US2424300A

US2424300A - Control system for hydraulic circuits

Info

Publication number: US2424300A
Application number: US470268A
Authority: US
Inventors: Becker Walter
Original assignee: Hydraulic Development Corp Inc
Current assignee: Hydraulic Development Corp Inc
Priority date: 1942-12-26
Filing date: 1942-12-26
Publication date: 1947-07-22
Anticipated expiration: 1964-07-22
Also published as: GB574475A; FR938596A; BE469620A

Description

July 22, 1947'. w. BECKER CONTRL SYSTEM FOR HYDRAULIC. CIRCUITS -Fled Dec. 26, 1942 INVENTOR WALTER BELKER ATI'ORNEY Patentel July 22, 1947 CoNrnoL SYSTEM Foa HYDRAULIC CIRCUITS Walter Becker, Dayton, Ohio, assignor to The Hydraulic Development Corporation, Inc., Wilmington, Del., a corporation of Delaware Application December 26, 1942, Serial No. 470,268

14 Claims. l This invention relates to control systems, and, in particular, to control systems for hydraulic circuits. i

It is `we11 known that, when a hydraulic press having a vertically reciprocable ram stands idle 5 for a relatively long period of time with the pump units idle, the press ram gradually settles downwardly due to leakage around the driving motor or press piston.

Also, it is customary to interconnect the press l platen or ram by means of linkage with a uid flow varying device, such as the ow control member of a variable delivery pump, whereby the ow of fluid to the retracting means of the hydraulic motor is neutralized at the end of the l retraction stroke of the press. In this manner the press ram automatically comes to a halt at the end of the retraction stroke. Therefore, when the press ram settles or slides downwardly,

as has been previously explained, the flow controlling means operated by the linkage inter connected with the platen is shifted to direct iiuid to the retraction area of the press. If the fluid is supplied by, say, a variable delivery pump,

the pump will start under load due to the settling of the ram. In turn, the prime moverfor driving the pump will also be started under load. and, in the case of an electric motor as the prime mover, expensive and complicated starting devices are required in order not to overload the power lines supplying energy to the driving motor.

Accordingly, it is an object of this invention to provide means whereby the prime mover driv- It is a still further object to provide a control system for use in connection with a uid source of variable delivery, which is operable selectively to bring about a temporary reduction in the delivery of said fluid source.

These and other objects and advantages of the invention will appear more `clearly from the following specification in connection with the accompanying drawings, in which:

Figure 1 diagrammatically illustrates the control system according to the invention in connection with a hydraulic press circuit; and

Figure 2 is a wiring diagram for the system of Figure l.

General arrangement The control Vsystem according to the invention com-prises a variable delivery pump including 'centering springs continuously urging the pump toward neutral, while servomotor means is connected with the pump for selectively shifting the pump into forward or retraction stroke delivery position.

T-he servomotor means includes a valve mem- 0 vents the supply of actuating fluid to the plunger ing the pump may vbe started under no load conditions, regardless of the position occupied by the. press ram. f

It is an object of this invention to provide a control system including a variable delivery pump having its shaft connected to the driving 4 shaft of a prime mover, in which the pump is automatically held in substantiallyV neutral or no delivery position until the prime mover has been brought up to the desired operating speed.

It is still another object of the invention provide a control system for use in connection with hydraulic systems, which includes a variable delivery pump drivingly connected with a prime mover, and pilot fluid operated servomotor means for controlling the delivery of said pump, and in which, responsive to the starting of said prime mover, the pilot uid from said servomotor means is by-passed to an exhaust until said prime mover has reached a predetermined minimum speed.

of the servomotor means for a predetermined time following the starting of the prime mover. After the said predetermined time the fluid supply for the plunger is re-established to actuate said plunger for shifting the pump on stroke. The press ram, controlled by the delivery of the pump, is then returned to its initialposition. In this way, the prime mover is prevented from starting under load, thereby protecting said prime mover 0 and reducing the power for actuating the same.

The control system according to the invention is also provided with safety means which prevents the operator from accidentally starting a working stroke of the press ram before the prime mover has come up to speed. To this end, the electric circuit for controlling the operation.of the ram and the driving motor for the pump, which includes 'a starter button for starting the motor or prime mover and a forward lbutton for starting the working stroke of the ram, is so arranged that closing of the forward button is not effective until after energzation of the motor and the elapse of the above mentioned predetermined time.

According to still another feature of the in- Structural arrangement Referring now to the drawings yin detail, the structure disclosed therein comprises a press cylv inder I having reciprocably mounted therein a press ram 2, which has connected thereto a press platen 3.. The platen 3 is provided with an arm 4 adapted t0 engage a collar 5 adjustably mounted on a push rod 6, which is reciprocably mounted and guided by any convenient guiding means. Also adjustably mounted on the push rod 6 is a collar 5a adapted to engage the arm Ia on the press cylinder I, to thereby limit the downward movement of the push rod 6.

