FR2834247A1 - Air conditioning for motor vehicle interior, has independent feeds into front and rear areas of passenger compartment - Google Patents

Abstract

The air conditioning for a motor vehicle interior has an air inlet (6) and a heater-cooler circuit (10-12) for the air with a mixing chamber (12). At least one of the outlets (19,23) opens into the mixing chamber and has an obturator (21,25). A rear duct (38) is fed with air from a breach of at least one of the outlets. Part of the inlet air is fed towards the front and part toward the rear, with the latter controlled to condition the air into the rear of the vehicle.

Description

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Process for air conditioning the passenger compartment of a motor vehicle

 The present invention relates to a method of air conditioning of a motor vehicle, in particular an air conditioning method for diffusing air to a rear space.

 An air conditioning device generally comprises an air intake, an air cooler, an air heating radiator, and means for mixing cooled air and heated air. The air conditioning device includes an outlet duct to de-icing vents, an air outlet duct to front seat ventilators, and an outlet duct to foot ventilators. The inlet of the outlet pipes can be closed completely or partially by means of shutter means. An adjustment panel makes it possible to control a diffused air temperature, an air flow rate according to several predetermined values, and a distribution of air between the different aerators, by complete or partial closure of each outlet pipe. The air conditioning device can optionally be automatically controlled by a control unit and associated sensors.

 It may be desired to provide motor vehicles comprising air conditioning devices offering the possibility of different settings between the front seats and the rear seats. A vehicle may include two air conditioning devices: a front device and a rear device. Such a solution is expensive. In addition, the consumption of the vehicle is increased, and the maintenance of the air conditioning devices may require more frequent stops of the vehicle.

 In order to bring treated air directly to a rear space of the vehicle, an air conditioning device may include a rear air outlet connected to a pipe opening into said rear space. Document EP 0 989 004 discloses an air conditioning module comprising a mixing chamber, from which de-icing lines, front aerator pipes, and rear aerator pipes start.

 Partition walls make it possible to obtain different air mixing chambers, and air diffusion towards the different pipes with different temperatures. Shutters of the various pipes allow, by complete or partial closure of the entrances of the pipes, and from

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 a flow rate provided by an air supply, an air distribution between the defrost lines, front aerators and rear aerators. However, such a device does not allow a rearward air supply with independent rear flow control.

 The present invention relates to an air conditioning method for front air diffusion and rear air diffusion, with independent adjustment of front and rear flow rates.

 The invention also relates to an air conditioning method for obtaining a rear air diffusion with independent flow control, without disturbing a distribution adjustment and air flow output of front aerators.

 The invention also relates to an air conditioning method for rear air diffusion, regardless of a distribution of air diffusion between different front aerators.

 In such a method of air conditioning the passenger compartment of a motor vehicle, after treatment, a portion of the intake air is directed forward and another part of the intake air is directed rearward, it increases the airflow directed rearward to effect the air conditioning of the rear part of the vehicle, and the air flow directed towards the front is corrected according to the increase of air flow towards the rear.

 The intake air is distributed to be diffused towards the rear and towards the front of the vehicle. Rearward-directed airflow disrupts airflow to the front. In particular, the forward air flow can be decreased, the increase in backward air flow causing a flow rate change in forward air outlet ducts.

 In one embodiment, the airflow directed towards the rear is increased by means of an air circulation means arranged in a rear pipe, intended for supplying air with at least a rear exit. The circulation means is of the fan type rotary actuator.

 In one embodiment, an air diffusion rear duct is fed to the rear of the vehicle from at least one air intake on an air diffusion outlet duct towards the front of the vehicle. vehicle. The increase of a flow rate in the rear pipe will cause a substantially proportional decrease in the flow rate at the outlet of an outlet pipe on which an air intake is arranged, and also at the outlet of a outlet pipe without a tap.

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 of air, but with a lower coefficient of proportionality. The forward air flow correction must compensate for a variation in output flow in different outlet lines.

