An opposed-piston, opposed-cylinder engine is disclosed that has the pistons symmetrically arranged in the opposed cylinders. In one embodiment, the inner pistons are exhaust pistons and the outer pistons are intake pistons. Alternatively, the inner pistons are intake pistons and the outer pistons are exhaust pistons. The pistons are coupled to the crankshaft that is situated between the opposed cylinders. Central axes of the two cylinders are offset by a predetermined distance. The connecting rods that couple between the crankshaft and the pistons are arranged adjacent to each other on journals of the crankshaft. The journal to which the pushrods couple is not a split-pin type. Instead, it is one that has a common central axis. Furthermore, the crankshaft is a one-piece or unitary structure.

FIELD

The present disclosure relates to an architectural arrangement for an opposed-piston, opposed-cylinder engine.

BACKGROUND AND SUMMARY

An opposed-piston, opposed-cylinder (OPOC) is disclosed in U.S. Pat. No. 6,170,443, which is incorporated herein in its entirety. The configuration in '443 has an asymmetrical arrangement of the pistons. That is, in one of the cylinders, the intake piston, i.e., that piston that uncovers intake ports, is located closer to the crankshaft than the exhaust piston. In the other cylinder, the exhaust piston is located closer to the crankshaft than the intake piston. Such an arrangement provides some distinct advantages such as nearly perfect balancing of the engine. However, some small detractors result due to the asymmetric arrangement and the phase offset between the intake and the exhaust pistons, the offset being provided for scavenging purposes. In particular, the crankshaft is a split-pin design. That is, the journals of the crankshaft, to which the pistons of the two cylinders couple, cannot be smooth cylinders to which two connecting rods couple, but instead includes two cylindrical crankpins that are offset from each other (as shown in FIGS. 9 and 10b in '443). This is a more costly and less robust design than the simpler single cylindrical journals to which two connecting rods couple. The highest stress location in a crankshaft tends to be located at the interface between the journal and the web portion of the crankshaft. There are techniques that can be used to harden that portion of the crankshaft such as: induction hardening or rolling. These are difficult and expensive for a split-pin design.

Additionally, as the inner pistons couple to the crankshaft in a different manner than the outer pistons, the '443 engine has four distinctly different pistons: an inner intake piston, an outer intake piston, an inner exhaust piston, and an outer exhaust piston. To reduce engineering costs, manufacturing costs, and complexity, it is desirable to have as few different parts as possible. Other detractors include optimizing two combustion chamber shapes and port heights, i.e., one for each of the two cylinders. One combustion chamber is formed by an inner intake piston and an outer exhaust piston and the other is formed by an outer intake piston and an inner exhaust piston. Part of the reason for the inconsistency from one cylinder to the other cylinder is due to differences in the flow characteristics by virtue of the asymmetric nature of the induction and exhaust systems.

To overcome these detractors, an OPOC with a symmetrical arrangement of the pistons is disclosed in U.S. Pat. No. 7,469,664, which is incorporated herein in its entirety. The two cylinders of the OPOC in '664 are collinear meaning that that the central axes of the two cylinders lay on essentially the same line. In the engine in '664, two connecting rods, that mesh together, couple to a single journal; this arrangement is commonly referred to as a forked rod design. Because the forked rod must be slid over the journal, the crankshaft is a “build-up”, meaning that it is assembled of multiple parts with the final assembly accomplished after the connecting rods have been installed. Such a crankshaft is more expensive to manufacture and assemble.

To overcome issues associated with a multi-piece crankshaft, alternative coupling strategies for inner pistons and for outer pistons are disclosed in commonly-assigned, published U.S. applications: 2012/0207415 A1 filed 3 Feb. 2012 and 2012/0247419 A1 filed 2 Apr. 2012. Although such disclosed solutions provide many advantages for the OPOC engine and provide the desired symmetrical arrangement of the pistons, these coupling arrangements are unique in the industry and are to date untested. For production purposes in the nearer term, some manufacturers prefer to use technologies that are well developed and thus are reticent to adopt the coupling arrangements disclosed in applications '415 and '419 until further proven.

An advantageous OPOC configuration, according to some embodiments disclosed herein, relies on proven mechanical technologies, provides a symmetric arrangement of the pistons, and uses a unitary crankshaft.

