US3225541A

US3225541A - Hydraulic anti-shock device

Info

Publication number: US3225541A
Application number: US430156A
Authority: US
Inventors: Piret Jean
Original assignee: Simca Automobiles SA
Current assignee: Simca Automobiles SA
Priority date: 1964-02-05
Filing date: 1965-02-03
Publication date: 1965-12-28
Anticipated expiration: 1982-12-28
Also published as: GB1055865A; DE1576152B; CH439987A; FR1426102A; BE659156A

Description

DC. 28, 1965 -r HYDRAULIC ANTI-SHOCK DEVICE 5 Sheets-Sheet 1 Filed Feb. 5, 1965 Emma Dec. 28, 1965 J. PlRET 3,225,541

HYDRAULIC ANTI-SHOCK DEVICE Filed Feb. 5, 1965 5 Sheets-Sheet 2 1 7M971??? ean /reT 14770 his 7;

Dec. 28, 1965 J, PlRET 3,225,541

HYDRAULIC ANTI-SHOCK DEVICE Filed Feb. 5, 1965 5 Sheets-Sheet 5 D66. 28, 1965 J, Pl

HYDRAULIC ANTI-SHOCK DEVICE 5 Sheets-Sheet 4.

Filed Feb. 5, 1965 Dec. 28, 1965 J. PIRET 3,225,541

HYDRAULIC ANTI-SHOCK DEVICE Filed Feb. 5, 1965 s Sheets-Sheet 5 6 [ZEN/M) 9 1M5 4 United States Patent HYDRAULIC ANTI-SHOCK DEVICE Jean Piret, Vernouillet, France, assignor to Societe Anonyme Simca Automobiles, Paris, France Filed Feb. 3, 1965, Ser. No. 430,156 Claims priority, application France, Feb. 5, 1964, 962,670 Claims. (Cl. 60-52) The present invention relates to a hydraulic anti-shock device for controlling a double-acting jack piston by means of a hydraulic fluid continually furnished by a pump, and particularly to devices of this type in which the hydraulic jack is actuated by a fluid to control machinetools.

In order to achieve the alternating displacement of a mechanical organ such as a tool holder, a pressure plate, or a mechanical shovel, it is known to use a hydraulic circuit which acts alternately on the double-acting piston of a jack, which piston is rigidly connected to the unit to be displaced.

To this end, each face of the control piston is connected, selectively and alternatively, on the one hand, to the delivery circuit under pressure and, on the other hand, to the hydraulic inlet circuit of the same pump.

The distributor comprises, in general, a principal element in the form of a slide valve carrying a piston which, when it assumes an intermediate, or central, position between its two extreme positions, connects the delivery circuit to the inlet circuit of the pump. The control of this slide valve is etfectuated most often by two electromagnets each mounted to push a respective end of the slide valve. Between the pump and the distributor is disposed in parallel a pressure regulator which determines the maximum pressure of the control fluid applied to the control piston and contained in the control jack.

In order to start the control piston in one direction, one of the windings of the electro-magnets is excited, which has the effect of provoking the displacement of the slide valve and the placing in communication of one of the faces of the control piston with the delivery circuit and of the other face of the piston with the circuit for returning hydraulic fluid to the pump inlet vat. After the movement of the slide valve in the distributor, and prior to the response of the regulator designed to short-circuit a portion of the delivery pressure, a hydraulic starting or compression shock wave appears in hydraulic circuits such as those associated with machine-tools, which wave particularly depends on the dimensions of the jack and of the masses to be placed in movement, and on the value of the operative pressure determined by the pressure regulator.

When the control piston has arrived at the end of its travel path, and when the slide valve is returned to its central position by the de-energization of the previously excited electro-magnet, the chamber which has previously been expanded by the delivery pressure abruptly liberates a large potential energy due to the fact that it is placed in communication with the circuit for returning fluid to the valve, the liberation of this potential energy creating a decompression shock wave.

Moreover, this decompression shock wave is reinforced by the placing under pressure of the opposed face of the control piston in the case where the Winding of the second electro-magnet is energized when the first electro-magnet is de-energized.

It may be readily appreciated that the shock waves which are produced at each starting or reversal of the movement of the control piston during the transient periods in the hydraulic circuit create serious drawbacks since they necessarily create leaks in the delivery circuit Patented Dec. 28, 1965 in the vicinity of connections and joints and, moreover, cause the premature deterioration of the hydromechanical transmissions as a result of the repeated and large strain produced by the elevated pressure points. To these inconveniences are added the considerable loss of hydraulic fluid due to the above-mentioned leaks and the replacement cost of prematurely deteriorated pieces, as well as the labour costs necessary for the replacement of these pieces.

The present invention is intended to be applied to a hydraulic jack within which there is found a double-acting control piston furnished with a straight, or partially straight shank, this jack being connected, on the one hand to a hydraulic fluid delivery circuit adapted to be placed in communication alternatively with one or the other surface of the control piston through the intermediary of a principal distributor furnished with a double-piston slide valve controlled alternatively by two electro-magnets, and on the other hand, a circuit for returning the hydraulic fluid to an inlet vat, which circuit communicates alternatively either with one or the other of the control-piston faces or simultaneously with the two faces of said piston and the delivery circuit of the pump through the intermediary of said principal distributor.

Devices are already known which function to damp the pressure shocks on the control piston by diminishing the acceleration of the hydraulic fluid in the delivery circuit. However, these devices do not prevent the creation of pressure shocks and although these shocks are no longer applied to the jack piston, the reactions of these shocks continue to act on the pump and on at least some of the joints of the delivery circuit.

A known hydraulic anti-shock device comprises, in the delivery circuit, between the delivery pump and the principal distributor, a pressure regulator capable of connecting the delivery circuit to the return circuit to the vat for two different pressure values, referred to as the maximum operative pressure and the minimum operative pressure, respectively. The pressure regulator comprises a valve interposed between the delivery circuit and the vat-return circuit and rigidly connected to a piston defining two chambers, one of which is situated below the piston and communicates directly with the return circuit and the other of which chambers is situated above the piston and communicates with the delivery circuit through the intermediary of a calibrated channel. The upper chamber is furnished with a restraining spring which urges the valve into its closing position and is adapted to be connected to the vat-return circuit through the intermediary of a master distributor controlled by means of an electromagnet.

In the case of a hydraulic anti-shock device associated with a hydraulic motor, it could be conceived to control the electro-magnets of the principal distributor and of the master distributor by means of an electronic timedelay circuit which could theoretically give acceptable results in so far as concerns the elimination of the formation of shock waves even for the case of extremely short work cycles. Such a device would neverthless present the drawback of not controlling the placing under minimum pressure of the delivery circuit by the master distributor and by the principal distributor. As a result the possibility of shock Waves which would be harmful to the apparatus would not be completely eliminated.

At the time of the stopping of the rotating motor prior to the reversal of the direction of rotation of said motor, the shock waves are established in a relatively slow manner, with the result that the response of the pressure regulator could intervene with a delay of one or two seconds with respect to the instant when this latter is commanded (anticipated command).

One could then control the displacement of the principal distributor in order to prepare the reversal of direction of rotation of the rotating hydraulic motor and then progressively reestablish the maximum operative pressure in the delivery circuit, by means of a pressure regulator, through the master distributor one to two seconds after having commanded the principal distributor. In order to definitively eliminate the formation of shock waves, the time-delay of the control of the distributors should be at least slightly greater than the response time of the pressure regulation of the device. It is known that the response time of the distributor depends in a large part on the temperature of the hydraulic fluid, on its viscosity, on the energization voltage of the electromagnets, on the friction of the various movable elements of the distributors, etc., so that the electronic time delay, for reasons of security, should be adjusted in accordance with the maximum response times of the distributors, if one desires to eliminate the formation of shock waves in all cases. The result thereof would be a considerable loss of time, particularly when it would be desired to apply the electronically controlled, hydraulic, anti-shock device to a hydraulic jack whose work cycle should be of the order of one to three seconds.

It has been noted that generally in a hydraulic jack the shock wave is established in /100 of a second. It would thus be desirable to provide a time interval of the order of of a second between the control of the two distributors in order to eliminate, with a margin of security, the possible shock waves, which would not increase in an excessive fashion the duration of a work cycle, even when this latter is of the order of l to 3 seconds. Similarly, in the decompression phase, the control of the principal distributor could intervene as soon after the response of the pressure regulator, i.e. when the delivery pressure is a minimum. For the above-noted reasons, it is not desirable to construct such a hydraulic anti-shock device using electronic means for the anticipated control of the master distributor controlling the pressure regulator and for the delayed control of the principal distributor. Moreover the electronic units are expensive and require highly skilled maintenance personnel.

It is an object of the present invention to eliminate all of the above-noted inconveniences and notably to provide a hydraulic anti-shock device for the control of the jack piston, which device, during starting, stopping and the reversal of the direction of motion of the jack piston at any point in its travel path, prevents the formation of pressure shocks and permits short work cycles for the jack while assuring the delivery of hydraulic fluid which is subjected to no pressure against one of the faces of said jack piston, the obtaining of a small operative pressure during a time period extending between the energization or deenergization of one or more electro-magnets and the response of the pressure regulator, as well as a progressive increase in the fluid pressure until reaching a maximum operative pressure and a progressive decrease of the pressure until attaining the minimum operative pressure during the reverse process.