 In one embodiment, desired flow rates are determined at the outlet of the forward air outlet ducts, the desired flow rates are corrected according to a rearward airflow increase. Forward air diffusion is generally through a plurality of forward diffusion air outlet ducts. Desired flow rates at the exit of the outlet pipes are determined to control a distribution of the air flow directed forwardly between the different outlet pipes. The flow rate variation at the outlet of the different outlet ducts, caused by an increase in the air flow directed towards the rear, is different at the outlet of each of the outlet ducts. For example, a backward diffusion air intake may be near an inlet of a first outlet conduit, while being remote from an inlet of a second outlet conduit. An increase in the air flow directed towards the rear will cause a greater variation in flow rate at the outlet of the first outlet pipe than at the outlet of the second outlet pipe. Likewise, if a rear line supply air intake is disposed on an intermediate portion of a forward air outlet duct, the variation of the outlet flow of said outlet duct due to the rearward directed air flow rate increase will be different from the output flow rate variation of an outlet duct devoid of air intake. A correction of the desired flow rate in each output line makes it possible to obtain at the output of each output line the initially desired flow rate.

 In one embodiment, a corrected input flow rate of a forward diffusion air outlet duct is determined to be the sum of a desired flow rate at the outlet of said outlet duct and a flow correction. The flow correction is a function of the air flow directed backwards.

 In one embodiment, corrected inlet flow rates of forward air outlet outlets are determined based on a desired flow distribution at the outlet of said outlets. The input flow rate correction required to achieve the desired output rates is a function of the flow distribution between the output lines. For example, if first and second outlets carry identical air intakes of a rear line, and if a larger air flow enters

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 the second output duct, for a rearward directed flow rate increase, the required flow rate correction at the inlet of the second outlet duct will be greater than the required flow rate correction at the inlet of the first outlet duct.

 In one embodiment, a flow rate correction is determined as the product of a rearward air flow rate and a correction coefficient. The necessary correction of the inlet flow rate of a forward diffusion air outlet duct is substantially proportional to the rearwardly directed airflow increase, which allows the use of a law of variation. linear flow rate correction, as a function of backward airflow.

 Advantageously, a correction coefficient is determined from a predetermined table. An input flow rate correction depends on the architecture of an air-conditioning device, the increase in backward air flow being able to change the flow rates of the air-handling system differently. forward airflow outlet. It is advisable to determine correction coefficients experimentally for a given air conditioning device. In the case of several forward air diffusion output ducts, the flow correction coefficients depend on an air distribution between said outlet ducts. Since a flow rate correction is functionally linearly dependent on a rearward flow rate increase, a predetermined table can be established for each outlet line from: an admitted air flow, an air flow directed to the reference rear, and for different front flow distributions in the outlet ducts.

 In one embodiment, a flow rate of the intake air and an air distribution between air distribution outlet ducts are corrected. The rearward-directed air flow rate increase must be compensated for by an increase in the intake air flow to maintain forward airflow. The intake air flow can be corrected by means of an air circulation means arranged in an air intake assembly. According to an architecture of an air conditioning device, the output flow of each outlet pipe is modified in a different manner by a rearward flow increase, which leads to modifying the air distribution at the inlet of the diffusion outlet pipes. air forward, from the airflow directed forward.

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 In one embodiment, the flow rate of air flowing in a rearward main air distribution rear duct is determined as a function of rotational speed information of a rotary actuator of a means of rotation. air circulation in the main rear pipe.

- la figure 1 est une vue schématique d'un dispositif de climatisation ; et - la figure 2 est un schéma bloc illustrant des étapes d'un procédé de climatisation d'un véhicule à partir du dispositif de climatisation de la figure 1. The present invention and its advantages will be better understood on studying the detailed description of embodiments taken as non-limiting examples and illustrated by the appended drawings, in which:

- Figure 1 is a schematic view of an air conditioning device; and FIG. 2 is a block diagram illustrating steps of a method of conditioning a vehicle from the air conditioning device of FIG. 1.

 In FIG. 1, an air conditioning device 1 comprises air intake means 2, an air heating / cooling assembly 3, a front ventilation assembly 4 and a rear aeration assembly 5.

 The air intake means 2 comprise an intake duct 6 provided with an inlet 7 and an outlet 8, and an air circulation means 9, in the form of a fan or a fan. pump. The heating / cooling assembly 3 comprises a cooling chamber 10, a heating chamber 11 and a mixing chamber 12. An opening 13 allows the passage of air from the cooling chamber 10 to the mixing chamber 12. opening 14 allows the passage of air from the cooling chamber 10 to the heating chamber 11.

