EP0719947B1 - Load-sensing circuit - Google Patents

Description

The invention relates to a load-sensing circuit according to the preamble of Claim 1.

Such load-sensing circuits are known from practice and for example in the "hydraulic training, issued by Mannesmann Rexroth, Drive and control technology in mobile drive machines ", RE 00 315 / 9.82 on page 68 in hydraulic-mechanical design described. These known load-sensing circuits are very susceptible to vibration, so that unstable conditions can often occur; aggravating in addition there are the high volume capacities in the relatively large distances between the hydraulic pump and the consumers bridging hoses and especially strong in mobile applications Fluctuations in oil temperature, drive speed and in vehicles such as such as excavators with multiple consumers the movement of changing masses (Boom, stick, spoon). Load sensing circuits in electro-hydraulic Execution show a more stable operating behavior, but a considerable one faces greater design effort.

Furthermore, a load-sensing circuit according to the preamble of claim 1 with a feedback device known from DE-A 29 10 611.

The volume flow feedback device comprises the first and second measuring surfaces, wherein the first measuring area is larger than the second measuring area. If for example the throttle cross section of the pressure difference between the Working pressure and the load pressure with the flow of a corresponding volume flow generating variable throttle increases and thus this pressure difference is reduced, the control valve controls the hydraulic pump for a longer time Delivery volume and thus larger volume flow until this at the variable throttle the original one, before enlarging the throttle cross section existing pressure difference generated. The larger volume flow accelerates the or the consumer, so that the working pressure and the load pressure in the same Dimensions increase. This increase in pressure creates the different sizes Measuring surfaces a force component corresponding to the measuring surface difference greater hydraulic force of the pressure difference. This force component is a measure of the increase in volume flow and thus represents the feedback force represents, which acts against the counterforce, which is preferably the adjusting force is a compression spring. To enlarge the hydraulic pump again Swinging out the delivery volume is one of the force components lower pressure difference required. This means a smaller increase of the volume flow and thus smaller control deviations or less Overshoot and consequently improved stability.

Another load-sensing circuit is known from DE-A 29 13 534, the feedback from a separate, on a control valve piston acting piston with two opposite measuring surface and the first measuring surfaces by the working pressure of the pump and the second measuring surface is acted upon by the load pressure. In addition to the considerable constructive Effort is the disadvantage of susceptibility to vibrations.

In the document DE 32 00 885 A1 there is a power controller for a hydrostatic pump disclosed to limit the control range the output control for large quantities at a first, with a second piston acting under a load pressure is provided is, the two opposite piston surfaces with the load pressure and are subjected to a working pressure. Exceeds that on the second Resulting force acting on the piston due to the corresponding movement Volume flow through a throttle pressure difference one through If a force can be specified by a spring, the second piston acts via the first Piston on the control valve, so that the pump towards smaller Flow rate is adjusted.

It is an object of the invention to provide a load-sensing circuit at the beginning mentioned type so that with little design effort more stable operating behavior is achieved.

This object is achieved by the characterizing features of claim 1 Interaction with its generic characteristics solved. The feedback device ensures that after each adjustment of the hydraulic pump greater or smaller delivery volume the resultant acting on the control valve the feedback force and the counterforce to a smaller or larger value is set. The setpoint setting of the Control valve changed so that a new adjustment of the hydraulic pump to an even larger or smaller delivery volume only with a smaller or larger, counteracting pressure difference between the Working pressure and the load pressure can be carried out. It results in in this way a decreasing with increasing funding volume and, conversely, with decreasing delivery volume increasing p-V characteristic curve, the one Load sensing circuit with so-called proportional behavior. This has in contrast to the load-sensing circuits known from the prior art with so-called integral behavior, i.e. with characteristic curves with the slope Zero, a significantly more stable operating behavior because of the delivery volume with a small control deviation only slowly, with a large control deviation however is changed quickly. The susceptibility to vibration of a such system is very small.

The feedback device is advantageously as one Flow feedback device designed, being the force generated by the feedback device can be mechanical force.

