Method for cooling a piston of an internal combustion engine and control unit

Abstract

A method for cooling a piston (1) of an internal combustion engine, wherein the piston (1) of the internal combustion engine is supplied with oil (4) from at least one piston cooling nozzle (5), wherein the supply of oil (4) to the piston (1) is dependent on a model of a piston temperature and the model defines at least one characteristic parameter for a load on the piston (1) and specifies a corresponding condition for the commencement of the supply of oil (4) to the piston (1), wherein corresponding conditions for several characteristic parameters include a respective threshold, characterized in that a certain number of several thresholds must be exceeded by the respective associated characteristic parameter, which includes at least one measured value for a temperature, before the supply of oil (4) to the piston (1) commences with a defined time delay.wherein the model for the piston temperature is derived from a model for a temperature in at least one area of ​​the internal combustion engine or at least a temperature in an area of ​​the motor vehicle to which the internal combustion engine is assigned, which is not located in the area of ​​the internal combustion engine.

Description

[0001] The invention relates to a method for cooling a piston of an internal combustion engine, in which the piston is supplied with oil from a piston cooling nozzle for the purpose of cooling, as well as a corresponding control device for carrying out the method.

[0002] German patent application DE 10 2007 042 405 A1 discusses the problems of pre-ignition and knocking combustion in a gasoline engine, which can occur as a result of secondary ignition points, such as hot spots in the combustion chamber. To solve these problems, fresh gas is introduced into the combustion chamber by means of a compression device during the intake stroke, and the intake valve is closed in such a way that the geometric compression is reduced compared to a compression-optimal closing angle.

[0003] The German patent specification DE 10 2009 008 960 B4 relates to a method for controlling a reciprocating piston engine, in which a combustion temperature in one or more cylinders is detected, wherein the ignition timing in one or more cylinders is controlled individually for each cylinder in such a way that the combustion chamber temperature deviates as little as possible from a predetermined target value.

[0004] German patent application DE 10 2010 064 186 A1 discloses a method for treating uncontrolled combustion in a motor vehicle's internal combustion engine. The number of uncontrolled combustion events within a monitoring period is recorded. If this number exceeds a threshold, the temperature in the combustion chamber of the internal combustion engine is reduced.

[0005] German patent application DE 10 2012 215 804 A1 describes a method for determining a defect in an internal combustion engine. A particle concentration, preferably of soot particles, is detected during and / or after the combustion of a fuel-air mixture. In particular, two measurements of the particle concentration can be taken, between which a function and / or operating state of the internal combustion engine is changed.

[0006] Further prior art includes the documents DE 199 33 363 A1, DE 10 2009 057 549 A1, DE 35 43 084 A1, DE 10 2014 203 930 A1, DE 102 06 769 A1, US 2013 / 0139768 A1, JP 4 599 785 B2 and DE 10 2007 060 160 A1.

[0007] In piston engines, such as gasoline or diesel engines, a piston moves within a cylinder. To reduce friction, the piston's running surface is coated with oil. It is also known to cool the piston by spraying it with oil from a piston cooling nozzle. Piston cooling is necessary for durability under high engine loads.

[0008] Because the piston is not tightly sealed to the cylinder, oil can enter the cylinder's combustion chamber and thus the mixture to be ignited. If the piston is cooled more effectively by spraying oil on the side of the piston facing away from the cylinder's combustion chamber, there is also the possibility of increased oil ingress into the combustion chamber and the mixture to be ignited. However, oil in the combustion chamber leads to particle formation during combustion of the mixture, and increased oil ingress into the combustion chamber thus leads to increased particulate emissions from the internal combustion engine. From an environmental perspective, this is undesirable and, given the relevant and increasingly stringent legal regulations, only acceptable to a limited extent.

[0009] This creates the problem that, on the one hand, the piston must be effectively cooled to avoid an unacceptable reduction in its service life and to prevent misfires, while, on the other hand, oil ingress into the combustion chamber must be kept to a minimum to avoid high particulate emissions. This problem becomes even more acute when driving at high power for long periods, and therefore the internal combustion engine must deliver high torque over long periods, because this is precisely when there is an increased need for piston cooling.

[0010] The object of the invention is therefore to provide a method which enables effective and sufficient cooling of a piston of an internal combustion engine, but which leads to only low particle emissions from the internal combustion engine.

[0011] A further object of the invention is to provide a control unit for the internal combustion engine for implementing the method according to the invention.

[0012] These objects are achieved by a method having the features according to claim 1 and a control device having the features according to claim 13.

