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

Connecting rod

The MCE‑5 rod is short compared to the piston’s effective stroke. Its small end is housed in the gearwheel rather than in the piston, as is the case for conventional engines. The body of this rod has a small section to avoid any interference with the gearwheel that houses it. The MCE‑5 rod has 2 axial guides: one on the bottom to guide it with respect to the crankshaft and the other at the top to guide the gearwheel. The main characteristic of the MCE‑5 rod is that it can resist tensile stress levels roughly 5 times higher than the maximum stresses applied to conventional car engine rods.

The MCE‑5 VCRi connecting rod is designed
for forging and is cracked, like most
conventional connecting rods

These high tensile stresses come from the reciprocating mass of the MCE‑5 piston and gearwheel that produce free inertia forces comparable to those of a small Diesel engine. In the end, these stresses are multiplied by 2 due to the MCE‑5 mechanism. The tensile stresses on the rod are roughly twice the inertia forces of a Diesel engine running not at 5000 rpm but at 6500 rpm. The compression forces are however lower than those found on modern Diesel engines operating with in-cylinder pressures that can reach up to 200 bar.

The lubrication of the small end of the MCE‑5 rod was previously ensured through ducts traversing the rod. This configuration has now been replaced by a more conventional solution for reasons of cost and because bringing the oil up through the rod made the operating conditions more severe for the crank bearings (need to create a groove in the rod). The latest versions of the MCE‑5 rod have tapered small ends and oil distribution grooves in the bushing that recovers the oil and brings it to the center of the joint.

The bushing of the small end of the rod is “double trumpet” shaped in the axial direction to follow the distortion of the pin, and is slightly oval in the radial direction to create an oil reservoir and improve oil convergence.

MCE‑5 rods are designed to be forged and cracked, using the same processes and materials as those currently used for mass-produced rods.

The main characteristic of the MCE‑5 VCRi connecting rod is its resistance to very high tensile stress

The MCE‑5 VCRi connecting rod no longer poses any manufacturing problems. This is particularly true
for its latest version that has no lubrication conduits from big end to small end

The main characteristics of the MCE‑5 VCRi connecting rod