FR3071895A1 - METHOD FOR PREVENTING A RISK OF SLIPPING A BELT CONNECTING A STARTING MEMBER TO AN ENGINE - Google Patents

Abstract

The invention relates to a method for preventing a sliding risk of a belt connecting a starting member to a heat engine of a motor vehicle, the risk being likely to be produced by a frost deposit. The method comprises estimating a temperature (Tcour) of the belt in real time according to a model simulating a heat balance (14) of the belt based on at least one estimate or measurement of the ambient temperature (Tamb) and at least an evaluation of the convection (15) and conduction (17) exchanges of the belt. If the temperature (Tcour) of the estimated belt is below a temperature threshold, when the engine is running, there is a prohibition of stopping the engine or, when the engine is stopped, a prohibition starting the engine by the starting member associated with the belt.

Description

The present invention relates to a method of preventing the risk of slipping by icing of a belt connecting a starting member. The present invention relates to a method of preventing a risk of slipping by icing of a belt connecting a starting member. to a heat engine of a motor vehicle. The starting device can advantageously be an alternator-starter or an electric machine.

The present invention finds a preferred application for hybrid vehicles having an engine other than a heat engine. Such hybrid vehicles may be vehicles in which the heat engine and the electric motor or electric machine are both propulsion engines, operating alternately or simultaneously, or alternatively vehicles in which the role of the heat engine is to drive an alternator. which recharges a battery for supplying the propulsion electric motor.

The present invention also finds a preferred application for hybrid vehicles or not provided with an automatic engine stop and restart system.

For a hybrid vehicle, it is frequent that, during taxiing, propulsion phases with the heat engine follow propulsion phases with the other engine. Similarly, in an automatic engine stop and restart system, automatic engine stop and restart phases are implemented in particular in the event of a temporary stop of the vehicle.

Several types of hybridization architecture are now envisaged with, in a first configuration, an electric machine driven by a belt on the drive of accessories of the heat engine, in a second configuration, an electric machine between the motor and the clutch, in a third configuration an electric machine after a first clutch between the engine and a gearbox, a second clutch can be arranged between this electric machine and the gearbox, in a fourth configuration an electric machine on the primary gearbox shaft, in a fifth configuration an electrical machine installed on one or more wheels, for example that can be installed on the rear axle of the vehicle.

In some configurations, a reversible alternator or alternator-starter can be used by being connected to the accessories drive on the engine, this reversible alternator can also be the main electric machine. This reversible alternator is currently driven by a ribbed belt which drives or transmits the movement of the latter by adhesion with the pulleys, themselves driving the rotary axes of the accessories.

As will be detailed later with reference to Figure 1, the axes which can typically be driven by this belt wound on the pulley of the reversible alternator can be at least one crankshaft of the heat engine, a water pump of the heat engine and an air conditioning compressor. The torque transmission capacity between the different axes is linked to the coefficient of adhesion or coefficient of friction of the belt on the pulleys.

One of the situations which requires good adhesion between pulley and belt is the starting of the engine by the reversible alternator or alternator-starter.

In normal conditions, that is to say belt and dry pulleys and temperature of the elements above a critical temperature threshold for the appearance of frost, conventionally 0 ° C., the coefficient of adhesion is at a level sufficient to guarantee the proper functioning of the system.

In cold conditions, that is to say a temperature of the elements below this critical temperature threshold and a wet belt, the coefficient of friction of the pulley belt can be very greatly degraded by the formation of frost on the belt. The adhesion between pulleys and belt is no longer sufficient to ensure the starting of the engine by the reversible alternator or alternator-starter.

It follows that the belt can slip. Belt slippage can also occur when the belt is very wet, for example during heavy rain or large splashes of water. The adhesion between the belt and the pulleys of the crankshaft and the alternator-starter is then insufficient. Thus, under these conditions when the heat engine proceeds to an assisted start, the pulley of the alternator-starter shaft can slip on the belt and the alternator-starter fails to implement an assisted start.

This is also the case for a frosted belt. As, at each start, it is primarily the start member connected by a belt to the engine that works, it follows that it is important that the belt fulfills its role by not sliding between the pulleys.

