Hydraulic Jack

Abstract

A hydraulic jack having two consecutive and completely different actions and its hydraulic operating means, the jack responding to the control order given by the operating means in the form of the supply pressure on a first input of the jack and the control pressure on a second input of the jack, while automatically effecting two consecutive actions in the same direction, the first action being a travel of large amplitude (naturally with a low force), while the second action develops a large force proportional to the control pressure (with a zero or very small travel), the disappearance of the control order resulting, by the operating means which apply the supply pressure to a third input of the jack, in the return movement of the travel of large amplitude only.

Description

THe invention relates to a hydraulic jack having two consecutive and completely different actions, and a hydraulic operating means, that is to say a hydraulic jack which responds to the control order given to it by the said operating means, in the form of the supply pressure on a first input of the jack and the control pressure on a second input of the jack, by supplying automatically two consecutive actions having the same direction, the first of which is a travel of large amplitude (naturally with a low force), while the second develops a large force proportional to the control pressure (at a zero or very small travel), the disappearance of the said control order resulting, by the said control means which apply the supply pressure to a third input of the jack, in the return of the travel of large amplitude only.

The said hydraulic control means according to the invention preferably but not necessarily comprise a hydraulic distributor controlled in dependence on the control pressure.

The invention also relates to the application of a jack of this kind to the braking of vehicles, and in this case the said jack solves the problem of taking up wear of the friction linings or other actuating members of the brake in a simple and economic manner, namely by the non-existence, upon the disappearance of the control order of the inverse of the said second action,

The invention is more particularly but not exclusively concerned with its application to the braking of vehicles in which, for any reason whatever, the position at rest of the actuating members of the brake must be relatively distant from their working position.

By way of non-limitative example, an arrangement of this kind is necessary for vehicles on a rail of concrete or the like, the thickness of the web of the rail or rails necessitating, when taking a curve, that the brake shoes in the position of rest should be held-off so as not to intersect the envelope diagram of the said web.

The jack according to the invention comprises briefly, in a body forming a first point of action, a large piston, the rod of which constitutes itself a cylinder for a small piston with a long travel, forming a second point of action. At rest, the supply pressure is applied by the said servo-controlled distributor, to the said third input of the jack, from which it goes to the small piston on the side opposite to the rod, which causes its outward movement.

Upon the appearance of the control pressure, the said controlled distributor applies the supply pressure to the said first input of the jack. From the and the control pressure to the said second input of the jack and the control pressure to the said second input of the jack. From the first input, the supply pressure is applied to the rod side of the small piston, which produces its return movement, which is the said travel of large amplitude. At the end of this return movement, the small piston locks itself automatically; this locking automatically causes the application of the control pressure from the second input on the rod side of the large piston, this being the said action at high force, proportional to the control pressure.

In the case of a brake in which the brake linings wear during the braking considered, it will be noted that the large piston becomes retracted during this wear. The disappearance of the control pressure causes the return of the control distributor to its position of rest, and therefore the application of the supply pressure to the said third input of the jack, which results in the automatic application of the supply pressure to the side opposite the rod of the small piston and the release of this small piston, together with its outward movement. It will also be observed that in the case of a brake, the large piston is not moved during release, and thus remains in the position corresponding to the instantaneous condition of wear of the linings.

THe brake and its operation described above, comprise auxiliary members which will be referred to later. It will be observed that the jack according to the invention does not comprise any spring or other elastic restoring device, either for the large piston or even for the small piston, the return of which in its extended position is ensured by the supply pressure.

