Abstract:
There is provided an outboard motor ( 1 ), comprising: an intake valve ( 17 ) and an exhaust valve ( 18 ) provided to a cylinder head ( 14 ); a camshaft ( 20 ) arranged substantially vertically in the cylinder head to open and close the intake and exhaust valves; a valve operation characteristics changing device ( 29 ) hydraulically operated to change operation characteristics of at least one of the intake and exhaust valves; a selector valve (electromagnetic valve  27 ) for controlling an oil pressure provided to the valve operation characteristics changing device; and an exhaust passage component part (exhaust manifold  23 ) secured on a side of the cylinder head, wherein the selector valve is disposed at a position (space G) beside the cylinder head and overlapping with a top-end surface of the exhaust passage component part.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to an outboard motor, and more specifically relates to an outboard motor comprising an engine in which valve operation characteristics of an intake or discharge valve of the engine can be variably controlled depending on an engine rotational speed.  
       BACKGROUND OF THE INVENTION  
       [0002]     It has been known to use a valve operation characteristics changing device in an outboard motor where the valve operation characteristics changing device is adapted to variably control operation characteristics of intake and exhaust valves for controlling supply of air-fuel mixture and discharge of combustion gas, respectively, depending on an operational condition of an engine of the outboard motor, to whereby achieve low fuel consumption and high output over a wide operation range (see Japanese Patent Application Laid-Open (kokai) No. 2000-186516).  
         [0003]     On the other hand, in order to optimally control the air-fuel ratio to achieve higher combustion efficiency, it is desired to provide an exhaust gas property sensor at an appropriate position in an exhaust passage (see Japanese Patent Application Laid-Open (kokai) No. 7-301135).  
         [0004]     However, in the conventional structure disclosed in the above-mentioned JPA Laid-Open No. 2000-186516, a selector valve for controlling the valve operation characteristics changing device is accommodated in a head cover for covering a valve gear mechanism, which results in a larger head cover. This leads to a larger engine cover and increases an amount of overhang in a tilt-up position, which is unfavorable in outboard motors where the engine cover having a smaller outer profile is preferred. Further, the exhaust gas property sensor protrudes from the component parts constituting the exhaust passage, and this can also hinder achieving a smaller engine cover.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In view of such problems of the prior art, a primary object of the present invention is to provide an outboard motor constructed to minimize the increase in size of the engine cover.  
         [0006]     According to the present invention, such objects can be accomplished by providing an outboard motor ( 1 ), comprising: an intake valve ( 17 ) and an exhaust valve ( 18 ) provided to a cylinder head ( 14 ); a camshaft ( 20 ) arranged substantially vertically in the cylinder head to open and close the intake and exhaust valves; a valve operation characteristics changing device ( 29 ) hydraulically operated to change operation characteristics of at least one of the intake and exhaust valves; a selector valve (electromagnetic valve  27 ) for controlling an oil pressure provided to the valve operation characteristics changing device; and an exhaust passage component part (exhaust manifold  23 ) secured on a side of the cylinder head, wherein the selector valve is disposed at a position (space G) beside the cylinder head and overlapping with a top end surface of the exhaust passage component part.  
         [0007]     In this way, the control valve of the valve operation characteristics changing device can be mounted at a place that otherwise would be a dead space in the engine, and thus increase in size of the engine cover can be avoided.  
         [0008]     According to a preferred embodiment of the present invention, the outboard motor further comprises an exhaust gas property sensor ( 28 ) for sensing an exhaust gas property of an engine, wherein the exhaust gas property sensor is secured on the top end surface of the exhaust passage component part. This allows the oil pressure control valve for the valve operation characteristics changing device and the exhaust gas property sensor to be placed at a position where they do not interfere with an engine cover, and therefore increase in the size of the engine cover can be avoided.  
         [0009]     Preferably, the selector valve and the exhaust gas property sensor are arranged in a front-to-back direction. This can improve an efficiency of utilization of the space inside the engine cover while preventing increase in the widthwise dimension of the engine cover.  
         [0010]     Further preferably, the exhaust passage component part extends from a joint with the cylinder head to a lateral side of the camshaft, and the exhaust gas property sensor of the engine is disposed at an end portion of the exhaust passage component part closer to the camshaft. This can achieve efficient utilization of a space that is formed for ensuring a sufficient length of the exhaust passage and that would otherwise be a dead space.  
