Variable Valve Timing, Lift, & Duration

[donjetman]

Will this turnout to be as problematic as GMs AFM/DOD system? or a win, win, win?

http://list.powerautomedia.com/lt.php?s=994065588c267f26a1bf1da2022ce5b6&i=9809A10042A26A1378799

 

[iamdub]

Can someone explain this to me in layman's terms? I know the lobe isn't "growing" or "shrinking". Is it more of a timing thing where the active part of the lobe is slowed down?

 

[wjburken]

Will this turnout to be as problematic as GMs AFM/DOD system? or a win, win, win?

http://list.powerautomedia.com/lt.php?s=994065588c267f26a1bf1da2022ce5b6&i=9809A10042A26A1378799

That’s pretty damn ingenious! I would say that this will be a lot more reliable than AFM/DOD as it doesn’t rely on the timing of oil pressure/flow.

 

[Larryjb]

I'll try. I looked at the video, which actually explains it fairly well. On our camshafts, and Fords as well, the lobes are fixed to the cam shaft. As the cam turns, the lobe turns exactly with the shaft. In Hyundai's new system, the lobe is not fixed to the cam shaft. So, as the cam shaft turns, the lobe is able to "pause" while holding the valve open. (The lobe is not actually "pausing", it is just rotating slower than the camshaft, keeping the valve open longer.)

However, this has a completely different purpose from GM's AFM or DOD. GM developed a way to keep the valves open on the disabled cylinders. VVT, VVD, and VVL would not be able to keep a valve open during a compression stroke.

As for reliability, I presume that oil quality will be just as critical as in VVT, and GM's AFM systems. The cam would need to have special requirements for lubrication, and I imagine that VVD would be controlled by oil pressurized solenoids. Poor quality or old oil would have a detrimental effect on the solenoid operation which would cause a failure of the VVD system.

OOPS... I didn't finish watching the video.... It is not operated with oil solenoids. But it does have small oil ports. If the oil sludges, you would still have trouble though.

 

[Larryjb]

That’s pretty damn ingenious! I would say that this will be a lot more reliable than AFM/DOD as it doesn’t rely on the timing of oil pressure/flow.

Didn't GM improve the lifter and oil system operating the DOD? I thought that as long as you kept up with oil changes and use quality oils that the DOD system was extremely reliable now.

 

[wjburken]

Didn't GM improve the lifter and oil system operating the DOD? I thought that as long as you kept up with oil changes and use quality oils that the DOD system was extremely reliable now.

I don’t know if I would say “extremely” reliable. GM definitely learned some lessons and made big improvements, but the basic design relies on precision timing of oil pressure changes. The chance of failure has been significantly reduced and regular oil changes are a key to that.

 

[iamdub]

... as the cam shaft turns, the lobe is able to "pause" while holding the valve open. (The lobe is not actually "pausing", it is just rotating slower than the camshaft, keeping the valve open longer.)

It slowing down was how I was trying to grasp the concept. It would have to slow down then snap back to it's originating position with every rotation, yet altering that position and time that it's slowed down based on RPM. Just seems like an astronomical amount of activity going on, and I'm sure that engine revs to 6,000 at least. I'm not nay-saying, just marveling at the mechanics... That I don't understand.

 

[Larryjb]

It slowing down was how I was trying to grasp the concept. It would have to slow down then snap back to it's originating position with every rotation, yet altering that position and time that it's slowed down based on RPM. Just seems like an astronomical amount of activity going on, and I'm sure that engine revs to 6,000 at least. I'm not nay-saying, just marveling at the mechanics... That I don't understand.

I see...

If you stand beside the center of a merry-go-round, and it takes 10 seconds to make one complete circle, you go a very small distance in 10 seconds so you are actually moving slowly. If you move to the edge of the merry-go-round, you are actually moving faster because you are having to travel a greater distance in the same 10 seconds. Note that the merry-go-round hasn't changed it's rotational speed of one revolution every 10 seconds.

What would happen if the pivot of the merry-go-round were actually not in the center, but off to one side? People sitting on the little horsey that's closest to the pivot would move slowly while those on the horsey farthest away from the pivot would be moving faster.

Now imagine a merry-go-round that can move it's pivot from side to side! When the pivot starts in the center, everyone moves at the same speed. Then the pivot moves to one side and people on one side start moving faster while the people on the opposite side move more slowly.

The valve stem only cares about how fast the cam lobe comes by. So, the faster moving cam lobe will result in a shorter opening time for the valve while a slower moving lobe would result in a longer opening time.

So far, this doesn't explain why the lobe seemed to move faster, then slower for each rotation. This is because our merry-go-round was attached to the pivot. If the cam lobe were attached directly to the cam shaft, the lobe would be moving farther and closer to the valve stem. Note that at 8:26, the camshaft center and lobe center did not actually change itself. Rather, the center of the "gearing" changed its center.

At 9:17, the "slider" is like our merry-go-round. As it slides one direction, the pivot moves to one side or the other like the pivot of our merry-go-round could change. But, the valve stem is not riding on the slider. Instead, the cam lobe is attached to the slider. Remember that the merry-go-round had a fast and slow end. So does the "slider". As the slider rotates the cam, the fast part of the slider will speed up the lobe for half the rotation, but then the slow end of the slider will slow the lobe for the other half of the rotation.

 

[iamdub]

I see...

If you stand beside the center of a merry-go-round, and it takes 10 seconds to make one complete circle, you go a very small distance in 10 seconds so you are actually moving slowly. If you move to the edge of the merry-go-round, you are actually moving faster because you are having to travel a greater distance in the same 10 seconds. Note that the merry-go-round hasn't changed it's rotational speed of one revolution every 10 seconds.

What would happen if the pivot of the merry-go-round were actually not in the center, but off to one side? People sitting on the little horsey that's closest to the pivot would move slowly while those on the horsey farthest away from the pivot would be moving faster.

Now imagine a merry-go-round that can move it's pivot from side to side! When the pivot starts in the center, everyone moves at the same speed. Then the pivot moves to one side and people on one side start moving faster while the people on the opposite side move more slowly.

The valve stem only cares about how fast the cam lobe comes by. So, the faster moving cam lobe will result in a shorter opening time for the valve while a slower moving lobe would result in a longer opening time.

So far, this doesn't explain why the lobe seemed to move faster, then slower for each rotation. This is because our merry-go-round was attached to the pivot. If the cam lobe were attached directly to the cam shaft, the lobe would be moving farther and closer to the valve stem. Note that at 8:26, the camshaft center and lobe center did not actually change itself. Rather, the center of the "gearing" changed its center.

At 9:17, the "slider" is like our merry-go-round. As it slides one direction, the pivot moves to one side or the other like the pivot of our merry-go-round could change. But, the valve stem is not riding on the slider. Instead, the cam lobe is attached to the slider. Remember that the merry-go-round had a fast and slow end. So does the "slider". As the slider rotates the cam, the fast part of the slider will speed up the lobe for half the rotation, but then the slow end of the slider will slow the lobe for the other half of the rotation.

Ok, that I can picture better. I'll watch it again!

Your first part reminds me of a discussion I had with an idiot. I was installing an automated driveway gate for a customer and his neighbor came over to inspect and question the speed of the electric operators. I told him the manufacturer lists them as taking 10 seconds to move the gate 90°. He said that spec was useless info and false advertising and wanted to know what size of gate the manufacturer was referencing because (in his example) "a single 12' gate would take twice as long as a 6' gate to swing 90°". He asserted that he was an engineer and I was wrong and that I should've sold the customer a dual 6' setup because 20 seconds is too long of a wait.