A motorsport-derived Quaife Automatic Torque Biasing differential, developed to work with innovative Ford RevoKnuckle suspension, allows one of the highest FWD outputs of any production car, with almost zero torque steer.
Differential technology from Quaife has helped Ford overcome one of the most challenging aspects of high performance front-wheel drive (FWD) cars. With its 2.5 liter five-cylinder turbocharged engine producing 300hp and 324 lb-ft of torque, the new Focus RS is one of the most powerful FWD production cars ever. Yet it's combination of Quaife Automatic Torque Biasing differential and new Ford RevoKnuckle suspension allows beautifully weighted steering with almost no torque steer, even under full acceleration out of corners.
"Ford wanted to retain front-wheel drive because it is lighter and more efficient than four-wheel drive and for many it gives a more tactile driving experience," explained Quaife technical director Michael Quaife. "The problem was how to put so much power through the front wheels without tremendous issues with traction and torque steer.
The solution chosen by Ford is a partnership between its new RevoKnuckle suspension and a Quaife Automatic Torque Biasing limited-slip differential (ATB).
RevoKnuckle uses the existing MacPherson strut architecture, but with a new two-piece knuckle that incorporates an innovative `C' shape lower suspension mount. This creates a king-pin offset less than half that of a conventional McPherson system with wide track - in effect, moving the turning line of each wheel closer to the wheel center. It also provides significantly greater freedom to optimize suspension parameters such as caster, camber and trail.
As well as substantially reducing torque steer, this new architecture is ideal for operation with a high-performance limited-slip differential as it allows the benefits of the ATB to be maximized without compromising steering feel and smoothness.
The Quaife ATB is a new development of technology thoroughly proven at the highest levels of motorsport. When one wheel starts to slip, the patented system automatically biases torque delivery to the wheel with most grip. In cornering, it maximizes the amount of power that can be used by biasing torque distribution to the outside wheel. This combination of functions allows the driver to apply more power through corners and on loose surfaces and makes the vehicle substantially safer and more stable in difficult conditions.
Power is delivered to a sun gear on each driveshaft by a set of six helical planet gears (12 in total) running within the input drive hub. As one wheel starts to slip, the torque differential across the two sets of planet gears increases, causing the set transferring the most torque to progressively lock. This reduces their rotational speed and progressively transfers more torque to the wheel with most grip.