Abstract:
A marine outboard engine is described, having an engine disposed in a cowling. The engine has a cooling system. A first pump is disposed inside the cowling below a water line of the outboard engine. The first pump is continuously driven by the engine during operation of the engine. The first pump is a centrifugal pump having an inlet in fluid communication with an exterior of the marine outboard engine below the water line and an outlet in fluid communication with the cooling system. A second pump is disposed inside the cowling below the water line. The second pump has an inlet in fluid communication with an exterior of the marine outboard engine below the water line and an outlet in fluid communication with the cooling system. An electric motor is operatively connected to the second pump for selectively driving the second pump during operation of the engine.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/109,780, filed Oct. 30, 2009, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to cooling systems for marine outboard engines, in particular marine outboard engines having open loop cooling systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    An internal combustion engine, such as those used in marine outboard engines, is powered by the combustion of fuel in one or more cylinders. During the operation of such an engine, the heat generated by the combustion of fuel in the cylinders must be dissipated to prevent overheating of the engine and consequent damage to engine components. Other components of the engine, such as fuel system, exhaust pathways, and electronics, can also experience an increase in temperature during use and require cooling to maintain normal operation. 
         [0004]    One common method of providing cooling in marine applications is with an open loop cooling system. Water is pumped from the body of water in which the engine is operating, for example using a pump driven by either the crankshaft or the driveshaft of the engine. Referring to  FIGS. 1A and 1B , one commonly used type of pump is a hybrid pump  10  that combines attributes of a centrifugal pump and a positive displacement pump. The pump  10  involves a flexible impeller  12  eccentrically mounted inside a housing  14 . At low speeds ( FIG. 1A ), the impeller  12  is in contact with the housing  14  and the pump  10  acts as a positive displacement pump. At high speeds ( FIG. 1B ), the impeller  12  flexes away from the housing  14  and the pump  10  acts as a centrifugal pump. As a result, this pump design provides a flow of water over a wide range of rotational speeds, but with lower efficiency than either a displacement pump at low speeds or a centrifugal pump at high speeds. The water is pumped to one or more components that require cooling, such as a water jacket of the engine, an exhaust manifold and electronic components. The water is then returned to the body of water. 
         [0005]    While this arrangement is adequate for cooling the engine, it has some drawbacks. The water drawn in by the pump  10  may contain salt or debris that can damage the impeller  12 , for example by getting caught between the impeller  12  and the housing  14  and causing wear on the impeller  12 , resulting in reduced flow of cooling water or even failure of the pump, potentially damaging the engine. In the event of damage to the pump  10 , the pump is often difficult to access and service because it is typically located above the cavitation plate of the engine so that it can be conveniently driven by the crankshaft or driveshaft. In addition, while the pump  10  is operational at all speeds, it may not provide a sufficient flow of water for adequate cooling, particularly at very low speeds when the speed of the pump  10  may not be sufficient to deliver the required volume of cooling water, and at very high speeds when the pump  10  experiences reduced efficiency. One alternative design, a centrifugal pump, is less susceptible to wear but provides insufficient cooling at low speeds. 
         [0006]    Therefore, there is a need for a method of providing improved cooling to a marine engine over a wide range of engine speeds. 
         [0007]    There is also a need for a marine engine having improved cooling over a wide range of engine speeds. 
         [0008]    There is also a need for a pump assembly requiring low maintenance and being easy to service and repair. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
         [0010]    In one aspect, the invention provides a method of cooling a marine outboard engine, the marine outboard engine comprising a cowling. An engine is disposed in the cowling. The engine has a cooling system. A driveshaft is disposed generally vertically. The driveshaft has a first end and a second end. The first end of the driveshaft is operatively connected to the engine. A gear case is disposed generally below the engine. Water is continuously pumped during operation of the engine from a body of water to the cooling system using a first centrifugal pump operatively connected to the engine and disposed below a water line of the outboard engine. Water is selectively pumped during operation of the engine from a body of water to the cooling system using a second pump operatively connected to an electric motor and disposed below the water line in response to at least one of: a current engine temperature being above a predetermined threshold temperature; a current engine speed being below a predetermined threshold engine speed; and a current speed of a watercraft to which the marine outboard engine is attached being above a predetermined threshold speed. Water is delivered from the cooling system to the body of water. 
