Patent Publication Number: US-2023145629-A1

Title: Outboard motor suspension structure and outboard motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-184081 filed on Nov. 11, 2021. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to suspension structures for outboard motors, and outboard motors. 
     2. Description of the Related Art 
     As disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2019-107995, suspension structures for suspending or hanging an outboard motor body onto a hull are known. A typical suspension structure includes a clamp bracket to be fixed to a hull, a tilt shaft attached to the clamp bracket, and a swivel bracket pivotally attached to the clamp bracket via the tilt shaft. An outboard motor body is fixed to the swivel bracket. With such a structure, the fixed outboard motor body is pivotable around the tilt shaft, and its inclination angle relative to the clamp bracket (relative to the hull) is changeable. 
     In order to tilt up/tilt down the outboard motor body, cylinders are provided between the clamp bracket and the swivel bracket. The cylinders typically include a trim cylinder for changing the inclination angle of the outboard motor body for trim adjustment purposes, and a tilt cylinder for tilting up the outboard motor body to a retracted position above the water surface or tilting down the outboard motor body into water. 
     During navigation, such a suspension structure bears a forward thrust force originated from the thrust of the outboard motor. In particular, when a hull leaves the water surface and then lands on the water during navigation, increased weight (G) of the outboard motor acts on a suspension structure. Due to the thrust force and the own weight of the outboard motor, a bending stress mainly occurs in the swivel bracket. 
     On the other hand, the weight of outboard motors is increasing as outboard motors become larger. Furthermore, there is a tendency to provide an increased backward thrust in recent outboard motors, and a bending moment caused by the weight of such an outboard motor is further increased. In this situation, the strength of the swivel bracket or other members in the suspension structure may increase by simply increasing the strength of the members of the suspension structure. However, the increase of the strength of the members results in an increase of the total weight of the suspension structure, and there is room for improvement. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide suspension structures for outboard motors and outboard motors, in each of which the strength is enhanced while significantly reducing or preventing an increase in the weight. 
     According to a preferred embodiment of the present invention, a suspension structure for an outboard motor includes a clamp bracket attachable to a hull, and a main load bearing portion to support an outboard motor body and mainly bear a weight of the outboard motor body. The suspension structure further includes a tilt shaft, a coupling, and a cylinder to change a trim angle or a tilt angle of the outboard motor body. The coupling includes a first end supported by the tilt shaft and rotatable about the tilt shaft, and a second end fixed to the main load bearing portion. The cylinder includes a first end supported by the clamp bracket at a position lower than the tilt shaft and rotatable about a first rotation shaft in an up-down direction relative to the clamp bracket, and a second end supporting the coupling and rotatable about a second rotation shaft in the up-down direction. The second rotation shaft is provided in the main load bearing portion or located near the main load bearing portion. 
     According to another preferred embodiment of the present invention, a suspension structure for an outboard motor includes a clamp bracket attachable to a hull, a swivel bracket to be fixed to an outboard motor body, a tilt shaft, and a cylinder to change a trim angle or a tilt angle of the outboard motor body. The cylinder has a first end supported by the clamp bracket at a position lower than the tilt shaft and rotatable about a first rotation shaft in an up-down direction relative to the clamp bracket, and a second end supporting the swivel bracket and rotatable about a second rotation shaft in the up-down direction. When the outboard motor body is in a tilted-down position, the second rotation shaft is located at a position lower than the first rotation shaft. 
     According to another preferred embodiment of the present invention, an outboard motor includes an outboard motor body, and any of the above-described suspension structures. 
     According to the above configurations, when an outboard motor body is, for example, in a tilted-down position, the weight of the outboard motor body causes a tensile force acting between the tilt shaft and the second rotation shaft on the coupling, and a compressive force acting between the first rotation shaft and the second rotation shaft on the cylinder. Therefore, it is less necessary to increase the strength of the coupling in order to cope with the bending stress. Therefore, it is possible to increase the strength of the suspension structure while significantly reducing or preventing an increase in its weight. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a marine vessel which uses a suspension structure for an outboard motor. 
         FIG.  2    is a perspective view of a suspension mechanism (in a tilted-down position). 
         FIG.  3    is a perspective view of the suspension mechanism (in a tilted-up position). 
