The subject of this paper is the review of advanced technology used in hydraulic systems. The technology in question is termed Independent Metering (IM); this is used in hydraulically driven mobile machinery, such as agricultural, construction, municipal, and forestry vehicles. The idea behind the concept is to modify the connection between the actuator, which could be a cylinder or a motor, and a flow control valve. Traditionally, spool hydraulic valves were used to control the fluid flow into and out of hydraulic actuators. This keeps the meter-in and the meter-out of the actuator mechanically connected due to the construction of these valves. This connection makes the control system blind to pressure changes in one of the hydraulic chambers in the actuator. This, in turn, reduces the overall system controllability. It also increases energy losses, especially under an overrunning load. These two main weaknesses led researchers to break this mechanical connection and get into a new technology with different characteristics. The proposed technology was called Independent Metering. New and more complex control techniques can now be applied to the hydraulic systems using this technology that were not possible before or could be applied to more conventional servo design. This paper reviews Independent Metering (IM) and the technologies used or developed in this field to date. The paper reviews the state of art hydraulic technologies and indicates the links between them and IM. It also reviews the different types of hydraulic valves used when implementing IM. This review also discusses some control algorithms, IM layouts, IM challenges, and identifies where further improvements may be achieved.

The hydraulic independent metering is an advanced actuator driving technique that allows the implementation of advanced control algorithms or methods. The main concept of independent metering is to control hydraulic actuators ports, which are the meter-in and meter-out, separately. In this article, a novel stepped rotary type valve has been developed for embedding in hydraulic independent metering systems, instead of conventional types such as poppet and spool. The insertion leads to developing different and novel control techniques, which require software-in-the-loop simulation and hardware-in-the-loop simulation of the proposed system. The paper explores the dynamic representation of this valve and defines its own performance limitations. This includes the development of a linear model comprising its two main subparts which are the stepper motor and the rotary orifice. Consequently, the linear time-invariant methods are used to explore the performance of the valve by considering the effect of different parameters namely the pressure drop, friction coefficient, damping coefficient, and bristle coefficient.

This paper presents the results of numerical and experimental performance evaluation of the rotary tubular spool valve. The aim of this work is to develop further the novel design of the tubular spool valve by confirming experimentally the validity of the simulation model and its results, thereby proving the valve's potential to represent a feasible and more efficient alternative to conventionally used translation spool valves avoiding the use of two stage valve configurations. In this research the valve performance is assessed through numerical modelling and experimental studies of its metering characteristic and pressure losses. This paper demonstrates that the used valve model yields the results, which agree well with the conducted experimental study. Therefore, validation of the numerical model and the modelling results in the form of theoretical valve characteristics was accomplished. Firstly, the paper presents details of a numerical approach employed to evaluate valve performance and then analyzes the simulation results. Next, the valve performance is experimentally validated by testing a prototype valve on a hydraulic test rig capable of measuring the volume flow rate, pressure levels in up-and downstream lines of the valve across the entire spool angular stroke. Initially, average discrepancies between modelling and test results were 52.46% for the metering and 82.78% for the pressure loss characteristics. Correcting the model geometry aimed at eliminating differences between the valve model and the practically used prototype-test rig system enabled reduction of the error between experiment and modelling by 47.75% for the pressure loss function. This confirmed validity of the simulated characteristics of the valve. The benchmark comparison of pressure losses confirmed average 71.66% energy dissipation reduction compared to the industry-available analogue valve.

This paper presents a control algorithm for a novel Mechatronics Electro-hydraulic Driving System, Micro-Independent Metering. The main idea of the independent metering is a separated control of the hydraulic actuator ports which are the meter-in and the meter-out. IM technique configuration relies upon different types of valves, especially on poppet valves. As these valves have stability limitations, a novel stepped rotary valve was developed to configure a novel IM form. This form is termed as micro-independent metering due to the activation technique of the valve. A novel algorithm was developed to control this new configuration. The algorithm implements the rules of the independent metering using the new valve. It is able to detect the different operation modes and make a real time changing between them. Also, it activates the enhanced performance technique which was especially developed for this new configuration. The paper includes the mathematical analysis of the developed algorithm and its State-flow representation. Also, it includes the simulation of the system performance, and the effect of MIM on the cylinder velocity.

This paper aims to investigate the performance of a hydraulic actuator controlled by the novel system micro-independent metering (MIM). This analysis has been performed by comparing the models of two systems which are the traditional independent metering, that depends on poppet valve, and the new hydro-mechatronics system micro-independent metering, that relies on a stepped rotary flow control valve. In general, independent metering is a hydraulic control system which guarantees a separation between the meter-in and the meter-out of the hydraulic actuator.A Valvistor valve, a special type of Poppet valves, was developed to be embedded into the independent metering (IM) system. This valve has controllability and stability shortcomings which prevent the system from spreading in the industrial applications. The Valvistor valve performance is highly affected by the fluid disturbances because the fluid is considered as a part of its control elements. A stepped rotary flow control valve has been developed to control hydraulic flow rate. The valve composed of a rotary orifice attached to a stepper motor. Using this valve instead of the traditional poppet type has led to a new configuration, that is termed by micro-independent metering. This form improves the hydraulic cylinder velocity performance by rejecting the fluid disturbances effect on the control circuit.