The openings 13 and 14 are adjacent. An opening 15 spaced from the openings 13 and 14 allows the passage of air between the heating chamber 11 and the mixing chamber 12. A shutter 16 allows to partially or completely close the openings 13 and 14.

 The air emerging from the outlet 8 of the intake duct 6 passes through a cooler 17 arranged in the cooling chamber 10, of the type of evaporator of a gas compression cycle air conditioning loop, of cooling the gas by expansion and heat exchange between the cooled gas and the intake air. At the outlet of the cooler 17, the cooled air can pass directly into the opening 13 to the mixing chamber 12. The air leaving the cooler 17 can also pass into the heating chamber 11 through the opening 14. A radiator heating 18 is disposed across the heating chamber 11. The air entering through the opening 14 passes through the radiator 18 before emerging through the opening 15 to the mixing chamber 12. The shutter 16 allows a distribution of the air cooled in cooled air

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 passing directly into the mixing chamber 12 and cooled air passing through the heating chamber 11 before passing to the mixing chamber 12, to obtain a mixture of air at the desired temperature. The cooler 17 may be in operation or stopped, the so-called cooled air being in this case substantially at the same temperature as the intake air.

 A defrost outlet pipe 19 has an inlet 20 opening into the mixing chamber 12, and can be closed completely or partially by a valve 21. An aerator 22 is disposed at the outlet of the outlet pipe 19, to bring the air towards the windshield of the vehicle. A dashboard output pipe 23 has an inlet 24 opening into the mixing chamber 12, and can be closed completely or partially by a valve 25. An aerator 26 is disposed at the outlet of the instrument panel output pipe 23 A foot outlet conduit 27 includes an inlet 28 opening into the mixing chamber 12 and being closable completely or partially by a valve 29. An outlet 30 is disposed at one end of the lower outlet conduit 27.

moyens mémoire 33, un programme stocké sur les moyens mémoire 33 et apte à être e-D exécuté par un microprocesseur 34. A control unit 31 comprises a processing module 32,

memory means 33, a program stored on the memory means 33 and able to be eD executed by a microprocessor 34.

 The rear aeration assembly 5 comprises an air intake 35 is disposed on an intermediate portion of the dashboard outlet pipe 23. An air intake 36 opens into the outlet pipe of feet 27 near the the exit 30.

The air intakes 35,36 meet in a manifold 37 opening also in a rear pipe 38. Rear outlets 39,40 are connected to the end of the rear pipe 38 opposite the manifold 37. Closing means 41 allow a distribution of air from the rear pipe 38 to the rear outlets 39,40. The rear outlets 39,40 are provided at their opposite ends to the rear line 38 of aerators 42,43. A rotary air circulation means 44 is disposed in an intermediate portion of the rear line 38. A control console 45 comprises a flow control knob 46 and a distribution adjustment knob 47, respectively controlling the circulation means. air 44 and the distribution means 41.

 Depending on a desired diffused air temperature, and desired airflows at the outlet of the defrost outlet lines 19, dashboard 23 and feet 27, the control unit 31 controls the circulation means. 9, the

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 cooler 17, the heating radiator 18, the closing means 16, and the valves 21, 25 and 29. The control unit 31 determines an admitted total air flow rate and controls the circulation means 9 for the purpose of sufficient air intake. Depending on the desired temperature, the control unit 31 controls the cooler 17, the heating radiator 18 and the shutter 16, to obtain the air at the desired temperature in the mixing chamber 12. The control unit 31 then determines a desired distribution of air between the defrosting outlet 19, the dashboard 23 and the feet 27. It then controls the opening and closing of the valves 21, 25 and 29. partial or complete closure of the corresponding inlets 20, 24 and 28. The control of the valves 21, 25, 29 can be independent and carried out with the aid of several actuators, or linked, and carried out by an actuator associated with a cam system for example for two valves 25,29.

 The control unit 31 can control the organs automatically, in function of sensor information and from a control program, or in manual mode, in which a user specifies on a control panel a ventilation rate and a diffused air temperature.

 If the dashboard outlet pipes 23 and feet 27 are supplied with air, air will be directed backwards, through the air intakes 35, 37 and the rear pipe 38. A passenger located at the rear can actuate the 46,47 setting buttons to increase a rear airflow and an air distribution between the rear outlets 39,40, one of which can be located at the feet, and the other in height in relation to the floor of the vehicle. The rear passenger adjusts the rear airflow independently of a forward setting. Depending on the requested reverse flow rate, the control console 45 causes rotation of a rotary actuator of the circulation means 44, with a suitable rotational speed.

