US2238110A - Hydraulic system for machine tools and the like - Google Patents

Description

April 15, 1941. w. J. GUILD 2,238,110

HYDRAULIC SYSTEM FOR MACHINETOOLS AND THE LIKE Filed May 5, 1937 3 Sheets-Sheet 1 w32' Waldo J. @und April 15, 1941. w. J. GUILD HYDRAULIC SYSTEM FOR MACHINE TOOLS AND THE LIKE Filed May 5, 1937 3 Sheets-Sheet 2 i @M a. Mm

Bmw/n April 15, 1941. w J, GUlLD 2,238,110

HYDRAULIC SYSTEM FOR MACHINE TOOLS AND THE LIKE Filed May 5, 1957 3 Sheets-Sheet 5 SMU/IMM Waldo J. Gu ld l @iff/@5% l pr. 15, 1941 OFFICE HYDRAULIC SYSTEM FOR MACHINE TUOTS AND THE LIKE Waldo J. Guild, Worcester, Mass., assignor to The Ileald Machine Company, Worcester, Mass., a corporation of Massachusetts Application May 5, 1937, Serial No. 140,991

(Cl. (t0-52) 4 Claims.

The present invention relates to hydraulic systems for the actuation of various machine parts, and it is particularly applicable to machine tools, for example boring, grinding, planing or milling machines.

In machines of this character a liquid of high viscosity is frequently used for the hydraulic actuation of the machine table-or other partor parts; it is well known that such hydraulically actuated parts, for a given setting of the throttle or other speed control device, will not always move at the same predetermined rate over a period of time, because of changes in the viscosity of the liquid, which may be caused by heating thereof, during prolonged'running of the machine.

Previous attempts Vto compensate for such changes in the viscosity of the actuating fluid have required mo're or less complicated additions to the hydraulic control devices ordinarily ernployed in such machines; see in' this connection the arrangements disclosed by the patent to Ernst et al. it 2,005,731 and Ernst et al. #i 2,005,- '732 both dated June 25, '1935. My invention as hereinafter described provides an exceedingly simple and inexpensive means for obtaining compensation for such changes in viscosity of the actuating fluid; these compensations instead of being effected by devices extraneous to the hy- `draulic control mechanism of the machine, are

effected, according to my invention, primarily by the control mechanisms themselves, the compensating instrumentalities being brought into action whenever the throttle becomes operative on the pressure fluid.

The arrangement shown in the cpending Blood application, Serial No. 138,424, led vApril 22, 1937, provides a constant speed or balancing valve which operates to compensate for changes in viscosity, and is satisfactory in operation in many types of installations. The compensation for 4viscosity changes in this Blood application is obtained by diverting a portion of the pressure fluid to this constant speed or balancing valve by Way of a narrow annular slot having its flow characteristics proportional to the ilow characteristics of the throttle valve. Such arrangement requires a carefully constructed compensating valve which is applicable to only a limited range of viscosity changes; furthermore, this arrangement requires the diversion of more or less of the pressure fluid supplied by the pump, away from the part or parts which are actuated by such pressure fluid.

l further feature of the present invention resides in a novel arrangement by which the de-l vices which provide the compensation for changes in viscosity of the pressure fluid thus to obtain a.

.speed must be kept substantially constant, so

that a pump of relatively small capacity may provide enough fluid for the actuation of other parts of the machine than the reciprocating table. By this arrangement, it is possib-le to so connect the pump in the system that parts of the machine can be under the control ofA fluid under full pump pressure, with the table, however, in its working zone maintaining the speed for which its throttle is set; this obviously necessitates the automatic imposition of pressure changes in the oil or other fluid admitted to the actuating mechanism.

Other and further objects and advantages of the invention will hereinafter more fully appear from the following detailed description taken in connection with the accompanying drawings in which- Fig. 1 is a front elevation of a boring machine, as illustrative of one type of machine tool to which my invention is applicable.

Fig. 2 is an end elevation of the machine of Fig. 1 with the work-holder and tool head removed.

Fig. 3 is a large scale front elevation illustrating the general arrangement of the hydraulic control devices for the boring machine shown by Fig. 1.

Fig. 4 is a sectional view of a certain balancing valve used in my improved system.

