JP3016777B1 - Multi-cylinder two-cycle engine - Google Patents

Abstract

An object of the present invention is to improve the output of the entire engine while making the exhaust system more compact in a multi-cylinder two-cycle engine. SOLUTION: In a multi-cylinder two-cycle engine having three cylinders having a phase difference of 120 °, each cylinder 11, 11,
The exhaust holes 23, 24, 25 of 12, 13 are combined into one
6 and connected to a common exhaust system. In the collecting part 36, the exhaust holes 23, 24, 25 of the cylinders 11, 12, 13 are provided.
A switching valve 38 is provided for switching one of the two to a state communicating with the exhaust system and the other two to a state communicating with the exhaust system.
The exhaust holes 23, 24, 2 of the cylinders 11, 12, 13 are also provided.
The distance from 5 to the collecting part 36 is made equal, and the switching valve 38
Is rotated, and is rotated synchronously with the crankshaft 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-cylinder two-stroke engine, and more particularly to a multi-cylinder two-stroke engine suitable for a vehicle having a straddle-type seat such as a personal watercraft or a snowmobile.

[0002]

2. Description of the Related Art FIG. 3 shows a general plan view of a personal watercraft, which is equipped with a straddle-type (saddle-type) seat 3 and a handle 4 on the upper side of a deck 1. An engine storage room is formed on the side, and the engine 10 is stored. In recent years, such small planing boats have been increasing in size such as two-seaters or three-seaters, and the displacement of an onboard engine has also been increasing in order to secure the performance required for the increase in size. In order to increase the engine displacement, the number of cylinders has been increased due to the restriction on the enlargement of the piston speed and bore.

[0003] At present, in response to the demand for multi-cylinders, a three-cylinder two-cycle engine 10 as shown in FIG. 2 is often mounted as an engine for a two-seater or three-seater planing boat. When such a three-cylinder engine is mounted, a tandem type in which the cylinders 11, 12, and 13 are arranged in a line in the front-rear direction so as to be arranged in a limited space below the seat is suitable.

However, even if the tandem engine 10 is mounted as described above, exhaust system equipment such as an exhaust muffler 16 and an intake system such as an air cleaner 109 are provided on the left and right sides of the engine body as shown in FIG. If parts are arranged and these equipments are provided with their own exhaust systems such as mufflers, the number of parts is increased by the number of cylinders accompanying the multi-cylinder, and the size of these equipments is increased. Note that FIG.
In the figure, 105 is a step surface, and 109 is an intake pipe.

On the other hand, it is difficult to increase the seat width W to a certain width or more due to ergonomics. Therefore, when a multi-cylinder system is used, if the exhaust system independent of each cylinder is provided as described above, the exhaust gas will be exhausted. It becomes difficult to arrange system equipment.

As a countermeasure, when a multi-cylinder engine such as a three-cylinder engine is adopted, the exhaust holes 23, 24, and 25 of the cylinders 11, 12, and 13 are gathered by an exhaust manifold 100 as shown in FIG. , Common exhaust muffler 1
6. The exhaust system is connected to the exhaust system to reduce the size of the exhaust system.

[0007]

The output of the two-stroke engine can be improved by devising the control of the exhaust system. This will be described briefly with reference to FIG. 9, which is a simplified diagram of the two-stroke engine. The exhaust muffler 16 connected to the exhaust hole 120 of the cylinder 101 has a diffuser portion 16a whose diameter gradually increases as it goes downstream of the exhaust gas, and a cone portion 16b whose diameter decreases relatively sharply as it goes downstream. I have. In the exhaust hole 120, the diffuser portion 1
A negative pressure is generated by the expansion action of 6a, and a positive pressure is generated by the compression action of the cone portion 16b. These negative and positive pressures are used to discharge combustion gas, suck out fresh air, and push in fresh air. It can create a kind of supercharging effect. When this phenomenon is represented by a pressure change curve in the exhaust hole 120, FIG.
The pressure waveform P2 shown in the middle stage of 0 is an ideal (at the time of tuning) waveform capable of effectively exhibiting the supercharging effect.

