it didn't make much sense to have all that hardware just to have a throttle. Now that I see BMW had no way to control valve lift AT ALL before Valvetronic, it makes sense.

The modest rpm limitations and complexity of valvetronic, along with the inability to control duration or overlap on both sides of the stroke are shortcomings of Double VANOS/Valvetronic compared to VTEC. The ability to control lift and timing continously instead of incrementally are advantages. The latest iVTEC is especially superior since it has VANOS-esque cam phasing (intake cam only) in addition to the regular VTEC cam profile switching features. iVTEC is essentially VANOS + VTEC. It's too bad they don't switch patents- it seems VTEC is better for performance, and D.VANOS/Valvetronic might be better for emissions and efficiency.

edit: nevermind that last part. It seems Honda is about to release "Advanced VTEC", which continously varies timing, lift, AND duration.


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## TRWham (Aug 21, 2004)

Think about it- if you can control lift, then you also can control duration by driving lift to zero earlier than the cam profile would normally allow.


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## carve (Nov 3, 2008)

TRWham said:


> Think about it- if you can control lift, then you also can control duration by driving lift to zero earlier than the cam profile would normally allow.


NO- it is a simple lift scaler. It varies the cams lift by a percentage. When lower-lift is selected, it takes just as much time to open and close the valve- the valve just moves slower since it's traveling a smaller distance.

VANOS can drive the valve closed sooner, but it must open it sooner in order to do that, and the total time the valve is open will be the same.


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## TRWham (Aug 21, 2004)

My last post on the topic: Study the kinematics of the design and you will see that the effective profile of the cam does, in fact, change, because the shape of the portion of the cam follower in contact with the cam changes. There are several videos out there that show enough detail for you to figure it out. Try this one:


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## DSXMachina (Dec 20, 2007)

Hi Carve, I have to agree with TRWham, the Variable Nockenwellen Steuerung (VANOS) setup seems to me to vary duration at the same time it is changing lift. Do we agree on these definitions?
Timing: The angular period of the camshaft, in relation to the crankshaft, during which the camshaft lobes cause intake or exhaust valves to open and close. (Note that the length of time, in degrees of rotation, during which the cam keeps a valve open does NOT change.) Like spark timing, the net effect is to open and close valves at a different point in a piston's travel.
Lift: The vertical travel of a valve, or the difference in diameter between the smallest and largest cross sections of a cam lobe. (Discounting valve lash as a variable.)
Duration: The total number of degrees of cam rotation during which a lobe keeps a valve open.


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## ProfessorCook (Jan 19, 2009)

They way I understand it, VANOS provides continuously variable valve timing and Valvetronic provides variable valve lift.


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## carve (Nov 3, 2008)

DSXMachina said:


> Hi Carve, I have to agree with TRWham, the Variable Nockenwellen Steuerung (VANOS) setup seems to me to vary duration at the same time it is changing lift. Do we agree on these definitions?
> Timing: The angular period of the camshaft, in relation to the crankshaft, during which the camshaft lobes cause intake or exhaust valves to open and close. (Note that the length of time, in degrees of rotation, during which the cam keeps a valve open does NOT change.) Like spark timing, the net effect is to open and close valves at a different point in a piston's travel.
> Lift: The vertical travel of a valve, or the difference in diameter between the smallest and largest cross sections of a cam lobe. (Discounting valve lash as a variable.)
> Duration: The total number of degrees of cam rotation during which a lobe keeps a valve open.


I'll agree with your definitions, but I disagree about VANOS. As professorcook said, it only controls the timing. Valvetronic controls the lift. There is no function to control duration on BMW engines.

All VANOS does is affect the camshaft position relative to the crankshaft. Please explain how that would affect lift or duration.

All valventronic does is very the leverage ratio, and therefore lift, between the cam and the valve. Please explain how that would affect timing or duration.


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## DSXMachina (Dec 20, 2007)

Hi carve. OK, here's how I thought Vanos varied duration. I know it can be done by this method but will admit that I could be wrong as to whether Vanos employs it: By having an adjacent cam type device, which acts on the pivot points of rockers activated by the primary cam, which acts on the valve stems, duration could be varied wirthout affecting lift. 
I "thought" this is how BMW did it (control duration) but you've got me wondering. I will research it for confirmation. TRWham's video references would be where I started. I wish he'd come back and take us through the mechanical aspects which vary duration.


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## carve (Nov 3, 2008)

Hi...I thought VANOS was like BMW VTEC and could control lift & duration, too (until yesterday). That's why I thought valvetronic didn't make sense. Now that I see VANOS did less than I though, valvetronic makes sense.


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## Andrew*Debbie (Jul 2, 2004)

FWIW,

A few minor points and corrections:

Valvetronic engines DO have a throttle butterfly. It is used during engine start and for limp home mode. During normal driving valvetronic controls throttle.

Single VANOS is not used on any current or recent BMW. First introduced in 1992, single VANOS engines vary the intake cam only. Single VANOS cars adjust the valve timing at two set points. You can see the points in the power / torque curves.

Dual VANOS engines vary the intake and exhaust timing continuously. There are no set points.

All Valvetronic cars are also dual VANOS. It is part of the system.

I think the first production car with a Valvetronic engine was the 2001 316ti. That car wasn't sold in the US. 2002 7 series had a valvetronic V8.



> What's the point of valvetronic?


Smoother more immediate power delivery.
Improved cold engine performance.
Reduced emissions.
Improved fuel economy.


