EP0582497B1 - Control system for a plurality of hydraulic actuators - Google Patents

Description

The invention relates to a control assembly for a plurality of hydraulic receivers, through which the receivers are supplied by the same generation of flow, each being connected thereto by means of a proportional distributor.

We know that distributors are devices that are available between a flow generation and a receiver to control the operation of the receiver by adapting the way it is connected to the flow generation.

Proportional type distributors include not only a controlled drawer whose position determines the section of a constriction, but also an automatic compensating drawer to maintain constant the pressure difference between the upstream and downstream of this constriction, so that at a given position of the controlled slide corresponds to a given flow of fluid. Consequently, when a receiver is controlled with a proportional distributor, its operating speed is fixed by the position of the controlled drawer, independently of the load that the receiver supports.

When the flow generation is used to supply a plurality of receivers to which each corresponds a proportional distributor, it may happen that the total flow requested by the receivers exceeds the maximum flow that the flow generation is able to supply. The respective compensating drawers are no longer in able to maintain the pressure difference between the upstream and downstream of the throttle at the prefix constant in each of the distributors, so that the most loaded receivers slow down or stop while the least loaded ones can continue to operate .

To avoid these disorders, it has already been proposed to take advantage of the regulation of the flow generation as a function of the power demanded, which is currently provided on most hydraulic circuits where the flow generation supplies a plurality of receivers. This regulation is carried out by providing load sensing means called "load-sensing" which bring the pressure of the most charged receiver towards the generation of flow, to which pressure responds the generation of flow by producing a working pressure equal to the load-sensing pressure increased by a constant. In reality, this constant is added as long as the total demand for flow is less than that capable of being supplied, but in the event of excess demand, the value added to the load-sensing pressure is smaller than the constant , and the smaller the excess demand for debit is important. It is this reduction in the added value which is used to avoid the abovementioned disorders.

FR-A-2.339.757 proposes to act on the actuation pressure of the slide controlled in each of the proportional distributors, by providing that the actuation valves are no longer supplied directly from a pilot pump, but with interposition between the pilot pump and the actuation valves of a maneuvering valve which varies the supply pressure of the control valves in the same way as the difference between the pressure of the flow generation and the pressure of load -sensing. As long as the flow generation works normally, the supply pressure of the control valves remains constant, just as if these valves were supplied directly by the pilot pump. In case of debit request excessive, the supply pressure of the control valves will decrease depending on the amount of excess demand, the actuation pressure of all the ordered drawers will decrease in the same way, and consequently all the throttles produced by the ordered drawers will increase in the same way, with the result that each distributor will be applied the same rate reduction rate so that all receivers will slow down with conservation of their speed ratio.

FR-A-2.548.290 proposes to achieve the same result in the case where the proportional distributors have a compensating drawer which is located upstream of the controlled drawer, by acting on the actuating means of the compensating drawer: it continues to be used in the direction of closing by the pressure upstream of the controlled drawer and in the direction of opening by the pressure downstream of the controlled drawer, but the conventional spring is replaced by a double pressure stress, respectively in the direction of closing by the load-sensing pressure and in the opening direction by the pressure of the flow generation. The pressure difference between the upstream and downstream of the throttle of the controlled slide is thus controlled by the difference between the pressure of the flow generation and the load-sensing pressure, which leads to the abovementioned result. DE-A-4,036,720 proposes to take similar measures, but instead of being directly the difference between the pressure of the flow generation and the load-sensing pressure, the servo reference is obtained from these pressures through adjustment means, for example a pressure lowering valve disposed between the generation of flow and the compensating slide.

The invention also aims to obtain the aforementioned result, but with improved performance.

• un tiroir commandé dont la position détermine la section d'un premier étranglement ;
• un tiroir compensateur pour réguler la différence de pression entre l'amont et l'aval dudit premier étranglement en produisant à l'amont de celui-ci un deuxième étranglement de section appropriée ; et
• des moyens d'actionnement du tiroir compensateur, pour lui faire prendre automatiquement une position où il produit ledit deuxième étranglement de section appropriée, en réponse :
  • . à la pression en aval du premier étranglement et à une première pression, agissant dans le sens de l'ouverture, et
  • . à la pression en amont du premier étranglement et à une deuxième pression, agissant dans le sens de la fermeture ;

• ensemble comportant en outre une valve auxiliaire alimentée par la génération de débit et produisant une pression constituant une dite première pression ;
• ensemble caractérisé en ce que :
  • chaque dite deuxième pression est une pression de régulation dépendant des conditions de charge desdits récepteurs hydrauliques ;
  • chaque dite première pression est produite par une dite valve auxiliaire ;
  • chaque dite valve auxiliaire produit, à partir de son alimentation et de ladite pression de régulation, qui lui est directement appliquée, une pression normalement égale à ladite pression de régulation augmentée d'une constante ; et
  • dans chaque distributeur proportionnel lesdits moyens d'actionnement du tiroir compensateur sont prévus pour qu'il soit en outre sollicité dans le sens de la fermeture par une force sensiblement constante.

To this end, it offers a control unit for a plurality of hydraulic receivers, through which the receivers are supplied by the same generation of each being connected to it via a proportional distributor comprising:

• a controlled drawer whose position determines the section of a first constriction;
• a compensating drawer for regulating the pressure difference between the upstream and downstream of said first throttle by producing upstream thereof a second throttle of appropriate section; and
• actuating means of the compensating drawer, to make it automatically assume a position where it produces said second throttle of appropriate section, in response:
  • . at the pressure downstream of the first constriction and at a first pressure, acting in the direction of opening, and
  • . at the pressure upstream of the first constriction and at a second pressure, acting in the direction of closure;

• assembly further comprising an auxiliary valve supplied by the generation of flow and producing a pressure constituting said first pressure;
• set characterized in that:
  • each said second pressure is a regulation pressure depending on the load conditions of said hydraulic receivers;
  • each said first pressure is produced by a said auxiliary valve;
  • each said auxiliary valve produces, from its supply and said regulating pressure, which is directly applied to it, a pressure normally equal to said regulating pressure increased by a constant; and
  • in each proportional distributor, said means for actuating the compensating drawer are provided so that it is further urged in the closing direction by a substantially constant force.

In the case where the regulating pressure is the load sensing pressure, the assembly according to the invention differs from that described in the last prior art aforementioned by the presence of the auxiliary valve whose pressure produced is applied in place of the pressure of the flow generation.

In reality, to make the prior assembly practical, it would have been convenient to apply the pressure upstream thereof to the compensating slide rather than the pressure of the flow generation. When the distributors are distributed in different places of a machine, however, difficulties would arise because the pressure upstream of the second throttle is not the same in the respective distributors, due to different pressure drops between the generation debit and the respective distributors.

Similar difficulties would occur also with the various distributors of a control block located at a distance from the flow generation, the pressure drops between the latter and the block increasing with the flow in the block supply pipe: it could for example happen that the controlled drawer of one of the block's distributors remains in the same position, and the flow passing through it decreases without there being an overshoot of the flow capacity. This would occur in particular as a result of an increase in the flow rate passing through a second distributor because the increase in the total flow rate of supply to the block increases the pressure losses between the generation of flow rate and the block, and therefore decrease the difference between the supply pressure of the block (i.e. the pressure upstream of the second throttle of all the distributors in the block) and the load sensing pressure.

The assembly according to the invention avoids this difficulty.

The invention also offers the advantage of being able to provide the desired result even if the generation of flow is not regulated as a function of the load supported by the receivers.

• une chambre d'alimentation reliée à la génération de débit ;
• une chambre de régulation dans laquelle règne ladite pression de régulation ;
• une chambre de sortie où règne ladite pression produite ;
• un tiroir dont la position détermine la section d'un étranglement entre la chambre d'alimentation et la chambre de sortie, comportant une première surface active disposée dans la chambre de régulation de sorte que ladite pression de régulation agit dans le sens de l'ouverture, et une deuxième surface active disposée dans la chambre de sortie de sorte que la pression produite agit dans le sens de la fermeture ; et
• un ressort, qui agit sur le tiroir dans le sens de l'ouverture.

