Single shaft dual expansion internal combustion engine

A single-shaft dual expansion internal combustion engine, comprising:

• an engine block, a cylinder head, a crankshaft, and a multi-link connecting rod assembly;
• first and second power cylinders and an expander cylinder being formed in the engine block and enclosed by the cylinder head;
• first and second power pistons being moveable in the first and second power cylinders, respectively, and being connected to respective first and second crankpins of the crankshaft;
• an expander piston being moveable in the expander cylinder and being connected via the multi-link connecting rod assembly to a third crankpin of the crankshaft;
• a first balance shaft arranged in a first longitudinal opening in the engine block;
• a second balance shaft arranged in a second longitudinal opening in the engine block;
• wherein the first balance shaft is disposed on a common lateral side of the engine block as the second balance shaft relative to a vertical axis that passes through a centerline of the crankshaft;
• wherein the first balance shaft is disposed on a common vertical side of the engine block as the second balance shaft relative to a lateral axis that passes through the centerline of the crankshaft;
• the first and second balance shafts having first and second counterweights, respectively, wherein the first and second balance shafts are disposed to generate respective first and second counter imbalance forces;
• and
• the crankshaft having a third counterweight, the third counterweight including an eccentric mass disposed at a radial distance from a centerline of the crankshaft to generate an imbalance force that compensates for the first and second counter imbalance forces.