Radial Piston Research Articles

Analysis of the Newest Design of Axial Piston Hydraulic Machines with Reduced Friction Losses and Leaks

Problem. Analysis of modern achievements in the field of volumetric hydraulic drives to improve the technical level of construction and road machines. Goal. Study of the design of the latest foreign development related to the improvement of the technical level of axial-piston volumetric hydraulic machines, in particular pumps and hydraulic motors according to the scheme of Innas floating cylinders. This design, according to the proposal of its inventors, is intended to work as pumps with a flow of up to 7400 l/min or hydraulic motors with a working volume of up to 5000 cm3 at a pressure of up to 50 MPa. Methodology. Analysis of the results of comparative bench tests of the Innas axial piston pump of the latest development and volumetric hydraulic machines of various designs, in particular axial and radial piston, as well as gear ones. Results. According to the results of comparative tests, the new design of the Innas axial-piston pump is significantly ahead of other serial hydraulic machines in terms of efficiency. The total efficiency value of 96 % achieved in the Innas pump shows the promise of such hydraulic machines. Originality. Analysis of the results of experimental studies with the determination of the features of the structures of hydraulic machines in terms of volumetric and hydromechanical power losses. It is concluded that Innas hydraulic motors can be used in trailing volumetric hydraulic drives with hydraulic power amplifiers, for which the characteristic of friction in the displacement mode is the main one from the point of view of the accuracy of the execution of the specified control signals. Practical value. The given materials are useful for specialists in the field of mechanical engineering, in particular, the design of volumetric hydraulic drives for construction and road machines

Investigation on combustion instability of electronic fuel injected multi-cylinder radial piston engine through multifractal technique – A comparative analysis

The main objective of the present study was to investigate combustion instability in a multi-cylinder radial piston engine with electronic fuel injection to ensure safety and reliability, maintain fuel efficiency, reduce harmful emissions, which has a positive impact on the environment. Multi-fractal analysis showed that IMEP (mean effective pressure) fluctuations are an anti-persistent process, meaning that there is no correlation between successive events. The return plots showed significant cyclic variability and instability in neighboring cylinders. The wavelet method and multiscale entropy analysis confirmed the results of the multifractal analysis, showing changes in the characteristics of the combustion process after the introduction of perturbations. The research-based on the first return map has shown an impact on the non-uniform and complex nature of the operation of the neighboring cylinders. The statistical analysis has shown that more than 60 % is slightly negatively skewness in most of the cases, and about 67 % of the cases indicate a leptokurtic distribution of IMEP. Finally, it is concluded that, the combustion of failure of one cylinder in a nine-cylinder engine affects the operation of the other cylinders, as demonstrated through advanced multifractal analysis techniques, return plots, return maps and multiscale entropy analysis.

Prediction and Dynamic Simulation Verification of Output Characteristics of Radial Piston Motors Based on Neural Networks

Radial piston motors are executive components in hydraulic systems, tasked with providing appropriate torque and speed according to load requirements in practical applications. The purpose of this study is to predict the output torque of radial piston hydraulic motors and confirm their suitable operating conditions. Efficiency determination experiments were conducted on physical models, yielding thirty sets of performance data. Torque (output torque) and mechanical efficiency from the experimental data were selected as prediction targets and fitted using two methods: multiple linear regression and neural networks. A dynamic simulation model was built using Adams2020 software to obtain theoretical torque values, enabling the verification of the alignment between the predicted values and simulation results. The results indicate that the error between the theoretical torque of the dynamic model and the physical experiments is 1.9%, with the error of the neural network predictions being within 2%. The dynamic simulation model can yield highly accurate theoretical torque values, providing a reference for the external load of hydraulic motors; additionally, neural networks offer accurate predictions of output torque, thus reducing experimental testing costs.

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.

