EP0902194B1 - Load-holding valve - Google Patents

Description

The invention relates to a load holding valve according to the preamble of claim 1.

In a load holding valve known from DE-C2-25 59 029 according to the preamble of claim 1, the pressure relief valve closing member against the spring force on the entire cross-sectional area of the valve seat with the pressure to be limited. With increasing too limiting pressure becomes that required to open the pressure relief valve Pilot pressure progressively lower. This can be undesirable for some applications be because it is cheaper from the respective consumer adjustment pressure low pressure to be limited and low to high pressure Pressure to derive higher pilot pressure. However, with this functional principle it is favorable that the check valve is structurally separate from the pressure relief valve and with large cross section can be designed so that in the first flow direction only low back pressure and low flow losses arise. The pressure relief valve closing member to be limited in the opening direction Pressure also enables a shock function and an automatic damping function, because in the event of a pressure surge, the pressure relief valve opens automatically and the Reduces or dampens pressure surge.

In practice, load holding valves are known from prior use, in which the Pressure relief valve closing member is relieved of the pressure to be limited. It there is an essentially linear relationship between the one to be limited Pressure and the pilot pressure to open the pressure relief valve. Indeed is a shock function or damping function by the pressure relief valve not given, so that separate valve components must be provided for this.

A 1992 from a brochure by Oil-Control, Nonantola, IT, Page CM3, known load holding valve has one with the pressure relief valve closing member one-piece control piston, the pressure surface slightly is smaller than the cross-sectional area of the valve seat. The pressure to be limited acts on the differential surface in the opening direction of the pressure relief valve to achieve a shock function or damping function in the event of pressure surges. The valve seat is for the check valve function in a sleeve that can be moved against spring force shaped. Because the same valve components for the non-return and pressure limiting functions cooperate, the pressure relief valve closing element is opened moved relative to the valve seat while in the one flow direction while being held Pressure relief valve closing element of the valve seat against spring force is shifted. Both valve functions performed with the same valve components affect each other. In the check valve is because of the small construction Cross-section high dynamic pressure to accept. Under unfavorable operating conditions no leakage can be achieved.

With a pressure relief valve not relieved of the pressure to be limited or with a partially relieved locking element, the desirable shock or damping function achieved because a pressure surge from the consumer pressure relief valve automatically opens and is dismantled. However, there is then the pressure relief valve suddenly a large cross section free, so that the consumer pressure falls off quickly, and with it the pilot print. This closes the pressure relief valve abruptly, if necessary with a hard serve. This calls mechanical Damage and vibrations and difficult when controlled opening sensitive movement control of the consumer.

Additional prior art is contained in GB-A-22 05 385, FR-A-23 62 290, FR-A-23 88 186 and EP-A-0 045 206.

The invention has for its object a load holding valve of the aforementioned Art to create that inexpensively with compact dimensions with high reliability is producible and despite the integrated shock-damping function under load one enables sensitive control of the consumer.

The object is achieved according to the invention with the features of claim 1 solved.

The one-piece design of the closing member with the control piston is manufacturing and technically inexpensive. The low back pressure of the pressure relief valve externally surrounding, structurally separate check valve Losses. The functions of the check valve and the pressure relief valve do not interfere with each other. The shooting link is partially relieved, i.e. the one to be limited Pressure only acts on the closing element in the opening direction for the shock-damping function sufficient size, but not on the entire cross-sectional area of the valve seat. This results in a favorable low tax ratio, the allows a high pilot pressure and precise and sensitive control of the consumer enables what to do with varying pressures with the consumer movement and instability to be feared is appropriate. The hydraulic system responds with the load holding valve stiff and low-vibration. Which is independent of the check valve function acting quantity control device supports the precision of the Control of the consumer significantly, since the pressure relief valve does not suddenly opens or closes, but the amount depending on the stroke of the closing element and / or controls the control piston according to a predeterminable characteristic curve. These effects are achieved with little structural effort, so that the Load holding valve can be manufactured inexpensively and insensitive to manufacturing tolerances is. Despite the volume control device, there is no leakage in the Closed position guaranteed because the quantity control device only depends on the stroke intervenes after opening the seat valve. This is essential for the load holding function.

According to claim 2, the partial relief of the closing member is structurally simple the annular shoulder that reaches between the housing chamber and the Pilot chamber is positioned so that in the stroke of the check valve, its closing member is guided on the pressure relief valve closing member.

