JP2002339751A - Cooling water passage structure of water-cooled engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the cooling water passage structure of a water-cooled engine capable of realizing a stable cooling water control by effectively cooling a cylinder head with a simple structure. SOLUTION: The water-cooled engine 2 comprises a water pump 50, allows cooling water discharged by the water pump 50 to be fed into a cooling water passage formed in the engine, and controls the flow of cooling water by a thermostat 60. A cooling water hose 57 is disposed separately from an engine body, and one end part thereof is connected to the discharge side of the water pump 50 and the other end is connected to a water jacket 32a in the cylinder head 32 of the engine 2 to introduce cooling water from the water pump 50 to the cooling water passage inside the engine from the cylinder head 32 side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a water-cooled engine, and more particularly to a structure of a water-cooled engine having a cooling water passage for cooling the engine.

[0002]

2. Description of the Related Art Conventionally, engines mounted on small snowmobiles such as snowmobiles are mainly two-stroke engines which have a relatively simple structure, are lightweight, compact and have high power. In general, a water-cooled engine is used as a two-cycle engine used in snowmobiles. By cooling the engine stably, it is possible to prevent overheating and overcooling, to improve output, and to suppress noise.

Here, the cooling structure of a water-cooled engine will be described with reference to the drawings. As shown in FIGS.
The cooling water cooled by the heat exchanger (heat exchanger) is supplied to the crankshaft 141 in the crankcase 138.
From the water pump 150 orthogonal to the crankcase 1
38, is introduced into a cooling water passage formed in the engine, cools the cylinder 131, and subsequently cools the thermostat 1
The cooling water, which flows to the thermocap 164 via the thermostat 60 or the thermostat manifold 163, is returned to the heat exchanger, passes through the engine 102, cools the high-temperature cooling water, and is again cooled by the water pump 150 into the engine 102. And circulated through the cooling water passage.

[0004]

However, in such a conventional cooling water passage structure, the cooling water is introduced from a crankcase 138 furthest from a combustion chamber (not shown) inside the cylinder head 132, and then is introduced. Since it flows to the cylinder 131 and further to the cylinder head 132, there is a problem that it is not effective for cooling the cylinder head 132 which is at the highest temperature.

The thermostat 160 for controlling the flow of the cooling water is conventionally installed in a thermostat manifold 163 for collecting the cooling water of each cylinder, and so-called outlet control is performed. Therefore, the time until the thermostat 160 is opened (the valve is opened) Time) is not stable, and has a characteristic that surging is apt to occur.

Further, as shown in FIG. 13, when the thermostat 160 is closed, the cooling water in the engine 102 is directly circulated to the water pump 150 through the cooling water bypass passage 167 to improve the above problem. Although the configuration is also known, there are problems that the number of components such as the cooling water hose increases, which increases the cost, complicates the cooling water piping path, impairs the appearance, and affects the workability. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a simple structure. The cooling water passage of a water-cooled engine can effectively cool a cylinder head and realize stable cooling water control. It is intended to provide a structure.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a cooling water passage structure for a water-cooled engine, and more particularly to a water pump for supplying cooling water to a cooling water passage formed inside the engine, and a cooling water discharged from the water pump. A water-cooled engine comprising: a thermostat for controlling supply of the water pump to the engine; and a thermostat provided in a pump housing of the water pump, wherein the water pump and the engine are provided between the water pump and a cooling water passage inside the engine. A cooling water bypass passage communicating with the internal cooling water passage; providing one end of the cooling water bypass passage with a cooling water passage inside the engine, and connecting the other end of the cooling water bypass passage with a water pump; At least part of the cooling water passing through the passage is directly led to the water pump without passing through the heat exchanger. It is characterized in that to enable.

Preferably, the cooling water discharged from the water pump is introduced from a cylinder head side into a cooling water passage inside the engine. Preferably, the water pump is provided on a side wall of a crankcase. Preferably, the thermostat is provided on a cooling water inlet side of a water pump. The thermostat includes a main valve that controls the introduction of cooling water sent from the heat exchanger to the water pump, and a sub-valve that controls the introduction of cooling water that is bypassed from the cooling passage inside the engine to the water pump. Preferably, it is provided.

It is preferable that the cooling water passage is provided separately from the engine body. Further, a cooling water intake manifold is provided on the exhaust side of the cylinder head, and a communication port for communicating the cooling water passage of the cylinder head with the manifold is provided, and a position facing the communication port in the cooling passage is provided. Preferably, a partial wall is provided. Preferably, the engine is mounted on a snowmobile.

