GB2536092A

GB2536092A - Method and system for increasing exhaust gas temperature

Info

Publication number: GB2536092A
Application number: GB1520086.8A
Authority: GB
Inventors: Ford Kim; Andreas Josephine Kees Don; Edward Caine Jonathan
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-11-13
Filing date: 2015-11-13
Publication date: 2016-09-07
Anticipated expiration: 2035-11-13
Also published as: GB201520086D0; DE102016121125A1; MX2016014898A; GB2536092B; RU2016143739A3; RU2016143739A

Abstract

A method of increasing exhaust gas temperature of an engine comprises the steps of: determining an exhaust gas aftertreatment temperature (steps 110, 120); determining whether the aftertreatment temperature is too low for efficient emission reduction (step 130); and, if so, controlling a variable valve timing (VVT) system (140) to reduce the air to fuel ratio at combustion of the engine. Exhaust gas aftertreatment temperature may be determined (a) at an exhaust port or any point downstream (step 110) and/or (b) at a portion of an exhaust gas aftertreatment system (step 120). The VVT system may be controlled to delay opening of an intake valve to increase the temperature of exhaust gas leaving the cylinder. The method may include determining the operational state of the engine (step 150), eg the air-fuel ratio may be reduced during light load and increased when increased torque is requested. The method may be adapted in response to the operational history of the engine. The VVT system may be controlled according to intake lambda value, EGR rate and/or mass airflow rate.

Description

Method and System for Increasing Exhaust Gas Temperature This disclosure relates to a method and system for increasing exhaust gas temperature and in particular, but not exclusively, relates to a method and system for increasing the temperature of the exhaust gasses of a variable displacement engine.

Introduction

It is becoming increasing important for vehicles to reduce the levels of emissions for all real driving conditions. For example, the New European Driving Cycle (NEDC) can be used to assess the levels of emissions from an engine. It is required for all real driving conditions (covered by the Real Driving Emissions (RDE) test process) that emissions are equivalent to the levels required for the NEDC cycle.

With continued development to improve fuel economy, waste heat is reduced and the exhaust system in consequence receives less heat. One problem in particular occurs during light-load driving conditions where an exhaust gas aftertreatment system for the vehicle may not reach a sufficient temperature to effect the required conversion of exhaust gasses.

One way of increasing the exhaust aftertreatment temperature is to increase the amount of fuel used for combustion, for example by retarding fuel injection and/or by introducing additional injections of fuel into the cylinder. It is desirable, however, to maintain the conversion efficiency of exhaust gas to achieve equivalent emissions to NEDC for all real driving conditions without increasing the amount of fuel used and reducing the fuel efficiency of the engine.

Statements of Invention

According to an aspect of the present disclosure there is provided a method of increasing exhaust gas temperature of an engine, for example a variable displacement engine. The method comprises the steps of: determining an exhaust gas aftertreatment temperature; and controlling a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.

Determining the exhaust gas aftertreatment temperature may comprise determining the temperature of the exhaust gas. The temperature of the exhaust gas may be determined at one or more points in an exhaust system of the engine. For example, the temperature of the exhaust gas may be determined in the exhaust manifold of the engine and/or at one or more points in an exhaust gas aftertreatment system.

Determining the exhaust gas aftertreatment temperature may comprise determining the temperature of a portion of an exhaust gas aftertreatment system, for example determining the temperature of a lean NOx trap (LNT) and/or a selective catalytic reduction (SCR) system. Sensors and/or models may be used to monitor gas and/or aftertreatment temperatures.

The air to fuel ratio of the combustion of the engine may be reduced by delaying the opening of at least one inlet valve of the engine to reduce the mass flow rate of gas through the engine. The air to fuel ratio of the combustion of the engine may be reduced when the exhaust gas aftertreatment temperature, for example the temperature of the exhaust gas, is below a predetermined temperature. For example, the predetermined temperature for the LNT and/or the SCR system may be a temperature at which the exhaust gas aftertreatment system is able to effect efficient conversion of exhaust gasses to meet the required levels.

