EP0870723A2 - Hydraulic gripper with pressure limiting valve - Google Patents

Abstract

A pressure control valve (1) is integrated in the hydraulic cylinder (26) and is inaccessible from outside. The valve has a conical piston (15) with seating co-operating with the spring (10). When a pre-set oil pressure (P) is exceeded for the hydraulic oil, the conical piston or the ball is pressed against the spring. The oil then passes it through a front opening (24) in the inner housing enclosing the conical piston or the ball into a chamber (25) in the pressure control valve and escapes from it to a hole for discharging the oil.

Description

The invention relates to a hydraulic gripper with hydraulic cylinders with pistons and Piston rod and a pressure relief valve and also affects one such a pressure relief valve.

It is known to offer excavators and car loading cranes with various attachments. Attachments are, for example, different types of grippers, in particular polyp grabs, clamshell grabs or the like. Excavator and loading cranes provide predetermined pressures available through connection of an appropriate attachment also work in this.

Hydrostatische Antriebe für Hüttenwerkskräne

, in: Klepzig Fachberichte 81 (1973), 51 - 59 erörtert, vorkommen, daß für bestimmte Anlagenbereiche höhere Drücke gewünscht werden als für die Anlage insgesamt. Dafür ist dort ein Druckübersetzer vorgesehen, der den Druck innerhalb eines Stripperzylinders auf das Doppelte des Druckes in den Rohrleitungen etc. erhöht. Dies ist jedoch ein Spezialproblem, das in Großanlagen, Hüttenwerken oder bei Zangenkränen in Hafenanlagen auftreten kann.It can be done by J. Martens,

Hydrostatic drives for metallurgical cranes

, discussed in: Klepzig Fachberichte 81 (1973), 51 - 59, that higher pressures are desired for certain plant areas than for the plant as a whole. For this purpose, a pressure intensifier is provided, which increases the pressure inside a stripper cylinder to twice the pressure in the pipelines, etc. However, this is a special problem that can occur in large systems, steelworks or with cranes in port facilities.

With excavators or other mobile devices used on construction sites Hydraulic grabs pose other problems. It often happens that the pressures provided by excavators and loading cranes exceed pressures, that may prevail in one attachment. To do this Avoid destruction of the attachment due to excessive pressures between the excavator or loading crane and the corresponding attachment Pressure relief valves provided. These are purchased as separate devices, for example, additionally offered by the manufacturers of the attachments. The separate pressure relief valves limit as an intermediate Element the maximum provided by the excavator or loading crane Pressure. A lower maximum pressure then acts on the attachment than on the excavator or loading crane. The attachments are thereby with regard to their hydraulic cylinders against destruction by too high effective Pressures protected.

A pressure relief valve is designed to reduce the working pressure of the hydraulic oil to one limit maximum pressure. It should also have a short response time and still work vibration-free. The hysteresis between opening and Closing pressure and the leakage oil flow should be as low as possible. Are known Pressure relief valves with a plug and spring tension screw, which can be operated and adjusted with a key or handwheel. Such Pressure relief valves have a damping piston with a valve cone, one Tension spring with stop and a set screw that is accessible and accessible from the outside is covered by a protective cap. Hydraulic oil is on the side of the Pressure relief valve fed in the area of a damping piston and valve cone connecting rod across this. A state of equilibrium arises between the oil pressure acting against the valve plug and the spring force a. With increasing oil pressure, the pressure on the valve cone also increases. This responds depending on the stiffness of the spring. By pressing the spring can be adjusted using the adjusting screw. The valve cone opens then set at a different pressure than before. This allows a with the pressure relief valve to various hydraulic cylinders Possible applications, in particular different types of hydraulic grippers, be adjusted with regard to the maximum pressures.

