Exhaust emission control system

• US 10,443,474 B2
• Filed: 01/08/2018
• Issued: 10/15/2019
• Est. Priority Date: 01/23/2017
• Status: Active Grant

• Current Assignee: Mazda Motor Corporation
• Original Assignee: Mazda Motor Corporation
• Inventors: Kanno, Masanobu, Yamaguchi, Takayuki, Tetsuno, Masayuki
• Primary Examiner(s): Lee, Brandon D
• Application Number:
  US15/864,414
• Publication Number:
  US 20180209316A1
• Time in Patent Office: 645 Days
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2900/08 said parameters being related to the engine
• CPC Class Codes: F01N 2900/1602 Temperature of exhaust gas apparatus
• CPC Class Codes: F01N 2900/1614 NOx amount trapped in catalyst
• CPC Class Codes: F01N 2900/1811 Temperature
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: F02D 2200/0802 Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 41/0245 by increasing temperature of the exhaust gas leaving the engine
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/064 at cold start F02D41/067 takes precedence
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/405 with post injections
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust emission control system is provided, which includes a NO_x storage catalyst provided in an exhaust passage of an engine and configured to store NO_x, a urea SCR catalyst provided in the exhaust passage, downstream of the NO_x storage catalyst, and a NO_x reduction controlling module configured to set a NO_x reduction condition and, when the NO_x reduction condition is satisfied, performs NO_x reduction processing in which an air-fuel ratio of exhaust gas is set to be one of near a stoichiometric air-fuel ratio and rich, and the NO_x stored in the NO_x storage catalyst is reduced, the NO_x reduction condition being set looser for the NO_x reduction processing performed the first time after the engine is started than the NO_x reduction processing performed the second and subsequent times after the engine is started.

Claims

1. An exhaust emission control system, comprising:

a fuel injector;

a NO_x storage catalyst provided in an exhaust passage of an engine and configured to store NO_x;

a urea selective catalytic reduction (SCR) catalyst provided in the exhaust passage downstream of the NO_x storage catalyst; and

a processor operatively coupled to the fuel injector and configured to execute a NO_x reduction controlling module to set a NO_x reduction condition and, when the processor determines that the NO_x reduction condition is satisfied, control the fuel injector to perform NO_x reduction processing in which an air-fuel ratio of exhaust gas is set to be one of near a stoichiometric air-fuel ratio and rich, and the NO_x stored in the NO_x storage catalyst is reduced, wherein

the NO_x reduction condition includes a condition in which a NO_x stored amount in the NO_x storage catalyst is larger than a given reference stored amount and the engine operates within a given reduction-allowed operating range determined based on an engine speed and an engine load,

the NO_x reduction controlling module sets a first operating range that is a reduction-allowed operating range for performing the NO_x reduction processing a first time after the engine is started, to be larger than a second operating range that is a reduction-allowed operating range for performing the NO_x reduction processing a second and subsequent times after the engine is started, and

the NO_x reduction controlling module sets the first operating range by expanding the second operating range toward at least one of a higher engine speed side and a higher engine load side.

2. The exhaust emission control system of claim 1, wherein

the processor is further configured to execute a urea-catalyst temperature acquiring module to acquire a temperature of the urea SCR catalyst, and

the NO_x reduction controlling module sets the first operating range to be larger as the acquired temperature of the urea SCR catalyst drops.

3. The exhaust emission control system of claim 1, wherein the NO_x reduction controlling module sets the air-fuel ratio of the exhaust gas to be one of near the stoichiometric air-fuel ratio and rich when a temperature of the NO_x storage catalyst is higher than a NO_x-catalyst purification start temperature and a temperature of the urea SCR catalyst is lower than a switching temperature at which a NO_x purification rate of the NO_x storage catalyst becomes higher than a NO_x purification rate of the urea SCR catalyst.

4. The exhaust emission control system of claim 1, wherein the NO_x reduction controlling module sets the air-fuel ratio of the exhaust gas to be one of near the stoichiometric air-fuel ratio and rich by performing a post injection of fuel on expansion stroke of the engine.