Virtual sensing system

A control system includes an electric heater disposed within an exhaust fluid flow pathway, and a control device for receiving at least one input selected from the group consisting of temperature readings along the exhaust fluid flow pathway, alternator power/current/voltage, battery power/current/voltage/state of charge, IAT and EAT profiles, mass flow rate of an exhaust fluid flow, NH3 slip, TCR characteristics of the heater, alternator speed, engine speed, state of aging of an aftertreatment component, state of aging of engine, aging degradation characteristics, a dosing rate and a temperature of DEF, NH3 storage condition of aftertreatment system, an ambient temperature, and combinations thereof. The control device modulates power to the heater based on the at least one input such that the heater provides different power output as a function of the at least one input and a continuously variable power output during operation of the exhaust system.

FIELD

The present disclosure relates to heating and sensing systems for fluid flow applications, for example vehicle exhaust systems, such as diesel exhaust and aftertreatment systems.

BACKGROUND

The use of physical sensors in transient fluid flow applications such as the exhaust system of an engine is challenging due to harsh environmental conditions such as vibration and thermal cycling. One known temperature sensor includes a mineral insulated sensor inside a thermowell that is then welded to a support bracket, which retains a tubular element. This design, unfortunately, takes a long amount of time to reach stability, and high vibration environments can result in damage to physical sensors.

Physical sensors also present some uncertainty of the actual resistive element temperature in many applications, and as a result, large safety margins are often applied in the design of heater power. Accordingly, heaters that are used with physical sensors generally provide lower watt density, which allows a lower risk of damaging the heater at the expense of greater heater size and cost (same heater power spread over more resistive element surface area).

Moreover, known technology uses an on/off control or PID control from an external sensor in a thermal control loop. External sensors have inherent delays from thermal resistances between their wires and sensor outputs. Any external sensor increases the potential for component failure modes and sets limitations of any mechanical mount to the overall system.

One application for heaters in fluid flow systems is vehicle exhausts, which are coupled to an internal combustion engine to assist in the reduction of an undesirable release of various gases and other pollutant emissions into the atmosphere. These exhaust systems typically include various aftertreatment devices, such as diesel particulate filters (DPF), a catalytic converter, selective catalytic reduction (SCR), a diesel oxidation catalyst (DOC), a lean NOxtrap (LNT), an ammonia slip catalyst, or reformers, among others. The DPF, the catalytic converter, and the SCR capture carbon monoxide (CO), nitrogen oxides (NOx), particulate matters (PMs), and unburned hydrocarbons (HCs) contained in the exhaust gas. The heaters may be activated periodically or at a predetermined time to increase the exhaust temperature and activate the catalysts and/or to burn the particulate matters or unburned hydrocarbons that have been captured in the exhaust system.

The heaters are generally installed in exhaust pipes or components such as containers of the exhaust system. The heaters may include a plurality of heating elements within the exhaust pipe and are typically controlled to the same target temperature to provide the same heat output. However, a temperature gradient typically occurs because of different operating conditions, such as different heat radiation from adjacent heating elements, and exhaust gas of different temperature that flows past the heating elements. For example, the downstream heating elements generally have a higher temperature than the upstream elements because the downstream heating elements are exposed to fluid having a higher temperature that has been heated by the upstream heating elements. Moreover, the middle heating elements receive more heat radiation from adjacent upstream and downstream heating elements.

The life of the heater depends on the life of the heating element that is under the harshest heating conditions and that would fail first. It is difficult to predict the life of the heater without knowing which heating element would fail first. To improve reliability of all the heating elements, the heater is typically designed to be operated with a safety factor to avoid failure of any of the heating elements. Therefore, the heating elements that are under the less harsh heating conditions are typically operated to generate a heat output that is much below their maximum available heat output.

