Abstract:
An exhaust gas recirculation valve comprises a drive, at least one rotatable drive element and at least one translationally drivable driven element. The drive element comprises a thread element that is configured to convert rotational motion of the drive element into translation of the driven element. A rotational axis of the drive element is inclined with respect to a translational axis of the driven element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to, and claims priority from, European Patent Application No. 08 165 906.2, filed Oct. 6, 2008, entitled “EXHAUST GAS RECIRCULATION VALVE,” the entirety of which is incorporated by reference herein and made a part of the present specification. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention concerns an exhaust gas recirculation valve. In the field of combustion engines, it is known to recirculate exhaust gas toward the fresh air side depending on operating conditions in order to reduce fuel consumption and noxious emissions. 
         [0004]    2. Description of the Related Art 
         [0005]    From EP 1 111 227 A2 an exhaust gas recirculation valve is known in which the rotary motion of a drive motor is converted into a translational motion of the valve element. At least at the beginning of the opening operation the valve element is given a rotary motion. 
         [0006]    EP 1 526 271 A1 concerns an exhaust gas recirculation valve in which the rotary motion of a drive motor is converted into a stroke movement of the valve element, wherein the valve element may rotate with the drive element upon opening, but is not urged to rotate along with it. The conversion of the rotary motion into a stroke movement is effected substantially by means of a driven threaded “worm” which engages a stationary but rotatable wheel. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide an exhaust gas recirculation valve which is improved in particular with regard to reliability during operation. 
         [0008]    This object is achieved by means of an exhaust gas recirculation valve as defined in claim  1  or claim  10 . 
         [0009]    Accordingly, it comprises a drive, at least one rotatable drive element and at least one translationally driven output-side element (driven element). Here, a rotational axis of the drive element is inclined with respect to a translational axis of the driven element. The drive of the exhaust gas recirculation valve is preferably configured as rotary drive, but not limited thereto. The rotatable drive element is a threaded element, for example a worm gear having a thread or a part of a thread. The worm gear might simply be referred to as a “worm” in the English language and is also referred to as a “worm” herein. The translationally driven element is engaged with the worm in such manner that a rotation of the worm leads to a translational motion of the driven element. For example, the driven element may be a portion protruding from the valve tappet (lifter), a wheel or pulley protruding thereon and engaging the worm, or an element having a counter-thread. 
         [0010]    According to the invention, the rotational axis of the drive element is inclined with respect to the translational axis of the driven element. In a geometrical sense, both axes are skew to each other. Substantially, this results in the force transmission between the drive and driven element occurring in a direction which is not inclined with respect to the contact face of the drive element or at least not that much inclined as hitherto. Conventionally, if the rotational axis of the drive element and the translational axis of the driven element are parallel to each other, the force transmission from the worm to the driven element occurs via a surface which is inclined with respect to the translational axis of the driven element. This has the result that a rectilinear force applied by the driven element, for instance due to the gas pressure, may result in a torsion (twisting) of the drive element, which may lead to an unintended displacement of the valve element. In the exhaust gas recirculation valve according to the invention such an inclination between the translational axis of the driven element and the rotational axis of the drive element is reduced so that higher forces are necessary for twisting the drive element. Thus, in practice it can largely be precluded that the valve is inadvertently displaced due to gas forces. 
         [0011]    Preferred embodiments are described in the dependent claims. In particular, it is preferred that the drive element comprises a surface with which at least a portion, for instance the mentioned protrusion or the described small wheel, of the driven element is in contact and which surface is largely perpendicular to the translational axis of the driven element. By this arrangement any force applied by the driven element acts in a direction largely perpendicular to the surface on the drive element and, thus, cannot cause an unintentional twisting of the same. 
         [0012]    Further, it is presently preferred that a location at which a portion of the driven element is in contact with the drive element is at least largely aligned with an axis of the translationally-moved valve element. Thus, no transverse or lateral forces are applied onto the arrangement consisting of the translationally-moved valve element and the driven element operatively connected therewith. This offers advantages for the steady (permanent) operation of the valve. The described orientation of a contact location on the drive element with respect to the translational axis of the valve element may, however, be advantageously combined with the above-described feature as well as with all of the features described in the following. 
         [0013]    For the exhaust gas recirculation valve according to the invention, it has proven to be advantageous if the valve element is only translationally movable but not twistable. Thus, delays and obstructions of the opening motion may advantageously be reduced in the response behavior. 
         [0014]    Further, with regard to the opening direction of the valve element, it is currently preferred that it is oriented (runs) against the exhaust gas pressure. Thus, the exhaust gas counterpressure may advantageously be used for assisting the closure of the valve and, thus, for minimizing the amount of leakage in the closed state. 
         [0015]    Preferably, a single-stage gear is provided between the drive and the drive element. Due to such a single-stage transmission the response behavior of the valve is improved, in particular due to reduced friction and lower mass inertia. Alternatively, the gear may also be a two- or multi-stage gear, which allows the generation of higher forces. 
         [0016]    Preferably, the drive element is further connected at least indirectly with a spring element, for instance a coil spring, which is solely twisted. Such a spring element advantageously ensures, in terms of a failsafe operation also during a fault or interruption in the electrical system, that the valve closes. 
         [0017]    Further, for a valve housing in which the valve element is arranged, it has proven advantageous to construct this valve housing in one piece, for instance as cast housing. Thus, the number of utilized parts may be advantageously reduced. 
         [0018]    Lastly, it is currently preferred to provide the valve housing with at least one cooling channel. Thus, the valve housing may be cooled in particular in proximity to the valve tappet so that the durability of the valve tappet and the plunger seal and plunger guide, and thus of the exhaust gas recirculation valve as a whole, may be improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the following, the invention is described in further detail by means of an embodiment illustrated by way of example in the figures. 
           [0020]      FIG. 1  shows a side view of the exhaust gas recirculation valve according to the invention; and 
           [0021]      FIG. 2  shows a partially cut-away view of the exhaust gas recirculation valve according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    As can be seen from  FIG. 1 , the exhaust gas recirculation valve  10  according to the invention comprises a drive  12  in the form of an inclined motor. In the illustrated embodiment, a pinion  14  is arranged on the motor shaft and drives a gear  16 . The drive element  18  in the form of a worm gear (or worm) is attached to the gear  16  and drives the valve tappet  20  as described in more detail below. In the illustrated embodiment, as can be seen in more detail from  FIG. 2 , the worm comprises an axis A that is supported both at its upper end and at its lower end. In the illustrated embodiment, the arrangement of gear  16  and worm  18  is connected to a coil spring  22  which is solely twisted upon opening and closing of the valve. In the illustrated embodiment, the combination of pinion  14  and gear  16  corresponds to a single-stage transmission having the above-described advantages. 
         [0023]    The conversion of the rotary motion of the worm  18  into a translational motion of the valve tappet  20  is effected by means of the driven element  24  which, in the illustrated embodiment, is configured as a small wheel and is in engagement with the thread of the worm  18 . The small wheel  24  is rotatably attached to a bracket  26  fixed to the valve tappet  20 . The valve tappet  20  is supported in a suitable bushing  28  which, in the illustrated embodiment, is provided in a valve housing  30  configured as a one-piece cast part. Moreover, as can be seen from  FIG. 2 , the valve housing  30  may be configured so as to additionally receive the drive  12  and the arrangement of drive element  18  and driven element  24 . Only the transmission in the form of the pinion  14 , the gear  16  and the coil spring  22  are located in the area of a lid  40 . This lid may further comprise a connector (socket)  42  for electric terminals. For example, a connection to a controller connected to an engine control unit may be performed by means of this socket in order to electronically control the operation of the valve. With the coolant parts  32  one may discern that the valve housing  30  may advantageously be cooled in order to cool the valve tappet  20  and its bearing and seal, too. 
         [0024]    A valve head (plate)  34  engaging a valve seat  36 , which advantageously is provided with rather sharp edges is attached to the valve tappet  20 . Advantageously, the valve element in the form of the valve head  34  is always, that is both in the open and the closed state, situated within the valve housing  30 . In the illustrated embodiment, the opening of the valve head  36  is effected against the exhaust gas pressure, that is, it opens downward according to the orientation of  FIG. 1 , so that the valve head  36  assists in closing the valve in response to exhaust gas pressure. At the same time, there is no danger that the exhaust gas pressure inadvertently displaces the valve, due to the following reasons. 
         [0025]    As can be seen from  FIG. 1 , the rotational axis A of the worm  18  serving as drive element is inclined with respect to the translational axis of the driven element  24 , in other words, with respect to the axis of the valve tappet  20 . Thus, in the illustrated embodiment, the surface in the region of the thread of the worm  18  engaging the small wheel  24  may be disposed largely perpendicular to the axis of the valve tappet  20 . Thus, if a force acts upon the valve tappet  20 , for example due to the exhaust gas pressure, this force will largely act perpendicular to the surface in the area of the thread of the worm  18 , and consequently cannot twist it. Thus, an inadvertent displacement of the valve may advantageously be avoided, a circumstance particularly relevant for small openings. 
         [0026]    The preferred embodiment illustrated in the figures provides a further advantage, which will be explained by means of  FIG. 2 . To begin with, in  FIG. 2  the gear  16  and the coil spring  22  are shown in section for better understanding. From  FIG. 2  one may further take that the worm  18  comprises a nearly complete turn of a thread. Further, from the illustration of  FIG. 2  one may take the additional advantage that the location at which the small wheel  24  engages the thread of the worm  18  is largely aligned with the axis of the valve tappet  20 . In this way, no transverse or lateral forces are generated, offering advantages for the durability of the valve. As mentioned, this arrangement is achieved by means of the largely U-shaped bracket attached at the upper end of the valve tappet  20  and rotatably supporting the small wheel  24  at its other end. 
         [0027]    As can additionally be taken from  FIG. 1 , a stationary guide  38  may be provided, which comprises a protrusion (not discernable in  FIG. 1 ) extending into a slit of the bracket  26 , for example, so that the bracket  26 , which translates together with the valve tappet  20  upon actuating the valve, is guided in the direction of motion.  FIG. 1  also shows that the guide  38  may be arranged on a plate  44  to which the drive  12  may additionally be attached and/or in which the axis of the worm  18  may be supported.