         [0011]    In a further aspect, selectively pumping the water using the second pump includes selectively pumping the water to an outlet of the second pump in fluid communication with an outlet of the first pump and upstream of the cooling system. 
         [0012]    In a further aspect, the first pump is primed using the second pump upon starting the engine. 
         [0013]    In a further aspect, selectively the pumping water using the second pump includes pumping water using the second pump only in response to a current engine speed being below a predetermined threshold speed. 
         [0014]    In a further aspect, the predetermined threshold speed is 1500 RPM. 
         [0015]    In a further aspect, pumping the water using the first pump to the cooling system includes pumping the water using the first pump to a water jacket of the engine. Selectively pumping the water using the second pump to the cooling system includes pumping the water using the second pump to the water jacket of the engine. 
         [0016]    In an additional aspect, the invention provides a marine outboard engine, comprising a cowling. An engine is disposed in the cowling. The engine has a cooling system. A driveshaft is disposed generally vertically. The driveshaft has a first end and a second end. The first end of the driveshaft is operatively connected to the engine. A gear case is disposed generally below the engine. A propeller shaft is disposed in the gear case and operatively connected to the second end of the driveshaft. A propeller mounted to the propeller shaft. A first pump is disposed inside the cowling below a water line of the outboard engine. The first pump is continuously driven by the engine during operation of the engine. The first pump is a centrifugal pump having an inlet in fluid communication with an exterior of the marine outboard engine below the water line and an outlet in fluid communication with the cooling system. A second pump is disposed inside the cowling below the water line. The second pump has an inlet in fluid communication with an exterior of the marine outboard engine below the water line and an outlet in fluid communication with the cooling system. An electric motor is operatively connected to the second pump for selectively driving the second pump during operation of the engine. 
         [0017]    In a further aspect, the electric motor drives the second pump when a current engine temperature is above a predetermined threshold engine temperature. 
         [0018]    In a further aspect, the electric motor drives the second pump when a current rotational speed of the engine is below a predetermined threshold rotational speed. 
         [0019]    In a further aspect, the outlet of the first pump fluidly communicates with the outlet of the second pump at a point upstream of the cooling system. 
         [0020]    In a further aspect, a cavitation plate is disposed generally above the gear case. The outlet of the first pump fluidly communicates with the outlet of the second pump above the cavitation plate. 
         [0021]    In a further aspect, the first and second pumps are self-priming pumps. 
         [0022]    In a further aspect, the first pump is driven by the propeller shaft. 
         [0023]    In a further aspect, the inlet of the first pump fluidly communicates with the front of the gear case. 
         [0024]    In this application, the term “water line” refers to the water level with respect to an outboard engine when the outboard engine is mounted on a watercraft with the drive shaft oriented vertically and the watercraft is at rest. 
         [0025]    Embodiments of the present invention each have at least one of the above-mentioned objects and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present invention that have resulted from attempting to attain the above-mentioned objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein. 
         [0026]    Additional and/or alternative features, aspects, and advantages of embodiments of the present invention will become apparent from the following description, the accompanying drawings, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
           [0028]      FIGS. 1A and 1B  are cross-sectional views of a prior art pump, operating at low and high speeds respectively; 
           [0029]      FIG. 2  is a side elevation view of a marine outboard engine to which the present invention can be applied; 
           [0030]      FIG. 3  is a side elevation view of a marine outboard engine showing a pump assembly according to a first embodiment; 
           [0031]      FIG. 4  is a side elevation view of a marine outboard engine showing a pump assembly according to a second embodiment; 
           [0032]      FIG. 5  is a side elevation view of a marine outboard engine showing a pump assembly according to a third embodiment; and 
           [0033]      FIG. 6  is a side elevation view of a marine outboard engine showing a pump assembly according to a fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Referring to  FIG. 2 , a marine outboard engine  40  will be described to which the present invention can be applied. It should be understood that the present invention is applicable to other marine applications, such as inboard engines and stern drives. 
