WO2008071639A1

WO2008071639A1 - Method for determining the oil quality

Info

Publication number: WO2008071639A1
Application number: PCT/EP2007/063561
Authority: WO
Inventors: Wolfgang Samenfink; Andreas Kufferath
Original assignee: Robert Bosch Gmbh
Priority date: 2006-12-14
Filing date: 2007-12-07
Publication date: 2008-06-19
Also published as: DE102006059071A1

Abstract

The invention proposes a method for determining the oil quality in an oil supply line (122) to a motor (112) and/or to a load (120). In this case, at least one temperature and at least one pressure in the oil supply line (122) are measured. Furthermore, at least one item of information is generated, from which conclusions are drawn about the volumetric flow through the oil supply line (122). Information about the oil quality, in particular information about the viscosity, is generated from the measured temperature, the measured pressure and the volumetric flow.

Description

description

title

Method for determining the quality of oil

State of the art

The invention relates to a method for determining the oil quality, which can be used in particular in internal combustion engines or in other types of engines. Furthermore, the invention relates to a device for carrying out the method.

In engines, especially in internal combustion engines, the quality of the lubricating oil is of great importance for the life of the engine. In addition to regular oil aging, quality can quickly deteriorate due to various operating conditions, such as extreme operating conditions. The latter is usually the more critical case for the engine. For example, at low temperatures, a larger amount of fuel is added to the lubricating oil, thus greatly diluting the lubricating oil. As a result, the viscosity of the oil decreases, which in turn leads to a sinking lubricity of the oil. This can lead to increased wear of the internal combustion engine up to engine failure. In addition, the oil level can increase unacceptably by a continuous cold operation, which can lead to catalyst damage in extreme cases.

Various systems are known from the prior art, by means of which the oil quality can be determined or estimated. Such systems are already partially commercially available.

Part of these systems uses simple predictive models to describe oil quality, which typically do not directly measure oil quality. As an example of a simple model, the calculation of the service interval, ie the remaining distance to the oil change service, can be estimated using several pieces of information become. Thus, for example, in each phase in which the ignition is switched on, the distance traveled in each case in a few seconds driving distance with the summed during the same time consumed fuel and thereby passed through oil temperature profile are coupled. This results in wear of the motor due to thermal stress. This value is used to determine the remaining distance to the required service on the basis of stored empirical values.

Another alternative option is the use of oil quality sensors. The oil quality can be measured by measuring one or more parameters, such as oil viscosity, permeability or temperature. These measuring principles can also be summarized in a single measuring system.

However, these known from the prior art methods or systems must be able to cope with high demands in practice. So it has been shown that simple models that work without direct oil quality sensor, are fraught with great uncertainties. Not in all cases, the reality is represented by the stored empirical values. The integration of a sensor oriented on the oil quality, however, causes not negligible additional costs due to the complexity of the known sensors and measuring principles. Known sensor systems, such as the combi sensors, are in many cases extremely expensive and associated with high production costs. Furthermore, in particular, the known combination sensors require a not insignificant space and a corresponding evaluation.

Disclosure of the invention

In contrast, a method is proposed which determines the oil quality in a simple manner as a function of the operating state and avoids the disadvantages of known systems and methods. The oil quality is determined in particular in the form of an oil viscosity (or a corresponding quantity from which the oil viscosity can be deduced). In this case, instead of a complex direct measurement of the oil viscosity or other directly coupled with the oil quality measurements (such as refractive index, dielectric or similar sizes) on the extremely easy to be determined Measured variables of temperature and pressure are used. These parameters are to be developed with favorable and reliable sensors. Coupled sensors are also possible and are described, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, 1st Edition, June 2001, pages 82-84. Such a sensor is already used today in numerous applications and is introduced as a mass product.

The proposed method is based on the fact that at least one temperature and at least one pressure is measured in an oil feed line to at least one consumer of the engine. Furthermore, at least one information is generated, from which it is concluded that there is a volume flow through the oil line. Information about the oil quality, in particular information about the viscosity, is generated from the measured temperature, the measured pressure and the volume flow.

