Noise Problem Resolution and Sound Quality Improvement of Valve Timing Belt in 4 Cylinders PFI Gasoline Engine

IC Engine Timing belt is a major noise prone area and it takes time during development to achieve acceptable NVH characteristics. In an existing engine under series production noise problem observed due to excitation of timing belt span by crank timing sprocket tooth. From vehicle perspective noise was heard in vehicle cabin at around idling RPM and a second peak observed around twice the initial RPM. This paper includes a methodology for use of computer based analytical simulation methods to predict timing belt dynamic behavior and NVH characteristics. Along with development of computer based multi body dynamic model for timing belt, validation of simulation model with actual testing was done and after correlation of testing and simulated results countermeasure were finalized based on iterations in multi body simulation model.

Multi body dynamics model of timing drive indicated resonance in one belt span when belt transverse vibration amplitude was converted from time domain to frequency domain using FFT. In an existing engine layout change to modify belt span length was not feasible to avoid resonance, 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 modifying the belt tension. 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.

Multi body dynamic simulation model helped to drastically reducing the number of testing trials/combination used to resolve the NVH issue of timing belt.