Design Of The Electronic Control System Of Variable Nozzle Turbocharger

As the high thermal-efficiency machines of power, diesel engines have been widely applied to the fields such as traffic transportation, agricultural machines and engineering machines. Since 1897 diesel engines have brought notable benefits to the society. However, the great noises and high emissions of particulate matter(PM) of diesel engines can also bring tremendous pressure to the environment. To control the emissions of diesel engines and enhance their performances, all sorts of methods have been suggested. The use of exhaust-gas turbocharger is the chief method to optimize the performance of the diesel engine because it can remarkably enhance the boost pressure, improve the quality of combustion, reduce the emissions and noises of the diesel engine. However, the exhaust-gas turbocharger can cause insufficient power at low speed and heavy smoke emission at transient operations due to its fixed geometry and turbo-lag. The Variable Geometry Turbocharger(VGT) can greatly overcome these disadvantages of exhaust-gas turbocharger because it can match with the diesel engine at all operating conditions.Variable Nozzle Turbocharger(VNT) is the chief type of VGT and it can match with the diesel engine by rotating its nozzle pivots. How can we precisely control the nozzle's geometry would be the key to achieve "variable" for VNT. These days, with the development of electronic technology, the studies of electronic control system of VNT become more and more popular because of its high precision and quick response. The foreign electronic control system of VNT usually has a high cost and a complexity structure, while there is less domestic research in this field.A set of electronic control VNT system has been designed while researching the matching of CA6DE1-21K DI TCA diesel engine and GT35V turbocharger in this dissertation. The components of this system include signal sensors, electronic control unit(ECU) and executing agency. Two sensors are used for getting input signals, one used for massuring the speed of diesel engine and the other used for massuring the control rod travel of diesel engine's accelerator. A MCS-51 single chip processor(SCP) and its extend circuits are chosen as the core of ECU. A step motor is the main part of executing agency, gearing(three-stage speed reducer), joining(plain connecting rod) and feedback mechanism(rheostat) are also important components of the executing agency. The electronic control system of VNT is excellent in its simple structure, low cost and convenient for fixing, detaching and repairing.Considering the simplicity of this designed system and its reliability of controlling, open-loop control is chosen as the control strategy of the system. At the same time, the speed of diesel engine, the control rod travel of accelerator and its change rate are chosen as input parameters, the current position of step motor's rotor is chosen as the feedback parameter. The controlling codes of the system which structure is modularized has been written in MCS-51 SCP language. The codes are composed of two parts: the part of pre-treatment and the part of main-circulation. The chief modules include executing agency reposition, start-up control, stop-overspeed control, steady and transient operation conditions control, step motor drive, and so on. We have chosen several methods to optimize the electronic control system such as enhance the response frequency of step motor.A pneumatic MAP has been gotten before the design of the electronic control system by the tests at steady operation conditions of CA6DE1-21K diesel engine which equipped with a GT35V turborcharger using a set of constant-pressure controle system, and the MAP has been changed to an electronic MAP after the electronic control system has been designed. The characters of the MAP show that the geometry of nozzle would become larger with the increasing of speed, the geometry of nozzle would become larger even when diesel runs in high load conditions.The matching of the GT35V turbocharger with electronic control system a...