The proposed method can in particular use a model for the oil circuit which is parameterized by the above-described measured values oil pressure and oil temperature. Due to the deviations of the oil pressure and the oil temperature from the predicted model sizes during operation, short-term and longer-term deviations from the setpoint can be used to determine the oil quality and the wear.

The proposed method and the proposed device for carrying out the method are thus distinguished from conventional systems by the use of inexpensive, readily available components, as well as by the use of well-practicable in practice measuring principles. The method can thus be implemented inexpensively, but at the same time the accuracy of the determination of the oil quality compared to most currently used systems is greatly improved.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show it: - A -

Figures IA and IB show the course of the oil viscosity as a function of an admixture of diesel fuel or gasoline;

2 shows an oil circuit of an internal combustion engine with an inventive

Device for determining oil quality; Figure 3 measured data of the course of oil pressure and oil temperature as a function of

Time; and

Figure 4 is a graph of viscosity as a function of temperature for various

Oils.

FIGS. 1A and 1B show the course of the dynamic viscosity η, indicated in millipascal seconds (mPas), as a function of the admixture of fuel (the concentration in percent by weight is shown). Here, Figure IA shows the course for the admixture of diesel oil, whereas Figure IB represents the course for the admixture of gasoline.

It can be clearly seen from the illustrations that there is a clear correlation between the viscosity and the contamination of the oil. The viscosity and thus the lubricity of the oil drops drastically with increasing contamination. This plot shows that viscosity is a useful measure of oil quality quantification.

FIG. 2 schematically shows an oil circuit 110 of an internal combustion engine 112 and an apparatus 114 according to the invention for determining the oil quality in an exemplary embodiment as a block diagram. On the basis of this embodiment of the device 114, the method according to the invention will be described in an exemplary embodiment. Of the

Internal combustion engine 112 may be configured in various ways and may include, for example, a gasoline engine and / or a diesel engine. However, other embodiments are also conceivable, for example hybrid motors or even operation with purely electric motors.

The oil circuit 110 has an oil pan 116 (oil sump) and an oil pump 118 connected to the oil pan 116. The oil pump 118 is related to the internal combustion engine 112. As further consumers 120 connected via one or more oil supply lines 122. From the oil supply line 122 branches off in front of the internal combustion engine 112 from a discharge line 124, in which a pressure relief valve 126 is received. From the internal combustion engine 112 or the consumers 120, in turn, a return line 128 leads back to the oil pan 116.

The device 114 comprises an oil pressure sensor accommodated in the oil feed line 122 and a temperature sensor, which in this embodiment shown in FIG. 2 are designed as an integrated sensor element (p, T sensor 130). The sensor element 130 can be designed, for example, as described in Robert Bosch GmbH: Sensors in the Motor Vehicle, 1st Edition, June 2001, pages 82-84.

Furthermore, the device 114 comprises a control device 132. This control device 132 is set up to receive measurement data from the sensor 130 directly or indirectly. In the exemplary embodiment illustrated in FIG. 2, the control unit 132 is configured as a control unit designed separately from an engine control unit 134 of the internal combustion engine 112. The control unit 132 and the engine control unit 134 are connected to each other via a line 136, which allows a bidirectional data exchange. For example, this line 136 may be a CAN bus. Other types of interfaces or systems for data exchange can also be used, whereby non-contact data exchange is also possible, for example by exchanging electromagnetic signals (for example radio waves or infrared signals).

As an alternative to the embodiment shown in FIG. 2, the control unit 132 and the engine control unit 134 may also be formed at least partially identically to the component or integrated in an instrument cluster. The controller 132 may include, for example, a microprocessor, including one or more electronic data storage in which corresponding data may be stored. The control unit can be set up according to the program in order to carry out the method described in full or in part and / or to control it. Furthermore, corresponding interfaces for programming and similar input and output means can be provided. The oil circuit 110 is operated such that in operation, the oil pump 118 sucks engine oil from the oil pan 116. Due to the oil production, an oil pressure p is built up in the oil supply lines 122 to the internal combustion engine 112 or the consumers 120. Depending on the state of wear of the oil pump 118, a more or less pronounced bypass volumetric flow occurs, which in the illustration according to FIG. 2 is designated symbolically as a gap loss 138 of the oil pump 118. The flow rate is dependent on the speed of the oil pump 118, which can be driven for example directly by the engine 112. In order to be able to provide the required volumetric flow (that is to say a volume of oil per unit time) for the internal combustion engine 112 and the consumers 120 at low rotational speeds, the oil pump 118 is designed oversized. At high speeds, therefore, the pressure in the oil supply line 122 must be partially removed and limited by the pressure relief valve 126 and the diversion line 124.

