Abstract:
An exhaust gas recirculation valve for an internal combustion engine includes a housing comprising an exhaust gas inlet and an exhaust gas outlet, and a valve closing body fastened to a valve rod. The valve rod is movable. A valve seat is arranged between the exhaust gas inlet and the exhaust gas outlet. A guide bushing comprising a first section guides the valve rod in the housing. A sealing ring is arranged at an end of the guide bushing remote from the valve closing body. The valve closing body is lowered onto the valve seat by a movement of the valve rod and lifted from the valve closing body by an opposite movement of the valve rod. A circumferential gap is formed between the valve rod and the guide bushing in the first section of the guide bushing directed toward the sealing ring.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
       [0001]    This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2011/063353, filed on Aug. 3, 2011 and which claims benefit to German Patent Application No. 10 2010 035 622.0, filed on Aug. 26, 2010. The International Application was published in German on Mar. 1, 2012 as WO 2012/025351 A1 under PCT Article 21(2). 
     
    
     FIELD 
       [0002]    The present invention relates to an exhaust gas recirculation valve for an internal combustion engine comprising a housing having an exhaust gas inlet and an exhaust gas outlet, a valve closing body, a valve rod on which the valve closing body is fixed and which can be moved by an actuator, a valve seat between the exhaust gas inlet and the exhaust gas outlet, wherein the valve closing body can be lowered onto said valve seat by moving the valve rod and the valve closing body can be raised from said valve seat by an opposing movement, a guide bushing via which the valve rod is guided in the housing, and a sealing ring which lies on the guide bushing end opposite the valve closing body. 
       BACKGROUND 
       [0003]    Exhaust gas recirculation valves for the recirculation of exhaust gas quantities adjusted to the respective operating state of the internal combustion engine in order to reduce environmentally harmful portions, in particular, nitrogen oxides, in the exhaust gas of an internal combustion engine are generally known and are described in a large number of applications. These exhaust gas recirculation valves typically comprise an actuator operatively connected with a valve rod which is guided in a housing of the valve by means of a guide bushing and comprises, at its end remote from the actuator, at least one valve closing body corresponding to a respective valve seat. Most such exhaust gas recirculation valves are configured such that, in the closed state of the valve, the guide bushing is located in the region containing fresh air and is separated from the exhaust gas side by the valve closing body. When the valve is opened (i.e., the valve closing body is lifted from the valve seat), however, exhaust gas flows in the direction of the intake pipe so that a connection is allowed between the exhaust gas, charged with soot or other caking and sticky substances, and the guide bushing, whereby, not least because of the temperature differences, accretions are formed on the valve rod and in the guide bushing, respectively, that can affect the functioning of the valve. 
         [0004]    Various suggestions have been made to avoid such accretions on the valve rod and in the guide bushing, but also in the interest of preventing functional disorders of electric components in the vicinity of the actuator, such as electromagnets, electric motors or potentiometers, by exhaust gas components. 
         [0005]    In order to avoid the ingression of dirt particles into the vicinity of the actuator, DE 103 36 976 describes providing a valve rod seal in the form of a radial sealing ring. Such a valve rod seal is, however, worn after a short operating time and thus loses its sealing function since accretions between the guide bushing and the valve rod cause scratching in the valve rod in the region adjacent to the sealing ring. These possibly sharp edges are passed along the sealing ring and may in turn cause small tears. Leakiness and/or jamming of the valve may result. 
         [0006]    Another form of sealing is described in DE 43 38 192 A1. With the valve disclosed therein, a rib is arranged in the region of the clean gas side, which rib is supposed to protect the guide body from thermal radiation and soiling. The valve rod is additionally connected with an elastic membrane that is to seal the control chamber from the exhaust gas outlet. Such a design is a rather complex structure, however, since a plurality of additional components must be used to seal the valve body. The provision of the sealing membrane, in particular, requires additional assembling effort and the production costs caused by a housing with a rib are higher than for a housing without a rib. Accretions moreover accumulate in the region between the guide bushing and the valve rod that lead to a jamming of the valve. 
