SE540931C2 - A cooling system for a WHR system - Google Patents

A cooling system for a WHR system

Info

Publication number
SE540931C2
SE540931C2 SE1551382A SE1551382A SE540931C2 SE 540931 C2 SE540931 C2 SE 540931C2 SE 1551382 A SE1551382 A SE 1551382A SE 1551382 A SE1551382 A SE 1551382A SE 540931 C2 SE540931 C2 SE 540931C2
Authority
SE
Sweden
Prior art keywords
condenser
coolant
line
radiator
cooling system
Prior art date
Application number
SE1551382A
Other versions
SE1551382A1 (en
Inventor
Ola Hall
Thomas Timrén
Zoltan Kardos
Original Assignee
Scania Cv Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania Cv Ab filed Critical Scania Cv Ab
Priority to SE1551382A priority Critical patent/SE540931C2/en
Priority to DE102016012528.4A priority patent/DE102016012528B4/en
Publication of SE1551382A1 publication Critical patent/SE1551382A1/en
Publication of SE540931C2 publication Critical patent/SE540931C2/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P3/00—Liquid cooling
    • F01P3/22—Liquid cooling characterised by evaporation and condensation of coolant in closed cycles; characterised by the coolant reaching higher temperatures than normal atmospheric boiling-point
    • F01P3/2285—Closed cycles with condenser and feed pump
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P3/00—Liquid cooling
    • F01P3/20—Cooling circuits not specific to a single part of engine or machine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/065—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle the combustion taking place in an internal combustion piston engine, e.g. a diesel engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P3/00—Liquid cooling
    • F01P3/22—Liquid cooling characterised by evaporation and condensation of coolant in closed cycles; characterised by the coolant reaching higher temperatures than normal atmospheric boiling-point
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G5/00—Profiting from waste heat of combustion engines, not otherwise provided for
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
    • B60K11/00—Arrangement in connection with cooling of propulsion units
    • B60K11/02—Arrangement in connection with cooling of propulsion units with liquid cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/10—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle
    • F01K23/101—Regulating means specially adapted therefor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/02—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using heat
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P7/00—Controlling of coolant flow
    • F01P7/14—Controlling of coolant flow the coolant being liquid
    • F01P2007/146—Controlling of coolant flow the coolant being liquid using valves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Engine Equipment That Uses Special Cycles (AREA)
  • Cooling, Air Intake And Gas Exhaust, And Fuel Tank Arrangements In Propulsion Units (AREA)
  • Air-Conditioning For Vehicles (AREA)

Abstract

The present invention relates to a cooling system for a WHR-system in a vehicle (1). The cooling system a first valve device (6, 27) configured to receive coolant from a coolant line (5) and direct it to a radiator line (7) and a radiator bypass line (9), a second valve device (23) configured to receive coolant from the radiator bypass line (9) and direct it to a condenser line (22) and a condenser bypass line (24), and a control unit (10) configured to control the first valve device (6, 27) and the second valve device (23 ) such that the coolant directed to the condenser (18) has a temperature and a flow rate which results in a cooling of the working medium in the condenser (18) to a desired condensation temperature/pressure at the actual operating condition.

Description

A cooling system for a WHR system BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a cooling system for 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 electric energy. A WHR system includes a pump which pressurizes and circulates a working medium in a closed circuit. The 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 electric 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 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 in the condenser is to be cooled to a condensation temperature as low as possible and substantially without subcooling. Consequently, in order to achieve a high thermal efficiency in a WHR-system, the working medium is to be cooled with a suitable cooling effect. However, the suitable cooling effect of the working medium in the condenser varies during different operating conditions such as with the heat effect supplied from, for example, the exhaust gases to the evaporator. Since the supplied heat from exhaust gases can vary rapidly, it is difficult to continuously provide a cooling effect of the working medium in the condenser resulting in a high thermal efficiency of a WHR-system.
US 2013/0118423 shows a cooling circuit with a circulating coolant which cools a motor. The cooling circuit comprises a cooling line where the coolant cools a working medium in a condenser of a WHR-system and a bypass line leading the medium past the condenser. The coolant flow through the bypass line is controlled by a relief valve which open at a specific pressure.
SUMMARY OF THE INVENTION The object of the present invention is to provide a cooling system which is able to adjust the cooling effect of a working medium in a condenser of a WHR-system in a quick and simple manner in order to substantially continuously establish a condensation temperature/pressure of the working medium in the condenser at which the WHR system receives a high thermal efficiency.
