US20110271657A1

US20110271657A1 - Control system and method for improved efficiency of particulate matter filter regeneration

Info

Publication number: US20110271657A1
Application number: US12/773,446
Authority: US
Inventors: Julian C. Tan; John Zeilstra; Christoph Thoele; Gustavo Tepedino
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-05-04
Filing date: 2010-05-04
Publication date: 2011-11-10
Also published as: CN102235216A; DE102011018928A1

Abstract

An engine control system includes an injection determination module and an injection distribution module. The injection determination module determines a desired amount of hydrocarbons (HC) to inject into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter. The injection distribution module controls a ratio of auxiliary injection to post-combustion injection based on engine load, engine speed, and the desired amount of HC injection, wherein auxiliary injection includes injecting HC into the exhaust gas, and wherein post-combustion injection includes injecting HC into cylinders of the engine during a period after combustion.

Description

FIELD

The present disclosure relates to internal combustion engines, and more particularly to a system and method for controlling hydrocarbon (HC) injection into exhaust gas produced by an engine to improve efficiency of particulate matter (PM) filter regeneration.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combine air and fuel to create an air/fuel (A/F) mixture that is combusted within a plurality of cylinders. The combustion of the A/F mixture drives pistons which rotatably turn a crankshaft generating drive torque. Specifically, air may be drawn into the cylinders and compressed using the pistons. Fuel may then be combined with (i.e., injected into) the compressed air causing the pressurized A/F mixture to combust (e.g., a compression ignition, or CI engine). For example, CI engines include diesel engines.
Alternatively, the air may be mixed with fuel to create the A/F mixture prior to compression. The A/F mixture may then be compressed until the A/F mixture reaches a critical pressure and/or temperature and automatically ignites (e.g., a homogeneous charge compression ignition, or HCCI engine). HCCI engines, however, may also “assist” ignition of the A/F mixture using spark from spark plugs. In other words, HCCI engines may ignite the A/F mixture using spark assist depending on engine operating conditions. For example, HCCI engines may use spark assist at low engine loads.
Exhaust gas produced during combustion may be expelled from the cylinders into an exhaust manifold. The exhaust gas may include carbon monoxide (CO) and hydrocarbons (HC). The exhaust gas may also include nitrogen oxides (NOx) due to the higher combustion temperatures of CI engines and HCCI engines compared to spark ignition (SI) engines. An exhaust treatment system may treat the exhaust gas to remove CO, HC, and/or NOx. For example, the exhaust treatment system may include, but is not limited to, at least one of an oxidation catalyst (OC), a particulate matter (PM) filter, a selective catalytic reduction (SCR) system, NOx absorbers/adsorbers, and catalytic converters.

SUMMARY

An engine control system includes an injection determination module and an injection distribution module. The injection determination module determines a desired amount of hydrocarbons (HC) to inject into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter. The injection distribution module controls a ratio of auxiliary injection to post-combustion injection based on engine load, engine speed, and the desired amount of HC injection, wherein auxiliary injection includes injecting HC into the exhaust gas, and wherein post-combustion injection includes injecting HC into cylinders of the engine during a period after combustion.
A method includes determining a desired amount of hydrocarbons (HC) to inject into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter, and controlling a ratio of auxiliary injection to post-combustion injection based on engine load, engine speed, and the desired amount of HC injection, wherein auxiliary injection includes injecting HC into the exhaust gas, and wherein post-combustion injection includes injecting HC into cylinders of the engine during a period after combustion.
In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a tangible computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an exemplary engine system according to the present disclosure;

FIG. 2 is a functional block diagram of an exemplary control module according to the present disclosure;

FIG. 3 is a functional block diagram of an exemplary injection distribution module according to the present disclosure;

FIG. 4 is a graph illustrating exemplary exhaust gas temperature (EGT) control during particulate matter (PM) filter regeneration according to the present disclosure; and

