Search Results (128)

This article analyzes statistics on the failure of technological equipment, assemblies, and mechanisms of agricultural (and other) machines associated with the breakdown or failure of gear pumps. It was found that the leading causes of gear pump failures are the opening of gear teeth contact during pump operation, poor assembly, wear of bushings, thrust washers, and gear teeth. It has also been found that there is a problem related to the restoration, repair, and manufacture of parts in the conditions of enterprises serving the agro-industrial complex of the Republic of Kazakhstan (AIC RK). This is due to the lack of necessary technological equipment, tools, and instruments, as well as centralized repair and restoration bases equipped with the required equipment. This work proposes to solve this problem by applying AM technologies to the repair and manufacture of parts for agricultural machinery and equipment. The study results on the stress–strain state of support bushings under various pressures are presented, showing that a fully filled bushing has the lowest stresses and strains. It was also found that bushings with 50% filling and fully filled bushings have similar stress and strain values under the same pressure. The difference between them is insignificant, especially when compared to bushings with lower filling. This means that filling the bushing by more than 50% does not provide a significant additional reduction in stresses. In terms of material and printing time savings, 50% filling may also be the optimal option. Full article

This study presents a computational fluid dynamics (CFDs) investigation of the hydrodynamic behavior of surface-textured lateral bushings in external gear pumps (EGPs), emphasizing the effects of combined sliding and squeezing motions within the lubrication gap. A comprehensive numerical model was developed to analyze how surface texturing implemented through different dimple shapes and texture densities influences pressure distribution and load-carrying capacity under transient lubrication conditions. The analysis demonstrates that the interaction between shear-driven flow and squeeze-film compression significantly amplifies pressure, particularly when optimal dimple configurations are applied. Results indicate that dimple geometry, depth, and arrangement critically influence hydrodynamic performance, while excessive texturing reduces effectiveness due to increased average gap height. Cavitation was intentionally not modeled in the early single dimple evaluations to allow clear comparison between configurations. The findings offer a design guideline for employing surface textures to enhance tribological performance and efficiency in EGP applications under realistic dynamic conditions. Full article

This study proposes an asymmetric pitch control technique for electric oil pumps with symmetric gear-type pumps in order to reduce noise and vibration. For vane pump noise reduction, mechanical asymmetric pitch arrangements of each vane are widely used. However, the mechanical asymmetric pitch arrangement approach is not applicable in gear-type pumps due to structural limitations. The proposed asymmetric pitch control method provides similar effects to the mechanical asymmetric pitch arrangement by employing instantaneous motor torque controls for an electric oil pump with a gear-type pump. The magnitude of motor torque for each pump tooth is determined with an asymmetric pitch formula, which has been widely used for mechanical vane pumps in previous studies and patents. A formula for the shape of instantaneous motor torque is proposed for the analysis of pressure fluctuations of pumps, which is a combination of trigonometric and exponential functions. The calibration factors for the magnitude and shape can be adjusted according to the characteristics of a given pump. The experimental results for a 400 W electric pump show that the proposed method reduced and dispersed the noise peak by approximately 4 dB(A) in comparison with the normal control, and affected hydraulic performance with a less than 1% decrease in flow rate in not only pump-level but also gearbox-level test environments. Full article

This paper presents a comparison of some different configurations of electro-hydrostatic actuators (EHA). The gear pump EHA has a simpler mechanical configuration, but the electronic power command circuits and the electric motor are in high demand due to the very frequent speed variations. The variable piston pump EHA has a more complicated mechanical configuration, but the electronic power command circuits and the main electric motor are less loaded due to the constant speed of the electric motor. The variable displacement pump control can be made either using an electric motor and mechanical transmission, or an additional hydraulic circuit, to modify the swash plate angle. In total, four EHA configurations are studied in this paper (one with a gear pump and three with variable axial piston pumps). The paper aims to advantages and disadvantages of each type of EHA, using numerical simulations. Full article

This study presents a systematic investigation on the thermal power characteristics of linear conjugate internal gear pumps. Through analyzing the heat sources of each friction pair in the internal gear pump, mathematical heat generation models for key friction pairs are derived based on mechanical efficiency and volumetric efficiency. Furthermore, the simulation model of the gear pump was established, and the losses of the internal gear pump under different working conditions were calculated and analyzed. The variation patterns of mechanical efficiency and volumetric efficiency under different pressures and speeds are studied, revealing significant declines in both efficiencies under complex operating conditions, with inefficiencies primarily occurring under low-speed high-pressure and high-speed low-pressure scenarios. The results show that the deviation between the simulation results of mechanical efficiency and the experimental value is less than 1.6%, and the deviation between the simulation results of volumetric efficiency and the experimental value is less than 1%. Variations in speed and pressure significantly impact both mechanical and volumetric efficiencies, with notable efficiency drops observed under low-speed/high-pressure conditions. In high-pressure environments, intensified radial unbalanced forces lead to increased frictional heat generation. Full article

