DE102020208932A1 - Valve with automatic return flow reduction for pulling loads - Google Patents

Abstract

The invention relates to a valve (20; 20') with an inlet connection (23), a return connection (24) and a first and a second working connection (21; 22), a movable control slide (30) being provided which has a first position (31) in which the first working port (21) is connected to the inflow port (23) via a first orifice (41) and the second working port (22) is connected to the return port (24) via a second orifice (42), wherein the control slide (30) is biased by at least one spring (34) into a second position (32) that differs from the first (31), the valve (20) having a first actuating pressure connection (25). According to the invention, a fluid flow path runs from the first control pressure connection (25) via a third orifice (43), further via a first control point (61), further via an adjustable fifth orifice (45) to a second control point (62), with a third control point ( 63) is arranged between the first orifice (41) and the first working connection (21), with the pressure at the first control point (61) acting on the control slide in the direction of an adjustment to the first position (31), with the fifth orifice (45 ) is acted upon in the opening direction by the pressure upstream of the fifth orifice (45), the fifth orifice (45) being acted upon in the closing direction by the pressure at the third control point (63).

Description

The invention relates to a valve according to the preamble of claim 1 and a hydraulic drive system with such a valve.

From the data sheet, which was available on May 25, 2020 at the Internet address https://www.boschrexroth.com/various/utilities/mediadirectory/download/index.jsp?ob iect nr=RD64322, a valve block is known, which consists of several individual valves is composed. The valves are always designed as hydraulic 4/2-way valves that are continuously adjustable. The corresponding control slides are adjusted hydraulically or electro-hydraulically. During operation, it can happen that a pulling load acts on the actuator that is connected to the valve. The case can arise that the fluid flow delivered by the pump is not sufficient to fill the inlet-side pressure chamber of the actuator, so that cavitation occurs there. In this case, the speed of movement of the actuator is determined by the second orifice of the valve in the return.

An advantage of the valve according to the invention is that cavitation to the inlet is avoided when pulling loads act on the associated actuator. It is no longer necessary to specially adapt the opening behavior of the second aperture in the return to the specific operating conditions. The second aperture does not have to be made excessively small, which would lead to unnecessary energy losses. Rather, one and the same valve can be used for many different operating conditions without fear of damage caused by cavitation.

According to claim 1, it is proposed that a fluid flow path, starting from the first actuating pressure connection, runs via a third orifice, further via a first control point, further via an adjustable fifth orifice to a second control point, with a third control point being arranged between the first orifice and the first working connection , wherein the pressure at the first control point acts on the control spool in the direction of displacement towards the first position, wherein the fifth orifice is acted upon in the opening direction by the pressure upstream of the fifth orifice, wherein the fifth orifice is acted upon in the closing direction by the pressure at the third control point. The pressure at the third control point drops when cavitation occurs. As a result, the fifth orifice opens so that the fluid flow path is released, whereas it is otherwise closed. As a result, the pressure at the first control point falls below the pressure at the first actuating pressure connection. Consequently, the opening cross-section of the second orifice in the return is reduced until the pressure at the third control point rises again and the cavitation condition has ended.

The second control point is preferably connected to the return port, the first working port or another point of the valve such that the pressure fluid flowing in the fluid flow path when the fifth orifice is open can flow off into a pressure fluid sink with a low back pressure. The pressure fluid sink can be a tank. However, it is also conceivable that at least part of the pressure fluid mentioned is routed to an actuator. The first screen and/or the second screen can preferably be continuously adjusted by moving the control slide. They are preferably delimited in sections by the control slide. The flow resistance of the first screen can be designed to be smaller than the flow resistance of the second screen. The valve is preferably used with a pressurized fluid, which is most preferably a liquid, particularly hydraulic oil. The control slide is preferably linearly movable.

Typically, pulling loads are caused by the action of gravity, so they only act in one direction. If exceptionally pulling loads occur in two opposite directions, a third position of the valve can be configured analogously to the first position of the valve, with the first and third positions differing in terms of the direction of movement of the actuator.

