Patent Publication Number: US-6336434-B1

Title: Engine unit of outboard motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an engine unit of an outboard motor particularly provided with an improved structure of a magneto device. 
     2. Prior Art 
     In an outboard motor, it is common to vertically dispose a crankshaft in an engine. The crankshaft is supported in the engine by a bearing, and lubricating oil is pumped to the bearing in a certain arrangement. An oil seal is provided above the bearing so that the lubricating oil will not leak outside from the bearing which supports an upper end of the crankshaft. The oil seal is mounted to the engine using a separate seal housing in many cases. 
     Meanwhile, in order to absorb variation in rotation of the engine and to deal with abrupt variation in load at the time of shifting, a rotation member having great moment of inertia is provided on an axis of revolution of the engine, usually on the crankshaft. 
     In the case of the engine unit of the outboard motor, the upper end of the crankshaft is usually projected above the engine body in an usual state to be mounted to a hull, for example, and the rotation member having great moment of inertial, i.e., a flywheel is provided on this projected portion. The flywheel constitutes a portion of a magneto device. In this case, it is a common method to integrally form the flywheel with a rotor constituting a part of the magneto device, and to fix a stator to which an electric generating coil is mounted to the seal housing which also serves as a mounting member of the stator. A recoil starter apparatus for manually starting the engine is provided above the magneto device in some cases. 
     A factor which determines a height of the outside shape of the outboard motor is a structural member provided on an upper portion of the engine, which, in generally, corresponds to the above-described magneto device and the recoil starter device. 
     Such location is not preferable because the height of the structural member is increased and the entire outboard motor is increased in size. Further, the shape of an engine cover must be considered in accordance with the structural member, and flexibility of styling is limited. 
     Further, the flywheel having great mass is supported in a cantilever manner by the bearing which supports the upper end of the crankshaft. Therefore, as the projecting length of the crankshaft outside from the engine is increased, even a slight deviation in revolution balance generated by the flywheel increases vibration, and this becomes a great burden to the crankshaft and the bearing. Even slight deviation in revolution balance generated by the engine and the crankshaft applied to an end of the crankshaft functions as a great moment, and this moment becomes a great burden to the crankshaft and the bearing and also becomes a factor for increasing the vibration. 
     It is not preferable to increase the crankshaft and the bearing in size and to change the material and producing method in order to prevent the vibration and to enhance the durability of the respective constitutional members. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in view of the above circumstances, and it is an object of the invention to provide an engine unit of an outboard motor capable of making compact the engine unit in size by shortening a projecting length of a crankshaft outward of an engine with a simple structure. 
     This and other object can be achieved according to the present invention by providing an engine unit of an outboard motor comprising: 
     an engine body; 
     a crank case in which a crankshaft is vertically perpendicularly arranged in a usable mounted state of the outboard motor; 
     a cylinder block which is disposed to a rear side of the crank case and in which cylinders are arranged; 
     a cylinder head disposed to a rear side of the cylinder block, the crank case, the cylinder block and the cylinder head being disposed in the engine body; and 
     a magnet device mounted to a top end portion of the crankshaft projecting upward and comprising a stator and a flywheel to which a rotor is integrally formed, 
     the crankshaft being supported by a bearing boss disposed to a mating portion of the cylinder block and the crank case through a bearing means and an oil seal is disposed between the bearing boss and the bearing means, the magnet device being mounted to the engine body through the stator through a mounting portion, wherein a diameter of the mounting portion of the stator is larger than an outer diameter of the oil seal. 
     In a preferred embodiment, the stator is directly mounted to the engine body. The engine body is formed with a hole through which the stator is mounted and the hole has a depth deeper than a position of a mounting portion of the oil seal. 
     The engine unit may further comprise a crank angle detecting sensor disposed to an upper surface of the engine body and a mounting boss for mounting the sensor disposed to be deviated sideways from a center line of the cylinder of the engine, the sensor being mounted to the mounting boss in an upside-down attitude. 
