Diesel particulate filter regeneration control and method

An after-treatment device that includes a diesel particulate filter (DPF) requiring periodic regeneration includes a sensor providing a signal indicative of a soot accumulation and at least one device providing an operating parameter indicative of a work mode of the machine. A controller determines a soot level and a readiness level based on the work mode of the machine, and further classifies the soot level relative to a desired range for initiating a regeneration event and initiates the regeneration event when the soot level falls within the desired range.

TECHNICAL FIELD

The present disclosure relates to a particulate trap regeneration system and, more particularly, to a particulate trap regeneration system and an associated control strategy.

BACKGROUND

One of the byproducts of fuel combustion in an internal combustion engine is carbon particles, which are typically referred to as soot. Emission standards will typically specify a limit to the amount of soot that an engine can emit to the environment, which limit will be below the level of soot generated by the engine during operation. Therefore, various components and systems are employed by engine or vehicle manufacturers that control and limit the amount of soot emitted to the environment.

One device commonly used to limit the amount of soot expelled into the environment from an engine is referred to as a particulate trap. Such a device includes a porous substrate, for example, made of ceramic material, that may be coated with various chemical compounds that alter the composition of exhaust constituents. The porosity of the substrate acts as a filter for physically trapping carbon particles or soot in an exhaust stream passing over and/or through the filter. One can appreciate that such physical removal of carbon particles from a gas stream will progressively saturate the filter with particulate matter.

One method of restoring the performance of a particulate trap becoming saturated with soot is by a process called regeneration. Regeneration involves the oxidation or burning of accumulated particulate matter in a filter. Such oxidation may include the introduction of a combustible agent, such as fuel, onto the particulate matter to aid in the combustion. Moreover, regeneration of particulate traps often includes an elevation of the temperature of the particulate matter, for example, by elevating the temperature of the exhaust gas stream passing therethrough, prior to combustion.

Commonly used methods of regenerating a particulate filter involve an active intervention to the normal operation of the engine. Such intervention may be perceptible to an operator of the engine, and may even interfere with the normal operation of the vehicle. In other words, processes that alter the fueling strategy of an engine to introduce fuel in the exhaust stream or, more commonly, operation of the engine to increase exhaust temperature, can alter the behavior and power output of a vehicle or machine. Such alterations may interfere with normal use of equipment, which can have repercussions in the uptime and cost of operating the equipment.

The time and duration of a regeneration event depends on many factors, such as the extent of accumulation of soot or carbon particulate matter on the filter, the operating conditions of the engine, and so forth. One example of a particulate trap system and control method therefor can be seen in U.S. Pat. No. 7,406,822 (hereafter, the '822 patent), which issued to Funke et al. and is assigned Caterpillar Inc. of Peoria, Ill. The '822 patent describes a system that includes a particulate trap and a regeneration device configured to reduce an amount of particulate matter in the particulate trap.

The system described in the '822 patent further includes a controller that activates the regeneration device in response to the first to occur of at least three trigger conditions. The trigger conditions may include, for example, operation of the engine for a predetermined period, consumption of a predetermined amount of fuel by the engine, detection of an elevated backpressure upstream of the particulate trap, detection of a pressure differential across the particulate trap that exceeds a threshold, or a calculated amount of particulate matter accumulated on the particulate trap that exceeds a limit. Such parameters may be independently evaluated to determine that a regeneration event is required. Thereafter, the controller may activate the regeneration device to oxidize the particulate matter found at the particulate trap.

Even though activation of a regeneration event for a particulate trap, whether such event involves use of a regeneration device or not, can be effective in removing trapped particulate matter when such concentration on a trap has exceeded a limit. Such regeneration may occur at any time during operation of the engine and may reduce, even temporarily, the effectiveness of any machine or vehicle, which heretofore has been an undesirable but necessary process. For example, a particulate trap installed on an on-highway truck may require the truck to be stopped on the side of the road while a regeneration event is taking place. It is desired to reduce or eliminate such intrusions to the normal operation of a vehicle or machine whenever possible.

SUMMARY

The disclosure describes, in one aspect, a machine having an after-treatment device that includes a diesel particulate filter (DPF) requiring periodic regeneration. The DPF receives a flow of exhaust gas provided by an engine associated with the machine. The machine further includes a sensor providing a signal indicative of a soot accumulation in the DPF, and at least one device providing an operating parameter indicative of a work mode of the machine. The sensor may directly measure soot and/or may generate a signal indicative of soot from indirect sources. A controller associated with the machine may receive the signal from the sensor and the operating parameter from the at least one device. The controller is arranged to determine a soot level based on the soot accumulation in the DPF, wherein the determination of soot accumulation is least partially based on the signal, and a readiness level based on the work mode of the machine, the work mode being at least partially based on the operating parameter. The controller may classify the soot level relative to a desired readiness level for initiating a regeneration event and initiate the regeneration event when the readiness level coincides with the desired readiness level or other suitable threshold.

In another aspect, the disclosure describes a method for initiating a regeneration event for a DPF. The method includes providing a signal indicative of a soot accumulation in the DPF and an operating parameter indicative of a work mode of the machine. A soot level may be determined based on the soot accumulation in the DPF, which may be at least partially based on the signal, and a readiness level may be determined based on the work mode of the machine, which is at least partially based on the operating parameter. Thereafter, the method includes classifying the soot level relative to a desired readiness level for initiating a regeneration event and initiating the regeneration event when the readiness level coincides with the desired readiness level.

