Crane hydraulic control system

Abstract

 A crane hoise drive assembly having a hydraulic motor (20) driven by a variable displacement hydraulic pump (21) and a control circuit (10) for the pump adapted to govern the pump displacement so that the lift generated by said motor is independent of line travel and is adjustably predetermined.

Description

[0001] The present invention relates to'cranes and more particularly but not exclusively to tag lines for cranes and cranes employed in ocean areas to lift loads from boats.

[0002] In ocean regions which are subjected to considerable wave action, such as the North Sea, it is very difficult to operate a crane to raise a load from a boat. This is due to movement of the ship relative to the crane. Motion of the load will subject the crane to shock loading while this problem is exacerbated since the weight of the load indicated to the crane operator may not be consistent with the actual weight of the load. Additionally the weight may not be fully uncoupled from the boat or may be caught on a rail and become jammed. In all these circumstances it is possible for the crane to be damaged and the operator subjected to danger. Thus, given any one of the above adverse conditions and the situation that the load is engaged at the crest of a wave, the crane may be subjected to excessive loading as the boat falls under the influence of wave action thereby subjecting the crane uncontrollably to the full load dynamically magnified.

[0003] In use of tag lines on cranes to date the controls for such tag lines must be continually manipulated if the tag line is to retain and support the load at a predetermined location. That is to say the controls are not generally adapted to maintain a constant tension in the tag line.

[0004] It is an object of the present invention to overcome or substantially ameliorate the above disadvantages.

[0005] There is disclosed herein a crane hoist drive assembly comprising a hydraulic hoist motor to provide a lift force for the crane; a variable displacement hydraulic pump operatively coupled to said motor to drive same by pumping hydraulic fluid therethrough, said pump having displacement control means adapted to govern the displacement of said pump; and a hydraulic control circuit operatively coupled to said displacement control means to thereby control displacement of said pump and therefore the lift force generated by said motor, said control circuit includingselectively operable valve means adapted to limit the pressure delivered by said control circuit to said control means to thereby limit the lift force generated.

[0006] A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 is a hydraulic control system to control the hoist hydraulic motor and hydraulic pump of a crane;

Figure 2 is a hydraulic circuit including a main hoist hydraulic motor and hydraulic pump to be controlled by the circuit of Figure 1; and

Figure 3 is a hydraulic circuit for a tag line control system to be employed with the circuit of Figure 2.

[0007] In Figure 1 there is depicted a control hydraulic circuit for the hoist motor and pump of a crane to be used in conjunction with the hydraulic circuit of Figure 2 which includes the hoist hydraulic motor 20 and pump 21.

[0008] With reference to Figure 2 in particular, there is schematically illustrated a hydraulic motor 20 which is driven by a hydraulic pump 21. The motor is provided with speed control valves 22 which in the case of a radial piston- type motor , selectively vary the hydraulic fluid displacement of the motor to thereby regulate the speed and torque of the motor 20, assuming a given pressure and fluid delivery to the motor 20. Also provided is a boost extraction valve 23.

[0009] The variable displacement pump 21 is provided with a control circuit 10, see Figure 1. The pump 21 is preferably an axial piston type with a variable angle swash plate to regulate the pump displacement and direction of flow through the pump 21. The pump 21 is controlled by circuit 10 via lines 24, 25 and 26, the line 26 being a vent line, extending from the pump 21 which vents control pressure governing the swash plate angle. The circuit 10 includes a main control panel 15 having two valves 12 and 13 which are manipulatable via an operator to control the main hoist motor and pump and are coupled to lines 24 and 25. The valves 12 and 13 are coupled via line 16 to a pump which provides hydraulic fluid under pressure to be used in circuit 10. Circuit 10 further includes a wave compensation selection valve 17 and a wave compensation valve 18. The valve 17 is a solenoid actuated valve and selects the position of valve 18. There is also provided a hoist up limit valve 19 which limits the maximum raised hoist position. Connected to the line 26 is a load capacity selection valve 27 which adjustably limits the maximum load force, and thus the load lift, applied to the main line by limiting the pump output pressure. Also connected to the line 26 is a light line selection valve 28 and a light line limit valve 29. The valve 28 is solenoid actuated'and can be simultaneously actuated with valve 17 in the light line wave compensation mode of operation.

[0010] In operation the lift provided by the hoist may be set at a predetermined magnitude by actuation of the wave compensation selection valve 17 and selection valve 28. By doing so, main control pressure is connected to the line 25 via actuation of valve 17 which would bias the pump 21 to maximum output. This is commonly known as biasing the pump to an "on-stroke" mode of operation. However, this is modified by venting pressure from vent line 26 as the output of the pump 21 exceeds a predetermined pressure. The predetermined pressure is adjustably set by valve 29 since valve 17 is simultaneously activated whti the valve 28. Under normal load lifting conditions the maximum output of the pump 21 is determined by valve 27, however upon wave compensation and lift line mode being selected, the limit is set by valve 29.

