Abstract:
An exhaust system for a marine propulsion device is configured to dispose two exhaust conduits in generally concentric overlapping relation with each other in order to minimize the potential cross sectional area of a leak path in the event that a seal fails. One of the exhaust conduits extends through a transom or other surface of a marine vessel and another exhaust conduit conducts exhaust gas from an engine to the exhaust conduit extending through the surface of the marine vessel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is generally related to exhaust systems of marine vessels and, more particularly, to an exhaust system which directs an exhaust flow to a point external to a marine vessel which is beneath the surface of a body of water in which the marine vessel is operated. 
         [0003]    2. Description of the Related Art 
         [0004]    Those skilled in the art of marine vessels and engine systems are aware of many different types of exhaust systems that direct exhaust gas away from an engine. Some marine systems direct the flow of exhaust gas to a location which is under the surface of a body of water. This is done for several reasons, including the silencing effect that can be obtained by exhausting the gases below the water level. The exhaust conduits of a marine propulsion system typically use more than one individual exhaust pipe, or conduit, to direct the exhaust gas from the engine to the point at which the gas is emitted from the exhaust system. The various components of the conduit system are connected together, either by flanges or intermediate elastomeric connectors, such as bellows structures. 
         [0005]    U.S. Pat. No. 3,802,491, which issued to Plank et al. on Apr. 9, 1974, describes a marine exhaust system. It comprises inner and outer concentrically arranged flexible conductors held in concentric relation by spacers and fittings at the opposite ends. The fitting at one end is adapted to connect the inner and outer conductors, respectively, to the manifold of an engine and to a coolant pump. The fitting at the other end is adapted to connect the inner and outer conductors, respectively, to a muffler and to an overboard line. 
         [0006]    U.S. Pat. No. 4,861,296, which issued to Wlezien on Aug. 29, 1989, describes a marine propulsion device exhaust system. It comprises a sterndrive unit including a gimbal housing adapted to be fixed to a boat transom. It also comprises an exhaust gas passage in a propulsion unit which includes an outlet normally located underwater and an inlet normally located above the water. A flexible exhaust gas bellows has a rearward end connected to the inlet of the gas passage in the propulsion unit and a forward end. An exhaust gas and coolant discharge conduit extends through the gimbal housing and comprises a forwardly located inlet passage adapted to receive combined exhaust gas and coolant discharge from an engine. 
         [0007]    U.S. Pat. No. 4,911,666, which issued to Gage et al. on Mar. 27, 1990, describes a boat propulsion device with an internal exhaust. A marine drive mounts through a hole in the bottom surface of a boat utilizing a driveshaft housing assembly. An engine mounted to the driveshaft assembly and a lower propeller drive unit mounted to the driveshaft housing assembly are also provided. The driveshaft housing assembly mounts the drive within the hole in the boat and includes a driveshaft housing. A steering assembly is constructed to rotate about a generally vertical axis within the driveshaft housing assembly to provide steering. A trimming assembly is connected to the steering assembly to pivotably swing the lower propeller drive unit to provide trimming and tilting. It also comprises a driveshaft and an exhaust passage therethrough. 
         [0008]    U.S. Pat. No. 5,421,756, which issued to Hayasaka on Jun. 6, 1995, describes an exhaust system for the marine propulsion machine. It provides an exhaust gas discharge system for a watercraft. The system has a first discharge path, including a first outlet, primarily for use during high speed vessel operation and a second discharge path, including a second outlet, for use during both low and high speed vessel operation. 
         [0009]    U.S. Pat. No. 6,022,254, which issued to Neisen on Feb. 8, 2000, discloses an exhaust system for an inboard/outboard marine propulsion system. The exhaust system includes intermediate exhaust pipes which are physically separate components than the water separator. A sealed latching mechanism connects an outlet portion of the intermediate exhaust pipes to an inlet portion of the water separator. The sealed latching mechanism is secure yet flexible and allows the orientation of the intermediate exhaust pipe to be adjusted relative to the water separator. This allows the exhaust system to be installed and serviced without dismounting or loosening the engine. The intermediate exhaust pipes also have a flared inlet part to facilitate alignment of the intermediate exhaust pipe at the exhaust elbow. 
