Sound Quality Improvement of Timing belt in Gasoline Engine 2019-01-1279
Timing belt is major noise prone area and takes time during development to achieve better NVH characteristics. This paper describes the solution of noise problem due to excitation of timing belt span by crank timing sprocket tooth on an existing engine under series production. Problem was noticed when engine was applied to commercial vehicle where NVH isolation package is much lower compared to conventional passenger car.
From vehicle operation perspective noise was heard in vehicle cabin at around idling RPM and a second peak around twice the initial RPM. To establish noise source engine was tested with timing cover removed by adjusted belt tension to different levels. AVL excite timing drive was used for analysis in parallel to study the phenomena and explore countermeasure. From tested frequency domain data it became apparent that resonance area corresponds to natural frequency of one of the timing belt spans. AVL excite timing drive model also indicated resonance in same belt span when belt amplitude was converted from to frequency domain from time domain using FFT.
In an existing engine layout change to modify belt span length was not feasible, other alternatives like reduction of belt natural frequency (by increasing belt mass density, tension reduction etc.) were explored using parametric simulation model. Final solution to avoid belt resonance in engine working RPM range was proposed as reduction of belt natural frequency by manual tensioner layout modification and increasing crank tooth excitation frequency by increasing engine idle RPM. Above proposal was checked on engine bench and anechoic vehicle test showed noise reduction of 5 and 11 dB at first and second harmonic respectively due to avoidance of resonance in engine working RPM range.
MBD simulation model helped to drastically reducing the number of testing trails/ combination used to resolve the NVH issue of timing belt.