Abstract:
A hydraulic valve for a pivot motor adjustment device of a camshaft, the hydraulic valve including a valve housing with a longitudinal axis and a valve piston that is axially moveable in the valve housing along the longitudinal axis, wherein a first operating connection of the valve housing and a second operating connection of the valve housing is openable and closable by the valve piston, wherein the first operating connection and the second operating connection are axially offset from one another; and a supply connection of the valve housing, wherein the supply connection supplies the hydraulic valve with hydraulic fluid fed by a feed device, wherein the hydraulic fluid flows through the hydraulic valve on different paths defined by a flowable channel system of the valve piston.

Description:
RELATED APPLICATIONS 
     This application claims priority from German patent application DE 10 2014 101 236.4 filed on Jan. 31, 2014 which is incorporated in its entirety by this reference. 
     FIELD OF THE INVENTION 
     The invention relates to a hydraulic valve for a pivot motor adjustment device of a camshaft according to the preamble of claim  1 . 
     BACKGROUND OF THE INVENTION 
     Hydraulic valves for pivot motor adjustment devices of a camshafts are well known in the art. Hydraulic valves include a valve piston that is axially moveable in a valve housing of the hydraulic valve. Typically the valve housing includes a first operating connection, a second operating connection and a supply connection. The first operating connection and the second operating connection are connected with the pivot motor adjustment device and a hydraulic fluid is feedable through these connections into the hydraulic valve and also from the hydraulic valve. In order to supply the hydraulic valve with the hydraulic fluid that is fed by a feed device the valve housing includes the supply connection. The hydraulic fluid can flow through the hydraulic valve in different paths controlled by a flowable channel system of the valve piston. In order to use a camshaft adjustment torques the hydraulic valve includes at least one check valve in the portion of the operating connections. Additionally a check valve is arranged in a flow portion of the supply connection. Thus, the check valves facilitate controlling the hydraulic fluid in the hydraulic valve as a function of a pressure. 
     Check valves for hydraulic valves whose closure elements are configured band shaped are also known. This can be derived from the French patent document FR 525 481 published in 1921 which discloses a check valve including a band shaped closure element. 
     The patent document DE 101 43 433 B4 discloses a band shaped closure element of a hydraulic valve wherein the closure element includes spring supported closure flaps. 
     A band shaped closure element of a check valve for a hydraulic valve can also be derived from the patent document EP 2 503 201 B1. The disclosed closure valve is characterized in that it includes a stop at a band end in order to limit its expansion. Since the closure element is only flowable within limits due to the stop different types of flow openings are provided. 
     The publication document US 2013 206 088 A1 discloses a hydraulic valve whose check valve is provided with a spring based closure element and received in the valve piston. 
     By the same token check valves with a band shaped closure elements for pivot motor adjustment devices for camshafts are known. The publication documents DE 10 2010 061 337 A1 and DE 10 2010 019 004 A1 disclose hydraulic valves with a band shaped closure element of the check valve. Contrary to the hydraulic valve known from DE 10 2010 061 337 A1 which respectively uses a check valve for the first operating connection and the second operating connection the hydraulic valve disclosed in DE 10 2010 019 004 A1 includes a single check valve through which the first operating connection and the second operating connection can be loaded as a function of a positioning of the valve piston that is axially moveable in the valve housing of the hydraulic valve along a longitudinal axis of the valve housing. The operating connection and the second operating connection are thus axially offset from one another wherein the supply connection of the valve housing is arranged between the first operating connection and the second operating connection. In order to flow the hydraulic valve through ring grooves in the valve housing are associated with the connections. 
     The check valve is arranged at the valve piston in a positioning groove of the valve piston that is oriented towards the ring grooves wherein the positioning groove is connected with the channel system in a flowable manner wherein the valve piston is moveable in the valve housing. Due to the axial move ability of the valve piston there is an option to use the first check valve for both operating connections. 
     The hydraulic fluid can flow through the hydraulic valve on different paths determined by the flowable channel system wherein a first tank connection of the hydraulic valve is configured at the valve housing providing a drain for the hydraulic fluid out of the hydraulic valve. 
     In order to quickly adjust the camshaft a quick and unimpeded response of the hydraulic valve, put differently a quick axial movement of the valve piston in the valve housing is required. Thus, it is necessary that the closure element of the check valve does not contact the valve housing during operations of the pivot motor adjustment device. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus, it is an object of the invention to provide a hydraulic valve for a pivot motor adjustment device of a camshaft which hydraulic valve provides improved response. 