We know the principle of detecting a risk of sliding of the combustion engine drive belt by the alternator-starter. Such a slip risk is detected, for example, by comparing the engine speed and the alternator-starter speed. An automatic stopping of the combustion engine is then prohibited in the event of a risk of slipping. This principle is proposed in particular in document FR-A2 965 880.

However, this type of slip detection is expensive to implement and produces a slip risk detection whose reliability is limited. Thus, the estimation of the potential slippage of the accessory belt is not reliable in all cases of life, and, to always guarantee the restart, the slipping detection system overestimates the risk of slipping of the belt. This results in an availability of the engine stop phases which is reduced compared to the real potential.

If the problem of wet belts at risk of slipping is known from the state of the art, there are few documents concerning this problem for frosted belts which nevertheless present a greater risk of slipping than wet belts.

It has been proposed to prohibit the stopping and restarting of a heat engine as soon as the outside temperature drops below 0 ° C. This is however too selective since the belt is present in the space below the hood of the motor vehicle, this space also housing the engine and being heated by the engine, therefore generally warmer than the outside temperature. We find ourselves in the case of an overestimation of the risk of slipping of a frosted belt which decreases the availability of the engine stop phases compared to what would be necessary.

Therefore, the problem at the root of the present invention is to implement a prevention of the risk of icing of a belt connecting a starting member to a specifically adapted heat engine by being neither too penalizing nor too lax.

To achieve this objective, there is provided according to the invention a method of preventing a risk of slipping of a belt connecting a starting member to a heat engine of a motor vehicle, the risk of slipping being susceptible to be produced by a deposit of frost on the belt, characterized in that the method comprises an estimation of a temperature of the belt in real time according to a model simulating a thermal balance of the belt based on at least one estimation or one measurement of the ambient temperature near the belt and at least one evaluation of the convection and conduction exchanges of the belt with its environment and if the estimated temperature of the belt is lower at a given time than a temperature threshold below which frost can be created on the belt, when the engine is running, the engine is stopped from being stopped rmique or, when the engine is stopped, a prohibition of starting the engine by the starting member associated with the belt.

The technical effect is to be able to manage the stoppages and restarts of the engine based on the belt temperature information estimated by the model. Risk prevention adapted to the estimated temperature of the belt, which is different from the outside temperature due to the heating action exerted by the engine, is obtained.

The temperature of the belt is indeed equal to the outside temperature only in the very specific case of a long shutdown of the heat engine which has allowed it to cool: there is then a substantial alignment of the temperature of the belt. on the outside temperature.

By cons, in a common context of use, the temperature of the belt is higher than the outside temperature. The frost will only be created if the belt has a temperature below 0 ° C. It is this criterion that is as close as possible to the real conditions that the prevention process according to the present invention applies.

To frost, it is of course necessary that the belt is at least slightly wet. The 0 ° C threshold can be calibrated according to external parameters to better follow the real conditions affecting the belt or compensate for the imprecision of the model.

The ambient temperature in the environment of the belt can be the temperature of the air under the hood, this air having penetrated through an opening in the cooling facade, having then been used for cooling one or more radiators d '' a motor-fan unit downstream of the facade then having been heated by the heat engine.

Advantageously, when the heat engine is stopped and the temperature of the estimated belt is higher than the threshold temperature by at most a predetermined temperature interval, the heat engine is put back into operation preventively.

When the engine is stopped, the temperature of the engine decreases appreciably taking into account the thermal inertia of the engine. The same goes for the air under the hood and for elements, such as the belt, located near the engine. The ventilation of the air under the hood is relatively weak.

The longer the vehicle has driven, the more its engine has reached its optimum operating temperature. The situation with the engine stopped and the vehicle moving only applies to a hybrid vehicle with an engine other than the combustion engine. The optional measure set out above prevents the belt from frosting in the near future by warming it up by running the heat engine preventively.

