LIFTING GEAR, AND METHOD FOR ADJUSTING THE BOOM OF SUCH A LIFTING GEAR

Abstract

A lifting gear, in particular a telescopic boom crane, including at least one boom, a boom adjustment unit including at least one hydraulic actuator for adjusting the boom, and a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having at least one pump for adjusting the hydraulic actuator.

Claims

1. A lifting gear comprising: a boom; a boom adjustment unit comprising at least one hydraulic actuator for adjusting the boom; and a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having a first pump for adjusting the hydraulic actuator.

2. The lifting gear according to claim 1, wherein the boom adjustment unit is free of throttle valves and brake valves, and speed-controlled.

3. The lifting gear according to claim 1, wherein the control device comprises a lowering brake mode; and wherein in the lowering brake mode, the hydraulic actuator is motion-controlled by means of the displacement controller.

4. The lifting gear according to claim 1, wherein the first pump connects two pressure chambers acting in opposite directions of the hydraulic actuator with each other and circulates pressure medium from one pressure chamber into the other pressure chamber.

5. The lifting gear according to claim 4, wherein the hydraulic actuator comprises a synchronous cylinder with equal pressure chamber cross-sectional areas or has a pair of differential cylinders arranged in opposition, the oscillating volumes of which at least approximately compensate each other.

6. The lifting gear according to claim 4 further comprising a second pump connected on the one hand to one of the pressure chambers and on the other hand to a tank; wherein the first and second pumps have displacement volumes whose ratio corresponds at least approximately to the cross-sectional area ratio of the pressure chambers of the hydraulic actuator.

7. The lifting gear according to 1 further comprising a second pump; wherein the first pump is connected to a pressure chambers of the hydraulic actuator and to a tank; wherein the second pump is connected to another pressure chamber of the hydraulic actuator acting in the opposite direction and to the tank; and wherein the first and second pumps have displacement volumes whose ratio corresponds at least approximately to the cross-sectional area ratio of the pressure chambers of the hydraulic actuator.

8. The lifting gear according to claim 1, wherein the first pump is configured as a pump selected from the group consisting of a fixed displacement pump with a variable speed drive and a variable displacement pump with an adjustable displacement volume.

9. (canceled)

10. The lifting gear according to claim 6, wherein a synchronization stage is provided for synchronizing the drive speed or synchronizing the displacement volume adjustment between the first and second pumps.

11. The lifting gear according to claim 1 further comprising a flushing arrangement and/or a feeding arrangement for compensating for excess quantities and/or sub-quantities occurring during circulation of pressure medium between pressure chambers acting in opposite directions of the hydraulic actuator.

12. The lifting gear according to claim 11, wherein the flushing arrangement and/or the feeding arrangement comprises a flushing valve for flushing excess quantities of the pressure medium occurring during displacement control of the hydraulic actuator into a tank.

13. The lifting gear according to claim 12, wherein the flushing valve flushes pressure medium into the tank on the low-pressure side of the hydraulic actuator.

14. The lifting gear according to claim 11, wherein the flushing arrangement and/or the feeding arrangement comprises a feed pump for feeding sub-quantities of the pressure medium occurring during displacement control of the hydraulic actuator.

15. The lifting gear according to claim 14, wherein the feed pump feeds the pressure medium on the low-pressure side of the hydraulic actuator.

16. The lifting gear according to claim 14, wherein a hydraulic circuit portion into which the feed pump feeds the pressure medium is connected to a tank via a pressure limiting valve.

17. The lifting gear according to claim 1 further comprising a check valve arrangement between the first pump and the hydraulic actuator for shutting off the inflows and/or outflows of the hydraulic actuator and thus locking the hydraulic actuator.

18. The lifting gear according to claim 17, wherein the check valve arrangement comprises two check valves provided for shutting off the inflows and outflows of the hydraulic actuator.

19. The lifting gear according to claim 18, wherein the check valves are hydraulically operated under pilot control; wherein the pilot pressure of the check valves is limited by a pressure limiting valve in such a way that when a predetermined pressure is reached in the hydraulic actuator, the pilot pressure is frozen and/or limited.

20. A method for controlling a lifting gear having a boom adjustable by a hydraulic actuator comprising: motion-controlling and/or speed-controlling the hydraulic actuator by a displacement controller.

21. The method according to claim 20 further comprising: speed-controlling lowering and/or luffing and/or retracting the boom without brake valves only by the displacement controller.

Description

[0032] The invention will be explained in more detail in the following with respect to preferred embodiments and to associated drawings. The drawings show:

[0033] FIG. 1: a side view of a revolving tower crane with a luffing boom that can be luffed up and down by a hydraulic actuator;

[0034] FIG. 2: a circuit diagram of the hydraulic system for actuating the hydraulic actuator with a displacement controller comprising two main pumps and a feed pump, and

[0035] FIG. 3: a circuit diagram of an alternative hydraulic system for displacement control of the hydraulic actuator, in which only one pump is provided, and a pressure accumulator compensates the oscillating volume.