An internal combustion engine is disclosed that includes a unitary crankshaft, a block into which the crankshaft is mounted, the block defining two cylinders wherein a first of the two cylinders is arranged substantially opposite a second of the two cylinders with respect to the crankshaft and a central axis of the first cylinder is offset from a central axis of the second cylinder by a predetermined distance, a first intake piston and a first exhaust piston inserted into the first cylinder with the first exhaust piston closer to the crankshaft than the first intake piston, and a second intake piston and a second exhaust piston inserted into the second cylinder with the second exhaust piston closer to the crankshaft than the second intake piston. The engine has a first pushrod that couples between a central journal of the crankshaft and the first exhaust piston; and a second pushrod that couples between the central journal of the crankshaft and the second exhaust piston wherein the first pushrod and the second pushrod are adjacent to each other and the predetermined distance that the cylinders are offset is substantially equal to a distance between the pushrods taken along an axis of rotation of the crankshaft.

In some embodiments, a first pair of shell bearings are placed on the central journal with the first pair of shell bearings located between the central journal and the first pushrod and a second pair of shell bearings placed on the central journal with the second pair of shell bearings located between the central journal and the second pushrod wherein the first pair of shell bearings is adjacent to the second pair of shell bearings. Alternatively, a single part of shell bearings are placed on the central journal with the first and second pushrods are coupled to the outer surface of the shell bearings. In some embodiments, at least one of the pair of shell bearings includes an outwardly extending tab; the first pushrod has a pocket defined on a surface of the first pushrod that nests with the shell bearings; and the tab engages with the pocket.

The crankshaft has at least five journals: a central eccentric journal, a front eccentric journal, a rear eccentric journal, a front main journal having an axis of rotation collinear with an axis of rotation of the crankshaft, and a rear main journal having an axis of rotation collinear with the axis of rotation of the crankshaft. The engine also includes: a first rear pullrod that couples between the rear journal of the crankshaft and the first intake piston, a first front pullrod that couples between the front journal of the crankshaft and the first intake piston, a second rear pullrod that couples between the rear journal of the crankshaft and the second intake piston, and a second front pullrod that couples between the front journal of the crankshaft and the second intake piston. In some embodiments, the engine further includes: a first rear pair of shell bearings placed on the rear journal with the first rear pair of shell bearings located between the rear journal and the first rear pullrod, a second rear pair of shell bearings placed on the rear journal with the second rear pair of shell bearings located between the rear journal and the second pullrod wherein the first rear pair of shell bearings is adjacent to the second rear pair of shell bearings, a first front pair of shell bearings placed on the front journal with the first front pair of shell bearings located between the front journal and the first front pullrod, and a second front pair of shell bearings placed on the front journal with the second front pair of shell bearings located between the front journal and the second pullrod wherein the first front pair of shell bearings is adjacent to the second front pair of shell bearings. Some embodiments include a rear pair of shell bearings placed on the central journal wherein the first and second rear pullrods are coupled to the outer surface of the rear pair of shell bearings and a front pair of shell bearing placed on the central journal wherein the first and second front pullrods are coupled to the outer surface of the front pair of shell bearings. In some alternatives, at least one of the rear pair of shell bearings includes an outwardly extending tab; the first rear pullrod has a pocket defined on a surface of the first rear pullrod that nests with the shell bearings; the tab associated with the rear pair of shell bearings engages with the pocket associated with the first rear pullrod; at least one of the front pair of shell bearings includes an outwardly extending tab; the first front pullrod has a pocket defined on a surface of the first front pullrod that nests with the shell bearings; and the tab associated with the front pair of shell bearings engages with the pocket associated with the first front pullrod.

The crankshaft in some embodiments the crankshaft is a unitary or one-piece crankshaft. The front and rear eccentric journals have a substantially identical crank throw and substantially equal phasing. The central journal has a crank throw greater than the crank throw of the front and rear eccentric journals and is offset between 150 to 180 degrees with respect to the front and rear eccentric journals.

Also disclosed is an internal combustion engine having a unitary crankshaft, a block into which the crankshaft is mounted, the block defining two cylinders wherein a first of the two cylinders is arranged substantially opposite a second of the two cylinders with respect to the crankshaft, two substantially identical inner pistons, one of which is inserted into the first cylinder and the other of which is inserted into the second cylinder, and two substantially identical outer pistons, one of which is inserted into the first cylinder and the other of which is inserted into the second cylinder wherein the inner pistons are located nearer the crankshaft than the two outer pistons. In some alternatives, a central axis of the first cylinder is offset from a central axis of the second cylinder by a predetermined distance. A first pushrod couples between a central journal of the crankshaft and the inner piston in the first cylinder. A second pushrod couples between the central journal of the crankshaft and the inner piston in the second cylinder. The first pushrod and the second pushrod are adjacent to each other and the predetermined distance that the cylinders are offset is substantially equal to a distance that first and second pushrods are displaced from each other taken along a central axis of the crankshaft.

