OVERTURNING-PREVENTING DEVICE FOR CRANE TRUCKS AND SIMILAR MACHINES

Abstract: The overturning-preventing device (1) for crane trucks (3) and similar machines is associated with the self-propelled truck (6) of the crane truck (3) in correspondence of the rear axle (8) of the same car, and is substantially composed by a pair of plate means (20, 21) hinged to each other (22) in correspondence of one of their edges. The necessary force in order to generate the rotation of the plate means (20, 21) relatively to each other is adjustable by means of suitable adjustment means (28A, 28B) which influence the minimum load transmitted by the rear axle (8) to the ground. In case the overturning torque is large, the rear portion of the self-propelled truck (6) tends to lift, whilts the rear axle (8), thanks to its own weight, tends to remain stably resting on the ground, causing the plate means (20, 21) of the overturning-preventing device (1) to divaricate. Such a divarica­ tion is used as a signal for enabling a circuit commanding the load-lifting operations by the crane truck (3) to be discontinued. The overturning-preventing device (1) is also suitable for applica­ tion to single-wheel-rear-axle crane trucks, with said rear axle being either of heavy or of light type, as well as to lift trucks.

Description: The present invention relates to an overturning-preventing device in crane trucks and similar machines, such as lift trucks, graders, and still other machines composed of a self-propelled truck which supports operating means. The overturning risk is constantly present during the operating steps of working machines, and, in particular, of crane trucks. It is known that an overturning occurs when the overturning torque, which causes it, exceeds determined threshold values which are a function of the structure, and of the weight of the crane truck. Mechanical overturning-preventing systems are known, which substantially provide for the crane truck-driving operator to verify, moment by moment, the load condition, on the basis of a suitable table which reports the maximum allowed values of lifted load as a function of the range reached by the crane. Unfortunately, such systems are affected by the shortcoming that they are only indicative of the approaching of the danger condition, in that not always the value of the lifted load can be exactly evaluated. In such cases, in order that a reasonable safety can be achieved, it is essential that the operator has matured a meaningful experience both in estimating the weight of the loads to be lifted, and in the use of the specific machine he is controlling and that he, on the basis of said experience is also capable of perceiving the danger premonitory signals, which are typical for that particular crane truck type. Devices have been developed at a later time, which are of electronic type. Such devices, which are particularly complex, expensive and delicate, are based on the principle of monitoring, by means of sensors installed at one or more suitably selected points on the crane truck structure, the value of the mechanical stresses generated by the lifted load, so as to be able to determine, at any time, the value of the overturning torque generated by the same load. The signals detected by the one or more sensors are processed by an on-board computer, which compares the value of the overturning torque generated by the lifted load, to the maximum allowed torque value for that crane truck. In case the value of the overturning torque becomes too similar to the value of the maximum allowed torque, the electronic device signals the danger condition, and stops the operation of the crane truck. The electronic devices, besides being (as already said) complex, delicate, and consequently expensive, are affected by the drawback that they give the operators a safety feeling, which is not always justified. In fact, the operators, aware of the fact that these devices automatically interrupt, with rapidity and precision, any dangerous operations, do not take very much care in evaluating the dynamics of the lifting. The lifting operation is carried out leaving to the electronic device only the task of supervising it, and of interrupting it in the event it becomes dangerous. But in case the device, owing to a large number of reasons, does not operate, or is affected by operating anomalies, the accident is practically immediate, unavoidable, and, most times, also with fatal consequences. Furthermore, often, both the above mentioned mechanical systems and electronic devices do not suitably exploit the lifting potential of the machine on which they are installed, due to a series of reasons, which we′ll illustrate very briefly, in that they are already well-known to those skilled in the art. As regards