EP0603722B1 - Hydraulic control system - Google Patents

Abstract

In a hydraulic control system (V) for at least one hydraulic consumer (5, 6) of a mobile crane (K), which control system (V) has a directional control spool, connected on the one side to a pressure line (15) and a return line (16) and on the other side to two working lines (17, 18) to the hydraulic motor and having an adjustable spool piston (21), as well as a volume-reducing device (M) which can be brought into engagement as a function of a critical loading state and with which at least the volume of the hydraulic medium flowing to the hydraulic motor can be reduced, the directional control spool is designed as a proportional directional control spool (S1 to S8) with a feed-control pressure balance (Z) connected upstream in the pressure line (15a), and the volume-reducing device (M) is arranged constructionally separate from the spool piston (21) so that it engages between the feed-control pressure balance (Z) and the proportional directional control spool (S1 to S8) or on the feed-control pressure balance (Z) or on the spool piston (21). <IMAGE>

Description

The invention relates to a hydraulic control device of the type specified in the preamble of claim 1.

In a control device for mobile cranes known from DE-A-37 10 699, the inflow regulating pressure compensator regulates the amount allocated to the proportional directional control slide valve to such an extent that the hydraulic consumer stops when a load limit is reached. This is brought about by the response of a pressure limiting valve connecting the control line to the return line to the load pressure prevailing in the control line. Until this load limit is reached, the hydraulic consumer can be moved independently of the load at the speed selected by the setting of the slide piston, ie, if necessary at the maximum speed. Because of the maximum speed of the hydraulic consumer or the respective load that is possible until the load limit is reached, a relatively high safety factor must be taken into account for a mobile crane equipped with this control device, which greatly limits the permissible load and / or the range.

When calculating a mobile crane, due to the load movement or the movement of components of the hoist, a relatively large safety factor must be taken into account for safety reasons, which limits the load capacity and / or the range. The safety factor depends on the speed of movement. In order to achieve a higher load capacity and / or a longer reach in a mobile crane, the amount of hydraulic medium flowing to the hydraulic consumer and thus the speed of movement of the hydraulic motor are reduced in a hydraulic control device according to EP-B-0 340 235 depending on the load. The safety factor to be taken into account when calculating the hoist is then lower as soon as the critical load condition is reached due to the reduced speed. In the known control device, a throttle travel control slide is used, in which a load-independent speed control is not possible. The quantity reduction device is built into the spool of the throttle travel control spool and uses the load pressure of the hydraulic motor to reduce the inflow quantity via a bypass control for the return. Since the load pressure controls the reduction in quantity, no load holding valve can be used to hold the load. The full pump pressure is applied to the throttle valve on the respective pressure side. Since hydraulic medium is drained to the tank via the bypass control means this results in a high mechanical load on the hydraulic medium and an undesirable development of heat. Furthermore, the bypass control is unsuitable if a plurality of directional control slides arranged in parallel control hydraulic motors which can be loaded at different levels simultaneously. A particularly serious disadvantage results from the scanning of the load pressure to reduce the feed quantity if the load pressure does not represent a meaningful reference value in special operating conditions. For example, in the case of an articulated cylinder that is inclined downward, the load pressure when the load is being pulled may be too low to reduce the supply quantity in spite of a critical operating state in the hoist. Finally, the throttle travel control spool is extremely complicated, and expensive and prone to failure.

The invention has for its object to provide a hydraulic control device of the type mentioned, which is structurally simple, enables load-independent speed control of the hydraulic consumer, and in which the quantity reduction can be controlled very reliably.

The object is achieved according to the invention with the features specified in claim 1.

