Outboard motor cooling system

[0002] This application is based on and claims priority to Japanese Patent Application No. 10-324303 filed Nov. 16, 1998.

[0003] 1. Field of the Invention

[0004] This invention relates to an outboard motor cooling system, and more particularly to an improved cooling system for an oil pan that depends from an engine into a driveshaft housing of an outboard motor.

[0005] 2. Description of Related Art

[0006] An outboard motor generally comprises a drive unit which includes a power head disposed at its top portion, a driveshaft housing depending from the power head and a lower unit further depending from the driveshaft housing. The power head incorporates a powering engine therein and a protective cowling encircling the engine. The driveshaft housing has a driveshaft extending from an output shaft of the engine and downwardly therethrough to the lower unit. The lower unit carries a propulsion device such as a propeller which is mounted on a propeller shaft driven by the driveshaft. The driveshaft housing and the lower unit further contain some sections of an exhaust system for discharging exhaust gasses from the engine outwardly. Actually, exhaust passages and expansion chambers are formed therein and exhaust gasses are discharged to the body of water surrounding the outboard motor through, for example, a hub of the propeller.

[0007] The outboard motor further comprises a bracket assembly which includes a swivel bracket and a clamping bracket. The swivel bracket carries the drive unit for pivotal movement about a steering axis extending generally vertically. The clamping bracket is mounted on a transom of an associated watercraft and supports the swivel bracket for pivotal movement about a tilt axis extending generally horizontally.

[0008] Some outboard motors recently have employed four-stroke engines as prime movers for such motors. One reason for this tendency is that emissions from a four-stroke engines is cleaner relative to a two-stroke crankcase compression engine. The four-stroke engine typically has a separate oil pan for lubrication of the engine, and usually the oil pan depend from the engine into the driveshaft housing of the outboard motor. Lubricant is pumped to the engine by a lubricant pump and oil drains to the oil pan after lubricating the engine. Because the engine commonly operate at high temperatures, the returning lubricant heats the oil pan.

[0009] The outboard motor has a cooling system for cooling the engine with coolant, usually water. More specifically, a water pump is provided in the cooling system and water pumped up by the water pump from the body of water surrounding the outboard motor is delivered to the engine. Conventionally, the cooling system utilizes the same water that has already cooled the engine to cool the oil pan. For this purpose, the oil pan is usually surround by a coolant pool through which the water that has circulated through at least a portion of the engine flows. The coolant pool is formed between an outer wall of the oil pan and an inner wall of the driveshaft. Because the water is already hot, however, the oil pan is not significantly cooled. As a result, an outer wall of the driveshaft is likely to be heated, and can become discolored. This harms the appearance of the outboard motor.

[0010] In addition, an exhaust manifold, which is one of the sections of the exhaust system, is positioned to pass through the oil pan. The exhaust gasses flowing through this exhaust manifold also are hot and further heat the oil pan. The heat sink provided by the water passing through the coolant pool in a conventional system therefore may not be sufficient to prevent discoloration of the driveshaft housing and overheating of the lubricant.

[0011] Other components of the outboard motor also are affected by the elevated temperature of the oil pan within the drive shaft housing. For instance, such heat may also affect an upper mount of the steering assembly. The steering assembly includes both an upper mount and a lower mount, which are affixed on the drive unit to pivotally support it on the swivel bracket. A steering shaft extends through forward portions of the respective mounts and a steering shaft housing disposed at the rear of the swivel bracket. Rear portions of the respective mounts are affixed to the forward portion of the driveshaft housing so as to be spaced apart vertically from each other. The rear portions contain elastic elements to absorb vibrations generated by the engine and the propeller or shocks exerted upon the drive unit, and to prevent transfer of such to the associated watercraft. The upper mount is usually positioned above and in the proximity to the oil pan. The elastic members of the upper mount tends to be deteriorated by heat transferred from the oil pan. Other components, particularly electrical components, within the protective cowling may be also damaged by the heat.

[0012] The present outboard motor cooling system enhances cooling of the oil pan vis-a-vis conventional outboard motor cooling systems. The cooling system also desirably inhibits discoloration of a driveshaft housing of the outboard motor, as well as deterioration of components positioned above the oil pan, such as, for example, but without limitation, elastic members of an upper mount and engine components.