         FIG.  4    is a side view of the suspension mechanism as viewed from the left (in the tilted-down position). 
         FIG.  5    is a side view of the suspension mechanism as viewed from the left (in the tilted-up position). 
         FIG.  6    is a rear view of a main portion of the suspension mechanism (in the tilted-down position). 
         FIG.  7    is an enlarged side view of the periphery of an upper pivot. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 
       FIG.  1    is a perspective view of a marine vessel to which a suspension structure for an outboard motor according to a preferred embodiment of the present invention is provided. The marine vessel  10  includes a hull  11 , a steering wheel  12 , a remote controller  13 , and an outboard motor  100 . The outboard motor  100  includes an outboard motor body  101  and a suspension mechanism  200  that supports the outboard motor body  101  to suspend or hang the outboard motor body  101  onto the hull  11 , which will be described below with reference to  FIG.  2   . The outboard motor body  101  is attached to a transom  14  at the rear of the hull  11  via the suspension mechanism  200 . 
     In the following description, unless otherwise specified, front, rear (or back), left, and right respectively mean front, rear (or back), left and right in the reference condition in which a steering axis  41  ( FIGS.  4  and  6   ) extends vertically and the outboard motor  100  is not inclined to the left or right relative to the hull  11 . In the reference position, left and right are defined with reference to the view of the marine vessel  10  from the rear. Reference signs F, B, L, and R in the drawings represent front, back, left, and right, respectively. For convenience, it is assumed that, when the steering axis  41  extends vertically, such a position of the outboard motor  100  (outboard motor body  101 ) belongs to the tilted-down position. 
     The steering wheel  12  is provided to steer the hull  11 . Due to an occupant of the marine vessel  10  operating the steering wheel  12 , the outboard motor body  101  rotates leftward or rightward relative to the hull  11 . The mode of the outboard motor  100  may change to a forward mode, a backward mode, or a neutral mode according to the operation of the remote controller  13  by the occupant (shift change). The outboard motor body  101  includes an engine  1  and a propulsion system with a propeller  15 . The engine  1  is provided with a throttle valve (which is not illustrated). The opening degree of the throttle valve may be adjusted by an occupant operating the remote controller  13 . An output of the outboard motor  100  is adjusted according to the adjustment of the opening degree of the throttle valve. 
       FIGS.  2  and  3    are perspective views of the suspension mechanism  200 .  FIGS.  4  and  5    are side views of the suspension mechanism  200  as viewed from the left.  FIGS.  2  and  4    illustrate a case where the outboard motor  100  is in the tilted-down position, and  FIGS.  3  and  5    illustrate a case where the outboard motor  100  is in a tilted-up position. Note that  FIGS.  4  and  5    also illustrate the lower case  38  and the exhaust guide  39  included in the outboard motor body  101 . In  FIG.  3   , illustration of a pair of frames  31 L and  31 R is omitted. Furthermore, in  FIG.  4   , illustration of a left frame  31 L is omitted. 
     As illustrated in  FIG.  4   , hereinafter, a direction parallel to the steering axis  41  is defined as a Z direction. In particular, when the outboard motor  100  is in the tilted-down position, the +Z direction is upward and the −Z direction is downward. 
     As illustrated in  FIGS.  2  to  5   , main components of the suspension mechanism  200  include a swivel bracket  30 , a pair of frames  31 L and  31 R, a pair of clamp brackets  24 L and  24 R, a pair of side swivel brackets  29 L and  29 R, and a PTT cylinder  25 . The frames  31 L and  31 R may be interpreted as being included in the outboard motor body  101 . The PTT cylinder  25  includes a cylinder body  26  and a rod  27 . 
     As illustrated in  FIGS.  2  and  4   , a mount holding portion  32  is fixed to the front lower portions of the frames  31 L and  31 R when the outboard motor body  101  is in the tilted-down position. The mount holding portion  32  is a holder that holds a lower mount  33 , and is U-shaped or substantially U-shaped as viewed from a side of the suspension mechanism  200  (in side view). The mount holding portion  32  holds the lower mount  33  from both sides in the steering axis  41  direction (Z direction). The lower mount  33  supports the outboard motor body  101  and mainly bears the weight of the outboard motor body  101 , which is preferably only one main load bearing portion in the suspension mechanism  200 . When the outboard motor body  101  is in the tilted-down position, the lower mount  33  is at the lowest position among portions that support the outboard motor body  101  except the clamp brackets  24 L and  24 R. The lower mount  33  holds a lower pivot  34  ( FIG.  4   ). 