With this design, the proportional directional spool valve with the inlet control pressure compensator always ensures load-independent speed control of the hydraulic motor. Since the quantity-reducing device is arranged separately from the slide piston, it can advantageously be operated with a hydraulic or electrical or Control mechanical signal that meaningfully represents a critical load condition of the hoist. This increases the reliability of the quantity reducing device, because it does not have to respond to the load pressure tapped off on the spool if this is not meaningful enough. The hydraulic control device is structurally simple because it works with proven proportional directional spool valves and inlet regulating pressure compensators, which only require simple and inexpensive modifications, which can be retrofitted if necessary, for the quantity reduction function. The use of load holding valves, which is advantageous for safety reasons, is possible without restriction. The gripping range and / or the load capacity of the hoist can be increased because the speed of movement can be freely reduced in the critical loading state of the hoist. If the quantity-reducing device intervenes between the inlet control pressure compensator and the proportional travel spool, then the quantity of hydraulic medium flowing in upstream of the spool is reduced, without any bypass control for the return, which is disadvantageous for other parallel consumers. If the quantity reduction device attacks the inlet control pressure compensator, then the quantity supplied to the proportional directional control slide is correspondingly withdrawn in the inlet control pressure compensator. If the quantity reduction device finally engages directly on the slide piston, the slide piston is either reset to a lower speed setting or prevented from reaching a setting for an impermissibly high speed. In any case, a meaningful signal can be used to control the pressure reducing device, so that the quantity reducing device is at a critical level Load condition intervenes reliably even if there is no critical load condition on the hydraulic motor itself. The control device is particularly useful for mobile cranes, but can also be used for other lifting equipment such as forklifts or lift trucks, tail lifts, concrete pumping devices or even rail-bound and stationary cranes. In principle, modified accordingly, it can also be used to reduce the speed of hoists with load hooks and / or trolleys, even when moving with an electric motor.

The hydraulic consumers can be moved at the maximum speed as long as there is no critical load in the hoist. The speed is only reduced when the critical load condition is reached. Then a large load can be moved up to the long range with a lower movement speed. This leads to an increased gripping range and a higher permissible load of the hoist, with the load being moved at a reduced speed at high load in the gripping range gained.

In the embodiment according to claim 2, when the orifice is switched on, the pressure difference across the slide piston and thus the amount flowing to the hydraulic consumer are reduced. The aperture can be switched on in at least one step or continuously. The load pressure in the control line or the signal from another signal transmitter that represents a critical load state of the lifting device can serve as a signal for switching on the diaphragm. A 2/2-way switching or control valve is inexpensive and reliable and can also be retrofitted.

In the embodiment according to claim 3, the prestressing of the control spring of the inlet control pressure compensator is withdrawn to reduce the supply quantity. The inlet control pressure compensator reduces the amount of hydraulic medium flowing into the spool. You can work with a pressure signal in the control line or with an external signal to operate the servo actuator.

A structurally simple embodiment is evident from claim 4. Regardless of whether the signal is a pressure signal is in the control line or an externally generated signal, the servo actuator is fed from the pressure line, which always carries sufficient pressure.

A structurally simple embodiment emerges from claim 5. The secondary pressure relief valve responds as soon as the control pressure in the control line generates a pressure signal that represents the critical load condition. The secondary pressure relief valve allows hydraulic pressure medium to flow off to the return, whereby the amount of hydraulic medium allocated by the inlet control pressure compensator for the proportional directional control slide is correspondingly reduced. The orifice and / or the characteristic curve of the pressure relief valve, which is set even steeper by the orifice as desired, ensures that the supply control pressure compensator increases the quantity reduction as the quantity increases.

In the embodiment according to claim 6, the quantity reduction is controlled only in one direction of movement of the hydraulic consumer.

In the embodiment according to claim 7, pressure-independent leakage via the two-way controller is used in a particularly advantageous manner to reduce the amount. The quantity reduction can be controlled in only one direction of movement or in both directions of movement of the hydraulic consumer. This embodiment can also be implemented retrospectively in the case of conventional proportional directional control slide valve concepts. The pressure-independent quantity reduction can be modulated with a control valve.

In order that the quantity reduction is not canceled out again by a load fluctuation or a pressure wave arising in some other way, the embodiment according to claim 8 is advantageous. The increased switching hysteresis or the hydraulic self-holding compensates for brief interferences. It is possible to use a time relay so that, for example, the quantity can only be reduced after e.g. 0.2 seconds, but the quantity reduction is only canceled when the signal is longer than e.g. 0.7 seconds no longer occurs.

The embodiment according to claim 9 is advantageous because usually several hydraulic consumers that can be operated simultaneously and simultaneously can be controlled in one hoist. By linking the two-way controller via the switching valve and the common return line, the speed reduction is only controlled if necessary with the proportional directional control valve, which is responsible for reaching the critical load condition or for which the greatest leakage occurs via the Two-way controller occurs. The hydraulic self-retention of the switching valve or the adjustable switching hysteresis of the switching valve prevent the quantity reduction from swinging in and out.

