Patent Publication Number: US-7581487-B2

Title: Pressure-compensating directional control valve

Description:
BACKGROUND OF THE INVENTION 
   The field of hydraulic systems, particularly with reference to circuits for controlling a plurality of actuators suitable to drive machines of various kinds, generally uses switching valves of the shuttle type provided with a compensating element arranged downstream. This technical solution is disclosed for example in U.S. Pat. No. 5,579,642. This compensating element is designed to keep as constant as possible the pressure drop across the control valve of the hydraulic actuator: this allows to operate the actuator with the chosen behavior. In such a case, the flow-rate delivered to the chambers of the actuator in fact depends exclusively on the passage section, which can be changed by the operator by way of the traditional means. 
   These switching valves are first of all typically associated with circuits for transmitting the load signal to the compensating elements; such circuits are designed to draw, by means of adapted selection valves, the highest load signal that is present in the various uses. This of course entails a certain constructive complication, which is often too expensive. 
   As an alternative to this, check valves are used which are directly integrated in the shuttle of the compensating element (as disclosed for example in U.S. Pat. No. 5,305,789), which in any case require the fitting of a so-called compensated “bleed-off” (which in the particular field is also known as “bleed”), which comprises a flow regulator. 
   A further alternative is constituted by the use of check valves fitted in parallel with respect to the compensating element, which is associated with a bleed-off. 
   Even these solutions, which in various situations have been optimized, are all characterized by high constructive complexity, which recommends against their use both as regards production costs and as regards installation and subsequent maintenance. 
   Secondly, moreover, in traditional applications the load signal is typically connected to the discharge by means of a so-called compensated bleed-off, which therefore entails installing additional hydraulic components, which considerably increase the complexity of the system. 
   Thirdly and finally, the load signal is usually drawn from the so-called bridge of the switching valve, and this fact entails a distinctly bulky design in the upper part of the component: in some applications, this is particularly disadvantageous. 
   EP-A-0 368 636 and DE 39 12 390 disclose hydraulic control systems with directional control valves having a combination of elements as set forth in the pre-characterizing portion of the appended claim  1 . 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is to obviate the above mentioned drawbacks, by providing a pressure-compensating directional control valve that allows to provide the effective actuation of hydraulic actuators with the desired behavior, i.e., with a preset speed, avoiding all the constructive complications and the high production costs that characterize the technical solutions that have been provided traditionally. 
   Within this aim, an object of the present invention is to provide a valve that is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost. 
   This aim and these and other objects, which will become better apparent hereinafter, are achieved by the present pressure-compensating directional control valve, particularly for actuating hydraulic actuators, of the type that comprises at least one modular valve body, which is affected by at least one through receptacle for at least one shuttle which can slide bidirectionally, by at least one driving fluid delivery port connected to a pump, by at least one discharge port for said fluid, by at least one first output opening and by a second output opening, which are connected respectively to the first chamber and to the second chamber of a hydraulic actuator, said shuttle being controlled by remote operation means and being adapted to selectively connect said delivery port to said first output opening and said discharge port to said second output opening and vice versa, in said valve body there being further at least one bridge for the selective communication, by way of said shuttle, of said delivery port with said first chamber or with said second chamber of said actuator, so as to actuate the actuator in one direction or the other, characterized in that it comprises at least one unidirectional hydrostat, which is connected to said bridge by means of a supply duct and is adapted to draw selectively a pressure signal of the load of said actuator, said signal being designed to adjust selectively the delivery pressure of the pump so as to keep substantially constant the pressure drop between said delivery port and said actuator in any load condition. 
   Advantageously, said modular valve body is associated with at least one actuation head, which comprises at least one main hydrostat adapted to connect selectively, under the action of at least one contrast spring and of said load pressure signal, the delivery duct of said pump to said discharge, so as to adjust said delivery pressure to an appropriate value, which is preset according to the load. 
