A hybrid electric-drive trailer tandem is being developed by group of engineers who promise substantial fuel savings and fast payback. The device, which for now has no official name, is under road testing and should be ready for the market in mid-2017, according to officials at Hyliion Inc., in Pittsburgh, Pa.

The system captures energy during braking and as a tractor-trailer runs downhill, and reapplies energy through a drive axle to help the truck launch and accelerate from a standstill and run uphill. Operation is completely autonomous and, except for an on-off switch, the driver has no involvement.

The system’s electronic controls read road, terrain and speed conditions and try to keep a vehicle at a desired speed, said Thomas Healy, the company’s founder and CEO.

Healy has raced various kinds of automobiles and said he had an "a-ha!" moment when he observed the 18-wheel transporters that hauled the cars. He wondered why the rigs couldn’t be altered to capture and use power like the hybrid electric car he now drives.

Hyliion, the company’s name, means hybrid lithium ion, which is the type of battery that’s part of the system, said Robert Culbertson, the company’s marketing director. The firm started up about a year ago to perfect the idea and market a product.

“We’ve been trying it out with different battery combinations and different motor combinations,” he said. “A lot of our supplies are going down in price, so it’s becoming cost-effective as well as environmentally beneficial” because of the fuel savings, which is estimated at 21% for the electric-drive tandem alone. Trailer aerodynamics would save more.

The system would more than meet trailer targets in the proposed Phase 2 federal greenhouse-gas and fuel economy regulations, Healy said.  

When its design is finalized, the product will be a complete tandem with axles, brakes and suspension that would replace a trailer’s existing tandem, he said. He said the switch can be done quickly, and three people at Hyliion have changed out a tandem in under 30 minutes. He envisions trailer builders eventually offering the electric-drive tandem on new trailers.

The suspension can be mechanical or air-spring, and a sliding tandem is the first type planned. A suspension supplier is being discussed. Included will be a fairing mounted ahead of the tandem to smooth air flow and protect electronic, electrical and mechanical components from grime and debris.

How It Works

A truck drive axle with a differential substitutes for one of the standard trailer axles. A 300-hp Remy motor-generator transmits energy to a battery pack that nestles between the rails of the slider box. When power is needed, electricity is sent to the motor, and it propels the trailer through the axle diff and shafts to the wheels.

The prototype uses a belt and pulleys to transfer power between the diff and the motor-generator that’s mounted above. Production models will mount the motor within the differential so the motor is gear driven.   

“We’ve been working with Dana on determining differential gear ratios,” said Healy, a mechanical engineer. “We think there’ll be one set for an operator who does pickup and delivery and another for highway use.”

Electronic controls use an algorithm to process data gotten from wheel sensors and GPS monitoring, then determine what road speed should be maintained. Controls know when there’s wheel slip and alter energy capture and power that’s applied, he said. It works with the tandem’s anti-lock braking system to become electronic stability control, enhancing safety. He said Hyliion is working with Bendix on the ABS-related apparatus.

The hybrid-electric tandem weighs 400 to 500 pounds more than a standard tandem, but much of that would be offset by changing from dual wheels to wide-base singles, suggested a test driver whose testimonial is featured on the company’s website, www.hyliion.com.  

An APU, Too

Energy captured in the battery pack can be tapped to run air conditioning and heating in a sleeper cab, Healy said. A reefer unit might also be powered from the batteries. For sleeper-cab cab HVAC, voltage would be stepped down from 400 to 110 by an inverter that’s part of the electronic controls. Depending on ambient temperatures, there’d be 20 to 30 hours’ worth of power available.

Because the system doubles as an auxiliary power unit,  federal law would exempt 400 pounds of its weight from the 80,000-pound gross weight limit, so “the truck wouldn’t lose any payload,” Healy said. The APU function would take total fuel savings to about 31%.

Projected price for a complete tandem is $29,500, but high projected fuel and dollar savings would supply a payback in as little as six months, he said. A lease-purchase plan would cost $500 per month for five years, and monthly fuel savings would more than cover that.  

“We’ve got this 80,000-pound vehicle moving around, so why can’t we get some energy out of it?” said Culbertson in recalling the idea that set development in motion. “The parts are pretty well tested, the motors, and it all works.”