Patent Publication Number: US-9896176-B2

Title: Marine propulsion device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The priority application number JP2014-199929, Marine Propulsion Device, Sep. 30, 2014, Takayoshi Suzuki, Noriyoshi Hiraoka, Akihiro Onoue, Atsushi Kumita, and Yoshiaki Tasaka, upon which this patent application is based is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a marine propulsion device, and more particularly, it relates to a marine propulsion device including an accelerator grip. 
     Description of the Background Art 
     A marine propulsion device including an accelerator grip is known in general. Such a marine propulsion device is disclosed in Japanese Patent Laying-Open No. 2014-046745, for example. 
     In general, a marine propulsion device is provided with an accelerator grip to adjust drive force in a forward movement direction or in a reverse movement direction generated from a power source. When finely adjusting forward/reverse movement of a boat body, a user repeats an operation of switching the accelerator grip from a rotatable state in one of a forward movement rotation region and a reverse movement rotation region to a rotatable state in the other of the forward movement rotation region and the reverse movement rotation region. In this case, there is a time lag until the boat body responds to the operation of switching the accelerator grip. Therefore, it is difficult for the user to recognize that the accelerator grip has been switched from the rotatable state in one of the forward movement rotation region and the reverse movement rotation region to the rotatable state in the other of the forward movement rotation region and the reverse movement rotation region. The aforementioned Japanese Patent Laying-Open No. 2014-046745 is known to solve this problem. 
     The aforementioned Japanese Patent Laying-Open No. 2014-046745 discloses a marine propulsion device including a power source, a steering handle that extends forward with respect to the power source, and an accelerator grip movably mounted on the steering handle. A movement region of the accelerator grip includes a forward movement rotation region where the accelerator grip is operated to rotate about a rotation axis so as to obtain drive force in a forward movement direction from the power source and a reverse movement rotation region where the accelerator grip is operated to rotate about the rotation axis so as to obtain drive force in a reverse movement direction from the power source. A shaft portion of the steering handle is provided with an engaging member that engages with the accelerator grip. The accelerator grip is not allowed to rotate in the forward movement rotation region and the reverse movement rotation region in a state where the accelerator grip and the engaging member engage with each other. A user presses down the engaging member while griping the accelerator grip. When the user presses down the engaging member, engagement between the accelerator grip and the engaging member is released, and the accelerator grip is allowed to rotate. Thus, when the accelerator grip is switched from a rotatable state in one of the forward movement rotation region and the reverse movement rotation region to a rotatable state in the other of the forward movement rotation region and the reverse movement rotation region, the accelerator grip engages with the engaging member to be temporarily fixed, and hence the user recognizes that the rotation region of the accelerator grip is switched by releasing this engagement. In the marine propulsion device described in the aforementioned Japanese Patent Laying-Open No. 2014-046745, however, it is necessary to release the engagement between the accelerator grip and the engaging member when the accelerator grip is switched from the rotatable state in one of the forward movement rotation region and the reverse movement rotation region to the rotatable state in the other of the forward movement rotation region and the reverse movement rotation region. Thus, although the user recognizes that the rotation region of the accelerator grip is switched, an operation of switching the accelerator grip from the rotatable state in one of the forward movement rotation region and the reverse movement rotation region to the rotatable state in the other of the forward movement rotation region and the reverse movement rotation region is complicated, and it is difficult for the user to smoothly perform the operation of switching the rotation region of the accelerator grip. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed in order to solve the aforementioned problem, and an object of the present invention is to provide a marine propulsion device that significantly reduces or prevents complication of an operation of switching a rotation region of an accelerator grip and allows a user to smoothly perform the operation of switching the rotation region of the accelerator grip while allowing the user to recognize that the rotation region of the accelerator grip is switched. 
     A marine propulsion device according to an aspect of the present invention includes a power source, a steering handle that extends forward with respect to the power source, and an accelerator grip movably mounted on the steering handle. A movement region of the accelerator grip includes a forward movement rotation region where the accelerator grip is operated to rotate about a rotation axis so as to obtain drive force in a forward movement direction from the power source, a reverse movement rotation region where the accelerator grip is operated to rotate about the rotation axis so as to obtain drive force in a reverse movement direction from the power source, and an axis movement region provided between the forward movement rotation region and the reverse movement rotation region, where the accelerator grip is moved in the extensional direction of the rotation axis. 
     In the marine propulsion device according to this aspect of the present invention, as hereinabove described, the movement region of the accelerator grip includes the axis movement region where the accelerator grip is moved in the extensional direction of the rotation axis between the forward movement rotation region and the reverse movement rotation region. Thus, the accelerator grip is switched from a rotationally operable state in one of the forward movement rotation region and the reverse movement rotation region to a rotationally operable state in the other of the forward movement rotation region and the reverse movement rotation region through the axis movement region, unlike the structure in which it is necessary to release an engaging state between the accelerator grip and an engaging member when the accelerator grip is switched from the rotationally operable state in one of the forward movement rotation region and the reverse movement rotation region to the rotationally operable state in the other of the forward movement rotation region and the reverse movement rotation region. In this case, complication of an operation of switching the rotation region of the accelerator grip is significantly reduced or prevented, and a user smoothly performs the operation of switching the rotation region of the accelerator grip while recognizing that the rotation region of the accelerator grip is switched. Consequently, the operability is improved when the user switches the rotation region of the accelerator grip. 
     Furthermore, the marine propulsion device is configured as hereinabove described, whereby when the accelerator grip is switched from the rotationally operable state in one of the forward movement rotation region and the reverse movement rotation region to the rotationally operable state in the other of the forward movement rotation region and the reverse movement rotation region, restriction of the posture of the user (restriction of a gripped position of the accelerator grip) is significantly reduced when the user operates the accelerator grip, unlike the structure in which it is necessary for the user to grip a position of the accelerator grip where the engaging state between the accelerator grip and the engaging member is released. 
     In the aforementioned marine propulsion device according to this aspect, the forward movement rotation region and the reverse movement rotation region are preferably arranged at positions different from each other in the extensional direction of the rotation axis. According to this structure, the forward movement rotation region and the reverse movement rotation region are arranged separately in the extensional direction of the rotation axis, and hence the user easily recognizes the forward movement rotation region and the reverse movement rotation region on the basis of a difference in the position in the extensional direction of the rotation axis. 
     In this case, the forward movement rotation region and the reverse movement rotation region are preferably arranged not to overlap each other, as viewed in the extensional direction of the rotation axis, and the rotation direction of the accelerator grip is preferably opposite in the forward movement rotation region and the reverse movement rotation region. According to this structure, the user more easily recognizes the forward movement rotation region and the reverse movement rotation region, unlike the case where the rotation direction of the accelerator grip is the same in the forward movement rotation region and the reverse movement rotation region. Furthermore, the user more easily recognizes the forward movement rotation region and the reverse movement rotation region on the basis of a difference in the position about the rotation axis. 
