WO1999058831A1

WO1999058831A1 - Compound engine having increased fuel efficiency and improved emissions

Info

Publication number: WO1999058831A1
Application number: PCT/US1999/010248
Authority: WO
Inventors: Rollin A. Armer; Andrew A. Frank
Original assignee: Armer & Frank Motors, Llc
Priority date: 1998-05-13
Filing date: 1999-05-10
Publication date: 1999-11-18
Also published as: AU3896599A

Abstract

The present invention provides an improved compound internal combustion engine designed efficiently from a thermodynamic standpoint. The present invention has improved fuel efficiency and emission control for both noxious gaseous outputs as well as emissions of carbon dioxide, a major constituent of greenhouse gases. On one aspect, the present invention comprises at least two chambers used in a multiple stage expansion design. Exhaust from the first chamber (302) is inlet for further expansion into the second chamber (304). A catalytic converter (318) is coupled to both chambers such that the exhaust gases from the first chamber are passed through the converter to undergo a catalytic process. The catalytic process serves to complete the combustion process from the first chamber, thereby cleaning the exhaust while increasing the heat content of the exhaust gases for further expansion.

Description

COMPOUND ENGINE HAVING INCREASED FUEL EFFICIENCY AND IMPROVED EMISSIONS Technical Field

The present invention relates to compound, multiple expansion engines in general and, in particular, to compound engines that are optimized for increased fuel efficiency and improved emissions.

Background Art

Ever since the advent of the heat engine (i.e. both internal and external combustion), fuel efficiency has been one of the major design considerations. The earliest engines (such as external combustion steam and hot air designs circa 1800) were typically not engineered in accordance with the principles of thermodynamics first enunciated by Sadi Carnot in the early 1800s; and, consequently, did not produce work efficiently for the amount of fuel consumed. One early method of improving the efficiency of heat engine was to construct a "compound" engine. Jonathan Hornblower, in 1781, patented a compound steam engine in which steam is exhausted from a primary, high pressure cylinder into a secondary, low pressure cylinder where the steam is further expanded before being exhausted to the air (or, later, to a condensor which creates a negative pressure to produce useable work). This compound engine design squeezed out additional work from the still-hot steam coming out the primary cylinder; whereas previous engines had thrown away this available source of heat.

Since Hornblower, compound engine design has been used in both external and internal combustion engines as one method to optimize thermal efficiency. Figure 1 shows a diagram of an early marine steam compound engine, as found on pages 56-57 in "Naval Machinery", Part III Naval Reciprocating Engines by the U.S. Naval Institute, Annapolis, Maryland (1941). This steam engine 100 employed a high pressure cylinder 102, an intermediate pressure cylinder 104, two low pressure cylinders 106, and piston valves 108 to exhaust steam from the high pressure to the low pressure cylinders, where the piston valve is coupled to the crankshaft for its actuation. Piston valves were used in the context of marine steam engines primarily for the ease of construction and relatively low number of parts. As discussed further below in connection with the present invention, piston valves have the desirable characteristic that they open quickly; and thus, tend to release gases at a high volumetric rate. This allows hot gases to keep their heat and exit "hot". The piston valves shown in Figure 1 are actuated by an eccentric drive off the crankshaft and communicated steam from the sides of the high, intermediate and low pressure cylinders, as was common for steam engine design of the day. Side- mounted pistons, as in Figure 1, in the steam engine context were "double acting" - i.e. steam pushed the piston from above and below its head. Thus, it was natural to mount such a double acting piston valve to one side of the high, intermediate and low pressure cylinders (that had their own double-acting pistons within each of these cylinders). This side-mounted piston valve design, however, suffered the disadvantage of increasing the total surface area of the cylinder, allowing some heat loss. Piston valves, however, did not survive the evolution to internal combustion engines. Internal combustion engines typically exhibit much greater temperature and pressure than external combustion engines, including steam engines. Additionally, internal combustion engines, by design, are generally not double-acting — i.e. the forces acting in a cylinder in an internal combustion engine act on only a single side of the piston. Double-acting pistons, as designed for steam engine use, were consequently not engineered for the internal combustion engine. Thus, perhaps not coincidentally, piston valves, which were also initially conceived and engineered for double-acting steam engines, are unheard-of in an internal combustion engine.

As discussed in greater detail below, internal combustion engines employed a different valve design, called the "poppet valve", which overcame the shortcomings of the piston valve in a high temperature and high pressure environment of the internal combustion engine.

