FR2815401A1 - Cooling system for fluid coolant comprises coolant inlet and outlet and auxiliary outlet allowing issuing fluid to be at lower temperature than from principal outlet - Google Patents

Abstract

The radiator (6) comprises an inlet (27) and an outlet (6a) for the coolant. There is an auxiliary outlet (6b) so that the coolant issuing from it is at a temperature lower than that of the principal outlet. An Independent claim is included for a method of cooling a hybrid vehicle comprising a heat engine and an electrical motor.

Description

<Desc / Clms Page number 1>

Device, system and method for cooling a heat transfer fluid.

The present invention relates to a cooling system for a hybrid propulsion vehicle.

Hybrid powered vehicles generally include a heat engine, one or two electric motors, an electric voltage generator, and an electronic power converter assembly which either powers the electric motor (s) or charges the batteries, all of which need to be cooled. in order to operate under the conditions for which they are intended. We are trying to take advantage of this dual engine to reduce consumption and polluting emissions as much as possible, so as to stay below authorized levels.

It has been found that the ranges of flow rate and temperature of the coolant are very different for an electric motor and for a heat engine. The coolant of an electric motor has a flow rate of the order of 100 to 500 l / hour at a temperature of 50 to 70. The coolant of a heat engine has a flow which can be twenty times higher, at a temperature of the order of 100 to 1100 maximum. These differences in flow and temperature make it difficult to use a single circuit and a single radiator operating under optimal conditions in all the situations encountered for a hybrid propulsion vehicle.

Document FR 2 748 428 (RENAULT) describes a cooling system for a hybrid propulsion vehicle comprising a heat engine and an electric motor, comprising a liquid

<Desc / Clms Page number 2>

 coolant circulating in the engines and in a radiator and means so that, the thermal engine being stopped and the electric motor being running, the coolant circulates in a first part of the radiator only, and so that the two engines being in operation, the heat transfer liquid circulates in the two parts of the radiator.

 However, when the two motors are running, the electric motor sees a coolant pass at relatively high temperature.

 The Japanese abstract 10 266 855 (TOYOTA) describes a cooling system comprising a radiator, an expansion tank common to a circuit dedicated to the heat engine and to a circuit dedicated to the electric motor. The radiator has two inputs and two outputs connected to two water boxes, one of which is divided by a partition. The other water box has no partition and the two circuits are in communication through it. During operation, the water in the two circuits hardly mixes.

 However, the heat released by the electric motor cannot be used to heat or preheat either the heat engine or the passenger compartment of the vehicle. The electric motor circuit pump operates as long as the electric motor is in operation, which reduces the service life of said pump. When the electric motor is not in service the radiator which is dedicated to it is useless and does not benefit the cooling of the heat engine and vice versa when the heat engine is not in service the radiator which is dedicated to it is used to nothing and does not benefit the cooling of the electric motor.

 The present invention proposes to overcome the limitations of conventional techniques by proposing a device and a cooling system operating optimally in all cases and making it possible to reduce energy consumption and polluting emissions.

 The present invention proposes to reduce the operating time of a coolant circulation pump in the electric motor.

 The present invention proposes to maintain the engine

<Desc / Clms Page number 3>

 electric at low temperature.

 The device for cooling a heat transfer fluid by heat exchange with another fluid, according to one aspect of the invention, comprises an inlet and an outlet for heat transfer fluid. The device includes an auxiliary outlet so that the heat transfer fluid from the auxiliary outlet is at a temperature lower than that of the main outlet.

 In one embodiment of the invention, the device comprises a first portion disposed between the main inlet and the outlet and a second portion disposed between the auxiliary inlet and outlet, the two portions being integrated into a radiator body.

 In one embodiment of the invention, the main output and the auxiliary output are arranged at opposite ends of the device.

 In another embodiment of the invention, the main output and the auxiliary output are arranged at the same end of the device.

 The device can be provided with a single inlet or with two close inlets, for example connected to the same water box.

 The path of the heat transfer fluid is longer between the auxiliary inlet and outlet than between the main inlet and outlet. In other words, the residence time in the device of the heat transfer fluid from the auxiliary outlet is greater than that of the heat transfer fluid from the main outlet.