The hydraulic anti-shock device associated with a hydraulic jack furnished with a piston whose two faces, through the intermediary of a principal distributor commanded alternately by two electro-magnets, are capable of being connected either alternately with the delivery circuit or the return circuit of a pump, or simultaneously with the two circuits, comprises: in the delivery circuit downstream of the principal distributor, a pressure regulator furnished with a valve interposed between the delivery circuit and the return circuit to the inlet vat, and rigidly connected to a piston defining two chambers, the lower chamber of which communicates directly with the delivery circuit and the upper chamber of which, furnished with a restraining spring urging the valve into its closing position, communicates through the intermediary of a calibrated channel with the delivery circuit; a master distributor connected, on the one hand to the upper cham ber of the valve piston and, on the other hand, to the vatreturn circuit, and capable of being controlled by an electro-magnet in such a manner as to destroy or establish the communication between the upper chamber of said valve piston and the vat-return circuit; and an electric circuit furnished with switches and relays for starting up and stopping the pump motor and for controlling the various electro-magnets, this hydraulic anti-shock device being characterized in that it comprises end-of-travel switches capable of being actuated by cams arranged in such a manner as to be able to follow the displacement of the armature of the corresponding electro-magnets of the distributors, the end-of-travel switch of the master distributor being disposed in the electric circuit of the electro-magnets of the principal distributor in such a way that it cannot be closed by its corresponding cam and does not permit the excitation of one of the electro-magnets of the principal distributor until the master distributor is in its neutral position, while the end-of-travel switches of the principal distributor are disposed in the circuit of the electro-magnet of the master distributor in such a way that neither can be closed by its corresponding cam and does not permit the excitation of the electro-magnet of the master distributor until the principal distributor occupies one of its two extreme positions.

These and other objects, features and advantages of the present invention will become more readily understood from the following description of various embodiments of the present invention, given only by way of non-limiting example, together with the attached drawings, in which:

FIG. 1 shows a hydraulic circuit of a jack, e.g. for a machine-tool, this jack being furnished with a hydraulic anti-shock device capable of being controlled according to the present invention;

FIG. 2 shows a hydraulic circuit of a jack, e.g. for a machine-tool, this jack being furnished with a second type of hydraulic anti-shock device capable. of being controlled according to the present invention;

FIG. 3 is a schematic diagram of a first embodiment of an electric control and monitoring circuit according to the present invention for the motor, pump and electromagnets of the distributors of the device of FIG. 1;

FIG. 4 shows a schematic diagram of a second embodiment of the control and monitoring circuit of the present invention; and

FIG. 5 is a schematic diagram of a third embodiment of the control and monitoring circuit of the present invention.

Turning first to FIG. 1, there is shown a jack 1, for a machine-tool e.g., comprising a double-acting piston 2 to which is rigidly connected a shank 3 furnished with a tool, not shown. The piston 2 defines two chambers 4 and 5 in the jack 1, each of these chambers communicating, through the intermediary of a respective one of

conduits

6 and 7, with a respective one of the end chambers 8 and 9 situated to either side of a central chamber 10 ofa principal distributor 11. Through the intermediary of a double piston slide valve 12, each of the end chambers 8 and 9 communicates with the central chamber 10 and, through the intermediary of said central chamber, with the delivery circuit 13 of a pump P driven by a motor M, these end chambers 8 and 9 also being connected to the return circuit 14 of the inlet vat 15 of pump P. In the description to follow, it should be understood that the term return circuit is intended to include all of the conduits leading to the vat 15 of pump P. When the double piston slide valve 12 is in its intermediate position, as shown in FIGS. 1 and 2, each of the chambers 4 and 5 of jack 1 communicates with the delivery circuit 13 as well as with the return circuit 14 leading to the inlet vat 15 of pump P.

.37. of electro-magnet EA to the shank 41 in order to diminish the speed of disregulator 16, comprising a piston 17 whose lower surface is rigidly connected to a valve 18 controlling an opening 19 through the intermediary of which the delivery circuit 13 communicates directly with the circuit 14 for returning fluid to the inlet vat 15 of pump P. On its upper surface, the regulator piston 17 carries a hollow cylinder 20 adapted to slide in an inpermeable manner in a cylindrical space 21 of the regulator. In this space 21 is housed a restraining spring 22 which urges the piston 17 downwardly in order to close the opening 19 by means of the valve 18, which valve comprises a central orifice 23 connecting said space 21 with the circuit 14 for returning fluid to the inlet vat 15. The piston 17 also comprises an eccentric calibrated channel 24 which creates a communication between a chamber 25, connected to the delivery circuit 13 and situated below the lower face of piston 17, and a chamber 25a, delimited by the upper surface 17, the housing of regulator 16, and the outer periphery of hollow cylinder 20. This annular chamber 25a is connected to the cylindrical space 21 through the intermediary of a calibrated channel 26, a retaining valve 27 urged by a regulatable spring 28 in a direction opposed to the flow of delivery fluid, a chamber 29 in which are housed said valve 27 and the regulatable spring 28, and a channel 26a. The calibrated channel 26 is also connected to a first connecting conduit 13, referred to as the master conduit, creating a communication between the delivery side of pump P and a first master distributor 30. This distributor 30 also comprises a pair of

chambers

31 and 32, each of which is disposed at a respective end of distributor 30, continually communicating with the return circuit 14 of the inlet vat 15 of the pump P. Distributor 30 also comprises a central chamber 33 into which empties the first master conduit 13. The first master distributor 30 further comprises a double piston slide valve 34 which, in its intermediate position, prevents any communication between the master conduit 13' and the

end chambers

31 and 32, and thus between conduit 13' and the return circuit 14.

At each of its ends, the principal slide valve 12 is urged by the

restraining springs

35 and 36 towards its intermediate position, this slide valve co-operating with the

armatures

37 and 33 of electro-magnets EA and EA respectively, each of which controls the displacement of said slide valve towards a respective end of distributor 11.

Armature 37 serves as an abutment for a control shank 41 which is guided in support bearing 44 and urged towards said armature 37 by springs 39 which are noticeably weaker than the spring 35 of slide valve 12. The

springs

35, 36 and 39 are calibrated in such a way that their forces are in equilibrium when the slide valve 12 occupies the neutral position shown in FIG. 1.

The shank 41 carries two

cams

42 and 43, each of which is intended to co-operate with a respective one of the switches FC and FC referred to as end-of-travel switches, these

cams

42 and 43 being mounted on said shank 41 in such a way that, on the one hand, the two switches FC and FC interposed in the electric control circuit in such a way as to control the excitation of electro-magnet EA of master slide valve 34, are open when the principal slide valve 12 is in its neutral position while, on the other hand, one or the other of these of these switches PC and PC, is closed when the principal slide valve 12 occupies one of its extreme positions corresponding to the advance or return of the piston 2 of jack 1.

The springs 39 are calibrated in such a way that the assembly of shank 41 and

cams

42 and 43 moves either at the same speed or at a slower speed than the armature A mass could also be added placement of the

assembly

41, 42 and 43 with respect to that of the armature 37. At its opposite end from electro-magnet EA the control shank 41 is furnished with a push button 46 which may, e.g., constitute the mass mentioned above and which permits the manual actuation of principal slide valve 12. The electromagnet EA the control shank 41, the bearings 44, the switches FC and FC.,, and a part of the push button 46 are all housed in a casing 47 attached to one of the end faces of distributor 11.

The master slide valve 34 comprises, at one of its ends, a restraining spring 48 which urges the master slide valve 34 into its extreme right-hand position, referred to as its neutral position, as shown in FIG. 1, which position permits the conduit 13 to communicate with the return circuit 14. This master slide valve 34 also carries, at its other end, an electro-magnet EA which, when it is energized, displaces the master slide valve 34 from its neutral position into a position where it prevents any communication between the conduit 13' and the return circuit 14. The armature 50 of electro-magnet EA co-operates with, and serves as an abutment for, a control shank 51 guided in support bearings 54 and carrying two

cams

52 and 53, each of which co-operates with a respective one of the end-of-travel switches FC and FC At its opposite end from electro-magnet AE the shank 51 is furnished with a push button 56 which permits the manual actuation of master slide valve 34. The electro-magnet EA the control shank 51, the bearings 54, the switches FC and PC and a part of the push button 56 are housed in a casing 57 attached to one end of master distributor 30. The shank 51 is urged towards the armature 50 by the springs 54 which are weaker than the spring 48 and which act against the push button 56, the

springs

48 and 54 being calibrated in such a way that the first master slide valve 34 occupies, under the sole efl ect of their urging, the neutral position shown in FIG. 1.

As in the case of the shank 41 of principal distributor 11, the shank 51 of the first master distributor 30 could be furnished with a mass, constituted e.g. by the push button 56, which serves to decrease the speed of displacement of the

assembly

51, 52 and 53 with respect to that of the armature 50.

The

cams

52 and 53 are mounted on the shank 51 in such a way that they alternately close their corresponding switches F0 and PC the switch FC being interposed in the electric control and monitoring circuit and being intended to control the energization and de-energization of one of the electro-magnets EA and EA of the principal distributor 11, while the other switch FC is connected to an audible or visual signalling device (not shown) and is intended to control said device in order to provide an indication of the position of master slide valve 34.

The end-of-travel switches FC FC FC and F0 are closed when they are actuated by their

respective cams

42, 43, 52 and 53, and open when they are not contacted by said respective cams. Each

cam

42, 43, 52 and 53 comprises a wedge-shaped portion and a cylindrical portion. The

cams

42 and 43 are arranged on the control shank 41 and the

cams

52 and 53 are arranged on the shank 51 in such a way that the cam 42 has its wedgeshaped portion directed towards electro-magnet EA the cam 52 has its wedge-shaped portion directed towards the electro-magnet EA and the cam 43 has its wedge-shaped portion directed towards the push button 46 and the cam 53 has its wedge-shaped portion directed towards the push button 56.

I. The operation of the first embodiment of the shockresisting hydraulic device is as f0ll0ws.It should first be noted that the description of this operation only refers to the various hydraulic processes, and that the various processes of electrical control and monitoring of the distributors will be described later in the present specification.

The positions of the principal and master slide valves 12 and 34, respectively, and of the piston 2 of jack 1 are as shown in FIG. 1. The pump P is started up. The pump P supplies a hydraulic fluid to the delivery circuit 7 13, this fluid passing through the return circuit 14 to the inlet vat 15 and into the chambers 4 and 5 of jack 1, due to the fact that the principal slide valve 12 is in its neutral position. The pressure of the fluid acting on either side of piston 2 is thus practically equal to the atmospheric pressure.

