EP0376023B1 - Electrohydraulic proportional valve - Google Patents

Description

State of the art

The invention is based on an electrohydraulic proportional directional valve according to the preamble of the main claim.

Such a proportional directional control valve is already known from the literature reference "Bosch hydraulics, proportional valves, hydraulics in theory and practice, 1983, Robert Bosch GmbH, division K6 hydraulics", in particular page 302, with which certain safety requirements can be met. The pilot spool, which can be actuated against spring force by a single proportional magnet, is moved there in the event of a power failure to a spring-centered, fourth switching position, in which at least pressure compensation is established between the two control chambers on the main control spool located at the end. The spring-centered main spool then takes up its central position and prevents malfunction of a hydraulic motor connected to the proportional valve. In addition to the four main connections A, B, P, T, this proportional valve also has control connections X and Y for external control oil supply and discharge in the main valve. There are also auxiliary connections C1 and C2 in the main valve, but these are used for the function of the load tap for the pressure compensator. This proportional valve can therefore not meet any further safety requirements such as those required by professional associations or accident prevention regulations for hydraulic machines and systems in the safety area. Also, in special applications, this proportional valve can be too slow in the event of an emergency stop because the main spool is reset by the springs in the main valve, which can only exert a restoring force corresponding to a few bar pressure and the pressure medium must flow through the small cross-sections of the pilot valve .

Furthermore, according to an older proposal (DE-A-3812116), the applicant has already been proposed to additionally connect a 3/2-way solenoid valve in the control circuit between the main valve and the pilot valve in order to meet the safety requirements for the aforementioned proportional valve. This allows e.g. meet the frequently existing requirement for systems and machines with protective devices that the connected working cylinder may only be actuated in one predetermined direction when opening a protective grille. For example, a mold is opened in order to remove defective parts. To achieve this, the proportional valve must be designed so that its main slide can only be switched in a certain flow direction. The disadvantage of this solution is that the effort for the intermediate plate solution, in which the 3/2 solenoid valve is housed, is relatively large. Even adapting to different security requirements is not always easy. In some cases, the poor dynamics mean that the requirement that the main slide should be quickly returned to its starting position in the event of an emergency stop or opening of a protective grille cannot be met.

Advantages of the invention

In contrast, the electrohydraulic proportional directional control valve according to the invention with the characterizing features of the main claim has the advantage that it can meet diverse security requirements with relatively little effort. In addition, the dynamic behavior can also be considerably improved if the resetting of the main control spool is supported hydraulically by the spring forces by an intermediate pressure in the pilot control circuit.

The measures listed in the subclaims enable advantageous developments and improvements of the proportional directional control valve specified in the main claim. Particularly advantageous embodiments result in a design according to claims 2 to 4, whereby a particularly simple and inexpensive solution can be achieved. For example, the standard version can be used as the housing for the main control valve, in which the auxiliary connections are available per se, but have previously been used for another function. Furthermore, a relatively small valve can be used as the switching valve, which only has to have the same nominal size as the regulating pilot valve, ie the switching valve must meet the flow of the pilot valve without increasing the pressure difference. Large-volume safety valves in the work lines can therefore be avoided. In addition, electrical position indicators can be arranged on the main control valve as well as on the pilot valve in the case of very high safety requirements. The main control spool can still be equipped with a leakage oil drain if the connected working cylinder is to be prevented from drifting. It is also advantageous if the tapping of the reliefs is incorporated directly in the main control slide, that is to say in an actuator which determines the flow. A design according to claim 12 is also particularly expedient, as a result of which pressure build-up in a control chamber can be prevented particularly effectively. Tapping the relief directly in the control oil supply allows a particularly compact solution. This self-monitoring of the valve also guarantees a high level of safety. Further particularly advantageous configurations result from the remaining claims, the description and the drawing.

drawing

Three embodiments of the invention are shown in the drawing and explained in more detail in the following description. 1 shows a first electrohydraulic proportional directional control valve in a simplified representation and partly in longitudinal section, FIG. 1a shows the switching symbol of the pilot stage in FIG. 1, FIGS. 2 to 6 different switching valves for use with the first proportional directional control valve according to FIG. 1 to implement different safety requirements, FIG. 7 shows a longitudinal section by a part of a second proportional directional control valve with a change in the tapping of the relief in the control circuit compared to FIG. 1 and FIG. 8 a partial section through a third exemplary embodiment.

