EP0828945B1 - Pilot controlled servo-valve - Google Patents

Abstract

PCT No. PCT/EP95/04454 Sec. 371 Date Sep. 16, 1997 Sec. 102(e) Date Sep. 16, 1997 PCT Filed Nov. 13, 1995 PCT Pub. No. WO96/15373 PCT Pub. Date May 23, 1996A pilot controlled servo-valve has four main flow connections, an axially sliding main control piston with four control edges and a front restoring spring that defines a spring-centered middle position of the main control piston. A control sleeve has ring shaped openings for the first, second and third main flow connections and a front opening for the fourth main flow connection. A first front face of the main control piston is axially opposed to the front opening. A pressure compensation surface is formed by the second front face of the main control piston in a spring chamber. The main control piston applies the pressure in the fourth main flow connection on said pressure compensating surface through a pressure relief channel. A traverse bore connects said pressure relief channel to an auxiliary connection chamber connected to the third main flow connection by the forth control edge. This valve may be space-savingly integrated in a hydraulic block and has a clearly defined middle position, as well as a remarkable dynamic performance.

Description

The invention relates to a pilot operated servo valve with four Power terminals.

Pilot operated electrohydraulic servo valves in two or more stages Version with four main power connections are used as 4-way valves Control of position, speed and force in cylinders for Linear movements, respectively position, speed and torque at Hydraulic motors for rotary movements. They are known in the Design as a panel-mounted valve, which means that they have one prismatic valve housing for mounting on a connection surface of a Hydraulic blocks on. The four main power connections of the valve are in one planar connection surface of the valve housing and its openings in the The guide bore of a main control piston is symmetrical. Control chambers are arranged in end caps on both sides of the Valve housing are flanged. These tax chambers are over Control holes connected to a pilot servo valve. The hydraulic The symmetrical main spool is actuated by Pressurization of its two end faces in the front Control chambers.

The well-known pilot operated 4-way servo valves all have one spring-centered rest position. In most cases this is done Centering of the main spool over two opposite Return springs which are arranged in the front control chambers and work against each other. However, centering is also known to accomplish by a single spring. This single spring is then in a spring chamber on the front clamped between two spring plates.

A pilot operated 4-way proportional valve with one one-sided spring centering is described in the book "Der Hydraulik Trainer Band 2", Publisher and publisher: Mannesmann Rexroth GmbH, DE-8770 Lohr am Main, 3rd edition 1989, page 31, picture 33 shown. The tax chambers of this Valves are arranged in end caps on both sides of the valve housing are flanged. DE-A-4011908 describes a multi-way valve (five ways) known with one-sided spring centering and opposite actuating piston. Both valves have a valve housing for mounting on a connection surface of a hydraulic block.

Pilot operated 4-way servo valves with valve body for mounting on a pad of a hydraulic block are very space consuming and require complicated drilling in the hydraulic block for the four Main power connections.

The invention is therefore based on the object of a piloted To create servo valve, which saves space in a hydraulic block can be integrated and has a clearly defined center position, without sacrificing good dynamic behavior of the servo valve to have to. According to the invention, this object is achieved by pilot control Servo valve according to claim 1 solved.

The pilot operated 4-way servo valve according to the invention has one Control sleeve on the directly in a stepped bore of a hydraulic block is mountable. This control sleeve includes openings for a first, second and third side working connection in the hydraulic block. The It opens into the control sleeve for the fourth main power connection on the other hand, arranged at the front end of the control sleeve that this fourth Main power connector opens axially into the control sleeve. The hydraulic block, in which the control sleeve is used, then has three lateral block holes for the first, second and third main power connection. Regarding the Arrangement of the block hole for the fourth main power connection exists however maximum freedom. This block hole for the fourth Main power connection can, for example, directly in the axial extension of the Stepped bore for the control sleeve to be carried out, which is conventional pilot operated servo valves with more than two main ports so far not possible. Bridge formation in the hydraulic block between individual Main power connections are also no longer required. With the servo valve according to the invention thus becomes a much more compact design of the control blocks than is the case with conventional servo valves is. This can also be done in more complex hydraulic controls servo valve according to the invention together with various additional valves, for example 2-way cartridge valves, space-saving in a hydraulic block to get integrated. A direct installation in the cylinder cover of larger ones Cylinders are also possible.

