WO2016089285A1

WO2016089285A1 - A method for controlling a waste heat recovery system and a waste heat recovery system

Info

Publication number: WO2016089285A1
Application number: PCT/SE2015/051263
Authority: WO
Inventors: Jan Dellrud; Alexander CHABO; Peter TYSK; Henrik FLEMMER
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2014-12-03
Filing date: 2015-11-25
Publication date: 2016-06-09
Anticipated expiration: 2017-06-03
Also published as: SE538742C2; SE1451471A1; DE112015004901T5

Abstract

A waste heat recovery (WHR) system for use in a drive system and a method for controlling such a system. The system includes a heat exchanger (3), an exhaust channel (4) for carrying exhaust gas from a combustion engine (1) through the heat exchanger, a bypass channel (5) connected to the exhaust channel and bypassing the heat exchanger, an adjustable valve (6) for adjusting the mass flow of exhaust gas through each of the exhaust channel and the bypass channel, and a coolant channel (7) for carrying a coolant fluid through the heat exchanger. The method comprises the steps of determining a current value of a mass flow MF_CF1of coolant flu id through the heat exchanger, an entrance temperature T_EG1 of the exhaust gas before entry into the heat exchanger, and an entrance temperature T_CF1of the coolant fluid before entry into the heat exchanger. A setpoint S₁ for a mass flow MF_EG1 of exhaust gas through the heat exchanger at which a net power gain P_net of the drive system is maximized is determined using said determined values. A current value of the mass flow MF_EG1 of exhaust gas through the heat exchanger is determined and the adjustable valve is controlled so that the mass flow M F_EG1 is adjusted toward the determined setpoint S₁.

Description

A method for controlling a waste heat recovery system and a waste heat recovery system

FI ELD OF THE I NVENTION

The invention relates to a method for controlling a waste heat recovery system for recovering waste heat from a combustion engine in a drive system, in particu lar in a drive system of a motor veh icle. The invention also relates to a waste heat recovery system, a computer program, a computer program product, an electronic control un it and a motor veh icle.

Waste heat recovery systems may be used in vehicles in order to extract waste heat energy from the exhaust gases and thereby increase the fuel economy of the veh icle. Thermoelectric generators (TEGs) may be used in such systems in order to convert waste heat into electricity, but also other kinds of heat exchangers may be used . PRIOR ART

WO201 1 /037526 d iscloses a waste heat recovery system includ ing a thermoelectric generator (TEG) for extracting electricity from a waste heat med ium in a veh icle powered by a combustion engine. The waste heat recovery system comprises a heat exchanger in the form of a TEG , an exhaust channel configured to carry an exhaust gas orig inating from the combustion engine through the TEG, a bypass channel connected to the exhaust channel upstream of the TEG and bypassing the TEG , an adjustable valve by means of which the mass flow of exhaust gas through each of the exhaust channel and the bypass channel can be adjusted , and a coolant channel configured to carry a coolant fluid through the TEG. The adjustable valve can be adjusted in response to the measured or estimated temperature of the exhaust gases. If the exhaust gases are too hot or too cold , a portion of the exhaust gases are led through the bypass channel in order to protect the TEG. Thus, the system is primarily configured to protect the TEG from overheating .

SUMMARY OF THE I NVENTION

It is an object of the present invention to provide on one hand a method for controlling a waste heat recovery system for recovering waste heat from a combustion engine in a drive system, and on the other hand a waste heat recovery system, which are in at least some aspect improved with respect to previously known methods and systems.

Accord ing to the invention , this object is with respect to the method ach ieved by means of a method accord ing to the appended claim 1 . With the inventive method , the waste heat recovery system can be controlled so that the net power gain P_net of the drive system is maximized , rather than the power gain of the at least one heat exchanger. The net power gain P_{n e}t is here defined as the sum of the total power gains obtainable from the waste heat recovery system and the total power losses arising in the drive system as a result of the waste heat recovery system. In consequence, in a vehicle with a drive system comprising said waste heat recovery system , the fuel economy may be improved by using the method accord ing to the present invention . Preferably, but not necessarily, the heat exchanger is placed in an after treatment system of the drive system.

