WO2015057129A1

WO2015057129A1 - Cooling system in a vehicle

Info

Publication number: WO2015057129A1
Application number: PCT/SE2014/051110
Authority: WO
Inventors: Zoltan Kardos; Mats EKMAN; Mattias STRINDLUND
Original assignee: Scania Cv Ab
Priority date: 2013-10-18
Filing date: 2014-09-26
Publication date: 2015-04-23
Also published as: SE538343C2; SE1351244A1; DE112014004338T5

Abstract

The present invention concerns a cooling system in a vehicle, whereby the cooling system comprises a first section of line (19) that comprises a first cooler (19b) and a first thermostat (15) that is adapted to regulate the flow of cooling fluid through the first cooler (19b), a second section of line (20) that is adapted to lead cooling fluid to a first zone (la) of the combustion engine, and a third section of line (21) that is adapted to lead cooling fluid to a second zone (lb) of the combustion engine (1) in which second zone a lower temperature is prevalent than the temperature in the first zone (1a) during operation of the combustion engine (1). The second section of line (20) comprises a second cooler (20b) that has the capacity to cool the cooling fluid to a temperature that is lower than the temperature in the first cooler (19b), and a second thermostat (16) that is adapted to regulate the flow of cooling fluid through the second cooler (20b).

Description

Cooling system in a vehicle

BACKGROUND AND PRIOR ART The present invention relates to a cooling system in a vehicle according to the preamble to claim 1.

Heat energy is created during combustion processes in the cylinders of a combustion engine that heats adjacent regions of the cylinder block and cylinder head. The regions that are located closer to the combustion chamber reach in general a higher temperature than the regions that are located at a greater distance from the combustion chamber. In this way, hotter and colder zones arise in the cylinder block and cylinder head of a combustion engine during the operation of a combustion engine. In operating conditions in which the combustion engine is placed under a heavy load for a long period, the hotter zones of the cylinder block and cylinder head can achieve a very high temperature.

Conventional cooling systems for the cooling of combustion engines circulate cooling fluid that can have a temperature within the range 80-90°C during normal operation. Since the cooling fluid circulates through the cooling channels combustion engine, all cooled zones in the combustion engine will receive a cooling effect from the cooling fluid of essentially the same temperature. In operating conditions in which the combustion engine is placed under a heavy load, the cooling may be inadequate in the hottest zones of the cylinder block and cylinder head.

DE 102011117102 reveals a cooling system with a circulating cooling fluid that can cool the crankcase and cylinder head of a combustion engine. The cooling system consists of a high-temperature cooling circuit and a low-temperature cooling circuit. Cooling fluid can be transferred between the two cooling circuits with the aid of valves. The temperature of the cooling fluid in the cooling circuits can in this way be varied. Cooling fluid from the low-temperature cooling circuit can be led through a lower warmer section of the cylinder head of the combustion engine, and cooling fluid from the high-temperature cooling circuit can be led through an upper cooler section of the cylinder head. The lower warmer section of the cylinder head can in this way be cooled with cooling fluid that has a lower temperature than the cooling fluid that cools

RECORD COPY TRANSLATION

(Rule 12.4) the upper cooler section of the cylinder head. It is complicated to control this cooling system, and it contains valves and other components that are expensive to obtain.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a cooling system that is simple to control and that has relatively few components that can be obtained for a relatively low cost, at the same time that it is able to cool in a reliable manner different zones in a combustion engine with cooling fluid at different temperatures.

