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    • 专利摘要:
    The invention relates to a method for controlling a waste heat recovery system (10) associated with a powertrain (3) of a vehicle (1), the powertrain (3) comprising a combustion engine (2) and a gearbox (4) connected to the combustion engine (2), the waste heat recovery system (10) comprising 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 coupled to the powertrain (3). The method comprises the steps of determining (s101 ) the pressure (P) and temperature (T) of the working fluid (WF) upstream of the expander (16); and controlling (s102) the rotational speed of the expander (16) based on the determined pressure (P) and temperature (T).The invention also relates to a waste heat recovery system (10), a vehicle (1) comprising such a system (10), a computer program (Pr) and a computer program product.(Fig. 2)
    公开号:SE1651039A1
    申请号:SE1651039
    申请日:2016-07-12
    公开日:2018-01-13
    发明作者:Johansson Bjoern；Hoeckerdal Erik；Timren Thomas
    申请人:Scania Cv Ab；
    IPC主号:
    专利说明:

    A method for controlling a waste heat recovery system and such a waste heat recovery system TECHNICAL FIELD The present invention relates to a method for controlling a waste heat recoverysystem, a waste heat recovery system, a vehicle comprising such a waste heatrecovery system, a computer program and a computer program product according to the appended claims.
    BACKGROUND Vehicie rnanutaeturers are today striving te increase engine ettioiency andreduce tuei consumption. "this is speciticaiiy an issue tor rnanutacturers ot heavyvehicies, such as trucks and buses. in vehioies with oornhustion engines sorneet the energy trorn the tuei is dissipated as heat through the exhaust pioes andthe engine eeoiing system. By the use ei a waste heat recovery system some etthe dissipated heat may instead he used te preduoe mechanicai work. Thernechanicai work may ter exampie he transterred to the oewertrain and thus heused te prepei the vehicie. This way the engine etticiency and the tuei consumption can he improved.
    Waste heat recovery systems are typieaiiy based en the Ftankine eycie and thuscemprise a yverking iiuid, a pump ter cireuiating the working tiuid in a Circuit, atieast ene evaporeter, an expansion device and at ieast ene eendenser. "theworking iiuid is suitaoiy in a iiquid state te start with. "the purnp pressurizes theworking tiuid which is purnped through the evaeorater. "the werking tiuid isheated ey the heat source (eg. exhaust gases, coeiing iiuid) iead through theevaporater and the working iiuid thereey evaporates. 'the vapour issuhsequentiy expanded in the expansion device. By irieans ot the expansiondevice the reeevered heat is converted inte mechanieai work. "the vapcur isthereatter cooied in the oondenser, such that the working tiuid is hreught ieack to its initiai iiquid state, The oendenser is thus typicaiiy connected to a coeiingoircuit, which eouid he part ot the engine cooiing system or a separate eoeiing circuit.
    The temperature and pressure et the working tiuid are iimited ey hardwareconstraints en the high pressure side, i.e. upstream ot the expander. "thehardware oonstraints iirrrit the arnount et heat that can ioe handied in the wasteheat recovery systern. iššxcessive heat may cause toe high pressure ot theworking tiuid upstrearn ot the expander, which may damage the components otthe systern. it the pressure is tee high the working tiuid may condensate whichtor exarnpie oouid damage the expander. in order to avoid too high pressure theexhaust gases are typicaiiy hypassed the evaporator, wherehy the temperatureet the evaporater and thus the working tiuid is reduced. Such soiutien thusresuits in some exhaust gas energy heing wasted.
    Other soiutiens aiso exist. Üoeurrtent Wtliäut åt Qïutšß At ter exarnpie disoiosesan exhaust gas system comprising a working tiuid reiease means arrarigedupstrearn ot the expander, such that working tiuid can he reieased te an exhaustgas cenveying arrangement in order to reduce the pressure. DocumenttšPt443t83 At describes a Ftankine eyoie systern associated with an internaioornioustion engine. "the systern comprises temperature centret means andpressure contrei means adapted te generate a gasphase working medium witha temperature and pressure at which the everati etticiency ieecomes a maximum.The temperature is contreiied hy controiiing the amount ot working mediumsuppiied to the evapcrater and the pressure is eontrciied oy centrotiirtg therotatienai speed ot the expander.
    SUMMARY OF THE INVENTIONDespite known solutions in the field, there is still a need to develop a method for controlling a waste heat recovery system, which optimizes the energy recoverywhile increasing the lifetime of the waste heat recovery system.
    An object of the present invention is to achieve an advantageous method forcontrolling a waste heat recovery system, which increases the lifetime of thesystem.
    Another object of the present invention is to achieve an advantageous methodfor controlling a waste heat recovery system, which optimizes the energy recovery.
    A further object of the invention is to achieve an advantageous waste heatrecovery system, which is adapted to be controlled such that the lifetime is increased.
    Another object of the invention is to achieve an advantageous waste heat recovery system, which optimizes the energy recovery.
    The herein mentioned objects are achieved by a method for controlling a wasteheat recovery system, a waste heat recovery system, a vehicle, a computerprogram and a computer program product according to the independent claims.
    According to an aspect of the present invention a method for controlling a wasteheat recovery system associated with a powertrain of a vehicle is provided. Thepowertrain comprises a combustion engine and a gearbox connected to thecombustion engine. The waste heat recovery system comprises a working fluidcircuit; an evaporator; an expander; a condenser; a reservoir for a working fluidand a pump arranged to pump the working fluid through the circuit, wherein theevaporator is arranged for heat exchange between the working fluid and at leastone heat source, wherein the waste heat recovery system further comprises acooling circuit arranged in connection to the condenser, and wherein theexpander is mechanically coupled to the powertrain. The method comprises thesteps of: - determining the pressure and temperature of the working fluid upstream of theexpander; and- controlling the rotational speed of the expander based on the determined pressure and temperature.
