 |
Description  |
|
|
TECHNICAL FIELD
1. Background Art
In the control of heavy duty internal combustion engines, the conventional practice utilizes electronic control units having volatile and non-volatile memory, input and output driver circuitry, and a processor that executes instructions to
control the engine and its various systems and sub-systems. A particular electronic control unit communicates with numerous sensors, actuators, and other electronic control units to control various functions, which may include various aspects of field
delivery, transmission control, and many others.
However, the heavy duty engine business is extremely competitive. Increased demands are being placed on engine manufacturers to design and build engines that provide better engine performance, improved reliability, and greater durability while
meeting more stringent emission and noise requirements.
For the foregoing reasons, there is a need for an improved method of controlling an internal combustion engine including an exhaust gas recirculation (EGR) system with improved performance and more precise control than existing systems.
2. Disclosure of Invention
It is, therefore, an object of the present invention to provide a method of controlling an internal combustion engine with improved performance and more precise emission controls than existing systems, with some embodiments including an exhaust
gas recirculation (EGR) system.
In carrying out the above object, a method of controlling an internal combustion engine is provided. The engine includes a variable geometry turbocharger (VGT) driven in response to a VGT command signal. The engine further includes a variable
flow exhaust recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake mixture. The method comprises determining the EGR command signal based on at least one engine condition, and determining the
VGT command signal based on at least one engine condition and at least partially based on the EGR command signal.
In a preferred embodiment, determining the VGT command signal further comprises determining a lead compensated signal based on the EGR command signal. The VGT command signal is determined at least partially based on the lead compensated signal.
Further, preferably, determining the EGR command signal further comprises determining a desired carbon dioxide quantity of the intake mixture. The EGR command signal is then determined based on the desired carbon dioxide quantity. More preferably,
determining the EGR command signal further comprises estimating an actual carbon dioxide quantity of the intake mixture. The desired carbon dioxide quantity is compared to the estimated actual carbon dioxide quantity to determine an error signal. The
EGR command signal is based on the error signal. Further, in a preferred embodiment, determining the desired carbon dioxide quantity further comprises determining the desired carbon dioxide quantity based in part on an oxygen to fuel ratio of the intake
mixture. Even further, in a preferred embodiment, determining the desired carbon dioxide quantity further comprises determining an engine torque demand and determining an engine speed. The desired carbon dioxide quantity is based on the oxygen to fuel
ratio of the intake mixture, the torque demand, and the engine speed.
Even further, in a preferred embodiment, determining the EGR command signal further comprises determining the EGR command signal further based on at least one controller gain term. More preferably, the EGR command signal is further based on a
gain normalization term.
Further, in carrying out the present invention, a method of controlling a compression-ignition internal combustion engine is provided. The engine includes a variable geometry turbocharger driven in response to a VGT command signal. The engine
further includes a variable flow exhaust gas recirculation system driven in response to an EGR command signal to recirculate exhaust to an engine intake mixture. The method comprises determining an engine torque demand, determining an engine speed based
at least partially on the driver accelerator demand and the engine speed. The method further comprises determining the EGR signal based at least partially on torque demand and engine speed. The method further comprises determining the VGT command
signal based on at least one engine condition and at least partially based on the EGR command signal.
Still further, in carrying out the present invention, a method of controlling an internal combustion engine is provided. The engine includes a variable geometry turbocharger driven in response to a VGT command signal, and a variable flow exhaust
gas recirculation system driven in response to an EGR command signal to recirculate exhaust to an engine intake mixture. The method comprises determining the EGR command signal based on at least one engine condition, determining a desired oxygen
quantity of the intake mixture, and estimating an actual oxygen quantity of the intake mixture. The method further comprises determining the VGT command signal based on the desired oxygen quantity, the estimated actual oxygen quantity, and the EGR
command signal.
In a preferred embodiment, determining the VGT command signal further comprises determining a feedforward term based on at least one engine condition, and determining the VGT command signal further based on the feedforward term. More preferably,
the feedforward term is determined based on an engine torque demand and an engine speed.
