WO2005001266A1

WO2005001266A1 - Method for controlling an internal combustion engine

Info

Publication number: WO2005001266A1
Application number: PCT/EP2004/050574
Authority: WO
Inventors: Hans-Peter Rabl; Hong Zhang
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-06-30
Filing date: 2004-04-21
Publication date: 2005-01-06
Also published as: DE10329328B4; DE10329328A1

Abstract

The invention relates to a method for controlling an internal combustion engine, whereby both NOx emission and particulate emission are reduced by post-injection.

Description

2003P02153

description

Method for controlling an internal combustion engine

The present invention relates to a method for controlling an internal combustion engine, with a fuel injection, a NOx sensor and a lambda sensor.

In internal combustion engines, in particular in diesel engines, the formation of the pollutants in the exhaust gas, in particular the particle concentration and the NOx concentration, is mainly determined by the fuel injection quantity, the cylinder charge and an exhaust gas recirculation, if present, in order to reduce the NOx emission and by In order to be able to comply with the exhaust gas limit values, exhaust gas recirculation is used, for example. The amount of exhaust gas returned reduces the oxygen concentration and increases the specific heat capacity of the load. Both influences lower the peak combustion temperature and therefore lead to a reduction in NOx emissions. The disadvantage here, however, is that the increase in the exhaust gas recirculation rate increases the particle emission. This phenomenon is known and is known as the NOx particle trade-off. In order for the internal combustion engine to operate optimally in terms of emissions, a compromise must therefore be sought for NOx reduction with a small increase in particle emissions. In order to be able to achieve this, it is necessary to set the setpoint of the exhaust gas return rate precisely depending on the operating point. The actual exhaust gas recirculation rate can deviate from the specified exhaust gas recirculation rate without this being able to be detected and corrected with sufficient accuracy by an air mass meter. The inaccuracy of the setting for the exhaust gas recirculation rate has a global effect in the control for similar cylinders. The inaccurate setting results, for example, from the uncertainties in the measurement of the 2003P02153

2 sucked air mass through the air mass meter and can lead to increased NOx and particle emissions.

Even small deviations in the measurement of the air mass flow lead to large deviations in the emission values. Measurements have shown that with a tolerance of the air mass meter of ± 4%, the NOx emission increases by up to 27% (if the air mass flow is too high) and the particle emission increases by up to 60% (if the air mass flow is too low).

In addition to these uncertainties in the air path, there are further uncertainties in the fuel path, which also have a negative impact on exhaust gas emissions and cannot be diagnosed with sufficient accuracy. For example, the amount of fuel injected can deviate from the specified target value if the fuel pressure does not correspond to the target value, which can occur, for example, due to measurement inaccuracies of the pressure sensor. The increase in fuel pressure leads to an increased injection quantity, which increases both particle emissions and NOx emissions. Furthermore, a drift occurs at the injection valves over the running time, which leads to a change in the injection quantity and thus changes the emission values. For the individual cylinders, there are additional tolerances for the individual control of the injection quantity by the injection valves. To ensure that the emission limit values can be met, high demands are placed on component scattering over the service life, which significantly increases the costs for component production.

The invention is based on the object of providing a method for controlling an internal combustion engine which, with simple means, makes it possible to operate the internal combustion engine with low emission values, in particular with regard to the NOx emission and the particle emission. 2003P02153

3 According to the invention the object is achieved by a method having the features of claim 1. Advantageous refinements form the subject of the subclaims.

In the method according to the invention, a value for the air ratio, known as the lambda value, is measured in a first step and compared with a target value. The setpoint is calculated using a lambda model. In a second step, which can also take place simultaneously with the first step, a measured NOx value is compared with a setpoint value of a NOx

Model compared. The lambda model and the NOx model calculate the respective target values for an operating point of the internal combustion engine. The control is now dependent on the comparison. According to the invention, the multiple injection is changed if the lambda deviation lies within a first lambda band and the NOx deviation likewise lies within a first NOx band. In other words, to control the lambda value and the NOx emission, an intervention takes place via the injection, in particular via the injection pattern and the amount of fuel injected afterwards, if the deviation from the target value is less than a first threshold value and greater than one second threshold is. The first and second threshold values each form a band of permissible values around the setpoint. In addition to the first band of lambda values and NOx values, second bands for lambda and NOx values are defined according to the invention. If the deviation of the measured lambda values and NOx values lies within the second bands, an intervention follows via changes in exhaust gas recirculation, fresh air supply, injection quantity and / or boost pressure.

