The recent electrification trend in the off-road market has incentivized research towards the proposal of compact, cost-effective and energy-efficient solutions for hydraulic actuators. As a result, increased attention has been given to electro-hydraulic actuator (EHA) architectures. The paper offers a study performed on a novel closed-circuit EHA architecture with the goal to maximize the overall system efficiency while meeting or exceeding traditional off-road applications performance, thereby enabling further electrification of off-road applications. Both numerical and experimental approaches are utilized to validate the functionality of the proposed EHA circuital configuration in four quadrants. Moreover, the actuator functionality at both high and low velocities are considered, which has never been explored in the past due to the limitations on the hydraulic machine driving speed. The good match between the experimental data and the simulation results confirms the potential of the simulation model for sizing such EHA architecture for different actuator sizes, duty cycles, and performance levels.

A novel Electro-Hydrostatic Actuator (EHA) prototype – designed to operate on subsea gate valves in deep and ultra-deep water – is analysed and qualified in terms of functionality under design and normative constraints. The prototype is assembled in a test bench for load control in a hyperbaric chamber where the high subsea environmental pressure can be emulated. The process variables under evaluation are monitored through a set of pressure and position sensors, which are part of the prototype design. The experimental results demonstrate a robust behaviour of the actuator concerning the imposed external pressure and load forces even with a forced limitation in its power input. Moreover, the prototype performs consistently throughout the entire endurance trial, asserting high reliability. With the results obtained, the subsea EHA concept is effectually eligible to a technology readiness level 4, according to the API 17N.

Today's economic and ecological directives demand for highly sustainable machine parts by low production cost and energy consumption. Consequently, it is crucial to guarantee a long service life by protecting all components against wear and corrosion. However, hydraulic components always include stressed surfaces, which suffer from heavy loads at high relative speeds. To prevent fretting, coating processes like thermal spraying or hard chrome have a long history in the field of hydraulics. New additive laser-based processes like EHLA and LPBF offer the potential to apply new coatings without environmentally hazardous substances such as chromium or to manufacture complex parts with new functionalities. So far, additively manufactured surfaces with relative movements are post-processed to obtain surface qualities similar to subtractive methods, as the tribological properties of additive surfaces have not been investigated to date. Therefore, this paper investigates the frictional behavior of 316L surfaces produced by laser-based EHLA and LPBF processes using a disc-disc tribometer.

In recent years, additive manufacturing (AM) has become one of the most revolutionary and promising technologies in manufacturing. The process of making a product layer by layer is also often referred to as 3D printing. Once employed purely for prototyping, AM is now increasingly used for small series production, for example in aerospace applications. The paper starts with a motivation for AM in hydraulic applications and the development of an AM internal gear pump. For a better understanding of the manufacturing process, a brief introduction to AM highlighting the advantages and challenges is given. The AM internal gear pump is part of an electrohydraulic power pack, which is used to power an electrohydraulic actuator (EHA). The power pack contains all necessary peripherals to realise the hydraulic system of the EHA. The AM process allows for new design possibilities, but the process differs strongly compared to subtractive manufacturing processes and therefore is outlined here. The paper concludes by presenting measurement results of the AM internal gear pump.

Hydraulic piston accumulators play a major role especially within the field of stationary hydraulics. The calculation of the amount of hydraulic energy which can be stored in such an accumulator is crucial when it comes to a precise system design. The knowledge of the temperature and pressure within the accumulator is required in order to calculate the amount of energy to be stored. The state of the art solution to estimate the state of change of such an accumulator is the implementation of a costly measurement system within the accumulator which tracks the position of the piston. The goal of this paper is to develop and to analyse a time efficient simulation approach for the gaseous phase within a piston accumulator depending on the accumulator’s load cycle. Temperature, pressure, density and velocity profiles inside of the gaseous phase are calculated transiently in order to achieve that goal. The simulation model is derived in one dimensional environment to save computational effort. Having derived a valid model of the gaseous phase it will be possible in future works to replace the expensive position measurement system by pressure and temperature transducers and then use the model to calculate the position of the piston and therefore estimate the state of change.

