JP7229845B2 - Outboard motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an outboard motor, and more particularly to an outboard motor that cools an engine with cooling water pumped up from a water intake.

Conventionally, in an outboard motor, the engine is cooled by pumping up cooling water from a water intake provided in a submerged portion of the outboard motor and supplying it to a water jacket formed around the cylinder block of the engine. is common.

For example, Patent Document 1 discloses an outboard engine in which cooling water pumped up from a water intake by a water pump flows into a water jacket to cool the engine, and is discharged from the lower end of a cylinder block into an undercover through a drainage channel. machine is disclosed.

Japanese Patent Application Laid-Open No. 2002-054438

However, in the outboard motor of Patent Document 1, the water pump is driven by the drive shaft that is directly connected to the crankshaft. The water pump is also driven to draw cooling water from the water intake. Therefore, even when the temperature of the engine is low, the cooling water pumped up from the water intake is supplied to the water jacket. As a result, when the temperature of the engine is low, there is a risk that the engine will be overcooled, and it is difficult to warm up the engine early.

SUMMARY OF THE INVENTION The present invention provides an outboard motor capable of preventing overcooling of the engine and early warming up of the engine.

The present invention
a water intake channel provided with a water intake;
a water pump for pumping cooling water from the water intake through the water intake channel;
an engine formed with a water jacket through which the cooling water passes;
a water supply passage for supplying the cooling water from the water pump to the water jacket;
an outlet passage through which the cooling water that has passed through the water jacket flows out;
a drainage channel through which the cooling water flowing out from the outlet passage flows, and a drainage port provided at a downstream end thereof;
The outboard motor, wherein the outlet passage is provided with a thermostat valve,
a bypass channel for circulating the cooling water from the drainage channel to the water intake channel;
a bypass flow rate adjustment mechanism that adjusts the flow rate of the cooling water flowing through the bypass path ;
The bypass flow rate adjustment mechanism includes a first throttle mechanism provided in the bypass passage to throttle the flow rate of the cooling water, and a second throttle mechanism provided in the drain passage to throttle the flow rate of the cooling water. .
In addition, the present invention
a water intake channel provided with a water intake;
a water pump for pumping cooling water from the water intake through the water intake channel;
an engine formed with a water jacket through which the cooling water passes;
a water supply passage for supplying the cooling water from the water pump to the water jacket;
an outlet passage through which the cooling water that has passed through the water jacket flows out;
a drainage channel through which the cooling water flowing out from the outlet passage flows, and a drainage port provided at a downstream end thereof;
The outboard motor, wherein the outlet passage is provided with a thermostat valve,
a bypass channel for circulating the cooling water from the drainage channel to the water intake channel;
a bypass flow rate adjustment mechanism that adjusts the flow rate of the cooling water flowing through the bypass path;
The bypass flow control mechanism has a valve mechanism provided at a branch portion between the drainage channel and the bypass channel.

According to the present invention, since the cooling water heated by cooling the engine can be supplied again to the water jacket from the bypass, overcooling of the engine can be prevented and the engine can be warmed up early.

1 is a schematic external view of an outboard motor according to a first embodiment of the invention; FIG. FIG. 2 is an elevational view of the main parts of the outboard motor shown in FIG. 1 with a part cut away; FIG. 7 is an elevational view of the essential parts of the outboard motor of the second embodiment of the invention, showing a partially cutaway outboard motor;

Each embodiment of the outboard motor of the present invention will be described below with reference to the accompanying drawings.

[First embodiment]
First, an outboard motor 1 according to a first embodiment of the invention will be described with reference to FIGS. 1 and 2. FIG.

<Outboard motor structure>
As shown in FIG. 1, an outboard motor 1 of this embodiment includes an engine cover 3 covering the upper portion of an engine 2, an undercover 5 including an engine mount 4, a reduction gear, a clutch, a forward/reverse switching device, and the like. A gear case 8 that houses the mission device 6 and supports a propeller 7 for propulsion, an extension case 9 that connects the undercover 5 and the gear case 8, and the outboard motor 1 are attached to the stern plate of the hull. (shown) and a vise stern bracket 10 for fixing to the stern bracket. An air intake duct 11 is opened in the engine cover 3 .

Between the undercover 5 and the extension case 9, upper and lower ends of a swivel shaft 14 rotatably supported by a pipe-shaped swivel case 13 to which a stern bracket 10 is connected via a tilt shaft 12 are connected. there is By operating a steering arm 15 fixed to the swivel shaft 14, the angle of the outboard motor 1 with respect to the hull can be changed to give the hull a turning motion. The swivel shaft 14 is hollow, and a rod 16 for switching the transmission device 6 between forward and backward movement is inserted through the center thereof.

