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Marton Pettendy28 Jun 2016
REVIEW

Mazda GVC 2016 Review

Japanese car-maker thinks outside the box again with innovative torque control system

First Drive
Mazda6 with G-Vectoring Control
Laguna Seca, California

Mazda presented its new G-Vectoring Control (GVC) technology to European media earlier this month and to Australian and US press last week. Claimed to improve cornering grip, straight-line stability and passenger comfort by limiting engine torque according to steering angle, GVC has been confirmed to make its local debut in the upgraded Mazda3 due on sale here in August. Requiring only additional software and -- in the Mazda6 we drove in California -- no chassis changes, it will eventually be rolled out as standard across all Mazda models.

Mazda has a tradition of thinking outside the box when it comes to engineering, as evidenced by the rotary engine it continues to develop and the diesel-style HCCI compression-ignition tech it will roll out across its SKYACTIV II petrol engines due within 12 months.

GVC is the latest example and, while the benefits are subtle, it makes a small but worthwhile difference to vehicle handling, stability and occupant comfort, if the Mazda6 prototype we drove on track and public roads in the US last week is any guide.

In the making since 2008, GVC is completely unrelated to the various torque-vectoring systems employed by a variety of manufacturers, which employ brake intervention or differential locks to transfer power across a driven axle to improve traction on the outside tyre.

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Instead, GVC works by momentarily reducing torque as steering angles increase, thereby transferring weight diagonally to the front tyre that's doing the most work in any given situation.

Mazda says the amount of torque reduction is so small it's imperceptible, but the result is effective enough to generate between 0.01 and 0.05 g of deceleration, providing up to 5kg of weight transfer to the tyre that needs the most grip.

Indeed, the degree of torque reduction is so minute that the technology couldn't be rolled out without the improved response of Mazda's latest direct-injection SKYACTIV engines. The reaction time between steering input and torque reduction is also miniscule, at just 50 milliseconds.

Furthermore, the complex algorithm that calculates it in any particular circumstance took a large part of the eight years chief engineer Umetsu Daisuke spent developing the patented GVC concept, which was first devised by a Japanese university professor.

There's no doubt the benefits are slight, but a series of closed-road exercises and a brief public road drive in a modified US-spec Mazda6, which unlike our revised Mazda3 required no accompanying suspension changes, proved it's far from a publicity stunt.

The first test involved a a tight, bumpy circular course marked out by orange cones, in both wet and dry with GVC on then off.

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Although the data recorded in real time via a laptop showed a bigger difference than we could feel behind the wheel, with GVC turned on there was slightly less steering wheel turning angle and speed required to lap the course at a constant 30km/h with the cruise control on.

In a nutshell, with GVC, the same corners at the same speed required slightly less steering angle to enter, and mid-corner bumps required slightly less wheel correction and slower steering wheel inputs to maintain a constant-radius line over.

Admittedly, we couldn't feel any difference in an 80km/h lane-change exercise, perhaps because – as Mazda sys – GVC is a subtle extension of what most experienced drivers already do when entering a corner: lift off before turning in to weight the outside front tyre in order to generate more grip.

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But we did feel a subtle difference in a narrow straight-line test on Laguna's main straight. At a higher speed between the pit wall and a straight row of cones, the Mazda6 required less steering wheel correction to keep the car in the narrow lane.

The same thing applied when attempting to trace the white line that marks the outside edge of the Laguna circuit at a slow, constant speed. Once again, steering corrections were less exaggerated and fewer in number than without GVC.

But the biggest difference we felt was on a near constant-radius gravel loop, where the front-drive Mazda6 understeered excessively without GVC but tracked tighter and with less steering input with it turned on, despite travelling at the same 30km/h.

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In all four exercises, the data showed small but discernible differences in steering angle and speed with GVC employed, and a corresponding reduction in the head movement of occupants. Yes, subtle though it may be, GVC reduced passenger 'head shake' and therefore fatigue, even at these low speeds in a relatively low-slung passenger car.

Mazda goes to great lengths to demonstrate how -- in line with its philosophy of 'Jinba-Ittai', which is Japanese for a feeling of unity between driver and vehicle – GVC applies the principles of equilibrioception (the sense of force on the body) and 'minimum jerk theory' – the human body's natural tendency to move with minimum jerk, or rate of change in velocity.

It claims GVC is the first attempt to apply science to the seat-of-the-pants feel everybody possesses in a car, to make it more of an extension of our bodies.

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"Until now, lateral and longitudinal acceleration (G) forces have been controlled separately," it claims. "GVC is the world’s first technology to adjust engine torque in response to steering inputs in order to control these forces in a unified way and optimize the vertical loading of each tire to realize smooth and efficient vehicle behavior."

"GVC maximizes tire performance by focusing on the vertical load on the tires. The moment the driver starts to turn the steering wheel, GVC controls engine drive torque to generate a deceleration G-force, thereby shifting load to the front wheels. This increases front-wheel tire grip, enhancing the vehicle’s turn-in responsiveness.

"Thereafter, when the driver maintains a constant steering angle, GVC immediately recovers engine drive torque, which transfers load to the rear wheels, enhancing vehicle stability. This series of load transfers extracts much more grip from the front and rear tires, improving vehicle responsiveness and stability according to the driver's intentions.

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"Regardless of the skill of the driver, GVC demonstrates its effect consistently over a range of driving situations, from low-speed everyday driving to high-speed straight-line driving, on winding roads and during emergency avoidance maneuvers."

Whatever the science behind it, the jury is in and you can take it from us: GVC is subtle, but it works. It's effective enough to make average drivers smoother and good drivers better, without them even knowing it. And the bumpier, tighter, slippery and faster the road is, the greater its advantages.

Combined with a full steering and suspension retune in this year's facelifted Mazda3, it should make one of Australia's top-selling models not only more dynamic and more stable, but more comfortable and easier to drive.

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