Patent Publication Number: US-6699086-B1

Title: Coolant management system for a marine propulsion device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to a coolant management system and, more particularly, to a system and method for cooling the outer surface of an oil sump of an outboard motor by an amount that varies with the operating speed of an internal combustion engine of the outboard motor. 
     2. Description of the Prior Art 
     Four cycle engines are provided with an oil reservoir, or sump, which stores liquid lubricant that is used to lubricate moving components of the internal combustion engine and associated parts. It is important that the liquid lubricant is prevented from being overheated by heat generated by the internal combustion engine. It is also important that the temperature of the lubricant in the oil sump be prevented from falling below an appropriate operating range. Various systems and methods are known to those skilled in the art for controlling the operating temperature of a liquid lubricant within an oil sump. 
     U.S. Pat. No. 6,416,372, which issued to Nozue on Jul. 9, 2002, describes an outboard motor cooling system that includes an improved construction to enhance cooling of the lubricant system. It includes an oil pan of the lubrication system. The oil pan depends from an engine of the outboard motor and into a driveshaft housing. A periphery coolant jacket is provided around the oil pan. A water pool is defined between the oil pan and the driveshaft housing. An exhaust manifold passes through in a hollow of the oil pan and a water curtain is defined between the hollow wall and the exhaust manifold. An upstanding water passage is also disposed through the oil pan. At least one of an upper and lower transverse water jacket extends transversely above or below the oil pan. No drain water from the engine flows through these jackets or passages. The oil pan therefore is sufficiently cooled. In addition, the upper transverse water jacket increases protection of engine components form heat deterioration. 
     U.S. Pat. No. 6,182,631, which issued to Kitajima et al on Feb. 6, 2001, describes a camshaft for an engine. It also describes a cooling and exhaust system for the engine which are formed with a minimum number of components and sealing joints and which incorporate a non-metallic camshaft for reduced cost and weight without sacrificing durability. The exhaust system includes an elongated expansion chamber formed in the driveshaft housing. In addition, the driveshaft housing has a cylindrical section that is journaled within a swivel bracket for its steering movement. The volume between the external portion of the driveshaft housing and the internal portion of the swivel bracket forms a second expansion chamber that is employed for the low speed above the water exhaust gas discharge. The flow of cooling water to and from the engine is controlled so that the exhaust gas interchange area between the powerhead and the driveshaft housing will be well cooled as will the oil reservoir for the engine and the oil returned to it. 
     U.S. Pat. No. 6,012,956, which issued to Mishima et al on Jun. 9, 1998, describes a cooling water passage structure of an outboard motor. The outboard motor is equipped with an engine, an engine holder, an oil pan disposed below the engine in a state of the outboard motor being mounted to a hull, a water pump disposed below the oil pan, and a cooling water passage structure. The cooling water passage structure includes a vertical cooling water passage vertically passing through the inside of the oil pan and communicated with the side of the engine, a lateral cooling water passage extending in a lateral direction along a bottom surface of the oil pan, a cooling water supply pipe extending upward from the water pump and connected to a side of the engine, and a water pressure relief valve provided for the lateral cooling water passage for controlling a pressure increase of the cooling water. The lateral cooling waster passage has one end communicated with a lower end of the vertical cooling water passage and has another end to which an upper end of the cooling water supply pipe is connected. 
     U.S. Pat. No. 5,937,801, which issued to Davis on Aug. 17, 1999, discloses an oil temperature moderator for an internal combustion engine. A cooling system is provided for an outboard motor or other marine propulsion system which causes cooling water to flow in intimate thermal communication with the oil pan of the engine by providing a controlled volume of cooling water at the downstream portion of the water path. As cooling water flows from the outlet of the internal combustion engine, it is caused to pass in thermal communication with the oil pan. Certain embodiments also provide a pressure activated value which restricts the flow from the outlet of the internal combustion engine to the space near the oil pan. One embodiment of the cooling system also provides a dam within the space adjacent to the outer surface of the oil pan to divide that space into first and second portions. The dam further slows the flow of water as it passes in thermal communication with the oil pan. 