     In the aforementioned structure in which the forward movement rotation region and the reverse movement rotation region are arranged at the positions different from each other in the extensional direction of the rotation axis, the forward movement rotation region and the reverse movement rotation region are preferably arranged to overlap each other, as viewed in the extensional direction of the rotation axis, and the rotation direction of the accelerator grip is preferably the same in the forward movement rotation region and the reverse movement rotation region. According to this structure, a space (rotation angle range) where the forward movement rotation region and the reverse movement rotation region are arranged is reduced in size, as viewed in the extensional direction of the rotation axis, unlike the case where the rotation direction of the accelerator grip is opposite in the forward movement rotation region and the reverse movement rotation region. 
     In the aforementioned marine propulsion device according to this aspect, the axis movement region preferably includes a neutral region where no drive force in the forward movement direction or in the reverse movement direction is generated. According to this structure, unless the accelerator grip passes through the neutral region, the accelerator grip does not rotate from one of the forward movement rotation region and the reverse movement rotation region into the other of the forward movement rotation region and the reverse movement rotation region. Consequently, complication of the operation of switching the rotation region of the accelerator grip is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip while recognizing that a state of forward movement drive or reverse movement drive switches to a state of opposite drive. Furthermore, the extra load on the power source is significantly reduced or prevented when the state of forward movement drive or reverse movement drive switches to the state of opposite drive. 
     In the aforementioned marine propulsion device according to this aspect, the forward movement rotation region and the reverse movement rotation region are preferably provided at substantially the same positions in the extensional direction of the rotation axis, the rotation direction of the accelerator grip is preferably opposite in the forward movement rotation region and the reverse movement rotation region, and the accelerator grip is preferably switched from a rotationally operable state in the forward movement rotation region to a rotationally operable state in the reverse movement rotation region through the axis movement region. According to this structure, even when the forward movement rotation region and the reverse movement rotation region are not arranged separately in the extensional direction of the rotation axis, the user easily recognizes the forward movement rotation region and the reverse movement rotation region by setting the rotation direction of the accelerator grip to be opposite in the forward movement rotation region and the reverse movement rotation region. Furthermore, unlike the case where the forward movement rotation region and the reverse movement rotation region of the accelerator grip are arranged separately in the extensional direction of the rotation axis, a space (the length in the extensional direction of the rotation axis) where the forward movement rotation region and the reverse movement rotation region are arranged is reduced in size in a plan view. 
     In this case, the forward movement rotation region and the reverse movement rotation region are preferably separated from each other by the axis movement region. According to this structure, even when the forward movement rotation region and the reverse movement rotation region are not arranged separately in the extensional direction of the rotation axis, the user more easily recognizes the forward movement rotation region and the reverse movement rotation region by the separation of the forward movement rotation region from the reverse movement rotation region by the axis movement region. 
     In the aforementioned structure in which the forward movement rotation region and the reverse movement rotation region are separated from each other by the axis movement region, the accelerator grip is preferably switched from the rotationally operable state in the forward movement rotation region to the rotationally operable state in the reverse movement rotation region through a neutral rotation region offset in the extensional direction of the rotation axis with respect to the forward movement rotation region and the reverse movement rotation region. According to this structure, complication of the operation of switching the rotation region of the accelerator grip is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip while recognizing that the accelerator grip is switched from the rotationally operable state in the forward movement rotation region to the rotationally operable state in the reverse movement rotation region through the neutral rotation region. 
     In the aforementioned marine propulsion device according to this aspect, the accelerator grip is preferably switched from a rotationally operable state in the forward movement rotation region to a rotationally operable state in the reverse movement rotation region through the axis movement region, and is preferably switched from the rotationally operable state in the reverse movement rotation region to the rotationally operable state in the forward movement rotation region not through the axis movement region. According to this structure, complication of the operation of switching the rotation region of the accelerator grip from the forward movement rotation region to the reverse movement rotation region is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip. Furthermore, the accelerator grip is easily switched from the rotationally operable state in the reverse movement rotation region to the rotationally operable state in the forward movement rotation region without a complicated operation. 
     In the aforementioned marine propulsion device according to this aspect, the maximum rotational operation angle of the accelerator grip in the forward movement rotation region is preferably larger than the maximum rotational operation angle of the accelerator grip in the reverse movement rotation region. According to this structure, the user easily recognizes whether the accelerator grip has rotated into the forward movement rotation region or the reverse movement rotation region and easily finely adjusts an output for forward movement. 
     In the aforementioned marine propulsion device according to this aspect, the axis movement region preferably includes a neutral region where no drive force in the forward movement direction or in the reverse movement direction is generated, and the marine propulsion device preferably further includes an urging member that urges the accelerator grip so as to locate the accelerator grip in the neutral region. According to this structure, the accelerator grip is located in the neutral region even when the user releases his/her hand from the accelerator grip in the case where the power source generates no output in the forward movement rotation region and the reverse movement rotation region. 
     In the aforementioned marine propulsion device according to this aspect, the power source is preferably an electric motor. According to this structure, in the marine propulsion device in which the electric motor is employed as the power source, complication of the operation of switching the rotation region of the accelerator grip is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip while recognizing that the rotation region of the accelerator grip is switched. 
     The aforementioned marine propulsion device according to this aspect preferably further includes a shaft member connected to the accelerator grip and a steering handle housing that supports the shaft member, the shaft member preferably includes a first engaging portion, the steering handle housing preferably includes a second engaging portion that engages with the first engaging portion, and in a state where the first engaging portion of the shaft member and the second engaging portion of the steering handle housing engage with each other, the shaft member preferably moves in the extensional direction of the rotation axis with respect to the steering handle housing in a first engaging region that corresponds to the axis movement region, and preferably rotates about the rotation axis with respect to the steering handle housing in a second engaging region that corresponds to the forward movement rotation region and a third engaging region that corresponds to the reverse movement rotation region. According to this structure, the accelerator grip rotates and axially moves in the state where the first engaging portion of the shaft member and the second engaging portion of the steering handle housing engage with each other, and hence the first engaging portion of the shaft member is guided by the second engaging portion of the steering handle housing and is moved to a prescribed position. Consequently, the accelerator grip is accurately operated. 