 The increase in the air flow in the rear pipe 38 causes a variation in the output flow rates of the outlet pipes 19, 23, 27. These flow variations are a function, for each outlet pipe 19, 23, 27, of the distribution of flow rates between the outlet ducts 19, 23, 27. These flow variations are also a function of an increase in air flow in the rear duct 38 caused by the circulation means 44 disposed in the rear duct 38.

 The rear flow control is done independently from the rear control console 45. In order that an increase in flow in the rear line 38 does not alter the outflows of the outlet lines 19, 23, 27, the unit of

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 control 31 determines corrected flow rates that are used for the control of the circulation means 9 and valves 21,25, 29. These corrected flow rates take into account the flow variations caused by the rear aeration assembly 5. The unit of control 31 takes into account rotational speed information of a rotary actuator of the circulation means 44 to determine a flow of air to the rear. The rear venting control can then be performed independently of the forward vent control, with respect to flow rates, and without disrupting the operation of the front vent.

 There is a plurality of different flow rate distributions. As the air inlets 35,37 are arranged on two outlet lines 23,27, as soon as one of these outlet lines 23,27 is supplied with air, the rear line 38 is supplied with air. The situation where the inputs of the two dashboard output lines 23 and feet 27 are completely closed corresponds to the case where the windshield must be defrosted quickly, for example when starting the vehicle, after a cold night.

In this case, the supply of the rear line 38 is in fact not desirable since the hot air must be sent to the windshield for rapid defrosting. However, it could of course be provided to have an additional air intake on the defrost outlet pipe 19.

 In FIG. 2, a block diagram illustrates an example of steps of an air-conditioning method according to the invention, adapted to the air-conditioning device of FIG. 1, and which can be implemented by the control unit 31. When of a processing step 50, input data symbolized by an arrow 51 are processed by the processing module 32 of FIG. 1 in order to determine the desired flow rates Q1, Q2, Q3 at the outlet of the deicing discharge lines 19, The data 51 include, by way of non-limiting example, the indoor temperature, the sunlight, the outside temperature, etc. These input data can be provided by suitable sensors arranged on a vehicle.

des débits souhaités Ql, Q2, Q3, définis par l'équation suivante :

. Qi (QI (ei+62+63) avec i = 1, 2, 3 During a step 52, distribution coefficients ql, q2, q3 are determined

desired rates Q1, Q2, Q3 defined by the following equation:

. Qi (IQ (ei + 62 + 63) with i = 1, 2, 3

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In a step 53, the distribution coefficients of q1, q2, q3 desired flow rates Q1, Q2, Q3 are used as predetermined table entries, and schematized by blocks 54, 55, 56, respectively corresponding to the output lines of defrosting 19, instrument panel 23, and feet 27. At the output, correction coefficients C1, C2, C3 are recovered.

 During steps 57 and 58, which can be simultaneous with steps 50, 52, 53, a rotational speed information o) is recovered from a rotary actuator of the circulation means 44 (FIG 1), and it is determined from FIG. this information a flow of air QA flowing in the rear pipe 38 (Figure 1). The rear air flow rate QA can be determined from a predetermined table whose input is the speed of rotation (0 of the rotary actuator QA can be a linear function or a refinement of the rotation speed M.

de la correction de débit correspondante AQ1, AQ2, AQ3. Un débit corrigé est donc défini par l'équation suivante :

QCi = 6 ! + 6a -C/l, < ? 2, q3) avec i = 1, 2, 3

Lorsque qu'une répartition de débits est spécifiée entre les conduites de sortie 19,23, 27, les corrections de débit AQ1, AQ2, AQ3 varient linéairement en fonction du débit arrière. L'utilisation des corrections de débit AQ1, AQ2, AQ3 déterminées comme fonctions linéaires du débit arrière QA permet un calcul fiable et rapide des corrections de débit AQ1, AQ2, AQ3. In a step 59, flow rate corrections AQ1, AQ2, AQ3 defined as the product of a correction coefficient C1, C2, C3 are determined by the flow rate in the rear line QA. In a next step 60, corrected rates QC1, QC2, QC3 are determined as the sum of a desired rate Q1, Q2, Q3, and

the corresponding flow rate correction AQ1, AQ2, AQ3. A corrected bit rate is therefore defined by the following equation:

QCi = 6! + 6a -C / l, <? 2, q3) with i = 1, 2, 3

When a flow distribution is specified between the output lines 19, 23, 27, the flow rate corrections AQ1, AQ2, AQ3 vary linearly as a function of the back flow. The use of flow rate corrections AQ1, AQ2, AQ3 determined as linear functions of the backward flow QA allows a reliable and fast calculation of the flow corrections AQ1, AQ2, AQ3.