The delivery volume feedback device comprises at least one displacement spring, on the actuator adjusting the delivery volume of the hydraulic pump and attacks on the valve body and the action of the latter by the Counterforce with increasing adjustment of the hydraulic pump to a larger or smaller funding volume reduced or increased. In this way a smaller or Larger pressure difference required to turn the hydraulic pump to a larger one or set a smaller delivery volume.

According to a development of the invention is between the valve body and a first, double-acting and stationary actuating cylinder, a second, single-acting, from the counterforce towards a fixed stop Actuated actuating cylinder clamped, the actuating piston under the Effect of the working pressure acts on the valve body against the counterforce, the actuating piston of the first actuating cylinder being the working pressure and has measuring surfaces acted upon by the load pressure and under which Effect of the pressure difference between the working pressure and the load pressure above the second actuating cylinder acts on the valve body against the counterforce. The valve body takes over together with the first actuating cylinder the load-sensing function and, with the second actuating cylinder, pressure control, which is superimposed on the load sensing, i.e. instead of the latter in Function occurs when the hydraulic force enters the second actuating cylinder System stops at the fixed stop.

The pressure control points when using the delivery volume feedback device the same proportional behavior as the load sensing control.

When designing the delivery volume feedback device with one or several measuring springs, the characteristics of which approximate a performance hyperbola there is a power regulation instead of the pressure. Their characteristic can as well as that of the aforementioned pressure control by simultaneous Use of the volume flow feedback device according to the measurement area difference be modified.

It is also possible to use an override device to Changing the size of the pressure difference acting on the measuring surfaces The characteristics of the load-sensing control between the working pressure and the load pressure and possibly the pressure or power control change.

Further features and advantages of the invention result from the remaining ones Claims.

Fig. 1

einen Schaltplan einer Load-Sensing-Schaltung in einer ersten Ausgestaltung nach dem Stand der Technik,

Fig. 2

ein Diagramm, das die Kennlinie der Load-Sensing-Schaltung nach Figur 1 zeigt,

Fig. 3

einen vereinfachten Schaltplan einer Load-Sensing-Schaltung in einer zweiten Ausgestaltung nach dem Stand der Technik,

Fig. 4

einen vereinfachten Schaltplan einer Load-Sensing-Schaltung in einer dritten Ausgestaltung nach dem Stand der Technik,

Fig. 5

einen vereinfachten Schaltplan einer Load-Sensing-Schaltung gemäß einem bevorzugten Ausführungsbeispiel der Erfindung,

Fig. 6

ein Diagramm, das die Kennlinie der Load-Sensing-Schaltung nach Figur 5 zeigt, und

Fig. 7

einen vereinfachten Schaltplan einer Load-Sensing-Schaltung gemäß einem weitere bevorzugten Ausführungsbeispiel der Erfindung.

The prior art and the invention are described in more detail below using two preferred exemplary embodiments with reference to the drawing. Show it:

Fig. 1

2 shows a circuit diagram of a load-sensing circuit in a first embodiment according to the prior art,

Fig. 2

2 shows a diagram showing the characteristic curve of the load-sensing circuit according to FIG. 1,

Fig. 3

a simplified circuit diagram of a load sensing circuit in a second embodiment according to the prior art,

Fig. 4

a simplified circuit diagram of a load-sensing circuit in a third embodiment according to the prior art,

Fig. 5

1 shows a simplified circuit diagram of a load-sensing circuit according to a preferred exemplary embodiment of the invention,

Fig. 6

a diagram showing the characteristic of the load sensing circuit of Figure 5, and

Fig. 7

a simplified circuit diagram of a load sensing circuit according to another preferred embodiment of the invention.

Figure 1 shows a load sensing circuit for a zero stroke controlled Hydraulic pump 1 adjustable delivery volume V, two in the open circuit consumers 2 connected in parallel, such as two hydraulic motors over two Working lines 3 drives hydraulically. The hydraulic pump 1 is with a Drive motor, not shown, mechanically coupled and via a main working line 4 to the two working lines 3 and via a suction line 5 connected to the tank 6. One of the consumers 2 leads Return line 7 also to tank 6.

