SE541668C2 - A cooling system for a combustion engine and a WHR system - Google Patents

A cooling system for a combustion engine and a WHR system

Info

Publication number
SE541668C2
SE541668C2 SE1750452A SE1750452A SE541668C2 SE 541668 C2 SE541668 C2 SE 541668C2 SE 1750452 A SE1750452 A SE 1750452A SE 1750452 A SE1750452 A SE 1750452A SE 541668 C2 SE541668 C2 SE 541668C2
Authority
SE
Sweden
Prior art keywords
coolant
condenser
combustion engine
radiator
cooling system
Prior art date
Application number
SE1750452A
Other versions
SE1750452A1 (en
Inventor
Thomas Sederholm
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 SE1750452A priority Critical patent/SE541668C2/en
Priority to DE102018002684.2A priority patent/DE102018002684B4/en
Publication of SE1750452A1 publication Critical patent/SE1750452A1/en
Publication of SE541668C2 publication Critical patent/SE541668C2/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
    • F01P3/02—Arrangements for cooling cylinders or cylinder heads
    • 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
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K9/00—Plants characterised by condensers arranged or modified to co-operate with the engines
    • F01K9/003—Plants characterised by condensers arranged or modified to co-operate with the engines condenser cooling circuits
    • 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
    • F01P7/16—Controlling of coolant flow the coolant being liquid by thermostatic control
    • F01P7/165—Controlling of coolant flow the coolant being liquid by thermostatic control characterised by systems with two or more loops
    • 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
    • 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
    • F01P3/02—Arrangements for cooling cylinders or cylinder heads
    • F01P2003/027—Cooling cylinders and cylinder heads in parallel
    • 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
    • F01P5/00—Pumping cooling-air or liquid coolants
    • F01P5/10—Pumping liquid coolant; Arrangements of coolant pumps
    • F01P2005/105—Using two or more pumps
    • 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
    • F01P2025/00—Measuring
    • F01P2025/08—Temperature
    • F01P2025/31—Cylinder temperature
    • 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
    • F01P2025/00—Measuring
    • F01P2025/08—Temperature
    • F01P2025/32—Engine outcoming fluid temperature
    • 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
    • F01P2025/00—Measuring
    • F01P2025/08—Temperature
    • F01P2025/33—Cylinder head temperature
    • 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
    • F01P2025/00—Measuring
    • F01P2025/08—Temperature
    • F01P2025/36—Heat exchanger mixed fluid temperature
    • 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
    • F01P2060/00—Cooling circuits using auxiliaries
    • F01P2060/02—Intercooler
    • 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
    • F01P2060/00—Cooling circuits using auxiliaries
    • F01P2060/14—Condenser
    • 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
    • F01P3/12—Arrangements for cooling other engine or machine parts
    • 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
    • F02G5/02—Profiting from waste heat of exhaust gases
    • 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)
  • Fluidized-Bed Combustion And Resonant Combustion (AREA)

Abstract

The present invention relates to a cooling system for a combustion engine (2) and a WHR-system (10). A control unit (8) receives information about a parameter related to the cooling demand of the combustion engine (2). When there is no virtually cooling demand of the combustion engine (2), the control unit (8) controls three valve devices (4, 20, 23) such that they divide the cooling system in a first circuit in which a first coolant pump (4) provides a non-cooled coolant flow to the combustion engine (2) and a second circuit in which a second coolant pump (21) provides a cooled coolant flow to a condenser (15) of the WHR-system and via an engine bypass line (19). The existence of the engine bypass line (19) and the second coolant pump (21), makes it possible to control the temperature and the flow of the coolant directed to the condenser (15) with a high accuracy which results in a high efficiency of the WHR system during operating conditions when there is no cooling demand of the combustion engine (2).

Description

A cooling system for a combustion engine and a WHR system BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a cooling system for a combustion engine and a WHR-system according to the preamble of claim 1. The present invention also relates to a vehicle comprising a cooling system.
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 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 working medium in the evaporator. Since the supplied heat effect 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 2012/0198840 shows a cooling system with a circulating coolant which cools a combustion engine and a working medium in a condenser of a WHR system. The cooling circuit comprises a condenser circuit comprising a coolant pump and a three way valve by which it is possible to direct the coolant flow from the condenser to the combustion engine or a radiator. During a warm- up phase of the combustion engine, the coolant from the condenser is directed, via said three way valve, to the engine for shortening the warm-up phase of it and to the radiator when the combustion engine has been heated to a regular operating temperature.