   In accordance with the invention, there is provided a pressure-compensating directional control valve, particularly for actuating hydraulic actuators, as defined in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a pressure-compensating directional control valve according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein: 
       FIG. 1  is a partially sectional schematic front view of a modular valve body associated with an adjustment head, according to the invention; 
       FIG. 1   a  is a partially sectional detail top view of the modular valve body; 
       FIG. 2  is a partially sectional detail front view of a modular valve body according to the invention; 
       FIG. 3  is a circuit diagram of two modular valve bodies associated with an actuation head, according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the exemplary embodiment that follows, individual characteristics may actually be interchanged with other different characteristics that exist in other exemplary embodiments. 
   Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer. 
   With reference to  FIG. 1 , the reference numeral  1  generally designates a pressure-compensating directional control valve according to the invention. 
   The valve is preferably but not exclusively adapted to provide integrated control and management, via remote operation on the part of the operators, of the fluid-operated actuators installed in machines (for example earth-moving machines and the like), typically a series of hydraulic actuators, which are subjected to often high loads. In greater detail, the valve is designed to ensure that all the actuators of the machine can operate with a load and a speed suitable for the specific applications and in any operating condition in relation to the commands imparted by operators. 
   As shown in  FIG. 1  and in greater detail in  FIG. 2 , the pressure-compensating directional control valve comprises at least one modular valve body, generally designated by the reference numeral  2 , which is affected by at least one through receptacle  3 , which is substantially cylindrical and has suitable cross-sections (as clarified hereinafter), and in which at least one shuttle  4  is fitted so that it can slide bidirectionally. The shuttle  4  has a first end  5 , which protrudes from the modular valve body  2  and is adapted to be associated with remote operation means, which are controlled by the operator and are not shown in the figure (for example a lever, an electric valve, and others), which provide the translational motion of the shuttle  4  along its own axis in the two directions; the shuttle  4  further has a second end  6 , which protrudes from the modular valve body  2  and is affected by a threaded end hole  7 , in which a screw  8  for fixing a cup  9  and a complementary cup  10 , provided with respective rims  9   a ,  10   a , is engaged. The rim  9   a  of the cup  9  abuts directly against the outer surface of the valve body  2 , while the rim  10   a  of the complementary cup  10  actuates a contrast spring  11 , which is interposed between the cup  9  and the complementary cup  10 , keeps the shuttle  4  in a preset position and contrasts its translational motion to the right with reference to  FIGS. 1 and 2 . The second end  6  of the shuttle  4  is covered by a protective cap  12 , which is fixed to the valve body  2  by means of screws  13 . 
   The modular valve body  2  is further affected by at least one delivery port  14  for actuation fluid (typically oil), which is connected to a hydraulic pump, which is not shown in the figures but is of a substantially traditional type, and by at least one discharge port  15  for said fluid, which is connected to the oil tank, not shown in the figures; the valve body  2  is also affected by at least one first output opening  16  and by at least one second output opening  17 , which are connected respectively to the first chamber and to the second chamber of a hydraulic actuator of the double-acting type, also not shown in the figures but of a traditional type. The first output opening  16  and the second output opening  17  are associated with respective safety valves  18 ,  19 , of a substantially traditional type, which connects the openings  16 ,  17  to the oil discharge if intolerable pressure peaks occur. 
   The shuttle  4 , which as mentioned is controlled by remote operation means operated by the operator, is adapted to connect selectively, by means of its bidirectional translational motion, by way of an impulse transmitted by the operator, the delivery port  14  to the first output opening  16  and the discharge port  15  to the second output opening  17  and vice versa: this is achieved, in a substantially traditional manner, by virtue of suitable passages obtained by virtue of expansions  20 ,  20   a ,  20   b ,  20   c ,  20   d ,  20   e  of the diameter of the receptacle  3  in preset positions and by virtue of corresponding grooves  21 ,  21   a ,  21   b ,  21   c ,  21   d  provided along the outer surface of the shuttle  4 . Along the shuttle  4 , and in portions having a larger diameter, there are also central flow-rate control recesses  21   e  and lateral flow-rate control recesses  21   f.    
