US3312146A

US3312146A - Fluid pressure jack with three stable positions

Info

Publication number: US3312146A
Application number: US427619A
Authority: US
Inventors: Quere Emile; Philippe Jacques
Original assignee: Nord Aviation Societe Nationale de Constructions Aeronautiques
Current assignee: Nord Aviation Societe Nationale de Constructions Aeronautiques
Priority date: 1964-01-27
Filing date: 1965-01-25
Publication date: 1967-04-04
Anticipated expiration: 1984-04-04
Also published as: FR1395635A; GB1092422A; DE1576139B1

Description

April 4, 1967 E. 'QUERE ETAL FLUID PRESSURE JACK WITH THREE STABLE POSITIONS Filed Jan. 25, 1965 2 Sheets-Sheet 1 April 4, 1967 E. QUERE ET-AL FLUID PRESSURE JACK WITH THREE STABLE POSITIONS Filed Jan. 25, 1965 2 Sheets-Sheet z United States Patent Ofiiice 3,312,146 Patented. Apr. 4, 1967 i 9 Claims. (lCl. sit-1st) The present invention relates generally to fluid-pressure jacks and more particularly to -a jack of this kind which can be brought into and kept at any one of three stable positions.

It is known to retain the piston of a double-acting fluid-pressure jack in one or the other of its end positions, by keeping under pressure the desired compartment of the cylinder while the other compartment is set to exhaust.

It is also known to seek to maintain the piston of a jack of this kind in a third central position by means of two restoring springs, both compartments of the cylinder being set to exhaust. However, this third position is then unstable because of the zero resultant of the contrary forces of the springs, and the slightest external force capable of overcoming the friction of the piston is then sufiicient to displace the said piston. The third position is furthermore not precise in consequence of this same friction, and the difliculty of balancing the springs. Finally, the presence of the springs constitutes a force to be overcome for movement to an end position and maintenance in this position by the fluid under pres-' sure.

The present invention proposes to produce a fluid-pressure jack with three positions:

Which can be brought into and maintained in any one of its three positions, exclusively by the fluid pressure;

Which can pass from any one of its end positions to its central position, or vice-versa, in an extremely short time;

Of which the central position is stable as the end positions;

Which is simple to manufacture and in consequence not expensive;

The operation of which can be eifected by simple devices, such as distribution slide valves and this by applying to these valves negligible forces, which, for example, enables them to be actuated by means of electro-magnets of low power.

With a view to attaining the particular objects enumerated above, the invention has for its object a fluidpressure jack which offers simultaneously the advantages of a double-acting jack and those of a differential jack.

To this, end, the fluid-pressure jack in accordance with the invention comprises essentially a main double-acting piston mounted between two auxiliary pistons of larger diameter and each moving between the corresponding end of the cylinder and an internal abutment.

With this arrangement, if one side only of the jack is put under pressure while the other is put to drainage, the

just as precise and as main piston and the auxiliary piston on the drainage side behave like a single double-acting piston and are brought into or maintained at the end position on the drainage side.

If the pressure which already existed on the opposite side is then applied to the drainage side, the two pistons which were in their end position behave like a single differential piston and are brought back into an intermediate position.

It is especially provided to utilize in a differential double-acting jack according to the invention a hydraulic fluid such as oil under pressure which, due to the fact that it is practically incompressible, enables all undesirable elastic effect to be eliminated.

By giving the main piston a length exactly equal to the distance between the internal abutments of the auxiliary pistons, the main piston can be maintained with great stability in an intermediate position (for example central) with great accuracy.

The jack according to the invention lends itself particularly well to obtaining an extremely rapid but controlled time of response by a suitable choice of the total section of the ports of the auxiliary pistons through which the fluid passes in order to act on the main piston, taking into account the pressure of this fluid, the working surfaces of the various pistons and the travel of the main piston.

The invention will be better understood with reference to the detailed description which follows below and from examination of the accompanying drawings which represent one form of embodiment of the invention, by way of example and without any limitative sense.

In the drawings:

FIG. 1 is a digrammatic view in axial longitudinal section of a simplified form of construction of the jack according to the invention, in its central position;

FIG. 2 is a view similar to FIG. 1 but showing the jack in the extreme lefthand position;

FIG. 3 is a view similar to FIGS. 1 and 2, but show ing the jack in the extreme right-hand position, and

FIG. 4 is a diagrammatic view partly in section in a diametral plane of the jack, showing also a control device for the jack constituted by two independent slide-valves which are in turn operated electro-magnetically.

