EP0918678B1 - Electrohydraulic control device - Google Patents

Description

State of the art

The invention is based on an electro-hydraulic Control device according to the preamble of claim 1 specified genus. It is already one electro-hydraulic control device from US 3,667,722 known with a sensitive proportional Volume flow control is possible. The hydraulic one Actuator with its load-securing check valve is here designed as a pilot operated seat valve, so that the leakage is as low as possible. This control device is as Lowering brake valve can be used, in which the operating forces are as small as possible and therefore the proportional magnet is small can build. The disadvantage of this control device is that only a 2/2 valve function can be represented with it, with the lower part made in poppet valve technology no additional valve functions can be carried out. Around Here Keeping the actuation forces low is between Proportional magnet and actual seat valve one-armed lever switched with which a power transmission is made. The force to operate the check valve is transmitted by an unlocking element that is pin-shaped and is designed with a small diameter so that it cannot take on any additional functions. The one at Lowering a load occurring volume flow is here only from a valve cone on a poppet valve body controlled so that especially at high loads occurring flow forces the proportional mode of operation of the shut-off valve can be sensitive. The one in here hydraulically controlled seat valve body therefore tends slightly to vibrations, especially when pulling loads or changing load directions occur. Also as Pilot valve working ball in the seat valve body has no pressure equalization. In addition, the control device builds relatively complex, especially the translation lever and contribute the valve sleeve for the check valve.

Furthermore, in an older patent application DE-A-19522746 (publication date: 02.01.97) already an electro-hydraulic control device proposed that works with 4/2 valve modules. Here are two such 4/2 valve modules with additional ones Check valves arranged in a circuit that a control valve for a double-acting actuator surrender. In each 4/2 valve module there is a seat valve part and a slide part combined so that they a have common, one-piece control member. At this not previously published control device performs this one-piece construction of the control element in the 4/2 valve module a relatively complex design; in addition arise at the Coordinating the control edges with each other in this 4/2 valve module Difficulties due to narrow longitudinal tolerances. Especially with relatively long slides are shape and Game tolerances difficult to control. Also require Step shifter in step holes with small clearance high Requirements for radial run-out; also can Do not grind the step shifter without a center ..

Advantages of the invention

The electrohydraulic control device according to the invention with the characterizing features of the main claim on the other hand the advantage that they have a simpler structure represents a 4/2 valve function, one in Seat valve technology designed sink part the leakage keeps as low as possible. The control device is with her 4/2 function versatile and also builds inexpensive and compact. The control device is as Lowering brake valve can be used, with which a sensitive, proportional volume flow control is possible. In the two-piece design can be a control edge adjustment simply by adjusting the length of the shoulder will be realized.

By the measures listed in the subclaims advantageous developments and improvements in Main claim specified electro-hydraulic Control device possible. So according to claim 2 achieve a particularly cheap, compact design that with their four working chambers to save space. Formations according to claims 3 are also advantageous and 4 by going through hydraulic unlocking low actuation forces and therefore small building proportional magnets can be used. Is cheap further an education according to claim 5, if the Seat valve body in the lower part and the control spool in Lifting part like a common, one-piece control element work together, the spool the Mechanically entrains the seat valve body, as is the case with a usual control unit is the case. Here are particular pulling loads more manageable. It is also useful an education according to claim 6, which is a particularly simple and inexpensive construction results, which are especially for small control valves with relatively low switching capacity is suitable. The training according to claim 8 increases versatile application in circuits. Particularly advantageous it is when the control device according to claim 9 with a flow force reduction is carried out, whereby still good at higher load pressures Control properties can be achieved if a direct Actuation by the proportional magnet is provided. It is also expedient to design the control device according to claim 10, whereby they are for control valves for higher switching capacities suitable for operating the Control spool provided hydraulic amplification becomes. According to claims 11 to 14, this can hydraulic amplification in a particularly simple, achieve cost-effective and compact design. Further is it is favorable if a in an embodiment according to claim 15 Valve characteristic is adjustable. More beneficial Refinements result from the remaining claims, the Description as well as the drawing.

drawing

Two embodiments of the invention are in the Drawing shown and in the description below explained in more detail. 1 shows a longitudinal section through a first control device in a simplified representation, Figure 2 shows a longitudinal section through a second Control device in a simplified representation, Figure 3 a Top view of part of the second control device according to Figure 2 and Figure 4 shows a circuit with the first or 2 control device according to FIG. 1 and 2.