Furthermore adjustably mounted on the push rod 6 is a collar 1 adapted to engage the arm 8 of a three-arm lever, generally designated 9. A second arm of the lever 9 is pivotally connected with a link I0 which, in its turn, is connected to an armature I I adapted to be actuated by the main solenoid I2 in such a manner as to cause the armature II to move downwardly, thereby shifting the three-arm lever 9 in clockwise direction about the pivot I3. The third arm of the lever 9 is connected through a link system, vgenerally designated I4, with a control rod I5, which has connected thereto a ange I6 an a valve member I1.

' The valve member I1 is reciprocably mounted in a servomotor plunger I8 which, in its turn, is reciprocably mounted in the servomotor casing I9 connected, in any convenient manner, with the pump 20, constituting a pump of reversible variable delivery. The pump 20 may be of any standard design, for instance of the radial piston type or the radial vane type.

The servomotor plunger I8 has a larger piston portion 2| reciprocable in the bore'22 of the casing I9 and a smaller portion 23 reciprocable in the bore 24 of the casing I9. The smaller portion 23 of the plunger I8 is provided with an annular groove 25 which communicates through longitudinal passageways 26 with the left side of the piston portion 2l, The said left side of .-he piston portion 2I constitutes the larger eective area thereof, while the oppositely located area of the piston portion 2| is smaller and is adapted, through bores 21, to communicate with the bore 28 in which the valve member I1 is reciprocable. The valve member I1 controls the bores 21 and the annular groove 25. The bore 28 is furthermore adapted to communicate with the bore 24 through the passageways 29.

The right hand end of the bore 22 is connected with a. conduit 30 comprising an adjustable choke 3I and leading to a control valve, generally designated 32. The choke 3I is adapted to be by-passed by fluid passing from the valve 32 toward the servomotor casing I9 through the conduit 33 and check valve 34 in said conduit.-

Branching oif from the conduit 38 is a conduit 35 comprising a check valve 36 and leading to the left hand end of the bore 22. 4

The bore 24 in the servomotor casing I9 is furthermore connected through a conduit31 with a fluid reservoir or tank 38. Branching oil.' from the conduit 3'I -are conduits 39 and 40 respectively leading to the right hand end and the left hand end of the valve casing 4I of the control valve 32. Reclprocably mounted in the casing 4 I is a valve member 42 with piston portions 43 and 44 and an armature 45 adapted to be controlled by the solenoid SI.

The valve member 42 is continuously urged, by means of a spring 46, into its left hand position, shown in the drawing, in which the conduit 38 communicates with the conduit 41 which is connected to the pressure side of a pilot pump 48. 'I'he pilot pump'48, which may be of any standard design, and may be a variable delivery or a' constant delivery pump, has its suction side connected through the conduit 49 with the tank 38.

Branching off from the conduit 41 is a conduit 60 comprising an adjustable pressure relief valve 5I and leading to the tank 38.

When the solenoid SI is energized, the valve member 42 moves into its right hand end position, in which the conduit 41 communicates with the conduit 39, while the conduit communicates with the conduit 48.

'I'he servomotor plunger I8 has furthermore arranged therein a spring 52, which continuously urges the valve member I1 to move toward the left with regard to the casing I8. 'I'he pump 26 has furthermore connected thereto a casing 53

housing centering springs

54 and 55, which act upon a control rod 56 connected to the ilow control member of the pump 20, so as to urge the -pump 20 into and tend to hold the same in its neutral or no delivery position.

One side of the pump 28 is connected through a conduit 51 with the upper portion of the press cylinder I,'while the lower portion of the press cylinder I is connected through conduit 58 with the other side of the pump 28. Also connected with the upper portlonof the press cylinder I is aiconduit 59 leading to a tonnage control valve 60, which latter is connected, through the conduit 6I, with the tank 38. The' tonnage control 'valve 60, which may be of any standard design,

for instance of the type disclosed in U. S. Patent No. 2,224,957, comprises a normally closed 'switch 60a (see Figure 2), which opens In response to a predetermined pressure in the conduit 59 and automatically closes again as soon as the pressure in the conduit 59 drops below the value o! said predetermined pressure. y

Extending into the upper portion of the press cylinder I is asurge valve 62, of any conventional design, for instance of the type disclosed in U. S. Patent No. 2,193,248, and adapted, in response to a suctio'n eifect in the upper portion of the press cylinder I, to open so as to eiect fluid connection between the tank 38 and the upper portion of the cylinder I. When a predetermined pressure develops in the upper portion of the cylinder I, the surge valve 62 closes. The surge valve 62 is connectedwith a pilot line 63 communicating with the conduit 58. The surge valve 82 is adapted, in response to a predetermined pressure in the pilot line 63, to open for establishing fluid connection between the tank 38 and the upper portion of the press cylinder I. Branching oi! from the conduit 63 is a conduit 64 comprising a check valve 65 adapted to allow the ow of fluid from the tank 38 into the conduit 64, while preventing the ilow of iluid in the opposite direction.

