Abstract:
A valve device for an internal combustion engine includes a multi-part housing. A drive unit generates a rotational moment. The drive unit is arranged in a motor chamber. A transmission unit is arranged in a transmission chamber. An eccentric is configured to be driven by the transmission unit. A valve rod is configured to be displaceable in translation. The valve rod extends into a valve rod displacement chamber. A coupling element converts a displacement of the eccentric into a translational displacement of the valve rod. A valve seat is arranged between an inlet and an outlet. A valve closing body is attached to the valve rod. The valve closing body is configured to be lowered onto the valve seat and lifted off the valve seat. A cover is disposed between the eccentric and the coupling element. The cover is configured to separate the transmission chamber from the valve rod displacement chamber.

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/EP2010/068019, filed on Nov. 23, 2010 and which claims benefit to German Patent Application No. 10 2009 056 251.6, filed on Dec. 1, 2009. The International Application was published in German on Jun. 9, 2011 as WO 2011/067138 A1 under PCT Article 21(2). 
     FIELD 
     The present invention relates to a valve device for an internal combustion engine, comprising a multi-part housing, a drive unit generating a rotational moment and arranged in an motor chamber, a transmission unit arranged in a transmission chamber, an eccentric that can be driven by means of the transmission unit, a valve rod that is displaceable in translation, said valve rod extending into a valve rod moving chamber, a coupling element by means of which the displacement of the eccentric can be converted into a translational displacement of the valve rod, a valve seat between an inlet and an outlet, and a valve closing body that is attached to the valve rod and can be lowered onto the valve seat and be lifted off the valve seat. 
     BACKGROUND 
     Such valve devices are used particularly as exhaust gas return valves. Via the drive unit, which in most cases is of the electromotive type, a transmission unit will be set into rotary movement, said transmission unit comprising a coupling element by which the rotary movement of the gears will be converted into a translatory movement of the valve rod. By means of these valves, an exhaust gas flow being returned from the exhaust manifold to the suction tube for thus reducing the emission of pollutants, can be controlled over a wide range. The electromotively driven valves with the intermediate transmission have a high control accuracy. Exhaust gas return valves are, however, subjected to high thermal stress and progressive contamination in their exhaust gas region. 
     EP 0 887 540 B1 describes an exhaust gas return valve wherein a gear transmission is driven by an electric motor. The last gear of the transmission comprises a guide opening with a pin extending into it, said pin being fixedly connected to the valve rod and extending vertically to it. Upon rotation of a drive gear, the pin will be displaced in the guide opening, resulting in a translatory movement, guided by the housing, of a rod actuating the valve. Ingress of blow-by gases into the transmission chamber is prevented in that the valve rod is divided into two axially superposed portions which are connected to each other by an attachment member, the outer side of said attachment member having a membrane arranged on it. 
     Even though such an arrangement does prevent an ingress of blow-by gases, the arrangement is very complex in regard to the number of component parts and also to the assembly process. There is also an increased space requirement. 
     EP 1 091 112 B1 describes an exhaust gas return valve with a planetary gear set. The last gear of this transmission is supported on an output shaft having an eccentric arranged on its opposite end. Said eccentric is connected to an axis which upon actuation of the drive motor will perform a circulating movement about a rotary axis. Arranged on said axis is a ball bearing, running in a slotted guide portion of a coupling element fixedly connected to the valve rod. The transmission chamber is closed by a pot-shaped cover having the rotary axis extending out therefrom and being connected to a further housing portion by bolts. 
     This arrangement prevents an ingress of blow-by gases into the transmission while, however, its opening towards the valve rod displacement chamber is located exactly in the region of the rotating axis so that the latter, being a particularly sensitive component, will still be affected by the hot exhaust gas. Due to the planetary gear set and the adjacent eccentric, the axial constructional space of such a valve is also relatively large. 
     SUMMARY 
     An aspect of the present invention to provide a valve device by which an ingress of contamination into a transmission and particularly into the sensitive rotating parts of the transmission can be prevented to the largest extent. Another aspect of the present invention is that, at the same time, the thermal stress acting on the sensitive parts of the valve device is reduced and the required constructional space is minimized. 
