METHOD AND DEVICE FOR PREVENTING THE PUNCTURE OF A LOAD-SENSING AND PRESSURE-COMPENSATING CONTROL SYSTEM FOR A HYDRAULIC CRANE

Abstract: In a method for preventing the puncture of a load-sensing and pressure-compensating control system for a hydraulic crane when the hydraulic flow requested to the different functions of the crane exceeds the maximum hydraulic flow available, the values of control signals Q1-QN from a means for controlling the different crane functions are added up, and the resulting sum QP is compared with the maximum hydraulic flow Qmax available from a pump. Should the hydraulic flow requested by the control signals exceed the maximum hydraulic flow available, the control signals are scaled down so as to define a flow which falls below the maximum flow available, thus ensuring that a hydraulic flow is at all times supplied to all the crane functions. A device for implementing the method can take the shape of a program in a computer which receives the control signals from the control means and transmits output signals to a directional-control-valve block in the control system.

Description: METHOD AND DEVICE FOR PREVENTING THE PUNCTURE OF A LOAD-SENSING AND PRESSURE-COMPENSATING CONTROL SYSTEM FOR A HYDRAULIC CRANE The present invention relates to a method for pre¬ venting the puncture of a load-sensing and pressure-com¬ pensating control system for a hydraulic crane when the hydraulic flow requested to the different functions of th crane exceeds the maximum hydraulic flow available. The invention further concerns a device for implementing the metho . Fig. 1 illustrates a conventional hydraulic crane which includes a body 1, a first boom section 2 articu¬ lated to the body 1 , an outer boom 3 articulated to the first boom section 2, and an extension boom 4 fixed to th outer boom 3. The first boom section is operated by means of a hydraulic lifting cylinder 5, the outer boom 3 is operated by means of a hydraulic outer boom cylinder 6, and the extension boom 4 is operated by means of a hydraulic extension boom cylinder 7. The control.system for controlling the different crane functions (lifting/lowering by means of the lifting cylinder, tilting by means of the outer boom cylinder, and extending/retracting by means of the extension boom cylinder) comprises a pump 10 which pumps hydraulic fluid from a tank 9 to a directional-control-valve block 12 containing a directional-control-valve section for each of the cylinders 5-7, to which the hydraulic fluid is supplied in conventional manner as a function of the position of the slide member in each valve section. The directional-control-valve sections are remote-controlled by a control means 13 with one lever for each crane func¬ tion. The signals from the control means 13 are trans¬ mitted via a cable or a wireless connection to a micro- processor 16 which in turn controls the position of the slide members in the valve sections of the directional- control-valve block 12 as a function of the value of the respective control signal from the control means. In advanced cranes, the control system, or more pre¬ cisely the directional-control-valve block 12, can be load-sensing and pressure-compensating, which means that a certain lever position on the control means 13 produces a certain flow to the associated crane function, regard¬ less of the load on this function and regardless of the flow to and load on the remaining crane functions. However, this only applies as long as the sum of the hydraulic flows requested by the levers of the control means 13 to the different crane functions, is smaller than or equal to the maximum hydraulic flow that the pump 10 can provide. When the total hydraulic flow requested to the different crane functions exceeds that available from the pump, the flow is primarily directed to the crane function(s) with the lightest load. At worst, no hydraulic flow at all is supplied to the function(s) with the heaviest load, and these will then stop working. If this happens suddenly, there may arise violent jerks in the movements of the crane which are extremely unpleasant and even may lead to overloading of the crane. This phenomenon of one or more crane functions being deprived of flow is called puncture. The only prior-art solution to this problem consists in oversizing the pump so that the flow therefrom will at all times be sufficient, regardless of the operations indicated by the operator on the control means. However, such oversizing renders the crane control system more expensive and energy-intensive. In mobile systems, it may in addition be difficult to make room for large pumps. The object of the present invention is, therefore, t provide a method and a device which solve the above-men¬ tioned problem and make it possible to use pumps with lower maximum flow without risking a puncture of the con¬ trol system. This object is achieved by a method which is charac¬ terised by a) measuring the value of each control signal repre¬ senting a flow requested to a crane function; b) adding up the measured values of the control signals; and c) comparing the sum of the control-signal values with maximum-flow value representing the maximum hydrauli flow available and, should the sum exceed the maxi- mum-flow value, multiplying each control signal by a scale factor k., wherein i = 1, ...N, and k. <1, before supply to a respective means for controlling the hydraulic flow to a crane function, and, should the sum fall below the maximum-flow value, supplying each control signal unmodified to the respective means for controlling the hydraulic flow to a crane function. This ensures that a hydraulic flow is supplied to all the controlled crane functions, thus avoiding a puncture of the control system and eliminating the risk of over¬ loading. As recited in appended claim 2, step c) is preferably repeated after the scaling down. The scale factors may then be so chosen that there is only a slight scaling down, since there will be a renewed check on whether the sum is smaller than the maximum-flow value, so that the scaling down can be repeated if need be. The scale factors can be the same for all the func¬ tions or, as recited in appended claim 3, be different for different crane functions, so that certain functions may be prioritised. The invention also concerns a device for implementing the method, which shows the features recited in appended claim 5. The invention can be applied to hydraulic cranes with load-sensing and pressure-compensating control systems. The crane functions of such a crane may, for instance, include lifting/lowering the first boom section, tilting the outer boom, extending/retracting the extension boom, lifting/lowering the jib boom, and rotating the crane. An embodiment of the present invention will be described below with reference to the accompanying draw¬ ings, in which Fig. 1, which already has been described, illustrates a conventional hydraulic crane with associated con¬ trol system, and Fig. 2 is a flow chart for implementing the method. In order to avoid that a load-sensing and pressure- compensating crane control system of the type illustrated in Fig. 1 is punctured when the hydraulic flow requested by an operator to the different crane functions exceeds the maximum hydraulic flow available, the control signals from the control means are processed in the following manner (see the flow chart in Fig. 2). In a first step 20 is measured the value of each of the control signals Q--Q N representing a flow requested to a crane function and being transmitted from the control means 13 to the micro¬ processor 16. In the subsequent step 21, the thus-estab¬ lished values of the control signals Q-,-Q N are added up, which gives the sum Q . Then, the sum Q is, in step 22, compared with a maximum-flow value Q representing the maximum hydraulic flow available from the pump. Should the sum Q exceed the maximum-flow value Q max/ "the system would be punctured unless the control signals Q.-Q N were modified before being transmitted to the directional- control-valve block 12. To prevent such a puncture, each control signal Q. is, in step 23, multiplied by a scale factor k., wherein i = 1, ...N, which optionally may be the same for all the control signals. Thereafter, the control signals Q. are, in step 24, scaled down to q., and the adding up of step 21 and the comparison of step 22 are repeated. Should the sum Q for the requested hydraulic flow still exceed the maximum-flow value Qma , another scaling down of the control signals is performed. If, on the other hand, the sum Q is smaller than or equal to the tr maximum-flow value Qmax, the control signals are, in step 25, transmitted as they are to the respective directional- control-valve section in the directional-control-valve block 12. This program is repeated at suitable intervals, thereby avoiding a puncture of the system. It should also be pointed out that the control-signal value need not be measured directly after the control means 13, but may instead be measured by establishing the displacement of the slide member in the valve 12 caused by the signal. The thus-established values are returned to the microprocessor 16, whereupon the method is implemented in the manner described above. This variant may be used not only in remote-controlled systems, but also in hand- lever-controlled, load-sensing and pressure-compensating valves. Finally, it should be observed that, by using the flow chart in Fig. 2, the expert may easily implement the invention to take the shape of a program in the micro- processor 16.

