Abstract:
A rotary feedthrough for a device to inflate and deflate a tire on a tractor wheel has a housing ( 13 ) with an inner member ( 28 ) arranged at a radial distance within the housing. The radial gap is bridged by two radially distanced closing elements ( 18, 22 ). The inner member ( 28 ) is supported in the closing elements ( 18, 22 ). Two seal combinations, including respectively, a first sealing ring ( 35 ) and a second sealing ring ( 41 ), are arranged mirror-invertedly to the inner member ( 28 ). The first sealing rings ( 35 ), with a first sealing face ( 36 ), abut a counter sealing face ( 21 ) or ( 25 ) of the closing elements ( 18, 22 ), respectively. Each first sealing ring ( 35 ) can be moved axially along the longitudinal axis Y. Each first sealing ring ( 36 ) is fixed rotationally to the inner member ( 28 ). Each first sealing ring ( 35 ) is acted upon by a second sealing ring ( 41 ). An annular edge of a sealing portion ( 43 ) abuts the second sealing face ( 36 ) of the first sealing ring ( 35 ) and presses the same against the counter sealing face ( 21 ) or ( 25 ), respectively, under the pressure present in the chamber K.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority to German Patent Application No. 10208024.0 filed Feb. 26, 2002, which application is herein expressly incorporated by reference.  
         FIELD OF THE INVENTION  
         [0002]    The invention relates to a rotary feedthrough for a device to inflate a tire on a vehicle wheel, especially a tractor wheel.  
         BACKGROUND OF THE INVENTION  
         [0003]    In tractors, a change in tire pressure is especially important. When working in the field, a lower tire pressure provides a lower ground compaction and higher traction. At high speeds, e.g. 40 km/h, tractors with low tire air pressure generally have a driving instability. In the trade paper, profi-magazin for agricultural technology, 10/1995 “The air pressure in the tire: Small causes, large effects” different regulating devices are found. According to this, the rotary feedthroughs are arranged on the wheel flange according to the axle type either on the inner side or the outer side of the wheel. In less expensive systems, the air feed is carried out passed the outside of the tire up to the rotary feedthrough. In an arrangement with an intermediate flange between the wheel and the wheel flange the attachment of the rotary feedthrough is achieved via the wheel screws. This embodiment has an advantage since conduits are not exposed to the outside. However, the critical screw connection is loaded even higher by the enlarged free bending length of the wheel screws.  
           [0004]    U.S. Pat. No. 4,804,027 describes a device for inflating and deflating a tire on a wheel of a vehicle fillable with air. The device is integrated into the wheel hub, which supports the wheel flange. The wheel hub forms the outer member with a channel, to which a connection line is connectable, which leads to the tire. An inner member is supported in the hub. The inner member is kept stationary and is connected to a pressure source. Two seals are non-rotatably arranged on the inner member and distanced from each other. The two seals together with a valve arrangement enclose an annular chamber. The valve arrangement includes a spring loaded valve. The valve is opened when a predetermined pressure is exceeded in the chamber. This allows the air to flow into the channel of the wheel hub. The valve, however, is formed so that it only opens when the seals abut the corresponding bore face of the wheel hub lying radially to the outside. The seals are always pressed against the corresponding counter face of the wheel hub with the total pressure that is present to inflate the tire. At high relative speeds this is disadvantageous. At high speeds, the high pressure leads to a high friction and, therefore, also to a corresponding high wear of the seals. A further disadvantage is that the hub and the inner member are supported independently from each other on a further component. Thus, radial deviations completely act on the seals.  
           [0005]    DE OS 1 605 743 describes a device that controls the tire pressure in vehicles. It describes a rotary feedthrough with an outer member and an inner member. The outer and inner members are rotatably sealed relative to each other and are sealed with contact seals towards each other and constantly carry out a relative movement.  
