Internal-combustion engines – Free piston – Single chamber; one piston
Reexamination Certificate
1999-02-22
2001-11-13
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Free piston
Single chamber; one piston
C123S0460SC
Reexamination Certificate
active
06314924
ABSTRACT:
TECHNICAL FIELD
The present invention relates to free piston internal combustion engines, and, more particularly, to a method of operating a free piston internal combustion engine with a hydraulic power output.
BACKGROUND ART
Internal combustion engines typically include a plurality of pistons which are disposed within a plurality of corresponding combustion cylinders. Each of the pistons is pivotally connected to one end of a piston rod, which in turn is pivotally connected at the other end thereof with a common crankshaft. The relative axial displacement of each piston between a top dead center (TDC) position and a bottom dead center (BDC) position is determined by the angular orientation of the crank arm on the crankshaft with which each piston is connected.
A free piston internal combustion engine likewise includes a plurality of pistons which are reciprocally disposed in a plurality of corresponding combustion cylinders. However, the pistons are not interconnected with each other through the use of a crankshaft. Rather, each piston is typically rigidly connected with a plunger rod which is used to provide some type of work output. In a free piston engine with a hydraulic output, the plunger is used to pump hydraulic fluid which can be used for a particular application. Typically, the housing which defines the combustion cylinder also defines a hydraulic cylinder in which the plunger is disposed and an intermediate compression cylinder between the combustion cylinder and the hydraulic cylinder. The combustion cylinder has the largest inside diameter; the compression cylinder has an inside diameter which is smaller than the combustion cylinder; and the hydraulic cylinder has an inside diameter which is still yet smaller than the compression cylinder. A compression head which is attached to and carried by the plunger at a location between the piston head and plunger head has an outside diameter which is just slightly smaller than the inside diameter of the compression cylinder. A high pressure hydraulic accumulator which is fluidly connected with the hydraulic cylinder is pressurized through the reciprocating movement of the plunger during operation of the free piston engine. An additional hydraulic accumulator is selectively interconnected with the area in the compression cylinder to exert a relatively high axial pressure against the compression head and thereby move the piston head toward the top dead center position.
In a free piston engine as described above, the piston includes a piston head, a compression head and a plunger head which are commonly carried by a plunger rod and respectively disposed in the combustion cylinder, compression cylinder and hydraulic cylinder. The piston including the three separate heads is quite long, which increases the overall package size of the free piston engine. Moreover, as a result of the relatively large size of the piston, the mass of the piston is relatively heavy. The energy which is required for combustion of fuel within the combustion cylinder is related to the required kinetic energy of the piston when the piston is at a TDC position. The kinetic energy is a function of the mass and square of the velocity of the piston. Since the piston is relatively heavy, the piston is accelerated to a velocity which is relatively low in order to provide the kinetic energy needed for combustion. Moreover, since the piston is relatively heavy and the hydraulic fluid used to move the piston toward the TDC position is at a limited pressure, the acceleration of the piston is relatively slow and thus the stroke length is relatively long in order for the piston to reach the desired velocity. The slow acceleration, velocity and frequency of a conventional free piston engine results in a relatively low power output.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the invention, a method of operating a free piston internal combustion engine includes the steps of: providing a housing with a combustion cylinder and a second cylinder, the combustion cylinder having a bore with an inside diameter; providing a piston including 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; and moving the piston between a top dead center position and a bottom dead center position during a return stroke, the return stroke having a stroke length between the top dead center position and the bottom dead center position, the moving step being carried out with a bore/stroke ratio represented by a quotient of the inside diameter divided by the stroke length which is between 1.2 and 1.5.
In another aspect of the invention, a method of operating a free piston internal combustion engine includes the steps of: providing a housing with a combustion cylinder and a second cylinder, the combustion cylinder having a bore and an air scavenging port in communication with the bore; providing a piston including 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; and moving the piston from a bottom dead center position to a top dead center position and back to the bottom dead center position during a cycle time period, the piston head opening and closing the air scavenging port during the movement of the piston, the air scavenging port being in fluid communication with the bore during between 50 and 70% of the cycle time period.
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TU Dresden—publication date unknown—earliest date 1993—Dresden University in Germany.
Application No. 08/974,326, filed Nov. 19, 1997, entitled “Two Cycle Engine Having a Mon-Valve Integrated Withy a Fuel Injector”.
Benton Jason
Caterpillar Inc.
Taylor & Aust P.C.
Wolfe Willis R.
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