US2375255A - Hydraulic transmission for machine tools - Google Patents

Description

4 Y J. SNADE-R #TAL 2,375,255

HYDRAULIC TRANSMISSION. FOR MACHINE TOOLS Fil ed Aug. 30,-1937 4 Sheets-Sheet 1 g 7- :u n

. HYDRAULIC TRAiLSMISSION FOR MACHINE TOOLS I. LSNVA'D-ER L 2 375,255

Filed Aug. so, 1937 4 smeets-sneet-z y 4 l. 1. SNADER El'AL 2,375,255

" HYDRAULIC TRANSMISSION FOR MACHINE TOOLS Fil d-Aug. so, 1937 4 Sheets-Sheet 3' @iin &

V V I hlw T? Q r \\\ll.ar .4 w, i..

9 m a m H y 8, 1945- l. .LS-NADER 'ET AL I 2,375,255 HYDRAULIC TRANSMISSION FOR MACHINE TOOLS 4 Sheets-Sheet 4 Filed Aug. 30, 1937 I r Mfg Patented May 8, 1945 HYDRAULIC TRAN SIVIISSION FOR MACHINE TOOLS Ira J. Snader and Max A. Mathys, Detroit, Mich, assignors to Ex-Cell-O Corporation, Detroit, Mich., a corporation of Michigan Application August 30, 1937, Serial No. 161,636

\ 17 Claims.

The present invention relates to improvements in machine tools and has particular reference to a new and improved hydraulic transmission.

One of the primary objects of the present invention is to provide a novel hydraulic transmission including a main control circuit and a pilot control circuit and including means for maintaining a constant relatively low pressure in the pilot control circuit regardless of pressure fluctuations in the main control circuit.

Another object is to provide a new and improved hydraulic transmission for a reciprocable carriage including selectively available dwell mechanisms for delaying the reversal at opposite ends of the reciprocation, the dwell mechanisms being connected in the pilot control circuit.

Still another object-resides in the provision of novel means including a pilot feed control valve selectively operable by the carriage to effect a plurality of feed movements in each direction.

Further objects and advantages will become apparent as the description proceeds.

In the accompanying drawings,

Figure l is a view in perspective and on a rc-. duced scale of a machine embodying the features of the invention.

Fig. 2 is a fragmentary view showing the machine control mechanism in front elevation.

Fig. 3 is a diagrammatic view of the hydraulic system.

Fig. 4 is an enlarged view showing the main direction valve and associated structure in longitudinal central section.

Fig. 5 is an enlarged view in longitudinal centrial section of the selective feed control mechan sm.

F gs. 6 and 7 are similar views of the dwell control and orifice pressure control mechanisms respectively. I

, Fi 8 is a view of the machine control mechanismin end elevation.

Referring more particularly to the drawings, the

- tion. Two inverted U-shaped bridge members 3 are mounted respectively on opposite ends of the base I, and each serves as a support for one or more, for example, three parallel spindle structures 4.

Suitable spindles 5 are journaled respectively in the structures 4. and are adapted to be driven electrically, with the spindles at opposite ends of the machine under the control respectively of two electric switches 6 and I. These switches are adapted to close and open the spindle drive circuits to start and stop the spindles, and may be operated by any suitable means. In the present instance, the switches '6 and 1 respectively have actuating stems 8 ands rigidly connected to pistons 50 and H reciprocable in stationary hydraulic motor cylinders l2 and i3. Pressure fluid supply lines M and is open to opposite ends of the cylinder l2, and similar lines l5 and H open to opposite ends of the cylinder is. This arrangement is shown diagrammatically in Fig. 3.

Each of the spindles 5 is provided with a brake Iii, and the brakes for the two sets of spindles at opposite ends of the machine are connected respectively for joint actuation by two pistons 59 and 2|! reclprocable in stationary hydraulic motor cylinders 2| and. 22. Opposite ends of the cylinders 2| and 22 are connected respectively to the.

two sets of pressure fluidsupply lines it and I6, and I5 and IT. The arrangement is such that if pressure fluid is supplied to the lines M and I5 and exhausted through the lines l6 and H, the switches 6 and 7 will be open and the brakes It will be applied, and if pressure fluid is supplied tothe lines It and I I, the left end spindles 3 will be idle and the right end spindles will be rotating, and if pressure fluid is supplied to the lines l5 and it the reverse condition will prevail.