In yet another aspect, the disclosure describes an after-treatment system associated with an engine of a machine. The after-treatment system includes an after-treatment device fluidly communicating with an exhaust conduit connected to the engine. A regeneration device is included between the engine and the after-treatment device along the exhaust conduit and has a first sensor providing a soot signal indicative of a soot accumulation within the after-treatment device. A second sensor associated with the machine provides a work signal indicative of a work mode of the machine. The second sensor, like the first sensor, generates a signal based on either direct or indirect measurements. A controller associated with the engine, the regeneration device, the first sensor, and the second sensor, determines a soot level of accumulation within the after-treatment device based on the soot signal and a readiness level of regeneration for the after-treatment device based on the work mode of the machine. Such work mode may be at least partially based on the work signal. The soot level is classified relative to a desired readiness level for initiating a regeneration event and the regeneration device initiates a regeneration event in the after-treatment device when the readiness level of regeneration reaches the desired readiness level or other suitable threshold.

DETAILED DESCRIPTION

A side view of a machine100, in this example a motor grader101, is shown inFIG. 1. The term “machine” is used generically to describe any machine having at least one drive wheel that is directly driven by a motor connected to the wheel, for example, by use of electrical or hydrostatic power, by a gear system or transmission interconnecting the wheel with an engine, or any other known drive arrangement. For instance, an alternative embodiment for the machine100may include a generator or another device capable of producing an alternative form of energy, such as electrical power.

The motor grader101shown inFIG. 1generally includes a two-piece frame made up of an engine frame102and an implement portion104. Alternatively, the motor grader101may include a single frame piece. The engine frame102in the embodiment shown is connected to the implement portion104by a pivot (not shown). The implement portion104includes an operator cab106and two idle wheels108(only one visible) that contact the ground. A shovel or blade110is suspended along a mid-portion of the implement portion104. The blade110can be selectively adjusted to engage the ground at various heights and angles to achieve a desired grade or contour while the motor grader101operates. Adjustment of the position of the blade110is accomplished by a system of actuators, generally denoted inFIG. 1as112, while support for the loading experienced by the blade110during operation is accomplished by a bar114, which pivotally connects the implement portion104to the blade110.

The engine frame102supports an engine (not visible), which is protected from the elements by an engine cover116. The engine provides the power necessary to propel the motor grader101as well as to operate the various actuators and systems of the motor grader101. As can be appreciated, other machines may have different configurations and/or various other implements associated therewith. The term “machine” as used herein may refer to any machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, a machine may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Similarly, although an exemplary blade110is illustrated as the attached implement, an alternate implement may be included. Any implements may be utilized and employed for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others.

In the illustrated machine, the engine in the engine frame102may be associated with a hydrostatic pump (not shown), which may be part of a hydraulic system operating a propel system of the motor grader101. In the embodiment shown, the motor grader101is driven by two sets of drive wheels118(only one set visible), with each set including two wheels118that are arranged in a tandem configuration along a beam120, which is connected to the frame102at a pivot joint or bearing122.

A block diagram of an after-treatment system200that may be associated with the machine100is shown inFIG. 2. The after-treatment system200includes an after-treatment device202disposed to receive a flow of exhaust gas from an engine204. The after-treatment device202may include one or more internal devices operating to chemically, or physically treat a flow of exhaust gas passing therethrough. Examples of such devices include oxidation catalysts, particulate filters, adsorbing filters, and others. Relevant to the present disclosure, the after-treatment device202essentially includes a diesel particulate filter (DPF)206, which is shown in dashed line and which may be included as part of the after-treatment device202or may be disposed as a stand-alone part in fluid communication with an exhaust pipe or conduit of an engine.

The illustration ofFIG. 2will now be described in more detail. Such illustration is exemplary and represents one potential embodiment of an after-treatment system associated with an engine that is installed in a vehicle or machine. The after-treatment system200includes an exhaust conduit or pipe208that is fluidly connected to the after-treatment device202and DPF206. Exhaust gas passing through the after-treatment device202and the DPF206flows through the exhaust pipe208.

In the embodiment shown inFIG. 2, the after-treatment device202is fluidly connected to a regeneration device210. The regeneration device210may be any device operating to initiate, maintain, and/or control the rate of a regeneration event occurring in the DPF206during operation of the engine204. One example of a regeneration device is described in the '822 patent discussed above. An additional example for a regeneration device is illustrated to include a burner (not shown) disposed to selectively yield a flame that can be used to initiate, maintain, and/or control regeneration of particulate matter that has accumulated on the DPF206. The illustrated regeneration device210includes an injector212disposed to inject a fuel, such as diesel, or a catalyst. When fuel is injected, a flow of fresh, compressed air is supplied via a conduit214to mix with the fuel and, in the presence of a spark, create the flame that introduces heat to the flow of exhaust gas and/or the DPF206. Such heat helps oxidize carbon and other deposits found on the DPF206during a regeneration event, which may produce byproducts, such as ash, that can be collected and/or removed from the DPF206during service.

