US2280190A - Self-centering servomotor - Google Patents

Description

April 21, 1942.

w. ERNST .SELF-CENTERING SERVOMOTOR Original Filed Oct. 21, 195'? 3Sheets-Sheet l v M am JW 2. y R 3 3 n .7 Nm & M a w w INQ 3. 5.3. Q.

April 21; 1942. ERN T 2,280,190

SELF-CEN'PERING SERV OMOTOR Original Filed Oct. 21, 1957 s Sheets-Sheet 2 Jvvueww WALTER ERNS'I;

'Ziril 21, 1942.

w. ERNST SELF- CENTERING' S ERVOMOTOR 3 Sheets-Shed 3 Original Filed 0ct.'2l, 193" v WALTER ERNST,

Patented AprLZI, 1942.

SELF-CENTERING SERVbMOTOR I Walter Ernst, Mount Gilead, Ohio, assignor to l The Hydraulic Development Corp. Inc., Wilmington, Del., a corporationof Delaware Original application October 21, 1937, Serial No.

Divided and this application Novembe! 6, 1939, Serial No. 302,99

7 Claims. 103-38) This invention relates to hydraulic machinery,

and in particular, to control devices and safety devices for hydraulic pump circuits.

The primary object of the present invention is to provide an improved servomotor for controlling the hydraulic pump circuit which operates a hydraulic press.

Still further objects are to provide an attach ment including a lever system by which the platen, or other moving part of the press, controls the servomotor, which in turn, initiates movement of the platen; to'provide a combined variable delivery pump and servomotor control mechanism, in the form of a compact structure of simple design and callingfor a relatively small number of castings; to provide an improved servomotor having a piston secured directly to and arranged in line with the flow-control member of the variable delivery pump; and to provide an improved servomotor and operating mechani'sm in which the valve for controlling the servoenlargement engaged on opposite sides by sliding collars, urged thereagainst by'springs. In the event that a failure of power occurs, one of these springs will force the rod and consequently the flow-control member or shiftring of the pump, to

its neutral position, thereby preventing the compression of the fluid by the weight of the press platen and piston, and consequently preventing the reverse operation of the pump as a motor when receiving this compressed fluid. The arrangement of the servomotor piston and control valve therefor on the same side of ,the pump shiftring prevents any possible entrapment of fluid, and consequently enables the centering springs to perform their workwithout being impeded by fluid entrapment.

Hitherto, when variable delivery pumpswere used in hydraulic press circuits, a failure of power would terminate delivery of pressure fluid to the main plunger, which would then start to drop by gravity, compressing the, fluid beneath it and motor piston is, actuated in response to themovef: ments of the press plunger through a lever system and thelatter is additionally controlled by plunger starting, reversing and stopping mechanism.

This application is Ia-division of my application Ser'. No. 170,250, filed pctober 21, 1937, and entitled self centeringservomotor.

In the drawingsz' v Figure 1 is a side elevation, partly in longitudinal section, of a variable delivery pump with the automatic centering device, servomotor and ,control mechanism of this invention, the pump through the tonnage control valve for regulating the pressing force of the'press.

In general, the servomotor control and automatic centering arrangement of this invention consistsof a centering rod attached tothe flow control member or shiftring of the variable depiston l'he centering rod is provided with an forcing the pressure fluid thus produced into the pump,,causing the latter to act as a motor. Even where the main pumpwas. in a neutral position at the time of the power failure, the pressure of the fluidthus produced by the weight of the platen and pressing plunger has been suflicient to force the pump onto stroke, and then to drive it backward like av motor. The result; of such operation was to cause the press platen to coast f downwardly at a rapid speed, thereby creating a hazard for the operator, whose hands may'have been in the press at the moment this occurred.

Furthermore, hydraulic failures hitherto have also caused a similar effect by the failure of a relief valve or a hydraulic line, so that the con trol mechanism failed to operate properly.

Referring to the drawings in detail, Figured shows a hydraulic press circuit containing a variable delivery pump, generally designated l, arranged to drive a press, generally designated 2, having a fluid or surge tank, generally designated 3. A main cylinder release and by-pass valve, generally designated 4, causes the pressure in the main cylinder of the press to be released at the moment of reversal of the pump l, and also causes the dischargeof the pump I to be temporarily by-passed through this valve 4 into the surge tank 3. The details of this valve 4 form no part of the present invention.

Also shown in the circuit of Figure 3 and more fully shown in the partial circuits of Figures 1 and 2, is a surge valve, generally designated 5,

during the initial coasting of the main platen. thereby prefilling the main cylinder with' fluid until the platen encounters resistance. This surge valve 5 is described in the Ernst Patent No. 1,892,568, of December 27, 1932, and its details likewise form no part of the present invention. The surge valve 5, as shown in the above-mentioned patent,,is adapted to be forcibly opened upon the return stroke of the press so as to release fluid directly from the main cylinder of the press 2 into the surge tank 3.

