FR2507984A1 - Laterally movable mobile crane - has double acting hydraulic cylinders to actuate outriggers to lift crane sideways - Google Patents

Abstract

The vehicle (10) has pivoted outriggers comprising telescopic beams (13,13'). Double-acting hydraulic cylinders (17,17') are pivoted on a vehicle body (11) and on otrigger boxes (15,15') for raising and lowering distal ends of the outriggers to support the vehicle. Double-acting hydraulic cylinders (18) extend and contract the outriggers. Control circuitry extends the outriggers on one side of the vehicle and contracts those on the other side to effect lateral translation of the vehicle. In a modification the raising and lowering cylinders are situated at the distal ends of the outriggers, and are pivoted directly onto floats (14,14').

Description

Vehicle capable of performing lateral translation movements, and hydraulic circuit equipping this vehicle.

 The present invention relates to a so-called "denor" vehicle, such as a chassis or a carriage fitted with tires and which, used as a support for a mobile crane, can be moved in the manner of a crab, that is to say in directions oriented at right angles to the normal direction of travel of the vehicle. The invention also relates to a hydraulic circuit making it possible to adapt known devices ensuring such lateral translation of the vehicle.

 When using a mobile crane or other earthmoving or industrial vehicles, it is often necessary to move the vehicle laterally in a small space on each side of the road. Since such a vehicle is generally not designed to be moved directly like a crab, it must be maneuvered backwards and forwards in a zigzag in the limited space, if the latter has a sufficient length, in a direction parallel to the road, to allow such a zigzag movement of the vehicle. Otherwise, this vehicle cannot be positioned properly in space.

 Chassis or carriages comprising tires, and used as supports for mobile cranes are usually delivered equipped with extension mechanisms actuated or not hydraulically. As has been done so far, all the hydraulic cylinders fitted to such a vehicle have been controlled by a single distributor allowing simultaneously either a deployment or a retraction of their rods, so that they have been used only to improve the stability in cantilevered.

 The object of the present invention is to allow direct lateral translation of a vehicle of the aforementioned type, using its jacks, therefore to improve the maneuverability of such a vehicle. In addition, the invention aims to use the existing organs as much as possible in conventional vehicles of the type under consideration, thus achieving an easy adaptation allowing these vehicles to move directly like the crabs do.

 According to the essential characteristics of the invention, the vehicle comprises two pairs of telescopic arms connected to the body of the vehicle so that it can be deployed in the direction of its opposite sides. In addition, the vehicle is equipped with means 3 for raising and lowering its body relative to the ground, by cooperating with the telescopic arms of means simultaneously ensuring the deployment and retraction of a pair of telescopic arms, as well as means simultaneously ensuring the deployment and retraction of the other pair of these arms. Consequently, given that the two pairs of telescopic arms can be deployed and retracted individually, the device can be used to allow the vehicle to be moved at an angle, by operating in a manner described below after the three aforementioned means.

Preferably, in the embodiments according to the invention, described in this specification, each telescopic arm is associated with a lifting cylinder, intended to raise and lower the body of the vehicle, as well as with an extension cylinder, allowing its proper deployment and retraction. A hydraulic circuit fitted to the vehicle includes three distributors independently controlling all of the lifting cylinders, a pair of extension cylinders (to deploy and retract a pair of telescopic arms), as well as the other pair of extension cylinders. The actuation of these three distributors in the manner mentioned allows the vehicle to move at an angle like a crab using its device provided for this purpose. It will be observed that a bias translation of conventional vehicles
of the above-mentioned door-type can be obtained by simply modifying the distribution device associated with the extension cylinders
extension of the telescopic arms.

The invention will now be described in more detail.
detail opposite the drawings appended as examples
in no way limiting and on which
Figure 1 is an end elevation with arra
checks illustrating a vehicle capable of performing a
direct lateral translation according to the invention, said vee
hicule being represented while performing this trans
lateral lation;
Figure 2 schematically illustrates a system
hydraulic allowing lateral translation of the vehicle
Figure 1;
Figure 3 schematically illustrates another
type of realization of a hydraulic system allowing
the lateral translation of the vehicle of Figure 1; and
the crack 4 is a view similar to FIG. 1,
but illustrates another form of realization of a vehicle
cule to which the present invention can be applied.

Figure 1 shows the embodiment
general of a vehicle in "door-outside", designated globally by the reference 10 and which can constitute the sup
carrying a mobile crane. This vehicle 10 comprises a body
11 equipped with organs in contact with the ground, which in
the example illustrated, consist of two pairs of wheels
12 with tires (only one pair shown), ensuring
the vehicle has a longitudinal translation
"outside" device comprising four transverse arms
telescopic 13 and 13 '(only two of which are illus
very), each connected by one end to one side of the body 11
of the vehicle in order to pivot about an axis oriented in the lon direction
gitudinal movement of the vehicle; stretching each
towards the respective opposite side; and ending cha
cun by a 14 or 14 'shoe. To facilitate the description,
the two telescopic arms 13 or i3 'connected to each side
of the vehicle body will be considered to form
one pair. Therefore, each pair of telescopic arms is spaced apart from the other pair in the longitudinal direction of the vehicle and Figure 1 illustrates only one telescopic arm of each pair.

1 G, de sorte que les vérins 17 et 17' seront appelés " vérins élévateurs dans le cadre du présent mémoire.Un autre verin hydraulique 18 ou 18' à double effet est logé à l'intérieur de chaque bras télescopique 13 ou 13' et ses extrémités opposees sont raccordées aux deux tiges télescopiques 15 ou 15' et 16 ou 16', afin de deployer et de rétracter chaque bras télescopique. De ce fait, les deux paires de vérins 18 et 18' seront repérees par l'appellation " vérins d'extension
La forme de réalisation du véhicule 10 telle que décrite jusqu'à present est classique et ne renferme aucune caractéristi-que propre à 1 'invention. L'invention est caractérisée par un circuit hydraulique qui, illustre sur la figure 2, comporte deux distributeurs 19 et 19' assurant individuellement le déploiement et la rétraction des tiges des pistons des deux paires de vérins d'extension 18 et 18'? en plus d'un distributeur 20 assurant le déploiement et la rétraction des tiges des pistons des quatre vérins élévateurs 17 et 17'. Ces trois distributeurs 19, 19' et 20 conjugués permettent au dispositif de déplacer le véhicule dans chacune des directions laterales opposes. Il s'est avéré que, jusqu'à présent, un seul dis tributeur était prévu pour permettre simultanément le déploiement et la retraction des tiges des pistons des deux paires de vérins d'extension.Each arm 13 or 13 'has a hollow rod 15 or 15', pivotally connected by one end to the body 11 of the vehicle, as well as a sliding hollow rod 16 or 16 'which, mounted telescopically in said rod 15 or 15' , has at its free end a pivoting pad 14 or 14 '. A hydraulic jack 17 or 17' with double interposed effect, is pivotally connected to the body II of the vehicle and at the other end of each hollow rod 15 or 15. This jack 17 or 17 'cooperates with the telescopic arm 13 or 13' to raise and lower the body 11 of the vehicle and its wheels 12 relative to the

1 G, so that the cylinders 17 and 17 'will be called "lifting cylinders for the purposes of this specification. Another hydraulic cylinder 18 or 18' with double effect is housed inside each telescopic arm 13 or 13 'and its opposite ends are connected to the two telescopic rods 15 or 15 'and 16 or 16', in order to deploy and retract each telescopic arm, therefore the two pairs of cylinders 18 and 18 'will be identified by the designation "cylinders extension
The embodiment of vehicle 10 as described so far is conventional and does not contain any characteristics specific to one invention. The invention is characterized by a hydraulic circuit which, illustrated in FIG. 2, comprises two distributors 19 and 19 'which individually deploy and retract the rods of the pistons of the two pairs of extension jacks 18 and 18'? in addition to a distributor 20 ensuring the deployment and retraction of the piston rods of the four lifting cylinders 17 and 17 '. These three distributors 19, 19 'and 20 combined allow the device to move the vehicle in each of the opposite lateral directions. It turned out that, until now, only one distributor was provided to simultaneously allow the deployment and retraction of the piston rods of the two pairs of extension cylinders.

 The hydraulic circuit of FIG. 2 comprises a pump 21 which, driven by a motor, supplies hydraulic fluid under pressure to the opposite chambers of the cylinders of the lifting cylinders 17 and 17 'and of the extension cylinders 18 and 18', by the distributor 20 and distributors 19 and 19 ', respectively. Although these three distributors 19, 191 and 20 are illustrated as each having six orifices, it is obvious that each distributor can have only four orifices to fulfill the functions assigned to it by the present invention. Consequently, these three distributors are mounted in parallel.

The distributor 20, interposed between the pump 21 and the clearance da veri.ns elevators 17 and 17 ', is of the type with three positions1 with closed center. The three positions of this dispenser are as follows
1. a central position N, in which the four openings are all closed;
2. a low position D, in which a pipe 22 for pumping pressure communicates with a pipe 23 connects to the chambers located on the rod side of the pistons of all the lifting cylinders 17 and 17 '; and in which a drain pipe 24 communicates with a pipe 25 connected to the chambers located on the head side of the pistons of all said lifting cylinders, by means of distributors 26 and 26 ′ of the “all or nothing” type and of non-return valves 27 and 27 '; and
3. a high position U, in which the pumping pressure line 22 communicates with the line 25; and in which the drain pipe 24 is connected to said pipe 23.

Preferably, the distributor 20 is controlled by electromagnets and for this purpose it has a pair of electromagnets 28 at its opposite ends.
The excitation of these electromagnets causes the switching of the distributor to its low position (D) or to its high position (U). The distributors 26 and 26 'are also individually controlled by electromagnets, in order to be switched from their normal closed positions to their open positions. Between these distributors 26 and 26' and the lifting cylinders 17 and 17 ', the valves non-return 27 and 27 'are intended to block the return flow from the chambers of the eieva- cylinders under the effect of the load. valves located on the piston head side, / These non-return valves are controlled from the conduits connected to the chambers, located on the piston rod side, the elevating cylinders 17 and 17 'respectively, thus allowing the fluid to escape from the chambers located on the head side when the pressurized fluid is supplied to the chambers located on the rod side.

 Consequently, when the distributor 20 is switched to its low position D, the pump 21 supplies pressurized fluid to the rod-side chambers of the pistons of the lifting cylinders 17 and 17 '. This results in a retraction of the rods of these jacks, therefore a lowering of the body 11 of the vehicle as well as of the wheels 12. On the other hand, it results from the switching of the distributor 20 to its high position U that a pumping pressure is delivered to the chambers on the head side of the pistons of the lifting cylinders 17 and 17 ', provided that the distributors 26 and 26' are open. At this time, the rods of the lifting cylinders are deployed, which causes a downward pivoting of the telescopic arms 13 and 13 'and, consequently, the lifting of the body 11 of the vehicle away from the ground G.

The first distributor 19 associated with the first pair of extension jacks 18 is also of the three-position type, with a closed center. The three positions of this distributor 19 are as follows
1. a central position N, in which the four openings are all closed;
2. a retraction position C, in which the pumping pressure conduit 22 communicates, via a conduit 29 with the chambers located on the piston rod side of the first pair of extension jacks 18; and in which the chambers of the cylinders of these jacks, situated on the head side of the pistons, communicate with the drain pipe 24 by a pipe 30; and
3. a deployment position E, in which the pumping pressure conduit 22 communicates with the chambers at the head side of the pistons of the first pair of extension jacks 18, via the conduit 30 and in which the chambers of the cylinders said cylinders, located on the piston rod side, communicate with the drain pipe 24 via the pipe 29.

 The first distributor 19 is provided with a pair of control electromagnets 31 at its opposite ends, in order to be switched to one of its retraction or deployment positions. When switched to its retraction position, this distributor 19 causes the retraction of the rods of the first pair of extension jacks 18 and, consequently, of the corresponding first pair of telescopic arms 13. On the other hand, when this distributor 19 is switched to its deployment position, it causes the deployment of the rods of the first pair of extension jacks 18 and, therefore, of the first pair of telescopic arms 13.

 The second distributor 1S ', cooperating with the second pair of extension verifiers 18', is of a design and an operation substantially similar to those of the first distributor 19. This second distributor 19 'can occupy three effective positions Nt, E 'and C' corresponding to positions N, E and C, respectively, of the first distributor 19. A pair of control electromagnets 31 ', situated at the opposite ends of the distributor 19', selectively switch the latter to its two positions E 'and C' from its central or neutral position N ', making the pump 21 communicate with the chambers on the head and rod side of the pistons of the second pair of extension cylinders 18'. Consequently, the second pair of telescopic arms 13 'is deployed when the second distributor 19' is switched to its deployment position E '; and is retracted when said distributor is switched to its retraction position C '.

 After having described the embodiment of the vehicle according to the invention, it is now necessary to describe the mode of operation thereof, when this vehicle must be moved diagonally to the left, as shown in FIG. 1. 'first that the three distributors 19, 19' and 20 all occupy their neutral position; that the rods of the four lifting cylinders 17 and 17 'are all retracted, allowing the body 11 with wheels to rest on the ground G; and that the rods of the two pairs of extension jacks 18 and 18 'are also all retracted, consequently causing the telescopic arms 13 and 13' to retract.

Under these conditions, when the user switches the first distributor 19 to its extended position
E by exciting one of the electromagnets 31, the pump 21 delivers pressurized fluid to the chambers located on the head side of the pistons of the first pair of extension cylinders 18, then causing a deployment to the left of the first pair of telescopic arms 13. The user then switches the distributor 20 to its high position U and all the distributors 26 and 26 'to their open position, energizing the corresponding electromagnets. As a result, the pump 21 delivers pressurized fluid to the chambers located on the head side of the pistons of all the lifting cylinders 17 and 17 '. The latter, whose rods are deployed, cause a downward pivoting of all the telescopic arms 13 and 13 'relative to the body 11 of the vehicle, which raises the latter away from the ground G. The position illustrated in solid lines in Figure 1 shows the vehicle in this phase of diagonal translation in the manner of a crab.

 The next step consists in switching the first distributor 19 to its retraction position C and the second distributor 19 'to its deployment position E'.

These distributors 19 and 19 ′ then direct the pressurized fluid coming from the pump 21 to the chambers situated on the rod side of the pistons of the first pair of extension jacks 18, and to the chambers situated on the head side of the pistons of the second pair of extension cylinders 18 ', respectively. When, therefore, the first pair of telescopic arms 13 is retracted and the second pair of arms 13 'is deployed, the body 11 of the vehicle is moved to the left, like a crab, to the position illustrated in lines mixed in Figure 1, being lifted off the ground. Then, the distributor 30 can be switched to its low position D, in order to establish communication between the pump 21 and the chambers situated on the rod side of the pistons of all the lifting cylinders 17 and 17 ′. The rods of the latter are controlled so as to be returned, until the wheels 12 of the vehicle come to rest on the ground.

 A lateral translation phase of the vehicle is thus completed. This same phase can be repeated if necessary to bring the vehicle to its desired position. It is obvious that this vehicle can be moved like a crab in the opposite direction, in a similar manner.

 In the presence of uneven ground, the vehicle body is subjected to torsional stresses when such a diagonal translation occurs. One solution to this problem consists in subdividing this body into anterior and posterior parts connected by a rotary articulation. Alternatively, the lifting cylinders can be controlled so as to compensate for the undulations of the ground, in a manner which will appear obvious to those skilled in the art.

 FIG. 3 illustrates another example of a hydraulic circuit ensuring the lateral movements of the vehicle 10 illustrated in FIG. 1. This circuit differs from that of FIG. 2 only by the arrangement of two distributors 119 and 119 '. The first distributor 119 is interposed between the pump 21 and the first pair of extension cylinders 18, just like the first distributor 19 of the previous embodiment, but the second distributor 119 'is interposed between this first distributor 119 and the second pair of 18 'extension cylinders.

The two distributors 119 and 119 ′ are of the three-position type with closed center. The two offset positions of the first distributor 119 are as follows
1. a retraction position C, communicating the pumping pressure conduit 22 with a conduit 129 opening into the chambers located on the rod side of the pistons of the first pair of extension cylinders 18; and communicating, with the drain pipe 24, a pipe 130 opening into the chambers located on the head side of the pistons of the first pair of said extension jacks; and
2. a deployment position E, making common the conduit 22 with the conduit 130 and the conduit 129 with the drain conduit 24.

In addition to its closed central position, the second distributor 119 'can occupy the following positions -
i. a first position / s talsant communicating the conduits 129 and 130 with the chambers on the rod side and on the head side of the pistons, respectively, of the second pair of extension jacks 18 '; and.

shifted
2. a second position / II, making the conduits 129 and 130 communicate with the chambers on the head and rod side of the pistons, respectively, of said second pair of jacks 18 '.

The other details of construction of this modified hydraulic circuit are identical to those of the circuit of FIG. 2. As shown in the foregoing, the modified system has the advantage that, when the second distributor 119 'is switched to its first position offset I, only the first distributor 119 must be actuated to simultaneously allow the deployment or retraction of all the telescopic arms 13 and 13 '. On the other hand, in the embodiment described in the first place, both the distributor 19 and the distributor 19 'must be actuated to allow the deployment and retraction of all the telescopic arms. The table below indicates the effective positions of the two distributors 119 and 119 'in various combinations, as well as the resulting functions of the extension cylinders 18 and 18
First distribution - Second distribution - Stopper function 119 stopper 119 '
CI Retraction of all arms
telescopic
C II Translation to the left
of the vehicle body
EI Deployment of all
telescopic arms
E Il Translation to the right
of the vehicle body
To obtain a translation to the left of the vehicle 10 (FIG. 1) using the hydraulic circuit of FIG. 3, the first distributor 119 can be switched to its deployment position E, the second distributor 119 'being held in its position central or neutral. The distributor 119 then directs the pressurized fluid discharged by the pump 21 to the chambers situated on the head side of the pistons of the first pair of extension jacks 18, thus causing a deployment to the left of the first pair of arms telescopic 13. The second pair of telescopic arms 13 'is then assumed to be retracted.

Then, the rods of all the lifting cylinders 17 and 17 ′ are deployed, as in the first embodiment described, in order to lift the body il of the vehicle with wheels away from the ground. While the vehicle body is raised, the first distributor 119 is switched to its retraction position C and the
second distributor 119 'at its second offset position
II. In this case, as shown in the table above,
the body of the vehicle translates to the left
since, at that time, the. stems of the first
pair of extension cylinders 18 and those of the second
pair of 18 'cylinders are retracted and deployed, respecting
vement. Then the rods of all the lifting cylinders
17 and 17 'are retracted in order to lower the body of the
vehicle to the ground. This operation can be repeated
if necessary. Of course, the vehicle can be moved
like a crab to the right in the same way.

Figure 4 illustrates another example of a vehicle
cule 110 to which the present invention can be applied.

This vehicle 110 differs from vehicle 10 in FIG. 1 by
the fact that its raising and lowering device located "outside" has a general configuration in H,
as seen in the figure. This device includes
two pairs of telescopic arms 113 and 113 'which, espa
lengthwise, are subject to the body 11 of the
vehicle fitted with wheels, so as to extend horizontally
lement. Each telescopic arm is associated with a jack
elevator 117 or 117 'hanging at its end deployed
ble and ending with a shoe 14 or 14 '. Each arm
telescopic also houses an extension cylinder 118 or
118 '.

Like the vehicle 10 in FIG. 1, the
elevating cylinders 117 and 117 'are used to lift and
lower the body 11 of the vehicle in cooperation with the
telescopic arms 113 and 113 ', while the cylinders
extension 118 and 118 'have the function of deploying
and retract these telescopic arms. That is why,
obviously, the hydraulic circuit of figure 2 or
3 is used in this vehicle 110 to allow it to
move like a crab. This vehicle presents
the advantage of performing such a crab movement without
be unduly hampered by uneven ground.

 Although the invention has been described in support of preferred embodiments intended for specific types of vehicles, it goes without saying that numerous modifications can be made to the vehicle and to the system described and shown, without going beyond the ambit of the invention.

Claims (9)

 1. Vehicle capable of performing lateral translation movements, characterized in that it comprises  a) a body (11) fitted with members (12) in contact with  the ground to ensure longitudinal translation;  b) two pairs of deployable telescopic arms (13, 13  or 113,113 ') connected to said body (11) and each extending  essentially in the transverse direction of said vehicle  cule (10 or 10) each pair of telescopic arms (13,  13 ') being spaced apart from the other in the longitu direction  dinal of said vehicle (10) ;;  c) means (17, 17 ′ or 117,117 t) cooperating with the two pairs  telescopic arms (13,13 '), in order to lift  away from the ground (G) and lower on the latter said  body (11) and said organs (12);  d) means (-18 or 118) intended to shrink and retract  simultaneously a pair of telescopic arms (13);  and  e) means (18 'or 118') intended to deploy and retract  simultaneously the other pair of telescopic arms  (13 '); and by the fact that said vehicle (10) can be moved in the manner of a crab by actuating the three means (17, 17 '; 18; 18') mentioned above.  2. Vehicle capable of performing lateral translation movements, characterized in that it comprises  a) a body (11) having organs in contact a  with the ground to ensure longitudinal translation  the ;  b) first and second pairs of telescopic arms  deployable (13,13 'or 113,113') connected to said body (11) and  each extending essentially in the trans direction  versal of said vehicle (10 or 110) each pair of arms  telescopic (113, 113 ') being spaced apart  in the longitudinal direction of said vehicle (110) ;;  c) a set of lifting cylinders (17.1? 'or 1779oop-  rant with pairs of telescopic arms (113,  113 '), in order to lift away from the ground and out of  be on the latter said body (11) and its organs  in contact with the ground;  d) first and second pairs of extension cylinders  (18.18 'or 118.118') associated with said first and  second pairs of telescopic arms (113, 113 '),  respectively, in order to independently ensure the  deployment and retraction of these arms; and  e) a fluid circuit enabling independent control  while the set of lifting cylinders (117,  117 '), the first pair of extension cylinders (118)  and the second pair of extension cylinders (118 '), said vehicle (110) being movable like a crab by selectively actuating all of the lifting cylinders (117, 117') and the first and second pairs extension cylinders (118, 113 ').  3. Vehicle according to claim 2, characterized in that each of the two pairs of telescopic arms (13, 13 ') is pivotally mounted by one end to the body (11), and by the fact that each lifting cylinder (17; 17 ') is effectively interposed between said body (11) and one (13; 13') of said telescopic arms.  4. Vehicle according to claim 2, characterized in that the two pairs of telescopic arms (113, 113 ') are secured to the body (11) so as to extend horizontally, and in that each lifting cylinder (117 * 117 ') hangs from one (113, 113') of said telescopic arms.  5. Vehicle according to claim 2, characterized in that its' fluid circuit comprises  a) a source (21) of pressurized fluid;  b) a distributor (20), interposed between said source  (21) of pressurized fluid and the elevating cylinders  teurs (17, 17 '), to order the communication  tion between these organs  c) a first distributor (19), inserted between the ladi  source (21) and the first pair of ex cylinders  voltage (18), to control communication  between these organs; and  d) a second distributor (19 '), interposed between ladi  source (21) and the second pair of ex-  voltage (18 '), to control communication  between these organs.  6. Vehicle according to claim 2, characterized in that its fluid circuit comprises  a) a source (21) of pressurized fluid  b) a distributor, interposed between said source (21)  and the lifting cylinders (17, 17 '), in order to control  communication between these bodies  c) a first distributor (119), interposed between ladi  source (21) and the first pair of ex cylinders  voltage (18), to control communication  between these organs; and  d) a second distributor (119 '), interposed between the  said first distributor (119) and the second pair  extension cylinders (18 '), to control the  communication between these bodies.  7. Hydraulic circuit intended to allow the lateral translation of a vehicle of the type comprising two pairs of deployable telescopic arms connected to the body of said vehicle and each extending for the essential in the transverse direction of the latter, a set lifting cylinders cooperating with the pairs of telescopic arms in order to raise the body of said vehicle away from the ground and lower it on the latter, as well as two pairs of extension jacks associated with the respective pairs of telescopic arms, in order to deploy and retract them, circuit characterized by the fact that it includes  a) a pump (21) ;;  b) a distributor (20), interposed between said pump  (21) and said lifting cylinders (17, 17 '), so  to selectively cause deployment and the  retraction of the piston rods of the latter,  therefore upward and downward displacements of the  body (11); and  c) distributors (19, 19 '), interposed between said  pump (21) and said extension jacks (18, 18 '),  in order to provoke independently and selectively  deployment and retraction of udder stems  tones from individual pairs of extension cylinders  sion (18, 18 '), so deployment and retrac  tion of the pairs of telescopic arms (13, 13 '), and by the fact that said vehicle (10) can be moved in the manner of a crab as a result of selective control of said distributor (20) and said distributors (19, 19 '), respectively.  8. Hydraulic circuit according to claim 7, characterized in that the device associated with the extension cylinders comprises  a) a first distributor (19), interposed between the  pump (21) and a pair of extension cylinders (18),  in order to control the commication between these gold  ganes-; and  b) a second distributor (19), interposed between said  pump (21) and the other pair of extension cylinders  (18 '), to control communication between  these organs.  9. Hydraulic circuit according to claim 7, characterized in that the device associated with the extension cylinders comprises  a) a first distributor (119 '), interposed between the  pump (21) and a pair of extension cylinders (18),  in order to control the communication between these orga  nes; and  b) a second distributor (119 '), interposed between the  said first distributor (119) and the other pair of extension jacks (18 '), in order to control the communication between these members.