Advantageously, the heat engine being in operation, the belt and the engine being housed in a space under the hood having a cooling facade traversed by an air flow coming from outside the vehicle at a flow speed of air in force and entering the space under the hood, said at least one evaluation of the convection exchanges of the belt with its environment takes account of the following parameters taken individually or in combination: the ambient temperature, the air flow speed in force in the space under the hood and an engine speed of the heat engine.

Advantageously, the heat engine being in operation and the belt being wound around at least two pulleys, said at least one evaluation of the conduction exchanges of the belt with its environment takes account of the conduction between the belt and each of said at least two pulleys according to a measurement or an estimate of a respective temperature for each of said at least two pulleys.

Advantageously, said at least two pulleys are a crankshaft pulley of the engine and a pulley associated with the starting member, the temperature of the crankshaft pulley being estimated according to at least one or more of the following parameters taken individually or in combination: a temperature of a lubricating oil for the heat engine, the ambient temperature near the belt, a speed of air flow in force entering a space under the hood housing the belt and the motor with a cooling front crossed by the air flow coming from outside the vehicle and an engine speed of the heat engine and the pulley temperature associated with the starting member being estimated according to one or more of the following parameters taken individually or in combination: a temperature of the starting device, the ambient temperature near the belt, the air flow speed and the engine speed engine.

Advantageously, the belt is wound around at least a third pulley, the third pulley being a compressor pulley, the conduction between the belt and the compressor pulley being estimated according to a measurement or an estimate. of a compressor pulley temperature and, in the case of an estimate, the temperature of the compressor pulley being estimated according to at least one or more of the following parameters taken individually or in combination: a torque of the compressor, a temperature of the compressor , the ambient temperature near the belt, the air flow speed and the engine speed of the heat engine.

Advantageously, account is taken of the mechanical losses by friction of the motor or of at least one element associated with the belt such as one or more pulleys or the starting member, these mechanical losses causing the belt to heat up, these mechanical losses being evaluated as a function of the following parameters taken individually or in combination: an engine speed of the heat engine, a engine torque of the heat engine, a torque of the starting member and a torque of the compressor when present.

Advantageously, when the temperature of the belt becomes greater than a temperature threshold beyond which the creation of frost on the belt is not possible or at the end of a minimum latency period after the ban, this minimum latency period being adjustable according to the outside temperature and / or the temperature of the belt, the stop or start prohibition is canceled by the starting member associated with the belt of the heat engine .

The minimum latency time makes it possible to take account of the thermal inertia in the space under the hood for the heating of the belt. This minimum time also allows the belt to rise to a temperature sharply above 0 ° C, for example above 50 ° C and therefore to stay longer, motejr stopped, at a temperature above the temperature threshold at least below 0 ° C even when the outside temperature is negative.

The invention also relates to a motor vehicle comprising at least one heat engine and a starting member with a belt connecting the starting member to the heat engine, a control-command unit controlling the starting member and the engine. thermal, characterized in that the control-command unit implements such a prevention method by presenting means for estimating the temperature of the belt, means for comparing the estimated temperature of the belt with a threshold of calibrable temperature at least less than 0 ° C memorized and means for prohibiting the engine from stopping or starting by the starting member associated with the belt.

Advantageously, the vehicle is a hybrid vehicle with a vehicle propulsion engine other than the heat engine or a vehicle equipped with an automatic engine stop and restart system, the vehicle having a starter other than the 'starting member associated with the belt, the starting member being an alternator-starter or an electric machine.

The advantage of the invention for a hybrid vehicle is to allow the driver to have limited availability of the electric mode for negative outside temperatures with an architecture involving an alternator-starter or an electric machine as the starting member. driven by a ribbed belt.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with regard to the appended drawings given by way of nonlimiting examples and in which:

- Figure 1 is a schematic representation of a perspective view of an accessory facade of a cylinder block of a heat engine according to the prior art, the method of preventing a risk of slipping of a belt connecting a starting member to a heat engine of a motor vehicle being used for the main belt of the accessory facade,

- Figure 2 is a schematic representation of a flow diagram of an embodiment of the method for preventing a risk of slipping of a belt connecting a starting member to a heat engine according to the present invention.

