JPH0941963A - Cooling system of two-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a good cooling performance conformed to each system up to a range from a medium and low speed area to the high speed one and to maintain output characteristics, in the cooling system which utilizes cooling water, taken out of a water jet propulsion pump, for the cooling of an engine and an exhaust system. SOLUTION: Cooling water to be taken out of a positive pressure part 3a of a water jet propulsion pump 2 is divided into two parts, a first cooling water route 41 to supply it to a cylinder and a cylinder head 7 and a second cooling water route 42 to supply it to an exhaust pipe unit including an exhaust expansion chamber 11 separately from the route. Dimension of exhaust expansion chamber 11 is set to be synchronized to an exhaust pressure wave in time of a medium and low speed area, for example, while in time of a high speed area, a cooling water quantity is held low by a control unit, whereby it is synchronized to the exhaust pressure wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling device for a two-cycle engine, and more particularly to a cooling device for a two-cycle engine used for driving a water jet propulsion pump mounted on a small boat such as a water slide boat.

[0002]

2. Description of the Related Art Conventionally, a cooling device of this type is often used in which the cooling water path 1 is one system, as shown in the schematic piping diagram of FIG. That is, the cooling water intake 3 opening to the positive pressure portion 3a of the water jet propulsion pump 2 is provided,
The cooling water taken out from the intake port 3 is sequentially supplied to the exhaust manifold 5, the cylinder 6, the cylinder head 7, the exhaust pipe device 8 and the water muffler 9 by one path 1,
The water muffler 9 is mixed with the exhaust gas and then discharged to the outside of the ship. The exhaust pipe device 8 includes an exhaust pipe 10 connected to the exhaust manifold 5 and an exhaust expansion chamber 11. There is also a configuration in which the gas is mixed with the exhaust gas in the expansion chamber 11 and then discharged to the outside of the ship.

There is also a device having two systems of cooling water paths, such as Japanese Utility Model Publication No. 7-11039. That is, FIG.
4, one cooling water path 14 introduces cooling water from the positive pressure portion 3 of the water jet propulsion pump 2 and supplies the cooling water to the exhaust expansion chamber 11 and the water muffler 9,
The remaining cooling water path (pipes 13a, 13b) is configured to be discharged to the outside, and the cooling water (internal water) pressurized by the circulation pump 15 is supplied to the cylinder and the cylinder head of the engine E, and then the pipe 13b. To the radiator 12 of the water jet propulsion pump 2 to exchange heat with the pipe 1
It is a circulation type path which is returned to the circulation pump 15 via 3a and is circulated to the engine again.

[0004]

In the one-system cooling device shown in FIG. 13, since the cooling water is taken out from the positive pressure portion 3a of the water jet propulsion pump 2, the cooling water amount increases as the engine speed increases. However, due to the relationship between the pulsation of the exhaust pressure wave and the size of the exhaust expansion chamber, the following problems occur with respect to the cooling of the exhaust pipe device 8. .

First, the relationship between the dimensions of the exhaust expansion chamber, the temperature of the exhaust gas, and the output performance will be described. Generally, in a two-cycle engine, the pulsation of the exhaust pressure wave is used to supply air and the charge ratio. In order to improve the efficiency, for example, as shown by the graph P1 of the exhaust port pressure wave in the upper part of FIG. 11, fresh air is drawn into the cylinder from the scavenging port with the negative pressure wave S1 in the scavenging stroke, and The air-supply ratio is improved, and in the stroke from the closing of the scavenging port to the closing of the exhaust port, the positive pressure wave S2 pushes the fresh air of the exhaust port portion back into the cylinder, thereby improving the charging efficiency. In order to exert the effect, the dimensions of the exhaust expansion chamber are set so that the pressure wave P1 in the desired rotation range is as shown in the upper part of FIG. Mind, it is a condition that is set so as to tune to the opening and closing of the exhaust port.

The dimensions of the exhaust expansion chamber can be variously set according to the purpose of use of the engine.
In general, it is considered that the tuning rotation range is matched to the medium-low speed rotation range and the tuning rotation range is matched to the high speed rotation range.

