Patent Publication Number: US-2006019558-A1

Title: Steering system for outboard drive

Description:
PRIORITY INFORMATION  
      The present application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2004-000219, filed on Jan. 5, 2004, Japanese Patent Application No. 2004-000264, filed on Jan. 5, 2004, and Japanese Patent Application No. 2004-000267, filed on Jan. 5, 2004, the entire contents of which are expressly incorporated by reference herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to a steering system for an outboard drive, and more particularly relates to an improved steering system that incorporates an electric motor for steering an outboard drive.  
      2. Description of Related Art  
      Many watercraft are propelled by one or more outboard motors mounted on a transom board. A typical outboard motor has a drive unit and a bracket assembly. The drive unit incorporates a propulsion device (e.g., a propeller) that propels the watercraft. The bracket assembly is mounted on the watercraft to support the drive unit and to enable pivotal movement of the drive unit about a steering axis. In a typical outboard motor, the steering axis is defined by a steering shaft coupled with the drive unit and extending vertically through the bracket assembly.  
      The typical watercraft includes a steering system that incorporates a steering handle (e.g., a steering wheel). The steering handle is operable by the operator of the watercraft. A steering device is responsive to movements of the steering handle and is coupled with the steering shaft to cause the steering shaft to move in accordance with the movement of the steering handle.  
      In some typical systems, a hydraulically operable steering device moves the steering shaft. Such a steering device includes a hydraulic system that occupies a relatively large space. The hydraulic system also includes a pipe arrangement that makes the steering device complicated.  
      A steering device incorporating an electric motor can replace the hydraulic steering device. For example, Japanese Patent No. 2959044 discloses an electrical steering device having an electric motor, a rack and pinion mechanism, and a link mechanism. The electric motor drives a pinion of the rack and pinion mechanism to axially move a rack thereof, and the link mechanism rotates the steering shaft in accordance with the axial movement of the rack. The drive unit can thus change its position about the steering axis, thereby, turning the watercraft left or right.  
      In the steering device disclosed in the above-referenced Japanese patent, the electric motor and the rack and pinion mechanism are disposed in a relatively large body positioned within the watercraft in front of the transom board. Thus, the steering device occupies a significant volume of space inside the watercraft or can interfere with other components in the watercraft.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention is recognition of the need for an outboard drive with an improved steering system with a simple and compact steering device for moving the steering shaft about the steering axis. To address such a need, an aspect of the present invention involves a steering system for an outboard drive that comprises a steering handle adapted to be finished on a watercraft, a steering device, a lever that has first and second ends, and a sensor. The first end of the lever is attached to the drive. The sensor senses an actual position of the steering handle to provide a position signal to the steering device. The steering device comprises an electric motor that has an outer casing and a ball screw arranged to extend through the outer casing. The ball screw and the outer casing move relative to one another in accordance with the actual position of the steering handle. The second end of the lever is attached to the ball screw or the outer casing. The ball screw or the outer casing steers the drive through the lever.  
      In accordance with another aspect of the present invention, an outboard drive system comprises a drive unit. A steering shaft is attached to the drive unit and extends generally vertically. A swivel bracket is arranged to journal the steering shaft for steering movement of the drive unit about a steering axis. A clamping bracket can be mounted on the watercraft. A tilt pin extends generally horizontally through the swivel bracket and the clamping bracket. The clamping bracket supports the swivel bracket with the drive unit for tilt movement about a tilt axis. A lever has first and second ends. The first end of the lever is attached to the steering shaft. A steering device includes an electric motor that has an outer casing and a ball screw arranged to extend through the outer casing. The ball screw and the outer casing move relative to each other. The second end of the lever is attached to the ball screw or the outer casing. The ball screw or the outer casing moves the steering shaft about the steering axis through the lever.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features, aspects and advantages of the present invention are described below with reference to the drawings of preferred embodiments, which embodiments are intended to illustrate and not to limit the present invention.  
       FIG. 1  illustrates a top plan view of an outboard motor mounted on a watercraft, and illustrates a steering system that is configured in accordance with certain features, aspects and advantages of the present invention.  
       FIG. 2  illustrates an enlarged top plan view of the outboard motor with a steering device of the steering system of  FIG. 1 .  
