DE102011055275B4 - Method for controlling the exhaust gas temperature of a direct-injection internal combustion engine - Google Patents

Abstract

Method for controlling the exhaust gas temperature of a direct-injection internal combustion engine (2),
in which the burning fuel injection is divided into several individual injections and
in which the engine exhaust temperature (T ₃ ) of the exhaust gas emerging from the internal combustion engine (2) at a predetermined load (PMI) is controlled by controlling the conversion rate area center of gravity (UFS) and the total injection quantity (q _inj ) of all combusting fuel injections.

Description

The invention relates to a method for controlling the exhaust gas temperature of a direct-injection internal combustion engine and to such an internal combustion engine.

The temperature of the exhaust gases leaving an internal combustion engine is of particular importance for the devices and units connected to the exhaust system. Exhaust aftertreatment devices in particular sometimes require minimum temperatures for efficient exhaust gas purification. In addition, minimum temperatures are also sometimes required for the regeneration of exhaust aftertreatment systems, and these must be achieved as efficiently as possible. On the other hand, certain temperature limits must not be exceeded in order to avoid thermal overloading of components such as the turbine of a turbocharger.

Furthermore, current and future emissions legislation is placing ever higher demands on internal combustion engines, especially diesel engines. In order to reduce the particle emissions emitted, closed particle filters have become widely established on the market. The use of such filters makes it necessary to regenerate them at certain intervals. This regeneration requires the temperature of the exhaust gas to be set precisely and as quickly as possible in order to keep the regeneration times as short as possible and to avoid damage to the particle filter. In addition to retarding the main injection, later, so-called post-injections are also used for this purpose. The interaction of the main injection and early post-injection, both of which burn and generate torque, must be adapted to all possible ambient conditions in complex tests during calibration.

DE 10 2006 015 503 A1 describes methods for controlling the injection curve of a direct-injection internal combustion engine, whereby the control causes a change in the injection curve at least during a first working cycle on the basis of at least one parameter recorded during the first working cycle. A combustion controller is provided which controls the start of injection and the injection characteristics on the basis of the combustion center position. The combustion center position is generally assumed to be after 50% of the injected fuel quantity has been converted, even if this is not exact in relation to the integrated area of the conversion rate. Combustion chamber pressure sensors are used to determine the combustion center position, by means of which the conversion rate can be deduced from the combustion chamber pressure.

The temperature of the exhaust gas exiting a direct-injection internal combustion engine corresponds to the temperature after the exhaust valve or, if a turbocharger is connected directly downstream of the internal combustion engine, the temperature before the turbine of the turbocharger. This temperature is usually controlled by known control methods. However, delays in the control of the controlled variable occur in every control loop, since this must first be determined or measured in order to then be fed back to the controller in the feedback loop. To counteract this problem, WO 2009/ 112 056 A1 proposes providing a temperature model of a gas in a combustion chamber of a cylinder in order to predictively determine the temperature of an exhaust gas exiting the combustion chamber of the cylinder and feed it to a controller. In the internal combustion engine described there, an HC emission model is also provided in order to determine the HC emission of an exhaust gas exiting the combustion chamber. This is used to control the regeneration of an exhaust gas purification system, in particular a particle filter.

The EP 2 075 442 A1 discloses a system for controlling a combustion process which has at least a main injection and a pilot injection, the system having a closed control loop by means of which the characteristics of the pilot injection are varied in order to regulate a noise emission and a combustion center of the entire combustion.

The DE 10 2007 004 265 A1 describes a method for controlling engine and injection parameters of an internal combustion engine depending on the position of a combustion center or combustion conversion point.

The object of the present invention is to provide a simple and accurate method for controlling the exhaust gas temperature.

The object is achieved according to the invention by a method for controlling the exhaust gas temperature of a direct-injection internal combustion engine, in which the combusting fuel injection is divided into several individual injections and in which the engine exhaust gas temperature of the exhaust gas exiting the internal combustion engine is controlled at a predetermined load by controlling the conversion rate area center of gravity and the total injection quantity of all combusting fuel injections.

