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 3 of this 6-part series examines’s “active” AWD center-differentials and yaw-control systems.
UTSUNOMIYA, Japan –Motors Corp.’s expertise with “active” all-wheel-drive center-differentials and yaw-control systems has made the auto maker a leader in advanced driveline torque management and is helping refine the performance of its future vehicles.
Mitsubishi also has a torque-vectoring AWD system ready to go, but management has yet to give a green light due to the auto maker’s poor – though improving – financial situation.
Torque-vectoring AWD, already in production at rivalMotor Co. Ltd., promises a safety and performance enhancement compared with conventional electronic stability control (ESC) systems but currently is costly and complex.
Kaoru Sawase, a senior engineer in Mitsubishi’s Drivetrain Design Div., says traction performance using actively controlled electronic limited-slip differentials (LSDs) in place of mechanical units also is another method of torque vectoring, although cost is nearly double a conventional LSD.
To bring electronic systems to market, Sawase estimates cost must come down by one-third, or to 50% more than mechanical devices, a target that could be achieved in three to four years, he says.
Concerning the auto maker’s Super-All Wheel Control system, portions of which (active center differential and yaw-control electronics) are featured on the high-performance Lancer Evolution, Sawase says the design objectives were “predictable handling” and “high-marginal performance.”
“Predictable handling” translates to “superior steering response, steering linearity and controllability even under sliding conditions,” he says, while high-marginal performance means “high traction performance during cornering and braking.”
In other words, the auto maker’s focus is on improving dynamic performance at higher speeds vs. pure safety concerns.
Mitsubishi says active steering control is under development, as well, eventually to join already adopted electronically managed AWD, active stability control, active center differentials and active yaw control.
Sawase adds that S-AWC is based on a 4WD controller and stands apart from other brake-based ESC systems.
“By employing a 4-wheel-drive controller, we improved traction and stability while avoiding interference with vehicle acceleration and deceleration, “ he says, noting Mitsubishi will consider adding active steering to its present system when costs come down.
For the time being, he says Mitsubishi’s stability-control “concept” is closer to’s and Heavy Industries Ltd.’s Subaru than to Motor Corp.’s, which is oriented towards improving safety.
“Our focus, like Honda’s and Subaru’s, is on vehicle dynamics and high-speed handling,” Sawase says.
Not that the auto maker has ignored antilock-brake and other brake-based chassis-management strategies. Almost all vehicles sold in its current lineup, including 0.66L minis, offer ABS.
Electronic brake-force distribution is available on all vehicles except minis, while a growing number of models, including the Outlander and remodeled Pajero, employ the auto maker’s Active Stability & Traction Control system (Mitsubishi’s brake-based ESC technology).
By 2015, Sawase expects vehicle stability controls to be installed in all Mitsubishi vehicles sold in the U.S., Japan and Europe. And in the future, he believes the technology will be fully integrated with ABS, electronic brake-assist and various automated climb-and-descent features, oriented largely toward SUVs.
When Mitsubishi’s torque-vectoring S-AWC system is fully market-ready, it will come on-stream first in Japan because of the positive impact on cornering performance.
“Japan has many narrow, winding roads,” Sawase says.
Next will be Europe, where a combination of narrow roads and autobahn-type highways highlight the road-handling features of the technology.
North America has the “least need for the technology (because of the market’s) long, straight and wide highway system,” Sawase says.
By 2010, he estimates 10% of Mitsubishi vehicles will be equipped with S-AWC, double the projected industry average, with the majority of sales in Japan and Europe. By 2015, he predicts penetration will reach 15%.
Mitsubishi currently markets three types of AWD systems: one employing mechanical or viscous differentials at each axle; the second featuring electronically controlled differentials; and the third a conventional center-differential type.
The auto maker generally adopts viscous AWD for vehicles with engine displacements less than 1.5L, including the 1.5L Colt and 0.66L i and eK series. Electronic differentials better suit midsize models with engines in the 1.6L to 3.0L range, including the 2.4L Outlander and 2.0L and 2.4L Grandis.
Meanwhile, Sawase notes conventional center-differential AWD systems are featured on larger or sportier vehicles, such as the 3.0L and 3.8L V-6 Pajero and 2.0L turbocharged Lancer Evolution.
While conventional viscous devices are adequate for most small vehicles, they generally do not provide sufficient torque capability for medium-size models, including the new generation of cross/utility vehicles.
In these segments, the auto maker must switch to electronic controls to enable additional clutch torque.
For heavier models, such as the Pajero, Sawase says adopting electronic controls requires a larger coupling, increasing drivetrain weight and nullifying any performance advantage gained.
“We feel that traction and handling are better with center differential-type units,” he says.
For these same reasons, Sawase says mechanical LSDs will be limited to fullsize SUVs and sporty vehicles going forward.
Mitsubishi was the first auto maker to introduce an integrated AWD, 4-wheel ABS, 4-wheel-steering and 4-wheel independent suspension system, in 1987, for the Galant VR-4, Sawase notes.
“and Honda introduced many of the same systems separately, but not in a combined package, until later,” he says.