         [0007]    A drawback of the known embodiments is that dirt particles entering between the guide bushing and the valve rod cause functional disorders of the valve by the formation of ridges or scratches in the valve rod or by the accretions themselves. This may also affect the protection of the actuator from dirt particles, resulting in malfunctions of the electric components. 
       SUMMARY 
       [0008]    An aspect of the present invention is to provide an exhaust gas recirculation valve where a long service life without malfunctions of the valve is provided and where the assembly effort is low. An alternative aspect of the present invention is to provide an exhaust gas recirculation valve where damage to the sealing elements and jamming by accretions or scratches in the valve rod is prevented. 
         [0009]    In an embodiment, the present invention provides an exhaust gas recirculation valve for an internal combustion engine which includes a housing comprising an exhaust gas inlet and an exhaust gas outlet, a valve closing body, and a valve rod to which the valve closing body is fastened. The valve rod is configured to be movable. A valve seat is arranged between the exhaust gas inlet and the exhaust gas outlet. A guide bushing comprising a first section is configured to guide the valve rod in the housing. A sealing ring is arranged at an end of the guide bushing remote from the valve closing body. The valve closing body is configured to be lowered onto the valve seat by a movement of the valve rod and to be lifted from the valve closing body by an opposite movement of the valve rod. A circumferential gap is formed between the valve rod and the guide bushing in the first section of the guide bushing directed toward the sealing ring. By forming a circumferential gap between the valve rod and the guide bushing in a first section of the guide bushing directed toward the sealing ring, friction between the valve rod and the guide bushing in said region is avoided. Scratches formed in this region that could cause the destruction of the radial sealing ring are therefore avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
           [0011]      FIG. 1  shows a sectional side elevational view of a detail of a first embodiment of an exhaust gas recirculation valve according to the present invention; and 
           [0012]      FIG. 2  shows a sectional side elevational view of a detail of a second embodiment of an exhaust gas recirculation valve according to the present invention 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In an embodiment of the present invention, the height of the gap can, for example, be larger or equal to the height of stroke of the valve closing body. It is thereby excluded that the section sliding in the guiding portion of the guide bushing, where scratches and edges could be formed due to their sliding directly on each other, can contact the sealing ring when the valve is closed. The tightness and the service life of the sealing ring are thereby increased. 
         [0014]    In an embodiment of the present invention, a guiding section of the guide bushing adjoins the first section, whose end facing toward the valve closing body is formed with a sharp edge. This sharp edge serves as a scraping edge at which accretions on the valve rod are sheared off as the valve is closed, whereby the intrusion of contaminations into the rather short sliding portion is largely avoided. 
         [0015]    In an embodiment of the present invention, the guiding section is joined by a third section in the direction towards the valve closing body in which a second gap is formed between the guide bushing and the valve rod, wherein the end of the guide bushing directed toward the valve closing member is provided with a constriction reducing the second gap. In this gap, dirt can accumulate without causing friction in the sliding portion which could lead to scratches in the rod or in the guide bushing. This section, which extends into the space through which exhaust gas flows, additionally serves as a shield for the valve rod. 
         [0016]    In an embodiment of the present invention, the axial ends of the guiding section can, for example, be provided with two guiding portions between which a further gap is formed. The sliding portion, in which friction could occur, is thus drastically reduced and additional space for collecting the accretions is created. A proper guiding of the valve rod is nonetheless provided by the two guiding portions. In an embodiment of the present invention, the guiding portions can, for example, be short in order to avoid larger friction surfaces. Jamming is thus easier to loosen. 
         [0017]    In an embodiment of the present invention, the axial height of the two guiding sections can, for example, be smaller or equal to the maximal height of stroke of the valve closing body, whereby, when the valve is in operation, dirt present in the guiding portion can be transported, respectively, into an area outside of the guiding portion. 
