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Technical Paper

Effect of Volume Viscosity on Traction Coefficient

The effect of volume viscosity or second vicosity on the traction coefficient has been investigated. The volume viscosity has been considered to cause the compression delay of the EHL film in the traction drive and as a result to decrease the shear force or the traction coefficient, because the oil film pressure changes from atmospheric pressure to several GPa in a shorter time interval than one millisecond. The volume viscosity and traction coefficient have been measured for five synthetic oils. The volume viscosity of oil has been estimated from the absorption coefficient of an ultrasonic wave which has been determined from the relation between a detected amplitude of ultrasonic pulse and the propagation distance. It has been found that the traction coefficient has increased as the volume viscosity has decreased.
Technical Paper

Development of Automatic Transmission Fluid for Slip-Controlled Lock-Up Clutch Systems

Slip-controlled lock-up clutch systems are very efficient and greatly improve fuel economy. On the other hand, these systems can cause unstable vibrations including those known as “shudder vibrations”. In this study, the authors made a theoretical analysis of these unstable vibrations to clarify the fundamental frictional properties of automatic transmission fluids (ATFs) required for slip-controlled lock-up clutch systems. Based on this analysis, we established lubricant technology having a sufficient anti-shudder property and high torque capacity. Further, we developed a new test apparatus to evaluate the anti-shudder durability for lubricant development.
Technical Paper

Lubricant Technology to Enhance the Durability of Low Friction Performance of Gasoline Engine Oils

This paper describes lubricant technology to enhance the durability of the low friction performance of gasoline engine oils which were formulated with molybdenum dithiodicarbamates (MoDTCs) as friction modifiers. This paper also describes an evaluation method which consists of three tests: (1) Our in-house rig test to simulate oil deterioration in an engine stand; (2) Quantitative analysis of MoDTC and ZnDTP in oils and; (3) A friction test (SRV). It was found that the low friction performance of fuel economy engine oils deteriorated primarily due to the consumption of MoDTC and ZnDTP. Calcium salicylates had better durability of low friction performance than calcium sulfonates. Furthermore, sulfurized compounds enhanced the durability. Based on these findings, an experimental oil was formulated.
Technical Paper

Experimental Study on Viscosity-Shear Characteristics of Lubricating Oils

The viscosity of automotive lubricants containing polymers decreases temporarily in the oil films of sliding parts with the increase in shear rate. This decrease sometimes causes surface damages such as bearing seizure and gear pitting. This paper describes the effect of polymers and base oils on viscosity under high shear rate conditions. The viscometer was newly developed to evaluate the viscosity at high shear rates. Shear rate can vary between 105 sec-1 and 106 sec-1. By using the viscometer, the effects of various factors such as polymer type, molecular weight, polar group and concentration on shear viscosity were investigated. The effects of polymer solubility and molecular weight distribution of base oils were also investigated.