Experimental analysis of influence of double-layer bump foils on aerodynamic thrust foil bearings performance

Purpose Gas thrust foil bearings (GTFBs) are used to balance the axial load of engines. However, in some working conditions of large axial force, such as the use of single impeller air compressor, the load capacity of GTFBs is still insufficient. To solve this problem, the load capacity can be improved by increasing the stiffness of bump foil. The purpose of this paper is to explore a scheme to effectively improve the performance of thrust foil bearings. In the paper, the stiffness of bump foil is improved by increasing the thickness of bump foil and using double-layer bump foil. Design/methodology/approach The foil deformation of GTFBs supported by three different types of bump foils, the relationship between friction power consumption and external force and the difference of limited load capacity were measured by experimental method. Findings The variation of the foil deformation, bearing stiffness, friction power consumption with the external force at different speeds and limited load capacity are obtained. Based on experimental results, the selection scheme of bump foil thickness is obtained. Originality/value This paper provides a feasible method for the performance optimization of GTFBs.

Study on Optimization of Operating Parameters of Contact Mechanical Seal Based on Orthogonal Test

The working condition parameters of common contact mechanical seals are experimentally studied by orthogonal experimental design. The effects of working condition parameters on mechanical seal performance are compared by variance and range analysis, and the optimal sealing working condition is put forward. The results show that the spring specific pressure has a great influence on the leakage of mechanical seal, and the leakage decreases rapidly with the increase of spring specific pressure; With the increase of spring specific pressure, the friction power consumption increases. According to the test results, considering the requirements of mechanical seal performance and service life, the optimal spring specific pressure is 0.028 MPa under the condition of medium pressure ps =0.60 MPa and motor speed n =2960 r/min. At this time, the leakage is 6.120 ml/h and the friction power consumption is 0.648 kW.

Research on the influence of key structural parameters on piston secondary motion

Piston secondary motion not only influences the side knocking of piston and frictional loss, but also influence the in-cylinder oil consumption and gas blow-by. An inline four-cylinder common rail diesel engine was chosen as the research object. Dynamic simulation model of piston assembly was built based on the piston and cylinder liner temperature field test. The impacts of pinhole offset, liner clearance and piston skirt ovality on piston secondary motion were researched. Based on the surface response method, the influence of multiple factors on friction power loss and slapping energy is estimated. The results indicate that: in-cylinder stress condition of piston will change with its structural parameters, then the secondary motion of piston will be affected as a result. Pinhole offset, liner clearance, piston skirt ovality and the interaction of the latter two all have significant effects on the friction power loss, while the slapping energy is significantly affected by liner clearance. Therefore, the parameters can be designed based on the significance level to optimize the secondary motion characteristics of the piston.

Study on Lubrication Efficiency and Friction Power Loss of Engine Based on a Hybrid Hydrodynamic Model

Friction loss is one of the main factors affecting engine power. Reducing friction power losses to improve the power of engines is a significant concern for designers. Especially, under the background of energy-saving and emission reduction, it is indispensable to carry out an in-depth investigation on engine bearing lubrication characteristics. Unlike the previous studies of separate modelling, a new modelling method of coupling the dynamic and lubrication model is proposed in this paper. The bearing capacity, friction force, friction coefficient and eccentricity ratio were taken as the evaluation criterion, and the influence of design parameters such as angular speed, bearing radius and width on the lubrication efficiency and friction power loss (LE-FPL) were studied. The results indicate that increasing the angular speed, bearing radius or width can effectively reduce the eccentricity ratio and raise the minimum oil film thickness, which is beneficial to improve the lubrication efficiency. However, the above methods to improve engine lubrication efficiency will lead to more power loss of engine to a certain extent. Therefore, studies on reducing the friction power loss for the engine and on improving the lubrication efficiency for the engine should be considered coordinately in the dynamic design and optimisation of the engine.

