Driving mechanism with energy storing feed system, particularly for the loading-travelling movements of portal cranes

Abstract

 A driving mechanism with energy storing feed system particularlyforthe loading-travelling motions of portal cranes having a hydraulic motor (3) in driving connection with an element (1) to be driven, a hydraulic supply unit (2) for operation of the hydraulic motor, the hydraulic supply unit being arranged to drive the motor (3) in synchronous operation with a hydraulic reversing unit (4) which is also in driving connection with the element (1) to be driven, and an energy storing unit (5) provided with a charger (6) in functional connection with the hydraulic reversing unit. The arrangement ensures that the energy necessary forthe driving mechanism to drive the element with direct energy input, also uses reserve power in the energy storing unit (5) derived from braking energy, this being transmitted through the separate reversing unit (4) when accelerating extra energy is required.
With use of the invention the amount of energy demand necessary for the operation of cranes can be reduced by over 50 per cent. The generally known energy saving expectations are met in an extremely high degree with the solution.

Description

[0001] The invention relates to a driving mechanism with energy storing feed system, suitable to carry out loading-travelling motions of portal cranes with extremely favourable energy requirements, and by means of which these tasks can be carried out at a considerably reduced energy utilization as compared with known mechanisms.

[0002] It is characteristic to our age, that the accelerated development and the participation in international division of labour significantly has increased the traffic of goods both by land and water. The development trend has required the handling of ever increasing unit weights of the goods, in the fast growing traffic of materials and goods arising partly from the labour shortage and partly from the effort of saving of loading time, for which purpose the 20 feet X 40 feet container traffic was developed (1 foot = 0.3048 m).

[0003] All these factors set off significant change in methods and means of material handling. As a result of the changes, faster moving crane types with higher load bearing capacity were developed and put into use in the goods receiving ports and terminals. Some of these cranes which meet the new demands were mobile, while others employ the fixed-track system. Installation of the latter type was due to the additional demand, whereby the development of the already highly energy-intensive loading equipment and capacity growth further increased the need even in the field of energy demand, and the goods receiving, and transfer terminals were forced to additional energy expansion wherever it was possible. Where the development for energy expansion was not possible, introduction of the much less favourable restriction on goods receipts was necessary, leading to diminished traffic in the ports and goods receiving terminals because of the incapacity to receive the goods in excess of the capacity of the loading equipment.

[0004] The realisation of this development trend suffered a new significant setback as a result of the worldwide energy shortage and price increases. All these facts and the goal of meeting the demands directed attention to the analysis of the crane and loading equipment and to the exploration of the existing reserves therein.

[0005] It is known that the existing increased demands are realized by the ports and good receiving terminals with the use of higher capacity, electric powered frame-, bridge-, container-cranes with the concomitant strengthening and expansion of the power network, loading space and crane track system, as well as by ensuring the extra electric power demands. A practice has been developed as further solution, whereby new mobile loading equipment was introduced for receiving the goods in the ports, where the network expansion and installation possibility were not feasible.

[0006] Both solutions require costly investment and substantially increased operating cost.

[0007] As a further development the most expedient and feasible way was found of making the crane operations more economical. These objectives formed the basis of analysing the economic efficiency of the crane operation. In connection with this it is known, that the rotary quay cranes have characteristically four main motions, such as: lifting-lowering, rotary, derricking and travelling motions.

[0008] The lifting-lowering and the rotary motions function regularly in each work cycle, the derricking motion not always, while the travelling motion is occasional, the demand for which is determined by the existing loading technology characteristics of portal cranes.

[0009] The parameters of the described loading and travelling activities are connected with and characterized in that the accelerating motion, the motion of constant velocity and the decelerating motion occur nearly for the same length of time in each phase of movement. On the basis of the frequency, the rotary and derricking motions of the crane usually do not even reach the rated velocity, the acceleration motion-phase passing directly into the braking phase of motion. This means that in the design of cranes, determination of the capacity requirement and dimension, are considered in relation to accelerating and braking in order that these may be achieved within a short time. As a result, the motors and brakes of the driving mechanisms are much more powerful and require much more energy, than they would be if only constant velocity were the objective.