The method may comprise determining the operational state of an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine. The method may comprise controlling the variable valve timing system of the engine depending on the operational state of the exhaust gas aftertreatment system.

The method may comprise the step of comparing the temperature of the exhaust gas to the temperature of the exhaust gas aftertreatment system. For example, the aftertreatment temperature may be a function of the temperature of the exhaust gas and the temperature of the exhaust gas aftertreatment system. The variable valve timing system of the engine may be controlled to reduce the air to fuel ratio of the combustion of the engine when the difference between the temperature of the exhaust gas and the temperature of the exhaust gas aftertreatment system is greater than a predetermined value and/or below a threshold.

The method may comprise determining the operational state of the engine. The method may comprises controlling the variable valve timing system of the engine depending on the operation state of the engine. The operational state of the engine may be a state of output torque from the engine. The step of determining the operational state of the engine may comprise determining the output torque from the engine, for example the output torque at any given time or over a period of time. The step of determining the operational state of the engine may comprise determining the operational history of the engine.

The method may comprise increasing the air to fuel ratio upon a request for increased output torque from the engine. For example, the control of the variable valve timing system to reduce the air to fuel ratio when aftertreatment temperatures are too low may be overridden when there is a request for increased output torque from the engine.

The method may comprise determining the oxygen content of the exhaust gas, for example using one or more lambda sensors. The method may comprise comparing the oxygen content of the exhaust gas to a target exhaust gas oxygen content level, for example the oxygen content of the exhaust gas may be compared to an exhaust lambda target map. The method may comprise controlling the variable valve timing system of the engine depending on the comparison of the oxygen content of the exhaust gas to the target oxygen content level.

According to another aspect of the present disclosure there is provided an exhaust gas control system for an engine, for example a variable displacement engine. The system comprises: a temperature sensor configured to determine an exhaust gas aftertreatment temperature; and a controller configured to adjust a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.

The temperature sensors may be configured to determine the temperature of the exhaust gas and/or the temperature of an exhaust gas aftertreatment system. The controller may be operatively connected to an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine. The controller may be configured to reduce the air to fuel ratio of the combustion of the engine depending on the operational state of the exhaust gas aftertreatment system.

There is provided an engine and/or a vehicle having one or more of the above-mentioned exhaust gas control systems.

The disclosure also provides software, such as a computer program or a computer program product for carrying out any of the methods described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein. A computer program embodying the disclosure may be stored on a computer-readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

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 arrangements of the disclosure. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or arrangement of the disclosure may also be used with any other aspect or arrangement of the disclosure.

Brief Description of the Drawing

For a better understanding of the present disclosure, and to show 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 flow chart of a method of increasing exhaust gas temperature.

Detailed Description

It is known for an internal combustion engine, for example a variable displacement engine (VDE) to be fitted with a variable valve timing (VVT) system configured to adjust the valve timing and/or the valve lift. Typically the WT system may be configured to adjust the operation of one or more intake valves and/or one or more exhaust valves of the engine by means of collapsible lash adjusters or moveable finger followers. However, the VVT system may have any appropriate configuration. During start-up of the engine or during an engine warm-up phase the VVT system may be configured to reduce compression to allow cranking speed to rise quickly before increasing compression to provide sufficient charge temperature for the combustion process to achieve sustained engine operation. During operation of the engine, the VVT can act to balance pumping work against fuel consumption for the required power.

An exhaust gas aftertreatment system can be used to reduce levels of pollutants in the exhaust gas, for example hydrocarbons, nitrogen oxides (NOx) and/or particulate matter. In some situations, for example during light-load driving conditions and/or the warm-up phase of the engine, the exhaust gas aftertreatment system of the vehicle may not reach a sufficiently high temperature to effect the required conversion of exhaust gasses or removal of particulate matter. For example, the required operating 10 temperature of a NOx absorber may be approximately 250°C for Lean NOx Trap (LNT) purge or approximately 170°C for active Selective Catalytic Reduction (SCR) dosing. It is desirable, therefore, to provide a sufficient aftertreatment temperature in order to achieve the desired emission conversion efficiency.

