Piston-by-Piston Detailed Modeling of A Novel Hydro-Mechanical Transmission

A hydro-mechanical transmission (HMT) is a continuously variable transmission that transmits power both mechanically and hydraulically. Typically, a HMT consists of one or more planetary gear-sets and a pair of hydraulic pump/motors, making it bulky and expensive. A novel structure of HMT named the Hondamatic only consisted a two-shafted piston pump and a variable displacement piston motor, making it very compact. The two-shafted piston pump plays the role of a planetary gear and the piston barrels of the pump and motor are dual-used for mechanical transmission. This paper analyzes the operating principle of the Hondamatic and its performance through detailed modeling. The model considering the kinematics, inertial and compressibility dynamics as well as the mechanical and volumetric losses. Modeling concepts for axial piston pump/motors are adapted to the Hondamatic to result in a dynamic model with tunable parameters to analyze the operation, dynamics and efficiency. The friction between the pistons and piston bores, the throttling loss of the distributor valves and the leakage from the piston bores are the main power losses in the Hondamatic. The overall efficiency of the Hondamatic is above 80% under most working condition according to the simulation results, which makes the Hondamatic high efficient and very compact meanwhile.