         [0010]    U.S. Pat. No. 6,508,681, which issued to Neisen on Jan. 21, 2003, describes a low friction exhaust bellows and techniques for constructing and assembling the bellows. A propulsion system has a low friction exhaust bellows relative to an engine located in the interior of a marine vessel. The engine has an exhaust discharge member in communication with a propulsion unit and an exhaust passage having an exterior coupling member flexibly connected to pass exhaust from the exhaust discharge member to the propulsion unit. The interior surface of the passage is configured to provide a relatively smooth surface to the exhaust passage therein. 
         [0011]    U.S. Pat. No. 7,018,255, which issued to Phillips et al. on Mar. 28, 2006, discloses an exhaust system for a marine propulsion device having two stationary tubes to define an annular exhaust passage. The system is provided with inner and outer bellows, or tubes, which are rigidly attached to both the transom bracket and the driveshaft housing of a sterndrive system. Neither the inner nor outer tubes rotate with the driveshaft. Both the inner and outer tubes, or bellows, allow the driveshaft to rotate relative to the transom bracket about either a steering axis or trim axis. An exhaust passage is defined between the outer surface of the inner tube and the inner surface of the outer tube. 
         [0012]    The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
         [0013]    When an exhaust system of a marine vessel conducts the flow of exhaust gases to a point below the surface of a body of water in which the marine vessel is operated, any leak or rupture of the exhaust system below the surface level of the water can cause water to flow into the marine vessel. Bilge pumps are typically provided and are intended to remove water from the bilge of the marine vessel but, in many instances, the bilge pump has a limited flow capability and may not be able to remove water from the bilge at the rate that it is leaking into the bilge. This is particularly true if a catastrophic failure occurs in an exhaust conduit at a point below the surface of the body of water. It would therefore be significantly beneficial if this potentially serious problem could be alleviated. 
       SUMMARY OF THE INVENTION 
       [0014]    An exhaust system of a marine vessel made in accordance with a preferred embodiment of the present invention comprises a first exhaust conduit and a second exhaust conduit. An end portion of the second exhaust conduit is disposed within an end portion of the first exhaust conduit. A seal is disposed between the end portion of the second exhaust conduit and the end portion of the first exhaust conduit. The seal can be disposed between an outer surface of the end portion of the second exhaust conduit and an inner surface of the end portion of the first exhaust conduit. 
         [0015]    In a preferred embodiment of the present invention, the seal can be an elastomeric seal which, in turn, can be a lip seal. The end portion of the second exhaust conduit and the end portion of the first exhaust conduit can be generally concentric. 
         [0016]    A preferred embodiment of the present invention further comprises an engine connected in fluid communication with the first and second exhaust conduits and a surface of a marine vessel. The first and second exhaust conduits are configured to conduct a stream of exhaust gas from the engine through the surface, which can be a transom of a marine vessel. 
         [0017]    In a preferred embodiment of the present invention, it further comprises a marine propulsion drive connected in torque transmitting relation with a crankshaft of the engine. The marine propulsion drive can be a sterndrive unit. The stream of exhaust gas can be conducted through the transom of the marine vessel and through the sterndrive unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    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: 
           [0019]      FIG. 1  shows an exhaust pipe connection known to those skilled in the art; 
           [0020]      FIG. 2  is an exploded view of a preferred embodiment of the present invention; 
           [0021]      FIG. 3  is an assembled view of the structure shown in  FIG. 2 ; 
           [0022]      FIGS. 4 and 5  show the geometric advantages of the present invention; 
           [0023]      FIG. 6  shows an embodiment of the present invention; 
           [0024]      FIG. 7  shows the present invention used in conjunction with a sterndrive system; and 
           [0025]      FIG. 8  shows the present invention used in conjunction with an inboard drive system. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
         [0027]      FIG. 1  shows the manner in which two exhaust conduits are typically connected in marine propulsion devices known to those skilled in the art. An exhaust pipe  10  which is connected to an engine (not shown in  FIG. 1 ) is attached to an exhaust pipe  12  which conducts the flow of exhaust gas E to and through a transom or hull of a marine vessel. Functionally, an engine and its exhaust manifold would be located to the left of the illustration in  FIG. 1  and the transom or lower hull of the marine vessel is located to the right of the schematic representation in  FIG. 1 . The ends of the exhaust pipes  10  and  12 , which face each other, are identified by reference numerals  16  and  18 , respectively. These ends,  16  and  18 , can be butted together or spaced apart as shown in  FIG. 1 . An elastomeric connection member  20  is typically attached to both exhaust pipes,  10  and  12 , by clamps which are schematically represented in  FIG. 1  and identified by reference numerals  22  and  24 . The elastomeric connection member  20  allows some relative movement between the two exhaust pipes,  10  and  12 , and provides a seal that prevents the escape of exhaust gas from the region within the elastomeric connection member  20 . Naturally, if a leak forms through the elastomeric connection member  20  or if the clamps,  22  and  24 , become disconnected, exhaust gas can escape from that region and, more importantly, water can flow from a point external to the marine vessel to the end face  18  and into the bilge of the marine vessel. This type of leak is possible when the stream of exhaust gas E is directed through the transom at a point which is below the surface of the water in which a marine vessel is operated. For example, the marine propulsion unit described in U.S. Pat. No. 4,911,666 extends through the bottom surface of a marine vessel. Any leak in the exhaust system below the level of the water can result in a flow of water from the body of water into the marine vessel bilge. Similarly, the marine propulsion system described in U.S. Pat. No. 6,022,254 can potentially develop a leak within the exhaust conduits inside the marine propulsion device and below the level of the body of water. 
