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Lumped parameter modeling is a consolidated technique for analyzing the fluid dynamic behavior of positive displacement machines, owing to their computational swiftness and the ease of integrating other physical domains affecting the operation of the machine. With some very limited exceptions, this modeling technique typically neglects fluid inertia and momentum effects. This paper proposes an approach to study the effects of fluid inertia affecting the pressurization and depressurization of the tooth space volumes of an external gear pump. The approach is based on considering the fluid inertia in the pressurization grooves and inside the control volumes with a peculiar subdivision. Further, frequency-dependent friction is also modeled to provide realistic damping of the fluid inside these channels. Validation of the model has been performed by comparing the lumped parameter model with a full three-dimensional Navier-Stokes solver. The quantities compared, such as tooth space volume pressures and outlet volumetric flow rate, show a good match between the two approaches for varying operating speeds. A comparison with the experiments supports the modeling approach as well. The paper finally, also discusses which operating conditions and geometries play a significant role that governs the necessity to model such fluid inertia effects in the first place. [ABSTRACT FROM AUTHOR]

This paper presents the formulation of a variable load sense control strategy suitable to achieve power savings in hydraulic systems using postcompensated load sensing (LS) hydraulic control architectures. Such architecture is typical in off-road construction machinery. The paper also describes the application of the proposed control strategy referred to as variable load sensing margin (VLM) on a full-size wheel loader. The paper first presents the rationale for the proposed strategy, showing how the state-of-the-art LS architecture present in commercial machines has a margin for lowering the throttling losses present at the control valves. A feedforward controller, derived from an empirical study on a reference vehicle, is used to control the flow to the front-end loader functions. Test results show improvements of the hydraulic power consumption up to 45%, based on the commanded speed of each front-end loader actuator. The paper also describes a gain scheduling pressure feedback control strategy, which is used to allow controlling also functions that include priority. For the case of off-road vehicles, this is typically the steering function. The experimental results show good performances with an error in controlled velocity below 5%, which is achieved when the front-end loader functions are used concurrently with the steering. [ABSTRACT FROM AUTHOR]

Counterbalance valves (CBVs) are widely used in hydraulic machines handling gravitational loads. They are usually adopted in hydraulic circuits that set the flow to the actuator with either metering control strategies or primary control strategies. In these circuits, the CBV does not determine the actuator velocity, but it establishes a proper counterpressure that balances the actuator during overrunning loads. A well-known problem of CBVs is the excessive power consumption introduced into the circuit, which is due to an excessive pressurization of the flow supply. This paper presents a solution for using CBVs to control the actuator velocity while also reducing energy consumption. The method consists in controlling the pilot port of the CBV through an external pressure source (adjustable pilot). The solution is first studied analytically, considering all the possible loading conditions at the actuator. Two different control strategies are presented: the "Smart CBV," where the CBV does not control the actuator velocity but it minimizes the system pressure; and the "Smart System" that uses the CBV to efficiently control the actuator velocity during overrunning load conditions. An experimental validation of the proposed solutions is also provided, taking as reference a truck-mounted hydraulic crane. The results of the proposed solutions are compared to those achieved by the traditional circuit of the reference hydraulic crane which uses standard CBVs. For both cases of smart CBV and smart system, a remarkable power saving, respectively, up to 75% and up to 90% is observed. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid power-split transmission to drive hydraulic implements in construction machinery. The highly efficient power-split hybrid transmission is combined with displacement-controlled (DC) actuators to eliminate throttling losses within the hydraulic system and achieve higher fuel savings. The architecture design, sizing, and power-management are addressed. Simulation results considering a realistic truck-loading cycle on a mini-excavator demonstrate the feasibility of the idea. A systematic comparison between the proposed system and the previously developed series-parallel hybrid is also carried out. The paper compares engine operation and fuel consumption of the previously mentioned hybrid system with the original nonhybrid load-sensing (LS) machine. It is shown that by implementing an efficient engine operation control, the proposed system can achieve up to 60.2% improvement in fuel consumption when compared to the original machine and consume 11.8% less than the previously developed series-parallel hybrid with DC actuation. Other advantages of the proposed solution include a much steadier engine operation, which open to the possibility of designing an engine for optimal consumption and emissions at a single operating point as well as greatly reduce pollutant emissions. A steadier prime mover operation should also benefit fully electric machines, as the battery would not be stressed with heavy transients. [ABSTRACT FROM AUTHOR]

The present work describes the modeling of a proportional relief valve actuated by an electromagnet. Two models were developed and compared each other: a detailed nonlinear model and its linearized version. The modeling approach presented has a general nature and can be applied to various types of electrohydraulic proportional valves (EHPV). The comparison between nonlinear and linear model results shows the limits of the linear approximation to study the real component. Substantially, the nonlinear model is composed by three submodels: the fluid-dynamic model (for the evaluation of the main flow features), the mechanical model (which solves the mobile body motion), and the electromagnetic model (which evaluates the magnetic forces and the electric transient). All submodels are based on a lumped parameter (LP) approach and they implement a specific set of nonlinear equations. However, to carefully model the main electromagnetic phenomena that characterize the proportional electromagnet behavior (including: magnetic losses, fringing effects, and magnetic saturation), a finite element analysis (FEA) 3D model was developed by the authors. The LP electromagnetic model is based on a particular use of the FEA 3D model steady state results. A series of transient simulations were performed through the FEA 3D model in order to quantify the effect of the eddy currents and to determine a second order transfer function used in the linear model to describe the electromagnet dynamics. The remaining parts of the linear model are obtained by linearizing the nonlinear model equations. The FEA 3D model was experimentally validated in steady-state conditions, while the results of the overall model of the valve were verified in both steady-state and dynamic conditions. [ABSTRACT FROM AUTHOR]