In the structurally particularly simple embodiment according to claim 10, the slide piston is reset by the return servo drive from a setting position for a higher speed to a setting position for a reduced speed when a critical load condition occurs.

In the embodiment according to claim 11, the reset device either resets the spool from a setting position for a higher speed to a setting position for a low speed or limits the spool stroke.

In the embodiment according to claim 12, the signal for controlling the quantity reduction is derived hydraulically or electrically from the lifting or articulating cylinder or from a working line of the lifting or articulating cylinder, at a point at which a signal that is meaningful under all operating conditions can be tapped, the represents a critical load condition in the hoist.

In the embodiment according to claim 13, the signal transmitter can be arranged at any point within the structure of the hoist at which a signal that is meaningful under all circumstances can be determined. In the case of electronically scanned signal transmitters, the signal transmission to the quantity reduction device is particularly simple in terms of construction.

Fig. 1

ein Schema eines Mobilkrans,

Fig. 2

ein Schaubild,

Fig. 3

ein Blockschaltbild einer hydraulischen Steuervorrichtung mit sechs Alternativen Mengenreduzier-Vorrichtungen,

Fig. 4

ein Blockschaltbild einer hydraulischen Steuervorrichtung mit drei Proportionalwegesteuerschiebern, und

Fig. 5

ein Blockschaltbild einer weiteren Ausführungsform.

Embodiments of the subject matter of the invention are explained with the aid of the drawing. It shows:

Fig. 1

a scheme of a mobile crane,

Fig. 2

a graph,

Fig. 3

a block diagram of a hydraulic control device with six alternatives Quantity reduction devices,

Fig. 4

a block diagram of a hydraulic control device with three proportional directional spool, and

Fig. 5

a block diagram of another embodiment.

In the case of a hoist, for example a mobile crane K, according to FIG. 1, a swivel boom 2 is arranged on a mast 1 in a joint 14, from which a pivotable telescopic boom 3 extends with an extension part 3a, on which a gripper 4 (or a Load harness, a lifting fork, or the like. The swing arm 2 can be pivoted by means of a lifting cylinder 5. An articulated cylinder 6 is inserted between the telescopic boom 3 and the swivel boom 2. The extension part 3a can be extended and retracted with an extension cylinder 7. The cylinders 5, 6, 7 and the gripper 4 are driven by a hydraulic control device (not shown in FIG. 1). In the mobile crane K, several signal transmitters 8, 9, 10, 11, 12 are indicated as examples, although one signal transmitter is usually sufficient. The signal generator 8 senses the pressure in the push-out space of the lifting cylinder 5. The signal generator 9 senses the pressure in the push-out space of the articulated cylinder 6. The signal generator 10 is a shuttle valve which transmits the higher pressure in the lifting cylinder 5 or in the articulated cylinder 6 as signal Y. The signal Y can be a hydraulic pressure signal or be an electrical signal that is generated, for example via a pressure switch. The signal generator 11 is arranged at the pivot pin 13 of the lifting cylinder 5 on the mast 1 and is designed as a strain gauge or pressure sensor or similar electronically scannable element. The signal generator 12 is arranged at the joint 14 between the mast 1 and the swivel arm 2 and electronically scanned as a strain gauge or the like.

One or more signal generators are used to operate in the hydraulic control device V, e.g. 3 to control a quantity reduction device M. In FIG. 3, different embodiments of quantity-reducing devices are shown in six units separated by dash-dotted lines. 4 and 5 illustrate further possible variations for quantity reducing devices M.

At the core of each unit in FIG. 3 is a proportional travel control slide valve S1 to S6 with an associated inlet control pressure compensator Z for load-independent speed control. The hydraulic consumer controlled by the proportional travel control spool S1 to S6 (e.g. cylinders 5, 6, 7 in Fig. 1) moves independently of the load at a speed which is based solely on the adjustment of the proportional travel control spool. This is achieved in that the inlet control pressure compensator Z keeps the pressure drop set on the proportional travel control valve constant regardless of the load.