     When the outboard motor body  101  is in the tilted-down position, an upper pivot  35  (held portion) is located at a position higher (in the +Z direction) than the lower mount  33  in the outboard motor body  101 . The lower pivot  34  and the upper pivot  35  function as a steering shaft. That is, a drive shaft (which is not illustrated) extends through a hole of the lower pivot  34  and a hole in the upper pivot  35 . The steering axis  41  is a common center line of the pivots  34  and  35  and coincides with an axis of the drive shaft. Details of the upper pivot  35  will be described below with reference to  FIG.  7   . 
       FIG.  6    is a rear view of a main portion of the suspension mechanism  200 .  FIG.  6    illustrates a case where the outboard motor  100  is in the tilted-down position. In  FIG.  6   , the frames  31 L and  31 R, the lower case  38 , and the exhaust guide  39  are omitted. 
     As illustrated in  FIGS.  4  and  5   , a pair of clamp brackets  24 L and  24 R are fixed to the hull  11 , specifically, to a rear surface of the transom  14  at the rear portion of the hull  11  by fasteners (which are not illustrated). A tilt shaft  20  is supported by the clamp bracket  24 L and the clamp bracket  24 R. The tilt shaft  20  extends in the left-right direction and is oriented horizontally or substantially horizontally. A tilt axis P 0  is a central axis of the tilt shaft  20 . The side swivel brackets  29 L and  29 R (coupling members) and the swivel bracket  30  (second coupling member) are supported by the tilt shaft  20  so as to be rotatable about the tilt shaft  20 , that is, about the tilt axis P 0 . 
     As illustrated in  FIG.  6   , a front end portion  29 Lb which is one end of the side swivel bracket  29 L is supported by the tilt shaft  20 , and a front end portion  29 Rb which is one end of the side swivel bracket  29 R is supported by the tilt shaft  20 . Therefore, the side swivel brackets  29 L and  29 R are rotatable about the tilt axis P 0 . 
     A front end portion  30   b  which is one end of the swivel bracket  30  is supported by the tilt shaft  20  in a region between the front end portion  29 Lb of the side swivel bracket  29 L and the front end portion  29 Rb of the side swivel bracket  29 R. As a result, the swivel bracket  30  is rotatable about the tilt axis P 0  in the up-down direction relative to the clamp brackets  24 L and  24 R. The swivel bracket  30  has a linear shape as viewed from a side of the suspension mechanism  200 . Here, the linear shape includes a substantially linear shape, that is, a case where a portion bent to some extent is present in the swivel bracket  30  in addition to a case where the swivel bracket  30  is strictly linear. 
     In the direction of the tilt axis P 0  (left-right direction), the front end portion  29 Lb is located at the left end portion of the tilt shaft  20 , and the front end portion  29 Rb is located at the right end portion of the tilt shaft  20 . As a result, the position (first position) of the front end portion  29 Lb and the position (second position) of the front end portion  29 Rb are separated from each other in the tilt axis P 0  direction. 
     As illustrated in  FIGS.  4  and  6   , the rear end portion  29 La that is the other end of the side swivel bracket  29 L and the rear end portion  29 Ra that is the other end of the side swivel bracket  29 R are both fixed to the lower mount  33  with a plurality of bolts, for example. In particular, referring to the left-right direction, the rear end portion  29 La is fixed to a support position  33   a  which is a left end portion of the lower mount  33 , and the rear end portion  29 Ra is fixed to a support position  33   b  which is a right end portion of the lower mount  33  ( FIG.  6   ). That is, the rear end portion  29 La and the rear end portion  29 Ra are fixed to the outboard motor body  101  via the lower mount  33  and the mount holding portion  32 . The rear end portion  29 La and the rear end portion  29 Ra are pivotally supported by the second rotation shaft  22 . A second rotation center P 2  is a central axis of the second rotation shaft  22 . The second rotation shaft  22  is located in the vicinity of the lower mount  33 . 