[0010] The foregoing leads to the fact, that a major part of the substantial energy provided for the acceleration phase is consumed during the intensive braking phase. These braking functions and the concomitant energy consumption have been solved with various methods including simple mechanical brakes and system, or eddy-current type braking solutions and methods. However, these have the common property that the braking energy will be lost in one way or another in every case. Thus this kind of consumption of the energy required for movement represents a significant loss or source of loss during crane operation. However, an even greater problem than the loss of energy and excess cost is represented by the technical selection and solution of the method of consumption. And this problem is increasing with high-capacity cranes being put into service, thus efforts are being made for the effective solution of this problem with novel braking mechanisms, e.g. with twin-disc brakes, combined electrical and mechanical brakes involving the additional drawback that both the production of the brake systems and their operation and maintenance entail substantial extra cost.

[0011] It is already known today, that loading capacity demand of operating cranes reached the limit, when the braking energy of the rotary motion can be practically no longer consumed.

[0012] The appearance of recent crane constructions was based on this situation. Such is the marine-type container crane, where the rotary motion of the load is substituted by another motion and by auxiliary machines moving on the wharf - such as container-loading machines. The price of these new loading apparatuses is about 2 to 2.5 times higher than that of the classical portal crane, which would be capable of yielding the same loading capacity, provided that the acceleration and braking of the rotary motion within adequately short time were technically possible.

[0013] It is similarly known, that increased capacity demand of the crane operations entailed also weight increase of the gripping apparatuses of the goods to be loaded. It is also known, that the gripping apparatuses have to be moved often in unloaded condition in order to meet the loading technology. In this case the decisive part of the lifting capacity and braking energy is aimed at moving a non-active load, since it is well known that, for instance with a bucket crane, the dead weight of the crane bucket and the payload, the grabbed material, appear nearly in the same proportion in respect of the effective load applied on the cables.

[0014] All these facts indicate that the drawback of the practice evolved in the course of present development appear in extra energy demand necessary for acceleration of the motions, in the loss of energy absorbed during braking, in the technical consumption of this energy and in their insolubility. When attempt is made to express the described drawbacks numerically, then taking into consideration a given portal crane capacity, separating the phases of constant velocity from the accelerating- decelerating phases, the following ratios are arrived at:

The capacity demand pertaining to the constant velocity with max. load and jib radius: N = xLE. The built- in capacity N = llxLE. The acceleration peak capacity: N = 50 x LE.

[0015] In view of above it is apparent that the greater part of the energy input is necessary for the acceleration of the masses in time, which energy during the next few seconds will have to be consumed on the brakes.

[0016] The invention has for its object to provide a driving mechanism with which, in given and known conditions, the energy demand of a crane is less than that in known mechanisms. Thus operation can be ensured with significant saving of electric power, and the material handling capacity of the cranes and/or goodsreceiving terminals can be increased without new network development and without the demand for extra energy. A further object is to allow operation of larger cranes at the same cost level. Again a further object is to provide a simpler and finer speed control in the operation of a crane, to reduce the weight of the structural elements, and to improve significantly the value of cos . The system is also to'be structurally simplified.

[0017] According to the invention there is provided a drive mechanism with energy storing feed system, particularly for carrying out loading and travelling motions of portal cranes, characterized in that the driving mechanism has a hydraulic supply unit (2) arranged to drive a hydraulic motor (3) in driving connection with an element (1) to be driven, the hydraulic supply unit (2) being arranged to drive the hydraulic motor in synchronous operation with a hydraulic reversing unit (4), which is also in driving connection with the element (1) to be driven, and an energy storing unit (5) provided with a charger (6) in functional connection with the hydraulic reversing unit (4).

[0018] The invention is thus based on the recognition that the described advantages and objectives can be realized with such a system which is capable of storing the braking energy adequately during the braking phase, and to feed back the same energy in the following acceleration phase, with at negligible loss, into the system to assist such acceleration. The recognition was based also on the fact, that several such stable structural masses can be found in the crane which may serve as means for storing the energy.

[0019] The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a diagrammatic arrangement of driving mechanism in accordance with the invention.

Figure 2 shows a rotating mechanism of a crane

Figure 3 shows an application in gripping operation mode and

Figure 4 is a diagrammatic view showing the application of the invention on a lifting mechanism of a multi-load bearing portal crane.

