EP3023619A1 - Adaptation of the amount of fluid in the system for injected additives of an internal combustion engine depending on the signal of the knock control - Google Patents

Abstract

In a method of controlling combustion in an internal combustion engine having at least one cylinder (30), a knocking strength in the cylinder (30) is detected by means of a knocking sensor (37). A predetermined target firing angle of the cylinder (30) corresponding to a target exhaust gas temperature is adjusted, and fluid addition to the cylinder (30) is controlled in dependence on the detected knock magnitude.

Description

The invention relates to a method for controlling a combustion in an internal combustion engine and an internal combustion engine with such controlled combustion.

In internal combustion engines, for example in gasoline engines, especially in highly-charged gasoline engines, knocking combustion can occur. This can result in power reduction and lower combustion efficiency. In extreme cases, this can even lead to component damage.

To counteract or prevent knock, it is known to retard the firing angle of the cylinder. As a result, however, the combustion efficiency deteriorates and the exhaust gas temperature increases. To counteract the higher heat load of the exhaust system, if necessary, the injected into the cylinder air-fuel mixture must be enriched, so be provided with higher fuel content. However, fuel consumption, performance, and emissions may degrade.

To reduce the tendency to knock, therefore, a fluid, such as water, is added directly into the combustion chamber or into the fuel, whereby the cylinder charge is cooled when the fluid is evaporated. As a result, the ignition angle can be adjusted toward early, and fuel consumption and performance of the engine improve.

The DE 31 42 729 A1 describes such a device for controlling an internal combustion engine as a function of the occurrence of knocking operations.

However, new and stricter emission control standards for combustion processes also require compliance with exhaust gas temperature limits. The exhaust gas temperature can through the Fluid addition can also be reduced. However, this requires that a certain amount of fluid must be kept permanently in order to ensure an admixture of fluid. The exact amount of fluid is dependent on many different factors, such as intake air temperature, engine temperature, fuel quality, component tolerances, for example, in terms of compression in the cylinder, signal tolerances, for example, during the filling of the cylinder, deposits in the combustion chamber and others. These factors can not be sufficiently pre-controlled or otherwise recorded. Therefore, always a large amount of fluid must be kept, and the fluid consumption increases.

It is therefore the object of the invention to provide a method and a device, with a reduced fluid consumption in the combustion control, at the same time a control of the exhaust gas temperature is possible, so that in particular exhaust gas temperature limits can be met.

To achieve the object, a method for controlling a combustion in an internal combustion engine, in particular an internal combustion engine in a motor vehicle, is provided, with at least one cylinder, wherein the method comprises a step in which a knock level is detected in the cylinder by means of a knock sensor. In a further step, a predetermined target ignition angle of the cylinder, which corresponds to a desired exhaust gas temperature, is set. In a further step, a fluid addition into the cylinder is controlled as a function of the detected knock intensity.

The fluid may in particular be water, ethanol or another fluid which is suitable for lowering the combustion temperature of the fuel or the exhaust gas temperature. Cooling takes place by the enthalpy of vaporization of the fluid in the cylinder. The admixture into the cylinder may be accomplished by injecting the fluid into the cylinder and / or injecting the fluid directly into the fuel.

According to the invention, a predetermined ignition angle is set when a knocking effect occurs, at which a certain exhaust gas temperature is reached. The dependence between the set ignition angle and the occurring knocking is preferably previously known and can be used in a control device, For example, the engine electronics, be deposited. The knocking effect can then be counteracted while maintaining a maximum exhaust gas temperature, for example, by targeted addition of fluid. Thus, a necessary amount of fluid can be better predetermined depending on the knock signal. This allows optimal use of the available fluid. In addition, the fluid consumption can be reduced, at the same time improved compliance with the exhaust gas temperature specifications can be achieved.

Also, such a fluid requirement can be detected earlier and the fluid can be kept reliably. Thus, a dead time can be reduced from a subsequent actual request of the fluid, and the fluid can be supplied to fluid injectors more quickly if necessary.

The controller may also determine a desired amount of fluid to inject into the cylinder based at least on the target exhaust gas temperature and / or on the detected knock level. In this way, a Vorhaltemenge of the fluid can be determined already on the basis of the detected signals.

As a result, a first plausibility check of the fluid consumption can be carried out by analyzing a fluid consumption and a knock strength change which takes place through the addition of fluid. A certain addition of fluid causes a predeterminable cooling of the cylinder charge and thus the combustion temperature in the cylinder. Consequently, this also causes a predeterminable cooling of the exhaust gas temperature. The temperature reduction also achieves a reduction in knocking. A predeterminable amount of fluid thus causes a predeterminable reduction in knocking.

If, despite sufficient fluid addition, a reduction in knocking does not occur to a predetermined extent, this may be determined in a controller and stored or output as an error message. Alternatively or additionally, the control device, in particular for the prevention of damage, issue control commands which, for example, cause a further increase in the fluid supply in the acute case or cause a shutdown of the affected cylinder or of the entire motor.

Analogously or additionally, this can be done for a determination of the exhaust gas temperature before and after the addition of fluid. Also analogously or additionally, a Zündwinkeleinstellung can be plausibility in this way, especially if an added amount of fluid can be defined exactly. The method according to the invention can thus form a self-contained control loop.

To check the plausibility of the addition of fluid, the knock intensity can be detected, for example, with the knocking strength sensor before the addition of the fluid and after the addition of the fluid, and stored in a memory device in the control device. Analogously, the calculated and / or the actually admixed amount of fluid, if different from the calculated fluid quantity, can be stored in the storage device. In the control device may be formed a comparator, which performs a comparison with predetermined values. The predetermined values can be present, for example, in the form of a data table, also referred to as a look-up table (LUT). With a predeterminable deviation of the actual values from the predetermined values, a predetermined sequence of a program, for example an error protocol, and / or the output of a corresponding control signal and / or further steps for error handling can then take place.

The data table can have theoretical values, general practical empirical values and / or cylinder-specific or engine-specific empirical values from trouble-free operation.

In an internal combustion engine having a plurality of cylinders, the method according to the invention can have a selective detection of the knock intensity for each cylinder and / or a selective control of the fluid admixture. Thus, a knock of a cylinder can be selectively reduced without affecting the performance and efficiency of other cylinders. This can make it possible to reduce the retained fluid quantity and to increase the efficiency of the internal combustion engine, in particular of the vehicle engine, at the knock limit.

The fluid admixture, that is the amount of admixed fluid, can be reduced, for example, if a knock intensity decreases in order to prevent this

Set knock to a predetermined desired knock value. Accordingly, the fluid addition may be increased as the knock intensity increases to set the knock to a predetermined desired knock value. In this way, a quick reaction to the current combustion characteristics can take place. In addition, an amount of fluid to be used for combustion may be predetermined, and a corresponding amount of reserve of the fluid may be provided. In particular, in cases where the fluid is added under high pressure in the cylinder or in the fuel system directly into the fuel, so only a calculated amount of fluid must be pressurized. Thus, a higher efficiency of the entire internal combustion engine can be achieved. Also can be made possible by setting a certain or determinable knock strength at the set ignition angle improved compliance with the exhaust gas temperature limits in this way.

In a further developed method, the nominal knock intensity can be compared with an actual knock strength and / or the setpoint exhaust gas temperature with an actual exhaust gas temperature in the control unit. The control unit can, analogously to the above descriptions, execute an error log at least in the case of a predetermined deviation from the setpoint and actual value. Alternatively or additionally, the control device can output a corrective control signal.

The respective desired values may in turn be theoretical values depending on various predetermined parameters, for example, a maximum permissible exhaust gas temperature independent of the ignition angle, a vehicle speed, an acceleration, etc. The desired values may also be the values determined by the control device certain set parameters are to be expected, for example, the exhaust gas temperature for a predetermined firing angle of the cylinder.

The controller may also compare an actual amount of fluid consumed and the desired amount of admixed fluid. In a case where a deviation of the fluid quantities thus compared is detected, an error log may be executed. A corrective control signal can also be output from the control device. The deviation may in particular be a predetermined, for example percentage, deviation of the Values of each other. In this way, a plausibility of the fluid consumption can take place. In addition, an error identification or the exclusion of a cause of error can take place when an error occurs in the internal combustion engine. Furthermore, in this way, an amount of fluid can be adjusted, which must be kept depending on an actual fluid consumption.

An error log that may be performed may include, for example, issuing a fault to an internal or external diagnostic device. When using a motor vehicle, the diagnostic device may be in particular an on-board diagnostic device (OBD).

A control signal of the control device, which can be output due to the occurrence of an error, can also be output in the context of execution of the error log in the control device. This control signal may be a signal that increases or decreases the fluid supply. It can also be a signal that adjusts the ignition angle, changes the fuel supply or completely deactivates the cylinder. The control signal may also be output as part of an acute fault correction loop, for example, to prevent damage.

According to a further aspect of the invention, to achieve the object of the invention, an apparatus for adding a fluid to at least one cylinder of an internal combustion engine is provided with a fluid pump and a metering device. In the device, a control device is embodied, which is designed to determine a quantity of admixing fluid, wherein the metering device meters the specific amount of fluid into a fluid reservoir, a fuel system and / or an air intake system. In the context of the invention, a fluid reservoir can also be understood as a fluid conduit through which the fluid flows.

This apparatus makes it possible to predetermine an amount of fluid to be mixed in a cylinder in a combustion process, whereby a reserve amount of the fluid can be accurately adjusted to the predetermined consumption. Thus, a consumption of fluid can be reduced. In addition, the amount of fluid held can be reduced.

The fluid reservoir can also be formed by a fluid line or by a fluid pump.

The device may further include a knock strength sensor. In this case, the control device may be configured to determine the amount of fluid to be admixed at least based on a knock intensity detected by the knocking strength sensor. Thus, the amount of fluid can be adapted to the current combustion characteristics. This may allow for improved control of the combustion process. This can also allow a fluid amount that is needed in the future to be detected in advance, since a higher knock strength requires a higher admixture of fluid, if the ignition angle is not to be adjusted.

The device may also include an exhaust gas temperature sensor. In this case, the control device may be configured such that an ignition angle of the cylinder is controlled such that an exhaust gas temperature is within a predetermined temperature interval, in particular does not exceed a predetermined exhaust gas temperature. In this way, knocking can be reduced or set to a predetermined value without violating emission standards. This can be achieved to reduce emissions, such as nitrogen oxides. At the same time, the cylinder output and thus also the engine power can be better utilized. An adjustment of the fluid supply can in this case allow an even finer adjustment of the knock level, without the exhaust gas temperature thresholds are exceeded or fallen below.

The device according to the invention can have such a metering device or a fluid reservoir for a plurality or all cylinders of an internal combustion engine. In some embodiments of the invention, for a plurality of cylinders, an individually controllable metering device or an individually fillable fluid reservoir may be formed for each cylinder. This allows each cylinder or group of cylinders to be adjusted separately. Thus, cylinder-specific characteristics, such as deposits, wear, etc., can also be taken into account in the control and use of the cylinder.

• Figur 1 eine schematisches Ansicht eines Fluidinjektorsystems für einen Verbrennungsmotor gemäß einer Ausführungsform der Erfindung;
• Figur 2 eine schematische Ansicht eines Fluidinjektorsystems für einen Verbrennungsmotor gemäß einer Ausführungsform der Erfindung;
• Figur 3 ein Diagramm zur Darstellung der zeitabhängigen Entwicklung der Fluidbefüllung und der Drehzahl des Motors gemäß einer Ausführungsform der Erfindung.

Further advantages and features can be found in the following description in conjunction with the accompanying figures. In these show:

• FIG. 1 a schematic view of a Fluidinjektorsystems for an internal combustion engine according to an embodiment of the invention;
• FIG. 2 a schematic view of a Fluidinjektorsystems for an internal combustion engine according to an embodiment of the invention;
• FIG. 3 a diagram illustrating the time-dependent development of the fluid filling and the rotational speed of the motor according to an embodiment of the invention.

FIG. 1 1 shows a schematic drawing of a fluid injector system 1. The fluid injector system 1 has a fluid system 10. The fluid system 10 includes a fluid pump 11 that holds the fluid or that delivers the fluid into the fluid system 10 at a predeterminable pressure. The fluid pump 11 may further include a fluid reservoir for storing a predeterminable amount of fluid (not shown). The fluid is already pressurized in the fluid system 10 with which it is injected into a fuel system 50 or directly into a cylinder 30.

The fluid is directed in the fluid system 10 through a fluid conduit 12 to a fluid injector 13. The fluid injector 13 may be designed in particular as a throttle valve. The fluid injector 13 connects in the in FIG. 1 In this embodiment, the intake pipe 21 is a common intake pipe, or the plenum, an internal combustion engine, in particular an internal combustion engine of a motor vehicle. The fluid injector 13 thus injects the fluid into the intake air of the engine. The fluid injector 13 is therefore also referred to as a plenum injection valve in this embodiment.

In addition, the fluid system 10 has a further fluid injector 14, here designed as a metering valve. The metering valve 14 connects the fluid system 10 to the fuel system 50. This allows fluid from the fluid system 10 to be injected directly into the fuel of the internal combustion engine. In alternative Embodiments, only the fluid injector 13 or only the metering valve 14 may be formed in the fluid system 10.

The fluid injector system 1 also has a control device 60. The control device 60, which in particular includes or represents the digital engine electronics, is connected via control lines 61 to the fluid injector 13 or to the metering valve 14. Furthermore, the control device 60 is connected to a high-pressure pump 51 of the fuel system 50. In this way, fuel delivery through a fuel line 53 and admixture of fluid through the metering valve 14 may be controlled, and a fluid-fuel mixture may be delivered via a supply line 52 to fuel injectors 41. The fuel injectors 41 are connected in the embodiment shown with a rail device 40, as known to those skilled in the art.

The fuel injector 41 injects the fluid-fuel mixture into the cylinder 30. The cylinder 30 is presently a cylinder for a four-stroke operation. In a first cycle, a piston 34 is adjusted via a connecting rod 35 by a crankshaft, not shown, such that the free volume of the cylinder 30, that is to say its combustion space 31, increases. This creates a negative pressure. An intake valve 32 connects the combustion chamber 31 to the intake system 20. The fluid-enriched air enters the combustion chamber when the intake valve 32 is opened. In a second cycle of the engine, the piston is adjusted so that the combustion chamber is reduced, and fuel is injected from the fuel injector 41 into the combustion chamber. By reducing the size of the combustion chamber, the fuel as well as the supplied air and the supplied fluid is highly compressed. In a third engine cycle, the ignition of the compressed fuel mixture is dependent on the ignition angle of the cylinder. The piston is displaced downwards, overcomes a bottom dead center, and in a fourth cycle, an exhaust valve 33 opens. Through a further piston stroke, the combusted mixture is expelled through an exhaust pipe 36.

On the cylinder 30, a knock sensor 37 is further provided. The knock sensor 37 detects whether or not there is a knocking combustion in the cylinder 30. The knock sensor 37 is connected to the control device 60 and transmits the detected data, ie whether a knocking Combustion and, where appropriate, their dimensions, to the control device 60th

Furthermore, a flow sensor, not shown here, may be formed in the fluid system 10, which detects a fluid volume which is transported through the fluid system to the fluid injector 13 and / or to the metering valve 14.

FIG. 2 shows an alternative embodiment of the present invention. The same components are provided with the same reference numerals, and a repetition of their description is omitted at this point.

The embodiment of the FIG. 2 is different from the one in FIG. 1 in that a fluid injection takes place via an intake pipe 22. In this case, each cylinder 30 of the engine has a separate intake pipe 22, so that a fluid injection takes place separately for each cylinder 30. The individual injectors 13 are supplied with fluid via a common plenum 15. The plenum 15 serves as the fluid reservoir to hold a sufficient amount of fluid for the combustion process can. In contrast, a separate control of the fluid supply for the individual cylinders was carried out in the previously described embodiment via a direct injection of water (DWI) into the fuel system and can be mapped accordingly in the control device 60.

In principle, the injection into the intake manifold is possible, similar to the embodiment according to FIG. 1 ,

FIG. 3 shows a diagram illustrating the fluid filling in case of need as a function of time. A comparison of the curves of the predicted desired fluid quantity, which is kept for the filling, with the actually held actual amount of fluid shows a time difference of about 1.5 seconds until the actual level reaches the required target level. In the period in which a discrepancy between the desired and actual level of the fluid, there is a risk of knocking combustion. Due to the prediction according to the invention of the required amount of fluid at a given load, the time for equalizing the desired and actual fluid filling quantity is reduced, and the risk of knocking combustion can be reduced. In this way, it is also possible to react faster and more flexibly to load changes.

As well as out FIG. 3 As can be seen, the speed of the engine is greatly increased during the time delay between requesting the fluid and actually providing the fluid to compensate for the delay time in the admixture of the fluid and to achieve the desired performance of the engine. This can in turn favor a knocking combustion, especially in highly charged gasoline engines. The load on the engine is increased. If the predicted amount of fluid is available, the increase in speed can be reduced. The load on the engine is reduced.

While FIG. 3 As an example of the time-dependent development of the filling and the speed of the engine in a case of direct water injection, a similar graph of the graphs is also to be expected for the case of injection into the plenum 21 or directly into the respective cylinder intake pipes 22.

Further, as not shown in the figures, in such a fluid injector system 1, a sensor for detecting the fuel quality and / or the engine temperature and / or the intake air temperature or the like may be further provided. Alternatively or additionally, this information can also be stored and / or collected in the control device. It is also conceivable that the current speed of the engine is detected. In addition, a predicted rotational speed of the engine and a predicted fluid filling can be stored or stored in the control device.

All or part of this information can, in particular in a case in which the fluid rests against the injector, be taken into account for the exact calculation of the injection time, the injection duration, the injection volume etc. by the control device. In addition, the detection of a current actual knock level in the control device can be processed in order to regulate a fluid admixture. For this purpose, a controller (not shown here) may be formed in the control device, which depends on the actual knock intensity and / or the nominal knock intensity and / or the desired or actual ignition angle and / or the target or actual exhaust gas temperature and / or other parameter determines a correction factor. The correction factor can then be used in the calculation or be taken into account in the regulation of the fluid filling in the control device.

The water can be filled by a fluid pump 11. The fluid pump 11 is for this purpose connected to the control device 60. Once the control device 60 has determined the amount of fluid to be supplied or the desired rate of fluid addition, the control of the fluid addition takes place. If necessary, then also the control of the knock strength, as described above. For this purpose, the control device outputs a delivery command to the fluid pump 11, which then provides the fluid accordingly.

The fluid pump 11 thus only promotes the actual volume of fluid to be consumed, thereby reducing fluid consumption and reducing power consumption for holding the fluid.

To FIG. 3 It should be noted that the required amount of water is mainly dependent on speed and load (and thus on the filling). Corrections for temperatures and fuel quality are only added as an offset.

When water in the form of an admixture is injected to the fuel, it is preferable to mix the fluid in front of the high-pressure fuel pump in order to manage with low fluid pressures. As a result, the volume of the high-pressure fuel system from the point of introduction of the fluid to the injector tip acts as a dead volume. At the start of the water injection, these volumes must first be flushed via the internal combustion engine before the fluid arrives in the combustion chamber and takes effect there.

In order to reduce the effective dead time, one tries to look into the future in order to prematurely start adding water to the fuel. For this purpose, the parameters speed and load are predicted. Ideally, so that the fluid arrives in the combustion chamber when the actual speed and load have reached the value provided in the map for this purpose. In reality, you can significantly reduce dead time.

The prediction of the rotational speed is made by determining, via the gradient of the actual rotational speed, where the value would lie in a certain time, if the rotational speed continues to change with the same gradient. at the prediction of the load is used instead of the actual charge, which is built up delayed over the exhaust gas turbocharger, the target filling.

Claims (10)

A method of controlling combustion in an internal combustion engine having at least one cylinder (30), the method comprising the steps of: Detecting a knocking strength in the cylinder (30) by means of a knocking sensor (37), - Setting a desired target exhaust gas temperature corresponding predetermined target ignition angle of the cylinder (30) and Controlling a fluid admixture into the cylinder (30) in dependence on the detected knock intensity. The method of claim 1, wherein a controller (60) determines a desired amount of fluid to inject into the cylinder (30) based at least on the target exhaust temperature and / or the detected knock magnitude. Method according to one of claims 1 or 2, wherein for each cylinder (30) there is a selective detection of the knock intensity and / or a selective control of the fluid addition. The method of any one of the preceding claims, wherein fluid addition is reduced when knock magnitude decreases and wherein fluid addition is increased as knock magnitude increases to set a desired knock level. Method according to one of the preceding claims, wherein the target knock intensity is compared with an actual knock strength and / or the target exhaust gas temperature with an actual exhaust gas temperature in the control device (60) and wherein by the control device (60) at least in the case of a predetermined Deviation from the setpoint and actual value, an error log is executed and / or a corrective control signal is output from the control device (60). Method according to one of the preceding claims, wherein the control device (60) compares an actually consumed amount of fluid and the desired amount of admixed fluid and at least in the case of a predetermined deviation of the fluid quantities executed an error log and / or a corrective control signal is output from the control device (60). Apparatus (1) for admixing a fluid to at least one cylinder (30) of an internal combustion engine, the apparatus comprising a fluid pump (11) and a metering device (13, 14, 15) and wherein a control device (60) is designed to accumulate an amount to determine admixing fluid, wherein the metering device (13, 14) metered the specific amount of fluid in a fluid reservoir (15), a fuel system (50) and / or an air intake system (20). The apparatus (1) of claim 7, wherein the apparatus (1) further comprises a knock strength sensor (37), and the controller (60) is configured to increase the amount of fluid to be mixed based at least on a knock magnitude sensed by the knock strength sensor (37) determine. Device (1) according to one of claims 7 or 8, wherein the device (1) further comprises an exhaust gas temperature sensor, and the control device (60) is adapted to control an ignition angle of the cylinder (30) such that an exhaust gas temperature within a predetermined Temperature interval is, in particular does not exceed a predetermined exhaust gas temperature. Device according to one of claims 7 to 9, wherein in a plurality of cylinders (30) for each cylinder (30) an individual metering device (13, 14, 15) is formed.

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