Toyota’s Proven Fuel-Cell Stack Reduces Cost, Complexity in H2 Semi-Truck

The latest iteration of Toyota’s hydrogen-powered Class 8 semi—shown pulling a Mirai-laden trailer—debuted on Earth Day at the Port of Los Angeles. (Sebastian Blanco)

Hydrogen proponents likely know that Mirai means “future” in Japanese, but Toyota is only just beginning to explore how important the fuel cell stack in its H2-powered passenger car will be to the future of the company.

Toyota’s philosophy is to specify small batteries and let the fuel cell take care of providing most of the power. (Sebastian Blanco)

Toyota debuted the third iteration of its hydrogen-powered Class 8 semi-truck on Earth Day at the Port of Los Angeles as part of the Zero and Near-Zero Emissions Freight Facilities Project (ZANZEFF) run by the California Air Resources Board (CARB). Using a Kenworth T680 Class 8 model as a starting point, this truck was developed in partnership with Kenworth and replaces the original diesel engines that displaced either 12.9 L or 10.8 L, with two solid polymer electrolyte fuel-cell stacks that are exactly like the one used in the Mirai.

Using Mirai stacks solved two engineering problems, said Takehito Yokoo, senior executive engineer for Toyota Motor Engineering & Manufacturing North America. First, it allowed the original hydrogen semi project to get going quickly, which was important to Yokoo and his team of three when they started three years ago.

“The new alternative powertrain has to be here now,” Yokoo said. “Toyota spent 20 years getting the Mirai to production. We do not have 20 years for this truck project. The market is waiting.”

Two solid polymer electrolyte fuel-cell stacks that are exactly like the one used in the Mirai (shown) replace the diesel engine in the Kenworth T680 tractor. (Toyota)

Yokoo has worked on powertrains at Toyota for years, including hybrid, plug-in hybrid and hydrogen. The easiest way he saw to power a semi using hydrogen was to use the existing fuel-cell stack.

“The good thing about the electric powertrain is that, basically, the components are connected by wire harnesses,” he said. “So, you can pick the motor, pick the inverter, pick the battery, pick the fuel cell and connect them to each other.”

The second reason the Mirai fuel-cell stack was used was that Yokoo knew it worked, and worked well.

“We spent 20 years of quality development on the Mirai, so I can steal what the Mirai team did.”

With the basics of the H2 semi-truck solution decided, Yokoo and his team realized that they had stumbled upon a way to power any size vehicle with hydrogen. While internal combustion engines come in many displacement sizes depending on the vehicle segment they are going to be used in, “we don’t want to develop those types of powertrains for fuel-cell systems,” Yokoo said. “It was our challenge to use one standard to scale up to even a Class 8 truck. So, if we can move a Class 8 truck with just the existing passenger size stack, that means we can cover all of the car segments. That’s a great opportunity for reducing costs, when one really good unit can be applied to any segment.”

Takehito Yokoo, senior executive engineer for Toyota Motor Engineering & Manufacturing North America. (Toyota)

Yokoo said Toyota is currently studying the middle spaces between the Mirai and a semi-tractor, to figure out the balance between one or two stacks and the associated battery that the powertrain uses. The Mirai uses a 1.6-kWh nickel-metal hydride battery for extra power, while the semi-trucks use a 12-kWh battery.

“The Mirai battery is very small, but maybe a pick-up will use one Mirai fuel cell and a larger battery,” he said. “When the battery becomes too large to cover the segment, maybe that’s when we move to two fuel cells. Our concept is to use small batteries and that the fuel cell would take care of most of the power. When more power is required for an uphill climb, for example, then the battery would contribute.”

So far, for over two years and 14,000 miles (22,530 km) of real-world drayage use in and around the ports of Los Angeles and Long Beach, Toyota’s first two Project Portal trucks have shown that a 12-kWh battery is enough. Toyota has not done any aggressive, on-road testing of its hydrogen semi in rougher terrain just yet, Yokoo said.

Toyota and Kenworth are planning to put 10 vehicles into service to move cargo in the warm and mostly flat lands of the Los Angeles basin around the Ports of Los Angeles and Long Beach as part CARB’s ZANZEFF project. These trucks have a range of over 300 miles (483 km), which is more than double the average daily duty cycle of drayage trucks. These specs work for now, but any future semis that will be designed for use in other areas might need a bigger battery or more hydrogen tanks for longer range, Yokoo said.

“I believe that 12 kWh will not be large enough for going across mountains,” Yokoo said. At least the type of fuel-cell stack in those potential trucks, that’s relatively set in stone.