GB2240080A

GB2240080A - Overload safety device for hydraulic winch of crane, preferably offshore crane

Info

Publication number: GB2240080A
Application number: GB9000711A
Authority: GB
Inventors: Christian Herzog
Original assignee: Liebherr Werk Nenzing GmbH
Current assignee: Liebherr Werk Nenzing GmbH
Priority date: 1990-01-12
Filing date: 1990-01-12
Publication date: 1991-07-24
Anticipated expiration: 2010-01-12
Also published as: GB9000711D0; NO901101L; GB2240080B; NO300837B1; NO901101D0

Abstract

Winch (2) is provided with means for preventing an overload comprising a relief valve (23), which in response to an overturning load in excess of a permissible value connects a hydraulic accumulator (16) to a hydraulic cylinder (4) for lifting the brake (3) of the hoisting mechanism and to the suction side (8) of the hydraulic motor (1) of the hoisting mechanism for a compensation of oil leakage so that the hoisting rope can be unwound from the hoisting drum (2). Characterisingly a second hydraulic motor (30) is provided, which is coupled to a hydraulic pump (31). Valves (24, 29) are provided, which are actuated by the hydraulic accumulator (16) and adapted to connect said hydraulic motor (30) to the pressure side of the hydraulic motor (1) of the hoisting mechanism, which latter hydraulic motor (1) operates as a pump during safety operation to feed motor 30 to cause pump 31 to feed oil to the circuit of the safety system even when accumulator 16 is empty. Said valves (24, 29) are also adapted to connect said hydraulic pump (31) to the hydraulic cylinder (4) for lifting the brake (3) and to the suction side (8) of the hydraulic motor (1) of the hoisting mechanism. <IMAGE>

Description

CR4XE, PREFERABLY OFvS-ORE CRANE This invention relates to a crane, preferably an offshore crane, comprising a jib, which is mounted on a rotatable post or sport and which is provided with a retracting mechanism for effecting a luffing motion, also comprising a hoisting winch provided with means for preventing an overload, which means comprise a relief valve, which in response to an o7erturning load in excess of a permissible value ccrnects a hydraulic accumulator to a hydraulic cylinder for lifting the brake of the hoisting mechanism and to the suction side of the hydraulic rotor of the hoisting mechanism for a compensation of oil leakage so that the hoisting rope can be unwound from the hoisting drum in response to the occurrence of forces in excess of those corresponding to the permissible overturning moment eve when the crane is out of operation.

Even when a crane is not in operation, the crane hook may be subjected to a force in excess of the overturning moment so that safety devices must be provided in order to avoid a tilting of or damage to the crane. Particularly offshore cranes must be protected from overload because sch cranes are used to unload ships and hoist loads from ships as such ships are raised and lowered in the waves. Wr.en a load to be hoisted has been welded to the deck, a descent of the ship into a trough between waves may cause the weight of the ship to be transmitted as a load on the crane.Besides, the crane hook may become caught in a ship which is driftite away or which descends into a trough between waves and tis will a' so result in a high overloading of the crane.

In order to protect a crane from sch osetloads, it is known in an arrangement which is of the kifld described first hereinbefore and serves to prevent an overload to lift te braces of the hoisting mechanism in response to measured loads or torRues and also to skort-circuit by a valve the hoisting side of the hydraulic mztor of the hoisting winch to the lowering side.When te crane is out of operation the brake of the hoisting mechanism should be lifted by a hydraulic cylinder ana losses d to an oil leakage in the hydraulic motor should be compensated in ormer to avoid cavitation. For that purpose 2 hydraulic accumulation must be provided, which feeds hydraulic oil to the hydraulic circuit at the required rate.

E a hydraulic accumulator can hold only 5 certain quantity of hydraulic oil so that te means for preventing an overload can act only for a limited time.Whet the crane hook of an offshore crane which is out of operation becomes caught in a ship which is drifting away or in supply boat r.ich is departing, it must be possible to unwind the rope of the hoisting mechanism entirely from the rope drum of the hoisting wine if damage to or a tilting of the crane is to be avoided. It is extremely expensive and therefore uneconomical to provide a hydraulic accumulator which is so large that it will supply hydraulic oil to the hydraulic system of the safety devices until the rope of the hoisting mechanism has entirely been unwound and has been torn from the hoisting drum.

