WO2001011212A1

WO2001011212A1 - A direct fuel-injected internal combustion engine using graphite-based pistons

Info

Publication number: WO2001011212A1
Application number: PCT/US2000/019642
Authority: WO
Inventors: Francis V. Bailey
Original assignee: Bombardier Motor Corporation Of America
Priority date: 1999-08-05
Filing date: 2000-07-19
Publication date: 2001-02-15
Also published as: AU6110500A

Abstract

A direct fuel injection internal combustion engine (30) rated to have an overall engine displacement that remains unchanged or higher notwithstanding that the engine may have a fewer number of cylinders than would be generally required to provide that overal engine displacement if the engine were to use metal alloy pistons is provided. The engine is made up of an engine block (62) that defines a plurality of cylinders (46). Each of the cylinders is configured to contribute a respective incremental displacement to the overall engine displacement, and the combination of the respective incremental displacements is selected to offset the reduction in the number of cylinders. The engine is further made up of a cylinder head (110) that closes each upper end of the cylinders to define a combustion chamber (118) in the cylinders. A piston (90) is reciprocally moveable in each of the cylinders. Each of the pistons is made up of a carbonaceous material.

Description

A DIRECT FUEL-INJECTED INTERNAL COMBUSTION ENGINE USING GRAPHITE-BASED PISTONS

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to fuel-injected internal combustion engines and, more particularly, to direct fuel-injected engines, such as two or four- stroke engines. Still more particularly, the invention relates to marine propulsion devices including such engines.

2. Related Prior Art

Two-stroke (or two-cycle) internal combustion engines using direct fuel injection have resulted in high performance engines generally having the relatively high power-to-weight ratio expected of a standard two-stroke engine plus the fuel economy and efficiency that matches the best of four stroke engines. For one example of a two-stroke direct fuel-injected engine used for marine propulsion devices, see U.S. Patent No. 5,699,468 assigned to the same assignee of the present invention.

As will be appreciated by those skilled in the art, a two-stroke direct fuel injection engine, on its compression cycle, compresses essentially plain air, as opposed to an air/fuel mixture. Since an air/fuel mixture would generally have superior thermal transfer characteristics as compared to plain air, internal components, e.g., pistons, of some direct fuel injected engines may experience hotter temperatures than the pistons of a standard two-stroke engine. Of course, the resulting higher temperatures could affect in the long run the durability of such pistons particularly since the pistons of such engines are typically made up of metal alloys, such as aluminum alloys. For example, hot spots on the surface of the pistons may cause undesirable damage to such piston surfaces. Further, any incremental thermally-induced expansion experienced by such metal alloy pistons may cause increased friction as the pistons reciprocate in their respective cylinders. The increased friction in turn may cause undue wear and tear of the pistons and associated components, and possibly result in higher engine maintenance and operational costs.

In addition to the above-described thermally-induced drawbacks, the relatively high density or weight of metal alloys have generally resulted in physical and/or economical constraints to the size of the respective pistons used by the engine since, if, for example, one were to increase the volume displaced by the piston (e.g., by increasing its bore and/or stroke), one would also have to use higher rated components, such as bearings, connecting crank pins, etc., in order to withstand the additional mechanical stresses resulting from the added weight of the piston or increased acceleration and deceleration forces.