The main volume flow of the oil flows through the engine 112. In addition to the portion of the oil needed to lubricate the engine 112, an amount of oil is needed for the consumers 120. The consumers 120 are made up, for example, of camshaft actuators which use the oil pressure to adjust actuators. Another consumer 120 may be an oil syringe for a piston cooling. Also in the area of the internal combustion engine 112 and the consumer 120, gap losses usually occur, which are indicated symbolically in FIG. 2 by the reference numeral 140. As with the oil pump 118, the gap losses 140 in the internal combustion engine 112 and in the consumers 120 are generally dependent on the wear of these components. Since the wear takes place very slowly, this leakage current changes only slowly over the entire service life of the internal combustion engine 112.

In FIG. 3, measured data of oil pressure p and oil temperature T are plotted, which were obtained by means of the device shown in FIG. 2 and which prove that an oil quality can actually be deduced from the two measured variables p and T determined. The measured data were obtained during a cold test, which is used to evaluate the oil dilution. Operating conditions with a constant operating point of 1000 rpm and full load were used. The coolant temperature was 50 ⁰ C. Plotted in FIG. 3, the pressure (diamond, left scale) in bar and the oil temperature (square, right scale) in ⁰ C, each as a function of the operating time t in hours.

It can be seen that the oil pressure in the long-term behavior, starting from originally 1.99 bar, has dropped to 1.83 bar after two hours. At the end of the test, an oil dilution of 6% was detected by gas chromatographic analysis.

In experiments in which by a corresponding parameterization of the internal combustion engine 112 even larger fuel inputs were caused in the oil, even significantly lower oil pressures could be detected after the corresponding operating time t. In each case fresh oil was used at the beginning of the test.

As can be seen from FIG. 3, fluctuations in the oil pressure, which correlate with fluctuations in the temperature, can be detected beyond the long-term drift. This is because the viscosity η changes with temperature. This temperature influence on the viscosity is explainable and can be predicted.

Thus, Figure 4 shows an example of the curve of the viscosity η (in arbitrary units) as a function of the temperature T in ⁰ C for different types of oil.

The example for a stationary operating point shown in FIG. 3 shows how the fundamental dependence of the oil pressure on the oil viscosity during engine operation is represented. The measurement data of pressure and temperature shown in FIG. 3, which were obtained by means of the device 114 shown in FIG. 2, can be compared either as "raw data" with predetermined nominal values in order to obtain information about the oil quality, for example about the viscosity to generate.

In order to be able to conclude the oil quality at various operating points, a volume flow through the oil feed line 122 is additionally taken into account. To make this procedure clear, it can be assumed, for example in the simplest case, that the law of Hagen-Poiseuille applies to the flow through the oil feed 122. After that, the volume flow through the oil supply line 122 is proportional to the pressure difference at both ends the oil supply 122, and inversely proportional to the viscosity. With known volume flow, known pressure (which in turn can be closed at least approximately to the pressure difference at both ends of the oil supply line 122) can thus be deduced the viscosity of the oil in the oil supply 122. The viscosity is again a function of temperature (see Figure 4), ideally the relationship is either known or can be calculated. In this way, a viscosity or a viscosity-correlating variable can be determined, which in turn (temperature-adjusted) can be compared with corresponding comparison curves in order to conclude on the oil quality.