In the context of internal combustion engines, Figure 2 shows an early (circa 1892) compound design of Rudolf Diesel, as found on page 186 of "Diesel Engines" by Lyle Cummins, published by Carnot Press 1993. The Diesel Series XIV

Compound Engine 200 shows a combination of two high pressure cylinders 202 (only one such cylinder is shown in cross-section view of Figure 2) and a low pressure cylinder 204 in a 4-stroke, 2-stroke configuration for the high pressure cylinders and the low pressure cylinder, respectively. A series of poppet valves 206 connected the inlet air to high pressure cylinders 202, to exhaust from high pressure cylinders 202 to low pressure cylinder 204, and final exhaust to air from low pressure cylinder 204. Diesel's poppet valves withstood the forces generated by the higher gas pressure and temperature during both the combustion and power stroke of the two high pressure cylinders. Additionally, Diesel's poppet valves were now located on the top ~ as opposed to the side — of the high and low pressure cylinders. This design improved on the side-mounted piston valve, as it tended to minimize the surface area of the combustion chamber — thus conserving heat for the exiting gases to perform useful work in the second stage expansion cylinder.

From a purely thermodynamic standpoint, however, the use of poppet valves for the transfer of hot gases from a high pressure to a low pressure cylinder in a compound engine is undesirable. Poppet valves are known to have a throttling and, therefore, a cooling effect on exiting gases as they slowly enter a chamber of lower pressure. This needlessly wastes the heat energy of the exhaust gases that might otherwise be converted into useful work in the second, low pressure expansion cylinder. Another notable feature of Diesel's engine is water cooling jacket 208 surrounding low pressure cylinder 204. Again, from a purely thermodynamic standpoint, water jacket 208 actually decreases the efficiency of the engine by robbing the expanding hot gases in the low pressure cylinder of useful heat that could be translated into usable work. Alternatively, the low pressure cylinder and manifold may have thermally insulated surfaces or be made of thermally low conductivity materials to keep the heat inside and working to a greater degree. Additionally, the low pressure cylinder and/or other parts of the engine may be preheated prior to starting to reduce condensing and enhance cold-engine efficiency and reduce smog. The development of the compound design for internal combustion engines tapered off around the turn of the century as more oil and gas reserves were located and developed and gasoline became plentiful and cheap. However, as the price of fuel has increased in recent decades, so has interest in more efficient engine design.

Fuel efficiency, however, is not the sole consideration in today's engine design. Today's engines must also address the increased concern for the environment. While increased fuel efficiency will naturally decrease the emissions of carbon dioxide, a known constituent of "greenhouse" gases, emissions of other hydrocarbons and other pollutants from the ubiquitous internal combustion engine are also of concern. Their elimination is a desired design goal for today's internal combustion engine. Currently, the most popular pollution control strategy has been to place a catalytic converter device in the exhaust manifold of the car. Hot gases being expelled from the engine pass through the catalytic converter before being exhausted into the air. As is well known, the catalytic converter process facilitates the reduction of hydrocarbon and other by-products of an incomplete combustion process while those gases are still hot. The present method of catalytic converting presents several sources of inefficiency. First, the heat in the exhausted gases after the catalytic conversion process is again thrown away — without all possible useful work being extracted from the heat. Second, the catalytic conversion process actually produces heat due to further combustion taking place in the exhaustion gases ~ thus; even more useful heat is produced and thrown away in the catalytic conversion process. These problems are particularly acute for the would-be designer of a compound internal combustion engine whereby any and all available useful heat in expanding gases should be used to drive pistons in secondary cylinders.

Thus, there is a need to design a fuel efficient compound internal combustion engine that uses all available heat in exhaust gases towards the driving of pistons in secondary cylinders.

There is also a need to design a compound internal combustion engine without the use of poppet valves to avoid the throttling and cooling effect on the exhaust gases as they pass through the high pressure cylinder exhaust valves on their way to the low pressure cylinder. There is also a need to design a compound internal combustion engine that keeps all the advantages of a catalytic conversion process without wasting the available useful heat that might otherwise be converted into useful work.

There is also a need to design a compound internal combustion engine with the use of poppet valves that minimizes the throttling and cooling effect of typical poppet valves.

