FR3016398A1 - THERMOSTAT DEVICE FOR AUTOMOTIVE VEHICLE COOLING SYSTEM, COOLING SYSTEM EQUIPPED WITH SUCH A THERMOSTAT DEVICE AND METHOD OF CONTROLLING A HEATING MODULE - Google Patents

Abstract

The invention relates to a thermostat device (4) for a motor vehicle cooling system comprising a valve, a heat-sensitive part, designed to cause the valve to open when the temperature of said sensitive part exceeds a temperature threshold. , and a controlled heating module of said sensitive part. A control module (40) is designed to control the heating module so that it delivers a non-zero heat output insufficient to cause an opening of the valve. A cooling system and a method of controlling a heating module are also described.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the cooling of the engine in a motor vehicle. It relates more particularly to a thermostat device for a motor vehicle cooling system comprising a valve, a heat sensitive part, designed to cause the opening of the valve when the temperature of said sensitive portion exceeds a temperature threshold, and a 10 controlled heating module of said sensitive portion. The invention also relates to a cooling system equipped with such a thermostat device and a method of controlling a heating module. BACKGROUND OF THE INVENTION In motor vehicle drive motor cooling systems, a thermostat is commonly used which regulates the amount of cold coolant delivered by the radiator to be injected into the engine cooling circuit to provide the engine coolant. obtain a set temperature. To do this, the thermostat generally comprises a valve and a heat-sensitive portion (typically a volume of wax), designed to cause the valve to open when the temperature of the sensing portion exceeds a temperature threshold: typically , the melting and the subsequent expansion of the wax causes the relative displacement of a rod (or pencil) relative to the body of the thermostat, which controls the opening of the valve. Thus, when the coolant heats up and reaches the temperature threshold, the valve opens mechanically so that cold coolant from the radiator is injected into the coolant circuit feeding the engine, allowing the desired regulation of the coolant temperature. It has been proposed to use a controlled heating module of the sensitive part, for example an electrical resistance heating the wax, in order to be able to control the opening of the valve: by putting the resistor under tension, the wax is heated artificially. , which makes it possible to force the opening of the valve. This technique is thus particularly used when it is desired to rapidly lower the temperature of the coolant in the engine, or, in general, when the desired temperature is lower than that obtained by the mechanical regulation of the thermostat. The drop (by controlled heating of the wax) of the temperature at which the valve opens can indeed be analyzed as an artificial drop in the temperature setpoint. The use of the controlled heating to obtain an early opening of the valve is for example described in the patent application FR 2 896 272. The heating of the heat-sensitive part, necessary for the opening of the valve, however, involves a non-negligible reaction time. It is therefore not possible to obtain a rapid forced opening of the valve. OBJECT OF THE INVENTION In this context, the present invention provides a thermostat device as evoked above, comprising a control module designed to control the heating module so that it delivers a non-heating power. none insufficient to cause an opening of the valve. The control module thus makes it possible to ensure a minimum heating of said sensitive part without, however, opening the valve. Thus, even when the valve is closed, the heat-sensitive portion is heated, which decreases the reaction time in a subsequent phase where the sensing portion is heated to cause the valve to open. According to optional features proposed by the invention: the sensitive part is a volume of wax whose expansion, above said temperature threshold, causes a mechanism designed to open the valve; the heating module comprises an electrical resistance; - The control module is designed to control the heating module according to a temperature at the thermostat; the thermostat device comprises a module for estimating the temperature at the thermostat as a function of a measured temperature; the thermostat device comprises a sensor for measuring the temperature at the thermostat; the thermostat device comprises a module for determining the opening proportion of the valve and the control module is designed to control the heating module as a function of the determined opening proportion; the thermostat device comprises a module for determining the flow rate of the valve and the control module is designed to control the heating module according to the determined flow rate. The invention also proposes a cooling system for a drive motor of a motor vehicle, comprising a radiator and a thermostat device as proposed above, designed to regulate the quantity of coolant coming from the radiator. inject into a motor cooling circuit. The invention also proposes a method of controlling a heating module controlled by a heat-sensitive part of a thermostat device for a motor vehicle cooling system, the thermostat device comprising a valve and the sensitive part. the heat being designed to cause the opening of the valve when the temperature of said sensing portion exceeds a temperature threshold, characterized by a step of controlling the heating module so that it delivers a non-heating power. none insufficient to cause an opening of the valve. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. 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 a first example of a control system of such a thermostat according to the teachings of the invention; 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 coolant at the level of the piloted thermostat; FIG. 8 represents a second example of a control system according to the teachings of the invention; FIG. 9 shows an example of a curve giving the useful voltage to be applied to obtain the total opening of the thermostat as a function of the temperature of the liquid in which the thermostat is immersed; - Figure 10 shows an example curve giving the useful voltage to be applied to obtain a preheating of the wax of the thermostat, without causing its opening, depending on the temperature of the liquid in which the thermostat is immersed. 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 coolant which ensures its operation at a given temperature of 25 given 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 conveyed by lines 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. temperature sensor 10 is also mounted in the coolant lines located at the output of the engine 2 in order to measure the temperature Ts of the coolant at the outlet of the engine 2. In the present embodiment, no means is provided. measuring the coolant temperature at the inlet of the engine 2 (temperature TE), or at the level of the thermostat 4 (temperature T4). Alternatively, as explained below, it could instead be provided to use a temperature sensor in the cooling circuit near the engine inlet to measure the temperature TE or at the thermostat 4 to measure the temperature T4. 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 is immersed in the temperature cooling liquid T4 at this location, as indicated above; the body 22 is therefore located downstream of the valve 26 in this pipe.

