GB2529925A

GB2529925A - A method of operating a vehicle

Info

Publication number: GB2529925A
Application number: GB1509234.9A
Authority: GB
Inventors: Nick John Shuter
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-05-29
Filing date: 2015-05-29
Publication date: 2016-03-09
Anticipated expiration: 2035-05-29
Also published as: GB2529925B; MX2016006475A; TR201606809A2; DE102016109812A1; RU2016119123A; RU2016119123A3; GB201509234D0

Abstract

A method of operating a motor vehicle, the motor vehicle comprises an engine (2, figure 1) and an exhaust gas after-treatment device in an exhaust line of the engine, the exhaust gas after-treatment device comprising a Passive NOx Adsorber (PNA, 10, figure 1); the method 200 comprises monitoring the air-fuel equivalence ratio of the engine 202, determining an ageing parameter of the exhaust gas after-treatment device by integrating the air-fuel equivalence ratio of the engine with respect to time 204, determining whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter 206 and regenerating the exhaust gas after-treatment device 208. The ageing parameter may also be determined by integrating a function of the exhaust gas temperature and air-fuel ratio with respect to time. The ageing parameter can relate to an anticipated oxidation of the catalyst of the exhaust gas after-treatment system, this system may also include a selective catalytic reduction device (SCR) and an exhaust gas recirculation system (EGR) in which the amounts of reductant and recirculated exhaust gas is adjusted based on the ageing parameter.

Description

A Method of Operafing a Vehicle

Technical Field

The present disclosure relates to a method of operating a vehicle and is particularly, although not exclusively, concerned with a method of operating a vehicle comprising a Passive NOx Adsorber (PNA).

Background

Motor vehicles are often fitted with exhaust gas after-treatment devices such as Diesel Particulate Filters (DPFs), Selective Catalytic Reduction (SCR) devices, Lean NOx Traps (LNTs) and/or Passive NOx Adsorbers (PNAs). These devices remove pollutants from the exhaust gases by capturing, oxidising or reducing the pollutant species.

Combinations of such devices may be implemented to provide the best emissions control over a range of operating conditions.

Exhaust gas after-treatment devices may be periodically regenerated in order to continue operating efficiently. Regeneration of after-treatment devices may come at a penalty to fuel consumption and/or may lead to an increase in emissions during regeneration. Hence, it may be desirable to regenerate after-treatment devices only when necessary to maintain their performance.

Some after-treatment devices, such as PNA5, may be regenerated periodically or following events which are know to cause significant degradation, such as the regeneration of a DPF or a desulphurisation event of a LNT in the same exhaust line as the PNA. However, the after-treatment devices may also become degraded under other driving conditions and hence may operate inefficiently until a regeneration event is triggered.

Statements of Invention

According to a first aspect of the present disclosure, there is provided a method of operating a motor vehicle, the motor vehicle comprising an engine and an exhaust gas after-treatment device in an exhaust line of the engine, the exhaust gas after-treatment device comprising a Passive NOx Adsorber (PNA) configured to: capture nitrogen oxides, from the exhaust gases, at or below a first temperature and release nitrogen oxides, into the exhaust gases, at or above a second temperature; and oxidise hydrocarbons and/or carbon monoxide by virtue of a catalyst.

The method comprises: monitoring an air-fuel equivalence ratio of the engine, e.g. a lambda value of exhaust gases from the engine, determining an ageing parameter of the exhaust gas after-treatment device by integrating the air-fuel equivalence ratio of the engine with respect to time, determining whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter and regenerating the exhaust gas after-treatment device, -In this specification, Passive NOx Adsorber (PNA) is taken to mean any device configured to be installed into an exhaust line of a vehicle such as a motor vehicle, which is configured to: capture nitrogen oxides, from the exhaust gases, at or below a first temperature and release nitrogen oxides, into the exhaust gases, at or above a second temperature; and oxidise hydrocarbons and/or carbon monoxide by virtue of a catalyst. Such a device may be known as a Passive NOx Adsorber or a Lean NOx Trap (LNT) lite.

