EP0972940B1 - Power control unit to control the hydraulic power in a drive line - Google Patents

Description

The invention relates to a power control device for controlling the hydraulic power in a working line.

[State of the art]

Power control devices are already known in a variety of designs. For example, DE 35 41 750 C2 discloses a power control device which consists of a simple control valve arranged in the working line. The pressure downstream of the control valve is tapped and returned via a control line to the control valve. By a special embodiment of the passage opening of the control valve ensures that the product of high pressure and flow through the control valve is adjusted to a constant value. However, a disadvantage is the immediate arrangement of the power function predetermining control valve in the working line, since the control valve and in particular its opening cross-section must be made relatively large. Furthermore, there is the risk of damage to the control valve by cavitation at high flow rates. The control valve can not be designed as a simple slide valve, since the geometry of the opening cross-section must meet special requirements because of the power control function.

A known for example from DE 196 26 793 C1 power control device comprises a so-called hyperbola controller, which acts back on a pivoting angle acting as a power control valve proportional valve. The reaction is dependent on the one hand by the pressure in the working line of the associated hydraulic pump and on the other hand by the lever arm, with which the pressure of the working line acts on the pivot lever. This constellation results in a hyperbolic control characteristic, ie at Achieving the predetermined maximum power controls the power control device, the hydraulic pump to a constant power, ie a constant product of working pressure in the working line and delivery volume of the hydraulic pump, a.

In this case, however, it is assumed that the delivery volume of the hydraulic pump depends solely on the predetermined by the adjustment swiveling. However, this condition only applies if the hydraulic pump is driven by the drive motor at a constant speed. Power control devices with a hyperbola controller are therefore not applicable for drive systems with variable input speed. Another disadvantage is the fact that this power control device must be connected to the actuator piston of the adjustment, d. H. must be mounted on the adjustment of the hydraulic pump. The corresponding connection between the pivot lever and the actuator piston requires additional design effort. In addition, the same constructive solution can not be realized in all types of hydraulic pumps to be used in the same way and it is for each type of hydraulic pump, a special construction required.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a power control device that does not require a structurally complex hyperbola and ensures proper functioning.

The object is solved by the features of claim 1.

The invention is based on the finding that the power control device is less susceptible to interference and the control function is more accurate when the elements that predetermine the power control punctuation are not directly in the Working line but are arranged in a side circuit. In the working line, there is only one main valve, which can be extremely simple, for example, designed as a slide valve and designed for the control of large volume flows, without causing constructive difficulties. From the input of the power control device according to the invention branches a side circuit. The secondary circuit is supplied via a flow control device, a constant volume flow, which is in particular independent of the prevailing in the working line high pressure. In the secondary circuit, a drain throttle is further provided, which is connected to the valve body of the main valve, so that the throttle cross-section depends on the position of the valve body of the main valve. The invention makes use of the fact that the supplied volume flow must be removed again from the outlet throttle. From this continuity condition results for each high pressure in the working line, a certain opening cross section of the outlet throttle and thus a certain secondary pressure in the secondary circuit between the Sromregeleinrichtung and the outlet throttle. This secondary pressure is supplied to a first valve chamber of the main valve to control the valve body.

Compared with an acting on the adjustment of an adjustable hydraulic pump power control device with hyperbola, there is the advantage of universal applicability in the power control device according to the invention. In particular, the power control is independent of the speed of the connected hydraulic pump. Furthermore, the power control device according to the invention can be used in any hydraulic lines to remote from the pump body, since it does not require a mechanical reaction to the pump.

Compared to the known power control device, the power-regulating element directly in the working line, Thus, in the main circuit, there is in the power control device according to the invention the advantage of a simple structural design of the arranged in the working line main valve and the more accurate control function. The actual flow control function taking over together with the flow control device flow restrictor can be designed to be relatively small, since it controls only a small flow of the secondary circuit. The flow control device and the outlet throttle can be integrated together with the main valve in a common valve block.

The subclaims contain advantageous developments of the invention.

