A METHOD FOR CONTROLLING A COOLING SYSTEM DELIVERING COOLANT TO HEAT EXCHANGER IN A VEHICLE

Abstract

A method for controlling a cooling system delivering coolant to a heat exchanger (18) in a vehicle (1). During operating conditions when a thermostat (6) in the cooling system is in the partly open position, the method comprises the steps of estimating a desired cooling temperature (T) of a medium in the heat exchanger (18), calculating the coolant flow rate ({dot over (m)}.sub.1) through a radiator (7b) and the coolant flow rate ({dot over (m)}.sub.2) through a radiator bypass line (9), calculating am coolant flow rate ({dot over (m)}.sub.3) and coolant temperature (t.sub.3) combination at 10 at which the medium in the heat exchanger (18) is cooled to a desired temperature (T), adjusting the flow regulating mechanism (23) such that coolant at the selected flow rate ({dot over (m)}3) and temperature (t.sub.3) combination is directed to the heat exchanger (18).

Claims

1. A method for controlling a cooling system delivering coolant to a heat exchanger in a vehicle, wherein the cooling system comprises: a radiator line configured to direct coolant to a radiator in which the coolant is cooled to a first temperature; a radiator bypass line directing coolant past the radiator; a heat exchanger line receiving coolant from the radiator line and from the radiator bypass line and directing the coolant to a heat exchanger; a heat exchanger bypass line receiving coolant from the radiator line and the radiator bypass line and directing the coolant past the heat exchanger; a thermostat receiving a coolant flow range ({dot over (m)}) at a second temperature, wherein the thermostat in a closed position directs the entire coolant flow range ({dot over (m)}) to the radiator bypass line, in a partly open position directs a first coolant flow range ({dot over (m)}.sub.1) to the radiator line and a second coolant flow range ({dot over (m)}.sub.2) to the radiator bypass line, and in a fully open position directs the entire coolant flow rate ({dot over (m)}) to the radiator line; and a flow regulating mechanism directing coolant from the radiator line and the radiator bypass line to the heat exchanger line and/or the heat exchanger bypass line, wherein; during operating conditions when the thermostat is in the partly open position, the method comprises the steps of: estimating a desired cooling temperature of a medium in the heat exchanger, estimating a cooling effect of the coolant in the radiator from information about the cooling air flow through the radiator and from perfoimance data of the radiator at varying air flows, calculating the coolant flow rate ({dot over (m)}.sub.1) through the radiator line from information of the cooling effect of the coolant in the radiator, temperature drop (t.sub.1-t.sub.2) of the coolant in the radiator and the specific heat capacity (c.sub.p) of the coolant, calculating the coolant flow rate ({dot over (m)}.sub.2) through the radiator bypass line; calculating a coolant flow rate ({dot over (m)}.sub.3) and coolant temperature combination at which the medium in the heat exchanger is cooled to the desired temperature; and adjusting the flow regulating mechanism such that coolant at the selected flow rate ({dot over (m)}.sub.3) and temperature combination is directed to the heat exchanger line and the heat exchanger.

2. A method according to claim 1, comprising the steps of calculating several coolant flow rate ({dot over (m)}.sub.3) and coolant temperature (t.sub.3) combinations at which the medium in the heat exchanger is cooled to the desired temperature (T) and selecting one of the combinations.

3. A method according to claim 1, wherein during operating conditions when the thermostat is in the closed position, the method comprises the steps of: estimating a desired cooling temperature of the medium in the heat exchanger; calculating a required coolant flow rate ({dot over (m)}.sub.3) at the second temperature to be directed to the heat exchanger at which the medium receives the desired temperature; and adjusting the flow regulating mechanism such that the calculated coolant flow ({dot over (m)}.sub.3) is directed to the heat exchanger.

4. A method according to claim 1, wherein during operating conditions when the thermostat is in the fully open position, the method comprises the steps of estimating a desired cooling temperature of the medium in the heat exchanger; calculating a required coolant flow ({dot over (m)}.sub.3) at the first temperature to be directed to the heat exchanger at which the medium receives the desired temperature; and adjusting the flow regulating mechanism such that the calculated coolant flow ({dot over (m)}.sub.3) is directed to the heat exchanger.

