EP1452701B1 - Method and device of oil temperature evaluation of a combustion engine - Google Patents

Abstract

The method involves calculating a predicted temperature of a coolant by a primary algorithm (A1), based on functioning parameters of an engine. An error between measured and predicted temperatures of the coolant is calculated. A predicted oil temperature is calculated by a secondary algorithm (A2), based on functioning parameters of the engine. The predicted oil temperature is corrected based on the calculated error. An independent claim is also included for a system to estimate oil temperature of an internal combustion engine.

Description

The invention relates to a method for evaluating the temperature of the oil of an internal combustion engine and a system for carrying out this method. It is applicable in particular to automobile engines.

Knowing the oil temperature of an engine is often used to control a gasoline or diesel engine. This information is sometimes indicated on the dashboard of the vehicle. It comes most often from an oil temperature sensor directly placed in the engine. This then requires to provide a sensor that is generally in contact with the engine oil, electronic circuits that translate this information into electrical signals and a link for transmitting these signals to the display device on the dashboard of the vehicle.

The present invention proposes to estimate the engine oil temperature of a vehicle from information available in the engine control devices without having to use an engine oil temperature sensor. In other words, the invention makes it possible to avoid the use of a sensor for the temperature of the engine oil and the associated electronic circuits (see for example DE-A-19 961 118 , US-A-5,633,796 , US Patent 4847768 , US Patent 6449538 , US-639337 ).

1. (a) Calcul de prédiction d'une température prédite du fluide de refroidissement en fonction de paramètres de fonctionnement du moteur,
2. (b) Mesure de la température du liquide de refroidissement à l'aide du dispositif de mesure,
3. (c) Calcul d'une erreur entre la température mesurée et la température prédite du fluide de refroidissement,
4. (d) Calcul de prédiction d'une température d'huile prédite en fonction de paramètres de fonctionnement du moteur,
5. (e) Correction de la température d'huile prédite à l'aide de ladite erreur pour fournir une température d'huile estimée.

The invention therefore relates to a method for estimating the temperature of the oil of an internal combustion engine including in particular a cooling fluid cooling circuit and a device for measuring the temperature of the cooling fluid providing a measured temperature of the engine. cooling fluid. This process comprises the following steps:

1. (a) Calculation of prediction of a predicted temperature of the coolant as a function of engine operating parameters,
2. (b) Measurement of the coolant temperature using the measuring device,
3. (c) calculating an error between the measured temperature and the predicted temperature of the coolant,
4. (d) Calculation of prediction of a predicted oil temperature as a function of engine operating parameters,
5. (e) correcting the predicted oil temperature using said error to provide an estimated oil temperature.

In this method, steps (e) and (d) can be performed in a single step. The prediction calculation then incorporates a correction taking into account the error calculated on the temperature of the water.

dans laquelle :

• Tpeau est la température d'eau prédite par la formule,
• teau est la constante de temps de l'évolution de la température du fluide de refroidissement,
• g(c,n) est une cartographie de différentes températures atteintes en régime permanent en fonction de paramètres de fonctionnement du moteur tels que le couple moteur réel et le régime de rotation du moteur.

The prediction of the cooling temperature is determined, for example, by solving the differential equation: $$\frac{\mathrm{d}{\mathrm{T}}_{\mathrm{skin}}}{\mathrm{dt}}\mathrm{=}\frac{{\mathrm{T}}_{\mathrm{skin}}}{{\mathrm{t}}_{\mathrm{water}}}\mathrm{+}\frac{\mathrm{boy\; Wut}\left(\mathrm{vs},,\mathrm{not}\right)}{{\mathrm{t}}_{\mathrm{water}}}$$

in which :

• Water is the water temperature predicted by the formula,
• water is the time constant of the evolution of the temperature of the cooling fluid,
• g (c, n) is a mapping of different steady-state temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed.

dans laquelle :

• Tphuile est la température de l'huile moteur prédite,
• thuile est la constante de temps de l'évolution de la température de l'huile,
• f(c,n) est une cartographie de différentes températures en fonction de paramètres de fonctionnement du moteur tels que le couple moteur réel et le régime de rotation du moteur,
• ϑhuile, est une valeur d'erreur à corriger sur la valeur de la température prédite de l'huile moteur.