Background/Objectives: Breastfeeding multiple birth infants (MBIs) poses unique challenges that require tailored support; however, research on these mothers’ experiences is limited. This study explored the breastfeeding journeys of Australian mothers of MBIs, highlighting barriers, facilitators, and support needs. Methods: Data were collected via an online survey (May–August 2024) and included quantitative data on breastfeeding initiation, duration, and challenges, as well as qualitative insights into mothers’ experiences. Thematic analysis was used to identify key themes, and statistical analyses were used to compare breastfeeding outcomes by parity. Results: While most mothers (87%) had an antenatal intention to breastfeed, they faced barriers such as latching difficulties (56%), inadequate milk supply (49%), and sore nipples (47%). Preterm births (58%) and neonatal unit admissions delayed the breastfeeding initiation. Most mothers (99%) used electric breast pumps to boost milk supply (68%) and enable expressed breast milk feeding by other caregivers (65% of mothers). While 72% were satisfied with hospital breastfeeding support and some mothers received excellent hands-on support, others felt neglected due to busy staff or conflicting advice. Mothers frequently reported that breastfeeding guidance was geared toward singletons, leaving them unprepared for the challenges of feeding multiples. Mothers’ suggestions for improving care included specialised guidance, better access to lactation support, and in-home practical support to alleviate the burden of feeding and expressing. Additionally, mothers reported that healthcare professionals should be trained to offer practical, non-judgemental support to help mothers navigate the elaborate challenges of breastfeeding MBIs. Conclusions: This study underscores the need for early postpartum support and tailored guidelines to enhance MBI breastfeeding outcomes and maternal-infant well-being. Full article

Compared with traditional gear pumps, circular-arc gear pumps have the advantages of silence and small flow pulsation, but the theory of design is underdeveloped. This paper presents a design method for gear pumps with circular-arc helical gear pairs, and the influence mechanism of flow characteristics is studied. First, a model of the gear pair is established, and a design method for the gear pair is proposed. Second, a CFD model is demonstrated, and the influences of the tooth profile parameters (tooth number, modules, and pressure angle) on the flow characteristics are analyzed. Finally, the significance of the influencing factors is analyzed. The results show that when the stagger angle of the two ends of the arc helical gear pair is an integral multiple of π/Z, there is no flow pulsation, and there is little noise. The tooth number and modules are positively correlated with the flow rate and flow pulsation, among which the modules have the most significant influence. The flow rate of the gear pump increases by 4–5 L/min for every 0.2 increase in the modules. The pressure angle and flow rate show a negative correlation trend, but the influence is insignificant. The flow rate is less than 1 L/min for every 2° change in the pressure angle. This paper provides a theoretical basis and reference value for the gear pair design of gear pumps. Full article

Cavitation is a critical phenomenon in hydraulic systems, particularly in gear pumps, where it can significantly affect performance and reliability. This study uses numerical simulations with the Full Cavitation Model and k-ε turbulence model to investigate the thermodynamic effects of cavitation in gear pump lubricating oil at varying temperatures. It focuses on the formation and evolution of cavitation vortex structures in the outlet bridge area. The simulations reveal significant heat exchange between liquid and vapor phases, causing a local temperature drop and a reduction in saturated vapor pressure, which suppresses cavitation development. As temperature increases, this effect diminishes due to the lower density of the hydraulic oil. Full article

To investigate the effect of the number of teeth on the cavitation characteristics of the cavity at high speed, a simulation model of the flow field with six to nine teeth of the gear pump is created. To study the influence of the number of teeth on the internal cavitation characteristics of the circular arc spiral gear pump and its outlet flow characteristics under high-speed conditions. The results show that the gear pump cavitation characteristics are significantly affected by the number of teeth and the speed; as the number of teeth increases, the extent of the effect of cavitation on the outlet flow decreases significantly. The critical speeds at which the gas volume fraction of the six- to nine-teeth gear pump changes significantly are 9000 RPM, 9000 RPM, 10,000 RPM, and 10,000 RPM, respectively, and after exceeding these critical speeds, the volumetric efficiency begins to decrease while the gas content in the cavity increases abruptly, which seriously affects the continuity and stability of the outlet flow. In addition, when designing gear pumps, increasing the number of teeth helps to inhibit cavitation, improve volumetric efficiency, and reduce pulsating flow. Full article

This paper investigates the design methodologies of pure rolling helical gear pumps with various tooth profiles, based on the active design of meshing lines. The transverse active tooth profile of a pure rolling helical gear end face is composed of various function curves at key control points. The entire transverse tooth profile consists of the active tooth profile and the Hermite curve as the tooth root transition, seamlessly connecting at the designated control points. The tooth surface is created by sweeping the entire transverse tooth profile along the pure rolling contact curves. The fundamental design parameters, tooth profile equations, tooth surface equations, and a two-dimensional fluid model for pure rolling helical gears were established. The pressure pulsation characteristics of pure rolling helical gear pumps and CBB-40 involute spur gear pumps, each with different tooth profiles, were compared under specific working pressures. This comparison encompassed the maximum effective positive and negative pressures within the meshing region, pressure fluctuations at the midpoints of both inlet and outlet pressures, and pressure fluctuations at the rear sections of the inlet and outlet pressures. The results indicated that the proposed pure rolling helical gear pump with a parabolic tooth profile exhibited 42.81% lower effective positive pressure in the meshing region compared to the involute spur gear pump, while the maximum effective negative pressure was approximately 27 times smaller than that of the involute gear pump. Specifically, the pressure pulsations in the middle and rear regions of the inlet and outlet pressure zones were reduced by 33.1%, 6.33%, 57.27%, and 69.61%, respectively, compared to the involute spur gear pump. Full article

