Control device for hydraulic winch

1. A control device for a hydraulic winch, comprising:

a hydraulic source;

a variable-displacement hydraulic motor that is caused to rotate by pressure oil from the hydraulic source and is used to drive a winch drum;

a winch operation member that outputs a low-speed hoisting/lowering command so as to hoist/lower a hook at low speed when operated to a low-speed side hoisting/lowering operating position and outputs a high-speed hoisting/lowering command so as to hoist/lower the hook at high speed when operated to a high-speed side hoisting/lowering operating position;

an accelerator operation quantity detection unit that detects an operation quantity of an accelerator operation member;

an engine control unit that controls an engine rotation speed at an engine within a range between a minimum rotation speed and a maximum rotation speed, in correspondence to the operation quantity at the accelerator operation member detected by the accelerator operation quantity detection unit;

a rotation speed detection unit that detects the engine rotation speed;

a line pull detection unit that detects a line pull at a hoisting rope;

a condition decision unit that decides that a fuel-efficient, high-speed operation condition is established in response to an operation performed at the winch operation member to switch from the low-speed side hoisting/lowering operating position to the high-speed side hoisting/lowering operating position when the engine rotation speed detected by the rotation speed detection unit is equal to or lower than a predetermined rotation speed and the line pull detected by the line pull detection unit is equal to or less than a predetermined value; and

a motor displacement control unit that reduces a motor displacement of the hydraulic motor and controls the motor displacement at a minimum displacement once the condition decision unit decides that the fuel-efficient, high-speed operation condition has been established, wherein:

once the condition decision unit decides that the fuel-efficient, high-speed operation condition has been established, the engine control unit sets an upper limit to the engine rotation speed at a predetermined rotation speed, lower than the maximum rotation speed.

2. A control device for a hydraulic winch according to claim 1 , wherein:

the hydraulic source includes at least two hydraulic pumps;

the control device further comprises two directional control valves each switched in response to a command output from the winch operation member, which individually control flows of pressure oil output from the two hydraulic pumps, to the hydraulic motor;

in response to the low-speed hoisting/lowering command output from the winch operation member, only one of the directional control valves is switched so as to deliver pressure oil from one of the two hydraulic pumps to the hydraulic motor; and

in response to the high-speed hoisting/lowering command output from the winch operation member, the directional control valves are both switched so as to deliver pressure oil from the two hydraulic pumps to the hydraulic motor.

3. A control device for a hydraulic winch according to claim 1 , wherein:

the rotation speed detection unit detects an actual rotation speed of the engine.

4. A control device for a hydraulic winch according to claim 1 , further comprising:

a mode selector operation member that selectively switches to a limit mode, in which the motor displacement at the hydraulic motor is controlled by the motor displacement control unit at the minimum displacement when the fuel-efficient, high-speed operation condition has been established or to a no-limit mode in which the motor displacement at the hydraulic motor is not controlled at the minimum displacement even if the fuel-efficient, high-speed operation condition has been established.

5. A control device for a hydraulic winch according to claim 4 , further comprising:

an auxiliary selector switch that either validates or invalidates the limit mode having been selected by the mode selector operation member, wherein:

the accelerator operation member includes a handle portion held by an operator seated in an operator's seat; and

the auxiliary selector switch is disposed at the handle portion of the accelerator operation member.

6. A control device for a hydraulic winch according to claim 1 , wherein:

if the winch operation member is moved from the high-speed side hoisting/lowering operating position to the low-speed side hoisting/lowering operating position while the motor displacement control unit is controlling the motor displacement at the hydraulic motor at the minimum displacement, the motor displacement control unit executes control so as to adjust the motor displacement at the hydraulic motor to a predetermined displacement, greater than the minimum displacement.

7. A control device for a hydraulic winch according to claim 1 , wherein:

if the line pull detected by the line pull detection unit becomes greater than the predetermined value when the upper limit to the engine rotation speed set by the engine control unit represents a predetermined rotation speed, which is lower than the maximum rotation speed, the engine control unit adjusts the upper limit to the engine rotation speed to the maximum rotation speed.

8. A control device for a hydraulic winch according to claim 1 , wherein:

if the winch operation member is determined to have been operated so as to switch from the high-speed side hoisting/lowering operating position to the low-speed side hoisting/lowering operating position and a command value detected by the accelerator operation quantity detection unit is determined to be less than the predetermined rotation speed while the engine control unit is controlling the upper limit to the engine rotation speed at the predetermined rotation speed, the engine control unit adjusts the upper limit to the engine rotation speed to the maximum rotation speed.

9. A control device for a hydraulic winch according to claim 1 , further comprising:

a cutoff unit that regulates the motor displacement when a circuit pressure of the hydraulic motor exceeds a predetermined cutoff pressure; and

a cutoff control unit that raises the predetermined cutoff pressure once the condition decision unit decides that the fuel-efficient, high-speed operation condition has been established.