Abstract:
A hydraulic valve for a cam phaser including a valve housing with a longitudinal axis and a valve piston that is axially moveable along the longitudinal axis, wherein the valve piston opens and closes a first operating connection of the valve housing and a second operating connection of the valve housing, wherein the first operating connection and the second operating connection are axially offset from one another; and a supply connection of the valve housing which is used for supplying the hydraulic valve with a hydraulic fluid fed by a feed device, wherein the hydraulic valve is configured to be flowed through by the hydraulic fluid on different paths controlled by a flow permeable channel system of the valve piston, and wherein a check valve opening and closing an inflow channel is arranged in the hydraulic valve in the inflow channel of the valve housing.

Description:
RELATED APPLICATIONS 
       [0001]    This applications claims priority from and incorporates by reference German patent application 10 2014 102 617.9 filed on Feb. 27, 2014. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a hydraulic valve for a cam phaser. 
         [0003]    Hydraulic valves for cam phasers in general are well known. The hydraulic valve includes a flowable valve piston which is received axially moveable in a valve housing of the hydraulic valve. The valve housing is configured with flowable channels so that a hydraulic fluid can flow through these channels and can flow in and out of the valve housing on different flow paths through a channel system configured in the valve piston. Typically the valve housing includes a flowable first operating connection, a flowable second operating connection and a flowable supply connection. The first operating connection and the second operating connection are connected with the cam phaser and the hydraulic fluid is feedable into the hydraulic valve and also out of the hydraulic valve through these connections. In order to supply the hydraulic valve with the hydraulic fluid fed by a feed device the valve housing includes the supply connection. In order to use cam shaft switching moments check valves are positioned in the flow paths of the operating connections, either in the valve housing or in the valve piston. Furthermore a check valve is configured in a flow path of the supply connection so that the hydraulic fluid can flow through the supply connection into the valve housing or into the valve piston, however, so that an exit of the hydraulic fluid through the flow path of the supply connection is blocked. Due to the check valves the hydraulic fluid in the hydraulic valve is controllable as a function of pressure. 
         [0004]    Thus, for example the publication document DE 10 2009 043 154 A1 discloses a hydraulic valve with a check valve configured as a ball check valve which is arranged in the flow path of the supply connection between the supply connection and the feed device. 
         [0005]    From the publication DE 10 2008 006 179 A1 a hydraulic valve is known which includes a support sleeve for the valve piston which is axially moveable in the valve housing. Openings are provided in the support sleeve which are configured for flowing through the hydraulic valve in combination with the flowable channels in the valve housing. A woven filter material is provided between the valve housing and the support sleeve. Typically the hydraulic fluid is filtered in a supply channel to which the supply connection is associated, wherein the filtering is performed with a respective separation device, for example an oil separator sleeve. The woven filter material is provided for filtering the hydraulic fluid for example for retaining chips which can be produced when mounting the separation device. Chips that reach the valve housing can on the one hand side impede movability of the valve piston, on the other hand side they can block the channels and the channel system so that the hydraulic valve cannot perform its function any more. A check valve configured as a ball check valve is arranged in the section of the supply connection in order to prevent a back flow of the hydraulic fluid from the valve piston into the supply connection. 
         [0006]    The publication document DE 10 2008 036 182 A1 discloses a hydraulic valve which is provided for simplifying a supply to cam bearings. In order to block a hydraulic fluid outflow from the hydraulic valve into the supply channel of the cam bearings a check valve configured as a ball check valve is arranged at a face of the hydraulic, which face is oriented towards the cam shaft. 
         [0007]    An improvement of responsiveness shall be achieved by the hydraulic valve with two spring loaded check valves that can be derived from publication document DE 10 2008 036 876 A1. The two check valves are provided for blocking an outflow of the hydraulic fluid in a direction towards the feed device. Using the two check valves contrary to just using one check valve shall safely prevent a back flow of the hydraulic fluid. Furthermore the two check valves facilitate adapting an effective pass through cross section to the respective conditions for quickly loading the hydraulic valve and thus to provide improved responsiveness of the hydraulic valve. This means for example operating an internal combustion engine including the cam shaft at high speeds feeds a correspondingly large hydraulic fluid flow which requires a large effective pass through cross section for quickly loading the hydraulic valve. By comparison a small effective pass through cross section is required for achieving a quick loading at low speeds. 