In view of the foregoing considerations, it would be desirable to have a direct fuel injection engine that uses a piston material which is substantially impervious to the higher temperatures and/or thermal transients generally encountered by the pistons in such direct fuel injection engine. Although it is believed that use of various light weight, high strength materials for pistons may have been alluded to in the prior art, due to cost considerations such use has been generally limited to specialized applications, such as car racing, military or aerospace applications, and the like where low cost is not necessarily a primary or even a secondary consideration. Applicant is not aware of any such use in relatively low-cost direct fuel injection engines that are manufactured to provide high quality while affording substantial performance and savings to the consumer. One way of overcoming the cost constraints of the prior art would be to reduce the number of cylinders in the engine so as to offset any incremental costs due the light-weight piston material with a corresponding decrease in the number of components in the engine. Needless to say, the reduction in the number of cylinders should preferably be implemented without sacrificing the overall engine displacement of the engine so that the power characteristics of the engine remain substantially unchanged so as to meet the high expectations of the consumer. In view of the foregoing considerations, it would be further desirable to provide a direct fuel injection engine rated to have an overall engine displacement that remains substantially unchanged notwithstanding that the engine may have a lesser number of cylinders as compared to a similarly sized engine using pistons made of metal alloys. The foregoing costs and thermal drawbacks may now, in accordance with the present invention, be jointly and advantageously addressed if the pistons are made of commercially available carbonaceous materials, such as graphite-based materials either in unitary or in composite form, having sufficient mechanical strength and thermal stability to withstand mechanical and/or thermal stress at least in a typical temperature range of engine operation (e.g., about 500° F to about 900° F) while being lighter in weight relative to such metal alloys.

SUMMARY OF THE INVENTION

Generally speaking, the foregoing needs are fulfilled by providing a direct fuel injection internal combustion engine rated to have an overall engine displacement that remains substantially unchanged or higher notwithstanding that the engine may have a fewer number of cylinders than would be generally required to provide that overall engine displacement if the engine were to use metal alloy pistons. The engine is made up of an engine block that defines a plurality of cylinders each having a respective longitudinal axis and an upper end. Each of the cylinders is configured to contribute a respective incremental displacement to the overall engine displacement, and the combination or sum of the respective incremental displacements is selected to offset the reduction in the number of cylinders. The engine is further made up of a respective cylinder head including a lower surface portion closing each upper end of the cylinders so as to define a respective combustion chamber in the cylinders. A respective piston is reciprocally moveable in each of the cylinders along the longitudinal axis. Each of the pistons is made up of a predetermined carbonaceous material (e.g., graphite, graphite fibers or whiskers, graphite- based composites, carbon-graphite fibers, etc.) that is sufficiently light relative to the metal alloys to enable each of the pistons to have a respective incremental piston volume substantially matching each respective incremental displacement contribution provided by each of the cylinders. The carbonaceous material should have at least comparable mechanical strength relative to the metallic alloys to withstand any mechanical or thermal stress induced as each respective piston reciprocates in its respective cylinder. It will be appreciated that in the event that the number of cylinders is not reduced then the incremental piston volume will advantageously result in additional engine displacement. In either case, the net result is that the ratio of horse power/cylinder is advantageously increased due to the use of pistons made of such carbonaceous material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a marine propulsion device embodying the invention;

FIG. 2 is a partial sectional view of the engine of the marine propulsion device.

FIG. 3 is an enlarged portion of FIG. 2; and

FIG. 4 is a view taken along line 4—4 in FIG. 3 and with the piston removed.

Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in the context of a marine propulsion device powered by a two-cycle direct fuel injection internal combustion engine. However, it will be appreciated by those skilled in the art that the teachings of the present invention need not be limited to marine propulsion devices or two-cycle engine operation since other applications, such as lawn and garden equipment, lightweight motorcycles, or other generally off-road vehicles, etc., may equally benefit from such teachings.

An exemplary marine propulsion device 10 embodying the invention is illustrated in FIG. 1. Marine propulsion device 10 may include an outboard drive unit 14 adapted to be mounted to a transom 18 of a boat for pivotal tilting movement relative thereto about a generally horizontal tilt axis 22 and for pivotal steering movement relative thereto about a generally vertical steering axis 26. Drive unit 14 includes a propeller shaft 30 having a propeller 34 fixed thereto. As suggested above, drive unit 14 may include a direct fuel-injected, two-cycle internal combustion engine 38 drivingly connected to propeller shaft 30 by a conventional drive train 42.

Engine 38 may be a six-cylinder or a four-cylinder V-type engine. It should be understood, however, that the invention is applicable to other types of engines with any number of cylinders.