The two inner pistons are exhaust pistons and the two outer pistons are intake pistons in one alternative. In another alternative, the two inner pistons are intake pistons, and the two outer pistons are exhaust pistons.

A plurality of ports are defined in each of the two cylinders with an inner plurality of ports that are located a first predetermined distance from the crankshaft and an outer plurality of ports that are located a second predetermined distance from the crankshaft with the second predetermined distance being roughly double the first predetermined distance. The engine further includes a first manifold system fluidly coupled to the inner plurality of ports and a second manifold system fluidly coupled to the outer plurality of ports. In some embodiments, the first manifold system is an intake system and the second manifold system is an exhaust system. In other embodiments, the first manifold system is an exhaust system and the second manifold system is an intake system.

In another embodiment, an engine has a crankshaft and a block into which the crankshaft is mounted. The block defines two cylinders with a first of the two cylinders arranged substantially opposite a second of the two cylinders with respect to the crankshaft and a central axis of the first cylinder is offset from a central axis of the second cylinder by a first predetermined offset. The engine includes: a plurality of inner ports defined in the first cylinder with an inner edge of the inner ports located at a first predetermined distance from the crankshaft and an outer edge of the inner ports located at a second predetermined distance from the crankshaft, a plurality of inner ports defined in the second cylinder with an inner edge of the inner ports located at the first predetermined distance from the crankshaft and an outer edge of the inner ports located at the second predetermined distance from the crankshaft, a plurality of outer ports defined in the first cylinder with an inner edge of the outer ports located at a third predetermined distance from the crankshaft and an outer edge of the outer ports located at a fourth predetermined distance cylinder from the crankshaft, and a plurality of outer ports defined in the second cylinder with an inner edge of the outer ports located at the third predetermined distance from the crankshaft and a outer edge of the outer ports located at the fourth predetermined distance from the crankshaft. In some embodiments, the engine further includes: a plurality of outermost ports defined in the first cylinder with an inner edge of the outermost ports located at a fifth predetermined distance from the crankshaft and an outer edge of the outermost ports located at a sixth predetermined distance from the crankshaft and a plurality of outermost ports defined in the second cylinder with an inner edge of the outermost ports located at the fifth predetermined distance from the crankshaft and an outer edge of the outermost ports located at the sixth predetermined distance from the crankshaft.

In some embodiments: the pluralities of inner ports are exhaust ports; the pluralities of outer ports are primary intake ports; the plurality of outermost ports is secondary intake ports; and all ports are shaped substantially as one of: a rectangle, a parallelogram, an oval, and a circle.

The various disclosed embodiments include one or more of the following advantages:a crankshaft without split pins;identical left and right cylinder blocks;only first-order unbalanced forces that can be overcome by weighting of the crankshaft such that the center of gravity is offset with respect to the axis of rotation of the crankshaft;symmetric arrangement of the pistons with common inner pistons and common outer pistons, i.e., two each of two piston designs as contrasted to some prior designs that had one each of four piston designs;the intake and exhaust flanges and ports are symmetrical;coupling of connecting rods to the journals draws upon well-known technologies used in the industry for decades;a stiffer, unitary crankshaft as contrasted with a built-up crankshaft or split-pin crankshafts used in some prior designs; andsubstantially identical combustion chamber configurations in the two cylinders.

DETAILED DESCRIPTION

As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.

An isometric view of an engine10according to an embodiment of the present disclosure is shown inFIG. 1. Engine10has a left cylinder12and a right cylinder14. Engine10has an exhaust system to conduct the exhaust from inside the cylinders; ducts16are part of the exhaust system. Air is provided to the cylinders through an intake system with ducts18being part of the intake system. Engine10has a crankshaft20. InFIG. 1, a single intake per cylinder is illustrated. Alternatively, each cylinder has two intakes: one fluidly coupled to primary intake ports and one fluidly coupled to secondary intake ports.

Referring now toFIG. 2, a crank train of engine10is shown. Crankshaft20couples with inner pistons30via pushrods34and to outer pistons32via pullrods36. In one embodiment, inner pistons30are exhaust pistons and outer piston32are intake pistons. Alternatively, inner pistons30are intake pistons and outer pistons32are exhaust pistons.

