SE1650837A1

SE1650837A1 - Starting an Internal Combustion Engine in a Parallel Hybrid Powertrain

Info

Publication number: SE1650837A1
Application number: SE1650837A
Authority: SE
Inventors: Kourie Afram; Carlson Peter
Original assignee: Scania Cv Ab
Priority date: 2016-06-15
Filing date: 2016-06-15
Publication date: 2017-12-16
Also published as: DE102017005334A1; SE1650837A2; SE541413C2

Abstract

The invention relates to a method for starting an internal combustion engine (4) in a parallel hybrid powertrain (2) in a vehicle (1) comprising an electric machine (14), a clutch (12) arranged between the electric machine (14) and the internal combustion engine (4) and a gearbox (6) with an input shaft (17) connected to the electric machine (14). The method comprises the steps of: a) providing torque (T) by the electric machine (14) to the powertrain (2); b) detecting a first signal (S) indicating that the internal combustion engine (4) should be started; c) starting the internal combustion engine (4) in response to the detected first signal (S); d) detecting a second signal (S) indicating that the clutch (12) should be controlled for connecting the internal combustion engine (4) to the electric machine (14); and e) controlling the clutch (12) in response to the detected second signal (S) for connecting the internal combustion engine (4) to the electric machine (14). The invention also relates to a vehicle (1) with a parallel hybrid powertrain (2).

Description

Starting an Internal Combustion Engine in a Parallel Hybrid Powertrain TECHNICAL FIELD The invention relates to a method for starting an internal combustion engine ina parallel hybrid powertrain, a vehicle comprising such a parallel hybridpowertrain, a computer program for starting an internal combustion engine anda computer program product comprising program code according to the appended claims.

BACKGROUND iiyhrid vehicles may he driven hy a primary ereeuisien means such as aninternai cemhustien engine and a secendary prepuisien means such as aneiectric machine. "ihe eiectrie machine is equipped tivith at ieast ene energysterage such as an eiectrecherriicai energy sterage ter stering eiectrieai energyand a centret unit te centrei the iiew et eiectricai energy hetween the energysterage and the eiectric machine. The eiectric machine may thus aiternateiyeperate as a meter and a generator, eased en the eperating cenditien ei thevehicie. When the vehicie is hraiting, the eiectric machine generates eiectricaienergy, which is stered in the energy sterage. This is usuaiiy caiiedregenerative hraiting, which means that the vehicie is hraking hy means ei theeiectric inachine and the internai eerrihustien engine. The stered eiecirieaienergy inay he utiiized iater ter the ereeuisien ei the vehicie.

Linder certain eperaiing cenditiens it is desirahie ie riurn ett the internaicemhustien engine, ter exarneie in erder te save tuei and te aveid ceeiing eithe internai cemhustien engine exhaust gas aiter treatment system due te iewiiety ei exhaust gases threugh the after treatment system. When a tergueincrease in the hyhrid pewertrain is needed er when the energy sierage musthe recharged, the internai cernhustien engine must start guickiy and eiiicientiy.iínewn seiutiens ter paraiiei hyierid pewertrains eemmeniy require the gearieex to be in netitrai in order to be abie to start the internai combustion engine byineans of the eiectric machine or a start engine. With the gearbox in neutrai nopropufsion torque can be provided white the internai combustion engine isstarted. This atfects the driveabiiity of the vehicie and the comfort ot the driveris oomprornised. Aiso, starting the internai combustion engine by means ot theeiectric machine iii/hen a gear in the gearbox is engaged may iniitience on thecorntort bf the driver. The reason for this is that a reduction of proptiision torque in the powertrain occurs when the internai combustion engine is started.

Aiso, starting the internaf combustion engine by means ct the efectric inaohinewhen the eiectrie machine runs at a high rotationai speed wiii resoit in that therotational speed of the internal combustion engine will increase from a lowlevel to a high level in a short period of time. Such increase of the rotationalspeed of the internal combustion engine is not comfortable for the driver andpassengers in the vehicle. Also, an undesired increase of fuel consumptionmay take place as a result of the increase of the rotational speed of the internal combustion engine.

Document US2013029183O discloses a method of starting rotation of astopped internal combustion engine if the predicted desired torque after thetransmission upshift is greater than a threshold amount of torque. An enginestart may be requested via an operator key or pushbutton input that has a solefunction of requesting an engine start. Alternatively, an engine restart may beautomatically requested by a control unit based on operating conditions. Theengine may be started via a starter or via an electric machine. The methodjudges if it may be desirable to start the engine based on transmission shifting or forecasted transmission shifting.

