2011 Kia Sportage's Proactive All-Wheel Drive System | National Post

2011 Kia Sportage Proactive All-Wheel Drive
2011 Kia Sportage’s Proactive All-Wheel Drive System
By Graeme Fletcher, National Post
Sportage sets new standard in grip
Kia’s launch of its third-generation Kia Sportage ushers in a level of sophistication not seen at the affordable end of the crossover segment before. To say it sets a new standard is an understatement.
Unlike many of its peers, the Sportage arrives with a proactive all-wheel-drive system. Many of the Sportage’s rivals feature the usual slip-first-grip-later (reactive) system. The problem with this strategy is that the car must go out of control (unwanted wheelspin) before it is brought under control (the all-wheel-drive system begins to reapportion the drive torque). In the worst case, if the car is understeering and the system reads this as wheelspin, it sends power rearward at the wrong time–the power transfer drives the car further into understeer. The sudden realization that the driver has lost the car is an unwelcome pucker moment at the best of times. The reason for the limited ability is that these reactive systems only monitor wheel speed, which means the front wheels must slip before the system picks up on the problem.
The Sportage’s new Dynamax all-wheel-drive system monitors both wheel speed and accelerator pedal input. If the system “sees” the driver tromp on the gas when vehicle speed is low, it knows that wheelspin is inevitable. Rather than waiting for the Sportage to lose traction, the system begins to close its electrohydraulically controlled multi-plate clutch, which reapportions the drive torque before the problem arises. The fact its action is proactive puts it in lofty company — Subaru and Audi are both revered for their proactive AWD systems.
The Sportage has a lock mode for those times when the going gets really slippery. The driver simply punches a button and the system locks the clutch, which splits the power evenly (50/50) front to rear. However, if the vehicle exceeds 30 kilometres an hour, the system automatically unlocks and returns to its proactive mode. This is done for handling considerations — trying to negotiate a fast corner with the centre clutch locked is not the smartest idea. The instant the vehicle drops back below the 30-km/h threshold, the system returns to its locked position.
The use of the lock mode could lead to an unwanted side effect during full-lock turns — it’s called crow hopping and is caused by drivetrain windup. To counter this negative effect, the Dynamax system looks at steering angle. The instant it sees a full-lock turn, it releases the clutch, which eliminates the potential windup. As soon as the driver begins to straighten the steering, the system resumes its locked duties.
This basic ability is layered with a good electronic stability/ traction control system. It is the traction side that’s used to control the Sportage’s power split left to right. If the right wheel begins to slip, the traction control brakes that wheel, which forces the drive to the wheel (left) with traction.
The second bit of the advanced equation is the ability to turn the front wheels and use this action as a level of electronic stability control. In simple terms, the system monitors driver input and compares it with the vehicle’s reaction. If the Sportage begins to oversteer, the steering side of the stability control system does what all good drivers would — steer into the skid. In this instant, it’s the electric motor that provides the power assist that turns the front wheels into the skid. It only turns them in by three or so degrees, but this is enough to help the regular electronic stability control system regain control in a more timely manner. The steering action is such that the driver is unaware of its helping hand — there’s no tugging at the steering wheel at all.
The system also turns the wheels during a hard stop when the left and right wheels are riding on different surfaces. Under normal circumstances, even with the anti-lock braking system doing its thing, any car will pull to the right when the right wheels are on tarmac and the left wheels are on ice or snow. Turning the front wheels to the left by just a couple of degrees counters the brake pull, which keeps the car in a straight line. Simple.
Obviously, if the car is in an understeer condition, turning the wheels only worsens a bad situation. Here the system ramps up the assist level so that when the front wheels do find some grip and the driver reefs on the steering wheel to avoid a house or tree, it requires much less effort. Few cars offer this level of technology regardless of vehicle cost.
Beyond these two significant pluses, the Sportage has a roll mitigation system that triggers the seat belt pretensioners and side curtain air bags when the car is in the final throes of flipping over — this keeps the shattered side window glass out of the cabin and the occupants inside. Then there are the semi-active shock absorbers — amplitude-selective damping in tech-talk. If the speed of the body’s motion is slow, the shocks deliver soft damping characteristics. When the body motion reaches a certain speed (hence the amplitude in the name), the damping automatically switches to a firmer setting by altering the internal valving. This controls unwanted body roll and brings much less nose dive under hard braking. It is a simple system that brings many of the benefits of a fully active damper system, but at considerably less cost.