BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a cooling system for cooling of a combustion engine and a WHR system according to the preamble of claim 1.

A WHR system (Waste Heat Recovery System) can be used in vehicles for recovering waste thermal energy and convert it to mechanical energy or electrical energy. A WHR system includes a pump which pressurizes and circulates a working medium in a closed circuit. The closed circuit comprises one or several evaporators where the working medium is heated and evaporated by one or several heat sources such as, for example, the exhaust gases from a combustion engine. The pressurized and heated gaseous working medium is directed to an expander where it expands. The expander generates mechanical energy which can be used to operate the vehicle or apparatuses on the vehicle. Alternatively, the expander is connected to a generator generating electrical energy. The working medium leaving the expander is directed to a condenser. The working medium is cooled in the condenser to a temperature at which it condenses. The liquefied working medium leaving the condenser is redirected to the pump which pressurizes the medium. Thus, the waste heat energy from, for example, the exhaust gases from a combustion engine in a vehicle can be recovered by means of a WHR-system. Consequently, a WHR-system can reduce the fuel consumption of a combustion engine. In order to achieve a high thermal efficiency in a WHR system, the working medium has to be cooled to a condensation temperature in the condenser as low as possible and substantially without subcooling. Consequently, in order to achieve a suitable condensation temperature in the condenser, the working medium has to be cooled by coolant of a specific temperature and a specific flow rate. The same cooling system may be used to cool the combustion engine and the working medium in the condenser. In order to achieve a high efficiency of the combustion engine, the coolant may be cooled to a temperature of about 90°C in a radiator before it is directed to the combustion engine. In order to achieve a high thermal efficiency of the WHR system, it is usually suitable to direct coolant of a different temperature to the condenser. In case the working medium is ethanol, it is suitable to direct coolant of a temperature of about 60-70°C to the condenser.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a cooling system which is able to cool a working medium in a condenser in a WHR system and a combustion engine by coolants of two different temperatures in a simple and effective manner.

The above mentioned object is achieved by the cooling system according to claim 1. A cooling system comprising two radiators have possibility to cool the coolant leaving the combustion engine to two different temperatures. The first valve device, which receives coolant from the combustion engine, directs a part of the coolant to the radiator bypass line without cooling and a remaining part of the coolant flow to the radiators for cooling to said two different temperatures. Thus, the cooling system has access to coolants of three different temperatures for cooling of the combustion engine and the working medium in the condenser. By means of the first valve device and the second valve device it is possible to mix the coolants of the three different

temperatures in a manner such that coolant of a suitable temperature is directed to combustion engine and coolant of a suitable temperature is directed to the condenser. The control unit may have access to stored information about suitable temperatures of the coolant to be directed to the combustion engine and suitable temperatures of the coolant to be directed to the condenser at different operating conditions.

According to an embodiment of the invention, the first radiator and the second radiator are arranged side by side in a common air stream passage. In this case, the coolants in the respective radiators may be cooled by air of the same temperature. The cooling requirement of modern combustion engines has decreased and thus the demand on a large radiator at a front portion of the vehicle. There is thus space to arrange a second radiator side by side with a first radiator at the front portion of the vehicle. The second radiator cools together with the first radiator the coolant which circulates in the cooling system and cools the combustion engine and the working medium in the condenser of the WHR system. Alternatively, it is possible to arrange the second radiator in a position upstream of the first radiator.

According to an embodiment of the invention, the first radiator and the second radiator are designed such that the coolant is cooled to a lower temperature in the second radiator than in the first radiator. In case, the coolant is cooled in parallel in a first radiator and a second radiator of the same size, it is possible to reduce the coolant flow to the second radiator such that the coolant flow through the second radiator will be smaller than the coolant flow through the first radiator. In this case, the coolant flows with a slower velocity through the second radiator than through the first radiator.

