VCT system having robust closed loop control employing dual loop approach having hydraulic pilot stage with a PWM solenoid
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United States of America Patent
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Feb 9, 1993
Grant Date -
N/A
app pub date -
Mar 5, 1992
filing date -
Mar 5, 1992
priority date (Note) -
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Abstract
A camshaft (26) has a vane (60) secured to an end thereof for non-oscillag rotation therewith. The camshaft also carries a sprocket (32) which can rotate with the camshaft but which is oscillatable with the camshaft. The vane has opposed lobes (60a, 60b) which are received in opposed recesses (32a, 32b), respectively, of the sprocket. 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 a chain drive extending therebetween. The camshaft tends to change in reaction to pulses which it experiences during its normal operation, and it is permitted to change only in a given direction, either to advance or retard, by selectively blocking or permitting the flow of hydraulic fluid, preferably engine oil, through the return lines (94, 96) from the recesses by controlling the position of a spool (100) within a valve body (98) of a control valve in response to a signal indicative of an engine operating condition determined from a closed loop feedback system.
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