Valve assembly for actuating a lifting mechanism

Abstract

Valve assembly (20; 20'; 20"), in particular for actuating a lifting mechanism (10) with a single-acting first cylinder (11) and a double-acting second cylinder (12), wherein the valve assembly (20; 20'; 20") has a housing (30) with a first, a second and a third outlet (31; 32; 33), a pump connection (34) and a tank connection (35), wherein a first cylinder (11) is assigned to the first outlet (31), wherein a second cylinder (12) is assigned to the second and the third outlet (32; 33), wherein a first and a second control valve (40; 70) are each linearly movable with respect to a first and a second axis (50; 72) respectively in the housing (30), wherein the first control valve (40) has a first and a second main orifice (61;62) which together with a main sealing surface (39) on the housing (30) can form a continuously adjustable aperture, wherein the first control slide (40) is biased into a central position (45) by means of at least one first spring (53), so that it can act in a first and an opposite second direction (51;52) is movable away from the central position (45) with respect to the first axis (50), wherein the second control slide (70) together with the housing (30) forms a continuously adjustable control orifice (71), wherein the second control slide (70) is acted upon by the pressure at a first control point (21) in a closing direction of the control orifice (71), wherein it is acted upon by a second spring (73) and by the pressure at a second control point (22) in an opening direction of the control orifice (71), wherein a fluid flow path (23) leads from the pump connection (34) via the control orifice (71), further via the first control point (21), through the main sealing surface (39), further to the second control point (22), characterized in that the first control slide (40) has a third main orifice (63) which together with the main sealing surface (39) can form the said continuously adjustable orifice, wherein the first, the second and third main aperture (61; 62;63) are arranged along the first axis (50) so distributed on the first control slide (40) that, depending on the position of the first control slide (40), only one of the aforementioned main apertures (61; 62; 63) together with the main sealing surface (39) forms the continuously adjustable aperture, wherein in a first position (41) of the first control slide (40), which is arranged immediately adjacent to the center position (45) in the first actuation direction, the first main aperture (61) interacts with the main sealing surface (39), wherein the first control slide (40) is designed such that in the first position (41) the second control point (22) is connected to the first output point (31) via the first control slide (40), wherein in the first position (41) the second and the third output point (32;33) are blocked by the first control slide (40), wherein in a second position (42) of the first control slide (40) the second main orifice (62) interacts with the main sealing surface (39), wherein in the second position (42) the second control point (22) is connected via the first control slide (40) to the second output point (32), wherein in the second position (42) the first output point (31) is blocked by the first control slide (40), wherein in a third position (43) of the first control slide (40) the third main orifice (63) interacts with the main sealing surface (39), wherein in the third position (43) the second control point (22) is connected via the first control slide (40) to the third output point (33), wherein in the third position (43) the first output point (31) is blocked by the first control slide (40).;

Description

[0001] The invention relates to a valve assembly according to the preamble of claim 1.

[0002] From EP 2 280 179 B1, a valve assembly with a first and a second control spool is known. The second control spool is designed as a pressure balance, which regulates the pressure drop across a continuously adjustable orifice of the first control spool to a predetermined value, so that the speed of movement of the cylinder connected to the valve assembly depends solely on the setting of the first control spool and essentially not on the load acting on the cylinder. The aforementioned pressure drop is the difference between the pressure at a first control point and the pressure at a second control point, wherein the first control point is located immediately upstream of the continuously adjustable orifice, and the second control point is located immediately downstream of the continuously adjustable orifice. The pressure at the second control point is also referred to as the individual load pressure.In a valve block with several valve assemblies or valve discs, the highest individual load pressure of all valve assemblies is determined in order to regulate the delivery pressure of the pump to a value that is above the highest load pressure by a predetermined pressure difference.

[0003] From the datasheet "Load-Sensing Directional Control Valves in Disc Design SB24-EHS4, SB34-EHS4", order number RD66174, edition 2021-11-11 of Bosch Rexroth AG, a modular system for valve blocks is known, with the valve blocks being used particularly in agricultural tractors. The individual valve discs or valve assemblies operate according to the principle of EP 2 280 179 B1. The first control spools can be actuated by a pilot control unit according to DE 10 2019 204 246 A1. In this case, the first control spool is hydraulically adjusted by means of an electrically actuated 4 / 3-way valve, whereby the position of the first control spool is measured by means of an inductive position sensor, and a position controller adjusts the measured actual position to a predetermined target position by adjusting the aforementioned directional control valve. This allows the position of the first control slide to be adjusted very precisely.

[0004] The linkage at the rear of an agricultural tractor can comprise a first and a second cylinder. The first cylinder moves the lower link of the linkage, while the second cylinder is part of the top link. Currently, the two cylinders are controlled by two separate valve discs in the valve block mentioned above.

[0005] From DE 10 2018 212 114 A1, a directional control valve is known which is intended for use in an agricultural tractor. The directional control valve comprises a second control spool as defined in the present application, which is also referred to as an LS pressure balance. The directional control valve is intended for controlling a single, double-acting cylinder. Two corresponding directional control valves are required for operating a lifting mechanism.