I'ig 5 is a sectional view along the line 5--5 of Fig. 4. y

Fig. 6 is a sectional view along the line 6--6 of Figyi. Fig. 7 is a partly diagrammatic View illustrating certain details of thehydraulic control devices for my improved system, as constructed to procure compensation for changes in viscosity of the pressure iiuid.

Fig. 8 is a perspective view of a fragmentary part of the balancing valve.

Like reference characters refer to like parts in the dlierent iigures.

Referring first to Fig. 1, in which is shown a boring machine as one example of a machine tool to which the present invention is applied. the machine has the reciprocatory table l usually provided in a boring machine. Either the boring head or the workpiece to be bored is carried on the table and the reciprocations of the latter serve in either case to produce a. relative longitudinal movement between the boring tool and the workpiece. In the construction shown. the table supports and carries a workholder 2 in the form of a. bracket, and the boring head 3 is mounted on a bridge i which spans the guideways 5, Fig. 2, provided by the machine base 6 for the movement of the table I. The boring head has a boring spindle l in the end of which is carried a tool 6 and the spindle is suitably rotated from a motor, not shown, in the base of the machine, to which the boring spindle is connected by belts 9 passing over pulleys I6 on the boring spindle and idler pulleys II secured to the bridge.

The workpiece a is mounted in alinement with the axis of the boring spindle and is here shown as held stationary against rotation in a suitable bore I2 of the bracket 2. It will be understood that any other suitable type of workholding mechanism can Ibe used and that the arrangement shown is merely illustrative.

With reference to Fig. 7, movement of the table I to the left to carry the workpiece into an operative position, relative to the boring tool, is procured by a iiuid pressure actuated mechanism comprising a cylinder I3 mounted in the base of the machine and having a piston I4 therein connected by a piston rod I5 to a lug I6 on the underside of the table. When fluid under pressure is directed to the right hand end of the cylinder the table is caused to move to the left. Movement of the table to the right is obtained by directing fluid under pressure to the left-hand end of the table cylinder.

The table I is reversed at the left-hand end of its movement by a reversing dog I1, Fig. l, mounted on the front of the table, and adapted to engage an arm I8 (see also Fig, 3) mounted on a stud I8 carried by the machine base 6. An oppositely extending arm 20, movable with the arm I8, engages a pin 2l carried by an arm 22 on a stud 23 which is pivotally mounted in the base. A depending arm 24 secured to the stud 23, has its lower end in position to engage and move a pilot valve 25 for the operation of a reversing valve 31, as hereinafter described in detail. 'I'he valve 25 is shiftable manually by a lever 26, also secured to the stud 23.

Still referring to Figs. 1 and 3, the table also has mounted on the front thereof a cam 21. which, as the workpiece arrives in position to be operated upon by the tool, engages and depresses an arm 28 secured to a stud 29 journalled in the base. An arm 30 also secured to the stud 29, engages the stem of a slow-down valve 3I, hereinafter described in detail, so that the rate of travel of the table I is reduced during the boring or other operations which the tool 8 performs on the workpiece.

With reference now to the fluid pressure dia- `gram of Fig. 7, a constant volume fluid pumpl 32 of Well known construction has its intake pipe 33 connected to a suitable supply of oil, not shown, and the pressure side of said pump is connected by a suitable conduit `34 to a port 35 in the casing 36 of the main reversing valve 31. A relief valve 38 determines the maximum pressure under which the pump operates, and the relief valve is connected to the supply tank by a return conduit 39.

The bore of the reversing valve casing 36 is convnected by a conduit 4I] to the bore of a casing 4I in which the pilot valve 25 is operable. The conduit 60 enters the bore of the reversing valve casing 36 at a point in line with the port 35, and said bore at this point has an annular groove 62 so that a constant supply of fluid is always directed to the pilot valve casing regardless of the position of the reversing valve 31. Spaced ports 63 and 66 in the pilot valve casing have a common connection [l5 to a return conduit 46 which leads from an exhaust port 41 at the right hand end of the reversing valve casing 36. In this same end of the bore of the reversing valve casing is a port 50 which is connected by a conduit 46 to a similar port 49 near the opposite end of said bore, for a purpose to be hereinafter described.

