Keiji Kyogoku

Relationship Between Temperature Distribution in EHL Film and Dimple Formation

This paper describes an experimental study on dimple formation under elastohydrodynamic lubrication (EHL) conditions. The oil film thickness between a ball surface and a glass disk was measured using optical interferometry, and the temperatures of both the surfaces and of the oil film averaged across it were measured using an infrared emission technique. It was found that the temperature profile across the oil film varies abruptly along the sliding direction, and the Couette flow decreases due to the viscosity wedge action as the oil flow is close to the dimple zone. The maximum temperature rise in the dimple zone sometimes reached over 400 K, thus, the phase transition of the oil from liauid to glass may not occur.

Experimental investigation of effects of slip ratio on elastohydrodynamic lubrication film related to temperature distribution in oil films

Abstract This article describes the mechanism of variations of elastohydrodynamic lubricated oil film under high slip ratio conditions. Experiments were conducted using a ball-on-disc apparatus. The thickness of the oil film was measured by optical interferometry. Temperature increase in the ball surface, disc surface, and oil film was determined by an improved infrared technique using a transparent disc without any coating and non-transparent disc with a comparatively thick Cr coating. The results reveal that the film thickness decreases with an increase in the slip ratio at constant entrainment velocities. The shape of the oil film indicates an increase in the thickness gradient at the inlet region and a slight increase in the oil film just behind the exit region. The temperature at the inlet region increases with the slip ratio and entrainment speed. Both the inlet region and the contact area exhibit a significant temperature difference between the surfaces. The variation of the shape of the oil film can be explained on the basis of the viscosity wedge action. The viscosity wedge action, heating at the inlet region, and inflow of heat from a slower surface to the inlet region reduce the film thickness considerably.

Measurements of Temperature Distributions around Longitudinally Grooved Rough Surfaces in Sliding Elastohydrodynamic Point Contacts

This paper describes the temperature measurements in the EHL conjunction area comprising a longitudinally grooved steel ball and a sapphire disk under high slip conditions. The authors measured the temperatures of the oil film as well as both the disk and ball surfaces; furthermore, they estimated the temperature profile across the oil film by means of experimental values. The experimental results show that the temperature of the grooved ball surface increased considerably compared with that of a non-grooved ball. The temperatures of the faster surface for the grooved ball became sensitive to the slip ratio, whereas that for the non-grooved surface was almost constant. The temperature distribution had a higher value at the land zones and a lower one at the grooved zones. The temperature rise in the grooved zones varied qualitatively depending on the thermal conditions of both the sliding surfaces.

Measurements of Two-Dimensional Distribution of Refrigerant Concentration in EHL Film Using Micro FT-IR and Effect of Variation of Concentration on Oil Film Thickness

The dissolution of refrigerant into a lubricant causes a decrease in viscosity of the oil and it gives a large effect on the lubrication of sliding parts in a refrigerant compressor. This paper describes an application of micro FT-IR to measure the two-dimensional concentration distribution of refrigerant held in solution in the EHL film surrounded by the refrigerant gas and discusses the refrigerant concentration variation in the vicinity of the Hertzian contact area. In order to measure the concentration distribution, an apparatus which can observe the EHL film in a point contact in the refrigerant atmosphere was developed. The refrigerant concentration was measured using micro FT-IR through a CaF2 window from outside of the apparatus with polyol ester as a base oil in an atmosphere pressurized with HFC-134a refrigerant gas. The results indicate that the concentration of HFC-134a refrigerant reduces in the inlet boost region of EHL contact and the Hertzian contact area but in the side region of Hertzian contact area it is greater than that in the bulk fluid. In addition, the effect of the variation on the oil film thickness is discussed.

The Effect of Interaction Between Neighboring Asperity Contacts on Wear Mode Transition in Sliding Contact of Rough Surfaces

Concerning the final aim, that is to make clear the mechanism of the wear mode transition from mild to severe belong to the increase of contact pressure in adhesive wear, estimation of the yielding condition in subsurface under contact boundary between rough surfaces was attempted in this study. Especially the effects of interaction between neighboring contacts as well as relative sliding on the yielding area were focused. The contacts between asperities were modeled by the contact between two neighboring hard wedges with the parallel axes and soft plane to be simplified. These models were calculated by commercial FEM solver in 2-dimension. Additionally, the effect of the difference between the heights of two wedges on the yielding region was evaluated by comparing the result with that obtained from the simple model of two wedges with the same height in non-sliding contact. The results showed that the effect of the interaction between adjacent contacts and existence of relative slip motion give significant factors to the yielding state, on the other hand, the height difference between neighboring asperities affects little the determination of the yielding region.Copyright

Measurements of EHL film temperature between sapphire disk and longitudinally grooved steel ball under high slip ratio conditions

This paper describes results of temperature measurements using longitudinally grooved steel balls and a sapphire disk under high slip EHL conditions. The authors measured the temperatures of both the sliding surfaces and the oil film, furthermore, estimated the temperature profiles across the oil film with experimental results. The experimental results show that the temperature of the ball surface with textured balls increase considerably in compared with that with a flat surface ball. The shape of the temperature distribution of both the surface and the oil film have higher value at the land zones and lower one at the grooved ones. The film thickness with increasing slip ratios decreases while previous results have indicated a constant thickness. The decrease of the thickness can be explained by the viscosity wedge action due to the temperature variations across the oil film.

Effect of surface roughness on friction loss between cam and follower

Friction forces between cam and follower have been calculated under conditions of non-steady state and partial EHL with asperity contacts. Non-Newtonian viscosity and thermal effect including the heat generation at asperity contacts have been taken into consideration. The results shows that the reduction of friction power loss due to the decrease in surface roughness appears remarkably under high temperature.