In the illustrated embodiment, the after-treatment device202is fluidly connected to an exhaust manifold216of the engine204. The engine204operates to combine fuel and air supplied to a plurality of cylinders via an intake manifold218to produce power or torque at an output shaft220. In a known configuration, each of the cylinders of the engine204includes a piston connected to a rotating crankshaft (not shown) via linkages (not shown). The reciprocating motion of the pistons generates a rotational motion of the crankshaft. Such rotational motion may be transferred to various components and systems of a machine, such as hydrostatic pumps, mechanical and/or hydraulic transmissions, electrical generators, work implements, and so forth. In the illustration ofFIG. 2, the output shaft220generically represents a mechanical linkage that can transfer torque and power generated by the engine204during operation to any such components and systems of the machine.

The after-treatment system200may further include a controller222. The controller222may be a single controller or may include more than one controller disposed to control various functions and/or features of a machine. For example, a master controller, used to control the overall operation and function of the machine, may be cooperatively implemented with a motor or engine controller, used to control the engine204. The term “controller” broadly encompasses one, two, or more controllers that may be associated with the machine100and that may cooperate in controlling various functions and operations of the machine100(FIG. 1) including control of a regeneration device or regeneration processes. The functionality of the controller, while shown conceptually in the figures that follow to include various discrete functions for illustrative purposes only, may be implemented in hardware and/or software without regard to the discrete functionality shown. Accordingly, various interfaces of the controller are described relative to components of the after-treatment system200shown in the block diagram ofFIG. 2. Such interfaces are not intended to limit the type and number of components that are connected, nor the number of controllers that are described. The interconnections between the controller222and the various sensors and actuators are denoted in dashed line, which represent communication lines for transferring information signals and commands to and from the controller222. As can be appreciated, any appropriate type of connection may be used, for example, electrical conductors carrying analog or digital electrical signals, and/or electronic communication channels such as those found in confined area network (CAN) arrangements.

The controller222is connected to various sensors and actuators that are disposed to measure various parameters during operation of the after-treatment system200. The controller222is thus disposed to receive information indicative of such operational parameters, to process such information, and to use such information to operate the after-treatment system200effectively and efficiently. As illustrated in the embodiment ofFIG. 2, the controller222may be connected to the injector212and to a flame or temperature sensor224associated with the optional regeneration device210. The controller222further maybe further connected to an engine speed sensor226and to an optional load sensor228disposed to measure a load being present at the output shaft220.

The controller222also may communicate with an upstream temperature sensor230and an upstream pressure sensor232. The upstream sensors230and232are disposed to provide signals to the controller222that are indicative of, respectively, the temperature and pressure of the exhaust gas flow before such flow enters or passes through the after-treatment device202and, in this case, before it passes through the DPF206. The controller222may further communicate with a downstream temperature sensor234and a downstream pressure sensor236. The downstream sensors234and236provide signals to the controller222that are indicative of, respectively, the temperature and pressure of the exhaust flow exiting the DPF206. Even though separate sensors are shown disposed upstream and downstream of the DPF206, for example, the upstream pressure sensor232and the downstream pressure sensor234, one can appreciate that a single sensor may be used instead, for example, a differential pressure sensor disposed to measure a difference in pressure between upstream and downstream locations relative to the direction of flow of exhaust gas through the after-treatment device202.

In one embodiment, the DPF206includes a soot sensor238. The soot sensor238, if present, operates to provide a signal that is indicative of the amount of material that has accumulated in the DPF206. In one embodiment, the soot sensor238emits radio frequency signals that pass through a filter element of the DPF206before being reflected back to the soot sensor238where they are received. The soot sensor238can provide a signal that is indicative of changes in amplitude between radio signals sent to the DPF206and radio signals received back from the DPF206. In one embodiment, such changes in amplitude are correlated to an extent of soot loading of the DPF206, such that an estimation of the amount of material having collected within the DPF206can be determined by, for example, logic integrated in the soot sensor238or logic present within the controller222.

In the embodiment ofFIG. 2, the controller222is further connected to other machine systems240, which are represented collectively as a single block inFIG. 2. Communication of information and command signals between the controller222and the other machine systems can be accomplished by any appropriate method. In one embodiment, a multi-channel CAN link242provides appropriate channels of communication between the controller222and each of the other machine systems240. Such other machine systems can include any component or system of the machine that provides functional information during operation of the machine. Examples of such systems include a neutral switch, which provides information about a transmission or traction system of the machine, a parking brake switch, which provides information about the engagement state of a parking and/or emergency brake, a throttle setting switch, which provides information indicative of the extent of throttle engagement of the engine204, an implement lockout engagement switch, an operator presence switch, and others. One can appreciate that different systems, and thus different information about such systems, may be available depending on the type of machine or vehicle involved.

An operator interface244is communicatively connected to the controller222and arranged to provide visual and/or audio information signals to an operator of the machine. Of course, such interface is optional and may include one or more operator controls, such as a manual enable or disable switch. The operator interface244may include a display for displaying information relative to the operational status of the after-treatment system200. The operator interface244may be a standalone or dedicated interface for displaying information and receiving commands relative to the after-treatment system200alone, for example, when such system is retrofitted to an existing machine, or may be integrated with a multi-functional or multi-purpose display that is arranged to interface with other systems of the machine.

