METHOD FOR CONTROLLING THE OPERATION OF AN ENGINE SYSTEM

Abstract

A method for controlling the operation of an engine system in a vehicle is provided The engine system includes an engine configured to operate in at least a two-stroke combustion mode and a four-stroke combustion mode, and an exhaust aftertreatment system, EATS configured to reduce emissions from the engine exhausts. The method comprising estimating or predicting the temperature of the EATS; estimating or predicting the emissions out of the EATS; n response of that the temperature of the EATS is below a predetermined temperature threshold, and that the emissions out of the EATS is above a predetermined emission threshold, performing a primary NOx emission reducing activity by operating the engine in a two-stroke combustion mode; subsequently to initiating the operation of the engine in a two-stroke combustion mode, and in response of that the emissions out of the EATS is below the predetermined emission threshold, changing engine operation from the two-stroke combustion mode to a four-stroke combustion mode.

Claims

1. A method for controlling the operation of an engine system in a vehicle, the engine system comprising an engine configured to operate in at least a two-stroke combustion mode and a four-stroke combustion mode, and an exhaust aftertreatment system, EATS configured to reduce emissions from the engine exhausts, the method comprising: estimating or predicting the temperature of the EATS; estimating or predicting the emissions out of the EATS; in response of that the temperature of the EATS is below a predetermined temperature threshold, and that the emissions out of the EATS is above a predetermined emission threshold, performing a primary NOx emission reducing activity by operating the engine in a two-stroke combustion mode; subsequently to initiating the operation of the engine in a two-stroke combustion mode, and in response of that the emissions out of the EATS is below the predetermined emission threshold, changing engine operation from the two-stroke combustion mode to a four-stroke combustion mode.

2. The method according to claim 1, further comprising: deactivating at least one engine cylinder of the engine during the operation of the engine in a two-stroke combustion mode.

3. The method according to claim 2, wherein the deactivated engine cylinder is controlled to perform engine compression brake, either as two-stroke or four stroke engine compression brake.

4. The method according to claim 1, further comprising: prior to changing engine operation from the two-stroke combustion mode to the four-stroke combustion mode, and in response of that the temperature of the EATS is below the predetermined temperature threshold, and that the emissions out of the EATS is above the predetermined emission threshold, performing a compensatory NOx emission reducing activity different to operating the engine in a two-stroke combustion mode.

5. The method according to claim 4, wherein the compensatory NOx emission reducing activity includes at least one of the following: using wastegate, late fuel injection, electrical heating of at least a part of the EATS, changing engine valves opening/closing, reduce the flow of exhaust through the engine and EATS.

6. The method according to claim 1, wherein the estimated or predicted emissions out of the EATS comprises the amount of NOx.

7. The method according to claim 1, further comprising: determining predicted vehicle operational information comprising at least a predicted upcoming road event and a predicted engine operation associated with the upcoming road event, wherein the emissions out of the EATS are calculated emissions associated with the predicted engine operation.

8. The method according to claim 7, wherein the emissions out of the EATS is predicted cold-start emissions associated with the predicted engine operation.

9. The method according to claim 7, wherein the predicted vehicle operational information is based on historical or statistical data of the vehicle operation, or is scheduled vehicle operational information based on a pre-determined planned vehicle operation.

10. The method according to claim 1, wherein changing engine operation from the two-stroke combustion mode to a four-stroke combustion mode is performed regardless of if the temperature of the EATS is below or above the predetermined temperature threshold.

11. An engine system of a vehicle, the engine system comprising and engine configured to operate in at least a two-stroke combustion mode and a four-stroke combustion mode, and an exhaust aftertreatment system, EATS configured to reduce emissions from the engine exhausts, the EATS comprising a control unit configured to: estimate or predict the temperature of the EATS; estimate or predict the emissions out of the EATS; in response of that the temperature of the EATS is below a predetermined temperature threshold, and that the emissions out of the EATS is above a predetermined emission threshold, instruct the engine system to perform a primary NOx emission reducing activity by operating the engine in a two-stroke combustion mode; subsequently to initiating the operation of the engine in a two-stroke combustion mode, and in response of that the emissions out of the EATS is below the predetermined emission threshold, instructing the engine to change its engine operation from the two-stroke combustion mode to a four-stroke combustion mode.