According to the present invention, the following effects can be obtained. That is, by providing the thermostat in the pump housing of the water pump, the number of components can be reduced as compared with the case where the thermostat is separately mounted on the engine, and the cost can be reduced. Also, by providing a cooling water bypass passage that connects the water pump and the cooling water passage inside the engine between the water pump and the cooling water passage inside the engine, and connecting the cooling water bypass passage to the water pump, Since at least a part of the cooling water heated through the cooling water passage can be directly introduced into the water pump without passing through the heat exchanger, the cooling water can be controlled without being overcooled.

Further, a cooling water passage is provided for communicating the discharge side of the water pump with the cooling water passage of the cylinder head.
By introducing the cooling water discharged from the water pump from the cylinder head side to the cooling water passage inside the engine, the cylinder head having the highest temperature can be cooled first and the engine can be effectively cooled.

Further, by providing the water pump on the side wall of the crankcase, it is possible to install the water pump with high space efficiency, and it is possible to reduce the number of components and reduce the cost as compared with a case where the water pump is provided separately. Can be planned.

Further, by providing the thermostat on the cooling water inlet side of the water pump, the thermostat can be arranged at a position separated from the cylinder head where the temperature becomes high, so that the cooling water can be controlled while the cooling water temperature is stable. At the same time, a thermostat with high space efficiency can be installed, and the number of components can be reduced as compared with a case where the thermostat is provided separately, so that the cost can be reduced. Further, the cooling water before being introduced into the engine, that is, the cooling water that has not yet been heated by the high-temperature engine can be controlled (inlet-side control), and the cooling water temperature can be stabilized.

The thermostat comprises a main valve for controlling the introduction of cooling water sent from the heat exchanger to the water pump, and a sub-valve for controlling the introduction of cooling water bypassed from the engine to the water pump. By controlling the circulation of the cooling water cooled by the heat exchanger by the main valve and the introduction of the cooling water heated to the engine by the sub-valve, by adjusting the cooling water Further, the cooling water temperature can be stabilized.

Further, since the cooling water passage is provided separately from the engine main body without being formed inside the engine main body, the cooling water passage is not directly affected by heat from the high temperature engine main body. The engine can be effectively cooled by the cooling water.

Further, a manifold for taking in cooling water is provided on the exhaust side of the cylinder head, and cooling water is introduced from the exhaust side of the cylinder head, so that the exhaust side at a high temperature can be effectively cooled. . Further, a communication port for communicating the cooling water passage of the cylinder head with the manifold is provided, and by providing a partial wall portion at a position facing the communication port in the cooling passage, the cooling water is directly directed to the non-exhaust side. The cylinder head on the high temperature side can be effectively cooled by preventing the inflow of the cylinder head.

Further, by mounting the engine configured as described above on a snowmobile, a snowmobile equipped with a highly efficient and space-saving engine can be provided.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 to FIG. 7 show an example of an embodiment of the present invention. In the drawings, portions denoted by the same reference numerals as those in the drawings represent the same items. FIG. 1 is an explanatory view showing the entire configuration of a snowmobile according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view showing the configuration of a water-cooled engine according to this embodiment, and FIG. FIG. 4 is a front view of the engine showing a configuration of a cooling water passage, FIG. 4 is a sectional view taken along the line AA of FIG. 2 showing a configuration of a cooling water introduction portion to a cylinder head of the engine, and FIG. FIG. 6 is a detailed sectional view showing the operation of the main valve and the sub-valve of the thermostat, and FIG. 7 is a detailed cross-sectional view showing the configuration of the thermostat (without the sub-valve) according to the present embodiment.

In the present embodiment, as shown in FIG. 1, a water-cooled engine 2 according to the present invention is mounted on a snowmobile 1. The snowmobile 1 has a pair of left and right steering sleds 13 rotatably installed below a frame front (engine mount frame) 11 of a body frame 10 extending in the front-rear direction so as to face left and right.
A driving crawler 16 for circulating the track belt 15 is arranged below the lower part. The crawler 16 is circulated around the drive wheels 17 disposed at the front end of the frame rear portion 12, the driven wheels 18 disposed at the rear end, the plurality of intermediate wheels 19, the suspension mechanism 20, and the respective wheels. A track belt 15 is provided.