It should be borne in mind that the figures are given by way of examples and are not limitative of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the dimensions of the various elements illustrated are not representative of reality.

In what follows, reference is made to all the figures taken in combination. When reference is made to a specific figure, this figure is to be taken in combination with the other figure for the recognition of designated numerical references.

As shown in Figure 1, a conventional accessory front of a cylinder block 13 of a heat engine of a motor vehicle comprises a belt 11 said accessory primary belt driven by a crankshaft pulley 2 and driving a machine pulley 8 electric 8a or alternator-starter and a return and / or tensioning element 5 of the belt, here illustrated by two tensioners but which can take other forms. The primary primary belt 11 connects the crankshaft pulley 2 to the pulley 8 of the electric machine 8a.

The accessory facade of the cylinder block 13 also advantageously carries an air conditioning compressor pulley 4 and a water pump carrying a pulley 6 whose drive is provided by a secondary drive belt 7 located in a plane other than that of the primary belt 11, this secondary drive belt 7 being conventionally integral with the crankshaft pulley 2 by turning on a raceway on the crankshaft pulley 2 other than that of the primary belt 11.

Referring to Figures 1 and 2, the present invention relates to a method of preventing a risk of slipping of a belt 11 connecting a starting member 8a to a heat engine of a motor vehicle, the risk of slippage being likely to be produced by a deposit of frost on the belt 11.

According to the invention, the method comprises an estimate of a temperature Tcour of the belt 11 in real time according to a model simulating a thermal balance 14 of the belt 11 based on at least one estimate or a measurement of the ambient temperature Tamb near the belt 11 and at least one evaluation of the convection 15 and conduction 17 exchanges of the belt 11 with its environment.

In FIG. 2 while referring to FIG. 1 for the references not present in FIG. 2, the oval 14 represents the heat balance made from different ovals of which the oval 15 represents the calculation by convection and the oval 17 represents the calculation by conduction, essentially in contact with the belt 11 with the pulleys 2, 8 and if necessary 4.

If the estimated temperature Tcour of the belt 11 is less than a given time at a temperature threshold below which the creation of frost on the belt is possible, it is proceeded, when the engine is running, to a ban stopping the engine or, when the engine is stopped, a prohibition of starting the engine by the starting member 8a associated with the belt 11. This temperature threshold is preferably 0 ° C, but can be calibrated and between + 5 ° C and -5 ° C to compensate for the inaccuracy of the estimated temperature of the Tcour belt.

The function of an engine control function is to estimate the belt temperature. This function calculates in real time an estimate of the temperature Tcour of the belt 11 using a calculation model simulating the thermal 14 of the belt 11. The information necessary for calculating the temperature Tcour of the belt 11 is given by the engine control. This information can be the engine speed Nmot and the engine torque Cmot of the heat engine, the power drawn supplied by the accessories, advantageously the starting member 8a and the air conditioning compressor 4 but other accessories can be taken into account and the oil temperature Th.

For the ambient temperature Tamb near the belt 11, the information circulating in the engine control can come from an estimator itself resulting from a calculation in real time by the engine control computer or from a physical sensor located close to the belt 11. This sensor can be identical to those used for the coolant temperature measurements of the heat engine.

When the engine is running, the engine heats the space under the hood and therefore the belt 11. If the vehicle is moving, cold air enters the space under the hood through an opening in the front of cooling. As the heat engine has a high thermal inertia, the temperature stabilizes in the space under the hood. It follows that the ambient temperature Tamb in the environment of the belt 11 gives a faithful estimate of the temperature Tcour of the belt 11, an estimate which is refined according to the method according to the present invention.

If the vehicle is not moving, the engine still running, the speed of the air flow entering under the hood of the vehicle is close to zero. There is therefore no air ventilation in the space under the hood and this is favorable to a gradual increase in temperature Tcour of the belt 11 as the engine is running and hot.

In the case of a recently stopped engine, the engine loses calories and its temperature gradually decreases. The ambient temperature Tamb in the space under the hood can therefore also decrease. For example, an internal combustion engine can cool down completely for 90 minutes and therefore perform increasingly moderate heating of the space under the hood during this time.