Investigation of the leakage in the flow distribution pair of radial piston hydraulic motors through CFD analysis and experiments

The internal leakage of a radial piston motor (RPM) is an unavoidable structural characteristic, and the amount of internal leakage has a critical effect on the volumetric efficiency of the motor. Using the distribution plate as the force body, an equation for the balance between the preload spring force and the hydrodynamic force is analytically derived, the variation range of the clearance of the flow distribution pair (FDP) is determined, and a model for the internal leakage flow of the FDP is developed. Based on computational fluid dynamics (CFD) simulations, the effects of the oil film thickness, inlet pressure, motor speed, and oil temperature on the leakage volume are investigated. An efficiency test system for RPMs is built and tests are performed on motor prototypes. The experimental results show that the error between experimental and simulation results decreases gradually with increasing motor speed. When the motor runs at the rated speed, the error is stable within 5%. The experimental results verify the correctness of both the theoretical and CFD models. The CFD analysis method can be used as a technical means to optimize the motor volumetric efficiency and the preload spring design.

ANALYSIS OF THE POSSIBILITY OF APPLICATION OF HYDRAULIC MOTOR-WHEELS IN TRANSMISSIONS HIGH-SPEED TRACTORS

Goal. The purpose of the article is to assess the possibility of developing a hydraulic fluid power in accordance with the standard traction-speed characteristics of the KhTZ-17021 wheeled tractor with the of using gearless drives of the driving wheels. For this purpose, the calculation of the hydraulic fluid power of the wheeled tractor was performed when using the latest radial piston multi-cycle hydraulic motor-wheels with a wide range of rotation frequency and adjustment of the working volume. Research methodology. An analysis of the traction-speed characteristics of the KhTZ- 17021 wheeled tractor and, based on it, a review of modern high-torque radial-piston multi-cycle hydraulic motors from the point of view of meeting the characteristics of torque and rotation frequency with power limitations relative to the serial model in the full speed range of the tractor. The maximum values of the working volumes of the 4 driving hydraulic motor-wheels and the power supply pump of these hydraulic motors, the torque and pressure drop in the hydraulic drive are calculated, and the modes in which it is necessary to change the working volume of the hydraulic motors from the maximum to the minimum values to work out the traction-speed characteristics. A comparative analysis of radial-piston multi-cycle hydraulic motors was carried out, and for the hydromotor-wheel model MHP27 of the "Poclain Hydraulics" company, which was chosen for the study, the hydraulic principle diagrams were considered with the use of a hydraulic regulation system of four stages of the working volume in hydraulic motors, the use of combined parking and service brakes, as well as an anti-skid system using means of proportional electro-hydraulic automation. The results. High-torque hydraulic motor-wheels of the radial piston type were selected, which make it possible to ensure the operation of the tractor transmission without intermediate gearboxes between the hydraulic motors and wheel hubs, and the calculated value of the working volume of the axial piston pump, which ensures the operation of the tractor transmission in the full speed range. Based on the results of the calculations, it was established that the pressure in the hydraulic drive does not exceed 35 MPa, while values from 40 MPa to 50 MPa are achieved in modern pumps and hydraulic motors. The possibility of increasing the speed of the tractor from standard 35 km/h to promising 50 km/h is shown.

Design and experimental validation of a valve-distributed water radial piston pump

In underground coal mining, there is an urgent need for reducing the noise, hydraulic shock, and leakage of reciprocating pumps. Flow pulsation is strongly dependent on the number of pistons for single-acting reciprocating pumps. Water hydraulic radial piston pumps (RPPs) allow the pistons to be radially distributed, which makes the multi-piston design easier compared to traditional single-acting reciprocating piston pumps. In this study, a novel valve-distributed water RPP was developed in which the star wheel assembled on the camshaft is used to drive the connecting rod-crosshead-piston assembly and realize the reciprocation of the piston and suction-discharge of the pump check valves. Mathematical and numerical models representing the RPP were built using MATLAB and AMESim, respectively. Three-dimensional computational fluid dynamics analyses were performed to investigate the internal flow field of the suction and discharge circuits as well as the flow characteristics of the discharge valve opening. A prototype pump was manufactured and tested for 200 h and then disassembled to evaluate the wear condition. The tested instant flow rates were lower than those obtained from the theoretical and simulation analyses. The experimental results also revealed that the average flow rates were almost independent of the output pressure and that the volumetric efficiency decreased with increasing rotational speed when the output pressure was larger than 25 MPa. Inspecting the disassembled water RPP revealed that scuffing problems occurred in the pistons, whereas the other components remained intact. The findings of this study offer a reference for water hydraulic power units in various applications and for investigating the intensity of water hydraulics.