     The engine unit may further comprise a starter motor, a mounting boss for mounting the starter motor to the engine body, and a crank angle detecting sensor which is mounted to a boss formed to the starter motor mounting boss. 
     The engine unit may further comprise a cam shaft driving mechanism which is disposed below the bearing means. 
     As explained above, in the engine unit of the outboard motor of the present invention, the crankshaft is vertically disposed in the engine (engine body), an upper end of the crankshaft is projected upward of the engine as a projection, and the projection is provided with the magneto device, a bearing boss above a bearing which supports an upper end of the crankshaft is provided with an oil seal, a diameter of a mounting portion of a stator constituting the magneto device to the engine is set greater than an outer diameter of the oil seal. Therefore, the stator can be disposed outward of the oil seal, the projecting length of the crankshaft outside of the engine is shortened, and the entire height of the engine is lowered. 
     Further, since the stator is directly mounted to the engine, the seal housing which was necessary in the conventional structure can be eliminated, the number of parts is reduced, the projecting length of the crankshaft outward of the engine is shortened, and the entire height of the engine is lowered. 
     Further, since the engine is formed with a hole for mounting the stator, and a depth of the hole is set deeper than a position of a mounting portion of the oil seal, the projecting length of the crankshaft outward of the engine is shortened, and the entire height of the engine can be reduced. 
     Furthermore, the engine is provided at its upper surface with the crank angle detecting sensor, the boss for mounting the sensor is disposed to be deviated sideways from the center line of the cylinder of the engine, and the sensor is mounted to the boss upside down. Therefore, the sensor does not interfere with the cooling water passage formed around the cylinder. 
     Further, the engine includes the starter motor, the boss for mounting the starter motor is formed on the engine, and the boss for mounting the motor is provided with another boss for mounting the other sensor. Therefore, the weight of the engine unit is reduced and the supporting rigidity thereof can be ensured sufficiently. 
     Furthermore, the engine includes the cam shaft driving mechanism, and the camshaft driving mechanism is disposed at a position lower than the bearing which supports the upper end of the crankshaft. Therefore, the distance between the flywheel and the bearing can be shortened. 
     The nature and further features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a left side view of an outboard motor showing a first embodiment according to the present invention; 
     FIG. 2 is an enlarged side view of an engine unit of the outboard motor shown in FIG. 1; 
     FIG. 3 is a plan view of the engine shown in FIG. 2; 
     FIG. 4 is a cross sectional view taken along the line IV—IV in FIG. 3; 
     FIG. 5 is an enlarged vertical sectional view of an upper end projecting portion of a crankshaft; 
     FIG. 6 is a plan view of a portion of the engine; 
     FIG. 7 is a cross sectional view taken along the line VII—VII in FIG. 3; and 
     FIG. 8 is an enlarged side view of an upper portion of the engine of the outboard motor showing a second embodiment according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be explained hereunder with reference to the accompanying drawings. 
     FIG. 1 is a left side view showing a first embodiment of an outboard motor to which the present invention is applied. 
     As shown in FIG. 1, the outboard motor  1  includes an engine holder  2 , and an engine (engine unit including an engine body)  3  is disposed above the engine holder  2 . The engine  3  is a vertical type engine in which a crankshaft  4  is disposed substantially vertically. An oil pan  5  is disposed below the engine holder  2 , a bracket  6  is mounted to the engine holder  2  for example, and the outboard motor  1  is mounted to a transom of a hull, not shown, through the bracket  6 . Further, it is to be noted that the description of the present invention made hereunder is substantially made with reference to the state of the outboard motor  1  mounted to the hull as illustrated in FIG.  1 . 
     Peripheries of the engine  3 , the engine holder  2  and the oil pan  5  of the outboard motor  1  are covered by an engine cover  7 . The engine cover  7  is divided into lower and upper two portions, i.e., into a lower cover section  7   a  for covering the peripheries of a lower portion of the engine  3 , the engine holder  2  and the oil pan  5  and an upper cover section  7   b  for covering an upper portion of the engine  3 . 