FIG. 5 is a flow diagram of an exemplary method for controlling injection of hydrocarbons (HC) into engine exhaust gas during PM filter regeneration according to the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.
As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
Compression ignition (CI) (e.g., diesel) and homogeneous charge compression ignition (HCCI) engines may include similar exhaust treatment systems. More specifically, exhaust treatment systems for CI and HCCI engines may include an oxidation catalyst (OC) located before (i.e., upstream from) a selective catalytic reduction (SCR) catalyst and a particulate matter (PM) filter. The OC oxidizes carbon monoxide (CO) and hydrocarbons (HC) to form carbon dioxide (CO₂) and water (H₂O). The SCR catalyst (in conjunction with a dosing agent, such as urea) removes nitrogen oxides (NOx) from the exhaust gas.
The PM filter, on the other hand, removes PM from the exhaust gas. The PM filter may remove PM from the exhaust gas until the PM filter is saturated. In other words, the saturation condition may correspond to when the PM filter is full of PM (e.g., soot), after which a regeneration cycle may begin. The regeneration cycle may introduce HC into the exhaust gas. The HC in the exhaust gas may be catalyzed by the OC in an exothermic reaction that generates heat and increases exhaust gas temperature (EGT). The increased EGT at the outlet of the OC (i.e., at the inlet of the PM) may burn and/or breakdown the PM trapped in the PM filter, thus “regenerating” the PM filter.
Exhaust treatment systems, therefore, may further include one or more HC injectors that inject HC (e.g., fuel) upstream from an OC in an exhaust stream. This may be referred to as “auxiliary injection.” Alternatively, exhaust treatment systems may introduce HO into the exhaust gas by performing post-combustion injection using fuel injectors of the engine. Conventional control systems control injection of HC into the exhaust stream during PM filter regeneration based on exhaust flow.
Auxiliary injection and post-combustion injection, however, both have disadvantages. More specifically, auxiliary injection may cause fuel to pool on exhaust pipe walls, resulting in a poor mixture of the fuel with the exhaust gas. The poor mixture may be difficult to catalyze by the OC, which may damage the OC and/or may result in decreased PM filter regeneration temperatures and increased emissions. Post-combustion injection, on the other hand, may cause fuel to pool on cylinder walls at low cylinder pressures (e.g., piston near bottom center). The pooling of fuel on the cylinder walls may dilute oil that lubricates the parts within the cylinder, thus requiring more frequent oil changes and/or decreased engine durability.
Accordingly, a system and method are presented that control a ratio of auxiliary injection to post-combustion injection during PM filter regeneration based on engine operating parameters. In other words, the system and method may achieve the advantages of both auxiliary injection and post-combustion injection while avoiding the corresponding disadvantages (discussed above). Therefore, the system and method may achieve more efficient regeneration of a PM filter, thereby protecting exhaust treatment system components (e.g., the OC, the PM filter, etc.) and/or decreasing emissions. Moreover, the system and method may command post-combustion injection in one bank of cylinders of the engine (e.g., half), thereby allowing for exhaust gas recirculation (EGR) to further improve the efficiency of the regeneration of the PM filter.
More specifically, the system and method may determine a desired amount of HC injection (i.e., a total quantity of HC injection) based on a temperature measured at an inlet of the PM filter. The system and method may also determine the desired amount of HC injection based on exhaust gas flow and a speed of the vehicle. The system and method may then control the ratio of auxiliary injection to post-combustion injection based on engine load and engine speed. In other words, the system and method may determine amounts of auxiliary injection and post-combustion injection. For example, the system and method may perform proportional-integral-derivative (PID) control of the ratio and/or the desired amount of HC injection based on the temperature measured at the inlet of the PM filter.