Advantageous developments and improvements of the invention are specified in the dependent claims.

Provision can be made for the second and third control points to coincide, with the fifth orifice being formed by a check valve. This embodiment is particularly simple. As can be seen in particular from the remarks on 2 results, said check valve can be easily integrated into the spool, so that it requires no additional space. A valve body of the check valve is preferably designed as a ball. A valve seat of the check valve is preferably formed by an edge running around in the shape of a circular ring.

Provision can be made for the second control point to be arranged between the second orifice and the return connection, with the fifth orifice being part of a pressure compensator. Compared to the previously described embodiment, this embodiment is more functionally reliable heit, since the low-resistance outflow of the pressure fluid from the fluid flow path is reliably guaranteed. However, the production of the pressure compensator is more complex and expensive than the production of the check valve.

Provision can be made for the fifth screen to be arranged inside the control slide. The valve therefore requires very little installation space. There are no fears of leaks escaping from the valve to the outside. Said non-return valve or said pressure compensator is preferably arranged inside the control slide.

Provision can be made for an adjustable fourth orifice to be arranged in the fluid flow path adjacent to the fifth orifice. The fourth orifice is intended to ensure that the fluid flow path according to the invention is only effective in the first position, being closed in a fluid-tight manner in all other positions of the control slide.

Provision can be made for the fourth aperture to be delimited directly by the control slide, at least in sections. In addition, the fourth orifice is preferably delimited by a housing of the valve. An opening cross section of the fourth panel is thus adjusted by moving the control slide.

Provision can be made for the fourth orifice to be adjustable by moving the control slide, with the fourth orifice being designed in such a way that the fluid flow path is blocked apart from the first position, and it can only be released in the first position. The fluid flow path according to the invention is thus only effective in the first position of the control slide.

It can be provided that the fourth screen is designed such that it opens later than the first screen when the control slide moves from the second to the first position. With small opening cross sections of the first and consequently the second screen, there is no risk of cavitation. As a result of the above design, at most minor leaks at the fourth diaphragm are to be feared, especially in the second position, which could disrupt the function of the valve.

Provision can be made for the third screen to have a constant flow resistance. The valve according to the invention is therefore particularly easy to produce, with the function according to the invention nevertheless being available without restrictions.

Protection is also claimed for a hydraulic drive system with a valve according to the invention, with an actuator being connected to the first and the second working port, with a tank being connected to the return port, with a pump being provided which can deliver pressurized fluid from the tank to the inflow port, A control device is assigned to the pump, with which a delivery pressure and/or a delivery flow of the pump can be regulated as a function of a predefinable desired value, the desired value depending on the pressure at the first actuating pressure connection. The pump can have an adjustable displacement volume, which can be adjusted by the control device. The pump can have a constant displacement volume, with the pressure fluid delivered by the pump being able to be returned to the tank via a circulating pressure compensator, with the circulating pressure compensator being adjustable by the control device. The actuator can be a hydraulic cylinder or a hydraulic motor.

Provision can be made for the valve to have a second control pressure connection, with the pressure at the second control pressure connection acting on the control slide in the direction of an adjustment away from the first position, with the setpoint value depending on the higher of the pressures at the first and second control pressure connection. The desired value can be formed using a shuttle valve, for example. The target value is preferably a predetermined pressure difference above said higher pressure.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 einen hydraulischen Schaltplan eines hydraulischen Antriebssystems mit einem erfindungsgemäßen Ventil gemäß einer ersten Ausführungsform;
• 2 eine grobschematische Schnittansicht des Ventils gemäß der ersten Ausführungsform der Erfindung;
• 3 einen hydraulischen Schaltplan eines hydraulischen Antriebssystems mit einem erfindungsgemäßen Ventil gemäß einer zweiten Ausführungsform;
• 4 eine grobschematische Schnittansicht des Ventils gemäß der zweiten Ausführungsform der Erfindung.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

• 1 a hydraulic circuit diagram of a hydraulic drive system with a valve according to the invention according to a first embodiment;
• 2 a rough schematic sectional view of the valve according to the first embodiment of the invention;
• 3 a hydraulic circuit diagram of a hydraulic drive system with a valve according to the invention according to a second embodiment;
• 4 a rough schematic sectional view of the valve according to the second embodiment of the invention.

