used to produce more subtle variations in engine valve timing amount of engine valve opening etc application ser no 08 512 528 which shows and describes this principle in somewhat related apparatus has been incorporated by reference herein fig9 a c herein also provide several examples of this principle an illustrative engine cam profile is shown in fig9 a various possible signals for controlling trigger valves like 52 82 etc are shown in fig9 b which is synchronized with fig9 a these signals are respectively identified as a b c and d the various openings of an engine valve such as 30 or 60 in response to the fig9 a cam profile and an associated trigger valve controlled by the fig9 b control signals are shown in fig9 c for example the engine valve opens as shown at a in fig9 c when the associated trigger valve is controlled by signal a in fig9 b signal a keeps the trigger valve closed throughout the entirety of the engine cam thereby causing the engine valve opening to follow the full engine cam profile as shown at b in fig9 c the engine valve opens by a lesser amount and closes earlier when the associated trigger valve is opened before the engine cam profile reaches its peak as shown by signal b in fig9 b as shown at c in fig9 c these trends are even more pronounced when the associated trigger valve is opened even earlier as shown by signal c in fig9 b as shown at d in fig9 c the opening of the engine valve can be delayed.