Abstract: In order to shorten the power shift time of hydro-mechanical transmission (HMT), the influence of bulk modulus for the oil containing gas on pressure building-up time of target range is explored based on the full power shift method. The oil tangent bulk modulus is theoretically analyzed and experimentally studied, and the change law of tangent bulk modulus of oil is obtained. A two-range arithmetic HMT is taken as the research object. The target range pressure building-up model in the power transition stage is established based on the full power shift method. The pressure building-up time of target range under the conditions of secant bulk modulus, tangent bulk modulus and pure oil bulk modulus was obtained by means of simulation analysis and protogype experiment. The results show that, when studying the pressure building-up time of target range in full power shift, the influence of oil gas content on the pressure building-up time must be considered, and the tangent bulk modulus should be used. The larger the oil gas content is, the smaller the tangent bulk modulus is, and the longer the pressure building-up time of target range is. Key

Key words: hydro-mechanical, variabletransmission, fullpowershift, oiltangentbulkmodulus, oilgascontent, powertransition, pressurebuilding-uptime