According to claim 3, the seat valve tightness important for the load holding function is simple reached. As soon as the seat is lifted off the valve seat, the result is between the cylinder guide and the cylindrical approach a slide function, in which the Control channels gradually open or close a variable cross-section depending on the stroke, spread the change in the passage cross-section over a large stroke range and prevent the pressure relief valve closing member from oscillating or e.g. in the event of a pressure surge after an opening stroke, the valve seat suddenly hits and causes vibrations in the system. Because the quantity control device Pressure fluid does not suddenly flow out, but after a predetermined one Characteristic curve, opens and closes the pressure relief valve damped in the event of a pressure surge. This results in a damping behavior that has so far only been possible with additional complex Action was possible.

According to claim 4, the closing member of the check valve works with the sealing surface unaffected by intensive flow dynamics in the pressure relief valve together. The check valve holds reliably when the pressure relief valve is opened its shut-off position. The pressure relief valve cannot supply any pressure medium bypass. When the check valve is opened it is without the flow control channels of the pressure relief valve closing member has its own flow path.

In terms of production technology, two structurally separate parts are simple Flow paths created for the pressure limiting and non-return function. The small cross-sectional passages come when the pressure relief valve is opened first of all to be carried in order to let the pressure medium flow out throttled, before further and larger passages are released with increasing opening stroke become. During the closing stroke, the passage is throttled gradually and depending on the stroke. Radial bores can be made easily and precisely.

According to claim 6, a relatively large opening or closing stroke of the Use the closing element to gradually change the flow cross-section.

According to claim 7, the additional control channels are alternatively of longitudinal grooves formed in the closing member to make changes in the flow cross-section to a large Distribute the stroke range of the closing element.

A particularly simple manufacture of the additional control channels is claimed 8 by grinding arch slots into the cylindrical longitudinal section of the closing link possible.

According to claim 9, it is appropriate to the longitudinal grooves at different intervals to end from the seat.

Alternatively, the longitudinal grooves can have different clear widths have.

The functional reliability is increased according to claim 11, if for each flow direction a sieve element is provided.

Fig. 1

ein schematisches Schaltbild einer Steuervorrichtung mit einem Lasthalteventil,

Fig. 2

einen Teil eines Längsschnittes einer ersten Ausführungsform eines Lasthalteventils, und

Fig. 3

einen Teil eines Längsschnittes einer weiteren Ausführungsform eines Lasthalteventils.

Embodiments of the subject matter of the invention are explained with the aid of the drawing. Show it:

Fig. 1

1 shows a schematic circuit diagram of a control device with a load holding valve,

Fig. 2

a part of a longitudinal section of a first embodiment of a load holding valve, and

Fig. 3

a part of a longitudinal section of a further embodiment of a load holding valve.

In a hydraulic control device S in Fig. 1, a hydraulic consumer V, e.g. a double-acting hydraulic cylinder or hydraulic motor, via one a directional control valve W connected to a pump P and a tank T. On a work line 1 is connected to the lower side of the consumer, while the Lifting side is connected to the directional control valve W via a working line 2. In at least one working line 2 (or in both working lines, not shown) A load holding valve L is provided between line sections 2a and 2b. The Load holding valve L includes a check valve R that is in the first flow direction to consumer V opens and in the second flow direction to the directional control valve W locks automatically. A pressure relief valve is located parallel to the check valve R. D provided that hydraulically from the working line 1 via a pilot line 3rd is controllable in the second direction of flow to the speed of the consumer V under load depending on the adjustment of the directional control valve W. Taxes.

In the position shown, a load is held by the load holding valve L. The load is too lift, the directional control valve is adjusted to its left switching position, so that the Consumer V is applied via the working line 2 and the open check valve R. becomes. Displaced pressure medium flows via the other working line 1 to Tank T. If the load is to be reduced, the directional control valve W is in its right switching position changed. Pressure built up in working line 1 acts via the pilot line 3 on the pressure relief valve D, which is opened and pressure medium flows out leaves. Indicated by the pilot line at the pressure relief valve D is a partially relieved pressure relief valve, which is the load pressure in the line section 2b acted upon in the opening direction. A shock or Damping function achieved during pressure surges in consumer V. Opens when there is a pressure surge the pressure relief valve D and allows pressure medium to flow out at least briefly, to reduce the pressure surge and dampen vibrations in the system.

In Fig. 2 is a closing member 4 of the pressure relief valve D in the manner of a cattail formed and provided with a conical seat 5, to which a cylindrical Approach 6 connects, which has a cylindrical longitudinal section 7 an annular shoulder 8 continues. In one piece with the closing member 4 is in the connection a control piston 9 is formed on the shoulder 8, which is connected to the pilot line 3 in a Pilot chamber 10 and a seal 11 is slidable.

