LIFT BOOM LINKAGE SYSTEM

Abstract: Handling apparatus of the type that includes a hydraulically actuated boom (18) or jib (18) has a support structure (14) carrying a boom pivot (28) to which a main boom (18) is pivoted. The boom actuator (24) is carried by a linkage (42) which is coupled to an additional actuator (48), this actuator (48) and the linkage (42) being pivoted on the fixed structure (14). The additional actuator (48) displaces the boom actuator (24) bodily as the boom (18) is raised and lowered. The invention is applicable especially to small excavators.

Description: LIFT BOOM LINKAGE SYSTEM This invention relates to mechanical handling apparatus of the general kind that includes a boom or jib movable by fluid-pressure operated means, which in this context usually means hydraulic means, but which also includes pneumatic means. Such apparatus may be static, such as a jib crane mounted on the ground or on a fixed structure, or mobile . Examples of mobile apparatus of the above kind include excavators and mobile cranes,- and cranes or other apparatus having a boom or jib and fitted to and/or carried by vehicles for transporting materials and/or equipment and/or other cargo. Such vehicles may be land vehicles such as trucks or construction equipment, or floating vehicles such as ships, barges, dredgers or pontoons used in civil engineering. For simplicity, this description will refer mainly to excavators, but it is to be understood that this is not to be taken as being in any way limiting. The invention is particularly applicable (subject to the foregoing) to small excavators of up to 15 kW power. A typical conventional excavator is a mobile vehicle, having a chassis which carries a support structure arranged to be rotated about a vertical axis on the chassis, and a jib which is pivoted on the support structure so as to be raised and lowered with respect to the latter, sideways displacement of the jib being obtained by rotation of the support structure on the chassis. The jib typically consists of two booms articulated together, the main boom being pivoted on the support structure and the other, or outer, boom carrying a scoop or bucket. Relative movements of the bucket, the outer boom and the main boom are effected by hydraulic actuators of the conventional piston and cylinder type. In such an excavator, the main boom is carried on a boom pivot which is in a fixed location on the support structure, and is raised or lowered by a boom actuator which is coupled at one end to a suitable point along the boom, the other end of the actuator being mounted on the support structure by a pivot which is again in a fixed location on the latter. The term "actuator" in this Application means a fluid- pressure operated actuating device, typically a piston- and-cylinder actuator or jack. Small excavators of this kind in current use are seldom able to dig to depths as great as 3 metres while also being capable of loading out at heights as great as 2.4 metres. In the case of such excavators that are capable of meeting one of these two requirements, it is found that the power and configuration of the machine tends to reduce its ability to meet the other requirement. One of the main considerations here is the fact that the boom actuator makes a small acute angle with the main boom. The greatest effort is required when the boom is at or near its maximum depression, so that the orientation of the boom actuator must be such that it exerts its greatest moment on the boom under these conditions. When the boom is raised, the angle, and therefore the length of the lever arm of the moment, is reduced, and this imposes limitations on the loading-out height. An object of the present invention is to overcome this problem by increasing the angle of depression of the boom, without detriment to its angle of elevation. In the context of an excavator, the invention aims to increase the depth to which the excavator can satisfactorily dig, without detriment to the range of loading-out heights at which it is capable of working. The document US-A-4, 393 , 607 describes a heavy-duty hydraulic excavator having a long boom consisting of three articulated sections, the lowest of which, described as a base boom, is raised and lowered by a boom actuator about a fixed boom pivot . The mechanism is arranged to enable the boom to be fully retracted and folded on the base of the excavator when the latter is travelling, so as to park the long boom in a compact, folded state. To this end the mechanism includes a parking actuator pivoted to one end of a pair of rocking levers, which are themselves pivoted on the axis of the base boom. The other end of these levers carries the base pivot of the boom actuator. In normal operations of digging, lifting and conveying spoil, the boom operates conventionally, with the parking actuator out of use and its associated levers stationary on the fixed platform of the machine. The parking actuator actually works in opposition to the boom actuator in order to achieve the required compact parking of the boom, and is activated by the operator when the boom is in a non-load carrying state. The arrangement does not aim to provide a means for continuously and automatically adjusting the position of the boom cylinder pivot with respect to the boom pivot whereby to increase the useful rotation of the boom when the machine is exerting a digging force or carrying a load. The two actuators have entirely separate hydraulic control systems. Another object is to improve the performance of the apparatus in terms of power utilisation throughout its work cycle, and generally to improve its mechanical efficiency. Another object is to achieve the above objects without intervention by the operator to that end, over the whole range of boom rotation, and