To accurately predict the brake performance of vehicular hydraulic retarder under oil partially filled condition,two math models were built based on different internal two-phase flow assumption.The braking torque of the hydraulic retarder was calculated using the mixture-density method or gas-hydraulic separating method.Compared with the experimental data obtained under oil fully filled condition,the calculation error is less than 5%.It is found that the separating method is more accurate in theory and the ...