STRATEGY FOR USING EXHAUST STROKE POST-INJECTION TO ELEVATE EXHAUST TEMPERATURE FOR DIESEL PARTICULATE FILTER REGENERATION

Abstract

An engine control system (28) causes combustion chambers (20) to be fueled during an engine cycle by a main injection (38) ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection (40) for elevating the temperature of the gases into a regeneration temperature range for regenerating a diesel particulate filter (36).

Description

FIELD OF THE INVENTION

This invention relates generally to internal combustion engines for propelling motor vehicles, particularly to diesel engines having diesel particulate filters (DPF's) as after-treatment devices in their exhaust systems.

BACKGROUND OF THE INVENTION

A known system for treating exhaust gases passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) associated with a diesel particulate filter (DPF). The combination of these two after-treatment devices promotes chemical reactions in the exhaust gases and traps diesel particulate matter (DPM) as the gases flow through the exhaust system from the engine, thereby preventing significant amounts of pollutants from entering the atmosphere.

A DPF requires regeneration from time to time in order to maintain particulate trapping efficiency. Regeneration involves creating conditions that will burn off trapped particulates whose unchecked accumulation would otherwise impair DPF effectiveness.

The creation of conditions for initiating and continuing regeneration generally involves elevating the temperature of exhaust gas entering the DPF to a suitably high temperature. Because a diesel engine typically runs relatively cool and lean, the post-injection of diesel fuel has been used as part of a DPF regeneration strategy to elevate exhaust gas temperatures entering the DPF while still leaving excess oxygen for burning the trapped particulate matter.

When a vehicle is being operated in a way conducive to DPF regeneration, such as cruising on a highway, the regeneration process may be conducted with little or no significant effect on vehicle driveability and may be initiated either by the driver or else automatically by a regeneration initiation strategy even before the DPF becomes loaded with DPM to an extent where forced regeneration would be mandated by the engine control system.

The inventors have discovered that a “close” post-injection of fuel—meaning an injection occurring during the expansion, or power, stroke within a range of about 60° after top dead center (ATDC)—makes a contribution to crankshaft torque having a sufficiently noticeable effect on vehicle driveability that some drivers may consider objectionable.

Compensating for the effect of “close” post injection in order to minimize its influence on vehicle drivability requires an extensive development effort in order to achieve the best possible calibration. One consideration that needs to be addressed is the ability of the fuel injectors to deliver “close” post-injections immediately following main injections. Certain fuel injectors that do possess desirable attributes may nonetheless have difficulty in delivering a “close” post-injection that is needed too soon after a main injection. The difficulty becomes more pronounced as engine speed increases into a high speed range.

While use of a “far” post-injection during the expansion stroke—meaning an injection occurring during later than a “close” post-injection—may address any issue of a fuel injector's ability to deliver a post-injection at a desired time during the expansion stroke, a post-injection that is too “far” in the expansion stroke may cause significant cylinder wall washing that can lead to motor oil dilution.

These discoveries and recognitions have led the inventors to seek an alternative and better solution for using post-injection to elevate exhaust temperature to levels for initiating and maintaining DPF regeneration.

SUMMARY OF THE INVENTION

The present invention relates to a novel strategy that provides such a solution.

In contrast to seeking an optimum calibration for post-injection by repeatedly initiating regeneration using different post-injection quantities and timings within a timing range immediately after TDC in the expansion stroke and then evaluating the results to ascertain an optimum, the inventors have discovered that a post-injection late in the exhaust stroke can be just as effective in initiating and maintaining DPF regeneration, with lesser affect on vehicle driveability and without requiring as extensive a development effort, as when “close” post-injection during the expansion stroke is used. Moreover, the invention avoids issues concerning the ability of a fuel injector to deliver a post-injection in close proximity to a main injection (thereby avoiding injector and/or injector driver and control modifications) and issues concerning excessive cylinder wall washing contributing to motor oil dilution.

Delaying post-injection to a time within a range spanning a later portion of the exhaust stroke has been found to create neither the potentially objectionable torque rise mentioned above nor objectionable cylinder wall washing while in doing so, giving fuel injectors, particularly hydraulically-driven ones, time to “re-charge” between the main injection and providing the same effect as “close” (expansion stroke) post-injection for initiating and maintaining DPF regeneration.