    The vvaste heat reccvery systern of the invention is suitahiy based on theFtankine cycie, preterahiy an organic Qankine cycie. The working fiuid is thussuitahiy organic, such as ethanci or acetone. The vvaste heat recovery systernbased on the Ftankine cycie is suitahiy coniigured such that the vvcrking fiuid,suitahiy in a iiquid state, is puntped through the evaporator. The working tiuid istherehy heated hy the at ieast one heat source connected te the evapcrator andthe working tiuie thus evaporates, The vapour is then expanded in the expandervvherehy rnechanicai tycrk is produced. The rnechanicai vvcrk is then suitahiytransierred to the povvertrain and ts thus used to propei the vehicie. The vanouris thereatter cccied in the concienser hy heat exchange vvith the cooiing tiuid inthe cooiing circuit, such that the Working tiuid is brought hack to its initiai iiquidstate. The at ieast one heat source in the vehicie cornprising the vvaste heatreccvery system rnay he exhaust gases ircrn the cornhusticn engine, an exhaustgas recircuiation systent, the cooiing iiuid of the cornhustion engine, theccrnhustion engine itseit or any other hot component in the vehicie. The at ieastone heat source ts preterahiy associated with the cornhustion engine. Theevaporator is suitahiy a heat exchariger connected to the at ieast one heatscurce and the working tiuid circuit. The heat transfer between the working iiuidand the heat source is an exchange ct energy resuiting in a change intemperature. Thus, the heat source is providing the energy entering the wasteheat recovery systern and the energy is ieaving the vvaste heat recovery systernas ntechanicai work via the expander and as heat via the cociing circuit. Thetemperature in the waste heat recovery systent thus aepends on the arrtount ot energy entering the systern anci the arncunt oi energy ieaving the systeni.
    The cperating temperature ct the waste heat recovery systern is ncrrnaiiy quitehigh. For ideai gases the pressure is directiy progortionai to the ternperature and tee high temperature et the werkirig tiuid may thus eause a tee high pressure etthe werkirtg tiuid en the high pressure side ot the waste heat reeevery systemwhere the werking tiuie is a vapeur. The high pressure side et the waste heatreeevery system is downstreain ot the pump and upstream et the expander. Teehigh pressure ot the working tiuie may damage the various components et thesystern. At tee high pressure the tfyerkirig tiuid ittay aise shitt te a iiquid phaseand this oeuid damage the expander. The pressure ot the working tiuie ean hedecreased er increased by eentreiiing the retatienai speed et the expander.When the retatiortai speed et the expander is increased, the mass tiow ot theworking tiuie haneiee by the expander is increased and the pressure et theworking tiuid in the eireuit upstream et the expander is thereby deereased. Ešydetermining the pressure of the working fluid upstream of the expander andcontrolling the rotational speed of the expander based on the determinedpressure, too high pressure upstream of the expander can be avoided. Also,since the temperature of the working fluid is linked to the pressure and affectsthe working fluid and the components of the system, it is advantageous to controlthe rotational speed of the expander based on the determined temperature. Thisway, the energy recovery is optimized and the lifetime of the waste heat recoverysystem is increased.
    The cooling circuit connected to the condenser may be part of the combustionengine cooling system or a separate cooling system. The cooling fluid coolingthe condenser may thereby be circulated in the cooling circuit by a cooling pump,driven by the combustion engine or by an electric machine.
    The waste heat recovery system may comprise one or more evaporators/heatexchangers. The waste heat recovery system may for example comprise arecuperator arranged to pre-heat the working fluid before entering theevaporator. The waste heat recovery system may also comprise one or morecondensers, such that cooling of the working fluid may be performed in multiplesteps. Furthermore, the system may comprise one or more expanders. Theexpander is suitably a fixed displacement expander or a turbine. The expander may be mechanically connected directly to the combustion engine or it may bemechanically connected to the gearbox or other components of the powertrain.This way, the mechanical work generated in the expander is transferred to the powertrain and helps propel the vehicle.
    The waste heat recovery system may be associated with a powertrain of a hybridvehicle. Such hybrid vehicle comprises an electric machine for propulsion, in addition to the combustion engine.
    According to an aspect of the invention the rotational speed of the expander iscontrolled based on a comparison between the determined pressure and apredetermined maximum pressure and a comparison between a differencebetween the determined temperature and the boiling point for the working fluidand a predetermined minimum temperature difference. The temperature of theworking fluid upstream of the expander is higher than the boiling point when it isa vapour. The boiling point for the working fluid depends on the pressure. Therotational speed of the expander is thus suitably controlled based on acomparison between the determined current pressure and a predeterminedmaximum pressure, and a comparison between a difference between thedetermined current temperature and the boiling point for the working fluid at thecurrent pressure and a predetermined minimum temperature difference. Thedifference between the actual temperature of the working fluid and the boilingpoint at the current pressure thus indicates the level of superheat of the workingfluid. A certain level of superheat is desired in order to obtain optimal efficiencyof the expander. The predetermined minimum temperature difference is suitablybetween 10-60 degrees, preferably between 20-30 degrees. The minimum levelof superheat is thus between 10-60 degrees, preferably between 20-30 degrees.lt is thus desired that the working fluid has a temperature which is between 10-60 degrees higher than the boiling point of the working fluid. The predeterminedmaximum pressure suitably depends on constraints of the components of thewaste heat recovery system. The predetermined maximum pressure thus depends on the configuration of the waste heat recovery system and may bedifferent for different systems.
