Control and Integration Challenges for Future Automatic Transmissions

The ever-increasing regulatory requirement on CO2 emissions drives efficiency improvement of vehicle powertrain systems. In this context, three mega trends have been happening in the automotive transmission industry. First, future automatic transmissions will have more gear steps to offer a broader ratio spread and finer ratio steps, which may enable the engine to operate at its efficient regions more often. Second, engine downsizing with boosted power and flexible cylinder deactivation have been become the technology trend to achieve better thermal efficiency. These engine technologies demand improved transmission dampers with greater isolation capabilities to drive future transmission dampers to be equipped with softer springs. Third, future transmissions will be more efficient due to new architectures and incremental subsystem improvements. We have discovered that all three trends can impose significant challenges to make the future transmission controls and powertrain integration more difficult. This paper starts with a fundamental study on the automotive drivetrain system. The powerful analytical modeling and sensitivity analysis method developed allows us to gain deep understandings of the drivetrain system dynamic nature. The results are general and can help answer some long-standing questions on transmission controls, such as, what is the physics behind the shift vibrations? why are some shifts intrinsically more difficult to control than others? Through the theoretical analysis, we can identify the latent shift vibration tendency and the dynamic structures behind. As the transmission system continue to evolve, it becomes clear that controls and integration will be more challenging for future transmissions. Simple adaption of the control systems from the existing transmissions today may no longer be adequate to the transmission systems tomorrow.