           [0006]    A tire inflating device is also described in DE-OS 1 907 082. This reference discloses that it is necessary for vehicles with relative high circumferential speeds, to switch off the rotary feedthrough during normal operation. Accordingly, during the non-actuation of the tire inflating device, no pressure is present. This eliminates problems that arise at the seal elements of the rotary connection. This problem is especially obvious, when large relative speeds are present, as is the case in the usage in tractors.  
           [0007]    In all the arrangements described above and belonging to the State of the Art, the seals, which are formed as soft seals, have a high wear at their seal lips, which leads to a short life span.  
         SUMMARY OF THE INVENTION  
         [0008]    The invention has an object to provide a rotary feedthrough where a secure seal is achieved over a long life span.  
           [0009]    This object is solved by a rotary feedthrough for a device to inflate and deflate a tire on a vehicle wheel, especially a tractor wheel, which includes a housing with a housing bore centered on a longitudinal axis. The housing bore forms an inner face. Also, the housing has a first connection bore. An inner member is arranged in the housing bore. The inner member has an outer face arranged to be radially distanced to the inner face. Two closing elements are axially arranged with a distance between each other. The closing elements bridge the radial distance between the inner face of the housing and the inner member. The closing elements rotatably support the housing and the inner member around each other. The closing elements along with the housing and inner member enclose a chamber and form a counter sealing face towards the chamber. At least one closing element is a separate component from the housing and the inner member. A sealing arrangement is positioned in the chamber. The sealing arrangement has, per each closing element, a first sealing ring. The sealing ring has a radially extending first sealing face to axially sealingly abut the counter sealing face of the corresponding closing element. The sealing ring has a second sealing face that extends parallel to the first sealing face and is axially displaceably guided along the longitudinal axis. The sealing arrangement has, per each closing element, a second sealing ring. The second sealing ring has an annular actuating portion and an attached annular membrane-like sealing portion. An annular edge, distanced from and facing away from the actuating portion, axially abuts the second sealing face of the first sealing ring.  
           [0010]    An advantage of this construction is that between the two sealing rings, formed as soft seals, and the two sealing faces of the first sealing rings no difference in the number of revolutions is present. Thus, the sealing rings practically show no wear. The first sealing rings are stable in shape and have a flat first sealing face and are preferably made from a form stable plastic. The corresponding counter sealing face of the mating closing element abuts the flat first sealing face. Also, a design with a base ring made from plastic or metal is possible. Here, the ring has a coating at least on the first sealing face. The first sealing rings seal the radial gap towards the closing element. The second sealing rings seal the axial gap between each first sealing ring and the component, to which the second sealing rings are arranged. The sealing portion of the second sealing ring acts upon the first sealing ring in the axial direction to abut the counter sealing face of the mating closing element. This is achieved by the pressure present in the chamber. The first sealing ring is displaceably arranged along the longitudinal axis. Thus, it is kept in abutment with the closing element to achieve wear compensation. The sealing portion of the second sealing ring can be formed such that its free annular edge, which abuts the second sealing face of the first sealing ring, even at the desired wear compensation effectively abuts the second sealing face of the first sealing ring.  
           [0011]    Preferably, the components belonging to the sealing arrangement in the chamber, namely the first sealing rings and the second sealing rings, are arranged on the inner member. The first sealing rings are attached axially displaceable and the second sealing rings with their attachment portion are fixed on the inner member. The first sealing rings are rotationably fixed to the inner member around the longitudinal axis to achieve distinctive movement relationships. Thus, a relative movement in the circumferential direction produced between the first sealing ring and the second sealing ring should be prevented.  
           [0012]    In cases where the closing elements are connected to the housing, the arrangement of the sealing arrangement is on the inner member. Here, one closing element is integrated into the housing and the other closing element is detachably connected to the housing. The detachable arrangement of one closing element is necessary to be able to mount the components belonging to the rotary feedthrough.  
