Abstract:
A rotary feedthrough for a compressed air supply system is provided between a stator and a rotor rotating relative to this stator. A compressed air channel disposed in the stator is connected to a compressed air line and leads into an annular chamber formed in the rotor, from which at least one working channel leading to a consumer proceeds. The stator is connected in the region of the rotary feedthrough to a control line. A moment of friction occurring in the region of the rotary feedthrough resulting in premature wear is reduced by providing a switchable non-return valve in the annular chamber. Blocking elements which extend within the annular chamber concentrically to the rotational axis of the rotor are moveable into an open position by an actuating element, which is displaced from the stator in the direction of the blocking elements.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     The invention described and claimed hereinbelow is also described in German Priority Document DE 10 2013 105890.6, filed on Jun. 7, 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). 
     The invention relates to a rotary feedthrough for a compressed air supply system positioned between a stator and a rotor rotating relative to this stator. A compressed air channel disposed in the stator is connected to a compressed air line and leads into an annular chamber formed in the rotor, from which at least one working channel leading to a consumer proceeds. The stator is connected in the region of the rotary feedthrough to a control line. 
     Rotary feedthroughs are used in order to transfer gaseous or liquid media between two components that are rotating relative to one another. In the case of a gaseous medium, this gaseous medium can be pressurized or can be transferred with an underpressure. In the latter case, a vacuum can be transferred via the rotary feedthrough. The components are usually a stationary component, which is referred to in the following as a stator, and a component rotating relative thereto, which is referred to as a rotor. It is also possible for the two components to be rotatably driven at different speeds or in opposite directions. 
     Such rotary feedthroughs are used on agricultural working vehicles (e.g., tractors and self-propelled harvesting machines), for tire pressure control systems in order to allow the pressure in the tires of the drive wheels to be changed during travel across a field or a road. During operation of the agricultural working vehicle on a field, the tire pressure is reduced, in particular, when the traction behavior of the tires should be improved due to certain ground conditions. In addition, the tire pressure can be lowered in order to reduce the ground compression resulting from the weight of the working vehicle as the ground contact surface of the tire is increased in this case. On the other hand, the tire pressure should be increased for road travel or for travel on a solid surface. The higher air pressure of the tires is required for road travel in order to achieve sufficient driving stability of the working vehicle and to reduce the tire wear overall. 
     A rotary feedthrough for a compressed air supply system is known from DE 10 2005 018 584 A1. This rotary feedthrough is used, within the framework of a tire filling system of an agricultural tractor, to transfer compressed air between a stator, which is connected to an axle body, and a rotor, which is provided on a wheel hub. In this case, a compressed air channel extending in the stator leads into a gap provided between the stator and the rotor, via which the compressed air can enter the working channel of the rotor in any position of the rotor. Two brush seals are disposed in the stator, concentrically to the longitudinal axis of the wheel hub. The brush seals seal the gap radially outwardly and radially inwardly. A control line connected to a control channel extends in the stator. 
     The control channel also is connected via a gap between provided the stator and the rotor to a control channel extending in the rotor. This connection is sealed off by concentrically extending brush seals. The brush seals disposed in grooves of the stator comprise metallic and/or non-metallic fibers or threads, the ends of which slide on the surface of the rotor facing these ends and thereby outwardly seal off the two intermediate spaces provided for the transfer of compressed air. A tire valve is provided in the tire, by which the tire is filled with compressed air from the working channel. In order to reduce the pressure in the tire, this tire valve is opened in a corresponding manner via the control channel until the intended tire pressure has been reached. 
     Document DE 10 2005 006 073 A1 makes known a rotary feedthrough having a design that substantially matches that of the rotary feedthrough according to DE 10 2005 018 584 A1. Seals are used in this case, however, instead of the brush seals disposed between the stator and the rotor. These seals have a U-shaped cross-section and are intended to be resiliently elastic. In the case of this previously known rotary feedthrough for a tire filling system as well, first compressed air channels for filling the tire are provided. The first compressed air channels communicate with one another via an annular chamber, and second compressed air channels are provided, which are designed as control channels and communicate with one another via a further annular chamber. The two U-shaped seals slide on the surfaces of the stator and the rotor that face one another. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the shortcomings of known arts, such as those mentioned above. 
