BorgWarner shows latest EV transmission

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  • Image: 31-03 3.png
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The lead program for BorgWarner’s 31-03 eGearDrive is the CODA Automotive sedan, which is expected to ramp up to 20,000 units per year by the end of 2011.

At the 2010 SAE World Congress, BorgWarner will display its 31-03 eGearDrive electric-drive transmission, the next generation of its technology developed for the emerging, higher-volume, lower-cost vehicle-electrification market. The first application will be in the all-electric CODA Automotive sedan scheduled for introduction in California in 2010, followed by the just announced application in the 2011 electric Ford Transit Connect commercial van.

The first variant of eGearDrive, the 31-01, was launched into limited production on the all-electric Tesla Roadster in 2008. In the CODA application, the new 31-03 single-speed transmission is paired with a UQM Technologies’ PowerPhase electric propulsion system. Power for that application will come from CODA Automotive’s transportation-battery joint venture with Lishen Power Battery, China's main state-owned battery manufacturer.

Targeted at urban delivery fleets, the all-electric Transit Connect will use the 31-03 single-speed transmission to reach a top speed of 75 mph (120 km/h) and offers a range of up to 80 mi (129 km) on a full charge. The conventional Transit will be upfitted to all-electric propulsion by Azure Dynamics, which will install its electric propulsion system driving the front wheels through the eGearDrive.

The eGearDrive transmission incorporates patented and proprietary technology, including a high-efficiency geartrain and compact low-weight design, that contributes to extended battery-powered driving range, which in turn reduces the required amount of battery capacity needed. The transmission achieves high torque capacity with 98% efficiency, says the company. Nearly all of the materials used in the transmission are recyclable.

The eGearDrive is specifically targeted at electric-axle applications in “through-the-road” parallel/series hybrids and range-extended and battery electric drives, according to John Barlage, Product Business Director for BorgWarner Drivetrain Systems.

The 31-03 is now BorgWarner’s core product for transverse and secondary axle drive systems, said Barlage. “Compared to the Tesla (31-01) unit, the 31-03 has a wide range of ratios, from 6.5:1 to 9:1,” he said. “That is really important because a lot of the electric vehicles are using different types of motors, either permanent magnet or induction, there is a range of sizes across the segment, and also certain vehicle [makers] want to target higher vehicle speed—say over 100 mph vs. just 80 mph.” Input torque is a bit lower at 200 N•m, 300 N•m peak, but input speed capability (14,000 rpm) is the same.

BorgWarner considers the three competitive attributes of the 31-03 to be its adaptability, efficiency and noise, and the ePark system, said Barlage.

“One aspect of adaptability is the single-speed unit’s wide range of gear-ratio options, which can easily be achieved by just changing two gears,” said Barlage. “Another is for the electric-motor interface. We don’t integrate the flange as part of the transmission case; it is a separate component that can be redesigned and recast to adapt to different motors.” The transmission also has a flexible drop angle and an adaptable emachine interface.

In the absence of a pump, the 31-03 uses splash lubrication. The high EV input speeds (vs. a conventional transmission) created “a lot of challenges to control where the oil is going,” said Barlage. “We developed a proprietary baffled vent system with an internal deflector. There is no [external] accumulator or tube required.”

In today’s conventional vehicles, the “bad boy of inefficiency is the internal-combustion engine (ICE), where you are losing 60% of the energy to heat,” said Barlage. “When you get rid of the ICE and replace it with an electric motor, [transmission] efficiencies become very important.”

BorgWarner engineers addressed efficiency through unique tooth forms in the helical gears not only to ensure low noise transmission but also efficiency. For noise, they made sure that the first gear mesh has at least four teeth in contact. For fatigue performance, they chose a specific gear class and surface finish, which was critical for efficiency as well as for high-speed performance. An offset architecture accommodates deep groove ball bearings, instead of tapered roller bearings, for improved efficiency.

With the ePark shift-by-wire park-lock system, the transmission uses a traditional mechanical (park pawl) lock typical in an automatic transmission, but it is engaged by wire signal via an actuator.

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