The invention and an application of the invention will now be described with reference to the accompanying drawings, given by way of non-limitative examples. In these drawings:

FIGS. 1 to 4 are diagrammatic figures explaining the operation of the jack according to the invention, FIG. 1 showing a condition of rest, FIG. 2 the automatic succession of the phases of the two actions, FIG. 3 the return and FIG. 4 a new condition of rest;

FIG. 5 gives the general diagram of the installation for an application of the invention to the actuation of the brakes of a vehicle running on a rail track with a thick center-rib or web;

FIG. 6 is a general axial cross-section of the jack shown in FIG. 5;

FIG. 7 is an explanatory detail of FIG. 6;

FIG. 8 shows the installation according to FIG. 5 when at rest;

FIG. 9 shows the operation of the installation as in FIG. 5 during the first action or approach travel;

FIGS. 10, 11 and 12 are three details explaining the automatic passage from the first action to the second in the installation according to FIG. 5;

FIG. 13 shows the operation of the installation according to FIG. 5 during the second action or application of the brakes;

FIG. 14 shows the return to rest of the installation according to FIG. 5;

FIGS. 15, 16 and 17 are three details explaining the automatic operations during the return, as shown in FIG. 14.

With reference to FIGS. 1 to 4, which are diagrammatic drawings explaining the operation of the jack according to the invention, the body 1 of the jack is provided with an eye 2 forming the first point of action and constitutes a double-acting cylinder for a large piston 3 placed between two chambers 4 and 5, and braked by a device 6 which will be described subsequently.

The hollow rod of the large piston 3 forms a double-acting cylinder for a small piston 7 having a long travel, placed between two chambers 8 and 9 and provided with an eye 11 forming the second point of action. THe jack is supplied from a hydraulic source S through a pressure-reducing valve 23 with manual operation 25, which actuates a controlled distributor 26. The said first input of the jack is the input 28, coupled to the controlled distributor 26, and the said third input of the jack which is the input 54; the said second input is the input 27, supplied by the reducing valve 23 and supplying a peripheral groove 51 of the large piston 3.

With reference to FIG. 1 which shows the jack in the position or rest, the pressure-reducing valve 23 connects the input 27 to the return R, and the controlled distributor 26 on the one hand connects the input 54 to the return R and on the other hand connects the input 28 to the supply pressure PA. Thus, the large piston 3 is maintained in the position in which it is located by the device 6, and the small piston 7 is maintained in the extended position by the supply pressure sent into the chamber 9.

With reference to FIG. 2, which represents the first action or travel with high amplitude, the pressure-reducing valve 23 regulates a control pressure PC, determined by the position of its manual control 25, and operates the control distributor 26, which on the one hand connects the input 28 to the return R, and on the other hand puts in input 54 to the supply pressure PA. This results automatically in three or four stages of operation. In a first stage (top left-hand side of FIG. 2), the supply pressure PA is sent into the chamber 8, which causes the retraction of the small piston 7 (arrow F1). In a second stage, the arrival of the small piston 7 at the limit of its travel (FIG. 2, bottom left-hand) automatically causes its locking by means of a bolt 12 (which will be described subsequently).

In a third phase, the locking action of the bolt 12 uncovers an orifice 52 (FIG. 2 right-hand top), by which the control pressure PC is transmitted from the peripheral groove 51 to the chamber 4. The large piston 3 is thus actuated by a force proportional to the said pressure. If wear takes place for example of the friction linings (FIG. 2 right-hand bottom), the large piston 3 is automatically retracted by the corresponding amount (arrow F2).

With reference to FIG. 3, manual re-setting of the control 25 to the zero position causes the control pressure to disappear and restores the controlled distributor 26 to its initial position. The disappearance of the control pressure causes the supply pressure to be sent into the chamber 9, thus releasing and extending the small piston 7 (arrow F3). FIG. 4 shows the new position of rest, which only differs from that of FIG. 1 (if wear has taken place) by a slight displacement of the moving parts, in particular of the large piston 3 which is held in position by the device 6.

There will now be described an application of the invention to the actuation of the brakes of a vehicle running on a track with a rail having a thick web, it being understood, as already stated, that this example is given without any limitation.

With reference to FIG. 5, which gives the general diagram of the installation, the hydraulic supply circuit comprises a central hydraulic station (not shown), permitting the supply to the control circuit of the jack of a substantially constant hydraulic supply pressure (arrow PA). This hydraulic station supplies, through the intermediary of a non-return valve 21, an oleo-pneumatic accumulator 22 which constitutes the pressure reserve of the control circuit of the jack.

