Arrangement for excavator buckets

Technical field:

The present invention relates to an arrangement for excavator buckets, more particularly those excavator buckets which are rotatably fastened to their supporting arms.

Background:

When excavating using an excavator bucket which is actuated by an excavator machine on many occasions it is an advantage if the excavator bucket can be swivelled around an axis which extends essentially in parallel with the movement path which covers the to-and-fro movement of the excavator bucket in its arm.system. If the excavator bucket can be swivelled, this can.be utilized not only for creating horizontal excavated surfaces, but it is also possible to bring about sloping excavation surfaces and also to excavate or to scrape on the underside of a cavern in the horizontal or sloping position. Furthermore this swivelling capacity can be utilized during the emptying of the bucket or the movement of objects by tilting it at a suitable angle.

The technical problem: Buckets capable of swivelling are already known but have exhiV ited certain disadvantages. Thus there are buckets which are more of the lifting bucket type than excavator bucket and which hang downwards from a vertical shaft around which the bucket- can be rotated. The rotating mechanism here however is not subjected to any major forces and this type of known mechanism cannot be employed with excavator buckets for the purpose described above. With other types the change-

over operation proved to be time-consuming because it was necessary to undertake a manual intervention to release and to fix the bucket before it could be swivelled. This signifies a considerable loss in time during work where rotation is often essential.

Solution:

By means of the present invention a simple and rational mechanism has been obtained for rotating the bucket and also for locking it. Rotation thus takes place by hydraulic means and the position of the bucket- can be controlled from the driver's cabin of the machine. In accordance with the invention the locking is carried out in such a way that the bucket is held locked up to a certain moment but, when loaded beyond this moment, is twisted by external forces.

Advantages:

By means of the arrangement in accordance with the invention an excavator bucket which functions extremely efficiently is obtained for the type of work mentioned above. At the same time a bucket is obtained which during normal work is kept locked, but which in the event of abnormal stresses permits rotation whereby the risk of destruction of the rotating mechanism is eliminated.

Brief description of drawings:

Two embodiments are envisaged, both of which relate to a bucket which can be swivelled through 360° and beyond. Fig.l illustrates a side view of a first embodiment and Fig.2 a seGtion along the line II-II in Fig.l. In Fig.3 the second embodiment is illustrated in section whilst Fig.4 illustrates an end view of a variation of an excavator bucket.

Best mode of carrying out the invention:

In the first embodiment the swivelling is brought about by means of a stepping mechanism which comprises a reciprocating force device, preferably an hydraulic piston jack, a driver device from the force device to the excavator bucket which enables the force device to be led in an initial direction without the excavator bucket rotating with it and in a second direction with drive connection to the bucket, also a braking arrange- ment for the bucket so that this can be held in fixed position. The driver arrangement can consist of a disengageable brake which is so arranged that it can be applied when the force device moves in its initial direction, and released when it moves in its second direction and vice-versa. By means of this arrangement, by changing the driver function it is possible to rotate the bucket in both directions inspite of the fact that the force device performs the same reciprocating motion throughout the entire period. The brake is designed to hold the bucket firmly during the return stroke of the force device, when there is no drive connection between the force device and the bucket. When the force device is in the stationary position as such no brake is required if the driver device is put into the applied position. The brake and the driver device can also be given such dimensions that the fairly low braking action required, which is needed during the return stroke of the force device, is exerted by the said braking arrangement whilst the locking of the bucket during excavation work when no movement is to be performed is undertaken by means of. the driver device or preferably by means of both the driver device and the brake. Futhermore the driver device does not need to be dimensioned for the braking action required during excavation, because generally movement does not take place under full

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loading. Thus the driver device and the braking device can each be dimensioned for roughly half of the braking action required during excavation.

It is also possible to select mountings for the bucket so that certain turning resistance is obtained, for example by means of a .brake which can certainly be applied, but is not instantaneously capable of actuation. By this means such a high driving resistance will be achieved that under the influence of its own weight and other lesser loadings the bucket will not be capable of rotating. By this mean ^' s the bucket is thus maintained in the position which it has adopted during the return stroke of the force device, but during this it cannot be selected to greater forces. On the other hand during rotation and during operation the bucket is locked by the said driver device for the force device which during rotation is by this means in movement and during operation is stationary. By this means it is sufficient to provide an instantaneously-applicable brake which represents the driver device, but if two instantaneously-applicable brakes are provided the arrangement can be designed for rotation during the desired application of force, because then the bucket can be locked also during the return stroke of the force device.