The prediction of the oil temperature can be obtained by solving the following differential equation: $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\left[\mathrm{f}\left(\mathrm{vs},,\mathrm{not}\right)\mathrm{+}\mathrm{\theta huile}\right]}{\mathrm{thuile}}$$

in which :

• Tphuile is the temperature of the predicted engine oil,
• the oil is the time constant of the evolution of the temperature of the oil,
• f (c, n) is a mapping of different temperatures according to engine operating parameters such as the actual engine torque and the rotational speed of the engine,
• oil, is an error value to be corrected on the value of the predicted temperature of the engine oil.

The error value of the predicted temperature of the oil to be corrected is substantially proportional to the error between the measured temperature of the coolant and the predicted temperature of the coolant.

To implement this method, provision is made beforehand to establish and store in memory a map of the coolant temperatures for different engine operating parameters and a map of the oil temperatures for the same parameters. engine operation.

The invention also relates to a system for estimating the temperature of the oil of a combustion engine (M) implementing this method. This system comprises a processing system implementing a first algorithm for predicting the temperature of the cooling fluid as a function of operating parameters of the engine and providing a predicted temperature of the cooling fluid. An error calculation circuit calculates the error between a measured temperature of the cooling fluid and the temperature thus predicted. In addition, the processing system implements a second algorithm for predicting the temperature of the engine oil as a function of engine operating parameters and provides a predicted oil temperature. Finally, a correction circuit corrects the predicted oil temperature using the error calculated by the error calculation circuit and provides an estimated oil temperature.

The system according to the invention makes use of non-linear functions (f (c, n), g (c, n)) approximated by maps of coolant temperatures and oil temperatures for different operating parameters. of the motor.

• La figure 1, un exemple d'organigramme du procédé de l'invention,
• Les figures 2a et 2b, des courbes d'évolution des température du liquide de refroidissement et de l'huile,
• les figures 3a et 3b, des cartographies des températures du liquide de refroidissement et de l'huile pour différentes valeurs du couple moteur et différentes valeur du régime,
• les figures 4a et 4b, des diagrammes de liaisons d'un système permettant de mettre en oeuvre l'invention,
• les figures 5a et 5b, des courbes de températures mettant en évidence la convergence correcte du système de l'invention,
• la figure 6, l'évolution de la chute de température lors d'un arrêt du moteur, et
• les figures 7a à 7d, des relevés d'essais mettant en évidence le fonctionnement de l'invention dans différentes conditions d'essais.

Other features and advantages of the invention will emerge more clearly with the description which follows and the appended figures which represent:

• The figure 1 an example of a flowchart of the method of the invention,
• The Figures 2a and 2b , curves of evolution of the coolant temperature and the oil,
• the Figures 3a and 3b , maps of coolant temperatures and oil for different values of the engine torque and different speed values,
• the Figures 4a and 4b , link diagrams of a system for implementing the invention,
• the Figures 5a and 5b , temperature curves highlighting the correct convergence of the system of the invention,
• the figure 6 , the evolution of the temperature drop during an engine stop, and
• the Figures 7a to 7d , test records highlighting the operation of the invention under different test conditions.

• de la vitesse du véhicule,
• de la température extérieure,
• de la charge du moteur (couple délivré par le moteur)
• et du régime moteur.

First of all, the temperature of an engine varies mainly according to:

• the speed of the vehicle,
• outside temperature,
• the motor load (torque delivered by the motor)
• and engine speed.

The temperature of the lubricating oil of the engine and the coolant (that is to say the cooling water) of an engine is also subject to variations according to these parameters.

A vehicle usually has a water temperature sensor, information on engine torque and engine speed.

The object of the invention is to determine the value of the oil temperature of an engine using the water temperature and various operating parameters of the engine and this without the aid of a sensor for measuring the temperature of the oil.

A first algorithm predicts the water temperature from an internal (mathematical) model that uses information such as load and engine speed. This predicted water temperature is then compared to the water temperature measured by the sensor.

A second algorithm predicts the oil temperature from an internal (mathematical) model that uses information such as engine load and engine speed. The error between the water temperature predicted by the first algorithm and the measured water temperature makes it possible to perform a correction of the oil temperature predicted by the second algorithm. This correction makes it possible to obtain an estimate of the temperature of the engine oil.