   The modular valve body is also affected, in a substantially traditional manner, by at least one bridge  22  for selective communication, provided by the appropriate translational motion of the shuttle  4 , alternately of the delivery port  14  with the first output opening  16  or with the second output opening  17 , i.e., with one or the other of the chambers of the actuator according to the specific operating situation. 
   According to the invention, the valve body  2  comprises advantageously at least one unidirectional hydrostat, generally designated by the reference numeral  23 , which is connected to the bridge  22  by virtue of a suitable supply duct  24 , which is adapted to selectively draw a load pressure signal (so-called “load sensing”) LS, to which the hydraulic actuator is subjected: said load pressure signal LS is conveniently intended to adjust selectively the delivery pressure of the pump, so as to keep substantially constant pressure drop between the delivery port  14  and the hydraulic actuator in any load condition. This allows to provide a flow-rate delivery that no longer depends on the pressure drop between upstream and downstream of the valve and on the passage section but depends exclusively on the latter: this, as it is known, allows to ensure the optimum operation of each actuator even in critical situations, such as for example situations with very high loads applied to the actuator itself, which require a high delivery pressure. 
   The unidirectional hydrostat  23  is engaged in a respective cylindrical seat  25 , which is provided in the modular valve body  2  and is substantially parallel to the receptacle  3  of the shuttle  4 . The unidirectional hydrostat  23  comprises a cylindrical slider  26 , which is associated with a respective contrast spring  27 , which is adapted to connect selectively the delivery port  14  to the bridge  22  across a secondary branch  28  connected to the expansion  20   c  of the receptacle  3 ; the contrast spring  27  of the cylindrical slider  26  is accommodated in a plug  29 , which is screwed in a respective recess  30  provided in the modular valve body  2 . 
   The unidirectional hydrostat  23  further comprises a spherical flow control element  31 , which is engaged in the opening of a bush  32 , which is threaded externally and is screwed into a recess  32   a  formed in the cylindrical slider  26 ; a contrast spring  33  of the spherical flow control element  31  is accommodated within the bush  32 . A channel  34  is formed in the cylindrical slider  26  and connects the outer surface of the slider  26  to the flow control element  31  and consequently connects the supply duct of the bridge  24  to an outlet hole  35  of said valve body by means of an expansion  36  of the diameter of the cylindrical seat  25 : the outlet hole  35  therefore allows to transfer the load pressures signal LS externally. 
   As mentioned earlier, practical applications generally use a plurality of modular valve bodies  2  fitted side by side and adapted to control the motion of respective hydraulic actuators, fitted for example on the same machine: this situation is shown in  FIG. 3 , with the corresponding circuit diagrams provided with the traditional symbols adopted universally in hydraulics. 
   As shown by  FIGS. 2 and 3 , the modular valve body is, according to the invention, conveniently associated with at least one actuation head, generally designated by the reference numeral  37 , which comprises at least one main hydrostat, designated by the reference numeral  38 , which is adapted to connect selectively, under the action of at least one respective contrast spring  39  and of the load pressure signal LS, the delivery duct P of the pump to the discharge S, so as to adjust said delivery pressure to a suitable value which is preset in relation to the load. 
   The actuation head  37  comprises advantageously at least one slide valve  40 , which is adapted to selectively connect the load pressure signal LS to the discharge S. Advantageously, the opening of the slide valve  40  is controlled by means of a line, designated by the reference numeral  41  in  FIG. 3 , which passes through each modular valve body  2  and is connected to the discharge S, so as to provide a controlled decompression of said load pressure signal: this allows to give optimum stability to the operation of the system in any load condition of all the actuators. 
   As can be seen in  FIG. 1   a , in greater detail each modular valve body  2  is affected by a pair of holes  41   a ,  41   b  (also shown in  FIG. 1  in broken lines), which allow to connect, by virtue of respecting expansions  41   c ,  41   d  of the diameter of the receptacle  3  and a groove  41   e  of the shuttle  4 , the discharge S to the slide valve  40  of the actuation head  37 , so as to drive the decompression of the signal LS. 
