Global regulations are driving the vehicle fleet toward econobox efficiency and/or increased electrification. But to succeed in a cheap-gas economy, these fuel/electron sippers will need to be as fun and comfortable to drive as our current favorite carbon spewers. GKN Driveline recently showed off several “life hack” technologies for preserving driving fun as the carbon screws tighten—including riffs on the company’s Twinster all-wheel-drive system, which gave the Ford Focus RS its drifting mojo and saves fuel by disconnecting the AWD hardware in myriad vehicles from GM, FCA, Jaguar Land Rover, and others.
Because these technologies are easiest to experience in low-traction conditions, I ventured to a frozen lake near Arjeplog, Sweden, to try them. First, a quickie refresher on Twinster: This AWD system eschews differential gears in favor of clutches on the left and right halfshafts. Engage them both fully, and you get a locked diff. Engage them variably, and they deliver torque vectoring. Release them both, and you can idle the engine and/or the driveline components to save fuel.
First up was a cost-reduced system that keeps two clutches but activates them simultaneously (Siamese-Twinster?), halving the number of valves and actuators needed. There’s no torque vectoring, but the system nevertheless made a Jeep Renegade much driftier than a similar open-diff Renegade on hand for comparison. Its locking function also delivers superior performance off-road and on surfaces with differing friction left and right. Pricing is only slightly more than an open-diff system with a single rear-axle disconnect clutch.
Next up was a mighty rear-drive BMW M3 fitted with a beefed-up Twinster axle in place of the limited-slip differential. This adds torque-vectoring capability, and I was abundantly assured that the clutches in this system can withstand repeated hard launches as easily as similar clutches in automatic transmissions. These clutches also serve as a smarter, less vulnerable “fuse” to prevent pricier driveline damage when enthusiasts go overboard boosting the engine and/or fitting ultra-grippy tires. And engineers claim that opening the clutches for engine-off “sailing” can reduce fuel consumption by 1 to 8 percent depending on the test cycle.
Other interesting innovations were presented in the hybrid and fully electric space. A new Multimode plug-in hybrid transaxle couples an electric motor to a combustion engine via a Prius-like planetary gearset—with the motor either acting as a generator to vary the output speed of the engine’s input at lower speeds or helping pull, sometimes with the engine locked to the output.
Pairing this setup with a peculiar second planetary gear (featuring no ring gear but two sets of planet gears engaging two different-diameter sun gears) delivers two gear ratios. High first-gear torque multiplication (17:1 on the demonstrator) allows a lighter, cheaper, less powerful motor to launch like a bigger, pricier one with the PHEV in full electric mode, while the second ratio optimizes engine and motor rpm at higher vehicle speeds (10:1 here). On two different vehicles, I never sensed a gear shift. Adding Twinster clutches to such a front-drive transaxle makes the vehicle feel vastly more eager to change directions.
GKN gutted another Jeep Renegade and fitted it with a battery pack and e-axles featuring the above two-speed setup at both ends. The front one featured Twinster clutches. By changing their programming, the car could deliver stock levels of understeer, feel completely neutral, or deliver modest drifty oversteer—with front drive and the rear motor idle. (Obviously, it drifts even more with the rears spinning, too.) The most fun demonstrator was a Mercedes-AMG GLA 45 fitted with a Twinster torque-vectoring front transaxle bolted to the stock engine and a two-speed rear Twinster e-axle in back. If one Twinster is fun, imagine the Ken Block hooning twin-Twinstering delivers!
Nobody inside GKN expects any manufacturer to spring for all-wheel-Twinster, and fitting the technology in front poses torque-steer challenges with powerful engines on dry pavement. But Twinster can boost driving dynamics—and fuel efficiency—wherever it’s fitted. Even our unfeeling robo-chauffeurs will appreciate the more neutral driving dynamics this technology affords.
Read more by Frank Markus here:
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Author: Erika Pizano