with both the said actuators controlled from a single valved supply. According to the invention in a first aspect, in a mechanical handling apparatus having a boom and a boom actuator, for raising and lowering the boom about a fixed boom pivot, the boom actuator is carried by an actuator pivot which is displaceable in a vertical plane by a second actuator as the boom is raised and lowered. According to the invention in another aspect, mechanical handling apparatus having a boom and a boom actuator, for raising and lowering the boom about a fixed boom pivot, wherein the boom actuator is carried by an actuator pivot which is displaceable in a vertical plane by a second actuator as the boom is raised and lowered, characterised in that the second actuator is a variable-geometry actuator coupled to the boom actuator through coupling means such that the second actuator varies the line of action of the boom actuator and works in tandem with the latter so as to tend to increase the force applied in operation of the apparatus at the free end of the boom as the orientation of the boom tends to decrease the said force. Mechanical handling apparatus in one form according to the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: - Figure 1 is a simplified side view of a typical small excavator incorporating features of the invention; Figure 2, which is included for purposes of explanation and comparison, shows diagrammatically the arrangement of a main boom and boom actuator in a conventional small excavator,- Figure 3, which is again diagrammatic, shows the actuating mechanism for the main boom in an excavator according to the invention, with the boom in its fully raised position; and Figure 4 is similar to Figure 3 but shows the boom in its fully extended position. The small excavator, part of which is shown in simplified form in Figure 1, is a machine having a maximum power output of 15 kW. It is to be understood that the invention is however applicable to excavators of any power output, including heavy excavators. It comprises a tracked chassis 10, on which a body 12 is mounted for rotation about a vertical axis. The body includes a cab, and also contains the power unit, not shown, of the machine. It also includes a support structure generally indicated at 14, projecting from the front of the cab. The structure 14 carries a jib 16, which consists of a main boom 18, an outer boom 20 articulated on the main boom, and a bucket 22 articulated on the outer end of the boom 20. The outer boom and the bucket are manoeuvred by means of hydraulic actuators. The main boom 18 is raised and lowered by means of a first, or boom, actuator 24, of the conventional piston and cylinder type. The outer end of the piston of the actuator 24 is coupled to a bracket 26 fixed about halfway along the boom 18. Thus far, the excavator is conventional. The mounting of the actuator 24 with respect to the support structure 14, in the machine shown in Figure 1, will be described below with reference to Figures 3 and 4. However, in a typical excavator according to current practice, the actuator 24 is mounted in the manner shown in Figure 2, to which reference is now made. In Figure 2, the boom 18 and actuator 24 are shown in full lines in the fully extended position of the boom, and in phantom lines in its fully raised position. The boom 18 is carried by a first or boom pivot 28, and the rear end of the cylinder of the actuator 24 is similarly carried by a second or actuator pivot 30. The pivots 28 and 30 are mounted in fixed locations on the support structure 14 (not shown in Figure 2) . In operation, the boom 18 is raised and lowered by the actuator 24, which exerts a moment on the boom the magnitude of which is a function of the lever arm indicated at R x in the fully raised position and R 2 in the fully extended position. It will be seen that R 2 is substantially greater than R 1( so that the maximum effort is available in the fully extended position for digging purposes. However, any further depression of the boom would reduce the lever arm and therefore the effort; and it will also easily be understood that any further elevation from the position indicated in phantom lines in Figure 2 will tend to reduce the lever arm still further, so that a definite limit is set on the loading-out height in practice, this limit being related to the angle of maximum extension of the boom 18. This arrangement in the embodiment of the excavator shown in Figure 1 is modified in accordance with the invention, in the way shown diagrammatically in Figures 3 and 4, to which reference is now made. Here, the boom 18 is again mounted on the fixed structure 14 (not shown in Figures 3 and 4) by means of a first pivot 28. The rear end of the boom actuator 24 is carried by means of a second pivot 40 on a linkage 42, shown here for simplicity as a simple crank. The other end of this linkage is mounted in a third pivot, which is in a fixed location on the support structure 14. In this example, this third pivot defines a common axis of rotation 44 with the first pivot 28, so that here the first and third pivots are in fact one and the same. The structure 14 also carries a fourth pivot 46, in a fixed location on the support structure. The rear end of the cylinder of a second (or "variable geometry") actuator 48 is mounted on the pivot 46. The piston 50 of this actuator is coupled, through a pivot 52, to the linkage 42. Both of the actuators 24 and 42 are controlled by the hydraulic control system of the excavator, and in this example they are both operated by the same hydraulic control circuit (which is not shown, but which is generally conventional) . Typically, these two actuators will be connected in parallel in that circuit. In operation, to lower the boom 18 from the position shown