Abstract:
A throttle valve positioning device is disclosed, The device has a housing with a bearing for a throttle valve shaft and a throttle valve support, within which a throttle valve pivots which sits on the throttle valve shaft, running into a shaft passage in the support. With the device, air leakage may be avoided, such that the periphery of the throttle valve is arranged at a separation from a passage for the throttle valve shaft in. the throttle valve support.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a throttle valve positioning device having a housing which forms a bearing arrangement for a throttle valve shaft and comprises a throttle body in which a throttle valve is pivotable, said throttle valve sitting on the throttle valve shaft, which leads through the shaft passage into the throttle body, the housing being of split design, and the circumference of the throttle valve, at least on one side, lying next to the throttle valve shaft at a distance from a passage of the throttle valve shaft in the throttle body. 
   In the hitherto known arrangements of throttle valves in the throttle body which sit centrally on the throttle valve shaft or in a slot in the throttle valve shaft, leakage air usually cannot be prevented from flowing past in the region between throttle valve shaft, throttle valve and throttle housing and also via the shaft apertures in the bearings. The avoidance of leakage air is made more difficult in particular in split housings having two housing shells, since the parting line of the two housing halves likewise lies in the region of the throttle valve, so that, on account of the very high vacuum produced in the region of the throttle valve, leakage air is drawn in in this region, which can scarcely be sealed off completely. 
   It has been attempted hitherto to reduce this problem by minimizing the shaft apertures and the mismatch in mold between the housing halves, it not being possible in this way to absolutely remove the problem, but rather it only being possible to provide for a certain improvement with regard to leakage air at increased production costs. 
   Throttle valve positioning devices of the type described at the beginning have been disclosed by U.S. Pat. No. 1,671,069, U.S. Pat. No. 3,556,475, U.S. Pat. No. 2,934,312 and U.S. Pat. No. 3,260,502. 
   SUMMARY OF THE INVENTION 
   The object of the present invention consists in providing a throttle valve positioning device in which leakage air is minimized. 
   According to the invention, the object is achieved in that the housing, between its halves, has an actuator and possibly gearing for positioning the throttle valve via the throttle valve shaft. 
   The displacement of the throttle valve margin away from the shaft passage and from the parting line of a split housing allows the leakage air to be minimized, since a sound seal between the circumference, preferably provided with a sealing ring, of the throttle valve and the inside of the throttle body, it being possible for the inside to be formed without joints away from the shaft passage and a housing parting line. The displacement may be achieved, for example, by a throttle valve attached with lateral offset to the throttle valve shaft, or preferably by the throttle valve lying at an acute angle to the throttle valve shaft, i.e. the throttle valve shaft passes through the throttle valve centrally at an acute angle. An elastic sealing ring, which preferably has certain radial mobility in a circumferential groove, can ensure that the deviations caused by the offset and/or the inclination of the throttle valve are compensated for. 
   In particular with the last-mentioned possibility, a design which exhibits very little leakage air is possible, in particular if the throttle valve circumference, at least on the side of the throttle valve shaft passage, lies on the suction side in the throttle body. In this design, the passage especially critical for the sealing is arranged toward the drive in a region which lies in front of the throttle valve so that the shaft passage is screened off from the vacuum occurring on the suction side. If, for example, the housing at the same time serves to accommodate an actuator and possibly gearing connected in between, the bottom shell can be designed as a closed-off, airtight unit, and vacuum is on no account applied to the gearbox. This in turn simplifies the sealing of the two housing halves, since the flange length in such positioning devices is relatively large. 
   With an inclined design of the throttle valve, in the embodiment described above, the shaft bearing arranged opposite the shaft passage lies in the region of the vacuum, a factor which, however, is relatively easy to cope with on this side of the positioning device. Especially preferred is an embodiment in which the throttle valve shaft is mounted at this point in a closed bearing boss, for example directly in the thermoset of the throttle body material. 
