Fuel injection pump control system
BACKGROUND OF THE INVENTION 
     The present invention relates to a fuel injection pump, especially for use in spark plug ignited internal combustion engines, wherein the injection quantity regulating member (control rod) is actuated by an r.p.m.-dependent centrifugal force governor acting through a lever linkage and via an interposed cam plate element. 
     In a known fuel injection pump of this type, the cam plate element is a member whose position depends on the position of the accelerator pedal, as well as on the position of the centrifugal weights rotated by the engine. When this known control mechanism is used, however, in low-load operation of the engine, i.e., when the accelerator pedal is only slightly depressed and in a region of low engine r.p.m., the air quantity aspirated by the engine may change without sufficiently precise fuel metering. In addition, the linkage mechanism in that system is also very complicated. 
     Another known control system in which the pressure within the induction tube is measured by means of a pressure sensor or pick-up system and correspondingly determines the position of the control rod, brings the disadvantage that the sensitivity becomes very poor at full-load operation, i.e., when the difference between the induction tube vacuum and the atmospheric pressure is very small. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a fuel injection pumping system which avoids these above-mentioned disadvantages. 
     This object is attained, according to the invention, in that the cam plate element is embodied as a three-dimensional cam which is set in one spatial direction -- preferentially the axial direction -- by the centrifugal force governor and in another spatial direction (rotational direction) by an air measuring member located in the induction tube of the internal combustion engine. 
     This construction results in an increase of the control precision over the entire r.p.m-domain of the engine. 
     An exemplary embodiment of the object of the invention is represented in the drawing and is described in detail below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic and partly cross-sectional representation of a fuel injection control system according to the invention. 
     FIG. 1A is an end view of cam 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A cam shaft 1 belonging to a fuel injection pump which is not further shown drives a centrifugal force governor with fly weights 2 whose lever arms 2a communicate with a control spring 3. The spring 3 acts on the lever arms 2a in opposition to the effect of the centrifugal force. The change of position of fly weights 2, caused by the centrifugal force, is transmitted to a three-dimensional cam 4 by an extension rod 2b whose one end engages a groove 4a provided for this purpose in the three-dimensional cam 4. 
     An induction tube 5 of the engine (not shown) contains a flap 6 which measures the aspirated air quantity and which is pivotably mounted about an axis 6a located outside of the induction tube. An extension 6b on the measuring flap 6 is attached to one end of a connecting rod 7 whose other end is attached to a pivot pin 4b fastened on the face of the three-dimensional cam 4, in such a manner that the rotary movement of the measuring flap 6 results in a change of the rotational position of three-dimensional cam 4 on the cam shaft 1. 
     A guide lever 8 is pivotably mounted about a locally fixed axis 9 and has a follower element 8a which follows the contour of the cam surface 4c of the three-dimensional cam 4. Changes in the spatial orientation of the three-dimensional cam 4 result in changes in the spatial position of the point of contact of the follower element 8a on the cam surface 4c. These changes are transmitted by guide lever 8 to an intermediate lever 10, pivotable about an axis 10a, which displaces control rod 11 controlling the injected fuel quantity. 
     In the fuel injection system described above, the axial position of the three-dimensional cam 4 is controlled by the r.p.m.-dependent rotational motion of cam shaft 1, causing the centrifugal force-induced position change of the fly weights 2 which is transmitted to the cam 4 by the extension rod 2b, whereas the rotation of the three-dimensional cam 4 about the cam shaft 1 is due to the motion of the measuring flap 6 within the induction tube 5, whose degree of opening is determined by the amount of air aspirated through the induction tube and whose rotary motion is transmitted to the cam 4 by the lever 6b, the connecting rod 7 and the pivot pin 4b. Thus, the degree of rotation of the three-dimensional cam corresponds to the degree of opening of the measuring flap 6, i.e., to the aspirated air quantity. These movements of the three-dimensional cam 4 cause the movement of the guide lever 8 and the intermediate lever 10 which displaces the control rod 11, changing the injected fuel quantity. 
     Thanks to this construction, the precision of the control process which regulates the injected fuel quantity is increased over the entire r.p.m. domain of the engine. Even in the case where the aspirated air quantity might change, for example, due to the plugged up air filter or because of a general deterioration of the suction system of the engine, for example due to wear in the intake valve, nevertheless the fuel quantity metered out always corresponds to the air quantity actually aspirated by the engine and this fact results in a correspondingly high efficiency and in the required low concentration of toxic or uncombusted components in the exhaust gas. 
     A damper 6c, constructed integrally with the measuring flap 6, is mounted pivotably about the axis 6a and in such a manner as to close or block a fan-shaped damper chamber 5a provided to the induction tube 5. The free end of the damper 6c defines a suitable gap A between itself and the inner wall of said damper chamber 5a so that, upon rotation or turning of said damper 6c, air is allowed to flow into and out of said damper chamber 5a. In this way, said damper 6c serves to prevent the occurrence of an overshooting in rotation of the measuring flap 6, which would otherwise tend to take place, when the degree of opening or the pedal position of the accelerator is subjected to a sudden change, so as to cause an excessive fuel supply, thus unbalancing the air fuel ratio.