A block diagram of an after-treatment control300is shown inFIG. 3. The functions may be implemented partially or entirely within controller222. The after-treatment control300is arranged to, essentially, perform two functions; a first function is to determine the soot loading of a DPF, which is illustrated as a DPF soot loading determinator302, and the second is to determine a readiness state for performing a regeneration of the DPF, which is illustrated as a regeneration readiness determinator304. During operation, the soot load is considered when deciding whether a regeneration event should be initiated based on the determination of the regeneration readiness of the system. In one embodiment, the after-treatment control300is arranged to initiate regeneration more aggressively when the soot loading of the DPF is increased. The operation of one embodiment of the after-treatment control300will now be described in more detail.

In the embodiment illustrated inFIG. 3, the DPF soot loading determinator302operates to quantify, for example, as a percentage of full loading, the loading state of a DPF that is associated with an after-treatment system installed on a machine, such as the DPF206installed as part of the after-treatment system200of the machine100shown inFIG. 1andFIG. 2. The DPF soot loading determinator302makes such determination based on a soot signal306and a pressure signal308. The soot signal306may be provided by an appropriate sensor that is associated with the DPF, such as the soot sensor238(FIG. 2), and the pressure signal308may be provided from a pressure sensor measuring exhaust gas pressure either upstream, downstream, or a pressure difference across the DPF. In one embodiment, such pressure sensor may be the upstream pressure sensor232(FIG. 2). In an alternate embodiment, the pressure sensor may be the downstream pressure sensor234, a differential pressure sensor measuring a pressure difference across the DPF206(FIG. 2), or both the upstream and downstream pressure sensors232and234, in which case a signal processing device may calculate the difference in value between the two sensors to yield the pressure signal308.

The DPF soot loading determinator302provides a soot loading determination signal310as an output thereof. The soot loading determination signal310may be expressed in any suitable quantification parameter. In the illustrated embodiment, the soot loading determination signal310is expressed as a “Soot Level,” which is a positive value ranging from 0 to 5 and which depends on the percentage of soot loading having been determined for the DPF according to Table 1, shown below:

TABLE 1DPF Soot Loading (%)05080100110120140Soot Level01233.545
As can be appreciated, the extent of soot loading in the particulate filter can be expressed as a percentage of the total capacity of soot that can be filtered by a filter element of a given size, with percentage values that exceed 100% indicating that the filter has been overloaded.

One embodiment of the DPF soot loading determinator302is shown in the block diagram ofFIG. 4. In this embodiment, an implementation using multiple methods of determining the soot loading of the DPF are operated in concert, but one can appreciate that any one of these, or other, equivalent methods, may be used. In the illustrated embodiment, the DPF soot loading determinator302employs four different methods of estimating the soot loading of a DPF filter, which methods include an estimation based on the soot signal306, the pressure signal308, a timer402, and a soot accumulation model404.

Beginning with the determination based on the soot signal306, such signal is provided to a transfer function, which is illustrated as a soot sensor table406. Information about the soot loading state of the DPF is provided by the soot signal306in the form of, for example, a voltage, which is then correlated to value representing the actual soot loading of the filter. The values populating the table406may be predetermined as a result of a calibration of the sensor providing the soot signal306, and can be provided as a sensor-based soot signal408to a soot load selector410.

In a similar fashion, the pressure signal308can be provided to a pressure difference table412, which provides a pressure-based soot signal414to the soot load selector410. The pressure difference table412may be calibrated to correlate values of pressure difference across the DPF to estimations of the corresponding soot loading of the DPF. In the case where a pressure value is used instead of a pressure difference across the DPF, the pressure table412may be calibrated accordingly.

In a third method of calculating soot loading on a DPF, the soot signal306and/or the pressure signal308may be provided to the soot accumulation model or function404. In one embodiment, both the soot signal306and pressure signal308are provided to the soot accumulation model404, but in alternate embodiments that include model-based soot accumulation calculators fewer, different, or no such signals may be provided. In the illustrated embodiment, a time signal416generated by the timer402is also provided to the soot accumulation model404. The time signal416may simply be indicative of the operating time of the engine since a previous or last regeneration event, or may alternatively be indicative of another operating parameter of the engine since the last regeneration event. Such other operating parameters of the engine may include total hours of operation, total amount of fuel used, total amount of power generated, and others, all calculated since a last regeneration event of the engine. One can appreciate that any parameter of the operation of the engine that is correlated to the amount of carbon produced by the engine may be tracked and its effect on carbon deposition quantified during intervals between regeneration of the DPF.

The time signal416is also provided to a time function418in one embodiment. The time function418may be a control device that correlates an estimated time-based soot signal420with, in this case, the time signal416. As in the other modes, the time-based soot signal420is provided to the soot load selector410.

In the illustrated embodiment, the soot accumulation model404may be an analytical or empirical function or model that estimates the soot accumulation on a DPF based on operating parameters of an engine, in this case, a signal from a soot accumulation sensor, an indication of a pressure across the DPF, and a time since the last regeneration was performed. The output of the soot accumulation function404is a model-based soot signal422that is provided to the soot load selector410.

The soot load selector410provides an estimated soot loading424to a table426, such as Table 1. The estimated soot loading424may be determined based on one or more of the various signals provided to the soot load selector410. In one embodiment, the soot load selector410may simply select the highest estimated value of soot loading among the signals provided, namely, the sensor-based soot signal408, the model-based soot signal422, the time-based soot signal420, and the pressure-based soot signal414. In such embodiment, selection of the highest estimation for soot loading ensures that the estimation of the soot loading will be conservative.