[0013] In the method according to the invention, a piston of an internal combustion engine is exposed to oil from at least one piston cooling nozzle, i.e., sprayed or squirted. It should be noted that the invention can, of course, also be used in the case of an internal combustion engine with a plurality of pistons for cooling the plurality of pistons, by cooling each piston of the internal combustion engine according to the method according to the invention.

[0014] The piston is supplied with oil depending on a model of the piston temperature. This means that the required cooling is determined from a model of the piston temperature, and the at least one piston cooling nozzle is controlled accordingly. The required cooling of the piston is determined at least with regard to the start of cooling, and advantageously also with regard to the duration of the cooling, i.e. the period of time during which oil is applied to the piston from the at least one piston cooling nozzle. The piston cooling nozzle can be controlled, for example, by controlling valves specifically provided for the piston cooling nozzle, which open or interrupt the oil supply to the piston cooling nozzle.Likewise, the piston cooling nozzle can be activated by increasing the oil pressure, i.e. the piston cooling nozzle opens from a certain oil pressure due to its design, and when the oil pressure subsequently drops, the piston cooling nozzle closes, for example due to the effect of a return spring.

[0015] In one embodiment, the model makes use of at least one parameter for the load on the piston. The at least one parameter is defined by the model. For this at least one parameter, a corresponding condition for the onset of the application of oil to the piston is specified by the model. The at least one parameter can comprise at least one measured value for the internal combustion engine or for a motor vehicle to which the internal combustion engine is assigned. Likewise, the at least one parameter can be a value calculated from at least one such measured value; in this case, evaluation factors, such as weightings, can be included in the calculated parameter in addition to the at least one measured value. Examples of possible measured values ​​are given below.

[0016] In a further development, the condition for at least one of the at least one characteristic variables includes a respective threshold, as well as a time delay between the respective threshold being exceeded by the at least one of the at least one characteristic variables and the onset of the application of oil to the piston. This means that the condition for the onset of the application of oil to the piston is met, for example, if at least one of the thresholds defined by the model is exceeded by the characteristic variable corresponding to the respective threshold, and a specific period of time, again defined by the model, has elapsed since this threshold was exceeded. The period of time can be defined separately for each threshold.

[0017] If the model defines multiple thresholds for corresponding parameters, the condition for the onset of oil supply to the piston can specify that at least a certain number of these thresholds must be exceeded by the respective parameter before the piston begins to be supplied with oil after a correspondingly defined time delay. In particular, the condition can specify that at least one threshold must be exceeded or that all thresholds must be exceeded.

[0018] In embodiments of the method, a moving average is determined for at least one of the at least one characteristic variable and incorporated into the model. In particular, this makes it possible to appropriately take into account power requirements of the internal combustion engine that fluctuate significantly over time. If, for example, a single, brief exceedance of a threshold for one of the at least one characteristic variable, for example if the threshold is only exceeded for 5 seconds, were to trigger cooling in the same way as if the threshold were exceeded for several minutes, this would result in unnecessary cooling of the piston and thus in unnecessary oil entry into the combustion chamber with subsequent high particulate emissions from the internal combustion engine. A moving average can compensate for such short-term fluctuations in the values ​​of characteristic variables.The moving average can be determined over a specific period of time or over a specific number of revolutions of the internal combustion engine's crankshaft. This specific period of time or this specific number of revolutions can be determined as variables from the model or can be fixed.

[0019] In embodiments of the method, the model for the piston temperature is derived from a model for a temperature in at least one region of the internal combustion engine or in at least one region of a motor vehicle, wherein the internal combustion engine is assigned to the motor vehicle. For example, a temperature in the combustion chamber of the cylinder in which the respective piston to be cooled is movably arranged can be modeled. The model can be designed to provide a temperature value for the combustion chamber or multiple temperature values ​​for different locations within the combustion chamber. A temperature distribution within the combustion chamber is also conceivable as a statement from the model. If a model for at least one temperature in the combustion chamber is available, in embodiments of the method the model for the temperature of the piston can be derived from the model for the temperature in the combustion chamber.In the simplest case, in which only a temperature value for the combustion chamber is supplied by the model, this temperature value can also be used as the value for the piston temperature. Likewise, a modeled temperature in a region of the internal combustion engine other than the combustion chamber can be used in the model for the piston temperature to model the piston temperature. A value for the piston temperature can also be derived in a manner determined by the model from another modeled temperature in a region of the internal combustion engine. A modeled temperature in a region of a motor vehicle, where the internal combustion engine is assigned to the motor vehicle but is not located in the specified region, can also serve as the starting point for modeling the piston temperature. For example, a modeled temperature in a catalytic converter can serve as the starting point for modeling the piston temperature.

