Date of Award

Summer 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor


Committee Chair


Committee Member 1


Committee Member 2


Committee Member 3



Improving energy efficiency, productivity, safety, and comfort of mobile machines is of utmost priority to original equipment manufacturers, suppliers, and consumers given the escalating fuel prices and increased awareness to the environment and workplace hazards. A major breakthrough in the realm of high power motion control is pump displacement controlled (DC) actuation, which does away with hydraulic valves for motion control and uses a variable displacement pump as both a flow source and final control element, thus eliminating throttling losses associated with hydraulic control valves. This work deals with researching and implementing DC technology for realizing the steering function of articulated frame steering mobile machines; however, the technology can be easily adapted to accommodate other applications and industries (aerospace, automotive, commercial, etc.) as well. ^ To realize the new steering technology, high fidelity dynamic models of the entire system including the electro-hydraulics and vehicle dynamics are first derived. Two controllers, linear and nonlinear (adaptive), are designed and validated in simulation and experimentally. System sizing and hardware implementation are then completed on a representative prototype test vehicle. Experimental testing results of a steering-only cycle performed on a compact wheel loader reveal a substantial improvement over the baseline machine in regards to fuel consumption reduction (-14.5%), productivity increase (+22.6%), and overall fuel efficiency improvement (43.5%). ^ A yaw stability control algorithm is developed to investigate the technology's capacity to increase the machine's safety via active steering control. The stability controller monitors the driver's desired trajectory, quickly intervenes when a deviation is detected, and smoothly relinquishes control back to the driver when the disturbance is attenuated. Advanced modern estimation techniques are employed to develop a virtual (soft) sensor for estimating the vehicle's yaw angle rate by combining available sensory data with the derived high-fidelity mathematical model. The output of the virtual yaw rate sensor is compared against that of an installed yaw rate sensor, and excellent correlation is obtained under various operating conditions.