 |
|
|
PWM Variable Cams describes the set of cam patterns that have X teeth of which half of the teeth are considered wide and the remaining teeth are considered narrow. The narrow teeth are grouped together, as are the wide teeth. The teeth are located so that one edge of each tooth is uniformily displaced about the cycle. This edge is called the synchronous edge and should be the edge selected in the Variable Cam Phase block. The variable cam phaser will not operate correctly if the incorrect edge is chosen. The figure illustrates a 6 tooth PWM cam. There are also 4 tooth and 8 tooth variants of this cam pattern style.
PWM style cam encoders are reliant upon pulse width information inorder to detect the difference between a wide tooth and a narrow tooth. The width information encodes engine half cycle information. The last observed tooth width that precedes a synchronization point on the crank encoder (like a missing tooth region) must be invariant for all possible cam phaser positions. Per the figure it can be seen that one missing tooth region always has a wide tooth precede it whilst the alternate missing tooth has a narrow tooth precede it.
A cam trigger shall be issued each time a synchronous edge is observed.
Variable Reluctance (VR) style of tooth sensing is not appropriate for this pattern because such sensors do not accurately convey tooth width information. Proximity sensors like hall-effect can be used because they operate in a digital like manner when detecting the prescense or absence of metal