EXPERIMENTAL ANALYSIS OF POWER LOSS AND NOISE CONTRIBUTION IN AXIAL PISTON MACHINES

In recent years, human activities have significantly contributed to climate change, with CO₂ being a primary driver, accounting for 75% of greenhouse gases (GHGs). This has led to noticeable increases in global temperatures. To mitigate these effects, effective strategies to reduce GHG emissions are essential. Off-highway vehicles (OHVs) contribute to 5% of the total CO₂ emission in the US and powertrain electrification has been identified as a solution to reduce their environmental impact. OHVs emissions, particularly from equipment like excavators, are highly influenced by the efficiency of their fluid power system components. At the core of these systems are hydrostatic machines, such as axial piston machines, which enable energy conversion between mechanical energy and fluid energy. These machines play a crucial role in the electrification of OHVs, where achieving a successful transition depends on developing highly efficient units with minimal noise emissions.

This thesis presents a detailed exploration of advancements in axial piston machine technology. A key contribution lies in the design and execution of experimental methodologies, including tribological investigations and noise, vibration, and harshness (NVH) analysis. This work emphasizes the complexity required in developing such experimental frameworks, highlighting the complex process of evaluating and enhancing axial piston machine performance for sustainable OHVs applications.

In particular, the work includes:

· Conceptualization, design, and procurement of a novel hydrostatic machine tribology test chamber.

· World-first measurement of piston-slipper interface frictional losses in an axial piston machine at low speeds, including near-zero rpm.

· Identification of high frictional losses in lubrication interfaces at low speeds.

· Discovery of a critical 5 rpm breakaway point, where peak torque is nearly 60% higher than 250 rpm. Highlighting the challenge of extreme low-speed friction, which can lead to startup stalls.

· Development of a simultaneous transfer path analysis method to pinpoint the root causes of axial piston machine noise (as part of a research team).

· Investigation of noise mitigation strategies, revealing that:

o Swashplate moment oscillations significantly contribute to machine noise.

o Displacement chamber pressure profiling techniques can effectively reduce swashplate moment oscillations.

· Experimental validation demonstrates a 6.4 dB noise reduction, confirming the effectiveness of the proposed technique.