One exemplary cylinder 46 of engine 38 is illustrated in FIG. 2. Engine 38 includes a crankcase 50 defining a crankcase chamber 54 and having a crankshaft 58 rotatable therein. An engine block 62 defines cylinder 46, which has a longitudinal axis 66 and an upper end (the upper end in FIG. 2). Engine block 62 may also define (see FIG. 4) a number of intake ports, e.g., three intake ports 70, 74 and 78 communicating with cylinder 46. Each of the ports communicates with crankcase chamber 54 via a respective transfer passage 82 (one shown in FIG. 2). Engine block 62 also defines an exhaust port 86 which communicates with cylinder 46 and which is located generally diametrically opposite intake port 74. This construction is well known in the art and will not described in greater detail. Engine 38 also includes a piston 90 reciprocally moveable in cylinder 46 along axis 66. Prior art direct fuel injection combustion engines have generally employed pistons made up of metal alloys, such as aluminum. In contrast to such prior art, the present invention provides a piston made up of carbonaceous or industrial carbon materials, such as synthetic graphite or graphite-based composites using suitable matrix fibers or whiskers, that although well-known in the art of light-weight and high- strength material design have not been used in low-to-moderately priced two-cycle internal combustion engines due to the generally prohibitive costs of such materials for such applications. By way of example, one potential supplier of the piston material may be Veejay Development Inc., based in Schaumburg, Illinois that offers a commercially available carbon- carbon composite (e.g., fiber matrix) under its proprietary name of VJD C/C, and advertised to have density comparable to that of Aluminum 40- 32/T6. Another potential supplier of the piston material may be Schank Graphite, a Germany-based supplier of graphite materials, having distribution operations in Menomonee Falls, Wisconsin, U.S.A., and offering a commercially available meso-phase graphite material. In one exemplary prior art six-cylinder engine rated to have an overall engine displacement of about 158 in (2589 cc) using a typical metal alloy for the pistons, each cylinder 46 may have a diameter D of 3.600 inches, so that the cross-sectional area of the cylinder 46 in a plane perpendicular to the axis 66 is approximately 10.18 square inches. In contrast to such prior art construction, by use of a graphite-based material for each piston 46, since the graphite-based material may be about 30% less dense than a typical metal alloy piston, one can advantageously configure each respective cylinder to provide a respective incremental displacement to offset a predetermined reduction in the number of cylinders in the engine. For example, assuming that the number of cylinders is reduced from six to four and further assuming that the overall engine displacement is to be substantially maintained, then one could increase the bore and/or stroke of each cylinder so that the combination or sum of each respective individual displacement contribution of each cylinder offsets the fewer number of cylinders. As will be further appreciated by those skilled in the art, although the advantages of the present invention can now be achieved by providing a graphite-based piston, it should be understood that other relatively light-weight materials capable of providing relatively high tensile strength under relatively high temperature conditions, such as those encountered in the operation of a direct injection engine, could also be employed in accordance with the teachings of the present invention. Thus, other materials, generally presently limited in use to aerospace or military applications due to their present high cost could also be employed presuming such materials were to become more economically attractive in the future. As will be readily understood by those skilled in the art of internal combustion engines, piston 90 is drivingly connected to the crankshaft 58 by a crank pin 94. By way of example and not of limitation, piston 90 could include (see FIG. 3) an upper surface 98 having therein a circular bowl 102. Bowl 102 has a planar bottom surface 106 perpendicular to the axis 66. The upper surface 98 surrounding the bowl 102 is convex, defining a portion of a sphere having a suitable radius of curvature. Engine 38 also includes a cylinder head 110 including a lower surface portion 114 closing the upper end of cylinder 46 so as to define a combustion chamber 118 between piston upper surface 98 and cylinder head lower surface portion 114. When piston 90 is at top dead center, the piston upper surface 98 is suitably spaced from cylinder head lower surface portion 114. Cylinder head lower surface portion 114 extends generally perpendicular to the cylinder axis 66 and may include therein an upwardly extending recess or dome 122. In the illustrated exemplary embodiment, cylinder head lower surface portion 114 surrounding recess 122 is generally concave and complementary with piston upper surface 98. In the exemplary embodiment shown in FIG. 3, recess 122 is located directly above bowl 102 and is generally cylindrical, and centered on the cylinder axis 66. However, it will be appreciated by those skilled in the art that in general the recess need not be either cylindrical or centered on the cylinder axis. The recess 122 has an upper end and a lower end (the upper and lower ends in FIG. 3). In the exemplary construction, recess 122 has an area in a plane perpendicular to the cylinder axis 66 suitably dimensioned relative to the cross-sectional area of the cylinder. For example, the recess area may be conveniently chosen to be approximately one-fifth the cross-sectional area of cylinder 46, so that the combustion chamber 118 has a squish factor of approximately three to two. (The squish factor is the ratio of the area of the cylinder 46 outside the recess 122 to the area of the recess 122.) Also, in the illustrated construction, the recess 122 has a height H conveniently chosen so that its height is approximately one-half the cylinder diameter. Engine 38 also includes a fuel injector 126 mounted on cylinder head 110 for injecting pressurized fuel into the upper end of recess 122. One exemplary fuel injector 126 is disclosed in U.S. Ser. No. 08/506,534, filed Jul. 25, 1995 and titled "Combined Pressure Surge Fuel Pump and Nozzle Assembly", now U.S. Patent No. 5,779,454. Fuel injector 126 conveniently creates a region, e.g., cone 130, of fuel spray surrounded by a volume of fuel vapor, cone 130 being centered on cylinder axis 66. Generally, most of the entirety of the fuel spray cone 130 strikes the bottom surface 106 of the bowl 102 before striking any other surface. As shown in FIG. 3, fuel spray cone 130 may be centered on a cone axis 134 (also cylinder axis 66) and has an outside envelope defining a line 138 in a plane including cone axis 134 (the plane of the paper), line 138 and cone axis 134 forming a suitably dimensioned acute angle A.

