Protection arrangement for rotator units.

Technical field

The following invention relates to a protection arrange¬ ment for rotator units, especially those which are intended for rotation of excavator buckets. The invention relates in particular to those units which comprise a housing and an output shaft, a motor, preferably a hydraulic motor coupled to a drive source for driving the output shaft in relation to the housing, and also a transmission between the motor and the output shaft. In the transmission, which is preferably of the self-braking type, such as a worm transmission, for a force-transmitt¬ ing element, in the case of a worm transmission its worm screw, a suspension arrangement is arranged for this element, which arrangement is designed to permit movement of the element under the effect of forces in the trans¬ mission. A spring arrangement is designed to hold the element in a normal position, up to a certain level of force effect, but, when the said level of force effect is exceeded, to allow the element to assume an actuation position deviating from the normal position in either direction. A detection member is designed to detect the position of the element.

Prior art

A worm transmission arrangement in which certain of the abovementioned elements are present is known from US patent 3,339,426, Karl-Heinz Borggrafe. The worm screw is movable from a normal position upon high axial forces. This movement actuates a stop member such that the movement of the worm screw is stopped if the resistance in the transmission becomes too great. The arrangement is designed to be used in drive arrangements for valve operation.

The present invention relates to rotator units, and especially those which are intended for rotation of excavator buckets. An excavator bucket is arranged on the supporting excavator in such a way that it can be pivoted in one plane and be guided into different positions in the same plane by means of the excavator arm. Alterna¬ tively, equipment other than a bucket, for example equipment for breaking up asphalt, can be suspended in the same way and thus have the same movement possi¬ bilities. However, in certain work, it is advantageous if the bucket or the alternative equipment can be pivoted about an axis extending in the said plane. In order to achieve this, it is known to arrange on the arm of the excavator a so-called rotator unit which is supported by the arm and in turn supports the equipment in question.

The rotator unit is generally designed with a housing, which has arrangements for securing to the excavator arm and, in the opposite position to these securing arrange¬ ments, an output shaft coupling which is designed for securing of the excavator bucket. In the housing there are drive arrangements for turning the shaft coupling and, with it, the excavator bucket or the alternative equipment. In a known embodiment of such a drive arrange¬ ment, a worm screw driven by a hydraulic motor is used, which drives a wheel on the shaft which bears the output coupling.

Technical problem

A rotator unit of this type for excavator buckets is subjected to extremely great forces. These arise, on the one hand, because the drive mechanism attempts to turn at extremely high load, but primarily because the turning mechanism attempts to hold the bucket in a certain position while it is subjected to high rotational forces as a result of the movement of the excavator arm or as a result of other external forces, for example from falling boulders or masses of earth. In this connection it has proven difficult to dimension the turning mechanism in

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such a way that it is not damaged when high forces of this type arise. Dimensioning the unit for such randomly occurring and very great forces is possible in the housing and securing arrangements of the unit, but would mean that the drive mechanism, in order to withstand such forces, would at the same time have to be dimensioned for corresponding drive forces, which would be uneconomical. The drive mechanism in rotator units of the said type is thus a sensitive part of the latter, and this sensitivity is difficult to eliminate at reasonable costs.

It is true that, after adapting the known arrangement mentioned in the introduction, its use would mean that the drive mechanism could be stopped in the event of excessively high drive resistance. However, as has emerged from the above, this would not be sufficient in those cases where a direct force effect on the bucket arises, which is in itself so great that it overloads the drive mechanism even if the latter is not subjected to any drive forces.

Solution

According to the invention a control arrangement is connected to the motor and coupled to the detection member and is designed, under action from the latter in either direction upon alteration of the position of the element by force effect above the said level, to couple the motor to the drive source for rotation in the direc¬ tion which the force effect exhibits. By this means, upon force effect against the output shaft relative to the housing, the shaft turns in the direction which the force effect exhibits until such a co-rotation has taken place that the said force actuation level is fallen short of and the detection member returns to the normal position.

Advantages

The invention provides a protection arrangement which protects the turning mechanism in a rotator unit even in the event of very high, unexpected loads, without having

to resort to a considerable dimensioning. This protection arrangement thus protects the drive mechanism even in cases where it is subjected to such high external forces in either drive direction that a stop of the drive is not itself sufficient to protect the mechanism.

Description of the figures

An embodiment of the invention is shown in the attached drawings. Fig. 1 shows a general view of a rotator unit according to the invention together with its attachment to an excavator arm and the excavator bucket supported by the unit; Fig. 2 -shows a perspective view of the unit, the housing having been partially removed in order to show the inner parts; and Fig. 3 shows the unit diagram- matically with its hydraulic equipment.