The paper presents a numerical and experimental study of the radial gap influence on the external gear pump performance. The numerical study is performed with a two-dimensional (2D) computational fluid dynamics (CFD) model developed and advanced in previous authors’ works. The experimental study is carried out on a laboratory test bench. The presented numerical results are accurate in the entire operating range (500–3500 RPM) of the pump, which is confirmed by comparisons between the CFD results, experimental data, and manufacturer’s technical documentation. The comparative analysis shows that the differences obtained during the verifications are in the range of −6.44% to 2.48%. An original methodology has been developed that allows us to obtain the volumetric efficiency and overall efficiency characteristics as a function of the rotation frequency of the pump at different values of the radial gap, using the manufacturer’s data for the same characteristics at a nominal radial gap and the results of CFD simulations. The analysis of the numerical and experimental results shows that a gap size of 0.04 mm is close to the limit value for the investigated pump, if it is not operated at a rotational frequency above the nominal. The presented methodology can also be applied to other types of hydraulic displacement pumps in order to evaluate their performance in the wear process and to predict the maximum allowable value of a specific design parameter under different operating modes. Full article

External gear pumps with an involute tooth profile are used in many applications because of their simple shape, low production cost, and excellent reliability. However, they can be characterized by the generation of vibration and noise, due to the pressure pulsation caused by the trapped volume resulting from the gear meshing. In this study, a one-point continuous contact helical gear pump with circular-involute teeth was designed to eliminate the trapped volume. A novel geometrical approach is described to analyze the kinematic flow of this pump. The morphology of the tooth space, which changes depending on the angular position of the rotating gear, is explained by a newly defined algorithm. Algorithms designed for the geometric approach are simple because they define tooth space morphology for specific angular positions and therefore do not require corrections. The area of tooth space calculated through numerical analysis is used to calculate the instantaneous theoretical flow rate. The kinematic flow rate of the numerically analyzed pump can quantify the compressibility effect of the fluid. In addition, the calculated instantaneous theoretical flow rate accurately reflects the physical characteristics compared to previous studies and can be used to identify the cause of flow ripple. Full article

A comprehensive model for evaluating the functionality of a multi-gear pump has been developed. The integrated model for assessing the functionality of a multi-gear pump contains a computational fluid dynamics analysis (CFD) model combined with a finite element method (FEM)-based strength model. Two submodels were linked: a CFD submodel to evaluate the internal pressure distribution of the pump and a structural FEM submodel to calculate the stresses and structural displacements of the pump due to fluid pressure. Finite element analysis in SolidWorks 2016 was used to evaluate the strength of the gear joints of the pump gears. As the pressure of the working fluid increases from 6 to 20 MPa, a linear increase in Mises stresses is observed. At the shaft, these stresses increase to 226.2 MPa, and at the tooth mouths, they reach a maximum value of 205.5 MPa. With the increase in torque on the drive shaft from 100 to 500 N·m, there is a significant increase in Mises stresses localized in the contact zones of the shaft with the drive gear. Analysis of the data obtained showed that the displacements caused by the pressure of the working fluid are insignificant compared to the displacements arising under the action of torque. With increasing pressure and torque, there is a tendency to decrease the safety factor, which indicates a decrease in the safety factor of the design of the multi-gear pump. The safety factor is not provided at a torque of 400–500 N·m. The simulation results are confirmed by correlation analysis. The average approximation error is 5–7%. Full article

A comprehensive analysis of in vitro pumps used in cardiovascular research is provided in this review, with a focus on the characteristics of generated flows and principles of flow generations. The cardiovascular system, vital for nutrient circulation and waste removal, generates complex hemodynamics critical for endothelial cell function. Cardiovascular diseases (CVDs) could be caused by the disturbances in these flows, including aneurysms, atherosclerosis, and heart defects. In vitro systems simulate hemodynamic conditions on cultured cells in the laboratory to study and evaluate these diseases to advance therapies. Pumps used in these systems can be classified into contact and non-contact types. Contact pumps, such as piston and gear pumps, can generate higher flow rates, but they have a higher risk of contamination due to the direct interaction of pump with the fluid. Non-contact pumps, such as peristaltic and lab-on-disk centrifugal pumps, minimize contamination risks, but they are limited to lower flow rates. Advanced pumps including piezoelectric and I-Cor diagonal pumps are focused on improving the accuracy of flow replication and long-term stability. The operational principles, advantages, and some disadvantages of these pump categories are evaluated in this review, while providing insights for optimizing in vitro cardiovascular models and advancing therapeutic strategies against CVDs. The outcomes of the review elaborate the importance of selecting an appropriate pump system, to accurately replicate cardiovascular flow patterns. Full article

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. Full article