SUMMARY

In one form, a control system for a heating system of an exhaust system is provided. The control system includes at least one electric heater disposed in an exhaust fluid flow pathway, and a control device adapted to receive at least one input. The at least one input is selected from the group consisting of temperature readings along the exhaust fluid flow pathway, alternator power, alternator current, alternator voltage, battery power, battery current, battery voltage, battery state of charge, inlet air throttle (IAT) and exhaust air throttle (EAT) profiles, exhaust gas recirculation (EGR), mass flow rate of an exhaust fluid flow, NH3slip, temperature coefficient of resistance (TCR) characteristics of the at least one electric heater, alternator speed, engine speed, state of aging of an aftertreatment component, state of aging of engine, aging degradation characteristics, a dosing rate of a diesel exhaust fluid (DEF), a temperature of the DEF, NH3storage condition of aftertreatment system, injection timing retard, cylinder cut-out, variable valve manipulation, turbocharger bypass, intake air pre-heating, late post injection, ambient temperature, ambient temperature, and combinations thereof. The control device is operable to modulate power to the at least one electric heater based on the at least one input such that a different power output is provided by the at least one heater as a function of the at least one input and such that the at least one heater provides a continuously variable power output during operation of the exhaust system.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the present disclosure, its application, or uses. It should also be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.

Referring toFIG. 1, an exemplary engine system10generally includes a diesel engine12, an alternator14(or generator in some applications), a turbocharger16, and an exhaust aftertreatment system18. The exhaust aftertreatment system18is disposed downstream from a turbocharger16for treating exhaust gases from the diesel engine12before the exhaust gases are released to atmosphere. The exhaust aftertreatment system18can include one or more additional components, devices, or systems operable to further treat exhaust fluid flow to achieve a desired result. In the example ofFIG. 1, the exhaust aftertreatment system18includes a heating system20, a diesel oxidation catalyst (DOC)22, a diesel particulate filter device (DPF)24, and a selective catalytic reduction device (SCR)26. The exhaust aftertreatment system18includes an upstream exhaust conduit32that receives a heater assembly28therein, an intermediate exhaust conduit34in which the DOC22and DPF24are provided, and a downstream exhaust conduit36in which the SCR26is disposed.

It should be understood that the engine system10illustrated and described herein is merely exemplary, and thus other components such as a NOxadsorber or ammonia oxidation catalyst, among others, may be included, while other components such as the DOC22, DPF24, and SCR may not be employed. Further, although a diesel engine12is shown, it should be understood that the teachings of the present disclosure are also applicable to a gasoline engine and other fluid flow applications. Therefore, the diesel engine application should not be construed as limiting the scope of the present disclosure. Such variations should be construed as falling within the scope of the present disclosure.

The heating system20includes a heater assembly28disposed upstream from the DOC22, and a heater control module30for controlling operation of the heater assembly28. Heater assembly28can include one or more electric heaters wherein each electric heater includes at least one resistive heating element. The heater assembly28is disposed within an exhaust fluid flow pathway in order to heat the fluid flow during operation. Heater control module30typically includes a control device adapted to receive input from the heater assembly28. Examples of controlling the operation of heater assembly28can include turning the heater assembly on and off, modulating power to the heater assembly28as a single unit and/or modulating power to separate subcomponents, such as individual or groups of resistive heating elements, if available, and combinations thereof.

In one form, the heater control module30includes a control device. The control device is in communication with at least one electric heater of the heater assembly28. The control device is adapted to receive at least one input including but not limited to an exhaust fluid flow, mass velocity of an exhaust fluid flow, flow temperature upstream of the at least one electric heater, flow temperature downstream of the at least one electric heater, power input to the at least one electric heater, parameters derived from physical characteristics of the heating system, and combinations thereof. The at least one electric heater can be any heater suitable to heat an exhaust fluid. Example electric heaters include but are not limited to a band heater, a bare wire resistive heating element, a cable heater, a cartridge heater, a layered heater, a strip heater, a tubular heater, and combinations thereof. The physical characteristics may include, by way of example, resistance wire diameter, MgO (insulation) thickness, sheath thickness, conductivity, specific heat and density of the materials of construction, heat transfer coefficient, and emissivity of the heater and fluid conduit, among other geometrical and application related information.