[0013] In accordance with one aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes a periphery coolant jacket generally surrounding the oil pan and being supplied with coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the periphery coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.

[0014] In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes an upstanding coolant passage extending generally vertically through the oil pan and the cooling system supplies coolant to the engine through the upstanding coolant passage.

[0015] In accordance with an additional aspect of the present invention, an outboard motor comprises a power head having an internal combustion engine. A housing depends from the power head and supports a propulsion device driven by the engine for propelling an associated watercraft. An oil pan contains lubricant for lubrication of the engine. The oil pan depends into the housing and is spaced from the housing. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes a coolant pool defined between the oil pan and the housing. The cooling system supplies coolant that has not cooled the engine to the coolant pool. The cooling system further includes a coolant discharge jacket bypassing the coolant pool. Coolant that has cooled the engine passes through the coolant discharge jacket.

[0016] In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. An exhaust system is provided for discharging exhaust gasses from the engine. The exhaust system includes an exhaust passage that passes through the oil pan. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes means for forming a heat sink between the exhaust passage and the oil pan when the engine is operated. In this manner, the amount of heat transfer between the exhaust passage and the oil pan is reduced, i.e., the oil pan and the exhaust passage generally are thermally decoupled from each other.

[0017] In accordance with yet another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system cools at least the engine and the oil pan. The cooling system includes a lower transverse coolant jacket that extends generally transversely below the oil pan. The cooling system supplies coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the lower transverse coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.

[0018] In accordance with a further aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system cools at least the engine and the oil pan. The cooling system includes an upper transverse coolant jacket extending generally transversely above the oil pan. The cooling system supplies coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the upper transverse coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.

[0019] Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follow.

[0020] These and other features of this invention will now be described with reference to the drawings of a preferred embodiment which is intended to illustrate and not to limit the invention.

[0021] FIG. 1 is a side elevational view showing an outboard motor in accordance with an embodiment of this invention. An engine, a driveshaft housing and a lower unit are shown largely in cross-section and some components are shown in a wire-frame format. An associated watercraft is also shown partially in section.

[0022] FIG. 2 is a diagram showing a flow of coolant through a cooling system employed in the outboard motor.

[0023] FIG. 3 is an enlarged cross-sectional side view of the driveshaft housing and shows an oil pan and some sections of the cooling system and an exhaust system in the outboard motor. Some components are shown in a wire-frame format again.

[0024] FIG. 4 is a top plan view showing an exhaust guide member of the outboard motor.

[0025] FIG. 5 is a top plan view showing the same exhaust guide member of FIG. 4 on which a pair of upper mount members are disposed.

[0026] FIGS. 6(A) and 6(B) illustrate the exhaust guide member. FIG. 6(A) is a side elevational view showing an appearance of the exhaust guide member looked from the position indicated by the arrow 6(A) in FIG. 5. FIG. 6(B) is a cross-sectional, side elevational view thereof taken along the line 6(B)—6(B) in FIG. 5.

[0027] FIG. 7 is a bottom plan view showing the same exhaust guide member of FIG. 4 on which the pair of upper mount members are disposed.

[0028] FIGS. 8(A), 8(B) and 8(C) illustrate a cover member which covers over an upper side of the oil pan. FIGS. 8(A), 8(B) and 8(C) are a top plan view, a cross-sectional side view taken along the line 8(B)—8(B) in FIG. 8(A) and a bottom plan view, respectively.

[0029] FIGS. 9(A), 9(B) and 9(C) illustrate the oil pan and are a top plan view, a bottom plan view and a cross-sectional rear view taken along the line 9(C)—9(C) of FIG. 9(A), respectively. An oil filter and an exhaust manifold are removed in this figure.

[0030] FIGS. 10(A), 10(B), 10(C) and 10(D) illustrate a lower plate attached to the bottom of the oil pan. FIGS. 10(A), 10(B), 10(C) and 10(D) are a top plan view, a side view taken along the line 10(B)—10(B) of FIG. 10(A), a bottom plan view and a cross-sectional rear view taken along the line 10(D)—10(D) of FIG. 10(A), respectively.

[0031] FIGS. 11(A), 11(B) and 11(C) illustrate a first exhaust expansion chamber member and are a top plan view, a cross-sectional side view taken along the line 11(B)—11(B) in FIG. 11(A) and a cross-sectional front view taken along the line 11(C)—11(C) in FIG. 11(A), respectively.

