EP0052065A2 - Effort-limiting reducer for the lifting gear of a self-lifting platform - Google Patents

Abstract

The subject of the invention is a force limiting reducer for a lifting pinion of a self-elevating platform in which the whole of the reducer is divided into two, namely a gear motor with brake mounted floating on the input shaft d '' a basic reducer which drives the pinion, the geared motor with brake having as its reaction arm a toothed wheel which meshes with a rack which slides while bearing both against a guide and against a hydraulic cylinder integral with the housing of the reducer basic. The invention applies to offshore drilling platforms.

Description

For the self-elevating platform legs having several leg corners each equipped with racks and pinion blocks with reduction gears, motors and brakes with lack of current, it is known that the pinions of a pinion block can undergo very significant overloads when , under the effects of wind, waves or currents, the leg changes position relative to the platform, this within the limits of the games existing between the leg and its guides.

In practice, the value of these clearances is such that in order to take up the overturning torque of the leg relative to the platform using the guides and not the pinions, the brakes of the motors must slip for several turns. These brakes are always oversized and to make them slip, it is necessary to overload the pinions and the reduction gear members.

Limiting an effort by relying on the slippage of a brake is of questionable viability; in order not to have damage, it is necessary to take a significant safety factor compared to the theoretical value, this leads to an expensive oversizing. Even if the sprockets have been calculated to take the weight plus the overturning torque, an equal distribution of the forces on the various sprockets after the brakes have fallen is not ensured and significant overloads from one sprocket to the other of the same row of gables can exist. The object of the present invention is a force limiting reduction gear for lifting pinion of self-lifting platform which allows, for the value of the rotation to be obtained at the pinion during a change in position of the tab between its guides, to reliably limit the forces transmitted by the pinion and the various gear units to a precise value, while allowing the load to be distributed equitably between the various pinions of the same leg corner or the same leg .

The reduction gear, according to the invention, makes it possible to measure the force acting on each pinion, force which can be part of the weight of the platform plus part of the vertical forces due to the overturning torque, this when this torque is taken up in partly vertically by the pinions and partly horizontally by the leg guides.

To this end, the entire gearbox is divided into two, a geared motor with brake mounted floating on the input shaft of a second gearbox which is the basic gearbox which drives the pinion.

The gear motor with brake is provided with a reaction arm which is connected to the structure by a hydraulic cylinder whose oil pressure is controlled; until a certain load on the pinion, the piston of the jack will not move, from a predetermined load the piston will sink and the pinion will rotate a few degrees without uncontrolled overloads since it is easy to maintain a limit value for pressure in a hydraulic cylinder. Each rotation of the pinion with the maximum controlled load corresponds to a rotation of the primary reduction gearbox with brake and motor which is mounted floating, the brake can be oversized, it does not need to slip to allow the pinion to rotate with these few degrees. If the ratio of the basic reducer directly connected to the pinion is relatively small, the rotation of the primary reducer, corresponding to the rotation of the pinion - when changing support on the tab guides, is small enough to directly attach the reaction arm of the primary reducer to the structure of the lifting mechanism with the interposition of a sufficiently long hydraulic cylinder.

If the ratio of the basic reducer is high, the geared motor with brake has as its reaction arm a toothed wheel which meshes with a rack which slides while bearing both against an appropriate guide of the base reducer housing and against a jack. hydraulic. The platform is suspended from the racks of the leg via the gables; when the tab changes position between its guides, the weight of the platform always remains on the pinions and to this weight is added a moment of reversal which overloads the teeth of the pinions which mesh with the rack or racks which tend to rise due to the above-mentioned overturning moment. If the pinions, whose racks tend to rise, let these racks rise by carrying out under a determined load the slight rotation which allows the racks to take the place corresponding to the desired support of the lug between its guides, the pinions, their control gearboxes as well as the teeth of the racks will not have to support a load greater than that which corresponds to the load determined for the aforementioned slight rotation of the pinion.

With the force limiting reducer according to the invention, the load for which the slight rotation of the pinion can take place is not a function of the engine brake but is a function of the oil pressure in the jack against which the motorcycle - floating reducer is supported, this by means of the rack which meshes with the toothed wheel which acts as a reaction arm.

The cylinder stroke and the corresponding length of the rack are long enough to allow a displacement corresponding to the slight rotation of the pinion multiplied by the reduction ratio of the basic reducer, reduction ratio which allows to decrease substantially in the same proportion the cylinder retaining force relative to the force acting between the pinion and rack of the lug. In principle, the rotation of the pinion is of the order of fifteen millimeters at the level of the pitch diameter for a displacement of the leg of twenty five millimeters at the level of the guides, with a reduction ratio of 1/80 for the basic reducer and a pitch diameter of the gear arm reaction arm equal to half the pitch diameter of the pinion, the jack must be adjusted for a force corresponding to 1/40 of the force on the teeth of the pinion, the stroke of the jack is then 40 x 15 or sixty centimeters, which is quite achievable.

