US3520270A - Tuned exhaust gas system for outboard motor - Google Patents

Description

G. E. MlLLER 3,520,270

TUNED EXHAUST GAS SYSTEM FOR OUTBOARD MOTOR Filed May 29, 1968 lUnited States Patent O 3,520,270 TUNED EXHAUST GAS SYSTEM FOR OUTBOARD MOTOR George E. Miller, Zion, Ill., assignor to Outboard Marine Corporation, Waukegan, Ill., a corporation of Delaware Filed May 29, 1968, Ser. No. 733,159 Int. Cl. B63h 21/26 U.S. Cl. 115-17 13 Claims ABSTRACT F THE DISCLOSURE,

The invention provides an exhaust gas passage extending in an outboard motor lower unit from an engine exhaust gas port to an exhaust gas discharge outlet located below the water level around the lower unit, and including an exhaust gas tube which extends through the lower unit driveshaft housing in spaced relation to the walls of said housing to prevent contact of exhaust gases with such outer walls and which is provided with an upper part and a lower part of greater transverse cross section than the transverse cross section of the upper part. Enlargement of the lower part of the exhaust gas tube in relation to the upper part serves to produce, in response to exhaust gas flow, negatively reflected pressure waves which arrive at the engine cylinder at about the time when the piston is at bottom dead center and thereby provide improved scavenging of the burnt combustion gases.

BACKGROUND OF INVENTION This invention relates generally to outboard motors. More particularly, the invention relates to exhaust gas discharge systems for outboard motors and specifically to exhaust gas systems including an exhaust gas tube which extends within the driveshaft housing in isolated and spaced relation to the outer housing walls and upwardly from below or approximately the normal level of the water surrounding the housing. Examples of such tubes are found in the Larsen Pat. 3,198,162, the Kollmann Pat. 3,310,022 and the Boda Pat. 3,350,879.

Such systems have not always achieved optimum horsepower output due to the construction of the exhaust gasl pasageway. In at least one instance, it is believed that the silencing features of the invention disclosed in the Larsen Pat. 3,198,162 were not employed because of adverse affect on horsepower output. The invention herein disclosed facilitates use of the silencing system disclosed in the Larsen Pat. 3,198,162 while at the same time maximizing horsepower output.

SUMMARY OF INVENTION The invention relates to maximizing the horse power output of an outboard motor having an exhaust gas passage comprising an exhaust gas tube located in a drive shaft housing in spaced relation to the outer walls of the drive shaft housing such that the exhaust gases are normally prevented from contacting such outer walls. Such maximization is provided by employing negatively reflected pressure waves, i.e., the negative reflection of the compressive wave produced by the discharging exhaust gases, to assist in scavenging the burned combustion ICC products. Specifically, the invention involves producing such negative pressure waves, i.e., pressure waves below the mean exhaust manifold pressure, by enlarging the lower portion of the exhaust gas tube and locating the commencement of enlargement at a distance from the engine cylinder or cylinders such that negative pressure waves arrive back at the cylinders approximately when the pistons are at bottom dead center.

The disclosed invention therefore provides an outboard motor having an exhaust gas tube which is situated in spaced relation from the drive shaft housing walls, which is arranged to prevent exhaust gas contact with the outer walls of the drive shaft housing, and which has upper and lower portions, with the lower portion having an enlarged cross sectional area as compared to the upper portion and with the upper and lower parts being connected at a juncture located above the cavitation plate or water line under normal operating conditions.

In addition to the foregoing, the invention involves the extension of the upper portion of the tube slightly into the lower portion to provide a depending lip or flange which projects into the lower portion and serves to increase the scavenging efficiency of the returning waves.

The invention is preferably embodied in an exhaust gas system in which the exhaust gas tube is resiliently mounted and water jacketed to diminish transmission of exhaust gas excitations to the outer walls of the drive shaft housing.

Other objects and advantages of the invention will become known by reference to the following drawings and accompanying description in which:

In the drawings:

FIG. 1 is a side-elevational view, partially broken away and in section, and partially schematically of an outboard motor embodying various of the features of the invention;

FIG. 2 is a view taken along line 2-2 of FIG. 1;

FIG.y 3 is 'a cross sectional elevational view of a modified exhaust gas tube for use in the motor shown in FIG. 1; and

FIG. 4 is a cross sectional elevational view of another modified exhaust gas tube for use in the motor shown in FIG. l.