In a preferred implementation, determining the VGT command signal further comprises determining a lead compensated signal based on the EGR command signal, and determining the VGT command signal based on the desired oxygen quantity, the estimated
actual oxygen quantity, the lead compensated signal, and the feedforward term. A preferred method further comprises determining an adjusted oxygen quantity error signal based on the desired oxygen quantity, the estimated actual oxygen quantity, and lead
compensated signal. The VGT command signal is determined based on the error signal and the feedforward term. In some implementations, the error signal is modified based on at least one controller gain term. In some embodiments, a gain normalization
term is determined and the error signal is modified based on the gain normalization term. Preferably, the gain normalization term is based on a determined engine air intake flow. More preferably, determining the air intake flow further comprises
determining an engine torque demand, determining an engine speed, and determining the engine air intake flow based on the torque demand and the engine speed. Most preferably, determining the gain normalization term further comprises determining the gain
normalization term such that the term effectively eliminates the error signal for a significantly low air intake flow.
Yet further, in carrying out the present invention, a method of controlling an internal combustion engine is provided. The engine includes a variable flow exhaust gas recirculation system driven in response to an EGR command signal to
recirculate exhaust to an engine intake mixture. The method comprises determining a desired engine intake mixture composed of a plurality of different components, estimating an actual engine intake mixture composition, and comparing the desired intake
composition to the estimated actual intake composition.
The method further comprises controlling the engine based on the comparison.
In some embodiments, controlling the engine further comprises determining the EGR command signal. In some embodiments, the engine includes a variable geometry turbocharger driven in response to VGT command signal, and controlling the engine
further comprises determining the VGT command signal. In a preferred embodiment, the engine includes a variable geometry turbocharger, and controlling the engine further comprises determining the EGR command signal based on the comparison, and
determining the VGT command signal based at least partially on the EGR command signal.
Yet further, in carrying out the present invention, a computer readable storage medium has instructions stored thereon that are executable by a controller to perform methods of the present invention. The instructions direct the controller to
control an internal combustion engine in accordance with one or more aspects of the various embodiments of the present invention.
The advantages associated with embodiments of the present invention are numerous. For example, methods of the present invention provide the integration of EGR and VGT controls to provide improved and more precise emission control. Further,
embodiments of the present invention employ other novel features that may be used separately or together as in the preferred embodiment. Embodiments of the present invention are suitable for compression ignition engines, but some embodiments are
suitable for spark ignition engines as well.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken into connection with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of an internal combustion engine and engine control system made in accordance with an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an EGR and VGT control system of the present invention;
FIG. 3 is a block diagram illustrating an engine control system of invention;
FIG. 4 is a block diagram illustrating an engine control system of the present invention; and
FIG. 5 is a graph depicting a gain normalization term versus air flow in an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIG. 1, an internal combustion engine and associated control systems and subsystems are generally indicated at 10. System 10 includes an engine 12 having a plurality of cylinders, each fed by a fuel injector. In a preferred
embodiment, engine 12 is a compression-ignition internal combustion engine, such as a heavy duty diesel fuel engine. The injectors receive pressurized fuel from a fuel supply in a known manner.
Various sensors are in electrical communication with a controller 22 via input ports 24. Controller 22 preferably includes a microprocessor 26 in communication with various computer readable storage media 28 via data and control bus 30.
Computer readable storage media 28 may include any of a number of known devices which function as read only memory 32, random access memory 34, and non-volatile random access memory 36.
Computer readable storage media 28 have instructions stored thereon that are executable by controller 22 to perform methods of controlling the internal combustion engine, including variable flow exhaust gas recirculation (EGR) valve 66 and
variable geometry turbocharger 52. The program instructions direct controller 22 to control the various systems and subsystems of the vehicle, with the instructions being executed by microprocessor 26, and optionally, instructions may also be executed
by any number of logic units 50. Input ports 24 receive signals from various sensors, and controller 22 generates signals at output ports 38 that are directed to the various vehicle components.