Most of the known pressure relief valves are outside the gripper provided between the hose connection of the excavator or loading crane and gripper. They are often preset in the form of a rectangular metal block and sealed, integrated there. Because these are accessible from the outside Arrangement of the pressure relief valve can be manipulated, too Damage caused by exceeding the originally set maximum pressure or by wrong setting, for example setting for another Attachment occur.

A similar arrangement is also provided, for example, in DE 195 00 606 A1. There is an additional one in the housing of a lowering brake valve Pressure relief valve provided. A valve spring is between the valve member and an adjustable locking screw clamped. The locking screw is sealed with a seal.

Experience has shown that such seals tear in rough operation on construction sites after a few months due to carelessness or even willful removed. A non-verifiable manipulation is easily possible.

The invention is therefore based on the object of having a hydraulic gripper To create pressure relief valve, which protects itself and which after commissioning no longer with regard to its set maximum pressure is manipulable.

The object is achieved in that the pressure relief valve in the hydraulic cylinder is installed and integrated inaccessible from the outside.

Further developments of the invention are defined in the subclaims.

This provides a hydraulic gripper with a pressure relief valve which is the cost of a separate pressure relief valve to protect a Attachment for an excavator or a loading crane can be saved. In order to costs of up to 20% of the gripper price can be saved. Because there is only a pressure relief valve that is specifically tailored to the special gripper is built in, is damage by too large acting pressure is no longer possible. Installation or correct setting not to be forgotten, as with known separate valves. Because the pressure relief valve is integrated in the hydraulic cylinder, is also no manipulation more possible from the outside.

The moment when the pressure is too high, for example more than 250 bar or 25 MPa, on the hydraulic cylinder, the pressure relief valve switches. There is then no greater pressure build-up in the cylinder, because that Incoming oil through the pressure relief valve arranged in the piston / cylinder through and through the piston rod of the hydraulic cylinder flows back into the oil tank. As a result, it no longer engages the piston on. A preset opening or closing pressure, for example of a gripper, can no longer be exceeded. Damage from exceeding a predetermined pressure can thereby on the hydraulic cylinders no longer occur.

Due to the manufacturer's installation of the valve in an attachment, such as the grippers, a device-specific pressure limitation is already provided in the device. Unconscious or deliberate misadjustments, as with known extreme ones Valves are avoided. The manufacturing effort of the hydraulic cylinder with the pressure relief valve according to the invention is compared to conventional Construction methods not bigger, because holes in the relevant place already available for plugging and connecting pressure lines are.

In principle, a pressure relief valve for hydraulic grippers with hydraulic cylinders created with piston and piston rod, in which the pressure relief valve can be preset, integrated and damped. The one time Presetting of the pressure relief valve is preferably by a spring a spiral spring, the one hand in a housing against one Wall mounted, on the other hand is pressed against a piston plate. Of the opposite side presses against this piston plate a conical piston. Of the Tapered piston has a tapered surface and is supported in a front opening an inner case. The hydraulic oil normally flows at the cone piston past. The hydraulic oil hits the conical surface at an angle. Will the Hydraulic oil pressure on the cone surface is greater than the preset force the spring, the conical piston is pressed against the piston plate and gives one Gap in the front opening of the inner housing for the passage of the hydraulic oil free. The hydraulic oil thereby gets into a chamber inside the Piston rod. From there it gets back into the oil tank. The pressure relief valve is inside the hydraulic cylinder in the area of pistons and Piston rod provided. So it is integrated in the hydraulic cylinder. By the Provide the spring in the direction of flow of the oil in the event of an overload vibrations and pressure surges of the flowing hydraulic oil are no longer immediately effective, but subdued. Instead of a tapered piston, too a ball can be provided.

An adjustable, directly controlled conical seat valve in is particularly preferred Cartridge design used. This works in comparison to known pressure relief valves reversed in cartridge design, which is why it is particularly preferred is used in hydraulic cylinders. The pressure relief valve is namely preferably constructed so that a hardened and ground seat of Tapered piston is provided, which ensures high tightness. The cone piston remains closed until the pressure acting in the hydraulic oil connection on the this exposed valve cone area a force greater than the set one Spring force generated. The valve opens and gives the flow on the cone piston past freely in the direction through the spring into the piston rod and into the Cylinder tube of the hydraulic cylinder.

