METHOD AND SYSTEM FOR CONTROLLING THE WASTE HEAT RECOVERY SYSTEM AT A PREDICTED DOWNHILL SLOPE

Abstract

Provided is a method for controlling a waste heat recovery system associated with a powertrain of a vehicle, the powertrain comprising a combustion engine and a gearbox connected to the combustion engine, the waste heat recovery system comprising a working fluid circuit; an 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 evaporator is arranged for heat exchange between the working fluid and at least one heat source, wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser, and wherein the expander is mechanically connected to the powertrain. The method comprises the steps of: predicting a downhill slope which will require braking of the vehicle; reducing the temperature of the evaporator to a predetermined temperature; and turning off the pump and thus the waste heat recovery system.

Claims

1. A method for controlling a waste heat recovery system associated with a powertrain of a vehicle, the powertrain comprising a combustion engine and a gearbox connected to the combustion engine, the waste heat recovery system comprising a working fluid circuit; an 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 evaporator is arranged for heat exchange between the working fluid and at least one heat source, wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser, and wherein the expander is mechanically connected to the powertrain, said method comprising: predicting a downhill slope which will require braking of the vehicle; reducing the temperature of the evaporator to a predetermined temperature; and turning off the pump, and thus the waste heat recovery system.

2. The method according to claim 1, wherein a downhill slope which will require braking of the vehicle is predicted based on road inclination, friction, and/or length of the slope.

3. The method according to claim 1, wherein the step of reducing the temperature of the evaporator is initiated when the vehicle is at a the crest of the predicted downhill slope.

4. The method according to claim 1, wherein the step of reducing the temperature of the evaporator is initiated when an auxiliary brake of the vehicle has been activated.

5. The method according to claim 1, wherein the step of reducing the temperature of the evaporator comprises to control the at least one heat source to bypass the evaporator.

6. The method according to claim 1, further comprising controlling the working fluid to bypass the evaporator.

7. The method according to claim 1, further comprising starting the pump when torque is requested once again or when the braking of the vehicle has stopped.

8. A waste heat recovery system associated with a powertrain of a vehicle, the powertrain comprising a combustion engine and a gearbox connected to the combustion engine, the waste heat recovery system comprising: a working fluid circuit; an 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 evaporator is arranged for heat exchange between the working fluid and at least one heat source; a cooling circuit arranged in connection to the condenser, and wherein the expander is mechanically coupled to the powertrain; and a control unit adapted to: predict a downhill slope which will require braking of the vehicle; reduce the temperature of the evaporator to a predetermined temperature; and turn off the pump and thus the waste heat recovery system.

9. The system according to claim 8, wherein the control unit is adapted to predict the downhill slope which will require braking of the vehicle based on road inclination, friction, and/or length of the slope.

10. The system according to claim 8, wherein the control unit is adapted to initiate the reduction of the temperature of the evaporator when the vehicle is at a crest of the predicted downhill slope.

11. The system according to claim 8, wherein the control unit is adapted to initiate the reduction of the temperature of the evaporator when an auxiliary brake of the vehicle has been activated.

12. The system according to claim 8, wherein the control unit is adapted to reduce the temperature of the evaporator by controlling the at least one heat source to bypass the evaporator.

13. The system according to claim 8, wherein the control unit is adapted to control the working fluid to bypass the evaporator.

14. The system according to claim 8, wherein the control unit is further adapted to start the pump when torque is requested once again or the braking of the vehicle has stopped.

15. A vehicle comprising a waste heat recovery system associated with a powertrain of the vehicle, the powertrain comprising a combustion engine and a gearbox connected to the combustion engine, the waste heat recovery system comprising: a working fluid circuit; an 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 evaporator is arranged for heat exchange between the working fluid and at least one heat source; a cooling circuit arranged in connection to the condenser, and wherein the expander is mechanically coupled to the powertrain; and a control unit adapted to: predict a downhill slope which will require braking of the vehicle; reduce the temperature of the evaporator to a predetermined temperature; and turn off the pump and thus the waste heat recovery system.

