Variable Displacement Pump Research Articles

Active Disturbance Rejection Control of Engine Speed in Series Hydraulic Hybrid Power System

Abstract: In this paper, a novel series hydraulic hybrid powertrain is proposed for a three-axis all-terrain vehicle. The engine drives two variable displacement pumps responsible for driving and steering, respectively. A variable displacement motor is connected to the ring gear of the planetary coupling mechanism to drive the vehicle and a fixed-displacement motor is connected to the sun gear to steer the vehicle. The active disturbance rejection control with feedforward control is employed to control the engine speed. The engine speed is controlled in a close-looped manner by adjusting the engine throttle. The controller parameters are decided by analyzing the influence of each parameter on the controller performance by means of the control variable method. The simulation results indicate that the proposed control strategy enables the vehicle to obtain better engine speed following and anti-disturbance performance. An all-terrain prototype is established and field tests are carried out to verify the effectiveness of the design and control strategy of the series hydraulic hybrid powertrain for the all-terrain vehicle.

The loose slipper fault diagnosis of variable-displacement pumps under time-varying operating conditions

Variable-displacement pumps (VDPs) are widely used as core power components of high-pressure hydraulic systems due to their superior power density. The loose slipper fault is a typical failure type of the VDP, which can cause premature damage or even unexpected shutdown. The on-site VDPs usually work under time-varying operating conditions (TVOCs), and their pressure varies with the changing speed. These unique characteristics pose a new challenge to the fault diagnosis (FD) of the VDPs. This study introduces an innovative FD method named the multi-scale attention mechanism residual network (MSARN). The MSARN is equipped with three well-chosen components: multi-scale convolution module (MSCM), attention mechanism (AM), and residual connection. The integration of these three components facilitates the efficient extraction and fusion of meaningful multi-scale fault features, thereby preventing the overfitting problem. The experimental results obtained on the VDP validate the effectiveness and accuracy of the MSARN. The suggested method trains the model using data collected under partial constant and representative operating conditions, enabling the achievement of FD under TVOCs.

Effect of Structural Parameters on Output Characteristics of a Novel Self-Supplied Aviation Intelligent Pump

The aviation intelligent pump system is an effective solution to aircraft hydraulic systems’ inefficient power consumption and temperature increase. A self-supplied aviation intelligent pump (SAIP) has a high power-to-weight ratio and compact structure, making it the optimal choice for an intelligent pump. To analyze the output characteristics of a novel aviation intelligent pump, it is crucial to establish an accurate mathematical model that describes its dynamic characteristics. This can be achieved by analyzing the working principle and exploring the influence of critical parameters. The paper introduces the composition and working principle of a self-supplied electro-hydraulic servo variable displacement pump. It then establishes a mathematical model of the whole pump, with a detailed analysis and modeling of the critical variable mechanism and the swash plate assembly’s load moment. A simulation model was created to examine the impact of crucial structural parameters, such as the offset spring’s stiffness and control piston’s diameter, on the output characteristics of the intelligent pump. An experimental platform was also constructed, and the experimental results confirm the accuracy of the SAIP model presented in this paper. The investigation of the output characteristics fully reveals the dynamic performance of the SAIP. This provides the basis for the subsequent design of high-performance flow and pressure control strategies and aids in researching intelligent aircraft hydraulic systems.

Enhancing Hydraulic System Performance through Intelligent Control and Energy Efficiency

In addressing the operational constraints of conventional hydraulic systems, significant advancements have been achieved through the development of an energy-efficient hydraulic system for press applications. This research identifies key inefficiencies, such as pressure losses and suboptimal flow rates, while proposing a novel architecture that utilizes advanced components, including energy-saving valves and variable displacement pumps. By automating critical processes, the integration of intelligent control algorithms - enabled by a programmable logic controller (PLC) - enhances fluid distribution and timing accuracy. The prototype notably employs gravity to propel fluid, significantly reducing energy consumption by minimizing the need for continuous pumping. Testing results confirm substantial energy savings, demonstrating the system’s potential to improve operational reliability and promote more environmentally sustainable industrial practices. Overall, this project exemplifies a holistic approach to hydraulic system design, addressing both performance enhancement and energy efficiency in a rapidly evolving industrial landscape.