Referring now to FIG. 1, an engine system 10 includes a CI engine 12. For example only, the engine 12 may be a diesel engine or an HCCI engine. The engine 12 combusts an air/fuel (A/F) mixture to produce drive torque. Air is drawn into an intake manifold 14 through an inlet 16. A throttle (not shown) may be included to regulate air flow into the intake manifold 14. Air within the intake manifold 14 is distributed into a plurality of cylinders 20. While six cylinders are shown, it can be appreciated that the engine 12 may include other numbers of cylinders. A MAF sensor 18 may measure a rate of airflow through the inlet 16. For example, the airflow rate measurement may be used to determine an engine load, which may correspond to a total amount of fuel required for combustion.
Fuel injectors 22 correspond to the cylinders 20. The fuel injectors 22 may inject fuel directly into the cylinders 20 (i.e., direct fuel injection). Alternatively, however, the fuel injectors 22 may inject fuel via intake ports of the cylinders 20 (i.e., port fuel injection). A piston (not shown) compresses and combusts the A/F mixture within the cylinder 20. The piston drives an engine crankshaft (not shown) during a power stroke to produce drive torque. In one embodiment, the cylinders 20 may include spark plugs (not shown) (e.g., for spark assist in an HCCI engine). The fuel injectors 22 may also inject fuel into the cylinders 20 after combustion of the A/F mixture (i.e., post-combustion injection) to introduce hydrocarbons (HC) into exhaust gas.
The crankshaft (not shown) rotates at engine speed or a rate that is proportional to engine speed. A crankshaft speed (CS) sensor 24 measures a rotational speed of the crankshaft. For example only, the CS sensor 24 may be a variable reluctance sensor. Drive torque from the engine crankshaft may be transferred to a driveline of a vehicle (e.g., wheels) via a transmission (not shown). A transmission output shaft speed (TOSS) sensor 26 measures a rotational speed of the output shaft of a transmission (not shown). In other words, the measurement from the TOSS sensor 26 may indicate vehicle speed. Both engine speed and vehicle speed, however, may be measured or calculated using other suitable sensors and/or methods.
The exhaust gas resulting from the combustion within the cylinders 20 is expelled into an exhaust manifold 28. An exhaust mass air flow (EMAF) sensor 30 generates an EMAF signal that indicates a rate of air flowing through the EMAF sensor 30. For example, the EMAF signal may indicate or be used to determine exhaust flow through an exhaust treatment system 32. Thus, the EMAF sensor 30 may be located between the exhaust manifold 28 and the exhaust treatment system 32.
The exhaust treatment system 32 may treat the exhaust gas. The exhaust treatment system 32 may include an auxiliary HC injector 34, an OC 36, and a PM filter 40. The auxiliary HC injector 34 selectively injects HC (e.g., fuel) into the exhaust stream. As previously described, however, the fuel injectors 22 may perform post-combustion injection to introduce HC into the exhaust gas. The OC 36 oxidizes CO and HC in the exhaust gas. The PM filter 40 removes PM from the exhaust gas.
The exhaust treatment system 32 also includes temperature sensors 37 and 39. Temperature sensor 37 may measure a temperature (T_out) of the exhaust gas at an outlet of the OC 36, and thus may be referred to as an “outlet temperature sensor.” Temperature sensor 39, on the other hand, may measure a temperature (T_in) at an inlet of the PM filter 40, and thus may be referred to as an “inlet temperature sensor.” The exhaust treatment system 32 may further include other temperature sensors (not shown) and/or NOx sensors (not shown) that measure exhaust gas temperature (EGT) and/or exhaust gas NOx concentration, respectively.
A control module 50 communicates with and/or controls various components of the engine system 10. The control module 50 may receive signals from the MAF sensor 18, CS sensor 24, the TOSS sensor 26, the EMAF sensor 30, the outlet temperature sensor 37, and the inlet temperature sensor 39. The control module 50 may also communicate with the PM filter 40 to determine when a regeneration cycle is required. Alternatively, the control module 50 may determine that regeneration of the PM filter 40 is required based on other parameters and/or modeling. For example, the control module 50 may determine that regeneration of the PM filter 40 is required when exhaust flow is less than a predetermined exhaust flow threshold (i.e., the PM filter 40 is restricted by PM).