It will be appreciated by those skilled in the art that the above- described fuel injector is one example of a type of injector that does not entrain the fuel in a gas or otherwise applies a gas under pressure to the fuel, commonly referred to as direct single fluid delivery. Other type of direct fuel delivery may be as described in US Patent No. 5,806,473. For example, this type of fuel delivery uses a high pressure pump for pressurizing a high pressure line to deliver fuel to the fuel injector through a fuel rail that delivers fuel to each injector. A pressure control valve may be coupled at one end of the fuel rail to regulate the level of pressure of the fuel supplied to the injectors to maintain a substantially constant pressure thereat. The pressure may be maintained by dumping excess fuel back to the vapor separator through a suitable return line. The fuel rail may incorporate nipples that allow the fuel injectors to receive fuel from the fuel rail. Thus, in this case, it is believed that a substantially steady pressure differential —as opposed to a pressure surge— between the fuel rail and the nipples causes the fuel to be injected into the fuel chamber. In either case, however, it should be appreciated that the present invention is not limited to fuel injectors that do not entrain the fuel delivered to the combustion chamber in a gas, since other types of fuel injection systems, such as injection systems that do entrain the fuel in a gas, commonly referred to as direct dual fluid injection or delivery, could be used and equally benefit from the teachings of the present invention. Examples of such direct dual- fluid injection systems that could be used include those that include a compressor or other compressing means configured to provide the source of gas under pressure to effect injection of the fuel to the engine, that is, fuel injectors that delivered metered individual quantity of fuel entrained in a gas. See, for example U.S. Patent No. 4,781,164 for general background information in connection with such type of dual fluid fuel injection system.