InFIG. 3, a horizontal, cross section of engine10is shown. Crankshaft20has a front main journal51, a rear main journal52. An axis of rotation50of crankshaft20is collinear with the axis of rotation of journals51and52. Crankshaft20also has a front eccentric journal53and a rear eccentric journal54. The journals are noticeably eccentric as their center does not line up with centerline50, even in this two-dimensional illustration. A center eccentric journal55of crankshaft20appears collinear with centerline50inFIG. 3. However, in the view inFIG. 3, center journal55is below the plane of the plane of cross section. A center axis56of the left cylinder and a center axis58of the right cylinder are offset as shown by60.

A plurality of inner ports64are defined in cylinder12and a plurality of inner ports74are defined in cylinder14. Cylinder12also defines a plurality of outer ports66; cylinder14defines a plurality of outer ports76. In the embodiment shown inFIG. 3, cylinder12defines a plurality of outermost ports68and cylinder14defines a plurality of outermost ports78. In the embodiment inFIG. 3, inner ports64and74are exhaust ports. Outer ports66and76are primary intake ports and outermost ports68and78are secondary intake ports. In another alternative, there is a single plurality of intake ports. In another alternative in which the intake pistons are closer to the crankshaft than the exhaust pistons, intake ports are located in the region where inner ports64and74are located and exhaust ports are located in the region where outer and outermost ports66,68,76, and78are located.

The ports inFIG. 3are symmetrically arranged. That is, an outer edge of inner ports64and74are located distance82from the axis of rotation50of crankshaft20. An inner edge of inner ports64and74are located a distance80from axis50. Additionally:inner edge of outer ports66and76are located a distance84from axis50;outer edge of outer ports66and76are located a distance86from axis50;inner edge of outermost ports68and78are located a distance88from axis50; andouter edge of outermost ports68and78are located a distance90from axis50.

When opening ports64and76, the pistons from toward the crankshaft. The port edge first opened is called the upper edge. The outer pistons (not shown) open ports66,68,76, and78are opened when the piston moves outwardly.

Crankshaft20is shown isometrically inFIG. 4. Eccentric journals53,54, and55are a single cylinder. This contrasts with the split pin design shown in '443, which results from having an asymmetric arrangement of the pistons.

Several embodiments of the bearing arrangement between the connecting rods and the crankshaft are described below. InFIG. 5, a crankshaft100rotates about axis101and has main bearings102. Outer eccentric journals have a center axis of103and center eccentric journal has a center axis of105. Pullrods104are placed over the outer eccentric journals and each is secured with a bearing cap106. A pair of shell bearing114(each covering 180° of circumference of the journal), is provided between each of the pullrods104and the associated journal. Pushrods108are placed over the center eccentric journal and each is secured with a bearing cap110. A pair of shell bearings118is provided between each of the pushrods and the associated journal. Oil passages (not shown) provide oil under pressure to the journals to provide an oil film between the eccentric journals and the shell bearings on the inner surface. Oil may also be provided to the outer surface of the shell bearings to provide a film of oil between the shell bearings and the associated pullrod or pushrod.

As described above, the cylinders are offset by a predetermined distance. A centerline107,107′,111,111′ of the pullrods104and a centerline109,109′ of the pushrods108are also indicated inFIG. 5. The distance between centerlines107and107′, as taken in the vertical direction, is substantially equal to the predetermined distance. The distance between centerlines107and107′ and the distance between centerlines111and111′ are substantially equal to the predetermined distance, as well.

The center eccentric journal carries the forces associated with two opposed pistons. In contrast, there are two outer eccentric journals to carry the forces associated with two opposed pistons. Because the load is shared, the outer eccentric journals can be made shorter than the center eccentric journal. However, the distance between centerlines of adjacent connecting rods should be substantially the predetermined distance, i.e., the offset between the cylinders. Such an arrangement is shown inFIG. 6. A crankshaft130has main bearings102and a center eccentric journal, which is very similar to those shown inFIG. 5. However, the outer eccentric journals inFIG. 6are shorter than the outer eccentric journals inFIG. 5. To retain the appropriate spacing between adjacent pullrods134, they are asymmetric. This can be seen in regard to bearing caps136. Centerlines137,137′,141,141′ of pullrods134pass through bearing caps136asymmetrically. By providing the arrangement shown inFIG. 6, the total length of the crankshaft is reduced slightly as a result of the shorter outside journals, which results in a smaller engine package and slightly less material to produce as well as a more rigid crankshaft.

