Patent Publication Number: US-9415850-B2

Title: Mount device for outboard motor

Description:
PRIORITY CLAIM 
     This patent application is a U.S. National Phase of International Patent Application No. PCT/JP2013/082010, filed 28 Nov. 2013, which claims priority to Japanese Patent Application No. 2012-267609, filed 6 Dec. 2012, the disclosures of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a mount device for an outboard motor that is arranged between an outboard motor body and an attachment device that attaches the outboard motor body to a hull. 
     BACKGROUND ART 
     Generally, in a mount device for an outboard motor disposed between an outboard motor body and an attachment device through which the outboard motor body is attached to a hull, a mount unit including an upper mount unit and a lower mount unit which are arranged in an upper portion and a lower portion of the outboard motor body, and vibration of an engine is prevented from transmitting to the hull by providing an elastic body, such as rubber material, in the mount unit. 
     In order to improve vibration prevention performance of such mount device, it is necessary to set a spring constant of the elastic body to be small to thereby prevent vibration particularly during low-speed rotation of the engine from transmitting to the hull. However, when a large load is applied to the outboard motor body as in a case in which a thrust of the outboard motor body rapidly changes, only the elastic body may not be able to prevent interference between a member on the outboard motor body side (e.g., an engine holder) and a member on the attachment device side (e.g., a swivel bracket). Patent Document 1 discloses a mount device for an outboard motor that solves the above-mentioned problem. 
     The mount device for an outboard motor disclosed in Patent Document 1 includes, as shown in  FIG. 10 , a first upper mount  101  that performs a function to prevent transmission of vibration, a second upper mount  102  that performs a function to restrict displacement of an outboard motor body during forward movement of a hull, a third upper mount  103  that performs a function to restrict displacement of the outboard motor body during backward movement of the hull, a fourth upper mount  104  that performs a function to restrict displacement in right-left and up-down directions of the outboard motor body, and a fifth upper mount  105  that performs a function to restrict rotational displacement in a yaw direction (a rotational direction about a gravity center position O within a horizontal plane of the outboard motor body) of the outboard motor body. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     Patent Document 1: Japanese Patent Laid-Open No. 2006-312379 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the mount device for an outboard motor shown in  FIG. 10 , the first upper mount  101  that performs the function to prevent the transmission of vibration during the low-speed rotation of an engine is desired to have a small spring constant relative to a vibration frequency of the engine or the like. Thus, a spring constant of mount rubber of the first upper mount  101  is set to be very small. 
     On the other hand, in the second upper mount  102  and the third upper mount  103  that perform a function to transmit the thrust from the outboard motor body to the hull as well as the function to restrict the displacement during the forward movement and the backward movement, and the fourth upper mount  104  that performs a function to transmit the steering force from the hull side to the outboard motor body as well as the function to restrict the displacement in the right-left and up-down directions, spring constants of the second upper mount  102 , the third upper mount  103  and the fourth upper mount  104  are set to be large in order to efficiently transmit the thrust and the steering force. A spring constant of the fifth upper mount  105  that restricts the rotational displacement is also set to be large. 
     By the way, when the spring constant of the first upper mount  101  is decreased, the displacement needs to be increased. Thus, for example, in order to prevent the fourth upper mount  104  and the fifth upper mount  105  from functioning, both of a gap M between a side wall  106 A of an upper mount housing section  106  to which the fourth upper mount  104  opposes and the fourth upper mount  104 , and a gap N between an abutment section  106 B of the upper mount housing section  106  to which the fifth upper mount  105  opposes and the fifth upper mount  105  are set to be large. 
     However, when the gaps M and N are set to be large as described above, a steering response and a displacement restricting function particularly at a time when the engine rotates at high speed are deteriorated. Therefore, in order to achieve both of the vibration transmission preventing function by the first upper mount  101  and the displacement restricting function and the steering response by the second to fifth upper mounts  102  to  105 , it is required for the gaps M and N to be as small as possible and also required for the fourth upper mount  104  and the fifth upper mount  105 , particularly, mount rubber, to be worked with high accuracy. 
     The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a mount device for an outboard motor capable of decreasing a manufacturing cost by reducing a requirement for machining accuracy of a mount device for restricting displacement in several directions including a lateral direction and etc. and also capable of improving a displacement restricting function and a steering response during high speed rotation of an engine. 
     Means for Solving the Problems 
     The above object can be achieved by the present invention by providing a mount device for an outboard motor having an outboard motor body generating a thrust by rotating a propeller that is driven by an engine mounted to the outboard motor and an attachment device configured to attach the outboard motor body to a hull, the mount device including an upper mount unit and a lower mount unit arranged between the outboard motor body and the attachment device for attaching the outboard motor body to the hull and configured to support an upper portion and a lower portion of the outboard motor body, respectively, the upper and lower mount units each further comprising first upper and lower mount sections that prevents vibration of the engine during low-speed rotation of the engine from being transmitted to the hull, a forward-movement side displacement restriction mount section that restricts displacement of the outboard motor body during high-speed rotation of the engine and during forward movement of the hull, a backward-movement side displacement restriction mount section that restricts displacement of the outboard motor body during backward movement of the hull, and a lateral displacement restriction mount section that restricts displacement in directions including a rolling direction and a yaw direction of the outboard motor body, and wherein the lateral displacement restriction mount section and a member opposing to the lateral displacement restriction mount section abut against each other at abutment surfaces thereof, the abutment surfaces being configured to be inclined with respect to a longitudinal direction of the outboard motor body. 