12. A vehicle comprising an engine system according to claim 11.

13. A computer program comprising program code comprising instructions to execute the steps of the method of claim 1 when said program is run on a computer.

14. A computer readable medium carrying a computer program comprising program code comprising instructions to execute the steps of the method claim 1 when said computer program is run on a computer.

15. A control unit for controlling the operation of an engine system in a vehicle, the control unit being configured to perform the steps of the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

[0077] FIG. 1 is a schematic side view of a vehicle comprising an engine system, and an exhaust aftertreatment system of the engine system, in accordance with an example embodiment of the invention,

[0078] FIG. 2 is a schematic view of an engine system, and an exhaust aftertreatment system of the engine system, of a vehicle in accordance with example embodiments of the invention; and

[0079] FIG. 3 is a flowchart illustrating the steps of a method in accordance with example embodiments of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0080] With reference to FIG. 1 a vehicle 1, here embodied as a heavy duty truck 1, comprising an engine system 10, is disclosed for which a control unit 17 of a kind disclosed in the present disclosure is advantageous. However, the control unit 17 may as well be implemented in other types of vehicles, such as in busses, light-weight trucks, passenger cars, marine applications etc having similar engine systems. The vehicle 1 of FIG. 1 is a hybrid vehicle 1 comprising an engine 15, which in this embodiment is a diesel engine 15, and an electric machine 22. The diesel engine 15 is powered by diesel fuel, typically comprised in a fuel tank (not shown) and the electric machine 22 is powered by electricity supplied from at least one energy storage or transformation device, e.g. a battery or a fuel cell. The diesel engine 15 and the electric machine 22 are typically arranged and configured to individually propel the vehicle 1, by being separately coupled to other parts of the powertrain of the vehicle 1, such as transmission, drive shafts and wheels (not shown in detail). That is, the vehicle 1 may be propelled by the diesel engine 15 alone, the electric machine 22 alone, or by the diesel engine 15 together with the electric machine 22.

[0081] In FIG. 1, at least the diesel engine 15 is comprised in the engine system 10, the engine system 10 further comprising an exhaust aftertreatment system, EATS, 20 having at least an SCR catalyst 32, an oxidation catalyst in the form of a DOC 30, and a particle filter in the form of a DPF 31. The DPF 31 is arranged upstream of the SCR catalyst 32, and is arranged and configured to remove particles, e.g. diesel particulate matter or soot, from the exhaust gas of the diesel engine 15. The SCR catalyst 32 is arranged and configured to convert nitrogen oxides, also referred to as NOx, with the aid of a catalyst, into diatomic nitrogen (N2), and water (H2O) (and potentially carbon dioxide CO2). A reductant, typically anhydrous ammonia, aqueous ammonia or urea solution (commonly referred to as urea in the present disclosure), is added to engine exhausts and is absorbed onto the catalyst in the SCR catalyst 32. The DOC 30 is arranged upstream of the DPF 31 and is configured to convert carbon monoxide and hydrocarbons into carbon dioxide. The SCR catalyst 32, the DOC 30 and the DPF 31 are examples of emission reducing components of the EATS 20, of which all need not to be included for the present invention. The engine system 10 is described in more detail with reference to FIG. 2.

[0082] FIG. 2 discloses the engine system 10 of vehicle 1 of FIG. 1 in more detail. The engine system 10 comprises, as already described with reference to FIG. 1, a diesel engine 15 and an EATS 20 having a fluid channel 26 for providing a fluid pathway for the engine exhausts to an EATS outlet 26b, the three emission reducing components already mentioned with reference to FIG. 1, i.e. the SCR catalyst 32, the DOC 30 and the DPF 31. As show in FIG. 2, a temperature sensor 33 is couped to the SCR catalyst 32 for measuring the temperature of the EATS 20, an in particular the temperature of the SCR catalyst 32. However, it should be noted that the temperature sensor may be arranged elsewhere in the EATS 20, and not necessarily at the SCR catalyst 32. Furthermore, a NOx sensor 35 is arranged at the EATS outlet 26b for measuring the NOx in the emissions out of the EATS 20 (also referred to as tailpipe NOx).