         [0035]      FIG. 2  is a side view of a marine outboard engine  40  having a cowling  42 . The cowling  42  surrounds and protects an engine  44 , shown schematically. The engine  44  may be any suitable engine known in the art, such as an internal combustion engine. An exhaust system  46 , shown schematically, is connected to the engine  44  and is also surrounded by the cowling  42 . 
         [0036]    The engine  44  is coupled to a vertically oriented driveshaft  48 . The driveshaft  48  is coupled to a drive mechanism  50 , which includes a transmission  52  and a bladed rotor, such as a propeller assembly  54  (shown schematically) mounted on a propeller shaft  56 . The propeller shaft  56  is generally perpendicular to the driveshaft  48 . A cavitation plate  57 , disposed generally above the gear case  68  and below the water line W, extends above the propeller assembly  54  to prevent air above the surface of the water from entering the flow of water in the vicinity of the propeller assembly  54  and potentially damaging the propeller assembly  54 . 
         [0037]    Other known components of an engine assembly are included within the cowling  42 , such as a starter motor and an alternator. As it is believed that these components would be readily recognized by one of ordinary skill in the art, further explanation and description of these components will not be provided herein. 
         [0038]    A stern bracket  58  is connected to the cowling  42  via a swivel bracket  59  for mounting the outboard engine  40  to a watercraft. The stern bracket  58  and swivel bracket  59  can take various forms, the details of which are conventionally known. 
         [0039]    A linkage  60  is operatively connected to the cowling  42 , to allow steering of the outboard engine  40  when coupled to a steering mechanism of a boat, such as a steering wheel. 
         [0040]    The cowling  42  includes several primary components, including an upper motor cover  62  with a top cap  64 , and a lower motor cover  66 . A lowermost portion, commonly called the gear case  68 , is attached to the exhaust system  46 . The upper motor cover  62  preferably encloses the top portion of the engine  44 . The lower motor cover  66  surrounds the remainder of the engine  44  and the exhaust system  46 . The gear case  68  encloses the transmission  52  and supports the drive mechanism  50 . 
         [0041]    The upper motor cover  62  and the lower motor cover  66  are made of sheet material, preferably plastic, but could also be metal, composite or the like. The lower motor cover  66  and/or other components of the cowling  42  can be formed as a single piece or as several pieces. For example, the lower motor cover  66  can be formed as two lateral pieces that mate along a vertical joint. The lower motor cover  66 , which is also made of sheet material, is preferably made of composite, but could also be plastic or metal. One suitable composite is fiberglass. 
         [0042]    A lower edge  70  of the upper motor cover  62  mates in a sealing relationship with an upper edge  72  of the lower motor cover  66 . A seal  74  is disposed between the lower edge  70  of the upper motor cover  62  and the upper edge  72  of the lower motor cover  66  to form a watertight connection. 
         [0043]    A locking mechanism  76  is provided on at least one of the sides of the cowling  42 . Preferably, locking mechanisms  76  are provided on each side of the cowling  42 . 
         [0044]    The upper motor cover  62  is formed with two parts, but could also be a single cover. As seen in  FIG. 2 , the upper motor cover  62  includes an air intake portion  78  formed as a recessed portion on the rear of the cowling  42 . The air intake portion  78  is configured to prevent water from entering the interior of the cowling  42  and reaching the engine  44 . Such a configuration can include a tortuous path. The top cap  64  fits over the upper motor cover  62  in a sealing relationship and preferably defines a portion of the air intake portion  78 . Alternatively, the air intake portion  78  can be wholly formed in the upper motor cover  62  or even the lower motor cover  66 . 