     A drive shaft housing  8  is disposed in a lower portion of the oil pan  5 . A drive shaft  9  is disposed substantially vertically in the engine holder  2 , the oil pan  5  and the drive shaft housing  8 , and an upper end of the drive shaft  9  is connected to a lower end of the crankshaft  4 . The drive shaft  9  extends downward in the drive shaft housing  8  for driving a propeller  13  through a bevel gear  11  and a propeller shaft  12  in a gear case  10  provided in a lower portion of the drive shaft housing  8 . 
     With reference to FIGS. 1,  2  and  3 , the engine  3  mounted in the outboard motor  1  is a water-cooled four-stroke-cycle three-cylinder engine comprising a combination of, e.g., a cylinder head  14 , a cylinder block  15  and a crankcase  16 . 
     The cylinder block  15  is disposed at the forefront of the engine  3 , i.e., behind (right side) of the crankcase  16  disposed at the leftmost position in FIGS. 1 and 2. The cylinder head  14  is disposed behind the cylinder block  15 . 
     As shown in FIG. 2, disposed on the left side surface of the engine  3  are a starter motor  17   a , an electrical equipment box  17   b  in which control electrical equipment, not shown, is accommodated, ignition coils  17   c , electrical equipment parts  17  such as a rectifier and a regulator  17   d , and an ignition plug  17   e , and an exhaust system part  18 . Disposed on the right side surface of the engine  3  are intake system parts  19  such as a carburetor  19   a , an intake pipe  19   b  and silencer  19   c.    
     FIG. 4 is a cross sectional view taken along the line IV—IV in FIG.  3 . As shown in FIG. 4, a cylinder  15   a  is substantially horizontally formed in the cylinder block  15  of the engine  3 , and a piston  20  is inserted in the cylinder  15   a  slidably in the axial direction of the crankshaft  15   a . The piston  20  and the crankshaft  4  are connected to each other by a connecting rod  21  so that reciprocating stroke of the piston  20  is converted into rotational motion of the crankshaft  4 . Although the piston  20  and the connecting rod  21  are illustrated in only one cylinder  15   a  in FIG. 4, pistons and connecting rods, not shown, are disposed also in other cylinders  15   a  in the similar manner. 
     Intake/exhaust valves, not shown, for opening and closing supply/discharge ports, not shown, are disposed in the cylinder head  14 , and a cam shaft  22  for opening and closing these valves is disposed in a rear portion of the cylinder head  14 . 
     A cam chain chamber  23  is formed in a space between a lower portion of the engine  3  and an upper surface of the engine holder  2 . A cam shaft driving mechanism  24  for transmitting rotation of the crankshaft  4  to the cam shaft  22  to rotate the latter is provided in the cam chain chamber  23 . The cam shaft driving mechanism  24  is driven by a chain for example and comprises a cam drive sprocket  25  provided on a portion of the crankshaft  4  projecting downward of the engine  3 , a cam driven sprocket  26  provided at the lower end of the cam shaft  22  projecting downward of the engine  3  similarly, and a timing chain  27  wound around these sprockets  25  and  26 . 
     A journal  4 a of each of the crankshafts  4  is pivotally supported by a bearing boss  29  formed on a juncture (mating portion) between the cylinder block  15  and the crankcase  16  through a bearing  28 , i.e., through a metal bearing in the present embodiment. The upper end of the crankshaft  4  projects upward of the engine  3  as a projection  4   b , and an oil seal  30  is provided on a bearing boss  29  located between this projection  4   b  and the bearing  28   a  supporting the journal  4   a  of the upper end of the crankshaft  4 . 
     FIG. 5 is an enlarged vertical cross sectional view of the projection  4   b  on the upper end of the crankshaft. As shown in FIG. 5, the oil seal  30  is formed at its outer peripheral surface with a falling-out preventing flange  30   a . The falling-out preventing flange  30   a  is fitted and fixed to a seal groove  29   a  which is a mounting portion of the oil seal  30  formed in the bearing boss  29  of the juncture between the cylinder block  15  and the crankcase  16  when the cylinder block  15  and the crankcase  16  are connected. 
