MCE-5 VCRi: Pushing back the fuel consumption reduction limits

We don’t know how to manufacture the parts

Many technologies did not see the light of day or were long to develop because of unresolved mass-production problems. This was the case of Diesel or gasoline direct injection applied to automobiles, as the required level of precision remained unreachable for a long time. However, it’s not because a technology is not manufacturable at a certain point in time that it will not be so 10, 20 or 30 years down the road. Progress made in computer-assisted design, in forging, forming and machining processes, in materials and surface treatments progressively offer more possibilities to manufacture parts that were previously impossible to produce. Similarly, the progress made in microelectronics, computing and mecatronics make it possible to intelligently and accurately control very demanding technologies.

The MCE‑5 VCRi production route sheet has been
studied and optimized according to multiple
industrial, functional and economic criteria

The characteristics obtained for mass-produced
MCE‑5 components meet the most
demanding specifications

Since the start of the MCE‑5 project, the developers have been conscious of the need to provide the required answers for mass-production and so, right from the outset, they integrated into their approach the need to find manufacturing solutions for the different engine components. It was indeed very important to start this work early since the design of the components was strongly impacted by manufacturing constraints. For example, for the forged parts, their shape and particularly the edges, the connecting radii and the way in which the material is offset by the pressure of the forge die have a direct incidence on the service life of the tooling. It was necessary to simultaneously set up the most appropriate forging route sheet, adapt the parts to the forge constraints and improve the forging process.

The complexity of these approaches lies in the fact that a part that is modified to take into account industrial constraints must be revalidated through testing. Moreover, different compromises must be found within a single manufacturing route sheet to ensure that the blanking, forming, machining and finishing processes all cooperate for the best result without overloading one or another stages of the process. For example, precision forging reduces the amount of material removed during machining, but it is more complex to develop. If the finishing process is naturally efficient and productive, it’s possible to accept a “rougher” forged part than if the process is slow and expensive. A deep hardening material will lead to less distortion and will reduce the material to remove from the part during finishing. Much iteration is necessary before reaching a functionally and economically convincing final result.

The trickiest MCE‑5 VCRi parts are undeniably the gearwheels and racks. These parts are complex, highly loaded and extremely precise. Moreover, they require a variety of chemical surface (carburizing), mechanical (shot peening, tribofinition) and thermal (hardening) treatments. The development of their manufacturing processes cost roughly 5 million euros and required 5 years of research and experimentation on mass-production tools. The main efforts were focused on “Netshape” or “near Netshape” forging (close to the finished shape). In parallel, the adaptation of precision electrochemical machining to the specific characteristics of the parts was an important topic of investigation: the hollowed racks do not provide room for the tool, making it impossible to use shaping or grinding wheels. The carburizing and hardening processes associated with the selected steel grades were also studied in depth.

The end result is that the innovative MCE‑5 parts can now be mass-produced under excellent functional and economic conditions, in the same way as its less innovative components nevertheless impacted by this new architecture: connecting rod, piston, crankshaft and crankcase.

The mass production of the MCE‑5 engine is now a problem solved. The learning phase during the first years of production will nevertheless be an opportunity to further improve in order to reduce by as much as possible the already very affordable price of MCE‑5 VCRi.

All of the MCE‑5 component manufacturing stages were optimized in terms of costs and product/process