EP0620932B1 - Electro-hydraulic control device and pressure reducing valve - Google Patents

Abstract

An electro-hydraulic control device (S) for a clamping device of an automatic lathe, with a pressure reducing valve (V) connected to a pressure source (1), the output of which can be connected via a directional control valve (W) to two user lines (11, 12) operable alternately, with a pressure switching device (D) fitted in the pressure reducing valve (V) and with a regulating input (20) to which control pressure can be applied, whereby in the directional control valve (W) there is a user pressure tapping (Z) at which the control pressure exists only in the control position (a and/or b) of the multi-way valve where the output (6) of the pressure reducing valve (V) is properly connected to a user line (11, 12), and in which the pressure tapping (Z) is connected to the control input (20). In the pressure reducing valve (V), between the control piston (14) and the pressure switching device (D) there is a mechanical, motion-transmitting link with which the pressure switching device (D) is actuatable directly by the control piston (14) once the monitoring pressure set via the force of the spring (22) has been reached.

Description

The invention relates to an electro-hydraulic control device according to the preamble of claim 1 as well a directly controlled pressure reducing valve according to the preamble of claim 8.

To secure workpiece clamping in a Machine tool, e.g. in a clamping device Automatic lathes, is used to control the machine tool a good signal if the required Clamping pressure is present, or an error signal is transmitted, if the clamping pressure is undercut. Will the tension pressure the good signal is not reached. Of the Clamping pressure is independent via a pressure reducing valve controlled by a supply pressure and in his Pressure value on the pressure reducing valve to the respective requirement set. Different workpieces or different Workpiece materials require different materials Clamping pressures.

From a publication 750 1614.05.02.86 from Herion Werke KG, D-7012 Fellbach, it is known to everyone Consumer line one assign adjustable pressure switch to the change of the clamping pressure must become. This poses a security risk because the correct adjustment of the pressure switches is often unintentional refrained from or performed incorrectly. Out the document is also known for disposal this security risk in a pressure switch to integrate the pressure reducing valve, automatically when the pressure reducing valve is adjusted is adjusted. However, it is an indirectly controlled one Pressure reducing valve, which a control pressure from each charged consumer line over either Common changeover valve supplied to consumer lines becomes.

From DE-C-35 32 592 is a directly controlled pressure reducing valve known, in addition to the control piston own pot piston loaded by its own spring is provided, the pressure switch as a measuring piston actuated independently of pressure.

DE-C-30 39 002 is a directly controlled pressure reducing valve in an electrohydraulic control device known in which in addition to the control piston a separate Throttle piston as volumetric piston for actuation two pressure switches is provided. The throttle piston is centered with two springs. The control pressure is on Output of the pressure reducing valve derived.

In an indirectly controlled known from DE-C-32 04 055 Pressure reducing valve in an electrohydraulic Control device for a machine tool component the pressure switch from the pilot valve of the Control piston of the pressure reducing valve actuated. The standard pressure for the control piston and for the closing element of the Pilot valve is made up of the via the directional valve Consumer line via one of two consumption lines common shuttle valve derived.

In a pressure reducing valve known from DE-C-23 10 193 in an electrohydraulic control device Machine tool component is the Control piston in one Auxiliary piston arranged the is adjusted depending on the pressure and actuated a pressure switch as a volumetric flask. The standard pressure for the control piston is upstream of the downstream one Directional valve derived. The switching pressure for the Auxiliary piston and the pressure switch, however, is from the acted upon consumer pressure line via a control line and derived a biased check valve. There are two control lines for the safety function with check valves and a common leakage line with a flow restrictor required. These additional Components not only increase construction costs, but create additional possible sources of error for the safety function. The pressure reducing valve is complicated and multi-part.

The invention has for its object an electrohydraulic Control device of the latter type as well as a suitable one to create a controlled pressure reducing valve, the structurally simple and in terms of desired security function are reliable, and just a few, the number of potential sources of error reducing parts exist.

The object is achieved with the im Claim 1 features contained solved.