That is, in the middle pressure waveform of FIG.
Fresh air is sucked into the exhaust system by the negative pressure (cross-line area Y1) in the section TO-TC in which the scavenging holes are open, and the positive pressure (hatched line) in the section from TC when the scavenging holes are closed to EC when the scavenging holes are closed. In the region Y2), fresh air sucked into the exhaust system is
1 (pushed back), and a high output is obtained by this supercharging action.

The above supercharging effect cannot be obtained even if the exhaust system length M1 is longer or shorter than the exhaust system length at the time of tuning. For example, if the length of the exhaust system is short, a pressure waveform P1 as shown in the upper part of FIG. 10 is obtained.
In C, the pressure becomes negative, so that the fresh air sucking and pushing action cannot be expected. If the exhaust system length is long, the pressure waveform P3 becomes as shown in the lower part of FIG. 10, and the scavenging hole closed section TO-TC
The section TC-EC also becomes a negative pressure continuously with the negative pressure of, and the pushing action of fresh air cannot be expected.

[0010] In the exhaust system of the conventional three-cylinder two-stroke engine shown in FIG.
The distances L1, L from the exhaust holes 23, 24, 25 of the exhaust manifolds 1, 12, 13 to the collecting portion 111 of the exhaust manifold 100.
2 and L3 are different. Here, for example, the passage length L2 from the exhaust hole 24 of the second cylinder 12 to the collecting portion 111
Is set to a length at which the pressure waveform P2 at the time of tuning shown in the middle part of FIG. 10 is obtained, the first and third cylinders 1
The pressure waveforms of the exhaust holes 24 and 25 of the exhaust valves 13 and 13 are non-tuned waveforms P1 and P3 as shown in the upper and lower sections of FIG. 10, and the supercharging effect is thin and does not lead to the improvement of the output of the three cylinders as a whole.

FIG. 8 shows a performance curve. According to a three-cylinder two-cycle engine having an exhaust manifold as shown in FIG. 11, a performance curve X3 shown by a broken line is obtained.
The output is lower overall as compared to the ideal performance curve X1.

By the way, if an independent exhaust system is to be connected for each of the three cylinders as described above in order to improve the output, a large arrangement space is provided below the seat 3 in FIGS. 2 and 3 as described above. And it is difficult to secure the boarding position of the pilot. Even if the independent exhaust system is arranged in a narrow space, a high output is obtained near the tuned rotation region N1 as shown in FIG. 8, but becomes non-tuned near the non-tuned rotation region N2. As shown by the performance curve X2, the rotation range N2 is larger than the ideal curve X1.
In the vicinity, the output decreases, and acceleration cannot be expected.

As a prior art document describing a two-cycle engine in which three cylinders are arranged in tandem in tandem and provided with an exhaust manifold, there is Japanese Patent No. 2767386, but the shape of the exhaust passage in the exhaust manifold is devised. By doing so, the mutual interference between the cylinders is reduced, and the output is maintained.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to improve the output of the entire engine while maintaining compactness of an exhaust system such as an exhaust muffler in a multi-cylinder two-cycle engine having three cylinders or a multiple of three cylinders. . In particular, the present invention provides a two-stroke multi-cylinder engine suitable for mounting on a vehicle such as a watercraft or a snowmobile where it is difficult to secure a sufficient space for an exhaust system.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an invention according to claim 1 of the present application is directed to a multi-cylinder two-cycle engine having three cylinders having a phase difference of 120 °, and having an exhaust hole of each cylinder. A single collecting portion is connected to a common exhaust system, and the collecting portion has a state in which one of the exhaust holes of each cylinder communicates with the exhaust system, and a state in which two of the exhaust holes of each cylinder are exhausted. It is characterized in that a switching valve for switching to a state communicating with the system is provided. As a result, most of the exhaust system equipment is made common to the three cylinders, so that the exhaust system can be kept compact. At the same time, each cylinder has an ideal pressure waveform that can exhibit the supercharging effect of the exhaust system. Can be changed, and the supercharging effect can be enhanced by utilizing the positive pressure of the next cylinder in the fresh air pushing stroke of one cylinder, and the engine output is improved.

