Identifier

etd-030613-094613

Abstract

Kinetic energy storage via flywheels is an emerging avenue for hybrid vehicle research, offering both high energy and power density compared to more established electric and hydraulic alternatives. However, connecting the high speed flywheel to the relatively low speed drivetrain of the vehicle is a persistent challenge, requiring a transmission with high variability and efficiency. A proposed solution drawing inspiration from the electrical domain is the Switch-Mode Continuously Variable Transmission (SM CVT), which uses a high speed clutch to transfer energy to a torsion spring in discrete pulses with a variable duty cycle. The greatest limitation to the performance of this system is the speed and efficiency of commercial clutch technology. It is the goal of this thesis to develop a novel clutch which meets the actuation speed, controllability, and efficiency requirements of the SM CVT, with potential for reapplication in other rotary mechanical systems with switching functionality.

The performance demands of the clutch were derived via a theoretical design case based on the performance requirements of a typical passenger vehicle, indicating the need for a sub-millisecond engagement and disengagement cycle. This is not met by any conventional clutch. Several concepts were considered across the fluid, electromagnetic and mechanical energy domains. A final concept was chosen which employs a friction disk style architecture, with normal force produced by compressing springs via an axial cam mounted to the flywheel. To control duty cycle, the cam was designed with a radially varying profile such that increasing radial position results in proportionally increasing ratio of high dwell to low dwell. Three synchronized followers are then translated radially on the cam by a control linkage. Analysis of the follower train dynamics and system stiffness were carried out to inform the design of a scaled benchtop prototype. Experimental testing was carried out to characterize the performance of the prototype. It was found that the intended functionality of the design was achieved, with discrete energy transfer accomplished via pulsing of the clutch. However, maximum efficiency was only 33% and torque capacity was only 65% of the intended 70Nm. Significant opportunity exists for improvement of the clutch performance in future research.

Publisher

Worcester Polytechnic Institute

Degree Name

MS

Department

Mechanical Engineering

Project Type

Thesis

Date Accepted

2013-03-06

Accessibility

Unrestricted

Subjects

transmission, CVT, clutch, switch-mode, flywheel, hybrid, cam

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