Investigation of Noise Sources on a Series Hybrid Transmission

Advanced hydrostatic transmissions and hydraulic hybrids show potential in new market segments such as commercial vehicles and passenger cars. Such new applications regard low noise generation as a high priority, thus, demanding new quiet hydrostatic transmission designs. The aim of this paper is to investigate noise sources on a series hybrid transmission through simulation and measurements.A model has been developed to capture the interaction of a pump and motor working in a hydrostatic transmission and to predict overall noise sources. The model describes dynamics of the system by coupling lumped parameter pump and motor models with a one-dimensional unsteady compressible transmission line model including a dynamic model of an accumulator. A semi-anechoic chamber has been designed and constructed for sound intensity measurements that can be used to derive sound power. Sound power measurements were conducted on a series hybrid transmission test bench inside the semi-anechoic chamber in order to study the relationship between sound power and two types of noise sources, fluid and structure borne. The focus of these measurements was to investigate the impact of an accumulator in the high pressure line as well as the influence of varying high pressure line length.Results show a strong influence of changing line length and the addition of an accumulator on pressure ripple, but with little impact on sound power. A high correlation was found between sound power levels and control moment amplitudes on the swash plate. This study demonstrates the usefulness of predicting transmission noise sources, and how this information is beneficial in the design process of a transmission.