Disclosure of Invention

The present invention meets the aforementioned needs by providing an improved compound internal combustion engine that is designed to be more efficient from a thermodynamic standpoint. Consequently, the present invention has improved fuel efficiency and emission control ~ for both noxious gaseous outputs (i.e. nitrous oxides, carbon monoxide, sulfur oxides, etc.) as well as emissions of carbon dioxide, a major constituent of greenhouse gases. In one aspect, the present invention comprises at least two chambers used in a multiple stage expansion design. Exhaust from the first chamber is inlet for further expansion into the second chamber. A catalytic converter is coupled to both chambers such that the exhaust gases from the first chamber is passed through the converter to undergo a catalytic process. The catalytic process serves to complete the combustion process from the first chamber, thereby cleaning the exhaust while increasing the heat content of the exhaust gases for further expansion. In one embodiment, the two chambers comprise a high pressure cylinder and low pressure cylinder. In another embodiment, the two chambers comprise a first cylinder and a turbine. In another aspect, the present invention comprises the use of piston valves for the inlet and/or exhaust ports for one or both chambers. Linkages coupled to the piston valves allow for quick opening of the ports and, in the case of a piston valve on the exhaust port of the first chamber, allow those gases to exit "hot" and improve the fuel efficiency of compound engines. In another embodiment, the linkages comprise an anchor pin that allows for valve timing to be advantageously changed according to driving conditions. Another aspect of the present invention allows the secondary piston to precompress the exhaust gasses to allow either a piston or poppet valve on the exhaust port of the primary piston time to open to prevent throttling or cooling of the gases from the primary expansion cylinder or process. Other features and advantages are disclosed in the specification below and in conjunction with the accompanying figures.

Brief Description of Drawings

Figure 1 is a view of an early compound marine steam engine. Figure 2 is a view of an early compound internal combustion engine.

Figure 3 is a top view of a current embodiment of a compound engine made in accordance with the principles of the present invention.

Figure 4 is a side, cross-sectional view of the compound engine as depicted in Figure 3. Figures 5 - 8 depict the action of the compound engine as shown in Figures 3 and 4 through a 4-stroke, 2-stroke cycle.

Figure 9 shows an alternative embodiment of the present invention employing poppet valves.

Figure 10 shows an alternative embodiment of the present invention wherein a turbine acts as an expander.

Figures 11 A, B, C show several alternative embodiments of the present invention wherein the secondary expansion cylinder has a horizontal axis, double acting and supercharging respectively.

Figure 12 shows an alternative embodiment of the linkages in which the anchor pin is part of an eccentric.

Figures 13A-G show alternative embodiments of how a compound internal combustion engine made in accordance with the principles of the present invention could couple to a drive crankshaft.

Figure 14 depicts a graph of the relative opening characteristics of a piston valve versus a poppet valve. Best Mode for Carrying Out the Invention

Referring now to Figure 3, a top view of one embodiment of the present invention is shown. Compound engine 300 comprises two high pressure cylinders 302, one low pressure cylinder 304, high pressure cylinder inlet valves 306, high pressure cylinder exhaust valves 308, water cooling jacket 310, low pressure cylinder inlet port 312, and low pressure cylinder exhaust valve 314. Cylinders 302 and 304 are a specific example of an "expander". Generically used, an "expander", for the purposes of the present invention, is any part involved with the input, expansion, and output of gases and is to be interpreted very broadly. "Expanders" include, but are not limited to: cylinders, turbines, pistons, positive displacement pumps and the like. Terms "expander" and "expansion chamber", for the purpose of the present invention, are given the same scope and may be used interchangeably.

Between high pressure cylinders 302 and low pressure cylinder is manifold 316. Manifold 316 takes in exhaust gases from high pressure cylinders 302 and inputs them into low pressure cylinder 304. In Figure 3, manifold 316 further comprises a catalytic converter 318 that (1) further reduces hydrocarbons formed from an incomplete combustion process in high pressure cylinders 302 and, (2) increases the heat content of the exhaust gases by their further combustion.

Catalytic converter 318 may be any commercially available catalytic converter on the market for the purposes of the present invention. However, the catalytic converter is preferably sized to fit in manifold 316 so that it does not take up excessive space in engine 300. One such small-sized catalytic converter is manufactured by Briggs & Stratton that is sized to fit on the outside of their small engines wherein the catalytic converter is coupled directly to the exhaust port of a single, primary cylinder.

As very advantageously positioned between the high and low pressure cylinders of a compound engine, catalytic converter 318 simultaneously accomplishes the twin goals of controlling emissions of hydrocarbons (by cleaning the exhaust gases) and improving fuel efficiency (by creating useful heat in the catalytic process and supplying the expansion, low pressure cylinder with even-hotter gases than would be supplied by the high pressure cylinders alone). Another advantage is to be found in the design of manifold 316. As seen in Figure 3, manifold 316 combines the exhaust of both high pressure cylinders and induces the gases to stream through catalytic converter 318. This minimizes the volume of the ports and fully utilizes catalytic converter 318 since the exhaust of both high pressure cylinders go through it, but in sequence in the 4-stroke, 2-stroke configuration as described below. Additionally, high pressure exhaust ports 308 may be located very close to each other and to the inlet port 312 of the low pressure cylinder to minimize the surface of the manifold. Catalytic converter 318 may also be inset some distance into the cooled high pressure cylinder head. This will further reduce the cooled port surface that the high pressure exhaust gases come in contact with on their way to the low pressure cylinder. It will be appreciated, however, that any manifold design is suitable for the purposes of the present invention.