The present invention relates primarily to an hydraulic operating mechanism for the carriage 2, the switch pistons ill and I I, andthe brake pistons I 9 and 20. In its preferred form, the operating mechanism comprises an hydraulic carriage motor having a cylinder 23 mounted in fixed position within the base I, and a piston 24 reciprocable in the cylinder and connected through a piston rod 25 to the carriage 2. Opening from the cylinder 23 respectively at opposite sides of the piston 2i are two fluid supply anddischarge passages, conduits or lines 26 and 21 leading to adirection valve 28 (Figs. 3 and 4) The direction valve may be ofany. desired construction, and preferably comprises an elongated bore 29 in a valve body 30. A valve piston 3| of the spool type, comprising axiallyspaced heads 32 33 and 34 separated by annular spaces 35 and 3B, is mounted for reciprocation in the bore 29."

Formed in longitudinally spaced relation in the periphery of the bore 29 are an annular groove or pressure port 31 open to a pressure supply respectively to the lines 26 and 21, two annular groovesor feedexhaust ports 4| and 42 at opp site sides of the ports 39 and 48am! open to restricted exhaust lines 43 and 44, and two annular grooves or rapid traverse exhaust ports 45 and 46 at opposite sides of the ports 39 and 48 and open to an unrestricted exhaust-line 41 leading to a sum 48. These ports are so arranged that when the valve piston 3| is in the left end position, both ports 45 and 4! will be open to the port 39, the port 48 will be open to the pressure port 31 and the ports 42 and 46 will be closed from the space 36, thereby establishing rapid traverse of the carriage 2 to the left; when the piston is moved one step to the right, the port 4| will still be open to the port 39, but the port 45 will be closed by the head 32, thereby establishing a feed movement to the left; when the piston is located in the central position, as shown, the pressure port 31 will be, closed by the head 33 and the ports 45 and 46 will be closed by the heads 32 and 34, thereby stopping the carriage 2; when the piston is moved partially to the right, the port 39 will be opened to the pressure port 31,

the port 40 will be opened to the exhaust port 42,

and the ports 45 and 46 will be closed from the spaces 35 and 36, thereby establishing a feed movement to the right; and when the piston is moved into the right end position, the port 46 will be opened to the port 40 to establish rapid traverse to-the right.

The pressure line 38 is adapted to be connected to any suitable source of pressure fluid, such as a power driven pump 49 having an intake line 50 opening from the sump 48.. The available pres-' sure from the pump 48 is under the control of a relief valve adapted to by-pass excess fluid from the passage 38 to the line 41. In the present instance, the. high pressure relief or control valve 5| comprises a valve bore 52 in the body 38 opening from the pressure line 38 at opposite ends respectively to the exhaust line 41 and a chamber 53 draining through a line 54 to the sum 48. A plunger 55 is reciprocable in the bore 52, and is formed in the periphery with a plurality of longitudinal grooves 56 in communication with the exhaust line 41 and adapted for movement into and out of communication with the pressure line 38. A coil compression spring 51 in the chamber 53 tends to urge the plunger 55 in a direction to decrease or interrupt communication of the grooves 55 with the line 38. The plunger 55 is also formed with an annular face 58 defining a pressure area which is exposed to the pressure in the line 38 and acts in opposition to the sprin 51. It will be evident that the relief valve 5| serves to limit the maximum pressure in the line 38. This pressure may be varied to suit the requirements of the machine work by means of an adjusting screw 59 acting against the fixed end of the spring 57.

The outer ends of the grooves 55 have a run out to the peripheral surface of the valve plunger 55. As a result, when the valve 5| is partially open, the increase in the eflective opening pressure area by the transverse area of the grooves 56 exposed in the line 38 is counteracted by the kinetic pressure of the lay-passing fluid against the outer end areas of the grooves. 'This substantial equalization of opposed forces serves to eliminate fluttering, and hence to maintain a more nearly uniform pressure in the line 38 under varying operating conditions.