According to a second aspect of the present invention, in the multi-cylinder two-stroke engine according to the first aspect, the distance from the exhaust hole of each cylinder to the collecting portion is made equal. As a result, changes in the exhaust hole pressure of each cylinder can be unified into a similar pressure waveform.

According to a third aspect of the present invention, in the multi-cylinder two-cycle engine according to the first or second aspect, the switching valve of the collecting portion is of a rotary type. This allows
Repeated switching operation can be performed smoothly.

According to a fourth aspect of the present invention, in the multi-cylinder two-cycle engine according to the first, second or third aspect, the switching valve is operated in synchronization with the crankshaft. Thus, high output can be maintained even when the rotation speed of the engine changes.

Also in a multi-cylinder two-stroke engine having a multiple of three cylinders, the present invention is also applicable to a three-cylinder two-cycle engine.
Or the configuration described in 4 can be provided.

[0020]

FIG. 3 shows a small personal watercraft equipped with a three-cylinder two-stroke engine according to the present invention. The boat body is composed of an upper deck 1 and a lower hull 2, and a deck is provided. A handle 4 and an openable / closable seat 3 are provided in order from the front side on the upper side of 1, an engine room is formed below the seat 3, and a three-cylinder two-cycle engine 10 is housed in the engine room. A jet pump 5 for propulsion is disposed at the rear end of the hull 2.

FIG. 2 is a plan view of the personal watercraft shown with the seat 3 removed. The engine 10 is of a tandem type and has first, second and third cylinders 11, 12, and
13 are arranged in a line in the front-back direction, and the ignition order is also in this order. The three cylinders 11, 12, and 13 are set such that the phase is delayed by 120 ° in crank angle in order from the front cylinder 11 to the rear. A crankshaft 19 projects from the rear end of the engine 10, and a propulsion shaft 21 is connected via a joint 20, and the jet pump 5 is driven by the propulsion shaft 21.

FIG. 1 is a left side view showing the engine 10 taken out. The cylinders 11, 12, 13 are fastened to the upper side of an integrated crankcase 22, and the cylinders 11, 12, 13 are fastened. Exhaust holes 23, 24, 25 are formed on the left side surface of the exhaust pipe 13, and exhaust pipes 28, 2, respectively.
9, 30 are connected. Each of the exhaust pipes 28, 29, 30 is formed to have the same length, and is connected to the collecting part 36 with a built-in switching valve. A single exhaust muffler 16 shared by three cylinders is connected to a front end exhaust outlet 36a of the collecting portion 36. The exhaust muffler 16 is curved upward and rearward, and extends rearward on the left side of the cylinder head 26. The downstream end of the exhaust muffler 16 projects into the water muffler 32 from above. In the middle of the exhaust muffler 16, a tapered diffuser portion 16a whose diameter increases as it goes downstream and a cone portion 16b whose diameter decreases as it goes downstream are sequentially formed. Water muffler 3
Although not shown, the second discharge pipe 33 extends outside the boat.

In the present invention, each exhaust hole 23, 2
The exhaust path from 4, 25 to the exhaust pipes 28, 29, 30, the collecting section 36, the exhaust muffler 16, the water muffler 32, and the outlet end of the exhaust pipe 33 is called an exhaust system. Since the lengths of the exhaust pipes 28, 29, 30 are equal, the exhaust system lengths of the cylinders 11, 12, 13 are also equal.

FIG. 6 is a sectional view of the collecting portion 36 taken along a plane perpendicular to the crankshaft 19.
Has a cylindrical inner peripheral surface and three ports 44, 45, 46 at 120 ° intervals in the circumferential direction. The first port 44 is configured to exhaust the first cylinder 11 through the exhaust pipe 28. The second port 45 communicates with the exhaust hole 24 of the second cylinder 12 via the exhaust pipe 29, and the third port 46 communicates with the exhaust of the third cylinder 13 via the exhaust pipe 30. Hole 25
Is in communication with As shown in FIG.
As shown in FIG. 7, a switching valve 38 formed by forming a cutout 43 for an exhaust passage in a cylindrical member is rotatably fitted via a seal ring 41.

