The Way of Suppressing Self-Excited Vibration in Small Pressure Regulator for Small Motorcycles

In recent years, the adoption of electronically-controlled fuel injection system (commonly called “FI”) of motorcycles is accelerating for the purpose of fuel efficiency improvement to meet tighter emission controls around the world and to protect global environment. The main stream of the motorcycle market is small motorcycles with an engine size of 100cc to 150cc, therefore downsizing and lowering the cost of FI products are being demanded. Pressure regulator (hereafter called P/R) installed in fuel pump module (hereafter called FPM), one of FI products for motorcycles, is being shifted to ball valve type from diaphragm type due to the downsizing demands. However, the ball valve type has problems such as abnormal noise and pressure adjusting defect that are caused by self-excited vibration. This time, we selected a structure to unite P/R with an aperture in view of downsizing and lowering costs, then we were able to suppress the self-excited vibration and have achieved 77% reduction in size of P/R by making resonance frequency between the pressure chamber and the valve chamber 0<f₂ ≦ 5.6×f_1. Here, f₁ is the resonance frequency of the first fuel passage that includes the pressure chamber and the fuel pipe and f₂ is the resonance frequency of the second fuel passage that includes the aperture and the valve chamber. As a result, we have increased the degree of freedom in installing on FPM and achieved 30% reduction in the size of FPM.