    According to an aspect of the invention the rotational speed of the expander isincreased when the determined pressure exceeds the predetermined maximumpressure and/or the difference between the determined temperature and theboiling point for the working f|uid is smaller than the predetermined minimumtemperature difference. The rotational speed of the expander is thus suitablyincreased if the determined level of superheat is lower than the predeterminedminimum level of superheat. When the level of superheat of the working f|uid issmaller than the predetermined minimum superheat, there is a great risk thatthe working f|uid will shift to liquid phase which may damage the expander. Thehigher the pressure of the working f|uid the higher is the boiling point of theworking f|uid. Thus, by decreasing the pressure the boiling point of the gas isdecreased and the difference between the determined temperature and theboiling point will thereby increase.
    According to an aspect of the invention the rotational speed of the expander isincreased if there is a risk that the pressure of the working f|uid will exceed thepredetermined maximum pressure and/or that the difference between thetemperature and the boiling point of the working f|uid will become smaller thanthe predetermined minimum temperature difference. By increasing the rotationalspeed of the expander when there is a risk that the difference between thetemperature and the boiling point of the working f|uid will become smaller thanthe predetermined minimum temperature difference, the pressure of the workingf|uid is pre-emptively decreased and the damage of the waste heat recoverysystem is avoided while optimizing the energy recovery. Similarly, by increasingthe rotational speed of the expander when there is a risk that the pressure willexceed the predetermined maximum pressure the pressure of the working f|uidis decreased pre-emptively and damage of the waste heat recovery system is avoided while optimizing the energy recovery.
    The risk that the pressure will exceed the predetermined maximum pressureand/or that the difference between the temperature and the boiling point of theworking fluid will become smaller than the predetermined minimum temperaturedifference is suitably determined based on a prediction of high load on thecombustion engine. When the load on the combustion engine is high, thetemperature of the at least one heat source will increase and the temperatureand pressure of the working fluid will thereby also increase. Thus, by predictingthat the load on the combustion engine will be high, it is predicted that thetemperature and pressure of the working fluid will increase. lf the determinedtemperature and/or pressure of the working fluid is close to the predeterminedmaximum pressure and the predetermined minimum temperature differencerespectively, an increase of load on the combustion engine will thus with greatprobability cause the pressure to become too high. The high load on thecombustion engine may be predicted based on the topography of the route ofthe vehicle. The load on the combustion engine may for example increasesignificantly when driving uphill. The risk that the pressure will exceed thepredetermined maximum pressure and/or that the difference between thetemperature and the boiling point of the working fluid will become smaller thanthe predetermined minimum temperature difference is thus suitably determinedbased on the current determined pressure and temperature of the working fluid and/or a prediction of high load on the combustion engine.
    According to an aspect of the invention the rotational speed of the expander iscontrolled by controlling the gearbox and thereby the rotational speed of thepowertrain. Since the expander is mechanically connected to the powertrain, therotational speed of the expander is directly connected to the speed of thepowertrain and thus the speed of the combustion engine. The rotational speedof the expander is thus suitably increased by controlling the gearbox to a lowergear. By controlling the gearbox, such that a lower gear is engaged, the speedof the combustion engine/ the powertrain will increase and the rotational speedof the expander will thereby also increase. lf the gearbox is controlled to shift toa higher gear, the speed of the combustion engine and the powertrain will decrease, and the rotational speed of the expander will thereby also decrease.ln the case where the cooling pump of the cooling circuit is driven by thecombustion engine the speed of the cooling pump will increase when the enginespeed is increased. Thus, when the gearbox is controlled to a lower gear in orderto increase the rotational speed of the expander and thereby decrease thepressure of the working fluid, the speed of the cooling pump will increase. Theflow of cooling fluid passing through the condenser will thereby increase and thecooling of the working fluid will increase. Lowering the temperature of theworking fluid will decrease the pressure of the working fluid upstream of theexpander. This way, increasing of the speed of the powertrain has a doublepositive effect on the pressure of the working fluid.
    According to an aspect of the invention the rotational speed of the expander iscontrolled based on the combustion engine efficiency, the expander efficiencyand/or the gearbox efficiency. The rotational speed of the expander may thusbe controlled based on the resulting impact on the overall efficiency of thepowertrain. By considering the overall efficiency of the powertrain the rotationalspeed of the expander can be controlled while obtaining the currently mostenergy optimal engine speed. The gearbox is thus preferably controlled basedon the resulting impact on the combustion engine efficiency, the expanderefficiency and/or the gearbox efficiency when controlling the rotational speed ofthe expander. The method suitably comprises to increase the rotational speedof the expander by controlling the gearbox to a lower gear, only if the negativeimpact on the overall efficiency of the powertrain is smaller than the increase ofenergy recovery. That is, if the decrease in overall efficiency of the powertrainwill be greater than the increase of recovered energy by shifting to a lower gear,the gearbox will not be controlled to a lower gear. lnstead, the at least one heatsource will be controlled to bypass the evaporator. By considering the overallefficiency of the powertrain it is ensured that the rotational speed of the expanderis controlled, such that the most energy optimal condition prevails in the powertrain.
    According to an aspect of the invention a waste heat recovery systemassociated with a powertrain of a vehicle is provided. The powertrain comprisesa combustion engine and a gearbox connected to the combustion engine. Thewaste heat recovery system comprises a working fluid circuit; an evaporator; anexpander; a condenser; a reservoir for a working fluid and a pump arranged topump the working fluid through the circuit, wherein the evaporator is arrangedfor heat exchange between the working fluid and at least one heat source, andwherein the waste heat recovery system further comprises a coo|ing circuitarranged in connection to the condenser, and wherein the expander ismechanically coupled to the powertrain. The waste heat recovery system furthercomprises a control unit adapted to determine the pressure and temperature ofthe working fluid upstream of the expander; and to control the rotational speed of the expander based on the determined pressure and the temperature.
