Systematic Synthesis of Dedicated Hybrid Transmission

The great diversity of dedicated hybrid transmissions(DHTs)requires a method to identify solutions among all potential concepts involved in each structure.Therefore,a DHT synthesis tool is developed on the basis of general transmission synthesis.In the first synthesis step,transmission structures are generated with only conventional functions such as driving with only the internal combustion engine.Electric machines are then installed in the transmissions to achieve further hybrid functions,including boosting,eCVT and electric driving modes.The number of generated transmission concepts increases exponentially with each synthesis step.Various evaluations are carried out successively to identify the most suitable DHT concepts among the many possible solutions.The generated DHT concepts are evaluated in terms of structural feasibility,driving modes,drivability and load factors on transmission components.An example of DHT synthesis involving planetary gear sets is explained in detail.The best five DHT structures are identified out of more than 120 billion solutions.

Highly Fuel-Efficient Transmission and Propulsion Concepts

The integration of one or more electricmachines into the drivetrain has resulted inmany different powertrain concepts in recent years,ranging from the P2 hybrid to dedicated hybrid transmission(DHT).Two types of DHT with different characteristics are investigated.The first type is the power split hybrid(PS-DHT),which has very low mechanical complexity but needs high electrical effort in the transmission.The second type is multi-mode DHT(MM-DHT),which has a slightly higher mechanical complexity but much less electrical effort when compared with the PS-DHT.A transmission synthesis is used to determine the concept of the MM-DHT.The three different powertrain concepts(i.e.,P2,PS-DHT,and MM-DHT)are analyzed and evaluated regarding fuel economy and performance.Legal driving cycles(e.g.,Worldwide Harmonized Light vehicles Test Procedure)and the 3D method(driver,driven vehicle,driving environs)are used to investigate the drivetrain in the context of real driving operation.Results show that the two DHT concepts offer better fuel economy than the P2 hybrid drivetrain while still providing the same or even better driving performance.The study also shows that new hybrid concepts created with transmission synthesis can lead to further improvements in hybrid powertrains.