Fault-Tolerant Control Algorithm for a Four-Corner Closed-Loop Air Suspension System

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Abstract
This paper presents a new systematic control and fail-safe design methodology for a four-corner closed-loop air suspension (CLAS) system. The proposed control algorithm consists of “system control” determining the target heights of the four corners of the vehicle body from driving conditions and from the driver's commands and “actuator control” achieving the target heights by controlling actuators. A sliding-mode control with phase-compensated feedback signal is applied as the main part of the system control. With the use of the sliding-mode control, the proposed system control can improve control accuracy and robustness against delays and disturbances as well as reduce the bounce oscillation of the vehicle body. This paper proposes a stepwise height control as the actuator control to overcome the limited power of the production CLAS system. The stepwise height control adjusts the front corners and the rear corners alternately until the four corners reach their corresponding target heights. A fail-safe algorithm (FA) is also proposed to provide the fault detection (FD), diagnosis, and management of the CLAS. In particular, a model-based FD method for the pressure sensor and the height sensors, which are critical components in the CLAS control system, has been proposed. A mathematical model of a CLAS system is developed for algorithm development and simulation. The proposed control algorithm and FA are verified by simulations and actual vehicle tests.

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