Development and control of electro-hydraulic fully flexible valve actuation system for diesel combustion research

Fully flexible valve actuation (FFVA) system, often referred to as camless valvetrain, employs electronically controlled actuators to drive the intake and/or exhaust valves. This technology enables the engine controller to tailor the valve event according to the engine operating condition in real-time to improve fuel economy, emissions and performance. At GM Research and Development Center, we have developed laboratory electro-hydraulic FFVA systems for single cylinder gasoline engines. The objective of this work is to develop a FFVA system for advanced diesel combustion research. There are three major differences between gasoline and diesel engines in terms of applying the FFVA systems. First, the orientation of the diesel engine valves and the location of the fuel injection system complicate the packaging issue. Second, the clearance between the valves and the piston for diesel engines are extremely small. The single cylinder engine we are working on has less than 1mm clearance when the piston is at top dead center (TDC). Third, different valve profile strategies are required for gasoline and diesel engines. For diesel low temperature combustion, we use late intake valve closing (LIVC) to change the effective compression ratio to reduce the combustion temperature. System hardware includes servo valves, power amplifiers, hydraulic pump and cylinders, sensors and signal conditioners. A robust tracking control was designed and implemented to control the system. The system is capable of generating real-time fully flexible motion for individual intake or exhaust valve and accommodates a large variety of valve profile strategies, such as late intake valve closing (LIVC). Both bench and combustion tests confirm that the system is able to provide the precision and flexibility required for diesel combustion research while operating safely under the small clearance between the valve and piston.