Patent Application
20130276761
The present disclosure relates generally to engines, and more particularly to variable-compression internal combustion engine assemblies.
Internal combustion engines (often referred to by the acronym “ICE”) convert chemical energy into mechanical energy typically through the combustion of a petroleum-based fossil fuel which is mixed with an oxidizer, such as air, in a combustion chamber. The resultant exothermic reaction of fuel and oxidizer creates gases of high temperature and pressure which expand to move a mechanical component. The two most common forms of internal combustion engines are the reciprocating engine, such as the modern-day automobile engine, and the continuous combustion engine, which includes jet engines and gas turbines. Reciprocating internal combustion engines include, for example, multi-stroke piston engines, and other well-known engine types.
In reciprocating-piston ICE designs, one or more pistons are used to drive a rotatable crankshaft. Each piston is slidably disposed inside a cylinder and connected to the crankshaft by a connecting rod. The stroke of the reciprocating assembly is determined by the offset of the crankshaft's connecting rod journal known as the crankshaft “throw.” This design can lead to numerous limitations and deficiencies. For instance, the crankshaft always generates the same stroke pattern for piston travel. It is a uniform motion and cannot be altered. Thus, the respective duration of intake strokes, exhaust strokes, compression strokes and power strokes, e.g., in a four-stroke ICE configuration, typically must coincide and are invariable. This is true of almost any engine utilizing a crankshaft no mater its size and number of cylinders.
Power is typically produced by filling each engine cylinder with an air-fuel mixture and inducing combustion of the mixture to generate heat and expansion to propel the pistons and, thereby, rotating the crankshaft. Filling the cylinder with an air-fuel mixture requires duration of time. Power produced by the ICE therefore has a direct correlation to the volumetric efficiency (VE) of the intake cycle. However, the time for the intake cycle is usually dictated by crankshaft speed and geometry; thus, volumetric efficiency is often compromised.
Achieving complete air-fuel mixture combustion, known as stoichiometric combustion, also takes time. To compensate for the restricted combustion interval, many conventional multi-stroke ICE designs advanced the ignition timing ahead of the piston achieving top dead center (TDC) during a compression stroke. The faster the speed of rotation, the more advancement of timing is used. This, in turn, wastes energy since additional power is required (during the compression stroke) to compress the expanding gases produced during the onset of the combustion process. This results in generated energy being used inefficiently. Due to the restrictions and other environment variables, stoichiometric combustion is briefly or never achieved.
A method commonly used to create additional compression time is to lengthen the connecting rod, thereby allowing the piston to “park” at top dead center for a longer than normal duration of time. However, there is a limitation to the length of the connecting rod used since longer rods will expand the physical size and weight of the engine. As such, additional time is inherently restricted.
The power output of conventional ICE designs is directly proportional to the work generated by the expansion of the combusted air-fuel mixture. Since the time within the power stroke to transfer power to the crankshaft is directly proportional to the rotational speed, unused heat and expansible energy are channeled out when the exhaust valve opens near the end of the power stroke and throughout the exhaust stroke as the piston approaches bottom dead center (BDC) and travels back to TDC. This leads to additional wasted energy.
As noted above, the piston within a traditional reciprocating-piston engine is driven up and down in the cylinder by the connecting rod which is directly connected to the connecting rod journal of the crankshaft. The 360-degree rotation of the crankshaft moves the piston forward from BDC to TDC and then back to BDC. Each cycle of reciprocation—e.g., piston movement to-and-from TDC, is known as the engine “stroke.”