In an alternate embodiment, the soot load selector410may determine the best estimation of soot loading based on the signals provided. More specifically, the soot load selector410may monitor the soot signals provided to ensure that any estimation is both accurate and consistent with the efficient operation of the engine. The soot load selector410further may consider the sensor-based soot signal408as the base for estimating the soot accumulation of the filter. The soot accumulation thus estimated may be compared with the model-based soot signal422to ensure that it is consistent or within an acceptable range, for example, a range of ±10%. This comparison may be performed as a check of the values provided by the sensor providing the soot signal.

An additional check of the sensor-based soot signal408may be made by comparing the time-based soot signal420and/or the pressure-based soot signal414with the sensor-based soot signal408. As before, such comparison may be used to discover potential issues with the accuracy of the soot signal306when the result of the comparison indicates a discrepancy between the compared values of more than a threshold value, for example, a discrepancy of about 10% or more.

The estimated soot loading424is provided to the table426, which yields the normalized soot level or soot loading determination signal310(FIG. 3). In one embodiment, the estimated soot loading424is expressed in terms of percentage of the soot loading capacity of the DPF. The soot loading determination signal,310is determined based on a lookup table, for example, Table 1 described above.

Returning now toFIG. 3, the after-treatment control300further includes the regeneration readiness determinator304, which provides a readiness level signal312based on one or more signals that are indicative of the state or work mode of the machine of vehicle. The regeneration readiness determinator304examines the functional state of various machine components or systems for indications of ongoing or imminent changes in operational status. The regeneration readiness determinator304provides an indication, in the form of the readiness level signal312, of the state of machine operation. Such readiness level signal312can provide multiple levels of the work status of the machine ranging from the machine being completely idle or not in a work mode to the machine being fully engaged at work. Such information may be used to determine when a regeneration event may be initiated.

As can be appreciated, a non-work mode of the machine is the desired time to initiate regeneration because a regeneration event may be intrusive to the machine's operation when the machine is in work mode. However, initiation of a regeneration may be conducted at other times should it become necessary due to high soot loading of the DPF. In other words, the importance of initiating a regeneration event may increase based on soot loading of the DPF and is balanced against the relative undesirability of initiating regeneration when the machine is working. In the embodiment presented, certain machine operating parameters are presented as inputs provided to the regeneration readiness determination, but one can appreciate that any other suitable parameters may be used. Further, different machines or vehicles may include components and systems onboard that are better suited to provide an indication of the work mode of the machine or vehicle, and in such instances, the regeneration readiness determination may be tailored to make use of such specialized parameters. The embodiment described below refers to parameters that may be available on a work machine and should not be construed as exclusive of other parameters that may be used in addition to or instead of the parameters presented.

The regeneration readiness determinator304in the embodiment illustrated is provided with a park brake signal314, a neutral transmission signal316, an implement status signal318, a throttle control signal320, a throttle signal322, a vehicle speed signal324, and potentially others, such as a signal indicating that an operator is present. Such signals are processed within the regeneration readiness determinator304to provide the readiness level signal312. In one embodiment, the readiness level312is an integer value between 0 and 8, with 0 indicating that the machine is in full work mode and 8 indicating that the machine is not in work mode. Readiness levels between 1 and 7 indicate various intermediate states of work mode.

A block diagram of one embodiment for the regeneration readiness determinator304is shown inFIG. 5. In this embodiment, the various machine operating parameters are provided to a table function502and used to determine the operating state of the machine. For example, the park brake signal314may be a simple ON/OFF indication of whether the parking or emergency brake of the machine has been set by the operator. Setting of the parking brake can be an indication of whether the machine is in work mode or not. The neutral transmission signal316is indicative of the gear selection in a transmission of a machine. The neutral transmission signal316may be a simple ON/OFF signal indicative of whether the transmission of a machine is in gear, which is an indication that the machine may be moving or preparing to move, or whether the transmission is in neutral. The implement status signal318may be a signal indicative of an activated implement status, or alternatively an interlock status of an implement control. The throttle control signal320may be an indication of whether a preset speed has been selected for the machine. The throttle signal322may be indicative of the extent of throttle activation of the machine, and the vehicle speed signal324may be indicative of the ground speed of the machine. One can appreciate that such signals may provide information as to the operating mode of the machine, but other parameters may be used, such as signals from an operator presence switch or sensor, a steering sensor, and so forth.

Such and other signals may be provided to a table, for example, Table 2 presented below, for categorization of the relative readiness level of the machine for regeneration of a machine based on the estimated work mode of the machine:

TABLE 2ReadinessLevelCriteria—No Regeneration Required8Not in Work Mode7(Park ON) and (Neutral) and (Implement Status OFF)and (Traction Sys. Control OFF)6(Park Brake ON) and (Neutral) and (Implement Status OFF)5(Park Brake OFF) and (Neutral), all other systems OFF4(Neutral) and (Implement Status OFF)3(Neutral) and (Traction Sys. Control OFF or SLOW)2(Implement Status OFF) and (Vehicle Speed = 0)1(No Throttle Command) and (Vehicle Speed = 0)0Regeneration disabled, Replace DPF
As can be seen from Table 2, the various parameters provided to the regeneration readiness determinator304are evaluated and such information is categorized to determine the relative state of work mode. Such categorization is tabulated against a range of readiness levels, which represent the relative level of work the machine is in at any time.