5. A method according to claim 1, comprising the steps of: receiving information of the actual cooling temperature of the medium in the heat exchanger; comparing the actual temperature with the desired temperature; and adjusting the flow regulating mechanism in order to eliminate a possible difference between the desired temperature and the actual temperature of the medium in the heat exchanger.

6. A method according to claim 1, comprising the step of: adjusting the coolant flow ({dot over (m)}.sub.3) to the heat exchanger line in a stepless manner.

7. A method according to claim 1, comprising the step of: regulating the coolant flow rate ({dot over (m)}.sub.3) to the heat exchanger by adjusting the flow resistance in the heat exchanger bypass line by the flow regulating mechanism.

8. A method according to claim 1, comprising the step of: delivering coolant at a variable flow rate ({dot over (m)}.sub.3) and a variable temperature to a condenser in which it cools a working medium of a WHR system to a specific condensation temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following a preferred embodiment of the invention is described, as an example, with reference to the attached drawing, in which:

[0018] FIG. 1 shows a cooling system cooling a working medium in a condenser of a WHR system and

[0019] FIG. 2 shows a flowchart describing an embodiment of a method according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0020] FIG. 1 shows a combustion engine 2 powering a schematically disclosed vehicle 1. The combustion engine 2 may be a diesel engine. The vehicle 1 may be a heavy vehicle. 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 provides a coolant flow rate {dot over (m)} through the combustion engine 2. When the coolant has circulated through the combustion engine 2, it is received in an engine outlet line 5. A thermostat 6 is arranged at an end of the engine outlet line 5. The thermostat 6 receives a coolant flow rate {dot over (m)} at a temperature t.sub.2. The cooling system comprises a radiator line 7 directing coolant through a radiator 8. The radiator line 7 comprises a radiator inlet line 7a, and a radiator outlet line 7b. The cooling system comprises a radiator bypass line 9 directing coolant past the radiator 8. The radiator bypass line 9 and the radiator outlet line 7b is connected to each other via a connection line 10. The connection line 10 is connected to the radiator bypass line 9 via a first connection point 9a and to the radiator outlet line 7b via a second connection point 7c.

[0021] The thermostat 6 is closed when the coolant temperature t.sub.2 is lower than a regulating temperature of the thermostat 6. In the closed position, the thermostat 6 directs the entire coolant flow rate {dot over (m)} to the radiator bypass line 9. The thermostat 6 is partly open when the coolant temperature t.sub.2 is within a somewhat higher temperature range than the regulating temperature. In the partly open position, the thermostat 6 directs a first part {dot over (m)}.sub.1 of the coolant flow rate to the radiator line 7 and a second part {dot over (m)}.sub.2 of the coolant flow rate to the radiator bypass line 9. In case the coolant has a higher temperature than the highest temperature of said temperature range at which the thermostat 6 is partly open, the thermostat 6 is fully open. In the fully open position, the thermostat 6 directs the entire coolant flow rate {dot over (m)} to the radiator line 7. The ram air and a radiator fan 11 provide a cooling air flow through the radiator 8. The coolant is cooled to a temperature t.sub.1 in the radiator 8.

[0022] The vehicle is provided with a WHR-system (Waste Heat Recovery system). The WHR-system comprises a pump 12 which pressurized and circulates a working medium in a closed a circuit 13. In this case, the working medium is ethanol. However, it is possible to use other kinds of working mediums such as for example R245fa. The pump 12 pressurizes and circulates the working medium to an evaporator 14. The working medium is heated in the evaporator 14, for example, by exhaust gases from the combustion engine. The working medium is heated in the evaporator 14 to a temperature at which it evaporates. The working medium is circulated from the evaporator 14 to the expander 15.

