US2601761A - Hydropneumatically controlled servomotor - Google Patents

Description

July l, 1952 P. FouRoN ErAL HYDROPNEUMATICALLY CONTROLLED SERVOMOTOR Filed Nov. 19, 1951 hm N vll/11111 w m EN f Y K l r EN f QN w `m N Patented July 1, "1952 UNITED STATES PATENT GFFICEl HYDROPNUMATICALLY CONTROLLED SERVOMOTOR France Application November 19, 1951, Serial No. 257,098 In France November 15, 1950 f 6 Claims.

The invention relates to servo-motors actuated by fluid pressure, of the reciprocating type, and it concerns more particularly an improved servomotor normally actuated by pneumatic means during the major portion of the cycle of operation, hydraulic actuating means coming into action during a minor portion of this cycle of operation to provide additional power.

The object of the invention is to provide an improved apparatus adapted to perform, with a minimum expenditure of power, an operation which, at a certain stage, presentsl a higher resistance than that offered during the other stages of the operation, by bringing into action an additional source of power enabling this higher resistance to be overcome, the rest of the operation being performed with more moderate power, thereby realising an economy of power.

As an example, the operation of casting aluminium alloys and other alloys in permanent chilled moulds can be mentioned. This operation calls for a, considerable force to separate the movable parts from the fixed parts of the mould, owing to the shrinking of the metal, whereas the further stages of the operation, which only require the displacement of the disengaged movable parts of the mould, require but little power. This is but one particular example among the many applications of the invention, and it will be selected as anillustration to explain it.

The invention has for its object, particularly, to provide servo-motor operated by pneumatic means during the stages of the operation which do not call for an exceptional supply of power, in combination with hydraulic means whichautomatically bring into play a supplementary source of power at the stage of the operation which requires additional power, for example, in the application mentioned above, for the purpose of extracting the movable parts of the moulds.

Referring to vthe drawing, which illustrates, by way of example only, a preferred arrangement of the apparatus according to the invention:

Fig. 1 is a diagram showing the disposition of the several devices the combination of which constitutes the invention.

Figs. 2 and 3 are cross-sectional views of the apparatus in two different positions, with the pistons at the ends of the working and of the idle stroke, respectively. i

Fig. 4 is a fragmentary cross sectionalview of a modification adapted to introduce a `time lagin the coming into action of the hydraulic means.

In its simplest form, the apparatus consists of two co-axial pneumatic cylinders I (at the front,

that is, towards the mechanism to be actuated) and 2 (at the back), in which reciprocate two pistons 3 and 4, respectively; these two cylinders are separated by a third co-axial cylinder disposed between the bottom of cylinder I and the head of cylinder 2, fullling the function of a hydraulic cylinder. In the iigures, the head 5 of the cylinder 2 is extended forward and bored to constitute the third cylinder, 5', in which is adapted to reciprocate a third piston 'I which it itself hollow and adapted to receive a plunger I0 integral with the piston 4 and guided by the head 5 of the cylinder 2, through which it passes, so that it acts also as a piston rod in connection with the piston 4 with which it constitutes a differential piston, of which this plunger is the portion of lesser diameter.

In the body of the head 5 is provided a circular chamber II, surrounding the said third cylinder with the interior of which it communicates by a passage II when the piston 4 is in the position shown in Fig. 2, with the plunger I0 almost entirely withdrawn from the cylinder 5. Means (not shown) enable a liquid to be introduced in the chamber II, whence, when the piston 4 and the plunger I0 are in the position just referred to, this liquid iiows along the passages III into the space I inside the hollow piston 1 and thence, through orifices I2 in the wall of the latter, into an annular space I3 behind the body, of larger diameter, of the piston 1; this in-flow of liquid is however cut off as soon as the piston 4, beginning its forward stroke, pushes the plunger IIJ through the neck of the open end of the space l', effectually closing the latter.

It will be seen that the differential `piston 4-I 0 constitutes an amplier for the duid pressure eX- erted on the back face of the piston 4 by iiuid (here a gaseous fluid) entering at 22, this pressure being transmitted by the plunger I0 and magnified in the ratio of the area of the piston 4 to the area of the plunger Ill, so that the liquid in the chamber I3 is subjected to a relatively considerable pressure which is applied on the face of the piston 1, pushing it away from the piston 3, that is, in the same direction as the motion of the piston 3 when it performs its power stroke under the action of gaseous fluid introduced in the cylinder I by the conduit 2U.

The piston 3 is provided with a piston rod 3 which is hollow and adapted to receive a rod 8 xed on the piston 1 and provided with a stop 9 so disposed that, as the piston 3 nears the end of its forward stroke, this stop butts against a nut or like member 3" on the piston 3 with the 3 result that the piston 1 is pulled forward, uncovering the passages I I', ready for the next power stroke.