16. A computer program product stored on a non-transitory computer-readable medium, said computer program product for controlling a waste heat recovery system associated with a powertrain of a vehicle, the powertrain comprising a combustion engine and a gearbox connected to the combustion engine, the waste heat recovery system comprising a working fluid circuit; an 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 evaporator is arranged for heat exchange between the working fluid and at least one heat source, wherein the waste heat recovery system further comprises a cooling circuit arranged in connection to the condenser, and wherein the expander is mechanically connected to the powertrain, said computer program product comprising computer instructions to cause one or more electronic control units or computers to perform the following operations: predicting a downhill slope which will require braking of the vehicle; reducing the temperature of the evaporator to a predetermined temperature; and turning off the pump, and thus the waste heat recovery system.

17. (canceled)

18. The computer program product according to claim 16, wherein a downhill slope which will require braking of the vehicle is predicted based on road inclination, friction, and/or length of the slope.

19. The computer program product according to claim 16, wherein reducing the temperature of the evaporator is initiated when the vehicle is at a crest of the predicted downhill slope.

20. The computer program product according to claim 16, wherein reducing the temperature of the evaporator is initiated when an auxiliary brake of the vehicle has been activated.

21. The computer program product according to claim 16, wherein reducing the temperature of the evaporator comprises to control the at least one heat source to bypass the evaporator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 drawings, and in which:

[0039] FIG. 1 schematically illustrates a vehicle according to an embodiment of the invention;

[0040] FIG. 2 schematically illustrates a waste heat recovery system according to an embodiment of the invention;

[0041] 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

[0042] FIG. 4 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] FIG. 1 schematically shows a &de view of a vehicle 1 according to an embodiment of the invention. The vehicle 1 has a powertrain 3 comprising a combustion engine 2 and a gearbox 4 connected to the combustion engine 2 and the driving wheels 6 of the vehicle 1. The vehicle 1 further comprises a waste heat recovery system 10 associated with the powertrain 3. 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.

[0044] FIG. 2 schematically shows a waste heat recovery system 10 associated with a powertrain 3 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; an 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 at least one heat source 24, wherein the waste heat recovery system 10 further comprises a cooling circuit 26 arranged in connection to the condenser 18 and wherein the expander 16 is mechanically connected to the powertrain 3.

[0045] 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 acetone. The waste heat recovery system 10 is configured such that the liquid working fluid WE is pumped from low pressure to high pressure and enters the evaporator 14. The working fluid WF is thereby heated by the at least one 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 transferred to the powertrain 3, whereby the temperature and the pressure of the vapour is decreased. 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. 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 of the working fluid WF 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.

[0046] The waste heat recovery system 10 comprises a control unit 30 adapted to predict a downhill slope which will require braking of the vehicle; reduce the temperature of the evaporator 14 to a predetermined temperature; and to turn off the pump 22 and thus shut down the waste heat recovery system 10. A computer 32 may be connected to the control unit 30.

[0047] 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. The waste heat recovery system 10 further comprises a first bypass device 36 arranged to control the at least one heat source 24 to bypass the evaporator 14. The first bypass device 36 is herein illustrated with a solid line in a position where the evaporator 14 is not bypassed and with a dotted line in a position where the evaporator 14 is bypassed. The control unit 30 is suitably adapted to control the first bypass device 36 such that the at least one heat source 24 is bypassing the evaporator 14 in order to reduce the temperature of the evaporator 14. The waste heat recovery system 10 may also comprise a second bypass device 38 arranged to control the working fluid WF to bypass the evaporator 14. The control unit 30 is suitably adapted to control the second bypass device 38 such that the working fluid WF is bypassing the evaporator 14. The control unit 30 is arranged in connection to the evaporator 14, the expander 16, the cooling circuit 26, the pump 22, the first bypass device 36 and the second bypass device 38.

