Hyundai has filed a patent application for a four-cylinder engine with variable cylinder displacement.
The patent application is officially for a “system and method for motor-assisted non-uniform displacement engine control,” but it details an engine that has cylinders with different displacements. As you may know, a conventional combustion engine is generally setup so that cylinders have uniform displacements, making it easy to control air-to-fuel ratio, exhaust gases and balance.
But according to Hyundai, the uniform displacement engine has a disadvantage: “a margin for operation point control is insufficient due to the fixed displacement thereof.” Additionally, excessive mechanical energy is consumed so that a uniform displacement engine can stably idle, which is also inefficient.
So the Korean automaker has an idea for a non-uniform displacement engine that would have two kinds of cylinders with different displacements, with a motor control unit being used to control the motor in at least three different modes.
In other words, imagine a four-cylinder engine with two pairs of different cylinder sizes, such as cylinders one and four displacing 0.4 liters and cylinders two and three displacing 0.35 liters. An electric motor is used to assist in balancing torque output, while helping counteract the extra noise and vibrations from the uneven displacements.
The patent application was originally filed on December 2, 2015 with the European Patent Office and was published on March 22, 2017.
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