In the system according to the invention, the evolution of the oil temperature is estimated using an internal model of water and oil temperature, the behavior of which is close to that of a system governed by two differential equations of the first order. It is based on observing measurements of changes in water and oil temperatures as a function of engine operating parameters, in particular the load, the engine speed and the time. It is a state model written in differential form.

A first differential equation of the first order makes it possible to estimate the temperature of the cooling water, a second differential equation of the first order makes it possible to estimate the temperature of the engine oil.

According to one embodiment of the invention, the model of evolution of the water temperature is identical to that used for the oil. The water temperature predicted by the model is corrected by measuring the actual temperature. This correction made on the water temperature makes it possible to correct the predicted temperature of the oil.

The invention thus makes it possible to dispense with an oil temperature sensor and the associated system for processing and transmitting electrical signals.

Referring to the figure 1 Therefore, an example of a general flowchart illustrating the process of the invention will first be described.

The method according to the invention therefore provides, as indicated above, from different operating information of the engine - such as the temperature of the cooling water, the engine load, its speed - to determine the temperature of the oil of the motor.

• élaboration d'un algorithme de prédiction de la température de l'eau de refroidissement en fonction de certains paramètres de fonctionnement du moteur tels que ceux indiqués précédemment. Cet algorithme peut être représenté par une équation différentielle représentant les évolutions de la température de l'eau de refroidissement du moteur: $$\frac{\mathrm{dTpeau}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tpeau}}{\mathrm{teau}}\mathrm{+}\frac{\mathrm{g}\left(\mathrm{c},,\mathrm{n}\right)}{\mathrm{teau}}$$
  

où :

• Tpeau est la température d'eau prédite par la formule,
• teau est la constante de temps de l'évolution de la température de l'eau,
• g(c,n) est une cartographie de différentes températures en fonction de paramètres de fonctionnement du moteur tels que le couple moteur réel et le régime de rotation du moteur.
  • mesure de la température réelle Teau de l'eau de refroidissement du moteur à l'aide du capteur de température de l'eau ;
  • comparaison de la température prédite Tpeau de l'eau lors de la première étape du procédé et de la température mesurée Teau et calcul de la différence ϑeau entre ces deux températures ;
  • élaboration d'un autre algorithme de prédiction d'une température prédite Tphuile de l'huile du moteur en fonction de paramètres de fonctionnement du moteur tels que ceux indiqués précédemment. Comme l'algorithme précédent, cet algorithme peut être représenté par une équation différentielle représentant les évolutions de la température de l'huile du moteur:
  $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\mathrm{f}\left(\mathrm{c},,\mathrm{n}\right)}{\mathrm{thuile}}$$
  
  où :
• Tphuile est la température de l'huile prédite par la formule,
• thuile est la constante de temps de l'évolution de la température de l'huile,
• f(c,n) est une cartographie de différentes températures en fonction de paramètres de fonctionnement du moteur tels que le couple moteur réel et le régime de rotation du moteur.
  • calcul d'une valeur de température estimée Thuile de l'huile du moteur par correction de la température prédite Tphuile à l'aide de la différence ϑeau obtenue précédemment entre la température prédite de l'eau et la température mesurée de l'eau. Cette correction peut prendre simplement la forme d'une somme algébrique de la température prédite Tphuile et de la différence veau.

This process comprises the following steps:

• development of an algorithm for predicting the temperature of the cooling water according to certain operating parameters of the engine such as those indicated above. This algorithm can be represented by a differential equation representing the changes in the temperature of the engine cooling water: $$\frac{\mathrm{dTpeau}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tpeau}}{\mathrm{teau}}\mathrm{+}\frac{\mathrm{boy\; Wut}\left(\mathrm{vs},,\mathrm{not}\right)}{\mathrm{teau}}$$
  

or :

