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Three-Pot Merc in the Works
by
Edward Niedermeyer
(IC: employee)
Published: June 18th, 2009
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In addition to offering hybrid options across its lineup, Mercedes-Benz will mount a three-cylinder engine in certain vehicles by 2012, reports Motor Authority. Mercedes R&D Boss Thomas Weber does mention that there’s a slight hitch to the plans, namely that “Mercedes is currently looking for a partner to help develop the new three-cylinder engine.” In what appears to be a case of car-before-horse(power), Weber confirms that this undeveloped engine will appear in future iterations of the C-Class, B-Class, A-Class and Smart ForTwo. The American market is not expected to receive three-banger benzes, although a 1.4-liter Kompressor engine is being considered for the C-Class.
Edward Niedermeyer
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Published June 18th, 2009 4:58 PM
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Here is what I do not understand. Back in the 50s there were lots of small fours. The original Mini started at 850. Fiat also had an 850. What is the point of a three?
A 3 cylinder engine has roughly 87% of the friction of a 4 cylinder of the same capacity and stroke, and is slightly lighter. It also has larger pistons, which in the case of small engines gives you smaller thermal losses. So for all those reasons you could expect slightly better economy. It is also significantly cheaper to make. On the other hand, it has a balance problem. A 4 cylinder basically jumps up and down, at 2/rev. A 3IL rocks at 1 per rev, and it is much more difficult to design around the rocking motion than the jumping up and down. They do sound nice tho.
So why not arrange the cylinders radially or "somewhat radially"? Would that make it doable, or am I way off here? I'm not an engineer, so I have no idea.
Sure, you could do the cylinders radially at 120 degrees apart (or certain fractions of that), but that would take up more space and probably require a separate head for each cylinder, which would make the intake and exhaust manifolds "interesting".