Belt driven variable camshaft timing system

摘要

A camshaft (326) has a vane (360) secured to an end thereof for a non-oscillating rotation therewith. The camshaft also carries a timing belt driven pulley (332) which can rotate with the camshaft but which is oscillatable with respect to the camshaft. The vane has opposed lobes (360a, 360b) which are received in opposed recesses (332a, 332b), respectively, of the pulley. The recesses have greater circumferential extent than the lobes to permit the vane and sprocket to oscillate with respect to one another and thereby permit the camshaft to change in phase relative to a crankshaft whose phase relative to the sprocket is fixed by virtue of the timing belt (338) drive extending therebetween. The camshaft tends to change in reaction to torque pulses which it experiences during its normal operation and it is permitted to advance or retard by selectively blocking or permitting the flow of engine oil from the recesses by controlling the position of a spool (400) within a valve body (392) of a control valve in response to a signal from an engine control unit (408). The spool is urged in a given direction by rotary linear motion translating means (682) which is rotated by an electric motor (686), preferably of the stepper motor type.