Vtec/Vtc - Honda Civic 2002-2003 Service Manual

•
•
•
VTEC/VTC
• The i-VTEC has a VTC (Variable Valve Timing Control) mechanism on the intake camshaft in addition to the usual
VTEC.
This mechanism improves fuel efficiency and reduces exhaust emissions at
all levels
of engine speed, vehicle speed,
and engine load.
• The VTEC mechanism changes the valve lift and timing by using more than one cam profile.
• The VTC changes the phase of the intake camshaft via oil pressure. It changes the intake valve timing continuously.
~i
<.-_LO_W_S_P_E_E_D_C_A_M _ _
X
HIGH SPEED CAM
' >
ENGINE
LOAD
!
LOW
L:::==:::. __________________ _
LOW--
ENGINE SPEED HIGH
Drivin Condition
VTC Control Descri tion
CD
Light-load
Base Position
@
Medium/high-load Advance Control
Cam angle is retarded to reduce the entry of exhaust
gas into the intake port and to achieve stable fuel
consurn tion durin lean burn.
Cam angle is advanced for EGR effect and to reduce
this pumping loss. The intake valve is closed quickly
to help reduce the entry of air/fuel mixture into the
______ . ____ -+-;-; ___
-;o-_-;;---cc-_ _
-+-oin-:'t~a~k~e_f'_'0~rt~a~n~d~im~=rove th_e~h'!rgi"n=e'_'ff"e"c"'t.~~
_ _
_I
QfHi-gh
speed Advance-Base Position Cam phase angle is controlled for optimum valve
timin and maximum en ine ower .
(cont'd)
11-29