Thus, the coolant in the second radiator is subjected to a cooling air stream during a longer time period than the coolant in the first radiator. As a result, the coolant in the second radiator is cooled to a temperature closer to the temperature of the cooling air than the coolant in the first radiator. Alternatively or in combination, the second radiator may be larger than the first radiator or having a design providing a more efficient cooling of the coolant than the first radiator. According to an embodiment of the invention, the cooling system comprises a coolant line directing coolant from an inlet tank of the first radiator to an inlet tank of the second radiator. The coolant line may be provided with a relatively small flow area such that a relatively small part of the coolant entering the inlet tank is passed on to the inlet tank of the second radiator. Alternatively, the tubes in the second radiator may provide a narrower flow path than the tubes in the first radiator. Alternatively, the first radiator comprises an inlet tank which at a bottom is fixedly connected, via a coolant passage, to an upper portion of an inlet tank of the second radiator. In this case, the coolant passage may be provided with a flow restricting area. According to an embodiment of the invention, the cooling system comprises a coolant line directing coolant from an outlet tank of the first radiator to an inlet tank of the second radiator. In this case, a first part of the coolant flow is directed through the first radiator and a remaining second part of the coolant flow is directed through the first radiator and the second radiator. Thus, the second part of the coolant flow is cooled in the first radiator and the second radiator in series which ensure that the coolant leaving the second radiator has a lower temperature than the coolant leaving the first radiator.

According to an embodiment of the invention, the cooling system comprises a condenser outlet line directing coolant from the condenser to the engine inlet line. Thus, the coolnt directed to the combustion engine is a mixture of coolant from the radiator bypass line, the first radiator and the condenser outlet line.

According to an embodiment of the invention, the first valve device is a first three way valve. The first three way valve may receive an inlet receiving a coolant flow from the engine outlet line and a first outlet directing a part of the received coolant to the radiator bypass line and a second outlet directing a remaining part of the received coolant to the radiators. The first valve device may have a substantially corresponding task as a thermostat in a conventional cooling system. Preferably, the first three way valve device is adjustable in a stepless manner. In this case, it is possible to vary the coolant flow rate to the radiators and the radiator bypass line with a high accuracy. In this case, the first valve device is designed as a single valve unit. Alternatively, the first valve device is designed as two two way valves wherein a first two way valve is arranged in the radiator bypass line and a second two way valve is arranged in a radiator inlet line.

According to an embodiment of the invention, the second valve device is a second three way valve. The second three way valve has an inlet receiving coolant from the first radiator and a first outlet directing a part of the received coolant to the condenser and a second outlet directing a remaining part of the coolant to a condenser bypass line. Preferably, the second three way valve valve device is adjustable in a stepless manner. In this case, it is possible to adjust the coolant flow rate from the first radiator to the condenser and the condenser bypass line with a high accuracy. In this case, the second valve device is designed as a single valve. Alternatively, the second valve device is designed as two two way valves wherein a first two way valve is arranged in the condenser inlet line and a second two way valve is arranged in the condenser bypass line.

According to an embodiment of the invention, the control unit is configured to receive information from a sensor sensing a parameter related to the actual condensing temperature/pressure of the working medium in the condenser. In case there is a difference between the actual temperature/pressure in the condenser and the desired condensation temperature/pressure, the control unit may adjust the first valve device and/or the second valve device in order to change the cooling of the working medium in the condenser in a manner such that said difference is eliminated.

According to an embodiment of the invention, the control unit is configured to control the first valve device and the second valve device such that the coolant directed to the condenser has a temperature and a flow rate which results in a cooling of the working medium in the condenser to a condensation pressure just above 1 bar. It is during the most operating conditions possible to direct a coolant flow to the condenser which results in a cooling of the working medium in the condenser to a desired condensation temperature/pressure. However, by practical reasons, it is many times suitable to avoid negative pressures in a WHR-system. In this case, it is suitable to obtain a

condensation pressure just above 1 bar. The desired pressure range may, for example, be in the range 1, 1 - 1, 5 bar. It is to be noted that a condensation pressure for a working medium has a corresponding condensation temperature. The working medium in the WHR-system may be ethanol. Ethanol has an evaporation temperature of about 78°C at 1 bar. It is relatively easy to accomplish a coolant temperature at a suitable level below the evaporation temperature of ethanol and cool the ethanol in a condenser to a condensation temperature just above 78°C. However, it is possible to use other working mediums such as for example R265fa.