In the context of the present disclosure, the term "aftertreatment temperature" is understood to mean the temperature of the exhaust gas and/or the temperature of the exhaust gas aftertreatment system. For example, the aftertreatment temperature may be a function of the exhaust gas temperature and temperature of the exhaust gas aftertreatment system. In one situation, the exhaust gas aftertreatment system may be 20 operating at a required temperature and the exhaust gas temperature may be lower than the temperature of the exhaust gas aftertreatment system, such that the temperature of the exhaust gas aftertreatment system is lowered by the cooler exhaust gas. In another situation, the exhaust gas aftertreatment system may be operating at a temperature that is lower than the temperature of the exhaust gas, such that the temperature of the exhaust gas is lowered by contact with the cooler exhaust gas aftertreatment system. The term "aftertreatment temperature" is therefore understood to mean the temperature at which efficient conversion of the exhaust gases is achieved, for example to meet the required standards. The present disclosure provides a method 100 in which the temperature of the exhaust gas itself and/or temperature of the exhaust gas aftertreatment system is used to determine if the aftertreatment temperature is above or below the required value.

Figures 1 depicts the method 100 for increasing aftertreatment temperature for a variable displacement engine, for example by controlling the VVT system of the engine to adjust the operation of at least one inlet and/or exhaust valve of the engine.

The method 100 comprises a step 110 of determining the temperature of the exhaust gas of the engine 103. The temperature of the exhaust gas may be determined at an exhaust port of a cylinder of the engine, and/or any appropriate point downstream of the exhaust port of the cylinder. For example, the temperature of the exhaust gas may be determined at an exhaust manifold and/or at one or more points of an exhaust gas aftertreatment system of the vehicle, such as an SCR system and/or an LNT.

The method 100 comprises a step 120 of determining the operational state of the exhaust gas aftertreatment system. For example, the method 100 may comprise a step of determining the temperature of at least one portion of the exhaust gas aftertreatment system. In this manner, steps 110 and 120 may be used in combination to determine if there is sufficient temperature to effect the efficient conversion of exhaust gases. It is understood, however, that the method 100 may comprise either of the steps 110 or 120 in order to determine if an exhaust gas aftertreatment process can be carried out in the desired manner. The method 100 may comprise determining the temperature of the exhaust gas and comparing the temperature of the exhaust gas to a predetermined temperature, for example a minimum temperature of the exhaust gas required to ensure a desired conversion level of exhaust gas. In a similar manner, the method may comprise determining temperature of one or more components of the exhaust gas aftertreatment system and comparing the temperature of the component to a minimum temperature required to ensure a desired level of the exhaust gas conversion. Hence, if it is determined that the aftertreatment temperature is too low for efficient emission reduction (step 130), the method comprises a step 140 of controlling the VVT system of the engine to reduce the air to fuel ratio at combustion of the engine.

One way of reducing the air to fuel ratio during combustion of the engine is to delay the opening of at least one intake valve to reduce the mass flow rate of gas through a cylinder of the engine. In operation, the inlet valve opening may be delayed so that the cylinder is part charged with just enough air to achieve a low lean air to fuel ratio. This will minimise the exhaust mass flow and the amount by which cold air entering the cylinder reduces the temperature of the exhaust gas. As a result, the exhaust gases leaving the cylinder will be hotter which will allow the exhaust gas aftertreatment system to function more effectively. Such a control strategy allows the exhaust gas temperature to the increased without having to retard fuel injection or add extra fuel into the cylinder during combustion.

The method may comprise a step of comparing the temperature of the exhaust gas to the temperature of the exhaust gas aftertreatment system in order to determine if the aftertreatment temperatures are too low for efficient emission reduction. For example, the VVT system may be configured to reduce the air to fuel ratio when the difference between the temperature of the exhaust gas and the temperature of the aftertreatment system is greater than or equal to a predetermined value and/or lower than a threshold.