FIG. 5A is a sectional view taken along line Va-Va of FIG.
6B is a cross-sectional view taken along line Vb-Vb of FIG. 6B. The downstream end (front end) of the switching valve 38 is open so as to always communicate with the inlet of the exhaust muffler 16. The notch 43 is bent radially outward on the way, and is opened on the cylindrical outer peripheral surface. That is, as the switching valve 38 rotates, a state is established in which only one port 44 and the like communicate with each other as shown in FIG. 5A, and two ports 44 and 4 as shown in FIG.
5 can be continuously switched to a state in which they are simultaneously communicated.

Specifically, the switching valve 38 makes one rotation in the direction R from the state shown in FIG.
The states of C, D, E, and F change sequentially and return to the state of A. That is, in the state of FIG. 6A, only the first port 44 communicates with the exhaust muffler 16 (FIG. 5), and in the state of B, the first and second ports 44 and 45 communicate with each other. In the state, only the second port 45 communicates, in the state D, the second and third ports 45 and 46 communicate, in the state E, only the third port 46 communicates, and in the state F, the third port 45 communicates. , And the first ports 46 and 44 are in communication with each other, and return to the state shown in FIG.

The switching valve 38 is also adapted to rotate synchronously with the crankshaft 19. In this embodiment, the valve driving shaft 37 connected to the switching valve 38 in FIG. It is linked to the crankshaft 19 via a pair of transmission gears 40 having the same diameter. Therefore, the crank angle is 360 °
Thus, the switching valve 38 makes one rotation.

The exhaust system of each of the cylinders 11, 12, 13 is common on the downstream side of the collecting section 36, and the exhaust pipes 28, 2
Since the lengths of 9, 30 are equal, each cylinder 11, 12, 13
Although the pressure waveforms of the exhaust holes 23, 24, and 25 are substantially the same, the exhaust system length is set such that the pressure waveform becomes the ideal waveform P2 shown in the middle part of FIG. are doing.

The lower part of FIG. 7 is a diagram showing the opening / closing change of each port 44, 45, 46 of the switching valve 38 which changes as shown in FIG. S1 in FIG. 7 indicates a range in which the first port 44 is open, and the first cylinder 11 is open 120 ° before and after each of the bottom dead center BDC (1) of the first cylinder 11. S2 indicates a range in which the second port 45 is open, and the second cylinder 12 is open 120 ° before and after each of the lower dead center BDC (2) of the second cylinder 12. S
Reference numeral 3 denotes a range in which the third port 46 is open, and the third port 13 is opened 120 ° before and after the bottom dead center BDC (3) of the third cylinder 13. S1 + S2 is the first and second port 4
4 and 45 indicate a range in which the cylinders are simultaneously open, and correspond to the area between the bottom dead centers BDC (1) and (2) of the first and second cylinders 11 and 12. S2 + S3 indicates a range in which the second and third ports 45 and 46 are simultaneously opened, and the second and third cylinders 12 and
13 corresponds to a position between the bottom dead center BDCs (2) and (3). S3
+ S1 indicates a range in which the third and first ports 46 and 44 are simultaneously open, and corresponds to between the bottom dead centers BDC (3) and (1) of the third and first cylinders 13 and 11.