In the current state of the art, it is very easy to precisely regulate a pressure inside a jack during its entire stroke, among other things it is sufficient to connect it to a sufficiently dimensioned oleopneumatic accumulator. Usually, the hydraulic cylinders of all the pinions of the same leg corner are hydraulically connected together; it is the hydraulic unit of each leg corner which distributes the overturning moment between leg guides and pinions. If the overturning moment is taken up only by the lug guides, then all the jacks on the same lug are hydraulically connected to each other.

To bring the jack back to the starting position, i.e. stroke available for a slight rotation of the pinion in the direction of descent from the platform, it is enough to energize the motor and the brake in the mounted direction and d '' supply the cylinder with a pressure higher than that which corresponds to the reaction due to the engine torque. This return to the starting point operation can be done individually for each pinion one after the other, especially when the torques of the motors are not provided for lifting operations during periods of major storms.

If the combination of basic reducer, primary reducer and hydraulic cylinder must allow significant rotations of the pinion, for example for the precise positioning of

1 the platform relative to the lug when using the known system of locking combs between lug and platform, a single stroke of the hydraulic cylinder is not enough and it is necessary to perform several strokes alternately; for this purpose, an additional brake or locking is provided between the input shaft and the base reducer housing, this allows the hydraulic cylinder to be returned to its starting position by opening the motor brake without energizing the motor. , the weight of the platform is then suspended during the return stroke of the jack, not on the motor magnetic field, but on the aforementioned additional brake or lock, the brake can be disc, jaw or band, the lock is a finger that fits into a notch or hole.

• La figure 1 est une vue de dessus avec coupes partielles selon le plan I, I de la figure 2.
• La figure 2 est une vue latérale avec coupe selon le plan II,II de la figure 1.
• La figure 3 est une vue de dessus avec coupe passant par le plan III, III de la figure 4.
• La figure 4 est une vue latérale passant par le plan IV, IV de la figure 3.

The attached figures show by way of non-limiting illustration a force limiting reduction gear for lifting pinion of a self-lifting platform according to the invention.

• FIG. 1 is a top view with partial sections along plane I, I of FIG. 2.
• FIG. 2 is a side view with section on plane II, II of FIG. 1.
• FIG. 3 is a top view with section passing through the plane III, III of FIG. 4.
• FIG. 4 is a side view passing through the plane IV, IV of FIG. 3.

The difference between Figures 1 and 3 as well as between Figures 2 and 4 is the additional locking device between the input shaft of the basic reducer and its casing, to avoid having to put the motor under tension during of multi-course operations with the hydraulic cylinder.

In these figures, the basic reducer and the floating gear motor with brake are not shown in section, this for the purpose of simplification; these reducers may as well be planetary reducers, monosatel reducers- lites, conventional multi-gear reducers than combinations of screw reducers with cylindrical or bevel gear trains, the only condition is that both the basic reducer and the floating gear motor must be reversible, this is that is to say that the slow shaft must be able to drive the fast shaft with a mechanical efficiency which is substantially constant over time; in the case of using a conventional planetary reducer, a ring with internal teeth of a planetary gear can serve as a reaction arm, this without changing the character of the invention, the mechanical elements which are downstream of this ring to internal teeth serving as reaction arms are then considered to be mounted floating on the mechanical elements which are downstream.

For FIGS. 1 and 2, the reducers chosen are a planetary reduction gear with hollow shaft for the basic reduction gear and a screw reduction gear with hollow shaft with primary with two cylindrical trains for the floating gear motor. 1 is the leg corner, 2 are the spacer tubes which join together the different leg corners, 3 are the pairs of guides located at the top and at the bottom of the platform, guides against which the edges 4 of the leg corner 1 are supported; there are generally about fifteen meters between the upper and lower guides, this makes it difficult to have less than twenty five millimeters of play between the edges 4 and each pair of guides 3. It is the catching up of these plays between the edges of corner 4 and guides 3 which is at the origin of the small vertical displacements of the rack 5, displacements which can be done with extremely great efforts when the modification of the position of the tab between its pairs of guides 3 is due to a storm.

6 is the pinion which meshes with the rack, 5, 7 and 8 are the bearings of the shaft 9 which is integral with the pinion 6. 10 is the support in which the shaft 9 of the pinion 6 rotates; in the same support there are generally several pinions with their own reducers and motors located one above the other; for the sake of simplification, a single pinion 6 is shown smelled; depending on the types of platform, this support 10 can be either rigidly fixed to the pontoon, or connected by articulations or elastic elements to the pontoon or to the upper guide supports. 11 is the basic reduction gear which is bolted to the support 10, the shaft 9 enters this reduction gear 11 and is driven by the key 12. 13 is the input shaft of the reduction gear 11, the screw reduction gear with hollow shaft 14 is mounted floating on the shaft 13 which is driven by the key 15. 16 is a primary reducer with two sets of cylindrical gears which is driven at 17 by the brake motor 18 of which 19 is the terminal box and 20 the wires supply, wires which lie substantially in the axis of rotation of the shaft 13. 21 is a ring gear which is concentric with the shaft 13 while being integral with the housing of the reduction gear 14, the ring gear 21 is the reducer reaction arm 14; 22 is a rack which is integral with the piston 23 of the jack 24 of which 25 is the pressure oil supply tube. 26 is a guide with end-of-travel stop 27 for the rack 22. The jack 24 and the guide 26 are integral with the casing of the basic reducer 11.