A data, diagnostics, and programming interface 44 may also be selectively connected to controller 22 via a plug 46 to exchange various information therebetween. Interface 44 may be used to change values within the computer readable storage media
28, such as configuration settings, calibration variables, instructions for EGR and VGT control and others.
In operation, controller 22 receives signals from the various vehicle sensors and executes control logic embedded in hardware and/or software to control the engine. In a preferred embodiment, controller 22 is the DDEC controller available from
Detroit Diesel Corporation, Detroit, Mich. Various other features of this controller are described in detail in a number of different U.S. patents assigned to Detroit Diesel Corporation.
As is appreciated by one of ordinary skill in the art, control logic may be implemented in hardware, firmware, software, or combinations thereof. Further, control logic may be executed by controller 22, in addition to by any of the various
systems and subsystems of the vehicle cooperating with controller 22. Further, although in a preferred embodiment, controller 22 includes microprocessor 26, any of a number of known programming and processing techniques or strategy may be used to
control an engine in accordance with the present invention.
Further, it is to be appreciated that the engine controller may receive information in a variety of ways. For example, engine systems information could be received over a data link, at a digital input or at a sensor input of the engine
controller.
With continuing reference to FIG. 1, controller 22 provides enhanced engine performance by controlling a variable flow exhaust gas recirculation valve 66 and by controlling a variable geometry turbocharger 52. Variable geometry turbocharger 52
includes a turbine 54 and a compressor 56. The pressure of the engine exhaust gasses causes the turbine to spin. The turbine drives the compressor, which is typically mounted on the same shaft. The spinning compressor creates turbo boost pressure
which develops increased power during combustion.
A variable geometry turbocharger has moveable components in addition to the rotor group. These moveable components can change the turbocharger geometry by changing the area or areas in the turbine stage through which exhaust gasses from the
engine flow, and/or changing the angle at which the exhaust gasses enter or leave the turbine. Depending upon the turbocharger geometry, the turbocharger supplies varying amounts of turbo boost pressure to the engine. The variable geometry turbocharger
may be electronically controlled to vary the amount of turbo boost pressure based on various operating conditions.
In a variable geometry turbocharger, the turbine housing is oversized for an engine, and the air flow is choked down to the desired level. There are several designs for the variable geometry turbocharger. In one design, a variable inlet nozzle
has a cascade of moveable vanes which are pivotable to change the area and angle at which the air flow enters the turbine wheel. In another design, the turbocharger has a moveable side wall which varies the effective cross-sectional area of the turbine
housing. It is appreciated that embodiments of the present invention are not limited to any particular structure for the variable geometry turbocharger. That is, the term VGT as used herein means any controllable air pressurizing device including the
above examples, and including a modulated waste gate valve.
An exhaust gas recirculation system introduces a metered portion of the exhaust gasses into the intake manifold. The EGR system dilutes the incoming fuel charge and lowers combustion temperatures to reduce the level of oxides of nitrogen. The
amount of exhaust gas to be recirculated is controlled by EGR valve 66 and VGT. In accordance with the present invention, the EGR valve is a variable flow valve that is electronically controlled by controller 22. The geometry of the variable geometry
turbocharger is also electronically controlled by controller 22. It is appreciated that there are many possible configurations for a controllable EGR valve, and embodiments of the present invention are not limited to any particular structure for the EGR
valve. Further, it is appreciated that various sensors at the EGR valve may detect temperature and differential pressure to allow the engine control to determine the mass flow rate through the valve. In addition, it is appreciated that various
different sensor configurations may be utilized in various parts of the exhaust flow paths to allow controller 22 to determine the various mass flow rates throughout the exhaust system, including flow through the EGR system and flow through the
compressor, and any other flows.
In some embodiments, it may be desirable to provide a cooler 62 to cool the charge air coming from compressor 56. Similarly, in some embodiments, it may be desirable to provide a cooler 68 to cool the flow through the EGR system prior to
reintroduction to engine 12 of the gasses.