         [0018]    In an embodiment of the present invention, the two guiding portions are formed with a sharp edge at at least one of their axial ends. These edges serve as scraping edges by which dirt is sheared off from the valve rod as it moves, whereby an intrusion of dirt into the sliding portion is largely prevented. This, in turn, leads to reduced friction and to the avoidance of scratches. 
         [0019]    In an embodiment of the present invention, a circumferential recess can, for example, be formed in the valve rod, which, in the closed state of the exhaust gas recirculation valve, is situated immediately adjacent the guiding section or has a short overlap with the guiding section. This section of the valve rod also serves to receive sheared off dirt and thus serves to prevent damage by friction with particles situated in between. 
         [0020]    An exhaust gas recirculation valve is thus provided with which the functional disorders of the valve can be minimized by providing a long-lasting tightness along the valve rod and by largely avoiding dirt in the guiding portion subjected to friction, thereby further preventing a jamming of the exhaust gas recirculation valve. 
         [0021]    Two embodiments of exhaust gas recirculation valves according to the present invention are illustrated in the drawings and will hereinafter be described. 
         [0022]    The exhaust gas recirculation valve illustrated in  FIG. 1  is configured as a snap-in valve that can be installed in a manner known per se in a correspondingly formed opening in an exhaust gas recirculation duct. It comprises a housing  2  in which an exhaust gas inlet  4  and an exhaust gas outlet  6  are formed. 
         [0023]    A flow cross section to be controlled exists between the exhaust gas inlet  4  and the exhaust gas outlet  6 , which cross section is surrounded by a valve seat  8  arranged in the housing  2  and cooperating with a valve closing body  10 . The valve closing body  10  is fixedly mounted to a valve rod  12  which is slidably supported in a guide bushing  14  for translational movement therein. The valve rod  12  here is a chrome-plated part sliding in the guide bushing  14  of stainless steel which is fixed in the housing  2  in a correspondingly formed throughbore  16  with a shoulder  17 . This shoulder  17  secures the axial position of the guide bushing  14  in the throughbore  16  against a movement of the guide bushing  14  towards the valve closing body  10 . 
         [0024]    Within this throughbore  16 , a lip sealing ring  18  with a support ring  20  is arranged on the side of the guide bushing  14  opposite the valve closing body  10 . 
         [0025]    At the end of the valve rod  12  opposite the valve closing body  10 , a non-illustrated, in particular, electromotive actuator is connected by which the valve rod  12  is movable in a translational manner. 
         [0026]    In the housing  2 , an annular recess  22  is formed around the valve rod  12  on the actuator side, the annular recess  22  concentrically surrounding the valve rod  12 . A helical spring  26  is supported on the bottom  24  of this annular recess  22 , which helical spring  26  also surrounds the valve rod  12  and whose opposite end abuts against a plate  28  which is fixed to the valve rod such that it is secured against axial displacement relative to the valve rod  12 . The helical spring  26  is situated in a biased state between the bottom  24  and the plate  28  so that the valve closing body  10  is urged against the valve seat  8  by the spring force. 
         [0027]    According to the present invention, the guide bushing  14  has a first section  30  facing to the lip sealing ring  18 , the inner diameter of the first section  30  being larger than the outer diameter of the valve rod  12  so that a concentric annular gap  32  exists in this first section  30  between the valve rod  12  and the guide bushing  14 . The axial extension of this concentric annular gap  32  is at least as large as the maximum stroke of the valve closing body  10 . 
         [0028]    This first section  30  is joined by a second section that serves as a guiding section  34  and in which the valve rod  12  is slidably supported. In this embodiment, this section  34  is also joined by an enlarged section  36  having a constriction  38  at its end facing to the valve closing body  10 , which constriction radially defines a second annular gap  40  arranged concentrically with respect to the valve rod  12 . 