     To that end, the present invention provides for reducing the moment of friction occurring in the region of a rotary feedthrough designed according to the conventional arts, such as that described above, wherein this moment of friction results in a temperature increase on the sliding surfaces of the seal and in the premature wear thereof. 
     The invention also provides a rotary feedthrough that can be produced in a more cost-favorable manner and that has a favorable installation-space requirement, as compared to those known in the conventional art. 
     In an embodiment, the invention provides a rotary feedthrough for a compressed air supply system disposed between a stator and a rotor rotating relative thereto, where a compressed air channel disposed in the stator is connected to a compressed air line and leads into an annular chamber formed in the rotor from which a working channel leading to a consumer proceeds and wherein the stator is connected in the region of the rotary feedthrough to a control line. Additionally, a switchable non-return valve is disposed in the annular chamber with blocking elements extending within the annular chamber concentrically to the rotational axis of the rotor. The blocking elements are moveable into an open position by an actuating element in this region, which is displaceable from the stator in the direction of the blocking elements. 
     The blocking elements used within the framework of the switchable non-return valve are therefore rotationally symmetrical. Consequently, in any position of the rotor that this rotor assumes relative to the stator, the actuating element impacts the blocking elements and can open these blocking elements in this region. As a result, a connection is established between the compressed air channel provided in the stator and the working channel disposed in the rotor. The connection allows the compressed air to flow into the working channel or to flow out of this working channel. Since the rotary feedthrough according to the invention does not establish a permanent connection between the two channels, which would have to be sealed by means of axial or radial sealing rings in this case, an increased moment of friction due to the actuating element engaging in the blocking elements takes effect only upon actuation of the switchable non-return valve. 
     The invention renders it possible to largely prevent wear and a temperature increase in the region of the rotary feedthrough. In addition, a corresponding rotary feedthrough can be produced cost-favorably within the framework of a large-quantity lot. Accordingly, the corresponding components can be favorably installed and removed, simplifying maintenance or repair work. 
     The inventive feedthrough arrangement also has the advantage that an axial offset that may occur between the stator and the rotor does not negatively affect the function of the rotary feedthrough. And, it is possible to arrange the components of the rotary feedthrough within the framework of a kinematic reversal such that the annular chamber is formed in the stator and accommodates the blocking elements of the is switchable non-return valve in a corresponding manner. As such, the actuating element is displaceably disposed in the rotor. 
     In contrast, documents DE 10 2005 018 584 A1 and DE 10 2005 006 073 A1 describe only a permanently acting sealing arrangement within the respective rotary feedthrough. The brushes or sealing lips of this sealing arrangement, which face in the axial direction, are guided on sliding surfaces of the rotor and of the stator. If corresponding rotary feedthroughs are formed with a large diameter, a considerable moment of friction occurs on a permanent basis, since this moment of friction increases over-proportionally to the diameter of the rotary feedthrough. This moment of friction also is considerably increased under the influence of the overpressure present in the rotary feedthrough when the corresponding floating-ring seals or brush seals are formed with a considerable diameter, which is usually the case. The overall friction that occurs on seals subjected to pressure has a negative effect on the efficiency of thusly equipped motor vehicles such that fuel consumption is increased. Furthermore, the known systems are very susceptible to interference in the case of axial offset of the stator and rotor, which rotate relative to one another, since this usually results in seal failure. 
     In contrast, the invention provides an embodiment wherein the annular chamber within the rotor is designed as a radial peripheral groove or as an end-face groove. When a radial peripheral groove is used, the actuating element extends radially to this peripheral groove and is radially displaced such that this actuating element engages into the blocking elements, which block the air flow, at points or across a small peripheral section. The actuating element opens these blocking elements, thereby allowing the compressed air to flow between the compressed air channel and the working channel. The compressed air channel and the working channel are therefore interconnected, during this phase, by the actuating element engaging into the blocking elements. As an alternative, the blocking elements are disposed in an end-face groove having an annular cross-section, wherein the actuating element is then displaced in the axial direction of the rotor in a corresponding manner, thereby allowing the actuating element to engage into the blocking elements and supply or block the compressed air. 
