Control system for exhaust gas recirculation

Claim 1

In an exhaust gas recirculation system having a valve having a valve stem, said valve being moveable between a first position blocking communication of an engine intake air passageway with an engine exhaust gas passageway and a second position at which said passageways are in communication, a frame mechanism, a stepper motor for moving the valve between the first and second positions, a driving element connected to the stepper motor, a one way clutch system connected to the driving element, and control means for rotating the stepper motor in preselected first and second directions and controllably stopping the stepper motor at preselected positions of the valve, the improvement comprising: said valve stem having a threaded first end portion; a spool having an axis and internal threads mated with the threads of the valve stem and being connected to the drive element of the stepper motor through the one way clutch; a clockwork spring connected to the spool and being adapted to store energy in response to rotation of the spool in a first direction and controllably release energy and rotate the spool in a second direction; a thrust mechanism operative to maintain the spool against axial movement; and an anti-rotation device operative to maintain the valve against rotation relative to the spool.