EP1728983A1

EP1728983A1 - A method for estimating the residual life of the lubricating oil of an internal-combustion engine

Info

Publication number: EP1728983A1
Application number: EP05425391A
Authority: EP
Inventors: M. C.R.F. Società Consortile per Azioni Gambera; C. C.R.F. Società Consortile per Azioni Borello; N. C.R.F. Società Consortile per Azioni Francone
Original assignee: Centro Ricerche Fiat SCpA
Current assignee: Centro Ricerche Fiat SCpA
Priority date: 2005-05-30
Filing date: 2005-05-30
Publication date: 2006-12-06
Anticipated expiration: 2025-05-30
Also published as: EP1728983B1; ATE524641T1

Abstract

Described herein is a method for estimating the residual life of the lubricating oil of an internal-combustion engine, in which there are determined; at least one recapitulatory quantity (30) summarizing the conditions of use of the engine from the last oil change; and at least one quantity (70) indicating the quality of the lubricating oil on the basis of said recapitulatory quantity (30), and in which the residual life (130) of the lubricating oil is estimated on the basis of said quantity indicating the quality of the lubricating oil.

Description

The present invention relates to a method for estimating the residual life of the lubricating oil of an internal-combustion engine.
As is known, lubricating oil for internal-combustion engines has principally the function of reducing friction between the mechanical parts of the engine, as well as that of cooling the engine and protecting it from the action of oxidizing agents. With use, lubricating oil undergoes a slow and irreversible deterioration, due principally to the absorption of carbon residue and particulate matter originating from the process of combustion, commonly known as soot, and other debris, which are generated by the rubbing of the various mechanical parts of the engine, as well as to the formation and absorption of lacquers and sludge.
Deterioration of the lubricating oil takes the form of a reduction in its lubricating power, or lubricating capacity, which depends, among other things, upon the chemico-physical characteristics of the lubricating oil, such as viscosity, total base number (TBN) or, alternatively, total acid number (TAN).
In particular, the viscosity depends upon the running temperature of the engine and decreases as the temperature increases on account of the formation of polymers and byproducts of oxidation, such as lacquers and sludge, and is affected by the presence of particles, the chemical formulation of the oil, and its contamination by water, fuel and coolant.
The reduction of the total base number is indicative of a progressive exhaustion of the anti-oxidizing additives present in the lubricating oil, which have the purpose of protecting the engine from corrosion, which is caused principally by the formation of acids deriving from the process of combustion.
In the automotive sector, to prevent damage to the engine on account of poor lubrication of its parts, automobile manufacturers recommend an oil change after the motor vehicle has covered a certain number of kilometres, and this distance is indicated, according to the category of the vehicle, either on the user operating and servicing instructions of the motor vehicle or else on a display of the motor vehicle as the distance that can still be covered before oil change.
Currently, the interval between two oil changes recommended by automobile manufacturers is estimated in the so-called "worst case", i.e., in the worst conditions of use of the motor vehicle, this being an approach that, by its very nature, is therefore generally conservative.
Furthermore, an oil change for an engine of a motor vehicle is usually carried out according to the programme established by the coupons for periodic maintenance prescribed by the automobile manufacturers, which, usually, involve a number of operations of maintenance to be carried out on the individual elements of the vehicle for the purpose of reducing the number of interventions and, consequently, are the result of a series of compromises between different requirements. This leads to an inevitable under-use of some components and expendable materials, of which lubricating oil is one.
There is thus increasingly felt the need to review the planning of the coupons for ordinary maintenance in such a way as to optimize the use of expendable materials and to enable, at the same time, a greater flexibility of use for the owner of the motor vehicle.
Recently, there have thus been proposed certain strategies of predictive diagnostics of the degradation of the lubricating oil that are aimed at personalized maintenance.
The document No. US 6.266,587 , for example, describes a method for determination of when it is necessary to carry out an oil change for the engine of a vehicle according to the recorded operating parameters of the engine. According to this solution, the engine r.p.m. and at least one other operating parameter important for the ageing of the oil are continuously recorded, and, on the basis of these recorded parameters, a fictitious distance is determined, which is subtracted from a pre-set total distance in order to establish the operating distance that remains up to the next oil change.
Instead, US 6.253,601 describes a system of determination of the interval of oil change, in which at pre-set intervals of time there are estimated, and accumulated separately, generation of soot, increase in viscosity, and reduction in the total base number of the lubricating oil, on the basis of current engine parameters measured, such as the temperature of the engine, the flow rate of fuel supplied to the engine, and the running rate and load of the engine. When at least one of the cumulative values of soot generation, increase in viscosity, and reduction of the total base number reaches a respective pre-set threshold, the driver is then warned of the need for an oil change. This system moreover envisages the use of sensors, such as an oil-level sensor, a soot sensor and a viscosity sensor, in order to validate in real time the calculated values of soot generated, of increase in viscosity of the oil and of reduction in the total base number, and in order to prevent operating conditions that might prove catastrophic for the engine and are not detectable by mere calculation.
The aim of the present invention is to provide a method for estimating in a reliable way the residual life of the lubricating oil of an internal-combustion engine, without having to resort to the use of any sensors.
According to the present invention, a method is provided for estimating the residual life of the oil of an internal-combustion engine, as defined in Claim 1.
For a better understanding of the present invention, there now follows the description of a preferred embodiment thereof, which is provided purely by way of non-limiting example, with reference to the attached plate of drawings, wherein:

