Abstract
Keywords:
Automatic transmission, Shift quality, Friction component, Clutch, Band, Test system
Abstract
A step-ratio automatic transmission (AT) system utilizes wet friction components to alter gear configurations for automatic shifting. Thus, their engagement behaviors have a direct impact on vehicle shift feel. In order to improve shift quality, a friction component test system is required to capture realistic engagement characteristics. Over the past 4 decades, the SAE#2 test system has served as the industry standard for evaluating engagement behaviors. However, the usefulness of SAE#2 test data is very much limited due to its test setups that are not consistent with actual AT shift conditions. This paper presents new friction component test system that replicates realistic shift conditions without complete AT hardware. It first reviews friction component engagement mechanisms as background. Then, an overview of typical AT shift kinematics is given to identify key engagement conditions that are not adequately represented in SAE#2 testing. Finally, the paper describes the enhanced friction component test system that accurately replicates those key conditions. It is based on a conventional SAE#2 test stand outfitted with a vector drive and a hydraulic control system. The vector drive permits a precise control of friction component slip speed during engagement. The hydraulic system is programmable and delivers a realistic pressure profile. A new control algorithm is developed to realize both torque phase and inertia phase of AT shifting. The enhanced system captures friction component engagement behaviors under far more realistic shift conditions compared with the conventional SAE#2 test stand. Thus, it greatly expands values and utilities of friction component testing during a vehicle development process.