BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to a cooling system for a vehicle powered by a combustion engine according to the preamble of claim 1.

The combustion engine of a vehicle is usually cooled by a cooling system with a circulating coolant. In heavy vehicles there is also a great need to cool various media such as, for example, charge air, recirculating exhaust gases, gearbox oil, refrigerant in an air conditioning system, oil in servo systems, fuel and hydraulic oil. A known practice is to use the combustion engine's cooling system for cooling one or more such media in the vehicle. During periods when the combustion engine is under heavy load, however, there is risk that the cooling system's temperature may become so high that such further media with connecting components may not receive sufficient cooling. If the cooling becomes deficient, this may lead to impaired operating characteristics of the vehicle and unnecessary wear of cooled components, with consequently reduced service life.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a cooling system for a vehicle which in addition to cooling the combustion engine also makes good cooling of other media and components in the vehicle possible even in situations where the cooling system is under heavy load.

This object is achieved with the cooling system of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. The cooling system thus comprises a first line circuit adapted to cooling the combustion engine and a second line circuit which comprises at least one heat exchanger in which another medium in the vehicle is intended to be cooled by coolant received from the first line circuit. In situations where the cooling system is not under heavy load, the coolant in the first line circuit will be at a temperature such that it can, without extra cooling, be received in the second line circuit and used for cooling the medium in the heat exchanger. In this case, the coolant is mainly led through a bypass line and thus past the extra radiator before it reaches the heat exchanger in which it cools the medium. The extra radiator is thus not used in this case for cooling the coolant. Using the bypass line ensures that the coolant in the cooling system is not cooled too much when the cooling system is not under heavy load, which would result in too low an operating temperature of the combustion engine. In situations where the cooling system is under heavy load, the coolant led to the second line circuit from the first line circuit will be at too high a temperature to be able, without extra cooling, to be used for cooling the medium in the heat exchanger. In this case, the coolant is led mainly through the extra radiator. The coolant is thus brought to a sufficiently low temperature for cooling the medium as necessary when it reaches the heat exchanger.

According a preferred embodiment of the invention, the valve means is arranged in the bypass line. Such a valve means can be placed in an open position whereby it allows coolant to be led through the bypass line, and in a closed position whereby it prevents coolant from being led through the bypass line. When the valve means is in a closed position, all of the coolant is led through the parallel line provided with the extra radiator. If the line with the extra radiator does not have a valve means of its own or is blocked in some other way, there is also a coolant flow through the line with the extra radiator when the valve means in the bypass line is open. In order to distribute the coolant flow between the lines, the bypass line may be so constructed that the coolant is led with a lower flow resistance through the bypass line than through the line with the extra radiator. It is thus possible to achieve a suitably smaller coolant flow through the extra radiator. This makes venting of the radiator possible and reduces the risk of thermal fatigue of the radiator and the risk of ice forming within the radiator when a cold ambient temperature prevails.

According to another preferred embodiment of the invention, the second line circuit comprises a temperature sensor adapted to detecting said medium's temperature and the control system is adapted to receiving information from said sensor and to controlling the valve means in such a way that at least a major part of the coolant is led through the line with the extra radiator when said medium is at a temperature above a highest acceptable temperature. With a suitably located temperature sensor, the control unit can immediately control the valve means so that at least a major part of the coolant is led through the extra radiator as soon as the medium reaches too high a temperature. This extra cooling of the coolant leads to its being able to cool the medium more effectively in the heat exchanger. This more effective cooling has the effect of lowering the temperature of the medium. As soon as the medium reaches a temperature which is a predetermined number of degrees lower than the highest acceptable temperature, the control unit opens the valve means so that the coolant is again led through the bypass line. Alternatively, the second line circuit may comprise a temperature sensor adapted to detecting the temperature of the coolant and the control unit may be adapted to receiving information from said sensor and to controlling the valve means so that at least a major part of the coolant is led through the line with the extra radiator when the coolant is at a temperature above the highest acceptable temperature. In that case, the control unit thus controls the valve means by means of the temperature of the coolant. When the coolant received in the second cooling circuit is too warm to cool the medium in the heat exchanger, it is led through the extra radiator before it is allowed to cool the medium in the heat exchanger. If the coolant is not too warm, it is led, without extra cooling, via valve means to the heat exchanger in order to cool the medium.

According to another preferred embodiment of the invention, the second line circuit comprises at least two heat exchangers for cooling a respective medium. In heavy vehicles in particular there is a need to cool a large number of media. Such media may be charge air, recirculating exhaust gases, gearbox oil, refrigerant in an air conditioning system, oil in servo systems, fuel and hydraulic oil. Said heat exchangers may be arranged in parallel in the second line circuit. This makes it possible for coolant at substantially the same temperature to be used for cooling the media in the respective heat exchangers. Alternatively, said heat exchangers may be arranged in series in the second line circuit. This results in the most effective cooling of the medium in the heat exchanger which the coolant flows through first. The heat exchangers are with advantage counterfiow heat exchangers. This makes it possible for the media to be cooled to a temperature close to the coolant's inlet temperature in the heat exchanger.