The hydraulic circuits thus far described con-- 'stitute the main operating circuits of the system, and are under the full pressure existing in the line 38. The main valve 28 is a five position valve, and is operable by a pilot control comprising pilot control circuits under a relatively low pressure, and a plurality of pilot valves,

namely, a start and stop valve 60, direction con- 5 trol valves GI. and 62, a rapid traverse valve 63 and a feed valve 64, operable by the carriage ,2. The pilot control also includes two dwell mechanisms 65 and 66 for preventing immediate institution of the rapid return at the ends of the feed strokes in opposite directions.

The various operating elements of the pilot control, together with the main control valve 28 are incorporated in a unitary control panel 61 which is mounted on the front of the base I, and which is so arranged that the pilot valves 60 to 64 are operable selectively by suitable control dogs 68 to 12 adjustably mounted in a T-slot 13 in the front side of the carriage 2. By selection and adjustment of the dogs, and by adjustment of the rate of feed and the selective use and adjustment of the dwell mechanisms 65 and 66, various machine cycles diiiering in movement rates and sequences may be obtained.

Fluid is supplied to the pilot control circuits at a relatively low pressure under the control of a regulating valve 14 in the body 30. The valve I4 comprises a bore opening from the line 38 at one end toa pressure chamber 76 and at the other end to the drain chamber 53. A plunger 1! is slidable in the bore l5,,and is urged against the pressure in the chamber 16 by a compression spring 18 having a pressure adjusting screw 19. The pl nger I7 is formed with a longitudinal bore 80 open to-the chamber 16, and adapted for communication with the line 36 or the chamber 53. It will be evident that the valve 14 serves to meter fluid from the line 38, which opens about the plunger 11, to the pressure chamber 16 which serves as the primary source of' fluid supply for the pilot control circuits. When the pressure in the chamber 16 acting on the end of the valve member Tl balances the spring 18, the supply of fluid will be cut oil. In the event of high pressure leakage past the valve M into the chamber 16, the resulting excess pressure will urge the plunger 17 to the right and allow fluid to escape through the bore 88 to the drain chamber 53. As a result, a balanced relatively low constant pressure is substantially maintained in the chamber T6 at all times.

The purpose in utilizing a uniform pressure in the pilot control lower than that in the operating circuits is to reduce the force required to operate the pilot valves 6|) to 64, and thereby to diminish the load on the table dogs 68 to 12 and to obtain greater sensitivity and accuracy. Also, the pilot pressure will remain constant at all times regardless of pressure variations in the main operating circuits.

The pilot valves 68 to 64 comprise a plurality of vertical bores 8| to 85 formed in and opening to the top of the panel 61, and a plurality of spool valve plungers 86 to 90 reciprocable in the bores and projecting therefrom through bushings SI for selective actuation by the dogs 68 to 72. Low pressure fluid from the chamber 16 is directed through a branched line 92 to the respective valve bore 8| to 85, and acts against the upper piston areas of the spool plungers 86 to 98. A leakage drain line 93 opens from the upper end portion of each of the valve bores 8| to 85 to the chamber 53.

The start and stop valve 60 is available to effect adjustment of the main oontrol valve 28 into neutral position. Thus, the valve bore 8| has appropriately arranged port connections 94 and 96 with a drain line 96 connected to the line 41, and a port connection with a branched line 91 opening to the outer ends of two cylinders 99 and 99 located at opposite end of the main valve bore 29. Two floating stop pistons I99 and I9! are slidable in the cylinders 98 and 99 and adapted for separable engagement with direction pins I92 and I93 engaging opposite ends of the main spool valve 3|. When the stop plunger 96 is depressed, the lines 92 and 91 are connected. and hence the pistons I99 and NI are held against the inner ends of the cylinders 96 and 99,

to center the spool valve 3|. When the plunger 96 is elevated, the line 91 is connected through the port connection 94 to the drain line 96, and the spool valve 3! is released for actuation under the control of the direction pilot valves GI and 62 as hereinafter described.

The plunger 86 may be operated manually from the front of the panel 6'! by means of a hand lever I99 to start and stop the carriage 2, and is self-maintained in either position. 'When the plunger 89 is elevated to start the operation, it is locked in operative position by pressure fluid in the lower 'end of the bore 8| supplied from the line 92 through a branch line I99 When the plunger 86 is depressed to stop the operation, the line I99 is closed, and the lower end of the bore 8| is vented through a passage I95 in the plunger and the port connection 95 to the drain line 96.

