ABSTRACT The achievable shift quality of a modern automatic transmission may be greatly affected by the equivalent rotational inertia of the gearbox and driveline components. New, more mass- and packaging-efficient higher number of gear powerflows are being developed. These new architectures often result in more components being attached to a given rotational node. The rotational speed multiplication of the components must be considered when determining their inertial torque contribution to a given speed change event. An example of this multiplication effect is presented, with a discussion of the resulting impact to shift quality disturbance. Opportunities to address the negative aspects of the higher inertial torque contribution to transmission output shaft disturbance are discussed. Coordination of engine torque control and clutch torque control is presented as a viable strategy to improve shift quality. Higher magnitudes of clutch torque and engine torque management are required to achieve fast shift times with desirable shift feel. The concerns with this approach may include customer perception of the torque interrupt, the ability to ramp in and out the engine torque in the allowable shift time, and the potential to affect emissions diagnostic compliance. Another concern may be the ability to ramp up and down the clutch torque in the allowable shift time. A discussion on the trade-off between faster inertia phase shift times and rate of change of transmission output torque is presented. Analysis is performed using system simulation via math models of the physical system. INTRODUCTION The number of speeds available in automatic transmissions has been on a steady climb over the past three decades. Additional number of speeds increase the overall ratio spread of the transmission, enabling improvements in both performance and fuel economy. Recent regulatory (greenhouse gas emissions) and competitive (marketing of advanced technology) pressures have accelerated the trajectory of this trend line, as illustrated in Figure 1. Figure 1. Trend of Increasing Number of Speeds While the number of speeds available in automatic transmissions has been on the increase, the available packaging space for the outer envelope of the transmissions has not increased correspondingly. This has challenged the automatic transmission designer to identify and develop innovative gearset configurations, or “powerflows”, that allow additional gear ratios to be obtained without extensive additional kinematic content. Automatic Transmission Rotational Inertia Effect on Shift Quality2011-01-0393 Published 04/12/2011 John Marano, Steven Moorman, John Czoykowski and Chinar Ghike General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-0393Downloaded from SAE International by Imperial College London, Monday, September 24, 2018These new, compact powerflows often result in high internal speed multiplication of rotational components. These relatively high internal speeds can generate high inertia torques during ratio changes. Compounding the engineer's challenge, the industry trend to reduce the time it takes to complete a ratio change results in higher inertial torques, which must be managed. While automatic transmissions with higher numbers of gears generally have smaller ratio steps between successive gears, the effects of the higher rotational speeds and desirable reduced ratio change times often more than offset this relative advantage. We will further explore this subject through the introduction of a concept of an “equivalent nodal inertia” and a descriptive “k-factor”. Analysis of a representative powerflow will follow, illustrating the effect of this higher inertia's contribution to shift dynamics. EQUIVALENT NODAL INERTIA A transmission powerflow may be described as a unique combination of “nodes”, or grouped components of non- variable kinematic connections. These nodes are connected via variable kinematic components, such as