Preferably, for reasons of simplicity and convenience, the auxiliary valve comprises:

• a feed chamber connected to the flow generation;
• a regulation chamber in which said regulation pressure prevails;
• an outlet chamber where said pressure produced prevails;
• a drawer whose position determines the section of a throttle between the supply chamber and the outlet chamber, comprising a first active surface disposed in the regulation chamber so that said regulation pressure acts in the direction of opening , and a second active surface arranged in the outlet so that the pressure produced acts in the closing direction; and
• a spring, which acts on the drawer in the opening direction.

In the case where the proportional distributors are divided into several groups of a distributor or of several neighboring distributors, the groups being distant from each other, it is preferable that the assembly includes for each group an auxiliary valve adjacent to the group.

This avoids problems related to pressure drops in line, and especially to have to provide a line between the auxiliary valve and a group of distributors distant from the latter.

• la figure 1 est une vue schématique en coupe d'un distributeur proportionnel faisant partie d'un ensemble conforme à l'invention ;
• la figure 2 est un schéma d'un circuit hydraulique comprenant cet ensemble de commande, qui comporte deux distributeurs similaires à celui montré sur la figure 1, accollés bout à bout ; et
• les figures 3 et 4 sont semblables aux figures 1 et 2 respectivement, mais pour une variante de réalisation.

The description of the invention will now be continued with the description of exemplary embodiments, given below by way of illustration and not limitation, with reference to the appended drawings, in which:

• Figure 1 is a schematic sectional view of a proportional distributor forming part of an assembly according to the invention;
• Figure 2 is a diagram of a hydraulic circuit comprising this control assembly, which includes two distributors similar to that shown in Figure 1, joined end to end; and
• Figures 3 and 4 are similar to Figures 1 and 2 respectively, but for an alternative embodiment.

The distributor 70 illustrated in FIG. 1 is similar to that described in FR-A-2,562,632, with the exception of its pressure compensating device.

It comprises a stator block 1, in the bore 2 of which slides a cylindrical controlled drawer 3. In the usual way, the switching of the hydraulic circuits is effected by displacement of the grooves of the drawer 3 in front of the lights of the stator.

At its left end, for example, the drawer 3 is provided with a spring return device of the type known, comprising a helical spring 4, compressed between the shoulders 5 and 6 of two rings 7 and 8, trapped between two shoulders of the end 9 of the drawer 3, around which they can slide. Thus, the drawer 3 is spontaneously returned to a neutral rest position, while it is pushed to the right (FIG. 1) when a pilot pressure is sent into an opening 10 of the fixed cap 61. On the contrary, it is pushed to the left when a pilot pressure is sent opposite, in an opening 11 of the cap 62 at its other end. In the example illustrated, it has been assumed that the three-position slide 3 is used to control a double-acting hydraulic cylinder 12. For this, one of the sections of the cylinder 12 is connected to a first channel use 13 of the stator 1, while the opposite section of the jack 12 is connected to a second use pipe 14 of the stator 1.

The distributor receives in an annular chamber 15, the pressure sent by a generation of flow 71.

The supply chamber 15 surrounds a compensating drawer 16, also called a balance, which is movable in a bore 80 of the stator 1. The drawer 16 is provided with a radial bore 22 communicating with a blind axial bore 23. The latter opens onto a seat capable of being closed off or unmasked by a ball 24 whose return spring 25 is compressed inside the compensating drawer 16. The chamber containing the ball 24 and the spring 25 opens out through a lateral opening 26 in a chamber ring 27 surrounding the central part of the controlled drawer 3.

At each of its two ends, the controlled slide 3 has an axial internal housing, 28 on the left, 29 on the right.

The housing 28 communicates with the outside of the drawer by two radial bores referenced respectively 30 and 31. Likewise, the housing 29 opens onto two radial bores 32 and 33.

When drawer 3 is in its neutral position of rest, the bore 30 faces a solid part 34 of the stator which closes it, between two annular chambers 35 and 36. The chamber 35 communicates with the first use pipe 13, while the chamber 36 is connected to the circuit of return.

Similarly, the bore 32 is closed at rest, by a solid part 37, located between two annular chambers 38 and 39. The chamber 38 communicates with the second use pipe 14, while the chamber 39 is connected to the return circuit .