According to claim 2, an additional proportional control valve may be provided that is acted upon by the pressure difference between the prevailing at the input high pressure and the pressure prevailing in the secondary circuit between the flow control device and outlet throttle secondary pressure. In this case, the flow control valve may be connected to a valve body of the main valve adjacent the second valve chamber, so that the valve body of the main valve is acted upon by increasing pressure difference between the high pressure and the secondary pressure in the direction of a decreasing opening cross section of the main valve. The proportional control valve supports and accelerates the actuation of the valve piston of the main valve. In principle, however, it is also conceivable to effect the return of the valve piston of the main valve against the application of the secondary pressure with a return spring and to save the proportional control valve. The proportional control valve may be designed according to claim 3, in particular as a 3/2-way valve. The flow control device preferably consists of a throttle arranged in the secondary circuit and a limiting valve arranged downstream or upstream of the throttle. In this case, the limiting valve is corresponding Claim 4 driven by the pressure drop across the throttle. The limiting valve is preferably designed as a 2/2-way valve according to claim 5.

The outlet throttle is preferably integrated on the valve body of the main valve according to claim 6. If the power control valve is to limit the power in the working line to a constant maximum power, the opening cross-section of the outlet throttle is designed so that it increases in proportion to the square root of the displacement of the valve body of the main valve. In addition to the power limitation realized by the power control device according to the invention, according to claim 9, a flow control valve and / or a pressure relief valve may be provided. Before reaching the maximum power of the connected hydraulic pump, the entire device then operates in a flow control mode in which the flow control valve adjusts the flow rate in the working line to a constant value. Upon reaching the maximum power of the hydraulic pump, the delivery volume is reduced so that the product of delivery volume and working pressure, so the hydraulic power remains constant. If, however, a maximum pressure is exceeded, the pressure limiting valve responds.

An embodiment of the invention will be described below with reference to the drawing. In the drawing show:

[Examples]

Fig. 1

a hydraulic circuit diagram of an embodiment of the power control device according to the invention;

Fig. 2

a section through an example structural design of the power control device according to the invention;

Fig. 3

a view of the outlet throttle of the power control device according to the invention in the direction A in Fig. 2; and

Fig. 4

a detail of Fig. 1 with the name of individual hydraulic variables that are required to describe the function of the power control device according to the invention.

1 shows an exemplary embodiment of the power control device according to the invention, which is designated generally by the reference numeral 1. The power control device 1 according to the invention is arranged in a working line 2 between an input 3 and an output 4. At the input 3, an adjustable hydraulic pump 17 is connected in the embodiment shown in FIG. 1, while at the output 4 any consumer, such as a hydraulic motor or a hydraulic piston can be connected.

The power control device 1 according to the invention comprises a arranged in the working line 2 main valve 5, depending on the position of a valve piston 6, the working line 2 releases, throttles or completely shuts off.

According to the invention a secondary circuit 7 is provided, which is fed via a flow control device 8 with a constant volume flow. The flow control device 8 is connected via a connecting line 29 to the input 3 and thus to the pressure prevailing in the working line 2 high pressure.

In the illustrated embodiment, the flow control device 8 consists of an example of 2/2-way valve designed limiting valve 9 and a downstream throttle 10. The throttle 10 has a preferably adjustable but fixed during operation of the power control device 8 throttle cross-section. The limiting valve 9 is driven by the pressure drop across the throttle 10. As the pressure drop across the throttle 10 increases, the restriction valve 9 reduces its opening area. Conversely, the opening cross section of the limiting valve 9 is increased when the pressure drop across the throttle 10 decreases. In this way, the pressure drop across the throttle 10 is kept constant, resulting in a constant volume flow, which is fed by the flow control device 8 in the secondary circuit 7. The flow of the volume flow from the secondary circuit 7 in a pressure medium tank 11 via an outlet throttle 12. The throttle cross section of the outlet throttle 12 is variable and determined by the position of the valve body 6 of the main valve 5. The smaller the opening cross section of the main valve 5, the lower the throttle cross section of the outlet throttle 12.