The above mentioned object is achieved by the cooling system according to the characterized part of claim 1. The first valve device makes it possible to divide the received coolant flow in a first coolant flow through the radiator and a second coolant flow through the radiator bypass line. The first coolant flow obtains a lower temperature than the second coolant flow when it is cooled in the radiator. Thus, it is possible to create two coolant flow of different flow rates and different temperatures by the first valve device. The first coolant flow leaving the radiator is directed to the condenser inlet line. The second coolant flow in the radiator bypass line enters the second valve device which directs a part of the second coolant flow to the condenser inlet line and a remaining part of the second coolant flow to the condenser bypass line. Thus, the second valve device makes it possible to supply an arbitrary part of the warmer second coolant flow to the cooler first coolant flow and direct the mixture to the condenser inlet line for cooling of the working medium in the condenser. A control unit controls the first valve device and the second valve device such that coolant directed to the condenser has a temperature and a flow rate resulting in a cooling of the working medium in the condenser to a desired condensation temperature/pressure.
According to an embodiment of the invention, the control unit is configured to estimate the required cooling effect of the cooling system and to control the first valve device such that it directs a coolant flow rate to the radiator which results in a cooling effect of the coolant in the radiator of a corresponding size as the required cooling effect of the cooling system. In this case, it is possible to maintain a thermal balance between input and output of thermal energy to the coolant in the cooling system.
According to an embodiment of the invention, the first valve device is a three way valve. The three way valve may comprises one inlet opening and two outlet openings. The three way valve receives, via the inlet opening, a coolant flow from a line of the cooling system and directs a first part of it, via a first outlet opening, to the radiator line and a second part of it, via the second outlet opening, to the radiator bypass line. In this case, the first valve device is designed as a single valve. Preferably, the first valve device is adjustable in a stepless manner. In this case, it is possible to vary the coolant flow rate to the radiator line and the radiator bypass line with a high accuracy. Alternatively, the first valve device is designed as two two way valves wherein a first two way valve is arranged in the radiator inlet line and a second two way valve is arranged in the radiator bypass line.
According to a further alternative, the first valve device comprises a thermostat, a thermostat bypass line and a valve controlling the flow rate through the thermostat bypass line. In this case, the thermostat directs a first coolant flow to the radiator line and a second coolant flow to the radiator bypass line depending on the temperature of coolant. When the coolant temperature is below a regulating temperature of the thermostat, it is possible to open the valve and provide a small first coolant flow through the thermostat bypass line and the radiator line as a complement to the second coolant flow through the radiator bypass line. Thus, it is also possible during such operating conditions to provide two coolant flows of different temperatures.
According to an embodiment of the invention, the first valve device and/or the second valve device are designed to conduct small coolant flow rates with a higher accuracy than larger coolant flow rates. During operating conditions when the coolant has a relatively low temperature, the first valve device directs a small coolant flow rate through the radiator line. This small coolant flow rate is mixed with a small warm coolant flow rate from the radiator bypass line by the second valve device before the mixture is directed to the condenser. In order to obtain a required coolant temperature of the mixture with a high accuracy, it is suitable to use a first valve device and a second valve device with the above mentioned design. The first valve devices may comprise a valve member movably arranged within a movement range having an extent between a first end position in which it directs no coolant flow to the radiator line and a second end position in which it directs the entire coolant flow to the radiator line. The movement range for the valve member at which it directs small coolant flows to the radiator line is greater than the movement range for the valve member at which it directs larger coolant flows to the radiator. The second valve device may have a corresponding design as the first valve device.
According to an embodiment of the invention, the second valve device is a three way valve. The three way valve receives a coolant flow from the radiator bypass line and directs a part of the coolant flow to the condenser inlet line and a remaining part of the coolant flow to the condenser bypass line. It may also direct coolant from the radiator line to the condenser bypass line. In this case, the second valve device is designed as a single valve. Preferably, the second valve device is adjustable in a stepless manner. In this case, it is possible to adjust the coolant flow rate to the condenser line and the condenser bypass line with a high accuracy. 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 temperature sensor about the temperature of the coolant flow in the condenser inlet line. In order to provide a cooling of the working medium in the condenser to a desired temperature, it is important that the coolant flow to the condenser has a required temperature. In this case, the control unit receives information about the actual temperature of the coolant in the condenser inlet line. In case there is a difference between the actual temperature and the required coolant temperature, the control unit may adjust the first valve device and/or the second valve device in order to eliminate this difference.
