Date of Graduation

2003

Document Type

Thesis

Degree Type

MS

Committee Chair

Victor H. Mucino

Committee Chair

Victor H. Mucino

Abstract

Continuously variable transmissions (CVTs) have an infinitely variable ratio, which allows the engine to operate more time in the optimum range given an appropriate control of the engine valve throttle opening (VTO) and transmission ratio. In contrast, traditional automatic and manual transmissions have several fixed transmission ratios forcing the engine to operate outside the optimum range. Usually CVTs are used in small vehicles due to power limitations of the variable elements. Continuously variable power split transmissions (CVPST) were developed in order to reduce the fraction of power passing through the variable elements. This configuration includes a planetary gear train (PGT), which allows the power to be split and therefore increase the power envelope of the system. The PGT also provides a branch that can be used in a hybrid electric vehicle (HEV) operation through an electric motor. HEVs are receiving special attention nowadays because they require a smaller internal combustion (IC) engine than they do in normal vehicles and consequently represent savings in fuel. HEVs generally employ conventional automotive transmissions. In this thesis a conceptual design for a CVPST for a HEV is presented, with increased power envelope in the system for a sport utility vehicle (SUV) application. A LabVIEW® program has been developed, which according to the vehicle characteristics, driving resistance coefficients and power source data, provides engine-vehicle velocity relationships, CVT ratio, variable pulley radii, belt force and power trace following the ideal fuel consumption curve. This thesis aims at extending CVT applications in the automotive industry to bigger vehicles (and engines) such as pickup trucks and perhaps small buses.

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