     U.S. Pat. No. 5,934,957, which issued to Sato et al on Aug. 10, 1999, describes an outboard motor having an oil pan positioned on the underside of the engine. It also has an exhaust passage, a water supply passage for cooling water, and a wastewater passage extending down from the engine and passing near the oil pan. The exhaust passage, the water supply passage, and the wastewater passage are molded as a single unit with the oil pan, and provide a simple, lightweight structure that does not result in an increase in the number of parts or assembly man hours necessary for construction. The oil pan is protected from the exhaust heat by the water passages, and a flush port to clean the cooling system is easily accessible. 
     U.S. Pat. No. 5,876,256, which issued to Takahashi et al on Mar. 2, 1999, describes an engine cooling system. A liquid cooling system for an internal combustion engine of an outboard motor includes a pump for delivering coolant to one or more coolant passages in the engine. At least one thermostat is provided for controlling the flow of coolant through the engine to one or more return lines which extend to a coolant pool extending about a lubricating oil reservoir. A pressure relief valve is provided between the pump and thermostat for relieving coolant from the engine upon excessive coolant pressure. The relief coolant is preferably either delivered to a drain, a second coolant pool extending about a muffler, or the first coolant pool. Preferably, a diverter is provided for controlling the flow of the relieved coolant. When a temperature of the lubricating oil is high, the relief coolant is preferably diverted to the first coolant pool for additional cooling of the oil in the reservoir, and when the temperature of the oil is low, the relieved coolant is preferably either diverted to the second coolant pool or the coolant drain for passage out of the motor. 
     U.S. Pat. No. 5,704,819, which issued to Isogawa on Jan. 6, 1998, describes an oil pan arrangement for a four cycle outboard motor. The outboard motor has a high performance V-type twin overhead cam four cycle internal combustion engine. The oil reservoir for the engine is disposed in a driveshaft housing below the engine and an oil pump is driven off the lower end of the engine crankshaft for circulating the oil from the oil tank to the engine. The oil supply system for the engine includes a vertically extending main gallery and a drain passage which extends in parallel side-by-side relationship and which are disposed over the oil tank for ease of oil return. The exhaust and cooling system for the engine is configured so as to minimize heat transfer between the exhaust system and the lubricating system and to maintain a compact assembly. 
     U.S. Pat. No. 5,487,687, which issued to Idzikowski et al on Jan. 30, 1996, discloses a midsection and cowl assembly for an outboard marine drive. The outboard marine drive has a midsection between the upper powerhead and the lower gearcase and has a removable midsection cowl assembly including first and second cowl sections. The midsection housing includes an oil sump in one embodiment and further includes an exhaust passage partially encircled by cooling water and partially encircled by engine oil for muffling engine exhaust noise. The midsection housing also has an oil drum arrangement providing complete and clean oil draining while the outboard drive is mounted on a boat and in the water wherein the operator can change oil without leaving the confines of the boat and entering the water. 
     U.S. Pat. No. 5,462,464, which issued to Ming on Oct. 31, 1995, describes an outboard motor with an oil sump cooling arrangement. A driveshaft housing includes outer side walls extending in spaced relation to each other, a forwardly located wall extending between the outer side walls, a rearwardly located wall spaced rearwardly from the forwardly located wall and extending between the outer side walls and a bottom wall extending between the outer side walls and between the forwardly and rearwardly located walls. The outer side walls, forwardly and rearwardly located walls, and bottom wall define an oil sump. A cooling passage extends vertically in one of the outer side walls. The forwardly located wall and the rearwardly located wall are adapted adjacent the upper end thereof for connection to a source of coolant. They terminate, at the lower end thereof, in a port located in the bottom wall and a deflector is fixed to the bottom wall and defines, with the bottom wall, a conduit extending along the bottom wall and having one end communicating with the coolant passage and a second end having an elongated discharge area, whereby to provide coolant flow along a substantial portion of the bottom surface of the bottom wall. 