In the known pressure relief valves, this flows when the pressure rises Hydraulic oil past the valve cone, but not through the spring into the piston rod / cylinder tube assembly. The hydraulic oil essentially retains its actual flow direction (from right to left), without one Redirection and damping, by the spring.

Cartridge design means that the valve housing with a screw-in cartridge is provided with an external thread and as a finished component on the corresponding Can be screwed into the hydraulic cylinder.

Figur 1

eine Schnittansicht eines Druckbegrenzungsventiles,

Figur 2

eine Schnittansicht eines Hydraulikzylinders mit eingebautem Druckbegrenzungsventil gemäß Figur 1,

Figur 3

eine Seitenansicht des Hydraulikzylinders gemäß Figur 2,

Figur 4

eine Seitenansicht eines Zweischalengreifers mit einem Hydraulikzylinder gemäß Figur 3, in geöffneter und in geschlossener Position und

Figur 5

eine Seitenansicht des Zweischalengreifers gemäß Figur 4 in 90°-Drehung.

For a more detailed explanation of the invention, an embodiment of a hydraulic gripper with a pressure relief valve is described below with reference to the drawings. These show in:

Figure 1

2 shows a sectional view of a pressure relief valve,

Figure 2

2 shows a sectional view of a hydraulic cylinder with a built-in pressure relief valve according to FIG. 1,

Figure 3

3 shows a side view of the hydraulic cylinder according to FIG. 2,

Figure 4

a side view of a clamshell bucket with a hydraulic cylinder according to Figure 3, in the open and in the closed position and

Figure 5

a side view of the clamshell grab according to Figure 4 in 90 ° rotation.

In Figure 1 , a sectional view of a pressure relief valve 1 is shown. The pressure relief valve has a cartridge design. A housing 2 is provided. In its thickened area 3, the housing has a vertical through bore 4. In the front narrower area 5 there is also a vertical through hole 6. In the front narrow area 5, a sleeve 7 is inserted with a through opening 8 in an end plate 9.

A coil spring 10 is arranged in the sleeve 7. The coil spring bears with her one end on the inside 11 of the end plate 9. With her other At the end, the coil spring rests on a piston plate 12. The piston plate protrudes an inner cantilever element 13 into the coil spring 10.

On the back of the cantilever element 13 of the piston plate 12 is one Recess 14 provided. A tapered piston 15 is supported in this recess with its almost spherical head part 16. The spherical head part goes over into a conical intermediate part. On the conical intermediate part 17 is followed by a rod-shaped part 18. The rod-shaped part 18 goes over in a provided with a groove 19 compared to the rod-shaped Part 18 projecting end part 20. The end part 20 is slidable in an inner Housing 21 stored. The inner housing is in turn in a recess 22 provided in the housing 2.

The inner housing 21 has in the region of the conical intermediate part 17 and the rod-shaped part 18 of the conical piston 15 obliquely on the conical surface of the conical intermediate part 17 tapering through holes 23 on. The tapered piston 15 is in a front opening 24 of the inner housing 21 inserted as a seat so that the spherical head part 16, the inner housing 21st closes towards the piston plate 12 opposite the housing 2.

