Study for the development of an electromechanical shifting system in a model-based approach

The model based design is a design approach that is spreading in the technical environment. The center of this development process is the creation of a virtual model of the system of interest that is then used to perform design and test activities such as validation, optimitazion and simulation on the designed object. It can also be used for automatic code generation or reporting, allowing companies to save money and time in the design phase and hence to be present early on the market scene. This project was developped in team with a student colleague, in a company that produces and distributes gear shifting systems. The shifting system is a component used in the automotive industry to convert the driver's will into an action on the vehicle. This is realised by moving a mechanical cable that operates on the vehicle gearbox. The aim of this thesis is to exploit and adapt the model based approach in the development of an electromechanical automatic shifter system in order to create in the future an industriable component. The starting point was an already existing mechanical prototype of the system and its functioning requirements. First step was the studying phase with the aim to better understand the mechanical system already implemented, its working conditions and the expected results. Once the system behaviour was understood, a first model of the actuator using the Simulink - Matlab environment was built, at this stage of the work only in continuous time. The hardware components needed to supply the electrical motor in the actuator and the sensors to take data were identify, purchased by the company and the needed code for them to run was implemented. As soon as the hardware part was working, the first few tests on the DC motor were run in order to validate the parameters on the DC motor datasheet provided by the electrical motor manufacturers. The Simulink model was improved and converted in discrete time in order to exploit it for the design of the PWM used to regulate the voltage supplied by the H bridge stage to the electrical DC motor. In order to modelling the remaing parts of the actuator, using a current sensor, different tests were performed to estimate the static and dynaminc friction present in the actuator. Once the model had reached a satisfying accuracy, it was also exploited for the design of a suitable closed – loop control system. The chosen control technique was the PID controller and the controlled variable the position of the mechanical cable to be moved. At last also the external loads oppositing the movement of the mechanical cable were modeled. The completed model was used to tune the PID controller. Finally, after performing multiple simulations in the different working conditions, practical tests on the implemented actuator were performed.