This purpose is achieved with the cooling system described in the introduction, and that is characterised by the distinctive features that are specified in the characterising part of the patent claim. Thus, the cooling system comprises a first section of line with a cooler and a first thermostat that regulates the supply of cooling fluid to the cooler, depending on the temperature of the cooling fluid. The first section of line has a design that corresponds to that of a conventional cooling system. The cooling system comprises further a second section of line that leads cooling fluid through at least a first zone of the combustion engine, and a third section of line that leads cooling fluid through a second zone of the combustion engine, which cooling fluid is heated to a lower temperature than the cooling fluid in the first zone during the operation of the combustion engine. The second section of line comprises a second cooler that has the capacity to cool cooling fluid to a lower temperature than the temperature in the first cooler, and a second thermostat that regulates the supply of cooling fluid to the second cooler depending on the temperature of the cooling fluid.

The temperature of the cooling fluid in the cooling system is related to the temperature of the combustion engine. When the cooling fluid has a low temperature in the cooling system, also the combustion engine has a low temperature. Under operating conditions in which the temperature of the cooling fluid is low, the warmer first zone of the combustion engine has a first warmer zone that has a temperature of an acceptable magnitude. The second thermostat is dimensioned such that it opens at a cooling fluid temperature that corresponds to a temperature in the hotter first zone of the combustion engine when extra cooling is required. Under such operating conditions, the second thermostat opens and cooling fluid is led through the second cooler, which has in this way the capacity to cool the cooling fluid to a lower temperature than the temperature in the first cooler. Cooling fluid can in this way be led to the first zone of the combustion engine, at a lower temperature than the temperature of the cooling fluid that is led to the second zone of the combustion engine. In this way, efficient cooling of the first zone of the combustion engine is obtained that ensures that the temperature in the first zone does not rise to a level that is too high.

According to one embodiment of the present invention, the second section of line comprises a bypass line and that the second thermostat is adapted to lead cooling fluid past the second cooler through the bypass line when the cooling fluid has a lower temperature than the regulation temperature of the second thermostat. Such a second section of line may have an inlet line that leads the cooling fluid to the second cooler and an outlet line that leads the cooling fluid from the cooler to the combustion engine. The bypass line extends in this case between the inlet line and the outlet line. The second thermostat is arranged in the inlet line in connection with the bypass line, where it may lead the cooling fluid through the bypass line or through the cooler, depending on the temperature of the cooling fluid in the second section of line.

According to one embodiment of the present invention, the second section of line and the third section of line receive cooling fluid in a line in the cooling system that is located essentially immediately downstream of the cooling fluid pump. The cooling fluid has a maximum pressure in this line, and the existing cooling fluid pump can therefore be used to circulate cooling fluid through both the second section of line and the third section of line.

According to one embodiment of the present invention, the second section of line comprises at least two cooling channels arranged parallel to each other that extend through first zones of the combustion engine. The cylinder head and the cylinder block of the combustion engine each comprise at least one hot first zone, and these first hot zones are located at a distance from each other. It is appropriate here to arrange a cooling channel through the relevant first zones in order for acceptable cooling to be obtained in the two first zones.

According to one embodiment of the present invention, the third section of line comprises at least two cooling channels arranged parallel to each other that extend through second zones of the combustion engine. The cylinder head and the cylinder block of the combustion engine each comprise at least one second zone, and these second zones are located at a distance from each other. It is appropriate also in this case to arrange a cooling channel through the relevant second zones, which are located at a distance from each other, in order for acceptable cooling to be obtained.

According to one embodiment of the present invention, the cooling system comprises a third thermostat that prevents cooling fluid being led through the third section of line to the second zone of the combustion engine when the cooling fluid has a lower temperature than the regulation temperature of the third thermostat, and that allows cooling fluid to be led through the third section of line to the second zone of the combustion engine when the cooling fluid has a higher temperature than the regulation temperature of the third thermostat. In this case, the colder second zone undergoes no initial cooling after a cold start as long as the cooling fluid has a lower temperature than the regulation temperature of the third thermostat. The combustion engine can in this way undergo more rapid heating after a cold start. The regulation temperature of the third thermostat defines thus when it is appropriate to start to cool the colder second zones of the combustion engine. The first zones are cooled from the start of the engine, by cooling fluid from the second section of line.

