Rubber V-belt Continuously Variable Transmissions (CVT's) are commonplace in the Baja SAE collegiate design competition, and are also used widely in the power sports industry. These transmissions offer benefits of simplicity in mechanical design, consisting of only two pulleys, and are easy to use. While most teams in the competition use commercially available designs, custom designs are becoming more common, and the Baja team at Virginia Tech has used custom CVT's since the 2014 season. The design of these CVT's has relied heavily on trial and error, requiring significant adjustments to be made during the testing phase. In addition, only qualitative information is known for the relationship between efficiency and design parameters, such as sheave angle. The goal of this thesis is to create an improved V-belt model that may be used as a design tool. This model provides quantitative information about efficiency that can be used to make more informed design decisions. The belt model also provides insight into the magnitude and relationship between the axial forces in the pulleys. This can be used to create an initial design that is more accurate, and possibly reduce the time required for tuning. A CVT dynamometer was constructed to validate the analytical results for efficiency, and this will also serve as a tuning tool for future Baja teams at Virginia Tech. This thesis will advance the state of the custom CVT design and testing process at Virginia Tech, and hopefully lead to improved results at competition in the future. / Master of Science / Baja SAE is an annual collegiate competition where students design and build an off-road vehicle. Many teams choose to use Continuously Variable Transmissions (CVT’s) in order to maximize the efficiency of the vehicle’s transmission. By continually shifting ratios, CVT’s allow internal combustion engines to always run at peak performance. There are several types of CVT’s, but the most common one used in Baja SAE and the power sports industry is a rubber V-belt design that is controlled mechanically with springs and flyweights. While these devices are used extensively, the underlying dynamics are not well-documented in literature. The Baja team at Virginia Tech builds a custom CVT every year for the vehicle, but the success of the design relies heavily on tuning through trial and error. A better understanding of the dynamics of the belt will result in better initial designs, and will help to reduce the amount of tuning required for the success of the design. This thesis offers an improved dynamic model for a CVT belt, and validates the results of this model through testing on a custom-built dynamometer. This model is also able to predict the efficiency of the transmission, and these results may be used to influence design decisions by predicting their effects on performance. The results of this research will improve the design process for a rubber V-belt CVT and hopefully lead to improved results at competition for the Baja team at Virginia Tech.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/85055 |
| Date | 19 September 2018 |
| Creators | Messick, Matthew James |
| Contributors | Mechanical Engineering, Kennedy, John Maurice, Wicks, Alfred L., West, Robert L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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