The vehicle body frame 10 is formed in a monocoque frame structure. A front portion 11 of the frame on which the engine 2 is mounted has a front portion formed to project upward from a main portion 11a. A front suspension housing 11b accommodating an upper portion of the front suspension 13a is formed, and the main portion 11a
A track housing 11c for accommodating a portion above the drive wheel 17 of the crawler 16 is formed continuously and integrally with the frame rear portion 12 in a shape in which a rear portion rises obliquely rearward and upward.

The frame rear portion 12 extends over the rear end portion in the vehicle front-rear direction, and also serves as a cover for housing the entire crawler 16 below. Also, the frame rear portion 12
A saddle-shaped seat 22 is disposed above the seat 22.
On both sides in the vehicle width direction, there are provided steps 23 which are one step lower than the seat 22. A steering shaft (not shown) is erected substantially at the center of the vehicle body between the seat 22 and the front cover 4, and a bar handle 26 is inclined slightly rearward at the upper end of the steering shaft and extends horizontally left and right. Has been established.

In front of the bar handle 26, a windshield 28 is erected, and the front cover 4 is gradually turned forward from the base of the windshield 28 in a substantially streamlined manner. It has a sparse shape. The steering sled 13 is operated by the bar handle 26 via a steering shaft.

Next, the configuration of the engine 2 will be described in detail. As shown in FIG. 1, in the engine room 30 inside the front cover 4, the cylinder 31 of the engine 2 is tilted rearward with respect to the traveling direction of the snowmobile (the center of the cylinder head 32 is positioned rearward of the crankshaft 41). ), And the position of the engine 2 including the cylinder 31 is retracted to near the lower portion of the steering shaft. An air cleaner box 33 for sending air-fuel mixture to the engine 2 is arranged in front of the engine 2, and an exhaust pipe 35 is similarly arranged in front of the engine 2.

As shown in FIG. 2, the engine 2 is a water-cooled two-stroke engine in which a cylinder head 32 is arranged above and two cylinders are arranged in parallel in the width direction. And the cylinder 31 side is largely inclined toward the rear of the vehicle body, and is disposed substantially at the center of the engine room 30 inside the front cover 4.

An exhaust manifold 36 is formed rearward of the cylinder 31 so as to face rearward. In an upper crankcase 38 provided below the cylinder 31, an intake manifold 39 is provided with the exhaust manifold 36.
And projecting rearward from the exhaust manifold 36.

A lower crankcase 40 is disposed below the upper crankcase 38. The lower crankcase 40 is provided with a pump that is substantially perpendicular to the axis of the crankshaft 41 and substantially horizontal. A shaft 42 is provided, and a drive from the crankshaft 41 is transmitted by a screw gear 44 provided integrally with the pump drive shaft 42 at a position facing the crankshaft 41.

As shown in FIG. 2, the pump drive shaft 42 has one end connected to an oil pump 46 provided on the front side of the engine 2 and the other end provided on the rear side of the engine. It is connected to the water pump 50.
The oil pump 46 supplies engine oil to each sliding portion of the engine component via an oil supply path (not shown). The water pump 50 cools the engine 2 by introducing cooling water into the engine via a cooling water passage.

As shown in FIGS. 2 and 3, the water pump 50 includes a rear side surface 40a of the lower crankcase 40.
A cooling water inlet 51 is disposed substantially below the center between the two cylinders 34 formed in the cylinder 31 and introduces cooling water into the water pump 50 through a heat exchanger 54 via a cooling water hose 54. (Not shown), while a cooling water outlet 52 for discharging cooling water is a water jacket 32 a which is a cooling water passage formed inside the cylinder head 32 via an inlet side hose nipple 55 and a cooling water hose 57. It is connected to the.

The inlet side hose nipple 55 is shown in FIG.
As shown in FIG. 4, the opening 55 a is protruded toward the lower crankcase 40 (the lower side in FIG. 2) at a substantially middle position on the rear side of the two combustion chambers 32 b arranged side by side. ing. The cooling water hose 57 is formed of a rubber material having heat resistance, and is disposed substantially linearly near the rear wall 31a of the cylinder 31 as shown in FIGS. The portion 52 and the inlet side hose nipple 55 are connected.

