EP0378789A2 - Electrohydraulic control system for controlling a hydraulic drive - Google Patents

Abstract

At least one control valve which has a control spool which is spring-loaded on one side and can be deflected against the spring force by a servomotor is used for controlling a hydraulic cylinder having a double-acting working piston. In the novel control system, at least one control valve each, belonging to each pressure space (16, 16a) of the hydraulic cylinder (15), is provided in a one-piece or multi-piece valve housing (1). The control spools (2, 2a) of the control valves are arranged coaxially and in mirror image to one another at a mutual distance apart. Here, a common control element (19, 20) of the servomotor (17), which control element (19, 20) is located between the inner ends of the control spools (2, 2a), serves to move the two control spools (2, 2a) in the same direction. Furthermore, each control spool (2, 2a) contains one auxiliary piston (8, 8a) each in one pressure space (26, 26a) each, in which arrangement the pressure spaces (26, 26a) can be acted upon via a manipulating valve (24) and the control spools (2, 2a) can thereby be moved into an inactive position in which they are removed from the effect of the control element (19, 20) of the servomotor (17). This inactive position can be activated directly as an "emergency stop function" from every operating position of the control spools (2, 2a). In addition, in the inactive position, the servomotor (17) can be moved into its zero or centre position and be orientated without this involving movements of the piston of the hydraulic cylinder (15). …<IMAGE>…

Description

The invention relates to an electrohydraulic control for controlling a hydraulic drive, such as a hydraulic cylinder, in which a double-acting working piston delimits a pressure chamber on each of its opposite sides, containing at least one control valve with a spring-loaded control slide, which can be deflected from its rest position against the spring force. and a servo motor for driving the control spool.

Directly controlled control valves, which are also referred to as electrohydraulic continuous valves, are generally used to form electro-hydraulic controls. Such a control valve contains a spring-loaded control slide in the valve housing, on which all the necessary control edges are arranged. These control edges must be "technically balanced"; they cannot be partially adjusted against each other afterwards. Through the action of a return spring, the control slide is held in a mechanically limited end position, which also represents the so-called "emergency stop function". From this end position, the control slide can be moved into the various valve positions by the force of a lifting magnet (control magnet) in order to to get the desired hydraulic symbol. The extent of the stroke movement of the control magnet (setpoint) is recorded via a position measuring system. With suitable control, a control loop can be built up with such an arrangement.

With such a directly controlled control valve, the middle position cannot be tapped off directly, but can only be determined indirectly via the behavior of the consumer to be controlled. This is extremely unsatisfactory, since it leads to unwanted and uncontrolled movements of the connected consumer when the control valve is set up or switched on.

Another disadvantage is that the so-called "emergency stop function" (control valve inactive) cannot be controlled separately, but is only possible by removing the setpoint generator. However, since the position of the control spool in the mechanical end position is not identical to the central position of the control valve (adjusted state), one or more symbol positions of the control valve are always run over when the "emergency stop function" is set. This inevitably leads to unwanted and uncontrollable movements on the consumer. Furthermore, when switching off from one of the possible control states with a larger setpoint specification, impermissibly high delays occur at the consumer, which is associated with the risk of damage to the hydraulic system. In order to counter these negative effects, one has started to take additional precautions by entering into the pressure medium supply line has a separate "emergency stop valve" and / or safety pressure valves installed in the consumer lines.

The invention aims to remedy these disadvantages. It is the object of the invention to provide an electrohydraulic control in which the control valve can be activated to control the control valve independently of the respective specification of the servo motor. The setting of the control valve to the "active" or "inactive" positions should always have priority over the setpoint specification. Furthermore, the control should be such that when the arrangement is switched on again, the setpoint can be adjusted independently of the position of the control valve, i.e. it should be possible to move the servomotor to the zero position without any movements of the consumer.

This object is achieved on the basis of an electrohydraulic control of the type described at the outset according to the invention in that in a one-part or multi-part valve housing at least one control valve, each associated with a pressure chamber of the hydraulic cylinder, is provided, the control slides of which are arranged coaxially in mirror image to one another with a mutual spacing from one another the inner ends of the control slide is a common control element of a servo motor, by means of which the spring-loaded control slide can be moved in the same direction by mechanical pressure contact, that each control slide in one pressure chamber each Auxiliary piston contains and that the pressure chambers can be acted upon by at least one switching valve with pressure medium in the sense of a movement counter to the spring force and thereby the control slide can be moved into an inactive position removed from the action of the control element, in which both pressure chambers of the hydraulic cylinder are connected to a line leading to the tank while the line coming from the pressure oil supply is blocked by the control valves.