The control module 50 may control a throttle (not shown), the fuel injectors 22, the auxiliary HC injector 34, and an exhaust gas recirculation (EGR) valve 46 (discussed in more detail below). The control module 50 may also implement the system and method of the present disclosure to improve efficiency of regeneration of the PM filter 40. More specifically, the control module 50 may actuate the fuel injectors 22 (i.e., post-combustion injection) and/or the auxiliary HC injector 34 to control EGT and control regeneration of the PM filter 40. In one embodiment, the control module 50 may actuate fuel injectors 22 corresponding to one bank of the cylinders 20 (e.g., half) to allow for EGR during regeneration of the PM filter 40.
The engine system 10 may further include an EGR system 42. The EGR system 42 includes the EGR valve 46 and an EGR line 44. The EGR system 42 may introduce a portion of exhaust gas from the exhaust manifold 28 into the intake manifold 14. The EGR valve 46 may be mounted on the intake manifold 14. The EGR line 44 may extend from the exhaust manifold 28 to the EGR valve 46, providing communication between the exhaust manifold 28 and the EGR valve 46. As previously described, the control module 50 may actuate the EGR valve 46 to increase or decrease an amount of exhaust gas introduced into the intake manifold 14.
The engine 12 may also include a turbocharger 48. The turbocharger 48 may be driven by the exhaust gas received through a turbine inlet. For example only, the turbocharger 48 may include a variable nozzle turbine. The turbocharger 48 increases airflow into the intake manifold 14 to cause an increase in intake MAP (i.e., manifold absolute pressure, or boost pressure). The control module 50 may actuate the turbocharger 48 to selectively restrict the flow of the exhaust gas, thereby controlling the boost pressure.
Referring now to FIG. 2, the control module 50 is shown in more detail. The control module 50 may include an injection determination module 60, an injection distribution module 70, and a regeneration control module 80. The injection determination module 60 receives an exhaust gas flow and a vehicle speed. For example, the exhaust gas flow may be measured by the EMAF sensor 30 and the vehicle speed may be measured by the TOSS sensor 26. The exhaust gas flow and the vehicle speed, however, may be measured using other sensors or modeled based on engine operating parameters. The injection determination module 60 also receives temperature T_in(measured by inlet temperature sensor 39).
The injection determination module 60 determines a desired amount of HC injection (i.e., a total quantity of HC injection) based on temperature T_in. The injection determination module 60 may also determine the desired amount of HC injection based on at least one of the exhaust gas flow and the vehicle speed. Moreover, in one embodiment the injection determination module 60 performs PID control of the desired amount of HC injection based on temperature feedback (i.e., T_in). For example, the injection determination module 60 may include a lookup table that includes a plurality of desired amounts of HC injection relating to various inlet temperatures of the PM filter 40, exhaust gas flows, and/or vehicle speeds. For example only, the desired amount of HC injection may decrease as exhaust gas flow increases. Alternatively, for example only, the desired amount of HC injection may increase when temperature T_indoes not increase or increases too slowly.
The injection distribution module 70 receives the desired amount of HC injection. The injection distribution module 70 also receives engine speed and engine load. For example, the engine speed may be measured using the CS sensor 22 and the engine load may be measured using the MAF sensor 18. The engine speed and the engine load, however, may be measured using other sensors or modeled based on engine operating parameters. The injection distribution module 70 determines an amount of auxiliary injection and an amount of post-combustion injection based on the desired amount of HC injection, the engine speed, and the engine load. More specifically, the injection distribution module 70 may determine a ratio of auxiliary injection to post-combustion injection. The injection distribution module 70 may then determine the amounts of auxiliary injection and post-combustion injection based on the desired amount of HC injection and the determined ratio. For example, the injection distribution module 70 may include a lookup table that includes a plurality of ratios relating to engine speed and engine load.
The regeneration control module 80 receives the determined amounts of auxiliary injection and post-combustion injection (AUX and PC, respectively). The regeneration control module 80 controls the auxiliary HC injector 34 and fuel injectors 22 based on the determined amounts of auxiliary injection and post-combustion injection, respectively. Alternatively, however, in one embodiment the injection distribution module 70 may determine rates of auxiliary injection and post-combustion injection and the regeneration control module 80 may control the auxiliary injector 34 and the fuel injectors 22 according to the determines rates, respectively.