Figure 1 shows a flowchart of the method of estimation forming the subject of the present invention;
Figures 2 and 3 show tables containing values assumed by quantities involved in the method forming the subject of the present invention; and
Figure 4 shows an example of linear model, represented by a line of regression, of a quantity involved in the method forming the subject of the present invention.

determining recapitulatory quantities summarizing the conditions of use of the engine from the last oil change;
then determining qualitative physico-chemical quantities of the lubricating oil on the basis of the aforesaid recapitulatory quantities; and
finally estimating the residual life of the lubricating oil on the basis of the aforesaid qualitative physico-chemical quantities of the lubricating oil.

Figure 1 is a flowchart of the method for estimating the residual life of the lubricating oil of an internal-combustion engine according to the invention, said method being implemented by an electronic control unit (not shown) on board the motor vehicle.
According to what is shown in Figure 1, in an initial programming step, stored in the electronic control unit of the engine are a series of values necessary for implementation of the method according to the invention (block 10).
In particular, stored in the electronic control unit of the engine is a first table, shown in Figure 2, containing, among other things, limit values of some quantities indicating the quality of the lubricating oil, in particular the amounts of soot, of lacquers, and of sludge present in the lubricating oil and designated, respectively, by Soot, Laq, Sld, the viscosity of the lubricating oil at 40°C, designated by Visc, and the total base number, designated by TBN (or, alternatively, the total acid number TAN) of the lubricating oil, the limit values of which represent thresholds, beyond which it is assumed that the degradation of the lubricating oil is such that the lubrication of the engine will no longer occur in an optimal way and it is thus advisable to carry out an oil change.
In particular, the first table shown in Figure 2 contains the following limit values:

a limit quantity of soot LimSoot in the lubricating oil, for example 4%;
a lower-limit viscosity LimViscInf and an upper-limit viscosity LimViscSup of the lubricating oil, at 40°C, for example -25% and +50%, respectively, of the viscosity of new lubricating oil, measured in cSt (centistokes);
a limit total base number LimTBN or, alternatively, a limit total acid number LimTAN, of the lubricating oil, for example comprised between 2-4 mgKOH/g and 1-2 mgKOH/g, respectively;
a limit value of lacquers LimLaq in the lubricating oil, for example comprised between 0.8-1.2 %; and
a limit value of sludge LimSld in the lubricating oil, for example 4%.

It should be noted how, for the viscosity of the lubricating oil, two limit values are stored instead of just one, the reason being that a viscosity that is too low does not allow the lubricating oil to separate in the best possible way the surfaces to be lubricated, whilst a viscosity that is too high does not allow the lubricating oil to penetrate into the narrower spaces between the surfaces to be lubricated.
Also stored in the electronic control unit of the engine is a second table (not shown) containing threshold values of some engine quantities used during operations of comparison carried out when estimating the residual life of the lubricating oil, in the way described in detail in what follows, and namely:

minimum and maximum threshold values of the temperature T _OIL of the lubricating oil;
a plurality of threshold values of the temperature T _COOL of the engine coolant;
a plurality of threshold values of the pressure P _BOOST of supercharging of the engine;
a plurality of threshold values of the engine running rate RPM;
particular areas identified in the dimensional diagram of the engine, each defined by a respective range of engine running rate RPM and by a respective range of engine torque TQ; and
particular operating conditions of the engine, each defined by a respective range of engine running rate RPM and by a respective range of temperature T _OIL of the lubricating oil.

