Issue link: https://read.dmtmag.com/i/287940
4 www.studentdriverplacement.com April '14 It Works How by Tom Kelley Know The Diff erence A xle gearing is used to get power from the driveshaft to the wheel-ends in the proper proportions. The largest gears in a drive axle are the pin- ion gear (input) and the ring gear (output). The layout of these two gears in the drive axle allows the power to make the 90-degree "turn" to reach the wheel-ends. There are other gears in a drive axle that balance power between the wheel-ends. On a straight road, all of a vehicle's wheels should be turning at nearly the same speed. But when driving through a curve in the road, distributing the force in the correct proportion between the left and right drive wheels requires "differen- tial" gearing to allow the wheels to turn at "different" speeds, as the wheels on the outside of the curve travel farther than the wheels on the inside of the curve. An axle's main differential is typically built inside the ring gear housing, transfer- ring power from the ring gear, through the differential gears, to the wheel-ends. When the drivetrain's pushing power can overcome the tires' ability to stick to the road, tandem drive axle confi gurations are used to divide force across a greater number of wheels, reducing the chance of spinning the wheels. Because a difference in tire sizes be- tween axles is almost unavoidable, and because axle spacing can add to the dif- ference in travel-distance at each wheel position when driving through a curve, an extra set of differential gearing, called the "inter-axle differential" or "power-divider," allows the two axles to turn at slightly dif- ferent speeds. The differential gearing that allows wheels to rotate at different rates when traveling through a turn, however, creates a problem when the wheels on either side of a differential do not have equal traction. With an "open" differential, the wheel with the least traction gets the most power, and there you sit, spinning one wheel and get- ting nowhere. With the potentially huge difference in traction across the wheel positions in a tandem drive axle confi guration, it's some- times necessary to be able to "lock" or dis- able the inter-axle differential in low-trac- tion situations. Today's ABS systems can perform this function by selectively braking any wheel that is spinning due to lack of traction. ◆ Turning The Corner With Differential Gearing how it works 0414.indd 1 3/20/14 1:42 PM