METHOD FOR REMOVING CONTAMINATION FROM A COMBUSTION CHAMBER PRESSURE SENSOR

Description

[0001] The invention relates to a method for operating an internal combustion engine, as well as an internal combustion engine, in particular a diesel engine, according to the preamble of the independent patent claims.

[0002] Current and increasingly stringent emissions legislation places high demands on raw engine emissions and exhaust aftertreatment in internal combustion engines. The demands for further reduced fuel consumption and the further tightening of emissions standards regarding permissible nitrogen oxide emissions pose a challenge for engine developers. In gasoline engines, exhaust gas purification is achieved in the usual way via a three-way catalyst, as well as additional catalysts upstream and downstream of the three-way catalyst. Diesel engines currently use exhaust aftertreatment systems that include an oxidation catalyst or NOx storage catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), a particulate filter for the separation of soot particles, and possibly additional catalysts. Ammonia is the preferred reducing agent.Because handling pure ammonia is complex, vehicles typically use a synthetic, aqueous urea solution that is mixed with the hot exhaust stream in a mixing device upstream of the SCR catalyst. This mixing heats the aqueous urea solution, releasing ammonia into the exhaust duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water. In addition to the emissions of the limited exhaust components, there is still a demand for further reductions in fuel consumption of combustion engines and an increase in thermal efficiency. To further improve and monitor the combustion process, more precise information about the combustion process is needed. For qualitative information, such as checking for the presence of pre-injection, knock sensors are currently the preferred means of providing structure-borne noise sensors.However, controlling the combustion process requires quantitative information on the energy released via the crank angle of each cylinder. Combustion chamber pressure sensors are ideal for this purpose. Combustion chamber pressure sensors enable cylinder-specific control of the internal torque, equalization of injection quantities, detection of pre-, main-, and post-injection events, control of the combustion center position, compensation for aging effects, and keeping the operating point indicator constant.

[0003] Since cylinder heads of modern combustion engines usually have little space for additional holes to install such a combustion chamber pressure sensor, such combustion chamber pressure sensors must be designed to be small and compact or integrated into existing components.

[0004] DE 10 2007 047 861 A1 discloses a multi-cylinder internal combustion engine in which each cylinder is monitored by its own combustion chamber pressure sensor. Each of the combustion chamber pressure sensors is connected to an engine control unit of the internal combustion engine, allowing individual cylinder-by-cylinder control of the respective combustion process in the individual combustion chambers of the internal combustion engine.

[0005] From WO 2009 112 056 A1 a method for regenerating a diesel particulate filter in the exhaust duct of a diesel engine is known, wherein each cylinder is assigned an individual temperature model, wherein the respective combustion chambers of the internal combustion engine are assigned a combustion chamber pressure sensor, via which a cylinder-individual pressure measurement is possible.

[0006] WO 2015 / 050 237 A1 discloses a control unit for an internal combustion engine, wherein a combustion chamber pressure sensor is arranged in a combustion chamber of the internal combustion engine, and the sensitivity of the combustion chamber pressure sensor is monitored by the control unit. It is provided that the combustion chamber pressure sensor is burned clear if the sensitivity decreases.

[0007] WO 2013 / 084309 A1 discloses an internal combustion engine with a combustion chamber pressure sensor arranged in the combustion chamber. A monitoring device is provided that monitors the thickness of a deposit on the combustion chamber pressure sensor and initiates a cleaning process for the combustion chamber pressure sensor if a defined layer thickness is exceeded.

[0008] From DE 10 2013 020 998 A1, a combustion chamber pressure sensor for detecting a pressure in a combustion chamber of an internal combustion engine is known, comprising at least one housing part, at least one transmission element which is translationally movable relative to the housing part for transmitting the pressure prevailing in the combustion chamber to at least one detection element of the combustion chamber pressure sensor (and at least one sealing element which is supported on the transmission element and on the housing part, wherein the sealing element is at least partially provided with at least one catalytic coating).

[0009] EP 2 693 029 A1 discloses a diesel engine with a control unit for monitoring the combustion in the combustion chambers of the internal combustion engine, wherein the pre-injection is adjusted in the event of an abnormal combustion signal.

[0010] EP 2 824 306 A1 describes a method for removing deposits in a combustion chamber of an internal combustion engine.

[0011] From DE 43 30 619 A1 an ignition angle control unit for an internal combustion engine is known, wherein in a warm-up phase of the internal combustion engine the ignition angle is adjusted so far in the early direction in order to clean the spark plugs that a knocking combustion with shock waves occurs in the combustion chamber to clean the deposits.

