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Get a grip, winter’s coming

When inclement weather approaches, particularly when you're driving through hilly terrain, improved traction on split road surfaces can mean the difference between keeping on track and wildly spinning...



When inclement weather approaches, particularly when you’re driving through hilly terrain, improved traction on split road surfaces can mean the difference between keeping on track and wildly spinning your wheels.

As we begin to eye the threat of the dreaded white stuff, the need becomes all that more apparent.

Take heart that there is a solution in the availability of Traction Control Devices (TCDs).

There are basically three types of these devices widely used on heavy-duty tractor-trailers:

Electronic Automatic

Traction Control Systems

Electronic Automatic Traction Control Systems are used in conjunction with Anti-lock Braking Systems (ABS), and are designed to minimize the slipping of wheels as you accelerate.

When a drive wheel begins to slip, the automatic traction control applies the brake on the affected wheel. When you’re on a split road surface – with one tire on ice and the other on dry pavement, for example – this allows the main differential to transfer power to the drive wheel that can grip the road.

If both drive wheels begin to slip, the automatic traction control uses the electronic engine throttle to automatically reduce power and allows the engine to more closely match the power that can effectively be transferred to the road surface.

The plus side of automatic traction control is that it doesn’t normally require a driver to turn it on.

In the end, you can better move a properly equipped vehicle on a slippery road surface, improve tire life, reduce expensive shock-related damage to the drivetrain, and in some cases eliminate the need for chains – a blessing when it’s 30 below zero and the wind is whipping around your ankles. It also reduces the potential of powering into a jackknife when you’re traveling on inclined surfaces or curves.

Just keep in mind that in some situations, and with some vehicle configurations, you need to engage the interaxle differential if you want the best traction enhancement.

Manual/Mechanical

Traction Systems

A driver-controlled differential lock, used in conjunction with an interaxle differential, helps your truck obtain the best traction in poor conditions by providing the maximum traction from each of an axle’s wheel ends, and more importantly, from each axle in a tandem.

A main differential divides the power equally between the axle’s two wheel-ends. And an inter-axle differential divides the power equally between a tandem’s two axles.

The term “power divider” is another term commonly used for an inter-axle differential.

A DCDL (driver controlled differential lock) operates by mechanically deactivating the main differential of an axle, to maximize the torque applied to each wheel end. And it allows operators to select optimum traction only when it’s needed, yet provides normal differential action when road conditions are fine.

The DCDL is typically activated with air pressure from the cab, triggering a shift assembly mounted on the axle. When activated, a shift collar moves laterally toward the differential case, along the axle shaft’s splines, to allow splines on the shift collar to engage with mating splines on the differential case. This action locks both the differential and axle shafts together as a solid unit, and effectively eliminates main differential action.

Maximum traction is then provided to both wheels, and you’re provided with added protection against spin-out damage to the differential.

A DCDL is used only at low speeds under poor traction conditions, and should be deactivated as soon as you encounter normal road surfaces.

Inter-Axle Differential Lock

An IADL 3/4 is also referred to as a “power divider”, or a third differential, and works in a manner similar to the main differential. The difference is that it divides power equally between the two axles of a tandem rather than between an axle’s two wheel ends.

You simply toggle a control lever in the cab to shift the rear side gear toward the inter-axle differential case. This effectively locks together the axle input and output shafts and differential assembly, and that also eliminates inter-axle differential action.

Therefore, by using the IAD lock you “lock out” the IAD action, and the percentage of tractive effort delivered to each wheel end on each axle is governed by the grip between the tire and road surface.

The tractive effort is not dependent on the wheel end or axle with the least amount of available traction. Unlike a DCDL, the IAD lock can be used at all speeds and for long periods of time.

It is generally recommended, however, that you use the IAD lock in conjunction with a DCDL. The reason for using both the DCDL and the inter-axle differential lock is to provide maximum traction when it’s needed for both the forward and rear drive axles in a tandem, as well as maximum traction at each axle’s individual wheel ends when the main differentials are locked.

In a “no-spin” differential when a vehicle is traveling down a straight road under poor weather conditions, each wheel will transmit only as much traction as conditions will allow. But, when the vehicle enters a curve in the road, the torque to the outside wheel will disengage, and all tractive effort will be provided by the inside wheel. Once a straight road is encountered, both wheels lock together once again.

The negative is that during a turn, only one-wheel is providing tractive effort, and that may not be enough to keep the rig moving if the inside wheel is spinning on poor road conditions. n

– Bob Brady is the president of Hitech Consulting in Burnaby, B.C.


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