The system ofFIG. 1includes the DOC22disposed downstream from the heater assembly28. The DOC22serves as a catalyst to oxidize carbon monoxide and any unburnt hydrocarbons in the exhaust gas. In addition, the DOC22converts nitric oxide (NO) into nitrogen dioxide (NO2). The DPF24is disposed downstream from the DOC22to assist in removing diesel particulate matter (PM) or soot from the exhaust gas. The SCR26is disposed downstream from the DPF24and, with the aid of a catalyst, converts nitrogen oxides (NOx) into nitrogen (N2) and water. A urea water solution injector27is disposed downstream from the DPF24and upstream from the SCR26for injecting urea water solution into the stream of the exhaust gas. When urea water solution is used as the reductant in the SCR26, NOx is reduced into N2, H2O and CO2.

In one form of the present disclosure, data from the engine system10described above is used in a mathematical model to predict various temperatures, including heater temperature, exhaust inlet temperature, and exhaust outlet temperature, among others, without the use of physical sensors. These models have been developed for both transient and non-transient systems and are applicable to a variety of heater types and fluid flow applications. Accordingly, the various forms provided herein of a tubular heater and an engine exhaust should not be construed as limiting the scope of the present disclosure. Further, the specific reference to a “heater sheath” temperature is merely exemplary, and the calculated temperature may be for any component of any type of heater such as a band heater, a bare wire resistive heating element, a cable heater, a cartridge heater, a layered heater, a strip heater, or a tubular heater, among others. A “layered heater” has been previously defined in U.S. Pat. No. 7,196,295, which is commonly assigned with the present application and the contents of which are incorporated herein by reference in their entirety.

Referring toFIG. 2, a tubular heater is used as an example type of heater used in the heater assembly28and is illustrated and generally indicated by reference numeral40. The tubular heater40comprises a resistive heating element42disposed within a sheath44, and an insulation material46disposed therebetween, such as by way of example, a compacted magnesium oxide (MgO). The tubular heater40also may include power pins50and seals52.

The present disclosure provides for a control system and methods of controlling an electric heater that generally include a device/apparatus that uses inputs, such as mass flow or flow velocity, flow temperature either upstream or downstream of the heater, heater power input, and parameters derived from physical characteristics of the system, to then modulate power to the heater based on these inputs. In order to calculate values for the system depending on a set of known variables, a variety of equations are disclosed herein. It should be understood that these equations are merely exemplary and should not be construed as limiting the scope of the present disclosure.

For example, in order to calculate the temperature of the sheath44without the use of physical sensors in an application such as a diesel exhaust as set forth above, mass flow rate, inlet temperature, and power to the heater40are used, along with heat transfer equations, for a variety of heater configurations. In one form, Equation 1 below is used to calculate the temperature of the sheath44(Ts):

where:Ac=heater cross-sectional area;As=sheath area;C=a first constant based on Reynolds number (Re) and Table 1 shown below;C2=offset based on number of heater elements;D=heater element diameter;K=thermal conductivity of air;kW=total heater power;Mfuel=mass flow rate of fuel;Min=inlet mass air flow (MAF) rate;m=a second constant based on Reynolds number (Re) and Table 1 shown below;Pr=Prandtl number of air taken at gas temperature;Prs=Prandtl number of air taken at sheath temperature;ST=transverse distance between elements;Tout=heater outlet temperature; andμ=viscosity of air.

TABLE 1ReD, maxC (“C1”)m10-1000.800.40100-1000(Single cylinder(Single cylinderapprox.)approx.)1000-200k0.270.63Single Cylinder40-40000.6830.466NL123456C20.700.800.860.890.900.92ReD,max=Reynolds number for a given diameter and velocity maximum;NL=Number of elements; andC2=When evaluating element1, use NL=1; when evaluating 6 elements,NLstarts at 0.7 and increases to 0.92 as each element is analyzed.

Further, in this Equation 1, radiation effects have not been incorporated, however, may be incorporated while remaining within the scope of the present disclosure.

In addition to heater sheath44temperature, an outlet temperature after each element within the fluid flow stream (seeFIG. 3) can be calculated/modeled, thus reducing the need for additional temperature sensors. In one form, the outlet temperature is calculated according to Equation 2 below:

where:As=sheath surface area;Cp=specific heat of air at constant pressure;h=convective heat transfer coefficient;{dot over (m)}=mass flow rate;Tout,1=outlet temperature after heating element1;Tin,1=inlet temperature of heating element1; andTs=sheath temperature.