[0048] The expander 16 is suitably a fixed displacement expander, such as a piston expander, or a turbine expander. The expander 16 may be mechanically connected directly to the combustion engine 2 or to the gearbox 4. The at least one 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 at least one heat source 24 is herein illustrated as a medium passing through the evaporator 14. The at least one heat source 24 is herein illustrated as arrows and may be exhaust gases originating from the combustion engine 2. The waste heat recovery system 10 may comprise a plurality of heat sources 24. The evaporator 14 is suitably a heat exchanger connected to the at least one heat source 24 and the working fluid circuit 12. The waste heat recovery system 10 may comprise one or more heat exchangers 14. The waste heat recovery system 10 may for example comprise a recuperator arranged to pre-heat the working fluid 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.

[0049] The pump 22 pressurizing and circulating the working fluid WF through the circuit 12 may be non-functional or even 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.

[0050] 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).

[0051] 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; an 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 at least one 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 predicting s101 a downhill slope which will require braking of the vehicle; reducing s102 the temperature of the evaporator 14 to a predetermined temperature; and turning off s103 the pump 22 and thus the waste heat recovery system 10.

[0052] When a vehicle has to be braked while driving down a slope the extra torque provided by the expander 16 is obviously not needed to propel the vehicle 1. It is therefore desired to conserve the energy in the waste heat recovery system 10 so that torque quickly can be provided when it is needed again. This can be achieved by turning off the waste heat recovery system 10. The operating temperature of the waste heat recovery system 10 is, however, normally quite high and the thermal inertia of the system 10 (specifically the thermal inertia of the evaporator 14) results in a high temperature long after the system 10 has been shut down. Too high temperatures could damage the working fluid WF and other components of the waste heat recovery system 10. It is therefore important that the waste heat recovery system 10 is cooled down before the system 10 is shut down. The evaporator 14 is the major energy reservoir in the waste heat recovery system 10. By predicting a downhill slope which will require braking of the vehicle 1, reducing the temperature of the evaporator 14 to a predetermined temperature and thereafter turning off the pump 22 and thus the waste heat recovery system 10, it is ensured that the energy in the system 10 is conserved in a safe and efficient way when it is not needed as mechanical work to propel the vehicle.

[0053] The method may comprise to predict s101 a downhill slope which will require braking of the vehicle 1 in order not to exceed a predetermined vehicle speed. Such predetermined vehicle speed may be a desired speed requested by the operator of the vehicle or it may be a speed limitation. The step of predicting s101 a downhill slope which will require braking of the vehicle 1 suitably comprises to predict such downhill slope based on road inclination, friction, length of the slope or similar. Such road data is available in the vehicle control system and may be determined by means of navigation systems, sensors and/or cameras. The step of predicting s101 a downhill slope which will require braking of the vehicle 1 suitably comprises to predict a driving situation where mechanical work provided by the expander 16 in the waste heat recovery system 10 is not needed to propel the vehicle 1.

[0054] The step of reducing s102 the temperature of the evaporator 14 may be initiated when the vehicle 1 is at the crest of the predicted downhill slope. This way, the extra torque provided by the expander 16 is used to propel the vehicle 1 up to the crest of the hill and the waste heat recovery system 10 is then cooled down before being shut down. The step of reducing s102 the temperature of the evaporator 14 may be initiated just before the vehicle 1 is at the crest of the predicted downhill slope. The step of reducing s102 the temperature of the evaporator 14 to the predetermined temperature suitably takes less than two minutes.

