A new active electric differential developed by Schaeffler's eMobility Systems division is slated for production in MY2014. The eDifferential, for which the company has patents pending, was the centerpiece of Schaeffler's eSolutions concept buck shown at the 2011 Frankfurt and 2012 Detroit auto shows.
The eSolutions display showcases more than 10 technologies designed for electrified vehicles. Along with the recently formed eMobility Systems group, it underscores the global supplier's intensified focus on the burgeoning electrified-vehicle sector.
By developing a systems approach to electric mobility, the aim is to create products "at an international level that will enable us to cover this important field in its entirety," according to Prof. Peter Gutzmer, Member of the Board of Management and Chief Technology Officer.
Schaeffler's expanding emphasis on electrified vehicle-related activities in Germany, China, and North America means 300 new jobs, including positions for engineers and technical specialists.
Modular motor solution
The eDifferential features two liquid-cooled permanent magnet synchronous motors (PMSM) made by IDAM, a Schaeffler Group unit. Each motor has a specific task. The larger, 60 kW (80.4 hp) machine handles drive power, while a smaller 8 kW (11 hp) motor regulates the distribution of torque.
"It's a modular solution, so we can do the primary drive motor at 40 kW, 60 kW, or 80 kW," Jeff Hemphill, Vice President and Chief Technology Officer for Schaeffler Group USA, told AEI. "In any of the sizes, the motors are very torque-dense and have a good efficiency over a wide speed range," he explained.
The system's architecture details include a planetary-type reduction gearset, a spur-gear differential, and a compound planetary headset. Electronic control is by an AFT unit also made by Schaeffler (as are the eDifferential's various rolling-element bearing sets.)
The active eDifferential can be front- or rear-axle mounted for two-wheel drive, or it can be mounted on both the front and rear axles for all-wheel drive. The system is capable of controlling each wheel individually to vector torque between the right and left wheels.
Schaeffler also has developed an electronic roll-stabilization system comprised of an electric motor with an engine control unit, a high-ratio rotational gear, a cam-drum, and coil spring.
"The coil spring stores energy in a manner similar to how a garage door opens, and this enables the system to provide roll stabilization with only 12 volts," said Hemphill. "Because it's a 12 V system, it can be used on conventional vehicles without the need of a voltage converter or an extra power bus," he noted.
Compared to a conventional hydraulic roll stabilization system, Schaeffler's electronic version is claimed to provide a 1 to 3% fuel economy improvement.
"We're currently doing both bench testing and vehicle testing of the electronic roll stabilization system and that will last for much of this year," Hemphill said.
Second-gen wheel motors coming
Schaeffler's eWheel Drive unit, also part of the eSolutions show buck, includes an electronically controlled in-hub motor, stator, friction brake, rotor, and wheel bearing.
"Our eWheel Drive motor uses hybrid synchronous commutation to provide high torque and efficiency over a wide speed range. For its power capacity, the unit is compact and lightweight," Hemphill said.
"The system has integrated power electronics and that helps simplify vehicle mounting, which is on the wheel side of the suspension," he explained.
Engineers currently are conducting vehicle tests on Schaeffler's second-generation eWheel motors, which provide an estimated output of 70 kW (94 hp) and 700 N·m (516 lb·ft).
In production applications, customers could opt to combine the supplier's eWheel unit with an active eDifferential.
"It's probably more likely, though, that an OEM would choose eWheel Drive for an electric city car and choose the active eDifferential for a two-wheel-drive electric vehicle of greater power," Hemphill speculated.
Schaeffler has filed approximately 100 patent applications in the U.S., Germany, Japan, South Korea, China, and elsewhere related to its eWheel and active eDifferential technologies.