In all the figures, the corresponding elements have been given the same reference numbers.

As can be seen from the basic diagrams of FIGS. 1 to 3, the fluid-pressure jack in accordance with the invention comprises essentially a main piston I mounted so as to be able to slide in a central portion 8 of a cylinder 7, the

end portions

9 and 10 of which are of larger diameter. In the example shown, the main piston 1 has a length exactly equal to that of the central portion 8 of the cylinder 7, and is provided with two

axial rods

40, 4b, which pass respectively through the: ends of the said cylinder and the length of which is suflicient for them to remain engaged in the ends of the cylinder over the entire travel of the main piston 1, and in order that one of them may transmit the movement of the said piston to the member to be driven. Two

auxiliary pistons

2 and 3 are mounted so as to be able to slide respectively in the

end compartments

14 and 15 of the cylinder 7 over the internal surface of the end portions 9 and ltl respectively of the said cylinder. The

auxiliary pistons

2 and 3 can furthermore slide freely on the

respective rods

4a, 4b of the main piston 1 and ports formed in the

auxiliary pistons

2 and 3 permit the fluid under pressure to pass through them so as to act on the main piston 1.

These ports which are not shown in the drawings for the sake of simplicity, are indicated symbolically by the

annular clearances

5 and 6 of the

auxiliary pistons

2 and 3 respectively. It will of course be understood that in practice these annular clearances are reduced to the minimum compatible with the free sliding movement of the

auxiliary pistons

2 and 3 on the

rods

4a and 4b of the main piston 1, the passage of the fluid under pressure being effected almost exclusively through the ports referred to above, When the position of the main piston 1 so permits, each of the

auxiliary pistons

2 and 3 can move freely between the corresponding end of the cylinder 7 and the abutment constituted by the radial shoulder coupling the corresponding end portion 9 or of the cylinder 7 to its central portion 8.

As described below in a more detailed manner, the end compartments 14 and can be put selectively into com- [munication under the control of appropriate means shown symbolically in FIGS. 1 to 3 by a five-way cock 54, with a source of fluid under pressure symbolized by the rectangle 52, or with a zone of pressure less than that of this fluid, shown symbolically in FIGS. 1 to 3 by a tank 53. The five-way cock 54 communicates, as described below, with the

end compartments

14 and 15 of the cylinder '7, through the respective conduits 4'7 and 48 terminating at

respective orifices

45 and 46 with the source of fluid under pressure 52 by a conduit 49, and with the tank 53 by conduits 50 and"51.

The operation of the jack according to the invention and shown in FIGS. 1 to 3 is as follows:

In the position shown in FIG. 1 the five-way cock 54 causes the source of fluid under pressure 52 to communicate simultaneously with the two

end compartments

14 and 15 of the jack through the intermediary of the

conduits

49, 47 and 48 and the

orifices

45 and 46. The assembly of the three

pistons

1, 2 and 3, is maintained in the central position shown in FIG. 1 by the pressure of the fluid acting on each side of the said assembly.

In fact if, for example, an external force of any kind tends to displace the main piston 1, for example towards the rig-ht, through the intermediary of the rod 4b (or of the rod 4a), the

pistons

1 and 3 tend to move as a whole towards the right, while the auxiliary piston 2 is held by its annular abutment at the left-hand extremity of the central portion 8 of the cylinder.

The pressure of fluid existing in the compartment 14 acts on the annular left-hand surface (in the drawing) of the main piston 1 through the ports of the auxiliary piston 2, while the fluid pressure existing in the compartment 15 acts on the full annular surface (that is to say with the exclusion of the ports) of the auxiliary piston 3. Since this latter surface is greater than the annular left-hand surface of the piston 1 and since the two fluid pressures are equal, the pressing force which acts on the assembly formed by the

pistons

1 and 3 towards the left is greater than that which tends to move the main piston 1 towards the right. Everything takes place as if the said assembly formed a single diiferential piston, and it is brought into the central position shown in FIG. 1. It would of course be the same if an external force sought to displace the main piston 1 towards the left, with this difference that the diflerential piston would then be constituted by the

pistons

1 and 2.

Experience has shown that the central position of FIG. 1 maintained by two oppositely-acting fluid pressures which are equal to each other is extremely stable, more stable even than the end position which, as will be seen later, are maintained by a single pressure of fluid applying the pistons against a mechanical abutment.