(a) Displacement of the principal slide valve 12 to its extreme left-hand position Electro-magnet EA is excited so that its armature 37 pushes the slide valve 12 of distributor 11 towards the left in such a way that communication between the delivery circuit 13 and the return circuit 14 connected to the distributor 11 is interrupted, the chamber 5 of jack 1 communicates with the delivery circuit 13, and the chamber 4 of jack 1 communicates with the return circuit 14 mounted on said distributor 11. When the pressure in circuit 13 exceeds a certain predetermined value, which is generally small, this pressure being called the minimum operative pressure, the fluid acts on the lower face of piston 17 of main pressure regulator 16 and urges said piston 17 and its valve 18 upward against the force exerted by restraining spring 22, the force produced by said spring 22 being relatively weak. In this way, the hydraulic fluid sent by the pump P through the delivery circuit passes through orifice 19 of regulator 16 and through the return circuit 14 to the inlet vat 15. The rest of the delivery circuit 13 and chamber 5 of jack 1, although they are filled with fluid, are under practically no pressure, or in other words, are at the minimum operative pressure.

A part of the hydraulic fluid arrives at the first master distributor 30 through the calibrated channel 24, the chamber 25a, the calibrated channel 26 and the master conduit 13'. Because the chamber 33 of master distributor 30 is connected to the return circuit 14, in the case where the master slide valve 34 is in the position shown in FIG. 1, this portion of the fluid also returns to the inlet vat 15. The pressure existing in chamber 25a above piston 17 is thus practically equal to the atmospheric pressure and because the force generated by the fluid delivered to chamber 25 and applied against the lower face of piston 17 is greater than the opposing force of spring 22, the valve 18 remains open.

(b) Displacement of the master slide valve 34 towards the left The displacement of the master slide valve 34 towards the left, in such a way that the communication of the chamber 34 of master distributor 30 with the return circuit 14 mounted on said distributor is interrupted, corresponds to a progressive augmentation of the fluid delivery pressure, or in other words, to a placing of the fluid under pressure until it attains a pressure called the maximum operative pressure. To this end, the electromagnet EA;, is excited with the result that it pushes the master slide valve 34 into its closing position against the opposing force of spring 48. The closing of the chamber 34 produces a progressive increase in the pressure of the fluid contained in the master conduit 13' and in the chamber 25a of the main regulator 16.

Since chamber 25a is then practically at the same pressure as the chamber 25 and the delivery circuit, the spring 22 progressively closes the orifice 19, which operation is accompanied by a continuous increase in the pressure of the delivery fluid, which circulates without inducing hydraulic shocks on the piston 2 of jack 1.

(c) Advance of the piston 2 of jack 1 When a certain pressure, called the maximum operative pressure, has been established in the delivery circuit 13 and in the chamber 5 of jack '1, the piston 2 advances towards the right, i.e. towards the other end of jack 1. During this displacement of piston 2 the fluid pressure remains constant; it does not begin to increase anew until the piston 2 has arrived at the right-hand end of its path of travel. This new increase in the fluid pressure is reflected against the lower face of piston 17 of regulator 16 as well as in chamber 25a, channel 26 and conduit 13. The spring 28 is adjusted in such a way that it permits, for a given pressure, the opening of retaining valve 27. As a result, a portion of the fluid in the chamber 25a escapes towards the return circuit 14 through valve 26, chamber 29, channel 26a, space 21 and channel 23, and thus permits the opening of valve =18. The fluid delivered by the pump P then arrives through the orifice 19 at the return circuit 14, but the maximum operative pressure corresponding to the displacement of of the piston 2 of jack 1 is maintained in the delivery circuit 13 and in the chamber 5. In this case, the valve 18 also plays the role of a maximum pressure regulator. However, the valve 18 is not necessarily combined with 'a regulatable retain ing valve 27 and a

canal

26a, 23 communicating with the atmosphere. The present invention may equally well be applied to the case where a valve 18 is interposed in the delivery circuit 13 and where the upper chamber 25a of the valve is only connected to the return circuit through the intermediary of a master distributor. In this case, any prior art type of maximum pressure regulator may also be provided in the delivery circuit.

(d) Displacement of the master slide valve 34 towards the right The displacement of the master slide valve 34 towards the right, in such a way as to permit the communication of the chamber '33 of master distributor 30, and thus of the master conduit 13', with the return circuit 14 fastened to said distributor 30, corresponds to a progressive decrease in the pressure of the fluid contained in the delivery circuit 13 and in the chamber 5 of jack 1. In other words, this corresponds to a progressive removal of pressure from the delivered fluid. In efiect, when the master slide valve 34 connects the chamber 25a, situated above piston -17 of regulator 16, to the return circuit 14 through the intermediary of channel 26, master conduit 13' and

chambers

31, 32 and 33 of master distributor 30, the fluid contained in this chamber 25a escapes progressively towards the return circuit '14. As a result, the valve 18 can open wide in proportion to the quantity of fluid driven from the chamber 25a through the channel 26 of regulator 16. A minimum operative pressure then exists in the delivery circuit 13 and in the chamber 5 of jack 1.

(e) Displacement of the principal slide valve 12 towards the right to its neutral position 'Electro-magnet EA is deactivated, which permits spring 35 to return the main slide valve to its neutral position, in which position the delivery circuit 13, the return circuit 14, and the chambers 4 and 5 of jack 1 are all interconnected through the intermediary of

chambers

8, 9 and 10 of principal distributor 11. As a result, the pressure of the fluid contained in the chambers 4 and 5 and the circuit 13 is equal to the atmospheric pressure.

(f) Displacement of the principal slide valve 12 towards its extreme right-hand position Electro-magnet EA is excited so as to cause its armature 38 to push the slide valve 12 towards the right in such a way that the communication between the delivery circuit 13 and the return circuit 14 attached to distributor 11 is interrupted, the chamber 4 of jack 1 is connected to the delivery circuit 13, and the chamber 5 of said jack 1 is connected to the return circuit 14 through the intermediary of the conduit 7 of the chamber 9 of principal distributor 11. The fluid contained in the delivery circuit 13 and in the chamber 4 is at the minimum operative pressure since the valve 18 opens automatically.

9 (g) Displacement of the master slide valve 34 towards the left The displacement of the master slide valve 34 towards the left in such -a way as to break the communication between the chamber 33 and the return circuit 14 attached to the distributor 30 corresponds, as has already been said, to a progressive placing under pressure of the fluid contained in the delivery circuit 13 and in the chamber 4 of jack 1. The difierent phases of this operation have already been described in paragraph Ib, above.

(h) Return of piston 2 of jack 1 When the maximum operative pressure has been established in the delivery circuit 13 and in the chamber 4, the piston 2 returns to the left. This process is practically identical with that described in paragraph Ic, above.

(i) Displacement of the master slide valve 34 towards the right This corresponds to a progressive decrease in the pressure of the fluid contained in the delivery circuit 13 and in the chamber 5 until a minimum operative pressure has been established. This process is identical with that described in paragraph Id, above.

(1') Displacement of the principal slide valve 12 towards the left to its neutral position The electro-magnet EA is deactivated, which permits the spring 36 to push the principal slide valve 12 into its neutral position, in which position the delivery circuit 13 as Well as the chambers 4 and 5 of jack *1 are all interconnected together and to the return circuit 14 and are, as a result, placed in communication with the atmosphere.

In order to permit a programming of the operative pressure so as to cause it to comprise one or several intermediate pressures between the minimum operative pressure and the maximum operative pressure, the present invention also provides one or several master distributors, identical with that shown in FIG. 1.

Turning now to FIG. 2, the hydraulic anti-shock device comprises two

master distributors

30 and 58. In this case, a second master conduit '13" is branched ofi of the first master conduit 13' between the output of pressure regulator 16 and the first master distributor 30. This conduit 13" is connected to a second master distributor 58 which, through the intermediary of an auxiliary pressure regulator 59 interposed in the return circuit 15 attached to said distributor 58, communicates with the inlet vat 15 of pump P.

This auxiliary pressure regulator 59 comprises a piston 65 whose lower face is furnished with a valve 66 adapted to close an orifice 67 to which is attached a portion of the return circuit 14. A restraining spring 68 suitably calibrated and acting on the upper face of piston 65 urges valve 66 into its closed position.

The second master distributor 58 also comprises, at each end, a respective one of

chambers

69 and 70 in permanent communication with the return circuit 14, and a central chamber 71 into which empties the second master conduit 13". This distributor 58 is furnished with a double-piston master slide valve 64 which, in its intermediate position, prevents any communication of the second master conduit 13" and the central chamber 71 with the

end chambers

69 and 70 of said distributor 58 and thus with the return circuit 14.

The second master slide valve 64 carries at one of its ends a restraining spring 72 which urges the slide valve 64 into its extreme right-hand position, called the neutral position, as shown in FIG. 2, and permits communication between the conduit 13" and the return circuit 14 through the intermediary of

chambers

69, 70 and 71 of master distributor 58.

At its other end, the master slide valve 64 carries an electro-magnet EA which, when it is activated, displaces the master slide valve 64 from its neutral position to a position, called the intermediate position, where it blocks communication between the second master conduit 13" and the return circuit 14. The armature of electromagnet EA co-operates with, and serves as an abutment for, a control shank 61 guided in support bearings 74 and carrying two

cams

62 and 63, each of which co-operates with a respective switch F0, and PC marking the ends of the path of travel of the shank. At the opposite end from electro-magnet EA the shank 61 is furnished with a push-button 75. The

elements EA

61, 62, 63, 75, PC and PC as in the case of the first master distributor 30, are housed in a casing 76 fastened to the side surfaces of the second master distributor 58.

Shank 61 is urged towards the armature 61} by springs 73, which are weaker than the spring 72 and which act on the push button 75.