The arrangement includes a control arrangement which is so designed that when an actuating device is actuated by the force device in a continuous cycle, it is given a reciprocating motion whilst the brake, if provided, will be released by being rotated, but applied during the return stroke, and thereby controlled as to its correct working cycle in relation to the force device and driver device which in accordance with the embodiment proposed will be applied

during the working stroke, but released during the return stroke, this too being controlled as to its correct cycle in relation to the force device. During . the actuation of the actuating device in a first manner 5 the cycle is thereby controlled in such a way that rotation is obtained in an initial direction, whilst during actuation in a second manner control occurs in such a way that rotation occurs in the other direction. Thus by this means full control is obtained over the 0 movement by means of a single clear actuating movement inspite of the complicated mode of operation of the rotating device.

An important feature of the arrangement in accordance with the invention is that the brake can only assert braking action up to a certain pre-determined moment. In the event of force application exceeding . this moment rotation of the bucket will be permitted with the aid of external forces. The aim here is to obtain sure fixing of the bucket in the set rotational position during work when the force application is normal and when there is no risk of damage to the rotating and braking mechanism. If however as a result of lack of care, or for example as a result of falling masses of material or stones, the bucket should be subjected to abnormal forces it can rotate without being held by the rotating and braking mechanism. This ensures that the said mechanism is not subjected to such abnormal forces as may damage it.

The said arrangement can be achieved with the jaw or belt brakes mentioned in connection with the embodiment described above by actuating these by means of an hydraulic medium which cannot reach a pressure greater than that which will ensure that the said _ braking moment is achieved but not exceeded. To

ensure that the pressure does not exceed a pre¬ determined value by-pass valves are provided in the system. By adjusting the opening pressure of the by¬ pass valves the braking moment can also be adjusted, e. 5 g. , having regard to different types of work or having regard to different transmission ratios in the drive mechanism.

Fig.l illustrates the bucket in accordance with the first embodiment in side view, and here a bearing pedestal O 1 is shown with bearing 2 for connecting the bucket to an excavating machine arm and its movement device. The bearing pedestal has a strong plate 3 in which a sleeve 4 is mounted. In turn inside the sleeve 4 is mounted a shaft 5 , at the outer end of which the bucket 6 is 5 attached which is to be actuated by a rotating mechanism. A brake 7which is carried by bearing pedestal 1 is placed against the sleeve 4. The brake comprises an hydraulic cylinder 8 which, by means of a lever arm 9 and an eccentric shaft 10, also arms 11, can bring about application and release of the brake against the sleeve 4. This is consequently connected with and released from the bearing pedestal 1. It is advisable if the brake is arranged to be applied at a certain braking moment so that the bucket can twist inspite of the brake being applied if the forces are so great that otherwise there would be a risk to the strength of the bucket.

As shown in Fig.2, from sleeve4 a lever arm 12 extends which is joined by means of a piston rod 13 with an hydraulic cylinder 14 which in turn by means of a bracket 15 is attached to the bucket 6. Like the hydraulic cylinder 8, hydraulic cylinder 14 is connected with the said control for the hydraulic medium which, for hydraulic cylinder 14, is obtained by means of a

torsional coupling 16 which permits hydraulic medium to be passed through the shaft 5 to the cylinder 6 regardless of bucket position.

During operation, when the bucket 6 is to be held in a fixed position up to the said safety moment, the brake 7 is applied and by actuation of the hydraulic cylinder 8 and at the same time the piston rod 13 is held in a fixed position by pressure being applied to both sides of the piston in hydraulic cylinder 14, whereby the piston preferably adopts a centre position. Since the sleeve is held by brake 7 at the bearing pedestal 1 and in turn bucket 6 is held by hydraulic cylinder 14 at the sleeve, thus the bucket cannot rotate. When rotation of the bucket is required the brake 7 is still kept applied whilst the hydraulic cylinder 14 is actuated so that the rod 13 is drawn into it or thrust out of it dependent on the direction in which swivelling of the bucket is required. Since the sleeve does not move, during actuation of the hydraulic cylinder instead the bucket must move, whereby the shaft 5 moves inside the? immovable sleeve 4. For continued movement a returu stroke of cylinder 14 is required, whilst sleeve 4 moves freely in relation to the bearing pedestal 1. Thus the brake 7 is disengaged during the return stroke. On the other hand the bucket 6 must not move in relation to the bearing pedestal 1 and its movement in the bearing pedestal must consequently encounter a certain resistance. As mentioned above a special actuatable brake can be arranged between the shaft 5 and the bearing pedestal 1. In such a case this will be locked during the return stroke of cylinder 14. When the piston in cylinder 14 has adopted a new starting position, the brake 7 is locked once more whilst the brake which has possibly been provided to

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lock the shaft 5 to bearing pedestal 1 is released. During a new stroke of cylinder 14 thus the bucket is allowed to rotate a bit more. By repeated strokes the bucket can be guided around for rotation at the desired angle and in any direction required.