     The object is achieved according to the invention through a hydraulic valve for a pivot motor adjustment device of a camshaft, the hydraulic valve including a valve housing with a longitudinal axis and a valve piston that is axially moveable in the valve housing along the longitudinal axis, wherein a first operating connection of the valve housing and a second operating connection of the valve housing is openable and closable by the valve piston, wherein the first operating connection and the second operating connection are axially offset from one another; and a supply connection of the valve housing, wherein the supply connection supplies the hydraulic valve with hydraulic fluid fed by a feed device, wherein the hydraulic fluid flows through the hydraulic valve on different paths defined by a flowable channel system of the valve piston, wherein a first tank connection of the hydraulic valve is configured at the valve housing and provides an outflow of the hydraulic fluid from the hydraulic valve, wherein a first check valve is positioned at the valve piston in a positioning groove of the valve piston so that the first check valve prevents an outflow of the hydraulic fluid from the positioning groove into the channel system, and wherein the hydraulic valve includes a limitation element at least partially enveloping the first check valve and limiting a radial expansion of the first check valve. 
     Advantageously embodiments with advantageous and non-trivial variations of the invention are provided in the respective dependent claims. 
     The hydraulic valve according to the invention for a pivot motor adjustment device of a camshaft includes a limitation element at least partially enveloping the check valve wherein the limitation element limits a radial expansion of the check valve. Through the at least partial envelopment of the check valve, in particular of a closure element of the check valve, the check valve is limited with respect to its radial expansion provided during operations of the hydraulic valve. This leads to improved and faster response of the hydraulic valve since a contact or a touching of the check valve at the valve housing is prevented. 
     The check valve is opened as a function of a pressure ratio provided at the check valve. Since the closure element of the check valve is band shaped, and the positioning groove is provided over its entire circumference the closure elements expands in radial direction as a function of the pressure ratio. Now put differently the closure element expands at least partially in a direction of the valve housing. The radial expansion is provided as a function of a provided pressure ratio. A high pressure ratio leads to a strong expansion. This means that the closure element can expand at least partially radially out of the positioning groove and that the closure element can contact an inner valve surface oriented towards the positioning groove or that it can touch this valve surface. This contact can lead to a damaging of the valve housing and/or to impeding an axial movement of the valve piston. 
     The limitation element prevents a respective contacting of the check element at the valve housing since the limitation element is configured so that it envelops the check element at least partially and therefore provides a resistance to the radial expansion of the check element. 
     In order to effectively limit the check element the limitation element is configured so that it is supported at the valve piston. Thus, the radial arrangement and also the axial arrangement of the limitation element relative to the check element is maintained in each position of the valve piston so that a touching or a contact of the check element or its closure element at the valve housing is safely prevented. Providing the limitation element at the valve housing would lead to a change of an axial arrangement relative to the stop element for an axial movement of the valve piston and the check element could contact the valve housing in a portion that is not enveloped by the limitation element. 
     Like the check valve the limitation element is arranged in the positioning groove of the valve piston. In order to provide a radial distance between the closure element of the check valve and the limitation element wherein the radial distance is required so that the check valve can open within this radial distance, the limitation element is received at a first shoulder and at a second shoulder of the positioning groove, wherein the shoulders are provided at walls of the positioning groove at a required radial distances from the closure element of the check valve. 
     In order for the hydraulic fluid to be able to flow in the direction released by the check valve the limitation element includes at least one pass through opening. Ideally pass through openings are arranged distributed over a circumference of the limitation element. These pass through openings have to be configured so that a flow resistance which is provided as a consequence by the limitation element in the flow path of the hydraulic fluid is as small as possible. This means that an effective flow cross section of the limitation element which is provided as a sum of the individual effective flow cross sections of the pass through openings should at least approximately correspond to the effective flow cross section of the positioning groove. This is necessary so that pressure losses or flow losses which can be caused by the limitation element are avoided to the largest possible extent. 
     In order to provide simple mounting for the limitation element the limitation element is made from a band. The band is introduced bent into the positioning groove so that it envelops the shoulders, thus with a small preload, wherein a first band portion of the band and a second band portion of the band are arranged overlapping in installed condition in order to produce the hollow cylindrical shape of the limitation element. 