     The PTT cylinder  25  changes a trim angle or a tilt angle of the outboard motor body  101 . The PTT cylinder  25  extends from the rear end portion  29 La and the rear end portion  29 Ra to the clamp brackets  24 L and  24 R. Here, one end of the PTT cylinder  25  is supported by the clamp brackets  24 L and  24 R so as to be rotatable about the first rotation shaft  21  in the up-down direction relative to the clamp brackets  24 L and  24 R. The other end of the PTT cylinder  25  supports the side swivel brackets  29 L and  29 R so as to be rotatable about the second rotation shaft  22  in the up-down direction. 
     As illustrated in  FIG.  3   , the rod  27  of the PTT cylinder  25  includes a connecting portion  28 . The connecting portion  28  is pivotally supported by the second rotation shaft  22  between the rear end portion  29 La and the rear end portion  29 Ra arranged in the left-right direction. With this structure, the side swivel brackets  29 L and  29 R and the PTT cylinder  25  are rotatable about the second rotation center P 2  relative to each other. The cylinder body  26  of the PTT cylinder  25  is connected to the clamp brackets  24 L and  24 R via a housing of the cylinder body  26  so as to be rotatable about the first rotation center P 1  ( FIGS.  4  and  5   ) of the first rotation shaft  21 . As a result, the clamp brackets  24 L and  24 R and the cylinder body  26  are rotatable about the first rotation center P 1  relative to each other. The first rotation center P 1  is located at a position lower than the tilt shaft  20 . That is, one end of the PTT cylinder  25  is supported by the clamp brackets  24 L and  24 R at a position lower than the tilt shaft  20 . 
       FIG.  7    is an enlarged side view of the periphery of the upper pivot  35 . A rear end portion  30   a  (see also  FIGS.  4  and  6   ), which is the other end of the swivel bracket  30 , supports the upper pivot  35  so as to be rotatable at least in the up-down direction about a third rotation center P 3  (third rotation shaft). The upper pivot  35  is regulated in position in the Z direction by the exhaust guide  39  and a plate  37 . The upper pivot  35  includes a spherical portion  23 . The rear end portion  30   a  of the swivel bracket  30  is slidably engaged with the spherical portion  23  via a bush (which is not illustrated). As a result, the rear end portion  30   a  of the swivel bracket  30  and the spherical portion  23  are relatively rotatable about the steering axis  41 , and are rotatable about the third rotation center P 3 . 
     A steering bracket  36  is engaged with the upper pivot  35  at a position shifted in the −Z direction from the spherical portion  23 , and a driver  42  is connected to the steering bracket  36  (see also  FIGS.  4  and  5   ). The frames  31 L and  31 R are fixed to the steering bracket  36 . The driver  42  rotates the steering bracket  36  about the steering axis  41 . As a result, the frames  31 L and  31 R are rotated about the steering axis  41 . By rotating the frames  31 L and  31 R, the orientation of the outboard motor body  101  is changed in the left-right direction. 
     The shapes of the side swivel brackets  29 L and  29 R are linear as viewed from a side of the suspension mechanism  200  ( FIGS.  4  and  5   ). As viewed also from the rear, the shapes of the side swivel brackets  29 L and  29 R extending from the front end portions  29 Lb and  29 Rb to the lower mount  33  are also linear ( FIG.  6   ). Here, the linear shape includes a substantially linear shape, that is, a case where a portion bent to some extent is present in each of the side swivel brackets  29 L and  29 R in addition to a case where each of the side swivel brackets  29 L and  29 R is strictly linear. 
     As illustrated in  FIG.  4   , when the outboard motor body  101  is in the tilted-down position, the third rotation center P 3  is located at a position lower than the tilt shaft  20 . That is, when the outboard motor body  101  is in the tilted-down position, the swivel bracket  30  is inclined downward toward the rear. Furthermore, when the outboard motor body  101  is in the tilted-down position, the second rotation shaft  22  is located at a position lower than the first rotation shaft  21 . That is, when the outboard motor body  101  is in the tilted-down position, the PTT cylinder  25  is inclined downward toward the rear. 
     As illustrated in  FIG.  6   , the lower mount  33  is located between the front end portion  29 Lb (first position) and the front end portion  29 Rb (second position) with respect to the direction (left-right direction) parallel to the tilt axis P 0 . When the outboard motor body  101  is in the tilted-down position, the lower mount  33  is located at a position lower than the front end portion  29 Lb and the front end portion  29 Rb. When the outboard motor body  101  is in the tilted-down position, a virtual triangle  50  defined by vertices of the front end portion  29 Lb, the front end portion  29 Rb, and the lower mount  33  is formed, as viewed from the rear. The center positions of the front end portions  29 Lb and  29 Rb and the lower mount  33  viewed from the rear define vertices Q 1 , Q 2 , and Q 3 , respectively. The vertices Q 1 , Q 2 , and Q 3  form the virtual triangle  50 . 
     Meanwhile, as illustrated in  FIG.  4   , a virtual triangle  40  defined by vertices of the tilt axis P 0  of the tilt shaft  20 , the first rotation center P 1  of the first rotation shaft  21 , and the second rotation center P 2  of the second rotation shaft  22  is formed, as viewed from a side of the suspension mechanism  200 . 
     Next, a description is provided of the operation of tilting up/down the outboard motor body  101  by the PTT cylinder  25 . The rod  27  extends from and retracts into the cylinder body  26  while being driven by a drive source (which is not illustrated). With an extension of the rod  27 , the connecting portion  28  ( FIG.  3   ) pushes the second rotation shaft  22 . As a result, the side swivel brackets  29 L and  29 R are subjected to a biasing force via the second rotation shaft  22 , and rotate upward (counterclockwise in  FIG.  4   ), which corresponds to a tilt-up direction, about the tilt axis P 0 . Since the distance between the second rotation center P 2  and the third rotation center P 3  is constant, the swivel bracket  30  also rotates in the tilt-up direction about the tilt axis P 0  in conjunction with the rotation of the side swivel brackets  29 L and  29 R. 
     Conversely, with a retraction of the rod  27 , which had been extended due to the tilting up process, the side swivel brackets  29 L and  29 R and the swivel bracket  30  rotate in a tilting down direction about the tilt axis P 0 . In the tilting up/down process, the triangular shape having the tilt axis P 0 , the second rotation center P 2 , and the third rotation center P 3  as vertices in the side view is maintained. 
     During navigation of the marine vessel  10 , a lateral load may be applied to the lower portion of the outboard motor body  101 . For example, a leftward or rightward water pressure may be applied to the lower portion of the outboard motor body  101  when the hull  11  turns. For another example, a lateral load may be applied to the lower portion of the outboard motor body  101  when the hull  11  leaves the water surface and then lands on the water in a situation where swells are large. Further, a forward thrust force originated from the thrust is applied to the suspension mechanism  200 . Conventionally, a large bending stress may occur in the constituent members of the suspension mechanism due to the thrust force, the lateral load, and/or the weight of the outboard motor body. On the other hand, when the strength of the constituent members of the suspension mechanism simply increases, it increases the total weight of the suspension mechanism. To solve this issue, the suspension mechanism  200  in the present preferred embodiment is devised so that the bending stress occurring therein is reduced. 
     As described above, the side swivel brackets  29 L and  29 R are substantially linear. As illustrated in  FIG.  6   , the lower mount  33  is located between the front end portion  29 Lb (first position) and the front end portion  29 Rb (second position) with respect to the direction parallel to the tilt axis P 0  (that is, the lower mount  33  is located between the front end portion  29 Lb and the front end portion  29 Rb when the lower mount  33 , the front end portion  29 Lb, and the front end portion  29 Rb are projected on a straight line parallel to the tilt axis P 0 ). When the outboard motor body  101  is in the tilted-down position, the lower mount  33  is located at a position lower than the front end portion  29 Lb and the front end portion  29 Rb, and the virtual triangle  50  is formed by the vertices Q 1 , Q 2 , and Q 3  as viewed from the rear. 
     As a result, when a thrust force is applied to the lower mount  33  from the right side, it causes a compressive force acting between the front end portion  29 Lb and the lower mount  33  on the side swivel bracket  29 L, and a tensile force acting between the front end portion  29 Rb and the lower mount  33  on the side swivel bracket  29 R. When a thrust force is applied to the lower mount  33  from the left side, an action opposite to this occurs. That is, in response to the thrust force applied to the lower mount  33  in the left-right direction, a compressive force acts on one of the side swivel brackets  29 L and  29 R, and a tensile force acts on the other. Bending stress hardly occurs in the side swivel brackets  29 L and  29 R. Therefore, it is less necessary to increase the member strength of the side swivel brackets  29 L and  29 R in order to cope with the bending stress. As a result, it is possible to increase the strength of the weight of the suspension mechanism  200  while significantly reducing or preventing an increase in its weight. 
     As illustrated in  FIG.  4   , the second rotation shaft  22  connecting the rear end portion of the PTT cylinder  25  and the side swivel brackets  29 L and  29 R is located in the vicinity of the lower mount  33 . As viewed from a side of the suspension mechanism  200 , the virtual triangle  40  defined by vertices of the tilt axis P 0 , the first rotation center P 1 , and the second rotation center P 2  is formed. Accordingly, at least when the outboard motor body  101  is in the tilted-down position, the weight of the outboard motor body  101  or the forward thrust force causes a tensile force acting between the tilt shaft  20  and the second rotation shaft  22  on the side swivel brackets  29 L and  29 R, and a compressive force acting between the first rotation shaft  21  and the second rotation shaft  22  on the PTT cylinder  25 . This reduces the bending stress that occurs in the side swivel brackets  29 L and  29 R originating from the weight of the outboard motor body  101  or the forward thrust force. Therefore, it is less necessary to increase the member strength of the side swivel brackets  29 L and  29 R in order to cope with the bending stress. Accordingly, it is possible to increase the strength of the suspension mechanism  200  while significantly reducing or preventing an increase in its weight. 
     Moreover, the upper pivot  35  is located at a position higher than the lower mount  33  when the outboard motor body  101  is in the tilted-down position. The front end portion  30   b  of the swivel bracket  30  is rotatably supported by the tilt shaft  20 , and the rear end portion  30   a  rotatably supports the upper pivot  35  about the third rotation center P 3 . As a result, the lower mount  33  which is the main load bearing portion bears most of the weight of the outboard motor body  101  and the forward thrust force. 
     Here, in a state where the weight of the outboard motor body  101  and the forward thrust force act, a force due to a rotational moment in the clockwise direction in  FIG.  4    around the second rotation center P 2  acts on the upper pivot  35 , but a load in the vertical direction and the forward direction hardly act on the upper pivot  35 . As a result, the lower mount  33  bears most of the weight of the outboard motor body  101  and the forward thrust force. This enhances the effect of reducing the bending stress that occurs in the side swivel brackets  29 L and  29 R. In addition, a tensile force is mainly generated in the swivel bracket  30  against the rotational moment about the second rotation center P 2 . This reduces the bending stress from occurring in the swivel bracket  30 , and it is also possible to reduce the weight of the swivel bracket  30  and improve its strength. 
     According to the present preferred embodiment, the lower mount  33  is located at the lowest position among portions supporting the outboard motor body  101  except the clamp brackets  24 L and  24 R, when the outboard motor body  101  is in the tilted-down position. The side swivel brackets  29 L and  29 R are rotatably supported by the tilt shaft  20  at the front end portion  29 Lb (first position) and the front end portion  29 Rb (second position), and are fixed to the lower mount  33  at the rear end portion  29 La and the rear end portion  29 Ra. The lower mount  33  is located between the front end portion  29 Lb (first position) and the front end portion  29 Rb (second position) with respect to the direction parallel to the tilt axis P 0 . When the outboard motor body  101  is in the tilted-down position, the lower mount  33  is located at a position lower than the front end portion  29 Lb (first position) and the front end portion  29 Rb (second position). As viewed from the rear, the virtual triangle  50  defined by vertices of the front end portion  29 Lb, the front end portion  29 Rb, and the lower mount  33  is formed ( FIG.  6   ). Since this reduces the bending stress that occurs in the side swivel brackets  29 L and  29 R due to the lateral load, the strength of the suspension mechanism  200  is increased while significantly reducing or preventing an increase in its weight. 
     The side swivel brackets  29 L and  29 R are linear, and the front end portion  29 Lb and the front end portion  29 Rb are separated from each other in the direction of the tilt axis P 0 . In such a structure, the bending stress is less likely to occur in the side swivel brackets  29 L and  29 R, and the lower mount  33  bears most of the weight of the outboard motor body  101  and the forward thrust force. This enhances the effect of reducing the bending stress from occurring in the side swivel brackets  29 L and  29 R and contributes to increasing the strength of the suspension mechanism  200 . 
