Online Auto School

[incawarrior]

Everything you wanted to know about cars/engines and theory etc. etc. etc.

Pretty kick ass site.

http://www.autozine.org/technical_school/tech_index.htm

[IndianStig]

nice find man

[EmminoDaGreat]

good 1

[incawarrior]

Can I get a sticky... this is fundamental knowledge .....

copy/paste from site.

Example - Honda's 3-stage VTEC

Honda's latest 3-stage VTEC has been applied in Civic sohc engine in Japan. The mechanism has 3 cams with different timing and lift profile. Note that their dimensions are also different - the middle cam (fast timing, high lift), as shown in the above diagram, is the largest; the right hand side cam (slow timing, medium lift) is medium sized ; the left hand side cam (slow timing, low lift) is the smallest.

This mechanism operate like this :

Stage 1 ( low speed ) : the 3 pieces of rocker arms moves independently. Therefore the left rocker arm, which actuates the left inlet valve, is driven by the low-lift left cam. The right rocker arm, which actuates the right inlet valve, is driven by the medium-lift right cam. Both cams' timing is relatively slow compare with the middle cam, which actuates no valve now.

Stage 2 ( medium speed ) : hydraulic pressure (painted orange in the picture) connects the left and right rocker arms together, leaving the middle rocker arm and cam to run on their own. Since the right cam is larger than the left cam, those connected rocker arms are actually driven by the right cam. As a result, both inlet valves obtain slow timing but medium lift.

Stage 3 ( high speed ) : hydraulic pressure connects all 3 rocker arms together. Since the middle cam is the largest, both inlet valves are actually driven by that fast cam. Therefore, fast timing and high lift are obtained in both valves.

Another example - Nissan Neo VVL

Very similar to Honda's system, but the right and left cams are with the same profile. At low speed, both rocker arms are driven independently by those slow-timing, low-lift right and left cams. At high speed, 3 rocker arms are connected together such that they are driven by the fast-timing, high-lift middle cam. You might think it must be a 2-stage system. No, it is not. Since Nissan Neo VVL duplicates the same mechanism in the exhaust camshaft, 3 stages could be obtained in the following way:

Stage 1 (low speed) : both intake and exhaust valves are in slow configuration.
Stage 2 (medium speed) : fast intake configuration + slow exhaust configuration.
Stage 3 (high speed) : both intake and exhaust valves are in fast configuration.

[IndianStig]

vote for sticky

aye