Design and Verification of a Flow Distribution Structure for a Water-Based Radial Piston Pump

Design and Verification of a Flow Distribution Structure for a Water-Based Radial Piston Pump

Evolution of friction couples in volume hydraulic machines due to achievements in material science and technology

The article analyses modern achievements in the field of volumetric axial and radial piston hydraulic machines for the mobile sector of application in terms of using the latest design solutions, friction pair materials and technologies. Goal. The aim is to acquaint specialists with directions for creating hydraulic machines of a modern technical level due to increased pressure and rotation frequency. Methodology. The evolution of constructive decisions regarding the selection of pairs of rolling and sliding friction and their change depending on the achievements in materials science, tribology and increasing the accuracy of machines for the finishing of friction surfaces are consistently considered. Results. It is shown that in axial-piston hydraulic machines with an inclined disk, the transition to hydrostatic piston pairs with heel pads was made, which made it possible to increase the pressure up to 52 MPa. In radial-piston high-torque multi-cycle hydraulic motors, almost all manufacturers have replaced the rolling friction piston pairs with sliding pairs due to the latest anti-friction materials and precision processing. Thus, the ratio of mass to power decreased almost 6 times. For radial-piston hydraulic transmissions with ball-pistons, a failure analysis was performed, respectively, regarding the materials used, quality and control of heat treatment. Originality and practical value. For promising high-speed hydraulic transmissions with ball-pistons, recommendations have been developed for the selection of steels and control of their manufacture on the basis of taking into account materials science tools. The work in the production of piston balls from ceramic materials are offered. The given informative and practical research results are planned to be taught to master's students in the discipline of "Design and Testing of Hydraulic Drives of Construction and Road Vehicles" at KhNAHU.

RADIAL PISTON PUMP WITH A COMPENSATING STATOR PROFILE FOR ELIMINATE FEED LOSSES DUE TO FLUID SUBSIDENCE

In this work, we consider an unregulated radial piston pump with a compensating profile of the stator surface. This design eliminates feed losses due to dynamic compression and subsidence of liquid in the working chamber under the pressure formed in the operating hydraulic system. Radial piston hydraulic machines operate at pressures of 40 – 60 mPa and higher. At a pressure of 45 mPa, i.e., the case considered in the paper, the volume of liquid subsidence in the working chamber and the connecting channel reaches almost 3 %. This results in a hydraulic shock that reduces the volumetric efficiency of the pump. The level of linear subsidence, equivalent to the reduction of the plunger stroke, equals 2.54 mm at a working chamber diameter of 25 mm, which is more than 10 %. According to the level of linear subsidence, the stator inner surface correction parameter δst is set, which increases the plunger stroke and displaced fluid volume as if the pressure in the hydraulic system were zero. The dimensions of the plunger shank are calculated, at which the suction conditions do not deteriorate while the subsidence is reduced to 2.6 % due to decreasing the volume of the connecting channel of the pump working chamber.

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.

Analysis of the technical level of hydraulic fluid power with motor-wheels

The analysis of the use of hydraulic fluid power of rotation of hydraulic motor-wheels for tracked and wheeled machines was carried out. The hydraulic principle schemes for the use of high-speed axial-piston hydraulic motors with planetary gearboxes and high-torque low-speed radial-piston hydraulic motors are considered, in particular, hydraulic devices for ensuring reliable movement in the event of obstacles from the road surface. The features of static and dynamic calculation methods using a mathematical model for the numerical solution of differential equations when calculating pressure fluctuations and the frequency of rotation of hydraulic motors depending on the tasks of changing the intensity of the pump supply and the working volume of the hydraulic motor, taking into account its efficiency, are shown. A comparative analysis of the technical level of hydraulic motor-wheels was carried out and a significant increase in the output parameters of high-torque radial piston hydraulic motors with respect to pressure, rotation frequency and mass-to-torque ratio was revealed. The article may be useful for engineers, scientists and master's students.