[0006] An advantage of the present invention is that only a single valve assembly is required to control both cylinders of a lifting mechanism. The load-independent adjustment described above remains possible regardless of whether the first or second cylinder is being adjusted. The valve disc according to the invention can be used within the existing modular system, and in particular, the connection dimensions of the valve assembly, which are important for interaction with other valve assemblies, can remain unchanged. This means, in particular, that the additional function can be implemented without a significant increase in the required installation space for the valve assembly. Additional control spools within the valve assembly can be avoided.

[0007] According to claim 1, it is proposed that the first control slide has a third main orifice which, together with the main sealing surface, can form the said continuously adjustable orifice, wherein the first, the second, and the third main orifices are arranged along the first axis such that, depending on the position of the first control slide, only one of the said main orifices together with the main sealing surface forms the continuously adjustable orifice, wherein in a first position of the first control slide, which is arranged immediately adjacent to the center position in the first actuation direction, the first main orifice interacts with the main sealing surface, wherein the first control slide is designed such that, in the first position, the second control point is connected to the first output point via the first control slide.wherein in the first position the second and the third output positions are blocked by the first control slide, wherein in a second position of the first control slide the second main orifice interacts with the main sealing surface, wherein in the second position the second control point is connected to the second output position via the first control slide, wherein in the second position the first output position is blocked by the first control slide, wherein in a third position of the first control slide the third main orifice interacts with the main sealing surface, wherein in the third position the second control point is connected to the third output position via the first control slide, wherein in the third position the first output position is blocked by the first control slide.

[0008] Within the scope of the present application, the first, second, and third main orifices each refer to the surface contours on the first control slide, which, together with the main sealing surface, can form the continuously adjustable orifice. Preferably, these surface contours on the first control slide include fine control notches by which the position-dependent flow resistance of the continuously adjustable orifice is primarily defined. The main sealing surface is preferably cylindrical with respect to the first axis. In the direction of the first axis, it is preferably bounded at both opposite ends by a control edge circumferentially around the first axis. The length of the main sealing surface in the direction of the longitudinal axis is preferably between 10% and 50% of the diameter of the main sealing surface.

[0009] The first, second, and / or third outlets can each be directly connected to a first, second, or third working port, respectively, which is located on the outside of the housing. Preferably, the first outlet is connected to the first working port via a load-holding valve. The load-holding valve is intended, in particular, to prevent the first cylinder from moving in the opposite direction to the desired position if the pressure at the pump port is insufficient to hold the external load acting on the first cylinder. The load-holding valve is preferably designed as a releasable check valve that can be released by the first control spool, for example, by means of a linearly movable plunger.

[0010] The first working port is preferably connectable to, or already connected to, the first cylinder. The second and third working ports are preferably each connectable to, or already connected to, the second cylinder. The switching valve described below can be connected between the second and third output points and the second and third working ports.

[0011] If the valve assembly is part of a valve block with several valve assemblies, the second control point is preferably connected to a changeover valve cascade, by means of which a maximum pressure is determined from the pressures at the various second control points of the valve block. This maximum load pressure is then used to control or regulate the delivery pressure of a pump, which in turn delivers pressurized fluid to the pump connection. In addition to the valve assembly according to the invention, the aforementioned various valve assemblies can also include valve assemblies according to EP 2 280 179 B1, which are likewise equipped with the second control valve.

[0012] The valve assembly is preferably designed as a valve disc, with several separate valve discs being assemblable to form a valve block. The tank connection can comprise one or more tank channels, each of which pressurizes all valve discs of a valve block, optionally being permanently connected to one another so that they can be connected to a single tank. The pump connection can comprise one or more pump channels, each of which pressurizes all valve discs of a valve block, optionally being permanently connected to one another so that they can be connected to a single pump.

[0013] The first to third positions each denote a continuous range of positions of the first control valve in which the aforementioned connections exist, whereby the respective first, second, or third main orifice interacts with the main sealing surface in this range such that the continuously adjustable orifice is at least minimally open. The same applies to the fourth position, where a return orifice, which is also continuously adjustable, is decisive.

[0014] The valve assembly is preferably used with a pressure fluid, which is preferably a liquid and in particular hydraulic oil.

[0015] The dependent claims specify advantageous further developments and improvements of the invention.

[0016] It can be provided that, in the second position of the first control valve, the third outlet is connected to the tank connection via the first control valve, and vice versa. This allows the pressurized fluid flowing back from the second cylinder to be directed into the tank.

[0017] It can be provided that in a fourth position of the first control valve, the first outlet is connected to the tank connection via the first control valve, with the second and third outlets being blocked by the first control valve, and the second control point being connected to the tank connection via the first control valve. The first, second, and third main orifices are designed such that the fluid flow path between the first and second control points is blocked in the fourth position. In the fourth position, the hoist is lowered by adjusting the first cylinder. The pressure at the second control point, which is reported to the changeover valve cascade of the valve block, is therefore low, even when the hoist is heavily loaded. This avoids energy losses caused by an unnecessarily high pump delivery pressure.