     According to the present preferred embodiment, one end of the PTT cylinder  25 , specifically the housing of the cylinder body  26  of the PTT cylinder  25 , is supported by the clamp brackets  24 L and  24 R at a position lower than the tilt shaft  20  so as to be rotatable about the first rotation shaft  21  (first rotation center P 1 ) in the up-down direction relative to the clamp brackets  24 L and  24 R. Further, the other end of the PTT cylinder  25 , specifically the connecting portion  28  of the rod  27  of the PTT cylinder  25 , supports the side swivel brackets  29 L and  29 R so as to be rotatable in the up-down direction about the second rotation shaft  22  (the second rotation center P 2 ). Further, the second rotation shaft  22  is located near the lower mount  33 . With such an arrangement, the virtual triangle  40  defined by vertices of the tilt axis P 0 , the first rotation center P 1 , and the second rotation center P 2  is formed, as viewed from a side of the suspension mechanism  200  ( FIG.  4   ). Since the bending stress that occurs in the side swivel brackets  29 L and  29 R due to the weight of the outboard motor body  101  and the forward thrust force is reduced, the strength of the suspension mechanism  200  is increased while significantly reducing or preventing an increase in its weight. 
     From the viewpoint of obtaining this effect, the distance between the lower mount  33  and the second rotation shaft  22  in a side view is preferably shorter than a distance between the lower mount  33  and the tilt shaft  20  in the side view. Alternatively, from the viewpoint of obtaining this effect, the second rotation shaft  22  is preferably provided in the lower mount  33 . That is, the second rotation shaft  22  (or the second rotation center P 2 ) may overlap the lower mount  33  in the side view. 
     Further, the lower mount  33  bears most of the weight of the outboard motor body  101  and the forward thrust force, and thus enhances the effect of reducing the bending stress from occurring in the side swivel brackets  29 L and  29 R and contributes to increasing the strength of the suspension mechanism  200 . 
     When the outboard motor body  101  is in the tilted-down position, the third rotation center P 3  is located at a position lower than the tilt shaft  20 , and the swivel bracket  30  is inclined downward toward the rear side ( FIG.  4   ). As a result, it is possible to prevent upward tensile stress from being generated in the clamp brackets  24 L and  24 R in the vicinity of the tilt shaft  20  when the outboard motor body  101  is in the tilted-down position. This strengthens the attachment of the clamp brackets  24 L and  24 R to the transom  14 . 
     Moreover, when the outboard motor body  101  is in the tilted-down position, the position of the second rotation shaft  22  is lower than the position of the first rotation shaft  21 , and the PTT cylinder  25  is inclined downward toward the rear side ( FIG.  4   ). In such a structure, when the outboard motor body  101  is in the tilted-down position, upward stress occurs in the clamp brackets  24 L and  24 R at the position of the first rotation shaft  21 . Therefore, this and the fact that the swivel bracket  30  is inclined downward toward the rear side make it possible to optimize the stress distribution applied to the clamp brackets  24 L and  24 R when the outboard motor body  101  is in the tilted-down position. As a result, it is possible to increase the strength of the clamp brackets  24 L and  24 R while significantly reducing or preventing an increase of their weight. 
     The mount holding portion  32  is U-shaped or substantially U-shaped as viewed from a side of the suspension mechanism  200 , and holds the lower mount  33  from both sides in the direction of the steering axis  41  ( FIG.  4   ). As a result, even when the mount holding portion  32  rotates about the steering axis  41  at the time of steering, it is possible to firmly hold the lower mount  33  while avoiding interference with the lower mount  33 . 
     The shapes of the side swivel brackets  29 L and  29 R are not limited to the illustrated shapes, and may be, for example, shapes closer to a linear shape. 
     The side swivel bracket is separated into two portions of the side swivel bracket  29 L as the first member and the side swivel bracket  29 R as the second member. However, these may be integral as one side swivel bracket. In this case, one side swivel bracket may have a substantially V-shape as viewed from the rear. 
     The marine vessel to which the suspension mechanism  200  according to a preferred embodiment of the present invention is provided may be any marine vessel to which an outboard motor can be attached, and the type is not limited. 
     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 from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.