     The projection  4   b  of the crankshaft  4  is provided with a magneto device  31 . The magneto device  31  comprises a stator  33  to which an electric generating coil  32  is mounted, and a flywheel  35  integrally formed with a rotor  34 . The flywheel  35  is formed at its outer periphery with a ring gear  36  which is operatively connected to the stator motor  17   a , a recoil starter apparatus  37  (see FIGS. 1 and 2) is provided above the magneto device  31 , and both the apparatus  31  and  37  are covered with a recoil cover  38 . 
     The flywheel  35  integrally formed with the rotor  34  is fitted to the projection  4   b  of the crankshaft  4  and is fixed to the crankshaft  4  by a bolt  39  such that the flywheel  35  rotates in unison with the crankshaft  4 . The fitting portion between the projection  4   b  and the flywheel  35  is formed into a tapered shape. Further, as shown in FIG. 6, the stator  33  is directly fixed to the cylinder block  15  and the crankcase  16  by a bolt  40  or the like. A knock pin  41  may be used for positioning the stator  33 . A magnet  42  is provided on an inner surface of the rotor  34  at a position opposed to the electric generating coil  32  of the stator  33 . 
     As shown in FIGS. 4 to  6 , a diameter A of a mounting portion of the stator  33  to the cylinder block  15  and the crankcase  16  is set greater than an outer diameter B of the oil seal  30  (see FIGS.  5  and  6 ), and the stator  33  is disposed outside of the oil seal  30 . A depth of a hole  43  for a bolt  40  for fixing the stator  33  formed on the cylinder block  15  and the crankcase  16  is set deeper than a position of a seal groove  29   a  for mounting the oil seal  30 . 
     As shown in FIGS. 3 and 4, a plurality of (three in the present embodiment) crank angle detecting sensors  44 ,  45  and  46  (simply, sensors, hereinafter) are provided on an upper surface of the engine  3 . These sensors  44 ,  45  and  46  detect the passing timing of a projection  47  (see FIG. 5) disposed on a reference crank angle position on an outer periphery of the flywheel  35  to judge the ignition timing of the ignition plug  17   e . These sensors  44 ,  45  and  46  are disposed at substantially equal distances from one another along the outer periphery of the flywheel  35 . 
     FIG. 7 is a cross sectional view taken along the line VII—VII in FIG.  3 . As shown in FIGS. 3,  6  and  7 , of the three sensors  44 ,  45  and  46 , the sensor  44  provided on the upper surface of the cylinder block  15  is deviated sideways from a center line  48  of the cylinder  15   a , and integrally formed with the cylinder block  15  and fixed to the sensor mounting boss  49  projecting upward by means of two bolts  50  for example. A portion of the sensor mounting boss  49  between its female screws is downwardly recessed to form a recess  51 , and the sensor  44  is mounted in the recess  51  upside down. 
     On the other hand, of the three sensors  44 ,  45  and  46  provided on an upper surface of the engine  3 , the sensors  45  and  46  disposed outer side from the width W (see FIG. 3) of the cylinder block  15  are mounted to a sensor mounting boss  54  integrally formed on a motor mounting boss  53  integrally formed on the crankcase  16  for supporting the starter motor  17   a  and the sensor mounting boss  52  integrally formed on the crankcase  16 , for example. 
     Next, operation of the first embodiment will be explained. 