The accumulator 22 applies a substantially-constant pressure to a hydraulic pressure-reducing valve 23, this valve delivering into the conduit system 24 a pressure which is variable (arrow PC) as a function of the control force applied to its control lever 25. The pressure-reducing valve 23 permits on the one hand a hydraulic control of a servo-controlled distributor 26 and on the other hand, through the conduit 24, the controlled distributor 26 and the conduit 27, it supplies a variable pressure PC to one of the working sections of the double-acting jack 1. Another working section of the jack 1 is supplied from the accumulator 22, the controlled distributor 26 and the conduit 28. A further distributor 29 with manual control enables the double-acting jack to be re-set under certain conditions of use, as will be seen later.

The double-acting jack 1 is shown as actuating by its eyes 2 and 11, two levers 31 articulated about fixed points 32 and carrying at their extremities brakeshoes 33 which, under the working action of the jack, come into engagement with a body 34. This illustration is solely employed in order to permit the explanation of the operation of the jack, it being understood that the jack according to the invention can co-operate with various other kinematic arrangements.

With reference to FIG. 6, which is a general axial cross-section of the jack shown in FIG. 5, the body 1 of the jack is in two parts, screwed one into the other in a fluid-tight manner, namely a bottom 41 with an eye-fork 2 and a cylinder 42 which is provided with two bores 43 and 44 in which the large piston 3 slides in a fluid-tight manner. The bottom 41 is provided axially with a hollow rod 45 on which is supported the brake device 6, constituted very simply by metal rings gripping the hollow rod and housed in a hollow plug 46 screwed into the large piston 3 (on the side of the chamber 5).

The large piston 3 is provided axially with a locking piston 47, sliding in a fluid-tight manner around the hollow rod 45 and in a fluid-tight manner in the large piston 3 and the plug 46, and is urged towards the left by a compression spring 48. This locking piston 47 and an internal shoulder 50 of the large piston 3, co-operate with a gripping clip 49 of the small piston 7, thus forming, as will be explained later with reference to FIGS. 10 to 12, the locking device having the reference numeral 12 in fIGS. 1 to 4. The large piston 3 is provided with a fluid-tight peripheral groove 51 which can be put into communication with the chamber 4 by a clapper-valve 52 which will be described later with reference to FIG. 7.

The jack 1 is connected to four conduit systems, namely: the conduit 28 which terminates at the chamber 8; the conduit 27 which terminates at the groove 51 and at the clapper 52; a conduit 53 which comes from the distributor 29 and terminates at the chamber 5; and a conduit 54 which comes from the controlled distributor 26 and terminates at the hollow rod 45 and at the chamber 9.

With reference to FIG. 7, which is a detail concerning the clapper-valve 52 of FIG. 6, this valve is housed in the large piston 3 and is held closed by its compression spring 56. It can be opened by mechanical thrust, as described later in connection with FIG. 12 on its end 57, and it then puts the peripheral groove 51 into communication with the chamber 4 by the conduits 58 and 59.

With reference to FIG. 8, which shows the installation of FIG. 5 in the condition of rest, the liquid under pressure from the accumulator 22, coming in through the intermediary of the controlled distributor 26 and the conduit 54, passes through the hollow rod 45 into the chamber 9, maintaining the small piston 7 in abutment on the left-hand side.

On the other hand, the liquid under pressure coming from the accumulator 22 reaches the supply position of the pressure-reducing valve 23 and is stopped there because the valve 23 is not actuated. The conduit 24 is therefore without pressure and the controlled distributor 26 occupies a position of rest by the action of its return spring; for this reason, the conduits 27 and 28 are connected to the tank.