Although Figure 3 depicts a compound engine with two high pressure cylinders and one low pressure cylinder, it will be also appreciated that for the purposes of the present invention other configurations are possible and are subsumed by the scope of the present invention. For example, the scope of the present invention includes, but is not limited to: a "one high-to-one low pressure cylinder" configuration, a "one high pressure-to-many low pressure cylinder" configuration, "many high pressure-to-one low pressure cylinder configuration", or a "many high pressure-to-many low pressure cylinder configuration". Moreover, the present invention should not be limited to merely a two-stage (i.e. from a single high pressure stage to a single low pressure stage) expansion processes as shown. In fact, the present invention contemplates multiple stage (three or more) expansion engines. Figure 3 merely depicts only one advantageous feature of the entire present invention ~ namely, that at least one catalytic converter be coupled between some high pressure cylinder and some low pressure cylinder to achieve the benefits as noted above. Indeed, other advantageous features of the present invention will be discussed below that do not even include such a catalytic converter.

Some other alternative embodiments involving use of an intermediate catalytic converter is depicted in Figure 10. Figure 10 shows high pressure cylinder 302 as a first stage expansion chamber exhausting through catalytic converter 318 into turbine 434, as second stage expander. All of the previous mentioned advantages for having the catalytic converter between first and second cylinders also apply to a cylinder-turbine combination. It will be appreciated that other configurations are possible and fall under the scope of the present invention. For example, a turbine could precede (e.g. be the first stage expander) a cylinder (either high or low pressure) as a follow-on expansion chamber. Likewise, one turbine could precede another turbine in a multiple expansion design.

Referring now to Figure 4, a side, cross-sectional view of the engine 300 is shown, the cross-section of which is depicted by the dashed line so labeled in Figure 3. As can be seen in Figure 4, inlet and exhaust valves 306, 308, and 314 comprise piston valves 400, 410 and 420 respectively. Piston valves 400, 410, 420 are advantageously positioned to operate on top of the high and low pressure cylinders, in contrast to the side-mounted position the piston valves obtained in prior art steam engine designs, such as shown in Figure 1. It is also to be noted that high pressure cylinder is surrounded by water jacket 310, whereas low pressure cylinder 304 is not so surrounded to help maintain a suitable average temperature. In the event that the end of the catalytic converter next to the low pressure cylinder does not reach sufficient temperature to work effectively (due to the average lower temperature of the head, then a gasket or separating ring of low conductivity material may be placed between the catalytic converter and the low pressure cylinder head.

Although Figure 4 depicts two separate cranks, coupled to the high pressure and low pressure cylinder pistons respectively, it will be appreciated that both the high pressure and low pressure cylinder pistons could be coupled to a single crank. Thus, for the purposes of the present invention, the two cranks in Figure 4 could be separate or represent the same crank.

The following are alternative design choices for the low pressure cylinder and are a part of the scope of the present invention: (1) the exhaust valve of the low pressure cylinder may be located as far from the low pressure inlet port as possible in order to minimize the heat loss of the inlet to the cold exhaust through conductivity of the low pressure cylinder head material; (2) a pressure relief valve may be installed in the low pressure cylinder head. In that event, the combustion of accumulated oil or other fuel in the low pressure cylinder will not result in damage to the engine; (3) the low pressure cylinder may be double acting (i.e. fluids acting on both sides of the piston) so that a single low pressure cylinder will serve four high pressure cylinders; (4) an anti-friction (needle, roller, or rolling element) bearing may be employed at the wristpin of the low pressure cylinder, since this cylinder may not have stress reversals due to the pressure always being down on the piston; (5) if the low pressure piston is made double acting, it may be made to supercharge (i.e. pump air above atmospheric pressure) two high pressure cylinders, by using the underside of the low pressure piston as a pump. Figures 11 A, B, and C depict yet another series of alternative embodiments.

Common among these embodiments (and depicted in Figure 11 A), low pressure cylinder 304 has a horizontal axis so that the low pressure exhaust valve may be located at the bottom of the system. This will allow the condensing water to be blown out of the exhaust especially when the engine is cold. Figure 11B shows low pressure cylinder 304 with a double acting piston, accepting exhaust from two high pressure sources (possibly four high pressure cylinders). Two catalytic converters 318 are in the intake path of cylinder 304 for all the aforementioned reasons and advantages. Additionally, crosshead 1100 is an enlarged piston rod that serves as a wristpin guide. Crosshead 1100 allows the wristpin and upper end of the connecting rod to enter one end of the double acting cylinder, which makes the assembly more compact. It also slightly reduces the volume of the left end of the low pressure cylinder.