[0032] With reference initially to FIG. 1, the general overall environment of an exemplary outboard motor will be described. In connection with the following description, including the appended claims, the terms “front,” “forward” and “forwardly” means at or toward the side where the clamping bracket 92 is located. The terms “rear” and “rearwardly” mean at or toward an opposite side of the front side unless stated otherwise.

[0033] An outboard motor 20 is shown as attached to a transom 22 of an associated watercraft 24. The outboard motor 20 generally comprises a drive unit 26 and a bracket assembly 28. The drive unit 26 includes a power head 30, a driveshaft housing 32 and a lower unit 34. The power head 30 is disposed at the top of the drive unit 26 and includes an internal combustion engine 38, a top protective cowling 40 and a bottom protective cowling 42.

[0034] The engine 38 is of the V6 type and operates on a four-stroke principle. The engine 38 comprises a cylinder block 46 that is formed with a pair of cylinder banks. Each of these cylinder banks defines three vertically spaced, horizontally extending cylinder bores 48 in which pistons reciprocate. The pistons are, in turn, connected to an output shaft or crankshaft 50 via connecting rods. The crankshaft 50 is journaled for rotation and extends generally vertically within a crankcase 52 which closes a forward opening of the cylinder block 46.

[0035] A cylinder head assembly 56 is affixed to the cylinder block 46 to close the other end of the cylinder block 46. The cylinder head assembly 56 defines a plurality of recesses in its inner face. Each of these recesses cooperate with the respective cylinder bore 48 and the head of the piston to define a combustion chamber. The cylinder head assembly 56 has intake ports and exhaust ports. The intake ports are provided for introducing air fuel mixture to the combustion chambers, while the exhaust ports are provided for discharging exhaust gasses from the combustion chambers. Intake valves 58 and exhaust valves (not shown) are provided for opening and closing the intake ports and exhaust ports. A camshaft 60 is journaled on the cylinder head assembly 58 to operate the intake valves 58 and exhaust valves. The intake valves 58 and exhaust valves are opened when cam lobes 64 of the camshaft 60 push them at proper timings. The camshaft 60 is driven by the crankshaft 50 by means of a timing belt 66.

[0036] An air induction system is provided for introducing air to the combustion chambers. The air induction system generally comprises a plenum chamber 70 and air intake ducts 72 which correspond to the respective cylinder bores 48. Carburetors or fuel injectors are provided between the plenum chamber 70 and the intake ports for supplying fuel with the air to make an air fuel charge for combustion in the combustion chambers.

[0037] Although not shown, spark plugs are affixed on the cylinder head assembly 56 for firing the air fuel charge. A generator 74 is placed at the top of the crankshaft 50 for generating electric power that is applied to the spark plugs and other electrical equipment.

[0038] Burnt charges or exhaust gasses are discharged through an exhaust system. Some sections of the exhaust system are contained in the driveshaft housing 32 and will be described below.

[0039] Since these types of four stoke engines are well known in the art, a further description is not believed to be necessary to permit those skilled in the art to practice the invention.

[0040] The top and bottom cowlings 40, 42 generally completely encircle the engine 38 to protect it. For instance, water is prevented from splashing over the engine 38. The top cowling 40 is detachably affixed to the bottom cowling 42 so as to ensure access to the engine 38 for maintenance.

[0041] The driveshaft housing 32 depends from the power head 30 and the lower unit 34, in turn, depends from the driveshaft housing 32. A driveshaft 78 extends generally vertically through the driveshaft housing 32 and is driven by the crankshaft 50. The driveshaft 78 drives a propeller shaft 80 which extends generally horizontally within the lower unit 34 through a forward, neutral, reverse transmission 82 including a bevel gear. The propeller shaft 80 has a propeller 84 at its outer end. Thus, the propeller 84 is powered by the engine 38 through the driveshaft 78 and propeller shaft 80.