When the engine is stopped and the estimated temperature Tcour of the belt 11 is greater than the threshold temperature by at most one predetermined temperature interval, relatively small interval of at most 5 ° C at above the icing temperature, the heat engine can be put back into operation preventively, this in order to avoid a frosted belt 11 and an impossibility of starting the heat engine by the alternator-starter 8a.

When the engine is in operation, the belt 11 and the engine being housed in a space under the hood having a cooling front through which an air flow from outside the vehicle passes at a flow speed of air Vase in force and penetrating into the space under the hood, said at least one evaluation of the convection exchanges represented by the oval 15 of the belt 11 with its environment takes account of the following parameters taken individually or in combination: the ambient temperature Tamb near the belt 11, the speed of air flow Vase in force in the space under the hood and an engine speed Nmot of the heat engine.

A possible duration of the heat engine running at the end of travel or as an alternative to propulsion other than heat can be used for drying and defrosting the belt 11. For a hybrid vehicle, it may be authorized after this time short period of driving by other propulsion by the heat engine but this period must be limited in particular by very low outside temperature, since the belt temperature Tcour of 0 ° C can be quickly reached again.

Thus, if the engine is in operation, the belt 11 heats up due to mechanical losses. When the engine stops, the belt 11 on the contrary cools. As previously mentioned, the engine control can restart the engine before the temperature Tcour of the belt 11 drops to a level for which the starting by the belt 11 could no longer take place under good conditions, the belt 11 probably being frosted.

The conduction represented by the oval 17 is calculated according to different stages. When the heat engine is in operation, the belt 11 being wound around at least two pulleys 2, 8 which are the crankshaft pulley 2 and the pulley of the starting member 8a, the latter advantageously an alternator-starter or a electric machine, part of the evaluation of the conduction exchanges 17 of the belt 11 with its environment takes account of the conduction between the belt 11 and each of the two above-mentioned pulleys 2, 8 according to a measurement or an estimate a respective temperature for each of said at least two pulleys 2, 8.

The oval 18 is dedicated to the calculation of the conduction of the belt 11 at the pulley of the starting member 8a, advantageously an alternator-starter or an electric machine and the oval 20 is dedicated to the calculation of the conduction of the belt 11 at the level of the crankshaft pulley 2.

For the oval 20, the temperature of the crankshaft pulley 2 can be estimated according to at least one or more of the following parameters taken individually or in combination: a temperature of a lubricating oil Th of the heat engine, the ambient temperature Tamb near the belt 11, a speed of air flow Vase in force penetrating into a space under the hood housing the belt 11 and the engine by having a cooling facade through which the air flow from outside the vehicle and an engine speed Nmot of the heat engine.

For the oval 18, the temperature of the pulley 8 associated with the starting member 8a can be estimated according to one or more of the following parameters taken individually or in combination: the ambient temperature Tamb near the belt 11, the temperature Tmel of the starting member 8a, the air flow speed Vase in force and the engine speed Nmot of the heat engine.

As shown in Figure 1, the accessory front belt 11 mainly connecting the crankshaft pulley 2 to the pulley of the starting member 8a, can be wrapped around at least a third pulley 4 and even more.

The third pulley can be a compressor pulley 4. In this case a conduction calculation between the belt 11 and the compressor pulley 4 is performed in the oval

21. The conduction calculation 21 for this compressor pulley 4 can be estimated as a function of a measurement or an estimate of a temperature of compressor pulley 4.

The temperature of the compressor pulley 4 can be estimated according to at least one or more of the following parameters taken individually or in combination: a torque of the compressor Cac, a temperature of the compressor Tac, the ambient temperature Tamb near the belt 11 , the air flow speed Vase and the engine speed Nmot of the heat engine.

In the calculation of the conduction 17, it can be taken into account the mechanical losses by sliding of the belt 11 on the pulley of the starting member 8a, this calculation being referenced 19 in Figure 2. The mechanical losses by slip of the belt 11 on the pulley of the starting member 8a can be estimated according to at least one or more of the following parameters taken individually or in combination: an engine speed Nmot of the heat engine, a torque Cmot of the engine and a torque Cmel of the starting member 8a.

