How the QX50’s variable compression engine works
The midsized SUV is set to be the world's first production vehicle with a variable compression engine, dubbed VC-Turbo. Effectively, it controls the combustion process within the cylinder and decides how powerfully or economically the engine works under the various load requirements. The result, Infiniti claims, is an engine that can boost efficiency by up to 25%, with increased power and torque.
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Chief engineer Shinichi Kiga has led the development of the VC-Turbo engine, having researched variable compression technology for around 20 years. “I knew that it was possible,” he said. “I’m convinced it will become a major technology trend in the years to come for internal combustion engines.” As with Mazda’s pursuit of compression ignition technology, Infiniti believes that electrification is not the only way to improve the efficiency of car powertrains.
Most current petrol engines have a fixed compression ratio of around 10:1 or more, largely set to maximise fuel economy. But a variable compression ratio can alter as needed. That means it can operate highly compressed at low speeds for maximum efficiency, and with far lower compression at higher speeds, boosting the engine’s power.
The challenge of developing variable compression wasn’t just an engineering one. Nissan North America’s propulsion development boss, Chris Day, said: “Seven or eight years ago we were sure we could make it. Not only did we need modern mechanical engineering for all the parts, but also the computing power needed to test the engine on the computer.”
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