Exhaust Line for Heat Engine

Abstract

The invention relates to an exhaust line ( 10 ) for a heat engine, comprising a nitrogen oxide trap ( 28 ) which is installed on a filter section ( 24 ) between an exhaust inlet ( 12 ) and an exhaust outlet ( 14 ). The invention also comprises: a bypass section ( 26 ) which is disposed between the nitrogen oxide trap ( 28 ) and the exhaust inlet ( 12 ) in order to divert the exhaust gas away from the nitrogen oxide trap ( 28 ), and exhaust gas switching means ( 32, 24 ) which enable the gases to flow through the filter section ( 24 ) or the bypass section ( 26 ).

1 - 10 . (canceled) 
   
   
       11 . Exhaust line ( 10 ) for a heat engine, comprising, between an exhaust inlet ( 12 ) and an exhaust outlet ( 14 ), a nitrogen oxide trap ( 28 ) which is fitted on a filtering portion ( 24 ), between the nitrogen oxide trap ( 28 ) and the exhaust inlet ( 12 ), a branching portion ( 26 ) which is capable of branching the exhaust gases away from the nitrogen oxide trap ( 28 ), switching means ( 32 ,  34 ) for the exhaust gases in order to cause them to flow through the filtering portion ( 24 ) or branching portion ( 26 ), a three-way catalyser ( 18 ) which is arranged between the inlet ( 12 ) and the upstream portion of the filtering portion ( 24 ) and the branching portion ( 26 ), characterised in that it comprises means ( 36 ) for controlling the switching means ( 32 ), which control means ( 36 ) comprise means ( 38 ) for acquiring the outlet temperature of the exhaust gases from the engine, the switching means ( 32 ) being capable of generally branching the gases off towards the branching portion ( 26 ) when the temperature of the gases is greater than 600° C., and in that the control means ( 36 ) comprise:
 means ( 40 ) for determining when the engine is operating with a rich mixture;   means ( 40 ) for determining whether the temperature measured by the temperature acquisition means ( 38 ) is greater than 600° C.;   means ( 40 ) for commanding the switching means ( 32 ) to branch the gases off towards the branching portion ( 26 ) when the engine operates with a rich mixture and when the temperature measured by the acquisition means ( 38 ) is greater than 600° C.; and   means ( 40 ) for commanding the switching means ( 32 ) to maintain the flow of the gases through the filtering portion ( 24 ) when the engine is not operating with rich mixture or when the temperature measured by the acquisition means ( 38 ) is less than 600° C.   
   
   
       12 . Exhaust line according to  claim 11 , characterised in that the switching means ( 32 ) comprise means for blocking the filtering portion ( 24 ) immediately downstream of the nitrogen oxide trap ( 28 ). 
   
   
       13 . Exhaust line according to  claim 12 , characterised in that the switching means comprise a three-way valve ( 32 ) which connects in parallel the branching portion ( 26 ) and the filtering portion ( 24 ) to the remainder of the line ( 10 ). 
   
   
       14 . Exhaust line according to  claim 13 , characterised in that it comprises a fork ( 22 ) which is arranged between the inlet ( 12 ) and, on the one hand, the upstream portion of the filtering portion ( 24 ) and, on the other hand, the upstream portion of the branching portion ( 26 ), and the three-way valve ( 32 ) is arranged downstream of the filtering portion ( 24 ) and the branching portion ( 26 ) and is capable of selectively connecting them to a common downstream portion ( 30 ) of the exhaust line. 
   
   
       15 . Exhaust line according to  claim 11 , characterised in that it comprises, on the one hand, at least one sensor selected from the group comprising a sensor ( 44 ) for sensing the position of at least one valve, a temperature sensor ( 46 ) and a gas composition sensor ( 48 ) and, on the other hand, means ( 42 ) for diagnosing the operating state of the switching means ( 32 ,  34 ) based on the or each sensor. 
   
   
       16 . Exhaust line according to  claim 11 , characterised in that the means ( 36 ) for controlling the switching means ( 32 ) comprise means ( 40 ) for acquiring the future occurrence of a phase for operating the engine with a lean mixture when it operates with a rich mixture, and in that the control means ( 36 ) comprise means for controlling the switching means ( 32 ) so as to branch the gases off towards the filtering portion ( 24 ) when such an operating phase of the engine with a lean mixture is detected. 
   
   
       17 . Exhaust line according to  claim 16 , characterised in that the control means ( 36 ) comprise means for, when the means ( 40 ) for acquiring the future occurrence of a phase for operating the engine with a lean mixture when it operates with a rich mixture do not detect such a phase, initiating a time delay following which the switching means ( 32 ) branch the exhaust gases off towards the filtering portion ( 24 ) for a shortened period of time. 
   
   
       18 . Line according to  claim 11 , characterised in that the means ( 36 ) for controlling the switching means ( 32 ) comprise means ( 40 ) for acquiring the stoichiometric operating conditions of the engine, and in that the switching means ( 32 ) are capable of generally branching gases off towards the branching portion ( 26 ) when the engine operates in a state which is superstoichiometric in terms of fuel. 
   
   
       19 . Exhaust line according to  claim 11 , characterised in that the control means ( 36 ) are capable of periodically controlling the switching means ( 32 ) so as to temporarily cause the exhaust gases to flow through the filtering portion ( 24 ) during the phases in which the exhaust gases generally flow through the branching portion ( 26 ). 
   
   
       20 . Propulsion assembly which comprises an engine which generally operates with a lean mixture and an exhaust line according to  claim 11 . 
   
   
       21 . Exhaust line according to  claim 11 , characterised in that the switching means comprise a three-way valve ( 32 ) which connects in parallel the branching portion ( 26 ) and the filtering portion ( 24 ) to the remainder of the line ( 10 ).