Description of the embodiments

FIG. 1 shows a simplified representation of an electrohydraulic proportional directional valve 10, which is used to control a double-acting working cylinder 11. The proportional directional control valve 10 essentially consists of a hydraulically controlled main control valve 12, an electrically controlled pilot control valve 13 and a switching valve 14 connected to the main control valve 12. The pilot control valve 13, which is flanged onto a housing 15 of the main control valve 12, is actuated by a proportional magnet 16. in which an additional displacement sensor is integrated. Main control valve 12 and attached pilot valve 13 are known per se with regard to their basic structure from the literature reference mentioned at the beginning, to which reference is expressly made.

The proportional main control valve 12 is designed as a 4/3-way valve with four controlled main connections A, B, P and T and a main control spool 17 which can be moved continuously in three switching positions. The main control slide 17 is in the housing 15 in one Slider bore 18 guided tight and sliding. The slide bore 18 penetrates a centrally located inlet chamber 19, which is connected to the main connection P, two adjacent motor chambers 21, 22, which are connected to the main connections A and B, and two return chambers 23 and 24, which are connected to the main connection T. . The main port P is supplied in a manner not shown by a pump with pressure medium, while the main port T is relieved to the tank. The two sides of the double-acting working cylinder 11 are connected to the main connections A and B.

The main control slide 17 projects with its front ends 25, 26 into a control chamber 27, 28, which each receive a spring 29, 31 to form a double-acting resetting device 32 for the main control slide 17. By pressurizing a control chamber 27, 28 while simultaneously relieving pressure on the other control chamber 28, 27, the main control slide 17 can be deflected in both directions from its drawn central position against the force of the resetting device 32.

The pilot valve 13 is designed as a 4/4-way valve, the control functions of which can be found in the associated, simplified illustration according to FIG. 1a. The pilot valve 13 has four controlled connections A, B, P, T and a pilot spool 33, which can be controlled by the single proportional magnet 16 against the force of a spring 34 in four switching positions 35, 36, 37 and 38. The switch position 37 is designed as a neutral control position in which all four connections A, B, P, T of the pilot valve 13 are closed. From this neutral control position, the pilot spool 33 can be transferred into the two working positions 38 and 36, respectively, by correspondingly controlling the proportional magnet 16, in which one of the connections A, B is alternately connected to the connection P, while the other connection B, A to Tank connection T is relieved. When the proportional magnet 16 is de-energized, the spring 34 presses the pilot spool 33 into its safety position 35, in which the two connections A, B are connected to one another and to the tank connection T and the P connection is shut off.

The pilot valve 13 is mounted on the main control valve 12 in such a way that its connection P is connected to a control connection X of the main control valve 12 via a supply channel 39 in the housing 15. Furthermore, from the port T of the pilot valve 13, a relief channel 41 in the housing 15 leads to a control port Y of the main control valve 12. These two control ports X, Y are used for external control oil supply and drainage and thus form parts of a control circuit together with the channels 39, 41 42. The supply channel 39 and the relief channel 41 cannot be influenced hydraulically by the main control slide 17 itself. The connection B of the pilot valve 13 is connected via a first control channel 43 to the A-side control chamber 27 in the main control valve 12, while in a corresponding manner the connection A has a connection to the B-side control chamber 28 via a second control channel 44.

The slide bore 18 receiving the main control slide 17 is expanded in the area between the first return chamber 23 and the associated control chamber 27 to form a first annular chamber 45 which is connected to an auxiliary connection C1 arranged in the housing 15. The main control slide 17 has in the area of this first annular chamber 45 a first annular groove 46 which, on the one hand, always has a connection with the first annular chamber 45 in the central position of the main control slide 17 and, on the other hand, is constantly connected to the A- via a longitudinal groove 47 on the outside of the slide end 25. side control room 27 is connected. In a corresponding manner, the slide bore 18 penetrates on the opposite valve side a second annular chamber 48, which has a connection to an auxiliary connection C2 and which has a corresponding second annular groove 49 in the main control slide 17 and an associated second longitudinal groove 51 with the B-side Control room 28 has connection. Furthermore, the main control slide 17 has a leak oil drain 52, which is not of interest in the present context, in order to prevent undesired drifting of the working cylinder 11.