The engine 2 mounted on the outboard motor 1 includes a cylinder block 19 integrally comprising a cylinder 17 and a crankcase 18, a crankshaft 20 vertically supported by the cylinder block 19, and pistons of the cylinder block 19 at top dead center. It is a four-cycle vertical crankshaft engine comprising a cylinder head 21 that is joined to a side end face to form a combustion chamber and a valve gear chamber, and a head cover 23 that closes the valve gear chamber in which a camshaft 22 is supported.

The crankshaft 20 has its lower end supported by a lower bearing wall integral with the cylinder block 19 and its upper end supported by an upper bearing provided on an upper cover 24 joined to the upper wall of the cylinder block 19 . A flywheel 25 and a recoil starter 26 are connected to the upper end of the crankshaft 20, and a drive shaft 27 that transmits power to the propeller 7 is connected to the lower end thereof. A belt/pulley mechanism 28 intervenes between the crankshaft 20 and the camshaft 22 .

As shown in FIG. 2 , the cylinder block 19 of the engine 2 has a water jacket 29 surrounding two horizontally extending cylinders 17 arranged vertically and connected to an exhaust port provided in the cylinder head 21 . an exhaust passage 30, an exhaust cooling passage 31 through which cooling water passes in the vicinity of the exhaust passage 30, and a breather passage for connecting the crankcase 18 and the cylinder head 21 to each other in order to reduce fluctuations in the crankcase internal pressure. 32, a suction oil passage 33 to a lubricating oil pump connected to the lower end of the camshaft 22, a discharge oil passage 34 from the lubricating oil pump, and a lubricating oil return passage 35 from the cylinder head 21 are formed respectively. It is

An engine mount 4 provided on the undercover 5 and an oil case 37 are joined to the lower surface of the cylinder block 19 to store lubricating oil. A cooling water supply passage 38 and an exhaust passage 39 are integrally formed in a part of the oil case 37 . The cooling water supply passage 38 is connected to a water supply passage 42 having a water pump 40 driven by a drive shaft 27 directly connected to the crankshaft 20 at its lower end. The water pump 40 is connected to a water intake channel 41 having a water intake port 41A opening at the top of the gear case 8 at its lower end (see FIG. 1). A cooling water supply passage 38 on the oil case 37 side communicates with a cooling water supply passage 46 on the cylinder block 19 side through an opening 45 of a gasket 44 interposed between the cylinder block 19 and the oil case 37 . ing.

An exhaust passage 30 formed in the cylinder block 19 is connected to an exhaust passage 39 formed in the oil case 37 , and the exhaust gas after combustion passes through the extension case 9 and enters the propeller boss 47 . It is exhausted into the water from the exhaust port 48 .

<Cooling water route>
While the outboard motor 1 is sailing, the cooling water pumped up by the water pump 40 from the submerged water intake 41A flows from the water supply passage 42 extending into the extension case 9 through the water intake passage 41 to the lower part of the cylinder block 19. The water flows into the water jacket 29 around the cylinder through the inlet passages 49a and 49b provided inside and the connecting passage 50 provided inside the cylinder head 21 . Then, the cooling water flows upward through the water jacket 29 and flows out from an outlet passage 51 formed on the upper left side of the cylinder block 19 in FIG. A thermostat valve 52 is provided in the outlet passage 51, and when the cooling water in the water jacket 29 reaches a predetermined temperature, the thermostat valve 52 opens, and the cooling water flows into the side machined surface 53 of the cylinder block 19 and the Through a water jacket cover 54 joined thereto and a drainage channel 56 provided in a thermostat cover 55 covering the thermostat valve 52, the water in the cylinder block 19 is discharged from a drainage port 57 provided at the downstream end of the drainage channel 56. It is discharged inside the undercover 5 through a drainage path (not shown). Similarly, the cooling water that has flowed through the exhaust cooling passage 31 near the exhaust passage 30 also passes through a drainage passage (not shown) between the side machined surface 53 of the cylinder block 19 and the water jacket cover 54 to the under cover. 5 inside.

A water test hole 43 is provided in the drainage channel 56 . By providing the water test hole 43 in the drainage path 56 through which the cooling water that has passed through the water jacket 29 flows, it is possible to more reliably detect whether or not the cooling water is being supplied to the water jacket 29 .

