vvt, cylinder deactivation etc.

[carnage1]

I am familiar with some of the types of VVT conceptually, but how are they really being implemented in production vehicles? Also what method are the manufacturers using to deactivate cylinders? It seems like you could just turn off injectors selectively but I'm guessing it is not that simple.

 

[dcasto]

VVT = Variable Valve Timinig, they are everywhere now. The last into the market was Mitsibishi on their 2 liter engine. GM, Ford, Toyota, Honda, Subaru all have VVT. The latest and most complex is the Toyota VVTL-i. It has variable valve timing and variable valve lift with a computer based "intellegent" system to optimize engine performance and to keep from over stressing the engine.

DOD = displacement on demand or cylinder deactivation. In this case solinoids open the intake and exhaust valves in a sequence where exhaust gases are trapped in the cylinder and just recirculate.

 

[patprimmer]

At least Honda has dual camshafts for both inlet and exhaust valves. It uses a locking pin in the rocker arm to lock the rocker to one cam follower to change camshafts on the run. I believe the Ivtec version runs big cam, 2 valve per cylinder at low speed, small cam at 4 valves per cylinder mid range and big cam 4 valve at top end. The locking pins are operated by oil pressure via solenoids controlled by the ECU. The two cam profiles have different duration and lift and probably also different lobe centres.

Most other manufacturers use a simple advance retard mechanism on the cam/s at the cam drive pulley and call it something like vtec, like vvtt or whatever.



Regards

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[MechanicalChef]

http://auto.howstuffworks.com/camshaft2.htm

DOD isn't quite as simple as just cutting fuel to the cylinder. Of course, that must be done, but there is also a valve control component as well. There are greater losses to be minimized by stopping the pumping action. So, the intake valve ceases to open, and the exhaust valve is always closed. Hence, no throughput of gasses.

It's much more efficient to let the piston compress the air, and then let the compressed air in turn push the piston back down. Work in = work out - frictional losses

By pumping air, less energy is conserved, and pumping losses (intake stroke and exhaust stroke) are added to frictional losses.

 

[SonyAD]

Doesn't DOD lead to uneven wear?

 

[patprimmer]

Yes, probably unless they change the deactivated cylinders regularly. That would also stop the plugs loading up.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TDIMeister]

Cylinder deactivation systems most commonly implemented at the moment use a lost-motion mechanism controlled by hydraulics.