Method for controlling the operation of an exhaust gas treatment device

Abstract

A method for controlling an engine assembly including an internal combustion engine and an exhaust gas treatment device is disclosed. The aftertreatment assembly may require cleaning from time to time, and if this involves active thermal management of the aftertreatment assembly, the method involves performing the steps of: (a) imposing a first limit on engine speed; (b) waiting for a safe condition of the engine; and (c) performing a cleaning process, the step including: (i) injecting fuel into the engine such that the fuel passes through the engine without burning in the diesel oxidation catalyst to target an increase in exhaust gas temperature in the diesel oxidation catalyst; and (ii) removing the first limit on engine speed and targeting an engine speed setpoint, the engine speed setpoint being faster than the first limit on engine speed.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to the field of exhaust gas treatment, and in particular to controlling the operation of exhaust gas treatment devices. [Background technology]

[0002] The exhaust gas treatment device may comprise a plurality of modules, each intended to treat one or more components of the exhaust gas. The modules may be arranged in series such that the exhaust gas passes through each module in turn. The exhaust gas treatment device may comprise a first aftertreatment module comprising a diesel oxidation catalyst (DOC) module and a second aftertreatment module downstream of the first aftertreatment module. The second aftertreatment module may comprise a diesel particulate filter (DPF) module and / or a selective catalytic reduction (SCR) module. If the second aftertreatment module comprises both a DPF module and an SCR module, the SCR module may be downstream of the DPF module.

[0003] A diesel oxidation catalyst module may oxidize components of the exhaust gas. A diesel particulate filter module, if present, may filter soot from the exhaust gas and prevent the soot from being emitted into the atmosphere. If an SCR module is present, it may filter NO 2 present in the exhaust gas. x may be caused to chemically react with ammonia to produce nitrogen and water.

[0004] Achieving and maintaining the proper temperature in each module can be important to achieving the desired results.

[0005] It is known to use a diesel oxidation catalyst module to increase the temperature of the exhaust gases before they reach the second aftertreatment module, to increase the temperature of the exhaust gases arriving downstream of the diesel oxidation catalyst, to increase the temperature of the exhaust gases passing through, which can be achieved by introducing unburned fuel upstream of the diesel oxidation catalyst module for oxidation in the diesel oxidation catalyst, thereby increasing the temperature of the exhaust gases leaving the diesel oxidation catalyst module.

[0006] Thus, in addition to injecting fuel for combustion, fuel may be injected into one or more of the cylinders of the engine as a post-combustion event with the intention that the fuel will exit the cylinder or cylinders without oxidation. This fuel may oxidize in the diesel oxidation catalyst module, thereby increasing the temperature of the exhaust gases therein. Injection of fuel in this manner may be referred to as HC dosing.

[0007] The performance of a diesel particulate filter module may be affected by the amount of soot trapped within the diesel particulate filter module, if any. Strategies known as regeneration or cleaning strategies may be used to seek to reduce the amount of soot trapped within the diesel particulate filter module. Such strategies may include techniques to ensure combustion of the soot within the diesel particulate filter module, as needed. For example, combustion may be promoted by an increase in temperature within the diesel particulate filter module.

[0008] The amount of soot trapped in the diesel particulate filter module may affect the performance of the exhaust gas treatment device, and therefore the engine performance. For example, if a large amount of soot is trapped in the diesel particulate filter module, the back pressure caused by the trapped soot may affect the engine performance.

[0009] The performance of an SCR module may also be affected by the buildup of deposits, if present, within the SCR module, which can be reduced or managed by proper thermal management of the exhaust gases passing through the SCR module.

[0010] Having an appropriate hierarchy of regeneration / cleaning strategies can improve exhaust gas treatment device performance, potentially reducing machine downtime, and even extending service intervals.

[0011] Cleaning strategies may be divided into two types of cleaning strategies. A first type of strategy may involve taking measures that affect the performance of the engine below a threshold that is likely to have a significant impact on the user of the engine. A second type of strategy may be more substantial that may not be implemented while allowing the user to continue to use the engine for useful work. For the purpose of distinguishing between the first type of cleaning strategies and the second type of cleaning strategies, for the sake of simplicity, the first type of strategies will be referred to herein as minor cleaning strategies and the second type of strategies as major cleaning strategies. The terms minor and major in this context are merely labeling terms and should not be understood as implying absolute requirements on the magnitude of cleaning achieved. Summary of the Invention

