Patent Application
20050016493
1. Field of the Invention
The field of the invention relates to internal combustion (IC) engines. More particularly, the invention relates to toroidal internal combustion engines.
2. Description of the Prior Art
The traditional reciprocating IC engine has been around for more than 100 years, yet its design has several inherent disadvantages. One major disadvantage is that the energy released by combustion is converted work via linearly moving pistons and is then converted to rotational work output when it is transmitted to the crankshaft. This transfer of work output from linear to rotational motion is inherently inefficient for several reasons. For one, the slider crank mechanism that receives the work output from the piston is not at an optimum position for producing high torque on the crankshaft when pressure in the combustion chamber peaks and, consequently, only a portion of the energy generated by the combustion process is transmitted to the crankshaft, with the rest being dissipated in side thrust resulting in frictional work. Piston rings are used to provide a seal between the pistons and the cylinder wall, and also absorb the side thrust of the pistons that results from the slider crank configuration. With this configuration, the scraping action of the piston assembly, i.e., piston and piston rings, along the cylinder wall accounts for 50-70% of the total friction losses of this engine design.
The poppet valves typically used in the reciprocating IC engine are also sources of energy loss for several reasons. First, they are subject to high friction, noise, and vibration, all of which dissipate energy. The typical valve configuration, in which both intake and exhaust valves are located in close proximity to each other in the cylinder head, is also a source of energy loss during valve overlap. During valve overlap, in which both valves are open at the same time for at least a portion of a stroke, some of the fresh charge being drawn into the cylinder escapes directly through the exhaust valve, thereby reducing the mass of fuel-air mixture entering the cylinder. The heat transfer from the exhaust gas to the incoming charge also contributes to the reduction in mass of fresh charge available for combustion.
Rotary or toroidal IC engine designs have been investigated in the past in an attempt to overcome some of the inherent shortcomings of the traditional reciprocating IC engine. Rotary engines include designs with reciprocating pistons within a rotating housing, such as the Selwood Orbital and Bradshaw Omega toroidal engines, as well as cat-and-mouse piston designs, such as the Tschudi and Kauertz engines, in which pistons travel with variable velocity in a circular path. Toroidal engines have some distinct advantages over the traditional reciprocating piston engine, such as excellent balance (Selwood and Bradshaw Omega), absence of valve mechanisms, small size, and high power-to-weight ratio. The Wankel engine, an eccentric, three-chamber rotary engine, has perhaps found the most success with its simple design and small size. Despite these advantages, problems of nonuniform heating, sealing, inertia effects, and/or lubrication have prevented these engines from taking hold in the market place. These and other rotary engines are described in: Chinitz: Walter; Rotary Engines, Scientific American, February 1999, pp. 90-99.
A number of toroidal engines of the prior art teach a toroidal construction in which a pair of rotors that operate in parallel, but spaced-apart planes are enclosed within a housing. Piston vanes are integrally formed or mounted on the rotors, with the faces of the vanes forming increasing or decreasing chambers as the rotors counter-rotate, i.e., rotate in opposite directions. Parmerlee (U.S. Pat. No. 3,702,746; 1972) discloses such a toroidal engine that is a free-piston gas generator. Intake and exhaust ports are provided in the wall of the housing, as are bypass recesses. Simultaneous combustion in two chambers, spaced 180 degrees apart, forces the vanes on each rotor that bound the combustion chamber to move apart, thereby causing the rotors to rotate and simultaneously increase the combustion and intake chambers and decrease the compression and exhaust chambers. Ports and/or bypass recesses are situated in the housing such that they are appropriately opened or closed by the side walls of the vanes as they rotate within the housing. Kim (U.S. Pat. No. 6,321,693; 2001) also discloses an internal combustion engine having a rotor-piston-housing configuration similar to that of Parmerlee. In the Kim engine, intake and exhaust valves are placed in close proximity to each other on the housing, spaced 90 degrees apart. These engines solve some of the inefficiencies and force-balance problems inherent in a linearly reciprocating piston engine design that converts work output to rotary motion, because combustion is simultaneously taking place at two places 180 degrees apart within a torus. However, due to the configuration and engine construction, the forces exerted on the rotors and, thus, the housing are very high and will necessarily require very high-performance seals, problems that the designs of these engines do not solve. None of the disclosures for the toroidal engines of the prior art addresses cooling techniques to prevent overheating, warping, or destruction of the engine during routine operation.