However, the velocity of the pressure wave changes in accordance with the change in temperature, like the velocity of sound, and the velocity increases when the temperature rises and the velocity decreases when the temperature falls.
Therefore, as described above, in the exhaust pipe device, the cooling water is taken out from the positive pressure portion of the water jet propulsion pump so that the cooling water amount automatically increases in accordance with the increase in the rotation speed. The following phenomena occur in the case where the tuning rotation range of the chamber is adjusted to the medium-low speed rotation range and the case where the tuning rotation range is adjusted to the high-speed rotation range.

When the dimensions of the exhaust expansion chamber are set so as to be tuned in the medium to low speed rotation range, the exhaust gas temperature, the output and the pressure wave are T1, H1 and P1 shown by the solid lines in FIGS. 9 and 11, respectively. To change. That is, as shown in the upper part of FIG. 11, the opening / closing timing of the exhaust port and the pressure wave are synchronized with each other in the medium to low speed rotation range, so that the effect of calling and pushing back can be efficiently exhibited. However, in the high-speed rotation region, as shown by the graph T1 in FIG. 9, the cooling water is excessively cooled, so that the rise in the exhaust gas temperature is suppressed more than necessary, and as shown by the solid line in the lower part of FIG. The speed of the wave P1 is relatively delayed with respect to the opening / closing timing of the exhaust port, and the synchronization is lost. Therefore, not only the above-mentioned calling effect and push-back effect cannot be expected, but also fresh air is blown out during scavenging or suction from the cylinder occurs, and sufficient output in the high-speed rotation range is obtained as shown in graph H1 in FIG. Can not be.

On the other hand, when the dimensions of the exhaust expansion chamber are set so as to be synchronized with the high speed rotation range, the exhaust gas temperature, output and pressure wave are T3, H3 and P3 shown by the solid lines in FIGS. 10 and 12, respectively. It changes like. That is, as shown in the lower part of FIG. 12, the opening / closing timing of the exhaust port and the speed of the pressure wave are synchronized with each other in the high-speed rotation range, so that the effect of calling and pushing back can be efficiently exhibited. However, in the medium to low speed rotation range, as shown in the graph T3 of FIG. 10, the temperature of the exhaust gas cannot be sufficiently lowered due to the decrease in the amount of cooling water, and as shown by the solid line in the upper part of FIG. Speed becomes relatively faster than the opening / closing timing of the exhaust port, and is not synchronized. Therefore, the graph H3 of FIG.
As described above, the output decreases in the medium and low speed rotation range.

In the two-system system as shown in FIG. 14, the second cooling water passage 14 for cooling the exhaust system is a one-way system using the external water from the positive pressure portion 3a of the water jet propulsion pump 2. On the other hand, the first cooling water paths 13a and 13b for cooling the engine E are of a circulation type in which the internal water is repeatedly used by the circulation pump 15, so that it takes time to manage the internal water and the circulation pump is used. It also takes time and effort to maintain the 15 and various circulation pipes 13b and 13b.

[0011]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention, in a two-cycle engine cooling device for driving a water jet propulsion pump, takes in from a positive pressure portion of the water jet propulsion pump. The cooling water is separately supplied into a first cooling water path for supplying to the cylinder and the cylinder head, and a second cooling water path for supplying to the exhaust pipe device including the exhaust expansion chamber independently of the path. It is characterized by doing so.

Here, the exhaust pipe device means an exhaust pipe and an exhaust expansion chamber connected thereto. Therefore, the second cooling water path is sufficient if it has a configuration for cooling at least the exhaust pipe and the exhaust expansion chamber. Exhaust system members other than these, that is, the upstream side exhaust manifold or the downstream side water muffler, are 1 cooling water path or 2nd
It does not matter which of the cooling water paths is connected to.

According to the configuration of claim 1, cooling water (external water) independent from the positive pressure portion of the water jet propulsion pump is supplied to the first cooling water passage and the second cooling water passage, In addition, the amount is supplied so as to increase as the engine speed increases. Then, it becomes possible to control the amount of cooling water according to the respective characteristics of the cylinder system and the exhaust pipe device system.