The invention can be implemented in existing systems through appropriate modifications of processor algorithms that control timing of fuel injections. Hence, no additional hardware is needed. Optimum timing during the exhaust stroke can be developed by calibration adjustment during driveability testing with lesser effort than that required when “close” (expansion stroke) post-injection is used.

Accordingly, one generic aspect of the present invention relates to a diesel engine comprising a fueling system for injecting diesel fuel into combustion chambers where the fuel combusts to power the engine, an exhaust system through which gases created by combustion pass to atmosphere and which comprises an after-treatment device that treats the gases before leaving the exhaust system but at times requires regeneration by elevation of temperature of the gases to a regeneration temperature range, and an engine control system for processing various data to control various aspects of engine operation including fueling performed by the fueling system and regeneration of the after-treatment device.

In consequence of a regeneration request, the control system causes the fueling system to fuel the combustion chambers during an engine cycle for a combustion chamber by a main injection ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection for elevating the temperature of the gases into the regeneration temperature range.

Another generic aspect relates to a motor vehicle powered by an engine as just described.

Still another generic aspect relates to a method for initiating regeneration of an exhaust gas after-treatment device in an exhaust system of a diesel engine having a fueling system for injecting diesel fuel into combustion chambers where the fuel combusts to power the engine and an engine control system for processing various data to control various aspects of engine operation including fueling performed by the fueling system and regeneration of the after-treatment device.

The method comprises initiating regeneration by causing the fueling system to fuel the combustion chambers during an engine cycle for a combustion chamber by a main injection ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection.

The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram of an exemplary internal combustion engine embodying a strategy for initiating and maintaining DPF regeneration in accordance with principles of the present invention.

FIG. 2 is a fuel injection timing diagram illustrating the strategy.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an example of a turbocharged diesel engine 10 having an intake system 12 through which charge air enters and an exhaust system 14 through which exhaust gas resulting from combustion exits, not all details of those two systems that are typically present being included. When used in a motor vehicle, such as a truck, engine 10 is coupled through a drivetrain 16 to driven wheels 18 that propel the vehicle.

Engine 10 comprises cylinders 20 forming combustion chambers into which fuel is injected by fuel injectors 22 to combust with the charge air that has entered through intake system 12. Energy released by combustion powers the engine via pistons 24 connected to a crankshaft 26 leading to drivetrain 16 for propelling the vehicle.

Fuel injectors 22 are under the control of an engine control system 28 that comprises one or more processors that process various data to develop data for controlling various aspects of engine operation including controlling pressure of hydraulic fluid supplied to fuel injectors 22 (reference numeral 30) and the timing of operation of valve mechanisms in the fuel injectors that use the hydraulic fluid to force fuel out of the injector tips into the combustion chambers.

Intake valves 32 control the admission of charge air into cylinders 20, and exhaust valves 34 control the outflow of combustion gases through exhaust system 14 and ultimately to atmosphere. Before entering the atmosphere however, the combustion gases are treated by one or more after-treatment devices. The one device shown here with which the present invention is concerned is a diesel particulate filter, or DPF, 36.

Various sensors are associated with the after-treatment devices for providing information to control system 28. One piece of information is the extent to which DPF 36 is loaded with particulates. Control system 28 contains algorithms that are repeated executed to process certain data for various control purposes. One such algorithm uses information about DPF particulate loading to initiate regeneration when conditions are suitable even if the DPF is loaded below a level requiring forced regeneration and to force regeneration when the DPF becomes loaded to the level calling for forced regeneration.

With engine 10 running, a main fuel injection occurs substantially at TDC between the compression stroke C and expansion, or power, stroke P, as represented by the injection 38 in FIG. 2 illustrating conventional diesel (CD) combustion.

When control system 28 requests regeneration of DPF 36, main injections such as 38 continue, but now a specific post-injection strategy is employed.

That strategy employs no post-injection during the expansion stroke, but rather a post-injection during the exhaust stroke E, preferably during a time toward the end of the exhaust stroke but ahead of the TDC that occurs between the end of the exhaust stroke and the beginning of the next intake stroke I, as represented by the post-injection 40 in FIG. 2.

