Abstract:
A system estimating temperature of a mechanical member of a vehicle once the vehicle has stopped, including: a temperature sensor of a first element of the vehicle, for example a fluid tank; a mechanism estimating air temperature outside the vehicle; a first module estimating temperature of the member when the vehicle is moving; a mechanism storing, while the vehicle is stopped, an outside air temperature, a temperature of the first element, and a temperature of the member; a second module to calculate how long the vehicle has been stopped according to the outside air temperature, the stored temperature of the first element, and the measured temperature of the first element; and a third module to calculate thermal history of temperature variation of the member while the vehicle is stopped, according to the outside air temperature, the stored temperature of the member, and the stoppage time of the vehicle.

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention lies in the field of monitoring the temperature of the mechanical members of a vehicle driven by an internal combustion engine. While the vehicle is traveling, in order to estimate the temperature of a mechanical member, generally the thermal energy dissipated by friction in this member is calculated, as well as the thermal energy given up by this member to the surrounding environment, i.e. to the air flowing under the engine cowling or under the vehicle. In the case of four-wheel drive vehicles, it is, for example, necessary to know the temperature of the coupler which transmits the available engine torque from one set of wheels of the vehicle to the other set of wheels of the vehicle. 
     2. Description of Related Art 
     Patent application EP 1 308 336 describes a method of managing a coupler according to the heating of the coupler. However, this document provides for assessing the heating of the coupler, either in terms of temperature difference with respect to an initial state, or in terms of thermal energy produced by friction. This document does not therefore provide a method for calculating the absolute temperature of the coupler. This temperature can be a crucial parameter, if, for example, the outside temperature is itself high, or if the coupler is already hot without this being taken into account by the system, following a start-up of the vehicle after a not very prolonged stop has not allowed the coupler to cool to the ambient temperature. For reducing the manufacturing costs and maintenance costs of the vehicle, the number of temperature sensors installed on the vehicle is limited to the minimum necessary. The monitoring methods developed should therefore preferably be able to forego having a temperature sensor on the member to be monitored (e.g. a coupler). 
     Incidentally, the monitoring methods developed will use, or preferably will not use a temperature sensor for the air outside the vehicle. Finally, for saving manufacturing costs and energy consumed by the vehicle, all the control electronics of the vehicle should be able to be switched off when the vehicle is at a prolonged stop. Thus solutions are sought that avoid maintaining an electronic clock on standby linked to the control system present. The moment the electronic control systems of the vehicle are powered up, they must therefore be capable of defining an initial value of temperature of the members from which they subsequently calculate the temperature variations by performing heat balances. 
     Using an arbitrary default value is risky since if the vehicle restarts after a short stoppage period, this default value risks being underestimated. There is a risk therefore of underestimating all the subsequently calculated temperatures of the coupler or of the member and damaging the member to be monitored. 
     BRIEF SUMMARY 
     The object of the invention is to provide a method for estimating an initial temperature of a dissipative vehicle member, enabling an initial temperature value to be assigned in the absence of temperature sensors on the member and in the absence of information, by a clock, from the time elapsed since the last use of the vehicle. 
     A system for estimating the temperature of a mechanical member of a vehicle after the vehicle is stopped, includes:
         a temperature sensor of a first element of the vehicle which may notably be a fluid tank of the vehicle;   a means for estimating the air temperature outside the vehicle;   a first module for estimating the temperature of the member while the vehicle is traveling.       

     The system further includes:
         means of storage, while the vehicle is stopped, of an outside air temperature value, a temperature value of the first element, and a temperature value of the member;   a second module capable of calculating a stoppage period of the vehicle according to an outside air temperature value, a stored temperature of the first element and a measured temperature of the first element;   a third module, capable of calculating a thermal history of temperature variation of the member while the vehicle is stopped, according to an outside air temperature value, a stored temperature of the member and a stoppage period of the vehicle calculated by the second module.       