The secondary pressure prevailing in the secondary circuit 7 between the throttle 10 of the flow control device 8 and the outlet throttle 12 is supplied to a first valve chamber 13 adjoining the valve piston 6 of the main valve 5. With increasing secondary pressure in the secondary circuit 7, therefore, the valve body 6 of the main valve 5 is acted upon in the direction of an increasing opening cross-section of the main valve 5.

Further, a proportional control valve 16 is provided, which is acted upon by the pressure difference between the prevailing in the working line 2 at the input 3 high pressure and the secondary pressure prevailing in the secondary circuit 7. If the secondary pressure prevailing in the secondary circuit 7 drops relative to the high pressure prevailing in the working line 2, the formed in the embodiment as a 3/2-way valve proportional valve 16 so that an adjacent to the valve body 6 of the main valve 5 second valve chamber 14 is increasingly pressurized via a connecting line 15 with pressure, so that the valve body 6 of the main valve 5 increasingly toward one decreasing opening cross section of the main valve 5 is acted upon. Conversely, when the secondary pressure in the secondary circuit 7 increases with respect to the pressure prevailing in the working line 2 high pressure, the second valve chamber 14 is relieved via the connecting line 15 and the proportional control valve 16 to the pressure medium tank 11 out. Overall, therefore, the valve body 6 of the main valve 5 with increasing secondary pressure in the secondary circuit 7 in Fig. 1 to the left in the direction of an increasing opening cross section of the main valve 5 and vice versa with decreasing secondary pressure in the secondary circuit 7 in Fig. 1 to the right towards one decreasing opening cross section of the main valve 5 is applied. In principle, the second valve chamber 14 and the proportional control valve 16 could also be dispensed with for simplifying the power control device 1 according to the invention and be replaced by a return spring, for example.

The operation of the power control device 1 according to the invention is the following:

When the high pressure in the working line 2 at the input 3 of the power control device 1 increases, regardless of the increasing high pressure by the flow control device 8, a constant, independent of the increase in the high pressure flow in the secondary circuit 7 continues to be fed. However, because of the increased pressure gradient, the outlet throttle 12 allows the flow to flow to the pressure medium tank 11 for a short time longer than the flow control device 8 continues to flow. This leads to a drop in the secondary pressure in the secondary circuit 7 and thus to a reduced pressure in the At the same time, the pressure difference across the proportional control valve 16 is reduced, so that the second valve chamber 14 is subjected to a higher pressure. Overall, the valve body 6 of the main valve 5 is moved in Fig. 1 to the right in the direction of a decreasing opening cross-section of the main valve 5. As a result, the throttle cross section of the outlet throttle 12 is reduced, since the outlet throttle 12 is connected to the valve body 6 of the main valve 5 accordingly. Only when the outflowing volume flow is in equilibrium with the inflowing constant volume flow, the equilibrium position of the valve body 6 of the main valve 5 is reached.

Conversely, when the high pressure at the inlet 3 decreases, the secondary circuit 7 continues to be supplied with a constant volumetric flow through the current control device 8. Due to the falling pressure gradient, however, a short-term volume flow compared to the volume flow supplied by means of the flow control device 8 is temporarily removed by the outlet throttle 12 from the secondary circuit 7. This results in a pressure increase in the sub-circuit 7 and thus an increase in the pressure in the first valve chamber 13. Further, the proportional control valve 16 is shifted so that the pressure in the second valve chamber 14 decreases by the second valve chamber 14 to the pressure medium tank 11 is relieved. The valve body 6 of the main valve 5 is deshald shifted in the direction of an increasing opening cross-section of the main valve 5. At the same time, the throttle cross-section of the outlet valve 12 coupled to the main valve 5 is increased, so that a new equilibrium is established between the constant volume flow supplied and the discharged volume flow.