Advantageous developments of the invention are described in the subclaims.

In contrast to previous methods, the center of gravity of the conversion rate area is used, and not the position of the conversion of 50% of the injected fuel, which already leads to a higher level of accuracy. This is due, among other things, to the fact that with multiple injections, the position of the conversion of 50% of the fuel may change abruptly if the position of one of the injections is shifted.

This is due, among other things, to the fact that in the case of multiple injections, shifting the position of one of the injections may not shift the position of the conversion of 50% of the fuel, e.g. if it is located exactly between the individual injections, but the area of gravity of the conversion in relation to all injections does shift.

In addition, this turnover rate area center of gravity is already regulated in the control loop. The controlled variable is therefore already the turnover rate area center of gravity, which means that a more quickly responsive control can be implemented.

Preferably, a required temperature difference is determined from a predetermined target value of the engine exhaust temperature and a measured actual value of the engine exhaust temperature, and from this a correction value for the conversion rate area center of gravity is regulated by means of a controller.

A corrected target value of the turnover rate area centre of gravity is determined from the correction value for the turnover rate area centre of gravity and a target value of the turnover rate area centre of gravity.

Furthermore, a difference value for the conversion rate area center of gravity is determined from the corrected target value of the conversion rate area center of gravity and an actual value of the conversion rate area center of gravity, and on the basis of this difference value, the position of the individual injections and/or the injection quantity distribution of the total injection quantity to the individual injections is controlled by means of a controller.

The target value of the conversion rate area center of gravity can be determined based on a characteristic map.

The actual value of the conversion rate area center of gravity is preferably determined using a combustion model or from measured pressure curves of the combustion chamber pressure. The use of a model has the advantage that the actual value can be determined predictively.

Preferably, the load, i.e. the indicated mean pressure, is also taken into account in the control, whereby a required load difference is determined from a setpoint value of the load and an actual value of the load and the total injection quantity is controlled from this by means of a controller.

Preferably, it is provided that a correction value for the total injection quantity is controlled directly by means of a controller as a function of a difference value for the conversion rate area center of gravity and that a corrected total injection quantity is determined from this and the total injection quantity.

The object is further achieved by a direct-injection internal combustion engine with a control unit for controlling the engine exhaust temperature of an exhaust gas exiting the internal combustion engine according to the method described above.

A turbocharger can be provided in the exhaust system and the engine exhaust temperature of the exhaust gas can be regulated upstream of the turbocharger turbine.

Furthermore, an exhaust gas aftertreatment device can be provided, which can be, for example, a particle filter, a NOx storage catalyst or an SCR catalyst, wherein a temperature required for the exhaust gas aftertreatment device, for example for regeneration, can be set by regulating the engine exhaust gas temperature.

At least one combustion chamber pressure sensor can be provided for combustion position control. In addition, temperature sensors can be provided for determining the engine exhaust gas temperature.

In the following, the invention is explained in more detail with reference to the drawings.

• 1 eine Gesamtstruktur einer Regelung nach einer ersten Ausführungsform,
• 2 die Gesamtstruktur einer Regelung nach einer zweiten Ausführungsform,
• 3 einen beispielhaften Umsatzratenverlauf,
• 4 den Brennverlauf bei einem Umsatzratenverlauf gemäß 3 und
• 5 eine schematische Darstellung einer Brennkraftmaschine mit Abgasanlage.

Herein show:

• 1 an overall structure of a control according to a first embodiment,
• 2 the overall structure of a control according to a second embodiment,
• 3 an example of a turnover rate trend,
• 4 the combustion process with a conversion rate according to 3 and
• 5 a schematic representation of an internal combustion engine with exhaust system.

1 shows a control for a special combustion process, for example for the particle filter generation operation of a diesel engine. The control system comprises two separate control circuits 1, 2. A first control circuit 1 for the integral position of the combustion, i.e. the conversion rate area center of gravity, and a second control circuit 2 for the load, which is determined, for example, by the indicated mean effective pressure or the internal moment.

