Thor Industries and Harbinger Electrify Class A Motorhomes

Motorhome manufacturer Thor Industries and the company’s technical partner and chassis supplier Harbinger make a strong case that series hybrid electrification is the ideal solution for big Class A motorhome powertrains.

The partners have revealed their Thor Test Vehicle, which they say is the world’s first hybrid-electric Class A motorhome. As a refresher on recreational vehicle terminology, “Class A” means those big motorhomes that are completely purpose-built as such, rather than the ones that are built into a van body or the ones that, like U-Haul trucks, use the chassis and cab of a van with a large box mounted on the back.

Conventional practice for these vehicles is for the RV maker to build a house atop an existing truck platform, with propulsion provided by either a large-displacement gasoline-fueled engine or turbodiesel and stationary electric power provided by a separate generator.

These chassis commonly use primitive solid beam axles and leaf springs. “There’s no reason to subject customers to that in 2024,” said Harbinger founder and CEO John Harris. “It is debatable whether there was a reason in 1964. There haven’t been any new trucks engineered in the past four decades,” he charged.

Harbinger’s chassis for the Thor Test Vehicle is completely different. It uses a smoother-riding De Dion axle at the rear and car-like double-wishbone front suspension for improved ride and handling.

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The Harbinger stripped chassis used for the Thor Test Vehicle shows its many advanced features, such as the independent double-wishbone front suspension and compact drivetrain packaging. HARBINGER

Using a De Dion axle on a vehicle with a 22,000-lb. gross vehicle weight is challenging because of the high loads involved, said Harris. Harbinger addresses this by using a forged axle made of micro-alloy steel. This design separates the motor mass from the axle’s unsprung weight, providing another contribution toward better ride and handling for the Thor Test Vehicle.

“We did that to separate the drivetrain from the axle,” said Harris. “The motor is chassis-mounted, vibration-isolated, sprung weight sending torque to the wheels via half shafts.”

The electric motor is mounted transversely, so there is no power loss from a hypoid gear, and the 1.4-liter gasoline range extender is not connected to the wheels at all. This motor serves only to charge the batteries when the vehicle is used for trips beyond the range of its battery pack and to provide electric power when the RV is parked if the battery is low and there is no shore power available.

Traditional RVs also have truck-like steering systems too. Because of the high loads involved, car-style rack-and-pinion steering isn’t suitable, so the Thor Test Vehicle also employs a conventional recirculating ball steering box, but pairs it with electric power steering rather than hydraulic power steering.

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Harbinger's electric drive is mounted transversely, avoiding the use of a power-sapping hypoid gear. HARBINGER

More significantly, Harbinger plans to replace that with a true steer-by-wire system soon that will provide low steering effort combined with quick-responding steering for campsite parking situations that is also steady and stable at highway speeds, according to Harris. “When you think of parking an RV there is a lot of hand-over-hand steering maneuvers,” he said. “There is a lot of room for improvement.”

The Thor Test Vehicle carries a 140-kilowatt-hour 800-volt battery pack that powers the motorhome like a conventional battery-electric vehicle until the charge is depleted. That’s when the gas engine runs, charging the battery so it can continue to power the electric motor.

Because the battery pack can provide hotel power for the RV’s appliances, lighting, and climate control and the gas motor can run to recharge it as needed, the Test Vehicle needs no auxiliary battery pack or generator.

The Thor Test Vehicle employs a Combined Charge System port for charging its 800-volt battery pack, but a future production version could use a North American Charge System port instead, if the market adopts that standard. HARBINGER

A future production model based on the Test Vehicle’s design would cost more than a gasoline-powered Class A motorhome, but it would probably be on par with the cost of a diesel-powered model while providing superior experiences both on the road and at the campsite, said Harris.

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