According to a second aspect of the invention, in a cooling device for a two-cycle engine that drives a water jet propulsion pump, a first aspect is to supply cooling water taken from a positive pressure portion of the water jet propulsion pump to a cylinder and a cylinder head. And a second cooling water path which is supplied independently to the second cooling water path to the exhaust pipe device including the exhaust expansion chamber, and the first cooling water path includes: It is characterized in that the cooling water path of the exhaust system portion on the upstream side of the exhaust pipe device is connected.

Here, the exhaust pipe device is the same as in the first aspect of the present invention, and the exhaust system portion on the upstream side of the exhaust pipe device mainly refers to the exhaust manifold.

The operation is the same as that of the first aspect.

According to a third aspect of the present invention, in the two-cycle engine cooling device according to the first or second aspect, a control device for controlling the amount of cooling water according to the engine speed is provided in the second cooling water passage. The feature is that it is provided.

Specific examples of the control device include a device having a function of suppressing an increase in the amount of cooling water in a high speed rotation region as will be described later, or a device for suppressing a decrease in the cooling water amount in a medium to low speed rotation region. is there.

The invention according to claim 4 is the same as the invention according to claim 3
In the cooling device for a cycle engine, the size of the exhaust expansion chamber is set to the medium-low speed type in which the pulsation of the exhaust pressure wave is synchronized with the scavenging of the medium-low speed rotation range and the opening / closing timing of the exhaust port. It is characterized in that a control device for suppressing an increase amount of cooling water is provided.

With such a control device, the pulsation of the exhaust pressure wave can be synchronized with the scavenging and opening / closing timing of the exhaust port from the medium to low speed range to the high speed range to improve the air supply ratio and the charging efficiency. You can

The invention according to claim 5 is the same as the invention according to claim 3
In the cycle engine cooling device, the size of the exhaust expansion chamber is set to a high-speed type that matches the exhaust pulsation during high-speed rotation, and the control device increases the amount of cooling water to the exhaust pipe device during medium-low speed rotation. It is characterized by that.

With such a control device, the pulsation of the exhaust pressure wave can be synchronized with the scavenging and opening / closing timing of the exhaust port from the medium to low speed rotation range to the high speed rotation range to improve the air supply ratio and the charging efficiency. You can

The invention according to claim 6 is the same as the invention according to claim 3.
In the cooling device for a cycle engine, as a control device, a second cooling path from the positive pressure part of the water jet propulsion pump to the exhaust pipe device is provided with a bypass path leading to the negative pressure part of the water jet propulsion pump. It has a feature.

With such a configuration, the suction amount by the negative pressure portion is increased in accordance with the increase in the cooling water amount from the positive pressure portion due to the increase in the rotation speed, so that the exhaust pressure from the medium to low speed rotation range to the high speed rotation speed range is increased. The pulsation of the wave can be synchronized almost automatically with the scavenging and opening / closing timing of the exhaust port, improving the air supply ratio and the charging efficiency.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIGS. 1 to 6 show an example in which the invention described in claims 1 to 4 is applied to a small planing boat equipped with a water jet propulsion pump. The same reference numerals are given to each component described in 14, the water jet propulsion pump 2, the exhaust manifold 5, the cylinder 6, the cylinder head 7, the exhaust pipe device 8, the exhaust pipe 10, the exhaust expansion chamber 11 and the water muffler 9. ing.

In FIG. 1, an exhaust pipe 5, an exhaust expansion chamber 11 and a water muffler 9 are sequentially connected to an exhaust manifold 5 attached to a cylinder 6, and a tail pipe 16 of the water muffler 9 is provided outside the small planing boat. It is open to.

As shown in FIG. 3, the exhaust expansion chamber 11 has a front divergent (dispersion) cone 25 that expands in a tapered shape, and a middle straight portion 26.
And a convergent cone 27 that is sharply squeezed thereafter.
a enters the water muffler 9 and is open upward at the upper part thereof.