According to an embodiment of the invention, the control unit is configured to receive information from a number of temperature sensors configured to sense the temperature of the coolant in different positions of the cooling system and to control the first valve device and the second member by means of this information. The control unit may be configured to receive information from temperature sensors configured to sense the temperature of the coolant in the engine outlet line, the temperature of the coolant leaving the first radiator and the temperature of the coolant leaving the second radiator. In this case, the control unit has temperature information of all accessible coolants which can be mixed by means of the first valve device and the second valve device and be delivered to the combustion engine and the condenser. Alternatively or in combination, the coolant may receive information about the temperature of the coolant in the engine inlet line and the temperature of the coolant in the condenser inlet line. In such a case, the control unit receives a direct feedback about the temperatures of the coolants directed to the combustion engine and the condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following preferred embodiments of the invention is described, as examples, with reference to the attached drawings, in which:

Fig. 1 shows a cooling system according to the invention,

Fig. 2 shows the first radiator and the second radiator in Fig. 1 more in detail,

Fig. 3 shows an alternative embodiment of the first radiator and the second radiator and

Fig. 4 shows a further alternative embodiment of the first radiator and the

second radiator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a schematically disclosed vehicle 1 powered by a combustion engine 2. The vehicle 1 may be a heavy vehicle and the combustion engine 2 may be a diesel engine. The vehicle 1 comprises a cooling system comprising an engine inlet line 3 provided with a pump 4 circulating a coolant in the cooling system. The pump 4 circulates the coolant through the combustion engine 2. When the coolant has cooled the combustion engine 2, it is received in an engine outlet line 5. A first valve device in the form of a first three way valve 6 is arranged at an end of the engine outlet line 5. The cooling system comprises a radiator inlet line 7 directing coolant to an inlet tank 8a of a first radiator 8. A connection line 9a directs coolant from inlet tank 8a of a first radiator 8 to an inlet tank 10a of a second radiator 10. A radiator fan 11 provides a cooling air stream through the first radiator 8 and the second radiator 10. The first radiator 8 and the second radiator 10 are arranged side by side. Thus, the coolant are cooled with air of the same temperature in the radiators 8, 10. The cooling system comprises a radiator bypass line 12 directing coolant past the first radiator 8 and the second radiator 10. The first three way valve 6 is controlled by a control unit 13. The first three way valve 6 is adjustable in a stepless manner. The first three way valve 6 receives coolant from the engine outlet line 5 and direct a part of the coolant to the radiator bypass line 12 and a remaining part of the coolant to the radiator inlet line 7.