It is easy to see that the rack 5 rotating a few degrees, with a great effort, the pinion 6 in the direction of clockwise and this rotation causing the toothed wheel 21 to rotate anticlockwise shows, the piston 23 will sink into the cylinder 24 by limiting the forces between pinion 6 and rack 5 as well as between the various members of the reducers 11 and 14 to the forces arising from the force of driving the piston 23 into the cylinder 24, effort which is very easy to control using the oil pressure in the tube 25. When the legs are raised, the pinions have only the weight of the legs to support, this weight is only a small fraction of the weight of the platform; on the other hand, the bending moments on the legs, during towing generally have no influence on the pinions, the clearances between guides and legs are then eliminated by blocking wedges or shims; consequently, limiting the forces at the pinions and their reducers is generally only important for the direction of the efforts corresponding to the retention of the weight of the platform when it is lifted above the water.

It is for this reason that FIGS. 1 and 2 represent a device with a single-acting cylinder; it is obvious that without changing anything in the character of the invention, the limit stop 27 can be replaced by another jack identical to 24 and that then the same anti-overload advantages can be achieved during towing with raised legs.

In FIG. 4, the double-acting hydraulic cylinder 30 with its supply pipes 3.1 and 32 is integral with the plate 33, itself integral with the casing of the basic reducer II. The piston rod 34 is secured at 35 to the rack 22 guided at 26. In FIG. 3, the toothed wheel 36 is secured to the input shaft 13 of the base reducer 11, this with the key 37; the double-acting hydraulic or pneumatic cylinder 38 is screwed onto the casing of the basic reducer 11, the finger 40 integral with the piston 39 can be retracted or removed from any notch of the toothed wheel 36.

It is easy to see that the platform being suspended from a rack 5 by the pinion 6, it is possible to fit the finger 40 into a notch of the wheel 36, this just for the time necessary for the return of the piston whose rod is 34, time during which the brake 28 is energized using the wires 29, therefore is open, the motor 18 with its wires 20 is not energized.

As soon as the piston whose rod is 34 has returned to its starting position, the brake 28 is no longer energized and is closed, the finger. 40 is out of the notch of the wheel 36 and the piston 34 and the rack 22 are ready to move in the direction which makes it possible to limit the forces on the pinion 6 or to be moved voluntarily in the desired direction either to resume vertically on the pinions part of the moment of reversal of the leg in the pontoon, either to make a slow movement and precise of the pontoon relative to the leg, that is to say at the limit to use the hydraulic sprockets of pinions as an emergency lowering or lifting system at very slow speed and low power, this in the case where the on-board power station is failure, a low-power emergency unit is sufficient to operate these hydraulic pinion cylinders.

Claims (4)

1. Force limiting reduction gear for lifting pinion of self-lifting platform, characterized in that the whole reduction gear is divided into two, ie a reduction gear motor with floating brake mounted (14, 16, 18, 28) on the shaft inlet (13) of a basic reducer (11) directly connected to the pinion (6), the motor assembly (18), brake (28) primary floating reducer (14,16) having a reaction arm (21 ) which is connected to a fixed point (33) of the lifting system by at least one hydraulic cylinder (30) whose fluid pressure is controlled, stops mechanically limiting the stroke of the cylinder. 2. Force limiting reduction gear for lifting pinion of self-lifting platform according to claim 1 characterized in that the whole of the reduction gear is divided into two or a gear motor with brake mounted floating on the input shaft d '' a basic reducer which drives the pinion, the motor-reducer with brake having a reaction arm connected to a fixed point by at least one hydraulic jack with controlled pressure, a toothed wheel which meshes with a rack which slides while being supported by both against a guide and a hydraulic cylinder secured to the base reducer housing. 3. Force limiting reducer for self-lifting platform lifting pinion according to any one of claims 1 or 2 characterized in that the hydraulic cylinder is single acting, acts in the direction of support of the weight of the platform and that an axial stop integral with the guide limits the travel of the rack in the support direction of the weight of the tab. 4. Force limiting reduction gear for lifting pinion of self-lifting platform according to any one of claims 1 or 2 characterized in that the jack is double-acting and that the races of the racks in the weight support direction of the platform and in the support direction of the weight of the leg are limited by the internal strokes of the double-acting cylinder.

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