[0011] Accordingly via lines 24, 25 and 26 the angle of the swash plate of pump 21 may be automatically varied to determine the pressure and direction of flow produced by the pump 21. Under wave conditions the pump 21 may be actually reversed in rotational direction to maintain a constant tension in the hoist cable, as for example when the boat is falling under the influence of wave action. The pressure output may be varied between a maximum set by valve 27 and 0 for the normal hoisting mode or the predetermined fixed setting of valve 29 in the case of light line, wave compensation mode and the flow may be reversed in direction.

[0012] An operator may regain manual control of the lifting operation by again actuating valves 12 and 13 which will cause actuation of sensor 30, which in turn will deactivate solenoid valve 17 and hydraulic control valve 28 and return circuit 10 to a normal mode of operation with a maximum tension setting controlled by valve 27. Under wave compensation mode of operation, the operator does not manipulate the valves 12 and 13 which will remain in a neutral position.

[0013] Turning now to Figure 3, there is depicted a tag line'control circuit 50 which is adapted to control a hydraulic pump.to apply constant tension to the tag line via a tag line hydraulic motor. The circuit 50 is adapted to be attached to a pump and motor of similar or identical construction to the pump 21 and motor 20 of Figure 2. The lines 24, 25 and 26 of Figure 3 correspond to the lines 24, 25 and 26 of Figure 1 for ease of description.

[0014] The circuit 50 includes a control panel 53 which includes spool valves manipulated by an operator and to which is connected control pressure via line 55, a variable setting and pilot operated constant tension control valve 56 connected to vent line 26, and an isolation valve 57 which upon selection of constant tension mode of operation applies full control pressure to the line 25. There is also provided an override valve 58.

[0015] The valves of control panel 53 are biased to a neutral position wherein control pressure is permitted to flow through valves 57 and 58 to bias the pump to maximum output. The pump will then maintain a constant output pressure as dictated by the adjustable setting of valve 56. For example, if the pressure drops, the valve 56 will cause the pump to increase in stroke, or if the pressure increases to the setting of the valve 56, the valve 56 will cause a decrease in stroke.

[0016] If the control valve 53 is operated to increase tension in the tag line , the output pressure is increased by increasing the stroke of the valve 53. The valve 56 is influenced by control pressure , proportional to the tension required, to adjust the pump pressure output.

[0017] If tag line tension is to be decreased and the tag line paid out, then the line 25 is dumped to tank via valve 58 and proportional control pressure is delivered to the line 24 via valve 53.

[0018] If the tag line tension is to be dropped to zero, then valve 57 is operated.

Claims

1. A crane hoist drive assembly comprising a hydraulic hoist motor (20) to provide a lift force for the crane, a variable displacement hydraulic pump (21) operatively coupled to said motor to drive same by pumping hydraulic fluid therethrough, said pump having displacement control means to govern the displacement of said pump, and a hydraulic control circuit (10) operatively coupled to said displacement control means to thereby control displacement of said pump and therefore the lift force generated by said motor;

characterised in that said control circuit (10) includes selectively operable valve means (18,27,28,29) adapted to limit the pressure delivered by said control circuit to said control means to thereby limit the lift force generated.

2. A crane hoist drive assembly comprising a hydraulic hoist motor (20) to provide a lift force for the crane; a variable displacement hydraulic pump (21) operatively coupled to said motor to drive same by pumping hydraulic fluid therethrough, said pump having displacement control means adapted to govern the displacement of said pump; and a hydraulic control circuit (10) operatively coupled to said displacement control means to thereby control displacement of said pump and therefore the lift force generated by said motor, said control circuit including selectively operable valve means (18,27,28,29) adapted to limit the pressure delivered by said control circuit to said control means to thereby limit the lift force generated.

3. An assembly according to claim 1 or 2, characterised in that said control circuit further includes manually operable controls (12,13,15) which are normally manipulated by an operator when controlling said crane by governing the control pressure delivered to said control means, and in that said valve means (18), when operated, isolates said manually operable controls from said control means.

4. An assembly according to any one of the preceding claims, characterised in that said valve means (27,29) is adjustable so that the pressure limit set thereby is variable.

5. An assembly according to claim 1 or 2, characterised in that said valve means is an adjustab1e valve (56) adapted to adjustably limit the control pressure.

6. An assembly according to claim 5, characterised in that said control circuit further includes manually operable controls (53) which are manipulated by an operator when co trolling said crane by governing the control pressure delivered to said control means, and said adjustable valve (56) adjustably limits the control pressure delivered to said control means.

7. An assembly according to any one of the preceding claims, characterised in that the hydraulic control circuit includes a tag line control circuit (50) having a respective hydraulic pump and motor to apply constant tension to a tag line.

Drawing