Description of the embodiments

Figure 1 shows a longitudinal section through a first electro-hydraulic control device 10 in simplified Representation as used for a hydraulic servomotor Control of the volume flows can be used. The Control device 10 is designed as a 4/2 valve module, at a lower part 11 in seat valve technology and a lifting part 12 are combined with one another in slide technology.

The control device 10 has a in a housing 13 through slide bore 14 on their End faces through a lid 15 and through a Proportional magnet 16 is closed. In the Slider bore 14 are through annular extensions Chambers formed, which are next to each other and which in Direction from the cover 15 in the direction of the proportional magnet 16 seen as a first motor chamber 17, a return chamber 18, a second motor chamber 19, and an inlet chamber 21 are executed. These chambers 17 to 21 are in correspondingly, a first motor connection B, a Return connection R, a second motor connection A and a Inlet port P assigned. In the slide bore 14 is in the area between the first motor chamber 17 and the return chamber 18 close to the latter, a valve seat 22 is formed, whose effective diameter is made smaller than that Diameter of the slide bore 14 and which valve seat 22 part of the sink part 11.

In the sink part 11 is a pilot operated as a check valve Seat valve arranged, the seat valve body 23 in the Slider bore 14 is slidably guided and in its interior receives a pilot cone 24. The seat valve body 23 limited with its end face loaded by a spring 25 26 a pressure chamber 27, the pressure of which together with the force the spring 25 the seat valve body 23 against the valve seat 22 presses. The seat valve body 23 is in the blocking position a seat edge 28 on the valve seat 22, the Diameter of the seat edge 28 is smaller than the diameter the slide bore 14. The seat valve body 23 is with a shaft 29 in the slide bore 14 and has on this shaft 29 a first control edge 31 to which 29 fine control recesses on the outer circumference of the shaft 32 connect. By grading the seat valve body 23 between the notch-like fine control recesses 32 and the Seat edge 28 with a reduced diameter is in the Slider bore 14 adjacent to the valve seat 22 Annular space 33 included, which an annular surface 34 on Seat valve body 23 is assigned. The cross section of the Slider bore 14 reduced by this annular surface 34 results a pressure surface 35, the size of which is from the effective seat edge 28 is determined. The shaft 29 is in with sufficient play the slide bore 14 is mounted, so that in the first Motor chamber 17 prevailing load pressure on the as Throttling points acting column also in the pressure chamber 27 and Annulus 33 can build.

The pilot control cone 24 arranged in the seat valve body 23 is pressure balanced, why the diameter of its Cone edge 36 and its shaft part 37 of the same size are trained. With its cone edge 36 controls Pilot cone 24 the connection from an annular space 38 to Return chamber 18, the annular space 38 via a bore 39 with the pressure chamber 27 has connection. Through that long building shaft part 37, which has only a small play, the pilot cone 24 seals the annular space 38 very well from a spring chamber 41, in which one the pilot cone 24 its pilot spring 42 is arranged. The Spring chamber 41 is located above the control cone 24 Channels 43 with the return chamber 18 in communication so that the pilot cone 24 is relieved of pressure on all sides.

Between the pilot operated check valve in the lower part 11 and the proportional magnet 16 is an unlocking member 44 switched, which here as a in the slide bore 14th slidably arranged longitudinal slide 45 is formed. The Longitudinal slide 45 controls with a second control edge 46 the connection between the inlet chamber 21 and the second Motor chamber 19, 46 on the second control edge notch-like fine control recesses 47 are also arranged are. The piston section carrying the second control edge 46 48 points to the fine control recesses 47 an auxiliary control edge 49 on the opposite end, which the connection from the second motor chamber 19 to Return chamber 18 controls. In the drawn The starting position of the longitudinal slide 45 is the inlet chamber 21 due to the positive overlap of the second control edge 46 shut off while the auxiliary control edge 49 the second Motor chamber 19 to the return chamber 18 is relieved. Further is the longitudinal slide 45 against the pressure in the inlet chamber 21 pressure balanced by its annular groove 51. The two End faces of the longitudinal slide 45 protrude Compensating holes 52 in connection. On his the end face facing the proportional magnet 16 is located Longitudinal slide 45 directly on an actuated by the anchor Ram 53 of the magnet 16. On the opposite lying end of the longitudinal slide 45 is an extension 54 formed, which projects into the return chamber 18 and with its outlet end forms an impact bolt 55 which is applied to the pilot cone 24. The extension 55 also forms additionally an abutment shoulder 56 that fits the poppet valve body 23 is assigned and the stop surface at a distance of the end face of the striker 55.