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 eliminate this difference.
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 nearly always possible to provide a coolant flow rate through the condenser which results in a cooling of the working medium in the condenser to a desired condensation temperature/pressure at different operating condition. 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.
According to an embodiment of the invention, the working medium in the WHR-system is 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 R245fa.
According to an embodiment of the invention, the control unit may be configured to receive information from a temperature sensor about the temperature of the working medium in a condenser outlet line. In this case, it is possible to detect the actual subcooling of the working medium in the condenser. In order to ensure that all working medium in the condenser is condensed, it is necessary to allow a certain subcooling of the working medium. However, it is important that the subcooling is relatively small since it reduces the thermal efficiency in a WHR-system. In this case, it is possible for the control unit to be informed of the actual subcooling and to adjust the first valve device and/or the second valve device in order to eliminate a possible difference between the actual subcooling and a desired subcooling.
According to an embodiment of the invention, the cooling system is also configured to cool a combustion engine. In this case, the cooling system is used to cool the combustion engine as well as the working medium in the condenser of the WHR system. Thus, no additional cooling system needs to be used. The control unit is configured to receive information from a temperature sensor sensing the temperature of the coolant in an engine outlet line. By means of this information, it is possible for the control unit to adjust the first control device and the second control device such that the combustion engine and the working medium in the condenser receive a required cooling of the coolant in the cooling system.
According to an embodiment of the invention, the working medium is heated in an evaporator of the WHR-system by means of exhaust gases from the combustion engine. The exhaust gases from a combustion engine contains a lot of heat energy, which usually is supplied to the environment. By means of a WHR-system, it is possible to recover a large part of the heat energy in the exhaust gases.
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 a first embodiment of the invention, Fig. 2 shows a cooling system according to a second embodiment of the invention and Fig. 3 shows graphs for three way valves with different properties which may be used in the cooling system.
DETAIFED 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. When the coolant has circulated through 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 first three way valve 6 has one inlet opening and two outlet openings. 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 first three way valve 6 is controlled by a control unit 10. The first three way valve 6 is adjustable in a stepless manner. Thus, it is possible for the first three way valve 6 to receive coolant from the engine outlet line 5 via the inlet opening and distribute a first part of it to the radiator line 7 via a first outlet opening and a second remaining part of it to the radiator bypass line 9 via a second outlet opening.
The vehicle is provided with a WHR-system (Waste Heat Recovery system). The WHR- system comprises a pump 12 which pressurizes 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. 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. 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 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 pressure in the receiver 19 can be varied by means of a pressure regulator 19a. 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 second control unit 20 controls the operation of the WHR-system. The second 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. A temperature sensor 21 or a pressure sensor senses the condensation temperature or the condensation pressure in the condenser 18.
The temperature of exhaust gases and thus the heating effect of the working medium in the evaporator 14 varies during different operating 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 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 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.
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 from a radiator outlet line 7b to the condenser 18. The condenser line 22 comprises a condenser outlet line 22b directing coolant from the condenser 18 to the engine inlet line 3. A second valve device in the form of a second three way valve 23 receives a coolant flow from the radiator bypass line 9. The second three way valve 23 is controlled by the control unit 10. The second three way valve 23 is adjustable in a stepless manner. The second three way 23 valve has one inlet opening receiving coolant from the radiator bypass line 9, one outlet opening directing coolant to a condenser bypass line 24 and a third opening which can be an outlet opening or an inlet opening. Consequently, the second three way valve 23 may receive coolant from the radiator bypass line 9 and direct a part of it to the condenser inlet line 22a and a remaining part of it to the condenser bypass line 24. Alternatively, the second three way valve 23 may receive coolant from the radiator outlet line 7b and direct it to the condenser bypass line 24. A temperature sensor 25 senses the temperature of the coolant in the engine outlet line 5. A temperature sensor 26 senses the temperature of the coolant in the condenser inlet line 22a.
During operation, the control unit 10 receives substantially continuously information from said temperature sensors 25, 26 about the actual coolant temperatures. The control unit 10 also receives information from the second control unit 20 about the operating condition of the WHR system. The control unit 10 may, for example, receive information from the sensor 21 about the actual condensation temperature in the condenser 18. The control unit 10 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 10 estimates a required flow rate and a required temperature of the coolant flow to be directed to the condenser inlet line 22a and the condenser 18 in order to provide the desired condensation temperature in the condenser 18.
