Radial hydraulic motor for a hydraulic hybrid vehicle

Abstract

A radial hydraulic pump/motor for use in place of a mechanical transmission for a hydraulic hybrid vehicle is described. Means for disengaging and reengaging individual working pistons are provided, allowing partial or zero effective displacement. Methods for using the radial pump/motor to supplement power from other pump/motors for the vehicle are also described.

1 . A hydraulic machine, comprising:
 a housing;   a power shaft, including an eccentric cam, configured to rotate about a common longitudinal axis;   a plurality of working pistons positioned in respective cylinders, wherein the cylinders are oriented in a radial arrangement each being substantially perpendicular to the axis, and wherein each piston has a connecting rod and wherein each connecting rod has a bearing surface for slidably bearing upon a bearing surface of the eccentric cam;   a high-speed control valve for each cylinder, configured to switchably connect the respective cylinder with a high pressure fluid source and a low pressure fluid source;   a high pressure fluid line connecting each high-speed control valve with the high pressure fluid source;   a low pressure fluid line connecting each high-speed control valve with the low pressure fluid source;   a shut off valve for isolating the high pressure fluid line from the high pressure fluid source; and   a pressure relieving valve on the high pressure fluid line for depressurizing fluid in the high pressure fluid line to facilitate disengagement of the connecting rod from the bearing surface.   
     
     
         2 . The hydraulic machine of  claim 1 , additionally comprising:
 one or more members, rigidly connected to each connecting rod and extending substantially perpendicularly to the central axis of the connecting rod; and   one or more grooves in the inner surface of the housing;   wherein each groove includes a first volume swept by an outer end of the respective member in a revolution of the cam when the respective bearing surface is in contact with the cam; and   each groove includes a second volume swept by an outer end of the respective member when the respective bearing surface moves to a position outside the maximum radius of the cam; and   wherein each member extends into a respective groove.   
     
     
         3 . The hydraulic machine of  claim 2 , wherein:
 said groove, when said second volume is occupied by the respective, member, acts to restrain the respective member from movement in such a way that the central axis of the respective connecting rod is prevented from swinging within the plane of rotation of the cam.   
     
     
         4 . The hydraulic machine of  claim 2 , wherein:
 said groove, when said second volume is occupied by the respective member, acts to restrain the respective member from movement in such a way that the central axis of the respective connecting rod is retained in an orientation substantially parallel with the plane of rotation of the cam.   
     
     
         5 . The hydraulic machine of  claim 2 , wherein:
 said groove, when said second volume is occupied by the respective member, acts to restrain the respective member from movement in such a way that the respective connecting rod is prevented from substantially rotating about its central axis.   
     
     
         6 . The hydraulic machine of  claim 1 , additionally comprising:
 a locking means for holding a piston in a position in which the bearing surface of the respective connecting rod is at or outside the maximum radius of the cam.   
     
     
         7 . The hydraulic machine of  claim 6 , wherein:
 said locking means includes a pin that enters a respective cylinder at a position that is below the position of the bottom of the respective piston when the respective connecting rod bearing surface is at or outside the maximum radius of the cam.   
     
     
         8 . The hydraulic machine of  claim 6 , wherein:
 said locking means is a permanent magnet or electromagnet configured to exert a magnetic force on said piston.   
     
     
         9 . The hydraulic machine of  claim 6 , wherein:
 said locking means is a fluid pressure force exerted on a surface of the piston and a surface of the cylinder.   
     
     
         10 . A method for deactivating and reactivating a radial hydraulic pump/motor having a plurality of working pistons positioned in respective cylinders, each piston having a connecting rod, each connecting rod having a bearing surface for slidably bearing upon an eccentric cam, the cam being connected to and rotating with a mechanical power shaft, comprising:
 deactivating a piston by causing the respective bearing surface of the respective connecting rod to move to a position at or beyond the maximum radius of the eccentric cam; and   reactivating a piston by causing the respective bearing surface of the respective connecting rod to be in contact with the cam.   
     
     
         11 . The method of  claim 10 , wherein:
 said deactivating includes the steps of:
 positioning each high-speed control valve to supply low pressure fluid to each cylinder; 
 closing a high pressure fluid supply line from a high pressure fluid source supplying the pump/motor; 
 opening a pressure relieving valve on the high pressure fluid supply line to a second low pressure that is lower than the first low pressure; 
 allowing rotation of the cam to push a piston to a top dead center position; 
 opening the cylinder space above said piston to the high pressure fluid supply line thereby causing fluid in said cylinder space to be at the second low pressure; and 
 positioning the piston at or beyond a top dead center position; and 
   said reactivating includes the steps of:
 allowing the cam to approach a rotational position at which a piston would be brought to a top dead center position if it were active; 
 opening the cylinder space above said piston to the low pressure fluid source; 
 allowing the low pressure active in the cylinder space above said piston to move the piston toward the cam until the bearing surface of the respective connecting rod is seated upon the cam; 
 closing the pressure relieving valve on the high pressure fluid supply line; and 
 opening the high pressure fluid supply line to the high pressure fluid source. 
   