The bore of the pilot valve casing All provides, on either side of the entrance of fluid supply conduit l0 thereto, the ports 5I and 52 which are connected by conduits 53 and 54 to ports 55 and 56 in the left and right hand ends respectively of the easing 36 for the main reversing valve. When iiuid enters either of the ports 55 or 56 the valve 31 is shifted to one or the other of its end positions for controlling the direction of the table movement. The position of the main reversing valve is thus controlled entirely by the pilot valve. The rate of movement of the main reversing valve from one end position to the other is controlled by the rate of admission of fluid to the ends of the casing 36 and this rate of admission may be controlled by throttle valves, not shown, in the conduits 53 and 54. It will be apparent that the table may have a dwell of a predetermined length at either end of the table stroke dependent upon the time interval between the shifting of the pilot valve and the resultant movement of the reversing valve. l

A port-l51 in the reversing valve casing 36 is connected by a conduit 58 directly to the left hand end of the table cylinder, and a similar port 59 in said casing is connected by a conduit 60 to a port 6I in a casing 62 in which the slow-down valve 3I is operable. At substantially the same level as the port 6I, the bore of casing 62 provides another port 63 which is connected by a conduit 64 to a Dort 65 which lets into the upper end of the bore 66 of a casing 61 in which operates the plunger 68 of my improved balancing or compensating valve. The casing 62 for the slow down valve 3| provides a throttle valve 'II which is adjustable to vary the speed of travel of the table I during the period in which the workpiece a is being operated upon by the tool; this throttle valve 1I as shown in Fig. '7 is arranged in a passage 69 which provides a connection between the conduit 64 (leading from port 63) and a casing passage 10 which is connected by conduit 12 to a port 13 opening into the bore of the balancing valve casing 61. -Another port 14 in the bore of casing 62 is spaced longitudinally from the port 63, and is connected by a conduit 15 to the conduit 12.

In spaced relation to inlet port 13, the bore of the balancing valve casing 61 provides an outlet port 16 which is connected by a conduit 11 to the right hand end of the table cylinder. A channel 18 in the casing 61 opens at one end to an annular groove 19 of said bore, which groove establishes constant communication of said channel 18 with the inlet 13. The opposite end of the channel 18 lets into the bore 66 at a substantially lower point. The valve plunger 68 is normally held approximately in the position shown by a coil spring disposed within a recess 8l, Fig. 4, of

"said plunger 60. The lower end of the spring engages the head 82 of a pin, surrounded by said spring and resting on a plurality of loi-metallic thermal elements 83 of well-known construction. rlhese elements are immersed in fluid from the supply pump which passes to the lower end of a bore lit by way of conduit 1,2, groove 19 and the channel 18. e

The reversing valve casing 36 provides, near its left hand end,a port 84 which is connected by a conduit 85 to the conduit 11, the latter, as shown in Fig. 7, leading from port 16 of the balancing valve to the right hand end of the table cylinder .03. The conduit 85 and port 84 provide as herev inafter described for the exhaust of fluid from the right hand of the table cylinder during Inovement of the table to the right, thereby permitting the table to move at a maximum of speed.

rlhe casing 62 for the slow-down valve has ax ially spaced ports 86 and 81 connected by a conduit 00, and a port 89 at substantially the same level as the port 81 is connected by a conduit 90 to the left hand end of a cylinder 9| in which a piston 92 is slidable. The right hand end of the cylinder 9| is connected by a conduit 93 to the return conduit 39; a coil spring 94 in the'cylinder 9|, at the right hand side of the piston, normally holds the piston 92 at the left hand of the cylinder. A projecting piston rod 95 connected to the piston is suitably connected to a clutch and brake mechanism, of well known construction, which controls the rotation of the boring tool 8, the brake being actuated when the piston is in the left hand position shown, and the clutch being engaged to transmit rotation to the tool, when the piston is moved to the right.

With reference to Figs. 4 and 5, each bi-metallic thermal element 83 is in the form of a three prong disk, Fig. 5, with the overall diameter corresponding to the diameter of the bore |50.` The lowermost element 83 rests centrally on the head of a pin 96, and a ring 91 is positioned between the peripheries of the two lowermost elements 83.

The uppermost pair of elements 83 have a similar ring 98 positioned between the peripheries thereof. A plate 99 having a central hub |00 is positloned between the upper and lower pairs of elements 83, as shown. By this arrangement any heating of the fluid in the uid pressure system causes a bending of each of the elements 83 which are so arranged as to cause a lowering of the pin 82 which supports spring 80, thus allowing the plunger 68 to move downwardly.

