Sound Quality Enhancement with Exhaust Manifold and Hot-End Structure Optimization on H8 Engine Systems

Idle sound quality for motorcycles is very important to the customers [1,2]. People would like to have a strong individualized sound in idle, linear and smooth sound in the driving condition. Since the idle fluctuation noise is based on the engine firing sequence, the exhaust manifold structure and the idle frequency eight or six cylinders engine are really hard to get a real good fluctuated tailpipe sound in the idle condition compared to the two or three cylinders engines. However, some surrogate methodology can be applied to these engines. Based on the noise cancellation process in amplitude and phase in the exhaust manifold system, engineers can manipulate the noise with several lower peaks, and the other higher peaks can be perceived by the masking effect in the time domain. In this scenario, people only feel the big noise fluctuation peaks, even the smaller peaks are still there in the background. In addition, waves can be further improved by the Hot-End structure. The structure could provide more opportunities to separate and cancel the waves in the duct system by phase. In this paper, a special case is presented by these methodologies and techniques. An eight-cylinder horizontal engine with an uneven firing sequence makes very irregular tailpipe noise in the idle condition originally. By optimizing the exhaust manifold structures in shapes and lengths by the DOE method, and also applying the new H Type Hot-End structure with the active-controlled valve in the middle of the connecting pipe, the tailpipe noise is finally optimized successfully. Good idle impulsiveness and less half-orders tone in running up can be achieved simultaneously with these techniques.