[0018] It may be designed so that the opening cross-section of the first main orifice increases more slowly during adjustment in the first actuation direction than the opening cross-section of the second main orifice during adjustment in the second actuation direction. In this context, an opening rate is considered, calculated by dividing the change in said opening cross-section by the associated travel distance of the first control valve. The above design takes into account the fact that the user of the valve assembly typically only wants to precisely adjust the first cylinder. For the second cylinder, it is sufficient if it can be moved to the desired position. Typically, there is no attempt to precisely meter a hydraulic force with the second cylinder.

[0019] The first control slide may have several annular webs distributed along the first axis, with immediately adjacent annular webs separated from each other by a boundary groove. These annular webs comprise a first and a second annular web, with the first and second main apertures arranged on opposite sides of the first annular web in the direction of the first axis. The third main aperture is arranged on the second annular web, with the second annular web being immediately adjacent to the first annular web, so that the first and third main apertures are bounded by a common boundary groove. With this arrangement of the first to third main apertures, the first control slide can be designed to be particularly space-saving while still being easy to manufacture.A large portion of the available travel of the first control slide is used for adjusting the first to third main apertures. The limit grooves, especially the common limit groove, are preferably designed as annular grooves circumferentially around the first control slide so that the first control slide can be installed in the housing in any desired rotational position. See below for further details. Fig. Section 5 explains that this principle is preferably deviated from in the case of a limit groove. Accordingly, the limit groove can also be designed in the form of a key surface or one or two parallel flats.

[0020] It can be designed so that in the fourth position, the first annular bridge interacts with the main sealing surface in such a way that the fluid flow path between the first and second control points is blocked. Accordingly, the first annular bridge is designed to be wide enough that the first and second main orifices are completely closed in the fourth position. This prevents pressurized fluid from reaching the first starting position from the pump connection in the fourth position.

[0021] It can be designed so that, in the neutral position, the first annular web interacts with the main sealing surface in such a way that the fluid flow path between the first and second control points is blocked. This prevents pressurized fluid from reaching the first starting position from the pump connection in the neutral position.

[0022] It can be provided that the fourth position in the second direction of actuation is arranged directly adjacent to the center position. In the fourth position and in the center position, the first annular web has a comparable sealing function. The proposed arrangement of the center position and the fourth position allows this commonality to be exploited to save installation space. Consequently, the first and fourth positions are arranged on opposite sides of the center position, both being directly adjacent to it.

[0023] It can be provided that, in the neutral and fourth positions, the second control point is connected to the tank connection via at least one bore in the first control valve, with this connection being blocked except in the neutral and fourth positions. The pressure at the second control point, which is reported to the changeover valve cascade of the valve block, is therefore low in the neutral and fourth positions. This avoids energy losses caused by an unnecessarily high pump delivery pressure.

[0024] It can be provided that a switching valve is arranged in the housing, which has two latching switching positions. The switching valve is subjected to pressure at the second and third output positions in the direction of an opposing adjustment between the two latching switching positions. The switching valve is connected to a second and a third working port, which are each arranged on the outside of the housing so that they can be connected to the second cylinder. The switching valve is preferably a 2 / 2-way valve with one open and one closed switching position. Due to the advantages of this second embodiment of the invention, reference is made to the descriptions in [reference to be added]. Fig. 7 referred.

[0025] A pilot control unit can be provided with which the position of the first control valve is hydraulically adjustable. This pilot control unit implements a control loop by means of which the position of the first control valve can be adjusted to a predefinable target position. A corresponding pilot control unit is known from DE 10 2019 204 246 A1. This allows the position of the first control valve to be set very precisely, so that the continuous adjustability of the first to third main orifices can be utilized to the best possible extent. The travel distance for the second and third main orifices can be designed to be very small.

[0026] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0027] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a circuit diagram of a valve assembly according to the invention in a first embodiment with an associated lifting mechanism; Fig. 2 a longitudinal section of the valve assembly according to Fig. 1 in the middle position of the first control slide; Fig. 3 one of the Fig. 2 corresponding view in the first position of the first control slide; Fig. 4 one of the Fig. 2 corresponding view in the fourth position of the first control slide; Fig. 5 one of the Fig. 2 corresponding view in the second position of the first control slide; Fig. 6 one of the Fig. 2 corresponding view in the third position of the first control slide; Fig. 7 one of the Fig. 2 corresponding view of a valve assembly according to a second embodiment of the invention; and Fig. 8 a circuit diagram of a valve assembly according to a third embodiment according to the invention.

