Hydraulic drive system for cable stringing apparatus

Apparatus for stringing aerial electrical cables and the like at relatively constant predetermined tension, said apparatus comprising:

• a rotary drum rotatably mounted on means for supporting said drum, said drum including a core on which a flexible line such as a messenger line or cable is wound in coils of increasing radius with respect to an axis of rotation of said drum, and a hydraulic drive system including:
• (a) a variable displacement hydraulic motor drivably connected to said drum, said motor including a pressure responsive motor controller for increasing motor displacement per revolution and motor output torque in response to sensing increasing pressure of fluid supplied to said motor;
• and
• (b) a variable displacement pressure compensated pump, including pump control means for maintaining a maximum pump discharge pressure setting at which pump fluid flow supplied to said motor may vary from a maximum to a minimum which is greater than the pressure at which said motor controller is actuated to increase said displacement of said motor, said pump control means comprising a pressure fluid operated pump displacement controller, and pressure regulator valve means for sensing pump discharge pressure and valving pressure fluid to said pump displacement controller to operate said pump displacement controller to maintain said maximum pump discharge pressure setting.

Apparatus for pulling cable at a substantially constant tension by winding one of a portion of said cable or a messenger line connected to said cable around a rotary drum, said apparatus comprising:

• a rotary drum including means forming a core portion for receiving said cable thereon in coils of increasing radius with respect to an axis of rotation of said drum;
• and
• hydraulic drive means connected to said drum for rotating said drum to wind said cable on said core at a substantially constant tension, said drive means comprising:
• (a) a variable displacement hydraulic motor drivably connected to said drum, said motor including a controller responsive to sensing a predetermined fluid pressure of fluid supplied to said motor to increase motor fluid displacement per revolution and motor output torque while winding said cable on said drum to maintain a substantially constant tension in said cable;
• (b) a hydraulic pump for supplying pressure fluid to said motor at a substantially constant preselected maximum supply pressure;
• and
• (c) control means for selecting said maximum supply pressure and including a pilot pressure control valve operable to change a pilot pressure fluid signal to said controller proportional to a change in said maximum supply pressure selected for changing the pressure setting of said controller at which motor displacement is increased in relation to said preselected maximum supply pressure.

Apparatus for pulling cable at a substantially constant tension by winding one of a portion of said cable or a messenger line connected to said cable around a rotary drum, said apparatus comprising:

• a rotary drum including means forming a core portion for receiving said cable thereon in coils of increasing radius with respect to an axis of rotation of said drum;
• and
• hydraulic drive means connected to said drum for rotating said drum to wind said cable on said core at a substantially constant tension, said drive means comprising:
• (a) a variable displacement hydraulic motor drivably connected to said drum, said motor including a controller responsive to sensing a predetermined fluid pressure of fluid supplied to said motor to increase motor fluid displacement per revolution and motor output torque while winding said cable on said drum to maintain a substantially constant tension in said cable;
• (b) a hydraulic pump for supplying pressure fluid to said motor at a substantially constant predetermined maximum pressure;
• and
• (c) control means for selecting said predetermined maximum pressure and including a pressure regulator valve in communication with a souce of pressure fluid and with said controller for supplying a selected pilot pressure signal to said controller to selectively vary the predetermined pressure setting at which said displacement of said motor is increased in relation to said predetermined maximum pressure.