Analysis of lubricating characteristics of high-pressure radial piston pump with thermo-elastohydrodynamic coupling

The behavior of piston-cylinder interfaces takes important influences on lubricating characteristics of the high-pressure piston pump. For the sake of revealing the lubricating characteristics of radial piston pumps, a transient thermo-elastohydrodynamic lubrication model to analyze the interface between piston and cylinder is established with considering the effects of the bushing elastic deformation, viscosity-temperature-pressure, heat conduction and piston tilting, on the basis of coupling the finite element method and finite difference method. Furthermore, the influences of design parameters (camshaft speed, inlet pressure and average clearance) on the load carrying capacity, leakage, viscous friction, and temperature rise of the friction-pair interfaces are analyzed. The results indicate that the average clearance has the most significant influence on the lubrication performance. Increasing the average clearance from 2 to 6 μm resulted in a substantial decrease in load carrying capacity by approximately 50% and friction force by approximately 65%. The temperature rise showed a significant reduction of 55%, while the leakage increased by approximately 3-fold.

Effect of Silencing Groove in Valve Plate on Efficiency of Radial Piston Pump

Effect of Silencing Groove in Valve Plate on Efficiency of Radial Piston Pump

ANALYSIS OF TECHNICAL CHARACTERISTICS OF HIGH TORQUE HYDROMOTORS WITH LIMITATIONS BASED ON DYNAMIC CALCULATIONS

The goal is to study the technical characteristics of the world's largest modern high-torque multi-acting hydraulic motor from the point of view of ensuring reliable operation by the manufacturer at elevated pressures, speeds and depending on the type of working fluid used. Analysis of the influence of dynamic loads on fluctuations in pressure and speed of the hydraulic motor in the modes of starting and braking, taking into account changes in the pump flow rate and inertial loads. Method. Dynamic calculation of a hydraulic fluid power with a high-torque hydraulic motor based on studies of external loads, changes in the pump feed time, providing the maximum speed. To solve nonlinear differential equations when calculating the pressure in the hydraulic drive and the rotational speed of the hydraulic motor, the VisSim application software package was used. The modes of change in the operation of the hydraulic motor over time in terms of rotational speed, pressure in the hydraulic fluid power, output power and hydromechanical efficiency, depending on the external load and pump flow, are presented on the corresponding oscillograms. The mathematical model of the hydraulic fluid power includes simulation modules for controlling the supply of an axial piston pump and changing the moment of resistance on the hydraulic motor. Results. Calculations of the dynamics of a hydraulic fluid power with a high-torque multi-acting radial piston hydraulic motor showed the need for preliminary modeling of its operation modes, taking into account the nature of the external loading, the moment of inertia and the intensity of the pump flow. Conclusion. The conducted studies can be used in the development of hydraulic fluid power with high-torque hydraulic motors to clarify the technological processes of work during the operation of a hydraulic machine.

TO THE MODERNIZATION OF HYDRAULIC FLUID POWER OF WHEEL EARTH MACHINE BASED ON HTZ TRACTORS

The purpose of the article is to scientifically search for the possibility of replacing mechanical drives of a chain working body and a rotary soil thrower of an earth-moving trenching machine with a hydraulic fluid power in order to increase reliability and effective protection against overloads.Studies have been carried out on the load characteristics of earth-moving machines of the PZM-2 (3) type and an assessment of the possibility of replacing the rotation of the chain working body and the rotary thrower of the dumped soil with the selection of hydraulic motors and pumps for a hydraulic fluid power. Hydraulic actuators must provide operation during the starting mode, minimal power loss during idling and effective protection in the event of a sudden stop of thehydraulic motors due to overloads.As a result of the calculations, it was found that for the hydraulic fluid power of the chain working body earthmoving trencher, high-torque low-speed radial piston hydraulic motors of single or multiple action with a working volume of 1800 ... 2500 cm3, as well as high-speed axial piston hydraulic motors with planetary gearboxes, for a rotary thrower of dumped soil, gerotor hydraulic motors with a working volume of about 200 cm3. The hydraulic motors required by the workingvolume are mass-produced by a number of foreign companies. To supply the working fluid to the hydraulic motors, axial piston tandem pumps with adjustable displacement, which are produced by the Hydrosila plant, are recommended.The results of the research can be used in the development of a new generation of earth-moving trenching machines when replacing the mechanical drive of the chain working body and the thrower of the dump soil with a hydraulic fluid power.