For this reason it is an object of the invention to provide for a crane of the kind described first hereinbefore a device which serves to prevent an overload and which will remain effective in case of need until the hoisting rope has entirely been unwound from the hoisting drum.

In a crane which is of the kind described first hereinbefore that object is accomplished in that a hydraulic motor is provided, which is coupled to a hydraulic pump, valves are provided, which are actuated by the hydraulic accumulator and adapted to connect said hydraulic motor to the pressure side of the hydraulic motor of the hoisting mechanism, which latter hydraulic motor operates as a pump during safety operation, and said valves are also adapted to connect said hydraulic pump to the hydraulic cylinder for lifting the brake and to the suction side of the hydraulic motor of the hoisting mechanism.

In the arrangement provided in accordance w-th the invention in order to prevent an overload, a set is provided, which is parallel to the pressure accumulator and consists of a hydraulic motor and a hydraulic pump and in which the hydraulic motor is supplied with hydraulic liquid by the hydraulic motor of the hoisting mechanism, which latter hydraulic motor operates as a pump when the hoisting rope is forcibly unwound from the hoisting drum. The hydraulic motor of the set then drives the hydraulic pump, which will supply hydraulic oil to the hydraulic circuit of the safety system even when the hydraulic accumulator has been emptied. In the arrangement in accordance with the invention to prevent overload the pressure accumulator serves only to supply hydraulic oil to the hydraulic circuit of the safety system at the beginning of the safety operation.When the pressure relief valve has opened, the pressure accumulator first acts to lift the brake of the hoisting mechanism so that the motor of the hoisting mechanism can start and can supply hydraulic oil to the hydraulic motor of the set. During a safety operation the pressure accumulator also actuates the corresponding valves for connecting the hydraulic motor of the set to the pressure side of the hydraulic motor of the hoisting mechanism and for connecting the pressure accumulator to the suction side of the hydraulic motor of the hoisting mechanism, which hydraulic motor then operates as a pump.

By the arrangement provided in accordance with the invention to prevent overload it is thus ensured that even when the pressure accumulator has been emptied the hydraulic circuit of the safety system will be supplied with hydraulic oil as long as the hoisting rope, which is under an overload, is unwound from the hoisting drum and via the hoisting drum drives the hydraulic motor of the hoisting mechanism.

In the arrangement provided in accordance with the invention to prevent an overload the hydraulic motor of the set by-passes any overpressure valve, which may be provided to connect the highpressure side of the hydraulic motor of the hoisting mechanism to the low-pressure side of that motor so that the low-pressure side of the set is then connected to the low-pressure side of the motor of the hoisting mechanism.

The pressure relief valve of the arrangement to prevent an overload may be actuated by any desired means which respond to loads or torques in excess of the overturning moment. But the pressure relief valve is suitably actuated by the torque-restraining member of the winch of the retracting mechanism. The retracting mechanism imparts a luffing motion to the jib and is suitably backed by a torquerestraining member, which can simply be provided with a switch, which is actuated by the torquerestraining member upon an occurrence of an overload.

An illustrstive embodiment of the invention will now be explained in more detail with reference to the drawing, the single figure of which is a diagrammatic representation of the hydraulic circuit of the arrangement for preventing an overload.

The motor 1 of the hoisting mechanism consists of a conventional hydrostatic motor, such as a reciprocating piston motor, and in the conventional manner drives via a transmission, not shown, the hoisting drum 2 of the hoisting winch. The indicated brake 3 of the hoisting mechanism acts on the shaft of the hoisting drum or on another member which is non-rot at ably connected thereto and can be controlled in a suitable manner and will be braked at least when the crane has been stopped. The brake 3 of the hoisting mechanism can be lifted by means of the spring-loaded hydraulic cylinder 4.