The method may further comprise monitoring the temperature of exhaust gases from the engine and the ageing parameter of the exhaust gas after-treatment device may be determined by integrating a function of the temperature and air-fuel equivalence ratio with respect to time.

The method may further comprise monitoring the operating time, and/or fuel consumption of the engine and the ageing parameter of the exhaust gas after-treatment device may be determined at least partly from the monitored operating time, and/or fuel consumption.

The method may further comprise determining a light-off temperature of the catalyst based on the ageing parameter. Determining whether the exhaust gas after-treatment device should be regenerated may be performed by comparing the light-off temperature to a threshold value.

The exhaust gas after-treatment device may be regenerated by operating the engine under rich combustion conditions. Regeneration of the exhaust gas after-treatment device may be performed during an acceleration event of the vehicle.

The method may further comprise determining the effect of the regeneration of the exhaust gas after-treatment device on the ageing parameter. The effect of the regeneration of the exhaust gas after-treatment device on the ageing parameter may determined by monitoring the air-fuel equivalence ratio of the engine during the regeneration and integrating the air4uel equivalence ratio of the engine with respect to time.

Additionally or alternatively, the effect of the regeneration of the exhaust gas after-treatment device on the ageing parameter may be determined by monitoring the temperature of exhaust gases from the engine and the air-fuel equivalence ratio of the engine during the regeneration and integrating a function of the temperature and air-fuel equivalence ratio with respect to time.

The ageing parameter may relate to an anticipated oxidation of the catalyst of the exhaust gas after-treatment device. The catalyst may comprise a platinum group metal.

The vehicle may further comprise a Selective Catalytic Reduction (8CR) device and the method may further comprise configuring the 8CR device to reduce the nitrogen oxides released by the PNA at or above the second temperature. Additionally or alternatively, the method may further comprise adjusting the amount of reductant introduced to the 8CR device according to the ageing parameter of the PNA.

The vehicle may further comprise an Exhaust Gas Recirculation (EGR) system and the method may further comprise adjusting the amount of exhaust gases recirculated by the EGR system according to the aging parameter of the PNA. Additionally or alternatively, the method may further comprise adjusting the amount of exhaust gases recirculated by the EGR system to reduce the temperature of exhaust gases entering the PNA whilst regenerating the PNA.

According to another aspect of the present disclosure, there is provded a controller configured to perform the method according to a previously mentioned aspect of the

disclosure.

S According to another aspect of the present disclosure, there is provided software, which when executed by a computing device causes the computing device to perform the method according to a previously mentioned aspect of the disclosure.

According to another aspect of the present disclosure, there is provided a motor vehicle comprising an engine, an exhaust gas after-treatment device in an exhaust line of the engine, the exhaust gas after-treatment device comprising a PNA configured to: capture nitrogen oxides, from the exhaust gases, at or below a first temperature and release nitrogen oxides, into the exhaust gases, at or above a second temperature; and oxidise hydrocarbons and/or carbon monoxide by virtue of a catalyst; and a controller configured to perform the method according to a previously mentioned

aspect of the present disclosure.

According to another aspect of the present disclosure, there is provided a method of operating a motor vehicle, the motor vehicle comprising an engine and an exhaust gas after-treatment device in an exhaust line of the engine, the method comprising: determining an ageing parameter of the exhaust gas after-treatment device, determining whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter and regenerating the exhaust gas after-treatment device.

The method may further comprise monitoring the temperature of exhaust gases from the engine and/or a lambda of the engine, wherein the ageing parameter of the exhaust gas after-treatment device is determined from the monitored temperature and/or lambda value.

The method may further comprise integrating a function of the temperature and/or lambda value with respect to time; wherein determining the ageing parameter of the exhaust gas after treatment device is performed using the result of the integration.

To avoid unnecessary duplication of effort and repetition of text in the specification certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention.