         [0011]     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Now the present invention is described in the following with reference to the appended drawings, in which:  
         [0013]      FIG. 1  is a side view showing an essential part of an outboard motor to which the present invention is applied, with part thereof being cut away;  
         [0014]      FIG. 2  is a top plan view showing an outboard motor to which the present invention is applied, with part thereof being cut away;  
         [0015]      FIG. 3  is a side view showing an essential part of an exhaust side of an engine for an outboard motor to which the present invention is applied;  
         [0016]      FIG. 4  is a schematic view of a valve operation characteristics changing device; and  
         [0017]      FIG. 5  is a structural view of an electromagnetic valve. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]      FIGS. 1 and 2  show a portion around an engine of an outboard motor constructed according to the present invention. This outboard motor  1  is a known type adapted to be attached to a stern plate  3  via a stern bracket  2 , and its engine  4  is mounted on a mount case  7  that is substantially integral with s swivel case  6  which in turn is connected to the stern bracket  2  so as to be pivotable around a laterally extending tilt shaft  5 . A substantially whole part of the engine  4  mounted on the mount case  7  is covered by a detachable engine cover  8 .  
         [0019]     The mount case  7  is fixed on top of an extension case  9 , and a drive shaft  10  extending to a screw is coupled to a crank shaft  11  inside the mount case  7 .  
         [0020]     The engine  4  may for example consist of a vertical crankshaft engine of a 4-cylinder in-line type, which comprises a crankcase  12 , cylinder block  13  and cylinder head  14 , and is arranged such that the crankcase  12  faces in a forward direction when the watercraft is traveling. The cylinder head  14  is formed with a combustion chamber  19  which is intermittently brought into flow communication with an intake port  15  and an exhaust port  16  via an intake valve  17  and an exhaust valve  18 , respectively ( FIG. 2 ). Further, a head cover  21  for covering a camshaft  20   s  for driving the intake valve  17  and a camshaft  20   e  for driving the exhaust valve  18  is coupled to a right end side of the cylinder head  14  in the drawing, with a gasket  72  ( FIG. 5 ) being interposed between the cylinder head  14  and the head cover  21 .  
         [0021]     An intake device  22  for supplying air/fuel mixture to the intake port  15  is disposed at one lateral side of the crankcase  12 , cylinder block  13  and cylinder head  14  so as to oppose them. On the other lateral side of the cylinder head  14  is disposed an exhaust manifold  23  for discharging combustion gas from the exhaust port  16 .  
         [0022]     The exhaust manifold  23  is formed with: exhaust passages  24  which are provided for respective cylinders and each extend substantially in parallel with a cylinder shaft from a coupling end coupled to an opening surface of the exhaust port  16  of the cylinder head  14  toward a lateral side portion of the head cover  21  covering the camshaft; an exhaust chamber  25  connected to a downstream end of each exhaust passage  24  and extending substantially in parallel with the crankshaft  11  (camshaft); and a water jacket  26  that surrounds the exhaust passages  24  and the exhaust chamber  25 . An end of the exhaust chamber  25  away from a crank pulley, i.e., a lower end, is connected to an upper surface of the mount case  7  so that the combustion gas is discharged into the extension case  9 . A portion of the exhaust manifold  23  connected to the upper surface of the mount case  7  is also attached with a hose  74  in order to allow discharge of engine cooling water from a thermostat case  73  which is provided on an end of the cylinder head  14  on the crank pulley side.  
         [0023]     As shown in  FIG. 3 , the end surface of the cylinder head  14  on the crank pulley side, i.e., an upper end surface, is offset from an upper end surface of the exhaust manifold  23  in an axial direction of the crankshaft  11  such that the offset defines a space G at the lateral side of an upper end portion of the cylinder head  14  away from the intake device  22 . In this space G, an electromagnetic valve  27  for controlling a valve operation characteristics changing device, which will be described later, is securely mounted. Further, on an end portion of the upper end surface of the exhaust manifold  23  close to the camshaft, an exhaust gas property sensor  28  is securely mounted so as to be adjacent to the electromagnetic valve  27 .  
         [0024]     The intake valves  17  of the engine  4  are provided with a valve operation characteristics changing device  29 . In the following, the valve operation characteristics changing device  29  is explained with reference to  FIG. 4 . It should be noted that the valve operation characteristics changing device  29  is provided for each of the cylinders although only one of them will be explained below.  
         [0025]     As seen in  FIG. 4 , the intake camshaft  20   s  is integrally formed with a pair of low-speed cams  31   a ,  31   b  for providing a relatively small valve operating angle and lift amount, and a high-speed cam  32  for providing a relatively large valve operating angle and lift amount where the high-speed cam  32  is interposed between the low-speed cams  31   a ,  31   b . Below the intake camshaft  20   s , three rocker arms  34   a ,  35 ,  34   b  are rotatably supported on a rocker shaft  33  extending in parallel with the intake camshaft  20   s , where the rocker arms  34   a ,  35 ,  34   b  are disposed one next to the other such that they can be angularly displaced relative to each other. The rocker arms  34   a ,  35 ,  34   b  are adapted to be rotatably driven by the corresponding cams  31   a ,  32 ,  31   b , respectively.  