InFIG. 7, instead of having a pair of shell bearings for each connecting rod, adjacent connecting rods share a pair of shell bearings. That is, a single bearing shell pair is placed over the eccentric journal and two adjacent connecting rods are placed over the shell bearing pair and secured via a bearing cap. For example, two pullrods104that are secured by bearing caps136have a single bearing shell pair124. Two pushrods108that are secured by bearing caps110have a single bearing shell pair128.

The embodiment inFIG. 7uses crankshaft130, which is shorter than crankshaft100ofFIG. 5. The width of front eccentric journal160and rear eccentric journal162(shown inFIGS. 6 and 7) are shorter than that of the front and rear eccentric journals of crankshaft100. (What is meant by the width of the journal is shown by numeral59inFIG. 3.) To maintain the predetermined distance between the pullrods, the embodiment inFIGS. 6 and 7use asymmetric pullrods134. A centerline through pullrods134is asymmetric with respect to the base of the pullrods. A great amount of such asymmetry in the pullrods is undesirable. However, a small amount of asymmetry can be tolerated to provide a shorter overall length of the crankshaft and hence a narrower engine and a more rigid crankshaft

InFIG. 5, there are two pair of shell bearings on each of the eccentric journals. Alternatively, a single pair of shell bearings is provided with a crankshaft100, i.e., the bearings ofFIG. 6or7, with the eccentric journal lengths shorter than that ofFIG. 5.

In one alternative, bearing shells124and128, inFIG. 7, are floating bearings. Alternatively, bearing shells are indexed with one of the connecting rods to prevent relative movement between the bearing shell pair and the connecting rod with which it is indexed. InFIG. 8, a portion of a bearing assembly is shown in an exploded view. A single shell bearing200has a tab202extending outwardly from the convex side of shell bearing200. A first bearing cap204has a pocket206. Tab202engages, or indexes, with pocket204to prevent relative movement of shell bearing200with first bearing cap204. Shell bearing200is double wide to accommodate two connecting rods (not shown inFIG. 8; only the bearing caps that couple to the connecting rods are illustrated) that are adjacent to each other. Thus, a second bearing cap208is shown inFIG. 8. Because the two connecting rods (not shown) that couple to first and second bearing caps204,208rotate independently of each other, shell bearing200engages with only one of the bearing caps (204in this embodiment) and floats with respect to bearing cap208. First and second bearing caps204,208are shown inFIG. 8as being next to each other. However, as assembled, they are on opposite sides of the crankshaft journal to which they couple, such as is illustrated inFIG. 2. InFIG. 2, pushrods34extend out in opposite directions so that the bearing caps are also opposite to each other. The same situation applies to pullrods36in which adjacent bearing caps (in an axial direction of the crankshaft) are substantially opposite each other with respect to the journal to which they couple.

Referring now toFIG. 9, an OPOC engine is illustrated that has a left cylinder300opposite a right cylinder302with a crankcase304between the two cylinders. An outer piston310and an inner piston312are disposed in left cylinder300. An outer piston320and an inner piston322are disposed in right cylinder302. As an OPOC engine has no cylinder head, access to the combustion chamber for ancillaries or sensors such as fuel injectors, spark plugs, glow plugs, and pressure transducers, can be a challenge. For some ancillaries or sensors, it is helpful to have access to the center of the combustion chamber as opposed to the periphery. Spark plugs330and332are shown disposed in pistons310and320, respectively. Other elements could be provided in the piston. If the desire is to mount the spark plug, or other element, in the intake pistons, the symmetric arrangement of the pistons facilitates this. The outer pistons reciprocate a lesser distance than the inner pistons, in most OPOC embodiments. Thus, the element mounted to the outer pistons is accelerated less than it would be if mounted to an inner piston. For most devices that would be mounted to the piston, such as the spark plugs shown, it is likely that wires, springs, or tubes will be coupled between the stationary block and the spark plug which is reciprocating with the piston. It is an advantage for the spark plugs to be mounted in outer pistons because the temperatures are lower at the outer edges and there is easier to access an entry for the wires, springs, or tubes where it is a little less crowded at the outer edges of the piston. Furthermore, replacing spark plugs in an outer piston is much easier than if mounted in an inner piston.