Design and Sensitivity Analysis of Mechanically Actuated Digital Radial Piston Pumps

One major challenge in fluid power is the improvement and optimization of the efficiency of mobile hydraulic systems. Conventional fluid power systems often exhibit relatively low overall efficiencies caused by inefficiencies in the various components, such as a prime mover, variable displacement pump, valves, fittings, hoses, and actuators. While each component contributes to the losses in the overall system, the pump converts the mechanical shaft energy from the prime mover to energy transmitted hydraulically and is one of the most crucial components impacting overall system efficiency. Using on/off technologies, new pump architectures have enabled the opportunity to increase the efficiency over conventional designs using positive sealing valves in place of conventional port plate designs. This work proposes, investigates, and assesses the development and optimization of a digital variable displacement pump using a novel cam actuation technique on radial piston pumps. The novelty of this work is the development and parameter optimization of a mechanically actuated digital radial piston pump that can achieve high efficiencies from minimum to maximum displacement compared to common conventional variable displacement pump technologies. In this study, a sensitivity analysis is conducted to study the parameters of the system to optimize the pump. The parameters assessed in this study include: the valve bore size, cam transition and compression angles, piston diameter, and dead volume in the pumping chamber. The simulation results show that after optimizing the parameters of the system, the pump in design could reach a maximum efficiency of approximately 93% and was capable of upholding efficiencies above 80% between 30–100% displacement.

A novel order-separated generalized feedforward design for motion control in energy-efficient electrohydraulic system with proportional and integral feedback

Existing feedforward, or FF, controllers are based on differentially flat models. For double-acting single-rod cylinders, more compact than the double-rod ones, flat models could be constructed either under an incompressible-flow assumption for low-pressure, slow-response applications or for a matched valve-cylinder combination. Contrasting the existing models tackling only a single nonlinear aspect like valve leakage, oil compressibility or friction, a novel FF controller, generalized for different types of valve-cylinder-pump combinations, has been developed here. It is based on the highest-order assumption of incompressible flow that sustains the piston motion. An FFPI controller has been implemented in a laboratory setup for displacement tracking against sinusoidal demands up to 9 Hz frequency. The FF parameters has been estimated by minimizing the deviation of simulation prediction from an offline experimental time-varying response. The PI gains have been selected through a stability analysis by extending Routh criteria for linearized time-variant error dynamics. Comparison against a PI-only controller with identical gains has established the energy-saving potential of the FFPI controller both working with the same variable-displacement pump. In comparison to existing nonlinear adaptive controllers, more precise and smoother responses have been obtained over wider frequency range at lower control expenses, admittedly with occasional marginal penalty in the phase variation. The FFPI controller has exhibited the shortest transient and the highest resilience against measurement noise.

Designing a Model Predictive Controller for Displacement Control of Axial Piston Pump

Variable displacement hydraulic pumps are widely used for energy efficiency, and they often have a mechanical feedback mechanism to ensure target tracking control performance and stability of tilt angle control. Furthermore, there are many examples which add electronic control to realize higher tracking control performance. However, in such cases, the control performance is significantly affected by the dynamic characteristics of the mechanical feedback mechanism, and this problem prevent its widespread use. Additionally, tilt angle control is susceptible to changes in dynamic characteristics and load pressure depending on the operating point, and there are constraints on the tilt angle. Hence, high control performance cannot be obtained without considering these nonlinearities. In this study, the variable displacement pump without mechanical feedback mechanism is focused on, and the objective of this study is to design a displacement control system for a hydraulic pump based on a model predictive control (MPC) that can consider various constraints on the design step. An adaptive system, which handles changes in dynamic characteristics and the effects of load pressure, is introduced. Additionally, the control performance of adaptive MPC is compared to adaptive model matching-based MPC with inverse optimization that can optimally design the weight matrices of the evaluation function without trial and error. Furthermore, in order to improve the transient response, a variable control input constraints are added in these two control systems. Experimental results of control performance have shown that the proposed method achieved a high tracking performance and short settling time, which confirmed the effectiveness of the variable control input constraints.