Preferred embodiment

According to Fig. 1, an excavator arm 1 has, at its outer end, an attachment, which is pivotable in relation to the arm 1 by means of a linkage 3 and a hydraulic cylinder 4. The arm 1 is movable in its entirety, and here it is assumed that the machine supporting the arm is an excavator of conventional design. The attachment 2 supports a rotator unit 5 designed according to the invention, which unit, in Fig. 1, has the form of a housing 6 with, on its top side, attachment elements 7 which are connected to the attachment 2 of the excavator arm and an output shaft coupling 8. An excavator bucket 9 is attached to the shaft coupling 8.

The rotator unit 5 has, in the housing 6, a hydraulically driven rotation mechanism which is able to rotate the output coupling 8 and, with it, the excavator bucket 9 in relation to the housing 6 and, thus, also in relation to the excavator arm 1. The said drive mechanism is here assumed to be driven hydraulically, as is indicated by two tubes 10 in Fig. 1. These tubes are connected to a hydraulic pump, as will be described hereinafter.

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Fig. 2 shows the rotator unit 5 with its housing 6. The output coupling 8 for securing of the excavator bucket can also be seen and is shown here turned upwards. The housing 6 is shown partially opened, so that most of the turning mechanism can be seen.

The said turning mechanism comprises, beside the output coupling 8, bearings (not shown) for the same, and a worm wheel 12 connected to the latter. The worm wheel 12 is in engagement with a worm screw 13 which is connected to a cylindrical gear wheel 14. The worm screw 13 and the gear wheel 14 are supported by a shaft 15 which, at its two ends, is mounted in bearings 16 and 17. These bearings are secured in the housing 6, as are the said bearing arrangements for the output shaft system 11.

In the housing, to the side of the shaft 15, a reversible hydraulic motor 20 is secured whose output shaft supports a cylindrical gear wheel 21 which is in engagement with the gear wheel 14 for driving the worm screw 13. The hydraulic motor is connected via tubes 22 to a supply system 23 for hydraulic fluid, which is connected to the said hydraulic pump by means of the tubes 10 shown in Fig. 1 which, in Fig. 2, are on the far side of the far wall of the housing, for which reason they cannot be seen.

The shaft 15, together with the worm screw 13 and the gear wheel 14, is movable in its axial direction in the bearings 16 and 17. It is acted upon in both directions by cup springs 25 (only the springs of the one shaft end are shown) with high spring action to assume a central normal position. The spring forces are adapted in such a way that this normal position is assumed the entire time that the drive mechanism is subjected only to those forces which it is dimensioned to absorb. These forces consist of torsional moments against the output coupling 8 which, via the worm wheel 12 and the worm screw 13, are converted to axial forces on the shaft 15 by virtue of

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the fact that the worm shaft is self-braking. It is thus these axial forces which are counteracted by the spring force of the cup springs. The shaft is connected to detection members which detect whether its position in the axial direction deviates from the said normal posi¬ tion and, if this is so, transmit control pulses to the supply arrangement 23 for hydraulic fluid for the motor 20. The two gear wheels 14 and 21 permit the said axial movement because the gear wheels 14, 21 are cylindrical.

Fig. 3 shows diagrammatically most of the parts mentioned in connection with the description of Fig. 2. Also shown diagrammatically are the cup springs 25 which attempt to hold the shaft 15 in the said normal position, and in addition the said detection member for the shaft 15 in the form of a rod 27 pivotable about a shaft 26. The supply arrangement 23 for hydraulic fluid is shown in detail. It can be seen that it comprises two valves 28 and 29 from which there extend the lines 22 to the hydraulic motor 20.

These valves can be manoeuvred by pivoting of the outer end of the rod 27. Three manoeuvring positions are thus obtained for the valves: a normal position when the shaft 15 is held in the central position by means of the cup springs 25, a first actuation position when the shaft 15 has moved upwards (shown in Fig. 3) and pivoted the outer end of the rod upwards, and a second actuation position when the shaft 15 has moved downwards (shown in Fig. 3) and the outer end of the rod in the same dir¬ ection.

The valves 28 and 29 are connected to the said hydraulic pump, which is designated 32, and to a hydraulic fluid sump 33 via a reversing valve 34. The reversing valve 34 is designed to be manoeuvred by an operator who is working the equipment and can thus bring about rotation by means of the unit in the desired direction.

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The valves 28 and 29 and the pump 32 are connected to a pressure accumulator 35 which, on the two sides of a membrane 36, has a fluid space 37 and an air space 38 respectively. It is the fluid space 37 which is connec¬ ted to the valves 28, 29 and to the pump 32. This is effected via a line 40 with a valve 41, which is designed to be manoeuvred between the open and closed position by a pressure sensor 42 which is connected to the air space 38.