       FIG. 3  illustrates an enlarged top plan view of a portion of the outboard motor and the steering device, wherein the portion of the outboard motor is partially cross-sectioned.  
       FIG. 4  illustrates a front elevation view of the portion of the outboard motor and the steering device shown in  FIG. 3 .  
       FIG. 5  illustrates a side elevation view of the portion of the outboard motor and the steering device shown in  FIG. 3 , wherein a swivel bracket of the outboard motor is positioned in a tilted down position.  
       FIG. 6  illustrates a side elevation view of the portion of the outboard motor and the steering device of  FIG. 3 , wherein the swivel bracket is positioned in a tilted up position.  
       FIG. 7  illustrates an enlarged top plan view of a portion of an outboard motor and another steering device modified in accordance with a second embodiment of the present invention, wherein the portion of the outboard motor is partially cross-sectioned.  
       FIG. 8  illustrates a front elevation view of the portion of the outboard motor and the steering device of  FIG. 7 .  
       FIG. 9  illustrates an enlarged top plan view of a portion of an outboard motor and a further steering device modified in accordance with a third embodiment of the present invention, wherein the portion of the outboard motor is partially cross-sectioned.  
       FIG. 10  illustrates a front elevation view of the portion of the outboard motor and the steering device of  FIG. 9 .  
       FIG. 11  illustrates an enlarged top plan view of a portion of an outboard motor and a further steering device modified in accordance with a fourth embodiment of the present invention, wherein the portion of the outboard motor is partially cross-sectioned.  
       FIG. 12  illustrates a front elevation view of the portion of the outboard motor and the steering device of  FIG. 11 .  
       FIG. 13  illustrates a top plan view of an outboard motor mounted on a watercraft, and illustrates a steering system that is modified in accordance with a fifth embodiment of the present invention.  
       FIG. 14  illustrates an enlarged top plan view of a portion of the outboard motor of  FIG. 13  and a steering device of the steering system of  FIG. 13 , wherein a portion of the outboard motor partially cross-sectioned.  
       FIG. 15  illustrates a front elevation view of the portion of the outboard motor and the steering device of  FIG. 13 , wherein a portion of the steering device associated with a left hand portion of the outboard motor in the figure illustrates a variation of the steering device of  FIG. 14 .  
       FIG. 16  illustrates a top plan view of an outboard motor mounted on a watercraft, and illustrates a steering system that is modified in accordance with a sixth embodiment of the present invention.  
       FIG. 17  illustrates an enlarged top plan view of a portion of the outboard motor of  FIG. 16  and a steering device of the steering system of  FIG. 16 .  
       FIG. 18  illustrates a front elevation view of the portion of the outboard motor and the steering device of  FIG. 16 .  
       FIG. 19  illustrates an enlarged top plan view of a portion of an outboard motor and a further steering device modified in accordance with a seventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION  
       FIGS. 1-6  illustrate a steering system  30  configured in accordance with certain features, aspects and advantages of one embodiment of the present invention for an outboard motor  32 . The outboard motor  32  merely exemplifies one type of outboard drive. The steering system  30  can be used with other types of outboard drives such as, for example, stern drives for inboard/outboard systems. Such applications will be apparent to those of ordinary skill in the art in view of the description herein.  
      The outboard motor  32  preferably comprises a drive unit  34  and a bracket assembly  36 . The drive unit  34  preferably comprises a housing unit and a power head disposed atop the drive unit  34  and above the housing unit. The housing unit preferably comprises a driveshaft housing and a lower unit extending below the driveshaft housing. The bracket assembly  36  supports the drive unit  34  on a transom  38  of an associated watercraft  40  and places a marine propulsion device (not shown) in a submerged position, with the watercraft  40  resting on the surface of a body of water. Preferably, the marine propulsion device is a propeller.  
      As used in this description, the terms “forward,” “forwardly” and “front” mean at or to the side where the bracket assembly  36  is located, and the terms “rear,” “reverse,” “backward” and “rearward” mean at or to the opposite side of the front side, unless indicated otherwise or otherwise readily apparent from the context use. As further used in this description, the term “horizontally” means that the subject portions, members or components extend generally parallel to the water surface when the watercraft  40  is substantially stationary with respect to the water surface and when the drive unit  34  is not tilted. The term “vertically” means that portions, members or components extend generally normal to those that extend horizontally.  