Figure 11C shows low pressure cylinder 304 again with a double acting piston, but only one intake path is coupled to a catalytic converter 318. The left end of this low pressure cylinder is used as a supercharging pump for the two high pressure cylinders. The left pumping end of the cylinder draws air in through check valve 431 and discharges the air through check valve 432 on its way to the high pressure cylinder inlet valves 400.

Each piston valve 400, 410 and 420 is operated by a set of linkages 401. 402, 403 404, 405 406 (coupled to piston valve 400); 411, 412, 413, 414, 415, 416

(coupled to piston valve 410); and 421, 422, 423, 424, 425, 426 and 427 (coupled to piston valve 420). As will be appreciated in conjunction with the discussion of their operation, linkages 401-406 and linkage 411-416 are designed to actuate piston valves 400 and 410 respectively to the "open" position once during a complete cycle. However, linkages 421-427 connected to low pressure cylinder piston valve 420 is a double acting toggle mechanism that actuates piston valve 420 to the "open" position twice during a complete cycle ~ as is keeping with the 4-stroke, 2-stroke operation of the engine.

These linkages, in turn, are coupled to and actuated by valve activating crank (VAC) 430. VAC 430 may be comprises as a short stroke crank or an eccentric that turns at half crankshaft speed, as is well known to those skilled in the art.

In order to gain appreciation of the operation of such arrangement, Figures 5 - 8 show the operation of this embodiment in a 4-stroke (of the high pressure cylinders), 2-stroke (of the low pressure cylinder) cycle. Figure 5 depicts the point in the cycle where cylinder 302 as shown is engaged in an "inlet" stroke, whereby piston valve 400 is actuated by its linkages to the "open" position and outside air rushes into cylinder 302. One advantageous feature of utilizing a piston valve in the inlet port of high pressure cylinder 302 is that its quick opening characteristics allows for free breathing of the high pressure cylinder; thus, avoiding throttling losses usually associated with the more constricted breathing characteristics of poppet valves. At the same time, piston valve 410 is actuated to the "closed" position, as is keeping with the general requirements of the inlet stroke. Piston valve 420 is actuated to the "open" position. The second high pressure cylinder (not shown) is involved in a power stroke. Low pressure cylinder 304 at this time is involved in an exhaust stroke, as is keeping with the 4-stroke, 2-stroke configuration. Low pressure cylinder 304 is exhausting gas during the cycle where the high pressure cylinders are engaged in an inlet and power stroke respectively. Low pressure cylinder 304. however, has its power stroke when the high pressure cylinders are engaged in a compression and exhaust stroke respectively. Thus, the low pressure cylinder cycles through two of its 2-strokes (exhaust and power) in the same time that each high pressure cylinder cycles through its 4-stroke (inlet, compression, power, and exhaust) cycle. It will be appreciated that although this embodiment depicts a two high pressure, one low pressure cylinder configuration, the present invention subsumes other configurations as previously noted above.

Figure 6 depicts the next phase in the cycle where high pressure cylinder is engaged in a compression stroke (both piston valves 400 and 410 are actuated in the "closed" position) and low pressure cylinder 304 is engaged in a power stroke (piston valve 420 is actuated in the "closed" position). Low pressure cylinder 304 is engaged in a power stroke because the other high pressure cylinder (not shown) is engaged in an exhaust stroke.

Figure 7 depicts high pressure cylinder engaged in a power stroke (piston valves 400 and 410 are "closed") as the compressed fuel and air mixture is ignited by a spark source (not shown). Low pressure cylinder 304 is engaged in an exhaust stroke (piston valve 420 is "open") as the second high pressure cylinder (not shown) is engaged in an inlet stroke.

Figure 8 depicts the final phase in the cycle wherein high pressure cylinder 302 is engaged in an exhaust stroke (piston valves 400 and 410 are "closed" and "open" respectively). Low pressure cylinder is engaged in a power stroke (piston valve 420 is "closed") while the other high pressure cylinder is engaged in a compression stroke.