During the second cycle of a four-cycle (or four-stroke) engine, the intake and exhaust valves for the specific cylinder are closed and the piston moves forward through its stroke distance and compresses the working volume of the cylinder into a chamber at the top of the cylinder. The change in combustion chamber volume created by the piston stroke is expressed numerically in a ratio, which is known as the Compression Ratio (CR). Compression Ratio can be expressed generally by the following formula:
CR=Cylinder volume when piston at BDC(A)/Cylinder volume when piston at TDC(B)
Fixed Compression Stroke distance is determined by the offset of the connecting rod journal which is shaped into the crankshaft profile. The offset is known as the crankshaft “throw”. The throw is a fixed distance and cannot be altered; thus, the stroke distance is fixed and cannot be altered. This directly affects the intake, compression, power and exhaust cycles limiting the operating parameters of the engine.
There are limited prior art designs where a piston interacts directly with an undulating flywheel surface. One design that arguably bears some relationship to an engine of this type is disclosed in U.S. Pat. No. 3,745,887, which issued to George Striegl on Jul. 17, 1973. Striegl discloses a reciprocating engine with pistons that interact with a hollow cylindrical “rotor” having a cam edge. Each piston of the Striegl device is nested in its own individual hollow rotor, with each rotor connected by an output/drive shaft to a flywheel. All of these elements are in axial alignment. However, there is nothing in Striegl that has off-axis pistons interacting with the surface of a flywheel. Nor, does Striegl provide the additional design flexibility necessary for the truly efficient functioning of piston-based internal combustion engines.
Based on the foregoing limitations and deficiencies associated with conventional reciprocating-piston ICE engines, including those that utilize flywheels, there is a continuing need for additional flexibility in designing the pattern, speed, and timing for various strokes in piston-based internal combustion engines.
Aspects of this disclosure are directed to an innovative engine design that incorporates opposing pistons which are located within the same cylinder and driven towards each other by two undulating flywheels at opposite ends of the engine assembly. Each flywheel has a precise cam-like surface profile that controls stroke height and duration interval of piston travel throughout the engines cycles. When both pistons are at TDC, the volume between the piston tops creates the combustion chamber. This configuration eliminates the need for a conventional crankshaft.
Rotation of the two flywheels in the above example can be held in synchronization by a main shaft that runs the length of the engine. In some embodiments, the main shaft has a key or external splines that mate with a complementary center hole in each flywheel which has a matching key slot or internal splines. This allows the combustion force applied to the flywheels to be transferred to the main shaft, which can also serve as the output shaft for the engine. The splined engagement also allows the flywheels freedom to move back-and-forth along the length of the main shaft.
By utilizing hydraulic, pneumatic, and/or mechanical forces applied to or removed from the flywheel—e.g., a surface of the flywheel which is opposite the cam-like surface for the piston—the flywheel can be selectively moved forward and/or backward along the main shaft. This results in the combustion chamber volume changing and, thus, a changing compression ratio. In real time and precisely controlled during engine operation, this innovative engine design has true variable compression.
Some advantages of the disclosed cam-like flywheel surfaces derive from the fact that the surface can be shaped and formed so as to provide specific engine cycle features desired by the designer. For instance, it provides extraordinary flexibility in adjusting the duration of the intake/exhaust cycle, the duration of the combustion/power cycle, the intake stroke pattern (e.g., to maximize cylinder fill volumetric efficiency), the power stroke pattern (e.g., to maximize transfer of power from the piston to the flywheel), and to park the piston at TDC during power stroke for a longer duration to achieve stoichiometric combustion. In comparison, the conventional crankshaft, piston, and connecting rod arrangement of traditional ICE assemblies provides limited design flexibility. In the conventional assembly, the offset shaped into the crankshaft fixes duration within the 360-degree crankshaft rotation. And, TDC and BDC durations can be only minimally altered through the use of different length connecting rods at a given crankshaft offset distance. Additional benefits associated with cam-like flywheel surfaces and expansible-chamber engines are disclosed in commonly owned U.S. Pat. No. 7,040,262, to Patrick C. Ho, which is incorporated herein by reference in its entirety and for all purposes.