Between the holes 30 and 31, the stator defines, in the bore, a solid part 40, in front of which is capable of moving a groove 41 of the drawer 3.

Around the drawer 3, in the zone situated around the bore 31 when the drawer 3 is pushed to the right (FIG. 1), there is an annular stator chamber 42.

Similarly, at its opposite end, the drawer 3 has a groove 43 movable in front of a solid part 44 of the stator. Around the passage 33 when the drawer 3 is pushed to the left, there is an annular stator chamber 45.

The two chambers 42 and 45 are connected by a pipe 46 called the load sensing pipe.

Progressivity notches equip the different grooves of the drawer, as indicated for example by the references 48, 49, 50, 51.

Finally, a first booster valve 52 is mounted in parallel on the first use pipe 13. Similarly, a booster valve 53 is mounted in parallel on the second user pipe 14. Behind the valves 52 and 53, is finds a chamber 54 connected to the oil return circuit.

A pressure relief valve, respectively 55 and 56, is provided on the side of each of the use pipes 13, 14, which can thus flow into the return chambers, respectively 36, 39.

The operation of the controlled drawer 3 will now be described.

In the neutral position, the chambers 27, 35 and 38 are closed, so that the jack 12 is immobilized while no flow passes through the distributor. In addition, the pipe 46 communicates through the grooves 41 and 43 respectively with the chamber 36 and the chamber 39, that is to say that it is connected to the return circuit.

When a pilot pressure is sent through the opening 10, as is the case in FIG. 1, the slide 3 slides to the right with an amplitude determined by the value of the pilot pressure, which is balanced with the opposing thrust of the spring 4, more or less compressed. The supply pressure of the chamber 27 is sent into the line 13 through the groove 49 and the chamber 35, while the line 14 communicates with the return chamber 39 through the groove 51. Each of the grooves 49 and 51 determines a throttle whose section is determined by the position of the slide 3. In addition, the pipe 46 communicates on the left with the pipe 13 through the passages 31, 28 and 30, while on the right it is closed. The pressure downstream of the throttle provided by the groove 49 is thus transmitted to the pipe 46.

When a pilot pressure is sent through the opening 11, the slide 3 slides to the left to a position determined by the amplitude of the pilot pressure. The supply pressure of the chamber 27 is sent into the line 14 passing through the groove 50 and the chamber 38, while the line 13 communicates with the return chamber 36 through the groove 48. Each of the grooves 48 and 50 determines a constriction, the section of which is determined by the position of the drawer 3. In addition, the pipe 46 communicates on the right with the pipe 14 by the holes 33, 29 and 32, while on the left it is closed. The pressure downstream of the throttle provided by the groove 50 is thus transmitted to the pipe 46.

It can thus be seen that in the neutral position, the pipe 46 is put under the pressure of the return circuit, while in each of the working positions, it is brought to the pressure downstream of the throttle provided by the slide 3 on the cylinder 12 supply line, that is to say the operating pressure thereof.

The circuit selector 99 (also called OR function) has one of its inputs which communicates with the pipe 46 by a channel 72, and its other input which communicates with a channel 73 connected to the output pipe of the circuit selector d '' a similar distributor. Here, the pressure in the line 46 is the highest, so that the circuit selector 99 adopts the illustrated position where it transmits by its output to the line 74 the operating pressure of the cylinder 12, which is the pressure of highest use of all the receivers supplied by the flow generation 71. More generally, as is clear from FIG. 2, it is always the pressure of the most loaded receiver which is applied to the pipe 74, this so-called "load sensing" pressure being transmitted to the generation of flow 71 which produces an operating pressure normally equal to the load sensing pressure increased by a constant.

The compensating slide 16 comprises around the channel 22 a groove 111 which produces, depending on the position of the slide, a more or less significant constriction upstream of the constriction provided by the slide 3 on the supply line of the jack 12, depending on the position taken by the drawer 16.

This comprises two active surfaces, on the left a surface 112 subjected to the pressure upstream of the throttle provided by the slide 3, and on the right a surface 301 subjected to the pressure prevailing in the pipe 46, that is to say tell the operating pressure of the jack 12.

