Whether you are racing a go-kart or a Formula One car, the bearings that allow the reciprocating parts to rotate are of vital importance to both durability and performance. The sphere of Formula One engine development, while not unique, provides one of the sternest tests for bearing design, notably thanks to the ever-present battle to find a compromise between strength and frictional efficiency. For example, the development of ever-lower viscosity lubricants to reduce parasitic losses presents a host of challenges for engineers trying to ensure bearings do not degrade at too rapid a rate. In this month’s article we will investigate the efforts of the Honda Formula One team in its development of bearings for its V8 era engine.
Although in the past Formula One engines have used rolling element bearings for applications such as the main and rod bearings, in recent times plain journal-type bearings have been the favoured solution. One area that Honda focused on with its bearing developments was the con rod big-end bearings. In physical terms, these were similar in size to those one would expect to find on a mass-production engine of 600 cc or so; however, the loads they experience are substantially greater. According to data from the bearing development programme, Honda showed that a standard production bearing can expect to experience loads in the region of 20 kN vertically and 5 kN horizontally. By contrast, the Formula One rod bearing saw loads of 50 kN and 20 kN respectively.
As engine speeds rose throughout the first decade of the 21st century, and regulations demanded longer service lives from power units, Honda began to find that its existing bearing solutions were not up to the task, and occurrences of bearing damage or failure started to become common. This led the team to investigate new bearing materials and designs. The solution was a move to a silicon-bronze bearing material, instead of the copper-steel bi-metal bearing type it had been using.
The existing bearings were of quite traditional construction, with a steel backing supporting a copper-lead intermediate layer that was topped with a thin coating of an alloy containing lead, copper and silicon. This bearing make-up provided low friction, but could not withstand the high contact pressures of the Formula One application and could not effectively dissipate the high levels of heat built up under running conditions.
The silicon-bronze bearing, however, was constructed without a steel backing, consisting instead simply of a silicon-bronze lining coated with a thin layer of lead-indium. While having marginally lower ‘slideability’ and a lower level of heat dissipation than the pure copper material, it provided a bearing shell that was stronger in all respects than the steel-copper item. Also, the heat transfer rate of the whole bearing assembly was higher than the copper-steel item, as the steel – which has relatively poor thermal conductivity – was removed from the equation.
The results of using the new material were impressive: its greater strength and heat dissipation characteristics allowed lower-viscosity oil to be used, reducing windage losses. More important, bearing failures became rare, allowing the engines to exceed the regulation-imposed working life of 1500 km.
Written by Lawrence Butcher