Each proportional travel control valve S1 to S6 is connected via a branch pressure line 15a to a common pressure line 15, in which the inlet control pressure compensator Z is arranged. A common return line 16 is connected via branch return lines 16a to all proportional directional control spools S1 to S6. Two working lines 17, 18 each lead from the proportional travel control spools S1 to S6 to the hydraulic motor. In the case of a hydraulic motor which can only be acted upon in one direction and adjustable in the opposite direction under load, only one working line 17 or 18 would be provided. The proportional travel control slides S1 to S6 shown in FIG. 3 have manual adjustment devices 19, with which a slide piston 21 can be adjusted from a zero position against a return spring device 20 into two control positions a and b. A control line 22 carrying the respective load pressure is connected to the control side of the inlet control pressure compensator Z. The control line 22 is connected via an orifice 23 to bleed lines 24a, 24b which can be connected to the working lines 17, 18 via the slide piston 21. A control line 25 connects the bleed lines 24a, 24b via a shuttle valve 26 to a common main control line 27, which leads to a control device of a constant pump or a control pump (not shown) for adjusting the pressure in the pressure line 15. A common return control line 28 is connected to a tank. A further control line 29 is subjected to a constant control pressure during operation of the control device, for example 25 bar.

In the inlet regulating pressure compensator Z, a regulating member 30 is continuously adjustable between a through position and a shut-off position. In the direction of the through position, the control element 30 is acted upon by the pressure in the control line 22 and by a control spring 31. In the opposite direction, the control element 30 via an auxiliary control line 32 with an orifice from the pressure in the pressure line 15a downstream of the inlet control pressure compensator Z.

The quantity reducing device M has for the proportional directional control valve S1, e.g. of the lifting cylinder 5 of FIG. 1, a control or switching valve 33 with a fixed or variable orifice 34, which can be activated when the signal Y occurs in the pressure line 15a. The control or switching valve 33 can be actuated by a magnet 35, to which the signal Y is supplied in electrical form. However, it is also possible to switch the control or switching valve 33 by means of a hydraulic pressure signal. In the zero position, the control line 22 can be relieved via an auxiliary return line 41 to the return line 16.

The aperture 34 is not effective during normal operation. The speed is determined by the setting position of the slide piston 21. The pressure difference across the spool 21 is kept constant by the inlet control pressure compensator. When signal Y occurs, the aperture 34 is switched on. This means a reduction in volume and thus a reduction in speed for the hydraulic consumer. The curve of FIG. 2 shows how (solid curve) the quantity Q increases over the stroke of the slide piston 21 without the orifice plate 34 being switched on. The dashed curve 20% means that only 20% of the original amount will flow in each point of the stroke of the slide piston 21 after the orifice 34 has been switched on. If, as indicated in FIG. 3 in the first unit, a control valve or a variable orifice 34 is used, then the orifice 34 can be switched on continuously and one for each Set the quantity curve adapted to the requirements, for example as indicated by the dot-dash line in FIG. 2 at "var".

For the second proportional travel control slide S2, the quantity reduction device M has a servo actuator 36 for the control spring 31 of the inlet control pressure compensator Z in order to reduce the preload of the control spring in order to reduce the quantity. A spring-loaded piston displaceable against a return spring is controlled with a switching valve 37 which is connected to the control line 28 via an auxiliary control line 38 and to the pressure line 15a via a further auxiliary control line 39. If the switching valve has a magnet 35, this is excited via the signal Y in order to remove the bias of the control spring 31. This can also be done continuously in one step. By reducing the spring preload, the control pressure difference becomes smaller and the quantity reduction in both working lines 17, 18 is the same in percentage terms. Another auxiliary control line 40 connects the pressure side of the spring-loaded piston to the outlet of the switching valve 37.

In the third proportional travel control slide S3, the quantity reducing device M is equipped with a secondary pressure limiting valve 43, which is arranged in an auxiliary control line 42 connected to the control line 22 to the return line 16a and is set to a pressure value in the control line 22 which represents a critical load state, for example in the hydraulic consumer . An orifice 44 is provided upstream of the secondary pressure relief valve 43. The secondary pressure relief valve 43 has - with or without an orifice 44 - a pressure characteristic curve that increases with an increasing flow rate, and thus from response with increasing load pressure an increasing amount flows through the valve 43. The quantity reducing device M acts in both directions of movement of the hydraulic consumer.

