Hydraulic motors

Abstract

A variable displacement bi-directional hydraulic motor 10 comprising a rotatable member 14 that has an axis of rotation and defines a plurality of cylinder bores, respective pistons 30 received in said bores and a yoke 34 provided with a bearing surface that is engaged by respective bearing members 32 carried at an end of the pistons that projects from the cylinder bores, said yoke being mounted for pivoting movement about a pivot axis to allow a swash angle of said bearing surface to be varied, whereby the displacement of the motor can be controllably varied and the direction of rotation of the motor can be changed and the arrangement being such that said bearing surface is inclined at a fixed angle in a plane perpendicular to the plane of said swash angle.

1 . A variable displacement bi-directional hydraulic motor comprising a rotatable member that has an axis of rotation and defines a plurality of cylinder bores, respective pistons received in said bores and a yoke provided with a bearing surface that is engaged by respective bearing members carried at an end of the pistons that projects from the cylinder bores, said yoke being mounted for pivoting movement about a pivot axis to allow a swash angle of said bearing surface to be varied, whereby the displacement of the motor can be controllably varied and the direction of rotation of the motor can be changed and the arrangement being such that said bearing surface is inclined at a fixed angle in a plane perpendicular to the plane of said swash angle.  
   
   
       2 . A motor as claimed in  claim 1 , wherein said fixed angle is substantially in the range 10 to 5°.  
   
   
       3 . A motor as claimed in  claim 2 , wherein said fixed angle is substantially 3°.  
   
   
       4 . A motor as claimed in  claim 3 , wherein said fixed angle is provided by forming said bearing surface on said yoke.  
   
   
       5 . A motor as claimed in  claim 2 , wherein said fixed angle is provided by forming said bearing surface on said yoke.  
   
   
       6 . A motor as claimed in  claim 1 , wherein said fixed angle is provided by forming said bearing surface on said yoke.  
   
   
       7 . A variable displacement bi-directional hydraulic motor comprising a body rotatable about an axis of rotation and defining a plurality of cylinder bores, respective pistons housed in said cylinder bores for reciprocating movement therein and each having an end projecting from the body, respective bearing shoes provided on said ends of the pistons and a bearing surface disposed opposite said body and engaged by said bearing shoes, said bearing surface being mounted for selective tilting movement about an axis extending perpendicular to said axis of rotation such that a ramp angle of said bearing surface can be selectively varied for varying the displacement and the direction of rotation of the motor and said bearing surface being canted at a fixed angle about an axis extending substantially perpendicular to said tilt axis and said axis of rotation.  
   
   
       8 . A variable displacement bi-directional motor in which each of a plurality of pistons carried in a body rotatable about an axis of rotation has an end projecting from the body and is provided with a bearing member that engages a bearing surface that is (i) inclined in a first direction with respect to said body to define a ramp for said bearing members, the angle at which said bearing surface is inclined in said first direction being controllably variable to permit the displacement and direction of the motor to be varied, and (ii) inclined in a second direction with respect to said body, which second direction is substantially perpendicular to said first direction.  
   
   
       9 . A motor as claimed in  claim 6 , in which the amount of the incline in said second direction is fixed.  
   
   
       10 . A variable displacement bi-directional hydraulic motor, said motor comprising: 
 a motor shaft rotatably mounted in a housing and having an axis of rotation;    a drum fixed on said motor shaft, said drum defining a plurality of bores extending parallel to said housing and having a first opening at a first end thereof and a second opening at a second end thereof;    a dedicated supply passage for supplying hydraulic fluid and a dedicated exhaust passage for exhausting hydraulic fluid, said passages being arranged to sequentially communicate with said first openings of said bores when, in use, said motor shaft rotates, whereby hydraulic fluid is supplied to and exhausted from said bores;    respective pistons housed in said bores and each having a leading end projecting from the second opening of the respective bore;    respective bearing members fixed on said leading ends of said pistons so as to be movable relative thereto;    a part defining a bearing surface engaged by said bearing members, said part being pivotally supported in said housing so as to be pivotable about a pivot axis extending perpendicular to the axis of rotation such that, in use, said bearing surface can be controllably pivotted about said pivot axis to provide a variable angle ramp having a ramp angle and said bearing surface being inclined at a fixed angle about an axis that is perpendicular to said pivot axis and said axis of rotation; and    a mechanism to allow a control system to act on said part defining a bearing surface to cause pivoting movement thereof such that said ramp angle is varied to control the displacement and direction of rotation of the motor.    
   
   
       11 . A variable displacement bi-directional hydraulic motor having a plurality of hydraulically actuated axially displaceable pistons arranged to react against a bearing surface to generate a torque for rotating a motor shaft, said bearing surface being inclined at a fixed angle in a first direction with respect to the respective axes of said pistons and at a variable angle in a second direction substantially perpendicular to said first direction, wherein, in use, variation of said variable angle controls the displacement and direction of rotation of said motor.  
   
   
       12 . A hydraulic control system in an aircraft comprising a variable displacement bi-directional hydraulic motor as claimed in any one of the preceding claims.