Experimental Research on the Dynamic Lubricating Performance of Slipper/Swash Plate Interface in Axial Piston Pumps

The interface between the slipper/swash plate is one of the most important frication pairs in axial piston pumps.The test of this interface in a real pump is very challenging.In this paper,a novel pump prototype is designed and a test rig is set up to study the dynamic lubricating performance of the slipper/swash-plate interface in axial piston machines.Such an experimental setup can simulate the operating condition of a real axial piston pump without changing the relative motion relationship of the interfaces.Considering the lubricant oil film thickness as the main measurement parameter,the attitude of the slipper under the conditions of different load pressure,rotation speed and charge pressure are studied experimentally.After the test,the wear state of the swash plate is observed.According to the friction trace on the surface of the swash plate,the prediction for the attitude of the slipper and the zone easy to wear are verified.

Tribological performance of MoS2 coating on slipper pair in axial piston pump

This study investigates tribological performance of MoS2 coating on slipper pair in axial piston pump.Firstly,the MoS2 coating on the surface of slipper pair was prepared by atmospheric plasma spraying treatment technology.Secondly,the tribological characteristics of slipper pair under various working conditions were evaluated on ring-on-block tester in oil lubrication.The original and worn surfaces of the specimens were analyzed with scanning electron microscope and energy dispersive spectrometer,and then the wear morphologies of the MoS2 coatings were imaged by X-ray photoelectron spectroscopy.The experimental results showed that the friction coefficients of Cu-based materials with MoS2 coating decreased by about 0.05 at 800 N.Especially,when the external load was set to 800 N,the wear rate of the ZY331608 decreased by about 16.4%after the substrates were treated by the MoS2 coating,which exhibited excellent anti-friction and wear resistance.The formation of the MoS2 lubricating film could be classified into four stages,including the initial friction stage,anchoring stage of MoS2 on friction surface,covering stage of the sliding surface by MoS2 and the formation stage of MoS2 film.The dominating wear mechanisms of Cu-based materials with MoS2 coating were adhesive wear and abrasive wear accompanied with oxidative wear.

Parametric analysis of thermal effect on hydrostatic slipper bearing capacity of axial piston pump

Hydrostatic slipper was often used in friction bearing design, allowing improvement of the latter's dynamic behavior. The influence of thermal effect on hydrostatic slipper bearing capacity of axial piston pump was investigated. A set of lumped parameter mathematical models were developed based on energy conservation law of slipper/ swash plate pair. The results show that thermal equilibrium clearance due to solid thermal deformation periodically changes with shaft rotational angle. The slipper bearing capacity increases dramatically with decreasing thermal equilibrium clearance. In order to improve the slipper bearing capacity, length-to-diameter ratio of fixed damper varies from 3.5 to 8.75 and radius ratio of slipper varies from 1.5 to 2.0. In addition, the higher slipper thermal conductivity is useful to improve slipper bearing capability, but the thermal equilibrium clearance is not compromised.

Prediction of Leakage from an Axial Piston Pump Slipper with Circular Dimples Using Deep Neural Networks

Oil leakage between the slipper and swash plate of an axial piston pump has a significant effect on the efficiency of the pump.Therefore,it is extremely important that any leakage can be predicted.This study investigates the leakage,oil film thickness,and pocket pressure values of a slipper with circular dimples under different working conditions.The results reveal that flat slippers suffer less leakage than those with textured surfaces.Also,a deep learning-based framework is proposed for modeling the slipper behavior.This framework is a long short-term memory-based deep neural network,which has been extremely successful in predicting time series.The model is compared with four conventional machine learning methods.In addition,statistical analyses and comparisons confirm the superiority of the proposed model.

Dynamic Characteristics of Lubrication and Wear Prediction of Slipper/Swash-Plate in Axial Piston Pumps

A novel dynamic model describing the slipper posture of the swash plate in axial piston pumps is proposed, taking into account the hydrodynamic and squeezing effects, which involves three degrees of freedom. The variation in the lubricating film thickness and the slipper tilt are accurately calculated. The influence of hydrodynamic effects and charging pressure on the slipper lubrication is discussed. The minimum film thickness, the overturning angle and the azimuth angle are obtained.Then, the trajectory of minimum thickness on the friction surface of the swash plate is predicted, the accuracy of which can be verified with the abrasion distribution of an actual swash plate. Research results can predict the durability and provide theoretical help for the design of the slipper.