FIG. 2 shows a vertical cross-sectional view of the water jet propulsion pump 2, in which the water jet propulsion pump 2 is arranged in a water duct 30 which is formed at the bottom of the small planing boat and has an open lower surface. A tubular steering nozzle 31 that can be swung left and right is attached to the throttle portion 4a formed in the rear portion.

The water jet propulsion pump 2 includes a tubular pump casing 32, a drive shaft 33 rotatably supported therein, and a drive shaft 33 interlockingly connected to the engine E.
A rotary impeller 34 fixed to the drive shaft 33 and a stationary blade 35 fixed in the pump casing 32 are provided. By rotating the impeller 34 on the drive shaft 33,
The external water sucked from the lower surface open portion 30a is pressurized and jetted rearward through the stationary blade 35 portion, the throttle portion 4a and the steering nozzle 31. Around the position where the vanes 35 are located behind the impeller 34 is the positive pressure portion 3a,
The positive pressure value increases as the number of rotations increases, and the casing portion of the positive pressure portion 3a is provided with a cooling water inlet 3 for extracting the positive pressure. On the other hand, since the flow velocity of the throttle portion 4a is high, the negative pressure take-out portion 4 is projectingly provided at that portion.

In FIG. 6, as a cooling device, a first cooling water passage 41 for cooling the exhaust manifold 5, the cylinder 6 and the cylinder head 7, and an exhaust pipe 10 and an exhaust expansion independent of the passage 41 are provided. Chamber 1
1 and the second cooling water path 4 for cooling the water muffler 9
2 is provided.

As the first cooling water passage 41, cooling water jackets (not shown) are formed in the exhaust manifold 5, the cylinder 6 and the cylinder head 7 in this order to communicate with each other, and the cooling of the exhaust manifold 5 is performed. The water inlet portion communicates with the positive pressure portion 3 of the water jet propulsion pump 2 via the cooling water pipe 43, and the cooling water outlet portion 17 of the cylinder head 7 is connected.
Is open to the outside of the planing boat via the discharge pipe 18.

As the second cooling water passage 42, annular cooling water passages 20 and 21 surrounding the outer circumferences of the exhaust passages 36 and 37 are formed in the exhaust pipe 10 and the exhaust expansion chamber 11 in FIGS. 4 and 5. As shown in FIG. 3, the cooling water passages 20 and 21 communicate with each other via a connecting pipe 22. The connecting pipe 22 is eliminated and the cooling water passage 20,
21 may be directly connected. The downstream end (rear end) of the exhaust expansion chamber 11 opens upward in the water muffler 9, and the exhaust passage 3 is provided in the middle of the cooling water passage 21.
7 are formed with a plurality of ejection holes 44, and a part of the cooling water is ejected into the exhaust passage 37. As shown in FIG. 3, the upstream end of the annular cooling water passage 20 of the exhaust pipe 10 of FIG. 4 is connected to the positive pressure portion 3a of the water jet propulsion pump 2 via the cooling water pipe 46 and the control valve 47. There is.

The control valve 47 is used as a relief bypass pipe 4.
8 is configured so that the bypass pipe 48 is closed when the engine speed is in the medium to low speed rotation range, and when the engine speed becomes the high speed range, the rotation speed is detected and the bypass pipe 48 is opened. . The bypass pipe 48 communicates with the outside of the planing boat, for example.

[Operation of Embodiment] Referring to FIG. 6, the first cooling water passage 41 and the second cooling water passage 42 are independent of the positive pressure portion 3a of the water jet propulsion pump 2 while the engine is operating. Cooling water (external water) is supplied.

In the first cooling water path 41, the cooling water is supplied from the positive pressure portion 3a to the jacket of the exhaust manifold 5 through the cooling water pipe 43, and sequentially passes through the jacket of the cylinder 6 and the jacket of the cylinder head 7. Then, they are cooled, and after being used for cooling, they are discharged to the outside through the discharge pipe 18.