Therefore, using Equation 2, temperatures can be predicted without the use of physical sensors throughout a fluid flow system. As a further advantage, using the equations as set forth herein results in a quicker response time due to the lag time associated with physical sensors, and especially in transient systems. Better accuracy and quicker response times also allows for using heaters that operate at higher temperatures, therefore providing improved performance and decreasing safety margins. Moreover, a failure mode of a physical sensor is removed by the present disclosure.

Because Equation 1 is for steady state, a further underlying equation is used for virtual sensing as disclosed herein, namely, Equation 3:

where:Ac=heater cross-sectional area;As=sheath area;C=constant based on Reynolds number (Re) and Table 1;C2=offset based on number of heater elements;Cp=specific heat of air at constant pressure;D=heater element diameter;K=thermal conductivity of air;Mfuel=mass flow rate of fuel;Min=inlet mass air flow (MAF) rate;m=constant based on Reynolds number (Re) and Table 1;{dot over (m)}=mass flow rate;Pr=Prandtl number of air taken at gas temperature;Prs=Prandtl number of air taken at sheath temperature;ST=transverse distance between elements;Tin=heater inlet temperature;Tout=heater outlet temperature; andμ=viscosity of air.

Generally, so as to not be limited to the specific equations disclosed herein, Tsis determined by a system of equations using inputs of set point, mass flow, and inlet temperature to calculate system temperatures.

The present disclosure further provides for predictive/proactive control of the heater40. For example, system data such as torque demand, pedal position, and increased manifold absolute pressure (MAP)/boost/engine timing can be converted into a mass flow rate, which can then be provided to the control system to determine desired heater power in advance of when the power is needed, rather than relying on a delayed response to a physical sensor.

One variation of the present disclosure takes into account radiation effects according to Equation 4:
Q=ε·σ·vf(Th+Tse)   EQUATION 4

Furthermore, the heater can be fully mathematically quantified such that the system frequency response of all materials comprising the heater can be determined from mass air flow (MAF) rate, heater inlet temperature, and applied power. The frequency response of the heater to changing engine and exhaust conditions or general system disruptions can be reduced, allowing the heater to have a faster feedback response. This then improves control over heater element temperature, allowing the heater to have a higher watt density (watts per unit length, watts per unit area, or watts per unit volume) and better durability, as temperature fluctuations are reduced. System representations can be simplified into a form the control microprocessor can utilize with reduced effort. Further, the present disclosure can simplify a relatively complex math process into tabulated form to reduce processing power and defined expected states. It should be understood that a variety of methods of obtaining mass air flow may be employed, such as by way of example, MAP and combining inlet air mass flow with fuel consumption. Accordingly, as used herein, the term “mass flow” shall be construed to include these and other methods of obtaining mass air flow.

Generally, the present disclosure takes inputs from a variety of devices, such as by way of example, engine, exhaust, electrical power, and heater, executes various algorithms, and then generates output such as actual power consumption, exhaust temperature, heater temperature, diagnostics, and exhaust mass flow. The engine inputs/parameters may include exhaust temperature and exhaust flow; and the heater inputs/parameters may include heater power, geometry, and coefficients. The system model may include a heater model, wire temperature and sheath temperature, and at least one control algorithm. The outputs may then include exhaust temperature, exhaust flow, and diagnostics.

In still another form, the virtual sensing system functions in a diagnostic mode to compare a response of the heater40to a known applied power to determine if the overall exhaust aftertreatment system18is degrading, has reduced efficiency, or if there is a defect in the exhaust aftertreatment system18. In addition, the virtual sensing system may allow for the removal of a catalyst inlet temperature sensor, thus reducing the cost and complexity of the overall exhaust aftertreatment system18. If the catalyst inlet temperature sensor remains in the exhaust aftertreatment system18, its output can be compared to the calculated/predicted heater outlet temperature provided by the virtual sensing system and any mismatch therebetween can trigger a diagnostic trouble code within an engine control unit (ECU). Furthermore, the virtual sensor system of the present disclosure can be integrated with a model-based design (e.g., Simulink) to improve transient performance and allow better characterization of the heater system. Furthermore, a model-based design can adjust parameters/characterization of the virtual sensor system based on a specific application other than the diesel exhaust application as used herein.

