The invention is directed to an improved exhaust valve throttling mechanism for a two-stroke engine -and has particular application to a multiple cylinder engine, such as a V-6 marine engine employ¬ ing two banks of three in-line cylinders.

Two-stroke engines include an exhaust port in the cylinder wall, which is opened and closed as the piston reciprocates in the cylinder. It has been rec¬ ognized that in multiple cylinder two-stroke engines reflected pressure fluctuations under idle or low speed conditions can adversely effect the combustion. At low or idle.speeds, the pressure waves are not nor¬ mally tuned so that reflected pressure waves from other cylinders in the bank, or from the same cylinder, can have an adverse effect on the engine combustion.

In viewof this, it has been proposed to utilize a butterfly valve in the exhaust port of a two-stroke motorcycle engine and control the operation of the valve through the intake manifold vacuum as disclosed in "Emission Control of Two-Stroke Motor Cycle Engines By The Butterfly Exhaust Valve", Society of Automotive Engineers Inc., September 8-11, 1980.

Our co-pending Application Serial No. PCT/US88/02090 filed June 15, 1988 also discloses an exhaust valve throttling mechanism for a two-stroke engine which can be incorporated with a multiple cylinder engine, such as a V-6 marine engine employing two banks of three in-line cylinders. As noted therein, the engine block is provided

with a pair of openings or passages, each of which in¬ tersects the exhaust ports of a bank of cylinders and a shaft is mounted for rotation with each passage and carries a plurality of shutters or valve members, 5 each of which is mounted within one of the exhaust ports. Advancement of the throttle will operate through a linkage to rotate the shafts to move the valves toward the open position. Conversely, a reduction of engine speed will act to move the valve members 10 toward the close _d position where the valve members will act to substantially block or restrict the propa¬ gation of pressure waves back to the cylinders at low and idle speeds.

The present invention provides an exhaust

H~~. port throttling means for a two-stroke engine including an engine block having a plurality of in¬ line cylinders, and exhaust passage means communicating with each cylinder, characterized in that said throt¬ tling means includes a tubular valve member mounted 20 or rotation relative to said block and having a plurality of apertures constructed and arranged to be moved into and out of registry with the respective exhaust passage means, and operating means for moving said valve member from a closed position at low 25 engine speeds where said apertures are substantially out of registry with the respective exhaust passage means to an open position at high speeds wherein said apertures are in full registry with said exhaust passage means, the interior of said tubular valve 30 member constituting a conduit to conduct exhaust gas. When used with a V-6 engine having two banks of in-line cylinders the device of the invention a shaft is connected to each tubular valve member and the corresponding ends of the shafts are interconnected _b y 5 meshing gear segments. One of the gear segments is connected through a linkage to the throttle lever for

the engine, so that the valve members will be rotated by actuation of the throttle lever between a substan¬ tially closed position at low speeds, where the valve members will substantially block the exhaust passages, to an open position at high speeds where the apertures in the valve members are in full registry with the corresponding ^• exhaust passages.

Preferably, 'a biasing mechanism can be in¬ corporated with the gear segments to bias the valve members to a closed position, and an adjusting mech¬ anism can also be employed to manually adjust the closed position of the valve members.

The exhaust valve throttling device of the invention substantially improves the performance of the engine by.'Providing quiet operation, better fuel economy and smoother running at low speeds. In ad¬ dition, the invention decreases hydrocarbon emissions and reduces engine surge that results from the ir¬ regular combustion inherent in a two-stroke engine. As the rotary valve members do not restrict or block the exhaust passages at high speeds, there is no power loss as occurs in prior systems in which the throttling valve partially restricts the exhaust passages at full throttle. Further features and advantages will appear in the course of the following description of a pre¬ ferred embo ^*" diment of the invention taken together with the accompanying drawings wherein:

FIGURE 1 is an elevational view partly in section of a six cylinder outboard motor engine in¬ corporating the exhaust valve throttling system of the invention;

FIGURE 2 is a section taken along line 2-2 Of FIGURE 1; FIGURE 3 is a ^' top plan view showing the mating gear segments;

FIGURE 4 is an enlarged fragmentary eleva- tional view showing ^' he gear segments and the biasing mechanism;

FIGURE 5 is a longitudinal section through a bank of cylinders showing the rotary valve member; and

FIGURE 6 is a perspective view of one of the rotary valve members.

The drawings illustrate a portion of an out- board motor power ead having a two-stroke, six cylin¬ der engine, such as that disclosed in U.S. Patent No. 4,187,809. The engine block 1 is provided with two banks in three cylinders 2 in a vertical in-line ar- ragnement. Each of the cylinders 2 includes an air- fuel intake port 3 and an exhaust port 4. As best shown in Fig. 2, each exhaust port 4 communicates with an exhaust passage 5 and the exhaust passages 5 of each of the banks of cylinders 2 register with ex¬ haust chambers 6a and 6b. A cover assembly 7 is connected to the engine block and encloses the exhaust chambers 6a and 6b, while an exhaust cavity separator 8, that is formed integrally with cover assembly 7 separates the two chambers.