As shown in Figure 1, the pump 20 is directly driven by a motor 11 while the pilot pump 4I is likewise directly driven by a second motor 18. 'As will be seen in the description of the wiring diagram of Figure 2 which follows, the motors 18 and 11 are permanently connected in parallel and operate in unison. Both pumps could, therefore, be

operated from a single motor as is indicated by the dotted line portion at the upper right of Figure 1. Hence, it is optional, and in no way affects this invention, whether the pumps are separately driven by individual motors parallelly connected or from a single motor drivingly connected to both.

Referring now to Figure 2, illustrating the wiring diagram for the system of Figure l, the main supply line 86 has connected thereto the line 81, which is adapted to be electrically connected with the line 68 by closure of the line switch 69. The line 68 is connected through the normally closed stop switch 18 with the line 1i, which latter is adapted, by closure of the forward switch 12, to be connected with the line 13. The line 13 is connected through the normally closed switch Rid with the line 14, comprising the main solenoid i2 and connected to the main supply line 15. Also connected to the Amain supply line' 15 is the line 18 leading to one terminal of the main motor 11, while the other terminal of the motor 11 is connected to the line 18. The main motor 11 has its driving shaft connected to the shaft of the pump 20 so that rotation of the motor 11 causes rotation of the pump 20. Preferably the driving shaft of motor 11 is connected to the shaft of pump .'iil by a flexible coupling. Arranged parallel to the motor 11 is an auxiliary or pilct'pump motor 18, having one terminal connected through line 80 with the line 18, while the other terminal is connected through line 8i with the main supply line 15. The motor 19 has its driving shaft connected with the shaft of the pilot pump 48 so that rotation of the pilot motor 18 causes operation of the pump 88.

Theline 18 is connected with a line 82 comprising the contactor solenoid R2, and having one end connected to the main supply line 15, while the other end leads to a terminal of a normally open contactor blade Rib which, in closed position, connects the line 82 with the line 83. The line 83 is connected with the line 1i and communicates through the normally closed tonnage control switch 88a. with the normally open main solenoid switch i2a. When the switch i2a is closed, the tonnage control switch 60a is connected through the normally closed reverse button 84 with the line 85, which latter is connected with the line 134 The line 83 is also adapted to be connected with the line 82 by closure of the contactor switch R2a.

Connected to the line 83 is furthermore a line 88 adapted, by closure of the starter button 81, to electrically communicate with the line 88, which latter communicates with the line 89 through the normally' closed timer switch Ti. The line 88 includes a contactor Ri and is connected with the main supply line 15. Also connected to the main supply line is one terminal of a timer T, the other terminal of which is connected to the line 89. Closure of the contactor switch Ria is adapted to eiect connection between the line 83 and the line 88. Furthermore connected with the line 83 is a line 90 adapted, by closure of the contactor switch Ric, to be connected with the line 9i, which latter comprises the solenoid Si, and is connected with the main supply line 15.

Branching off from the line 9i is a line 92 adapted, by closure of the limit switch 83, to be connected with the line 83. The limit switch 93 is normally held in open position and is closed by engagement of the roller 94 (Fig. 1) with the cam 85 carried by the press platen 3.

Operation sumed to occupy a position intermediate its end positions so that the valve member I1 is moved somewhat to the left with regard to the position in which it is shown in Figure 1. It may furthermore be assumed that the driving motors for the pumps 2li and 48 are ata standstill.

If it is now desired to cause the press ram 2 to perform a working cycle, it ls first necessary to retract the ram 2 to its uppermost or retracted position, i. e., the position shown in Figure 1.

To this end, the operator closes the line switch 89 and furthermore closes the starter button 81. As 'a result thereof, the energizing circuit for the contactor Ri ands the timer T is closed, which circuit comprises the main supply line 66, switches 69 and 18, line 83, now'closed starter button 81,

lines

88 and 89, contactor Ri and timer T, and the main supply line 15. Energization of the contactor Ri causes closure of the contactor switches Ria, Rib and Ric, while causing the contactor switch Rid to open. Opening o f the contactor switch Rid has no effect at this time.

Closure of the contactor switch Ria establishes a holding circuit for the contactor Ri and the timer T so that the contactor Ri and the timer T will remain energized when the starter button 81 is released and thereby returns to its open position. The said holding circuit comprises the main supply line 66, switches 89 and 10, line 83, contactor switch Ria, lines 88 and 89, contactor Ri and timer T and the main supply line 15. The timer T is now operating for a predetermined time for which it has been set. This predetermined time corresponds to a period necessary to bring the main motor 11 up to a desired speed. After this said predetermined time has expired, the timer switch Ti opens temporarily to thereby stop the timer T, and immediately thereafter the timer switch Ti again closes.