Springs

72 and 73 are calibrated in such a way that the second master slide valve 64 occupies, when exclusively under their influence, the neutral position shown in FIG. 2. As in the case of

shanks

41 and 51 of

distributors

11 and 30, respectively, the shank 61 of the second master distributor 58 can be furnished with a mass, constituted e.g. by push button 75, so as to decrease the displacement speed of the

assembly

61, 62 and 63 with respect to that of the armature 60 and of the master slide valve 64.

The switch PO, is open and the switch FC is closed when they are activated by their

respective cams

63 and 62. The

cams

62 and 63 are mounted on the shank 61 in such a way that they control, or simultaneously permit, the opening, or the closing, of switches F0 and FC The switch FC which is connected to a signalling device, is closed and controls the emission of a luminous or acoustic signal when the second master slide valve 64 breaks the hydraulic connection between the main regulator 16 and the auxiliary regulator 59, while the switch FC interposed in the electric command and monitoring circuit, is open and disconnects the excitation of electromagnet EA of the first master distributor 30 when the slide valve 64 of the second master distributor 58 is in its neutral position, i.e. when the latter establishes a hydraulic connection between the

regulators

16 and 59.

It should also be noted/that in the case of a hydraulic anti-shock device having two master distributors, the switch FC marking one end of travel in the first master distributor 31 no longer controls a luminous or audible signalling device, but this switch is interposed in the electric control and monitoring circuit of the hydraulic anti shock device and is particularly intended to only permit the actuation of the electro-rnagnet EA of the second master distributor 58 when it is closed, i.e. when the first master slide valve 34 breaks the communication between the principal pressure regulator 16 and the return circuit 14 attached to the first master distributor 30.

II. The operation of this embodiment of a hydraulic anti-shock device is as f0llows.-As before, the description of this operation only concerns the various hydraulic processes effectuated by the device of the present invention. The positions of the principal slide valve 12 and the

master slide valves

34 and 64, as well as those of the

pressure regulators

16 and 59 are as shown in FIG. 2. When the motor M is placed in operation, the pump P supplies hydraulic fluid to the delivery circuit 13, this fluid passing through the return circuit 14 attached to the principal distributor 11 and through the chambers 4 and 5 of jack 1, since the principal slide valve 12 is in its neutral position (FIG. 3). As a result, the pressure of the fluid acting on both sides of the piston 2 of jack 1 is substantially equal to atmospheric pressure.

(a) Displacement of the principal slide valve towards its extreme left-hand position The electro-magnet EA is excited so that its armature 37 pushes the slide valve 12 of distributor 11 towards the left. These operations and the eilects thereof have already been described in paragraph Ia. The fluid passing through the channel 26 of main regulator 16 arrives not only at the first master distributor 30, and from there to the return circuit 14, but also at the second master distributor 58 and its return circuit 14. However, the auxiliary regulator 59 does not permit the fluid passing through the second master distributor 58 to flow into the inlet vat 15, since valve 66 is closed.

([2) Displacement of the first master slide valve 34 towards the left When the electro-magnet EA of the first master distributor 30 is excited, its armature 50 pushes the master slide valve 34 towards the left in such a way as to cause an interruption of the communication between the chamber 33 and the return circuit 14 attached to the first master distributor 30. As has already been described in paragraph 'Ib, there is then established in the chamber 25a of the main regulator 16 a certain counter-pres sure applied against the upper face of piston 17 which, by acting on the valve 18, determines progressively, and without producing hydraulic shocks, the establishment of a pressure, called the average operative pressure, in the delivery circuit 13 and in the chamber of jack 1. This average pressure is determined by the spring 68 of auxiliary regulator 59. From the moment when this average pressure is exceeded in the delivery circuit 13, the valve 66 of auxiliary regulator 59 opens and creates a pressure drop in the chamber 25a of main regulator 16, so that its valve 18 also opens and leads the pressure of the fluid in the delivery circuit to arrive at the average operative pressure.

(c) Displacement of the second master slide valve 64 towards the left This displacement, produced by the actuation of electro-magnet EA of the second master distributor 58, places the slide valve 64 in a position in which the communication between the central chamber 71 of said distributor and the return circuit 14 is interrupted. This causes a progressive increase in the pressure of the delivery fluid, commencing from the average operative pressure and terminating at the maximum operative pressure. This process is similar to that described in paragraph Ib.

(d) Advance of the piston 2 of jack 1 The piston 2 advances under the effect of the maximum operative pressure which is applied thereagainst (see paragraph 16).

The processes for removing the pressure from the delivery circuit 13 and the chamber 5 of jack 1, for the reversal of the movement of principal slide valve 12, for the placing under pressure of the chamber 4 of jack 1, for the return of piston 2 of jack 1, for the removal of pressure from the delivery circuit 13 and the chamber 4, and for the displacement of principal slide valve 12 into its intermediate position, are similar to those described in paragraphs Id to If, above.

The only essential difference consists in the fact that the establishment of the maximum operative pressure and the removal of pressure are carried out in two steps, but these operations are always progressive.

In order to place the delivery circuit under pressure, in order to control either the advance or the return of the piston 2 of jack 1, the following operations are carried out in the following order:

Displacement of the principal slide valve 12 from its neutral position to an extreme position, corresponding to the advance or return of piston 2;

Displacement of the master slide valve 34 into its closing position;

And displacement of the second master slide valve 64 into its closing position.

After the advance or return of jack-piston 2, the system is caused to operate in an inverse fashion in first returning the second master slide valve 64, then the first master slide valve 34, and finally the principal slide valve 12 to their neutral positions.

For the control and monitoring of the activation and the de-activation, several electric circuit arrangements are provided which permit either a semi-automatic control or an entirely automatic control of the hydraulic anti-shock device.

Turning now to FIG. 3, the electric control and monitoring circiut for the hydraulic anti-shock device shown in FIG. 1 comprises several groups G G G G G and G of electric elements, these groups being energized in parallel by a single-phase alternating current source In this figure, there is also shown, schematically, the motor M of pump P, this motor being exicted by a threephase mains RT.

In a general manner, the various contacts and switches shown in FIGS. 3, 4 and 5, are of two dilferent types. Assuming that a current flows through the system of FIG. 3 in the sense of the arrow F, all of the contacts and switches to the left of the direction of curent flow in the conductors with which they are associated are open when they are not activated by their respective control organs or, on other words, when their corresponding relays are not actuated or when they are not depressed by their corresponding cams. Similarly, the contacts and switches to the right of this direction of current flow are closed when they are not actuated by their respective control organs. The contacts controlled by the same relay are indicated by the same main reference, but each bears a difierent sufi'ix.

In FIG. 3, the first group of electrical elements G comprises a relay C called the control switch for motor M; this relay C is mounted in series with a manual control switch Mm which is generally open so as to permit the starting of motor M, and with another manual control switch Am which is normally closed, permitting the stopping of motor M.

A contact C called the holding contact for relay C is connected in parallel across the terminals of switch Mm, a second contact C of relay C is interposed in the line L feeding the other groups G to G and a third group C of three contacts is placed in the lines supplying energy to motor M, these contacts C C and the three contacts C being closed when their relay C is actuated.

The second group of electrical elements G comprises two relays R and R called relays for monitoring the advance and return of the piston jack, mounted in parallel with one another. A manual switch DCAV, referred to as the switch for starting the advance cycle, is mounted in parallel with a contact R referred to as the holding contact for advance-monitoring relay R the switch DCAV and the contact R being each mounted in series with said relay R Another manual switch DCAR, referred to as the switch for starting the return cycle, is mounted in parallel with a contact R referred to as the holding contact for the return-monitoring relay R this contact R and the switch DCAR each being mounted in series with the relay R A third manual switch Ac, called the cycle-stopping switch, is normally closed and is mounted in series with the contacts R R and the switches DCAV and DCAR, the contacts R and R closing when their corresponding relays R and R are actuated.

The third group of electrical elements G comprises a relay, called the advance-control relay C the winding of the first electro-magnet EA of the principal slide valve 12, and a first contact C which is normally open and which is operated by said relay C this contact C and this winding EA being mounted in series with one another, but in parallel with respect to said relay C As shown in FIG. 3, the winding EA is connected across the terminals of relay C through the intermediary of contact C which, in the present case, is not indispensable. However, the series connection of contact C and winding EA could also be connected between the lines L and L, in parallel with relay C without being directly connected across the terminals of said relay C The preceding considerations are, in addition, also valid for the connection of the windings of the other electromagnets EA EA and EA and for their corresponding control relays.

The third group G, also comprises a second contact C which is normally closed, is mounted in series with relay C and is controlled by the relay C of the fifth group G a third contact R which is normally closed, is mounted in series with the contact C and is controlled by the relay R of the sixth group G a fourth contact R which is normally open, is mounted in parallel with the contact R and is controlled by the advance-monitoring relay R a fifth contact R which is normally open, is mounted in series with the contact R but in parallel with the contact R and is controlled by the relay R and a sixth contact, called a holding contact C which is normally open, is mounted in parallel with the contact R and is commanded by the relay C The fourth group of electrical elements 6,; comprises a relay C referred to as the control relay for the first distributor 30; the winding of electro-magnet EA of master slide valve 34; a first contact C which is normally, open, this winding EA and contact C being mounted in series with one another and in parallel with relay C a second and a third contact R and R respectively, both of which are normally open and which are mounted in parallel with one another and in series with relay C the contact R being controlled by the relay R and the contact R being controlled by the relay R and the two switches FC and FC each of which is associated with a respective one of the ends of the path of travel of the movable element of distributor 11, each of these switches co-operating with a respective one of the cams 42 and 43 mounted on the shank 41 of principal slide valve 12, these switches FC and PG; being mounted electrically in parallel with one another, but in series with the contacts R and R 2, and being normally open when they are not acted upon by their corresponding cams 42 and 43.

The fifth group of electrical elements G comprises: a relay C referred to as the return-control relay, the winding of the second electro-magnet EA of the principal slide valve 12; a first contact C which is normally open and which is controlled by the relay C this Winding EA and this contact C being mounted in series with one another but in parallel with relay C a second contact C which is normally closed, mounted in series with said relay C and controlled by the relay C of the third group G a third contact R which is normally closed, mounted in series with contact C and controlled by the relay R of the sixth group G a fourth contact R which is normally open, mounted in parallel with the contact R3 and controlled by the return-monitoring relay R a fifth contact R which is normally open, mounted in series with the contact R but in parallel with the contact R and controlled by the relay R and a sixth contact, called the holding contact C which is normally open, mounted in parallel with the contact R and controlled by the relay C The sixth group of electrical elements G comprises: a relay R referred to as the maximum operative pressure monitoring relay, mounted in series with the switch FC which is responsive to the end of travel of the movable elements of master distributor 30, this switch being closed when it is acted on by its corresponding cam 53, Le. when the master slide valve 34 is in its neutral position.

A manual switch, called the emergency switch Au, is also interposed in the supply line L feeding the various groups of electrical elements.

III. The above described electrical circuit functions in combination with the hydraulic anti-shock device of FIG.

1 in the following manner.This description concerns particularly the order of the various electrical control operations of the device of the present invention, which operations relate to the various hydraulic phenomena described earlier in this specification.

All of the switches and contacts are initially in the positions shown in FIG. 3. These positions correspond to those of slide valves 12 and 34 as indicated in FIG. 1.

(a) The starting of motor M of pump P The switch Mm is closed. The relay C is then actuated and closes the switches C C and C The relay C remains actuated when the switch Mm is opened, since the holding contact C remains closed. Because the switch C is closed, the motor M is supplied with current. The switch C being closed, as is the end-of-travel switch PC the relay R is actuated and its contacts R and R are opened while its contacts R and R close. When the contacts R and R on the one hand, and R and R on the other hand, are opened, the relays C and C cannot be actuated.

(b) Control of the electro-magnet EA of principal slide valve 12 This control corresponds to a displacement of the principal slide valve 12 towards the left (FIG. 1). To this end, the switch DCAV is closed in order to permit the actuation of relay R thereby controlling the closing of its contacts R R and R After the opening of switch DCAV, the actuation of relay R is maintained due to the fact that its holding contact R is closed.

The relay C is then supplied with current through the intermediary of closed switches R R and C The actuated relay C closes its holding contact C as well as the contact C this latter contact thus permitting the actuation of electro-magnet EA so as to permit it to displace the principal slide valve 12 towards the left.

(0) Control of the electro-magnet EA for the first master slide valve 34 This control corresponds to a displacement of the slide valve 34 towards the left and to the causing of a progressive increase in pressure of the fluid contained in the delivery circuit 13 and in the chamber 5 of jack 1.

The control shank 41 of the principal distributor 11 follows the displacement of slide valve 12 towards the left so that the cam 42 moves to close the switch FC The relay C is then supplied with current through the intermediary of the switch PC and the switch R both of which are closed. The relay C closes the contact C and thus permits the actuation of electro-magnet EA which urges the master slide valve 34 towards the left.

The control shank 51 follows the displacement of master slide valve 34. The cam 53 moves away from the switch FC permitting the switch to open, and the cam 52 closes the switch FC when the slide valve 34 has reached its closing position. An audible or visual signal, controlled by the switch FC indicates this position of slide valve 34. However, prior thereto, the switch FC has disconnected the supply of current to relay R so that its contacts R and R re-open, and its contacts R and R close.

Electro-magnet EA remains actuated since the relay C is supplied with current through the intermediary of the closed contacts C R andC On the other hand, the relay C controlling the actuation of electro-magnet EA cannot be supplied with current, despite the closing of contact R because the contact C remains open as long as the relay C is actuated.

The piston 2 of jack 1 advances towards the right-hand end of its path of travel under the effect of the maximum operative pressure. It should also be noted that follow each other automatically.

(d) Termination of the advance cycle of piston 2 The end of the advance cycle corresponds to successive de-actuations of the electro-magnets EA and EA i.e. to the progressive reduction in pressure in delivery circuit 13 and in the chamber 5 of jack 1.

T this end, the switch Ac is momentarily opened so as to disconnect the supply of current to relay R causing the contacts R R and R thereof to re-open. The relay C remains actuated through the intermediary of closed contacts R and C When the contact R opens, the relay C is de-energized, the contact C opens and the electro-magnet EA is de-energized. The master slide valve 34 is then urged to its neutral position by the spring 48. Due to this fact, the switch FC opens and the switch FC then closes and permits a re-energization of the relay R causing the opening of contact R and, as a result, the de-energization of relay C The contact C opens and the electro-mag'net EA is de-energized. The spring then urges the principal slide valve 12 into its neutral position, causing the cam 42, which follows this movement, to move away from the switch FC permitting the latter to open.

(e) Control of the electro-magnet EA of principal slide valve 12 This control corresponds to the displacement of slide valve 12 towards the right and to the preparation for the return of piston 2 of jack 1.

The switch DCAR is closed, permitting the energization of the return-monitoring relay R the contacts of which R R and R also close. Owing to its holding contact R the relay R remains energized after the release of switch DCAR.

The relay C is then energized through the intermediary of the closed contacts R R and C The contact C closes and permits the energization of electro-magnet EA which urges the principal slide valve 12 towards the right.

(f) Control of the electro-magnet EA 3 of master slide valve 34 This control corresponds to the displacement of slide valve 34 towards the left and to the progressive increase in pressure of the fluid in the delivery circuit and in the chamber 4 of jack 1.

The control shank 41 of the p rincipal distributor 11, under the efiect of electro-magnet EA displaces towards the right and the cam 43 closes the switch FC The relay C is then energized through the intermediary of the switch F0 and the closed contact R The energization of relay C3 closes the contact C energizing electro-magnet EA The process which follows is then the same as that described in paragraph III (c).

The control shank 41 of the principal distributor 11,

(g) Termination of the return cycle of piston 2 The end of the cycle corresponds to the successive deenergizations of electro-magnets EA and EA as well as the progressive reduction of pressure in the delivery circuit 13 and the chamber 4 of jack 1.

The switch Ac is momentarily opened, causing the deenergization of relay R and the resulting re-opening of contacts R R and R of this relay. The relay C remains energized through the intermediary of the closed contacts R and C but the relay C becomes de-energized because of the opening of contact R The electromagnet EA is therefore de-energized since the contact C also re-opens and the spring 48 urges the cam 53 against the switch FC which closes the switch and thus permits the re-excitation of relay R The contacts R and R open and the relay C becomes de-energized, as does the electro-magnet EA The spring 36 then urges the principal slidevalve 12 into its neutral position and the cam 43 of the shank 41 follows this movement under the influence of springs 39 and moves away from switch FC In case of emergency the apparatus can be turned off by the switch Au.

It might be desirable to automatically control the stopping of the advance cycle, the reversal of the principal slide valve, the return of the piston 2 and the stopping of the return cycle.

For this purpose, in accordance with the present invention, there is provided on the shank 3 of the jack-piston 2 a cam which. is adapted to co-operate alternately with two switches FC and FC referred to as switches for monitoring the ends of the advance travel and the return travel, respectively, of piston 2, this co-operation taking place when the piston 2 of jack 1 is in one of its extreme positions in such a way that the end-of-advance travel monitoring switch FC through the intermediary of the electric circuit, controls the de-energization of the electro-magnet EA of the first master slide valve 34, then the de-energization of the first electro-magnet EA then the energization of the second electro-magnet EA; of the principal slide valve 12, and then the re-energization of the electro-magnet EA while the end-of-return travel monitoring switch FC controls, also through the intermediary of the electric circuit, the de-energization of the electro-magnet EA of the master slide valve 34, then that of the second electro-magnet EA of the principal slide valve 12.

When the shank 3 of jack-piston 2 is adapted to selectively operate, through the intermediary of its cam 80, the two switches FC and FC the electric control and monitoring circuit comprises, in addition two groups of supplementary electrical elements G and G mounted in parallel with the other groups, while the group G comprising the advance and return monitoring relays R and R is modified.

As shown in FIG. 4, the electric circuit, fed by the three-phase mains RT, through the itermediary of a single-phase transformer Tr, comprises in addition to groups G to G a group G constituted by a relay R referred to as the end-of-advance travel and reversal monitoring relay, this relay R being mounted in series with the switch FC said switch being normally open when it is not acted on by the cam 80; and an eighth group G consituted by a relay R referred to as the endof-return travel monitoring relay, mounted in series with the switch FC this switch being normally open when it is not acted on by the cam 80.

The group G comprises, in addition to the elements shown in group G of FIG. 3, normally closed contact R connected in series on the one hand with relay R and the contact R and on the other hand with the switch Dc, referred to as the cycle-starting switch. This annual switch Dc corresponds moreover to the switch DCAV of FIG. 3. In the circuit associated with the relay R in place of the manual return-cycle-starting switch, there are provided four contacts C R R and R the first contact C being normally closed and being controlled by the advance-control relay C the second contact R being normally closed and being commanded by the monitoring relay R the third contact R being normally closed and being controlled by the advance monitoring relay R and the fourth contact R being normally opened and being controlled by the end-of-advance travel monitoring relay R the two contacts R and R being mounted in parallel and the two contacts R and C in the immediate vicinity of relay R being mounted in series with the holding contact R of relay R The manual switch Ac, as in the preceding circuit, is mounted in series with all of the other contacts and relays of the group G IV. The operation of the electric circuit provided for a hydraulic anti-shock device having a master distributor and permitting the automatic control of a complete work cycle of the piston 2 is as follows.All of the contacts and switches are initially in the positions shown in FIG. The positions correspond to those of the slide valves 12 and 34 as indicated in FIG. 1 and' correspond to the state of the complete device when it is at rest (including the stoppage of pump P).

A. Starting of the motor M and the pump P.This starting is eifectuated in the manner described above in paragraph IIIa.

B. Automatic control of a complete cycle of piston 2.The various processes carried out during the course of a complete cycle serve to initiate one another, but for the sake of clarity these processes will be described below as separate phases of operation.

(a) Control of the electro-magnet EA of the principal slide valve 12 The switches RT are permanently closed. Starting switch Mm is closed, causing the energization of relay C through the intermediary of normally closed switch Au, normally closed switch Am and switch Mm. Energized relay C closes holding contact C motor-energizing contact C and circuit-power-supply contact C Because of the closure of holding switch C the relay C will remain closed even after the opening of switch Mm. The switch Dc is momentarily closed, thereby energizing relay R through the intermediary of contact R The energization of relay R opens contact R thereby preventing any energization of relay R as long as relay R is energized.

The energization of electro-magnet EA is then effectuated in the manner described in paragraph IIIb.

Because relay C is energized, the cont-act C opens and prevents any energization of the return-travel monitoring relay R Similarly, the contact R is open when the relay R is energized, thereby preventing any energization of the relay R when the switch F is closed, i.e. when the piston 2 is in its extreme left-hand position.

(b) Control of the electro-magnet EA of the first master slide valve 34 This operation is identical to that described in paragraph Illc. The piston 2 advances towards the extreme right-hand side of jack 1 under the influence of the maximum operative pressure and the cam 80 moves away from the switch FC permitting this switch to open. As a result, the relay R is de-energized and the contact R re-closes, but the relay R remains in its de-energized state, since the contacts C R R and R are still open.

(c) Automatic stopping of the advance cycle of piston 2 When the piston 2 arrives at the end of its advance travel, the cam 80 closes the switch FC causing the relay R to be energized. Due to this fact, the contact R opens, the relay R becomes de-energized, and the contacts R R and R re-open, but on the other hand, the contact R re-closes.

The procedures by which the electro-magnets EA and EA are successively de-energized is the same as that described in paragraph IIId.

(d) Control of the eIectro-magnet EA of the principal slide valve 12, corresponding to a reversal of the principal slide valve 12 Because the relays R and R are no longer energized while the relay R is energized, the contacts R R and R are closed and when the relay C is de-energized, the contact C re-closes, thereby permitting the energization of relay R The rest of this procedure is identical with that described in paragraph IIIe.

(e) Control of the electro-magnet E11 of the master slide valve 34 This procedure is identical with that described in paragraph IIIf. However, when the piston 2 commences to return, the cam 80 moves away from the switch FC interrupting the supply of current to the relay R so that contact R recloses and contact R re-opens. The opening of contact R does not affect the energization of relay R since this contact R is in parallel with the holding contact R which remains closed as long as relay R is energized.

(f) Automatic halting of the return cycle of piston 2 I At the end of the return travel of piston 2 the cam closes the switch FC so that the relay R is energized. Its contacts R opens and the relay R becomes deenergized. The remainder of this procedure is identical to that described in paragraph IIIg.

FIG. 5 shows an electrical circuit permitting the auto matic control of a complete cycle (advance, reversal and return of the piston 2, and the progressive increase or decrease of pressure between each of the procedures) of the piston 2 of jack 1 furnished with a hydraulic antishock device having two

master distributors

30 and 58, as shown in FIG. 2.

In this case, the energization of the various electromagnets EA, each of which is mounted in series with its respective control contact but all of which are mounted in parallel with one another, is assured by a single-phase transformer Tr connected across the mains RT in parallel with the transformer Tr feeding the various relays R and C mounted in parallel with respect to one another. It thus results that the electro-magnets EA are mounted in parallel with their corresponding relays C, as is true for the systems shown in FIGS. 3 and 4.

The electric circuit for a hydraulic anti-shock device having two master distributors, of the type shown in FIG. 2, is characterized in that it comprises in addition to the groups of circuits shown in FIG. 3 (permitting a semiautomatic control of the advance and return cycles) or of the circuit of FIG. 4 (permitting an automatic command of a complete cycle): a group of electrical elements G adapted to control the energization and the de-energization of the electro-magnet EA of the second master slide valve 64, as well as an end-of-travel switch FCF, provided in group G this switch being controlled by the second master slide valve 64 and being adapted to disconnect the energizing current to the electro-magnet EA of the first master slide valve 34 when the second master slide valve 64 has returned to "its neutral position.

The switch FC7 is mounted in parallel with the contacts R and R one of the terminals of this parallelarrangement also being connected to the relay C while the other terminal thereof is connected to the parallel arrangement of switches FC and FC The switch F07 is open when it is acted on by the cam 63 rigidly connected to the control shank 61 of the second master distributor 53. The opening of the switch FC corresponds to the neutral position of the second master slide valve 64. e

The group of electrical elements G is constituted by a relay C referred to as the control relay for the second master distributor 58, by the winding of the electromagnet EA of the second master slide valve 64, by a contact C which is normally open and which is controlled by the relay C this winding EA, and this contact C being mounted in series with one another but in parallel with respect to the relay C Group 6,, also comprises the end-of-travel switch FC of the first master distributor 30, this switch FC being operated by the cam 52 of shank 51 so as to be closed when acted on by this cam when the first master slide valve 34 is in its neutral position, assuring communication between the principal pressure regulator 16 and the return circuit 14 attached to said distributor 30. Group G further comprises two contacts R and R both of which are normally open and are mounted in parallel with one another and in series with the relay C through the intermediary of switch FC the contacts R being controlled by the controlled by the return-control relay R V. The operation of the electric circuit provided for a hydraulic anti-shock device having two master distributors and permitting the automatic control of a complete work cycle of the piston. 2 is as follows.-All of the contacts and switches are initially in the positions shown in FIG. 5. These positions correspond to those of the

slide valves

12, 34 and 64, as indicated in FIG. 2 when the apparatus is at rest, the pump P also being at rest.

A. Starting the motor M and the pump P.-This starting is eifectuated in the same manner as that described in paragraph IIIa, above.

B. Automatic control of a complete cycle of piston 2.- The various operations effectuated during the course of a complete cycle serve to trigger one another, but for the sake of clarity these procedures will be described as separate phases of operation.

(a) Control of the electro-magnet EA of principal slide valve 12 This procedure is identical with that described in paragraph IVB-a, except that the relay R when energized, also closes the contacts R (b) Control of the electro-magnet EA first master slide valve 43 When the energized electro-magnet EA displaces the slide valve 12 towards the left, the control shank 41 follows this movement and the cam 42 closes the switch F0 Since the contact R has been previously closed, the relay C is energized and closes the contact C with the result that the electro-magnet EA is also energized. As a result, the master slide valve 34 is urged into its closed position, which corresponds to the progressive establishment of the average operative pressure in the delivery circuit 13 and in the chamber of jack 1.

(c) Control of the electro-magnet EA, of the second master slide valve 64 When the first master slide valve 34 is displaced towards the left, the shank 51 follows this movement and its cam 52 closes the switch FC Because the energization of relay R had previously closed the contact R the relay C is energized. The contact C closes, and thereby permits the energization of the electro-magnet HA causing the latter to urge the second master slide valve 46 towards the left into its closing position. There is then produced a progressive increase in the pressure in the delivery circuit 13 and in the jack-chamber 5 until the maximum operative pressure is reached, which pressure controls the advance of piston 2 towards the right-hand end of jack 1. The shank 61 follows the displacement of the second master slide valve 64 so that, firstly, its cam 63 separates from switch FC causing the switch to close, and then, when the slide valve 64 is in its closed position, the cam 62 closes the switch FC so as to control the emission of an audible or visible signal. Because the piston 2 advances towards the right-hand end of jack 1, the cam 80 separates from the switch FC permitting this switch to open. The relay R is thus de-energized and the contact R re-closes.

(d) Automatic termination of the advance cycle of piston 2, corresponding to a successive de-energization of the electro-magnet EA EA and EA This procedure corresponds to a progressive reduction in the pressure of the fluid in the delivery circuit 13 and the chamber 5.

When the piston 2 arrives at the end of its forward travel path, the cam 80 closes the switch FC and the relay R is energized, causing its contact R to open. As a result, the relay R is de-energized, its contact R re-closes and its other contacts R R R and R reopen. Relay C remains energized because contacts R and C remain closed due to the fact that relays R and R are not energized. The relay C remains energized through the intermediary of the closed switches FC and PC7- But the relay C becomes de-energized because the contact R has opened and the contact R has not closed.

The contact C re-opens and the electro-magnet EA, is tie-energized, thereby permitting the spring 72 to urge: the second master slide valve 64 into its neutral position, which corresponds to a progressive return to the average operative pressure in the delivery circuit 13 and in the chamber 5 of jack 1. When the master slide valve 64 is urged towards the right, the cam 62 frees the switch FC which opens, then the cam 63 opens the switch FC7.. As a result, the relay C is de-energized, the contact C opens, and the electro-magnet EA;, is de-energized, thus permitting the spring 48 to urge the first master slide valve 34 into its neutral position (progressive return to the minimum operative pressure).

The shank 51 is also urged towards the right so that the cam 52 permits the opening of switch FC and so that the cam 53 then re-closes the switch FC so as to thus permit the energization of relay R As a result, the contacts R and R re-close while the contacts R and R re-open. The energization of relay C is then disconnected'by the contact R causing the contact C to open and the electro-magnet EA to be de-energized, with the result that spring is permitted to urge the principal slide valve 12 towards the right into its neutral position (progressive elimination of pressure). On the other hand, the contact C closes. The shank 41 follows this movement and the cam 42 frees the switch FC permitting this switch to re-open.

(e) Automatic control of the return cycle of piston 2, corresponding to a reversal of the principal slide valve 12 and the successive energization of electro-magnets E142, EA3 and E144.

This procedure corresponds to a progressive creation of pressure in the delivery circuit 13 and the chamber 4 of jack 1.

The contacts R and R are closed since their corresponding relays R and R are not energized. The contact R is closed since the switch P0 is closed while the relay R is energized.

