Helical Camshaft - Practical Considerations

Practical Considerations

The disadvantage of this system is its cost. Even though it is a fairly simple device it requires very accurate helical machining and very careful assembly. The Helical Camshaft prototypes typically cost about $1500 in machining and materials. This figure would reduce greatly in production. The cost of the Helical Camshaft is really only high when considered in comparison to a conventional camshaft which reportedly cost the manufacturers only a few dollars per unit to make. This fact does tend to make the Helical Camshaft look more expensive than it really is. Having said this, the cost of the Helical Camshaft (and associated controls etc.) is probably very similar to (or even cheaper) than other production VVA systems.

The various prototypes have never shown any wear or ultimate strength (breakage) problems in the many hours of testing (some at very high RPM) they have undergone. But as a production car camshaft must ideally last for the life of the vehicle, there must remain some doubt until really long-term testing is carried out. However, indications are that there would probably be no insoluble long-term problems.

A helical camshaft must operate through a lift-multiplying pivoting follower. The Helical Camshaft could not really be used with an inverted bucket type of follower. Even though the inverted bucket is still used, it is being increasingly replaced both in road and racing engines by the pivoting “finger” follower. As well as needing a pivoting follower, if the engine has four valves per cylinder then the follower must be forked so that the one Helical Camshaft lobe operates two valves. This is more a characteristic than a problem. If a really wide duration range is required, because axial space is somewhat limited along the camshaft, usually only room for one Helical Camshaft lobe (and its operating space) can be found.

A helical camshaft cannot do very short durations or variable lift. Many companies and manufacturers have made it appear that it is something of a virtue that their particular VVA system produces very short durations and the linked low valve lift as they really have had no choice.

It should be noted that there is no physical reason why a Helical Camshaft could not be the “driving” cam in a Valvetronic-type oscillating cam setup. (But it would be quite complex and the Valvetronic part of the arrangement would limit the Helical Camshaft’s high RPM capabilities). The result would be an almost unbelievable array of possible duration/lift combinations. This could be very useful in research. However, in the real world probably 95% of the combinations have no really useful relevance to the four-stroke cycle. This, of course also applies to the Helical Camshaft to some extent. It is hard to imagine a use for more than about 400 degrees – and the Helical Camshaft potentially has another 300 or so degrees in hand.