Optimization and Influence of Micro-Chamfering on Oil Film Lubrication Characteristics of Slipper/Swashplate Interface within Axial Piston Pump

The overturning and eccentric abrasion of the slipper worsens the lubrication characteristics and increases the friction power loss and kinetic energy consumption of the slipper/swashplate interface to reduce the axial piston pump efficiency. A coupling lubrication numerical model and algorithm and a micro-chamfering structure are developed and proposed to predict more precisely and improve the lubrication characteristics of the slipper/swashplate interface. The simulation results reveal that the slipper without micro-chamfering overturns and contacts with the swashplate, while the one with micro-chamfering forms a certain oil film thickness to prevent this contact effectively. The minimum total power loss of the slipper/swashplate interface has to be effectively ensured under the worst working conditions, such as the high pressure, the low speed, the maximum swashplate inclination angle and the minimum house pressure. The optimal micro-chamfering width and depth are 1.2 mm and 3.5 μm or C1.2-3.5, the simulation average oil film thickness of which is approximately equal to the optimal analytical value. The experimental friction power loss of the slipper/swashplate interface is basically consistent with the simulation one, confirming the correctness and effectiveness of the coupling lubrication numerical model, and the optimization method and providing the further design direction of axial piston pumps.

Analysis and Experimental Validation of the Tribological and Dynamic Characteristics of Journal Bearings

Sliding bearings are the main kinematic pair of a Stirling engine, and one of the main sources of friction power loss and excitation force. There is a coupling effect between the lubrication state and the excitation force. In this paper, the dynamic model of a Sapphire bearing fatigue test bed, which includes thermo-elasto-hydrodynamic (EHD) property, is established and the accuracy of the model is verified by the experimental data. Based on the model, the effects of the load, the oil supply temperature, the oil supply pressure, the bearing clearance on the tribological and dynamic characteristics are studied. With an increase in the load, the orbital path of the journal moves downward, the lubrication state changes from the full hydrodynamic lubrication to the boundary lubrication, the friction power loss increases, and the bearing excitation frequency increases. Due to the decrease of the oil viscosity, the hydraulic friction power loss decreases, but the friction power loss derived from the asperity contact increase, so does the total friction power loss. With the increase of the radial clearance, the shape of the orbital path and the minimum oil film thickness remain unchanged. The increase of the bearing clearance results in the collisions between the journal and bearing bush, thus the amplitude of the frequency multiplication component in the bearing load increases, and the asperity and the total friction power loss increase.

Parameter Influences on Rail Corrugation of Metro Tangential Track

Rail corrugation can reduce riding comfort by vibration and noise, and even cause running accident. In this paper, the vehicle–track coupled dynamic model was developed for a metro’s tangential track considering the wear in rail materials. The influences of different track structure parameters and vehicle speed on the generation and development of rail corrugation of the tangential track were analyzed using the developed model by the control variable method. The results show that for different parameters, the friction power in wheel–rail contact patch fluctuates with time, but the overall fluctuation range is relatively uniform. Meantime, an analysis of one-third octave curves of the friction power reveals that the characteristic frequencies of friction power are mainly concentrated in the middle and low frequency bands. At the dominant characteristic frequency, the longitudinal stiffness and damping of fasteners, and lateral and vertical damping of fasteners have less influence on rail corrugation, while the lateral and vertical stiffnesses of fasteners, spacing of fasteners, wheel–rail friction coefficient and vehicle speed have greater effect on rail corrugation. The changes in vertical stiffness and spacing of fasteners will cause the characteristic frequency of friction power to be offset, resulting in a shift from 80[Formula: see text]Hz to 100[Formula: see text]Hz, which will further lead to rail corrugation of the corresponding wavelength. Thus, it can be concluded that the vertical stiffness and spacing of fasteners have an important impact on the generation and development of rail corrugation at the specific frequency. Besides, the variations of the other variables bring little change to the characteristic frequencies of friction power as well as on rail corrugation. The mechanism of parameters unveiled here provides some guides for the parameter optimization problem on restraining the generation or development of rail corrugation on the tangential track.