' As shown in Figs. 4 and 7, although the inlet port 13 in the casing 61 is normally covered by a full-diameter portion of the plunger 68, still the pressure fluid can pass from the inlet port 13 to the outlet port 16 (the latter normally left uncovered by a reduced portion |02 of the plunger) through small slots |03 in the full-diameter portion |0|. As best shown in Fig. 8, these slots are located at an angle to the axis of the plunger 68 so that a slow turning of the plunger tends to occur as the rpressure fluid ows through the slots to the space around the reduced portion |02. This turning of .the plunger substantially overcomes any tendency of the plunger to resist endwise movements. The slots |03 preferably decrease in cross-sectional area. toward the upper ends thereof to provide for varying the quantity of fluid passing through said slots as the position of the plunger 68 changes, a downward movement of the plunger obviously cutting down the quantity of fluid which is thus supplied to the outlet port 18.

In the operation of the machine, movement of the table to the left to carry the workpiece toward the tool, is initiated by movement of the control lever 28, Fig. 3. Rocking of this lever shifts the pilot valve 25 into its illustrated right hand position, thereby causing the reversing valve 31 to be moved by the pressure uid into its right hand position (Fig. 7), in which fluid under pressure is directed around a reduced portion |04 of the reversing valve, and through the conduit to the port 0| which opens to the bore of the slow-down valve casing.

A reduced portion |05 of the slow-down valve 3| normally provides fluid connection between the ports 6| and 1t, and fluid under full pump pressure is thus supplied to the port 13 passing thence by way of the groove 19 and channel 18 to the underside of the balancing valve plunger 68. Fluid at the same pressure also enters the upper end of the bore 60 by way of port 03 and the conduit 64. As the effective areas of the opposite ends of the plunger 68, are equal, the pressures exerted by the iluid on opposite ends of the plunger are equal, and the spring 80 is therefore eifective to produce more or less upward movement of the plunger 68 to allow the flow of pressure uid through slots |03 and thence by way of conduit 11 to the right hand end of cylinder I3; this moves the table I to the left, at a speed unaffected by the setting of the adjustable throttle valve 11, since the pressure fluid in this unlowered position of the slow-down valve 3| ls permitted to by--pass said throttle valve.

At the completion of this high-speed table movement, just before the tool is engaged by the workpiece, the slow-down valve 3| is moved downwardly by the cam blocking 21; this movement, in the following manner, starts the rotation of the boring tools and also procures a reduction in the rate of table travel. As the valve 3| moves downwardly the reduced portion |05 establishes fluid connection between the ports 6| and 86, and fluid under pressure is thus directed to the port 81, around an upper reduced portion |06 of the valve 3| and through the conduit 90 to the clutch and brake operating mechanism. The fluid entering the cylinder 9| is at full pump pressure and thus positively engages the clutch mechanism by movement of the piston 92 to the right thereby obtaining rotation of the boring tool 8.

The downward movement of the slow-down valve also procures, as above stated, a reduction in the rate of table travel.. This is effected by the closing of the port 14, so that all the fluid which goes to the right hand end of cylinder I3, by way of the inlet port 13 must pass through the throttle Valve 1|. It will be noted that the port 14 is gradually closed by a conical shoulder |01 on the valve 3|. With the port I4 thus closed, the setting of the throttle valve 1| determines theamount of fluid entering the table cyllnder and thus reduces the rate of table travel to Ia desirable boring speed.

It is well known that, at a given viscosity of a fluid, a throttle maintains a constant flow of the fluid only when the pressure drops across the Vthrottle (the difference between the pressure entering -the throttle and that against which the throttle is discharging) is maintained constant. If the `pressure drop becomes less, by reason of an increase of back pressure built up against the discharge of the throttle, or by reason of a decrease in pump pressure, the rate of flow decreases, and when the pressure drop increases, the rate of ilow increases. It is the function of of the maximum pressure required in the conduit v11 leading to the cylinder I3 to secure motion of the table I, the balancing valve 68 interposes a second but variable throttle |03 between the port 19 and the conduit 11. The variable throttle |83 is arranged automatically to reduce the pressure required at the port 10 (to maintain a uniform pressure drop across the throttle 1I) to that pressure which may, at the moment, be required in conduit 11 necessary to procure movement of the table at the desired rate. This automatic compensation is controlled by the diierence in pressures across the throttle 1|, that is, at ports 63 and 10, by means of the valve plunger 68.