On the left side of the drawer 16 is arranged a piston 114 movable coaxially, which comes into contact with the drawer compensator by a stud, and slides in a cylinder 116 screwed into the stator 1 coaxially with the bore 80, the cylinder 116 being open on the internal side and closed on the external side, and sealingly passing through the pipe 46.

The piston 114 has an L-shaped passage which makes it possible to communicate the chamber 115 situated between the piston and the bottom of the cylinder with the pipe 119, which is connected to the load-sensing pipe for the generation of flow, so that it is brought to the load sensing pressure. The piston 114 has two opposite surfaces, a surface 121 facing the active surface 112 of the drawer 16, and subjected to the same pressure, and an active surface 123 subjected to the load sensing pressure.

A spring 125, the force of which is adjustable with the screw 126, applies the piston 114 against the drawer 16.

This comprises on the right a third active surface 302 which is subjected to the pressure produced by an auxiliary valve 303.

The surfaces 301 and 302 look to the right, and the pressures to which they are subjected urge the drawer 16 in the direction of opening.

The surface 301 is subjected to the pressure prevailing downstream of the throttle provided by the slide 3 because it is disposed in the pipe 46, and the surface 302 is subjected to the pressure produced by the valve 303 because it is disposed in a chamber 304 connected by a pipe 305 to the valve 303.

The surfaces 112 and 123 look to the left, the pressures to which they are subjected therefore urge the drawer 16 in the closing direction. The surface 121 looking to the right, urges the piston 114 to the left, that is to say that everything happens as if the pressure upstream of the throttle provided by the slide 3 applied to the effective value of the surface 112 minus the effective value of the surface 121. We denote by S ₂ the effective value of this difference in active surfaces, which for convenience will call "dimensioning of the active surface 112", and S ₁ the effective value of the active surface 123.

The effective value of the active surface 301 is also S ₂ , and that of the active surface 302 is S ₁ .

If we also note F the force applied by the spring 125, P _i the pressure prevailing upstream of the throttle provided by the controlled slide 3, P _ls the load sensing pressure, PU _i the pressure prevailing downstream of the constriction provided by the controlled slide 3, and P _p the pressure produced by the auxiliary valve 303, it is demonstrated that at equilibrium: $${\mathit{\text{P}}}_{\mathit{\text{i}}}\text{-}{\mathit{\text{COULD}}}_{\mathit{\text{i}}}\text{=}\frac{{\mathit{\text{S}}}_{\text{1}}}{{\mathit{\text{S}}}_{\text{2}}}\text{((}{\mathit{\text{P}}}_{\mathit{\text{p}}}\text{-}{\mathit{\text{P}}}_{\mathit{\text{ls}}}\text{) -}\frac{\mathit{\text{<figure-callout id="2" label="F S" filenames="imgf0001.png,imgf0003.png" state="{{state}}">F </figure-callout>}}}{{\mathit{\text{S}}}_{}}$$

We see that the pressure difference P _i - PU _i depends on the pressure difference P _p - P _ls according to a linear function with strictly positive coefficient and strictly negative constant.

The auxiliary valve 303 comprises a stator body 306 which defines a supply chamber 307 connected to the discharge orifice of the flow generation 71; a regulation chamber 308 in which P _ls prevails; an outlet chamber 309 where said pressure produced prevails; a drawer 310 whose position determines, thanks to a groove 311, the section of a constriction between the chambers 307 and 309; and a spring 312 which acts on the slide 310 in the opening direction, a screw 313 being provided to adjust the force with which the spring acts.

P _ls prevails in the chamber 308 because this chamber is connected to the pipe 74.

The drawer 310 comprises a first active surface 314 disposed in the chamber 308, and therefore subject in the direction of opening to P _ls and a second active surface 315 disposed in the chamber 309, which means that the pressure produced acts on the surface 315 in the closing direction. We demonstrate, in case the effective value of surfaces 314 and 315 is similar, and if we note S this value and F the force exerted by the spring, which we obtain: $${\mathit{\text{P}}}_{\mathit{\text{p}}}\text{=}{\mathit{\text{P}}}_{\mathit{\text{ls}}}\text{+}\frac{\mathit{\text{F}}}{\mathit{\text{S}}}$$

The pressure produced is therefore normally independent of the pressure supplied by the flow generation.

