Kia 2004.5 Spectra Service Technical Training page 61

2004.5 Spectra Technology
CVVT OPERATING RANGE
Powertrain
• Reduced emission
• Reduce NOx through an EGR effect due to
optimization of valve overlap
• Small overlap (Retard) causes increased burning
time resulting in reduced HC emission
• Large overlap (Advance) causes an EGR effect
by lowering NOx
• Improved performance
• Improved volumetric and thermodynamic
efficiency by variable valve timing
• Advanced valve timing at low and middle speed
improves volumetric efficiency
• Retarded valve timing at high speeds improves
volumetric efficiency by inertia energy
• Improved idle stability
• Reduced valve overlap to burn A/F mixture at idle
The CVVT will retard or advance intake valve timing,
based on engine RPM and load. The chart shows the
CVVT operating range for different engine loads and
RPM. At idle and low load (starting from the lower left
corner), the timing is retarded for stable combustion.
As load increases (upward on the chart), timing is
advanced to improve torque. Timing advances as RPM
increases (shown as moving to the right) under partial
load for fuel economy and emission. When both RPM
and load increase, the CVVT retards timing to improve
power. When load and RPM becomes constant, intake
valve timing is maintained based on the amount of
load and RPM (see chart).
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