GENERAL DESCRIPTION Shown in the drawings is an outboard Imotor 11 comprising a transom clamp or bracket 13 which is pivotally connected by a horizontal pivot 15 to a swivel bracket 17. In turn, the swivel bracket 17 is pivotally connected about a vertical pivot 19 to a propulsion unit 21 including a power head 23 and a lower unit 25 which supports the power head 23 and includes an intermediate housing or strut 27 connected to the power head 23, together with a gear box 29 which is located at the bottom of the housing 27, which is suitably connected to the housing 27 by a series of bolts 30, and which, in normal operation, is submerged in water. Above the gear box in the conventional location is a cavitation plate 32 which, under normal operating conditions, is located at or slightly below the water level aft of the boat transom. The power head 23 includes an engine 31 having one or more cylinders 33 with pistons 35 reciprocable therein, an output or crankshaft 37, and an exhaust gas discharge port 39.

Also included in the outboard motor 11 is an engine cooling system including an engine cooling jacket 45 having an inlet 47 and a discharge outlet or port 49. Water for the cooling jacket is supplied to the inlet 47 through a conduit 51 from a water pump 53 which is communicable with a lake or stream and which is driven by a drive shaft 55 extending through the housing 27 and connected to the crankshaft 37. The driveshaft 55 extends into the gear box 29 and connects with a transmission or `clutch 57 controlling delivery of power to a propeller shaft 59 carrying -a propeller 61 rearwardly of the gear box 29.

The engine cooling system can take various forms and can be either of the recirculating type or of the non-reciroulating type. The clutch or transmission can also take various forms and can be either mechanical, electro-mechanical, hydraulic or electro-hydraulic.

Included in the lower unit 25 is an exhaust gas system for conducting exhaust -gases from the engine exhaust gas discharge port to an underwater discharge outlet which is located below the surrounding water level during normal operation and more or less near the bottom of the lower unit. In the disclosed construction, the exhaust gas system includes an exhaust gas passage 65 having an underwater exhaust gas discharge outlet 67 provided by a passage section 69 formed in the hollow interior of the hub of the propeller 61. In turn, the propeller hub passage section 69 communicates with a gearbox passage section 71 which, in turn, communicates with an exhaust Igas tube or pipe 73 extending upwardly from approximately at or below the water level 75 during normal operations. The exhaust gas tube or pipe 73 communicates with the engine exhaust gas port 39 and is arranged to prevent contact of the exhaust gases with the 'walls of the drive shaft housing. If desired, the exhaust gas discharge outlet could be provided in a iin portion of the lower unit as shown in the Larsen Pat. 3,198,162.

As also disclosed in the Larsen Pat. 3,198,162, the tube 73, at least at the bottom, is preferably vibrationally isolated from the drive shaft housing by means of one or more resilient elastomeric mounts or supports 77, such as for instance a rubber ring or blocks of rubber or the like, to prevent vibration transmission from the tube 73 to the drive shaft housing 27.

As also disclosed in the Larsen Pat. 3,198,162, the tube 73 is preferably surrounded with a jacket 79 of water to assist in deadening transmission of exhaust gas excitations to the outer walls of the drive shaft housing 27 In this regard, in the disclosed construction, the drive shaft housing 27 includes a generally vertically extending cross partition 83 which forms, together with other portions of the drive shaft housing 27, a chamber for the water jacket. Water can be supplied to the jacket or chamber in various ways. In the disclosed construction, such water is supplied from the engine water jacket discharge port 49. Excess water from the exhaust gas tube water jacket 83 overflows over a ledge 87 and to the exterior of the drive shaft housing 27 through a port 89 in the rear outer wall 91 of the drive shaft housing. If desired, the overow discharge water can be conducted within the lower unit 25 to a discharge point below the normal level of the surrounding water.

In accordance with the invention, the exhaust gas tube is constructed to maximize power output from the engine by causing the production of negatively reflected pressure waves which travel back to the engine cylinders 33 and can be -employed to assist in scavenging the engine cylinder or cylinders. Thus, in the disclosed construction, the exhaust gas' tube 73 includes a lower part or portion 94 which is materially larger in horizontal cross section than an upper part or portion 97 of the tube 73. As shown in FIG. 1 of the drawings, the lower tube part 94 is joined to the upper `tube part 97 adjacent the lower end of the upper tube part along a junction located above the cavitation plate 32 or water line 75 under normal operating 75 conditions. Very high efciency in producing negative or reflected pressure waves can Ibe obtained by designing such that `the ratio of the lower portion horizontal cross section to the upper portion horizontal cross section is 5 to 1. Because of size and mass flow limitations, as well as other considerations in the construction of outboard motors, achievement of such a relatively large ratio has thus far not seemed practical. However, the advantages of the invention can be obtained with a material increase in horizontal cross sectional size or area between the upper and lower portions of the exhaust gas tube. One engine which has been constructed and which has a ratio of 2.3 to 1 provides substantial advantages. However, this invention is not limited to a ratio of 5 to 1 or 2.3 to 1 and it is expressly stated that ratios smaller than 2.3 to 1 can be used to achieve the advantages of the invention.