Returning toFIG. 3, the soot level310and the readiness level312are provided to a regeneration control326. The regeneration control326is arranged to schedule the initiation of a regeneration event based on the soot level310and the readiness level312. Moreover, the regeneration control326may, at times, command a controller in the machine to reduce the power output of the engine, especially when the DPF has become overloaded. The regeneration control326operates, for example, to initiate a regeneration event whenever the machine is not in a work mode and the soot loading of the DPF is at least 50%. Such initiation of regeneration is performed on a regular basis to maintain a relatively low soot accumulation in the DPF. In certain machine applications, however, favorable non-working conditions of the machine may not occur often. In such situations, a regeneration event may be delayed and may be performed under less than favorable conditions or at conditions beneath a threshold readiness level. Under some circumstances, operation of the engine may be adjusted, for example, to increase the flow of exhaust gas through the DPF during regeneration, or to reduce the power rating of the engine when the extent of soot loading of the DPF exceeds 100%.

In one embodiment, the regeneration control326operates to schedule the initiation of a regeneration event when a predetermined soot level310coincides with a predetermined readiness level312that has been selected as suitable for regeneration. Such relationship between the soot level310, the readiness level312, and an indication of whether engine control or engine power reduction is required is presented in Table 3 below:

TABLE 3Soot Level (%)3.5 (110%)5to 4321(140%)(120%)(100%)(80%)(50%)Readiness Level012345678EngineNONONOYESYESYESYESYESYESControlAllowedEngine—20% to20%NONONONONODe-rate100%
As can be seen from this exemplary table, no engine control is allowed when the soot accumulation in the DPF exceeds the capacity of the filter. Moreover, regeneration initiation is enabled for soot accumulations exceeding 50% of the capacity of the DPF, and is disabled when the soot level exceeds a threshold, e.g., soot Level 4. At other times during operation, the regeneration control326may first determine the readiness level of the machine, and based on the readiness level, determine a suitable time to initiate a regeneration event based on the soot level in accordance with the schedule presented in Table 3. When the regeneration control determines that a regeneration event should be initiated, an appropriate regeneration command328is provided at the output of the after-treatment control300.

INDUSTRIAL APPLICABILITY

An exemplary control strategy is illustrated in the flowchart ofFIG. 6. The flowchart illustrates one embodiment of a control strategy for initiating a regeneration event for a DPF in accordance with the disclosure. Such control strategy may be implemented in the form of computer executable instructions that reside in a computer readable or accessible medium that is integrated with a logic device in a machine, such as an electronic controller. In the exemplary embodiment, the control strategy includes a determination of the soot loading of the DPF at602. Such determination may include receipt of sensor signals that are indicative of the soot loading on the DPF and/or an estimation of such loading based on various operating parameters of an engine.

The control strategy further includes a determination of the application readiness level for initiation of regeneration at604. As described above, the application readiness level is, in one embodiment, a determination or estimation of the degree to which the machine or vehicle is determined as being in a work mode or in a non-working mode. Initiation of a regeneration event is favored under conditions when it has been determined that machine or vehicle is not working, but a regeneration may be initiated at other times depending on the extent of soot accumulation in the DPF even though such action may adversely affect the performance of the operation of the machine. The determination of the work mode of the machine may be based on monitoring any appropriate operating parameter of the machine or vehicle for indications of use. For example, such operating parameters may involve operator switches, idle timers, emergency or park brake sensors, occupant switches, implement status, vehicle speed, engine speed, and/or other parameters.

In certain applications, especially those involving regular machine work schedules, the control strategy may be arranged to include a programmable regeneration initiation feature. Such feature may, for example, include a schedule for initiating regeneration at times selected by the user, which would be especially useful for machine applications that involve a substantially constant mode of the machine that otherwise may not have provided an appropriate time to regenerate. In an alternate embodiment, such feature may further include functionality that can discern a regular jobsite schedule and adaptively determine when machine downtime is forthcoming. Such information may be used to defer or schedule regeneration during jobsite downtime periods such that intrusion on the normal operation of the machine may be minimized. In certain applications including fleets of machines operating collectively in a single site and according to similar schedules, information indicative of the soot accumulation of each machine may be transmitted to a central information processing station. Such central station may be located at the jobsite, or may alternatively be part of a larger network of stations that are monitored by a local equipment servicing entity or an equipment manufacturer. Such collecting monitoring of fleet operations can enable a scheduling or staggering of regeneration of machines belonging to a work group such that overlapping downtimes of the machines can be minimized or avoided. Hence, the central information processing station may be capable of sending regeneration commands to each of the machines it monitors.

Having determined or estimated the soot accumulation in the DPF at602, the control strategy may monitor the application readiness level for an opportune time to initiate regeneration at606. Such initiation may occur based on a predetermined function or schedule that becomes more aggressive in initiating regeneration as the soot accumulation increases. During initiation, the control strategy may monitor the regeneration readiness level of the machine while the regeneration is underway at608. In the event that an operator command or a change in a machine operating parameter alters the previously determined readiness level during regeneration, a decision may be made at610to interrupt the regeneration at612. In other instances, the regeneration may be completed at614and the process repeated.