The described method, in which the law of Hagen-Poiseuille is utilized, preferably requires the measurement of pressure and temperature in two places with an exact procedure. Alternatively, it would also be possible to work with approximations, for example with an assumption about a specific, constant oil pressure at the end of the oil feed 122. However, such multiple measurements or simplifications are not technically feasible or sufficiently precise in all cases. Furthermore, for example, the assumption of a flow according to the Hagen-Poiseuille law is based on the assumption of a laminar flow, which is not the case in many lines due to the complex line geometry. Rather, turbulent flow profiles often occur. Therefore, in order to be able to conclude the oil quality at various operating points, as an alternative or in addition to the described analytical or semiempirical method, an empirical method may be used in which, as explained below, for example, an evaluation of the volumetric flow by means of maps above the pump speed respectively. Furthermore, in this way, a correction of the evaluation over the lifetime take place, which could be required for example due to wear effects occurring.

Stationary operating points of the internal combustion engine 112 are particularly suitable for the measurement and analysis, since here the influence of unsteady oil volume flows of the consumers 120 on the oil pressure can be neglected. Whether a consumer 120 and / or the internal combustion engine 112 requires an oil volume flow and how large this oil volume flow is can be queried, for example, as information via the engine control unit 134 become. For example, the control of camshaft actuators is triggered directly via the engine control unit 134. In this way, the at least one piece of information can thus be generated, from which it is possible to deduce the volume flow through the oil feed line 122. Alternatively, however, additional sensors could be used to generate appropriate information about the oil flow.

Instead of using stationary operating points, it is also possible to use unsteady operating points at which none of the consumers 120 requires an additional oil volume flow. This information is usually present in the engine control unit 134.

The oil volume flow may be indicated, for example, as a function of the rotational speed of the internal combustion engine 112, in particular in the case in which the oil pump 118 is driven directly or indirectly by the internal combustion engine 112. The information about the speed is directly available in the engine control unit 134 and can be interrogated, for example, via the line 136.

To implement the method described above, ie the inference of the pressure and the temperature and the flow or the speed of the oil quality, various technical refinements are available. Thus, for example, the measured pressure can be compared with at least one output characteristic in which an oil pressure is stored as a function of the volume flow, parameterized with the temperature. This output characteristic can be stored, for example, in an electronic data store, for example in a lookup table. The influence of the oil temperature on the oil viscosity can be calculated by appropriate approximation functions (see for example FIG. 4) or determined empirically or semiempirically.

Alternatively or additionally, the measured pressure can also be compared with at least one characteristic map, for example with a characteristic map, which comprises the pressure above the temperature and the volume flow. Instead of the volume flow, the speed can also be used here again. The map can in turn be stored, for example, in a lookup table in the control unit 132 or another data memory. Preferably the at least one output characteristic and / or the at least one characteristic field is stored for the oil type provided in the initial filling.

Instead of these data technology particularly easy to implement procedures which work with given, stored output characteristics or maps, alternatively or additionally, an analytical or semiempirisches method can be used in which from the measured pressure, the measured temperature and the flow / the speed current viscosity is calculated. This calculated viscosity can then be compared to a predetermined desired viscosity to obtain information about the oil quality.

If, after the start of the internal combustion engine 112, a large deviation in the oil viscosity for the last evaluation exists at a point which can be used for the evaluation (for example a deviation above a predefined threshold value), then an oil change that has occurred in the meantime getting closed. In this case, the output characteristic curves or output characteristics for the dependencies of the oil viscosity, which will be assumed below, can be reset.

In further operation, the viscosity, determined via the oil pressure, is compared with the stored characteristic map. If the viscosity is outside a specified range, which is defined for a non-critical engine operation, for example, a warning can be issued to the driver.

Furthermore, in addition to driver information, an action by the device 114 or the control device 132 can also be made on the internal combustion engine 112 or the entire engine operation. In particular, in an extreme case where the viscosity is outside a specified range, engine operation may be restricted. Furthermore, the proposed method offers the possibility of determining the oil change interval from a real operation and possibly output this information to the driver. As described with reference to FIG. 2, at high rotational speeds, it is necessary to control the oil pressure through the overpressure valve 126. With knowledge of the oil quality and the origin map, the speed for that point can be predicted. Shifts this speed over the lifetime of the internal combustion engine 112 to higher speeds, it can be concluded from this from wear due to increased gap losses 140. This wear can in turn be used to correct the dependencies of the maps described above, for example, deposited. This can increase the accuracy of the analysis of the oil quality.

