Steering gear for boat

Abstract

A steering gear for a boat includes a steering mechanism that moves a rudder, and a driving source. The steering mechanism has: a housing that is fixed to a hull; an output shaft that is rotatably supported by the housing; a first conversion mechanism that is provided inside the housing and converts power from the driving source into rotation of the output shaft; and a second conversion mechanism that is provided outside the housing and converts rotation of the output shaft into motion of the rudder.

What is claimed is: 
     
         1 . A steering gear for a boat, the steering gear comprising:
 a steering mechanism that moves a rudder provided at a stern of the boat; and   a driving source of the steering mechanism, wherein   the steering mechanism has: a housing that is fixed to a hull; an output shaft that is rotatably supported by the housing; a first conversion mechanism that is provided inside the housing and converts power from the driving source into rotation of the output shaft; and a second conversion mechanism that is provided outside the housing and converts rotation of the output shaft into motion of the rudder.   
     
     
         2 . The steering gear according to  claim 1 , wherein the first conversion mechanism has: a ball screw shaft that is rotatably supported inside the housing and rotates as the driving source operates; a ball screw nut that is screwed on the ball screw shaft through a plurality of balls and has rack teeth provided on an outer circumferential surface along an axial direction; and a sector gear that is integrally rotatably coupled to the output shaft and meshes with the rack teeth of the ball screw nut so as to swing around the output shaft as the ball screw nut moves in the axial direction. 
     
     
         3 . The steering gear according to  claim 1 , wherein the driving source is a motor. 
     
     
         4 . The steering gear according to  claim 2 , wherein:
 the driving source is a motor; and   the steering gear has a speed reducer that reduces speed of rotation of the motor and transmits the rotation at a reduced speed to the ball screw shaft.   
     
     
         5 . The steering gear according to  claim 2 , further comprising a control valve that, on the assumption that the driving source is an electrically powered pump that discharges a hydraulic fluid, and that the ball screw nut is slidably provided in the housing, with an inside of the housing being divided by the ball screw nut into two fluid chambers, controls supply or discharge of the hydraulic fluid to or from the two fluid chambers, wherein the control valve moves the ball screw nut as a piston along the axial direction by selectively supplying the hydraulic fluid discharged from the electrically powered pump to one of the two fluid chambers according to manipulation of a steering wheel that is manipulated to change a direction of the hull. 
     
     
         6 . The steering gear according to  claim 1 , wherein the rudder is an outboard motor that is provided as a propulsion unit of the boat on an outer side of the stern so as to be able to rotate around a pivot shaft and functions also as the rudder of the boat by rotating around the pivot shaft. 
     
     
         7 . The steering gear according to  claim 1 , wherein the rudder is provided separately from a propulsion unit of the boat on an outer side of the stern so as to be able to rotate around a support shaft. 
     
     
         8 . The steering gear according to  claim 1 , wherein power transmission between the rudder and a steering wheel that is manipulated to change a direction of the hull is isolated. 
     
     
         9 . The steering gear according to  claim 1 , wherein:
 the rudder is coupled to a steering wheel that is manipulated to change a direction of the hull; and   the driving source generates an assisting force that assists in moving the rudder through manipulation of the steering wheel.