CA1079692A

CA1079692A - Hydraulic winch system for pivoting a cargo boom

Info

Publication number: CA1079692A
Application number: CA293,224A
Authority: CA
Inventors: Harald Hagenes
Original assignee: BERGENS MEKANISKE VERKSTEDER AS
Current assignee: BERGENS MEKANISKE VERKSTEDER AS
Priority date: 1977-02-16
Filing date: 1977-12-16
Publication date: 1980-06-17
Also published as: NL7714036A; NO138839B; DK554477A; DK146175B; NO770507L; NO138839C; DK146175C; DE2755673A1

Abstract

ABSTRACT OF THE DISCLOSURE
A hydraulic winch system for pivoting a cargo boom by means of two winches which are adapted to pull the boom to their respective sides and which are controlled by a maneuvering valve and driven by a common pressure medium source, having the cable-tautening sides of both motors coupled to a separate, common, pressure-medium source, which provides a somewhat higher pressure than the pressure which at any time is highest on the cable-slackening sides of the two motors.

Description

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The invention relates to a cargo boom which can be pivoted about the boom needle by means of two winches which, r through a system of cables and tackles, also called guys, affect the boom such that one obtains the moment required to pivot the boom and its cargo sideways, without slack in any of the cables.
One previously known system for this purpose utilizes a winch with two drums, where one drum winds in and the other pays out simultaneously. This sort of arrangement has several disadvantages. Owing to the geometric ratios, the sum of the cable lengths between the two drums has to change during a -pivoting operation if a slackening or tautening of the cables is to be avoided. This compensation of cable length cannot be effected ~hen both drums rotate together, with the result that one has an alternating slackening or tautening of the cable system, depending on the boom's angle of swing.
Another problem with this type of system is that wXen the cables stretch with time, the slack will increase, and readjustment is very difficult.
Any slack in the guys will result in imprecision in the control of the boom, and can lead to dangerous situations.
In an attempt to compensate to some degree for slack, -~
springs or other elastic members between the boom and tackles have been used. However, this is merely a makeshift solutlon;
it is still not possible to avoid slack under certain loading and heeling conditions, and the tension in the elastic members will also decrease as the guys gradually stretch with time.
Another system which utilizes two winches is Xnown from Norwegian Patent No. 124,022. The way in which slack in the guys is avoided in this system is that "a braking force is applied to the slacking winch motor such that the slacking guy -- 1 -- ~,~

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1 wire has to be drawn off the drum against a certain force."
This effect is obtained because the slacking hydraulic winch motor is pulled around ~y the motor that hauls in, oil from the - slacking motor being made to pass through a counterpressure valve which produces a braking moment on the slacking motor. To hold the guy wires taut when the winch system is not in operation, a certain pressure is applied to the motors on the drive side.
A decided disadvantage of the latter system is that the winch motor that pays out cable receives a significant 10 braking moment owing to the counterpressure valve! this in addition to the friction and resistance already present in the system. Therefore, in order to be able to effect a certain moment on the boom about the boom needle, the winch motor that hauls in must necessarily be dimensioned so large that it can overcome both the boom-force and the braking force from the slackening winch. -This means that one is forced to utilize larger and more expensive winch motors than one really needs for a specific boom, cargo, heeling angle and the normal friction conditions.
To obtain the desired pivoting velocity, therefore, a larger pump and increased applied power are required to over-come the braking effect caused by the counterpressure valve.
It is obvious that the costs involved in such a system are dependent on the dimensions and installed power of the machinery that is utilized. This results in an increase both in the initial investment for procuring the machinery and in the running costs during operation, owing to the increased energy consumption.
The present invention is the result of work to find a solution to the problems of previous systems, as described 30 above.

1 Briefly, the invention is characterized in that pressure from a separate pressure source is led into a pipeline which connects up the respective sides of the two motors which indi-vidually try to draw the boom to one side or the other, respectively. By ensuring that the pressure in this pipeline is always somewhat higher than the highest pressure existing elsewhere in the system, the guys will always be under tension without any application of braking force on the motor which is paylng out cable being necessary, and one thus obtains the 10 desired savings in power consumption.
The supply of pressure medium (oil) from said separate pressure source is very small. In the non-operational state, it will merely refill enough oil to compensate for a small inner leak in the system, and with a pivoting of the boom it will compensate for the changes in volume which are the result of the aforementioned geometric ratios which cause the one motor to pay out more cable than the other motor hauls in, or vice-versa.
The surplus of pressure medium from the two motors when the total length of cable is shortened is led out of the connective 20 line between the motors through a pressure-regulating valve.
In the ~ollowing, the method of operation will be explained with reference to the accompanying diagram.
The pivotable boom is symbolically drawn ànd designated (B). The two winch drums are designated Tl and T2, and the guys, the cables gl and g2, are attached to the top of the boom and pull it to either side. In practice, there would normally be multi-sheaved tackles between the drum and boom in o~der to obtain the most advantageous ratio, but this simplified drawing has been chosen merely for the purpose of illustrating the 30 system.