[0028] Fig. Figure 1 shows a circuit diagram of a valve assembly 20 according to a first embodiment of the invention, with an associated lifting mechanism 10. The lifting mechanism 10 shown is, for example, mounted on the rear of an agricultural tractor. It carries an interchangeable implement 14, which is, for example, a plow. The height of the implement 14 above the ground on which the tractor is driving is adjusted by means of the pivotable lower link 13 of the lifting mechanism 10. The lower link 13 can be raised by pressurizing the single-acting first cylinder 11. The lower link 13 can be lowered by the action of gravity. The double-acting second cylinder 12 forms a top link of the lifting mechanism 10. When the second cylinder 12 is adjusted, the length of the top link changes, thereby changing the inclination of the implement 14 relative to the ground.

[0029] The valve assembly 20 comprises a first and a second control spool 40; 70. The second control spool 70 forms a pressure balance with which the pressure difference between a first and a second control point 21; 22 is regulated to a predetermined value, which corresponds to the pressure equivalent of the pre-tensioned second spring 73. The second control spool 70, together with the housing (No. 30 in Fig. 2) The valve assembly 20 includes a continuously adjustable control orifice 71. In the opening direction of the control orifice 71, the second control slide 70 is acted upon by the pressure at the second control point 22 and by the second spring 73. In the closing direction of the control orifice 71, the second control slide 70 is acted upon by the pressure at the first control point 21.

[0030] A fluid flow path leads from tank 17 via pump 16, then via pump connection 34, then via the first control orifice 71, then via the first control point 21 and then via the first control valve 40 to the second control point 22. The further course of this inlet-side fluid flow path is described below with reference to Fig. 2 explained.

[0031] By adjusting the first control valve 40, the flow resistance between the first and second control points 21; 22 can be continuously adjusted. Furthermore, different connections between the second control point 22 and the first, second, or third output point 31; 32; 33 can be set. The first control valve 40 is preferably adjusted by a pilot control assembly 27, which is designed according to DE 10 2019 204 246 A1. The position of the first control valve 40 is accordingly adjusted hydraulically by a 4 / 3-way valve, whereby the actual position of the first control valve 40 is measured, preferably inductively, and a position controller is provided which, by adjusting the aforementioned directional control valve, adjusts the actual position to a predetermined target position.This type of adjustment is characterized by the fact that any intermediate position of the first control slide 40 can be precisely set. This is of great advantage for the present invention.

[0032] The first control valve 40 is biased into a central position 45 by a first spring 53, in which the first, second, and third output positions 31, 32, and 33 are locked. Furthermore, the first control valve 40 has a first, second, third, and fourth position 41, 42, 43, and 44, which can be set by means of the pilot control assembly 27, with reference to Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6 will be explained in more detail.

[0033] The first, second and third working connections 36; 37; 38 are located on the outside of the housing (No. 30 in Fig. 2) of the valve assembly 20, so that the first and second cylinders 21 and 22, respectively, can be connected there. In the first embodiment, the second working port 37 forms the second outlet 32, and the third working port 38 forms the third outlet 33. A load-holding valve 24 is connected between the first working port 36 and the first outlet 31. This valve is intended to prevent the first cylinder 11 from moving in the opposite direction if the pressure at the pump port 34 is insufficient to hold the load acting on the first cylinder 21. The load-holding valve 24 is designed as an unlockable check valve, which, in the active state, allows only fluid flow from the first outlet 31 to the first outlet port 36. In the unlocked state, both flow directions are possible. Unlocking is performed mechanically with a plunger (No. 92 in [reference missing]). Fig. 2), which interacts with the first control valve 40, with reference to DE 10 2011 013 176 A1 as an example. Hydraulic unlocking is also conceivable.

[0034] Furthermore, the pressure relief valve 26 should be noted, which limits the pressure at the first working port 36 upwards, with the pressure relief valve 26 opening towards the tank 17.

[0035] Fig. Figure 2 shows a longitudinal section of the valve assembly 20. Fig. 1 in the central position 45 of the first control valve 40. The first control valve 40 has a total of seven annular webs 80, which are arranged distributed along the first axis 50, defining a common circular cylinder that is arranged concentrically to the first axis 50. In particular, the second, first, fourth, third, fifth, sixth and seventh annular webs 82; 81; 84; 83; 85; 86; 87 are arranged in the aforementioned order distributed along the first axis 50.

[0036] The housing 30 has a bore that is essentially fluid-tight and adapted to the aforementioned circular cylinder. Two immediately adjacent annular webs 80 are each separated from each other by an associated limit groove 90. The in Fig. The rightmost ring bar 80 is the second ring bar 82, on which the fine control notches 54 of the third main aperture 63 are arranged. The one in Fig. The first ring 81, located immediately to the left of the two adjacent ring ribs 80, is the ring rib 81, on which the fine control notches 54 of the first and second main orifices 61; 62 are arranged. The first and second ring ribs 81; 82 are separated from each other by the common limit groove 91. In the present central position, the first ring rib 81 rests against the main sealing surface 39 of the bore in the housing 30 such that the fluid flow path 23, indicated by a dashed line, is fluid-tight. The limit grooves 90, marked No. 96, run in an annular shape around the first control slide 40. The limit groove 90, marked No. 97, in the area of ​​the second tap 48, is designed in the form of a key surface, with the second tap 48 opening away from this limit groove 97 onto the circular cylindrical outer circumferential surface of the first control slide 40.