     Advantageously a second tank connection of the hydraulic valve is configured at the valve housing so that a respective tank connection can be associated with the first operating connection and the second operating connection independently from one another. 
     In another embodiment of the hydraulic valve according to the invention the valve piston includes a throttling element for throttling a fluid drainage of the hydraulic fluid at the valve piston, in particular so that the throttle element envelops the valve piston over its radial circumference. Typically throttle elements are arranged at the valve housing in portions of faces of the valve piston. This arrangement leads to an axial force that impacts the accordingly loaded face of the valve piston. When the throttle element is configured as suggested at the valve piston, in particular at its circumference, the axial force is eliminated so that a position change of the valve piston in the hydraulic valve can be provided very quickly since the valve piston does not have to be moved against an axial force caused by the throttle element. 
     In a particularly economical embodiment the throttle element has a polygon shaped circumference. This polygon shaped circumference can be implemented in a simple manner e.g. through so called eccentrical turning. 
     The hydraulic valve is advantageously configured as a central valve so that reduced installation space and improved response are provided compared to an external hydraulic valve since conduction paths for the hydraulic fluid can be kept short. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features and advantages of the invention can be derived from the subsequent description of advantageous embodiments with reference to appended drawing figures. 
       The features and feature combinations recited in the description and individual features and feature combinations recited in the description of the drawings and/or in the drawings and feature combinations are not only useable in the respectively provided combination but in also other combinations or by themselves without departing from the spirit and scope of the invention. Identical reference numerals are associated with identical or functionally equivalent elements. In order to provide clarity it may be the case that elements are not provided with numerals in all drawing figures, wherein: 
         FIG. 1  illustrates a cross section of a pivot motor adjustment device according to the invention; 
         FIG. 2  illustrates a longitudinal sectional view of a hydraulic valve according to the invention; 
         FIG. 3  illustrates a detail of a longitudinal sectional view of the hydraulic valve according to  FIG. 2 ; 
         FIG. 4  illustrates a three dimensional sectional view of a valve piston of the hydraulic valve according to  FIG. 2 ; 
         FIG. 5  illustrates a perspective view of a cage of the hydraulic valve according to  FIG. 2 ; and 
         FIG. 6  illustrates a perspective of the valve piston according to  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A pivot motor adjustment device  1  according to  FIG. 1  facilitates adjusting opening and closing times of gas flow control valves of the internal combustion engine during operations of the internal combustion engine that is not illustrated in more detail. Thus, a relative angular position of a camshaft that is not illustrated in more detail of the internal combustion engine is adjusted continuously variable by the pivot adjustment motor device  1  relative to a crank shaft that is not illustrated in more detail of the internal combustion engine, wherein the camshaft is rotated relative to the crank shaft. A relative rotation of the crank shaft moves opening and closing times of the gas flow control valves so that the internal combustion engine provides optimum power at a respective speed. 
     The pivot motor adjustment device  1  includes a cylindrical stator  2  which is connected torque proof with a drive gear  3  of the camshaft. In the illustrated embodiment the drive gear  3  is a sprocket over which a non illustrated chain is run as a drive element. The drive gear  3  can also be a timing belt cog over which a timing belt is run forming a drive element. Through this drive element and the drive gear  3  the stator  2  is drive connected with the crank shaft. 
     The stator  2  includes a cylindrical stator base element  4  on which radially inward extending bars  6  are configured at even distances on an inside  5  wherein an intermediary cavity  7  is formed between two respectively adjacent bars  6 . A pressure medium, typically hydraulic fluid, is introduced in a controlled manner into this intermediary cavity  7 , through a hydraulic valve  20  that is illustrated in more detail in  FIG. 2 . 
     A lobe  8  is positioned so that it protrudes into the intermediary cavity  7 , wherein the lobe is arranged at a rotor hub  9  of the rotor  10 . Corresponding to the number of intermediary cavities  7  the rotor hub  9  includes a number of lobes  8 . 
     Through the lobes  8  the intermediary cavities  7  are respectively divided into a first pressure cavity  11  and a second pressure cavity  12 . In order to reduce a pressure loss in the first pressure cavity  11  and the second pressure cavity  12 , the bars  6  are configured so that they contact an outer enveloping surface  14  of the rotor hub  9  with their first faces  13  providing a seal through the contact. By the same token the lobes  8  contact an inner wall  16  of the stator base element  4  with their second faces  15  wherein the inner wall  16  is positioned opposite to the outer enveloping surface  14  and a seal is provided through the contact. 