     U.S. Pat. No. 5,439,404, which issued to Sumigawa on Aug. 8, 1995, describes a cooling system for an outboard motor. The cooling system for an outboard motor and specifically for the lubricating reservoir thereof is described. The lubricating reservoir depends into the driveshaft housing and is surrounded by an open trough-like water manifold to which cooling water is delivered from the engine. This manifold has lower restricted openings that direct the cooling water to the outer peripheral wall of the oil pan of the lubricant reservoir. The water level is maintained by a weir-like structure and the water that overflows the weir is also directed toward the outer surface of the lubricant reservoir. 
     U.S. Pat. No. 5,232,387, which issued to Sumigawa on Aug. 3, 1993, describes an exhaust device for a four cycle outboard motor. An arrangement is provided for the lubricating, cooling and exhaust systems of a four cycle outboard watercraft motor. Coolant is drawn from the body of water within which the watercraft is operated for circulation through the engine cooling system. Subsequently, the coolant is brought into proximity with an exhaust pipe extending downwardly from the engine within an encasing member. After passing downwardly along the exhaust pipe the coolant is finally directed towards an exhaust gas expansion chamber and a cooling water jacket provided around the expansion chamber. In order to prevent any of the cooling water from splashing back up against an oil reservoir, also located within the casing, a cover is provided across the tops of the expansion chamber and its accompanying cooling water jacket. Cooling water or air may fill the voids separating the various components contained within the encasing. The arrangement is particularly effective in preventing the corrosion of the oil reservoir housing due to back-splashed coolant when the watercraft is operated in saltwater; cooling the components contained within the encasing; and, minimizing heat transfer from higher temperature operating components to lower temperature operating components. 
     U.S. Pat. No. 5,215,164, which issued to Shibata on Jun. 1, 1993, describes a lubricating device for a four stroke outboard motor. A number of embodiments of outboard motors including dry sump lubricated four cycle internal combustion engines is described. The dry sump lubrication system includes a scavenge pump for drawing lubricant drained from the engine lubricating system through an inlet port and returns it to a dry sump reservoir through an outlet port and a pressure pump that draws lubricant from the dry sump lubricant reservoir through an inlet port and delivers it to the engine lubricating system through an outlet port. At least one of the ports of each of the pumps is positioned above the normal lubricant level in the lubricant reservoir when it is filled with the normal volume of lubricant so as to insure that lubricant will not drain back into the engine when the pump system is not operating. Various arrangements for achieving this result and for cooling the lubricant are described. 
     U.S. Pat. No. 4,735,590, which issued to Mondek on Apr. 5, 1988, describes a lubrication system for a marine propulsion device. The marine propulsion device comprises a propulsion unit including an internal combustion engine, a pump driven by the engine, a transom bracket for mounting the propulsion unit to the transom of a boat, a fluid reservoir carried by the transom bracket, a fluid cooler is carried by the transom bracket for cooling the fluid contained in the reservoir and a conduit for communicating the cooled oil to the pump is provided. 
     U.S. Pat. No. 4,498,875, which issued to Watanabe on Feb. 12, 1985, describes an outboard motor. Two embodiments of water cooled, four cycle internal combustion engines used for outboard motors is described. In each embodiment, an arrangement is provided that offers a compact nature and which issued the coolant delivered to the engine for cooling the oil in the oil pan. In addition, an arrangement is provided whereby the exhaust pipe may pass through the oil pan and yet avoid significant heat transfer from the exhaust system to the lubricating system. In each embodiment of the invention, coolant is delivered to this clearance for further cooling the exhaust system. In one embodiment of the invention, an arrangement is provided for limiting the discharge of coolant from the clearance so as to maintain a level of coolant around the exhaust pipe. 
     The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
     Although it is very important that the oil within an oil reservoir or sump is maintained at a temperature less than an upper limit which can degrade and deteriorate the lubricating characteristics of the oil, it is also very important that the oil in the oil sump or reservoir be maintained at a temperature above a lower limit. In certain situations, the oil in the oil sump can be cooled to an excessive degree, particularly when the internal combustion engine of the marine propulsion device is operating at a low speed. When the internal combustion engine is initially started and while it is operating at relatively low operating speeds, such as idle speed, it is beneficial if the oil in the oil reservoir is allowed to absorb sufficient heat to maintain its temperature within an appropriate temperature range. It would be significantly beneficial if a coolant management system could assist in maintaining the operating temperature of the oil in the oil sump within the desired temperature range while requiring a minimum number of components to accomplish this function. 