• Water is the water temperature predicted by the formula,
• water is the time constant of the evolution of the temperature of the water,
• g (c, n) is a mapping of different temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed.
  • measuring the actual temperature Water cooling water of the engine using the water temperature sensor;
  • comparing the predicted temperature of the water in the first step of the process and the measured temperature of the water and calculating the difference in water between these two temperatures;
  • developing another algorithm for predicting a predicted temperature of the engine oil as a function of engine operating parameters such as those indicated above. Like the previous algorithm, this algorithm can be represented by a differential equation representing the changes in the temperature of the engine oil:
  $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\mathrm{f}\left(\mathrm{vs},,\mathrm{not}\right)}{\mathrm{thuile}}$$
  
  or :
• Tphuile is the temperature of the oil predicted by the formula,
• the oil is the time constant of the evolution of the temperature of the oil,
• f (c, n) is a mapping of different temperatures according to operating parameters of the such as the actual engine torque and engine rotation speed.
  • calculating an estimated temperature value Thuile of the engine oil by correcting the predicted temperature Tphuile using the difference θeau previously obtained between the predicted water temperature and the measured water temperature. This correction can take the simple form of an algebraic sum of the predicted temperature Tphilus and the difference calf.

The last two steps can be carried out in a single step by integrating an oil uncertainty of the value of the predicted temperature of the oil into the differential equation of prediction of this temperature: $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\left[\mathrm{f}\left(\mathrm{vs},,\mathrm{not}\right)\mathrm{+}\mathrm{\theta huile}\right]}{\mathrm{thuile}}$$

In the above procedure, it is necessary to know the time constants of water and oil as well as the functions f (c, n) and g (c, n).

To identify the time constants τeau and τuile, it is possible to provide temperature rise tests on a test bench. By way of example, it will be considered that the variables to be taken into account are load echelons and engine speeds and that they allow the identification of time constants.

For example, by measuring the time required to reach a value of the temperature at 63% (t = T) of the final value and then at 95% (t = 3.T) of the final value, it is possible to deduce the constant of system time. For both oil and water, we find that time constants have similar values, for example 150s. The figure 2a and 1a. figure 2b show curves of evolution of cooling water temperatures and oil temperatures respectively, with the time constants identified previously. These curves are compared with the actual temperature curves.

Nonlinearities appearing on the figure 2a at 100s and 300s are respectively the opening of the thermostat and the start of motorcycle fan units. Under these conditions, to keep a simple model, these phenomena will not be taken into account. However, alternatively, for a better accuracy on the estimation of the oil temperature, the thermostat and the start of the GMVs are taken into account.

• fonctionnement du banc d'essai en mode iso vitesse (vitesse constante),
• le véhicule est sur le second rapport de boîte de vitesse,
• le régime du moteur est fixé par la vitesse de rotation des rouleaux du banc d'essai,
• la charge est ajustée par la pression sur la pédale d'accélérateur,
• le refroidissement est assuré par un ventilateur dont la vitesse de l'air pulsé est égale une vitesse de déplacement simulée,
• le capot moteur est ouvert (pour des raisons d'instrumentation).

To obtain the functions f (c, n) and g (c, n), maps of possible operating points are provided. These maps can be performed on a bench by setting typical operating conditions. For example, the following operating conditions can be provided:

• operation of the test bench in iso speed mode (constant speed),
• the vehicle is on the second gearbox ratio,
• the speed of the motor is fixed by the speed of rotation of the rollers of the test bench,
• the load is adjusted by the pressure on the accelerator pedal,
• the cooling is provided by a fan whose pulsed air speed is equal to a simulated displacement speed,
• the engine hood is open (for instrumentation reasons).

• vitesses : 2000 tr/min, 3000 tr/min et 4000 tr/min
• couples : 30 Nm, 74 Nm et 130 Nm (mesurés grâce à la variable « Couple Réel » sur un réseau CAN (« Control Area Network ») inter système.

By way of example, operating points are chosen over the range of use of the motor:

• speeds: 2000 rpm, 3000 rpm and 4000 rpm
• torques: 30 Nm, 74 Nm and 130 Nm (measured using the variable "Real torque" on a CAN ("Control Area Network") inter-system network.

In this example, there is therefore a total of nine calibration points for each fluid (water and oil).

Tests have therefore made it possible to establish constant-load maps according to the load such as that of the figure 3a for the mapping of the engine cooling water temperature, and that of the figure 3b for mapping the engine oil temperature.