     In an embodiment, the present invention provides a valve device for an internal combustion engine which includes a multi-part housing. A drive unit is configured to generate a rotational moment. The drive unit is arranged in a motor chamber. A transmission unit is arranged in a transmission chamber. An eccentric is configured to be driven by the transmission unit. A valve rod is configured to be displaceable in translation. The valve rod extends into a valve rod displacement chamber. A coupling element is configured to convert a displacement of the eccentric into a translational displacement of the valve rod. A valve seat is arranged between an inlet and an outlet. A valve closing body is attached to the valve rod. The valve closing body is configured to be lowered onto the valve seat and lifted off the valve seat. A cover is disposed between the eccentric and the coupling element. The cover is configured to separate the transmission chamber from the valve rod displacement chamber. The eccentric is thus arranged with its rotary axis in the encapsulated transmission chamber. In comparison to known arrangements, the rotary axis is thus given added protection against intruding blow-by gases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a sectional lateral view of a valve device of the present invention; 
         FIG. 2  shows a perspective view of the valve assembly; and 
         FIG. 3  shows a perspective view of the transmission unit and of the drive unit of the valve device of the present invention shown in  FIG. 1 , with parts of the transmission unit being represented in an exploded view. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment of the present invention, a motor cap can, for example, be arranged in a receiving portion of the housing, said motor cap separating the transmission chamber from the motor chamber. In this manner, ingress of burned or abraded brush particles from the motor chamber into the transmission chamber is prevented to the largest extent. 
     In an embodiment of the present invention, an axis can, for example, be fastened to the eccentric, said axis being moveable on a circular path around the rotary axis of the eccentric. This arrangement allows for an especially simple coupling to the valve rod. 
     A special arrangement is provided in that a drive gear of the transmission unit serves as an eccentric and said axis is arranged on the drive gear. The eccentric is consequently integrated into the drive gear, thus obviating the need for an eccentric as an additional component, with resultant reduction of the number of component parts and assembly times. In this embodiment, the drive wheel and the axis can be produced as one integral piece, or the axis can have material injection-molded around it. 
     In an embodiment of the present invention, the coupling element is fastened to the valve rod and comprises a slotted guide portion guiding therein a roll or bearing arranged on said axis. The rotational movement of the gear is thereby converted in a particularly simple manner into a translatory movement of the valve rod. Frictional forces are minimized so that only small actuating forces are required. 
     In such an arrangement, the cover can, for example, comprise an opening shaped as part of a circular arc, said opening having said axis extending therethrough. Said opening forms the sole connection between the valve rod displacement chamber and the transmission chamber and is not located in the immediate vicinity of the axes supported for rotational movement. While a relatively high shielding effect is achieved by the cover, the functionality is nonetheless provided. 
     In an embodiment of the present invention, the cover can, for example, be formed as a plate having outer edges bent vertically to said plate. Such a cover can be placed in the housing without additional fastening elements. In such a case, attachment is realized by form-locking engagement. 
     In an embodiment of the present invention, the outer edges are arranged in at least partial abutment on abutment faces of the housing which extend in the same direction. The sealing length on the outer periphery of the cover is thereby increased so that an additional flow resistance is created which will act against an intrusion of gases into the transmission chamber. 
     In an embodiment of the present invention, the housing comprises a pot-shaped motor housing portion, a transmission housing portion in which the transmission chamber is formed and in which the rotary axes of the gears are attached, and a valve housing portion in which the inlet and the outlet together with the valve seat are formed. This arrangement makes it possible to achieve a high sealing effect toward the outer atmosphere while allowing for a simple assembly process. 
     In an embodiment of the present invention, the abutment faces for the outer edges of the cover are formed on the transmission housing portion, thus preventing a displacement of the abutment faces in the housing relative to the outer edges of the cover. 
     A particularly advantageous embodiment of the transmission is obtained when using a spur gear transmission wherein the transmission unit comprises a drive pinion meshing with the larger gear of a double gear of which the smaller gear meshes with the output gear which is formed as a gear segment. Such a transmission, even though offering a high gear ratio, requires only little constructional space and can be easily mounted. 
     In an embodiment of the present invention, the transmission housing portion includes a recess concentric with the rotary axis of the output gear, said recess having arranged therein a helical spring of which the first leg is in abutment on the transmission housing portion and of which the second leg is in abutment on the output gear, such that, upon rotation of the gear from the closed position of the valve, energy for turning the output gear back into the starting position is stored in the spring. Such an arrangement makes it possible to enlarge the angle of rotation of the eccentric. This will result in a favorable force development across the angle of rotation so that, in the extreme positions, high forces can be applied to break loose the valve or to overcome differences in pressure. 