The pilot valves BI and 62 are operable respectively to institute the right and left movements of the carriage 2, and to reset each other alternately for coaction with the dogs 69 and I9.

Each has port connections with the supply and drain lines 92 and 96, and with cross lines I99 and. I91 opening respectively to the lower ends of the valve bores 83 and 92 and also to the inner ends of the cylinders 99 and 99. The port connections are so arranged that when the'plunger 81 is depressed, the line 92 will be connected to the line I99, thereby causing upward movement of the plunger 88 to connect the line I91 to the drain line 96. As aresult, the plunger 81 is locked in depressed position, the plunger 99 is held in its upward position, and the directional pin I93 is shifted to the left, thereby shifting the spool valve 3I in the same direction to institute the carriage movement to the left. Conversely, when the plunger 89 is depressed, pres sure fluid is supplied through the line I91 .to the lower end of the bore 82 to raise the plunger 81 and connect the line I96 with the drain line 96 and to the inner end of the cylinder 98. 'As a result of the attendant outward movement of the plunger 91, fluid is exhausted from the inner end of the cylinder 99 while the directional pin I92, together with the spool valve 3|, is moved to the right to institute carriage movement to the right.

The pilot valves 89 and 99 control each other' and also the valve 28 for selective rapid traverse against whatever pressure may exist in the inner end of one or the other of the cylinders 99 and 99, and serve to limit the range of movement of the valve member 3| so that the exhaust ports ,45 and 96 will remain closed during the previously described feed movement of the table.

Suitable spring actuated plungers II3 (shown only in connection with stop collar I99) tend to urge the stop collars I98 and I99 into their outermost positions when the line H2 is connected to the drain line 96.

The rapid traverse valve 63 has appropriate port connections with the pressure line 92, the drain line 96 and a cross line II; leading to the lower end of the feed valve bore 85. The line I I2, leading from the feed valve 69 has a branch cross line I I5 opening to the lower end of the bore 84. Hence, the rapid traverse plunger 99 is elevated when the feed plunger 99 is depressed, and thereupon relieves the line 9 to lock the latter in depressed position. Likewise, the feed plunger 99. is moved into elevated position when the plunger 89 is depressed, and thereupon relieves the line M5 to lock the latter in depressed position.

The feed valve 69 also controls connection of the exhaust lines as and 99 to the drain to obtain the line 53 is connected to the line H6 and the, line 99 is connected to the line H9; and when.

the plunger is fully depressed, the lines 99 and 99 are connected respectively to the lines in and I29.

Suitable flow restrictions, preferably adjustable orifice valves 822 to B25, are interposed respectively in the parallel lines H6, H1, H9 and I29.

Preferably, these orifice valves are alike-in con- III] and feed. The feed positions of the main spool valve 28 are determined by stop collars I99 and I99 reciprocable in cylinders H9 and III defined by enlargements of the-opposite ends of the valve the plunger 99 is depressed, as shown in Fig. 3,'

or to the drain line 96 when the plunger is fully elevated. Upon supply of pressure fluid to the line II2, the stop collars I99 and I99 are moved into their innermost position, as shown in F18. 4,

struction, each comprising a rotary valve plug I26 (Fig. 7) independently adjustable from the front of the panel 61. The orifice valves control the escapement of motive fluid from the motor cylinder 23, and hence their adjustment determines the rate or rates of feed in either direction of carriage travel The two valves I22 and I29 may be adjusted to obtain a fast feed and the two valves I 23-and I25 may be adjusted to obtain a slow feed. Assuming the valves to be so adjusted, partial depression of the plunger 99 will institute a rapid feed and full depression of the plunger -will institute a slow feed, in either direction of carriage movement depending on which of the direction valves 6| and 62 is depressed.

To maintain the intermediate adjustment of the valve 64 for fast feed, the plunger 99 (Fig. 5) is rigid at the lower end with a hollow differential piston I2! reciprocable in a cylinder I29 connected at opposite ends'to the line Ill. The piston I27 defines an internal cylinder I29 open .to an axial bore I39 in the plunger 99. A piston I3I is reciprocable in the cylinder I29 and has an axial stem' I32 adapted to project through the depressed with the drain Lne 93. The lower end of the cylinder I29 is vented through a passage I36 in the piston I3I to the lower end of the cylinder I28.

In operation, when the plunger 90 is partially depressed into fast feed position, as shown in' Fig. 5, the opposite ends of the cylinder I28 are ,exhausted. Fluid pressure acting on the upper end of the difierential plunger 90 tends to urge the latter downwardly, but also projects the stem I32 to limit the downward movement. When the plunger 90 is fully depressed, the upper end of the cylinder I29 is also exhausted, and thereupon V the pressure actingon the upper end of the plunger serves to position.

A suitable spring detent I3I is selectively engageable in parallel annular grooves I38 in the piston I27, and serves to hold the valve 64 in position of adjustment when the pump 49 is shut off. A spring friction detent I39 (Fig. 3) engages the side of the direction valve plunger 88 for the same purpose. As a result, the cycle is maintained under control when the machine is stopped, and will continue .its cycle when the machine is again started.

Interposed respectively in the drain lines IIS and I2I at the outlet sides of the orifice valves I 22 to I25 are two governor or orifice pressure control valves I40 and MI. Preferably, the two valves are alike in construction and correspondlock the latter in the slow feed ing parts thereof are therefore identified by the same reference numerals. The valve I40 comprises a differential cylinder I42 connected at the small end to the line 43 and at the large end to the section of the line II8 exhausting from the orifices I22 and I23. An annular groove I43 in the large end portion ofthe cylinder I42 is open to the other section of the line H8 connected with the drain 96. Freely reciprocable in the cylinder I42 is a hydraulically balanced difierential valve piston I44. A plurality of peripherally spaced generally longitudinal V-shaped notches or grooves I45 are formed in the periphery of the large end of the piston I44 and are movable into various degrees of communication with the annular groove- I43 to provide a restricted adjustable orifice in the line H8.

The adjustable orifice defined by the grooves I45 at their points of communication with the groove I43 is in series with the orifices I22 and I23. Consequently, the pressure drop in the exhaust side of the system is divided between the orifices as determined by the ratio of the areas of the difierential piston I44. For example, ifv

the large end area of the piston is twice the size of the small end area, there will be a fifty percent pressure drop across the orifice I 22 or I23 and a fifty percent pressure drop across thevalve I 40.

- This ratio will be automatically maintained regardless of pressure variation and regardless of different size adjustments of the orifices I22 and I23. Since the pressure drop is subdivided by the two orificesin series, each of the orifice flow areas is larger than if a single control orifice were employed for a ,given rate of table movement. The larger orifice flow area is less likely to become clogged by foreign matter in the oil, particularly when the table ismoving at a slow rate of feed. In the case of the valve Hi, the large end of the cylinder is connected to the inlet section of the line I2I and the annular groove I43 is connected to the outlet section of this line, and the small end of the cylinder is connected to the exhaust line 44.

In operation, when the selective feed control plunger is partially depressed into fast feed position, as shown in Figs. 3 and 5, the pressure line 92 is connected with line H2 for holding the stop collars I08 and I09 in their innermost positions, and through the line H5 to lock the rapid traverse valve 69 in its upward non-operative position. At the same time, the rapid feed control orifice valves I22 and I24, with the associated orifice pressure control valves I40 and I, are connected to control the passage of fluid out of the motor 23 through lines 43 or 44. When the selective feed valve plunger 90 is further depressed to its slow feed position, the connections remain unchanged exceptthat the slow feed orifice valves I23 and I25 are connected into the lines 43 and 44. Upon depression of the rapid traverse plunger 89, pressure line 92 is connected to line H4 to lift the selective feed plunger 90 to its uppermost position. Line H2 is thereby connected to exhaust line 96 to relieve the pressure from the outer ends' of the stop collars I08 and I09, allowing these collars to move to their outermost position and permitting the valve piston 3I to move in the direction determined by the directional valves 6! or 62 to connect lines 26 or 21 directly with the sump through rapid traverse exhaust ports 45 or 46. For any setting of the selective feed valve 64, the direction of table travel will be determined by the direction valves BI and 62. Thus, by proper setting of the machine controls, practically any desired series of table movements is obtainable.

On occasion, it may be desirable to delay the reversal of the carriage 2 at either end of the reciprocation, and the two dwell mechanisms 65 and 66 are selectively available for this purpose. Preferably, the dwell mechanisms are alike in construction so that a description of one will sumce for both. The mechanism 65 comprises a cylinder I46 in which a differential spool piston I41 is. reciprocably disposed. One end of the cylinder I46, exposed to the small area of the piston I41, is constantly connected through an adjustable restricted orifice valve I 48 to the pressure line 92. The other end of the cylinder I46, exposed to the large area of the piston I41, opens to a line I49.. Another line I50 opens from an intermediate point in the cylinder I46. and is adapted to be uncovered by the piston I4I, when the latter is moved into one extreme position by the application of a difierential pressure. A manually adjustable two-position valve I5I is availableselectively to connectthe line I49 to the section of line I06 opening to the valve bore 82 for communication with the pressure line 92 when the directional feed plunger 8'! is depressed, and the line I56 to the other section of line I06, or to connect the line I49 to the line I50 and the line I06 through the valve I 5| directly to the valve bore 82. The valves I48 and lil are mounted in the control panel 61, the valve- I48 being associated in a unitary mounting with the orifice valves I22 and I23 for adjustment from the front of the machine.

The dwell mechanism 66 is identical except for the line connections, the valve Iil in this case being interposed in the line I01 to time the upplunger 81. The ends of the cylinders I46 opposite to the lines I49 are connected with the exhaust line 96 and the pistons I41 preferably have an intermediate peripheral recess I60" which communicates through a bore I6I in the piston and in a connected stem I62 with the exhaust line 96 to permit the expulsion of fluid respectively from the lines I06 and I01 when the associated piston is returned to its upward position.

When a dwell is not desired, the valve II is adjusted, as shown by the position of dwell mechanism 66, to connect the lines I49 and I50 and to pass fluid directly from one section of line I01 to the other. In this adjustment, the system will operate to efiect immediate reversal. When the dwell is desired, the valve I5I is adjusted into the other position, as shown by dwell mechanism 65, so that the line I06 is not directly connected to the pilot valve 6I, but will receive pressure fluid from the cylinder I46 or will exhaust through the piston I41. Assuming that the dwell mechanism 65 is conditioned for. operation, depressingv the plunger 81 at the end of the stroke will not immediately direct pressure fluid into the line I06. Instead, the carriage 2 will move into a fixed limit position, and

pressure fluid will be directed through the line I49 to the large end of the cylinder I46. The

piston I41 will move in response to the diiferconnections obtain -through the stop collar I09, respectively, for the lines I5 and I1, and in this position of the main direction valve 28 the pistons I9 and are actuated to apply the brakes and the pistons I0 and II are moved to open the switches 6 and 1. The spindles are, therefore, idle. When the pilot valves are actuated to initiate a feed stroke, the brakes and switch 10 (gm that end of the machine, toward which the able moves, are respectively released and closed toefiect spindle operation.

Presuming that thesyste'm is actuated to establish a feed stroke to the left, the valve 3| moves to the left as limited by the stop collar I08 to establish the' feed connections. The stop collarI08 is not moved, 'so that the connection between the line I13 and bore I64 remains established. The pin I02, however, moves to the left sure fluid to the line I06 and thereby effect reversal of the main valve 28. The disposition of the switches 6 and I and the'brakes I8, in operative or inoperative condition, is preferably under the control of the main directional valve 28. Referring. to Figs. 3 and 4, thepressure fluid'supply lines I4 and I6 to the left end switch 6 and brakes I8 lead through the valve body to terminate at longitudinally spaced'intervals opposite the stop collar I 08, and the supply lines I5 and I1 for the right end switch land brakes I8 similarly 'terminate opposite the stop collar I09. Since the stop collars I08 and I09 are substantially identical, only one need be described, but it should be noted that in Fig. 4 the lines of section through the stop collars are taken,on difierent planes for better illustration of the passageways to carry the head I10 to the opposite side of the bore I64 efiecting a reversal of the application of pressure fluid through th lines I4 and I6 tothe valve be moved in the opposite direction to effect a feed toward the right, the normal fluid pressure connections through the lines I5 and I! would be reversed in the same manner to enable operation of the right end spindles.

When the valve 3I is'in its rapid traverse position, either in right or left direction, the stop collars I08 and I09 will move to their outermost positions, thereby blocking line I13 and drain groove I14. The relative positions of the pin I02 and I03 to the stop collars I08 and I09 prevent drainage from the recesses I68 and I69. Hence, when the valve is in position for rapidtraverse in either direction, both pressure and drain lines leading to the brake andswitch cylinders at both ends of the machine are blocked and no action affecting any of these cylinders will take place. An interrupted or jump out may, therefore, be performed without stopping the spindles during a rapid traverse jump between HI surrounding the pin I02 and communicating through a bore I12 (see stop collar I09) with the inner face of the collar. A line I13 leads from the pressure port 31 to a-point opposite the stop collar I08. The arrangement is such that, when the main direction valve 28 is in its centered or locked position, as shown in Fig. 4, and the feed plunger 90 is in depressed position, in which instance the stop collar I08 occupies its innermost position, pressure fluid is supplied to the line I4 throug'hline I13; radial bore I64, recess I68 and bore I63. At the same time, the line I5 is conpassage I14 to the exhaust line 41. The same feeds, and the spindles will only stop when the machine is reversed or,brought' to acomplete stop. The stopped conditio of the spindles will be maintainediuntil a feed movement of the machine in one direction or the other is initiated, at which time only those spindles located at the end of the machine, toward which the feed table moves,-will be started.

We claim as our invention:

1. An hydraulic operating mechanism for a reciprocable element of a machine tool comprising, in combination, a reversible hydraulic piston and cylinder motor for reciprocating said element, an hydraulic operating system including control valve means for supplying-pressure fluid to said motor to eifect reciprocation thereof, an hydraulic pilot control system including at least one pilot valve for operatively positioning said control valve means to govern the operative movements of said motor, pump means having a discharge passage for supplying pressure fluid under pressure fluid under a relatively low constant pressure from said discharge passage.

member for'operativ'ely adjusting said control element and having a low pressure fluid supply pas-- sage, and a pressure reducing valve for automatically supplying pressure fluid to said low pressure passage up to a predeterminedrelatively low max imum pressure from said high pressure passage and for discharging excess pressure fluid above said predetermined low maximum pressure in said movable element oi a machine tool comprising, in combination, a reversible hydraulic motor for driving said element; a sourcev of fluid under pressure, a direction valve for connecting said source reversibly to said motor, hydraulic means for reversing said direction valve and including two fluid supply passages, pilot valve means oper-v low pressure passage from said pilot control system, whereby to maintain a substantially constant pressure in said low pressure passage 7egardless of varying demands of said pilot control,

system.

10. A hydraulic operating mechanism for a movable machine tool element comprising, in combination, a reversible hydraulic motor for actuating said element, a hydraulic operating system for supplying pressure fluid to said motor and including a hydraulically operable control element and a high pressure fluid supply passage, v--

draulic pilot control system including at least one low pressure passage and terminating at the other end in a port movable selectively in opposite directions into communication respectively with said high pressure passage and said drain, adjustable spring means tending to urge said member in a direction to establish communication of said port with said high pressure passage, said valve member being opposed to the pressure in said low pressure passage acting in opposition to said spring means, whereby fluid under pressure will be supplied from said high pressure passage through said flow passage to said low pressure passage up to a predetermined relatively low maximum pressure and excess pressure fluid above said predetermined pressure will be discharged from said low pressure passage through said flo passage to said drain.

able to connect said source alternately to said passages, and two dwell mechanisms associated re..

spectively with said pusages, each mechanism being operable to interrupt the flow of fluid through the associated passage for a, predetermined time after connection of said associated passage by said pilot valve means to said source.