the mechanical systems, such a situation is clearly purposely wished, in order to secure a safety margin which is large enough for compensating for any possible inaccuracies in load situation evaluation. In case of electronic devices, the missed full exploitation of the power of the machine derives most times by the fact that owing to cost reasons only one type of electronic device is manufactured, with the individual devices being then adapted, with marginal modifications, to heavy-axle crane trucks, as well as to light-axle crane trucks. But, as well-known, inasmuch as the rear axle of the crane truck is in the opposite position relatively to the position of the lifted load, it has a major influence on the useful load the same crane truck can lift; not taking this fact into due account, is obviously to the detriment, according to cases, either of the machine (in case of a heavy-axle machine) or of the safety (in case of a light-axle machine). From FR-A-2 574 389 an overturning-preventing device of a mechanical type has become known, having the features of the preamble of claim 1. In this device, the elastic means are operatively interposed between the pivotally connected plate means and act in the sense of opening the same. The axis about which the plate means are pivoted extends transverse to the truck, i.e. parallel to the axis of the rear wheels. When the load conditions of the machine approach to the maximum admissible load conditions, the plate means open angularly owing to the interposed compressed elastic means which are no longer counteracted by a sufficient load, and this causes a safety device to intervene to stop operation. This known device is satisfactory only when used in trucks having light rear axle arrangements. In fact, the known device does not take advantage from the weight of the axle arrangement, which rather favours the aperture of the plate means to cause the intervention of the safety device. It would instead be advantageous, particularly in case of heavy axle arrangements, to exploit the weight thereof to increase the maximum load which can be handled by the machine without danger. The purpose of the present invention is to provide an overturning-preventing device which is capable of substantially obviating the shortcomings which derive from the use of the above mentioned overturning-preventing devices, without thereby giving up the relevant advantages. Such purpose is achieved by an overturning-preventing device having the features claimed in claim 1. The advantages deriving from the device according to the present invention are the following: safety in operation, simpleness and low cost of manufacturing, precision; possibility of suitably exploiting, with full safety, the maximum lifting potential offered by a whatever type of operating machine, whether it is a crane truck, or another type of machine, whether of the heavy-rear-axle or of the light-rear-axle type; possibility of adjusting the sensitivity of intervention of the device; possibility of predetermining, according to requirements, and by means of the same adjustment of the sensitivity of intervention, the minimum load to be transmitted by the axle to the ground before the device stops the operations of the crane; possibility of applying the device to double-wheel or single-wheel axles, whether of heavy or of light type. The invention is illustrated for merely illustrative, non-limitative purposes, in the figures of the hereto attached drawing sheets, wherein: Figure 1 shows a schematic side view of a crane truck equipped with a device according to the invention; Figure 2 shows a schematic rear view of the rear axle of a heavy-rear-axle crane truck, with said rear axle being equipped with an overturning-preventing device according to the present invention; Figure 3 shows a schematic view of the rear axle of Figure 2, wherein the overturning-preventing device is in the condition of interruption of the lifting operation; Figure 4 shows a schematic rear view of the rear axle of a heavy-rear-axle crane truck with single-wheel rear axle, with said rear axle being equipped with an overturning-preventing device according to the invention; Figure 5 shows a schematic view of the rear axle of Figure 4, wherein the overturning-preventing device is in the condition of interruption of the lifting operation; Figure 6 shows a schematic side view of the rear axle of Figures 4 and 5. Referring to the above cited figures, and in particular to Figures 1 through 3, the overturning-preventing device, generally indicated by the reference numeral 1, is part of a steering, driving rear axle arrangement 2 of a crane truck 3. The crane truck 3 comprises a crane 4, with a telescopic arm 5, constituting operating means borne by a self-propelled truck 6. The