   To avoid passage of air between throttle valve and throttle valve shaft in the case of a throttle valve inclined relative to the shaft, measures for sealing in this region are expedient. The throttle valve itself may consist of a thermoset or of a thermoplastic, for example filled PEI or filled PPS. The throttle valve may be integrally molded on a sleeve which is made of metal or plastic and which completely or partly encloses the shaft and can be secured to the latter in the case of a sleeve made of plastic, said sleeve may in turn also be integrally molded on the throttle valve shaft in one piece with the throttle valve, whereas in the case of metallic sleeves, said sleeves are preferably screwed to the throttle valve shaft or are welded to the latter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Exemplary embodiments of the invention are dealt with in more detail below with reference to the attached drawings, in which: 
       FIG. 1  shows an oblique view of a throttle valve positioning device, with top housing half removed; 
       FIG. 2  shows a sectional illustration of the throttle valve positioning device according to  FIG. 1 , with housing top part; 
       FIG. 3  shows a view of a further embodiment of a throttle valve positioning device, with lifted housing top part. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Shown in  FIG. 1  is a throttle valve positioning device  10  which essentially comprises a housing  12  with a bottom housing half  14  and a top housing half  16 , an actuator  18 , a throttle valve shaft  20 , which is coupled to the actuator  18  via gearing  22 , and a throttle valve  24  which sits on the throttle valve shaft  20  and is pivotable in a throttle body  26  formed by the two housing halves  14 ,  16 . In addition to a receptacle for the actuator  18  and the gearing  22 , the housing also forms a bearing arrangement for the throttle valve shaft  20  at a first, drive-side bearing  28  in the parting line  30  between the two housing halves  14 ,  16  and at a second bearing  32  on the side opposite the drive in the throttle body  26 . The second bearing  32  is at a distance from the parting line  30  between the housing halves and may also be designed as a closed bearing boss, whereas in  FIG. 2  the bearing  32  is shown open outward. 
   The actuator  18  and the gearing  22  and also those regions of the two housing halves  14 ,  16  which enclose them are designed in a manner known per se and are therefore slot to be discussed in more detail here. 
   In deviation from conventional solutions, the throttle valve  24  does not sit centrally on the throttle valve shaft or in a split throttle valve shaft, but rather is designed to be offset relative to the throttle valve shaft in such a way that the circumference  34  of the throttle valve  24  bears next to the throttle valve shaft  20  on the inside against the throttle body  26 . To this end, in the exemplary embodiment shown, the throttle valve  24  is arranged inclined relative to the throttle valve shaft  20 , an angular range of between 5° and 25° being expedient. In the contact region of the circumference  34  of the throttle valve  24 , the throttle body  26  is formed with a correspondingly inclined region  36 , the walls of which lie perpendicularly to the plane defined by the throttle valve  24  in its completely closed position. The adaptation of the wall of the throttle body to the inclination of the throttle valve relative to the throttle valve shaft reduces the actuating forces and avoids jamming in the closed position. 
   In the exemplary embodiment shown in  FIGS. 1 and 2 , the inclined region  36  is formed essentially by the bottom housing half  14 , i.e., in the closed position of the throttle valve, the inclined region  36 , which together with the throttle valve provides for the sealing, is designed without joints. This provides for an excellent sealing effect, so that the leakage air is reduced to a minimum. 
   The throttle valve  24  is connected to the shaft in a rotationally fixed manner by means of a sleeve  38 , it being possible for the throttle valve to be integrally molded with the sleeve directly on the throttle valve shaft  20 , which is made of steel, or for it to be secured to the shaft via a metal insert which is welded or screwed to the shaft. In the solution with a metal insert, the throttle valve can again be integrally molded on said metal insert. Suitable materials for the body of the throttle valve are thermosetting plastic or thermoplastic, such as, for en-ample, filled PEI (polyether imide) or filled PPS (polyphenylene sulfide). 
