Method and device for determining the quality of oil in an internal combustion engine

Abstract

The invention relates to a method and a device for determining the oil quality of an internal combustion engine (1), wherein the oil quality is determined after starting the internal combustion engine (1) by evaluating the switching time of an oil pressure switch (2) of the internal combustion engine (1).

Description

Technical Field

[0001] The invention relates to a method and a device for determining the quality of engine oil of an internal combustion engine. Background Art

[0002] Motor oils for internal combustion engines have the task of ensuring constant lubrication properties in all operating ranges of the internal combustion engine at the lowest possible friction for the moving mechanical components of the internal combustion engine.

[0003] In order to reduce fuel consumption and thus also reduce CO2 emissions of internal combustion engines, it is known to reduce the viscosity of the engine oil, but thereby reduce the lubricating properties of the engine oil. If additional fuel penetrates into the engine oil, the lubricating properties of the engine oil may drop so sharply that engine damage occurs.

[0004] Even today's friction-optimized engine designs lead to a high level of fuel ingress into the engine oil via the piston rings, especially during the warm-up phase of the internal combustion engine. These fuel ingresses temporarily reduce the quality of the engine oil. An additional problem is the increase in the oil level caused by these fuel ingresses. This can lead to foaming of the engine oil via the crankshaft of the internal combustion engine.

[0005] Therefore, there is a need to continuously understand the quality of the engine oil in order to resolve the conflicting objectives between the lubricating properties of the engine oil and friction reduction without causing engine damage.

[0006] It is already known to determine the quality of the engine oil using an oil level sensor and / or a special oil quality sensor. Resistive and capacitive measuring principles are used here, wherein the chemical properties of the engine oil are inferred by resistance measurement, conductivity measurement or dielectric constant measurement.

[0007] DE 100 53 250 A1 discloses an oil condition sensor device which comprises an ultrasonic sensor, a temperature sensor and an oil level sensor and an evaluation unit which derives an oil condition variable from the output signals of the sensors mentioned.

[0008] A system for monitoring the oil quality of an internal combustion engine is known from DE 10 2006 009 910 A1, in which the oil quality is calculated by correlating measured variables provided by the engine. The viscosity of the oil is determined from the rotational speed of the oil pump, the measured oil pressure and the oil temperature.

[0009] DE 10 2006 059 071 A1 discloses a method for determining the quality of oil in an oil supply line to an engine and / or a consumer. In this method, at least one temperature and at least one pressure are measured in the oil supply line. In addition, at least one information is generated from which the volume flow through the oil supply line is inferred. Information about the quality of the oil, in particular information about the viscosity of the oil, is determined from the measured temperature, the measured pressure and the volume flow. Summary of the invention

[0010] The object of the present invention is to specify a method and a device for determining the oil quality of an internal combustion engine which can be realized cost-effectively and does not require a special oil quality sensor.

[0011] This object is achieved by a method having the features specified in claim 1 and by a device having the features specified in claim 12. Advantageous embodiments and developments of the invention are specified in the dependent claims.

[0012] The present invention provides a method for determining the oil quality of an internal combustion engine, wherein the oil quality is determined after starting the internal combustion engine by evaluating a switching time of an oil pressure switch of the internal combustion engine.

[0013] According to one specific embodiment of the invention, the oil quality is determined after a cold start of the internal combustion engine by evaluating a switching time of an oil pressure switch of the internal combustion engine.

[0014] According to one specific embodiment of the invention, the oil quality is determined after a hot start of the internal combustion engine by evaluating a switching time of an oil pressure switch of the internal combustion engine.

[0015] According to one specific embodiment of the invention, the engine oil quality is determined as a function of an engine temperature which is present when the internal combustion engine is started.

[0016] According to one specific embodiment of the present invention, the engine oil quality is determined using a stored oil quality model.

[0017] According to one specific embodiment of the invention, the engine oil quality is determined by means of a repeated evaluation of the switching times of the oil pressure switch.

[0018] According to one specific embodiment of the invention, short-term engine oil quality information is determined.

[0019] According to one specific embodiment of the invention, long-term engine oil quality information is determined.

[0020] According to one embodiment of the present invention, a change in viscosity of the engine oil is detected.

[0021] According to one embodiment of the present invention, the determined oil quality information is compared with other models.

[0022] According to one specific embodiment of the invention, the engine oil quality is determined during operation of the internal combustion engine using a targeted change in the oil pressure setpoint value.

