The Full Journal Bearing

Application of the Reynolds Equation to the Full Journal Bearing 

In applying the Reynolds equation to a real bearing, the film thickness h is expressed as a function of position in the bearing. In the journal bearing this is done as follows. Let a be the radius of the shaft and let us define the radial clearance c between the shaft and the 

Equation 2-35 gives the thickness of the oil film in a journal bearing at any point in terms of the angular distance of that point from F, where the film thickness is at a maximum (Fig. 2-7). 

To use the Reynolds equation for a journal bearing we change from 

Equation 2-39 cannot be readily solved as it is written. Osborne Reynolds obtained a solution for it in the form of a Fourier series which converges for eccentricity ratios less than 0.5 and is therefore useful only for lightly loaded bearings. The exact solution of A. Sommerfeld, details of which can be found in most of the standard texts on hydrodynamic lubrication of bearings, yields the following expression  

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Plain radial, or journal, bearings also are referred to as sleeve or Babbit bearings. The most common type is the full journal bearing, which has 360° contact with its... 

Figure 2-8. Comparison of theoretical and experimental friction for the full journal bearing.

To calculate the friction in a full journal bearing we have recourse to Eqn 2-26, using the fact that at the surface of the journal the velocity is U and 1 = 0. The tangential stress at the journal surface is then... 

The classical Reynolds boundary conditions are associated with Reynolds equation. An inlet groove is located on the load line for a full journal bearing and at the beginnning of each pad for a multilobe bearing. 

Experiments with journal bearing have put forward a higher load capacity for cylindrical bearings, and, on the other hand, a better whirl resistance for lobed bearings [4,5] (especially the full offset bearing). 

Herzig" also studied the effect of dispersed molybdenum disulphide in a hydrodynamic bearing, and showed that, where full fluid film lubrication Is not present, dispersed molybdenum disulphide can decrease friction. The coefficient of friction in an oil-lubricated journal bearing is related to the Sommerfeld Number ZN/P where Z Is the viscosity, N the rate of rotation, and P the bearing pressure or specific load. Figure 13.2 shows some empirical relationships between coefficient of friction and the Sommerfeld Number for an oil with different concentrations of dispersed molybdenum disulphide in a foil bearing . 

BEARING, FULL JOURNAL - A journal bearing that surrounds the journal by a full 360°. 

This Is given In full by Lamor (14) but as It concerns us so closely I thought It worth reproducing In full (Figure 2). It shows clearly that Stokes had found the solution of hydrodynamic lubrication of a Journal bearing. 

The process of flow mixing at the inlet to a starved hydrodynamic bearing differs in a number of respects from that of a full-film bearing. A schematic of flow mixing in a journal bearing is shown in Figure 3. The major differences for starved conditions are ... 

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