DE102012020706A1 - Method for operating internal combustion engine i.e. diesel engine, for passenger car, involves varying preinjection based on signal characterizing temperature of internal combustion engine - Google Patents

Abstract

The method involves carrying out pre-injections of predeterminable preinjection of fuel into a corresponding combustion chamber of an internal combustion engine before main injections adjacent to the pre-injections by an injection element. The preinjection is varied in time compared with the following pre-injections. The preinjection is varied based on a signal characterizing temperature of the combustion engine. Larger preinjection of the fuel at certain value of temperature is injected in relation to another value of temperature, where the latter value is greater than the former value.

Description

The invention relates to a method for operating an internal combustion engine according to the preamble of patent claim 1.

From the general state of the art, it is known to operate internal combustion engines, in particular diesel engines, for motor vehicles in such a way that fuel is injected into a corresponding combustion chamber of the internal combustion engine by means of at least one injection element, which is also commonly referred to as an injector.

If the internal combustion engines, as is the case in particular with diesel engines, have high compression pressures, it may - if no appropriate countermeasures are taken - result in combustion noise which is perceptible, for example, in the interior of the motor vehicle by vehicle occupants and is perceived as unpleasant.

In order to keep these combustion noises low, it is known, by means of the injection element during operation of the internal combustion engine, to carry out pre-injections of a respective predefinable pre-injection quantity of fuel into the corresponding combustion chamber before respective respective main injections following the pre-injections. Such a pilot injection is usually also referred to as pilot injection.

Such a method for operating an internal combustion engine, in which such pilot injections are performed, is for example the DE 103 15 817 A1 to be known as known. In this method, the pilot injection quantity is varied on the basis of a first of the pilot injections in comparison to a temporally following of the pilot injections. In other words, in a first of the pre-injections, which is carried out in time before a corresponding, first of the main injections, a first pre-injection amount of fuel is injected into the combustion chamber. In a subsequent to the first pilot injection, second pilot injection, which is performed in time after the first main injection and in time before a corresponding, the second of the main injections, a second pilot injection quantity of fuel is injected into the combustion chamber. In this case, the first and the second pilot injection amount are different from each other. This means that in the second pilot injection, a smaller or larger pilot injection quantity is injected into the combustion chamber than in the first pilot injection.

It has been found that in such methods for operating internal combustion engines - if no appropriate measures are taken - to misfires due to a delayed or lack of combustion in the combustion chamber, increased emissions, speed fluctuations especially at idle the internal combustion engine as well as unpleasant noises in particular Idle can come. Furthermore, it has been found that a so-called dying of the internal combustion engine can occur because it can no longer overcome the frictional and / or applied loads. Moreover, due to bad burns, undesirably high main injection amounts of the fuel in the main injections may occur, which is caused by a control unit for controlling and / or controlling the internal combustion engine, resulting in deterioration of the combustion.

It is therefore an object of the present invention to develop a method for operating an internal combustion engine of the type mentioned in such a way that the problems mentioned can be avoided.

This object is achieved by a method for operating an internal combustion engine having the features of patent claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the remaining claims.

In order to provide a method for operating an internal combustion engine, in particular for a motor vehicle, of the type indicated in the preamble of patent claim 1, by which said problems can be avoided, it is provided according to the invention that the pre-injection quantity varies as a function of a signal characterizing a temperature of the internal combustion engine becomes. In other words, the pilot injection quantity, which may also be referred to as a pilot injection quantity, varies depending on the temperature, which is referred to as a temperature-dependent adaptation of the pilot injection quantity. As a result, the pre-injection amount can be adapted to the temperature of the internal combustion engine, so that it can not come to the initially described problems such as misfires, increased emissions, speed fluctuations, unwanted noise, autonomous engine shutdown and undesirably high main injection rates due to not matched to the temperature pre-injection quantities. It has been shown that the above-mentioned problems, especially at cold temperatures of the internal combustion engine and thus occur during a cold start this. These problems can now be avoided due to the temperature-dependent adjustment of the pilot injection.

