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How the Escape's 4x4 System Works

In my opinion, this article from the July 2000 issue of Car and Driver has the best description of how the Escape's four wheel drive system works.  It is a little technical, but it is also understandable.  It also explains one of several reasons the Escape is not for serious off-roading.

Yet Another All-New All-Wheel Drive
by Frank Markus from the July 2000 issue of Car and Driver

Contrary to what you’ll be told by the dashboard markings, your Ford Outfitter salesperson, and even Ford’s press materials, the Escape’s Control Trac II system does not offer fully locked four-wheel drive.  Rather, this on-demand all-wheel-drive setup only sends power to the rear axle when the front wheels slip.  Here’s how it works: 

In the “4x4 Auto” mode, 100 percent of the torque is sent to the front wheels until a wheel slips.  When that happens, a rotary blade coupling (RBC) generates enough pressure to activate a multiplate clutch, like that found in an automatic transmission, which sends torque (as much as 100 percent of it) to the rear.  At the heart of the RBC is a “fan” with three blades in a chamber filled with a silicone fluid like that used in viscous couplings.  The fan is shaped kind of like the warning symbol for radiation.  When the front wheels slip, this fan spins through the fluid, heating and expanding it, which generates the pressure to activate the clutch.  Then the clutch – not the viscous fluid – bears the burden of transmitting the torque. 

When set to “4x4 On”, an electromagnet energizes a small clutch pack, locking a ball ramp to the input shaft.  Now when the wheels spin, they turn the ball ramp, which overrides the RBC and pressurizes the same multiplate clutch pack.  In the “4x4 On” mode, the rear axle is engaged quicker and more securely.  The front and rear axles are, however, never locked together except during front wheel slippage.  That way there is never any crabbing or binding in tight turns, and there is no need for a center differential.

With no limited-slip differentials, it is possible – with opposite corners in full droop and airborne, for example – for an Escape to get totally stuck.  And that’s why this ain’t a true four-ba-four.

Escape 4x4 system cut-away view

This is from the Escape's Owners Guide:

4x4 System General Information

Your vehicle is equipped with a 4x4 system. This system can use all four wheels to power the vehicle. This helps traction, enabling you to drive your vehicle over terrain and road conditions not normally traveled by two-wheel drive vehicles.

Power is always supplied to the front wheels and to the rear wheels through the transaxle and Rotary Blade Coupling (RBC) unit that allows you to select a four-wheel drive mode best suited for your current driving conditions.

Operating modes of the 4x4 system:

The 4x4 system functions in two modes:

bullet The 4x4 AUTO mode provides four wheel drive with full power delivered to the front axle at all times and to the rear axle as required for increased traction. This is appropriate for normal on-road operating conditions, such as dry road surfaces, wet pavement, snow and gravel.
 
bullet The 4x4 ON mode provides four-wheel drive with power to both axles at all times. It is only intended for severe off-road driving conditions, such as deep snow and ice (where no dry or wet pavement remains uncovered) and shallow sand or mud.
 
bullet The vehicle should not be operated in the 4x4 ON mode on dry or merely wet pavement. Doing so will produce excessive noise, increase tire wear and may damage driveline components. The 4x4 ON mode is intended for use only on consistently slippery or loose surfaces.

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(c) R. Romaine
This page was last updated on 04/11/13.