    The control unit is suitably connected to the evaporator, the expander, the pumpand the coo|ing circuit. The control unit is suitably connected to at least onepressure sensor and at least one temperature sensor arranged upstream of theexpander on the high pressure side of the waste heat recovery system. Thecontrol unit may be the engine control unit or may comprise a plurality of differentcontrol units. A computer may be connected to the control unit.
    According to an aspect of the invention the control unit is adapted to control therotational speed of the expander based on a comparison between thedetermined pressure and a predetermined maximum pressure and acomparison between the difference between the determined temperature andthe boiling point for the working fluid and a predetermined minimum temperature difference. The boiling point for the working fluid is different for different pressure.
    Also, the boiling point is different for different types of working fluid. The normalboiling point for the working fluid is the boiling point in atmospheric pressure.The boiling point of the working fluid is thus lower than the normal boiling pointat a pressure lower than the atmospheric pressure. The boiling point of theworking fluid in relation to the pressure is known and is suitably saved in the 11 control unit. The temperature of the working fluid upstream of the expander ishigher than the boiling point when it is a vapour irrespective of the type ofworking fluid. The difference between the actual temperature of the working fluidand the boiling point at the current pressure thus indicates the level of superheatof the working fluid. The control unit is thus suitably adapted to control therotational speed of the expander based on a comparison between thedetermined pressure and a predetermined maximum pressure and acomparison between a determined level of superheat and a predeterminedminimum level of superheat. A certain level of superheat is desired in order toobtain optimal efficiency of the expander. The predetermined minimumtemperature difference is suitably between 10-60 degrees, preferably between20-30 degrees. The minimum level of superheat is thus between 10-60 degrees,preferably between 20-30 degrees. The predetermined maximum pressuresuitably depends on constraints of the components of the waste heat recoverysystem. The predetermined maximum pressure and the predeterminedminimum temperature difference/superheat level are suitably saved in the control unit.
    According to an aspect of the invention the control unit is adapted to increasethe rotational speed of the expander when the determined pressure exceeds thepredetermined maximum pressure and/or the difference between thedetermined temperature and the boiling point for the working fluid is smaller thanthe predetermined minimum temperature difference. The control unit may furtherbe adapted to increase the rotational speed of the expander if there is a risk thatthe pressure will exceed the predetermined maximum pressure and/or that thedifference between the temperature and the boiling point for the working fluidwill become smaller than the predetermined minimum temperature difference.The control unit is thus suitably adapted to increase the rotational speed of theexpander if the determined level of superheat is lower than the predeterminedminimum level of superheat. The control unit is suitably adapted to increase therotational speed of the expander pre-emptively, when there is a risk that the pressure will exceed the predetermined maximum pressure and/or that the 12 difference between the temperature and the boiling point for the working fluid will become smaller than the predetermined minimum temperature difference.
    The control unit may be adapted to determine if there is a risk that the pressurewill exceed the predetermined maximum pressure and/or that the differencebetween the temperature and the boiling point of the working fluid will becomesmaller than the predetermined minimum temperature difference based on aprediction of high load on the combustion engine. The control unit may beadapted to predict a high load on the combustion engine based on thetopography of the route of the vehicle. The control unit may be adapted todetermine if there is a risk that the pressure will exceed the predeterminedmaximum pressure and/or that the difference between the temperature and theboiling point of the working fluid will become smaller than the predeterminedminimum temperature difference based on the current determined pressure andtemperature of the working fluid and/or a prediction of high load on the combustion engine.
    According to an aspect of the invention the control unit is adapted to control therotational speed of the expander by controlling the gearbox and thereby thespeed of the powertrain. Since the expander is mechanically connected to thepowertrain, the rotational speed of the expander is directly connected to thespeed of the powertrain and thus the speed of the combustion engine. Thecontrol unit is thus suitably adapted to increase the rotational speed of theexpander by controlling the gearbox to a lower gear. By controlling the gearbox,such that a lower gear is engaged, the speed of the combustion engine/ thepowertrain will increase and the rotational speed of the expander will therebyalso increase and the pressure of the working fluid is decreased.
    According to an aspect of the invention the control unit is adapted to control therotational speed of the expander based on the combustion engine efficiency, theexpander efficiency and/or the gearbox efficiency. The control unit is thusadapted to control the rotational speed of the expander based on the resulting 13 impact on the overall efficiency of the powertrain. This way, the rotational speedof the expander can be controlled while obtaining the currently most energyoptimal engine speed. The control unit is thus adapted to control the gearboxbased on the resulting impact on the combustion engine efficiency, the expanderefficiency and/or the gearbox efficiency. The control unit is suitably adapted toincrease the rotational speed of the expander by controlling the gearbox to alower gear, only if the energy recovery gained by changing gear exceeds thenegative impact on the overall efficiency of the powertrain. That is, if thedecrease in overall efficiency of the powertrain will be greater than the increaseof recovered energy by shifting to a lower gear, the control unit is adapted tocontrol the at least one heat source to bypass the evaporator.
    Further objects, advantages and novel features of the present invention willbecome apparent to one skilled in the art from the following details, and also byputting the invention into practice. Whereas the invention is described below, itshould be noted that it is not restricted to the specific details described.Specialists having access to the teachings herein will recognise furtherapplications, modifications and incorporations within other fields, which arewithin the scope of the invention.
    BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects andadvantages of it, the detailed description set out below should be read togetherwith the accompanying drawings, in which the same reference notations denote similar items in the various drawings, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment ofthe invention;Figure 2 schematically illustrates a waste heat recovery system according to an embodiment of the invention; 14 Figure 3 illustrates a diagram over the temperature-pressure relationshipfor working fluids according to an embodiment of the invention; Figure 4 schematically illustrates a flow chart for a method for contro|ing awaste heat recovery system according to an embodiment of theinvention; and Figure 5 schematically illustrates a control unit or computer according to an embodiment of the invention.
    DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 soiietnatioaiiy shows a side view of a vehicie f according to anembodiment of the invention. The vehicle f has a powertrain 3 comprising acombustion engine 2 and a gearbox 4 connected to the combustion engine 2and the driving wheeis 6 of the vehioie f. The vehioie f further comprises awaste heat recovery system fO associated with the powertrain 3. The vehicle 1may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternativelybe a passenger car. The vehicle may be a hybrid vehicle comprising an electricmachine (not shown) in addition to the combustion engine 2.
    Figure 2 sohernatioaiiy shows a waste heat recovery system 10 associated witha powertrain 3 of a vehicle 1 according to an embodiment of the invention. Thevehicle 1 is suitably configured as described in Figure 1. The waste heatrecovery system 10 comprises a working fluid circuit 12; an evaporator 14; anexpander 16; a condenser 18; a reservoir 20 for a working fluid WF and a pump22 arranged to pump the working fluid WF through the circuit 12, wherein theevaporator 14 is arranged for heat exchange between the working fluid WF andat least one heat source 24, wherein the waste heat recovery system 10 furthercomprises a cooling circuit 26 arranged in connection to the condenser 18 andwherein the expander 16 is mechanically connected to the powertrain 3.
    The waste heat recovery system 10 comprises a control unit 30 adapted todetermine the pressure P and temperature T of the working fluid WF upstreamof the expander 16 and to control the rotationa| speed of the expander 16 basedon the determined pressure P and temperature T. A computer 32 may beconnected to the control unit 30. The waste heat recovery system 10 furthercomprises at least one pressure sensor 36 and at least one temperature sensor38 for determining the current pressure P and the current temperature T of theworking fluid WF. The at least one pressure sensor 36 and the at least onetemperature sensor 38 are suitably arranged in communication with the workingfluid circuit 12 upstream of the expander 18 and downstream of the pump 22.The control unit 30 is arranged in connection to the evaporator 14, the expander16, the cooling circuit 26, the pump 22, the at least one pressure sensor 36 and the at least one temperature sensor 38.
    The at ieast one heat source 24 connected to the evaporator te ihay he exhaustgases from the coinoustion engine 2, an exhaust gas recircuiation system(EGR), the oooiing fiuioi ot the oornoustion engine 2, the contoustion engine 2itself or any other hot component associated with the oornioustion engine 2. Theat ieast one heat source 24 is herein iiiustrateo as a medium passing throughthe evaporator tri. The at ieast one heat source 24 is herein iiiustrated as arrowsand may tue exhaust gases from the cornioustion engine 2. The waste heatrecovery system ti) may oomprise a piuraiity ot heat sources 24. The evaporator“iii is suitahiy a heat exchanger connected to the at ieast one heat source 24and the yyoriting tiuid circuit i2. The heat transfer between the Working tiuid WPand the heat source 24 is an exchange of energy resuiting in a change intemperature, The Waste heat recovery system tt) is suitaoiy haseo on an organicRanirtine cycie. The working fiuid WP is thus suitahiy organic, such as ethanoi oracetone, The waste heat recovery system to is thus configureo such that theiiouici working fiuid WP is purnpeo ironi iow pressure to high pressure and entersthe evaporator tft. The working fiuid WP is thereoy heated hy the at ieast oneheat source 24 connected to the evaporator te and the working fiuid WP is thuseyaoorated. The vapour is then exoanded in the expander i6 whereoy 16 ntechanicai work is produced and transferred to the powertraih 3, whereby thetemperature and the pressure ot the vapour is decreased. The vapour thereafterenters the condenser tå where condensation through heat exchange betweenthe vapour and the cooiing fiuid ot the cooiing circuit 26 brings the working fiuidWP back to its iriitiai iiouid state. Thus, the heat source 24 is providing the energyentering the waste heat recovery system it) and the energy is ieaving the wasteheat recovery systern ti) as mechanicai work via the expander 16 and as heatvia the oooiing circuit 26 cooiing the condenser 18. The temperature ot theworking fiuid WF in the waste heat recovery systern tu thus depends on theamount of energy entering the system to and the amount of energy ieaving thesystem tu.
    Only vapour should enter the expander 16 and the waste heat recovery system10 therefore comprises a bypass arrangement 34, such that in the case wherethe 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 bypassarrangement 34. The expander 16 is suitably a fixed displacement expander,such a piston expander. The expander 16 may be mechanically connecteddirectly to the combustion engine 2 or to the gearbox 4.
    The purnp 22 pressurizirtg and circuiating the working fiuid WF through thecircuit i2 may be darnaged if the working fiuid WP entering the pump 22 is notin a iiouid state. Thus in the case where the teinperature downstream ot thecondenser ta is too high, such that the working tiuid WF is not in a iiduid state,the pressure in the reservoir 2G may be increased. This way., the working fiuidWF is brought to a iiouid state and may be ournped by the pump 22. The pump22 is suitabiy eiectricaiiy driven.