In the fourth proportional travel control spool S4, the quantity reduction device M is designed analogously to that of the third proportional travel control spool S3 and is equipped with a secondary pressure valve 43 and an upstream orifice 44 in the auxiliary control line 42 '. This quantity reduction device M is only effective in one direction of movement of the hydraulic motor, namely in the control position a of the proportional travel control spool S4. For this purpose, the auxiliary control line 42 'is guided through a passage 45 in the slide piston 21, which is only open in the control position a. This passage is blocked in the neutral position and in the control position b.

In the fifth proportional travel control spool S5, the quantity reduction device M works with pressure-independent leakage and only in one direction of movement. The auxiliary control line 42, which is led through the passage 45 in the spool 21 to a tank T, contains a two-way controller 46 to which a switching or control valve 47 is assigned, e.g. downstream, is. When signal Y occurs, the control or switching valve 47 is adjusted so that a pressure-independent leakage occurs via the two-way controller 46, which leads to a reduction in the quantity in the control position a of the spool 21.

In the sixth proportional directional control valve S6, two variants of the quantity reducing device M are indicated. In one variant, the slide piston 21, which is manually adjustable by means of the adjusting device 19, is a reset servo drive 48 is provided which engages via a valve 49 controllable with the signal Y. The valve 49 is connected to a tank control line 51 and, via a line 50, the control line 29 (which carries a constant pressure). As soon as the signal Y occurs, the reset servo drive is activated and the spool 21 is either pushed back from the previously selected setting or is prevented from any further adjustment at all. If the quantity reduction device is to work in both directions of movement, then two counter-acting return servo drives 48 are required.

If the spool 21 - as is often the case - is hydraulically or electro-hydraulically piloted (indicated at 61), e.g. Via an electromagnetic (magnet 54a) adjustable pressure reducing valve 54 in a control line 52, a further pressure reducing valve 56 can then be inserted into the control line 52, which is activated by the signal Y and reduces the pressure for adjusting the slide piston 21. The further pressure reducing valve 55 can be controlled either hydraulically or electromagnetically. In both variants it is ensured that the speed of the hydraulic motor is reduced from the occurrence of a signal Y or that the low speed is not exceeded.

4 shows three proportional directional control spools S5, S7 and S8. The first proportional travel control spool S5 corresponds to the proportional travel control spool S5 of FIG. 3, with the difference that an electro-hydraulic pilot control 61 is also provided, which is connected to the control line 29 and the control line 28 (to the tank). Any quantity reduction device M has in the auxiliary control line 42 to a common collective control line 57 a two-way controller 46 with a check valve 58, which is expediently spring-loaded and opens in the flow direction to the collective control line 57. With each proportional travel control spool S5, S7, S8, the quantity is reduced in both directions of movement when the quantity reduction device responds. In the collective control line 57 there is a switching valve 59 with an actuator 60, for example a switching magnet, which can be switched between a through position and a shut-off position. 4, the switching valve 59 is a 2/2-way switching valve or a magnetically lockable check valve 62. As soon as the signal Y occurs, the switching valve 59 is put into the open position. In the open position, a pressure-independent leak occurs via the two-way controller 46 of the proportional travel control spool S5, S7 or S8, which contributes to the critical load state, which leads to a reduction in the quantity because the respective inlet control pressure compensator Z now only allocates a reduced quantity.

The switching valve 59 is designed with an increased switching hysteresis so that pressure or load fluctuations occurring during the speed reduction or an unwanted change in the signal Y lead to the switching valve 59 being reset immediately. When actuated by means of an electrical signal Y, a time relay can be used which holds the signal for a pre-settable time period and does not cancel the quantity reduction until the signal change remains beyond the set time period.