The mode of operation of the first control device 10 is explained as follows:
When the proportional magnet 16 is not energized, the lower part 11 and the lifting part 12 assume the initial position shown, as this corresponds to a neutral position. The inlet connection P is hydraulically blocked by the longitudinal slide 45, since the second control edge 46 shuts off the connection to the motor connection A. On the other hand, the motor connection A is relieved via the auxiliary control edge 49 to the return chamber 18, so that no pressure can develop in it even if a leakage current occurs. The servomotor is generally connected to the motor connection B with its load side, the pressure in the first motor chamber 17 being able to build up in the pressure chamber 27 and the annular chamber 33 via the gaps formed by the shaft 29. On a remaining differential surface, which corresponds to the pressure surface 35, the seat valve body 23 is pressed onto the valve seat 22 by the pressure in the pressure chamber 27 and by the force of the spring 25 and thereby ensures a low-leak sealing of the motor connection B. The load pressure in the motor connection B can change build up from the pressure chamber 27 via the bore 39 also in the annular space 38, where it is, however, securely sealed off from the return chamber 18 by the cone edge 36 and the long shaft of the pilot cone 24. In the initial position shown, the pilot spring 42 holds the pilot cone 24 in its seat and, via the push-on bolt 55, the longitudinal slide 45 in the position shown, wherein it rests on the tappet 53 of the proportional magnet 16.

Now the proportional magnet 16 is excited and the Longitudinal slide 45 deflected to the left in the working position, so he first opens the push pin 55 to Pilot cone 24, whereby the pressure chamber 27 for Return chamber 18 is relieved. About the as a throttle acting gap of the shaft 29 can less pressure medium in flow through the pressure chamber 27 than via the pilot cone 24 flows out, so that the pressure in the pressure chamber 27 is reduced. Any pressure remaining in the annular space 33 acts onto the annular surface 34 and pushes the seat valve body 23 against the force of the spring 25 to the left, so that this Annulus 33 via the seat edge 28 to the return chamber 18 relieved. The seat valve body 23 is made in this way hydraulically unlocked and is when the left movement of the Longitudinal slide 45 now through the push shoulder 56 taken, which is on the front of the Seat valve body 23 has created. Now open the first Fine control recesses 32 on the seat valve body 23 and connect the motor connection B to the return chamber 18, and then - if there is a negative overlap - open the Fine control recesses 47 on the longitudinal slide 45 the connection from the motor connection A to the inlet chamber 21. With these Fine control recesses thus become the volume flows of B proportional to R on the one hand and on the other hand from P to A controlled. The switching capacity of the control device 10 is essentially dependent on those pressure drops, which are effective on the control edges 31 and 46, respectively. For the Lifting part 12, it is relatively easy to over the pressure drop the second control edge 46 is relatively small and constant hold. This can e.g. with a pressure compensator, with which a load pressure compensated volume flow can be controlled leaves.

In the case of the lower part 11, the switching power is then relative low if the load pressure is present at motor connection B. The tried volume flow flowing through the sink part 11 the seat valve body 23 as a result of flow forces occurring to move to the right, i.e. to move. This closing The greater the volume flow and that, the greater the force Are pressure drops. By appropriate interpretation of the Seat angle 58 on the valve seat 22 and the effective Seat diameter can now be achieved that the pressure in the Annulus 33 is pent up. This pent-up pressure acts in the Annulus 33 on an annular surface 34 of the seat valve body 23 and thus against the flow force. So that one achieve significant fluid power reduction that too a significant increase in switching power also high load pressures. With the present control device 10 is the after unlocking the check valve Seat valve body 23 mechanically from the longitudinal slide 45 taken away, as is the case with a slide device Case is, so that a stable operation can be achieved. In particular, in contrast to hydraulic controlled locking blocks, where with a pulling load Instabilities occur due to mechanical coupling of seat valve body 23 and longitudinal slide 45 also at unfavorable operating conditions stable employment relationships to reach. Through the direct, direct actuation of the Longitudinal slide 45 results from the proportional magnet 16 an extremely simple, inexpensive and compact Construction, which is especially with smaller switching capacities can be used advantageously. Due to the Fluid power reduction can be done in spite of direct actuation still with relatively small proportional magnets relatively high switching capacity can be achieved. In The proportional magnet 16 pushes the working positions Longitudinal slide 45 against seat valve body 23 against the force of the spring 25 to the left, the size of the stroke is proportional to the magnitude of the magnetic force. According to the The fine control recesses 32 become the size of the deflection and 47 turned on, so that the two volume flows of B according to R or P according to A proportional to the size of the electrical Input signal on the proportional magnet 16 can be controlled.