[0042] The drive unit 26 is mounted on the associated watercraft 24 by the bracket assembly 28 which comprises a swivel bracket 90 and a clamping bracket 92. The swivel bracket 90 carries the drive unit 20 for pivotal movement about the axis of a steering shaft 94 which extends generally vertically through a steering housing section 96 of the swivel bracket 90. An upper mount 100 and a lower mount 102 are affixed on the drive unit 26 to pivotally support it on the swivel bracket 90. That is, the steering shaft 94 extends through forward portions of the respective mounts 100, 102 and the steering shaft housing section 96 disposed at the rear of the swivel bracket 90. The steering shaft 94 is fitted in the forward portions of the respective mounts 100, 102 in spline connections. Meanwhile, rear portions of the respective mounts 100, 102 are affixed to the forward portion of the driveshaft housing 32 so as to be spaced apart vertically from each other. The rear portions of the respective mounts 100, 102 contain elastic elements 104 to absorb vibrations generated by the engine 38 and the propeller 84 or shocks exerted upon the drive unit 26 and prevent them from being conducted to the associated watercraft 24. A steering lever 106 extends forwardly from the upper mount 100 so that an operator of the outboard motor 20 can steer it with the lever 106. A throttle control lever (not shown) may be also attached on the steering lever 106.

[0043] The clamping bracket 92 is mounted on the transom 22 of the associated watercraft 24 and supports the swivel bracket 90 for pivotal movement about the axis of a tilt shaft 108. A hydraulic tilt device 110 is affixed between the swivel bracket 90 and the clamping bracket 92 for tilt and trim movements of the drive unit 26.

[0044] The hydraulic tilt device 110 comprises a housing having a cavity, a piston slidably supported within the cavity and a piston rod affixed on the piston and extends beyond the cavity. The housing is affixed to a pivot shaft 120 which extends generally horizontally and journaled on a lower portion of the clamping bracket 92 for pivotal movement. The piston rod, in turn, is affixed to a pivot shaft 122 which also extends generally horizontally and is journaled on and between upper portions of the clamping bracket 92 and the swivel bracket 90 for pivotal movement.

[0045] When the piston rod expands and contracts with the reciprocal movement of the piston, the drive unit 26 as well as the swivel bracket 90 is tilted up or down within a trim adjusted range or a tilt range. The tilt range exists higher than the trim adjusted range. In the view of FIG. 1, because the drive unit 26 is in a fully trimmed down position, the swivel bracket 90 almost entirely conceals itself within the clamping bracket 92.

[0046] The bottom cowling 42 is configured as a tray-shape. At the bottom of the bottom cowling 42, an exhaust guide member 126 is affixed. The engine 38 is anchored to the exhaust guide member 126. An Exhaust manifold 128 depends from the exhaust guide member 126. The exhaust ports of the cylinder head assembly 56 communicate with the exhaust manifold 128. A first exhaust expansion chamber 130 is defined in an expansion chamber member 131 disposed downstream of the exhaust manifold 128 within the driveshaft housing 32. A second expansion chamber 132 is defined downstream of the first expansion chamber 130 and in the lower unit 34.

[0047] Exhaust gasses from the exhaust ports of the cylinder head assembly 56 are collected by the exhaust manifold 128 and then flow through the exhaust expansion chambers 131, 132. When passing through the expansion chambers 131, 132, the exhaust gasses are expanded and lose their energy. Exhaust noise is attenuated accordingly. The exhaust gasses are finally discharged to the body of water surrounding the outboard motor 20 through a bore 134 formed in a hub of the propeller 84.

[0048] As is typical, the outboard motor 20 includes a lubrication system provided for lubricating engine components. An oil pan 138 depends from the exhaust guide member 126 although a cover member 140 is inserted between the guide member 126 and the oil pan 138. The upper mounts 100 are positioned above and in the proximity to the oil pan 138. Further, engine components exist above the upper mounts 100 within the protective cowlings 40, 42. A lower member 144 is affixed to the bottom of the oil pan 138. The structure of the oil pan 138 including the cover member 140 and the lower member 144 will be described in more detail shortly.

[0049] Lubricant is reserved in this oil pan 138 and an lubricant pump 146 is provided around the driveshaft 78 for circulating the lubricant in the oil pan 138 within the engine 38. The lubricant pump 146 is driven by the driveshaft 78.

[0050] The lubricant is pumped up from the oil pan 138 by the lubricant pump 146 and circulates around internal portions of the engine for lubrication of engine components such as the crankshaft 74, piston and the camshaft 60. The lubricant then returns to the oil pan 138 again.

