Just like the Toyota Prius range of cars, the Mirai’s specific hydrogen drivetrain-based platform could allow Toyota to breed a family of models, according to Toyota Mirai chief engineer Yoshikazu Tanaka.
Speaking ahead of the 2015 Tokyo motor show, Tanaka explained the reasons behind the choice for a sedan body style for the first production fuel-cell vehicle (FCV) despite the fact the company had previously used Toyota Kluger SUV mules as the test bed for the technology.
“Actually Toyota used to use the SUV as the test pilot FCV when we were doing the development back in the early 2000s, but, I mean, if you want to widely sell the car in many different markets, you have to do it with a compact, small [car],” Tanaka said.
The Mirai isn’t compact by conventional standards. Its long, sleek body spans 4.89 metres in length – a few centimetres longer than a Toyota Camry (4.85m).
Tanaka indicated that building the Mirai as an SUV could have meant a much bigger footprint and more weight, something the company wasn’t willing to experiment with on its first attempt at a production FCV.
“This vehicle has very high response, because it’s electric motor-driven. If you want to drive a car as a fashion [accessory], I mean probably SUV would be your choice. But this is the first generation of FCV, and we really want people to know what it can do.
“In order for us to do that, we don’t want to start to be a fashion, we want this car to be fun to drive,” he said.
Tanaka suggested the engineering team had been “very meticulous in developing and designing these cars”, claiming that the driving enjoyment on offer was a key consideration for the car. That push is lead by the brand’s chief, Akio Toyoda, who says he wants all Toyota cars to offer waku doki, or the feeling of having your pulse race when you drive your car.
The Mirai’s construction has a lot to do with the brand’s claims of the car being fun to drive. The fuel-cell stack is located low, beneath the front passenger seat, and the vehicle itself has a lower centre of gravity than conventional vehicles built by the brand.
“The heaviest components are focused toward the centre of the car, so weight balance is very good. It’s very fun to drive. And it has very strong torsional rigidity, if you don’t have to have an engine under the hood, so we have tightly monitored the stiffness using cross members in the engine room and on top of that we have the motor,” Tanaka said.
“The stacks are mounted rigidly using carbon. This vehicle has 60 per cent extra torsional rigidity compared with an ordinary front-wheel-drive car,” he said.
What about other body styles, then? Tanaka admitted he is already considering the next-generation models that will come after the Mirai, and they could include different body styles if development and engineering allows it.
“We don’t know yet. I’m thinking right now,” he said.
When asked specifically if the second round of Mirai models will include an SUV, Tanaka responded “maybe”.
He explained that the bigger body of an SUV – even in conventional models – means there is more energy loss at higher speed, and that would dictate the approach for how to make it more efficient.
“This has a very important implication. All the SUVs have very bad mileage or fuel consumption at high speed.
“So I’m not ruling out the possibility of a FCV SUV, but we will have to pace out the design plan evolution of FCV together with the design of the core technology.
“So at the point we believe a FCV will be very attractive as an SUV, we will do that,” he said.
Speaking of attractiveness, the design of the Mirai is clearly a polarising one. But Tanaka suggested that producing a two-door coupe to match those sporty driving claims could make sense.
“That’s an option as well,” he said of the notion of a coupe. “The design is very important as well.”
But would a performance-focused FCV in front-drive form be what buyers want? What about a rear-drive sports car? That’s on the table, too, according to Tanaka.
“There’s one very unique feature about FCV, one significant constraint to this technology. If it’s a conventional gasoline vehicle, you can design the fuel tanks to be any shape. But for hydrogen, because you need a very rigid tank, the shape has to be cylindrical.
“In the future if the cost of one single hydrogen tank comes down, then we can use many number of skinnier hydrogen tanks. That would give us more flexibility in designing the vehicle.
“For the time-being we will have to live with the very fat cylindrical tank. Right now we would not be able to install a fuel stack in to the 86,” he said to make an example.
Tanaka suggested that it would be possible to make rear-drive work on the architecture, with the motor at the rear axle and two hydrogen tanks to help with weight balance.
“If we could come up with a different layout of the stack, motor and hydrogen tank, we could have a FR, the rear drive,” he said.
“I will not say we are doing that right now, but again we are open to many options.”