           [0013]    The first sealing face of the first sealing ring is formed as an annular face. The first sealing ring has a small diameter and a large diameter. The first sealing ring, furthermore, has an inner diameter and an outer diameter. In the arrangement of the first sealing ring in the inner member, the small diameter is equal to or larger than the inner diameter and that the large diameter is equal to or smaller than the outer diameter. Thus, the first sealing face is smaller than an annular face limited by the inner diameter and the outer diameter. The abutment relationships with reference to the abutment of the first sealing ring with its first sealing face on the counter sealing face of the corresponding closing element is such that under the existing pressure conditions in the chamber no excess loading and no excessive wear is present, however, the necessary sealability is achieved. The pressure, acting on the annular face of the first sealing ring, which limits the relief chamber, acts against the pressure of the sealing portion of the second sealing ring. The residual face of the second sealing face of the first sealing ring, which is not covered by the sealing portion of the second seal, is acted upon by the same pressure as the chamber. By changing the position of the first sealing face in the radial direction by a means of different size lay-out of the small diameter and corresponding change of the large diameter to achieve the same area, the resulting abutment forces of the first sealing ring with its first sealing face against the corresponding counter sealing face and resulting surface pressure can be changed.  
           [0014]    In one embodiment of the invention, the arrangement of the first sealing ring on the inner member and the lay-out of the larger diameter to a value smaller than the outer diameter forms a relief chamber between these and the counter sealing face of the corresponding closing element. The relief chamber is connected to the chamber. Thus, the relief chamber is acted upon by the same pressure. In this arrangement, the first sealing face is always smaller than the face limited by the inner diameter and the outer diameter. To keep the friction small with reference to the support of the inner member in the housing small, a friction bearing element is arranged, respectively, to the closing elements.  
           [0015]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0017]    [0017]FIG. 1 shows a sectional view of a tractor wheel arranged to an axle housing of a tractor;  
         [0018]    [0018]FIG. 2 shows a longitudinal sectional view of a rotary feedthrough according to the invention with a first embodiment of first sealing rings;  
         [0019]    [0019]FIG. 3 shows a half longitudinal sectional view of a first sealing ring according to the embodiment of FIG. 2; and  
         [0020]    [0020]FIG. 4 shows a half longitudinal sectional view of a second embodiment of the first sealing ring. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0022]    The tractor wheel  1  represented in FIG. 1 includes a wheel rim  2 , a wheel center member  3  supporting the wheel rim  2  and a tire  4  on the wheel rim  2 . The inner chamber  5  is enclosed by the tire  4  and the wheel center member  3 . The tractor wheel  1 , arranged on the axle body  6  of a tractor, is only partially represented. It is especially mounted on the flange  8  of the axle shaft  7 . The rotary feedthrough  9  is arranged relative to the wheel center member  3 . The inner member is kept stationary by a holder  10  attached, for example, to the axle body  6 . The outer member of the rotary feedthrough  9  rotates with the tractor wheel  1 . The valve  11  is attached to the outer member of the rotary feedthrough  9 . This valve  9  is connected by an air duct  12  to the inner chamber  5 . The feed of air pressure is achieved through the holder  10  to the rotary feedthrough  9  and therefrom by the valve and the air duct  12  to the inner chamber  5 .  
         [0023]    The design of the rotary feedthrough  9  is described in detail by means of FIGS.  2  to  4 .  
         [0024]    The rotary feedthrough  9  includes housing  13  with a bore  14  as well as a housing bore  15 . The bore  15  has an enlarged diameter compared to the bore  14 . The housing bore  15  is open to the left front face of the housing  13 . In the area of the housing bore  15  a first connection bore  16  is provided. The connection bore  16  extends through the wall of the housing  13  in the area of the housing bore  15 . The connection bore  16  connects with the valve, shown in FIG. 1.  
