Patent Publication Number: US-11041514-B2

Title: Hydraulic distributor with valve device with active discharge in load sensing circuits

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Italian patent application 102017000023749 filed on Mar. 2, 2017, the contents of which are incorporated herein by reference. 
     APPLICATION FIELD 
     The invention is in the field of the hydraulic valve devices within directional control valves used in agricultural applications, such as in “front loader” vehicles. 
     The invention relates to a hydraulic distributor, with a closed center and multiple working sections, and comprising a logic discharge element. 
     According to an implementation example said logic element is an adjusting device. 
     The invention also relates to the above-mentioned discharge adjusting device configured to be associated with a hydraulic valve distributor with multiple sections, particularly on the inside thereof. 
     More specifically, said discharge adjusting device is a pilot-operated valve with differential areas. 
     The driving of said valve having differential areas is carried out by different pressure “signals” of connection channels inside the distributor. 
     STATE OF THE ART 
     In industrial and agricultural applications, such as those of front loaders, a known problem is that of an even heating of the hydraulic distributor. In fact, said vehicles are often left outdoors overnight and/or during the winter season. Upon its actuation, the distributor has a temperature that is equal to that of the outer environment; often, before actuating said distributor, it is necessary to translate the vehicle for a few kilometers. The drive oil, which is the same one used for the hydraulic application of the front loader, heats until reaching temperatures above 100° C. In the case the distributor is of an open center type, through a free circulation, the oil flows through the same distributor and allows a gradual heating thereof. 
     On the contrary, in the case the distributor is of a conventional closed-center type, the body is passed through by hot oil only upon the first actuation of at least one hydraulic section thereof. In this condition, it turns out that the hot oil contacts zones and components of the distributor itself that are still cold with a high temperature differential, compared to that of the same oil used in the transmission. Local deformations of the components are triggered, due to the different thermal expansion coefficients and the different geometries of the components. 
     Therefore, upon the first actuations, it is usual that a blocking of the distribution spool occurs in such positions whereby the flow rate continues to be delivered without the operator being able to bring it back to a central position, resulting in a considerable risk in the safety of the operator him/herself, but also for the working environment and the surrounding people. 
     In the prior art, such problem is solved for said applications by inserting a discharging valve located in by-pass to the delivery line of a closed-center, load sensing distributor that discharges to the low-pressure line, passing through the whole distributor, a part of the flow rate delivered by the pump until when it is switched to close by the signal of the delivery pressure exceeding a predetermined threshold dictated by a spring opposite the active area on which said signal acts. 
     Since, in agricultural applications the stand-by pressure (or margin) of the LS pump supplying the system can be very high (even up to 60 bar), the switching pressure of the discharging valve has to be of slightly higher than the stand-by margin pressure itself. 
     When at least one utility is actuated, upon which a low load, or a load for small openings acts, and since the oil keeps flowing towards the low-pressure line through the discharging valve until the switching thereof is completed, it is necessary that the pump sends a higher flow rate than that required by the same utility. 
     OBJECT OF THE INVENTION 
     An object of the present invention is to provide to the art a closed-centre, load sensing distributor which allows improving the known solutions in the context of a rational, simple, and rather cost-effective solution. 
     A further object of the present invention is to provide a hydraulic distributor, of the closed-center, load-sensing type, which can obviate one or more of the drawbacks defined with reference to the prior art. 
     It is also an object of the present invention to provide a hydraulic closed-center distributor which is less prone to problems of an uneven temperature distribution. 
     Such and other objects are achieved by virtue of the characteristics of the invention set forth in the independent claim  1 . The dependent claims outline preferred and/or particularly advantageous aspects of the invention. 
     Particularly, an embodiment of the present invention provides a logic element configured to send to the low-pressure line, passing through the whole distributor, a flow rate dispensed by the pump to minimize the temperature differential between the distributor body and the oil used under a non-operative condition of the spool that adjust the oil distribution towards the actuations. 
     A further object of the invention is also to minimize the dissipation of the flow rate delivered in the case that at least one hydraulic utility requires oil for the pump and the load present at the utility is minimum or the opening of the adjusting cursor is reduced. 
     An embodiment provides to the art a logic element composed of at least one bi-directional, two-position pilot-operated slide  2 , on which, on the one hand, a spring, or another equivalent elastic member, and the discharge pressure act, while, on the other hand, both the oil delivery pressure and the load sensing pressure present at the utilities act (once at least one section has been actuated). 
     Preferably, said oil delivery pressure and said load sensing pressure act on two corresponding active areas of the logic element. 
     In one embodiment, the valve device element is a logic element connectable on the outside of the distributor body. 
     A further object of the invention is to solve the problem whereby, under some operative conditions, the LS pressure remains trapped along its own channel even if no utility has been actuated. 
     Said misfunctioning may cause an abnormal adjustment of the pump LS and the logic element itself. 
     In order to solve such drawback, a further embodiment of the invention uses a logic element adapted to:
         again, create the connection between the abovementioned high and low-pressure lines, and   at the same time, create a second connection configured to join, in the usually open condition of the logic element, the chamber of the LS signal with the low-pressure line, closing when the logic element (slide) is actuated.       