Furthermore, once again with reference to block 10 of Figure 1, at each oil change the electronic control unit resets the values of physico-chemical quantities for the previous session of estimation of the residual life of the lubricating oil, in particular the recapitulatory quantities determined in the previous estimation session, the distance covered by the vehicle from the last updating of the qualitative physico-chemical quantities of the lubricating oil, the distance covered by the vehicle from the last oil change, and the table shown in Figure 2.
With reference again to Figure 1, at each starting of the engine the electronic control unit starts to acquire continuously the engine quantities listed below, which are used for estimating the residual life of the lubricating oil (block 20) :

the running rate RPM and the load L of the engine,
the distance KM covered by the vehicle,
the temperature T _OIL of the lubricating oil of the engine,
the temperature T _COOL of the engine coolant, and
the pressure P _BOOST of supercharging of the engine,

the engine torque TQ; and
the duration t _TRIP , in hours, of each trip of the vehicle, i.e., the interval of time elapsing between each ignition and the next turning-off of the engine.

After resetting the aforementioned quantities, or else in the case where the oil change has not yet been carried out, the electronic control unit calculates the following recapitulatory quantities summarizing the conditions of use of the engine from the last oil change on the basis of the engine quantities acquired and calculated in block 20 (block 30):

the summation RPM _TOT of the engine running rate from the last oil change;
the distance KM _OIL , in kilometres, covered by the vehicle from the last oil change;
the time h _TOT , in hours, of ignition of the engine from the last oil change;
the number N _{_} AVV _TOT of engine starts performed from the last oil change;
the number N _{_} START _{_} COLD _TOT of engine cold starts performed from the last oil change, i.e., the number of engine starts with temperature of the engine below a given minimum threshold, for example 60°C;
the number N _{_} START _{_} COLD _{_} SHORT _TOT of short cold starts of the engine performed from the last oil change, i.e., the number of engine starts with the temperature of the engine below a given minimum threshold T _OILMin1' for example 60°C, and for a duration below a given threshold t _min1 , for example 20 minutes;
the duration h _{TOT SHORT} , in hours, in which the engine has run with a temperature of the oil T _OIL below a given threshold, for example 40°C, during a short trip, for example less than 40 minutes;
the duration h _{_} T _{OIL_MAX} , in hours, and/or the distances KM _{_} T _{OIL_MAX} travelled by the vehicle, in kilometres, in which the engine has run with temperature T _OIL of the lubricating oil above pre-set thresholds, for example 90°C, 95°C, 98°C and 101°C;
the durations h _{_} T _{OIL_MIN} , in hours, in which the engine has run with temperature T _OIL of the lubricating oil below pre-set thresholds, for example 40°C, 0°C and -10°C;
the durations h _{_} T _{COOL_MAX} , in hours, and/or the distances KM _{_} T _{COOL_MAX} travelled by the vehicle, in kilometres, in which the engine has run with temperature T _COOL of the engine coolant above two thresholds, for example 95°C and 100°C;
the durations h _{_} P _{BOOST_MIN} , in hours, and/or the distances KM _{_} P _{BOOST_MIN} travelled by the vehicle, in kilometres, in which the engine has run with pressure P _BOOST of supercharging of the engine below two thresholds, for example 1000 mbar and 1200 mbar;
the durations h _{_} P _{BOOST_MAX} , in hours, and/or the distances KM _{_} P _{BOOST_MAX} travelled by the vehicle, in kilometres, in which the engine has run with pressure P _BOOST of supercharging of the engine above two thresholds, for example 2000 mbar and 2200 mbar;
the duration h _{ENG_BRAKE} in hours, in which the engine has run in the presence/absence of the engine brake;
the durations h _{ENG_BRAKE_RPM} , in hours, in which the engine has run in the presence/absence of the engine brake and with the engine rate RPM above two thresholds, for example 1500 and 2000 r.p.m.;
the amount of oil Q _OIL , in litres, consumed by the engine in the presence/absence of the engine brake;
the amount of oil Q _{OIL_RPM} , in litres, consumed by the engine in the presence/absence of the engine brake and with the engine rate RPM above two thresholds, for example 1500 and 2000 r.p.m.;
the durations h _RPM,TQ , in hours, in which the engine has run in the following areas of the dimensional diagram of the engine:
- a) in a first area of the dimensional diagram of the engine defined by an engine rate RPM below a first threshold, for example 800 r.p.m., and by an engine torque TQ below a first threshold, for example 50 N·m,
- b) in a second area of the dimensional diagram of the engine defined by an engine rate RPM below a second threshold, for example 1200 r.p.m., and by an engine torque TQ above a second threshold, for example 900 N·m,
- c) in a third area of the dimensional diagram of the engine defined by an engine rate RPM above a third threshold, for example 2200 r.p.m., and by an engine torque TQ above a third threshold, for example 700 N·m, and
- d) in a fourth area of the dimensional diagram of the engine defined by an engine rate RPM above a fourth threshold, for example 2400 r.p.m., and by an engine torque TQ below a fourth threshold, for example 200 N·m; and
the durations h _RPM,TOILi , in hours, in which the engine has run in the following operating conditions:
- a) in a first operating condition defined by an engine rate RPM above a threshold, for example 2300 r.p.m., and by a temperature T _OIL of the lubricating oil below a first threshold, for example 40°C, and
- b) in a second operating condition defined by an engine rate RPM above the said threshold (2300 r.p.m.) and by a temperature T _OIL of the lubricating oil above a second threshold, for example 98°C.