[0023] The pressurised and heated working medium expands in the expander 15. The expander 15 generates a rotary motion which may be transmitted, via a suitable mechanical transmission 16, to a shaft 17 of the power train of the vehicle 1. Alternatively, the expander 15 may be connected to a generator transforming mechanical energy into electrical energy. The electrical energy may be stored in a battery. After the working medium has passed through the expander 15, it is directed to a condenser 18. The working medium is cooled in the condenser 18 by coolant from the cooling system to a temperature at which it condenses. The working medium is directed from the condenser 18 to a receiver 19. The pump 12 sucks working medium from the bottom of the receiver 19 ensuring that only working medium in a liquid state is supplied to the pump 12. A first control unit 20 controls the operation of the WHR-system. The first control unit 20 controls the operation of the pump 12 and the expander 15. The WHR-system makes it possible to transform thermal energy from the exhaust gases to mechanical energy or electrical energy.

[0024] The temperature of exhaust gases and thus the heating effect of the working medium in the evaporator 14 varies during different operation conditions. In order to maintain a substantially continuously high thermal efficiency in the WHR-system, the working medium in the condenser 18 is to be cooled with an adjustable cooling effect. It is favourable to establish a condensation pressure as low as possible at the different operating conditions. 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 18 to a condensation pressure just above 1 bar. Consequently, in order to maintain a high thermal efficiency it is necessary to adjust the cooling effect of the working medium in the condenser 18 in view of the supplied heat energy from the exhaust gases 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 18.

[0025] The cooling system comprises a condenser line 22 directing coolant through the condenser 18. The condenser line 22 comprises a condenser inlet line 22a directing coolant to the condenser 18. The condenser inlet line 22a receives coolant from the radiator outlet line 7b and/or the connection line 10 via the second connection point 7c. The condenser line 22 comprises a condenser outlet line 22b directing coolant from the condenser 18 to a third connection point 22c with the engine inlet line 3. The third connection point is arranged in a position downstream of a valve 23 arranged in the engine inlet line 3 and upstream of the pump 4. The part of the engine inlet line 3 which is arranged between the first connection point 9a and the third connection point 22c defines a condenser bypass line 3a. The valve 23 provides an adjustable flow resistance in a stepless manner for the coolant in the condenser bypass line 3a. The condenser line 22 provides a constant flow resistance for the coolant. By means of the valve 23, which may be a throttle vale, it is possible adjust the flow resistances in the condenser bypass line 3a in relation to the constant flow resistance in the condenser line 22 and thus an adjustable coolant flow rate {dot over (m)}.sub.4 through the condenser bypass line 3a in relation to a coolant flow rate {dot over (m)}.sub.3 through the condenser line 22.

[0026] A second control unit 24 controls the valve 23. A first temperature sensor 25 measures the ambient temperature. A second temperature sensor 26 measures the temperature t.sub.2 of the coolant in the engine outlet line 5. A third temperature sensor 27 measures the temperature t.sub.1 of the coolant in the radiator outlet line 7b. The second control unit 24 receives substantially continuously information from said temperature sensors 25-27 about actual temperatures. The second control unit 24 also receives information from the first control unit 20 about the operating condition of the WHR system. Furthermore, the second control unit 24 receives information about operation parameters 28 of the vehicle such as vehicle speed and the speed of the radiator fan 11. The second control unit 24 has access to stored information about performance data of the radiator 8 at varying air flows. An expansion tank 29 is connected to the engine inlet line 3 in a position downstream of the valve 23 and upstream of the pump 4 via a static line 30. A temperature senor 21 or a pressure sensor measures the condensation temperature or the condensation pressure in the condenser 18.

[0027] FIG. 2 shows a flowchart describing a method for directing coolant at a variable flow rate {dot over (m)}.sub.3 and at a variable temperature t.sub.3 to the condenser 18. The method starts at step 31. At step 32, the control unit 24 receives information about relevant operating parameters of the vehicle 1. The operating parameters include the velocity of the vehicle 1 and the speed of the radiator fan 10. The operating parameters may include engine load and temperature of the exhaust gases. The control unit 24 also receives information about relevant operating parameters of the WHR system. The control unit 24 receives, for example, information from the temperature sensor 21 about the actual condensation temperature T.sub.a in the condenser 18. At step 33, the control unit 24 estimates a desired condensation temperature of the working medium in the condenser 18. When ethanol is used as working medium, a condensation temperature of about 80 C. is desirable during most operating conditions. The control unit 24 estimates, at step 34, the required cooling effect Q.sub.c of the working medium in the condenser 18 at which the working medium receives the desired condensation temperature T.