Various packingsl I4, I5, I6, I'I, I8 and I9 ensure the fluid-tightness of the several sliding contacts.

A conduit 2i) between ports provided at the outer ends of the cylinders I and 2 puts these two cylinders, in permanent communication; another conduit 2I between ports provided at the innerends of these two cylinders puts them likewise in permanent communication; a. pipe 22 opening inv the cylinder 2 at its outer end either admits a.

compressed gaseous fluid in this cylinder` or .is open to exhaust and another pipe 23 opening 1n the conduit 2I either admits a compressedgaseous uid in both the cylinders I and 2, or'opens these two cylinders to exhaust. A suitable distributor 24 (Fig. 1) opens these pipes 22 and 23 alternatively to admission or to exhaust, one being open to admission while the other one is open to exhaust, and reci-procally.

In operation the various parts being. in the p osition shown in Fig. 2, with the servo-motor at the end of its forward stroke (that is, the stroke towardsl the mechanism to be actuated), the Complete operation is performed .on the. double. acting principle, in four stages, as follows:

First stage-A gaseous fluid under pressure is introduced in the cylinder 2 b y thel pipe 22, the piston 4begins to move, uncovering the port,2.0:, thereby enabling the uid to proceed by they conduit Ztill the port 20", blocked by thenpiston 3.; the plunger II] enters the space I andcompresses the duid in the spaces I and I3, the piston 1 .begins to move in the opposite .direction to that of the plunger, and pulls the piston 3 which uncoversv the port 20" slightly, enabling the fluid to enter the cylinder; the motion proceeds under the combined action of both pistons 3. and-l', exerting their maximum power. This stage` corresponds, ior example, to the beginning of the withdrawal of the moulds, as explained above.

.SfecQnd.stctge.--When the piston 'I Areachesthe endof its power stroke, the. piston 3 continues` to more alone under pneumatic pressure only-.tillit reaches the end of the cylinder; meanwhile, any iiuid behind this piston escapes to exhaustby. the passages, 2I and 23; similarly, any fluid infront ofthe piston 4 passes through these passages to exhaust. This stage corresponds to the furtherdisengagement of the movable partsof the. chilled moulds, enabling the castings to be removed from the moulds.

Third stage.-The passage 22 is open to exhaust while 2,3; is open to admission; the two pistons 3 and'4'move in opposite directions towards the outer ends of their respective cylinders; the. pistot!` `3;.drives the fluid in front of it by the conduit 2-0," the cylinder 2 and the pipe 22. The hydraulic cylinder is, of course, idle (Fig. 3)

loatlzv stage-Near the end of its stroke, the piston 3 engages the 'stop 9. on the rod 8, thereby pullingv the piston 'I forward, back to the position shown in Fig. 2; liquid is again admitted inthe spaces I and I3, to make up for anyseepage; they reaction of the piston 'I provides abraking action and prevents a shockat the moment whenl the moulds are closedfor a new casting operation.

Thegacton of the hydraulicpart of themachine may-take place during` the whole power stroke of the-piston 3 or only during aportion offthis stroke.

The. moments whenV this action begins and ceases may also be varied: they dependonrthe; position ofthe stop S on the rod, 8 and of; the, apertures.

I2 in the wall of the piston 'I or on the length of the plunger I 0.

In the embodiment described above, it is seen that. at the beginning ofthe stroke of-the piston 4 in the forward direction, the conduit 20 becomes open to pneumatic pressure; it may vbe useful to introduce a time lag between these two operations, so that the opening of the passage 20 to admission onlytakesplace after the piston 4 has performed a certain displacement. To obtain this result,l the bottom. ofthe cylinder 2 is provided with a hollowboss- 25 (Fig. 4) which enters in a corresponding.- recess in the piston 4 and the conduit 20 is madefto open inside the hollow boss, so that it is only when the displacement of the plston 4 is suiiiciently pronounced to uncover the opening of this conduit 20 in the hollow boss, that the gaseous fluid under pressure can enter this passage 2l).

The hydraulic part of the machine being independentof the pneumatic part, it is possible-to obtain diierent combinations of displacements and of the power of one or the other arrangement. For. example, oneJmay provide fluidylinders the stroke; ofwhich is longer or vshorter or-one may mount on one of thepneumatic cylinders diiferent k1nds of fluid-pressure ampli'ers, with variable strokes.

The'distributor 24shown in Fig. 1 is-intended formanual operation. Any other equivalentv arrangement coul-d. of coursebefemployedforthe samepurpose.

Insteadof the rst stage -of-operations being performed underthe jointvaction of the pneumatic piston 3 and of the hydraulic piston, it can be performed under. the action of the hydraulic piston alone, the port 20." remaining closed to adm1ssion' until the operation can be pursued with pneumatic power only.