Since, as mentioned above, the contactor switch Ric closes, the energizing circuit for the solenoid Si is closed, which energizing vcircuit comprises the main supply line 66,

lines

61, 88, 1i, 83 and 98, the now closed contactor switch Ric, line 9i, solenoid Si and main supply line 15.

Energization of the solenoid Si causes the valve member 42 to move toward the right against the thrust of the spring 48, thereby establishing fluid connection between the conduits 39 and 41, while simultaneously connecting the conduit 30 with the conduit 48.

Since, as likewise mentioned above, the contactor switch Rib closes, the energizing circuit for the contactor R2 is closed, which energizing circuit comprises the main supply line 66,

lines

61, 88, 1i and 83, the now closed contactor switch Rib, line 82, contactor R2 and the main supply line 15. Energization of the contactor R2 causes closure of the contactor switch R2a, thereby establishing a holding circuit for the contactor R2, which maintains the latter energized When the contactor switch Rib opens.

-tion of the main motor 11 merely rotates the rotor of the pump 20 without, however, causing Simultaneously with the contactor R2, also the motors 11 andA the pump 28 to deliver fluid. In other words, at this time no load acts upon the motor 11. and the motor 11 gradually increases its speed until it reaches its normal speed. Since, as mentioned above, the valve member 42 is in its right hand end position. operation of the motor 18 causes the pump 48 merely to run idle, and the fluid delivered by the pump 48 is passed through conduits 41, 39 and 31 into the tank 38. In other words, the fluid delivered by the pump 48 is merely circulated without performing work.

When the motor 11 has reached its desired or normalspeed, the timer switch TI, as explained above, opens temporarily, thereby breaking the holding circuit for the contactor RI and the timer T. This causes deenergization of the timer T and the contactor RI and, as a result thereof, the contactor switches Rla, RIb and Rlc open, whereas the contactor switch RId closes. the timer switch TI then again closes, it will not re-establish theenergizing circuit for the contactor RI and the timer T.

Opening of the contactor switch RIb-has no eiect at this time, since the contactor R2 remains energized by the holding circuit established by the contactor switch R2a. Consequently, also the motors 11 and 18 remain energized and continue to drive the

pumps

28 and 48.

Opening of the contactor switch RIc causes deenergization of the solenoid SI, so that the spring 46 returns the valvemember 42 to the position shown in Figure- 1, in which fluid connection is established between the conduits 41 and 38, while the fluid connection between the conduits 41 and 38 is interrupted. Therefore,.the fluid delivered by the pump 48 now passes through the conduit 41, valve 32, conduit 33, check valve 34 and conduit 38 into the bore 22, where it acts upon the smalleror right hand area of the piston portion 2 I. This causes the plunger I8 to move toward the left, thereby placing the pump28 on retraction stroke. The iluid expelled during the leftward movement of the plunger I8 from the left hand side ofthe bore 22 passes through the passageways 26, bore 28, passageways 28 and conduit 31 into the tank 38. The pump 28 now delivers pressure fluid through the conduit 58 into the lower Iportion of the press cyl.. inder I and causes the ram 2 to move upwardly.

The iluid expelled during this upward movement of the ram 2 from the upper portion of the press cylinder I passes, in part, through the conduit 51 to thenow suction side of the pump 20 and escapes, in part, through the surge valve $2 into the tank 38. It will be appreciated that at this time the surge valve 82 has been opened by the pressure conveyed from the conduit 58 through the pilot line 83 to the surge valve 82.

When the ram 2 approaches its upper or retracted position, the platen arm 4 engages the collar 5 and thereby shifts the push rod 8 into the position shown in the drawing, so that the three-arm lever 8, through its linkage I4, causesl the valve member I1 to move toward the right, with regard to the position it last occupied, into the position shown in Figure 1.

Since, as previously mentioned, the plunger I8 was shifted toward its left hand position, the rightward movement of the valve member I1 brings-about iluid connection between the right side or smaller effective area of the piston portion 2| and the left side or larger effective area of the said piston portion. Consequently, pressure uid passes from the conduit 38 through the bores 21 and 28 into the left hand end of the bore 22 where it acts upon the larger efective area of the piston` portion 2| and shifts the plunger I8 toward the right until it occupies the position shown in Figure 1. The pump 28 is then When in its neutral or no delivery position and, since now fluid is neither delivered to nor withdrawn from the press cylinder I, the ram 2 comes to a stop. The ram 2 is now in its position for starting a pressing cycle. The iluid delivered by the pilot pump 48 is now by-passed through the pressure relief valve 5I into the tank 38.