Embodiments of the present invention include control logic that processes various inputs representing various engine conditions, and in turn, provides an EGR command signal and a VGT command signal. The EGR command signal commands a position for
the variable flow EGR valve 66 to control gas flow through path 64, while the VGT command signal commands a geometry for VGT 52 to control gas flow through path 60. In a preferred embodiment of the present invention, the various techniques utilized to
determine the EGR and VGT command signals are best shown in FIG. 2.
In FIG. 2, a block diagram 80 illustrates the functions of the control logic, including instructions, executed by controller 22 to provide enhanced engine performance and improved emission control. Embodiments of the present invention are
particularly useful to improve emissions on heavy-duty diesel engines. Using EGR technology to mix a portion of exhaust gas with the intake charge reduces emissions of oxides of nitrogen (NO.sub.x), while minimizing fuel economy impact and improving
durability, in accordance with the present invention. In a turbo charged diesel engine, the back pressure necessary to drive the EGR flow from exhaust to intake manifolds is accomplished with the variable geometry turbocharger. The control of the EGR
flow rate may be achieved via VGT geometry change (for example, vane position change), via EGR valve position change, and preferably via both. In preferred embodiments, the method of control employed results in interactions between EGR and VGT systems
that are above the capabilities of existing systems.
There are many aspects of the present invention that may be used separately or together. In the preferred embodiment, the EGR valve and the VGT are controlled simultaneously and continuously. That is, preferred embodiments provide a
continuously adjusting EGR/VGT controller. Preferred implementations of the present invention utilize desired intake manifold composition in terms of chemical species (O.sub.2, N.sub.2, CO.sub.2 and H.sub.2 O) as a set point for the controller. The
actual quantity of these chemical species is preferably calculated from a simplified combustion model.
With continuing reference to FIG. 2, in the embodiment illustrated, a driver accelerator position sensor input and an engine speed (rpm) input are received at block 82. Block 82 utilizes a look up table to determine an engine torque demand. The
engine torque demand represents a fuel quantity that may be adjusted for other aspects of engine control that are not specifically described herein such as, for example, cylinder balancing. Further, it is appreciated that FIG. 2 illustrates a preferred
implementation and that various aspects of the control strategy shown are preferred, but not specifically required. At block 84, a one way, second order filter adds some delay to the torque demand. Delay is added to allow the slower, air flow aspects
of engine control to catch up to the faster responding torque demand aspects of engine control. At block 86, engine speed and filtered torque demand are received, and processed along with other engine conditions, resulting in desired fuel injection
timing, quantity, and rail pressure. These factors control fuel delivery, indicated at 88.
At block 90, a desired chemical composition for the engine air intake is determined. The desired composition is in terms of chemical species (N.sub.2, O.sub.2, CO.sub.2, and H.sub.2 O). The fuel per cycle is provided to block 90 from injection
control block 86, and block 90 provides a fuel limit per cycle to block 86 (for example, fuel may be limited in low air flow conditions). At block 92, actual flow values for the EGR system and turbo charging system, the oxygen to fuel ratio, and
chemical composition of the intake gasses are calculated. The calculations are based on a simplified combustion model and engine sensor inputs. The desired or set point values in block 90 are based on interpolation of values contained within five pairs
of look up tables. For each pair of look up tables, the first table (94,98) corresponds to stabilized turbocharger boost pressure and the second table (96,100) corresponds to zero turbocharger boost pressure. That is, the first table corresponds to
maximum oxygen per fuel (per cycle) while the second table corresponds to minimum oxygen per fuel. Depending on the current oxygen per fuel as determined from various measurements, desired values are interpolated between the two tables for the
particular value.
For example, desired carbon dioxide and air values are determined with an interpolation between tables 94,96 (block 94 and block 96 each represent two look up tables, one table for CO.sub.2 and one table for oxygen quantity/cycle, for a total of
four tables). Similarly, desired values for timing parameters, quantity, and rail pressure are determined by interpolation (based on oxygen per fuel) between tables 98 and 100 (block 98 and block 100 each represent three tables). In accordance with
preferred embodiments of the present invention, controller 22 adjusts VGT and EGR operation to achieve the d | | |