[0023] According to one embodiment of the present invention, a device for determining the oil quality of an internal combustion engine is provided, the device having an engine control unit and an oil pressure switch, the oil pressure switch transmitting binary switching information to the engine control unit when a predetermined pressure threshold is exceeded after starting the internal combustion engine, wherein the engine control unit is constructed to determine the oil quality by evaluating the switching time of the oil pressure switch.

[0024] The invention is particularly advantageous in that the desired oil quality information can be determined inexpensively without using a special oil quality sensor. In the method according to the invention, use is made of the fact that after starting the internal combustion engine, when the oil pressure is built up, the analysis of the pressure gradient allows inferences about the oil quality. The pressure gradient is approximated by using the switching time of the oil pressure switch which is present anyway and which has hitherto only been used to signal to the engine control unit after starting the engine that the engine has reached the minimum oil pressure required for engine operation when a predetermined oil pressure is exceeded. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Further advantageous characteristics of the invention are apparent from the following exemplary description thereof with reference to the figures.

[0026] Figure 1 A block diagram of a device for determining the oil quality of an internal combustion engine is shown,

[0027] Figure 2 shows a diagram illustrating the switching times of the oil pressure switch after a cold start of the internal combustion engine with a fuel introduction of 1% into the oil,

[0028] Figure 3 shows a diagram illustrating the switching times of the oil pressure switch at a 10% introduction of fuel into the oil after a cold start of the internal combustion engine,

[0029] Figure 4 shows a diagram illustrating the switching times of the oil pressure switch at a fuel introduction of 1% into the oil after a hot start of the internal combustion engine,

[0030] Figure 5 shows a diagram illustrating the switching times of the oil pressure switch at a 10% fuel introduction into the oil after a hot start of the internal combustion engine, and

[0031] Figure 6 A graph illustrating short-term oil quality information and long-term oil quality information is shown. DETAILED DESCRIPTION

[0032] Figure 1 The block diagram of a device for determining the oil quality of an internal combustion engine is shown. The device has an engine control unit 1, an oil pressure switch 2, an engine temperature sensor 3, a memory 4, a storage device 5 and a display 6.

[0033] The output signals of the oil pressure switch 2 and the engine temperature sensor 3 are in particular supplied to the engine control unit 1. In addition, the engine control unit 3 controls the display 6 so that, for example, a warning message as will be explained below is displayed there. In addition, the engine control unit 1 communicates with memories 4 and 5. In the memory 4, data corresponding to an empirically determined oil quality model are stored. In the memory 5, the following data corresponding to other empirically determined models, such as the fuel introduction of the engine oil based on the blow-by behavior and the modeling of the exhaust gas when the engine operating temperature is reached are stored.

[0034] The oil pressure switch 2 is arranged in the oil circulation system and outputs binary switching information to the engine control device 1 after the internal combustion engine is started if the oil pressure established after the internal combustion engine is started exceeds a mechanically calibrated pressure threshold value. This binary switching information is provided, for example, in the form of a transition from a high level to a low level, for example from level 1 to level 0. This binary switching information provided by the oil pressure switch has the following task: signaling to the engine control device that the oil pressure established after the internal combustion engine is started has reached the minimum oil pressure required for the engine operation. According to the present invention, the engine control device is further configured to detect the switching time of the oil pressure switch 2. Here, the switching time of the oil pressure switch is understood to be the period of time that elapses from the start of the engine until the binary switching information is output by the oil pressure switch 2. In addition, the engine control device 1 is configured to determine the oil quality by evaluating the switching time of the oil pressure switch. Here, the following fact is used, that is, the analysis of the pressure gradient when the oil pressure is established allows the oil quality to be inferred, wherein the pressure gradient is approximated by the switching time of the oil pressure switch 2.

[0035] Information about the introduction of fuel into the engine oil can be determined by means of the above-described pressure gradient analysis.

[0036] Furthermore, the viscosity of the engine oil changes over the service life of the engine oil and during motor operation of the internal combustion engine as fuel is introduced into the engine oil. These viscosity differences also manifest themselves in different response behaviors of the oil pressure switch, ie, different switching times of the oil pressure switch.

[0037] After the internal combustion engine is started, the oil is delivered by the mechanical oil pump in the oil sump and the pressure build-up of the engine oil is thus started. During the engine ramp-up, fluctuations in the oil pressure occur which are greater when there is a cold start, in which the oil circuit is initially still empty, than when there is a subsequent hot start, in which the oil circuit is already filled. However, in both cases, it can be seen from the measurement and evaluation of the switching time of the oil pressure switch that a high level of fuel introduction into the engine oil leads to a shorter switching time of the oil pressure switch, as will be explained exemplarily below.