     Advantageously, the third module is configured for calculating the change in temperature of the member during a preset period after the vehicle is stopped, then for switching off until another vehicle start-up. 
     According to a preferred embodiment, the third module is configured for assigning to the estimated temperature of the member when the vehicle is restarted, the last temperature value calculated for the member before the third module is switched off, if the stoppage period of the vehicle that the second module transmits to it is less than or equal to the preset period. 
     The second and third modules respectively can calculate the stoppage period and the temperature history at the stoppage of the member, or its last temperature on stopping, respectively by performing a heat balance on the exchanges between the first element and the air outside the vehicle, or respectively by performing a heat balance on the exchanges between the member and the air outside the vehicle. 
     Preferably, the second and third modules use exponential profiles of variation, with respect to time, of the difference of a temperature with respect to the temperature outside the vehicle, for estimating the stoppage period or for estimating the extent of a temperature variation. 
     The system may include one or more first modules capable of calculating one or more internal temperatures of a coupler transferring the torque of one set of wheels of the vehicle to another set of wheels of the vehicle, and comprise one or more third modules capable of calculating one or more internal temperatures of the coupler after an indeterminate stoppage period of the vehicle. 
     According to an advantageous embodiment, each estimated temperature value is associated with a Boolean validity indicator and a default temperature value, which replaces the estimated value if the Boolean indicator takes a preset value. 
     Preferably, the first element is cooling liquid present in the vicinity of the engine. 
     According to another aspect, an internal combustion engine vehicle is equipped with the preceding system for estimating the temperature of a mechanical member after the vehicle is stopped, and is equipped with a module for estimating the temperature outside the vehicle connected to an engine intake air temperature sensor, to an engine cooling liquid temperature sensor, and to a means for estimating the speed of the vehicle. 
     According to a third aspect, a method for estimating the temperature of a mechanical member of a combustion engine vehicle after the vehicle is stopped, includes the following steps:
         when the vehicle stops, a last measured temperature of the vehicle&#39;s cooling liquid, a last measured or estimated temperature of air outside the vehicle, a last estimated temperature of the member, are written to read-only memories;   when the vehicle is restarted, the vehicle&#39;s cooling liquid temperature is measured, and from this temperature and the three preceding stored temperatures, a new temperature of the member is deduced,   this new temperature of the member is used as an initial temperature for a subsequent estimate of the temperature of the member while the vehicle is traveling.       