As previously described, the chamber above the valve plunger 68 in the casing 61 is connected by the conduit 64 to the port 63 above the throttle 1|. 'I'he chamber below the valve plunger 68 is connected by the conduit 18 and the groove 19 in the casing 61 to the port 13 leading by the conduit 12 to the port 10 below vthe throttle 1|. The pressures existing on opposite sides of the throttle 1I are therefore imposed on opposite ends of the balancing plunger 68. With the port 14 closed, the fluid pressurein the port 10 is reduced by the throttle valve 1I and the pressure on the underside of the plunger 68 is correspondingly reduced. The -pressure above the plunger 68 remains that of port 63 on the pressure side of the throttle (-full pump pressure). The valve plunger 68 is thus moved down into approximately the position of Fig. 7 or until the combined forces exerted by the spring 88 and by the iluid on the underside of the plunger become balanced by the force exerted by the fluid above the plunger. The lthrottling passages |03 are brought into action between ports 13 and 16 by the downward movement of the valve 68, thereby increasing the pressure in the conduit 12 and thus at the port 10 until the valve 68 is again in balance. Since the pressure areas are uniform on the valve 68, this balance is obtained when the pressure on the 'top of the valve 68 (or -that at port 63) minus the pressure on the underside of the valve 68 (or that at port 10) is equal to the pressure of the spring 80.

If the table encounters increased resistance, the pressure in the table cylinder increases, tending to increase the pressures at all points in the system back to the throttle valve 1| But with the proportionate increase at port 19, the ressure on the underside of the valve 68 overbalances the pressure on the upper side of the valve, raising the valve until a new balance is established, thereby reducing the pressure drop through the throttle passages |03 and reestablishing the fixed pressure drop across the throttle 1I, as governed by the spring 88. The spring 88 will have a diiierent pressure at every setting of balance which the valve may take and may result in a slight variation in the difference of pressures across the throttle 1I. These variations, may, however, be made negligible in practice by proper design and pressure selections.

This balancing valve also compensates for changes in the viscosity of the actuating :fluid so as to keep the rate of table travel substantially constant for any given setting of the throttle valve 1|, and substantially independent of such changes. As the temperature of the fluid increases, the viscosity decreases and the table would under these conditions tend to travel faster, except for the automatic operation of the balancing valve which offsets vand compensates for the changed condition of the pressure fluid. The bi-metallic elements 83 are arranged to provide for a lowering of the pin 82 as the temperature of the nuid increases, thus decreasing the pressure exerted by the spring 88 (by lengthening it) so that when a. balanced condition is again established, the diierence in pressures above and below the valve will be lessened and the pressure drop across the throttle 1I, from ports 63 to 18, will be correspondingly lessened. Since a throttle oiers less resistance to the flow of uid of lower viscosity (or greater uidity), a smaller pressure drop across the throttle is required to pass a given rate of flow when the fluid becomes less viscous.

As the table continues its throttled-down movement to the left the boring tool performs a boring operation, and the table is then reversed by the reversing dog I1 which shifts the pilot valve 25 to the left, causing a movement of the reversing valve to the left whereupon the pressure fluid is admitted by way of port 51 and conduit 58 to the left hand end of cylinder |3, to obtain a full speed return of the table I to its extreme right hand position of rest. 'I'he reversing valve 31, in its left hand position, directs fluid under pressure around a. reduced portion |08 thereof to the conduit 58 leading directly to the left hand end of the table cylinder. Fluid from the right hand end of the cylinder exhausts through the conduit 85, around the reduced portion |04 of the reversing valve 31 and through the conduit 48 and ports 50 and 41 to the return conduit 46, the ports 50 and 41 each communicating with an'annular groove |09 in the bore of casing 36.

The slow-down valve is held down during the first part of the run-out of the table but this does not prevent the movement of the table at miximum speed as the exhaust from the cylinder I3 is by-passed around the slow-down valve through the conduit 85. 'I'he table comes to rest at the right hand position of Fig. 1 by engagement between the piston I4 and the end of the cylinder I3.

