EP3094842B1 - Method for controlling a heatable thermostatic valve - Google Patents

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

The present invention relates generally to the cooling of the drive motor in a motor vehicle.

It relates more particularly to a method for controlling a controlled thermostat of a cooling circuit of a heat engine driving a vehicle.

TECHNOLOGICAL BACKGROUND

Motor vehicles are conventionally equipped with a system for cooling their drive engine (for example, an internal combustion engine).

Such a cooling system generally comprises at least one radiator having the function of cooling a liquid transported by pipes between the radiator and a cooling circuit internal to the engine.

Other elements can also be connected to the external cooling circuit formed by the radiator and the pipes, such as, for example, an air heater, a turbocharger or a water-oil exchanger.

The cooling circuit may further include a thermostat controlled by a heating element, as described in DE10318355-A1 .

In order to be able to control the operation of all of these elements within predefined parameter ranges, in particular with regard to the temperature of the coolant, it is desirable to know this temperature, ideally at various points in the system.

US2005 / 006487-A1 describes a cooling circuit comprising several sensors for measuring the temperature of the liquid transported.

The use of a plurality of sensors, however, entails a non-negligible cost and is thus frequently limited to a single temperature sensor, positioned for example at the outlet of the engine, as described. EP0731261 -A1 , which is detrimental to precise control of the entire system.

OBJECT OF THE INVENTION

In this context, the present invention provides a method according to claim 1.

DETAILED DESCRIPTION OF AN EXAMPLE OF AN IMPLEMENTATION

The description which will follow with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented.

• la figure 1 représente schématiquement les éléments principaux d'un système de refroidissement d'un moteur à combustion interne ;
• les figures 2a et 2b représente schématiquement un thermostat piloté utilisé dans le système de la figure 1 ;
• la figure 3 représente un exemple d'un système de pilotage d'un tel thermostat ;
• les figures 4a et 4b présentent des éléments d'un exemple de modèle utilisé pour évaluer la course du thermostat piloté ;
• la figure 5 représente un exemple de module d'évaluation de la course du thermostat piloté ;
• la figure 6 présente les échanges de chaleur impliqués dans le système de refroidissement au niveau du thermostat piloté et du moteur ;
• la figure 7 représente un exemple de module d'évaluation de la température du liquide de refroidissement au niveau du thermostat piloté conforme aux enseignements de l'invention.

In the accompanying drawings:

• the figure 1 schematically represents the main elements of a cooling system of an internal combustion engine;
• the figures 2a and 2b schematically represents a controlled thermostat used in the system of the figure 1 ;
• the figure 3 shows an example of a control system for such a thermostat;
• the figures 4a and 4b show elements of an example model used to evaluate the stroke of the controlled thermostat;
• the figure 5 represents an example of a module for evaluating the stroke of the controlled thermostat;
• the figure 6 presents the heat exchanges involved in the cooling system at the level of the controlled thermostat and the engine;
• the figure 7 represents an example of a module for evaluating the temperature of the coolant at the level of the controlled thermostat in accordance with the teachings of the invention.

The figure 1 shows the main elements of a cooling system of an internal combustion engine 2 of a motor vehicle. This engine is here a compression ignition engine (Diesel). As a variant, it could be a spark ignition engine (gasoline).

There is a dotted line on the figure 1 elements which are present in accordance with certain variant embodiments of the invention.

The cooling system comprises a radiator 6, mounted for example at the front of the motor vehicle in order to receive the air flow generated by the movement of the vehicle, and an air heater 8 which allows the heating of the vehicle interior.

The internal combustion engine 2 is traversed by a cooling liquid which ensures its operation at a set temperature. given as explained below.

On leaving the engine 2, the coolant (heated by the engine 2) is transported by pipes to the thermostat 4 on the one hand, to the radiator 6 and to the heater 8 on the other hand. After cooling in these elements, the cooling liquid is transported by pipes to the engine 2 for cooling thereof.

The coolant is transported from engine 2 (outlet) to engine 2 (inlet) through thermostat 4 permanently so that thermostat 4 is always in contact with a flow of coolant regardless of the state. thermostat 4 (open or closed).

The cooling system may optionally further include a water-oil exchanger 12 which receives the cooling liquid from the engine 2 as input. After passing through the water-oil exchanger 12, the cooling liquid is reinjected into the circuit described below. above, for example at the thermostat 4. The use of the water-oil exchanger does not fall within the scope of the present invention and will therefore not be described in detail here.

The coolant is however transported from the radiator 6 to the engine 1 through a thermostatic valve or thermostat 4 which regulates the quantity of cooled coolant (from the radiator 6) to be injected into the inlet of the engine 1 in order to obtain the desired temperature. engine operating mode, as explained below.

Likewise, the coolant at the outlet of the engine 2 can be used to regulate the temperature within a turbocharger 14 supplied for this purpose with coolant by a bypass of the circuit linking the engine 2 and the air heater 8.