     SUMMARY OF THE INVENTION 
     A coolant management system for a marine propulsion device, made in accordance with a preferred embodiment of the present invention, comprises an internal combustion engine having a coolant passage disposed in thermal communication with at least one heat producing portion of the internal combustion engine, a water pump having an inlet connected in fluid communication with a body of water in which the marine propulsion device is operated and an outlet connected in fluid communication with the coolant passage. It also comprises a cavity formed within the marine propulsion device and an oil reservoir disposed at least partially within the cavity. An inlet passage is connected in fluid communication within the coolant passage and the cavity. A drain passage is connected in fluid communication with the cavity to allow the water to drain from the cavity and return to the body of water in which the marine propulsion device is operated. The drain passage is sized to cause the water within the cavity to rise to a level which is at least partially a function of the operating speed of the internal combustion engine, whereby the magnitude of the surface area of the oil reservoir disposed in thermal communication with the water within the cavity is a function of the operating speed of the internal combustion engine. 
     In a particularly preferred embodiment of the present invention, the system further comprises a first wall within the cavity which defines a first containment and a second containment. The inlet passage is positioned to conduct water from the coolant passage to the first containment. The drain passage is disposed in the second containment. 
     In a preferred embodiment of the present invention, the system further comprises a second wall disposed within the second containment to define a first compartment and a second compartment. The drain passage comprises a first opening in the first compartment and a second opening in the second compartment. The first wall has an upper edge that, in one embodiment, is generally straight and, in another embodiment, a portion of the oil reservoir, or sump, is lower than the upper edge of the first wall. The cavity is disposed within a driveshaft housing of the marine propulsion device which, in a preferred embodiment is an outboard motor. The method of the present invention for managing the coolant flow in a marine propulsion device, in a preferred embodiment, comprises the steps of providing a pump for drawing water from a body of water in which the marine propulsion device is operating, directing the water into thermal communication with an internal combustion engine of the marine propulsion device, conducting the water into a cavity formed within the marine propulsion device at a first rate of flow which is a function of the operating speed of the internal combustion engine, wherein the cavity is shaped to contain an oil reservoir of the internal combustion engine, and conducting the water out of the cavity at a second rate of flow, whereby the first and second rates of flow determine the height of a level of water within the cavity as a function of the operating speed of the internal combustion engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
     FIG. 1 is a simplified silhouette representation of a marine propulsion device; 
     FIGS. 2,  3 A, and  3 B illustrate a first embodiment of the present invention; 
     FIGS. 4,  5 A, and  5 B show a second embodiment of the present invention; 
     FIGS. 6,  7 A, and  7 B show a third embodiment of the present invention; 
     FIG. 8 is a section view of a driveshaft housing incorporating the present invention; 
     FIG. 9 is generally similar to FIG. 8 but with additional components illustrated; and 
     FIG. 10 is generally similar to FIG. 9, but with additional components illustrated. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
     FIG. 1 is a side view of an outboard motor  10 . The outboard motor  10  is shown in silhouette in order to allow the basic structure to be described. The outboard motor  10  is attachable to a transom  12  of a marine vessel. The outboard motor comprises a cowl structure  14  that encloses an internal combustion engine  20  and associated components. The cowl  14 , shown in FIG. 1, is a two piece cowl. The engine  20  is supported by an adapter plate which is located in the general vicinity identified by reference numeral  22 . A driveshaft  26  extends downwardly from the engine  20  for rotation about a vertical axis. The driveshaft  26  is contained within a driveshaft housing  30 . A gearcase  34  is supported below the driveshaft  30  and a propeller shaft (not shown in FIG. 1) is connected in torque transmitting relation with the driveshaft  26  and supported by the gearcase  34  for rotation about a propeller shaft axis  38 . A skeg  40  is located at the lowermost portion of the outboard motor  10 . As will be described in greater detail below, an oil sump is supported below the engine  20  and contained within a cavity of the driveshaft housing  30 . A water pump is connected in torque transmitting relation with the driveshaft  26  and draws water upwardly, through inlet openings in the gearcase  34 , and causes the water to be pumped upwardly toward the internal combustion engine  20  through appropriate conduits and into coolant passages formed within the structure of the engine  20 . The coolant passages within the internal combustion engine  20  can be in various shapes and configurations which are very well known to those skilled in the art. The coolant passages typically comprise cavities and channels cast into the structure of the engine block and cylinder head structure of the engine  20 . 