[0020] In the figures a hydraulic motor 3 is shown in functional connection with a hydraulic supply unit 2. The motor 3 is drivingly connected with a element 1 to be driven. There is also a hydraulic reversing unit 4 in driving connection with the element 1 to be driven and this reversing unit 4 is coupled for synchronous operation with the hydraulic motor 3. An energy storiny unit 5 provided, with a charger 6. This is in functional connection with a stationary counterweight block 7 and/or an oil-air cataract type storage tank 8.

[0021] The structural units of the driving mechanism according to Figure 1 are connected to each other in such a way, that when brought into motion with the driven element 1, the hydraulic supply unit 2 starts the hydraulic motor 3, which is in driving connection with the element 1 to be driven. At the same time the reversing unit 4 starts and the energy for which is supplied by the energy storing unit 5.

[0022] Thus the driven element 1 receives starting power from two sides, partly from the hydraulic motor 3 and partly from the reversing unit 4.

[0023] In the course of further operation of the mechanism, the reversing unit 4 functions, during bracing not as a driving unit, but as a braking motor transmitting. the energy into the energy storing unit, while making use of the braking energy transmitted into the energy storing unit 5, for instance to shift the counterweight block 7, the opposite movement of which is capable of providing the extra energy, through the reversing unit 4, necessary for acceleration, as described.

[0024] The charger 6 built into the energy storing unit supplies the first charge and renews the loss during operation.

[0025] The driving mechanism, depending on the capacity and demand, may consist of one or several hydraulic supply units 2, one or several hydraulic motors 3, one or several reversing units 4, which are in functional connection with the element 1 to be driven.

[0026] Switching the mechanism on and off can be carried cut by conventional automatic means. In the case of a lifting mechanise) an overload inhibiting device 9 shown in Figure 4 sensing the force capability may be provided. Such a means may sense the force acting on the cable of the lifting mechanism to switch on or off, for acceleration or deceleration, the hydraulic motors 3 and reversing units 4. In this case an economic apparatus can be developed-in the lifting mechanism of a crane, where various load bearings and pertaining speed demands exist.

[0027] The energy storing unit 5 may be for instance a hydraulic storing cylinder. The weight 7 carried on it, may also be the stabilizing counterweight of the crane. Alternatively it may be the rotary part of the crane itself, provided that, in this case, the hydraulic cylinder is built in between the thrust bearing of the crane and its tower. One arrangement of rotating mechanism is shown in Figure 2.

[0028] Figure 3 shows the arrangement as applied to the lifting mechanism of a crane and Figure 4 shows a similar system in a multiple load bearing portal crane. This figure also shows an oil-air cataract type storage tank 8 serving as the energy storing unit. It is possible to employ such a storage tank arrangement with a counterweight arrangement in combination, to serve as the energy storing unit. unit.

[0029] The energy storing unit 5 and hydraulic supply unit 2 are not necessarily arranged on the rotary part of the crane. For instance in case of floating cranes they can be arranged on the floating bridge, if in this way, the height of the centre of gravity of the floating crane can be favourably improved, In this case hydraulic conduits may be conducted through the centre of the thrust bearing with hydraulic connections ensuring the conventional degree of rotational freedom. Naturally these are unnecessary if the floating crane is of non-rotary typs and the principle is applied to the lifting mechanism or to the jib motion.

[0030] The driving mechanism thus described is suitable for realization of the objectives and is capable of meeting known development requirements by ensuring energy saving with so far unknown efficiency compared with the solutions existing up to now.

Claims

1. A driving mechanism with energy storing feed system, particularly for carrying out loading and travelling motions of portal cranes, characterized in that the driving mechanism has a hydraulic supply unit (2) arranged to drive a hydraulic motor (3) in driving connection with an element (l) to be driven, the hydraulic supply unit (2) being arranged to drive the hydraulic motor in synchronous operation with a hydraulic reversing unit (4), which is also in driving connection with the element (l) to be driven, and an energy storing unit (5) provided with a charger (6) in functional connection with the hydraulic reversing unit (4).

2. Apparatus as claimed in Claim 1, characterized in that the energy storing unit (5) has a functionally connected counterweight block (7) and/or an oil-air cataract-type storage tank (8).

Drawing