What is needed, therefore, is an IC engine that provides superior performance with greater efficiency and reduced emissions. What is further needed is such an engine that is lighter in weight, smaller in size, and has fewer moving parts. What is yet further needed is such an engine in which the mechanical forces are dynamically balanced and the thermal stresses evenly distributed. What is still yet further needed is such an engine with reduced loads and requirements on seals, lubrication, and cooling.
For the reasons given above, it is an object of the present invention to provide an IC engine that provides superior performance and reduced emissions. It is a further object to provide such an engine that has fewer moving parts, is lighter in weight, and small in size than a conventional IC engine of comparable power. It is a yet further object to provide such an engine in which the mechanical forces are dynamically balanced and the thermal stresses evenly distributed. It is a still further object to provide such an engine that requires fewer and simpler seals and has reduced requirements for cooling and lubrication.
The above-cited objects have been achieved by providing a toroidal IC engine with free-moving pistons within an engine ring that is a torus. The torus is formed of two concentric rings, an inner engine ring and an outer ring. The two rings are sealed along two ring seams to form the complete torus. One set of pistons is affixed to the outer ring and another set of pistons is affixed to the inner engine ring. The pistons of each set are at a fixed interval relative to each other. The torus thus forms the chamber walls and the faces of the pistons form the boundaries of the chambers within the torus. Pressure applied to the faces of pistons forces the pistons to move, with the result that the inner and outer rings of the torus counter-rotate relative to one another and the pistons slide in the torus along the walls of the ring to which they are not affixed. For purposes of illustration and simplicity, the toroidal IC engine according to the present invention will be described hereinafter as being a four-stroke engine having eight pistons and eight chambers. Thus, four of the eight pistons are affixed to the outer ring at 90 degree intervals, and the four other pistons are affixed to the inner engine ring, also at 90 degree intervals. In an engine of this configuration, the torus contains two chambers for each stroke of the 4-stroke cycle, that is, two combustion chambers, two intake chambers, two compression chambers, and two exhaust chambers. Any two chambers going through the same stroke are spaced 180 degrees apart on the torus. When combustion occurs, the pressure change forces the two pistons bounding the two combustion chambers apart, effectively forcing the two rings to counter-rotate. Because the four pistons on a ring are fixed in a 90-degree spatial relationship to each other, the pressure changes in the two combustion chambers simultaneously force four chambers to increase and four chambers to decrease in volume. It should be understood that this engine is configurable with any number of pistons greater than one, depending on the size and power requirements of the engine. For example, the toroidal IC engine may also be constructed as a 2-stroke engine with six pistons. In this case, at any one stroke of the engine cycle, three chambers of the six chambers are combustion chambers and are fixed in a 120-degree spatial relationship to each other on the engine ring.
In the engine according to the invention, the inlet and exhaust valves are assembled directly on the piston faces, with one valve only on each face. Each piston has two faces and, ideally, either an exhaust valve or an intake valve is assembled on each face of a piston and all pistons with intake valves are assembled on one ring and all pistons with exhaust valves on the other ring. This arrangement simplifies the construction of the engine because each piston requires only one connection to the respective intake or exhaust maniforld and all pistons on one ring are fed from the same manifold. Thus, all pistons connected to one ring allow the introduction of a fresh charge into the engine, while all pistons connected to the other ring allow exhaust products to exit the engine. This construction provides the further advantage that the fresh air charge enters through a piston face at one end of the chamber and the exhaust gases exit through a piston face at the other end of the chamber. This arrangement reduces the portion of fresh air charge being swept out through the exhaust valve during any intake and exhaust valve overlap and improves scavenging (the elimination of exhaust gas) and control over the amount of fresh charge taken in during the intake stroke. Placing the intake and exhaust valves at opposite sides of the chamber also enhances mass flow into the engine, because the intake valve stays cooler than in the traditional valve arrangement in which intake and exhaust valves are placed close together on the cylinder head. Furthermore, by forcing the fresh air into one end of the chamber while venting exhaust at the other end of the chamber, fresh air bathes and cools the exhaust valve only after it has entered one end of the chamber and traveled to the opposite end.
