Automotive Engineering - February 2023 - 14

ROAD READY
High-performance hybrid headlines Lexus's re-engineered RX lineup
Electrification is a pillar of Lexus's " next
chapter. " The fifth-generation Lexus RX
progresses this objective, offering four
new powertrains including a high-performance
hybrid and the company's firstever
plug-in hybrid (PHEV) - though the
latter is not available in the U.S. at launch.
Other " foundational elements " include
bold design, intuitive technology and
Lexus driving signature. Experienced firsthand
by SAE Media on the hilly, twisty
terrain north and west of Santa Barbara,
the 2023 RX, which rides on the lighter,
stiffer GA-K platform that also underpins
the smaller Lexus NX, hits on all marks.
Overall, the new RX is just 4.9 kg (11
lb) lighter than the previous generation,
but the GA-K platform is 90 kg (198 lb)
lighter than its predecessor. Its center of
gravity is 0.6 inches (15 mm) lower.
Panel thickness has been reduced on the
side members and front and rear door
assemblies thanks to the use of higherstrength
steels such as 1180-MPa grade
on side rockers, 1470-MPa for the roof
and 2-GPa hot-stamp steel for B-pillars.
Additional bracing at the radiator support,
center floor, rear suspension towers
and back door opening improves overall
rigidity. Although the 2023 RX retains its
overall length at 192.5 inches (4890
mm), its 112.2-inch (2850-mm) wheelbase
is 2.36 inches (59.9 mm) longer
and its track is widened by 0.59 inches
(15 mm) to 65 inches (1651 mm) in front,
and by 1.77 inches (45 mm) to 66 inches
(1676 mm) at the rear. The new RX overall
is 1-inch (25-mm) wider and 0.4-inch
(10-mm) lower than before, giving it a
more muscular stance.
Lexus says its engineers thoroughly
revised the suspension to better absorb
high-frequency vibrations and shocks. Up
front are MacPherson struts. An all-new
five-arm multi-link rear setup reportedly
is more compact, which for hybrid models
aids battery-pack placement beneath
the rear seat while yielding more legroom
(37.36 inches/948.9 mm) for rear passengers
and additional cargo volume (29.6
cu. ft./0.84 cu. m. with all seats up).
First-ever RX 500h
While the RX 350h hybrid model was
designed with efficiency in mind, developers
envisioned drivers having a more
visceral connection with the all-new RX
500h F Sport Performance AWD. A 271hp
(202-kW) 2.4-L turbocharged inlinefour
is matched to a six-speed automatic
A new vertical-standing trapezoidal grille sets
a bold design statement for the 2023 RX. For F Sport models,
front vents regulate airflow around the tires, aiding straight-line stability.
gearbox and integrated power control
unit and electric motor. An 80-kW rear
eAxle consisting of an inverter and motor
provides power to the rear wheels.
Lexus opted for nickel-metal hydride
batteries in both the 500h (288 V, 240
battery cells) and 350h (259 V, 216
cells), claiming their overall performance
is comparable to that of lithiumion
batteries. Engineers will continue to
evolve both battery types and use them
accordingly, a spokesperson said.
In total, the system produces 366 hp
(273 kW) and 406 lb-ft (550 Nm) - figures
worthy of the vehicle's F Sport
Performance nomenclature. Lexus's
more-traditional hybrid, the RX 350h,
couples the fourth-generation hybrid system
with a 2.5-L four-cylinder Atkinsoncycle
gasoline engine and CVT, resulting
in a total system output of 246 hp (183
kW) and max. 233 lb-ft (316 Nm).
The RX 500h features a new Direct4
RX 500h Sport
Performance cabin.
AWD system that utilizes the rear eAxle
to provide nearly double the max output
of the MGR (motor at rear axle) in the
eFour AWD system employed on the RX
350h and the RX 450h+ plug-in hybrid
model. Relying on sensors for wheel
speed, acceleration and steering angle,
the " performance-oriented " Direct4 adjusts
the driving force to the front and
rear wheels between 70:30 and 20:80.
Engineers explained that during departure
and straight-line acceleration, the
system controls the front-to-rear ratio
between 60:40 to 40:60 " to suppress
14 February 2023
AUTOMOTIVE ENGINEERING
BOTH IMAGES: LEXUS

Automotive Engineering - February 2023

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