[0038] Figure 2 The diagram illustrates the switching time t of the oil pressure switch after a cold start of the internal combustion engine with a fuel introduction of 1% into the oil. s Here, the engine speed N in revolutions per minute (rpm) is plotted upward on the left, the level PO of the output signal of the oil pressure switch is plotted upward on the right, and the time t in seconds is plotted to the right. In the graph, line L1 represents the time point t1 when the engine is started, line L2 represents the time point t2 when the oil pressure switch 2 outputs the switching signal, curve K1 represents the level of the output signal of the oil pressure switch, and curve K2 represents the change process of the engine speed N. From Figure 2 It can be seen that the engine speed N is about 1220 rpm, at which the oil pressure switch outputs a switching signal, and the switching time of the oil pressure switch is t s , that is, the duration between starting the engine and outputting the switching signal is approximately 2.1 s.

[0039] Figure 3 The diagram illustrates the switching time t of the oil pressure switch after a cold start of the internal combustion engine with a fuel introduction of 10% into the oil. s Here, the engine speed N in revolutions per minute (rpm) is plotted upward on the left, the level PO of the output signal of the oil pressure switch is plotted upward on the right, and the time t in seconds is plotted to the right. In the graph, line L1 represents the time point t1 when the engine is started, line L2 represents the time point t2 when the oil pressure switch 2 outputs the switching signal, curve K1 represents the level of the output signal of the oil pressure switch, and curve K2 represents the change process of the engine speed N. From Figure 3 It can be seen that the engine speed N is about 1250 rpm, at which the oil pressure switch outputs a switching signal, and the switching time of the oil pressure switch, ie, the duration between starting the engine and outputting the switching signal, is about 1.55 s.

[0040] Figure 4 The diagram illustrates the switching time t of the oil pressure switch after a subsequent start or hot start of the internal combustion engine with a fuel introduction of 1% into the oil. sHere, the engine speed N in revolutions per minute (rpm) is plotted upward on the left, the level PO of the output signal of the oil pressure switch is plotted upward on the right, and the time t in seconds is plotted to the right. In the graph, line L1 represents the time point t1 when the engine is started, line L2 represents the time point t2 when the oil pressure switch 2 outputs the switching signal, curve K1 represents the level of the output signal of the oil pressure switch, and curve K2 represents the change process of the engine speed N. From Figure 4 It can be seen that the engine speed N is about 590 rpm, at which the oil pressure switch outputs a switching signal, and the switching time of the oil pressure switch, that is, the duration between starting the engine and outputting the switching signal, is about 0.35 s.

[0041] Figure 5 The diagram illustrates the switching time t of the oil pressure switch after a subsequent start or hot start of the internal combustion engine with a fuel introduction of 10% into the oil. s Here, the engine speed N in revolutions per minute (rpm) is plotted upward on the left, the level PO of the output signal of the oil pressure switch is plotted upward on the right, and the time t in seconds is plotted to the right. In the graph, line L1 represents the time point t1 when the engine is started, line L2 represents the time point t2 when the oil pressure switch 2 outputs the switching signal, curve K1 represents the level of the switching signal, and curve K2 represents the change process of the engine speed N. Figure 5 It can be seen that the engine speed N is about 380 rpm, at which the oil pressure switch outputs a switching signal, and the switching time of the oil pressure switch, that is, the duration between starting the engine and outputting the switching signal, is about 0.20 s.

[0042] If the detected switching times are assigned to the start types (cold start or subsequent start or hot start) at different engine starting temperatures, an oil quality model can be determined empirically, which is stored in the memory 4 and based on which the oil quality can be inferred during operation of the internal combustion engine based on the detected switching times and the detected engine temperature.

[0043] The oil quality is determined by repeated measurement of the switching times and subsequent evaluation using a stored oil quality model.

[0044] An advantageous embodiment is to determine short-term oil quality information and long-term oil quality information. The short-term oil quality information provides information about short-term fuel introduction into the oil. The long-term oil quality information provides information about the effects of long-term oil aging.

[0045] The increased introduction of fuel into the engine oil takes place during repeated cold starts with a fully warmed-up engine without significant driving (Fahrbetreib), that is, when driving a number of short distances in succession with a cold engine. Due to the introduction of fuel, the viscosity of the engine oil decreases dynamically. As a trend, shorter switching times of the oil pressure switch can be measured over a number of measured engine starts. If the warmed-up engine operating state is reached during driving, fuel components are vented from the engine oil. This leads to a very rapid increase in viscosity.