Placing only one valve on a piston face provides a greater surface area available for the valve and makes it possible to use types of valves other than the traditional poppet valve. The valve types most suitable to the toroidal IC engine are slider or slot valve types. Valve systems using these types of valves allow faster opening and closing operation and are much lighter, smaller, and require less energy to operate than conventionally used poppet valve or sleeve valve systems. Preferably, the valves are hydraulically, pneumatically, or electromechanically controlled, as the actuation has shown to be fast, efficient, and light for similar applications, such as the operation of clutches. With these three actuation types, all valves are independently actuatable, allowing optimization of the engine under various conditions, which further contributes to increased performance and decreased emissions. As described earlier, the intake and exhaust valves are on opposite sides of the chambers, providing optimal scavenging for both two and four stroke cycle modes (no piston contouring needed), and enabling independently operable valves as a function of piston position. This independent operation of the valves, along with their ideal placement on the piston face, allows the engine to be switched from a four stroke to a two stroke mode during operation. This capability theoretically doubles the power output of the engine, nearly instantaneously, without an increase in engine speed. This opens up the possibility of an entire new class of engines having dual-cycle-mode operating characteristics. The power-to-weight ratio of the engine is again doubled, having a major impact on the power output range of the toroidal IC engine according to the invention. In addition, ability to independently operate the valves enables optimization of valve time as a function of engine speed and load, and this further reduces emissions. The power-to-weight ratio of the engine is doubled again, having a major impact on the power output range of the toroidal IC engine. Note that the engine is still dynamically balanced in both the four or two stroke cycle modes, because the combustion strokes occur at every 90° in the described configuration.
Since only one valve is placed on the piston face, the entire surface area of the piston face is available as working surface for the valve. The surface area is sufficiently large that it is possible to place an appropriate device in the center of the piston face for spark-ignition or fuel injection. Placing the spark plug in the center of the piston face has the advantage that is provides the shortest possible flame travel during combustion. This has proven to prevent detonation and decrease emissions in the engine. For compression ignition engines, the direct fuel injection would ideally be located near the center of a piston face.
The toroidal IC engine according to the invention requires two different types of seals, a piston seal and a ring-seam seal. The engine ring-seam seal has two major tasks which prescribe a different design than that of the piston ring seal in the traditional engine. First, the engine ring-seam seal must act as a sliding surface for the inner and outer engine rings and prevent blowby of high pressure gas from the combustion chambers to the surrounding area outside the torus. Second, the engine ring seam seal must provide a gas seal between adjacent chambers. It is known that the o-rings used in the past inherently lead to leakage. The seal requirements for the toroidal IC engine are very different. For one thing, combustion occurs evenly around the toroidal IC engine, which reduces thermal stresses in the engine torus and, thus, prevents engine warping. The engine is also constructed from advanced composites having a low thermal expansion coefficient, which further reduces thermal stresses and prevents engine warping. The lack of side thrust, the low thermal expansion coefficient, and the known self-lubricating characteristics of advanced composite materials (to be discussed below) make it possible to operate the toroidal IC engine without an O-ring-type seal at the engine ring seam and without the traditional oil lubrication system. The ring seam on the engine torus is constructed to be self-sealing, that is, the seam surfaces on the inner and outer rings are machined to act in a self-sealing manner. The pressures on the inside surface of each engine ring have a resultant force in opposite directions, which effectively forces the seam surfaces together. Ideally, the seam surface on the inside of the chamber is flush with the cross section of the torus shape. When the piston passes over the ring-seam seal, there is no gap for high pressure gas to leak through into the adjacent chamber. This design requires that the engine ring seam surfaces be accurately and precisely machined to obtain even surface contact around the inner circumference of the torus.
