Mitsubishi Motors' S-AWC Integrally Controls Vehicle Behaviors with 2 ECUs
Mitsubishi Motors Corp. announced July 10, 2007, that it will mount Super All Wheel Control (S-AWC), a newly-developed technology for the integration control of vehicle motion, in the new models of Lancer Evolution, which will be released in fall 2007.
S-AWC was developed by integrating four functions to control vehicle motion. Those four functions are "sports ABS," "active center differential (ACD)" to control braking force of front and rear wheels, "active yaw control (AYC)" to regulate yaw driving force of rear wheels, and "active stability control (ASC)" to control a brake and engine.
Mitsubishi Motors has been developing the first three functions for some time.
The company exhibited an integration control technology that also controls suspensions and steering as S-AWC in the 39th Tokyo Motor Show in 2005. However, S-AWC that the company announced in 2007 controls neither of them.
Dedicated CAN Controls 2 ECUs
In this integration control system, two electronic control units (ECU) regulates vehicle motion. One is an ECU developed by Mitsubishi Electric Corp. to control ACD, AYC and ASC. The other is an ECU that is accompanied by the ABS developed by Continental Teves Inc. of Germany.
The two ECUs can communicate with other ECUs through a CAN, an in-vehicle LAN interface standard. In addition, the two ECUs are communicating with each other through a dedicated CAN, enabling to control vehicle motion with faster response speed.
The cable and communication standard for the dedicated CAN are the same as those for other CANs.
The company considered adopting FlexRay, a next-generation in-vehicle LAN interface standard used by BMW. But, according to the company, with the dedicated CAN, it is possible to ensure enough communication speed that does not bring discomfort to the users.
As for sensors, a longitudinal acceleration sensor, lateral acceleration sensor and yaw rate sensor are installed as one module near the gravity center of a vehicle, which is located between a driver's seat and passenger seat.
Other sensors, such as a wheel-speed sensor and steering-angle sensor, are installed in different places. However, no vertical acceleration sensor is used.
Cooperation with Twin Clutch SST is One-Way Communication
Mitsubishi Motors also announced the details of Twin Clutch SST, a newly-developed automatic transmission and that this transmission operates in cooperation with S-AWC.
For example, when S-AWC analyzes a behavior of a turning vehicle and judges it safer not to shift gears, it sends a signal to tell Twin Clutch SST that the gear must not be changed. However, S-AWC does not control vehicle motion by using control information from Twin Clutch SST, according to the company.
Model-Based Method Develops Control Algorithms of Vehicle Motion
With Matlab/Simulink, a control-system-modeling tool, the control algorithms of vehicle motion were developed by Mitsubishi Motors. The company adopted model-based method, which combines an algorithm and physical model of a vehicle to run a simulation.
The physical model of a vehicle was constructed with CarSim, a simulation-package software developed by Mechanical Simulation Corp. of the United States.
The algorithms were developed for each function such as ACD and AYC, not for each vehicle type. Therefore, the algorithms can be employed by various types of vehicles.
"If ECUs are integrated, it will become more difficult to use a part of the softwares installed in an ECU for other vehicles," said Seiichi Ohta, executive officer and corporation general manager of the Development and Engineering Office of Mitsubishi Motors, when asked about Toyota Motor Corp., which aims to integrate several ECUs.
"Unless the prices of ECUs drastically drop, it is more efficient to use multiple ECUs," he said, expressing a negative view on the integration of ECUs at this point.