At first, reading the words “Ferrari” and “all-wheel drive” (AWD) seem as compatible as “oil” and “water,” but with the company's original FF entering its fifth year of production, the Maranello engineers decided it was time for its unique AWD system to get an update by incorporating a new, patented torque-vectoring capability and rear-wheel steering.
The first Ferrari to feature this integrated capability is the new GTC4 Lusso, a nameplate that conjures both the GTC and Lusso classics, with the '4' denoting not the number of driven wheels but the seating capacity.
“In general we wanted to improve the torque vectoring, with more flexibility to put the right amount of torque to the correct wheel," explained Ferrari Chief Technology Officer Michael Leiters during the new Lusso's debut at the 2016 Geneva Salon. "Therefore, we had to do two things: firstly, to estimate and control more precisely the slip of any wheel and, secondly, to improve the flexibility of the system to distribute the torque,”
He added: “We are now able to put up to 20% more torque to the front axle with a maximum of 1400 N·m (1032 lb·ft) to either wheel and up to 90% of torque to the outer wheel during cornering."
To view an animation of the new Ferrari driveline: https://www.youtube.com/watch?v=JVsZ2A3mXgs.
Rapid response time
Leiters told Automotive Engineering at Geneva that his team's idea for the new driveline was "to increase driveability in low-grip situations, which is why we decided to have AWD available through to fourth gear of the main transmission: We wanted to improve that system, especially in low-grip, wet and snow conditions.”
To achieve that, Ferrari developed a new software algorithm to estimate wheel slip. Known as ‘Slip Control Version 4’ it employs a different suite of sensors, including speed sensors for the wheels and acceleration sensors, to more accurately calculate the precise manner in which the wheels slip, while improving reaction time over the outgoing technology by between “10 to 20%,” according to Leiters.
Although ZF provides the GTC4 Lusso's mechanical hardware, the software and algorithm development has all been done in-house at Ferrari and is subjected to its own patents.
The second major update was increasing the amount of torque available to the front wheels by optimizing the AWD system’s thermal management. “Previously that was one of our limits, but the cooling system and heat exchanger is more efficient than the previous one,” claimed Leiters.
From its original concept, Ferrari's AWD was intended to be much more than a stand-alone system.
"It was our initial idea to combine it with electrically-actuated rear-wheel steering; when you drive on snow with torque vectoring on the front axle you get increased control," Leiters explained. "But also having rear-wheel steering, that helps us a lot compared to other cars which have a very neutral behavior but can be very difficult to control when they start to oversteer."
With the GTC4 Lusso, the car is "very precise and predictable, so you feel how the car is at the back. It’s much easier [to control] than the previous FF when we tested it on ice," Leiters noted.
Although the system alters the rear-wheel angle by no more than 3º, Leiters maintained that the speed of reaction is most important. Beyond saying that it’s “very, very” fast" he wouldn’t divulge reaction time. He added that the keys to the system's enhanced effect on stability are the new algorithms that predict both the car’s behavior and the driver’s inputs.
Comparing the rear-wheel steering to that introduced on the F12tdf (where it remains in parallel production), Leiters explained that the GTC4 Lusso system has two modes.
“On the FF we do both parallel and counter-steering depending on the situation: on a dry road and you want to drive through a dynamic curve, we always [rear steer] in parallel [with the front wheels], because if you go in counter-steer the car feels as if it’s slipping away. That gives a strange feeling, not emotional driving," he said. Meanwhile, "if you go on ice and you have to correct the slip angle of the car, you have to do both.”
From the nose of the V12
While Leiters admitted that Ferrari will develop rear-wheel steering "for further applications and cars,” he made it clear that agile cars like the 458 will remain resolutely focused as driver’s cars without any dynamic enhancements.
The AWD drive unit takes its power directly from the nose of the 680-hp (507-kW) V12 engine’s crankshaft, so there is no transfer case or forward-leading propshaft. The engine is mounted far enough back in the vehicle structure that the whole front-drive system can be fixed to its nose. The rear wheels drive thru a 7-speed dual-clutch sequential transaxle similar to that used in Ferrari's rear-drive California model.
Within the front drive-unit casing are a 2-speed gearbox and a pair of electronically controlled multi-plate oil-bath clutches. When the car’s ECU determines that drive to the front is required, it progressively closes the clutches. The two clutches are independently controlled; one drives the left front wheel, the other the right. Thus there is no need for a front differential and torque vectoring is provided.
The front gearbox’s two ratios are similar to second and fourth gears in the primary rear-axle gearbox. Any discrepancy in the drive ratio between front and rear wheels is taken care of by the slippage of the clutch packs.Continue reading »