Model-Based Performance Analysis of a Hybrid Summation Drive Used in Off-Highway Vehicles

摘要

High power density, wide speed range and overall good efficiency are the primary demands of a modern hydrostatic transmission used in heavy earth moving machineries (HEMM). Conventional hydrostatic drive consisting of a displacement controlled pump and motor is sometimes inadequate to meet such requirements. Therefore, there is a need for examining alternative concepts of drives for HEMM. This article studies one of such alternatives where the motors are connected in parallel. In another solution, one motor is permanently connected to the load and the other one is connected to the load through gear unit. The latter is used during high-torque, low-speed demand of the vehicle. The challenge with the concept is the reconnection procedure, where the disconnected motor is accelerated, synchronized to the main motor output speed and finally locked to the output shaft, all in fraction of a second. Two different principles for the reconnection are proposed: to control the connection using a disc-type clutch, or to control it from the fluid power system. The performances of the two systems are compared through bond graph model simulation with respect to pressure, speed and efficiency for the varying load demand usually catered by a HEMM.