         [0029]    If the actuator is actuated against the spring force, the valve rod is moved slidingly in the guide bushing  14  towards the valve closing body  10  so that the valve closing body is lifted from the valve seat  8 . A free flow cross section is thus formed through which particle-loaded exhaust gas can flow from the exhaust gas inlet  4  toward the exhaust gas outlet  6 . As a consequence, conditions may arise, in particular due to the existing exhaust gas pulsations, which conditions cause a pressure gradient in the direction towards the actuator so that small exhaust gas quantities flow along the valve rod towards the actuator. This exhaust gas contains dirt that settles on the valve rod  12  or the guide bushing  14 . When the valve is moved, this may lead, due to the necessary small tolerances, to the formation of scratches in the portion sliding in the guide section in any position of the valve. However, these can no longer contact the lip sealing ring  18 , since the portion of the valve rod  12  contacting the lip sealing ring  18  does not slide in the guiding section  34  in any position. Thus, no scratches are formed in this portion of the valve rod, which could cause the destruction of the lip sealing ring  18 . Instead, the concentric annular gap  32  offers enough space to collect the existing dirt. The same is true for gap  40 . It is further possible to remove the dirt from the guiding section  34  by the movement and to contain it in one of the gaps  32 ,  40 . 
         [0030]    The exhaust gas recirculation valve illustrated in  FIG. 2  represents a development of the first embodiment, where like reference numerals are used for like components. 
         [0031]    Compared to the first embodiment, modifications have been made to the valve rod  12  and the guide bushing  14 . In the long, contiguous guiding section  34  of the embodiment in  FIG. 1 , soot may gather in particular in the middle of the guiding portion, which soot is no longer transported off and eventually causes increased friction. Therefore, the rather long guiding section  34  of the first embodiment is divided into two guiding portions  42 ,  44  in the embodiment in  FIG. 2  which are arranged at the axial ends of the guiding section  34 , a gap  45  being formed between the two guiding portions  42 ,  44  by widening the inner diameter of the guide bushing  14 , which gap is longer than the portions. This distance between the two guiding portions  42 ,  44  is necessary in order to prevent a tilting of the valve rod  12 . By reducing the guiding to the two guiding portions  42  and  44  most distant from each other in opposite directions, the guiding geometry with the rod is maintained. At their axial ends, the two guiding portions  42 ,  44  have edges  46 ,  48 ,  50 ,  52  serving as scraping edges. Dirt on the valve rod  12  are sheared off by these edges  46 ,  48 ,  50 ,  52  as the valve rod  12  moves and therefore, for the greater part, does not reach the two guiding portions  42 ,  44  at all, but is collected in the gaps  32 ,  40 ,  45 . It is now achieved by the guiding portions, which are much shorter than the valve stroke, that each contact point of the valve rod  12  with the guiding travels through the respective short two guiding portion  42 ,  44  more than completely during a full stroke and, thus, the greater part of the particles can be transported out from the contact portion. Moreover, an accumulation of particles is also prevented by the rather large radial force component in these two guiding portions  42 ,  44  given during the movement of the valve rod  12  and the direct contact of both components. 
         [0032]    The guiding portion  44  closer to the valve closing body  10  is located inside the space through which the exhaust gas flows. In the closed state of the exhaust gas recirculation valve, a recess  54  in the valve rod  12  is situated immediately adjacent this guiding portion  44  or with a slight overlap with this guiding portion  44 . This recess  54  also serves to receive dirt and causes turbulences that make a straight inflow into the guide portion  44  more difficult. 
         [0033]    It is evident that the embodiments described are suited to extend the service life of an exhaust gas recirculation valve, since the portions subjected to mechanical load are reduced. Friction is essentially avoided so that the tightness of the lip sealing ring is maintained and a jamming is largely prevented by a reduction of the sliding portions. 
         [0000]    The scope of protection of the claims is not limited to the embodiments described; but various structural modifications are conceivable, in particular, with respect to the scraping edges or the dimensions of the components. Reference should also be had to the appended claims.