     In the embodiment of the mount device for an outboard motor having the above characteristic features, the following preferable modes or aspects may be provided. 
     It may be preferred that the lateral displacement restriction mount section is arranged on respective sides of the longitudinal direction of the outboard motor body with the vibration prevention mount section being disposed therebetween. 
     It may be preferred that the lateral displacement restriction mount section is installed on each of opposing lateral side surfaces of a core metal member at which the forward-movement side displacement restriction mount section and the backward-movement side displacement restriction mount section are mounted. 
     It may be preferred that the lateral displacement restriction mount section of the upper mount unit is installed on an engine holder of the outboard motor body that supports the engine in a manner opposing to an upper mount bracket that is the opposing member. 
     It may be preferred that the lateral displacement restriction mount section of the lower mount unit is mounted on a lower mount bracket with a portion of a drive shaft housing of the outboard motor body being formed as the opposing member. 
     It may be preferred that the respective mounts have spring constants that are respectively set so as to satisfy the vibration prevention mount section&lt;the forward-movement side displacement restriction mount section=the backward-movement side displacement restriction mount section&lt;the lateral displacement restriction mount section. 
     Effects of the Invention 
     According to the present invention of the characters mentioned above, a gap between the respective abutment surfaces of the lateral displacement restriction mount section (i.e., lateral displacement restriction mount section including a rolling direction and a yaw direction) and the opposing member is decreased during the high-speed rotation of the engine and during the forward movement of the hull, and therefore, a displacement restricting function during the high-speed rotation of the engine and a steering response can be improved. Furthermore, since the gap between the respective abutment surfaces of the above lateral displacement restriction mount section and the opposing member is set to be large enough not to interfere the abutment surfaces with each other even by the vibration of the engine during the low-speed rotation of the engine, it is possible to reduce a requirement for machining accuracy of the above lateral displacement restriction mount section, and to reduce a manufacturing cost of the right-left etc. displacement restriction mount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a left side view illustrating an outboard motor to which one embodiment of a mount device for an outboard motor according to the present invention is applied. 
         FIG. 2  is a sectional view of an upper mount unit taken along the line II-II in  FIG. 1 . 
         FIG. 3  is a sectional view taken along the line III-III in  FIG. 2 . 
         FIG. 4  is a sectional view corresponding to  FIG. 2  illustrating a state of the upper mount unit during forward movement of the outboard motor. 
         FIG. 5  is a sectional view corresponding to  FIG. 2  illustrating a state of the upper mount unit during backward movement of the outboard motor. 
         FIG. 6  is a sectional view of a lower mount unit taken along the line VI-VI in  FIG. 1 . 
         FIG. 7  is a sectional view taken along the line VII-VII in  FIG. 6 . 
         FIG. 8  is a sectional view corresponding to  FIG. 6  illustrating a state of the lower mount unit during forward movement of the outboard motor. 
         FIG. 9  is a sectional view corresponding to  FIG. 6  illustrating a state of the lower mount unit during backward movement of the outboard motor. 
         FIG. 10  is a sectional view illustrating a conventional upper mount unit. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     An embodiment for carrying out the present invention is described hereinafter with reference to the accompanying drawings.  FIG. 1  is a left side view illustrating an outboard motor to which one embodiment of a mount device for an outboard motor according to the present invention is applied. It is to be noted that terms indicating directions such as “upper”, “lower”, “right”, “left” and like indicating direction are used herein with reference to an illustrated state or in a state in which the outboard motor is attached to a hull. 
     As shown in  FIG. 1 , an outboard motor  10  includes an outboard motor body  11  that generates a thrust to a front side or a rear side of the outboard motor by transmitting a drive force of a mounted engine  14  to a propeller  15  to rotate the propeller  15 , an attachment bracket device  12  as an attachment device that supports the outboard motor body  11  and attaches the outboard motor body  11  to a transom  16 A of a hull  16 , and a mount device  13  that is disposed between the outboard motor body  11  and the attachment bracket device  12  and includes an upper mount unit  17  and a lower mount unit  18 . 
     The outboard motor body  11  includes an engine holder  20 , and the engine  14  is incorporated in the engine holder  20 . An oil pan  21  is arranged below the engine holder  20 . A drive shaft housing  22  and a gear case  23  are arranged in a lower portion of the oil pan  21  and in a lower portion of the drive shaft housing  22 , respectively. The engine  14 , the engine holder  20 , and the oil pan  21  are covered with an engine cover  24 . 
     In the engine  14 , a crankcase  25 , a cylinder block  26 , and a cylinder head  27  are sequentially arranged from the front side to the rear side of the outboard motor. A cylinder in which a piston reciprocates (both of which are not shown) is formed in the cylinder block  26  in a substantially horizontal direction. A crankshaft  28  is arranged between the crankcase  25  and the cylinder block  26  in a substantially vertical direction. 