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 accurate manner in order to substantially continuously establish a condensation temperature 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 defined in claim 1. The first valve device makes it possible to create two coolant flows with different temperatures. The second valve device makes it possible to mix said two coolant flows in a manner such that the mixture obtains a temperature at which it cools the working medium in the condenser to a desired condensation temperature. However, during certain operating conditions, it is difficult to control the temperature of the mixed coolant directed to the condenser with a desired accuracy. In order to address this problem, the cooling system comprises an engine bypass line with a second coolant pump able to pump coolant leaving the condenser, via the engine bypass line, to the radiator. A third valve device is designed to direct coolant leaving the condenser to the engine or the engine bypass line. A control unit is configured to receive information about a parameter related to the cooling demand of the combustion engine and to control the three valve devices such that they, when there is no cooling demand of the combustion engine, divide the cooling system in a first circuit in which non-cooled coolant is directed to the combustion engine and a second circuit in which cooled coolant is directed to the condenser. It is relatively easy to control the speed of the second coolant pump such that it pumps a coolant flow through the radiator at which the coolant is cooled to a desired temperature with a high accuracy. The ability of the second circuit to give the coolant a desired temperature with high accuracy before it is directed to the condenser results in a high efficiency of the WHR system during operating conditions when there is no cooling demand of the combustion engine. There is substantially only a cooling demand of a modem combustion engine when it is highly loaded. A modem combustion engine provided with a WHR system is not frequently highly loaded. In view of this fact, it is possible to use the second circuit and provide a very accurate cooling of the working medium in the condenser during a relatively large part of the operation time of the combustion engine.
According to an embodiment of the invention, the second coolant pump may be an electric pump. An electric pump is driven by an electric motor. It is relatively easy to control the speed of the electric motor and thus the coolant flow pumped by the electric pump. The first coolant pump may be a mechanical pump driven by a component in a powertrain of a vehicle. The first coolant pump may be arranged in an engine inlet line.
According to an embodiment of the invention, the cooling system comprises a control unit configured to start the operation of the second coolant pump when there is no cooling demand of the combustion engine and to shut off the operation of the second coolant pump when there is a cooling demand of the combustion engine. In case there is a cooling demand of the combustion engine, the first coolant pump circulates the coolant in the entire cooling system. Thus, the second coolant pump is only used during operating conditions when the WHR system is in operation and there is no cooling demand of the combustion engine.
According to an embodiment of the invention, the control unit is configured to control the speed of the second coolant pump such that the coolant entering the condenser has a temperature which results in a cooling of the working medium in the condenser to a desired condensation temperature. The control unit may have access to stored data about suitable speeds of the second coolant pump at different operating conditions. Alternatively, the control unit may calculate a suitable speed of the second coolant pump by information of suitable operating parameters. According to a further alternative, the control unit controls the speed of the second coolant pump by means of feedback information from a temperature sensor sensing the temperature of the coolant entering the condenser.
According to an embodiment of the invention, the engine bypass line comprises a check valve designed to allow a coolant flow from the condenser outlet line towards the radiator and to prevent a coolant flow in the opposite direction. Such a check valve ensures a coolant flow in an incorrect direction through the engine bypass line when the second coolant pump is not in operation.
According to an embodiment of the invention, the third valve device is a two way valve which is settable in a first position in which it directs the coolant flow from the condenser to the combustion engine and a second position in which it directs the coolant flow from the condenser, via the engine bypass line, to the radiator. In this case, the third valve device is designed as a single valve settable in two positions. The two way valve may be a solenoid valve.
According to an embodiment of the invention, the first valve device is a three way valve. In this case, the first valve device is designed as a single valve. Alternatively, the first valve device is designed as two two way valves wherein a first two way valve is arranged in a radiator inlet line and a second two way valve is arranged in the radiator bypass line. The three way valve may comprise an inlet opening receiving coolant from the engine outlet line, a first outlet opening directing coolant to the radiator bypass line and a second outlet directing coolant to the radiator. During operating conditions when there is no cooling demand of the combustion engine, the first valve device is configured to direct the entire coolant flow from the combustion engine to the radiator bypass line. During operating conditions when there is a cooling demand of the combustion engine, the first valve device is adjusted such that it directs a suitable part of the coolant flow to the radiator and a remaining part of the coolant flow to the radiator bypass line. Preferably, the first valve device is adjustable in a stepless manner. In this case, it is possible to distribute the coolant flow between the radiator and the radiator bypass line with a high accuracy.
