Japan’s six major auto makers are divided into two camps on future strategies for stability-enhancing driveline technologies: safety benefits vs. performance improvements. Part 4 of this 6-part series examines’s Vehicle Dynamic Control technologies.
UTSUNOMIYA, Japan – Despite its proficiency in developing electronic all-wheel-drive systems,Motor Co. Ltd. has not made development of the latest torque-vectoring AWD technologies a priority.
Shigeo Murata, chief powertrain engineer of Nissan’s powertrain engineering unit, says the auto maker has yet to determine the value of torque-vectoring compared with conventional brake-based electronic stability control (ESC).
Torque-vectoring uses AWD or active differentials to actively manage torque apportionment between drive wheels on the same axle, influencing vehicle handling. Proponents say such systems, although currently costly, offer a performance advantage over contemporary ESC systems, which selectively apply braking at a single wheel to bring a vehicle in line with the driver’s intended path.
To date, only one Nissan car has employed an electronically managed limited-slip differential (LSD) or torque-vectoring device: the Japan-market Skyline GT-R, which ended production in 2005.
Murata says the auto maker’s initial focus, if it decides to pursue the technology more extensively, will be on high-performance, sporty vehicles such as the Skyline GT-R.
“When system costs eventually come down, we believe that torque-vectoring systems have potential in crossover vehicles,” he says.
Murata points out most sporty cars built by Nissan andMotor Corp. are rear-wheel drive vs. competitors produced by Motors Corp. and Motor Co. Ltd.
’s current Super Handling All-Wheel-Drive torque-vectoring system primarily is aimed at improving the handling behavior (and safety) of its front-wheel-drive-based vehicles, such as the Acura RL sedan and RDX cross/utility vehicle.
“We feel that torque-vectoring may not be suitable for ‘sporty’ rear-wheel-drive vehicles for safety reasons,” Murata says. “In this sense, safety is our first priority.”
He adds, Heavy Industries Ltd., maker of Subaru cars, and other auto makers that have model ranges comprised of mainly FWD vehicles “may need electronic drive controls, including electronic LSDs, to boost the performance of their cars.”
Conversely, Murata says LSDs – both mechanical and electronic – may cause RWD vehicles to oversteer excessively, making conventional ESC systems a priority for such drivetrain layouts.
In adopting electronic torque management controls, Murata says Nissan’s first priority is improving traction on slippery surfaces, followed by fuel economy and high-speed handling.
The auto maker’s main chassis-manipulation focus for SUVs is traction on ice and snow, with passenger cars geared more toward better cornering.
Murata says Nissan’s most advanced car, from an electronic torque-management standpoint, is not the Skyline but the Japan-market Fuga, known as the Infiniti M35 and M45 in North America. A new Nissan model due out next year will exceed the Fuga’s performance, he says.
Meanwhile, the auto maker is forecasting sharp growth in U.S. demand for its brake-based ESC system known as Vehicle Dynamic Control.
Murata expects VDC penetration to approach 100% in the U.S. by 2010, with similar inroads in Europe due to new safety regulations. In Japan, he says VDC currently is installed in 5% of new cars and will grow to 30% in 2010 and 50% in 2015.
In other parts of Asia, Murata expects penetration to increase to 10% in 2015, up from less than 1% today.
Cost is the biggest obstacle to increasing VDC demand, he says, noting prices must come down nearly 50% before installation rates take off.
Nissan plans to introduce an integrated AWD and 4-wheel-active-steering system in 2007.
“We’re not ready to do so with a fully integrated system like’s (Vehicle Dynamics Integrated Management),” Murata says, noting his research team feels it can achieve performance comparable to Toyota’s VDIM, which also can actively steer the vehicle in emergencies, using separate electronic control units.
“We believe the steering, handling (stability) and braking performance of our new car will equal or exceed that of Toyota’s current VDIM lineup,” he says.
“Of course, the situation could change if Toyota were to further improve its current VDIM system,” he says, adding Nissan plans to introduce a VDIM-type technology in 2010.
On the issue of “batching,” or combining ABS, ESC and brake-assist controllers into a single ECU, as Toyota currently does, Murata says Nissan will integrate the first two but not brake-assist.
Nissan employs mechanical brake-assist for most of its cars vs. the electronic systems used by Toyota.
“Mechanical systems enable us to achieve satisfactory braking performance at more reasonable cost,” Murata says.
“They also are quieter, vibrate less and offer better pedal ‘feel’ than electronic units,” he says. “The biggest advantage is that they can be used across our product line.”
Murata expects to see a steady switch to electronic units over the next five years in the European market, where Nissan will integrate all three systems.