The upper part of FIG. 7 shows each cylinder 11, 11 as described above.
The exhaust system length is set so that the independent pressure waveforms of the exhaust holes 12 and 13 become the ideal waveforms shown in the middle part of FIG. 10, and the switching of the exhaust passage by the switching valve 38 is performed as shown in the lower part of FIG. FIG. 9 shows pressure waveforms actually generated in the exhaust holes of the respective cylinders when set. However, each exhaust hole 2
Opening / closing timing of 3, 24, 25 (EO-EC section)
Is a range of approximately 90 ° before and after the bottom dead center BDC of each cylinder. It is well known that EO is when the exhaust hole is open, EC is when the exhaust hole is closed, TO is when the scavenging hole is open, TC is when the scavenging hole is closed, TDC is at top dead center, and BDC is at bottom dead center. . In the section (TC-E) where the fresh air pushing action works in the first cylinder 11
C) and the immediately preceding section are the exhaust holes 23 of the second cylinder 12.
Is positive pressure. Similarly, in the section (TO-EC) where the fresh air pushing action works in the second cylinder and the section immediately before that, the exhaust hole 25 of the third cylinder 13 has a positive pressure, and the fresh air pushing action works in the third cylinder 13. In the section (TO-EC), the exhaust port 24 of the first cylinder 11 has a positive pressure.

[0031]

During operation of the engine, the switching valve 38 shown in FIG. 6 rotates synchronously with the crankshaft 19 in the direction of arrow R, and the crank angle 360
In the range of °, each port 44, 4 in the order shown in AF of FIG.
5 and 46 are opened and closed, and the opening and closing timing is as shown in the lower part of FIG. 7 as described above.

The change in the pressure of the exhaust hole during operation of the engine is determined by the first
Explaining with reference to the cylinder 11 described above, in the upper part of FIG. 7, after the exhaust hole is opened (EO), the pressure in the exhaust hole increases,
After the scavenging holes are closed (TO) by the diffuser section 16a of the exhaust muffler 16, pressure reduction is started, and the bottom dead center B of the first cylinder 11 is reduced.
In the vicinity of DC, as shown by S1 + S2 at the bottom, the first and second
The ports 44 and 45 communicate with each other. After that, due to the positive pressure after the exhaust hole opening EO of the second cylinder 12, the pressure in the exhaust hole of the first cylinder 11 becomes smaller than the scavenging hole closing TC of the first cylinder 11. The pressure suddenly starts rising immediately before, and the positive pressure between TC and EC of the first cylinder 11 becomes sufficiently high as indicated by oblique lines. In this way, in the first cylinder 11, ideal exhaust air suction and ideal fresh air pushing by the positive pressure of the second cylinder 12 can be achieved. The above relationship indicates that the switching valve 38 is connected to the crankshaft 1
Due to the synchronous rotation with No. 9, even if the engine speed changes, there is almost no effect.

Regarding the second and third cylinders 12 and 13,
Ideal fresh air can be pushed in by the positive pressures of the third and first cylinders 13 and 11 respectively acting. Therefore, an ideal output performance as shown by a performance curve X1 in FIG. 8 can be obtained for the entire engine.

[0034]

[Other Embodiments] (1) The present invention is applicable to a multi-cylinder engine having a multiple of three cylinders such as a six-cylinder engine, in addition to a three-cylinder two-cycle engine. In this case, a collecting portion is provided for each of the three cylinders to collect the exhaust gas and connect it to one exhaust muffler. Therefore, the six cylinders are equipped with two collecting parts and two exhaust mufflers.

(2) In the illustrated embodiment, the first, second, and third cylinders 11, 12, and 13 are rotated by 120 ° in this order.
The three cylinders 2 have a phase difference of 120 ° in the order of the first, third, and second cylinders.
Applicable to cycle engines. In this case, the switching valve is opened and closed according to the above order (that is, the ignition order).

(3) As a drive mechanism of the switching valve, an electric motor or a hydraulic motor can be used in addition to the mechanism driven by the crankshaft 19 as shown in FIG. In this case, it is preferable to provide a detection mechanism for detecting the rotation speed of the crankshaft 19, and to configure the motor to rotate synchronously with the crankshaft.

(4) The switching valve is not limited to a rotary valve, and may be, for example, a spool type that slides linearly in the axial direction.

