Prodrive fixes Focus RS

New active diff adds traction and stops 'wheel fight'

By PH Staff / Friday, 4 March 2005 / Loading comments

Prodrive is putting its Active Torque Dynamics (ATD) system onto a front wheel drive (FWD) car for the first time. The motorsport and automotive technology specialist is building its first FWD prototype and using the Ford Focus RS as a demonstrator.

Prodrive has already built 11 ATD prototype vehicles; nine based on four-wheel drive vehicles and two on rear-drive cars. With the increasing popularity of high performance, FWD cars, like Focus RS, maintaining traction without compromising the ride and handling is becoming an issue.

“To give these cars better traction and excellent handling characteristics on smooth roads and circuits, some high performance front wheel drive vehicles have a limited slip differential on the front axle,” said chief dynamics engineer Damian Harty. “The consequence of this is that such cars can suffer from ‘wheel fight’, with the vehicle wanting to steer itself from side to side, as it is accelerated on surfaces that are slightly uneven or with differing levels of traction at each wheel. It can be unnerving for a driver and lead to a poor impression.”

On the Prodrive ATD Focus, the standard limited slip differential is replaced with an active differential, which can be opened or closed to give the best solution in any scenario. As a result, the differential can be locked when traction is required, but in an event where ‘wheel fight’ may occur the differential lock can be softened enabling the wheels to turn at different speeds and finding the optimum balance between traction and wheel fight.

Through mapping of the ATD software, the tendency to understeer can also be suppressed, while the differential can help ‘steer’ the car into a slide to help correct oversteer.

“This represents an exciting opportunity, delivering some of the benefits of active steering without the difficult failure modes,” said Harty.

In production, the ATD system would use all the existing sensors on a car and replace the existing differential with an active unit. As a result, the additional cost to the consumer would only amount to a matter of a few hundred dollars.