     The present invention will be described in terms of three alternative embodiments. One embodiment will be described below in conjunction with FIGS. 2,  3 A, and  3 B. Another embodiment will be described in conjunction with FIGS. 4,  5 A, and  5 B. A third embodiment will be described in conjunction with FIGS. 6,  7 A, and  7 B. FIGS. 2-7B are illustrated in a highly simplified schematic manner in order to allow the basic principles of the present invention to be described. Beginning with FIG. 8, the present invention will be described in conjunction with illustrations that more accurately depict a prototype of the present invention in the general form of the embodiment described in a more basic manner in conjunction with FIGS. 2,  3 A, and  3 B. 
     FIG. 2 is a section view, viewed in a downward direction through a structure  50 , within the driveshaft housing  30  that defines a cavity  52 . A first wall  56  within the cavity  52  defines a first containment  61  and a second containment  62 . In other words, the first wall  56  divides the cavity  52  into the first and second containments,  61  and  62 . A second wall  70  is disposed within the second containment  62  to define a first compartment  71  and a second compartment  72 . A drain passage comprises drain opening  81  and drain opening  82 . As can be seen, drain opening  81  is in the first compartment  71  and drain opening  82  is in the second compartment  72 . 
     FIG. 3A is a front section view of this structure  50  that defines the cavity  52 . FIG. 3B is a port side section view of the structure  50  with its internal components. In addition to the elements described above in conjunction with FIG. 2, an oil reservoir  90  is disposed at least partially within the cavity  52 . The oil reservoir  90  is an oil sump that contains a quantity of liquid lubricant for use in lubricating moving components of the internal combustion engine  20 . 
     An inlet passage  94  is schematically represented in FIGS. 3A and 3B for the purpose of showing the location at which water is conducted into the first containment  61  after it is passed through the coolant passages of the engine and through other conduits of the coolant system. The water flows through the inlet passage  94  into the first containment  61  and fills that containment to a level which is determined by both the upper edge  96  of the first wall  56  and the rate of flow of water from the inlet passage  94 . Although the inlet passage  94  is represented as a single conduit in FIGS. 3A and 3B, it should be understood that water can be directed to flow into the first containment  61  from more than one source. 
     In FIG. 3A, the second wall  70  is shown in dashed lines because it is located behind the first wall  56  in that figure. In FIG. 3B, the higher portion of the first wall  56  extends partially behind the oil reservoir  90 . As can be seen in FIGS. 3A and 3B, the upper edge  96  of the first wall  56  is curved. It has an upper end  100  and a lower end  102  which are represented by dashed lines in FIGS. 3A and 3B. It can also be seen that the lower surface of the oil reservoir  90  is slanted, with the front portion of the oil sump, represented by dashed line  106  being lower than the back edge of the bottom surface. Dashed line  108  represents the height of the second wall  70 . 
     In operation, water flowing through the entire cooling system, under the pressure provided by a water pump, flows into the first containment  61 . As a result, the water level in the first containment  61  will rise until it reaches a height coincident with dashed line  102 . At that height, the water can begin to spill over the first wall  56  from the first containment  61  into the second containment  62  and, more particularly, into the first compartment  71 . This spill over of water is represented by arrow  110  in FIG.  3 B. As the water pours over the upper edge  96  of the first wall  56  into the first component  71  of the second containment  62 , some of that water drains out of the first compartment  71  through drain opening  81 . If the water spilling over the upper edge  96  of the first wall  56  is insufficient to overcome the amount draining through the drain opening  81 , the water level within the first compartment  71  will not rise appreciably. However, if the rate of water flow from the inlet passage  94  is sufficiently high, the rate of water pouring over the upper edge  96  of the first wall  56  will be greater than the water draining through drain opening  81 . As a result, the water level within the first compartment  71  will rise until it eventually reaches the top  114  of the second wall  70 . The water will then begin to spill over the top  114  of the second wall  70  from the first compartment  71  into the second compartment  72  which has a much larger drain opening  82 . Depending on the rates of flow of water through the inlet passage  94 , the water level within the second compartment  72  may begin to rise as the water flowing into it exceeds the drain capacity of drain opening  82 . As a result, the water level within the cavity  52  will rise. 