The hydraulic pump 1 is designed, for example, as an axial piston pump, the Actuator 8 for adjusting its delivery volume V via the piston rod 9 with the actuating piston 10 of a hydraulic cylinder 11 in a differential design is mechanically coupled. The actuating piston 10 defines in the hydraulic cylinder 11 with its smaller, circular end face a pressure chamber 12 and with its opposite, larger, circular end face one Pressure chamber 13. The pressure chamber 12 is connected via a first signal pressure line 14 the main working line 4 and via a second signal pressure line 15 to the Pressure chamber 13 connected.

The load sensing circuit consists of a control valve 16 in the second Signal pressure line 15, a volume flow feedback device 17 and each an adjusting throttle 18 in the two working lines 3. The control valve 16, which is shown symbolically in FIG. 7, divides the second Signal pressure line 15 in a first, connected to the pressure chamber 12 Signal pressure line section 19 and a second, to the pressure chamber 13 connected signal pressure line section 20. It is considered a throttling 3/2-way valve with a working connection P to the first signal pressure line section 19, a working connection A to the second signal pressure line section 20 and a working connection T to a leading to the tank 6 Relief line 21 formed.

The valve body 22 of the control valve 16 has at its two ends a first measuring surface MF ₁ and a second measuring surface MF ₂ . The first measuring area MF ₁ is larger than the second measuring area MF ₂ and defines a working pressure control chamber 23 which is connected to the first signal pressure line section 19 via a working pressure control line 24. The second measuring surface MF ₂ defines a load pressure control chamber 25, which is connected via a load pressure control line 26 to a shuttle valve 27 in a connecting line 28. The connecting line 28 connects those working line sections 3, 29 to one another which are arranged in the flow direction after the adjusting throttles 18, ie between these and the consumers 2. A preloaded compression spring 30 is arranged in the load pressure control chamber 25, which acts on the valve body 22 in FIG. 1 to the left in the direction of a first working position, in which the working connections A and T are connected to one another, while the working connection P is blocked.

The volume flow feedback device 17 comprises the two differently sized measuring surfaces MF ₁ and MF ₂ on the valve body 22 and serves to generate a feedback force F _R acting on the valve body, as described below.

The function of the load-sensing circuit according to FIG. 1 is as follows: The zero-stroke-controlled hydraulic pump 1 is actuated by the actuating or working pressure p _A, which may be present in the pressure chamber 12 of the hydraulic cylinder 11, and is removed from the main working line 4 via the first actuating pressure line 14. acted upon by a compression spring, not shown, in the pressure chamber 12 in the direction of the maximum delivery volume, as long as the control valve 16 assumes its aforementioned first working position. In this, the pressure chamber 13 of the hydraulic cylinder 11 is relieved via the second signal pressure line section 20, the opened working connections A and T of the control valve 16 and the relief line 21 to the tank 6, while the full setting or Working pressure p _A builds up and acts on the actuating piston 11 in the direction of its right end position in FIG. 1, which corresponds to the maximum delivery volume V of the hydraulic pump 1.

The preload (setting force or counterforce F _G ) of the compression spring 30 is selected such that it is equal to the hydraulic force of that pressure difference Δp between the working pressure p _{A of} the hydraulic pump 1 which was reduced in front of the adjusting throttle 18 and the load pressure p _{L of} the consumer which was reduced after the adjusting throttle 18 2, which, acting on both measuring surfaces MF ₁ and MF _{2 of} the valve body 22, is formed on the adjusting throttle 18 which is set to the largest throttle cross section and through which the maximum volume flow Q of the hydraulic pump 1 flows; in this case the other adjustment throttle 18 is completely closed.

Under these conditions, the hydraulic force of the pressure difference Δ p generated by the maximum volume flow Q at the adjusting throttle 18 is in equilibrium with the pretension or counterforce F _{G of} the compression spring 30, so that the control valve 16 assumes its starting position shown in FIG. 1, in which all working connections A, P and T are locked.

