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Re: Variable valve timing...how does this work? 900 1995

posted by  someone claiming to be Jim Bowers on  Wed Dec 13 08:37 CST 2000 [RELATED]

I'm not sure about the new Volvo but I know that BMW and Porsche have been doing this for several years. (I gave shop manuals to #1 son for his BMW and #2 son for his Boxster. Chips don't fall far from the tree re interest in fine cars.)

Basic concept is that at each engine speed there is an optimum time, angle, for the cam to open and close the valves to obtain maximum torgue. (Remember that Torgue x RPM = power.) The variable system allows the designers to alter the timeing based on RPM, or some control method to get closer to the optimum. This as apposed to a fixed compromise value on all our older Volvos.

Usually the hardware is a hydraulic cylinder changing the effective length of timing belt or chain on either side of the cam gear. The cylinder in turn can be controled by the ECU or just a mechanical governer.

This isn't teribly specific but I hope it helps.





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