In an advantageous embodiment of the invention, a movement signal, in particular an acceleration, of a piston of the internal combustion engine recorded in the combustion chamber is used as the signal. The variation or adaptation of the pilot injection quantity is preferably carried out so that - if the internal combustion engine has a plurality of combustion chambers - combustion chamber selectively the motion signal and thus the motion or acceleration behavior of the piston is evaluated. For this purpose, for example, a speed change of a shaft of the internal combustion engine coupled to the piston in a region of a bottom dead center of the piston is compared with a speed change in a region of a top dead center of the piston, in particular during one revolution of the shaft. On the basis of the comparison can be drawn conclusions about a quality of combustion in the combustion chamber, for example, the pilot injection is varied depending on the quality of combustion. The quality of combustion can be dependent on the temperature in the combustion chamber.

If an incorrect movement behavior of the piston in the corresponding combustion chamber is detected by this comparison, then the pre-injection quantity can be varied as a result in order to bring about a desired movement or acceleration behavior of the piston.

For this purpose, it is provided in one embodiment of the invention that based on the comparison of the speed changes, a movement of the piston characterizing actual value is determined, which is compared with a predetermined, the movement characterizing target value, wherein the pilot injection in dependence on the comparison Actual value is varied with the target value. The predefinable desired value can be calculated, for example, by means of a model.

In a particularly advantageous embodiment of the invention, it is provided that at least a first value of the temperature, a larger pilot injection quantity of the fuel is injected than at least one, compared to the first value higher, second value of the temperature. In other words, at lower temperatures of the internal combustion engine, higher pilot injection quantities of the fuel are injected than, on the other hand, higher temperatures. As a result, the movement behavior of the piston and the behavior of the internal combustion engine can be adapted to a desired desired behavior in a temperature-adapted manner. As a result, misfires can be avoided and hydrocarbon emissions of the internal combustion engine can be kept particularly low. Furthermore, it is possible, in particular in a cold operation, d. H. during a warm-up phase of the internal combustion engine, to avoid speed fluctuations of its shaft. In addition, the internal combustion engine also during cold operation an advantageous noise behavior due to only low combustion noise as well as quiet running, especially idle on.

The internal combustion engine may in particular be designed as a reciprocating internal combustion engine and comprise as a shaft crankshaft, with which the piston is coupled via a connecting rod. The combustion chamber is a cylinder of the reciprocating internal combustion engine.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and with reference to the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Serve 1 and 2 to explain the background of the invention.

The drawing shows in:

1 a diagram with six curves, which illustrate respective accelerations of pistons in respective combustion chambers of an internal combustion engine, wherein in two of the six combustion chambers to an undesirable combustion behavior comes;

2 another diagram illustrating respective combustion and pressure curves in the respective combustion chambers;

3 the diagram according to 1 wherein the undesirable combustion behavior in the two combustion chambers is avoided due to a temperature-dependent variation of a pilot injection quantity of pilot injections; and

4 a diagram for illustrating respective combustion and pressure curves in the combustion chambers according to 3 ,

Based on 1 to 4 In the following, a method for operating an internal combustion engine for a motor vehicle, in particular a passenger car, is explained. The internal combustion engine is designed as a reciprocating internal combustion engine and includes six combustion chambers in the form of cylinders in which burns occur during a fired operation of the internal combustion engine. For this purpose, the internal combustion engine sucks in air, which flow into the cylinder. The cylinders are each assigned an injection element. The injection element is also commonly referred to as an injector and serves to inject a liquid fuel in the respective associated cylinders. The internal combustion engine is, for example, a diesel engine, so that the liquid fuel is present as diesel fuel.

By injecting the fuel into the cylinders, a respective fuel-air mixture is formed in the cylinders, which burns as a result of ignition. This ignition can be done in a diesel engine without a spark plug and as a result of compression of the respective fuel-air mixture in the cylinder.