To start a. working cycle of the ram 2, the operator closes the forward switch 12, thereby clos- `41, 33 and 38 and the bores 21 and 28 and causes the plunger I8 to move toward the right against the thrust of the centering

springs

54 and 85. As a result thereof, the pump 28 is placed on forward stroke, and now delivers fluid through the conduit 51 into the upper portion of the press cylinder 'I, while withdrawing fluid through the conduit 58 from the lower portion of the press cylinder I.

The press ram 2 now moves downwardly by gravity as fast as iluid is withdrawn from the lower portion of the cylinder I. The suction effect created in the upper portion oi.' the cylinder I maintains the surge valve 82 open, so that the 'iiuid delivered by the pump 28 into the upper portion of the cylinder I is supplemented by fluid passing from the tank 38 through the surge valve 82 into the cylinder I. When the ram 2, during its downward movement, approaches the position at which the platen 3 or a die connected thereto engages the work piece to be shaped, the cam 85 engages the roller 84 and closes the switch 83. Closure of the'switch 83 establishes a by-pass circuit for the now open contactor switch RIc, thereby closing the energizing circuit for the solenoid SI. Energization of the solenoid SI causes the valve member 42 to move toward the right, thereby again effecting fluid connection between the conduits 41 and 38, while connecting the

conduits

38 and 48 with each other. Since now fluid' may escape from the left hand portion of the bore 22 through the conduit 35, check valve 38, conduit 38, choke 3| and conduits 48 and 31 into the tank 38, the centering

springs

54 and 55 move the plunger I8 toward the left, thereby decreasing the withdrawn from the lower portion of the cylinder I, so that the ram 2, in its downward movement. is slowed down.

As soon as the cam has passed the roller 84, at which` time the platen or a die connected thereto, has engaged a work piece, the switch 83 again opens. As a result thereof, the energizing circuit for the solenoid SI is again interrupted and the spring 48 moves the valve member 42 again to the left, thereby restoring the position shown in Figure 1.of the valve 32.

Pressure uid delivered by the pump 48 now `amanece again shifts the plunger la toward the right in the manner described previously, thereby returning the pump to its full delivery forward Astroke position. The ram 2 now performs its actual pressing stroke.

When, at the end of the pressing stroke, a predetermined pressure has built up in the upper yportion of the press cylinder I, this pressure is conveyed through the pilot line 59 to the tonnage control valve 80 and causes the tonnage control switch 80a to open. This breaks the holding circuit for the main solenoid I2 so that the latter becomes deenergized. As a result thereof, the spring 52, which was previously loaded, shiftsl the valve member I1 toward its extreme left hand position, thereby causing the valve member I1 to release the annular groove 25, while preventing iluid connection between the larger and the smaller eective areas of the piston portion 2|. As a result thereof, the fluid delivered by the pump 48 into the conduit 30 now acts upon the smaller effective areaof the piston portion 2| and causes the plunger I8 to move toward the left, while the fluid expelled during this leftward movement of the plunger i8 from the left hand portion of the bore 22 passes through the passageways 26, annular groove 25, passageways 29 and conduit 31 into the tank 38.

The pump 20 is now in its retraction stroke position, in which it delivers pressure fluid through conduit 58 into the lower portion of the press cylinder I, and causes the ram 2 to move upwardly, while the fluid expelled from the upper portion of the cylinder I passes, in part, through the conduit 51 vto the now suction side' of the pump 28 and, in part, into the tank 38 through the surge valve 82 which, as previously explained, has been opened by pressure fluid conveyed from the conduit 58 through the pilot line 63 to the surge' valve 62. 'The ram 2 now performs its upward movement or retraction stroke in the man-y ner set forth above in connection with vthe description of the conditioning of thepress for a working cycle after a period of idleness.

When the ram 2 reaches its retracted' position,

it causes the 4pump 20 to move into neutral or no delivery position and, thereby, comes to a stop, as was also previously explained. p

If it is desired, during the advancing stroke of the press ram, to returnthe ram to its retracted position before theramjha's reached the end of its forward stroke, it is merely necessary to open the reverse switch 84, thereby breaking the energizing 1 circuit for the main solenoid I2, so that the spring 52 in the servomotor plunger I8 causes the pump to move, into retraction stroke position. The ram then performs a retraction stroke in the manner described above.

If it is desird, in case Aof. an emergency, or for some other reason, to stop the press ram atits respective position, the operator opens the stop switch 10, thereby deenergizing all parts of the electric circuit including the pump motor 11.

Particular attention is directed to the fact that if the press ram, Adue to leakage during a period of idleness of the press, has moved -to a position intermediate its end positions, and if now the operator, in order to return the ram from this intermediate position to its retracted position, ac-

cidentally closes the forward switch 12 instead of the starter button 81, this will not result in an accidental downward movement of the -ram 2. All that will happen is that the main solenoid i2 will be energized, thereby shifting the valve member I1 toward the left. However, since this will not close the energizing circuits for the main motor 11 and the auxiliary or pilot pump motor 19, the pumps 20 and 48 will not be started, and no movement of the ram will be brought about.