The main control piston of the valve according to the invention is axial slidably arranged in the control sleeve. One of the two Piston face of the main control piston lies the fourth axial Working connection axially opposite. The second piston face of the The main control piston forms in an extension of the spring chamber Control sleeve one, the first piston face hydrostatic counteracting, pressure compensation surface of the piston. The spring chamber is through a pressure relief duct in the main spool with the fourth Main power connection hydraulically connected. This pressure relief channel also connects an auxiliary connection chamber to the fourth Main power supply. A return spring is in the spring chamber clamped and engaged with the main spool via spring plates that them in both stroke directions of the piston of the hydraulic actuating force in the Control chambers opposed a spring force proportional to the piston stroke and one for the main control piston in unpressurized control chambers pressure-centered position defined. A pilot valve with regulator is hydraulically connected to the two control chambers. On Position sensor of the main control piston delivers a feedback signal for the regulator of the pilot valve.

In the valve according to the invention, the asymmetrical hydrostatic Load the main control piston through appropriate dimensioning of the Pressure compensation area of the main control piston compensated. Through this hydrostatic compensation are the required actuation forces for the main control piston is reduced, whereby the actuating surfaces in the Control chambers can be designed smaller. It follows smaller control oil volumes, that is, with the same large pilot valve shorter positioning times can be achieved. This hydrostatic compensation for the Main control piston also enables the easy use of a one - sided return spring for the spring centering of the main control piston in both stroke directions. As a result, with the same signal for each stroke direction ensures an equal deflection. Furthermore, the mechanical Return spring acting directly on the main control piston Center position of the main spool reliably determined.

der erste Hauptstromanschluß wird hydraulisch mit einer ersten Verdrängerkammer eines Verbrauchers verbunden und bildet somit einen ersten Arbeitsanschluß (A),

der zweite Hauptstromanschluß wird hydraulisch mit einem Tank verbunden und bildet somit einen Tankanschluß (T),

der dritte Hauptstromanschluß wird hydraulisch mit einer zweiten Verdrängerkammer eines Verbrauchers verbunden und bildet somit einen zweiten Arbeitsanschluß (B),

der vierte Hauptstromanschluß wird hydraulisch mit einer Pumpe verbunden und bildet somit einen Pumpenanschluß (P).

The connections of the servo valve are preferably assigned as follows:

the first main flow connection is hydraulically connected to a first displacement chamber of a consumer and thus forms a first working connection (A),

the second main flow connection is hydraulically connected to a tank and thus forms a tank connection (T),

the third main flow connection is hydraulically connected to a second displacement chamber of a consumer and thus forms a second work connection (B),

the fourth main flow connection is hydraulically connected to a pump and thus forms a pump connection (P).

In this version, the pump connection (P) can axially into the Control sleeve are introduced; the tank connection (T) is between the first and second work connection. Other assignments of the Main power connections are also possible, however, without the to dispense with the main advantages of the servo valve according to the invention.

It should be noted that hydraulic is generally under pump Pressure source, under the tank a vessel or a line without essential Back pressure and under consumer a hydraulic consumer with two Displacement chambers (for example a rotary or linear drive) is understood.

die erste axiale hydraulische Verbindung ist durch die erste Steuerkante verschlossen,

die zweite axiale hydraulische Verbindung ist freigegeben,

die dritte axiale hydraulische Verbindung ist freigegeben,

die vierte axiale hydraulische Verbindung ist durch die vierte Steuerkante verschlossen.

In a preferred embodiment of the servo valve, with the spring-centered central position of the main control piston, the control edges assume the following position:

the first axial hydraulic connection is closed by the first control edge,

the second axial hydraulic connection is released,

the third axial hydraulic connection is released,

the fourth axial hydraulic connection is closed by the fourth control edge.