A total of two controllers are provided in the first control circuit 1. A first controller 3 is fed a control deviation from the setpoint value of the temperature upstream of the turbine as a reference variable and the actual value of the temperature upstream of the turbine as feedback. The temperature upstream of the turbine corresponds to the engine exhaust temperature of the exhaust gases exiting the internal combustion engine. With the help of the first controller 3, a correction value for the conversion rate area center of gravity is determined, via which the setpoint value of the conversion rate area center of gravity, which can be taken from a characteristic map, for example, is corrected. The current actual value of the conversion rate area center of gravity can be determined from the measured or modeled pressure curve using a thermodynamic model of the combustion chamber. The actual value of the conversion rate area center of gravity is compared with the corrected setpoint value, whereupon a second controller 4 changes an injection profile in accordance with the specifications. The injection profile can include the positions of the individual injections, such as the main injection and the post-injection. Furthermore, this can include the injection quantity distribution to the individual injections. For robust, transient operation, the control loop can be supplemented with a map-based or model-based feedforward control.

The first control circuit 1 changes the setpoint value of the conversion rate area center of gravity so that the desired temperature is regulated upstream of the turbine. The second control circuit 2 regulates the load. A third controller 5 is provided for this purpose. The control deviation for the third controller 5 is determined from the setpoint value of the load, for example in the indicated mean pressure, and the actual value of the load and is fed to the third controller 5. A total injection quantity is determined from this.

Since the two control loops 1, 2 are strongly coupled, the overall structure can be supplemented by a decoupling element 6. Here, based on the control deviation of the conversion rate area center of gravity, based on the corrected setpoint value of the conversion rate area center of gravity and the actual value of the conversion rate area center of gravity in the decoupling element 6, a pre-control can take place in order to correct the total injection quantity behind the third controller 5. The decoupling element can be a DT1 element, for example.

2 shows a regulation according to 1 , where corresponding elements are given the same reference numerals. In the regulation according to 2 However, no decoupling element is provided. Instead, a combustion model 8 is provided, which has the setpoints for the temperature before the turbine and for the load as input variables. A setpoint for the conversion rate area center of gravity is determined from the combustion model 8, as well as a pre-correction of the total injection quantity, so that the combustion model 8 serves not only to provide the setpoint but also to decouple the two control loops 1, 2.

3 shows an example of a conversion rate curve with a main injection and a post-injection, both of which are burned and thus converted and thus generate torque. The conversion rate curve is shown over the crank angle, whereby it can be seen that the main injection takes place at a crank angle just before 200° and the post-injection takes place between 225° and 250°. The corresponding combustion curve is shown in 4 The combustion curve indicates what percentage of the total injection quantity was converted or burned. In 3 The turnover rate area centre of gravity is also indicated. This is calculated based on the centre of gravity of the areas below the curve of the turnover rate. This lies between 200° and 225°. In 4 However, it can be seen that 50% of the injection quantity is converted at a position after 225°. The two values, i.e. the conversion rate area center of gravity and the position of the conversion of 50% of the fuel, are clearly different. If the injection quantity of the main injection were to be increased slightly and the injection quantity after injection were to be reduced accordingly, the curve of the combustion process would be as follows: 1 shift their saddle point 7. The saddle point 7 would rise, for example to a value above 0.5. Thus, the position of the turnover of 50% of the fuel would be shifted abruptly from over 225° to significantly below 225°. The turnover rate area center of gravity, on the other hand, would hardly change.

This makes it clear that using the turnover rate area center of gravity results in a much more stable and robust control.

5 shows schematically the structure of an internal combustion engine with an exhaust system 9. A diesel internal combustion engine 10 is connected to a first exhaust pipe 11, which leads to a turbine 12 of a turbocharger. The first exhaust pipe 11 can contain one or more exhaust manifolds in which the exhaust gas flows from various combustion chambers or cylinders of the diesel internal combustion engine 10 are brought together. Here Further components, such as EGR valves and branches, may also be provided.