According to an embodiment of the invention, the second valve device is a three way valve. 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 engine inlet line. During operating conditions when there is no cooling demand of the combustion engine, the second valve device is configured to direct the entire coolant from the radiator bypass line to the combustion engine. During operating conditions when there is a cooling demand of the combustion engine, the second valve device is adjusted such that it directs a part of the coolant flow from the radiator bypass line to a condenser inlet line to be mixed with the coolant flow from the radiator. A remaining part of the coolant flow from the radiator bypass line is direct to the combustion engine. When said mixed coolant flow has been directed to the condenser and cooled the working medium it is directed to the combustion engine. Preferably, the second valve device also is adjustable in a stepless manner.
According to an embodiment of the invention, the control unit is configured to receive information about a parameter in the form of the temperature of the coolant leaving the combustion engine in order to determine the cooling demand of the combustion engine. The temperature of the coolant leaving the combustion engine is related to the temperature of the combustion engine and the cooling demand of the combustion engine. In case the coolant temperature is lower than a specific temperature, there is no cooling demand of the combustion engine. In case the coolant temperature is higher than a specific temperature, there is a cooling demand of the combustion engine.
According to an embodiment of the invention, the control unit is configured to control the valve devices such that the coolant directed to the condenser has a temperature 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 temperature of the coolant which results in a cooling of the working medium in the condenser to a desired condensation temperature. 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 temperature for a working medium has a corresponding condensation pressure.
According to an embodiment of the invention, the control unit is configured to receive information from a sensor sensing the temperature or the temperature/pressure 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 first circuit comprises a heat exchanger by which it is possible to provide a cooling of coolant leaving the combustion engine. By means of such a heat exchanger, it is possible to reduce the operating time at which the combustion engine needs to be cooled by means of the radiator. Thus, the use of such a heat exchanger increase the operating time when it is possible to divide the cooling system into said two circuits. The coolant may be cooled in the heat exchanger by air, coolant or another medium. The cooling of the coolant may be controlled by the control unit.
The invention is also related to a vehicle comprising a cooling system according to any one of the preceding claims 1-14.
BRIEF DESCRIPTION OF THE DRAWING In the following a preferred embodiment of the invention is described, as an example, with reference to the attached drawing, in which: Fig. 1 shows a cooling system according to an embodiment of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 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 a first coolant pump 3. The first coolant pump 3 may be a mechanical pump operated by a component in the powertrain of the vehicle 1. The first coolant pump 3 is arranged in an engine inlet line 2a. Thus the first coolant pump 3 pumps coolant through cooling channel in the combustion engine 2. The coolant leaving the combustion engine 2 is received in an engine outlet line 2b. A first three way valve 4 is arranged at an end of the engine outlet line 2b. The cooling system comprises a radiator inlet line 5 a directing coolant to a radiator 5 and a radiator outlet line 5b receiving coolant from the radiator 5. The cooling system comprises a radiator bypass line 6 directing coolant past the radiator 5. A radiator fan 7 and ram air provides a cooling air flow through the radiator 5 during operation of the vehicle 1. The first three way valve 4 is controlled by a control unit 8. The first three way valve 4 has one inlet opening receiving coolant from the engine outlet line 2b, a first outlet directing coolant to the radiator inlet line 5a and a second outlet directing coolant to the radiator bypass line 6. Thus, it is possible for the first three way valve 4 to receive coolant from the engine outlet line 2b and distribute it between the radiator inlet line 5 a and the radiator bypass line 6. The first three way valve 4 is adjustable in a stepless manner.
The vehicle is provided with a WHR-system (Waste Heat Recovery system). The WHR- system comprises a working medium pump 9 which pressurizes and circulates a working medium in a closed a circuit 10. 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 working medium pump 9 pressurizes and circulates the working medium to an evaporator 11. The working medium is heated in the evaporator 11, for example, by exhaust gases from the combustion engine to a temperature at which it evaporates. The working medium is circulated from the evaporator 11 to the expander 12. The pressurised and heated working medium expands in the expander 12. The expander 12 generates a rotary motion which may be transmitted, via a suitable mechanical transmission 13, to a shaft 14 of the powertrain of the vehicle 1. Alternatively, the expander 12 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 1 or a component on the vehicle 1 in a later state.