In the electro-hydraulic control device according to claim 1, the control pressure is structurally simple directly in the directional control valve and only tapped there if the directional control valve properly with a consumer line connected to the outlet of the pressure reducing valve. A separate monitoring of the directional valve for its correct Function is eliminated, as is the need for separate Control lines, a shuttle valve or Check valves. The control device is simple and consists of a few components. The safety function is reliable because the pressure switching device only if the directional control valve functions properly is operated. The pressure switch device is at a Adjustment of the pressure reducing valve set with. Should the directional valve get stuck when pressed and the monitored Do not assume the tax position correctly, then none a response of the pressure switch device Control pressure generated. The Pressure switch device does not emit or enter a good signal Error signal, so that warnings or damage-preventing Measures can be taken. The standard pressure is only derived if the directional control valve, if necessary with a remaining stroke, is so far adjusted that the proper Supply of the clamping device is guaranteed is. Since the clamping pressure of the clamping device most important criterion for security is it expedient, the control pressure to reduce the supply pressure only when the consumer line is charged to derive for tensioning. On the other hand, can be used to release the tensioning device refrain from reducing the pressure and the supply pressure be used. For this purpose, when connecting the other consumer line via the directional valve no control pressure is derived from the outlet of the pressure reducing valve, so that the pressure reducing valve then opens and does not intervene regulatively.

With the motion-transmitting connection between the control piston and the pressure switching device the safety function is reliable because the Pressure switching device directly on movements or the Position of the control piston responds.

According to claim 3 it is ensured that in intermediate positions and / or in a middle position of the directional control valve no control pressure arises, but any existing pressure is even reduced. The easiest the pressure relief can be achieved through a connection to return.

According to claim 4 is an inexpensive 4/2 or 4/3 directional spool used in Housing has a control channel, the mouth part is the consumer pressure tap. To accommodate the Tapping is not a modification of the basic concept of the directional spool valve is required. The pressure tap can if necessary for only one or both consumer lines to be used.

According to claim 5 is for Pressure tapping in each or only one control position of the longitudinal channel incised the spool or milled in. It is through training and arrangement the longitudinal channel ensures that in intermediate positions no control pressure is derived, and the pressure switching device only generates a signal when the directional spool properly switched to continuity.

According to claim 6, the pressure relief directly across the cross slot to the tank connection ensured. If the pressure tap is not used, the tank connection can be closed. With the three aforementioned embodiments can to save space and to create short, low loss flow paths the directional spool and the pressure reducing valve with the Switching device in a common, compact housing be arranged.

The measure of claim 7 is important so that the flow paths always open in the predetermined manner and are closed. The locking device holds the slide piston in the event of a power failure in the control position, so the tensioning device does not release immediately. It would be conceivable the latch with two scans for proper Monitor snapping to ensure the correct one Switching the directional spool signal to tap. This is useful for embodiments where the control pressure does not have the pressure tap but tapped elsewhere on the pressure reducing valve becomes. Alternatively, the actuating magnets could or the spool is monitored with position sensors.

The directly controlled pressure reducing valve according to claim 8 is characterized by a few individual parts, a compact one Construction and high reliability because of the pressure switching device Actuated directly by the control piston via the tappet becomes. If the control spring of the The pressure switching device needs a pressure reducing valve not to be adjusted separately. The pressure reducing valve can be used universally for use hydraulic control devices where for pressure monitoring using a pressure switching device a rule print is available.

The execution according to claim 9 has the advantage of direct actuation of the Pressure switch through the control piston. The pressure reducing valve consists of only a few individual parts and builds compact.

According to claim 10, the movement or position of the control piston mechanically via the tappet transfer to the pressure switch plunger. Of the The tappet does not become pressure-dependent, but depends on the path Control piston adjusted. It can be the pressure switch Arrange sideways, what compact dimensions of the pressure reducing valve and an exact adjustment of the pressure switch enables.

According to claim 11 can through the progressive characteristic of the spring or spring arrangement the smallest possible pressure difference on Switching point of the pressure switch, e.g. when pressure builds up on Output of the pressure reducing valve or when changing the Delivery rate.

Movement transmission is structurally simple according to claim 12. It can be a conventional one Control pistons are used because of the spring abutment the coupling takes over.