The variable compression features disclosed herein provide controllable compression ratio, increased combustion efficiency, controllable power output and combustion characteristics and improved emission performance of the engine. By way of example, variable compression allows the engine to adapt to initial startup conditions and then maintain correct parameters during normal operation under various load conditions. It also allows the engine to adapt to various compositions of fuel types, quality, and combustion characteristics. Moreover, the CR can be continuously adjusted in real-time during engine operation to compensate for varying engine load, temperature, and operating changes to achieve optimal performance.
According to aspects of the present disclosure, an engine assembly is presented. The engine assembly includes an output shaft and a flywheel with a variable cam surface. The flywheel is slidably mounted onto the output shaft and rotatable about a flywheel axis. The engine assembly also includes an internal combustion device with a piston that is movable along a central axis in a cycle between retracted and extended positions. The piston engages the variable cam surface. The central axis of the piston is spaced from the flywheel axis. The cycle includes a power stroke when the piston moves from the retracted position to the extended position whereby the piston presses against the variable cam surface and thereby rotates the flywheel, and a compression stroke when the piston moves from the extended position to the retracted position responsive to the variable cam surface.
Other aspects of the present disclosure are directed to a variable-compression engine assembly. The variable-compression engine assembly includes an output shaft that is rotatable about a common axis, and a flywheel with a variable cam surface that is mounted onto the output shaft for common rotation therewith. The flywheel is rotatable about the common axis and selectively slidable on the output shaft along the common axis. The variable-compression engine assembly also includes an internal combustion device with a piston disposed in a cylinder. The piston is movable along a central axis in a cycle between retracted and extended positions. An outboard end of the piston engages the variable cam surface. The central axis of the piston is radially spaced from the common axis. A prime mover is configured to move the flywheel longitudinally along the output shaft to thereby selectively change a compression ratio of the internal combustion device. The cycle includes a power stroke when the piston moves from the retracted position to the extended position whereby the piston presses against the variable cam surface and thereby rotates the flywheel, and a compression stroke when the piston is moved by the flywheel from the extended position to the retracted position responsive to the variable cam surface.
Additional aspects of this disclosure are directed to an engine assembly. This engine assembly includes an output shaft, first and second flywheels and an internal combustion device. The output shaft is rotatable about a common axis. The first flywheel has a first variable cam surface and is slidably mounted onto the output shaft and rotatable about the common axis. The second flywheel is coaxial with and spaced from the first flywheel. The second flywheel has a second variable cam surface that is facing the first variable cam surface. The second flywheel is mounted onto the output shaft and rotatable about the same common axis as the first flywheel and output shaft. The internal combustion device is disposed between the first and second flywheels. The internal combustion device has first and second opposing pistons each of which is movable along a central axis in a cycle between respective retracted and extended positions. The central axis of the pistons is spaced from the common axis of the output shaft and flywheels. The first piston engages the first variable cam surface whereas the second piston engages the second variable cam surface. Each cycle includes a power stroke, whereat a respective one of the pistons moves from respective retracted to extended positions whereby the respective piston presses against a respective one of the variable cam surfaces and thereby rotates a respective one of the flywheels, and a compression stroke, whereat the respective piston moves from respective extended to retracted positions responsive to the respective variable cam surface.
The above summary is not intended to represent each embodiment or every aspect of the present disclosure. Rather, the foregoing summary merely provides an exemplification of some of the novel and inventive features included herein. The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiments and best modes for carrying out the present invention when taken in connection with the accompanying drawings and appended claims.
While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
This invention is susceptible of embodiment in many different forms; herein, there are shown in the drawings and described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated. To that extent, elements and limitations that are disclosed, for example, in the Abstract, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference or otherwise. For purposes of the present detailed description, unless specifically disclaimed: the singular includes the plural and vice versa; the words “and” and “or” shall be both conjunctive and disjunctive; the word “all” means “any and all”; the word “any” means “any and all”; and the words “including” and “comprising” mean “including without limitation.” Moreover, words of approximation, such as “about,” “almost,” “substantially,” “approximately,” and the like, can be used herein in the sense of “at, near, or nearly at,” or “within 3-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof, for example.
