This thesis deals with the design of a level controller for an Electronic Level Control system (ELC). After the introduction of the air suspension systems of commercial vehicles, the model of the trailer truck, and the model of the five channel magnet valve block applied in the software-in-the-loop controller design are described in chapter 2 and chapter 3 respectively. The differential equations realizing the state-space representation of the ELC system are based on physical laws like conservation of gas energy, conservation of momentum, mass flow and thermodynamical equations.
The controller requirements are set up, and the development work is presented in details in chapter 4. The focus is on the precise and fast operation, with low magnet valve actuation numbers. The main challenge is to harmonize the effect of the two control goals (level and axle load distribution control). The operation is based on a state observer, so thus the controller works in a feed-forward way. During axle lifting, a state-machine takes over the control. The developed high level controller supervises the cooperation of the observer, the feed-forward controller and the lifting state-machine. The sensitivity to system parameters is also investigated.
The operation of the system is simulated in software-in-the-loop environment, the results are presented in chapter 6. A hardware-in-the-loop environment was built for fine tuning and to verify the accordance to the requirements. The prototype controller was implemented on a Mercedes Actros commercial vehicle, using a National Instrument Industrial computer. The test results are presented in chapter 7. The system has proven to operate in the specified way.
In the last chapter comments and proposals are put forward.