LUBRICATION FILM FORMATION MECHANISM OF SLIPPER PAIRS IN LOW SPEED HIGH TORQUE HYDRAULIC MOTORS

Pressure-flow analytical formulas of lubrication film of slipper pairs on camshaft connecting rod type low speed high torque （LSHT） hydraulic motors are put forward. The bottom surface of slipper pairs is rectangle, and the effect of squeeze flow and pressure differential flow is considered. The dynamic process of lubrication film formation through squeezing is numerically studied by computer simulation. Effects of supply pressure, initial lubrication film thickness, velocity damping coefficient, loading impact and gravity, etc are studied. Advantages of novel slipper pairs with large oil cavity area are pointed out.

Pressure distribution of combining center cavity slipper for axial piston pump

In order to improve lubricating characteristics of slippers in an axial piston pump, the combining center cavity slipper approach was proposed based on slipper shape and moving characteristic. The cylindrical coordinate was used in the lubricant area and mesh was made. The blockweight approach was implemented to deal with non-coincidence of mesh and shallow recess border in numerical method. The finite control volume method was applied in calculating pressure distribution. The flow conservation equation and film thickness model were resolved through Gauss-Siedel relaxation iteration. The calculation and analysis results indicate that compared to the slipper （1） slip- per pressure distribution is improved; （2） hydrodynamic pressure of the combining slipper is greatly increased; （3） inclining degree is greatly reduced; （4） negative pressure in lubricant film disappear. So the combining center cavity slipper is lubricated better.

基于分形理论的静压支承滑靴系统摩擦自适应特性分析

静压支承滑靴副比一般的滑动摩擦副具有更好的摩擦自适应特性,对滑靴的早期磨损有一定的修复效果,但其摩擦自适应机理目前尚不明确。为此,基于分形理论,采用分形维数、尺度系数等分形参数描述滑靴表面形貌,对摩擦自适应过程进行理论分析,开展磨损试验并以分时段更换试件的试验方法观察分形参数的变化情况,得到分形参数对摩擦学特性的影响规律,揭示滑靴摩擦自适应机理。结果表明,滑靴副在发生早期磨损后,分形维数呈增大-减小-再增大-再减小的变化过程,尺度系数和摩擦系数呈减小-增大-再减小-再增大的变化过程,滑靴在早期磨损阶段呈现出显著的摩擦自适应特性,其表面性能表现出劣化-修复-再劣化-再修复的变化特征。

Integrated slipper retainer mechanism to eliminate slipper wear in high-speed axial piston pumps

he power density of axial piston pumps can greatly benefit from increasing the speed level.However,traditional slippers in axial piston pumps are exposed to continuous sliding on the swash plate,suffering from serious wear at high rotational speeds.Therefore,this paper presents a new integrated slipper retainer mechanism for high-speed axial piston pumps,which can avoid direct contact between the slippers and the swash plate and thereby eliminate slipper wear under severe operating conditions.A lubrication model was developed for this specific slipper retainer mechanism,and experiments were carried out on a pump prototype operating at high rotational speed up to 10000 r/min.Experimental results qualitatively validated the theoretical model and confirmed the effectiveness of the new slipper design.

高压大排量径向柱塞泵定子运动规律分析

为改善高压大排量径向柱塞泵定子-滑靴副摩擦状况,实现泵的精确变量,提出定子圆周方向非固定安装结构。通过滑靴柱塞组件力学特性分析,建立单个滑靴滑动摩擦力矩和11个滑靴摩擦合力矩,求解得到定子角速度变化曲线。结果表明,定子在滑靴滑动摩擦力矩作用下能够运动,且排油区滑靴摩擦力矩大于吸油区滑靴摩擦力矩。径向柱塞泵正常工作后,定子角速度稳定在89.5~90.6 rad/s,呈周期变化,对定子运动起阻碍作用的滑靴个数为4、5交替变换。为高压大排量径向柱塞泵滑靴副设计、提高泵的性能提供一定参考。

外负载对径向柱塞泵滑靴副流场特征和强度的影响

针对高压大排量径向柱塞泵在重载领域出现的滑靴副失效问题,在考虑油液黏温黏压特性的基础上,对滑靴副流体域展开数值计算和流固耦合仿真分析,探讨外负载对滑靴副流体域压力、流速、泄漏以及滑靴结构强度的影响。结果表明:当外负载从1.1×10^(8)N增加到1.2×10^(8)N时,吸油区滑靴副流体域的压力分布和数值基本不变,排油区滑靴副中心油腔压力增大1.5 MPa,流体域油膜的高压区面积增大,油液压力增大了0.05 MPa,油液流速稍有增加;滑靴副油液泄漏主要位于滑靴副边界处,高、低阻尼孔泄漏较小,随着外负载的增大,3处泄漏量都增大,单个滑靴副总泄漏量增大0.05 mL/s;外负载对滑靴强度影响较小,在排油区滑靴最大应力与变形发生在中心油腔处,此处是滑靴结构强度较为薄弱的地方。