As an alternative embodiment to Figures 4-8, it is noted that while anchor pins 405, 415, and 425 are normally anchored and stationary, some or all of these anchor pins may be made eccentric to vary valve timing while the engine is running, as discussed further below in conjunction with Figure 12. Assuming, however, that the anchor pins are stationary, the crank centers on VAC 430 may be spaced to secure appropriate valve timing as follows: the high pressure exhaust crank leads the inlet by approximately 100 degrees and the low pressure exhaust crank lags the high pressure inlet by approximately 150 degrees. Thus, the high pressure inlet valves open about 5 degrees before top center and close about 35 degrees after bottom center. The low pressure exhaust valve opens about 20 degrees before bottom center and closes about 40 degrees before top center. It will be appreciated that different spacings may be implemented and that the present invention is not limited by the particular spacings disclosed. If spacings are, however, chosen such that the low pressure exhaust valve opens some degree before bottom center and closes some degree before top center, then some advantage is gained in the compression during the last part of the exhaust stroke in the low pressure cylinder. As the low pressure piston is coming up on its exhaust stroke ~ expelling the exhaust gasses through the open exhaust valve, that valve closes before the piston gets all the way up (i.e. before top center). Thus, a small fraction of the exhaust gasses are trapped and compress to a desired pressure by the time the low pressure piston is all the way up and its crank is at top center. The function of this short compression period is to equalize the pressure on both sides of the high pressure exhaust valve and prevent the loss of some small part of the high pressure exhaust gasses being required to fill the volume of the passage (manifold) between the high pressure and low pressure cylinders. Additionally, the short compression period tends to oppose the large pistons upward flight and reduce its tendency to "yank" the bearings. One additional advantage to this short compression is relevant with respect to poppet valves. The short compression stroke builds up some pressure behind the exhaust poppet valves of the high pressure cylinder and, as a result, minimizes the initial rush of flame through the high pressure exhaust valve reducing throttling losses (expansion cooling losses) and valve temperature. In this fashion, the performance of poppet valves in a compound internal combustion engine design may be significantly improved.

Piston valves — as opposed to poppet valves ~ on the exhaust port of the high pressure cylinder may have several advantages of their own. First, piston valve 410 cannot be blown open from high pressure behind it. This feature eliminates the need for a second high pressure exhaust valve or a heavy spring downstream. To illustrate this feature, reference is made to Figure 3. Suppose the upper high pressure cylinder has just completed its power stroke and its exhaust valve has just opened. The lower high pressure cylinder has, at that point, just completed its inlet stroke and is full of gasoline vapor at very low (i.e. near atmospheric) pressure. Since the upper and lower high pressure exhaust ports 308 are connected together by manifold 316. there will be a puff of high pressure exhaust fire from the upper port 308 that may be sufficient to blow open lower port 308 and ignite the charge of fuel vapor in lower high pressure cylinder 302. If lower port 308 comprised a poppet valve, it is possible that such a poppet valve may be blown open against its spring.

That this was a problem in previous engines is evidenced by the fact that many previous poppet valve compounds had two exhaust valves in series from each high pressure cylinder. In fact, this design is seen in Diesel's compound engine of Figure 2. Thus, the non-blow back feature of the piston valve simplifies the system and allows a single catalytic converter to alternately serve two high pressure cylinders. A second advantage to piston valve 410 on the exhaust port of the high pressure cylinders is that a piston valve should run much cooler than a conventional poppet valve since it is operating in a water cooled bore and does not have the exhaust flames surrounding its head as does the poppet valve. Therefore, the compression ratio of the high pressure cylinders may be increased without ensuing detonation normally caused by the glowing poppet valves presence in the combustion chamber.

A third advantage to piston valve 410 on the exhaust port is quick opening, as noted in conjunction with Figure 14 and its accompanying discussion below. Piston valve 410 opens at a much quicker volumetric rate than a comparable poppet valve; thus, eliminated the throttling and cooling effect due to the slow squeezing of exhaust gases around a poppet valve opening. Exhausting gases hotter is a desirable feature, as that heat can then be converted to useful work in driving the piston in the low pressure expansion cylinder. In addition, since the piston valve opens so much more quickly than the poppet valve, it can open somewhat later in the power stroke of the high pressure piston, allowing the high pressure piston to have a somewhat longer expansion (power) stroke.

Another advantage is that the piston valve can be constructed using fewer parts than a conventional poppet valve. Yet another advantage is that variable compression ratios may be achieved using piston valves as shown in Figure 12. The stroke of piston valve 400 could be varied to extend into the high pressure cylinder (e.g. to go further into, or further away from high pressure cylinder) during the high pressure cylinder's compression stroke. This may be accomplished by the mechanism of Figure 12, which can change both the compression ratio and the timing as described in greater detail below.

These advantageous features utilizing piston valves is independent of the use of a catalytic converter in the manifold between the high and low pressure cylinders. In fact, manifold 316 could be merely metal piping without a catalytic converter 318 for the purposes of the present invention. However, in the preferred embodiment, both piston valves and catalytic converter are employed.

