Watch Lucid engineers tweak the 1200 HP Air Sapphire EV
From April 2023 issue car and driver.
Especially at Virginia International Raceway, it’s best to clip as many as you can to set up competitive laps. Snake is one such section he is. The Lucid Air Sapphire prototype I’m piloting glides over concrete serrations and rockets toward Climbing Esses as if it were built to do nothing. More careful and selective curb skimming works well here. Then a tight oak tree corner offers another mild apex clobbering. The right-hand detour to the VIR’s inner loop appears quickly, but Sapphire’s massive 10-piston front brake caliper squeezes a trajectory-friendly carbon-ceramic rotor to smartly pull this cruise missile down to turning speed. The car turns smoothly around a low-speed horseshoe, with possible hiccups on exit. It then continues on to the Spiral and a left-right combination of dives just above the blind crest.
“Whoa! That was a big cramp.” There’s another slight interruption in power as you graze the low curb at the exit of the Spiral, but the car reclaims the rest of the infield.Sapphire loves roller coasters. Sounds good, but when you exit the Hog Pen and aim down the front straight, the car goes to the left edge of the track and you don’t have the confidence to take your right foot. After completing one lap, I will return to the pits and report back. Then consider making some changes.
This process is not entirely new territory for me. Before journalism, my food-on-the-table job was evaluating and fine-tuning the suspension of prototypes in development on proving grounds, racetracks and even public roads when everyday driving characteristics were being scrutinized. But I was always focused on tweaking the hardware (springs, dampers, anti-roll bars, tires, bushings, etc.). Because the suspensions I worked on didn’t have lines of software code associated with them.
Ace driver and Senior Technical Specialist in Lucid’s Chassis and Vehicle Dynamics division, John Culliton, has a job similar to the one I once had. He rode a shotgun so we could discuss the car’s behavior on the fly, let loose from his 5-point harness on the prototype, full roll, dive under his cage, calibrate and validate Manager Esther Unti joins the trunk of the car. Laptop.
They seem happy to corroborate my feedback with their own feedback. This is important because it is important to distinguish between what the car is doing and what the driver is doing. This is the first time Sapphire has ventured onto the grand course of his VIR, and the test crew must achieve a certain level of track proficiency before driver tuning gives way to vehicle tuning.
But this is far from Sapphire’s first tuning session. Quite the opposite. CHASSIS AND VEHICLE His dynamics director David Rickford and his team visited numerous tracks and proving grounds. They have so far adjusted the specs of the purely mechanical bits (which I was tuning) and the internals of the bespoke Michelin Pilot Sport 4S tires.
Lickfold and company also decided on a basic mechanical valve for the electronically controlled Bilstein dampers. It works mostly without electronic valving in basic smooth driving mode. Software-controlled rebound and compression damping valves add supplemental damping during extreme events in this mode, while Swift mode automatically adapts to the extra damping and Sprint takes it up another notch . The team also landed on the power steering assist profile for each mode, as well as the mode-dependent behavior of Bosch’s electromechanical brake booster, which blends powerful friction braking with the car’s high regenerative braking potential.
These basic elements felt well worked out and although Lucid didn’t officially lock them down, they are almost in production. What’s left of this his VIR session the engineer is still tweaking the damper software in Swift mode but Sapphire’s ability to shrug the curbs tells me they’re getting closer . It’s mostly something I’ve never had to deal with in my engineering career. It’s all about managing the torque produced by Sapphire’s three very powerful motors.
A regular Lucid Grand Touring features one motor on each end with a differential cleverly integrated within a surprisingly compact coaxial motor housing with the output on the centerline of the motor. Each motor is capable of 670 hp, but the GT’s 1050 hp total is less than both combined. That’s because the GT’s 112.0 kWh battery can’t put out as much power as the Sapphire’s 118.0 kWh pack. This difference also eliminates the cause of uneven high load torque splitting.
On the Sapphire, the same 670-horsepower unit is placed up front, but the rear end contains a pair of these motors within a shared housing. Each rear wheel is individually controlled, so the rear axle has a terrifying 1340 horsepower potential, and all three motors combined add up to a staggering 2010 horsepower. In total Lucid can only put out over 1200 horsepower, with final numbers a few weeks away. But the difference between what that placeholder means and 2010 suggests that the torque vectoring potential is huge here Unti’s laptop and why Lucid joins his VIR Let’s go back to what we did.