With reference to FIG. 9, which shows the operation of the installation of FIG. 5 during the travel of large amplitude or approach travel, when the control lever 25 of the pressure-reducing valve 23 is actuated, a reduced pressure or control pressure appears in the conduit 24. For a given value of this pressure PC, the controlled distributor 26 is actuated hydraulically and then ensures the distribution shown in FIG. 9. This distribution reconnects the conduit 54 to the tank R.

On the other hand, the conduit 27 receives the reduced pressure PC existing in the conduit 24; this pressure terminates in the groove 51 and has no action as long as the clapper-valve 52 remains against its seating. Finally, the conduit 28 receives the liquid under pressure coming from the accumulator 22. The chamber 8 is thus supplied and for this reason the said piston 7 of the jack 1 is sent towards the right and the piston 3 and body 1 to the left. This achieves the approach travel; the shoes 33 have been brought up to the body 34.

With reference to FIGS. 10, 11 and 12, which are three details explaining, for the installation shown in FIG. 5, the automatic transition from the first action to the second: When the first action or approach travel comes towards its end, the grip-clip 49, carried by the small piston 7 and constituted by a series of flexible blades, passes into the bore 50 and pushes back the locking piston 47 while compressing its spring 48. When the extremity of the grip-clip reaches the extremity of the bore 50, it expands and permits the extremity of the locking piston 47 to pass into the interior of the clip.

From this moment, the small piston 7 is locked in position with respect to the large piston 3 by means of the simultaneous action of the clip 49 and the locking piston 47 (FIG. 12). In addition, the extremity of the clip 49 is applied against the end 57 of the clapper-valve 52, opening this valve which sends the pressure PC into the chamber 4.

With reference to FIG. 13, which shows the operation of the installation shown in FIG. 5 during the second action or gripping engagement, the control pressure PC existing in the chamber 4 thus acts on the annular section of the large piston 3. This action effects the working travel which applies the shoes 33 against the body 34. Depending on the force applied to control the pressure-reducing valve 23, the value of the pressure PC acting on the chamber 4 is more or less high, and the gripping force of the shoes 33 is more or less great.

If the shoes 33 are subjected to wear during the course of the use of the device (the case for example in which the shoes 33 are friction linings and the body 34 is a disc of a disc-brake), the travel of the large piston 3 would become increasingly great as and when this wear increased if special measures were not taken to prevent this. It is for this reason that there have been placed in the hollow plug 46, elastic metal rings 6 which grip the hollow rod 45. In the present stage of operation, these elastic rings yield (if wear exists) and permit the large piston 3 to move back towards the right by an amount corresponding to the said wear.

With reference to FIG. 14 which shows the return to rest of the installation shown in FIG. 5, when the actuation of the control lever 25 of the pressure-reducing valve 23 ceases, the control pressure falls to zero in the conduit 24, and as the control distributor 26 is no longer actuated hydraulically, it returns to the distribution of FIG. 8 due to the action of its return spring. The conduit 27 becomes connected to the tank R; there is therefore no longer any pressure existing in the chamber 4. The elastic metal rings 6 which grip the hollow rod 45 maintain the large piston 3 in the position in which it was located.

For the case of wear of the shoes 33, there is thus obtained a device which permits the consumption of the least possible quantity of liquid for the control of the piston 3, and in consequence the shortest response time for the effective engagement of the shoes 33 is obtained.

The conduit 28 is also connected to the tank R, while the conduit 54, that is to say the chamber 9, is again connected to the accumulator 22. The pressure existing in the chamber 9 acts on the locking piston 47 and causes it to return, compressing its spring 48. The extremity of the locking piston 47 thus passes out of the clip 49 and frees it (FIG. 15). The small piston 7 being subjected to the pressure PA is displaced towards the left, the clip 49 is withdrawn and passes into the bore 50.

The clapper-valve 52 is returned against its seating by the action of its restoring spring 56, which is calculated in such manner as to overcome the force of the pressure on the tail of the valve. The small piston returns, carrying out the whole of its travel up to abutment. The device has returned to rest. The situation is identically the same as that of FIG. 8, except that the position of the large piston 3 is slightly different if wear of the shoes 33 has taken place.