A temperature sensor 10 is also mounted in the coolant pipes located at the outlet of the engine 2 in order to measure the temperature Ts of the coolant at the outlet of the engine 2.

In the present exemplary embodiment, no means are provided for measuring the temperature of the cooling liquid at the inlet of the engine 2 (temperature T _E ), or at the level of the thermostat 4 (temperature T ₄ ). As a variant, as explained below, on the contrary, provision could be made to use a temperature sensor in the cooling circuit near the engine inlet in order to measure the temperature T _E or at the level of the thermostat 4 in order to measure the temperature T ₄ .

The figures 2a and 2b represent the thermostat 4 in two distinct operating positions, respectively a first position in which the thermostat closes the pipe connecting the radiator 6 to the engine 2 and a second position in which the thermostat opens this pipe.

The thermostat 4 comprises a rod (or "pencil" ) 20 on which is slidably mounted an assembly formed of a brass body 22 and a valve (or flap) 26. The space left free between the body 22 and the rod 20 is filled with a material sensitive to heat, here wax 24 sealed in this space delimited by body 22, valve 26 and rod 20.

The thermostat 4 is positioned in the pipe connecting the radiator 6 to the engine 2 so that its body 22 bathes in the coolant of temperature T ₄ at this location, as indicated above; the body 22 is therefore located downstream of the valve 26 in this pipe.

When the temperature T ₄ of the cooling liquid at the level of the thermostat 4 is below a predetermined threshold (defined by the design of the thermostat), and in particular when cold (when the engine 2 is stopped), the wax 24 is solid and the valve 26 occupies the position shown in figure 2a in which it obstructs the pipe: the cooling liquid coming from the radiator 6 is therefore not injected into the cooling circuit of the engine 2 and therefore does not participate in its cooling.

When the temperature T ₄ of the cooling liquid at the level of the thermostat 4 reaches, or even exceeds, the aforementioned threshold, due in particular to the heating of the cooling liquid by the engine 2 and the absence of cooling by the cooling liquid from the radiator 6, the wax 24 melts and expands, which causes the volume between the body 22 and the rod 20 to increase, so that the body 22 and the rod 20 are forced to move away, causing the displacement of valve 26 and thermostat opening 4.

Cooling liquid from the radiator 6 (cooled by the latter) is thus injected into the cooling circuit of the engine 2 and therefore participates in the cooling of the engine.

A mechanical regulation of the temperature of the coolant is thus obtained.

A return spring (not shown) is generally provided to facilitate the return of the valve 26 to its closed position when the temperature T ₄ of the cooling liquid decreases and the wax cools and contracts.

The thermostat 4 also comprises an electrical resistance (not shown), installed for example inside the rod 20 and electrically connected to an electrode 28.

The application of a voltage V to the electrode 28 causes a current to flow through the resistor which releases heat by the Joule effect and therefore accelerates the rise in temperature of the wax 24. The thermostat 4 will therefore open more. rapidly than in the absence of heating by the resistance, that is to say for a coolant temperature T ₄ below the aforementioned threshold.

The use of the heating of the wax 24 (here by means of the resistance) thus makes it possible to artificially lower the regulation temperature of the coolant of the engine 2: the thermostat 4 is a controlled thermostat.

The continuous application of a nominal voltage V ₀ (maximum useful voltage) makes it possible to obtain the generation by the resistance of a maximum heating power (which depends on the design of the thermostat). A calorific power lower than the maximum calorific power can be obtained by applying the nominal voltage V ₀ on a proportion only of the period of time considered (principle of the modulation by width of pulses or PWM of the English " Pulse Width Modulation" ): it is considered in the following that one applies in this case a useful voltage V lower than the nominal voltage V ₀ .

The figure 3 shows an example of a control system for thermostat 4 in accordance with the teachings of the invention.

The control system of the figure 3 includes several modules, shown here in functional form. Several functional modules can however in practice be implemented by the same processing unit programmed to carry out the processing operations assigned respectively to these functional modules. This processing unit is for example an engine control computer 30 (or ECU standing for “Engine Control Unit ”) fitted to the vehicle, or a processing unit dedicated to controlling the thermostat 4.

Regardless of the physical architecture of the thermostat control system, load information C (expressed in Nm) and engine speed information N (expressed in rpm), representative of the operation of engine 2, are available in the calculator 30.

This information C, N is transmitted on the one hand to a module 32 for determining a temperature setpoint T _C and on the other hand to a module 36 for evaluating the temperature T ₄ of the cooling liquid at the thermostat. 4.

The setpoint determination module 32 develops the temperature setpoint T _C as a function of the engine speed N and of the load C on the basis of a map stored in the processing unit which implements the module 32. In other words, the module 32 is designed to determine the temperature setpoint T _C by reading a value associated with the engine speed N and load C values received from the computer 30 in a correspondence table (mapping) stored in the processing unit concerned .

