Design and Development of a Roller Follower Hydraulic Lash Adjustor to Eliminate Lash Adjustment and Reduce Noise in a Serial Production Diesel Engine

摘要

Commercial vehicles require continual improvements in order to meet fuel emission standards, improve diesel aftertreatment system performance and optimize vehicle fuel economy. Aftertreatment systems require significant space claim which makes vehicle packaging a challenge. Today’s diesel engines require valvetrain lash adjustment settings at distinct intervals to ensure proper valvetrain performance. This requires removing the engine rocker cover to access the valvetrain rocker arms for setting lash. Setting lash for compact vehicle applications sometimes requires removing the aftertreatment system to provide access to the rocker cover prior to setting lash. Then, the rocker cover is reinstalled followed by the aftertreatment system making the lash setting process time consuming and complex. This paper focuses on the design, development and validation of adapting hydraulic lash adjusters (HLAs) into a type V (camshaft in block) diesel engine thus eliminating the lash adjustment process. The flat mechanical tappets were replaced with roller follower HLAs on both the intake and exhaust valves. The roller was included to reduce valvetrain friction over flat tappets. An anti-rotation design was included to maintain alignment between the roller and the camshaft. A major advantage of using the HLA was reduced engine valvetrain noise. Minor engine block changes were required to accommodate the roller follower HLAs. The HLA design ensured reliable and repeatable valve motion from engine build thru cold start and normal engine operation over the useful life of the engine. Reliability was key for the roller follower HLA as it is embedded inside the block which makes replacement impractical. This paper highlights the major design aspects for including roller follower HLAs in a type V diesel engine.