According to an embodiment of the invention , the step of determining the setpoint Si for the mass flow M F _EGI of exhaust gas through the first heat exchanger comprises the steps of:

choosing a set of test values representing the mass flow M F Ed of exhaust gas through the first heat exchanger,

iteratively calculating the net power gain P_{n e}t using said test values until said net power gain P_net is at a maximum,

outputting the test value at which the net power gain P_{n e}t is at a maximum as said setpoint Si .

I n this embodiment, the setpoint Si is determined using an iterative algorithm for calculating the net power gain P_net. The set of test values is preferably chosen such that the initial net power gain P_{n e}t is small. After each iteration , it is checked whether the net power gain P_net is larger than in the previous iteration , and if so, the algorithm continues to calculate the net power gain for the successive test value. If not, the preceding test value is output as the setpoint Si . In th is way, the setpoint Si can be found with in a short runn ing time.

According to another embod iment of the invention , wherein the system further comprises a cooler connected to the first coolant channel and a coolant flu id pump, the method further comprises the steps of: determin ing a setpoint S₂ for the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump at wh ich the net power gain P_net of the drive system is at a maximum,

controlling the coolant flu id pump so that the mass flow M F_CF of coolant flu id pumped through the coolant flu id pump is adjusted toward the determined setpoint S₂.

In this embodiment, the method is implemented in a system comprising a cooling system with a coolant flu id pump. In addition to controlling the first adjustable valve controlling the amount of exhaust gas carried through the heat exchanger and the bypass channel respectively, the method according to this embodiment allows to control the coolant flu id pump such that the net power gain P_net is optimized . Th is allows for a more accurate control of the waste heat recovery system.

According to another embodiment of the invention , the step of determin ing a setpoint S₂ for the mass flow M F_CF of coolant flu id pumped through the coolant fluid pump comprises determin ing a power consumption P_pump of the coolant fluid pump. In th is way, also power losses occurring at the coolant flu id pump are taken into account in the optimization of the net power gain P_net.

According to another embodiment of the invention , wherein the cooler comprises at least one radiator for cooling the coolant fluid , and a charge air cooler for cooling an air flow coming from a turbo charger and flowing through the charge air cooler toward an air in let of the combustion engine, the method further comprises the step of: determin ing a power loss P_CAC in the charge air cooler due to a temperature increase of the air flowing through the charge air cooler caused by the at least one rad iator. I n this way, an even more accurate control of the heat recovery system can be ach ieved , since the method allows to control the waste heat recovery system such that the power losses P_CAC in the charge air cooler have a minimum impact on the net power gain P _NET. The method according to this embod iment is suitable for use in a drive system in which a coolant fluid flowing through the charge air cooler is separate from the coolant fluid flowing through the at least one rad iator, i.e. wherein separate closed cooling systems are used , wh ich are arranged so that they interact with each other.

According to another embodiment of the invention , the power loss PCAC in the charge air cooler is used in the step of determin ing a setpoint S₂ for the mass flow M F_CF of coolant flu id through the coolant flu id pump. Accord ing to another embodiment of the invention , the power loss P_CAC in the charge air cooler is used in the step of determining a setpoint Si for a mass flow M F Ed of exhaust gas through the first heat exchanger. Of course, it is possible to simultaneously use the power loss P_CAC in the charge air cooler in the step of determining a setpoint Si and in the step of determining a setpoint S₂.

According to another embodiment of the invention , wherein the system further comprises

a second heat exchanger, a second exhaust channel connected to the first exhaust channel and configured to carry an exhaust gas orig inating from the combustion eng ine through the second heat exchanger,

a second bypass channel connected to the second exhaust channel upstream of the second heat exchanger and bypassing the second heat exchanger,

a second adjustable valve by means of which the mass flow of exhaust gas through each of the second exhaust channel and the second bypass channel can be adjusted ,

- a second coolant channel connected to the first coolant channel and configured to carry a coolant fluid through the second heat exchanger,

the method further comprises the steps of:

determining an entrance temperature T_EG2 of the exhaust gas before entry into the second heat exchanger,

controlling the second adjustable valve in response to said determined entrance temperature T_EG2 of the exhaust gas before entry into the second heat exchanger. In this embodiment, the method is used in a system comprising at least two heat exchangers, of which the first one may for example be placed in an after treatment system and the second one may for example be placed in an exhaust gas recirculation system. The method allows the exhaust gas flow through the second heat exchanger to be controlled such that damages due to h igh temperatures of the exhaust gases are avoided . A heat exchanger placed in the exhaust gas recirculation system may otherwise reach relatively high temperatures at which e.g . a thermoelectric generator may be damaged . According to another embodiment of the invention, wherein the system further comprises a third adjustable valve connecting the first coolant channel and the second coolant channel, the method further comprises the step of:

- determining a current value of the mass flow MFCF of coolant fluid pumped through the coolant fluid pump,

determining a setpoint S₃ for a ratio

of the mass flow MF_CFI of coolant fluid through the first heat exchanger to the mass flow MF_CF2 of coolant fluid through the second heat exchanger at which a net power gain P_NET of the waste heat recovery system is maximized using the determined current value of the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump as an input value for calculating the net power gain P_NET,

- controlling the third adjustable valve so that said ratio R of the mass flows of coolant fluid is adjusted toward the determined setpoint S₃.

In this embodiment, the waste heat recovery system can be controlled such that the mass flow of coolant fluid through the first and the second heat exchanger respectively is adjusted such that the net power gain P_NET is optimized. This has proved to be efficient for increasing the net power gain P_net of the drive system, since it enables reduction of the total mass flow MF_CF of coolant fluid, thereby reducing energy consumption of the coolant fluid pump.

According to another embodiment of the invention, the power loss PCAC in the charge air cooler is used in the step of determining a setpoint S3 for the ratio MFCFI IMF CF2 of the mass flow M FcFi of coolant fluid through the first heat exchanger to the mass flow M F_CF2 of coolant flu id through the second heat exchanger. Th is allows for increased accuracy in the determination of the setpoint S₃.

According to another embodiment of the invention , the method further comprises the step of determining a torque of the combustion engine. According to another embodiment of the invention , the method further comprises the step of determining a rotational speed of the combustion eng ine. These embodiments enable theoretical modeling of the temperature of the exhaust gases and reduce the need for temperature sensors mounted in the waste heat recovery system , thus decreasing the complexity of the system. Preferably, both the torque and the rotational speed are determined and used for temperature modeling .

The object of the present invention is, with respect to the system, achieved by means of a waste heat recovery system for recovering waste heat from a combustion engine in a drive system accord ing to the independent appended system claim. Advantages and embodiments of such a system appear from the method described above and also from the following detailed description . In other aspects, the invention also relates to a computer program having the features of claim 14, a computer program product having the features of claim 15, an electronic control unit having the features of claim 16 and a motor veh icle according to claims 1 7 and 1 8. Other advantageous features as well as advantages of the present invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described by means of example with reference to the appended drawings, wherein

Fig. 1 shows a schematic overview of a drive system including a waste heat recovery system according to a first embodiment of the invention,

Fig.2 shows a schematic overview of a drive system including a waste heat recovery system according to a second embodiment of the invention,

Fig.3 shows a flow chart of a method according to a first embodiment of the invention, and

Fig.4 shows a schematic drawing of a control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A drive system including a combustion engine 1, an after treatment system 2, and a waste heat recovery (WHR) system according to an embodiment of the invention is schematically shown in fig. 1. The WHR system includes a heat exchanger in the form of a thermoelectric generator (TEG) 3 placed in connection with the after treatment system 2, an exhaust channel 4 configured to carry an exhaust gas originating from the combustion engine through the TEG 3, and a bypass channel 5 which is connected to the exhaust channel 4 u pstream of the TEG 3 and which bypasses the TEG 3. The WHR system further includes an adjustable valve 6 by means of which the mass flow of exhaust gas through each of the exhaust channel 4 and the bypass channel 5 can be adjusted . The WH R system also comprises a coolant channel 7 connected to a cooler 8 , which coolant channel 7 is configured to carry a coolant fluid through the TEG 3. A pump 9 is arranged to pump the coolant fluid through the TEG 3 and the cooler 8.