Document WO2013091946 A1 discloses a parallel hybrid powertraincomprising an internal combustion engine, an electric machine, a clutchbetween the internal combustion engine and the electric machine, an outputclutch downstream of the electric machine and a gearbox downstream of theoutput clutch. The document further describes a method for starting the internal combustion engine while the electric machine is driving the vehicle,wherein the clutch is closed such that the internal combustion engine can bestarted by the electric machine. At the same time, the output clutch is openedsuch that the output clutch slips and the output torque maintains constant. Thissolution requires an additional clutch device and is thus complex and affectsthe size of the powertrain.

However, the above-mentioned prior art documents do not discuss whether itis convenient or not to start the internal combustion engine by means of theelectric machine when the electric machine is running at a particular rotationalspeed and if it may be convenient to connect the internal combustion engine tothe powertrain when the electric machine is running at that particular rotational speed.

SUMMARY OF THE INVENTION Despite known solutions in the field, there is still a need to develop a methodfor starting an internal combustion engine in a parallel hybrid powertrain, whichdoes not affect the driveability of the vehicle, which entails a great comfort ofthe driver and passengers of the vehicle, which save fuel and which alsoinstantly may start the internal combustion engine for delivering torque to thepowertrain.

An object of the present invention is thus to achieve a method for starting aninternal combustion engine in a parallel hybrid powertrain, which maintains thedriveability of the vehicle.

Another object of the invention is to achieve a method for starting an internal combustion engine in a parallel hybrid powertrain, which is quick and efficient.

A further object of the invention is to achieve a method for starting an internalcombustion engine in a parallel hybrid powertrain, which maintains the comfortof the vehicle driver and passengers.

Another object of the invention is to achieve a method for starting an internalcombustion engine in a parallel hybrid powertrain, which save fuel.

Another object of the present invention is to achieve a new and advantageouscomputer program for starting an internal combustion engine in a parallel hybrid powertrain.

The herein mentioned objects and other objects are achieved by a method forstarting an internal combustion engine in a parallel hybrid, a vehicle comprisingsuch a hybrid powertrain, a computer program for starting an internalcombustion engine and a computer program product comprising program codeaccording to the independent claims.

According to an aspect of the present invention a method for starting aninternal combustion engine in a parallel hybrid powertrain is provided. Theparallel hybrid powertrain comprises an electric machine, a clutch arrangedbetween the electric machine and the internal combustion engine and agearbox with an input shaft connected to the electric machine and the clutch.The method comprises the steps of: a) providing torque by the electric machine to the powertrain; b) detecting a first signal indicating that the internal combustion engine shouldbe started; c) starting the internal combustion engine in response to the detected firstsignal; d) detecting a second signal indicating that the clutch should be controlled forconnecting the internal combustion engine to the electric machine; and e) controlling the clutch in response to the detected second signal forconnecting the internal combustion engine to the electric machine.

When the internal combustion engine is turned off in the parallel hybridpowertrain, the electric machine solely provides torque in the powertrain to apropeller shaft arranged in connection to the gearbox and driving wheels of thevehicle. ln this situation a gear is engaged and the clutch is disengaged. Theclutch is connected to a crank shaft of the internal combustion engine and tothe input shaft of the gearbox and thus also to the electric machine. When theelectric machine provides the output torque, the input shaft rotates and thecrank shaft is still. Controlling the clutch such that clutch torque is providedmeans that the clutch is controlled to a partly engaged state and thereby slips,whereby the crank shaft of the internal combustion engine will start rotatingand the clutch torque is thus transferred to the internal combustion engine. Theprovided clutch torque will thus affect the speed of the internal combustionengine. When the internal combustion engine reaches an idling speed, theinternal combustion engine may be controlled such that it ignites and theinternal combustion engine is thereby started.

