Page 360 - The Tribology Handbook

C16 Dip, splash systems

WORM GEARS GENERAL DESIGN NOTES
Typical under-driven worm gear unit Gears

In dip-splash systems, a large oil quantity is beneficial in
removing heat from the mesh to the unit walls and thence
to the atmosphere.
However, a large quantity may mean special care has to
be paid to sealing, and churning losses in gears and bearings
may be excessive. It is necessary to achieve a balance be-
tween these factors.
Other applications

The cylinders and small-end bearings of reciprocating
compressors and automotive internal combustion engines
are frequently splash lubricated by oil flung from the
Figure 16.6 rotating components. In these applications the source of
Oil is churned by the worm and thrown up to the top the oil is usually the spill from the pressure-fed crankshaft
and sides of the case. From here it drips down via the wheel bearings. In some small single-cylinder compressors and
bearings to the sump. four-stroke engines, the cap of the connecting rod may be
A simple lip seal on a hard, ground shaft surface, prevents fitted with a dipper which penetrates up to 10 mm into the
leakage. oil in the sump and generates splash lubrication as a result.
Oil level generally just below worm centre-line. In lightly loaded applications the big-end bearings may also
An oil scraper scrapes oil into a trough to feed the wheel be splash lubricated in this way, and in some cases the
bearings. dipper may be in the form of a tube which scoops the oil
directly into the big-end bearing. In small domestic
refrigeration compressors, a similar system may also be
Typical over-driven worm gear unit used to scoop oil into the end of the crankshaft, in order to
lubricate all the crankshaft bearings.
Similar to under-driven worm gear unit except that the
worm is over the wheel at the top of the unit, and the oil
level varies in depth from just above wheel tooth depth to
almost up to the centre line of the wheel, depending upon
speed. The greater the speed, the higher the churning loss,
therefore the lower should be the oil level. At low speeds,
the churning loss is small and a large depth of oil ensures
good heat-transfer characteristics.

C16.2