If the operator now, noticing that the motors 11 and 19 remain at a standstill, closes the starter button 81 'simultaneously 'with the forward button 12, this will likewise not bring about an accidental downward movement of the ram 2.

It will be appreciated that, as soon as the starter button 81 is closed, the contactor RI is energized, thereby opening the contactor switch l Rid, so that the main solenoid I2 is deenergized and the spring 52 moves the valve member I1 to its left hand end position. However, since the energization of the contactor RI also causes energization of the solenoid SI, as previously explained, with the result that the valve member 42 is moved to its right hand end position, the

fiuid delivered by the pump 48, when the motorA 19 is energized, is by-passed to the tank 38 and, therefore, does not bring about a movement of the plunger I8. On the other hand, the

springs

54 and 55 maintain the pump 20 in its neutral position, so that the energization of the main motor 11 merely rotates the rotor of the pump 20 without load. In other words, the condition .by two separate motors, it will be appreciated that, if desired, the motor 19 may be omitted and the pump 48 drivingly connected with the motor 11, without in any way affecting the operation' of'A the control system described above.

If desired, the pilot pump'4'8 may be replaced by an accumulator, in which instance the conduit 39 and the motor 19 with the lines 80 and 8| will be omitted. It will then beappreciated that when the solenoid SI is energized, the escape of uid from the accumulator is prevented, whereas when the solenoid SI is deenergized and the valve member 42 occupies the position Ashown in-Figure 1, fluid connection is established between the accumulator and the conduit 39.

While the system according to the invention has been described in connection with automatic manually when the pump 'motor 11 has reached its Vdesired speed.;

It will also be appreciated that, if the above described slow-down arrangement for Aslowing down the ram 2 at. a predetermined point of travel thereof should not be required or be ren placed by other means, the conduits 33 and 35 together with thel valves 34 and 3B and also the choke 3| and switch93 may be omitted. In this instance, the bore shown in Figure 1 at the left side of the larger piston portion 2| and directly communicating with the conduit will either be omitted or plugged ,without affecting the control system of the present invention for preventing the starting of the pump motor 'I1 under load.

It will be understood that I do not wishl to be limited by the specific structure shown in the drawings and described in the specification, except as required by the appended claims.

Having thus fully described my invention, what I claim as new anddesire to secure by Letters Patent is:

l. In a hydraulic system, a double-acting plunger, a fluid source of reversible delivery for supplying actuating iluid to said plunger, a prime mover drivingly connected to said source, yielding means normally urging said source toward neutral, a fluid operable servomotor normally positioning said source to deliver to said plunger in one direction, control means energlzable to move said servomotor to position said source to deliver to said plunger in the other direction, means operated by said plunger in a predeterminedposition of movement thereof in said one direction for actuating said servomotor for moving said fluid source into no delivery position, and

means operable automatically in response to the starting of said prime mover for exhausting said servomotor whereby said yielding means moves said source to neutral and for interrupting the energizing circuit to said control means to prevent movement of said servomotor into position to move said source to deliver to said plunger in the said other direction upon the restoration of the supply of pressure fluid to said servomotor, said automatically operable means being enective for a predetermined length of time.

2. In a hydraulic system, a vertically reciprocable plunger, a pump of reversible delivery connected te supplsr said plunger, meanscontinuously urging said pump toward neutral, a prime mover directly connected with said pump. a fluid operable servomotor associated with said pump normally urging the same to deliver to said plunger to move the same upwardlyand adapted for actuation by said plunger in a predetermined' upper position thereof for moving said pump to neutral, control means energizable to actuate said servomotor to move said pump to deliver to said plunger to move the same downwardly, a source of nuid for supplying said servomotor, means` operable automatically in response to the starting of said prime mover forinterrupting the supply of :duid to said servomotor while simultaneously exhausting said servomotor and for interrupting the energizing circuit for said control means, said automatically operable means being effective for a predetermined length ofvtime during which said prime mover comes up to speed, and other means operated by said plunger during its downward movement for momentarily at least partially exhausting said servomotor for momentarily slowing down the downward movement o! said plunger.

