JPH0563607B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust system for an internal combustion engine, and more particularly to an exhaust system for an internal combustion engine having a plurality of cylinders, particularly for use in an outboard motor, for example.

[Prior art] In general, when the exhaust timing of a two-stroke engine is advanced, the maximum output of the internal combustion engine increases, but the torque in the low and medium speed range decreases.On the other hand, when the exhaust timing is delayed, the maximum output decreases, but the maximum output of the internal combustion engine decreases. It is known that torque in the speed range increases. here,
In a two-stroke engine that has multiple cylinders, the exhaust timing of all cylinders is set constant in order to obtain a predetermined output and torque, but the effect of changing the exhaust timing on the maximum output and torque depends on the number of cylinders. The larger the number, the greater the increase, and therefore it has been extremely difficult to set the exhaust timing to ensure maximum output and maintain torque in the low to medium speed range without decreasing it.

For this reason, in the past, the exhaust timing was determined depending on whether emphasis was placed on maximum output or torque in the low and medium speed range, and there was no system that satisfied both.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the prior art as described above, and its purpose is to secure maximum output in an engine having a plurality of cylinders, and to An object of the present invention is to provide an exhaust system for an internal combustion engine that prevents a decrease in torque in the low and medium speed range.

[Means for Solving the Problems] In order to achieve this object, the present invention provides an exhaust system for an internal combustion engine having a plurality of cylinders, in which the end of the exhaust port of at least one cylinder is closest to the top dead center. The piston is characterized in that the distance between the cylinder and the upper end surface when the piston is located at the top dead center is different from the distance in other cylinders.

[Function] With this configuration of the present invention, the exhaust timing for one cylinder is set with emphasis on maximum output, and the exhaust timing on other cylinders is set with emphasis on torque in the low and medium speed range, and as a result, the output of the engine is adjusted. The maximum output can be maintained, and the torque in the low and medium speed range can also be prevented from decreasing.

[Example] The present invention will be described below based on an example shown in the drawings.

FIG. 1 shows a three-cylinder, two-stroke internal combustion engine. Here, a piston 10 is inserted into each of the three cylinders 12 of the engine block so as to be able to reciprocate, and each piston 10 is inserted into the connecting rod 14.
It is connected to the crankshaft 16 via. The crankshaft 16 extends vertically over three cylinders, and each crank chamber 18 containing the crankshaft 16 is communicated with a carburetor 22 via an intake passage 20. 24 is a reed valve provided in each intake passage 20.

Each crank chamber 18 is opened to the inner surface of the cylinder 12 through a scavenging passage 26 formed in the cylinder 12, and the opening of this scavenging passage 26 is opened and closed by the reciprocating movement of the piston 10. There is.

In addition, exhaust ports 28 and 3 are provided on the inner surface of each cylinder 12.
0 and 32 are provided, respectively, and the burned gas is discharged to an exhaust passage (not shown) through these exhaust ports. Here, the positions of the exhaust ports are slightly shifted so that the exhaust timing differs between cylinders. That is,
The distance a between the right end of the first exhaust port 28, that is, the end closest to the top dead center of the piston 10 and the upper end surface at the top dead center of the piston 10, and the second exhaust port 30
The similar distance b at the third exhaust port 32 and the similar distance c at the third exhaust port 32 are arranged to be slightly shifted from each other. In particular, in this example, b and c are provided at the same position, but a is 1 with respect to b and c.
mm, and the difference in distance is that the first cylinder has an exhaust timing of 94 degrees in terms of crankshaft rotation angle, while the second and third cylinders have an exhaust timing of 94 degrees. This leads to the difference that the exhaust timing is 96 degrees.

That is, in this embodiment, the second and third
The exhaust timing in the first cylinder is the same, and
The exhaust timing of only the cylinders is made about 2 degrees earlier in terms of crankshaft rotation angle than the other cylinders. This change in exhaust timing is achieved by changing the position of the exhaust port in each cylinder, especially the distance between the end of the exhaust port closest to top dead center and the top end surface when the piston is at top dead center. I'm trying to get the hang of it.

According to the configuration of this embodiment, the relationship between engine speed and output for the entire internal combustion engine is determined by the second
A curve like the solid line in the figure will be drawn. In this Figure 2, the horizontal axis shows the engine speed and the vertical axis shows the output. For comparison, the dotted line curve indicates the exhaust timing of all cylinders at 94 degrees in terms of crank rotation angle. The curve shown by the one-dot chain line is the curve when all exhaust timings are matched to 96 degrees. In addition, the relationship between engine speed and torque is shown in Figure 3. In the above example, the curve shown by the solid line is drawn, and when all exhaust timings are set to 94 degrees as in Figure 2, the curve is shown by the dotted line. On the other hand, if the exhaust timing is set to 96 degrees, the curve will be as shown by the dashed line.

As can be seen from Figures 2 and 3, the maximum output is highest when all exhaust timings are set to 94 degrees, but the torque is highest in the low and medium speed range as shown in Figure 3. On the other hand, if the exhaust timings are all set to 96 degrees, the torque in the low and medium speed range will be high, but the maximum output will be lower. The above-described embodiment according to the present invention exhibits an output and torque approximately intermediate between the dotted line and the dashed-dotted line in FIGS. This is achieved by making the exhaust timing different.

[Effect] As described above, according to the present invention, at least one
By making the exhaust timing in one cylinder different from that in other cylinders, there is an excellent effect that the maximum output and the torque in the low and medium speed range can be simultaneously maintained as high as possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of an exhaust system for an internal combustion engine according to the present invention, FIG. 2 is a graph showing the relationship between engine speed and output in the same embodiment, and FIG. 3 is an engine in the same embodiment. It is a graph showing the relationship between rotation speed and torque. 10... Piston, 28... Exhaust port, 30...
Exhaust port, 32...exhaust port.

Claims (1)

[Claims] 1. In an exhaust system for an internal combustion engine equipped with multiple cylinders, the distance between the end of the exhaust port of at least one cylinder closest to top dead center and the upper end surface when the piston is located at top dead center relative to other cylinders. The exhaust system of an internal combustion engine configured to be different from the distance in question.