Effective Torque Arm – the RoundEngine Advantage

The effective torque arm in a reciprocating engine varies because the angle of force relative to the angle of the torque arm varies. The effective torque arm in a RoundEngine never changes because the 90 degree relationship between the angle of force and the physical torque arm is always maintained. A graphical summary of the effective torque arm of reciprocating engines and RoundEngine is as follows:

Two items are worth noting:

• Reciprocating engines have a maximum effective torque arm, and thus maximum torque, at only one point in an entire revolution. In the RoundEngine, the effective torque arm is always at its maximum during its expansion or power stroke.

• The maximum pressure in the combustion chamber is the largest at TDC, a point where reciprocating engines have zero effective torque arm.

In the graph below, the shaded red area shows the relative effective torque arm advantage of the RoundEngine over a 4-stroke engine. The green shaded area shows the additional advantage over a 2-stroke engine where 20% of the power stroke is lost due to the exhaust port opening prior to the piston reaching BDC.