A bypass 60 that branches off from the drainage channel 56 and circulates the cooling water to the water intake channel 41 is provided in the vicinity of the drainage port 57 of the drainage channel 56 . Therefore, the cooling water flowing through the drainage channel 56 is either discharged inside the undercover 5 from the drainage port 57 or circulated from the bypass channel 60 to the water intake channel 41 and supplied to the water jacket 29 again. split up.

Therefore, at least part of the cooling water heated by cooling the engine 2 circulates from the bypass passage 60 to the water intake passage 41 and is supplied to the water jacket 29 again.

In the outboard motor 1, the temperature of the engine 2 is low, for example, when the engine 2 is started or during low-speed trolling. Even in such a case, the water pump 40 is driven by the drive shaft 27 directly connected to the crankshaft 20, so when the engine 2 is driven, the water pump 40 is also driven to pump up cooling water from the water intake 41A. Therefore, cooling water is supplied to the water jacket 29 even when the temperature of the engine 2 is low. In this embodiment, in such a case, the cooling water heated by cooling the engine 2 can be circulated from the bypass passage 60 to the water intake passage 41 and supplied to the water jacket 29 again. Since the cooling water having a higher temperature than the cooling water alone can be supplied to the water jacket 29, overcooling of the engine 2 can be prevented and the engine 2 can be warmed up early.

Further, the outboard motor 1 is provided with a bypass flow rate adjusting mechanism 70 that adjusts the flow rate of cooling water flowing through the bypass passage 60 . The bypass flow rate adjusting mechanism 70 has a first orifice 71 provided in the bypass passage 60 for restricting the flow rate of cooling water, and a second orifice 72 provided in the drainage path 56 for restricting the flow rate of cooling water.

The first orifice 71 is arranged near the junction of the bypass 60 and the intake channel 41 . The water pump 40 not only pumps up the cooling water from the intake channel 41 but also sucks the cooling water from the bypass channel 60 by the suction force of the pump. Therefore, due to fluctuations in the suction force of the water pump 40, the flow rate of the cooling water flowing through the bypass passage 60 also fluctuates. However, in the present embodiment, since the first orifice 71 is arranged near the junction of the bypass passage 60 and the water intake passage 41 , the cooling water flowing through the bypass passage 60 due to fluctuations in the suction force of the water pump 40 Fluctuations in the flow rate can be reduced. By using the first orifice 71 having an appropriate flow path diameter, the flow rate of the cooling water can be throttled and an appropriate amount of cooling water can be supplied to the water intake path 41. Therefore, an appropriate temperature according to the state of the engine 2 can be obtained. Cooling water can be supplied to the water jacket 29 . In addition, since the flow rate of the cooling water is throttled by the orifice, the amount of the cooling water can be adjusted accurately with a simple structure.

The second orifice 72 is located near the outlet passage 51 of the drainage channel 56 . When the cooling water in the water jacket 29 reaches a predetermined temperature, the thermostat valve 52 opens and the cooling water is discharged to the drainage path 56. Therefore, the cooling water flows through the drainage path 56 before and after the thermostat valve 52 is opened and closed. The flow rate of cooling water fluctuates greatly. However, in this embodiment, since the second orifice 72 is arranged near the outlet passage 51 of the drainage channel 56, the opening and closing of the thermostat valve 52 reduces the fluctuation of the flow rate of the cooling water flowing through the drainage channel 56. Therefore, fluctuations in the flow rate of cooling water flowing through the bypass 60 can also be reduced. By using the second orifice 72 having an appropriate flow path diameter, the flow rate of the cooling water can be throttled and an appropriate amount of cooling water can be supplied to the water intake path 41 via the drainage path 56 and the bypass path 60. It is possible to supply the water jacket 29 with cooling water having an appropriate temperature according to the state of the engine 2 . In addition, since the flow rate of the cooling water is throttled by the orifice, the amount of the cooling water can be adjusted accurately with a simple structure.

In this manner, the bypass flow rate adjustment mechanism 70 having the first orifice 71 and the second orifice 72 can adjust the flow rate of the cooling water flowing through the bypass passage 60, so that an appropriate temperature according to the state of the engine 2 can be obtained. of cooling water can be supplied to the water jacket 29 .

[Second embodiment]
Next, an outboard motor 1A according to a second embodiment of the invention will be described with reference to FIG. In the following description, the same components as those of the outboard motor 1 of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted or simplified. In the outboard motor 1 of the first embodiment, the bypass flow rate adjusting mechanism 70 has the first orifice 71 and the second orifice 72. However, in the outboard motor 1A of the second embodiment, the bypass flow rate adjusting mechanism 70 has a pressure valve 73 . Differences between the outboard motor 1 of the first embodiment and the outboard motor 1A of the second embodiment will be described in detail below.

As shown in FIG. 3, the bypass flow control mechanism 70 provided in the outboard motor 1A of the second embodiment has a pressure valve 73. As shown in FIG.

The pressure valve 73 is provided near the drain port 57 of the drain channel 56 and at the branching portion between the drain channel 56 and the bypass channel 60 . The pressure valve 73 of this embodiment is closed when the pressure of the cooling water is less than a predetermined value, and is opened when the pressure of the cooling water is equal to or higher than the predetermined value.

More specifically, when the pressure of the cooling water is less than the predetermined value, the pressure valve 73 is closed, the cooling water does not flow to the drain port 57 , and all the cooling water flows to the bypass passage 60 . On the other hand, when the pressure of the cooling water is equal to or higher than the predetermined value, the pressure valve 73 is in an open state, a part of the cooling water flows to the bypass passage 60, and the remaining cooling water flows through the pressure valve 73 to the drain port 57. , and discharged to the inside of the undercover 5 through the drain port 57 .

Since the water pump 40 is driven by the drive shaft 27 directly connected to the crankshaft 20, when the rotation speed of the engine 2 is low, the suction force of the water pump 40 is small and the pressure of the cooling water is small. Therefore, the pressure valve 73 is in a closed state, the cooling water does not flow to the drain port 57 , and all of the cooling water heated by cooling the engine 2 flows to the bypass passage 60 . As a result, all of the cooling water heated by cooling the engine 2 can be circulated from the bypass passage 60 to the water intake passage 41 and supplied to the water jacket 29 again. Therefore, it is possible to more effectively prevent overcooling of the engine 2 and warm up the engine 2 early.

On the other hand, when the rotation speed of the engine 2 is high, the suction force of the water pump 40 is large and the pressure of the cooling water is large. Therefore, the pressure valve 73 is in an open state, and although a portion of the cooling water, which has been heated by cooling the engine 2, flows to the bypass passage 60, the rest all flows to the drain port 57, and from the drain port 57, the cylinder It is discharged to the inside of the undercover 5 through a drainage path (not shown) inside the block 19 . Also, the higher the rotation speed of the engine 2, the greater the suction force of the water pump 40, and a large amount of cooling water is pumped up from the water intake port 41A. Therefore, the higher the rotation speed of the engine 2, the smaller the ratio of the cooling water circulating from the bypass passage 60 to the water intake passage 41 with respect to the cooling water pumped up from the water intake port 41A. Therefore, as the rotation speed of the engine 2 increases, the temperature of the cooling water supplied to the water jacket 29 is almost the same as the temperature of the cooling water pumped up from the water intake port 41A. As a result, when the engine speed is high, the pressure valve 73 is open, and the higher the engine speed, the more cooling water is discharged from the drain port 57 to the inside of the undercover 5 and the water jacket. Since the temperature of the cooling water supplied to 29 is almost the same as the temperature of the cooling water pumped up from the water intake port 41A, the engine 2 can be cooled more effectively.

In this manner, the bypass flow rate adjustment mechanism 70 having the pressure valve 73 can more accurately adjust the flow rate of the cooling water flowing through the bypass passage 60, so that the cooling water can be adjusted to an appropriate temperature according to the state of the engine 2. can be supplied to the water jacket 29.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be modified, improved, and the like as appropriate.

For example, the bypass flow rate adjustment mechanism 70 of the outboard motor 1 of the first embodiment has a first orifice 71 and a second orifice 72, and the bypass flow rate adjustment mechanism 70 of the outboard motor 1A of the second embodiment has: Although the bypass flow control mechanism 70 has the pressure valve 73 , the bypass flow control mechanism 70 may have both the first orifice 71 and the second orifice 72 and the pressure valve 73 .

Further, for example, the bypass flow rate adjustment mechanism 70 of the outboard motor 1 of the first embodiment has the first orifice 71 and the second orifice 72, but the bypass passage 60 is not limited to the first orifice 71. Any throttle mechanism that is provided to throttle the flow rate of cooling water may be used. may be used.

Further, for example, the bypass flow control mechanism 70 of the outboard motor 1A of the second embodiment is closed when the pressure of the cooling water is less than a predetermined value, and is opened when the pressure of the cooling water is equal to or higher than the predetermined value. Although the pressure valve 73 is used, any valve mechanism may be used, for example, a three-way valve that switches between the flow path flowing to the bypass passage 60 and the flow path flowing to the drain port 57 depending on the pressure of the cooling water. Alternatively, it may be an electromagnetic valve whose opening can be electrically adjusted.

In addition, at least the following matters are described in this specification. In addition, although the parenthesis shows the components corresponding to the above-described embodiment, the present invention is not limited to this.

(1) a water intake channel (water intake channel 41) provided with a water intake (water intake port 41A);
a water pump (water pump 40) for pumping cooling water from the water intake through the water intake channel;
an engine (engine 2) formed with a water jacket (water jacket 29) through which the cooling water passes;
a water supply passage (water supply passage 42) for supplying the cooling water from the water pump to the water jacket;
an outlet passage (outlet passage 51) through which the cooling water that has passed through the water jacket flows;
a drainage channel (drainage channel 56) in which the cooling water flowing out from the outlet passage flows, and a drainage port (drainage port 57) is provided at a downstream end,
The outboard motor (outboard motor 1, 1A) is provided with a thermostat valve (thermostat valve 52) in the outlet passage,
a bypass passage (bypass passage 60) for circulating the cooling water from the drainage passage to the intake passage;
and a bypass flow rate adjustment mechanism (bypass flow rate adjustment mechanism 70) that adjusts the flow rate of the cooling water flowing through the bypass passage.

According to (1), the outboard motor has a bypass passage that circulates cooling water from the drainage passage to the water intake passage, and the cooling water that has been heated by cooling the engine can be resupplied from the bypass passage to the water jacket. Therefore, overcooling of the engine can be prevented and the engine can be warmed up early.
Furthermore, since the outboard motor can adjust the flow rate of cooling water flowing through the bypass passage by means of the bypass flow rate adjusting mechanism, it is possible to supply the water jacket with cooling water at an appropriate temperature according to the state of the engine.

(2) The outboard motor according to (1),
The outboard motor, wherein the drainage channel is provided with a water test hole (water test hole 43).

According to (2), since the outboard motor is provided with the water test hole in the drainage channel through which the cooling water that has passed through the water jacket flows, it is possible to more reliably check whether the cooling water is being supplied to the water jacket. can be detected.

(3) The outboard motor according to (1) or (2),
The bypass flow rate adjustment mechanism includes a first throttle mechanism (first orifice 71) that is provided in the bypass passage and throttles the flow rate of the cooling water, and a second throttle mechanism that is provided in the drainage channel and throttles the flow rate of the cooling water. and a mechanism (second orifice 72).

According to (3), the bypass flow rate adjustment mechanism includes a first throttle mechanism provided in the bypass channel to throttle the flow rate of the cooling water, and a second throttle mechanism provided in the drainage channel to throttle the flow rate of the cooling water. Therefore, the flow rate of cooling water flowing through the bypass can be adjusted with a simple structure.

(4) The outboard motor according to (3),
The outboard motor, wherein the first throttle mechanism is an orifice.

According to (4), since the first throttle mechanism is an orifice, the flow rate of the cooling water can be adjusted accurately with a simple structure.

(5) The outboard motor according to (3) or (4),
The outboard motor, wherein the second throttle mechanism is an orifice.

According to (5), since the second throttle mechanism is an orifice, the flow rate of the cooling water can be adjusted accurately with a simple structure.

(6) The outboard motor according to any one of (3) to (5),
The outboard motor, wherein the first throttle mechanism is arranged in the vicinity of a junction of the bypass passage and the water intake passage.

According to (6), since the first throttling mechanism is arranged in the vicinity of the confluence with the water intake channel of the bypass channel, the flow rate of cooling water flowing through the bypass channel fluctuates due to fluctuations in the suction force of the water pump. can be reduced.

(7) The outboard motor according to any one of (3) to (6),
The outboard motor, wherein the second throttle mechanism is arranged in the vicinity of the outlet passage of the drainage channel.

According to (7), since the second throttle mechanism is arranged near the outlet passage of the drainage channel, it is possible to reduce fluctuations in the flow rate of cooling water flowing through the drainage channel due to opening and closing of the thermostat valve.

