Truckin’ on Hydrogen
Toyota’s hydrogen fuel cell powertrain provides an electrifying ride with SAE Media on board.
The hydrogen-fueled electrified Class 8 road tractor doesn’t move or sound like a diesel-fueled behemoth. “This advanced prototype is production-intent for shape, power, virtually everything, and its performance is much more capable than the previous prototypes,” Luke Rippelmeyer, Toyota’s senior program manager responsible for developing a heavy-duty hydrogen fuel cell electric powertrain, told SAE Media as we settled into the passenger seat of the prototype Kenworth T680.
The Toyota-developed powertrain was being demonstrated on a two-mile highway loop at the American Center for Mobility in Ypsilanti, Michigan. The truck’s acceleration was impressively quick, while light on noise and vibration, and moderate rattle and squeak – essentially a byproduct of not having the diesel engine masking in-cabin noises.
At the start of the closed-track drive, Chris Rovik, Toyota’s executive program manager for the heavy-duty hydrogen fuel cell, steadily depressed the accelerator. As vehicle speed increased, the whirl-sound of electric motors cascaded into the cabin. “A traditional diesel truck uses pulley-driven systems for the brake air compressor, A/C compressor and power steering pump. But in this former diesel-engine truck, the engine compartment’s pulley-driven systems have been replaced with electric motors to run the ancillaries,” Rovik noted.
In roughly 15 seconds, the tractor accelerated to more than 55 mph (88 km/h). “We’ve gone from zero mph to highway speeds in 30 seconds with truck and trailer” during previous testing, Rovik said. The vehicle’s four-speed automatic transmission – part of the eDrivetrain module that also includes two electric motors to provide up to 450 kW of peak power and 2400 Nm (1,770 lb-ft) of peak torque – quickly completed its tasks. The first-gear shift occurred around 25 mph (40 km/h), followed by another upshift at 40 mph (64 km/h) and a final upshift at 60 mph (97 km/h). “If we had a trailer with a load on it, the ride would feel even smoother because the load would help damp out some of the shifting,” Rovik said, referring to the slight vehicle sway felt during the automatic gear shifts.
Under the Kenworth’s tilting hood are two second-generation fuel cell stacks based on the stack used in the Toyota Mirai sedan. The overall package dimensions of the fuel cell module, which includes the stacks, air compressors, pumps and fans, is essentially the same size as a diesel engine, Rovik pointed out. Toyota’s fuel-cell powertrain kit will enable buyers to replace their diesel engines with hydrogen-fueled electrification. In the prototype vehicle, hydrogen storage tanks and related components are housed in a cabinet behind the cab. The 60 kg (132 lb) of onboard hydrogen provides approximately 1,800 kWh of usable energy. That represents more than three times the 565-kWh battery capacity of the Volvo VNR Electric Class 8 truck.
The advanced prototype’s 200-kWh lithium-ion battery pack is located below the cab. It provides supplemental power when needed and regenerative braking assistance. “We have built several different versions of the truck with different battery capacities. As our goal grew from supporting only port drayage applications to include regional haul applications, the specification for overall battery capacity grew,” Rovik explained.
California’s Los Angeles and Long Beach ports and surrounding areas have served as fleet testing locations for the prototypes. The tests provide Toyota’s engineering teams with feedback on so-called soft topics, like sound and other ride/drive impressions. “We’ve also been evaluating this advanced prototype vehicle – usually paired with a trailer loaded with 80,000 lb (36,287 kg) of cinder blocks – in hot and cold weather over rough roads and long-grade climbs,” Rippelmeyer said. More than 10,000 miles (16,093 km) have been logged on the prototype vehicle to date.
Toyota is slated to begin producing its heavy-duty hydrogen fuel cells in 2023 at the company’s Kentucky plant. The hydrogen fuel cell electric trucks are projected to have a 300-mile (483-km) driving range when fully loaded to 82,000 lb (37,194 kg) gross combination weight. “That’s about 5 miles (8 km) per kg of hydrogen when at maximum vehicle load,” Ripplemeyer said.