In a method for controlling the WH R system according to a first embodiment of the invention , a current value of a mass flow M F cFi of coolant fluid through the TEG 3, equal to the mass flow M FCF of coolant fluid through the coolant flu id pump 9, is determined in a step A1 , see fig . 3. This can be performed e.g . by determining the temperature increase and the pressure drop across the TEG 3 or across the pump 9, but also by sensing the mass flow M F_CFI directly or by theoretical modeling . In a step A2, an entrance temperature T_EGI of the exhaust gas before entry into the TEG 3 is determined . This can be performed either by measuring the temperature using a sensor, or by modeling using e.g . the torque and the rotational speed of the combustion engine 1 as input parameters. In a step A3, an entrance temperature T cFi of the coolant fluid before entry into the TEG 3 is determined . In a step A4, a setpoint Si for a mass flow M FEGI of exhaust gas through the TEG 3 is determined , at which a net power gain P_net of the drive system is maximized . The setpoint Si is determined using said determined entrance temperature T_EG1 of the exhaust gas, said determined entrance temperature TCFI of the coolant fluid, and said determined current value of the mass flow MFc_Fi of coolant fluid through the first heat exchanger as input values for calculating the net power gain P_net. This is preferably done iterativeiy by first calculating the net power gain P_net for a first test value MF_EGi_;min representing the mass flow MF Ed of exhaust gas through the TEG 3, thereafter iterating for a second test value MF_EGi_;min + AMF_EGi, wherein AMF_EGi represents a small change in mass flow MF_EG1, and checking whether the net power gain P_net is larger or smaller for this second test value. As soon as a test value MF_EGI_;x has been found at which the net power gain P_net is at a maximum, this test value MF_EGI;_X is output as the setpoint Si. In a step A5, a current value of the mass flow MF_EGi of exhaust gas through the TEG 3 is determined, e.g. by a mass flow sensor (not shown) or by measuring temperature and pressure differences across the TEG 3. In a step A6, the adjustable valve 6 is controlled so that the current value of the mass flow MF_EG1 of exhaust gas through the TEG 3 is adjusted toward the determined setpoint Si and so that the remaining exhaust gas is led through the bypass channel 5. In this way, the WHR system can be controlled to maximize the net power gain P_net of the drive system. The calculation of the setpoint Si can e.g. be carried out by a control unit (not shown) which is also used for controlling the adjustable valve 6. Before outputting the setpoint S-i, it is preferably checked that the setpoint Si represents a mass flow MF_EGi within an allowed span, so that overheating of the TEG 3 is avoided.

To further increase the net power gain P_net of the drive system, also a setpoint S₂ for the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump 9, which here equals the mass flow M FcFi of coolant fluid pumped through the TEG 3, can be determined . Preferably, the power consumption P_{pu mp} of the coolant fluid pump is determined for th is purpose, and the setpoint S₂ is calcu lated as the mass flow M F_CF of coolant fluid pumped through the coolant fluid pump 9 that g ives rise to the largest net power gain P_net of the drive system. The coolant fluid pump 9 is controlled so that the mass flow M F_CF of coolant fluid pumped through the coolant flu id pump 9 is adjusted toward the determined setpoint S₂.

Another drive system includ ing a WH R system according to the invention is shown in fig . 2. The drive system includes a combustion engine 1 , an after treatment system 2 and further an exhaust recircu lation system 10. The WHR system includes a first heat exchanger in the form of a first TEG 3 placed in connection with the after treatment system 2 , a first exhaust channel 4 configured to carry an exhaust gas originating from the combustion engine 1 through the first TEG 3, and a first bypass channel 5 wh ich is connected to the first exhaust channel 4 upstream of the first TEG 3 and wh ich bypasses the TEG 3. The WHR system further includes a first adjustable valve 6 by means of which the mass flow of exhaust gas through each of the first exhaust channel 4 and the first bypass channel 5 can be adjusted . The WHR system also comprises a first coolant channel 7 configured to carry a coolant fluid through the TEG 3. A coolant flu id pump 9 is arranged to pump the coolant flu id through the TEG 3 and a cooler includ ing a first radiator 1 1 and a second radiator 12. The cooler further includes a charge air cooler 13. The WHR system also includes a second heat exchanger in the form of a second TEG 14 placed in connection with the exhaust recirculation system 10, a second exhaust channel 1 5 connected to the first exhaust channel 4 and configured to carry an exhaust gas orig inating from the combustion engine 1 through the second TEG 14, and a second bypass channel 16 which is connected to the second exhaust channel 15 upstream of the second TEG 14 and wh ich bypasses the second TEG 14. The WH R system further includes a second adjustable valve 1 7 by means of wh ich the mass flow of exhaust gas through each of the second exhaust channel 15 and the second bypass channel 16 can be adjusted . The WH R system also includes a second coolant channel 18 for carrying coolant fluid through the second TEG 14, and a three-way adjustable valve 19 placed between the first coolant channel 7 and the second coolant channel 18 , by means of wh ich the ratio R=M Fc_Fi/M F_CF2 of mass flow of coolant fluid through the first TEG 3 and the second TEG 14 respectively can be varied .

