Degree Type


Date of Award


Degree Name

Master of Science


Mechanical Engineering


Mechanical Engineering

First Advisor

Atul G. Kelkar


The research presented in this thesis provides a methodology of designing, modeling and controlling a fully pneumatic semi-active vibration isolator system. The prototype vibration isolator system has the ability to adjust the damping and natural frequency characteristics of the system. It consists of an air spring, a variable orifice valve, and an accumulator. In this conguration, the spring characteristics are provided by the air spring and accumulator, while the variable orifice valve provides the damping characteristics. The valve is computer regulated according to the innovative control laws that were developed for the pneumatic system. The

vibration isolator system is designed to work in the vibration environment that is typically observed in the case of Class 7 and 8 vehicles as dened by the U.S Department of Transportation Federal Highway Administration. In order to design a vibration isolator system for the intended application, a benchmarking study was conducted to gain additional insight on OEM vibration isolator systems features and limitations. Based on the insights obtained from this study, the design requirements for the system were dened.

This paper presents a methodology of producing a plant model that is based on supplier's engineering specications and experimental characterization. The plant model includes a complete characterization of nonlinear pressure to volume and eective area to ride height relationships. A detailed design process of selecting and implementing components to optimize system performance is also provided. The plant model was then used to design three semiactive controllers that use position and pressure feedback signals that exploit the nonlinear characterizations to measure direct force generation. The semi-active controllers that were designed for this novel pneumatic vibration isolator system include: a LQI (Linear Quadratic Impulse) optimal controller, Modied Skyhook controller, and a Relative Displacement controller. This vibration isolator system was designed, fabricated, and tested using a prototype

electronic height control system. A comprehensive design process for the specialized height control system is also presented.The performance of the system was evaluated using a custom testing apparatus that was built specically for this vibration isolator research. The testing apparatus was designed to accommodate dierent isolator systems and excite them with simulated road disturbances to obtain head-to-head system comparisons. This research presents a comparison between the system performances of an OEM Peterbilt cab suspension unit and the innovative fully pneumatic semi-active vibration isolator prototype using the three dierent control laws. It was found that the properly tuned controllers were able to provide desired dynamic characteristics

over the range of common ride frequencies.


Copyright Owner

Hans William Schaeffer



File Format


File Size

135 pages