According to an essential concept of the invention, the main control valve contains in a common valve housing at least two mirrored control spools which can be moved in the same direction and the control pistons arranged thereon for controlling one pressure chamber of the consumer. The setpoint is transferred to both control spools simultaneously via a common control element of the servo motor. For the "emergency stop function", each spool contains an auxiliary piston in each pressure chamber. The "emergency stop function" can thus be reached directly with the aid of a switching valve, regardless of the respective control state of the two control valves. In the "emergency stop function" position, ie in the inactive position of the control valves, the central position of the control element of the servo motor can be aligned without moving the consumer, even though the pressure oil supply is present. This also provides two-channel control of the control valves. Another advantage in the structural division of the control valves and the symmetrically opposite arrangement of the control slides is the compensation the hydraulic contact forces.

Advantageous further developments of the electro-hydraulic control are described in the subclaims. After that it is advantageous to design the control element of the servo motor as an eccentrically mounted cam ring, the outer lateral surface of which serves as a contact surface for the inner end of the two control slides.

In order to be able to adjust the spool axially against each other, it is expedient to have axially adjustable components at their inner end, e.g. a screw or a spindle. Each individual control valve is expediently designed as a 3/3-way valve known per se.

The inactive position of the spool, i.e. the position "emergency stop function" can be determined mechanically by a mechanical stop for the auxiliary spool of the control slide, e.g. the end wall of the cylinder space is provided.

To adjust the center position of the servo motor, it is advisable to connect a switch cam to the rotating lifting ring, which can actuate a zero point switch in the center position.

• Fig. 1 einen Axialschnitt einer Ausführungsform eines Doppel-Steuerventils zum Steuern eines zweiseitig beaufschlagbaren Hydraulikzylinders gemäß der Erfindung,
• Fig. 2 einen Schaltplan einer elektrohydraulischen Steuerung gemäß der Erfindung zum Steuern eines Hydraulikzylinders im Schaltzustand "inaktive Stellung" der Steuerventile,
• Fig. 3 den Schaltplan nach Fig. 2 im Schaltzustand "aktive Stellung" der Steuerventile,
• Fig. 4 den Schaltplan nach Fig. 2 im Schaltzustand Betätigung des Hydraulikzylinders und
• Fig. 5 den Schaltplan nach Fig. 2 im Schaltzustand Betätigung des Hydraulikzylinders in entgegengesetzter Richtung.

Further details of the invention are explained below using an exemplary embodiment shown schematically in the drawing. It shows:

• 1 shows an axial section of an embodiment of a double control valve for controlling a hydraulic cylinder which can be acted upon from two sides according to the invention,
• 2 shows a circuit diagram of an electrohydraulic control according to the invention for controlling a hydraulic cylinder in the "inactive position" switching state of the control valves,
• 3 in the switching state "active position" of the control valves,
• Fig. 4 shows the circuit diagram of Fig. 2 in the switching state actuation of the hydraulic cylinder and
• Fig. 5 shows the circuit diagram of Fig. 2 in the switching state actuation of the hydraulic cylinder in the opposite direction.

In the embodiment illustrated in FIG. 1, two identical control slides (2, 2a) are arranged coaxially in a housing (1) and mirror-inverted to one another in relation to the central plane (3). In view of the same design of the two control slides (2, 2a) and thus also the control valves, only one of the two control valves is described for the following description. The same applies to the second control valve, the letter a being added to the individual reference numbers.

The control valves are individually designed in the manner of a conventional 3/3-way valve. The spool (2, 2a) contains two spools (4, 5) each a control edge (6, 7) and also an auxiliary piston (8). The control pistons (4 and 5) and the auxiliary piston (8) are connected to one another and, together with an end piston rod (9) that emerges from the valve housing (1), form the axially movable control slide (2). Between the free end face of the piston rod (9) and an end cap (10) a helical compression spring (11) is arranged, which tries to move the control slide (2) from the mechanical end position shown in the opposite direction.

