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TUD and Romax collaborate on two-drive transmission for hybrid powertrains

University institute and software specialist develop transmission design for electric range-extended vehicles  

 

Above: Romax model of the two-drive transmission.

German research university Technische Universität Darmstadt (TUD) and Romax Technology have combined expertise for a project designing a two-drive transmission for hybrid vehicles.

Romax – which provides software and services for the analysis and design of bearings, gearbox and driveline systems – supplied modeling, simulation and analysis capabilities to TUD’s Institute for Mechatronic Systems in Mechanical Engineering (IMS), assisting in a project to design a new transmission system for use in electric range-extended vehicles.

Design of the new transmission was carried out in RomaxDesigner software – which enabled the creation of simulations and subsequent efficiency analysis.

“Efficiency maps of transmissions can be very hard to calculate,” said Ruben König, a research associate at IMS. “We needed Romax to provide this information.”

The two-drive concept was created in an attempt to optimize efficiency in an electric drive system fitted with an internal combustion range-extender engine – providing the best possible operation in both all-electric and hybrid modes.

Above: CAD model of the two-drive-transmission including e-motors and shift actuators. 

Existing system configurations include the parallel hybrid system often implemented in plug-in hybrid vehicles, and the series hybrid system commonly used in electric range-extended vehicles. Different systems have different respective advantages and drawbacks.

“Our project looked into different PHEV concepts,” said König. “We’re mainly interested in parallel layouts as they are generally agreed to be the most efficient. Parallel two-clutch systems are interesting but costly, and have complex transmission technology. The two-drive transmission has less complexity: only two gears in both transmission sub-systems, and fewer parts. There are also no friction elements, no friction couplings, no synchronizers, so it’s highly efficient. We identified potential to make improvements in terms of efficiency and cost.”

After formulating optimization strategies, IMS used Romax software to run simulations to analyze the efficiency of the two-drive transmission – a system that König and his colleagues determined would provide efficient electric operation, offer efficient parallel hybrid modes, and also make it possible to implement series hybrid modes during specific conditions. The two-drive transmission concept met the project’s criteria: two parallel 2-speed transmission sub-systems for efficiency, high starting torque and high maximum speed; two small electric machines avoiding interruption of traction during shifts and providing efficiency in low-load conditions; and range-extender capabilities as a result of implementing parallel and series hybrid modes.

“Romax software allows us to design systems and components at a level of detail that’s not too deep but still provides the right level of information,” König says. “For example, we need efficiency maps of the transmission but didn’t have a detailed design – so we could create the first model and then scale the efficiency map.”

Above: CAD model of the complete powertrain.

IMS set a range of parameters for optimization work – including power ratings for the electric machines and combustion engine, and gear ratios – allowing project requirements for minimum torque, minimum electric high speed and minimum hybrid high speed to be satisfied.

Further design of the system was carried out using Romax’s CAD Fusion software, ensuring package and operational constraints were met, before switching the model back to RomaxDesigner. IMS were sufficiently impressed with this functionality to take the decision to implement it in future projects.

“We have created a promising powertrain concept, offering high efficiency in both electric and hybrid driving, good driving performance, and simple transmission technology,” König added. “All design and efficiency calculations, as well as modeling and simulations, were done using Romax.”

IMS currently has plans to build prototypes of the new two-drive transmission.

April 27, 2015 

 

27 April 2015

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