[0028] At step 35, the control unit 24 receives information about the coolant temperature t.sub.2 in the engine outlet line 5. At operating conditions when the coolant temperature t.sub.2 in the engine outlet line 5 is lower than the regulating temperature of the thermostat 6, the method continues at step 36. The control unit 24 notes that the thermostat 6 is in a closed position and it directs the entire coolant flow rate {dot over (m)} at the temperature t.sub.2 to the radiator bypass line 9. In this case, the control unit 24 has information about the temperature t.sub.2 of the coolant directed to the condenser 18 and the required cooling effect Q.sub.c in the condenser. Furthermore, the control unit 24 has access to necessary parameters such as the heat capacity of the coolant and the working medium, and performance data of the condenser 18. In view of this fact, it is possible for the control unit 24, at step 37, to calculate the required coolant flow rate {dot over (m)}.sub.3 at the temperature t.sub.2 to be directed to the condenser 18 in order to cool the working medium in the condenser 18 with the estimated cooling effect Q.sub.c at which the working medium condenses at the desired condensation temperature T.

[0029] At step 38, the control unit 24 regulates the valve 23 such that it provides a flow resistance in the heat exchanger bypass line 3a at which the coolant flow rate {dot over (m)} in the radiator bypass line 9 is divided in a coolant flow rate {dot over (m)}.sub.3 through the heat exchanger line 22 and a remaining coolant flow rate {dot over (m)}.sub.4 through the heat exchanger bypass line 3a. The remaining coolant flow rate {dot over (m)}.sub.4 can be calculated as {dot over (m)}-{dot over (m)}.sub.3. At step 39, the control unit 24 receives information from the temperature sensor 21 about the actual condensation temperature T.sub.a. The control unit 24 compares, at step 39, the actual condensation temperature T.sub.a with the desired condensation temperature T. In case there is a difference between the actual condensation temperature T.sub.a and the desired condensation temperature T, the control unit 24 provides, at step 39, a further valve adjustment in order to eliminate such a possible difference. Thereafter, the method restarts at step 31.

[0030] If instead, at step 35, the coolant temperature t.sub.2 in the engine outlet line 5 is within the temperature range where the thermostat 6 is partly open, the method continues at step 41. In this case, the thermostat 6 directs a first coolant flow rate {dot over (m)}.sub.1 of the to the radiator line 7 and a second coolant flow rate {dot over (m)}.sub.2 to the radiator bypass line 9. The first coolant flow rate {dot over (m)}.sub.1 is cooled to the temperature t.sub.1 in the radiator 8. At step 42, the control unit 24 estimates the cooling effect Q.sub.r in the radiator 8 by means of performance data of the radiator 8 at varying air flows and air temperatures. The air flow through the radiator 8 is estimated by means of information of the velocity of vehicle 1 and the speed of the radiator fan 10. The control unit 24 receives information from the temperature sensor 25 about the temperature of the ambient air. At step 43, the control unit 42 calculates the coolant flow rate {dot over (m)}.sub.1 through the radiator 8 according to the formula Q.sub.r={dot over (m)}.sub.1.Math.c.sub.p.Math.(t.sub.2t.sub.1). The cooling effect Q.sub.r in the radiator has been estimated above, c.sub.p is the heat capacity of the coolant, t.sub.2 is received from the temperature sensor 27 and t.sub.1 is received from the temperature sensor 27. Thus, the coolant flow rate {dot over (m)}.sub.1 through the radiator 8 is calculable since it is the only unknown parameter in the formula. The coolant flow rate {dot over (m)}.sub.2 through the radiator bypass line 9 can be calculated as {dot over (m)}.sub.2={dot over (m)}{dot over (m)}.sub.1, where {dot over (m)} is the total coolant flow rate in the cooling system which is defined by the pump 4.