In a housing chamber 12, a seat insert 13 is positioned, which the closing member 4th supports and on an underside sealing surface 15 for a plate-shaped check valve closing member 16 ending flow passages 14 contains. The check valve closing member 16 is e.g. on the cylindrical longitudinal section 7 of the closing member 4 out and loaded by a weak closing spring 17, which is a bell-shaped Screen 18 holds on the closing member 16. The lower part of the housing chamber 12 is connected to the line section 2b. The upper part of the housing chamber 12 forms the connection to the line section 2a with a screw-in insert 23. A suitably adjustable spring 22 is accommodated in the screw-in insert 23, which loads the closing member 4 downwards and determines at what pressure the pressure relief valve D opens.

A circular valve seat 19 is formed in the seat insert 13 and is in contact with the seat surface 5 of the closing member 4 cooperates in the manner of a seat valve (in the shown Shut-off position leak-free tightness). Adjacent to the valve seat 19 is a cylindrical one Guide section 20 shaped, the slide-like with the cylindrical approach 6 of the locking member 4 works together (e.g. sliding fit). In connection to the guide section 20, the seat insert 13 is slightly enlarged inside, so the longitudinal section 7 slides smoothly.

The closing member 4 contains a chamber 24 which is connected to the lower one via connections 25 Part of the housing chamber 12 is connected, and additionally molded control channels K adjacent to the seat 5, for example radial bores 21 with different Diameters. The contours of the radial bores 21 may overlap each other in the axial direction. With increasing distance from the seat 5, the radial bores 21 have increasing diameters.

The guide section 20 forms with the extension 6 and the control channels K. Quantity control device M, which is relative to the stroke of the closing member 4 relative to the valve seat 19 takes effect to control the amount. In the seat insert 13 is in A further screen disk 26 is provided in the upper part of the housing chamber 12.

In Fig. 2, the pressure relief valve D and the check valve R are in their shut-off positions.

In order to move the consumer V in the lifting direction, the closing member 16 of the Check valve R by the control pressure between the line sections 2a, 2b lifted off the sealing surface 15. Pressure medium flows in from the line section 2a the line section 2b and to the consumer V. The pressure relief valve D remains in the shut-off position. If the load is to be reduced, the working line 1 is pressurized acted upon, which reaches the pilot chamber 10 via the pilot line 3. The pressure in Line section 2b rises. Pressure on the control piston 9 and in the line section 2b on the area difference between the cross-sectional areas of the valve seat 19 and the seal 11 act in the opening direction of the closing member 4. Is the spring 22nd overcome, the seat 5 rises from the valve seat 19. The following come Control channels K to effect to pressure medium in a controlled amount from the line section 2b let in the line section 2a. The higher the load pressure in the line section 2b, the lower the pilot pressure in the pilot chamber 10 is by that Pressure relief valve D to open, and vice versa.

The duty ratio of the load holding valve should be greater than 1: 2.5, expediently are around 1: 3.

A pressure surge rises above the area difference between the valve seat 19 and the Seal 11, the closing member 4 against the spring 22 from the valve seat 19. It is dismantled or steamed. The control channels K also participate in this as soon as the seat surface 5 has lifted off the valve seat 19. After the pressure surge has been reduced, the closing element sets 4 on the valve seat 19.

In Fig. 3 (function as in Fig. 2), the quantity control device M is different from that shown in FIG. The closing member 4 in Fig. 3 is in one piece with the control piston 9. In its cylindrical longitudinal section 7 are distributed over the circumference Longitudinal grooves 27 shaped as additional control channels K, the groove depths in the direction to the seat 5 or the cylindrical extension 6. The longitudinal grooves 27 can be ground in with a grinding wheel, the diameter of which curvature and their strength determine the clear width of the longitudinal grooves 27. It can several longitudinal grooves 27 of identical size and width distributed over the circumference and length can be molded, or also different widths or different lengths Longitudinal grooves 27. As shown, the longitudinal grooves 27 end in the same axial area. It would be conceivable, as with the radial bores 21, for the ends of the longitudinal grooves 27 to be different position far from the seat 5.

By means of the additional control channels K it is achieved that the cross section at Stroke movement of the closing member 4 is only gradually opened or closed, in order to control the quantity and to prevent a large passage cross section is suddenly opened or closed.

For a high control ratio, the load holding valve of FIGS. 2 and 3 could be used with a larger control pistons can be combined in the pilot chamber 10.

