Polaris system adds true four-wheel driveto ATV spec
ATV development has taken yet another turn with the introduction by Polaris of the Visco-Lok system, which is designed to help ensure that maximum traction is maintained.
Available for the companys 325 and 500 Magnum machines Visco-Lok is an advanced form of limited slip differential working on the front axle but, through its design allows full torque to be delivered to wheels that have grip at any one time.
It works like this: In normal operation, the front gear case acts like a normal differential and allows different wheel speeds for turns. If one front wheel should lose traction the Visco-Lok system is activated and the differential is progressively locked to provide power to the wheel which has traction.
Understanding just how the unit works is not easy, but, for the technically minded, here goes. The front gear case contains two fluids – one is a normal gear oil and the other is a silicone-based fluid with a high viscosity (thick). This second fluid is contained in the sealed Visco drive unit which is inside the front gear case.
When the front wheels turn at different speeds they turn clutch plates – very much like motor cycle clutch plates – against the reservoir containing the viscous fluid.
This draws the fluid from the reservoir which takes up the space to create pressure which forces the clutch plates together, locking the differential.
When the wheels are both turning at the same speed a spring forces the fluid back into the reservoir unlocking the differential.
With the Magnums four-wheel-drive system the total effect of the system is to provide just that – true four-wheel-drive.
Used in conjunction with the Polaris engine braking system (EBS), which provides effective engine braking, despite use of an automatic transmission, the Visco-Lok system provides a radically new dimension to ATV operation.
Driving up or down steep slopes is when its use is most obvious. When climbing, no longer is there any violent spinning of non-gripping wheels, which even limited slip clutches can allow to some degree. And when descending there is the added security that one wheel is not going to suddenly slip away.
lPolaris ATVs are built in Minneapolis, Minnesota and imported into the UK by EP Barrus. *