If hydraulic oil is pumped into the through hole 4 by a hydraulic system, this usually occurs through the through holes 23 of the inner housing 21 through and on the other side of the through hole 4 out again. This is indicated by arrows in Figure 1. The coil spring 10 presses the cone piston 15 against its seat and thereby locks in the rest position the connection of the hydraulic system hydraulic oil to the oil tank. If the Resistance from outside via a hydrometer in the hydro system acts, the resulting one Pressure on all sides, also perpendicular to the active surface, the cone of the cone piston 15, the valve. If the pressure of the hydraulic oil is increased so far, that it is greater than the counter pressure of the coil spring 10 is over the conical surface of the conical intermediate part 17 of the conical piston 15 of the latter pressed against the coil spring 10. As a result, the spherical head part 16 lifted from the seat of the cone in the inner housing 21 and pushed away. It thereby opens the front opening 24 of the inner housing 21, thereby the hydraulic oil past the spherical head part 16 of the conical piston a chamber 25 formed in the housing 2 can enter. Out of the chamber 25 the hydraulic oil then passes through the through hole 6 and / or Through opening 8, in the direction of the arrows out of the housing 2, since it was not removed by the consumer (hydraulic cylinder). Preferably it becomes converting the pressure energy into thermal energy returned to the oil tank for the hydraulic oil. This is shown in Figure 1 "T" indicated. The pressure of the hydraulic oil that passes through the through hole 4 enters the housing is indicated by "P".

As the flow rate increases, the flow cross section also increases. This means that the stroke of the conical piston increases and against the Spring presses. The restoring force of the spring increases accordingly Characteristic too.

The pressure relief valve shown in Figure 1 is controlled directly Designated poppet valve in cartridge design. It is preferably with one hardened and ground seat and cone. This makes a high one Ensures tightness of the valve. By the interaction of tapered pistons 15 and coil spring 10 will swing the valve, which by a change of static and dynamic forces on the cone could occur, prevented. The opening width of the valve, i.e. the degree of lifting of the spherical Head part 16 of the inner housing 21 is dependent on the pressure increase at "P". The maximum effective hydraulic oil force before the Pressure relief valve is selected by suitable selection of the characteristic of the coil spring 10 made. For example, the pressure with clamshell buckets limited to 250 bar + 10 bar (25 MPa + 1 MPa) if this is for one Maximum pressure of approx. 250 bar corresponding to 25 MPa.

The screwing in of the groove 19 in the piston 15 helps to ensure that it acts as a relief groove acts and through them the hydraulic shear force acting on the piston can be significantly reduced. There is pressure equalization on the piston circumference achieved. This can be done with different pressures applied circumferential surface of the piston can be kept small. By the Floating the tapered piston in hydraulic oil is a clean fit, a good one Functionality and low-wear work enables.

FIG. 2 shows a sectional view of a hydraulic cylinder 26 with a built-in pressure relief valve 1. The hydraulic cylinder 26 has a housing 27. Four connection elements 28 are provided on the housing 27 for connecting joints of an attachment, for example a polyp gripper or a clamshell gripper. For this purpose, the connection elements have through holes 29 and small, front sleeves 30.

In its two end plates 31, 32 there are bores 33, 34 for the oil supply and removal provided. At the holes are on the outside End plate 31, 32 threaded plug 35 provided for connecting oil lines. The holes shown are drawn rotated by 90 °.

A cylinder tube 36 is welded to the end plate 32. At the end of A guide bush 37 is provided in the cylinder tube 36. In this guide bush slidably supports a piston rod 38. The piston rod is connected to the End plate 31 welded. The piston rod is opposite the guide bush 37 38 sealed by seals 39 and a wiper 40.

A through bore 41 is provided within the piston rod 38. The Through hole leads to a chamber 42. In this chamber 42 that is Pressure relief valve 1 according to Figure 1 inserted. In the transition area from Piston rod 38 to the piston 44 is perpendicular to the through bore 41 of the Piston rod 38 a further through hole 43 is provided. The Through hole 43 connects the chamber 42 with the space between the cylinder tube 36 and piston rod 38 twice.

The piston rod 38 is in the area of the pressure relief valve 1 with a Piston 44 firmly connected, for example welded. The piston 44 is over a piston seal 45 and a piston guide ring 46 opposite Cylinder tube 36 slidably sealed.

