Patent Publication Number: US-8109800-B2

Title: Outboard motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an outboard motor including a transmission device arranged to change the speed or the direction of rotation of an engine and to transmit the rotation to a propeller. 
     2. Description of the Related Art 
     WO 2007-007707 A1 proposes an outboard motor including a hydraulic clutch type transmission mechanism that shifts the speed of rotation of an engine between high speed and low speed positions and transmits the rotation to a propeller, an oil pump for supplying hydraulic pressure to the hydraulic clutch type transmission mechanism, and a hydraulic pressure control valve for controlling hydraulic pressure supplied to the hydraulic clutch type transmission mechanism. A solenoid type hydraulic pressure control valve in which an electromagnetic coil is energized to open or close a valve body is generally applied to the hydraulic pressure control valve. 
     However, when the solenoid type hydraulic pressure control valve is applied, it is necessary to cool the valve at a position that depends on where the valve is located because the hydraulic pressure control valve generates heat. In this case, if the hydraulic pressure control valve is constructed to be cooled by a separate cooling mechanism, it results in a complicated construction and a cost increase. 
     Depending on how the hydraulic pressure control valve is arranged, there is concern that the outboard motor may increase in size and the distance from the center of gravity of the outboard motor to a hull may increase, thereby increasing an applied load on a clamp bracket supporting the outboard motor on the hull. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide an outboard motor capable of ensuring a cooling characteristic of a hydraulic pressure control valve without causing structural complexity and an increase in cost and without increasing the size of the outboard motor and the load applied to a clamp bracket. 
     A first preferred embodiment of the present invention provides an outboard motor including an engine arranged to generate power, and a transmission device arranged to change the speed of rotation of the engine and to transmit the rotation to a propeller, in which the transmission device includes a hydraulic type transmission mechanism arranged to change a rotational operation of the engine and a hydraulic pressure control valve arranged to control hydraulic pressure supplied to the hydraulic type transmission mechanism, and the hydraulic pressure control valve is disposed on one side in the watercraft width direction. 
     A second preferred embodiment of the present invention provides the outboard motor in accordance with the first preferred embodiment, in which the hydraulic pressure control valve is arranged to protrude in a direction toward the one side of the watercraft. 
     A third preferred embodiment of the present invention provides the outboard motor in accordance with the second preferred embodiment, in which a transmission housing arranged to house the hydraulic type transmission mechanism includes upper and lower housings connected by a fastening bolt, for example, and the hydraulic pressure control valve protrudes in the direction toward the one side in the rear of the fastening bolt disposed on a front side in the watercraft in a fore-and-aft direction. 
     A fourth preferred embodiment of the present invention provides the outboard motor in accordance with the first preferred embodiment, in which a hydraulic housing arranged to house the hydraulic pressure control valve is detachably mounted on a side wall of a transmission housing arranged to house the hydraulic type transmission mechanism, and at least a portion of a hydraulic circuit is arranged on a mating surface between the side wall of the transmission housing and the hydraulic housing. 
     A fifth preferred embodiment of the present invention provides the outboard motor in accordance with the fourth preferred embodiment, in which at least a portion of a cooling circuit arranged to cool the hydraulic pressure control valve by oil injection is arranged on the mating surface between the side wall of the transmission housing and the hydraulic housing. 
     A sixth preferred embodiment of the present invention provides the outboard motor in accordance with the first preferred embodiment, in which the hydraulic pressure control valve is disposed with its valve shaft oriented in the watercraft fore-and-aft direction, and an input passage and an output passage of hydraulic pressure to and from the hydraulic pressure control valve are arranged to extend in directions perpendicular, or substantially perpendicular, to the valve shaft. 
     A seventh preferred embodiment of the present invention provides the outboard motor in accordance with the first preferred embodiment, in which the hydraulic pressure control valve is disposed above a lower mount member arranged to support the outboard motor. 
     An eighth preferred embodiment of the present invention provides the outboard motor in accordance with the seventh preferred embodiment, in which the hydraulic pressure control valve is disposed to protrude in a direction toward the one side, a level to which the hydraulic pressure control valve protrudes in the direction toward the one side is equivalent, or substantially equivalent, to a level to which the lower mount member protrudes in the direction toward the one side. 
     The hydraulic pressure control valve is disposed on one side in the watercraft width direction in the outboard motor in accordance with the first preferred embodiment of the present invention. This facilitates contact between a headwind and the hydraulic pressure control valve during traveling, thus ensuring the cooling characteristics of the hydraulic pressure control valve. As a result, it is not necessary to provide a separate cooling mechanism, thus preventing a complex structure and an increase in cost. 
     Because the hydraulic pressure control valve is disposed on one side in the watercraft width direction, it allows for the prevention of an increase in the size of the outboard motor in the fore-and-aft direction due to a disposition of the hydraulic pressure control valve. As a result, it prevents both a size increase of the outboard motor and an increase in the load applied to the clamp bracket. 
     In the second preferred embodiment of the present invention, the hydraulic pressure control valve is arranged to protrude in a direction toward one side. This facilitates contact between a headwind and the hydraulic pressure control valve during traveling, thus enhancing the cooling characteristics. 
     In the third preferred embodiment of the present invention, the hydraulic pressure control valve protrudes in the direction toward one side in the rear of the fastening bolt disposed on the front side in the watercraft fore-and-aft direction. Therefore, a cover arranged to cover the hydraulic pressure control valve is prevented from contacting with the clamp bracket and so forth when the outboard motor is steered to a maximum steering angle. As a result, both a size increase of the outboard motor and an increase in the load applied on the bracket can be prevented while also securing sufficient steering angles. 
     In the fourth preferred embodiment of the present invention, at least a portion of the hydraulic circuit is arranged on the mating surface between the transmission housing and the hydraulic housing. This allows for a downsizing of the hydraulic circuit by utilizing the mating surface between both the housings and facilitates forming the hydraulic circuit. 
     In the fifth preferred embodiment of the present invention, at least a portion of the cooling circuit arranged to cool the hydraulic pressure control valve is arranged on the mating surface between the transmission housing and the hydraulic housing. Therefore, the hydraulic pressure control valve can be cooled by both a headwind and oil, thus achieving an improvement in the cooling rate and a further improvement in the durability of the hydraulic pressure control valve. 
     In the sixth preferred embodiment of the present invention, the valve shaft of the hydraulic pressure control valve is disposed in the watercraft fore-and-aft direction, and the input passage and the output passage between the hydraulic pressure control valve are arranged in the directions perpendicular, or substantially perpendicular, to the valve shaft. Therefore, hydraulic pressure can come and go directly between the hydraulic pressure control valve and the transmission mechanism, thus achieving a simple configuration of the hydraulic circuit and savings in cost. 
     In the seventh preferred embodiment of the present invention, the hydraulic pressure control valve is disposed above the lower mount member. Therefore, the hydraulic pressure control valve can be disposed without interfering with the lower mount member. Further, the whole outboard motor can be arranged compactly. 
     In the eighth preferred embodiment of the present invention, the level to which the hydraulic pressure control valve protrudes on the side is equivalent, or substantially equivalent, to the level to which the lower mount member protrudes on the side. Therefore, the hydraulic pressure control valve does not protrude higher than the lower mount member that is originally installed. Thus, a size increase of the outboard motor can also be prevented in this manner. 
     Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an outboard motor including a transmission device in accordance with a preferred embodiment of the present invention. 
         FIG. 2  is across-sectional rearview of a transmission device in accordance with a preferred embodiment of the present invention. 
         FIG. 3  is a cross-sectional front view of a transmission device in accordance with a preferred embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of a power transmitting portion in which an oil pump of a transmission device in accordance with a preferred embodiment of the present invention is disposed. 
         FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 2 . 
         FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 2 . 
         FIG. 7  is a side view of a housing in which a transmission device in accordance with a preferred embodiment of the present invention is housed. 
         FIG. 8  is a cross-sectional view taken along line VIII-VIII in  FIG. 7 . 
         FIG. 9  is a cross-sectional view taken along line IX-IX in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described hereinafter with reference to the attached drawings. 
       FIGS. 1 through 9  are drawings for describing an outboard motor in accordance with preferred embodiments of the present invention. Front, rear, right, and left in descriptions of the preferred embodiments denote front, rear, right, and left in the view as seen from the rear of a watercraft unless otherwise specified. 
     In the figures, reference numeral  1  denotes an outboard motor installed at a stern  2   a  of a hull  2 . The outboard motor  1  is supported swingably in the vertical direction by a clamp bracket  3  fixed to the hull  2  via a swivel arm  4  and supported to be steerable to the right and left via a pivot portion  5 . 
     The outboard motor  1  has an engine  6  in which a crankshaft  6   a  is oriented generally vertically, an exhaust guide  7  on which the engine  6  is mounted, a cowling  8  connected to an upper surface of the exhaust guide  7  to cover an outer periphery of the engine  6 , an upper case  9  connected to a lower surface of the exhaust guide  7 , and a lower case  10  connected to a lower surface of the upper case  9 . 
     The outboard motor  1  is supported by the clamp bracket  3  via an upper mount member  11  mounted on the exhaust guide  7  and a lower mount member  12  mounted on a lower end of the upper case  9 . 
     The outboard motor  1  includes the engine  6  arranged to generate power and a transmission device  15  arranged to change the speed of rotation of the engine  6  and to transmit the rotation to a propeller  13 . 
     The transmission device  15  includes a first input shaft  24  connected to the crankshaft  6   a  arranged to output power of the engine  6 , a hydraulic type and planetary gear type transmission mechanism  20  connected to the first input shaft  24  and arranged to change the speed of rotation of the engine  6 , and a hydraulic type forward-reverse switching mechanism  21  connected to the transmission device  20  and arranged to change the direction of rotation of the engine  6 . 
     The propeller  13  is attached to a propeller shaft  13   a . The propeller shaft  13   a  is connected to a drive shaft  14  via a bevel gear mechanism  13   b . The propeller shaft  13   a  is disposed in a direction perpendicular, or substantially perpendicular, to the crankshaft  6   a  in the lower case  10 . The drive shaft  14  is coaxially disposed with the crankshaft  6   a.    
     The transmission mechanism  15  is housed in a generally cylindrical transmission housing  22  that is preferably oil-tight. The transmission housing  22  is housed in the upper case  9  to be positioned in a front portion thereof. An exhaust system  16  arranged to discharge exhaust gas from the lower case  10  into the water is disposed in the rear of the transmission device  15  in the upper case  9 . 
     The transmission housing  22  is divided into an upper housing  22   a  in which the transmission mechanism  20  is housed and a lower housing  22   b  in which the forward-reverse switching mechanism  21  is housed. The lower housing  22   b  and the upper housing  22   a  are combined together preferably by front bolts B 1 , for example, disposed on the left and right sides on the front side in the watercraft fore-and-aft direction and preferably by rear bolts B 2 , for example, disposed on the left and right sides on the rear side (see  FIG. 5 ). 
     The planetary gear type transmission mechanism  20  preferably includes a first internal gear  25 , a first sun gear  27 , a first output shaft  28 , a first carrier  29 , first planetary gears  30 , and a second clutch  31 . 
     The first internal gear  25  is connected to the first input shaft  24  to rotate together therewith. The first sun gear  27  is connected toward the housing  22  via a first clutch  26 . The first output shaft  28  is coaxially disposed with the first input shaft  24 . The first carrier  29  is connected to the first output shaft  28  to rotate together therewith. The first planetary gears  30  are supported by the first carrier  29  to be capable of relative rotation and are meshed with the first sun gear  27  and the first internal gear  25 . The second clutch  31  is located between the first sun gear  27  and the first carrier  29 . 
     The first input shaft  24  is coaxially disposed with the crankshaft  6   a  and combined with the crankshaft  6   a  to rotate together therewith. 
     The first sun gear  27  is fixedly housed in or rotatably supported by the housing  22 . The first sun gear  27  is connected to or disconnected from a support housing  33  for rotatably supporting the first output shaft  28  via the first clutch  26 . 
     As shown in  FIG. 5 , the first clutch  26  is a one-way type clutch which permits only rotation of the first sun gear  27  in rotational direction (a) (clockwise) of the crankshaft  6   a  but prohibits rotation in the opposite direction (counterclockwise). 
     The second clutch  31  is preferably a wet type multi-plate clutch and has a clutch housing  31   a  combined with the first sun gear  27  to rotate together therewith, a number of clutch plates  31   b  disposed between the clutch housing  31   a  and the first carrier  29 , a piston  31   e  disposed in a hydraulic chamber  31   d  arranged in the clutch housing  31   a , and a spring member  31   c  urging the piston  31   e  in a direction to disconnect power transmission. The piston  31   e  brings the clutch plates  31   b  into contact with each other by hydraulic pressure supplied to the hydraulic chamber  31   d.    
     When an operator of the watercraft operates a shift lever or a shift button (neither shown) to a low speed position, the first clutch  26  is engaged, the first sun gear  27  is locked, and the second clutch  31  is disengaged. When rotation of the engine  6  is transmitted from the first input shaft  24  to the first internal gear  25  in this state and the internal gear  25  rotates, each of the planetary gears  30  rotates, rotates relatively to the first internal gear  25 , and revolves with respect to the first sun gear  27 . Thereby, the speed of engine rotation is reduced and the rotation is transmitted to the first output shaft  28 . 
     On the other hand, when operation is changed to a high speed position, the first clutch  26  is disengaged, the first sun gear  27  enters a free state, and the second clutch  31  is engaged. When rotation of the engine  6  is transmitted from the first input shaft  24  to the first internal gear  25  in this state, the first internal gear  25 , each of the first planetary gears  30 , and the first sun gear  27  rotate unitarily. Rotation of the first input shaft  24  is transmitted to the first output shaft  28  without speed reduction. 
     The forward-reverse switching mechanism  21  has a second internal gear  36 , a second input shaft  37 , a second output shaft  38 , a second sun gear  39 , a second carrier  40 , a second planetary gear  41 , a third planetary gear  42 , and a fourth clutch  43 . 
     The internal gear  36  is connected to the housing  22  via a third clutch  35 . The second input shaft  37  is coaxially disposed with the first output shaft  28  and connected to the first output shaft  28  to rotate together therewith. The second output shaft  38  is coaxially disposed with the second input shaft  37 . The second sun gear  39  is unitarily disposed with and connected to the second output shaft  38 . The second carrier  40  is connected to the second input shaft  37  to rotate together therewith. The second planetary gear  41  is rotatably supported by the second carrier  40  and meshed with the second sun gear  39 . The third planetary gear  42  is meshed with the second internal gear  36 . The fourth clutch  43  is installed between the second carrier  40  and the second output shaft  38 . 
     The fourth clutch  43  and the third clutch  35  are preferably multi-plate wet type clutches having constructions similar to the second clutch  31  described above. 
     When a shift lever or a shift switch (neither shown) arranged to switch between forward and reverse is in a neutral position, the third and fourth clutches  35  and  43  are disengaged. The second input shaft  37  idles. Accordingly, rotation of the second input shaft  37  is not transmitted to the second output shaft  38 . 
     When shifting from the neutral position to a forward position, the third clutch  35  is disengaged, and the fourth clutch  43  is engaged. The second internal gear  36 , the second and third planetary gears  41  and  42 , and the second sun gear  39  rotate unitarily. The second output shaft  38  rotates in the forward travel direction which is the same as rotational direction (a) of the engine  6 . 
     On the other hand, when shifting from the neutral position to a reverse position, the third clutch  35  is engaged, and the fourth clutch  43  is disengaged. The second internal gear  36  is fixed to the housing  22  to be unable to rotate. The second and third planetary gears  41  and  42  revolve while rotating in directions opposite to each other. The second sun gear  39  rotates in the opposite direction. Thereby, the second output shaft  38  rotates in the reverse travel direction which is the direction opposite to rotational direction (a) of the crankshaft  6   a.    
     The transmission device  15  preferably has a planetary gear type speed reducing mechanism  18  arranged to reduce the speed of rotation of the second output shaft  38  and transmit the rotation to the drive shaft  14 . 
     The planetary gear type speed reducing mechanism  18  has an internal gear  55 , a planetary gear  57 , and a sun gear  58 . 
     The internal gear  55  is connected to the second output shaft  38  to rotate together therewith. The planetary gear  57  is meshed with the internal gear  55  and rolls on the internal gear  55 . The sun gear  58  is meshed with the planetary gear  57  and disposed to be unable to rotate. 
     The speed reducing mechanism  18  has a speed reducer housing  56  fixed to the lower case  10  and rotatably supporting a boss  55   a  of the internal gear  55  and a carrier  59  rotatably supporting the planetary gear  57 . 
     The sun gear  58  is fixed to the lower case  10  to be incapable of rotation. The carrier  59  is rotatably supported by the sun gear  58 . The carrier  59  is combined with the drive shaft  14  to rotate together therewith. 
     The transmission device  15  includes the first input shaft  24  constructing the power transmitting portion, an oil pump  45  disposed on the first input shaft  24 , and a driving force acquisition mechanism  46  arranged to acquire driving force from the first input shaft  24 . 
     The oil pump  45  supplies hydraulic pressure to the second through fourth clutches  31 ,  35 , and  43  and supplies oil for lubricating and cooling each slide portion of the transmission device  15 . The oil pump  45  is independent from an oil pump arranged to supply lubricating oil to each sliding portion of the crankshaft  6   a  and so forth of the engine  6 . 
     The first input shaft  24  extends upward from the housing  22  and is housed in a first housing  47  connected to an upper surface of the housing  22 . A second housing  48  arranged to house the oil pump  45  is disposed in and fixed to the first housing  47 . The first input shaft  24  is rotatably supported by the second housing  48 . 
     A third housing  49  arranged to house the driving force acquisition mechanism  46  is connected to the outside of the first housing  47 . The third housing  49  is disposed to extend outward on the starboard side of the first housing  47  in the watercraft width direction. 
     The driving force acquisition mechanism  46  has a driving force acquisition shaft  46   a  extending in a direction toward the starboard side and perpendicular, or substantially perpendicular, to the axis of the first input shaft  24 . The driving force acquisition shaft  46   a  is connected to the first input shaft  24  to rotate together therewith via a bevel gear mechanism  46   b.    
     A water pump  50  is connected to the driving force acquisition mechanism  46 . The water pump  50  has a pump shaft  52  disposed in the third housing  49  in parallel, or substantially parallel, with the driving force acquisition shaft  46   a  and on which a reduction gear  52   a  meshed with a driving gear  46   c  of the driving force acquisition shaft  46   a  is arranged and a pump cover  51  arranged to house the water pump  50 . The pump cover  51  is detachably connected to the third housing  49 . 
     A portion of coolant drawn up by the water pump  50  is supplied to the engine  6  side by a coolant hose  51   a  connected to the pump cover  51 . The remaining coolant is supplied to the transmission device  15  side by a branch hose  51   b  connected to the coolant hose  51   a.    
     Coolant jackets  22   c  and  22   d  extending in the circumferential direction are arranged on the starboard and the rear sides of the housing  22 . The branch hose  51   b  is connected to the coolant jackets  22   c  and  22   d.    
     The oil pump  45  has an inner rotor  45   a  housed in a pump chamber  48   a  arranged in the second housing  48  and combined with the first input shaft  24  to rotate together therewith and an outer rotor  45   b  fixed to the second housing  48 . The oil pump  45  pressurizes and discharges oil drawn by rotation of the inner rotor  45   a.    
     An oil inlet  48   b  fluidly connected to a suction port of the oil pump  45  and an oil outlet  48   c  fluidly connected to a discharge port are defined in the second housing  48 . 
     An oil reservoir  22   e  is arranged at a bottom of the housing  22 . The oil reservoir  22   e  and the oil inlet  48   b  are fluidly connected together by an oil drawing passage  22   f  provided in the housing  22  and extending in the axial direction. 
     An oil discharge passage  22   g  extending in parallel, or substantially parallel, with the oil drawing passage  22   f  is provided in the housing  22 . An upstream end of the oil discharge passage  22   g  is fluidly connected to the oil outlet  48   c . A downstream end thereof is fluidly connected to hydraulic chambers  31   d ,  35   d , and  43   d  of the second through fourth clutches  31 ,  35 , and  43  via respective clutch hydraulic passages  22   i.    
     The oil drawing passage  22   f  and the discharge passage  22   g  are disposed on the port side in the watercraft width direction with respect to a straight line “A” extending in the traveling direction through the center of the first input shaft  24  (shown in  FIG. 5 ). In addition, the oil drawing passage  22   f  is disposed in a portion downstream of the oil discharge passage  22   g  in rotational direction (a) of the crankshaft  6   a  (on the front side in the watercraft traveling direction). 
     An oil return passage  22   h  extending in the circumferential direction along the inside of the coolant jacket  22   c  is arranged on the side generally opposite to the oil drawing passage  22   f  across the second input shaft  37  in the lower housing  22   b . The oil return passage  22   h  is fluidly connected to the oil reservoir  22   e.    
     Oil passages  24   a ,  28   a ,  37   a , and  38   a  are arranged to be fluidly connected to each other in the axes of the first input shaft  24 , the first output shaft  28 , the second input shaft  37 , and the second output shaft  38 , respectively. Oil supplied from the oil outlet  48   c  to the oil passages  24   a ,  28   a ,  37   a , and  38   a  is supplied to each of bearings, slide parts, and so forth. 
     In this case, oil supplied into the upper housing  22   a  returns to the oil reservoir  22   e  through the oil return passage  22   h  of the lower housing  22   b . Oil supplied into the lower housing  22   b  drops and returns to the oil reservoir  22   e.    
     A relief passage  48   d  fluidly connecting the oil discharge passage  22   g  and the oil drawing passage  22   f  together is defined in the second housing  48 . A relief valve  61  is interposed in the relief passage  48   d . A valve body  61   a  is urged in the closing direction by a spring member  62  in the relief valve  61 . An elastic force of the spring member  62  is set so that a valve body  61   a  opens when pressure in the relief passage  48   d  exceeds a predetermined value (see  FIG. 6 ). 
     The transmission device  15  includes second through fourth hydraulic pressure control valves  65 ,  66 , and  67  arranged to control hydraulic pressure supplied to the second through fourth clutches  31 ,  35 , and  43 , respectively, of the planetary gear type transmission mechanism  20  and the forward-reverse switching mechanism  21  independently of each other. 
     Each of the second through fourth hydraulic pressure control valves  65  through  67  is controlled by a controller (not shown) to open or close based on a speed shifting signal, a forward-reverse switching signal, and so forth. 
     The hydraulic pressure control valves  65  through  67  are housed in respective hydraulic housing  65   a  through  67   a  arranged independently of each other. The hydraulic housing  65   a  through  67   a  have respective housing main bodies  65   b  through  67   b  detachably mounted on a left side wall surface  22   k  of the housing  22  by a plurality of bolts  68  inserted from the outside and respective lid members  65   c  through  67   c  detachably mounted on the housing main bodies  65   b  through  67   b  in a state that the hydraulic pressure control valves  65  through  67  are preferably fixed by a plurality of bolts  69 , for example, inserted from the front side. 
     Each of the hydraulic pressure control valves  65  through  67  is disposed in parallel, or substantially parallel, in the vertical direction on the port side in the watercraft width direction of the housing  22  and is disposed to protrude outward from the housing  22  in the watercraft width direction. 
     The hydraulic pressure control valves  65  through  67  protrudes toward the port side in a portion between the front bolt B 1  and the rear bolt B 2  on the left side arranged to combine the upper housing  22   a  and the lower housing  22   b  together. The front bolts B 1  preferably arranged to fasten the upper and lower housings  22   a  and  22   b  together are designed so that an outer surface of a portion of the upper case  9  covering the bolts do not contact with the clamp bracket and so forth at the maximum steering angles. The hydraulic pressure control valves  65  through  67  protrude toward the port side in the rear of the front bolt B 1 . Therefore, a portion  9   a  of the upper case  9  covering the hydraulic pressure control valves  65  through  67  can be prevented from contacting with the clamp bracket and so forth when the outboard motor is turned to the maximum steering angle. 
     Each of the hydraulic pressure control valves  65  through  67  is disposed on the side opposite to the water pump  50  across the center line C of the transmission device and is positioned below the water pump  50  in a view from the rear of the watercraft (see  FIG. 2 ). This stabilizes the weight balance between the left and the right sides of the transmission device  15 . 
     Each of the hydraulic pressure control valves  65  through  67  is positioned above the lower mount member  12  in a view from a side of the watercraft. A level to which each of the hydraulic pressure control valves  65  through  67  protrudes toward the port side is substantially equivalent to a level to which the lower mount member  12  protrudes toward the port side (see straight line B in  FIG. 3 ). 
     The hydraulic pressure control valves  65  through  67  have respective valve shafts  65   d  through  67   d  whose axes are disposed in the fore-and-aft direction that is the watercraft traveling direction and respective electric drivers  65   e  through  67   e  connected to front sides of the respective valve shafts  65   d  through  67   d  and reciprocally driving the valve shafts  65   d  through  67   d  in the axial directions (shown in  FIG. 7 ). 
     A hydraulic circuit  70  and a cooling circuit  71  are arranged on a mating surface between the left side wall surface  22   k  of the housing  22  and each of the hydraulic housings  65   a  through  67   a . Here, since the hydraulic circuits  70  and the cooling circuits  71  of the second through fourth hydraulic pressure control valves  65  through  67  have similar constructions, descriptions will be made only about the hydraulic circuit  70  and the cooling circuit  71  of the fourth hydraulic pressure control valve  67  for controlling hydraulic pressure supplied to the fourth clutch  43 , that are shown in  FIG. 8 . 
     The cooling circuit  71  is arranged to cool the hydraulic pressure control valve  67  through the injection of oil. Specifically, hydraulic cooling passages  22   q  and  67   j  fluidly connected to the oil discharge passage  22   g  are arranged to extend in the watercraft width direction in the housing  22  and the hydraulic housing  67   a . The hydraulic cooling passage  67   j  opens toward the driver  67   e  in the hydraulic housing  67   a.    
     Oil pressurized by the oil pump  45  passes through the oil discharge passage  22   g  and the hydraulic cooling passages  22   q  and  67   j  and is injected to the driver  67   e , thereby cooling the driver  67   e . Oil injected to the driver  67   e  returns into the housing  22  via a return passage  67   k  and a return hole  67   i  arranged in the hydraulic housing  67   a.    
     The hydraulic circuit  70  is constructed to disconnect or connect hydraulic pressure to the fourth clutch  43  and specifically has the following construction. 
     The clutch hydraulic passage  22   i  arranged in the housing  22  is bifurcated into a hydraulic pressure input passage  22   m  fluidly connected to the oil discharge passage  22   g  and a hydraulic pressure output passage  22   n  fluidly connected to the hydraulic chamber  43   d  of the fourth clutch  43 . 
     A hydraulic pressure input passage  67   f  fluidly connecting the valve shaft  67   d  of the hydraulic pressure control valve  67  and the hydraulic pressure input passage  22   m  together and a hydraulic pressure output passage  67   g  fluidly connecting the valve shaft  67   d  and the hydraulic pressure output passage  22   n  together are arranged in the hydraulic housing  67   a.    
     Hydraulic pressure releasing passages  22   p  and  67   h  arranged to release hydraulic pressure supplied to the hydraulic chamber  43   d  are defined in the housing  22  and the hydraulic housing  67   a . The hydraulic pressure releasing passage  67   h  is fluidly connected to the housing  22  through the hydraulic pressure releasing passage  22   p.    
     The hydraulic pressure input passages  22   m  and  67   f , the hydraulic pressure output passages  22   n  and  67   g , and the hydraulic pressure releasing passages  22   p  and  67   h  are arranged to extend in directions perpendicular, or substantially perpendicular, to the axis of the valve shaft  67   d.    
     The hydraulic pressure output passages  22   n  and  67   g  and the hydraulic pressure input passages  22   m  and  67   f  are arranged on the rear side of the hydraulic housing  67   a . Thereby, the oil discharge passage  22   g  and so forth can be disposed in a rear portion of the transmission housing  22 . 
     Hypothetically, if the hydraulic pressure output passages and the hydraulic pressure input passages were arranged on the front side of the hydraulic housing  67   g , the oil line would be complicated, or it would be required to dispose the oil discharge passage in a front portion of the transmission housing  22 . However, if the oil discharge passage were disposed in the front portion, a front portion of the transmission housing  22  would become large, and the second input shaft (i.e., whole outboard motor) would have to be disposed in the rear. This would results in an increase in the load applied on the bracket. 
     Oil pressurized by the oil pump  45  is supplied to the hydraulic pressure input passages  22   m  and  67   f  through the oil discharge passage  22   g . The hydraulic pressure input passage  67   f  is blocked by the valve shaft  67   d . Thereby, the fourth clutch  43  is disengaged. 