Electric machine sizing consideration for ePumps in mobile hydraulics

AbstractEnvironmental concerns have pushed toward electrified technologies for off‐road vehicle actuations that can lower greenhouse gas emissions and reduce energy consumption. Replacing a central diesel engine with a dedicated electric machine (EM) as a prime mover for the hydraulic supply offers several opportunities for so‐called ePumps (aka electric‐driven pumps) to maximize energy efficiency and limit the usage of electric materials. This paper discusses the impact of different choices for the ePumps architecture (i.e., fixed vs. variable displacement pump; variable speed vs. fixed speed electrical machine), and on their main design parameters in terms of size and efficiency. Although the procedure followed in the study could be extended to different types of electric and hydraulic units, the paper particularly considers ePumps based on permanent magnet synchronous machines combined with axial piston machines. The importance of properly considering the ePump drive cycle and its cooling requirements is taken into account while addressing energy efficiency, mass, and overall compactness of the solution. The results show that an ePump based on a variable displacement pump, when compared to fixed displacement ePumps, reduces the electrical machine size both in volume and mass up to 40%, when the high‐pressure demand is not combined with high flow rate demand, thus decreasing the cost of the EM. In all drive cycles, the variable speed EM–fixed displacement pump architecture has a higher efficiency, ranging from 1% to 5%, compared to the case of fixed speed EM–variable displacement pump. Finally, the paper compares the advantages and shortcomings of each ePump architecture presented, based on representative drive cycles.

Position control performance analysis of linear actuator in swashplate-controlled electro hydrostatic actuation system

The position control of an energy efficient electrohydraulic actuation system is a decisive characteristic of its performance. In position control applications, a servo valve and/or variable displacement pump are vital to control the position of the linear actuator. In this open-loop control experimental work, the position of a linear actuator having a stroke length of 0.2 m is controlled by a swashplate-controlled electro hydrostatic actuation system. LabVIEW is used to create the control algorithm, and the National Instrument compact-RIO controller is used to control the voltage supply. The National Instruments controller processes sinusoidal and square demand signals at frequencies of 1/16, 1/12, 1/8, and 1/4 Hz. Open-loop control performance is predominantly dependent on the appropriate tuning of the voltage supply. Control performance is evaluated using the parameters integrated absolute error, integrated square error, integrated time absolute error, and integrated time square error. In comparison to square demand, it has been found that sinusoidal demand offers better position control accuracy, and square demand also offers appropriate control accuracy only at lower frequencies (1/16 Hz).

Digitalization of Radial Piston Pumps through Internal Mechanically Actuated Designs

Digital hydraulics is a technology gaining perceptible growth in fluid power research. The advantages of digital fluid power systems can be realized through improved system efficiencies, energy savings, increased productivity, and system performance compared to traditional fluid power systems. Conventional check valve pumps use differential pressures to deliver pressurized flow to the system. Digital fluid power pumps enable conventional check valve pumps to achieve variable displacements by enhancing the controllability of the inlet and outlet valves through digital hydraulic technologies and techniques. The benefit of this technology is the use of positive sealing check valves with lower leakage losses compared to typical variable displacement pumps, increasing the unit’s overall efficiency. The primary focus of prior digital pump/motor research has been on digital actuation using electronic solenoids to actuate or latch the valves. While these electrical systems provide a platform for digital hydraulic techniques, they come with a cost: added energy sources, advanced controls, and expensive data acquisition systems. Research has also shown that minor valve timing inconsistencies can limit the potential energy savings of digital pumps in electrically actuated systems. A system configuration that promotes the advantages of digital hydraulics while mitigating the disadvantages associated with electrical systems is mechanically actuated systems. This work discusses variable cams and their advantages/disadvantages in digital radial piston pump/motor technologies. The significance of this work is the investigation of the digitalization of radial piston pumps through mechanically actuated valving systems, which has yet to be implemented in prior research. This paper evaluates various design concepts for commercializing digital radial piston pumps using mechanically actuated cams. A two-quadrant pump and a four-quadrant pump/motor design are simulated to assess their potential efficiency across the bandwidth of their displacement. The results show that the two systems can achieve relatively high efficiencies across their displacement bandwidth but show room for further improvement by optimizing these systems. This study is the first step in designing an integrated mechanically actuated variable cam system in digital radial piston pumps.

