Electrically powered camshaft?

[Nico3d3]

Did anyone ever though of an electrically powered camshaft? It would remove the need for a timing belt/chain and it would then be a lot easier to have infinite variable valve timing. The only possible problem is the size of the electric motor we would need. I know it take around 20% of the power of an engine to drive the timing belt/chain so I'm not sure if it would be feasible

 

[patprimmer]

I think maybe absolutely guaranteed accurate, consistent, reliable synchronisation between crank and cam might be an issue or more to the point, syncronysation between pistons and valves.

While belts have a limited life and have common maintenance issues and chains can be noisy and occasionally have maintenance issues, a well designed gear will be very durable and reliable. Gear driven cams have existed on automotive engines since the 19th century. As this solution is very rare, w must presume i is lack of incentive rather than a lack of technology that gives us cam drives that need expensive maintenance or fail all to often.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[PedroCG]

the fluctuations in rpm of the motor would need to be precisely monitored as well as the ones in the camshaft and "matched" to keep the timing acurate and avoid piston to valve contact... i think theres better ways of CVVT besides, those 20% would stil need to be produced by the engine rigth? CVVT in this case would mean that the motor would need to constantly adjust his speed, the power losses in overcoming the inertial forces would be a bit high i guess.

 

[BrianPetersen]

Heaven help if the electrical system ever blows the wrong fuse ...

Chains, gears, belts guarantee no valve-to-piston collisions as long as components don't physically fail. Phase-shifting by conventional means only happens within defined mechanical bounds, so that there are no collisions.

Using a camshaft still locks you to the same lift and duration. I think your estimate of 20% of engine power to run the camshaft is way high, but whether it's run by mechanical means or by electrics, the power demand is still there.

Lots of disadvantages, no advantages that I can see.

 

[BuntaGR]

Instead of electronic camshaft why don't you think about electomagnetic valves...?

 

[SomptingGuy]

I have never found the camshaft & poppet valve approach technically pleasing. It's almost like a plan B that is merely good enough. So many compromises and constraints. Operating the valves in an even more complicated way is (in my view) adding to the complexity rather than removing it.

I wonder if sleeve valves or equivalent will ever come back. If they do, there may be easier ways to alter their open area profiles dynamically.

- Steve

 

[BrianPetersen]

Sleeve valves have way more friction and are more difficult to seal. So do rotary valves. There have been plenty of other inventions over the years.

The nice thing about a poppet valve is that, when sealed, the parts sealing against each other are not moving relative to each other. Keep in mind that the exhaust side is subject to an extremely nasty environment.

Some people find reliance on springs to close it (and avoid piston-to-valve collisions) to be disconcerting. There is an alternative ... Ducati's desmodromic system that uses another cam lobe to push the valve closed. But, expensive!! Springs work well enough for most people. Pneumatic valve closure works well enough for most of the rest.

It would be nice to infinitely vary valve timing and lift, but that gets complicated and expensive. (BMW Valvetronic)

 

[SomptingGuy]

I wasn't advocating sleeve valves, or a return to piston-ported 2-strokes. Or even any of today's new fangled "paradigm-changing" rotary valve systems.

It's just that whenever I see a fully assembled multi-valve cylinder head (or worse, the bits all laid out) I find myself thinking "Bloody hell, that's complicated", whereas many of the best engineering solutions are beautiful in their simplicity.


- Steve

 

[marcusaurailius]

SomptingGuy, yes 2 strokes, there has been a remarkable advancement over the years,,

direct injection, separate oil system,

its just that they got a bad name in the pollution area,

is this the way,??

regards Marcus

 

[Lou Scannon]

The most advanced IC engines on the planet in the arena of efficiency are low-speed marine diesels. Two-stroke, with overhead valves! I guess the poppet valves have quite a bit to offer, even to the inherently elegant 2-stroke.

 

[malbeare]

Here is an interesting thread
cheers malbeare

http://www.f1technical.net/forum/viewtopic.php?f=4&t=3045

 

[waross]

Years ago I had an automotive manual that was published in the early 1900's. The intuitive perception of the limitations of the poppet valve were recognized even back then. There was a lot of development on alternate valve strategies. There were two main survivors of the many valve schemes that were tried. Poppet valves and cylinder ported valves. The very low compression ratios in use 100 years ago were a lot more forgiving than the higher ratios and combustion chamber pressures common now.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Lou Scannon]

I'm no expert, but sleeve valves had a run for a while in the 30's and 40's. IIRC, the Napier Sabre achieved a record for absolute (for an aero engine) and specific hp at one time.