Adiabatic, two-stroke cycle engine having piston-phasing and compression ratio control system

#This invention relates to uncooled, two-stroke-cycle, opposed-piston, uniflow-scavenging internal combustion engines, and to piston phasing and compression ratio controls for such engines. Specifically, the engine relates to an axial-cylinder, twin-barrel-cam engine, wherein the control system provides independently controllable compression ratio and port timing, offering improved power density, efficiency, smoothness, compactness, torque and thermal tolerance. 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.

#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.

#FIG. 1 is a simplified section and cutaway view of an engine assembly constructed according to the present invention showing the axial-cylinder, opposed-piston layout utilizing twin, double-harmonic cams;

#FIG. 2 is a simplified schematic diagram of a four-cylinder engine assembly at Section A--A indicated in FIG. 1;

#FIG. 3 is a pictorial illustration of a double harmonic barrel cam of the present invention, with roller followers;

#FIG. 1 shows a simplified longitudinal section and cutaway view of the engine assembly of the present invention. Shaft 10 passes axially through the center of the assembly, is carried by a pair of bearings 11 in a fixed axial position and mounts a pair of double-harmonic barrel cams 12, one fixed on each end. Cams 12 are radially and axially indexed and placed on shaft 10 with respect to opposed piston pairs 14 such that piston pairs 14 of diametrically opposite cylinders 16 and 18 are in approximately the same position with respect to the center of their respective cylinders so that there is axial and longitudinal symmetry at all times. Cams 12 may be located on shaft 10 with a small angular displacement with respect to each other in order to cause one of piston pairs 14 to be displaced in the cylinder slightly ahead of its opposite. This asymmetric piston phasing feature will be explained more fully in the following in connection with scavenging operations.

#As discussed above, opposed pistons 14 in diametrically opposite cylinders are in approximately the same position for purposes of axial and longitudinal symmetry. However, in FIG. 1 cylinder 18 is shown as though shaft 10 had been rotated 90.degree. from the actual position shown. In FIG. 1 opposed pistons 14 are located in cylinder 16 (denoted as No. 1) at their innermost positions as determined by their respective cam follower assemblies 20 which straddle cams 12 and act on pistons 14 through piston rods 22. As shaft 10 is rotated through a 90.degree. angle the followers are displaced in equal and opposite directions by an amount equal to the amplitude of cams 12, which determines the stroke of each piston 14. The positions of pistons 14 at this position (90.degree. out of phase) is indicated by the illustration of cylinder 18 (denoted as No. 3) in FIG. 1 which shows opposed pistons 14 in their outermost positions. Further, rotation of shaft 10 causes pistons 14 to move in and out synchronously and cyclically such that pistons 14 traverse cylinders 16 and 18 in and out four full strokes for each complete revolution of the shaft 10.

#Pairs of cylinders 16 and 18, such as those designated Nos. 1 and 3 in FIG. 1, which are symmetrical about the shaft 10, are fully balanced dynamically in that all motions of reciprocating masses are in equal and opposite directions and pairs of diametrically opposite cylinders 16 and 18, like those denoted Nos. 1 and 3, are symmetrical about the shaft axis of the engine. Additional pairs of cylinders 16 and 18, e.g. Nos. 2 and 4, may be disposed about the shaft, as in the four cylinder arrangement shown in FIG. 2, without disturbing the balance of the engine. The cam and follower arrangement corresponding to the layout of FIG. 2 is indicated in FIG. 1, where the cylinder pair out of plane are denoted Nos. 2 and 4.