         [0028]      FIG. 2  is a schematic representation of an exhaust system joint made in accordance with a preferred embodiment of the present invention. It comprises a first exhaust conduit  31  and a second exhaust conduit  32 . An end portion  42  of the second exhaust conduit  32  is disposable within an end portion  41  of the first exhaust conduit  31 . A seal  40  is disposed between the end portion  42  of the second exhaust conduit  32  and the end portion  41  of the first exhaust conduit  31  as will be described below in conjunction with  FIG. 3 . In the exploded view of  FIG. 2 , the first and second exhaust conduits,  31  and  32 , are shown spaced apart and the seal  40  is shown between them. In a preferred embodiment of the present invention, the seal  40  is made of an elastomeric material and, in a particularly preferred embodiment, is a lip seal. 
         [0029]      FIG. 3  is similar to  FIG. 2 , but with the components assembled together. In  FIG. 3 , the seal  40  is shown disposed between the end portion  42  of the second exhaust conduit  32  and the end portion  41  of the first exhaust conduit  31 . In this preferred embodiment shown in  FIG. 3 , the seal  40  is disposed between an outer surface  52  of the end portion  42  of the second exhaust conduit  32  and an inner surface  51  of the end portion  41  of the first exhaust conduit  31 . The seal  40  can be an elastomeric seal, as described above, and a lip seal. In a preferred embodiment of the present invention, the end portion  42  of the second exhaust conduit  32  and the end portion  41  of the first exhaust conduit  31  are generally concentric. 
         [0030]      FIGS. 4 and 5  are provided to illustrate the primary advantage provided by the present invention.  FIG. 4  is a simplified representation of a cross section of an exhaust pipe. The cross section shown in  FIG. 4  is the cross section through which water would flow from the body of water into the bilge of a marine vessel if the two exhaust conduits are separated. As an example, the illustration in  FIG. 4  shows a section view of the exhaust pipe  12  described above in conjunction with  FIG. 1 . The flow of water, from a body of water and into the boat, would flow through the internal area of the exhaust pipe  12 . If, on the other hand, the exhaust system incorporated the principles of the present invention, as illustrated in  FIG. 3 , and the elastomeric seal  40  fails, water is limited to flowing in the region identified by reference numeral  140  in  FIG. 5 , between the outer surface of the second exhaust conduit  42  and the inner surface  51  of the first exhaust conduit  41 . If clearances between the first and second exhaust conduits are limited appropriately, this cross sectional area  140  can be significantly less than the area within the exhaust pipe  12  shown in  FIG. 4 . 
         [0031]      FIG. 6  shows an embodiment of the present invention in which an external clamp is used to maintain the axial relative positions of the first  31  and second  32  exhaust conduits. The seal  40  is shown with the radially inward extension deformed slightly as a result of the contact with the outer surface  52  of the second exhaust conduit  32 . A circumferential ridge  200  of the second exhaust conduit facilitates the clamping of the first and second exhaust conduits together as shown. A plurality of bolts  202 , nuts  204 , washers  206  and springs  208  facilitate the retention of the two exhaust conduits in relation to each other. In addition, two clamp rings,  210  and  212 , assist in providing the axial retention forces. 
