Operation
The duration of the Helical Camshaft is changed by moving the outer shaft of the coaxial arrangement in a lengthwise (or axial) direction. The helix angle of the Helical Camshaft is probably always going to be around 30 to 35 degrees. The helix angle has its origin in the width of the segment used (normally about 10 mm or 0.39 in) and the 20-degree region of constant radius on the nose of the lobe (this usually measures about 7 mm in circumference). The diagonal split line across this area thus must generally be at about 35 degrees to the axis of the camshaft. This translates to a figure of around 3.5 (crankshaft) degrees per millimetre of axial movement. 30 mm (1.2 in) of movement would give 105 degrees of duration change. Although the Helical Camshaft is capable of far more than this, it has been found in testing that this amount is sufficient for most purposes.
Little force is needed to move the shaft axially so there is a possibility that when using the Helical Camshaft for LIVC load control alone the axial movement could be could be connected directly and mechanically to the accelerator pedal. Similarly, if the Helical Camshaft is used to improve high RPM power only a simple self-contained centrifugal controller/actuator could be used.
Some prototypes have run very well using centrifugal controller/actuators. If it was desired to operate the Helical Camshaft to use both the LIVC and the high RPM aspects of the cam it would probably require hydraulic actuators on each cam to enable the LIVC to be used. Each Helical Camshaft would also need a phase-changing mechanism for the high RPM use. At low RPM and part-load the Helical Camshaft would be all LIVC. At high RPM and full load it would still require long duration from the Helical Camshaft but the phase changing mechanism would need to alter the all-on-the-closing-flank duration increase to something of a more symmetrical duration increase. All this possibly could be done mechanically but the sensible arrangement probably would be an externally-powered arrangement with a computer/microprocessor to sort out the required amounts LIVC and phasing. For HCCI operation the picture is less clear but the very short (and thus very fast) axial movement that would be needed to change the compression pressure would seem to make the Helical Camshaft very suitable for this process.
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