The first signal according to the invention indicates that the internalcombustion engine should be started. There may be different reasons whysuch a first signal is generated. The electrical energy for the electric machine,which is stered in an energy storage rnay be empty er is at a few level. Anotherreason rnay be that a driver of the vehicle demands higher cutput torque te thedriving tfvheeie than may be delivered by the electric machine. ln response tothe detected first signal the internal combustion engine is started. However,depending on the rotational speed of the electric engine and the next comingdriving conditions of the vehicle it may be more and less suitable to connectthe internal combustion engine to the powertrain. lf the rotational speed of theelectric machine is increased due to shifting of gears in the gearbox it is mostlikely that the rotational speed of the electric machine is decreased duringshifting of gears. Thus, it is not suitable to connect the internal combustionengine to the powertrain when the rotational speed of the electric machine hasbeen increased, because the rotational speed of the internal combustionengine will then increase from a low level to a high level in a short period of time. Thereafter, the rotational speed of the internal combustion engine willdecrease to a low level due to shifting of gears. Such increase of the rotationalspeed of the internal combustion engine is not comfortable for the driver andpassengers in the vehicle, especially the sound generated when increasing therotational speed of the internal combustion engine, is not comfortable for thedriver and passengers in the vehicle. Also, an undesired increase of fuelconsumption may take place as a result of the increase of the rotational speed of the internal combustion engine. ln order to avoid these shortcomings a second signal is generated anddetected, which indicates that the clutch should be controlled for connectingthe internal combustion engine to the electric machine. The second signal maybe generated after shifting of gears and when the rotational speed of the electric engine is low.

The method for starting an internal combustion engine in a parallel hybridpowertrain thus maintains the driveability of the vehicle and also maintains thecomfort of the vehicle driver and passengers. The method is also quick andefficient and saves fuel.

The inventors have realized that the starting of the internal combustion engineand connecting the internal combustion engine to the powertrain may takeplace at different occasions in time. The internal combustion engine may bestarted by means of a starter motor arranged at the internal combustion enginewhen the clutch is disengaged or by means of the electric machine when theclutch is partly engaged, as discussed above, and thereafter disengaged whenthe internal combustion engine has been started. However, the internalcombustion engine may thereafter, at a suitable occasion in time, beconnected to the powertrain in order to avoid inconvenient increase of the rotational speed of the internal combustion engine.

After step c) and before step d) the method may further comprise the step of:f) running the internal combustion engine on idle speed. When the first signalhas been detected and the internal combustion engine has been started, theinternal combustion engine may be running at idle speed until it is suitable toconnect the internal combustion engine to the powertrain. Depending on thedriving conditions of the vehicle, it may also be possible to increase therotational speed of the internal combustion engine above the idle speed whenwaiting for the suitable moment to connect the internal combustion engine tothe powertrain. A suitable moment to connect the internal combustion engineto the powertrain may be after shifting of gears in the gearbox, when therotational speed of the electric machine has decreased to a rotationalsynchronizing speed between the internal combustion engine and the electric machine.

According to an aspect of the invention the internal combustion engine in stepc) is started when the speed of the electric machine is predicted tosubstantially reach a rotational synchronizing speed between the internalcombustion engine and the electric machine. lt may be suitable to delay thestart of the internal combustion engine even if the first signal is detected at asubstantially earlier point of time. Thus, fuel may be saved. The point of timewhen the internal combustion engine is started may be when the speed of theelectric machine is predicted to substantially reach a rotational synchronizingspeed between the internal combustion engine and the electric machine.During shifting of gears in the gearbox, the rotational speed of the electricmachine will be different from the rotational speed before shifting of gears. Therotational speed of the electric machine after shifting of gears may bepredicted when having information of the gear ratio in the gearbox. Also, thetime when the electric machine reaches the rotational speed after shifting ofgears may be predicted. The rotational synchronizing speed between theinternal combustion engine and the electric machine should be the rotationalspeed of the electric machine after shifting of gears. Also, it may be suitable to connect the internal combustion engine to the powertrain shortly after theinternal combustion engine has been started.

According to an aspect of the invention the internal combustion engine is instep c) started by means of a starter motor arranged at the internal combustionengine. When starting the internal combustion engine by means of the startermotor the clutch is open. Thus, the internal combustion engine may be startedindependent of the condition of the electric machine or the driving condition of the vehicle.

According to an aspect of the invention the internal combustion engine isstarted by controlling the clutch in step c) such that it provides a clutch torquegenerated by the electric machine. The clutch may be controlled so that itreaches a partly engaged state corresponding to the clutch torque required forstarting the internal combustion engine. The provided clutch torque dependson the degree of clutch engagement. The more engaged the clutch is, thegreater clutch torque may be provided and transferred to the internalcombustion engine. When the clutch is completely engaged, the transferredtorque to the internal combustion engine is the same as the torque provided bythe electric machine, less any torque required for propelling the vehicle.

According to an aspect of the invention the clutch is disengaged when theinternal combustion engine has been started. Since the speed of the electricmachine may be different from the idle speed of the internal combustionengine the clutch is disengaged and the internal combustion engine runsindependently of the electric machine and waits for a suitable moment to beconnected to the powertrain.