     In the context of such aspects, a first advantage of the present invention is as follows: when the slide is open, the distributor is heated through an oil flow rate which passes through it, generated by the pump at the stand-by pressure (i.e. only of the margin) of the pump itself. 
     A further advantage is that the double driving on the logic element, in which the LS signal coming from the utilities is also present, and which acts on the active area of said element, allows a switching at a lower pressure. Therefore, a lower power dissipation follows, given by the product between the flow rate discharged through the valve and the delivery pressure. 
     A further advantage is that, when, as a by-pass to the delivery of the pump, also a second distributor is inserted in addition to the closed-center LS distributor, as it is the case, for example, in agricultural applications (rear distributor), the operation of the distributor which is the subject-matter of the invention is not subjected to operative alterations, thus maintaining/ensuring the same functional advantages. Under such condition, the logic element is pilot-operated to close (chamber opposite the spring) only by the signal of the delivery pressure on its own active area. 
     Another advantage is that it is possible to solve the problem whereby, under some operative conditions, the LS pressure remains trapped along its own channel, even if no utility has been actuated. 
     Such objects and advantages are all achieved by the valve device, which is the subject-matter of the present finding, which is characterized by that is provided for in the claims set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       This and other characteristics will be more pointed out by the following description of some embodiments that are illustrated, by way of non-limiting example only, in the attached drawing tables. 
         FIG. 1  illustrates the hydraulic scheme of the system in which the valve device which is the subject-matter of the invention is inserted; 
         FIG. 2  illustrates the hydraulic scheme of the valve device and the corresponding distributor which is the subject-matter of the invention; 
         FIG. 3  illustrates a sectional view of the valve device used in the distributor which is the subject-matter of the invention; 
         FIG. 4  illustrates the adjustment curve of said device; 
         FIG. 5  illustrates the hydraulic scheme of a second embodiment of the valve device and the corresponding distributor which is the subject-matter of the invention; 
         FIG. 6  illustrates a sectional view of the valve device of  FIG. 5 ; and 
         FIGS. 7A and 7B  illustrate a sectional view of still another variation of the valve device, in two operative positions, used in the distributor of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , an operative example of a hydraulic circuit of a distributor comprising a valve device in accordance with the invention is illustrated. 
     The circuit is composed of a variable displacement pump  1 , connectable to a closed-center, load sensing distributor generally indicated by the reference number  3 . The connection between the pump and the distributor takes place via a high-pressure channel  2 , formed by a series of corresponding conduits. 
     In a possible embodiment, the load sensing distributor  3  is schematized by a dashed line, and it is provided with three general sections E 1 , E 2 , and E 3 , each of which controls a corresponding actuator through the utilities A 1 , B 1 , A 2 , B 2 , A 3 , and B 3 . 
     Each section E 1 , E 2 , E 3  comprises therein at least one slide C 1 , C 2 , C 3  and, preferably, at least one selector S 1 , S 2  and S 3  configured to capture the highest signal LS among all the utilities. Therefore, via a channel  6  the signal LS is sent to the pump  1 , which provides the flow rate to the system based on its own margin, i.e., the stand-by pressure of the pump. 
     The distributor  3  also comprises a low-pressure channel  4 , through which the oil is discharged from the utilities, for example, into a tank  5 . 
     In one embodiment, the first high-pressure channel  2  inside the distributor is divided into a first delivery line  7  is adapted to connect the pump to the sections of the distributor E 1 , E 2  and E 3 , and a second line  9  suitable to pass through the entire distributor before reaching a valve device  10 , the characteristics of which will be best specified herein below. Preferably, also a third line  8  is present, which is suitable to connect the high-pressure channel to an outer distributor, not shown in the figure, arranged in another part of the vehicle. 
     With reference to  FIGS. 2 and 3 , the valve device  10  comprises a cursor  11 , preferably of the bi-directional type with continuous positioning, housed in a respective valve body. 
     In one embodiment, the valve body is defined inside the body of the distributor itself. However, it will be appreciated that, alternatively, the valve device  10 ,  100  may be formed by a logic element attachable to the outside of the distributor body and, therefore, having a distinct body. 
     As it can be seen from  FIG. 3 , the cursor  11  is pushed to open by an elastic member  12 , such as a spring, and by the pressure PB that is present on the low-pressure line  4 . According to a preferred embodiment, the pressure PB that is present on the low-pressure line  4  acts onto a first surface  13 . 
     Furthermore, the cursor is pushed to close by the pressure P that is present on the second high-pressure line  9  and by the LS pressure that is present in the respective channel  6 . 
     According to an aspect of the invention, the equivalent switching pressure of the slide through the compression of the spring  12  with just the pressure present in the line  9  is higher than the stand-by pressure of the pump. 
     The high-pressure signal P present in the second high-pressure line  9  and the load sensing signal (LS) in the respective channel  6  act on respective areas  14 ,  15 . Preferably, the two areas are located on a same side, opposite the one of the first surface  13 . The sum of the areas  14 ,  15  is equal to the area of the first surface  13 . 
     In other words, the surfaces  14  and  15  are located on a same side, while the surface indicated with  13  is on the opposite side of the slide cursor  11 . 
     While the size of the area of the driving surface  13  is indicated by A 13 , the size of the area  14  is indicated by A 14  and the size of the area  15  is indicated by A 15 , the ratios between the areas are preferably such that:
 