Brief Description of the Drawings

For a better understanding of the present disclosure, and to shown more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a schematic view of the flow of air and exhaust gases through a previously proposed engine system and exhaust after-treatment system; Figure 2 shows a method for operating a vehicle according to the present disclosure; and Figure 3 shows a schematic view of a controller configured to operate a vehicle

according to the present disclosure.

Detailed Description

With reference to Figure 1, a vehicle 1 may comprise an engine 2, an air inlet 4, an exhaust gas recirculation (EGR) system 6 and an exhaust system 8. The engine 2 may comprise a diesel engine, however it is equally envisaged that the present disclosure could also apply to any other type of vehicle engine, such as a petrol engine.

Additionally or alternatively, the engine may be naturally aspirated or comprise a turbocharger and/or a supercharger and/or be provided with some other form of enhanced induction. The vehicle may comprise an additional motor, such as an electric motor, and the engine 2 may be part of a hybrid drive system.

As depicted in Figure 1, the engine 2 may comprise an inlet manifold 2a and an exhaust manifold 2b. The inlet manifold 2a may be supplied with inlet air from the inlet 4 which can be drawn into the engine 2 via the inlet manifold 2a. The inlet air may be mixed with fuel within the engine 2 arid combusted to provide power to drive the vehicle, as well as to power any ancillary systems, such as electrical systems, provided on the vehicle. The combustion of the fuel and inlet air produces exhaust gases including water vapour, carbon dioxide (GO2), carbon monoxide (CO), nitrous oxides (N04 and other gases, which may be exhausted via the exhaust manifold 2b.

As depicted in Figure 1, the EGR system 6 comprises a high pressure EGR system.

Additionally or alternatively the EGR system 6 may comprise a low pressure EGR system, in which exhaust gases are recirculated subsequently to being expanded through a turbocharger turbine. Alternatively, the vehicle may not comprise an EGR system. The EGR system 6 allows a portion of the exhaust gases to be recirculated back to the inlet of the engine 2. Replacing a portion of the oxygen rich air with burnt exhaust gases reduces the proportion of the contents of each cylinder which is available for combustion. This results in a lower heat release and lower peak cylinder temperature and thereby reduces the formation of NON.

Exhaust gases which are not recirculated via the EGR system 6 may enter the exhaust system 8. As shown in Figure 1, the exhaust system 8 may comprise one or more exhaust gas after-treatment devices, for example a Passive NOx Adsorber (PNA) 10.

The exhaust system 8 may further comprise a selective catalytic reduction (SCR) device 12. The exhaust gas after-treatment devices may be provided upstream of an exhaust outlet 14. The SCR device 12 may be actively controlled, as described below, or may be a passive SCR device. Additionally or alternatively, the exhaust gas after treatment system may comprise a diesel particulate filter (DPF), Lean NOx Trap (LNT), diesel oxidation catalyst (DOC) and/or any other exhaust gas after-treatment device.

Again additionally or alternatively, the exhaust system may comprise a combined after-treatment device such as a combined SCR/DPF device. The exhaust after-treatment systems may be provided in any order within the exhaust system.

The vehicle 1 may further comprise exhaust outlet sensors 16 and/or engine sensors 18. The sensors may comprise one or more temperature sensors and/or one or more lambda sensors. The lambda sensors may comprise narrow band or wide band oxygen sensors. Additionally or alternatively, the lambda sensors may comprise any other sensor capable of measuring the amount of oxygen present in the exhaust gases andlor determining the air-fuel ratio and/or air-fuel equivalence ratio of combustion within the engine 2. The engine sensors 18 may be provided downstream of the exhaust manifold 2b. Addfticnally or alternatively, exhaust oufiet temperature and/cr lambda sensors 16 may be provided at or near the outlet 14, which may be configured to measure the temperature and/ar oxygen content of the exhaust gases once they have passed through the exhaust gas after-treatments devices 10,12. Again additionally or alternatively, exhaust temperature and/or lambda sensors (not shown) may be provided at another point in the exhaust system, e.g. between the PNA 10 and the SCR device 12.