In the embodiment according to claim 13, the control pressure either directly from the one charged Consumer line or derived directly in the pressure reducing valve. The pressure reducing valve can also be used for other operating modes be used where the control pressure not derived from the way to the consumer becomes.

The embodiment according to claim 14 is universal different modes of operation customizable by each required channel connected, the other is closed.

Fig. 1

ein Blockschaltbild einer elektrohydraulischen Steuervorrichtung,

Fig. 2 + 3

zwei einander zugeordnete Schnitte eines Druckminderventils in den Schnittebenen II-II in Fig. 3 und III-III in Fig. 2,

Fig. 4,5,6

drei einander zugeordnete Schnitte eines Wegeventils in den Ebenen IV-IV, V-V und VI-VI,

Fig. 7

einen Schnitt einer geänderten Ausführungsform des Druckminderventils, und

Fig. 8

einen Schnitt einer weiteren geänderten Ausführung des Druckminderventils.

Embodiments of the subject matter of the invention are explained with the aid of the drawing. It shows:

Fig. 1

2 shows a block diagram of an electrohydraulic control device,

Fig. 2 + 3

two associated cuts of a pressure reducing valve in the sectional planes II-II in Fig. 3 and III-III in Fig. 2,

Fig. 4,5,6

three associated cuts of a directional valve on levels IV-IV, VV and VI-VI,

Fig. 7

a section of a modified embodiment of the pressure reducing valve, and

Fig. 8

a section of another modified version of the pressure reducing valve.

An electrohydraulic control device S according to FIG. 1 is used for the safety-monitored actuation of a Machine tool component K, like a double-acting one Hydraulic cylinder of a tensioning device Automatic lathes. An air-cooled driven by an engine M. Constant pump 1 sucks from a tank 2 and charges against a pressure relief valve via a pressure line 3 a pressure accumulator 4. From the pressure line 3 branches a line 3a to a pressure reducing valve V. A return line 5a leads from the pressure reducing valve V. a return line 5 and to the tank 2. With the pressure reducing valve V is a pressure switch device D structurally connected. The pressure reducing valve V is on the outlet side via a line 6 to a directional valve W, namely one 4/2 directional spool, connected, from which a return line 5b leads to the return line 5 (connections P and T on the directional valve W). The directional valve W is on the output side via consumer lines 11, 12 with the machine tool component K connected (connections A and B). The directional valve W has a consumer pressure tap Z (indicated schematically in the directional valve symbol), via a control line 7 with a control input 20 of the pressure reducing valve V is connected. The directional valve W contains a slide piston 8 by two actuating magnets 9, 10 between two control positions a and b is convertible. In intermediate positions between the the two control positions is the pressure tap Z with the Return line 5b connected and the control line 7 depressurized.

The structure of the pressure reducing valve V is shown in FIG. 2 and 3 (1st embodiment) can be seen in detail. The Pressure reducing valve V contains 13 in a housing bore a control piston 14 with two control edges 15 which are aperture-like the output connected to line 6, which cuts the housing bore 13 with its mouth 18, alternately with a pressure connection 19 (to the Line 3a connected) and a tank connection 17 (to the return line 5a connected) connects to Output 6 to set a certain pressure. The control piston 14 has a piston end 16 which with the Control input 20 fed control pressure can be applied is opposite to the force of a spring 22, which are arranged in a pressure-relieved chamber 28 and is adjustable in its bias, and the control piston 14 applied via a spring abutment 23. In the spring abutment 23, a groove 24 is provided, into which a Head part 27 in a parallel to the housing bore 13 Bore 25 displaceable plunger 26 in a form-fitting manner intervenes. The plunger 26 is mechanical via the spring abutment 23 motion transmitting with the control piston 14 coupled. The plunger 26 is sealed to one pressure ram 28 guided out of the bore 25, with which a pressure switch 29 of the pressure switching device D can be actuated.