 The cooling system, according to one aspect of the invention, is intended for a hybrid propulsion vehicle comprising a heat engine and at least one electric motor. The system is of the type comprising a heat transfer fluid capable of cooling the thermal and electric motors, a radiator capable of cooling the heat transfer fluid by heat exchange with a stream of air and comprising a plurality of cooling channels, an inlet and an outlet, a first pipe between the outlet of the radiator and the heat engine and a second pipe between said engine and the inlet of the radiator. The radiator includes an auxiliary outlet so that the heat transfer fluid from the auxiliary outlet is at

<Desc / Clms Page number 4>

 a temperature lower than that of the main outlet connected to the first pipe, said auxiliary outlet being connected to a bypass pipe capable of cooling the electric motor.

 Preferably, the bypass pipe comprises a first branch connected to the auxiliary output and a second branch connected to a pipe upstream of the heat engine.

 Preferably, the first branch is able to be connected to the first pipe.

 The first branch can pass through the electric motor and an electronic power unit of the electric motor.

 The first branch can be equipped with a circulation pump for the heat transfer fluid.

 In one embodiment of the invention, the second branch is connected to an outlet pipe of a radiator for heating a passenger compartment of a vehicle.

 In one embodiment of the invention, the bypass pipe comprises a third branch connected to the second pipe.

 In one embodiment of the invention, the bypass pipe comprises a fourth branch connected to the output of the heat engine upstream of a thermostat.

 In one embodiment of the invention, the branches of the bypass pipe are connected together by a multi-way valve. A thermostat can be integrated into said multi-way valve. The multi-way valve may include a rotary control core.

 In one embodiment of the invention, said circulation pump for the heat transfer fluid is driven by the electric motor.

 In another embodiment of the invention, said heat transfer fluid circulation pump is driven independently of the electric motor.

 The invention also relates to a vehicle comprising a cooling system as above.

 The invention also provides a cooling method for a hybrid propulsion vehicle comprising a heat engine and at least one electric motor cooled by the circulation of a fluid.

<Desc / Clms Page number 5>

 heat transfer medium in said motors, a heat exchange means capable of cooling the heat transfer fluid by heat exchange with another fluid and provided with an inlet and an outlet, process in which the flow of heat transfer fluid is divided in the means d heat exchange between a main outlet and an auxiliary outlet so that the heat transfer fluid from the auxiliary outlet has a temperature lower than that of the main outlet, said auxiliary outlet being connected to a bypass line capable of cooling the electric motor .

 Cooling can be carried out in series, the heat transfer fluid passing through the bypass pipe then passing into the heat engine, which is preferable in the event of a high temperature at the outlet of the heat exchange means.

 Advantageously, the flow of heat transfer fluid in the bypass line is varied as a function of the temperature at the outlet of the heat exchange means.

 In one embodiment of the invention, if the temperature of the heat transfer fluid is insufficient to cause the opening of a thermostat disposed at the outlet of the heat engine, the heat transfer fluid is circulated in the bypass line connected thirdly to the inlet of the heat exchange means, for cooling the electric motor in the absence of circulation of heat transfer fluid in the heat engine. This operating mode can also be adopted when the engine is stopped.

 In one embodiment of the invention, in the event of a temperature of the heat transfer fluid significantly lower than the opening temperature of a thermostat disposed at the outlet of the heat engine, the heat transfer fluid is circulated in the connected bypass pipe of fourth leaves at the outlet of the heat engine upstream of the thermostat, to cool the electric motor while warming up the heat engine. It is thus possible to obtain a faster rise in temperature of the heat engine when it starts and to reduce the formation of polluting elements.

 This operating mode can also be adopted when the

<Desc / Clms Page number 6>

 engine is stopped, if the pump associated with the engine is electrically driven or if said pump can be bypassed. It is thus possible to preheat the heat engine.

- la figure 2 est une vue schématique d'un radiateur ; - les figures 3 à 8 sont des vues schématiques d'un système de refroidissement selon d'autres modes de réalisation de l'invention ; et - la figure 9 est une vue schématique d'un autre radiateur. The invention will be better understood and other advantages will appear on reading the detailed description of some embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which: - Figure 1 is a schematic view a cooling system according to an embodiment of the invention;

- Figure 2 is a schematic view of a radiator; - Figures 3 to 8 are schematic views of a cooling system according to other embodiments of the invention; and - Figure 9 is a schematic view of another radiator.

électrique, et le terme"électronique de puissance"définit l'ensemble des électroniques qui convertissent du courant alternatif en courant continu, du courant continu en courant alternatif, du courant de haute tension en courant de faible tension, ou encore du courant de faible tension en courant de haute tension. To simplify our description, the term "electric motor" defines all the machines which convert electrical energy into mechanical energy, or mechanical energy into energy

electric, and the term "power electronics" defines all the electronics that convert alternating current into direct current, direct current into alternating current, high voltage current into low voltage current, or even low voltage current in high voltage current.

