Spark ignition engine including three-way catalyst with nox storage component

Abstract

A spark ignition engine with an exhaust system having a catalyst, which includes a three-way catalyst (TWC) and a NOx storage component, and an engine control unit is provided. The engine control unit is programmed to control the air-to-fuel ratio of the engine to run at the stoichiometric air-to-fuel ratio during normal running conditions and to run lean of the stoichiometric air-to-fuel ratio during a defined portion of an engine speed/load. The engine control unit also determines the amount of NOx contacting the TWC during lean running operation in response to data input from a sensor means, thereby a remaining NOx storage capacity of the TWC is determined. The control unit is programmed to return the air-to-fuel ratio to stoichiometry when the NOx storage capacity is below a pre-determined value. The engine and its components are arranged such as to substantially prevent passing more NOx to atmosphere during an engine cycle compared with a spark ignition engine run continuously at stoichiometric conditions.

1 . A spark ignition engine comprising an exhaust system comprising a catalyst and an engine control unit programmed to control the air-to-fuel ratio of the engine to run at a stoichiometric air-to-fuel ratio during normal running conditions and to run lean of the stoichiometric air-to-fuel ratio during a defined portion of an engine speed/load map, which catalyst comprising a three-way catalyst (TWC) including a NOx storage component, wherein the engine control unit is programmed to determine an amount of NOx contacting the TWC during lean running operation in response to data input from sensor means, thereby a remaining NOx storage capacity of the TWC is determined, and the control unit is programmed to return the air-to-fuel ratio to stoichiometry when the NOx storage capacity is below a pre-determined value.  
   
   
       2 . An engine according to  claim 1 , wherein the defined portion of the engine speed/load map is engine idle.  
   
   
       3 . An engine according to  claim 1 , wherein the defined portion of the engine speed/load map comprises driving conditions, wherein a level of NOx emitted by the engine at the driving conditions is up to ten times more than the level of NO x  emitted at engine idle conditions.  
   
   
       4 . An engine according to  claim 1 , further comprising a clock, wherein the data input sensor means includes a predetermined or predicted time elapsed from the start of lean running operation.  
   
   
       5 . An engine according to  claim 4 , wherein the predicted time is subsequently adjusted in response to data input.  
   
   
       6 . An engine according to  claim 1 , wherein the sensor means detects a value of airflow over the TWC and the data input includes that detected value.  
   
   
       7 . An engine according to  claim 1 , wherein the sensor means detects a manifold vacuum value and the data input includes that detected value.  
   
   
       8 . An engine according to  claim 1 , wherein the sensor means detects an ignition timing value and the data input includes that detected value.  
   
   
       9 . An engine according to  claim 1 , wherein the sensor means detects an engine speed value and the data input includes that detected value.  
   
   
       10 . An engine according to  claim 1 , wherein the sensor means detects a throttle position value and the data input includes that detected value.  
   
   
       11 . An engine according to  claim 1 , wherein the sensor means is a lambda value sensor, and the data input includes the lambda value detected upstream and/or downstream of the TWC.  
   
   
       12 . An engine according to  claim 1 , wherein the sensor means detects a quantity of fuel injected in the engine and the data input includes that detected quantity.  
   
   
       13 . An engine according to  claim 1 , further comprising an exhaust gas recirculation (EGR) circuit, wherein the sensor means detects an amount of exhaust gas recirculation by the position of an EGR valve and the data input includes the detected amount of EGR.  
   
   
       14 . An engine according to  claim 1 , wherein the sensor means detects an engine coolant temperature value and the data input includes that detected value.  
   
   
       15 . An engine according to  claim 1 , wherein the sensor means comprises a NOx sensor and the data input includes an amount of NOx detected by the NO x  sensor upstream and/or downstream of the TWC.  
   
   
       16 . An engine according to  claim 1 , wherein the engine is a gasoline engine.  
   
   
       17 . An engine according to  claim 16 , wherein the engine is a port fuel injection engine.  
   