In a method accord ing to an embodiment of the invention , the method is implemented for the drive system shown in fig . 2. In this embodiment, a setpoint Si for the mass flow M FEGI of exhaust gas through the TEG 3, a setpoint S₂ for the mass flow M FCF of coolant fluid pumped through the coolant flu id pump 9 and a setpoint S₃ for the ratio R=M FCFI IM F CF2 of mass flow of coolant flu id through the first TEG 3 and the second TEG 14 respectively are set. As described above, a current value of a mass flow M F_CF of coolant fluid through the coolant fluid pump 9 is determined , as well as an entrance temperature TEGI of the exhaust gas before entry into the first TEG 3, and an entrance temperature T_CFI of the coolant fluid before entry into the first TEG 3. The power consumption P_{pu mp} of the coolant fluid pump is also determined and used in the step of determining the setpoint s₂.

Also, a power loss P_CAC in the charge air cooler is determined . This power loss P_CAC is mainly due to a temperature increase of the air flowing through the charge air cooler 13 caused by the radiators 1 1 , 1 2. With the air flow shown in fig . 2, the second radiator 12, placed before the charge air cooler 13, is the main source for the temperature increase in the charge air cooler 1 3. The power loss P_CAC is used both in the step of determin ing the setpoint Si and in the step of determining the setpoint S₂.

The setpoint S 3 for a ratio R= M FCFI /M F CF2 of the mass flow M FCFI of coolant flu id through the first TEG 3 to the mass flow M FCF2 of coolant fluid through the second TEG 14 is determined as the ratio R at which the net power gain P _NET of the waste heat recovery system is maximized . The setpoint S₃ is determined using the determined current value of the mass flow M F_CF of coolant fluid through the coolant fluid pump 9 and the power loss P cAc in the charge air cooler 13 as input values for calcu lating the net power gain P_{n e}t - The three-way adjustable valve 1 9 is controlled so that said ratio R= M FCFI /M F CF2 of the mass flows of coolant flu id is adjusted toward the determined setpoint S₃. In this embod iment, it is also possible to determine an entrance temperature T_EG2 of the exhaust gas before entry into the second TEG 14, either by means of sensing or by modeling . The second adjustable valve 1 7 can then be controlled in response to the determined entrance temperature T_EG2. If the temperature T_EG2 is too high , the second adjustable valve 1 7 is controlled so that all or part of the exhaust gases are led through the second bypass channel 16. If the temperature T_EG2 is within a predetermined acceptable span, all or part of the exhaust gases are led through the second TEG 14.

In a preferred embodiment of the inventive method, it is checked before outputting each of the setpoints Si, S₂, S₃ that the setpoint Si represents a mass flow MF_EG1 within an allowed span, that the setpoint S₂ represents a mass flow MF_CF within an allowed span and that the setpoint S₃ represents a mass flow ratio within an allowed span, so that overheating of each of the TEGs 3, 14 is avoided.

In a preferred embodiment of the inventive method, the setpoints S-i, S₂, S₃ are calculated using the algorithm Alg 1 presented at the end of the detailed description. In this algorithm, the net power gain P_NET is calculated for a system such as the one shown in fig.2. In the first for loop, a value of the mass flow MF_CF of coolant fluid pumped through the pump 9 is set, and the power loss P_CAC occurring at the charge air cooler 13 due to a temperature increase herein is determined. This loop also calculates the power loss P_PUMP at the pump 9, which is related to the total mass flow MFCF of coolant fluid pumped through the pump 9.

Inside the first for loop, the second for loop has the purpose of determining how to divide the mass flow MF_CF of coolant fluid through the pump 9 between the first TEG 3 and the second TEG 14. The loop sets a value of the ratio R=MFCFI IMF CF2 and calcu lates the power gain P₂ obtainable at the second TEG 14 for said ratio R .

Inside the second for loop, the third for loop steps through different mass flows M F_EGI of exhaust gas through the first TEG 3 placed in the after treatment system 2. It calcu lates the power gain and the power loss Pn_oss in the first TEG 3, occurring due to back pressure in the after treatment system 2, and it also calculates the total net power gain P_{n e}t by summing up all power gains and power losses.

When the third for loop is finished , a new value representing the mass flow M F_CF of coolant flu id through the pump 9 is set and the calcu lations are repeated . In this way, the net power gain P_net will start out as a small value and will successively increase. When the net power gain P_{n e}t starts to decrease, the iteration is aborted . The setpoints S-i , S₂, S₃ that are output by the algorithm are the values set by the previous iteration for the mass flow M F Ed of exhaust gas through the first TEG 3, for the mass flow M FCF of coolant fluid through the pump 9, and for the ratio R=M FCFI /M FCF2 , respectively. Before sending the setpoints Si , S₂, S₃ to a respective control unit, it is checked that the setpoints Si , S₂, S₃ are within an allowed span . If not, the setpoints are set to predefined values so that overheating of any of the TEGs 3, 14 is prevented .

The intervals of the for loops are thereafter mod ified by the ranges r_EGi , ^C F ^{a n d r}D'v respectively, and moved in the direction of where the optimum is most likely to be found the next time the algorithm is run . The algorithm is preferably run with a predetermined frequency, for example such that the setpoints S-i, S₂, S₃ are updated at a frequency of 1 Hz.

In other embodiments, the method may be implemented in a WHR system in which it is only necessary to determine a setpoint Si for the mass flow MF_EGI of exhaust gas through a first or a single heat exchanger. In this case, the algorithm may be simplified by reducing the amount of for loops. In a simple WHR system used in a method according to the invention, the coolant fluid may also be carried through the first and the second heat exchanger through one single coolant channel, without a three-way valve for dividing the mass flow MFCF of coolant fluid between the first and the second heat exchanger. In this case, the mass flow MF_CFI through the first heat exchanger equals the mass flow MF_CF through the pump located in the coolant channel.

Computer program code for implementing a method according to the invention is suitably included in a computer program which is readable into an internal memory of a computer, such as the internal memory of an electronic control unit of a motor vehicle. Such a computer program is suitably provided through a computer program product comprising a data storing medium read- able by an electronic control unit, which data storing medium has the computer program stored thereon. Said data storing medium is for example an optical data storing medium in the form of a CD-ROM-disc, a DVD-disc, etc., a magnetic data storing medium in the form of a hard disc, a diskette, a tape etc., or a Flash memory or a memory of the type ROM , PROM , EPROM or EEPROM .

Fig . 4 illustrates very schematically an electronic control unit 40 comprising an execution means 41 , such as a central processor unit (CPU), for executing a computer program . The execution means 41 communicates with a memory 42, for example of the type RAM , through a data bus 43. The control un it 40 comprises also a non-transitory data storing medium 44, for example in the form of a Flash memory or a memory of the type ROM , PROM , EPROM or EEPROM . The execution means 41 communicates with the data storing med ium 44 through the data bus 43. A computer program comprising computer program code for implementing a method according to the invention is stored on the data storing medium 44.

The invention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with skill in the art without departing from the scope of the invention as defined in the appended claims.

Algorithm Alg1: Optimization pseudo code

Data: Input values from sensor signals or modeled input values Result: Outputs setpoints S₂, S₃

for MF_CF = MF_CF;min : MFcF;maxClO

Remember_MFcF

Ppump ⁼ f (■■■)

for R = Div_min : Div_maxdo

Remember_R

P₂= f (...)

for MFEGI = F_EG1;min: MF_EG1;max dO

Remember_MF_EG1;MIN

Pi = f (...)