According to one embodiment of the present invention, the thermostats are of the type that comprises a wax body that changes phase at the regulation temperature. The wax body changes phase from a solid to a liquid at the regulation temperature. The volume of the wax body thus changes, which change is used to open or close a valve at the thermostat. Such thermostats are very cheap to purchase and at the same time function very reliably. At least one of the thermostats may have a regulation temperature that can be varied. It may be desirable under certain operating conditions to regulate the opening temperature of the thermostat. The thermostats mentioned above may in this case be provided with an electrical heating unit, with which the regulation temperature of the wax body can be varied.

According to one embodiment of the present invention, is, the cooling system comprises a fourth section of line in which the cooling fluid is used for the cooling of a component or a medium in the vehicle. The cooling system that cools a combustion engine is also advantageously used for the cooling of other components and media in the vehicle. The fourth section of line can in this case comprise a cooler that cools a medium. The cooler may be an EGR cooler for the cooling of recirculating exhaust gases, an intercooler for the cooling of charge air, a cooler for the cooling of engine oil, a cooler for the cooling of gearbox oil, etc. The cooling fluid can be used also for the cooling of components, such as electrical control units, in the vehicle.

According to one embodiment of the present invention, comprise the fourth section of line receives cooling fluid from a line in the cooling system that is located essentially immediately downstream of the cooling fluid pump. The existing cooling fluid pump can in this way be used also to circulate cooling fluid through the fourth section of line. An additional cooling fluid pump is not required in this case, either. BRIEF DESCRIPTION OF THE DRAWING

One preferred embodiment of the invention will be described below as an example, with reference to the attached drawing, of which: Figure 1 shows a cooling system in a vehicle according to one embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Figure 1 shows a combustion engine 1 that is arranged in a vehicle 2, shown schematically. The combustion engine 1 may be a diesel engine and the vehicle a heavy vehicle. The combustion engine 1 comprises an exhaust gas line 3 that is provided with a turbine 4 at a turbocharger unit. A return line 5 for the recirculation of exhaust gases leads a fraction of the exhaust gases back from the exhaust gas line 3 to the combustion engine 1. The return line 5 comprises an EGR valve 7 with which it is possible to regulate the flow of exhaust gases in the return line 5, and an EGR cooler 6 for the cooling of the recirculating exhaust gases. The vehicle 2 comprises an air line 8 that leads air to the combustion engine 1. A compressor 9 draws in air by suction and compresses it in the air line 8. The compressed air is led to an intercooler 11 that is arranged at a front part of the vehicle 2. A cooling fan 10 draws a cooling flow of air of the surrounding air through the intercooler 11 by suction. After the charge air has been cooled in the intercooler 11, it is mixed with the recirculating exhaust gases in the return line 5, after which the mixture is led to the cylinders 12 of the combustion engine. The combustion engine 1 is cooled by a cooling system with a circulating cooling fluid. The cooling fluid is circulated in the cooling system with the aid of a cooling fluid pump 13. The cooling fluid pump 13 may be driven in conventional manner by the combustion engine 1 using a suitable transmission, not shown in the drawings. The cooling system comprises an inlet line 13a that leads cooling fluid to the cooling fluid pump 13 and an outlet line 13b that receives cooling fluid from the cooling fluid pump 13. The cooling system comprises an expansion tank 14 for the filling of cooling fluid in the cooling system and to ensure the required pressure in the system when the cooling fluid becomes hot and expands. The expansion tank 14 is united with the inlet line 13a of the cooling fluid pump through what is known as a "static line" 14a. The required pressure in the inlet line 13a to the suction side of the cooling fluid pump 13 is in this way created, such that cavitation is prevented. The cooling system comprises a first thermostat 15 that regulates the flow of cooling fluid through a first section of line 19 at the cooling system, a second thermostat 16 that regulates the flow of cooling fluid through a second section of line 20 at the cooling system, and a third thermostat 17 that regulates the flow of cooling fluid through a third section of line 21 at the cooling system. It is an advantage if the thermostats are of the type that contains a wax body that undergoes a phase transformation at the regulation temperature. Such thermostats are very cheap to purchase and at the same time function very reliably. They can also be equipped with an electrical heating unit with which the regulation temperature can be regulated under different operating conditions.