 Flow rate corrections AQI, AQ2, AQ3 each depend differently on the flow distribution between the outlet lines 19, 23, 27. For example, the air flow at the outlet of the outlet pipe 27 may important, the output flow of the instrument panel output conduit 23 being low. The increase in the air flow in the rear line 38 will cause a greater flow variation in the foot exit line 27 than in the dashboard outlet line 23.

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 different. The flow corrections in the defrost outlet line 19, where no air intake is disposed, are generally smaller than the flow rate corrections in the other outlet lines 23,27.

 The correction coefficients C1, C2, C3 therefore depend on the distribution of flow rates in the outlet pipes 19, 23, 27. Furthermore, the correction coefficients C1, C2, C3 depend on the architecture of the air conditioning device 1. It is advantageous to use tables 54, 55, 56 of correction coefficients C1, C2, C3 determined experimentally.

ec ! qci = Qci (QC1+ QC2 + QC3) avec i = 1, 2, 3

Le moyen de circulation 9 permet de commander un débit d'entrée suffisant pour obtenir les débits souhaités QI, Q2, Q3, QA en sortie des conduites de sortie de dégivrage 19, de tableau de bord 23, de pieds 27, et de la conduite arrière 38. Les clapets 21,25, 29 permettent une répartition de débit entre les conduites de sortie de dégivrage 19, de tableau de bord 23, et de pieds 27, dans les entrées desquelles circulent les débits corrigés QC1, QC2, QC3. Les prises d'air 35,37 prélèvent suffisamment d'air pour obtenir le débit d'air arrière QA souhaité. La variation de débit dans les conduites de sortie de dégivrage 19, de tableau de bord 23, de pieds 27 est telle que l'on obtient en sortie desdites conduites de sortie de dégivrage 19, de tableau de bord 23, de pieds 27 les débits souhaités en sortie QI, Q2, Q3. During a step 61, the circulation means 9 (FIG 1) are controlled according to the sum of the corrected flow rates QC 1, QC 2, QC 3, and the valves 21, 25 and 29, as a function of the corrected flow rates QC 1, QC 2 , QC3, and more particularly as a function of corrected flow coefficients q1, qc2, qc3 QC1, QC2, QC3, defined by the following equation:

ec! qci = Qci (QC1 + QC2 + QC3) with i = 1, 2, 3

The circulation means 9 makes it possible to control an input flow rate sufficient to obtain the desired flow rates QI, Q2, Q3, QA at the outlet of the defrost outlet pipes 19, the dashboard 23, the feet 27 and the pipe 38. The valves 21, 25, 29 allow a distribution of flow between the defrost outlet 19, instrument panel 23, and feet 27, in whose inputs flow corrected flows QC1, QC2, QC3. The 35.37 air intakes take enough air to obtain the desired rear airflow QA. The flow rate variation in the defrost outlet pipes 19, dashboard 23, feet 27 is such that the output of said defrost outlet pipes 19, dashboard 23, feet 27 flow rates are obtained. desired at the output QI, Q2, Q3.

 When the circulation means 44 (FIG 1) operates, during step 61, the control of the circulation means 9 (FIG 1) and the valves 21, 25, and 29 (FIG.

1) identically to the situation where the circulation means 44 does not work, for example using predetermined control tables. The compensation of the output flow variations of the outlet lines 19, 23, 27 (FIG 1), caused by a rearward-directed air flow increase, is achieved by a

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 control during step 61 not according to the desired flow rates QI, Q2, Q3 at the output of the output lines 19, 23, 27, but according to the corrected flow rates QC1, QC2, QC3, determined using the tables 54,55,56 correction coefficient, dependent on the distribution of desired flow rates between the outlet lines 19,23,27.

