In modern day diesel engines, measures are taken to minimize fuel consumption and harmful emissions. The emissions of diesel soot and NOx can be reduced in an engine aftertreatment system (EAS). Typical components of such an aftertreatment system may be a diesel particulate filter to capture soot, and a catalytic converter more specifically an SCR (Selective Catalytic Reduction) catalyst that converts NOx into harmless products also known as the deNOx process and a diesel oxidation catalyst (DOC) to (inter alia) increase the deNOX efficiency and oxydize unburned hydrocarbon and CO. In normal operation, the aftertreatment system can be heated by residual heat from the combustion engine, however, at very low loads, the temperature of the exhaust gas may be too low. The temperature may be influenced by an engine efficiency mode, which controls the efficiency of the engine and an engine out temperature. For high efficiency engine power settings, the temperature may be too low to accommodate a required NOx conversion efficiency of the catalytic converter, in which case the engine aftertreatment system temperature should be increased to provide a better performance of the SCR system.
A possible method to meet these new regulations is to (locally) release heat in a component of the exhaust after treatment system, by applying a thermal measure, and thereby increasing the temperature of the downstream SCR system. To this end aftertreatment systems may further include a heater system, which may include: an electrical heater; a fuel burner, but may also include engine measures or a combination of these. Typically, the reactivity of aftertreatment systems increases when temperature of the catalyst material and the exhaust gas increases at least up to a certain temperature. In order to quickly reach a high conversion efficiency of the aftertreatment system after engine start, the heater system may be used to heat the aftertreatment system to an operating temperature, which may be around 200-300° C. The control objective for the thermal management strategy is to maintain the SCR temperature robustly on the SCR light-off temperature. Applying insufficient heat could lead to loss of deNOx performance and applying too much heat will lead to an increase of the fuel consumption, leading to a CO2 penalty for increasing the aftertreatment temperature when a higher temperature is not necessary. A robust controller with good tracking behaviour allows for lowering the target temperature closer to the SCR light-off temperature and thus lower the fuel penalty associated with thermal management.
A problem with the control of this type of system is the long lead times between applying heat via the thermal measure and to have an effect downstream of the system, due to the long lead times (deadtime) and the large thermal inertia.
It is an object of this invention to more efficiently control the heater system, while at the same time generate an amount of enthalpy necessary for a sufficient SCR conversion.
It is an aspect of the present invention to alleviate, at least partially, the problems discussed above. It is aimed to provide an internal combustion engine comprising a heater system to generate heat to the exhaust aftertreatment system including a catalytic converter. A control system is arranged to control the heater system; wherein the control system is programmed to heat the exhaust after treatment system based on a setpoint value. The control system comprises a controller having an error input and an output; that outputs a heating power setpoint value that is adjusted by a feedback signal, said adjusted setpoint value provided in parallel to a branch including the heater system and a branch including a dynamic response system. The dynamic response system comprises a dynamic response part and a delay part. A first subtractor subtracts a measured heat output and an output of the dynamic response system; an adder adds an output of the dynamic response part and an output of the first subtractor. A second subtractor subtracts a heating power setpoint from the output of the adder to provide a control error signal for the error input of the controller. It is noted that conventional PID control will face stability issues if the phase delay of the system is close to the systems deadtime. This can be solved by adding phase margin (conservative calibration), but this comes at the cost of performance (heat-up time).
By providing the added output of the dynamic response part and the output of the first subtractor, a faster response can be obtained, without a need for a large phase delay to prevent stability problems of the controller.
The specific position of the heater system may be dependent on practical conditions. It may be a system that can be integral to the aftertreatment system.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs as read in the context of the description and drawings. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some instances, detailed descriptions of well-known devices and methods may be omitted so as not to obscure the description of the present systems and methods. The term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising” specify the presence of stated features but do not preclude the presence or addition of one or more other features. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.
During cold start or in other conditions where the operating temperature of the EAS 30 is insufficient, the heater system 20 may also be activated. Heater system 20 may be an electric heater system or it may be a burner or other heat source. A turbo can be controlled to achieve certain boost pressure for the engine intake line 12 and may be a turbo compressor of a known type, where mechanical energy derived from the exhaust turbine may be electrically boosted by an electric motor. The compressor may also be all-electric or may be hybrid—that is, the compressor can be mechanically driven by the turbine and at the same time boosted by an electric motor. The control system 50 may calculate the heat addition delivered by the heater system/burner. This can be determined by a temperature sensor or a model, in view of the exhaust gas flow, that is provided by the heater system 20.
