<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>

Electrohydraulic drives are primarily used whenever a low power/weight ratio, a compact build and/or large forces are required for individual applications. These drives are often used together with electric drive technology in machines. However, in terms of automation, unlike electric drives, electrohydraulic drives are still largely connected via analog interfaces and centralized closed control loops today. To compensate for this competitive disadvantage of hydraulic drive technology and, at the same time, significantly enhance its performance and diagnostics capability, a consistent automation solution has been developed that can be configured for both centralized and decentralized solutions. This contribution firstly gives an overview over this complete solution already available and its classification in the automation world. In a second step, the subset of decentralized drive solutions contained therein is presented in more detail and their benefits are explained on the basis of some exemplary applications.

Modern control design is sometimes accompanied by the challenge of dealing with nonlinear systems or plants. In some situations, due to the complexity of the plant and the unavailability of suitable models, the controls engineer opts for developing control schemes based on look-up tables. These tables, typically populated with the steady state inverse input-output characteristics of the plant, are used to compensate the plant via open-loop or closed-loop to solve the control problem. In an effort to present a new alternative, a general theoretical framework for online auto-calibration and control of general nonlinear systems is developed in this dissertation. This technique simultaneously learns the inverse input-state mapping (i.e. the calibration mapping) of the plant while forcing its state to follow a prescribed desired trajectory. The main requirements for the successful application of the novel control law are knowledge of the order of the plant and some generic data to initialize the inverse mapping. This last requirement can be easily fulfilled by using steady-state data or the equilibrium points of the plant. In this approach, the inverse mapping is learned from the current and past states. The learning is accomplished in a composite manner by employing input and state errors. The map is used simultaneously in the feedforward path to control the plant. The performance of the plant subject to this novel controller is validated through simulations and experimental data. The new control method is applied to a novel Electro-Hydraulic Poppet Valve (EHPV). These valves are used in a Wheatstone bridge arrangement for motion control of hydraulic actuators. This is preferred over the conventional use of spool valves due to the energy savings potential. It is shown in this dissertation that this method improves the value of using these types of valves for motion control in hydraulics. This is due to the combination of self-learning (auto-calibration) and better performance for a more efficient operation of hydraulic equipment. Additionally, it is shown that the auto-calibration of the valves can be used for health monitoring of the same, which consequently improves their reliability and expedites maintenance downtime.

The thesis focuses on a hydraulic system design for a specific application of hydrostatic drive with regard to energy efficiency of proposed solution. Standard hydraulic and electronic components are used, mostly products of Bosch Rexroth. The aim of the thesis is to carry out a complex design from mechanic through hydraulic up to the electronic part of the system. After a short introduction in the beginning of the thesis is the particular application described and analyzed. Then the elemental principles of hydraulic devices and systems are explained. In the following part the actual solution is presented, which expands to several different alternatives. These alternatives are compared according to set criteria and the selected alternative is then further developed. At the end of the thesis, the outputs are evaluated and the direction of further possible improvements in the design is outlined.

Due to good energy-efficiency of electrohydraulic compact drives a cooling aggregate often is not installed. The operating temperature is governed by the complex interaction between dissipative heat input and passive heat output. This paper targets the simulation of the thermo-energetic behaviour of an electrohydraulic compact drive by means of a lumped parameter model in order to predict the operating temperature. The developed thermo-hydraulic model is validated against measurements utilising thermocouples and a thermographic camera to capture temperatures. The results show, that the presented methodology enables a satisfying accurate prediction of the thermo-energetic behaviour of electrohydraulic compact drives. A further analysis of simulation results is given, highlighting the power losses and heat rejection capabilities of different components. Finally, measures for the improvement of the heat rejection capabilities are studied.

Electrohydraulic drives are primarily used whenever a low power/weight ratio, a compact build and/or large forces are required for individual applications. These drives are often used together with electric drive technology in machines. However, in terms of automation, unlike electric drives, electrohydraulic drives are still largely connected via analog interfaces and centralized closed control loops today. To compensate for this competitive disadvantage of hydraulic drive technology and, at the same time, significantly enhance its performance and diagnostics capability, a consistent automation solution has been developed that can be configured for both centralized and decentralized solutions. This contribution firstly gives an overview over this complete solution already available and its classification in the automation world. In a second step, the subset of decentralized drive solutions contained therein is presented in more detail and their benefits are explained on the basis of some exemplary applications.

<div>Pressure compensated vane pump systems are an attractive solution in many automotive applications to supply hydraulic power required for cooling, lubrication, and actuation of control elements such as transmission clutches. These systems feature variable displacement vane pumps which offer reductions in parasitic loads on the engine and in wasted hydraulic energy at high engine speeds when compared to traditional fixed displacement supply pumps. However, oscillations in a currently available pressure compensation system limits the achievable performance and therefore the application of this solution.</div><div>This dissertation presents the development and experimental validation of a lumped parameter model in MATLAB/Simulink of a current pressure compensated vane pump system for an automatic transmission oil supply application. An analysis of the performance of this system using the validated pump model and a developed black box control system model reveals that the low cost solenoid valve present in the control circuit to set the regulation pressure limits the achievable bandwidth to 1.84Hz and causes a significant time delay in the response. To address this limitation, as well as eliminate a non-minimum phase zero introduced by the case study’s control circuit architecture, an actively controlled electrohydraulic pressure compensation system is proposed. This proposed system is explored both experimentally and in simulation making use of the accuracy of the presented variable displacement vane pump model. Significant improvements in the achievable system performance are shown with both a simple PI control law (47% reduction in the pressure response time) and an advanced cascaded model following controller based on feedback linearization (58% reduction in the pressure response time). An analysis of these results reveals that implementing the proposed control system with a 5(L/min)/bar proportional valve with a 20Hz at ±100% (60Hz at ±50%) amplitude bandwidth and a PI control law is an economical path to achieving the best performance improvements for this automotive application.</div>

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.

Hydraulic systems are widely applied in industry for position or force control. However, due to hydraulic system nonlinearities, it is difficult to achieve a precise model valid over a large range of frequencies and movements. The work in this dissertation focuses on a high performance hydraulic test bench which involves three main hydraulic components, i.e. two high performance servovalves, a double rod actuator, and a specific intermediate block connecting the servovalves and actuator. This rig has been designed for testing aerospace or automotive components in real conditions (e.g. wear and ageing effects). The main objectives of this dissertation are first the development of a virtual prototype based on a precise model which is derived from the physical principles and experimental works, and then second the synthesis of several nonlinear control laws of this actuation system in a large operating range with a good robustness to the perturbations. The proposed model based on Bond Graph shows a very good agreement with experimental results not only at low frequencies, but also at high frequencies. Moreover, its performances are improved at high frequencies by introducing the dynamic effects due to the intermediate block. Besides, multivariable and monovariable control strategies, based on respectively the backstepping and the model-free method, are developed and implemented on the test bench. All the control strategies proposed have been validated by simulations and experiments. Results show they lead to better tracking precision and robustness performance compared to the conventional control techniques.