When the relay C is de-energized (see paragraph VB-d), the contact C closes and the relay R is energized. Its contacts R R R and R close and, because the relay R is energized (see paragraph VB-d) the contact R is closed. The contact C is also closed (see paragraph VB-d). The relay C is then energized through the intermediary of the closed contacts R R and C The contact C closes and permits the energization of the electro-magnet EA which urges the principal slide valve 42 from its neutral position towards its extreme right-hand position. The shank 41 is also displaced in this direction and its cam 43 closes the switch PC, which, through the intermediary of closed contact R permits the excitation of relay C The contact C closes and permits the excitation of the electro-magnet EA of the first master distributor 30, the slide valve 34 of which is urged towards the left. This corresponds to the progressive establishment of the average operative pressure in the delivery circuit 13 and in the chamber 4 of jack 1.

The shank 51 follows this movement. The cam 53 permits the opening of the switch FC and the de-energization of the relay R As a result, the contacts R and R re-close and the contacts R and R re-open.

The relay C continues to be energized through the intermediary either of the closed contacts C R and R or of the closed contacts R and C The relay C cannot be energized since the contact C is open, due to the fact that the relay C is energized.

Then, when the slide valve 34 occupies its closed position, the cam 52 closes the switch F0 so that the relay C can be energized through the intermediary of tlns switch and of the closed contact R The contact C 21 closes and the electro-magnet EA; is energized; the latter then urges the second master slide valve 64 into its closed position. This corresponds to the progressive establishment of the maximum operative pressure in the delivery circuit 13 and in the chamber 4 of jack 1.

The shank 61 follows the displacement towards the left of the second slide valve 64. The cam 63 then moves away from the switch FC permitting the switch to reclose and then the cam 62 operates the switch PC indicating that the slide valve 64 occupies its closed position, i.e. which indicates that the maximum operative pressure has been established.

The piston 2 of jack 1 moves in its reverse direction under the effect of this pressure. The cam 80 moves away from the switch FC permitting the latter to open, thereby removing the energization from relay R The contact R re-closes, but the relay R cannot be energized since the switch Dc and the contact R are open. Simultaneousely with the de-energization of the relay R the contact R opens. However, the excitation of relay R is maintained through the intermediary of the closed contaCtS R21, R51 and C22.

(f) Automatic stopping of the return cycle, i.e. of the complete work cycle of piston 2 This operation corresponds to the progressive removal of the pressure in the delivery circuit 13 and in the chamber 4 of jack 1.

At the end of the return travel of piston 2 the cam 80 closes the switch FC thereby permitting the energization of the relay R causing the opening of contact R The relay R becomes de-energized with the result that its contacts R R R and R open.

The relay C remains energized through the intermediary of the closed switches F and FC while the relay C remains energized through the intermediary of the closed contacts R and C On the other hand, the relay C becomes de-energized since the contact R opens and the contact R was previously opened (prior to the reversal of the principal slide valve 12).

The contact C opens and the electro-magnet EA; is de-energized, thus permitting the spring 72 to urge the second master slide valve 64 into its neutral position.

As a result, the cam 62 moves away from the switch PC and then the cam 63 opens the switch FC so that the latter switch disconnects the energizing current from the relay C The contact C opens and the electro-magnet EA is de-energized, permitting the spring 48 to urge the first master slide valve 56 into its neutral position. The shank 51 also moves towards the right under the influence of said spring 48. The cam 52 moves away from switch FC permitting the switch to open, and the cam 53 closes the switch FC thereby permitting the re-energization of relay R At this moment, the contacts R and R open and the contacts R and R close. The opening of contact R results in a de-energization of relay C The contact C opens and the electro-magnet EA is de-energized, which permits spring 36 to urge the principal slide valve 12 into its neutral position. In following this movement, the cam 43 moves away from the switch FC permitting the latter to open.

The stopping of the entire apparatus is etfectuated by the momentary depression of switch Am.

The hydraulic anti-shock device having two master slide valves could also be controlled in a semi-automatic fashion. To this end, one may use the electric circuit shown in FIG. 3, completed by the group G of FIG. 5 and in which the group G of FIG. 3 is replaced by the group G of FIG. 5. The operation of this embodiment is the same as that described in paragraphs III and V, above.

Of course, the various embodiments have only been given by way of example, and numerous modifications can be made thereto without departing from the spirit of this invention. For example, the master slide valves could also be of simple stop-valve type. In place of the master distributors utilizing slide valves, one could also provide electro-magnetic valves of any known type. The operation of the device of the present invention could deviate from that which has been describedabove. Thus, it would be possible to manually actuate the various distributors. After the energization of the advance-control relay R it is also possible to anticipate the operation of the master distributors by manually actuating them in the direction which they would be given by the excitation of their corresponding electro-magnets. Similarly, because of the addition of a mass to the control shank of the distributors, the successive energizations of the electro-magnets of the master distributors could be delayed. It should also be noted that the arrangement of the present device permits the advance and return of the jack-piston to be stopped at any desired moment, at any position in its travel path, and this could be carried out in an extremely rapid fashion and without the formation of any shock waves or vibrations. The fact that the sequence of operations is constantly monitored by the end-of-travel switches, and in such a manner that the following operation can only be carried out after the accomplishment of the preceding operation, and the fact that this monitoring is linked to the positions of the distributors, gives to this hydraulic anti-shock device a high degree of effectiveness, security, and rapidity of operation. The hydraulic antishock device could also be applied to the control of a jack comprising a single acting piston. It should also be noted that the application of the present invention is not limited to a jack in which the piston moves in an alternating linear path, but it may also be used for pistons having non-linear alternating or continuous movements and to rotating hydraulic motors.

The present invention has been described in connection with embodiments which consist in the utilization of distributors referred to as having open centres; but it would be possible, according to operating requirements, to utilize distributors having closed ends, or semi-closed ends, i.e. in so far as concerns the principal distributor, the delivery circuit and the vat-return circuit, as well as the two jack-feeding circuits, could be blocked.

I claim:

1. A hydraulic anti-shock device associated with a hydraulic jack furnished with a piston the two faces of which, through the intermediary of a principal distributor controlled alternately by two electro-magnets, are adapted to be connected either alternately with the delivery circuit of a pump or the pump inlet by its return circuit, or simultaneously with said two circuits, and comprising: in the delivery circuit downstream of the principal regulator, a pressure regulator furnished with a closing valve interposed between the delivery circuit and the return circuit, and rigidly connected to a piston defining two chambers the lower chamber of which communicates directly with the delivery circuit and the upper chamber of which, furnished with a restraining spring urging the valve into its closing position, communicates through the intermediary of a calibrated channel with the delivery circuit; a master distributor connected, on the one hand, to the upper chamber of the valve piston and, on the other hand, to the return circuit, and adapted to be controlled by an electro-magnet in such a manner as to destroy or establish the communication between the upper chamber of said valve piston and the return circuit; and an electric circuit furnished with switches and relays for starting and stopping a motor driving the pump and for controlling the various electro-magnets, said device being characterized in that it comprises: end or travel switches adapted to be actuated by cams arranged in such a manner as to be able to follow the displacements of the armatures of the corresponding electromagnets of the distributors, the end of travel switch for the master distributor being disposed in the electric circuit of the electromagnets of the principal distributor in such a way that they can only be closed by their corresponding cams and can only. permit the energization of the electromagnets of the principal distributor when the master distributor is in its neutral position, while the end of travel switches of the principal distributor are disposed in the circuit of the electromagnet of the master distributor in such a way that neither can be closed by its corresponding cam and does not permit the energization of the electromagnet of the master distributor until the principal distributor occupies one of its two extreme positions.

2. A device according to claim 1 wherein the cams of the end of travel switches of the principal distributors are mounted on a control shank cooperating with the corresponding slide valve of the distributor through the intermediary of the electromagnets.

3. A device according to claim 1 characterized in that the cam of the end of travel switch of the master slide valve is mounted on a control shank cooperating with the corresponding slide valve of the master distributor through the intermediary of its electromagnet.

4. A device according to claim 1, characterized in that a shank cooperating with the electro-magnet of the master distributor is furnished with two cams each of which cooperates with a corresponding end of travel switch, these two cams being mounted on said shank in such a way that, when one of the cams closes its corresponding switch, the other cam permits the opening of the other switch, one of the switches being closed when the master slide valve occupies its neutral position and being interposed in the electric control and monitoring circuit and adapted to monitor the energization and the deenergization of one or the other of the electro-magnets of the principal distributor, while the other switch is closed when the master slide valve occupies its closing position and is interposed in the electric supply line for a device for producing a visible or audible signal.

5. A device according to claim 1, characterized in that, at one of their ends, the control shanks associated with the principal and master distributors are furnished with weak springs adapted to urge their respective shanks against the armature of the electro-magnet of the corresponding distributor.

6. A device according to claim 1, characterized in that, at one of its ends, each of the control shanks associated with the principal and master distributors is furnished with a push-button which permits the manual actuation of the slide valve of the corresponding distributor.

7. A device according to claim- 6 characterized in that each push button is constituted by a certain inertia mass adapted to slow down the displacements of each respective control shank with respect to the speed of displacement of the corresponding distributor slide valve and electro-magnet armature.

8. A device according to claim 1 characterized in that the electric control and monitoring circuit is connected to a source of alternating current and comprises several groups of electrical elements, which groups are mounted in parallel with one another and include, a first group adapted to control the starting and stopping of the pump motor and to simultaneously control the supply of current to the other groups; a second group adapted to control the energization and deenergization, on the one hand, of one of the electromagnets of the principal distributor and, on the other hand, of the electro-magnet of the master distributor; a third group adapted to control the first electro-magnet of the principal distributor in such a manner that, when it is energized, this electromagnet urges the slide valve of the principal distributor into a position corresponding to the advance of the jack piston; a fourth group adapted to control the electromagnet of the master distributor in such a way that,

in its energized state, this electromagnet urges the master distributor slide valve into a position which produces a progressive increase in the pressure of the fluid in the delivery circuit; a fifth group, adapted to control the second electromagnet of the principal distributor in such a man her that, in its energized state, this electromagnet urges the slide valve of the principal distributor into a position corresponding to the return of the jack piston; and a sixth group adapted to monitor the supply of current to the third and fifth groups.