         [0045]    Referring now to  FIG. 3 , the water pump arrangement of the outboard engine  40  will be described according to a first embodiment. 
         [0046]    A primary water pump, in the form of a centrifugal pump  102 , is disposed in the gear case  68 . The pump  102  is driven by the rotation of the propeller shaft  56 . It is contemplated that the axis of the pump  102  may be offset from the axis of the propeller shaft  56 , with a gear reduction arrangement (not shown) disposed therebetween. As a result, the pump  102  is in continuous operation when the engine  44  is in operation. In order to maintain the continuous operation of the pump  102 , it is preferable for the propeller assembly  54  to be a variable pitch propeller assembly such as the one described in U.S. patent application Ser. No. 11/962,372, which is incorporated herein by reference in its entirety. This variable pitch propeller assembly allows the outboard engine  40  to provide thrust in either the forward or the reverse direction, as well as a neutral position, without reversing the direction of rotation of the propeller shaft  56  or disengaging the propeller shaft  56  from the engine  44 . It is contemplated that continuous operation of the pump  102  may alternatively be provided in other ways, which will be described below in further detail. The pump  102  draws water from the surrounding body of water through a primary inlet  104 , preferably located at the front of the gear case  68 . The pump  102  pumps the water upwardly through the primary outlet  106 , toward the cooling system  120  of the engine  44 . 
         [0047]    An auxiliary water pump, in the form of a positive displacement pump  108 , is also disposed in the gear case  68 . Alternative positions of the pump  108  are also contemplated, and will be described below with reference to alternative embodiments. The pump  108  is driven by an electric motor  110 , which is controlled by an electronic control unit (“ECU”)  202  of the engine  44 . The ECU  202  preferably causes the pump  108  to operate at times when the pump  102  is either expected or observed to provide insufficient water flow. The pump  108  may be caused to operate when the engine is operating at low speeds, preferably below 1500 RPM, when the pump  102  experiences reduced efficiency. The pump  108  may also be caused to operate when the watercraft is traveling at a speed below a predetermined threshold speed, such as below 5 miles per hour, including when the engine is in a neutral or reverse mode, when the pump  102  may not provide enough water to cool the engine. The pump  108  may also be caused to operate when an elevated temperature is detected by the ECU  202 , indicating the need for additional cooling. The pump  108  may also be caused to operate at engine startup, as will be described below in further detail. When the pump  108  is in operation, the pump  108  draws water from the surrounding body of water through the auxiliary inlet  112 , and pumps the water upward through the auxiliary outlet  114 . In conditions when the pump  102  would normally provide adequate cooling for the engine  44 , such as during cruising at high speeds, the ECU  202  does not cause the pump  108  to operate, and water is supplied to the cooling system  120  only by the pump  102 . It is contemplated that the pump  108  may include a check valve (not shown) to prevent water flow from the outlet  106  into the outlet  114  and out of the engine via the inlet  112  without first passing through the cooling system  120 . It is contemplated that the pump  108  may alternatively operate at all times when the engine  44  is operating. 