[0012] The invention is based on the object of preventing sooting or coking of a combustion chamber pressure sensor or of removing deposits already present on the combustion chamber pressure sensor and thus enabling reliable operation of the combustion chamber pressure sensor and avoiding incorrect measurements or measurement deviations due to coking or sooting.

[0013] According to the invention, this object is achieved by a method for operating an internal combustion engine with a plurality of combustion chambers and at least one combustion chamber pressure sensor arranged on at least one of the combustion chambers, which method comprises the following steps: Operating the internal combustion engine in normal operation, in which all combustion chambers are operated with the same fuel quantity and the same injection start, so that a substantially identical combustion chamber pressure results in all combustion chambers during combustion, detecting a degree of contamination of the combustion chamber pressure sensor or a load profile of the internal combustion engine which is highly likely to lead to contamination of the combustion chamber pressure sensor, operating the combustion chamber in which the combustion chamber pressure sensor is arranged with a combustion chamber pressure that is higher than during normal operation, whereby the contamination is removed from the combustion chamber pressure sensor, whereby the injection quantity of fuel into the combustion chamber in which the combustion chamber pressure sensor is arranged is increased, while in parallel the efficiency of the corresponding combustion chamber is reduced, and whereby the remaining combustion chambers continue to operate with unchanged operating parameters,so that the combustion chamber pressure in the combustion chamber where the combustion chamber pressure sensor is located is significantly higher than the combustion chamber pressures in the other combustion chambers.

[0014] By means of a method according to the invention, sooting and coking can be removed from a combustion chamber pressure sensor arranged in the combustion chamber of the internal combustion engine, in particular from a combustion chamber pressure sensor extending into the combustion chamber of the internal combustion engine, and the combustion chamber pressure sensor can be cleaned in this way. This increases the measurement accuracy of the combustion chamber pressure sensor, which is negatively affected by contamination.

[0015] The features listed in the dependent claims enable advantageous improvements and further developments of the method for operating an internal combustion engine specified in the independent claim.

[0016] According to the invention, the combustion chamber pressure of the combustion chamber in which the combustion chamber pressure sensor is arranged is increased compared to the combustion chamber pressure in the other combustion chambers. Especially with driving profiles with low load, as occurs, for example, in small vans in inner-city distribution traffic, there is a particularly high tendency for deposits, coking, and sooting of the combustion chamber pressure sensor to form. In these driving profiles, the internal combustion engine is often not under a sufficiently great load to remove this contaminant from the combustion chamber pressure sensor. By specifically increasing the combustion chamber pressure for the cylinder and combustion chamber in which the combustion chamber pressure sensor is arranged, a sufficient combustion chamber pressure and a correspondingly high temperature can be achieved even with low load profiles to remove coking and sooting of the combustion chamber pressure sensor.

[0017] The method for selectively increasing combustion chamber pressure is characterized by shifting the start of fuel injection into the combustion chamber of the respective cylinder toward "advance." Shifting the start of injection toward "advance" increases the combustion chamber pressure and the combustion chamber temperature, causing the contaminants on the combustion chamber pressure sensor to be detached. The remaining cylinders continue to operate normally. For this purpose, the engine control software is adapted and expanded by degrees of freedom to enable cylinder-selective advancement of the start of injection.

[0018] According to the invention, it is provided that the injection quantity of fuel into the combustion chamber in which the combustion chamber pressure sensor is arranged is increased, while in parallel the efficiency of the corresponding combustion chamber is deteriorated.

[0019] In a further method, which is not claimed, it is provided that the injection quantity of fuel for the combustion chamber in which the combustion chamber pressure sensor is arranged is increased, while in parallel the injection quantity into the combustion chambers without a combustion chamber pressure sensor is reduced. Alternatively, the injection quantity for the combustion chamber in which the combustion chamber pressure sensor is arranged can be increased accordingly and in parallel the injection quantity for the other combustion chambers can be reduced accordingly. This measure can also increase the combustion chamber pressure and the combustion chamber temperature in the combustion chamber in which the combustion chamber pressure sensor is arranged, while the overall torque of the internal combustion engine is also kept constant. However, the different injection quantities can result in minimal losses in the smoothness of the internal combustion engine and thus in driving comfort.