The turbine 12 is connected via a second exhaust pipe 13 to an exhaust aftertreatment device in the form of an oxidation catalyst 14 and a particle filter 15. This is followed by a third exhaust pipe 16. Further components can be provided in both the second exhaust pipe 13 and the third exhaust pipe 16.

In order to regulate the temperature of the exhaust gas exiting the diesel internal combustion engine 10 in front of the turbine 12, which is usually designated T ₃ , in the first exhaust pipe 11, the aforementioned control circuits are provided.

list of reference symbols

1

first control loop (load)

2

second control loop (sales rate area center of gravity)

3

first controller

4

second controller

5

third controller

6

decoupling element

7

saddle point

8

combustion model

9

internal combustion engine with exhaust system

10

diesel engine

11

first exhaust pipe

12

turbine

13

second exhaust pipe

14

oxidation catalyst

15

particulate filter

16

third exhaust pipe

Claims (13)

Method for controlling the exhaust gas temperature of a direct-injection internal combustion engine (2), in which the combusting fuel injection is divided into several individual injections and in which the engine exhaust gas temperature (T ₃ ) of the exhaust gas emerging from the internal combustion engine (2) at a predetermined load (PMI) is controlled by controlling the conversion rate area center of gravity (UFS) and the total injection quantity (q _inj ) of all combusting fuel injections. procedure according to claim 1 , characterized in that a required temperature difference is determined from a predetermined target value of the engine exhaust temperature and a measured actual value of the engine exhaust temperature, and from this a correction value for the conversion rate area center of gravity (UFS) is regulated by means of a controller. procedure according to claim 2 , characterized in that a corrected target value of the turnover rate area centre of gravity (UFS) is determined from the correction value for the turnover rate area centre of gravity (UFS) and a target value of the turnover rate area centre of gravity (UFS). procedure according to claim 3 , characterized in that a difference value for the conversion rate area center of gravity (UFS) is determined from the corrected target value of the conversion rate area center of gravity (UFS) and an actual value of the conversion rate area center of gravity (UFS), and on the basis of this difference value, the position of the individual injections and/or the injection quantity distribution of the total injection quantity to the individual injections are regulated by means of a controller. Method according to one of the Claims 3 or 4 , characterized in that the target value of the conversion rate area center of gravity (UFS) is determined based on a characteristic map. Method according to one of the Claims 4 or 5 , characterized in that the actual value of the conversion rate area center of gravity (UFS) is determined by means of a combustion model or from measured pressure curves of the combustion chamber pressure. Method according to one of the preceding claims, characterized in that a required load difference is determined from a target value of the load and an actual value of the load and the total injection quantity is regulated from this by means of a controller. Method according to one of the preceding claims, characterized in that a correction value for the total injection quantity is regulated directly by means of a controller as a function of a difference value for the conversion rate area center of gravity (UFS), and a corrected total injection quantity is determined from this and the total injection quantity. Direct-injection internal combustion engine (2) with a control unit for controlling the engine exhaust temperature (T ₃ ) of an exhaust gas exiting the internal combustion engine (2) according to one of the preceding claims. Direct injection internal combustion engine according to claim 9 , characterized in that a turbocharger is provided and the engine exhaust temperature (T ₃ ) of the exhaust gas upstream of the turbine (4) of the turbocharger is controllable. Direct injection internal combustion engine according to claim 10 , characterized in that an exhaust gas aftertreatment device, in particular a particle filter (7), a NOx storage catalyst or an SCR catalyst, is provided, wherein a temperature required for the exhaust gas aftertreatment device can be set by regulating the engine exhaust gas temperature (T ₃ ). Direct injection internal combustion engine according to one of the Claims 9 until 11 , characterized in that at least one combustion chamber pressure sensor is provided for combustion position control. Direct injection internal combustion engine according to one of the Claims 9 until 12 , characterized in that a temperature sensor is provided for determining the engine exhaust temperature (T ₃ ) of the exhaust gas emerging from the internal combustion engine.

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