If precise machining is not practical or economically feasible, a flexure piece may be used to provide the ring-seam seal. A small slit or cavity is cut into one of the two surfaces of each seam to form a flexure piece. Flexion in this small piece allows the seal surface to flex/bend slightly to form a seal against the adjacent surface of the ring seam. Note that the flexion of this piece is effected during high pressures in the chamber. The appropriate size and location of the slit is dependent upon the material properties and anticipated irregularities in the seam surfaces. It is also within the scope of the present invention to provide a separate engine ring seam seal. The advantage of using a separate engine ring seal is that the wear resulting from the motion of the inner and outer engine rings is carried by the seal and, thus, wear on the engine ring is minimal. It is, of course, much more economical to replace the engine seal, rather than the engine ring. The applicant has determined that a separate seal with a delta geometry crossection provides excellent sealing characterisitics.
The pistons are machined to fit with minimal clearance within the torus cross section, with one half of the piston being rigidly attached to either the inner or the outer engine ring and and the other half fitted with an integrated seal that will allow the piston to slide in the other engine ring, while maintaining a sealed chamber. Thus, the pistons are not fitted with an independent ring seal. As mentioned above, the engine ring and the pistons are constructed of composite materials. Because the thermal expansion coefficient of the composite materials is very low and the pistons and engine rings are machined to close tolerances, the pistons provide an adequate seal between the chambers without requiring separate piston seals. Ringless pistons provide the advantage of reduced friction, as the absence of piston rings eliminates additional piston ring friction resulting from increased cylinder pressure during combustion, and also reduces emissions, as there is no gap between piston and chamber wall to harbor unburned fuel.
The toroidal IC engine according to the invention is operable in a two or four stroke cycle mode, with spark ignition or compression ignition. The following is a brief summary of the four stroke, compression ignition cycle operation. Refer also to
The reciprocating action of the pistons in the torus allows adjacent pistons to share chamber volume. Thus, the swept volume (engine displacement) of the toroidal IC engine of the present invention is substantially double that of a conventional engine with the same volume. For example, an engine having a torus diameter of 12 inches measured from seam to seam, a piston-face diameter of 3.5 inches, and a piston thickness of 3.0 inches will have 263 cubic inches of swept volume. The swept volume is essentially equal to twice the actual volume of the engine (volume of the eight chambers), assuming an infinite compression ratio.
The geometry of the torus and the fact that combustion occurs simultaneously at two locations 180 degrees apart and in all chambers around the torus in the course of the four-stroke cycle, are factors that contribute to a dynamically and thermally balanced engine. During combustion, the pressure applied to the chamber walls tends to force the inner and outer rings apart at that location. The shape of the torus and a self-sealing construction of the ring seam, however, hold the rings together. The self-sealing effect results from the fact that the ring seam is designed such that the equal but opposite forces on the engine rings force the seam edges against each other to effect a tighter seal, rather than forcing them apart. In addition, the forces on the chamber walls (inner and outer ring walls) during combustion in one chamber cancel out the forces from the other chamber 180 degrees out. This attribute eliminates adverse forces on the engine mounting shaft, resulting in reduced friction (higher thermal efficiency) and a completely balanced engine during operation. In addition, the reduced friction reduces wear and lubrication requirements, increases reliability, and reduces maintenance.
The mass inertia of the inner and outer rings is balanced so that the momentum of the rings during the rotation is essentially the same. This and the fact that the rings counter-rotate and that the rotation stops and starts at the same time eliminates adverse inertia effects, such as are inherent in the Tschudi and Kauertz engines. The toroidal IC engine of the present invention is dynamically balanced, with much reduced vibration and smoother operation. Furthermore, the inertia loads on the torus (including the pistons) are opposed by the pressures in the combustion and compression chambers, instead of being absorbed by connecting rod-crankshaft bearings, as in the traditional reciprocating design. By contrast, the configuration of the Kim design has axially opposing side walls. The forces on the walls translate into friction forces on the sliding surface, which reduces efficiency.
