Engine NVH performance improvements with polymer gears

Abstract

Legislation drives the automotive megatrend to reduce fuel consumption and CO2 is resulting in small high output 3 and 4 cylinder engines. While customers have raised expectations on driving comfort, the smaller high output engines have inherent vibration noise, vibration and harshness (NVH) issues. Thus gear rattle in mass balance systems, cam gears, pump and accessory drives is an NVH issue. The most common approach is to use a split (scissor) gear assembly; the solution is complex, high in cost and heavy. High performance polymer injection molded net shape gears made from VICTREX® PEEK have gained growing attention and acceptance as cost effective, low mass and highly efficient solution to significantly reduce NVH in engine related application areas like mass balancer, cam and pumps. This paper presents test data done with validation customers and independent research institutes. It also references and discusses technical publications at SAE and VDI. With a successful case study it further it demonstrates the benefits of a net shape polymer gear solution offering a 3 dB (~50%) improvement in NVH, a 68% weight reduction resulting in 78% reduction of the moment of inertia and therefore 9% less torque required to operate compared to a cast iron gear set.