The pitch trim actuator is a hydraulic powered electro-mechanical flight control device of UH-60 helicopters which converts a mechanical input and an electrical command into a mechanical output with trim detent capabilities. In this thesis study, pitch trim actuator is investigated and a mathematical model is developed. From these mathematical equations, the actuator is modeled in MATLAB Simulink environment. While constructing the mathematical model, pressure losses in hydraulic transmission lines and compressibility of hydraulic oil are considered. To achieve a more realistic model for valve torque motor, particular tests are carried out and the torque motor current gain and the stiffness of torque motor flexure tube and the flapper displacement are obtained. Experimental data to verify the Simulink model is acquired with KAM-500 data acquisition system. A test fixture is designed for acquiring the experimental data. This test fixture can also be used to test the pitch trim actuator during depot level maintenance and overhaul. To verify the consistency of Simulink model, acquired experimental data is implemented in Simulink environment. The output of Simulink model simulation and the experimental data are compared. The results of comparison show that the model is good enough to simulate the steady state behavior of the actuator.

Many problems in tracking control have been identified over the years, such as the availability of systems states, the presence of noise and system uncertainties, and speed of response, just to name a few. This thesis is concerned with developing novel integrated control and estimation algorithms to overcome some of these problems in order to achieve an efficient tracking performance. Since there are some significant advantages associated with Sliding Mode Control (SMC) or Variable Structure Control (VSC), (fast regulation rate and robustness to uncertainties), this research reviews and extends new filtering concepts for state estimation, referred to as the Variable Structure Filter (VSF)and Smooth Variable Structure Filter (SVSF). These are based on the philosophy of Sliding Mode Control.<p>The VSF filter is designed to estimate some of the states of a plant when noise and uncertainties are presented. This is accomplished by refining an estimate of the states in an iterative fashion using two filter gains, one based on a noiseless system with no uncertainties and the second gain which reflects these uncertainties. The VSF is combined seamlessly with the Sliding Mode Controller to produce an integrated controller called a Sliding Mode Controller and Filter (SMCF). This new controller is shown to be a robust and effective integrated control strategy for linear systems. For nonlinear systems, a novel integrated control strategy called the Smooth Sliding Mode Controller and Filter (SSMCF), fuses the SMC and SVSF in a particular form to address nonlinearities. The gain term in the SVSF is redefined to form a new algorithm called the SVSF with revised gain in order to obtain a better estimation performance. Its performance is compared to that of the Extended Kalman Filter (EKF) when applied to a particular nonlinear plant.<p>The SMCF and SSMCF are applied to the experimental prototype of a precision positioning hydraulic system called an ElectroHydraulic Actuator (EHA) system. The EHA system is known to display nonlinear characteristics but can approximate linear behavior under certain operating conditions, making it ideal to test the robustness of the proposed controllers.<p>The main conclusion drawn in this research was that the SMCF and SSMCF as developed and implemented, do exhibit robust and high performance state estimation and trajectory tracking control given modeling uncertainties and noise. The controllers were applied to a prototype EHA which demonstrated the use of the controllers in a real world application. It was also concluded that the application of the concepts of VSC for the controller can alleviate a challenging mechanical problem caused by a slip-stick characteristic in friction. Another conclusion is that the revised form of the SVSF could obtain robust and fast state estimation for nonlinear systems.<p>The original contributions of the research include: i) proposing the SMCF and SSMCF, ii) applying the Sliding Mode Controller to suppress cross-over oscillations caused by the slip-stick characteristics in friction which often occur in mechanical systems, iii) the first application of the SVSF for state estimation and iv) a comparative study of the SVSF and Extended Kalman Filter (EKF) to the EHA demonstrating the superiority of the SVSF for state estimation performance under both steady-state and transient conditions for the application considered.<p>The dissertation is written in a paper format unlike the traditional Ph.D thesis manuscript. The content of the thesis discourse is based on five manuscripts which are appended at the end of the thesis. Fundamental principles and concepts associated with SMC, VSF, SVSF and the fused controllers are introduced. For each paper, the objectives, approaches, typical results, conclusions and major contributions are presented. Major conclusions are summarized and original contributions reiterated.

