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

Synchronized roller

The MCE‑5 synchronized roller guides the lower part of the piston-rack assembly. It always remains at the same altitude from the gearwheel so that the lowest possible radial stress is applied to the combustion piston skirt. This altitude does however vary when the compression ratio varies. The roller offset with respect to the gearwheel can reach up to 3.15 mm at minimum compression ratio.

Weighing only 72 grams, the synchronized roller
is the smallest and lightest component of
the MCE‑5 VCRi moving parts assembly

The synchronized roller indirectly serves as a support for the MCE‑5 rod to generate torque on the crankshaft by reaction with the crankcase. Thus, the rod no longer pushes against the cylinder via the piston as is the case in a conventional engine. It pushes on the synchronized roller and the rolling surfaces of the gear system, which comprises the gearwheel, the piston rack and the control rack. This configuration is responsible for the highest reduction in friction losses generated by MCE‑5 technology: the radial stress ordinarily taken up by piston is replaced by pure rolling taken up by the synchronized roller and the rolling surfaces. Hence, only the cylinder head and the crankcase react with the rod via the rolling system to transmit forces to the crank. The cylinder no longer participates.

The MCE‑5 synchronized roller is placed between two rolling surfaces, one on the crankcase and the other on the backside of the piston rack. The synchronized roller is maintained in a vertical position by three synchronization racks: one placed behind the piston rack, the two other on the crankcase. The synchronization racks on the crankcase side have a low operational clearance and guarantee the roller’s horizontalness, while the synchronization rack on the piston rack side has a higher clearance and enables the combustion piston to orient vertically without damaging the synchronization racks.

The small module teeth of the synchronized roller principally take up its inertia forces. In practice, the inertia of the synchronized roller is essentially taken up by the friction between it and the rolling surfaces on the piston and crankcase. In this context, the main function of the small module teeth of the roller is to correct position deviation due to its sliding. The synchronized roller is guided axially by a groove (1) in its center, which cooperates with a guide rail on the rolling surface side of the crankcase. The MCE‑5 synchronized roller is today made as a single part.

The synchronized roller is largely responsible for the
low-friction performance of the MCE‑5 VCRi

The MCE‑5 VCRi synchronized roller cooperates with
3 synchronization racks: two of them are on a plate
fixed to the crankcase while one is on the
back side of the piston rack

The main characteristics of the MCE‑5 VCRi synchronized roller