Infiniti is destined to become the first major automaker with a variable compression engine.
The engine, dubbed the VC-T (Variable Compression-Turbo), has the ability to alter the compression ratio, i.e. the volume of the combustion chamber when a piston is at the bottom of the stroke compared to when it reaches the top, whereas in conventional engines this ratio is fixed.
The result is an engine whose displacement changes as required, i.e. a larger displacement for high-load situations and a smaller displacement at other times. According to Infiniti, the VC-T will offer improvements in efficiency as well as NVH levels. The engine is also said to be lighter and more compact than a conventional engine with similar performance, while being cheaper to produce than a modern diesel.
Infiniti is saving full details for next month’s 2016 Paris auto show but there are some details we can confirm. The first VC-T will be a turbocharged inline-4 that will offer the performance of a naturally-aspirated V-6. The compression ratio can vary anywhere between 8:1 (for high performance) and 14:1 (for high efficiency). The low 8:1 compression ratio also enables higher boost pressure from the turbo without fear of detonation or engine knock. Everything is done automatically, depending on what the driving situation demands.
Infiniti VC-T (Variable Compression-Turbocharged) engine
To be able to adjust the compression ratio, the VC-T relies on a rotating unit called the Harmonic Drive. By way of mechanical linkages, this unit can alter the connection between the piston and the crank shaft, so that the maximum height the piston can reach within the cylinder (and therefore the compression ratio) can be controlled. Infiniti and its parent Nissan have over 300 patents for the design.
A few automakers have toyed in the lab with variable compression technology, including Saab which came close to utilizing it in the early 2000s. Infiniti says it’s been working on the VC-T for more than two decades. The automaker will start rolling it out in 2018, most likely initially in the next-generation QX50 SUV.
"[VC-T] is a revolutionary next-step in optimizing the efficiency of the internal combustion engine," Infiniti boss Roland Krueger said in a statement. "This technological breakthrough delivers the power of a high-performance 2.0-liter turbo gasoline engine with a high level of efficiency at the same time."
More details on the engine and its future applications will be announced at the 2016 Paris auto show, which gets underway September 29. For more from the show, visit our dedicated hub.