Many problems in tracking control have been identified over the years, such as the availability of systems states, the presence of noise and system uncertainties, and speed of response, just to name a few. This thesis is concerned with developing novel integrated control and estimation algorithms to overcome some of these problems in order to achieve an efficient tracking performance. Since there are some significant advantages associated with Sliding Mode Control (SMC) or Variable Structure Control (VSC), (fast regulation rate and robustness to uncertainties), this research reviews and extends new filtering concepts for state estimation, referred to as the Variable Structure Filter (VSF)and Smooth Variable Structure Filter (SVSF). These are based on the philosophy of Sliding Mode Control.<p>The VSF filter is designed to estimate some of the states of a plant when noise and uncertainties are presented. This is accomplished by refining an estimate of the states in an iterative fashion using two filter gains, one based on a noiseless system with no uncertainties and the second gain which reflects these uncertainties. The VSF is combined seamlessly with the Sliding Mode Controller to produce an integrated controller called a Sliding Mode Controller and Filter (SMCF). This new controller is shown to be a robust and effective integrated control strategy for linear systems. For nonlinear systems, a novel integrated control strategy called the Smooth Sliding Mode Controller and Filter (SSMCF), fuses the SMC and SVSF in a particular form to address nonlinearities. The gain term in the SVSF is redefined to form a new algorithm called the SVSF with revised gain in order to obtain a better estimation performance. Its performance is compared to that of the Extended Kalman Filter (EKF) when applied to a particular nonlinear plant.<p>The SMCF and SSMCF are applied to the experimental prototype of a precision positioning hydraulic system called an ElectroHydraulic Actuator (EHA) system. The EHA system is known to display nonlinear characteristics but can approximate linear behavior under certain operating conditions, making it ideal to test the robustness of the proposed controllers.<p>The main conclusion drawn in this research was that the SMCF and SSMCF as developed and implemented, do exhibit robust and high performance state estimation and trajectory tracking control given modeling uncertainties and noise. The controllers were applied to a prototype EHA which demonstrated the use of the controllers in a real world application. It was also concluded that the application of the concepts of VSC for the controller can alleviate a challenging mechanical problem caused by a slip-stick characteristic in friction. Another conclusion is that the revised form of the SVSF could obtain robust and fast state estimation for nonlinear systems.<p>The original contributions of the research include: i) proposing the SMCF and SSMCF, ii) applying the Sliding Mode Controller to suppress cross-over oscillations caused by the slip-stick characteristics in friction which often occur in mechanical systems, iii) the first application of the SVSF for state estimation and iv) a comparative study of the SVSF and Extended Kalman Filter (EKF) to the EHA demonstrating the superiority of the SVSF for state estimation performance under both steady-state and transient conditions for the application considered.<p>The dissertation is written in a paper format unlike the traditional Ph.D thesis manuscript. The content of the thesis discourse is based on five manuscripts which are appended at the end of the thesis. Fundamental principles and concepts associated with SMC, VSF, SVSF and the fused controllers are introduced. For each paper, the objectives, approaches, typical results, conclusions and major contributions are presented. Major conclusions are summarized and original contributions reiterated.

<p>Emission regulations and global policies to tackle climate change have forced industries and businesses to take measures to curb their impact on the environment. According to the United Nations Environment Program 2022 report on emissions [1], the transportation sector contributes to one-quarter of all energy-related CO2 emissions, and it is set to double by 2050. A recent report [2] suggests that off-road vehicles and equipment account for three-quarters of particulate matter and one-quarter of the nitrogen oxides emitted from mobile transportation sources in the US. The major challenge in decarbonizing or electrifying off-road machines is that they come in a wide range of sizes, weights, and functions, creating barriers to bringing down costs through economies of scale. Fluid power systems which are ubiquitous in these machines have been electrified in a compact and efficient manner to break even the costs of electrification. </p> <p>In off-road applications, where actuation systems heavily depend on hydraulics, there is a high demand for novel systems based on electric prime movers that can enable zero-carbon emission vehicles. An appropriate combination of electric prime movers and hydraulic machines commonly known as electrohydraulic units (EHUs) can help leverage the benefits of both these technologies. The integration of these two technologies in a single casing shaftless EHU can further maximize compactness and reduce cost. However, to achieve such an integrated EHU there is no standard procedure or recommended guidelines for equipment manufacturers owing to the interdisciplinary nature of the problem. </p> <p>This study proposes a generic design methodology to design electrohydraulic units (EHUs). As a starting point, a survey study was undertaken to compare different combinations of electric and hydraulic machines when designing an EHU. The different combinations were investigated for different operating drive cycles for their performance as well as other factors such as power-to-weight, cost, and the possibility of variable displacement. An axial piston machine (APM) was selected as a hydraulic machine (HM) to be integrated with a permanent magnet synchronous motor (PMSM) as the electric machine. </p> <p>The design methodology is demonstrated for an integrated electrohydraulic architecture with the APM housed inside the core of the PMSM. Such an architecture not only makes the overall integration much more compact but also allows for better thermal management of the EM. In such an architecture, the EM governs the overall power density of the integration and the total mass of the integration owing to inherent torque density differences. An EM design optimization is adopted for a predefined HM architecture to design the proposed EHU integration. The design optimization is used to quantify the effect of key EHU design specifications on the EM size and performance. EHU specifications such as sizing torque, operating voltage, aspect ratio, cooling efficacy, number of poles, and power-to-weight ratio have been studied to draw generic trends. These generic trends in the design specifications are used to outline clear guidelines on the impact of each of the EHU specifications for future EHU designers.</p> <p>Using the generic design trends, the design methodology is extended to size the EHU based on typical operating demands using the HM variable displacement, EM overload capability, and the EM flux weakening operation. These sizing studies allow the designers to size the EHU for the specific drive cycle operating demands and avoid oversizing the EHU. The EM flux weakening mode of operation allows the EM to be sized for a peak power level lower than the corner power of operation. The EM overload operation allows a reduction in the sustainable sizing torque lower than that of the maximum torque demand. The variable displacement in the HM can be used for improving overall EHU efficiency when selecting a low voltage or using a compact EM as well as to reduce the EM sizing torque. Two operation algorithms are proposed to define the EHU operation using variable displacement. Additionally, the sizing of a single EHU for multiple applications is also demonstrated. Such multi-utility EHU sizing can promote mass production and improve the rate of electrification in off-road machines.</p> <p>Finally, a prototype-tested EHU design based on the sizing study is demonstrated and the design considerations in such a design process are discussed. The prototype of the integrated EHU with a fixed displacement APM was able to reach the full capability of the reference APM. Thermal considerations are made on the EM sizing, to ensure the reliability of the designed EHU.  A novel self-sustained EHU architecture using the HM working fluid as a cooling fluid for the EM was designed. This was achieved by proposing a three-port valveplate design to divert part of the delivery stroke to cool the EM. A lumped parameter HM model was used to optimize this third port for an EHU prototype.</p>