In steady state, the water temperature is measured and compared with the predicted water value. We deduce the value of water, the error committed on the temperature of the water being: $$\mathrm{\theta eau}\mathrm{=}\mathrm{teau}\mathrm{-}\mathrm{Tpeau}$$

If we consider that the dissipated energy losses for oil and water are almost identical, we obtain a relationship between water and oil which is of the form: $$\mathrm{\theta huile}\mathrm{=}\mathrm{\theta eau}\left[\mathrm{f}\left(\mathrm{vs},,\mathrm{not}\right)\mathrm{/}\mathrm{boy\; Wut}\left(\mathrm{vs},,\mathrm{not}\right)\right]$$

As described above, the maps f (c, n) and g (c, n) are defined, for example, for nine operating points recorded on a chassis dynamometer. Between these operating points, a linear interpolation is performed to determine a determined operating temperature which will be called the target temperature.

In order to determine f (c, n) / g (c, n), the system was simplified by dividing the "target" temperatures for the nine operating points recorded, and then calculating the average value of these ratios. . In the model thus implemented, f (c, n) / g (c, n) is considered as a constant.

Referring to Figures 4a and 4b an embodiment of a system for implementing the previously described method will now be described.

The figure 4a represents a general example of realization of this system.

The engine M is equipped with a temperature sensor TE capable of measuring the water temperature of the water of engine cooling. The motor M comprises devices such as P1 and P2 capable of indicating engine operating parameters such as, for example, the torque developed by the engine and the rotational speed as has been considered in the previous examples.

The values of these operating parameters are applied to the inputs of two processing devices A1 and A2 which respectively provide a predicted temperature of the cooling water and a predicted temperature of the engine oil.

A calculation circuit D1 receives the measured temperature of water at the temperature predicted from the water of cooling, compares these temperatures and provides a calf value representing this difference.

Furthermore, another calculation circuit D2 receives the predicted temperature Tphil of the engine oil as well as the value calf previously calculated and provides a value of the corrected oil temperature Thuile.

The figure 4b represents a more detailed system for implementing the invention. This system includes, as in figure 4a , devices P1 and P2 providing engine operating parameters and a TE temperature sensor providing the temperature of the cooling water of the engine.

In addition the system has in memory a mapping G (c, n) of the cooling water temperatures according to a type of parameter (the torque for example) for different values of another parameter (the engine speed for example). It also has a similar mapping f (c, n) for the engine oil temperatures.

The mapping g (c, n) is exploited in an A1 algorithm using the parameters c and n provided by the devices P1 and P2. The algorithm provides a predicted temperature for the skin. A difference circuit receives this predicted temperature as well as the water temperature measured by the TE sensor. and provides a difference value θwater. This difference is transmitted to an operator OP1 which multiplies it by an average value of different ratios f (c, n) / g (c, n) calculated for different operating points of the engine. The operator OP1 provides an oil value which substantially represents the uncertainty in calculating the value of the oil temperature to be reached in steady state.

Moreover, the mapping G (c, n) is exploited in an algorithm A2 using the parameters c and n provided by the devices P1 and P2. The algorithm also takes into account the value of oil and provides a temperature Thuile.

In the foregoing description, two operating parameters (motor torque and speed) were used as examples, but other parameters could be used without departing from the scope of the invention.

To initialize the system, the water temperature at start-up is used as the initial value of the oil temperature. If the engine is cold at start-up, the water is substantially equal to Thuile. If the engine is hot, the two temperatures may be different (in principle, a difference of less than ten degrees). Initializing the oil temperature estimator to an erroneous value does not disturb its convergence, as shown by the Figures 5a and 5b . In what follows, the initial value of the oil temperature will be initialized to the initial value of the water temperature.

The convergence of the estimator is observed regardless of the initial value of the oil temperature.

Furthermore, it is observed that the system is effective during a shutdown of the engine followed by a restart (so hot). Indeed, the estimation of the oil temperature during the engine shutdown is used to initialize the estimator at the next start. The figure 6 shows a decrease in temperature when the engine is stopped. It can be seen that, in the example, the oil and water temperatures are substantially equal to the time 0 (engine stop time), then, both temperatures decrease almost identically. After about 1800s, there is a difference of about 5 ° C between water and oil. If the water temperature is used at this time to initialize the estimator, an error of about 5 ° C is made.

However, as described above in relation to the Figures 5a and 5b thanks to the rapid convergence of the behavioral estimator, an error of 5 ° C on the initial temperature of the oil does not disturb its convergence. It is therefore not necessary to use a particular estimator model for the stopping phase of the engine, the difference between the water temperature and the oil temperature during engine stopping. being not important enough.

