EP0897062A2 - Pressure control circuit for more than one hydraulic pump with a pressure averager - Google Patents

Abstract

The pressure regulating device (1) has at least one setting device (6a,b) for setting the displacement volume of the hydro-pumps (2a,b) and a hydraulic regulator (30,11a,b,19a,b,20a,b) controlling the setting devices, provided with a pressure equaliser (30) coupled to the working line pressures (P1,P2) and having a source (33) employing an electromagnet, providing an electrical signal representing the mean pressure.

Description

The invention relates to a control device for several in separate work lines promotional hydraulic pumps.

A control device according to the preamble of claim 1 gives from the EP 0 133 870 B1. From this document, a control device for several in separate working lines promoting hydraulic pumps known. The double hydraulic pumps are controlled by a control unit acting on a common adjustment device driven, which includes a power controller. Furthermore, a is in the control unit Diaphragm seal provided with the separate working lines of the two Hydraulic pumps is connected and from the prevailing in the separate working lines Working pressures generate an average working pressure. The average working pressure serves to control the adjustment device. Such a diaphragm seal goes in detail, for. B. from DE 34 07 827 C2. The diaphragm seal disclosed there comprises one in one Piston chamber displaceable stepped piston, being between the piston chamber and the Step pistons a first and a second control edge are formed. The first control edge is with a first pressure line and the second control edge with a second pressure line connected. Downstream of the control edges, annular grooves are provided, each over a check valve is connected to an outlet line. The stepped piston will both with the inlet pressures present in the inlet lines and with the Existing outlet pressure applied in the outlet line. This results in one such adjustment of the stepped piston within the piston chamber that at the A mean pressure is applied to the outlet line.

A disadvantage of the known control device, however, is that a change in Overall control characteristic, in particular that specified by the power controller Total output of the two double pumps is not easily achieved by a control signal is changeable. This is desirable in practice because of the different operating states require different operating performance of the hydraulic pumps. When changing the Operating states should be between different performance limits as quickly as possible can be switched. This problem arises not only in the EP 0 133 820 B1 known power controller, but also in other control devices for several hydraulic pumps conveying in separate working lines, e.g. B. in a pressure control device or a torque control device.

The invention is therefore based on the object of one control device for several to specify separate work lines promoting hydraulic pumps, which a fast Switching of the control characteristic enables.

The object is in connection with the characterizing features of claim 1 solves with the generic features.

The invention is based on the finding that by changing the outlet pressure of the diaphragm seal a particularly efficient change in the control characteristics of the Control device can be achieved. According to the invention is at the diaphragm seal Provided encoder that acts on the diaphragm seal so that the diaphragm seal generated average working pressure not only from those prevailing in the work lines individual working pressures, but also from one acting on the encoder Is dependent on the encoder signal.

Claims 2 to 11 contain advantageous developments of the invention.

The diaphragm seal can have a valve piston according to claim 2, wherein the Encoder elastically acts on the valve piston via a first diaphragm seal spring. By the additional force exerted by the transmitter on the valve piston becomes one Encoder signal proportional adjustment of the valve piston and thereby the Output pressure of the diaphragm seal depending on the sensor signal and still in Dependence on the working pressures of those connected to the pressure medium Working lines vary. According to claim 3, a second can on the valve piston Attack diaphragm seal that opposes the valve piston to the sender acted on, so that the valve piston by the two diaphragm seals in his Piston housing is centered. The preload is at least one of the diaphragm seals advantageously adjustable according to claim 4 to fine-tune the To enable diaphragm seals. According to claim 5, the donor Electromagnet and the encoder signal thus be an electrical signal. The electromagnet ensures a quick response of the diaphragm seal and thus the control device to the electrical encoder signal.

The control device according to the invention has particular advantages if everyone Hydraulic pump according to claim 6 each have a separate adjusting device is assigned and each adjustment device is controlled by the diaphragm seal. Here Two conventional valve units can be used, as is usually the case with Single hydraulic pumps can be used. For a double hydraulic pump or multiple hydraulic pump therefore no special valve units are to be constructed or manufacture, which significantly reduces the cost. However, it is necessary that To control valve units together by means of a uniform control signal, and via this common control signal uniformly the control characteristics of both control units to change. If the valve units e.g. B. work as a power controller can by averaged working pressure generated by the diaphragm seal the total output of the two Hydraulic pumps can be specified. Since according to the invention the averaged working pressure the sensor provided on the diaphragm seal can also be varied by a z. B. electrical control signal, which on the z. B. trained as an electromagnet encoder acts, the overall performance of the hydraulic pumps can be changed quickly and effectively and thus be adapted to the operating conditions.