The working connections (A) and (B) are thus spring-centered Center position of the main control spool connected to the tank connection (T). in other words, the two displacement chambers of one connected Consumers are in the spring-centered center position of the main control spool both relieved of pressure. In this version, the four control edges of the Main control piston preferably has a zero overlap. This will For example, excellent positioning accuracy when using the Valve in a position control loop of a hydraulic cylinder, and a excellent dynamic behavior when using the valve Pressure control achieved. However, other arrangements of the control edges are also possible. For example, in a spring-centered center position of the main control piston all connections through the control edges to be introverted.

The spring centering is preferably designed as follows. The The main control piston has an axial one in the spring chamber Extension shaft on. A first and a second spring plate are axial slidably guided on this extension shaft. At rest of the The return spring presses the first spring plate against a valve Stop surface on the main control piston and the second spring plate against one Stop surface at the free end of the extension piston. The spring chamber is then dimensioned such that in this rest position both spring plates in the Apply spring chamber axially.

• Figur 1 einen Längsschnitt durch ein erfindungsgemäßes Servoventil;
• Figur 2 einen vergrößerten Ausschnitt der Figur 1.

An embodiment of the invention is illustrated in the accompanying drawings and will be described in more detail below. Show it:

• 1 shows a longitudinal section through an inventive servo valve;
• FIG. 2 shows an enlarged section of FIG. 1.

In Figure 1, the servo valve according to the invention is as such with the Reference number 10 denotes. A control sleeve 12 is in a stepped bore 14 one (only indicated) hydraulic block 16 used. The control sleeve 12 forms an axial guide bore into which a main control piston 18 axially is slidably fitted.

The servo valve 10 shown in the figures is a 4-way servo valve and has a pump connection (P), a tank connection (T), and a first working connection (A) and a second working connection (B). The Pump connection (P) is hydraulically connected to a pressure line (Not shown). The tank connection (T) is in hydraulic connection with an unpressurized line (not shown). The working connections (A) and (B) are in hydraulic connection with a first or second Displacement chamber of a hydraulic linear or rotary drive (not shown).

Three block bores 22, 20, 24 in the hydraulic block 16 for the Tank connection (T) 22, the first working connection (A) 20 and the second Working connection (B) 24, are arranged transversely to the stepped bore 14 and open laterally into the stepped bore 14. In the stepped bore 14 forms the Control sleeve 12 each have an annular junction 22 ', 20', 24 'in the area the corresponding block bores 22, 20, 24. Any of these Mouths 22 ', 20', 24 'has several transverse bores 25 through the wall the control sleeve 12, which each have a hydraulic connection with the Make the guide bore of the main control piston 18. A fourth Block bore 26 for the pump connection (P) is in a coaxial extension the stepped bore 14 arranged. The control sleeve 12 has this fourth Block bore 26 an end opening 26 '.

Within the control sleeve 12 connects a first axial hydraulic Connection 28 the end opening 26 'for the pump connection (P) with the lateral mouth 20 'for the work connection (A); a second axial hydraulic connection 30 the mouth 22 'for the tank connection (T) with the mouth 20 'for the working connection (A); a third axial hydraulic connection 32 with the mouth 22 'for the tank connection (T) the mouth 24 'for the work connection (B); and a fourth axial hydraulic connection 34 the mouth 24 'for the working connection (B) with one inside the control sleeve 12 by the main control piston 18th delimited auxiliary connection chamber 36. Due to the arrangement of the annular outlets 22 ', 20', 24 'is the axial distance between the second and third (30 and 32) axial hydraulic connection by far larger than the axial distance between the first and second (28 and 30), respectively the third and fourth 32 and 34) axial hydraulic connection.

The main control piston 18 has a first coaxial piston collar 38 on which is assigned to the working connection (A) and axially in the first and second axial hydraulic connection 28 and 30 is slidable. He also has a second coaxial piston collar 40, which the Working connection (B) is assigned and axially in the third and fourth axial hydraulic connection 32 and 34 is displaceable. The first piston collar 38 forms a first, assigned to the first hydraulic connection 28 Control edge 28 'and one of the second hydraulic connection 30 assigned second control edge 30 '. Both control edges 28 ', 30' point a zero coverage. The second piston collar 40 forms one, the third hydraulic connection 32 assigned, third control edge 32 ', and a fourth control edge assigned to the fourth hydraulic connection 34 34 '. Both control edges 32 ', 34' also have a zero overlap on. The auxiliary connection chamber 36 is annular in the control sleeve around the Main control piston 18 is formed. It is on one side through the Piston collar 40 and on the other side by a piston collar 42 axially sealed.