[0012] Against this background, a method for controlling an engine assembly including an internal combustion engine and an exhaust gas treatment device is provided, The exhaust gas treatment device includes a first aftertreatment module including a diesel oxidation catalyst and a second aftertreatment module downstream of the first aftertreatment module; the engine assembly is configured to provide a numerical indication of an efficiency of the second aftertreatment module; The method is comparing the efficiency indication to a first threshold value; and if the efficiency indication is such that the efficiency is below the first threshold value; (a) enforcing a first limit on engine speed; (b) waiting for an engine safe condition; (c) performing a primary cleaning process of the second post-treatment module, the primary cleaning process comprising: (i) injecting fuel into the engine after an engine combustion event such that the fuel passes through the engine without being combusted to combust in the diesel oxidation catalyst to target a first increase ΔT1 in exhaust gas temperature in the diesel oxidation catalyst; (ii) performing a primary cleaning process including removing a first limit on engine speed and targeting an engine speed set point, the engine speed set point being faster than the first engine speed limit, sequentially or simultaneously removing the first limit on engine speed and targeting the engine speed set point.

[0013] Thus, advantageously, the temperature of the exhaust gas is increased due to both (a) increased combustion within the engine because the second engine speed limit is higher than the first, and (b) combustion after fuel injection in the DOC module.

[0014] In certain arrangements, the method further includes an escalation architecture in which increasing limitations on the useful work output of the internal combustion engine are imposed as the efficiency numerical indication decreases.

[0015] Thus, advantageously, the method of the present disclosure provides an escalating aftertreatment cleaning strategy that presents the user with increasing limitations on the useful work achievable with the engine until aftertreatment efficiency is restored by implementation of an appropriate aftertreatment cleaning process within the strategy. [Brief description of the drawings]

[0016] Embodiments of the present disclosure will now be described with reference to the accompanying drawings.

[0017] [Figure 1] FIG. 1 shows a highly schematic representation of an engine assembly to which the methods of the present disclosure may be applied. [Diagram 2] FIG. 2 shows a flow chart of a first embodiment of a method for controlling an engine assembly according to the present disclosure. [Diagram 3] FIG. 3 shows a flow chart of a second embodiment of a method for controlling an engine assembly according to the present disclosure. [Figure 4] FIG. 4 shows a flow chart of a third embodiment of a method for controlling an engine assembly according to the present disclosure. [Diagram 5] FIG. 5 illustrates a representation of a first embodiment of an escalation strategy for a post-treatment system cleaning process according to the present disclosure. [Figure 6] FIG. 6 illustrates a representation of a second embodiment of an escalation strategy for a post-treatment system cleaning process in accordance with the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] To understand the context of the disclosed method, a description of a possible exhaust gas treatment device 550 of an engine assembly 500 that may be controlled by the disclosed method is provided below. As one of ordinary skill in the art will readily appreciate, the disclosed method is applicable to a wide variety of exhaust gas treatment devices and is not limited to the specific examples described below, which are provided merely to assist the reader in understanding the context of the disclosed method.

[0019] The exhaust gas treatment device 550 of FIG. 1 includes fluid flow paths 515, 520, 525, 530, 535, through which fluid may flow sequentially through various modules 520, 530 for treatment of the exhaust gases prior to release into the atmosphere.

[0020] The fluid flow path downstream of the engine 510 may include, in series, a first conduit 515 connecting an inlet of a first aftertreatment module 520 comprising a DOC module to an outlet of the engine 510, a second conduit 525 connecting an inlet of a second aftertreatment module 530 to an outlet of the first aftertreatment module 520, and a third conduit 535 providing an outlet from the second aftertreatment module 530 to the atmosphere. The second aftertreatment module may include a DPF module and / or an SCR module. If the second aftertreatment module includes both a DPF module and an SCR module, the SCR module may be downstream of the DPF module. Additional modules (not shown) may be present downstream or upstream of the other modules. If such additional modules are present, they may include a separate DPF module or a separate SCR module.

[0021] The engine 510 may include a combustion unit (not shown) having an exhaust conduit 515 and one or more combustion cylinders (not shown). Each of the one or more cylinders may include a piston, a fuel injector, an intake valve, and an exhaust valve that leads to the exhaust conduit. Fuel may be injected into the (or each) combustion cylinder via the fuel injector. The fuel injector may be configured to inject fuel according to a controlled timing pattern.