In one general aspect, the regeneration control described herein may include additional functionality for use during regeneration of the DPF. As described in the '822 patent, the contents of which are incorporated herein by reference, a regeneration device may operate to create a flame that initiates and/or maintains the combustion of soot accumulated on the DPF during regeneration. In one embodiment of the present disclosure, as shown inFIG. 2, a valve246may be disposed to modulate the flow of fresh air supplied to the regeneration device210via the conduit214. The valve246may be a proportional air control valve that is responsive to air flow commands from the controller222or another controller (not shown) operating to modulate the flow of air provided to the regeneration device210during a regeneration event. Such event that may be initiated under engine operating conditions that may not provide an optimal airflow required by the regeneration device210for proper operation. One may appreciate that, in accordance with the foregoing discussion, less than optimal circumstances may occur when the soot level of the DPF is relatively high and regeneration is initiated under machine or engine work conditions that are less desirable.

Even though the valve246may be useful in certain applications, its use is optional and may further increase the cost and complexity of a machine or vehicle system. For this reason, the function of controlling the flow of air provided to the regeneration device210may be substituted, when the valve246is not present, or is present but not used, by appropriately controlling the operation of the engine204. More specifically, the controller222or another controller (not shown) may receive information indicative of pressure in the intake manifold218of the engine204via a boost sensor248, information about the pressure in the exhaust manifold216via a backpressure sensor250, information about the airflow into the engine204via a mass airflow (MAF) sensor252, and/or information about the ambient pressure in the operating environment of the machine as an indication of operating altitude via a barometric pressure (BP) sensor254.

The controller222may use such information to adjust the speed of the engine204and the intake manifold or boost pressure to achieve a desired flow of air through the conduit214. Such desired flow of air through the conduit214may be arranged to suffice for operation of the regeneration device210without additional control, i.e., without control by the valve246. Such airflow through the conduit214may be especially relevant when the regeneration device210is attempting to initiate a regeneration event. Engine control under such conditions may include an adjustment of engine speed and/or engine torque output performed in a known fashion to achieve a desired airflow through the conduit214. One can appreciate that a desired airflow through the conduit214may be a function of more than one parameter, which can include boost pressure, backpressure, engine speed, engine load, and others.

In one embodiment, an estimation of the airflow through the conduit214, especially in the absence of any effects from the valve246, and through the engine204in general, may be refined by limiting the operating window of the engine during regeneration. As is known, one method of initiating and/or controlling a regeneration event is to transition between lean and rich engine combustion. Such transitions may adjust the content of combustible compounds in the exhaust gas of the engine, which can affect the rate of regeneration. In the past, engines were operated using a rich combustion mixture during most of the regeneration event. Use of the regeneration device, however, permits operation of the engine with a lean combustion mixture because the regeneration event may be controlled by use of the regeneration device.

One parameter requiring adjustment during operation of the regeneration device210is the flow of air through the conduit214, which may depend on, or may be calculated based on, the intake airflow of the engine as measured by the MAF sensor252. As such, the accuracy of the MAF sensor252may be relevant to the operation of the regeneration device210. In one embodiment, the MAF sensor252may be selected to provide improved accuracy over a relatively narrow portion of its operating range. The controller222may provide a narrow range of operation of the engine having an engine intake air flow that falls within the narrow portion of the operating range of the MAF sensor252such that improved accuracy in the air flow measurement of the MAF sensor252may be achieved when the regeneration device210is active.

In general, the soot loading estimation can be adjusted to avoid prolonged regeneration events and increased thermal stresses in the DPF. One exemplary collection of data relevant to regeneration frequency is shown in the graph ofFIG. 7. The graph illustrates one correlation between regeneration frequency, soot loading of the DPF, and operating conditions of the engine. Specifically, the graph has regeneration frequency in hours plotted against the horizontal axis702. A smoke number, such as those acquired by testing equipment manufactured by AVL Emission Test Systems, of Germany, that is indicative of particulate concentration in the exhaust gas of the engine is plotted against the vertical axis704such that the smoke number increases as the density of particulates in the exhaust gas increases.

The graph shown inFIG. 7includes a first curve706and a second curve708. The first and second curves706and708represent two concentrations of soot loading on a DPF and the relationship between time intervals for regeneration and smoke density yielding such regeneration. In the graph shown, the first curve706represents a soot concentration of about 3.5 grams of soot per liter of filter material (g/L), and the second curve708represents a soot concentration of about 7 g/L. An operating point710of the engine is plotted for illustration.

As can be seen from the graph, an after-treatment control arranged to initiate regeneration at a soot level of about 3.5 g/L, with the engine operating at a smoke level of about 1, may do so at an intervals of about 5 hours. The same after-treatment control arranged to initiate regeneration at a soot level of 7 g/L at the same engine smoke level may cause regeneration to occur at intervals of about 10 hours. One can appreciate that as the interval between regenerations increase, the total amount of soot accumulated on the filter also increases, which in turn increases the time required for completion of regeneration and also increases the temperature of the DPF during regeneration as the increased combustible soot material prolongs the duration and intensity of soot combustion. Such factors may influence the level of thermal stress within the DPF as the altitude of operation of the machine changes.