[0036] As FIG. 1 shows, the lifting gear 1 can be configured as a tower revolving crane in the form of a so-called luffer, which comprises a boom 2 that is mounted on a tower 3 so that it can be luffed up and down. In this respect, the boom 3 can carry a ballast weight 4 on a counter boom portion.

[0037] Regardless thereof, the boom 2 can be luffed up and down by a hydraulic actuator 5, wherein the hydraulic actuator 5 can advantageously be configured as a hydraulic cylinder. It should be understood that more than one hydraulic actuator 5 can also be provided to be able to adjust the boom 2, for example in the form of a pair of double hydraulic cylinders. Regardless thereof, the hydraulic actuator 5 can be articulated on the tower 3 on the one hand and on the boom 2 on the other hand in order to be able to luff the boom 2 up and down relative to the tower about the horizontal luffing axis 6.

[0038] In this respect, the hydraulic actuator 5 is controlled by a control device 7, which, considered as a whole, may comprise hydraulic control components for controlling the pressure fluid flow and electrical or electronic control components for controlling the hydraulic components.

[0039] The control device 7 may, for example, comprise input means on a control station or remote control to be able to input an adjustment request for adjusting the boom 2, the input means may, for example, comprise a joystick or slide switch or a touch screen or other control command input means. The crane operator's input request is converted into control commands that adjust the hydraulic actuator 5 in order to adjust boom 2 according to the crane operator's request.

[0040] As FIG. 2 shows, the control device 7 comprises a displacement controller to move the hydraulic actuator 5 in a displacement-controlled manner.

[0041] The displacement controller 8 comprises at least a first pump 9, which connects the two pressure chambers 10 and 11 of the hydraulic actuator 5 acting in the opposite direction with each other and circulates pressure fluid from one pressure chamber 10 into the other pressure chamber 11 or vice versa from the pressure chamber 11 into the pressure chamber 10, thereby actuating the hydraulic actuator 5 in a displacement-controlled manner. Depending on the direction in which the displacement volume is circulated, the hydraulic cylinder extends or retracts.

[0042] As FIG. 2 shows, the displacement controller 8 may comprise a second pump 12 connected to one of the pressure chambers 10 and, on the other hand, to the tank 13 in order to discharge the pressure fluid from the chamber 10 into the tank 13 or, conversely, to supply the pressure medium from the tank into the pressure chamber 10. By means of the second pump 12, the quantity of pressure fluid caused by the piston rod of the hydraulic actuator 5 or, in general, its differential volume, which occurs due to the difference in cross-section of the pressure chamber 10 and 11 when the hydraulic actuator 5 is adjusted, can be replaced or discharged.

[0043] As FIG. 2 shows, the second pump 12 can advantageously be connected to the piston side or the larger pressure chamber 10 to supply additional pressure fluid on the piston side when the piston rod is to be extended.

[0044] Advantageously, the first pump 9 is configured to be resistant to high pressure on both sides. In the case of the second pump 12, it is sufficient if only one side or one of the two hydraulic working ports is configured to be resistant to high pressure, since the other hydraulic working port communicates only with the tank 13.

[0045] The two the pumps 9 and 12 can be configured as fixed displacement pumps with a variable speed drive, wherein advantageously a common pump drive 14 can be provided for both pumps 9 and 12 in order to drive the pumps 9 and 10 synchronously at the same speed or in a fixed speed ratio to each other. This also allows torque compensation via the shaft, which can reduce the drive torque.

[0046] Alternatively, each pump 9 and 12 can also have its own drive, for example in the form of a variable-speed controllable electric motor, wherein a synchronizing stage 15 can be provided, if necessary, in order to coordinate the speeds and thus the delivery rates of the pumps.

[0047] Advantageously, the two pumps 9 and 12 have displacement volumes the ratio of which corresponds at least approximately to the cross-sectional area ratio of the pressure chambers 10 and 11, acting in the opposite direction, of the hydraulic actuator 5.

[0048] As an alternative to fixed displacement pumps with variable speed drive, however, variable displacement pumps 9 and 12 can also be provided, the displacement volume of which is adjustable. Here, too, a synchronization stage can be provided which then adjusts the displacement volume synchronously or in a fixed ratio to one another. Such variable displacement pumps can then be operated with a constant speed drive, if necessary, although variable speed drives can also be provided for variable displacement pumps, if necessary.

[0049] As FIG. 2 further shows, a flushing arrangement and/or a feeding arrangement 16 can be provided to flush excess circulation accumulating during displacement control into the tank or to feed circulation shortages. In practice, there may be deviations in the displacement volume, for example due to the limited control quality of the variable displacement pumps or tolerances in the grading of the fixed displacement pumps, so that this does not correspond exactly to the cross-sectional area ratio of the pressure chambers 10 and 11. As a result, the quantity of the pressure fluid circulated back and forth between pressure chambers 10 and 11 does not correspond to the exact area ratio of the pressure chambers 10 and 11. As a result, a pressure increase, which can build up to a pressure limit, or a pressure drop, which can lead to cavitation, would occur in itself.

[0050] However, these undesirable consequences can be avoided by the flushing arrangement and/or feeding arrangement 16.