     In an embodiment, the actuating element comprises a longitudinally displaceable peg having a head piece and a control element, which cooperates with the control line. The head piece engages, radially or axially, into the blocking elements of the non-return valve in order to establish a connection between the compressed air channel and the working channel. The longitudinally displaceable peg can be embodied as a piston, for example, which is guided in a longitudinally displaceable manner in a housing of the actuating element affixed in the stator. On the end thereof facing the blocking elements of the switchable non-return valve, the corresponding head piece is preferably fastened by a threaded connection. As explained in detail in the following, this head piece has an outer contour that assists in opening the blocking elements without damaging these blocking elements or inducing a substantial moment of friction. 
     Furthermore, the head piece has a boat-like shape, wherein one tip of the boat-shaped head piece points in the direction of rotation and the other tip points opposite the direction of rotation. As a result, the boat-shaped head piece has a longitudinal extension that is greater than the width thereof. One keel of this boat-shaped head piece can have flat outer jacket surfaces and a narrower width. This keel has rounded edges or be pointed in the direction of rotation and opposite the direction of rotation. The head piece penetrates the blocking elements by this keel and therefore induces the exchange of compressed air between the compressed air channel and the working channel. 
     To this end, a longitudinal bore extending through the peg and the head piece of the actuating elements is provided. The compressed air channel leads into this longitudinal bore and, therefore, proceeding therefrom, a connection to the working channel is established by the corresponding actuating element. 
     The non-return valve also can be designed as a plate valve. The blocking elements of this plate valve are retained in the blocking position thereof. In the blocking position, the blocking elements bear against one another, in a sealing manner, due to an inherent preload and by the pressure that is present in the working channel and, therefore, in the annular chamber. The only way to eliminate this blocking effect in the corresponding region is by moving the actuating element against the blocking elements in that the head piece of the actuating element impacts the blocking elements. As a result, the blocking elements lift off of one another along the length of the aforementioned keel, whereupon the keel penetrates the gap that forms. Since the rotor is rotating at this time, this region becomes correspondingly displaced, whereby the blocking elements open in a zipper-like manner in front of the keel and close in a zipper-like manner behind the keel, as viewed in the direction of rotation. 
     To this end, the blocking elements are produced as cylindrical or circular rings disposed on side walls of the annular chamber and which block the flow of compressed air by the edges thereof that face one another. In the closed state of the plate valve, the adjoining ends of the circular or cylindrical rings extend toward one another in the shape of a “V”. In order to lift these ends off of one another, as explained above, the head piece is moved into the acute-angled region thereof formed by the rings. 
     In an embodiment, the control element embodies an annular piston connected to the peg. In order to displace the head piece in the direction of the blocking elements, this annular piston is acted upon, on at least one end face, by a control pressure from a control channel proceeding from the control line. The annular piston is spring-loaded by a return spring on an end face remote from the end face acted upon by the control pressure. Therefore, the peg is displaced together with the head piece by a control pressure. In this context, the peg is furthermore guided, in a sealing manner, in a receiving bore extending substantially along the same axis as a compressed air channel proceeding from the compressed air line. 
     As an alternative to the actuation of the peg and the head piece fastened thereon by a control pressure, the control element may comprise an electromagnetic actuator system, thereby making it possible to eliminate a separate connection for a control pressure. 
     The head piece, which tapers in the direction of the end thereof pointing toward the blocking elements, as described above, can have lateral jacket surfaces with a concave or convex contour, at least in sections, as viewed in a longitudinal sectional view. The shape of the head piece by which the blocking elements can implement this procedure with low friction and low wear in the region in which the head piece lifts these blocking elements off of one another is decisive. Moreover, it is advantageous to provide the head piece with a coating that reduces the friction occurring between the blocking elements and the head piece. 
