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In recent years, several new types of automatic transmissions have been developed and launched such as CVT, AMT, DCT and Multi Step AT. The operating condition of wet friction material in automatic transmission has become more severe in order to achieve further improvement of fuel economy and compact size with high power engine. Under higher speed engagement, the sliding interface between friction material and separator plate (steel) must absorb a large amount of energy in a very short time. Recently, there is increasing to focus on the hot spot phenomenon that is appeared as some discoloration and distortion on reaction plate for wet friction material. This hot spot phenomenon is known as a typical failure mode of wet clutch system, because it influences the durability and shift quality in clutch system. [1][2] Hot spots can cause degradation of friction performance during shift change in automatic transmission.

In recent years, several new types of automatic transmissions were developed and launched. Especially, the multi-step automatic transmission as a 6 speed can provide good shift quality and better fuel economy. Improved technology for torque converter clutches is important in order to achieve further improvement of fuel economy and efficiency. This paper describes the development of new friction material optimized for high energy and high speed slipping condition of slipping control torque converter clutch.

Various products with paper-based wet-friction material have been developed for smoother shifting of automatic transmissions. Band brakes have been featured as friction engagement elements for planetary gears, which provide higher holding-torque capacity than same-size multiple friction-disk brakes caused by a self-energizing mechanism. The advantages that should be focused on are better shift quality for the release element during up shifting because of the different torque capacity in the drum rotating direction. In 1988, BorgWarner developed the Maji-Band for band brakes (coiled-steel straps joined into bands), which is lightweight and compact, and provides approximately 3.5 times higher torque capacity than single wrapped band brakes and lower drag torque than multiple friction-disk brakes. However, it is difficult to control shift quality as the engaging element for upshifting is caused by instability in attaining the required torque to dynamically follow the servo-applied force.

It has been past over 10 years since the slip-controlled clutch has adopted to torque converters as improvement technology of fuel consumption. In the recent trend, the updated demand is use of expanded slipping control for further improvement of the transmission efficiency. However, there are the cases of vibration issues in slip-controlled torque converter clutches. This issue is called shudder as typical problem of vehicle vibration. In design of torque converter, it is known as the importance to manage μ -V property preventing from shudder vibration. However, it was difficult to predict μ -V property on the actual system, because of its complex interface phenomena are caused by various changeable factors include physical and chemical. Therefore, if prototype design was never satisfied anti- shudder properties, we need to change design and lost much time to redesign it.

The approximate torque response model for the engagement of a wet friction clutch, developed by Berger [1, 2], was modified and enhanced. The modified Reynolds equation for the film thickness and force balance for the wet clutch pack are solved numerically. The Reynolds equation relates the film hydrodynamic pressure to the film thickness, physical properties of friction materials, and operating parameters. The torque is calculated from the film and asperity pressure distribution at the friction interface. The applied pressure and the interface temperature as a function of time during engagement are considered in the model. The correct average flow factors of Patir and Cheng [3, 4] for ATF flow between rough surfaces are incorporated into the model. The permeability of friction materials and the temperature gradient inside the friction material are considered.