     In an embodiment of the present invention, the transmission housing portion can comprise a lead frame injection-molded into it, said lead frame comprising connection pins of a plug formed on the transmission housing portion, of a sensor and of the drive unit. The electric supply to the valve and the positional feedback can thus be safeguarded throughout the lifespan because a detachment of contacts due to vibrations of the valve is excluded. 
     An additional sealing effect already in the transition between the exhaust-conducting region and the valve rod displacement chamber is obtained in that the valve rod is guided, via a guiding element, for translatory movement in the housing, and that a sealing element is arranged on the valve rod between the guiding element and the coupling element. 
     By providing a contour on the transmission housing portion, which contour serves for guiding the coupling element, twisting of the coupling element and thus the valve rod is prevented. 
     There is thus created a valve device which is largely resistant to contamination particularly by blow-by gases and to thermal stresses and, further, while offering high actuating accuracy, requires only little constructional space and consequently is inexpensive in production. 
     The valve device illustrated in  FIG. 1  comprises a multi-part housing  2  composed of a pot-shaped motor housing portion  4 , a transmission housing portion  6  and a valve housing portion  8 . 
     The transmission housing portion  6  is, on its first side, provided with an annular projection  10  on whose outer periphery, with interposition of a sealing  12 , the motor housing portion  4  is fastened and whose inner periphery forms a receiving portion  14  into which an electric motor is inserted as a drive unit  16 . On its end facing toward the transmission housing portion  6 , the electric motor  16  is largely closed by a motor cap  18 , so that a motor chamber  20  is separated from the transmission housing portion  6 . Only a drive shaft  22 , with a drive pinion  24  of a transmission unit  26  arranged thereon for common rotation therewith, and two motor connector terminals, not shown, extend through corresponding opening of motor cap  18 . 
     Within the transmission housing portion  6 , transmission unit  26  is arranged and supported in a transmission chamber  28 . Said transmission unit comprises a drive pinion  24  meshing with the larger gear  30  of a double gear  32  of which the smaller gear  34  meshes with an output gear  36  which is formed as a gear segment, as can be seen particularly in  FIG. 3 . Said double gear  32 , as also holds true for the output gear  36 , is supported on an axial bolt which serves as a rotary axis  38 , 40  and which is fastened in the transmission housing portion  6 . 
     In transmission chamber  28 , there is further formed an annular recess  42  which is arranged concentrically with the rotary axis of the output gear  36 , said recess having arranged therein a helical spring  44 , biased in the direction of rotation, wherein the first leg of said spring, not visible in the drawings, is in abutment against the transmission housing portion  6  and the second spring leg  46  is in abutment on the output gear  36 . Upon rotation of the output gear  36  from its starting position, said spring will be further twisted, so that spring  44  can be used as a return spring which will turn the drive unit  26  in a known manner back into its starting position, e.g. in case that the drive unit  16  should fail. 
     On output gear  36 , outside of rotary axis  40 , an axis  48  is arranged which extends parallel to rotary axis  40  and, upon rotation of output gear  36 , will be moved on a segment of a circle around rotary axis  40 . Said axis  48  can be provided with injection-molded material around it during manufacture of output gear  36  or can be produced in one piece with the latter, or be attached to gear  36  in another manner. Accordingly, output gear  36  will also act as an eccentric  37  so that no additional eccentric component will be required. 
     Said axis  48  extends through an opening  50 , also formed as a segment of a circle, of a cover  52  which according to the present invention separates the transmission chamber  28  from a valve rod displacement chamber  54  into which the axis  48  extends. 
     Cover  52 , its shape being shown in  FIG. 3 , is substantially formed as a flat plate  56 , with outer edges  58  extending from said plate at an angle of 90° thereto. Said outer edges  58  are in abutment on correspondingly shaped abutment faces  60  of transmission housing portion  6 , resulting in a form-locked attachment in transmission housing portion  6  without the need for additional fastening elements. This extended abutment area further increases the sealing tightness of transmission chamber  28  which on a first side thereof is separated from its ambience by motor cap  18 , and on the opposite side by cover  52 . A connection exists only by way of the openings  50  through which extend the shafts  22  and respectively the axes  48  for drive transmission out from and respectively into transmission chamber  28 . 