     A drive shaft  29  is connected to a lower end portion of the crankshaft  28  of the engine  14  on the same straight line. The drive shaft  29  extends in the substantially vertical direction within and through the engine holder  20 , the oil pan  21 , the drive shaft housing  22 , and the gear case  23 , and is then connected to a propeller shaft  31  via a bevel gear  30  in the gear case  23 . Accordingly, the drive force of the engine  14  (that is, a rotational force of the crankshaft  28 ) is transmitted to the propeller  15  coupled to the propeller shaft  31  through the drive shaft  29 , the bevel gear  30 , and the propeller shaft  31 . 
     A shift device  32  that switches a rotating direction of the propeller shaft  31  to a normal rotating state (forward movement), a reverse rotating state (backward movement), or a neutral state by a remote operation is provided in the gear case  23 . A shift rod, not shown, extends upward from the shift device  32 , and the shift rod is operated from the outside of the outboard motor body  11  via a clutch rod, not shown. 
     The above-mentioned attachment bracket device  12  includes a clamp bracket  35 , a swivel bracket  36 , a steering shaft  37 , an upper mount bracket  38 , and a lower mount bracket  39  as also shown in  FIG. 1 . The clamp bracket  35  is provided so as to be able to grasp the transom  16 A of the hull  16 . The swivel bracket  36  is supported on the clamp bracket  35  to be rotatable in the vertical direction via a pivot shaft  40 . 
     The steering shaft  37  is rotatably provided so as to extend in a direction perpendicular to the swivel bracket  36 . The upper mount bracket  38  as a base end portion of a steering bracket  41  and the lower mount bracket  39  are coupled to an upper end and a lower end of the steering shaft  37 , respectively, so as to be rotatable together with the steering shaft  37 . The outboard motor body  11  is attached to the upper mount bracket  38  via the upper mount unit  17  and to the lower mount bracket  39  via the lower mount unit  18 . 
     Accordingly, the outboard motor body  11  is pivoted to be rotatable about the steering shaft  37  in the lateral (i.e., right-and-left or horizontal) direction with respect to the clamp bracket  35  and the swivel bracket  36 , and is also pivoted to be rotatable (to enable a tilt operation and a trim operation) about the pivot shaft  40  together with the swivel bracket  36  in the vertical direction with respect to the clamp bracket  35 . 
     The upper mount unit  17  constituting the mount device  13  is installed in a front portion of the engine holder  20  and is connected to the upper mount bracket  38  (the steering bracket  41 ) by means of upper mount bolts  42 , and further, a detailed description is made later by using  FIGS. 2 to 5 . The lower mount unit  18  constituting the mount device  13  is provided in each of opposite side portions of the drive shaft housing  22 , and a detailed description is made later by using  FIGS. 6 to 9 . The respective lower mount units  18  are connected to the lower mount bracket  39  by means of lower mount bolts  43 . Reference numeral  44  denotes a lower mount cover covering the lower mount unit  18 . The upper mount unit  17  and the lower mount units  18  prevent vibration of the engine  14  of the outboard motor body  11  from being transmitted to the hull  16 , and restrict excessive displacement of the outboard motor body  11  with respect to the hull  16 . 
     It is further to be noted that, as shown in  FIG. 1 , in the outboard motor  10 , the outboard motor body  11  supported by the upper mount unit  17  and the lower mount units  18  is inclined by an inclination angle θ by a forward thrust force generated by the rotation of the propeller  15 . Further, by such thrust force, an upper half portion supported by the upper mount unit  17  and including the engine holder  20  is also displaced backward, and a lower half portion supported by the lower mount units  18  and including the drive shaft housing  22  is also displaced forward. 
     As shown in  FIGS. 2 and 3 , an upper mount accommodation (housing) section  45  that accommodates the upper mount unit  17  is formed in the front portion of the engine holder  20 , and an upper mount holding section  46  is formed in the upper mount accommodation (housing) section  45  integrally with the engine holder  20 . The upper mount unit  17  is fixed to the upper mount bracket  38  with front end portions of the upper mount bolts  42  penetrating the upper mount bracket  38  (the steering bracket  41 ) and fastening nuts  47  screwed to the front end portions in a state in which the upper mount unit  17  is accommodated in the upper mount accommodation section  45  of the engine holder  20 . 
     The upper mount unit  17  is composed of first to fifth upper mount sections or members described below. 
     That is, the upper mount unit  17  includes first to fifth upper mount sections  51  to  55 . The first upper mount section  51  formed of an elastic body such as rubber is wound around each of inner tubes  48  through which the right and left pair of upper mount bolts  42  are inserted, and is fitted to the upper mount holding section  46 . The second upper mount section  52  formed of an elastic body such as rubber is interposed between a front surface of a core metal member  49  provided at rear end portions of the right and left pair of upper mount bolts  42 , and the upper mount holding section  46 . The third upper mount section  53  formed of an elastic body such as rubber is interposed between a rear surface of the core metal member  49  and a rear wall  50 A of the upper mount accommodation section  45 . The fourth upper mount section  54  formed of an elastic body such as rubber or a resin material is interposed between right and left opposite side surfaces of the core metal member  49  and the upper mount holding section  46 . The fifth upper mount section  55  formed of an elastic body such as rubber or a resin material is interposed between a front portion of the upper mount accommodation section  45  and the upper mount bracket  38  (the steering bracket  41 ). Each of the above first to fifth upper mount sections  51  to  55  will be described hereinafter in more detail. 
     The first upper mount section  51  functions as a vibration prevention mount member that prevents vibration generated during low-speed rotation of the engine  14  from being transmitted to the hull  16 , and this first upper mount section  51  has a very small (soft) spring constant that enables vibration in a longitudinal (i.e., front-and-rear) direction and the lateral (i.e., right-and-left) direction. The first upper mount section  51  is arranged around a gravity center position G of the outboard motor body  11  so as to easily hold a load of the outboard motor body  11  in the tilt or trim operation of the outboard motor body  11 . Therefore, the spring constant of the first upper mount section  51  in the vertical direction is set to an appropriate value required for holding the load of the outboard motor body  11 . 
     The second upper mount section  52  is attached to the front surface of the core metal member  49 . A slight gap is formed between the front surface of the second upper mount section  52  and a rear surface  46 A of the upper mount holding section  46 , which is a member opposing to a front surface of the second upper mount section  52 . The engine holder  20  of the outboard motor body  11  is displaced backward (in a direction shown with an arrow A in  FIG. 4 ) by the forward thrust generated by the propeller  15  during the high-speed rotation of the engine  14  in the forward movement. The second upper mount section also  52  functions as a forward movement-side displacement restriction mount member that restricts the backward displacement of the engine holder  20 . For example, when the engine holder  20  of the outboard motor body  11  is displaced backward, the first upper mount section  51  is first deformed, and a displacement exceeding the displacement absorbed by the first upper mount section  51  is restricted with the front surface of the second upper mount section  52  abutting against the rear surface  46 A of the upper mount holding section  46 . 
     Therefore, the spring constant of the second upper mount section  52  is set to a spring constant large enough to prevent the vibration from transmitting of a constant level and restrict the displacement by the forward thrust of the propeller  15 , that is, a medium level larger than the spring constant of the first upper mount section  51 . When the forward thrust is generated by the propeller  15 , the front surface of the second upper mount section  52  is maintained in a state in abutment against the rear surface  46 A of the upper mount holding section  46 , and a steering force is transmitted to the entire outboard motor body  11  through the engine holder  20 . 
     The third upper mount section  53  is attached to the rear surface of the core metal member  49 . A slight gap is formed between the rear wall  50 A of the upper mount accommodation section  45 , which is a member opposing to the rear surface, and a rear surface of the third upper mount section  53 . The engine holder  20  of the outboard motor body  11  is displaced forward (in a direction shown with an arrow B in  FIG. 5 ) by a backward thrust of the propeller  15  during the backward movement. The third upper mount section  53  functions as a backward movement-side displacement restriction mount member that restricts the forward displacement of the engine holder  20 . 
     For example, when the engine holder  20  of the outboard motor body  11  is displaced forward, the first upper mount section  51  is first deformed, and a displacement exceeding the displacement absorbed by the first upper mount section  51  is restricted with the rear surface of the third upper mount section  53  abutting against the rear wall  50 A of the upper mount accommodation section  45 . A spring constant of the third upper mount section  53  is set to a medium level similarly to the second upper mount section  52 . 
     The fourth upper mount section  54  and the fifth upper mount section  55  are arranged on respective sides of the longitudinal direction (i.e., front-and-rear direction or hull travelling direction) a of the outboard motor body  11  with the first upper mount section  51  therebetween as shown in  FIGS. 2 and 3 . That is, the fourth upper mount section  54  is attached so as to cover the both lateral side surfaces of the core metal member  49 , and an upper surface and a lower surface close to the opposite side surfaces. A slight gap is formed with a rear surface  46 B of the upper mount holding section  46 , and a rear side (wall) surface  50 B, an upper surface  45 A, and a lower surface  45 B of the upper mount accommodation section  45 , which are opposing members. 
     The fifth upper mount section  55  is attached so as to cover lateral (right and left) side surfaces of the front portion of the upper mount accommodation section  45 , and an upper surface and a lower surface close to the opposite side surfaces. A slight gap is formed with side surfaces  38 A and  38 B of the upper mount bracket  38  (the steering bracket  41 ), and the upper surface  45 A and the lower surface  45 B of the upper mount accommodation section  45 , which are opposing members. 