In the second cooling water path 42, the annular cooling water passage 20 (FIG. 4) of the exhaust pipe 10 is introduced from the positive pressure portion 3a through the cooling water pipe 46 and the control valve 47, and the inside of the exhaust pipe 10 is closed. After cooling the exhaust gas, it enters the cooling water passage 21 of the exhaust expansion chamber 11 through the connecting pipe 22 of FIG. 3 and flows rearward. In the middle of the cooling water passage 21, a part of the cooling water is ejected from the ejection holes 44 into the annular cooling water passage 21. At this time, the latent heat of vaporization is removed from the exhaust gas to enhance the cooling effect of the exhaust gas. . The remaining cooling water that is not jetted is discharged from the rear end of the annular cooling water passage 21 into the water muffler 9, mixed with the exhaust gas, and then discharged from the tail pipe 16.

The pressure of the positive pressure portion 3a increases as the number of revolutions increases, so that the amount of cooling water taken in from the positive pressure portion 3a also increases accordingly.

In the second cooling water path 42, the bypass pipe 48 of the control valve 47 is closed in the medium to low speed rotation range (N1 to N2), and all the cooling water is passed through the exhaust manifold 5. It is sent to the jacket of the cylinder 6 and the cylinder head 7. In this case, since the size of the exhaust expansion chamber 11 is set to the medium-low speed type as described above, the scavenging in the medium-low speed rotation range and the opening / closing timing of the exhaust port are set as shown in the upper graph P1 in FIG. The pulsation of the exhaust pressure wave P1 is synchronized. Therefore, the negative pressure wave S1 during the exhaust and scavenging strokes exerts a pull-in action, and the positive pressure wave S2 during the scavenging-close to exhaust-closed strokes exerts a pushing action. As a result, the air supply ratio and the charging efficiency can be kept good, and good output characteristics can be kept in the medium to low speed rotation range (N1 to N2) as shown by the graph H1.

When the rotation speed exceeds N2 and enters the high-speed rotation range, the control valve 47 of FIG. 6 is actuated by the detection of the rotation speed to open the bypass pipe 48, and a part of the cooling water from the positive pressure portion 3a is opened. Let it escape. As a result, the amount of increase in the amount of cooling water due to the increase in the number of revolutions is suppressed, and the exhaust gas temperature is raised as compared with the conventional low pressure type (solid line graph T1), as shown by the broken line graph T2. As a result, as indicated by a broken line P2 in the lower part of FIG. 11, the speed of the exhaust pressure wave P2 is made faster than that of the conventional type (solid line P1), and synchronized with the scavenging and opening / closing timing of the exhaust port. Therefore, as in the case of the medium to low speed rotation, the air supply ratio and the charging efficiency are kept good, and the output in the high speed rotation range is improved as shown by the broken line H2 in FIG.

[Second Embodiment] FIG. 7 is a schematic piping diagram of a cooling device to which the invention according to claim 6 is applied. As a control device, instead of the control valve 47 of FIG. 6, a second cooling water path is provided. A negative pressure bypass passage 50 is connected in the middle of the cooling water pipe 46 of 42, and the bypass passage 50 is connected to the throttle portion 4 a of the water jet propulsion pump 2. Other configurations are similar to those of FIG. 6, and the same components are denoted by the same reference numerals.

In the second cooling water path 42, the positive pressure part 3
At the same time as supplying the cooling water from a to the exhaust pipe 10 and the exhaust expansion chamber 11 via the cooling water pipe 46, the negative pressure of the throttle portion 4a causes excess cooling water to be removed from the middle of the cooling water pipe 46. The amount of cooling water is controlled by discharging (sucking) inward.

In this control, as the positive pressure of the positive pressure portion 3a increases in accordance with the increase in the rotational speed, the negative pressure in the throttle portion 4a also increases in accordance with the increase in the rotational speed. At the time of increase, the amount of suction due to the negative pressure also increases as the amount of cooling water from the positive pressure portion 3a increases, whereby the amount of increase is automatically controlled.

[Third Embodiment] FIG. 8 is a schematic diagram of piping of a cooling device to which the invention of claim 5 is applied. As the exhaust expansion chamber 11, a high-speed type which is synchronized with the opening / closing timing of the exhaust port in the high-speed rotation range is shown. I'm using it.