[0020] In other embodiments of the method, the piston temperature is modeled directly, without relying on a model for the temperature in the combustion chamber or for a temperature in another region of the internal combustion engine or of a motor vehicle to which the internal combustion engine is assigned. In certain embodiments, the piston temperature results, depending on details of the piston temperature model, from at least one measured value for at least one temperature in a region of the internal combustion engine or in a region of a motor vehicle, wherein the internal combustion engine is assigned to the motor vehicle.

[0021] In one embodiment of the method, at least one temperature value is determined at at least one location on the piston by at least one sensor and included in the piston temperature model.

[0022] In embodiments, the piston temperature model takes into account at least one of the following measured variables of the internal combustion engine or of a motor vehicle to which the internal combustion engine is assigned: engine speed, engine torque, water temperature in a cylinder crankcase, oil temperature, combustion air ratio, ignition angle, residual gas content, combustion pressure, exhaust back pressure, temperature in a catalytic converter of the motor vehicle, driving speed, ambient temperature, ambient air pressure. The respective measured variable is determined by suitable known sensors.

[0023] In the aforementioned embodiments of the method, in which the model for the piston temperature is derived from a model for a temperature in a region of the internal combustion engine or in a region of a motor vehicle, one or more of the aforementioned measured variables can of course also be included. The measured variables can be included in the model for the temperature in a region of the internal combustion engine or in a region of the motor vehicle and / or taken into account when modeling the piston temperature based on the modeled temperature in a region of the internal combustion engine or in a region of the motor vehicle.

[0024] Variables determined by the piston temperature model, in particular a delay between exceeding a threshold for at least one of the at least one characteristic variable and the onset of the piston being supplied with oil from the at least one piston cooling nozzle, can be determined in embodiments by the model via an equation into which, in a manner dependent on details of the model, the at least one characteristic variable and, if applicable, measured variables of the internal combustion engine or of a motor vehicle to which the internal combustion engine is assigned, for example one, some or all of the above-mentioned measured variables, are included. Instead of an equation, a characteristic curve or a characteristic map can also be used. A delay can also be determined indirectly.If, for example, a moving average or the result of a mathematical filter operation is determined from the measured values ​​in a model-dependent manner, threshold values ​​for these variables may be exceeded later than the threshold value is exceeded by the measured variable itself. For example, if a threshold value is set for torque, and the measured torque provided by the internal combustion engine suddenly rises above the threshold value and remains above it, a moving average of the torque will only exceed the same threshold value later.

[0025] A control unit according to the invention for the internal combustion engine is designed to carry out the method according to the invention in one or more of its embodiments. The control unit does not need to be a separate control unit for the piston cooling system; rather, the corresponding functionality can be implemented as software in an engine control unit already assigned to the internal combustion engine.

[0026] The hardware ensures that the engine control unit can control the respective piston cooling nozzles, for example by controlling valves for the respective piston cooling nozzle or by changing the oil pressure. In particular, the control unit is designed to receive at least one measured value from at least one sensor from the internal combustion engine or the motor vehicle to which the internal combustion engine is assigned and, taking into account the at least one measured value, to control the supply of oil from at least one piston cooling nozzle to a piston of the internal combustion engine as a function of a piston temperature model. The at least one measured value comprises at least one of the measured variables mentioned above in the context of the method.

[0027] In the following, the invention is explained in more detail in a specific embodiment with reference to the attached schematic drawing. Fig. 1 shows a piston in a cylinder of an internal combustion engine, with the piston being pressurized with oil.

[0028] Fig.1 shows a piston 1, which is movably arranged in a cylinder 2 of an internal combustion engine (not shown in detail) in a known manner. Torque is transmitted to a crankshaft (not shown) of the internal combustion engine via a connecting rod 9. Valves 8 are provided to supply combustion educts to a combustion chamber 3 of the cylinder 2 and to discharge combustion products therefrom. Any further elements such as spark plugs and fuel injection have been omitted from the illustration, as they are not essential to the principle of the invention. Gaps 10 between the piston 1 and a wall 11 of the cylinder 2 are shown exaggeratedly wide. They are intended to clarify that the piston 1 does not form a tight seal with the wall 11 of the cylinder 2, and thus the piston 1 does not tightly seal the combustion chamber 3 from an outer region 12.

