Patent ID: 8863500

Claim:
An apparatus comprising: at least one control unit, wherein the control unit implements a method of operating an electromagnetically actuated metering valve, the method comprising: loading the metering valve with a pulse-width modulated metering signal that stipulates a dosage of a precursor of a reagent introduced into an exhaust gas region of an internal combustion engine; forming ammonia by a thermolysis process of the precursor, the ammonia acting as the reagent; providing a clock signal having a clock signal period, wherein the clock signal period is smaller than a period of the pulse-width modulated metering signal; setting the period of the pulse-width modulated metering signal as a function of a metering request signal to a multiple of the clock signal period; and adjusting at least one of the period of the pulse-width modulated metering signal and a pulse duration of the pulse-width modulated metering signal in order to adapt the dosage of the reagent; calculating a minimum pulse duration based on a type of the metering valve and conditions in the exhaust gas region, the minimum pulse duration calculated to enable the metering valve to completely open, the minimum pulse duration further calculated so that a spray mist is produced during metering which prevents the reagent from crystallizing; limiting the pulse duration of the pulse-width modulated metering signal to a minimum pulse duration; and setting the pulse duration of the pulse-width modulated metering signal as a multiple of the clock signal period.