     The rotor  10  is connected torque proof with the camshaft of the internal combustion engine. In order to adjust an angular position between the camshaft and the crank shaft the rotor  10  is rotated relative to the stator  2 . For this purpose the pressure medium in the first pressure cavity or in the second pressure cavity  12  is pressurized as a function of a selected direction of rotation, whereas the second pressure cavity  12  or the first pressure cavity  11  is unloaded. The unloading is provided through a tank access which is opened for unloading. This can be a single tank access that is accessible to the first pressure cavity  11  and the second pressure cavity  12  or as illustrated in the embodiment according to  FIG. 2  a first tank inlet T 1  is associated with the first pressure cavity  11  and a second tank access T 2  is associated with the second pressure cavity  12 . 
     In order to rotate the rotor  10  clock wise relative to the stator, radial first hub bore holes  17  are pressurized by the hydraulic valve  20  wherein the hub bore holes  17  are evenly distributed over a circumference of the rotor hub  9 . In order to rotate the rotor  10  relative to the stator  10  counter clockwise radially oriented second hub bore holes  18  are pressurized through the hydraulic valve  20  wherein the radially oriented second bore holes are also arranged distributed over the circumference of the rotor hub  9 , wherein the second hub bore holes  18  are positioned axially offset from the first hub bore holes  17 . 
     In  FIG. 2  the hydraulic valve  20  according to the invention is illustrated in a longitudinal sectional view in a first valve position. The hydraulic valve  20  is configured similar to a cartridge valve and includes a valve housing  21  in which a valve piston is arranged axially moveable. 
     In order to move the valve piston  22  a first face  23  of the valve piston  22  that is oriented away from the internal combustion engine is closed so that a plunger  24  of an electromagnetic linear actuator  25  can contact this first face  23 . Providing power to the linear actuator  25  causes an axial movement of the valve piston  22  towards the internal combustion engine wherein a retaining element arranged at a second face  26  of the valve piston  22 , wherein second face  26  if oriented away from the first face  23 , imparts a retaining force onto the valve piston  22  against which retaining force the valve piston  22  has to be moved. The retaining element  27 , in this embodiment configured as a compression coil spring, is supported at a hollow cylinder  28  which is arranged with a press fit in the valve housing  21  in a portion of a housing face  29  that is oriented towards the internal combustion engine. 
     The sleeve shaped valve housing  21  includes a supply connection P, a first operating connection A and a second operating connection B. A first ring groove  30  is associated with the supply connection P a second ring groove  31  is associated with the first operating connection A and a third ring groove  32  is associated with the second operating connection B, wherein the respective ring grooves are connected with the connections through respective linking channels. The linking channels are configured so that they completely penetrate a housing wall  34  of the valve housing  21 . 
     The supply connection P is configured to connect with an oil pump that is not illustrated in mover detail, so that the hydraulic valve  20  is supplyable with the hydraulic fluid which is oil in this embodiment. The first operating connection A is connectable with the first hub bore holes  17 , the second operating connection B is connectable with the second hub bore holes  18 . The first tank access T 1  is arranged at the housing face wall  29 . The second tank access T 2  is connectable with a fourth ring groove  33  of the valve housing  21  which ring groove is axially offset from the supply connection B, wherein the connection can be provided through an additional linking channel that is not illustrated in more detail and which leads into the fourth ring groove  33 . The fourth ring groove  33  is arranged between the first face  23  and the third ring groove  32 . 
     The valve piston  22  is configured so that it can be flowed through and it includes a channel system  35  which can be flowed through by the hydraulic fluid. A supply channel  37  of the channel system  35  is provided along a longitudinal axis  36  of the valve piston  22 , wherein a first channel group  38 , a second channel group  39  and a third channel group  40  traverse the supply channel  37  respectively axially offset from one another. The first channel group  38 , the second channel group  39  and the third channel group  40  are flow connected with one another through the supply channel  37 , so that hydraulic fluid for example from the first channel group  38  can flow through the supply channel  37  into the second channel group  39  and/or the third channel group  40 . A channel group in this embodiment respectively includes two transversal bore holes that intersect each other and that are positioned perpendicular relative to one another, wherein the transversal bore holes are configured so that they extend over a diameter D of the valve piston  22  so that they penetrate the valve piston  22  in its entirety. By the same token the channel group could also include a different number of transversal bore holes. 