In the case where the proportional distributors of the control assembly are divided into several groups of a distributor or of several neighboring distributors, the groups being distant from each other, for example in the case of a public works machine, divided into a first group of two distributors which control the right and left engines for advancing the vehicle, a second group of a single distributor which controls the rotation of a turret, and a third group of several distributors which control the different arms of the vehicle, it is preferable to provide an auxiliary valve for each of the groups, not only to avoid pressure drop problems, but also to avoid having to provide a pipe between a centralized auxiliary valve and the different groups.

FIG. 2 shows a control assembly according to the invention, formed of a single group of two contiguous distributors, respectively the distributor 70 illustrated in FIG. 1, and an identical distributor 70 ', all the elements of the latter carrying the same reference as distributor 70, but assigned a prime index.

It will be noted that the pipes 73 and 74 form with the selector 99 an assembly which crosses the entire distributor 70 and that the same is true for the pipes 119 and 305, so that it is possible to make the connections between distributors, by simply joining these end to end.

In the variant of the control unit according to the invention shown in FIGS. 3 and 4, the same reference numbers have been kept for the identical elements while the number 100 has been added to them for similar elements.

The proportional distributor 170 shown in FIG. 3 includes a compensating drawer 116, the left part of which is different from that of the drawer 16: in the position illustrated in FIG. 3, the compensating drawer 116 closes the passage between the chambers 15 and 27, but when it moves to the left it produces, depending on its position, a more or less significant constriction upstream of the constriction provided by the slide 3 on the supply line of the jack 12.

The drawer 116 has two surfaces 83 and 300 subjected to the pressure upstream of the throttle provided by the drawer 116, an active surface 84 subjected to the pressure upstream of the throttle provided by the drawer 3, and an active surface 85 subjected to the pressure prevailing in a chamber 86 located to the left of the drawer 116.

The surfaces 83 and 300 are opposite and have the same dimensioning, the slide 116 therefore does not react to the pressure upstream of the constriction which it provides.

Surfaces 84 and 85 look to the left. Since the drawer 116 closes the constriction it provides when it moves from the left to the right and vice versa, the pressures to which the surfaces 84 and 85 are subjected urge it in the closing direction. A spring 87 is provided in the chamber 86 between the bottom of the latter, located on the left, and the surface 85, which means that the drawer 116 is also biased in the closing direction by a substantially constant force. To adjust the latter, a screw 88 is provided which forms the bottom of the chamber 86.

The surface 84 is subjected to the pressure prevailing upstream of the constriction provided by the drawer 3 because it is disposed in a chamber 91 communicating with the room 27 via a duct 92.

The drawer 116 is provided with a radial bore 93 communicating with a blind axial bore 94 which opens onto a seat capable of being closed off or unmasked by a ball 95 whose return spring 96 is compressed in a chamber 98 which opens out an axial opening 100 in the chamber 86. This communicates via a passage 101 with a pipe 102 closed at one end and opening into the flow generation reservoir through a restriction 104 at the other end, the pipe 102 being common to all distributors, who have their room corresponding to 86 which is connected to it.

We see in Figure 4 that for each distributor 170 and 170 ', the common pipe 102 is connected upstream of the throttle provided by the drawer 3 via a non-return valve whose ball 95 forms the shutter, this non-return valve passing towards the pipe 102. Consequently, there prevails in the latter the pressures prevailing upstream of the throttles provided by the drawers 3 and 3 ′, the restriction 104 achieving a decompression of the pipe 102 which allows the continuous adjustment of the latter to the maximum of the pressures upstream of the drawers 3 and 3 '. It is therefore this last pressure which prevails in the chamber 86 and in the corresponding chamber of the distributor 70 '.

It is also this last pressure which prevails in the chamber 308, since here it is connected to the pipe 102.

In the example illustrated, the surface 84 has a similar dimension to the surface 301, that is to say S ₂ , and the surface 85 has a similar dimension to the surface 302, that is to say S ₁ .

Given the arrangement and dimensioning of surfaces 84 and 85, the action of the load sensing pressure has in fact been replaced by the maximum of the pressures prevailing upstream of the throttle provided by the slide ordered in the respective drawers, noted MAX (P _i ).