     The foregoing and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for illustrating the overall structure of a marine propulsion device according to a first embodiment of the present invention; 
         FIG. 2  is a diagram for illustrating the structure of a steering handle of the marine propulsion device according to the first embodiment of the present invention; 
         FIG. 3  is a diagram schematically showing an engaging state between a first engaging portion and a second engaging portion of the marine propulsion device according to the first embodiment of the present invention, as viewed in a direction Z 2 ; 
         FIG. 4  is a diagram for illustrating a shaft member of the marine propulsion device according to the first embodiment of the present invention; 
         FIG. 5  is a diagram showing the shaft member and a friction plate of the marine propulsion device according to the first embodiment of the present invention; 
         FIG. 6  is a diagram schematically showing the operation of an accelerator grip of the marine propulsion device according to the first embodiment of the present invention; 
         FIG. 7  is a sectional view taken along the line VII-VII in  FIG. 3 ; 
         FIG. 8  is a plan view showing the accelerator grip of the marine propulsion device according to the first embodiment of the present invention; 
         FIG. 9  is a side elevational view of the accelerator grip of the marine propulsion device according to the first embodiment of the present invention, as viewed in the extensional direction of a rotation axis; 
         FIG. 10  is a diagram schematically showing an engaging state between a first engaging portion and a second engaging portion of a marine propulsion device according to a second embodiment of the present invention, as viewed in a direction Z 2 ; 
         FIG. 11  is a diagram schematically showing the operation of an accelerator grip of the marine propulsion device according to the second embodiment of the present invention; 
         FIG. 12  is a diagram schematically showing an engaging state between a first engaging portion and a second engaging portion of a marine propulsion device according to a third embodiment of the present invention, as viewed in a direction Z 2 ; 
         FIG. 13  is a diagram schematically showing the operation of an accelerator grip of the marine propulsion device according to the third embodiment of the present invention; 
         FIG. 14  is a diagram schematically showing an engaging state between a first engaging portion and a second engaging portion of a marine propulsion device according to a fourth embodiment of the present invention, as viewed in a direction Z 2 ; 
         FIG. 15  is another diagram schematically showing the engaging state between the first engaging portion and the second engaging portion of the marine propulsion device according to the fourth embodiment of the present invention, as viewed in the direction Z 2 ; 
         FIG. 16  is a diagram schematically showing the operation of an accelerator grip of the marine propulsion device according to the fourth embodiment of the present invention; and 
         FIG. 17  is a diagram showing the relationship between the rotational operation angle of an accelerator grip and torque generated from a power source in a marine propulsion device according to a modification of the first embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the present invention are hereinafter described with reference to the drawings. 
     First Embodiment 
     The structure of a marine propulsion device  1  according to a first embodiment of the present invention is now described with reference to  FIGS. 1 to 9 . In the figure, arrow FWD represents the forward movement direction of a boat body, and arrow BWD represents the reverse movement direction of the boat body. 
     As shown in  FIG. 1 , the marine propulsion device  1  includes a power source  2 , a drive shaft  3 , a gear portion  4 , a propeller shaft  5 , and an ECU (engine control unit)  6 . Electric power is supplied from a battery  7  arranged in a boat body  50  to the power source  2  and the ECU  6 . The marine propulsion device  1  also includes a steering handle  8 . The marine propulsion device  1  is mounted on the boat body  50  through a bracket  50   a.    
     The power source  2  includes a normally and reversely rotatable electric motor. 
     An upper end of the drive shaft  3  is connected to the power source  2 . A lower end of the drive shaft  3  is mounted with a pinion gear  4   a  described later. The drive shaft  3  is rotated about a rotation axis A 1  following the drive of the power source  2 . 
     The gear portion  4  includes the pinion gear  4   a  and a bevel gear  4   b . The pinion gear  4   a  and the bevel gear  4   b  engage with each other. 
     The propeller shaft  5  extends in a direction orthogonal to the drive shaft  3 . A back end of the propeller shaft  5  is mounted with a propeller  5   a . The drive force of the drive shaft  3  is transmitted to the propeller shaft  5  through the gear portion  4  so as to rotate the propeller shaft  5  about a rotation axis A 2 . 
     The ECU  6  includes a CPU, a storage portion, etc. The ECU  6  controls the operation of the power source  2  on the basis of the operation of an accelerator grip  82  performed by a user. 
     As shown in  FIG. 2 , the steering handle  8  includes a steering handle housing  81 , the accelerator grip  82 , a shaft member  83 , and a friction plate  84   a . The steering handle  8  also includes a neutral correction plate  85   a , urging members  86 , a rotation angle detecting sensor  87 , and an emergency stop switch  88 . The steering handle  8  extends forward (the extensional direction of the propeller shaft  5 , see  FIG. 1 ) with respect to the power source  2 . The steering handle  8  has a function of turning the marine propulsion device  1  with respect to the boat body  50  and changing a direction in which the thrust force of the marine propulsion device  1  is applied by rotation in a right-left direction of the boat body  50  about the bracket  50   a  arranged on a back end of the boat body  50 . At this time, the power source  2  is controlled by operating the accelerator grip  82  in either a forward movement rotation region  910  (see  FIG. 6 ) or a reverse movement rotation region  920  (see  FIG. 6 ) described later. 
     The steering handle housing  81  is a case member that stores the shaft member  83 , the neutral correction plate  85   a , etc. The steering handle housing  81  includes a second engaging portion  811 . 
     The second engaging portion  811  is a groove provided in an upper side portion of the inner surface of the steering handle housing  81 . As shown in  FIG. 3 , the second engaging portion  811  has a schematic shape in which a straight line is bent. Specifically, an axis guide portion of the second engaging portion  811  that corresponds to a first engaging region  930   a  described later is longitudinal in a direction X. A forward movement rotation guide portion  811   d  Portions of the second engaging portion  811  that correspond to a second engaging region  910   a  described later and a reverse movement rotation guide portion  811   e  of the second engaging portion  811  correspond to a third engaging region  920   a  described later are longitudinal in a direction (direction Y) perpendicular to the direction X. The forward movement rotation guide portion  811   d  of the second engaging portion  811  that correspond to the second engaging region  910   a  and the reverse movement rotation guide portion  811   e  of the second engaging portion  811  that correspond to the third engaging region  920   a  extend in opposite directions. The forward movement rotation guide portion  811   d  that correspond to the second engaging region  910   a  and the reverse movement rotation guide portion  811   e  of the second engaging portion  811  that correspond to the third engaging region  920   a  are connected to the vicinities of one edge portion  811   f  and the other edge portion  811   g  of the axis guide portion  811   c  that corresponds to the first engaging region  930   a  in the direction X, respectively. The second engaging portion  811  engages with a first engaging portion  833  of the shaft member  83 . The second engaging portion  811  includes a stopper  811   a  that restricts rotation of the first engaging portion  833  of the shaft member  83  in a direction Y 2  in the second engaging region  910   a  described later. The second engaging portion  811  includes a stopper  811   b  that restricts rotation of the first engaging portion  833  of the shaft member  83  in a direction Y 1  in the third engaging region  920   a  described later. In this description, the direction X is a concept indicating the longitudinal direction of the shaft member  83 . 
     As shown in  FIG. 2 , the accelerator grip  82  is arranged in an end of the steering handle  8  in a direction X 1 . The accelerator grip  82  is movably mounted on the steering handle  8 . The accelerator grip  82  moves into the forward movement rotation region  910  where the accelerator grip  82  is operated to rotate about a rotation axis A 3 , the reverse movement rotation region  920  where the accelerator grip  82  is operated to rotate about the rotation axis A 3 , and an axis movement region  930  where the accelerator grip  82  is moved in the extensional direction (direction X) of the rotation axis A 3 , as shown in  FIG. 6 . In  FIG. 6 , the accelerator grip  82  arranged in the axis movement region  930  is shown by diagonal lines. The accelerator grip  82  is described later in detail. In this description, the direction X 1  is a concept indicating a direction away from the marine propulsion device  1 , and a direction X 2  is a concept indicating a direction toward the marine propulsion device  1 . 