Engine 38 also includes a spark plug 142 which is mounted on cylinder head 110 and which extends into recess 122. In the illustrated exemplary construction, spark plug 142 may extend along a plug axis 146 which is located in the plane of cone axis 134 and line 138 and which is perpendicular to line 138. Also, spark plug 142 could readily located directly above intake port 74. Spark plug 142 includes a spark gap 150 that may be located outside fuel spray cone 130 and within the fuel vapor volume, so that spark plug 142 initially ignites fuel vapor rather than directly igniting the fuel spray. The distance from spark gap 150 to upper end of recess 122 may be greater than the distance from spark gap 150 to e piston upper surface 98 when piston 90 is at top dead center. In the illustrated exemplary construction, spark gap 150 is conveniently spaced approximately twice as far from the upper end of the recess 122 as it is from piston upper surface 98 when piston 90 is at top dead center. Ignition is timed by a suitable control unit (not shown) so that spark plug 142 ignites the fuel spray before the fuel spray strikes piston upper surface 98.

Using techniques well understood in the art, engine 38 also includes a source of primary lubricant, i.e. an oil tank 154 (shown schematically in

FIG. 2), and a lubricant supply system 158 for supplying oil from oil tank

154 to crankcase 50 of engine 38. The lubricant supply system may include an oil pump 162 communicating between oil tank 154 and crankcase chamber 54. An exemplary lubricant supply system 158 is disclosed in part in U.S. Ser. No. 08/507,051, filed Jul. 25, 1995 and titled "Oil Lubricating System For A Two-Stroke Internal Combustion Engine", now U.S. Pat. No. 5,632,241. Lubricant supply system 158 supplies oil directly to the various crankcase chambers 54 of the engine 38.

The engine also includes a source of fuel, i.e. a fuel tank 166 (shown schematically in FIG. 2), and a fuel supply system 170 for accurately supplying pressurized (e.g., 250 psi) fuel to the various respective fuel injectors 126 of engine 38. The fuel supply system 170 includes a fuel pump 174 communicating between the fuel tank 166 and the fuel injectors 126.

The engine may also include a source of secondary lubricant which is mixed with the fuel injected into the cylinders 46. Although a separate lubricant source could be employed, in the illustrated exemplary construction, the source of fuel and the source of secondary lubricant are a single tank ( fuel tank 166) of mixed fuel and oil. The ratio of fuel to secondary lubricant by volume is preferably within the range of 50:1 to 300:1 and does not necessarily vary with engine speed. Usually, the ratio is approximately 250:1, i.e., substantially greater than 200:1, at all engine speeds. In other words, the amount of secondary lubricant injected into the cylinders 46 by the fuel injectors 126 is substantially less than is necessary to adequately lubricate the engine 38. The purpose of the secondary lubricant is not lubrication of the engine 38, but is reduction of spark plug fouling. It has been found that mixing a relatively small amount of oil with the injected fuel significantly reduces spark plug fouling. In an alternative exemplary construction, the secondary lubricant is provided by a combined fuel and oil pump drawing fuel and oil from separate tanks. Any suitable fuel and oil pump can be employed. Another alternative would be using a completely separate oil pump drawing from a separate oil tank.

It will be understood that the specific embodiment of the invention shown and described herein is exemplary only. Numerous variations, changes, substitutions and equivalents will now occur to those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, it is intended that all subject matter described herein and shown in the accompanying drawings be regarded as illustrative only and not in a limiting sense and that the scope of the invention be solely determined by the appended claims.

Claims

1. A direct fuel injection internal combustion engine (30) rated to have an overall engine displacement that remains substantially unchanged or higher notwithstanding that said engine has a fewer number of cylinders than would be generally required to provide said overall engine displacement if the engine were to use metal alloy pistons, said engine comprising: an engine block (62) defining a plurality of cylinders (46) each having a respective longitudinal axis (66) and an upper end, each of said cylinders configured to contribute a respective incremental displacement to the overall engine displacement, the combination of said respective incremental displacements being selected to offset the fewer number of cylinders in said engine; a respective cylinder head (110) including a lower surface portion (114) closing each upper end of said cylinders so as to define a respective combustion chamber (118) in said cylinders; and a respective piston (90) reciprocally moveable in each of said cylinders along said axis, each of said pistons made up of a predetermined carbonaceous material that is sufficiently light relative to said metal alloys to enable each of said pistons to have a respective incremental piston volume substantially matching each respective incremental displacement contribution provided by each of said cylinders, the carbonaceous material further having at least comparable mechanical strength relative to said metallic alloys to withstand any mechanical stress induced as each respective piston reciprocates in its respective cylinder.