Referring now to the drawings, wherein like reference numerals are used to refer to the same or similar components throughout the several views, there is shown in
The internal combustion device 12, as shown, is an expansible chamber device that includes an elongated hollow cylinder 16 within which is housed a first (left) piston 18A in opposing spaced relation to a second (right) piston 18B, as best seen in the cross-sectional views of
In the embodiment shown, the cylinder 16 includes four ports: an air inlet port 20, a first (left) exhaust port 22A, a second (right) exhaust port 22B, and a fuel inlet port 24 (see
Rotation of the two flywheels 14A and 14B can be held in synchronization by a main shaft 30 (also referred to herein as “output shaft”) that runs the length of the engine assembly 10. The first flywheel 14A of the illustrated embodiment is coaxial with and spaced from the second flywheel 14B. In this regard, both flywheels 14A, 14B are mounted on, concentrically aligned with, and circumscribe the main shaft 30 to rotate about a common axis A2 (also referred to herein as “flywheel axis”). The flywheels axis A2, as shown, is generally parallel to and radially spaced from the central axis A1 of the pistons 18A, 18B.
In the illustrated embodiment, both flywheels 14A, 14B are mounted onto the output shaft 30 for common rotation therewith. That is, the output shaft 30 and flywheels 14A, 14B all rotate in the same direction Dl and, in at least some embodiments, at the same rotational velocity R1. Alternative designs could have two main shafts (shown schematically at 30A and 30B in
With reference back to
According to the example shown in the drawings, the first piston 18A engages the first variable cam surface 34A while the second piston 18B engages the second variable cam surface 34B but not the first cam surface 34A.
At least one, and in the illustrated embodiments both flywheels 14A, 14B are slidably mounted onto the output shaft 30. Some configurations allow the flywheels 14A, 14B to slide rectilinearly back-and-forth on the output shaft 30 along the common axis A2 such that the flywheels 14A, 14B can translate along the longitudinal length of the shaft 30 towards each other and the internal combustion device 12, as illustrated by arrows 46A and 46B in
Altering the position of one or more of the flywheels 14A, 14B relative to the internal combustion device 12 operates to change the compression ratio of the internal combustion device 12. Because the pistons 18A, 18B ride on the variable cam surfaces 34A, 34B of the flywheels 14A, 14B, they too will move back-and-forth with the flywheels 14A, 14B. As a result, the space between the tops of the opposing pistons 18A, 18B at TDC, which is the combustion chamber 26 for the ICE assembly 16, will likewise change in volume relative to flywheel position. The change to a larger or smaller volume results in lower or higher compression ratio, respectively. By way of non-limiting example, the first flywheel 14A can be moved on the output shaft 30 from a first longitudinal position (e.g.,
The positional changes of each flywheel 14A, 14B can be effectuated in “real time”—i.e., while the engine assembly 10 is in operation. For the flywheels 14A, 14B to move back and forth along the main shaft 30, a force is applied to or removed from the flywheels 14A, 14B, for example, at the surface that is opposite the variable cam surface 34A, 34B. In a non-limiting example, the engine assembly 10 includes one or more prime movers, designated generally at 60A and 60B in
The introduction of additional pressurized fluid 68 into the fluid cavities 64A, 64B increases cavity pressure. In so doing, the flywheel pistons 66A, 66B are urged against the flywheels 14A, 14B thereby moving the flywheels 14A, 14B longitudinally along the output shaft 39 towards the internal combustion device 12, as seen in
Alternatively, the cavities 64A, 64B could contain mechanical means to increase or decrease the force on the backside of the flywheel pistons 66A, 66B. For instance, a cam or series of cams positioned against the backside of the flywheel pistons 66A, 66B could be rotated or otherwise actuated, e.g., by external electric, hydraulic, mechanical or manual means, to move the pistons 66A, 66B. In other optional configurations, the cavities 64A, 64B could contain a worm gear or series of worm gears that operatively engage and move the flywheel pistons 66A, 66B. Gear movement could be effectuated by external electric, hydraulic, mechanical or manual means. The cavities 64A, 64B could alternatively contain a lever or series of levers that are attached by a pivot. Lever movement is actuated by external electric, hydraulic, mechanical or manual means.