[0031] The control unit 24 has now information about the coolant flow rate {dot over (m)}.sub.1 and the coolant temperature t.sub.1 in the radiator line 7 and information about the coolant flow rate {dot over (m)}.sub.2 and the coolant temperature t.sub.2 in the radiator bypass line 9. In this case, the entire coolant flow rate {dot over (m)}.sub.1 at the temperature t.sub.1 from the radiator line 7 is directed to the heat exchanger line 22 and the condenser 18. However, it is possible to introduce a variable amount of the coolant flow rate {dot over (m)}.sub.2 at the temperature t.sub.2 in the heat exchanger line 22 by means of the valve 23. At step 44, the control unit 24 calculates possible coolant flow rate {dot over (m)}.sub.3 and temperature t.sub.3 combinations which provide the required cooling effect Q.sub.c in the condenser at which the working medium is condensed at the desired condensation temperature T. During some operating conditions the number of such combinations can be relatively large. Combinations with a too small coolant flow rate {dot over (m)}.sub.3 to the condenser 18 can be excluded. The control unit 24 selects, at step 45, the most favorable combination of coolant flow rate {dot over (m)}.sub.3 and coolant temperature t.sub.3 to be directed to the condenser 18. The control unit 24 performs, at step 46, an adjustment of the valve 23 and the flow resistance in the heat exchanger bypass line 3a in order to direct coolant with the selected combination of flow rate {dot over (m)}.sub.3 and temperature t.sub.3 to the heat exchanger line 22 and the condenser 18.

[0032] The control unit 24 receives information from the temperature sensor 21 about the actual condensation temperature in the condenser 18. At step 39, the control unit 24 compares the actual condensation temperature T.sub.a with the desired condensation temperature T. If there is a difference between the actual condensation temperature T.sub.a and the desired condensation temperature T, the control unit 24 performs a further adjustment of the valve23, at step 40, in order to eliminate such a possible difference. Thereafter, the method restarts at step 31.

[0033] If instead, at step 35, the coolant temperature t.sub.2 in the engine outlet line 5 is higher than the highest temperature in said temperature range in which the thermostat 6 is partly open, the method continues at step 47. The thermostat 6 is fully open and it directs the entire coolant flow rate m from the engine outlet line 5 to the radiator line 7 and the radiator 8. At step 48, the control unit 24 calculates the required coolant flow rate {dot over (m)}.sub.3 at the temperature t.sub.1 to be directed to the condenser 18 in order to cool the working medium in the condenser 18 with the estimated cooling effect Q.sub.c at which the working medium condenses at the desired condensation temperature T. In this case, the control unit 24 receives information about the coolant temperature t.sub.1 from the temperature sensor 27. Furthermore, the control unit 24 has access to necessary parameters such as the heat capacity c.sub.p of the coolant and the working medium and performance data of the condenser 18. In view of this fact, it is possible for the control unit 24 to calculate the required coolant flow rate {dot over (m)}.sub.3 at the temperature t.sub.1 to be directed to the condenser 18.

[0034] At step 49, the control unit 24 regulates the valve 23 such that it provides a flow resistance in the heat exchanger bypass line 3a at which the coolant flow rate {dot over (m)} in the radiator line 7 is divided in a coolant flow rate {dot over (m)}.sub.3 through the heat exchanger line 22 and a remaining coolant flow rate {dot over (m)}.sub.4 through the heat exchanger bypass line 3a. At step 39, the control unit 24 receives information from the temperature sensor 21 about the actual condensation temperature T.sub.a. The control unit 24 compares, at step 39, the actual condensation temperature T.sub.a and the desired condensation temperature T. In case there is a difference between the desired condensation temperature T and the actual condensation temperature T.sub.a, the control unit 24 provides, at step 39, a further valve adjustment in order to eliminate such a possible difference. Thereafter, the method restarts at step 31.

[0035] The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims. It is, for example, possible to use other kind of a flow regulating mechanisms than a single adjustable valve 23 arranged in the radiator bypass line 3a. Furthermore, it is possible to cool other mediums in a heat exchanger than a working medium in a condenser 18. It is, for example, possible to cool charged air in a charged air cooler, recirculating exhaust gases in an exhaust gas cooler, an a working medium of a AC system in a condenser.