The water pump 50 is shown in FIG.
As shown in FIG. 6, a thermostat 60 that controls the flow rate of the cooling water according to the temperature of the cooling water is provided at the cooling water inlet 51 of the water pump housing 58. The thermostat 60 is connected to the water pump housing 5.
8, a main valve 61 for controlling the introduction of cooling water supplied from the heat exchanger to the water pump 50, and cooling water directly supplied to the water pump 50 by bypassing the cooling water from the engine 2 main body. And a sub-valve 62 for controlling the introduction.

On the cooling water inlet side of the water pump housing 58, a water pump cover 59 in which a thermostat 60 is disposed is formed so as to protrude rearward, and a thermostat mounting side of the water pump cover 59 and the thermostat 60 are provided. A thermostat cap 64 is provided so as to cover the upstream side in the cooling water flow direction. The thermostat cap 64 has a cooling water inlet 5
1 is formed.

The side wall 59 of the water pump cover 59
3, a bypass hose nipple 68 to which a cooling water bypass hose 67 bypassed from a part of the cooling water passage of the upper crankcase 38 is connected as shown in FIGS. ing. A bypass opening 69 is formed inside the side wall 59a, and a sub-valve 62 is provided at a position facing the bypass opening 69 so as to be able to protrude and retract so as to open and close the bypass opening 69.

A water jacket (not shown) formed inside the rear side surface of the lower crankcase 40.
Hose nipple 40 for bypass which communicates with the outside
b protrudes outward. The bypass outlet-side hose nipple 40b is connected to the bypass hose nipple 68 via a cooling water bypass hose 67.

Next, the operation of the cooling water passage structure of the water-cooled engine according to this embodiment will be described with reference to the drawings. First, when the cooling water is supplied to the water pump 50 from a heat exchanger (not shown), the water pump 50 is provided via a thermostat 60 provided at the cooling water inlet 51 of the water pump housing 58.
Introduced within.

The cooling water introduced into the water pump 50 is discharged from a cooling water outlet 52 and is supplied to a cooling water hose 5.
7 and is introduced into the engine 2 from the hose nipple 55 on the inlet side of the cylinder head 32. The introduced cooling water is supplied to the water jacket 32 in the cylinder head 32.
a through a water jacket 31b formed in each part of the cylinder 31 and a cooling water passage (not shown) in the upper crankcase 38 and the lower crankcase 40.
The engine is cooled and warmed while passing through the engine, and is sent out of the engine through an outlet hose nipple 56 provided on the lower crankcase 40 side.

The warmed cooling water is sent to the heat exchanger through a cooling water hose 70 connected to the outlet hose nipple 56. Then, the cooling water cooled while passing through the cooling water passage in the heat exchanger is supplied to the water pump 50 again, sent to the engine 2 and repeated the cooling process described above to cool the engine 2. Will be

Here, when the engine is in the warm-up operation state, the thermostat 6
0, the main valve 61 is closed and the sub-valve 62 is opened, no new cooling water is introduced from the cooling water inlet side of the water pump 50, and the engine 2 The warmed coolant is introduced into the engine 2 and the warm coolant is circulated and supplied to the engine 2 side. Thus, an efficient warm-up operation of the engine can be performed without unnecessary cooling of the engine 2.

On the other hand, when the engine 2 is operating, the water pump 50 is in a state in which the main valve 61 is opened and the sub-valve 62 is closed by the action of the thermostat 60, contrary to the warm-up operation. , Bypass opening 69
From the cooling water inlet side of the water pump 50, only new cooling water is introduced. As a result, the engine that has become hot in the operating state can be efficiently cooled.

With the above-described structure, according to the cooling water passage structure of the water-cooled engine of the present embodiment, the thermostat 60 is provided in the water pump housing 58 of the water pump 50, so that the thermostat 60 is separately attached to the engine 2. Compared to the case, the number of components can be reduced, and the cost can be reduced. Further, the water pump 50 and the water jacket 3 inside the engine are disposed between the water pump 50 and the water jacket 32a inside the engine.
2a is provided with a hose 67 for cooling water bypass communicating with 2a.
By connecting the cooling water bypass hose 67 to the water pump 50, at least a portion of the cooling water heated through the water jacket 32a is directly introduced into the water pump 50 without passing through the heat exchanger. The cooling water can be controlled by stabilizing the temperature of the cooling water without overcooling, and the engine 2 is not excessively cooled during the warm-up operation of the engine 2.

Further, according to the present embodiment, the cooling water discharged from the water pump 50 is introduced from the cylinder head 32 side into the cooling water passage inside the engine to cool the cylinder head 32 having the highest temperature first. Thus, the engine 2 can be effectively cooled.

