QJMotor Patents Reveal Unique New Single-Cylinder Engine

China’s QJMotor, the sister brand of Benelli under the Qianjiang Group has filed patents for a new single-cylinder engine design, shaped like a v-twin. The idea behind the design is that the engine has only one active cylinder, and the second cylinder and piston will be used as a counterbalancer. The second inactive cylinder and piston is mounted at 90 degrees to the main one. The second cylinder has a much smaller bore than the active one with a weighted piston designed to act as a counterbalancer.

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The dummy piston is actually a counterweight with a hole in it.

The second piston has a large hole in the middle so it won’t be compressing air, and the inactive rear cylinder is cast in a single piece with its head to keep the engine sealed. A cross section image of the crankshaft show a pair of connecting rods to which are attached a tradition working piston on one, and a dummy piston which is actually a counterweight.

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The benefit of this single-cylinder engine design is that its balance is the same as a 90-degree v-twin, without the addition of balance shafts or other weights. QJMotor’s patent filings don’t reveal the capacity of the engine, or what sort of model it’s intended for, but considering the drawings, the Chinese firm seems to be working on expanding its technological capabilities to look for new innovations to make more efficient motorcycle engines in future. So far, though, there’s no word on when or if at all this engine concept will actually make it to production.

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The idea behind this kind of engine design isn’t entirely new. In the 1990s, Ducati created its Supermono racer with a similar concept, using the brand’s Desmoquattro v-twin and removing the rear cylinder. Ducati retained the rear connecting rod, and attached it to a weighted rocking linkage that replicated the mass of the rear piston. The concept gave the single-cylinder engine the balance it needed to have a higher rev limit and also to make more power.

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