     Advantageously, the relationship that connects the last measured or estimated outside air temperature T a , the last estimated temperature of the member T max , the last temperature T 0  measured at the same moment for the vehicle&#39;s cooling liquid, the temperature T 1  of the cooling liquid at start-up, and the new temperature of the member T ini , is an exponential relationship of the form: 
                     T   o     -     T   a           T   1     -     τ   a         =       (         T   ini     -     T   a           T   max     -     T   a         )     A       ,         
where A is a positive real value.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, advantages and characteristics of the invention will become apparent on scrutiny of the detailed disclosure of some embodiments given as non-restrictive examples and illustrated in the accompanying drawings, in which: 
         FIG. 1  illustrates a four-wheel drive vehicle equipped with a system for estimating the temperature of a coupler according to the invention; 
         FIG. 2  illustrates a possible mode of operation of a module for estimating vehicle stoppage time between two journeys; 
         FIG. 3 , with the aid of measured and estimated temperature curves, illustrates the principle of determining an initial coupler temperature according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As illustrated in  FIG. 1 , a vehicle  1  includes a front set of wheels  2  and a rear set of wheels  3 , the front set  2  and rear set  3  being connected by a coupler  4  capable of being completely or partly joined together in rotation with the front axle  2  and rear axle  3 . Each of the wheels of the front set  2  is fitted with a rotational speed sensor  12  and each of the wheels of the rear set  3  is fitted with a rotational speed sensor  13 . The values recorded by the sensors  12  and  13  are used notably to calculate the difference in rotational speed between the front axle  2  and the rear axle  3 , together with the instantaneous speed of the vehicle  1 . Such sensors are generally present on the four wheels of a four-wheel drive vehicle, or more generally on the four wheels of vehicles equipped with a traction control system of the ABS type, or of a trajectory correction system of the ESP type. 
     The front axle  2  is connected via a power train system (not shown) to an internal combustion engine  5 , notably including an air inlet  6 , leading fresh air through an air filter  9  to cylinders  7  of the engine. The engine  5  is equipped with a cooling circuit  10 . A temperature sensor  8  is arranged at the air inlet circuit  6 , between the air filter  9  and the inlet of the cylinders  7 . A temperature sensor  11  is arranged in the vicinity of the engine  5  in contact with the liquid of the cooling circuit  10 . The wheel speed sensors  12  and  13 , and the temperature sensors  8  and  11  are respectively connected by connections  16 ,  17 ,  14 ,  15  to an electronic control unit  18 . The electronic control unit (ECU)  18  notably includes a module  19  for estimating the temperature of air outside the vehicle, a module  20  for estimating the time elapsed since the last use of the vehicle, and a module  21  for estimating the temperature of the coupler  4  at the end of the stoppage of the vehicle. The ECU  18  further includes storage means  22  connected to the three preceding modules  19 ,  20 ,  21 , enabling the ECU  18  to write to read-only memories certain values from calculations or measurements which it has in random access memory just before the engine  5  is switched off, or just before the ECU  18  itself is switched off. 
     The module  20  is connected via the connection  15  to the cooling liquid temperature sensor  11 , as well as to modules  19  and  21 . 
     The module  19  is connected via connections  16  and  17  to the wheel speed sensors  12  and  13 , via connections  14  and  15  to the two temperature sensors  8  and  11 . Alternatively, the module  19  can be simply connected to a temperature sensor for air outside the vehicle. In the first case, the module  19  may, for example, use the values measured by sensors  8  and  11 , of the engine intake air temperature and the cooling liquid temperature, for determining a probable initial temperature of the air outside the vehicle. The module can then determine the estimated variations in outside air temperature by performing mathematical filtering on the temperature measured by the sensor  8  of the engine intake air temperature, this filtering being designed to limit the estimated outside temperature gradients, by imposing two different maximum gradient values according to whether the instantaneous speed of the vehicle is higher or lower than a threshold value. The instantaneous speed of the vehicle can be deduced by the module  19  from the values of the instantaneous rotational speeds of the wheels, provided by the two sensors  12  and by the two sensors  13 . 
     The ECU  18  also includes a module  23  for calculating the temperature of the coupler  4 , when the vehicle is traveling. This temperature of the coupler  4  is, for example, calculated by performing a heat balance, taking into account the energy generated by friction in the coupler, based on the difference in rotational speed between the front axle  2  and the rear axle  3 , and the energy given up to the air flowing around the coupler. 
     When the vehicle&#39;s engine has been stopped and the dashboard ignition has been switched off, the ECU  18  writes to one of the memory storage means  22 , the last estimated temperature value of the coupler  4  during its operation calculated by the module  23 . It also writes to another memory means  22 , the last temperature estimated by the module  19  (or, in other variant embodiments of the invention, the last measured value of air outside the vehicle). Finally it writes, to a third read-only memory, the last value measured by the sensor  11 , of the cooling liquid temperature. 
     After the ignition is switched off, the electronic control unit  18  remains active during a preset period, in order to better take into account a possible vehicle restart in quick succession. This preset period may be, for example, a few minutes to a few tens of minutes, according to the compromise that is to be chosen, between the reactivity of the vehicle control system during a warm restart, and the power consumption caused by the standby mode. During this preset period, the electronic control unit may possibly calculate, at regular time intervals, the temperature of the coupler  4 , by taking into account its last temperature at the moment the engine is switched off, and by taking into account the heat exchanges with the outside air during the preset standby period of the electronic control unit. 
     In addition to the estimated temperature of the coupler  4  at the moment the engine is switched off, the electronic control unit  18  can write to memory means  22 , the estimated temperature of the coupler  4  just before an electronic control unit  18  is finally switched off. The preset standby period of the electronic control unit is also recorded as a calculation parameter in a read-only, writable or non-rewritable memory of the electronic control unit  18 . When the electronic control unit  18  is powered up again for restarting the vehicle, the module  20  for estimating the time elapsed since the last use of the vehicle records a current value of the cooling liquid temperature, which is provided by the sensor  11 . The module  20  also accesses the last cooling liquid temperature value recorded in the storage means  22 , as well as the last temperature of the air outside the vehicle recorded in the storage means  22 . 
     For calculating the time elapsed since the engine has been switched off, the module  20  uses a first-order model representing the heat exchanges between the cooling liquid and the air outside the vehicle, assuming that there is a global exchange coefficient C liq  enabling the following equation to be written: 
     
       
         
           
             
               
                 
                   
                     
                       ⅆ 
                       
                         T 
                         liq 
                       
                     
                     
                       ⅆ 
                       t 
                     
                   
                   = 
                   
                     - 
                     
                       
                         ( 
                         
                           
                             T 
                             liq 
                           
                           - 
                           
                             T 
                             a 
                           
                         
                         ) 
                       