In addition to the cooling water pipe 46, an auxiliary cooling water pipe 54 connected to the positive pressure portion 3a of the water jet propulsion pump 2 is connected to the control valve 52. In the high speed rotation range, the auxiliary cooling water pipe is connected. 54 is closed, and the auxiliary cooling water pipe 54 is opened to increase the amount of cooling water in the second cooling path 42 in the medium to low speed rotation range.

The operation will be described. In the high speed rotation range, the auxiliary cooling water pipe 54 is closed, and the second cooling water path 4
In 2, only the cooling water from the main cooling water pipe 46 is supplied to the exhaust pipe 10 and the exhaust expansion chamber 11. In this case, since the size of the exhaust expansion chamber 11 is set to the size of the high speed type corresponding to the amount of cooling water from the main cooling water pipe 46, as shown in the lower graph P3 of FIG. The opening / closing timing of the exhaust port and the exhaust pulsation are synchronized.
Therefore, the negative pressure wave S1 during the exhaust and scavenging strokes exerts a pull-in effect, and the positive pressure wave S2 during the exhaust closing-scavenging closed stroke exerts a pushing-in effect. As a result, the air supply ratio and the charging efficiency are kept good, and good output can be kept in the high speed rotation range (N2 to N3) as shown in the graph H3 of FIG.

In the medium to low speed rotation range, the control valve 52 shown in FIG. 8 is actuated by the detection of the number of rotations to open the auxiliary cooling water pipe 54 to increase the amount of cooling water, as shown by the broken line graph T4 in FIG. , Conventional low pressure type (solid line graph T
Lower exhaust gas temperature than 3). As a result, FIG.
As shown by the broken line graph P4 in the upper part of the figure, the speed of the exhaust pressure wave is made slower than that of the conventional type (solid line P3), and synchronized with the scavenging and opening / closing timing of the exhaust port. Therefore, as in the high speed rotation, the air supply ratio and the charging efficiency are kept good, and the output in the medium to low speed rotation range is improved as shown by the broken line graph H4 in FIG.

[Other Embodiments] (1) In the invention described in claim 5, when a high-speed type exhaust expansion chamber is used, as a control device for increasing the amount of cooling water in the medium-low speed rotation range, for example, a distribution system is used. A flow control valve having a variable cross-sectional area may be provided to suppress the opening at high speed and increase the opening at medium to low speed rotation to increase the amount of cooling water.

(2) In any of the above embodiments, the cooling water jacket of the exhaust manifold is connected to the first cooling water passage of the same system as the cooling of the cylinder and the cylinder head.
You may connect to the 2nd cooling water path of the same system as the cooling of an exhaust pipe apparatus.

(3) In any of the above embodiments, the water muffler is connected to the second cooling water passage for cooling the exhaust pipe device, but it is also possible to connect it to the first cooling water passage.

[0050]

【The invention's effect】

(1) According to the invention of claim 1 or 2, the cooling water taken in from the positive pressure portion of the water jet propulsion pump is independent of the first cooling water path for cooling the cylinder and the cylinder head. Therefore, the exhaust pipe device including the exhaust expansion chamber is divided into the second cooling water path for cooling and the independent cooling system is provided for each, so that there is no need for a special drive device such as a circulation pump.
Both the cylinder system and the exhaust pipe system can be cooled so as to automatically increase the amount of cooling water in accordance with the increase in the number of revolutions, and it is possible to cool each cooling water path as needed. The amount of water can be controlled, and the cooling performance of the cylinder and the cylinder head and the cooling performance of the exhaust pipe device including the exhaust expansion chamber can be improved.

(2) According to the third, fourth, fifth and sixth aspects of the present invention, the controller controls the amount of cooling water in the second cooling water path for supplying the cooling water to the exhaust expansion chamber, thereby controlling the medium and low speed. Since output reduction is prevented in either the rotation speed range or the high speed rotation speed range, good output characteristics can be obtained from the medium to low speed rotation speed range to the high speed rotation speed range.