Figure 2 shows a longitudinal section through a second Control device 60, which differs from that of Figure 1 differs as follows, being for the same components same reference numerals are used.

In the second control device 60, the sink part 11, the proportional magnet 16 and the slide bore 14 with their chambers unchanged, but the lifting part 12 another longitudinal slide 61, which from Proportional magnets 16 via a hydraulic Sequence control 62 can be actuated. In this way, the second control device 60 compared to the first Control device 10 achieve higher switching powers. The Longitudinal slide 61 is hollow here and takes in a blind hole-like, centrally arranged, and for Proportional magnet 16 open longitudinal bore 63 a Pilot spool 64 on. The pilot spool 64 is with a piston section 65 in the longitudinal bore 63 tight and slidably guided and forms together with radial bore 66 in Longitudinal slide 61 an adjustable throttle point 67, which switched into a control line 68 of the sequence control 62 is. This control line 68 leads from the inlet chamber 21 via the radial bores 66, the adjustable throttle point 67, the hollow pilot valve 64, a part the longitudinal bore 63, a throttle 69 in an unlocking piston 71 and via oblique bores 72 in the longitudinal slide 61 for Return chamber 18. The pilot spool 64 projects with a cylindrical section 73 in a between the longitudinal slide 61 and proportional magnet 16 in the slide bore 14 trained control room 74 into it. In this control room 74 is an axial by an unspecified screw adjustable adjusting screw 75 arranged on the one Rule spring 76 is fixed to the housing with its other End is supported on the cylindrical portion 73 and the Pilot spool 64 abutting the plunger 53 of the Proportional magnet 16 holds.

In the longitudinal bore 63 of the pilot spool 64 is on the inner end of the unlocking piston 71 slidingly guided, which is operatively connected to a push pin 77. This push pin 77 is sliding in the extension 54 stored and is in the starting position of the control device 60 on the pilot control cone 24 of the check valve. Especially It is useful here that the spool 64 with his Piston section 65 and the unlocking piston 71 the same Have outer diameter so that they together in one single longitudinal bore 63 can be arranged sliding. In this way, the longitudinal slide 61 through the blind hole-shaped longitudinal bore 63 is a one-piece Construction, the manufacturing technology particularly cheap can be produced.

Figure 3 shows a partial longitudinal section according to III-III in Figure 2, the seat valve body 23, the longitudinal slide 61 and the set screw 75 shown in plan view are.

The operation of the second control device 60 corresponds in principle to that of the first Control device 10 of Figure 1, but by the hydraulic sequence control 62 higher switching capacities are achievable.

In the drawn starting position the second Control device 60, which corresponds to a neutral position, are the first motor chamber 17 and the inlet chamber 21 hydraulically blocked. In the starting position the Pilot valve 64 by the control spring 76 adjacent to Tappet 53 and thus held in a position fixed to the housing.

This also means the axial position of the longitudinal slide 61 fixed, the adjustable throttle point 67 straight controls.

When operating the second control device 60, the Proportional magnet 16 only against the force of The control spring 76 works because the pilot spool 64 is balanced on all sides. If the spool 64 controls the adjustable throttle point 67, forms a control oil flow via the control line 68, the pressure pent up at throttle 69 unlocking piston 71 actuated and thus opens the pilot cone 24, so that Lock valve in the lower part 11 is unlocked. Furthermore the longitudinal slide 61 follows the stroke of the pilot slide 64, with an intermediate pressure in the control chamber 74 Operating the longitudinal slide 61 builds up and the magnetic force reinforced. Longitudinal spool 61 and pilot spool 64 work in a manner known per se hydraulic sequence control together. With the help of Adjusting screw 75 can be the bias of the control spring 76th change and thus adjust the position of the valve characteristic.