                       
                         C 
                         liq 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     where: 
     T liq  is the cooling liquid temperature, 
               ⅆ     T   liq         ⅆ   t           
is the derivative of this cooling liquid temperature with respect to time,
 
     T a  is the air temperature outside the vehicle, and 
     C liq  is a coefficient of exchange between the cooling liquid and the parts of the engine in thermal contact with this liquid and the air outside the vehicle. 
     The elapsed period between the two cooling liquid temperature measurements can therefore be written: 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     t 
                   
                   = 
                   
                     
                       C 
                       liq 
                     
                     ⁢ 
                     
                       ln 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               T 
                               0 
                             
                             - 
                             
                               T 
                               a 
                             
                           
                           
                             
                               T 
                               1 
                             
                             - 
                             
                               T 
                               a 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     where 
     Δt is the time interval separating the first temperature measurement, of result T 0  and the second temperature measurement, of result T 1  of the cooling liquid; 
     T a  is the air temperature outside the vehicle, and 
     C liq  is a constant representing the global exchange coefficient between the engine and the cooling liquid and the air outside the vehicle. 
     In the case where the result of the calculation of Δt is less than a value Δt extinct  representing the preset standby period of the electronic control unit, the module  20  will interpret it that the period of the electronic control unit  18  being switched off is reduced to zero, i.e. the module  20  will consider that the vehicle has been restarted just after the electronic control unit  18  has been switched off. 
     Once the elapsed time estimation module  20  has determined the stoppage period of the vehicle, the module  20  transmits to the module  21  at least one value expressing this stoppage time. To this end it may transmit either the value Δt separating the last instant that the engine was switched off and the instant it is restarted, or the value Δt mission  representing the period separating the complete switching off of the electronic control unit and the new restarting of the engine, the two periods being connected by the relationship:
 
Δ t=Δt   extinct   +Δt   mission   (equation 3)
 
     where Δt extinct  represents the preset standby period of the electronic control unit  18  after the engine is stopped  5 . 
     Once the module  21  has the time interval separating the last stoppage and restarting of the engine, it will read in the storage means  22  the last temperature recorded as the temperature of the air outside the vehicle T a  and it will read a last recorded value of estimated temperature of the coupler, which may be either a temperature T max  of the coupler at the moment the engine is switched off, or a temperature T coff  of the coupler calculated by the electronic control unit as being the temperature of the coupler at the moment the electronic control unit  18  is switched off. 
     The electronic control unit  18  then estimates the temperature T ini  of the coupler at the moment the vehicle starts up by performing a heat balance of the exchanges of the coupler with the air outside the vehicle, between the last moment when the temperature of the coupler was calculated, and the moment when the cooling liquid temperature T 1  at the moment the engine starts up, is measured again. 
     It is again assumed that there is a global exchange coefficient C 2  between the coupler and the air outside the vehicle, so that the electronic control unit  18  may, for example, estimate the temperature of the coupler T ini  at the moment of restarting according to one of the following equations: 
     
       
         
           
             
               
                 
                   
                     
                       T 
                       ini 
                     
                     = 
                     
                       
                         T 
                         a 
                       
                       + 
                       
                         
                           ( 
                           
                             
                               T 
                               max 
                             
                             - 
                             
                               T 
                               a 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           exp 
                           ⁡ 
                           
                             ( 
                             
                               - 
                               
                                 
                                   Δ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   t 
                                 
                                 
                                   C 
                                   2 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   or 
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     T 
                     ini 
                   
                   = 
                   
                     
                       T 
                       a 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             T 
                             coff 
                           
                           - 
                           
                             T 
                             a 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         exp 
                         ⁡ 
                         
                           ( 
                           
                             - 
                             
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   t 
                                   mission 
                                 
                               
                               
                                 C 
                                 2 
                               
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
           
         
       
