Monitoring operation of exhaust gas particle filter, e.g. for diesel engine, involves monitoring characteristic property downstream of filter

摘要

The value of at least one characteristic property for the interaction of the particles with the filter (1) is determined downstream of the filter. A filter monitoring signal is generated as a function of this value and compared with a comparison value. A fault indication is generated as a function of the result of the comparison : The values of the characteristic property are measured at successive time intervals and are subtracted from each other. The quantity of particles accumulated in the exhaust gas flow downstream of the filter on a defined measuring surface (4) which can be heated electrically by a detector (5) is determined as the characteristic property from the heat capacity of the measuring surface and the heat capacity of the quantity of particles from a curve of rising temperature. The curves of rising temperature for the measuring surface with particle deposits are compared with at least one curve of rising temperature obtained by a calibration of the measuring surface with and without particle deposits. Influences exerted on the measurement by the exhaust gas pressure, temperature and flow rate are eliminated by measuring these properties and compensating for them on the curve of rising temperature. Alternatively, the quantity of particles is determined as the characteristic property by measuring the capacity of a detector-condenser exposed to the exhaust gas flow downstream of the particle filter. At the end of each measurement, the measuring surface of each detector exposed to the exhaust gas flow is brought to a temperature at which the particle deposits are burned. Alternatively, the characteristic property measured is the back-pressure on the particle filter, measured at preset intervals and compared to a comparison back-pressure value which is preferably below the value of back-pressure when the particle filter is empty. An independent claim is included for a device for carrying out this process, with at least one detector (5) placed downstream of a particle filter (1) and connected to an evaluation unit (6) which is in turn connected to a display (11). The detector can be a measuring surface with defined heat capacity mounted on a support (3) and with a temperature detector (5) connected to the evaluation unit. Alternatively, it can be a condenser which can be electrically heated, exposed to the exhaust gas flow by two electrodes and connected to a capacitative measuring circuit from the evaluation unit. Alternatively, it can be a pressure detector downstream of the particle filter and connected to the evaluation unit and a second pressure detector in the wall of the pipe to measure the volume gas flow in combination with the first pressure detector and a temperature detector.