     As the water rises within the cavity  52 , ever increasing magnitudes of the outer surface of the oil sump  90  are placed in contact with the water. Since the water rises within the cavity  52  as a function of the relative rates of flow of water through the inlet passage  94  and through the drain openings,  81  and  82 , the cooling effect on the oil reservoir  90  increases as a function of increasing engine speed. 
     With continuing reference to FIGS. 2,  3 A, and  3 B, dashed line arrows  120  represent the water draining through drain opening  81 , dashed line arrows  122  represent the water draining through drain opening  82 , and arrows  120  in FIG. 3B also represent the water draining through drain opening  81 . 
     It should also be understood that the rate of water draining through drain openings  81  and  82  is also affected by the height of the water level above those drain openings. In other words, the pressure head caused by the depth of water within cavity  52  affects the rate of draining. As a result, the flow rate of water flowing into the first containment  61  through the inlet passage  94 , in combination with the rate of flow through the drain passage will determine the height of water within the cavity  52 . These variables will also determine the amount of outer surface area of the oil sump  90  that is wetted by the rising water within cavity  52 . In many types of marine propulsion devices, the water pump operates at a speed that is directly related to the rotational speed of the driveshaft  26  because the water pump is connected in torque transmitting relation with the driveshaft  26 , usually by a set of gears. 
     FIGS. 4,  5 A, and  5 B show an alternative embodiment of the present invention that is similar to the embodiment shown in FIGS. 2,  3 A, and  3 B, but with several noticeable differences. First, as can be seen in FIG. 4, no second wall  70  is shown. Instead, the first wall  56  divides the cavity  52  into first and second containments,  61  and  62 . The drain passage comprises drain openings  81 . The second containment  62  is not divided into first and second compartments. With reference to FIGS. 5A and 5B, water is conducted into the first containment  61  by an inlet passage similar to the inlet passage  94  described above in conjunction with FIGS. 3A and 3B. The water level in the first containment  61  rises until it reaches the upper edge  96  of the first wall  56 . It then spills over the first wall  56 , as represented by arrow  110 , and begins to drain out through the drain openings  81 . If the drain openings  81  are appropriately sized, the level of water in the second containment  62  will depend on the relative rates of flow of cooling water through the inlet passage  94  and the flow of water through the drain openings  81 . When the engine is operating at a relatively high speed, the pump will create a flow of cooling water into the system that exceeds the rate at which the water is draining out of the second containment  62  through drain openings  81 . This will cause the water to rise and immerse some of the outer surface of the oil sump  90  in cooling water. At even higher speeds, the water level will rise sufficiently to immerse a greater amount of surface area of the oil sump  90  and thereby reduce the temperature of the oil. The relative positions of the top edge  96  of the first wall  56 , as represented by dashed line  100 , and the lowest portion of the oil sump  90 , represented by dashed line  106 , will determine the amount of surface area of the oil sump  90  that is in contact with the cooling water for various heights of water in the cavity  52 . 
     The embodiment shown in FIGS. 4,  5 A, and  5 B, differs from the previously described embodiment by the absence of the second wall  70  within the second containment  62  and the shape of the upper edge  96  of the first wall  56 , which is generally straight in FIG. 5A but curved in FIG.  3 A. In addition, the two drain openings  81  in FIG. 4 are generally equal in size while drain opening  82  in FIG. 2 is significantly larger than drain opening  81 . 
     Another embodiment of the present invention is shown in FIGS. 6,  7 A, and  7 B. Comparing this embodiment to the embodiment shown in FIGS. 2,  3 A, and  3 B, it can be seen that the first wall  56  in FIG. 7A has upper edges,  96 A and  96 B, which are located at different heights. Upper edge  96 A is identified by dashed line  100  while upper edge  96 B is identified by dashed line  102 . Drain opening  82  is noticeably larger than drain opening  81 . The other components shown in FIGS. 6,  7 A, and  7 B, are identified by the same reference numerals as used to describe and identify those same components in the Figures described above. 
