Internal-combustion engines – Free piston – Single chamber; one piston
Reexamination Certificate
1999-09-29
2001-09-25
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Free piston
Single chamber; one piston
C060S413000
Reexamination Certificate
active
06293231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to free-piston type internal combustion engines, compressors or pumps, and in particular, to innovations which improve the controllability and efficiency of the free-piston engine or pump and reduce the toxic emissions, the weight and the size of such engines.
2. Background Art
Although advantageous in applications where pressurized fluid is used to transmit the energy, the simple concept of free-piston internal combustion engines or pumps, transferring the chemical energy of a combustible fuel direct into mechanical energy of pressurized hydraulic fluid, is rarely utilized due to the inability to control their operating characteristics, and in particular, the top and bottom end positions of the piston, sufficiently.
Free-piston Control
In one known free-piston engine, disclosed in U.S. Pat. No. 4,791,786, the hydraulic piston control mechanism of the free-piston requires three hydraulic control surfaces in axial direction to control the top-end position and the bottom-end position somewhat sufficiently. The free-piston has a combustion end and a hydraulic end, consisting of a plunger with one outer control surface acting in opposite direction to the combustion forces, and a piston with one larger control surface acting also in the opposite direction and a smaller control surface acting in the same direction as the combustion force.
During the compression stroke, pressurized fluid at the outer plunger surface advances the free-piston toward the top-end position while the chamber at the larger piston surface draws fluid in from a reservoir. The smaller piston surface, acting in opposite direction and being smaller than the plunger surface, is permanently pressurized with hydraulic fluid and provides a buffer function at the end of the compression stroke in top-end position by depressurizing the plunger surface. During the expansion stroke, all three control surfaces are exposed to pressurized fluid, advancing the fluid, drawn in during the compression stroke, to the accumulator. The bottom-end position of the free-piston can be obtained by readjusting the position after a stop.
In this prior art free-piston engine, the top-end position is determined by the balance of the buffer force, depending on the fluid pressure in the accumulator, and the dynamic mass forces of the heavy free-piston, depending on its velocity. The bottom-end position is determined by the balance of combustion and dynamic piston mass forces versus hydraulic forces, and depends on the insufficiently controllable, variable velocity of the piston (rpm.) and the fluid pressure in the accumulator. During a cycle interruption, the bottom-end position can be corrected.
The variations in top-end position and bottom-end position are too high to allow for an overall sufficient control of the compression ratio and combustion conditions, reducing the efficiency and increasing the amount of toxic emissions. Furthermore, the requirement for three hydraulic control surfaces increases the cost and size of the free piston engine and reduces the efficiency of the free-piston engine.
In another known free-piston engine, which is disclosed in U.S. Pat. No. 5,556,262, the hydraulic piston control mechanism consists of four control surfaces in axial direction to control the top-end position and the bottom-end position. The free-piston has a hydraulic end, consisting of a compression section, having a larger and a smaller control surface, and a pump section, also having a larger and a smaller control surface in which the larger surfaces are acting in opposite direction to the combustion end of the free-piston assembly.
During the compression stroke, the smaller control surface of the compression section is in communication with the fluid reservoir and the larger control surface is pressurized with fluid from a compression (bouncing) accumulator, advancing the free-piston toward the top-end position, while the pump section of the hydraulic end draws fluid in from the reservoir. During the expansion stroke, the hydraulic section, controlled by non-return valves, advances the fluid to the pressure accumulator, while the pressure conditions in the compression section remain unchanged. The bottom-end position is determined by decreasing combustion forces and increasing hydraulic forces. The hydraulic section has no noticeable influence in the control of the free-piston.
The top-end position is determined by the balance of nearly constant hydraulic forces and mass forces of the free-piston, varying with the velocity of the free-piston, and the compression forces acting in opposite direction. The bottom-end position is controlled by the mass forces of the free-piston in addition to the combustion pressure and the increasing hydraulic forces. Increased accuracy of the bottom-end position is obtained with increasing hydraulic losses to brake the free-piston. The compression ratio, which determines efficiency and combustion conditions as well as the amount of toxic emissions, can only be controlled by changing the pressure in the compression (bouncing) accumulator. However, this results in loss of energy and is very time consuming. Moreover, the need for four control surfaces and the requirement of an additional accumulator increase expense, and require additional space and reduce the efficiency of the free-piston engine.
Charge Mechanism
The utilization of exhaust gas energy increases the efficiency and reduces weight and size by increasing the specific power output, resulting in a smaller engine with less heat and friction losses.
In U.S. Pat. No. 5,261,797, there is disclosed a pressure wave charger (pulse pressure booster) which consists of a compressor, driven by an exhaust turbine or the crankshaft, and a booster, having a spring loaded booster piston, which is reciprocally mounted in a piston bore of a booster housing. The ingress of fresh air from the compressor to one chamber at the first end of the booster piston is controlled by a non-return valve. The egress to the combustion chamber is controlled by a rotary valve. A chamber at the second end of the booster piston, opposite to the first end, is in communication with the sump of the two-stroke combustion engine, controlled by a valve. A second chamber, being in communication with the exhaust port of the combustion engine, can be arranged at the second end of the booster piston, further increasing the pressure of the pressurized air from the compressor in the booster chamber.
Starting in the top-end position after the ignition, the combustion piston advances toward the bottom-end position, compressing the air in the sump while the compressor charges the first booster chamber with fresh, pressurized air. Near the bottom-end position of the combustion piston, the exhaust port and the valve to the sump of the engine open and provide pressure to their respective chambers at the second end of the booster piston in opposition to the compressed air. Pressure, sufficient to overcome the forces of the compressed air and a spring at the opposite side of the booster piston, will advance the piston toward the top-end position and increase the pressure of the compressed fresh air being forced through the intake port into the combustion chamber. Due to the spring force, the booster piston will return in its original position when the ports of the combustion engine are closed during the compression stroke.
The charge apparatus is complex and the overall efficiency low due to friction, leakage and larger amounts of compressed air, not participating on the combustion process.
Fuel Injection Apparatus
Known fuel injection systems provide fuel of increasingly higher pressure levels to a single, centrally or nearly centrally located fuel injector with one or several closely spaced nozzles to provide improved conditions for a more efficient combustion with reduced toxic emissions. The higher injection pressure provides an improved air-fuel mixture for a more efficient and cleaner combustion/lower toxic emissions, but th
Moulis Thomas N.
Reinhart, Boerner, Van Deuren, Norris & Rieselbach, s.c.
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