According to an aspect of the invention the electric machine is controlled suchthat the torque provided by the electric machine is increased with an additionaltorque, wherein the additional torque corresponds to the provided clutch torque. When starting the internal combustion engine by means of the electric machine, the clutch torque and the torque provided by the electric machine arecounteracting. The torque provided by the electric machine to propelling thevehicle may therefore be increased with additional torque for compensating theclutch torque needed for starting the internal combustion engine. The torquefor propelling the vehicle will as a result be maintained. Thus, the driveability ofthe vehicle and also the comfort of the vehicle driver and passengers will be maintained.

According to an aspect of the invention the first signal in step b) is generatedwhen the torque provided by the electric machine cannot be maintained or isnot enough for the driving characteristics demanded by the vehicle. Theelectrical power for the electric machine, which is stored in the energy storagemay be empty or at a lovv level or the driver ot the vehicle demands higheroutput torque to the driving wheels than rnay be delivered by the eiectricmachine. There rnay aiso be other reasons tvhy the internal combustionengine should be started. Under such conditions the first signal indicating that the internal combustion engine should be started is generated.

According to an aspect of the invention the second signal in step d) isgenerated when the torque provided by the electric machine cannot bemaintained or is not enough for the driving characteristics demanded by thevehicle. ln a situation when the eiectrical power in the energy storage isrunning out in a very short period ot tirne, or when the driver of the vehicleimmediately demands higher output torque to the driving vvheels than inay bedelivered by the electric machine, the internal combustion engine may beconnected to the powertrain immediately even though it may not becomfortable for the driver or the passengers in the vehicle.

According to an aspect of the invention a computer programme product isprovided, comprising a programme code stored on a computer-readablemedium for performing the method steps according to the herein mentionedmethod for starting an internal combustion engine, when said computer programme is run on an electronic control unit or another computer connected to the electronic control unit.

Further objects, advantages and novel features of the present invention willbecome apparent to one skilled in the art from the following details, and alsoby putting the invention into practice. Whereas the invention is describedbelow, it should be noted that it is not restricted to the specific detailsdescribed. Specialists having access to the teachings herein will recognisefurther applications, modifications and incorporations within other fields, whichare within 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 diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment ofthe invention; Figure 2 schematically illustrates a parallel hybrid powertrain according toan embodiment of the invention; Figure 3 illustrates a flow chart for a method for starting an internalcombustion engine according to an embodiment of the invention; Figure 4a illustrates a diagram of rotational speed variations during a methodfor starting an internal combustion engine according to anembodiment of the invention, and Figure 4b illustrates a diagram of torque variations during a method for starting an internal combustion engine according to an embodiment of the invention. 11 DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 schernaticaiiy shows a side view cf a vehicie 1 which cornpnses aparaiiei hybrid powertrain 2 according td an enibodinient of the invention. Thehybrid powertrain 2 cernprises an internet ceinbiisticn engine 4 connected te agearbox 6. The gearbox 6 is aiso connected te the driving wheeis 8 of thevehicie t, via a prepeiier shaft 16.

Figure 2 schematicaiiy shows a parallel hybrid powertrain 2 of a vehicleaccording to an embodiment of the invention. The powertrain 2 comprises aninternal combustion engine 4, a clutch 12, an electric machine 14 and agearbox 6. The crankshaft 16 of the internal combustion engine 4 is connectedto the clutch 12 and the electric machine 14 is connected to the clutch 12. Theclutch 12 is thus arranged between the internal combustion engine 4 and theelectric machine 14. The electric machine 14 and the clutch 12 are connectedto an input shaft 17 of the gearbox 6. An cutput shaft ef the gearbex 6 isconnected td the propeiier shaft 1G, which in ttiirn is connected tc the drivingwheeis 8 bf the vehicie 1. Ûniy iwb driving wheeis 8 are iiitistrated in Figure 2,hcvvever, any number ef driving wheeis 8 rnay be driven by the hybridpowertrain 2 within the scope of the invention.

