INTRODUCTION More recently, the legislative and market pressure for CO2 reduction and fuel efficient powertrains has led to the development of automatic transmissions that include large number of gears (around 10), [ 1, 2]. The increased number of gears in ATs, however, increases the number of shift types and shift events progressively, thus making the development of new ATs significantly more time-consuming. Therefore, new approaches for dynamic analysis of vehicles with large number of gears AT have been developed [ 3]. Still, most of the AT dynamics modeling and control research work published in literature relates to conventional ATs, typically those with four or six gears [ 4, 5, 6]. The emphasis is on analysis and compensation (typically by means of controls) of distinct effects of AT shift dynamics such as inertia bump, torque hole, engine flare, and transmission tie-up effects [ 4, 7]. There are, however, several publications that analyze specific effects and related unconventional controls, which are directly or indirectly related to advance ATs with a large number of gears. This relates to double-transition shift [ 8], where four clutches are active, and single-transition shifts (STS) using an extra, normally-open clutch (three clutches are active) [ 9]. For better understanding of optimal shift behavior and development of related control strategies, various optimization techniques have been considered in [ 6, 10, 11].This paper presents two contributions in the field. Firstly, it analyzes the aforementioned, well-known AT dynamics effects, but by using a new, systematic and illustrative graphical approach based on the bond graph methodology [ 12]. Although the approach was already applied to ATs [ 13] (and also to hybrid electric transmissions [ 14, 15]), it is employed in this paper in a broader sense in terms of covering a wide set of AT single-transition shift dynamics effects. Secondly, the bond graph approach is applied to develop a set of conditions for beneficial use of extra clutch in the inertia phase of single-transition upshifts and downshifts. Compared with [ 9], where a specific structure of transmission model is used, the extra clutch conditions are derived and analyzed herein for a more general case of any STS in an AT with a large number of gears. The derived condition-based prediction of beneficial use of extra clutch is verified by comparing the prediction results with control trajectory optimization results for a wide range of subsequent and skipping-gear shifts of a 10-speed AT from [ 16]. POWER TRAIN MODEL The structure of a power train equipped with a torque converter AT can be depicted by the block scheme shown in Figure 1 [5]. The corresponding model equations are given in Appendix A based on [ 5, 17].Bond Graph Analysis of Automatic Transmission Shifts including Potential of Extra Clutch Control Vanja Ranogajec, Joško Deur, and Mirko Coric Univ of Zagreb ABSTRACT New generation of torque converter automatic transmissions (AT) include a large number of gears for improved fuel economy. Control requirements for such transmissions become more demanding, which calls for the development of new shift optimization and analysis tools. This paper presents two contributions to the field of transmission dynamics analysis: (i) bond graph method-based shift transient analysis, and (ii) deriving a unique set of conditions for beneficial use of a third (normally-open) clutch for any upshift or downshift, with emphasis on inertia phase. The derived conditions are examined on an example of 10-speed AT based on the clutch torque input trajectory optimization results. The examination results point out that the extra clutch has a potential of significant performance improvement for any single-transition upshift in the inertia phase, in terms of reduced vehicle jerk RMS value due to the suppressed inertia bump effect. The shift quality improvement is possible in the