     
     Once the module  21  for estimating the temperature of restarting of the coupler has calculated the new value T ini , it can transmit this value to the module  23  which continues to evaluate the temperature of the coupler while the vehicle is traveling. 
       FIG. 2  illustrates a possible embodiment of the module  20  for estimating the time elapsed since the last powering down of the vehicle monitoring systems. Some elements found in  FIG. 2  are common to  FIG. 1 , the same elements then being designated by the same references. The module  20  will read in the storage means  22  a temperature T 0  which is the last cooling liquid temperature stored before the system is switched off, and a temperature T a  which is a last temperature of the air outside the vehicle stored before the system is switched off. It then sends these two values to a subtractor  30  which calculates the absolute value of the difference between the two temperatures and sends it to a comparator  32  that performs a test for ascertaining whether the difference is less in absolute value than a parameter Δt min . 
     Via the connections  15 , the module  20  receives a cooling liquid temperature T 1  measured at the moment the engine is restarted. A subtractor  31  calculates the absolute value of the difference between this temperature T 1  and the temperature T a  stored as a temperature of the air outside the vehicle. This difference is sent to a comparator  33  which looks to see whether it is less than a parameter of minimum duration Δt min . The comparators  32  and  33  send their result to a Boolean “OR” operator  34 , which sends its result to the control input of a three-way switch  35 . The result of the operator  34  is, for example, 1 if at least one of two differences in absolute value is less than the Δt min  parameters, and otherwise is zero. The differences calculated by the subtractors  30  and  31  are then respectively thresholded by the thresholding operators  36  and  37 . A divisor  38  then produces the quotient of the differences T 0 −T a  and T 1 −T a . The quotient is then sent to another thresholding operator  39 . A logarithmic converter  40  then calculates the logarithm of the result of the operator  39  and transmits it to a multiplier  41  which multiplies it by a value C liq . Another thresholding operator  42  performs a thresholding of the result so that it is between a value Δt extinct  and the parameter Δt max . The value Δt extinct  used by the thresholding operator  42  may be either a fixed parameter, written to a rewritable or non-rewritable memory, or may be a variable parameter written each time the system is switched off, to the storage means  22 . The result of the operator  42  is sent to the negative input of the switch  35 , which receives the value of the parameter Δt max  at its positive input. According to the results of the Boolean operator  34 , the output of the switch  35  takes the value Δt max , if one of the temperature differences calculated by the operators  30  and  31  is less than the threshold Δt min , or otherwise takes the value calculated by the operator  42 . The value Δt extinct  corresponding to the electronic control unit  18  standby period can then be subtracted from the result leaving the switch  35 , for obtaining a period Δt mission , corresponding to the period that has elapsed between the electronic control unit  18  being switched off, and the vehicle being restarted. This value Δt mission  is then sent to the module  21  which uses it for estimating the new temperature of the coupler  4 . 
     With the aid of temperature curves  FIG. 3  illustrates the principle used in the invention for calculating the temperature T ini  of the coupler when the vehicle is restarted. Notations common to the previous figures are found in  FIG. 3 , the same notations representing the same variables. On the abscissa axis, graduated in hours, three instants are shown of a stop-restart sequence of the engine  5  from  FIG. 1  which are: 
     A: the moment the engine is switched off, 
     B: the moment the electronic control unit  18  is switched off, 
     C: the moment the vehicle is restarted. 
     Three temperature curves  50 ,  51  and  52  are shown in the figure. 
     Curve  52  shows the estimated temperature of the air outside the vehicle. It is shown in the form of a curve of constant value T a , since over the time intervals prior to A and subsequent to C, the outside air temperature is estimated with temporal filtering which tends to reduce these variations; over the time interval AC, there is no estimation of outside air temperature, so it is considered that the temperature remains constant, equal to the last value T a  stored in the means  22  at the moment the engine is switched off. 
     The temperature curve  50  shows the estimated temperature variations of the coupler  4 , and breaks down into two portions  50   a  and  50   c  calculated by the module  23  while the engine is traveling, and a portion  50   b  calculated by the module  21  of the electronic control unit  18 . 
     Curve  51  shows the temperature variations of the cooling liquid, and breaks down into two portions  51   a  and  51   c  corresponding to the time intervals prior to A and subsequent to C and a portion  51   b  corresponding to the time interval AC. The curve portions  51   a  and  51   c  result from measurements made by the temperature sensor  11 , and the portion  51   b  is deduced from the calculation performed by the elapsed time estimation module  20 . 
