More bite for the snake - New Technology

Automotive Industries, June, 2002 by Gerry Kobe

The components of Jeep's highly acclaimed Quadra-Drive system --first introduced on the 1999 Grand Cherokee -- have finally been tapped for passenger car duty. And not just any passenger car either -- this is Viper duty.

Dana's Hydra-Lok differential features a progressive coupling that uses a gerotor-type pump to transfer torque back and forth. The inner rotor portion of the pump is splined to one output on the axle and the outer drum portion of the pump is splined to the other. As long as both wheels are turning at the same speed, the axle is open and no pumping is taking place. When there is a difference in speed, the two halves of the pump move relative to each other, gradually building pressure that engages a clutch plate. This locks the inner portion of the pump to the outer case effectively transferring torque.

Specifically, Dodge was looking for a drop-in differential that would offer the traction advantages of a traditional limited-slip design, but without the inherent handling drawbacks caused by clutch pre-loading and abrupt side-to-side torque transfer. It found exactly what it wanted inside the Dana-supplied axles in the Grand Cherokee.

"The Hydra-Lok is speed-sensing rather than torquesensing," says Bob Keister, director of global core engineering at Dana's Traction Technologies Group. "That means it reacts to wheel slip so it ramps up and is easier to tune for handling. It will make the car track better so that it seems to be in a 'groove' in a transition from a straightaway to a turn or in a slalom."

Keister also points out that unlike traditional limited slip designs, Hydra-Lok will not change characteristics or wear out over the life of the vehicle.

"On a typical limited-slip, you start to get performance degradation after 20,000 miles because clutches wear," he says. "Since this doesn't have pre-loading it normally runs in a free state and engages only when needed. This will last a lot longer and always be there when you need it"

Viper is the first performance application for Hydra-Lok although other domestic manufacturers are also negotiating with Dana, possibly for front-wheel-drive duty