By the same token, the present invention subsumes an embodiment in which no valves are piston valves. Figure 9 depicts one embodiment utilizing the familiar poppet valves (valves 900, 904, and 908). Poppet valves 900, 902, and 908 are actuated by cams 902, 906, and 910 in the conventional way to facilitate the 4-stroke. 2-stroke cycle as described above. The main advantageous feature of Figure 9 is the use of catalytic converter 318 coupled in between high and low pressure cylinders 302 and 304 respectively. Additionally, the scope of the present invention subsumes any embodiment where any of the valves are piston valves, either in concert with a catalytic converter or not. It will be appreciated that circular, disc shaped, or slide valves may also be used in lieu of piston or poppet valves, and that the present invention contemplates their use as alternative embodiments. As noted above, piston valves did not survive the transition from steam engines to internal combustion engines — primarily because steam engines were double acting in nature, whereas the internal combustion engine is single acting by design. In a double acting environment, high pressure gas (e.g. steam) is admitted between the two ends of the piston valve; and thus the valve is pressure balanced. The working gas pressure exerts no net force on the valve and the valve driving apparatus (e.g. eccentrics, cams, levers, etc.) can be light and not prone to wear. In a single acting cylinder, piston valves must have the gas pressure exerted against one end only, and cannot be balanced. Thus, when the fire goes off in the cylinder, a strong force tends to blow the piston valves out of the cylinder head. The linkages as displayed in the current embodiments (e.g. linkages 402. 404, and 406 actuating piston valve 400) are designed for this exacting environment of high pressure and temperature. Such linkages, however, were first used in application for punch presses ~ and not internal combustion engines. Punch presses need to apply a stamp to sheet metal with such force as to stamp out a particular design. Thus, these linkages were designed to withstand great impact forces ~ as linkages 402 and 404 are induced to be collinear by linkage 406. By contrast, poppet valves also exhibit the same ability to withstand the great forces of the compression and power strokes in an internal combustion engine.

However, in the context of the internal combustion engines, these linkages provide two altogether surprising and unexpected results -- (1) they hold the piston valve practically motionless (i.e. "closed") during the three of the four strokes of a full cycle; and (2) they open very quickly and allow gas to enter or exit at a great volumetric rate during the fourth stroke. For example, a piston valve on the inlet port of the high pressure cylinder is held "closed" by the linkages during the compression, power and exhaust strokes; but is "open" for the inlet stroke. Likewise, a piston valve on the exhaust port of the high pressure cylinder is held "closed" by the linkages during the inlet, compression and power strokes; but opens for the exhaust stroke. This was clearly not a concern of engineers of the punch press.

The second surprising advantage of the piston valves as actuated by these linkages is quick opening to a high rate of volumetric gas exchange. Poppet valves, by contrast (and as shown in Figure 14), have relatively slow opening characteristics; thus, making it a less desirable candidate for the transfer valve from high pressure to low pressure cylinders of a compound engine. This slow opening valve with its concomitant throttling and cooling of exhaust gasses lessens the thermal efficiency of a compound internal combustion engine design. It can be estimated that a piston valve of the design herein disclosed opens approximately fifteen times faster than a poppet valve.

Referring now to Figure 12, a manner of adjusting the valve timing while the engine is running is shown. Although this feature is shown in connection with inlet valve 400, it will be appreciated that all valves could have their timing adjusted accordingly. Anchor pin 405 is now part of an eccentric wherein the larger part of the eccentric is journaled in the engine frame 434 and is free to rotated therein. Lever 433 is attached to eccentric anchor pin 405 and may be operated back and forth as indicated by arrow 435.

When lever 433 is moved to the right, the center of the anchor pin 405 will move down a small amount causing piston valve 400 to open late and close early as would be desired for low speed - high torque operation of the engine. When the engine is running fast and very high power is desired, as when passing another vehicle, lever 433 is moved to the left. Such movement could be accomplished under computer or microprocessor control, as is well known in the art. This action raises the center of anchor pin 405 a small amount causing piston valve 400 to open early and close late. This has the net effect of increasing the amount of opening as well as the open time duration, allowing the engine to exert maximum power at high speed.

A further desirable effect is that when lever 433 is moved left, piston inlet valve 400 is raised somewhat during the compression and power strokes of the engine. This lowers the compression ratio a small amount during full throttle operation and reduces the tendency of the engine to detonate. Additionally, it allows the compression ratio to be controlled during various load operations of the overall engine. It will be appreciated by one skilled in the art that lever 433 may be moved by any appropriate servo device which, in turn, can be controlled by a computer.

Yet another desirable effect is that the eccentric anchor is an inherently strong device which can be moved by modest forces even when under operating load.