[0051] The outboard motor 20 further has a cooling system for cooling down heated components including engine components, exhaust system components and the oil pan 138. The water out of and surrounding the motor 20 is utilized as coolant for this cooling system. The cooling system includes a water pump 150, a pressure control valve 152, a water inlet port 154, a water outlet port 156, water supply conduits or jackets and drain conduits or jackets. The water pump 150 is provided around the driveshaft 78 to be driven thereby. Although the cooling system will be described in more detail later, a supply conduit 158, a water pool 160 and drain jacket 162 are shown in FIG. 1.

[0052] It should be noted that basically the components including the power head 30 except the top cowling 40, driveshaft housing 32, the lower unit 34, the exhaust guide member 126, the oil pan 138, the cover member 140, lower member 144, the exhaust manifold 128 and the exhaust expansion chamber member 131 are made of metal such as aluminum alloy. In addition, they are assembled with each other by bolt connections whether they are shown or not.

[0053] With reference to FIGS. 2 through 11, the structure or construction of the oil pan 138 and the cooling system will be described.

[0054] For easy understanding of the exhaust gas flow paths and water channels, these components will be indicated by suffix letters after the respective reference numerals which are assigned in these figures. The respective letters will indicate the specific exhaust gas flow or water channels as follows:

[0055] (a): exhaust gas flow;

[0056] (b): water channel from the water pump 150 before a branch to the pressure control valve 152;

[0057] (c): water channel to the engine 38 after the branch to the pressure control valve 152;

[0058] (d): water channel discharged from the engine 38;

[0059] (e) and (g): water channel branched off from the channel (c) to an internal wall 166 (see FIG. 9(C)) in the oil pan 138 surrounding the exhaust manifold 128:

[0060] (f): water channel branched off from the channel (b) and having the pressure control valve 152;

[0061] (k): water channel branched off from the channel (b) to a periphery water jacket 138k.

[0062] Incidentally, letters (i), (j), (o) and (z) are also assigned to indicate an inlet port, a water jacket, an outlet port and lubricant reservoir, respectively.

[0063] With reference to FIG. 2, the flow of cooling water in these channels (a) to (k) will be described. The water is introduced into the cooling system by operation of the water pump 150. The water goes through the channel (b) toward the channel (c). Before reaching the channel (c), some water goes to the pressure control valve 152 in the channel (f). The pressure control valve 152 includes a ball 172 and a spring 174 that urges the ball 172 to close the channel (f) and only permits a water flow from the channel (b) to the channel (f) when the pressure of the water is greater than a preset magnitude. Meanwhile, the water that has reached the channel (c) is directed into one of two banks, each of which goes to exhaust passages 176 of the cylinder bores 48. The water then passes along the periphery of an exhaust collector portion 180 and the combustion chambers 182. The water joins together downstream of the combustion chambers 182 and again is split to the banks and still goes to the respective cylinder bores 48. Downstream of the cylinder bores 48, thermostats 184 are provided in both split channels (c). The thermostats 184 open unless water temperature is lower than a preset value (for example, more than 60° C.) and the water goes to the discharge channel (d). If the water temperature is lower than the preset value, the thermostats 184 will not open (a very small amount can still flow under this condition) and the water pressure exceeds the predetermined magnitude to open the pressure control valve 152. The pressure is relieved accordingly by the pressure control valve 152 and the water, in turn, goes to the channel (f).

[0064] It should be noted that the pressure control valve 152 may open for other reasons and that an only condition for opening of the pressure control valve 152 is that the pressure of the water flowing the channels exceeds the preset magnitude.

[0065] The actual water channels (b) to (k), as well as the exhaust gas flow (a), will be described by reference to FIGS. 3 through 11.

[0066] As seen in FIGS. 4 through 7, the exhaust guide member 126 has a pair of recesses 190 to receive the upper mount 100. A bore 126ais formed at almost the center position of the exhaust guide member 126 through which the exhaust gasses flow downwardly. In front of the bore 126aand also at both lateral sides of the bore 126a, slits 126eare formed. Also, behind the bore 126a, a pair of openings 126care formed. A pair of discharge openings 126dare formed at both outer sides of the lateral slits 126efurther. The pressure control valve 152 is affixed on the exhaust guide member 126 in a valve chamber 188.

