page_title: Variable compression ratio
section_title: Peugeot MCE-5
hierarchical_section_title: Variable compression ratio / Engine designs / Peugeot MCE-5
caption_attribution_description: English: Working principle of MCE-5 Variable compression ratio Engine Français&#160;: Principe de fonctionnement d'un moteur MCE-5 à compression variable
context_page_description: Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume above the piston at top dead centre to be changed. Higher loads require lower ratios to increase power, while lower loads need higher ratios to increase efficiency, i.e. to lower fuel consumption. For automotive use this needs to be done as the engine is running in response to the load and driving demands. The 2019 Infiniti QX50 is the first commercially available vehicle that uses a variable compression ratio engine.
context_section_description: The Peugeot design works by varying the effective length of the con-rods connecting the piston to the crank. When the con-rod is shorter, the compression ratio is lower and vice versa. On the left hand-side of the diagram is the conventional piston of an internal combustion engine. On the right is an hydraulic cylinder with double-acting piston. This acts through a rod-crank system with a gear wheel, whose movement adjusts the effective con-rod length and thus the compression ratio in the left cylinder.
caption: Principle of the MCE-5 ("Multi Cycle Engine - 5 parameters"), the variable compression ratio engine made by Peugeot.