Provided that P _{ls is} replaced by MAX (P _i ), the equations given above apply to the variant shown in Figures 3 and 4.

It will be noted that there is no non-return valve in the distributor 170 between the chambers 15 and 27, unlike the distributor 70.

et dans le sens de l'ouverture par : $${\text{P.S}}_{\text{1}}\text{.}$$

Indeed, it is certain that at rest, when all the controlled drawers 3 are neutral, that all the compensating drawers 116 are in the closed position illustrated: if we keep the same notations as before and by noting P the discharge pressure of the flow generation, observing that P _p is at most equal to P and that at rest P _i = P in all the distributors, even if the drawer 116 is closed taking into account the minute leaks between the upstream and downstream of it which are inevitable, we see that the drawer 116 is biased in the closing direction by: $${\text{F + PS}}_{\text{1}}{\text{+ <figure-callout id="2" label="PS" filenames="imgf0001.png,imgf0003.png" state="{{state}}">PS</figure-callout>}}_{\text{2}}$$

and in the direction of opening by: $${\text{PS}}_{\text{1}}\text{.}$$

Since F + PS ₂ is strictly positive, we are sure that the forces acting in the direction of closing will always be greater than those acting in the direction of opening.

In service, in each of the illustrated assemblies, in the event that the total flow demand of receivers 12 and 12 'exceeds that capable of being supplied by flow generation 71, the speed ratios between receivers are maintained because in case of excess demand for flow, chamber 307 is not supplied with sufficient pressure for F / S to be added to P _ls or to MAX (P _i ), it is only a lower value which is added, all the smaller as the excess demand for flow is large.

• le tiroir 16 ou 116 doit assurer en service normal, où P_p - MAX(P_i) ou P_p - P_ls = a, une valeur b à P_i - PU_i de sorte que : $$\mathit{\text{b}}\text{=}\frac{{\mathit{\text{S}}}_{\text{1}}}{{\mathit{\text{S}}}_{\text{2}}}\mathit{\text{a}}\text{-}\frac{\mathit{\text{<figure-callout id="2" label="F S" filenames="imgf0001.png,imgf0003.png" state="{{state}}">F</figure-callout>}}}{{\mathit{\text{S}}}_{}}$$
  
• le tiroir 16 ou 116 doit se fermer pour une certaine valeur minimum c de P_p - MAX(P_i) ou de P_p - P_ls, en deçà de laquelle on estime que la surcharge est trop importante pour que les rapports de vitesse entre les récepteurs puissent être maintenus, de sorte que : $${\text{S}}_{\text{1}}\text{.c = F.}$$
  

The values S ₁ , S ₂ and F are chosen in particular according to the following requirements:

• drawer 16 or 116 must ensure normal service, where P _p - MAX (P _i ) or P _p - P _ls = a, a value b to P _i - PU _i so that: $$\mathit{\text{b}}\text{=}\frac{{\mathit{\text{S}}}_{\text{1}}}{{\mathit{\text{<figure-callout id="2" label="S" filenames="imgf0001.png,imgf0003.png" state="{{state}}">S</figure-callout>}}}_{\text{2}}}\mathit{\text{at}}\text{-}\frac{\mathit{\text{<figure-callout id="2" label="F S" filenames="imgf0001.png,imgf0003.png" state="{{state}}">F </figure-callout>}}}{{\mathit{\text{S}}}_{}}$$
  
• drawer 16 or 116 must close for a certain minimum value c of P _p - MAX (P _i ) or P _p - P _ls , below which the overload is considered to be too great for the speed ratios between the receivers can be maintained, so that: $${\text{S}}_{\text{1}}\text{.c = F.}$$
  

Depending on the circumstances, it is possible to choose a regulation pressure other than MAX (P _i ) or the load-sensing pressure. In these variants, the advantages of using an auxiliary valve are retained.

More generally, many variations can be made to the examples described. In this regard, it is recalled that the invention is not limited to the latter.

