Simulations and Measurements of the Vibroacoustic Effects of Replacing Rolling Element Bearings With Journal Bearings in a Simple Gearbox

Schematic of the NASA GRC test gearbox: (left) top view with lid cut away, and (right) side view

Finite element model of the NASA GRC gearbox: (right) part of the top cover and front and side walls removed to reveal the inner shafting and gear blanks, and (bottom) enlarged view of the shafting and gear blanks

Approach for coupling shafting and housing models—nodes and constraints

Ball bearing schematic and force-displacement relationships

Radial load-deflection and stiffness-deflection curves for the NASA GRC gearbox ball and roller bearings

Journal bearing stiffness coefficients around the bearing circumference at 79.1 N m (700 in.-lb) torque and 3000 rpm

Journal bearing damping coefficients around the bearing circumference at 79.1 N m (700 in.-lb) torque and 3000 rpm

Comparison between the (top) journal bearing radial stiffnesses, and (bottom) rotational stiffness magnitudes to those of the ball and roller bearings at the input side of the gearbox at 79.1 N m (700 in.-lb) torque

Journal bearing radial damping at 79.1 N m (700 in.-lb) torque and variable rpm

Measured and simulated top panel modes attached to the housing

Simulated and measured drive point mobility of the top panel at two drive points on the top plate

Measured gearbox mode loss factors, along with averaged curve fits for the top plate, shaft, top housing, and miscellaneous modes (no curve fit)

Simulated (right) and measured (left) transfer accelerances between the gear tooth loads (in line of action) and bearing accelerometers with the top panel removed: (top) vertical, and (bottom) horizontal (without accelerometer 3, which malfunctioned)

Radiated sound power and high frequency limit (piston) radiated sound power for the gearbox with rolling element bearings and drive in the LOA of the meshing gears

Measured averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 1 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

Measured averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 2 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

Vertical vibration at the rolling element bearing on the gearbox input side at 1 × GMF (upper left). Measurements at the NASA GRC, (upper right) simulations, (lower left) differences between gearbox vibrations with rolling element and journal bearings, 79.1 N m (700 in.-lb) torque.

Differences between the vibrations and noise from the gearbox with rolling element and journal bearings for measured and simulated averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 1 × GMF for several operational speeds (rpm), 79.1 Nm (700 in-lb) torque

Differences between vibrations and noise from gearbox with rolling element and journal bearings for measured and simulated averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 2 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

Standard single land journal bearing

Fluid film pressure distribution for the journal bearing

Effect of rotation about x (vertical) on the film pressure: (left) no rotation, and (right) with rotation—notice the slight asymmetry in the pressure field

Static gear transmission error for two torque conditions. The function is periodic around the shaft between 0 deg and 360 deg.

Harmonics of the gear transmission error at two torque conditions