EP3023619B1 - 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

Description

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

In internal combustion engines, for example in Otto engines, in particular in highly charged Otto engines, knocking combustion can occur. This can lead to a reduction in output and lower combustion efficiency. In extreme cases, this can even lead to component damage.

In order to counteract or prevent knocking, it is known to move the ignition angle of the cylinder late. However, this degrades the combustion efficiency and the exhaust gas temperature rises. In order to counteract the higher thermal load on the exhaust system, the air-fuel mixture injected into the cylinder must, if necessary, be enriched, i.e. provided with a higher proportion of fuel. However, this can degrade fuel consumption, performance and emissions.

In order to reduce the tendency to knock, a fluid, for example water, is therefore added directly to the combustion chamber or to the fuel, as a result of which the cylinder charge is cooled when the fluid is evaporated. As a result, the ignition angle can be adjusted in the early direction, and fuel consumption and engine performance are improved.

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

The US 8,370,049 B1 Fig. 11 shows a method of controlling an engine that burns ammonia as fuel. This engine needs a second fuel to allow the ammonia to burn. The ratio of ammonia to the second fuel is, among other things, a function of one determined with a knock sensor measured knock strength. Independently of this, the ignition angle of the cylinder is set so that the exhaust gas temperature is in an optimal temperature range for a catalytic converter.

The DE 10 2012 207 904 A1 discloses a method for injecting water into a cylinder in response to the signal from a knock sensor.

In the DE 10 2008 003 581 A1 A method is shown in which the ignition angle of an engine is shifted early to carry out an advance ignition in order to bring about a suitable lowering of an exhaust gas temperature when the temperature of a component and / or the exhaust gas exceeds a threshold value assigned to it. It also shows which aspects can be used to determine an engine's tendency to knock in order to shift the ignition angle to advance and carry out the associated advanced ignition without triggering (significant) knocking.

However, new and tightened standards with regard to the emission control of combustion processes also require compliance with limit values for exhaust gas temperatures. The exhaust gas temperature can also be reduced by adding fluid. However, this requires that a certain amount of fluid must be kept permanently available in order to ensure an admixture of fluid. The exact amount of fluid depends on many different influencing variables, such as intake air temperature, engine temperature, fuel quality, component tolerances, for example with regard to compression in the cylinder, signal tolerances, for example when filling the cylinder, deposits in the combustion chamber and others. These influencing variables cannot be sufficiently pre-controlled or otherwise recorded. Therefore, a large amount of fluid must always be kept available, and the fluid consumption increases.

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

To achieve the object is a method for controlling combustion in an internal combustion engine, in particular an internal combustion engine in one

Motor vehicle, provided with at least one cylinder, the method having a step in which a knock intensity in the cylinder is detected by means of a knock sensor. According to the invention, in a further step, a predetermined target ignition angle of the cylinder, which corresponds to a target exhaust gas temperature, is set when a knocking effect occurs, the set target ignition angle being dependent on the knocking that occurs. In a further step, an admixture of fluid into the cylinder, that is to say the amount of fluid admixed to the fuel, is controlled as a function of the detected knock intensity.

The fluid can in particular be water, ethanol or another fluid that is suitable for lowering the combustion temperature of the fuel or the exhaust gas temperature. A cooling takes place through the evaporation enthalpy of the fluid in the cylinder. It is mixed into the cylinder by injecting the fluid directly into the fuel.

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

In this way, a fluid request can also be recognized earlier and the fluid can be reliably held. In this way, a dead time from a subsequent actual demand for the fluid can be reduced, and the fluid can be delivered to fluid injectors more quickly if necessary.

The control device can also determine a target amount of fluid to be mixed in, which is to be injected into the cylinder, at least based on the target exhaust gas temperature and / or on the detected knock intensity. To this In this way, a reserve amount of the fluid can already be determined 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 change in knock strength that occurs due to 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 brings about a predeterminable cooling of the exhaust gas temperature. The temperature reduction also reduces knocking. A predeterminable amount of fluid thus brings about a predeterminable reduction in knocking.

If the knocking is not reduced to a predetermined extent despite sufficient fluid addition, this can be determined in a control device and stored or output as an error message. Alternatively or in addition, the control device can output control commands, in particular to prevent damage, which, for example, in an acute case, cause a further increase in the fluid supply or cause the affected cylinder or the entire motor to be switched off.

This can be done analogously or additionally for a determination of the exhaust gas temperature before and after the fluid addition. Similarly or in addition, an ignition angle setting can also be checked for plausibility in this way, in particular if an added amount of fluid can be precisely defined. The method according to the invention can thus form a closed control loop.

To check the plausibility of the addition of fluid, the knock intensity can for example be detected with the knock intensity sensor before the addition of the fluid and after the addition of the fluid and stored in a storage device in the control device. Analogously, the calculated and / or the actually added fluid quantity, if this differs from the calculated fluid quantity, can be stored in the storage device. A comparator which carries out a comparison with predetermined values can be embodied in the control device. The predetermined values can, for example, in the form of a data table, also as a look-up table (LUT) referred to. In the event of 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 or engine-specific empirical values from fault-free operation.

The method according to the invention can have a selective detection of the knock intensity and / or a selective control of the fluid admixture in an internal combustion engine with a plurality of cylinders for each cylinder. In this way, knocking from one cylinder can be reduced in a targeted manner without impairing the performance and efficiency of the other cylinders. This can make it possible to reduce the amount of fluid held and to increase the efficiency of the internal combustion engine, in particular of the vehicle engine, at the knock limit.

The admixture of fluid, that is to say the amount of admixed fluid, can be reduced, for example, if a knock intensity is reduced in order to set the knock to a predetermined setpoint knock value. Correspondingly, the admixture of fluid can be increased when the knock intensity increases in order to set the knock to a predetermined setpoint knock value. In this way, a quick reaction to the current combustion characteristics can take place. In addition, an amount of fluid that is to be used for the combustion can be predetermined and a corresponding reserve amount of the fluid can be provided. In particular in cases in which the fluid is fed into the cylinder or into the fuel system directly into the fuel under high pressure, only a calculated amount of fluid needs to be pressurized. A higher efficiency of the entire internal combustion engine can thus also be achieved. In this way, by setting a specific or determinable knock intensity at the set ignition angle, improved compliance with the exhaust gas temperature limits can be made possible.

In a further developed method, the target knock intensity with an actual knock intensity and / or the target exhaust gas temperature with an actual exhaust gas temperature in compared to the control unit. Analogous to the above descriptions, the control device can run an error log at least in the event of a predetermined deviation between the setpoint and the actual value. Alternatively or additionally, the control device can output a corrective control signal.

The respective target values can 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 target values can also be the values determined by the control device that are certain set parameters are to be expected, for example the exhaust gas temperature for a predetermined ignition angle of the cylinder.

The control device can also compare an actually consumed amount of fluid and the target amount of fluid to be admixed. In the event that a discrepancy between the amounts of fluid thus compared is found, an error log can be carried out. A corrective control signal can also be output from the control device. The deviation can in particular be a predefined, for example a percentage, deviation of the values from one another. In this way, the fluid consumption can be checked for plausibility. In addition, a fault can be identified or a fault cause can be excluded if a fault occurs in the internal combustion engine. Furthermore, in this way it is also possible to adapt an amount of fluid that has to be kept available, depending on an actual fluid consumption.

An error log that can be carried out can contain, for example, the output of an error to an internal or an external diagnostic device. When using a motor vehicle, the diagnostic device can in particular be 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 the execution of the error log in the control device. This control signal can be a signal that increases or decreases the supply of fluid. It can also be a signal that adjusts the ignition angle, changes the fuel supply or completely deactivates the cylinder. The control signal can also be used as Part of a control loop for acute troubleshooting, for example to prevent damage, are output.

According to a further aspect of the invention, to achieve the object of the invention, a device for admixing 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 formed which is designed to carry out the method according to the invention and to determine an amount of fluid to be admixed, the metering device metering the determined amount of fluid into a fluid reservoir, a fuel system and / or an air intake system. A fluid line through which the fluid flows can also be understood as a fluid reservoir in the context of the invention.

This device makes it possible to predetermine an amount of fluid that is to be mixed in during a combustion process in a cylinder, as a result of which a reserve amount of the fluid can be precisely adapted to the predetermined consumption. In this way, consumption of fluid can be reduced. In addition, the amount of fluid that is kept available can be reduced.

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

The device can furthermore have a knock intensity sensor. In this case, the control device can be designed to determine the amount of fluid to be admixed at least based on a knock intensity detected by the knock intensity sensor. In this way, the amount of fluid can be adapted to the current combustion characteristics. This can allow improved control of the combustion process. This can also allow an amount of fluid that will be required in the future to be recorded in advance, since a higher knock intensity requires a higher admixture of fluid if the ignition angle is not to be adjusted.

The device can also have an exhaust gas temperature sensor. The control device can be designed in such a way that an ignition angle of the cylinder is controlled in such a way that an exhaust gas temperature lies within a predetermined temperature interval, in particular a predetermined exhaust gas temperature does not exceed. In this way, knocking can be reduced or set to a predetermined value without a violation of exhaust gas standards occurring. This makes it possible to reduce emissions, for example of nitrogen oxides. At the same time, the cylinder output and thus also the engine output can be better used. In this case, an adjustment of the fluid supply can enable an even finer adjustment of the knock intensity without exceeding or falling below the exhaust gas temperature threshold values.

The device according to the invention can have such a metering device or such a fluid reservoir for a plurality or all of the cylinders of an internal combustion engine. In some embodiments of the invention, with a plurality of cylinders, an individually controllable metering device or an individually fillable fluid reservoir can be formed for each cylinder. This allows each individual cylinder or a group of cylinders to be set separately. In this way, cylinder-specific characteristics, for example deposits, wear and tear, etc., can be taken into account when controlling and using 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 nicht unter die Erfindung fallenden Alternative;
• 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:

• Figure 1 a schematic view of a fluid injector system for an internal combustion engine according to an embodiment of the invention;
• Figure 2 a schematic view of a fluid injector system for an internal combustion engine according to an alternative not falling under the invention;
• Figure 3 a diagram to illustrate the time-dependent development of the fluid filling and the speed of the motor according to an embodiment of the invention.

Figure 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 comprises a fluid pump 11 which holds the fluid in reserve or which conveys the fluid into the fluid system 10 at a predeterminable pressure. The fluid pump 11 can also have a fluid reservoir for storing a predeterminable amount of fluid (not shown). The fluid is already at a pressure in the fluid system 10 applied, with which it is injected into a fuel system 50 or directly into a cylinder 30.

The fluid is conducted in the fluid system 10 through a fluid line 12 to a fluid injector 13. The fluid injector 13 can in particular be designed as a throttle valve. The fluid injector 13 connects in the in Figure 1 The embodiment shown is the fluid system 10 with an intake pipe 21 of an intake system of the cylinder 30. In this embodiment, the intake pipe 21 is a common intake pipe, or the plenum, of 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, designed here as a metering valve. The metering valve 14 connects the fluid system 10 to the fuel system 50. As a result, fluid is also injected from the fluid system 10 directly into the fuel of the internal combustion engine. In alternative embodiments, only the metering valve 14 can be embodied in the fluid system 10.

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

The fuel injector 41 injects the fluid-fuel mixture into the cylinder 30. In the present case, the cylinder 30 is a cylinder for four-stroke operation. In a first cycle, a piston 34 is adjusted via a connecting rod 35 by a crankshaft (not shown) in such a way that the free volume of the cylinder 30, that is to say its combustion chamber 31, increases. This creates a negative pressure. A Inlet valve 32 connects the combustion chamber 31 to the intake system 20. The air enriched with fluid enters the combustion chamber when the inlet valve 32 is opened. In a second stroke of the engine, the piston is adjusted in such a way that the combustion chamber is made smaller, and fuel is injected into the combustion chamber by the fuel injector 41. By reducing the size of the combustion chamber, the fuel, as well as the air and fluid supplied, are strongly compressed. In a third engine cycle, the compressed fuel mixture is ignited depending on the ignition angle of the cylinder. The piston is shifted downwards, overcomes a bottom dead center, and an exhaust valve 33 opens in a fourth cycle. The burned mixture is expelled through an exhaust pipe 36 by a further piston stroke.

A knock sensor 37 is also provided on the cylinder 30. The knock sensor 37 detects whether there is knocking combustion in the cylinder 30 or not. The knock sensor 37 is connected to the control device 60 and transmits the recorded data, that is to say whether there is a knocking combustion and, if applicable, its extent, to the control device 60.

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

Figure 2 shows an alternative which does not fall under the claimed invention. The same components are provided with the same reference numerals, and a repetition of their description is omitted at this point.

The alternative of Figure 2 differs from that in Figure 1 in that fluid injection is tracked through an aspiration tube. Each cylinder 30 of the engine has a separate intake pipe 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 in order to be able to hold a sufficient amount of fluid for the combustion process. In contrast, in the embodiment described above, the fluid supply for the individual cylinders was controlled separately via direct water injection (DWI) into the Fuel system and can be mapped accordingly in the control device 60.

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

Figure 3 shows a diagram which shows the fluid filling when required as a function of time. A comparison of the curves of the predicted target amount of fluid that is kept available for filling with the actually kept actual amount of fluid shows a time difference of approx. 1.5s until the actual level reaches the required target level. During the period in which there is a discrepancy between the target and actual level of the fluid, there is a risk of knocking combustion. The prediction according to the invention of the required amount of fluid at a specific load reduces the time required to match the target and actual fluid fill amounts, 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.

How also from Figure 3 As can be seen, the speed of the motor is greatly increased during the time delay between the fluid request and the actual supply of the fluid in order to compensate for the delay time in the admixing of the fluid and to achieve the desired output of the motor. This can in turn promote knocking combustion, especially in highly charged Otto 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 Figure 3 represents an example of the time-dependent development of the filling and the engine speed in a case of direct water injection, a similar course of the graphs can also be expected for the case of injection into the plenum 21 or directly into the respective cylinder intake manifolds.

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

All or part of this information can be taken into account by the control device, in particular in a case in which the fluid is applied to the injector, for the exact calculation of the injection time, the injection duration, the injection volume, etc. In addition, the detection of a current actual knock intensity can be processed in the control device in order to regulate the addition of fluid. For this purpose, a regulator (not shown here) can be configured in the control device, which is dependent on the actual knock intensity and / or the target knock intensity and / or the target or actual ignition angle and / or the target or actual exhaust gas temperature and / or other parameters determine a correction factor. The correction factor can then be taken into account in the calculation or in the regulation of the fluid filling in the control device.

The water can be filled with a fluid pump 11. To this end, the fluid pump 11 is connected to the control device 60. As soon as the control device 60 has determined the amount of fluid to be supplied or the setpoint rate of the fluid admixture, the fluid admixture is controlled. If necessary, the knock intensity is also regulated as described above. For this purpose, the control device issues a delivery command to the fluid pump 11, which then makes the fluid available accordingly.

The fluid pump 11 thus only conveys the fluid volume that is actually to be consumed, as a result of which fluid consumption is reduced and energy consumption for holding the fluid can be reduced.

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

If water is injected in the form of an admixture to the fuel, the fluid is preferably mixed in upstream of the high-pressure fuel pump in order to be able to manage with low fluid pressures. This is how the volume works of the high-pressure fuel system from the point at which the fluid is introduced to the injector tip as dead volume. When the water injection is started, this volume 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 be able to start adding water to the fuel early. For this, the parameters speed and load are predicted. Ideally in such a way that the fluid arrives in the combustion chamber when the actual speed and load have reached the value provided for in the map. In reality, the dead time can be reduced considerably.

The prediction of the speed is done by using the gradient of the actual speed to determine where the value would be in a certain time if the speed continues to change with the same gradient. When predicting the load, the target filling is used instead of the actual filling, which is built up with a delay via the exhaust gas turbocharger.

Claims (8)

1. Method for controlling a combustion in an internal combustion engine having at least one cylinder (30), having a fluid system (10), having a fuel system (50) and having a control device (60), wherein the method has the following steps:

   - detecting a knocking intensity in the cylinder (30) by means of a knocking sensor (37),

   - setting a predetermined setpoint ignition angle, corresponding to a setpoint exhaust-gas temperature, of the cylinder (30) in the event of the occurrence of a knocking effect, wherein the set setpoint ignition angle is dependent on the occurring knocking,

   - controlling an admixing of fluid into the cylinder, that is to say the quantity of fluid admixed to the fuel, in a manner dependent on the detected knocking intensity, wherein the fluid is dispensed by the fluid system (10) into the fuel system (50) directly into the fuel, and

   wherein the control device (60) determines a setpoint quantity of fluid for admixing at least on the basis of the setpoint exhaust-gas temperature and on the basis of the detected knocking intensity.
2. Method according to Claim 1, wherein a selective detection of the knocking intensity and selective control of the fluid admixing is performed for each cylinder (30).
3. Method according to either of the preceding claims, wherein fluid admixing is reduced if a knocking intensity decreases, and wherein fluid admixing is increased if the knocking intensity increases, in order to set a setpoint knocking intensity.
4. Method according to any of the preceding claims, wherein the setpoint knocking intensity is compared with an actual knocking intensity and/or the setpoint exhaust-gas temperature is compared with an actual exhaust-gas temperature, in the control device (60), and wherein, at least in the event of a predetermined deviation of setpoint and actual values, fault logging is performed by the control device (60), and/or a corrective control signal is output by the control device (60).
5. Method according to any of the preceding claims, wherein the control device (60) compares an actually consumed fluid quantity and the setpoint quantity of fluid for admixing, and, at least in the event of a predetermined deviation of the fluid quantities, fault logging is performed and/or a corrective control signal is output by the control device (60).
6. Device (1) for admixing a fluid to at least one cylinder (30) of an internal combustion engine, wherein the device has a fluid pump (11) and a dosing device (13, 14, 15), and wherein a control device (60) is designed to carry out the method according to any of the preceding claims and determine a quantity of fluid for admixing, wherein the dosing device (13, 14) doses the determined quantity of fluid into a fluid reservoir (15), a fuel system (50) and/or an air intake system (20), wherein the device (1) comprises an exhaust-gas temperature sensor and a knocking intensity sensor (37), and the control device (60) is designed to determine the quantity of fluid for admixing at least on the basis of a knocking intensity detected by the knocking intensity sensor (37).
7. Device (1) according to Claim 6, wherein the control device (60) is designed to control an ignition angle of the cylinder (30) such that an exhaust-gas temperature lies within a predetermined temperature interval, in particular does not overshoot a predetermined exhaust-gas temperature.
8. Device according to either of Claims 6 and 7, wherein, in the case of a multiplicity of cylinders (30), an individual dosing device (13, 14, 15) is formed for each cylinder (30).

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