Claims (10)

1. Unit for controlling a plurality of hydraulic receivers (12, 12'), through which the receivers are supplied by one and the same flow generator (71), each being connected thereto by means of a proportional control valve having:

   - a controlled spool (3), whose position determines the cross-section of a first constriction;

   - a compensating spool for regulating the difference between the pressures upstream and downstream of the said first constriction by producing a second constriction of appropriate cross-section upstream of the latter; and

   - means of actuating the compensating spool, in order to make it automatically take up a position where it produces the said second constriction of appropriate cross-section, in response:

   . to the pressure downstream of the first constriction and to a first pressure, acting in the direction of opening, and

   . to the pressure upstream of the first constriction and to a second pressure, acting in the direction of closure;

   a unit additionally having an auxiliary valve supplied by the flow generation (71) and producing a pressure constituting a said first pressure;

   a unit characterised in that:

   - each said second pressure is a regulation pressure depending on the load conditions of the said hydraulic receivers;

   - each said first pressure is produced by a said auxiliary valve (303) ;

   - each said auxiliary valve produces, from its feed and the said regulation pressure, which is applied directly to it, a pressure normally equal to the said regulation pressure increased by a constant; and

   - in each proportional control valve (70, 70'; 170, 170') the said means of actuating the compensating spool are designed so that it is also forced in the direction of closure by a substantially constant force.
2. Unit according to Claim 1, characterised in that, in each proportional control valve, the said means of actuating the compensating spool include on the latter a first active surface (301) subjected to the pressure downstream of the first constriction, a second active surface (302) subjected to the pressure produced by the auxiliary valve, a third active surface (84, 112) subjected to the pressure upstream of the first constriction, and a fourth active surface (85, 123) subjected to the said regulation pressure, the said first and second surfaces (301, 302) being opposite the said third and fourth surfaces (84, 85; 112, 123); and a spring (87, 125) forcing the compensating spool (16, 116) in the direction of closure.
3. Unit according to Claim 2, characterised in that the said first and third active surfaces (301, 84; 301, 112) of the compensating spool (16, 116) are of similar dimensions, and in that the said second and fourth surfaces (302, 85; 302, 123) of the compensating spool are of similar dimensions.
4. Unit according to any one of Claims 1 to 3, characterised in that the said auxiliary valve (303) has:

   - a feed chamber (307) connected to the flow generator (71) ;

   - a regulation chamber (308) in which the said regulation pressure prevails;

   - an outlet chamber (309) in which the said produced pressure prevails;

   - a spool (310) whose position determines the cross-section of a constriction between the supply chamber (307) and the output chamber (309), having a first active surface disposed in the regulation chamber (308) so that the said regulation pressure acts in the direction of opening, and a second active surface (315) disposed in the outlet chamber (309) so that the pressure produced acts in the direction of closure; and

   - a spring (312) which acts on the spool (310) in the direction of opening.
5. Unit according to any one of Claims 1 to 4, characterised, the proportional control valves being divided into several groups of one control valve or several adjacent control valves, the groups being distant from one another, in that for each group it has a said auxiliary valve adjacent to the group.
6. Unit according to any one of Claims 1 to 5, characterised in that it has means (73, 74, 99, 99') for detecting the pressure of the most heavily loaded receiver, referred to as the "load sensing pressure", and in that the regulation pressure is the load sensing pressure.
7. Unit according to Claim 6, characterised in that for each proportional control valve the detection means have a duct which connects the area downstream of the first constriction to a circuit selector (99, 99'), and in that, where there are several of them, the circuit selectors are disposed in a cascade.
8. Unit according to any one of Claims 1 to 5, characterised in that it has means (95, 95', 102, 104) for detecting the highest of the pressures prevailing upstream of the first constriction in the respective proportional control valves (170, 170'), and in that the said regulation pressure is the highest of the upstream pressures thus detected.
9. Unit according to Claim 8, characterised in that in each proportional control valve (170, 170') there is no non-return valve between the said second and first constrictions.
10. Unit according to either one of Claims 8 or 9, characterised in that the said means for detecting the maximum pressure upstream of the respective first constrictions have a common duct (102) closed at a first end and opening into the reservoir through a restriction (104) at a second end; and for each proportional control valve a non-return valve (95) disposed so as to pass between the area upstream of the first constriction and the common duct.

Images