The power controller can be according to claim 8 by a so-called Hyperbola controls are formed in which each adjustment device has a swivel lever is associated with associated power control valves and that of the diaphragm seal generated averaged working pressure via an acting on the pivot lever Control spool and the pivot lever is transferred to the power control valve. According to claim 9, the control spool in a displacement adjusting piston. Here is the lever arm with which the Control slide engages the pivot lever from the position of the actuating piston and thus dependent on the displacement volume of the associated hydraulic pump.

According to claim 10, the control unit for each adjustment device can be a separate one Have stroke control valve that the pivoting of the associated hydraulic pump in Regulates dependence on a signal pressure. The signal pressure is transmitted to the stroke control valve supplied to each hydraulic pump separately assigned signal pressure line. It is Stroke control valve via a stroke control valve spring with the control piston elastic connections. Below the performance control characteristic (hyperbolic characteristic) of the by Power control valve, the pivot lever and the control slide formed Output controller is the displacement volume of the corresponding hydraulic pump in Dependence on the signal pressure in the signal pressure line through the Stroke control valve regulated. If the power controller characteristic curve is exceeded by the set displacement volume or that set in the work line The power regulator intervenes at working pressure and regulates the displacement volume corresponding to the power controller characteristic (hyperbolic characteristic, characteristic the same Performance). According to claim 11, the control unit for each Adjustment device additionally or alternatively a separate pressure cut-off valve have, which is subjected to the working pressure in the associated work and the working pressure in the working line to a predetermined maximum pressure limited. A further swing out of the corresponding hydraulic pump is at Exceeding the maximum pressure in the work line prevented.

Fig. 1

ein Ausführungsbeispiel der erfindungsgemäßen Regelvorrichtung in einem hydraulischen Prinzipschaltbild; und

Fig. 2

ein Ausführungsbeispiel des bei der erfindungsgemäßen Regelvorrichtung verwendeten Druckmittlers.

The invention is described below with reference to the drawing based on a preferred embodiment. The drawing shows:

Fig. 1

an embodiment of the control device according to the invention in a hydraulic block diagram; and

Fig. 2

an embodiment of the diaphragm seal used in the control device according to the invention.

The control device according to the invention is described in more detail with reference to FIG. 1. The Control device of the embodiment shown in Fig. 1 works as a combined Power regulator and pressure regulator. In addition, the displacement volume of each one Hydraulic pump under the power regulator and pressure regulator predetermined control limits by a control pressure acting on a stroke control valve separately controllable. However, the control device according to the invention can also be used in the after other control principles working control devices, which are a diaphragm seal operate, find use.

The control device according to the invention, generally designated by reference number 1 is used to control two conveying lines 1a and 1b that promote separate working lines Hydraulic pumps 2a and 2b. The hydraulic pumps 2a and 2b are common Drive shaft 3 z. B. driven by an internal combustion engine, not shown. The Hydraulic pumps 2a and 2b suck pressure fluid through an associated, with a Pressurized fluid tank 4 connected suction line 5a or 5b and feed the pressurized fluid under a working pressure into the working lines 1a or 1b. By doing Embodiment, the two hydraulic pumps 2a and 2b work as a double hydraulic pump. However, further hydraulic pumps can also be provided within the scope of the invention be.

Each hydraulic pump 2a and 2b is assigned an adjustment device 6a or 6b, which serves to adjust the displacement volume V _g between a minimum value V _{g min} and a maximum value V _{g max} . For better understanding of the invention, the adjusting devices in the direction of the maximum displacement volume V _{g max} and the minimum displacement volume V _{g min are identified} by a double arrow in FIG. 1. In the exemplary embodiment shown, each adjusting device 6a, 6b consists of two adjusting pistons 7a or 7b and 8a or 8b, which can be moved in actuating cylinders 9a or 9b and 10a or 10b. The adjusting pistons 7a and 8a or 7b and 8b adjust the displacement volume of the assigned hydraulic pump 2a or 2b depending on the piston stroke.