In the cylinders, a respective piston is arranged, which can move translationally relative to the corresponding cylinder. The piston is used in particular to compress the respective fuel-air mixture and to transfer forces resulting from the combustion and from an associated expansion of the fuel-air mixture to an output shaft in the form of a crankshaft of the internal combustion engine. For this purpose, the pistons are pivotally coupled via a respective connecting rod with the crankshaft, so that the translational movements of the pistons in the cylinders can be converted into a rotational movement of the crankshaft.

In order to provide a presettable by the driver of the motor vehicle torque via the crankshaft, a corresponding amount of fuel is injected by means of the respective injection element in the respective cylinder. In order to keep combustion noises particularly low, respective pre-injections of fuel into the cylinders are carried out before the respective so-called main injections of fuel into the cylinders during the fired operation of the internal combustion engine. As part of the main injections, a respective main injection quantity of fuel is injected into the associated cylinder by means of the respective injection element. The main injections have in particular the purpose of causing the torque given by the driver.

As part of the pilot injections, a respective pre-injection quantity of fuel is injected into the respective associated cylinder by means of the respective injection element. The pre-injections serve in particular the purpose of keeping the combustion noise in a small frame.

1 now shows a diagram 10 , on the abscissa 12 a variable is plotted, above the respective, by gradients 14a -F in the diagram 10 illustrated accelerations of the pistons are plotted in the cylinders. For example, this variable is the time. The running variable may also be a degree of crank angle, which characterizes the rotational movement of the crankshaft. On the ordinate 16 of the diagram 10 For example, another variable may be plotted to characterize the burns in the cylinders.

Like the progressions 14a -F can be seen, it comes - if no appropriate countermeasures are taken - to one in the diagram 10 through a body 18 illustrated point despite the performance of a pilot injection and a subsequent main injection into the respective cylinders that in two of the six cylinders no or only sporadic burns occur. The history 14a Characterized by the corresponding acceleration the burns in a first of the cylinders, during the course 14b characterized by the acceleration of the burns in a second of the cylinders. Accordingly, the course characterizes 14c about the acceleration of the corresponding piston the burns in a third of the cylinders, the course 14d about the acceleration of the corresponding piston the burns in a fourth of the cylinders, the course 14e about the acceleration of the corresponding piston the burns in a fifth of the cylinder and the course 14f about acceleration of the corresponding piston burns in the sixth cylinder. As based on the gradients 14b and 14c it can be seen, it comes in the place 18 not in the second cylinder and in the third cylinder only sporadic burns. In the other cylinders, the burns run off as desired.

The courses 14a -F illustrate the accelerations in the cylinders during a so-called cold operation of the internal combustion engine, ie during a warm-up this time after a cold start, with the internal combustion engine is idling.

This undesirable acceleration and thus combustion behavior is also based on 2 illustrated. 2 shows a diagram 20 , on the abscissa 22 the crank angle of the Crankshaft is applied. On the ordinate 24 of the diagram 20 the pressure in the unit bar is plotted in the respective cylinders as well as values for the respective combustion process in the cylinders.

courses 26 in the diagram 20 illustrate a respective combustion history in the first, in the fourth, in the fifth and in the sixth cylinder, while a course 28 illustrates the evaporation of the main injection. Accordingly, courses illustrate 30 in the diagram 20 a respective pressure curve in the first, in the fourth, in the fifth and in the sixth cylinder, during courses 32 illustrate a respective pressure profile in the second and in the third cylinder. As in 2 through a straight line 34 is illustrated, it is due to the sporadic or incipient combustion in the second and third cylinder to a respective combustion and pressure curve, which differs significantly from the combustion and pressure curves in the first, the fourth, the fifth and the sixth cylinder. In other words, the second and third cylinders do not burn while the remaining cylinders are burning cleanly, ie, desirably burning.

As a result of these undesirable combustion behaviors in the second and third cylinders, there may be increased emissions, speed variations, undesirable noise, and increased fuel consumption, particularly during cold operation. In addition, it can come to a dying of the internal combustion engine due to excessive friction and high external loads.