 As can be seen in FIG. 1, the cooling system is associated with a heat engine 1 and an electric motor 2 provided with an electronic power unit 3. There is also provided a heating radiator 4 making it possible to heat the passenger compartment of the vehicle in which the cooling system is installed, as well as an exchanger 5 making it possible to cool any fluid, for example lubricating oil, gearbox oil, etc. or any organ, for example a turbocharger bearing, ...

 The cooling system comprises a radiator 6, a main outlet 6a of which is connected to a pipe 7 and the inlet of which is connected to a pipe 8. The pipe 7 is connected to a pump 9, the outlet of which is connected to the heat engine 1. Pump 9 can be driven

<Desc / Clms Page number 7>

 by the heat engine 1 or by an electric motor which is dedicated to it and which has not been shown. The output of the motor 1 is provided with a thermostat 10, itself connected to the pipe 8. The radiator 6 is generally provided with a motorized fan II, capable of accelerating the flow of air through said radiator 6 .

 The cooling system comprises a temperature sensor 12 disposed at the outlet of the engine 1, immediately upstream of the thermostat 10, a temperature sensor 13 mounted on the pipe 7 at the outlet of the radiator 6, and a control unit 14 receiving information temperature from the sensors 12 and 13. The connection between the control unit 14 and the sensors 12 and 13 can be carried out by dedicated electrical wires or via a communication bus.

 The input of the heating radiator 4 is connected to an output of the heat engine 1 and the output of the radiator 4 is connected to the pipe 7. Likewise, the input of the exchanger 5 is connected to an output of the heat engine 1 and its output is connected to line 7.

 The cooling system further comprises a bypass line referenced 15 as a whole and provided with several branches, and a multi-way valve 16 to which said branches are connected.

 More specifically, a first branch 17 is connected, on the one hand to an auxiliary output 6b of the radiator 6 and, on the other hand to the multi-way valve 16. The branch 17 passes through the electric motor 2 and through the unit of power 3. The circulation of the coolant in said branch 17 makes it possible to maintain the electric motor 2 and the power unit 3 at a normal operating temperature, if possible sufficiently low so that common industrial components, both electric and electronic, can be used in the construction of these elements.

 There is also an electric pump 21 arranged on the branch 7, controlled by the control unit 14 and circulating the cooling fluid in said branch 17. A second branch 18 is connected at one end to the first pipe 7 to near pump 9 and at the opposite end to the multi-valve

<Desc / Clms Page number 8>

 tracks 16.

A third branch 19 is connected, on the one hand to the pipe
8 and, on the other hand to the multi-way valve 16. A fourth branch 20 is connected, on the one hand to an output of the heat engine 1 upstream of the thermostat 10 and, on the other hand to the multi-way valve 16. The multi-way valve 16 is able to connect the branches 17 and
18 by closing off the branches 19 and 20, putting the branches 17 and 19 into communication by closing the other branches and putting the branches 17 and 20 into communication by closing the other branches, on the order of the control unit 14 to which it is linked.

In other words, the multi-way valve 16, which is here four-way, has the function of ensuring the selective passage of the cooling fluid between the branch 17 and one of the three other branches
18,19 or 20.

 In addition, the bypass line 15 comprises a fifth branch 22 and a 3-way valve 23. The valve 23 is mounted on the branch 17 near the outlet 6b of the radiator 6, in other words between the outlet 6b and the pump 21. The fifth branch 22 is connected, on the one hand to the valve 23 and, on the other hand to the pipe 7 downstream of the temperature sensor 13.

 The structure of the radiator 6 is illustrated in more detail in FIG. 2. The radiator 6 comprises a plurality of parallel pipes and two water boxes 24 and 25 into which the ends of the pipes open. The water box 24 is divided into an upstream part 24a and a downstream part 24b by a partition 26 forming a sealed separation. The upstream part 24a is connected to an input 27 of the radiator 6. The downstream part 24b is connected to the main output 6a.

 The water box 25 is divided into an upstream part 25a and a downstream part 25b by a partition 28 forming a watertight separation. The upstream part 25a connects pipes connected to the upstream part 24a and pipes connected to the downstream part 24b. The radiator 6 is said to have a U-shaped circulation, the upstream part 25a forming the bottom of the U. The downstream part 25b is connected to the auxiliary output 6b. The downstream part 24b connects pipes connected to the upstream part 25a and pipes connected to the downstream part 25b.

