Development and Validation of Diamond-Like Carbon Coating for a Switching Roller Finger Follower

An advanced variable valve actuation system is developed that requires a coating with high stress loading capability on the sliding interfaces to enable compact packaging solutions for gasoline passenger car applications. The valvetrain system consists of a switching roller bearing finger follower (SRFF) combined with a dual feed hydraulic lash adjuster and an oil control valve. The SRFF contains two slider pads and a single roller to provide discrete variable valve lift capability on the intake valves. These components are installed on a four cylinder gasoline engine. The motivation for designing this type of variable valve actuation system is targeted to improve fuel economy by reducing the air pumping losses during partial load engine operation. This paper addresses the technology developed to utilize a Diamond-like carbon (DLC) coating on the slider pads of the SRFF. Slider interfaces that are able to withstand high stress levels enable compact packaging options for valvetrain solutions. Initial screening for materials and surface preparations showed DLC to be the most viable alternative. The slider pad surface finish and form is shown to be essential prior to applying the DLC coating. Process development for high volume production is developed to meet the surface preparation requirements. Testing results show that the SRFF including all DLC coating interfaces is durable well beyond the useful life of the valvetrain.