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Variable Swirl and Internal Egr By Vvt Application on Small Displacement 2 Valve SI Engines: An Intelligent Technology Combination
Technical Paper
2004-05-0406
Sector:
Language:
English
Abstract
During recent years several VVT devices have been developed in
order to improve either peak power and low end torque, or part-load
fuel consumption of SI engines. When the target of the VVT
application was an improvement of part-load fuel consumption these
VVT devices were often combined with devices for variable charge
motion such as port deactivation, valve deactivation or tumble
flaps, in order to allow acceptable combustion stability at part
load with high EGR rates.
This paper describes an experimental activity concerning the
integration of a continuously variable cam phaser (CVCP) and a
special intake and exhaust port geometry on a family of small
displacement 4- cylinder, 2-valve engines. The target was to
achieve significantly lower fuel consumption under normal driving
conditions, compared to a standard MPFI application, without the
need for a separate variable charge motion device.
A hydraulic vane-type cam phaser is used to shift the single
overhead camshaft to retarded positions at constant overlap. Thus
high EGR rates in the combustion chamber are generated by
re-aspiration of burnt gas from the exhaust port into the cylinder.
This re-aspiration phase is used to generate increased swirl with
the help of a unique exhaust port design to enable stable
combustion under high residual gas operating conditions. The
consecutive aspiration phase through the intake port creates an
additional moderate swirl motion. In this way a conventional
tangential intake port can be adopted, allowing at the same time
good combustion stability with high EGR rates, with a good trade-
off between part-load fuel consumption and full-load performance.
Late intake valve closure ("reverse Miller cycle") is
combined with these measures in order to further reduce pumping
losses at part load.
Using 1.2 and 1.4 dm3 4-cylinder 8V engines equipped with
these devices the concept was developed on the engine test bed with
respect to functionality, durability and cost.
Two demonstration cars with these engines were prepared. ECU
calibration was performed on the test bed and in the vehicles with
given targets for driveability and emissions. EURO 4 exhaust
emission limits were reached using a conventional catalyst aged for
100,000 km. Fuel consumption was reduced by 5% in the NEDC cycle
due to the thermodynamic effects achieved with VVT, high residual
gas content and late intake closing. Additional measures on the
valve train in order to reduce friction resulted in a total fuel
consumption reduction of more than 6% for both vehicles compared to
a standard (without any conventional EGR system) 4-cylinder 8V MPFI
application.