INTRODUCTION Friction clutches or brakes are commonly used in automatic transmissions during shifts. This approach can provide smooth clutch engagement and disengagement and good shift quality. However, efficiency losses occur during the energized mode because of slip or during de-energized mode due to the viscous drag between the friction plates. Further, multi-plate friction clutches consume considerable space and thus pose challenges when designing a compact transmission. Driven by the demand for better fuel economy, the concept to replace friction clutches with dog clutches is worthwhile to be investigated. Compared to friction clutch, the dog clutch is more compact and provides lower drag losses. The dog clutch without a synchronizer has been applied in commercial and military vehicles [ 1-2]; however, very limited information on dog clutch modeling and simulation is available. Also, controlling a dog clutch during shifts (without synchronizers) has not been fully researched nor validated within integrated vehicles. Several papers discussed the manual transmission synchronizer modeling from the design perspective [ 3,4,5], but only a few papers have investigated the contact dynamics of synchronizers [ 6,7,8,9]. Most of this research focused on FEM analysis for multi-body dynamics systems, which has limited potential to be implemented into a transmission system model for drivability evaluation. The major challenge associated with the dog clutch mathematical modeling is the requirement to capture the high frequency transients without sacrificing computational efficiency. These high frequencies result from the chamfer to chamfer contact in this application [ 10]. This research focuses on developing a physics-based component level model that describes the contact and impact dynamics while maintaining computational accuracy and speed. The component model is implemented in a powertrain system model to evaluate the drivability of the automatic transmission designed with a dog clutch under different driving scenarios. COMPONENT LEVEL DOG CLUTCH MODELING To better understand the contact dynamics of dog clutch, a physics-based model is first developed at component level. Assuming one dog (designed as g for grounded) is completely grounded, the other dog (designated as e for engaging) with an initial rotating speed is actuated axially, as shown in Figure 1. Similar to [7], the normal contact force F normal between two dogs is represented by a contact stiffness Knormal and contact damping Cnormal, where xnormal is the relative displacement and ẋnormal is the relative velocity along the normal direction. (1) Through kinematic analysis, the following relationships are determined: (2a) (2b)Analytical Study of a Dog Clutch in Automatic Transmission Application Chengwu Duan General Motors Co. ABSTRACT A dog clutch, if successfully implemented in an automatic transmission, provides better packaging and the potential for improved fuel economy. The technical requirements for this concept are examined through modeling and simulation. As a first step, a physics-based component level model is developed that provides an understanding of the basic contact and impact dynamics. The model is compared to a built-in AMESim block to establish confidence. This component level model is then integrated into a powertrain system model within the AMESim environment. As a test bed, the powertrain model is exercised to simulate a friction plate to dog clutch shift in a 6-speed automatic transmission. The analysis helps to define the slip speed target at the onset of the dog clutch engagement while ensuring shift requirements are met. Finally, the model is validated by comparing the simulated results with measured dynamometer data. CITATION: Duan, C., "Analytical Study of a Dog Clutch in Automatic Transmission Application," SAE Int. J. Passeng. Cars - Mech. Syst. 7(3):2014, doi:10.4271/2014-01-1775.2014-01-1775 Published 04/01/2014 Copyright © 20