[0020] According to the invention, the combustion chamber pressure of the combustion chamber in which the combustion chamber pressure sensor is arranged is increased compared to the combustion chamber pressure in the normal process. In this case, the combustion chamber pressure is raised, for example, to at least 80% of the maximum combustion chamber pressure, preferably to at least 90% of the maximum combustion chamber pressure, particularly preferably to at least 95% of the maximum combustion chamber pressure, in particular to the maximum combustion chamber pressure. In order to remove the contaminants and clean the combustion chamber pressure sensor, a correspondingly high temperature and a correspondingly high combustion chamber pressure are necessary. It is therefore advantageous if a correspondingly high combustion chamber pressure is achieved in the combustion chamber in which the combustion chamber pressure sensor is arranged, even at low partial load in correspondingly low-load driving cycles.

[0021] An advantageous improvement to the method provides for the increase in the combustion chamber pressure of the combustion chamber where the combustion chamber pressure sensor is located to occur for a defined time interval depending on the degree of contamination of the cylinder pressure sensor. Since the combustion chamber where the combustion chamber pressure sensor is located is operated with an increased pressure gradient during the method, the noise level also increases. It is therefore advisable to keep this operating state as short as possible while achieving a sufficient cleaning effect. Therefore, after a defined time interval, the combustion engine switches back to normal operation, during which the combustion engine reaches an ideal operating point for emissions and / or fuel consumption.

[0022] In an alternative advantageous embodiment of the method, the increase in the combustion chamber pressure sensor of the combustion chamber on which the combustion chamber pressure sensor is arranged takes place for a defined number of combustion cycles, which depends on the degree of contamination and the driving profile. Since the combustion chamber on which the combustion chamber pressure sensor is arranged is operated with an increased pressure gradient during the method, the noise level also increases. It is therefore sensible to keep this operating state as short as possible, but to achieve a sufficient cleaning effect. Therefore, after a defined number of combustion cycles, the combustion engine switches back to normal operation, during which the combustion engine reaches an ideal operating point for emissions and / or consumption.

[0023] Furthermore, it is advantageously provided that the combustion chamber temperature of the combustion chamber in which the combustion chamber pressure sensor is arranged exceeds a defined threshold temperature, preferably a threshold temperature of 300°C, particularly preferably a threshold temperature of at least 400°C, in particular of at least 450°C, as a result of the method. To ensure sufficient cleaning of the combustion chamber pressure sensor, a corresponding combustion chamber pressure and a corresponding combustion chamber temperature are necessary. In this case, it is necessary that the temperature at the combustion chamber pressure sensor exceeds a threshold temperature above which detachment and / or combustion of coking and sooting is possible, thus bringing the combustion chamber pressure sensor back to its initial state and increasing the measurement accuracy of the combustion chamber pressure sensor.

[0024] According to the invention, an internal combustion engine with multiple combustion chambers is proposed, wherein a combustion chamber pressure sensor is arranged in at least one of the combustion chambers, and with an engine control unit which is configured to carry out a method according to the invention when a machine-readable program code is executed by the engine control unit. For cost reasons, in internal combustion engines, a combustion chamber pressure sensor is not arranged in each combustion chamber, but rather, for example, one combustion chamber pressure sensor is arranged for a series of combustion chambers, wherein the combustion chamber pressure in the other combustion chambers can be modeled accordingly. Alternatively, the use of multiple combustion chamber pressure sensors is also possible, for example two combustion chamber pressure sensors, particularly with two different cylinder banks of a V-engine.By using only one combustion chamber pressure sensor, costs can be kept low and transmitted to the other cylinders through appropriate modulation, whereby additional signals such as the combustion chamber temperature, the fuel injection quantity and / or the current consumption of a glow plug can be evaluated to monitor the combustion chamber.

[0025] In an advantageous embodiment of the invention, the combustion chamber pressure sensor is arranged in a cylinder head of the internal combustion engine. To enable a comparatively simple and cost-effective arrangement of the combustion chamber pressure sensor in the combustion chamber of the internal combustion engine, it is advantageous if the combustion chamber pressure sensor is arranged in a cylinder head of the internal combustion engine.

[0026] In a further advantageous embodiment of the invention, the combustion chamber pressure sensor is integrated into a glow plug, which is assigned to the combustion chamber in which the combustion chamber pressure is to be determined. Since installation space is limited in modern internal combustion engines, it is advantageous to integrate the combustion chamber pressure sensor into an existing component of the internal combustion engine in order to avoid an additional bore for a combustion chamber pressure sensor. In a diesel engine, integrating the combustion chamber pressure sensor into a glow plug is particularly preferred, as this is structurally simpler than other components, in particular simpler than integration into a fuel injection nozzle of a fuel injector.