     As shown in  FIG. 2 , the shaft member  83  is fixedly connected to the accelerator grip  82  in the vicinity of an end in the direction X 1 . The shaft member  83  is supported by the steering handle housing  81 . The shaft member  83  is schematically a shaft-shaped (see  FIG. 4 ) member that extends in the direction X. The shaft member  83  includes a recess portion  831 , a diameter reduction portion  832 , and the first engaging portion  833 . The first engaging portion  833  is in the form of a boss that protrudes upward. 
     As shown in  FIG. 5 , the friction plate  84   a  is a ring-shaped plate member. The friction plate  84   a  includes a projecting portion  841   a  that projects upward (in the direction Z 1 ) from a lower portion of an inner peripheral portion. The projecting portion  841   a  does not engage with the recess portion  831  of the shaft member  83  in the extensional direction of the rotation axis A 3  to not limit movement of the shaft member  83  within a certain distance along the extensional direction, but engages therewith in a rotation direction to rotate with the shaft member  83  in the rotational direction. Thus, the shaft member  83  moves in the extensional direction (direction X) of the rotation axis A 3  independently of the friction plate  84   a . The shaft member  83  rotates together with the friction plate  84   a  in the rotation direction of the shaft member  83 . As shown in  FIG. 2 , a friction adjustment mechanism  84   b  is provided adjacent to the friction plate  84   a . A degree of contact between the friction plate  84   a  and the friction adjustment mechanism  84   b  is adjusted such that resistance generated when the shaft member  83  rotates is adjusted. 
     The neutral correction plate  85   a  is a plate-like member that includes a magnet  851   a  in a lower end. The neutral correction plate  85   a  includes a hole  852   a  in a substantially central portion, as viewed in the direction X. The hole  852   a  of the neutral correction plate  85   a  engages with the diameter reduction portion  832  of the shaft member  83 . The inner diameter of the hole  852   a  is smaller than those of both outside portions of the diameter reduction portion  832  of the shaft member  83 . The neutral correction plate  85   a  is held by both the outside portions of the diameter reduction portion  832 . Thus, the shaft member  83  moves in the extensional direction (direction X) of the rotation axis A 3  together with the neutral correction plate  85   a . The shaft member  83  moves independently of the neutral correction plate  85   a  in the rotation direction of the shaft member  83 . In other words, rotation of the shaft member  83  does not cause rotation of the neutral correction plate  85   a.    
     The position of the magnet  851   a  in the extensional direction (direction X) of the rotation axis A 3  of the shaft member  83  is detected by magnetic sensors  85   b  ( 851   b ,  852   b ) provided in the steering handle housing  81 . The ECU  6  acquires information detected by the magnetic sensors  85   b  and determines the position of the accelerator grip  82  in the direction X. Specifically, when the magnetic sensor  851   b  in the direction X 1  detects the magnet  851   a , the ECU  6  determines that the accelerator grip  82  is arranged in the forward movement rotation region  910 . When the magnetic sensor  852   b  in the direction X 2  detects the magnet  851   a , the ECU  6  determines that the accelerator grip  82  is arranged in the reverse movement rotation region  920 . When neither the magnetic sensor  851   b  nor  852   b  detects the magnet  851   a , the ECU  6  determines that the accelerator grip  81  is arranged in the axis movement region  930 . 
     A pair of urging members  86  are provided. The pair of urging members  86  hold an upper portion of the neutral correction plate  85   a  therebetween from both sides in the direction X. The urging members  86  urge the neutral correction plate  85   a  so as to locate the accelerator grip  82  in a neutral region  930   n  (see  FIG. 6 ) when the accelerator grip  82  moves into the axis movement region  930 . 
     The rotation angle detecting sensor  87  is arranged in the vicinity of an end of the shaft member  83  in the direction X 2 . The end of the shaft member  83  in the direction X 2  is rotatably inserted into the rotation angle detecting sensor  87 . The rotation angle detecting sensor  87  detects the rotation angle of the shaft member  83  when the accelerator grip  82  is rotationally operated. The ECU  6  acquires information detected by the rotation angle detecting sensor  87  and determines the rotational operation angle of the accelerator grip  82 . 
     An emergency stop cord  881  is pulled to remove a clip  882  such that the emergency stop switch  88  brings the marine propulsion device  1  to an emergency stop. 
     The accelerator grip  82  is now described in detail. 
     As shown in  FIG. 6 , a movement region  900  of the accelerator grip  82  includes the forward movement rotation region  910  where the accelerator grip  82  is operated to rotate about the rotation axis A 3  so as to obtain drive force in the forward movement direction from the power source  2  (see  FIG. 2 ). The movement region  900  of the accelerator grip  82  also includes the reverse movement rotation region  920  where the accelerator grip  82  is operated to rotate about the rotation axis A 3  so as to obtain drive force in the reverse movement direction from the power source  2 . The accelerator grip  82  rotates to draw a track along an arc centered on the rotation axis A 3  in each of the forward movement rotation region  910  and the reverse movement rotation region  920 . Specifically, the rotation starting point Ps 1  of the accelerator grip  82  moves to draw a track along the arc centered on the rotation axis A 3  in the direction Y 2  in the forward movement rotation region  910 . The rotation starting point Ps 1  is a position in the forward movement rotation region  910  that is neutral such that minimal or no drive force is generated. The rotation starting point Ps 2  of the accelerator grip  82  moves to draw a track along the arc centered on the rotation axis A 3  in the direction Y 1  in the reverse movement rotation region  920 . The rotation starting point Ps 2  is a position in the reverse movement rotation region  930  that is neutral such that minimal or no drive force is generated. In this description, the forward movement rotation region  910  is a concept indicating a region where the rotation starting point Ps 1  of the accelerator grip  82  moves in the direction Y 2  about the rotation axis A 3 . The reverse movement rotation region  920  is a concept indicating a region where the rotation starting point Ps 2  of the accelerator grip  82  moves in the direction Y 1  about the rotation axis A 3 . 
     The movement region  900  of the accelerator grip  82  includes the axis movement region  930  provided between the forward movement rotation region  910  and the reverse movement rotation region  920 , where the accelerator grip  82  is moved in the extensional direction (direction X) of the rotation axis A 3 . The axis movement region  930  is the neutral region  930   n  where no drive force in the forward movement direction or in the reverse movement direction is generated. The forward movement rotation region  910  and the reverse movement rotation region  920  are separated from each other by the axis movement region  930 . The rotation direction of the accelerator grip  82  is changed such that the normal rotation and the reverse rotation of the electric motor (see  FIG. 1 ) that the power source  2  includes are switched. In this description, the axis movement region  930  is a concept indicating a region between the rotation starting point Ps 1  of the accelerator grip  82  and the rotation starting point Ps 2  of the accelerator grip  82 . 
     The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged at positions different from each other in the extensional direction of the rotation axis A 3 . Specifically, the forward movement rotation region  910  is connected to the vicinity of an end of the axis movement region  930  in the direction X 1 , and the reverse movement rotation region  920  is connected to the vicinity of an end of the axis movement region  930  in the direction X 2 . The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged to hold the axis movement region  930  therebetween. The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged not to overlap each other, as viewed in the extensional direction of the rotation axis A 3 . The rotation direction of the accelerator grip  82  is opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . That is, as illustrated in  FIG. 6 , in the forward movement rotation region  910 , a rotation direction away from the rotation starting point Ps 1  of the accelerator grip  82  is in a first direction. In the reverse movement rotation region  920 , a rotation direction away from the rotation starting point Ps 2  of the accelerator grip  82  is in a second direction opposite the first direction. 