     The fourth upper mount section  54  and the fifth upper mount section  55  function as a displacement restriction mount member for restricting displacement in lateral direction that includes a rolling direction and a yaw direction (hereinafter, which may be called lateral displacement restriction displacement mount section, for the sake of convenience) of the outboard motor body  11  with respect to the hull  16  generated during the steering operation or when the hull  16  lands on water after jumping. For example, during the steering operation, a lift (lift force) is generated on the underwater gear case  23  of the outboard motor body  11 , and the outboard motor body  11  is displaced in the lateral direction including the roiling direction and the yaw direction by the lift. At this time, the first upper mount section  51  is deformed first. When a larger load is applied, the fourth upper mount section  54  abuts against the rear surface  46 B of the upper mount holding section  46  and the rear side surface  50 B of the upper mount accommodation section  45 , and the fifth upper mount section  55  abuts against the side surfaces  38 A and  38 B of the upper mount bracket  38  to thereby restrict the displacement, respectively. Further, it is herein to be noted that the rolling direction means a direction in which the outboard motor body  11  rolls (i.e., tilts) in the lateral direction within a perpendicular plane with the gravity position G of the outboard motor body  11  being the center of rolling, and the yaw direction means a direction in which the outboard motor body  11  rotates (turns its direction) within a horizontal plane about the gravity position G. 
     Therefore, the spring constants of the fourth upper mount section  54  and the fifth upper mount section  55  are set to the spring constants capable of restricting the displacement of the outboard motor body  11  even when an excessive load is applied, that is, to the spring constants larger than the spring constants of the second upper mount section  52  and the third upper mount section  53 . 
     Further, a side surface  54 A acting as an abutment surface of the fourth upper mount section  54  and the rear surface  46 B acting as an abutment surface of the upper mount holding section  46  opposing to the side surface  54 A are formed so as to provide a tapered shape in which a front side is inclined inward in the lateral direction with respect to the longitudinal direction α of the outboard motor body  11 . A side surface  54 B acting as an abutment surface of the fourth upper mount section  54  and the rear side surface  50 B acting as an abutment surface of the upper mount accommodation section  45  opposing to the side surface  54 B are formed in parallel to the longitudinal direction α of the outboard motor body  11 . 
     On the other hand, a side surface  55 A acting as an abutment surface of the fifth upper mount section  55  and the side surface  38 A acting as an abutment surface of the upper mount bracket  38  (the steering bracket  41 ) opposing to the side surface  55 A are formed in parallel to the longitudinal direction α of the outboard motor body  11 . A side surface  55 B acting an abutment surface of the fifth upper mount section  55  and the side surface  38 B acting as an abutment surface of the upper mount bracket  38  (the steering bracket  41 ) opposing to the side surface  55 B are formed so as to provide a tapered shape in which a front side is inclined inward in the lateral direction with respect to the longitudinal direction α of the outboard motor body  11 . 
     Both of the side surface  54 A of the fourth upper mount  54  section and the rear surface  46 B of the upper mount holding section  46 , and both the side surface  55 B of the fifth upper mount section  55  and the side surface  38 B of the upper mount bracket  38  are formed to provide the tapered shape as described above. Thus, a gap X between the side surface  54 A of the fourth upper mount section  54  and the rear surface  46 B of the upper mount holding section  46 , and a gap Y between the side surface  55 B of the fifth upper mount section  55  and the side surface  38 B of the upper mount bracket  38  become relatively large (see  FIG. 2 ) at a time when the rotating speed of the engine  14  is low and the forward thrust of the propeller  15  is small, while the gaps X and Y are decreased with the engine holder  20  being displaced backward (the direction of the arrow A in  FIG. 4 ) as shown in  FIG. 4  at a time when the rotating speed of the engine  14  is high and the forward thrust of the propeller  15  is large. 
     Therefore, when the rotating speed of the engine  14  is high and the forward thrust of the propeller  15  is large, the side surface  54 A of the fourth upper mount section  54  abuts against the rear surface  46 B of the upper mount holding section  46 , and the side surface  55 B of the fifth upper mount section  55  abuts against the side surface  38 B of the upper mount bracket  38  even with a slight displacement in the lateral direction including the rolling direction and the yaw direction. As a result, there can be attained an effect such that both of the lateral displacement restriction function and the steering response when the rotating speed of the engine  14  is high and the forward thrust of the propeller  15  is large can be improved. 
     When the rotating speed of the engine  14  is low and the forward thrust of the propeller  15  is small, both of the gap X between the side surface  54 A of the fourth upper mount section  54  and the rear surface  46 B of the upper mount holding section  46 , and the gap Y between the side surface  55 B of the fifth upper mount section  55  and the side surface  38 B of the upper mount bracket  38  are relatively large. More specifically, the gaps X and Y are set to be sufficiently large such that the side surface  54 A and the rear surface  46 B, and the side surface  55 B and the side surface  38 B do not interfere with each other even by occurrence of the vibration of the engine  14  during the low-speed rotation of the engine  14 . As a result, there can be attained effects such that it is possible to ensure a favorable vibration transmission preventing function by the first upper mount section  51  during the low-speed rotation of the engine  14 , and to reduce a requirement for machining accuracy of the fourth upper mount section  54  and the fifth upper mount section  55 , thus reducing the manufacturing cost of the fourth and fifth upper mount sections  54  and  55 . 
