THE FUTURE OF TRACTION CONTROL: IT'S FUN NOW
Lucid’s 1,234-horsepower Air Sapphire has reinvented traction control, and it’s meant to keep you out of the ditch—while never being noticed.
We know that you, Mr. Car Guy, do not need traction control. You communicate with a car purely via the gentle caress of your palms and the rhythmic beat of your soles. Traction control simply interrupts your tango with the machine, and to suggest leaving it on is sacrilege.
This might be fine with gas cars, but electric cars do not want to dance. Electric motors—with 100 percent torque available from a standstill—operate on a timescale human beings cannot process. In absurdly powerful electric cars like the 1,234-horsepower Lucid Air Sapphire—with three motors to coordinate—traction control is a necessity to keep the car on the road, but engineers are determined to let us have our fun while keeping the car at least close to the road.
The Name's Max. Max Trac
Traction control dates back to the early 1970s, when Buick offered “Max-Trac” as an option on its full-size models. Max-Trac was rudimentary by modern standards, with just two sensors communicating to a central control unit. One sensor was located on the (unpowered) front left wheel, and the other was on the output shaft of the transmission. If the transmission output shaft sensor indicated higher speeds than the front wheels, the computer determined the rear wheels were slipping, and the ignition system would cut in proportion to the amount of slip measured.
Max-Trac was unpopular and discontinued entirely in 1973, just two years after its introduction, but it proved incredibly prescient. Modern traction control operates on the exact same principles: Sensors at the wheels—generally, the same sensors used for ABS monitoring—and the transmission output shaft need to agree on what speed the car is going. If the wheels lose traction (and spin faster than they should be), power is reduced either by cutting throttle (like the early Buick design), or in performance cars, by selectively braking slipping wheels. Modern traction control helps prevent losing control on slippery surfaces, but it also prevents drivers from reaching the edge of control when driving hard. Proactive systems cut power long before the true limits of grip, which generally is where the fun is to be had.
19,500 RPM Needs More Than A Gentle Foot
Most modern internal-combustion traction control comes with an off switch for this reason. But EVs, which produce hundreds or thousands of foot-pounds of torque on tap from a standstill and use motors that spin up to 20,000 RPM, can go from “I got this” to backward in moments. I spoke to Esther Unti, who was responsible for developing traction systems on the 1,234 horsepower Lucid Air Sapphire, to understand how engineers put power to the ground in an era of electrification.
Unti explained that for the Sapphire project, off-the-shelf traction control systems were not fast enough for the torque of the Sapphire’s three motors, as they operated on a glacial time scale of tens of milliseconds. (A human takes roughly 572 milliseconds to blink.) Instead, the Air uses a in-house traction control algorithm built directly into each of its motors’ controllers for a virtually instant response to wheel spin.
This is orders of magnitude faster and more predictable. In a physical, brake-based system, the act of braking itself introduces lag, as the computer waits for fluid to pressurize and pads to contact the rotor. Even when brakes engage, they don’t do so consistently—heat can change how much bite the pads have over the course of a single track session. With EVs, cutting power at the motor prevents this mechanical variance and allows for perfect consistency.
Benchmark: Blackwing
Unti explained that motor-based traction control has two other key advantages.
“With brakes… you’re wasting the torque that goes to the wheel you’re going to apply the brake to,” Unti explained; that waste is simply energy lost and more heat created. Additionally, with a motor at each wheel (as on the rear axle of the Air Sapphire), “we can positively apply torque on one side, and negatively apply torque on the other side.”
A vehicle control unit (VCU) coordinates the motors based on driving mode, road surface, and driver input. On a single-motor car such as the Air Pure, the VCU’s job is to fine-tune the motor’s response, but “on a three-motor configuration [as found in the Sapphire], it’ll say ‘let’s cut some rear [power] and add some front [power]... it’s a big part of what makes the car ‘shrink down’ and rotate.” It’s not dissimilar from an active torque-vectoring differential found in some gas cars, but the VCU allows for more fine tuning of the car’s behavior.
This flexibility allowed Sapphire engineers to design a more-fun driving experience, rather than purely a lap-time focused one.
“If you’re a good driver, and you can drive at the limit confidently, you know what rotating the car [with] throttle feels like, or rotating the car on lift. With torque vectoring, you can access that feeling at, say, six tenths… way below the screeching tires limit that you would need” with a typical ICE sports car. The feeling the engineers aimed for with this torque vectoring was a fun, “hoonable” one, benchmarked off of the Cadillac CT5-V Blackwing and BMW M5 CS.
"TC On" Means You Can Still Go In The Ditch, Mind You
Although the Air Sapphire has a “traction control off” setting in its Track Mode, allowing the Sapphire to burn rubber and drivers to drift up to (and past!) the edge of control, the traction control is never truly off. Without it, the car would be literally undriveable. The success of the Sapphire has shown that electrification and always-on traction control doesn’t spell the end of fun in the automotive world. Instead, the hyper-powered sedan might just hold the key to a more accessible experience for us all.
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2024-04-19T14:20:30Z dg43tfdfdgfd