In addition to a conduction 17 and convection 15 calculation, it can be carried out in parallel a calculation of the mechanical losses by friction which is illustrated by the oval 16 in FIG. 2. It can therefore be taken into account mechanical losses by friction of the motor or of at least one element associated with the belt 11 such as one or more pulleys 2, 8, 4 or the starting member 8a, these mechanical losses causing heating of the belt 11.

These mechanical losses can be evaluated as a function of the following parameters taken individually or in combination: an engine speed Nmot of the heat engine, an engine torque Cmot of the engine, a torque Cmel of the starting member 8a and a torque of the Cac compressor when present.

When the temperature Tcour of the belt 11 becomes greater than a temperature threshold beyond which the creation of frost on the belt is not possible or at the end of a minimum latency period after the ban, this minimum latency period being adjustable according to the outside temperature and / or the temperature Tcour of the belt 11, the stop or start prohibition can be canceled by the start-up member 8a associated with the belt 11 of the heat engine. This illustrates a return to normal operation of the starting of the heat engine, the belt 11 is not likely to frost in the near future. This temperature threshold is preferably 0 ° C, but can be calibrated to compensate for the model's inaccuracy.

In addition, an estimate can be made of an amount of water retained on the belt 11, the amount of water having to be greater than a minimum threshold for a ban on stopping or starting the heat engine. Account can also be taken of the external humidity advantageously near the belt 11.

The invention also relates to a motor vehicle comprising at least one heat engine and a starting member 8a with a belt 11 connecting the starting member 8a to the heat engine, a control unit controlling the starting member 8a and the heat engine.

According to the invention, the control-command unit implements such a prevention method by presenting means for estimating the temperature Tcour of the belt 11 at least by conduction 17 and convection 15 calculations, means for comparing the measured or estimated temperature of the belt 11 with a temperature threshold below which the creation of frost on the belt is possible memorized and means for prohibiting the engine from stopping or starting by the starting member 8a associated with the belt 11. This temperature threshold is preferably 0 ° c, but can be calibrated and between + 5 ° C and -5 ° C to compensate for the inaccuracy of the estimation of the belt temperature Tcour.

This can be done using a belt temperature estimation module Tcour 11 sending this information to a stop and restart coordinator of the heat engine via a sliding belt estimator module 11. The coordinator's role is to send stop and restart orders to the engine and restart orders to the starting member 8a associated with the belt 11, advantageously an alternator-starter or an electric machine.

The vehicle can be a hybrid vehicle with a vehicle propulsion engine other than the heat engine or a vehicle equipped with an automatic engine stop and restart system. In this case, the vehicle may have a starter other than the starting member 8a associated with the belt 11, the starting member 8a being an alternator-starter or an electric machine.

The invention is in no way limited to the embodiments described and illustrated which have been given only by way of examples.

Claims (10)

