The crankcase forms the core structural component of the engine, on to which all other components are mounted. The design aims for the crankcase were to increase the structural robustness whilst minimising mass, increase efficiency of oil passages, and simplify assembly operations.

During the FE study of the crankcase it became apparent that to meet the life targets it would be necessary to use a high performance casting aluminium. Ilmor worked closely with its casting supplier and through technical collaboration it was decided that A354 would be a suitable material for the crankcases, barrels and cylinder heads.

A354 shows good fluidity, resistance to hot cracking and pressure tightness. It is more difficult to machine than other casting alloys, but in return it gives excellent mechanical properties and fatigue life across the entire engine operating temperature range.

Crankcase main bearing inserts

In some automotive engines, cast-in spherical graphite iron or alloy steel inserts are used in areas of high stress concentration. This locally enhances the structural properties whilst still largely maintaining the mass benefits of using an aluminium alloy for the bulk of the component.

The use of steel inserts for engine main bearing housings provides increased strength and favourable thermal expansion properties over aluminium.

It is believed that the use of cast-in steel main bearing inserts in an aerospace application is novel.

Each half of the Ilmor crankcase design uses five individual 817M40 steel inserts cast into the A354 aluminium bulk structure. This arrangement replaced the SMA design of separate alloy steel ‘Main Bearing Saddles’ which were clamped between the aluminium crankcase halves during engine assembly. This not only gives a more robust design solution by reducing the number of joint faces in the assembly, but simplifies the manufacture significantly.

Illustration showing the steel main bearing inserts of the prototype engine

Figure 2 - Illustration showing the steel main bearing inserts of the prototype engine

The design of the inserts focussed on generating a shape which maximised strength without compromising the mass of the complete crankcase. The inserts feature several details which ensured good ‘mechanical’ locking to the aluminium casting.

A comparison with the original SMA arrangement is shown below:

Comparison of main bearing inserts

Figure 3 - Comparison of main bearing inserts
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This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 686533