The invention is directed to an exhaust valve throttling mechanism for a two-stroke engine and in particular to an exhaust valve throttling mechanism that can be incorporated with multiple cylinder engines, such as a V-6 marine engine employing two banks of three in-line cylinders.

Two stroke engines include an exhaust port in th cylinder wall, which is opened and closed as the piston reciprocates in the cylinder. It has been recognized 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 normally 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 view of this, it has also been proposed to utilize a butterfly valve in the exhaust port of 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.

The present invention provides an exhaust port throttling means for a two-stroke engine having an engine block with a plurality of in-line cylinders and having piston means disposed for reciprocal movement in each cylinder, each cylinder including exhaust port means disposed to be closed by said piston means, characterized in that said block includes a passage intersecting each of said exhaust port means, said throttling means includes a shaft journalled for rotation within said passage, a plurality of valve members disposed in spaced relation on said shaft, each valve member being movable between a closed position where said valve member substantially

closes off the respective exhaust port means and an open position, each valve member disposed in registry with one of said exhaust port means, and operating means for rotating said shaft in accordance with a variation in engine speed to move said valve members from said closed position at low throttle speed to said open position at high throttle speed, said valve members when in said closed position at low speed acting to restrict the propagation of pressure waves to the cylinders. The present invention also involves the provision in a two-stroke engine of an engine block having a plurality of in-line cylinders, piston means disposed for reciprocal movement in each cylinder, each cylinder including exhaust port means disposed to be closed by said piston means, said block including a passage intersecting each of said exhaust port means, throttle means for controlling the speed of the engine and movable between a high speed position and an idle speed position, and means responsive to movement of said throttle means toward said idle speed position for blocking the propagation of reflected pressure waves through each exhaust port means to the respective cylinder.

Preferably, a biasing mechanism is incorporated with each shaft, and acts to urge the valve members to a closed position so that the valve members will automatically be returned to the closed position on termination of operation of the engine. In addition, an adjusting mechanism can be incorporated in the valve operation means to adjust the closed position of the valves.

The exhaust valve throttling mechanism of the invention substantially improves the performance of the engine by providing quieter operation, better fuel economy and smoother running at low speeds. In addition, the mechanism system decreases hydrocarbon emissions and

mechanism system decreases hydrocarbon emissions and reduces engine surge that results from the irregular combustion inherent in a two-stroke engine.

Further features and advantages will appear in the course of the following description of a preferred embodiment of the invention taken together with the accompanying drawings wherein:

Fig. 1 is an elevational view partly in section of a six cylinder outboard motor engine incorporating the exhaust valve throttling system of the invention;

Fig. 2 is a section taken along line 2-2 of Fig. l;

Fig. 3 is a top plan view showing the mating gea segments; Fig. 4 is an enlarged fragmentary elevational view showing the gear segments and the biasing mechanism; and

Fig. 5 is a perspective view of one of the shaft carrying the valve members. The drawings illustrate a portion of an outboard motor powerhead having a two-stroke, six cylinder engine, such as that disclosed in U.S. Patent No. 4,187,809. The engine block 1 is provided with two banks of three cylinders 2 in a vertical in-line arrangement. 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 exhaust 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.

In accordance with the invention, engine block 1 is provided with a pair of parallel openings or passages

9, each of which intersects the exhaust passages 5 of one of the cylinder banks. A shaft 10 is mounted within each of the openings 9, and each shaft 10 includes a plurality of spaced collars 11 which serve as bearing means to journal the shaft 10 within the respective passage 9.

Located between collars 11 on each shaft are three valve members or shutters 12, which are disposed in the respective exhaust passages 5. Through rotation of shaft

10, the valve members 12 can be moved between closed and open positions.

The upper end of each shaft 10 extends through a collar or boss 13 on block 1 and carries a gear segment 14. As best shown in Fig. 3, the gear segments 14a and 14b each include a central hub 15, which is mounted on the end of the corresponding shaft 10, and a plurality of meshing gear teeth 16.

Arms 17 extend outwardly from opposite sides of each hub 15 and are connected to block 1 through bolts 18. Valve members 12 are biased to a closed position and to provide this biasing action, a torsion spring 19 is disposed around each of the hubs 15. One end of each torsion spring is engaged with a lug 20 on boss 13, while the opposite end of the torsion spring is engaged with a pin 21 on the respective gear segment. The force of torsion springs 19 will thus bias the gear segments 14 and shafts 10 in a direction such that on termination of operation of the engine the valve members will be returned to the closed position.

The invention also includes a mechanism for adjusting the closed position of valve members 12. 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 peripheral edge of gear segment 14b. 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 12 in exhaust passages 5 can be controlled to obtain the optimum exhaust opening. In practice, valve members 12 will not be fully closed at idle speed and adjusting screw 22 can be employed to adjust the amount of opening of the valve when in the closed position. Alternatively, the valve members 12 can be provided with one or more small holes or cut-outs, in which case the valve members can be moved to a fully closed position and the holes will provide for the discharge of exhaust at idle conditions. Thus, the term

"closed position" as used in the description and claims is intended to cover a condition where the valve members do not completely close off the exhaust passages.

Valve members 12 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 15 of gear segment 14b and the arm is connected through a suitable linkage 27 to the throttle lever 28 for the outboard engine. As the throttle lever 28 is advanced toward full engine speed, the valve members 12 will be moved 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 substantially 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 12 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 incorporating 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 cylinders 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, by preventing the propagation of pressure fluctuated back to the cylinders, substantially improves engine performance, producing a quieter and smoother running engine at low speeds, as well as increasing fuel economy and reducing engine surge. In addition, the mechanism substantially reduces hydrocarbon emissions from the engine.