Composites
The FIA regulations governing the materials used for the construction of Formula One engines prohibits the use of composites for major structural components, and this is set to continue, despite the fact that it is planned to use composite cylinder blocks on a much lower budget race engine soon. However, just one bolted joint away from the engine is the transmission, and there are no such regulations which affect the transmission case. Although composites have not been universally adopted, they are legal and have been used by several Formula One teams for more than a decade.
In a previous RET-Monitor article giving an overview of the use of composites in the racing powertrain, some of the potential advantages of a composite main case were mentioned. These were not simply concerned with mechanical or physical properties; the complex manufacture of a composite case means there are inherent risks compared to a metallic case. Without wanting to over-simplify the manufacturing route of a metallic case, it is generally a question of making a casting and then machining it. A composite case is much more laborious and requires much greater human input. There is a large number of individual plies that are manually positioned, having been automatically cut, and there are a lot of metallic ‘hard points’ to be incorporated into the composite case which then require machining.
Where metallic cases are essentially homogenous, composites have the advantage that their properties can be ‘tuned’ to achieve a desired result. For example, this can be through judicious use of unidirectional fibres to increase stiffness in a given direction. This is the main mechanical benefit of a well designed composite case, but it is not the only potential improvement over one made from metal. Composites have a low thermal conductivity compared to metals, so the transmission of heat through the walls of the main case is reduced.
Some time ago I discussed the merits of composite transmission cases with an engineer from a now-defunct Formula One team. He said the decrease in thermal energy being transferred through the case resulted in a net reduction in cooling requirement. There is clearly going to be lower heat rejection through the walls of the case, which one might expect to lead to increased transmission oil temperatures and increased cooling requirements. However, this was more than compensated for by a reduction in the amount of heat absorbed by the transmission from nearby hot components, notably parts of the exhaust system from which the transmission case was not sufficiently protected by heat shields. Of course, the amount of heat transfer to the transmission oil through the walls of the case is affected greatly by the proximity of the exhaust, and the current regulation requiring the exhaust to exit on the top deck of the rear bodywork might reduce the amount of heating that would affect the transmission oil.
With the adoption of turbocharged engines in Formula One from 2014 onwards, plus some high-powered electrical machines being used to increase efficiency, we might expect the matter of heat transfer to play a greater part in the selection of transmission case materials in future.
Written by Wayne Ward