Via an axial piston bore 44 and a piston transverse bore 46 through the main control piston 18 is the auxiliary connection chamber 36 with the Pump connection (P) connected. The main spool can therefore over its coaxial piston collar 38 the first working port (A) and over its coaxial piston collar 40 optionally the second working port (B) connect to the pump connection (P) or the tank connection (T), whereby the respective flow of the hydraulic fluid over the four control edges 28 ', 30 ', 32', 34 'is regulated.

About its pressurized piston face 48, the Main control piston 18 loaded hydrostatically asymmetrically. On hydrostatic pressure equalization of the main control piston is carried out by Continuation of the coaxial piston bore 44 to the second end of the Main control piston 18, where it via a piston cross bore 50 in a Pressure compensation or spring chamber 52 opens out. This upper part of the Valve is closer with reference to the enlarged section of Figure 2 described.

The spring chamber 52 is in the axial extension of the control sleeve 12 in a valve cover 54 is arranged. This valve cover 54 is on the Hydraulic block 16 fastens and fixes the control sleeve 12 in the stepped bore 14. The second end of the main spool 18 is axially sealed by a sealing insert 56 is inserted into the spring chamber 52 and forms one therein Pressure equalization approach 58. This points in the pressure compensation chamber 52 one hydrostatically counteracting the first piston face 48 Pressure compensation surface 60. The pressure compensation area 60 is equal to that Piston face 48 so that there is a complete hydrostatic Pressure equalization of the pump pressure results.

The main control piston 18 is actuated via a processed coaxial actuating piston collar 62, by appropriate Pressurizing its ring-shaped first, respectively second Actuating surface 64, 66. Between the piston collar 42 and the Actuating surface 64 becomes a first annular in the control sleeve Control chamber 68 and between sealing insert 56 and the actuating surface 66 a second annular control chamber 68 is formed. The first tax chamber 68 is via a pilot port 72 in the valve cover 54 with the Working port (A ') and the second control chamber 70 is via a pilot port 74 in the valve cover 54 with the working connection (B ') one Flanged 4-way pilot servo valve 76 connected. The Actuating surfaces 64, 66 are designed so large that the Overflow of the control edges 28 ', 32' or 30 ', 34' Flow forces are surely overcome. That’s why Control oil volumes are very small and very short positioning times can be achieved to reach.

In the spring chamber 52 there is a return spring 78 between a first one and second spring plate 80 and 82 axially clamped. An extension shaft 84 is rigidly connected to the second end of the main control piston 18. On the spring plates 80 and 82 are guided axially displaceably in this shaft 84. The Shaft 84 has at its free end an axial stop surface 86 for the second spring plate 82. The second piston end face 60 forms an axial one Stop surface for the first spring plate 80. In Figure 2, the Return spring 78 the first spring plate 80 against the stop surface 60 and the second spring plate 82 against the stop surface 86. In this position is the first spring plate 80 also in the housing stop on Sealing insert 56 and the second spring plate 82 in the housing stop on one axially opposite stop surface 88 of the valve cover 54. Both Spring plates 80 and 82 are therefore in the housing stop, and the Main control piston 18 is over the extension shaft 84 between the two spring plates 80 and 82 clamped by the return spring 78 in opposite directions are spring loaded. In other words, the The main control piston 18 is in a spring-centered rest position is also referred to as the center position.