After calculating the aforementioned recapitulatory quantities, the electronic control unit updates the distance KM _{_EST} , in kilometres, covered by the vehicle from the last updating of the qualitative physico-chemical quantities of the lubricating oil (block 40).
With reference once again to Figure 1, the electronic control unit then checks whether the vehicle has covered a given distance, for example 1000 km, from the last updating of the qualitative physico-chemical quantities of the lubricating oil (block 50). If it has not (output NO from block 50), the electronic control unit once again repeats the operations previously described starting from block 20, continuously updating the distance covered by the vehicle from the last updating of the qualitative physico-chemical quantities of the lubricating oil and the recapitulatory quantities referred to above; otherwise (output YES from block 50), the electronic control unit resets the distance covered by the vehicle from the last updating of the qualitative physico-chemical quantities of the lubricating oil (block 60) and then calculates the values of the following qualitative physico-chemical quantities of the lubricating oil (block 70) according to at least one recapitulatory quantity in the following way:

the quantity of soot in the lubricating oil according to the following formula: $Soot = a_{s} + b_{s} \cdot {RPM}_{_TOT} + c_{s} \cdot {KM}_{_TOIL_MAX} + d_{s} \cdot {h_T}_{OIL_MAX} + e_{s} \cdot {h_P}_{BOOST_MIN} + f_{s} \cdot {KM_P}_{BOOST_MIN} + g_{s} \cdot h_{_RPM, TOIL} + h_{s} \cdot h_{_RPM_T} + i_{s} \cdot h_{_TOT_SHORT}$

where the constant term as assumes values comprised between 0.5 and 1 and the other weighting coefficients from b _s to is assume values comprised between 10^-8 and 10⁵;
the viscosity of the lubricating oil at 40°C according to the following formula: $Visc = a_{v} + b_{v} \cdot {RPM}_{_TOT} + c_{v} \cdot {KM}_{_TOIL_MAX} + d_{v} \cdot {h_T}_{OIL_MAX} + e_{v} \cdot {h_P}_{BOOST_MIN} + f_{v} \cdot {KM_P}_{BOOST_MIN} + g_{v} \cdot h_{_RPM, TOIL} + h_{v} \cdot h_{_RPM_T} + i_{v} \cdot h_{_TOT_SHORT}$

where the constant term a _v assumes values comprised between 90 and 130 and the weighting coefficients from b_v to i _v assume values comprised between 10^-8 and 10⁵;
the total base number according to the following formula: $TBN = a_{t} + b_{t} \cdot {RPM}_{_TOT} + c_{t} \cdot {KM}_{_TOIL_MAX} + d_{t} \cdot {h_T}_{OIL_MAX} + e_{t} \cdot {h_P}_{BOOST_MIN} + f_{t} \cdot {KM_P}_{BOOST_MIN} + g_{t} \cdot h_{_RPM, TOIL} + h_{t} \cdot h_{_RPM_T} + i_{t} \cdot h_{_TOT_SHORT}$

where the constant term a _t assumes values comprised between 8 and 14, and the weighting coefficients from b _t to it assume values comprised between 10^-8 and 10⁵ ;
the quantity of lacquers present in the lubricating oil according to the following formula: $L a q = a_{l} + b_{l} \cdot {RPM}_{TOT}$

where the constant term a _l assumes values comprised between 0 and 0.5, and the coefficient b _l assumes values comprised between 10^-9 and 10⁵ ;
the quantity of sludge present in the lubricating oil according to the following formula: $S l d = a_{s l} + b_{s l} \cdot {RPM}_{TOT}$

where the constant term a _sl assumes values comprised between 0 and 3, and the coefficient b _sl assumes values comprised between 10^-9 and 10⁵.

