18-04-2013, 02:40 PM
Variable Valve Timing
Variable Valve.ppt (Size: 2.33 MB / Downloads: 58)
Spark-Ignition Focus
Many factors have steered commercial market away from standard IC-engine with spark-ignition
Growing competition from alternative power sources
More efficient fuel consumption due to heightened emission restrictions
Individual company commitments toward higher performance demands and safety regulations without compromising comfort level or retail value
Effects of Reduced Fuel Consumption
Pumping losses
Combustion efficiency
Minimal friction from Direct Injection
Downsizing
Higher pressure charging
Thermodynamic Solutions
Thermodynamic conditions must operate at higher loads
Or reduce gas exchange/heat loss at part load
Supercharging
Turbo-charging
Fully Variable Valve Timing
Direct-Injection
Current Design: Delphi Automotive Systems
Cylinder Deactivation System
Enables cut-out of half cylinder count to boost fuel economy.
Intake stroke of exhaust valves are disabled with target cylinders using oil pressure or electric solenoids
Simultaneously FI is cut off to target cylinders
“Forward-tumble Direct-Injection”- A/F mixture stabilized near ignition source zone
Produces 8 to 10% decrease in emission levels.
Movement towards Efficiency
Many companies have shifted away from throttle to improve efficiency
Hydraulic actuation and electronic control is incorporated
All available VVT advancements still involve camshaft or rocker arm