The circuit shown in Figure 3 likewise contains a pilot pump generally designated 6, for delivery of pilot pressure fluid to the servomotor of the variable delivery pump I. The details of the pilot pump 6 and itsdriving connection with the variable delivery pump I form no part of the present invention and are disclosed and claimed in my Patent No. 2,168,669, granted August 8, 1939. The circuit of Figure 3 also con tains a relief valve generallydesignated 1, connected to the pilot circuit. This relief valve 1 is described in Ernst Patent No. 2,086,295, of July 6, 1937, and its details form no part of the present invention.

Within the surge tank 3 are pressure relief valves 8 and 9. connected on opposite sides of the main cylinder and by-pass valve 4, a check valve I being associated with the relief valve 9. The pressure which the press exerts is controlled by a tonnage control valve, generally designated II, and shown in longitudinal section in Figure 4. The press 2 contains a double-acting main plunger I2 attached to a platen I3, which has an arm I4 adapted to engage a collar I5 upon a control rod I1, the latter being guided by brackets, such as the bracket I8 projecting from the main cylinder I9 of the press 2. The main cylinder I9 contains a bore 29 for the reciprocation of the main plunger I2, and has ports 2i and 22 communicating therewith on opposite sides of the main plunger I2. The ports 2| and 22 are connected respectively to the lines 23 and 24 leading to the forward and return pressure connections 25 and 26 of the variable delivery pump I. A branch 21 runs from the pipe 24 to the check valve Ill, the pressure relief valve 9 and the main cylinder release and by-pass valve 4, the branch 28 continuing from the latter to the port 29 in the main cylinder I9 and containing the pressure relief valve 8. From the port 30 in the main cylinder I9, above the main plunger I2, the line 3I runs to the tonnage control valve I I, from which the line 32 leads to the surge tank 3.

The pilot circuit, including the pilot pump 6 and the pilot pressure relief valve 1, includes the line 33 running from the surge tank 3 to the pilot pump 6, the line 34 serving to convey the fluid discharged by the relief valve 1 back to the surge tank 3, and the lines 35 and 36 for conveying pressure fluid from the pilot pump 6 to the servo-motor casing 31 of the variable delivery pump I. The discharge line 38 leads from the servomotor casing 31 back to the surge tank 3.

The variable delivery pump I includes a pump casing 40, having a chamber 4I containing bearing pads 42, supporting and guiding the horizontal reciprocation of the pump shift ring or flow control member 43. The latter, as is known to those skilled in the art, controls the delivery of the variable delivery pump I so as to advance or return the main plunger I2, or to cause it to remain in a neutral position, depending upon the eccentricity of the shift ring 43 from its neutral position.

Secured, as at 44, to the shift ring 43 is the threaded end 45 of the servomotor piston rod 46, which passes through bore 41 in the pump casing 40 and carries atits opposite end the piston head 48. The latter reciprocates within the stepped cylinder bores 49 and 50 in the servomotor casing 31. The bores 49 and 50 are provided with annular enlargements 5| and 52, having ports 53 and 54 to which are connected the lines 36 and 38, respectively.

The piston 48 contains a central longitudinal bore 55, which carries a fixed sleeve 56 having ports 51 and 58 opening into its inner bore 59. The piston 48 likewise is' provided with ports 68 communicating with the ports 51, and likewise with an annular enlargement 6| of the bore adjacent the ports 58. The piston 48 is provided with axially bored passageways 62, running from the left-hand side of the piston 48 to the annular enlargement 6|, thereby conveying fluid therebetween, but not communicating with the piston ports 60. The piston rod 46 contains a. longitudinal bore 63, from which ports 64 communicate with the annular enlargement 52. The piston rod bore 53 is provided with a coil spring 65, one end of which engages the end of the bore 63, and the other end engages the reduced diameter portion 66 of the servomotor control valve rod 61, which carries a valve head 68, movable to and fro within the inner bore 59 of the sleeve 56. The valve rod 61 carries a disc-like bafile member 69 before it enters a bore 10 within a plug 1|, carried by a bore 12 in the servomotor cylinder head 13. A packing 14 and gland 15 reduce the fluid leakage around the valve rod 61.

18, which is pivoted as at 19 to the upper end of a lever 80. The latter is mounted upon a pivot pin 8|, supported by a link 82, pivotally mounted upon a pin 83 supported by the ears 84 upon the servomotor cylinder head 13. Secured to the side of the pump casing 40, opposite the servomotor casing 31, is the centering device casing 85, having a cap 86 mounted upon the opposite sidethereof.