For each hydraulic pump 2a or 2b, a power controller is provided in the illustrated embodiment, which comprises a power control valve 11a or 11b. A control slide valve 12a or 12b is provided in each of the actuating pistons 7a and 7b and can be acted upon by a pressure chamber 13a or 13b formed in the actuating piston 7a or 7b. The pressure chamber 13a or 13b is connected to the associated actuating cylinder 9a or 9b via a connecting line 14a or 14b formed in the actuating piston 7a or 7b. An increase in the pressure in the actuating cylinder 9a or 9b causes a displacement of the actuating piston 7a and 7b in FIG. 1 to the left in the direction of the maximum displacement volume V _{g max} . At the same time, the control slide 12a or 12b is acted upon via the connecting line 14a or 14b and the pressure chamber 13a or 13b in the direction perpendicular to the direction of movement of the actuating piston 7a or 7b and acts on a fixed pivot lever 16a mounted on a bearing 15a or 15b or 16b. The arm of the pivot lever 16a or 16b opposite the control slide 12a or 12b acts on the power control valve 11a or 11b via a linkage 17a or 17b. The valve piston of the power control valve 11a or 11b is displaced against a preferably adjustable power control valve spring 18a or 18b, so that via the power control valve 11a or 11b, the stroke control valve 19a or 19b still to be described and the pressure cut-off valve 20a, which is also yet to be described or 20b and the line 21a or 21b of the actuating cylinder 10a or 10b of the respectively opposite actuating piston 8a or 8b is acted upon by the pressure p _m . As a result, the hydraulic pump 2a or 2b is pivoted back in the direction of the minimum delivery volume V _{g min} .

Since the lever arm with which the control slide 12a or 12b acts on the pivoting lever 16a or 16b depends on the position of the actuating piston 7a or 7b and thus on the displacement volume V _{g of} the hydraulic pump 2a and 2b, a hyperbolic characteristic curve results overall between the average working pressure p _m present in the lines 22a and 22b and the displacement volume V _{g of} the corresponding hydraulic pump 2a and 2b. The hyperbolic power controller characteristic curve represents a characteristic curve of constant work power in a working pressure displacement volume diagram, so that the power controller limits the working range of the corresponding hydraulic pump 2a or 2b to a maximum power.

Before the capacity control valve 11a or 11b responds, ie before the maximum output is reached, the stroke control valve 19a or 19b regulates the displacement volume V _{g of} the corresponding hydraulic pump 2a and 2b. The hydraulic control inputs Y ₁ and Y ₂ are connected to the respective stroke control valve 19a and 19b via signal pressure lines 23a and 23b. The control signal supplied via the inputs Y ₁ and Y ₂ in the form of a control pressure displaces the valve piston of the stroke control valve 19a or 19b against a preferably adjustable first stroke control valve spring 24a or 24b. The greater the control pressure at the inlet Y ₁ or Y ₂ , the more the control piston 8a or 8b is subjected to the corresponding working pressure p ₁ or p ₂ and the associated hydraulic pump 2a or 2b in the direction of the minimum displacement volume V _{g min} pivoted back. The displacement volume V _{g of} the hydraulic pump 2a or 2b is therefore inversely proportional to the signal pressure at the inputs Y ₁ and Y ₂ (negative control characteristic). The adjustment position of the adjusting device 6a or 6b is fed back to the lift control valve 19a or 19b via the extension arm 25a or 25b and the second lift valve spring 26a or 26b. The control signal supplied to the inputs Y ₁ and Y ₂ can also be an electrical signal, for example.

In addition, in the exemplary embodiment shown in FIG. 1, a pressure cut-off valve 20a or 20b is provided for each hydraulic pump 2a or 2b. The valve piston of the pressure cut-off valve 20a or 20b is acted upon by the working pressure p ₁ or p ₂ prevailing in the working line 1a or 1b of the corresponding hydraulic pump 2a or 2b against a preferably adjustable pressure cut-off valve spring 27a or 27b. When the working pressure p ₁ or p ₂ in the corresponding working line 1a or 1b increases, the valve piston of the pressure cut-off valve 20a or 20b is displaced such that the actuating piston 8a or 8b increasingly via the line 21a or 21b and the pressure cut-off valve 20a or 20b is acted upon by the working pressure p ₁ or p ₂ and thus the associated hydraulic pump 2a or 2b swings back in the direction of the minimum displacement volume V _{g min} . The pressure cut-off valve 20a or 20b therefore effects a pressure limitation in the corresponding working line 1a or 1b.