   
       18 . An engine according to  claim 16 , wherein the engine is a direct injection engine.  
   
   
       19 . An engine according to  claim 1 , wherein the engine is fuelled by a fuel selected from the group consisting of liquid petroleum gas, natural gas, methanol, and hydrocarbon mixtures including ethanol or hydrogen gas.  
   
   
       20 . An engine according to  claim 1 , wherein the TWC comprises at least one platinum group metal (PGM).  
   
   
       21 . An engine according to  claim 20 , wherein the at least one PGM is selected from the group consisting of platinum (Pt), palladium, rhodium (Rh), ruthenium, osmium or iridium and combinations of any two or more thereof.  
   
   
       22 . An engine according to  claim 1 , wherein the NOx storage component comprises an alkali metal, an alkaline-earth metal or a rare-earth metal or a combination of any two or more thereof.  
   
   
       23 . An engine according to  claim 22 , wherein the alkali metal is potassium or caesium.  
   
   
       24 . An engine according to  claim 22 , wherein the alkaline-earth metal is magnesium, calcium, strontium or barium.  
   
   
       25 . An engine according to  claim 22 , wherein the rare earth metal is a lanthanide group metal.  
   
   
       26 . An engine according to  claim 1 , wherein the TWC comprises an oxygen storage component (OSC).  
   
   
       27 . An engine according to  claim 26 , wherein the OSC comprises a component selected from the group consisting of stabilised ceria, perovskites, NiO, MnO 2 , manganese-based compounds supported on alumina-containing mixed oxide, a mixed oxide of manganese and zirconium, Pr 2 O 3  and combinations of any two or more thereof.  
   
   
       28 . An engine according to  claim 27 , wherein the ceria stabiliser selected from the group consisting of zirconium, lanthanum, aluminium, yttrium, praseodymium and neodymium.  
   
   
       29 . An engine according to  claim 1 , wherein the TWC comprises an inner layer comprising a first PGM and the NOx storage component, and an outer layer comprising an OSC and a second PGM.  
   
   
       30 . A vehicle including an engine according to  claim 1 .  
   
   
       31 . A vehicle according to  claim 30 , wherein the TWC is in a close-coupled position.  
   
   
       32 . A vehicle according to  claim 30 , wherein a fresh TWC includes a sufficient amount of the NOx storage component to retain sufficient NOx storage capacity after high temperature ageing.  
   
   
       33 . An engine control unit for a spark ignition engine comprising an exhaust system comprising a TWC including a NOx storage component, which engine control unit is programmed to control the air-to-fuel ratio of the engine to run at a stoichiometric air-to-fuel ratio during normal running conditions and to run lean of stoichiometry during a defined portion of an engine speed/load map and to determine an amount of NOx contacting the TWC during lean running operation in response to data input from sensor means, thereby a remaining NOx storage capacity of the TWC is determined, and the control unit is programmed to return the air-to-fuel ratio to stoichiometry when the NOx storage capacity is below a pre-determined value.  
   
   
       34 . A method of treating exhaust gas of a spark ignition engine run at the stoichiometric air-to-fuel ratio during normal running conditions, which engine comprising an exhaust system comprising a TWC including a NOx storage component, which method comprising the steps of controlling the engine air-to-fuel ratio to run lean of stoichiometry during a defined portion of an engine speed/load map, determining the amount of NOx contacting the TWC during lean running operation in response to data input from sensor means thereby determining the remaining NOx storage capacity of the TWC, and returning the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a pre-determined value.  
   
   
       35 . (canceled)  
   
   
       36 . (canceled)  
   
   
       37 . An engine according to  claim 29 , wherein the first PGM is platinum.  
   
   
       38 . An engine according to  claim 29 , wherein the second PGM is rhodium.  
   
   
       39 . An engine according to  claim 11 , wherein the lambda value sensor is a linear lambda sensor.  
   
   
       40 . An engine according to  claim 25 , wherein the rare earth metal is lanthanum.