[0037] The fluid flow path 23 mentioned above leads from a pump port 34, via the control orifice 71 of the second control valve 70, via the first control point 21, through the main sealing surface 39 to the second control point 22. The pump port 34 is formed by a permanently open channel that carries all valve assemblies 20 of a valve block perpendicular to the plane of the drawing. Fig. 2 permeated.

[0038] The tank connection 35 is also formed by a permanently open channel, which connects all valve assemblies 20 of a valve block perpendicular to the plane of the drawing. Fig. 2. The bore 46 and the associated first and second radial taps 47; 48 in the first control valve 40 permanently connect the two left limit grooves 90, which separate the fifth, sixth, and seventh annular webs 85; 86; 87, so that a connection exists between the tank connection 35 and the second control point 22 via this flow path in the neutral position. Therefore, the present valve assembly 20 is not used when determining the maximum load pressure of the entire valve block, even if a high pressure is present at the first to third working ports 36; 37; 38.

[0039] In the first embodiment, the second outlet 32 ​​directly forms the second working port 37, which is located on the outside of the housing 30. In the central position, the second outlet 32 ​​is sealed off fluid-tight by the fifth annular web 85. In the first embodiment, the third outlet 33 directly forms the third working port 38, which is located on the outside of the housing 30. In the central position, the third outlet 33 is sealed off fluid-tight by the sixth annular web 86.

[0040] The first outlet 31 is formed by a U-shaped channel in the housing, the legs of which lead to two different annular webs 80, with the base of the U being connected to the load-holding valve 24 described above. In the neutral position, the plunger 92 is in a position where it is closest to the first axis 50, so that the check valve function of the load-holding valve 24 is active. Since the load-holding valve 24 is a poppet valve, no pressurized fluid can flow from the first working port 36 to the first outlet 31. In the reverse direction, small leakage flows are possible because the first annular web 81 does not completely seal the fluid flow path 23 without leakage.

[0041] It should also be noted that the return orifice 64 in the third ring web 83 is completely closed in the middle position, so that no fluid exchange between the tank connection 35 and the first outlet point 31 is possible.

[0042] The pressure in the pressure chamber 75 acts on the second control slide 70 in the closing direction of the control orifice 71. Fig. Figure 2 shows the control orifice 71 in a fully closed position, with the pressure chamber 75 at its maximum volume. A permanent fluid exchange connection between the first control point 21 and the pressure chamber 75 is established via the tap 74 and a central bore in the second control slide 70. In the opposite direction, the pressure at the second control point 22 and the force of the second spring 73 act on the second control slide 70.

[0043] Fig. 3 shows one of the Fig. 2 corresponding view in the first position 41 of the first control slide 40. The first control slide 40 is opposite Fig. 2 in the first actuation direction 51 slightly to the left. The fine control notches 54 of the first main aperture 61 now interact with the main sealing surface 39 on the housing 30, showing a maximally open position of the corresponding continuously adjustable aperture, the first position encompassing every position of the first control slide 40 in which the respective continuously adjustable aperture is less open, as long as it is open. Both ends of the main sealing surface 39 opposite each other in the direction of the first axis 50 form an annular edge around the first axis 50, which is also called the control edge because it can interact with at least one main aperture 61; 62; 63 to form the continuously adjustable aperture.

[0044] The fine control notches 54 of the second and third main orifices 62; 63 have no influence on the flow resistance between the first and second control point 21; 22 in the first position, since they do not interact with the main sealing surface 39, which is located in the fluid flow path 23.

[0045] As in the middle position, in the first position the second and third exit points 32; 33 are each fluid-tightly sealed off from the fifth and sixth ring webs 85; 86, respectively. The in Fig. 3. The left first radial tap 47 of the bore 46 is now displaced so far that the connection between the tank connection 35 and the second control point 22, as described above, is blocked. Contrary to the illustration in Fig. 3 preferably covers the bore for the first control valve 40 in the housing, the aforementioned first tap 47 and the associated limit groove 90. The third annular web 83 closes the connection between the tank connection 35 and the first outlet 31, as in the central position.

[0046] The load-holding valve 24 is shown in an open position because in the first position there is typically a fluid flow from the second control point 22 via the limit groove 90 between the first and the fourth annular web 81; 84, further via the first outlet point 31, further via the load-holding valve 24 to the first working port 36, in order to supply the first cylinder (No. 11 in Fig. 1) to drive out.

[0047] In Fig. Figure 3 shows the second control slide 70 in the fully open position of the control orifice 71, the position of the second control slide 70 being different from that on the first cylinder (No. 11 in Fig. 1) depends on the attacking load or on the pressure at the second control point 22.