The vehicle is provided with a WHR-system (Waste Heat Recovery system). The WHR- system comprises a pump 14 which pressurizes and circulates a working medium in a closed circuit 15. In this case, the working medium is ethanol. However, it is possible to use other kinds of working mediums such as for example R265fa. The pump 14 pressurizes and circulates the working medium to an evaporator 16. The working medium is heated in the evaporator 16, for example, by exhaust gases from the combustion engine. The working medium is heated in the evaporator 16 to a temperature at which it evaporates. The working medium is circulated from the evaporator 16 to the expander 17. The pressurised and heated working medium expands in the expander 17. The expander 17 generates a rotary motion which may be transmitted, via a suitable mechanical transmission 18, to a shaft 19 of the power train of the vehicle 1. Alternatively, the expander 17 may be connected to a generator transforming mechanical energy into electrical energy. The electrical energy may be stored in a battery. The stored electrical energy can be supplied to an electrical engine for driving of the vehicle or a component on the vehicle in a later state. After the working medium has passed through the expander 17, it is directed to a condenser 20. The working medium is cooled in the condenser 20 by coolant from the cooling system to a temperature at which it condenses. The working medium is directed from the condenser 20 to a receiver 21. The pressure in the receiver 21 can be varied by means of a pressure regulator. The pump 14 sucks working medium from the receiver 21. A second control unit 22 controls the operation of the WHR-system. The second control unit 22 controls the operation of the pump 14 and the expander 17. The WHR-system makes it possible to transform thermal energy from the exhaust gases to mechanical energy or electrical energy. A temperature sensor 23 or a pressure sensor senses the condensation temperature or the condensation pressure in the condenser 20. It is favourable to establish a condensation pressure as low as possible. However, it is suitable to avoid negative pressure in the WHR-system by practical reasons. In view of these facts, it is suitable to provide a cooling of the working medium in the condenser 20 to a condensation pressure just above lbar. Consequently, in order to maintain a high thermal efficiency it is necessary to adjust the cooling effect of the working medium in the condenser 20 such that the condensation pressure will be just above 1 bar. The working medium ethanol has a condensation temperature of 78°C at 1 bar. In this case, it is suitable to accomplish a condensation temperature of just above 78°C in the condenser 20.

The cooling system comprises a condenser inlet line 24a directing coolant to the condenser 20. Coolant from an outlet tank 10b of the second radiator is directed, via a second radiator outlet line 25, to the condenser inlet line 24a. A return line 24b directs coolant from the condenser 20 to the engine inlet line 3. A second valve device in the form of a second three way valve 26 receives coolant from an outlet tank 8b of the first radiator 8a via a first radiator outlet line 27. The second three way valve 26 is controlled by the control unit 13. The second three way valve 26 is adjustable in a stepless manner. The second three way 26 valve directs a part of the coolant flow from first radiator outlet line 27, via a coolant line 28, to the condenser inlet line 24a. The coolant flow from the first radiator 8 and the second radiator 10 is mixed in the condenser inlet line 24a. The second three way 26 valve directs a remaining part of the coolant flow to a condenser bypass line 29. An initial temperature sensor 30 senses the temperature To of the coolant in the engine outlet line 5. A first temperature sensor 31 senses the temperature Ti of the coolant in the first radiator outlet line 27 and a second temperature sensor 32 senses the temperature T ₂ of the coolant in the second radiator outlet line 25.

Fig. 2 shows a view of the first radiator 8 and the second radiator 10 in Fig. 1. The coolant from the radiator inlet line 7 is, via an inlet port 8a', directed to the inlet tank 8a of the first radiator 8. A first part of the coolant flow is cooled in the first radiator 8. The first part of the coolant flow is received in an outlet tank 8b before it is directed, via an outlet port 8b', to the first radiator outlet line 27. A second part of the coolant flow entering the inlet tank 8a of the first radiator 8 is directed, via an outlet port 8a", a coolant line 9a and an inlet port 10a', to an inlet tank 10a of the second radiator 10. When the second part of the coolant has been cooled in the second radiator 10, it is received in the second radiator outlet tank 10b and directed, via an outlet 10b 'to the second radiator outlet line 25. In this case, a coolant passage in the form of a coolant line 9a is used for directing coolant from the first radiator 8 to the second radiator 10. The coolant line 9a has a relatively small cross section area. Consequently, the flow resistance through the second radiator will be higher than the flow resistance through the first radiator 8. Thus, the second part of the coolant flow through the second radiator 10 will be smaller than the first coolant flow through the first radiator 8. The smaller coolant flow through the second radiator 10 makes it possible to cool the coolant to a lower temperature in the second radiator than in the first radiator. An alternative way to provide a higher flow resistance in the second radiator 10 than in the first radiator 8, it is to design the coolant tubes in the second radiator 10 with narrower coolant tubes than in the first radiator 8. A further alternative is to provide the coolant line 9a or the second radiator outlet line 25 with a throttle.