If, for example, the throttle cross section of the adjusting throttle 18 is reduced, the pressure difference Δp increases accordingly and shifts the valve body 22 in FIG. 1 to the right into a second working position, in which when the working connection T is blocked, the working connections A and P are open and the two signal pressure line sections 19 and 20 connect with each other. The actuating or working pressure p _A now acts on the larger, circular piston surface of the actuating piston 10, thus displacing it to the left in FIG. 1 and thus swiveling the hydraulic pump 1 back to a smaller delivery volume V until it delivers the reduced volume flow Q that starts the adjusting throttle 18 causes the original pressure differential pressure difference Δp corresponding to the preload F _{G of} the compression spring 30, ie until a force equilibrium is established again on the valve body 22. In accordance with the reduced volume flow Q, the load on the hydraulic pump 1 is reduced, so that the working pressure p _A and the load pressure p _L fall by the same value. However, since the load pressure p _L acts on the smaller of the two measuring surfaces MF ₁ and MF ₂ , its hydraulic force decreases by a smaller amount corresponding to the measuring surface difference MF ₁ -MF ₂ than the hydraulic force of the working pressure p _A acting on the larger measuring surface MF ₁ , The difference between the hydraulic force of the pressure difference Δp before and that after the aforementioned pivoting back of the hydraulic pump 1 to a smaller delivery volume V is a measure of the resulting reduction in the volume flow Q. This difference in force at the measuring surfaces MF ₁ and MF ₂ forming the feedback device 17 becomes here referred to as feedback force F _R , which acts on the valve body 22 in the same direction as the preload F _{G of} the compression spring 30. The feedback force F _R thus increases the action on the valve body 22 by the counterforce F _G and thus sets the control valve 16 to a larger setpoint of the volume flow Q. This results in the pQ characteristic curve shown in FIG. 2, which increases with decreasing volume flow Q and characterizes a proportional operating behavior of the hydraulic pump 1.

The operating behavior of the hydraulic pump 1 follows the same characteristic curve if the throttle cross section of the variable throttle 18 is increased. The pressure difference Δ p thus falls, so that the valve body 22 transfers to the first working position and the hydraulic pump 1 is swung out to a larger delivery volume V until it promotes the larger volume flow Q which causes the original pressure difference Δp at the adjusting throttle 18 , ie until force equilibrium is established on valve body 22. The larger volume flow Q increases the load on the hydraulic pump 1, so that the working pressure p _A and the load pressure p _{L increase to} the same extent. The hydraulic force of the working pressure p _A acting on the larger measuring surface MF ₁ increases by a larger amount corresponding to the measuring surface difference than the hydraulic force of the load pressure p _L acting on the smaller measuring surface MF ₂ . The resulting feedback force F _R acts on the valve body 22 in the opposite direction to the counter force F _G , whereby the control valve 16 is set to a smaller setpoint of the volume flow Q. The result is the same pQ characteristic curve, shown in FIG. 2 and falling with increasing volume flow Q, which characterizes a proportional operating behavior of the hydraulic pump 1.

That according to the above description for controlling the hydraulic pump 1 Control valve 16 also takes over the function of a Regulation with which the delivery volume V of the hydraulic pump 1 changes Loads are adjusted such that the volume flow Q delivered with the adjusting throttle 18 matches the setpoint.

For example, if the load on the consumer 2 increases so much that the drive motor is pressed and thus the hydraulic pump 1 one Speed drop corresponding smaller volume flow Q promotes the Valve body 22 in the same manner as in the control described in shifted the first working position and thus the hydraulic pump 1 for so long larger delivery volume V swung out until it reaches that volume flow Q promotes the original pressure difference Δ p on the adjusting throttle 18 generated. In a corresponding manner, the load on the Consumer 2 and accordingly cranking up the drive motor and Hydraulic pump 1 the latter set to a smaller delivery volume until the volume flow Q is adapted to the needs of the consumer.

