DE102009046417A1 - Method for detecting fuel input in lubricant of internal combustion engine, particularly of motor vehicle, involves determining lambda-value during overrun cut-off operating phase which is completed on fuel input in lubricant - Google Patents

Abstract

The method involves determining a lambda-value during an overrun cut-off operating phase which is completed on a fuel input in a lubricant. The fuel input is detected by a lambda-sensor, where the lambda-value is determined, according to a pre-determined operating time. The lambda value deviates from the reference value around a predetermined threshold value on a strong dilution of the lubricant. Independent claims are also included for: (1) a controller for operating an internal-combustion engine, particularly a motor vehicle; (2) a computer program for executing the fuel input detecting method; and (3) a computer program product with a program code.

Description

The invention relates to a method for detecting a fuel input in the lubricating oil of an internal combustion engine, in particular of a motor vehicle according to the preamble of claim 1.

The invention also provides a control device for operating an internal combustion engine and a computer program and a computer program product which are suitable for carrying out the method.

State of the art

In today's internal combustion engines, depending on the operating conditions in the combustion chambers of the individual cylinders, the case may occur that fuel does not burn and partly condenses on the cylinder walls and in this way gets past the piston rings into the crankcase. This leads to oil dilutions by fuel entry into the lubricating oil. In today's internal combustion engines, the fuel injection is very often by way of gasoline direct injection. This fuel pressures of up to 200 bar are provided. In some areas of direct injection, such as in spray-guided combustion processes or highly supercharged internal combustion engines, even higher pressures occur. To be able to transfer the forces required to generate these pressures from a camshaft or a crankshaft of the internal combustion engine to a high-pressure pump, pump rams known to be used in these pumps must be supplied with lubricating oil from the oil circuit of the internal combustion engine.

If there is now an increased leakage of seals arranged between the oil circuit and the fuel circuit, fuel can enter the oil circuit with the prefeed pressure of a low-pressure circuit arranged in the internal combustion engine. The resulting dilution of the lubricating oil (engine oil) of the internal combustion engine is disadvantageous and can even lead to destruction of the internal combustion engine in extreme cases. Since fuel input into the lubricating oil is practically unavoidable in practice, there is an interest in knowing the presence of fuel input into the lubricating oil.

From the DE 10 2006 059 675 A1 For this purpose, a method and a device has become known, which enable the detection of a continuous fuel input into the lubricating oil of an internal combustion engine during cold start. The fuel input is detected here by means of a lambda control. The leaning of adaptation values is taken as the basis for the lambda control.

In this method and the device of the entry of fuel vapors from a crankcase ventilation is evaluated in an intake manifold of the internal combustion engine. Such an entry leads to a mixture enrichment in the combustion chamber or in the combustion chambers of the internal combustion engine and thus to a change in the measured value at the lambda sensor of the lambda control. It is provided to detect the leaning of the adaptation values of an idle control cooperating with the lambda control.

In addition, oil quality sensors are used to monitor the oil quality. The use of such oil quality sensors also requires additional assembly and manufacturing costs and thus increases the cost. The detection of an increased fuel input by means of these sensors also leads to greatly shortened oil change intervals, which although prevents damage to the engine, but rather counteracts the acceptance of the said engine due to the shortened service intervals and the associated increased costs of acceptance of said internal combustion engine.

The invention is therefore the object of developing a method for detecting a fuel entry in the lubricating oil of an internal combustion engine to the effect that it is readily usable even with turbocharged engines and that can be completely dispensed with additional sensors in its implementation.

Disclosure of the invention

Advantages of the invention

This object is achieved by a method for detecting a fuel input into the lubricating oil of an internal combustion engine having the features of claim 1. The basic idea of the invention is to detect the lambda value during a fuel cut operating phase and to deduce the fuel input into the lubricating oil , During a fuel cut operating phase, there are hydrocarbons in the intake air that are largely due to crankshaft vents. In the fuel cut-off operating phase, the throttle valve is closed, so that the negative pressure in the intake manifold and thus in the crankcase is maximum. This vacuum forces most of the hydrocarbons into the intake air during the fuel cut phase of operation, thus changing the fuel-air composition and thus the lambda value. Has already a large fuel input into the oil occurred, so the oil is already "diluted" by the fuel, compared to unconsumed, that is fresh oil very many hydrocarbons into the exhaust gas and change the lambda value. This change is sufficient to detect whether fuel has entered the oil or not.

The measures listed in the dependent claims advantageous refinements and improvements of the method specified in the independent claim 1 are possible. Thus, an advantageous embodiment provides that after making an oil change, the lambda value is detected in a fuel cut-off operating phase and stored as a reference value. This reference value characterizes an unconsumed, that is, an oil not diluted by fuel inputs.

In principle, however, it is also possible to deduce a fuel input on the basis of absolute lambda values. The inclusion and storage of a reference value has the advantage that any age-related wear and tear of the internal combustion engine, which lead, for example, to an immediate entry of fuel into the oil even after an oil change, can be considered.

An advantageous embodiment provides that a lambda value is detected after a prescribable operating time or mileage of the vehicle in a fuel cut operating phase and this lambda value is compared with the reference value and then when the detected lambda value of the reference value by a predetermined Threshold deviates, is closed to a strong dilution of the lubricating oil by fuel input and this is optionally signaled to the driver.