When the temperature T4 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 T4 of the coolant at the thermostat 4 reaches or even exceeds the aforementioned threshold, in particular because of the heating of the coolant by the engine 2 and the lack of cooling by the coolant 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 T4 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 resistance heating, that is to say for a coolant temperature T4 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 Vo (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 power can be obtained by applying the nominal voltage Vo to a proportion only of the period of time considered (principle of pulse width modulation or PWM of the English language "Pulse Width Modulation") In the following it is considered that in this case a useful voltage V is applied which is lower than the nominal voltage Vo. FIG. 3 represents a first 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. 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 engine 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 Tc and on the other hand to a module 36 for evaluating the temperature T4 of the coolant at the level of the thermostat 4. The setpoint determination module 32 generates the temperature setpoint Tc 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 Tc 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, setpoints Tc of between 90.degree. C. and 110.degree. 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 instruction Tc can take a discrete set of values, for example 90 ° C, 100 ° C or 110 ° C. The temperature set point Tc generated by the reference determination module 32 is transmitted to a regulation module 34, which also receives the temperature Ts of the engine output coolant measured by the temperature sensor 10. On the basis of the measured temperature Ts and the temperature set point Tc, the regulation module 34 determines the raw useful voltage VR to be applied to the electrode of the driven thermostat 4 so as to converge the temperature of the coolant towards the setpoint T.

The regulation law applied by the regulation module 34 to determine the raw useful voltage VR as a function of the measured temperature Ts and the set temperature Tc depends on the intended application. For example, we can consider the following in the case indicated above where the setpoint Tc can take a discrete set of values: - when the setpoint Tc is equal to 110 ° C (high temperature control), the gross useful voltage VR 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 temperature of the coolant is carried out mechanically by the thermostat (whose design is here provided for regulation at 110 ° C); when the setpoint Tc is strictly lower than 110 ° C. (low temperature regulation), and therefore equal to 90 ° C. or 100 ° C. in the case described here, the gross useful voltage VR is, for example, determined as a function of the temperature error (Ts-Tc) according to a PI (proportional-integral) control mechanism. The gross useful voltage VR 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 T4 of the coolant at the level of the thermostat 4 receives as input the temperature Ts measured by the measurement sensor 10 and an estimated value L of the stroke of the thermostat 4, as well as, as already indicated, the load information C and the engine speed N representative of the operation of the engine 2. The estimated value L of the stroke 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 as input, the module 36 evaluates the temperature T4 of the coolant at the level of 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 stroke evaluation module 38 already mentioned receives the inlet temperature T4 coolant level the thermostat (produced by the evaluation module 36 in the example described) and the useful voltage value actually applied to the controlled thermostat 4 (corrected useful value Vc 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 produced by implementing a digital model, as described below with reference to FIGS. 4a, 4b and 5. In a variant, this evaluation can be performed by reading the associated path L in a pre-recorded correspondence table, with the values of temperature T4 and applied voltage Vc received at the input. The prerecorded values have, for example, been determined in this case by means of prior tests or simulations, carried out beforehand, using the numerical model described with reference to FIGS. 4a, 4b and 5. The module 38 may thus be provide a value L representative of the stroke of the thermostat 4 to the correction module 40, which also receives as input the gross useful voltage VR calculated by the control module 34 as already indicated. When the gross useful voltage VR 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 effectively applied to the electrode 28 of the driven thermostat 4 so that the resistance provides a non-zero heating power, which allows to pre-heat 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 system of 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 finds the closing of the thermostat 4 (that is to say if L = 0), it generates at the output a corrected voltage value Vc 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 VR generated by the regulation module 34 is lower than this minimum preheating voltage. Indeed, when the regulation module 34 controls a gross useful voltage VR greater than the minimum preheating voltage, this raw useful voltage VR is applied as it is by the correction module 30 to the electrode 28 of the driven thermostat 4 ( in this case we have Vc = VR).

