For his first job as a chief engineer, Satoki Oya got a big one: managing the development of Toyota’s 2023 Prius.The new fifth-generation version’s heavy revision is most apparent in its brazenly sleek sheetmetal. But letting go of the Prius’ hallmark stylistic oddness was just one part of Oya’s mission to just as shockingly upgrade the hybrid’s dynamics while sacrificing virtually none of its signature fuel-efficiency.
The Prius’ new design has earned near-unanimous praise. Its markedly upgraded power and performance take it to a driving-dynamics place difficult to believe could be achieved in concert with a 57-mpg city/highway combined fuel-economy rating. SAE Media editorial director Bill Visnic interviewed Oya, assisted by a translator, at a media-drive program in December 2022.
You retained the TNGA (Toyota New Generation Architecture)-C for the 2023 Prius, but what were some of the chief areas of revision?
The biggest difference was for weight reduction. Weight reduction of the underbody and increase in structural body rigidity, structural rigidity. For more specifics, the front suspension components’ design is slightly different. The crossmembers are different. And the rear structure of the platform has been remade exclusively for the Prius in order to accommodate the packaging for the design — the floorpan itself. The reason is that we had to change the layout of the fuel tank and the hybrid batteries.
We've reported on Toyota's attempts to get to 40% brake thermal efficiency with non-turbocharged combustion engines and you've achieved that. Can you relate to me where the Prius engine is in terms of brake thermal efficiency?
For the 2.0-L Dynamic Force engine, the fourth generation already had a thermal efficiency of 41 percent and the fifth generation [used for the 2023 Prius] maintains the same 41 percent. There weren't any major changes for the engine.
The 2.0-L’s 150 hp is 56-percent more powerful than the Prius’ outgoing 1.8L engine, yet the new Prius manages essentially the same fuel efficiency. What kind of choices did you make?
For dynamic performance, switching to a larger-displacement engine and the improvements in the hybrid system almost automatically gave the increased performance factor. For maintaining fuel economy, it's a combination of smaller adjustments and techniques — such as, even though we went with a larger-diameter wheel and tire, we minimized tire width to reduce rolling resistance.
In terms of aerodynamics, the new Prius certainly looks sleeker than the fourth-generation model. Has there been aerodynamic improvement?
If we just look at aerodynamic characteristics, the fourth-generation had an advantage. The reason is the peak of the roof is more forward on the fourth generation – and that's purely for aerodynamics.
But this time, for styling, we moved it rearward. Aerodynamics though, is not just about the Cd coefficient figure. If we're talking about the frontal resistance, what we did – because we lowered the overall height of the vehicle – we reduced the surface area. So it's actually the CdA calculation. And we've matched that of the fourth generation, so [the new sheetmetal] doesn't affect [overall aerodynamic] performance.Continue reading »