The setpoint determination module 32 generates for example setpoints T _C between 90 ° C and 110 ° C adapted to the different operating conditions of the engine 2 encountered (represented by the load C and the engine speed N). In practice, the setpoint T _C can take a discrete set of values, for example 90 ° C, 100 ° C or 110 ° C.

The temperature setpoint T _C generated by the setpoint determination module 32 is transmitted to a regulation module 34, which also receives the temperature T _s of the cooling liquid at the outlet of the engine measured by the temperature sensor 10.

On the basis of the measured temperature T _s and the temperature setpoint Tc, the regulation module 34 determines the gross useful voltage V _R to be applied to the electrode of the controlled thermostat 4 in order to make the temperature of the coolant converge towards the setpoint Tc.

The regulation law applied by the regulation module 34 to determine the gross useful voltage V _R as a function of the measured temperature T _s and of the setpoint temperature T _C depends on the envisaged application.

• lorsque la consigne T_C est égale à 110 °C (régulation haute température), la tension utile brute V_R est égale à 0 V, c'est-à-dire que la résistance de chauffage de la cire n'est pas utilisée et que la régulation de la température du liquide de refroidissement est réalisée mécaniquement par le thermostat (dont la conception est ici prévue pour une régulation à 110 °C) ;
• lorsque la consigne T_C est strictement inférieure à 110 °C (régulation basse température), et donc égale à 90 °C ou à 100 °C dans le cas décrit ici, la tension utile brute V_R est par exemple déterminée en fonction de l'erreur en température (Ts-Tc) selon un mécanisme de régulation PI (proportionnel-intégral).

For example, the following can be considered in the case indicated above where the setpoint T _C can take a discrete set of values:

• when the setpoint T _C is equal to 110 ° C (high temperature regulation), the gross useful voltage V _R is equal to 0 V, that is to say that the resistance for heating the wax is not used and that the temperature of the coolant is regulated mechanically by the thermostat (the design of which is here provided for regulation at 110 ° C);
• when the setpoint T _C is strictly less than 110 ° C (low temperature regulation), and therefore equal to 90 ° C or 100 ° C in the case described here, the gross useful voltage V _R is for example determined as a function of l temperature error (Ts-Tc) according to a PI (proportional-integral) regulation mechanism.

The raw useful voltage V _R generated by the regulation module 34 is transmitted to a correction module 40, the operation of which will be described below.

The module 36 for evaluating the temperature T ₄ of the coolant at the level of the thermostat 4 receives as input the temperature T _s measured by the measurement sensor 10 and an estimated value L of travel of the thermostat 4, as well as, as already indicated, the load C and engine speed N information representative of engine operation 2.

The estimated travel value L of the thermostat 4 is produced as explained in more detail below by a module 38 intended for this purpose.

On the basis of this information received at the input, the module 36 evaluates the temperature T ₄ of the coolant at the level of the thermostat 4, for example according to the method described in detail below with reference to the figures 6 and 7 .

As already indicated, according to a possible variant, the module 36 could be replaced by a temperature sensor immersed in the cooling liquid at the level of the thermostat 4.

The already mentioned stroke evaluation module 38 receives as input the temperature T ₄ of the cooling liquid at the thermostat (produced by the evaluation module 36 in the example described) and the useful voltage value actually applied to the thermostat. controlled 4 (corrected useful value Vc generated by the correction module 40 as explained below).

On the basis of this information received at the input, the module 38 evaluates the travel L of relative displacement of the rod 20 and of the body 22, which gives an estimate of the proportion of opening of the thermostat 4. The evaluation carried out by the controller. module 38 is for example carried out by implementing a digital model, as described below with reference to figures 4a, 4b and 5 . As a variant, this evaluation can be carried out by reading the travel L associated, in a prerecorded correspondence table, with the values of temperature T ₄ and of useful applied voltage Vc received at the input. In this case, for example, the preset values were determined by means of preliminary tests or simulations, carried out beforehand, using the digital model described with reference to figures 4a, 4b and 5 .

The module 38 can thus supply a value L representative of the travel of the thermostat 4 to the correction module 40, which also receives as input the gross useful voltage V _R calculated by the regulation module 34 as already indicated.

When the gross useful voltage V _R calculated by the regulation module 34 is low, or even zero, the correction module 40 corrects this value so that a minimum useful voltage is effectively applied to the electrode 28 of the controlled thermostat 4 so that the resistance delivers a non-zero calorific power, which makes it possible to preheat the wax 24 to a limit temperature for opening the thermostat 4. Thus, any additional heating of the wax 24 (in response to a command from the system control to open the thermostat) will immediately open the valve.

In practice, thanks to the knowledge of the estimated value L of travel of the thermostat 4 (received from the module 38), the correction module 40 can determine what proportion of opening of the thermostat 4 is produced by the useful voltage value actually applied. If the correction module 40 notes the closing of the thermostat 4 (that is to say if L = 0), it generates at output a corrected useful voltage value Vc slightly higher than that previously applied, until a slight opening of thermostat 4 (always using the estimated travel value L).