Next, the electronic control unit stores the calculated values of the qualitative physico-chemical quantities of the lubricating oil in a table of the type shown in Figure 3 (block 80). In particular, if for each of the qualitative physico-chemical quantities of the lubricating oil in the table of Figure 3 there has not yet been stored a given number of values, for example ten (corresponding to a distance covered by the vehicle of 10 000 km), then the electronic control unit updates the table of Figure 3 by simply storing the new calculated values of the qualitative physico-chemical quantities of the lubricating oil, and the distance at which they have been calculated, whilst, if for each of the qualitative physico-chemical quantities of the lubricating oil in the table of Figure 4 there has already been stored the aforesaid given number of values (ten), then the electronic control unit updates the table of Figure 3 eliminating the "older" values of the qualitative physico-chemical quantities of the lubricating oil, i.e., those calculated at the shorter distance covered by the vehicle present in the table (column furthest to the left), then storing the new values of the qualitative physico-chemical quantities of the lubricating oil. In this way, the subsequent calculations are carried out on a data base(observation window) always having the same length, in the example indicated, ten values.
Next, the electronic control unit checks whether the aforesaid given number of values (ten) is stored in the table of Figure 3 for each qualitative physico-chemical quantity of lubricating oil (block 90). If it is not (output NO from block 90), then the operations resume from those previously described starting from block 20, i.e., continuing updating of the distance covered by the vehicle from the last updating of the qualitative physico-chemical quantities of the lubricating oil and the recapitulatory quantities referred to above for the calculation of new values of the qualitative physico-chemical quantities of the lubricating oil. If said number of values is stored (output YES from block 90), then the electronic control unit calculates, on the basis of the values contained in the table of Figure 3, the residual life of the lubricating oil in terms of distance that can still be covered by the vehicle before the oil change (blocks 100-140).
In particular, for each of the qualitative physico-chemical quantities of the lubricating oil referred to above the electronic control unit determines and stores in Table 2 the values of characteristic parameters a, band F of a respective line of regression, which is determined using the least-squares method and represents a linear modelling of said quantity as a function of the distance covered by the vehicle (block 100).
In order to be able to establish whether the linear relation introduced by the line of regression calculated is correct and reliable, a quantity F is calculated indicating the significance of the model according to the formula: $F = \frac{\sum {({\hat{y}}_{i} - y_{a v})}^{2}}{(\sum {(y_{i} - y_{a v})}^{2}) / (n - 2)}$

where:

y _i are the values of the qualitative physico-chemical quantity of lubricating oil contained in the table of Figure 3;
ŷ _i are the values of the qualitative physico-chemical quantity of lubricating oil calculated via the line of regression;
y _av is the mean value of the values y _i; and
n-2 are the degrees of freedom of the model.

On the basis of the values stored of the characteristic parameters of the lines of regression and of the quantity F, the electronic control unit then checks whether the model of each qualitative physico-chemical quantity of lubricating oil, represented by the respective line of regression, is statistically significant (block 110), and, according to the outcome of this check, calculates, for each qualitative physico-chemical quantity of lubricating oil considered irrespective of the others, the corresponding residual autonomy of the vehicle, in kilometres, before it is necessary to carry out the oil change, i.e., the distance that can still be covered by the vehicle before said quantity exceeds the corresponding limit value (block 120).
In particular, the electronic control unit performs the following operations:

• Soot, Lacquers and Sludge

For each of these quantities, the electronic control unit checks whether the angular coefficient (slope) b of the respective line of regression is greater than or equal to 0, and whether the quantity F of the respective model is greater than or equal to a threshold value, for example 2.
For those qualitative physico-chemical quantities of the lubricating oil for which the aforesaid conditions are satisfied, the respective modellings are considered statistically significant, and hence the electronic control unit calculates and stores, for each quantity and using the respective line of regression, the total distance, in kilometres, that the vehicle can cover altogether, starting from the previous oil change, before said quantity reaches the respective limit value stored (LimSoot, LimLaq, LimSld) and it is thus necessary to carry out a oil change, according to the formulas: $kmSoot = \frac{LimSoot - a_{Soot}}{b_{Soot}}$
$km L a q = \frac{Lim L a q - a_{L a q}}{b_{L a q}}$
$km S l d = \frac{Lim S l d - a_{S l d}}{b_{S l d}}$
For those qualitative physico-chemical quantities of the lubricating oil for which none of the aforesaid conditions is satisfied, the respective modellings are considered statistically not significant, and for these the electronic control unit considers, as total distance that can be covered by the vehicle between one oil change and the next, the last value calculated in conditions of statistically significant modelling. If upon the first execution of the calculation of the total distance that can be covered by the vehicle the modelling is not statistically significant, used as total distance that can be covered is a maximum distance stored, which is, for example, equal to the one indicated in the user operating and servicing instructions for the oil change.

• Viscosity

In a way similar to what has been said above, the electronic control unit checks whether the quantity F of the respective model is greater than or equal to a threshold value, for example 2.
In the case where said condition is satisfied, the model is then considered statistically significant, and hence the electronic control unit calculates a first total distance and a second total distance, in kilometres, that the vehicle can cover altogether, starting from the previous oil change, before the viscosity of the lubricating oil reaches a lower-limit viscosity LimViscInf and, respectively, an upper-limit viscosity LimViscSup, at 40°C, according to the formulas: $kmViscInf = \frac{LimViscInf - a_{Visc}}{b_{Visc}}$
$kmViscSup = \frac{LimViscSup - a_{Visc}}{b_{Visc}}$
Between these two values, only one will be greater than zero, so that this, designated in what follows by kmVisc, is considered as total distance, in kilometres, that the vehicle can cover altogether, starting from the previous oil change, before the viscosity reaches a value such as to render the oil change advisable.
In the case, instead, where said condition is not satisfied, the model is then not considered statistically significant, and hence the electronic control unit considers, as total distance that can be covered by the vehicle between one oil change and the next, the last value calculated in conditions of reliable modelling. In a way similar to what has been said above, if upon the first execution of the calculation of the total distance that can be covered by the vehicle the model is not statistically significant, as total distance that can be covered a maximum stored distance is used, which is, for example, equal to the one indicated in the user operating and servicing instructions for the oil change.

• Total base number or Total acid number

In a way similar to what has been said above, the electronic control unit checks whether the angular coefficient (slope) b of the corresponding line of regression is smaller than or equal to 0 and whether the quantity F of the respective model is greater than or equal to a threshold value, for example 2.
If the aforesaid conditions are satisfied, then the model is considered statistically significant, and the electronic control unit hence calculates a total distance, in kilometres, that the vehicle can cover altogether, starting from the previous oil change, before the total base number (or total acid number) of the lubricating oil reaches a stored limit value LimTBN (or LimTAN), according to the formulas: $kmTBN = \frac{LimTBN - a_{TBN}}{b_{TBN}}$
$kmTAN = \frac{LimTAN - a_{TAN}}{b_{TAN}}$
In the case where, instead, none of the aforesaid conditions are satisfied, then the model is not considered statistically significant, and the electronic control unit hence considers, as total distance that can be covered by the vehicle between one oil change and the next, the last value calculated in conditions of reliable modelling. In a way similar to what has been said above, if upon first execution of the calculation of the total distance that can be covered by the vehicle the model is not statistically significant, a stored maximum distance, for example equal to the one indicated in the user operating and servicing instructions for the oil change, is used as total distance that can be covered.
With reference once again to Figure 1, the electronic control unit then determines the residual distance that can still be covered by the vehicle before it is advisable to change the lubricating oil as the difference between the minimum value of the total distances previously calculated for the various quantities and the current covered distance according to the formula: $km = \min (kmSoot, kmVisc, kmTBN, kmSld, kmLag) - {km}_{OIL}$
(block 130) and then supplies the driver of the vehicle with an indication of said residual distance displaying it on a display on board the vehicle (block 140).
Then the operations resume from those previously described with reference to block 10.
Finally, it is clear that modifications and variations can be made to the method described and illustrated herein without thereby departing from the sphere of protection of the present invention, as defined in the annexed claims.
For example, the residual distance that can still be covered by the vehicle before having to change the lubricating oil could be calculated also considering any subset of the quantities indicating the aforementioned quality of the lubricating oil, as likewise the qualitative physico-chemical quantities of the lubricating oil could be determined on the basis of recapitulatory quantities other than those indicated.
In addition, the method according to the invention could be further enriched in order to take into account also any possible topping-up of lubricating oil that can occur between two subsequent oil changes.
In particular, in the first place, a check is made on whether the topping-up has been performed and on the amount of oil involved, and, at each key-on of the vehicle, the level of the lubricating oil is stored (information that is known to the electronic control unit and is supplied by a level sensor purposely provided in the tank of the lubricating oil) and then the level of the lubricating oil between one key-on and the next is compared. In the case where the difference between the levels of the lubricating oil at one key-on and the next exceeds a given threshold, for example, 1 kg, then the amount of oil involved in topping-up is equal to said difference.
In the presence of topping-up, the ratio r between the amount R of oil involved in topping-up and the capacity C of the tank of the lubricating oil, i.e., r = R/C, is initially calculated, after which, for each qualitative physico-chemical quantity of lubricating oil, the value y _{_fil} of the qualitative physico-chemical quantity of lubricating oil is calculated, taking into account the effect of topping-up, according to the formula: $y_{_fil} = (y - (y_{0} * r)) / (1 - r)$

where:

y represents the value of the qualitative physico-chemical quantity of lubricating oil stored in the table of Figure 3 and calculated according to the recapitulatory quantities, in the way previously described; and
y ₀ represents the initial value of the qualitative physico-chemical quantity of lubricating oil, i.e., the value assumed by the qualitative physico-chemical quantity of lubricating oil when the latter is new.

For each qualitative physico-chemical quantity of lubricating oil a respective corrective factor gap is then calculated and additionally stored in the table of Figure 2, according to the formula: $gap = y - y_{_fil}$
On the basis of the corrective factors, the lines of regression of the qualitative physico-chemical quantity of lubricating oil calculated in the way previously described are modified accordingly. In particular, the characteristic parameters a and b of each line of regression are modified according to the respective corrective factor, setting: $a_{_fil} = a + gap$
$b_{_fil} = b$

where a _{_fil} and b _{_fil} are the characteristic parameters of the line of regression modified so as to take into account the effect of topping-up.
The modifications of the known terms but not of the angular coefficients (slopes) of the lines of regression in practice result in a parallel translation of the lines of regression by an amount equal to the respective corrective factor, with consequent increase of the residual life of the lubricating oil.
What has been said previously as regards an individual topping-up can be readily extended also to the case of multiple operations of topping-up. In particular, at the second topping-up we have: $y_{_fil} = (y + gap - (y_{0} * r)) / (1 - r)$
$gap = y - y_{_fil}$
and so forth for the subsequent operations of topping-up.
Furthermore, in the case where the total amount of oil involved in the various operations of topping-up exceeds a given threshold, for example half of the capacity of the oil tank, the driver can be warned of an excessive consumption of the lubricating oil and of the need to carry out a check.

Claims

A method for estimating the residual life of the lubricating oil of an internal-combustion engine, in particular for a vehicle, characterized in that it comprises:
• determining at least one value of at least one recapitulatory quantity summarizing the conditions of use of said engine from the oil change;

• determining a value of at least one qualitative physico-chemical quantity of lubricating oil on the basis of said value of said recapitulatory quantity; and

• estimating the residual life of the lubricating oil on the basis of said value of said qualitative physico-chemical quantity.
The method according to Claim 1, further comprising:
• determining a plurality of values of said qualitative physico-chemical quantity of lubricating oil on the basis of the value of said recapitulatory quantity; and

• estimating the residual life of the lubricating oil on the basis of the values of said qualitative physico-chemical quantity of lubricating oil.
The method according to Claim 1, further comprising:
• determining at least one value of a plurality of qualitative physico-chemical quantities of the lubricating oil on the basis of the value of said recapitulatory quantity; and

• estimating the residual life of the lubricating oil on the basis of the values of said qualitative physico-chemical quantities of the lubricating oil.
The method according to Claim 1, further comprising:
• determining a plurality of values of a plurality of qualitative physico-chemical quantities of the lubricating oil on the basis of the value of said recapitulatory quantity; and

• estimating the residual life of the lubricating oil on the basis of the values of said qualitative physico-chemical quantities of the lubricating oil.
The method according to any one of the preceding claims, further comprising:
• determining the value of a plurality of recapitulatory quantities summarizing the conditions of use of said engine from the oil change; and

• determining each value of each qualitative physico-chemical quantity of lubricating oil on the basis of the value of said recapitulatory quantities.
The method according to any one of the preceding claims, in which each qualitative physico-chemical quantity of lubricating oil is chosen in the group comprising:
• the quantity of soot (Soot) present in the lubricating oil;