rear axle 2 comprises a wheel axle 8 with two wheels 7, a differential 9, a pair of vertical elements 10, the same overturning-preventing device 1, a hinge 11, with a respective rotation-limiting device 14, a steering unit 12, and a bearing-carrier sleeve 13 directly linked to the self-propelled truck 6. In the depicted case the vertical elements 10 are rigid, but they could be constituted as well by traditional leaf springs or spiral springs associated with shock absorbers in case the hinge 11 is replaced by a rigid link. The rotation-limiting device 14, which limits the rotation about the axis of the hinge 11, comprises a pair of horizontal arms 15 bearing adjusting screw means 16. The steering unit 12 comprises at least one hydraulic cylinder 18 rigid with the structure of the self-propelled truck 6 and acting by its piston on the rear axle arrangement 2 through at least one lever element 17 rigid with a shaft 19 protruding from the sleeve 13, and the axis of which coincides with the steering axis 25. The shaft 19 is linked through the hinge 11 to the overturning-preventing device 1. The overturning-preventing device 1 comprises a first plate means 20 and a second plate means 21, pivotally linked together along one of their edges by means of a hinge 22, the axis 26 of which is perpendicular to the revolution axis 27 of the wheels 7. As visible in the drawings, the plate means 20 is linked to the truck structure, whereas the plate means 21 is rigid with the axle arrangement 2. The edges of the plate means 20 and 21 opposite to the edges engaged by the hinge 22 are connected with means for discontinuing the operation of the crane 4, which are constituted by a switch 23 and a respective electrical circuit not shown in the figures, with these latter means being enabled by the rotation of the first plate means 20 and of the second plate means 21 relatively to each other about the hinge 22. The rotation of the plate means 20 and 21 about the axis of the hinge 22 is limited by a bridge element 24 which, in case of need, is capable of supporting the weight of the wheel axle 8, of the wheels 7, of the vertical elements 10, and, obviously, of the second plate means 21. The overturning-preventing device 1 operates associated with means 28 for adjusting the minimum load transmitted by the axle to the ground, i.e. for properly exploiting the weight of the axle arrangement. The means 28 are particularly suitable for application to heavy axles, wherein the weight of the axle is exploited as extensively as possible, of course within the safety limits, in order to generate a torque opposing the overturning torque. The means 28 comprises a fulcrum 29, integral with either one of the vertical elements 10, possibly through a connecting rod 30, a lever 31 having one end pivoted at the fulcrum 29 and the other end connected to an elastic means in form of an adjustable-pre-load spring 32, and a flange 33 rigid with the first plate means 20 and pivotally connected with the lever 31. The configuration taken by the means 28 is the configuration of a third class lever, wherein the power force derives from the flange 33, the resistance force is constituted by the adjustable-pre-load spring 32, and the fulcrum is in 29, wherein the spring 32 and the fulcrum 29 are respectively connected to members rigid with the plate means 21 and the spring 32 acts in the sense opposing angular aperture of the plate means 20 and 21. Advantageously, the point of connection of the flange 33 with the lever 31 has a distance from the fulcrum which is shorter than the distance from the lever end to which the spring 32 is connected. During the lifting operations carried out by the crane 4, the overturning torque generates on the rear axle 2 a force F, vertically directed from bottom to top, which causes the first plate means 20 to separate from the second plate means 21, due to the effect of the rotation of the same plate means about the axis 26 of the hinge 22. Such a separation causes the means which command the interruption of the operation of the crane 4, constituted by the switch 23 and the relevant circuit, to operate on reaching an angular aperture between the plate means 20 and 21 exceeding a safety angular aperture. The load-adjustment means 28 act, by using the weight of the wheel axle 8, in the sense of preventing the plate means 20 and 21 from separating from each other, for values of the force F which are smaller than a certain threshold limit, which is a function of the pre-load given to the spring 32, which anyway can never be such as to allow the axle 8 with its wheels 7 to lift completely from the ground, with the practical exclusion of the device 1. When the intensity of the force F exceeds the threshold limit - which is a function of the pre-load