In order to avoid these problems now, it is provided that the pre-injection quantity is varied depending on the temperature. In other words, the pilot injection quantity is varied starting from a first of the pilot injections in comparison to a temporally following one of the pilot injections as a function of a signal characterizing a temperature of the internal combustion engine.

This means, for example, that during a first of the pre-injections, which is carried out in time before a corresponding first of the main injections, a first pilot injection quantity of fuel is injected into the cylinders. In a subsequent to the first pilot injection, second pilot injection, which is performed in time after the first main injection and in time before a corresponding, the second of the main injections, a second pilot injection quantity of fuel is injected into the combustion chamber. In this case, the first and second pilot injection quantities differ from one another, the different pilot injection quantities being set as a function of the temperature.

If the internal combustion engine thus has a low temperature, the pilot injection quantity is increased in comparison with the higher temperatures of the internal combustion engine. This variation of the pilot injection takes place cylinder-selectively, d. H. for each of the cylinders individually or independently of the corresponding other cylinders. Thus, any combustion behavior in the respective cylinder can be taken into account.

3 shows the diagram 10 according to 1 with the courses 14a -F, where, unlike 1 a temperature-dependent variation, ie adaptation, of the pilot injection quantities is performed. As the Fig. 14a -F can be seen, so the undesirable and unfavorable combustion behavior of the second and third cylinder can be avoided.

This is also based on 4 recognizable which the diagram 20 with the courses 26 . 28 . 30 . 32 shows, with the gradients 26 . 28 . 30 . 32 now with the progressions 14a -F according to 3 correspond. As 4 can be seen, correspond to the gradients 28 of the second and third cylinders now at least substantially the courses 26 of the first, fourth, fifth and sixth cylinders. Correspondingly, the courses also correspond 32 of the second and third cylinders at least substantially the courses 30 the first, the fourth, the fifth and the sixth cylinder. In other words, all cylinders burn clean.

The variation of the pilot injection quantity takes place, for example, in such a way that a pre-injection output quantity stored, for example, in a characteristic map or the like, is corrected by a correction quantity. This is carried out, for example, such that a factor which is 1, for example, corresponds to the pre-injection output quantity. In order to increase the pre-injection amount, the factor is increased. For example, to reduce the pilot injection amount from the pilot injection output amount, the factor is reduced.

Alternatively or additionally, the variation, ie the adaptation of the pilot injection quantity, can take place in the manner described below: in a first step, a correction value for the pilot injection quantity is learned. In a second step, this correction value is stored as a function of the temperature and used in a renewed start of the internal combustion engine as a pilot control value for the pilot injection quantity. New correction values are permanently taught in as long as at least one predefinable condition for this teach-in is fulfilled. This means that several, taught-in correction values or correction quantities are used instead of one once learned correction value permanently is used for adaptation. As a result, a particularly advantageous adaptation is possible.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10315817 A1 [0005]

Claims (5)

Method for operating an internal combustion engine, in particular for a motor vehicle, in which by means of at least one injection element pre-injections of a respective predetermined pilot fuel quantity in a corresponding combustion chamber of the internal combustion engine in time before respective, following the pilot injections main injections are performed, the pilot injection starting from a the pilot injection is varied in comparison with a temporally following of the pilot injections, characterized in that the pilot injection quantity is varied in dependence on a signal characterizing a temperature of the internal combustion engine. Method according to Claim 1, characterized in that the signal used is a movement signal characterizing a movement, in particular an acceleration, of a piston of the internal combustion engine accommodated in the combustion chamber. A method according to claim 2, characterized in that for generating the motion signal, a speed change of a shaft of the internal combustion engine coupled to the piston in a region of a bottom dead center of the piston is compared with a speed change in a region of a top dead center of the piston. A method according to claim 3, characterized in that based on the comparison, an actual value is determined, which is compared with a predetermined target value, wherein the pilot injection quantity is varied in dependence on the comparison of the actual value with the desired value. Method according to one of the preceding claims, characterized in that at least a first value of the temperature, a larger pre-injection amount of the fuel is injected than at least one, compared to the first value higher, second value of the temperature.

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