Figure 4 shows a simplified representation Circuit in which two first control devices 10 after Figure 1 to a control valve 80 for a double-acting actuator are arranged. Here are the two P-connections of both control devices 10 in parallel connected to a control pump 82, both of which Connections R to a tank 83 are relieved. Of each Port A of each control device 10 carries one Inlet line 84 or 85 to one of the consumer connections 86 or 87 on the servomotor 81. Each feed line is there 84, 85 via a check valve 88 securing the load or 89 led. The two connectors B on each Control devices 10 are each via a drain line 91 or 92 with the respective other consumer connection 87 or 86 connected. A load pressure signal is generated by the Inlet lines 84, 85 tapped and the control pump 82nd reported. With the control valve 80 is a 3-position valve realized that with non-actuated control devices 10th the actuator 81 seals securely. To keep the leakage low hold, the consumer connection 86 is on the one hand by the Check valve 88 and on the other hand by the check valve in the lower part 11 of the right control device 10 safely cordoned off. The same applies to the other Consumer connection 87. By pressing the left Control device 10, the servomotor 81 in one Actuate the direction with the piston rod extending while by actuating the right control device the servomotor Steer 81 in the opposite direction with a moving piston rod leaves, whereby a proportional mode of operation is achieved. By processing the load pressure signal in the Control pump 82 can the pressure drop across the second Control edge 46 in the lifting part 12 are kept constant, so that load-compensated volume flow control is possible.

Of course, are shown on the Embodiments changes possible without thinking to deviate from the invention. Although the piloted Check valve in the control device is particularly advantageous a directly controlled shut-off valve can also be used be a largely pressure relieved Has check valve body. The continuous can also Run the slide hole so that it is in the area of Sink part has a slightly larger diameter than in Lifting part so that the inside diameter of the valve seat 22nd corresponds approximately to the diameter of the slide bore. Also can be in the circuit of Figure 4 instead of first control devices 10 the second Use control devices 60. The control valve 80 can also be designed so that there are four working positions having. Instead of the control pump 82 there is also one Constant pump with pressure compensator conceivable.

Claims (17)