一次性拖鞋产品企业标准现状探讨

我国尚未制定一次性拖鞋的国家标准和行业标准。文章通过梳理现行有效的一次性拖鞋企业标准,发现一次性拖鞋企业标准的相关问题,并结合国家政策提出行业技术发展路径和一次性拖鞋行业标准制修订方向,对于推动我国一次性拖鞋行业的高质量发展具有现实意义。

基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解方法

通过改进轴向柱塞泵的滑靴副与柱塞的结构设计以稳定建立滑靴油膜,这是轴向柱塞泵当前的研究热点之一。柱塞泵滑靴副油膜厚度的动态特性对分析柱塞泵滑靴副的支撑特性至关重要,为此,提出了一种基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解新方法。首先,对滑靴副的受力平衡机理进行了分析,并构建了柱塞泵运动学和动力学模型;然后,构建了柱塞泵整泵流场仿真模型,求解了包含滑靴底部支撑力、柱塞腔压力等在内的滑靴副支撑动态边界,并采用容积效率试验数据验证了整泵流场仿真的准确性;最后,建立了滑靴副油膜承载模型,分析了滑靴副油膜支撑特性,提出了基于插值计算理论的柱塞泵滑靴副油膜承载尺度动态求解方法,对1600 r/min与600 r/min两种典型工况的滑靴副油膜动态进行了计算。研究结果显示:大排量柱塞泵转速为1600 r/min时,柱塞惯性力导致高压侧油膜厚度进一步减薄,高压转低压过程中,柱塞腔内出现压力骤降,使滑靴副油膜无法形成,导致滑靴与斜盘发生刚性接触,在该区域内发生异常磨损;而在低转速工况(600 r/min)时,滑靴底面能够有效形成油膜,保证柱塞泵低速运行的可靠性。这表明基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解方法可以快速地对不同工况下的柱塞泵滑靴副油膜厚度进行求解。

柱塞泵滑靴磨损信号随机森林算法故障诊断

为了提高低负载下柱塞泵滑靴磨损故障状态诊断精度,提出基于随机森林算法的柱塞泵滑靴磨损故障状态识别方法。重点分析了低负载条件下各类柱塞泵滑靴故障信号的频域特征值,构建了特征数据库。验证了上述方法的适应性,并测试了柱塞泵不同程度松靴故障的诊断情况。研究结果表明:滑靴磨损后频域表现出明显的波动性,袋外错误率和决策树数量呈现反比变化规律,基本都在0.05附近,将决策树最优棵数n设定在400。以随机森林算法诊断特征数据库时,在250组样本中只发生了1组误识别情况,达到了98.75%的识别准确度。随机森林方法训练时间、训练准确度与测试准确度都比其它各算法更优。松靴故障诊断结果获得了高于99.5%的总体诊断准确度。采用随机森林方法柱塞泵磨损故障状态诊断表现出优异适应性,能够对柱塞泵各故障状态进行准确诊断。

表面织构对微型轴向柱塞泵滑靴副摩擦学性能的影响研究

为减小微型轴向柱塞泵滑靴副的摩擦因数并提高油膜润滑性能,在滑靴底部设计椭圆微织构,建立滑靴副几何模型,并采取流场仿真对滑靴底部的油膜压力场以及剪切场进行求解分析,发现采取微织构能够减小滑靴底部的摩擦因数。为了进一步增强动压效应的作用,提升支承力并减小摩擦因数,通过Design-Expert响应面分析设计实验水平表进行计算分析,以泄漏量最小、支承力最大及摩擦因数最小为目标函数建立数学模型,最终得到微织构的优化尺寸。优化后滑靴副的油膜润滑性能得到提高,优化后的参数可作为柱塞泵结构优化的依据。

Investigation on structural optimization of anti-overturning slipper of axial piston pump

Improving the carrying ability of oil film between slipper and swash plate and reducing the partial abrasion of slipper are important to improve the service life and reliability of axial piston pump.In this paper,a numerical simulation model was developed for slipper/swash-plate friction pair based on the elastohydrodynamic theory.The dynamic micro-motion and pressure distribution of slipper were analyzed and it was pointed out that the tilt of slipper was the main reason for its partial abrasion.The simulations about the slippers with different slopes on the outer edge of the sealing belt showed that the partial abrasion could reduce the carrying ability and increase the leakage of the slipper/swash-plate pair.The proper slope on the inner edge helped to improve the carrying ability and reduce the leakage of slipper.The experimental tests were in accord with the simulation results to a great extent,showing that the simulation model had a high accuracy and could be applied to the design and optimization of slipper,and that the slipper with optimal inner slope provided an encouraging method to improve the efficiency and reliability of axial piston pump.