    The cooling circuit 26 connected to the condenser 18 may be part of thecombustion engine cooling system or a separate cooling system. The coolingfluid 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). 17 The waste heat recovery system 10 may comprise one or more heat exchangers14. The waste heat recovery system 10 may for example comprise a recuperatorarranged to pre-heat the working fluid WF before entering the evaporator 14.The waste heat recovery system 10 may also comprise one or more condensers18, such that cooling down of the working fluid WF may be performed in multiplesteps. Furthermore, the system 10 may comprise one or more expanders 16.
    Figure 3 shows a diagram over the relationship between temperature T andpressure P for working fluids WF according to an embodiment of the invention.Two different working fluids WF are illustrated in this diagram and just as anexample the solid line may represent ethanol and the dashed line may representacetone. Any of the working fluids WF may constitute the working fluid in thewaste heat recovery system 10 as disclosed in Figure 2. The diagram shows thenormal boiling point BP1n, BP2n for the respective working fluid. The normalboiling point is the temperature at which the working fluid WF evaporates inatmospheric pressure. The relationship between temperature T and pressure Pis thus different for different types of working fluid WF. The boiling point BP fora working fluid WF varies with the pressure P. lf the pressure increases, theboiling point BP increases.
    The diagram further illustrates the temperature difference AT between adetermined temperature T1, T2 and the boiling point BP1, BP2 at the determinedpressure P1 , P2 for the respective working fluid WF. This temperature differenceAT is also called the level of superheat. A certain level of superheat is desiredin the waste heat recovery system 10 in order to obtain optimal efficiency of theexpander 16. The diagram shows the desired level of superheat defined as apredetermined minimum temperature difference ATmin, for the working fluid WFillustrated as a dashed line. The predetermined minimum temperature differenceATmin is suitably between 10-60 degrees, preferably between 20-30 degrees. 18 The components of the waste heat recovery system 10 set a constraint on themaximum pressure Pmax of the working fluid WF that the system 10 can handlewithout problems. lf the pressure P of the working fluid WF is higher than themaximum pressure Pmax on the high pressure side of the waste heat recoverysystem 10, the various components may be damaged. Such maximum pressurePmax is predetermined for the relevant waste heat recovery system 10.
    Figure 4 shows a flowchart for a method for controlling a waste heat recoverysystem 10 associated with a powertrain 3 of a vehicle 1. The powertrain 3comprises a combustion engine 2 and a gearbox 4 connected to the combustionengine 2. The waste heat recovery system 10 comprises a working fluid circuit12; an evaporator 14; an expander 16; a condenser 18; a reservoir 20 for aworking fluid WF and a pump 22 arranged to pump the working fluid WF throughthe circuit 12, wherein the evaporator 14 is arranged for heat exchange betweenthe working fluid WF and at least one heat source 24, wherein the waste heatrecovery system 10 further comprises a cooling circuit 26 arranged in connectionto the condenser 18, and wherein the expander 16 is mechanically coupled tothe powertrain 3. The method comprises the steps of: - determining s101 the pressure P and temperature T of the working fluid WFupstream of the expander 16; and - controlling s102 the rotational speed of the expander 16 based on thedetermined pressure P and temperature T.
    The waste heat recovery system 10 is suitably configured as disclosed in Figure2, wherein the control unit 30 is adapted to perform the method steps described herein.
    The rotational speed of the expander 16 may be controlled based on acomparison between the determined pressure P and a predetermined maximumpressure Pmax and a comparison between a difference between the determinedtemperature and the boiling point for the working fluid AT and a predeterminedminimum temperature difference ATmin. The temperature T of the working fluid 19 WF upstream of the expander 16 is higher than the boiling point BP when it is avapour. The boiling point BP for the working fluid WF depends on the pressureP. The difference between the actual temperature of the working fluid and theboiling point AT at the current pressure P thus indicates the level of superheatof the working fluid WF. An example of the relationship between the pressure Pand temperature T of the working fluid is illustrated in Figure 3.
    The rotational speed of the expander 16 is suitably increased when thedetermined pressure P exceeds the predetermined maximum pressure Pmaxand/or the difference between the determined temperature and the boiling pointfor the working fluid AT is smaller than the predetermined minimum temperaturedifference ATmin. When the rotational speed of the expander 16 is increased agreater mass flow of working fluid WF can be handled by the expander 16 andthe pressure of the working fluid WF in the circuit 12 upstream of the expander16 will decrease. When the temperature difference AT is smaller than thepredetermined minimum temperature difference ATmin, there is a great risk thatthe working fluid WF will shift to liquid phase which may damage the expander16. The higher the pressure P of the working fluid WF the higher is the boilingpoint BP of the working fluid WF. Thus, by decreasing the pressure P the boilingpoint BP of the vapour is decreased and the difference between the determined temperature and the boiling point AT will thereby increase.
    The rotational speed of the expander 16 may be increased if there is a risk thatthe pressure P of the working fluid WF will exceed the predetermined maximumpressure Pmax and/or that the difference between the temperature and the boilingpoint of the working fluid AT will become smaller than the predeterminedminimum temperature difference ATmin. The rotational speed of the expander 16is thus suitably increased if the determined level of superheat is lower than thepredetermined minimum level of superheat. This way, the pressure P of theworking fluid WF is pre-emptively decreased and the damage of the waste heatrecovery system 10 is avoided while optimizing the energy recovery.
    The risk that the pressure P will exceed the predetermined maximum pressurePmax and/or that the difference between the temperature and the boiling point ofthe working fluid AT will become smaller than the predetermined minimumtemperature difference ATmin may be determined based on a prediction of highload on the combustion engine 2. When the load on the combustion engine 2 ishigh, the temperature of the at least one heat source 24 will increase and thetemperature T and pressure P of the working fluid WF will thereby also increase.Thus, by predicting that the load on the combustion engine 2 will be high, it ispredicted that the temperature T and pressure P of the working fluid WF willincrease. The high load on the combustion engine 2 may be predicted based onthe topography of the route of the vehicle 1.