         [0026]     The low-speed rocker arms  34   a ,  34   b  which are driven by the low-speed cams  31   a ,  31   b  essentially have an identical shape and their free ends abut stern ends of the two intake valves  17  which are always spring-urged in the closing direction. The high-speed rocker arm  35  which is driven by the high-speed cam  32  is always kept in a slidable contact with the high-speed cam  32  by a spring member not shown in the drawing.  
         [0027]     Inside the mutually adjoining three rocker arms  34   a ,  35 ,  34   b  is provided a selective coupling mechanism for selectively achieving a low-speed mode in which the rocker arms are allowed to be angularly displaced relative to each other and a high-speed mode in which the rocker arms can be rotated in a unit. In the following, the selective coupling mechanism is described in detail.  
         [0028]     Referring to  FIG. 4 , the low-speed rocker arm  34   a  on the left is formed with a first guide hole  36  which opens out towards the center-positioned high-speed rocker arm  35  and is closed at the other end, where the guide hole  36  extends in parallel with the axis of the rocker shaft  33  and a first selective coupling pin  37  is slidably received therein. The high-speed rocker arm  35  is formed with a second guide hole  38  passing therethrough such that the second guide hole  38  is aligned with the first guide hole  36  in a rest position where a round base portion of the high-speed cam  32  is slidably contacts the cam slipper. Further, a second selective coupling pin  39  is received in the second guide hole  38  so that one end of the second selective coupling pin  39  abuts the first selective coupling pin  37 .  
         [0029]     Like the left low-speed rocker arm  34   a , the right low-speed rocker arm  34   b  in  FIG. 4  is formed with a third guide hole  40  which is substantially closed at one end, and a stopper pin  41  is slidably received therein such that one end of the stopper pin  41  abuts the other end of the second selective coupling pin  39 . The stopper pin  41  is always urged toward the high-speed rocker arm  35  by a compression coil spring  42 .  
         [0030]     The rocker shaft  33  is internally provided with an oil supply passage  43  for conducting engine oil pumped up from an oil pan by a pump P. The oil supply passage  43  is in flow communication with a bottom of the first guide hole  36  as well as with passages (not shown in the drawing) for supplying the engine oil to the contact surfaces between the rocker shaft  33  and each of the rocker arms  34   a ,  35 ,  34   b , the sliding surfaces between each of the cams  31   a ,  32 ,  31   b  and the cam slippers, and the cam journals.  
         [0031]     The above described selective coupling mechanism is operated by open/close controlling the electromagnetic valve  27  depending on an operating condition of the engine  4  and thereby intermittingly transmitting an oil pressure to the first selective coupling pin  37  in the first guide hole  36  through the oil supply passage  43 .  
         [0032]     In the low-speed mode, the first selective coupling pin  37  is not applied with a high oil pressure, and a resilient force from the compression coil spring  42  brings each pin  37 ,  39 ,  41  into alignment with the corresponding guide hole  36 ,  38 ,  40  (a state shown in  FIG. 4 ). In this state, the rocker arms  34   a ,  35 ,  34   b  can be angularly displaced relative to each other. In other words, the rocker arms  34   a ,  35 ,  34   b  can individually undergo a rocking motion. Therefore, the high-speed rocker arm  35  driven by the high-speed cam  32  would not affect the other rocker arms  34   a ,  34   b , and the two intake valves  17  are simultaneously driven by the low-speed rocker arms  34   a ,  34   b  which are driven by the low-speed cams  31   a ,  31   b  having a relatively small lift amount and valve operating angle.  
         [0033]     In the high-speed mode, a high oil pressure is applied to the fist selective coupling pin  37  through the oil supply passage  43 , and the first and second selective coupling pins  37 ,  39  are pushed out from the first and second guide holes  36 ,  38 , respectively, against the resilient force of the compression coil spring  42 . This causes the first and second selective coupling pins  37 ,  39  to sit across adjoining ones of the rocker arms  34   a ,  35 ,  34   b . Therefore, the rocker arms  34   a ,  35 ,  34   b  are joined to each other so as to be rotatable as a unit, and accordingly the two intake valves  17  are simultaneously driven by the high-speed cam  32  having a relatively large lift amount and valve operating angle.  
         [0034]     Next, an explanation is made as to the electromagnetic valve  27  for operating the above-described valve operation characteristics changing device  29  between the low-speed mode and the high-speed mode. As shown in  FIG. 5 , the electromagnetic valve  27  comprises a valve body  51 , a spool valve  52 , a pilot valve  53 , and a solenoid  54  for driving the pilot valve  53 , where the valves  52 ,  53  are received in the valve body  51  so as to be moveable along respective axial lines which are parallel to each other.  
