How engineers use intentional distortion to achieve perfect engine alignment
In short: Most precision components are built to be perfect, but the Renault-Nissan MR engine family uses a clever trick called 'under stress' manufacture. By temporarily distorting the engine block during boring, engineers ensure it pulls into its exact, intended shape only once the head is torqued into place.
The MR engine family, developed by Renault and Nissan, includes a variety of three and four-cylinder, all-aluminium, water-cooled engines. To achieve high efficiency, these engines incorporate several sophisticated features, such as offset cylinder placement, a 'silent' timing chain, and mirror-finished crankshaft and camshaft journals. They also utilize acoustically equal runner lengths and tumble control valves within the intake manifold.
A defining characteristic of the MR family's manufacturing is the 'under stress' process. During the boring of the engine block, a torque plate is applied to purposefully distort the block. This distortion is temporary; once the cylinder head is torqued onto the block, the component is pulled into its correct, final shape, ensuring precise alignment.
The family's versatility is evident in its diverse applications. For instance, the 1.6 L MR16DDT engine was introduced in the Nissan Juke in the autumn of 2010, while the 2.0 L MR20DE was the first in the series, replacing the QR20DE and debuting in early 2005. The family has even expanded to include hybrid technology, such as the third-generation E-power system, which uses a 1.5 L three-cylinder engine designed specifically to charge a battery with a high compression ratio of 13.5 to 1.
Beyond passenger cars, the technology has reached high-performance limits, such as the 2012 Nissan Deltawing race car, which utilized a non-production version of the MR series to produce 221 kW (296 hp) at 7400 rpm.
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- Summary by Intellect · source: Nissan MR engine
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