9. A device according to claim 8, characterized in that each group of electrical elements comprises at least one relay.

10. A device according to claim 8, characterized in that the first group of electric elements comprises: a relay for controlling the motor; a first manual switch, which is normally open, for starting the device, and a second manual switch, which is normally closed, for stopping the device; these switches being mounted in series with one another and with said relay, said relay comprising: a first holding contact connected in parallel across the terminals of the first-recited switch; a second contact mounted in series with the line feeding the other groups; and a group of three contacts interposed in the line feeding the pump motor, these five contacts being closed when their relay is energized.

11. A device according to claim 8 characterized in that the second group of electric elements comprises: two monitoring relays, one of which monitors the advance of the jack piston and the other of which monitors the return of the jack piston, the two relays being mounted in parallel, a first manual switch for starting the advance cycle of the jack and mounted in parallel with a holding contact of the advance monitoring relay, these contacts and said first switch each being mounted in series with said advance monitoring relay; a second manual switch for starting the return cycle of the jack and mounted in parallel with a holding contact of the return monitoring relay, this contact and the second switch each being mounted in series with the return monitoring relay; and a third manual switch for stopping the cycle of operations, this switch being normally closed and being mounted in series with the holding contacts and with said cycle starting switches, the latter being normally open, said holding contacts being closed when their corresponding relay is energized.

12. A device according to claim 8 characterized in that the third group of electrical elements comprises: an advance control relay; the winding of the first electromagnet of the principal slide valve; and a first contact which is normally open and which is controlled by said relay, this contact and this winding being mounted in series with one another and in parallel with said relay; a second normally closed contact mounted in series with said relay and controlled by a relay of the fifth group of elements; a third normally closed contact mounted in series with the second contact and controlled by a relay of the sixth group of elements; a fourth normally open contact mounted in parallel with the third contact and controlled by the advanced monitoring relay; a fifth normally opened contact mounted in series with the fourth contact and in parallel with the third contact, and controlled by the relay of the sixth group; and a sixth holding contact, which is normally opened, mounted in parallel with the fifth contact and controlled by the advanced control relay.

13. A device according to claim 8 characterized in that the fourth group of electric elements comprises: a relay for controlling the master distributor; the winding of the electro-magnet of the master slide valve and a first normally opened contact, this winding and this contact being mounted in series with one another and in parallel with said relay; second and third normally opened contacts mounted in parallel with one another and in series with said relay, the second contact being controlled by the advanced monitoring relay and the third contact being controlled by the return monitoring relay; and the two end of travel switches of the principal distributor, which switches cooperate with the two cams mounted on the shank of the principal slide valve, these switches being mounted in parallel With one another and in series with the second and third contacts and being normally opened when they are not actuated by their corresponding cams.

14. A device according to claim 8 characterized in that the fifth group of electric elements comprises: a return control relay; the Winding of the second electro-magnet of the principal slide valve and a first normally open contact controlled by said relay, this winding and this contact being mounted in series with one another and in parallel with said relay; a second normally closed contact mounted in series with said relay and controlled by the advanced control relay; a third normally closed contact mounted in series with the second contact and controlled by the relay of the sixth group; a fourth normally open contact mounted in parallel with the third contact and controlled by the return monitoring relay; a fifth normally open contact mounted in series with the fourth contact and in parallel with the third contact and controlled by the relay of the sixth group; and a sixth normally opened holding contact mounted in parallel with the fifth contact and controlled by the return control relay.

15. A device according to claim 8 characterized in that the sixth group of electrical elements comprises: a minimum operative pressuremonitoring relay mounted in series with that one of the end of travel switches of the master distributor which is closed when the master slide valve is in its neutral position.

16. A device according to claim 1, characterized in that it comprises a second master distributor having a slide valve which is also furnished with an electromagnet adapted to act against the force of a restraining spring of said slide valve; this second master distributor being connected, on the one hand, to the conduit between the principal pressure regulator and the first master distributor and, on the other hand, to the inlet vat return circuit through the intermediary of an auxiliary pressure regulator; the slide valve of said second master distributor being adapted to displace a shank furnished with two cams each of which is adapted to cooperate with an end of travel switch, one of these end of travel switches being adapted to interrupt the energization current of the electromagnet of the first master distributor when the slide valve of the second master distributor establishes a hydraulic communication between the principal pressure regulator and the auxiliary regulator, while the other end of travel switch is mounted to control a unit producing and audible or visual signal when said slide valve interrupts the hydraulic communication between the principal pressure regulator and the auxiliary pressure regulator.

17. A device according to claim 1, characterized in that the shank of the jack piston is furnished with a cam adapted to cooperate alternately with an end of advance travel switch and an end of return travel switch when said piston is in a respective one of its extreme positions, in such a way that the end of advance travel switch, through the intermediary of the electric circuit, controls the denergization of the electromagnet of the master distributor, then the deenergization of the first electro-magnet, then the energization of the second electro-magnet, of the principal distributor, and then the reexcitation of the electro-magnet f the master distributor, and also in such a way that the end of return travel switch, also through the intermediary of the electric circuit, controls the deenergization of the electro-magnet of the master distributor, and then the denergization of the second electromagnet of the principal distributor.

18. A device according to claim 1 characterized in that, when the shank of the jack piston is adapted to selectively actuate, through the intermediary of a cam, two end of travel switches, the electric control and monitoring circuit further comprises a seventh and an eighth group mounted in parallel with the other groups of the elements; the seventh group comprising an end of advance travel and reversal monitoring relay mounted in series with the end of advance travel switch, which switch is normally open when it is not actuated by said cam; the eighth group comprising an end of return travel monitoring relay mounted in series with the end of return travel switch, which switch is normally open when it is not actuated by said cam; and the second group of electrical element comprising, on the one hand, a normally closed contact controlled by the end of travel relay and mounted in series with the advanced monitoring relay and, on the other hand, in place of the return cycle manual starting switch, four contacts mounted in series with the return monitoring relay; said four contacts comprising: a first normally closed contact controlled by the advance control relay; a second normally closed contact controlled by the end of return travel monitoring relay; a third normally closed contact controlled by the advanced monitoring relay; and a fourth normally opened contact controlled by the end of advance travel monitoring relay, the last two of said contacts being mounted in parallel and the first two of said contacts being mounted in series with the holding contact of the return travel monitoring relay.

19. A device according to claim 1, characterized in that the group of electric elements comprising the relay for the first master distributor includes one of the end of travel switches of the second master distributor, this switch being mounted in parallel with the two parallel connected contacts and being controlled, respectively, by the advanced monitoring relay and the return monitoring relay, and being opened when it is actuated by its corresponding cam.

26. A device according to claim 16, characterized in that it further comprises a group of electrical elements controlling the displacements of the slide valve of the second master distributor, this group comprising: a second master distributor control relay; the winding of the electromagnet of the second master distributor; a normally open contact controlled by said relay, this winding and this contact being mounted in series with one another and in parallel with said relay; one of the end of travel switches of the first master distributor, this switch being mounted in series with said relay and being closed when the first master distributor assures the communication between the principal pressure regulator and the inlet vat return circuit, and two normally open contacts, mounted in parallel with one another and in series With said relay through the intermediary of said switch, one of these two contacts being adapted to be controlled by the advanced monitoring relay while the other of these contacts is adapted to be controlled by the return monitoring relay.

References Cited by the Examiner UNITED STATES PATENTS 2,267,177 12/ 1941 Twyman 60-52 2,277,640 3 1942 Harrington 6052 2,287,559 6/1942 Nye.

2,318,851 5/1943 Griflith 60-97 X EDGAR W. GEOGHEGAN, Primary Examiner.

Claims

1. A HYDRAULIC ANTI-SHOCK DEVICE ASSOCIATED WITH A HYDRAULIC JACK FURNISHED WITH A PISTON THE TWO FACES OF WHICH, THROUGH THE INTERMEDIARY OF A PRINCIPAL DISTRIBUTOR CONTROLLED ALTERNATELY BY TWO ELECTRO-MAGNETS, ARE ADAPTED TO BE CONNECTED EITHER ALTERNATELY WITH THE DELIVERY CIRCUIT OF A PUMP OR THE PUMP INLET BY ITS RETURN CIRCUIT, OR SIMULTANEOUSLY WIITH SAID TWO CIRCUITS, AND COMPRISING: IN THE DELIVERY CIRCUIT DOWNSTREAM OF THE PRINCIPAL REGULATOR, A PRESSURE REGULATOR FURNISHED WITH A CLOSING VALVE INTERPOSED BETWEEN THE DELIVERY CIRCUIT AND THE RETURN CIRCUIT, AND RIGIDLY CONNECTED TO A PISTON DEFINING TWO CHAMBERS THE LOWER CHAMBER OF WHICH COMMUNICATES DIRECTLY WITH THE DELIVERY CIRCUIT AND THE UPPER CHAMBER OF WHICH, FURNISHED WITH A RESTRAINING SPRING URGING THE VALVE INTO ITS CLOSING POSITION, COMMUNICATES THROUGH THE INTERMEDIARY OF A CALIBRATED CHANNEL WITH THE DELIVERY CIRCUIT; A MASTER DISTRIBUTOR CONNECTED, ON THE ONE HAND, TO THE UPPER CHAMBER OF THE VALVE PISTON AND, ON THE OTHER HAND, TO THE RETURN CIRCUIT, AND ADAPTED TO BE CONTROLLED BY AN ELECTRO-MAGNET IN SUCH A MANNER AS TO DESTROY OR ESTABLISH THE COMMUNICATION BETWEEN THE UPPER CHAMBER OF SAID VALVE PISTON AND THE RETURN CIRCUIT; AND AN ELECTRIC CIRCUIT FURNISHED WITH SWITCHES AND RELAYS FOR STARTING AND STOPPING A MOTOR DRIVING THE