1. INTRODUCTION Traction-drive has been developed as, for example, an element of a continuously variable transmission (CVT) for automobiles. An oil film is constantly formed in the contact between rolling elements that transmit power to each other. This oil film is solidified and sheared at a GPa-level contact pressure, and its shearing properties are af fected by the heat-generated temperature rise itself. That is, the temperature in the contact area can be considered the most important factor in estimating traction transmission force. With the goal of improving estimation accuracy for the maximum traction coefficient, the authors have been working to estimate and measure the temperature rise in the contact area using a thin film temperature sensor [ 1, 2]. One of the calculation methods that precisely handles temperature rise in oil film is Thermal- Elasto Hydrodynamic Lubrication (T-EHL) [3], which is a method that couples an energy equation with normal EHL analysis. However, this numerical analysis requires such advanced and large-scale calculation that the calculation method used for convergence could become a research subject in itself. In CVT for automobiles, sequentially estimating the maximum traction coefficient under driving conditions and properly controlling the normal force at the contact improves power transmission efficiency . However, incorporating large-scale calculation into such sequential control is certainly impossible. Therefore, it is necessary to build a model with the goal of understanding the physical characteristics of μ and expressing μ in as simple calculation as possible while retaining its characteristics. Through a traction coefficient estimation method using a calculation model suggested in the past [ 1], estimation accuracy was improved by combining the viscosity and plasticity regions of an oil film inside the contact ellipse in a μ measurement test using a four-roller experimental apparatus. However, under certain conditions, the change slope of μ relative to the slip ratio still differed from measured values (See in Figure 1). That is, μ estimation accuracy was observed to decrease as the heat generated by shearing inside the oil film increased. It seems that the physical characteristics of μ necessary under certain conditions could not be sufficiently expressed as the model was simplified. The slip ratio in the contact of a typical variator unit is not large, that is under 1%. However, as the slip Improvement of Temperature Prediction Method for Traction Contact Toshinari Sano Toyota Motor Corporation Masashi Inoue Nippon Soken Inc Fumihiro Itoigawa Nagoya Institute of Technology ABSTRACT This report proposes a method of improving the temperature prediction model for traction drive contact portion in order to improve prediction accuracy of the maximum traction coefficient, and then describes verification of this method. In our previous report, a method of estimating the maximum traction coefficient by expressing conditions inside the contact ellipse using a simple combination of viscosity and plasticity was proposed. For the rise in oil film temperature, a calculation model is used that considers maximum temperature to be the typical value. Furthermore, a thin film temperature sensor technology was developed to directly measure the temperature of traction contact of a four-roller experimental apparatus and a variator in an actual transmission, and its validity was confirmed. When measured values of the traction coefficient μ were compared with calculated ones, it was learned that μ estimation accuracy decreased under certain low-contact-pressure and high-sliding conditions. The factor that caused μ estimation accuracy to decrease under these load conditions was presumed to be an error in oil film temperature estimation. Therefore, by partially improving the temperature prediction model, that factor was identified and examined. In the end, the maximum traction coefficient was est