Abstract:
An improved and simplified marine power steering device that provides assist by selectively operating an electric motor driven hydraulic motor to provide the assist. This eliminates pumps that are constantly driven by the watercraft engine. Also the entire assist unit is formed as a single assembly to minimize the hydraulic conduits and their assembly.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to a marine power steering system and more particularly to an improved, compact, high efficiency hydraulically assisted system.  
           [0002]    There have been proposed power assisted marine steering systems. These types of systems generally employ hydraulic assist motors that are mechanically coupled to the watercraft steering device to apply a force that assists the manual inputted steering force. These prior art systems have several disadvantages as will become apparent by reference to FIG. 1, that shows a conventional type of system now used.  
           [0003]    Referring now to FIG. 1, a manually operated steering control, such as a steering wheel  11  is mounted in the operator&#39;s area of the associated watercraft and its output is connected to a vessel steering device  12  by a Bowden wire actuator, indicated generally at  13 . The watercraft steering device  12  may comprise any known type of watercraft steering device such as a rudder or pivotally supported propulsion device such as an outboard motor or the outboard drive portion of an inboard outboard drive.  
           [0004]    The Bowden wire actuator is comprised of an inner, actuating wire  14  and a surrounding protective sheath  15 . One end of the inner wire is connected to the steering wheel  11  and the other end is connected to the watercraft steering device  12 . These connections are of any known type.  
           [0005]    A hydraulic assist motor  59  is also connected to the vessel steering device  12  to assist in the steering operation. The assist motor is generally a reciprocating motor comprised of an outer cylinder  17  having a cylinder bore  18  in which a piston  19  is reciprocally mounted to define a pair of fluid chambers  21  and  22 . During steering assist one or the other of the chambers  21  and  22  is pressurized and the fluid from the other is returned to an oil reservoir  23 . How this is done will be described shortly.  
           [0006]    A piston rod  24  is connected to the piston  19  at one end and extends through the chamber  22 , externally of the cylinder  17  for connection to the vessel steering device  12 .  
           [0007]    The power assist is controlled by controlling the pressurization of either the chamber  21  or  22  from a fluid pump  25  that is continuously driven by an engine  26  which generally is the engine that powers the associated watercraft. The supply and return of the fluid to the motor  26  is controlled by a spool valve, indicated generally at  27 . The spool  28  of the valve  27  is connected to the sheath  15  of the Bowden wire actuator  13 . As is well known, the force applied to the wire  14  from the steering wheel  11  causes a reactive force on the sheath  15  and this force is utilized to actuate the valve spool  28 .  
           [0008]    This type of system has a number of disadvantages. For example, the hydraulic pump  25  is constantly driven by the engine  26  while the engine  26  is powering the watercraft, resulting in loss of the engine output. In addition, the hydraulic cylinder  16  and the hydraulic pump  25  are separately installed in the watercraft requiring, complicated hydraulic piping arrangement for connection. This also results in more burdensome installation as well as a risk of foreign matter entering into the hydraulic circuit.  
           [0009]    It has been proposed to utilize an electric motor to drive the pump  25 , but this does not simplify the plumbing problems. In addition the motor is operated continuously to insure the availability of hydraulic assist, putting added load on the watercraft electrical system and its batteries. Also it means that the system must be constantly pressurized and this reduces the life of the system.  
           [0010]    It is, therefore, a principal object of this invention to provide an improved and simplified water craft steering assist system that has a reduced and simplified hydraulic system and a simplified control and operator therefore.  
         SUMMARY OF INVENTION  
         [0011]    This invention is adapted to be embodied in an assisted marine steering system that is comprised of a manually operated steering control, a watercraft steering device controlling the direction of travel of a watercraft and a manual connection between the manually operated steering control and the watercraft steering device for manually operating the watercraft steering device. A force sensor is provided for sensing the manual force applied to the manually operated steering control. A hydraulic assist motor is coupled to the watercraft steering device for applying a hydraulic assist to the steering operation thereof. Finally, a control varies the amount of hydraulic assist outputted to the watercraft steering device by the hydraulic assist motor in response to the amount of manual force sensed by the force sensor. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]    [0012]FIG. 1 is a partially schematic, cross sectional view of a prior art type of watercraft power steering system.  
         [0013]    [0013]FIG. 2 is a partially schematic, cross sectional view, in part similar to FIG. 1, but shows a system embodying the invention.  
         [0014]    [0014]FIG. 3 is a cross sectional view showing how the power assist mechanism is integrated into the watercraft steering system.  
         [0015]    [0015]FIG. 4 is an enlarged cross sectional view showing the connection of the protective sheath to the force sensor and the output thereof.  
         [0016]    [0016]FIG. 5 is a top plan view in part similar to FIG. 3 but shows the actual connection to the watercraft steering device, in this case an outboard motor.  
