Automotive Engineering - March 2023 - 31

Q&
Making over the world's leading hybrid
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
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 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. Where
is the Prius engine is in
terms of BTE?
For the 2.0-L Dynamic Force
engine, the fourth generation
already had a thermal
AUTOMOTIVE ENGINEERING
efficiency of 41 percent and the fifth generation [used for the
2023 Prius] maintains the same 41 percent. There were no
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.
For the 2023 Prius, Chief engineer
Satoki Oya delivered vastly sleeker
styling and drastically more power
- without compromising the Prius'
exemplary fuel efficiency.
Switching to a largerdisplacement
engine and the
improvements in the hybrid
system almost automatically gave
the increased performance factor.
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.
March 2023 31
A
TOYOTA
Automotive Engineering - March 2023

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