Toymods Car Club Inc: Tech & Conversions => New stepless throttless valvetrain

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manolis
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Registered:
July 2003

Re: New stepless throttless valvetrain

Wed, 02 July 2003 09:33

oldcorollas wrote on Tue, 01 July 2003 18:30

it looks like an interesting idea, although i think there are a few issues to .... a toyota K type enigne i'll be glad to try it Wink

Cya, Stewart

Hello from Greece.
The flattening of the valve opening graph at max lift is only because the cam lobe profile was selected to have a specific simple form, for demo reasons.
The real cam profile of the prototype is shown many times in the Theory, images and photos page of the site, and the resulting valve lift graph is quite different than the demo one.
The top curve could be, according the profile of the cam lobe, even a pure sinusoidal curve. We have already an easy method to calculate and create the necessary cam lobe profile in order to achieve any desirable valve opening graph. Just note that even with a pure sinusoidal top curve, the lower curves are somewhat deformed, but there the inertia loads are very light in comparison.

The expected longevity of the mechanism in real driving conditions is better than the conventional valve train system.
The normal car operates most of its life in low revs and partial loads, where the new system operates actually unloaded, as the valve springs are only partially compressed. Compare this case to the idling (or low revs) operation of the conventional engine having the 80lbs/240lbs valve seat pressure you mentioned. The cam lobe has to compress completely the strong springs, while the timing belt or chain has to provide the necessary impact torque.
No matter how strong the valve springs are, you can rotate at idling (which means 0.15 to 0.2 mm valve lift) the camshaft of the new system (with the timing belt removed) easily, just by your small finger. Try the same in a conventional head.
The new system is loaded as the conventional system only at its maximum valve lift operation. And this maximum valve lift is necessary only at high revs with full load. Anywhere else the new system operates with lower loads than conventional.

On the other hand, if by real driving you mean racing use, things are not significantly different. Any moment you operate the engine at lower than maximum revs or at partial load, the valve springs, valve seats, cam lobes, timing belt and the rest components of the valve train system take a short or long breath that extends their life and delays fatigue.
By the way, what is the percentage of time that a racing engine operates at its maximum revs with full load?

The small push rods with the spherical ends, do seem weak.
But their 4 mm diameter, their 25 mm length form center to center and the 6 mm diameter of their spherical ends could easily change to 8 mm, 25 mm and 12 mm without changing the basic design.
In practice the small push rods gave no indication that they are overloaded.
Just compare the contact surface between the small spherical end and the corresponding hemispherical cavity to the case of Toyota Celica GTS (or VVTLi), where the rocker arm and the top valve stem have an actually point or line contact. Surface contact against line or point contact.

Thanks
Manolis Pattakos

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