     
     
         12 . The method of  claim 11 , wherein:
 the second low pressure is substantially equal to case pressure below the pistons.   
     
     
         13 . The method of  claim 11 , wherein:
 a piston is locked at its top dead center position or beyond.   
     
     
         14 . The method of  claim 11 , wherein:
 the second low pressure is below case pressure.   
     
     
         15 . A method for providing torque to a drivetrain, comprising:
 providing a first variable displacement pump/motor having a range of allowable displacements;   providing a second pump/motor having a substantially fixed displacement larger than the maximum displacement of the first pump/motor and having a power shaft connected to the output shaft of the first pump/motor;   determining a torque demand of the drivetrain; and   apportioning the torque demand between the first pump/motor and the second pump/motor by selecting a displacement and/or state of utilization of each, wherein the first pump/motor, if utilized, is utilized at a displacement within its range of allowable displacements, and wherein the second pump/motor, if utilized, is utilized at its substantially fixed displacement.   
     
     
         16 . The method of  claim 15 , wherein said apportioning includes the steps of:
 determining a first torque as the torque that the first pump/motor can provide at its maximum positive displacement;   comparing the torque demand to the first torque; and
 if the torque demand is less than or equal to the first torque, operating the first pump/motor at a positive displacement that would deliver the first torque, and having the second pump/motor in an inactive state delivering no torque; and 
 if otherwise, then:
 determining a second torque as the torque that the second pump/motor can provide at its fixed positive displacement; 
 determining a third torque as the torque demand minus the second torque, wherein the third torque may thereby be a positive, negative, or substantially zero quantity; 
 operating the second pump/motor at its fixed positive displacement, and 
 if the third torque is positive, operating the first pump/motor at a positive displacement that would deliver the third torque; 
 otherwise if the third torque is negative, operating the first pump/motor at a negative displacement that would absorb the third torque; 
 otherwise if the third torque is substantially zero, operating the first pump/motor at a substantially zero displacement. 
 
   
     
     
         17 . The method of  claim 15 , wherein said apportioning includes the steps of:
 determining a first rotational speed of the drivetrain;   comparing the first rotational speed to a maximum rotational speed of the second pump/motor; and   if the first rotational speed is not greater than the maximum rotational speed, then:
 determining a first torque capacity, as the torque available from the first pump/motor if acting as a motor at maximum displacement; 
 determining a second torque capacity, as the torque available from the second pump/motor if acting as a motor; 
 comparing the torque demand to the first torque capacity and the second torque capacity; and 
 if the torque demand does not exceed the first torque capacity,
 determining a first displacement value, as a displacement of the first pump/motor necessary to supply the torque demand if acting as a motor, 
 utilizing the first pump/motor as a motor at the first displacement value, and 
 having the second pump/motor in an inactive state; 
 
 if the torque demand exceeds the first torque capacity and does not exceed the second torque capacity,
 determining a torque surplus as the difference between the second torque capacity and the torque demand, 
 determining a second displacement value, as a displacement of the first pump/motor at which it would require a torque input equal to the torque surplus if acting as a pump, 
 utilizing the second pump/motor as a motor, and 
 utilizing the first pump/motor as a pump at the second displacement value; 
 
 if the torque demand exceeds the second torque capacity and does not exceed the sum of the first and second torque capacities,
 determining a torque deficit, as the difference between the torque demand and the second torque capacity, 
 determining a third displacement value, as a displacement of the first pump/motor necessary to supply the torque deficit if acting as a motor, 
 utilizing the second pump/motor as a motor, and 
 utilizing the first pump/motor as a motor at the third displacement value; and 
 
 if the torque demand exceeds the sum of the first and second torque capacities, utilizing the first pump/motor as a motor at maximum displacement, and utilizing the second pump/motor as a motor; 
   and if the first rotational speed is greater than the maximum rotational speed, then:
 determining a fourth displacement value, as a displacement of the first pump/motor necessary to supply at least a portion of the torque demand if acting as a motor, 
 utilizing the first pump/motor as a motor at the fourth displacement value, and 
 having the second pump/motor in an inactive slate. 
   
     
     
         18 . The method of  claim 15 , wherein:
 the first pump/motor is an axial piston pump/motor, and   the second pump/motor is a radial pump/motor.   
     
     
         19 . The method of  claim 18 , wherein:
 the second pump/motor has a mechanically fixed displacement.   
     
     
         20 . The method of  claim 18 , wherein:
 the second pump/motor is the hydraulic machine of  claim 1 .