         [0035]     The solenoid  54  is fastened to an end surface of the valve body  51  on the side of the camshaft  20 , i.e., an upper end surface in  FIG. 5 . Within an air-core of the solenoid  54  is received a plunger  56  which is connected to the pilot valve  53  and always urged downward by a compression coil spring  55 . In this way, a lower end of the pilot valve  53  is pressed against an opening of an orifice  58  provided at an outlet of an upstream-side pilot oil passage  57  that supplies a pilot pressure to the spool valve  52 .  
         [0036]     Opened in a surface of the valve body  51  facing the cylinder head  14  and arranged from top to down are: a drain port  60  connected to an engine oil return passage  59 ; an outlet port  62  connected to a supply passage  61  which in turn is connected to the oil supply passage  43  of the rocker shaft  33 ; and an inlet port  64  connected to an engine oil discharge passage  63  from the pump P. Among these ports, the inlet port  64  is directly connected to the upstream-side pilot oil passage  57  while the outlet port  62  is connected to the upstream-side pilot oil passage  57  via an orifice  65 .  
         [0037]     The spool valve  52  is formed with, from top to down, a piston portion  66 , an annular recessed portion  67  for allowing communication between the inlet and outlet ports, and a land portion  68  for blocking communication between the inlet and outlet ports, where these portions are arranged serially and the spool valve  52  is always urged in the upward direction resiliently by a compression coil spring  69  which is disposed at a lower end side of the spool valve  52  in a compressed state.  
         [0038]     In a deactivated state of the electromagnetic valve  27  as shown in  FIG. 5 , the pilot valve  53  closes the orifice  58  due to the downward resilient force which is applied thereto from the coil spring  55  via the plunger  56 . Therefore, the high oil pressure transmitted from the inlet port  64  to the upstream-side pilot oil passage  57  is blocked there. In this state, the land portion  68  of the spool valve  52  which is lifted by an upward resilient force of the coil spring  59  blocks the direct communication between the inlet port  64  and the outlet port  62 . Thus, the engine oil which has flowed into the upstream-side pilot oil passage  57  from the inlet port  64  only flows into the outlet port  62  via the orifice  65  by an amount necessary for lubricating the valve gear mechanism. Consequently, the high oil pressure does not act upon the outlet port  62 , keeping the valve operation characteristics switching device  29  in the low-speed mode.  
         [0039]     When an electric current is supplied to the solenoid  54 , the plunger  56  is lifted against the urging force of the coil spring  55 , causing the pilot valve  53  to move upward. This opens the orifice  58  so that the high oil pressure in the upstream-side pilot oil passage  57  is transmitted to an upper surface of the piston portion  66  of the spool valve  52  through a downstream-side pilot oil passage  70  which is formed in the valve body  51  so as to extend obliquely in a downward direction. The high oil pressure causes the spool valve  52  to move downward against the resilient force of the coil spring  69 . As a result, the land portion  68  moves downward, and the inlet port  64  and the outlet port  62  are directly connected to each other via the annular recessed portion  67 . This allows the high oil pressure to be transmitted to the outlet port  62 , causing the selective coupling pins  37 ,  39  to move to the right in the drawing so that the high-speed mode is achieved. In this state, excessive oil is discharged from the drain port  60  via an orifice  71  formed in the piston portion  66 .  
         [0040]     In the outboard motor  1  where an outer profile of the engine cover  8  should be as small as possible, it is not preferable that the above-described electromagnetic valve  27  projects out from the outer profile of the engine  4 . Therefore, according to the present invention, the upper end surface of the exhaust manifold  23  and the upper end surface of the cylinder head  14  are offset from each other in the direction of axis of the crankshaft to thereby define the space G therebetween, and the electromagnetic valve  27  is disposed in the space G such that the electromagnetic valve  27  overlaps the upper end surface of the exhaust manifold  23 . This can prevent the electromagnetic valve  27  from projecting out from the outer profile of the engine. Particularly, if the exhaust gas property sensor  28  is disposed on a camshaft-side end of the exhaust manifold  23 , which extends from a joint with the cylinder head  14  to a lateral side of the camshaft  20 , the open space formed for ensuring a sufficient length of the exhaust passage  24  can be utilized even more efficiently.  
         [0041]     As described above, according to the present invention, the electromagnetic valve and the exhaust gas property sensor are disposed so as to be adjacent to each other in the front-to-back direction in a space which is formed beside an upper end portion of the cylinder head and which usually would be a dead space. This can allow the electromagnetic valve and the exhaust gas property sensor to be attached to the engine without an increase in the outer profile of a crank pulley-side end surface of the engine of the outboard motor. Therefore, the present invention is quite advantageous in achieving a more compact outboard motor.  
         [0042]     Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.