Hybrid trucks? Sure, though they’re somewhat complex and expensive, and interest has waned in the face of cheap fuel. Hybrid trailers? Comin’ up, and they’ll be comparatively simple and quicker to pay back their extra investment.

That’s the plan for a hybrid electric-drive trailer tandem being developed by a group of engineers at Hyliion Inc. in Pittsburgh, Pa. The device, which for now has no official name, is undergoing road testing and should be ready for the market in mid-2017, they say.

The system captures energy as a tractor-trailer runs downhill, and reapplies energy through a drive axle to help the truck run uphill. Operation is completely autonomous and, except for an on-off switch, the driver has nothing to do, explains Thomas Healy, the company’s founder and CEO. Electronic controls read road, terrain and speed conditions and try to keep a vehicle at a desired speed.

Healy has observed big rigs and wondered why their mass couldn’t be captured for reuse, 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, says Robert Culbertson, the company’s marketing director. The firm started 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,” Culbertson says. “A lot of our supplies are going down in price, so it’s becoming cost-effective as well as environmentally beneficial.” The fuel savings 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 greenhouse-gas and fuel economy regulations, Healy says.  

When its design is finalized, the product will be a complete tandem with axles and a suspension that would replace a trailer’s existing tandem. Three people at Hyliion have changed out a tandem in less than 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.

How it works

A truck drive axle with a differential, now sourced from Dana, 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 differential 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,” says Healy, a mechanical engineer. “We think there’d be one set for an operator who does pickup and delivery and another for highway use.”

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

An APU, too

In addition, energy captured in the battery pack can be tapped to run air conditioning and heating in a sleeper cab, Healy says. A reefer unit might also be powered from the batteries. For sleeper-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 would be 20 to 30 hours’ worth of power available.

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

Projected price for a complete tandem is $29,500, but the projected fuel and dollar savings would supply a payback in as little as six months, according to the company. 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?” Culbertson says in recalling the idea that set development in motion. “The parts are pretty well tested, the motors, and it all works.”