If the previously closed adjustment throttle 18 is also opened, the volume flow Q delivered by the hydraulic pump 1 is divided into two partial volume flows, which the consumers 2, in accordance with the set throttle cross sections and the loads acting on the consumers 2 at the branches of the working lines 3 from the main working line 4 drive at appropriate speed. The respectively higher load pressure p _L acts via the shuttle valve 27 and the load pressure control line 26 on the second measuring surface MF _{2 of} the valve body 22, while the same working pressure p _A in both working lines 3 acts on the first measuring surface MF ₁ . In this way, the smaller of the pressure difference Δ p occurring at both adjusting throttles 18 acts on the valve body 22; in other words, the control and regulation described above only controls or regulates the consumer 2 which is subject to greater loads in the manner described above.

The load-sensing circuit according to FIG. 3 differs from that according to FIG. 1 with an otherwise identical construction and function by an override device 31 for changing the size of the first and second measuring surfaces MF ₁ , MF ₂ . pressure difference Δp. The override device 31 comprises a third measuring surface MF ₃ , which is formed on the valve body 22, defines a control pressure chamber 32 and can be acted upon by an external control pressure p _S against the counterforce F _{G of} the compression spring 30 via a control pressure line 33 connected thereto, by the pressure difference Increase Δp as required; this function of the override device 31 which causes the hydraulic pump 1 to pivot back to a smaller delivery volume as the control pressure p _S increases is also referred to as a negative control function. On the other hand, a so-called positive control function is also possible, with which the hydraulic pump 1 is pivoted out to a larger delivery volume V when the control pressure increases; For this purpose, the control pressure line 33 can be connected to the pressure space opposite the control pressure space 32, designated by reference numeral 34 in FIG.

FIG. 4 shows a load-sensing circuit which, instead of the hydraulic override device 31, comprises an override device 35 which is designed as an electrically controllable input part, for example in the form of a switching magnet or control magnet, for the control valve 16 and, with appropriate control, the valve body 22 with a Additional force is applied, which either acts against the counterforce F _{G of} the compression spring 30 (when performing the negative control function) or in the opposite direction (when performing the positive control function).

The load sensing arrangement according to FIG. 5 differs from that according to FIG. 1 with otherwise the same construction and function in that instead of the volume flow feedback device 17 with measuring surfaces MF ₁ and MF _{2 of} different sizes, they are of the same size and therefore have the reference symbols MF ' ₁ and MF ' ₂ designated measuring surfaces and a delivery volume feedback device 36 are used in the form of a displacement measuring spring which acts on the actuator 8 of the hydraulic pump 1 and on the end of the valve body 22 opposite the compression spring 30. The measuring spring 36 detects the delivery volume setting of the hydraulic pump 1 by acting on the valve body 22 with increasing delivery volume V with a correspondingly increasing feedback force F _R and with decreasing delivery volume V with a correspondingly decreasing feedback force F _R against the counterforce F _{G of} the compression spring 30. In this way, the action on the valve body 22 by the counterforce F _G and thus the setpoint setting of the control valve 16 is changed such that the pV- shown in FIG. 6 decreases with increasing delivery volume V and, conversely, increases with decreasing delivery volume V. Characteristic results that characterizes a load-sensing circuit with so-called proportional behavior.

The invention also extends to exemplary embodiments, both the Volume flow feedback device 17 and the delivery volume feedback device 36 use.

Figure 7 shows a load sensing circuit with superimposed pressure or power control. It comprises a first, double-acting and stationary actuating cylinder 37, a second, single-acting actuating cylinder 38 and the control valve 16 according to FIG. 1, but without the measuring surfaces acted upon by the differential pressure Δp. These are designed as measuring surfaces MF ' ₁ and MF' _{2 of the} same size on the actuating piston 39 of the first actuating cylinder 37. The first measuring surface MF ' ₁ defines the working pressure control chamber 23, which is connected to the main working line 4 via the working pressure control line 24. The second measuring surface MF ' ₂ defines the load pressure control chamber 25, which is connected via the load pressure control line 26 to the shuttle valve 27 in the connecting line 28 connecting the working line sections 29. The pressure difference .DELTA.p taken off at the adjusting throttle 18 associated with the higher-load consumer acts on the actuating piston 39 of the first actuating cylinder 37 and acts on the second actuating cylinder 38 in FIG. 7 to the left in the direction of the valve body 22 via its piston rod 40.