According to the present embodiment, the water pump 50 and the water jacket 3 in the cylinder head 32 are provided.
The cooling water hose 57 is disposed outside the engine 2 separately from the engine 2 main body without forming a cooling water passage communicating with the engine 2a inside the engine 2 main body. The engine 2 can be effectively cooled by the cooled cooling water without being directly received.

According to the present embodiment, the water pump 50 is provided on the rear side surface 40a of the lower crankcase 40, and the thermostat 6 is provided on the discharge side of the water pump 50.
By providing 0, the cooling water before being introduced into the engine 2, that is, the cooling water that has not yet been heated by the engine 2, can be controlled, so that the cooling water temperature can be stabilized. In addition, the cooling water can be controlled in a state where the temperature of the cooling water is stabilized while being isolated from the cylinder head 32 which becomes high in temperature. In addition, the thermostat 60 with high space efficiency can be installed, and the number of components can be reduced as compared with the case where the thermostat 60 is provided separately, so that the cost can be reduced.

According to the present embodiment, the thermostat 60 is disposed in the water pump housing 58,
By including a main valve 61 that controls the introduction of cooling water sent from the heat exchanger side to the water pump 50 and a sub-valve 62 that controls the introduction of cooling water bypassed from the engine side to the water pump 50 side, Since the circulation of the cooling water can be controlled by the main valve 61 and the introduction of the high-temperature cooling water sent from the engine side can be controlled by the sub-valve 62, the cooling water can be adjusted to further stabilize the cooling water temperature. it can.

Further, according to the present embodiment, since the cooling water hose 57 is arranged so as to introduce the cooling water from the water pump 50 into the cooling water passage inside the engine from the side opposite to the exhaust side of the cylinder head 32, the structure is complicated. It is also possible to configure the cooling water passage substantially linearly without taking a path, and it is possible to configure the cooling water passage with a simple configuration and in a small space, and to shorten the cooling water passage. It is possible to minimize the influence of heat on the engine during liquid transfer.

The structure of the cooling water passage of the water-cooled engine according to the present invention is not limited to the above-described example, but various modifications can be made without departing from the scope of the present invention. .

In this embodiment, the thermostat 60
Although the main valve 61 and the sub-valve 62 are provided, the present invention is not limited to the configuration of the thermostat. For example, as shown in FIG.
Only one may be provided.

In this embodiment, the cylinder head 32
The cooling water is introduced into the cooling water passage inside the engine 2 from the side opposite to the exhaust, but the present invention is not limited to this. For example, as a modification, as shown in FIG. The cooling water may be introduced into the water jacket 32a in the cylinder head 32 from the exhaust side of the cylinder head 32. More specifically, a cooling water manifold 32c is formed on the exhaust side of the cylinder head 32, and a partial wall portion 32d is formed between cylinders in the water jacket 32, so that the introduced cooling water flows directly to the non-exhaust side. This is to prevent that. Reference numeral 32e in the figure is an air bleeding nipple. According to this configuration, the exhaust side of the cylinder head 32 that is in a high temperature state can be effectively cooled.

Although the present embodiment describes a water-cooled engine, the present invention can be applied to other liquid-cooled engines that cool the engine using oil or the like. Effects can be achieved.

[0050]

As described above, the first aspect of the present invention is as described above.
According to the cooling water passage structure of the water-cooled engine described in
With a simple configuration, an excellent effect of effectively cooling the cylinder head and realizing stable control of the cooling water can be achieved. Specifically, by providing the thermostat in the pump housing of the water pump, the number of components can be reduced as compared with a case where the thermostat is separately mounted on the engine, and the cost can be reduced. Also, by providing a cooling water bypass passage that connects the water pump and the cooling water passage inside the engine between the water pump and the cooling water passage inside the engine, and connecting the cooling water bypass passage to the water pump, Since at least a part of the cooling water heated through the cooling water passage can be directly introduced into the water pump without passing through the heat exchanger, the cooling water can be controlled without being overcooled.