• en roulage urbain par temps frais (figure 7a),
• en roulage urbain par temps chaud (figure 7b),
• en roulage extra urbain (figure 7c),
• en roulage autoroutier avec un moteur chaud (figure 7d) .

To validate the operation of the system for estimating the oil temperature, various tests were carried out in different traffic conditions:

• in urban running in cool weather ( figure 7a )
• in urban running in hot weather ( figure 7b )
• in extra urban traffic ( Figure 7c )
• when driving on a motorway with a hot engine ( figure 7d ).

• le graphique du haut représente les températures d'eau en degrés C en fonction du temps, en secondes, et cela durant une variation du régime du moteur et du couple,
• le graphique du milieu fournit les températures estimées de l'huile et les températures d'huile qui ont été mesurées pour vérification, en degrés C en fonction du temps,
• le graphique du bas fournit les écarts, en degrés, en fonction du temps, entre les températures d'huile mesurées et les températures estimées.

Each of these figures has three graphs:

• the graph at the top shows the water temperatures in degrees C as a function of time, in seconds, and this during a variation of the engine speed and the torque,
• the middle graph provides the estimated oil temperatures and oil temperatures that were measured for verification, in degrees C as a function of time,
• the bottom graph provides the deviations, in degrees, as a function of time, between the measured oil temperatures and the estimated temperatures.

As can be seen on the figure 7a during an urban run in temperate conditions (21 ° C for example) there is a convergence of the estimator towards values close to real values after about 600s. In addition, the error committed remains within a range of 2.4 to 7 percent.

In urban running in hot weather ( figure 7b ), for example by 33 ° C outdoor temperature, with a dense circulation period between times 400s and 2200s, the temperature has increased sharply. Water temperatures up to 97 ° C were recorded. It is found that the error on the estimate of the oil temperature is less than about 6%. It was also found that when the circulation was more fluid, the error fell to 3%.

In extra urban traffic illustrated in Figure 7c , the stabilization time of the system to obtain an error reduced to less than 2% is about 600s. In addition, it can be seen that during the test, two maximum temperatures were produced at times 1500s and 1800s, and the estimated temperatures took these maxima into account.

Finally, in hot-air motorways, represented in figure 7d , the system tends to overestimate the actual temperature. The maximum relative error is 11.2%. Then, during a slowdown (motorway exit), and a return to a moderate run (at about 1050s time), the system returns to a level of performance corresponding to a 5% error.

It can therefore be seen that the system of the invention gives good results both as regards the respect of the oil temperature dynamics as for the steady state value.

An advantage of this system is the speed of convergence of the estimate which makes it insensitive to the initialization value. This removes the problem of stopping temperature estimation because it is possible to initialize the system with the water temperature at startup.

• prendre en compte d'autres paramètres de fonctionnement que le couple ou le régime : la vitesse du véhicule, la température extérieure par exemple,
• réaliser les cartographies des températures avec un plus grand nombre de points de fonctionnement.

Without departing from the scope of the invention, one could:

• take into account other operating parameters than the torque or the speed: the speed of the vehicle, the outside temperature for example,
• perform temperature mapping with a greater number of operating points.

Claims (13)

1. Method of estimating the oil temperature of a combustion engine (M) comprising a coolant cooling circuit, a device (TE) for measuring the temperature of this coolant providing a measured temperature (Teau) of said coolant, characterized in that it involves the following steps:

   • (a) a predictive calculation (A1) of a predicted temperature (Tpeau) of the coolant on the basis of engine operating parameters,

   • (b) measuring the temperature (Teau) of the coolant using the measurement device (TE),

   • (c) calculating an error between the measured temperature (Teau) of the coolant and the predicted temperature (Tpeau) of the coolant,

   • (d) predictive calculation (A2) of a predicted oil temperature (Tphuile) on the basis of engine operating parameters, and

   • (e) correcting the predicted oil temperature (Tphuile) using said error in order to provide an estimated oil temperature (Thuile).
2. Method according to Claim 1, characterized in that steps (e) and (d) are performed in a single step, the predicted calculation of oil temperature (A2) incorporating a correction to take account of the calculated error in water temperature.
3. Method according to Claim 1 or 2, characterized in that the predictive calculation (A1) of coolant temperature is based on the following differential equation: $$\frac{\mathrm{dTpeau}}{\mathrm{dt}}=\frac{\mathrm{Tpeau}}{\mathrm{teau}}+\frac{\mathrm{g}(\mathrm{c},\mathrm{n})}{\mathrm{teau}}$$