Overall, therefore, the opening cross section of the main valve 5 is reduced by the power control device 1 according to the invention, when the high pressure in the working line 2 increases and vice versa, the opening cross section of the power control device 5 increases when the high pressure in the working line 2 falls. As will be shown below, with a suitable choice of the opening cross-section of the outlet throttle 12 as a function of the valve lift of the main valve 5 can be achieved that the product of high pressure in the working line 2 and from the flow through the main valve 5, ie the hydraulic power, is adjusted to a constant value, which corresponds for example to the maximum power of the hydraulic pump 17.

In Fig. 1, the adjustable hydraulic pump 17 sucks from the pressure medium tank 11, the pressure medium and feeds it into the working line 2 a. To adjust the hydraulic pump 17 is an adjusting device 18, which has a first actuating piston 19a and a first actuating cylinder 20a and a second actuating piston 19b and a second actuating cylinder 20b. In the second actuating cylinder 20b is a spring 21 which swings the hydraulic pump 17 to maximum displacement.

In addition to the power control device 1 according to the invention, a flow control valve 22 and a pressure relief valve 23 are provided in the embodiment shown in FIG. The flow control valve 22 compares the pressure in the working line 2 at the input 3 of the power control device 1 with the pressure at the output 4 of the power control device 1, ie it detects the pressure drop across the main valve 5 of the power control device 1. When this pressure drop increases, the first actuating cylinder 20a is the Actuator 18 increasingly acted upon with control pressure, so that the adjustable hydraulic pump 17 pivots back. Conversely, the first actuating cylinder 20a of the actuator 18 is relieved when the pressure drop across the main valve 5 falls, so that the hydraulic pump 17 is swung to a larger displacement volume.

The flow control valve 22, a pressure relief valve 23 is connected downstream, which responds as soon as the high pressure in the working line 2 exceeds a predetermined maximum pressure. The pressure limiting valve then increases the actuating pressure in the first actuating cylinder 20a of the adjusting device 18 and pivots the hydraulic pump 17 back.

The power device 1 according to the invention, the flow control valve 22 and the pressure relief valve 23 work together as follows:

As long as the set power of the hydraulic pump 17 is not reached, the output from the hydraulic pump 17 via the main valve 5 flow rate is adjusted by the flow control valve 22 to a constant value, so that the connected load a constant flow is supplied. However, if a predetermined power is reached, the power control device 1 according to the invention responds and ensures that the product does not exceed a predetermined power from the high pressure prevailing in the working line 2 and the flow rate flowing in the working line 2. However, if the maximum allowable pressure in the working line 2 is exceeded, the pressure limiting valve 23 responds and pivots the hydraulic pump 17 back so far that the permissible maximum pressure of the working line 2 is not exceeded.

It should be emphasized that the power control device 1 according to the invention can of course also be used with another external circuit. In general, the power control device 1 serves to limit the power in any hydraulic working line 2. The power control device 1 according to the invention can therefore also be arranged as a compact valve assembly on a position spatially remote with respect to the hydraulic pump 17, for example immediately before the user.

In the case of a plurality of consumers arranged parallel to one another, each consumer may be assigned a separate power control device 1, which is in each case tuned such that a permissible maximum power of the connected consumer is not exceeded.

FIG. 2 shows a constructive realization of the power control device 1 according to the invention shown in FIG. 1 in a cutaway view. Evident are the input 3, the output 4 and a terminal 30 for connection to the flow control valve 22. In an outer housing body 31, the proportional control valve 16 is integrated. In a cylinder bore 32, a valve piston 33 is axially displaceable. The valve piston 33 has a thickening 34 and two tapers 35 and 36. The valve piston 33 is biased by a return spring 37. The axial position of the valve piston 33 is determined by the pressure difference between a connected to the input 3 first valve chamber 38 and connected to the secondary circuit 7 second valve chamber 39 and the position of the mouth of the bore 34. When the high pressure at the inlet 3 with respect to the secondary pressure in the secondary circuit 7 increases, the valve piston 33 is displaced in Fig. 2 upwards, so that the connecting line 15 is increasingly acted upon by the prevailing at the input 3 high pressure and thus the pressure in the second valve chamber 14 of the main valve 5 increases. Conversely, the second valve chamber 14 of the main valve 5 is relieved when the high pressure at the inlet 3 against the secondary pressure in the secondary circuit 7 drops.

