Development and performance of a velocity control system for modern combustion-powered scooters
This doctoral thesis covers the development of a velocity-controlled Throttle-by-Wire-System for modern four-stroke 50 cc scooters (Euro 5). Further, the system performance, fuel-saving effect and exhaust optimization was investigated. The European Parliament has adopted major CO2 emission reductions by 2030. But modern combustion-powered scooters are inefficiently restricted and emit unnecessary amounts of CO2. Replacing the original restriction method with the velocity-controlled Throttle-by-Wire-System, the engines operating point is being improved significantly. Controlling the throttle valve opening prevents an inefficient ignition timing shift. The Throttle-by-Wire-System consists of an anisotropic magnetoresistance throttle position sensor and a position controlled stepper motor-driven throttle valve actuator. The sensor unit comes with a measurement deviation of less than 0.16% whereas the actuator unit can approach throttle valve positions with a deviation of less than 0.37%. The actuators settling time does not exceed 0.13 seconds in the case of stable, step-loss free and noiseless operation. A redundant wheel speed sensor measures the vehicle velocity using the Hall effect with a precision of 0.04 km/h. The entire system is managed by a central ECU, executing the actual velocity control, fail-safe functions, power supply and handling inputs/outputs. For velocity control, an adaptive PI-controller has been simulated, virtually tuned and implemented, limiting the top speed regulated by legal constraints (45 km/h). By implementing a humanmachine interface, including a virtual dashboard, the system is capable of interfacing with the rider. For sensor evaluation, Hardware-in-the-Loop test benches have been developed. During test drives, a specially developed measurement box logs vehicle orientation, system/control variables and engine parameters. A Peugeot Kisbee 50 4T (Euro 5) severed as test vehicle. The system has been evaluated regarding performance and fuel efficiency both through simulation and road testing. Fuel savings of 13.6% in real-world test scenarios were achieved while maintaining vehicle performance. Finally, the system behavior, the combustion process and the exhaust gas composition were investigated. The original and the optimized restriction were subjected to various load points on a roller dynamometer at top speed. The resistance parameters required, were previously determined in a coast down test. When driving on level ground, a difference of 50% in the throttle opening leads to a 17% improvement in fuel economy. By measuring the engine parameters, the optimum ignition timing could be proven with increasing internal cylinder pressure. Further, 17% reduction in exhaust gas flow was demonstrated. CO emissions decreased by a factor of 8.4, CO2 by 1.17 and HC by 2.1 while NOx increased by a factor of 3. Overall, the exhaust emissions at top speed have been significantly improved with regard to the existing emission standards. By comparing the CO2 equivalents of the test vehicle with a modern electric scooter, a CO2 saving of 21% could be estimated over the life cycle favoring the combustion engine.
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