The regeneration control module 80 may control auxiliary injection and post-combustion injection by generating control signals for the auxiliary HC injector 34 and the fuel injectors 22, respectively. As previously described, however, in one embodiment the regeneration control module 80 may generate control signals for fuel injectors 22 associated with one bank of cylinders 20 to allow for EGR during regeneration of the PM filter 40. While one regeneration control module 80 is shown, two separate modules may be implemented to control auxiliary injection and post-combustion injection, respectively.
Referring now to FIG. 3, an exemplary implementation of the injection distribution module 70 is shown in more detail. The injection distribution module 70 may include a ratio determination module 90. The ratio determination module 90 receives the engine load and the engine speed. The ratio determination module 90 determines the ratio of auxiliary injection to post-combustion injection. For example, the ratio determination module 90 may generate a factor (e.g., between 0 and 1). The injection distribution module 70 may multiply the desired amount of HC injection by the factor to determine the amount of post-combustion injection. The injection distribution module 80 may then subtract the determined amount of post-combustion injection from the desired amount of HC injection to determine the amount of auxiliary injection.
Referring now to FIG. 4, a graph is shown illustrating EGT control for a vehicle traveling at 75 miles per hour (mph) according to the system and method of the present disclosure. More specifically, the graph illustrates EGT control during regeneration of a PM filter using 50% auxiliary injection and 50% post-combustion injection (i.e., a 1:1 ratio). As shown, temperature T_inat the inlet of the PM filter 40 accurately tracks the desired temperature steps (e.g., 565° C., 585° C., etc.) throughout the regeneration process. The accurate tracking of the desired temperature steps may result in improved efficiency during PM filter regeneration.
Referring now to FIG. 5, a method for controlling injection of HC into exhaust gas produced by the engine 12 begins in at 100. At 100, the control module 50 determines whether the engine 12 is on. If true, control may proceed to 104. If false, control may return to 100. At 104, the control module 50 may determine whether regeneration of the PM filter 40 is required. For example, regeneration of the PM filter 40 may be required when exhaust flow is less than a predetermined threshold. If true, control may proceed to 108. If false, control may return to 104.
At 108, the control module 50 may determine the desired amount of HC injection. At 112, the control module 50 may determine the ratio of auxiliary (AUX) injection to post-combustion (PC) injection. For example, the control module 50 may determine a factor using a lookup table that includes a plurality of factors relating to engine load and engine speed
At 116, the control module 50 may determine the amounts of auxiliary (AUX) injection and post-combustion (PC) injection based on the desired amount of HC injection and the determined ratio (or factor). For example, the control module 50 may determine the amount of auxiliary (AUX) injection based on a product of the factor and the desired amount of HC injection and may determine the amount of post-combustion injection based on a difference between the desired amount of HC injection and the determined amount of auxiliary injection
At 120, the control module 50 may control HC injection according to the determined amounts of auxiliary injection and post-combustion injection. At 124, the control module 50 may measure the temperature T_inat the inlet of the PM filter 40.
At 128, the control module 50 may determine whether the regeneration operation has completed. For example, the regeneration operation may be completed after the inlet temperature T_inis greater than or equal to a predetermined temperature threshold for a predetermined period. If true, control may return to 104. If false, control may then return to 108 where control of the desired amount of HC injection and the ratio of auxiliary injection to post-combustion injection may continue (e.g., PID control) until the regeneration operation has completed.
The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.

