Mitsubishi Lancer Ralliart equipped with competition-derived active center differential (ACD) 4-wheel drive
The 2009 Mitsubishi Lancer Ralliart is the latest in a long line of high-performance 4-wheel drive (4WD) Mitsubishi models. The Lancer Ralliart All-Wheel Control (AWC) system is based on the Mitsubishi Active Center Differential (ACD), which uses an electronically controlled multi-plate clutch center differential to distribute drive torque between the front and rear wheels in response to driving conditions. The system is controlled by the AWC computer, which takes input from a variety of engine and wheel speed sensors, G-force sensors and steering angle sensor information.
The AWC computer uses a proprietary Mitsubishi algorithm to calculate action of the ACD unit in response to road conditions. The ACD provides an excellent balance between steering response and traction characteristics and allows the driver to set system response parameters using a "Tarmac, Gravel, Snow" selector.
The ACD is essentially the same that was used in the previous-generation Lancer Evolution (Evolution IX in other markets.) Likewise, the helical limited-slip front and mechanical limited-slip front rear differentials are adapted from the previous-generation Lancer Evolution.
(The new-generation Lancer Evolution, in comparison, is equipped with the Super All-Wheel Control system featuring both the Active Center Differential and the Active Yaw Control torque-vectoring rear differential.)
Active Center Differential (ACD)
The heart of any four-wheel drive system is the means of power distribution, which is a key to establishing the vehicle's handling behavior. First employed on the Japanese-market Evolution VII model, Mitsubishi's Active Center Differential (ACD) made its North American debut in the previous-generation Lancer Evolution models. (The track-handling capability of that model was only recently eclipsed by the new-generation Lancer Evolution with Super All-Wheel Control system featuring both ACD and the Active Yaw Control torque-vectoring rear differential.)
The ACD splits torque up to 50:50 between the front and rear wheels using an electronically controlled hydraulic multi-plate clutch. The All-Wheel Control computer optimizes ACD clutch cover clamp load for different driving conditions, regulating the differential limiting action between a free state (where torque is split equally between front and rear wheels) and a locked state to optimize the torque split and thereby produce the best balance between traction and steering response.
The maximum limited-slip torque of the ACD multi-plate clutch is about three times that of a conventional viscous coupling. The hydraulic unit housed in the engine compartment regulates the hydraulic pressure of the multi-plate clutch within the range of zero to 145 PSI.
The All-Wheel Control computer takes data input from various sensors to continuously calculate the ACD 's limited-slip torque. Steering wheel angle, throttle opening, wheel speeds, and the vehicle's longitudinal and lateral movements are constantly measured to determine the vehicle's path of travel. Using this data, the AWC computer determines whether limited-slip torque should be increased or decreased at any given time.
As in the Lancer Evolution, the Lancer Ralliart offers three driver-selectable traction modes for the ACD, changeable while the car is moving using a switch on the dash: "Tarmac" for dry, paved surfaces; "Gravel" for wet or rough surfaces, and "Snow" for snow-covered surfaces.
In each mode, the ACD adjusts center differential locking behavior to suit the road conditions. The car's other dynamic handling systems respond to the road conditions and driver input. The multi-information monitor, located between the tachometer and speedometer, displays the selected ACD mode and also provide status indicators for ACD operation.
Active Stability Control (ASC) with Traction Control (TCL)
Integrated management of the ASC and ABS systems allows seamless control of vehicle dynamics when accelerating, decelerating or cornering. The ASC system, which includes stability control and traction control, helps to maintain optimum traction by regulating engine power and the braking force at each wheel. ASC helps the driver follow a chosen line more closely by comparing the car's path (as determined from yaw rate sensor data) to the desired path (as determined from steering inputs) and applies individual wheel braking or throttle control to correct any divergence. ASC also enhances vehicle stability by helping to prevent wheel spin on slippery surfaces, and helping to prevent sliding as the result of sudden steering inputs. Communication between ASC and the TC-SST ensures that the transmission selects and holds the best gear during cornering.
Increasing braking force on the inside wheel during understeer and on the outer wheel during oversteer situations, ASC helps maintain stability through cornering, and also enhances stability for hazardous road conditions. ASC is programmed to allow performance driving and can be turned off by pressing and holding the ASC button for five seconds. Turning off ASC does not compromise operation of the car's 4WD.
Limited-Slip Front and Rear Front Differentials
A helical gear-type limited-slip front differential reacts to torque input to govern side-to-side torque distribution at the front wheels. A mechanical limited-slip differential performs that task for the rear wheels.
The helical limited slip front differential, which is installed in the ACD transfer case, constantly biases torque to the wheel that has more traction. This type of differential reacts to torque input. Under straight-line acceleration, power remains evenly split between the front wheels. While cornering or accelerating out of a turn, the helical LSD directs power away from the inside wheel and toward the outside wheel, allowing the driver to begin accelerating earlier and exit the turn at a higher speed, without losing traction.
The helical front differential can also compensate for loss of traction when the front wheels are on slippery surfaces, biasing torque to the wheel with the best traction. In the rear, a plate-style, 1.5-way limited slip differential (also inherited from the previous-generation Lancer Evolution) is a competition-proven design for providing traction and durability.
Lancer Ralliart Warranty
Lancer Ralliart is covered by a bumper-to-bumper, New Vehicle Limited Warranty of 36 months or 36,000 miles (whichever comes first). The restraints system and the highly technical powertrain are covered by a 5-year or 60,000 miles Powertrain Limited Warranty, an Anti-Corrosion Perforation Limited Warranty for 7-years or 100,000 miles and a generous 5-year, unlimited miles timeframe for roadside assistance. All warranties are transferable to subsequent owners; coverage time begins on the original in-service date (does not start over with resale.)