[0048] Fig. 4 shows one of the Fig. 2 corresponding view in the fourth position 44 of the first control valve 40. The first control valve 40 is opposite Fig. 2 in the second actuation direction 52 is shifted slightly to the right. This initially causes the plunger 92 to be moved away from the first axis 50 by the first control slide 40. This unlocks the load-holding valve 24, allowing a fluid flow from the first working port 36 to the first outlet 31. The pressurized fluid then flows on through the open return orifice 64 on the third annular web 83 to the tank port 35. This activates the first cylinder (No. 11 in Fig. 1) driven in by the effect of gravity.

[0049] The second and third outlets 32; 33 remain blocked by the fifth and sixth ring webs 85; 86, respectively. As in the neutral position, the bore 46 in the first control valve 40 creates a connection between the tank port 35 and the second control point 22, resulting in a low pressure at the latter. Therefore, when determining the maximum load pressure of the entire valve block, the present valve assembly 20 is not used, even if a high pressure is present at the first to third working ports 36; 37; 38.

[0050] As in the middle position, the first ring bridge 81 seals fluid-tight against the main sealing surface 39, whereby neither the first nor the second main aperture 61; 62 on the first control slide 40 become effective.

[0051] Fig. 5 shows one of the Fig. 2 corresponding view in the second position 42 of the first control slide 40. The first control slide 40 is opposite Fig. 4 in the second direction of operation 52 shifted even further to the right, whereby it is in Fig. Figure 5 shows the second main aperture 62 in an end position where it rests against the right end stop. This initially causes the second main aperture 62 to interact with the main sealing surface 39 on the first ring bridge 81, thus determining the flow resistance of the continuously adjustable aperture between the first and second control points 21; 22. The fine control notches 54 of the second main aperture 62 are designed such that the travel from the closed position of the second main aperture 62 to the fully open position of the second main aperture 62 is significantly smaller than the analogous travel of the first main aperture 61.

[0052] The connection between the first outlet 31 and the second control point 22 is blocked by the fourth ring bridge 84. The connection between the first outlet 31 and the tank connection 35 is blocked by the fifth ring bridge 85. The limit groove 90 between the fifth and sixth ring bridges 85; 86 allows a connection between the second control point 22 and the second outlet 32 ​​or the second working port 37. Thus, pressurized fluid can flow from the pump port 34 to the second working port 37. Consequently, the second cylinder (No. 12 in Fig. 1) extended. The load acting on the second cylinder determines the pressure at the second control point 22. This allows the extension speed of the second cylinder to be set essentially independently of its external load.

[0053] The third working port 38 from the second cylinder (No. 12 in Fig. 1) The backflowing pressurized fluid flows over the boundary groove 90 between the sixth and seventh ring webs 86; 87 to the tank connection 35. It is understood that the channel 93 lies in a different plane than the channels corresponding to the second and third outlet points 32; 33, so that these channels do not intersect each other. This fact is indicated by the modified hatching around the channel 93.

[0054] In Fig. In Figure 5, it appears as if the bore system 46; 47; 48 would cause a hydraulic short circuit between the tank connection 35 and the second control point 22. This is not actually the case because the limit groove 97 is designed in the manner of a key face, so that it does not surround the first control valve 40 over its entire circumference. The second tap 48 opens outside the first control valve 40, away from this limit groove 97. Consequently, in the second position, the circular cylindrical bore in the housing 30 fluid-tightly covers the second tap 48. The first control valve 40 is preferably secured against rotation to ensure that this coverage is reliably maintained.

[0055] Fig. 6 shows one of the Fig. 2 corresponding view in the third position 43 of the first control valve 40. The first control valve 40 is opposite Fig. 4 in the first actuation direction 51 shifted even further to the left, whereby it was in Fig. Figure 6 shows the orifice in an end position where it rests against the left end stop. This initially causes the third main orifice 63 to interact with the main sealing surface 39 on the second annular web 82, thus determining the flow resistance of the continuously adjustable orifice between the first and second control points 21 and 22. The connection between the first outlet point 31 and the second control point 22 is blocked by the first annular web 81, while the connection from the first outlet point 31 to the tank connection 35 is blocked by the third annular web 83.

[0056] From the second control point 22, pressurized fluid can flow via the limit groove 90 between the fifth and sixth annular webs 85; 86 to the third outlet point 33 or to the third working port 38. Subsequently, the second cylinder (No. 12 in Fig. 1) Retracted. The load acting on the second cylinder determines the pressure at the second control point 22. This allows the retraction speed of the second cylinder to be set essentially independently of its external load.

[0057] The second working port 37 from the second cylinder (No. 12 in Fig. 1) Backflowing pressure fluid flows over the limit groove 90 between the third and the fifth ring web 83; 85 to the tank connection 35.

[0058] Fig. 7 shows one of the Fig. 2. Corresponding view of a valve assembly 20' according to a second embodiment. The second embodiment is identical to the first embodiment except for the differences explained below, so that reference is made to the descriptions of the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6 is referred to. In the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. 7 are identical or corresponding parts marked with the same reference numbers.

