Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Subaru Impreza 2001-2002.2004-2007 Approved Subaru Impreza 2004 WRX STi 08. MECHANISM AND FUNCTION 25. MECHANICAL (STi) 10. Variable Valve Timing System
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W1860BE.book Page 13 Tuesday, January 28, 2003 11:01 PM
VARIABLE VALVE TIMING SYSTEM
MECHANICAL
10.Variable Valve Timing System
This engine has a variable valve timing system, which adjusts the opening and closing timings of
the intake valves optimally by continuously changing the phase angle of the camshaft sprocket rel-
ative to the camshaft.
The ECM determines the optimal cam angle relative to the crank angle by making reference to
the engine speed, vehicle speed, throttle opening and other relevant parameters.
Under the control of the ECM, the oil flow control valve moves its spool to switch the hydraulic
passage to/from the advance and retard chambers that are formed in the camshaft sprocket to
change continuously the phase angle between the camshaft sprocket and camshaft.
A: PHASE ANGLE ADVANCES
In response to an advance signal from the ECM, the oil flow control valve moves its spool such that
hydraulic pressure is applied to the advance chamber in the camshaft sprocket. The sprocket is then
turned in the direction in which its phase angle advances relative to the camshaft.
(3)
(6) (1)
(5)
(2)
(4)
(1)
(2)
ME-00747
(1) Variable valve timing controller (attached to camshaft sprocket)
(2) Vane (attached to intake camshaft)
(3) ECM
(4) Oil flow control valve
(5) Oil pressure
(6) Turns in advance direction
ME(STi)-13
W1860BE.book Page 14 Tuesday, January 28, 2003 11:01 PM
VARIABLE VALVE TIMING SYSTEM
MECHANICAL
B: PHASE ANGLE RETARDS
In response to a retard signal from the ECM, the oil flow control valve moves its spool such that hy-
draulic pressure is applied to the retard chamber in the camshaft sprocket. The sprocket is then
turned in the direction in which its phase angle retards relative to the camshaft.
(3)
(1)
(5)
(2)
(6)
(4)
(1)
(2)
ME-00748
(1) Variable valve timing controller (attached to camshaft sprocket)
(2) Vane (attached to intake camshaft)
(3) ECM
(4) Oil flow control valve
(5) Oil pressure
(6) Turns in retard direction
ME(STi)-14
W1860BE.book Page 15 Tuesday, January 28, 2003 11:01 PM
VARIABLE VALVE TIMING SYSTEM
MECHANICAL
C: A CERTAIN PHASE ANGLE IS RETAINED
When the ECM issues a signal to keep the phase angle unchanged, the oil flow control valve moves
its spool to the position at which the hydraulic pressures to/from both the chambers are blocked.
The pressures in the chambers are thus maintained, so the phase angle does not change and the
intake valves' opening and closing timings also remain unchanged.
(3)
(1)
(5)
(2)
(4)
ME-00749
(1) Variable valve timing controller (attached to camshaft sprocket)
(2) Vane (attached to intake camshaft)
(3) ECM
(4) Oil flow control valve
(5) Oil pressure
ME(STi)-15
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