CASE STUDY USING PISDYN OF THE EFFECT ON ... - Ricardo

Wear and friction simulation
Simulation type A showed that increasing the connecting rod length would reduce skirt friction
loss by 1.0%. The maximum instantaneous wear load and maximum cumulative wear load were
also predicted to be lower if the longer connecting rod is used, so scuffing or excessive wear
should not occur if the longer conrod is used.
The wear pattern predicted by simulation type B if the longer connecting rod is used is shown in
Figure 7. This is clearly suitable and as seen by comparison with Figures 1 and 2, quite
comparable to that produced when the original connecting rod was used.
CONCLUSIONS
The conclusions of the feasibility study using PISDYN of the effect on piston performance of
increasing the connecting rod length by 7.9% in the particular four-cylinder petrol engine are:
1. There will not be a danger of piston scuffing and the wear pattern will have little change.
2. There will be little change in skirt frictional power loss.
3. There will be little change in “croak” noise.
4. There will be a significant increase in “rattle” noise amounting to about five decibels.
Given the piston was found to be very quiet under “rattle” conditions when the original
conrod was used, it is possible that the “rattle” noise with the new connecting rod will
still be acceptable.
The broader conclusions of this work are that:
1. The PISDYN simulation package can be used to successfully optimise skirt profile, skirt
contour, pin offset and other piston specifications to meet quietness, wear resistance,
friction and durability design requirements.
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