[0027] Alternatively, it is advantageous for the combustion chamber pressure sensor to be integrated into a spark plug associated with the combustion chamber in which the combustion chamber pressure is to be determined. For gasoline engines, integration into a spark plug is preferred, as this is relatively simple and cost-effective to implement and does not require an additional access hole in the cylinder head of the internal combustion engine.

[0028] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0029] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Identical components or components with the same function are designated by the same reference numerals. In the drawings: Figure 1 shows an embodiment of an internal combustion engine according to the invention for carrying out a method according to the invention. The internal combustion engine is shown in a plan view of the cylinder head of the internal combustion engine; Figure 2 shows a schematic representation of a section through a cylinder of an internal combustion engine according to the invention, wherein the combustion chamber pressure sensor is arranged in the cylinder head of the internal combustion engine.

[0030] Figure 1shows a plan view of a cylinder head 36 of an internal combustion engine 10 according to the invention. The internal combustion engine 10 is preferably designed as a diesel engine, but can alternatively also be designed as a gasoline engine. The internal combustion engine 10 has a plurality of combustion chambers 12, preferably four combustion chambers 12 arranged in series. The internal combustion engine 10 can be connected to an air supply system for the internal combustion engine 10 via an inlet 14. The internal combustion engine 10 can also be connected to an exhaust system of the internal combustion engine 10 via an outlet 16. A combustion chamber pressure sensor 24 is arranged on at least one of the combustion chambers 12, preferably on exactly one of the combustion chambers 12, and can be used to measure the combustion chamber pressure p B in the corresponding combustion chamber. The combustion chambers 12 each have at least one inlet valve 18 and one exhaust valve 20.Preferably, two intake valves 18 and two exhaust valves 20 are arranged in each combustion chamber. Furthermore, each combustion chamber 12 is assigned a fuel injection valve 22, in particular an electronically controllable fuel injector with an injection nozzle. The internal combustion engine 10 is also assigned an engine control unit 26, which is connected to the respective fuel injection valves 22 via signal lines 28 and to the combustion chamber pressure sensor 24 via at least one further signal line 30. The combustion chamber pressure sensor 24 can be designed either as a separate combustion chamber pressure sensor 24 or integrated into another component, in particular a glow plug or a spark plug.

[0031] In Figure 2A further exemplary embodiment of an internal combustion engine 10 according to the invention is shown in a sectional view through a combustion chamber 12, in which a combustion chamber pressure sensor 24 is arranged. The internal combustion engine 10 has a crankshaft 38, which is connected to a piston 32 of the internal combustion engine 10 via a connecting rod. The internal combustion engine 10 further has an engine block 34 and a cylinder head 36, which, together with the piston 32, delimit the combustion chamber 12. At least one inlet channel 40 and one outlet channel 42 are provided on the cylinder head 36 for each combustion chamber 12. Fresh air or a fresh air-fuel mixture can be introduced into the combustion chamber 12 through the inlet channel 40. The exhaust gas produced during combustion in the combustion chamber 12 can be discharged into an exhaust channel of the internal combustion engine 10 through the outlet channel.At least one intake valve 18 is provided on the intake port 40, with which the intake port 40 can be fluidically separated from the combustion chamber 12. At least one exhaust valve 20 is arranged between the combustion chamber 12 and the exhaust port 42, with which the combustion chamber 12 can be fluidically separated from the exhaust port 42. At least one intake camshaft 44 and one exhaust camshaft 46 are provided for opening and closing the intake and exhaust valves 18, 20. The piston 32 has a combustion chamber bowl 48, with a fuel injection valve 22 arranged in the cylinder head 36 having at least one injection opening, preferably a plurality of injection openings distributed evenly over the circumference, which are aligned with the combustion chamber bowl 48.

[0032] During normal operation of the internal combustion engine 10, fuel is injected into the combustion chambers 12 of the internal combustion engine 10 through the fuel injection valves 22. The injection timing and injection quantity are selected to be identical for all combustion chambers 12 to enable uniform and harmonious torque generation with high efficiency and low emissions. Combustion in at least one of the combustion chambers 12 is monitored by the combustion chamber pressure sensor 24, and the injection quantity, injection timing, and combustion center position are controlled accordingly.