The correction module 40 also causes a limitation of the applied operating voltage Vc (and therefore of the heating power delivered by the resistance Joule effect) so that the application of this voltage Vc does not cause heating greater than that resulting a total opening of the thermostat 4 (that is to say a stroke L equal to the maximum stroke Lmax). 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 Lmax, the correction module 40 applies to the piloted thermostat 4 a useful voltage Vc that does not depend on the gross useful voltage VR received from the regulation module 34, but which is chosen to maintain the race L at its maximum value Lmax. For example, a servo-control of the applied operating voltage Vc is used, for example, so that the evaluated travel L is maintained between a predetermined value (in this case 0.951, a,) and the maximum travel Lmax. 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 VR generated by the regulation module 34 is greater than this limited voltage. Indeed, since the control module 34 controls a gross useful voltage VR less than the limited voltage determined by the servocontrol described above, this raw useful voltage VR is applied as such by the correction module 30 to the electrode 28 of the piloted thermostat 4 (in this case Vc = VR). It can also be provided, in addition to the above limitation, that the correction module 40 causes a limitation of the actually applied voltage Vc as a function of the stroke L received at input for a range of values of this stroke 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 assembly valve body.

The processing unit which implements the correction module 40 stores a correspondence table which indicates the maximum allowable voltage Vmax 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 Vmax 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 VR is lower at Vmax, Vc = VR - If VR is greater (or equal) than Vmax, VC = Vmax. For the sake of simplicity of the disclosure, in the foregoing paragraph the additional limitation of the applied voltage is not taken into account 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 piloted thermostat 4 a useful voltage Vc equal to the raw payload VR received at the input from the regulation module 34. In practice, the application of a given useful voltage to the thermostat 4 is carried out by applying a nominal voltage Vo during a proportion of the total time such that an electric power equal to that which would have been obtained by continuous application of the desired voltage wanted (according to the principle of Pulse width modulation or PWM module), 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); the following are defined: the mass m22, the specific heat capacity C22 and the temperature T22 of the body 22; the mass m24, the specific heat capacity C24 and the temperature T24 of the wax 24; the mass m20, the specific heat capacity C20 and the temperature T20 of the rod. It is furthermore considered that these various 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 h2 and a surface S2 for the interface between the wax 24 and the body 22; a transfer coefficient h3 and a surface S3 for the interface between the body 22 and the cooling liquid at the temperature T4. 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 Vc applied to the piloted thermostat 4); a heat exchange takes place between the rod 20 and the wax 24 of power E1 = hi.S1 (T20-T24) (counted positively for a 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 E2 = h2.S2 (T24-T22) (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 E3 = h3.S3 (T22-T4) (counted positively for a heat transfer from the body 22 to the cooling liquid). By performing a heat balance for each part of the thermostat, the following equations are obtained which relate the temperatures T20, T22, T24 of the different parts and the variation AT20, AT22, AT24 of each of these temperatures in the time (per second when the Above powers are expressed in W) M20.C20.A1-20 = PJ-E1 = PJ h1.S1. (T24-1-20) M24.C24.3,1-24 = E1 E2 = h1.S1. (T20-1-24) h2.S2. (T22-1-24) M22.C22.A1-22 = E2 E3 = h2.S2. (T24-1-22) h3. S3. (T4-1-22). Thanks to these equations, and on the basis of evaluations or measurements of the temperature T4 of the coolant at the thermostat 4 and the useful voltage Vc applied to the thermostat 4 (which gives directly the power Pj dissipated by the placed resistance 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, it can be considered that at start-up (the resistor being inactive in the previous instants), the temperature is homogeneous in the thermostat 4 and is equal to the temperature of the coolant: the initial values of T20 are chosen, T22, T24 as equal to that T4 of the coolant. Thus, in particular, the temperature T24 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, by Figure 4b. These data (relationship between the temperature T24 of the wax and the stroke L of the thermostat) are for example determined by preliminary 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 m20.C20, m22.C22, m24.C24 and h1.S1, h2.S2, h3.S3, and not each characteristic separately.) Figure 5 shows a example module 38 for evaluating the stroke of the piloted thermostat that uses the model just described. This module is for example implemented within a processing unit which notably stores the correspondence table connecting the temperature values of T24 wax and L-stroke of the thermostat. The module 38 receives as input the temperature T4 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 useful voltage Vc applied to the thermostat 4. The module 38 comprises a unit 102 for storing the instantaneous value for evaluating the temperature T22 of the body 22, a unit 104 for storing the instantaneous value of the evaluation of the temperature T24 of the wax 24 and a unit 106 for storing the instantaneous evaluation value of the temperature T20 of the rod 20. As indicated above, at the beginning of the evaluation process, these units are initialized with the temperature value T4 of the coolant received at the inlet. Each iteration of the process begins with an estimation of the new temperature values T20 and T22 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 .