The strategy continues until regeneration is initiated and also thereafter in order to maintain regeneration. When the strategy terminates regeneration, the post-injection during the exhaust stroke concludes.

Certain diesel engines are at times capable of operating by alternative diesel combustion, as distinguished from CD combustion, and while the engine that has been described here operates by CD combustion, it is believed that principles of the invention are applicable to an engine running by alternative diesel combustion provided that the control system allows DPF regeneration while the engine is so running. Alternative diesel combustion is a generic term for certain processes and systems such as Homogeneous Charge Compression Ignition (HCCI), Controlled Auto-Ignition (CAI), Dilution Controlled Combustion Systems (DCCS), and Highly Premixed Combustion Systems (HPCS). When an engine is running by an alternative diesel combustion process, the effect of whatever injections occur until main combustion occurs may be considered equivalent to a main injection of CD combustion.

It should also be understood that the use of post-injection during the exhaust stroke instead of during the expansion stroke may be only one element of a more comprehensive regeneration strategy that uses other than merely fuel injection to initiate and maintain DPF regeneration.

While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.

Claims

1. A diesel engine comprising:

a fueling system for injecting diesel fuel into combustion chambers where the fuel combusts to power the engine;

an exhaust system through which gases created by combustion pass to atmosphere and which comprises an after-treatment device that treats the gases before leaving the exhaust system but at times requires regeneration by elevation of temperature of the gases to a regeneration temperature range;

an engine control system for processing various data to control various aspects of engine operation including fueling performed by the fueling system and regeneration of the after-treatment device;

wherein in consequence of a regeneration request, the control system causes the fueling system to fuel the combustion chambers during an engine cycle for a combustion chamber by a main injection ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection for elevating the temperature of the gases into the regeneration temperature range.

2. A diesel engine as set forth in claim 1 wherein the post-injection is caused to occur nearer TDC than BDC.

3. A diesel engine as set forth in claim 1 wherein the main injection causes the engine to operate by conventional diesel combustion.

4. A diesel engine as set forth in claim 1 wherein the after-treatment device comprises a diesel particulate filter.

5. A diesel engine as set forth in claim 4 wherein the post-injection is caused to occur nearer TDC than BDC.

6. A motor vehicle comprising:

a diesel engine for turning driven wheels through a drivetrain to propel the vehicle:

a fueling system for injecting diesel fuel into combustion chambers of the engine where the fuel combusts to propel the vehicle;

an exhaust system through which gases created by combustion pass to atmosphere and which comprises an after-treatment device that treats the gases before leaving the exhaust system but at times requires regeneration by elevation of temperature of the gases to a regeneration temperature range;

an engine control system for processing various data to control various aspects of engine operation including fueling performed by the fueling system and regeneration of the after-treatment device;

wherein in consequence of a regeneration request, the control system causes the fueling system to fuel the combustion chambers during an engine cycle for a combustion chamber by a main injection ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection for elevating the temperature of the gases into the regeneration temperature range.

7. A motor vehicle as set forth in claim 6 wherein the post-injection is caused to occur nearer TDC than BDC.

8. A motor vehicle as set forth in claim 6 wherein the main injection causes the engine causes the engine to operate by conventional diesel combustion.

9. A motor vehicle as set forth in claim 6 wherein the after-treatment device comprises a diesel particulate filter.

10. A motor vehicle as set forth in claim 9 wherein the post-injection is caused to occur nearer TDC than BDC.

11. A method for initiating regeneration of an exhaust gas after-treatment device in an exhaust system of a diesel engine having a fueling system for injecting diesel fuel into combustion chambers where the fuel combusts to power the engine and an engine control system for processing various data to control various aspects of engine operation including fueling performed by the fueling system and regeneration of the after-treatment device, the method comprising:

initiating regeneration by causing the fueling system to fuel the combustion chambers during an engine cycle for a combustion chamber by a main injection ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection.

12. A method as set forth in claim 11 comprising causing the post-injection to occur nearer TDC than BDC.

13. A method as set forth in claim 11 comprising injecting the main injection so as to cause the engine to operate by conventional diesel combustion.