Use of the returning negative pressure waves to assist in scavenging the cylinders is afforded by locating the enlargement in the exhaust gas tube 73 at such distance from the cylinders that the returning pressure waves will arrive at about the time the piston is at bottom dead center. The distance chosen can be such as to have maximum effect when at high, low, or middle engine speeds.

The enlarged portion 95 of the exhaust gas tube 73 can take various forms. For example, in FIG. 1 the enlarged lower portion has a fore and aft length A approximately twice the transverse width B which, in turn, is somewhat larger than the diameter D of the circular cross section of the upper portion 97 of the exhaust gas tube 0r pipe 73.

The cross section of the lower portion of the exhaust gas tube shown in FIG. 1 is essentially generally constant throughout its vertical length. However, at least some of the advantages of the invention can be obtained when using an enlarged portion which, as shown in FIG. 4, diverges downwardly, i.e., gradually increases in horizontal cross section in a downward direction from a junction between the lower portion 195 and the lower end of the upper portion 197, which junction is located above the cavitation plate 32 or normal water line under normal operating conditions. Thus, the tube 173 shown in FIG. 4 diverges at its lower end to provide a horizontal cross section of gradually increasing size in the downward direction.

Another embodiment of an exhaust gas tube 273 in accordance with the invention is shown in FIG. 3, which tube includes an upper part 297, and a lower part or enlarged portion 295, and a junction between the lower part 295 and the upper part 297 adjacent the lower end thereof, which junction is located above the cavitation plate 32 or normal water line 7'5 under normal operating conditions. The lower enlarged portion 295 includes two subparts, the upper sub-part 201 having a horizontal cross section larger than that of the upper portion 297 of the exhaust gas tube 273 and the lower sub-part 203 having a horizontal cross sectional area greater than the horizontal cross sectional area of the upper sub-part 201.

As already indicated, the increase in cross sectional area of the lower portion as compared to the upper portion of the exhaust gas tube need not be symmetrical about a vertical axis.

As also shown in FIG. 1, it is preferred to construct the exhaust gas tube 73` so that the upper portion 97 extends slightly into the lower portion 95, rather than terminating the upper portion 97 at the top of the lower or enlarged portion 95. Thus, in FIG. 1, there is provided a lip or ange 98 which constitutes an extension of the upper portion 97 of the pipe 73 and which extends slightly 'into the lower portion 95 beyond the upper wall 99 of the lower portion. A similar lip or flange 298 is shown in FIG. 3 extending from the upper portion 297 into the upper sub-part 201 of the lower or enlarged portion 296. Likewise, a lip or flange 398 extends a slight distance from the upper sub-part 201 into the lower sub-part 203 of the enlarged portion 295. If' desired, such a lip or flange can also Ibe employed in the tube 173 between the upper portion 197 and the lower portion 195.

The use of lips 98, 2.98y and 398 serves to increase the magnitude of the returning wave as compared to a returning wave which is produced without such a lip.

In operation, exhaust gases discharged froml the engine .31 travel through the exhaust pipe 73, and incident to passage from the upper part 97 to the lower part 95 of thepipe 73,'produce negatively reected pressure waves which travel .rearwardly and -upwardly through the exhaust gas tub'e 73 toward the cylinder,`arriving at the cylinder at approximately the time when the piston is at bottom dead center. The negative pressure which therefore occurs adjacent to the cylinder serves to assist in removing from the cylinder all of the burnt combustion gases, thereby improving scavenging eiciency.

In operation, various of the features of the invention are set forth in the following claims.

I claim:

1. In an outboard motor, the combination of a propulsion unit including a power head having an exhaust gas port and a lower unit including a housing supporting said power head, an exhaust gas discharge outlet located below the water level around said lower unit under normal operating conditions, and an exhaust gas passage extending from said exhaust gas port to said exhaust gas discharge outlet and including an exhaust tube extending through said housing interiorly of the walls of said hous ing, said exhaust gas tube including an upper part, a lower part of greater transverse cross section than the transverse cross section of said upper part, and a junction between said lower part and said upper part adjacent the lower end of said upper part, said junction being located above the water line under normal operating conditions.

2. An outboard motor in accordance with claim 1 wherein said upper part extends slightly into said lower part to provide a lip projecting slightly into said lower part.

3. An outboard motor in accordance with claim 1 wherein said tube extends upwardly from adjacent to or below said water level.

4. An outboard motor in accordance with claim 1 wherein said lower part includes a series of sub-parts, the lower sub-part of each adjacent pair of sub-parts having a horizontal transverse cross section larger than the horizontal transverse cross section of the upwardly adjacent sub-part.