     In an embodiment, the rotary feedthrough is provided for a tire pressure control unit of a motor vehicle, wherein the stator is fixedly disposed on an axle housing and the rotor is disposed on a wheel hub, which is rotating relative to the axle housing. As such, the air pressure in a tire of a drive wheel is adjusted during travel by the switchable non-return valve disposed within the annular chamber. To this end, the working channel provided in the rotor is connected to the tire via a working line. The tire pressure is increased or decreased during travel by means of the rotary feedthrough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  presents a longitudinal sectional view of a rotary feedthrough arrangement between a stator and a rotor configured according to the invention; 
         FIG. 2  presents a perspective representation of the rotary feedthrough depicted in  FIG. 1  to highlight an actuating element used in the rotary feedthrough; and 
         FIG. 3  presents a perspective view of the rotary feedthrough arrangement of  FIGS. 1 and 2  within a wheel drive of a motor vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
       FIG. 1  shows a stator  1 , in which a drive shaft  2  is supported via non-illustrated rolling bearings. The drive shaft  2  is connected on the drive side to a transmission, such as a final drive or a differential gear, and, on the output side, drives a drive wheel of the motor vehicle. Furthermore, a rotor  3  is disposed on the drive shaft  2 , for example, a wheel hub of the motor vehicle. Since a consumer  5  is supplied with a pressure medium or pressure medium will be removed from this consumer  5  by way of a compressed air source  4  disposed on the stator  1 , a rotary feedthrough  6  is disposed between the stator  1  and the rotor  3 , wherein this rotary feedthrough is the subject matter of this invention. 
     In this case, the compressed air is fed from the compressed air source  4  via a compressed air line  7  to the pressure-medium feedthrough  6 , wherein the pressure-medium feedthrough  6  comprises a compressed air channel  8 . This compressed air channel  8 , which is formed by a coupling  10  screwed into a housing  9  of the pressure-medium feedthrough  6 , extends into the interior of an actuating element  11 . The actuating element  11  comprises a tubular peg  12 , an annular piston  13 , and a head piece  14  connected to the peg  12 . The peg  12  is provided with a longitudinal bore  15  in the interior thereof. The longitudinal bore extends from the compressed air channel  8  to the head piece  14 . The head piece  14  has a connecting bore  16 , which terminates at an end of the head piece  14  remote from the peg  12 . The peg  12  extends, in the upper region thereof, in a guide bore  17  of the housing  9  and, in the lower region thereof, in a receiving bore  18  of a cover  19 , which closes the housing  9  in the axial direction. 
     A control channel  20  is located in the housing  9 , extends substantially parallel to the peg  12  and is connected to a control unit  22  via a control line  21 . The control line  21  extends into a pressure chamber  23 , which annularly encloses the peg  12  and is provided on one side of the annular piston  13 . In addition, the annular piston  13  comprises a piston ring  24 , by which the annular piston  13  is guided in a sealing manner in a cylinder  25  formed within the housing  9 . The annular piston  13  is acted upon, on the end face thereof remote from the pressure chamber  23 , by the force of a return spring  26 . The return spring  26  bears against a cover  19  at the other end thereof. The housing  9  comprises a mounting flange  27 , via which this housing is fixed on the stator  1  by screws  28 . 
     The rotary feedthrough  6  also has an annular chamber  29  formed in the rotor  3 , which is embodied as a U-shaped, radial peripheral groove of the rotor  3 . A switchable non-return valve  30  embodied as a plate valve  31  is disposed within the annular chamber  29 . The plate valve  31  comprises blocking elements  32  and  33 , which are assigned to the side walls  34  and  35 , respectively, of the annular chamber  29 . The two blocking elements  32  and  33 , which are embodied as profiled, annular rings  36  and  37 , each have a first radially extending section  38  and  39 , respectively, by which the blocking elements are affixed on said side walls  34  and  35  of the annular chamber  29 . Diagonally extending sections  40  and  41  proceed from the radially extending sections  38  and  39 , respectively, and extend toward one another, thereby forming an acute angle. These diagonally extending sections  40  and  41  form second radially extending sections  42  and  43 , which bear against one another in a sealing manner and therefore radially outwardly seal off the annular chamber  29 . Adjoining the annular chamber  29  is a working bore  44 , which first extends radially and then axially, into the end of which a coupling  46  connected to a working line  45  is screwed. The consumer  5  is connected to this working line  45 , to which said consumer compressed air shall be supplied or from which compressed air shall be removed during rotation of the rotor  3 . 
       FIG. 2  presents a perspective sectional representation of the arrangement of the rotary feedthrough  6  between the stator  1  and the rotor  3  to highlight the special configuration of the head piece  14 , which is connected to the peg  12  via a screw  47 . As shown, the head piece  14  has a boat-like shape. The head piece has a collar  48 , the longitudinal sides of which transition into a keel  50  via a concavely curved section  49 . 