Piioss⁼ f (■■■)

Pnet ⁼ P2 ⁺ Pi " PcAC^— Plloss ^" Ppump

end

If Pnet< Pnet;old hen

Break

end

if Remember_/MFcF/R/MF_EG1 in allowed span then

Si = Remember_MF_EG1 - previous

S₂ = Remember_MFcF <^~ previous

S₃ = Remember_R <- previous

else

51 = PreDefined

5₂ = PreDefined

S₃ = PreDefined

end

MF_EGi;min ⁼ Si - r_EG1

DiVmin = S3 - Γοίν

DiVmax ⁼ S₃ + r_Div

Claims

CLAI MS

1 . A method for controlling a waste heat recovery system for recovering waste heat from a combustion engine ( 1 ) in a drive system, the waste heat recovery system including :

a first heat exchanger (3) ,

a first exhaust channel (4) configured to carry an exhaust gas originating from the combustion engine ( 1 ) through the first heat exchanger (3) ,

- a first bypass channel (5) connected to the first exhaust channel (4) upstream of the first heat exchanger (3) and bypassing the first heat exchanger (3) ,

a first adjustable valve (6) by means of which the mass flow of exhaust gas through each of the first exhaust channel (4) and the first bypass channel (5) can be adjusted ,

a first coolant channel (7) configured to carry a coolant fluid through the first heat exchanger (3) ,

characterized in

that the method comprises the steps of:

- determin ing a current value of a mass flow M F_CFI of coolant fluid through the first heat exchanger (3) ,

determining an entrance temperature T_EG1 of the exhaust gas before entry into the first heat exchanger (3) ,

determin ing an entrance temperature T_CFI of the coolant fluid before entry into the first heat exchanger (3) ,

determin ing a setpoint Si for a mass flow M F_EGI of exhaust gas through the first heat exchanger (3) at which a net power gain P_net of the drive system is maximized using said determined entrance temperature T_EG1 of the exhaust gas, said determined entrance temperature T_CFI of the coolant fluid , and said determined current value of the mass flow M F_CFI of coolant fluid through the first heat exchanger (3) as input values for calcu lating the net power gain P_net,

determin ing a current value of the mass flow M FEGI of exhaust gas through the first heat exchanger (3),

controlling the first adjustable valve (6) so that the mass flow

M F Ed of exhaust gas through the first heat exchanger (3) is adjusted toward the determined setpoint S-| .

2. The method according to claim 1 , wherein the step of determining the setpoint Si for the mass flow M F _EGI of exhaust gas through the first heat exchanger (3) comprises the steps of: choosing a set of test values representing the mass flow

M F Ed of exhaust gas through the first heat exchanger (3),

- iteratively calculating the net power gain P_net using said test values until said net power gain P_net is at a maximum,

outputting the test value at which the net power gain P_net is at a maximum as said setpoint Si .

3. The method according to claim 1 or 2 , wherein the system further comprises a cooler (8) connected to the first coolant channel (7) and a coolant fluid pump (9), the method further comprising the steps of:

determin ing a setpoint S₂ for the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump (9) at wh ich the net power gain P_{n e}t of the drive system is at a maximum,

controlling the coolant fluid pump (9) so that the mass flow M FCF of coolant flu id pumped through the coolant fluid pump (9) is adjusted toward the determined setpoint S₂.

4. The method according to claim 3, wherein the step of determining a setpoint S₂ for the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump (9) comprises determining a power consumption P_PUMP of the coolant fluid pump (9).

5. The method according to claim 3 or 4, wherein the cooler comprises at least one radiator (11, 12) for cooling the coolant fluid, and a charge air cooler (13) for cooling an air flow coming from a turbo charger and flowing through the charge air cooler (13) toward an air inlet of the combustion engine (1), wherein the method further comprises the step of:

determining a power loss P_CAC in the charge air cooler (13) due to a temperature increase of the air flowing through the charge air cooler caused by the at least one radiator (11 , 12).

6. The method according to claim 5, wherein the power loss PCAC in the charge air cooler (13) is used in the step of determining a setpoint S₂ for the mass flow MF_CF of coolant fluid through the coolant fluid pump (9).

7. The method according to claim 5 or 6, wherein the power loss PCAC in the charge air cooler (13) is used in the step of determining a setpoint Si for a mass flow MF_EG1 of exhaust gas through the first heat exchanger (3).