[0083] The control unit 17 is configured to control at least part of the operation of the engine system 10 and/or the EATS 20. It should however be mentioned that the control unit 17 may be provided outside of the EATS 20 and/or the engine system 10 and instead be comprised in another part of the vehicle 1. Moreover, as a further example an ammonia slip catalyst, ASC, may be arranged downstream of the SCR catalyst 32 for handling any ammonia slip from the SCR catalyst 32. Moreover, the EATS 20 may comprise a pre-SCR catalyst arranged upstream of the DOC 30.

[0084] A reductant injector 34 is in the embodiment in FIG. 2 arranged upstream the SCR catalyst 32 for providing reductant to the SCR catalyst 32. The reductant injector 34 is typically fluidly connected to a reductant dosing system comprising a storage tank for the reductant and a pressuring means, typically a pump, for pressurising the reductant prior to injection.

[0085] The EATS 20 may comprises means for providing determination/measurement of the emissions out of the diesel engine 15 (e.g. engine out NOx), ammonia storage of the SCR catalyst 32, the temperature of the SCR catalyst 32 (e.g. temperature sensor 33 previously mentioned), the temperature at the EATS outlet 26b, the emissions at the EATS outlet 26b (e.g. the NOx emissions, or tailpipe NOx emissions). For such purposes, the EATS 20 may comprise suitable a temperature sensors and/or ammonia sensors and/or NOx sensors.

[0086] As also indicated in FIG. 2, the control unit 17 is communicatively connected to the diesel engine 15. Thus, the diesel engine 15 may be instructed by the control unit 17 to perform various engine operations, such as e.g. setting the combustion mode as two-stroke or four-stroke, and/or individual setting of the engine cylinders.

[0087] As described with reference to FIG. 1, the engine system 10 may comprise an electric machine 22 powered by electricity supplied from at least one energy storage or transformation device, e.g. a battery or a fuel cell. In FIG. 2 the electric machine 22 is shown as being operable by a rechargeable energy storage system, RESS 12, comprising at least one battery. The diesel engine 15 may be coupled to the RESS 12 for charging the battery.

[0088] For example, during initial operation of vehicle, e.g. up to a point in time at which the (normal) operating temperature of the engine system has been reached, the emissions (e.g. emissions per travelled distance, or emissions per unit operational time or emission per energy, g/kWh) out of the EATS are typically higher compared to when the operating temperature of the engine system has been reached. Such emissions are referred to as cold-start emissions and they typically comprises undesired compounds (such as NOx, particles, and CO or unburned HC) in the exhaust out from the EATS as a result of the cold-start of the engine system. The initial operation of the vehicle may e.g. span over the near future to the engine operational initialization time, e.g. over a time span of e.g. 0 s or 1 s to 30 min, or 0 s or 1 s to 20 min, or 0 s or 1 s to 15 min, or 0 s or 1 s to 10 min. Thus, the cold-start emissions of the vehicle are the emissions in the exhausts out from the EATS 20 during such initial operation of the vehicle. There are also other vehicle operational conditions for which the operating temperature (or normal operating temperature) of the engine system, or at least the operating temperature of the EATS, is not achieved. Such vehicle operational conditions may also load to elevated, or at least unnecessarily high, emissions.

[0089] In order to avoid, or at least reduce, elevated emissions of NOx, at least one NOx emission reducing activity can be applied. That is, at least a part of the engine system 10 may be operated in such a way that the NOx emissions during vehicle operations suffering from low temperatures in the engine system is reduced.

[0090] A method for controlling the operation of an engine system in a vehicle by performing at least a primary NOx emission reducing activity will now be described with reference to the flowchart of FIG. 3, schematically illustrating steps of such method. The engine system, such as the engine system 10 of FIGS. 1 and 2, comprises an engine configured to operate in at least a two-stroke combustion mode and a four-stroke combustion mode, such as e.g. the diesel engine 15 of FIGS. 1 and 2, and an exhaust aftertreatment system, EATS, such as EATS 20 of FIGS. 1 and 2.

