Electro-Magnetic Valve Actuation System: First Steps toward Mass Production 2008-01-1360
Market expectations for the next generation of gasoline engines are: improved performance for better driveability, lower toxic emissions to meet future legislation, and reduced fuel consumption to help meet future legislation linked to Green House Gas emissions (including CO2) and to counter the recent increase in fuel price. In addition, any new technical solution must be cost effective and applicable to a large volume of engines.
In order to improve fuel efficiency, the combustion process needs to be optimized. A key technology to achieve this is fully variable valve actuation for both naturally aspirated and turbocharged engines (variable displacement, reduced pumping losses, Miller-Atkinson cycles). To futher improve, accurate control of ignition and the air/fuel ratio will also be required and are necessary for CAI-HCCI combustion.
VALEO Engine Management Systems has, since 1998, been working on an infinitely variable valve actuation system based on a linear spring-mass actuator. The VALEO electro-magnetic variable valve actuation system replaces the intake camshaft with electromagnetic valve actuators that are driven by a Valve Control Unit (VCU). This VCU receives commands (mainly the engine running mode and the valve event timing) from the Engine Management System through a dedicated CAN bus. The main function of the system is to ensure consistent valve lift profiles in accordance with Engine Management System request.
The technical challenge of this concept are the trade-offs between the functional characteristics of the system and the expectations (from the OEM) in terms of specific power, NVH, reliability, cold start ability, and fuel consumption. These expectations are therefore translated into system characteristics which are respectively: transition time, noise emitted (number of impacts and impact velocity control), reliability, viscous friction and electrical power consumption.
The electromagnetic valve actuation system improves engine and vehicle attributes with improved low-end torque (10%-20%) and improved fuel economy (16%-19% on the European drive cycle). This makes the technology well positioned to meet future market expectations for the next generation of gasoline engines.
This paper describes the level of maturity and robustness of the spring-mass concept actuator technology. In addition, we look at the trade-offs required to properly master the system and ready it for mass production. At first, in the half-camless architecture for traditional combustion engines and in the meantime readying the technology for future CAI-HCCI combustion engines with the full camless architecture.