     As shown in  FIG. 3 , the forward movement rotation region  910  corresponds to the second engaging region  910   a  where the first engaging portion  833  of the shaft member  83  (see  FIG. 4 ) and the second engaging portion  811  of the steering handle housing  81  engage with each other. The reverse movement rotation region  920  corresponds to the third engaging region  920   a  where the first engaging portion  833  and the second engaging portion  811  engage with each other. The axis movement region  930  corresponds to the first engaging region  930   a  where the first engaging portion  833  and the second engaging portion  811  engage with each other. 
     The shaft member  83  (see  FIG. 4 ) moves in the extensional direction (direction X, see  FIGS. 6 and 7 ) of the rotation axis A 3  with respect to the steering handle housing  81  in the first engaging region  930   a  (the axis guide portion  811   c ) that corresponds to the axis movement region  930  (see  FIG. 6 ) in a state where the first engaging portion  833  of the shaft member  83  and the second engaging portion  811  of the steering handle housing  81  engage with each other (hereinafter referred to as the engaging state). The shaft member  83  rotates (see  FIG. 6 ) about the rotation axis A 3  with respect to the steering handle housing  81  in the second engaging region  910   a  (the forward movement rotation guide portion  811   d ) that corresponds to the forward movement rotation region  910  (see  FIG. 6 ) in the engaging state. The shaft member  83  rotates (see  FIG. 6 ) about the rotation axis A 3  with respect to the steering handle housing  81  in the third engaging region  920   a  (the reverse movement rotation guide portion  811   e ) that corresponds to the reverse movement rotation region  920  (see  FIG. 6 ) in the engaging state. Thus, the shaft member  83  moves or rotates with respect to the steering handle housing  81  while the first engaging portion  833  of the shaft member  83  is guided by the second engaging portion  811  of the steering handle housing  81 . 
     As shown in  FIG. 6 , the accelerator grip  82  is switched from a rotationally operable state in the forward movement rotation region  910  to a rotationally operable state in the reverse movement rotation region  920  through the axis movement region  930  in the extensional direction of the rotation axis A 3 , and is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  through the axis movement region  930  in the extensional direction of the rotation axis A 3 . 
     The accelerator grip  82  rotates in the direction Y 2  by a maximum rotational operation angle θf at which a maximum output is generated during forward movement in the forward movement rotation region  910 . At this time, the ECU  6  determines that the accelerator grip  82  is arranged in the forward movement rotation region  910  on the basis of information about the magnet  851   a  of the neutral correction plate  85   a  detected by the magnetic sensor  851   b . Then, the first engaging portion  833  of the shaft member  83  comes into contact with the stopper  811   a  (see  FIG. 3 ) in the second engaging region  910   a , and the rotation angle detecting sensor  87  (see  FIG. 2 ) detects the rotation angle (maximum rotational operation angle θf) of the shaft member  83 . Thus, the ECU  6  controls the power source  2  to generate maximum thrust force in the forward movement direction. The accelerator grip  82  rotates in the direction Y 1  by a maximum rotational operation angle θr at which a maximum output is generated during reverse movement in the reverse movement rotation region  920 . At this time, the ECU  6  determines that the accelerator grip  82  is arranged in the reverse movement rotation region  920  on the basis of information about the magnet  851   a  of the neutral correction plate  85   a  detected by the magnetic sensor  852   b . Then, the first engaging portion  833  of the shaft member  83  comes into contact with the stopper  811   b  (see  FIG. 3 ) in the third engaging region  920   a , and the rotation angle detecting sensor  87  detects the rotation angle (maximum rotational operation angle θr) of the shaft member  83 . Thus, the ECU  6  controls the power source  2  to generate maximum thrust force in the reverse movement direction. 
     The maximum rotational operation angle θf of the accelerator grip  82  in the forward movement rotation region  910  is larger than the maximum rotational operation angle θr of the accelerator grip  82  in the reverse movement rotation region  920 . In other words, the accelerator grip  82  has the maximum amount of rotation different in the direction Y 2  and the direction Y 1 . At the maximum rotational operation angles θf and θr of the accelerator grip  82 , the rotation directions of the power source  2  are opposite to each other, but the generated outputs are the same. 
     As shown in  FIG. 8 , the accelerator grip  82  is provided with a mark portion  821  that indicates the output of the power source  2  associated with the rotation region (rotation direction) and the rotation angle of the accelerator grip  82 . In the mark portion  821 , the forward movement rotation region  910  (see  FIG. 6 ) is indicated by “F”, and the reverse movement rotation region  920  (see  FIG. 6 ) is indicated by “R”. The steering handle housing  81  is provided with an arrow portion  812  that indicates an accelerator position in the mark portion  821  of the accelerator grip  82 . Thus, when the accelerator grip  82  rotates to either the forward movement rotation region  910  or the reverse movement rotation region  920 , the user easily recognizes that the output in the rotation region (rotation direction) indicated by the arrow portion  812  is generated from the power source  2 . The mark portion  821  and the arrow portion  812  may be printed on the accelerator grip  82  and the steering handle housing  81 , respectively, or may be seal-shaped members. 
     As shown in  FIG. 9 , the accelerator grip  82  is provided with a protrusion  822 . The protrusion  822  protrudes downward (in a direction Z 2 ) in a state where the accelerator grip  82  is arranged in the neutral region  930   n  (see  FIG. 6 ). The protrusion  822  is arranged to extend in the extensional direction (direction X) of the rotation axis A 3 . Thus, the user easily tactually recognizes that the accelerator grip  82  is arranged in the neutral region  930   n.    
     According to the first embodiment, the following effects are obtained. 
     According to the first embodiment, as hereinabove described, the movement region  900  of the accelerator grip  82  includes the axis movement region  930  where the accelerator grip  82  is moved in the extensional direction of the rotation axis A 3  between the forward movement rotation region  910  and the reverse movement rotation region  920 . Thus, the accelerator grip  82  is switched from the rotationally operable state in one of the forward movement rotation region  910  and the reverse movement rotation region  920  to the rotationally operable state in the other of the forward movement rotation region  910  and the reverse movement rotation region  920  through the axis movement region  930 , unlike the structure in which it is necessary to release the engaging state when the accelerator grip  82  is switched from the rotationally operable state in one of the forward movement rotation region  910  and the reverse movement rotation region  920  to the rotationally operable state in the other of the forward movement rotation region  910  and the reverse movement rotation region  920 . In this case, complication of an operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the rotation region of the accelerator grip  82  is switched. Consequently, the operability is improved when the user switches the rotation region of the accelerator grip  82 . Furthermore, the marine propulsion device  1  is configured as hereinabove described, whereby when the accelerator grip  82  is switched from the rotationally operable state in one of the forward movement rotation region  910  and the reverse movement rotation region  920  to the rotationally operable state in the other of the forward movement rotation region  910  and the reverse movement rotation region  920 , restriction of the posture of the user (restriction of a gripped position of the accelerator grip  82 ) is significantly reduced when the user operates the accelerator grip  82 , unlike the structure in which it is necessary for the user to grip a position of the accelerator grip  82  where the engaging state is released. 