The area difference between the valve seat 19 and the seal 11 or the contact surface of the control piston 9 is matched to the application, i.e. the force or preload of the spring 22 and the pressure conditions in the system, such that the shock and damping function for pressure surges of a certain extent is achieved with which the pressure relief valve is independent of the control piston 9 opens briefly.

Claims (11)

1. A load holding valve (L) for high-pressure hydraulic systems, comprising a check valve (R) permitting flow in one direction of flow and a pressure limiting valve (D) which is arranged in said check valve (R) and which controls a flow in the opposite direction of flow in a pressure-dependent manner, further comprising a stationary seat insert (13) in a housing chamber (12) which said valves (R, D) have in common, said seat insert (13) comprising as structurally separate components a valve seat (19) for a spring-loaded closure member (4) of the pressure limiting valve (D) and a sealing surface (15) for a check-valve closure member (16), and further comprising a coaxial opening piston (9) which is coupled to the closure member (4) of the pressure limiting valve (D) and which is arranged in the pilot chamber (10), said closure member (4) of the pressure limiting valve (D) being provided with an effective area which, in a direction opposite to the direction of spring loading, is adapted to be acted upon by a pressure to be limited, characterized in that the opening piston (9) is formed integrally with the closure member (4) of the pressure limiting valve (D) and has in the pilot chamber (10) a pressure surface which is effective in the opening direction of the pressure limiting valve (D) and which is slightly smaller than the cross-sectional area of the valve seat (19), and that the valve seat (19) in combination with control passages (K) formed in the closure member (4) of the pressure limiting valve (D) define a stroke-dependent quantity control device (M) for the opposite direction of flow.
2. A load holding valve according to claim 1, characterized in that the differential area constituting the difference between the opening piston (9) in the pilot chamber (10) and the valve seat (19) is provided on an annular shoulder (8) forming the effective area and arranged between the housing chamber (12) and the pilot chamber (10), and that said shoulder (8) is adapted to be acted upon from the housing chamber (12) and is sealed off from the pilot chamber (10).
3. A load holding valve according to claim 1, characterized in that the seat insert (13) has provided therein, adjacent the valve seat (19), a cylindrical guide means (20) for a cylindrical projection (6) of the closure member (4) of the pressure limiting valve (D), said cylindrical guide means (20) bordering on a conical seat surface (5) on the closure member (4) of the pressure limiting valve (D), and that at least one of the control passages (K) ends in the projection (6).
4. A load holding valve according to at least one of the preceding claims, characterized in that there is a sliding fit between the cylindrical guide means (20) and the cylindrical projection (6), and that the cylindrical guide means (20) and the cylindrical projection (6) are arranged in said seat insert at a substantial axial distance from the sealing surface (15).
5. A load holding valve according to at least one of the preceding claims, characterized in that the closure member (4) of the pressure limiting valve (D) includes a chamber (24), which is connected to the housing chamber (12) on the check-valve side of the seat insert (13), and that openings (21) leading from the chamber (24) to the outer circumference of the closure member (4) of the pressure limiting valve (D) are provided as additional control passages (K), said openings (21) being preferably holes with different opening widths, and said openings widths increasing as the distance from the seat surface (5) increases.
6. A load holding valve according to claim 5, characterized in that the contours of axially adjacent openings (21) overlap.
7. A load holding valve according to at least one of the claims 1 to 4, characterized in that the closure member (4) of the pressure limiting valve (D) includes in a cylindrical longitudinal portion (7), which extends towards the opening piston (9), a plurality of circumferentially distributed longitudinal grooves (27) which bypass the check valve (R) and which extend with decreasing groove depth up to or up to and into the cylindrical projection (6).
8. A load holding valve according to claim 7, characterized in that the longitudinal grooves (27) are curved cut-out portions which are radially formed in the cylindrical longitudinal portion (7), preferably approx. 100% of the radius of curvature of said curved cut-out portions corresponding to the outer diameter of said cylindrical longitudinal portion (7) and preferably approx. 25% of the maximum depth of said curved cut-out portions corresponding to the outer diameter of said cylindrical longitudinal portion (7).
9. A load holding valve according to claim 8, characterized in that the longitudinal grooves (27) end at different distances from the seat surface (5).
10. A load holding valve according to at least one of the claims 7 to 9, characterized in that the longitudinal grooves (27) have different inside widths.
11. A load holding valve according to at least one of the preceding claims, characterized in that the seat insert (13) has arranged on both sides thereof respective perforated elements (18, 26) upstream of the check valve (R) and upstream of the pressure limiting valve (D), respectively.

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