         [0048]    The outlets  106 ,  114  of the pumps  102 ,  108  fluidly communicate at a point  116  located above the cavitation plate  57 , and extend upwardly from the point  116  via a common conduit  118 . In this configuration, the pump  108  can be operated at engine startup to prime the pump  102  by pumping water to the point  116 , which then descends via the primary outlet  106  toward the pump  102  to fill the pump  102  with water. It is contemplated that the pump  102  may alternatively be self-priming, in which case the pump  102  may include a check valve (not shown) to prevent water flow from the outlet  114  into the outlet  106  and out of the engine via the inlet  104  without first passing through the cooling system  120 . The conduit  118  supplies water to a cooling system  120  (shown schematically) of the engine  44 . The cooling system  120  may include water passageways arranged to cool one or more components of the engine  44  that either generate heat or require cooling due to the heat generated by surrounding components. Components for which the cooling system  120  provides cooling may include the engine  44  via a water jacket  204 , the exhaust manifold  206  of the engine  44 , one or more fuel injectors or carburetors  208  that supply fuel to the engine  44 , a lubrication system  209  of the engine  44 , and or one or more electronic systems  210  such as the ECU  202  that are electrically connected to the engine  44 . After the water from the conduit  118  has cooled one or more components of the cooling system  120 , the water is returned to the body of water via an outlet (not shown) in a known manner. 
         [0049]    Referring now to  FIG. 4 , the water pump arrangement of the outboard engine  40  will be described according to a second embodiment. 
         [0050]    A primary water pump, in the form of a centrifugal pump  302 , is disposed in the gear case  68 . The pump  302  is driven by the rotation of the propeller shaft  56 , similarly to the pump  102  of  FIG. 3 . The pump  302  draws water from the surrounding body of water through a primary inlet  304 , preferably located at the front of the gear case  68 . The pump  302  pumps the water upward through the primary outlet  306  toward the cooling system  320  (shown schematically) of the engine  44 . 
         [0051]    An auxiliary water pump, in the form of a positive displacement pump  308 , is disposed above the cavitation plate  57  and below the water line W. The pump  308  is driven by an electric motor  310 , which is controlled by the ECU  202 . The ECU  202  controls the pump  308  in a similar way to the auxiliary pump  108  of  FIG. 3 . When the pump  308  is in operation, the pump  308  draws water from the surrounding body of water through the auxiliary inlet  312 , and pumps the water upward through the auxiliary outlet  314 . 
         [0052]    In this embodiment, the outlets  306 ,  314  of the pumps  302 ,  308  do not fluidly communicate upstream of the cooling system  320  (shown schematically) of the engine  44 . In this embodiment, it is preferred that the pumps  302 ,  308  both be self-priming pumps. Each outlet  306 ,  314  supplies a separate flow of water to the cooling system  320 . The cooling system  320  includes the same components as the cooling system  120  of  FIG. 3 , and as such will not be described again in detail. After the water from either or both of the outlets  306 ,  314  has cooled one or more components of the cooling system  320 , the water is returned to the body of water via an outlet (not shown) in a known manner. 
         [0053]    Referring now to  FIG. 5 , the water pump arrangement of the outboard engine  40  will be described according to a third embodiment. 
         [0054]    A primary water pump, in the form of a centrifugal pump  402 , is disposed above the cavitation plate  57  and below the water line W. The pump  402  is disposed around the drive shaft  48  and is driven by the rotation of the drive shaft  48 . It is contemplated that the pump  402  may be driven by a gear reduction arrangement, in which case the axis of the pump  402  may be offset from the axis of the drive shaft  48 . In this arrangement, the pump  402  remains in continuous operation while the engine  44  is in operation, even if the drive shaft  48  is disengaged from the propeller assembly  54  or the direction of rotation of the propeller shaft  56  is reversed by the transmission  52  disposed in the gear case  68 . The pump  402  draws water from the surrounding body of water through an inlet  404  disposed in the gear case  68 . The pump  402  pumps the water upward through the primary outlet  406  toward the cooling system  420  (shown schematically) of the engine  44 . 
         [0055]    An auxiliary water pump, in the form of a positive displacement pump  408 , is disposed above the cavitation plate  57  and below the water line W. The pump  408  is driven by an electric motor  410 , which is controlled by the ECU  202 . The ECU  202  controls the pump  408  in a similar way to the auxiliary pump  108  of  FIG. 3 . When the pump  408  is in operation, the pump  408  draws water from the surrounding body of water through the inlet  404 , and pumps the water upward through the auxiliary outlet  414 . 