     Furthermore, both of the side surface  54 B of the fourth upper mount section  54  and the rear side surface  50 B of the upper mount accommodation section  45 , and both the side surface  55 A of the fifth upper mount section  55  and the side surface  38 A of the upper mount bracket  38  are formed in parallel to the longitudinal (front-and-rear) direction α of the outboard motor body  11  as described above. Thus, a gap Z between the side surface  54 B of the fourth upper mount section  54  and the rear side surface  50 B of the upper mount accommodation section  45 , and a gap W between the side surface  55 A of the fifth upper mount section  55  and the side surface  38 A of the upper mount bracket  38  are substantially constant without being changed even if the engine holder  20  is displaced forward (in the direction shown with the arrow B in  FIG. 5 ) as shown in  FIG. 5  due to the generation of the backward thrust of the propeller  15 . Therefore, there can be attained effects such that it is possible to prevent a decrease in the lateral displacement restriction function and the steering response when the backward thrust is generated by the propeller  15 , and to ensure a favorable vibration transmission preventing function by the first upper mount section  51 . 
     Although the side surface  54 B of the fourth upper mount section  54  has an area smaller than the side surface  54 A and the side surface  55 A of the fifth upper mount section  55  has an area smaller than the side surface  55 B, the displacement in the lateral direction including the rolling direction and the yaw direction when the backward thrust is generated by the propeller  15  can be sufficiently restricted because the speed of the hull  16  is low and the lift generated on the gear case  23  during the steering operation is also small when the backward thrust is generated by the propeller  15 . 
     On the other hand, as shown in  FIGS. 1, 6, and 7 , the lower mount accommodation sections  57  that accommodate the lower mount units  18  are formed in both the opposite side surface portions of the drive shaft housing  22 . Each of the lower mount accommodation sections  57  is closed by the lower mount cover  44  to be removable in a width direction. A pair of lower mount holding sections  58  are formed in the lower mount accommodation section  57  and the lower mount cover  44  in the width direction of the outboard motor body  11  integrally with the lower mount accommodation section  57  and the lower mount cover  44 . The lower mount units  18  are fixed to the lower mount bracket  39  with front end portions of the right and left two lower mount bolts  43  penetrating the lower mount bracket  39  and rear end portions thereof screwed to a core metal member  59  in a state in which the lower mount units  18  are accommodated in the lower mount accommodation sections  57  of the drive shaft housing  22 . 
     Each of the lower mount units  18  includes first to fifth lower mount sections  61  to  65 . The first lower mount section  61  formed of an elastic body such as rubber is wound around each of inner tubes  60  through which the right and left pair of lower mount bolts  43  are inserted, and the first lower mount section  61  is fitted to the lower mount holding sections  58  of the drive shaft housing  22  and the lower mount cover  44 . The second lower mount section  62  formed of an elastic body such as rubber is interposed between the rear surface of the core metal member  59  and the rear wall  66  of the lower mount accommodation section  57  of the drive shaft housing  22 , and between the rear surface center portion of the lower mount bracket  39  and the front surface of the mount holding section  58  of the drive shaft housing  22 . The third lower mount section  63  formed of an elastic body such as rubber is interposed between the front surface center portion of the core metal member  59  and the rear surface of the lower mount holding section  58  of the drive shaft housing  22 , and between opposite-side front ends of the core metal member  59  and the mount holding section  58  of the lower mount cover  44 . The fourth lower mount section  64  formed of an elastic body such as rubber or a resin material is interposed between right and left opposite side surfaces and the upper surface and the lower surface close to the opposite side surfaces of the core metal member  59 , and the lower mount cover  44 . The fifth lower mount section  65  formed of an elastic body such as rubber or a resin material is interposed between an area of the lower mount bracket  39  around the lower mount bolt  43  inserted therein, and the lower mount holding section  58  of the drive shaft housing  22  and the lower mount cover  44 . 
     The first lower mount section  61  functions as a vibration prevention mount member that prevents the vibration generated during the low-speed rotation of the engine  14  from being transmitted to the hull  16  and has a very small (soft) spring constant that enables movement in the longitudinal direction and the lateral direction. The spring constant of the first lower mount section  61  in the vertical direction is set to an appropriate value required for holding the load of the outboard motor body  11 . 
     The second lower mount section  62  is attached to the rear surface of the core metal member  59  and the rear surface center portion of the lower mount bracket  39 . A slight gap is formed between the rear wall  66  of the lower mount accommodation section  57  and the front surface of the lower mount holding section  58  of the drive shaft housing  22 , which are members opposing to the rear surface of the second lower mount section  62 . The drive shaft housing  22  of the outboard motor body  11  is displaced forward (in a direction shown with an arrow C in  FIG. 8 ) by the forward thrust generated by the propeller  15  during the high-speed rotation of the engine  14  in the forward movement of the hull. 
     The second lower mount section  62  functions as a forward movement-side displacement restriction mount member that restricts the forward displacement of the drive shaft housing  22 . 
     For example, when the drive shaft housing  22  of the outboard motor body  11  is displaced forward, the first lower mount section  61  is first deformed, and a displacement exceeding the displacement absorbed by the first lower mount section  61  is restricted by the rear surface of the second lower mount section  62  abutting against the rear wall  66  of the lower mount accommodation section  57  of the drive shaft housing  22  and the front surface of the lower mount holding section  58  of the drive shaft housing  22 . 