After the working medium has passed through the expander 12, it is led to a condenser 15. The working medium is cooled in the condenser 15 by coolant from the cooling system to a temperature at which it condenses. The working medium is led from the condenser 15 to a receiver 16. The pressure in the receiver 16 can be varied by means of a pressure regulator 16a. The pump working medium 9 sucks working medium in a liquid state from the receiver 16. A second control unit 17 controls the operation of the WHR-system. The second control unit 17 controls the operation of the working medium pump 9 and the expander 12. The WHR-system makes it possible to transform thermal energy from the exhaust gases to mechanical energy or electrical energy. A temperature sensor or a pressure sensor 18 senses the condensation temperature or the condensation pressure in the condenser 15.
The temperature of exhaust gases and thus the heating effect of the working medium in the evaporator 11 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 15 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 15 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 15 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 15.
The cooling system comprises a condenser inlet line 15a directing coolant from a radiator outlet line 5b to the condenser 15 and a condenser outlet line 15b directing coolant from the condenser 15 to the engine inlet line 2a or an engine bypass line 19. The engine bypass line 19 directs coolant from the condenser outlet line 15b to the radiator inlet line 5 a. A two way valve 20 is arranged in a portion of the condenser outlet line 15b located downstream of its connection point to the engine bypass line 19 and upstream of its connection point to the engine inlet line 3. When the two way valve 20 is in an open position, the coolant flow in the condenser outlet line 15b is directed, via the two way valve 20, to the engine inlet line 2a. When the two way valve 20 is in a closed position, the coolant flow in the condenser outlet line 15b is directed to the engine bypass valve 19. A second coolant pump 21 and a check valve 22 are arranged in the engine bypass line 19. The second pump 21 is a pump with a controllable speed. The second pump 21 may be an electric pump driven by an electric motor. A second three way valve 23 in configured to receive coolant from the radiator bypass line 6 or the radiator 5. The second three way valve 23 directs the coolant to the engine inlet line 2a and the condenser inlet line 15 a. The second three way valve 23 is controlled by the control unit 8. The second three way valve 23 is adjustable in a stepless manner.
A first temperature sensor 24 senses the temperature of the coolant in the condenser inlet line 15 a. A second temperature sensor 25 senses the temperature of the coolant in the engine outlet line 2b. A heat exchanger 26 is arranged in the engine outlet line 2b. The coolant may receive a cooling in the heat exchanger 26 by air, coolant or another kind of cooling medium. The control unit 8 may be able to control the cooling in the heat exchanger 26. It may, for example, control an air fan forces air through the heat exchanger 26 or valve member controlling the flow of a cooling medium to the heat exchanger. It can be an advantage to use such a heat exchanger 26 but it is not necessary.
During operation, the control unit 8 receives information from the second control unit 17 about the operating condition of the WHR system. The control unit 8 may, for example, receive information indicating when the WHR system is in operation. In such a case, the control unit may receive information from the sensor 18 about the actual condensation temperature in the condenser 15. The control unit 8 estimates a desired condensation temperature of the working medium in the condenser 15. When ethanol is used as working medium, a condensation temperature of about 80°C is desirable during most operating conditions.
The control unit 8 receives substantially continuously information from the second temperature sensor 25 about the actual coolant temperature in the engine outlet line 2b. In case the control unit 8 receives information indicating that the coolant temperature in the engine outlet line 2b is lower than a threshold value, there is no cooling demand of the combustion engine 2. If also the WHR system is in operation, the control unit 8 sets the cooling system in a first mode. This means that the control unit 8 sets the first three way valve 4 in a position in which it directs the entire coolant flow from the engine outlet line 2b to the radiator bypass line 6, the second three way valve 23 in a position in which it directs the entire coolant flow from the radiator bypass line 6 to the engine inlet line 2a and the two way valve 20 in the closed position such the entire coolant flow in the condenser outlet line 15b is directed via the engine bypass line 19 to the radiator 5.
Consequently, the control unit 8 controls the first three way valve 4, the second three way valve 23 and the two way valve 20 such that they divide the cooling system in a first cooling circuit and a second cooling circuit. The first cooling circuit and the second cooling circuit are separate closed circuit. The first cooling circuit includes the engine inlet line 2a, the combustion engine 2, the engine outlet line 2b, the first three way valve 4, the radiator bypass line 6, the second three way valve 23 and the engine inlet line 2a. The first coolant pump 3 provides the coolant flow through the first circuit. The second circuit includes the condenser inlet line 15a, the condenser 15, the condenser outlet line 15b, the engine bypass line 19, the radiator inlet line 5a, the radiator 5, the radiator outlet line 5b and condenser inlet line 15a. The second coolant pump 21 provides the coolant flow through the second circuit.