    The rotational speed of the expander 16 may be controlled by controlling thegearbox 4 and thereby the rotational speed of the powertrain 3. Since theexpander 16 is mechanically connected to the powertrain 3, the rotational speedof the expander 16 is directly connected to the speed of the powertrain 3 andthus the speed of the combustion engine 2. The rotational speed of the expander16 is thus suitably increased by controlling the gearbox 4 to a lower gear. Bycontrolling the gearbox 4, such that a lower gear is engaged, the speed of thecombustion engine 2/ the powertrain 3 will increase and the rotational speed ofthe expander 16 will thereby also increase. lf the gearbox 4 is controlled to shiftto a higher gear, the speed of the combustion engine 2 and the powertrain 3 willdecrease, and the rotational speed of the expander 16 will thereby alsodecrease.
    The rotational speed of the expander 16 may be controlled based on thecombustion engine efficiency, the expander efficiency and/or the gearboxefficiency. The rotational speed of the expander 16 may thus be controlledbased on the resulting impact on the overall efficiency of the powertrain 3. Byconsidering the overall efficiency of the powertrain 3 the rotational speed of theexpander 16 can be controlled while obtaining the currently most energy optimalengine speed. The gearbox 4 is thus preferably controlled based on the resulting 21 impact on the combustion engine efficiency, the expander efficiency and/or thegearbox efficiency when controlling the rotational speed of the expander.
    The method may comprise to increase the rotational speed of the expander 16by controlling the gearbox 4 to a lower gear, only if the resulting negative impacton the overall efficiency of the powertrain 3 is smaller than the resulting increaseof energy recovery. That is, if the decrease in overall efficiency of the powertrain3 will be greater than the increase of recovered energy by shifting to a lowergear, the gearbox 4 will not be controlled to a lower gear. lnstead, the at leastone heat source 24 will be controlled to bypass the evaporator 14.
    Figure 5 schematically illustrates a device 500. The control unit 30 and/orcomputer 32 described with reference to Figure 2 may in a version comprise thedevice 500. The term “link” refers herein to a communication link which may bea physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link ormicrowave link. The device 500 comprises a non-volatile memory 520, a dataprocessing unit 510 and a read/write memory 550. The non-volatile memory 520has a first memory element 530 in which a computer program, e.g. an operatingsystem, is stored for controlling the function of the device 500. The device 500further comprises a bus controller, a serial communication port, I/O means, anA/D converter, a time and date input and transfer unit, an event counter and aninterruption controller (not depicted). The non-volatile memory 520 has also asecond memory element 540.
    There is provided a computer program P which comprises routines for a methodfor controlling a waste heat recovery system 10 associated with a powertrain 3of a vehicle 1 according to the invention. The computer program P comprisesroutines for determining a pressure P and temperature T of the working fluid WFupstream of the expander 16. The computer program P comprises routines forcontrolling the rotational speed of the expander 16 based on the determinedpressure P and temperature T. The computer program P comprises routines for 22 contro|ing the rotational speed of the expander 16 based on a comparisonbetween the determined pressure P and a predetermined maximum pressurePmax and a comparison between a difference between the determinedtemperature and the boi|ing point for the working f|uid AT and a predeterminedminimum temperature difference ATmin. The computer program P comprisesroutines for increasing the rotational speed of the expander 16 when thedetermined pressure P exceeds the predetermined maximum pressure Pmaxand/or the difference between the determined temperature and the boi|ing pointfor the working f|uid AT is smaller than the predetermined minimum temperaturedifference ATmin_ The computer program P comprises routines for increasing therotational speed of the expander 16 if there is a risk that the pressure P of theworking f|uid WF wi| exceed the predetermined maximum pressure Pmax and/orthat the difference between the temperature and the boi|ing point of the workingf|uid AT wi| become sma|er than the predetermined minimum temperaturedifference ATmin_ The computer program P comprises routines for contro|ing therotational speed of the expander by contro|ing the gearbox 4 and thereby therotational speed of the powertrain 3. The computer program P comprisesroutines for contro|ing the rotational speed of the expander 16 based on thecombustion engine efficiency, the expander efficiency and/or the gearboxefficiency. 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.
    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 programstored in the memory 560 or a certain part of the program stored in the read/writememory 550.
    The data processing device 510 can communicate with a data port 599 via adata bus 515. The non-vo|ati|e memory 520 is intended for communication withthe data processing unit 510 via a data bus 512. The separate memory 560 isintended to communicate with the data processing unit 510 via a data bus 511. 23 The read/write memory 550 is adapted to communicating with the dataprocessing unit 510 via a data bus 514.
    When data are received on the data port 599, they are stored temporarily in thesecond memory element 540. When input data received have been temporarilystored, the data processing unit 510 is prepared to effect code execution asdescribed above.
    Parts of the methods herein described may be effected by the device 500 bymeans of the data processing unit 510 which runs the program stored in thememory 560 or the read/write memory 550. When the device 500 runs theprogram, methods herein described are executed.
    The foregoing description of the preferred embodiments of the present inventionis provided for i|ustrative and descriptive purposes. lt is not intended to beexhaustive or to restrict the invention to the variants described. l/lanymodifications and variations will obviously be apparent to one ski|ed in the art.The embodiments have been chosen and described in order best to explain theprinciples of the invention and its practical applications and hence make itpossible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.
