The use of electrically driven throttle flaps as part of en E-GAS system is already known. Usually, structures are used wherein, at a lower mechanical stop, a position of the throttle flap with minimal air leakage is reached as shown in FIG. 5a. The throttle flap is identified in FIG. 5a by reference numeral 1. FIG. 5d shows a typical position of the throttle flap during driving operation. An upper mechanical stop lies in the vicinity of the maximum possible air throughput. In order to ensure an emergency driving when there is a malfunction of the E-GAS system, there is, as a rule, still a rest position just above the lower mechanical stop and this is the so-called emergency air position of the throttle flap 1 as shown in FIG. 5b. 
Systems having a so-called through-plunging throttle flap as shown in FIGS. 4a to 4c are also known. Here, the emergency air position can lie at the lower mechanical stop shown in FIG. 4a or on the side lying opposite the lower mechanical stop as shown in FIG. 4a in phantom outline. The minimum air throughput results with a perpendicular position of the throttle flap 1 as shown in FIG. 4b. FIG. 4c, in turn, shows a typical position of the throttle flap 1 during driving operation wherein the upper mechanical stop lies in the vicinity of the maximum possible air throughput. A system of this kind with a through-plunging throttle flap 1 has some advantages. On the one hand, a simpler mechanical structure of the reset mechanism results and, on the other hand, the control path, which results with the control of the position of the throttle flap 1, has, depending upon the emergency air position, no turning point at the emergency air position and is therefore simpler to master. In FIG. 4a, such an emergency air position without a turning point is the emergency air position shown in phantom outline and lying opposite to the lower mechanical stop. Thirdly, a flatter ascending characteristic line for the air throughput is achieved which, in any event, facilitates reaching the necessary precision in the adjustment of the throttle flap 1 for the idle control of the internal combustion engine.
What is problematic with the through-plunging throttle flap is, however, that the position of the throttle flap 1 with minimum leakage air, that is, the position with minimum air throughout, must be known to the E-Gas system in order to make possible an idle control with very small air mass flows. In a conventional throttle flap according to FIGS. 5a to 5c, the position of the throttle flap 1 with minimum air leakage can be simply learned because, for this purpose, simply the lower mechanical stop can be approached and the read-back values of a sensor (not shown) for the position of the throttle flap 1 can be stored in a control apparatus.
In a through-plunging throttle flap, only the lower mechanical stop can be learned in this way which, however, is of no consequence during normal operation. The position of the throttle flap 1 with minimal air leakage must now either be known very accurately with respect to the mechanical stop(s) or be very accurately known absolutely as a read-back voltage of the sensor for the position of the throttle flap 1 in order to ensure that, on the one hand, positions of the throttle flap 1 with very low air leakage can be approached and, on the other hand, it is avoided to come to the again increasing portion of the air mass flow in the closing direction of the throttle flap, that is, in the direction of the lower mechanical stop. The air mass flow as a function of the throttle flap angle is shown by way of example in FIG. 3. Here, it can be seen that, in the direction of the lower mechanical stop in the region of negative angles of the throttle flap 1, the air mass flow again increases. The air mass flow is plotted in kg/h as a function of the angle of the throttle flap. Furthermore, it must be ensured that this position with minimum air leakage changes only very slightly over the service life of the internal combustion engine which imposes high requirements on the mechanics, read-back tolerances and manufacturing tolerances.
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USPTO Backgrounds