Assignment

The curves shown in the diagrams could also have been taken from an exhaust-gas testing. They show various Lambda sensor voltages, always around approx. 0,5 V, at idling speed, higher RPM and with or without air-volume disturbance values.

Function

At cold idling-speed (see picture 1), the Lambda sensor does not deliver any voltage. What can be seen is the comparator voltage of the control device (approx. 0,45 V). Picture 2 shows the typical, slow, swinging movement during idling. This could also be made visible through an analog multimeter. The speed of this movement increases with higher RPM (see picture 3).

To be able to test the responsiveness of the entire system, as is done during the mandatory exhaust-gas emission test, as shown in picture 4, foreign air is introduced into the system during idling. The sensor voltage remains, for a moment, at a voltage which reflects the lean mixture. Then the control device compensates for the additional amount of air by increasing the amount of fuel through the injection valves. The same thing occurs in picture 5, only faster.

In the world of electronics, the comparator (lat. comparare) is, as the name suggests, a comparer, e.g., in the case of two input points, to see which of the two has the higher voltage and to switch the output accordingly. In the Lambda sensor, the comparator voltage (mostly 0,45 - 0,5 V) serves as the comparative value (reference voltage) stated by the manufacturer. Regulation-wise, this is the reference- or the specified value.

In every moment, there is a voltage generated by a given- and the actual value (integrator-voltage), which is given to the control device, this then determines the momentary injection timing. Should the Lambda sensor voltage be higher than the comperator voltage, the up to now, still gradually increased integrator voltage is gradually reduced, that means, it's not abruptly changed. It is in fact, actually desired, that the regulation, for a certain amount of time, actually occurs in the wrong direction.

The slowing down of the reaction is important, so that it does not come to a so-called over-regulation. The gas-flow- and computing-time must be taken into consideration. The values of course, may also not deviate too far from the ideal-value (Lambda-range). Should, by the way, the same correction of the starting values in the Lambda-grid be frequently necessary, the control device can also change and permanently store them (adaption). 08/13