Hyliion, a start-up founded by a group of graduate students at Carnegie Mellon, has developed an add-on hybrid system for semi-trailers. Combining regenerative braking and power boost for the trailer to reduce on-the-road fuel consumption, the system also functions as an auxiliary power unit to reduce engine-on idling. Their patent application describing the basics of the system was published earlier this month.

The Hyliion System—comprising motor, battery and control electronics—can power a truck cab for 20 hours, out-performing an industry standard, idle-free all-electric APU. Overall fuel savings are upwards of 30%, according the company.

Hyliion’s aerodynamic packaging also reduces air resistance, saving more fuel. The company also offers additional tools that keep track of trailers in real-time and make real-time route decisions.

The Hyliion System replaces the existing axle system, and can be installed in an hour (8 bolts and 2 lines). The system is designed to retrofit all 6 million box trailers on the road today. The system’s data logic analyzer interprets certain variable conditions (such as brake status of the trailer; accelerometer position; GPS indicator; acceleration status of the trailer; velocity status of the trailer; measured incline of the trailer; a gyroscope reading; a microphone reading; driver behavior; or currently operating engine status) and is used to determine when to apply supplemental power to the wheels of a trailer to reduce fuel usage.

Shifting the mechanical stress of braking onto the Hyliion System enables brake pads and engines to go further and last longer, requiring less maintenance and fewer replacements.