Better by Design – The Case for Predictive AWD
When Mazda development engineer Dave Coleman talks about all-wheel drive, he compares it to walking on an icy sidewalk.
“You know that’s dangerous, and you walk more carefully so you don’t slip,” Coleman observes. “You can predict how the sidewalk is going to be, and you adapt to it in advance.”
Mazda’s goals for i-ACTIV AWD are similar. Simply stated, i-ACTIV AWD was designed to preserve the precise, intuitive, Jinba Ittai—”horse and rider as one”—feeling Mazda builds into all of its vehicles, even on low-grip surfaces. The i-ACTIV AWD system must function seamlessly and invisibly, with no input from the driver. And the impact on fuel economy should be negligible.
“What we’re trying to do with the i-ACTIV predictive all-wheel-drive system is to have the car feel as precise and controllable on snow as it does on pavement,” Coleman says.
Predictive AWD Eliminates Compromises
“We needed to make our AWD system intelligent enough to understand the current road conditions and anticipate when the tires were going to slip. Then, we needed to direct power to the rear wheels to take the load off the fronts and prevent the slip in the first place,” Coleman said.
The solution to the inefficiencies of traditional AWD systems turned out to be ingeniously simple.
“We have so much data flying around the car from existing systems. If we can read that data intelligently, we can accurately interpret what the surface conditions are without having to add any more systems to the car,” Coleman said.
Where traditional AWD systems measure only relative wheel speed, the i-ACTIV AWD system monitors 27 different variables more than 200 times per second. The i-ACTIV system considers not only wheel speed and engine dynamics, but G-forces, driver inputs to the braking and steering systems, outside temperature and even windshield wiper activity. All that information comes together to create a snapshot of driving conditions as they change from moment to moment.
By constantly monitoring that information, the i-ACTIV system recognizes any pre-slip condition and delivers power to maintain traction before the driver can feel any change in driving dynamics.
To deliver power to the rear wheels before a front wheel can slip, Mazda uses a unique electromagnetic multi-plate clutch. To eliminate the engagement backlash commonly encountered with traditional on-demand AWD systems, the i-ACTIV system maintains one to two percent of clutch pre-load under most conditions, so the system is always ready to maintain traction.
Maintaining Fuel Economy
Seamless control on ice and snow is revolutionary, but it was only half of the goal set by the i-ACTIV AWD development team. The other half was to dramatically reduce the fuel-economy penalty traditionally associated with AWD.
“Ideally, we’d like to have no fuel economy penalty at all for AWD. At the moment, we’d like the penalty to be as small as possible,” Coleman said.
By employing Mazda’s “gram strategy,” Mazda’s engineering team was able to reduce the weight of the i-ACTIV system components by 40 percent compared to Mazda’s previous AWD system. Then, by using the electromagnetic clutch to control rear wheel engagement, the i-ACTIV system reduces friction losses that lead to decreased fuel economy and lag.
“In the snow, we’re actually more efficient in all-wheel-drive mode than in two-wheel drive,” Coleman said.
Driving Matters – Under any Conditions
For Coleman, it all comes back to the concept of Hashiru Yorokobi: joy derived from driving.
By creating an AWD system that predicts and corrects traction problems before the driver can even feel them happening, the i-ACTIV AWD system maintains control, stability and forward momentum – the soul of Jinba Ittai. What that means to the driver is control, confidence and peace of mind.