    权利要求:
    Claims (17)
    [1] 1. A method for controlling a waste heat recovery system (1 O) associated with apowertrain (3) of a vehicle (1), the powertrain (3) comprising a combustionengine (2) and a gearbox (4) connected to the combustion engine (2), the wasteheat recovery system (1 O) comprising 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 thecircuit (12), wherein the evaporator (14) is arranged for heat exchange betweenthe working fluid (WF) and at least one heat source (24), wherein the waste heatrecovery system (10) further comprises a coo|ing circuit (26) arranged inconnection to the condenser (18), and wherein the expander (16) ismechanically coupled to the powertrain (3), characterized by the steps of: - determining (s101) the pressure (P) and temperature (T) of the working fluid(WF) upstream of the expander (16); - controlling (s102) the rotational speed of the expander (16) based on the determined pressure (P) and temperature (T).
    [2] 2. The method according to c|aim 1, wherein the rotational speed of theexpander (16) is controlled based on a comparison between the pressure (P)and a predetermined maximum pressure (Pmax) and a comparison between a difference (AT) between the temperature (T) and the boiling point (BP) for the working fluid (WF) and a predetermined minimum temperature difference (ATmin).
    [3] 3. The method according to c|aim 2, wherein the rotational speed of theexpander (16) is increased if there is a risk that the pressure (P) will exceed thepredetermined maximum pressure (Pmax) and/or that the difference (AT)between the temperature (T) and the boiling point (BP) of the working fluid (WF)will become smaller than the predetermined minimum temperature difference(ATmin).
    [4] 4. The method according to claim 3, wherein the risk is determined based on aprediction of high load on the combustion engine (2).
    [5] 5. The method according to any of the preceding claims, wherein the rotationa|speed of the expander (16) is controlled by controlling the gearbox (4) andthereby the speed of the powertrain (3).
    [6] 6. The method according to any of the preceding claims, wherein the rotationa|speed of the expander (16) is controlled based on the combustion engineefficiency, the expander efficiency and/or the gearbox efficiency.
    [7] 7. A waste heat recovery system associated with a powertrain (3) of a vehicle(1), the powertrain (3) comprising a combustion engine (2) and a gearbox (4)connected to the combustion engine (2), the waste heat recovery system (10)comprising a working fluid circuit (12); an evaporator (14); an expander (16); acondenser (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 theevaporator (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 thecondenser (18), and wherein the expander (16) is mechanically coupled to thepowertrain (3), characterized in that the waste heat recovery system (10)comprises a control unit (30) adapted to determine the pressure (P) andtemperature (T) of the working fluid (WF) upstream of the expander (16); and tocontrol the rotationa| speed of the expander (16) based on the determinedpressure (P) and the temperature (T).
    [8] 8. The system according to claim 7, wherein the control unit (30) is adapted tocontrol the rotationa| speed of the expander based on a comparison betweenthe pressure (P) and a predetermined maximum pressure (Pmax) and acomparison between the difference (AT) between the temperature (T) and the 26 boiling point (BP) for the working fluid (WF) and a predetermined minimum temperature difference (ATman).
    [9] 9. The system according to claim 8, wherein the control unit (30) is adapted toincrease the rotational speed of the expander (16) if there is a risk that thepressure (P) will exceed the predetermined maximum pressure (Pmax) and/orthat the difference (AT) between the temperature (T) and the boiling point (BP)for the working fluid (WF) will become smaller than the predetermined minimum temperature difference (ATman).
    [10] 10. The system according to claim 9, wherein the control unit (30) is adapted todetermine the risk based on a prediction of high load on the combustion engine (2)-
    [11] 11. The system according to any of claims 7-10, wherein the control unit (30)is adapted to control the rotational speed of the expander (16) by controlling the gearbox (4) and thereby the speed of the powertrain (3).
    [12] 12. The system according to any of claims 7-11, wherein the predeterminedmaximum pressure (Pmax) depend on constraints of the components of the waste heat recovery system (10).
    [13] 13. The system according to any of claims 7-12, wherein the predeterminedminimum temperature difference (ATmin) is between 10-60 degrees, preferably20-30 degrees.
    [14] 14. The system according to any claims 7-13, wherein the control unit (30) isadapted to control the rotational speed of the expander (16) based on thecombustion engine efficiency, the expander efficiency and/or the gearboxefficiency. 27
    [15] 15. A vehicle, characterized in that it comprises a waste heat recovery system (10) according to any of the claims 7-14.
    [16] 16. A computer program (Pr), wherein said computer program comprisesprogram code for causing an electronic control unit (30; 500) or a computer (32;500) connected to the electronic control unit (30; 500) to perform the steps according to any of the claims 1-6.
    [17] 17. A computer program product comprising a program code stored on acomputer-readable medium for performing the method steps according to anyof claims 1-6, when said computer program is run on an electronic control unit(30; 500) or a computer (32; 500) connected to the electronic control unit (30;500).
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    同族专利:
    公开号 | 公开日
    KR20190022748A|2019-03-06|
    US20190309655A1|2019-10-10|
    BR112019000480A2|2019-04-24|
    SE541953C2|2020-01-14|
    EP3485156A4|2020-03-11|
    CN109415997A|2019-03-01|
    WO2018013027A1|2018-01-18|
    EP3485156A1|2019-05-22|
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    PCT/SE2017/050484| WO2018013027A1|2016-07-12|2017-05-12|A method and system for controlling the rotational speed of an expander in a waste heat recovery system|
    EP17828051.7A| EP3485156A4|2016-07-12|2017-05-12|A method and system for controlling the rotational speed of an expander in a waste heat recovery system|
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