As FIG. 1 also shows, the two auxiliary connections C1, C2 are each connected via a line 53, 54 to the connections A, B of the switching valve 14, which is designed as a simple, spring-centered, electromagnetically actuated 4/3-way valve. The switching valve 14 has a central, spring-centered zero position 55, in which it relieves both auxiliary connections C1, C2 to the tank connection T, while the connection P is hydraulically blocked. In a left switch position 56, all connections A, B, P, T are blocked, while in a right switch position 57, connection B to the tank is relieved and connections A and P are blocked.

The mode of operation of the electrohydraulic proportional directional valve 10 to meet special safety requirements is described as follows, the basic function of the two-stage proportional valve being assumed to be known, according to which the control oil supplied at the control connection X from the pilot valve 13, depending on the control position of the pilot valve 33, builds up pressure in the control spaces 27, 28 causes, while at the same time the other control chamber 28, 27 is relieved in order to deflect the main control slide 17 proportionally to the two sides from the center position shown.

In the present proportional directional control valve 10, at least in the central position of the main control slide 17, its control spaces 27, 28 are each connected via the longitudinal grooves 47, 51, the annular grooves 46, 49 and the annular chambers 45, 48 to the auxiliary connections C1 and C2, which in turn are connected the switching valve 14 are connected. Depending on the currently active switching symbol on the switching valve 14, different ones can now be used Safety requirements are realized on the main control valve 12, as is often required in systems and machines with protective devices.

One of these requirements can e.g. be that, when the protective grille is open, the working cylinder 11 must be prevented from making an unauthorized closing movement, i.e. the main control slide 17 must not reach its flow direction P-A. This requirement is met with the aid of the zero position 55 of the switching valve 14, since in this spring-centered neutral position both auxiliary connections C1, C2 to the tank are relieved and thus a deflection of the main control slide 17 is not possible even with a regulating pilot valve 13. This can already be achieved with a relatively small switching valve 14, which only has to have the same nominal flow rate as the pilot valve 13, so that the pressure medium possibly controlled by the pilot valve 13 into a control chamber can also be safely discharged to the tank, so that no disturbing pressure build-up takes place.

An additional requirement for accident prevention regulations requires that, with an open protective grille, there should be the possibility that the mold can only be opened, for example to remove defective parts, ie the main control slide 17 may only be switched in the flow direction PB. This requirement can be achieved with the help of the right switching position 57 of the switching valve 14, the auxiliary connection C2 being relieved of pressure to the tank, while the other auxiliary connection C1 is blocked. With a regulating pilot valve 13, a pressure build-up can only take place in the left control chamber 27, so that a deflection of the main control slide 17 to the right is possible for controlling a flow from P to B, but not a flow control from P to A.

For normal control operation of the proportional directional control valve 10, the switching valve 14 is brought into its left switching position 56, in which it shuts off both auxiliary connections C1, C2.

In normal control operation, ie when the pilot valve 13 is energized, an improved dynamic behavior of the proportional directional control valve 10 can also be achieved. It is assumed that in Figure 1 the main spool 17 e.g. is deflected in the direction P → A, that is to the left, and the switching valve 14 assumes its position 56, a rapid return to the position predetermined by the desired value now being desired. For this purpose, the switching valve 14 is switched to its position 57 and at the same time the pilot valve 13 is energized in such a way that the full control pressure is present in the left control chamber 27. The right control chamber 28 is relieved with the switching valve 14, so that the pressure medium from the right control chamber 28 does not have to flow back solely through the small cross sections of the pilot valve 13. As a result, shorter positioning times are achieved. When the protective grille is opened, the switching valve 14 can then be brought into its position 55; this prevents any deflection of the main control slide 17.