in Figure 3, when the control circuit is energised the actuators 24 and 48 become extended, so that the actuator 24 exerts a moment directly on the boom 18 to lower it, while the actuator 48 exerts a moment on the linkage 42, so rotating the latter about the pivot 28 in a vertical plane and displacing the pivot 40 (to the right in Figure 3) accordingly. In other words, the variable geometry actuator displaces the boom actuator 24 bodily, in such a way that when the latter is in its fully extended position, the boom 18 is depressed by a greater amount than in the conventional arrangement shown in Figure 2. This is illustrated in Figure 4, which also shows the lever arm R, of the moment then exerted by the actuator 24. The magnitude of this moment (which is preferably a maximum in this condition) is such that the same effort can be exerted for digging at the greater depth afforded by this arrangement as would be available at the lesser maximum depth of dig in a machine having the arrangement shown in Figure 2 but otherwise identical. The arrangement shown in Figures 3 and 4 also extends the range of height between the maximum digging depth and the maximum load-out height. The two actuators 40 and 48 are hydraulically balanced and connected in parallel in a single valved hydraulic circuit of the apparatus, and it should be noted that the actuators 40 and 48 work in tandem with each other and not in opposition. The operation of the mechanism to compensate for loss of effort (i.e. of the digging, lifting and carrying force exerted by the bucket 22 at the free end of the boom in the embodiment shown) caused by unfavourable orientation of the boom, is automatic, the hydraulic system being adapted accordingly in any known way. These actuators work as an extension of each other to vary the radius of the line of action of the boom actuator in order to achieve the above compensation, continuously throughout the range of boom movement and with no other external stops or limits. The resultant actuator lever arm is improved. As shown, the pivots 40 and 52 are spaced apart on the linkage 42. It may be envisaged that these two pivots could be combined on a common axis. The linkage 42 can take any convenient form. It may be pivoted on the support structure at a location spaced away from the boom pivot 28. It will be observed from Figures 3 and 4 that the lever arm of the moment exerted by the variable geometry actuator 48 undergoes only a small variation between its value R 5 , in the raised position of Figure 3, and R β in the extended position of Figure 4. It will be understood that the geometry of the arrangement may be modified in any convenient way from that shown in Figures 3 and 4, within the scope of the invention, provided that the required displacement of the boom actuator is achieved as the boom is raised and lowered, so that this actuator is enabled to exert the required effort in the fully raised and fully extended positions of the boom and at all intermediate positions. It will also be readily understood that the arrangements described above may easily be adapted, by a person of ordinary skill in the technology of mechanical handling apparatus having a hydraulically or pneumatically actuated boom, to any other form of such apparatus, such as those mentioned by way of example earlier in this document. Where the apparatus is mobile (e.g. an excavator) , the vehicle of which it consists, or (as the case may be) the vehicle on which it is mounted, need not be a tracked vehicle. Skids or wheels, for example, may be used instead of tracks.

Claims: CLAIMS 1. Mechanical handling apparatus having a boom (18) and a boom actuator (24) , for raising and lowering the boom about a fixed boom pivot (28) , characterised in that the boom actuator is carried by an actuator pivot (40) which is displaceable in a vertical plane by a second actuator (48) as the boom is raised and lowered. 2. Mechanical handling apparatus having a boom (18) carried by a first pivot (28) , a first actuator (24) coupled between the boom and a second pivot (28) , for moving the boom in a vertical plane about the first pivot, characterised by a linkage (42) carrying the second pivot (40) and carried on a third pivot (28) , and a second actuator (48) coupled between the linkage and a fourth pivot (46) for displacing the second pivot in a vertical plane about the third pivot, the first, third and fourth pivots being in fixed locations on a support structure (10) of the apparatus. 3. Apparatus according to Claim 2, characterised in that the first and third pivots (28) define a common axis of rotation. 4. Apparatus according to Claim 2 or Claim 3, characterised in that the second actuator (48) is coupled to the linkage (42) at a location (52) on the latter spaced away from the axis of the second pivot (40) . 5. Apparatus according to any one of the preceding Claims, being an excavator. 6. Mechanical handling apparatus having a boom (18) and a boom actuator (24) , for raising and lowering the boom about a fixed boom pivot (28) , wherein the boom actuator is carried by an actuator pivot (40) which is displaceable in a vertical plane by a second actuator (48) as the boom is raised and lowered, characterised in that the second actuator (48) is a variable-geometry actuator coupled to the boom actuator (24) through coupling means (42) such that the second actuator varies the line of action of the boom actuator and works in tandem with the latter so as to tend to increase the force applied in operation of the apparatus at the free end of the boom as the orientation of the boom tends to decrease the said force.

Inventors: EVANS EMLYN THOMAS, EVANS, EMLYN, THOMAS
Applicants: EVANS EMLYN THOMAS, EVANS, EMLYN, THOMAS
Application year: 1996
Main classification: E02F3
IPC codes: E02F3