In the hydraulic control device V according to FIG. 5 two proportional directional control spools S5 and S7 for the lifting cylinder 5 and the articulated cylinder 6 of a mobile crane are connected to the pressure and return line, to which further directional control spools, not shown, can also be connected. For the lowering movement of the lifting cylinder 5, a load holding valve 65 is provided in the working line 18, which can be opened from the working line 17. With the articulated cylinder 6, load holding valves are included in both working lines. The working line 18, to which the control line 64 is connected between the load holding valve 65 and the lifting cylinder 5, serves as the signal generator for the pressure signal Y. The quantity-reducing devices M of both proportional travel control spools S5, S7 are designed similarly to FIG. 4, ie the auxiliary control line 42 leads to the control line 57. In each auxiliary control line 42, a two-way controller 46 with an associated check valve 58 is provided. The two-way controller 46 enables pressure-independent leakage as soon as the switching valve 59 switches to passage when a signal Y occurs in the control line 64. The switching valve 59 can be a so-called snap holder or a valve 63 with hydraulic self-holding, which, for example, holds its respective position, for example when the pressure signal Y disappears, for a predetermined period of time. The check valves 58 prevent the pressure prevailing in the collective control line 57 from acting back into a control line 22 with a lower control pressure.

If the control pressure in the control line 64 (pressure signal Y) switches the switching valve 59 into the through position, then only the reduced amount is fed to the lifting cylinder 5, so that it moves at a reduced speed. However, the proportional directional control spool becomes S7 adjusted to move the articulated cylinder 6, then the amount fed to the articulated cylinder 6 is reduced due to the pressure-independent leakage via the two-way controller 46. If both proportional travel control spools S5, S7 are actuated, then only a slight reduced movement speed is permitted for both cylinders 5, 6 or only for that of the two cylinders which is responsible for the critical load condition.

The signal Y controlling the respective quantity reducing device M in the control devices V according to FIGS. 4 and 5 can also come from any of the signal transmitters indicated in FIG. 1 or also from another external signal transmitter not shown but meaningfully representing a critical load condition . The components of the quantity reducing devices M used in each case can either be integrated in the proportional directional control slide valve or can be provided on its housing or in the connection block which is usually provided. The proportional directional control spool can therefore also be retrofitted with regard to the speed reduction function. Basic modifications of the proportional directional spool are not necessary for this.

Claims (13)