According to another preferred embodiment of the invention, the second line circuit receives coolant from the first line circuit at a first location and returns the coolant to the first line circuit at a second location and the coolant is at a higher pressure at the first location than at the second location. With such a connection of the second line circuit to the first line circuit, the coolant pump in the first line circuit can also be used for circulating the coolant in the second line circuit. To achieve a pressure difference for ensuring a continuous coolant flow through the second line circuit, the second line circuit needs to receive coolant relatively near to the pressure side of the coolant pump and to return coolant relatively near to the suction side of the coolant pump.

According to another preferred embodiment of the invention, the second line circuit comprises a fan and the control unit is adapted to activating the fan to provide a cooling air flow through the extra radiator when there is an extra cooling requirement for the medium in the heat exchanger. The cooling effect of the coolant in the extra radiator is thus increased. The control unit preferably activates an electric motor which drives the fan when the coolant is led through the extra radiator. The extra radiator is with advantage situated at a peripheral surface in the vehicle so that it has air at the temperature of the surroundings flowing through it when the fan is activated. The coolant can thus undergo very effective cooling in the extra radiator.

BRIEF DESCRIPTION OF THE DRAWING

Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which:

Fig. 1 depicts a cooling system according a first embodiment of the invention and

Fig. 2 depicts a cooling system according a second embodiment of the invention .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 depicts schematically a vehicle 1 powered by a combustion engine 2 which may be a diesel engine. The vehicle 1 is with advantage a heavy vehicle. The combustion engine 2 is cooled by a cooling system with a circulating coolant. A coolant pump 3 is adapted to circulating coolant through the cooling system. The cooling system comprises a first line circuit 4 and a second line circuit 5. The first line circuit 4 comprises schematically depicted cooling ducts 4a which extend through the combustion engine 2 in such a way that the latter undergoes desired cooling. After the coolant has cooled the combustion engine 2, it is received in a line 4b which leads the coolant to a thermostat 6. The thermostat 6 leads a variable amount of the coolant to a line 4c and a line 4d depending on the temperature of the coolant. The line 4c leads the coolant back to the fuel pump 3 and the combustion engine 2, whereas the line 4d leads coolant to a radiator 7 fitted at a forward portion of the vehicle 1. A radiator fan 8 is adapted to generating a cooling air flow through the radiator 7. When the coolant has reached a normal operating temperature, substantially all of the coolant is led to the radiator 7 in order to be cooled before it is led back to the fuel pump 3 and the combustion engine 2 via a line 4e. The first line circuit 4 of the cooling system thus has the configuration of a conventional cooling system for cooling a combustion engine 2 in a vehicle 1.

The cooling system's second line circuit 5 comprises a line 5a which receives coolant from the first line circuit 4 at a location 4a' situated close to the pressure side of the coolant pump 3. The line 5a divides successively into two parallel lines 5b, 5c. The first parallel line 5b comprises an extra radiator 9. The extra radiator 9 is fitted in a peripheral region of the vehicle 1. In this case the peripheral region is situated at a front portion of the vehicle 1. A radiator fan 10 driven by an electric motor 11 is adapted to generating a cooling air flow through the extra radiator 9. The second parallel line 5c is a bypass line which comprises a valve 12. A control unit 13 is adapted to controlling the electric motor 11 and the valve 12. The parallel lines 5b, 5c join together in a line 5d which leads the coolant to a first heat exchanger 14a and a second heat exchanger 14b. In this case the coolant is led in parallel to the respective heat exchangers 14a, 14b. The coolant is intended to cool a medium in the respective heat exchangers 14a, 14b. In this case oil from the vehicle's gearbox is cooled in the first heat exchanger 14a. Another medium, which may for example be charge air, recirculating exhaust gases, the refrigerant in an air conditioning system, oil for servo systems, fuel, a medium which cools electrical components in the vehicle 1 or hydraulic oil, is cooled in the second heat exchanger 14b. There are thus a number of media and components which need to be cooled in a heavy vehicle 1. A temperature sensor 15 is adapted to detecting the temperature of the gearbox oil at a suitable location. The temperature sensor 15 measures and sends signals about the temperature of the oil substantially continuously to the control unit 13 during operation of the vehicle. After the coolant has cooled the media in the heat exchangers 14a, 14b, it is led back to the first line circuit 4 via a line 5e. The coolant is led back to the line 4e in the first line circuit 4 at the location 4e' which is here situated between the radiator 7 and the coolant pump 3.

