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68 Chapter Three
Figure 3.21 Rocker pivot tilting-pad journal bearing.
(Salamone Turbo Engineering, Houston, Tex.)
symmetric about the vertical axis, the cross-coupled stiffness terms are
eliminated. The number of pads utilized in the tilting-pad bearing can
be three, four, five, or seven. However, the most common tilting-pad
bearing arrangements have four or five pads. The rocker pivot and the
spherical pivot arrangements are illustrated in Figs. 3.21 and 3.22,
respectively. The rocker design has a line-contact pivot between the
pad and the bearing retainer. As the name implies, the spherical design
has a semispherical surface-contact pivot. Both of these designs allow
the pads to pitch in the conventional manner. However, the spherical
design has the additional ability to accommodate shaft misalignment.
3.2 Key Design Parameters
The discussion of preload brought out the distinction between two dif-
ferent bearing bores. These are pad machined bore and bearing set
bore. Note that the plain journal, axial groove, and pressure dam bear-
ings have only one bore (the set bore is the same as the pad bore). The
difference between the pad machined bore radius and the journal
radius is the pad machined clearance. The difference between the bear-
Figure 3.22 Spherical pivot tilting-pad journal bearing.
(Salamone Turbo Engineering, Houston, Tex.)
