[musv]

I have to preface this question by saying that i do not know THAT much about engines, but I do know a little. so here goes
I know that the valve timing is mechanincally controlled by the camshaft, so how does variable valve timing work? Does it use some other method, not the camshaft?

 

[Crazyquik]

Re: Question about Variable Valve Timing (musv)

Its sorta hard to explain (at least for me), without a diagram to show, I'll look for one online. There are also various methods of VVT, a cam with 2 sets of lobes on it, with the cam sliding back and forth would be one method. In a pushrod motor, if the pushrods got longer and shorter, or if the fulrum of the rocker arm changed position, those would also give VVT. I forget how the infinently variable BMW setup works.

 

[jaydub]

Re: Question about Variable Valve Timing (Crazyquik)

http://www.howstuffworks.com/question229.htm
that's the best i can do

 

[Crazyquik]

Re: Question about Variable Valve Timing (jaydub)

Here is a diagram of one method, you can see as the tensioning arm moves back and forth it advances and retards the cam, but uses the same single set of cam lobes.

 

[garbage]

Re: Question about Variable Valve Timing (Crazyquik)

F1 or CART engines use pneumatically-actuated valves, giving them unlimited variable-valve timing. http://****************.com/smile/emthup.gif I'm not sure which leauge uses them; I know one does, and the other banned them. I'm pretty sure it's the F1 cars that use them. The lack of camshafts is one of the reasons they can rev up to 18,000 rpms. http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif

 

[Crazyquik]

Re: Question about Variable Valve Timing (garbage)

Its F1, but they do have cams. They dont have valve springs though, they use a compressed gas. The reason revs stabilized for a number of years was the metal valve springs would fatigue and loose thier springiness, so, they got rid of the valvesprings. I think it was Renualt

GM I know has a camless inline 6 test engine. Some other companies surely do as well. Hopefully someone will replace poppet valves with a valve like a camera iris http://****************.com/smile/emthup.gif

 

[FowVay]

Re: Question about Variable Valve Timing (musv)

Here is a good example of the BMW VANOS system:
http://www.bmwworld.com/technology/vanos.htm
Hope this helps. I didn't realize those things were this complicated.

 

[l5gcw0b]

Re: Question about Variable Valve Timing (FowVay)

Some systems change the timing using valves inside the sprocket (to get the same end results as moving the tensioner).
Valves can be "turned on" or "turned off" by disconnecting the valve from the cam using a valve in the follower(this geves you a 2-valve motor below, let's say 4500rpm, and a 4-valve motor above).
BMW's variocam(DUH! sorry, but variocam is Porsche, but BMW calls its new infinitely variale cams valvetronic) is my favorite (short of neumatic F1 valves), using a fulcrum to raise or lower the followers.
My ideal would be a K04 1.8T using Saabs variable compression, and BMW's variocam

[Modified by l5gcw0b, 5:37 PM 2-9-2002]

 

[Jaw]

Re: Question about Variable Valve Timing (l5gcw0b)

quote:[HR][/HR]
Valves can be "turned on" or "turned off" by disconnecting the valve from the cam using a valve in the follower(this geves you a 2-valve motor below, let's say 4500rpm, and a 4-valve motor above).[HR][/HR]​

VTEC-E is kinda like that, except it has one set of intake valves opening normally, and the other opening just a little bit to "swirl" the intake air. At high revs they all open normally.

 

[Double-V]

Re: Question about Variable Valve Timing (Jaw)

It is also important to distinguish between duration and lift when discussing these systems. Some vary only one, some vary both.

 

[Tugz_Vr6]

Re: Question about Variable Valve Timing (Double-V)

Here you go...Straight from the horses mouth...

VTEC IMPLEMENTATIONS
http://asia.vtec.net/spfeature/vtecimpl/vtec1.html
i-VTEC IN DETAIL
http://asia.vtec.net/article/ivtec/index.html
HONDA CVT MULTIMATIC
http://asia.vtec.net/article/mmt/index.html
VTEC MODEL-IMPLEMENTATION CHART
http://asia.vtec.net/spfeature/hondaxref/index.html

Read all this and you will understand VTEC very well.....
http://****************.com/smile/emthup.gif

 

[usdm]

Re: Question about Variable Valve Timing (Tugz_Vr6)

And there is also this. Check the sig below

 

[Crazyquik]

Re: Question about Variable Valve Timing (usdm)

Pretty slick looking setup there usdm. I might try to have some made in about a year or so. Hopefully the size I will need will be available then.
J.

 

[usdm]

Re: Question about Variable Valve Timing (Crazyquik)

quote:[HR][/HR]Pretty slick looking setup there usdm. I might try to have some made in about a year or so. Hopefully the size I will need will be available then.
J.[HR][/HR]​

The ABA is fisrt, and then the AAA, hopefully. What size or motor do you have?