The first thermostat 15 receives cooling fluid in a return line 18 from the combustion engine 1. The first thermostat 15 opens when the temperature of the cooling fluid in the return line 18 exceeds the regulation temperature Ti of the first thermostat 15. When the cooling fluid in the return line 18 has a lower temperature than the first regulation temperature Ti, it leads the cooling fluid to the inlet line 13a of the cooling fluid pump without cooling. When the cooling fluid in the return line 18 has a higher temperature than the first regulation temperature T_1; the first thermostat 15 opens and cooling fluid is led through the first circuit 19. The first circuit comprises an inlet line 19a that receives cooling fluid from the return line 18 and leads it to a first cooler 19b that is arranged at the front part of the vehicle in a position downstream of the intercooler 11, with respect to the direction of the cooling flow of air through the intercooler 11. The cooling fluid in the first cooler 19b is cooled in this case by the same flow of air that has first passed through the intercooler 11. The air that flows through the first cooler 19b has as a consequence of this a higher temperature than that of the surrounding air. The first section of line 19 comprises an outlet line 19c that leads the cooling fluid from the first cooler 19b to the inlet line 19b of the cooling fluid pump. The second thermostat 16 is arranged in a second section of line 20. The second section of line 20 comprises an inlet line 20a that receives cooling fluid from the outlet line 13b of the cooling fluid pump. The inlet line 20a is connected at an opposing end to a second cooler 20b. The second cooler 20b is arranged at the front part of the vehicle in a position that is at the same height as the intercooler 11. It may be arranged, as an alternative, in front of the intercooler 11. The cooling fluid also in this case is cooled by a cooling flow of air that is led through the second cooler 20b with the aid of the cooling fan 10. The air that is led through the second cooler 20b has, however, the temperature of the surroundings, and thus a lower temperature than that of the air that is led through the first cooler 19b. The second section of line 20 comprises an outlet line 20c that leads cooling fluid from the second cooler 20b to two cooling channels 20d that are arranged parallel and that extend through first zones la of the combustion engine that requires a very high cooling effect. The first zones la constitute regions of the cylinder block and cylinder head combustion engine that attain a high temperature during operation. The second thermostat 16 is arranged in the inlet line 20a. The second thermostat has a second regulation temperature T₂. When the cooling fluid in the inlet line 20a has a lower temperature than the second regulation temperature T₂, the second thermostat 16 will lead cooling fluid, through a bypass line 20e, from the inlet line 20a to the outlet line 20c without it being cooled in the second cooler 20b. When the cooling fluid in the inlet line 20a has a higher temperature than the second regulation temperature T₂, the second thermostat 16 will lead cooling fluid to the second cooler 20b for cooling, before it is led onwards to the cooling channels 20d that extend through the combustion engine 1.

The third section of line 21 comprises an inlet line 21a that leads cooling fluid from the outlet line 13b of the cooling fluid pump to the third thermostat 21. The third section of line 21 comprises two parallel outlet lines 21b that lead cooling fluid from the third thermostat 17 when it is open to two cooling channels 21c that are arranged parallel to each other and that each extend through a second zone lb of the combustion engine. The second zones lb comprise regions of the cylinder block and cylinder head of the combustion engine that do not attain the same high temperature during operation as the temperature in the first zones la. The third thermostat 17 determines the temperature of the cooling fluid in an outlet line 13b from the cooling fluid pump. The third thermostat 17 opens when the cooling fluid has a temperature that is higher than a third regulation temperature T₃. The cooling system comprises also a fourth circuit 22 that receives cooling fluid from the outlet line 13b of the cooling fluid pump. The circuit 22 comprises an inlet line 22a that receives cooling fluid and leads it to the EGR cooler 6. The fourth circuit 22 comprises a return line 22b that leads cooling fluid back from the EGR cooler 6 to the inlet line 13a of the cooling fluid pump.