In the method according to the invention, different intervention options are used to optimize NOx and particle emissions depending on the values for the deviation. This method is based on the knowledge that the intervention via injection, in particular via multiple injection, is a very effective method 2003P02153

4 set to reduce NOx and particle emissions, which avoids the well-known NO _x particle trade θff.

A multiple injection consists of several individual injections, each of which is defined by an injection quantity and its respective injection time. The injection time in this case comprises the start of injection and the injection duration, which in turn is linked to the injection quantity.

When selecting whether an intervention takes place via the multiple injection, the defined first and second bands for the lambda and NOx values are preferably disjoint, that is to say they have no common values.

To change the post-injection, an amount of fuel is preferably injected after a main injection or the amount injected is changed, the amount of post-injected fuel being less than the amount of fuel introduced during the main injection. It is also possible for the main injection to be preceded by one or more injections.

In the method according to the invention, the amount of post-injected fuel is selected such that the emissions assume a minimum. The sum of the NOx and particle emissions is preferably turned off, the sum also being weighted. This process step is based on the knowledge that multiple injection is a method for reducing particle and NOx emissions. With a change in the emission via the multiple injection, the possibility is created to set a target value for the NOx emission.

In a preferred embodiment, the changes, in particular the changes in the post-injection cylin 2003P02153

5 derspecific. It is also possible to make changes for defined groups of cylinders or bank by bank.

Depending on the current measured value and the operating point, characterized by speed, load, temperature and injection, the model for the lambda or NOx values yields a lambda setpoint value that corresponds to a minimum NOx emission and a minimum particle emission. The method according to the invention is explained in more detail below using an exemplary embodiment. It shows:

FIGS. la, lb the dependence of the particle emission on NOx emission or on the lambda value in the event of an intervention in the exhaust gas recirculation rate, intake air throttling, injection quantity and / or the boost pressure,

2 shows a qualitative diagram for the dependency of particle and NOx emissions when the multiple injection changes,

3 shows the emission of NOx and particles depending on an amount of fuel injected,

4 shows a flow diagram for lambda control,

Fig. 5 is a flowchart for NOx control and

Fig. 6 is a flowchart for pπorization of the interventions.

Figure la shows the relationship between particle and NOx emissions for the internal combustion engine. An increase in the exhaust gas recirculation rate and / or a throttling of the intake air and / or an increase in the injection quantity lead to an increase in the quantity of particles and a reduction in the NOx emission. Along 2003P02153

6 of the curve 10 shown in FIG. 1 a, the exemplary operating point 12 shifts in the direction of B. A reduction in the exhaust gas recirculation rate and / or a reduction in the intake air throttling and / or a reduction in the injection quantity and / or the reduction in the boost pressure move the Working point 12 in the direction of A, which leads to an increase in NOx emission and a reduced particle emission. The operating point 12 is characterized by a lambda value. According to FIG. 1, a predetermined lambda target value leads to a target value 14 for the NOx emission and a target value 16 for the particle emission. The operating point 12 is additionally characterized by the speed, load, temperature and injection. Fig. Lb shows the setting of the target value for the particle emission via the lambda value.

2 shows the qualitative relationship between NOx emission and particle emission in the context of post-injection. While the above-mentioned measures of exhaust gas recirculation, intake air throttling and injection quantity can only shift the working point 12 along the double arrow C, multiple injection leads to a new working point 18, for example by post-injection of a small amount of fuel. The working point is shifted here is associated with a simultaneous reduction of NOx emissions and particle emissions.