given to the spring 32 (adjustable by screw means as shown in the drawings) -, the elasticity of the same spring allows the lever 31 to rotate relatively to the fulcrum 29, and the plate means 20 and 21 to consequently rotate relatively to the axis 26 of the hinge 22, with the consequent tripping of the switch 23. It is important to observe that, in order that the overturning-preventing device 1 may operate correctly, it is necessary that the axis 26 of the hinge 22 is always perpendicular to the revolution axis 27 of the wheels 7, in the case that a driving torque is applied to the wheels. Should it be not so, the reaction torque, deriving from the driving torque transmitted to the ground by the same wheels, would tend to disturb the correct operation of the overturning-preventing device 1, in that it would add to those torques which act on the same device, by increasing or decreasing the level of intervention of said device, according to the direction of revolution of the same driving torque. The overturning-preventing device 1 can be also used on single-wheel-axle crane trucks, whether of light, or of heavy type, as shown in Figures 4 to 6. For the sake of simplicity, in said Figures 4 to 6, the elements equal to such elements as illustrated in the preceding Figures 1 through 3 are marked by the same reference numerals. The single-wheel axle arrangement 37, whether of light or of heavy type, is conventionally associated with a drive unit comprising a motor means 38 and a transmission 39 acting on the single rear wheel 7. The overturning-preventing device 1 of the embodiment of Figures 4 to 6 is disposed opposite to that of the embodiment of Figures 2 and 3, i.e. with the flange 33 rigid with the plate means 21 which is rigid with the axle arrangement 37 and with the fulcrum 29 and the spring 32 connected to members rigid with the plate means 20 which is liked to the truck structure. The overturning-preventing device 1 can be finally also applied to lift trucks, in this case too the risk being avoided that said lift trucks may overturn owing to wrong lifting operations.

Claims: Overturning-preventing device in a crane truck (3) or a similar machine, composed of a self-propelled truck (6) which supports operating means (5), wherein the truck (6) comprises a rear axle arrangement (2,37) constrained to the truck (6) and having one or two wheels (7) on a wheel axle (8), the device (1) comprising two plate means (20,21) pivotally connected to each other, one of said plate means (20,21) being rigid with the axle arrangement (2,37) and the other of said plate means (20,21) being linked to the truck structure, elastic means (32) acting on said plate means (20,21), and means (23) for discontinuing operation of the crane (4) or the operating means (5) on reaching an angular aperture between said pivotally connected plate means (20, 21) exceeding a safety angular aperture, characterised in that the pivot axis (26) of said plate means (20,21) is perpendicular to the wheel axis (27) and in that a lever system is provided between said elastic means (32) and said plate means (20,21), the lever system comprising a flange (33) rigid with one of said plate means (20,21) and a lever (31) pivotally connected with said flange (33) and having ends respectively connected by a fulcrum (29) and by said elastic means (32) to members (10,30) rigid with the other of said plate means (20,21), the elastic means (32) acting in the sense opposing angular aperture of said plate means (20, 21). Overturning-preventing device according to claim 1, characterised in that said flange (33) is rigid with the plate means (20) linked to the truck structure and said fulcrum (29) and said elastic means (32) are connected to respective vertical elements (10) of a two-wheel axle arrangement (2) (Figs.2 and 3). Overturning-preventing device according to claim 1, characterised in that said flange (33) is rigid with the plate means (21) rigid with the axle arrangement (37) and said fulcrum (29) and said elastic means (32) are connected to members rigid with the plate means (20) linked to the truck structure, said axle arrangement (37) comprising a single wheel (Figs.4 to 6). Overturning-preventing device according to one of the preceding claims, characterised in that the point of connection of the flange (33) with the lever (31) has a distance from the fulcrum (29) which is shorter than the distance from the lever end to which said elastic means (32) are connected. Overturning-preventing device according to one of the preceding claims, characterised in that screw means are provided for adjusting the pre-load of said elastic means (32).

Inventors: MASO, ROBERTO
Applicants: VALLA S.P.A.
Application year: 1988
Main classification: B66C23
IPC codes: B66F17, B66C23