For this purpose, the module 38 determines the evolution AT20 of the temperature T20 of the rod 20 during an iteration on the basis of the instantaneous values T20, T24 of temperature and of the useful voltage Vc (received as input) as follows. A subtracter 148 receives the instantaneous value T20 from the unit 106 and subtracts it from the instantaneous value T24 received from the unit 104. The value generated by the subtractor 148 is multiplied by h1.S1 within a multiplier 150. then, by means of an adder 152, 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 Vc applied to the resistor by means of a conversion unit 108. The output of the adder 152 is multiplied by 1 / (m20.C20) within a multiplier 154 in order to obtain the desired AT20 evolution (in accordance with the formula given above). The output of the multiplier 154 (AT20 evolution) is added to the instantaneous value T20 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 T20 of the rod 20, which will be used by the unit 106 at the next iteration (after passing through this purpose through a retarder 116). Likewise, the module 38 determines the evolution AT22 of the temperature T22 of the body 22 during an iteration on the basis of the instantaneous values T4 (received at the input), T22, T24 of temperature as follows. A subtractor 120 receives the instantaneous value T22 from the unit 102 and subtracts it from the instantaneous value T4 received at the input; likewise, a subtractor 122 receives the instantaneous value T22 from the unit 102 and subtracts it from the instantaneous value T24 received from the unit 104. The values generated by the subtractors 120, 122 are respectively multiplied by h3.S3 within a multiplier 124 and by h2.S2 within a multiplier 126, then summed by an adder 128. The output of the adder 128 is multiplied by 1 / (m22.C22) within a multiplier 130 in order to obtain the desired AT22 evolution (according to the formula given above). The output of the multiplier 130 (AT22 evolution) 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 112). The module 38 determines the evolution AT24 of the temperature T24 of the wax 24 during an iteration (here of a duration of one second) on the basis of the instantaneous values T20, T22, T24 of temperature as follows. Here, the temperatures T20 and T22 used are those which have just been calculated as described above.

A subtractor 134 receives the instantaneous value T24 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 T24 from the unit 104 and subtracts it from the instantaneous value T20 (as just calculated) received from the adder 156. The values generated by the subtracters 134, 136 are respectively multiplied by h2.S2 within a multiplier 138 and by h1.S1 within a multiplier 140, then summed by an adder 142. The output of the adder 142 is multiplied by 1 / (m24. C24) within a multiplier 144 to obtain the desired evolution T24 (according to the formula given above). The output of the multiplier 144 (ATM evolution is added to the instantaneous value T24 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 T24 of the wax 24, which will be used by the unit 104 at the next iteration (after passing through this purpose through a retarder 114) The new instantaneous temperature evaluation value T24 is also transmitted to the input of a conversion unit 110 of the temperature value of wax in stroke value L of the thermostat, based on the correspondence table mentioned above, which relates the wax and stroke temperature values of the thermostat, thus obtaining an estimate of the stroke value at each iteration. L of the thermostat 4. Figure 6 shows the heat exchanges involved in the cooling system at the controlled thermostat and the motor.