13. A hydraulic operating mechanism for a movable element of a machine tool comprising, in combination, a reversible hydraulic motor for driving said element, a source of fluid under pressure, a direction valve for connecting said source reversibly to said motor, hydraulic means for reversing said direction valve and including two fluid supply passages, pilot valve nieans operable to-connect said source alternately to'said passages, two dwell mechanisms associated respectively with said passages, and two selector valves independently operable at will to connect said mechanisms respectively into; said passages-in the path of fluid flow or to shunt said mechanisms, each mechanism when interposed in its associated passage being operable to interrupt the flow of fluid therethrough for a predetermined time after connection of said associated passage by said pilot valve means to said source whereby to delay the reversal of said direction valve.

14. A hydraulic operating mechanism for a I movable element of a machine tool comprising, in combination, a reversible hydraulic motor for driving said element, a source of fluid under pressure, a direction valve for connecting said source reversibly to said motor, hydraulic means for reversing said direction valve and including two fluid supply passages, pilot valve means operable I to connect said source alternately to said pas- 11. A hydraulic operating mechanism for a mov- I able element of a machine tool comprising, in combination, a reversible hydraulic motor for moving said element, a hydraulic operating system including control valves for governing the operation orsaid motor, asource of fluid under pressure communicating with said system, and means for controlling the pressure of the fluid delivered to said system, said last mentioned means including a pressure chamber open to said source, an exhaust chamber open to drain, a. valve passage con- Y necting said chambers, a diflerential valve reciprocable in said passage and having a longitudinal groove open to said exhaust chamber and movable into and out of communication with said pressure chamber and having a pressure area exposed to the pressure in said pressure chamber and acting in a direction toweifect graduated opening of said groove to said pressure chamber, adjustable spring said pressure area in diiirent degrees of valve opening.

12. A hydraulic operating mechanism for a sages, a two position selector valve interposed in one passage, a by-pass passage across said valve, said valve in one position connecting said pilot valve means directly to said hydraulic means and in the other position connecting said pilot valve means through'said by-pass passage to said hydraulic means, and a dwell mechanism interposed in said by-pass passage, said mechanism comprising a differential valve, and means including an adjustable restricted orifice connecting said source to the small end-,of said diiierential valve normally to maintain said diflerential valve in closed position, the large end of said .diflerential valve being connected to said'suppiy passage at the up stream side of said difierential valve when said selector valve is adjusted to c'oneach position being adjustable to connect the supply passage receiving fluid from said motor selectively to said unrestricted passage or the associated restricted passage, pilot valve means operable by said elements to eflect adjustment of said direction valve selectively into its said positions of adjustment, and two sets of parallel restricted orifices interposed respectivel in said restricted passages, said pilot valve means being operable to connect said orifices of each set selec-- tively ins-aid associated restricted passage concurrently with location oi said direction valve in position to connect said motor to the selected one or the other of said restricted passages.

16. A hydraulic operating mechanism for a movable element of a machine tool comprising, in combination, a reversible hydraulic motor for driving said element, a source of fluid under pressure, two supply passages connected to opposite sides of said motor, a relatively unrestricted exhaust passage, two restricted exhaust passages associated respectively with said supply passages,

a reversible direction valve operable in reverse positions to connect one or th other of said supply passages respectively to-said source and in each position being adjustable to connect the supply passage receiving fluid from said motor selectively to said unrestricted passage or the associated restricted passage, pilot valve means" operable by said element to eflect adjustments of said direction valve selectively into its said positions or adjustment, and two parallel restricted orifices interposed in one of said restricted passages, said pilot valve means being operable to connect said orifices selectively in the associated restricted passage concurrently with location of said direction valve in position to connect said motor to said associated restricted passage.

17. A hydraulic operating mechanism for a movable element of a machine tool comprising, in combination, a reversible hydraulic motor for driving said element, a source of fluid under pressure, a direction valve for connecting said source alternately to opposite sides of said motor, a relatively unrestricted exhaust passage, a relatively restricted exhaust passage, pilot control means operable by said element for adjusting said direction valve selectively into position to direct fluid CERTIFICATE OF CORRECTION.

Patent No. 2, 7 ,255. May 19m..-

' IRA J. SNADER, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 6 first column, line 50, claim )4, for "controlling" read --d-irecting-; and thatthe said Letters Patent should be read with this correct-ion therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of October, A. D. 1916.

Leslie Frazer (Seal) First Assistant Commissioner of Patents.

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