Abstract:
A valve formed with a valve sleeve formed with at least a first port, at least a second port and a pressure-compensated valve tappet movable between a closed position and at least one open position. The valve tappet is formed as two parts that move relative one another and are acted upon relative to one another by a hydrostatic pressure present at the first port.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Priority Document DE 10 2013 004108, filed on Mar. 11, 2013. The German Priority Document, the subject matter of which is incorporated herein by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a valve for controlling the flow of a hydraulic fluid, in particular for supplying a single-acting or double-acting consumer. Such valves having pressure-compensated and non-pressure-compensated designs are known. Non-pressure-compensated valves make it possible to utilize the pressure differential between a high-pressure connection and a low-pressure connection of the valve in order to press a closing element against a valve seat. Therefore, these are also suitable for obtaining a secure seal even in the presence of high pressure differentials. Disadvantageously, however, the hydrostatic pressure differential acting on the closing element must be overcome in order to release the closing element from the valve seat. The force required to open the valve therefore increases as the pressure differential increases, and when such a valve is supposed to be actuated by means of an actuator, the actuator must be powerful enough to overcome the greatest pressure differential that can occur at the valve. Such actuators are naturally large and expensive. 
         [0003]    A valve having a pressure-compensated design is known, for example, as the “WEDT-08” from Bosch-Rexroth. This conventional valve has a substantially cylindrical sleeve, in the case of which a first port is formed on an end face of the sleeve and a second port is formed on the circumferential surface thereof. A valve tappet, which can move in the valve sleeve, has an axial bore, via which the pressure of the first port is present at two end faces of the tappet that face away from each other. The hydrostatic pressure forces acting on the end faces of the tappet cancel each other out, and therefore, in order to switch the valve, only a slight actuating force is required by one of the actuators acting on the end face of the tappet remote from the first port. 
         [0004]    However, the pressure-compensated design not only prevents high pressure at the first port from holding the tappet on the seat, but also prevents high pressure at the second port from releasing the tappet from the seat. If the aim is to use the valve in a hydraulic system in which the pressure at the second port can temporarily exceed the pressure at the first port and thereby endanger components of the system, a non-return valve must be installed in parallel in order to prevent such pressure peaks, which markedly increases costs and space requirements of a valve assembly for such an application. Such pressure peaks can occur, for example, on a self-propelled harvesting machine, when an assembly that is mounted so as to be displaceable by hydraulic cylinders, such as a front harvesting attachment, is exposed to external forces during use. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention overcomes the shortcomings of known arts, such as those mentioned above. 
         [0006]    To that end, the present invention provides a simply designed valve that enables a strong flow to be controlled with a low actuating force and is simultaneously capable of counteracting excess pressures at one of the ports thereof. 
         [0007]    For example, in the case of a valve comprising a valve sleeve having at least one first and one second port and a pressure-compensated valve tappet, which is movable between a closed position and at least one open position, the valve tappet comprises two parts configured to move relative to one another and to be acted upon relative to one another by a hydrostatic pressure present at the first port. 
         [0008]    Provided the pressure at the first port is sufficiently greater than at the second port, the two parts of the valve tappet are held tightly together by the pressure present at the first port and can be moved jointly between the closed position and the first open position, as is the case with the tappet of the conventional valve. The fact that one part of the valve tappet can move independently of the other part makes it possible to obtain a second open position, in which the two parts of the valve tappet are separated from one another and fluid can flow from the second port to the first port. In order to specifically achieve a transition into the second open position when high pressure is present at the second port, the two parts can advantageously touch one another in a cavity, which communicates with the second port. Therefore, fluid from the second port can easily enter the area between the two parts and drive them apart. 
         [0009]    Advantageously, the two parts comprise end faces that face away from one another and are exposed to the hydrostatic pressure present at the first port. The pressure forces acting on the end faces in opposing directions hold the two parts in contact with one another in the closed position and in the first open position and, given that these pressure forces compensate for one another; it is ensured that the valve tappet can move easily as a whole. 
         [0010]    The valve may be designed as a 2/2 directional control valve or a 3/2 directional control valve having a third port, which, in the closed position, is fluidically connected to the second port and, in the first open position, is disconnected from the second port. Upon transitioning between the closed position and the first open position, such a 3/2 directional control valve passes through a transition region in which either all three ports are connected to one another or all three ports are disconnected from one another. Depending on the intended use of the valve, one of these two variants can be unusable, and it is generally desired to make the transition region as short as possible. The two-part design of the valve tappet makes it possible, by a replacement or a subsequent contour change of one of the two parts of the valve tappet, to minimize the extension of the transition region or to convert a valve having negative overlap, i.e., convert a valve in which all ports are connected in the transition region into a valve having positive overlap (meaning having ports which are disconnected from one another in the transition region), and vice versa. 