In addition, there is often the requirement that the main control slide 17 should be quickly returned to its central position in the event of an emergency stop or when the protective grille is opened. This requirement is also improved in the proportional directional control valve 10, in that when the main control spool 17 is reset, the pressure medium can flow out via the pilot control valve 13 and the switching valve 14 due to the relatively weak forces of the springs 29 and 31, so that a quick reset can be achieved.

With the present proportional directional control valve 10, a wide variety of safety requirements can thus be met, an inexpensive standard housing, which already can be used as the housing 15 a control circuit 42 is provided with the auxiliary connections C1, C2.

FIGS. 2 to 6 show different switching valves which can be used instead of the switching valve 14 in the proportional directional control valve 10 according to FIG. 1. These switching valves differ as follows, the spring-centered zero position 55 and the left (56) and right switching position 57 always being identified by the same reference numerals as in the switching valve 14.

FIG. 2 shows a switching valve 61, in which the spring-centered zero position 55 is designed so that normal control can be controlled with the proportional directional control valve 10. While in the right switch position 57 the auxiliary connection C2 is relieved, in the left switch position 56 the auxiliary connection C1 to the tank is relieved, so that in these switch positions 56, 57 the main control slide 17 can only be deflected in one direction and thus depending on the pin assignment the connections PA or PB are monitored.

FIG. 3 shows a third switching valve 62, which differs from the first switching valve 14 only in that, in the zero position 55, the two auxiliary connections C1 and C2 are connected to one another, while the tank connection T is blocked. This promotes rapid pressure equalization, especially if the switching valve has larger cross sections than the pilot valve 13.

FIG. 4 shows a fourth switching valve 63, which differs from the first switching valve 14 only in that, in the right switching position 57, the auxiliary connection C1 associated with the A side to the tank is relieved.

FIG. 5 shows a fifth switching valve 64, which is designed as a 4/2 solenoid valve and only has the positions 55, 57, in which it alternately relieves one of the connections A, B to the tank T. With the fifth switching valve 64 it is achieved that the main control slide 17 can only ever be deflected in one direction. If the switching valve 64 sticks, a change in direction cannot be carried out. This ensures self-monitoring of the valve.

FIG. 6 shows a sixth switching valve 65, which is designed as a spring-loaded 2/2 solenoid valve and which only controls an auxiliary connection C2, which can also be assigned C1 if required.

FIG. 7 shows a longitudinal section through part of a second proportional directional control valve 70 which works with other control means to avoid pressure build-up in a control room. The second proportional directional control valve 70 differs from the first proportional directional control valve 10 as follows, the same reference numerals being used for the same components.

In the case of the second proportional directional control valve 70, the supply channel 39 starting from the control connection X is guided to the pilot control valve 13 in a manner which can be influenced by the main control slide 17. For this purpose, the supply channel 39 runs through an annular chamber 71 which is formed in the housing 15 between the first annular chamber 45 and the left return chamber 23. The main control slide 17 has in the area of this annular chamber 71 an annular groove 72 which forms an auxiliary control edge 73. This auxiliary control edge 73 has a positive overlap 74 with respect to the first annular chamber 45, which is smaller than the positive overlap with which the main control slide 17 is equipped between the main connections P and A. A hydraulic cross-connection as in FIG. 1 is omitted between the left control chamber 27 and the first annular chamber 45.

The mode of operation of the second proportional directional control valve 70 with regard to its safety function is explained as follows: It is assumed that in the event of an unwanted deflection of the main control spool 17 from its spring-centered center position to the left into a working position, the switching valve 65 connected to line 53 assumes its zero position, whereby it relieves the auxiliary connection C1 to the tank. When the main control slide 17 begins to move to the left, its auxiliary control edge 73 opens a connection from the control connection X to the auxiliary connection C1, so that control oil supplied in the control connection X is no longer guided from the regulating pilot valve 13 into the control chamber 28, but rather via the annular groove 72 to the auxiliary connection C1 and further to the tank. The main control slide 17 thus relieves itself, as a result of which no pressure can be built up in the pilot valve 13. An unwanted deflection of the main control slide 17 to the left is therefore not possible. The positive overlaps 74 on the main control slide 17 are matched to one another in such a way that the connection from the main connection P to A is not opened.

