Journal Bearing Pressure-Fed

Hydraulic portion of pressure-fed journal bearing

Orifices

Description

The Journal Bearing Pressure-Fed block simulates the hydraulic portion of a pressure-fed journal bearing, shown in the following illustration.

The lubricant under pressure p is pumped into the circumferential groove at the center of the bearing. The groove divides the bearing into two half-bearings. The lubricant exits through the end grooves located at a distance l from the central groove. The model is intended to be used in lubrication system simulation to assess the flow consumption through the pressure-fed journal bearing. The flow regime is assumed to be laminar due to very small clearances between the journal and the bushing.

The flow rate is computed using the Hagen-Poiseuille equation (see [1]):

`$q=\frac{\pi pr{c}^{3}}{3\mu l}\left(1+1.5{\epsilon }^{2}\right)$`

where

 q Volumetric flow rate p Pressure differential across the bearing r Journal radius c Radial clearance at neutral position μ Dynamic viscosity l Length of the half-bearing ε Relative eccentricity, ε = e / r e Eccentricity or journal deflection from the central position

The journal radial displacement, which controls the bearing eccentricity, is imported through the physical signal port J. Connections A and B are hydraulic conserving ports associated with the bearing inlet and outlet, respectively. The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B and the pressure differential is determined as $p={p}_{A}-{p}_{B}$. Positive signal at the physical signal port J increases the eccentricity and is limited to the radial clearance of the bearing.

Basic Assumptions and Limitations

The flow regime is assumed to be laminar due to small clearances.

Dialog Box and Parameters

The radius of the journal. The parameter must be positive. The default value is `0.05` m.

The radial clearance between the journal and the bushing at neutral position. The parameter must be positive. The default value is `2e-4` m.

Bearing half-length

The length of the half-bearing, that is, the distance between each of the end grooves and the central groove. The parameter must be positive. The default value is `0.025` m.

Global Parameters

Parameters determined by the type of working fluid:

• Fluid density

• Fluid kinematic viscosity

Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.

Ports

The block has the following ports:

`A`

Hydraulic conserving port associated with the bearing inlet.

`B`

Hydraulic conserving port associated with the bearing outlet.

`J`

Physical signal port that controls the journal deflection.

References

[1] Shigley, J., C. Mischke, and R. Budynas. Mechanical Engineering Design. New York: McGraw-Hill, 2004.