In the embodiment, the two pneumatic pistons. movein: opposite` directions; the apparatus may however .be designed so that they-move in the samed-irection What we. claim is:

l. -In' aservoemotor of thetype-described, three coaxial. huid-pressurecylinders,y namely, a rst cylinder, meansfor admittinga' compressed gaseous fluid tothe .said rsc'cyimder, a piston lo the said first cylinder, a piston-rod; integralwith. the said piston, connectedmechanically to-themechamsmto bel actuated, a second cylinder, means` fory admittmg acompressed gaseousv uid tothis second cylinder, a diierential piston. in thesaid. second. cylinder, comprising'two: piston elements. of dilerentr diameters and constituting a ,iiuidpressure magnifying device, a third cylinder, a, piston in thisthird cylinder, means for admitting a .liquid in this third cylinder, meansfor trans.- mittlng thefnuid pressure onl the piston in the second cylinder,v magnifiedy by the. saidluidepressure magnifying device, to the. piston in thesaid thlrd cylinder, in the same direction asthe. power. stroke of the first rcylinder and meansy for temporarnyconnecting positively. the pistons in .thev iirst and in the third cylindery duringv thestage.` of the operation which requiresadditiona-l power for its performance.. l

2. In a servo-motor of thetypedescribedthree. co-axial duid-pressure cylinders, namely, arst cylinder, a piston in this rst cylinder,means for admitting a gaseousfluid under pressure. in the. sa1dl first cylinder; on either sidev of thefsaid p1ston, alternately, a piston rod, integral with the said piston, connectedvmechanically to the mechanism to be actuated, asecond cylinder, a

piston in this second cylinder, means for admitting a gaseous fluid under pressure to the said second cylinder, on either side of theK piston in this second cylinder, alternately, a plunger of lesser diameter than the latter said piston, constituting, together with the latter said piston, a fluid-pressure magnifying device, a third cylinder, a piston in this third cylinder bored cylindrically along a portion of its length to such a diameter as to just receive the said plunger, the assembly of second cylinder, piston in-thissecond cylinder, plunger and bored piston in the third cylinder constituting a fluid-pressure magnifying device, means for admitting a liquid to the said third cylinder and to the said bored piston, means for transmitting the fluid pressure on the piston in the second cylinder to the liquid in the third cylinder, against the piston in the said third cylinder, in the direction of the power stroke of the iirst cylinder and means for temporarily connecting positively the pistons in the iirst and in the third cylinder during the stage of the operation which requires additional power for its performance.

3. The servo-motor defined in claim 2, in which the space inside the bored piston in the third cylinder communicates by oriices in the wall of this bored piston with the space in the iront part of the third cylinder, both spaces being cut 01T from the means for admitting the liquid in the third cylinder by the plunger when it enters into the first aforementioned space.

4. The servo-motor defined in claim 2, in which the mechanical means temporarily connecting the first and the third piston comprise a rod fixed on the said third piston, on the side thereof towards `the first cylinder, a stop on the said rod and means for engaging said stop with the first piston, positively, during the stage which requires additional power for its perfomance.

5. 'I'he servo-motor defined in claim 2v, in which the means for the admission of a compressed gaseous iiuid against the pistons in the iirst and the second cylinders comprises a conduit having connecting ports opening into the said cylinders at the outer ends thereof and putting them in communication at the beginning of their working stroke, and a pipe opening into the second cylinder, at the back thereof, adapted to be connected to a' source of compressed gaseous fluid. and the means for the admission of a compressed gaseous uid in the saine cylinders at the beginning of the back or return strokes of the pistons in these two cylinders, respectively, comprises a conduit adapted to be connected to a source of compressed gaseous iiuid, connecting ports opening into the said two cylinders at the inner ends thereof, said means for the admission of a compressed gaseous uid at the beginning of a working stroke and of a back or return stroke, respectively, serving also, alternatively, for the exhaust of the used gaseous fluid, each of said two conduits serving for the admission while the other conduit is open to exhaust.

6. The servo-motor dened in claim 2, in combination with means for delaying the beginning of the power stroke of the rst piston with respect to the beginning of the power stroke of the second piston, said means comprising a conduit putting in communication the outer or front end of the first cylinder and the inside of a hollow boss provided on the bottom of the second cylinder. internally thereof, said boss being adapted to fit in a recess in the piston in the second cylinder when this piston is at the end of its back or return stroke and to be uncovered by the said piston thereby opening the admission to the rst cylinder, when the said piston has moved a predetermined distance.

PIERRE FOURONT. GEORGES BOURRET.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 825,301 Coddington July 10, 1906 2,319,950 Schleicher et al. May 25, 1943 2,324,149 Gray July 13, 1943 2,365,536 Fischer et al Dec. 19, 1944 2,396,539 Smith et al Mar. 12, 1946 2,396,778 Flowers Mar. 19, 1946 2,432,088 Caldwell Dec. 9, 1947 FOREIGN PATENTS Number Country Date 929,959 France July 28, 1947

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