Differential engagement
To explain to you how the system operates, I randomly chose the Traxlok from Honda as my reference.

In most cases, you can only engage the differential at a certain speed. For example, the Traxlok differential won't engage until the ATV reaches 10 kph.


This system consists of an electromagnetically-controlled, two-way roller clutch located inside the driveshaft. It was initially fitted to all Foreman, Rincon 650 and Rancher AT models. It's a sealed mechanism that requires no maintenance whatsoever.

The component assembly is a bit complex to grasp but nonetheless ingenious. The bearing-mounted shaft runs through a ring gear and is driven by the engine which, in turn, drives the outer ring gear connected to the cam ring gear (via ten rollers). The cam ring gear is then connected to a 10-face pinion axle.

When the rollers occupy the center space on the cam ring gear, the system is in slip mode and does not transfer any motion to the differential. That's 2WD. As soon as the electromagnetic force steps in, the rollers move toward the bottom of the mechanism, on the cam faces. The ring gear and cams then lock, which engages 4WD. The roller cage pivots on a steel plate held by tongues. A spring controls the roller cage and maintains the 2WD mode as long as the electromagnetic module is not hit by an electric current. When it does, however, the module magnetizes the rotor which, in turn, attracts the plate and moves the rollers in a certain direction, depending on whether the vehicle is accelerating or decelerating. When the rider switches to 4WD, an indicator light will turn on (on the instrument panel) to inform that the system is engaged and operational.

I told you it was difficult to grasp. It just goes to show you how sophisticated these on-demand differential systems are.




Photo Credit : Henri Lebarbé, Honda, Yamaha