Automotive Engineering - April 2023 - 19

COVER STORY
The BEV system includes a larger
motor, along with the onboard
charger and inverter, up front,
with a smaller one powering the rear.
Chassis star: steer-by-wire
The RZ's chassis is conventional, with front
MacPherson struts and double-wishbone rear suspension
striking a nice balance between performance and
comfort, at least over the relatively smooth roads of
Provence. Frequency reactive dampers are used at the
rear to " control the damping force on the extension
stroke in response to road surface frequency input. "
Essentially, the technology helps maintain tight control
over the sprung weight throughout driving, which is
one of the Lexus Driving Signature goals.
Though it won't be available on RZs sold in North
America until late 2024 at the earliest, Lexus' steer-bywire
was the star of the cars Lexus' provided for journalists.
The system consists of the yoke (Lexus considers
this to be a four-letter word and vows not to use it
- more about that later), a steering-torque actuator
for steering feedback and a control actuator on the
steering rack that turns the wheels. The motors were
developed by Toyota, JTEKT and Denso.
Unlike Infiniti's Direct Adaptive Steering introduced
on the Q50s in 2013, there is no mechanical steering
column backing up the by-wire system. Instead,
Higashiyama said the system is fully redundant. He
also said that steer-by-wire and the yoke will be core
components of future Lexus EVs. He referenced the far
future when he said that " When we reach Level 5
[driving automation], you will be able to fold it away. "
It took less than 30 seconds of driving to acclimate
to the Lexus system, which provides a great user experience
a few ways:
AUTOMOTIVE ENGINEERING
Cutaway of the RZ body shows some of the effort to reduce NVH by using hightensile-strength
steel (in blue) with high-density foam adding ridgidity.
* The yoke's lock-to-lock movement is only 300 degrees, so there is
never any need for the hand-over-hand movement of standard
steering wheels. This was a common complaint about Tesla's yoke,
which had some drivers grabbing for air during turns.
* The steering ratio is elegantly optimized based on speed. Turns to
full lock are only necessary at slow, parking-lot-like speeds.
Moderate speeds through the hills on the twisty roads of Provence
April 2023 19
FROM TOP: LEXUS; CHRIS CLONTS

Automotive Engineering - April 2023

Table of Contents for the Digital Edition of Automotive Engineering - April 2023

Automotive Engineering - April 2023 - INTRO1
Automotive Engineering - April 2023 - SPONSOR1
Automotive Engineering - April 2023 - CVRA
Automotive Engineering - April 2023 - CVRB
Automotive Engineering - April 2023 - CVR1
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