WO2008074559A1

WO2008074559A1 - A method and sensor for measuring concentration of particulate in lubrification oil in an internal combustion engine

Info

Publication number: WO2008074559A1
Application number: PCT/EP2007/061728
Authority: WO
Inventors: Giorgio Girondi
Original assignee: Ufi Innovation Center S.R.L.
Priority date: 2006-12-20
Filing date: 2007-10-31
Publication date: 2008-06-26
Also published as: ITRE20060159A1

Abstract

In a method and sensor for measuring a concentration of particulate in lubrication oil contained in a lubrication circuit (1) of an internal combustion engine (2), the method comprises a stage of performing a first measurement of a predetermined lubrication oil impurity parameter which depends on a particulate concentration in the lubrication oil. The method also comprises performing a second measurement of the impurity parameter on a portion of the lubrication oil contained in the lubrication circuit, which is in the same conditions as the lubrication oil subjected to the first measurement but has been purified of the particulate contained therein. An index is then calculated for the particulate concentration in the lubrication oil on the basis of the values obtained from the first and second measurements.

Description

A METHOD AND SENSOR FOR MEASURING CONCENTRATION OF PARTICULATE IN LUBRICATION OIL IN AN INTERNAL COMBUSTION ENGINE

Technical Field

The present invention concerns a method and a sensor for measuring particulate concentration in lubrication oil in an internal combustion engine, typically a Diesel engine.

Background Art As is known, lubrication is one of the most important factors that contribute to ensuring the efficiency and long working life of an internal combustion engine.

Lubrication is generally obtained by means of a hydraulic circuit provided with a pump which constantly forces lubrication oil into contact with the moving parts of the engine, in such a way as to prevent reciprocal friction from causing serious, often irreparable damage.

The lubrication circuit is generally provided with an oil filter which traps any solid pollutants in the lubricating oil, such as for example large dust particles, or wear particles. Solid pollutants are very dangerous because they can scratch and erode the moving parts of an engine, and block conduits.

During use, however, lubrication oil undergoes a progressive reduction in performance, making protection of the engine less effective, and making it necessary to replace the lubrication oil periodically. The progressive reduction in performance depends on numerous factors including, especially with Diesel engines, the presence in the lubrication oil of large carbon particles produced by combustion, generally known by the term particulate.

The oil filter does not trap particulate particles in relevant quantities, and the progressive increase in their concentration in the lubrication oil contributes very significantly to a progressive reduction in the performance of the oil. For this reason, lubrication circuits are usually provided with special sensors that measure particulate concentration in the lubrication oil, which warn a user of the need to replace the lubrication oil when the concentration exceeds a predetermined threshold value. At present the market offers numerous particulate concentration sensors, which often differ from one another in their structure, how they function and their strategies for analysing the oil.

However most of the known sensors are based on measuring a predetermined characteristic parameter of the lubrication oil which depends directly on the particulate concentration in the oil.

This parameter, henceforth termed the impurity parameter, can be, for example, the dielectric permittivity of the lubrication oil, the impedance as a function of the dielectric spectrum thereof, or the electric conductivity thereof. Therefore the sensors are provided with a processor which implements a calculation algorithm that associates a value of particulate concentration to each value of the impurity parameter, making it possible to evaluate, at each measurement, whether the particulate concentration is within a tolerable range of values. Should this not be the case, the processor activates appropriate warning instruments ot inform the user that the lubrication oil needs replacing.

A drawback of known sensors is that the impurity parameters do not depend only on particulate concentration, but also on many other contingent conditions relating to the lubrication oil. For example, the permittivity of the lubrication oil also depends on the temperature and oxidation of the oil, on the concentration of polar molecules, such as water or antifreeze, on the concentration of electrically charged particles, such as various types of ions, on the possible presence of additives, and on the presence of diesel fuel, which might have leaked through the cylinder seals and gaskets. In particular, these conditions generally depend on the amount of use to which the lubrication oil has been subjected, that is, how long it has already been in use within the hydraulic circuit.

They are however not always a symptom of an effective decline in the performance of the lubricating oil, and thus can present an error in measurement which in some circumstances can render the reading taken so inaccurate as to be unreliable.

A known technique for overcoming this drawback is to compare the measurement of the impurity parameter of the lubrication oil with the measurement of other lubrication oil parameters that depend principally on the aforementioned error conditions, so as to weight the effects of the latter and make measurement reliable.

To do this, however, the sensor processor must adopt a calculation algorithm that takes a very high number of variables into account, which often lead to an increase in the degree of inaccuracy of analysis; also, the electronic equipment required for this have costs that are incompatible with the cost of the sensor.

The aim of this invention is to make available a method and a sensor for measuring particulate concentration that overcomes the aforementioned drawbacks, within the ambit of a simple, rational, low-cost solution.

This aim is achieved by the invention as characterised in the attached claims.

Disclosure of Invention

In particular a method is provided which includes performing a first measurement of a preset impurity parameter in the lubrication oil contained in the lubrication circuit, which initial measurement relates to the quantity of particulate contained therein.

The invention also includes the following further stages: performing a second measurement of the same impurity parameter in a portion of the lubrication oil contained in the lubrication circuit, which portion is in the same condition as the lubrication oil which ws subjected to the first measurement but which has been purified of the particulate contained in it, and then calculating a lubrication oil particulate concentration index, on the basis of the values obtained from both the first and the second measurements.

This index can, for example, be calculated as the difference between the value obtained from the first measurement, and the value obtained from the second measurement.

In this way, all the desired aims are achieved in a simple and effective way. In fact, both measurements are performed on lubrication oil that has been used in the lubrication circuit.

Further, both measurements are performed on oil of the same type that is in the same conditions, both in terms of temperature and in terms of degree of wear. In particular, this lubrication oil possesses the same degree of oxidation, the same concentration of polar molecules, ions and diesel fuel particles, the same additives and, in general, the same characteristics that usually contribute to invalidating particulate concentration measurements.

The only characteristic that distinguishes the two measurements is that the second is performed on lubrication oil that is substantially free of particulate, while the first is carried out on lubrication oil that contains the same particulate concentration that is present in the lubrication circuit at that moment in time.

Thus the differential index obtained with the method in question depends solely on particulate concentration and on no other condition.

Obviously the conclusions deriving from the measurements are to be considered valid, since both the first and the second measurements assess the same impurity parameter of the lubrication oil.

According to the invention, the impurity parameter measured can be the conductivity of the lubrication oil, or a parameter derived from the dielectric spectroscopy, such as for example the impedance or the dielectric permittivity of the lubrication oil.

In particular, it is preferable to choose as the impurity parameter the dielectric permittivity of the lubrication oil, since it is in general easier and less expensive to measure.

For correct application, the method is preferably carried out in the following stages: taking a sample of the lubrication oil contained in the lubrication circuit, dividing the sample into a first portion and a second portion, - performing the first measurement on the first portion, purifying the second portion, and performing the second measurement on the second purified portion. It must be specified that the sample need not necessarily be separated and isolated from the lubrication oil that remains in the lubrication circuit, but can also be defined as a quantity of oil contained within the lubrication circuit, or within a housing communicating with the circuit, so long as the conditions of the sample thus defined are maintained practically unchanged during implementation of the subsequent stages of the method. The first and second measurement are preferably done simultaneously. To apply the method, the invention also makes available a sensor of the particulate concentration in the lubrication oil of an internal combustion engine, which sensor includes: a first chamber communicating with a lubrication oil inlet and a second chamber communicating with a lubrication oil outlet, wherein the first and second chambers are reciprocally separated by a porous barrier which allows oil to pass through and prevents only the particulate contained in the oil from passing through, two measuring devices each capable of measuring the same lubrication oil impurity parameter which depends on the quantity of particulate therein contained, a first measuring device thereof being situated within the first chamber and a second measuring device thereof being situated within the second chamber, and a processing device, connected to both measuring devices, which calculates a particulate concentration index on the basis of the values obtained from both the first and second measuring devices.

The sensor inlet and outlet are connected to the lubrication circuit of the internal combustion engine, preferably downstream of the oil filter. In this way, a part of the used oil circulating in the lubrication circuit enters the first chamber of the sensor, and from there flows into the second chamber through the porous barrier which prevents the particulate from passing.

When the engine is working normally, the used lubrication oil contained in the second chamber is then purified of particulate, while the used lubrication oil contained in the first chamber contains the same particulate concentration that is present in the lubrication circuit.

In this way, the measuring devices can effectively measure the lubrication oil impurity parameter, following the procedures of the method outlined above. The passage of the lubrication oil through the porous barrier occurs due to a difference of pressure between the first and the second chamber of the sensor.

The pressure difference can be obtained by connecting the sensor outlet at a point in the lubrication circuit downstream of the point where the sensor inlet is connected, relative to the direction in which the lubrication oil circulates in the circuit. Alternatively, the passage of the lubrication oil through the porous barrier can be performed via a diffusion process, by which spontaneous transfer of the lubrication oil from the first to the second chamber takes place, due to the different concentration of the various types of chemical substances present in the chambers. In a preferred aspect of the invention, the porous barrier consists of one or more porous membranes that allow the passage of oil and prevent the passage of the particulate contained in the oil. In a further preferred aspect of the invention, each of the measuring devices measures the dielectric permittivity of the lubrication oil.

In this case, each measuring device includes at least one capacitor housed within the respective chamber of the sensor, in such a way that the lubrication oil contained within the chamber acts as a dielectric between the capacitor plates. The plates can consist of flat electrodes facing each other, or of preferably cylindrical tubular electrodes arranged coaxially one inside the other. Alternatively, each of the measuring devices can contain at least one chemFET semiconductor inside the chamber of the sensor with which it is associated, an electric reaction of which semiconductor, when submitted to a preordained electric current, varies its electric reaction according to the chemical substances contained in the liquid with which it comes into contact. In conclusion, the invention makes available a filter unit for the oil in an internal combustion engine that includes a filtering cartridge which performs the actual filtering of the lubrication oil contained in the lubrication circuit, and a particulate concentration sensor having the innovative characteristics described above.

Preferably, this sensor is situated downstream from the filtering cartridge relative to the direction of the oil in the filtering unit, in such a way that it analyses lubrication oil that has already been filtered and therefore purified of any solid pollutants.

Brief description of the Drawings

Further characteristics and advantages of the invention will become clear from the following description provided by way of a non-limiting example, with the aid of the figures of the attached drawings, wherein: - figure 1 schematically shows the sensor of the invention applied to a lubrication circuit of an internal combustion engine; figure 2 is detailed diagram of the sensor in figure 1 ; figure 3 is a first variant of the sensor in figure 2; figure 4 is a second variant of the sensor in figure 2; figure 5 shows an alternative embodiment of the sensor in figure 1 ; - figure 6 shows a graph which links the difference of the variations in dielectric permittivity of the lubrication oil measured in the two chambers, to the percentage in weight of particulate contained therein.

Best Mode for Carrying Out the Invention

Figure 1 schematically illustrates a lubrication circuit 1 of a Diesel engine 2. The lubrication circuit 1 is a closed circuit which includes an oil pump 3, which oil pump 3 forces the lubrication oil into a series of conduits 4 which reach the moving parts of the engine 2.

The lubrication oil thus reaches the moving parts of the engine 2, effectively reducing friction and removing a part of the heat produced in operation, and is then collected in an oil sump 5, situated below the engine 2, from which it returns to the oil pump 3.

The lubrication circuit 1 includes an oil filter 6, which traps the solid pollutants such as for example particles due to wear and/or dust of various types, that may be dispersed in the lubrication oil. During operation, sooty residues of combustion, known as particulate, can accidentally escape from the combustion chambers of the engine 2 and mix with the lubrication oil.

Therefore the lubrication circuit 1 is provided with a sensor 10, which measures particulate concentration in the lubricating oil. This sensor 10 includes a hollow housing 11 provided with a lubrication oil inlet 12 and a lubrication oil outlet 13.

Both the inlet 12 and the outlet 13 are in communication with a branch of the lubrication circuit 1.

In particular, this branch is located downstream of the oil filter 6, relative to the direction of flow of the oil imposed by the pump 3, in such a way that the sensor 10 cannot be damaged by any solid pollutants that might be present in the lubrication oil.

Further, the outlet 13 is connected at a point of the branch of the lubrication circuit 1 where the pressure is lower than at the point where the inlet 12 is connected.

This ensures that the lubrication oil can pass through the sensor 10 only in the direction from the inlet 12 to the outlet 13.

It should be noted that the inlet 12 and the outlet 13 may be simple calibrated orifices afforded in the hollow housing 11 , or they may include a valve with commanded opening.

The internal space of the hollow housing 11 is divided by a porous barrier 14 into two distinct chambers, a first chamber 15 communicating with the inlet

12 and a second chamber 16 communicating with the outlet 13.

The porous barrier 14 is capable of allowing the lubrication oil to pass through and of preventing the passage only of particles belonging to the particulate .

Preferably the porous barrier 14 consists of one or more porous membranes arranged in series.

Porous membranes generally ensure a better barrier to particulate than any other porous filtering material.

A respective measuring device 17 is housed inside each of the first and second chambers, 15 and 16, and measures a characteristic property of the lubrication oil, the property being one which depends on the concentration of particulate contained in the oil. Both measuring devices 17 measure the same characteristic property of the lubrication oil which, in the example illustrated, is dielectric permittivity.

Each measuring device 17 includes at least one capacitor 18, the plates of which consist of a flat and reciprocally-facing pair of electrodes 19.

These electrodes 19 are separated by a space and are contained within the relative first chamber 15 or second chamber 16 of the sensor 10, in such a way that the space between them is filled with lubrication oil. In this way, the lubrication oil functions as a dielectric for the capacitors 18.

As is known, the electrical capacitance of a capacitor depends on the permittivity of the dielectric between the plates.

Therefore the electric capacitance of the two capacitors 18 depends on the permittivity of the lubrication oil contained respectively in the first chamber 15 and the second chamber 16 of the sensor 10.

Each capacitor 18 is included in a simple electric circuit 20 comprising a current generator (not shown) which applies a predetermined difference of potential across the terminals of the capacitor 18, so that it is possible to establish the permittivity of the lubrication oil from the intensity of the current in the electric circuit.

A further porous barrier 24, having a greater degree of porosity compared with the porous barrier 14, and made of electrically insulating material, is positioned between the porous barrier 14 and each capacitor 18. The further porous barriers 24 have the mechanical function of supporting the porous barrier 14 without influencing the measurement of the dielectric permittivity carried out by the capacitors 18.

The electrical circuits 20 of both capacitors 18 are connected to a processing device 21 , typically a microprocessor. The microprocessor 21 in turn is connected to a thermometer 22 which is inserted in the lubrication circuit 1 , in order to measure the temperature of the lubrication oil.

Further, the microprocessor 21 is connected to a signalling device 23, such as a warning light or an acoustic signal. The microprocessor 21 applies an algorithm capable of performing a preordained operation on the basis of the values of permittivity measured by both capacitors 18, in such a way as to obtain a single index of the particulate concentration in the lubrication oil.

Further, the algorithm is capable of comparing this index with a preset threshold value stored in the microprocessor 21. -li¬

lt should be noted that the measuring devices 17 can be constructed with different shapes.

For example, in the variant of figure 3, each capacitor 18 comprises a pair of electrodes 19' of a cylindrical tubular shape, which are coaxially inserted one inside the other, in such a way that a space is left between them that can be filled with lubrication oil.

In the variant of figure 4, each measuring device 17 comprises a plurality of capacitors 18, each of which includes a pair of disc-shaped electrodes 19" facing each other and separated by a space which will then be filled by lubrication oil. The disc-shaped electrodes 19" of each measuring device 17 are identical and reciprocally coaxial.

In operation, a part of the lubricating oil circulating in the lubrication circuit 1 enters the first chamber 15 of the sensor 10 through the inlet 12 .

As a consequence of the difference of pressure between the two chambers of the sensor 10, the lubrication oil contained in the first chamber 15 tends to pass through the porous barrier 14 and to fill the second chamber 16.

At the same time, the oil contained in the second chamber 16 exits through the outlet 13 and returns to the lubrication circuit 1 , at a point where the pressure is lower. As it passes through the porous barrier 14, the lubrication oil is purified of substantially all the particles of particulate that it contains.

During normal operation, the oil flow described above results in both chambers, 15 and 16, of the sensor 10 always being full of the lubrication oil that is circulating in the lubrication circuit 1. In particular, the lubrication oil contained in the chambers 15 and 16 exhibits the same temperature, the same degree of oxidation, the same concentration of polar molecules, of ions and of diesel fuel particles, the same additives and in general the same characteristics that usually contribute to modifying the electrical permittivity of the oil. The only distinctive characteristic is the fact that the lubrication oil in the second chamber 16 is free of particulate, while the oil in the first chamber 15 contains the same concentration of particulate that is present in the lubrication circuit 1.

The microprocessor 21 of the sensor 10 contemporaneously acquires the values of permittivity of the lubrication oil in the first chamber 15 and of the lubrication oil in the second chamber 16 by means of the measuring devices 17.

This measurement is repeated at predetermined time intervals, for example, once a week, and only when the temperature of the lubrication oil in the lubrication circuit 1 , measured by the thermometer 22, is within a predetermined range of values.

In particular, the above measurements can be performed during operation of the engine 2 or, alternatively, when the engine 2 is off. In the first case, the range of temperatures at which to perform acquisition will be between 80° and 100°; while in the second case it will be close to ambient temperature, between approximately 10° and 30°.

At each measurement, the microprocessor 21 preferably calculates the difference between the values of permittivity measured in the first chamber 15 and in the second chamber 16 of the sensor 10. This difference of permittivity between lubrication oil containing particulate and lubrication oil with no particulate is in fact an index that depends exclusively on the concentration of particulate contained in the oil circulating in the lubrication circuit 1 , which index is not influenced by any other factor linked to the properties of the oil or to the process of aging to which it is subjected. In particular, the greater the difference in absolute value, the greater the concentration of particulate, as a percentage in weight relative to the lubrication oil.

At this point, the microprocessor 21 compares the index thus obtained with a stored threshold value, which indicates when a concentration of particulate that might compromise the efficiency of the lubrication oil has been reached. If the index is higher than the threshold value, the microprocessor 21 commands the signalling device 23 to generate a warning signal to inform the user that the lubrication oil should be replaced. In the embodiment of the invention illustrated in Figure 5, the porous barrier 14 maintains the property of trapping the particulate, while allowing the lubrication oil to pass from the first chamber 15 to the second chamber 16 by means of molecular diffusion.

Molecular diffusion takes place thanks to the different characteristics of the lubrication oil contained in the two chambers, and not because of pressure differences.

Therefore a continuous bi-directional flow of lubrication oil through the porous barrier 14 is established, with the oil passing from the first chamber 15 to the second chamber 16 and vice-versa, which ensures that the second chamber 16 always contains the same lubrication oil contained in the first chamber 15, only with the particulate removed.

In this way it is neither necessary for the second chamber 16 to be provided with an outlet pipe, nor for it to be kept at a different pressure relative to the first chamber 15, and it can thus remain completely isolated. This solution makes it possible to further simplify construction of the sensor 10, and to simplify its installation in the lubrication circuit 1.

Figure 6 shows as an explanatory aid a graph illustrating the influence of the particulate on the dielectric permittivity of the lubrication oil. Δεn indicates the variation in dielectric permittivity of the lubrication oil contained at a certain moment in the first chamber 15, compared with the condition of fresh oil.

Δεr₂ indicates the variation in the dielectric permittivity of the lubrication oil contained at the same moment in the second chamber 16, also compared with the condition of fresh oil. The graph in Figure 6 shows the difference Δεn - Δεr₂ between the variations of dielectric permittivity of the lubrication oil measured in the two chambers, as a function of the percentage in weight of particulate contained in the lubrication oil circulating in the lubrication circuit 1.

As can be seen in the graph, the value of Δεn - Δεr₂ is obviously zero when the lubrication oil is free of particulate, and then rises as the percentage of particulate increases.

Since the lubrication oil contained in the chambers 15 and 16 differs only regarding the concentration of particulate, which is substantially present only in the chamber 15, the value of Δεη - Δεr₂ is a valid index of the concentration of particulate in the lubrication oil circulating in the system, Obviously a person skilled in the art could make numerous modifications of a practical/technical nature to the sensor 10 as herein described, and to the method of analysis described therein, without for this reason forsaking the ambit of the invention as claimed herein below.

Particularly noteworthy is the fact that the oil filter 6 and the sensor 10 can be integrated into a filter unit (not shown), for installation along the lubrication circuit 1.

The filter unit can for example include an external housing which contains a filter cartridge, of a known type, which filters the oil.

The filter cartridge divides the internal space of the housing into two distinct chambers, one of which is a chamber for oil to be filtered, communicating with an inlet of the filter unit, while the other is a chamber of filtered oil, communicating with an outlet from the filter unit.

The sensor 10 can be installed in an appropriate seating afforded in the external housing of the filter unit, in such a way that the inlet 12 is in communication with the chamber of filtered oil downstream from the filter cartridge.

Claims

1 ). A method for measuring a concentration of particulate in lubrication oil contained in a lubrication circuit (1 ) of an internal combustion engine (2), which method comprises a stage of performing a first measurement of a predetermined lubrication oil impurity parameter, which parameter depends on a concentration of particulate contained therein, characterised in that it comprises the stages of: performing a second measurement of the impurity parameter on a portion of lubrication oil contained in the lubrication circuit, which portion is in the same conditions as the lubrication oil submitted to the first measurement but has been purified of particulate, calculating an index of particulate concentration in the lubrication oil, based on the values obtained from the first and second measurements.

2. The method of claim 1 , characterised in that it comprises the stages of: taking a sample of the lubrication oil contained in the lubrication circuit, dividing the sample into a first and second portion, performing the first measurement of the first portion, performing purification of the particulate in the second portion and performing the second measurement of the second purified portion.

3. The method of claim 2, characterised in that the first and second measurements are taken contemporaneously.

4. The method of claim 1 , characterised in that the particulate concentration index is obtained by calculating the difference between the values obtained from the first and second measurements.

5. The method of claim 1 , characterised in that it includes the further stages of: comparing the index with a predetermined reference value, generating a signal when the index exceeds the reference value.

6. The method of claim 1 , characterised in that the impurity parameter is the dielectric permittivity of the lubrication oil.

7. The method of claim 1 , characterised in that the impurity parameter is the impedance of the lubrication oil.

8. The method of claim 1 , characterised in that the impurity parameter is the electrical conductivity of the lubrication oil.

9. The method of claim 1 , characterised in that purification is obtained by making the portion of the lubrication oil pass through a porous barrier (14), which allows passage of the lubrication oil and prevents the passage of the particulate contained therein.

10. The method of claim 1 , characterised in that the passage of the oil through the porous barrier (14) is obtained by means of a different pressure upstream and downstream of the porous barrier (14).

11. The method of claim 9, characterised in that the passage of the oil through the porous barrier (14) is obtained by means of diffusion phenomena.

12. The method of claim 1 , characterised in that the first measurement and the second measurement are performed by means of at least one capacitor (18).

13. A sensor of a concentration of particulate contained in lubrication oil in a lubrication circuit (1 ) of an internal combustion engine (2), characterised in that it contains: a first chamber (15) communicating with a lubrication oil inlet (12) and a second chamber (16) separated from the first chamber by a porous barrier (14), which allows the lubrication oil to pass from the first chamber (15) to the second chamber (16) and prevents passage of the particulate contained therein, two measuring devices (17) each of which measures the same lubrication oil impurity parameter which depends on the quantity of particulate contained in the oil, a first measuring device thereof being located inside the first chamber (15) and a second measuring device thereof being located inside the second chamber (16), and a processing device (21 ), connected to the two measuring devices (17), which calculates a particulate concentration index on a basis of values obtained both from the first measuring device and the second measuring device (17).

14. The sensor of claim 13, characterised in that the processing device (21 ) compares the index with a reference value, and is connected to signalling means (23) which generate a signal when the index exceeds the reference value.

15. The sensor of claim 13, characterised in that both measuring devices (17) comprise at least one capacitor (18) which can be immersed in the lubrication oil present in the relative chamber (15, 16).

16. The sensor of claim 15, characterised in that the capacitor (18) includes two flat electrodes (19, 19") that face each other.

17. The sensor of claim 15, characterised in that the capacitor (18) includes two coaxial tubular electrodes (19'), one being inserted within the other.

18. The sensor of claim 15, characterised in that each measuring device (17) includes a plurality of capacitors (18).

19. The sensor of claim 13, characterised in that the porous barrier (14) includes al least a porous membrane.

20. The sensor of claim 13, characterised in that a barrier (24) is interposed between the porous barrier (14) and each of the measuring devices (17), which barrier (24) exhibits greater porosity than the porous barrier (14) and is made of electrically insulating material.

21. The sensor of claim 13, characterised in that a second chamber (16) communicates with an outlet (13) of the lubrication oil.

22. A filter unit for lubrication oil contained in a lubrication circuit of an internal combustion engine (2), comprising a filter cartridge that filters the lubrication oil, characterised in that it comprises a sensor (10) of particulate concentration according to any of the claims from 12 to 19.

23. Filter unit according to claim 22, characterised in that the sensor (10) is located downstream of the filter cartridge.