         [0017]    [0017]FIG. 6 is a schematic hydraulic diagram of the system. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring now in detail to the drawings and initially to FIG. 1, a steering control such as a steering wheel  51  is connected to the inner wire  52  of a Bowden wire actuator, indicated generally by the reference number  53 . The inner wire  52  is received in a sheath  54  to be connected to a steering device (not shown in this figure) in the boat via a connection  55 . The push-pull type of inner wire  52  is operated in its push and pull directions. Operating the steering wheel  51  to drive the connection  55  in the directions shown by the arrow A allows the drive to rotate around its swivel shaft (not shown in this figure). Therefore, the thrust direction of the drive is changed to steer the boat.  
         [0019]    The piston rod  56  of a hydraulic cylinder assembly, indicated generally at  57 , is also connected to the connection  55 . The hydraulic cylinder  57  serves as a steering assist to the steering wheel  51  and drives the connection  55  in the directions shown by the arrow A to provide auxiliary, assist power in response to the steering force from the steering wheel  51 . A hydraulic pump  58  supplies hydraulic pressure to the hydraulic cylinder  57  as required in a manner to be described. The hydraulic pump  58  is driven by a reversible electric motor  59 .  
         [0020]    A link  61  is connected to the protective sheath  54 . The link  61  is pivotal about a rotational shaft  62 . When the steering wheel  51  is rotated by a force exceeding a value preset, in a manner to be described, it provides either a pulling force or a pushing force that acts on the inner wire  52 . In practice, the protective sheath  54  for guiding the inner wire  52  does not move linearly but bends at an angle of, for example, 90 degrees. Thus, when the inner wire  52  is subjected to pulling force or pushing force the protective sheath  54  is acted on accordingly thereby producing reactive force.  
         [0021]    Therefore, the link  61  connected to the sheath  54  rotates around the rotational shaft  62  by force equal to the reactive force. The degree of rotation of the link  61  is detected as a change in electrical resistance by a variable resistor  63 . Thereby, the steering force in the inner wire  52  according to the steering force for the steering wheel is detected. The steering force corresponds to the displacement of the link  61  rotating between positions. Thus, the positions of the link  61  are detected by the potentiometer (the variable resistor  63  in this embodiment), so that the steering force for the steering wheel is detected to provide auxiliary steering power accordingly.  
         [0022]    A pair of oppositely acting springs  64  are disposed on opposite sides of the link  61  to adjust the steering force applied to the steering wheel  51  necessary to effect steering, as above noted. Thus the link  61  and the variable resistor  63  described above make up a steering force sensor, indicated generally by the reference numeral  65 . The steering force sensor  65  is preferably integrally connected to the above hydraulic cylinder  57 , the hydraulic pump  58  and electric motor  59  to form into a unit of single-piece configuration, indicated generally at  66 .  
         [0023]    The output of the variable resistor  63  in the steering force sensor  65  is connected to a variable resistor  67  in a controller  69  by a conductor  68  for controlling the drive of the electric motor  59 . The variable resistor  67  is designed to adjust the stand-still position of the motor  59 . The variable resistor  67  for adjusting the stand-still position of the motor is designed to correct installation errors of the variable resistor  63  in the steering force sensor  65 , and to adjust to the input value for which no steering force is produced in the inner wire  52 .  
         [0024]    The controller  69  is supplied with electric power from a watercraft battery  71  under the control of a key controlled switch  72 . The controller  69  has a control signal generation circuit  73  to which the output of the variable resistor  67  is connected or integrally incorporated. Its output is delivered to a motor drive circuit  74  connected to the circuit, and a safety device  75 . The control signal generation circuit  73  calculates the amount of controlling of the electric motor  59  according to the control input (the tension of the inner wire  52  detected by the steering force sensor  65  to generate pulse width modulation signals as motor control signals.  
         [0025]    PWM signals generated are inputted to the motor drive circuit  74  to control motor current by an FET. The motor drive circuit  74  drives the electric motor  59  by control current according to the steering force via the safety device  75  comprised of fuses and relays.  
         [0026]    When input to the controller  69  is changed depending on changes in steering force, the electric current changed with the input operates the motor  59 . The hydraulic cylinder  57  is allowed to extend or retract in the direction to restore the link  61  and the hydraulic cylinder  57  to their original relative location, which reduces steering force required for the steering wheel  51 . When the variable resistor  63  is returned to the neutral position, the operation of the electric motor  59  and pump  58  is stopped.  
         [0027]    Having described the general construction and operation by reference to the primarily schematic FIG. 2, more detailed description of the physical structure will now be made by reference to the remaining, more detailed figures and initially, primarily to FIG. 3. As has been noted, the system body  66  is configured as a power steering unit of single-piece configuration in which the hydraulic cylinder  57 , the hydraulic pump  58 , the electric motor  59  and the steering force sensor  65  are integrally connected. The power steering unit  66  (system body) is mounted inside on the transom board of the boat via three mounting holes  76 . The connection  55 , to which the inner wire  52  and the piston rod  56  of the hydraulic cylinder  57  are both connected, is connected to a steering section  77  of the boat via a steering rod  78 .  