After a cold start of the combustion engine 1 the cooling fluid pump 13 starts the circulation of cooling fluid in the cooling system. The cooling fluid initially has the temperature of the surroundings, which may be very low in the winter. The inlet line 20a at the second circuit 20 receives cooling fluid continuously from the outlet line 13b of the cooling fluid pump. The second thermostat 16 determines the temperature of the cooling fluid in the inlet line 20a. The cooling fluid has, at least initially, a temperature that is lower that the regulation temperature T₂ of the second thermostat. Thus the second thermostat 16 leads cooling fluid, through the bypass line 20e, to the outlet line 20c without it being cooled in the second cooler 20b. The cooling fluid is subsequently led through the cooling channels 20d that extend through first zones la of the combustion engine. The cooling fluid provides cooling of the cylinder block and cylinder head in the first zones. After the cooling fluid has passed through the combustion engine 1, it is collected in the return line 18 and is led towards the first thermostat 15 that controls the flow of cooling fluid in the first section of line 19. The third thermostat 17 determines the temperature of the cooling fluid in the outlet line 13b of the cooling fluid pump. The cooling fluid has, at least initially after a cold start, a temperature that is lower that the regulation temperature T₃ of the third thermostat. The third thermostat 17 thus prevents cooling fluid being led through the cooling channels 21b that extend through one the second zones lb of the combustion engine. Thus, no cooling of the second zones lb of the combustion engine 1 takes place during this phase. The combustion engine 1 in this way undergoes a more rapid heating.

The return line 18 receives cooling fluid that has circulated through the cooling channels 20d through the second circuit 20. The first thermostat 15 determines the temperature of the cooling fluid in the return line 18. The cooling fluid during this phase has a significantly lower temperature than the regulation temperature Ti of the first thermostat 15. The first thermostat 15 thus leads the cooling fluid to the inlet line 13a of the cooling fluid pump without it being cooled in the first cooler 19b. The fourth circuit 22 receives cooling fluid continuously from the outlet line 13b of the cooling fluid pump. This cooling fluid is led to the EGR cooler 6 where it cools the recirculating exhaust gases in the return line 5. The cooling fluid is subsequently led to the inlet line 13a of the cooling fluid pump for repeated circulation in the cooling system. During the initial phase after a cold start that is described above, cooling fluid acquires heat from the first zones la of the combustion engine and from the recirculating exhaust gases in the EGR cooler 6. The cooling fluid does not provide cooling in either the first cooler 19b or the second cooler 20b. The cooling fluid in the cooling system thus acquires a rapidly rising temperature.

The temperature of the cooling fluid reaches the regulation temperature T₃ of the third thermostat 17 relatively soon after a cold start. The third thermostat 17 opens, and a flow of cooling fluid through the inlet line 21a is established. The third thermostat 17 now leads cooling fluid, through the two outlet lines 21b, to the cooling channels 21c that extend through second zones lb of the combustion engine. The cooling fluid in the inlet line 20a of the second circuit still has, however, a temperature that is lower than the regulation temperature T₂ of the second thermostat 16. The second thermostat thus also in this phase leads cooling fluid, through the bypass line 20e, to the outlet line 20c without it being cooled in the second cooler 20b. The cooling fluid is subsequently led through the cooling channels 20d that extend through first zones la of the combustion engine. Cooling fluid that has passed through the cooling channels 20d, 21c of the combustion engine 1 is collected in the return line 18 and is led towards the first thermostat 15. The first thermostat 15 determines the temperature of the cooling fluid in the return line 18.

