Having spent most of my driving life in the tropics, I don’t consciously make a distinction between driving on snow and on ice – something which I need to fix immediately if I am to drive safely in this minus 10 degrees Celsius weather in Hokkaido. Snow doesn’t get you in trouble, most of the time at least. Ice however – that’s the surface that will make you skid and crash.
Compounding the problem is that snow is visible to the naked eye but icy surfaces tend to appear as clear. Drivers from these cold climate regions have been trained to be careful of ice when ambient temperature drops below 4 degrees Celsius. This is also another reason why all cars have a display showing ambient temperature outside, something which has little or no value to us in the tropics.
As icy surfaces are the most extreme of all slippery surfaces, many car makers spend a lot of time doing winter testing to fine tune their traction and stability control systems and drivetrain. Chassis control systems that work well enough on ice, will work well enough on rain soaked roads in the tropics.
Rural places like Lapland in Finland and Arjeplog in Sweden are typically busy with prototype vehicles during winter but the problem is that these places are also public areas so spy photographers often hang out there.
Mazda sidesteps the problem by supplementing their winter testing at their own Kenbuchi Proving Ground in Hokkaido, a public area that’s closed off by the local city council at every winter to be used exclusive by Mazda. Recently, Carlist.my was recently granted a rare opportunity by Mazda to witness how development work for their i-Activ AWD was carried out in Kenbuchi.
Before that, let’s do a quick recap on Mazda’s i-Activ AWD. In Malaysia, this feature is available in the AWD variants of the CX-5 and CX-9. Elsewhere, it’s also offered as an option in the Mazda 3 and Mazda 6. The one used in the BT-50 pick-up truck is a different, off-road biased Part-Time 4WD system.
Unlike more off-road bias systems used by part-time 4WD pick-up trucks or heavy duty full-time 4WD SUVs like a Toyota Land Cruiser, Mazda’s i-Activ AWD prioritizes on-road use and lacks a low-ratio (4WD Lo) transfer case and a locking centre differential. It can only split torque between the front and rear wheels but not side to side.
As such, it’s not suitable for heavy duty off-road operations but this is fine because few Mazda customers are interested in driving off-road. The priority is to deliver good traction on slippery roads while keeping fuel consumption low.
But what makes Mazda’s i-Activ AWD different from a similarly equipped Honda CR-V? To put it simply, Mazda says its system is predictive in nature and is active at all times. Most of its peers are using a passive, reactive-based system that require at least one wheel to slip before engaging the rear axles.
There is an interesting back story to the i-Activ AWD’s development. Over the many years of working in Hokkaido during winter, Mazda engineers have learned, from the local residents, how to tell if someone is local or not simply by looking at how they walk on snow/ice.
The visitors or tourists tend to keep their hands close to their body for warmth, and walk in normal steps, both of which will make you lose your balance and slip. The locals however, tend to spread their hands out and walk in smaller steps.
“Walk like a penguin, feet pointing out, hands out, small steps,” said our host to us fumbling visitors from the tropics, who were slipping and falling on the icy surfaces.
By studying the difference in the way the locals adapt to slippery conditions, Mazda engineers began exploring the idea – why not build a simple, fuel-efficient AWD that adapts to the changing conditions in the same manner as a local Hokkaido resident is able to walk safer and faster than a tourist without relying on any special foot wear.
So instead of adding more heavy hardware to the drivetrain, Mazda engineers attempted to make better use of existing hardware tht’s already in the car. They started by linking the i-Activ AWD system to 27 different sensors, some of which have no relation to the drivetrain but have been co-opted by Mazda’s engineers to function as the ‘eyes and ears’ of the car. In the same way a human uses their eyes, ears, skin to make better sense of the conditions around them, and instinctively adapt their walking posture, so too will Mazda vehicles.
If the wipers are turned on, it could only mean that visibility is poor. Readings from the ambient temperature will also tell the car if there is risk of ice. A Hokkaido resident is always sensitive to the amount of grip that can be felt from the shoe soles. A car can be programmed to do the same. What is the slip angle between the power steering’s input versus the driving wheels? What is the throttle and brake pedal’s position? As you drive along, the system is continuously taking 200 readings every second. All these data are used by the system to predict what the surface conditions are like, and allows Mazda’s predictive i-Activ AWD to react faster and more precisely than rival AWD/4WDs systems in its class.
The downside on many reactive-type AWD/4WD drivetrains used by Mazda’s rivals is that they need least one wheel has to start slipping before the rear axles are engaged. It’s not only slower to react but sometimes could also result in a noticeable jerk when torque is transferred between the front and rear axles. This is less preferred because it upsets the vehicle’s balance.
Through their development work at Kenbuchi, Mazda engineers have learned that to avoid this jerk; torque needs to be transferred within this small window of just a fraction of a second – between the moment when a wheel slip is picked up by the sensors and the moment when the driver realizes any loss in traction. Thus they concluded that the key to building an predictive AWD system that meets Mazda’s ‘Jinba Ittai’ philosophy of balance, of feeling of oneness between the car and the driver, is to build an AWD that is capable of distributing torque between the two axles within this tiny window period.
For a lightning fast response, the rear axle is permanently engaged but to keep fuel consumption low, only 2 percent of torque of transferred to the rear under normal conditions. This minimal ‘pre-torque’ is there only to maintain tension in the driveline, allowing the services of the rear axle to be summoned immediately.
The system is capable of delivering front-to-rear torque split from 98:2 to a maximum of 50:50.
All of this culminates in a very precise control of torque delivery to the rear axle, which Mazda’s test drivers were very keen to demonstrate on the icy surfaces of Kenbuchi, on AWD variants of the Mazda 3 which we don’t get here. Balance and precision – everything Mazda needs to deliver the Jinba Ittai character.
Even when driving on normal studless winter tyres, the AWD CX-5 stops and accelerates and tackles corners on the icy Kenbuchi Proving Ground without any hesitation. You simply get in and drive with your instincts, with all of Mazda’s intelligent bits working quietly behind the scene, never once making its presence known and that’s exactly how Mazda engineers intended it to be.
Keyword: How Turning On The Wipers Can Alter The Way Mazda’s Predictive i-Activ AWD Works