[0059] In contrast to the first embodiment, the second and third outlets 32; 33 no longer directly form the second and third working ports 37; 38, respectively. Rather, the second and third working ports 37; 38 are connected to a switching valve 25 with two switching positions. In the Fig. In the first switching position shown in Figure 7, a fluid exchange connection exists between the second and third working ports 37; 38. In the other, second switching position, this connection is blocked. The two switching positions are locked by the detent device 94, so that the last set switching position is retained if the first control slide 40 is, for example, in the fourth position. The switching valve can be switched by the pressure at the second or third outlet 32; 33, i.e., by setting the second or third position of the first control slide 40.

[0060] The second embodiment is used, for example, when an implement is mounted on the lifting mechanism that, in a lowered position, is intended to follow the ground largely freely, while in a raised position it is to be firmly connected to the tractor. A rotary mower is one example. In the lowered position, its weight is largely distributed via the first cylinder (No. 11 in Fig. 1) supported, with the rotary mower bearing a residual force against the ground, allowing it to follow the uneven terrain as the tractor moves. For this purpose, the top link is preferably freely movable, which is achieved with the in Fig. The first switching position shown in Figure 7 can be achieved. However, when the rotary mower is lifted from the ground, the top link should be rigid. This can be achieved by setting the second switching position.

[0061] Fig. Figure 8 shows a circuit diagram of a valve assembly 20" according to a third embodiment of the invention. The third embodiment is derived from the first embodiment, except that no lifting mechanism is provided. Instead, the second and third working ports 37; 38 are each closed with a sealing screw. In this application as well, the second and third positions of the first control slide 40 according to the invention are advantageous.

[0062] The second position, 42", allows the pressure fluid to be warmed up after the hydraulic system has been out of operation for an extended period, particularly during winter. For this purpose, the pressure fluid is pumped from the pump connection 34 to the tank connection 35 via the second main orifice 62. Only the [unclear text] needs to be adjusted. Fig. The connecting bore 95, shown as a dashed line, is to be produced. No further changes compared to the first embodiment are necessary.

[0063] The third position 43" ensures that the pump delivers at maximum pressure, regardless of the loads acting on the various actuators of the valve block. For this, the valve assembly according to the first embodiment does not need to be modified. It is sufficient to screw the previously mentioned sealing screws into the second and third working ports 37; 38. Reference sign 10 hoist 11 first cylinder 12 second cylinder 13 lower links 14 attachments 16 pump 17 Tank 20 Valve assembly (first embodiment) 20' Valve assembly (second embodiment) 20" valve assembly (third embodiment) 21 first tax office 22 second tax office 23 Fluid flow path 24 Load holding valve 25 switching valve 26 Pressure relief valve 27 Input control unit 30 cases 31 first starting point 32 second starting point 33 third exit 34 Pump connection 35 Tank connection 36 first work connection 37 second work connection 38 third work connection 39 Main sealing surface 40 first control valve 41 first position 42 second position 42" second position of the third embodiment 43 third position 43" third position of the third embodiment 44 fourth position 45 Middle position 46 bore in the first control valve 47 First radial tap of the bore in the first control valve 48 second radial tap of the bore in the first control valve 50 first axis 51 first direction of operation 52 second direction of operation 53 first spring 54 Fine control notch 61 first main aperture 62 second main aperture 63 third main aperture 64 Return orifice 70 second control valve 71 Control aperture 72 second axis 73 second spring 74 Tapping hole 75 Pressure chamber 80 Ring Bridge 81 first ring bridge 82 second ring bridge 83 third ring bridge 84 fourth ring bridge 85 fifth ring bridge 86 sixth ring bridge 87 seventh ring bridge 90 Border groove 91 common border 92 pestles 93 Channel to tank connection 94 Locking device 95 Connecting hole 96 circular circumferential boundary grooves 97 key-shaped boundary grooves

