FYI: I just stumbled on this site-
The strange geometry of Gleason's Impossible Differential
Constantly responding to changing road conditions, this unique differential automatically
varies the distribution of torque to a vehicle's rear wheels. Result: two-wheel-drive traction
approaching that of a four-wheel drive. It could make its Detroit debut in 1985.
As I approached the stop sign, I noticed an icy patch on the street in front of the left side of my International Scout. Several cars
had already spun their wheels on the ice, and it was polished to a slippery, glassy smoothness. I had recently installed one of the
new Torsen (torque-sensing) differentials in my four-wheel-drive Scout, and this was a perfect opportunity to test the maker's
claims. In two-wheel drive, I gently accelerated and began to turn. The left rear wheel was now on the ice, but it didn't slip. I
pushed harder on the accelerator. The rear tires grabbed, and I maintained a perfect are through the intersection as if there had
been no ice at all.
Throughout the winters of 1981 and 1982, 1 never had to use four-wheel drive. The amazing improvement in my Scout's
performance was due to the Gleason Torsen differential. This uniquely designed differential applies torque to both rear wheels
and distributes torque as required. It will deliver as much as 90 percent of the torque to one wheel, with 10 percent going to the
The new differential has been proving itself in vehicles ranging from Mario Andretti's race car to the U.S. Army's Jeep
replacement. And Detroit is definitely interested. The way engine power is conveyed to the wheels by the drive train affects the
way a vehicle gets traction on a road surface. Most of us know about the first two components of the drive train: the engine and
transmission. The third part, the differential is not nearly as familiar. That part has traditionally been a major source of mysterious
traction problems for many cars.
To understand the characteristics of the Gleason differential, it is necessary first to review the "differential problem," as engineers
describe it. The problem stems from the basic nature of power-driven wheels on axles. The best way to propel a vehicle is with
power to both wheels. But in many situations, the wheels are not turning at the same speed. For example, when a car makes a left
turn, the inside (left) wheel makes a smaller are than the right wheel. The right wheel must travel farther, and the differential must
"differentiate," or compensate, between these two arcs. If both wheels were solidly driven by the drive shaft (as on some dirt-track
racing cars) and the vehicle took a sharp turn, the tires would skid, squeal, wear unevenly, and possibly throw the vehicle off a
curve at high speed.
Until now, there have been three basic ways to handle this problem. The first is the conventional differential. In normal operation
(driving in a straight line), it distributes torque equally to both wheels. But because of its internal gearing, it has a built-in preference
for the wheel with less rolling resistance (traction). This allows the wheels to make turns, but it has traction drawbacks. A
conventional differential can't tell whether you're losing traction on a slippery surface or turning. The "limited-slip" differential tries
to overcome the conventional differential's limitations. It's been offered as an option on many makes of cars for over two decades.
Through the compression of clutch packs