The existing from the limiting valve 9 and the throttle 10 flow control device 8 is located in Fig. 2 below the input 3. The valve piston 40 of the limiting valve 9 has two thickened portions 41 and 42 and a taper 43. The limiting valve 9 is connected via the connecting line 29 with the input 3 in connection. Over two connecting lines 44 and 45, the pressure in front of and behind the throttle 10 is detected and respectively supplied to a first valve chamber 47 and a second valve chamber 48. Further, a return spring 46 is provided. When the pressure drop across the throttle 10 increases, the opening area of the restriction valve 9 is reduced. This ensures that the flow control device 8 the secondary circuit 7 regardless of the high pressure at the input 3 supplies a constant volume flow.

The process from the secondary circuit 7 is regulated via the outlet throttle 12. The outlet throttle 12 is integrated with the valve piston 6 of the main valve 5 and adjoins the first valve chamber 13 of the main valve 5. The first valve chamber 13 is connected via a connecting line 50 and an annular groove 51 with the secondary circuit 7. The outlet throttle 12 is formed by a stationary pin 52 cooperating with an annular body 53 and releasing a gap 54 which depends on the valve stroke b and which is rectangular in the exemplary embodiment. In Fig. 3 the area of the outlet throttle 12 is shown in a sectional view corresponding to the viewing direction A in Fig. 2 again, wherein the annular body 53, the pin 52 and rectangular in the embodiment gap 54 can be seen. In the exemplary embodiment, the gap 54 has a constant gap length a and a gap width h dependent on the valve stroke b. The valve lift is indicated in Fig. 2 by an arrow. In this case, the smallest valve lift b results when the thickening 55 of the valve body 6 completely closes the annular groove 56 in the inner housing body 57. The largest valve lift b results when the annular groove 58 of the valve body 6 completely overlaps with the annular groove 56 leading to the outlet 4, as shown in FIG.

As already stated, the geometric dependence of the throttle opening of the outlet throttle 54 as a function of the valve lift b determines the control characteristic of the invention Power control device 1. Preferably, the power control device 1 according to the invention is operated so that it limits the hydraulic power to a predetermined constant power. As will be shown below, this can be achieved if, at a constant gap length a, the gap width h (b) dependent on the valve lift b is proportional to the square root of the valve lift b. As can be seen from Fig. 2, therefore, the flank of the pin 52 is formed accordingly. The specified geometric relationship between the gap width h and the valve lift b results from the considerations described below.

For a better clarification of the mathematical variables used in the following, a section from FIG. 1 is again shown enlarged in FIG. 4 and the mathematical variables used below are illustrated there.

As explained, there is an equilibrium situation when the inflowing volume flow Q corresponds to the outflow volume flow Q _ab : $$Q_{zu}=Q_{ab}$$

$${\mathrm{Q}}_{\mathrm{a}\mathrm{b}}={\mathrm{A}}_{\mathrm{a}\mathrm{b}}\cdot {\mathrm{v}}_{\mathrm{a}\mathrm{b}}={\mathrm{A}}_{\mathrm{a}\mathrm{b}}\sqrt{\frac{2\cdot {\mathrm{p}}_{\mathrm{x}}}{\zeta \cdot \alpha }}$$