Secured to the shift ring 43 of the pump I, as at 81, is the threaded end 88 of the centering rod 89. The latter is provided with an enlargement 90, beyond which is a reduced portion 9I. On opposite sides of the enlargement 90 are collars 92 and 93, slidably mounted upon the centering rod 89 and reduced portion 9| thereof, respectively. The centering device casing is provided with an annular internal flange 94, against which the collars 92 and 93 are urged by coil springs 95 and 96 within the casing 85 and a cap 86, respectively. A threaded Port 91, normally closed by a plug, permits access to the interior of the cap 86 so as to check the condition of the spring 96.

The lower end of the lever 80 is pivotally connected, as at 98, to a link 99 (Figure 3), which is pivoted at Inn to the upper end of a lever IN. The latter is pivotally mounted upon a fixed pivot I02 and at its lower end is pivoted at I93 to a link I04, pivotally connected at I05 to an arm I06 mounted upon the shaft I01. The latter closing the switch in the usual manner.

likewise carries a lever I08, one end of which ,has a rounded yoke I09 engaging the collar I6 upon the control rod II. The other end of the lever I08 is pivoted at IIO to a rod III, connected to the armature II2 of a solenoid H3. The sole- .noid H3 is energized by electricity reaching it over the wires H4 and H5.

The tonnage control valve II (Figure 4) consists of a block "6, containing a longitudinal bore I I1 reciprocably receiving a plunger II8, the

upper end of which carries ahead II9 urged downwardly by the coil spring, I20, the upper end of which is engaged by the end I2I of the threaded shaft I22, mounted in the threaded bore I23. A hand wheel I24 serves to adjust plunger II8 upwardly, opening the .normally closed limit switch I30, and thereby deenergizing I the solenoid II3 by breaking its energizing cirthe position of the threaded shaft I22, thereby varying the. force exerted by thecoil spring I upon the plunger H8. The plunger II8 carries an annular portion I reciprocating in the guide chamber I26, leakage being prevented by the packing consisting of dihe washer I21, packing I28 and gland I29. A limit switch I30 is positioned with its switch arm I3I adapted to be engaged by the head II9 as it moves upwardly when the plunger H8 is shift d by a predetermined pressure exerted against its lower end I32 by pressure fluid arriving along the line 3|, leading to the main cylinder bore 20 above the pressingjplunger I2. The limit switch I30 is connected in circuit for energizing the solenoid II3 by way of the wires H4 and H5. The limit switch I30 is normally closed, and thus permits the solenoid I I3 to be energized until the plunger II8 of the tonnage control valve II' rises and opens the switch I30, thereby denergizing the solenoid II3. I

In the operation of the circuit shown in Figures 1 to 3, the solenoid H3 is energized by The energization of the solenoid I I3 draws its armature I I2 downwardly, this motion being conveyed through the lever I08, arm I06,-link I04, lever I II, link 99 and lever 80 to urge theservomotor control valve rod 61 inwardly. This, in turn,

. compresses thecoil spring 65 and. shifts thvalve head 68 to the right, permitting pressure fluid from the pilot pump 6 and lines 35 and 36 to pass through the ports and 51, into the inner chamber 59 of the sleeve 56, and thence into tering'springSG. The motion of the servomotor piston 48 causes a correspond ng motion of the sleeve 56 in the same direction, thereby causing the ports 51 to pass over and be closed by the valve head 68. The stroke of the valve head 68, however, is arranged to be slightly greater in each direction than the stroke of the servomotor piston 48 so as to allow a small amount of overtravel. While the piston 48 has been moving to the right the fluid within the annular enlargement 52 is discharged through the port 54 and line 38, into the surge tank 3.

With the pump shift ring 43 shifted to the right of its neutral position in this manner, the pump I discharges pressure fluid into the space above the main pressing plunger I2 by way of the line 23 and port 2|, thereby forcing the plunger I2 downwardly. Ordinarily, the surge valve 5 opens automatically in response to the gravitational descent of the plunger I2 and admits fluid into the space above the plunger I2 cuit. When the solenoid H3 is deenergized in this manner, the coil spring within the servomotor piston rod 46 forces the servomotor valve rod 61 to the left, causing its head 68 to uncover the ports 58. Fluid then escapes from the lefthand side of the servomotor piston head 48, through the axial passageways 62, into the annular enlargements 6I, thence through the ports 58, inner chamber 59 of thesleeve 56, ports 64,

annularchamber 52, port 54 and line 38, back to the surge tank 3.

the variable delivery pump I and causes.-pressure fluid to pass thruthe connection 26, line 24 and port 22, into the main cylinder bore 20 beneath the piston head I2, forcing the platen I3 upwardly. This movement continues until the platen arm I4 lifts the collar I5 and the control rod IT. This motion is transmitted through the lever I08, arm I06, link I04, lever IOI, link 99 i and lever 88 to the servomotor control valve rod 61, forcing the latter inwardly to the right thru a partial stroke, thereby moving the shift ring 43 of the pump I toits neutral position. The pump I thereupon ceases to deliver pressure fluid, and

the platen I3 and plunger I2 remain in a retracted position.