The main control piston 18 by pressurizing the first Control chamber 68 from its central position in the direction of spring chamber 52 is moved, the return spring 78 by the, on the end face 60 of Main control piston 18 adjacent, first spring plate 80 in the spring chamber 52 compressed. As a result, she exercises one on the main control piston 18 Spring force that opposes this movement and its module is proportional to the stroke of the main control piston 18. Will the Main control piston 18 by pressurizing the second control chamber 70 moves from its central position in the direction of the pump connection 26, exercises the extension shaft 84 on the second spring plate a tensile force, so that the return spring 78 now through the second spring plate 82 in the Spring chamber 52 is compressed. This spring force arises here against the movement of the main control piston 18 and its module proportional to the stroke of the main spool 18. By using a single return spring 78, which acts as a compression spring for both stroke directions works, it is ensured that the main control piston 18 in both directions is subjected to exactly the same restoring force.

From the partial section of Figure 2 it can be seen that the Extension shaft 84 is screwed into the main control piston and through a pin 90 is secured. The axial piston bore 44 is in the Extension shaft 84 continued to the transverse bore 46. Another Cross bore 92 is located directly above the end face 60 of the Main control piston 18. This second transverse bore 92 has one for the purpose To ensure pressure equalization above and below the spring plate 80. In the second spring plate 82, this pressure equalization through holes 94 in Spring plate 82 reached.

As can be seen from Figure 1, the main control piston is over a Position sensor 96 in a closed position control loop involved. A shaft 98 of the position sensor 96 is mechanical connected to the extension shaft 84 of the main control piston. The Output signal of the position sensor 96 (that of the position of the Main control piston 18) is included in a control amplifier 100 compared to a target value (S), and the pilot servo valve 76 is in the Ratio to the determined target / actual value difference. The Pilot control valve 76 then regulates the control oil pressure in the two Control chambers 68 and 70 of the main stage and places, against the action of Return spring 78, the piston stroke firmly, so that a closed, electro-hydraulic Control loop is formed.

• die erste Steuerkante 28' die erste hydraulische Verbindung 28 zwischen Pumpenanschluß (P) und Arbeitsanschluß (A) verschließt;
• die zweite Steuerkante 30' die zweite hydraulische Verbindung 30 zwischen Tankanschluß (T) und Arbeitsanschluß (A) freigibt;
• die dritte Steuerkante 32' die dritte hydraulische Verbindung 30 zwischen Tankanschluß (T) und Arbeitsanschluß (B) freigibt;
• die vierte Steuerkante 34' die vierte hydraulische Verbindung zwischen Arbeitsanschluß (B) und Hilfsanschlußkammer 36 verschließt, und dadurch die hydraulische Verbindung über die axiale Kolbenbohrung 44 zwischen Arbeitsanschluß (B) und Pumpenanschluß (P) unterbindet.

The main control piston 18 is also shown in FIG. 1 in the spring-centered rest or center position. The control edges 28 ', 30', 32 ', 34' are arranged on the main control piston 18 such that in this central position:

• the first control edge 28 'closes the first hydraulic connection 28 between the pump connection (P) and the working connection (A);
• the second control edge 30 'enables the second hydraulic connection 30 between the tank connection (T) and the working connection (A);
• the third control edge 32 'enables the third hydraulic connection 30 between the tank connection (T) and the working connection (B);
• the fourth control edge 34 'closes the fourth hydraulic connection between the working connection (B) and the auxiliary connection chamber 36, and thereby prevents the hydraulic connection via the axial piston bore 44 between the working connection (B) and the pump connection (P).

The work connections are thus in this spring-centered center position (A) and (B) depressurized to the tank. The main spool 18 is off this center position in the direction of the pump connection (P) remains the work connection (A) to the tank is relieved. The work connection (B) will however via the auxiliary connection chamber 36 and the axial piston bore 44 the pump connection (P) hydraulically connected. However, if the Main control piston 18 from this central position in the direction of the spring chamber 52 driven, the work connection (B) to the tank remains unloaded. The However, the working connection (A) becomes the tank through the second control edge 30 ' blocked, and via the first control edge 32 'with the pump connection (P) hydraulically connected. In the event of a control pressure failure, the main spool takes off 18 in its spring-centered center position, in which both working connections (A) and (B) are relieved to the tank as described above.