[0029] If the piston 1 is now exposed to oil 4 from a piston cooling nozzle 5 on the side facing the outer region 12 for the purpose of cooling the piston 1, oil 4 can enter the combustion chamber 3. During combustion in the combustion chamber 3, unwanted particles are then produced, and as a result, the internal combustion engine exhibits increased levels of unwanted particle emissions.

[0030] To reduce these undesirable particulate emissions while simultaneously ensuring adequate cooling of the piston 1, the supply of oil 4 from the piston cooling nozzle 5 to the piston 1 is controlled according to the method according to the invention. In the embodiment shown, this is achieved by a correspondingly configured control unit 7. The control unit 7 controls the piston cooling nozzle 5 based on a piston temperature model implemented in the control unit 7. To do this, the control unit in this embodiment accesses the torque and / or speed of the internal combustion engine. The control unit 7 can also access other measured variables relating to the internal combustion engine itself or its environment.

[0031] Speed, torque, and other measured variables can be measured using suitable, known sensors. A sensor 6 is shown on the wall 11 of cylinder 2 as an example. Such a sensor 6 can, for example, measure a combustion pressure in the combustion chamber 3 or a temperature in the combustion chamber 3. List of reference symbols 1 piston 2 cylinders 3 combustion chamber 4 Oil 5 Piston cooling nozzle 6 Sensor 7 Control unit 8 valve 9 connecting rods 10 Gap between piston and cylinder wall 11 Wall of the cylinder 12 Outdoor area

Claims

[1] Method for cooling a piston (1) of an internal combustion engine, in which the piston (1) of the internal combustion engine is supplied with oil (4) from at least one piston cooling nozzle (5), wherein the supply of oil (4) to the piston (1) takes place as a function of a model of a piston temperature and the model defines at least one characteristic for a load on the piston (1) and specifies a corresponding condition for the onset of the supply of oil (4) to the piston (1), wherein corresponding conditions for several characteristic values include a respective threshold, characterized bythat a certain number of thresholds must be exceeded by the respectively associated characteristic variable, which comprises at least one measured value for a temperature, before the piston (1) is supplied with oil (4) with a defined time delay, wherein the model for the piston temperature is derived from a model for a temperature in at least one region of the internal combustion engine or at least one temperature in a region of the motor vehicle to which the internal combustion engine is assigned, which region is not in the region of the internal combustion engine. [2] Method according to claim 1, characterized by that the model from which the model for the piston temperature in the area of the internal combustion engine is derived provides a temperature value in the combustion chamber of the cylinder in which the respective piston (1) to be cooled is movably arranged. [3] Method according to claim 2, characterized bythat the model from which the piston temperature model is derived provides only one temperature value for the combustion chamber or several temperature values for different locations within the combustion chamber. [4] Method according to claim 3, characterized by that the model from which the piston temperature model is derived provides a temperature distribution of the temperature values within the combustion chamber. [5] Method according to claim 1, characterized by that the model from which the piston temperature model is derived provides a temperature value in the region of the motor vehicle which is not in the region of the internal combustion engine, with a modeled temperature in a catalytic converter serving as the starting point for modeling the piston temperature. [6] Method according to claim 2, characterized bythat at least one measured value for at least one temperature in the region of the internal combustion engine is included in the model for the piston temperature, wherein the at least one measured value is a temperature value of the piston temperature, which is determined at at least one point on the piston (1) by a sensor and is included in the model. [7] Method according to claim 1, characterized by that all thresholds are exceeded by the respective associated parameter before the piston (1) is pressurized with oil (4) with a defined time delay. [8] Method according to claim 1, characterized by that a corresponding condition includes a moving average for at least one of the parameters. [9] Method according to claim 1, characterized by that a certain period of time, determined by the piston temperature model, has elapsed since the respective threshold(s) were exceeded. [10] Method according to claim 9, characterized by that the time period is set separately for each threshold. [11] Method according to claim 1, characterized by that in the model of the piston temperature at least one measured value of the following measured variables in the area of the internal combustion engine or in the area of the motor vehicle to which the internal combustion engine is assigned is taken into account: a speed of the internal combustion engine, a torque of the internal combustion engine, a water temperature in a cylinder crankcase, an oil temperature, a combustion air ratio, an ignition angle, a residual gas content, a combustion pressure, an exhaust gas back pressure, a driving speed, an ambient temperature, an ambient air pressure. [12] Method according to claim 11, characterized by that one or more measured variables are included in the model from which the model for the piston temperature is derived. [13] Control unit (7) for an internal combustion engine, which is designed to carry out the method according to one of claims 1 to 12.

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