Chunhao Lee

Study of a Non-Circular Gear Infinitely Variable Transmission

Improving automobile fuel efficiency is an important research and development effort in the automotive industry. In the transmission area, it is generally understood that optimum fuel economy can be achieved via a combination of highly efficient power transfer (gears, for example) and an ability to transmit power at an infinite number of ratios (CVT, for example). In this paper, a geared infinitely variable transmission (IVT) is analyzed for efficiency through static analysis. This IVT is based on a non-circular gear concept described in [1, 2]. This IVT consists of multiple function generators with each function generator comprising two sets of non-circular gear sets whose outputs are combined with a summing planetary gear set. Each function generator provides the desired gear ratio for only a part of the driving rotation. So, multiple function generators are combined along with multiple one-way clutches to provide an infinitely variable transmission.This paper first explains the operating principle of the geared IVT. A static analysis of the IVT powerflow is derived and it is shown that this powerflow exhibits a torque recirculation phenomenon, which is not desired. This recirculation phenomenon is expected to be present in all similarly arranged IVTs where two inputs are combined using a planetary gear set to provide infinite gear ratio capability. The efficiency of the IVT is calculated based on assumed individual component efficiency and it is shown that, owing to torque recirculation, the efficiency of this transmission may not compare well with that of current automatic transmissions for a passenger car application.© 2014 ASME

Design, modeling, and analysis of wedge-based actuator with application to clutch-to-clutch shift:

Clutch-to-clutch shift technology is a key enabler for fast and smooth gear shift process for multi gear transmissions. However, conventional hydraulic actuation systems for clutches have drawbacks of low efficiency, oil leakage and inadequate robustness. Electromechanical devices offer potential alternative actuators. In this paper, a novel motor driven wedge-based clutch actuator, featuring self-reinforcement, is proposed. The design concept and physical structure are thoroughly described. Dynamic models for the actuation system and vehicle powertrain are validated by experiments. Upshift and downshift processes at different engine throttle openings, clutch clearances and friction coefficients are discussed. The results show that, the self-reinforcement ratio is tested as 9.6; at the same time, the shift quality is comparable to that of the conventional hydraulic actuated clutch in automatic transmissions in terms of the shift duration (about 1 s) and vehicle jerk (<10 m/s3). Taking advantage of fast response of the actuation DC motor, the wedge-based actuator is robust dealing with uncertain clutch clearance and friction coefficient. Therefore, the wedge-based clutch actuator has potential to provide acceptable performance for clutch-to-clutch shift.

Experimental and Control Study of Slipping Decay Time of a Wedge Clutch in an Automatic Transmission

A wedge clutch with a wedge ramp transfers the tangential force into an axial force. It has unique features of self-reinforcement, and can be packaged into tight spaces. This wedge clutch is developed to apply to an automatic transmission as an implementation example.The slipping decay time is found to be critical for the shifting quality. This paper focuses on the experimental study and control of slipping decay time of the wedge clutch through the influencing factors. The mechanical system of the wedge clutch applied in an automatic transmission is described and the sensors for measuring signals are installed. A transmission dynamometer is set up for experiments.The torque magnitude and direction of the motor motion are considered as actuation factors; the driveline input speed, load torque, and oil temperatures are considered as the driveline factors. The results show how influencing factors affect the slipping decay time during gear shifting.© 2012 ASME