Before the table begins its right hand return movement the rotation of the boring tool is stopped, by movement of piston 92, to disengage the clutch and to apply the brake. To this end, the movement of the reversing valve 31 to the left allows the uid in the cylinder 9| to exhaust through the conduits 6|) and 48, the slow-down valve 3| being in its lower position for a uid connection between the ports 6I and 86. 'Ihe reversing valve 31 establishes fluid connection between the ports 49 and 59 before the table is reversed so that the tool may come to rest before the runout of the table is started.

As above stated, the table dwells at the end of the table at the left hand end of its stroke. 'I'he dwell is controlled by the time interval required for the movement of the main valve from a position cutting off the flow of fluid from the port 35 to the port 59 around the portion |04, until the valve reaches a position providing fluid connection between the ports 35 and 51 around the reduced portion |08.

From the foregoing it will be apparent that the machine incorporates a balancing valve in the fluid pressure system in series with the main throttle valve and between the throttle valve and the reciprocatory table with the balancing valve providing for a uniform rate of table travel independently of changes in the viscosity of the fluid and independently of the resistance encountered by the table. Moreover, with the balancing valve in the position described, it is possible to have available the full pump pressure in any other part of the uid pressure system for the actuation of any other mechanism controlled by fluid under pressure. The compensation for viscosity changes is eiected by mechanism responsive to temperature changes in the actuating iiuid.

I claim:` e

I.`In a machine tool, a reciprocatory table, fluid pressure actuated means for moving the table, a source of fluid under pressure, a balancing valve in the uid connection between the source and said means for providing a uniform rate of table travel, said balancing valve comprising a casing having a plunger slidable therein, an inlet port in the casing, and an outlet port connected to the fluid pressure actuated means, said plunger being adapted to vary the amount of opening of one of said ports by movement within the casing, a connection from the source to one end of the casing, a throttle valve in the fluid connection from the source to the i'nlet port, a connection between the other end of the casing and the inlet port, a spring for normally urging the plunger toward one end of the casing, and means responsive to changes in the temperature of the Huid in the system for varying the action of the spring.

2. In a machine tool, a reciprocatory table, fluid pressure actuated means for moving the table, a source of fluid under pressure, a balancing valve in the uid connection between the source and said means for providing a uniform rate of table travel, said balancing valve comprising a casing having a plunger slidable therein, an

inlet port in the casing, and an outlet port connected to the fluid pressure actuated means, said plunger' being adapted to vary the amount of l opening of one of said ports by movement Within the casing, a connection from the source to one end of the casing, a throttle valve in the fluid connection from the source to the inlet port, a connection between the other end of the casing and the inlet port, and means responsive to changes in the temperature of the fluid in the system for shifting said balancing valve.

3. In.. a machine tool, a reciprocatory table, fluid pressure actuating means for moving the table, a source of uid under pressure, a balancing valve in the fluid connection betwen the source and said means for providing a uniform rate of table travel, said balancing valve comprising a casing having a plunger slidable therein, said casing having an inlet port connected to said source and an outlet port connected to the fluid pressure actuated means, said plunger being adapted to 'vary the amount of fluid passing through said outlet port by movement within the casing, a connection from the source to one end of the casing, a throttle valve in said connection, a connection from the other end of the casing to said source, ahead of said throttle valve, afspring for normally urging the plunger toward one end of the casing, and means responsive to changes inthe temperature of the fluid in the system for varying the action of the spring.

4. In a machine tool, a reciprocatory table, fluid pressure actuating means for moving the table, a source of uid under pressure, a balancing valve in the fluid connection between the source and said means, for providing a uniform rate of table travel, said balancing valve comprising a casing having a plunger slidable therein, Vsaid casing having an inlet port connected to said source and an outlet port connected to the fluid pressure actuated means, said plunger being adapted to vary the amount of fluid passing through said outlet port by movement within the casing, a connection lfrom the source to one end of the casing, a throttle valve in said connection, a connection from the other end of the casing to said source, ahead of said throttle valve,

means responsive to changes in the temperature of the fluid in the system for shifting said balancing valve, and a normally open slow-down valve in parallel with the throttle valve and shifted to closed position in response to the table movement for rendering the throttle valve operative during a portion only of the table movement.

WALDO J. GUILD.

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