Internal-combustion engines – Multiple cylinder – Having rotary output shaft parallel to cylinders
Reexamination Certificate
2000-07-17
2001-08-28
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Multiple cylinder
Having rotary output shaft parallel to cylinders
C123S056500
Reexamination Certificate
active
06279520
ABSTRACT:
FIELD OF INVENTION
This invention relates to uncooled, two-stroke-cycle, opposed-piston, uniflow-scavenging internal combustion engines, and to certain structural improvements thereto. Specifically, the engine relates to an axial-cylinder, twin-barrel-cam engine, having a novel intake/exhaust valve configuration, a novel combustion chamber configuration and a novel external piston rod alignment structure. The engine system herein has particular value in aviation propulsion and other engine power applications demanding maximum performance over wide load, speed and altitude range.
BACKGROUND—DESCRIPTION OF PRIOR ART
Heretofore, internal combustion engines of the reciprocating type have been constructed of metals in forms best suited for their fabrication in such materials. However, due to these materials prior art engines require supplemental cooling and lubrication in order to function properly with adequate durability. These cooling and lubrication requirements further require provisions for fluid circulation and heat rejection accessories that can be burdensome in many applications. Aircraft applications of such engines are particularly sensitive to the installation of such accessories because of the weight and aerodynamic drag associated with their proper usage. In addition, the control of fluids in aircraft engines and their remote accessories such as radiators, oil coolers, pumps, oil sumps and the like is complicated because a fixed gravitational orientation can not be relied upon to disengage vapors and liquids and establish fluid levels.
A further disadvantage of most prior art engine constructions for aircraft applications is their dependence on increased output shaft speed as a means of reducing weight per unit of power output. Because propellers function efficiently only with limited rotational speeds, most light-weight engines of the prior art type require speed-reducing gear boxes, and perhaps even variable ratio transmissions, to properly match their outputs to suitable propellers. Such mechanical accessories have cooling and lubrication requirements of their own and can add significant weight, cost and complexity to the installation, particularly for small-engine and high-altitude applications. Such speed constraints are not limited to aircraft applications. Certain alternators and compressors represent other important drive applications that are so limited.
Most prior art engines employ structural arrangements, assemblies and mechanisms that are highly dependent on the tensile properties of the customary metallic materials which have limited temperature tolerance, expand significantly when heated and are prone to galling under sliding and rubbing contact. They require sophisticated cooling and lubrication schemes to maintain their mechanical and structural integrity and their weight and balance is highly sensitive to increases in cylinder working pressures and rotational speeds. Thus, prior art engines that operate on the diesel cycle are somewhat heavier and larger than their spark ignition counterparts and they also present greater lubrication, cooling and balancing burdens. This accounts, to a large extent, for the lack of acceptance, heretofore, of prior art type diesel engines for aircraft applications notwithstanding their potentially superior flight-worthiness, safety, fuel economy and fuel flexibility characteristics.
Various attempts have heretofore been made to overcome some of these problems by designing diesel engines with large heat retention capacities. Examples of such “adiabatic engine” are those manufactured by Adiabatic Inc. and Cummins. These adiabatic engines utilize insulated parts, heat tolerant components and high-temperature tribology or friction controls. However, such friction controls require advanced chemistry for liquid lubrication. What is needed is an adiabatic engine that overcomes these shortcomings.
With rare exceptions, prior art reciprocating engines, adiabatic or otherwise, utilize crankshafts and connecting rods for the translation of reciprocating to rotary motion. This arrangement has been successfully applied to engines comprised of from one to many cylinders laid out in various configurations such as in a single line of cylinders parallel to the crankshaft, banks of inline cylinders disposed around the crankshaft, radial cylinder dispositions and opposed-piston arrangements using one or more crankshafts geared together. A few crankshaft-type engines are known which have been constructed with parallel cylinders axially aligned in a barrel arrangement around the crankshaft or with inline cylinders transverse to the crankshaft. Both of these types rely on additional auxiliary mechanisms such as gear trains, rocker arms, wobble plates, universal ball joints and the like for the translation of power.
Prior art engines that utilize crankshafts provide no mechanical advantage in the conversion of piston motion to shaft torque. Furthermore, eccentricities in connecting rods and the like produce side loads in the reciprocating pistons which give rise to friction and vibration. Another disadvantage of crankshaft-type engines is the complex load path that must be structurally accommodated in maintaining the mechanical integrity of the engine. Typically, such loads are passed through the cylinder walls which must also handle the stresses due to combustion. As a result, the cylinders must be constructed of materials having high tensile strengths. Due to the complex forms of the structures required, metallic materials constitute the only economic and durable means of construction, and then only if an abundance of cooling and lubrication is used. Furthermore, crankshafts, by nature, must span the length of the engine. Because of this, as well as a poor structural geometry for the loads imposed, crankshaft engines require somewhat more weight, strength and stiffness in the shaft, bearings and supporting structure to obtain an adequate degree of torsional rigidity and structural integrity.
The axial piston or barrel configuration typified by the prior art engines of Herrmann, Sterling/Michel and others offers improved compactness, structural efficiency and frontal area. These characteristics are desirable for an engine. However, none of these characteristics has been obtained in the prior art with the use of thermally tolerant and self-lubricated materials in the principal parts. All of these prior art engines rely on the established principles of ironmongery, which succeeds only with proper cooling and lubrication. None of the prior art engines suggests the use of non-metallic construction or arrangements, hence, the burdens of supplemental cooling and lubrication remains.
Many of these prior art engines, such as Junkers, Hill and Sterling/Michel, have utilized opposed-piston arrangements which avoid the use of cylinder heads and the stresses, dynamic forces, seals, attachments and fastenings attendant thereto. Although this arrangement is limited to two-stroke-cycle operation, this can be advantageous for some applications, provided aspiration and cylinder scavenging can be properly attended. Other advantages of the opposed-piston arrangement include reduced combustion chamber heat losses, improved compactness for a given cylinder displacement and reduced piston speed for a given power output.
For example, the Sterling/Michel engine includes an opposed piston arrangement that utilizes a double swashplate for translating axial to reciprocating motion (see, Heldt, P. M.,
High Speed Diesel Engines
, 4th Ed., Nyack, N.Y., 1943, pp. 308-309). However, the Sterling/Michel engine has swashplate followers which impart significant side loads. Furthermore, the engine requires a separate scavenging system and supplemental lubrication. Finally, the Sterling/Michel swashplates are single harmonic, thereby yielding only one power stroke per revolution.
The Junkers engine utilizes two crankshafts in an inline cylinder, opposed piston configuration, thus also yielding only one power stroke per revolution (see Heldt, pp. 320-326). Furthermore, the ar
Canter Bruce M.
McMahon Marguerite
Oppenheimer Wolff & Donnelly LLP
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