[0067] As best seen in FIG. 3, the oil pan 138 is affixed to the cover member 140 by bolts 192 and anchored to the exhaust guide member 126 along with the cover member 140 and also the exhaust manifold 128 by bolts 194. The cover member 140 not only covers the oil pan 138 but also forms an upper transverse water jacket 126fj(see FIGS. 7 and 8(A)) with the exhaust guide member 126 therebetween. A pair of inlet ports 126fifor the water jacket 126fjare formed at both sides of the pressure control valve 152 in the valve chamber 188. A water channel 126bis also formed under the pressure control valve 152 (see FIG. 6) at the bottom of the exhaust guide member 126. The water flowing through the channel 126b, thus, passes through the pressure control valve 152 if it is opened and flows into the upper transverse water jacket 126fj. If the pressure control valve 152 is not opened, the water flowing the channel 126bgoes to the channel (c) including the openings 126c. The channel (c) is formed in the cover member 140 as described shortly.

[0068] As seen in FIGS. 8(A), 8(B) and 8(C), the cover member 140 has a bore 140acommunicating with the bore 126a, three slits 140ecommunicating with the slits 126eand a pair of openings 140cocommunicating with the openings 126c. The channel (c) or 140cis formed as a hollow passage and runs from the rear to the forward in the cover member 140. The water flows therethrough and goes out from the openings 140cotoward the engine 38. A conduit 140bpasses through the conduit 140bvertically and hence an inlet port 140biand an outlet port 140boare defined at both lower and upper ends. A pair of discharge openings 140dcommunicating with the discharge openings 126dare further formed at both outer sides of the lateral slits 140e. The conduit 140chas an opening 140gelongating transversely at its forward end bottom portion.

[0069] The upper transverse water jacket 126fjhas a certain extent that can isolate the oil pan 138 from the upper mount 100 and extends generally horizontally. To put it more precisely, it slightly inclines forwardly. Drains 140fare formed at the most forward and rear portions of the jacket 126fj. The water flowing through the transverse water jacket 126fj, therefore, can remove the heat existing at the upper portion of the oil pan 138. Besides, the upper transverse jacket 126fjprevents the heat in the oil pan 138 from being radiated to the upper mount 100.

[0070] As seen in FIG. 8(C), the drains 140fexist out of a circular rib 198 which meets with a circular rib 200 (see FIG. 9(A)) of the oil pan 138 so that no water falls down into a lubricant reservoir 138zof the oil pan 138.

[0071] As described above, the oil pan 138 depends from the cover member 140. The lubricant reservoir 138zis configured generally as a circular shape so as to make the hollow 202 at its center portion. The hollow 202 narrows at its top portion to form an inner flange 204 there. An opening 138astill exists therein. Bolt holes 206 are provided at the four corners of the inner flange 204 and the bolts 194 are affixed therethrough. The exhaust manifold 128 extends generally vertically through the hollow 202.

[0072] Slits 138ecommunicating with the slits 140eof the cover member 140 are formed in front of the opening 138aand also both sides thereof. An aperture 138gcommunicating with the opening 140gis also formed behind the opening 138a. The water branched off from the channel (c) and passing through the slits 126e, 140e, 138e, the opening 140gand the aperture 138gfalls down along the wall 166 of the hollow 202. This down flow of the water makes a water curtain between the wall 166 of the hollow 202 and the exhaust manifold 128. The heat that the exhaust manifold 128 as well as the exhaust gasses passing therethrough holds is prevented from conducting to the lubricant reservoir 138z.

[0073] The oil pan 138 has a periphery water jacket 138k. Actually, as best seen in FIG. 9(B), the periphery water jacket 138kconsists of three jacket sections and generally surrounds the lubricant reservoir 138z. The periphery water jacket 138kis unitarily formed with the oil pan 138 and extends upwardly from the bottom of the oil pan 138 and almost halfway thereof.

[0074] The water to the periphery water jacket 138kis supplied from the supply conduit 158 (see FIG. 3) through a lower transverse water jacket 144bj(see FIG. 10(A)) which is formed between the bottom of the oil pan 138 and the lower member 144. For this purpose, the lower member 144 is affixed to the oil pan 138 by bolts, although they are not shown. The lower transverse water jacket 144bjhas a certain extent like the upper transverse water jacket 126fjand extends generally horizontally. It may slightly incline rearwardly.