[0022] It is known to combust fuel in the DOC module 520 to increase the temperature of the exhaust gas in the exhaust gas treatment device, for example as part of an aftertreatment cleaning process. While it is possible to inject fuel directly into the DOC module 520 for this purpose, it is also possible to avoid the need for a separate injector by using the fuel injectors already present in the combustion cylinders of the engine 510. This may involve injection of fuel for combustion in the DOC module 510 by injecting fuel into the combustion cylinders of the engine at a time in the combustion cycle (e.g., during the exhaust stroke of the cylinder) when conditions are such that the fuel passes directly through the cylinder without combustion and is therefore available for combustion in the DOC module 510. Such injection may be referred to as auxiliary injection or post-combustion injection, as distinguished from the primary injection that is timed to combust in the cylinder and drive the piston in the conventional manner.

[0023] Processes intended to result in improved efficiency of exhaust gas treatment devices (eg, by removal of soot deposits from a DPF module) may be described as aftertreatment system cleaning processes or regeneration processes.

[0024] The extent to which post-treatment cleaning is required may depend on the extent to which the post-treatment efficiency has decreased.

[0025] In the case of a DPF module, the extent to which DPF cleaning is required may depend on the amount of soot sensed or estimated to be present in the DPF. The amount of soot sensed or estimated may be described as soot loading. A moderate soot loading may prompt a different cleaning strategy than that required if the soot loading is more severe. It is known to provide different DPF cleaning processes in response to soot loading. Additionally, it is known to escalate a series of increasingly effective DPF cleaning processes in response to increasing soot loading.

[0026] In the case of an SCR module, the extent to which SCR cleaning is required may depend on the extent to which deposits have built up within the SCR module. Rather than sensing deposits, it may simply be assumed that deposits have likely built up after a predetermined period of time since a previous cleaning event, and therefore the timing of SCR cleaning may simply be based on a predetermined time interval since the previous cleaning event.

[0027] An embodiment of a method 100 for controlling an engine assembly according to the present disclosure is shown in Figure 2. The method involves invoking a primary cleaning strategy, which effectively prevents the operator from using the engine to perform useful work.

[0028] The method involves receiving aftertreatment efficiency data (which may be sensed or estimated) at step 110, and determining at step 120 whether a decrease in aftertreatment efficiency (e.g., caused by the accumulation of soot deposits) is such that the aftertreatment efficiency falls below a threshold. The threshold may represent an absolute efficiency level or a percentage efficiency, or some other variable that is a function of efficiency. In other words, it is determined whether the efficiency deficit is large enough to cause the efficiency to fall below a threshold level. Efficiency, whether measured or estimated, may be expressed numerically.

[0029] If the efficiency numerical indication is determined to be below the first threshold, the method involves implementing a first engine speed limit at step 130 .

[0030] The first engine speed limit may be intended to limit the amount of useful work that the engine 110 can perform. This may provide a very noticeable signal to the operator of the engine assembly 100 that an aftertreatment cleaning process is required that is incompatible with normal engine operation, without forcing the operator to immediately cease all useful work.

[0031] As a result of the introduction of this first speed limit, the driver may be intended to reach a suitable opportunity to stop all useful work and park the machine (without shutting down the engine).

[0032] A condition for proceeding with the method may involve determining whether a "safe state" condition has been reached. A safe state condition may include determining that useful work has ceased (e.g., the engine is idling) without shutting down the machine.

[0033] The method may further include determining if a safe state condition has been reached, at step 140. If the safe state condition has been reached, the method may involve invoking a dedicated DPF cleaning process, at step 150.

[0034] A dedicated aftertreatment cleaning process may be referred to as dedicated because it may occur during a dedicated cleaning phase, rather than in parallel with the engine performing other useful work, during which the engine control strategy may be primarily or exclusively targeted at cleaning the aftertreatment.

[0035] A dedicated post-treatment cleaning process may include two or more elements.

[0036] One element may involve targeting an engine speed set point 152 that may be higher than a first engine speed limit (so that more combustion may occur in the engine 510 when operating at the engine speed set point than when operating under the first engine speed limit) to increase cylinder combustion and raise the temperature of the exhaust gases exiting the engine 510 and reaching the aftertreatment device 550.

[0037] Another element may be to inject fuel with supplemental injections 151 such that the fuel does not burn in the cylinders of the engine 510, but instead arrives at the DOC module 520 where it is burned, thereby further increasing the temperature of the exhaust gases in the DOC module 520. These supplemental injections may be configured to target a temperature increase of ΔT1.

[0038] In summary, an increase in engine speed may result in an increase in the temperature of the exhaust gases exiting the engine and entering the aftertreatment device, while the supplemental injection may combust within the DOC module 520, thereby resulting in an increase in the temperature of the exhaust gases within the DOC module 520 upstream of the second aftertreatment module.

