Marine propulsion device

A marine propulsion device (12) has an internal combustion engine (10) which includes a cooling water passage (20, 22, 32, 40) provided in an engine main body (14) of the internal combustion engine, a thermostat valve (34, 42) provided in the cooling water passage for opening and closing the cooling water passage according to a temperature of cooling water in the cooling water passage, and a cylindrical cooling water introduction member (96) surrounding the thermostat valves.

TECHNICAL FIELD

The present invention relates to a marine propulsion device, and in particular to a marine propulsion device having an internal combustion engine provided with an improved cooling system.

BACKGROUND ART

A water-cooled internal combustion engine is typically fitted with a thermostat valve that opens and closes a cooling water passage according to the temperature of the cooling water to maintain the engine temperature within a desired range for the optimum operation of the engine. The thermostat valve includes a housing typically made of a copper alloy while the engine main body is made of an aluminum alloy. Since copper and aluminum are far apart in the galvanic series, and aluminum has a greater tendency to undergo a galvanic reaction, an accelerated corrosion of the material of the engine main body surrounding the thermostat valve may be caused. This problem is particularly acute in internal combustion engines for marine propulsion devices which typically use the surrounding body of water including seawater for the cooling medium. Seawater is a highly electrolytic solution.

To overcome this problem, it was proposed in JP2015-86974A to enlarge the cross sectional area of the part of the cooling water passage where the thermostat valve is located so that the thermostat valve may be positioned far away from the inner wall of the cooling water passage.

However, when the cross sectional area of the cooling water passage near the thermostat valve is increased, a large temperature gradient may be created in the flow of the cooling water in a region immediate upstream of the thermostat valve. Therefore, the thermostat valve may be subjected to erratic changes in temperature with the result that the unstable operation of the thermostat valve such as hunting may be caused.

This has a negative impact on the durability of the thermostat valve, and may even impair the performance of the engine.

SUMMARY OF THE INVENTION

In view of such a problem of the prior art, a primary object of the present invention is to provide a marine propulsion device having an internal combustion engine provided with an improved cooling system in which galvanic corrosion of a part of the engine surrounding a thermostat valve thereof can be reduced in a favorable manner.

To overcome such a problem, a certain aspect of the present invention provides a marine propulsion device (12) having an internal combustion engine (10), the internal combustion engine comprising: a cooling water passage (20,22,32,40) provided in an engine main body (14) of the internal combustion engine; a thermostat valve (34,42) provided in the cooling water passage for opening and closing the cooling water passage according to a temperature of cooling water in the cooling water passage; and a cylindrical cooling water introduction member (96) surrounding the thermostat valves.

The cylindrical cooling water introduction member separates the thermostat valve from the surrounding wall surface of the cooling water passage so that the galvanic reaction between the thermostat valve and the surrounding wall surface can be minimized. Also, since the cooling water passage immediately upstream of the thermostat valve is not enlarged, the thermostat valve is prevented from hunting or otherwise behaving in an unstable manner.

Preferably, in this marine propulsion device, the cooling water introduction member is made of a material that has a higher ionization tendency (a greater tendency to undergo a galvanic reaction) than materials of the thermostat valve and the engine main body or is electrically insulating.

Thereby, progress of electrolytic corrosion of the engine main body is delayed, and the durability of the engine is improved.

Preferably, in this marine propulsion device, a cross-sectional area of a flow path defined between the cooling water introduction member and the thermostat valve is larger than an opening area of the thermostat valve when the valve is open.

Thereby, the cooling water is allowed to flow through the thermostat valve with an adequate flow rate, and an increase in pressure loss due to the cooling water introduction member can be avoided.

Preferably, in this marine propulsion device, the cooling water introduction member is provided with a tapered shape such that an inner diameter thereof progressively increases from an upstream side to a downstream side of the thermostat valve.

Thereby, a stable and smooth flow through the thermostat valve can be ensured. Furthermore, the process of mounting the cooling water introduction member can be facilitated.

Preferably, in this marine propulsion device, the cooling water introduction member extends further upstream than the thermostat valve.

Thereby, the inner wall of the cooling water passage surrounding the thermostat valve can be particularly favorably protected from galvanic corrosion.

Preferably, in this marine propulsion device, a part of the cooling water passage downstream of the thermostat valve is jointly defined by an outer surface (16A) of the engine main body having a first opening (32A) directly communicating with a part of the cooling water passage receiving the thermostat valve therein, and a second opening (38A) communicating with a part of the cooling water passage further downstream of the thermostat valve, a lid plate (51) attached to the outer surface of the engine main body and having a first hole and a second hole aligning with the first opening and the second opening, respectively, and a cover member (62) attached to the lid plate so as to define a communicating passage communicating the first opening with the second opening via the first hole and the second hole.

Thereby, the cooling water passage can be formed in such a manner that the assembling of the thermostat valve and the cooling water introduction member is facilitated. By forming the cooling water introduction member integrally with the lid plate, no gap is created between the two parts or there is no interface between the two parts. In particular, the cooling water that has passed along the thermostat valve is prevented from making a shortcut.

Preferably, in this marine propulsion device, the thermostat valve includes a body portion (76) defining a valve seat and provided with a radial flange (76A) in a downstream end part thereof, the radial flange being interposed between a shoulder surface (51A) of the lid plate and the cover plate.

Thereby, the cooling water passage can be formed in such a manner that the assembling of the thermostat valve and the cooling water introduction member is facilitated.

Preferably, in this marine propulsion device, the cooling water introduction member is integrally formed with the lid plate.

Thereby, the assembling of the cooling water passage can be facilitated.

Preferably, in this marine propulsion device, the cooling water introduction member is provided with a radial flange (96A) in a downstream end thereof, the radial flange being interposed between a shoulder surface (51A) of the lid plate and the radial flange of the thermostat valve.

Thereby, the assembling of the cooling water passage can be facilitated.

Preferably, in this marine propulsion device, the body part of the thermostat valve is made of plastic material, and the cooling water introduction member is integrally molded with the body part.

Thereby, the assembling of the cooling water passage can be facilitated.

Thus, the present invention provides a marine propulsion device having an internal combustion engine provided with an improved cooling system in which galvanic corrosion of a part of the engine surrounding a thermostat valve thereof can be prevented in a favorable.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A marine propulsion device (outboard motor) according to an embodiment of the present invention will be described in the following with reference to the appended drawings.

FIG.1shows a marine propulsion device10according to an embodiment of the present invention mounted on watercraft consisting of a boat1. The marine propulsion device10is encased in a housing2, and is mounted to the transom T of the boat1by using a per se known clamp mechanism4. The clamp mechanism4allows the marine propulsion device10to be swung sideways, and tilted up and down in a per se known manner.

An internal combustion engine12having a vertical crankshaft is provided inside the housing2. The output end of the crankshaft is connected to a drive shaft5that extends downward, and the lower end of the drive shaft5is connected to a gear mechanism6that transmits the power of the internal combustion engine12to a propeller shaft7that extends rearward from the gear mechanism6. The rear end of the propeller shaft7is fitted with a propeller8. The gear mechanism6not only transmits power from the drive shaft to the propeller shaft7, but also allows the rotational direction of the propeller shaft7to be reversed via a shift mechanism not shown in the drawings.

As shown inFIG.2, the internal combustion engine12consists of a water-cooled V-8 engine having a pair of banks of cylinders, and a crankshaft extending vertically in normal use.

The internal combustion engine12includes an engine main body14made of metal such as aluminum alloy. The engine main body14includes a cylinder block18defining cylinder bores therein, and a pair of cylinder heads16(seeFIG.3) for the respective cylinder banks.

As shown inFIGS.3to6, the cylinder head16of each cylinder bank is provided with a head-side cooling water passage20extending along either side of the corresponding cylinder row. The cylinder block18is provided with a bore-side cooling water passage22extending along either side of the cylinder row of each bank. The head-side cooling water passages20and the bore-side cooling water passages22both communicate with a cooling water supply passage24provided in a lower end part of the internal combustion engine12.

The cooling water for this internal combustion engine12is drawn from the surrounding body of water. For this purpose, a pump26is provided in a cooling water inlet passage30connected to the lower end of the cooling water supply passage24at one end thereof, and having a water inlet28at the other end thereof. The water inlet28is submerged in the water under normal condition, and is fitted with a filter29.

The cooling water supply passage24communicates with various parts of the internal combustion engine12which are required to be cooled, in addition to the head-side cooling water passages20and the bore-side cooling water passages22.

The cylinder head16of each cylinder bank is provided with a head-side cooling water discharge passage32that communicates with an upper end of the corresponding head-side cooling water passage20. The downstream end of the head-side cooling water discharge passage32opens at a flat surface16A of the cylinder head16, and defines an upper opening32A. Another opening or a lower opening38A is formed on this flat surface16A of the cylinder head16immediately under the upper opening32A. The lower opening38A communicates with an outlet passage38which is defined mostly in the cylinder head16. The downstream end of the outlet passage38communicates with a cooling water release passage36whose lower end is positioned so as to be submerged in the surrounding water.

A lid plate51made of plastic material is overlaid on the flat surface16A of the cylinder head16. The lid plate51is formed with a pair of holes54and56which are conformal to and aligned with the upper opening32A and the lower opening38A, respectively, and is attached to the flat surface16A by using bolts52. A cover member62is attached to the outer surface of the lid plate51by using bolts60. The inner surface of the over member62is provided with a cavity64which encompasses both the upper hole54and the lower hole56of the lid plate51(the upper opening32A and the lower opening38A).

A lower end part of the cover member62is provided with a hose nipple66extending downward to define a drain passage44therein. The drain passage44is connected to a downstream part of the cooling water release passage36via a hose48. To ensure water tight attachment of the lid plate51and the cover member62, a first seal member58is provided on the lid plate51so as to surround the upper opening32A and the lower opening38A, and a second seal member68is provided on the cover member62so as to surround the upper hole54and the lower hole56of the lid plate51.

Thus, a continuous passage extends from the head-side cooling water discharge passage32to the outlet passage38via the upper opening32A and the lower opening38A. the holes54and56in the lid plate51, and the cavity64of the cover member62.

The lid plate51is integrally formed with a cooling water introduction member96which is tubular in shape, and extends from the periphery of the upper hole54into the head-side cooling water discharge passage32via the upper opening32A. The cooling water introduction member96has a substantially constant wall thickness, and is slightly tapered such that the upstream end is slightly smaller in diameter than the downstream end thereof, or the inner diameter thereof progressively increases from an upstream side to a downstream side of the thermostat valve34.

The part of the outer surface of the lid plate51surrounding the upper hole54is recessed so as to form an annular shoulder surface51A which is recessed from the outer surface of the lid plate51. A thermostat valve34is positioned inside the cooling water introduction member96. The thermostat valve34is provided with a valve housing70. The valve housing70includes a disk-shaped body portion76centrally provided with an opening that defines a valve seat74(seeFIG.5). The disk-shaped body portion76of the thermostat valve34is provided with a radial flange76A that rests upon the annular shoulder surface51A of the lid plate51. The cover member62is provided with a peripheral flange and a projection62A projecting from the inner surface of the cover member62toward the lid plate51. When the lid plate51and the cover member62are assembled to the engine main body, the peripheral flange and the projection62A of the cover member62firmly press the radial flange76A of the thermostat valve34against the annular shoulder surface51A of the lid plate51.

The part of the head-side cooling water discharge passage32immediately upstream thereof is provided with a bullet-shaped flow guide98which is attached to the wall of the head-side cooling water discharge passage32by three legs (not shown in the drawings). The flow guide98smooths the flow of water along the thermostat valve34. The cover member62is provided with a stopper62B projecting from the bottom wall of the cavity64. The flow guide98additionally serves as a heat mass. In addition to reducing the flow resistance of the cooling water passage, the flow guide98warms the part of the cooling water that is about to flow into the thermostat valve34by the heat stored in the flow guide98so that the hunting of the thermostat valve34can be minimized.

The valve housing70further includes a frame portion78having a cage-like structure and extending into the head-side cooling water discharge passage32in the upstream direction inside the cooling water introduction member96. The valve housing70is made of a copper alloy which has a less tendency to undergo a galvanic reaction than aluminum.

A bottom end (upstream end) of the frame portion78is closed, and contains therein a temperature sensing element80which includes an elastomeric diaphragm84and a thermo-wax86enclosed between the bottom end of the frame portion78and the diaphragm84.

The thermostat valve34further includes a valve member90configured to cooperate with the valve seat74, a valve stem88extending from the valve member90into the frame portion78, a tubular spring retainer92surrounding and attached to the valve stem88, and having a radial flange92A at an end thereof remote from the valve member90, and a compression coil spring94surrounding the valve stem88and the spring retainer92, and interposed between an end of the frame portion78adjacent to the body portion76and the radial flange92A of the spring retainer92.

The thermo-wax86expands and contracts according to the temperature thereof in a reversible manner. When the temperature of the surrounding cooling water is low, the thermo-wax86is in the contracted state, and the valve member90closes the valve seat74under the spring force of the compression coil spring94. As a result, the thermostat valve34essentially closes the flow of the cooling water. As shown inFIG.5, the valve member90is provided with four recesses90A to allow a small amount of cooling water to flow through even when the valve member90is in the closed state. When the temperature of the surrounding cooling water is high, the thermo-wax86is in the expanded state, and pushes the free end of the valve stem88in the direction to lift the valve member90away from the valve seat74against the spring force of the compression coil spring94. The fully open position of the valve member90is determined by the abutting of the valve member90against the stopper62B projecting from the inner surface of the cover member62. As a result, the thermostat valve34freely allows the flow of the cooling water.

Preferably, the cross-sectional area of a flow path defined between the cooling water introduction member96and the thermostat valve34is larger than the opening area of the thermostat valve34when the valve is open. Thereby, the cooling water is allowed to flow through the thermostat valve34with an adequate flow rate, and an increase in pressure loss due to the cooling water introduction member96can be avoided.

The cylinder block18is provided with a bore-side cooling water discharge passage40, for each cylinder bank, that communicates with an upper end of the corresponding bore-side cooling water passages22. The downstream end of the bore-side cooling water discharge passage40opens at a flat surface of the cylinder block18, and defines an upper opening100. Another opening or a lower opening101is formed on this flat surface of the cylinder block18immediately under the upper opening100. The lower opening101communicates with an outlet passage39which is defined mostly in the cylinder block18. The downstream end of the outlet passage39is connected to the cooling water release passage36.

A lid plate102made of plastic material is overlaid on the flat surface of the cylinder block18. The lid plate102is formed with a pair of holes which are conformal to and aligned with the upper opening100and the lower opening101, respectively. A cover member106is overlaid on the outer surface of the lid plate102. The lid plate102and the cover member106are jointly attached to the cylinder block18by using bolts104. The inner surface of the cover member106is provided with a cavity which encompasses both the upper opening100and the lower opening101. Thus, a continuous passage extending from the bore-side cooling water passage22to the outlet passage39via the upper opening100and the lower opening101is defined by the lid plate102and the cover member62.

The lid plate102is integrally formed with a cooling water introduction member (not shown in the drawing) which is similar to that of the lid plate51. Another thermostat valve42is placed in the downstream end part of the bore-side cooling water discharge passage40surrounded by the cooling water introduction member. The mounting structure for the thermostat valve42is similar to that of the thermostat valve34for the head-side cooling water discharge passage32.

A lower end part of the cover member106is provided with a hose nipple108extending downward to define a drain passage46therein. The drain passage46is connected to a downstream part of the cooling water release passage36via a hose48. To ensure water tight attachment of the lid plate and the cover member, a first seal member is provided on the lid plate102so as to surround the upper opening100and the lower opening101, and a second seal member is provided on the cover member106so as to surround the upper hole and the lower hole of the lid plate102.

Since the structure, positioning and mode of operation of the thermostat valve42are similar to those of the thermostat valve34provided at the downstream end of the head-side cooling water discharge passage32, the description related to this thermostat valve42is omitted from this disclosure.

The mode of operation of the cooling system described above will be described in the following with reference toFIG.3.

The fresh water or seawater drawn by the cooling water pump26via the cooling water inlet28is filtered by the filter29, and forwarded to the cooling water supply passage24via the cooling water inlet passage30. The cooling water in the cooling water supply passage24is distributed to the left and right head-side cooling water passages20and to the left and right bore-side cooling water passages22.

The cooling water flowing through each head-side cooling water passage20cools the head portion of corresponding cylinder bank, passes through the head-side cooling water discharge passage32and reaches the corresponding head-side thermostat valve34. When the head-side thermostat valve34is open, the cooling water passes through the head-side thermostat valve34and flows through the outlet passage38to the cooling water release passage36.

The cooling water flowing through each bore-side cooling water passage22cools the bore portion of the corresponding cylinder bank, passes through the bore-side cooling water discharge passage40, and reaches the corresponding bore-side thermostat valve42. When the bore-side thermostat valve42is open, the cooling water passes through the bore-side thermostat valve42and flows through the outlet passage39to the cooling water release passage36.

The cooling water that has flowed into the cooling water release passage36is discharged from the lower end of the cooling water release passage36into the surrounding body of water. When the marine propulsion device10is tilted up with respect to the hull (not shown), the cooling water remaining in the head-side cooling water passages20and the bore-side cooling water passages22is drained to the cooling water release passage36via the thermostat valves34and42, the drain passages44and46, and the hoses48.

In the illustrated embodiment, the cooling water introduction member96surrounds the outer periphery of the thermostat valve34, and separates the thermostat valve34from the surrounding wall defining the head-side cooling water discharge passage32. Thereby, migration of ions between the surrounding wall (cylinder head) and the thermostat valve34, in particular the frame portion78thereof, is effectively prevented. As a result, the material of the surrounding wall which has a greater tendency to undergo a galvanic reaction than the frame portion78of the thermostat valve34is favorably protected from galvanic corrosion. In this regard, it is desirable that the upstream end of the cooling water introduction member96extends beyond the upstream end of the thermostat valve34. Thereby, the cooling water that contains hydroxide ions dissolved from the material of the thermostat valve at a high concentration is more effectively restricted from migrating to the side of the cylinder head16, with the result that a particularly high corrosion preventing result can be obtained.

Furthermore, the cooling water introduction member96prevents creation of spaces where cooling water may stagnate, and keeps the cooling water near the thermostat valve34to be concentrated in and around the thermostat valve34. As a result, creation of excessive temperature gradients around the thermostat valve34is prevented, and this contributes to the stable operation of the thermostat valve34free from hunting.

According to the present embodiment, the cooling water introduction member96is integrally formed with the lid plate51so that the assembly process is simplified, and the number of component parts can be reduced. In particular, the installing of the cooling water introduction member96can be performed with an improved precision.

The cooling water introduction member96has a tapered shape that decreases in diameter from the downstream side to the upstream side of the head-side thermostat valve34, thereby suppressing an increase in pressure loss and allowing stable control of the flow rate by the thermostat valve34. In addition, the process of installing the cooling water introduction member96in the head-side cooling water discharge passage32, and the process of installing the thermostat valve34into the cooling water introduction member96are both simplified.

The advantages mentioned above are equally applicable to the arrangement associated with the thermostat valve42provided at the downstream end of the bore-side cooling water discharge passage40.

FIG.7shows a modified embodiment of the present invention. In this case, the cooling water introduction member96is made of a separate member, instead of being an integral part of the lid plate51. The downstream end of the cooling water introduction member96is provided with a radial flange96A which is interposed between the radial flange76A of the thermostat valve34and the shoulder surface51A. In this case also, the main part of the cooling water introduction member96consisting of a tubular member has a taper such that the diameter of the cooling water introduction member96progressively decreases toward the upstream side, and extends beyond the upstream end of the thermostat valve34.

Since the lid plate51is simplified, and the cooling water introduction member96can be formed as a small component having a simple configuration, the manufacturing cost can be minimized, Since the cooling water introduction member96can be fixedly secured by interposing the radial flange96A of the cooling water introduction member96between the lid plate51and the shoulder surface51A, the assembling process can be simplified.

FIG.8shows another modified embodiment of the present invention. In this case, the disk-shaped body portion76of the thermostat valve34along with the radial flange76A thereof is made of plastic material while the remaining part of the thermostat valve34is generally made of a copper based alloy. While the metallic part of the thermostat valve is insert molded with the disk-shaped body portion76, the cooling water introduction member96is integrally molded with the disk-shaped body portion76. In other words, the cooling water introduction member96is integrally formed with the thermostat valve34.

Since the radial flange76A extends radially beyond the outer circumference of the cooling water introduction member96, the thermostat valve34can be fixedly secured by interposing the radial flange76A between the lid plate51and the shoulder surface51A. In this case also, the assembling process is simplified.

The present invention has been described in terms of specific embodiments thereof, but is not limited by such embodiments, and can be modified in various ways without departing from the scope of the present invention as can be readily appreciated by a person skilled in the art. For example, the cooling water introduction member96is not necessarily required to be integrally formed with the lid plate51, and may also be a separate member from the lid plate51. The cooling water introduction member96may also be made of other electrically insulating materials such as ceramic, or may be formed of a material having a higher ionization tendency (a greater tendency to undergo a galvanic reaction) than the material of the thermostat valve and the engine main body. Moreover, all of the components shown in the above embodiment are not necessarily essential, and can be appropriately substituted or omitted without departing from the spirit of the present invention. The contents of any cited references in this disclosure will be incorporated in the present application by reference.