Thus, the coolant circulated in the first circuit is not cooled in the radiator 5. The coolant circulated in the first circuit is only cooled by heat losses to the environment and by an optional heat exchanger 26. During many operating condition, such transfer of heat energy is enough for maintaining a regular operating temperature of the combustion engine 2. The second coolant pump 21 provides a coolant flow through the second circuit. The coolant circulated in the second circuit is transferred between the condenser 15 and the radiator 5. The control unit 8 estimates a required temperature of the coolant to be directed to the condenser 15 in order to cool the working medium to the desired condensation temperature in the condenser 15. The control unit 8 controls the speed of the second coolant pump 21 such that it provides a coolant flow at which the coolant is cooled to the requested temperature in the radiator 5. The control unit 8 receives information from the temperature sensor 24 about the actual temperature of the coolant directed to the condenser. In view of this information, it is possible to adjust the speed of the second coolant pump 21 in case the actual coolant temperature does not corresponds to the requested coolant temperature in the condenser inlet line 15a.
On the other hand, in case the control unit 8 receives information from the temperature sensor 25 indicating that the coolant temperature in the engine outlet line 2b is higher than a predetermined threshold value, there is a cooling demand of the combustion engine 2. The control unit 8 sets the cooling system in a second mode. This means that the control unit 8 sets the two way valve 20 in the open position and it shut off the second coolant pump 21. Consequently, the entire coolant flow in the condenser outlet line 15b is directed to the engine inlet line 2a. Furthermore, the control unit 8 adjusts the three way valve 4 such it directs a relatively large part of the coolant flow from the engine outlet line 2b to the radiator 5 and a remaining small second part of the coolant flow to the radiator bypass line 6. Thus, the coolant flow to the radiator 5 and the coolant flow to the radiator bypass line 6 can be varied by the first three way valve 4. The check valve 22 prevents a flow in an incorrect direction through the engine bypass line 19 when the second coolant pump is not in operation. The coolant flow is cooled to a lower temperature in the radiator 5 than the coolant flow through the radiator bypass line 6. In this case, the first three way valve 4 is used to provide two coolant flows of different temperatures.
The part of the coolant flow which is cooled in the radiator 5 is directed from the radiator outlet line 5b to the condenser inlet line 15a. However, the coolant in the radiator outlet line 5b has usually a too low temperature for cooling the working medium in the condenser 15 to the desired condensation temperature. The control unit 8 adjust the second three way valve 23 such that it directs a part of the warmer coolant flow from the radiator bypass line 6 to the condenser inlet line 15 a. In this case, a mixture of a cold coolant from the radiator 5 and warm coolant from the radiator bypass line 6 is directed to the condenser 15. The second three way valve 23 directs the remaining part of the coolant from the radiator bypass line 6 to the engine inlet line 2a.
The control unit 8 receives information from the temperature sensor 24 about the temperature of the coolant in the condenser inlet line 15 a. In case the actual temperature of the coolant is not corresponding to the desired temperature, the control unit 8 adjusts the first three way valve 4 and/or the second three way valve 23 in order to change the temperature of the coolant in the condenser inlet line 15a to the desired temperature. Possible temperatures of the coolant to be directed to the condenser 15 are within a temperature range having a minimum temperature defined by the temperature of the coolant in the radiator outlet line 5b and a maximum temperature defined by the temperature of the coolant in the radiator bypass line 6. By adjustment of the first three way valve 4 and the second three way valve 23 it is possible to give the coolant directed to the condenser 15 an arbitrary temperature within this temperature range. In case the first three way valve 4 directs substantially the entire coolant flow to the radiator 5, it is possible to direct a variable part of the coolant flow in the radiator outlet line 5b to the engine inlet line 2a. In this case, it is possible to reduce the coolant flow of the minimum temperature to the condenser 15. The coolant leaving the condenser 15 is directed, via the condenser outlet line 15b and the open second valve 20, to the engine inlet line 2a. Since the radiator inlet line 5a is located upstream of the condenser outlet line 15b in view of the flow distance from the first coolant pump 3, the pressure difference prevents a coolant flow from the condenser outlet line 15b, via the engine bypass line 19, to the radiator inlet line 5a when the second coolant pump 21 is not in operation.