     At the moment the engine is switched off, i.e. at instant A, the value T max  corresponding to the temperature of the coupler being switched off at point  53  of curve  50 , and the value T 0  corresponding to the measured cooling liquid temperature at point  56  of curve  51 , are stored in the storage means  22 . The value T a  of temperature outside the vehicle, estimated by the module  19  at this same instant, is also stored in the means  22 . At the moment the engine is switched on again, i.e. at instant C, the temperature sensor  11  gives the temperature T 1  corresponding to point  58  at which the temperature T 1  is known, but not the temporal coordinate. From the values T 0  and T a  the elapsed time estimation module  20  is able to plot curve portion  51   b  starting from point  56 , and find the point where this curve passes through an ordinate of temperature T 1 , corresponding to the new liquid temperature measured by the sensors  11 . The module  20  deduces the abscissa of point  58  from this and transmits it to the module  21 , either by specifying a value Δt mission  representing the time that has elapsed since the electronic control unit  18  was switched off, or by specifying the sum Δt=Δt extinct +Δt mission  of the elapsed times over the time intervals AB and BC since the engine was switched off. 
     The module  21 , at the moment the engine is restarted, will search in the storage means for the values T max  and T a  corresponding to the values stored for the last temperature of the coupler and for the last outside air temperature, and is able, from these two values, to deduce portion  50   b  of curve  50  giving the cooling history of the coupler  4  starting from point  53 . By searching for point  55  where this curve passes through the time abscissa C that module  20  has transmitted to it, the module  21  may deduce the value T ini  of the coupler  4  at the moment the vehicle starts up. 
     Even if the module  21  only provides, for the needs of controlling the coupler, the temperature of the coupler at point  55 , corresponding to the moment of the vehicle being restarted, the module  21  is able to calculate the entire cooling history corresponding to portion  50   b  of curve  50 . In fact, for ascertaining the temperature of the coupler at any instant of the time interval AC, it would suffice to provide module  21  with any time interval separating instant A and another instant prior to C, instead of the time interval AC corresponding to restarting the vehicle. 
     According to variant embodiments, it may happen that the time interval provided by the module  20  is less than or equal to Δt extinct . In this case, the module  21  considers that the stoppage period is exactly equal to Δt extinct . The module  21  then provides the temperature value corresponding to point  54 , which gives the temperature of the coupler at the moment the electronic control unit  18  is switched off. According to variant embodiments, the temperature value corresponding to point  54  may be stored at the moment the electronic control unit  18  is switched off, or may be recalculated after the event, only if it is decided that it is needed as the temperature of the coupler when the vehicle is restarted. If the temperature of point  54  is stored before the electronic control unit  18  is switched off, the module  21  may use it for calculating the temperature T ini , without reusing the value T max  calculated at the moment the engine is switched off. 
     Variant embodiments are conceivable where the cooling liquid temperature continues to be recorded after some of the engine functions are switched off, until the electronic control unit is switched off, so that the temperature value corresponding to point  57  of curve  51  is recorded in the memory means  22 . 
     At the moment the vehicle is restarted, the module  20  then estimates the time interval Δt mission  from the stored value T a  of air and the temperature of point  57 . This variant is more accurate since the temperature of point  57  is measured this time and not calculated. On the other hand, this method requires leaving some of the engine functions on standby, notably that associated with the management of the sensor  11 . 
     The invention is not limited to the embodiments disclosed and may be the subject of numerous variants, notably with respect to the models used for calculating the cooling of the engine in contact with the cooling liquid, and for calculating the cooling of the coupler. The temperature of the air outside the vehicle may be measured by an outside air sensor. A choice may then be made, when the vehicle is restarted, to use either the air temperature at the moment of switching off, or the air temperature at the moment of restarting, or a weighted average of the two measured temperatures. Each measured or estimated temperature may be associated with a Boolean validity indicator which will indicate whether the information necessary for its calculation or its measurement is sufficiently reliable. A choice can then be made, when the Boolean indicator indicates a lack of reliability, either to retain, for the value in question, the last value it has taken with a positive Boolean indicator, or to impose an arbitrary default value on it. 
     The temperature estimation system according to the invention can be used to assign a temperature value to a mechanical member when a vehicle is restarted, by using the minimum of temperature sensors, the temperature sensors used further forming a part of the practically unavoidable sensors on an internal combustion engine vehicle. The estimation system according to the invention enables the electronic management system of the vehicle to be completely switched off while the vehicle is stopped. The system is not likely to cause overheating of the dissipative members, which would be caused by too low an arbitrary initialization of the estimated temperatures of these members. The system is economical, robust and safe for the members for which it is used.