Inherent in the design of the toroidal IC engine according to the invention is uniform heating of the engine. This is because combustion occurs once in all chambers of the toroidal IC engine in the course of operation of a full cycle. With reference to a four-stroke cycle engine with eight chambers, combustion occurs in each of the eight chambers once in the four-stroke cycle. This intermittent heating at eight equally spaced positions around the torus results in uniform heating and significantly reduces thermal stress on the engine.
Ideally, the toroidal IC engine of the present invention is constructed entirely of carbon-reinforced carbon (CRC) material. The thermal expansion of the CRC material is extremely low, thus, engine warping due to nonuniform heating is minimal. The CRC material has the potential to reduce the weight of the engine on average by a factor of two or more. It is known that carbon-carbon composite materials have oxidation problems at elevated temperatures. To avoid this problem, the engine is coated, in oxygen exposed areas, with a suitable coating, such as silicon carbide, which prevents oxidation and provides additional insulative properties. The CRC material and the coating drastically reduce the cooling requirements of the engine. In addition, the advanced materials allow higher operating temperatures, which reduces heat transfer losses and results in a higher fuel conversion efficiency of the engine. The use of the CRC material plays a significant role in the ability to switch from a 4-stroke to a 2-stroke operating mode and still retain thermal equilibrium while operating. This is because the CRC material allows higher operating temperatures, whereby the 2-stroke mode requires the higher operating temperatures because it undergoes twice as many combustion strokes as the 4-stroke does in one cycle.
The combination of uniform heating, the extremely low thermal expansion of the CRC material, and the fact that all combustion chamber walls are surrounded by air makes this toroidal IC engine ideal for air cooling. Elimination of a water cooling system further reduces the weight and size of the engine, while increasing its reliability. This, together with the weight savings due to engine design mentioned above, provides a potential increase in power-to-weight ratio of this toroidal IC engine over the traditional engine design of at least 6:1.
As with traditional free piston engines, the compression ratio of the toroidal IC engine of the present invention is variable and is dependent upon the ignition point of the fuel and/or fuel injection for both spark and compression cycle modes. This characteristic allows optimization of the operating cycle (increased thermal efficiency) based on the type of fuel utilized, reducing both fuel consumption and emissions. Unlike the traditional free piston engine, the toroidal IC engine does not rely on a bounce cylinder to return the piston on compression, which severely limited the speed/power output of the conventional free piston engine. Since combustion occurs on both sides of the pistons, the engine is capable of much higher operating speeds. In addition, the engine is operable in a four stroke or two stroke cycle mode, whereas the traditional free piston engine operates strictly on the two stroke cycle. Note that the inner and outer rings must be linked to ensure that they move with the same angular velocity and acceleration. This is necessary in order for the mass inertia of the reciprocating rings to balance each other out for smooth operation, and to keep the rings from rotating around the center shaft. A mechanism similar to a dual rack and pinion gear, in which one rack is connected to the outer ring, the other rack to the inner engine ring, is a suitable mechanism for linking the two racks together to ensure that both rings move through the same angle of rotation. The movement of the pinion is used to measure the location of the rings during operation. Note that no load is to be extracted by this mechanism and, hence, a small, fine tooth gear system is suitable for effective operation.
Ideally, the toroidal IC engine according to the invention is mounted on a central shaft, along with intake and exhaust manifolds that have passages that connect to the intake and exhaust valves, respectively, in the pistons. The exhaust passages head from the pistons toward the center shaft. This provides an ideal arrangement for installing a turbocharger/turbocompounding/turboalternator unit with radial flow compressor and turbine. The compressor and turbine are aligned on the same center shaft as the engine, resulting in a very compact and light weight system.