2. The internal combustion engine of claim 1 wherein said engine is a two-cycle engine.

3. The internal combustion engine of claim 1 wherein said engine is a four-cycle engine.

4. The internal combustion engine of claim 1 wherein said carbonaceous material is selected from the group consisting of graphite, graphite composites, graphite fibers, and carbon graphite fibers.

5. The internal combustion engine of claim 1 wherein said engine further comprises a fuel injector (126) for directly injecting fuel into the combustion chamber.

6. The internal combustion engine of claim 5 wherein said engine comprises a spark plug (142) having a spark gap located within the chamber to ignite the fuel delivered by the fuel injector.

7. The internal combustion engine of claim 5, wherein the fuel injector is configured to deliver to the chamber fuel that is entrained in a predetermined gas.

8. The internal combustion engine of claim 7 wherein the predetermined gas is air.

9. The internal combustion engine of claim 7 wherein the fuel is compressed to be entrained within the predetermined gas by a compressor.

10. The internal combustion engine of claim 5 wherein the fuel injector is configured to deliver fuel to the chamber not entrained in a gas.

11. The internal combustion engine as set forth in claim 10 wherein the fuel injector delivers fluid due to a predetermined pressure surge or by a pressure differential.

12. The internal combustion engine of claim 1 wherein the number of cylinders is reduced from a number N, where N is a positive integer representing the number of cylinders that would be generally required if metal alloy pistons were to be used, to a positive number of N-P cylinders, where P is a positive integer representing the number of cylinders eliminated when using the carbonaceous material so as to maintain the overall engine displacement substantially unchanged notwithstanding said reduction in the number of cylinders.

13. The internal combustion engine of claim 12 wherein the number N corresponds to eight or six cylinders and the number P corresponds to one, two, three, or four cylinders.

14. An internal combustion engine (38) comprising: an engine block (62) defining a cylinder (46) having a longitudinal axis (66) and an upper end; a piston (90) reciprocally moveable in said cylinder along said axis, said piston being made of a carbonaceous material; a cylinder head (110) including a lower surface portion (114) closing said upper end of said cylinder so as to define a combustion chamber (118) between said piston upper surface and said cylinder head lower surface portion; a fuel injector (126) supported relative to said cylinder head for injecting fuel directly into said combustion chamber to create a region of fuel spray surrounded by a volume of fuel vapor; and a spark plug (142) which is supported relative to said cylinder head, which extends into said combustion chamber, and which includes a spark gap located outside said fuel spray region and within said fuel vapor volume.

15. The engine of claim 14 wherein the carbonaceous material for said piston is selected from the group consisting of graphite, graphite composites, graphite fibers, and carbon graphite fibers.

16. The internal combustion engine of claim 14 wherein said engine is a two-cycle engine.

17. The internal combustion engine of claim 14 wherein said engine is a four-cycle engine.

18. The internal combustion engine of claim 14 wherein said cylinder head lower surface portion extends generally perpendicular to said axis, and has therein an upwardly extending recess.

19. The internal combustion engine of claim 14 wherein the fuel injector delivers fluid to the chamber due to a predetermined pressure surge without entraining the fuel in a gas.

20. An internal combustion engine (30) having direct fuel injection comprising: (a) an engine block (62) having a cylinder;

(b) a piston (90) moveable in the cylinder, the piston being made of carbonaceous material;

(c) a cylinder head (110) connected to the engine block;

(d) a chamber (118) formed between the piston and the cylinder head;

(e) a fuel injector (126) which is positioned to deliver fuel directly into the chamber; and

(f) a spark plug (142) having a spark gap, the spark plug being positioned such that the spark gap is located within the chamber to ignite the fuel delivered by the fuel injector.

21. The internal combustion engine as set forth in claim 20 wherein the carbonaceous material is selected from the group consisting of graphite, graphite composites, graphite fibers, and graphite fiber composites.