[0033] If the engine control unit 26 detects a load profile of the internal combustion engine 10 in which coking or sooting of the combustion chamber pressure sensor is to be expected, or if coking, sooting, or other contamination of the combustion chamber pressure sensor 24 is detected in another way, a regeneration process or a cleaning process of the combustion chamber pressure sensor 24 is initiated in which the start of injection of the fuel injector 22 at the combustion chamber 12 where the combustion chamber pressure sensor 24 is located is shifted toward "early" and, if necessary, the injection quantity is increased in order to increase the combustion chamber pressure p BS . The remaining combustion chambers 12 continue to operate with unchanged operating parameters, so that the combustion chamber pressure p BS in the combustion chamber 12 where the combustion chamber pressure sensor 24 is located is significantly higher than the combustion chamber pressures p B in the remaining combustion chambers 12.In parallel with the combustion chamber pressure p BS in the combustion chamber 12, where the combustion chamber pressure sensor 24 is arranged, the combustion chamber temperature TB also rises, whereby the coking or sooting on the combustion chamber pressure sensor 24 can be removed and at least partially thermally converted. This cleans the combustion chamber pressure sensor 24, so that precise combustion chamber pressure measurement is still possible. The adaptation of the start of injection and / or the injection quantity to the combustion chamber 12, where the combustion chamber pressure sensor 24 is arranged, is only shifted to parameters that deviate from normal operation for a short, limited period of time, thereby limiting any deterioration in efficiency and / or raw emissions. List of reference symbols

[0034] 10Combustion engine 12Combustion chamber 14Inlet 16Exhaust 18Inlet valve 20Exhaust valve 22Fuel injection valve 24Combustion chamber pressure sensor 26Engine control unit 28Signal line 30Signal line 32Piston 34Engine block 36Cylinder head 38Crankshaft 40Intake port 42Exhaust port 44Intake camshaft 46Exhaust camshaft 48Combustion chamber bowl

Claims

1. Method for operating an internal combustion engine (10) having a plurality of combustion chambers (12) and at least one combustion chamber pressure sensor (24) arranged on at least one of the combustion chambers (12), comprising the following steps: - operating the internal combustion engine (10) in a normal mode in which all combustion chambers (12) are operated with the same fuel quantity and the same injection period, so that a substantially identical maximum combustion chamber pressure (ps) of combustion results in all combustion chambers (12), - detecting a degree of contamination of the combustion chamber pressure sensor (24) or a load profile of the internal combustion engine (10) which is highly likely to lead to contamination of the combustion chamber pressure sensor (24), the method is characterized by - operating the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged with a combustion chamber pressure that is higher than during normal operation (p > ps), thereby removing the contamination from the combustion chamber pressure sensor (24), the injection quantity of the fuel for the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged being increased, while in parallel the efficiency of the corresponding combustion chamber being impaired, and - the remaining combustion chambers (12) continuing to be operated with unchanged operating parameters, so that the combustion chamber pressure (pBS) in the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged is significantly above the combustion chamber pressures (pB) in the remaining combustion chambers (12).

2. Method according to claim 1, characterized in that the combustion chamber pressure (pss) of the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged is increased by shifting the start of injection of the fuel into this combustion chamber (12) in the "early" direction.

3. Method according to one of claims 1 or 2, characterized in that the combustion chamber pressure (pss) of the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged is increased for a defined time interval.

4. Method according to any of claims 1 to 3, characterized in that the combustion chamber pressure (pss) of the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged is increased for a defined number of combustion cycles.

5. Method according to any of claims 1 to 4, characterized in that a combustion chamber temperature (Tes) of the combustion chamber (12) on which the combustion chamber pressure sensor (24) is arranged exceeds a defined threshold temperature (Ts) by use of the method.

6. Internal combustion engine (10) comprising a plurality of combustion chambers (12), wherein a combustion chamber pressure sensor (24) is arranged on at least one of the combustion chambers (12), and comprising an engine control unit (26) which is configured to carry out a method according to any of claims 1 to 5 when a machine-readable program code is executed by the engine control unit (26).

7. Internal combustion engine (10) according to claim 6, characterized in that the combustion chamber pressure sensor (24) is arranged in a cylinder head (36) of the internal combustion engine (10).

8. Internal combustion engine (10) according to claim 6 or 7, characterized in that the combustion chamber pressure sensor (24) is integrated into a glow plug which is assigned to the combustion chamber (12) in which the combustion chamber pressure (pB) is to be determined.

9. Internal combustion engine (10) according to claim 6 or 7, characterized in that the combustion chamber pressure sensor (24) is integrated into a spark plug which is assigned to the combustion chamber (12) in which the combustion chamber pressure (pB) is to be determined.