Hybrid motors find new efficiencies and markets

Tom Shelley reports on advances in automotive hybrid technology at this year's Hannover Fair.

A motor for hybrid transmissions sets a new benchmark in electrical efficiency thanks to improved stator windings. It also a step forward in a process that is seeing such transmissions diversifying out of conventional cars into small excavators, off road vehicles and trucks. The Heinzmann Generation 3 hybrid drive motor is the latest development to come from a German Black Forest-based company that has been going since 1897 and has been making electric drives since 1985.

At the 2011 Hannover Fair, technical director Frank Böhler showed us how it was more efficient because it used what he called "Concentrated windings" on each stator tooth. He explained that in most motors, there is "Copper without any use, which does not produce magnetic field". There are still resistance losses in these parts of the windings that represents energy that is being consumed for no useful purpose.

In the new design of motor, the ends of the rotor tooth windings are only 5mm from the permanent magnet rotor, whereas in previous designs, Böhler claims the distances were 35mm to 45mm. The change in design also makes the motors more compact. Efficiency improvement in these motors, which are rated at 25kW continuous and 40kW peak, is about 1%, which might not sound a lot, but represents a more than 10% reduction in heat output, since the motors were already more than 90% efficient.

The company makes motors for electric and hybrid drives that are rated up to 60kW and are used in Atlas wheel loaders, the Mecalac 12 MTX excavator and Ladog multipurpose municipal vehicles. Böhler favours what he calls, "Mild hybrids", where there is a traditional transmission system, either mechanical or hydraulic, and the motor is switched on during load peaks to provide additional torque.

At the same time, the motor functions as a generator during braking and as a starter motor that allows the internal combustion engine to be turned off when the vehicle is stopped and started again in 150 to 300ms. He sees forklift trucks and wheel loaders as ideal applications, because of their frequent stops and starts, However tests with the municipal vehicles, which are not considered to be an ideal use, still showed fuel savings of around 20%.

Also on show in the same hall as the motors were a plethora of battery electric and hybrid cars and vans ranging from electric tricycles to large luxury limousines, the most notable of which came from Mercedes and its MB Tech offshoot. However, outside, was a large hybrid truck which visitors described as looking like a cross between Concorde and a German ICE train.

This drive by wire and streamlined juggernaut turned out to have been developed by Professor Gernot Spiegelberg of Siemens, in the context of a Rudolf Diesel industry fellowship at the University of Munich Institute for Advanced Study. The project has been given the title, "Diesel reloaded". Three post doctoral researchers are engaged in the three principle tasks of: "Electric power train and energy management," "Electronic system architecture of all interconnected functions," and "Development of a novel human-machine interface with side stick controller."

Design is being coordinated with the aid of Teamcenter from Siemens PLM. The vehicle is currently fitted up as a mobile exhibition centre.

Tom Shelley

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