         [0032]      FIG. 7  is a schematic representation of the general location of the present invention in relation to a marine vessel and its engine and drive unit. The engine  300  has a manifold  302  from which exhaust gases are emitted. It should be understood that the engine  300 , manifold  302  and drive unit  304  are represented in a highly schematic manner in  FIG. 7 . The purpose of  FIG. 7  is to illustrate the relative positions of the various components and not to show the precise way in which they are connected to each other. As those skilled in the art of marine propulsion devices are well aware, many different configurations are provided in exhaust systems and many types of interconnections between various components are well known. The general direction of the exhaust flow is represented by arrows E in  FIG. 7 . The first exhaust conduit  31  extends through the transom  310  of a marine vessel. This directs the flow of exhaust gas E through the marine drive unit  304  which can be a sterndrive unit. 
         [0033]    With continued reference to  FIG. 7 , it can be seen that the connection between the first and second exhaust conduits,  31  and  32 , is relatively low within the bilge of the boat. In some applications, the exhaust connection in the region of the seal  40  can be below the water line of the surface of the body of water in which the marine propulsion system is being operated. In those cases, hydrostatic pressure will cause water to rise within the first exhaust conduit toward the engine. A failure of the seal between the first and second exhaust conduits can therefore lead to a flow of water into the bilge of the boat. One advantage of the present invention is that such a failure, of the seal  40 , will lead to a significantly reduced flow of water into the bilge if the seal fails, whereas a failure of the connector  20  in  FIG. 1 , as typically used in the prior art, can lead to a much more catastrophic failure. This difference is described above in conjunction with  FIGS. 4 and 5 . 
         [0034]      FIG. 8  is a schematic representation of a section view of a marine vessel with an inboard drive system. The crankshaft  400  of the engine  300  provides torque to a transmission device  402  which, in turn, provides torque to a propeller shaft  404 . The propeller shaft has a propeller attached to its distal end (not shown in  FIG. 8 ). The basic configuration of the exhaust conduit is generally similar to that described above. If the connection region between the first and second exhaust conduits,  31  and  32 , is below the water level of the body of water in which the marine propulsion system is operated, a failure of the seal between the two exhaust conduits can lead to the flow of water into the bilge of the boat as a result of the hydrostatic pressure experienced by that region of the exhaust conduit structure. Again, the present invention limits that flow of water. 
         [0035]    With reference to  FIGS. 2-8 , it can be seen that an exhaust system for a marine vessel made in accordance with a preferred embodiment of the present invention, comprises a first exhaust conduit  31 , a second exhaust conduit  32 , and end portion  42  of the second exhaust conduit  32  which is disposed within an end portion  41  of the first exhaust conduit  31 , and a seal  40  disposed between the end portion  42  of the second exhaust conduit  32  and the end portion  41  of the first exhaust conduit  31 . The seal  40  is disposed between an outer surface  52  of the end portion  42  of the second exhaust conduit  32  and an inner surface  51  of the end portion  41  of the first exhaust conduit  31 . The seal  40  can be an elastomeric seal and, in certain embodiments of the present invention, can be a lip seal. The end portion  42  of the second exhaust conduit and the end portion  41  of the first exhaust conduit are generally concentric in a preferred embodiment of the present invention. An engine  300  is connected in fluid communication with the first and second exhaust conduits,  31  and  32 , and a surface of a marine vessel, such as a transom surface, is provided such that the first and second exhaust conduits direct a stream of exhaust gas from the engine  300  through the surface. The surface can be a transom  310  of a marine vessel. The marine propulsion drive, such as a sterndrive unit  304  or a propeller shaft  404  is connected in torque transmitting relation with a crankshaft  400  of the engine. 
         [0036]    It should be understood that many different sizes of first and second exhaust conduits can be used in various embodiments of the present invention. The advantage of the physical arrangement provided by the present invention is that the outer diameter of the second exhaust conduit  32  and the inner diameter of the end  41  of the first exhaust conduit  31  can be selected to minimize the circumferential gap between those surfaces. This gap defines the radial thickness of the seal and further defines the area through which water can pass if the seal fails. This area can be selected to limit the flow of water, in the event of a catastrophic failure, to that which can be accommodated by a bilge pump. On the other hand, if the flow of water in this type of failure mode is limited only to the internal area of the first exhaust conduit, the flow of water into the bilge can easily exceed the capability of the bilge pump. These relative areas are discussed above in conjunction with  FIGS. 4 and 5 . The primary advantage of the present invention is, therefore, its ability to inherently limit the flow of water into the bilge of a boat from the body of water in which the boat is operated when a catastrophic failure occurs in the seal between the first and second exhaust conduits. 
         [0037]    Although the present invention has been described with particular specificity and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.