Topology Synthesis Of Planetary Gear Train With Multiple Degrees Of Freedom For Vehicle

Planetary gear trains (PGTs) have long been applied in Automatic transmissions (ATs)because of a smaller volume, higher power density and easier power-shift manipulationcompared to the standard parallel axis gear trains. In order to satisfy the new additionalrequirements for vehicle powertrain, such as multiple speeds, wider ratio range and higherpower density, PGTs with multiple degrees of freedom (DOFs) are widely developed for ATbased on the methods of in-series, switched-input or switched-output and variable structure.To obtain multi-speed PGTs with the same magnitude, the planetary variable structuretransmission has less control units than the PGTs designed by the other two methods.However, there is lack of theory to provide guidance for the design of variable structure.Therefore, based on the concept from2-DOF PGT to multi-DOF PGT, a deduced method isproposed for the topology synthesis of the2-DOF PGTs. And a graph model withconnection characteristic of fixed interconnection edge is built to provide guidance for thedesign of variable structure. Based on the graph model, a performance analysis model isdeveloped for the multi-DOF multi-speed PGTs.According to the structure and function analysis, PGT can be divided into twomodules, including the module of PGSs and the fixed interconnections between PGSs andthe module of external links consisting of the input, output and frame link. Based on thelever model of PGT, a deduced synthesis method based on excellent structure is proposedfor2-DOF PGTs with multiple planetary gear sets (PGSs). A composite lever analogy and acomplete graph model for isomorphism test are applied to synthesize the2-DOF PGTs. Andan example with three PGSs is considered to highlight the capabilities of the deducedsynthesis method. The results show it is valid to shorten the design period.Based on power-flow analysis for each speed ratio of the2-DOF PGT, the connectioncharacteristic of fixed interconnection edge is defined as its frequency of constructing theoriginal speed ratios. A PGT graph model with connection characteristic is built to provideguidance for the design of variable structure multi-DOF PGTs. On the basis of the graphmodel and lever analogy, the variable structure multi-DOF PGTs are synthesized throughthe methods of deleting and adding fixed interconnection edges.A generalized properties analysis model for multi-DOF PGT is built based on theidentification algorithm of links and the torque analysis method. All the possible speed ratios are synthesized and the corresponding properties are analyzed, including the angularspeed and torque of units, efficiency and circulating power of each speed ratio. Based onthe requirements of single-transition shift and step ratio, a synthesis algorithm for clutchingsequence is developed. And the graph models of full-closed and half-closed boundary areproposed for planarity test of longitudinal and transverse AT with PGT. Finally, theexamples for multi-DOF PGTs with multi-PGS are developed to validate the proposedsynthesis and analysis methods. And several multi-speed multi-DOF PGTs are obtained forvehicles, such as8-and9-speed PGTs.