The effect of the post-injection is summarized again in FIG. 3. Here the total emission is plotted against the amount of fuel injected. If no post-injection takes place, the post-injected fuel quantity corresponds to 0, then there is a base value 20 for the emission. If the amount of post-injected fuel is increased, the total emission drops to a value of 22. With regard to Fig. 2, this means that the operating points in

Shift in the direction of arrow D and so do the emission values 2003P02153

7 probably be reduced for Nθ _x as well as the particle emission.

4 shows a flow chart for regulating the lambda values. After an engine start 24, a measurement of the lambda

Value 26. The measured La bda value is forwarded to an evaluation unit 28 which takes into account the change over time in the lambda values. Likewise, the measured lambda value 26 is forwarded to an emission model 32 together with the current engine operating variables 30. The emission model 32 uses a lambda model 34 to determine the change over time for the lambda value and its absolute magnitude. The lambda model 34 generates a desired lambda model value 36, which is applied to the query 40 together with the lambda value 38. Query 40 checks whether:

SW1 <λ_Value - λ_Modell_Soll <SW2,

where SW1 and SW2 are two engine-specific threshold values.

Query 40 checks whether the deviation of the lambda values lies within a predetermined interval. If the values lie outside the interval, an intervention takes place in step 42 to regulate the current lambda measured value to the predefined model value. The intervention 42 is limited to the possibilities of exhaust gas recirculation, intake air throttling, the intervention via the injection quantity and the boost pressure.

As long as the motor vehicle is in operation, the method returns to step 26 in order to measure the current lambda value again. If there is a signal for the engine stop 44, the values set in the course of the method are stored for the later operation of the internal combustion engine in order to achieve an adaptation over the service life. 2003P02153

Fig. 5 shows the NOx control. After an engine start 48, a NOx measurement is carried out via a NOx sensor 50. The measured value is processed in a NOx evaluation unit 52, taking into account its time profile, in particular smoothed. The measured NOx value 50 is also forwarded to an emission model 54. A set of engine operating variables 56 is also present on the emission model 54. The value for the NOx target value output by the emission model 54 is processed in step 56 with regard to its temporal course and its absolute value to the NOx model target value 58.

The NOx value 60 from the NOx evaluation device 52 and the NOx model setpoint are compared with one another in the query 62. Query 62 checks whether:

SW3 <NOx value - NOx model setpoint <SW4, whereby SW3 and SW4 are engine-specific threshold values. If the deviation is not within the predetermined interval, an intervention is carried out in step 64 to regulate the NOx emission. In addition to the interventions 42 provided in the lambda control, the intervention 64 also involves an intervention in the injection pattern, i.e. the number of injections and / or the injection times. After intervention 64, the method returns to its starting point, where a new NOx measurement takes place.

When the engine stops 66, the adapted values are stored.

6 now shows the sequence of the method according to the invention in more detail. The method according to the invention is based on a common lambda / NOx emission model 70, against which the current engine operating variables 72, the measured lambda value 74 and the measured NOx value 76 are applied. Because of the connection with FIGS. 1 and 2 described relationships 2003P02153

Model 70 calculates a lambda deviation Δ and a NOx deviation ΔNOx between NOx and particle emissions. When determining the deviations, the optimal value to be achieved is specified in model 70.

A subsequent query 72 checks whether:

SW5 <λ <SW6 and SW7 <ΔNOx <SW8,

wherein the threshold values SW5 to SW8 lead to one or more of the interventions listed in step 74, which relate to the exhaust gas recirculation rate, the intake air throttling and the injection quantity.

The deviations determined in the emission model 70 are checked in the query 76 to determine whether: SW9 <h λ <SW10 and

SW 11 <ΔNOx <SW12, whereby SW9 to SW12 are specific threshold values. If it is determined in query 76 that the deviations from lambda and NOx lie within the threshold value intervals, then the injection pattern is followed in step 78, i.e. the number of injections and their timing or amount of fuel in the injection quantities is changed.