Claims

1. An engine control system, comprising:

an injection determination module that determines a desired amount of hydrocarbons (HC) to inject into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter; and

an injection distribution module that controls a ratio of auxiliary injection to post-combustion injection based on engine load, engine speed, and the desired amount of HC injection, wherein auxiliary injection includes injecting HC into the exhaust gas, and wherein post-combustion injection includes injecting HC into cylinders of the engine during a period after combustion.

2. The engine control system of claim 1, wherein the injection distribution module determines amounts of auxiliary injection and post-combustion injection based on the engine load, the engine speed, and the desired amount of HC injection.

3. The engine control system of claim 2, further comprising:

a regeneration control module that generates control signals for an auxiliary HC injector and fuel injectors based on the amounts of auxiliary injection and post-combustion injection, respectively.

4. The engine control system of claim 3, wherein the auxiliary HC injector is located upstream from an oxidation catalyst (OC) in an exhaust treatment system, and wherein the fuel injectors correspond to cylinders of the engine.

5. The engine control system of claim 4, wherein the regeneration control module generates control signals for fuel injectors corresponding to one bank of cylinders of the engine.

6. The engine control system of claim 2, wherein the injection distribution module determines a factor using a lookup table that includes a plurality of factors relating to engine load and engine speed.

7. The engine control system of claim 6, wherein the injection distribution module determines the amount of auxiliary injection based on a product of the factor and the desired amount of HC injection, and wherein the injection distribution module determines the amount of post-combustion injection based on a difference between the desired amount of HC injection and the determined amount of auxiliary injection.

8. The engine control system of claim 1, wherein the injection determination module determines the desired amount of HC injection based on a temperature of the exhaust gas at an inlet of the PM filter.

9. The engine control system of claim 8, wherein the injection determination module determines the desired amount of HC to inject into the exhaust gas based on at least one of exhaust gas flow and vehicle speed.

10. The engine control system of claim 9, wherein the injection determination module performs proportional-integral-derivative (PID) control of the desired amount of HC to inject into the exhaust gas.

11. A method, comprising:

determining a desired amount of hydrocarbons (HC) to inject into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter; and

controlling a ratio of auxiliary injection to post-combustion injection based on engine load, engine speed, and the desired amount of HC injection, wherein auxiliary injection includes injecting HC into the exhaust gas, and wherein post-combustion injection includes injecting HC into cylinders of the engine during a period after combustion.

12. The method of claim 11, further comprising:

determining amounts of auxiliary injection and post-combustion injection based on the engine load, the engine speed, and the desired amount of HC injection.

13. The method of claim 12, further comprising:

generating control signals for an auxiliary HC injector and fuel injectors based on the amounts of auxiliary injection and post-combustion injection, respectively.

14. The method of claim 13, wherein the auxiliary HC injector is located upstream from an oxidation catalyst (OC) in an exhaust treatment system, and wherein the fuel injectors correspond to cylinders of the engine.

15. The method of claim 14, further comprising:

generating control signals for fuel injectors corresponding to one bank of cylinders of the engine.

16. The method of claim 12, further comprising:

determining a factor using a lookup table that includes a plurality of factors relating to engine load and engine speed.

17. The method of claim 16, further comprising:

determining the amount of auxiliary injection based on a product of the factor and the desired amount of HC injection; and

determining the amount of post-combustion injection based on a difference between the desired amount of HC injection and the determined amount of auxiliary injection.

18. The method of claim 11, further comprising:

determining the desired amount of HC injection based on a temperature of the exhaust gas at an inlet of the PM filter.

19. The method of claim 18, further comprising:

determining the desired amount of HC to inject into the exhaust gas based on at least one of exhaust gas flow and vehicle speed.

20. The method of claim 19, further comprising:

performing proportional-integral-derivative (PID) control of the desired amount of HC to inject into the exhaust gas.