The method comprises a step 150 of determining the operational state of the engine 103. For example, the method may comprise determining the torque output from the 10 engine and/or a requested level of torque output from the engine. The VVT system may be configured to control one or more of the inlet valves of the engine depending on the operational state of the engine. For example, during light load conditions the operational state of the engine may be such that there is a low level of heat delivered into the exhaust gas. As a result, the VVT system is controlled to reduce the air to fuel ratio of the combustion, thereby increasing the temperature of the exhaust gas. As soon as a request for increased torque is received, the VVT system is controlled to increase the air to fuel ratio of the combustion for the increased torque demand which increases the temperature of the exhaust gas for the given operational state of the engine. In this manner, transient operation of the engine is not affected by application of the method 100, and a request for increased torque output of the engine may set new target levels for operation of the VVT system.

The control of the VVT system may vary to achieve a low but lean air to fuel ratio over a range of different operational conditions of the engine. For example, transient operation of the engine is not affected since the amount by which the opening of the inlet valve is delayed can be matched to the required torque output from the engine. When a request for increased torque is received, the controller may set new operational parameters for the WT system in order to reduce the air to fuel ratio of the combustion by an amount corresponding to the amount by which aftertreatment temperature is below an optimum value. For example, if the difference between the actual aftertreatment temperature and required aftertreatment temperature is relatively high, the system may be configured to delay the opening of one or more inlet valves by a relatively long period. In this manner, the temperature of the exhaust gas may be increased by a larger amount to compensate for a larger differential between the actual aftertreatment temperature and the desired aftertreatment temperature, thereby effecting efficient exhaust gas conversion.

In the context of the present disclosure, the term "operational state" it is understood to mean the operating condition of the engine at any given point in the operational lifecycle. As such, operational state may includes one or more parameters relating to the operational history of an engine, for example age and/or wear parameter& In this manner, the method 100 may comprise a step of adjusting the control strategy depending upon how many cycles of the operation the engine has performed. For example, if the engine has performed a high number of operational cycles the temperature of the exhaust gas may be different from that of an engine that has performed a lower number of operational cycles. In this manner, the method 100 may be adapted in response to the operational history the engine 103.

The method may comprise a step of determining one or more environmental conditions in which the engine operates. For example, a method may comprise a step of determining the environmental temperature and/or pressure using one or more sensors. In this manner, it may be determined if the vehicle is operating at an increased altitude having a lower oxygen content. Signals from the sensors may be fed into the controller and the opening of the inlet valve may be delayed by a different amount in order to compensate for the environmental conditions in which the engine operates.

The method may comprise a step of determining the oxygen content of the exhaust gas using one or more oxygen sensors (lambda sensors). The oxygen content of the exhaust gas may be determined at any point downstream of the exhaust port of the engine, such as in the exhaust manifold and/or at a point of the exhaust gas aftertreatment system. If it is determined that the aftertreatment temperature is below a desired level, the oxygen content of the exhaust gas may be compared to a target exhaust oxygen content level (exhaust lambda map) and the control of the VVT system may be adjusted depending on the comparison between a lambda value of the exhaust 30 gas and the exhaust lambda map. As soon as the operational state of the engine changes, and an increased level of torque is requested, the control of the VVT system may be adjusted according to a control strategy incorporating an intake lambda value, an exhaust gas recirculation rate and/or a mass airflow rate.

It will be appreciated by those skilled in the art that although the disclosure has been described by way of example with reference to one or more arrangements, it is not limited to the disclosed arrangements and that alternative arrangements could be constructed without departing from the scope of the disclosure as defined by the appended claims.