[0075] Drains 138ko(see FIG. 3) are formed at each top portion of the jacket sections of the periphery water jacket 138kand the water overflowing in the periphery water jacket 138kis drained to the water pool 160 defined between the oil pan 138 and the driveshaft housing 32.

[0076] The periphery water jacket 138kis effective to remove the heat held by the oil pan 138 because it is unified with the oil pan 138 and fresh water is supplied thereto. The term “fresh” means that the water has not circulated within the engine 38 and is directly supplied from the water pump 150.

[0077] The oil pan 138 has an upstanding water passage 138bat the rear thereof. The remainder of the water that does not go to the periphery water jacket 138kflows into this upstanding water passage 138band goes up toward the upper transverse water jacket 126fj. As a matter of course, the water passing through the upstanding passage 138bis fresh and hence the heat in the oil pan 138 is removed more effectively. Besides, the isolation of the upper mount 100 from the heat of the oil pan 138 is also achieved efficiently, because this fresh water may flow through the upper transverse water jacket 126fj.

[0078] The water drained to the water pool 160 from the periphery water jacket 138kis discharged to the second expansion chamber 132 or directly to the water outlet port 156 through apertures 205, 207 formed at almost the bottom portion of the driveshaft housing 32 (see FIG. 3). The water drained to the second expansion chamber 132 is discharged to the body of water surrounding the outboard motor 20 through the bore of the propeller 84 with exhaust gasses. Meanwhile, the water drained to the outlet port 156 is directly to the surrounding water. However, because the apertures 205, 207 are relatively small, usually the water accumulates in the water pool 160. An overflow port 160do(see FIG. 9(C)) is formed at nearly the top portion of the discharge passage 138dof the oil pan 138. When the water in the water pool 160 reaches the level of the overflow port 160do, it flows into the discharge passage 138d. The water pool 160 is particularly effective for preventing the driveshaft housing 32 from being discolored, although it is still effective for removing the heat of the oil pan 138.

[0079] The water discharge passages 138dextends downwardly therethrough. The discharge passages 138dcommunicate with the discharge openings 140dof the cover member 140. Thus, the water circulated around the engine water jackets flows down through the discharge openings 126dof the exhaust guide member 126, the discharge openings 140dof the cover member 140 and the discharge passages 138dtoward the lower member 144.

[0080] As seen in FIG. 3, an oil strainer 208 is affixed to the bottom of the cover member 140 so as to exist in the lubricant reservoir 138z. A strainer element 210 is fitted at the inlet portion of the strainer 208. Lubricant in the oil pan 138 is supplied to the engine 38 through the strainer 210 by the lubricant pump 146. Foreign particles are removed by the strainer element 210 before entering the lubricant pump 146.

[0081] As seen, for example, in FIG. 10(A), the lower member 144 has a bore 144acommunicating with the exhaust manifold 128 through which the exhaust gasses pass. Around the bore 144a, a water receiver 144eis formed. The water of the water curtain falling down along the wall 166 of the hollow 202 is received by this water receiver 144e. The water receiver 144ehas a drain slit 144eoin front of the exhaust bore 144aand a pair of drain apertures 144ehat sidelong behind thereof. Further around the water receiver 144e, the lower transverse water jacket 144bjis formed. An inlet opening 144bifor the water jacket 144bjis provided at the most forward portion of the lower member 144.

[0082] The opposite side (bottom) of the lower member 144 is mated with the top of the exhaust expansion chamber member 131. A water discharge jacket 144dcommunicating with the discharge openings 144diis formed on this side with the exhaust expansion chamber member 131 so as to collect the drain behind the exhaust bore 144a. The drain apertures 144ehare also opened to the water discharge jacket 144d.

[0083] As seen in FIGS. 11(A) through 11(C), the exhaust expansion chamber member 131, in turn, has a discharge opening 131d. The discharge opening 131dis connected with the drain jacket 162 (see FIG. 3) in the driveshaft housing 32. The water going down through the drain jacket 162 is, then, discharged to the body of water surrounding the outboard motor 20 through the water outlet port 156 formed in the lower unit 34. The expansion chamber member 131 has also a slit 131ewhich communicates with the slit 144eof the lower member 144 and the water coming down through the slit 131egoes down to the second expansion chamber 132 through the aperture 205 and is finally discharged to the surrounding body of water.