Further, a cooling water passage communicating between the discharge side of the water pump and the cooling water passage of the cylinder head is provided.
By introducing the cooling water from the water pump into the cooling water passage inside the engine from the cylinder head at the top of the engine, the cylinder head having the highest temperature can be cooled first and the engine can be effectively cooled. Moreover, since the cooling water passage is formed separately from the engine body without being formed inside the engine body, the cooling water is not directly affected by the heat from the engine body where the temperature becomes high. The engine can be cooled effectively. In addition, a thermostat that controls the supply of cooling water is provided upstream of the cooling water passage inside the engine, and by controlling the cooling water that has not yet been warmed by the engine before being introduced into the engine, cooling is performed. This has the effect of stabilizing the water temperature and bringing the engine to an optimal cooling state.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a snowmobile according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view illustrating a configuration of a water-cooled engine according to the embodiment.

FIG. 3 is a front view of the engine showing a configuration of a cooling water passage around a water pump according to the embodiment.

FIG. 4 is a sectional view taken along the line AA of FIG. 2, showing a configuration of a cooling water introduction portion of the cylinder head of the engine.

FIG. 5 is a detailed sectional view showing an operation of a sub-valve of the thermostat.

FIG. 6 is a detailed sectional view showing the operation of a main valve and a sub valve of the thermostat.

FIG. 7 is a thermostat according to the present embodiment (without a secondary valve).
2 is a detailed sectional view showing the configuration of FIG.

FIG. 8 is a plan view showing a configuration of a cylinder head according to a modified example of the embodiment.

FIG. 9 is a front view showing a configuration of a cooling water passage of a conventional water-cooled engine.

FIG. 10 is a view as viewed in the direction of arrow A in FIG. 9;

11 is a view as viewed in the direction of arrow B in FIG. 10;

FIG. 12 is an explanatory diagram showing a configuration of a conventional pump drive shaft.

FIG. 13 is a front view showing an example of a cooling water bypass passage of a conventional water-cooled engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Snowmobile 2 Engine 31 Cylinder 31b Water jacket 32 Cylinder head 32a Water jacket 38 Upper crankcase 40 Lower crankcase 40b Exit side hose nipple for bypass 50 Water pump 51 Cooling water inlet 52 Cooling water outlet 54 Cooling water hose 57 Cooling water hose 58 Water pump housing 59 Water pump cover 60 Thermostat 61 Main valve 62 Secondary valve 67 Hose for cooling water bypass 70 Cooling water hose

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02F 1/36 F02F 1/36 C 7/00 301 7/00 301Z F16K 31/68 F16K 31/68 Q F Terms (reference) 3G024 AA01 AA11 AA47 AA53 BA27 BA29 CA05 CA13 DA12 DA18 EA01 3H057 AA02 CC06 CC13 EE01 FB01 FD11 HH03 HH17

Claims (8)

[Claims] 1. A water-cooled engine comprising: a water pump for feeding cooling water to a cooling water passage formed inside the engine; and a thermostat for controlling supply of cooling water discharged from the water pump to the inside of the engine. A cooling water bypass passage communicating between the water pump and a cooling water passage inside the engine is provided between the water pump and a cooling water passage inside the engine; One end of the water bypass passage communicates with the cooling water passage inside the engine, and the other end communicates with the water pump.
A cooling water passage structure for a water-cooled engine, wherein at least a portion of the cooling water passing through the cooling water passage can be directly introduced into a water pump without passing through a heat exchanger. 2. A cooling water passage structure for a water-cooled engine according to claim 1, wherein cooling water discharged from said water pump is introduced from a cylinder head side into a cooling water passage inside the engine. . 3. The cooling water passage structure for a water-cooled engine according to claim 1, wherein the water pump is provided on a side wall of a crankcase. 4. The thermostat is provided on a cooling water inlet side of a water pump.
The cooling water passage structure for a water-cooled engine according to any one of claims 3 to 3. 5. The thermostat has a main valve that controls the introduction of cooling water sent from the heat exchanger to the water pump, and a sub valve that controls the introduction of cooling water bypassed from the cooling passage inside the engine to the water pump. The cooling water passage structure of a water-cooled engine according to any one of claims 1 to 4, further comprising a valve. 6. The cooling water passage structure for a water-cooled engine according to claim 1, wherein the cooling water passage is provided separately from an engine main body. 7. A cooling water intake manifold is provided on an exhaust side of the cylinder head, and a communication port is provided for communicating a cooling water passage of the cylinder head with the manifold, and the communication port is opposed to the communication port in the cooling passage. The cooling water passage structure for a water-cooled engine according to claim 1, wherein a partial wall portion is provided at a position where the cooling water passes. 8. The cooling water passage structure for a water-cooled engine according to claim 1, wherein the engine is mounted on a snowmobile.