During normal operation, oil enters a chamber through the bore 33 for the oil supply 47 in the end plate 32. The oil pressure acts on the piston 44. The Piston 44 is thereby moved within the cylinder tube 36 in the direction of the arrow. The piston rod 38 is pushed away from the oil in the direction of the arrow. The hydraulic cylinder is extended. The through hole 4 of the pressure relief valve, which is connected to the chamber 47 is of the oil without actuation of the pressure relief valve flows. To retract the hydraulic cylinder oil flows into the bore 34. It enters chamber 42, from there through the opening 8 of the pressure relief valve in this inside. It presses against the piston plate 12 and thereby the cone of the conical piston 15 in its seat. The oil flows through the slots of the spring 10 the through holes 6 out of the valve through the holes 43 into the chamber between cylinder tube 36 and piston rod 38. The oil pressure of the oil flowing into this chamber is directed against the Piston 44, whereby this is moved back against the direction of the arrow. Of the Hydraulic cylinder is retracted.

By providing two through bores 6 and one through opening 8, the bores 6 have the same passage as the opening 8.

In known hydraulic cylinders, a bore 6 is sufficient, because in these no piston rod through bore 41 is provided.

Only at the moment when - by the spring force of the coil spring 10 of Pressure relief valve predetermined - oil pressure is exceeded, that will Pressure relief valve actuated. The oil then occurs, as described in Figure 1, from the pressure relief valve. As a result, it enters chamber 42 inside the piston rod 38. From there it passes through the through hole 41 to hole 34 for oil drainage. So the oil flows directly from the Hole for the oil supply to the hole for the oil drain. The piston 44 not actuated. The hydraulic cylinder remains in the one previously held Position. The piston can only be actuated again when the oil pressure drops respectively. This mode of action is contrary to that of conventional known ones Pressure relief valves, which are set manually and accessible from the outside are provided on a hydraulic cylinder and in which the oil transversely to Valve cone flows past this, but not through the spring.

FIG. 3 shows a side view of the hydraulic cylinder according to FIG. 2. The connecting elements 28 with their through holes 29 and the front sleeves 30 can be seen. The approximate course of the piston rod 38 is indicated by a dash-dotted line.

Figure 4 shows an example of an attachment with pressure relief valve in a side view of a clamshell bucket 48 in the closed position A and only partially in the open position B. Via joints 49, the connecting elements 28 are articulated to the two shells 50, 51 of the clamshell bucket 48.

When the hydraulic cylinder is extended, the two shells close 50, 51 of the clamshell bucket 48. If the hydraulic cylinder is reversed moved together, the two shells 50, 51 open, as indicated in a stylized manner in position B.

FIG. 5 shows a side view of the clamshell bucket 48 according to FIG. 4 in the position rotated by 90 °, in the top view of shell 50.

The pressure relief valve shown in Figures 1 and 2 has a cone piston with conical surface on. This ensures an optimal response of the Pressure relief valve enables. There is good damping. In a another alternative embodiment can also use a ball instead of the cone be provided. The front shape of such a ball piston is similar to that of the cone piston. Instead of the conical intermediate part is the ball piston the spherical surface in the front opening 24 of the inner housing 21 inserted as a seat. The hydraulic oil hits this spherical surface. Through the Bulging does not result in a uniform transmission of the force exerted, but due to different angles of incidence everywhere a non-uniform Forwarding. There is a risk that undamped vibrations or Fluttering of the valve can occur with fluctuations in the pressure load. these are undesirable effects, as this causes a certain unrest in the hydraulic cylinder is introduced. A tapered piston is therefore preferred for the pressure relief valve used.