It will be observed that the clamping force provided by the elastic metal ring 6 on the hollow rod 45 is determined in such manner that the movement of the large piston 3 cannot take place in spite of the action of the pressure existing in the chamber 9 against a section equal to the section of the hollow rod 45.

Under normal conditions of use, the distributor 29 (FIG. 5) does not play any part in the operation of the device; it continuously ensures the connection of the chamber 5 to the tank R through the conduit 53.

In the case of a device in which wear occurs (that of the shoes 33 in the case of a brake for example), resulting in a gradual movement of the large piston 3 towards the right-hand side of the drawing, it may be necessary at a certain moment to replace the piston 3 in its initial position which it occupied when the device was new. It is at this moment that the distributor 29 is utilized so as to put the chamber 5 in direct connection with the accumulator 22 under pressure, thus causing the return of the piston 3 by the action of the liquid under pressure.

It will be observed that the device according to the invention may advantageously find an application in the operation of a disc-brake necessitating a very large liberating travel of the brakeshoes, at the same time providing an acceptable response time. The presence of the pressure-reducing valve 23 enables the braking pressure to be varied at will while actuating the jack 1 by a single control.

It will be noted that this jack, by reason of the relative action of the clip 49 and the clapper-valve 52, comprises a device with an incorporated sequence, first ensuring the approach travel and then immediately and automatically effecting the working travel.

Claims

What we claim is:

1. A hydraulic jack having two consecutive and complete different actions and a hydraulic operating means for furnishing a supply pressure under the action of a control pressure, said jack comprising a body, said body forming a first point of action and constituting a first cylinder, a first piston in said first cylinder and a first rod fast with said first piston and directed towards the side opposite to said first point of action, said first piston defining in said first cylinder a chamber on the rod side and a chamber on the side opposite to said rod, said first piston being provided with a peripheral groove, a clapper-valve between said groove and said rod-side chamber, said first rod forming a second cylinder, a second piston in said second cylinder, a second rod fast with said second piston and directed towards the side opposite to said first piston and forming a second point of action, said second piston defining in said second cylinder a chamber on the rod side and a chamber on the side opposite to said rod, and said hydraulic operating means responding to the control pressure when said pressure exceeds a selected threshold, by sending the supply pressure into said rod side chamber of said second piston on the one hand, and the control pressure into said peripheral groove of the said first piston on the other hand, and when said control pressure does not reach said threshold value, by sending the supply pressure into the chamber of said second piston on the opposite side to its rod.

2. A jack and its hydraulic operating means as claimed in claim 1, in which said hydraulic operating means comprises a hydraulic distributor controlled in dependence on the control pressure.

3. A jack and its operating means as claimed in claim 2, in which said jack comprises a braking means for maintaining by friction said first piston in the position in which it is located.

4. A jack and its operating means as claimed in claim 3, in which said jack body comprises an end member, an eye head, and a hollow axial rod, and forming a cylinder with two bores in which said first piston is adapted to slide.

5. A jack and its operating means as claimed in claim 3, in which said braking means comprises metal rings adapted to grip said hollow rod, and a hollow plug fast with said first piston and housing said rings.

6. A jack and its operating means as claimed in claim 1 comprising locking means including an elastic grip-clip fast with said second piston and adapted to engage in a shoulder of said first piston, and a locking piston with a compression spring adapted to slide in said first piston and to lock said clip in said position.

7. A jack and its operating means as claimed in claim 6, in which said elastic clip is adapted to open said clapper valve in the locked position.

8. A jack and its operating means as claimed in claim 1 in which said hydraulic operating means comprises a pressure-reducing valve which regulates the control pressure under the manual action of an operator.

9. A jack and its operating means as claimed in claim 1, in which said hydraulic operating means comprises a distributor which, under the manual action of an operator, sends the supply pressure into the chamber of said second piston on the side opposite to its rod.