[0091] In an optional step S5, which may be performed prior (or simultaneously with) any one of steps S10 and S20 described below, predicted vehicle operational information comprising at least a predicted upcoming road event and a predicted engine operation associated with the upcoming road event is determined. The predicted vehicle operational information may be based on historical or statistical data of the vehicle operation, or may be scheduled vehicle operational information based on a pre-determined planned vehicle operation. Typically, such pre-determined planned vehicle operation is based on map data. The predicted vehicle operational information may furthermore comprises an engine or vehicle operational initialization time (i.e. at point in time in which the engine is started, or in which the vehicle is started). Moreover, the predicted engine operation associated with the upcoming road event typically comprises predicted engine speed and/or predicted engine torque in response to the upcoming road event. The predicted vehicle operational information may further comprise at least one external parameter such as predicted traffic and/or weather conditions associated with, or comprised in, the upcoming road event.

[0092] In a step S10, e.g. being a first step S10, the temperature of the EATS 20 is estimated or predicted. For example, the temperature of the EATS may be estimated based on a temperature measurement. For example, the temperature of at least one the previously mentioned emission reducing components of the EATS can be measured using a temperature sensor. As exemplified in FIG. 2, the temperature of the SCR catalyst 32 may be measured by temperature sensor 33, but it should be mentioned that any one of the other emission reducing components, such as the DOC 30 and the DPF 31 could be coupled to a temperature sensor for measuring the temperature thereof. As a further alternative, the temperature could be estimated using a temperature sensor arranged at the EATS outlet 26b. Predicting the temperature of the EATS 20 may alternatively be achieved by modelling the temperature of the EATS 20 in response to a known thermal model of the EATS 20 and predicted vehicle operation using predicted vehicle operational information from the step S5. That is, in a step S15, a predicted temperature of the EATS 20 associated with the predicted engine operation may be determined.

[0093] In a step S20, e.g. being a second step S20, the emissions out of the EATS 20 is estimated or predicted. Typically the estimated or predicted emissions out of the EATS 20 comprises the estimated or predicted amount of NOx emissions. For example, the emissions out of the EATS 20 may be estimated based on a measurement based on a NOx sensor, e.g. arranged at the EATS outlet 26b as shown in FIG. 2. Correspondingly to the prediction of the temperature, the emissions out of the EATS may be predicted (calculated) by modelling the emissions out of the EATS in response to a known emission model and predicted vehicle operation using predicted vehicle operational information. The emissions out of the EATS 20 may e.g. be the predicted cold-start emissions associated with the predicted engine operation associated with the upcoming road event of the predicted vehicle operational information. That is, in a step S25, a predicted emission out of the EATS 20 associated with the predicted engine operation may be determined.

[0094] For example, the cold-start emissions of the predicted engine operation may be based on the cold-start emissions associated with the predicted engine speed and/or predicted engine torque. The cold-start emissions of the predicted engine operation may for example be estimated from the engine operational initialization time to a time at which the engine system has reached (or is predicted to have reached) its (normal) operating temperature.

[0095] It should be noted that, at least one of, or each one of, the steps S10 and S20 may be performed continuously. Hereby, the temperature of the EATS 20 and/or the emissions out of the EATS 20 may be continuously estimated (or measured), or continuously predicted. The steps S10 and S20 may be performed simultaneously, or subsequently, in any order. In case the steps S10 and S20 are performed discretely, subsequent steps of estimating or predicting the temperature of the EATS 20 and/or the emissions out of the EATS 20 are typically repeated as will be described in the following.

[0096] In a step S27, performed subsequently to at least steps S10 and S20, the estimated or predicted temperature of the EATS 20 is compared to a predetermined temperature threshold, and the estimated or predicted emissions out of the EATS 20 is compared to a predetermined emission threshold.

