Browsing by Subject "Mechatronics"

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    Design and control of fully flexible valve actuation systems for camless engines
    (2012-12) Gillella, Pradeep Kumar
    The motivation to improve the fuel efficiency and reduce emissions of the internal combustion engine comes from the dwindling oil reserves and the increased concerns about climate change. A key step towards realizing these improvements is to introduce flexibilities into the mechanisms used for air and fuel management by replacing the mechanical devices with mechatronic systems. The introduction of fuel injection systems in place of the carburetors resulted in significant improvements due to the additional flexibilities in fuel management. The traditional air management systems use camshaft based mechanisms to actuate the intake/exhaust valves. The benefits offered by fully flexible valve actuation and the limitations of the camshaft based systems motivate the development of a "Camless valve actuation system". Research in this area during the past two decades has led to the development of several concepts. However, the stringent performance requirements to ensure reliable operation and the shortcomings of the previously developed concepts has impeded the widespread deployment of these systems. In this research, we propose to address the problem from two perspectives. A design based solution capable of achieving fully flexible operation using inexpensive components while requiring simplified controllers is first introduced. It is followed by the development of a systematic procedure for optimizing the design of a key component in this system to improve it performance and robustness. The second topic focuses on the implementation aspects of a new control algorithm to enable precise tracking of the engine valve reference profile. The effectiveness of the linear time invariant controllers based on the internal model principle for steady state operation of the engine is leveraged to enable tracking control during engine speed transients by extending the control framework to the time-varying setting. The challenges associated with the time-varying nature of the controller are revealed and the developed solutions help its implementation and validation on experimental hardware. The proposed framework can easily be extended to other engine subsystems as well as other general rotational machinery.
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    System Configuration and Control Using Hydraulic Transformer
    (2018-05) Lee, Sangyoon
    Hydraulic power transmission offers multiple benefits over competing technologies including an order of magnitude higher power density than electric systems, relatively low cost, fast response, and flexible packaging. Hydraulics are often used in high-performance mobile robots that demand power, precision, and compactness. However, typical hydraulic systems suffer from low system efficiency from the wide usage of throttle valves. The research described in this dissertation focuses on developing hydraulic transformers that transforms hydraulic power from one set of pressure and flow to the other set of pressure and flow to replace throttle valves such that a compact and efficient fluid power system can be realized. A dynamic model capable of capturing operating characteristics and losses is developed to establish a quantitative comparison between two major designs of the hydraulic transformer. A traditional design where a pump and motor are coupled together in a single package is chosen for the research. This design has three possible configurations with unique operating characteristics, and if these configuration modes can be switched, the resulting transformer is shown to be more compact and efficient. A trajectory tracking controller for a cylinder and force controller for a hydraulic human power amplifier is developed to demonstrate potential applications for the hydraulic transformer. The controller developed proves that utilizing hydraulic transformer need not sacrifice the control performance. Control methodologies ensuring efficiency of the transformer driven system are developed. Transformer operating speed is optimized to minimize the power loss through the transformer. Transformer configuration is switched actively to operate the transformer in its most optimal mode. These methods further improve the efficiency benefit of using the transformer. A hydraulic transformer system utilizing developed controllers compared against a throttle valve system tracking a trajectory with various loading conditions reveals that transformer system can achieve an efficiency of 81.2% which is more than threefold increase over the throttling system with an efficiency of 26.2%. This efficiency improvement is possible with the ability of a transformer to capture regenerative energy to reduce the net energy consumption. This dissertation successfully presents the controller development for a hydraulic transformer that captures both precision and efficiency.