(8) The outboard motor according to any one of (1) to (7),
The outboard motor, wherein the bypass flow control mechanism has a valve mechanism (pressure valve 73) provided at a branching portion between the drainage channel and the bypass channel.

According to (8), since the bypass flow rate adjustment mechanism has a valve mechanism provided at the branching portion between the drainage channel and the bypass channel, it is possible to more accurately adjust the flow rate of the cooling water flowing through the bypass channel. .

(9) The outboard motor according to (8),
The valve mechanism is a pressure valve,
when the pressure of the cooling water is less than a predetermined value, the pressure valve is closed and the cooling water does not flow to the drain port;
When the pressure of the cooling water is equal to or higher than a predetermined value, the pressure valve is in an open state, and the cooling water flows through the pressure valve to the drain port.

According to (9), the valve mechanism is a pressure valve. When the pressure of the cooling water is less than a predetermined value, the cooling water does not flow to the drain port. It flows through the valve to the drain. Therefore, when the engine speed is low, the suction force of the water pump is small and the pressure of the cooling water is low, so the cooling water does not flow to the drain port. Since it can be supplied to the water jacket, overcooling of the engine can be prevented more effectively, and the engine can be warmed up early. On the other hand, when the engine speed is high, the suction force of the water pump is large and the pressure of the cooling water is large, so the cooling water flows to the drain port, so that the engine can be cooled more effectively.

1, 1A outboard motor 2 engine 29 water jacket 40 water pump 41 water intake channel 41A water intake port 42 water supply channel 43 water test hole 51 outlet passage 52 thermostat valve 56 drain channel 57 drain port 60 bypass channel 70 bypass flow control mechanism 71 first Orifice (first throttle mechanism)
72 second orifice (second diaphragm mechanism)
73 pressure valve (valve mechanism)

Claims (8)

a water intake channel provided with a water intake;
a water pump for pumping cooling water from the water intake through the water intake channel;
an engine formed with a water jacket through which the cooling water passes;
a water supply passage for supplying the cooling water from the water pump to the water jacket;
an outlet passage through which the cooling water that has passed through the water jacket flows out;
a drainage channel through which the cooling water flowing out from the outlet passage flows, and a drainage port provided at a downstream end thereof;
The outboard motor, wherein the outlet passage is provided with a thermostat valve,
a bypass channel for circulating the cooling water from the drainage channel to the water intake channel;
a bypass flow rate adjustment mechanism that adjusts the flow rate of the cooling water flowing through the bypass path;
The bypass flow rate adjustment mechanism is provided in the bypass path and has a first throttle mechanism that throttles the flow rate of the cooling water, and a second throttle mechanism that is provided in the drainage path and throttles the flow rate of the cooling water. Outboard motor. The outboard motor according to claim 1,
The outboard motor, wherein the drainage channel is provided with a water test hole. 3. The outboard motor according to claim 1 , wherein
The outboard motor, wherein the first throttle mechanism is an orifice. The outboard motor according to any one of claims 1 to 3 ,
The outboard motor, wherein the second throttle mechanism is an orifice. The outboard motor according to any one of claims 1 to 4 ,
The outboard motor, wherein the first throttle mechanism is arranged in the vicinity of a junction of the bypass passage and the water intake passage. The outboard motor according to any one of claims 1 to 5 ,
The outboard motor, wherein the second throttle mechanism is arranged in the vicinity of the outlet passage of the drainage channel. a water intake channel provided with a water intake;
a water pump for pumping cooling water from the water intake through the water intake channel;
an engine formed with a water jacket through which the cooling water passes;
a water supply passage for supplying the cooling water from the water pump to the water jacket;
an outlet passage through which the cooling water that has passed through the water jacket flows out;
a drainage channel through which the cooling water flowing out from the outlet passage flows, and a drainage port provided at a downstream end thereof;
The outboard motor, wherein the outlet passage is provided with a thermostat valve,
a bypass channel for circulating the cooling water from the drainage channel to the water intake channel;
a bypass flow rate adjustment mechanism that adjusts the flow rate of the cooling water flowing through the bypass path;
The outboard motor, wherein the bypass flow control mechanism has a valve mechanism provided at a branching portion between the drainage channel and the bypass channel. The outboard motor according to claim 7 ,
The valve mechanism is a pressure valve,
when the pressure of the cooling water is less than a predetermined value, the pressure valve is closed and the cooling water does not flow to the drain port;
When the pressure of the cooling water is equal to or higher than a predetermined value, the pressure valve is in an open state, and the cooling water flows through the pressure valve to the drain port.

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