Purifying internal combustion engine exhaust gases, where triple effect, NOx storage and RCS catalyzers are in series and the NOx storage catalyzer can be bypassed when its temperature rises

The installation has a bypass line (5) to allow exhaust gases leaving the triple effect catalyzer to be channeled to the RCS catalyzer, short-circuiting the NOx storage catalyzer. The fraction of exhaust gases leaving the triple effect catalyzer and passing through the bypass line is adjusted as a function of the installation temperature, in particular the NOx storage catalyzer temperature The installation comprises an exhaust gas pipe (1) on which is mounted one after another a triple effect catalyzer (2), a NOx storage catalyzer (3) and an RCS catalyzer (4). Above a predetermined threshold value TS1 for a temperature T1 measured in the NOx storage catalyzer, the fraction of exhaust gases passing through the bypass is at least approximately equal to 100% of the gases leaving the triple effect catalyzer. When the temperature T1 of the NOx storage catalyzer is above the threshold value TS1 and the temperature T2 of the RCS catalyzer is above a threshold value TS2, the engine is fed only with a stoichiometric or rich combustion mixture, or the throttle on the engine air inlet is open and the exhaust gases leaving the triple effect catalyzer are all or nearly all sent to the NOx storage catalyzer. L'invention concerne une installation comportant une conduite (1) pour les gaz d'échappement sur laquelle sont montés l'un derrière l'autre et dans la direction du flux, un catalyseur à triple effet (2), un catalyseur (3) d'emmagasinage des oxydes d'azote et un catalyseur à RCS (4). Selon l'invention, l'installation pour l'épuration des gaz présente une conduite en dérivation (5) qui permet d'acheminer des gaz d'échappement sortant du catalyseur à triple effet (2) au catalyseur à RCS (4), en court-circuitant le catalyseur (3) d'emmagasinage des oxydes d'azote. Utilisation dans un véhicule automobile.