     During operation, water is conducted into the first containment  61  by an inlet passage similar to the inlet passage  94  shown in FIGS. 3A and 3B. For the purpose of simplifying the illustrations, the inlet passage  94  is not shown in FIGS. 7A and 7B. As the first containment  61  fills with water, its level eventually reaches the upper edge  96 B, at which time it begins to spill over the upper edge  96 B as represented by arrow  110 . This water flows into the first compartment  71  of the second containment  62 . If the water flowing through the inlet passage  64  exceeds the rate of the water flowing out of drain opening  81 , the water level will rise to the upper edge  96 A of the first wall  56  and eventually will flow into the second compartment  72  from both the first containment  61  and the first compartment  71 . Again, as described above in conjunction with the first two embodiments, the water level rising within the cavity  52  will move into thermal communication with the outer surface of the oil sump  90  and this thermal communication will increase as a function of engine speed because the water pump operates at a speed that is directly related to the rotational speed of the driveshaft  26  which was described above in conjunction with FIG.  1 . 
     The three embodiments described above, in conjunction with FIGS. 2-7B, illustrate different ways in which the basic concepts of the present invention can be implemented to manage the coolant system of a marine propulsion device such as an outboard motor. 
     FIG. 8 is an actual containment  50  which implements the embodiment of the present invention described in conjunction with the simplified schematic representations in FIGS. 2,  3 A, and  3 B. The oil sump  90  is not shown in FIG.  8 . However, the first wall  56  with its upper edge  96  can be seen, extending from left to right, in its position to define the first containment  61  and second containment  62  within the cavity  52 . Represented by dashed lines, the second wall  70  is perpendicular to the representation in FIG.  8  and disposed behind the first wall  56 . As described above, the function of the second wall  70  is to divide the second containment  62  into first and second compartments,  71  and  72 . The illustration in FIG. 8 is a section view from the front of the outboard motor. An exhaust opening  130 . Reference number  134  identifies an anti-ventilation plate. 
     FIG. 9 is a section view, viewed from the front of the driveshaft housing, which is similar to the section view of FIG. 8, but with certain additional components added to the illustration. An adaptor plate  140  is shown at the top portion of FIG.  9 . As is generally known to those skilled in the art, the adaptor plate  140  is located within the outboard motor and supports the internal combustion engine  20 . The driveshaft housing  30  is supported downwardly from the adaptor plate  140 . In FIG. 9, an exhaust conduit  144  conducts exhaust gases downwardly through the driveshaft housing  30  from an opening in the adaptor plate  140 . The exhaust gases, which result from the operation of the internal combustion engine  20 , are conducted downwardly toward and through the exhaust opening  130 . A water jacket  146  surrounds a portion of the exhaust conduit  144 . The first wall  56  is shown in FIG. 9 directly behind the unjacketed portion of the exhaust conduit  144 . A pressure regulator is located in the compartment identified by reference numeral  150 . A drain conduit allows water to flow from the pressure regulator  150  to allow the water to drain into the first containment  61 . 
     FIG. 10 is a section view of a driveshaft housing  30  with the oil reservoir  90  disposed within a cavity  52 . An adaptor plate region  22  is shaped to support an internal combustion engine having a crankshaft disposed in torque transmitting relation with the driveshaft  26 . Although not directly related to the concepts of the present invention, FIG. 9 also shows a fuel vapor separator  160  attached to the aft portion of the driveshaft housing  30 . The water pump  170  has a rotatable portion that turns in coordination with the driveshaft  26  to pump water from a plurality of water inlets  180  in the gearcase  34 . The water is drawn into the inlets  180 , which is below water level, and pumped upwardly from the pump  170  to its outlet  182 . From the outlet  182  of the pump  170 , water is caused to flow upwardly through conduit  186  and, eventually, into cooling passages of the internal combustion engine  20  described above in conjunction with FIG.  1 . 
     With continued reference to FIG. 10, a propeller  190  is attached to a propeller shaft within the gearcase  34  for rotation about axis  38  as described above. A skeg  192  extends downwardly from the gearcase  34 . 
     The outboard motor, made in accordance with the preferred embodiment of the present invention, is subjected to various water levels within the cavity  52  of the driveshaft housing  30 , depend on the operating speed of the internal combustion engine  20  and the rotational speed of the driveshaft  26 . At higher rotational speeds of the driveshaft  26 , the pump  170  will provide cooling water to the engine at increasing rates of flow. These increasing rates of flow will result in the cooling water within the cavity  52  rising to increased heights around the oil reservoir  90 . The precise height of the water level within the cavity  52  and surrounding the oil reservoir  90  will vary as a function of the flow rate of coolant provided by the pump  170  to the coolant passages of the internal combustion engine  20 , the relative sizes of the drain openings,  81  and  82 , and the height of the water itself which provides a pressure head that can affect the rate at which water flows through the drain openings. As an example, when the internal combustion engine  20  is operating at maximum speed, one particularly embodiment of the present invention will cause the water within cavity  52  to rise to a level represented by dashed line  200 . A significant portion of the outer surface area of the oil reservoir  120  is submerged in water contained within the cavity  52  when the upper level of the water in the cavity is at dashed line  200 . In comparison, when the internal combustion engine  20  is operating at very low speeds, and the boat is still on plane, the level of water within the cavity  52  of the driveshaft housing  30  can fall to a level which is represented by dashed line  202 . At idle speed the driveshaft housing fills to the outside water level which can be as high or higher than line  200 . For purposes of reference, dashed line  204  represents the minimum height of water necessary to maintain the water pump  170  in a submerged state. Dashed line  106  illustrates the bottom edge of the oil reservoir  90 . 
     With reference to FIGS. 1-10, it can be seen that the present invention provides a coolant water management system for a marine propulsion device which causes the depth of water within the cavity  52  of the driveshaft housing  30  to vary in magnitude as a general function of the operating speed of the internal combustion engine  20 . At increased operating speeds, the water pump  170  draws water through inlet  180  at a rate which exceeds the rate of draining through various drain openings, such as those identified by reference numerals  81  and  82 . This causes the water level to rise within the cavity  52 . The rate at which water drains through the drain openings,  81  and  82 , is a function of the height of water above the drain passage. Therefore, as the water level within the cavity  52  of the driveshaft housing  30  increases, the rate of draining also increases. If the drain openings are properly sized, as appropriate high speed water depth  200  can be empirically determined for any particular style of propulsion device. The first and second walls,  56  and  70 , are used to divide the cavity  52  into first and second containments,  61  and  62 . The second wall  70 , in particular, is used to divide the second containment  62  into first and second compartments,  71  and  72 , in certain embodiments of the present invention. By directing coolant into the first containment  61 , after it is passed through various passages of the internal combustion engine and related components, the flow of coolant water from the engine can be sequentially directed to the first containment  61 , the first compartment  71  of the second containment  62 , and then the second compartment  72  of the second containment  62 . By appropriately placing the empirically sized drain openings,  81  and  82 , in the first and second compartments,  71  and  72 , of the second containment  62 , the water level within the cavity  52  can be selected for the range of operating speeds of the engine  20 . By controlling the depth of coolant within the cavity  52  of the driveshaft housing  30 , the amount of outer surface area of the oil reservoir  90  can be controlled. This, in turn, allows the rate of cooling of the oil within the oil reservoir  90  to be controlled as a function of engine speed. 
     Several different embodiments of the present invention have been described. A first embodiment is described in conjunction with FIGS. 2,  3 A, and  3 B. The second embodiment is described in conjunction with FIGS. 4,  5 A, and  5 B. A third embodiment is described in conjunction with FIGS. 6,  7 A, and  7 B. The embodiment illustrated in FIGS. 2,  3 A, and  3 B is illustrated in greater detail in FIGS. 8-10. 
     Although the present invention has been described with particular detail to show these various embodiments and has been illustrated with specificity, it should be understood that alternative embodiments are also within its scope.