[0046] The short-term behavior of the oil quality is masked by the long-term reduction in viscosity due to the aging of the oil. Multigrade oils are additive-infused oils with a specific base viscosity. Additives cause a single grade oil to cover a range of viscosities. With increasing aging, the oil adopts its base viscosity.

[0047] Figure 6 A diagram is shown which illustrates short-term and long-term oil quality information. In this diagram, the decreasing oil viscosity V and thus also the decreasing oil quality Q are plotted downwards on the vertical axis and the time t is plotted to the right. The curve K3 shown in the diagram describes the short-term oil quality information. The curve K4 shown in the diagram describes the long-term oil quality information. Interval This corresponds to the interval in which the engine has been started for several short periods in succession without reaching the operating temperature state. In the interval, the fuel incorporation in the oil increases. As a result, the oil quality Q and the oil viscosity V decrease. This corresponds to a range in which there is a drive with an engine at operating temperature. In the case of , the fuel incorporation into the engine oil is reduced. As a result, the engine oil quality Q and the engine oil viscosity V increase. Figure 6 The time t at which the oil change is due is also specified. w This point in time is reached when the long-term oil quality information does not exceed a predefined oil quality.

[0048] According to one specific embodiment of the invention, the oil quality information determined using the stored oil quality model can be compared with information from one or more other models whose data are stored in Figure 1 These other models may correspond, for example, to the modeling of the fuel introduction of the oil based on the Blow-By behavior and the exhaust gas when the engine operating temperature is reached.

[0049] If the engine configuration includes a regulated oil pump with adjustable pressure levels, there is the possibility of determining the oil quality during the drive by selectively changing the oil pressure setpoint value. In this case, switching is performed between high and low oil pressure levels. The oil quality is then determined from the delayed switching time of one or more oil pressure switches.

[0050] Using the determined oil quality, a recommendation for a variable oil change interval can be output. During operation, a warning of an excessively high fuel content in the oil can also be displayed on the display 6. A simplified oil level plausibility check can also be performed by temporarily reducing the viscosity of the oil. In addition, a warning of foaming of the oil by the crankshaft can be displayed on the display 6.

Claims

1. A method for determining the quality of oil in an internal combustion engine, characterized in that After starting the internal combustion engine, determining the oil quality by evaluating the switching time of the oil pressure switch of the internal combustion engine, Therein, analysis of the pressure gradient during the build-up of oil pressure after starting the internal combustion engine allows conclusions to be drawn about the oil quality, wherein the switching time of the oil pressure switch is understood to be the period of time that elapses from starting the engine until the output of binary switching information by the oil pressure switch.

2. The method according to claim 1, characterized in that After a cold start of the internal combustion engine, the engine oil quality is determined by evaluating a switching time of an oil pressure switch of the internal combustion engine.

3. The method according to claim 1, characterized in that After a warm start of the internal combustion engine, the engine oil quality is determined by evaluating a switching time of an oil pressure switch of the internal combustion engine.

4. The method according to any one of claims 1 to 3, characterized in that The engine oil quality is determined as a function of an engine temperature which is present when the internal combustion engine is started.

5. The method according to any one of claims 1 to 3, characterized in that The engine oil quality is determined using a stored oil quality model.

6. The method according to any one of claims 1 to 3, characterized in that The engine oil quality is determined by means of repeated evaluation of the switching times of the oil pressure switch.

7. The method according to any one of claims 1 to 3, characterized in that Determines short-term oil quality information.

8. The method according to any one of claims 1 to 3, characterized in that Determines long-term oil quality information.

9. The method according to any one of claims 1 to 3, characterized in that A change in viscosity of the engine oil is detected.

10. The method according to any one of claims 1 to 3, characterized in that The determined oil quality information is compared with other models.

11. The method according to any one of claims 1 to 3, characterized in that The engine oil mass is determined during driving operation of the internal combustion engine while causing a targeted change in the oil pressure setpoint value.

12. A device for determining the oil quality of an internal combustion engine, the device comprising an engine control unit and an oil pressure switch, the oil pressure switch transmitting binary switching information to the engine control unit when a predetermined pressure threshold is exceeded after starting the internal combustion engine, characterized in that The engine control unit is designed to determine the oil quality by evaluating the switching time of the oil pressure switch, wherein an analysis of the pressure gradient when the oil pressure is built up after starting the internal combustion engine allows the oil quality to be inferred, wherein the switching time of the oil pressure switch is understood to be the period of time that elapses from starting the engine until the output of binary switching information by the oil pressure switch.

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