<b>Innovative methods for electro-hydraulic actuation and fluid power education</b>

<p dir="ltr">After decades of incremental improvement in fluid power actuation systems, nowadays commercial off-road vehicles are experiencing a strong push toward the implementation of more energy efficient actuation architectures, driven by the need of reducing emissions. As a result, off-road vehicles in agriculture, mining, and construction, are adopting electrified or hybrid technologies, affecting the design of their fluid power systems. State of the art fluid power systems have a large power to weight ratio, but have an overall energy efficiency of about 30%, therefore there is a high opportunity for improvement.</p><p dir="ltr">However, due to the number of actuators typically present in an off-road vehicle and the large variability of their drive cycle, the electrification of actuation system to allow low energy consumption and high battery up time present high complexities. In particular, several circuit layouts and different forms of integration between the electric prime mover and the hydraulic power supply are possible, each one with proper strengths and limitations.</p><p dir="ltr">This thesis addresses this trend towards novel circuit designs from two different angles: 1) how to educate and prepare current and future generations of engineers for this trend, especially considering the lack of skilled workforce in the fluid power industry capable of proposing new efficient systems, and 2) the development of a new self-contained Electro-Hydraulic Actuator (EHA) that can is suitable for machine electrification on a wide range of applications. The two topics are presented in a distinct way for clarity.</p><p dir="ltr">Hands-on experiences constitute a high-value, perhaps unreplaceable, element of applied engineering disciplines such as FP. Hydraulic and pneumatic trainers have been developed over the years to expose students to applications of fluid power technology. However, the traditional approach for educating students through hands-on lab is recently under high pressure due to the following aspects: a) the outdated design of the traditional trainers that seldom integrate modern electro-hydraulic components, data acquisition systems, and visual aids; b) the increased need for online education. These factors have been endangering the number of students – already low compared to the industry needs – enrolled in fluid power programs.</p><p dir="ltr">Consequently, A novel physical trainer was formulated to allow 29 lab experiences that span from basic concepts of single actuator control to more sophisticated layouts for controlling multiple actuators. The trainer largely uses electro-hydraulic components, sensors as well as a DAQ system connected with a touch base screen, aimed at maximizing the student’s feeling of experiencing modern technology.</p><p dir="ltr">Additionally, there is a notable absence of virtual tools that can provide students with a realistic feeling of assembling, troubleshooting, and operating an actual hydraulic circuit. This thesis describes the effort made to develop an original virtual trainer that fulfills these needs. This virtual trainer is designed to replicate existing physical trainers but on a virtual platform. The virtual trainer is implemented in Unity3D software, using CAD drawings of the components from the actual trainer, and provides the user with an interactive environment that reproduces all the aspects of a real lab experience. The tool allows the students to learn by mistake, as in typical activities with a physical trainer, and includes realistic operating noise. The core part of the virtual trainer is the object-oriented simulation model that is behind every hydraulic component.</p><p dir="ltr">The physical and virtual trainers are used in Purdue fluid power graduate (ME/ABE 535) and undergraduate (ABE 435) classes. First successfully used in the Fall of 2020, and subsequently utilized in both Spring and Fall 2021, 2022 courses.</p><p dir="ltr">The proposed EHA addresses the key challenges of actuators to be used in electrified systems: it minimizes the energy loss due to throttling, it allows for energy recuperation, it minimizes spatial requirements, and it is conceived as a self-contained actuator, minimizes chances of oil leakage. The EHA design is ergonomic and suitable for applications in harsh environments, but most importantly it implements new principles for reducing the size of the power supply unit (the electric machine and the hydraulic machines), to integrate different components (such as the actuator and the oil reservoir) and to optimize the cooling features thought internal recirculation. A numerical simulation and optimization approach that ensures the highest level of integration, the proper sizing of the EHA components, and the control formulation were followed. To validate the behavior of the system and the energy performance a lumped parameter model was built using the commercial software Simcenter Amesim followed by an experimental setup on a stationary test rig that can reproduce both resistive and overrunning loads is utilized to perform tests on the proposed hydraulic circuit. The measured hydraulic energy efficiency of this technology goes up to 80 % with an average of 70% compared to 30% of the current state-of-the-art. A mild drive and aggressive working cycles for the reference application are considered to evaluate the steady-state temperature of the working fluid suggesting that the EHA does not require external cooling in mild working cycles with hydraulic oil temperature kept less than 80, while a coolant is required for continuous operation under aggressive operation.