1. Electrohydraulic control device for a hydraulic actuator motor for controlling a volume flow, having a shut-off valve which is arranged in a housing and whose movable seat valve element is switched into a connection between a motor chamber and a return flow chamber and in this arrangement protects the motor chamber, and having a proportional magnet with armature-activated tappet for activating the shut-off valve and with a longitudinally movable release element which is separated from the shut-off valve, is guided in a sliding fashion in the housing and is connected into the operative connection between the tappet of the proportional magnet and the shut-off valve, characterized in that the seat valve element (23), the release element (44) and the tappet (53) of the proportional magnet (16) are arranged on the same axis as one another, and in that the release component is embodied as a longitudinal slide (45, 61) which controls the connection between an inflow chamber (21) and a second motor chamber (19) using a control edge (46), said motor chamber (19) being arranged in the slide hole (14), which receives the longitudinal slide (45, 61) and is next to the return flow chamber (18), and in that the longitudinal slide (45, 61) has essentially the same external diameter as the seat valve element (23), and in that, in the case of activation by the proportional magnets (16), both connections are opened or closed in the same direction.
2. Electrohydraulic control device according to Claim 1, characterized in that the seat valve element (23) and the longitudinal slide (45, 61) are guided in a continuous slide hole (14), in particular with a diameter of the same size, in which hole (14) four chambers (17, 18, 19, 21) for the first motor port (B), the return flow port (R), the second motor port (A) and the inflow port (P) are provided lying one next to the other and veered in the direction of the proportional magnet (16), and in that formed in this slide hole (14), between the first motor chamber (17) and the return flow chamber (18), is a valve seat (22) which is assigned to the seat valve element (23) and has, in particular, a smaller diameter than the slide hole (14).
3. Electrohydraulic control device according to Claim 1 or 2, characterized in that the shut-off valve in the sink component (11) is a pilot-controlled valve whose seat valve element (23) receives a pilot-control element (24) which can be released by the longitudinal slide (45, 61) by means of a push-up bolt (55, 77).
4. Electrohydraulic control device according to Claim 3, characterized in that the pilot-controlled element is a pressure-compensated pilot control cone (24).
5. Electrohydraulic control device according to one of Claims 1 to 4, characterized in that between the longitudinal slide (45,61) and the seat valve element (23) on one of the two construction elements, in particular on the longitudinal slide at its end face turned away from the proportional magnet (16) there is arranged an axially extending projection (54), which projects into the return flow chamber (18) , has the push-up bolt (55, 77) at its end and is arranged on the push-up shoulder (56) which is assigned to the seat valve element (23).
6. Electrohydraulic control device according to one or more of Claims 1 to 5, characterized in that the longitudinal slide (45) can be actuated directly by the armature tappet (53), and in that it is designed with pressure-equalization in relation to the pressures in the inflow chamber (21), the second motor chamber (19) and the return flow chamber (18).
7. Electrohydraulic control device according to one of Claims 1 to 6, characterized in that the longitudinal slide (45) has notch-like fine-control cut-outs (47) on its control edge (46).
8. Electrohydraulic control device according to one of Claims 1 to 7, characterized in that the piston section (48) which has the control edge (46), on the longitudinal slide (45, 61) has an auxiliary control edge (49) which, in the home position, relieves the second motor chamber (19) to the return flow chamber (18) and shuts off this connection in the working position.
9. Electrohydraulic control device according to one or more of Claims 1 to 8, characterized in that the seat valve element (23) in the slide hole (14) bounds a pressure space (27) in which there is arranged a spring (25) which loads the seat valve element (23), together with the pressure acting on the end side of said pressure space (27), in the direction of the shut-off position in which it bears, with its seat edge (28), with a diameter which is smaller than the diameter of the slide hole (14), on the valve seat (22) which is fixed to the housing, and includes in the process an annular space (33) which lies upstream of the valve seat (22) and is bounded by the seat valve element (23) and whose pressure loads the seat valve element (23) in the opening direction by means of an associated annular face (33) and which annular space (33) is separated from the first motor chamber (17) by means of a control edge (31), fine-control cut-outs (32) being arranged, lying in particular on the circumference of the seat valve element.
10. Electrohydraulic control device according to one or more of Claims 1 to 5, 7 to 9, characterized in that the longitudinal slide (61) can be activated by the proportional magnet (16) by means of a hydraulic follower controller (62) (Fig. 2).
11. Electrohydraulic control device according to Claim 10, characterized in that the follower controller (62) has a pilot-control slide (64) which can be activated by the proportional magnet (16) counter to a control spring (76), which is arranged centrally in the longitudinal slide (61) and is guided in a sliding fashion.
12. Electrohydraulic control device according to Claim 10 or 11, characterized in that a release piston (71), which is used to release the shut-off valve in the sink component (11) by means of a push-up bolt (77) which is guided in the longitudinal slide in a sliding fashion, is arranged in the longitudinal slide (61).
13. Electrohydraulic control device according to one of Claims 10 to 12, characterized in that the pilot-control slide (64) and the release piston (71) have the same external diameter and are guided in a sliding fashion in the same longitudinal hole (63) in the longitudinal slide (61).
14. Electrohydraulic control device according to Claim 12 or 13, characterized in that the control oil flow which is used for the hydraulic follower controller (62) and is conducted from the inflow chamber (21) to the return flow chamber (18) is conducted by means of a throttle (69) which is arranged in the release piston (71).
15. Electrohydraulic control device according to one of Claims 10 to 14, characterized in that the longitudinal slide (61) bounds, with its end side facing the proportional magnet (16) in the slide hole (14), a control space (74) which receives an adjustment screw (75) on which the control spring (76) which loads the pilot-control slide (64) counter to the magnetic force is supported fixed to the housing.
16. Electrohydraulic control device according to one of Claims 11 to 15, characterized in that the pilot-control slide (64) is of pressure-compensated design.
17. Electrohydraulic control device according to one of Claims 10 to 16, characterized in that the control line (68) which is assigned to the hydraulic follower controller (62) is guided through the hollow pilot-control slide (64), the longitudinal hole (63) and the release piston (71), the pressure upstream of the throttle (69) and downstream of an adjustable throttle point (67) being fed to the control space (74) and driving the longitudinal slide (61).

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