[0097] In response of an outcome of step S27 being that the temperature of the EATS is below the predetermined temperature threshold, the temperature e.g. be estimated by measuring the temperature of the EATS 20 during the step S10, and that the emissions out of the EATS 20 is above the predetermined emission threshold, the emissions e.g. be estimated by measuring the NOx emissions out of the EATS 20 during the step S20, a primary NOx emission reducing activity is performed in step S30 by operating the engine 15 in a two-stroke combustion mode. As mentioned previously, the step S30 may be carried out in response to a prediction of the temperature of the EAST 20 in step S10, and thus performing the step S30 may be carried out in response to that predicted temperature of the EATS 20 is below the predetermined temperature threshold. Additionally, or alternatively, the step S30 may be carried out in response to a prediction of the emissions out of the EATS 20 in step S20, and thus performing the step S30 may be carried out in response to that predicted emissions out of the EATS 20 is above the predetermined emission threshold.

[0098] Thus, the engine 15 is operated in the two-stroke combustion mode in order to increase the heating of the EATS 20. The operation of the engine 15 in the two-stroke combustion mode may continue for time period until a new criterium is met which enables the operation of the engine 15 to be operated in a four-stroke combustion mode.

[0099] During the operation of the engine 15 in the two-stroke combustion mode, at least one engine cylinder may be deactivated in a step S31. Hereby, not all engine cylinders of the engine 15 need to be operating in the two-stroke combustion mode. For example, half of the engine cylinders may be deactivated, while the other half are operated in the two-stroke combustion mode. The deactivated engine cylinder(s) needs not to be passive, but the term “deactivated” should be understood as not participating in the combustion of fuel.

[0100] In a subsequent step S32, the deactivated engine cylinder may be controlled to perform engine compression brake, either as two-stroke or four stroke engine compression brake. Thus, the two-stroke combustion mode may be used together with the deactivation of at least one engine cylinder and engine compression brake.

[0101] The engine 15 may be operated in a four-stroke combustion mode prior to initiating the operation of the engine 15 in the two-stroke combustion mode. Thus, the engine 15 may be operated in a four-stroke combustion mode, e.g. as the initial operation of the engine 15 subsequently to engine start (e.g. during the first seconds or minutes), while the (first) estimation or prediction of the temperature of the EATS and the emissions out of the EATS in steps S10 and S20 are performed. Moreover, in response of an outcome of step S27 being that the temperature of the EATS is above the predetermined temperature threshold, the temperature e.g. be estimated by measuring the temperature of the EATS 20 during the step S10, and that the emissions out of the EATS 20 is below the predetermined emission threshold, the emissions e.g. be estimated by measuring the NOx emissions out of the EATS 20 during the step S20, a step S40 of operating the engine 15 in the four-stroke combustion mode may be performed. Thus, the operation of the engine 15 may be continued in the four-stroke combustion mode, or in case the engine 15 was operating in the two-stroke combustion mode, be changed into the engine operation of the four-stroke combustion mode.

[0102] During the operation of the engine 15 in the two-stroke combustion mode, and prior to changing engine operation from the two-stroke combustion mode to the four-stroke combustion mode, and in response of that the temperature of the EATS 20 is below the predetermined temperature threshold, and that the emissions out of the EATS 20 is above the predetermined emission threshold, a compensatory NOx emission reducing activity may be performed in a step S34. The compensatory NOx emission reducing activity is different to the primary NOx emission reducing activity of operating the engine 15 in a two-stroke combustion mode. The temperature of the EATS 20, and the emissions out of the EATS 20, may be estimated or predicted continuously as previously described. In an alternative, a separate step S35 of estimating or predicting the temperature of the EATS 20 is performed as a sub-step of step S34, and/or a separate step S36 of estimating or predicting the emissions out of the EATS 20 is performed as a sub-step of step S34 (typically prior to actual activation of the compensatory NOx emission reducing activity).