     When the camshaft driving mechanism  24  is disposed on the side of the lower end of the crankshaft  4 , the oil seal  30  is provided on the bearing boss  29  between the projection  4   b  on the upper end of the crankshaft  4  and the bearing  28   a  supporting the journal  4   a  of the upper end of the crankshaft  4 , the diameter A of the mounting portion of the stator  33  constituting the magneto device  31  to the engine  3  (cylinder block  15  and the crank case  16 ) is set greater than the outer diameter B of the oil seal  30 , and the stator  33  is disposed outer side of the oil seal  30 . With this layout, since the fixing bolt  40  for fixing the stator  33  does not interfere with the oil seal  30  and thus, a seal housing which also functions as a mounting member of the stator  33  which was necessary in the prior art can be eliminated. As a result, the stator  33  can be directly fixed to the engine  3 , and the entire height of the engine  3  can be reduced by the same length as the height of the seal housing, the outboard motor  1  can be reduced in size, the weight of the entire outboard motor  1  can be reduced, and the flexibility in styling of the engine cover  7  is enhanced. Further, since it is possible to shorten the crankshaft  4  by the same length as the height of the sealing housing, load that the vibration caused by deviation in rotation balance generated from the flywheel  35 , and moment caused by deviation in rotation balance generated from the engine  3  and the crankshaft  4  apply to the crankshaft  4  and the bearing  28   a  is reduced, the reliability of the engine  3  is enhanced, and the durability is extended. 
     Further, since the diameter A of the mounting portion of the stator  33  to the engine  3  is set to be greater than the outer diameter B of the oil seal  30 , it is possible to increase the diameters of the electric generating coil  32  mounted to the stator  33  and the flywheel  35  integrally formed with the rotor  34 . For example, by increasing the outer diameter of the flywheel  35  as compared with the conventional structure, a peripheral speed of the projection  47  disposed in the reference crank angle position of the outer periphery of the flywheel  35  is increased as compared with the conventional structure, and it is possible to detect a stable reference signal from lower engine revolution number. The starting performance and stability in a low revolution region of the engine  3  can be enhanced. 
     Further, by increasing the outer diameter of the flywheel  35  as compared with the conventional structure, a mass  35   a  can easily be mounted at outer side of the flywheel  35  in the diametrical direction, and it is possible to increase the moment of inertia as compared with the conventional structure even if the same weight is added, and absorbing ability of revolution variation of the engine  3  is enhanced. 
     Furthermore, by increasing the outer diameter of the flywheel  35  as compared with the conventional structure, a peripheral speed of the magnet  42  mounted to the rotor  34  is also increased, and the electric generating amount is increased. If the required electric generating amount is the same as that of the conventional structure, the length of the magnet  42  can be shortened, the flywheel  35  can be made thinner, i.e., its height can be lowered. 
     Further, by increasing the outer diameter of the stator  33  as compared with the conventional structure, if the number of poles  32   a  of the electric generating coil  32  is the same as that of the conventional structure, a distance between poles  32   a  is increased, and the number of windings of a coil wire, not shown, can be increased. As a result, the electric generating amount can be increased. If the required electric generating amount is the same as that of the conventional structure, the thickness T of the core of the electric generating coil  32  can be reduced, the stator  33  can be made thinner, i.e., its height can be lowered. 
     Further, since the diameter A of the mounting portion of the stator  33  to the engine  3  is set greater than the outer diameter B of the oil seal  30 , and the stator  33  is directly fixed to the engine  3 , a contact area of the stator  33  with the engine  3  is increased, and it is easy to transmit the heat generated at the time of generation of electric power to the engine  3 . As a result, heat resistance of the coil wire is enhanced, and the reliability of the magneto device  31  is enhanced. 
     Furthermore, it is possible to lower the heat resistance of the coil wire, resulting in the cost reduction. 
     Further, since the diameter A of the mounting portion of the stator  33  to the engine  3  is set greater than the outer diameter B of the oil seal  30 , a diameter C of the boss  35   b  for mounting the flywheel  35  to the crankshaft  4  can be increased as compared with the conventional structure. As a result, fastening torque of the bolt  39  for fixing the flywheel  35  to the crankshaft  4  can be increased, and a tapering length of the fitting portion between the crankshaft  4  and the flywheel  35  can be shortened, and the height of the flywheel  35  can be reduced. 