A symmetric OPOC engine is disclosed in commonly-assigned U.S. application 61/549,678, filed 20 Oct. 2011, which is incorporated herein in its entirety. The engine disclosed in '678 has collinear cylinders rather than offset cylinder axes according to embodiments disclosed herein. In '678 and in the present disclosure, the pistons are symmetrically arranged, which provides balance characteristics that are superior to conventional engines, but slightly poorer than the OPOC engine as disclosed in U.S. Pat. No. 6,170,443, which has asymmetrically-arranged pistons. In the present disclosure, the unbalanced forces in the direction of the cylinder axis are only of first order. For applications in which exceptionally low vibration is desired, balancing measures can be applied to the symmetric OPOC by counter weights on the crankshaft (integral with the crankshaft or applied to the crankshaft) and with counter rotating masses with crankshaft speed to attain asymmetric OPOC balancing or better. These measures apply equally well to the '678 and present disclosures.

The inertia forces404in the direction of reciprocation of the pistons of the OPOC engine inFIG. 1is plotted as function of crank angle degrees for a moderate engine speed. Also plotted (with a dashed line) on the same scale at the same engine speed are the inertia forces406for a comparable, conventional four-cylinder, four-stroke engine. OPOC engine10has about one-quarter of the unbalanced inertia forces compared to that of a conventional in-line, four-cylinder engine. The imbalance in OPOC engine10is a first-order imbalance, i.e., at crankshaft speed. The inertia force imbalance in the 1-4 engine is of second order, i.e., the imbalance has two periods in 360 crank degrees. Although the inertia force imbalance for the OPOC engine10with symmetrically-arranged pistons is quite small, there are applications in which the least amount of imbalance is desired, e.g., aviation applications, in which measures to lower the imbalance may be desired.

As a first measure to overcome a portion of the imbalance, webs between journals on crankshaft20may be designed such that the center of gravity of crankshaft20is displaced from the axis of rotation. If crankshaft20is weighted to overcome about half of the imbalance due to the reciprocating pistons and rods, the imbalance introduced by the offset center of gravity is shown as curve412.

Referring now toFIG. 12, an isometric representation of an accessory drive for an internal combustion engine is shown. Crankshaft450has a gear452that engages with a gear454that couples to an oil pump or other accessory (not shown). A counterweight456is coupled to gear wheel454. Crankshaft450is also coupled to a pulley458that is part of a front end accessory drive system460. A belt466engages with multiple pulleys462,463,464,465, and467. Pulleys462,463,464,465, and467may be coupled to additional accessories such as: an air-conditioning compressor, a power-steering pump, and a water pump. Some of the pulleys may be idler pulleys. Furthermore, at least one belt tensioner may be included in the system. A counterweight470is applied to pulley464and a counterweight468is applied to pulley468. Pulleys464and468are the same diameter as pulley458so that pulleys464and468counterrotate at crank speed. Gear454has the same number of teeth as gear452so that gear454counterrotates at crankshaft speed.

Crankshaft450rotates counter clockwise inFIG. 12as shown by arrow472. Gear454, pulley462, and pulley464, rotate clockwise, as shown by arrows474and476, and478thereby facilitating the counterweights associated with the gear and/or pulleys to counteract the imbalance in a direction orthogonal to the axis of the cylinders and the axis of rotation of the crankshaft created by the counterweighting of the crankshaft.

The counterweight(s) (i.e., offset of the center of gravity) applied to crankshaft460overcomes about one-half of the inertia force imbalance of the pistons in the axial direction of the cylinders but introduces an inertia force imbalance in an orthogonal direction. Counterweight456on gear454is sized to overcome about one-quarter of the inertia force imbalance due to reciprocation of the pistons in the axial direction of the pistons. And, because gear454rotates in an opposite direction from crankshaft460, it overcomes about one-half of the orthogonal imbalance introduced by a counterweight on crankshaft460. Counterweights468and470on pulleys462and464, respectively, are sized to overcome about one-eighth of the inertia force imbalance due to reciprocation of the pistons. Again, because pulleys462and464rotate in the opposite sense of crankshaft60, they collectively overcome about one-half of the orthogonal imbalance introduced by a counterweight on crankshaft460. The engine is balanced with the set of counterweights as described.

Referring back toFIG. 11, the imbalance due to counter weights468and470is shown as curve412and the imbalance due to counterweight456is shown as curve424. By summing curves404,410,412, and424, the resultant curve is426, which shows that the balance is perfect or nearly perfect.

While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.