The actuating piston 42 of the second actuating cylinder 38 has an annular piston surface 43 which, together with an annular cylinder surface 44 of the same size, defines a likewise annular pressure chamber 45 which is penetrated by the piston rod 46 and is connected to the second actuating pressure line section 15, 20 via a control line 47 , The actuating piston 42 acts on the valve body 22 of the control valve 16 against the counterforce F _{G of} the adjustable compression spring 30 in the direction of the second, under the action of the working pressure p _{A of} sufficient size present in the pressure chamber 45 and taken from the first actuating pressure line section 15, 20 by the first actuating pressure line 14 working position.

The feedback device is designed here as a delivery volume feedback device 36 which, in the case of the aforementioned pressure control, comprises a position measuring spring and, in the case of the aforementioned power control, an arrangement of a plurality of travel measuring springs connected in series with different characteristic curves which approximate a performance hyperbola. The displacement spring or displacement spring arrangement 36 engages on the piston rod 9 of the actuating piston 10 of the hydraulic cylinder 11 and on the end of the valve body 22 opposite the actuating cylinders 37, 38 and acted upon by the compression spring 30. Thus, the measuring spring or measuring spring arrangement 36 is tensioned with increasing swiveling back of the hydraulic pump 1 to a smaller delivery volume V, so that the resulting feedback force F _R acts in the same direction with the compression spring 30, ie the valve body 22 in the direction of the first working position and via this and the actuating piston 42, the second actuating cylinder 38 is urged against a stationary stop 48.

The valve body 22 takes over together with the first actuating cylinder 37 Load-sensing function and together with the second actuating cylinder 38 Pressure or power control, with the p-V characteristics of both the load sensing control as well as the pressure or power control of the characteristic of Displacement spring 36, for example the characteristic shown in FIG. 6, or the Power hyperbola correspond to the position measuring spring arrangement 36.

The measuring surfaces MF ' ₁ and MF' ₂ are larger than the piston surface 43 and the cylinder surface 44, in such a way that during the load sensing function the hydraulic force of the pressure difference Δp acting on the measuring surfaces MF ' ₁ and MF' _{2 is} greater than the hydraulic force of the working pressure p _A acting on the cylinder surface 44 and thus keeps the second actuating cylinder 38 at a distance from the fixed stop 46; as a result, the effect of the working pressure p _A on the actuating piston 42 and thus the valve body 22 is switched off. If the value at which the pressure or power control is to override the load-sensing function is exceeded, the hydraulic force of the working pressure p _A acting on the piston surface 43 and on the cylinder surface 44 exceeds the hydraulic force of the pressure on the measuring surfaces MF ' ₁ and MF ' ₂ acting pressure difference Δ p and displaces the second actuating cylinder 38 against the fixed stop 48. As a result, the second actuating cylinder 38 and the actuating piston 39 of the first actuating cylinder 37 are shut down, and the working pressure p _A displaces the actuating piston 42 of the second actuating cylinder 38 in Figure 7 to the left and in this way transfers the valve body 22 into the second working position; the hydraulic pump is pivoted back to a smaller delivery volume V in accordance with the characteristic curve of the displacement spring 36 or the power hyperbola of the displacement spring arrangement 36.