As can be seen in FIG. 1, the flow rate of coolant entering and flowing through the engine 2 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 output of the thermostat, which depends on the stroke L of the thermostat.

The warming of this flow of coolant in the engine, because of the heat output P (C, N) yielded by the engine, generates the increase of the temperature of the coolant of its input value TE at its value. Ts at the output, which is expressed by the following equation: P (C, N) = k. [Q0 + Q (L)]. (Ts-TE), where k is a characteristic constant of the coolant (k = p.Cp where p is the density of the coolant 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 TE at the engine inlet, and then the coolant temperature T4 at the driven 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 T4 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 operating point 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 Ts of the engine output coolant, here measured by the sensor The processing unit which implements the module of FIG. 7 stores a mapping of the power P (C, N) transferred to the cooling liquid by the engine as a function of the load C and the engine speed. N. This map is a table which indicates the values of power P given to the coolant by the engine respectively associated with pairs of values C, N.

This processing unit also stores a plurality of coolant flow rate values Q (L) through the thermostat respectively associated 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 stroke value L received at the input and the power P (C, N) associated with the values of load C and engine speed N received at the input. Sub-module 70 thus evaluates, at each instant t, the engine coolant temperature TE (t) using the model described above with reference to FIG. 6: TE (t) = Ts - P (C, N) / (k, [Qo + Q (L)]). The temperature information TE (t) determined by the sub-module 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 T4 of the coolant at the level of the thermostat 4 which is at each instant: T4 = TE ( t) - a + b [TE (t) - TE (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 T4 of the coolant at the level of the thermostat 4 on the basis of the estimated value of engine coolant temperature TE 2.

In this sub-module 71, the correction made to the temperature TE (t) by the terms a and b [TE (t) - TE (t-1)] makes it possible to take into account the fact that the thermostat is situated slightly in upstream of the engine inlet into the coolant circuit and that 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 ° G 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 above description, the calculation of the evaluation of the temperature T4 of the coolant at the thermostat as a function of the evaluation of the engine coolant temperature TE is presented in the form of functional modules. performing the various operations. In practice, these operations can be performed by the execution of a program by the processing unit which implements the module of FIG. 7.

FIG. 8 represents a second example of a control system according to the teachings of the invention. In this figure, the numbering of the modules identical to those present in the first example described above with reference to FIG. 3 is retained. As in FIG. 3, the control system of FIG. 8 comprises several modules represented in form. functional. 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. The engine management computer 30 delivers a load information C (expressed in Nm) and an engine speed information N (expressed in rpm), representative of the operation of the engine 2. This information C, N is transmitted to the module 32 for determining a temperature setpoint T. As in the first example described with reference to FIG. 3, the setpoint determination module 32 generates the temperature setpoint Tc 20 as a function of the engine speed N and of the load C by reading. in a correspondence table (cartography). The temperature setpoint Tc generated by the setpoint determination module 32 is transmitted to the regulation module 34, which also receives the temperature Ts of the engine output coolant measured by the temperature sensor 10. On the basis of the measured temperature Ts and the temperature setpoint Tc, the regulation module 34 determines the raw useful voltage VR to be applied to the electrode of the controlled thermostat 4 so as to converge the temperature of the coolant towards the setpoint T. It will be possible to Refer to the explanations given above in the context of FIG. 3 for more details on the regulation module 34. A correction module 44, the operation of which is described below, receives as input the gross useful voltage VR generated. by the regulation module 34 and the temperature T4 of the cooling liquid at the thermostat 4, measured for example by a temperature sensor 42 Alternatively, the temperature T4 of the coolant at the thermostat 4 could be evaluated by an evaluation module as the evaluation module 36 of Figure 3, optionally on the basis of an evaluation of the stroke of the thermostat such as that provided by the evaluation module 38 of FIG. 3. The processing unit which implements the correction module 44 stores: a first correspondence table which indicates the useful voltage Vlim to be applied to obtain the total opening of the thermostat according to the temperature T4 of the liquid in which the thermostat is immersed, for example according to the curve shown in Figure 9; a second correspondence table which indicates the useful voltage Vmin to be applied to obtain a preheating of the wax of the thermostat, without however causing it to be opened, as a function of the temperature T4 of the liquid in which the thermostat is immersed, for example according to the curve represented in FIG. 10. The stored values are determined in advance, for example by means of tests; they can in particular be provided by the manufacturer of the thermostat. The correction module 44 reads at each instant the associated value Vlim in the first correspondence table at the temperature T4 received from the sensor 42 and the associated value Vmin in the second correspondence table at this same temperature T4. The correction module 44 then determines the useful voltage Vc to be applied to the thermostat by correcting the gross useful voltage VR so as to limit the useful voltage applied to the thermostat to the Vlim value and to apply at least a useful voltage Vmin. Specifically, the correction module 44 determines the useful voltage Vc to be applied to the thermostat 4 as follows: - if VR> Viim, VC = Vlim - If VR <Vmin, VC = Vmin - in other cases, Vc = VR. Thus, when the correction module 44 does not modify the value of the useful voltage (in which case Vc = VR), the heating of the piloted thermostat will tend to open it so that the temperature Ts converges towards the set temperature Tc, according to the regulation mechanism implemented regulation module 34.