   The actuation head  37  comprises a substantially parallelepipedal body affected by a delivery orifice  42 , which is connected to the delivery duct P, and a withdrawal orifice  43 , which is connected by means of a withdrawal duct  44  to each hole  35  of each modular valve body  2 , so as to transmit the signal LS of all the actuators to the actuation head  37 . 
   The actuation head  37  forms a first cylindrical chamber  45 , which accommodates the main hydrostat  38 ; the first cylindrical chamber  45  is connected to the withdrawal orifice  43  by means of a first branch  46 . A closure plug  47  is fitted in the first cylindrical chamber  45  and has an abutment surface  48  for the helical contrast spring  39  of the main hydrostat  38 . 
   The actuation head  37  further forms a second cylindrical chamber  49 , which accommodates the slide valve  40 . The second cylindrical chamber  49  is connected to the withdrawal orifice  43  by means of a second branch  50 ; it is further connected to the delivery orifice  42  by means of a third branch  50   a , in which a check valve with a choke  51  is inserted. 
   The second cylindrical chamber  49  is further connected to an opening  52  for the discharge of the signal LS by means of a fourth branch  53  and to a driving opening  54  by means of a fifth branch  55 ; the driving opening  54  is connected to the line  41 , as also shown in  FIG. 3 . 
   The slide valve  40  is associated with a respective contrast spring  56 , which abuts against a hermetic closure element  57 , and is affected by a through channel  58 , which is connected to the discharge opening  52 . 
   Finally, the actuation head  57  comprises at least one maximum pressure valve  58 , which allows to connect the pump to the discharge in functional situations in which the pressure is too high. 
   The operation of the valve according to the invention is summarized hereinafter. 
   The pump delivers pressurized oil through the delivery duct P, and said oil must flow into one chamber or the other of each actuator depending on the commands imparted by the operator, which are transmitted by means of the translational motions of the shuttles  4 . The shuttle  4 , during its full stroke, provides a series of connections, which allow the oil, which at present is at low pressure in the secondary branch  28 , to flow at a pressure defined by the load in the output openings  16 ,  17 . In the first step of the stroke of the shuttle  4 , the groove  41   e  closes the discharge circuit of the slide valve  40 ; a further movement of the shuttle  4  allows the load signal LS, drawn through the bridge  22  and sent to the main hydrostat  38  across the spherical flow control element  31  of the unidirectional hydrostat  23 , to activate the system at the pressure of the load. At this point, with a further movement of the shuttle  4 , the pressurized oil contained at the delivery port  14  flows, through the central flow-rate control recesses  21   e , into the secondary branch  28 , thus opening, when the load pressure is reached, the unidirectional hydrostat  23  and from there, across the bridge  22 , to the output openings  16 ,  17 , through the lateral flow-rate control recesses  21   f  that have opened last in the sequence of functions. 
   Advantageously, the load signal LS is selectively connected to the discharge by the slide valve  40 , so as to ensure operating stability of the set of actuators provided in the machine. 
   The valve according to the invention is particularly advantageous in particular situations in which one of the actuators of the machine is subjected to a very high load: the compensation of each of the modular valve bodies in fact ensures that all the actuators of the machine are actuated independently of each other at the chosen speed. 
   As described, an important and considerable advantage achieved by the present invention is the presence of the slide valve  40  for managing the load signal LS, generated by the movement of the shuttle  4  across the line  41 . 
   Further, the withdrawal of said load signal LS, and particularly the highest one among all the actuators that are present, occurs by opening the flow control element  31  provided in the unidirectional hydrostat  23  and not, as in traditional systems, by moving all the selection valves of all the sections: this last method in fact entails an inevitable delay in the transmission of the load signal LS, and consequently entails excessive slowness in starting the actuators and therefore in performing the corresponding mechanical functions. 
   The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. 
   All the details may further be replaced with other technically equivalent ones. 
   In practice, the materials used, as well as the shapes and the dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims. 
   The disclosures in European Patent Application No. 06425362.8 from which this application claims priority are incorporated herein by reference.