The reduction of oil demand for automotive engines has been
driven recently by the need to reduce oil pump capacity so that
benefits from having a smaller size, including a reduction in power
loss and CO₂ emissions. Crankshaft bearings are generally
attributed to be the largest consumers, main bearings in particular
since the supply pressure in the upper bearing shell oil groove
over a large arc (circumferentially) coincides with high average
clearance.
Measurements of oil flow indicate that the main bearing groove
is significant and there is a trade-off between lower oil flow and
higher bearing temperatures. All solutions must ensure that the oil
supply to the big-end bearings via crank drillings is not
compromised.
Numerical simulation tools can be used to predict and optimize
the total oil flow required by the engine lubrication system. In
this work, the Elasto-Hydrodynamics Simulation (EHL) was used to
analyze the oil flow required by the crankshaft main bearings. In
addition, the influence of some crankshaft and bearing feature
designs such as, bearing clearances, bearing oil groove
configurations and crankshaft oil drilling among others, were
investigated in terms of oil flow requirements.
For the tested engine, the total oil flow requirement could be
reduced by 20% by reducing the size/capacity of the oil pump by
this amount with plain upper main bearings, using a
"1-to-2" crank drilling configuration. With the maximum
flow reduction via "plain" upper main bearings, a
temperature rise of 5-10°C was measured, but this did not
jeopardize the performance of the big end bearings in durability
tests.