Two channels 30, 32 are via a connecting channel 33 connected to the control input 20. The channel 30 intersects the mouth 18 and then the channel 33. The channel 32 leads to a connection 7 'in the outside of the pressure reducing valve V to which the control line 7 can be connected is. In the embodiment shown, the channel is 30 by a plug between the mouth 18 and the channel 33 shut off and to the outside by a screw plug 31 sealed. The connection 7 ', however, is open and connected to the control line 7. Will the Port 7 'closed, then the connection to Mouth 18 opened so that the control input 20 with the Control pressure is fed from outlet 6. To the connection 7 'a control line could also be connected be the higher one via a shuttle valve Consumer pressure in one of the two consumer lines 11, 12 leads.

The spring 22 could be a progressive spring arrangement Be characteristic. For this purpose, several can be done in stages springs to come into effect are provided or one with differently wound sections Feather. A progressive characteristic has the advantage that the switching pressure of the pressure switch 29 with increasing Flow rate or near increasing working pressure is at the working pressure.

4, 5 and 6 in one Slider bore 34 of the slide piston 8 sealed displaceable guided and reciprocally by plunger 37 slidable. The plunger 37 are from the actuating magnet 9, 10 adjusted. A locking device 36 secures mechanically the two control positions of the spool 35. In the slide bore 34 is centered a connected to the output 6 of the pressure reducing valve V. Inlet 38, on both sides of which outlets 39, 40 are arranged in the form of turned grooves. At that Inlet 38 facing away from each outlet 39, 40 a tank connection 43, T is provided to which the return line 5b (Fig. 1) is connected. Im with a cylindrical Sealing section 42 formed slide piston 8 are two diametrically opposed flow pockets 41 molded, which are connected inside the slide piston 8 and the inlet 38 in each control position connect to an outlet 39 or 40, while via a Constriction 35 in the spool 8 of the other outlet 40, 39 connected to the adjacent tank connection 43 is. There would be a flow pocket 41 on one side of the Slide piston 8 are sufficient; for reasons of pressure equalization and the smooth running of the slide piston 8 are two diametrically opposed flow pockets 41 expedient.

The flow pockets 41 are offset in the circumferential direction two diametrically opposed longitudinal channels 44 (milled grooves in the sealing section 42) provided that connected to each other via an oblique through hole 48 are. On the one longitudinal channel 44 (in FIG. 5 below) is a control channel mouth 45 in the slide bore 34 aligned with a control channel 51 (with the Control line 7 connected) belongs. The opposite Longitudinal channel 44 is cut by a transverse slot 49, the movement of the slide piston 8th runs over a tank connection 46 of a tank channel 50 and then a flow connection between the longitudinal channels 44 and the return line 5b (Fig. 1) produces about which the control line 7 is relieved of pressure. The tank connection 46 is offset to the side relative to the longitudinal channel 44, so that it is only run over by the transverse slot 49.

4 to 6, the spool 8 is in its Control position b shown, in which the outlet 40 with the Inlet 38 is connected, while the outlet 39 with the Tank connection 43 is connected. The one in the consumer line 12 prevailing pressure is the control pressure of the Control channel mouth 45 abandoned, so that it over the Control line 7 to the control input 20 of the pressure reducing valve (Fig. 1) is transmitted. To tank connection 46 there is no connection because the transverse slot 49 (FIG. 5) is to the right of the tank connection 46. It's going on this way not only the correct pressure in the consumer line 12 reported as standard pressure, but also ensures that the spool 8 actually in has reached its correct tax position b. Remains the slide piston 8 hang in the intermediate position, e.g. without the latching device 36 having intervened, then the control channel opening is via the transverse slot 49 45 connected to the tank and no control pressure reported.

It is particularly important that in all embodiments the pressure reducing valve with a single control element, namely the adjusting screw for the preload of the spring or spring arrangement 22 the setting of the pressure reducing valve and the pressure switching device D synchronously are changeable. In a particularly convenient manner the control piston, e.g. 14 in Fig. 2, the pressure reducing valve V at the same time as the measuring piston of the pressure switch 29 used because between the control piston and the pressure switch no further, pressure-dependent adjustable element is provided.