     At ends of a first channel group  38  which ends are oriented towards an enveloping surface  41  of the valve piston  22 , of the second channel group  39  and of the third channel group  40  the valve piston  22  respectively includes an annular groove, this means a positioning groove  42 , a fifth ring groove  42   a , and a sixth ring groove  42   b  wherein the ends of the first channel group  38  lead into the positioning groove  42 , the ends of the second channel group  39  lead into the fifth ring groove  42   a  and the ends of the third channel group  40  lead into the sixth ring groove  42   b . In the positioning groove  42  a first check valve  43  is received, whose closure element is configured band shaped. A check valve with a band shaped closure element is known and can be derived e.g. EP 1 703 184 B1. It is appreciated that a check valve per definition includes a housing and a closure element opening or closing the flow through opening of the housing. In case of a band shaped closure element walls that define the flow through opening can be used to form the housing for the band shaped closure element as illustrated in the embodiment. Therefore the first check valve  43  is subsequently interpreted as the closure element and vice versa. 
     The first closure element  43  prevents an inflow of the hydraulic fluid from the first ring groove  30 , from the second ring groove  31  and from the third ring groove  32  into the first channel group  38 . On the other hand side the first check valve  43  opens when hydraulic flows through the first channel group  38  from the supply channel  37 . Put differently, the first check valve  43  closes in a direction towards the supply channel  37  and opens in a direction towards the ring grooves  30 ,  31 ,  32 . 
     A second check valve  4  is provided outside of the valve housing  21  between the supply connection P and the oil pump in order to prevent a back flow of the hydraulic fluid into the oil pump. 
     The first valve position of the hydraulic valve  20  illustrated in  FIG. 2  corresponds to a valve position in an unpowered condition of the linear actuator  25 . In this condition the fifth ring groove  42   a  at least partially covers the second ring groove  31 , so that the hydraulic fluid from the first pressure cavities  11  can flow through the first hub bore holes  17 , the first operating connection A and the second ring groove  31  into the fifth ring groove  42   a  and further into the second channel group  39 , provided a first pressure in the first pressure cavities  11  exceeds a second pressure that is provided in the channel system  35 . The hydraulic fluid flowing out of the second ring groove  31  is separated into a first fluid flow and second fluid flow while providing pressure compensation. The first fluid flow can flow out of the second ring groove  31  due to the partial overlap of the fifth ring groove  42   a  and the second ring groove  31  through a first gap  44   a  into the first tank access T 1  according to the arrow direction PR 1 , c.f.  FIG. 3 , wherein the first gap  44   a  is configured in the portion between the second face  26  and the fifth ring groove  42   a  between the enveloping surface  41  and a valve inner surface  49  of the valve housing  21 . The gap  44   a  is configured in sections over the circumference of the valve piston  22 . 
     The second fluid flow flows according to the second arrow direction PR 2  into the second channel group  39  and from there into the supply channel  37  wherein the fluid flow moves into the third ring groove  32  through the first check valve  43 . The third ring groove  32  is covered in this valve position at least partially by the positioning groove  42 , so that the inflow of the hydraulic fluid from the first channel group  38  can be provided through the positioning groove  42  into the third ring groove  32 . The hydraulic fluid flowing out of the supply connection P onto the first check element  43  flows through a third gap  44   e  which is configured in the first valve position between the positioning groove  42  and the inner valve surface  49  according to the third arrow direction PR 3  into the third ring groove  32 . 
     The hydraulic fluid thus moves through the second operating connection B into the second hub bore holes  18  which are connected with the second pressure cavities  12 , so that the pressure in the second pressure cavities increases and the drive wheel  3  is rotated counter clock wise relative to the stator  2 . 
     As soon as the camshaft due to its switching torques tends to rotate into the intended adjustment direction, the pressure in the first pressure cavities  11  increases. When this pressure is large enough so that the preloaded first check valve opens sufficient hydraulic fluid is provided through the second operating connection B to the second pressure cavities  12  which have a suction effect due to a vacuum so that a rotation of the rotor  10  is provided. A fast rotation is provided that could not be provided by the oil pump alone. 