The volume flow is given by the product of opening cross-section and flow velocity, so that: $$Q_{zu}=A_{zu}\cdot v_{zu}=A_{\mathrm{<figure-callout\; id="2"\; label="z\; u"\; filenames="imgf0001.png"\; state="\{\{state\}\}">z\; </figure-callout>}u}\sqrt{\frac{2\cdot \Delta p}{\zeta \cdot \alpha }}$$

$${\mathrm{Q}}_{\mathrm{a}\mathrm{b}}={\mathrm{A}}_{\mathrm{a}\mathrm{b}}\cdot {\mathrm{v}}_{\mathrm{a}\mathrm{b}}={\mathrm{A}}_{\mathrm{a}\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png"\; state="\{\{state\}\}">b</figure-callout>}}\sqrt{\frac{2\cdot {\mathrm{p}}_{\mathrm{x}}}{\zeta \cdot \alpha }}$$

In this case, A _is the inflow cross section, A _from the outflow cross section, V _to the inflow velocity and V _from the Outflow velocity. The relations used for the inflow velocity v _to and the outflow velocity v _ab are derived from the Bernoulli equation of motion for incompressible fluids (see, for example, BHJ Matthies "Introduction to Oil Hydraulics", Teubner Studienbücher, page 35). In this case, ζ denote the density of the pressure medium used, if α a friction value, Δp the pressure drop at the throttle 10 and p _x the secondary pressure in the secondary circuit 7. The pressure in the secondary circuit 7 p _x corresponds to the pressure drop at the outlet throttle 12, since this leads directly to the pressure medium tank 11.

gilt folgende Beziehung: $$A_{zu}\cdot \sqrt{\Delta p}=A_{ab}\cdot \sqrt{{\mathit{p}}_{\mathrm{HD}}}$$

Under the approximation $$p_x=p_{\mathrm{HD}}-\Delta p\approx p_{\mathrm{HD}}$$

the following relationship applies: $$A_{zu}\cdot \sqrt{\Delta p}=A_{ab}\cdot \sqrt{{\mathit{p}}_{\mathrm{HD}}}$$

wobei a die konstante Spaltenlänge und h die von dem Ventilhub b abhängige Spaltbreite ist. Wesentlich ist, daß der Ventilhub b für das Hauptventil 5 und der Ventilhub für die Abströmdrossel 12 einander gleich sind, da das Hauptventil 5 mit der Ablaufdrossel 12 starr gekoppelt ist. Soll eine Leistungsregelung in der Weise erreicht werden, daß das Produkt aus dem Hochdruck p_HD an dem Eingang 3 und dem das Hauptventil 5 durchströmenden Fördervolumen konstant gehalten wird, so entspricht dies folgender Bedingung $$p_{\mathrm{HD}}\cdot A_{bgr}=\mathrm{const}$$

The inflow cross section A _to and the pressure difference Δp at the inflow throttle 10 are constant quantities. For the outflow cross section at the outflow throttle 10 applies $$A_{ab}=a\cdot H$$

where a is the constant column length and h is the gap width dependent on the valve lift b. It is essential that the valve lift b for the main valve 5 and the valve lift for the outflow throttle 12 are equal to each other, since the main valve 5 is rigidly coupled to the outlet throttle 12. If a power control is to be achieved in such a way that the product from the high pressure p _HD at the inlet 3 and the main valve 5 flowing through the delivery volume is kept constant, this corresponds to the following condition $$p_{\mathrm{HD}}\cdot A_{bGr}=\mathrm{const}$$

$$p_{\mathrm{HD}}=\mathrm{const}/b$$

In this case, A _{bgr means} the limiting cross-section of the main valve 5, which determines the flow rate flowing through the main valve 5. Since the limiting cross section A _bgr due to the constant diameter of the groove 58 depends exclusively on the valve lift b, applies $$p_{\mathrm{HD}}\cdot b=\mathrm{const}$$

$$p_{\mathrm{HD}}=\mathrm{const}/b$$

oder $$h\left(b\right)\sim \sqrt{b}$$

Substituting equations (9) and (6) into equation (5) gives $$A_{zu}\cdot \sqrt{\Delta p}=a\cdot H\left(b\right)\cdot \sqrt{\frac{\mathrm{const}}{b}}$$

or $$H\left(b\right)~\sqrt{b}$$

With the power control device 1 according to the invention therefore provides a constant power when the gap width h is proportional to the square root of the valve lift b, which can be achieved by a corresponding geometric configuration of the pin 52 readily in the embodiment shown in FIG. Basically it is possible, the functional relationship between the gap width h and the flow cross-section _A, and the valve b in other ways to choose a different control characteristics of the power control device 1 according to the invention which can be achieved.