• the quantity of lacquers (Laq) present in the lubricating oil;

• the quantity of sludge (Sld) present in the lubricating oil;

• the viscosity (Visc) of the lubricating oil; and

• the total base number (TBN) or total acid number (TAN) of the lubricating oil.
The method according to Claim 6, further comprising:
• estimating the residual life of the lubricating oil on the basis of the values of said quantity of soot (Soot), of lacquers (Laq) and of sludge (Sld) present in the lubricating oil, of said viscosity (Visc) of the lubricating oil, and of said total base number (TBN) or of said total acidity (TAN) of the lubricating oil.
The method according to any one of the preceding claims, in which each recapitulatory quantity is chosen in the group comprising:
• the summation (RPM _TOT) of the engine running rate (RPM) from the last oil change;

• the distance (KM _{OIL_MAX}) over which the engine has run at certain given temperatures (T _OIL) of the lubricating oil;

• the duration (h _{_BOOST_MIN}) in which the engine has run at certain given boosting pressures (P _BOOST) ;

• the duration (h _RPM,TQ) in which the engine has run in certain given areas of the dimensional diagram of the engine;

• the duration (h _RPM,TOIL) in which the engine has run in certain operating conditions each defined by a respective range of engine running rate (RPM) and by a respective range of temperature (T _OIL) of the lubricating oil; and

• the duration (h _{TOT_SHORT}) in which the engine has run at a given temperature (T _OIL) of the lubricating oil for a given period of time.
The method according to any one of the preceding claims, further comprising:
• updating the value of each recapitulatory quantity at pre-set time intervals.
The method according to Claim 2 or Claim 4, further comprising:
• determining the value of each qualitative physico-chemical quantity of lubricating oil at pre-set distances covered by said vehicle.
The method according to any one of the preceding claims, further comprising:
• estimating the residual life of the lubricating oil at pre-set distances covered by said vehicle.
The method according to any one of the preceding claims, in which estimating the residual life of the lubricating oil comprises:
• determining a residual distance that can still be covered by said vehicle up to the next oil change.
The method according to Claim 12, in which determining a residual distance comprises:
• for each qualitative physico-chemical quantity of lubricating oil, estimating the total distance that can be covered by the vehicle from the oil change before the value of said qualitative physico-chemical quantity of lubricating oil satisfies a given relation with respect to at least one respective limit value; and

• determining said residual distance according to the total distance calculated for each qualitative physico-chemical quantity of lubricating oil and of the current distance covered by the vehicle.
The method according to Claim 13, in which determining, for each qualitative physico-chemical quantity of lubricating oil, the total distance that the vehicle can cover before the value of said qualitative physico-chemical quantity of lubricating oil satisfies a given relation with respect to at least one respective limit value, comprises:
• constructing a mathematical model of said qualitative physico-chemical quantity of lubricating oil as a function of the distance covered by the vehicle; and

• estimating said total distance on the basis of said mathematical model.
The method according to Claim 13 or Claim 14, in which said relation is defined by the condition that the value of said qualitative physico-chemical quantity of lubricating oil exceeds the respective limit value.
The method according to Claim 14 or Claim 15, in which constructing a mathematical model of said qualitative physico-chemical quantity of lubricating oil comprises:
• determining characteristic parameters of a line of regression, comprising a known term and an angular coefficient (slope), and a coefficient indicating the significance of said mathematical model.
The method according to Claim 16, in which determining said total distance comprises:
• verifying the statistical significance of said mathematical model on the basis of said coefficient of significance; and

• in the case where said mathematical model is statistically significant, determining said total distance on the basis of said mathematical model and of said limit value.
The method according to Claim 17, in which verifying the statistical significance of said mathematical model comprises:
• verifying whether said coefficient of significance satisfies a given relation with respect to a respective threshold value.
The method according to Claim 18, in which verifying the statistical significance of said mathematical model further comprises:
• verifying whether said angular coefficient (slope) of said line of regression satisfies a given relation with respect to a respective threshold value.
The method according to any one of Claims 16 to 19, further comprising:
• in the case where said mathematical model is not statistically significant, setting said total distance equal to the last total distance calculated in conditions of statistical significance of said mathematical model.
A device for estimating the residual life of the lubricating oil of an internal-combustion engine, in particular for a vehicle, configured in such a way as to implement the method of estimation according to any one of the preceding claims.