MITSUBISHI Lancer Evolution X: Sport-ABS & S-AWC - 2/2

MITSUBISHI Lancer Evolution  X:  Sport-ABS & S-AWC

S-AWC = ACD + S-AYC + Sports ABS + ASC

The Super All Wheel Control (S-AWC) for LANCER EVOLUTION X is an integrated vehicle

dynamics control system for handling the Active Center Differential (ACD), Active Yaw Control (AYC), Active Stability Control (ASC) and Antilock Brake System (ABS). It is based on the All Wheel Control (AWC) philosophy advocated by Mitsubishi Motors Corporation (MMC). To ensure predictable handling and a high performance margin, the S-AWC system calculates the yaw moment by using the yaw rate feedback control and distributes the yaw moment to each component taking into consideration its characteristics. S-AWC can improve the vehicle cornering performance seamlessly at various driving conditions. 

The All Wheel Control (AWC) is a MMC’s four-wheel dynamic control philosophy for maximally exploiting the capability of all four tires of a vehicle in a balanced manner to realize predictable handling and high margin of performance, which in turn yield the driving pleasure and utmost safety that MMC sees as fundamentals in producing vehicles.

The Super All Wheel Control (S-AWC) is an integrated vehicle dynamics control system that combines various components based on the four-wheel drive (4WD) control, and controls all components integrally to embody the AWC philosophy.

The S-AWC system on the LANCER EVOLUTION X delivers all of the following functions under integrated control: Active Center Differential (ACD), Active Yaw Control (AYC), Active Stability Control (ASC), and Antilock Brake System (ABS). As shown in Fig. 1, by adding braking control to the ACD-AYC combination, which has superior controllability among the currently existing 4WD systems, the S-AWC can control both the driving and braking forces and so handle both longitudinal and lateral behaviour of the vehicle. As a result, the S-AWC seamlessly improves the vehicle’s dynamic performance for various vehicle operations such as acceleration, deceleration and cornering. 

The system includes a Torsen-type front differential, Active Center Differential (ACD), Active Yaw Control (AYC) rear differential, Active Stability Control (ASC), and Sport ABS brakes. Additionally, the driver can choose between Tarmac, Gravel and Snow modes for the ACD and the ASC can be turned off for performance driving.
As an added bonus, if you hold the ASC button down for 3 seconds it will deactivate the AYC's brake control function. Turning off the ASC is imperative for a fast autocross run, but we found during our road course run that ASC was a useful aid in the rain.
ASC On = cuts power and uses individual braking control
-The new chassis is more than 50 percent stiffer than the old one, and the EVO gets a V-shaped brace behind the rear seats. It's also more robust in the rear shock mount area.

There are three types of direct yaw moment control technology currently available: 

The lateral torque distribution control unequally dis- tributes the engine torque to the left and right wheels. The resulting difference in driving torque between the left and right wheels generates the yaw moment. This control, therefore, cannot effectively generate the yaw moment during cruising or deceleration when the engine torque is not large enough.

The lateral torque vectoring control transfers the torque from the left wheel to the right wheel, and vice versa, to generate an amount of braking torque on one wheel while generating the same amount of driving torque on the other wheel. The control of this type, therefore, can generate the yaw moment at any time regardless of the engine torque. Another merit of this control is that it does not affect the total driving and braking forces acting on the vehicle, which means that the control does not conflict with acceleration and deceleration operations by the driver. Although this control affects the steering reaction force when applied to the front wheels, it does not produce any adverse effects when applied to the rear wheels.

The lateral braking control applies different braking forces to the four wheels independently so as to produce a difference in braking force between the left and right wheels, which generates the yaw moment. As this control uses braking forces, it feels to the driver like deceleration, but the control is effective because it can generate yaw moment under a wide range of conditions of vehicle operation. 

  

In view of the characteristics of these three yaw moment control technologies, a combination of the lateral torque vectoring control applied to the rear wheels and the lateral braking control is the most effective way of providing the yaw rate feedback control seamlessly under varying vehicle driving conditions from acceleration to deceleration. The AYC differential introduced by MMC to its products in 1996 is the world’s first component to use lateral torque vectoring control. The braking control can be achieved by using ASC or other exist- ing brake control systems.


For the reasons mentioned above, the S-AWC system consists of ACD, AYC, ASC, and ABS. This configuration is based on the LANCER EVOLUTION IX’s system to which the braking control system is added. 

Table 1 summarizes the characteristics of the longitudinal differential limiting control, lateral torque vectoring control, and braking control. The longitudinal differential limiting control has a stabilizing effect on the vehicle when it is likely to spin, in other words, it can restrain cornering. The lateral torque vectoring control works effectively during acceleration, when loads on the rear wheels increase. It is most effective in improv- ing cornering when the torque is transferred to the out- er wheels, on which the load increases. The braking control is most effective in restraining cornering during deceleration where it can provide control effects with- out causing the driver to perceive excessive deceleration. Seamless and high-quality yaw moment control can be achieved by appropriately combining these control effects based on their characteristics. The control logic shown in Fig. 4 is designed in line with this concept. 

Fig. 6 shows the steering wheel angles and the steering wheel angular velocities plotted on the same graph for when the vehicle was put in sporty driving on a 2.4-km dry handling circuit. It shows that the With S- AWC presented smaller values for both the steering wheel angle and steering wheel angular velocity and that the lap time of the With S-AWC was about 1.5 seconds shorter than the Without S-AWC.

Fig. 7 shows the steering wheel angles and steering wheel angular velocities plotted on the same graph for when the vehicle was turned around a 15-m radius circle as fast as possible on a snow packed road. It shows that the With S-AWC presented substantially smaller values in both the steering wheel angles and steering wheel angular velocities than the Without S-AWC.

These test results clearly show that the S-AWC improves the vehicle’s response to operation of the steering wheel regardless of the road surface conditions and helps drive the vehicle reliably at faster speeds with less operation of the steering wheel. In other words, the S-AWC system improves the cornering performance, stability and controllability of the vehicle. 

With the integrated vehicle dynamics control capability realized using the yaw rate feedback control as the base technology, the S-AWC system on the LANCER EVOLUTION X has succeeded in dramatically improving the vehicle dynamics performance under various driving conditions, thereby achieving both predictable handling and high margin of performance.

MMC will continue to evolve the S-AWC system by adding novel components and improving the control logic, aiming to improve the dynamics performance of our products even further.