The cooling fluid has also during this phase a temperature that is lower than the regulation temperature Ti of the first thermostat 15. The first thermostat 15 thus leads the cooling fluid to the inlet line 13a of the cooling fluid pump without it being cooled in the first cooler 19b. The circulation of cooling fluid in the fourth circuit 22 is unchanged. Thus, cooling of the second zones of the combustion engine 1 will be added during this phase. The cooling fluid is thus supplied with heat energy from the first la and the second zones lb of the combustion engine and from the recirculating exhaust gases in the EGR cooler 6. The cooling fluid does not provide cooling in the cooling system, and the temperature of the cooling fluid continues to rise. As operation of the vehicle 2 continues, the cooling fluid eventually becomes heated to a temperature that is higher than the regulation temperature Ti of the first thermostat 15. The first thermostat 15 opens and leads cooling fluid through the first circuit 19. The cooling fluid is led, through the inlet line 19a, to the cooler 19b where the cooling fluid is cooled by air that is forced through the cooler 19b with the aid of the cooling fan 10 and vehicle headwind. The cooling fluid is subsequently led, through the outlet line 19c, to the inlet line 13a of the cooling fluid pump for repeated circulation in the cooling system. Thus the cooling fluid undergoes during this phase cooling in the cooler 19. The task of the cooler 19 is to cool the cooling fluid such that it can ensure, with the aid of the first thermostat 15, a stable operating temperature of the cooling fluid, at which temperature the combustion engine 1 achieves its optimal properties. The cooling power that the cooling fluid undergoes in the cooler corresponds here essentially to the heating power that the cooling fluid receives when it is heated by the combustion engine and the recirculating exhaust gases in the EGR cooler 6.

The load on the combustion engine, however, varies during operation and thus the heating power that is to be withdrawn in the first cooler 19b also varies. In operating conditions in which the combustion engine 1 is placed under heavy load, the first cooler 19b does not always have the capacity to withdraw the heating effect that the cooling fluid absorbs as it cools the combustion engine 1 and the recirculating exhaust gases in the EGR cooler 6. This results in the temperature of the cooling fluid in the return line 18 rising to a level that is higher than the regulation temperature Ti of the first thermostat. Since the first cooler 19b does not have the capacity to maintain the temperature of the cooling fluid at the desired operating temperature, the second thermostat 16 opens. The second thermostat 16 has a regulation temperature T3 that determines when the temperature of the cooling fluid after the cooling in the first cooler 19b is too high. When this occurs, the second thermostat 16 leads cooling fluid in the second section of line 20 to the second cooler 20b. In this way, cooling fluid that has already been cooled in the first cooler 19b is cooled in the second cooler 20b in a second stage, by air that has the temperature of the surroundings. It can in this way attain a temperature that is lower than that of the cooling fluid that is led through the third circuit 21 and through the second zones of the combustion engine 1. This relatively cold cooling fluid is led from the second cooler 20b, through the outlet line 20c, to the cooling channels 20d that extend through first zones la of the combustion engine. The first zones receive in this way efficient cooling. Thus, all cooling fluid is cooled in the first cooler 19b during this phase. That fraction of the cooling fluid that is led through the second section of line receives cooling also in a second step in the second cooler 20b to an even lower temperature than that of the cooling fluid that is cooled only in the first cooler 19b. Since also the second cooler 20b is used for cooling the cooling fluid, the cooling system provides an increased cooling capacity. At the same time, the extra cooling power that is provided can be provided at the regions in which cooling is most needed, namely the hot first zones la of the combustion engine 1. The risk that the temperature in the first zones la of the combustion engine 1 will become unacceptably high if the combustion engine 1 is placed under a very high load for a long period is in this way essentially eliminated. A further advantage of the cooling system is that it requires only one cooling fluid pump to circulate the cooling fluid in all sections of line 19, 20, 21, 22 of the cooling system. This can be achieved through the second circuit 20, the third circuit 21 and the fourth circuit 22 receiving cooling fluid from the outlet line 13b of the cooling fluid pump in inlet lines 20a, 21a, 22a that are arranged in parallel. A further advantage of the cooling system is that it is very simple to control. The thermostats 15, 16 and 17 provide a simple and efficient control of the cooling system. Thermostats are components that can be obtained at very low cost.

