Humanizing Cars to Make Them Ride and Handle Better – Technologue

Mazda always talks about developing vehicles with Jinba Ittai—“horse and rider as one.” Recently the company disclosed that it accomplishes this in part by studying the way humans move and engineering vehicles that mimic or facilitate such movements. Two terms that emerged from this research caught my ear: minimum jerk theory and equilibrioception. “Jerk” is the rate of change of acceleration, and apparently when we move objects or ourselves, we naturally minimize jerk. Equilibrioception is our ability to experience and maintain physical balance, which we endeavor to do while holding our heads upright.

When we walk or run, our view of the world is smooth and level, meaning our brains steady cam out the sinusoidal up-and-down and side-to-side motions our heads go through. Mazda found that many cars lauded for their smooth ride (such as E36 and E39 vintage BMWs) feature suspensions that allow very similar vertical motions, damped so as to transmit minimal jerk, with the front and rear generally moving in unison with no front/rear pitching motions. Our internal steady cams may well improve our perceptions of cars that move like this.

Achieving and maintaining equilibrioception when belted into a moving car primarily requires neck muscle exertion to resist the various g forces trying to sway our heads. By placing electrodes on driver and passenger necks and measuring the voltage potential across these muscles, Mazda has been able to plot electromyographs of the neck muscle effort expended during various vehicle maneuvers. An interesting discovery in this research: When the brain anticipates an impending g force before the neck feels it, the neck-muscle effort ramps up more gradually with less jerk and hence greater comfort. Drivers innately anticipate the reactions to their own control inputs, but a way to trigger this perception in passengers, too, is to design the chassis to induce some early “diagonal roll.” Then, when passengers see the outboard corner of the hood dip a split second before the g-forces hit, their necks can prepare.

Don’t be surprised if GVC so endears you to your Mazda that you anthropomorphize it.

The Skyactiv Vehicle Dynamics systems that are just rolling out are informed by these studies. The first is G-Vectoring Control, which endeavors to foster a bit of diagonal roll and to minimize neck jerk by smoothing g-load transitions in turns. The system automates a basic tenet of performance driving: To improve turn-in, you want to load the steering tires by shifting weight forward with some deceleration, then settle the rear at the corner exit by shifting it aft again. Here’s how it works: As the driver turns in, the CAN bus informs the engine controller, which retards the ignition timing within 50 milliseconds. This reduces torque just enough to produce between 0.01 and 0.05 g of deceleration (undetectable to human neck muscles), inducing a slight diagonal roll that increases the load on the outer front tire by between 2 and 10 pounds. Torque resumes as the driver unwinds the wheel, settling the car. The driver feels more in control, and the passenger’s neck strains less.

In a Mazda6 equipped with a GVC-on/off switch, the amount of steering required to negotiate a tight oval was noticeably increased with it off. That’s because without that little bit of front-tire loading, the turn-in response was delayed just enough to cause me to input a bit too much steering, then back it out—again maybe too much, then dial it back in again, and so forth. The results are more pronounced in slippery conditions or at higher speeds.

GVC adds no cost to the car and will gradually roll out across all product lines starting with the Mazda6. It might not be advertised, and it won’t have an off switch, so you might never “feel” it. But don’t be surprised if it so endears you to your Mazda that you anthropomorphize it.

Read more Technologue columns here:

• What I Learned at Valvoline’s Sesquicentennial
• Another Batter Swings at the Compression-Ignition Gas Engine
• What the Bentley Mulsanne and Acura NSX Have in Common
• Road Hard (If Not Put Down Wet): Rethinking Concrete Science

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