The use of a virtual sensor system further reduces the uncertainty of knowing the actual resistive element (e.g., wire) temperature and allows safety margins to be reduced, increased watt density and less heater surface area, thus resulting in a more efficient and less costly heater.

The control system as disclosed herein may also control power to the heater by a calculated, or virtual temperature of the resistive heating element, such as a resistive wire. Reference is made to copending application titled “Advanced Two-Wire Heater System for Transient Systems,” which has been incorporated herein by reference. In some applications such as a tubular heater, controlling by virtual wire temperature overcomes the thermal inertia of the insulation and sheath. This results in less temperature variation on the wire, which improves reliability. Such an approach also reduces the cyclic load on a power source, allowing for smoother power delivery and less strain on the power source.

The present disclosure further provides for an engine system10including a control system for the heating system of the exhaust system as previously described. The control device is adapted to receive engine inputs selected from the group consisting of engine parameters, exhaust parameters, electrical power output, heater parameters, and the device is operable to generate output selected from the group consisting of power consumption, exhaust temperature, heater temperature, diagnostics, exhaust mass flow rate, and combinations thereof. The control system is further operable to diagnose degrading engine system components. In this example, the control system is in communication with an engine control unit and adapted to trigger a diagnostic trouble code when a determined parameter is mismatched with a preset parameter.

Referring toFIG. 4, the present disclosure further includes a method100of predicting temperature of at least one location in a fluid flow system having a heater disposed in a heating system for heating fluid. The method includes obtaining a mass flow rate of fluid flow of the fluid flow system110, obtaining at least one of a fluid outlet temperature and a fluid inlet temperature of the heater120, obtaining power provided to the heater130, and calculating temperature at the at least one location based on a model of the fluid flow system and the obtained mass flow rate and fluid outlet and inlet temperatures140. The at least one location can be on a heating element of the at least one electric heater of the heating assembly. The model can include the temperature prediction models as previously described above. The process can further be integrated with a model-based design.

Referring toFIG. 5, the present disclosure further provides another method200of predicting outlet temperature after each of a plurality of resistive heating elements in a heater system disposed in a fluid flow system for heating fluid. The method includes obtaining a mass flow rate of fluid flow of the fluid flow system210, obtaining a fluid inlet temperature to at least one resistive heating element220, obtaining power provided to each resistive heating element and characteristics of the fluid flow system that relate power input to each resistive heating element to power transferred to the fluid flow230, and calculating the outlet temperature based on a model of the fluid flow system240.

As used herein, the term “model” should be construed to mean an equation or set of equations, a tabulation of values representing the value of a parameter at various operating conditions, an algorithm, a computer program or a set of computer instructions, a signal conditioning device or any other device that modifies the controlled variable (e.g., power to the heater) based on predicted/projected/future conditions, wherein the prediction/projection is based on a combination of a priori and in-situ measurements.

Accordingly, a variety of different forms of heaters, sensors, control systems, and related devices and methods have been disclosed herein for use in fluid flow systems. Many of the different forms can be combined with each other and may also include additional features specific to the data, equations, and configurations as set forth herein. Such variations should be construed as falling within the scope of the present disclosure.

Referring toFIG. 6in conjunction withFIG. 1, as previously noted, the heater control module30may be configured to control operation of the heater assembly28and to modulate power to the heater assembly28. In the present embodiment, the heater control module30may be integrated or communicated with the engine12to allow for treatment of the exhaust gas in the exhaust aftertreatment system18without compromising the fuel efficiency or with less disturbance to the fuel efficiency.

In a prior art heating system for an exhaust system, the heater may be activated solely based on the conditions of the exhaust system, such as the temperature of the exhaust gas, without considering the conditions of the engine and the battery. Such control may compromise the fuel efficiency. For example, when the vehicle is operated in a charge-depleting or EV mode where the vehicle operation is dependent on the energy from the battery pack, actuating the heater in this state causes an increased demand for power. The increased demand for power may cause the vehicle to switch from the charge-depleting mode to an engine running mode if the battery state of charge is low, thereby undesirably increasing fuel consumption.