[0055] The step of reducing s102 the temperature of the evaporator 14 may be initiated when an auxiliary brake of the vehicle 1 has been activated. The auxiliary brake may be a retarder, an exhaust brake or a compression release brake and is associated with the powertrain 3. When an auxiliary brake of the vehicle 1 is activated while driving downhill, it is indicated that the torque from the waste heat recovery system 10 is not needed. It is thereby suitable to initiate the reduction of the evaporator temperature. Also, when the cooling circuit 26 of the waste heat recovery system 10 is part of the engine cooling system, the auxiliary brake is connected to the same cooling circuit as the waste heat recovery system 10. When the auxiliary brake is activated it thereby increases the load on the cooling circuit. In order not to load the cooling circuit 26 unnecessarily, the temperature of the evaporator 14 is suitably reduced when an auxiliary brake is activated. This way, the waste heat recovery system 10 will transfer less heat to the cooling system.

[0056] The step of reducing s102 the temperature of the evaporator 14 may comprise to control the at least one heat source 24 to bypass the evaporator 14. This way, less heat is exchanged through the evaporator 14. By controlling the heat source 24 to bypass the evaporator 14 the temperature of the evaporator 14 is reduced and the heat transfer to the working fluid WF is reduced. The circulation of the working fluid WF can thereafter be stopped without damaging the components of the waste heat recovery system 10. In the case where the heat source 24 is exhaust gases from the combustion engine 2, the step to reduce the temperature of the evaporator 14 may comprise to control the exhaust gases 24 such that they bypass the evaporator 14. The at least one heat source 24 is suitably controlled to bypass the evaporator 14 by controlling a first bypass device 36, such as a bypass valve, arranged in fluid communication with the at least one heat source 24. The at least one heat source 24 is suitably controlled to bypass the evaporator 14 as long as the pump 22 is turned off and the waste heat recovery system 10 thus is shut down.

[0057] The method may comprise the further step of controlling the working fluid WF to bypass the evaporator 14. If the evaporator 14 is bypassed on the working fluid side, the evaporator 14 does not need to be cooled down as much as if it is not bypassed on the working fluid side. By bypassing the evaporator 14 on the working fluid side, heat transfer from the evaporator 14 to the cooling circuit 26 is avoided and the full capacity of the cooling circuit 26 can instead be used to cool for example an auxiliary brake. The working fluid WF may be controlled to bypass the evaporator 14 by controlling a second bypass device 38 arranged in fluid communication with the working fluid WF. When the evaporator 14 is bypassed on the working fluid side and the heat source side the temperature of the evaporator is reduced, which will affect the ability to vaporize the working fluid. If the working fluid WF is in liquid phase when entering the expander 16, the expander 16 may be damaged. By controlling the pump 22 to decrease the mass flow of the working fluid WF, the temperature of the evaporator 14 may be enough to vaporize and superheat the working fluid WF. The expander 16 may therefore not need to be bypassed. The method may alternatively comprise to bypass the expander 16 if the temperature of the evaporator 14 is not enough to vaporize the working fluid WF.

[0058] The method may further comprise the step of starting the pump 22 when torque is requested once again or when braking of the vehicle 1 has stopped. Torque may be requested by the operator of the vehicle 1 by depressing the accelerator pedal, Torque may alternatively be requested by a vehicle system, such as a downhill speed control system. The braking of the vehicle 1 may be stopped by the operator by inactivating a previously activated auxiliary brake. The braking of the vehicle 1 may alternatively be stopped by a vehicle system inactivating a previously activated auxiliary brake. This way, it is indicated that the extra torque provided by the expander 16 is useful once again. The method suitably comprises to stop bypassing the evaporator 14 on the heat source side and the working fluid side when torque is requested once again or when braking of the vehicle 1 has stopped. The waste heat recovery system is thereby active again and heat from the at least one heat source 24 can be converted to mechanical work by the expander 16.

[0059] 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 ND 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.

[0060] 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 downhill slope which will require braking of the vehicle 1 in order not to exceed a predetermined vehicle speed. The computer program P comprises routines for reducing the temperature of the evaporator to a predetermined temperature. The computer program P comprises routines for turning off the pump and thus the waste heat recovery system 10. 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.