Systems and methods for exhaust catalyst temperature control

Patent metadata

Field	Value
Publication number	US-9297320-B2
Application number	US-201414341484-A
Country	US
Kind code	B2
Filing date	Jul 25, 2014
Priority date	Jul 25, 2014
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

Methods and systems are provided for exhaust catalyst temperature control by metering exhaust bypass flow from a dedicated EGR cylinder. A continuously variable bypass valve may be adjusted to vary an amount of exhaust directed to an exhaust catalyst from a dedicated EGR cylinder via a bypass passage relative to exhaust recirculated to the engine intake via an EGR passage. At lower catalyst temperatures, more exhaust is metered via the bypass passage to enable catalyst temperature to be maintained above an activation level.

First claim

The invention claimed is:

1. A method for an engine, comprising:
flowing exhaust from a dedicated EGR cylinder to each of an exhaust catalyst via a bypass passage and an engine intake via an EGR passage;
adjusting, responsive to a catalyst temperature, a relative flow through the bypass passage and EGR passage via a bypass valve by increasing the relative flow through the bypass passage while correspondingly decreasing flow through the EGR passage as the catalyst temperature falls below a threshold, the threshold including a catalyst light-off temperature, and decreasing the relative flow through the bypass passage while correspondingly increasing flow through the EGR passage as the catalyst temperature exceeds the threshold;
determining a required bypass flow rate to maintain the catalyst temperature at the threshold; and
enriching the dedicated EGR cylinder based on each of the catalyst temperature and the required bypass flow rate.

2. The method of claim 1 , wherein the bypass valve is a continuously variable bypass valve.

3. The method of claim 1 , wherein a degree of richness of the enriching is increased as a difference between the catalyst temperature and the threshold increases.

4. The method of claim 3 , wherein the enriching includes, after increasing a flow rate of exhaust through the bypass passage up to a threshold rate, maintaining the bypass valve flow while increasing a degree of richness of the enriching as the difference between the catalyst temperature and the threshold increases.

5. The method of claim 4 , further comprising, enleaning remaining engine cylinders, the enleaning based on the enriching of the dedicated EGR cylinder and flow through the bypass passage to maintain a stoichiometric air-fuel ratio at the exhaust catalyst.

6. An engine system, comprising:
an engine having a first and a second cylinder group;
an EGR passage selectively routing exhaust from the first cylinder group to an intake manifold of the engine, the EGR passage including a water-gas shift catalyst;
a bypass passage coupling the EGR passage, downstream of the water-gas shift catalyst, to an exhaust manifold of the engine, upstream of an exhaust catalyst;
a continuously variable bypass valve at a junction of the EGR passage and the bypass passage for varying a portion of exhaust from the first cylinder group routed via the bypass passage relative to the EGR passage;
a temperature sensor coupled to the exhaust catalyst configured to measure a catalyst temperature; and
a controller with computer-readable instructions for:
enriching the first cylinder group while enleaning the second cylinder group;
determining a required bypass flow rate to maintain the catalyst temperature at a threshold temperature, wherein said threshold temperature includes a catalyst light-off temperature; and
adjusting an opening of the bypass valve, continuously, to vary a proportion of exhaust routed from the first cylinder group to the exhaust catalyst via the bypass passage relative to exhaust recirculated to the engine intake manifold to maintain the catalyst temperature at the threshold temperature based on each of the catalyst temperature and the required bypass flow rate.

7. The system of claim 6 , wherein the enriching of the first cylinder group is based on a difference between an estimated exhaust catalyst temperature and the threshold temperature, a degree of richness being increased as the difference increases.

8. The system of claim 7 , wherein the enleaning of the second cylinder group is based on the enriching of the first cylinder group and the proportion of exhaust routed via the bypass passage, a degree of leanness being increased as a degree of richness increases or as the proportion of exhaust routed via the bypass increases to maintain a stoichiometric air-fuel ratio at the exhaust catalyst.

9. The system of claim 8 , wherein the controller includes further instructions for: in response to the estimated exhaust catalyst temperature being higher than the threshold, reducing a degree of richness of the first cylinder group while adjusting the opening of the bypass valve to decrease routing of exhaust via the bypass passage to the exhaust catalyst.

10. The system of claim 6 , wherein the controller includes further instructions for: combining rich exhaust from the enriched first cylinder group received via the bypass passage with lean exhaust from the enleaned second cylinder group at the exhaust catalyst.

Assignees

• Ford Global Tech Llc

Inventors

• Hilditch James Alfred
• Shelby Michael Howard
• Styles Daniel Joseph
• Glugla Chris Paul
• Czekala Michael Damian

Classifications

• F01N9/00

  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 title

• F02D43/00

  Conjoint electrical control of two or more functions, e.g. ignition, fuel-air mixture, recirculation, supercharging or exhaust-gas treatment · CPC title

• F02M26/02

  EGR systems specially adapted for supercharged engines · CPC title

• F02D41/00

  Electrical control of supply of combustible mixture or its constituents (F02D43/00 takes precedence {; control of engine starters F02N11/08, electrical control of engine ignition timing F02P5/145}) · CPC title

• F02D41/0055

  Special engine operating conditions, e.g. for regeneration of exhaust gas treatment apparatus · CPC title