By this comparison after a predetermined operating time or mileage of the vehicle optimal and safe monitoring of engine oil quality is possible.

The invention also relates to a control device in which the method sequence according to the invention is stored as a program. The control unit preferably contains a data carrier, that is to say a computer program product which is described with the computer program which represents the method.

Brief description of the drawings

Embodiments and other advantages and features of the invention are the subject of the following description and the drawings of the embodiments. In this case, the described features can be realized both for themselves and in combination with each other.

Show it

1 the lambda value over time at an engine operated in a fuel cut-off operating phase with freshly changed oil;

2 the lambda value over time in an engine operated in a fuel cut-off operating phase with aged oil and

3 schematically a flowchart for explaining the method according to the invention.

Embodiments of the invention

In 1 is shown schematically the time course of the supplied by a lambda probe (not shown) raw signal "lambda", which was detected on a test bed engine during a fuel cut operating phase at a speed of 2000 revolutions per minute. The internal combustion engine was filled with fresh, that is freshly changed oil or, in other words, with oil, which could have no age-related fuel input, filled. As the figure can be seen, a substantially constant lambda value of 25.4 is detected over a longer period of time.

In 2 In contrast, the lambda value over time in a fuel cut-off operating phase of the same engine at a speed of 2000 revolutions per minute is shown, in which case the oil used, however, a strong fuel input, that had a dilution by fuel. As can be seen from the figure, the lambda value drops to about 21.0 after a brief phase of about 15 seconds and remains at this value for a relatively long period of time. This drop in lambda value from 25.4 for unused oil to 21.0 for heavy fuel oil, each measured in the fuel cut-off operating phase, when the throttle valve is closed and hydrocarbons from the fuel injected into the lubricating oil, allows one Statement about the oil dilution.

The inventive method is described below in conjunction with 3 explained. First follows in one step 305 the start of the procedure. This is always the case when the oil of the internal combustion engine has been changed. After an oil change is in one step 310 In a fuel cut-off operating phase, the lambda value is detected by means of a lambda probe and stored as a reference value. After a predetermined mileage of the vehicle or after a predetermined time is then in one step 320 , which is later in time, made a new lambda determination in a fuel cut operating phase, their motor operating data those in step 310 set fuel cut operating phase. It will then be in step 330 an "oil dilution" determined, for example, by forming the difference in step 310 detected lambda value and in step 320 recorded lambda value. If this difference exceeds a predefinable threshold, which is in step 340 is checked, it must be assumed that the oil is diluted too much. Where "too strong" means that the risk of damage to the internal combustion engine exists. This will be in step 350 output as a signal and signaled for example to the driver of the vehicle. Then the process in step 360 completed. If, on the other hand, the oil dilution is not yet so great that there is a danger to the internal combustion engine, a further definable mileage or a predefinable time is awaited and in step 370 in turn, determines a lambda value in a comparable fuel cut-off operating phase. It will turn the oil dilution in step 380 determined, for example, by forming the difference of in step 310 certain lambda value and that in step 370 certain lambda value. Then, a return occurs before step 340 and it is again checked whether this difference exceeds the predefinable threshold value, wherein the threshold value is selected such that when the threshold value is exceeded there is a risk of damaging the internal combustion engine. The procedure repeats until this threshold is exceeded and an error message is signaled (step 350 ). The method takes place in a fuel cut-off operating phase of the internal combustion engine. This operating phase has the great advantage that the throttle valve is closed and thus a precise statement about the stored in the engine oil hydrocarbons of the fuel can be made due to the thus dense system. In addition, it is advantageous that during a fuel cut-off operating phase no disturbance of the comfort characteristics of the internal combustion engine occur.

The method is implemented in the control unit of the internal combustion engine, either as a circuit or as a computer program. The program code can be stored on a machine-readable carrier, for example a DVD, a CD-ROM, a flash memory and the like, so that a retrofitting of the control unit of the internal combustion engine is possible at any time.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102006059675 A1 [0005]

Claims (7)

A method for detecting a fuel input into the lubricating oil of an internal combustion engine, in particular of a motor vehicle, wherein the fuel input is detected by means of a lambda sensor, characterized in that due to a lambda value, which is detected during a fuel cut operating phase, a fuel entry into the Lubricating oil is closed. A method according to claim 1, characterized in that after making an oil change, the lambda value is detected in a fuel cut operating phase and stored as a reference value. A method according to claim 1, characterized in that a reference lambda value can be predetermined, which represents a non-existent fuel input into the lubricating oil. A method according to claim 2 or 3, characterized in that a lambda value is detected after a predetermined operating time or mileage of the vehicle in a fuel cut operating phase and this lambda value is compared with the reference value and then when the detected lambda value deviates from the reference value by a predetermined threshold, is concluded on an excessive dilution of the lubricating oil by fuel input. Control unit for operating an internal combustion engine, in particular a motor vehicle, characterized by means for carrying out the method according to one of the preceding claims 1 to 4 for detecting a fuel input into the lubricating oil of the internal combustion engine. Computer program that executes all the steps of a method according to one of claims 1 to 4, when it runs on a computing device, in particular the control unit of an internal combustion engine. Computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to one of claims 1 to 4, when the program is executed on a computer or a control unit of a vehicle.

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