The PNA 10 may comprise a honeycomb structure provided with a wash coat, which may comprise a platinum group metal (PGM) catalyst, e.g. a platinum, palladium, osmium, iridium, ruthenium or rhodium catalyst. When the PNA 10 has been heated, e.g. by the exhaust gases, to a temperature that is at or above a light-off temperature of the catalyst, the PGM catalyst within the PNA 10 may begin to catalyse a reaction through which N0 compounds may be adsorbed from the exhaust gases and captured within the PNA 10. The light-off temperature of the catalyst may be sufficiently low that the FNA 10 may effectively adsorb NOx from the exhaust gases at lower temperatures than other after-treatment devices configured to adsorb NOx, such as an LNT. The F'NA 10 may also begin to adsorb NOx at lower temperatures than the SCR device 12 is able to operate, as described below. The PNA 10 may be configured to release the stored NOx when it reaches higher operating temperatures. Unlike an LNT, the PNA 10 may be configured to allow stored Wax to be released without the operation of the engine being specifically adjusted, for example by initiating a rich combustion mode of the engine.

ri addition to catalysing the adsorption of NOx into the PNA 10, when the PGM catalyst within the PNA is at or above the light-off temperature, oxidation reactions of other exhaust gases, such as CO and/or unburnt hydrocarbons (HC), may be catalysed by the PGM catalyst. These gases may be oxidised within the PNA to form 002 and water.

In the exhaust system depicted in Figure 1, the SCR device 12 uses a controlled injection of a reductant, for example from a SCR dosing system (not shown), to convert NOx compounds, present in the exhaust gases, to nitrogen gas and water through a chemical reduction process. In the example shown in Figure 1, urea is injected into the exhaust system and undergoes thermal decomposition and hydrolysis to produce ammonia. The ammonia produced may act as the reductant in the SCR device. The dosage of urea added may be controlled to affect the efficiency Mth which NO is removed from the exhaust gases. Additionally or alternatively, another reductant may be introduced by the 8CR dosing system. Again additionally or alternatively, the reductant may be provided through a reformation process of another exhaust gas after treatment device installed upstream of the 8CR device 12.

The exhaust system 8 and/or the SCR device 12 may be required to heat up to a suitable temperature before the urea can thermally decompose and the 8CR device can operate effectively. The PNA 10 may therefore operate at lower temperatures than the 8CR device 12. However, the 8CR device 12 may continue to operate at higher temperatures than those at which the PNA 10 begins to release the NOx, which was previously captured by the device, as descried above. By providing the PNA 10 upstream of the 8CR device 12, as shown in the exhaust system 8 of Figure 1, the exhaust system 8 may operate effectively to remove NOx from the exhaust gases over a wider range of temperature than either of the devices are capable of individually.

As described above, pollutant species, such as HC and/or CO, may be oxidised within the PNA 10. The PGM catalyst may act a catalyst in these oxidation reactions. During such reactions the PGM catalyst itself may be oxidised. Additionally, at higher temperatures, the PGM catalyst may be directly oxidised by oxidising species within the exhaust gases, e.g. the PGM catalyst may be a reactant in the oxidation reaction.

This effect may be increased when the engine is operating with leaner combustion conditions, which may lead to greater concentrations of oxidising species within the exhaust gases. Oxidation of the PGM catalyst may cause the light-off temperature of the catalyst to increase, which may increase the temperature at which the PNA begins to efficiently capture NOx from the exhaust gases and/or cause other pollutant species such as CO and HC to be oxidised. An increase in the light-off temperature of the catalyst may therefore result in ageing of the PNA 10.

In order to reduce the light-off temperature of the catalyst and improve the efficiency of the PNA 10, the PNA may be regenerated. A rich combustion mode of the engine 2 may be imposed in order to increase the concentration of reducing species, such as HG and GO, within the exhaust gases. The oxidised PGM catalyst may be reduced by the reducing species, reversing the FNA ageing process and reducing the light-off temperature of the PGM catalyst. The reaction in which the oxidised PGM catalyst is reduced may proceed with a higher reaction rate, relative to the oxidation reaction of the PGM catalyst, when the operating temperature of the PNA is reduced and hence the operation of the engine and/cr EGR system may be controlled to reduce the temperature of the exhaust gases.

