There is a lot more to designing and manufacturing modern crankshaft bearings than many people realise. Designed to run reliably over a wide range of operating conditions, and using lubricants with viscosities so low they would have made engineers laugh as recently as 15 years ago, the high power ratings of modern engines places a growing demand on them. But with bearing shapes nowhere near circular and clearances between shell and journal measured in microns these days, how do we...
Readers may well be familiar with the concept of torsional vibration in an engine crankshaft. The situation where the intermittent torques fed into the crankshaft by the successive firing of the cylinders induces cyclical strain within the shaft – which, unchecked, can lead to component failure – is something most power unit engineers will have come across during their lifetimes. When the shaft is revolving at a speed such that the frequency of the repeated applied torques or one...
We could successfully argue that many plain bearings are actually little more than coatings, and that the shell is simply a carrier for the very thin layer of material which is doing the hard work for us. That would be ungenerous though, as plain bearings rely heavily on their backing to provide strength, adhesion and thermal conductivity. The shells also have a very important role to play in controlling clearances. However, some applications are sufficiently lightly loaded to allow...
In the RET-Monitor collection of articles, there are already dozens of articles covering con rods, many of them covering individual design features. The aim of this article though is to bring some elements of these together and give some of the basics of the design process. The first element we need to fix is size, which for many engine development projects will be fixed by the size of the existing crankshaft and the availability of bearings to suit. Where a bespoke engine is concerned, we...
In life there are many instances where we have to make decisions based on insufficient information or experience. I mention this because in applications where we have rotating axial flow fluid movers – a cooling fan, for instance – there are times when we as engineers do not have enough data, and decisions have to be made quickly as to the effectiveness of the design or installation. These decisions may not be potentially calamitous or affect the lives of many innocent people,...