<Desc / Clms Page number 9>

 The cooling fluid performs, by passing through the radiator 6, a first pass from the upstream part 24a of the water box 24 to the upstream part 25a of the water box 25, then a second pass from the upstream part 25a of the box 25 to the downstream part 24b of the water box 24 and is divided into two flows, one passing through the main outlet 6a, the other making a third pass from the downstream part 24b of the water box 24 to the downstream part 25b of the water box 25. Said other flow takes advantage of a longer heat exchange and leaves the radiator 6 at a temperature lower than that of the flow passing through the main outlet 6a. In some cases one of the flows may be zero.

It is therefore possible to maintain the electric motor 2 and the power unit 3 at a low temperature allowing the use of large-scale industrial components at low cost.

 The operation of the cooling system is as follows.

 1) Heat engine 1 running.

généralement comprise entre 83 et 89OC, la vanne multi-voies 16 met en communication les branches 17 et 20 et permet de laisser passer le fluide de la branche 20 vers la branche 17. La pompe 21 est à l'arrêt. If the water temperature as measured by the sensor 12 is less than a predetermined temperature Tel and which is less than or equal to the total opening temperature of the thermostat 10,

generally between 83 and 89OC, the multi-way valve 16 puts branches 17 and 20 into communication and allows the fluid to pass from branch 20 to branch 17. The pump 21 is stopped.

The cooling fluid which is in the heat engine 1 is subjected to a high pressure due to the pump 9, pressure higher than that prevailing in the branch 17. The valve 23 puts the branches 17 and 22 in communication and allows to leave pass the fluid from branch 17 to branch 22. The valve 23 cuts the outlet 6b.

 In this state, which is that of an operation at the start of the heat engine 1 or at very low load, no energy is consumed by the pump 21 which is stopped. The heat released by the operation of the electric motor 2 and of the power unit 3 makes it possible to increase the temperature of the heat engine 1 and therefore to reduce the duration of its rise in temperature, which results in the reduction of the quantity of pollutants generated by the

<Desc / Clms Page number 10>

 combustion of the heat engine 1. Keeping the pump 21 stopped reduces its operating time and therefore allows a longer overall service life.

 If the sensor 12 indicates a water temperature greater than or equal to the temperature Tel but lower than the total opening temperature of the thermostat 10, the multi-way valve 16 connects the branches 17 and 19. The pump 21 is put on running at low speed, for example with a low supply voltage Ul.

The valve 16 is maintained as before or on the contrary cuts the branch 22 and opens the outlet 6b. The electric motor 2 and its power unit 3 are then cooled by means of the radiator 6, the heat exchange capacity of which is much greater, for example by a factor of the order of 3 to 5, than the heat capable of be released by the electric motor 2 and its power unit 3. The pipe 8, the radiator 6 and the pipe 7 being dimensioned for the high flow rates of coolant required by the heat engine 1, the pressure drops are low. The energy consumed by the pump 21 is therefore also low. Its wear is also.

 If the sensor 12 indicates a water temperature greater than or equal to the temperature Tot, the multi-way valve 16 communicates the branches 17 and 18. The pump 21 is started. The valve 23 cuts the branch 22 and opens the outlet 6b.

 In other words, the flow rate of the output 6b of the radiator 6 passes through the branches 17 and 18. The electric motor 2 and its power unit 3 are cooled by coolant at low temperature.

 In addition, it can be provided that if the temperature sensor 13 at the outlet of the radiator 6 indicates a coolant temperature below a predetermined temperature T the pump 21 operates at low flow rate, for example with the low supply voltage U and on the other hand if the sensor 13 indicates a temperature higher than the temperature T the pump 21 operates at high flow rate, for example supplied by a voltage U2 greater than U, to obtain a higher flow rate in the branch 17. It will be understood that Te2 is greater than Tot.

<Desc / Clms Page number 11>

 Of course, the control unit 14 of the cooling system can control the operation of the fan II as a function of the temperature measured by the sensor 13.

 2) Heat engine 1 stopped, fully electric vehicle.

 If the water temperature measured by the sensor 12 is lower than the temperature, the multi-way valve 16 puts branches 17 and 20 into communication and allows the fluid to pass from branch 17 to branch 20. The valve 23 connects the branches 17 and 22 and allows the fluid to pass from the branch 22 to the branch 17. The valve 23 cuts the outlet 6b. The pump 21 is started at low flow rate, for example supplied by the voltage U. It is thus possible to heat the heat engine 1 and, if necessary, the passenger compartment by the radiator 4.