[0039] The step of injecting fuel with supplemental injection 151 may begin before, after, or simultaneously with the step of targeting the engine speed setpoint 152 .

[0040] The nature of the post-combustion fuel injection (eg, timing and volume) may be such that it results in dedicated aftertreatment cleaning processes that are incompatible with normal engine operation.

[0041] The combination of the increase in exhaust temperature entering the aftertreatment device along with the combustion in the DOC module of the fuel injected into the engine in the post-combustion event results in a significant increase in temperature in the second aftertreatment module. This temperature increase may result in the combustion of accumulated soot in the DPF, if present, which means that the soot loading is reduced and / or may result in the combustion of ammonia deposits in the SCR, if present.

[0042] An alternative embodiment of the method is shown in Figure 3. This embodiment is similar to that shown in Figure 2 and provides additional functionality, including interrupting the aftertreatment cleaning process if the safe state condition ceases, step 260. The safe state condition may cease, for example, if a user attempts to take control of the machine, such as to perform useful work. Furthermore, the interruption of the aftertreatment cleaning process may be followed, step 130, by the return of the first engine speed limit and a repeat of the process of the first embodiment, such that the aftertreatment cleaning process can be resumed only when the safe state condition is returned.

[0043] A further alternative embodiment of the method is shown in Figure 4. This embodiment is similar to that shown in Figure 3, but provides further functionality.

[0044] This embodiment recognizes that there may be situations where the driver deems it imperative to perform useful work. For example, it may be deemed imperative to move a machine with an engine out of a dangerous situation (e.g., away from other machines). The embodiment of FIG. 4 shows how such an opportunity may be made available to the driver.

[0045] In the embodiment of Figure 4, the method initiates, in step 370, the termination of the aftertreatment cleaning process and allows the possibility of returning to normal engine operation by restarting the engine. This results in at least a partial interruption of the method and initiates a limited time delay before initiating the method again. Once the delay has ended, the method may be resumed at an appropriate point in the method loop, such as at receiving aftertreatment efficiency data (step 110) as shown in Figure 4, or alternatively (not shown in Figure 4), at implementing a first engine speed limit in step 130.

[0046] The engine restart condition may be limited to a quick restart, which may be one in which the engine is shut off and restarted within a limited time period, for example, 5 or 10 seconds. In this manner, the possibility of initiating a termination of the aftertreatment cleaning process is not merely available by leaving the machine unused for a longer period and then restarting it.

[0047] 4 embodiment (not shown), initiating an exit from the aftertreatment cleaning process and returning to normal engine operation by restarting the engine may be available as an option only a limited number of times, such as one, two, three, or more than three times. In this manner, the driver has a limited number of opportunities to regain normal driver control before the driver is effectively unable to avoid the aftertreatment cleaning process.

[0048] The embodiments described above, as well as those illustrated in Figures 2, 3 and 4, may be part of an escalation strategy to increase the likelihood that the aftertreatment cleaning process will occur while decreasing the opportunities for the driver to control the engine in order to perform normal engine operation at each stage.

[0049] The embodiments of Figures 2, 3 and 4 may all result in a primary after-treatment cleaning strategy that effectively prevents the use of the engine to perform useful work. The embodiments of Figures 2, 3 and 4 may form part of a broader set of strategies that include minor cleaning processes that occur before the primary cleaning process is carried out, where user control of the engine is not interrupted.

[0050] According to one particular embodiment, a first level strategy may be to provide modest intervention for thermal management that is not apparent to the user, involving merely minor thermal management and occasional post-combustion fuel injection, such post-combustion fuel injection may be configured to target a temperature rise of T2.

[0051] In the second level strategy, large amounts of post-combustion injection may occur which results in a slightly more subtle effect that may be slightly apparent to the user, without preventing the user from using the engine to perform useful work.

[0052] In a third level strategy, the driver may be provided with a visible warning that a dedicated aftertreatment cleaning process is required, intended to alert (but not force) the user to find an opportunity to stop normal operations to allow the primary aftertreatment cleaning process to take place, perhaps by manually initiating a aftertreatment cleaning sequence.

[0053] The fourth level strategy may be identical to the third level strategy, except that the visual alert of the third level strategy may be substituted for the audible alert of the fourth level strategy.

[0054] A fifth level strategy may then be to initiate the method of the embodiment of FIG.

[0055] FIG. 6 illustrates an embodiment of an escalation strategy that has even more escalation levels than the embodiment of FIG.