     A second valve position can be adjusted by providing power to the linear actuator  25 . The valve piston  22  is pushed into its end position against a force of the retaining element  27  in a direction towards the first tank access T 1 . In this end position the second face  26  contacts the hollow cylinder  28 . Thus the valve piston  22  was axially moved far enough so that the overlap of the fifth ring groove  42   a  and the second ring groove  31  is removed so that the second ring groove  31  is closed by the enveloping surface  41 . 
     Due to the axial movement of the valve piston  22 , an overlap is provided between the positioning groove  42  and the second ring groove  31  and the first ring groove  30  so that an overflow of the hydraulic fluid is provided from the supply connection P into the first operating connection A. Furthermore at least a partial overlap of the sixth ring groove  42   b  and the third ring groove  32  is provided. The hydraulic fluid which now flows from the second operating connection B separates into a third fluid flow and a fourth fluid flow, wherein the third fluid flow can enter the first channel groove  38  through the third channel group  40  and the supply channel  37 . 
     After opening the first check valve  43  the third fluid flow continues to flow from the positioning groove  42  into the second ring groove  31 . The fourth fluid flow flows through a second gap  44   b  that is configured between the valve inner surface  49  and the enveloping surface  41  into the second tank connection T 2 . 
     This context and the basic principle of the hydraulic valve  20  are also described in more detail in DE 10 2010 019 004 A1 so that they are not described herein in more detail. 
       FIG. 4  illustrates the valve piston  22  in a longitudinal sectional view along the longitudinal axis  36  in three dimensions. The positioning groove  42  is configured in steps so that in its radial extension a first shoulder  51  is configured at a first wall  50  that is oriented towards its first face  26  and a second shoulder  53  is configured at its second wall  52  that is arranged opposite to its first wall  50 , so that the positioning groove  42  has a first axial extension E 1  and a second axial extension E 2 , wherein the first axial extension E 1  is configured smaller than the second axial extension E 2 . 
     The first check valve  43  is received in the portion of the positioning groove  42  which has the first extension E 1 , wherein the first wall  50  and the second wall  52  are used for axially securing the check valve  43 . Axial end portions of the band shaped closure element of the check valve  43  overlap each other slightly so that an opening pressure can be kept small. 
     In order to limit a radial expansion of the check valve  43  or the closure element of the check valve  43  an annular limitation element  45  which envelops the check valve  43  is arranged at the valve piston  22 . The limitation element  45  is illustrated in more detail in a perspective view in  FIG. 5 . The limitation element  45  is made from a band  45   d  which includes transversal struts  45   c  of the band  45   d  between a first longitudinal strut  45   a  of the band  45   d  and a second longitudinal strut  45   b  of the band  45   d , wherein the transversal struts  45   c , the first longitudinal strut  45   a  and the second longitudinal strut  45   b  are configured so that they connect with each other. 
     In order to position the limitation element  45  at the valve piston  22  and thus to envelop the first check valve  43  the band shaped limitation element  45  is bent so that a first band portion  46  and a second band portion  47  overlap one another and the band  45   d  contacts the valve piston  22  like a ring. 
     Between the transversal struts  45   c  and the longitudinal struts  45   a ,  45   b  pass through openings  48  of the limitation element  45  are configured rectangular for a free pass through of the hydraulic fluid in this embodiment. 
     The limitation element  45  can be also made from a band shaped perforated sheet material, to that the limitation element  45  that is provided with numerous pass through openings  48  is configured similar to a sieve. Additional modifications of the limitation element are conceivable, wherein the pass through openings  48  have to be configured so that a pressure loss which can be provided by the limitation element  45  in the flow path of the hydraulic fluid from the first channel group  38  into the positioning groove  44  is kept as small as possible or so that it is eliminated. 
     The limitation element  45  is arranged at the valve piston  22  so that it is supported at the first shoulder  51  and at the second shoulder  52  by the first longitudinal strut  45   a  or the second longitudinal strut  45 . Put differently the first longitudinal strut  45   a  and the second longitudinal strut  45   b  contact over their axial extension at least partially at the first shoulder  51  or the second shoulder  52  wherein the pass through openings  48  form a free flow cross section for the hydraulic fluid. A radial extension of the first check valve  43  is limited by the transversal struts  45   c , so that a contact of the first check valve  43  or the closure element of the check valve  43  with the inner valve surface is prevented. 