Naturally, this mechanism for applying a minimum preheating voltage is maintained only as long as the gross useful voltage V _R generated by the regulation module 34 is less than this minimum preheating voltage. Indeed, as soon as the regulation module 34 controls a gross useful voltage V _R greater than the minimum preheating voltage, this gross useful voltage V _R is applied as it is by the correction module 30 to the electrode 28 of the controlled thermostat. 4 (in this case we have Vc = V _R ).

The correction module 40 also causes a limitation of the useful voltage Vc applied (and therefore of the calorific power delivered by the resistor by the Joule effect) so that the application of this voltage Vc does not cause heating greater than that resulting in total opening of thermostat 4 (i.e. a stroke L equal to the maximum stroke L _max ). Additional heating is in fact unnecessary; it is furthermore detrimental to the weather reaction of the system when it is then desired to close the thermostat (since the additional heating of the wax 24 makes its cooling longer, then possibly its solidification).

In practice, when the value L of the travel of the thermostat 4 received by the correction module 40 reaches the maximum travel L _max , the correction module 40 applies to the controlled thermostat 4 a useful voltage Vc which does not depend on the gross useful voltage V _R received from the regulation module 34, but which is chosen to maintain the stroke L at its maximum value L _max . To do this, for example, a slaving of the useful applied voltage Vc is used so that the evaluated stroke L is maintained between a predetermined value (here 0.95.L _max ) and the maximum stroke L _max . It is therefore in this case a closed loop control.

Naturally, this mechanism for limiting the applied voltage (and therefore the calorific power delivered by the resistor) is only maintained as long as the gross useful voltage V _R generated by the regulation module 34 is greater than this limited voltage. Indeed, as soon as the regulation module 34 controls a raw useful voltage V _R less than the limited voltage determined by the control described above, this raw useful voltage V _R is applied as it is by the correction module 30 to the electrode 28 of the controlled thermostat 4 (in this case we have V _C = V _R ).

Provision can also be made, in addition to the above limitation, for the correction module 40 to cause a limitation of the voltage effectively applied Vc as a function of the stroke L received at the input for a range of values of this stroke L.

In fact, for certain types of controlled thermostats, it is contraindicated to control a high heating power in certain opening positions of the thermostat because the heating then risks damaging the seals which ensure the seal between the rod and the body-valve assembly.

The processing unit which implements the correction module 40 stores for this purpose a correspondence table which indicates the maximum authorized useful voltage V _max as a function of the travel L of the thermostat. These data are for example provided by the manufacturer of the thermostat.

• si V_R est inférieur à V_max, Vc = V_R ;
• si V_R est supérieur (ou égal) à V_max, V_C = V_max.

The correction module 40 therefore reads at each instant the maximum authorized useful voltage V _max in the table as a function of the travel value L received from the evaluation module 38 and thus determines the corrected useful voltage to be applied:

• if V _R is less than V _max , Vc = V _R ;
• if V _R is greater than (or equal) to V _max , V _C = V _max .

To simplify the description, the preceding paragraph does not take into account the possible additional limitation of the useful voltage applied in order to avoid excessive heating of the wax, as proposed above.

It is understood that, apart from the situations described above, the correction module 40 applies to the controlled thermostat 4 a useful voltage Vc equal to the gross useful voltage V _R received at the input from the regulation module 34.

It is noted that in practice, the application of a useful voltage given to the thermostat 4 is carried out by applying a nominal voltage V ₀ for a proportion of the total time such that one generates an electric power equal to that which one would have obtained by continuous application of the desired working voltage (according to the module principle of pulse width, or PWM of English "pulse width Modulation"), as already explained above.

The figure 4a presents the model used in the example described here to simulate the thermal behavior of the different parts of the controlled thermostat 4 with a view to evaluating its stroke as explained below.

• la masse m₂₂, la capacité thermique massique C22 et la température T₂₂ du corps 22 ;
• la masse m₂₄, la capacité thermique massique C24 et la température T₂₄ de la cire 24 ;
• la masse m₂₀, la capacité thermique massique C₂₀ et la température T₂₀ de la tige 20.

In this model, each part of the controlled thermostat 4 is represented by its mass, its specific heat capacity and its temperature (which is considered uniform over the whole of the part concerned); we define as follows:

• the mass m ₂₂ , the specific heat capacity C22 and the temperature T ₂₂ of the body 22;
• the mass m ₂₄ , the specific heat capacity C24 and the temperature T ₂₄ of the wax 24;
• the mass m ₂₀ , the specific heat capacity C ₂₀ and the temperature T ₂₀ of the rod 20.

• un coefficient de transfert h₁ et une surface S₁ pour l'interface entre la tige 20 et la cire 24 ;
• un coefficient de transfert h₂ et une surface S₂ pour l'interface entre la cire 24 et le corps 22 ;
• un coefficient de transfert h₃ et une surface S₃ pour l'interface entre le corps 22 et le liquide de refroidissement à la température T₄.

It is also considered that these different elements, as well as the coolant, are separated by interfaces each characterized by a surface heat transfer coefficient and a surface, which makes it possible to define:

• a transfer coefficient h ₁ and a surface S ₁ for the interface between the rod 20 and the wax 24;
• a transfer coefficient h ₂ and a surface S ₂ for the interface between the wax 24 and body 22;
• a transfer coefficient h ₃ and a surface S ₃ for the interface between the body 22 and the cooling liquid at temperature T ₄ .

• la résistance chauffe la tige par effet Joule en lui apportant une puissance thermique P_J (directement liée à la tension utile Vc appliquée au thermostat piloté 4) ;
• un échange de chaleur a lieu entre la tige 20 et la cire 24 de puissance E₁ = h₁.S₁.(T₂₀-T₂₄) (comptée positivement pour un transfert de chaleur de la tige 20 vers la cire 24) ;
• un échange de chaleur a lieu entre la cire 24 et le corps 22 de puissance E₂ = h₂.S₂.(T₂₄-T₂₂) (comptée positivement pour un transfert de chaleur de la cire 24 vers le corps 22) ;
• un échange de chaleur a lieu entre le corps 22 et le liquide de refroidissement de puissance E₃ = h₃.S₃.(T₂₂-T₄) (comptée positivement pour un transfert de chaleur du corps 22 vers le liquide de refroidissement).

The heat exchanges are therefore modeled as follows:

• the resistance heats the rod by the Joule effect by providing it with a thermal power P _J (directly linked to the useful voltage Vc applied to the controlled thermostat 4);
• a heat exchange takes place between the rod 20 and the wax 24 of power E ₁ = h ₁ .S _1. (T ₂₀ -T ₂₄ ) (counted positively for a transfer of heat from the rod 20 to the wax 24);
• a heat exchange takes place between the wax 24 and the body 22 of power E ₂ = h ₂ .S ₂ (T ₂₄ -T ₂₂ ) (counted positively for a transfer of heat from the wax 24 to the body 22);
• a heat exchange takes place between the body 22 and the cooling liquid of power E ₃ = h ₃ .S _3. (T ₂₂ -T ₄ ) (counted positively for a transfer of heat from the body 22 to the cooling liquid) .

$${\mathrm{m}}_{24}.{\mathrm{C}}_{24}.{\mathrm{\Delta T}}_{24}={\mathrm{E}}_1-{\mathrm{E}}_2={\mathrm{h}}_1.{\mathrm{S}}_1.\left({\mathrm{T}}_{20}-{\mathrm{T}}_{24}\right)+{\mathrm{h}}_2.{\mathrm{S}}_2\left({\mathrm{T}}_{22}-{\mathrm{T}}_{24}\right)$$

$${\mathrm{m}}_{22}.{\mathrm{C}}_{22}.{\mathrm{\Delta T}}_{22}={\mathrm{E}}_2-{\mathrm{E}}_3={\mathrm{h}}_2.{\mathrm{S}}_2.\left({\mathrm{T}}_{24}-{\mathrm{T}}_{22}\right)+{\mathrm{h}}_3.{\mathrm{S}}_3.\left({\mathrm{T}}_4-{\mathrm{T}}_{22}\right).$$

By making a heat balance for each part of the thermostat, we obtain the following equations which link the temperatures T ₂₀ , T ₂₂ , T ₂₄ of the different parts and the variation ΔT ₂₀ , ΔT ₂₂ , ΔT ₂₄ of each of these temperatures in the time (per second when the powers above are expressed in W): $${\mathrm{<figure-callout\; id="20"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_{20}.{\mathrm{<figure-callout\; id="20"\; label="VS"\; filenames="imgf0001.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{20}.{\mathrm{<figure-callout\; id="20"\; label="\Delta T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\Delta T</figure-callout>}}_{20}={\mathrm{P}}_{\mathrm{J}}-{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}}_1={\mathrm{P}}_{\mathrm{J}}+{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">h</figure-callout>}}_1.{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">S</figure-callout>}}_1.\left({\mathrm{T}}_{24}-{\mathrm{T}}_{20}\right)$$

$${\mathrm{<figure-callout\; id="24"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_{24}.{\mathrm{<figure-callout\; id="24"\; label="VS"\; filenames="imgf0001.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{24}.{\mathrm{<figure-callout\; id="24"\; label="\Delta T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\Delta T</figure-callout>}}_{24}={\mathrm{E}}_1-{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_2={\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">h</figure-callout>}}_1.{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">S</figure-callout>}}_1.\left({\mathrm{T}}_{20}-{\mathrm{<figure-callout\; id="24"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_{24}\right)+{\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="imgf0001.png"\; state="\{\{state\}\}">h</figure-callout>}}_2.{\mathrm{S}}_2\left({\mathrm{T}}_{22}-{\mathrm{T}}_{24}\right)$$

$${\mathrm{<figure-callout\; id="22"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_{22}.{\mathrm{<figure-callout\; id="22"\; label="VS"\; filenames="imgf0001.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{22}.{\mathrm{<figure-callout\; id="22"\; label="\Delta T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\Delta T</figure-callout>}}_{22}={\mathrm{E}}_2-{\mathrm{E}}_3={\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="imgf0001.png"\; state="\{\{state\}\}">h</figure-callout>}}_2.{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_2.\left({\mathrm{T}}_{24}-{\mathrm{<figure-callout\; id="22"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_{22}\right)+{\mathrm{h}}_3.{\mathrm{S}}_3.\left({\mathrm{T}}_4-{\mathrm{<figure-callout\; id="22"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_{22}\right).$$

Thanks to these equations, and on the basis of evaluations or measurements of the temperature T ₄ of the coolant at the level of the thermostat 4 and of the useful voltage Vc applied to the thermostat 4 (which directly gives the power P _J dissipated by the resistance placed in the thermostat 4), it is possible to determine at any time the evolution of the temperatures of the different parts of the thermostat. For the initialization of the system, we can consider that at start-up (the resistance being inactive in the preceding moments), the temperature is homogeneous in the thermostat 4 and is equal to the temperature of the coolant: we choose the initial values of T ₂₀ , T ₂₂ , T ₂₄ as equal to that T ₄ of the coolant.

We therefore know in particular the temperature T ₂₄ of the wax 24 which allows directly obtain the thermostat travel value L, for example by means of a correspondence table which indicates the relationship between these two quantities, as illustrated for example in figure 4b . These data (relationship between the temperature T ₂₄ of the wax and the stroke L of the thermostat) are for example determined by preliminary tests; they can be supplied by the thermostat manufacturer.

Likewise, when the characteristics of the different parts of the thermostat (mass, heat capacity) and of the interfaces (surface area, transfer coefficient) are not known, it is possible to determine them by prior tests or using experimental curves. thermostat operation: the characteristics of the different parts and interfaces are adapted so that equivalent results or curves, determined using the model, correspond to the test results or to the experimental curves. (Note that in this case it suffices to determine the products m ₂₀ .C ₂₀ , m ₂₂ .C ₂₂ , m ₂₄ .C ₂₄ and h ₁ .S ₁ , h ₂ .S ₂ , h ₃ .S ₃ , not each feature separately.)

The figure 5 represents an example of module 38 for evaluating the stroke of the controlled thermostat which uses the model which has just been described. This module is for example implemented within a processing unit which notably memorizes the correspondence table linking the values of wax temperature T ₂₄ and stroke L of the thermostat.

The module 38 receives as input the temperature T ₄ of the coolant at the level of the thermostat 4 (evaluated by a dedicated module, such as the module 36 visible in figure 3 and described below with reference to figure 7 , or measured by a temperature sensor) and the useful voltage value Vc applied to thermostat 4.

The module 38 comprises a unit 102 for memorizing the instantaneous evaluation value of the temperature T ₂₂ of the body 22, a unit 104 for memorizing the instantaneous evaluation value of the temperature T ₂₄ of the wax 24 and a unit 106 for memorizing the instantaneous evaluation value of the temperature T ₂₀ of the rod 20. As indicated above, at the start of the evaluation process, these units are initialized with the value T ₄ of the temperature of the cooling liquid received in entrance.

Each iteration of the process begins with an estimate of the new temperature values T ₂₀ and T ₂₂ respectively of the rod 20 and of the body 22. This is done because these elements are close to the heat sources and their temperature. temperature is likely to change from the previous iteration.

To do this, the module 38 determines the change ΔT ₂₀ of the temperature T ₂₀ of the rod 20 during an iteration on the basis of the instantaneous values T ₂₀ , T ₂₄ of temperature and of the useful voltage Vc (received at the input ) as following.

A subtracter 148 receives the instantaneous value T ₂₀ from the unit 106 and subtracts it from the instantaneous value T ₂₄ received from the unit 104. The value generated by the subtracter 148 is multiplied by h ₁ .S ₁ within a multiplier 150. Then, by means of an adder 152, the value obtained at the output of multiplier 150 and the power P _J generated by the resistor, determined as a function of the useful voltage Vc applied to the resistor by means of a conversion unit 108.

The output of adder 152 is multiplied by 1 / (m ₂₀ .C ₂₀ ) within a multiplier 154 in order to obtain the desired change ΔT ₂₀ (in accordance with the formula given above).

The output of the multiplier 154 (change ΔT ₂₀ ) is added to the instantaneous value T ₂₀ by an adder 156, which makes it possible to obtain at the output of the adder 156 the new instantaneous evaluation value of the temperature T ₂₀ of the rod 20, which will be used by unit 106 in the next iteration (after passing for this purpose through a retarder 116).

Likewise, the module 38 determines the change ΔT ₂₂ of the temperature T ₂₂ of the body 22 during an iteration on the basis of the instantaneous temperature values T ₄ (received at input), T ₂₂ , T ₂₄ as follows.

A subtracter 120 receives the instantaneous value T ₂₂ from the unit 102 and subtracts it from the instantaneous value T ₄ received as input; similarly, a subtracter 122 receives the instantaneous value T ₂₂ from the unit 102 and subtracts it from the instantaneous value T ₂₄ received from the unit 104. The values generated by the subtractors 120, 122 are respectively multiplied by h ₃ .S ₃ within a multiplier 124 and by h ₂ .S ₂ within a multiplier 126, then summed by an adder 128. The output of adder 128 is multiplied by 1 / (m ₂₂ .C ₂₂ ) at within a multiplier 130 in order to obtain the desired change ΔT ₂₂ (in accordance with the formula given above).

The output of the multiplier 130 (change ΔT ₂₂ ) is added to the instantaneous value T ₂₂ by an adder 132, which makes it possible to obtain at the output of the adder 132 the new instantaneous evaluation value of the temperature T ₂₂ of the body 22, which will be used by the unit 102 at the next iteration (after passing for this purpose through a retarder 112).

The module 38 determines the change ΔT ₂₄ of the temperature T ₂₄ of the wax 24 during an iteration (here lasting one second) on the basis of the instantaneous values T ₂₀ , T ₂₂ , T ₂₄ of temperature as follows. Here, the temperatures T ₂₀ and T ₂₂ used are those which have just been calculated as described above.

A subtracter 134 receives the instantaneous value T ₂₄ from the unit 104 and subtracts it from the instantaneous value T ₂₂ (as it has just been calculated) received from the adder 132; similarly, a subtracter 136 receives the instantaneous value T ₂₄ from the unit 104 and subtracts it from the instantaneous value T ₂₀ (as it has just been calculated) received from the adder 156. The values generated by the subtractors 134, 136 are respectively multiplied by h ₂ .S ₂ within a multiplier 138 and by h ₁ .S ₁ within a multiplier 140, then summed by an adder 142. The output of adder 142 is multiplied by 1 / (m ₂₄ .C ₂₄ ) within a multiplier 144 in order to obtain the desired change ΔT ₂₄ (in accordance with the formula given above).

The output of the multiplier 144 (change ΔT ₂₄ ) is added to the instantaneous value T ₂₄ by an adder 146, which makes it possible to obtain at the output of the adder 146 the new instantaneous evaluation value of the temperature T ₂₄ of the wax 24, which will be used by unit 104 in the next iteration (after passing for this purpose through a retarder 114).

The new instantaneous evaluation value of the temperature T24 is also transmitted to the input of a unit 110 for converting the wax temperature value into the stroke value L of the thermostat, on the basis of the correspondence table mentioned above relating the wax temperature and thermostat stroke values.

An estimate of the travel value L of the thermostat 4 is thus obtained at each iteration.

The figure 6 shows the heat exchanges involved in the cooling system at the level of the controlled thermostat and the motor.

As visible in figure 1 , the flow of cooling liquid which enters the engine 2 and passes through it in order to ensure its cooling is the sum of the flow Qo at the outlet of the air heater (and possibly of the turbocharger) and of the flow Q (L) at the outlet of the thermostat, which depends on the stroke L of the thermostat.

The heating of this coolant flow in the engine, due to the calorific power P (C, N) transferred by the engine, generates an increase in the temperature of the coolant from its value T _E at the inlet to its value T _s at the output, which is translated by the following equation:
P (C, N) = k. [Q ₀ + Q (L)]. (T _S -T _E ), where k is a constant characteristic of the coolant (k = ρ.C _P where is p the density of the coolant and C _P its specific heat capacity, or specific heat).

Note that, as indicated by its expression in the form P (C, N), the calorific power yielded by the engine depends on its operating point, defined by load C and speed N.

It is proposed to use these considerations to evaluate the temperature of the coolant T _E at the inlet of the engine, then the temperature of the coolant T ₄ at the level of the controlled thermostat 4 by means of the evaluation module 36 already mentioned, for example. as described now.

The figure 7 thus represents an example of a module for evaluating the temperature T ₄ of the cooling liquid at the level of the controlled thermostat.

This evaluation module receives as input a piece of information L representative of the travel of the thermostat 4 (determined here by means of the evaluation module 38, an example of which has been described with reference to figures 4a, 4b and 5 ), information relating to the operating point of the engine, here load C and engine speed N (supplied for example by the engine management unit or ECU), and the temperature T _s of the coolant at the outlet of the engine , here measured by the temperature sensor 10.

The processing unit that implements the module of figure 7 stores a map of the power P (C, N) transferred to the coolant by the engine as a function of load C and engine speed N. This map is a table which indicates the power values P transferred to the coolant by the motor respectively associated with pairs of values C, N.

This processing unit also stores a plurality of values Q (L) of coolant flow through the thermostat associated respectively with the different possible values for the stroke L.

Thus, on the basis of the information received as indicated above, a submodule 70 determines at each instant, by reading from the memory of the processing unit, the rate Q (L) associated with the stroke value L received. as a starter and power P (C, N) associated with the load C and engine speed N values received as input.

The sub-module 70 thus evaluates, at each instant t, the temperature T _E (t) of the coolant entering the engine using the model described above with reference to the figure 6 : T _E (t) = T _s - P (C, N) / (k. [Q ₀ + Q (L)]).

The temperature information T _E (t) determined by the submodule 70 is applied to a retarder 72, to a subtracter 73 (which also receives the output of the retarder 72) and to an adder 76. The adder also receives the input. output of the subtractor 73 after multiplying in a multiplier 75 by a constant b.

The output of adder 76 is applied to a subtractor 78 of a constant a, which thus generates at output an estimated value of the temperature T ₄ of the cooling liquid at the level of the thermostat 4 which is equal at each instant: $${\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">T</figure-callout>}}_4={\mathrm{T}}_{\mathrm{E}}\left(\mathrm{t}\right)-\mathrm{at}+\mathrm{b}.\left[{\mathrm{T}}_{\mathrm{E}}\left(\mathrm{t}\right)-{\mathrm{T}}_{\mathrm{E}}\left(\mathrm{t}-1\right)\right].$$

The arrangement of the elements 72, 73, 75, 76, 78 which has just been described thus forms a sub-module 71 which determines the estimated value of the temperature T ₄ of the coolant at the level of the thermostat 4 on the basis of the estimated value of the temperature T _E of the coolant entering the engine 2.

In this sub-module 71, the correction made to the temperature T _E (t) by the terms a and b. [T _E (t) - T _E (t-1)] makes it possible to take into account the fact that the thermostat is located slightly upstream of the engine entering the coolant circuit and the fact that the engine inlet temperature results from the combination of coolant from the thermostat and coolant from the air heater.

The constants a and b are determined by preliminary tests and can be stored in the processing unit which implements the module of the figure 7 . In the embodiment described here, for example a = 4 and b = 15 (for temperatures expressed in ° C or in K).

It is possible, according to a conceivable variant, for the parameters a and b to be variable as a function of the thermal power taken by the water heater. During the preliminary tests, in this case the parameters a and b are determined for various heating powers of the vehicle interior. During operation, the values a and b are then determined at each moment as a function of the heating power (as indicated by a dedicated information received for example from the cabin heating management module).

In the above description, the calculation of the evaluation of the temperature T ₄ of the coolant at the thermostat as a function of the evaluation of the temperature T _E of the coolant entering the engine is presented in the form of functional modules performing the various operations. In practice, these operations can be performed by executing a program by the processing unit which implements the module of the figure 7 .

Claims (1)

1. Method for operating a controlled thermostat (4) of a cooling circuit of a driving combustion engine (2) of a vehicle, the method comprising the following steps:

   a) measuring the temperature (T_S) of the liquid coolant circulating in a first pipe of the cooling circuit at the outlet of the combustion engine (2),

   b) acquiring at least one item of information (C, N) representative of an operating parameter of the combustion engine (2),

   c) estimating the travel (L) of the controlled thermostat (4) by means of a numerical model modelling the exchange of heat between an electrical resistive element of the controlled thermostat and a rod (20) of the controlled thermostat during the heating of the controlled thermostat by the resistive element, the exchange of heat between the rod (20) and the wax (24) of the controlled thermostat, the exchange of heat between the wax (24) and the body (22) of the controlled thermostat, the exchange of heat between the body (22) of the controlled thermostat and the liquid coolant and drawing up a heat balance sheet for each part of the thermostat,

   d) estimating the temperature (T_E) of the liquid coolant circulating in a second pipe of the cooling circuit at the inlet of the combustion engine as a function of the temperature (T_S) measured in step a), of the information (C, N) acquired in step b), and of the travel (L) estimated in step c), the second pipe being connected to a radiator with interposition of the controlled thermostat, a unit heater being connected to the second pipe,

   e) estimating the temperature (T₄) of the liquid coolant at the thermostat on the basis of the temperature (T_E) estimated in the second pipe, the temperature (T₄) at the thermostat being obtained on the basis of the temperature (T_E) estimated in the second pipe by correction by means of at least one coefficient determined as a function of a heating power of the unit heater,

   f) generating a useful voltage value to be applied to the controlled thermostat (4) as a function of a temperature setpoint (T_C), of the temperature (T_S) measured in step a) and of the travel (L) estimated in step c),

   g) applying the useful voltage (V_C) to the controlled thermostat (4).

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