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## DSXMachina (Dec 20, 2007)

Thanks AD. Can you shed any light on the duration variation discussion?


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## carve (Nov 3, 2008)

Andrew*Debbie said:


> FWIW,
> 
> Smoother more immediate power delivery.
> Improved cold engine performance.
> ...


I think, more to the point, Valvetronic is there *to have a variable valve lift system* in order to realize those advantages. When I started this thread, I thought VANOS also varied lift and Valvetronic was _only for throttleing the engine_. If that were the case, you'd have just as much of a pumping loss as with a butterfly throttle, prompting the question "what's the point". However, using valvetronic to throttle the engine is more of a 'why not?...we can quickly adjust lift to any level', than the main point of the system.


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## invariant (Jun 19, 2007)

Yes, the way I understand it, valvetronic only controls (scales) valve lift, and VANOS advances/retards valve timing.

*Theoretically* speaking, valvetronic could be used to control duration by continuously scaling lift while the cam lobe slides along the follower (i.e. effectively changing cam lobe geometry) via complicated control algorithms, but it would require a very fast electric motor. I think it can't be done with the one that has a reaction time of 300 ms end-to-end (a cam lobe strikes the follower every 20 ms at 6000 RPM).

Edit: I just re-read TRWham's post "the effective profile of the cam does, in fact, change, because the shape of the portion of the cam follower in contact with the cam changes". Still, in this case the valve lift can't be controlled separately from duration.


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## Andrew*Debbie (Jul 2, 2004)

carve said:


> I think, more to the point, Valvetronic is there *to have a variable valve lift system* in order to realize those advantages.


Correct. Valvetronic minimizes pumping losses by controlling valve lift.

The way I best understand this is that the motor isn't working to pump air out of the intake manifold. During normal operation there isn't significant manifold vacuum. One of the uses for the throttle butterfly is to develop manifold vacuum during engine start.

Combining variable valve lift with variable valve timing, and the variable length intake manifold allows very precise tuning of airflow through engine.

Our last two cars, X3 3.0si and MINI Cooper both have valvetronic motors. It does work.

BMW added a valvetronic head to a 1.4L 75HP Peugeot engine. The results are a 95HP 1.4L and a 120HP 1.6L motor that get better gas milage then the original 75HP motor. I've driven the same car with both versions of the 1.4L engine and there is no comparison.

Found these BMW drawings on the 'web. Best I've found.


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## jesimmons (Jan 11, 2008)

Here's another... From a 2007 BMW Technical Pub.


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## gtxragtop (Feb 25, 2008)

invariant said:


> Yes, the way I understand it, valvetronic only controls (scales) valve lift, and VANOS advances/retards valve timing.
> 
> *Theoretically* speaking, valvetronic could be used to control duration by continuously scaling lift while the cam lobe slides along the follower (i.e. effectively changing cam lobe geometry) via complicated control algorithms, but it would require a very fast electric motor. I think it can't be done with the one that has a reaction time of 300 ms end-to-end (a cam lobe strikes the follower every 20 ms at 6000 RPM).
> 
> Edit: I just re-read TRWham's post "the effective profile of the cam does, in fact, change, because the shape of the portion of the cam follower in contact with the cam changes". Still, in this case the valve lift can't be controlled separately from duration.


So we agree that duration is modified at the same time lift is modified.


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## gtxragtop (Feb 25, 2008)

carve said:


> From wikipedia....
> _
> "volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions"_
> 
> So, throttling an engine reduces volumetric efficiency intentionally. Valvetronic may help at wide open throttle, but in that scenario it is like any other engine and any of the myriad of variable timing and lift systems out there would do the same even with their butterfly throttle valves. It still doesn't make any sense.


Read this http://www.bimmerfest.com/pdf/2007-BMW-Engine-Mechanical.pdf Then decide on my comments on VE. 

And this http://autospeed.com/cms/A_110859/article.html


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## DSXMachina (Dec 20, 2007)

A*D, thanks for posting those pictures. Wow, they quickly illustrate what I was stumbling around trying to say in an earlier post! The mechanism is complicated (compared to a non variable OHC) but very effective in accomplishing its mission. What staggers me is the software mapping that must be behind optimizing all that movement. I tried to find an illustration before I posted my comment but couldn't, your series did the trick.


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## Andrew*Debbie (Jul 2, 2004)

carve said:


> Valvetronic may help at wide open throttle, but in that scenario it is like any other engine and any of the myriad of variable timing and lift systems out there would do the same even with their butterfly throttle valves. It still doesn't make any sense.


BMW's overall goal for the fleet is increased performance, increased fuel economy and decreased emissions. That's why these cars have valvetronic.

Valvetronic isn't there to help at full power. At full power it would be running at full valve lift, same as a fixed lift system. If anything peak performance is limited because of the additional complexity in the valve train. I'd guess a valvetronic motor's power would fall off at 7000+ RPM.

BMWs highest performance motors don't use valvetronic. In the N54 turbo it would be redundant. The turbocharge also minimizes pumping losses.

The N45B20S motor in the 320si does not have valvetronic. You also get a 7300 RPM red line and a car that is one seconds faster 0-60 than an N46B20 powered 320i.

The S65 motor in the M3 doesn't have valvetronic either.

===

Valvetronic improves daily drivability and emissions. Wider torque and power bands make for an easy drive. And you get improved economy. We are getting an honest 40mpg in our MINI Cooper. Even our big heavy X3 3.0si without full Efficient Dynamics gets 20mpg in city driving.


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