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1 Each of the two drums Tl and T2 is driven by its own hydraulic motor, Ml and M2, respectively. These motors are coupled to the pipeline 1 in such a way that supplying an over-pressure in the pipeline 1 produces a moment on each of the two motors Ml and M2, each of which then tries to pull the boom to its side via the drums Tl and T2 and the guy wires gl and g2.
Both winches are alike and are supplied the same pressure, and when the boom is in the position shown on the drawing, the winches are in equilibrium and the boom is stationary. To make the boom pivot, the moment on one motor must be reduced such that the other motor has the upper hand. This is accomplished by guiding the control lever for the maneuvering valve 2 to the side toward which one wants the boom to swing. The control slide ~a 4-way valve of known type) is arranged such that it will then conduct pressure medium from the pump 3 to the motor that is supposed to pay out cable~ The moment on this motor, which is approximately proportional to the pressure difference over the motor, will thus be reduced,and the other motor, which retains its moment, will draw the boom toward its side.
It is essential that the pressure in the pipeline 1 always be higher than the highest of the two pressures that can exist in the pipelines 4 and 5. This can be achieved, for example, by ensuring that the maximum-pressure valve 6 is adjusted somewhat lower than the pressure in the separate pressure source 12 which is coupled to the pipeline 1.
In a preferred embodiment, the use of a pressure-regulating valve 7 of a known type has been chosen, as shown on Fig. 1. As is known, this valve functions such that the pressure in the line 1 will be higher than the pressure in lines 4 or 5 by an amount equal to the spring force F that is set. The slide in the valve 7 is in equilibrium when PF A Pl ' where PF = pressure in the spring housing, F = the spring force, A = the end cross section of the slide valve, and Pl = the pressure in the pipeline 1.

The spring housing is automatically coupled via a relay 8-to whichever of the pipelines 4 or 5 has the highest pressure at the moment.
To prevent an unnecessarily high pressure build-up in pipelines 4 and 5 when the maneuvering valve is in the stop ~ -~
position, the pipeline which has the lowest pressure is auto- `
matically coupled to a reservoir tank 9 through a relay 10 and a choke valve 13. In this way, pressure medium which leaks from line 1 through the motors Ml and M2 to line 4 or S can flow back to the return side of the auxiliary pump 12, which also is connected to the reservoir tank 9. This tank is dimensioned such that it can refill or receive that volume of ~ .

pressure medium brought about as a result-of temperature changes, an~ can also compensate for the changes in volume occurring when the motors Ml and M2, owing to the geometry of the rigging, are forced to rotate at different speeds during a pivoting `~
operation. The surplus fluid from line 1 is led off through valves 7 and 13 to the reservoir 9.
Also shown on Fig. 1 is a valve 11 of conventional design and function. This valve's job is to ensure that the pressure on the pump's intake side will not be too high if the cargo pulls the boom to the same side as the one toward which it is pivoting. This valve also ensures that the pressure on the pump's outlet side is sufficient to prevent cavitation in the ~0796g2 1 motor that pays out cable in the same situation.
Standard symbols or schematic representations with which a person skilled in the art will be familiar and whose functions he will understand have been utilized for the purpose of illustrating the method of operation for the invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hydraulic winch system for pivoting a pivotally mounted cargo boom comprising:
first and second motor driven winches, a first side of each motor being connected to a common first pressure medium source, a second side of each motor being connected through a maneuvering valve to a second pressure medium source, operation of the motors being controlled by the pressure differentials between their respective first and second sides, the motor driven winches being operatively connected to the boom whereby operation of the first winch pivots the boom in one direction, while operation of the second winch pivots the boom in the opposite direction, the pressure of the first medium source being greater than that of the second medium source whereby each motor tends to drive its respective winch to pull the boom in said opposite directions, thus maintaining the boom in a state of equilibrium until the maneuvering valve is operated to apply sufficiently different pressures to the second sides of the motors to cause the winches to pivot the boom.

2. A hydraulic winch system as claimed in claim 1 wherein operation of the maneuvering valve increases the pressure to the second side of one motor, thereby decreasing the pressure differential across said one motor to allow the winch driven by the other motor to pull the boom in said opposite direction.