Camless Variable Valve Actuation Designs with Two-Spring Pendulum and Electrohydraulic Latching 2007-01-1295
Camless variable valve actuation (VVA) technologies have been known for improving fuel economy, reducing emissions, and enhancing engine performance. A family of VVA designs from LGD Technology, LLC (called LGD-VVA) has been configured to include a two-spring actuation, a bypass passage, and an electrohydraulic latch-release mechanism. The two-spring pendulum system provides efficient conversion between the moving mass kinetic energy and the spring potential energy and is less influenced, than a hydraulic actuation means, by operating conditions such as temperature. The electrohydraulic mechanism is used primarily for latch-release function, and it is also flexible enough in its design to offer different levels of energy input to overcome engine cylinder pressure, which can be substantial for exhaust valves.
The LGD-VVA designs offer better lift variability, higher power density, and lower electrical demand relative to electromagnetic VVA systems. They include three types of lift-control: fixed-lift, two-step-lift, and continuously-variable-lift. The engine valve release and actuation is triggered by one simple switch action of a four-way directional valve or its equivalent, and the engine valve completes the rest of the stroke, including soft-seating, without active control.
The combination of the two-spring pendulum and bypass design is able to reduce fluid flow during most of the engine valve travel, thus achieving actuator power consumption comparable to that of a conventional cam system. At 8-mm valve lift, up to 64% of the kinetic energy is converted to the spring potential energy before the snubber is engaged, and the energy conversion continues even after the snubber is engaged. The combination makes it possible to achieve a “short-tailed” soft-seating without the need for closed-loop control.
A numerical model of the designs is developed, and the simulation validates some benefits of the LGD-VVA philosophy.