Claims

[1] Valve assembly (20; 20'; 20"), in particular for actuating a lifting mechanism (10) with a single-acting first cylinder (11) and a double-acting second cylinder (12), wherein the valve assembly (20; 20'; 20") has a housing (30) with a first, a second and a third outlet (31; 32; 33), a pump connection (34) and a tank connection (35), wherein a first cylinder (11) is assigned to the first outlet (31), wherein a second cylinder (12) is assigned to the second and the third outlet (32; 33), wherein a first and a second control valve (40; 70) are each linearly movable in the housing (30) with respect to a first and a second axis (50; 72), respectively, wherein the first control valve (40) has a first and a second main orifice (61;62) which together with a main sealing surface (39) on the housing (30) can form a continuously adjustable aperture, wherein the first control slide (40) is biased into a central position (45) by means of at least one first spring (53), so that it can act in a first and an opposite second direction (51;52) is movable away from the central position (45) with respect to the first axis (50), wherein the second control slide (70) together with the housing (30) forms a continuously adjustable control orifice (71), wherein the second control slide (70) is acted upon by the pressure at a first control point (21) in a closing direction of the control orifice (71), wherein it is acted upon by a second spring (73) and by the pressure at a second control point (22) in an opening direction of the control orifice (71), wherein a fluid flow path (23) leads from the pump connection (34) via the control orifice (71), further via the first control point (21), through the main sealing surface (39), further to the second control point (22), ; characterized by, that the first control slide (40) has a third main aperture (63) which, together with the main sealing surface (39), can form the said continuously adjustable aperture, wherein the first, second and third main apertures (61; 62; 63) are arranged along the first axis (50) in such a way that, depending on the position of the first control slide (40), only one of the said main apertures (61; 62;63) together with the main sealing surface (39) forms the continuously adjustable aperture, wherein in a first position (41) of the first control slide (40), which is arranged in the first actuation direction immediately adjacent to the center position (45), the first main aperture (61) interacts with the main sealing surface (39), wherein the first control slide (40) is designed such that in the first position (41) the second control point (22) is connected to the first output point (31) via the first control slide (40), wherein in the first position (41) the second and the third output point (32;33) are blocked by the first control slide (40), wherein in a second position (42) of the first control slide (40) the second main orifice (62) interacts with the main sealing surface (39), wherein in the second position (42) the second control point (22) is connected via the first control slide (40) to the second output point (32), wherein in the second position (42) the first output point (31) is blocked by the first control slide (40), wherein in a third position (43) of the first control slide (40) the third main orifice (63) interacts with the main sealing surface (39), wherein in the third position (43) the second control point (22) is connected via the first control slide (40) to the third output point (33), wherein in the third position (43) the first output point (31) is blocked by the first control slide (40).; [2] Valve assembly (20; 20'; 20") according to claim 1, wherein in the second position (42) of the first control slide (40) the third outlet (33) is connected to the tank connection (35) via the first control slide (40), wherein in the third position (43) of the first control slide (40) the second outlet (32) is connected to the tank connection (35) via the first control slide (40). [3] Valve assembly (20; 20'; 20") according to one of the preceding claims, wherein in a fourth position (44) of the first control valve (40) the first outlet (31) is connected to the tank connection (35) via the first control valve (40), wherein the second and third outlets (32; 33) are blocked by the first control valve (40), wherein the second control point (22) is connected to the tank connection (35) via the first control valve (40), wherein the first, second and third main orifices (61; 62; 63) are designed such that the fluid flow path (23) between the first and second control points (21; 22) is blocked in the fourth position (44). [4] Valve assembly (20; 20'; 20") according to one of the preceding claims, wherein an opening cross-section of the first main orifice (61) increases more slowly when adjusted in the first actuation direction (51) than an opening cross-section of the second main orifice (62) when adjusted in the second actuation direction (52). [5] Valve assembly (20; 20'; 20") according to one of the preceding claims, wherein the first control slide (40) has several annular webs (80) distributed along the first axis (50), wherein immediately adjacent annular webs (80) are each separated from each other by a limit groove (90), wherein said annular webs (80) comprise a first and a second annular web (81; 82), wherein the first and the second main orifice (61; 62) are arranged on sides of the first annular web (81) opposite each other in the direction of the first axis (50), wherein the third main orifice is arranged on the second annular web, wherein the second annular web (82) is arranged immediately adjacent to the first annular web (81), so that the first and the third main orifice (61; 63) are bounded by a common limit groove (91). [6] Valve assembly (20; 20'; 20") according to claim 5, referring back to claim 3, wherein in the fourth position (44) the first annular web (81) interacts with the main sealing surface (39) such that the fluid flow path (23) between the first and the second control point (21; 22) is blocked. [7] Valve assembly (20; 20'; 20") according to claim 5 or 6, wherein in the central position (45) the first annular web (81) interacts with the main sealing surface (39) such that the fluid flow path (23) between the first and the second control point (21; 22) is blocked. [8] Valve assembly (20; 20'; 20") according to claim 7, referring back to claim 3, wherein the fourth position (44) in the second actuation direction (52) is arranged immediately adjacent to the middle position (45). [9] Valve assembly (20; 20'; 20") according to one of claims 3 to 8, wherein in the middle position (45) and in the fourth position (44) the second control point (22) is connected to the tank connection (35) via at least one bore (46) in the first control slide (40), wherein this connection is blocked away from the middle position (45) and the fourth position (44). [10] Valve assembly (20") according to one of the preceding claims, wherein a switching valve (25) is arranged in the housing (30), which has two latching switching positions, wherein the switching valve (25) is acted upon with the pressure at the second and at the third output point (32; 33) in the sense of an opposite adjustment between the two latching switching positions, wherein the switching valve (25) is connected to a second and a third working port (37; 38), which are each arranged on the outside of the housing (30) so that they can be connected to the second cylinder (12). [11] Valve assembly (20; 20'; 20") according to one of the preceding claims, wherein a pilot control assembly (27) is provided with which a position of the first control valve (40) can be hydraulically adjusted, wherein the pilot control assembly (27) implements a control loop by means of which the position of the first control valve (40) can be adjusted to a predefinable target position.

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