Spend time with Mazda's talented vehicle-dynamics engineers as they fine-tune a new model before production release and you may hear the Japanese term jinba ittai—the concept of driver and car (more literally, horse and rider) as one. And that concept was very much at play during development of the automaker's latest technology for improving steering response, smoothness and precision.
It's called G-Vectoring Control (GVC), a name that is a bit of a misnomer. It is not a torque-vectoring system aimed at dramatically improving race-circuit lap times. Rather, the purpose of the system is to endow the vehicle with refined and natural smoothness in normal day-to-day driving environments.
To hear Daisuke Umetsu, Mazda's 35-year-old development leader explain it, "Longitudinal acceleration is modulated in response to lateral jerk for harmonious G transition. The GVC control applies minute, almost imperceptible longitude deceleration, less than 0.05 g—far less than normal engine braking—sensing two input sources: steering input angle and vehicle velocity.” He says the resulting system, standard on the 2017 Mazda3 (Axela in Japan) and Mazda6 (Atenza) and expected to spread to other models, is designed to provide "peace of mind."
Controller integrated with PCM
A simpler explanation is that GVC, co-developed with Hitachi Automotive and Kanagawa Institute of Technology, closely monitors the speed of steering-wheel inputs then signals the engine to reduce torque to a minute degree. The resulting deceleration, hardly perceptible to the driver and without drama, delicately loads the front axle and thus tightens up compliance in the car's steering and front suspension.
Umetsu likens the function to that of the top expert drivers, citing the example of the legendary Yoshimi Katayama, who drove various Mazda works racing cars at Le Mans and elsewhere. Turning into a bend or curve, Katayama would have smoothly increased vertical force up front, through steady-state, to accelerating with vertical force shifting rearward.
Developed over a nearly eight-year period, GVC performs the expert-like function seamlessly and smoothly while using the engine as "the actuator, with no additional hardware required,” Umetsu explained to Automotive Engineering during a technical presentation and ride-and-drive event earlier this year. He noted that the GVC controller is integrated within the powertrain control module (PCM), occupying a scant 3-kB in Mazda’s 3-MB passenger car PCM.
Mazda dispatched a development team to Europe with the GVC-equipped Mazda6 prototype to obtain subjective responses and evaluations on public roads including high-speed motorways in the hands of 20 drivers of different nationalities and varying driving skills. Reactions were most positive, noted Umetsu.
Unique development team
The cross-functional GVC team of about 40 members is an interesting and unique joint R&D entity of OEM, supplier and academic engineers. There is no middle-management supervision, but the organization has the full support of Mazda Chairman Seita Kanai, R&D head Kiyoshi Fujiwara and his predecessor. Hirotaka Kanazawa.
Umetsu, an-art-major-turned-neuroscience-graduate of the University of Tsukuba, joined Mazda in 2006. He is a senior specialist in the vehicle development department, responsible for chassis dynamics. Like the team's other members he does not specialize in GVC; his primary job function is a vehicle development engineer-driver. Umetsu has been involved in the development of such vehicles as the CX-5, the new MX-5 roadster and its near-twin Fiat 124 Spider, spending a year with the latter in Italy.
The initial proposal came from Hitachi, employing brakes for vehicle dynamics control with higher deceleration intervention. This ordinary approach was quickly abandoned. Umetsu’s first encounter with the GVC concept was on the Tsukuba race circuit where he met Prof. Yamakado, at the time a Hitachi researcher specializing in engine control and fuel injection and a fellow track-day enthusiast. Their meeting, and conversations with others at J-SAE events, spawned ideas that led to G-Vectoring Control.
Umetsu also attributes quantum leaps in powertrain control and chassis technologies. Included were learnings from development of the Mazda Demio (Mazda2) battery-electric vehicle that the company offered to selected lease customers. That car's brake- or electrically-actuated deceleration was in the order of 0.1 to 0.3 g, versus the production GVC system’s 0.05 g. But a key enabler is the Skyactiv engine family, both gasoline and diesel, that incorporates extremely high control precision and responsiveness.
Technical details of the G-Vectoring Control can be found in JSAE technical papers 20165248, 49, 50 (in Japanese).