2018-01-1165 Published 0 3 Apr 2018 © 2018 SAE International; Ford Motor Company.Dynamic Lever: Key to Automotive Transmission and Drivetrain Dynamics Dongxu Li General Motors LLC Citation: Li, D., “Dynamic Lever: Key to Automotive Transmission and Drivetrain Dynamics,” SAE Technical Paper 2018-01-1165, 2018, doi:10.4271/2018-01-1165. Abstract Lever analogy has been developed for more than 30 years. The powerful tool can greatly simplify transmission analysis and has been widely used for transmission powerflow analysis, selection and control synthesis. In the past two decades, automatic transmissions have undergone a rapid growth with continual increase in the number of speeds and electrification. The increase in the system complexity has presented great challenges to system integrations. Many unpredicted issues have been NVH related and difficult to troubleshoot, partially due to the lack of proper modeling and analysis tool to capture the drivetrain dynamics including transmission components. Although the lever analogy has played important roles in the system design, the current form is not adequate and has never been used for dynamic analysis for the transmission and drivetrain system. In this paper, we will introduce the dynamic lever model framework and analysis method to address the dynamic aspect of a transmis - sion and drivetrain system. This analytical model framework allows one, for the first time, to systematically comprehend all possible dynamic structures within a drivetrain system. We will show that the dynamic lever framework can add the desired dynamic analysis capability to the existing lever analogy based methods, and will be a powerful tool proven to be effective in transmission analysis, control design and troubleshooting. Introduction Lever analogy introduced 30 years ago has been a key tool and widely used for transmission powerflow analysis, selection and control synthesis [ 1]. Since its invention, it is solely an inertia-based modeling tool for the transmission and drivetrain systems, which is not adequate to address the dynamic aspect of a transmission system, so that important NVH tendencies driven by certain drivetrain structures can be overlooked. As the transmission system grows with increased complexity due to more gear steps and electrification, new transmission related NVH issues emerges, some of which are closely tied to particular transmission architecture and its underlying dynamic properties [ 8]. Any architecture related issue can be difficult to resolve at a later stage due to the limited options. Therefore, the awareness and understanding of possible drivetrain structures and its dynamic nature has become important at the early stage of transmission design, and the transmission configurations with undesired dynamic properties can be avoided. To achieve this goal, an adequate drivetrain modeling and dynamic analysis tool are highly desired. Drivetrain NVH characteristics are important to vehicle drive quality, potential issues may be perceived by the driver include audible sound, drive torque and chassis, etc. To date, the drivetrain NVH-related studies have been mostly focused on the driving conditions with the transmission in gear, and the excitation forces mainly come from the exogenous inputs like the engine or brakes. Until recently, transmission design engineers have only focused on system inertias and their impact on shift quality and controls, the dynamic aspect of the transmission and drivetrain systems has largely been over - looked. In dynamic drivetrain system models, the transmis-sion is usually over simplified as lumped inertias and ratios. The drivetrain system dynamic characteristics involving transmission components during gear shifting are not comprehended in those models. As the industry raced toward transmission systems with more gear steps and different levels of electrification, new NVH related drive quality issues have merged. Such issues can usually be tra