Operating the engine in order to reduce the light-off temperature of the PGM catalyst within the PNA may be performed periodically, e.g. after a certain engine running time or distance travelled or after a certain amount of fuel has been combusted within the engine 2. Additionally or alternatively the engine may be operated to regenerate the PNA following specific events which are know to have a detrimental effect on the performance of the PNA, for example after the regeneration of a DPF of the exhaust system, or a de-sulfurisation event of an LNT of the exhaust system. These events may require a period of high temperature, lean operation of the engine 2 which may lead to oxidation of the PGM catalyst and hence ageing of the PNA 10. Additionally or alternatively, the ageing of the PNIA 10 may be monitored directly and regeneration of the PNA may be performed based on the ageing of the PNA.

With reference to Figure 2, a method 200 for operating a vehicle according to an example of the present disclosure is shown. The method 200 may comprise a first step 202 in which the air-fuel equivalence ratio, e.g. lambda value, of the engine is monitored. In a second step 204, a function dependent on the air-fuel equivalence ratio may be integrated with respect to time to determine an ageing parameter of an exhaust gas after-treatment device, e.g. the PNA 10. In a third step 206, it may be determined whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter. In a fourth step 208, the exhaust gas after-treatment device may be regenerated.

In addition to monitoring the air-fuel equivalence ratio in the first step 202, the temperature of exhaust gases from the engine may also be monitored. If the temperature of the exhaust gases is monitored in the first step, the function, which is integrated in the second step 204 in order to determine an ageing parameter of the exhaust gas after-treatment device, may additionally depend on exhaust gas temperature.

As described above, with reference to Figure 1, the ageing of an exhaust gas after-treatment device, for example the PNA 10, may correspond to oxidation of a catalyst of the device. The rate of the oxidation reaction of the catalyst may depend on the temperature of exhaust gases and/or the concentration of oxidising species within the exhaust gases. By monitoring the air-fuel equivalence ratio of the engine and/or the temperature of exhaust gases in the first step 202, for example by using the engine temperature and/or lambda sensors 18 and/or the outlet temperature and/or lambda sensors 16, the oxidation rate of the catalyst may be determined. For example, a function of temperature and/or air-fuel equivalence ratio may be used to calculate the rate of oxidation of the catalyst, or a parameter that is representative of the rate of oxidation. Alternatively, a look-up table may be referred to and a value for the oxidation rate or the representative parameter may be determined according to the temperature and/or air-fuel equivalence ratio. The value, which has been calculated or determined from the look-up table, may be integrated with respect to time in order to determine an oxidation of the catalyst, which may provide an ageing parameter of the exhaust gas after-treatment device.

Integration of the calculated or determined rate of oxidation may be performed continuously whilst the vehicle is operating. Alternatively, the integration may be performed by considering discrete values which are recorded at predetermined intervals. Alternatively again, the integration may only be performed whilst the temperature and/or air-fuel equivalence ratio are within predetermined ranges.

Additionally or alternatively to applying the monitored temperature and/or air-fuel equivalence ratio to determine an ageing parameter of the exhaust gas after-treatment device, an operating time, distance travelled and/or fuel consumption of the engine may be monitored and may be used to determine or adjust the ageing parameter of the exhaust gas after-treatment device, for example by referring to an alternative look-up

table.

In order to determine whether the exhaust gas after-treatment device should be regenerated in the third step, a light-off temperature of a catalyst of the exhaust gas after-treatment device may be determined. For example, a second look-up table may be referred to and a light-off temperature may be determined according to the ageing parameter of the exhaust gas after-treatment device. The light-off temperature may be compared to a threshold value and, if the determined light-off temperature is equal to or greater than the threshold value, it may be determined that the exhaust gas after-treatment device should be regenerated. ii

If the exhaust system 8 comprises another exhaust gas after-treatment device, which may be controfled to affect the rate at which NOx compounds are removed from the exhaust gases, such as the 8CR 12, the method may comprise an additional step of controlling the other exhaust gas after-treatment device in order to remove any additional NOx which has not been captured due to ageing of the PNA 10.