Biped robots with serial links driven by an electric motor experience problems because the motor and transmission are installed in each joint, causing the legs to become very heavy. Previous solutions involved robots using servo valves, a type of highly responsive proportional valve. However, high supply pressure is necessary to realize high responsiveness and the resulting energy losses are large. To address this problem, we proposed a hydraulic direct-drive system in which the pump controls the cylinder meter-in flow, while a proportional valve controls the meter-out flow. Furthermore, our hydraulic interlocking drive system connects two hydraulic direct-drive systems for biped humanoid robots and concentrates the pump output on one side cylinder. The meter-in flow rate of the other side cylinder is controlled by the meter-out flow rate of the cylinder on which the pump is concentrated. A comparison of the walking simulation performance with that of the conventional independent system shows that our proposed system reduces the motor output power by 24.3%. These results prove the feasibility of constructing a two-legged robot without having to incorporate highly responsive servo valves.

Inverse, multidimensional input-output flow mapping is very important for use of valves in precision motion control applications. Due to the highly nonlinear characteristic and uncertain model structure of the cartridge valves, it is hard to formulate the modelling of their flow mappings into simple parameter estimation problems. This contribution conducts a comprehensive analysis and validation of three- and four-dimensional input-output-mapping approaches for a proportional pilot operated seat valves. Therefore, a virtual and a physical test-rig setup are utilized for initial measurement, implementation and assessment. After modeling and validating the valve under consideration, as a function of flow, pressure and temperature different mapping methods are investigated. More specifically, state of the art approaches, deep-learning methods and a newly developed approach (extPoly) are examined. Especially ANNs and Polynomials show reasonable approximation results even for more than two inputs. However, the results are strongly dependent on the structure and distribution of the input data points. Besides identification effort, the invertibility was investigated.

The field of self-contained linear hydraulic drives based on variable-speed electrical motors and fixed displacement pumps is gaining interest from both industry and academia. Some of the main reasons for this is the possibility to improve the energy efficiency of such drives compared to conventional valve controlled drives, and the possibility for electrical regeneration allowing power sharing between multiple drives [1]. The main drawback for such types of drive concepts is a low pressure in the nonload carrying cylinder chamber. This induces a low drive stiffness limiting the achievable drive bandwidth and hence the application range. However, a so-called self-locking compact drive architecture recently proposed allows maintaining a proper drive stiffness by virtue of separate forward and return flow paths, combining the advantages of efficient flow control into the cylinder and a throttle driven flow out of the cylinder. The multiple inputs available in this architecture allow the control to target several objectives concurrently, for example piston motion, drive stiffness and fluid temperature. The purpose of the study presented is to analyse the dynamic couplings between the control objectives via relative gain array (RGA) methods, and the realization of input- and output transformations effectively decoupling relevant dynamic interactions. These transformations allow the usage of simple SISO-controllers for each control objective, and a method for controlling motion and fluid temperature concurrently, is proposed and experimentally verified.

In the presented paper, the applicability of pressure-decay methods to determine the diffusivities of gases in hydraulic fluids is analysed. First, the method is described in detail and compared to other measurement methods. Secondly, the thermodynamics and the mass transfer process of the system are studied. This results in four different thermodynamic models of the gaseous phase in combination with two diffusion models. Thirdly, the influence of the models on the pressure-decay method is evaluated computationally by examining the diffusion process of air in water as all system parameters are available from literature. It is shown that ordinary pressure-decay methods are not applicable to gas mixtures like air and therefore a new method for calculating the diffusivities is suggested.

In hydraulic pumps, typically in axial piston pumps, reduction of pressure and flow ripples was attempted by providing relief grooves and pre-compression for noise reduction. Pre-compression is normally achieved by using the dead space between pump ports in the valve plate. Also valve plate profile modification is required, if system operating conditions such as pump output pressure and flowrate change, to maintain optimum operating conditions for reduced pressure/flow ripple. An earlier simulation study confirmed effectiveness of varying dead centre position to reduce pressure and flow ripples. A specifically designed mechanism, outlined in the earlier work, achieves this goal by varying the dead centre position of the pump swash plate. This study reports on the findings of the effect of varying dead centre position and groove configurations on forces and moments acting on the swash plate for various operating conditions. The simulation model cited in the earlier work was used in this study. This information is vital for the design of an actuating mechanism to vary dead centre position of a pump valve plate. These simulations were run using MATLAB/Simulink and S-functions. Results of this study are promising.