 If the temperature of the water measured by the sensor 12 is greater than the temperature, the multi-way valve 16 puts branches 17 and 19 into communication and allows the fluid to pass from branch 17 to branch 19. The valve 23 cuts the branch 22 and opens the outlet 6b. The pump 21 is started at low flow rate, for example supplied by the voltage U This mode allows excellent cooling of the electric motor 2 and of the power unit 3 because the cooling fluid passes through all of the radiator 6 (three passes ).

 An intermediate cooling performance can also be obtained by passing water only through the third pass of the radiator 6 using the multi-way valve 16 which connects the branches 17 and 19. This intermediate configuration can be advantageous for reduce the possible oscillation of the water temperature during the transition from the temperature rise and heating phase to the super cooling phase described above.

 If the sensor 13 indicates a temperature higher than the temperature T 2, the fan 11 is started up, however, this will only rarely happen, resulting in a reduction in the operating time of said fan II and a reduction in the consumption d 'energy.

<Desc / Clms Page number 12>

 3) Electric motor 2 stopped, without the need to cool electronic components.

 The pump 21 can be started to pass cooling fluid into the third pass and thus provide additional cooling of the heat engine. The valve 16 puts the branches 17 and 18 into communication. The valve 23 puts the branch 17 into communication with the outlet 6 b and closes the branch 22.

 As a variant, provision may be made to keep the pump 21 stopped and to communicate the branch 22 with the outlet 6b and while closing the branch 17 by means of the valve 16.

 Thus, the water temperature at the inlet of the electric motor 2 and of the electronic power unit 3 remains very low in all operating cases. For cases where the temperature measured by the sensor 13 is greater than T 2, an increase in the flow rate of the pump 21 and / or the triggering of the fan 11 makes it possible to maintain this temperature within the desired limits.

 Thanks to the invention, the pump 21 needs a low power, runs slower and less frequently. In an operating case, the pump 21 is stopped. In two other operating cases where the thermostat is closed, the heat exchange capacity of the radiator 6, dimensioned for the heat losses of the heat engine 1, is largely in excess of the heat losses of the electric motor 2 and of the electronic unit. of power 3 and therefore allows the pump 21 to operate at low flow rate. Finally, the branches 17, 18 and 19 are connected to pipes 7 and 8 of large diameter, which minimizes the pressure drop undergone by the fluid entrained by the pump 21.

 It has been assumed above that the pump 21 was driven by an independent electric motor. It is also conceivable that the pump 21 is driven by the electric traction motor 2. This is advantageous for the cost and the service life of the system. Indeed, a conventional electric pump is generally direct current. Compared to a mechanical pump, the electric motor is the main additional cost of an electric pump and generally has a lifetime

<Desc / Clms Page number 13>

 significantly lower than that of the mechanical pump. The operation of the system is then as follows.

If the water temperature measured by sensor 12 is lower than the Tot opening temperature of the thermostat, the branches
17 and 19 are connected. If the water temperature measured by the sensor 12 is greater than or equal to the Tot temperature, and if the vehicle is in electric traction mode, thermal engine
1 when stopped, the fluid communication between the branches 17 and 19 is maintained. If the coolant temperature measured by the sensor 12 becomes greater than or equal to the Top temperature and if the heat engine is in operation, the valve 16 connects the branches 17 and 18. In addition, if the sensor 13 measures a temperature higher than the predetermined temperature Te2 'the fan 11 is put into action, in particular if the vehicle speed is low, for example less than a value between 60 and 80 km / h.

 In FIG. 3, a variant is illustrated in which the electric motor 2 and the electronic power unit 3 are cooled in parallel, the branch 17 dividing into a sub-branch 17a passing through the electric motor 2 and into a sub- branch 17b passing through the electronic power unit 3.

 In FIG. 4, a variant is illustrated in which the valve 23 and the branch 22 are eliminated. The branch 17 is permanently in communication with the output 6b. This economic variant is advantageous if the heating of the heat engine 1 is not a priority.

 In FIG. 5, a variant close to the previous one is illustrated except that the branch 20 is deleted. The valve 16 is three-way. This economic variant is advantageous if the heating of the heat engine 1 is not a priority and if the life of the pump 21 is not critical, for example if the pump 21 is driven by the electric motor 2.