3. In a hydraulic system, a vertically reciprocable double-acting plunger, a variable delivery pump for supplying fluid to said plunger, yielding means normally urging said pump toward neutral, a iiuid operable servomotor associated with said pump normally urging the same to deliverto the underneath side'of said plunger and adapted for actuation by said plunger in a predetermined upper position thereof for moving said pump to neutral, first electrical means energizable to move said servomotor to position said pump to deliver to the upper side of said plunger,

l2 iluid to said servomotor, a prime mover directly connected to drive said pump, an electric starter for `initiating movement of said prime mover, valve means normally connecting said auxiliary source with said servomotor, second electrical means energiz'able to move said valve means to exhaust said servomotor whereby it loses effect on said pump, a control circuit interlocking said electrical means and said starter means and operable upon energization of the latter to open the energizing circuit for said nrst electrical means and to energize said second electrical means, and after a predetermined length of time to re-establish the energizing circuit for said ilrst electrical means and to de-energlze said second electrical means. f

4. In a hydraulic system, a reciprocable plunger,

` fluid operable advancing and retracting means reversing the delivery thereof to selectively supply pressure iluid to said advancing and retracting means, an auxiliary fluid source for supplying actuating fluid to said servomotor means to move said pump into delivery position in either of two directions to control the direction of flow therefrom, centering means continuously urging said pump into and tending to hold the same in substantially neutral or no delivery position, means operated by said plunger at least in one position thereof to actuate said servomotor for moving, and holding said pump in neutral position as long as said plunger is in said one position, electric motor means drivingly connected with said pump, starter means for initiating operation of said motor means, control means for actuatingsaid servomotor means to move said pump into delivery 'position to supply pressure iluidstosaid advancing means, and electrically actuated means operatively connected with said startenlmeans and said control means and responsiveltgjlhe actuation of said starter means and operab ffor a predetermined length of time to prevntroperative operation of said control means and for preventingdelivery of iluid from said auxiliary fluid source to said servomotor means.

5. In a hydraulic system, a reciprocable plunger having iluid'operable advancing and retracting means, a pump of reversible delivery for supplylng actuating fluid to said means, iiuid operable servomotor. means for positioning said pu'mp to deliver ln either direction, means for supplying actuating iiuid to said servomotor including valve means movable to exhaust said servomotor, centering means continuously urging said pump toward neutral position, means operated by said 50 plunger at least in one position thereof to actuate said servomotor for moving and holding said pump in neutral position as long as said plunger is in said one position, a prime mover drivingly of said plunger to hold said servomotor in neutral position until said prime mover reaches a predetermined minimum speed, and other means operable by said plunger during the movement thereof for momentarily actuating said an auxiliary fluid source for supplying actuating valve means to exhaust said servomotor.

6. In a hydraulic system, a reciprocable plunger having fluid operable advancing and retracting means, a pump of reversible delivery for supplying actuating uid to said means, iluid operable servomotor means associated with said pump for determining the direction of delivery thereof, means for supplying actuating fluid to said servomotor including valve means actuatable to exhaust said servomotor, centering means continuously urging said pump toward neutral position, control means selectively operable to actuate said servomotor to move said pump todeliver to said advancing area, means operated by said plunger in its retracting direction of movement to actuate said servomotor for moving said pump toward neutral position, a prime mover drivingly connected with said pump, starter means for energizing said prime mover, and means interlockingr said starter means and said control means and operable for a predetermined time after the actuation of said starter means to initiate movement of said prime mover to prevent actuation of said control means, during which time said prime mover reaches a predetermined minimum speed, said means also being operable during the same period to actuate said valve means to` exhaust said servomotor.

` 7. In a hydraulic system, a reciprocable plunger having fluid operable advancing and retracting means, a pump of reversible variable delivery for supplying pressure fluid selectively to said advancing or said retracting means, fluid operable servomotor means associated with said pump for reversing the delivery thereof to selectively supply pressure uid to` said advancing and retracting means, an auxiliary uid source for supplying actuating fluid to said servomotor, centering means continuously urging said pump into and tending to hold the same in substantially neutral or no delivery position, means operated by said plunger at least in one position thereof to actuate said servomotor for moving and holding said pump in neutral position as long as said plunger is in said one position, an electric motor drivingly connected-to the drive shaft of said pump for positively driving the same, starter means for starting operation of said electric motor, electrically operable control means operable in response to the operation of the said starter means and eiective for a predetermined length of time for preventing delivery of iluid to said servomotor means to thereby prevent movement of said pump thereby into delivery position upon loss of effect of said plunger to hold said servomotor in neutral position, a second starter means for causing said servomotor. means to place said pump into position for delivering pressure iliiid to said advancing means, and means actuated in response to the actuation of said iirst starter means to render such second starter means ineffective for a predetermined time to permit said prime mover to reach a predetermined minimum speed.