1 shows a hydraulic circuit diagram of a hydraulic drive system 10 with a valve 20 according to the invention according to a first embodiment. In the present case, the hydraulic drive system 10 is designed as an open hydraulic circuit, the invention also being able to be used in a closed hydraulic circuit. All tank symbols 12 in 1 denote the same tank. The hydraulic drive system 10 is preferably used with pressurized fluid in the form of a liquid, and most preferably hydraulic oil.

The main pump 13 draws in pressurized fluid from the tank 12 and delivers it to an actuator 11 via the valve 20 according to the invention. The pressurized fluid flowing back from the actuator 11 flows through the valve 20 into the tank 12 can supply in parallel, each actuator 11 is assigned a valve 20. The direction of movement and the speed of movement of the relevant actuator 11 are set with the valve 20 . The actuator 11 can be a cylinder or a hydraulic motor.

In the present case, the main pump 13 has an adjustable displacement volume, being designed, for example, as an axial piston pump with a swash plate design. The main pump 13 is assigned a control device 14 which can adjust the displacement volume of the main pump 13 . In the present case, the displacement volume is set as a function of the highest actuating pressure. In the present case, the valve 20 is adjusted hydraulically with two actuating pressures, which are supplied by a first and a second pressure-reducing valve 51; 52 are provided. The two control pressures are connected on the input side to a shuttle valve 50, the output pressure of which is supplied to the control device 14 as a setpoint value 60. The pressure reducing valves 51; 52 are supplied, for example, by a separate control oil pump 15 with pressure fluid.

In a hydraulic drive system 10 of this type, it can happen that pulling loads act on the actuator 11 . In the present case, the actuator 11 is designed as a hydraulic cylinder, which can raise and lower a load 16 against the effect of gravity. When lowering, the load 16 pulls on the actuator 11. In this operating state, it can happen that the load 16 is lowered so quickly that the main pump 13 no longer delivers enough pressure fluid to move the in 1 fill the upper cylinder chamber completely. Cavitation occurs. This is avoided with the present invention.

The valve 20 has a first, a second and a third position 31; 32; 33, which are arranged next to each other in the order given, whereby further positions may be present. The middle second position 32 is a locked position in which the actuator 11 is clamped hydraulically. The inlet port 23, the return port 24 and the first and second working port 21; 22 on the valve 20 are locked in the second position 32 accordingly. The valve 20 is preferably biased into the second position 32 by at least one spring 34 . The valve 20 can be moved into the first position 31 with the actuating pressure which is present at the first actuating pressure connection 25 . The valve 20 can be moved into the third position 33 with the control pressure applied to the second control pressure connection 26 . In the third position 33, the load 16 is lifted against the effect of gravity, so that there is no risk of cavitation from the outset. The inflow port 23 is accordingly connected to the second working port 22 , with the return port 24 being connected to the first working port 21 .

The load 16 is critically lowered in the first position 31. The inlet connection 23 is then connected to the first working connection 21 via a continuously adjustable first orifice plate 41, with the second working connection 22 being connected to the return flow connection 24 via a continuously adjustable second orifice plate 42 . The first and second aperture 41; 42 are adjusted by moving a control slide 30 of the valve 20. In the second position 32 they are completely closed, with their opening cross-section increasing steadily and monotonously towards the end of the first position 31 . The opening cross section of the first orifice 41 is preferably always smaller than the opening cross section of the second orifice 42. The speed of the actuator 11 is preferably determined by the flow rate of the main pump 13 or by suitable additional valves (not shown). The opening cross section of the first screen 41 is preferably at least large enough to prevent an undesired reduction in the inflow quantity.