During operation of the combustion engine, the coolant pump 3 circulates coolant through the first line circuit 4 so that the combustion engine receives necessary cooling. The second line circuit 5 is so dimensioned that it receives via the line 5a at the location 4a' a specified proportion of the coolant which is circulated in the first line circuit 4. The control unit 13 receives information from the temperature sensor 15 about the temperature of the gearbox oil. The control unit 13 contains stored information about a highest acceptable temperature which the gearbox oil should not exceed. When the gearbox oil is at a temperature within the acceptable range, the control unit 13 is adapted to keeping the valve 12 in an open position. The control unit 13 is at the same time adapted to keeping the electric motor 10 switched off so that the fan 11 does not provide a cooling air flow through the extra radiator 9.

The second line system 5 is so constructed that the flow resistance through the bypass line 5c is considerably less than the flow resistance through the line 5b with the extra radiator 9. When the valve 12 is open, the major part of the coolant which circulates in the second line circuit 5 will therefore be led through the bypass line 5c. Only a small portion of the coolant will be led through the line 5b and the extra radiator 9. Even if the extra radiator 9 need not be used in this case for cooling the coolant in the second line circuit 5, it is nevertheless advantageous for several reasons to cause a small portion of the coolant to pass through the extra radiator 9. Such a small coolant flow makes it possible to vent the extra radiator 9, thereby ensuring that the extra radiator 9 maintains a temperature such that the risk of thermal fatigue is reduced, as also the risk of ice forming within the extra radiator 9 when a cold ambient temperature prevails. When the gearbox oil is at an acceptable temperature, the coolant is used without any extra cooling in the extra radiator 9 for cooling the media in the respective heat exchangers 14a, 14b. The coolant is thereafter led back via the line 5e to the first line circuit 4 at the location 4e'. The second line circuit 5 thus receives coolant from a location 4a' in the first line circuit 4 close to the pressure side of the coolant pump 3 and leads the coolant back to the first line circuit at a location 4e' close to the suction side of the coolant pump 3. The pressure difference between said locations 4a' and 4e' in the first line circuit 4 ensures that the circulation of coolant through the second line circuit 5 can be maintained by the same coolant pump 3 as circulates coolant in the first line circuit 4.

If the temperature of the gearbox oil rises above the acceptable temperature, the control unit 13 finds that the coolant in the first line circuit 4 is at too high a temperature for cooling the gearbox oil in a desired manner. The control unit 13 thereupon closes the valve 12 while at the same time activating the electric motor 11 and the fan 10. All of the coolant in the second line circuit 5 is then led through the line 5b and the extra radiator 9, in which it undergoes cooling by the air which is forced through the extra radiator 9. The coolant in the second line circuit 5 thus undergoes effective cooling to a temperature which is definitely lower than the temperature of the coolant in the first line circuit 4 before it is used for cooling the media in the heat exchangers 14a, 14b. As the heat exchangers 14a, 14b are in this case arranged in parallel, the media in the respective heat exchangers 14a, 14b will be cooled by coolant at the same low temperature. The cold coolant provides effective cooling of the media in the respective heat exchangers 14a, 14b. The effective cooling of the gearbox oil in the heat exchanger 14a results in the gearbox oil being cooled relatively quickly to an acceptable temperature. When the control unit 13 receives information which indicates that the gearbox oil has cooled to a temperature which is a predetermined number of degrees below the highest acceptable temperature, it opens the valve 12 while at the same time switching off the electric motor 11 and the fan 10. The major part of the coolant will therefore again be led through the bypass line 5c and only a small portion through the line 5b and the extra radiator 9.

Fig. 2 depicts an alternative embodiment of the cooling system. In this embodiment, the control unit 13 receives information from a temperature sensor 16 about the temperature of the coolant which is received in the second line circuit 5. If the coolant is at a temperature above a highest acceptable temperature, the control unit 13 finds that the media in the heat exchangers 14a, 14b cannot receive desired cooling by such a warm coolant. The control unit 13 thereupon closes the valve 12 while at the same time activating the electric motor 11 and the fan 10. All of the coolant in the second line circuit 5 is then led through the line 5b and the extra radiator 9, in which it undergoes cooling by the air which is forced through the extra radiator 9. The coolant which is led to the heat exchangers 14a, 14b after the cooling in the extra radiator 9 will then be at a significantly lower temperature and can therefore provide effective cooling of the gearbox oil in the first heat exchanger 14a. The coolant is thereafter led to the second heat exchanger 14b, in which it cools the second medium, hi this case, the heat exchangers 14a, 14b are thus arranged in series, which is advantageous when one of the media requires cooling to a lower temperature than the other medium. The extra cooling of the coolant in the extra radiator 9 results in the coolant throughout the cooling system being at a lower temperature. When the control unit 13 receives information which indicates that the coolant has cooled to a temperature which is a predetermined number of degrees below the highest acceptable temperature, it finds that the coolant can again be used for cooling said media without any extra cooling in the extra radiator 9. The control unit 13 thereupon opens the valve 12 while at the same switching off the electric motor 11 and fan 10. The major part of the coolant will thus be led through the bypass line 5c and only a small portion through the line 5b and the extra radiator 9.

The invention is in no way limited to the embodiment to which the drawing refers but may be varied freely within the scopes of the claims.