Claims (9)

1. Load-sensing circuit for a zero-stroke-regulated hydraulic pump (1) with adjustable delivery volume (V) driving at least one consumer (2) via at least one working line (3), with a control valve (16) which can be set to a nominal value of the volume flow (Q) of the hydraulic pump (1),
   the valve body (22) of which, under the effect of a counter-force (F_G) setting the nominal value, can be pressurised via a first measurement surface (MF₁, MF'₁) by the working pressure (p_A) of the hydraulic pump (1) against the counter-force (F_G) towards a working position and via a second measurement surface (MF₂, MF'₂) by the load pressure (p_L) of the consumer (2) in the same direction as the counter-force (F_G) towards another working position,
   or the valve body (22) of which, under the effect of the counter-force (F_G) setting the nominal value, can be pressurised via a pressure difference (Δ_p) acting on an actuator piston (39) in the opposite direction to the counter-force (F_G),
   where the control valve (16) in the one working position provokes an adjustment of the hydraulic pump (1) towards a smaller and in the other working position towards a greater delivery volume (V),
   characterised by
   a feedback device (17, 36) to generate a feedback force (F_R) corresponding to the set delivery volume (V) of the hydraulic pump (1) which acts on the valve body (22) and changes the pressurisation of the valve body (22) by the counter-force (F_G) and hence the nominal value setting of the control valve (16) in the opposite direction to the changes of the delivery volume (V),
   where the feedback device comprises a delivery volume feedback device (36) which is formed with at least one position measurement spring (36) which acts on the actuator (8) adjusting the delivery volume (V) of the hydraulic pump (1) and on the valve body (22).
2. Load-sensing circuit according to claim 1, characterised in that the characteristic curve(s) of the position measurement spring (36) resemble a power hyperbola.
3. Load-sensing circuit according to claim 1 or 2, characterised in that the working pressure (p_A) is taken in the flow direction before and the load pressure (p_L) in the flow direction after a choke point (18) in the working line (3).
4. Load-sensing circuit according to claim 3, characterised in that the choke position (18) is an adjustment choke.
5. Load-sensing circuit according to at least one previous claim,
   characterised by an overdrive device (31, 35) to change the size of the pressure difference (Δ_p) acting on the measurement surfaces (MF₁, MF₂) between the working pressure (p_A) and the load pressure (p_L).
6. Load-sensing circuit according to at least one previous claim,
   characterised in that between the valve body (22) and a first double-action stationary actuating cylinder (37) is clamped a second single-action actuating cylinder (38) pressurised by the counter-force (F_G) in the direction of a stationary stop (48), the actuating piston (42) of which cylinder, under the effect of the working pressure (p_A), pressurises the valve body (22) against the counter-force (F_G), and in that the adjustment piston (39) of the first actuating cylinder (37) has the measurement surfaces (MF'₁, MF'₂) which can be subjected to the working pressure (p_A) and the load pressure (p_L), and under the effect of the pressure difference (Δ_p) between the working pressure (p_A) and the load pressure (p_L) via the second actuating cylinder (38) pressurises the valve body (22) against the counter-force (F_G).
7. Load-sensing circuit according to claim 6, characterised in that the piston surface (43), pressurised by the working pressure (p_A), of the actuating piston (42) of the second actuating cylinder (38) is smaller than the measurement surfaces (MF'₁, MF'₂) of the adjustment piston (39) of the first adjustment cylinder (37) which can be subjected to the working pressure (p_A) and the load pressure (p_L).
8. Load-sensing circuit according to at least one previous claim,
   characterised in that between the valve body (22) and a first double-action stationary actuating cylinder (37) is clamped a second single-action actuating cylinder (38) which is pressurised by the counter-force (F_G) in the direction of a stationary stop (48), the actuating piston (42) of which cylinder, under the effect of the working pressure (p_A), pressurises the valve body (22) against the counter-force (F_G), and that the actuating piston (39) of the first actuating cylinder (37) has the measurement surfaces (MF'₁, MF'₂) which can be subjected to the working pressure (p_A) and the load pressure (p_L) and under the effect of the pressure difference (Δ_p) between the working pressure (p_A) and the load pressure (p_L) via the second actuating cylinder (38) pressurises the valve body (22) against the counter-force (F_G).
9. Load-sensing circuit according to claim 8, characterised in that the piston surface (43), pressurised by the working pressure (p_A), of the actuating piston (42) of the second actuating cylinder (38) is smaller than the measurement surfaces (MF'₁, MF'₂) of the actuating piston (39) of the first actuating cylinder (37) which can be subjected to the working pressure (p_A) and the load pressure (p_L).

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