[0056] A comprehensive strategy might be to try to actively manage aftertreatment efficiency through engine use, and encourage the driver not to attempt to perform useful work when the degradation of aftertreatment efficiency reaches a threshold sufficient to warrant more significant aftertreatment cleaning, but instead to allow a dedicated aftertreatment cleaning process to take place. A comprehensive strategy might then introduce increasingly stringent steps to convince the user to allow the primary aftertreatment cleaning process to take place if the user does not allow the primary aftertreatment cleaning process to begin. By stringent steps, we mean steps that are likely to convince the user to take action, such as by providing visible and audible warnings that subsequently limit the user's ability to control the engine in a way that will perform useful work. [Industrial Applicability]

[0057] The strategies described in this disclosure may be particularly suitable for engines that do not have backpressure valves. When present, backpressure valves are often used in aftertreatment thermal management to control pressure for temperature rise purposes. For engines that do not have backpressure valves and the technology involving such valves is not available, the technology set forth herein is particularly applicable.

[0058] In engines that do not have a backpressure valve, the intake throttle valve may be controlled as part of the process described herein to appropriately limit engine speed.

[0059] However, the strategies described herein may be applied to any internal combustion engine having an aftertreatment device where efficiency can be improved through proper thermal management.

Claims

1. 1. A method of controlling an engine assembly including an engine and an exhaust gas treatment device, comprising: the exhaust gas treatment device comprising a first aftertreatment module including a diesel oxidation catalyst; a second post-treatment module downstream of the first post-treatment module, the engine assembly is configured to provide aftertreatment efficiency data of the second aftertreatment module; The method further comprising: comparing the post-processing efficiency data to a first threshold; and if the post-processing efficiency data is such that the efficiency is below the first threshold, (a) enforcing a first limit on engine speed; (b) waiting for an engine safe state; (c) performing a primary cleaning process of the second post-treatment module, the primary cleaning process comprising: (i) the fuel is cooled to a temperature within the diesel oxidation catalyst such that a first increase in exhaust gas temperature, ΔT 1 injecting fuel into the engine after an engine combustion event such that the fuel passes through the engine without being combusted for combustion in the diesel oxidation catalyst to target (ii) performing a primary cleaning process including, sequentially or simultaneously, removing the first engine speed limit and targeting an engine speed set point, the engine speed set point being faster than the first engine speed limit; If the engine safe state condition is interrupted during the step of implementing the primary cleaning process of the second aftertreatment module, the method returns to the step of implementing a first limit on the engine speed.

2. 2. The method of claim 1, wherein if the engine is restarted, the method includes removing (ii) the first engine speed limit and targeting an engine speed set point for a predetermined delay period before resuming the method of claim 1, the first engine speed limit and targeting an engine speed set point being faster than the first engine speed limit.

3. 3. The method of claim 2, wherein the step of (ii) restarting the engine to remove the first engine speed limit and target an engine speed set point for a predetermined delay period, the engine speed set point being faster than the first engine speed limit, is available for only a limited number of engine restarts.

4. The method of any of claims 1 to 3, further comprising an escalation architecture, whereby as the after-processing efficiency data decreases, increasing limitations are placed on the useful work output of the engine.

5. The method of any of claims 1-4, wherein the second aftertreatment module comprises a diesel particulate filter module, and the aftertreatment efficiency data includes a function of DPF soot loading.

6. An engine assembly comprising an engine and an exhaust gas treatment device, The exhaust gas treatment device includes a first aftertreatment module including a diesel oxidation catalyst; a second post-treatment module downstream of the first post-treatment module, the engine assembly is configured to provide aftertreatment efficiency data of the second aftertreatment module; The engine assembly includes: comparing the post-processing efficiency data to a first threshold, and if the post-processing efficiency data is such that the efficiency is below the first threshold; (a) enforcing a first limit on engine speed; (b) waiting for an engine safe state; (c) performing a primary cleaning process of the second post-treatment module, the primary cleaning process comprising: (i) the fuel is cooled to a temperature within the diesel oxidation catalyst such that a first increase in exhaust gas temperature, ΔT 1 injecting fuel into the engine after an engine combustion event such that the fuel passes through the engine without being combusted for combustion in the diesel oxidation catalyst; (ii) performing a primary cleaning process including, sequentially or simultaneously, removing the first engine speed limit and targeting an engine speed setpoint, the engine speed setpoint being faster than the first engine speed limit; the engine assembly returning to the step of implementing a first limit on engine speed if the engine safe state condition is interrupted during the step of implementing the primary cleaning process of the second aftertreatment module.

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