The second orifice 42 only determines the speed of the actuator 11 when a pulling load acts on it, with the delivery flow of the main pump 13 no longer being sufficient to fill the cylinder chamber connected to the first working port 21 . The pressure at the third control point 63, which is arranged between the first orifice plate 41 and the first working connection 21, then falls. If this occurs, the opening cross section of the second orifice plate 42 is reduced by the fluid flow path according to the invention to such an extent that the pressure at the third control point 63 increases again. Accordingly, the flow of the main pump 13 is sufficient again to the to fill said cylinder chamber, with no more cavitation occurs.

The fluid flow path according to the invention runs, starting from the first actuating pressure connection 25, via a third orifice 43, further via a first control point 61, further via an optional fourth orifice 44, further via an adjustable fifth orifice 45 to a second control point 62. The second control point 62 acts it is any pressurized fluid sink selected such that when the fifth orifice 45 is open, the pressurized fluid can drain from the fluid flow path with substantially no back pressure. In the first embodiment, the second control point 62 coincides with the third control point 63 . At the with regard to the 3 and 4 explained second embodiment, a different second control point 62 was selected in the first place.

The control slide 30 is not acted upon directly by the pressure at the first actuating pressure connection 25, as is otherwise usual, but by the pressure at the first control point 61.

As long as the fifth orifice 45 is closed, these two pressures are essentially the same. As soon as the fifth orifice 45 opens, the third orifice 43 causes a pressure drop, so that the pressure at the first control point 61 falls compared to the pressure at the first control pressure connection 25 . As a result, the control slide 30 shifts to a second aperture 42 that is less open. The third screen 43 preferably has a constant opening cross section or a constant flow resistance.

The adjustable fifth orifice 45 is designed to be closed when the pressure at the third control point 63 is high and open when the pressure at the third control point 63 is low. In the simplest case, the fifth orifice 45 is formed by a non-return valve 40, which only allows a flow of fluid from the first 61 to the second control point 62, with the second 62 and third control point 63 coinciding. The check valve 40 is preferably biased into the closed position by a spring 48, so that it opens only above a predetermined pressure difference.

Because of the optional fourth panel 44, the statements are made 2 referred. With the fourth screen 44 is achieved that the fluid flow path is released only in the first position 31, wherein it is in the second and the third position 32; 33 is permanently closed.

2 shows a rough schematic sectional view of the valve 20 according to the first embodiment of the invention. The control slide 30 is accommodated in a linearly movable manner in a circular-cylindrical bore 29 of a housing 27, with 2 the housing 27 is shown only on one side of the bore 29 . The housing 27 is provided with a plurality of housing openings 28 arranged next to one another in the direction of movement, which can be designed as circular openings or as annular grooves running around the control slide 30 . The housing openings 28 are, for example, as in 2 shown fluidically permanently connected to each other, forming the inlet port 23, the return port 24 and the first and the second working port 21, 22.

A part of the housing orifices 28 is permanently fluidly connected to one another via a connecting channel 70 exclusively within the valve 20, whereby they do not form a connection.

The spool 30 is adapted in a substantially fluid-tight manner to the bore 29, having a plurality of reduced diameter neck portions 36 which, depending on the position of the spool 30, provide the various fluid connections between said ports 21; 22; 23; 24 manufacture. The control slide 30 is provided with at least one control notch 37 in particular in the region of the first aperture 41 , the control notches 37 possibly being arranged uniformly distributed over the circumference of the control slide 30 . The desired continuous adjustability of the first diaphragm 41 is thus achieved.

In the present case, the control slide 30 is shifted minimally towards the first position, starting from the second position. Accordingly, the second orifice 42 is minimally opened in the connection from the second working port 22 to the return port 24 . Furthermore, the first screen 41, which connects the inlet connection 23 to the connecting channel 70, is minimally open. The neck section 36a in turn connects the connecting channel 70 to the first working connection 21.