If .the cock 54 is brought from the position of FIG. 1 to that of FIG. 2, only the compartment 15 is maintained under pressure through the intermediary of the conduit 49, the cock 54, the conduit 48 and the orifice 46, while the compartment 14 is put into communication with the zone of low-pressure shown diagrammatically by the tank 53, through the intermediary of the orifice 45, the conduit 47, the cock 54 and the conduit 51.

The section of passage of this drainage circuit is chosen to be as large as possible in order to reduce the resistance to movement of the main piston 1 under the action of the pressure of the fluid. This pressure, passing through the ports represented by the annular space 6, acts on the ananular right-hand face of the main piston 1 which moves towards the left, pushing back the auxiliary piston 2, until the latter comes into abutment against the left-hand end of the cylinder 7. As long as the cock 54 remains in the position of FIG. 2, the main piston 1 remains in its extreme left-hand position shown in this figure.

If furthermore the cock 54 is brought from the position of FIG. 1 to the position of FIG. 3, the operation is identical with that which has just been described, with this difference that the main piston 1 is brought and held in its extreme right-hand position, as shown in FIG. 3.

Conversely, if the cock 54 is brought back to the position of FIG. 1 from one or the other of the positions of FIGS. 2 and 3, the fluid pressure acts in the two

compartments

14 and 15 and brings back and then retains the assembly of the pistons at the central position shown in FIG. 1, as described above.

The chamber in center portion 8, it will be noted, is always connected to low pressure tank 53 in all three positions of the pistons in FIGS. 1, 2 and 3. One method of showing this connection is disclosed in FIG. 4.

It will be observed that if a hydraulic fluid such as oil under pressure is utilized, by placing the cock 54 in an intermediate position, it is possible literally to block the piston 1 in any one of its three positions by enclosing a column of liquid on one side and/ or on the other of the piston 1 in the jack and in the conduits 47 and/ or 48.

In this case cf course, it would be necessary to provide safety devices in order to take into account the possible thermal expansion of the oil, but this possibility shows quite clearly the stability with which the piston 1 can be maintained in any one of its three position. In particular, the stability in the central position is valuable, especially in the case of controlling a device which can be displaced on each side of a neutral position, the stability of this latter position being particularly important.

The control device shown diagrammatically in FIGS. 1 to 3 by a five-way cock 54 can be produced in any desired manner.

In accordance with a form of embodiment of the invention shown diagrammatically in FIG. 4, this control device is constituted by two independent slide-valves 19 and 20 capable of sliding in a common cylinder 18. The slide-valve 19 comprises essentially two cylindrical bearing surfaces 22 and 23 connected to each other by a rod 21 which is extended into the exterior of the cylinder 18.

In the same Way, the slide-valve 20 is essentially constituted by two cylindrical bearing surfaces 25 and 26 connected to each other by a rod 24 which is extended to the exterior of the cylinder 18. The fitting of the distribution slide-valves in their cylinder is obtained by grinding-in.

In the position shown in FIG. 4, which corresponds to the central position of the main piston 1, the annular groove 31 of the slide-valve 19 communicates by a conduit 37 with the compartment 14 of the cylinder 7, and by a conduit 34 with the intake of fluid under pressure 33. In the same way, the annular groove 32 of the slidevalve 20 communicates, in the position shown in FIG. 4, by a conduit 39 with the compartment 15 Of the cylinder 7, and by a conduit 35 with the intake of fluid under pressure 33.

The extreme left-hand and right-hand compartments of the cylinder 18 communicate respectively by conduits 38 and 40 with the evacuation 36 towards a zone of low pressure. The central compartment 43 of the cylinder 18 communicates continuously by the conduits 44 and 38 with this same evacuation 36. In addition, the central position 41 of the cylinder 8 is put into communication with this evacuation through the intermediary of a conduit 42, of the said central compartment 43 of the cylinder 18, and of the conduits 44 and 38, in order to evacuate the leakages of fluid under pressure.

The

rods

4a and 4b of the main piston 1 pass through the respective ends of the cylinder 7 by packing

glands

13a, 13b or the like.

Experience has shown that it is possible in certain cases to dispense with sealing joints for the main piston 1 and for the

auxiliary pistons

2 and 3. However, as shown in FIG. 4, there may be provided, if required, a sealing joint 11 for the main piston 1 and/or sealing joints 12a and 12b for the

auxiliary pistons

2 and 3.