The control unit 10 receives substantially continuously information about the coolant temperature in the engine outlet line 5. The temperature of the coolant in the engine outlet line 5 indicates the cooling requirement of the coolant in the cooling system. In case the coolant has a too low temperature the control unit 10 adjusts the three way valve 6 such that it directs a relatively small first part of the coolant flow to the radiator line 7 and a remaining relatively large second part of the coolant flow to the radiator bypass line 9. On the other hand, in case the coolant has a high temperature, the control unit 10 adjusts the three way valve 6 such it directs a relatively large first part of the coolant flow from the engine outlet line 5 to the radiator line 7 and a remaining relatively small second part of the coolant flow to the radiator bypass line 9. Thus, the coolant flow rate to the radiator line 7 and the coolant flow rate to the radiator bypass line 9 can be varied by the first three way valve 6. Furthermore, the first part of the coolant flow is cooled to a lower temperature in the radiator 8 than the temperature of the second part of the coolant flow. Consequently, it is possible to create two coolant flows of different temperatures and flow rates by means of the first three way valve 6.
The first part of the coolant flow which is cooled in the radiator 8 is directed from the radiator outlet line 7b to the condenser inlet line 22a. However, the coolant in the radiator outlet line 7b has usually a too low temperature for cooling the working medium in the condenser 18 to the desired condensation temperature. The control unit 10 adjust the second three way valve 23 such that it directs a part of the warmer coolant flow from the radiator bypass line 9 to the condenser inlet line 22a. In this case, a mixture of a cold coolant from the radiator line 7 and warm coolant from the radiator bypass line 9 is directed to the condenser 18. The second three way valve 23 directs the remaining part of the coolant from the radiator bypass line 9 to the condenser bypass line 24. The control unit 10 receives information from the temperature sensor 26 about the temperature of the coolant in the condenser inlet line 22a. In case the temperature of the coolant is not the required temperature, the control unit 10 adjusts the first three way valve 6 and/or the second three way valve 23 in order to change the temperature of the coolant in the condenser inlet line 22a to the required temperature. Possible temperatures of the coolant to be directed to the condenser 18 are within a temperature range having a minimum temperature defined by the temperature of the coolant in the radiator outlet line 7b and a maximum temperature defined by the temperature of the coolant in the radiator bypass line 9. By adjustment of the first three way valve 6 and the second three way valve 23 it is possible to give the coolant directed to the condenser 18 an arbitrary temperature within this temperature range. In case the first three way valve 6 directs substantially the entire coolant flow rate to the radiator line 7, it is possible to direct a variable part of the coolant flow rate in the radiator outlet line 7b to the condenser bypass line 24. In this case, it is possible to reduce the coolant flow rate of the minimum temperature to the condenser 18.
In order to control the cooling system, the control unit 10 may estimate the required cooling effect of the cooling system. In this case, the required cooling effect is the sum of the required cooling effect of the working medium in the condenser 18 and the required cooling effect of the combustion engine 2. When the combustion engine 2 has a lower temperature than a desired operating temperature, the combustion engine 2 does not need to be cooled. The temperature of the combustion engine is indicated by the sensor 25 sensing the temperature of the coolant in the engine outlet line 5. In this case, the required cooling effect of the cooling system is defined by the required cooling effect of the working medium in the condenser 18. As a consequence, the control unit 10 controls the first three way valve 6 such that it directs a coolant flow rate to the radiator line 7 such that the coolant receives a cooling effect in the radiator 8 of the same value as the required cooling effect of the working medium in the condenser 18. In this case, a thermal balance is maintained between input and output of thermal energy in the cooling system.
During operating conditions when combustion engine is to be cooled, the required cooling effect of the cooling system is the sum of the required cooling effect of the working medium in the condenser 18 and the required cooling effect of the combustion engine 2. In this case, the control unit 10 controls the first three way valve 6 such that it directs a coolant flow rate to the radiator line 7 such that the coolant receives a cooling effect in the radiator 8 of the same value as the sum of the required cooling effect of the working medium in the condenser 18 and the required cooling effect of the combustion engine 2.