FIG. 8 shows a longitudinal section through part of a third proportional directional control valve 80, which differs from the second proportional directional control valve 70 as follows, the same reference numerals being used for the same components. In the third proportional directional control valve 80, a second auxiliary control edge 82 is formed via an additional, second annular groove 81, which has a positive overlap 83 with respect to the first annular chamber 45. The two annular grooves 72, 81 are connected to one another via transverse bores 84 in the main control slide 17.

With this arrangement it is achieved that with the third proportional directional control valve 80 a self-relief is possible in both directions when the main control slide 17 is deflected from its central position.

This means that the proportional directional control valves 70, 80, with their extremely compact design and relatively little additional effort, can fulfill a wide range of safety requirements for systems and machines with protective devices.

Of course, changes are possible to the embodiments shown without departing from the spirit of the invention. Instead of the pilot valve with a single proportional solenoid, a pilot control stage can also be used that works with two proportional solenoids. Furthermore, it is also possible, in the embodiment according to FIG. 1, to dispense entirely with the annular grooves 46, 49 pierced in the control slide 17 and to produce the cross-connections solely through the longitudinal grooves 47, 51, which must then be made sufficiently long.

Instead of the type of construction shown in FIG. 1, in which the control rooms 27, 28 are permanently connected to the auxiliary connections C1, C2 in the middle position shown as a result of negative coverage, it may also be expedient to equip these cross connections with a low positive coverage, which, however is always made smaller than the associated positive overlap of the control spool between the main connections. Such a covering has the advantage that it allows the control slide to be reset more quickly, since the full control pressure in the pressurized control chamber can be maintained longer when the control is reset. If there is a positive overlap in the cross-connection, it is also possible in an advantageous manner to specifically specify a certain stroke on the control slide, after the passage of which the safety shutdown is to take effect.

Under certain circumstances it can also be useful to combine cross connections with positive and negative overlap in the proportional directional control valve.

Claims (20)