     When the valve shaft  67   d  of the hydraulic pressure control valve  67  moves and the hydraulic pressure input passage  67   f  opens, oil is supplied to the hydraulic chamber  43   d  of the fourth clutch  43  through the hydraulic pressure output passage  67   g . Thereby, the fourth clutch  43  is engaged. The hydraulic pressure input passage  67   f  is blocked when the valve shaft  67   d  returns to the original position. Hydraulic pressure in the hydraulic chamber  43   d  is released into the hydraulic housing  67   a  through the hydraulic pressure releasing passages  67   h  and  22   p.    
     Each of the hydraulic pressure control valves  65  through  67  is preferably disposed on the port side of the transmission housing  22  in the watercraft width direction. This facilitates contact between a headwind and the hydraulic pressure control valves  65  through  67  via the upper case  9  when traveling. Accordingly, the cooling characteristics of the hydraulic pressure control valves  65  through  67  can be secured. As a result, it is not required to separately provide a cooling mechanism, thus preventing complexity in structure and increase in cost. 
     Each of the hydraulic pressure control valves  65  through  67  is preferably disposed on the port side of the housing  22 . Therefore, the control valves can be disposed by utilizing an open space in the upper case  9 , thus allowing for a reduction in the size of the transmission device  15  in the fore-and-aft direction. Thereby, the transmission device  15  can be positioned forward. As a result, the center of gravity of the outboard motor  1  can be positioned closer to the hull  2 . This allows for a reduction in the load applied on the clamp bracket  3  arranged to support the outboard motor  1  and reduction in the weight and the size of the whole outboard motor. 
     In the present preferred embodiment, each of the hydraulic pressure control valves  65  through  67  is preferably disposed on the housing  22  to protrude in the direction toward the port side. Therefore, the hydraulic pressure control valves  65  through  67  can be disposed in positions facilitating contact with a headwind when traveling, thus enhancing the cooling characteristics of each of the hydraulic pressure control valves  65  through  67 . 
     In the present preferred embodiment, the hydraulic circuit  70  is preferably arranged on the mating surface between the transmission housing  22  and each of the hydraulic housings  65   a  through  67   a . This allows downsizing of the hydraulic circuit  70  by utilizing the mating surface between both the housing  22  and the hydraulic housings  65   a  through  67   a  and facilitates a forming of the hydraulic circuit. 
     Further, the cooling circuit  71  arranged to cool the hydraulic pressure control valves  65  through  67  is arranged on the mating surface between the transmission housing  22  and the hydraulic housings  65   a  through  67   a . Therefore, the hydraulic pressure control valves  65  through  67  can be cooled by both a headwind and oil, thus enhancing the cooling characteristics, and further improving durability of the hydraulic pressure control valves  65  through  67 . 
     In the present preferred embodiment, the valve shafts  65   d  through  67   d  of the respective hydraulic pressure control valves  65  through  67  are preferably disposed in the watercraft fore-and-aft direction. The hydraulic pressure input passages  65   f  through  67   f  and the hydraulic pressure output passages  65   g  through  67   g  between the hydraulic pressure control valves  65  through  67  are formed in the directions perpendicular, or substantially perpendicular, to the valve shafts  65   d  through  67   d . Therefore, hydraulic pressure can directly come and go between the hydraulic pressure control valves  65  through  67  and the respective clutches  31 ,  35 , and  43 . This achieves a simple configuration of the oil circuit and cost reduction. 
     In the present preferred embodiment, each of the hydraulic pressure control valves  65  through  67  is preferably disposed above the lower mount member  12 . In addition, the level to which each of the hydraulic pressure control valves  65  through  67  protrudes toward the port side is substantially equivalent to the level to which the lower mount member  12  protrudes toward the port side. Therefore, each of the hydraulic pressure control valves  65  through  67  can be disposed without interfering with the lower mount member  12 . This prevents an increase in the size of the upper case  9  in the watercraft width direction, thus allowing downsizing of the whole outboard motor  1 . That is, if the hydraulic pressure control valves  65  through  67  are disposed to adjoin the lower mount member  12  in the watercraft width direction, the lower mount member  12  needs to protrude outward for the width of the hydraulic pressure control valves  65  through  67 . This would result in a problem of size increase of the upper case  9 . 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.