         [0025]    Slip-ring transmitters  17  are arranged in the housing  13 . The slip-ring transmitters  17  serve to transmit signals to the valve. The housing bore  15  is closed by a first closing element  18 . The closing element  18  supports a first friction bearing element  19  within the first bearing bore  20 . A second closing element  22 , which is a separate component from the housing  13 , closes the other end of housing bore  15 . The first closing element  18  forms a first counter sealing face  21 . The second closing element  22  has a second counter sealing face  25  that opposes the first sealing face  21 . The second closing element  22  supports a second friction bearing element  23  in the second bearing bore  24 . A seal  26 , in the form of an O-ring, is mounted in a groove of the housing  13 . The seal  26  serves to seal between the second closing element  22  and the housing  13 . The two closing elements  18 ,  22  are arranged with an axial distance between each other. The second closing element  22  is detachable from the housing  13 . The second closing element  22  is kept in its axial position by a retaining ring  27 .  
         [0026]    The inner member  28  is supported in the housing  13 . The inner member  28  has an air channel  29 . Air channel  29  leads to the chamber K, enclosed by the housing  13 , the inner member  28  and the two closing elements  18 ,  22 . The pressurisation of the chamber K is achieved, via the air channel  29 , by a compressed air reservoir or a compressor, not represented, and mounted stationarily on the tractor. The inner member  28  has a portion which sits in the bore  14 . The portion includes components belonging to the slip-ring transmitter  17  for the transmission of signals.  
         [0027]    The inner member  28  has a first seat face  30  in the area of the first closing element  18  and a second seat face  31  closes to the second closing element  22 . The inner member  28  has a first bearing face  32  reduced in diameter compared to the first seat face  30  and the second seat face  31  and a second bearing face  33 . The inner member  28  is supported by the first bearing face  32  in the first bearing bore  20  of the first friction bearing element  19 . The inner member  28  is supported by the second bearing face  33  in the second bearing bore  24  of the. second friction bearing element  23  belonging to the second closing element  22 . A first sealing ring  35  and a second sealing ring  41  are arranged on the first seat face  30  and the second seat face  31 , respectively, in a mirror-inverted arrangement. The two first sealing rings  35  are formed according to FIG. 3.  
         [0028]    The further description of the first sealing rings  35  is made with reference to FIG. 3. The two first sealing rings  35  together with the first sealing face  36  interact with the corresponding first counter sealing face  21  or second counter sealing face  25 , respectively. Parallel to the radially extending first sealing face  36  the first sealing ring  35  has a second sealing face  37 . The second sealing face  37  is facing away from the first sealing face  36  and has a larger area than the first sealing face  36 . The first sealing rings  35 , according to FIGS. 2 and 3, have a first sealing face  36  which has a small diameter DK, which corresponds to the inner diameter DI of the first sealing ring  35 .  
         [0029]    The first sealing rings  35  are arranged with the bore  39  with the inner diameter DI on the first seat face  30  or the second seat face  31 , respectively, such that they are adjustable in the axial direction along the longitudinal axis Y, in rotational direction. However, the sealing rings  35  have to rotate around the axis Y together with the inner member  28 . This can be achieved, for example, by the arrangement of one or more axially extending grooves  45  in the first sealing ring  35 . The grooves  45  interact with a not represented wedge, partially embedded in the first seat face  30  and the second seat face  31  and extending parallel to the longitudinal axis Y.  
         [0030]    As the large diameter DG of the first sealing ring  35  is smaller than the outer diameter DA of the first sealing ring  35 , a relief chamber  38  is formed between the first counter sealing face  21  and the second counter sealing face  25  and the first sealing rings  35 . These relief chambers  38  are connected to the chamber K since the outer diameter DA of the first sealing rings  35  is smaller than the diameter of the housing bore  15 . A pressure present in the chamber K is also present in the relief chambers  38 . The annular face between the large diameter DG and the outer diameter DA in the area of the chamber tries to lift off the first sealing rings  35  from the corresponding counter sealing face  21  or  25 , respectively, under the influence of the pressure, present in the chamber K. The first sealing rings  35  are however acted upon by the preloading force of the sealing portions  43  of the second sealing rings  41  and by the pressure acting on these sealing portions  43  in the chamber K, so that their first sealing face  36  are correspondingly pressed against the counter sealing face  21  or  25 , respectively. Thus, the residual face acts practically in a non supporting way outside of the annular edge of the sealing portion  43  to the outer face  40  with the outer diameter DA. Thus, in the area of the relief chamber  38  a correspondingly large area acting in a reliefing way is produced. This is, however, different, when the large diameter DG of the first sealing face  36  corresponds in size to the outer diameter DA of the first sealing ring  35 .  