Variations in engine operating conditions, such as engine and ambient temperatures, fuel mixture, rpm, engine load, and so forth, have an effect on the engine's efficiency. Often times, the best engine efficiency stems from consistent Stoichiometric combustion under any operating condition. The variable-compression engine assembly 10 disclosed herein provides the ability to change to any compression ratio necessary, e.g., at any time in the engine cycle—even during combustion if sensor feedback and flywheel movement is quick enough, to maintain a consistent Stoichiometric event. In so doing, the engine assembly 10 is more efficient than its conventional counterparts. Another potential benefit is that the engine assembly 10 can operate with a variety of different fuels. For example, the engine assembly 10 could run on gasoline at 10:1 and switch to diesel at 20:1 (in real time) or any other fuel thereof.
The overall operation of the engine assembly 10 can be understood by considering the illustrated configuration in use as a two-stroke engine. In this application,
Notwithstanding the foregoing description of the illustrated embodiment, it should be realized that the engine assembly 10 could also be structured with a single piston interacting with a single flywheel and corresponding variable cam surface. This configuration can, in effect, be illustrated by taking either side of
There are several advantages to be realized from the variable-compression engine assembly 10. For example, the engine assembly 10 does not include a traditional crankshaft or connecting rods, so the dynamic loads and stresses associated with such rapidly accelerating, decelerating, rotating, and reciprocating members are eliminated. Fewer rotating and reciprocating parts also reduces friction losses. The engine assembly 10 is also lighter in weight because of fewer components, and because reduced internal antagonistic forces allow for lighter construction. Other advantages stem from the variable cam surface configurations, which can be designed to vary or control numerous engine parameters, for example, by varying piston movement. In a non-limiting example, the amplitude of the wave pattern can be increased or decreased to increase/decrease the structural compression ratio (and piston travel/stroke).
Numerous variations to the cam surfaces are possible that can alter the structural compression ratios, duration of intake/exhaust stroke, duration of combustion/power stroke, compression stroke pattern (to maximize cylinder fill volumetric efficiency), and power stroke pattern to maximize transfer of power from piston to flywheel. Overall, the amplitude of a stroke is based on crest to trough amplitude, while the length of time allowed for any event in the engine cycle is related to the slope of the portion of the undulating surface corresponding to the event. A steeper slope dictates a shorter time, while a flatter or flat slope extends the time. The aforesaid ability to freely vary, shape and determine various engine performance parameters stands in stark contrast to conventional crankshaft-piston-connecting rod assemblies. In these assemblies, rotational duration is fixed by the radius of the crankshaft, and piston TDC and BDC duration can be only minimally altered by use of connecting rods of different lengths.
The expansible chamber itself can also be designed and configured to enhance certain characteristics. As previously noted, the expansible chamber engine configuration reduces the weight of the reciprocating assemblies by eliminating connecting rods, a crankshaft, and counterweights, and with fewer cylinders for a given number of power strokes per flywheel revolution. As the tops of the two pistons form the combustion chamber at their top dead center, there is enormous flexibility in designing the shape of the combustion chamber for complete and efficient combustion, flame propagation, and maximum combustion pressure. Intake and exhaust ports can also be located to enhance the discharge of exhaust gas, influx of incoming air, and tumbling and turbulence within the cylinder. Additional advantages and alternatives are disclosed in commonly owned U.S. Pat. No. 7,040,262, to Patrick C. Ho, which is incorporated herein by reference.
While exemplary embodiments and applications of the present disclosure have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