      As shown in  FIGS. 3 and 4 , the bracket assembly  36  preferably comprises a swivel bracket  44 , a clamping bracket  46 , a steering shaft  48  and a tilt pin (or pivot pin)  50 . The steering shaft  48  preferably extends generally vertically through the swivel bracket  44  and is affixed to the housing unit through upper and lower mount assemblies. The steering shaft  48  is pivotally journaled within the swivel bracket  44  for steering movement about a steering axis defined by the steering shaft  48 . The steering axis extends vertically along a center plane CP ( FIGS. 2-4 ) that extends vertically and fore to aft relative to the outboard motor  32 . The drive unit  34  pivots about the steering axis relative to the swivel bracket  44  because the steering shaft  48  is affixed to the drive unit  34 .  
      In the illustrated embodiment, a steering lever  52  preferably is affixed to a top end of the steering shaft  48  to extend forward. The steering lever  52  has a forward end  54  and a rear end  55 , and the steering lever  52  preferably is affixed to the steering shaft  48  at the rear end  55  thereof. As thus constructed, the drive unit  34  is steerable about the steering axis when the steering lever  52  moves the steering shaft  48  right and left. In the illustrated embodiment, a steering device  56  is provided on the bracket assembly  36  to move the steering lever  52 .  
      The clamping bracket  46  comprises two bracket arms  58  that are spaced from each other to interpose the swivel bracket  44  there between, and the respective bracket arms  58  are affixed to the watercraft transom  38  ( FIG. 2 ) by clamping bolts. Preferably, the clamping bolts are previously inserted into suitable bolt holes  60  in the bracket arms  58 . The tilt pin  50  extends generally horizontally through the swivel bracket  44  and the bracket arms  58  of the clamping bracket  46  to complete a hinge coupling between the swivel bracket  44  and the clamping bracket  46 . The clamping bracket  46  thus supports the swivel bracket  44  and the drive unit  34  for pivotal movement about a tilt axis defined by the tilt pin  50 . The tilt pin  50  preferably is pivotally affixed to the bracket arms  58  by nuts  62  shown in  FIG. 3 . In the illustrated embodiment, each end portion of the tilt pin  50  extends outward beyond the nuts  62 .  
      A tilt and trim adjustment device  64  ( FIG. 4 ) preferably is provided between the swivel bracket  44  and the clamping bracket  46  to tilt (raise or lower) the swivel bracket  44  together with the drive unit  34  relative to the clamping bracket  46 . The tilt and trim adjustment device  64  preferably comprises a hydraulically operated mechanism that includes a hydraulic cylinder  66 , a hydraulic piston that reciprocates within the cylinder  66 , a hydraulic pump  68  that powers the piston, and a fluid reservoir  70  that stores a working fluid such as oil. A piston rod extends outward beyond one end of the cylinder  66 . Preferably, a bottom end of the cylinder  66  is pivotally affixed to the clamping bracket  46  while a top end of the piston rod is pivotally affixed to the swivel bracket  44 .  
      When the hydraulic pump  68  operates, the piston rod extends from the cylinder  66  or retracts into the cylinder  66  in response to the movement of the working fluid within the cylinder  66 . When the piston rod extends, the swivel bracket  44  and the drive unit  34  are tilted upward. With the piston rod retracts, the swivel bracket  44  and the drive unit  34  are tilted downward. Preferably, the drive unit  34  moves between a fully tilted down position that is the most lowered position of the drive unit  34  and a fully tilted up position that is the most raised position of the drive unit  34  when the tilt and trim adjustment device  64  is activated. Preferably, a lower tilt range is a trim adjustment range.  
      The power head comprises a prime mover, which in this embodiment is an internal combustion engine such as, for example, a four-cycle engine or two-cycle engine. Other prime movers such as, for example, an electric motor, can replace the engine. The power head further comprises a protective cowling assembly. Preferably, the protective cowling assembly defines a generally closed cavity, and the engine is disposed within the protective cowling assembly.  