Therefore, the heater control module30of the heating system20for the exhaust aftertreatment system18may be configured to control one or more electric heaters of the heater assembly28in a way to reduce emissions from the exhaust aftertreatment system18while taking fuel efficiency into consideration. The one or more electric heaters of the heater assembly28are disposed in an exhaust fluid flow pathway. The heater control module30includes a control device31configured to receive at least one input relating to the conditions of the engine, the battery, the alternator, the heater, the aftertreatment component of the exhaust aftertreatment system18, as well as the temperature along the exhaust fluid flow pathway of the exhaust aftertreatment system18and to modulate power to the heater assembly28accordingly.

When the at least one input is an engine-related condition, the engine-related condition may be represented by a predetermined or desired temperature profile. The at least one input may also relate to the conditions of the battery, the alternator, the heater, the aftertreatment component of the exhaust aftertreatment system18. Therefore, the at least one input may be selected from the group consisting of temperature readings along the exhaust fluid flow pathway, alternator power, alternator current, alternator voltage, battery power, battery current, battery voltage, battery state of charge (SOC), inlet air throttle (IAT) and exhaust air throttle (EAT) profiles, exhaust gas recirculation (EGR), mass flow rate of an exhaust fluid flow, NH3slip, temperature coefficient of resistance (TCR) characteristics of the electric heater, alternator speed, engine speed, state of aging of an aftertreatment component, state of aging of engine, aging degradation characteristics, a dosing rate of a diesel exhaust fluid (DEF), a temperature of the DEF, NH3storage condition of aftertreatment system, injection timing retard, cylinder cut-out, variable valve manipulation, turbocharger bypass, intake air pre-heating, late post injection, ambient temperature, and combinations thereof. Based on the at least one input, the control device31is operable to modulate and adjust power to the heater assembly28continuously or at a predetermined interval. Different power/heating output is provided by the heater assembly28to heat the exhaust gas in the exhaust aftertreatment system18as a function of the at least one input.

Among the plurality of inputs, state of aging of a component refers to the time and temperature history of the component. The IAT-EAT profiles may include a temperature-mass flow profile, a temperature-engine speed profile, a temperature-load profile, or a temperature-engine condition profile. All of these profiles have different temperature targets based on engine conditions. The one or more electric heaters of the heater assembly28may include one or more resistive elements. The control device31may modulate power to the heater assembly28based on a calculated temperature of the resistive element(s).

As an example, when the at least one input includes the temperature readings along the exhaust fluid flow pathway, the temperature readings are relative to a threshold value to adjust or modify the output of the heater assembly28such that different power outputs are provided by the heater assembly28below and above the threshold value. In one example, the temperature readings may be an inlet temperature of a selective catalytic reduction (SCR) device26. A higher power output is provided by the heater assembly28when the SCR inlet temperature is below the threshold value. A lower power output is provided by the heater assembly28when the SCR inlet temperature is above the threshold value. The higher power output includes an increase in magnitude and/or rate of power increase.

The control device31may include a power switch60, a controller62, a mass flow limit table64, and a power output limit device66. The controller62may be a PID controller, a predictive feedback controller, a model based controller, or any controller known in that art that can control heater power output.

When the at least one input, such as the temperature readings, is above the threshold value, the controller62may be used to control the heater power based on the temperature readings. However, when the temperature readings are below the threshold value and higher heater power output or a fast heating is desired, the control device31may bypass or override the controller62and the heater power is provided using a mass flow limit table64and a power output limit device66. The at least one input is constantly or regularly monitored. When the at least one input has increased to reach the threshold value, the control of the heater assembly28may be switched to the PID control with limits. Alternatively, the control of the heater assembly28may be based on a predetermined algorithm48.

