Patent ID: 7603858

Claim:
An engine comprising: a reciprocating-piston expander comprising: an expander cylinder; an expander piston head axially slidable in said expander cylinder and together enclosing an expansion chamber; a piston rod connected at one end to the expander piston head; an inlet valve for controlling the flow of working fluid into the expansion chamber to effect a power stroke of the expander, said inlet valve being a harmonic oscillator having an equilibrium position outside the expansion chamber so that the inlet valve is open at equilibrium and displaceable to a closed position against an equilibrium restoring force; latch means for automatically re-latching the inlet valve in the closed position after being unlatched to experience a harmonic oscillation; an outlet valve for controlling the flow of working fluid out from the expansion chamber during a return stroke of the expander, said outlet valve being a harmonic oscillator having an equilibrium position inside the expansion chamber so that the outlet valve is open at equilibrium and displaceable to a closed position against an equilibrium restoring force; an intake header connectable to a pressurized fluid source for channeling pressurized working fluid into the expansion chamber via the inlet valve; and an exhaust header for channeling working fluid exhausted out from the expansion chamber via the outlet valve; and periodic return means for effecting the return stroke of the expander after each power stroke.