     Further, since the diameter A of the mounting portion of the stator  33  to the engine  3  is set greater than the outer diameter B of the oil seal  30 , a diameter of the crankshaft  4  can be increased as compared with the conventional structure. As a result, since a surface area of the tapered portion is increased, the tapering length can be shortened, and the height of the flywheel  35  can be reduced. 
     On the other hand, since the diameter A of the mounting portion of the stator  33  to the engine  3  is set greater than the outer diameter B of the oil seal  30 , the outer diameter of the flywheel  35  is also increased, and its height is also reduced. Therefore, if the sensor  44  is mounted upside down, the height of the sensor  44  is reduced so as not to be interfered with the flywheel  35 . 
     If the sensor  44  is disposed on the center line  48  of the cylinder  15   a , a mounting depth of the sensor  44  is limited so as not to be interfered with a cooling water passage  15   b  (see FIG. 7) formed around the cylinder  15   a , but if the sensor  44  is deviated sideways from the center  48  of the cylinder  15   a  and mounted upside down, it is possible to reduce the height of the sensor  44  only by making shallow a portion of the cooling water passage  15   b  corresponding to the immediately below the sensor  44 , and the height of the sensor  44  is further lowered so as not to be interfered with the flywheel  35 . The sensors  45  and  46  disposed outer side of the width W of the cylinder block  15  are overhanging from the engine  3 , but if the sensor mounting boss  54  is provided on the motor mounting boss  53  formed in the crankcase  16 , it is possible to reduce the weight as compared with a boss  52  which is formed singly, and sufficient supporting rigidity can be ensured. 
     Further, since the cam shaft driving mechanism  24  is disposed at a height lower than the bearing  28   a  which supports the upper end of the crankshaft  4 , it is possible to shorten the distance between the flywheel  35  and the bearing  28   a  , and a load applied to the crankshaft  4  and the bearing  28  can be reduced. 
     FIG. 8 is an enlarged side view of an upper portion of an engine of an outboard motor showing a second embodiment to which the present invention is applied. Constituent members similar to those of the engine  3  shown in the first embodiment are designated by the same reference numerals and its explanation will be omitted herein. 
     As shown in FIG. 8, an engine (engine unit having an engine body)  61  has basically the same structure as that of the engine  3  shown in the first embodiment except for the placement of the cam shaft driving mechanism  24  of the first embodiment. In the second embodiment, the engine  61  is provided at its upper portion with a chain cover  62 , and a cam chain chamber  63  is formed in the chain cover  62 . A cam shaft driving mechanism  64  for transmitting the rotation of the crankshaft  4  to the cam shaft  22  to rotate the cam shaft  22  is provided in the cam chain chamber  63 . 
     A cam drive sprocket  65  is provided on a portion of the crankshaft  4  projecting upward of the engine  61 , and a cam driven sprocket  66  is provided on an upper end of the cam shaft  22  projecting upward of the engine  61 . A timing chain  67  is wound around these sprockets  65  and  66 . 
     The chain cover  62  also serves as a supporting member of the oil seal  30 , and further serves as a mounting member of the stator  33  constituting the magneto device  31  and includes a boss  69  for mounting the crank angle detecting sensor  68 . A diameter J of the mounting portion of the stator  33  to the chain cover  62  is set greater than an outer diameter K of the oil seal  30  as in the first embodiment, and the stator  33  is disposed outside of the oil seal  30 . Further, the sensor mounting boss  69  is arranged such that the sensor  68  can be mounted upside down as in the first embodiment. 
     The operation of the second embodiment of the present invention will be explained. 
     The cam shaft driving mechanism  64  is provided the upper portion of the engine  61 , and the chain cover  62  for covering the cam shaft driving mechanism  64  also functions as the mounting member of the stator  33 , and as a boss  69  for mounting the crank angle detecting sensor  68 . Therefore, it is possible to largely reduce the number of parts. 
     Further, if the diameter of the mounting portion of the stator  33  to the chain cover  62  is set greater than the outer diameter of the oil seal  30  as in the first embodiment, the same operation and effect can be obtained. 
     It is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scope of the appended claims.