Frictional behaviour of experimental synthetic and semi‐synthetic gear oils

The use of synthetic and semisynthetic lubricants combined with a proper selection of additives, can help reduce friction between gear teeth, as shown on a tribometer simulating gear tooth contact. Accurate efficiency measurements on a loaded industrial power divider show good agreement with friction measurements on the tribometer, except for the viscosity effects that appear not to be significant in the simulated gear tooth contact and are an influencing parameter in the gear box. Changing the viscosity grade from 320 to 100 can reduce the friction losses by about 20%, but such an improvement has been found with a fully synthetic lubricant with a very high performance additive treatment, without any risk since the viscosity grade was 220. The effect of the additive was assumed to be about 5%; the overall friction reduction was about 20%. In worm gears, significant improvements are also achieved with the synthetic oil (about 8% efficiency increase), but the best energy saving fluids appear to be polyglycol base lubricants (with a measured efficiency improvement of about 17%).