Power Drive Architectures for Industrial Hydraulic Axes: Energy-Efficiency-Based Comparative Analysis

In hydraulic systems, energy dissipation can be significant. The pressure losses that can occur in the hydraulic circuit, which are influenced by the adopted drive architecture, result in power consumption that is often significantly higher than that required by the mechanical system. This paper presents a comparative study of the energy efficiency of five common drive architectures in industrial hydraulic axes. The analysis is applied to a variable speed and force hydraulic blanking press, a fairly common industrial system, e.g., in the manufacture of semi-finished brass products. Standard, regenerative, high–low, variable-displacement pumps and variable speed drive configurations for a fixed-displacement pump were analyzed and compared. In each case, an appropriate and optimized sizing of the different components of the system was performed, and then the energy consumption was estimated for a load cycle common to all the considered cases. The results show that the choice of the power generation architecture of the hydraulic system has a very significant impact on the energy efficiency and consequently on the operating costs and the carbon footprint. The performed quantification of the potential energy efficiency of the considered drive architectures can be very useful in helping to make energy-conscious decisions.

Performance evaluation of adjustable stroke piston pump with varying fulcrum position

Lubrication of machines is done manually or using automatic systems, the purpose of the automatic lubrication system is to provide specified amount of lubrication at specified lubrication points using a controlled pump system. The proposed work is based on auto control variable displacement pump and referencing to literature survey it is a novel work involves, an innovative kinematic link base stroke changing mechanism. The stoke variation mechanism serves to alter the stroke of the piston pump in controlled manner to control the flow rate of the pump precisely. The design of the linkage for stoke variation has been done. The previous studies deal with the theoretical design and analysis of the components of the variator mechanism. The variator mechanism is used to vary the angle of oscillation of the output and thereby the stroke of the piston of the pumping element. The variator mechanism design includes the design of the worm gear box and its components, variator screw and nut arrangement. Selection of the motor to operate the linkage and the force analysis based on the motor specifications has been carried out. The present work deals the manufacturing and preliminary testing of the device. In that testing was carried out at various input speeds to the pump and the actual discharge from the pump was measured and the volumetric efficiency of the pump at the particular speed and fulcrum position was determined. Results of the two fulcrum positions were compared and evaluated. Further testing will be carried out in the next six months and the optimization of the fulcrum position for desired discharge will be done. The IOT circuit and mechanism will then be configured suitably.

Limits on the Range and Rate of Change in Power Take-Off Load in Ocean Wave Energy Conversion: A Study Using Model Predictive Control

Previous work comparing power take-off (PTO) architectures for ocean wave-powered reverse osmosis suggests that variable displacement in the wave energy converter (WEC)-driven pump does not offer a significant performance advantage. A limitation of that study is that the WEC was subject to a constant load within a given sea state (“Coulomb damping”) and did not account for controlled, moment-to-moment variation of the PTO load enabled by a variable displacement pump. This study explores the potential performance advantage of a variable PTO load over Coulomb damping. Model predictive control is used to provide optimal load control with constraints on the PTO load. The constraints include minimum and maximum loads and a limit on the rate of load adjustment. Parameter studies on these constraints enable conclusions about PTO design requirements in addition to providing an estimated performance advantage over Coulomb damping. Numerical simulation of the Oyster 1 WEC is carried out with performance weighted by historical sea state data from Humboldt Bay, CA. The results show a performance advantage of up to 20% higher yearly-average power absorption over Coulomb damping. Additionally, the parameter studies suggest that the PTO load should be adjustable down to at least 25% of the maximum load and should be adjustable between the minimum and maximum loads within a few seconds.