Fig 2 shows an alternative embodiment of the cooling system. In this case, a first valve device 27 comprises a conventional thermostat 27a which opens automatically when the coolant in the engine outlet line 5 has a temperature above a regulating temperature of the thermostat 27a. The first valve device 27 comprise further a thermostat bypass line 27b and a valve 27c controlled by the control unit 10. The valve 27c is adjustable in a stepless manner between a closed position and a fully open position. Furthermore, a temperature sensor 30 is configured to sense the temperature of the working medium in a condenser outlet line 18a of the WHR-system.
During operation, the control unit 10 receives information from the second control unit 20 about the operating condition of the WHR system. The control unit 10 receives information from the sensor 21 about the actual condensation temperature in the condenser 18 and from the temperature sensor 30 about the temperature of the working medium leaving the condenser 18. The difference between the condensation temperature and the temperature of the working medium leaving the condenser 18 is the subcooling of the working medium. In order to achieve a high thermal efficiency in a WHR-system, the working medium in the condenser is to be cooled to a condensation temperature as low as possible and substantially without subcooling. The control unit 10 estimates a desired condensation temperature of the working medium in the condenser 18 which may be about 80°C when ethanol is used as working medium. Furthermore, the control unit 10 estimates a required flow rate and a required temperature of the coolant to be directed to the condenser inlet line 22a and the condenser 18 in order to provide the desired condensation temperature in the condenser 18 and a small subcooling of the working medium in the condenser 18.
In case the coolant in the engine outlet line 5 has a lower temperature than the regulating temperature of the thermostat 27a, the thermostat 27a only directs coolant to the radiator bypass line 9. In order to provide a coolant flow through the radiator line 7, the control unit 10 may open the valve 27c and provide a coolant flow through the thermostat bypass line 27b. In this case, a relatively small first part of the coolant flow in the engine outlet line 5 is directed to the radiator line 7 and a remaining relatively large second part of the coolant flow is directed to the radiator bypass line 9. Since the first part of the coolant flow is cooled in the radiator 8, it has a lower temperature than the coolant flow through the radiator bypass line 9.
The first part of the coolant flow which is cooled in the radiator 8 is directed from the radiator outlet line 7b to the condenser inlet line 22a. The coolant in the radiator outlet line 7b has usually a too low temperature for cooling the working medium in the condenser 18 to the desired condensation temperature. Therefore, the control unit 10 adjust the second three way valve 23 such that it directs a part of the warmer coolant flow from the radiator bypass line 9 to the condenser inlet line 22a. In this case, a mixture of the coolant flow from the radiator outlet line 7b and a part of the coolant flow from the radiator bypass line 9 is directed to the condenser 18. The second three way valve 23 directs the remaining part of the coolant from the radiator bypass line 9 to the condenser bypass line 24.
The control unit 10 receives information from the sensor 21 about the actual condensation temperature in the condenser 18 and from the temperature sensor 30 about the actual temperature of the working medium leaving the condenser 18. In case the condensation temperature and/or the subcooling of the working medium are not of desired values, the control unit 10 adjusts the valve 27c and/or the second three way valve 23 in order to change the flow rate and the temperature of the coolant directed to the condenser 18 such that the working medium obtains the desired condensation temperature and the desired small subcooling.
Fig. 3 shows schematically a graph of certain relevant properties of the first three way valve 6 used in the cooling system. The three way valve 6 comprises a valve member which is movably arranged within a movement range between a first end position and a second end position. The movable member of the first three way valve 6 may divide the coolant flow from the engine outlet line 5 in a first coolant flow through the radiator line 9 and a second coolant flow through the radiator bypass line 9. The valve member may provide an arbitrary movement such as a rotary movement or a rectilinear movement between the end positions. In the first end position, it directs no coolant flow rate to the radiator line 7 and in the second end position it directs the entire coolant flow rate to the radiator bypass line 9. The graph depicts the percentage proportion of the flow rate directed to the radiator line 7 as a function of the valve member distance D from the first position. A first curve 31 shows such a function for a conventional three way valve. In this case, the valve member distance D from the first end position is directly related to the flow rate to the radiator line 7. A second graph 32 shows an embodiment of a three way valve 6 according to the invention. When the coolant has a relatively low temperature, the three way valve 6 is used to direct a small coolant flow rate to the radiator line 7. In order to direct a small coolant flow rate to the radiator line 7 with a high accuracy, the valve member has an increased movement range for small coolant flows to the radiator line 7. This is indicated by the curve 32, where a first part 32a including 40 % of the movement range of the valve member is used to direct coolant flow rates from 0 to 10 % to the radiator line 7. The remaining 60 % of the movement range of the valve member is used to direct coolant flow rates from 10 to 100 % to the radiator line 7. Curve 33 indicates a further alternative relationship between the percentage proportions of the flow rate directed to the radiator line 7 as a function of the valve member distance D from the first position. In this case, the flow rate accuracy increases continuously in direction towards the first end position of the valve member. The second three way valve 23 may have a corresponding design as the first three way valve 6.
