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BMWs Valvetronic: How It Works

ExplorerDMB

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vt_works.jpg

Valvetronic


Note: This doesn't have to deal with Explorers, but is just a good way to understand how evolved the automotive world is becoming with computers.


Valvetronic is currently only available on the V-12 and the V-8 (7 series). It is a great concept in engine "breathing." It varies valve lift to such a great degree, that the intake valves efectively assume the function of the traditional engine throttle (it replaces the butterfly). Since intake air does not have to snake around the throttle - the engine delivers quicker, more spontaneous response to the accelerator pedal, along with high power output, more refined operation, excellend cold starting, and low engine friction.

The Valvetronic system has a conventional intake cam, but it also uses a secondary eccentric shaft with a series of levers and roller followers, activated by a stepper motor. Based on signals formerly taken mechanically from the accelerator pedal, the stepper motor changes the phase of the eccentric cam, modifying the action of the intake valves. Most accelerator pedals are no longer attached with a cable; they are now just sensors that will send the information to the computer (seen now on some Chevrolets).

The Valvetronic engine does not require a timing belt or chain. Valvetronic has its own computer housed in a separate unit away from the engine management system, networked with the digital engine management system incorporating a 40-megahertz, 32-bit computer.

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Operating Parameters:

-Valve lift is variable between 0 and 9.7 mm.
-Adjustment of the worm gear from one extreme to the other takes 300 milliseconds.
-Combined with double-Vanos valve timing technology, the camshaft angle relative to the crankshaft can be adjusted by up to 60°.
-The intermediate arm is finished to a tolerance of 0.008 mm.
-The cams controlling the eccentric shaft are machined to tolerances of a few hundredths of a millimeter.

Additional Benefits:

-In Valvetronic engines coolant flows across the head, resulting in a temperature reduction of 60%.
-The water pump size is cut in half, reducing power consumption by 60%.
-The power steering fluid is warmed quickly, reducing the power used by the hydraulic pump.
-Mounting the water and power pump on the same shaft and a heat exchanger between coolant and engine oil reduces oil temperature by 30%.

The downside is that at above 6,000 RPM valvetronics effeciency drops quickly since stronger valve springs are required. The stronger springs create higher friction losses. Don't except to see the Valvetronic system on any M series vehicles produced by BMW.



-Drew
 




ExplorerDMB

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Dodge/Chrysler is using a similar design which controls the cylinders. MDS is what it's called. On the Hemi's - it'll shut down 4 cylinders while crusing, but when needed will kick the 8-cylinders back in. Saves a great amount of fuel.

-Drew
 




BrooklynBay

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I was just wondering if those engines are the "interference type", meaning if the timing goes haywire, will the valves collide with the cylinders? That was a common problem on some of the older engines that have a timing belt. I'm sure that some engines with timing chains might have been susceptible. A while ago, engineers were designing engines that used individual electric solenoid valves with each cylinder. Did anything happen with that idea? Valvetronic seems to be more on the simple side compared to the complexity of that design, since it is only partially electronic. If they would use all electric valves, they wouldn't have the 6,000 RPM drawback, since they wouldn't have to worry about spring tension. The computer would control which valves would be open, and closed for a given period of time.
 




gijoecam

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OK, here's the million-dollar question: If valve lift goes to zero, how does the engine keep running?? I suspect that in normal operation, it can't go to zero. The engine would stop breathing.

MDS technology is really nothing new (but this valvetronic concept is completely different).... MDS is being touted as something revolutionary, but it was around back in the 70s. The electronics have simply progressed to make it more reliable. It's a completely different beast than this though. MDS still opens and closes the valves normally, just like a conventional engine.

Personally I prefer the old mechanical stuff. The more we count on electronics to run our engiens, the closer we get to having Bill Gates run our engines. I don;t want to re-boot on the freeway when my engine freezes at WOT!

-Joe
 




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