</p><p dir="ltr">After decades of incremental improvement in fluid power actuation systems, nowadays commercial off-road vehicles are experiencing a strong push toward the implementation of more energy efficient actuation architectures, driven by the need of reducing emissions. As a result, off-road vehicles in agriculture, mining, and construction, are adopting electrified or hybrid technologies, affecting the design of their fluid power systems. State of the art fluid power systems have a large power to weight ratio, but have an overall energy efficiency of about 30%, therefore there is a high opportunity for improvement.</p><p><br></p><p dir="ltr">However, due to the number of actuators typically present in an off-road vehicle and the large variability of their drive cycle, the electrification of actuation system to allow low energy consumption and high battery up time present high complexities. In particular, several circuit layouts and different forms of integration between the electric prime mover and the hydraulic power supply are possible, each one with proper strengths and limitations.</p><p dir="ltr">This thesis addresses this trend towards novel circuit designs from two different angles: 1) how to educate and prepare current and future generations of engineers for this trend, especially considering the lack of skilled workforce in the fluid power industry capable of proposing new efficient systems, and 2) the development of a new self-contained Electro-Hydraulic Actuator (EHA) that can is suitable for machine electrification on a wide range of applications. The two topics are presented in a distinct way for clarity.</p><p dir="ltr">Hands-on experiences constitute a high-value, perhaps unreplaceable, element of applied engineering disciplines such as FP. Hydraulic and pneumatic trainers have been developed over the years to expose students to applications of fluid power technology. However, the traditional approach for educating students through hands-on lab is recently under high pressure due to the following aspects: a) the outdated design of the traditional trainers that seldom integrate modern electro-hydraulic components, data acquisition systems, and visual aids; b) the increased need for online education. These factors have been endangering the number of students – already low compared to the industry needs – enrolled in fluid power programs.</p><p dir="ltr">Consequently, A novel physical trainer was formulated to allow 29 lab experiences that span from basic concepts of single actuator control to more sophisticated layouts for controlling multiple actuators. The trainer largely uses electro-hydraulic components, sensors as well as a DAQ system connected with a touch base screen, aimed at maximizing the student’s feeling of experiencing modern technology.</p><p dir="ltr">Additionally, there is a notable absence of virtual tools that can provide students with a realistic feeling of assembling, troubleshooting, and operating an actual hydraulic circuit. This thesis describes the effort made to develop an original virtual trainer that fulfills these needs. This virtual trainer is designed to replicate existing physical trainers but on a virtual platform. The virtual trainer is implemented in Unity3D software, using CAD drawings of the components from the actual trainer, and provides the user with an interactive environment that reproduces all the aspects of a real lab experience. The tool allows the students to learn by mistake, as in typical activities with a physical trainer, and includes realistic operating noise. The core part of the virtual trainer is the object-oriented simulation model that is behind every hydraulic component.</p><p dir="ltr">The physical and virtual trainers are used in Purdue fluid power graduate (ME/ABE 535) and undergraduate (ABE 435) classes. First successfully used in the Fall of 2020, and subsequently utilized in both Spring and Fall 2021, 2022 courses.</p><p dir="ltr">The proposed EHA addresses the key challenges of actuators to be used in electrified systems: it minimizes the energy loss due to throttling, it allows for energy recuperation, it minimizes spatial requirements, and it is conceived as a self-contained actuator, minimizes chances of oil leakage. </p>