The connecting channel 70 forms the second and third control points 62; 63, which coincide in the first embodiment. The fourth orifice 44 is formed by a channel 38 within the control slide 30, which opens out radially from the control slide 30 in the area of a housing opening. In the first position, the fourth shutter 44 is open, being otherwise closed. Said channel 38 is part of the fluid flow path explained above, and it opens out at the end face of the control slide 30 associated with the first control pressure connection 25 . In this channel 38 is the check valve 40 arranged, which only allows a flow of fluid from the first control pressure port 25 to the fourth orifice 44 out. The corresponding valve body, which is preferably designed as a ball, is biased by a spring 48 into the closed position. The corresponding valve seat is preferably designed in the shape of a circular cone or in the form of an edge running around in the shape of a circular ring, it being possible for it to be arranged directly on the valve slide 30 or on a separate insert.

The first control point 61 is preferably formed by the interior of a separate, pot-like control cover 71 which is firmly connected to the housing 27 . The control cover 71 covers the front side of the control slide 30 facing the first actuating pressure connection 25. A spring (no. 34 in 1 ) be included, which biases the spool 30 in the second position. The third orifice 43 is preferably arranged on the mentioned control cover, in particular in the area of the first actuating pressure connection 25.

For the sake of order, it should be noted that the location of the fourth orifice 44 is within the fluid flow path 1 not according to the actual and preferred location 2 is shown. It is preferably arranged between the fifth screen 45 and the second control point 62 .

3 shows a hydraulic circuit diagram of a hydraulic drive system 10 with an inventive valve 20 'according to a second embodiment. Except for the differences explained below, the second embodiment is designed identically to the first embodiment, so that in this regard the explanations 1 and 2 is referenced. In the 1 , 2 , 3 and 4 Identical or corresponding parts are marked with the same reference numbers.

In the second embodiment, the second and third control locations 62; 63 executed differently from each other. The second control point 62 is arranged between the second aperture 42 and the return connection 24 . The pressurized fluid from the fluid flow path according to the invention can thus flow off almost directly to the tank 12, being subjected to a small back pressure. The fifth panel 45 is now formed by a pressure compensator 46, the fifth panel 45 between the first and the third control point 61; 63 is switched. In the opening direction of the fifth orifice 45, the pressure compensator 46 is acted upon by the pressure upstream of the fifth orifice 45. In the closing direction of the fifth orifice 45, the pressure compensator 46 is acted upon by the pressure at the third control point 63.

The fourth aperture 44 is in 3 according to their actual position in the fluid flow path between the fifth orifice 45 and the second control point 62, as is also the case in FIG 4 is shown.

4 shows a rough schematic sectional view of the valve 20 'according to the second embodiment of the invention. The pressure compensator 46 comprises a circular-cylindrical piston 73, which is accommodated in a substantially fluid-tightly adapted bore 72 in the control slide 30 in a linearly movable manner. A channel 74 in the control slide 30 opens radially into this bore 72 and is preferably permanently connected to the housing opening 28a at least in the first position of the control slide 30 . The housing opening 28a is in turn fluidly connected between the second orifice plate 42 and the return connection 24 . in the in 4 right position of the piston 73 this covers the channel 74. In the in 4 Left position, a fluid connection from the channel 74 to the interior of the bore 72 and from there to the front side of the control slide 30 and thus to the first control point 61 is released. The channel 74 forms, together with the piston 73, the adjustable fifth screen 45. In 4 from the right, ie in the opening direction of the fifth orifice 45, the piston 73 is acted upon by the pressure at the first control point 61 or by the pressure upstream of the fifth orifice 45. In the closing direction of the fifth orifice 45, the piston 73 is acted upon by the pressure at the third control point 63, which is formed by the connecting channel 70 in the second embodiment.

Incidentally, the explanations 2 referred.