Claims (7)

1. A pilot-operated servo valve with four main-stream ports comprising:

   a valve housing (12, 54) having:

   a guide bore for a main control piston (18),

   a first hydraulic connection (28) in the guide bore between the fourth and first main-stream ports,

   a second hydraulic connection (30) in the guide bore between the first and second main-stream ports,

   a third hydraulic connection (32) in the guide bore between the second and third main-stream ports,

   a fourth hydraulic connection (34) in the guide bore between the third main-stream port and an auxiliary port chamber;

   a main control piston (18), which is axially displaceable in the guide bore, having:

   a first control edge (28'), which is assigned to the first axial hydraulic connection (28) for control of the throughflow,

   a second control edge (30'), which is assigned to the second axial hydraulic connection (30) for control of the throughflow,

   a third control edge (32'), which is assigned to the third axial hydraulic connection (32) for control of the throughflow,

   a fourth control edge (34'), which is assigned to the fourth axial hydraulic connection (34) for control of the throughflow,

   the main control piston (18) delimiting a first and second control chamber (68, 70) within the valve housing and forming within the first control chamber (68) a first actuating surface (64) and within the second control chamber (70) a second actuating surface (66) axially opposing the first actuating surface (64);

   a return spring (78), which is clamped in an end spring chamber (52) in such a way and engages with the main control piston (18) in such a way that in both lifting directions of the main control piston (18) it opposes the latter with a spring force and thus defines a spring-centered centre position of the main control piston (18);

   a pilot valve (76), which is connected hydraulically to at least one of the two control chambers (68, 70);

   a controller (100) for the pilot valve (76);

   a position transducer (96), which is connected to the main control piston (18) and supplies the position of the main control piston (18) as a feedback signal for the controller (100) of the pilot valve (76);

   characterised in that
   the valve housing comprises a control sleeve (12), which can be inserted axially in a bore (14) of a hydraulic block (16) and is designed in such a way that it delimits annular openings (20', 22', 24') in this bore (14) for the first, second and third main-stream port,
   an opening (26') for the fourth main-stream port is arranged axially at the end of the control sleeve (18), a first piston end surface of the main control piston (18) being positioned axially opposite this opening (26'),
   a pressure-equalising surface (60) is formed by the second piston end surface of the main control piston (18) in the spring chamber (52),
   a pressure-relief duct (44) hydraulically connects the spring chamber (52) to the fourth main-stream port through the main control piston (18), so that the pressure equalising surface (60) is loaded with the pressure in the fourth main-stream port, and
   a cross-bore (46) hydraulically connects this pressure-relief duct to the auxiliary port chamber (36).
2. Valve according to claim 1, characterised in that
   the first main-stream port forms a first working port (A),
   the second main-stream port forms a tank port (T),
   the third main-stream port forms a second working port (B), and
   the fourth main-stream port forms a pump port (P).
3. Valve according to claim 1, characterised in that the control edges are arranged in such a way that they assume the following positions when the main control piston (18) is in the spring-centered centre position:

   the first axial hydraulic connection (28) is closed by the first control edge (28'),

   the second axial hydraulic connection (30) is opened,

   the third axial hydraulic connection (32) is opened, and

   the fourth axial hydraulic connection (34) is closed by the fourth control edge (34').
4. Valve according to one of claims 1 to 3, characterised in that the first and second actuating surfaces (64, 66) are annular surfaces.
5. Valve according to one of claims 1 to 4, characterised by
   an axial extension shaft (84) of the main control piston (18) in the spring chamber (52),
   a first and second spring plate (80, 82), which are axially displaceable on this extension shaft (84),
   an axial stop surface (60) on the main control piston for the first spring plate (80),
   an axial stop surface (86) on the displacement shaft (84) for the second spring plate (82),
   the return spring (78) forcing each of the two spring plates (80, 82) against its stop surface (60, 86) when the valve is in the rest position, and
   the spring chamber (52) being dimensioned in such a way that in this rest position both spring plates (80, 82) abut axially in the spring chamber.
6. Valve according to claim 5, characterised in that the pressure-relief duct (44) is introduced as an axial bore into the extension shaft (84) and there terminates in the spring chamber (52) via a first cross bore (50).
7. Valve according to claim 6, characterised in that the extension shaft (84) has a second cross-bore (92) in the immediate vicinity of the first stop surface (60) for the first spring plate (80).

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