The invention is not in any way limited to the embodiment that has been described in the drawing: it can be freely varied within the scope of the patent claims.

Claims

1. A cooling system in a vehicle, whereby the cooling system comprises a cooling fluid pump (13) that is adapted to circulate cooling fluid in the cooling system, a first section of line (19) that comprises a first cooler (19b) and a first thermostat (15) that is adapted to lead the flow of cooling fluid through the first cooler (19b) when the cooling fluid has a temperature that is higher than the regulation temperature (T of the thermostat, and past the first cooler (19b) without cooling when the cooling fluid has a temperature that is lower than the regulation temperature (TO of the thermostat, a second section of line (20) that is adapted to lead the cooling fluid to a first zone (la) of the combustion engine, and a third section of line (21) that is adapted to lead cooling fluid to a second zone (lb) of the combustion engine (1) in which a lower temperature is prevalent than the temperature in the first zone (la) during operation of the combustion engine (1), characterised in that the second section of line (20) comprises a second cooler (20b) that has the capacity to cool the cooling fluid to a temperature lower than the temperature in the first cooler (19), and a second thermostat (16) that is adapted to lead the cooling fluid in the second section of line to the second cooler (20) when the cooling fluid has a temperature that is higher than the regulation temperature (T₂) of the second thermostat (16) and past the second cooler (20b) without cooling when the cooling fluid has a temperature that is lower than the regulation temperature (T₂) of the second thermostat (16).

2. The cooling system according to claim 1, characterised in that the second section of line comprises a bypass line (20e) and that the second thermostat (16) is adapted to lead the cooling fluid past the second cooler (20b), through the bypass line (20e), when the cooling fluid has a temperature that is lower than the regulation temperature (T₂) of the second thermostat.

3. The cooling system according to claim 1 or 2, characterised in that the second section of line (20) and the third section of line (21) receive cooling fluid from a line (13b) in the cooling system that is located essentially immediately downstream of the cooling fluid pump (13).

4. The cooling system according to any one of the preceding claims, characterised in that the second section of line (20) comprises at least two cooling channels (20d) arranged parallel to each other that extend through first zones of the combustion engine (1).

5. The cooling system according to any one of the preceding claims, characterised in that the third section of line (21) comprises at least two cooling channels (21c) arranged parallel to each other that extend through second zones of the combustion engine (1).

6. The cooling system according to any one of the preceding claims, characterised in that it comprises a third thermostat (17) that prevents cooling fluid being led through the third section of line (21) to the second zone of the combustion engine (1) when the cooling fluid has a temperature that is lower than the regulation temperature (T₃) of the third thermostat (17), and allows cooling fluid to be led through the third section of line (21) to the second zone (lb) of the combustion engine (1) when the cooling fluid has a temperature that is higher than the regulation temperature (T₃) of the third thermostat (17).

7. The cooling system according to any one of the preceding claims, characterised in that the thermostats (15, 16, 17) are of the type that comprises a wax body that changes phase at the regulation temperature.

8. The cooling system according to any one of the preceding claims, characterised in that at least one of the thermostats has a regulation temperature that can be varied.

9. The cooling system according to any one of the preceding claims, characterised in that it comprises a fourth section of line (22) that comprises a cooler (6) for the cooling of a medium.

10. The cooling system according to any one of the preceding claims, characterised in that the fourth section of line (22) receives cooling fluid from a line (13b) in the cooling system that is located essentially immediately downstream of the cooling fluid pump (13).