The invention is not limited to the illustrated embodiment. In particular, the gap length a of the outlet throttle 54 need not be constant. Thus, it is conceivable, for example, to use an annular throttle gap and form the pin 52, for example, as a rotationally symmetrical body, which can be realized in manufacturing technology easier. The function of the radius of the rotationally symmetric pin 52 as a function of the valve lift b can be determined either numerically or by experiments in a simple manner and manufacture easily in a numerically controlled manufacturing machine.

Claims (9)

1. Capacity control device (1) for controlling the hydraulic capacity in an operating line (2) with a main valve (5), arranged between an input (3) and an output (4) in the operating line (2) and having a valve body (6) which releases or throttles the operating line (2) irrespective of its position,
   with a current control device (8), connected to the input (3), which supplies an auxiliary circuit (7) with a constant volume flow (Q_zu),
   with a discharge throttle (12), arranged in the auxiliary circuit (7), the throttle cross-section (A_ab) of which depends on the position of the valve body (6) of the main valve (5) and
   with a first valve chamber (13), adjacent to the valve body (6) of the main valve (5), which is arranged in the auxiliary circuit (7) between the current control device (8) and the discharge throttle (12) and which charges the valve body (6) with increasing auxiliary pressure (p_x) in the auxiliary circuit (7) in the direction of an increasing opening cross-section (A_bgr) of the main valve (5),
   wherein a proportional control valve (16) is provided which is charged by the pressure difference between the high pressure (p_HD) prevailing at the input (3) and the auxiliary pressure (p_x) prevailing in the auxiliary circuit (7) between the current control device (8) and the discharge throttle (12).
2. Capacity control device according to claim 1, characterised in that the proportional control valve (16) is connected to a second valve chamber (14) adjacent to the valve body (6) of the main valve (5), so that the valve body (6) of the main valve (5) is charged with increasing pressure difference between the high pressure (p_HD) and the auxiliary pressure (p_x) in the direction of a decreasing opening cross-section (A_bgr) of the main valve (5).
3. Capacity control device according to claim 1 or 2, characterised in that the proportional control valve (16) is a 3/2 port directional control valve.
4. Capacity control device according to one of claims 1 to 3, characterised in that the current control device (8) consists of a throttle (10) arranged in the auxiliary circuit (7) and a limiting valve (9) arranged in the auxiliary circuit (7) downstream or upstream the throttle (10), the limiting valve (9) being triggered by the drop in pressure on the throttle (10).
5. Capacity control device according to claim 4, characterised in that the limiting valve (9) is a 2/2 port directional control valve.
6. Capacity control device according to one of claims 1 to 5, characterised in that the discharge throttle (12) is constructed on the valve body (6) of the main valve (5), wherein the throttle cross-section (A_ab) of the discharge throttle (12) enlarges with increasing opening cross-section (A_bgr) of the main valve (5).
7. Capacity control device according to claim 6, characterised in that the capacity control device (1) limits the capacity in the operating line (2) to a constant capacity, wherein the opening cross-section (A_ab) of the discharge throttle (12) increases in proportion to the square root of the valve lift (b) of the main valve (5).
8. Capacity control device according to one of claims 1 to 7, characterised in that the capacity control device (1) is integrated in the operating line (2) of an adjustable hydraulic pump (17) and the drop in pressure over the main valve (5) serves to trigger an adjusting device (18) of the hydraulic pump (17).
9. Capacity control device according to claim 8, characterised in that arranged between the input (3) and the output (4) of the capacity control device (1) and the adjusting device (18) is/are a delivery flow control valve (22) and/or a pressure-limiting valve (23).

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