Abstract:
An electropneumatic converter for connection with an exhaust recirculation valve in a motor vehicle. The electropneumatic converter includes a vacuum port and an atmospheric pressure port configured to connect with a valve chamber using a valve device, wherein a mixed pressure is formed in the valve chamber and supplied to a mixed pressure port. An armature is affixed to a valve body of the valve device movable in an axial direction, the valve body being connected to a suspension device, wherein the armature is displaceable in the axial direction using a solenoid. The electropneumatic converter also includes a damping element configured to dampen the axial movement of the armature and the valve device affixed thereto. The damping element includes at least one of an elastomer or a foamed material.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2007/058009, filed on Aug. 2, 2007 and which claims benefit to German Patent Application No. 10 2006 038 920.4, filed on Aug. 18, 2006. The International Application was published in German on Feb. 21, 2008 as WO 2008/019949 A1 under PCT Article 21(2). 
     FIELD 
     The present invention refers to an electropneumatic converter such as is used, for example, for pneumatic control in motor vehicles, where a mixed pressure is obtained from the intake pressure of an internal combustion engine and atmospheric pressure, said mixed pressure being supplied to a load, such as an exhaust recirculation valve, for example. 
     BACKGROUND 
     Such a converter is described, for example, in DE 41 10 003 C1. This converter has three ports, a vacuum being applied to the first port, atmospheric pressure being applied to the second port and a mixed pressure of the first and the second port being applied to the third port which mixed pressure is supplied to a load, such as an exhaust recirculation valve, for example. Moreover, this converter comprises a valve means as well as a plunger-type armature fixedly attached thereto, which is displaceable by means of a solenoid so that the position of the valve means can be changed and the mixed pressure supplied to the load can be controlled. The valve means and the armature attached thereto are suspended from a membrane such that they are movable in the axial direction. 
     It is a drawback of such a pressure converter that the armature and the valve means can swing freely in the axial direction, whereby undesirable vibrations can be caused especially by engine vibrations or by pressure pulsations on the part of the connected components. This undesirable effect occurs particularly frequently in connection with vacuum pulsations. 
     Moreover, pulsations can occur in a state in which no current flows through the solenoid and the solenoid can exert no forces on the plunger-type armature and the valve means. Undesirable vibrations of the plunger-type armature and the valve means result in troubles in the operation of the internal combustion engine. 
     SUMMARY 
     An aspect of the present invention is to provide an electropneumatic pressure converter that allows for an improved, trouble-free operation of the internal combustion engine. 
     In an embodiment, the present invention provides an electropneumatic converter for connection with an exhaust recirculation valve in a motor vehicle. The electropneumatic converter includes a vacuum port and an atmospheric pressure port configured to connect with a valve chamber using a valve device, wherein a mixed pressure is formed in the valve chamber and supplied to a mixed pressure port. An armature is affixed to a valve body of the valve device movable in an axial direction, the valve body being connected to a suspension device, wherein the armature is displaceable in the axial direction using a solenoid. The electropneumatic converter also includes a damping element configured to dampen the axial movement of the armature and the valve device affixed thereto. The damping element includes at least one of an elastomer or a foamed material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is a detailed description of preferred embodiments of the present invention with reference to figures. 
       In the Figures: 
         FIGS. 1-5  are sectional views of different embodiments of the electropneumatic converter, and 
         FIGS. 1   a - 5   a  details of the damping elements of the electropneumatic converters illustrated in  FIGS. 1-5 . 
     
    
    
     DETAILED DESCRIPTION 
     For the dampening of the axial movement of the armature and the valve means attached thereto, a damping element is provided. This effectively avoids undesirable axial vibrations of the armature and the valve means attached thereto, so that a trouble-free operation of the internal combustion engine is possible. 
     In particular, the present invention allows for a reduction of pulsations in a non-energized state as well as in the operational range of the electropneumatic converter. Furthermore, the present invention leads to better large signal behavior and a better small signal behavior of the electropneumatic converter during the venting operation. 
     The damping element may be located in particular between the valve means and a housing. Further, the damping element may also be situated between the armature and a iron core located beneath the armature. 
     Moreover, the damping element may be configured, for example, as a membrane. 
     Independent of the material used, the damping element may be mounted at different positions of the electropneumatic converter, as described above, so that a damping of the axial movement of the armature and the valve means attached thereto becomes possible. 
     In an embodiment, the damping element can be integrated in the suspension means by which the valve body and the armature attached thereto are suspended so as to be movable in the axial direction. For example, the damping element may be realized by damping legs integrated in the suspension means, whereby the assembly of an additional damping element can be omitted. Further, the damping element may be integrated in other existing components of the electropneumatic converter, i.e., besides their actual function, these components may also have a damping function with respect to the axial movement of the armature and the valve means attached thereto. Using an additional damping element is not required in such an arrangement. In the present context, the term integrated means that the further component and the damping element are formed integrally, the damping element and the further component being two components that are fixedly connected with each other, or the damping element and the further component being a single component of monolithic design. 
     In an embodiment, the damping element can be arranged at the venting side of the electropneumatic converter to which atmospheric pressure is applied. Thereby, the closing operation of the valve means can be delayed for a short moment, whereby the behavior of the electropneumatic converter is improved especially in the small signal range. Here, the valve plate of the bellows closes the vacuum pipe, which may in particular be configured as a brass pipe, and the venting occurs past the bellows. The force exerted on the armature by the damping element causes a delayed closing of the second valve seat integrated in the armature. The sealing surface of the bellows keeps the vacuum port (vacuum source/pump) closed for as long as possible, so as to allow venting. In particular, such an arrangement causes an improved large signal and small signal behavior upon venting. The atmosphere port should stay open for as long as possible. Thus, for example, a vacuum can be relieved more quickly. When the effective pressure and the force, which is exerted by the solenoid on the armature, are almost at an equilibrium, the valve plane of the bellows closes both valve seats. Now, the further venting takes place via the valve bypass until the final balance of forces has been reached. 
     In another embodiment, the damping element may be designed as a damping membrane in the form of an elastomeric ring in which the armature is supported. 
     With reference to  FIG. 1 , an electropneumatic converter has a vacuum port  10 , an atmospheric pressure port  12  and a mixed pressure port  14  to which is applied a mixed pressure of the vacuum port  10  and the atmospheric pressure port  12 . The mixed pressure is supplied to a load, in particular an exhaust recirculation valve, via the mixed pressure port  14 . 
     The valve means  18 ,  28  comprises a valve body  18  with a valve plate  28 . The valve body is connected with a housing  32  via a membrane  20  such that it is movable in the axial direction  30 . The membrane  20  annularly surrounds the valve body  18  and is fixed in a clamping manner in an annular recess  32  in the housing or a housing cover. Between the valve body  18  and the housing  32  or the housing cover, the membrane  20  follows a substantially arcuate path. At the valve body  18 , the membrane  20  is also mounted in a recess that extends annularly around the valve body  18 . 
     An armature  16  is fixedly attached to the valve body  18 , the armature also being movable in the axial direction. The armature  16  comprises magnetic material and can be moved by supplying electric current to a solenoid  17 . 
     The electric coil of the solenoid  17  is enclosed by an iron casing  38  to bundle the magnetic field lines. Moreover, an air gap  40  is formed between the armature  16  and the iron casing  38 , in which air gap an adjustable iron core  34  is arranged such that the length of the air gap  40  is variable. In addition, a second iron core  36  is provided that protrudes into a recess  37  of the armature  16 . A cavity  24  is formed between the first iron core  34  and the armature  16 . 
     The mixed pressure supplied to a load via the mixed pressure port  14  is formed in a valve chamber  11  defined by the membrane  20 . The mixed pressure is obtained from the pressure supplied to the solenoid via the vacuum port and the air pressure supplied to the electropneumatic valve via the atmospheric pressure port  12 . 
     By varying the current supplied to the solenoid  17 , the mixed pressure supplied to the load can be regulated precisely. An exact adjustment of the air gap  40  is possible by an adjustment of the iron cores  34 ,  36 , so that possible effects of mechanical and/or electromagnetic tolerances can be eliminated. 
     According to  FIGS. 1 and 1   a , the valve plate  28  is formed monolithically with the elastomeric bellows  19 , whereby it is resiliently connected with the armature  16 . The vacuum port can be opened and closed by means of the valve plate  28 . 
     An important feature of the electropneumatic converter of the present invention is the damping element  26 , designed as a bellows of elastomeric material and arranged between a valve seat collar  56  and the coil rib  27 . This bellows serves to effectively avoid undesirable axial vibrations of the armature and the valve means attached thereto, so that a trouble-free operation of the internal combustion engine is possible. 
     In the following Figures, identical or similar components will be identified by the same reference numerals. 
     As illustrated in  FIGS. 2 and 2   a , the damping element  26  is formed as a part of the membrane  20  and may be formed integral with the membrane  20  in an injection molding process. In analogy to  FIGS. 1 and 1   a , the effect of the damping element  26  is realized by one side of the element being supported at the coil rib  27  and the opposite side introducing a force into the membrane  20  connected therewith. Here, the damping element  26  is arranged on the venting side of the electropneumatic converter, i.e. on the side that is immediately connected with the atmospheric pressure port  12 . 
     As illustrated in  FIGS. 2 and 2   a , the damping element  26  is also arranged within the cavity  22 . 
     In  FIGS. 3 and 3   a , a damping element  26  of elastomer is illustrated that is arranged within a cavity  24  formed between the armature  16  and the iron core  34 . 
     At the same location,  FIGS. 4 and 4   a  show a damping element formed by a foam material member. 
     In another embodiment according to  FIGS. 5 and 5   a , the damping element may be configured as a damping membrane  50 , and in particular as an elastomeric ring, in which the armature  16  is supported. The elastomeric ring can, for example, comprise silicone. As an alternative or in addition, the strokes of the armature  16  and the valve means  18 ,  28  may be damped by abutments  44 ,  46 ,  48  provided on the housing  32 . These can, for example, be provided at the location of the housing  32  towards which the valve body  18  moves as it moves in the direction of the force exerted by the membrane  20 . 
     An exact matched positioning of the stroke-preventing or stroke-limiting abutments  44 ,  46 ,  48  as well as a matching of the spring force or the membrane force allows to realize an excitation acceleration of 20 g. It is particularly advantageous in this context to use a damping membrane  50  of a thickness between 2 mm and 3 mm, so that limitations to the functions of the electropneumatic converter, such as the characteristic (gradient and hysteresis) or dynamic (large and small signal) can be minimized. 
     As an alternative or in addition, a thicker damping membrane  30  may also be used, which has recesses that make it more flexible. For receiving the damping membrane  50 , the valve body  18  comprises a preferably annular groove  52 . 
     To allow a passage towards the atmospheric pressure port  12 , the abutment  46  has a groove-shaped recess  54  through which venting may take place. The abutments  46 ,  48  can, for example, be made of plastic material. 
     For an additional damping of the movement of the valve body  18 , a spring  42  may be provided between the valve body  18  and the housing  32 . According to the present invention, the same is used in combination with further damping elements  26 ,  50 . 
     Only a single damping element may be provided, for example, only on one side of the armature or the valve means, or a plurality of damping elements may be provided, which are arranged on a plurality of sides of the armature and the valve means.