Figures 13A-G shows various possible ways in which a compound internal combustion engine made in accordance with the principles of the present invention could couple to the drive crankshaft. Figure 13 A shows a top view of a four high pressure cylinder (302) in line-type configuration with a double acting low pressure cylinder 304 whose crankshaft 1302 is bevel geared 1304 to the main crankshaft 1300. Figure 13B is a top view of a two high pressure cylinder type with a rocker arm 1306 coupled to main crankshaft 1300 with a bellcrank 1308. Figure 13C shows a way of linking a single acting horizontal low pressure cylinder 304 to high pressure cylinders and main crankshaft via a rocker arm 1310 on a fixed pivot 1312. Figure 13D is an end view of a Vee four or Vee eight high pressure cylinder arrangement with horizontal low pressure cylinders in the Vee with a scotch yoke 1313 driving an eccentric 1315 on the crankshaft 1300. Figure 13E is a variation on the Zee crank engine where two opposing horizontal low pressure cylinders 304 actuate a ball bearing output shaft 1314 whose axis is parallel to theirs. This machine would have simple harmonic motion; thus minimizing piston inertia loads and would be perfectly balanced. Figure 13F shows a top view of a Vee eight high pressure cylinder layout with the arrangement of two low pressure cylinder units as shown in Figure 13E. Figure 13G is a variation on Figure 13D using a conventional connecting rod 1316 and bellcrank 1317 to communicate motion from the horizontal low pressure cylinder or cylinders. It will be appreciated the numerous mechanisms and means of connecting the present compound internal combustion engine to the drive crankshaft are well known to those skilled in the art. It should be further appreciated that the scope of the present invention should not be limited to the mechanisms and means shown herein; but instead encompasses all such mechanisms and means. Referring now to Figure 14, a "valve percent open" performance graph versus

"crankshaft degree rotation" is shown according to a supposed valve timing. Curve A shows the opening of a piston valve whereas Curve B depicts the opening for a typical poppet valve. Most of the cooling by expansion effect of the gasses passing through the valve takes place in the first twenty percent of valve opening. Curves A and B show that approximately 20% opening takes fifteen degrees of travel for the piston valve and 46 degrees for the poppet valve. At the beginning of the opening, the contrast is even greater. The difference in the shape of these curves illustrates that the piston valve can breathe a great deal easier in a short open duration than can the poppet valve.

Claims

1. An internal combustion engine comprising: a first expansion chamber; a second expansion chamber; a catalytic converter coupled to both said first expansion chamber and said second expansion chamber, wherein exhaust from said first expansion chamber passes through said catalytic converter into said second expansion chamber.

2. The internal combustion engine as recited in Claim 1 wherein at least one of said first expansion chamber or said second expansion chamber is a high pressure cylinder.

3. The internal combustion engine as recited in Claim 1 wherein at least one of said first expansion chamber or said second expansion chamber is a low pressure cylinder.

4. The internal combustion engine as recited in Claim 1 wherein at least one of said first expansion chamber or said second expansion chamber is a turbine.

5. An internal combustion engine comprising: a first high pressure cylinder; a second high pressure cylinder; a low pressure cylinder; a manifold comprising a catalytic converter, a first opening and a second opening, said manifold coupled to said first high pressure cylinder at said first opening, said second high pressure cylinder at said first opening, and said low pressure cylinder at said second opening; such that exhaust from said first and said second high pressure cylinders enters said manifold through said first opening and passes through said catalytic converter and exits said manifold through said second opening into said low pressure cylinder.

6. The internal combustion engine as recited in Claim 5 wherein said first and said second high pressure cylinders perform a 4-stroke cycle and said low pressure cylinder performs a 2-stroke cycle.

7. The internal combustion engine as recited in Claim 5 wherein said first and said second high pressure cylinder further comprises a water jacket.

8. The internal combustion engine as recited in Claim 3 wherein said low pressure cylinder does not comprise a water jacket.

9. The internal combustion engine as recited in Claim 3 wherein said low pressure cylinder has a substantially horizontal axis.

10. An internal combustion engine comprising: a cylinder comprising a port, said port allowing the passage of gas through said cylinder; a valve actuating crank; and a piston valve coupled to said valve actuating crank, said piston valve positioned over said port and said piston valve actuated by said valve actuating crank such that the passage of gas through said cylinder via said port is controlled by said piston valve.

11. The internal combustion engine as recited in Claim 10 wherein said cylinder is a high pressure cylinder in a compound engine.

12. The internal combustion engine as recited in Claim 11 wherein said port is the inlet port for said high pressure cylinder.

13. The internal combustion engine as recited in Claim 11 wherein said port is the exhaust port for said high pressure cylinder.

14. The internal combustion engine as recited in Claim 10 wherein said cylinder is a low pressure cylinder in a compound engine.

15. The internal combustion engine as recited in Claim 14 wherein said port is the inlet port for said low pressure cylinder.

16. The internal combustion engine as recited in Claim 14 wherein said port is the exhaust port for said low pressure cylinder.

17. The internal combustion engine as recited in Claim 10 wherein said valve actuating crank further comprises: an anchor pin; a linkage coupled to said anchor pin; and said linkage coupled to said piston valve.

18. The internal combustion engine as recited in Claim 17 wherein said anchor pin comprises an eccentric such that the opening and closing timing of said piston valve is controllable by positioning said eccentric.