Reference List

10

hydraulic drive system

11

actuator

12

tank

13

main pump

14

control device

15

control oil pump

16

load

20

valve (first embodiment)

20'

valve (second embodiment)

21

first working port

22

second working port

23

inlet connection

24

return connection

25

first control pressure connection

26

second control pressure connection

27

casing

28

housing outlet

28a

housing outlet

29

drilling

30

spool

31

first position

32

second position

33

third position

34

feather

36

neck section

36a

neck section

37

control notch

38

channel

40

check valve

41

first aperture

42

second aperture

43

third aperture

44

fourth aperture

45

fifth aperture

46

pressure compensator

48

Spring on the fifth aperture

50

shuttle valve

51

first pressure reducing valve

52

second pressure reducing valve

60

setpoint

61

first control station

62

second control station

63

third control station

70

connecting channel

71

control cover

72

drilling

73

Pistons

74

channel

Claims (11)

Valve (20; 20') with an inlet connection (23), a return connection (24) and a first and a second working connection (21; 22), a movable control slide (30) being provided which has a first position (31). , in which the first working port (21) is connected to the inflow port (23) via a first orifice (41) and the second working port (22) is connected to the return port (24) via a second orifice (42), the control slide (30 ) is biased by at least one spring (34) into a second position (32) different from the first (31), the valve (20) having a first control pressure connection (25), characterized in that a fluid flow path starting from the first control pressure connection ( 25) via a third screen (43), further via a first control point (61), further via an adjustable fifth screen (45) to a second control point (62), with a third control point (63) between the first screen (4th 1) and the first working connection (21), the pressure at the first control point (61) acting on the control slide in the direction of an adjustment to the first position (31), the fifth orifice (45) in the opening direction being influenced by the pressure upstream of the fifth orifice (45) is acted upon, wherein the fifth orifice (45) is acted upon in the closing direction by the pressure at the third control point (63). valve (20) after claim 1 , wherein the second and the third control point (62; 63) coincide, wherein the fifth orifice (45) is formed by a check valve (40). valve (20') after claim 1 , wherein the second control point (62) is arranged between the second orifice (42) and the return connection (24), the fifth orifice (45) being part of a pressure compensator (46). Valve (20; 20') according to one of the preceding claims, wherein the fifth orifice (45) is arranged inside the control slide (30). A valve (20; 20') according to any one of the preceding claims, wherein an adjustable fourth orifice (44) is arranged in the fluid flow path adjacent to the fifth orifice (45). valve (20; 20'). claim 5 , wherein the fourth screen (44) is limited at least in sections directly by the control slide (30). Valve (20; 20') according to a claim 5 or 6 , wherein the fourth orifice (44) is adjustable by movement of the spool (30), wherein the fourth orifice (44) is designed such that the fluid flow path is blocked away from the first position (31), wherein it is only in the first position ( 31) can be released. valve (20; 20'). claim 7 , wherein the fourth panel (44) is designed so that it at a movement of the control slide (30) from the second (32) to the first position (31) opens later than the first diaphragm (41). Valve (20; 20') according to any one of the preceding claims, wherein the third orifice (43) has a constant flow resistance. Hydraulic drive system (10) with a valve (20; 20') according to one of the preceding claims, wherein an actuator (11) is connected to the first and the second working connection (21; 22), wherein a tank is connected to the return connection (24). (12) is connected, with a pump (13) being provided which can deliver pressure fluid from the tank (12) to the inlet connection (23), with the pump (13) being assigned a control device (14) with which a delivery pressure and/or or a delivery flow of the pump (13) can be regulated as a function of a predefinable desired value (60), the desired value (60) depending on the pressure at the first actuating pressure connection (25). Hydraulic drive system (10) after claim 10 , wherein the valve (20; 20') has a second control pressure connection (26), wherein the pressure at the second control pressure connection (26) acts on the control slide (30) in the direction of an adjustment away from the first position (31), the desired value ( 60) depends on the higher of the pressures at the first and second control pressure connection (25; 26).

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