Method of operating a free piston internal combustion engine with high pressure hydraulic fluid upon misfire or initial start-up

Abstract

A method of operating a free piston engine of the present invention, includes a housing with a combustion cylinder and a second cylinder. A piston includes a piston head reciprocally disposed within the combustion cylinder, a second head reciprocally disposed within the second cylinder, and a plunger rod interconnecting the piston head with the second head. A supply of hydraulic fluid is pulsed from a high pressure hydraulic accumulator into a pressure chamber in the second cylinder adjacent the second head during a beginning portion of a compression stroke to cause the piston head to move toward a top dead center position. The high pressure hydraulic accumulator is decoupled from the pressure chamber after the pulsing step. A low pressure hydraulic accumulator is coupled with the pressure chamber during a remaining portion of the compression stroke. The high pressure hydraulic accumulator is coupled with the pressure chamber when the piston head is traveling toward a BDC position during a return stroke. A sensor senses a position of the piston which is at or near the BDC position and provides a corresponding signal. The coupling between the high pressure hydraulic accumulator and the pressure chamber is maintained for a period of time, dependent upon the sensor signal.