         [0011]    In the case of the 3/2 directional control valve in the first open position, the valve tappet forms a gap seal between the first port and the third port. The gap seal makes it possible for the valve tappet to move slightly away from the first open position without this necessarily immediately establishing the connection between the second and third ports. 
         [0012]    In the case of a conventional two-part valve tappet, a connection between the two end faces extending through the valve tappet in a conventional manner would be difficult to seal off from the second port. The invention overcomes this shortcoming by providing a valve with a pressure-compensating fluidic connection between the two opposing end faces of the tappet preferably formed by a channel, which extends in the valve sleeve in a manner separated from the valve tappet. 
         [0013]    The first part of the valve tappet is preferably a closing element, which seals at the valve seat in the closed position, and the second part is a transfer pin, which holds the closing element away from the valve seat in the first closed position. The aforementioned gap seal is then preferably formed by the transfer pin. 
         [0014]    In the second open position, the closing element is disposed with separation from the valve seat and from the transfer pin, preferably in the same direction. The closing element and the transfer pin are separated from one another in the axial direction of the sleeve by a gap filled with hydraulic fluid. 
         [0015]    An actuator can act on the transfer, pin in order to transfer an actuating force to the closing element. 
         [0016]    The actuator is preferably controllable in a proportional manner in order to permit this actuator to stably assume stop positions corresponding to the first open position and the closed position, as well as positions located therebetween. As a result, for example, quantitative control of the throughput of the valve is made possible. Alternatively, the 3/2 directional control valve can be expanded into a 3/3 directional control valve in that a position of the valve tappet between the first open position and the closed position can be set, in which the three ports are either all disconnected from each other or are all connected to each other. 
         [0017]    Since an overpressure present at the first port is incapable of acting upon the closing element in the direction of the closed position, at least one first spring element is preferably provided for this purpose. 
         [0018]    A second spring element acts on the transfer pin in order to act upon this transfer pin in the direction of the closed position. As a result of the support by the second spring element, the force that the first spring element must apply in order to press the closing element against the valve seat is reduced. The first spring element can therefore be kept small and avoid significantly inhibiting the flow of hydraulic fluid through the valve in the opened position. 
         [0019]    The actuator and the valve sleeve delimit a chamber, into which the pressure-compensating channel leads. The chamber is formed, in particular, in that the valve sleeve is screwed into a housing of the actuator. 
         [0020]    In order to ensure that an overpressure at the second port acts on the closing element quickly and directly, it is advantageous for the closing element to delimit the cavity in the axial direction of the valve sleeve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Further features and advantages of the invention will become apparent from the description of exemplary embodiments that follows, with reference to the attached figures, wherein: 
           [0022]      FIG. 1  depicts a section through a valve assembly comprising two 3/2 directional control valves constructed according to the invention; 
           [0023]      FIG. 2  presents a perspective view of one of the directional control valves from  FIG. 1 ; 
           [0024]      FIG. 3  depicts an axial section through the directional control valve from  FIG. 2 ; 
           [0025]      FIG. 4  depicts an axial section through a 2/2 directional control valve; and 
           [0026]      FIG. 5  depicts a closing element according to a developed embodiment of the valve. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The following is a detailed description of example embodiments of the invention depicted in the accompanying drawings. The example embodiments are presented in such detail as to clearly communicate the invention and are designed to make such embodiments obvious to a person of ordinary skill in the art. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention, as defined by the appended claims. 
         [0028]      FIG. 1  shows two directional control valves  1  constructed according to the invention, arranged for an exemplary application. The directional control valves  1  each comprise a valve cartridge or valve sleeve  2 , which is screwed into a through-bore  4  of a valve plate  3 , the through-bore extending in the plane of the drawing. The directional control valves  1  each further comprise an actuator  40  outside of the valve plate  3 . 
         [0029]    The valve plate  3  comprises two bores  5 ,  6  oriented perpendicularly to the plane of the drawing, wherein one bore  5  leads to the through-bore  4 , between opposing end faces  7  of the valve cartridges  2 , in order to direct hydraulic fluid under high pressure from a pump toward the end faces  7  of the valves. The other bore  6  is connected via branch lines  8  to annular chambers  9  extending around the valve cartridges  2 , in order to direct hydraulic fluid under low pressure from there back to a tank. Further annular chambers  10  enclose the valve cartridges  2  and are each connected to consumer ports  11  of the valve plate  3 . The annular chambers  9 ,  10  are therefore second and third ports, respectively, of the valves. 
         [0030]    In the  FIG. 2  perspective view, a central passage  13  and a plurality of passages  12  grouped around said central passage are shown on the end face  7  of the valve sleeve  2 . The passages  12 ,  13  form a first port of the directional valve  1 , which is exposed to the high pressure of the pump. As indicated in  FIG. 2  by dashed lines III-III, the axial section through the directional control valve  1  shown in  FIG. 3  extends through one of the passages  12  in the upper half of  FIG. 3 , and between two passages  12  in the lower half. 
         [0031]    As shown in  FIG. 3 , the central passage  13  extends across the entire length of the valve sleeve  2  and contains a two-part valve tappet  14 . The two parts of the valve tappet  14  are a closing element  15  and a transfer pin  16 . The closing element  15  comprises a cylindrical shaft  17  and a hemispherical dish  18 . The shaft  17  extends into an inlet section of the passage  13 , which leads into the end face  7 . The high pressure of the pump acts via the passage  13  on an end face  37  of the shaft  17 . A chamber  19  having a larger diameter adjoins the inlet section, into which said chamber the passages  12  lead. A valve seat  20  is formed by a tapering of the passage  13  at the side of the chamber  19  remote from the end face  7 . The spherical surface  39  of the hemispherical dish  18  is pressed, in a sealing manner, against the valve seat  20  by a coil spring  21  accommodated in the chamber  19 . 
         [0032]    The transfer pin  16  has a plunger section  22 , which fills the passage  13  in a manner having a narrow tolerance, and has a tapered section  23 , the tip  38  of which touches the spherical surface  39  of the hemispherical dish  18  in the center. 
         [0033]    A cavity  25  extends annularly around the tapered section  23 . Branch bores  26 , which connect the cavity  25  to the annular chamber  10 , form a second port of the directional control valve  1 . The cavity  25  is delimited toward the end face  7  by the hemispherical dish  18 . A third port is formed by branch bores  27 , which lead to the side of the cavity  25  opposite the hemispherical dish  18  and connect said cavity to the annular chamber  9 . 
         [0034]    A channel  28  extends through the valve sleeve  2 , from the chamber  19  to an end face  29  opposite the end face  7 , parallel to the passage  13 . Together with a cup-shaped housing  30  of the actuator  40 , into which the valve sleeve  2  is screwed, the end face  7  delimits a second chamber  31 , in which a solenoid armature  32  driven by a solenoid coil disposed outside of the housing  30  bears against an end face  33  of the transfer pin  16 . The actuator  40  is designed for binary operation, i.e., the solenoid armature  32  thereof has only two reproducibly adjustable stop positions at the ends of the displacement path thereof that the actuator assumes in the energized or de-energized state, respectively, of the solenoid coil. Preferably, actuator  40  permits proportional operation, i.e., a supply circuit acts upon the solenoid roil with various non-disappearing current intensities, to which positions of the solenoid armature  32  between the stop positions reproducibly correspond. 
         [0035]    The channel  28  ensures that the pressures in the chambers  19 ,  31  are the same. Therefore, in order to displace the valve tappet  14 , the solenoid armature  32  substantially only needs to overcome the force of the spring  21  and a spring  34  that holds the transfer pin  16  pressed against the solenoid armature  32 . An excessively high pressure can occur on the end face  7  of the directional control valve  1 , for example, when a consumer supplied by the line  6  parallel to the valve  1  is exposed to an external force, and is therefore incapable of blocking the directional control valve  1 . 
         [0036]    A groove  24  is provided on the plunger section  22  in order to accommodate a sliding seal, which seals the cavity  25  with respect to the chamber  31 . As shown in Fig:  3 , the chamber  19  is disconnected from the cavity  25 , and therefore hydraulic fluid cannot flow from the bore  5  to the bore  6  or the consumer port  11 . Since the branch bore  27  is connected to the cavity  25 , hydraulic fluid from the consumer port  11  can reach the bore  6 , however. When the transfer pin  16  is displaced by the solenoid armature  32  in the direction of the end face  7 , this transfer pin releases the closing element  15  from the valve seat  20 , thereby permitting hydraulic fluid from the bore  5  to enter the cavity  25  via the chamber  19 . From the cavity  25 , the fluid can continue to the annular chamber  10  and ultimately reach the consumer port  11 . Alternatively, the fluid can flow, unused, to the bore  6  via the branch bores  27  and the annular chamber- 9  and ultimately to the tank, provided the transfer pin  16  is not advanced far enough forward to close the branch bore  27 . 
         [0037]      FIG. 4  shows an alternative embodiment of the directional control valve  1 , as 2/2 directional control valve. As compared to  FIG. 3 , the branch bore  27 , which can be blocked by the movement of the transfer pin  16 , and the associated annular chamber  9  on the jacket surface of the valve sleeve  2  are eliminated, where the branch bore  26  and the associated annular chamber  10  remain. 
         [0038]    A further difference between the representations in  FIGS. 3 and 4  is the two-part design of the valve sleeve  2  shown in  FIG. 4 . This two-part design also can also implemented in the 3/2 directional control valve in  FIG. 3 . In greater detail, a main body  35  of the valve sleeve is bored through from the end face  7  to the valve seat  20  with a large diameter in order to form the chamber  19 . A cover  36  is pressed into the bore, which supports the coil spring  21  and guides the shaft  17  of the closing element  15 . 
         [0039]    As shown in  FIG. 4 , the central passage  13  also extends through the cover  36 . Alternatively, the cover  36  can also completely close the passage  13  and in that case comprise a blind hole that is open toward the chamber  19 . Such blind hole, therefore, accommodates the shaft  17  of the closing element  15 . In such design, the end face  37  of the shaft  17  is not directly exposed to the pressure present externally at the end face  7 , but rather is exposed to the pressure of the chamber  19 . This can simplify switching of the valve  1  in particular when the pressure is lower in the chamber  19  than at the end face  7 , due to a high throughput. 
         [0040]      FIG. 5  shows a perspective view of an alternative closing element  41 , for use instead of the closing element  15  in the above-described directional control valves  1 . Alternative closing element  41  is used to simplify proportional operation and/or to convert a 3/2 directional control valve having negative overlap into one having positive overlap. 
         [0041]    The closing element  41  comprises (as does the closing element  15 ), a shaft  17 , a hemispherical dish  18  and an adapter  42  placed onto the hemispherical dish  18  that engages into the cavity  25 . The adapter  42  in this case has a flat cylindrical section  43 , the outer diameter of which corresponds, with slight play, to the inner diameter of the cavity  25 . As soon as the closing element  41  is released from the valve seat  20 , the flat cylindrical section  43  forms a gap seal with the wall of the cavity  25 . The gap seal delimits the throughput of hydraulic fluid from the chamber  19  to the cavity  25  in proportion to the extent of the deflection of the closing element  41 . Fingers  4  projecting from the cylindrical section  43  wrap around and guide the tip of the transfer pin  16 , which engages therebetween (not shown in  FIG. 5 ). 
       REFERENCE CHARACTERS 
       [0042]      1  directional control valve 
         [0043]      2  valve sleeve 
         [0044]      3  valve plate 
         [0045]      4  through-bore 
         [0046]      5  bore 
         [0047]      6  bore 
         [0048]      7  end face 
         [0049]      8  branch line 
         [0050]      9  annular chamber 
         [0051]      10  annular chamber 
         [0052]      11  consumer connection 
         [0053]      12  passage/first port 
         [0054]      13  passage/first port 
         [0055]      14  valve tappet 
         [0056]      15  closing element 
         [0057]      16  transfer pin 
         [0058]      17  shaft 
         [0059]      18  hemispherical dish 
         [0060]      19  chamber 
         [0061]      20  valve seat 
         [0062]      21  coil spring 
         [0063]      22  plunger section 
         [0064]      23  tapered section 
         [0065]      24  groove 
         [0066]      25  cavity 
         [0067]      27  branch bore/second port 
         [0068]      27  branch bore/third port 
         [0069]      28  channel 
         [0070]      29  end face 
         [0071]      30  housing 
         [0072]      31  chamber 
         [0073]      32  solenoid armature 
         [0074]      33  end face 
         [0075]      34  spring 
         [0076]      35  main body 
         [0077]      36  cover 
         [0078]      37  end face 
         [0079]      38  tip 
         [0080]      39  surface 
         [0081]      40  actuator 
         [0082]      41  closing element 
         [0083]      42  adapter 
         [0084]      43  cylindrical section 
         [0085]      44  finger 
         [0086]    As will be evident to persons skilled in the art, the foregoing detailed description and figures are presented as examples of the invention, and that variations are contemplated that do not depart from the fair scope of the teachings and descriptions set forth in this disclosure. The foregoing is not intended to limit what has been invented, except to the extent that the following claims so limit that.