By correcting input instructions when the circulation means 44 operates using correction coefficient tables 54, 55, 56, it is possible to use predetermined control tables for the device in step 61 when the means circulation 44 is not in operation. This makes it possible to use smaller memory means.

 No air intake is disposed on the defrost outlet pipe 19.

When the rearward flow increase QA caused by the circulation means 44 is non-zero, and the flow distribution coefficient in the defrost output pipe is small, the flow variation in the defrost outlet pipe 19 is low. Moreover, the increase of the rear flow rate QA causes the control of the circulation means 9 (FIG 1) for an increase of a flow of air admitted, so that it is equal to the sum of the flow rates of desired output at the front QI, Q2, Q3 and backflow QA. Consequently, the increase in the inlet flow rate, despite the flow rate variation in the defrost outlet pipe, may tend to cause an increase in the flow rate flowing in the defrost outlet pipe 19. In other words, it there are flow distribution configurations in which the flow rate correction of the defrost line 19 may be negative, i.e. flow correction coefficients may be negative.

The circulation means 44 (FIG 1) allows an increase of a rearward air flow compared to a situation where the rear pipe 38 would be devoid of circulation means. The circulation means 44 can be controlled from the rear seats by means of the flow control knob 46 of the control console 45 (FIG 1). From a situation of significant rearward airflow, a passenger may control a decrease in the rearward directed airflow increase. The passenger will have a feeling of decreased airflow directed to the rear.

The air conditioning device 1 of FIG. 1 is described as comprising three outlet ducts, two of which are provided with air intake. Of course, more outlet pipes and a different number of air intakes can be provided. The

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 Air conditioning process can then be easily adapted. The air conditioning method can also be easily adapted to the case of an air conditioning device comprising air intakes arranged not on the outlet pipes, but directly in a mixing chamber, or a combination of air intakes on pipes. outlet and in a mixing chamber.

 Thanks to the invention, there is obtained an air conditioning process for air diffusion to a rear space, without disturbing a front air diffusion, with independent front and rear flow settings.

Claims (10)

1. A method of air conditioning the passenger compartment of a motor vehicle in which, after treatment, a portion of the intake air is directed forward and another part of the intake air is directed rearward, characterized in that the rearward airflow is increased to effect the rearward air conditioning of the vehicle, and the forward airflow is corrected according to the increase in flow rate of air towards the rear.  2. Method according to claim 1, characterized in that the air flow directed towards the rear is increased by means of an air circulation means (44) arranged in a main rear pipe ( 38).  3. Method according to any one of claims 1 or 2, characterized in that it feeds a main rear air duct (38) towards the rear of the vehicle from at least one outlet. air (35,37) on an air outlet duct (23,27) to the front of the vehicle.  4. Method according to any one of the preceding claims, characterized in that the desired flow rates (QI, Q2, Q3) are determined at the outlet of the air outlet ducts (19, 23, 27) to at the front, the desired flow rates (IQ, Q2, Q3) are corrected according to an increase in air flow towards the rear.  5. Method according to any one of the preceding claims,

 characterized in that a ZD input corrected flow (QC1, QC2, QC3) of a forward air outlet pipe (19, 23, 27) is determined as the sum of a desired flow rate (IQ, Q2, Q3) output from said output pipe (19, 23, 27) and a flow rate correction (AQ1, AQ2, AQ3).  6. Method according to claim 5, characterized in that corrected flow rates (QC1, QC2, QC3) of the output pipe lines (19,

 23, 27) as a function of a distribution (q1, q2, q3) of desired flow rates (Q1, Q2, Q3) at the output of said outlet lines (19, 23, 27).  7. Method according to any one of claims 5 or 6, characterized in that a flow rate correction (δ-Q1, AQ2, AQ3) is determined as the product of an air flow (Qa) directed towards the rear and a correction coefficient (C1, C2, C3). <Desc / Clms Page number 14>  8. Method according to claim 7, characterized in that a correction coefficient (C1, C2, C3) is determined from a predetermined table (54, 55, 56).  9. A method according to any one of claims 4 to 8, characterized in that one controls a flow of air intake and an air distribution between the output ducts (19,23,27) of diffusion of 'air.  10. Method according to any one of the preceding claims, characterized in that it determines the air flow (Qa) flowing in a rear main duct (38) of air diffusion backwards as a function of a rotational speed information (M) of a rotary actuator of an air circulation means (44) in the main rear pipe (38).