8. The method according to any one of the preceding claims, wherein the system further comprises:

a second heat exchanger (14), a second exhaust channel (15) connected to the first exhaust channel (4) and configured to carry an exhaust gas orig inating from the combustion eng ine (1 ) through the second heat exchanger (14),

- a second bypass channel ( 16) connected to the second exhaust channel (15) upstream of the second heat exchanger (14) and bypassing the second heat exchanger (14) ,

a second adjustable valve ( 1 7) by means of wh ich the mass flow of exhaust gas through each of the second exhaust channel (15) and the second bypass channel (1 6) can be adjusted ,

a second coolant channel (1 8) connected to the first coolant channel (7) and configured to carry a coolant fluid through the second heat exchanger (14) ,

the method further comprising the steps of:

- determin ing an entrance temperature T_EG2 of the exhaust gas before entry into the second heat exchanger (14),

controlling the second adjustable valve (1 7) in response to said determined entrance temperature T_EG2 of the exhaust gas before entry into the second heat exchanger (14).

9. The method according to claim 8 in combination with any of claims 3-7, wherein the system further comprises a th ird adjustable valve (1 9) connecting the first coolant channel (7) and the second coolant channel ( 18), the method further comprising the step of:

determin ing a current value of the mass flow M F_CF of coolant fluid pumped through the coolant fluid pump (9) ,

determin ing a setpoint S₃ for a ratio R= M F_CFI /M F_CF2 of the mass flow M F_CFI of coolant flu id pumped through the first heat exchanger (3) to the mass flow M F_CF2 of coolant flu id through the second heat exchanger (14) at which a net power gain P_NET of the waste heat recovery system is maximized using the determined current value of the mass flow MF_CF of coolant fluid pumped through the coolant fluid pump (9) as an input value for calculating the net power gain P_NET,

controlling the third adjustable valve (19) so that said ratio R of the mass flows of coolant fluid is adjusted toward the determined setpoint S₃.

10. The method according to claim 9, wherein the power loss PCAC in the charge air cooler (13) is used in the step of determining a setpoint S₃ for the ratio

of the mass flow MF_CFI of coolant fluid through the first heat exchanger (3) to the mass flow MF_CF2 of coolant fluid through the second heat exchanger (14).

11. The method according to any one of the preceding claims, further comprising the step of determining a torque of the combustion engine (1).

12. The method according to any one of the preceding claims, further comprising the step of determining a rotational speed of the combustion engine (1).

13. A waste heat recovery system for recovering waste heat from a combustion engine (1) in a drive system, the waste heat recovery system including:

a first heat exchanger (3), a first exhaust channel (4) configured to carry an exhaust gas originating from the combustion engine ( 1 ) through the first heat exchanger (3) ,

a first bypass channel (5) connected to the first exhaust channel (4) upstream of the first heat exchanger (3) and bypassing the first heat exchanger (3) ,

- a first coolant channel (7) configured to carry a coolant fluid through the first heat exchanger (3) ,

characterized in that the system further comprises:

means for determining a current value of a mass flow M F_CFI of coolant flu id through the first heat exchanger (3) ,

- means for determining an entrance temperature TEG-I of the exhaust gas before entry into the first heat exchanger (3) ,

means for determin ing an entrance temperature TCFI of the coolant fluid before entry into the first heat exchanger (3) ,

means for determining a setpoint Si for a mass flow M F EGI of exhaust gas through the first heat exchanger (3) at which a net power gain P_{n e}t of the drive system is maximized using said determined entrance temperature T_EG1 of the exhaust gas, said determined entrance temperature T_CFI of the coolant flu id , and said determined current value of the mass flow M F_CFI of coolant fluid through the first heat exchanger (3) as in put values for calcu lating the net power gain P_net,

means for determin ing a current value of the mass flow

M F Ed of exhaust gas through the first heat exchanger (3) , means for controlling the first adjustable valve (6) so that the mass flow M F _EGI of exhaust gas through the first heat exchanger (3) is adjusted toward the determined setpoint S-| .

14. A computer program comprising computer program code for causing a computer to implement a method according to any one of the claims 1 -12 when the computer program is executed in the computer.

15. A computer program product comprising a data storage medium (44) wh ich can be read by a computer and on wh ich the program code of a computer program according to claim 14 is stored .

16. An electron ic control unit (40) of a motor vehicle comprising an execution means (41 ), a memory (42) connected to the execution means (41 ) and a data storage med ium (44) wh ich is connected to the execution means (41 ) and on which the computer program code of a computer program accord ing to claim 14 is stored .

1 7. A motor vehicle comprising an electronic control unit (40) according to claim 1 6.

18. A motor veh icle accord ing to claim 1 7, wherein the motor vehicle is a truck or a bus.