     According to the first embodiment, the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged at the positions different from each other in the extensional direction of the rotation axis A 3 . Thus, the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged separately in the extensional direction of the rotation axis A 3 , and hence the user easily recognizes the forward movement rotation region  910  and the reverse movement rotation region  920  on the basis of a difference in the position in the extensional direction of the rotation axis A 3 . 
     According to the first embodiment, the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged not to overlap each other, as viewed in the extensional direction of the rotation axis A 3 . The rotation direction of the accelerator grip  82  is set to be opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . Thus, the user more easily recognizes the forward movement rotation region  910  and the reverse movement rotation region  920 , unlike the case where the rotation direction of the accelerator grip  82  is the same in the forward movement rotation region  910  and the reverse movement rotation region  920 . Furthermore, the user more easily recognizes the forward movement rotation region  910  and the reverse movement rotation region  920  on the basis of a difference in the position about the rotation axis A 3 . 
     According to the first embodiment, the neutral region  930   n  where no drive force in the forward movement direction or in the reverse movement direction is generated is provided in the axis movement region  930 . Thus, unless the accelerator grip  82  passes through the neutral region  930   n , the accelerator grip  82  does not rotate from one of the forward movement rotation region  910  and the reverse movement rotation region  920  into the other of the forward movement rotation region  910  and the reverse movement rotation region  920 . Consequently, complication of the operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that a state of forward movement drive or reverse movement drive switches to a state of opposite drive. Furthermore, the extra load on the power source is significantly reduced or prevented when the state of forward movement drive or reverse movement drive switches to the state of opposite drive. 
     According to the first embodiment, the forward movement rotation region  910  and the reverse movement rotation region  920  are separated from each other by the axis movement region  930 . Thus, even when the forward movement rotation region  910  and the reverse movement rotation region  920  are not arranged separately in the extensional direction of the rotation axis A 3 , the user more easily recognizes the forward movement rotation region  910  and the reverse movement rotation region  920  by the separation of the forward movement rotation region  910  from the reverse movement rotation region  920  by the axis movement region  930 . 
     According to the first embodiment, the maximum rotational operation angle θf of the accelerator grip  82  in the forward movement rotation region  910  is larger than the maximum rotational operation angle θr of the accelerator grip  82  in the reverse movement rotation region  920 . Thus, the user easily recognizes whether the accelerator grip  82  has rotated into the forward movement rotation region  910  or the reverse movement rotation region  920  and easily finely adjusts an output for forward movement. 
     According to the first embodiment, the urging members  86  are provided to urge the accelerator grip  82  so as to locate the accelerator grip  82  in the neutral region  930   n . Thus, the accelerator grip  82  is located in the neutral region  930   n  even when the user releases his/her hand from the accelerator grip  82  in the case where the power source generates no output in the forward movement rotation region  910  and the reverse movement rotation region  920 . 
     According to the first embodiment, the power source  2  including the electric motor is provided. Thus, in the marine propulsion device  1  in which the power source  2  includes the electric motor, complication of the operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the rotation region of the accelerator grip  82  is switched. 
     According to the first embodiment, the shaft member  83  moves in the extensional direction of the rotation axis A 3  with respect to the steering handle housing  81  in the first engaging region  930   a  that corresponds to the axis movement region  930  in the state where the first engaging portion  833  of the shaft member  83  and the second engaging portion  811  of the steering handle housing  81  engage with each other. Furthermore, the shaft member  83  rotates about the rotation axis A 3  with respect to the steering handle housing  81  in the second engaging region  910   a  that corresponds to the forward movement rotation region  910  and the third engaging region  920   a  that corresponds to the reverse movement rotation region  920 . Thus, the accelerator grip  82  rotates and axially moves in the state where the first engaging portion  833  of the shaft member  83  and the second engaging portion  811  of the steering handle housing  81  engage with each other, and hence the first engaging portion  833  of the shaft member  83  is guided by the second engaging portion  811  of the steering handle housing  81  and is moved to a prescribed position. Consequently, the accelerator grip  82  is accurately operated. 
     Second Embodiment 
     The structure of a marine propulsion device  200  according to a second embodiment of the present invention is now described with reference to  FIGS. 10 and 11 . 
     In the second embodiment, the marine propulsion device  200  in which a forward movement rotation region  910  and a reverse movement rotation region  920  overlap each other, as viewed in the extensional direction of a rotation axis A 3  is described, unlike the first embodiment in which the forward movement rotation region  910  and the reverse movement rotation region  920  do not overlap each other, as viewed in the extensional direction of the rotation axis A 3 . Portions of the marine propulsion device  200  similar to those of the marine propulsion device  1  according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIG. 10 , in the marine propulsion device  200  according to the second embodiment, a second engaging portion  891   a  is substantially U-shaped. Specifically, a forward movement rotation guide portion  891   d  of the second engaging portion  891   a  that correspond to a second engaging region  910   a  and a reverse movement rotation guide portion  891   e  of the second engaging portion  891   a  that correspond to a third engaging region  920   a  extend in the same direction. The second engaging portion  891   a  includes a stopper  811   a  that restricts rotation of a first engaging portion  833  of a shaft member  83  in a direction Y 2  in the second engaging region  910   a . The second engaging portion  891   a  includes a stopper  811   b  that restricts rotation of the first engaging portion  833  of the shaft member  83  in the direction Y 2  in the third engaging region  920   a.    
     As shown in  FIG. 11 , the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged at positions different from each other in the extensional direction of the rotation axis A 3 . The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged to overlap each other, as viewed in the extensional direction of the rotation axis A 3 . The rotation direction of an accelerator grip  82  is the same (direction Y 2 ) in the forward movement rotation region  910  and the reverse movement rotation region  920 . 
     More specifically, the shaft member  83  (see  FIG. 4 ) moves in the extensional direction (direction X, see  FIG. 10 ) of the rotation axis A 3  with respect to a steering handle housing  81  in a first engaging region  930   a  (an axis guide portion  891   f ) that corresponds to an axis movement region  930  in an engaging state where the first engaging portion  833  of the shaft member  83  and the second engaging portion  891   a  of the steering handle housing  81  engage with each other, as shown in  FIG. 10 . The shaft member  83  rotates (see  FIG. 10 ) about the rotation axis A 3  with respect to the steering handle housing  81  in the second engaging region  910   a  (the forward movement rotation guide portion  891   d ) that corresponds to the forward movement rotation region  910  in the engaging state. Furthermore, the shaft member  83  rotates (see  FIG. 10 ) about the rotation axis A 3  with respect to the steering handle housing  81  in the third engaging region  920   a  (the reverse movement rotation guide portion  891   e ) that corresponds to the reverse movement rotation region  920  in the engaging state. Thus, the shaft member  83  moves with respect to the steering handle housing  81  while the first engaging portion  833  of the shaft member  83  is guided by the second engaging portion  891   a  of the steering handle housing  81 . 