Impact of the thermal effect on the load-carrying capacity of a slipper pair for an aviation axial-piston pump

A thermal hydraulic model based on the lumped parameter method is presented to analyze the load-carrying capacity of a slipper pair in an aviation axial-piston pump under specified operating conditions. Both theoretical and experimental results are presented to demonstrate the validity of the thermal hydraulic model. The results illustrate that the squeezing force and thermal wedge bearing force are the main factors that affect the film thickness and load-carrying capacity.At high oil temperature and high load pressure, the film thickness decreases with increasing clamping force due to a combined action of the squeezing bearing force and the thermal wedge bearing force, but the load-carrying capacity will increase. An increase of the film thickness is proven to be beneficial under high shaft rotational speed but especially dangerous as it strongly increases the ripple amplitude of the film thickness, which leads to decreasing the load-carrying capacity. The structural parameters of the slipper can be optimized to achieve desired performance, such as the slipper radius ratio and orifice length diameter ratio. To satisfy the requirement of the load-carrying capacity, the slipper radius ratio should be selected from 1.4 to 1.8, and the orifice length diameter ratio should be selected from 4 to 5.

Performance optimization of grooved slippers for aero hydraulic pumps

A computational fluid dynamics （CFD） simulation method based on 3-D Navier Stokes equation and Arbitrary Lagrangian Eulerian （ALE） method is presented to analyze the grooved slip- per performance of piston pump. The moving domain of grooved slipper is transformed into a fixed reference domain by the ALE method, which makes it convenient to take the effects of rotate speed, body force, temperature, and oil viscosity into account. A geometric model to express the complex structure, which covers the orifice of piston and slipper, vented groove and the oil film, is constructed. Corresponding to different oil film thicknesses calculated in light of hydrostatic equilibrium theory and boundary conditions, a set of simulations is conducted in COMSOL to analyze the pump characteristics and effects of geometry （groove width and radius, orifice size） on these characteristics. Furthermore, the mechanics and hydraulics analyses are employed to validate the CFD model, and there is an excellent agreement between simulation and analytical results. The simulation results show that the sealing land radius, orifice size and groove width all dramatically affect the slipper behavior, and an optimum tradeoff among these factors is conducive to optimizing the pump design.

Study on friction performance and mechanism of slipper pair under different paired materials in high-pressure axial piston pump

High-pressure axial piston pumps operate in high-speed and high-pressure environments. The contact state of the slipper against the swashplate can easily change from an oil film lubrication to a mixed oil film/asperity contact, or even dry friction. To improve the dry friction performance of slipper pairs and to avoid their potentially rapid failure, this study examined the effects of material matching on the dry friction performance of the slipper pair for high-pressure axial piston pumps. A FAIAX6 friction and wear tester was developed, and the dry friction coefficients of the slipper pairs matched with different materials were studied using this tester. Based on the thermo-mechanical coupling of the slipper pair with the working process, the contact surface temperatures of the slipper pairs matched with different materials were calculated and analyzed for the same working conditions. Following this, the effects of the material properties on the temperature increase at the slipper sliding contact surfaces were revealed. The reliabilities of the temperature calculations and analysis results were verified through orthogonal tests of slipper pairs matched with different materials. The results indicate that the influence of the material density on the friction coefficient is greater than that of the Poisson's ratio or the elastic modulus, and that the slipper material chosen should have a high thermal conductivity, low density, and low specific heat, whereas the swashplate material should be high in specific heat, density, and thermal conductivity;in addition, the slipper pair should be a type of hard material to match the type of soft material applied;that is, the hardness of the swashplate material should be greater than that of the slipper material.

Transient tribo-dynamic analysis of crosshead slipper in lowspeed marine diesel engines during engine startup

A crosshead slipper-guide system,which bears a significant thrust force,is an essential friction pair in low-speed marine diesel engines.Owing to the low moving speed of the crosshead slipper during engine startup,it is difficult to form good hydrodynamic lubrication between the crosshead slipper and guide.Therefore,a detailed analysis of the crosshead slipper during engine startup is needed.In this study,a new transient tribo-dynamic model for a crosshead slipper during the engine startup process is presented.The model consists of a mixed lubrication model of the crosshead slipper-guide and dynamic models of the piston assembly,crosshead assembly,connecting rod,and crankshaft.The tribo-dynamic performances of the crosshead slipper during startup and under the rated conditions were simulated and compared.The results show that the tribo-dynamics of the crosshead slipper during the startup process are significantly different from those under the rated conditions.Some measures beneficial for the low friction of a crosshead slipper-guide under the rated conditions may significantly increase the friction loss of the crosshead slipper-guide system during the startup process.