Design of Hydrostatic Power Shift Compound Drive System for Cotton Picker Experiment

To meet the working performance demand of cotton pickers, a hydrostatic power shift composite drive system design is proposed. This study aims to enhance the driving function of the cotton picker in various working conditions and improve its adaptability by combining a hydrostatic speed control system with a mechanical power shift structure. To achieve this, a single variable pump + double variable motor closed circuit is adopted. By adjusting the pump and motor displacement in stages, the driving speed of the cotton picker can be optimized for different working conditions. Additionally, the power shift mechanism is employed to increase the speed range and improve the transmission efficiency, enabling higher speeds to be achieved. Firstly, the main components of the composite drive system were calculated and selected, and then AMESim software was used for modeling and simulation analysis, and the results are as follows: When the cotton picker starts and picking operation stage variable displacement pump + fixed displacement dual motor speed control, the highest driving speed is 8.5 km/h. During the field and road transport operation stage fixed displacement pump + variable displacement dual motor speed regulation, the highest speed of 14.5 km/h was achieved in the field. When transferring to the road, the instant mechanical power shift speed and, the highest speed on the road was up to 27.5 km/h. Finally, the field experiment and speed ratio analysis of the drive system was conducted, and the average error of the experimental speed measurement was 0.588%. The speed ratio matching was in line with the design expectation. The results show that the hydrostatic power shift composite drive system designed in this study has good driving adaptability and can effectively meet the functions of cotton picker field picking, transport operation and road transportation in transit, which provides theoretical support for the design of cotton picker chassis drive system.

Kinematic Design of Adaptive Control Adjustable Stroke Piston Pump for Automated Lubrication System

Lubrication is done either manually or using automatic systems, the purpose of the automatic lubrication system is to provide certain amount of lubricant at given time to the machines the proposed work is based on auto control variable displacement pump and referencing to literature survey it is a novel work involves, an innovative kinematic link base stroke changing mechanism. The stoke variation mechanism serves to alter the stroke of the piston pump in a controlled manner to control the flow rate of the pump precisely. The present work pertains to the design theoretically and kinematic synthesis of the components of the kinematic linkage. The theoretical design of the kinematic linkage is done using graphical method by overlay method, and the analysis of the kinematic linkage is done using adam’s software. The linkage motion for various angle of crank and corresponding output link are derived from this kinematic synthesis. The kinematic analysis of the linkage is done in using adam’s software and the motion study of the link is done to determine the parameters velocity of link and acceleration of link used in the mechanism.

Thermal management of cylindrical battery pack based on a combination of silica gel composite phase change material and copper tube liquid cooling

The lithium-ion battery(LIB) generates severe heat when discharging. In this study, a silica gel(SG) composite phase change material(CPCM) that is easy to fill was prepared, and its performance was tested, so as to ensure the safe operation of the battery. Besides, a battery cooling system combining CPCM and liquid cooling was established. Finally, simulation and experiment were performed to demonstrate the effectiveness of the battery pack cooling module. As revealed by analyzing the characterization results of the CPCM, the decomposition temperature of CPCM is more than 150 °C, the leakage rate of CPCM is less than 4 %, and the latent heat of phase change is 63 J/g. The thermal field simulation and discharge experiment of the battery module suggest that when the battery spacing changes from 5 mm to 15 mm and the thermal conductivity changes from 0.05 W/m·K to 0.75 W/m·K, the maximum temperature of the battery pack decreases by 10 °C, and the temperature difference between the batteries also decreases. When the flow of the variable displacement pump was maximum, the liquid cooling scheme of 3 inlets/3 outlets can still control the maximum temperature of the battery below 45 °C and make the battery temperature difference not exceed 2 °C, though the battery pack is subject to 3C(Discharge current rate) discharge - 1C(Charging current rate) charging cycle.

