Method for controlling a waste heat recovery system and such a waste heat recovery system

Abstract

The invention relates to a method for controlling a waste heat recovery system associated with a combustion engine of a vehicle, the waste heat recovery system comprising a working fluid circuit; at least one evaporator; an expander; a condenser; a reservoir for a working fluid and a pump arranged to pump the working fluid through the circuit, wherein the at least one evaporator is arranged for heat exchange between the working fluid and a heat source, and wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser. The method comprises the steps of: predicting a shutdown of a combustion engine associated with the system; determining if a predetermined requirement is fulfilled; and if so reducing the temperature in the waste heat recovery system prior to combustion engine shutdown.

Claims

1. A method for controlling a waste heat recovery system associated with a combustion engine of a vehicle, the waste heat recovery system comprising a working fluid circuit; at least one evaporator; an expander; a condenser; a reservoir for a working fluid and a pump arranged to pump the working fluid through the working fluid circuit, wherein the at least one evaporator is arranged for heat exchange between the working fluid and a heat source, and wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser, wherein said method comprises, via at least one control unit: monitoring, via at least one sensor, at least one of a current operation and an expected operation of the combustion engine associated with the waste heat recovery system; predicting a future shutdown of the combustion engine, based on said monitored at least one of the current operation and the expected operation; determining if a predetermined requirement is fulfilled after predicting the future shutdown of the combustion engine; and if so reducing a temperature in the waste heat recovery system prior to combustion engine shutdown.

2. The method according to claim 1, wherein predicting the combustion engine shutdown is based on a determination that the vehicle comprising the combustion engine is standing still.

3. The method according to claim 2, wherein determining a predetermined requirement is fulfilled comprises determining that a parking brake in the vehicle is activated.

4. The method according to claim 1, wherein predicting the combustion engine shutdown is based on the final destination of the vehicle comprising the combustion engine.

5. The method according to claim 4, wherein the predetermined requirement comprises that the vehicle is within a predetermined distance or time from the final destination.

6. The method according to claim 1, wherein predicting the combustion engine shutdown is based on a next required stop of the vehicle comprising the combustion engine.

7. The method according to claim 1, wherein the predetermined requirement comprises that the vehicle comprising the combustion engine is operating in a specific mode.

8. The method according to claim 1, wherein the predetermined requirement comprises that a current temperature in the waste heat recovery system is above a critical temperature.

9. A method according to claim 1, wherein reducing the temperature in the waste heat recovery system comprises controlling the cooling circuit connected to the condenser.

10. The method according to claim 1, wherein reducing temperature in the waste heat recovery system comprises controlling the heat source connected to the at least one evaporator.

11. The method according to claim 1, wherein reducing the temperature in the waste heat recovery system comprises reducing the temperature, such that a target temperature is reached, wherein the target temperature is below a normal operation temperature.

12. The method according to claim 1, wherein monitoring further comprises monitoring both a current and an expected operation of the combustion engine associated with the waste heat recovery system.

13. A waste heat recovery system associated with a combustion engine of a vehicle, the waste heat recovery system comprising: a working fluid circuit; at least one evaporator arranged for heat exchange between a working fluid and a heat source; an expander; a condenser; a reservoir for a working fluid; a pump arranged to pump the working fluid through the working fluid circuit; a cooling circuit arranged in connection to the condenser; and a control unit including executable instructions stored in a non-transitory computer readable medium, which when executed are configured to: monitor, via at least one sensor, at least one of a current operation and an expected operation of the combustion engine associated with the waste heat recovery system; predict a future shutdown of the combustion engine, based on said monitored at least one of the current operation and the expected operation; determine if a predetermined requirement is fulfilled after predicting the future shutdown of the combustion engine; and if so reduce a temperature in the waste heat recovery system prior to combustion engine shutdown.

14. The waste heat recovery system according to claim 13, wherein the executable instructions associated with said control unit are further configured to monitor both a current and an expected operation of the combustion engine associated with the waste heat recovery system.

15. A vehicle comprising a waste heat recovery system comprising: a working fluid circuit; at least one evaporator arranged for heat exchange between a working fluid and a heat source; an expander; a condenser; a reservoir for a working fluid; a pump arranged to pump the working fluid through the working fluid circuit; a cooling circuit arranged in connection to the condenser; and a control unit including executable instructions stored in a non-transitory computer readable medium, which when executed are configured to: monitor, via at least one sensor, at least one of a current operation and an expected operation of the combustion engine associated with the waste heat recovery system; predict a future shutdown of the combustion engine, based on said monitored at least one of the current operation and the expected operation; determine if a predetermined requirement is fulfilled after predicting the future shutdown of the combustion engine; and if so reduce a temperature in the waste heat recovery system prior to combustion engine shutdown.

16. The vehicle according to claim 15, wherein the executable instructions associated with said control unit are further configured to monitor both a current and an expected operation of the combustion engine associated with the waste heat recovery system.

17. A computer program product comprising computer program code stored on a non-transitory computer-readable medium, said computer program code for controlling a waste heat recovery system associated with a combustion engine of a vehicle, the waste heat recovery system comprising a working fluid circuit; at least one evaporator; an expander; a condenser; a reservoir for a working fluid and a pump arranged to pump the working fluid through the working fluid circuit, wherein the at least one evaporator is arranged for heat exchange between the working fluid and a heat source, and wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser, said computer program code comprising computer instructions stored on the non-transitory computer-readable medium and configured, such that when accessed and performed by at least one control unit, to execute the following operations: monitoring, via at least one sensor, at least one of a current operation and an expected operation of the combustion engine associated with the waste heat recovery system; predicting a future shutdown of the combustion engine, based on said monitored at least one of the current operation and the expected operation; determining if a predetermined requirement is fulfilled after predicting the future shutdown of the combustion engine; and if so reducing a temperature in the waste heat recovery system prior to combustion engine shutdown.

18. The computer program product according to claim 17, wherein monitoring further comprises monitoring both a current and an expected operation of the combustion engine associated with the waste heat recovery system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

(2) FIG. 1 schematically illustrates a vehicle according to an embodiment of the invention;

(3) FIG. 2 schematically illustrates a waste heat recovery system according to an embodiment of the invention;

(4) FIG. 3 schematically illustrates a flow chart for a method for controlling a waste heat recovery system according to an embodiment of the invention; and

(5) FIG. 4 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 schematically shows a side view of a vehicle 1 according to an embodiment of the invention. The vehicle 1 comprises a combustion engine 2 and a waste heat recovery system 10 associated with the combustion engine 2. The vehicle 1 further comprises a gearbox 4 connected to the driving wheels 6 of the vehicle 1. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car. The vehicle may be a hybrid vehicle comprising an electric machine (not shown) in addition to the combustion engine 2.

(7) FIG. 2 schematically shows a waste heat recovery system 10 associated with a combustion engine 2 of a vehicle 1 according to an embodiment of the invention. The vehicle 1 is suitably configured as described in FIG. 1. The waste heat recovery system 10 comprises a working fluid circuit 12; at least one evaporator 14; an expander 16; a condenser 18; a reservoir 20 for a working fluid WF and a pump 22 arranged to pump the working fluid WF through the circuit 12, wherein the evaporator 14 is arranged for heat exchange between the working fluid WF and a heat source 24, and wherein the waste heat recovery system 10 further comprises a cooling circuit 26 arranged in connection to the condenser 18. The waste heat recovery system 10 comprises a control unit 30 adapted to predict a shutdown of a combustion engine 2 associated with the system 10; determine if a predetermined requirement is fulfilled; and if so reducing the temperature in the waste heat recovery system 10 prior to combustion engine shutdown.

(8) The control unit 30 is arranged in connection to the evaporator 14, the expander 16, the cooling circuit 26 and the pump 22. A computer 32 may be connected to the control unit 30. The predetermined requirement is suitably stored in the control unit 30. The control unit 30 is adapted to predict a combustion engine shutdown based on various vehicle operation data. The control unit 30 is adapted to reduce the temperature in the waste heat recovery system 10 by controlling the cooling circuit 26 and/or controlling the heat source 24 connected to the evaporator 14.

(9) The heat source 24 connected to the evaporator 14 may be exhaust gases from the combustion engine 2, an exhaust gas recirculation system (EGR), the cooling fluid of the combustion engine 2, the combustion engine 2 itself or any other hot component associated with the combustion engine 2. The heat source 24 is herein illustrated as a medium passing through the evaporator 14. The heat source 24 is herein illustrated as arrows and may be exhaust gases from the combustion engine 2.

(10) The waste heat recovery system 10 may comprise a plurality of evaporators 14, each connected to a different heat source 24. The evaporator 14 is suitably a heat exchanger connected to the heat source 24 and the working fluid circuit 12. The heat transfer between the working fluid WF and the heat source 24 is an exchange of energy resulting in a change in temperature.

(11) The waste heat recovery system 10 is suitably based on an organic Rankine cycle. The working fluid WF is thus suitably organic, such as ethanol or R245fa. The waste heat recovery system 10 is thus configured such that the liquid working fluid WF is pumped from low pressure to high pressure and enters the evaporator 14. The working fluid WF is thereby heated by the heat source 24 connected to the evaporator 14 and the working fluid WF is thus evaporated. The vapour is then expanded in the expander 16 whereby mechanical work is produced and the temperature and the pressure of the vapour is decreased. The mechanical work may for example be transferred to the crankshaft of the combustion engine 2 and thus be used to propel the vehicle 1 or the mechanical work may be used to drive for example a generator. The vapour thereafter enters the condenser 18 where condensation through heat exchange between the vapour and the cooling fluid of the cooling circuit 26 brings the working fluid WF back to its initial liquid state.

(12) Thus, the heat source 24 is providing the energy entering the waste heat recovery system 10 and the energy is leaving the waste heat recovery system 10 as mechanical work via the expander 16 and as heat via the cooling circuit 26 cooling the condenser 18. The temperature in the waste heat recovery system 10 thus depends on the amount of energy entering the system 10 and the amount of energy leaving the system 10.

(13) It is crucial that the waste heat recovery system 10 is cooled down before being shut down. The thermal inertia of for example the evaporator 14 will otherwise cause a high temperature in the waste heat recovery system 10 after shutdown. A too high temperature in the waste heat recovery system 10 may damage the working fluid WF and other components of the waste heat recovery system 10. Only vapour should enter the expander 16 and the waste heat recovery system 10 therefore comprises a bypass arrangement 34, such that in the case where the working fluid WF is still in a liquid state downstream of the evaporator 14, the working fluid WF is bypassing the expander 16 through the bypass arrangement 34.

(14) The pump 22 pressurizing and circulating the working fluid WF through the circuit 12 may be damaged if the working fluid WF entering the pump 22 is not in a liquid state. Thus in the case where the temperature downstream of the condenser 18 is too high, such that the working fluid WF is not in a liquid state, the pressure in the reservoir 20 may be increased. This way, the working fluid WF is brought to a liquid state and may be pumped by the pump 22. The pump 22 is suitably electrically driven.

(15) The cooling circuit 26 connected to the condenser 18 may be part of the combustion engine cooling system or a separate cooling system. The cooling fluid in the cooling circuit 26 may thereby be pumped by a cooling pump (not shown) driven by the combustion engine 2 or by an electric machine (not shown). In the case where the cooling pump is driven by the combustion engine 2 it is important that the waste heat recovery system 10 is cooled down prior to engine shutdown, since the cooling pump will stop working when the combustion engine 2 is turned off. If the condenser 18 is not cooled by the cooling circuit 26, the working fluid WF in the waste heat recovery system 10 will not be cooled and reducing the temperature in the waste heat recovery system 10 will be difficult. In the case where the cooling pump is driven by an electric machine the waste heat recovery system 10 may be cooled down after engine shutdown. However, the driver will then have to wait until the waste heat recovery system 10 has reached a sufficiently low temperature to be safely shut down. Also, if the waste heat recovery system 10 is cooled down after engine shutdown, the electric machine driving the cooling pump will use energy from an energy storage such as a battery in the vehicle 1. This is not advantageous. By reducing the temperature in the waste heat recovery system 10 prior to engine shutdown the electric machine driving the cooling pump will instead use energy from a generator, which will increase the lifetime of the battery. Also, by reducing the temperature in the waste heat recovery system 10 prior to engine shutdown, the driver comfort is increased since the waste heat recovery system 10 may be shut down essentially at the same time as the combustion engine 2.

(16) The waste heat recovery system 10 may comprise one or more heat exchangers. The waste heat recovery system 10 may for example comprise a recuperator arranged to pre-heat the working fluid WF before entering the evaporator 14. The waste heat recovery system 10 may also comprise one or more condensers 18, such that cooling down of the working fluid WF may be performed in multiple steps. Furthermore, the system 10 may comprise one or more expanders 16. The expander 16 may be a turbine or a piston expander.

(17) FIG. 3 shows a flowchart for a method for controlling a waste heat recovery system 10 associated with a combustion engine 2 of a vehicle 1. The waste heat recovery system 10 is suitably configured as described in FIG. 2. The waste heat recovery system 10 thus comprises a working fluid circuit 12; at least one evaporator 14; an expander 16; a condenser 18; a reservoir 20 for a working fluid WF and a pump 22 arranged to pump the working fluid WF through the circuit 12, wherein the evaporator 14 is arranged for heat exchange between the working fluid WF and a heat source 24, and wherein the waste heat recovery system 10 further comprises a cooling circuit 26 arranged in connection to the condenser 18. The method comprises the steps of:

(18) predicting s101 a shutdown of a combustion engine 2 associated with the system 10;

(19) determining s102 if a predetermined requirement is fulfilled; and if so

(20) reducing s103 the temperature in the waste heat recovery system 10 prior to combustion engine shutdown.

(21) The waste heat recovery system 10 associated with the combustion engine 2 is typically activated mainly when the combustion engine 2 is operating. Thus, the waste heat recovery system 10 is commonly shut down when the combustion engine 2 has been turned off. When the combustion engine 2 is turned off, the heat source 24 may no longer heat the evaporator 14 but the thermal inertia of the evaporator 14 means that the evaporator 14 will maintain a very high temperature for a certain time. If the waste heat recovery system 10 is immediately shut down as the combustion engine 2 is turned off, the high temperature of the evaporator 14 may damage the working fluid WF and other components of the waste heat recovery system 10. The temperature in the waste heat recovery system 10 therefore needs to be reduced before the system 10 is shut down. However, the efficiency of the waste heat recovery system 10 is increased with the temperature of the evaporator 14. The temperature of the evaporator 14 should therefore be maintained as high as possible during normal operation. The waste heat recovery system 10 should thus not be unnecessarily cooled down. By performing the method steps it is ensured that the waste heat recovery system 10 is cooled down only when necessary. A method for controlling a waste heat recovery system 10 is thereby achieved, which optimizes engine efficiency and fuel consumption. By predicting an engine shutdown and determining if a predetermined requirement is fulfilled a shutdown of the waste heat recovery system 10 is predicted. The waste heat recovery system 10 may thereby be cooled down prior to combustion engine shutdown and the waste heat recovery system 10 may be shut down essentially at the same time as the engine shutdown.

(22) The prediction of a combustion engine shutdown is suitably based on that a vehicle 1 comprising the combustion engine 2 is standing still. The predetermined requirement then suitably comprises that a parking brake in the vehicle 1 is activated. By reducing the temperature in the waste heat recovery system 10 only when the parking brake is activated, and thus only when it is very likely that the waste heat recovery system should be shut down, it is ensured that the efficiency of the waste heat recovery system 10 is optimized and the engine efficiency and the fuel consumption is thereby optimized.

(23) The prediction of a combustion engine shutdown is suitably based on the final destination of a vehicle 1 comprising the combustion engine 2. The final destination of the vehicle 1 is suitably determined by means of a navigation system. The predetermined requirement may comprise that the vehicle 1 is within a predetermined distance or time from the final destination. The predetermined requirement may comprise that the vehicle 1 is between 1-3 minutes from the final destination, which may correspond to a distance corresponding to said period in time. It is very probable that the combustion engine 2 will be turned off when the vehicle 1 has reached its final destination. It is thus also very probable that the waste heat recovery system 10 will be shut down at the final destination. By pre-emptively reducing the temperature in the waste heat recovery system 10 when the vehicle 1 is close to the final destination the waste heat recovery system 10 will be ready for shutdown at the time of combustion engine shutdown. This way, a method for controlling a waste heat recovery system is achieved, which optimizes driver comfort.

(24) The prediction of a combustion engine shutdown is suitably based on the next required stop of a vehicle 1 comprising the combustion engine 2. The next required stop of the vehicle 1 is suitably determined by means of a tachograph. The next required stop is determined based on how long the driver has been active and is thus the time or position where the driver must rest. The predetermined requirement may thus comprise that the vehicle 1 is within a predetermined distance or time from the next required stop. The predetermined requirement may comprise that the vehicle is between 1-3 minutes from the next required stop. It is very probable that the combustion engine 2 and thus the waste heat recovery system 10 will be turned off at the next required stop. By pre-emptively reducing the temperature in the waste heat recovery system 10 when the vehicle 1 is close to the next required stop the waste heat recovery system 10 will be ready for shutdown at the time of combustion engine shutdown. This way, a method for controlling a waste heat recovery system is achieved, which optimizes driver comfort.

(25) Alternatively, the combustion engine shutdown may be predicted based on a different vehicle system requesting engine shutdown. This may be advantageous in the case where the vehicle 1 comprising the waste heat recovery system 10 is a hybrid vehicle. For example, in order to avoid noise and emissions it may be desirable to turn off the combustion engine 2 and propel the vehicle 1 with the electric machine. In this case, the combustion engine 2 may the turned off and the waste heat recovery system 10 is not needed.

(26) The predetermined requirement suitably comprises that a vehicle 1 comprising the combustion engine 2 is operating in a specific vehicle performance mode, such as an economy mode, a normal mode or a power mode. Depending on the vehicle performance mode different aspects are considered when controlling the vehicle 1. When operating in an economy mode the fuel consumption should be minimized and the temperature in the waste heat recovery system 10 should therefore be preserved as long as possible. In order to maximize the engine power in a power mode the temperature of the waste heat recovery system 10 should also be preserved as long as possible. The temperature of the waste heat recovery system 10 is thus suitably only reduced based on a predicted engine shutdown in the case where the vehicle performance mode is a normal mode.

(27) The predetermined requirement suitably comprises that the current temperature in the waste heat recovery system 10 is above a predetermined critical temperature. If the temperature in the waste heat recovery system 10 is not too high, there is no need to reduce the temperature further prior to engine shutdown. Thus, the temperature in the waste heat recovery system 10 is reduced only when the current temperature in the waste heat recovery system 10 is above a predetermined critical temperature. The predetermined critical temperature may be between 100-150 degrees Celsius.

(28) The step to reduce s103 the temperature in the waste heat recovery system 10 suitably comprises to control the cooling circuit 26 connected to the condenser 18. By controlling the cooling circuit 26 connected to the condenser 18 the amount of energy leaving the waste heat recovery system 10 through the cooling circuit 26 may be increased and the temperature in the waste heat recovery system 10 is thereby reduced. The cooling circuit 26 may be controlled such that the flow of cooling fluid through the condenser 18 is increased and/or such that the temperature of the cooling fluid is reduced. In addition or alternatively, the step to reduce s103 the temperature in the waste heat recovery system 10 comprises to control the heat source 24 connected to the evaporator 14. The heat source 24 is suitably controlled such that it is bypassing the evaporator 14. The temperature of the evaporator 14 is thereby reduced and the heat transfer to the working fluid WF is reduced. This way, the amount of energy entering the waste heat recovery system 10 may be reduced and the temperature in the waste heat recovery system 10 is thereby reduced.

(29) The step to reduce s103 the temperature in the waste heat recovery system 10 suitably comprises to reduce the temperature, such that a target temperature is reached, wherein the target temperature is below a normal operation temperature. The target temperature is suitably a temperature desired to safely shut down the waste heat recovery system 10. When a combustion engine shutdown has been predicted and the predetermined requirement is fulfilled the temperature in the waste heat recovery system 10 is suitably reduced to a target temperature lower than the normal operation temperature. This way, the waste heat recovery system 10 is cooled down such that it can be safely shut down at the time of engine shutdown. The target temperature and the normal operation temperature are suitably associated with the working fluid WF immediately downstream of the evaporator 14 or immediately downstream of the condenser 18. The temperature of the working fluid WF immediately downstream of the condenser 18 may be determined by the temperature in the cooling circuit 26. The waste heat recovery system 10 is thus suitably controlled such that the working fluid WF has a normal operation temperature during normal operation and such that the working fluid WF reaches a target temperature prior to shutdown of the waste heat recovery system 10.

(30) FIG. 4 schematically illustrates a device 500. The control unit 30 and/or computer 32 described with reference to FIG. 2 may in a version comprise the device 500. The term link refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

(31) There is provided a computer program P which comprises routines for a method for controlling a waste heat recovery system 10 associated with a combustion engine 2 of a vehicle 1 according to the invention. The computer program P comprises routines for predicting a combustion engine shutdown of a combustion engine 2 associated with the waste heat recovery system 10. The computer program P comprises routines for determining if a predetermined requirement is fulfilled. The computer program P comprises routines for reducing the temperature in the waste heat recovery system 10 if the predetermined requirement is fulfilled. The program P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

(32) Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the program stored in the memory 560 or a certain part of the program stored in the read/write memory 550.

(33) The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

(34) When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

(35) Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, methods herein described are executed.

(36) The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.