         [0031]    The two second sealing rings  41  are fixed with their attachment portion  42  on the first seat face  30  or the second seat face  31 , respectively. The sealing portion  43  is attached near the corresponding seat face  30  or  31  and extends in an inclined way in the direction of the second sealing face  37 . The sealing portion  43  abuts the second sealing face  37  with a predefined preloading. If this preloading is not sufficient, springs can be provided, which press the two first sealing rings  35  into abutment with the corresponding counter sealing faces  21  or  25  of the closing elements  18  or  22 , respectively. Since the two second sealing rings  41  and the corresponding first sealing rings  35  are fixed to the inner member  28 , no relative rotation is produced between the two. The sealing portions  43  of the two second sealing rings  41  enable a specific axial path. Thus, during wear of the first sealing faces  36  of the two first sealing rings  35  an adjustment in the axial direction by the allowed wear X is possible.  
         [0032]    Then, when the inner member  28  experiences a relative rotational movement around the longitudinal axis Y compared to the housing  13 , no relative movement is produced in the rotational direction between the annular edge and the second sealing face  37 . The annular edge of the sealing portion  43  of the second sealing ring  41 , in rotational direction around the longitudinal axis Y, is relatively soft compared to the second sealing face  37  of the first sealing ring  35 . The wear takes place at the first sealing face  36 . The wear compensation by the allowed amount X, which the sealing portion  43  also undergoes, enables a high life span.  
         [0033]    The pressure conditions of the first sealing ring  35  with its first sealing face  36  against the first counter sealing faces  21  or  25 , respectively, can be varied, on the one hand, by size. The area of the first sealing face  36  and its radial arrangement between the inner diameter DI and the outer diameter DA can be altered. With the same size of the first sealing face  36 , as in FIG. 3, an arrangement according to FIG. 4 can be chosen, so that a first sealing face  136  is achieved.  
         [0034]    The first sealing face  136  is formed as an annular face and has the same area as the sealing face  36  in the embodiment according to FIG. 3. However, it is arranged on a different diameter. The small diameter DK is larger than the inner diameter DI and the large diameter DG is, with consideration of the area, correspondingly larger than the small diameter DK. Therefore, the relief chamber  138  acted upon by the pressure in the chamber K, the annular face remaining to the outside, is reduced. The face, acting in a relief way, between the large diameter DG and the outer diameter DA is smaller than that in the embodiment according to FIG. 3. The pressure acting on the annular sealing portion  43  of the second sealing ring  41  and the residual face between the outer annular edge of the sealing portion  43 , with which the second sealing ring  41  abuts the second sealing face  137 , and the outer diameter DA of the outer face  140  leads to a higher surface pressure on the first sealing ring  135  with its first sealing face  136  against the corresponding counter sealing face of the two closing elements, than it is the case in the embodiment according to FIG. 3. According to the desired pressing conditions, the first sealing face  136  can be displaced radially to the outside of the longitudinal axis Y in such a way, that its larger diameter DG corresponds to the outer diameter DA, so that practically the complete face of the sealing portion and the residual face, if provided, produce a high pressing force under the pressure, as no relief chamber is produced.  
         [0035]    From FIGS. 3 and 4 it is visible that two first sealing rings  35 ,  135  include a reinforcement inlay  44 ,  144  for reinforcement. The inlays  44 ,  144  enable a high stability to ensure that the first sealing face  36  or  136 , respectively, over a long life span provide an exact abutment to the corresponding counter sealing face. In the extreme case the reinforcement inlay  44 ,  144  can be formed as a metal plate ring. The plate ring is provided with a low friction coating made from synthetic material, which can be machined in the area of the two sealing faces  36 ,  136  or  37 ,  137 , respectively.  
         [0036]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.