Acceleration Waves in Cylindrical Shrinking Gas Bubbles

The paper studies the case of shrinking cylindrical gas bubbles acting as a radial piston and generating acceleration waves. The behavior of such waves and their improbable transformation into shocks are illustrated theoretically, as well as through some examples inspired by experimental data. The use of rational extended thermodynamics enables us to highlight the relevance of the dissipation and the possible role played by dynamic pressure and stress tensor in bubble evolution or shock formation. These results constitute an extension and a completion of a previous work dedicated to the analysis of acceleration waves generated in oscillating spherical bubbles.

Dynamic Modelling and Experimental Validation of a Pneumatic Radial Piston Motor

A pneumatic radial piston motor is studied in this paper in order to establish a dynamic modelling and simulation method. As a result of using geometric parameters, the piston cylinder volume change was calculated, and the heat transfer equation, thermodynamic energy balance equation, and motion equation were combined in order to create a complete model of the piston cylinder. With the aid of compressed air, several experimental tests were conducted, and the results of rotational speed with varying inlet pressure were fed into the simulation to determine one of the critical unknown parameters, such as the overall friction coefficient of the system. For the studied piston motor, this coefficient was 0.0625 Nm. Computer simulations can be used to adjust design parameters in order to reach a higher rotation speed by using an accurate model. As a result, better efficiency and performance present several opportunities that would not be possible when running experimental tests in a lab. The mathematical model yielded higher rotational speeds of 50 RPM on average, with an increased piston diameter of 1.775 mm; by increasing the diameter of the cylinder to 25.8 mm, it was possible to achieve faster rotational speeds. The performed precise simulation could be used for further motor design and optimisation, and performance estimates under a broader range of operational conditions. Simulations should be conducted on multiple sets of experimental test results to determine the correct foverall value for each motor. In addition to guiding the design and optimisation of the motor, simulations could also predict its performance under a broader range of operating conditions by utilising effective parameters such as geometrical characteristics, flow conditions, and motion equations.

Tribological behavior of tribo-pairs in water hydraulic radial piston pumps

Friction and wear tests were performed on five Cu-based materials and three polyether ether ketone (PEEK)-based composites sliding against 17-4PH and 42CrMo4 coated with tungsten carbide-reinforced Ni-based coating. Two types of pin-on-disk specimens were used to represent the slipper/eccentric drive and piston/sleeve gap seal tribo-pairs in water hydraulic radial piston pumps. The experimental results showed that the QSn8-0.3 slipper material exhibited the highest steady-state friction coefficients for sliding against both 17-4PH (0.156) and coated-42CrMo4 (0.894). Glass fiber-reinforced PEEK exhibited the highest steady-state friction coefficients for sliding against the two specimens (0.540 and 0.420). The ZCuPb15Sn8/17-4PH showed the highest wear rate for the representative slipper/eccentric drive tribo-pair (26.86 × 10−6 mm/Nm); glass fiber-reinforced PEEK/17-4PH showed the highest wear rate for the representative piston/sleeve gap seal tribo-pair (46.91 × 10−6mm/Nm). The wear mechanisms of the two types of tribo-pairs were characterized through scanning electron microscopy, profilometry, and energy-dispersive spectroscopy analyses. Furthermore, the effects of hardness, pv values, coating, and reinforcement on the tribological behavior of the two types of tribo-pairs were analyzed.

Study of aircraft radial piston engines noise

The results of the study of acoustic characteristics of aircraft radial piston engines ASH-62IR and M-14P are presented. The tests were carried out during the race of the power plants of the AN-2 and Yak-18T light propeller-driven aircrafts under static conditions at the local aerodrome. It is shown that the method of organizing the exhaust of a multi-cylinder engine determines the main tone frequency. The influence of the engine power condition on the directivity of the tonal noise components is considered. The dependences of the sound power on the engine speed are obtained.