In the embodiment according to FIG. 7, the control piston has 14 'of the pressure reducing valve V' at its the control input 20 adjacent end a molded axial Tappet 54, which is aligned with the pressure switch 29 is and operated it. The plunger 54 penetrates one Sealing arrangement of the housing bore. The control pressure is here derived from output 6 via channel 30, 33. Is this channel is closed, then the control input 20 also as shown to the pressure tap Z in Fig. 1 or also directly to the two consumer lines via a shuttle valve 11, 12 may be connected.

In the embodiment according to FIG. 8 of the pressure reducing valve V "is the plunger 26 'as in Fig. 2 via the spring abutment with the control piston 14 transmitting motion coupled. A switching link 56 is provided on the plunger 26 ′, on which a probe arm 55 of a pressure switch 29 ' is present, which is on one side of the pressure reducing valve V " arranged outside and part of the pressure switching device D is.

Instead of a 4/2 directional spool valve, W a 4/3 directional spool can be provided (indicated in Fig. 1). The consumer pressure tap Z is excluded in the correct tax position or positions (a and / or b) - either by connection with the Tank connection or by a connection to the tank connection or through a connection with the straight with the Return line open consumer line unloaded. In the 4/3 directional spool, the middle position is above the Slide the control line for the control pressure directly connected to the return line while either both consumer lines blocked or connected together the return line are connected. Will rule pressure derived only in a tax position, then the Control line in the other control position with the straight one connected to the return open consumer line and relieved. These measures - individually or in combination - Are faulty good signals from the pressure switch device exclude the otherwise the higher-level control the tensioning device would react.

Claims (14)

