Navigant Research Blog

Schaeffler Shows One Path to Better Fuel Economy

David Alexander — January 30, 2015

January in Detroit heralds the annual North American International Auto Show (NAIAS), where many manufacturers launch new models and technology.  It’s less well known as a supplier event, but many of the Tier One companies hold press and industry events to showcase their developments, primarily during the media and industry days that are held before the show opens to the general public.

This year, German supplier Schaeffler chose to highlight its project on fuel economy, with a view to meeting the upcoming more stringent American CAFE requirements.  As well as developing specific components and products, the company has incorporated them into an existing vehicle to demonstrate the integration potential.  Phase 1 of the implementation shows one way to meet the 2020 CAFE target on an existing vehicle by making a series of small, low-cost changes; Phase 2 will add additional features to meet the 2025 fuel economy goal.

Hunker Down

The target vehicle chosen was a model year 2013 Ford Escape AWD (all-wheel drive), which features a 2.0-liter engine and Ford’s 6-speed automatic transmission.  For phase 1, Schaeffler engineers implemented an AWD disconnect feature to eliminate additional friction when only two-wheel drive is necessary, a new torque converter damper to allow a lower lockup speed, and an automatic engine stop-start system.  A new thermal management module enabled faster engine warming from cold.  Other detail changes included coated tappets, new balance shaft bearings, and low rolling-resistance tires.

To reach the 2025 target fuel economy, phase 2 houses two main features: ride height adjustment and disconnecting vehicle accessory drives from the engine.  Automatically reducing the ride height as speed increases is a straightforward way to reduce aerodynamic drag, a topic that I discussed in a previous blog.  The idea of disconnecting accessory drives has been around for some time, and is key to extending the value of stop-start systems, but replacing a traditional crankshaft belt drive with individual electric motors is a very expensive solution.

Clutch Move

Schaeffler solves this dilemma by setting up a separate 48V motor generator to power the accessories when the engine is switched off.  The system is controlled by a pair of clutches that can connect the electric motor to either the engine or the transmission.  Using a 48V subsystem allows more powerful regenerative braking than a 12V system, and therefore greater energy recovery, and the motor can also be used to supplement the drive.

Navigant Research has recently released a detailed report on this topic: Automotive Fuel Efficiency Technologies.  The Schaeffler approach nicely illustrates our conclusion that there is no single solution for meeting future fuel economy targets, and future vehicles will have to incorporate many small changes that will combine to deliver measurable results.  Schaeffler’s concept of creating a separate 48V accessory drive subsystem can keep costs manageable while allowing the industry to transition from 12V to 48V.

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