Nonlinear Model Predictive Control for Efficient Control of Variable Speed Variable Displacement Pumps

Hydraulic pumps are a key component in manufacturing industry and off-highway vehicles. Paired with diesel engines or electric motors, they provide hydraulic flow that can conveniently be used to power a variety of actuators. Hydraulic power transmission has numerous advantages, unfortunately energy efficiency is usually not one of those. The use of Variable Speed Variable Displacement pumps has been proven to be advantageous with respect to constant speed or constant displacement solutions: It allows to achieve higher efficiency and faster flow tracking dynamics. This paper presents the development of a Model Predictive Control for this system, considering the nonlinearities and look-up-tables that characterize the system dynamics. The Model Predictive Controller is then compared both in simulation and on test bench with a reference controller for such system, showing potential both regarding efficiency and flow tracking dynamics.

A Fault Detection Method for a Practical Electro-Hydraulic Variable-Displacement Pump With Unknown Swashplate Moment

Electro-hydraulic controlled variable-displacement pump (EHVDP) is a power source of the hydraulic system, which is extensively used in the electro-hydraulic system due to the high efficiency and controllability. Thus, for a good operation of the hydraulic system, effective fault diagnosis techniques are crucial to avoid unexpected breakdown and failure. However, the data-driven fault diagnosis methods, which are commonly adopted in axial piston pumps, suffer from a lack of considerably effective data. Modelling uncertainty due to the swashplate moment has not been adequately considered, though some attempts have been made for the model-based methods. In this paper, the pressure transition is assumed to simplify the swashplate moment. A Kalman filter with unknown input for the EHVDP is used to estimate the additional uncertainty due to the simplification of the swashplate moment. A cumulative sum (CUSUM) based residual evaluation is utilized to detect the fault of the EHVDP. The test bench has been established and three typical failure modes of the EHVDP, including the control valve, displacement regulation mechanism, and rotating group are investigated by the experiments. Experimental results under different working conditions validate the effectiveness of the proposed fault detection method. Comparative results show the superiority of the proposed method in sensitivity and rapidity over the general method not considering unknown swashplate moment.

Research on a power smoothing control strategy for energy storage hydraulic wind turbines

AbstractTo solve the problem of large output power fluctuations in wind turbines and improve grid adaptability, a hydraulic energy storage system is introduced in traditional hydraulic wind turbines. Based on the working principle of energy storage hydraulic wind turbines, an energy storage hydraulic wind turbine state space model is established, and the feedback linearization method is introduced to solve the multiplication nonlinear problem in the modeling process. The output power is taken as the control output, and the torque compensation controller is established with the feedback linearization method. The displacement of the variable displacement pump motor is controlled to realize hydraulic energy storage system energy charging and discharging, and the wind turbine output power smoothing control is realized with the fluctuating wind speed. The power smoothing control strategy is verified with the 24 kW energy storage hydraulic wind turbines semi‐physical simulation experimental platform. The proposed control strategy lays the groundwork for the wide application of the energy storage hydraulic wind turbines.

A single stage spool valve for the pressure compensator of a variable displacement pump: design, dynamic simulation and comparative study with a real pump

The study is focused on the design of a simplified spool valve to be incorporated in the pressure compensator of a variable displacement axial piston pump in order to perform a comparative study with a commercial pump having a two-stage spool valve in its compensator. The design involves the evaluation of the spool size and selection of spring from static equilibrium conditions to satisfy cut-in and cut-off pressure. Following the development of a dynamic model of the system, a design sensitivity analysis of the spool valve has been carried out through simulation to identify the critical sizes of the parameters, which affect the pump performance. By systematic design, it is possible to have a single-stage spool valve-controlled pressure compensator that can produce a performance of the variable displacement axial piston pump at par with a similar commercially available pump.