Method for determining the quantity of reducing agent in a tank

Abstract

The present invention relates to a method for determining the quantity of reducing agent in a tank (10) of a system intended to reduce the amount of NOx in the exhaust gases of a motor vehicle. The system comprises: a storage material (11) arranged in the tank (10) and capable of storing and of releasing the reducing agent reversibly according to the demand for reducing agent which may vary over the course of time; a heating device (12) designed to supply heat in order to release the reducing agent from the storage material (11), and a control device (13) for driving the heating device (12) in order to release the reducing agent. The method involves the following steps: a) as soon as the motor vehicle is started, driving the heating device (12) so that it delivers constant power during a phase known as the initial phase over which the pressure inside the tank (10) increases until it reaches a predetermined value, the driving of the heating device (12) then being adapted in order to regulate the pressure around a datum value; b) measuring the time of the initial phase or the derivative of pressure with respect to time during this initial phase; c) comparing the measured time of the initial phase, said derivative of pressure with respect to time or a combination of both against various calibrated values of the initial phase according to the quantity of reducing agent in the tank (10) in order to determine said quantity of reducing agent in said tank (10).

Dependencies are inferred from the claim text.