The control characteristic of the valve unit consisting of the output control valve 11a or 11b, the lift control valve 19a or 19b and the pressure cut-off valve 20a or 20b can therefore be summarized to the extent that the output control valve limits the output of the hydraulic pump 2a or 2b to a maximum output, while the pressure cut-off valve 20a or 20b limits the working pressure in the working lines 1a or 1b. Within the control range defined by these limits, the displacement volume V _{g is} predetermined by the control pressure supplied to the hydraulic inputs Y ₁ and Y ₂ .

In addition to the valve units 11a, 19a, 20a and 11b, 19b, 20b described above, the hydraulic control unit according to the invention further comprises a diaphragm seal 30 which is connected to the working lines 1a and 1b via connecting lines 31a and 31b. A valve piston 32 of the diaphragm seal 30 is acted upon by the working pressures p ₁ and p ₂ prevailing in the working lines 1a and 1b. The diaphragm seal 30 serves to generate an averaged working pressure p _m , which is fed to the adjustment device 6a or 6b via the connecting lines 22a or 22b already described. In the opposite direction, the valve piston 32 is acted upon by the averaged working pressure p _m , so that an averaging working pressure p _m which corresponds to the arithmetic mean between the two working pressures p ₁ and p ₂ is established on the valve piston 32 if the further development according to the invention is disregarded. However, the balance on the valve piston 32 is disturbed by an encoder 33 according to the invention, which acts on the valve piston 32 via a first diaphragm seal spring 34 arranged between the encoder 33 and the valve piston 32. The transmitter 33 is therefore elastically coupled to the valve piston 32. At the opposite end, a preferably adjustable second diaphragm seal spring 35 acts on the valve piston 32, so that the transmitter 33 acts on the valve piston 32 against the second diaphragm seal spring 35. The transmitter 33 is preferably an electromagnet and is controlled via an electrical connecting cable 36 with an electrical transmitter signal.

As already described, the maximum output of the hydraulic pumps 2a and 2b is predetermined by the averaged working pressure p _m . By changing the equilibrium position of the valve piston 32 of the diaphragm seal 30 by means of the transmitter 33, the averaged working pressure p _m can be varied within certain limits, deviating from the arithmetic mean of the two working pressures p ₁ and p ₂ , which leads to a change in the maximum output of the two hydraulic pumps 2a and 2b leads. Due to the arrangement of the transmitter 33 on the diaphragm seal 30 according to the invention, the control device 1 can thus be expanded in a structurally relatively simple and inexpensive construction such that the maximum output of the two hydraulic pumps 2a and 2b can be changed within certain limits by the preferably electrical transmitter signal which adjusts the transmitter 33 is. When the operating state of the control device according to the invention changes, the maximum output of the hydraulic pumps 2a and 2b can therefore be changed relatively easily and quickly by the sensor signal.

Fig. 2 shows a preferred construction of the diaphragm seal 30 in one Sectional view.

The diaphragm seal, designated as a whole by 30, has a valve piston 32 designed as a stepped piston, the two stepped surfaces 40 and 41 of which have the same size. The working surface 42 arranged opposite the stepped surfaces 40 and 41 has an area A which is equal to the sum of the areas A1 and A2 of the two step surfaces 40 and 41. The valve piston 32 is arranged in a housing 43, of which only the inner working spaces are shown. The housing thus has a first working space 44, into which the feed line 31a opens at the working pressure p ₁ . Furthermore, a second working space 45 is provided, to which the feed line 31b with the second working pressure p _{2 is} connected. An annular groove 48 and 49 is assigned to each of the two working spaces 44 and 45 or the control edges 46 and 47 of the step surfaces 40 and 41. The control edges 46 and 47 cooperate with an edge of the ring grooves 48 and 49, respectively. A lead 50 and 51 lead away from the ring grooves 48 and 49, respectively. A check valve 52 or 53 is arranged in each of the discharge lines 50 and 51. Both derivatives 50 and 51 are combined with a line 22, from which in turn a branch 54 leads to the work surface 42 and a further branch 55 to the connecting lines 22a and 22b. The control edges 46, 47 each form an edge of the associated annular groove 48 or 49 chokes, which are denoted by 56 and 57.

The diaphragm seal 30 works as follows:

If the working pressures p ₁ and p _{2 are} supplied to the diaphragm seal 30 via the feed lines 31a and 31b, then these pressures p ₁ and p _{2 act} on the step surfaces 40 and 41 of the valve piston 32, respectively. You will move the valve piston 32 to the right so that the control edges 46 and 47 of the annular grooves 48 and 49 are released. This allows the pressurized fluid to penetrate the discharge lines 50 and 51 and reach the line 22 via the check valves 52 and 53.

If the two working pressures are the same, ie p ₁ = p ₂ , the pressure p ₁ = p _{2 will} build up on the working surface 42 via the line 22 and the branch 54. This acts on the valve piston 32 from both sides with the same forces. The right stop position of the valve piston 32 is consequently the equilibrium position when the working pressures are identical, since the mean pressure p _{m is} identical to the respective working pressures p ₁ and p ₂ .

However, if the case occurs that one of the two working pressures p ₁ , p _{2 is} higher, the equilibrium position of the valve piston 32 will change. If, for example, the pressure p _{2 is} greater than the pressure p ₁ , then after the valve piston 32 has been pushed into its right stop position, the pressure fluid with the higher pressure p ₂ after it flows through the discharge line 51 will flow into the line 22. As a result, the check valve 52 is closed. The pressure p ₂ is on the work surface 42. Since the higher pressure p _{2 is} now present on the work surface 42, the left thrust force generated on this side is greater than that of the pressures p ₁ and p ₂ on the step surfaces 40, 41 caused right-hand thrust. The valve piston 32 is consequently shifted to the left until the control edge 47 of the step surface 41 throttles the pressure fluid flow with the pressure p ₂ to such an extent that the balance of forces is restored. This equilibrium is reached when the working pressures are averaged, i.e. when:

The valve piston 32 will consequently, depending on the difference between the two operating pressures p ₁ and p _2, more or less restrict the flow of pressurized fluid or also go completely free. However, he will always be able to maintain an equilibrium position.

As already mentioned, the diaphragm seal can be made in the same way as this using the Drawing was described for two working pressures, also for the working pressures of more than two working lines can be designed. The valve piston 32 is always in its Equilibrium pushed so that the multiple working pressures on the multiple equally large areas over the control edges and check valves with the pressure at the Work surface 42 are in balance.

ergibt sich die Gleichgewichtsbeziehung:

The pressure conditions on the valve piston 32 also result from the following equilibrium consideration: if the step surface 40 has the area A ₁ , the step surface 41 has the area A ₂ and the working surface 42 has the area A and the following also applies:

the equilibrium relationship results:

According to the equilibrium position of the valve piston 32 of the diaphragm seal 30 is not only influenced by the working pressures p ₁ and p ₂ but also by the transmitter 33. The transmitter 33, which is preferably designed as an electromagnet, is elastically connected to the valve piston 32 via the first diaphragm seal spring 34 and an extension 60. An extension 61 is also provided on the opposite side of the valve piston 32. Between the housing 43 and the extension 61 of the valve piston 32, a second diaphragm spring 35 is provided, which is adjustable in the preferred embodiment shown. A plunger 62 of the transmitter 33 is influenced in its axial position by a transmitter signal supplied via the electrical lines 35 and exerts a corresponding force on the valve piston 32 via the first diaphragm seal spring 32, which displaces it to the right in FIG. 2.

A corresponding counterforce is exerted by the second pressure medium spring 35, so that there is an equilibrium position. When the valve piston 32 is shifted to the right in FIG. 2, the average working pressure p _m in the line 22 increases and thus no longer exactly represents the arithmetic mean of the working pressures p ₁ and p ₂ . B. the power limitation of the power controller can be influenced. The extent of the variations in the average working pressure p _m by the transmitter 33 can be adjusted by means of the adjustable second diaphragm seal spring 35. In the design of the control unit shown in the exemplary embodiment, consisting of two hydraulic individual regulators assigned to each of the hydraulic pumps 2a and 2b and the use of a central pressure transmitter 30, it can be achieved by the transmitter 33 that the hydraulic pumps 2a and 2b largely operate in parallel despite the use of hydraulic individual regulators or swivel back.

The invention is not limited to the illustrated embodiment, in particular The diaphragm seal 30 varied according to the invention can also be used in connection with others Control characteristics working control units are used, the z. B. only provide a pressure cut-off and no power regulation or as so-called load-sensing controllers are designed.

Claims (11)

Control device (1) for a plurality of hydraulic pumps (2a, 2b) delivering in separate working lines (1a, 1b) at least one adjusting device (6a, 6b) for adjusting the displacement volumes (V _g ) of the hydraulic pumps (2a, 2b), and a hydraulic control unit (30, 11a, 11b, 19a, 19b, 20a, 20b) with a diaphragm seal (30) for controlling the at least one adjusting device (6a, 6b), the diaphragm seal (30) with the separate working lines (1a, 1b ) the hydraulic pump (2a, 2b) is connected and generates an average working pressure (p _m ) from the working pressures (p ₁ , p ₂ ) prevailing in the separate working line (1a, 1b) which is used to control the at least one adjusting device (6a, 6b) serves
characterized, that the diaphragm seal (30) with an encoder (33) can also be acted on so that the averaged working pressure (p _m ) not only from the working pressures (p ₁ , p ₂ ) prevailing in the working lines (1a, 1b), but also from is dependent on an encoder signal acting on the encoder (33). Control device according to claim 1,
characterized, that the diaphragm seal (30) has a valve piston (32) which can be acted upon elastically by the transmitter (33) via a first diaphragm seal spring (34). Control device according to claim 2,
characterized, that a second diaphragm spring (35) acts on the valve piston (32) of the diaphragm seal (30) and acts on the valve piston (32) in the opposite direction to the transmitter (33). Control device according to claim 3,
characterized, that the bias of at least one of the diaphragm seals (34, 35) is adjustable. Control device according to one of claims 1 to 4,
characterized, that the transmitter (33) is an electromagnet and the transmitter signal is an electrical signal. Control device according to one of claims 1 to 5,
characterized, that each hydraulic pump (2a, 2b) is assigned a separate adjusting device (6a, 6b), and that the control unit (30, 11a, 11b, 19a, 19b, 20a, 20b) each adjusting device (6a, 6b) in dependence on the working pressure (p ₁ ; p ₂ ) in the working line (1a, 1b), the associated Hydraulic pump (2a; 2b) prevails, and controls the averaged working pressure (p _m ). Control device according to claim 6,
characterized, that the control unit (30, 11a, 11b, 19a, 19b, 20a, 20b) has a separate power control valve (11a, 11b) for each adjustment device. Control device according to claim 7,
characterized, that each adjustment device (6a, 6b) is connected to the associated power control valve (11a, 11b) via a swivel lever (16a, 16b) and the average working pressure (p _m ) is connected to a control slide (12a.) acting on the swivel lever (16a, 16b) , 12b) and the pivot lever (16a, 16b) acts on the power control valve (11a, 11b). Control device according to claim 8,
characterized, that the control slide (12a, 12b) is integrated in an adjusting piston (7a, 7b) adjusting the displacement volume (V _g ) and the lever arm with which the control slide (12a, 12b) engages on the swivel lever (16a, 16b) from the Position of the actuating piston (7a, 7b) and thus on the displacement volume (V _g ) of the associated hydraulic pump (2a, 2b) is dependent. Control device according to claim 8,
characterized, that the control unit (30, 11a, 11b, 19a, 19b, 20a, 20b) has a separate stroke control valve (19a, 19b) for each adjusting device (6a, 6b), which swings out the associated hydraulic pump (2a, 2b) as a function of controls a control pressure which is fed to the stroke control valve (19a, 19b) by means of a control pressure line (23a, 23b) separately assigned to each hydraulic pump (2a, 2b), the stroke control valve (19a, 19b) via a stroke control valve spring (26a, 26b) ) is elastically connected to the actuating piston (7a, 7b). Control device according to one of claims 6 to 10,
characterized, that the control unit (30, 11a, 11b, 19a, 19b, 20a, 20b) has a separate pressure cut-off valve (20a, 20b) for each adjustment device (6a, 6b), which with the working pressure (p ₁ ; p ₂ ), which in the working line (1a, 1b) of the assigned hydraulic pump (2a, 2b) prevails, is acted upon and limits the swiveling out of the assigned hydraulic pump (2a, 2b) when a predetermined maximum pressure in the working line (1a, 1b) is exceeded.

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