Improving NOx conversion during cold exhaust conditions can achieve optimal fuel saving. Faster heating during cold exhaust conditions can improve NOx conversion when the exhaust is cold, thereby allowing the engine to be run at relatively lower temperature when the exhaust later becomes warmer to save fuel. Faster heating during cold exhaust conditions may be achieved by ramping up the power to the heater to provide more heat. Advancing fuel injection timing can also improve fuel savings. Therefore, the engine calibration may be modified to supply additional heat along with operation of the heater assembly28when more heat is needed.

The fuel used during cold exhaust conditions is typically a smaller portion of the overall fuel usage. By using more fuel than typically required when exhaust temperatures are low, a faster heating can be achieved, thereby achieving better NOx conversion. The better NOx conversion during cold exhaust conditions enables a reduced NOx conversion when the exhaust later becomes warmer. Therefore, the temperature for NOx conversion when the exhaust is warmer may be lowered to reduce fuel consumption. The heater power can also be minimized when the exhaust is warmer.

While extra fuel is used to achieve fast heating during cold exhaust conditions, fuel is saved during the subsequent warmer exhaust conditions when the engine will be run at a relatively lower temperature. As a result, the extra fuel that is used during cold exhaust conditions is recouped by lowering the temperature (and consequently fuel consumption) during the subsequent warming exhaust conditions. While this strategy will increase NOx emissions during the subsequent warmer exhaust conditions, the amount of NOx emissions will still be within the controlled range according to government regulations. The effect of this fuel saving strategy can be further enhanced by combining engine heating for fast heating up, such as retarded timing for fuel injection, multiple injections and injection pressure.

To reduce fuel consumption during low load operations, condition-based setpoints, instead of a single fixed setpoint, are used to more closely match a desired engine-condition-based temperature profile. In other words, the desired setpoints vary with engine conditions.

In another example, the at least one input may include battery current or battery state of charge. In this case, the heater power is limited when the battery state of charge is lower than a threshold value. Therefore, the heater assembly28may be controlled to be limited based on engine/alternator speed or based on change in voltage over time.

NH3slip occurs when excessive ammonia is injected in the SCR device26or when SCR temperature increases and NH3storage capacity is reduced. When the at least one input includes NH3slip, the heater power is lower when the NH3slip exceeds a threshold value and is higher when the NH3slips is below the threshold value.

The power switch60of the control device31may be used to control the power to the heater assembly28. The power switch60may cause pulsed current/power to be supplied to the heater assembly28. Power is pulsed to control current supply to the heater assembly28. When the current is pulsed, voltage and average current are used to calculate the power to the heater assembly28. By using the pulsed power along with power measurements, combined with information about exhaust mass flow, a mass flow limit table44or an algorithm48may be used to protect the heater assembly28and the heater assembly28can be made smaller.

In summary, the heater assembly28is controlled to provide heating to the exhaust gas in the exhaust aftertreatment system18taking the fuel efficiency into consideration. Therefore, the heater assembly28is operated in a way to provide more precise thermal control to meet emission requirements while conserving fuel through optimization. The heater assembly28may be controlled differently based on whether at least one input is below or above a threshold value or may be controlled differently in a plurality of heating modes. The at least one input includes parameters relating to the conditions of the engine, the conditions of the battery, the conditions of the alternator, the conditions of an aftertreatment component, and the conditions of the heater, as well as temperature of the exhaust aftertreatment system. The plurality of heating modes are also based on the conditions of the engine, the battery, the alternator, the aftertreatment component, the heater, as well as the temperature of the exhaust aftertreatment system.

The heater power is limited based on power measurement and based on duty cycle to reduce fuel consumption. By limiting the heater power, heating the exhaust gas to a single setpoint particularly during a time of generally lower engine speed and load is avoided. By limiting the heater power, switching the vehicle from an EV mode to an engine running mode (where the alternator recharges the battery) is avoided. Power limit varies with mass flow (or engine-based map). The heater assembly28may also be used to manage NH3 storage, thereby controlling NH3 slip. The temperature of the heater assembly28is controlled based on power measurement (in the context of engine, alternator, battery, etc.). Moreover, in order to conserve fuel, the temperature setpoints vary at different engine conditions. As a result, fuel can be used more efficiently while NOx emissions can be controlled within a range to meet government regulations.