Turning to
The internal combustion engine 10 may comprise an exhaust gas recirculation (egr) line 11 for use, in egr mode, to supply exhaust gas to the intake line 12.
A dynamic response system (A) capturing theses long lead times and the large thermal inertia is added to the feedback controller (
The adjusted setpoint value of the controller actuation (uFF+uFB=utot) will be fed to the actual electrical heater, but also will be used to feed (B) the simple model, i.e. said adjusted setpoint value provided in parallel to a branch including the heater system 20 and a branch including a dynamic response system A.
The temperature measured—representing the SCR system (mv)—is not directly compared to the target setpoint for the temperature (sp or G) (as in a normal arrangement), but the target setpoint (sp or G) is in part compared to a modelled temperature (D) according to the dynamic response part 341. To this end adder 310 adds an output of the dynamic response part 341 and an output of the first subtractor 320, which subtracts a measured temperature of the SCR system (mv) and an output (C) of the dynamic response system 340—see further below. Thus, output D is a result of how the control action (utot) forces the dynamic response part 341 to react to controller actuation without including a delay, which corresponds to an actual predicted response of the SCR system.
As mentioned already, the modelled temperature result of 341 is also used to estimate what the system would do if the dead time was actually taken into account, by delay part 342. This results in output C that is provided to first subtractor 320. The output C will accordingly be compared the actual behaviour of the system (mv), and then this results in (E), which can be described as a predicted error. A second subtractor 330 subtracts heating power setpoint (sp) from the output of the adder 310 to provide a control error signal for the error input of the controller 300.
This predicted error (E) will be added to the predicted (undelayed) estimation of the system (D ). Together (E) this will be used to compare against the desired temperature target (G) and finally (error) used to feed into the controller 300.
The effect of applying dynamic response system 340 in the feedback will result in that the large lead time is effectively cancelled out with the (E) and (D) loops, and thereby speeding up the control loop. The best results are obtained when the simple model matches exactly the dynamic of SCR system, reality is that this will not happen, but still there is enough improvements to speed up the control loop.
Where:
TSCRSS=Steady state SCR temperature
TICE out=Engine exhaust gas temperature
PTM=Power added to the exhaust gas by a thermal measure
Ploss=Calculated power losses over the aftertreatment system
m′exh=Exhaust gas massflow
cp(TICE out)=Specific heat of exhaust gas at constant pressure, determined for TICE out
Ploss may be calculated by solving the convective heat transfer equation per EAS component or be a calibratable loss as a function of m′exh and TICE out with a vehicle speed and ambient temperature dependency.
In the ideal situation that everything is perfectly known and stable, then PTM can be set equally to Ploss, which in terms of control represents that the feedforward term uFF is PTM. The added heat power may be provided by the heater system to be controlled.
The heat loss may be calculated as a sum of heat losses over exchange surfaces of the exhaust after treatment system, with ambient temperature.
In detail, the convective heat losses are calculated by:
Where:
Ploss componenti=Powe loss of the ith aftertreatment component
n=total number of evaluated aftertreatment components
Ai=Outer surface area of ith aftertreatment component
hi=heat transfer coefficient ith aftertreatment component
Ti=The surface temperature of the ith aftertreatment component
Tamb=The ambient temperature
The heat loss may calculate with a transfer coefficient that is dependent on vehicle speed. The heat transfer coefficient can be dependent on the local wind speed and on the geometric shape. Assuming the aftertreatment is a flat surface, the heat transfer coefficient is given by:
h
i=6.2+4.2·νveh·ki
Where:
νveh=Vehicle speed
ki=Wind speed fraction of the vehicle speed at the ith component
The output of the dynamic response part, corresponding to a calculated SCR temperature, is an undelayed response that is low pass filtered with a massflow dependent variable time constant. The time constant is a function of the exhaust massflow and is tuned to resemble the thermal inertia of the system (A1). This output of the model component (A) resembles signal (D) of the figure, and it is the undelayed description of the behaviour.
T
SCR dyn=lowpass(TSCR SS, τ(m′exh))
Where:
TSCR dyn=dynamic model value of the SCR temperature
lowpass=any type of low pass filter
τ(m′exh)=variable time constant as a function of exhaust gas massflow
In the representation of
The representation of
The representation of
By way of example,
Other variations to the disclosed embodiments can be understood and by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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2033137 | Sep 2022 | NL | national |