Internal-combustion engines – Multiple cylinder – Having rotary output shaft parallel to cylinders
Reexamination Certificate
2003-11-01
2004-08-24
Denion, Thomas (Department: 3748)
Internal-combustion engines
Multiple cylinder
Having rotary output shaft parallel to cylinders
C123S056200
Reexamination Certificate
active
06779494
ABSTRACT:
FEDERALLY SPONSORED RESEARCH
Not applicable.
SEQUENCE LISTING OR PROGRAM
Not applicable.
BACKGROUND—FIELD OF INVENTION
This invention relates to barrel-cam internal-combustion engines (reciprocating piston internal-combustion engines where motion conversion takes place via a pair of conjugate axial cams) that are specifically improved by assuring naturally balanced operation under a greater variety of as well as simpler configurations than before.
BACKGROUND—DISCUSSION OF PRIOR ART
Cost reduction has always been an area of strong interest for internal-combustion engines considering their market span and production quantities. The barrel-cam engine (a reciprocating piston internal-combustion engine where motion conversion takes place via a pair of conjugate axial cams) has been one of the attempts at cost reduction for internal-combustion engines. Prior art of barrel-cam engines claim reduction of the number of parts relative to conventional crank-type engines without sacrificing reliability, performance/efficiency, or increasing NVH (Noise and Vibrational Harshness). Though the motion conversion mechanism for barrel-cam engines uses the same number and complexity of parts as a conventional crank-type engine, the prior art anticipates reducing the components needed for valve actuation and avoiding the need for balance shafts in certain configurations.
Patent applications by those including Gresse (251,607:United Kingdom) and Herrmann (U.S. Pat. No. 2,237,621 and related subsequent patents) anticipated certain engine simplifications due to the structure of the barrel-cam engine. Specifically, they anticipated the ability to actuate cylinder valves by secondary cams directly coupled to the barrel-cam shaft (the shaft analogous to the crankshaft of conventional IC engines). This is made possible because of two reasons: Firstly, the barrel-cam shaft can always be extended to be close to the cylinder heads due to the planetary arrangement of the piston-assemblies about the barrel-cam. Secondly, and more importantly, barrel-cam engines are not restricted to a single piston-assembly reciprocation per shaft revolution. Therefore the engine can be easily designed such that the rate of rotation of the valve-actuating-cams and barrel-cam shaft arc compatible. For example, in a four cycle engine, the intake and exhaust valve groups per cylinder each lift once every four cycles, or every 2 piston-assembly oscillations. Therefore, in order for the rotation rates of the valve-actuating-cams and barrel-cam shaft to be compatible, for n defined as the # single piston-assembly oscillations defined through one rotation of the barrel-cam's piston-assembly displacement profile, n must be divisible by 2 and the intake and exhaust cam must each have n/2 lobes. Directly coupling the valve-activation-cams to the barrel-cam shaft, as proposed, avoids the need for a rotational power transfer mechanism such as gear and belt or chain and sprocket which are needed in OHC crank-type engines. The planetary arrangement of piston-assemblies also reduces the member of cam surfaces needed since the engine can be designed such that each planetary bank of cylinders per side of the barrel-cam (across the plane normal to the barrel-cam shaft) can share the same pair of cam surfaces unlike crank-type engines where each cylinder has its own pair of cams, at minimum. Because of the unique arrangement of the pistons relative to the output shaft, the barrel-cam engine can easily accomodate axial cams or radial cams with rocker arms to actuate the valves.
A number of patents such as those by Herrmann (U.S. Pat. No. 2,237,621 and associated patents) and Trimble et al. (U.S. Pat. No. 4,090,478) set one of their objectives to have a balanced engine without balance shafts. Certain cylinder configurations of crank-type engines require balance shafts that spin at twice the crankshaft speed to balance the 2nd harmonics of vibration. Avoiding the need for balance shafts and their associated rotational power transfer mechanisms results in yet another reduction in part numbers. The series of patents by Herrmann (U.S. Pat. No. 2,237,621 and related subsequent patents) use 6 double-ended piston-assemblies in a planetary arrangement about a barrel-cam having a 4 lobe sinusoidal piston-assembly displacement profile corresponding to 2 oscillations per revolution per piston-assembly. This configuration has the piston-assemblies naturally balanced. The configuration allows partial balancing of valve-assembly forces in the direction of piston motion by generally opposing actuation of valves. Valve-assembly forces in the direction of piston motion account for a large portion of the valve-assembly forces because the angle between the valves' direction of motion and that of the pistons is typically not very large. However cycle ordering constraints restrict opposing valves from being paired exclusively on a per piston-assembly basis and hence torque imbalances by valve-assembly actuation still exist. Trimble et al. offer an approach to have a completely balanced engine in a more general case at the expense of more parts and increased size. Trimble et al. anticipate balancing by placing along a common barrel-cam shaft both an arbitrary barrel-cam engine and its “mirror image” across the plane normal to the barrel-cam shaft. This balances all piston-assembly and valve-assembly forces as well as moments. However, a pair of “mirrored” barrel-cam engines require that the piston-assemblies from both units along the same line of motion simultaneously move inward and outward. Therefore, the piston-assemblies, in line between both opposite units, cannot be connected. As a result, each unit requires its own barrel-cam. Consequently, for the same number of cylinders, this engine occupies more space than an engine using double-ended piston-assemblies with a single barrel-cam.
Fortunately, barrel-cam engines share the same fluid dynamics and thermodynamics as conventional crank-type engines since their combustion chambers, piston shape, and valve arrangement can be made identical to their conventional counterparts. This simplifies development since the only new considerations in design are the structural and reliability issues for the motion conversion mechanisms. Operational prototypes of barrel-cam engines have been constructed to date. Extensive development has been conducted by Dyna-Cam Engine Corp. At the time of the present invention, Dyna-Cam Engine Corp. claims to have developed their seventh generation engine based on the work by Herrmann (U.S. Pat. No. 2,237,621 and related subsequent patents). Their series of engines consisted of 12 cylinder, 6 double-ended piston-assembly, barrel-cam engines. Dyna-Cam Engine Corp. presently has a barrel-cam engine of this type in production for sale. Also Dyna-Cam Engine Corp. claims to have demonstrated a number of advantages in using a barrel-cam engine including quieter vibration-free operation and a significant reduction in number of parts compared to an equivalent crank-type internal-combustion engine. The ReJen Company is also developing a barrel-cam engine that is diesel powered with a regenerated cycle for general aviation aircraft propulsion and shipboard power generation. The ReJen company has received support from government contracts through NASA and the US Navy as well as support through partnerships with Caterpillar, Inc and Alvin Lowi & Assoc.
BACKGROUND—OBJECTS AND ADVANTAGES
The 12 cylinder, 6 double-ended piston-assembly, barrel-cam engine developed by Dyna-Cam Engine Corp. is particularly useful when a high number of cylinders are needed as in marine, industrial, heavy automotive, and aviation applications. However it is not well suited for applications that are cost sensitive and historically have a low number of cylinders such as in the personal automotive market. The idea proposed by Trimble et al. to utilize two “mirrored” barrel-cam engine units along a common barrel-cam shaft allows the use of as few as 2 cylinders for a fully balanced engine, but this comes at the expens
Denion Thomas
Eshete Zelalem
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