         [0028]    The output shaft of the electric motor  59  is connected to the hydraulic pump  58  via a dog clutch  79 . The protective sheath  54  is connected to a wire mounting section  81  in the steering force sensor  65 . Rather than operating on the lever  61 , as previously described, the wire mounting section  81  is connected to a transmission arm  82  and a transmission shaft  83  integral with the transmission arm. The transmission shaft  83  has a drive gear  84  (not shown in FIG. 3 but see FIG. 4) attached to its end  83   a.  The drive gear  84  is connected to the variable resistor  63  via a driven gear  85 .  
         [0029]    The variable resistor  63  in the steering force sensor  65  is connected to the variable resistor  67  (FIG. 2) in the controller  69  via the wire  68 . The controller  69  is, as previously described, made up of a control circuit  86  including the variable resistor  67  and the control signal generation circuit  74  (FIG. 2) and a driver  87  that includes the motor drive circuit  74  and the safety device  75  (FIG. 2)The detailed construction of the steering force sensor  65  will now be described by reference to FIG. 4. The wire mounting section  81  to which the protective sheath  54  is connected, is coupled via the transmission arm  82  and the transmission shaft  83  integral with the transmission arm  82  to the drive gear  84  at the end  83   a  of the transmission shaft (FIG. 3). The drive gear  84  is engaged with the driven gear  85  to rotate the variable resistor  63 . The variable resistor  63  is, as described above, connected to the controller  69  via the wire  68 .  
         [0030]    The actual connection to the watercraft steering device will now be described by reference to FIG. 5. FIG. 4 is a top view in which the power steering unit of the invention is mounted.  
         [0031]    The above power steering unit  66  as shown in FIG. 3 is mounted inside on the transom board through the three mounting holes  76 . A piston rod  56  of the hydraulic cylinder  57  is coupled to the steering rod  78  via the connection  55 . The steering rod  78  is coupled to the steering section  77  of the steering unit, which in this case comprises an outboard motor  88  to steer the boat.  
         [0032]    The hydraulic circuit associated with the steering assist system will now be described by particular reference to FIG. 6. The hydraulic pump  58  is driven by the electric motor  59  as described above. The electric motor  59  is a reversible DC motor and the hydraulic pump  58  is driven by the electric motor  59  either in the reverse or forward direction depending on the desired direction of turning determined by the direction of rotation of the steering control  51 .  
         [0033]    The hydraulic pump  58  communicates with one chamber of the hydraulic cylinder  57  via a main shuttle valve  89  and a hydraulic passage  91  on the oil discharging side when the hydraulic pressure pushes the piston rod to the right as seen in this figure. Pressure is relieved from the other side of the hydraulic cylinder  57  to the hydraulic pump  58  via a further hydraulic passage  53  and a further shuttle valve  93  on the oil returning side.  
         [0034]    As is well known in the art a shuttle piston  94  is disposed between both the main valves  89 ,  93 . This opens the valve on the side not pressurized when one of the main valves  89 ,  93  is opened by discharge pressure from the hydraulic pump. When the shuttle piston  94  is positioned in the middle, the main valves  89 ,  93  are closed so that oil circulation stops and the piston movement of the hydraulic cylinder  57  is stopped.  
         [0035]    A manual valve  95  is provided between the hydraulic passages  91 ,  53 , which allows manual steering. The manual valve  95  is communicated with an oil reservoir tank  96  (the common oil tank used for the hydraulic pump  58 ).  
         [0036]    A piston  97  of the hydraulic cylinder  57  is provided with a pair of relief valve check valves  97   a,    97   b  located in opposite orientations from each another. When the force acting from the piston rod side is larger than the hydraulic pressure from the hydraulic cylinder, the respective relief valve  97   a  or  97   b  allows the piston to operate in the opposite direction against the hydraulic pressure. This allows the steering wheel  51  to be operated by large manual steering force even if pressure is locked in the hydraulic circuit. In addition, if large external force, generated when the boat hits pieces of driftwood, acts on the drive, the drive is protected by dissipating the external force.  
         [0037]    On one of the oil discharging sides of the hydraulic pump  58 , an up-relief valve  98  and a check valve  99  are provided while a down-relief valve  101  and a check valve  102  are provided on the other side. If the pressure in the hydraulic cylinder is equal to a predetermined value or higher when steering the boat, the up-relief valve  98  and the down-relief valve  101  respectively allow oil to return to the oil tank  96  according to the amount of oil stayed in the hydraulic cylinder  57 . The check valves  99 ,  102  refill the hydraulic cylinder  57  with oil provided from the oil tank  96  if running out of oil when the boat is steered.  
         [0038]    Thus from the foregoing description it should be readily apparent that the described construction overcomes the problems attendant with the prior art constructions. Of course those skilled in the art will readily understand that the foregoing description is that of a preferred embodiment of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.