     In the valve rod displacement chamber  54 , axis  48  has arranged on it a roll  62  guided in a slotted guide portion  64  of a coupling element  66 , the latter in turn being fixedly connected to a valve rod  68  of the valve device. The slotted guide portion  64 , which is shown in  FIG. 2 , can have a curved shape for realizing special required force/stroke developments. 
     Valve rod  68  extends through a corresponding opening of the valve housing portion  8  in which a guide element  70  is arranged for supporting the valve rod  68  in a manner allowing only for a pure lifting movement. Between said guide element  70  and the valve rod displacement chamber, a sealing element  72  is arranged in the valve housing portion  8 , surrounding the valve rod  68  and significantly reducing a blow-by gas flow entering the valve rod displacement chamber  54  along valve rod  68 . Arranged on the opposite end of the guide element, again surrounding the valve rod, is a shielding element  74  which will detach depositions on valve rod  68  and also improve the sealing effect on valve rod  68 . 
     To the end of valve rod  68 , there is fastened in a known manner a valve closing body  76  which in the illustrated position separates an inlet  78  of the valve from an outlet  80 . For this purpose, the valve closing body is resting on a valve seat  82 . 
     On the opposite axial end of valve rod  68 , beyond coupling element  66 , a carrier element  84  is fastened to the coupling element  66 , said carrier element being arranged for movement together with the valve rod  68 . Carrier element  84  comprises a ceramic insulating body  86  which extends across the cross section of carrier element  84 , thus creating a thermal separation between the valve rod, which in the given case may be subjected to high thermal stress, and the part of the carrier element  84  arranged beyond insulating body  86 . In this thermally separated region, carrier element  84  comprises an opening in which a permanent magnet  88  is fastened. This magnet communicates with a contactless sensor  90  which is arranged, with material injection-molded around it, in the transmission housing portion  6  parallel to the direction of movement of carrier element  84  adjacent to the latter. 
     Sensor  90  is connected via a lead frame  92  to a plug  94  whose connector pins  96  are formed by the ends of the lead frame  92 . Further lines of the lead frame  92  serve as motor connectors which will be plugged together with motor contacts so that both the controlling of drive unit  16  and the positional feedback of the valve device can be performed via plug  94 . During the manufacturing process, lead frame  92  will be placed into the injection mold of transmission housing portion  6  and by injection molding enclosed with material around it, thus reliably preventing detachment of the electrical contacts. 
     If, now, it is desired to at least partially open the connection from inlet  78  to outlet  80 , a required voltage will be supplied by a control unit via the connector pins  96  of plug  94  of drive unit  16 . By rotating the drive unit  16 , the transmission unit  26  and thus also the drive gear  36  will be caused to rotate. Thereby, axis  48  will be rotated on circular arc around rotary axis  40 , with resultant movement of roll  62  in slotted guide portion  64 . Enforced thereby is a translatory movement of coupling element  66  and consequently of valve rod  68  and valve closing body  76  which will be lifted off the valve seat  82  so that a gas flow can stream from inlet  78  to outlet  80 . During this movement, twisting of valve rod  68  will be prevented by a contour  98  on valve housing portion  8 , as evident from  FIG. 2 . 
     In the process, the position of the valve closing body  76  will be fed back in a known manner via plug  94  by means of the magnetic field which, on sensor  90 , is changed by the movement of permanent magnet  88  with carrier element  84 , so that, once the desired position has been reached, the drive unit will be switched off. 
     In the region of outlet  80 , pressure pulsations are occurring which have the effect that, in spite of the sealing element  72 , blow-by gases will enter the valve rod displacement chamber  54  along valve rod  68 . Ingress of these gases into the transmission chamber, however, can be prevented in large part by the additional cover  52 . Particularly, the opening  50  of cover  52  is not arranged directly opposite a rotatably supported part of transmission  26  so that a predominant intrusion of the gas which is nonetheless reaching the transmission chamber  28  will also have lesser consequences. 
     While being highly unaffected by contamination, this valve device requires only little constructional space. Assembly will be simple while also the number of constructional parts has been minimized, which allows for a distinct cost reduction and an increased useful life. 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims.