SE540350C2

SE540350C2 - A WHR system for a vehicle comprising a combustion engine and a hydraulic retarder

Info

Publication number: SE540350C2
Application number: SE1651574A
Authority: SE
Inventors: Zoltan Kardos; Thomas Hällqvist
Original assignee: Scania Cv Ab
Priority date: 2016-11-30
Filing date: 2016-11-30
Publication date: 2018-07-24
Also published as: SE1651574A1; DE102017010531A1

Abstract

The present invention relates to a WHR-system for a vehicle (1) comprising a combustion engine (2) and a hydraulic retarder (20). The WHR system comprises a WHR circuit (16) comprising a pump (5) configured to pressurize and circulate a working medium, a first evaporator (18) in which the working medium is configured to be heated by exhaust gases from the combustion engine (2), an expander (24) configured to transform heat energy from the working medium into mechanical energy for propulsion of the vehicle (1) and a condenser (13) in which the working medium is configured to be cooled. The WHR system comprises a heat storage (28) configured to store heat energy from a braking process of the hydraulic retarder (20), a second evaporator (19) in which the working medium is configured to be heated by heat energy from said heat storage (28) and a valve arrangement (21, 22, 23, 33) configured to direct the working medium flow in the WHR circuit (16) to the first evaporator (18) or the second evaporator (19).

Description

A WHR system for a vehicle comprising a combustion engine and a hydraulic retarder BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a WHR system for a vehicle comprising a combustion engine and a hydraulic retarder according to the preamble of claim 1. The present invention also relates to a vehicle comprising a WHR 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 an evaporator where the working medium is heated and evaporated by a heat source 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 working 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.

Heavy vehicles are often equipped with one or several supplementary brakes in order to reduce wear on the ordinary wheel brakes of the vehicle. Such a supplementary brake may be a hydraulic retarder. A hydraulic retarder comprises a toroidal chamber defined by a static vane and a dynamic vane which is connected to the wheels to be braked. A fluid is supplied to the toroidal chamber during activation of the retarder. The viscous drag forces between dynamic vane and static vane provides retardation of the dynamic vane and the wheels. During the braking process, the fluid obtains a rapid heating. The fluid may be heated to a temperature of about 300°C before it leaves the retarder. The hot fluid leaving the retarder is led to a retarder cooler where it is cooled by coolant circulating in a cooling system of the vehicle. In this case, the heat energy generated during the braking process is dissipated, via a radiator of the cooling system, to ambient air.

JP 2010077901 shows a waste heat recovery device for a vehicle. The device comprises a first cooling water heater heating water of a cooling water circuit by heat of a retarder and a second cooling water heater heating the cooling water of the cooling water circuit by exhaust gas of an engine. The water of the cooling water circuit is made to flow to the first cooling water heater when the retarder operates and to the second cooling water heater when the retarder does not operate. The absorbed heat is used for a Rankine cycle.

SUMMARY OF THE INVENTION The object of the present invention is to provide a WHR system for a vehicle which is able to utilize heat energy from the exhaust gases of a combustion engine as well as heat energy from a hydraulic retarder and convert the heat energy to mechanical energy for propulsion of the vehicle.

The above mentioned object is achieved by the WHR system according to claim 1. During operating conditions when exhaust gases from a combustion engine has a high temperature, it is suitable to use the exhaust gases for heating and evaporation of the working medium in the first evaporator of the WHR circuit. During operating conditions when the retarder is activated, the vehicle is braked and there is no need to supply mechanical energy for propulsion of the vehicle. In view of this fact, the heat energy generated from retarder braking processes is stored in a heat storage. When the retarder braking process is completed, it is possible to use the stored heat energy from the retarder braking process or heat energy from the exhaust gases for propulsion of the vehicle. The stored heat energy from a retarder braking process may be used during operating conditions when the energy level in the exhaust gases is low. During a braking process of a hydraulic retarder, a large amount of heat energy is generated. The possibility to save this heat energy and use it during suitable operating conditions when the heat energy in the exhaust gases is low increases the capacity of the WHR system.

According to an embodiment of the invention, said heat storage is configured to absorb heat energy from the retarder fluid used in the hydraulic retarder. The retarder fluid may be a suitable oil. The retarder fluid leaving the retarder has usually a very high temperature and it contains a large amount of heat energy, which can be absorbed and stored in the heat storage.

According to an embodiment of the invention, said heat storage comprises a tank configured to receive and store retarder fluid leaving the retarder. Such a heat storage may have a very simple design. The container may be provided with a heat insulating layer in order to maintain a high temperature of the retarder fluid during a relatively long period of time. However, the heat storage may have another design. It may, for example, comprise a suitable material absorbing heat energy from the retarder fluid.

According to an embodiment of the invention, the WHR system comprises a heat transfer arrangement configured to transfer heat from the heat storage to the second evaporator. The heat transfer arrangement may comprise a heat transfer circuit, a pump configured to circulate a heat transfer fluid in the circuit from the heat storage to the second evaporator. When it is time to use the stored heat energy, the pump is started and it provides circulation of the heat transfer fluid in the heat transfer circuit. During this circulation, the heat transfer fluid transfers heat energy from the heat energy storage to the working medium in the second evaporator. The heat transfer circuit may be a closed circuit such that the heat transfer fluid is directed back to the heat storage after it has delivered heat energy to the working medium in the second evaporator. However, it is possible to use other kinds of heat transfer arrangements such as, for example, heat pipes.

According to an embodiment of the invention, said heat transfer fluid is the same fluid as used in the retarder circuit. In case, the heat storage comprises a container with hot retarder fluid, it is possible to circulate the stored retarder fluid to the second evaporator for heating of the working medium in the WHR circuit. Alternatively, said heat transfer fluid may be a separate fluid in relation to the retarder fluid. In such a case, the heat transfer fluid may absorbs heat energy in the heat storage and releases the absorbed heat energy to the working medium in the second evaporator.

According to an embodiment of the invention, the WHR system comprises a control unit configured to control said valve arrangement in view of information about at least one operating parameter. In view of such information, the control unit may determine whether the heat energy in the actual exhaust gases or the heat energy in the heat storage are to be used for heating the working medium in the WHR circuit. Said parameter may be the temperature of the exhaust gases and/or the temperature in the heart storage. In this case, it is possible to use the heat source having the highest temperature for heating of the working medium. However, it is possible to receive information from further relevant parameters. The control unit may for example receive information from a GPS unit about the topography of the road ahead.

According to an embodiment of the invention, the first evaporator and the second evaporator are arranged in parallel lines in the WHR circuit. Such a design make it possible to use a relatively simple valve arrangement for directing the circulating working medium to the evaporator to be used for evaporation of the working medium. The valve arrangement may comprises a three way valve arranged in a branched point of the two parallel lines in an upstream position of the evaporators. Such a three way valve makes it possible to direct the working medium flow to the parallel line and the evaporator to be used in a very simple manner. Alternatively, each parallel line may include a two way valve arranged in a position upstream of the respective evaporators. In this case, one of the two way valves is set in an open position while the other two way valve is set in a closed position.

According to an embodiment of the invention, the valve arrangement comprises check valves arranged in a respective position downstream of the evaporators in the parallel lines. The check valves prevent a working medium flow in an incorrect direction to the evaporator that is not used. Alternatively, the valve arrangement may comprise a three way valve arranged in a connection point of the two parallel lines in a position downstream of the evaporators. Such a three way valve direct the working medium from the evaporator in use towards the expander at the same time as it prevents a working medium flow in an incorrect direction to the evaporator that is not in use.

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 and Fig. 2 shows a cooling system according to a first embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a schematically disclosed vehicle 1 powered by a combustion engine 2. The vehicle 1 may be a heavy vehicle and the combustion engine 2 may be a diesel engine. An exhaust line 3 directs exhaust gases from the combustion engine 2. The vehicle 1 comprises a cooling system comprising an engine inlet line 4 provided with a pump 5 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 6. The engine outlet line 6 comprises a retarder cooler 7. A first three way valve 8 is arranged at an end of the engine outlet line 6. The first three way valve 8 directs coolant to a radiator 9 or a radiator bypass line 10. The first three way valve 8 is controlled by a control unit 11. The first three way valve 8 is adjustable in a stepless manner. Thus, it is possible for the first three way valve 8 to distribute a part of coolant flow to the radiator 9 and a remaining part of the coolant flow to the radiator bypass line 10. The cooling system comprises a second three way valve 12. The second three way valve 12 is controlled by the control unit 11. The second three way valve 12 is adjustable in a stepless manner. The second three way valve 12 may receive coolant from the radiator bypass line 10 and direct a part of it to a condenser line 13 and a remaining part of it to a condenser bypass line 14. Alternatively, the second three way valve 12 may receive coolant from the radiator 9 and direct it to the condenser bypass line 14. The condenser line 13 directs coolant from the radiator 9 to a condenser 15 of a WHR circuit 16.

The WHR circuit 16 comprises a pump 17 which pressurizes and circulates a working medium in the WHR circuit 16. In this case, the working medium is ethanol. However, it is possible to use other kinds of working mediums such as for example R145fa. The pump 17 pressurizes and circulates the working medium to a first evaporator 18 or a second evaporator 19. The working medium can be heated in the first evaporator 18 by exhaust gases flowing through the exhaust line 3 of the combustion engine 2. The working medium can be heated in a second evaporator 19 by heat energy from a hydraulic retarder 20. The first evaporator 18 is arranged in a first parallel line 16a and the second evaporator 19 are arranged in a second parallel line 16b of the WHR circuit 16. The WHR circuit comprises a three way valve 21 by which working medium is directed to the first parallel line 16a and the first evaporator 18 or to the second parallel line 16b and the second evaporator 19. Each parallel line 16a, 16b comprises a check valve 22, 23 in a position downstream of the respective evaporators 18, 19. The object of the check valves 22, 23 is to prevent a working medium flow in an incorrect direction towards the evaporator 18, 19 that is not in use. The working medium is heated in one of the evaporator 18, 19 to a temperature at which it evaporates. The evaporated working medium is directed to an expander 24. The expander 24 may be a turbine or a piston. The pressurised and heated working medium expands in the expander 24. The expander 24 generates a rotary motion which may be transmitted, via a suitable mechanical transmission 25, to a shaft 26 of the power train of the vehicle 1. Thus, the expander 24 converts thermal energy to mechanical energy for propulsion of the vehicle 1. The expander 24 may alternatively convert thermal energy to electrical energy which may be stored in a battery.

The working medium leaving the expander 24 is directed to the 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 temperature and the flow rate of exhaust gases and thus the heating effect of the working medium in the evaporators 18, 19 varies during different operating conditions. In order to maintain a substantially continuously high thermal efficiency in the WHR circuit 16, it is favourable to establish a condensation pressure as low as possible. However, it is suitable to avoid negative pressure in the WHR circuit 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. In order to maintain a high thermal efficiency, the control unit 11 controls the three way valves 8, 12 such that coolant of a variable temperature and flow rate cools the working medium in the condenser 15 in a manner 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 working medium is directed from the condenser 15 to a receiver 27. The pump 17 sucks working medium from the receiver 27 and directs it towards one of the evaporators 18, 19. The control unit 11 also control the operation of the pump 15 and the expander 24.

The vehicle comprises a retarder circuit 29. The retarder circuit 29 comprises a retarder pump 30 configured to direct a retarder fluid such as an oil to the retarder 20 when the control unit 11 initiates a braking process of the retarder 20. The retarder fluid is usually heated to a high temperature in the retarder 20 during the braking process. The retarder fluid leaving the retarder 20 is received and stored in a container in the form of a heat storage 28. During activation of the retarder, the fluid is directed from the heat storage 28 to the retarder cooler 7 where it is cooled by coolant circulating in the above mentioned cooling system before it again is directed to the retarder 20. The vehicle comprises a heat transfer circuit 31 configured to transfer heat from the heat storage 28 to the second evaporator 19 during operating conditions when the stored heat energy is used to heat the working medium in the second evaporator 19. A pump 32 circulates a heat transfer fluid in the heat transfer circuit 31.

During operating conditions when the vehicle 1 is traveling down a long hill, the driver may activate the hydraulic retarder 20 in order to travel down the hill at a selected constant speed. The control unit 11 activates the retarder pump 30 which directs a suitable fluid flow to the retarder 20 such that the vehicle 1 travels down the hill at the selected speed. The hot retarder fluid leaving the retarder 20 is collected in the heat storage 28. As long as the braking process continuous, a part of the retarder fluid in the heat storage 28 is led further, via the retarder cooler 6, to the retarder 20. As soon as the control unit 11 receives information indicating that the retarder braking process has terminated. The control unit 11 shuts off the retarder pump 30 and the hot retarder fluid is collected in the heat storage 28. The retarder pump 30 can be replaced by a valve which is set in an open position when the retarder is activated. In this case, the retarder 20 provides the circulation of the retarder fluid in the retarder circuit 29. The control unit 11 receives information about operating parameters p such as the temperature of the fluid in the heat storage 28 and the temperature of the exhaust gases in the exhaust line 3.

When the control unit 11 receives information indicating that there is a propulsion demand of the vehicle, the control unit 11 activates the combustion engine 2. The control unit compares the temperatures of the retarder fluid in the heat storage 28 and the temperature of the exhaust gases in the exhaust line 3. In case the exhaust gases has a higher temperature than the retarder fluid in the heat storage 28, the control unit 11 indicates a movement of the three way valve 21 to a first position in which it directs the working medium flow to the first parallel line 16a and the first evaporator 18. The hot exhaust gases heats the working medium in the first evaporator 19 such that it is evaporated. The pressurised and heated working medium leaves the first evaporator 18 and enters the expander 24. The working medium expands in the expander 24. The expander 24 generates a rotary motion which is transmitted, via the mechanical transmission 25, to the shaft 26 of the power train of the vehicle 1.

On the other hand, in case the exhaust gases has a lower temperature than the retarder fluid in the heat storage 28, the control unit 11 initiates a movement of the three way valve 21 to a second position in which it directs the working medium flow to the second parallel line 16b and the second evaporator 19. At the same time, the control unit 11 activates the pump 32 such that it starts to circulate the heat transfer fluid in the heat transfer circuit 31. The heat transfer fluid may be the same fluid as used in the retarder circuit 29. In this case, the pump 31 circulates hot retarder fluid from the heat storage 28 to the second evaporator 19 where it heats the working medium to an evaporation temperature. The pressurised and heated working medium leaves the second evaporator 19 and enters the expander 24. The working medium expands in the expander 24 such that the expander 24 generates a rotary motion which is transmitted, via the mechanical transmission 25, to the shaft 26 of the power train of the vehicle 1. The used retarder fluid is circulated back to the heat storage 28. Thus, the temperature of the retarder fluid in the heat storage decreases as long as the braking process continuous. As soon as the control unit 11 receives information indicating that the exhaust gases has a higher temperature than the retarder fluid in the heat storage 28, it shuts off the pump 31 and initiates a movement of the three way 21 valve to the first position such that the working medium is directed to the first evaporator 18.

Fig 2 shows an alternative embodiment of the WHR system. In this case, the heat transfer fluid is a separate fluid in relation to the retarder fluid. The heat transfer fluid absorbs heat from the retarder fluid in the heat storage 28 by means of a heat exchanger 34. Furthermore, the valve arrangement comprises, except the three way valve 21, a further three way valve 33 arranged in a connection point of the parallel line 16a, 16b in a position downstream of the evaporators 18, 19. The further three way valve 33 prevents a working medium flow in an incorrect direction to the evaporator 18, 19 that is not used.

The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims

1. A WHR system for a vehicle (1) comprising a combustion engine (2) and a hydraulic retarder (20), wherein the WHR system comprises a WHR circuit (16) comprising a pump (5) configured to pressurize and circulate a working medium, a first evaporator (18) in which the working medium is configured to be heated by exhaust gases from the combustion engine (2), an expander (24) configured to transform heat energy from the working medium into mechanical energy for propulsion of the vehicle (1) and a condenser (13) in which the working medium is configured to be cooled, characterized in that the WHR system comprises a heat storage (28) configured to store heat energy from a braking process of the hydraulic retarder (20), a second evaporator (19) in which the working medium is configured to be heated by heat energy from said heat storage (28) and a valve arrangement (21, 22,23, 33) configured to direct the working medium flow in the WHR circuit (16) to the first evaporator (18) or the second evaporator (19).

2. A WHR system according to claim 1, characterized in that said heat storage (28) is configured to receive heat energy from a retarder fluid used in the hydraulic retarder (20).

3. A WHR system according to claim 2, characterized in that said heat storage (28) comprises a tank configured to receive and store retarder fluid leaving the retarder (20).

4. A WHR system according to any one of the preceding claims, characterized in that the WHR system comprises a heat transfer arrangement configured to transfer heat from the heat storage (28) to the second evaporator (19).

5. A WHR system according to claim 4, characterized in that said heat transfer arrangement comprises a heat transfer circuit (31), a pump (32) configured to circulate a heat transfer fluid in the heat transfer circuit (31) from the heat storage (28) to the second evaporator (19).

6. A WHR system according to claims 5, characterized in that said heat transfer fluid is the same fluid as used in the retarder (20).

7. A WHR system according to claim 5, characterized in that said heat transfer fluid is a separate fluid in relation to the retarder fluid used in the retarder circuit.

8. A WHR system according to any one of the preceding claims, characterized in that the WHR system comprises a control unit (11) configured to control said valve arrangement (21, 22, 23, 33) in view of information about at least one operating parameter (p).

9. A WHR system according to claim 9, characterized in that the said parameter (p) is the temperature of the exhaust gases and/or the temperature in the heat storage (28).

10. A WHR system according to any one of the preceding claims, characterized in that the first evaporator (18) and the second evaporator (19) are arranged in parallel lines (16a, 16b) in the WHR circuit 16.

11. 1 1. A WHR system according to claim 10, characterized in that the valve arrangement comprises a first three way valve (21) arranged in a branched point of the two parallel lines (16a, 16b).

12. A WHR system according to claim 11, characterized in that the valve arrangement comprises check valves (22, 23) arranged in the respective parallel lines (16a, 16b) in a downstream position of the respective evaporators (18, 19).

13. A WHR system according to claim 11, characterized in that the valve arrangement comprises a three way valve (33) arranged in a connection point of the two parallel lines (16a, 16b) in a position downstream of the evaporators (18, 19).

14. A vehicle comprising a WHR-system according to any one of the preceding claims 1 to 13.