As long as the torsional moment against the output shaft system 11 is below a predetermined value which is adapted to the dimension of the turning arrangement, the shaft 15 assumes the normal position and the rod 27 a central position in which the two valves 28 and 29 take up their first manoeuvring positions. In the latter, they leave a free passage for hydraulic fluid from the reversing valve 34 to the hydraulic motor 20 via the lines 22. In this position the accumulator 35 has no function. Depending on the position of the reversing valve 34, one of the lines 22 is connected to the hydraulic pump 32 and the other one to the hydraulic fluid sump 33. In this way the output shaft of the motor 20 is turned in a defined direction. In an opposite manoeuvring position of the reversing valve 34, the connection of the lines 22 is the reverse, and the motor is driven in the other direction. In a neutral position the reversing valve is closed and the hydraulic motor braked by means of the confined fluid. The pump must then be stopped or dis¬ charged to the fluid sump 33. As a result of the move¬ ment of the hydraulic motor in the said manner in both directions, it turns the shaft 15 and the worm screw 13 via the gear wheels 21 and 14 and turns the output shaft system with its output coupling 8 via the worm wheel 12. This turning in relation to the housing 6 means that the excavator bucket 9 is turned in relation to the excavator arm 1. If the reversing valve 34 is set in the neutral position, the drive arrangement is held in the assumed position by means of the confined fluid pressure.

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If the output shaft system 11 were to be subjected to torsional moment above the predetermined value, the cup springs 25, by virtue of their dimensions, allow the shaft 15 to be displaced axially in either direction. In this displacement, one of the valves 28 and 29 is thus actuated, such that it connects its respective line 22 and, with it, the corresponding motor side to the fluid space 37 of the accumulator 35, while the connection to the pump 32 at the reversing valve 34 is interrupted, in which respect the pump may require to be discharged to the fluid sump 33. In contrast, the other valve is acted upon so as* to set' its respective line 22 in connection with the fluid sump 33. This coupling means that the first-mentioned side of the motor is set under pressure from the accumulator 35, while its other side is decom¬ pressed to the fluid sump 33. This means that the motor is driven in a defined direction as a result of the pressure from the accumulator. This turning movement means that the output coupling 8 is turned in the direc¬ tion in which it is acted upon by the torque. In other words, the excavator bucket "dodges" the acting force and thus keeps the torque effect below the predetermined value. In this way the drive mechanism and the equipment are protected from breakdown and from the effect of excessively great force.

The manoeuvring function of the valves is adapted in such a way that a movement of the rod in one direction, corresponding to a torque against the coupling 8 in a first direction, provides such connection that the turning of the motor 20 takes place in this direction and vice versa. The said turning takes place for as long as the abnormal torque remains and the shaft 15 is thus dis¬ placed. However, the accumulator 35 has a limited output volume from the fluid space 37. The pressure in the latter is generated by means of the counter-pressure of compressed air in the air space 38, which decreases as a result of the discharge of hydraulic fluid. However, because the pressure in the air space 38 is controlled by

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means of the pressure sensor 42, out-flowing hydraulic fluid can be replaced by means of the valve, upon decrea¬ sing pressure in the air space, connecting the fluid space 37 to the pump 32, which replaces the out-flowing fluid.

The valves 28, 29 could themselves be connected to the pump 32 without the accumulator 35, and, as long as the pump emitted pressure fluid, one would still be able to obtain the function described. This system is a simplif¬ ication in comparison to the one described, because the accumulator 35 is omitted, and this application also lies within the scope of the invention. However, if one takes into consideration the fact that the equipment may come to be subjected to high torques even when the pump is not in operation, for example as a result of falling boulders or earth when the equipment is not being driven, the said evasive movement is also obtained in these situations as a result of the function of the accumulator. In such a case, the said compensation for the out-flowing fluid is not obtained until the pump 32 is started. By means of suitable dimensioning of the accumulator, it is however possible to achieve a sufficiently great evasive turn in order to protect the mechanism from overloading in all foreseeable cases.

Industrial use

The embodiment can be modified within the scope of the invention in relation to the exemplary embodiment descri¬ bed. Thus, other valve couplings are conceivable within the scope of the anticipated function: that the turning of the output shaft system will take place in the direc¬ tion in which it is acted upon by the abnormal torque. The arrangement can also be used in control systems other than the mechanical-hydraulic system described, for example with electrical manoeuvring members, and in drive systems other than hydraulic ones, for example electrical systems. As mentioned in the introduction, a rotator unit of the type to which the invention relates is not

restricted to use together with excavator buckets, but instead other equipment can also be connected.