If, by a failure of power or other reason, pilot pressure fails to be delivered through the lines 36,

when the plunger I2 and platen I3 are in their retracted positions the weight of these moving parts exerted upon the fluid in the circuit generates pressure fluid which momentarily runs the pump I backward as a motor, and thepump I then runsthe pilot pump' 6 backward since both pumps are connected to the same motor. As the. pilot pump 6 runs backward it sucks the oil out of the line 36 and this relieves the pressure in the chamber 5I. The instant this pressure is relieved, the centering spring 96 shifts the pump.

flow control member or shift ring-43 into its neutral position, thereby preventing the pump pistons from reciprocating and, therefore, preventing the weight of the platen I3 and plunger I2 from creating further pressure fluid to continue to move the pump I backwardly as a motor. Thus, a failure of power or other reason for cutting off the flow of pilot pressure fluid through the line 36, permits the platen I3 to coast downwardly but a negligible distance before it halts, while the press is in its retracted position. If the press is on its return stroke and the platen I3 is moving upwardly, the pilot valve rod 61 is urged to'the left by the coil spring 65 within the servomotor piston rod 46, the stroke of this valve rod 61 being slightly greater than the stroke of the servomotor piston 48 and shift ring 43.

If, now, there is a failure of power or failure of pilot pressure fluid from the line 36 while the press platen I3 is executing a return stroke the above-described action permits the centering spring 85, which is now in a compressed condition, to urge the collar 92 and centering rod 8 9 to the right, thereby bringing the shift ring 43 of the pump back to its neutral position. Since the servomotor piston 48 and its servomotor cylinder bores 49 and 50 are in constant communication with the pipe lines 36 and 38, respectively, entrapment of fluid therein is prevented in the event that a failure of pilot pressure occurs, such as by failure of power to the pilot pump 6.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully describcd my invention, what I claim as new and desire-to secure by Letters Patent, is:

1. In combination in a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for operating said piston, said piston having a chamber therein with valve ports, and a valve member within said chamber cooperating with said ports for controlling the supply of pressure fluid from said source to said piston.

2. In combination in a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for operating said piston, a control valve adjacent said piston for controlling the supply of pressure fluid from said source to said piston, and yielding means contained entirely within said servomotor cylinder for urging said valve member in one direction.

3. In combination in a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for operating said piston, said piston having a chamber therein with valve ports, a valve member within said chamber cooperating with said ports for controlling the supply of pressure fluid from said source to said piston, and yielding means contained entirely within said servomotor cylinder for urging said valve member in one direction.

4. In combination in a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for opera ing said piston, said piston having a chamber therein with a transverse valve port extending between said cylinder and said chamber on one side of said piston and an axial passageway extending from the other side of said piston to another port opening into said chamber, a discharge line connected to said chamber, and a valve member in said chamber with a valve portion cooperating with said ports for selectively connecting one side of said piston with said source and said discharge line.

5. In combination in a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for operating said piston, said piston having a chamber therein with a transverse valve port extending between said cylinder and said chamber on one side of said piston and an axial passageway extending from the other side of said piston to another port opening into said chamber, a discharge line connected to said chamber, and a valve member in said chamber with a valve portion cooperating with said ports for selectively connecting one side of said piston with said source and said discharge line, the other side of said piston being constantly in communication with said source.

6. In combination in a variable delivery pump With a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid for operating said piston, said piston having oppositely disposed head portions of differing areas, a longitudinal chamber within said piston having a port communicating with the smaller piston head portion, a discharge line connected to said chamber, an axial passageway leading from the larger piston head portion to another port communicating with said chamber, and a valve member in said chamber arranged in one position to connect said source through one of said ports to the larger piston head portion and in another position to connect said source to the smaller piston head portion while connecting the larger piston head portion to said discharge line.

'7. In combination in a self centering servomotor control mechanism for a variable delivery pump with a pump shift ring, a servomotor cylinder, a servomotor piston therein connected to said pump shift ring, a source of pressure fluid fOr operating said piston, said piston having oppositely disposed head portions of differing areas, a longitudinal chamber within said piston having a port communicating with the smaller piston head portion, a discharge line connected to said chamber, an axial passageway leading from the larger piston head portion to another port communicating with said chamber, a valve member in said chamber arranged in one position to connect said source through one of said ports to the larger piston head portion and in another position to connect said source to the smaller piston head portion while connecting the larger piston head portion to said discharge line.

WALTER ERNST.

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