8. A control system for a hydraulic pu'mp which is drivingly connected to a prime mover to prevent the pump from being placed on a delivery stroke before the prime mover has reached a predetermined minimum speed that includes in combinatiom servomotor means operably connected to the pump to place the same on a delivery stroke in either direction or in neutral, yielding means normally urging said pump into neutrai position, control means operably connected to said servomotor having on position for placing said servomotor in position to place said pump on delivery stroke in one direction and a second position to place said servomotor in position to place said pump on delivery stroke in the other direction, means for supplying iluid to said servomotor for actuating the same in response to movements of said control means, and other means operable automatically upon initiation of movement of said prime mover for preventing the supply of :duid to said servomotor thereby to permit said yielding means to position said pump in neutral and to render said control means ineffective to change the position of said servomotor, said other means being operable for a predetermined length of time to permit said prime mover to attain a predetermined minimum speed.

9. A control system for a hydraulic pump that is directly connected to a prime mover to prevent the pump from being placed on a delivery stroke before the prime mover has reached a predetermined minimum speed, that includes in combination, a pump of variable delivery, a prime mover directly connected to the pump for driving the same servomotor means operably connected to the pump to place the same on a delivery stroke or on neutral, means normally urging said pump into neutral position, control means operably connected to said servomotor having one position for placing said servomotor in position to place said pump on a delivery stroke and a second position to place said servomptor in position to place said pump on neutral stroke, electrically operated means for preventing delivery of actuating iiuid to said servomotor, means for energizing said prime mover to start said pump and including means to operate said electrically actuated means to prevent delivery of actuating uid to said servomotor whereby to prevent said servomotor from changing the position of said pump from neutral position as retained therein by the said aforesaid means irrespective of` the position of said control means, means operable after a period of time during-which said motor has attained a predetermined minimum speed for rendering said electrically actuated means ineiective topermit flow of actuating iluidV to said servomotor for actuation in response to said control means, means for rendering said control means active to position said servomotor in a position to place said pump on a delivery stroke, and means actuated in response tosaid means for energizing said motor for rendering said last-mentioned means ineffective.

10. In a hydraulic system, a iluid operable motor, a pump of variable delivery for supplying fluid to said motor, means continuously urging said pump toward neutral, iiuid operable servomotor means for moving said pump to delivery position, a prime mover directly connected with said pump, an auxiliary source of pressure uid for supplying said servomotor, valve means connecting said auxiliary source with said servomotor, means responsive to the starting of said prime mover for actuating said valve to prevent the supply of iluid from said auxiliary source of said servomotor', said means being eiective during a predetermined period of time to allow said prime mover to come up to speed under no load, means operable in response to a predetermined movesaid pump toward neutral, fluidoperable servomotor means for moving said pump to delivery position, a prime mover directly connected with said pump, an auxiliary source of pressure iluid for supplying said servomotor, valve means connecting said auxiliary source with said servomotor, means responsive to the starting of said prime mover for actuating said valve to prevent the supply ofiluid from said auxiliary source to said servomotor, said means being effective during a predetermined period of time to allow said prime mover to come up to speed under no load, means operable iny response to a predetermined movement o! said motor for actuating said valve` means to interrupt the supply of ,fluid to said servomotor while exhausting the same, ilow restricting means connected to control the rate Aoi' exhaust from said servomotor; and means responsive to a predetermined further movement oi' said motor for again bringing about the supply oi' actuating fluid from said auxiliary source to said servomotor.

12. In a hydraulic system, the combination with a pump having pressure operated delivery control means, yielding means continuously urging said pump toward neutral and eil'ective to so position said pump in the absence of pressure in said control means, power means directly connected to drive said pump, a source of pressure iiuid, a valve connecting said source of pressure iluid with said control means, valve actuating means operable automatically in response to the starting of said power means for actuating said valve to prevent the supply oi' fluid from said source to said control means whereby said pump is retained in neutral by said yielding means, and means automatically responsive to the elapse of a predetermined period of time following the starting o! said power means for rendering said valve actuating means for a predetermined time after the starting oi the power means to actuate said valve means for disconnecting said control means trom said source and for connecting it instead with exhaust, means permitting free supply of fluid from said valve to said control means and a restricted exhaust o! uid from said control means, and other means selectively operable for energizing said valve actuating means irrespective of whether or not said prime mover is being started.

14. In combination with a vertically reciprocableuid actuated plunger, a iluid source for supplying actuating fluid to said plunger, means normally urging said source into neutral position for preventing the delivery of tluidto or the removal of iluid from said plunger, control means REFEBENCES CITED The following references are of record in the ill'e of this patent:

'.UNITED STATES PATENTS Number Name Date 473,949 McGowan May 3, 1892 823,118 Gurney June 12, 1906 1,847,229 Swanson Mar. l, 1932 1,910,000 Buehler May 23, 1933 1,911,105 Buehler May 23, 1933 2,145,404 Osborne Jan. 3l, 1939 2,167,623 Britter Aug. 1, 1939 2,184,665 Ernst Dec. 26, 1939 2,260,175 Ernst Oct. 2l, 1941 2,280,291 Jaseph Apr. 21, 1942 2,286,358 Geiger June 16, 1942 Tucker Nov. 24, 1942 I