In the area of the stroke movement of the control pistons (4, 5), a circumferential annular groove (12, 13) is contained in the guide bore of the valve housing (1), the line (P) and (4) coming from the pressure medium source, not shown, being connected to the annular groove (12) the line (T) leading to the tank is connected to the annular groove (13). Between the two ring grooves (12, 13) there is a central ring groove (14) to which a line (B) is connected which leads to the hydraulic cylinder (15), namely to the pressure medium chamber of the same.

A setpoint motor (17), for example an electric stepper motor, is flanged to the side of the valve housing (1). The drive shaft (18) of the setpoint motor (17) is coupled to an eccentric ring (19) which carries a roller bearing, for example a ball bearing with an outer ring (20). The outer ring (20) serves as a mechanical support for the spring-loaded control spool (2, 2a). In order to be able to adjust the axial position of the two control slides (2, 2a) independently of one another, a component (21), for example a screw or a spindle, which is adjustable in its axial length is attached to the free end face of the control piston (4). As long as the auxiliary piston (8), the meaning of which will be discussed below, the component (21) is in pressure contact with the outer ring (20) of the eccentric ring under the action of the force of the compression spring (11).

The setpoint motor (17) can be moved to a middle position. To set this middle position, a switch cam (22) is connected to the drive shaft (18) of the setpoint motor, which actuates a known zero point switch (23) when the middle position is reached.

The eccentric ring (19) is arranged so that, in the aforementioned central position, the components (21 and 21a) lying on the outer ring (20) of the eccentric ring (19) are at the same radial distance from the axis of rotation of the shaft (18). When the setpoint motor (17) rotates, this radial distance increases on one side and decreases to the same extent on the other side and vice versa. In this way, by turning the setpoint motor (17), the two control slides (2, 2a) can be moved from their central position to one or the other end position simultaneously.

As long as the control spools (2, 2a) are in pressure contact with the outer ring (20), the two control valves are "active". With the help of the auxiliary pistons (8 and 8a) already mentioned, the control valves can also be brought into an "inactive" position will. A switching valve (24) known per se is provided for this control, which in the exemplary embodiment consists of a 4/2-way valve with magnetic actuation by a magnet (25). In the illustrated embodiment, it is assumed that the pressure chambers (26 and 26a), which are delimited by the auxiliary pistons (8 and 8a), can be controlled simultaneously by a single switching valve (24).

The connections (P and T) are always connected to the supply line (P) coming from the pressure medium source or the line (T) leading to the tank. This can be done either by direct connecting lines or, as in the exemplary embodiment shown in FIG. 1, via connections within the valve housing (1). The switching valve (24) is shown in the rest position, in which it is held by the compression spring (27) when the actuating magnet (25) is not energized. In this position, the pressure chambers (26, 26a) are acted upon; the control slides (2, 2a) consequently assume the mechanical end position shown in the drawing, i.e. the control valves are in the inactive position. In this inactive position there is no contact between the components (21, 21a) and the outer ring (20) of the eccentric ring (19). The setpoint motor (17) can thus be aligned without the control slides (2, 2a) being moved.

The individual possible switching states are explained below using the circuit diagrams in FIGS. 2 to 5. The directional control valves with the usual hydraulic symbols are in these circuit diagrams shown.

• 1. Steuerventile inaktiv (Fig. 2)
• 2. Steuerventile aktiv, "ausgeregelte Mittellage" (Fig. 3)
• 2.1 Steuerventile in einer ersten Schaltstellung (Fig. 4) und
• 2.2 Steuerventile in der zweiten, entgegengesetzten Schaltstellung (Fig. 5).

The following switching states are possible:

• 1. Control valves inactive (Fig. 2)
• 2. Control valves active, "adjusted middle position" (Fig. 3)
• 2.1 control valves in a first switching position (Fig. 4) and
• 2.2 control valves in the second, opposite switching position (Fig. 5).

To 1.

The switching valve (24) is in the rest position. The control slide (2, 2a) assume the end position according to FIG. 1. Mechanical contact with the outer ring (20) is eliminated. The hydraulic symbol shown in FIG. 2 is set on the control valves. The position of the setpoint motor (17) has no influence on this symbol. The pressure oil supply (P) is blocked, the hydraulic cylinder (15) is relieved to the tank (T) in both pressure chambers (16, 16a). In this operating state, the setpoint motor can, if necessary, be aligned without the control valves being actuated.