 A 13= A 14+ A 15, where
 
 A 15&gt; A 14
 
     I.e., the area A 13  of the driving surface  13  is equal to the sum of the areas  14  and  15 , considering the constraint that the area  15  is larger than the area  14 . 
     In one embodiment, the cursor  11  is slidable in a hole  18  obtained inside the valve body or, more generally of the distributor  3 . Consequently, the corresponding section of the hole corresponds to the area A 13  of the first surface  13 . 
     According to a preferred embodiment, two recesses  19  and  20 , preferably having an annular shape, are present in the hole  18 . 
     A first recess  19  is configured to receive the pressurized fluid via the high-pressure channel  2  (and via its second channel  9 ) supplied by the pump  1 . 
     A second recess  20  is connected with the low-pressure channel  4  at the tank  5 . 
     Usually, the cursor  11 , i.e. when it is in a non-operative configuration, keeps the connection between the recesses  20  and  19  open, preferably through a throttled passage  16 . The opening is obtained by the combined action of the spring  12  and the PB pressure in a corresponding chamber  21 . It should be noted that, in the context of the present invention, by the term throttled is meant that the passage defines a narrowing to the fluid, thereby allowing the passage inside thereof in a calibrated and controlled manner. 
     According to a preferred embodiment, the chamber  21  which is obtained at the end of the surface  13  and the abutment  17  thereof is obtained on the spring  12  side. 
     In one embodiment, inside the cursor  11  a hole  22  parallel to the same axis of the cursor  11  (on the side opposite the surface  13 ) is obtained, and defines the area  14  mentioned above. 
     As it can be seen from the figures, a piston  23  can slide in the above-mentioned hole  22 , which has two surfaces at the ends thereof, a first surface indicated by  24  facing the side of the cursor  11 , and a second surface indicated by  25  facing the side  26  of the abutment of the cursor  11  opposite the spring. 
     In one embodiment, the piston  23  defines a further chamber  27  between the first surface  24  and the area  14  on which the pressure P acts, by virtue of one or more holes  28 , preferably inside the slide  11 , which connect it with the recess  19 . 
     The area  15  of the cursor  11  and the second surface  25  of the piston  23  together with the abutment  26  inside the hole  18 , define a chamber  29  to which the LS pressure arrives. 
     According to a further aspect, one or more throttled passages  16  are defined between the cursor  11  and the corresponding hole  18 . 
     Under a stand-by condition, i.e., when no slide C 1 , C 2 , C 3  is actuated, the LS pressure is null, thanks to the spring  12 , therefore all the minimum flow rate passes through the valve device via the throttled passage  16 . In this manner, the hot oil is allowed to evenly heat the whole distributor at the stand-by pressure of the pump. 
     Referring as F 12  the switching force of the spring  12 , the equilibrium of the slide  11  is given by the following relationship:
 
 pP*A 14+ pLS*A 15= F 12+ pPB*A 13
 
     where pP is the pressure present in the chamber  27 , pLS the one in the chamber  29 , and finally, pPB the one in the chamber  21 . 
     Assuming the PB pressure as almost null, it follows that
 
 pP*A 14+ pLS*A 15= F 12
 
In order to switch the cursor  11  from the usual opening position, i.e. piston  23  on the abutment  26  and, in turn, in abutment on the cursor  11 , at the closure position thereof, i.e. with the cursor  11  on the abutment  17 , two distinct cases may exist. A first case I occurs with a null LS (the slides C 1 , C 2  and C 3  are not moved), in which a utility of the outer distributor is actuated along the line  8 . In this manner, the pressure P increases until reaching the switching pressure value given by F 12 /A 14 . In this case, the cursor  11 , upon moving, closes the passage  16  and it is switched to close. Therefore, all the oil is sent by the pump P along the high-pressure pump  8 .
 