[0051] The flushing arrangement and/or feeding arrangement 16 can on the one hand comprise a flushing valve 17, via which advantageously an oil volume flow, in particular a constant oil volume flow, can be taken from the low-pressure side of the hydraulic circuit with which the hydraulic actuator 5 is operated and fed back into the tank, cf. FIG. 2. Here, cooling and/or filtering of the pressure medium fed back can take place and a corresponding cooling and/or filtering device can be provided.

[0052] The flushing arrangement and/or the feeding arrangement 16 may further comprise at least one feed pump 18, which may replace the oil quantity returning to the tank via the flushing valve 17. Regardless thereof, the feed pump 18 can also compensate for deviations in the volume flow ratio of the two the pumps 9 and 12, in that the feed pump 18 occasionally feeds in more or less pressure medium.

[0053] The feed pump 18 can advantageously feed pressure medium to the low pressure side of the hydraulic circuit, wherein, if necessary, via a valve arrangement 19, which can comprise, for example, check valves or directional valves, a feed can always be made to the low pressure side, irrespective of the direction in which the hydraulic actuator 5 is actuated or which side is the low pressure side.

[0054] In further development of the invention, the feed pump 18 can supply fluid to a pressure limiting valve 20, or pressure fluid supplied by the feed pump 18 can be supplied directly into the tank through the pressure limiting valve 20 after the corresponding pressure level is reached.

[0055] Since hydraulic pumps are generally not leak-free, a slow downward movement of the boom 12 can occur even when the pumps 9 and 12 are stopped or swiveled to the zero position, since the hydraulic actuator 5 is under corresponding pressure due to the weight of the boom 2.

[0056] In order to avoid such an unwanted downward movement as a result of a pump leakage, a check valve arrangement 21 can be provided by means of which the outflows and/or inflows of the hydraulic actuator 5 can be shut off. Such a check valve arrangement 21 may be provided, in particular, between the pumps 9 and 12 and the hydraulic actuator 5.

[0057] As FIG. 2 shows, the check valve arrangement 21 can advantageously comprise two check valves 22, 23 which can be opened and closed in a defined manner to hydraulically lock the hydraulic actuator 5.

[0058] The check valves 22, 23 may be hydraulically operated under pilot control, and the level of pilot pressure may be limited by a pressure limiting valve 24. This can ensure that the maximum permissible pressures in the hydraulic cylinder are not exceeded. In particular, the pilot pressure for the check valves 22, 23 can be limited by the pressure limiting valve 24 in such a way that the respective check valve 22 or 23 opens as soon as a critical or predetermined maximum pressure is reached in the hydraulic actuator 5.

[0059] As FIG. 3 shows, the displacement control system does not necessarily need several pumps as is the case with the design according to FIG. 2. In particular, the second pump 12 and the feed pump 18 can be dispensed with, wherein advantageously a hydraulic accumulator 25 can be provided, which can accommodate the oscillating volume of the hydraulic actuator 5, which can be configured as a differential cylinder, and advantageously hydraulically preload the low-pressure side of the hydraulic system.

[0060] If necessary, however, only the second pump 12 can be dispensed with, in particular if a synchronous cylinder is used as the hydraulic actuator 5 or a pair of differential cylinders arranged in opposite directions are used, so that the oscillating volume is at least approximately zero. In this case, the flushing arrangement and/or the feeding arrangement 16, in particular its flushing valve 17 and its feed pump 18, can suffice for the volume flow compensation that may still occur.

[0061] Other than shown in FIG. 2, a different connection or wiring of the two the pumps 9 and 12 can also be provided. For example, the first pump 9 may be connected to the pressure chamber of the hydraulic actuator 5 and the tank on one side, while the second pump 12 may be connected to the pressure chamber 11 of the hydraulic actuator 5 and the tank on the other side.

[0062] The displacement controller 8 can be used to adjust the boom 2, in particular, as follows: If a crane operator enters an adjustment request via the input device of the control device 7, in particular a desired speed for an up luffing or a down luffing of the boom 2, the control device 7 controls the at least one pump 9 in order to circulate a corresponding pressure medium volume. If first and second pumps 9 and 12 are provided, as shown in FIG. 2, the control device 7 controls both pumps 9 and 12 to produce a corresponding flow rate of both pumps. For this purpose, the control device 7 can directly adjust or control the swivel angle of the two pumps 9 and 12 or, in the case of fixed displacement pumps, adjust the speed of the drive shaft or the common pump drive 14 so that the desired volume flow is generated.

[0063] The speed of the hydraulic actuator 5 is proportional to the volume flow circulated by the two pumps 9 and 12. Due to the immediate adjustment and the omission of pressure-dependent controls such as a lowering brake, a fast response and precise control of the adjustment movement of the boom 2 can be achieved without any tendency to vibrate. At the same time, the system is characterized by higher energy efficiency, as in regard to the previous brake valve controls, losses at volume flow control valve edges are eliminated. This makes it possible to reduce the connected or drive power or to increase the travelable adjustment speeds of the boom 2. Furthermore, the general pressure level in the system can also be lowered, which reduces the demands on the components.