     Therefore, the spring constant of the second lower mount section  62  is set to a spring constant large enough to prevent vibration transmission of a constant level, and restrict the displacement by the forward thrust of the propeller  15 , that is, is set to an intermediate level larger than the spring constant of the first lower mount section  61 . When the forward thrust is generated by the propeller  15 , the rear surface of the second lower mount section  62  is maintained in a state in abutment against the rear wall  66  of the lower mount accommodation section  57  of the drive shaft housing  22  and the front surface of the lower mount holding section  58  of the drive shaft housing  22 , and a steering force is transmitted to the entire outboard motor body  11  through the drive shaft housing  22 . 
     The third lower mount section  63  is attached to the front surface center portion of the core metal member  59  and the opposite-side front ends of the core metal member  59 . A slight gap is formed between the rear surface of the lower mount holding section  58  of the drive shaft housing  22  and the lower mount holding section  58  of the lower mount cover  44 , which are members opposing to the front surface center portion of the core metal member  59  and the opposite-side front ends of the core metal member  59 . The drive shaft housing  22  of the outboard motor body  11  is displaced backward (in a direction shown with an arrow D in  FIG. 9 ) by the backward thrust of the propeller  15  during the backward movement of the hull. The third lower mount section  63  functions as a backward movement-side displacement restriction mount member that restricts the backward displacement of the drive shaft housing  22 . 
     For example, when the drive shaft housing  22  of the outboard motor body  11  is displaced backward, the first lower mount section  61  is first deformed, and a displacement exceeding the displacement absorbed by the first lower mount section  61  is restricted by the front surface of the third lower mount section  63  abutting against the lower mount holding section  58  of the drive shaft housing  22  and the lower mount holding section  58  of the lower mount cover  44 . The spring constant of the third lower mount section  63  is set to an intermediate level similarly to the second lower mount section  62 . 
     The fourth lower mount section  64  and the fifth lower mount section  65  are arranged on the respective sides of the longitudinal direction α of the outboard motor body  11  with the first lower mount section  61  being disposed therebetween as shown in  FIGS. 6 and 7 . That is, the fourth lower mount section  64  is attached so as to cover the right and left opposite side surfaces and the upper surface and the lower surface close to the opposite side surfaces of the core metal member  59 . A slight gap is formed between the side surfaces  44 A and  44 B of the lower mount cover  44 , and an upper surface  57 A and a lower surface  57 B of the lower mount accommodation section  57 , which are opposing members. The fifth lower mount section  65  is attached to the area of the lower mount bracket  39  around the lower mount bolt  43  that is inserted therein. A slight gap is formed between the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  and a front-side inner surface  44 C of the lower mount cover  44 , which are opposing members. 
     The fourth lower mount section  64  and the fifth lower mount section  65  function as displacement restriction mount members for restricting displacement in the vertical direction, the lateral direction including the rolling and yaw directions of the outboard motor body  11  with respect to the hull  16  generated during the steering operation or when the hull  16  lands on water after jumping. For example, during the steering operation, a lift forth is generated to the underwater gear case  23  of the outboard motor body  11 , and the outboard motor body  11  is displaced in the lateral direction by the lift. At this time, the first lower mount section  61  is first deformed. When a larger load is applied, the fourth lower mount section  64  abuts against the side surfaces  44 A and  44 B of the lower mount cover  44 , and the fifth lower mount section  65  abuts against the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  and the front-side inner surface  44 C of the lower mount cover  44  to thereby restrict the displacement, respectively. 
     Therefore, spring constants of the fourth lower mount section  64  and the fifth lower mount section  65  are set to spring constants capable of restricting the displacement of the outboard motor body  11  even when an excessive load is applied, that is, spring constants larger than the spring constants of the second lower mount section  62  and the third lower mount section  63 . 
     Further, a side surface  64 B acting as an abutment surface of the fourth lower mount section  64  and the side surface  44 B acting as an abutment surface of the lower mount cover  44  that opposes the side surface  64 B are formed in a tapered shape in which a rear side is inclined with respect to the longitudinal direction α of the outboard motor body  11 . Furthermore, a side surface  64 A acting as an abutment surface of the fourth lower mount section  64  and the side surface  44 A acting as an abutment surface of the lower mount cover  44  that opposes the side surface  64 A are formed in parallel to the longitudinal direction α of the outboard motor body  11 . 
     On the other hand, a side surface  65 A acting as an abutment surface of the fifth lower mount section  65  and the front-side inner surface  44 C acting as an abutment surface of the lower mount cover  44  that opposes the side surface  65 A are formed in parallel to the longitudinal direction α of the outboard motor body  11 . A side surface  65 B acting as an abutment surface of the fifth lower mount section  65  and the front portion side surface  58 A acting as an abutment surface of the lower mount holding section  58  of the drive shaft housing  22  that opposes the side surface  65 B are formed in a tapered shape in which a rear side is inclined to the inner side in the lateral direction with respect to the longitudinal direction α of the outboard motor body  11 . 