Claims: 1. Method for preventing a risk of slipping of a belt (11) connecting a starting member (8a) to a heat engine of a motor vehicle, the risk of slipping being likely to be produced by a deposit of frost on the belt (11), characterized in that the method comprises an estimation of a temperature (Tcour) of the belt (11) in real time according to a model simulating a thermal balance (14) of the belt (11) on at least one estimate or measurement of the ambient temperature (Tamb) near the belt (11) and at least one evaluation of the convection (15) and conduction (17) exchanges of the belt (11) with its environment and if the temperature (Tcour) of the estimated belt (11) is lower at a given time than a temperature threshold below which the creation of frost on the belt is possible, it is proceeded, when the heat engine is running, to a ban on stopping the m heat engine or, when the engine is stopped, a prohibition of starting the engine by the starting member (8a) associated with the belt (11). 2. Method according to the preceding claim, in which, when the heat engine is stopped and the temperature (Tcour) of the estimated belt (11) is higher than the threshold temperature by at most one predetermined temperature interval , the heat engine is put back into operation preventively. 3. Method according to any one of claims 1 or 2, wherein, the engine being in operation, the belt (11) and the engine being housed in a space under the hood having a cooling front through which a flow of air coming from outside the vehicle at an air flow speed (Vase) in force and entering the space under the hood, said at least one evaluation of the convection exchanges (15) of the belt (11) with its environment takes account of the following parameters taken individually or in combination: the ambient temperature (Tamb) near the belt (11), the air flow speed (Vase) in force in the space under the hood and an engine speed ( Nmot) of the engine. 4. Method according to any one of the preceding claims, in which, the heat engine being in operation and the belt (11) being wound around at least two pulleys (2, 8), said at least one evaluation of the exchanges in conduction (17) of the belt (11) with its environment takes account of the conduction between the belt (11) and each of said at least two pulleys (2, 8) according to a measurement or an estimate of a respective temperature for each of said at least two pulleys (2, 8). 5. Method according to the preceding claim, wherein said at least two pulleys (2, 8) are a crankshaft pulley (2) of the engine and a pulley (8) associated with the starting member (8a), the temperature of the crankshaft pulley (2) being estimated according to at least one or more of the following parameters taken individually or in combination: a temperature of a lubricating oil (Th) of the heat engine, the ambient temperature (Tamb) near the belt (11), an air flow speed (Vase) in force entering a space under the hood housing the belt (11) and the motor by having a cooling front through which the air flow from outside the vehicle and an engine speed (Nmot) of the heat engine and the temperature of the pulley (8) associated with the starting member (8a) being estimated according to one or more of the following parameters taken individually or in combination: a temperature (Tmel) of organ starting temperature (8a), the ambient temperature (Tamb) near the belt (11), the air flow speed (Vase) and the engine speed (Nmot) of the heat engine. 6. Method according to the preceding claim, in which the belt (11) is wound around at least a third pulley (4), the third pulley being a compressor pulley (4), the conduction between the belt (11) and the compressor pulley (4) being estimated as a function of a measurement or an estimate of a compressor pulley temperature (4) and, in the case of an estimate, the temperature of the compressor pulley (4 ) being estimated according to at least one or more of the following parameters taken individually or in combination: a torque of the compressor (Cac), the ambient temperature (Tamb) near the belt (11), a temperature of the compressor (Tac), the speed of air flow (Vase) and the engine speed (Nmot) of the heat engine. 7. Method according to any one of the preceding claims, in which account is taken of the mechanical losses by friction (16) of the motor or of at least one element associated with the belt (11) such as one or pulleys (2, 8, 4) or the starting member (8a), these mechanical losses resulting in heating of the belt (11), these mechanical losses being evaluated according to the following parameters taken individually or in combination: an engine speed (Nmot) of the heat engine, engine torque (Cmot) of the heat engine, torque (Cmel) of the starting device (8a) and torque (Cac) of the compressor (4) when present. 8. A prevention method according to any one of the preceding claims, in which, when the temperature (Tcour) of the belt (11) becomes greater than a temperature threshold beyond which the creation of frost on the belt is not not possible or at the end of a minimum latency period after the ban, this minimum latency period being calibrable according to the outside temperature and / or the temperature (Tcour) of the belt (11), it is carried out cancellation of the prohibition of stopping or starting by the starting member (8a) associated with the belt (11) of the heat engine. 9. Motor vehicle comprising at least one heat engine and a starting member (8a) with a belt (11) connecting the starting member (8a) to the heat engine, a control-command unit controlling the starting member ( 8a) and the heat engine, characterized in that the control-command unit implements a prevention method according to any one of the preceding claims by presenting means for estimating the temperature (Tcour) of the belt ( 11), means for comparing the estimated temperature of the belt (11) with a stored temperature threshold below which the creation of frost on the belt is possible and means for preventing the engine from stopping or starting. by the starting member (8a) associated with the belt (11). 10. Motor vehicle according to claim 9, which is a hybrid vehicle with a vehicle propulsion engine other than the heat engine or a vehicle equipped with an automatic engine stop and restart system, the vehicle having a starter other than the starting member (8a) associated with the belt (11), the starting member (8a) being an alternator-starter or an electric machine.