Hydraulic oil is supplied to the motor 1 of the hoisting mechanism by a variable-displacement hydraulic pump 5, which is driven by the drive motor 6, which may consist of an electric motor or of an internal combustion engine. The hydraulic pump 5 is connected to the motor 1 of the hoisting mechanism by hydraulic lines 7, 8 on the high-pressure side and on the low-pressure side. The drive motor 6 also drives a hydraulic feeding pump 10, which is connected by non-return valves 11, 12 and lines 13, 14 to the lines 7, 8 as illustrated and compensates any loss of oil caused by leakage.

The arrangement for preventing an overload comprises the pressure accumulator 16, which is connected by the lines 17 to 22 with the interposed pressure relief valve 23 and the valve 24 interposed to the hydraulic cylinder 4 of the brake of the hoisting mechanism and to the low-pressure side of the motor 1 of the hoisting mechanism. The lines 18, 19 are connected by lines 25, 26, 27 to the hydraulic actuators for the valves 24, 29.

The valve 29 is hydraulically operable against spring force and when actuated connects a hydraulic motor 30 to the high-pressure side 7 and the low-pressure side 8 of the motor 1 of the hoisting mechanism. That hydraulic motor 31 is included in a set 32, which also comprises a hydraulic pump 31.

The hydraulic prp 31 of the set 32 is connected by a line 36 which contains the nan-return valve 33 to the lines 18,19.

The hydraulic pump 10 which serves as a feed pump is also connected by lines 37, 38, 39 to the hydraulic accumulator 16 so that the latter will be re-charged during an operation of the crane when that accumulator has been emptied during a safety operation. A non-return valve 40 is incorporated in the line 39 which leads to the hydraulic accu emulator 16.

The mechanically operable pressure relief valve 23 has an actuating member, which is supported by the torue-restrainng member of the retracting winch. In response to a torque which acts on the torRue-restrainlng member and corresponds to the overturning moment, the pressure relief valve 23 will be actuated to connect the hydraulic accumu- motor 16 to the line 18.As soon as pressure is a-plleS to the line 18., the valves 24 and 29 wll be opened in the first place so that the brake of the hoisting mechanism will be lifted and hydraulic oil will be fed to the low-pressure side of the motor 1 of the hoisting mechanism in order to prevent cavitation and in the second place the hydraulic motor of the set 32 is connected to the pressure side of the motor 1 of the hoisting mechanism. NMnen the hoisting rope 42 is then unwound from the hoisting drum 2, the motor 1 of the hoisting mechanism will be driven to act as a pump. By that pumping operation, hydraulic oil is supplied to the hydraulic motor 30 of the set 32 so that that motor drives the pump 31 and the latter will supply hydraulic oil to the hydraulic system of the arrangement for preventing overload when the hydraulic accumulator 16 has been emptied.

During a normal operation of the crane the solenoid valve 45 connects the discharge side of the feed pump 10 via the lines 37, 38, 20, 21 to the hydraulic cylinder for lifting the brake of the hoisting mechanism. As soon as the crane has been shut down the solenoid valve assumes the position which is apparent from the drawing.

Claims

CLAI;

1. A crane, preferably an offshore crane, comprising a jib, which ip mounted on a rotatable post or support and is provided with a retracting mechanism for effecting a luffing motion, also comprising a hoisting winch provided with means for preventing an overload, which means comprise a relief valve, which in response te an overturning load in excess of a pe missible value connects a hydraulic accumulator to a hydraulic cylinder for lifting the brake of the hoisting mechanism and to the suction side of the hydraulic motor of the hoisting mechanism for a compensation of oil leakage so that the hoisting rope can be unwound from the hoisting drum in response to the occurrence of forces in excess of those corresponding to the permissible overturning moment even when the crane is out of operation, characterized in that a hydraulic motor is provided, which is coupled to a hydraulic pump, valves are provided, which are actuated by the hydraulic accumulator and adapted to connect said hydraulic motor to the pressure side of the hydraulic motor of the hoisting mechanism, which latter hydraulic motor operates as a pump during safety operation, and said valves are also adapted to connect said hydraulic pump to the hydraulic cylinder for lifting the brake and to the suction side of the hydraulic motor of the hoisting mechanism.

2. A crane substantially as described hereinbefore with reference to and as shown on the drawing.