     A second case II occurs by actuating at least one of the slides C 1 , C 2  or C 3  of the distributor  3 . The LS pressure, which is the highest among those of the actuated utilities, directly acts on the area  15 . In this case, the cursor  11 , upon moving, closes the passage  16  and is switched to the closure position. Therefore, all the oil is sent by the pump along the first high pressure line  7 . 
     As it can be seen from the graph in  FIG. 5 , not drawn in scale, in the case II a considerably lower pressure than the pressure needed is required to switch the valve device  10  to close compared to case I. 
     The operative advantages that are obtained are as follows:
         by actuating at least one of the cursors C 1 , . . . or Cn and by driving the slide with the signal LS present in the channel  6 , besides the signal P present in the second line  9 , the percentage of power dissipated by the system, which is given by the oil flow which, through the cursor  11 , is lower than that dissipated through said slide when the same flow rate is required from a general utility located along the third line  8  without actuating any slides C 1  . . . or Cn.   by actuating at least one of the slides C 1 , . . . or Cn and by driving the cursor  11  with the LS signal present in the channel  6  besides the signal P present in the line  9 , the percentage of power dissipated by the system, which is given by the oil flow that passes through the cursor  11  is lower than that dissipated through a similar device that carries out the same connection of the cursor  11 , but which uses only the P signal to switch the cursor and does not involve the use of the LS signal, which acts on an active area thereof.       

     Intermediate conditions of the valve device  10  described can also be present, between the two cases given by the overlapping of the operation of the distributor  3  supplied by the first line  7  and the external one, supplied by the third line  8  and by the change in the margin by the pump according to the vehicle on which said hydraulic application is installed. 
       FIGS. 5 and 6  show a possible example or variation of the valve device in question. 
     Now the device is indicated with  100  and the cursor is indicated with  110 . 
     The present implementation variation will be described only with reference to different aspects compared to the version described above. Therefore, the preferred embodiments described above will be applicable also to this case, unless otherwise stated. 
     The cursor  110  comprises one or more calibrate passages  30  which, under a usual opening condition, bring the chamber  29  connected to the LS line  6  into communication with the recess  20  connected with the low-pressure line. By virtue of such solution, the calibrated passage is suitable to discharge the LS pressure that could be trapped in the circuit even when the slides C 1 , C 2  and/or C 3  are not operated, causing a misfunctioning of the pump and/or of the same valve device  10 . 
     When the cursor moves to the closure position, such connection is inhibited. 
     Preferably, the calibrated passage  30  is configured so that the connection between the chamber  29  and the recess  20  closes with a lesser stroke with respect to the one needed to carry out the switching of the slide  110 , thus closing the connection through the throttled passages  16  between the recess  20  and the recess  19  connected to the high-pressure line. 
     In other words, the calibrated passage between the second high-pressure line  9  and the low-pressure channel  4  is configured to allow, even in a switching position, a controlled passage of fluid therebetween. 
     In  FIGS. 7A and 7B , a further variation of the valve device of the present invention is illustrated. 
     In such embodiment, in which the valve device may have similar characteristics to those of the two previous embodiments, the cursor  11  has a further throttled passage  40  that brings the chamber  21 , in which the counter-pressure PB of the low-pressure channel acts, in communication with a third annular recess  41  defined in the hole  18  and also connected with the low-pressure channel  4 . 
     Preferably, the third recess  41  is defined between the recess  19  and the chamber  21 . In one embodiment, the further throttled passage  40  brings the recess  41  and the chamber  21  into communication through a housing cavity  42  of the spring  12 , which opens in the same chamber  21 . 
     Thus, it will be appreciated that the further throttled passage  40  allows obtaining an advantageous damping effect during the switching of the cursor  11 . 
     Therefore, the invention solves the proposed problem, while achieving a plurality of advantages, among which an improvement in the safety and reliability of the distributor is exhibited, particularly in the case of a start in cold settings, by virtue of the passage of oil even when the slides are not moved.