     Both the side surface  64 B of the fourth lower mount section  64  and the side surface  44 B of the lower mount cover  44 , and both the side surface  65 B of the fifth lower mount section  65  and the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  are formed in a tapered shape as described above. Thus, a gap Q between the side surface  64 B of the fourth lower mount section  64  and the side surface  44 B of the lower mount cover  44 , and a gap R between the side surface  65 B of the fifth lower mount section  65  and the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  are relatively large (see  FIG. 6 ) at a time of the low rotating speed of the engine  14  and the small forward thrust of the propeller  15 , while the gaps Q and R are decreased with the drive shaft housing  22  displaced forward (the direction of the arrow C in  FIG. 8 ) as shown in  FIG. 8  at a time of high rotating speed of the engine  14  and the large forward thrust of the propeller  15 . 
     Therefore, in the operation at the time when the rotating speed of the engine  14  is high and the forward thrust of the propeller  15  is large, the side surface  64 B of the fourth lower mount  64  section abuts against the side surface  44 B of the lower mount cover  44 , and the side surface  65 B of the fifth lower mount section  65  abuts against the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  even with slight displacement in the lateral direction including the rolling and yaw directions. As a result, there can be attained an effect such that both of the displacement restricting function and a steering response at the time of the high rotating speed of the engine  14  and the large forward thrust of the propeller  15  can be improved. 
     During the low rotating speed of the engine  14  with the small forward thrust of the propeller  15 , both of the gap Q between the side surface  64 B of the fourth lower mount section  64  and the side surface  44 B of the lower mount cover  44 , and the gap R between the side surface  65 B of the fifth lower mount section  65  and the front portion side surface  58 A of the lower mount holding section  58  of the drive shaft housing  22  became relatively large. More specifically, the gaps Q and R are set to be large enough not to interfere the side surface  64 B and the side surface  44 B, and the side surface  65 B and the front portion side surface  58 A with each other even by the vibration of the engine  14  during the low rotating speed of the engine  14 . As a result, there can be attained effects such that it is possible to ensure a favorable vibration transmission preventing function by the first lower mount section  61  during the low rotating speed operation of the engine  14 , and to reduce a requirement for machining accuracy of the fourth and fifth lower mounts  64  and  65 , thereby reducing the manufacturing cost of these fourth and fifth lower mounts  64  and  65 . 
     Furthermore, both of the side surface  64 A of the fourth lower mount section  64  and the side surface  44 A of the lower mount cover  44 , and the side surface  65 A of the fifth lower mount section  65  and the front-side inner surface  44 C of the lower mount cover  44  are formed in parallel to the longitudinal direction α of the outboard motor body  11  as described above. Thus, a gap S between the side surface  64 A of the fourth lower mount section  64  and the side surface  44 A of the lower mount cover  44 , and a gap T between the side surface  65 A of the fifth lower mount section  65  and the front-side inner surface  44 C of the lower mount cover  44  are substantially constant without being changed even if the drive shaft housing  22  is displaced backward (in the direction shown with the arrow D) as shown in  FIG. 9  due to the generation of the backward thrust of the propeller  15 . Accordingly, there can be attained effects such that it is possible to prevent a decrease in the lateral displacement restriction function and the steering response when the backward thrust is generated by the propeller  15 , and to ensure a favorable vibration transmission preventing function by the first lower mount section  61 . 
     Although the side surface  64 A of the fourth lower mount section  64  has an area smaller than the side surface  64 B and the side surface  65 A of the fifth lower mount section  65  has an area smaller than the side surface  65 B, the displacement in the lateral direction including the rolling and yaw directions when the backward thrust is generated by the propeller  15  can be sufficiently restricted because the speed of the hull  16  is low and the lift generated on the gear case  23  during the steering operation is also small when the backward thrust is generated by the propeller  15 . 
     It is to be noted that although the embodiment of the present invention has been described above, the embodiment is merely illustrative, and does not intend to limit the scope of the present invention. The present invention may be carried out other than the embodiment described above in various other forms, and various omission, replacements, and changes may be also made without departing from the scope of the present invention. 
     REFERENCE NUMERAL 
       10 —outboard motor,  11 —outboard motor body,  12 —attachment bracket device (attachment device),  13 —mount device,  14 —engine,  15 —propeller,  16 —hull,  17 —upper mount unit,  18 —lower mount unit,  20 —engine holder,  22 —drive shaft housing,  38 B—side surface (abutment surface),  44 —lower mount cover,  44 B—side surface (abutment surface),  46 B— 44 B—rear surface (abutment surface),  51 —first upper mount section (vibration preventing mount),  52 —second upper mount section (forward-movement side displacement restriction mount),  53 —third upper mount section (backward side displacement restriction mount),  54 —fourth upper mount section (lateral direction displacement restriction mount),  55 —fifth upper mount section (lateral direction displacement restriction mount),  54 A,  54 B—side surface (abutment surface),  57 —lower mount accommodation portion,  58 —lower mount holding portion,  58 A—front-side side surface (abutment surface),  59 —core metal member,  61 —first lower mount section, (vibration prevention mount),  62 —second lower mount section (forward-movement side displacement restriction mount),  63 —third lower mount section (backward side displacement restriction mount),  64 —fourth lower mount section (lateral direction displacement restriction mount),  65 —fifth lower mount section (lateral direction displacement restriction mount),  64 B,  65 A,  65 B—side surface (abutment surface), α—longitudinal (front-and-rear) direction.