Claims

Claims 1 A method of increasing exhaust gas temperature of an engine, the method comprising the steps of: determining an exhaust gas aftertreatment temperature; and controlling a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.
2. A method according to claim 1, wherein the step of controlling the variable valve timing system comprises delaying the opening of at least one inlet valve of the engine to reduce the mass flow rate of exhaust gas from the engine.
3 A method according to claim 1 or 2, wherein the air to fuel ratio of the combustion of the engine is reduced when the exhaust gas aftertreatment temperature is below a predetermined temperature.
4. A method according to any of the preceding claims, the method further comprising the steps of determining the operational state of an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine; and controlling the variable valve timing system of the engine depending on the operational state of the exhaust gas aftertreatment system 5 A method according to claim 4, the method further comprising the step of comparing the temperature of the exhaust gas to the temperature of the exhaust gas aftertreatment system.6. A method according to claim 4 or 5, wherein the temperature of the exhaust gas is determined at the exhaust gas aftertreatment system.7. A method according to any of the preceding claims, the method further comprising the steps of: determining the operational state of the engine; and controlling the variable valve timing system of the engine depending on the operation state of the engine.8. A method according to claim 7, wherein the step of determining the operational state of the engine comprises determining the output torque from the engine.9. A method according to claim 7 or 8, wherein the step of determining the operational state of the engine comprises determining the operational history of the engine.10. A method according to claim 9, the method further comprising increasing the air to fuel ratio upon a request for increased output torque from the engine.11 A method according to any of the preceding claims, the method further comprising: determining the oxygen content of the exhaust gas; comparing the oxygen content of the exhaust gas to a target exhaust gas oxygen content level; and controlling the variable valve timing system of the engine depending on the comparison of the oxygen content of the exhaust gas to the target oxygen content level.12. An exhaust gas control system for an engine, the system comprising: a temperature sensor configured to determine an exhaust gas aftertreatment temperature; and a controller configured to adjust a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.13. An exhaust gas control system according to claim 12, wherein the controller is configured to reduce the air to fuel ratio of the combustion of the engine depending on the operational state of an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine.14. An engine and/or a vehicle comprising one or more control systems of any of claim 12 or 13.15. A method of increasing exhaust gas temperature as described herein, with reference to, and as shown in the accompanying drawings.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSClaims 2 cr) 15 CO 4 o C\I 5 6.A method of increasing exhaust gas temperature of an engine, the method comprising the steps of: determining an exhaust gas aftertreatment temperature; and controlling a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.A method according to claim 1, wherein the step of controlling the variable valve timing system comprises delaying the opening of at least one inlet valve of the engine to reduce the mass flow rate of exhaust gas from the engine A method according to claim 1 or 2, wherein the air to fuel ratio of the combustion of the engine is reduced when the exhaust gas aftertreatment temperature is below a predetermined temperature.A method according to any of the preceding claims, the method further comprising the steps of: determining the operational state of an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine; and controlling the variable valve timing system of the engine depending on the operational state of the exhaust gas aftertreatment system.A method according to any of the preceding claims, wherein the exhaust gas aftertreatment temperature is a function of the temperature of the exhaust gas and the temperature of the exhaust gas aftertreatment system.A method according to claim 4 or 5, wherein the temperature of the exhaust gas is determined at the exhaust gas aftertreatment system.A method according to any of the preceding claims, the method further comprising the steps of: determining the operational state of the engine; and controlling the variable valve timing system of the engine depending on the operation state of the engine.8. A method according to claim 7, wherein the step of determining the operational state of the engine comprises determining the output torque from the engine.9 A method according to claim 7 or 8, wherein the step of determining the operational state of the engine comprises determining the operational history of the engine.10. A method according to claim 9, the method further comprising increasing the air to fuel ratio upon a request for increased output torque from the engine.11 A method according to any of the preceding claims, the method further comprising: determining the oxygen content of the exhaust gas; comparing the oxygen content of the exhaust gas to a target exhaust gas oxygen content level; and controlling the variable valve timing system of the engine depending on the comparison of the oxygen content of the exhaust gas to the target oxygen content level.12. An exhaust gas control system for an engine, the system comprising: a temperature sensor configured to determine an exhaust gas aftertreatment temperature; and a controller configured to adjust a variable valve timing system of the engine to reduce the air to fuel ratio at combustion of the engine depending on the exhaust gas aftertreatment temperature.13. An exhaust gas control system according to claim 12, wherein the controller is configured to reduce the air to fuel ratio of the combustion of the engine depending on the operational state of an exhaust gas aftertreatment system that is configured to treat the exhaust gas from the engine.14. An engine and/or a vehicle comprising one or more control systems of any of claim 12 or 13.15. A method of increasing exhaust gas temperature as described herein, with reference to, and as shown in the accompanying drawings.