     An implementation of throttling the flow of the hydraulic fluid into the first tank access T 1  without axial force and into the second tank access T 2  is provided with a first throttle element  54  or a second throttle element  55 . The first throttle element  54  is provided between the fifth ring groove  42   a  and the second face  26  adjacent to the fifth ring groove  42   a  and the second throttle element  45  is provided between the sixth ring groove  42   b  and the first face  23  adjacent to the sixth ring groove  42   b . These throttle elements  54 ,  55  completely envelop the radial circumference of the radial valve piston  22 . 
     The first throttle element  54  and the second throttle element  55  include a polygon shaped radial circumference c.f. in particular  FIG. 6  so that over the radial circumference of the valve inner surface  49  alternatively the first gap  44   a  and a first seal surface  44   c  or the second gap  44   b  and the second seal surface  44   d  are configured by the first throttle element  54  or the second throttle element  55 . 
     The first throttle element  54  extends adjacent to the fifth ring groove  42   a  over an axial first length L 1  and the second throttle element  22   b  extends adjacent to the sixth ring groove  42   b  over an axial second length L 2 . In this embodiment the first length L 1  corresponds to the second length L 2 . By the same token the first length L 1  can deviate from the second length L 2 . The first length L 1  and the second length L 2  correspond to a desired throttle effect. 
     The polygon shaped radial circumference has the shape of a pentagon. It could also have the shape of another polygon wherein due to reducing the pressure loss the polygon shaped radial circumference of the first throttle element  54  and of the second throttle element  55  should not have less than 5 polygon edges. By the same token the number of the polygon edges should not exceed a certain number that is a function of the diameter D of the valve piston  22 . This would mean too little differentiation between the circular radial circumference of the valve piston  22  so that an outflow of the hydraulic fluid through the first tank connection T 1  and the second tank connection T 2  would be throttled too much. As illustrated in particular in  FIGS. 2 and 3  the first gap  44   a  is provided by the first polygon shaped throttle element  54 . This first gap  44   a  does not extend over the entire radial circumference of the valve piston  22  but the first throttle element  54  partially contacts the valve inner surface  49 , thus the first gap  44   a  is only formed in sections. 
     In the portion of the sixth ring groove  42   b  a second gap  44   b  is implemented through the polygon shaped radial circumference of the second throttle element  55  so that the hydraulic fluid can Flow in a throttled manner from the third channel group  40  over the second gap  44   b  into the second tank access T 2 . 
     REFERENCE NUMERALS AND DESIGNATIONS 
       1  pivot motor adjustment device 
       2  stator 
       3  drive gear 
       4  stator base element 
       5  inner side 
       6  bar 
       7  intermediary cavity 
       8  lobe 
       9  rotor hub 
       10  rotor 
       11  first pressure cavity 
       12  second pressure cavity 
       13  first face 
       14  outer enveloping surface 
       15  second face 
       16  inner wall 
       17  first hub bore hole 
       18  second hub bore hole 
       20  hydraulic valve 
       21  valve housing 
       22  valve piston 
       23  first face 
       24  plunger 
       25  linear actuator 
       26  second face 
       27  retaining connection 
       28  hollow cylinder 
       29  housing face wall 
       30  first ring groove 
       31  second ring groove 
       32  third ring groove 
       33  ring groove 
       34  housing wall 
       35  channel system 
       36  longitudinal axis 
       37  supply channel 
       38  first channel group 
       39  second channel group 
       40  third channel group 
       41  enveloping surface 
       42  positioning groove 
       42   a  fifth ring groove 
       42   b  sixth ring groove 
       43  first check valve 
       44   a  first gap 
       44   b  second gap 
       44   c  first seal surface 
       44   d  second seal surface 
       44   e  third gap 
       45  limitation element 
       45   a  first longitudinal strut 
       45   b  second longitudinal strut 
       45   c  transversal strut 
       45   d  band 
       46  first band portion 
       47  second band portion 
       48  pass through opening 
       49  inner valve surface 
       50  first wall 
       51  first shoulder 
       52  second wall 
       53  second shoulder 
       54  first throttle element 
       55  second throttle element 
     A first operating connection 
     B second operating connection 
     D diameter 
     DI inner diameter 
     E 1  first axial extension 
     E 2  second axial extension 
     L 1  first length 
     L 2  second length 
     P supply connection 
     PR 1  first arrow direction 
     PR 2  second arrow direction 
     PR 3  third arrow direction 
     T 1  first tank access 
     T 2  second tank access