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Fuel economy of both highway and off-highway vehicles is a major driver for new technology development. One of the technologies to meet this driver is a digital valve based hydraulic system. Digital Hydraulics technology employs high speed on/off valves to achieve the same functionality with no throttling loss. Furthermore, by forming various architecture by using digital valves, it provides the system level capability and flexibility for energy saving and productivity improvement. There are many challenges in fully realizing the full efficiency benefits of the system in an actual application. These challenges include packaging, durability, a change in the operator's perception of the vehicle as well as hydraulic system performances during operation. One significant issue is the noise, vibration and harshness (NVH) of the system. Due to the nature of the digital valve operation, there are severe transient dynamics in the fluid system.

Vehicle electrification is being actively expanded into coming generations of passenger and commercial vehicles. This technology trend is helping vehicles to become more energy efficient. For electric vehicle (EV) city bus application, the system designers have been experimenting with a number of options including direct drive and multi-speed gearbox architectures. Direct drive scenario offers simplified drivetrain system, however requires a large and powerful electric motor. Multi-speed transmission system provides an opportunity to reduce motor size and optimize its operating points, but increases complexity from the architecture and controls point of view. This paper provides an overview of several common system layouts and examines their advantages and disadvantages. Vehicle simulation results are presented to compare direct drive vs. multi-speed technology from the gradeability, acceleration and energy consumption points of view.

Extensive experimental and numerical investigations were done to improve the vibration and acoustic performance due to excitation at the timing gears of automotive supercharger. Gear excitation, system response, and covers have been studied to find the most cost efficient method for reducing gear whine noise. Initially, gear excitation was studied where it was found that transmission error due to profile quality was the dominant source parameter for gear whine noise. To investigate the system effects on gear noise, a parametric study was carried using FEM model of the supercharger, with special interests in optimizing dynamic characteristics of internal components and the coupling to supercharger housing. The BEM model of the corresponding supercharger was built to predict the noise improvement after dynamic optimization of the system. Good correlations were observed between experimental and numerical results in both dynamic and acoustic parameters.

Supercharger timing gears have been a source of rattle noise due to torsional vibration from the engine and sometimes have required torsional isolators to reduce the rattle noise significantly. Supercharger gear rattle is studied analytically and experimentally in this paper in order to understand to what extent basic design parameters could impact gear rattle noise to eliminate the need for isolators. A 3 DOF (degree of freedom) discrete model is used to represent a geared rotor system in the supercharger. A mathematical dynamic model is established in Matlab handling the non-linearity due to gear backlash. The fluctuation of input torque is used as source of excitation. A real time simulation technique is used for the analysis. Good correlation has been obtained between the experimental and analytical results. An index for comparing analytical results to gear noise and vibration level has been proposed.

An extensive experimental and numerical investigation was completed to improve the vibration and acoustic performance of a piston pump. A parametric study was carried out using an FEM model of the pump. The BEM model of the corresponding model was built to predict the noise levels and document the improvements during the dynamic optimization process of the system. Experimental modal and acoustic tests were done in order to verify the numerical results. Good correlation was observed between experimental and numerical results in both dynamic and acoustic parameters. Based on the modeling results, which were validated experimentally, design improvements were made.