The toroidal IC engine according to the invention decreases the actual total chamber length (cylinder volume) by 50% because adjacent pistons share chamber space. In addition, cylinder heads, crankshaft, or connecting rods are eliminated. Hence, weight and size of the engine are radically reduced, each by approx. 70%. Because of the substantially lower friction losses, the toroidal IC engine of the present invention produces more power than a conventional slider crank engine for the same volume displacement. This attribute alone increases the power-to-weight ratio of the toroidal IC engine by greater than a factor of three. This in turn reduces the weight of the vehicle, which translates into lower fuel consumption and reduced emissions.
One major difference between compression ignition engine and spark ignition is the compression ratio. Compression ignition requires higher compression ratios for auto-ignition of the fuel to take place. Since the compression ratio of the toroidal IC engine according to the invention is variable, the engine is operable in either mode. Unlike the traditional diesel engine, which is much heavier than the spark ignition engine, the toroidal IC engine does not require a significant change in engine housing construction in order to accommodate a variable compression ratio feature that allows the toroidal IC engine to switch between low and high compression ratios. This is because of the elimination of the cylinder head of the traditional design. In the toroidal IC engine, the forces on the engine rings do not increase at high compression ratios because the area of the exposed engine ring decreases linearly with the compression ratio. As a result, the forces remain nearly constant in an engine with a variable compression ratio. Auto-ignition temperatures vary for different fuels and the variable compression ratio feature of the engine automatically optimizes the engine cycle, based on the type of fuel used.
Various methods of power extraction are suitable for the toroidal IC engine according to the invention and are not discussed to any extent herein. The most suitable method of power extraction will depend to some extent on the particular application of the engine. Three different suitable methods of extracting energy from the engine are: a mechanical power train, an exhaust turbine, or an electric alternator.
It is possible to use other seals, other than the self-sealing ring seam seal 10C described above.
Each chamber 11 is bounded by two pistons 3 in the torus 10. As shown in
Each of the
It should be clear from the previous discussion of
A preliminary study was completed by the applicant of the present application to determine whether the toroidal IC engine 100 according to the invention could operate at similar power output range of traditional engines. The study considered a 12 inch diameter torus shape, 3.5 inch piston face, and 3.0 inch piston thickness, which provided an engine of approximately 260 in3 swept volume. The toroidal IC engine was to operate at an equivalent 5000 rpms of a traditional engine. The proposed engine ring velocity was assumed sinusoidal, from which an equation for engine ring acceleration was derived. A standard indicator diagram for a spark ignition engine, with a peak pressure of 750 psi, was used for pressures in the chambers of the proposed engine. Estimates for ring seam and piston friction were included in the calculations, and mass inertia was calculated based on an engine construction of carbon-carbon composite (approximate engine weight was calculated to be 35 pounds). The study showed that with the cylinder pressures of the traditional engine, acceleration rates of the engine rings were above those needed to operate at 5000 rpm, indicating that the engine was still producing power. From the calculations, an estimated power output of approximately 600 horsepower was found (neglecting power train and valve losses). Although this study was not complete, it indicates that the toroidal IC engine according to the present invention has a very high potential to provide superior performance compared to the traditional design.
The toroidal IC engine 100 according to the invention is preferably constructed of carbon-reinforced carbon (CRC) composite material. In oxygen-exposed areas, the engine surfaces are coated with a coating to prevent oxidation. Silicon carbide, for example, is a suitable coating material that also provides insulative properties, which further reduce the cooling requirements of the engine. It should be noted that no oil lubrication system is shown in the Figures. The toroidal IC engine 100 according to the invention is a self-lubricating engine that requires no oil lubrication system. In the conventional internal combustion engine, a crankshaft for power extraction applies a powerful side thrust to pistons. This side thrust is completely lacking in the toroidal IC engine 100. The use of the composite, self-lubricating CRC material, the even distribution of thermal stresses on the engine due to multiple combustion strokes that take place all around the engine ring in the course of an engine cycle, and the much reduced friction forces due to the lack of the side thrust all contribute to the embodiment of a self-lubricating engine that is continuously operable for extended periods of time with air-cooling and without oil lubrication and oil cooling.
It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the toroidal IC engine may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.