 In FIG. 6, a variant close to that of FIG. 1 is illustrated. The radiator 6 is of the two pass type with a water box 24 devoid of a partition. The coolant performs a

<Desc / Clms Page number 14>

 passes between entrance 27 and exit 6a.

 In FIG. 7, a variant close to that of FIG. 5 is illustrated except that the branch 19 and the valve 16 are eliminated. When the thermostat 10 is closed with the pump 21 running and for certain speeds of the heat engine 1, the cooling fluid coming from the radiator 4 and from the exchanger 5 can enter via the outlet 6a of the radiator 6, make a pass, and exit by exit 6b. The cooling fluid coming from the branch 18 can pass through the pump 9 and the heat engine 1.

 In FIG. 8, a variant close to that of FIG. 7 is illustrated except that the branch 18 is connected to the pipe 7 closer to the outlet 6a, in other words between the sensor 13 and the branch towards the exchanger 5.

 FIG. 9 shows a variant of a radiator close to that of FIG. 2, except that the water box 24 is divided into three upstream parts 24a, central 24b, and downstream 24c by partitions 26 and 29. The downstream part 24c is connected to the auxiliary output 6b. The downstream part 25b of the water box 25 connects the pipes connected to the central part 24b and the pipes connected to the downstream part 24c. The radiator 6 is said to have four passes with circulation in double U. An even lower temperature at the auxiliary output 6b is obtained.

 The main output 6a can be provided for current operation around 90 to 105 ° C., temperature desired for the heat engine, without risk of overconsumption of fuel linked to a temperature that is too low. The auxiliary output 6b can provide for current operation at a significantly lower temperature, allowing good efficiency of the electric motor and the electronic power unit and their construction from inexpensive standard components.

Claims (12)

1. Cooling device (6) of a heat transfer fluid by heat exchange with another fluid, comprising an inlet (27) and an outlet (6a) of heat transfer fluid, characterized in that it comprises an auxiliary outlet (6b ) so that the heat transfer fluid from the auxiliary outlet is at a temperature lower than that of the main outlet.  2. Device according to claim 1, characterized in that it comprises a first portion arranged between the inlet and the main outlet and a second portion disposed between the inlet and the auxiliary outlet, the two portions being integrated into a body of radiator.  3. Device according to claim 1 or 2, characterized in that the main outlet and the auxiliary outlet are arranged at opposite ends of the device.  4. Device according to claim 1 or 2, characterized in that the main output and the auxiliary output are arranged at the same end of the device.  5. Cooling system for a hybrid propulsion vehicle comprising a heat engine (1) and at least one electric motor (2), of the type comprising a heat transfer fluid capable of cooling the heat and electric motors, a radiator (6) capable of cooling the heat transfer fluid by heat exchange with an air stream and comprising a plurality of cooling channels, an inlet and an outlet, a first pipe (7) between the outlet of the radiator and the heat engine and a second pipe (8) between said heat engine and the radiator inlet, characterized in that the radiator (6) comprises an auxiliary outlet (6b) so that the heat transfer fluid from the auxiliary outlet is at a temperature lower than that of the main outlet (6a) connected to the first pipe, said auxiliary outlet being connected to a bypass pipe (15) capable of cooling the electric motor.  6. System according to claim 5, characterized in that <Desc / Clms Page number 16>  that the bypass pipe comprises a first branch (17) connected to the auxiliary output and a second branch (18) connected to a pipe upstream of the engine.  7. System according to claim 5 or 6, characterized in that the first branch (17) is adapted to be connected to the first pipe (7).  8. System according to any one of claims 5 to 7, characterized in that the bypass pipe comprises a third branch (19) connected to the second pipe.  9. System according to any one of claims 5 to 8, characterized in that the bypass pipe comprises a fourth branch (20) connected to the outlet of the heat engine upstream of a thermostat (10).  10. System according to any one of claims 5 to 9, characterized in that the branches of the bypass pipe are connected to each other by a multi-way valve (16).  11. Vehicle comprising a system according to any one of claims 5 to 10.  12. Cooling method for a hybrid propulsion vehicle comprising a heat engine, and at least one electric motor, cooled by the circulation of a heat transfer fluid in said engines, a heat exchange means capable of cooling the heat transfer fluid by heat exchange with another fluid and provided with an inlet and an outlet, in which the heat transfer fluid flow is divided in the heat exchange means between a main outlet and an auxiliary outlet so that the heat transfer fluid from the auxiliary output has a temperature lower than that of the main output, said auxiliary output being connected to a bypass line capable of cooling the electric motor.