5. An outboard motor in accordance with claim 1 wherein said lower part diverges downwardly.

6. An outboard motor in accordance with claim 1 wherein said power head includes a plurality of cylinders and pistons reciprocable in said cylinders, and wherein said lower part is spaced from said cylinders such that negative pressure waves reliected incident to exhaust gas passage from said upper part to said lower part return to said cylinders approximately when said pistons are at bottom dead center.

7. In an outboard motor, the combination of a propulsion unit including a power head having an exhaust gas port and a lower unit including a housing supporting said power head, an exhaust gas discharge outlet located below the water level around said lower unit under normal operating conditions, an exhaust gas discharge passage extending from said exhaust gas port to said exhaust gas discharge outlet and including an exhaust tube extending through said housing in spaced relation to the walls of said housing, said exhaust gas tube including an upper lpart, a lower part of greater transverse cross section than the transverse cross section of said upper part, and a junction between said lower part and said upper part adjacent the lower end of said upper part, said junction being located above the water line under normal operating conditions, a water pump, and means for supplying water from said pump to the space between said tube and the walls of said housing to provide a water jacket around said tube.

8. An outboard motor in accordance with claim 7 including a resilient mount supporting said tube from said lowere unit.

9. An outboard motor in accordance with claim 7 wherein said upper part extends slightly into said lower part to provide a lip projecting slightly into said lower part.

10. An outboard motor in accordance with claim 7 wherein said power head includes a plurality of cylinders and pistons reciprocable in said cylinders and wherein said lower part is spaced from said cylinders such that negative pressure waves reflected incident to exhaust gas passage from said upper part to said lower part return to said cylinders approximately when said pistons are at bottom dead center.

11. In an outboard motor, the combination of a transom bracket, a swivel bracket connected to said transom bracket about a horizontal pivot, and a propulsion unit connected to said swivel bracket about a vertical pivot, said propulsion unit including a power head having an internal combustion engine with a plurality of cylinders, a plurality of pistons reciprocable in said cylinders, an exhaust gas port and a water jacket having a discharge port, and a lower unit including a housing supporting said power head, a gear box connected to the bottom of said housing and extending into the water under normal operating conditions, an exhaust gas discharge outlet located below the water level around said lower unit under normal operating conditions, an exhaust gas passage extending from said exhaust gas port to said exhaust gas discharge outlet and including an exhaust tube extending through said housing in spaced relation to the walls of said housing and upwardly from adjacent to or below said water level, said exhaust gas tube including a lower part, an upper part, and a junction between said lower part and said upper part adjacent the lower end of said upper part, said junction being located above the water line under normal operating conditions, said upper part having a horizontal transverse cross section less than the horizontal transverse cross section of said lower part, said upper part extending slightly into said lower part to provide a lip projecting slightly into said lower part, said lip being spaced from said cylinders such that pressure waves reflected incident to exhaust gas passage from said upper part to said lower part return to said cylinders approximately when said pistons are at bottom dead center, a resilient mount supporting said tube from said lower unit, a water pump communicating with said engine water jacket, and means for supplying water from said engine water jacket discharge port to the space between said tube and the walls of said housing to provide a water jacket around said tube.

12. In an outboard motor, the combination of a propulsion unit including a power head having an exhaust gas port and a lower unit including a housing supporting said power head, a cavitation plate, an exhaust gas discharge outlet located below the water level around said lower unit under normal operating conditions, and an exhaust gas passage extending from said exhaust gas port to said exhaust gas discharge outlet and including an exhaust tube extending through said housing interiorly of the walls of said housing, said exhaust gas tube includingg and upper part, a lower part of greater transverse cross section than the transverse cross section of said upper part, and a junction between said lower part and said upper part adjacent the lower end of said upper part, said junction being located above said cavitation plate.

13. In an outboard motor, the combination of a propulsion unit including a power head having an exhaust gas port and a lower unit including a housing supporting said power head, a cavitation plate, an exhaust gas discharge outlet located below the water level around said lower unit under normal operating conditions, an exhaust gas discharge passage extending from said exhaust gas port to said exhaust gas discharge outlet and including an exhaust tube extending through said housing in spaced relation to the Walls of said housing, said exhaust gas tube including an upper part, a lower part of greater transverse cross section than the transverse cross section of said upper part, and a junction between said lower part and said upper part adjacent the lower end of said upper part, said junction being located above said cavitation plate, a water pump, and 1 neans for supplying water from said pump to the space between said tube and the walls of said housing to provide a water jacket around said tube.

References Cited UNITED STATES PATENTS Hansson 181-72 Ringles 181-57 Nowak 181-72 Larsen 115,-17 Kollman 115-,-17

Walther et i. 181-57 X 10 ANDREW H. FARRELL, Primary Examiner

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