A graph illustrating the effects of soot accumulation and altitude on thermal stresses within the DPF during regeneration, for a particular DPF arrangement operating under the same set of engine operating conditions, is shown in the graph ofFIG. 8for illustration of the principle of operation of the altitude compensation in the after-treatment control300(FIG. 3). The graph shown inFIG. 8is a time trace of estimated or measured stress in the DPF during a regeneration event. The graph plots time, expressed in seconds (sec.), along the horizontal axis802and corresponding stress in the DPF, expressed in Mega Pascal (MPa), along the vertical axis804. Such graph may be created by the real-time measurement of stress within the DPF or, alternatively, by real-time measurement of DPF temperature and subsequent correlation of temperature to thermal stress in the DPF.

The graph includes three stress trace curves representing the stress within the DPF under different soot concentration and altitude conditions of operation, which have been time-aligned to better illustrate the differences observed between the three individual tests conducted. In each test, the regeneration was initiated with the engine running at a specific engine speed, which engine speed was reduced to an idle speed 500 sec. after the regeneration had begun. The 500 sec. time point at which the engine speed was reduced is indicated by the vertical line806in the graph. Such reduction in engine speed was performed to illustrate the effects of reduced engine exhaust flow at idle on the thermal stress of the DPF during regeneration. As can be seen from the graph, the thermal stresses in all three stress curves increase following the reduction of engine speed.

More particularly, a first stress trace curve808represents the time evolution of stresses within the DPF during regeneration initiated with the machine operating at sea level and with the DPF including a soot load concentration of about 7.5 g/L. As can be seen from the graph, the regeneration represented by the first stress trace curve808increases the stress in the DPF shortly after combustion of soot begins, and remains relatively steady thereafter while the engine operates at an elevated speed during the first 500 seconds. The reduction in engine speed at 500 seconds causes the stress to increase by about 35% while remaining well below a stress limit of about 1.48 MPa, which is represented by the horizontal line810on the graph.

A second stress trace curve812represents the same operating condition of the machine as the first stress trace curve812with the exception that the machine is operating at an altitude of about 10,000 feet (3.05 km). As can be seen from the graph, operation at this altitude yields an increase of stress in the DPF by a factor of about 1.8 while the engine is operating at the higher engine speed within the first 500 seconds of the test. Such increase may be due to the elevated temperature of exhaust gas provided by the engine at the high altitude. As can also be seen from the graph, the stress in the DPF dramatically increases by over 220% compared to the stress before the engine speed was reduced following the reduction in engine speed. The peak stress in the second stress trace curve812is still below but approaches the stress limit810. The degree of increase in stress both before and after a change in engine speed between the first and second stress trace curves808and812illustrates the effect of altitude.

A third stress trace curve814illustrates the effect of soot accumulation on stress in the DPF during regeneration. More specifically, the third stress trace curve814represents an operating condition that is the same as the operating condition used for generating the second stress trace curve812, i.e. operation at high altitude, but the soot accumulation at the initiation of regeneration was about 6 g/L. As can be seen from the graph, the stresses in the DPF begin rising later than in the other two illustrated conditions, are about 10% lower than the stresses represented by the second stress trace curve812during the initial 500 seconds before the reduction in engine speed, and the stress spike following the reduction in engine speed is about 25% lower than the spike illustrated by the second stress trace curve812. The degree of decrease in the stresses between the second and third stress trace curves812and814illustrates the effect of soot accumulation.

As can be understood, the exemplary conditions presented illustrate that stress due to thermal effects in the DPF during regeneration may dramatically increase when the altitude of operation of the engine increases, but it can also decrease for regeneration conducted at a lower total soot accumulation in the DPF. Returning now toFIG. 3, an estimation of the altitude of operation of the machine may be used to adjust the estimation of soot accumulation in the DPF, and particularly, to set a soot accumulation limit for the DPF. Such limit may simply be used to initiate regeneration or may alternatively be used as the soot accumulation capacity of the DPF for calculating the soot level as discussed above and as shown in Table 1. Operation of internal combustion engines at altitudes above seal level may tend to increase exhaust temperatures due to the lower density of air at the high altitude and the lower concentration of oxygen available for combustion. Such increase in exhaust temperature may alter the rate of cooling of the DPF during regeneration due to the flow of exhaust gas passing therethrough, and may increase the core temperature of the DPF. One can appreciate that thermal stresses in the DPF should be considered when selecting a particular size and configuration of the DPF for a specific application.

To address such and other issues, one embodiment of the after-treatment control300shown inFIG. 3includes an optional, additional input330that is indicative of the barometric pressure of operation of the machine, such as a signal from the BP sensor254shown inFIG. 2. The barometric pressure330is shown in dotted line to indicate that such input is optional for the illustrated embodiment of the after-treatment control300shown inFIG. 3. In accordance with this alternate embodiment, the barometric pressure330is input to a barometric pressure compensation table426. In one embodiment, the barometric compensation table426may include tabulated values correlating barometric pressure values, which are indicative of operating altitude, with desired or appropriate compensation values for the soot limit or soot capacity permitted for the DPF. An output of the barometric pressure table426may be provided in the form of an altitude-based soot compensation428that is provided to the soot load selector410. As an additional functionality of the soot load selector410, the soot load selector410may adjust or compensate the estimated soot loading424by the altitude-based soot compensation428. In one embodiment, such adjustment can decrease the soot limit by an amount that will increase the estimated soot loading percentage or soot level of the DPF, such that a regeneration is initiated at an earlier time when the machine is operating at a high altitude. Even though one embodiment is presented for adjusting the estimated soot loading herein, other methods may be used.