     According to the second embodiment, the following effects are obtained. 
     According to the second embodiment, the marine propulsion device  200  is configured as hereinabove described, whereby complication of an operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and a user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the rotation region of the accelerator grip  82  is switched, similarly to the first embodiment. Furthermore, restriction of the posture of the user is significantly reduced when the user operates the accelerator grip  82 . 
     According to the second embodiment, the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged to overlap each other, as viewed in the extensional direction of the rotation axis A 3 . The rotation direction of the accelerator grip  82  is set to be the same in the forward movement rotation region  910  and the reverse movement rotation region  920 . Thus, a space (rotation angle range) where the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged is reduced in size, as viewed in the extensional direction of the rotation axis A 3 , unlike the case where the rotation direction of the accelerator grip  82  is opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . 
     The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment. 
     Third Embodiment 
     The structure of a marine propulsion device  300  according to a third embodiment of the present invention is now described with reference to  FIGS. 12 and 13 . 
     In the third embodiment, the marine propulsion device  300  in which a forward movement rotation region  910  and a reverse movement rotation region  920  are provided at the same positions in the extensional direction of a rotation axis A 3  is described, unlike the first embodiment in which the forward movement rotation region  910  and the reverse movement rotation region  920  are provided at the positions different from each other in the extensional direction of the rotation axis A 3 . Portions of the marine propulsion device  300  similar to those of the marine propulsion device  1  according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIG. 12 , in the marine propulsion device  300  according to the third embodiment, an axis guide portion  891   g  of a second engaging portion  891   b  that corresponds to a first engaging region  930   a  is substantially U-shaped. A forward movement rotation guide portion  891   h  of the second engaging portion  891   b  that correspond to a second engaging region  910   a  and a reverse movement rotation guide portion  891   i  of the second engaging portion  891   b  that correspond to a third engaging region  920   a  are longitudinal in a direction (direction Y) perpendicular to a direction X. The forward movement rotation guide portion  891   h  of the second engaging portion  891   b  that correspond to the second engaging region  910   a  and the reverse movement rotation guide portion  891   i  of the second engaging portion  891   b  that correspond to the third engaging region  920   a  extend in opposite directions. The forward movement rotation guide portion  891   h  that correspond to the second engaging region  910   a  and the reverse movement rotation guide portion  891   i  of the second engaging portion  891   b  that correspond to the third engaging region  920   a  are connected to the vicinities of two (different) ends (one edge portion  891   j  and the other edge portion  891   k ) of the axis guide portion  891   g  that corresponds to the first engaging region  930   a  in a direction X 1 . 
     As shown in  FIG. 13 , a movement region  900  of an accelerator grip  82  includes an axis movement region  930  provided between the forward movement rotation region  910  and the reverse movement rotation region  920 , where the accelerator grip  82  is moved in the extensional direction (direction X) of the rotation axis A 3 . According to the third embodiment, the axis movement region  930  is substantially U-shaped in a plan view. The axis movement region  930  is a neutral region  930   n  where no drive force in a forward movement direction or in a reverse movement direction is generated. The axis movement region  930  includes a neutral rotation region  930   i  where the accelerator grip  82  rotates about the rotation axis A 3 . The neutral rotation region  930   i  is a region of the axis movement region  930  (neutral region  930   n ) that corresponds to a position offset in a direction X 2  along the rotation axis A 3  with respect to the forward movement rotation region  910  and the reverse movement rotation region  920 . More specifically, the neutral rotation region  930   i  is located in an end of the axis movement region  930  in the direction X 2 . 
     The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged at the same positions in the extensional direction of the rotation axis A 3 . The forward movement rotation region  910  and the reverse movement rotation region  920  are arranged not to overlap each other, as viewed in the extensional direction of the rotation axis A 3 . The rotation direction of the accelerator grip  82  is opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . 
     The accelerator grip  82  is switched from a rotationally operable state in the forward movement rotation region  910  to a rotationally operable state in the reverse movement rotation region  920  through the axis movement region  930 , and is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  through the axis movement region  930 . Specifically, the accelerator grip  82  is switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  through the neutral rotation region  930   i , and is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  through the neutral rotation region  930   i . Thus, a user operates the accelerator grip  82  while sequentially confirming the movement region where the accelerator grip  82  is arranged. 
     According to the third embodiment, the following effects are obtained. 
     According to the third embodiment, the marine propulsion device  300  is configured as hereinabove described, whereby complication of an operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the rotation region of the accelerator grip  82  is switched, similarly to the first embodiment. Furthermore, restriction of the posture of the user is significantly reduced when the user operates the accelerator grip  82 . 
     According to the third embodiment, the forward movement rotation region  910  and the reverse movement rotation region  920  are provided at substantially the same positions in the extensional direction of the rotation axis A 3 . The rotation direction of the accelerator grip  82  is set to be opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . Furthermore, the accelerator grip  82  is switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  through the axis movement region  930 . Thus, even when the forward movement rotation region  910  and the reverse movement rotation region  920  are not arranged separately in the extensional direction of the rotation axis A 3 , the user easily recognizes the forward movement rotation region  910  and the reverse movement rotation region  920  by setting the rotation direction of the accelerator grip  82  to be opposite in the forward movement rotation region  910  and the reverse movement rotation region  920 . Furthermore, unlike the case where the forward movement rotation region  910  and the reverse movement rotation region  920  of the accelerator grip  82  are arranged separately in the extensional direction of the rotation axis A 3 , a space (the length in the extensional direction of the rotation axis A 3 ) where the forward movement rotation region  910  and the reverse movement rotation region  920  are arranged is reduced in size in the plan view. 
     According to the third embodiment, the accelerator grip  82  is switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  through the neutral rotation region  930   i  offset in the extensional direction of the rotation axis A 3  with respect to the forward movement rotation region  910  and the reverse movement rotation region  920 . Thus, complication of the operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the accelerator grip  82  is switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  through the neutral rotation region  930   i.    
     The remaining effects of the third embodiment are similar to those of the aforementioned first embodiment. 
     Fourth Embodiment 
     The structure of a marine propulsion device  400  according to a fourth embodiment of the present invention is now described with reference to  FIGS. 14 to 16 . 
     In the fourth embodiment, the marine propulsion device  400  in which an accelerator grip  82  goes through an axis movement region  930  or a detour region  940  when switched from a rotationally operable state in a reverse movement rotation region  920  to a rotationally operable state in a forward movement rotation region  910  is described, unlike the first embodiment in which the accelerator grip  82  goes through the axis movement region  930  when switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910 . Portions of the marine propulsion device  400  similar to those of the marine propulsion device  1  according to the aforementioned first embodiment are denoted by the same reference numerals, to omit the description. 