As best shown in FIQURE 2, exhaust chambers 6a and 6b are partially cylindrical in cross section and the lower end of each, exhaust chamber 6a, 6b is connected to an exhaust discharge passage 9, formed in the block 1.

Mounted for rotation within each exhaust chamber 6a, 6b is a tubular valve member 10. The up¬ per end of each valve member 10 is enclosed by a cap 11 and an axial shaft 12 projects upwardly from the cap 11 and is journalled within an opening in the block 1. As best shown in FIGURE 5, the lower end of each valve member 10 is open and communicates with

the respective discharge passage 9.

Each valve member 10 is provided with a plurality of apertures 13, each of which is adapted to register with one of the exhaust passages 5. Through rotation of the valve member 10, apertures 13 can be moved from an open position, where the apertures are in full registry with the exhaust passages 5, to a closed position where the apertures are substantially out of registry and act to block the exhaust passages 5. As illustrated, apertures 13 extend through an arc of approximately 160 to 170 , but this of course lepends on the diameter of the tube and the cross sectional area of the exhaust passages. It is, of course, important that the area of the apertures 13 be equal to, or greater, than the cross sectional area of the exhaust passages 5, so that when the valve members are in the open position, there will be no restriction to gas flow from the exhaust passages into the interior of the valve members. In the closed position, apertures 13 are substantially out of registry with exhaust ports 5. In practice, about 85% to 95% of the area of the pas¬ sages 5 will be blocked off by the valve members 10. Alternately, valve members 10 can be provided with one or more small holes separate from the apertures 13, so that when the valve members are in the closed position, the small holes will register with the exhaust passages 5. Thus, at low or idle speed the valve members 10 will substantially block or restrict the propagation of pressure waves back to the cyli- inders.

The term "closed position", as used in the description and claims is intended to cover a condition where the valve members 10 do not completely close off

the exhaust passages 5.

Valve members 10 are moved between the closed and openpositions in accordance with engine speed. In this, regard the upper end of each shaft 12 extends through a collar or boss 14 on block 1 and carries a gear segment 15. As best shown in FIGURE 3, the gear segments- 15a and 15b each include a central hub 16, which is mounted on the end of the corresponding shaft 12, and a plurality of meshing gear teeth. Arms 17 extend outwardly from opposite sides of each hub 16 and are connected to block 1 through bolts 18.

Valve members 10 are biased to a closed position and to provide this biasing action, a torsion spring 19 is disposed around each of the hubs 16.

One end of each torsion spring is engaged with a lug 20 on boss 14, while the opposite end of the torsion spring is engaged with a pin 21 on the respective gear segment 15. The force of torsion springs 19 will thus bias the gear segments 15 and shafts 12 in a di¬ rection such that on termination of operation of the engine the valve members 10 will be returned to the closed position.

The invention can also include a mechanism for adjusting the closed position of valve members 10. In this regard an adjusting screw 22 is threaded within a bracket 23 that extends upwardly from block 1 and the end 24 of screw 22 is engaged with the peri¬ pheral edge of gear segment 15b. Lock nut 25 is threaded onto screw 22 and bears against bracket 23. By adjustment of screw 22, the closed position of the valve members 10 can be controlled to obtain the opti¬ mum exhaust opening at idle speed.

Valve members 10 are moved between the closed and open positions in accordance with operation of the engine throttle. To provide this operation, an arm 26

extends outwardly from the hub 16 of gear segment 15a and the arm is connected through a suitable linkage 27 to the throttle lever 28 for the engine. As the throttle lever 28 is advanced toward full engine speed the valve members 10 will be rotated toward the open position, against the force of torsion springs 19, and conversely, as the throttle lever is moved toward idle speed, the valve members will be moved toward the closed position so that the valve members will sub¬ stantially block the reflection of pressure waves back to the cylinders.

Linkage 27 and throttle lever 28 are shown diagrammatically and may take various forms depending upon the nature and location of the throttle of the marine craft. In general, the movement of the valve members 10 is proportional to movement of the throttle lever 28 and can be calibrated for each type of engine. The invention provides a simple and effective exhaust valve throttling mechanism for engines incor¬ porating a plurality of in-line cylinders. While the above description has shown the mechanism as utilized with a V-6 engine employing two banks of three cylin¬ ders each, it is contemplated that the invention can be used with any engine having a plurality of in-line cylinders.

The exhaust valve throttling mechanism pre¬ vents the propagation of pressure fluctuated waves back to the cylinders at low and idle speeds and thus sub¬ stantially improves engine performance, producing a quieter and smoother running engine at low speeds, as well as increasing fuel economy and reducing engine surge. At high speeds the exhaust valve throttling mechanism does not interfere or restrict the exhaust passages so that the mechanism does not reduce the power output at full throttle.

While the description and drawings have

illustrated the valve members 10 being rotated between the open and closed positions, it is contemplated that the valve members could be moved axially or with a combination of axial and rotational movement.