[0038]

As described above, according to the present invention, (1) an exhaust system such as an exhaust muffler, which is provided with a collecting portion for collecting the exhaust holes of three cylinders having a phase difference of 120 ° and is downstream of the collecting portion; Is common to three cylinders, thereby reducing the number of equipment for the exhaust system and making the exhaust system compact. This makes it possible to easily mount a vehicle such as a personal watercraft with a limited engine arrangement space.

(2) A switching valve for switching between a state in which one of the exhaust holes of the three cylinders communicates with the exhaust system and a state in which the two exhaust holes are simultaneously connected to the exhaust system. Therefore, for each cylinder, the exhaust port internal pressure can be set so as to have an ideal pressure waveform in which a supercharging effect by fresh air suction and fresh air intrusion can be expected. The supercharging action can be enhanced by affecting the positive pressure of the next cylinder on the pushing action, and the output can be improved by controlling the exhaust system.

(3) By making the exhaust pipes of the respective cylinders up to the converging portion equal in length, the change in the exhaust hole internal pressure of each of the cylinders can be uniformly changed to an ideal waveform, thereby further improving the output. Can be achieved.

(3) When the switching valve is configured to operate synchronously with the crankshaft, the above-described supercharging effect can always be exerted regardless of the low and high engine speeds.

(4) By making the switching valve a rotary type,
The switching of the exhaust passage in the collecting portion can be continuously and smoothly performed, the structure is simplified, and the generation of noise is reduced. Further, it can be easily synchronized with the rotation of the crankshaft.

[Brief description of the drawings]

FIG. 1 is a side view of a three-cylinder two-stroke engine to which the present invention is applied.

FIG. 2 is a plan view of a personal watercraft equipped with an engine according to the present invention.

FIG. 3 is a left side view of the same personal watercraft shown in FIG.

FIG. 4 is a perspective view of a switching valve.

FIG. 5 is an enlarged vertical cross-sectional view of the collecting portion, in which A shows a state communicating with one exhaust hole, and B shows a state communicating with two exhaust holes.

6 is a cross-sectional view taken along the line VI-VI of FIG. 5, in which A to F sequentially show changes in the rotational position for one rotation of the switching valve.

FIG. 7 is a diagram illustrating a change in the exhaust port pressure of each cylinder with respect to the crank angle, and a lower diagram illustrating a change in opening and closing of each cylinder port of the switching valve with respect to the crank angle.

FIG. 8 is an output characteristic diagram of an engine.

FIG. 9 is a sectional view of an exhaust system in the case of a single cylinder.

10 is a diagram showing different pressure waveforms depending on the length of the exhaust system in the exhaust system of FIG. 9;

FIG. 11 is a side view of a conventional engine.

FIG. 12 is an enlarged cross-sectional view taken along the line XII-XII of FIG. 11;

FIG. 13 is a vertical sectional view of a personal watercraft equipped with a conventional engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Engine 11, 12, 13 1st, 2nd, 3rd cylinder 16 Exhaust muffler 19 Crankshaft 23, 24, 25 Exhaust hole 28, 29, 30 Exhaust pipe 36 Collecting part 38 Switching valve

Claims (5)

(57) [Claims] In a multi-cylinder two-stroke engine having three cylinders having a phase difference of 120 °, the exhaust holes of each cylinder are gathered into one gathering part and connected to a common exhaust system. A switching valve for switching between a state in which one of the exhaust holes of each cylinder communicates with the exhaust system and a state in which two of the exhaust holes of each cylinder communicate with the exhaust system. Cylinder 2-cycle engine. 2. The multi-cylinder two-stroke engine according to claim 1, wherein the distance from the exhaust hole of each cylinder to the collecting portion is
A multi-cylinder two-stroke engine characterized by being of equal length. 3. The multi-cylinder two-stroke engine according to claim 1, wherein the switching valve at the collecting part is a rotary type. 4. The multi-cylinder two-stroke engine according to claim 1, wherein the switching valve is operated in synchronization with the crankshaft. 5. A multi-cylinder two-stroke engine comprising a multiple of three cylinders and the configuration according to claim 1, 2, 3, or 4 provided for every three cylinders.