         [0056]    The outlets  406 ,  414  of the pumps  402 ,  408  fluidly communicate at a point  416  located above the cavitation plate  57 , and extend upwardly from the point  416  via a common conduit  418 . In this configuration, the pump  408  can be operated at engine startup to prime the pump  402  in the same manner as the pump  108  of  FIG. 3 . The conduit  418  supplies water to the cooling system  420  (shown schematically) of the engine  44 . The cooling system  420  includes the same components as the cooling system  220  of  FIG. 3 , which will not be described again in detail. After the water from the conduit  418  has cooled one or more components of the cooling system  420 , the water is returned to the body of water via an outlet (not shown) in a known manner. 
         [0057]    Referring now to  FIG. 6 , the water pump arrangement of the outboard engine  40  will be described according to a fourth embodiment. 
         [0058]    A primary water pump, in the form of a centrifugal pump  502 , is disposed in the gear case  68 . The pump  502  is driven by the rotation of the propeller shaft  56 , similarly to the pump  102  of  FIG. 3 . The pump  502  draws water from the surrounding body of water through a primary inlet  504 , preferably located at the front of the gear case  68 . The pump  502  pumps the water upward through the primary outlet  506  toward the cooling system  520  (shown schematically) of the engine  44 . 
         [0059]    An auxiliary water pump, in the form of a positive displacement pump  508 , is disposed above the cavitation plate  57  and below the water line W. The pump  508  is driven by an electric motor  510 , which is controlled by the ECU  202 . The ECU  202  controls the pump  508  in a similar way to the auxiliary pump  108  of  FIG. 3 . When the pump  508  is in operation, the pump  508  draws water from the surrounding body of water through the auxiliary inlet  512 , and pumps the water upward through the auxiliary outlet  514 . 
         [0060]    The outlets  506 ,  514  of the pumps  502 ,  508  fluidly communicate at a point  516  located above the cavitation plate  57 , and extend upwardly from the point  516  via a common conduit  518 . In this configuration, the pump  508  can be operated at engine startup to prime the pump  502  in the same manner as the pump  108  of  FIG. 3 . The conduit  518  supplies water to the cooling system  520  (shown schematically) of the engine  44 . The cooling system  520  includes the same components as the cooling system  220  of  FIG. 3 , and as such will not be described again in detail. After the water from the conduit  518  has cooled one or more components of the cooling system  520 , the water is returned to the body of water via an outlet (not shown) in a known manner. 
         [0061]    Using any one of the above arrangements, an ample and uniform flow of cooling water can be delivered to the cooling system  220  under a wide range of conditions. In the arrangement shown in  FIG. 3 , the pump  102  is a centrifugal pump having an impeller (not shown) with rigid vanes rotatably mounted within a housing (not shown). This pump design provides more efficient cooling at high speeds than the conventional hybrid pump  10 , and the auxiliary pump  108  supplements the cooling at lower speeds. The auxiliary pump  108  does not experience reduced efficiency at low speeds, because it is powered by the electric motor  110  at a speed independent of the rotational speed of the engine  44 . In addition, the pump  102  is more durable than the pump  10  because the vanes of the pump  102  do not contact the housing and are therefore not subject to the same degree of wear. In addition, the vanes of the pump  102  are more resistant to corrosion or damage due to salt or debris entering the pump housing than the flexible impeller  12  of the pump  10 . In the event of damage or wear, the location of the pump  102  in the gear case  68  permits easy access for servicing or replacement. In addition, the useful life of the auxiliary pump  108  is extended, and its maintenance requirements correspondingly reduced, by using the auxiliary pump  108  only when needed to supplement the flow of cooling water from the pump  102 , rather than constantly while the engine  44  is in operation. Similar advantages are provided by the embodiments shown in  FIGS. 4 ,  5  and  6 . 
         [0062]    Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.