During operation, the control unit 13 receives substantially continuously information from said temperature sensors 30, 31, 32 about the actual coolant temperatures. The control unit 13 also receives information from the second control unit 22 about the operating condition of the WHR system. The control unit 13 may, for example, receive information from the sensor 23 about the actual condensation temperature in the condenser 20. The control unit 13 estimates a desired condensation temperature of the working medium in the condenser 20. When ethanol is used as working medium, a condensation temperature of about 80°C is desirable during most operating conditions. The control unit 13 estimates a suitable temperature of the coolant to be directed to the condenser 20 in order to provide the desired condensation temperature. Furthermore, the control unit 13 estimates a suitable temperature of the coolant to be directed to the combustion engine 2. A suitable temperature of the coolant directed to the combustion engine 2 may be of about 90°C. A suitable temperature of the coolant directed to the condenser 20 may be within the temperature range 60-70°C.

The initial temperature To of the coolant in the engine outlet line 5 indicates the cooling demand of the coolant in the cooling system. In case the initial temperature To of the coolant in the engine outlet line 5 is low, the control unit 13 adjusts the three way valve 6 such that it directs a small part of the coolant flow to the radiator line 7 and a remaining large part of the coolant flow to the radiator bypass line 12. In case the initial temperature To of the coolant in the engine outlet line 5 is high, the control unit 13 adjusts the three way valve 6 such that it directs a large part of the coolant flow to the radiator inlet line 7 and a remaining small part of the coolant flow to the radiator bypass line 12. Thus, the coolant flow rate to the radiator inlet line 7 and the coolant flow rate to the radiator bypass line 12 can be varied by the first three way valve 6. A first part of the coolant flow directed to the radiator inlet line 7 is cooled in the first radiator 8 to a first temperature Ti and a second part of the coolant flow is cooled in the second radiator to a second temperature T ₂ . The second temperature T ₂ is lower than the first temperature Ti.

In view of information from the temperature sensors 30, 31, 32 about the actual coolant temperatures To, Ti, T ₂ , the control unit 13 estimates a suitable positioning of the first three way valve 6 and the second three way valve 26. The first valve device 6 and the second valve device 26 are controlled in a manner such that the coolant directed to the combustion engine 2 obtains a temperature of about 90°C. The coolant flow to the combustion engine is a mixture of the coolant flows in the radiator bypass line 12, the condenser bypass line 29 and the condenser return line 24b. The first valve device 6 and the second valve device 26 are controlled in a manner such that the coolant directed to the condenser 20 obtains a temperature of about 60-70°. The coolant flow to the condenser is a mixture of the coolant flows in first radiator outlet line 27 and the second radiator outlet line 25.

Fig. 3 shows an alternative embodiment of the first radiator 8 and the second radiator 10. In this case, the inlet tanks 8a, 10a of the first radiator 8 and the second radiator 10 are connected to each other, via a coolant passage 9b, such that they form a coherent inlet tank body. The coolant passage 9b comprises a reduced flow area in relation to the flow areas in the respective inlet tanks 8a, 10a. The coolant passage 9b restrict the coolant flow to the second inlet tank 10a, such that a main part of the coolant flow is directed through the first radiator 8. Consequently, the coolant flow through the second radiator 10 will be lower than the coolant flow through the first radiator which results in cooling of the coolant to a lower temperature in the second radiator 10 than in the first radiator 8. Fig. 4 shows a further alternative embodiment of the radiators 8, 10. In this case, the entire coolant flow from the radiator inlet line 7 is directed through the first radiator 8. A first part of the coolant flow leaving the first radiator 8 is directed to the first radiator outlet line 27 and a remaining second part of the coolant flow leaving the first radiator 8 is directed, via a coolant line 9c, to an inlet tank 10a of the second radiator 10. The second part of the coolant flow is cooled in a second step in the second radiator 10.

The cooling of the coolant in the second step in the second radiator 10 ensures that the coolant is cooled to a lower temperature in the second radiator 10 than in the first radiator 8. The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.