Equipment Type

Hyliion Hybrid Trailer Tandem Adds Drive Power

The electric-powered system captures braking energy that helps propel the trailer to save fuel

January 20, 2017

You can’t drive a trailer, but the Hyliion hybrid electric tandem can help propel your rig down the road. From the driver’s seat, you feel nudging from the powered trailer behind. Its primary purpose is to save fuel, and a lot of it, say engineers at Hyliion, which is developing and testing the system for upcoming release.

Powered Trailer Axles in Europe

Drive axles on trailers are unusual, even in Europe where higher-tech solutions to operating problems are often used. Recently, two products using powered trailer axles were announced. One is electric and is being fleet-tested, and the other hydraulic and is aimed right at dump vehicles, which often encounter poor off-road traction.

Here’s some background: The usual Class 8 configuration in Europe is a single-rear-axle, 4x2 tractor pulling a three-axle trailer. The 4x2 works fine on pavement, especially with a locking differential, but a single drive axle on end-dump rigs sometimes can’t grab enough traction while on loose gravel or muddy trails. So such operators often use 4x4 tractors, according to Markus Heuser, Germany-based director of global marketing communications for SAF-Holland. Of course, a front-driving axle adds considerable weight and cost to the tractor. The company’s SAF Trak alternative is essentially a hydraulic booster for the trailer.

SAF Trak is powered from the tractor’s hydraulic wet kit that operates the trailer’s hoist. On the trailer, two Poclain hydraulic motors, one at each axle end, turn the wheels to help get the rig moving in slippery conditions. A driver pushes a switch on the dash and compressed oil is sent to the motors to get the traction boost. It works only at low speeds. The hydraulic motor is a 10-cylinder radial, a layout similar to old gasoline aircraft engines. Heuser says the hydraulic tank on the tractor would need to hold a few more gallons of fluid, and of course, the trailer needs to be set up with hydraulic lines extending to the powered axle. There are no plans to bring SAF Trak here because our 6x4 tractors with twin-screw tandems seem to have enough traction for on/off-road work.

The electric unit, called the Kinetic Energy Recovery System, or KERS, is from SDC Trailers in the United Kingdom. It uses an axle-mounted motor-generator that performs regenerative braking, capturing energy and storing it in a bank of “graphene ultracapacitors.” Upon acceleration, electricity is sent back to the axle motor to help propel the vehicle. Controls are mounted in both trailer and tractor so they communicate and coordinate the powering effort. It’s being fleet-tested, and SDC claims that fuel savings are up to 25 percent.

The name Hyliion is a contraction of “hybrid lithium ion,” which is the operating style and the type of battery that’s part of the system. The Hyliion tandem captures kinetic energy available while the rig is braking, coasting, or running downhill, as hybrid cars and trucks now do. A motor-generator converts forward momentum to electricity that’s stored in a battery pack, and electricity flows back to the motor when the rig needs a boost. The tandem’s hybrid action saves 10 to 20 percent in fuel while on the move, and another 10 percent or more when its batteries are tapped to run other systems on the vehicle or act as an auxiliary power unit, according to Hyliion’s founder and CEO, Thomas Healy.

Parts include a Dana truck-type drive axle with differential, a short driveline to the motor-generator, a battery pack, and a control box. Development included writing the software that controls hybrid action and determining proper gear ratios in the axle, which may vary depending on the application. The powered tandem replaces a trailer’s standard tandem slider, and the drive axle replaces one of the “dead” axles. On a van trailer, Hyliion technicians can do a swap of the tandems in under an hour, Healy says. Non-slider assemblies will also be available.

Healy and his colleagues plan to market the system to operators of on-highway semis, who place great value in fuel economy. Falling into that category, though owners might not think so, are flatbeds delivering building supplies, and bulk tankers and hopper trailers carrying cement, liquid asphalt, and aggregates to batch plants. In a meeting with Healy, I suggested that his hybrid system might also be useful for on/off-road dumpers that could use extra traction, and that’s still a possibility. More recently, I learned that there is such a system for dump trailers now on the market in Europe. (See the video below and the sidebar.)

Healy rode along on a demonstration run to answer questions I posed from the driver’s seat of the company’s Volvo tractor. The trailer was a common van whose tandem had been pulled off and replaced with a Hyliion unit. This was on freeways near the company’s base in Pittsburgh, Pa., one of the hillier areas in the country and therefore a good testing ground for the concept. I can relate that with the power boost and retarding action from the trailer, I didn’t have to push very hard on the tractor’s accelerator or brake pedals. The Hyliion system helped propel the rig on the level and while climbing hills, and held it back on downgrades, capturing braking energy in the process.

Healy said only enough power is used to help move the trailer, and “it never pushes the tractor.” That was my sensation. The tractor’s engine still did some work, but not as much as when power from the trailer was turned off. A readout in the tractor’s sleeper showed fuel usage was cut substantially compared to when the tandem was purposely cut out.

On this run, engineer Morgan Culbertson sat at a control box in the sleeper compartment and operated the tandem. On production models, the system will operate on its own and require no link to the tractor. Thus any tractor of whatever age, like the 2010-model Volvo, can pull a Hyliion-equipped trailer and be aided by it. The only control the driver will have is an on/off switch on the dash.

Wouldn’t a powered axle on slick pavement cause a jackknife, either by pushing the tractor’s drive axles or the trailer’s rear out of line? Not likely, because the Hyliion’s controls are tied into the trailer’s anti-lock braking system, whose sensors determine wheel slip. In such cases, the Hyliion’s activity is minimized. And the driver can simply switch off the trailer system when roads are slick, as he might do with an engine brake.

The company’s test data, which indicate savings from 10 percent to 30 percent or more, suggest that fleets wanting to save fuel ought to consider the product. Several are, Healy says, and have requested units to test. They’ll be built in an expanded facility starting soon. And if all goes well, regular production, perhaps by a contract manufacturer, will start this summer. Hyliion engineers, who include Healy, have also designed a single-axle system for use in Europe, where it would replace one of the three axles under a semitrailer, a common configuration over there. 

Fleet testing here will determine if the system is rugged enough for everyday use. Healy expects that it will prove out fine. Its suggested list price of $29,500 might be a choker, but executives have also prepared leasing plans that take care of financing. Purchased or leased, the powered hybrid axle’s claimed fuel-saving benefits should provide a decent payback and make it more reality than fancy.

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