In a further development of the method according to the invention, an oil dilution by fuel is concluded from the oil quality. If such an oil dilution over a predetermined level, so appropriate action can be taken. For example, in turn, the operation of the internal combustion engine 114 can be acted upon. Alternatively or additionally, the temperature level of cooling water and / or oil can be increased if such control interventions are possible. In this way, for example, the fuel can be expelled faster from the oil, so that the oil quality is improved again.

Furthermore, it is conceivable to store maps for the oil consumption of the actuators. If the oil pressure deviates from the stored oil pressure during the setting process, it can be concluded that the corresponding actuator is wearing out. This can be used, for example, for information and diagnostic purposes, which is a further advantage of the proposed device 114. Furthermore, due to the provision of the oil pressure sensor 130 can be dispensed with a conventional oil pressure switch.

Another option is to use suitable models to determine the engine temperature by measuring the oil temperature. In extreme cases, even a motor temperature sensor can be dispensed with.

Claims

claims

A method for determining the oil quality in at least one oil supply line (122) to at least one engine (112) and / or at least one consumer (120), comprising the following steps: a) in the oil supply line (122) is at least one temperature and at least one Pressure measured; b) at least one information is generated, from which a volume flow through the oil feed line (122) is closed; c) information about the oil quality, in particular information about a viscosity, is generated from the measured temperature, the measured pressure and the volume flow.

2. Method according to the preceding claim, characterized in that in method step c) the measured pressure and the measured temperature are compared with setpoint values specific for the respective volume flow.

3. The method according to any one of the preceding claims, characterized in that in step b) generated information about the volume flow contains at least one rotational speed of the motor (112).

4. The method according to any one of the preceding claims, characterized in that the method steps a) and b) are carried out at a stationary operating point of the motor (112).

5. The method according to any one of the preceding claims, characterized in that in step c) at least one of the following sub-steps is performed: - the measured pressure is compared with at least one output characteristic in which an oil pressure is stored as a function of the volume flow, wherein the output characteristic is parameterized with the temperature; - The measured pressure is compared with at least one map on the temperature and the flow rate;

From the measured pressure, the measured temperature and the volume flow, a viscosity is calculated by means of an analytical or semiempirical method, wherein the calculated viscosity is preferably compared with a predetermined desired viscosity.

6. The method according to any one of the preceding claims, characterized in that the information generated in step c) information about the oil quality with predetermined setpoints is compared, wherein according to the result of this comparison one or more of the following measures are performed:

an information is output to a driver, in particular a warning,

- Engine operation is adjusted according to the oil quality, especially limited in poor oil quality.

7. The method according to any one of the preceding claims, characterized in that is closed from the information about the oil quality to an oil dilution by fuel and, accordingly, a temperature level of a cooling water and / or the oil is raised.

8. The method according to any one of the preceding claims, characterized in that the motor (112) further comprises at least one pressure relief valve (126) for the control of oil pressure, being closed from the information about the oil quality to a Absteuerdrehzahl, wherein the pressure relief valve (126 ) opens to Absteuern.

9. The method according to the preceding claim, characterized in that it is concluded from the Abdrehdrehzahl on a motor wear.

10. The method according to one of the two preceding claims, characterized in that the Absteuerdrehzahl for generating the information about the oil quality in step c) is used.

11. The method according to any one of the preceding claims, characterized in that the temperature and / or the pressure for at least one of the following diagnostic purposes are used:

- From a deviation of the pressure during a control operation of an actuator of a given command pressure is concluded that a malfunction and / or wear of the actuator;

- From the temperature is closed to a temperature in the engine (112).

12. Device (114) for determining the oil quality in at least one oil supply line (122), wherein the device (114) at least one oil pressure sensor (130) for measuring an oil pressure in the oil supply line (122) and at least one temperature sensor (130) for measuring a temperature in the oil supply line (122), wherein the device (114) further comprises at least one control device (132) and wherein the device (114) is arranged to perform a method according to one of the preceding method steps.

13. Device (114) according to the preceding claim, characterized in that the device (114) is set up to query the information about the volume flow in method step b) on an engine control unit (134), wherein the control device (132) of the device ( 114) is formed as part of the engine control unit (134) or as a separate control unit (132) which is in communication with the engine control unit (134).