In the example shown in FIG. 4, the slide-valves 19 and 20 are respectively operated in their turn by electromagnets, the windings of which are shown at 27 and 28 respectively and the

cores

29 and 30 respectively, which are rigidly fixed to the corresponding rods 21 and 24. In the position shown in FIG. 4, the two electro-magnets are excited (position P of the outer extremities of the rods 21 and 24). The position of the slide-valves 19 and 20 which corresponds to this simultaneous excitation of the two electro-magnets enables the fluid pressure to be applied in the two compartments 14 and of the jack 7, and corresponds to the basic diagram of FIG. 1.

If, starting from these conditions, the left-hand electromagnet 27-29 is de-excited, the outer extremity of the rod 21 is brought to the position P under the action of a restoring spring 29 and the slide-valve 19 cuts-off the communication between the intake conduit 34 of fluid under pressure and the conduit 37 which supplies the compartment 14 and on the contrary causes this latter to communicate throughthe intermediary of the said conduit 37 with the conduit 38 and the fluid evacuation 36. On the other hand, the slide-valve continues to permit the intake of fluid under pressure to the compartment 15. These conditions correspond to the basic diagram of FIG. 2.

Conversely, if the right-hand electro-magnet 28-30 is alone de-excited, the rod 24 is brought into the position P by the action of a restoring spring and the slidevalve 20 puts to exhaust the compartment 15, while the slide-valves 21 continue to supply fluid under pressure to the compartment 14. These conditions correspond to the basic diagram of FIG, 3.

The main piston 1 can actuate a driven member of any kind, shown diagrammatically in FIG. 4 by an oscillating bar 54 which, in the arrangement of FIG. 4, is held in the central or neutral position as shown in full lines, while when the lef-hand electro-magnet is de-excited, this bar is brought into the position in broken lines on the left and while, if the right-hand electro-magnet is de-excited, it is brought into the right-hand position in broken lines.

It will be noted that, contrary to what took place in the basic diagrams of FIGS. 1 to 3, the arrangement of FIG. 4 comprises a possible fourth combination of the positions of the slide-valves 19 and 20, namely that for which these two slide-valves put the

compartments

14 and 15 simultaneously to exhaust. In the applications in which this combination proves undesirable, various means can be employed to exclude it or to remedy its effects.

For example, as shown in FIG. 4, the excitation and selective -de-excitation of the electro-magnets can be effected from a source of electric current shown diagrammatically by the battery 55, under the control of an appropriate circuit enclosed by the rectangle 56, permitting exclusively either the selective excitation of one of the two electro-magnets or their simultaneous excitation, while preventing them from being both de-excited.

By way of non-limitative example, the circuit 56 may be constituted by a two-pole change-over switch with three directions, as shown in FIG. 4, in which the two fixed end contacts and the two fixed central contacts are supplied in parallel from the source 55, and in which the moving contacts supply respectively the excitation circuits of the two electro-magnets. In the central position of this switch, shown in FIG. 4, it can be seen that the two electro-magnets are simultaneously excited by the source 55, while in the left or right-hand position of the change-over switch, one of them only is excited. No position of the switch permits the two electromagnets to be simultaneously de-excited.

If so desired, it is also possible to retain the ability of simultaneous connection of the two

compartments

14 and 15 to the exhaust tank and to provide restoring means internal or external to the jack. For example, in FIG. 4 there have been indicated external restoring forces F which tend to maintain the driven member 54, and in consequence the piston 1, in the neutral position.

The double-acting and differential fluid pressure jack in accordance With the invention lends itself particularly well to obtaining a very short response time of the control of the piston 1. Thus, for example, in a hydraulic jack of practical construction in accordance with the invention, with an annular surface of 1 sq. cm. of the faces of the piston 1, a full annular surface of 2 sq. cm. of each of the

auxiliary pistons

2 and 3, by the application of an oil pressure of kg./sq. cm., the total surface area of the ports of each piston being of the order of 25 sq. mm. and the travel of the piston 1 towards the left or towards the right being 3 mm., it was possible to obtain a response time of 6 milliseconds from the neutral position to one of the end positions or vice-versa, it being understood that this was the response time of the hydraulic portion, to which it is necessary to add the response time of the distribution, which is substantially of the same order of magnitude when the control is effected by electro-magnets.