[0084] At the most forward portion of the expansion chamber member 131, an opening 131bis formed and the top of the supply conduit 158 is fitted therein (see FIG. 3). The water passing up through the water conduit 158 is supplied to the lower transverse water jacket 144bj.

[0085] The first expansion chamber 130 is defined in the expansion chamber member 131 as described above. The capacity of the expansion chamber 130 is relatively large and the exhaust gasses passing through the exhaust manifold 128 is abruptly expanded in this chamber 130. Because of this, energy of the exhaust gasses is released and exhaust noise is reduced accordingly. The lower end of this chamber 130 is narrowed and the second expansion chamber 132 again has a large capacity. The same situation, therefore, occurs again in this second expansion chamber 132.

[0086] In summary, exhaust gasses from the engine 38 are collected by the exhaust manifold 128 and are directed down to the first exhaust expansion chamber 130 and then the second exhaust expansion chamber 132. Finally, they are discharged to the body of water surrounding the outboard motor 20 through the bore 134 formed in the hub of the propeller 84.

[0087] On the other hand, cooling water is introduced from the surrounding water through the water inlet port 154 by the water pump 150 and goes up to the lower transverse water jacket 144bjformed between the lower member 144 and the bottom of the oil pan 138 through the supply conduit 158. The water flows transversely below the oil pan 138 within the lower transverse water jacket 144bjand then primarily goes up to the engine 38 through the upstanding water passage 138b. Some of the water, however, goes to the periphery water jacket 138k. If the pressure control valve 152 is opened, the reminder of the water flows transversely through the upper transverse water jacket 126fjformed between the cover member 140 and the exhaust guide member 126.

[0088] Before going to the engine 38, some water is branched off and falls down through the slits 126e, 140e, 138e, the opening 140gand the aperture 130galong the wall 166 of the hollow 202 in the oil pan 138. By this flow, the water curtain is made. The water then goes down through the slit 144eor the drain jacket 162 to the apertures 205, 206 to be discharged.

[0089] The water discharged from the engine 38 goes down through the water discharge jacket comprising the openings 126d, 140dand the discharge passage 138d. The water discharge jacket bypasses the periphery water jacket 138k, the water pool 160 and the upper and lower transverse water jackets 126fj, 144bj.

[0090] The water in the periphery water jacket 138kis discharged to the water pool 160 through the drains 138k. Also, the water passing through the upper transverse water jacket 126fjis discharged to the water pool 160 through the drains 140f. Then, the water goes to the apertures 205, 207 to be discharged or flows into the discharge passage 138dthrough the overflow port 160doand then yes to the aperture 207.

[0091] As described above, the oil pan 138 is surrounded by the periphery water jacket 138kin one aspect of the present invention and the water pool 160 in another aspect thereof. The water curtain is also made to prevent the heat of the exhaust manifold 128 from conducting to the oil pan 138 in a further aspect of this invention. Also, the upper transverse water jacket 126fjand/or the lower transverse water jacket 144bjare provided in other aspects of the present invention. Further, the cooling water supplied to the engine 38 passes through the upstanding passage 138bwhich is disposed through the oil pan 138. No drain water from the engine 38 passes through these water jackets or flows as the water curtain. The water from the engine 38 rather flows through the water discharge jacket comprising the openings 126d, 140dand the discharge passage 138d. Thus, the oil pan 138 in the cooling system of the embodiment is cooled down more powerfully than in the conventional cooling system.

[0092] Also, the water pool 160 is defined between the oil pan 138 and the driveshaft housing 32 and the water into the water pool 160 has not been circulated within the engine 38. This water pool 160 can, therefore, prevent the driveshaft housing 32 from becoming discolored.

[0093] Further, the upper transverse water jacket 126fjis disposed above the oil pan 138 and hence the radiant heat of the oil pan 138 is precluded from being radiated to the components within the protective cowling 40. The components cannot be jeopardized by the heat of the oil pan 138. If the upper mount 100 is positioned above the upper transverse water jacket 126fjlike in this embodiment, the elastic members 104 of the upper transverse water jacket 126fjis also prevented from being deteriorated by the heat of the oil pan 138. In other words, the elastic members 104 should not have greater heat-resistance. The nature of anti-vibration can be given much priority in selecting a material for the elastic member 104.

[0094] Although this invention has been described in terms of a certain preferred embodiment, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims that follow.