1. Hydraulic control device (V) for at least one hydraulic user (5, 6) in a lifting gear (K), in particular in a mobile crane, having a proportional directional control valve (S1 to S8) which, on the one hand, is connected to a pressure line (15, 15a) and to a return line (16, 16a) and, on the other hand, to two working lines (17, 18) to the hydraulic user and has a valve piston (21), which can be adjusted by a manual or a pilot-controlled adjusting device, for speed control up to a predetermined maximum speed and for directional control of the hydraulic user (5, 6), and having a meter-in control compensator (Z) which is connected upstream of the proportional directional control valve (S1 to S8) in the pressure line (15a) and can be acted upon in the opening direction depending on the load pressure from a control line (22) and by a control spring (31) and, in contrast, in the closing direction from the pressure line (15a), it being possible for the speed of movement of the hydraulic user (5, 6) to be preselected independently of the load with the respective setting of the valve piston (21), characterized in that a quantity-reducing device (M) which is separate from the valve piston (21) in terms of construction is provided in the control device (V), in that the quantity-reducing device (M) can be moved, on account of a signal (Y) representing a load state of the lifting gear (A) which is critical owing to the preselected speed, into engagement which limits the quantity of the hydraulic medium flowing to the hydraulic user (5, 6) and thus solely reduces the preselected speed, and in that the quantity-reducing device (M) acts between the meter-in control compensator (Z) and the proportional directional control valve (S1) or on the meter-in control compensator (Z) of the proportional directional control valve (S2, S3, S4, S5, S7, S8) or on the valve piston (21) of the proportional directional control valve (S6) when the signal (Y) occurs.
2. Hydraulic control device according to Claim 1, characterized in that the quantity-reducing device (M) has an orifice plate (34), which can be connected, in the pressure line (15a) downstream of the meter-in control compensator (Z), preferably in a 2/2 directional switching valve or in a 2/2 directional control valve (33), and in that the connection of the orifice plate can be controlled, preferably in at least one stage or infinitely variably, by means of the signal (Y) of a signal transmitter (8, 9, 10, 11, 12) or in the control line (22).
3. Hydraulic control device according to Claim 1, characterized in that the quantity-reducing device (M) has a servo-adjusting drive (36) which changes the prestress of the control spring (31) of the meter-in control compensator (Z) and can be actuated by means of the signal (Y), preferably in at least one stage or infinitely variably.
4. Hydraulic control device according to Claim 3, characterized in that the servo-adjusting drive (36) has a spring-tension piston which can be hydraulically adjusted counter to the force of a restoring spring and whose actuation side can be connected selectively to the pressure line (15a) or the return line (16) via a 3/2 directional switching valve (37), and in that the 3/2 directional switching valve (37) can be controlled electromagnetically or hydraulically.
5. Hydraulic control device according to Claim 1, characterized in that the quantity-reducing device (M) has a secondary pressure-reducing valve (43) which is connected to the control line (22), is connected to the return line (16), and can be controlled to open by means of the signal (Y) in the control pressure line (22), in that an orifice plate (44) is provided in the control line (22) between the secondary pressure-reducing valve (43) and the meter-in control compensator (Z), and/or in that the secondary pressure-reducing valve (43) has a pressure characteristic which rises with an increasing throughflow quantity.
6. Hydraulic control device according to Claim 5, characterized in that the secondary pressure-reducing valve (43) is arranged with the orifice plate (44) in at least one auxiliary control line (42, 42') which branches off from the control line (22) of the meter-in control compensator (Z), and in that the auxiliary control line (42') is routed via the proportional directional control valve (S4) and can be switched in the latter only to a control position (a) of the valve piston (21) for passage.
7. Hydraulic control device according to Claim 1, characterized in that the quantity-reducing device (M) has a two-directional flow controller (46) which leads to the return line (16) and to which the control line (22) can be connected directly via an auxiliary control line (42) or via a passage (45) in the valve piston (21) which is only open in one control position of the proportional directional control valve (S5, S6, S7, S8), and in that, for the two-directional flow controller (46), a switching or control valve (47, 59) is provided, which can be controlled by the signal (Y) of a signal transmitter (64) or in the control line (22).
8. Hydraulic control device according to Claim 7, characterized in that the switching valve (47, 59, 63) is designed with an increased switching hysteresis or with hydraulic self-holding.
9. Hydraulic control device according to at least one of Claims 1 to 8, characterized in that a plurality of proportional directional control valves (S6 to S8) which are connected in parallel to the pressure line (15) and to the return line (16) are provided in the control device (V), each having a meter-in control compensator (Z), each having an auxiliary control line (42) which branches off from the control line (22) with a two-directional controller (46) and a nonreturn valve (58) which is arranged upstream or downstream of the latter and opens for return flow (T), in that the two-directional controllers (46) are connected to a common return collector line (57) to a tank (T), in that the return collector line (57) contains, ahead of the tank (T), a 4/2 directional switching valve (63) or a magnetic switching valve (62), and in that the said valve (63 or 62) can be actuated by means of the signal (Y).
10. Hydraulic control device according to Claim 1, characterized in that the quantity-reducing device (M) has at least one hydraulically or electrically controllable partial restoring servo drive (48) for the valve piston (21) which can be adjusted manually from a zero position counter to the force of a restoring spring.
11. Hydraulic control device according to Claim 1, characterized in that, for the valve piston (21) which can be adjusted hydraulically or electrohydraulically from a zero position counter to the force of a restoring spring, the quantity-reducing device (M) has at least one electrical or electrohydraulic restoring device (55) which returns the valve piston (21) in the direction of the zero position or reduces the setting pressure for the valve piston (21) when the signal (Y) occurs.
12. Hydraulic control device according to at least one of Claims 1 to 11, characterized in that the signal (Y) can be generated by means of a signal transmitter (8, 9, 10, 11, 12) which is a hydraulic or electrical pressure sensor in a lifting or pivoting cylinder (5, 6) or in a working line (18) of the lifting cylinder (5) or the pivoting cylinder (6) of the lifting gear designed as a mobile crane (K).
13. Hydraulic control device according to Claim 12, characterized in that the signal transmitter (11, 12) is an electronically scannable strain gauge or a pressure sensor in a joint (14), which provides significant information regarding a critical load state of the lifting gear or in an attachment point (13) within the lifting gear construction, e.g. in the attachment stalk of the lifting or pivoting cylinder (5, 6).

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