   

   
   in which:

   • Tpeau is the predicted water temperature,

   • Teau is the time constant for the change in water temperature,

   • g(c, n) is a map of various temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed.
4. Method according to one of Claims 1 to 3, characterized in that the predictive calculation of water temperature is based on the following differential equation: $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\left[\mathrm{f}\mathrm{(}\mathrm{c}\mathrm{,}\mathrm{n}\mathrm{)}\mathrm{+}\mathrm{\vartheta huile}\right]}{\mathrm{thuile}}$$

   

   
   in which:

   • Tphuile is the engine oil temperature predicted by the formula,

   • thuile is the time constant for the change in oil temperature,

   • f(c, n) is a map of various temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed,

   • ϑhuile is an error value to be corrected in the predicted engine oil temperature value.
5. Method according to Claim 4, characterized in that the error value (ϑhuile) to be corrected is substantially proportional to the error between the measured coolant temperature (Teau) and the predicted coolant temperature (Tpeau).
6. Method according to Claim 1, characterized in that it comprises a prior step of establishing and of recording in memory a map (g(c, n)) of coolant temperatures for various engine operating parameters and a map (F(c, n)) of oil temperatures for the same engine operating parameters.
7. System for estimating the oil temperature of a combustion engine (M) comprising a coolant cooling circuit, a device (TE) for measuring the temperature of said coolant providing a measured temperature (Teau) of said coolant, characterized in that it comprises a processing system comprising:

   • a first means (A1) of predicting the coolant temperature on the basis of engine operating parameters and providing a predicted coolant temperature (Tpeau),

   • an error calculating means (D) calculating the error between the measured coolant temperature (Teau) and the predicted coolant temperature (Tpeau),

   • a second means of predicting the engine oil temperature on the basis of engine operating parameters and supplying a predicted oil temperature (Tphuile),

   • a correction means correcting the predicted oil temperature (Tphuile) using the error calculated by the error calculation means and providing an estimated oil temperature (Thuile).
8. System according to Claim 7, characterized in that the predicted oil temperature (Tphuile) is corrected in the second prediction means.
9. System according to Claim 7 or 8, characterized in that the first prediction means (A1) comprises a means for solving the differential equation: $$\frac{\mathrm{dTpeau}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tpeau}}{\mathrm{teau}}\mathrm{+}\frac{\mathrm{g}\mathrm{(}\mathrm{c}\mathrm{,}\mathrm{n}\mathrm{)}}{\mathrm{teau}}$$

   

   
   in which:

   • Tpeau is the water temperature predicted by the formula,

   • Teau is the time constant for the change in water temperature,

   • g(c, n) is a map of various temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed.
10. System according to one of Claims 7 to 9, characterized in that the second prediction means (A2) comprises a means of solving the differential equation: $$\frac{\mathrm{dTphuile}}{\mathrm{dt}}\mathrm{=}\frac{\mathrm{Tphuile}}{\mathrm{thuile}}\mathrm{+}\frac{\left[\mathrm{f}\mathrm{(}\mathrm{c}\mathrm{,}\mathrm{n}\mathrm{)}\mathrm{+}\mathrm{\vartheta huile}\right]}{\mathrm{thuile}}$$

    

    
    in which:

    • Tphuile is the engine oil temperature predicted by the formula,

    • thuile is the time constant for the change in oil temperature,

    • f(c, n) is a map of various temperatures as a function of engine operating parameters such as actual engine torque and engine rotational speed,

    • ϑhuile is an error value to be corrected in the predicted engine oil temperature value.
11. System according to Claim 10, characterized in that it comprises a means such that the error value (ϑhuile) to be corrected is substantially proportional to the error between the measured coolant temperature (Teau) and the predicted coolant temperature (Tpeau).
12. System according to Claim 7, characterized in that it comprises means (f(c, n), g(c, n)) for establishing and recording in memory a map (g(c, n)) of coolant temperatures for various engine operating parameters and a map (f(c, n)) of oil temperatures for the same engine operating parameters.
13. Combustion engine comprising a system according to one of Claims 7 to 12.

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