[Brief description of drawings]

FIG. 1 is a perspective view of an engine, an exhaust device, and the like provided with a cooling device according to the present invention.

FIG. 2 is a vertical sectional view of a water jet propulsion pump.

FIG. 3 is a vertical cross-sectional view of the cooling device of FIG.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

5 is a sectional view taken along line VV of FIG.

FIG. 6 is a schematic piping diagram of a cooling device to which the inventions according to claims 1 to 4 of the present application are applied.

FIG. 7 is a piping diagram of a cooling device to which the invention according to claim 6 of the present application is applied.

FIG. 8 is a schematic piping diagram of a cooling device to which the invention according to claim 5 of the present application is applied.

FIG. 9 is a graph showing the relationship between engine speed, exhaust gas temperature, and output when a low-speed exhaust expansion chamber is provided.

FIG. 10 is a graph showing the relationship between engine speed, exhaust gas temperature, and output when a high-speed exhaust expansion chamber is provided.

FIG. 11 is a graph showing an exhaust pressure wave when a low speed type exhaust expansion chamber is provided.

FIG. 12 is a graph showing an exhaust pressure wave when a high-speed exhaust expansion chamber is provided.

FIG. 13 is a schematic diagram of piping of a conventional example.

FIG. 14 is a plan view of another conventional example.

[Explanation of symbols]

 2 Water jet propulsion pump 3 Cooling water intake 3a Positive pressure part 4 Cooling water discharge port 4a Throttling part 5 Exhaust manifold 6 Cylinder 7 Cylinder head 8 Exhaust pipe device 10 Exhaust pipe 11 Exhaust expansion chamber 36, 37 Annular cooling water passage 41 No. 1 1 cooling water path 42 2nd cooling water path 44 Jet hole 47,52 Control valve (control device) 48,50 Bypass pipe

Claims (6)

[Claims] 1. A cooling device for a two-cycle engine that drives a water jet propulsion pump, comprising: a first cooling water path for supplying cooling water taken from a positive pressure portion of the water jet propulsion pump to a cylinder and a cylinder head; A cooling device for a two-cycle engine, wherein the cooling water is separately supplied to a second cooling water path that is supplied to an exhaust pipe device including an exhaust expansion chamber independently of the path. 2. In a cooling device for a two-cycle engine that drives a water jet propulsion pump, a first cooling water path for supplying cooling water taken from a positive pressure portion of the water jet propulsion pump to a cylinder and a cylinder head. The second cooling water path is independently supplied to the second cooling water path that is supplied to the exhaust pipe apparatus including the exhaust expansion chamber, and the first cooling water path is provided on the upstream side of the exhaust pipe apparatus. A cooling system for a two-cycle engine, characterized in that a cooling water path of the exhaust system part of is connected. 3. The cooling device for a two-cycle engine according to claim 1 or 2, wherein a control device for controlling the amount of cooling water according to the engine speed is provided in the second cooling water passage. Cooling system for 2-cycle engine. 4. The two-cycle engine cooling device according to claim 3, wherein the size of the exhaust expansion chamber is a medium-low speed type in which the pulsation of the exhaust pressure wave is synchronized with the opening / closing timing of the exhaust port in the medium-low speed rotation range, and a high speed rotation is performed. A cooling device for a two-cycle engine, characterized in that a control device for suppressing the amount of cooling water to the exhaust pipe device is provided in the region. 5. The cooling system for a two-cycle engine according to claim 3, wherein the size of the exhaust expansion chamber is a high-speed type in which the pulsation of the exhaust pressure wave is synchronized with the opening / closing timing of the exhaust port in the high-speed rotation range, and at the time of medium-low speed rotation. 2. A cooling device for a two-cycle engine, wherein a control device for increasing the amount of cooling water to the exhaust pipe device is provided. 6. The cooling device for a two-cycle engine according to claim 3, wherein the control device is provided with a bypass passage communicating with the negative pressure portion of the water jet propulsion pump in the second cooling water passage portion. A characteristic two-cycle engine cooling device.