Fully-controlled, free-piston engine

Details Fully-controlled, free-piston engine Fully-controlled, free-piston engine

2003-02-20

2003-11-25

Walberg, Teresa (Department: 3742)

Pumps

Motor driven

Internal-combustion engine

C123S090120

Reexamination Certificate

active

06652247

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the conversion of chemical energy (fuel) into hydraulic, electric or pneumatic energy. The general field of application is the efficient production of hydraulic, electric or pneumatic power for mobile and non-mobile power needs.
2. The Prior Art
Hydraulic power is currently produced by rotating the drive shaft of a hydraulic pump by a drive motor, usually an electric motor or an internal combustion engine. Power from a rotating shaft must be converted into a linear motion to drive reciprocating pistons which serve as the pumping means for the most efficient hydraulic pumps. When a reciprocating piston pump is driven by a conventional crankshaft internal combustion engine, pistons within the engine are driven linearly by the expansion of combustion gases, which in turn are connected by rods to a crankshaft, to produce rotating power output, which in turn is connected to the drive shaft of a piston pump which must then create the linear motion of the pumping pistons to produce hydraulic power.
The idea of directly (and usually axially) coupling the engine combustion piston to the hydraulic piston to produce hydraulic power directly from the linear motion of the combustion piston, avoiding the cost and inefficiencies of converting linear motion to rotation and back to linear, is not new. However, a variety of challenges associated with prior art designs have prevented any commercial success of this basic idea.
Connecting the combustion piston to the hydraulic piston eliminates the need for an engine crankshaft, and in doing so forms a free-piston assembly. Since the piston assembly is not connected mechanically to an apparatus which could in turn be used to control thernovement of the free-piston assembly, one major challenge associated with the basic idea of free-piston engines is how to accurately and repeatably (for millions of events) control the exact position of the stoppage of the assembly as it approaches the top dead center (TDC) position of the combustion piston during its compression stroke. For a combustion engine to be efficient, the control of the degree of compression (that is the compression ratio) is critical, and the high compression ratios of efficient combustion processes result in the need to take and stop the combustion piston very near (often within 1 millimeter) the opposite end of the combustion chamber (usually the engine “head”). A similar challenge is associated with the control of the exact position of the stoppage of the assembly as it approaches the bottom dead center (BDC) position of the pumping piston during the expansion or power stroke. The friction of each stroke can vary (especially during warm-up or transient operation), the quantity of fuel provided for each combustion event can vary, the beginning of the combustion process can vary, the rate of combustion and its completeness can vary, the pressure of the hydraulic fluid being supplied to the pump can vary, the pressure of the hydraulic fluid being expelled can vary, and many other operating parameters that influence each stroke can vary; therefore, the accurate control of the TDC and BDC positions is very challenging. The consequences of inadequate control can go beyond unacceptable performance, and be destructive to the engine if the combustion piston contacts the opposite end of the combustion chamber or the pumping piston contacts the opposite end of the pumping chamber.
Free-piston engines of the prior art operate on the two stroke cycle (with one exception to be described later) because of the challenge of operational control. Even with a two stroke cycle, stoppage of the combustion piston at the correct position at TDC during the compression stroke is very difficult. If the engine were operating on the four stroke cycle, an additional TDC stroke would be required to exhaust the spent combustion gases. In this exhaust stroke, unlike the compression stroke, there would be no trapped gases to increase in pressure as the combustion piston moved toward TDC and thereby decelerate the piston assembly. Some other means would be necessary to restrain the piston assembly from impact. Additional means would also be needed to move the assembly through the two additional strokes. Other problems or disadvantages of prior art designs will be apparent as they are contrasted with the present invention.
There are several informative technical papers, Society of Automotive Engineers (SAE) papers numbers 921740, 941776, 960032 and the reference listed therein, which provide review and analysis of the various free-piston engine concepts. There are also several United States free-piston hydraulic pump and related technology patents which might be considered relevant to the present invention and are as follows:
U.S. Pat. No. 4,087,205 Heintz: Free-Piston Engine-Pump Unit
U.S. Pat. No. 4,369,021 Heintz: Free-Piston Engine Pump
U.S. Pat. No. 4,410,304 Bergloff et al: Free Piston Pump
U.S. Pat. No. 4,435,133 Meulendyk: Free Piston Engine Pump with Energy Rate Smoothing
U.S. Pat. No. 3,841,707 Fitzgerald: Power Units
U.S. Pat. No. 6,152,091 Bailey et al: Method of Operating a Free Piston Internal Combustion Engine
U.S. Pat. No. 5,983,638 Achten et al: Hydraulic Switching Valve, and a Free Piston Engine Provided Therewith
U.S. Pat. No. 5,829,393 Achten et al: Free Piston Engine
U.S. Pat. No. 4,891,941 Heintz: Free-Piston Engine-Pump Propulsion System
U.S. Pat. No. 4,791,786 Stuyvenberg: Free-Piston Motor with Hydraulic or Pneumatic Energy Transmission
U.S. Pat. No. 4,382,748 Vanderlaan: Opposed Piston Type Free Piston Engine Pump Unit
U.S. Pat. No. 6,029,616 Mayne et al: Free Piston Engine
U.S. Pat. No. 5,556,262 Achten et al: Free Piston Engine Having a Fluid Energy Unit
U.S. Pat. No. 5,363,651 Knight: Free Piston Internal Combustion Engine
U.S. Pat. No. 5,261,797 Christenson: Internal Combustion Engine/Fluid Pump Combination
U.S. Pat. No. 4,415,313 Bouthors et al: Hydraulic Generator with Free Piston Engine
There is also a free-piston, hydraulic-pump engine, which can operate in either the two stroke or four stroke cycles, disclosed in U.S. Pat. No. 5,611,300 (
FIGS. 6-8
and claims
11
-
12
). This engine utilizes a conventional crankshaft and combustion piston to intake and compress air and to exhaust the spent combustion gases for the four stroke cycle.
Free-piston engines of prior art design are generally classified as single piston, opposed piston or dual piston. The present invention would be classified as a dual piston-configuration. Like prior art free-piston engines, the present invention utilizes the stroke of the combustion piston to directly produce hydraulic, pneumatic or electric energy. However, for ease of description of the essential features of the present invention, only hydraulic energy production will be described.
Additional challenges associated with the various prior art free-piston engine designs include:
(1) Difficulty in achieving mechanical balance. Each stroke of a free-piston assembly transmits an acceleration and a deceleration force to the engine housing, and to the structure to which the engine is mounted unless these forces are somehow counteracted (i.e., balanced) within the engine. Proponents of opposed piston engines usually stress as a primary advantage the potential for good balance, but the difficulty of exactly controlling the movement of each free-piston makes this potential difficult to realize in practice.
(2) Accurate control of timing and quantity of fuel introduction. This challenge is primarily related to control of the piston assembly motion as previously discussed, but the elimination of this sensitivity would be highly beneficial.
(3) Operation utilizing two stroke cycle. There are currently no two stroke cycle automotive engines sold in the United States. This is because it is extremely difficult to control air pollution exhaust emissions from such engines. This challenge would apply to two stroke cycle free-piston engines as well.
(4) Difficulty of providing a wide rang

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