To 2.

The switching valve (24) is in the working position as a result of the excitation of the magnet (25). The pressure chambers (26, 26a) are relieved to the tank. The springs (11, 11a) press the control spool (2, 2a) against the outer ring (20). Due to the symmetrical arrangement of the control spools (2, 2a), the contact forces cancel each other out, so that no additional torque occurs for the setpoint motor (17).

If the setpoint motor (17) is in the middle position, the hydraulic symbol shown in FIG. 2 is set on the control valves. The control valves are in the active position. The hydraulic cylinder is hydraulically clamped via the connections (A and B).

To 2.1

If the setpoint motor (17) is rotated in one direction in accordance with the setpoint specification, the control slides (2, 2a) move in the same direction to the right as shown in FIG. 4 by the eccentric cam ring (19). The hydraulic symbol shown in FIG. 4 is set on the control valves. This means that the pressure chamber (16a) is applied to the hydraulic cylinder (15) and the pressure chamber (16) is relieved.

To 2.2

The setpoint motor (17) has been rotated from the central position in the opposite direction. The control spools (2, 2a) move in the same direction from the central position to the left as a result of the action of the eccentric cam ring (19) as shown in FIG. 5. With the control valves, this is shown in FIG. 5 Hydraulic symbol on. This means that the pressure chamber (16) is now acted upon and the pressure chamber (16a) of the hydraulic cylinder (15) is relieved towards the tank.

In the two switching states of FIGS. 4 and 5, the flow rate of the pressure medium to the pressure medium spaces (16 and 16a) and vice versa depends on the angle of rotation of the setpoint motor (17), so that a control circuit can be set up in connection with a suitable control. The maximum flow rate is achieved in each case when the eccentric cam ring (19) is rotated from its central position in one direction or the other by 90 °.

The separate actuation of the switching valve (24) has the great advantage in the described electrohydraulic control that the "emergency stop function" can be activated at any time, regardless of which control state is present. The "emergency stop function" can be reached directly without going through another "hydraulic symbol".

Claims (6)

1.Electro-hydraulic control for controlling a hydraulic drive, such as a hydraulic cylinder in which a double-acting working piston delimits a pressure chamber on each of its opposite sides, containing at least one control valve with a spring-loaded control slide, which can be deflected from its rest position against the spring force, and one Servo motor for controlling the control slide, characterized in that in a one-piece or multi-piece valve housing (1) there is at least one control valve associated with each pressure chamber (16, 16a) of the hydraulic cylinder (15), the control slide (2, 2a) of which is coaxial and mirror image are mutually spaced from each other that between the inner ends of the spool (2, 2a) there is a common control element (19) of a servo motor (17), by means of which the spool (2, 2a) spring-loaded at its outer ends in the same direction mech Anical pressure contact are movable, that each control slide (2, 2a) in each pressure chamber (26, 26a) contains an auxiliary piston (8, 8a) and that the pressure chambers (26, 26a) via at least one switching valve (24) with pressure medium in Actuable in the direction of a movement counter to the spring force, and thereby the control slides (2, 2a) can be moved into an inactive position, removed from the action of the control element (19) of the servo motor (17), in which both pressure chambers (16, 16a) of the hydraulic cylinder (15) are connected to the line leading to the tank (T), while the line (P) coming from the pressure oil supply is blocked by the control spool (2, 2a). 2. Control according to claim 1, characterized in that the control element of the servo motor (17) is designed as an eccentric cam ring (19, 20), the outer lateral surface serves as an attachment for an inner end of the control slides (2, 2a) located on diametrically opposite sides. 3. Control according to claim 1 or 2, characterized in that at the inner end of each control slide (2, 2a) an axially adjustable component (21, 21a), such as a screw or spindle is arranged. 4. Control according to one of claims 1 to 3, characterized in that with the rotatable cam ring (19, 20) a switching cam (22) for actuating an electrical O-point switch (23) is connected. 5. Control according to one of claims 1 to 4, characterized in that each control valve is designed as a 3/3-way valve. 6. Control according to one of claims 1 to 5, characterized in that each control slide (2, 2a) abuts a mechanical stop in the inactive position.

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