On the other hand, when this mechanism controls (via the value VR generated by the regulation module 34) heating of the wax beyond what is necessary to fully open the thermostat 4 (as indicated by first correspondence table), the correction module 44 limits the voltage (and therefore the heating power delivered by the resistance) to that which allows this total opening. A greater heating of the wax would in fact have no interest but would be detrimental to the reaction time of the system when the control mechanism will later wish to control the closure (possibly partial) of the thermostat.

Similarly, when the control mechanism does not control (via the VR value generated by the control module 34) no heating of the wax (VR = O), or control a low heating, so that a subsequent heating it would be necessary to bring the wax to the temperature at which it generates a start of opening of the thermostat 4, the correction module 44 makes it possible to apply to the thermostat 4 a preheating useful voltage (in accordance with the indication of the second table of correspondence); the heating power delivered by the resistance due to this preheating voltage makes it possible to heat the wax to the temperature at which any subsequent heat input will cause the immediate opening of the thermostat.

The reaction time of the system when opening the thermostat (for example due to a setpoint change) is reduced. In this embodiment, the limiting value VI ', and the preheating value Vrnin are determined solely on the basis of the temperature T4 received at the input: it is therefore an open-loop control system.

Claims (10)

REVENDICATIONS1. A thermostat device (4) for a motor vehicle cooling system comprising a valve (26), a heat-sensitive portion (24) adapted to cause the valve (26) to open when the temperature of said sensing portion ( 24) exceeds a temperature threshold, and a controlled heating module of said sensing portion (24), characterized by a control module (40; 44) adapted to control the heating module so that it delivers power. insufficient non-zero heat to cause an opening of the valve (26). Thermostatic device (4) according to claim 1, wherein the sensitive portion is a volume of wax (24) whose expansion, above said temperature threshold, causes a mechanism for opening the valve (26). 3. Thermostat device (4) according to claim 1 or 2, wherein the heating module comprises an electrical resistance. 4. Thermostat device (4) according to one of claims 1 to 3, wherein the control module (44) is adapted to control the heating module according to a temperature (T4) at the thermostat (4). ). 5. Thermostat device (4) according to claim 4, comprising a module (36) for estimating the temperature at the thermostat (4) as a function of a measured temperature (T8). 6. Thermostat device (4) according to claim 4, comprising a sensor (42) for measuring the temperature (T4) at the thermostat (4). 7. Thermostat device (4) according to one of claims 1 to 3, comprising a module (38) for determining the proportion (L) of opening of the valve (26), wherein the control module (40) ) is designed to control the heating module according to the determined opening proportion (L). The thermostat device (4) according to one of claims 1 to 3, comprising a valve flow rate determining module, wherein the control module is adapted to control the heating module according to the determined flow rate. 9. Cooling system of a driving motor of a motor vehicle, comprising a radiator (6) and a thermostat device (4) designed to regulate the amount of coolant from the radiator (6) to be injected into a motor cooling circuit (2), the thermostat device (4) according to one of claims 1 to 8. A method of controlling a controlled heating module of a heat-sensitive portion of a thermostat device (4) for a motor vehicle cooling system, the thermostat device comprising a valve (26) and the portion Heat-sensitive device (24) adapted to cause the valve (26) to open when the temperature of said sensing portion (24) exceeds a temperature threshold, characterized by a step of controlling the heating module so as to it delivers a non-zero heating power insufficient to cause an opening of the valve (26).