Subaru Impreza 2002 Service Manual page 31

Mechanical
11. Variable Valve Timing System
The STi model's engine has the variable valve timing system, which adjusts the opening and clos-
ing timings of the intake valves optimally by continuously changing the phase angle of the cam-
shaft sprocket relative to the camshaft.
D
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.
D
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.
(1) Variable valve timing controller (attached to camshaft sprocket)
(2) Vane (attached to intake camshaft)
(3) ECM
(4) Oil flow control valve
(5) Hydraulic pressure
(6) Turns in advance direction
VARIABLE VALVE TIMING SYSTEM
ME-6
NF0581