Camshafts ensure that the charge-cycle valves in internal combustion engines are opened and closed reliably and precisely. These valves are located in the camshaft module, the standard material for which is still aluminium metal but automotive manufacturers and suppliers are putting great effort into making powertrains and components using lightweight designs. Weight reduction is one of the most effective methods for reducing CO2 emissions.
Researchers at Fraunhofer ICT in Pfinztal have developed a camshaft module made of thermosetting composite materials. This lightweight camshaft module was realised in cooperation with the MAHLE Group and associated partners Daimler AG, SBHPP/Vyncolit NV and Georges Pernoud. The German Federal Ministry for Economic Affairs and Energy (BMWi) has been funding the project.
For this project, the research team opted for high-strength, fibre-reinforced thermoset polymers, as they are well able to withstand high temperatures and mechanical and chemical stresses such as those caused by synthetic motor oils and coolants, for instance. The camshaft module is located in the cylinder head, so normally in the upper installation space of the powertrain. Here, it makes particular sense to reduce weight, since doing so also contributes to lowering the vehicle’s centre of gravity.
Castings made from aluminium require extensive reworking, resulting in high costs. Fibre-reinforced thermoset polymers allow near-net-shape manufacturing, thus requiring comparatively little reworking and which again leads to reduced production cost. Also, at up to 500,000 units, the service life of thermoset polymer injection moulds is significantly higher than that of aluminium high-pressure die-cast moulds. Furthermore, plastics reinforced with a high fibre content have a much lower CO2 footprint compared with aluminium, since this light metal is very energy-intensive to manufacture.
Another advantage of using these materials is the reduction in noise emissions. Rattling cars are not only annoying, but they are also a clear competitive disadvantage, so noise, vibration and harshness (NVH) characteristics are high up on the list of factors used to assess vehicle quality. Polymers have good damping characteristics.
The camshaft module features a monolithic design with integrated bearings – in other words, it is manufactured in one piece, thus reducing assembly time in the engine manufacturing plant. Car manufacturers receive a pre-assembled module from their supplier and can mount it on the engine with just a few simple mounting operations. This eliminates the need for separate, time-consuming installation of the camshaft. This innovative solution boasts an additional advantage: aluminium inserts in highly stressed areas of the camshaft bearings absorb the direct forces.
During initial tests on the engine, researchers observed positive operating performance, and weight savings were demonstrated compared with the aluminium reference part. They can produce camshaft modules made of thermoset polymer material much more easily than their counterparts made of light metal, and can even do it economically in an injection moulding process. Simulation calculations help engineers design and validate the prototype before the manufacturing process begins. Although the stiffness of the thermoset polymer is only a quarter of that of aluminium, design measures enable researchers to adhere to the maximum allowable deformation. After 600 hours of testing, the lightweight design element demonstrated flawless functionality in a state-of-the-art internal combustion engine. With the aid of the planned fuel injection tests, the project partners want to prove the functionality and the NVH characteristics taking the gas forces of the combustion process into account.