   To improve the sealing between throttle valve and throttle body  26 , a piston ring or sealing ring  40 , which can be made of an elastic plastic, for example PEEK (polyaryletherketone, polyetheretherketone) with PTFE filling or pure PTFE, is embedded in the circumference  34  of the throttle valve  24 . This piston ring  40  is held in a circumferential groove  42 , which is designed to be so deep that the piston ring  40  can be pressed in elastically in the radial direction. The radial mobility of the elastic piston ring  40  and its inherent elasticity ensure that the deviations of the path of movement, which are caused by the inclination of the throttle valve, during the pivoting of the throttle valve are compensated for, so that an optimum sealing effect can nonetheless be achieved. Furthermore, the piston ring  40  is suitable for compensating for production tolerances, so that the latter likewise cannot be the cause of leakage air. 
   Due to the special arrangement of the throttle valve  24  in the throttle valve positioning device  10  shown in  FIGS. 1 and 2 , the passage  44  of the throttle valve shaft  20  into the throttle body  26  is relieved of vacuum, since the vacuum side, in accordance with the illustration, lies on the fresh-air side below the throttle valve  24  and the throttle valve shaft. This means that, in particular the case of a closed design of the second bearing  32 , especially sound sealing against leakage air is achieved, since vacuum cannot be applied to the closed housing  12  via the passage location  44 . As a result, the sealing of the two housing halves  14 ,  16  relative to one another is simplified, 
   The two housing halves  14 ,  16  may be produced from plastic, in particular a thermoset, which is also suitable for directly forming the bearing  32 , so that the throttle valve shaft, during assembly, merely needs to be inserted there into the closed bearing boss. 
   In the embodiment of a throttle valve positioning device  110  shown in  FIG. 3 , in which the drive and that region of a housing  112  which surrounds said drive have been omitted, a parting line  130  between the two housing halves  114 ,  116  runs both through the first drive-side bearing  128  of the throttle valve shaft  120  and through the opposite second bearing  132 , i.e. the parting line  130  lies essentially in the plane defined by the position of the throttle valve shaft  120 . Only in the region of the throttle body  126  is the parting line  130  designed so as to be inclined in accordance with the inclined region  136 , with a slope corresponding to the throttle valve inclination. This makes it necessary for a wall section  150  formed parallel to the flow direction in the throttle body  126  to be provided between the region of the top housing half  116 , this region forming part of the throttle body  126 , and the remaining housing region, so that two parting lines are produced in the contact region of the sealing ring  140  at the circumference  134  of the throttle valve  120 . However, these parting lines are not critical for the sealing on account of their essentially perpendicular course relative to the direction of movement of the sealing ring in this region during the positioning of the throttle valve. The advantage of the embodiment shown in  FIG. 3  consists in the simpler assembly, since the unit of drive, gearing, throttle valve shaft and throttle valve, when housing halves  114 ,  116  are separated, can be inserted into its bearings in a simple manner and the housing  112  can then be closed in a simple manner. The embodiment shown in  FIGS. 1 and 2  offers even further improved sealing, with certain difficulty during the assembly on account of the second bearing  32 , which is not split, since first of all the throttle valve shaft can be inserted into this bearing and only after that can the unit of gearing and actuator be inserted into the receptacles of the bottom housing half  114 . 
   In principle, further embodiments of the throttle valve positioning devices are conceivable which have the common feature that the throttle valve circumference lies laterally next to the throttle valve shaft, at least in the region of the passage location in the throttle valve shaft, in the throttle body. A simple lateral offset of the throttle valve with respect to the throttle valve shaft without or with only very slight inclination is likewise possible in principle, even though a corresponding adaptation of the inner contour of the throttle body to the path of movement of the pivotable throttle valve could be necessary in this respect in order to achieve a good sealing effect. In principle, it is also conceivable to arrange the drive not directly between the two housing halves but rather at a distance from the throttle valve shaft, so that the two housing halves merely form the throttle body and the bearing arrangement for the throttle valve shaft.