         [0008]    A hydraulic valve that is configured as a check valve but not as a ball check valve can be derived from the publication document WO 2009/089 960 A1. In order to obtain quick response of the hydraulic valve and an increase of the adjustment speed of the cam phaser a closure element of the check valve in a flow cross section of the supply connection is disclosed which closure element is configured disc shaped and arranged in an inflow channel of the hydraulic valve for the supply connection. The disc for opening and closing the inflow channel includes a closure element which is supported at the disc in a spring elastic manner. A disc is disclosed with a ring that is configured with spring elements, wherein the closure element is arranged within the ring. The closure element is integrally connected with the ring in one piece. The spring elements are illustrated with groove shaped channels completely penetrating the disc along its thickness so that a spring element that is respectively configured between two channels is moveable in a spring elastic manner along a longitudinal axis of the disc. The idea is to achieve quicker closing or opening of the check valve due to a greater effective inflow surface and lower mass inertia compared to a ball check valve. An inflow of hydraulic fluid from the supply connection into the valve piston is provided through the spiral or wave arc shaped channels which are simultaneously used for providing the spring elements and through a lift off of the closure element from the inflow channel, however so that the disc is fixated at its outer circumference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    Thus, it is an object of the present invention to provide a hydraulic valve for a cam phaser which assures safe closure and sufficient supply for the hydraulic valve at low camshaft speeds and also at high camshaft speeds and which has a simple and cost effective configuration. 
         [0010]    The object is achieved according to the invention by a hydraulic valve for a cam phaser including a valve housing with a longitudinal axis and a valve piston that is axially moveable along the longitudinal axis, wherein the valve piston opens and closes a first operating connection of the valve housing and a second operating connection of the valve housing, wherein the first operating connection and the second operating connection are axially offset from one another; and a supply connection of the valve housing which is used for supplying the hydraulic valve with a hydraulic fluid fed by a feed device, wherein the hydraulic valve is configured to be flowed through by the hydraulic fluid on different paths controlled by a flow permeable channel system of the valve piston, and wherein a check valve opening and closing an inflow channel is arranged in the hydraulic valve in the inflow channel of the valve housing which inflow channel is associated with the supply connection, wherein the check valve includes a disc shaped flow permeable first closure element with a first pass through opening and a spring element, characterized in that the check valve includes a flow permeable second closure element with a second pass through opening, wherein the first pass through opening is arranged opposite to a non flow permeable second outer section of the second closure element, and wherein the second pass through opening is arranged opposite to a non flow permeable first inner section of the first closure element, so that a relative movement between the first closure element and the second closure element causes an opening or closing of the check valve. 
         [0011]    Advantageously embodiments with useful and non trivial variations of the invention are provided in the dependent claims. 
         [0012]    The hydraulic valve according to the invention for a cam phaser with a valve housing and a valve piston that is moveable along a longitudinal axis of the valve housing includes a check valve which is received in a flow channel of the valve housing upstream of the valve piston and downstream of a supply connection of the valve housing. The supply connection is used for supplying hydraulic fluid to the hydraulic valve. The check valve is arranged in the supply channel so that the supply channel is openable or closeable by the check valve so that the hydraulic fluid cannot flow back from the inflow channel towards the supply connection. 
         [0013]    The check valve includes a flowable disc shaped first closure element including at least a first pass through opening and a flowable second closure element including at least a second pass through opening. Since both closure elements include a pass through opening it is required for achieving a sealing effect or closing the check valve that the closure elements are arranged so that the first pass through opening is arranged opposite to a non flowable first section of the second closure element and the second pass through opening is arranged opposite to a non flowable second section of the first closure element so that opening or closing the check valve is performed based on a movement of the two closure elements relative to each other. The two accordingly configured closure elements provide a secure closure of the check valve in a simple manner since the pass through openings of the two closure elements can be closed by the respective opposite closure element as a result of a relative movement. Put differently this means that in case the two closure elements move towards each other a sealing contact between the two closure elements can be established, wherein the pass through openings are closed due to their positioning. 
         [0014]    Opening the check valve can be performed rather quickly since the pass through openings are released already for a small movement of the two closure elements relative to one another where they move away from each other so that hydraulic fluid can flow from the first pass through opening between the first closure element and the second closure element already for a small displacement of the two closure elements from each other so that the hydraulic fluid flows through the second closure element into the valve piston. 
         [0015]    In a second embodiment of the hydraulic valve according to the invention the first pass through opening is arranged in an outer section of the first closure element and the second pass through opening is configured in a center of the closure element. 
         [0016]    Compared to the check valves known in the art the advantage is that on the one hand side an assured sealing effect is obtainable due to the pass through openings that are arranged relative to another accordingly and on the other hand side it is possible to release a sufficiently large flow cross section as quickly as possible so that a quick response of the hydraulic valve is provided. 
         [0017]    Advantageously the first closure element is configured independently from the second closure element so that an uncomplicated and thus cost effective production can be implemented. 
         [0018]    In another embodiment of the hydraulic valve according to the invention the first pass through opening is configured in a first outer section of the first closure element and the second pass through opening is configured in a second inner section of the second closure element. This has the advantage that the hydraulic fluid when flowing into the valve piston from the second pass through opening does not go through any or almost no change in flow direction so that flow loses are largely prevented so that also this configuration facilitates a quick response of the hydraulic valve. 
         [0019]    It is another advantage of the solution according to the invention that disc shaped closure elements with the accordingly arranged pass through openings can be produced in a cost effective manner. Thus, the closure elements can be made for example from a sheet material which can be worked in a simple manner. The pass through openings can be introduced into the disc through a stamping method simultaneously with fabricating the disc. 
         [0020]    Another advantage of the disc shaped closure elements is little wear of components that contact each other during operations when closing the check valve due to a greater contact or impact surface compared to the known check valves. 
         [0021]    An axial movement of one of the two closure elements, advantageously of the second closure element arranged proximal to the valve piston is easily supported by a spring element which is advantageously configured as a coil spring. Thus, the spring element only has a supporting effect in that it causes on the one hand side a quicker closure and on the other hand side a safe closure since already a pressing force impacting the second closure element due to pressure spikes at the valve piston achieves an axial movement of the second closure element in a direction of the first closure element. When the second closure element reaches the first closure element the spring element additionally imparts a pressure force for safe closure. 
         [0022]    Overall the hydraulic valve according to the invention is characterized by a simple configuration of its check element so that simple and quick assembly can be provided. Axially securing the spring element is provided by a second shoulder configured in the hollow cylinder and axially securing the first closure element is obtained in a simple manner with a first shoulder provided in the inflow channel and a retaining ring received in an inflow channel in a ring groove. The shoulders are thus produced e.g. through internal turning. This means the check valve of the hydraulic valve according to the invention is characterized by simple production of the closure elements and simple assembly, and the hydraulic valve is influenced very little by its installation position. 
         [0023]    The first pass through opening is configured groove shaped over a circular circumference and the second pass through opening is configured circular so that a large effective flow cross section of the check valve is achievable so that a quick response of the hydraulic valve can be provided even for high engine speeds since a sufficient amount of the hydraulic fluid can flow in a respectively required short time period through the pass through openings into the supply channel of the valve piston. 
         [0024]    Due to the configuration of the check valve sensitivity with respect to contamination is greatly reduced. Thus, the check valve can be adjusted in the same simple manner that is used for mounting. Materials optimization facilitates further improvement of the reaction time and leak tightness. Overall the check valve is characterized by a low loading of the disc shaped closure elements and overall of the components that are configured adjacent to the closure elements since only the second closure element has to be moved in addition to the spring element. 
         [0025]    Secure closure of the check element prevents an opposite pressure on a filter that is provided upstream of the check element in the flow path of the supply connection, in particular a sieve, so that a loading of the sieve is reduced and its service life is extended. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Further advantages, features and details of the invention can be derived from a subsequent description of advantageous embodiments with the reference to drawing figures. The features and feature combinations recited in the preceding description and the features individually recited in the subsequent figure description or illustrated in the figures are not only useable in the respectively provided combination but are also useable by themselves or in other combinations without extending beyond the scope of the invention. Identical or functionally equivalent elements have identical reference numerals. For reasons of clarity it is possible that the elements are not provided with respective reference numerals in all figures, while maintain their association, wherein: 
           [0027]      FIG. 1  illustrates a longitudinal sectional view of a hydraulic valve for a cam phaser with a check valve configured as a ball check valve that is known in the art; 
           [0028]      FIG. 2  illustrates a longitudinal sectional view of a hydraulic valve according to the invention; 
           [0029]      FIG. 3  illustrates a longitudinal sectional view of the hydraulic valve according to the invention according to  FIG. 2 ; 
           [0030]      FIG. 4  illustrates a top view and a longitudinal sectional view of a first closure element of a check valve of the hydraulic valve according to  FIG. 2 ; 
           [0031]      FIG. 5  illustrates a top view and a longitudinal sectional view of the check valve of the hydraulic valve according to  FIG. 2 ; 
           [0032]      FIG. 6  illustrates a view in principle of the first closure element and the second closure element according to  FIGS. 4 and 5  in a longitudinal sectional view in a first relative position; 
           [0033]      FIG. 7  illustrates a view in principle of the first closure element and the second closure element in a longitudinal sectional view in a second embodiment in a second relative position; and 
           [0034]      FIG. 8  illustrates a view in principle of the first closure element and the second closure element in a third embodiment in the second relative position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    A cam phaser that is not illustrated in more detail facilitates changing opening and closing times of gas control valves of an internal combustion engine which is not illustrated in more detail. Thus, the cam phaser according to the invention continuously adjusts a relative angular position of a cam shaft of the internal combustion engine relative to a crank shaft of the internal combustion engine wherein the cam shaft and the crank shaft are not illustrated in more detail and wherein the cam shaft is not rotated relative to the crank shaft. 
         [0036]    Rotating the cam shaft moves the opening and closing times of the gas control valves so that the internal combustion engine produces optimum power at a respective speed. Controlling the cam phaser is typically provided by an electronic control unit which controls an inflow and an outflow of hydraulic fluid in pressure chambers provided in the cam phaser based on parameters of the internal combustion engine. A hydraulic valve  1  controlled by electrical signals from a control unit is used for controlling inflow and outflow of the hydraulic fluid, wherein the hydraulic valve according to the prior art as illustrated in  FIG. 1  is configured with a check valve configured as a ball check valve. 
         [0037]    The hydraulic valve  1  includes a valve housing  2  and a valve piston  4  that is axially moveable along a longitudinal axis  3  of the valve housing  2 . In order to move the valve piston  4  a first face  5  of the valve piston  4  that is oriented away from the internal combustion engine is closed so that a plunger that is not illustrated in more detail of an electromagnetic linear actuator that is not illustrated in more detail can contact the first face  5 . Providing power to the linear actuator leads to an axial movement of the valve piston  4  towards the internal combustion engine, wherein a retaining element  7  arranged at a second face  6  of the valve piston  4  which is configured oriented away from the first face  5  imparts a reset force upon the valve piston  4  against which reset force the valve piston  4  has to be moved. The retaining element  7  configured in this embodiment as a compression coil spring is supported at a hollow cylinder  8  which is arranged in the portion of the second face  6  with a press fit and non moveable in the valve housing  2 . 
         [0038]    The valve piston  4  is configured flowable and includes a channel system  14  with a supply channel  15  and a channel groove  16  intersecting the supply channel. The supply channel  15  extends along a longitudinal axis of the valve piston  4  which longitudinal axis is configured coaxial to the longitudinal axis  3 , wherein the supply channel  15  is closed at a first channel end  17  oriented towards the first face and open at a second channel end  18  oriented towards the second face  6  so that hydraulic fluid can flow into the supply channel  15  through an inlet opening  19  of the valve piston  4  configured at the second channel end  18 . 
         [0039]    The channel group  16  is configured as intersecting bore holes, wherein each bore hole extends completely over a diameter D of the valve piston  4  and forms two respective outlet openings  21  at an enveloping surface  20  of the valve piston  4 . The bore holes are arranged star shaped, wherein they form a joint intersection surface which is arranged flowable in the supply channel  15 . 
         [0040]    The valve housing  2  which is configured bushing shaped includes a supply connection P, a first operating connection A, a second operating connection B, a first tank access T 1  and a second tank access T 2  which are respectively configured flowable. The first operating connection A and the second operating connection B are connected with accordingly associated pressure chambers of the cam phaser so that the hydraulic fluid can load the pressure chambers in a manner controlled by the hydraulic valve  1 . 
         [0041]    A first channel  10  in the valve housing  2  is associated with the first operating connection A and a second channel  11  in the valve housing  2  is associated with the second operating connection B, wherein the operating connections facilitate loading the channels  10 ,  11  with the hydraulic fluid flowing through the hydraulic valve using a first opening  23  and a second opening  24  configured at an inner surface  22  of the valve housing  2 , which inner surface is oriented towards the valve piston  4 . 
         [0042]    Depending on a selected direction of rotation the hydraulic fluid flows in or out of the pressure chambers. Thus, for example in the position of the valve piston illustrated in  FIG. 1  the pressure chambers associated with the operating connection B are loaded with the hydraulic fluid. In this position of the valve piston  4 , the hydraulic fluid flows out of the supply connection P through a check valve  13  arranged in an inflow channel  12  of the valve housing  2 , which inflow channel is configured between the supply connection P and the hollow cylinder  8 , and through the hollow cylinder  8  through the inlet opening  19  into the supply connection  15 . 
         [0043]    The outlet openings  21  at least partially cover the second opening  24  so that the hydraulic fluid can flow out of the supply channel  15  through the outlet openings  21  and the second opening  24  into the second channel  11  through the second operating connection B into the respective pressure chambers. 
         [0044]    The pressure chambers associated with the second operating channel B are thus loaded with the hydraulic fluid. This has the effect that hydraulic fluid exits the pressure chambers associated with the first operating connection A, wherein the hydraulic fluid flows from the first channel  10  through its first opening  23  and a first gap  25  arranged between the enveloping surface  20  and the inner surface  22  into a third channel  26  which includes a third opening  27  arranged at an inner surface  22  wherein the third channel  26  is connected with the first tank access T 1  for relief, this means for draining the hydraulic fluid. 
         [0045]    The second tank access T 2  through which the hydraulic fluid can flow from the second channel  11  when the valve piston  4  is positioned accordingly is arranged in a portion of the cam phaser downstream of the first face  5 . 
         [0046]    In a non-illustrated additional position of the valve position  4 , the valve piston  4  is axially moved in a direction towards the internal combustion engine so that the first gap  25  is closed whereas an axially opposite second gap is configured between the first opening  23  and the enveloping surface  20 , wherein the outlet openings  21  now at least partially cover the first opening  23 . Through this second gap the hydraulic fluid can flow through the outlet openings  21  out of the supply channel  15  into the first opening  23  and thus into the first channel  10 . From the first channel  10  the hydraulic fluid flows through the first operating connection A into the pressure chambers associated with the first operating connection A wherein the pressure chambers are loaded with the hydraulic fluid. 
         [0047]    As a consequence of this loading hydraulic fluid exits the pressure cavities associated with the second operating connection B wherein the hydraulic fluid flows out of the second channel  11  through its second opening  24  and a third gap which is configured between the enveloping surface  20  and the inner surface  22  so that the hydraulic fluid eventually flows into the second tank access T 2 . 
         [0048]    The supply connection P is configured to be connected with an oil pump which is not illustrated in more detail so that the hydraulic valve  1  is flowable with hydraulic fluid which is oil in this embodiment. 
         [0049]    The supply connection P is arranged at a housing face of the valve housing  2  which housing face is oriented towards the internal combustion engine. In order to prevent a back flow of the hydraulic fluid from the valve housing  2  to the supply connection P a check valve  13  is arranged in the inflow channel  12 . The check valve  13  is configured as a ball check valve and fixated in the valve housing  2  by a retaining element  29  configured as a Seeger ring and by a form element  47  wherein the retaining element is axially supported at a first annular shoulder  28  configured in a supply channel  12 . 
         [0050]    A hydraulic valve  1  according to the invention is configured according to  FIG. 2 . A detail drawing for illustrating the check valve  13  depicts a longitudinal sectional view of a detail of the hydraulic valve  1  according to the invention in  FIG. 3 . The check valve  13  is configured disc shaped including a first disc shaped closure element  30  which is fixated in the inflow channel  12  downstream of the supply connection P in the valve housing. Between the valve piston  4  and the first closure element  30  a disc shaped second closure element is moveably received in the inflow channel  12 . The first closure element  30  is configured independent from the second closure element  31 . The two closure elements  30 ,  31  are positioned in the inflow channel  12  so that a first inflow surface  40  of the first closure element  30  and a second inflow surface  41  of the first closure element  30  which is oriented away from the first inflow surface  40  or a third inflow surface  42  of the second closure element  31  and a fourth inflow surface  43  of the second closure element  31  that is oriented away from the third inflow surface  42  are oriented parallel to a flow cross section  44  of the inflow channel  12 . 
         [0051]    The first closure element  30  is secured against axial movement by the first annular shoulder  28  in the inflow channel  12  and by the retaining element  29  and the formed element  47 . Additionally a radial rotation of the first closure element  30  is blocked through a press fit of the first closure element  30  in the inflow channel  12 . 
         [0052]    Like typical check valves the check valve  13  opens when a pressure of the hydraulic fluid upstream of the check valve  13  is greater than a pressure downstream of the check valve  13  wherein the flow direction is counted from the direction of the supply connection P.  FIG. 2  illustrates the hydraulic valve  1  according to the invention in a position in which the check valve  13  is flowable. 
         [0053]    The hydraulic fluid presses the second closure element  31  against the hollow cylinder  8  where it is supported. A spring element  32  supported at the hollow cylinder  8  by a second shoulder  45  configured in the hollow cylinder  8  is arranged oriented towards the second closure element  31  for establishing contact and is preloaded in this position. 
         [0054]    In closed condition the hydraulic fluid can flow in arrow direction PR from the supply connection P through a first pass through opening  33  of the first closure element  30  into the inflow channel  12  and from there through the second closure element  31  through its second pass through opening  34  so that the hydraulic fluid can enter the supply channel  15  through the hollow cylinder  8 . 
         [0055]    When sizing the second pass through opening  34  care has to be taken that its diameter is on the one hand side smaller than a smallest diameter configured in the hollow cylinder  8  and on the other hand side that it is large enough so that the hydraulic fluid can flow into the valve piston  4  in a sufficiently short time period also at high engine speeds. The advantage of sizing the diameter of the second pas through opening  34  smaller is that hydraulic fluid flowing out of the valve piston  4  in a direction towards the check valve  13  at least partially directly impacts the third inflow surface  42  and can move the third inflow surface against the first closure element  30  so that closing the check valve  13  is accelerated. 
         [0056]    The first pass through opening  33  is configured in an annular first outer section  35  of the first closure element  30 , wherein the term “outer section” is thus interpreted so that a radial distance of the outer section  35  from a center of the first closure element  30  is greater than a radial distance of the first inner section  36  of the first closure element  30 . The first pass through opening  33  is divided into four pass through opening sections by bars  46 , wherein the bars  46  are required to implement a simple configuration of the first closure element  30  and are only used for defining the first pass through opening  33  in radial direction. The first pass through opening  33  is configured groove shaped providing an effective flow cross section with maximum size in the first outer section  35 , c.f.  FIG. 4 . 
         [0057]    The second closure element  31  is configured not flowable in its second outer section  37 , wherein its second inner section  38  is flowable and includes the circular second pass through opening  34 . Put differently the second closure element  31  is configured as a circular disc, cf.  FIG. 5 . 
         [0058]    The pass through openings  33 ,  34  are arranged to that the first pass through opening  33  is arranged opposite to the non flowable second outer section  37  and the second pass through opening  34  is arranged opposite to the un flowable first section  36 . 
         [0059]    In case a pressure downstream of the check valve  13  is greater than a pressure upstream of the check valve  13  or in case a pressure spike due to cam phasing moments downstream of the check valve  13  impacts the second closure element  31 , the second closure element  31  is pressed onto the first closure element  30  through a force of the pressure spike impacting a third inflow surface  42  of the second closure element  31  oriented towards the valve piston  4 , so that accordingly positioned pass through openings  33 ,  34  are blocked by the respective other closure element  31 ,  30  so that they are not flowable. 
         [0060]    The axially moveable second closure element  31  is supported in a sliding bearing in a radial direction at its circumference in the inflow channel  12  so that a wear caused by cavitation or abrasion is very small depending on an axial thickness d of the second closure element  31 . The axial thickness d can be kept very small since the second closure element  31  performing its sealing function only has to cover the first pass through openings  33  with a fourth inflow surface  43  of the second closure element since the second closure element  31  is pressed against the first closure element  30  due to a pressure acting downstream. 
         [0061]    The shape of the first closure element  30  and of the second closure element  31  illustrated in this embodiment and of the accordingly configured pass through openings  33 ,  34  facilitates advantageous sizing of the pass through openings  33 ,  34  so that sufficient hydraulic fluid can flow from the supply connection P into the valve piston  4  also under high engine speeds so that a quick response of the hydraulic valve  1  or a quick reaction time or switching time is implemented. 
         [0062]    It is also favorable for a quick reaction time to use appropriate materials to implement a low weight of the moveable second closure element  31 . 
         [0063]    The spring element  32  supports the axial movement of the second closure element  31  and presses the second closure element  31  against the first closure element  30  which supports safe closure. Using the spring element  32  significantly improves responsiveness of the hydraulic valve  1  due to improved dynamics of the check valve  13  over known check valves. Additionally the spring element  32  helps to dampen pressure spikes which can occur in the inflow channel  12  coming from the supply connection P and thus achieves loading the valve piston  4  by the hydraulic fluid without pressure spikes. 
         [0064]      FIG. 6  illustrates the first closure element  30  and the second closure element  31  in a longitudinal sectional view in a first relative position. Depending on the pressures applied at the check valve  13  the second closure element  31  moves in an axial direction. When a pressure caused by pressure spikes on a side of the check valve  13  is greater than a pressure on a side of the supply connection P the second closure element  31  impacts the first closure element  30  until a sealing contact is established between the first closure element  30  and the second closure element  31 . 
         [0065]    Improved sealing of the check valve  13  can be achieved by a seal element  39  between the first closure element  30  and the second closure element  31 . According to a second embodiment, c.f.  FIG. 7  the seal element  39  is configured at the first inflow surface  40  arranged opposite to the second closure element  31 . By the same token the sealing element  39  can be arranged at a fourth inflow surface  43  arranged opposite to the first closure element  30  as illustrated in the third embodiment according to  FIG. 8 . 
       REFERENCE NUMERALS AND DESIGNATIONS 
       [0000]    
       
         
           
               1  hydraulic valve 
               2  valve housing 
               3  longitudinal axis 
               4  valve piston 
               5  first face 
               6  second face 
               7  retaining element 
               8  hollow cylinder 
               9  housing face 
               10  first channel 
               11  second channel 
               12  inflow channel 
               13  check valve 
               14  channel system 
               15  supply channel 
               16  channel group 
               17  first channel end 
               18  second channel end 
               19  inlet opening 
               20  enveloping surface 
               21  outlet opening 
               22  inner surface 
               23  first opening 
               24  second opening 
               25  first gap 
               26  third channel 
               27  third opening 
               28  first shoulder 
               29  safety element 
               30  first closure element 
               31  second closure element 
               32  spring element 
               33  first pass through opening 
               34  second pass through opening 
               35  first outer section 
               36  first inner section 
               37  second outer section 
               38  second inner section 
               39  sealing element 
               40  first inflow surface 
               41  second inflow surface 
               42  third inflow surface 
               43  fourth inflow surface 
               44  flow cross section 
               45  second shoulder 
               46  bar 
               47  form element 
           
         
       
     
         [0113]    A first operating connection 
         [0114]    B second operating connection 
         [0115]    D diameter 
         [0116]    D 1  first diameter 
         [0117]    D 2  second diameter 
         [0118]    P supply connection 
         [0119]    PR arrow direction 
         [0120]    T 1  first tank access 
         [0121]    T 2  second tank access
       d thickness