This powertrain gives the Cariton and Antti a lot of tuning freedom, but a wide variety of performance-driven scenarios must be considered. Linearly, nothing but sanity and physics will stop you from sending all your battery cans to the rear axle. Having two or more tires torquing the ground will always give you a faster, more stable takeoff. Because of that, they told me about 75% of the launch torque goes to the rear. Even at the drift end of the spectrum, it sends a small amount of torque to the front “to make the slide more predictable and achieve higher sideslip angles.” nice.
The Grand Course at VIR is halfway between these two performance extremes, with a wide variety of corners. That’s why it’s the perfect place for the annual Lightning Lap test and a handy place to sort out Sapphire’s intricate torque his vectoring. This goes far beyond simulating the differential action that occurs naturally in single-motor drivetrains. With two motors on one axle, torque vectoring in an EV can produce power faster, more accurately, and smoothly than typical brake-based torque vectoring. Also, one motor regenerates power while the other advances, so the degree of splitting is highly variable.
Unti’s laptop, equipped with a control program developed by Lucid, manages all these settings. In fact, about 90% of the lines of code within Sapphire were written in-house. The application Unti uses today allows Unti and Cullton to change parameters and rewrite the underlying code accordingly. For example, the wheelbase module redistributes torque to mimic the feeling of the wheelbase physically shortening or lengthening depending on the conditions.
Culliton and Unti made some tweaks to address issues I encountered. For high-speed exits, such as when coming out of a hogpen, increase the level of rear torque vectoring when transitioning from parts throttle to add a little rev (use the word “throttle” instead of “accel” or “accel” use). Since there are other terms to complain about, I also (only this once) add to the front straight acceleration, so I get over the feeling that adding it increases understeer. A dramatic spiral transition softens the turn and reduces turn-in moments so as not to overwhelm the rear tires. It also adds a bit more front torque bias for rear stability in scenarios where the backend cramps on corner exit.
They didn’t tell me any of this before I went out to Sapphire again. His two small bumps on corner exit are gone and the car is much more stable when culminating in slow transitions on spirals. Best of all, I was able to take in power better when exiting the final turn.
There were side effects. As is often the case in tuning, when you improve one thing, you lose out elsewhere. It happened on a roller coaster where Sapphire was a bit twitchy. The car appeared to have tried to help, but two mistakes were right here. Back in the pits for another thought and software tweaks.
At this point my time was up, but Cullton, Unti, and Lickfold planned to stay in the VIR for another round or two before packing up and moving to another test locale. It’ll be great to see where the Lucid Air Sapphire ends up when it’s finished, but it actually looks very promising, let’s hope he gets one next Lightning lap.
Sapphire vs. Plaid
It’s tempting to look at the Tesla Model S Plaid and Lucid Air Sapphire through the same lens. After all, each one is powered by his tri-motor powertrain, which he produces over 1000 horsepower. But there is a fundamental difference.
For one thing, Sapphire has been part of the Lucid Air game plan from the beginning, coming into the model’s second year of production. David Rickford said when his team first conceived the suspension, they knew it needed to drop all that monstrous power and torque. This means the 10-piston front caliper and carbon-ceramic brakes his rotors are not retrofitted.
The Plaid, on the other hand, is the tenth model of the Model S. Since Tesla built its brand around the induction motor invented by Nikola Tesla, and the cross section of it is the Tesla logo, it is doubtful whether Tesla planned the existence of the Plaid that much. But he said in 2019, Tesla began quietly ditching the Model S’s induction motors, switching to permanent magnet synchronous motors.
Additionally, the Model S Plaid shares tires and brakes with its less powerful variant. All-season 19-inch tires remain standard, but 21-inch summer rubber is an option. Plaid is mostly a motor swap. A $20,000 carbon-ceramic brake upgrade kit is slated for later this year, but should have been in the Plaid package from the start.
technical editor
Dan Edmonds was born into the automotive world, but it’s not what you might think. His father, a retired racing driver, opened his Autoresearch, a manufacturing shop for racing cars, where Dan gained experience as a metal fabricator. He then went on to engineering school, SCCA Showroom Stock, where he went through racing and got a job in suspension development at two different automakers. His writing career began when he was featured by Edmunds.com (unrelated) to build a testing department.
https://ift.tt/4RSBpjY Watch Lucid engineers tweak the 1200 HP Air Sapphire EV
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