The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims (14)

Claims
1. A cooling system for a WHR-system in a vehicle (1), wherein the cooling system comprises - a radiator line (7) directing a first coolant flow through a radiator (8), - a radiator bypass line (9) directing a second coolant flow past the radiator (8), - a condenser line (22) directing coolant through a condenser (18) of the WHR system, - a condenser bypass line (24) directing the coolant past the condenser (18), characterized in that the cooling system comprises - a first valve device (6, 27) configured to receive coolant from a coolant line (5) and direct it to the radiator line (7) and the radiator bypass line (9), - a radiator outlet line (7b) directing at least a part of the first coolant flow from the radiator line (7) to the condenser line (22), - a second valve device (23) configured to receive coolant from the radiator bypass line (9) and direct it to the condenser line (22) and the condenser bypass line (24), and - a control unit (10) configured to control the first valve device (6) and the second valve device (23) such that the coolant directed to the condenser (18) has a temperature and a flow rate which results in a cooling of a working medium in the condenser (18) to a desired condensation temperature/pressure at the actual operating condition.
2. A cooling system according to claim 1, characterized in that the control unit (10) is configured to estimate the required cooling effect of the cooling system and to control the first valve device (6) such that it directs a coolant flow rate to the radiator (8) which results in a cooling effect in the radiator of a corresponding size as the required cooling effect of the cooling system.
3. A cooling system according to claim 1 or 2, characterized in that the first valve device is a three way valve (6).
4. A cooling system according to claim 1 or 2, characterized in that the first valve device (27) comprises a thermostat (27a), a thermostat bypass line (27b) and a valve (27c) controlling the flow rate through the thermostat bypass line (27c).
5. A cooling system according to any one of the preceding claims, characterized in that the first valve device (6) and/or the second valve device (23) are designed to conduct small coolant flow rates with a higher accuracy than larger coolant flow rates.
6. A cooling system according to any one of the preceding claims, characterized in that the second valve device is a three way valve (23).
7. A cooling system according to any one of the preceding claims, characterized in that the control unit (10) is configured to receive information from a temperature sensor (26) about the temperature of the coolant flow in a condenser inlet line (22a).
8. A cooling system according to any one of the preceding claims, characterized in that the control unit (10) is configured to receive information from a sensor (21) about the temperature or the pressure in the condenser (18).
9. A cooling system according to any one of the preceding claims, characterized in that the control unit (10) is configured to receive information from a temperature sensor (30) about the temperature or the working medium in a condenser outlet line (18a).
10. A cooling system according to any one of the preceding claims, characterized in that the control unit (10) is configured to control the first valve device (6, 27) and the second valve device (23) such that the coolant directed to the condenser (18) has a temperature and a flow rate which results in a cooling of the working medium in the condenser (18) to a condensation pressure just above 1 bar.
11. 1 1. Cooling system according to any one of the preceding claims, characterized in that the working medium in the WHR-system is ethanol.
12. A cooling system according to any one of the preceding claims, characterized in that the cooling system is also configured to cool a combustion engine (2).
13. A cooling system according to claim 12, characterized in that the control unit (10) is configured to receive information from a temperature sensor (25) sensing the temperature of the coolant in an engine outlet line (5).
14. Cooling system according to any one of the preceding claims, characterized in that the working medium is heated in an evaporator (14) of the WHR-system by means of exhaust gases from a combustion engine (2).
SE1551382A 2015-10-27 2015-10-27 A cooling system for a WHR system SE540931C2 (en)

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SE541554C2 (en) 2017-01-26 2019-10-29 Scania Cv Ab A cooling system for cooling of objects with coolant at three different temperatures and a vehicle comprising such a system
US10570784B2 (en) 2017-09-22 2020-02-25 Tenneco Gmbh Rankine power system for use with exhaust gas aftertreatment system
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