     The function of the arrangement  6  shall now be described with reference to  FIGS. 1 and 2 . For example, when the objective is to convey compressed air from the compressed air source  4  into the consumer  5 , pressure is applied to the pressure chamber  23  proceeding from the control unit  22 , via the control line  21  and the control bore  20 . The annular piston  13  is therefore displaced in the direction of the cover  19  against the force of the return spring  26 . As a result, the peg  12  moves the head piece  14  radially in the direction of the blocking elements  32  and  33  of the switchable non-return valve  30 . The keel  50  is thereby guided between the second radially extending sections  42  and  43  of the rings  36  and  37 . Since, in this state, the rotor  3  rotates together with the drive shaft  2 , the engagement point of the keel  50  is continuously displaced between the blocking elements  32  and  33 . In this state, compressed air is fed via the longitudinal bore  15  of the peg  12 , subsequently enters the working channel  44  and is therefore fed to the consumer  5  via the working line  45 . 
     In this case, in which the head piece  14  engages via the keel  50  thereof into the switchable non-return valve  30 , compressed air can is directed out of the consumer  5  in the direction of the compressed air source  4  or a compressed air outlet. Once the entire procedure has ended, the pressure on the annular piston  13  is reduced and the peg  12  therefore moves the head piece  14  out of the engagement position thereof between the blocking elements  32  and  33 . As a result, the blocking elements  32  and  33 , which are embodied as rings  36  and  37 , once more bear against one another in a sealing manner, via the second radially extending sections  42  and  43  thereof, around the entire circumference. The pressure-medium connection is therefore blocked. 
       FIG. 3  illustrates the use of the rotary feedthrough  6  in a tire filling system of a motor vehicle, preferably an agricultural working vehicle. In this case, an axle tube  51  of the vehicle is embodied as a stator. A supported axle shaft  52  extends within this axle tube. This axle shaft  52  comprises a flange  53 , on the end thereof, upon which a wheel disk  54  of a rim  55  is fastened. In the complete state of the wheel, this rim  55  accommodates a non-illustrated wheel, which shall be filled with air or relieved of pressure. In addition, a wheel hub  56  is disposed on the axle shaft  52  in a rotationally locked manner, wherein the coupling  46  (as shown in  FIG. 1 ) proceeds from this wheel hub. This coupling connects the working line  45  to the working channel (explained by reference to  FIG. 1 ) while the working line  45  is connected to the rim  55 . As such, the working line extends into the interior of the tire or into the interior of a tube provided in the tire.  FIG. 3  also shows that the rotary feedthrough  6  is disposed on the axle tube  51  embodied as a stator, wherein this rotary feedthrough is designed as shown in  FIGS. 1 and 2  to provide this function. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  stator 
           2  drive shaft 
           3  rotor 
           4  compressed air source 
           5  consumer 
           6  rotary feedthrough 
           7  compressed air line 
           8  compressed air channel 
           9  housing of  6   
           10  coupling 
           11  actuating element 
           12  peg 
           13  annular piston 
           14  head piece 
           15  longitudinal bore 
           16  connecting bore 
           17  guide bore 
           18  receiving bore 
           19  cover 
           20  control channel 
           21  control line 
           22  control unit 
           23  pressure chamber 
           24  piston ring 
           25  cylinder 
           26  return spring 
           27  mounting flange 
           28  screw 
           29  annular chamber 
           30  switchable non-return valve 
           31  plate valve 
           32  blocking element 
           33  blocking element 
           34  side wall of  29   
           35  side wall of  29   
           36  ring 
           37  ring 
           38  first radially extending section of  36   
           39  first radially extending section of  37   
           40  diagonally extending section of  36   
           41  diagonally extending section of  37   
           42  second radially extending section of  36   
           43  second radially extending section of  37   
           44  working channel 
           45  working line 
           46  coupling 
           47  screw 
           48  collar of  14   
           49  concavely curved section of  14   
           50  keel of  14   
           51  axle tube 
           52  axle shaft 
           53  flange 
           54  wheel disk 
           55  rim 
           56  wheel hub 
       
    
     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.