Reference list

1

Pressure relief valve

2nd

casing

3rd

thickened area

4th

Through hole

5

narrow area

6

Through hole

7

Sleeve

8th

Through opening

9

End plate

10th

Coil spring

11

inside

12th

Piston plate

13

cantilevered element

14

Recess

15

Tapered piston

16

spherical headboard

17th

conical intermediate part

18th

rod-shaped part

19th

Groove

20th

End part

21

inner housing

22

Recess

23

Through hole

24th

front opening

25th

chamber

26

Hydraulic cylinder

27

casing

28

Connector

29

Through hole

30th

superior sleeve

31

front end plate

32

front end plate

33

Hole for oil supply

34

Hole for oil drainage

35

Threaded plug

36

Cylinder barrel

37

Guide bushing

38

Piston rod

39

Seals

40

Wipers

41

Through hole

42

chamber

43

Through hole

44

piston

45

Piston seal

46

Piston guide ring

47

chamber

48

Clamshell buckets

49

Joints

50

Bowl

51

Bowl

A

closed position

B

open position

Claims (13)

Hydraulic gripper with hydraulic cylinder (26) with piston (44) and piston rod (38) and a pressure relief valve (1),
characterized by
that the pressure relief valve (1) in the hydraulic cylinder (26) is installed and integrated inaccessible from the outside. Hydraulic gripper according to claim 1,
characterized by
that the pressure relief valve (1) can be preset and damped once. Hydraulic gripper according to claim 1 or 2,
characterized by
that a spring (10) is provided in the pressure relief valve (1) to create a presetting. Hydraulic gripper according to one of claims 1 to 3,
characterized by
that the pressure relief valve (1) has a tapered piston (15) with a tapered seat which interacts with the spring (10). Hydraulic gripper according to one of claims 1 to 3,
characterized by
that the pressure relief valve (1) has a ball with a seat which interacts with the spring (10). Hydraulic gripper according to one of claims 1 to 5,
characterized by
that when a predetermined oil pressure (P) of the hydraulic oil is exceeded, the pressure relief valve (1) responds directly and switches the piston (44) without force. Hydraulic gripper according to claim 6,
characterized by
that when a predetermined oil pressure (P) of the hydraulic oil is exceeded, the tapered piston (15) or the ball is pressed against the spring (10) so that the oil past it through a front opening (24) of an inner, the tapered piston (15) or the housing (21) surrounding the ball enters a chamber (25) of the pressure relief valve (1) and out of this to a bore (34) for the oil discharge. Hydraulic gripper according to one of claims 1 to 7,
characterized by
that a through hole (23) has such an inclined position to the conical surface on a conical intermediate part (17) of the conical piston (15) or to the spherical surface of the ball, that the conical piston or the ball only at one predetermined by the bias of the spring (10) Pressure of the oil responds. Hydraulic gripper according to one of claims 1 to 8,
characterized by
that the pressure relief valve (1) is provided in cartridge design within the hydraulic cylinder (26). Hydraulic gripper according to one of claims 1 to 9,
characterized by
that the piston (44), the piston rod (38) and the hydraulic cylinder (26) have recesses into which the pressure relief valve (1) is inserted, in particular screwed. Hydraulic gripper according to one of claims 1 to 10,
characterized by
that the pressure relief valve (1) is a directly controlled cone seat valve in cartridge design. Hydraulic gripper according to one of claims 1 to 11,
characterized by
that the pressure relief valve (1) has a fixed valve seat in the piston (44) which a head part (16) can close, which is acted upon by a spring (10) which is supported on the piston (44), and by which Pressure limiting valve (1) oil flowing through from a first space, formed by the piston (44) with the cylinder (26), and flows from outside into a second space inside the piston rod (38) and forms oil from a third annular cylindrical space from the piston rod (38) with the hydraulic cylinder (26) as well as delivering oil to an oil drain, a single piston (44) with the hydraulic cylinder (26) forming the first and second space, the second space via bores (43) in the piston rod (38) is connected to the third space and the second space is connected to the oil drainage through a bore (41) emerging in the longitudinal axis of the piston rod (38) and leading out of the annular space is. Pressure relief valve for a hydraulic gripper according to one of the preceding Expectations.

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