The other exhaust gas after-treatment device may also be configured to remove any NOx compounds which are released once the PNA 10 has reached a higher temperature at which it begins to release the stored NOx, as described above.

When the vehicle is accelerating, the difference in the fuel consumption and/or emissions values of the vehicle, between ideal engine operation and rich operation of the engine, may be less than at other points in the vehicle drive cycle. Regeneration of the exhaust gas after-treatment device in step 208 may therefore be performed when the vehicle is accelerating.

During regeneration of the exhaust gas after-treatment device, the rate of the reduction of the oxidised PGM catalyst may depend on the temperature of the exhaust gases and/or the concentration of reducing species within the exhaust gases. The effect of a period of regeneration on the catalyst may therefore be determined from exhaust temperature and/or air-fuel equivalence ratio measurements in a similar way to how the ageing parameter was determined. The function of temperature and/or air-fuel equivalence ratio, or the look-up table described previously may allow for negative values which may be integrated, as described above, to determine the reduction to the ageing parameter.

The method 200 may further comprise an additional step, in which the effect of the regeneration of the exhaust gas after-treatment device on the ageing parameter is determined. As described above, this may be achieved by monitoring the temperature of exhaust gases from the engine and/or the air-fuel equivalence ratio of the engine during the regeneration, and integrating a function of the temperature and/or air-fuel equivalence ratio with respect to time. Additionally or alternatively, the look-up table may be referred to and a reduction rate of the catalyst may be determined from the

look-up table.

Updating the ageing parameter during regeneration, as well as during normal operating conditions, may allow the length of a regeneration event to be controfled in order to provide the desired reduction in ageing of the after-treatment device, and hence the desired reduction in light-off temperature. Monitoring the effect of regeneration may also allow the regeneration to be split between multiple regeneration events. This may be useful if regeneration must be stopped or abandoned, for example if it is no longer possible to operate the engine with rich combustion conditions. Additionally, regeneration may be deliberately split into shorter regeneration events which can be performed during periods when it is most efficient to run the engine with rich combustion conditions, for example which the vehicle is accelerating.

Referring now to Figure 3, a controller 300 for operating a vehicle according to an example of the present disclosure is shown. The controller 300 may comprise a first module 302 which is configured to monitor an air-fuel equivalence ratio of the engine andlor a temperature of exhaust gases from an engine of the vehicle. The controller 300 may comprise a second module 304, configured to integrate a function of the air-fuel equivalence ratio and/or the temperature of exhaust gases to determine an ageing parameter of an exhaust gas after-treatment device, e.g. the PNA 10. The controller 300 may comprise a third module 306, configured to determine whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter. The controller 300 may comprise a fourth module 308, which may control the vehicle to regenerate the exhaust gas after-treatment device.

As described above, in order to determine the ageing parameter of the exhaust gas after-treatment device, the second module 304 may comprise a memory 304a in which a look-up table is stored. The look-up table may allow an ageing rate of the after-treatment device, such as an oxidation rate of a catalyst of the after-treatment device, to be determined based on exhaust temperature and/or engine air-fuel equivalence ratio values. The look-up table may also comprise negative values for the ageing rate, which may correspond to values of exhaust temperature and/or engine air-fuel equivalence ratio experienced during a regeneration event.

In order to determine whether the exhaust gas after-treatment device should be regenerated based on the ageing parameter, the third module 306 may comprise a second memory 306a in which a second look-up table is stored. The second look-up table may allow a light-off temperature of a catalyst of the after-treatment device to be determined from the ageing parameter. The third moduie 306 may be configured to compare the determined light-off temperature value to a threshold value to determine whether the exhaust gas after4reatment device should be regenerated It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims