EP3094842A1

EP3094842A1 - Method for estimating a temperature of a cooling liquid and system for cooling a driving engine of a motor vehicle

Info

Publication number: EP3094842A1
Application number: EP14827828.6A
Authority: EP
Inventors: Christophe Piard; Stephane Ruby; Christophe VIEL
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2014-01-15
Filing date: 2014-12-12
Publication date: 2016-11-23
Anticipated expiration: 2034-12-12
Also published as: JP6552508B2; FR3016400A1; EP3094842B1; JP2017503112A; WO2015107278A1; FR3016400B1

Abstract

The invention relates to a method for estimating the temperature (T_E) of a cooling liquid flowing in a cooling circuit of a driving engine (2) of a motor vehicle, which includes the following steps: a) measuring the temperature (T_s) of the cooling liquid flowing in a first pipe of the cooling circuit; b) acquiring at least one piece of information representing an operating parameter of the engine (2); and c) estimating the temperature (T_E) of the cooling liquid flowing in a second pipe of the cooling circuit, which is separate from said first pipe, in accordance with the temperature (T_s) measured in step a) and the information acquired in step b). The invention also describes a cooling system of the engine.

Description

Method for estimating a coolant temperature and cooling system of a motor vehicle drive motor

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the cooling of the drive motor in a motor vehicle.

It relates more particularly to a method for estimating the temperature of a coolant circulating in a cooling circuit of a motor vehicle drive motor.

The invention also relates to a cooling system of a motor vehicle drive motor.

BACKGROUND

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

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

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

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

The use of a plurality of sensors, however, leads to a non-negligible cost and is thus frequently limited to a single temperature sensor, positioned for example at the output of the motor, which is detrimental to precise control of the entire system.

OBJECT OF THE INVENTION

In this context, the present invention proposes a method for estimating the temperature of a cooling liquid flowing in a cooling circuit of a motor vehicle drive motor, characterized by the following steps:

a) measuring the temperature of the coolant circulating in a first pipe of the cooling circuit,

b) acquisition of at least one piece of information representative of an operating parameter of the engine,

c) estimating the temperature of the coolant circulating in a second cooling circuit line, distinct from said first pipe, as a function of the temperature measured in step a) and the information acquired in step b) .

This results in an evaluation of the coolant temperature in a pipe separate from that in which the temperature sensor is placed. This improves the control of the system on the basis of information delivered by a sensor.

The first pipe and the second pipe are, for example, pipes for connecting the cooling circuit to an internal cooling circuit of the engine: the first pipe may be located at the outlet of the engine, while the second pipe may then be located at the inlet of the engine. engine.

According to optional features proposed by the invention:

the second pipe is connected to a radiator with the interposition of a thermostat;

the method comprises a step of estimating the temperature of the coolant at the thermostat on the basis of the estimated temperature in the second pipe;

the temperature at the thermostat is obtained on the basis of the estimated temperature in the second pipe by correction by means of at least one coefficient stored in a processing unit implementing the temperature estimation step at the level of the thermostat; thermostat;

- a heater is connected to the second pipe;

the temperature at the thermostat is obtained on the basis of the estimated temperature in the second pipe by correction by means of at least one coefficient determined as a function of a heating power of the heater;

the estimation of the temperature in the second pipe uses a flow rate through the thermostat determined as a function of a stroke value of the thermostat evaluated by a thermostat stroke estimation module; - The acquisition step comprises a step of receiving the information representative of an engine operating parameter from an engine management module.

The invention also proposes a cooling system for a motor vehicle drive motor comprising an engine cooling circuit and a temperature sensor for a cooling liquid circulating in a first pipe of the cooling circuit, characterized in that it comprises a module for acquiring at least one piece of information representative of an operating parameter of the engine and a module for estimating the temperature of the coolant circulating in a second pipe of the cooling circuit, distinct from said first pipe, depending on the temperature measured by the sensor and the information acquired by the acquisition module.

Such a system may also include the optional features presented above in the context of the method proposed by the invention, in particular the following optional features:

the system comprises a module for estimating the temperature of the coolant at the thermostat on the basis of the estimated temperature in the second pipe;

the temperature estimation module at the thermostat is designed to determine the temperature at the thermostat on the basis of the estimated temperature in the second pipe by correction by means of at least one coefficient stored in a processing unit implementing the temperature estimation module at the thermostat;

the thermostat temperature estimation module is designed to determine a coefficient as a function of a heating power of the heater and / or to determine the temperature at the thermostat on the basis of the estimated temperature in the thermostat. the second conduct by correction by means of said coefficient;

- The temperature estimator module at the thermostat is designed to receive a thermostat stroke value from a thermostat stroke estimation module and / or to determine a flow through the thermostat as a function of said stroke value and / or for estimating the temperature at the thermostat using said flow rate; - The temperature estimation module in the second pipe is designed to receive the information representative of an engine operating parameter from an engine management module.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

In the accompanying drawings:

- Figure 1 shows schematically the main elements of a cooling system of an internal combustion engine;

- Figures 2a and 2b schematically shows a piloted thermostat used in the system of Figure 1;

FIG. 3 represents an example of a control system of such a thermostat;

FIGS. 4a and 4b show elements of an exemplary model used to evaluate the stroke of the piloted thermostat;

FIG. 5 represents an example of a module for evaluating the stroke of the piloted thermostat;

FIG. 6 shows the heat exchanges involved in the cooling system at the controlled thermostat and the engine;

FIG. 7 represents an exemplary module for evaluating the temperature of the cooling liquid at the level of the piloted thermostat according to the teachings of the invention.

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). Alternatively, it could be a spark ignition engine (gasoline).

Dashed lines in FIG. 1 show elements that are present according to certain variant embodiments of the invention.

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

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

At the output of 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 other parts. After cooling in these elements, the coolant is transported by pipes to the engine 2 for cooling thereof.

The coolant is conveyed from the engine 2 (output) to the engine 2 (input) through the thermostat 4 permanently so that the thermostat 4 is always in contact with a flow of coolant whatever the state thermostat 4 (open or closed).

The cooling system may optionally further comprise a water-oil exchanger 12 which receives the cooling liquid coming from the engine 2 as input. After passing through the water-oil exchanger 12, the cooling liquid is reinjected into the circuit described herein. above, for example at the thermostat 4. The use of the water-oil heat exchanger is not 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 amount of cooled coolant (from the radiator 6) to be injected at the input of the engine 1 in order to obtain the desired temperature engine operation, as explained below.

Similarly, the coolant output of the engine 2 can be used to regulate the temperature in a turbocharger 14 supplied for this purpose in cooling liquid by a bypass of the circuit linking the engine 2 and the heater 8.

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

In the present exemplary embodiment, no means is provided for measuring the temperature of the coolant at the inlet of the engine 2 (temperature T _E ), or at the level of the thermostat 4 (temperature T). Alternatively, as explained below, it could instead provide 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 .

Figures 2a and 2b show the thermostat 4 in two different operating positions, respectively a first position in which the thermostat closes the pipe connecting the radiator 6 to the motor 2 and a second position in which the thermostat opens the pipe.

The thermostat 4 comprises a rod (or "pencil") 20 on which is slidably mounted an assembly formed of a body 22 of brass and a valve (or valve) 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 to this space delimited by the body 22, the valve 26 and the 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 temperature T at this location, as indicated above; the body 22 is therefore located downstream of the valve 26 in this pipe.

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

When the temperature T of the coolant at the thermostat 4 reaches, or even exceeds, the above-mentioned threshold, notably because of the heating of the coolant by the engine 2 and the absence of cooling by the coolant coming from the radiator 6, the wax 24 melts and expands, causing the volume located 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 the valve 26 and the opening of the thermostat 4.

Coolant from the radiator 6 (cooled by it) is thus injected into the cooling circuit of the engine 2 and thus participates in cooling the engine.

This gives a mechanical regulation of the temperature of the coolant. A return spring (not shown) is generally provided to facilitate the return of the valve 26 to its closed position when the coolant temperature T ₄ 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 passes a current in the resistor which releases heat by the Joule effect and thus accelerates the rise in temperature of the wax 24. The thermostat 4 will open thereby more rapidly in the absence of heating by the resistance, that is to say for a coolant temperature T below the aforementioned threshold.

The use of the heating of the wax 24 (here by means of the resistor) thus makes it possible to artificially lower the control temperature of the engine 2 engine coolant: 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 heat output (which depends on the design of the thermostat). A heating power lower than the maximum heating capacity can be obtained by applying the nominal voltage V ₀ to a proportion only of the period of time considered (principle of the pulse width modulation or PWM of the English "Pulse Width Modulation" ): it is considered in the following that is applied in this case a useful voltage V less than the nominal voltage V ₀ .

FIG. 3 represents an example of a control system of the thermostat 4 according to the teachings of the invention.

The control system of FIG. 3 comprises several modules, represented here in functional form. Several functional modules can, however, in practice be implemented by the same processing unit programmed to perform the processing assigned respectively to these functional modules. This processing unit is for example an engine control unit (ECU or engine control unit) on 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 the motor 2, are available within the computer 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 of the coolant at the thermostat 4 .

The setpoint determination module 32 generates the temperature setpoint T _c as a function of the engine speed N and 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 values of engine speed N and load C received from the computer 30 in a correspondence table (map) stored in the processing unit concerned .

The setpoint determination module 32 generates, for example, instructions T _c between 90 ° C and 1 10 ° C adapted to different operating conditions of the engine 2 encountered (represented by the load C and the engine speed N). In practice, the set T _c can take a discrete set of values, for example 90 ° C, 100 ° C or 1 10 ° C.

The temperature setpoint T _c generated by the reference determination module 32 is transmitted to a regulation module 34, which also receives the temperature T _s of the engine output coolant measured by the temperature sensor 10.

Based on the measured temperature T _s and the temperature setpoint T _c , the regulation module 34 determines the raw useful voltage V _R to be applied to the driven thermostat electrode 4 in order to converge the temperature of the coolant. towards the instruction T _c .

The regulation law applied by the regulation module 34 for determining the gross useful voltage V _R as a function of the measured temperature T _s and of the set temperature T _c depends on the application envisaged.

For example, the following can be envisaged 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 1 10 ° C (high temperature control), the gross useful voltage V _R is equal to 0 V, that is to say that the heating resistance of the wax is not used and that the regulation of the coolant temperature is carried out mechanically by the thermostat (whose design is here provided for a regulation at 1 10 ° C);

when the setpoint T _c is strictly lower than 1 10 ° 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 according to of the temperature error (T _s -T _c ) according to a PI (proportional-integral) control mechanism.

The gross useful voltage V _R generated by the regulation module 34 is transmitted to a correction module 40 whose operation will be described later.

The module 36 for evaluating the temperature T 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 the stroke of the thermostat 4, as well as, as already indicated , load information C and engine speed N representative of the operation of the engine 2.

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

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

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

The aforementioned stroke evaluation module 38 receives as input the temperature T of the cooling liquid at the thermostat (produced by the evaluation module 36 in the example described) and the value of the useful voltage effectively applied to the piloted thermostat. 4 (corrected useful value V _c generated by the correction module 40 as explained below).

On the basis of this information received as input, the module 38 evaluates the travel L of relative displacement of the rod 20 and the body 22, which gives an estimate of the opening proportion of the thermostat 4. The evaluation carried out by the For example, module 38 is implemented by implementing a digital model, as described below with reference to FIGS. 4a, 4b and 5. Alternatively, this evaluation can be performed by reading the associated path L in a pre-recorded correspondence table, at temperature values T ₄ and applied applied voltage V _c received at the input. The prerecorded values have, for example, been determined in this case by means of preliminary tests or simulations, carried out beforehand, using the numerical model described with reference to FIGS. 4a, 4b and 5.

The module 38 can thus provide a value L representative of the stroke of the thermostat 4 to the correction module 40, which also receives as input the raw voltage V _R calculated by the control module 34 as already indicated.

When the gross useful voltage V _R calculated by the regulation module 34 is small, or even zero, the correction module 40 corrects this value so that a minimum useful voltage is actually applied to the electrode 28 of the driven thermostat 4 so that the resistor delivers a non-zero heating power, which makes it possible to preheat the wax 24 to a limit opening temperature of the thermostat 4. Thus, any additional heating of the wax 24 (in response to a control of the system piloting to open the thermostat) will have an immediate effect of opening the valve.

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

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 lower than this minimum preheating voltage. Indeed, since the regulation module 34 controls a gross useful voltage V _R greater than the minimum preheating voltage, this raw useful voltage V _R is applied as such by the correction module 30 to the electrode 28 of the controlled thermostat. 4 (in this case V _c = V _R ).

The correction module 40 also causes a limitation of the applied voltage V _c (and therefore of the heating power delivered by the resistance Joule effect) so that the application of this voltage V _c does not cause heating higher than that resulting in a total opening of the thermostat 4 (that is to say a stroke L equal to the maximum stroke L _max ). An additional heating is indeed useless; it is also detrimental to the reaction time 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 stroke of the thermostat 4 received by the correction module 40 reaches the maximum stroke L _max , the correction module 40 applies to the piloted thermostat 4 a useful voltage V _c that does not depend on the useful voltage Gross V _R received from the regulation module 34, but which is chosen to maintain the stroke L at its maximum value L _max . For example, this is done by controlling the applied operating voltage V _c 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 heating power delivered by the resistor) is maintained only as long as the gross useful voltage V _R generated by the regulation module 34 is greater than this limited voltage. Indeed, since the regulation module 34 controls a gross useful voltage V _R less than the limited voltage determined by the servocontrol described above, this raw useful voltage V _R is applied as it is by the correction module 30 to the electrode 28 of the piloted thermostat 4 (in this case V _c = V _R ).

It can also be provided, in addition to the above limitation, that the correction module 40 causes a limitation of the applied voltage V _c as a function of the stroke L received at input for a range of values of this race L.

Indeed, for certain types of controlled thermostats, it is contraindicated to control a large heating power in certain opening positions of the thermostat because the heating may then damage the seals that seal between the rod and the thermostat. body-valve assembly.

The processing unit which implements the correction module 40 stores for this purpose a correspondence table which indicates the maximum allowable voltage V _max as a function of the stroke L of the thermostat. This data is for example provided by the manufacturer of the thermostat. The correction module 40 thus reads at each instant the maximum allowable voltage V _max in the table as a function of the value L of travel received from the evaluation module 38 and thus determines the corrected useful voltage to be applied:

if V _R is less than V _max , V _c = V _R ;

if V _R is greater (or equal) than V _max , V _c = V _max .

For the sake of simplicity of the exposition, the preceding paragraph does not take into account the additional limitation, if any, of the applied voltage with a view to preventing 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 piloted thermostat 4 a useful voltage V _c equal to the raw payload voltage V _R received as input from the regulation module 34.

Note that in practice, the application of a given useful voltage to the thermostat 4 is performed 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 wanted voltage (in accordance with the principle of pulse width module or PWM of the English "Pulse Width Modulation"), as already explained above.

FIG. 4a shows the model used in the example described here to simulate the thermal behavior of the different parts of the piloted thermostat 4 in order to evaluate its stroke as explained below.

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

the mass m ₂ 2, the specific heat capacity C22 and the temperature T22 of the body 22;

the mass m ₂₄ , the specific heat capacity C2 ₄ and the temperature T ₂₄ of the wax 24;

the mass m ₂ o, the specific heat capacity C20 and the temperature T ₂ o of the rod 20.

It is furthermore 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 hi and a surface Si 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 the body 22;

a transfer coefficient h ₃ and a surface S 3 for the interface between the body 22 and the cooling liquid at the temperature T.

The heat exchanges are thus modeled as follows:

the resistance heats the rod by Joule effect by providing a thermal power Pj (directly related to the voltage V _c applied to the controlled thermostat 4);

a heat exchange takes place between the rod 20 and the wax 24 of power Ei = hi .Si. (T ₂ o-T2 ₄ ) (counted positively for heat transfer 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 ₂ 2) (counted positively for a heat transfer of the wax 24 towards the body 22) ;

a heat exchange takes place between the body 22 and the power coolant E ₃ = h ₃ .S _3. (T ₂ 2 -T ₄ ) (counted positively for a heat transfer from the body 22 to the coolant) ).

By making a heat balance for each part of the thermostat, we obtain the following equations which bind the temperatures T ₂ o, T ₂₂ , T ₂₄ of the different parts and the variation ΔΤ ₂₀ , ΔΤ ₂₂ , ΔΤ ₂ of each of these temperatures in the time (per second when the powers above are expressed in W):

m ₂₀ .C ₂ o.AT ₂₀ = Pj - E1 = Pj + hi .Si. (T ₂₄ -T ₂₀ )

m ₂₄ .C ₂ .AT ₂₄ = E ₁ - E ₂ = hi .Si. (T ₂₀ -T ₂₄ ) + h ₂ .S _2. (T ₂₂ -T ₂₄ )

m ₂₂ .C ₂₂ .AT ₂₂ = E ₂ - E3 = h ₂ .S ₂ (T ₂₄ -T ₂₂ ) + i3.S3. (T ₄ -T ₂₂ ).

With these equations, and based on evaluations or measurements of the temperature T of the coolant at the thermostat 4 and the useful voltage V _c applied to the thermostat 4 (which gives directly the power Pj dissipated by the resistance placed in the thermostat 4), it is possible to determine at each moment the evolution of the temperatures of the different parts of the thermostat. For the initialization of the system, we can consider that at startup (the resistance being inactive in the previous instants), the temperature is homogeneous in the thermostat 4 and is the coolant temperature: the initial values of T ₂₀ , T ₂₂ , T ₂₄ are chosen to be equal to that T of the coolant.

Thus, in particular, the temperature T ₂₄ of the wax 24 is known, which makes it possible to obtain directly the stroke value L of the thermostat, 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 prior tests; they can be provided by the thermostat manufacturer.

Similarly, when the characteristics of the different parts of the thermostat (mass, heat capacity) and the interfaces (area, transfer coefficient) are not known, it is possible to determine them by preliminary tests or by means of experimental curves. operating the thermostat: the characteristics of the different parts and interfaces are adapted so that equivalent results or curves, determined by the model, correspond to the test results or to the experimental curves. (Note that it is sufficient in this case to determine the products m ₂₀ .C ₂ o, m ₂₂ .C ₂₂ , m ₂₄ .C ₂₄ and hi .Si, h ₂ .S ₂ , h ₃ .S3, and not each feature separately.)

FIG. 5 represents an exemplary module 38 for evaluating the stroke of the piloted thermostat that uses the model that has just been described. This module is for example implemented within a processing unit which notably stores the correspondence table connecting the temperature values of wax T ₂ and stroke L of the thermostat.

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

The module 38 comprises a unit 102 for storing the instantaneous evaluation value of the temperature T ₂₂ of the body 22, a unit 104 for storing the instantaneous evaluation value of the temperature T ₂ of the wax 24 and a unit 106 storing the instantaneous evaluation value of the temperature T ₂₀ of the rod 20. As indicated above, at the beginning of the process these units are initialized with the value T of the temperature of the coolant received at the inlet.

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

To do this, the module 38 determines the evolution ΔΤ20 of the temperature T ₂ o of the rod 20 during an iteration on the basis of the instantaneous values T ₂ o, T 24 of temperature and of the useful voltage V _c (received in input) as follows.

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 subtractor 148 is multiplied by hi .Si within a multiplier 150 The value obtained at the output of the multiplier 150 and the power Pj generated by the resistance, determined as a function of the useful voltage V _c applied to the resistance by means of a unit of unity, are then summed by means of an adder 152. conversion 108.

The output of the adder 152 is multiplied by 1 / (m ₂₀ .C ₂ o) in a multiplier 154 to obtain the desired evolution ΔΤ ₂₀ (according to the formula given above).

The output of the multiplier 154 (evolution ΔΤ 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 value for evaluating the temperature T ₂₀ of the rod 20, which will be used by the unit 106 at the next iteration (after passing through this purpose through a retarder 1 16).

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

A subtractor 120 receives the instantaneous value T ₂₂ from the unit 102 and subtracts it from the instantaneous value T received at the input; likewise, a subtractor 122 receives the instantaneous value T ₂₂ from the unit 102 and subtracts it from the instantaneous value T ₂ received from the unit 104. The values generated by the subtractors 120, 122 are respectively multiplied by h ₃ .S3 within a multiplier 124 and by h ₂ .S ₂ within a multiplier 126, then summed by an adder 128. The output of the adder 128 is multiplied by 1 / (m ₂₂ .C ₂₂ ) within a multiplier 130 in order to obtain the evolution ΔΤ22 sought (in accordance with the formula given above).

The output of the multiplier 130 (evolution ΔΤ22) is added to the instantaneous value T22 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 T22 of the body 22, which will be used by the unit 102 at the next iteration (after passing through this purpose through a retarder 1 12).

The module 38 determines the evolution ΔΤ ₂₄ of the temperature T ₂₄ of the wax 24 during an iteration (here of a duration of one second) on the basis of the instantaneous values T ₂ o, T22, T24 of temperature as following. Here, the temperatures T ₂ o and T 22 used are those which have just been calculated as described above.

A subtractor 134 receives the instantaneous value T ₂₄ from the unit 104 and subtracts it from the instantaneous value T22 (as just calculated) received from the adder 132; likewise, a subtractor 136 receives the instantaneous value T ₂₄ from the unit 104 and subtracts it from the instantaneous value T ₂ o (as just calculated) received from the adder 156. The values generated by the subtractors 134, 136 are respectively multiplied by h ₂ .S2 within a multiplier 138 and by hi .Si within a multiplier 140, then summed by an adder 142. The output of the adder 142 is multiplied by 1 / (m ₂₄ .C2 ₄ ) within a multiplier 144 to obtain the desired evolution ΔΤ ₂₄ (according to the formula given above).

The output of the multiplier 144 (evolution ΔΤ 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 the unit 104 at the next iteration (after passing through this purpose through a retarder 1 14).

The new instantaneous temperature evaluation value T24 is also transmitted to the input of a unit 1 for converting the wax temperature value into a stroke value L of the thermostat, on the basis of the correspondence table mentioned above. connecting the wax temperature and stroke temperature values of the thermostat.

This gives an estimate of the stroke value L of the thermostat 4 at each iteration.

Figure 6 shows the heat exchanges involved in the system cooling at the controlled thermostat and motor.

As can be seen in FIG. 1, the coolant flow rate that enters the engine 2 and travels it in order to ensure its cooling is the sum of the flow rate Q ₀ at the outlet of the heater (and possibly the turbocharger) and the flow rate Q (L) at the thermostat output, which depends on the L-stroke of the thermostat.

The warming of this flow of coolant in the engine, due to the heat output P (C, N) yielded by the engine, generates the increase of the coolant temperature of its value T _E at its inlet. value T _s output, which is translated by the following equation:

P (C, N) = k. [Qo + Q (L)]. (T _s -T _E ), where k is a characteristic constant of the coolant (k = p.Cp where p is the density of the liquid cooling and Cp its specific heat capacity, or specific heat).

It should be noted that, as indicated by its expression in the form P (C, N), the calorific power yielded by the motor depends on its operating point, defined by the load C and the regime N.

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

FIG. 7 thus represents an example of a module for evaluating the temperature T of the coolant at the level of the piloted thermostat.

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

The processing unit which implements the module of FIG. 7 stores a mapping of the power P (C, N) yielded to the cooling liquid by the engine as a function of the load C and the engine speed N. This mapping is a table which indicates the values of power P ceded to the coolant by the engine respectively associated with couples of values C, N.

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

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

The sub-module 70 thus evaluates, at each instant t, the engine coolant temperature T _E (t) at the input of the engine using the model described above with reference to FIG. 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 output of the subtracter 73 after multiplication in a multiplier 75 by a constant b.

The output of the adder 76 is applied to a subtractor 78 of a constant a, which thus generates an output value of the temperature T of the coolant at the level of the thermostat 4 which is worth at each instant:

T ₄ = T _E (t) - a + b. [T _E (t) - T _E (t-1)].

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

In this submodule 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 slightly upstream of the engine inlet in the coolant circuit and the engine inlet temperature results from the combination of coolant from the thermostat and coolant from the heater.

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

According to one conceivable variant, it is possible to envisage that the parameters a and b are variable as a function of the thermal power taken by the heater with water. During the preliminary tests, in this case the parameters a and b are determined for various heating powers of the passenger compartment of the vehicle. During operation, the values a and b are then determined at each instant as a function of the heating power (as indicated by dedicated information received for example from the cabin heating management module).

In the description above, the calculation of the evaluation of the temperature T of the coolant at the thermostat according to the evaluation of the engine coolant temperature T _E is presented in the form of modules. functionalities performing the different operations. In practice, these operations can be performed by the execution of a program by the processing unit that implements the module of FIG. 7.

Claims

1. Method for estimating the temperature (T _E ) of a cooling liquid circulating in a cooling circuit of a motor vehicle drive motor (2), characterized by the following steps:

a) measuring the temperature (T _s ) of the coolant circulating in a first pipe of the cooling circuit,

b) acquisition of at least one piece of information (C, N) representative of an operating parameter of the engine (2),

c) estimation of the temperature (T _E ) of the coolant circulating in a second pipe of the cooling circuit, distinct from said first pipe, as a function of the temperature (T _s ) measured in step a) and of the information (C, N) acquired in step b).

The method of claim 1, wherein the first conduit and the second conduit are connecting lines of the cooling circuit to an internal cooling circuit of the engine (2).

3. Estimation method according to claim 1 or 2, wherein the second pipe is connected to a radiator (6) with the interposition of a thermostat (4), the method comprising a step of estimating the temperature (T ₄ ) of the coolant at the thermostat (4) based on the estimated temperature (T _E ) in the second pipe.

The estimation method according to claim 3, wherein the temperature (T) at the thermostat (4) is obtained on the basis of the estimated temperature (T _E ) in the second pipe by correction by means of at least a coefficient (a, b) stored in a processing unit implementing the step of estimating the temperature (T) at the thermostat (4).

The estimation method according to claim 3, wherein a heater (8) is connected to the second conduit and wherein the temperature (T) at the thermostat is obtained based on the estimated temperature (T _E ) in the second conduct by correction by means of at least one coefficient determined according to a heating power of the heater.

6. Cooling system of a motor vehicle engine (2) comprising an engine cooling circuit (2) and a temperature sensor (10) of a cooling liquid circulating in a vehicle. first pipe of the cooling circuit,

characterized in that it comprises a module (30) for acquiring at least one piece of information (C, N) representative of an operating parameter of the engine and a module (70) for estimating the temperature (T _E ) coolant circulating in a second pipe of the cooling circuit, separate from said first pipe, as a function of the temperature (T _s ) measured by the sensor and the information (C, N) acquired by the module of acquisition.

The cooling system of claim 6, wherein the first conduit and the second conduit are connecting conduits of the cooling circuit to an internal cooling circuit of the engine (2).

8. Cooling system according to claim 6 or 7, wherein the second pipe is connected to a radiator (6) with the interposition of a thermostat (4), the system comprising a module (71) for estimating the temperature ( T) of the coolant at the thermostat (4) based on the estimated temperature (T _E ) in the second pipe.

9. Cooling system according to claim 8 wherein the module (71) for estimating the temperature (T) at the thermostat (4) is designed to determine the temperature (T) at the thermostat (4) on the basis of the estimated temperature (T _E ) in the second pipe by correction by means of at least one coefficient (a, b) stored in a processing unit implementing the temperature estimation module (T) at the level thermostat (4).

10. Cooling system according to claim 8, wherein a heater (8) is connected to the second pipe and wherein the module (71) for estimating the temperature (T) at the thermostat (4) is designed to determining a coefficient as a function of a heating power of the heater (6) and for determining the temperature at the thermostat (T) based on the estimated temperature (T _E ) in the second conduit by correction by means of said coefficient.