Claims: CLAIMS 1. Method for preventing the puncture of a load- sensing and pressure-compensating control system for a hydraulic crane when the hydraulic flow requested to the different functions of the crane exceeds the maximum hydraulic flow available, c h a r a c t e r i s e d by a) establishing the value of each control signal Q ι -Q N representing a flow requested to a crane function; b) adding up the established values of the control signals Q,-Q N ; and c) comparing the sum Q of the control-signal values with a maximum-flow value Q_max representing ~ the maximum hydraulic flow available and, should the sum Q exceed the maximum-flow value Q max , mul¬ tiplying each control signal by a scale factor k. , wherein i = 1, ...N, and k. <1, before supply to a respective means (12) for controlling the flow to a crane function, and, should the sum fall below the maximum-flow value, supplying each control signal unmodified to the respective means (12) for controlling the flow to a crane function. 2. Method as claimed in claim 1, c h a r a c ¬ t e r i s e d by repeating step c) after the multipli¬ cation by the scale factors k.. 3. Method as claimed in claim 1 or 2, c h a r ¬ a c t e r i s e d by using scale factors k. with different values for the control signals to different crane functions. 4. Method as claimed in any one of the preceding claims, c h a r a c t e r i s e d by establishing the value of each control signal Q..-Q., by measuring the displacement caused by said signal of a control element provided in each means (12) for controlling the flow to a crane function. 5. Device for preventing the puncture of a load- sensing and pressure-compensating control system for a hydraulic crane, said control system comprising load- sensing and pressure-compensating valve means (12) for controlling the hydraulic flow to the different crane functions, and means (13) for controlling the valve means (12) by control signals, c h a r a c t e r i s e d by means for establishing the value of each control signal 0^-Q j ,, means for adding up the established values of the control signals Q,-Q N , means for comparing the sum Q of the measured values with a maximum-flow value Q_ ax representing the maximum hydraulic flow available, and means for multiplying the control signals by a scale factor k., wherein i = 1, ...N, and k. <1, should the sum Qp exceed the maximum-flow value Qmax 6. Device as claimed in claim 5, c h a r a c - t e r i s e d in that the means for establishing the control-signal values include means for establishing the displacement of a slide member in the valve means (12).

Inventors: ANDERSSON LARS, ANDERSSON, LARS
Applicants: HIAB AB
Application year: 1991
Main classification: B66C13
IPC codes: B66C13, G05D7