1. Electrohydraulic proportional directional valve (10, 70, 80) with a hydraulically controlled main control valve (12), the control slide (17) of which is centred in a middle position by spring force and can be deflected towards both sides into working positions via control spaces (27, 28) located on the end faces, in order to control the hydraulic connections between four main connections (A, B, P, T), and with an electromagnetically actuated pilot-control valve (13) which controls the main control valve (12) via a pilot-control circuit (42), for which purpose the two valve connections of the pilot-control valve (13) are connected via control channels (43, 44) to the control spaces (27, 28), in order alternately to load these with control pressure medium or to relieve them, and with at least one auxiliary connection (C1, C2) which is arranged in the main control valve (12) and which, in dependence on the position of the control slide (17), can be connected to another space filled with pressure medium, characterized in that there are arranged on the control slide (17) of the main control valve (12) control means (46, 47, 49, 51; 72, 73; 81, 82), via which a portion (27, 28; 39) of the pilot-control circuit (42), the said portion being loaded with pressure when the pilot-control valve (13) is regulating, is connected to the auxiliary connection (C1, C2), and in that inserted into a line (53, 54) outgoing from the auxiliary connection (C1, C2) is a switching valve (14; 61-65), by means of which the pressure-loaded portion (27, 28, 39) can be relieved.
2. Proportional directional valve according to Claim 1, characterized in that the pressure-loaded portion of the pilot-control circuit (42) is a control space (27, 28) which is connected to the auxiliary connection (C1, C2) via the cross-connection (47, 46; 51, 49) which can be influenced by the main control slide (17).
3. Proportional directional valve according to Claim 1 or 2, characterized in that the cross-connection is arranged on the main control slide (17) and, in particular, is designed essentially as a longitudinal groove (47, 51) extending on the outer circumference of the latter.
4. Proportional directional valve according to Claim 3, characterized in that the longitudinal groove (47, 51) extends between the control space (27, 28) and an annular groove (46, 49) in the control slide (17), which annular groove (46, 49) is located in the region of an annular chamber (45, 48) fixed relative to the housing and connected to the auxiliary connection (C1, C2).
5. Proportional directional valve according to one or more of Claims 1 to 4, characterized in that the main control valve (12) has a second auxiliary connection (C2) with an associated cross-connection (49, 51) in the other second control space (28), and the line (54) outgoing from the auxiliary connection (C2) leads to a switching valve (14).
6. Proportional directional valve according to Claim 5, characterized in that the two connections (C1, C2) are connected to a common switching valve (14) via their outgoing lines (53, 54).
7. Proportional directional valve according to Claim 6, characterized in that the switching valve is designed as a 4-way/3-position valve (14, 61, 62, 63) with a spring-centred neutral position (55).
8. Proportional directional valve according to Claim 7, characterized in that the switching valve (62), in its spring-centred neutral position (55), connects the two auxiliary connections (C1, C2) to one another.
9. Proportional directional valve according to Claim 7, characterized in that the switching valve (14; 63), in its spring-centred neutral position (55), relieves the two auxiliary connections (C1, C2) to the tank (T).
10. Proportional directional valve according to one of Claims 5 to 9, characterized in that the switching valve (14; 61, 62, 63) has at least one switching position, in which the two auxiliary connections (C1, C2) are blocked hydraulically, and has at least one switching position (57), in which one of the auxiliary connections (C2, C1) is relieved and the other (C1, C2) is blocked.
11. Proportional directional valve according to one of Claims 5 and 6, characterized in that the switching valve is designed as a 2-position valve (64, 65), in particular a spring-centred 3/2 solenoid valve (64), which, in each switching position (55, 57), relieves one of the auxiliary connections (C1, C2) to the tank (T) and shuts off the other auxiliary connection.
12. Proportional directional valve according to Claim 1, characterized in that the pressure-loaded portion of the pilot-control circuit is a channel (39) which serves upstream of the pilot-control valve (13) to a control connection (X) for the inflow of control pressure medium and which is connected to an annular chamber (71) assigned to the control slide (17), and in that this annular chamber (71) can be connected to the auxiliary connection (C1) via an auxiliary control edge (73) and the control slide (17).
13. Proportional directional valve according to Claim 12, characterized in that the auxiliary control edge (73) has, in the middle position of the control slide (17), a positive overlap (74) which is smaller than the associated positive overlap of the control slide (17) in relation to a connection between the main connections for the inflow (P) and the motor (A/B).
14. Proportional directional valve according to Claim 12 or 13, characterized in that a second auxiliary control edge (82) is arranged on the control slide (17), so that in the event of a deflection of the control slide (17) out of its middle position in opposite directions, the inflow (X) of the control pressure medium can be connected to the auxiliary connection (C1).
15. Proportional directional valve according to one of Claims 12 to 14, characterized in that the auxiliary connection (C1) is connected to the tank (T) via the outgoing line (53), and the switching valve located in this line (53) is designed as a spring-centred magnet-actuated 2/2 valve (65).
16. Proportional directional valve according to one or more of Claims 1 to 15, characterized in that the control means (47, 46, 49, 51; 72, 73; 81, 82) in the main valve (12) for each auxiliary connection (C1, C2) are arranged respectively essentially between a return-flow chamber (23; 24) and the adjacent control space (27, 28).
17. Proportional directional valve according to one or more of Claims 1 to 16, characterized in that the pilot-control valve is a 4/4 valve, the pilot-control side of which can be deflected counter to the force of a spring (34) by a single proportional magnet (16).
18. Proportional directional valve according to one of Claims 1 to 17, characterized in that the load pick-ups for a pressure balance, which are present per se in a housing (15) of the proportional directional valve (10; 70; 80), are used as auxiliary connections (C1, C2).
19. Proportional directional valve according to one of Claims 1 to 11, characterized in that, in the middle position of the control slide (17), the cross-connection (47, 46, 45, C1) is designed as a negative overlap.
20. Proportional directional valve according to one of Claims 1 to 11, characterized in that, in the middle position of the control slide, the cross-connection is designed as a positive overlap which is smaller than the associated positive overlap of the control slide in relation to an associated connection between the main connections for the inflow (P) and the motor (A/B).

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