Steer-By-Wire Stars on the New Lexus RZ 450e

March 13, 2023

Chris Clonts

Even while Toyota was being criticized about its electrification strategy and its pace in embracing BEVs, the company’s engineers were quietly prepping the Lexus brand’s first EV, the 2023 RZ 450e crossover.

SAE Media recently drove the RZ and spoke with engineers about its development at an event in Provence, France. While not underpowered, with a total of 230kW (313 hp) available when both front and rear motors are at peak output, some will question the vehicle’s below-average range.

The RZ’s 71.4kW, 355V lithium-ion battery — developed by Tokyo-based Prime Planet Energy & Solutions, a Toyota affiliate company — has 96 cells, is sealed with urethane and cooled and heated with water that circulates through it. Lexus says the RZ’s EPA-estimated range is 220 miles (354 km) fitted with 18-inch wheels and 196 miles (315 km) with 20-inch wheels. Charging from 0 to 100% with a Level 2 240V / 32-amp charger takes 9.5 hours, the company claims. A 400-amp DC fast charger requires 30 minutes to go from 0 to 80%.

When asked about the range, engineers and officials said two things. One, that the range is plenty for the RZ’s strongest use case: A two-car household whose other car is an ICE or hybrid vehicle. Why include more capacity than needed for day-to-day local use, Toyota argues, when it would just increase cost and mass?

As an interesting hedge against range anxiety, Lexus will launch a program called Lexus Reserve that allows RZ buyers 30 days’ free access to ICE or hybrid models during the first three years of ownership. So, road tripping from the U.S. coasts to Yellowstone isn’t out of the question. Lexus is also partnering with ChargePoint and Qmerit to guide new owners on charger installation.

And besides, said Yushi Higashiyama, assistant chief engineer for RZ performance, the design is locked in. “The only way for this platform [called e-TNGA] to have higher capacity is to make it longer,” he said through a translator. Interestingly, Lexus’ new CEO Koji Sato has seemingly marked the RZ as a bridge project. He has said a next-generation BEV platform would arrive around 2026. Toyota and Lexus together have plans to release 28 new electric vehicles by 2030.

The dual-motor nature of the RZ presents some interesting challenges when talking about power distribution. For instance, when engineers say that the vehicle’s Direct 4 AWD system can transfer 100% of drive torque to the rear wheels, it comes with an asterisk. Because there is no driveline connecting the front motor (150 kW/201 hp) to the rear, it means that only the 80kw (107 hp) motor is driving the rear wheels.

One can imagine a lack of power in situations that would call for rear bias, such as spirited exits from curves and around corners. But that’s not the case. While no one is going to take the RZ to the track, there is plenty of power available, in any combination, to make driving the RZ enjoyable. Lexus claims the RZ can accelerate to 60 mph (96.5 km/h) in five seconds. Delivering power to the ground are high-torque eAxles with three-point mounting. Left/right stability control is handled via brake-vectoring only.

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-by-wire 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 [autonomy], you will be able to fold it away.”

It took less than 30 seconds of driving to get used to the Lexus system, which provides a great user experience a few ways:

• 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 require less yoke travel, and at highway speeds only tiny adjustments are necessary as the ratio is set at its highest.
• Controls such as turn signals aren’t on a (non-existent) steering column. Attached to and rotating with the yoke, they’re always in the same position relative to your hands.

The system is so good that driving cars with the standard steering setup felt a bit disappointing, even though the experience had no obvious flaws and meets the standards of other Lexus vehicles. With either wheel, the RZ has a tendency to understeer, though stabbing the throttle and the resulting high proportion of power at the back wheels is a noticeable remedy.

The only thing worth wishing for is some place at the bottom of the yoke for one-handed cruising down straight, open roads.

New sunroof, active battery cooling

The RZ features an electrochromic, one-touch dimming sunroof. Lexus product marketing manager Sakiko Aono said deleting the mechanical sun shade in favor of the electrochromic sunroof increases headroom for front-seat passengers.

Aono said one distinguishing feature of the RZ is its available interior accent lighting, which projects a texture onto interior surfaces like doors. On the front fascia, the “L” logo is lighted, a first for the brand. It also indicates charging status at a glance.

Up front, Lexus’ signature spindle grille is replaced by what designers call the “spindle body.” This is a small grille above the bumper that is used to vector supplemental cool air to the liquid-cooled battery and motors. Assistant chief engineer Higashiyama said an active shutter inside closes when cooling isn’t needed. The vehicle’s traction motors circulate coolant through a jacket around the permanent magnet cores.

Radiant heating and safety

The RZ’s curb weight is listed at about 4,600 lb (2086 kg) in the Luxury trim level equipped with 20-inch wheels. The Premium model, with 18-inch wheels, is approximately 40 lb (18 kg) lighter.

Both trim levels come with a 14-inch touchscreen with controls easy to use for anyone who has a smartphone. The USB-C era has arrived with authority in the RZ, with three ports up front and two in the rear.

Without a steering column in the way, Lexus has made available a radiant heat panel that can warm the front driver and passenger’s legs and feet. One reason to do it, Higashiyama said, was for energy management. With radiant heat from the seats and the front panel, the main cabin HVAC system may be called on less, saving energy overall. This is similar to a proposition supplier ZF said at CES earlier this year when it offered up a heated seat belt with a similar thesis.

The 450e comes with a full suite of standard and available driver-assistance and safety tech, including:

• Pre-Collision System with Pedestrian Detection, powered by a camera and millimeter-wave radar.
• Risk Avoidance Emergency Steer Assist, which can gently brake and steer away from trouble during daytime parameters.
• Left Turn Oncoming Vehicle Detection/Braking, to first warn then automatically brake the vehicle if the driver is turning left in front of oncoming traffic.
• All-speed Dynamic Radar Cruise Control, which can maintain safe distances from cars in front while slowing to a complete stop and accelerating again.
• Advanced Park, which can automatically park with minimal driver input.
• Traffic Jam Assist.

The RZ is assembled at Toyota’s Lexus factory in Motomachi, Japan. U.S. retail pricing starts just below $60,000.

We mentioned above that Lexus really doesn’t want to call the steer-by-wire interface a yoke. Asked what they want to call it, the U.S. contingent said they haven’t named it yet, but that the definitely will not call it what it’s being called in Europe: One Motion Grip, or OMG... LOL.

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