     As shown in  FIGS. 14 and 15 , in a steering handle housing  81 , a portion of a second engaging portion  891   c  that corresponds to a fourth engaging region  940   a  described later is connected to an end of a third engaging region  920   a  in a direction Y 1  and an end of a second engaging region  910   a  in the direction Y 1 . The fourth engaging region  940   a  extends so as to be inclined at about 45 degrees counterclockwise with respect to a direction X, as viewed in a direction Z 2 . A portion of the second engaging portion  891   c  that corresponds to the fourth engaging region  940   a  described later is provided with a ratchet mechanism  820  that allows a first engaging portion  833  to move only in a direction Y 2  but does not allow the same to move in the direction Y 1 . The first engaging portion  833  of a shaft member  83  engages with the second engaging portion  891   c  of the steering handle housing  81  in a first engaging region  930   a  (an axis guide portion  891   l ), the second engaging region  910   a  (a forward movement rotation guide portion  891   m ), the third engaging region  920   a  (a reverse movement rotation guide portion  891   n ), and the fourth engaging region  940   a.    
     As shown in  FIG. 16 , a movement region  900  of the accelerator grip  82  includes the detour region  940  in addition to the forward movement rotation region  910 , the reverse movement rotation region  920 , and the axis movement region  930 . The detour region  940  corresponds to the fourth engaging region  940   a  (see  FIG. 14 ) where the first engaging portion  833  of the shaft member  83  (see  FIG. 4 ) and the second engaging portion  891   c  of the steering handle housing  81  engage with each other. The axis movement region  930  and the detour region  940  are neutral regions  930   n.    
     The detour region  940  is a region where the accelerator grip  82  moves from a position Ps 3  rotated by a maximum rotational operation angle θf in the reverse movement rotation region  920  to a rotation starting point Ps 1  in the forward movement rotation region  910 . The accelerator grip  82  is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  through either the axis movement region  930  or the detour region  940 . 
     According to the fourth embodiment, the ratchet mechanism  820  is provided such that the accelerator grip  82  does not move from the rotation staring point Ps 1  (see  FIG. 16 ) in the forward movement rotation region  910  to the reverse movement rotation region  920  (the position Ps 3 , see  FIG. 16 ) through the detour region  940 , as shown in  FIG. 15 . Thus, the accelerator grip  82  is not switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  unless the accelerator grip  82  goes through the axis movement region  930 . 
     According to the fourth embodiment, the following effects are obtained. 
     According to the fourth embodiment, the marine propulsion device  400  is configured as hereinabove described, whereby complication of an operation of switching the rotation region of the accelerator grip  82  is significantly reduced or prevented, and a user smoothly performs the operation of switching the rotation region of the accelerator grip  82  while recognizing that the rotation region of the accelerator grip  82  is switched, similarly to the first embodiment. Furthermore, restriction of the posture of the user is significantly reduced when the user operates the accelerator grip  82 . 
     According to the fourth embodiment, the accelerator grip  82  is switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  through the axis movement region  930 , and is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  not through the axis movement region  930  but through the detour region  940 . Thus, complication of the operation of switching the rotation region of the accelerator grip  82  from the forward movement rotation region  910  to the reverse movement rotation region  920  is significantly reduced or prevented, and the user smoothly performs the operation of switching the rotation region of the accelerator grip  82 . Furthermore, the accelerator grip  82  is easily switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  without a complicated operation. 
     The remaining effects of the fourth embodiment are similar to those of the aforementioned first embodiment. 
     The embodiments disclosed this time must be considered as illustrative in all points and not restrictive. The range of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and all modifications within the meaning and range equivalent to the scope of claims for patent are further included. 
     For example, while the power source according to the present invention is the electric motor in each of the aforementioned first to fourth embodiments, the present invention is not restricted to this. According to the present invention, the power source may alternatively be an engine. 
     While both the forward movement rotation region  910  and the reverse movement rotation region  920  are connected to the vicinities of the ends of the axis movement region  930  in the direction X in each of the aforementioned first to fourth embodiments, the present invention is not restricted to this. According to the present invention, so far as the axis movement region is provided between the forward movement rotation region and the reverse movement rotation region, both the forward movement rotation region and the reverse movement rotation region may not be connected to the vicinities of the ends of the axis movement region in the direction X, or only one of the forward movement rotation region and the reverse movement rotation region may be connected to the vicinity of the end of the axis movement region in the direction X. 
     While the maximum rotational operation angle θf of the accelerator grip  82  in the forward movement rotation region  910  is larger than the maximum rotational operation angle θr of the accelerator grip  82  in the reverse movement rotation region  920  in each of the aforementioned first to fourth embodiments, the present invention is not restricted to this. According to the present invention, the maximum rotational operation angle of the accelerator grip in the forward movement rotation region may alternatively be equal to the maximum rotational operation angle of the accelerator grip in the reverse movement rotation region (the maximum amount of rotation in the direction Y 2  may alternatively be equal to the maximum amount of rotation in the direction Y 1 ). 
     In the case where the maximum rotational operation angle of the accelerator grip in the forward movement rotation region is equal to the maximum rotational operation angle of the accelerator grip in the reverse movement rotation region, the following structure may be possible. Specifically, the response characteristics of the output (torque) generated by the power source may be different according to the rotational operation angle of the accelerator grip in the case of rotating the accelerator grip in the direction Y 2  and in the case of rotating the accelerator grip in the direction Y 1 . More specifically, the amount of torque generated from the power source that has a non-linear relationship with the rotation angle of the accelerator grip may be different in in the case of rotating the accelerator grip in the direction Y 2  and in the case of rotating the accelerator grip in the direction Y 1 , as shown in a graph (a graph showing the relationship between the rotational operation angle of the accelerator grip and the torque generated from the power source according to the rotational operation angle of the accelerator grip) in  FIG. 17 . In this case, the power source is more responsive to the rotational operation angle of the accelerator grip in the direction Y 2  than that in the direction Y 1  such that the user easily recognizes whether the accelerator grip has rotated into the forward movement rotation region or the reverse movement rotation region due to the difference in the rotational operation angle of the accelerator grip. 
     While the neutral rotation region  930   i  is provided at the position offset in the extensional direction of the rotation axis A 3  with respect to the forward movement rotation region  910  and the reverse movement rotation region  920  in the aforementioned third embodiment, the present invention is not restricted to this. According to the present invention, no neutral rotation region may be provided at the position offset in the extensional direction of the rotation axis with respect to the forward movement rotation region and the reverse movement rotation region. 
     While the accelerator grip  82  is not switched from the rotationally operable state in the forward movement rotation region  910  to the rotationally operable state in the reverse movement rotation region  920  unless the accelerator grip  82  goes through the axis movement region  930 , and the accelerator grip  82  is switched from the rotationally operable state in the reverse movement rotation region  920  to the rotationally operable state in the forward movement rotation region  910  without going through the axis movement region  930  if the accelerator grip  82  goes through the detour region  940  in the aforementioned fourth embodiment, the present invention is not restricted to this. According to the present invention, the accelerator grip may not be switched from the rotationally operable state in the reverse movement rotation region to the rotationally operable state in the forward movement rotation region unless the accelerator grip goes through the axis movement region, and the accelerator grip may be switched from the rotationally operable state in the forward movement rotation region to the rotationally operable state in the reverse movement rotation region without going through the axis movement region if the accelerator grip goes through the detour region.