Ride Comfort, Efficiency and Compact Package

IAV presented the optimized version of its modular electric drive concept at the Vienna Engine Symposium. Combining e-motor and transmission, it provides up to three speeds and, because of its modular concept, can be made to suit various vehicle platforms and requirements. The aim is to combine a high level of ride comfort, efficiency and compact package at competitive cost.

In the long term, electric drive systems will play a key part in mobility because they permit zero-emission mobility and are not reliant on fossil energy. Besides the environmental aspect, however, manufacturers also need to consider their customers’ demands on ride comfort. At the same time, consumers expect top efficiency to give them maximum traveling range on one battery charge, good hillclimbing performance, high vehicle speed and good acceleration.

Many of today’s electric drives use a combination of an e-motor and transmission with fixed transmission ratio. Although solutions of this type are relatively simple in terms of structure, they cannot meet all of the demands made on them at the same time. For instance, high hill-climbing ability and maximum efficiency demand very different transmission ratios. It is for this reason that IAV has chosen a modular concept based on an e-motor and a transmission with one to three speeds. “As a result, we can match the electric drive unit to different vehicle platforms and demands”, explains Matthias Krause, head of department in the IAV Powertrain System Development division. “Our solution delivers a high level of torque across a wide vehicle speed range.”

IAV’s solution is also flexible in use – as the main drive for battery electric vehicles, for fuel cell vehicles or as a component of plug-in hybrids. Its power output is sufficient for vehicles from classes A (subcompact car), B (compact car), C (standard size) and D (upper standard size). It represents a further development of a solution IAV presented back in 2010.

In the modular electric drive unit, an e-motor developed by IAV delivers a continuous power output of 50 kilowatts and maximum power of 80 kilowatts. It generates constant torque of 150 newton meters which can be increased to 300 newton meters for short periods of time. It was designed using IAV’s emotor synthesis tool which finds the optimum solution for the given application from an almost unlimited number of potential variants.

Providing a maximum of three speeds, the planetary transmission is installed at the side of the e-motor and is capable of generating output torque levels of up to 3,000 newton meters. At the same time, this makes it possible to limit the motor’s maximum speed to 8,000 revolutions per minute. The differential is accommodated in the emotor, making optimum use of limited package.

“Our modular electric drive unit meets the demands on torque with more speeds than comparable solutions”, says Jens Liebold, Technical Consultant for Electromechanical Drive Systems at IAV. “Instead of a multiplespeed transmission, these use a larger motor with means they need more package and encounter problems because of the higher speeds involved, such as with NVH.” Developing the casing also presented a particular challenge. Compact design, a high level of functional integration and temperature management were combined to provide additional benefits.

With IAV’s solution, for example, the power electronics are accommodated in the casing to reduce costs from copper wiring, ensure good EMC shielding as well as include the power electronics in the electric motor’s cooling circuit. “In our case, we use the stator’s circuit to control the temperature of the power electronics because we can bring it into contact with a large area of the casing’s cooled sections”, Krause says. “The transmission’s lubrication system, in turn, also cools the e-machine’s rotor.”

Besides this, the project also placed exacting demands on the casing’s structural stiffness. “Otherwise there is a risk of getting problems with acoustic behavior and mechanical strength”, Liebold explains. “So the casing had to be as stiff as possible to avoid vibration but also to absorb forces and transfer them to the vehicle.” In developing the casing, IAV’s experts cooperated closely with Nemak, a globally operating aluminum casting specialist. This has resulted in a casing that combines compact size, high stiffness, a high level of functional integration and competitive costs.