According to the second embodiment movement is brought about by a rotating device consisting of a rotating hydraulic motor with a type of planetary gear in which the planetary wheel travels in a gear rim and imparts rotation to a second gear rim. Such a gear arrangement is suitable for extremely large gear transmissions and high load moments. By this means it is possible to transmit the relatively rapid movements of the hydraulic motor to the slow swivelling motion of the excavating bucket.

It has been found that very great difficulties occur during attempts to mount excavator buckets in rotatable fashion because of the high forces which are encountered. However in connection with the present invention it has been established that a suitable and stable mounting arrangement of he bucket is obtained of a shaft which is mounted in at least two spherical slide bearings located at a distance from each other. These spherical slide bearings at the same time provide a radial and axial bearing arrangement.

The second embodiment of the bucket is shown in form of a central section in Fig.3 and here again we see a bearing pedestal 17 with bearings 18 for connection to the. arm of the excavating machine. On the bearing pedestal a sleeve 19 is arranged with two bearing rings 20. These have the previously mentioned spherical bearing surface 21. Inside the bearing 20 inner rings 22 are mounted having a

corresponding spherical surface. The inner rings 22 are fastened to a shaft 23 which in turn supports the excavator bucket 24 which is to be connected to the rotating mechanism.

On the shaft 23 a chain wheel 25 is fastened. This is joined by means of a drive chain 31 with a somewhat smaller chain wheel 26. The chain wheel 26 is mounted on shaft 27 which proceeds as drive shaft from a gearbox 28 of the said type and which is mounted in a bearing 29. The gearbox 28 is attached at the bearing pedestal 17 and on its input side it carries a hydraulic motor 30.

The hydraulic motor 30 is so connected to the hydraulic system of the excavating machine that it can be driven in both directions. It is connected with by-pass valves which are set to pass the hydraulic medium at a certain pressure. This pressure is so adapted that if the moment ^• at the bucket reaches a certain value and this consequently tries via the chain gears and differential gears 28 to drive the hydraulic motor 30, this can take place at a drive force exceeding the pre-determined value by the by-pass valves opening, as a result of which the hydraulic motor starts to function as hydraulic pump and pumps out medium via a shunt type or a return type to the hydraulic system tank. Provided that the pre-determined moment is not exceeded, the bucket is held in a fixed position against the pressure exerted by the hydraulic medium against the pressure-loaded surfaces of the hydraulic motor. Thanks to the said design it is possible for the bucket and mechanism to be protected in a simple manner against overloading because, at the pre-determined safety value, rotation of the bucket is obtained before any breakdown can occur. The pre-determined moment value can very easily be adjusted by adjusting the

opening pressure of the by-pass valve.

During rotation of the bucket the hydraulic motor 30 is started in the desired direction and thus drives the shaft 23 and together with this the bucket 24 via the gear drive 28 and the said chain gear drive, of which gear wheels 25 and 26 form a part. The gear drive gives an extremely high speed reduction which is necessary to accomodate the very large moments required to rotate the bucket and to hold this in the working position. Hence no special brake is required in the system, the position-maintaining forces being generated by the enclosed hydraulic medium. A suitable output ratio for the gear drive is 1:97 whilst the output shown on the chain gear drive can for example be 1:2. Thanks to its design the gear drive can accommodate extremely high moments which are accommodated by several sets with planetary wheels. On the other hand it is extremely rigid and does not provide any spring capacity. However the latter is achieved in the chain gear drive because the chain does provide some elasticity. This serves to reduce impulse loadings on the drive and hydraulic motor.

As already mentioned, the type of mounting shown has proved extremely suitable for the purpose involved and it is also appropriate to provide this to the first embodiment.

Fig.4 illustrates a gripping function exercised by the bucket. By means of a separate servo cylinder 32 the bucket which is provided along a line 33 can be opened by swivelling around a shaft 34, which can be used partly for emptying material in the bucket and partly fur "plucking" objects, e.g., rocks.