If the queries 72 and 76 show that the deviations are not within the band, a control is carried out in a manner known per se via step 80.

The method according to the invention consists of two parts: in a first part, the fuel is generated via the lambda signal 2003P02153

10 air ratio considered in order to intervene in the fuel and / or air path so that the global / cylinder-specific setpoint is reached depending on the operating point.

In a second part, the NOx sensor signal is used to diagnose, regulate and adapt the exhaust gas recirculation rate and multiple injection with regard to low emissions:

With knowledge of the air-fuel ratio, a global or cylinder-specific lambda control can be carried out to an emission-optimal, operating point-dependent setpoint. Global intervention is therefore taking place in the air path. In a further development, it is conceivable that a bank or even cylinder-specific regulation to bank or cylinder-specific fuel ratios is carried out. Furthermore, especially when it comes to a quick intervention in the power-air ratio, the injection quantity can first be adjusted so that the target value of the global or bank or cylinder-specific fuel-air ratio is reached. The intervention via injection generally takes place globally or individually for each bank or cylinder, as does intervention in the air path.

The injection quantity tolerances of the injection valves can be selected by means of cylinder-specific measurements of the air-fuel ratio and by correcting the injection times, the setpoint of the cylinder-specific power / air mixture can be regulated.

With knowledge of the NOx emission, a diagnosis of exhaust gas recirculation rate and multiple injection can be carried out with regard to the target values of the emission. The NOx setpoint can be controlled directly, and the particle emissions are recorded via the NOx particle emission relationships. 2003P02153

It is important in the method according to the invention that a lambda and a NO _x setpoint are regulated by intervening in exhaust gas recirculation, intake air throttling, fuel injection quantity and boost pressure. This achieves a balance between particle and NO _x emissions. The regulation to the lambda setpoint (FIG. 4) and the No _x setpoint (FIG. 5) are coupled via models 34 and 56.

Claims

2003P0215312 claims

1. A method for controlling an internal combustion engine, with a fuel injection, a NOx sensor and a La bda probe, comprising the following steps:

- In a first step, a measured lambda value (26) is compared with a target value (36) of a lambda model (32, 34), - in a second step, a measured NOx value (50) is compared with a target value (58 ) of a NOx model (54, 56) compared, - the lambda model (32, 34) and the NOx model (34, 56) determining the respective target values for an operating point (30, 56) of the internal combustion engine, - dependent A multiple injection is changed from the comparison if the La bda deviation lies within a first lambda band and the NOx deviation lies within a first NO _x band (76), and there is a change in exhaust gas recirculation and / or a fresh air supply and / or an injection quantity (74) and / or a boost pressure if the lambda deviation lies within a second lambda band and the NOx deviation lies within a second NOx band (72).

2. The method according to claim 1, characterized in that the first lambda band and the second lambda band have no common values as well as the first NOx band and the second NOx band.

3. The method according to claim 1 or 2, characterized in that to change the multiple injection, an amount of fuel is injected after a main injection or the post-injected amount is changed, the amount of post-injected fuel being less than that 2003P02153

13 is the amount of fuel introduced at the main injection.

4. The method according to claim 3, characterized in that the main injection is preceded by one or more injection processes.

5. The method according to claim 3 or 4, characterized in that the amount of post-injected fuel is selected such that the emissions assume a minimum.

6. The method according to any one of claims 1 to 5, characterized in that the change made depending on the comparison takes place cylinder-specifically.

7. The method according to any one of claims 1 to 5, characterized in that the change made depending on the comparison is carried out for a group of cylinders.

8. The method according to any one of claims 1 to 7, characterized in that the lambda model (54, 56) depending on the speed, load, temperature, injection and measured lambda value specifies a target lambda value (58) that a minimum NOx emission and a minimum particle emission corresponds.

9. The method according to any one of claims 1 to 8, characterized in that the NOx model (32, 34) depending on speed, load, temperature, injection and measured NOχ value specifies a NOx setpoint, which is a minimal NOx emission and corresponds to a minimal particle emission.