      As illustrated in  FIG. 1 , the steering system  30  comprises a steering handle such as, for example, a steering wheel  72 , a steering column  74 , a steering position sensor  76 , an electric cable  78 , a steering controller  80  and the foregoing steering device  56 . The steering column  74  preferably extends upward and rearward from a forward bottom of a cockpit of the watercraft  40  and is supported by a journal for rotation. The steering wheel  72  is disposed atop the steering column  74  in a position so that an operator of the watercraft  40  can turn the wheel  72 . The steering position sensor  76  is positioned at a bottom of the steering column  74  to sense an actual angular position of the steering wheel  72  when the wheel is turned by the operator. The sensor  76  senses a pivot angle of the steering column  74  that corresponds to an amount of the angular movement of the steering wheel  72  from a reference position (e.g., the neutral position of the steering wheel when the watercraft is moving straight ahead without turning). The cable  78  electrically connects the sensor  76  in the forward area of the cockpit to the steering controller  80  positioned in the proximity of the steering device  56 . The sensor  76  provides a position signal to the steering device  56  through the cable  78 .  
      Alternatively, the steering controller  80  can be placed in the cockpit, for example, in the proximity of the sensor  76 . In this variation, the electric cable  78  interconnects the controller  80  and an electric motor  84  of the steering device  56 , which is described below.  
      When the operator turns the steering wheel  72  clockwise or counterclockwise, the steering column  74  rotates with the steering wheel  72 , and the steering position sensor  76  senses a position of the steering wheel  72 . A signal indicating the sensed position of the steering wheel  72  is transmitted to the steering controller  80 . The controller  80  controls the steering device  56  to move the steering lever  52  to the right or to the left in accordance with the position of the steering wheel  72 .  
      The cable  78  can be formed in a variety of configurations. For example, electrical conductors or optical fibers can be used. In one variation, the cable  78  is replaced by a wireless transmitter placed at or near the sensor  76  and a wireless receiver placed at or near the controller  80 .  
      As illustrated in  FIGS. 2-5 , the steering device  56  preferably comprises the electric motor  84 . The electric motor  84  has an outer casing  86  and has a ball screw  88  extending through the outer casing  86 . The outer casing  86  and the ball screw  88  together form a direct drive type motor (“a DD motor”). The outer casing  86  includes the remainder of the motor elements such that the outer casing  86  and the ball screw  88  together function as a motor. The steering controller  80  is electrically connected to the electric motor  84  to control the motor  84 . The ball screw  88  comprises an elongated screw and a plurality of balls (not shown) placed in the grooves of the screw in an area of the casing  86 . The casing  86  and the screw  88  are coupled with each other via the balls in a known manner. The casing  86  and the ball screw  88  move axially relative to each other when the motor  84  is activated. More specifically, the controller  80  activates and controls the motor  84  to move the outer casing  86  or the ball screw  88  relative to one another in response to the actual position of the steering wheel  72 . The steering lever  52  converts the axial movement of the outer casing  86  or the ball screw  88  to a pivotal movement of the steering shaft  48 . Additionally, the electric motor  84  is connected to receive electrical power from a battery or batteries (not shown).  
      In the illustrated embodiment shown in  FIG. 3 , a cylindrical motor housing  92  extends parallel to the tilt pin  50  and holds the outer casing  86 . The ball screw  88  also extends parallel to the tilt pin  50 . Preferably, the outer casing  86  is affixed to an inside wall of the motor housing  92  at a center location by bolts or by other suitable fixing elements such as, for example, a bonding agent. Preferably, the motor housing  92  is sufficiently longer than the casing  86  to protect the ball screw  88 , because the ball screw  88  in the illustrated embodiment is longer than the tilt pin  50 .  
      A support member or support unit preferably extends from the tilt pin  50  to support the ball screw  88 . In the illustrated embodiment, the support unit is formed by two support members  94  that are mounted onto respective end portions of the tilt pin  50  and that generally extend forwardly from the tilt pin  50 . The respective support members  94  are positioned symmetrically relative to the center plane CP.  
      Each support member  94  is generally configured as a shape of the letter “S.” A rear end of the support member  94  has an opening through which an end portion of the tilt pin  50  extends. A forward end of the support member  94  also has an opening through which an end of the ball screw  88  extends. The rear end of each support member  94  is attached to one end portion of the tilt pin  50  such that a spacer  96  is interposed between the nut  62  and the rear ends of the support member  94 . The forward end of each support member  94  is attached to a respective end of the ball screw  88 . Preferably, a distance between the forward ends of the support members  94  is longer than a distance between the rear ends of the support members  94 , because the ball screw  88  is longer than the tilt pin  50 . In the illustrated embodiment, nuts  98  fix the rear ends of the support members  94  onto the tilt pin  50 , while nuts  100  fix the forward ends of the support members  94  onto the ball screw  88 . In alternative embodiments, a single support member  94  of sufficient strength may be used to support the ball screw  88 . As thus constructed, the ball screw  88  is affixed to the tilt pin  50  and can pivot about the tilt axis when the drive unit  34  tilts up or down.  
      A link unit couples the forward end  54  of the steering lever  52  with the outer casing  86  of the electric motor  84 . The link unit preferably comprises a link member  102  and a connecting pin  104 . In the illustrated embodiment, the motor housing  92  is coupled with the link member  102  to be a part of the link unit.  
      The link member  102  preferably is a metal plate that generally has a half elliptic shape. As shown in  FIG. 4 , a center area  102   a  of the link member  102  is slightly recessed such that both side areas  102   b  of the link member  102  are positioned higher than the center area  102   a  when the link member  102  is positioned above the motor housing  92 . As shown in  FIG. 3 , the link member  102  preferably has a slot  105  in the center area  102   a . The connecting pin  104  preferably extends from the lever  52  and extends through the slot  105  of the link member  102  to couple the lever  52  and the link member  102  with each other. The slot  105  is loose enough for the pin  104  to move back and forth therein. In the illustrated embodiment, both the steering axis and an axis of the pin  104  are positioned on the center plane CP when the drive unit  34  is not steered. The recessed configuration of the link member  102  is advantageous because the position of the drive unit  34  can be lowered to lower the center of gravity of the outboard motor  30  to increase the stability of the watercraft  40 .  
      The motor housing  92  has two bosses  108  ( FIG. 4 ) that extend upward from a top surface of the motor housing  92 . The link member  102  is affixed to the motor housing  92  by bolts  110  at the respective bosses  108 . The bolts  110  enable the motor housing  92  and the link member  102  to be easily and rigidly coupled together. In one variation, the link member  102  is unitarily formed with the motor housing  92  such that the link unit is simpler.  
      As thus constructed, the motor housing  92  is movable along the ball screw  88 , and the ball screw  88  is not movable because the ball screw  88  is rigidly affixed to the tilt pin  50 . The motor housing  92  thus moves axially along the ball screw  88  accordingly in this embodiment when the electric motor  84  is activated.  
      The motor housing  92  is placed in the center of the ball screw  88  such that the center of the outer casing  86  is positioned on the center plane CP when the steering wheel  72  is in a neutral position (e.g., a non-turning position). Thus, the illustrated steering device  56  is positioned symmetrically relative to the center plane CP when the steering angle is zero. The motor housing  92  and the outer casing  86  are positioned at a reference position that corresponds to a reference position of the steering wheel  72 . The steering angle is zero at those reference positions. The pin  104  is positioned at the forward-most end of the slot  105  under these conditions.  
      When the operator turns the steering wheel  72  clockwise or counterclockwise, the sensor  76  senses an actual position of the steering wheel  72  and transmits a position signal to the controller  80  through the cable  78 . The controller  80  activates and controls the electric motor  84 . The outer casing  86  of the electric motor  84  and the housing  92  move along the ball screw  88  to the right or to the left as indicated by the arrow A of  FIG. 2  under control of the controller  80 . The movement of the housing  92  causes the pin  104  to move rearward within the slot  105  and causes the lever  52  turn with a certain angle that the controller  80  indicates. For example, as illustrated in  FIG. 1 , when the operator turns the steering wheel  72  clockwise as indicated by the arrow B, the lever  52  turns counterclockwise as indicated by the arrow C, and the drive unit  34  also turns counterclockwise as indicated by the arrow D. This position of the drive unit  34  causes the watercraft  40  to turn right in response to the operator action.  
      As illustrated in  FIGS. 5 and 6 , the steering device  56  is able to pivot about the tilt axis because the support members  94  are affixed to the tilt pin  50 . As shown in  FIG. 5 , the link member  102  generally extends horizontally when the drive unit  34  is in a tilted down position. In contrast, when the drive unit  34  is fully tilted up as illustrated in  FIG. 6 , the link member  102  is inclined and the steering device  56  is positioned lower than the tilt pin  50 .  
      In the illustrated embodiment, the connecting pin  104  extends from the steering lever  52 , and the slot  105  is located at the link member  102 . Alternatively, the connecting pin  104  can extend from the link member  102  with the slot  105  located at the steering lever  52 . In this alternative, the pin  104  is positioned at the rear-most end of the slot  105  when the drive unit  34  is positioned for straight ahead movement (e.g., no turning).  
      The steering device  56  of the steering system  30  in the illustrated embodiment has a simple and compact arrangement because the electric motor  84  is disposed in the motor housing  92  that extends along the ball screw  88  and has no rack and pinion mechanism. The illustrated ball screw  88  is located close to the tilt pin  50  because the ball screw  88  is supported by the tilt pin  50 . This arrangement makes the portion of the steering device  56  situated within the watercraft  40  smaller than in a system using known steering devices.  
       FIGS. 7 and 8  illustrate a steering system  116  modified in accordance with a second embodiment of the present invention. The members, components, and devices that are the same as those described above are assigned the same reference numerals in the embodiment of  FIGS. 7 and 8  and in other embodiments described below, and will not be described again unless required in the context of the description of another element.  
      The steering system  116  of  FIGS. 7 and 8  includes a steering device  118 . The steering device  118  incorporates a modified motor housing  120  that preferably has a housing body  122  and two housing arms  124 . The housing body  122  generally extends parallel to the tilt pin  50  and holds the outer casing  86  of the electric motor  84 . The respective housing arms  124  extend from respective ends of the housing body  122  toward the tilt pin  50  and are affixed to the end portions of the tilt pin  50 .  
      Preferably, a link rod  128  connects the steering lever  52  with the ball screw  88 . In this second embodiment, the steering lever  52  does not have a slot Instead, the link rod  128  is affixed to the lever  52  by a ball joint  130  that has a pin  132 . Also, the link rod  128  is affixed to one end of the ball screw  88  by another ball joint  134  that has a pin  136 .  
      Because the outer casing  86  is affixed to the tilt pin  50  via the motor housing  120 , while the ball screw  88  is free to move relative to the outer casing  86  in the second embodiment, the ball screw  88  extends from or retracts into the housing  120 . With the movement of the ball screw  88 , the steering lever  52  pivots about the steering axis. Thus, the drive unit  34  moves clockwise or counterclockwise to turn the watercraft  40  to the left or to the right respectively. The ball joints  130 ,  134  allow the swivel bracket  44  with the drive unit  34  to tilt up and down even though the motor housing  120  is affixed to the tilt pin  50 . Also, the ball joints  130 ,  134  allow greater tolerance in the dimensions of the components of the steering system  116 . The arrangement of the second embodiment also allows the tilt pin  50  to be shorter.  
       FIGS. 9 and 10  illustrate a further steering system  140  modified in accordance with a third embodiment of the present invention. The steering system  140  incorporates a modified steering device  141  that has a movable motor housing  92 . In the third embodiment, modified support members  142  are applied to support the ball screw  88  on the swivel bracket  44  rather than on the tilt pin  50 . The steering device  141  includes two bosses  143  that preferably project toward the motor housing  92  from top forward ends of the swivel bracket  44 . The support members  142  are affixed to the respective bosses  143  by bolts  144 . Because the ball screw  88  is affixed to the swivel bracket  44 , the tilt pin  50  does not need to extend outward and can be shorter in the third embodiment.  
       FIGS. 11 and 12  illustrate a further steering system  148  modified in accordance with a fourth embodiment of the present invention. The steering system  148  incorporates a modified steering device  150  that has the movable ball screw  88 . The motor housing  92  preferably has bosses  152  that project toward the bosses  143  of the swivel bracket  44 . The motor housing  92  is affixed to the swivel bracket  44  at the bosses  152  by bolts  154 . The bolts  154  are schematically shown in actual lines in the figure, although a large part of each bolt  154  is hidden by the motor housing  92  during normal viewing.  
       FIGS. 13-15  illustrate a further steering system  160  modified in accordance with a fifth embodiment of the present invention. The steering system  160  incorporates a modified steering device  162  that has the movable ball screw  88 . The illustrated ball screw  88  extends coaxially with a modified tilt pin  164  that is hollowed. Thus, the illustrated tilt pin  164  is configured as a pipe, and the ball screw  88  extends through the pipe. The ball screw  88  has a center axis E that is identical to the tilt axis of the tilt pin  164 . The tilt pin  164  preferably has a relatively large diameter so that the tilt pin  164  is also a motor housing that holds the outer casing  86 . Preferably, the steering device  162  includes collars  166  that are inserted into the tilt pin  164  to hold the ball screw  88  therein. The collars  166  space the ball screw  80  apart from the swivel bracket  44 .  
      Alternatively, as shown in the left hand side of the tilt pin  164  of  FIG. 15 , each bracket arm  58  of the clamping bracket  46  has a cylindrical projection or boss  168  that unitarily extends from the bracket arm  58 . Each projection  168  is inserted into an opening  169  of the swivel bracket  44  to space the ball screw  88  apart from the swivel bracket  44 .  
      When constructed as shown in  FIGS. 13-15 , the steering device  162  in the fifth embodiment is extremely compact and does not protrude into the watercraft.  
       FIGS. 16-18  illustrate a further steering system  170  modified in accordance with a sixth embodiment of the present invention. The steering system  170  incorporates a modified steering device  172  that has the movable ball screw  88 . A motor housing  174  of the sixth embodiment is attached to the transom  38  of the watercraft  40 . A bracket  176  preferably is affixed to a portion of the transom  38  by bolts  178  in close proximity to one side corner of the watercraft  40 . Preferably, a first end portion  180  of the motor housing  174  is affixed to the bracket  176  via a ball joint  182 . A second end portion, which is opposite to the first end portion  180 , comprises the outer casing  86 . The ball screw  88  extends through the motor housing  174  and further extends outward from the outer casing  86 . An end  184  of the ball screw  88  is affixed to a forward end  54  of the steering lever  52  via a ball joint  186  by a pin  188 . In  FIG. 18 , one nut  62  couples the tilt pin  50  with the clamping bracket  46 . Preferably, another nut is affixed to another side of the tilt pin  50  to couple the tilt pin  50  to another side of the clamping bracket  46 .  
      Because the motor housing  174  is attached to the transom  38  of the watercraft  40 , the tilt pin  50  can be short enough to be covered by the power head of the drive unit  34 . The electric cable  78  in the sixth embodiment is located away from the drive unit  34 . Thus, the cable  78  does not bend and stretch much even though the drive unit  34  tilts up and down. The life span of the cable  78  may thus be extended.  
      In the illustrated embodiment, the controller  80  is attached to the electric motor  86 . As noted above, the controller  80  can be separated from the electric motor  86  and can be placed close to the sensor  76 . In this variation, the steering device  172  can be more compact.  
       FIG. 19  illustrates a further steering system  190 , which is modified in accordance with a seventh embodiment of the present invention. The steering system  190  incorporates a modified steering device  192  that has the movable motor housing  92 . In the seventh embodiment, two support members  194  preferably are affixed to the transom  38  of the watercraft  40  by bolts to support the ball screw  88 . The illustrated motor housing  92  is rigidly coupled with a link member  198 . The link member  198  in turn is affixed to the steering lever  52  via a ball joint  200  that has a pin  202 . The pin  202  preferably is inserted into a slot (not shown) which is disposed at the lever  52 .  
      The motor housing  92  does not move with the tilt movement of the drive unit  34  because the ball screw  88  is affixed to the transom  38 . The controller  80  is affixed to the housing  92 . Thus, the electric cable  78  does not bend and stretch much even though the drive unit  34  tilts up and down. The life span of the cable  78  in the seventh embodiment may also be extended, accordingly.  
      Although this invention has been disclosed in the context of certain preferred embodiments, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.