1. An electrohydraulic control device (S) for a holding fixture (K), in particular for a holding fixture of a machine tool such as an automatic lathe, comprising an adjustable pressure reducing valve (V, V', V"), which is connected to a pressure source (1) and the outlet (6) of which cooperates with a control piston (14, 14') and is adapted to be alternately connected to one of two consumer lines (11, 12) of the holding fixture (K) via a downstream directional control valve (W) which is connected to the reservoir (2) and which is adapted to be changed over between control positions (a, b), further comprising a pressure switch means (D) which is functionally incorporated into the pressure reducing valve (V, V', V"), said pressure switch means (D) monitoring a pressure which is set by the pressure reducing valve (V, V', V") and which prevails in at least one consumer line (11, 12) acted upon via the directional control valve (W) as intended, and still further comprising a control input (20) in the pressure reducing valve (V, V', V"), said control input (20) being adapted to have applied thereto a pilot pressure derived from the output pressure of the pressure reducing valve (V, V', V") for the consumer line (11, 12) acted upon, characterized in that the directional control valve (W) has provided therein a consumer pressure tapping point (Z), which is used for deriving the pilot pressure and from which the pilot pressure can only be derived at the control position (a and/or b) of the directional control valve (W) at which the outlet (6) of the pressure reducing valve (V, V', V") is connected to a consumer line (11, 12) via the directional control valve (W) as intended, and that the consumer pressure tapping point (Z) is connected to the control input (20) of the pressure reducing valve (V, V', V").
2. A control device according to claim 1, characterized in that the control piston (14, 14') is coupled to the pressure switch means (D) in a motion-transmitting manner.
3. A control device according to claim 1, characterized in that the pressure tapping point (Z) in the directional conrol valve (W) is relieved from pressure between the control positions (a and b) of a slide piston (35) of the directional control valve (W), preferably at a central position at which the consumer lines (11, 12) are blocked or relieved due to communication with the reservoir (2) and/or at intermediate positions between the control positions (a and b) or between the central position and the control positions (a and b).
4. A control device according to claims 1 and 3, characterized in that the directional control valve (W) is a 4/2 or a 4/3 way slide valve comprising a slide piston (35) which is adapted to be displaced in a bore (34) for the slide piston between two control positions (a or b) by at least one operating magnet (9, 10) and which opens at each control position a connection between an inlet (38), which is connected to the outlet (6) of the pressure reducing valve (V), and an outlet (39, 40), which is connected to a consumer line (11, 12), and connects simultaneously an outlet (40, 39), which is connected to the other consumer line (11, 12), to a reservoir connection (T), that the bore (34) for the slide piston has provided therein a consumer pressure tapping control passage mouth (45) which the slide piston (35) connects at each control position (a or b) to at least one outlet (39, 40) and which said slide piston (35) separates from both outlets (39, 40) between the control positions, and that the pressure reducing valve (V) and the directional control valve (W) are preferably arranged in one common casing.
5. A control device according to claim 4, characterized in that, in a cylindrical sealing section (42), the slide piston (35) has on at least one side thereof a flow pocket (41) delimited axially and in the circumferential direction, that the control passage mouth (45) is arranged outside of the contour of the flow pocket (41) such that it is displaced relative to the flow pocket (41) when seen in the circumferential direction of the bore (34) for the slide piston, and that an axially delimited longitudinal passage (44) is provided in the sealing section (42) of the slide piston (35), said longitudinal passage (44) being in alignment with the control passage mouth (45) and establishing a connection between said control passage mouth (45) and an outlet (39, 40) at at least one control position.
6. A control device according to claim 5, characterized in that the longitudinal passage (44) can be connected to a reservoir connection (46) of the bore (34) for the slide piston via a transverse slot (49), which is provided in the slide piston (35) and which intersects the longitudinal passage (44), exclusively at intermediate positions and/or at the central position between the control positions (a, b) of the slide piston (35).
7. A control device according to claims 4 to 6, characterized in that the slide piston (35) is secured against rotational displacement within the bore (34) for the slide piston, and that said bore (34) has provided therein a detent means (36) with two defined detent positions corresponding to the control positions (a or b), said detent means (36) acting on the slide piston (35).
8. A directly controlled pressure reducing valve (V, V', V") for an electrohydraulic control device according to claim 1, comprising a control piston (14, 14'), which is adapted to be displaced within a valve bore (13) in response to a pilot pressure and against the force of a spring (22) and which, by means of axially spaced control edges (15), alternately controls the communication of an outlet (6) with a pressure connection (19) and a reservoir connection (17), and further comprising the signal-generating pressure switch means (D), which is provided on the pressure reducing valve and which is used for the purpose of monitoring the pressure at said outlet (6), characterized in that the control piston (14, 14') and the pressure switch means (D) have provided between them a tappet (54, 26, 26'), which is adapted to be displaced together with the control piston (14, 14') and which mechanically transmits movements of the control piston (14, 14') and actuates the pressure switch means (D) when the output pressure set by means of the force of the spring (22) has been reached.
9. A pressure reducing valve according to claim 8, characterized in that the tappet (54) is arranged on the control piston (14') such that it is adapted to be sealingly displaced and that it is in alignment with a pressure switch (29).
10. A pressure reducing valve according to claim 8, characterized in that the tappet (26 or 26') is arranged parallel to the control piston (14), that it is mechanically coupled to said control piston (14), and that it is either in alignment with a sealingly displaceable pressure switch tappet (28) or provided with a cam surface (56) for a cam follower arm (53) of the pressure switch (29').
11. A pressure reducing valve according to claims 8 to 10, characterized in that the control piston (14, 14') is acted upon by a spring or a spring arrangement (22) consisting e.g. of a plurality of springs which become effective in steps or of differently wound helical springs and having a progressive characteristic.
12. A pressure reducing valve according to claims 8 to 11, characterized in that a spring abutment (23) is arranged between said spring or spring arrangement (22) and the control piston (14), and that the tappet (26, 26') is mechanically coupled to said spring abutment (23).
13. A pressure reducing valve according to claims 8 to 12, characterized in that a pilot pressure for displacing the control piston (14, 14') is derived from the outlet (6) of the pressure reducing valve (V, V') or from a consumer line (11, 12) connected to said outlet (6).
14. A pressure reducing valve according to claims 8 to 13, characterized in that in said pressure reducing valve (V, V') a control input (20) leading to the control piston (14) is adapted to have selectively applied thereto the pilot pressure via one of two passages (32, 30), one of said passages (30) leading from the outlet (6) of the pressure reducing valve (V) to said control input (20) and the other passage (32) leading from a casing connection (7') to said control input (20).

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