Browse Publications Technical Papers 2006-01-0040
2006-04-03

2-step Variable Valve Actuation: System Optimization and Integration on an SI Engine 2006-01-0040

2-step variable valve actuation using early-intake valve closing is a strategy for high fuel economy on spark-ignited gasoline engines. Two discrete valve-lift profiles are used with continuously variable cam phasing. 2-step VVA systems are attractive because of their low cost/benefit, relative simplicity, and ease-of-packaging on new and existing engines.
A 2-step VVA system was designed and integrated on a 4-valve-per-cylinder 4.2L line-6 engine. Simulation tools were used to develop valve lift profiles for high fuel economy and low NOx emissions. The intake lift profiles had equal lift for both valves and were designed for high airflow & residual capacity in order to minimize valvetrain switching during the EPA drive cycle. It was determined that an enhanced combustion system was needed to maximize fuel economy benefit with the selected valve lift profiles. A flow-efficient chamber mask was developed to increase in-cylinder tumble motion and combustion rates.
A 2-step valvetrain mechanism was developed that features hydraulically-actuated switchable rocker arms and hydraulic lash adjusters (Type II valvetrain). The rocker arm is a dual-roller, single-slider design for compact packaging and low friction. The engine management system was modified for control and calibration of 2-step VVA, and to realize the full fuel economy potential of the system.
Dynamometer tests on a multicylinder engine indicated a 6.9 percent fuel economy benefit relative to the production engine with exhaust cam phasing alone on the EPA city cycle. Combustion enhancement significantly contributed to the overall fuel economy benefit. Vehicle tests showed less fuel economy improvement than steady state dynamometer tests due, in part, to cam phaser control limitations. For warmed-up Phase 3 EPA tests (cycles 19-23), a 5.5% improvement was measured with 46% reduction in NOx. For the whole EPA city test including cold start, a 4.8% improvement was measured. Further improvements in vehicle fuel economy are expected with refinement in transient control and calibration.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Preview Document Add to Cart
Members save up to 17% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:
TECHNICAL PAPER

An Assessment and Comparison of De-Throttling Approaches and Technologies for Further Reductions in Fuel Consumption in a Modern GDI Engine

2017-01-2224

View Details

TECHNICAL PAPER

The New Changan Inline 4 Cylinder 1.6 L Gasoline Naturally Aspirated GDI Engine

2018-01-1129

View Details

TECHNICAL PAPER

Fuel Sulfate Content Influence in the Formation of Inorganics Components Deposits in the Engine Injectors with Technologies of Gasoline Direct Injection

2012-36-0314

View Details

X