There is substantially no cooling demand of a modem combustion equipped with a WHR system when it is normally loaded. The existence of the engine bypass line 19 and the second coolant pump 21 makes it possible to set the cooling system in the first mode during a relatively large part of its operation time. When the cooling system is in the first mode, it is possible to obtain a simpler and a more accurate control of the temperature of the coolant which is directed to the condenser 15. Such a control used to cools the working medium in the condenser 15. When the cooling system is in the first mode, it is possible to obtain an increased efficiency of the WHR system.
The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims (15)

Claims
1. A cooling system for a combustion engine (2) and a WHR-system (10), wherein the cooling system comprises a radiator (5), a radiator bypass line (6) configured to direct coolant past the radiator (5), a condenser (15) of the WHR system in which a working medium is cooled by coolant, a first valve device (4) configured to receive coolant from the engine (2) and direct it to the radiator (5) or the radiator bypass line (6), a second valve device (23) configured to control the coolant flow from the radiator (5) and the radiator bypass line (6) to the combustion engine (2) and the condenser (15), characterized in that the cooling system comprises an engine bypass line (19) configured to direct coolant from the condenser (15) to the radiator (5), a third valve device (20) which in a first position direct coolant from the condenser (15) to the engine (2) and in a second position directs coolant from the condenser (15) to the engine bypass line (19), and a control unit (8) configured to receive information about a parameter related to the cooling demand of the combustion engine (2) and to control the valve devices (4, 20, 23) such that they, when the parameter indicates that there is no cooling demand of the combustion engine (2), are configured to divide the cooling system in a first circuit in which a first coolant pump (3) provides a coolant flow from the radiator bypass line (6) to the combustion engine (2) and a second circuit in which a second coolant pump (21) provides a coolant flow from the radiator (5) to the condenser (15).
2. A cooling system according to claim 1, characterized in that the second coolant pump (21) is an electric pump.
3. A cooling system according to claim 1 or 2, characterized in that the control unit (8) is configured to start the operation of the second coolant pump (21) when there is no cooling demand of the combustion engine (2) and to shut off the operation of the second coolant pump (21) when there is a cooling demand of the combustion engine (2).
4. A cooling system according to claim 3, characterized in that the control unit (8) is configured to control the speed of the second coolant pump (21) such that the coolant entering the condenser (15) has a temperature and a flow which results in a cooling of the working medium in the condenser (15) to a desired condensation temperature.
5. A cooling system according to any one of the preceding claims, characterized in that the engine bypass line (19) comprises a check valve (22) designed to allow a coolant flow through the engine bypass line (19) in direction from the condenser (15) to the radiator (5) and to prevent a coolant flow in the opposite direction.
6. A cooling system according to any one of the preceding claims, characterized in that the third valve device (20) is a two way valve which is settable in a first position in which it directs the coolant flow from the condenser (15) to the combustion engine (2) and a second position in which it directs the coolant flow from the condenser (15), via the engine bypass line (19), to the radiator (5).
7. A cooling system according to any one of the preceding claims, characterized in that the first valve device (4) is configured to be set in a position in which it directs the entire coolant flow from the combustion engine (2) to the radiator bypass line (6) when there is no cooling demand of the combustion engine.
8. A cooling system according to any one of the preceding claims, characterized in that the first valve device is a three way valve (4).
9. A cooling system according to any one of the preceding claims, characterized in that the second valve device (23) is configured to be set in a position in which it directs the entire coolant flow from the radiator bypass line (6) to the combustion engine (2) when there is no cooling demand of the combustion engine.
10. A cooling system according to any one of the preceding claims, characterized in that the second valve device is a three way valve (23).
11. A cooling system according to any one of the preceding claims, characterized in that the control unit (8) is configured to receive information about a parameter in the form of the temperature of the coolant leaving the combustion engine (2) in order to determine the cooling demand of the combustion engine (2).
12. A cooling system according to any one of the preceding claims, characterized in that the control unit (8) is configured to control the valve devices (4, 20, 23) such that the coolant directed to the condenser (15) has a temperature and a flow at which it cools the working medium in the condenser (15) to a condensation pressure just above 1 bar.
13. A cooling system according to any one of the preceding claims, characterized in that the control unit (8) is configured to receive information from a sensor (18) about the temperature or the pressure in the condenser (15).
14. A cooling system according to any one of the preceding claims, characterized in that the first circuit comprises a heat exchanger (26) by which it is possible to provide a cooling of the coolant circulating through the combustion engine (2).
15. A vehicle comprising a cooling system according to any one of the preceding claims 1-14.
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