It will of course be understood that the invention is in no way limited to the form of embodiment described; it is capable of numerous alternative forms according to the application contemplated, without thereby departing from the scope of the invention. In particular, the hydraulic or pneumatic and electro-magnetic control devices shown have only been given by way of example Without any limitation, and it would also be possible to utilize other devices such as rotary distributors; the control ofthese devices could be effected for example by impulses, in a periodic manner, with any desired programming, etc.

We claim:

1. A double-acting differential fluid-pressure jack, especially hydraulic, with three stable positions, comprising:

a cylinder with three compartments, a central compartment and two outer compartments, each of greater diameter than said center compartment; means for communication of said compartments with each other; three pistons adapted to slide individually, each fitting in one of said three compartments; means for applying and maintaining selectively a fluid under pressure in at least one of said outer compartments; means acting at the same time for putting the outer compartment opposite to said compartment connected to the fluid under pressure into communication with a Zone in which exists a pressure less than that of said fluid under pressure; and means for operatively coupling said central piston to the element to be actuated.

2. A double-acting differential fluid-pressure jack with three stable positions as claimed in claim 1, in which said central piston can pass into said outer compartments.

3. A double-acting differential fluid-pressure jack with three stable positions as claimed in claim 1, in which the length of said central piston is exactly equal to that of said central compartment, and in which said central piston is adapted to slide up to two extreme positions, in each of which it applies one of said outer pistons against the adjacent end of said cylinder.

4. A double-acting differential fluid-pressure jack with three stable positions as claimed in claim 1, in which said means for operatively coupling said central piston to the element to be actuated comprise at least one rod which couples said central piston to said element to be actuated.

5. A double-acting differential fluid-pressure jack with three stable positions as claimed in claim 1, in which said means for communication of said compartments with each other are constituted by ports disposed on said outer pistons and ensuring said communication with a predetermined loss of pressure.

6. A double-acting differential fluid-pressure jack with three stable positions, as claimed in claim 1, in which said pistons of the outer compartments are of the same diameter.

7. A double-acting differential fluid-pressure jack With three stable positions, as claimed in claim 1, in which the rod of said central piston passes through the end of said cylinder in a packing gland sealing device.

8. A double-acting differential fluid-pressure jack, especially hydraulic, with three stable positions, comprising a cylinder With three compartments, a central compartment and two outer compartments, each of greater diameter than said center compartment; means for communication of said compartments with each other; three pistons adapted to slide individually, each fitting in one of said three compartments; means for applying and maintaining selectively a fluid under pressure in at least one of said outer compartments; means acting at the same time for putting the outer compartment opposite to said compartment connected to the fluid under pressure into communication with a zone in Which exists a pressure less than that of said fluid under pressure; means for constant communication of said center compartment With said Zone References Cited by the Examiner UNITED STATES PATENTS 2,005,387 6/ 1935 Pelton 92--65 2,915,043 12/1959 Neiner 92-62 FOREIGN PATENTS 1,339,103 10/1963 France. 1,002,202 2/1957 Germany.

939,035 10/ 1963 Great Britain. 319,349 3/ 1957 Switzerland.

MARTIN P. SCHWADRON, Primary Examiner.

PAUL E. MASLOUSKY, Examiner.

Claims

1. A DOUBLE-ACTING DIFFERENTIAL FLUID-PRESSURE JACK, ESPECIALLY HYDRAULIC, WITH THREE STABLE POSITIONS, COMPRISING: A CYLINDER WITH THREE COMPARTMENTS, A CENTRAL COMPARTMENT AND TWO OUTER COMPARTMENTS, EACH OF GREATER DIAMETER THAN SAID CENTER COMPARTMENT; MEANS FOR COMMUNICATION OF SAID COMPARTMENTS WITH EACH OTHER; THREE PISTONS ADAPTED TO SLIDE INDIVIDUALLY, EACH FITTING IN ONE OF SAID THREE COMPARTMENTS; MEANS FOR APPLYING AND MAINTAINING SELECTIVELY A FLUID UNDER PRESSURE IN AT LEAST ONE OF SAID OUTER COMPARTMENTS; MEANS ACTING AT THE SAME TIME FOR PUTTING THE OUTER COMPARTMENT OPPOSITE TO SAID COMPARTMENT CONNECTED TO THE FLUID UNDER PRESSURE INTO COMMUNICATION WITH A ZONE IN WHICH EXISTS A PRESSURE LESS THAN THAT OF SAID FLUID UNDER PRESSURE; AND MEANS FOR OPERATIVELY COUPLING SAID CENTRAL PISTON TO THE ELEMENT TO BE ACTUATED.