[0103] Turning briefly back to the engine system 10 of FIG. 2. The engine system 10 typically comprises various valves, such as wastegate, inlet throttle valve, intake and exhaust valves (not shown). For example, the wastegate may be operated in such a way that the flow of exhaust gases to the turbine wheel in a turbocharger of the engine system is varied. Moreover, the engine system 10 may comprise electrical heaters arranged in one or various positions of the EATS 20, e.g. arranged to heat at least one of the emission reducing components. For example, and as seen in FIG. 2, heaters 50, 52, may be arranged in various positions of the engine system 10. In the example embodiment of FIG. 2, two heaters 50, 52, here being a first heater 50 arranged to heat the DOC 30 (or exhaust gases entering the DOC 30) and a second heater 52 arranged to heat the injected reductant and/or the SCR catalyst 32 (by heating exhaust gases upstream of the injection point of the reductant injector 34 and/or upstream of the SCR catalyst 32). However, only one of the two heaters 50, 52 may be provided in the engine system 10, and the heaters may be arranged elsewhere in the engine system 10. The first and second heaters 50, 52 may be electrical heating elements, or combustion units configured for combustion of e.g. HC to produce heat. Each one of heaters 50, 52 may e.g. comprise a lattice or a grating, or a coil or a plate, configured to be heated by electricity led through the lattice, grating, coil, or plate.

[0104] Compensatory NOx emission reducing activities may chosen from at least one of the following: using wastegate, late fuel injection, electrical heating of at least a part of the EATS, changing engine valves opening/closing, reduce the flow of exhaust through the engine and EATS. Another example of a compensatory NOx emission reducing activity may be to increase the load, e.g. by charging the battery of the RESS 12, resulting in an increased temperature of the exhausts and an increased temperature of the EATS 20.

[0105] In a step S37, during the operation of the engine 15 in the two-stroke combustion, and optionally while performing at least one of the compensatory NOx reducing activities, and in response of that the emissions out of the EATS is below the predetermined emission threshold, the engine operation is changed in a step S37 from the two-stroke combustion mode to the four-stroke combustion mode. Again, the emissions out of the EATS 20 may be estimated or predicted continuously as previously described. In an alternative, a separate step S39 of estimating or predicting the emissions out of the EATS 20 is performed as a sub-step of step S37 (typically prior to actual changing of the engine operation into the four-stroke combustion mode). The step S37 of changing engine operation from the two-stroke combustion mode to the four-stroke combustion mode may be performed regardless of if the temperature of the EATS 20 is below or above the predetermined temperature threshold. However, as an alternative embodiment, the temperature of the EATS 20 is estimated or predicted continuously as previously described, or a separate step S38 of estimating or predicting the temperature of the EATS 20 is performed as a sub-step of step S37 (typically prior to actual changing of the engine operation into the four-stroke combustion mode). Thus, the step S37 of changing engine operation from the two-stroke combustion mode to the four-stroke combustion mode may be performed in further response to that the temperature of the EATS 20 is above the predetermined temperature threshold. As a further alternative, and in response to that the temperature of the EATS 20 is higher than the temperature of the exhaust gases from the engine (i.e. engine out temperature), the engine operation is changed from the two-stroke combustion mode to the four-stroke combustion mode.

[0106] For example, the control unit 17 of the vehicle 1 may be configured to perform, or initiate, or at least instruct components of the engine system 10 to achieve said at least one primary NOx reducing activity by operating the diesel engine 15 in a two-stroke combustion mode, and any one of the other steps described with reference to the flow chart of FIG. 3. Thus, the control unit 17 of FIGS. 1 and 2 may be configured to:

[0107] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. The present invention is not limited to a certain type of engine system and/or EATS. For example, the EATS 20, or a similar one, may be used for cleaning exhaust gases of other engines than diesel engines. For example, the EATS may be used to clean exhaust gases by converting NOx emissions from the exhaust of internal combustion engines using CNG (Compressed Natural Gas), LPG (Liquified Pressurized Gas), DME (DiMethylEther), and/or H2 (Hydrogen) as fuel. Thus, the engine system may comprise another combustion engine than a diesel engine, e.g. a hydrogen engine.

[0108] It should be noted that the naming of the steps of FIG. 3 is not necessarily, but might according to at least one example embodiment, relate to the order in which the steps are carried out. Thus, the order of the steps may be different than that explained here, unless explicitly being dependent on each other. Moreover, one or more steps may be omitted, and/or two of the steps may be carried out simultaneously.

[0109] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed inventive concept, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.