The internal combustion engine 4, the clutch 12, the electric machine 14 andthe gearbox 6 are connected to a control unit 18. The control unit 18 isadapted to control the internal combustion engine 4, the clutch 12, the electricmachine 14 and the gearbox 6, for example for starting the internal combustionengine 4 while the vehicle 1 is propelled by the electric machine 14. Acomputer 20 may be connected to the control unit 18. The control unit 18and/or the computer 20 comprises a computer program P, which can includeroutines to control the start of the internal combustion engine 4 of theinvention. A program P may be stored in an executable form or compressedform in a memory l\/I and/or in a read/write memory. A computer program product may be provided, which comprises a program code stored on a 12 computer readable medium for performing the start of the internal combustionengine 4, when said program is run on the control unit 18 or the computer 20connected to the control unit 18. Said code may be non-volatile, stored in said computer readable medium. ln order to drive the driving wheels 8 and thus propel the vehicle 1, the internalcombustion engine 4 and/or the electric machine 14 generates a torque whichis transferred via the gearbox 6 to the propeller shaft 10. The torque on thepropeller shaft 10, called output torque, is the torque that propels the vehicle 1.When the internal combustion engine 4 provides output torque on the propellershaft 10 and propels the vehicle 1, the clutch 12 is engaged and a gear isengaged in the gearbox 6. The electric machine 14 may in this case eitherprovide additional output torque on the propeller shaft 10 or it may operate asa generator. ln some situations it may be desirable to turn off the internalcombustion engine 4 and propel the vehicle 1 by means of the electricmachine 14. For instance, in order to save fuel and to avoid coollng of aninternal combustion engine 4 exhaust gas after treatment system. ln thesesituations the clutch 12 is disengaged and a gear is engaged in the gearbox 6.When, however, the internal combustion engine 4 is needed again it isimportant that it can be started in a quick and efficient way.

When the internal combustion engine 4 is turned off in the parallel hybridpowertrain 2, the electric machine 14 solely provides torque in the powertrain 2to the propeller shaft 10 and drives the driving wheels 8 of the vehicle 1. Thetorque provided by the electric machine 14 may be increased by increasing thecurrent from an energy storage 19 to the electric machine 14. ln this situation agear is engaged in the gearbox 6 and the clutch 12 is disengaged. When theelectric machine 14 provides the output torque, the input shaft 17 rotates andthe crank shaft 16 is standing still, i.e. not rotating. Controlling the clutch 12such that a clutch torque Tc is provided means that the clutch 12 is controlledto a partly engaged state and thereby slips, whereby the crank shaft 16 of theinternal combustion engine 4 will start rotating and the clutch torque Tc is thus 13 transferred to the internal combustion engine 4. The provided clutch torque Tcwill thus affect the rotational speed of the internal combustion engine 4. Theprovided clutch torque Tc for starting the internal combustion engine 4 may begradually increased. When the internal combustion engine 4 reaches an idlingspeed the internal combustion engine 4 may be controlled such that it ignitesand the internal combustion engine 4 is thereby started. According to theinvention the clutch 12 may be disengaged when the internal combustionengine 4 has started and be engaged later at a suitable moment. Alternatively,it is possible to start the internal combustion engine 4 by means of a startermotor 22 arranged at the internal combustion engine 4.

Figure 3 shows a flowchart for a method for starting an internal combustionengine 4 in a parallel hybrid powertrain 2 according to an embodiment of theinvention. The parallel hybrid powertrain 2 may be configured as described inFigure 2. The method comprises the steps of: a) providing torque Te by the electric machine 14 to the powertrain 2; b) detecting a first signal S1 indicating that the internal combustion engine 4should be started; c) starting the internal combustion engine 4 in response to the detected firstsignal S1; d) detecting a second signal S2 indicating that the clutch 12 should becontrolled for connecting the internal combustion engine 4 to the electricmachine 14; and e) controlling the clutch 12 in response to the detected second signal S2 for connecting the internal combustion engine 4 to the electric machine 14. ln step a) the internal combustion engine 4 is turned off, i.e. not running, andthe electric machine 14 solely provides torque Te in the powertrain 2 to thepropeller shaft 10 and to the driving wheels 8 of the vehicle 1. ln this situationa gear is engaged and the clutch 12 is disengaged. When the electric machine14 provides the output torque, the input shaft 17 is rotating and the crank shaft16 is standing still. ln step b) the first signal S1 according to the invention 14 indicates that the internal combustion engine 4 should be started. There maybe different reasons why the first signal is generated. For example, theelectrical energy for the electric machine 14, which is stored in the energystorage 19 may be empty or is at a low level. Another reason may be that adriver of the vehicle 1 demands higher output torque to the driving wheels 8than may be delivered by the electric machine 14. ln step c) the internalcombustion engine 4 is started in response to the detected first signal S1. Theinternal combustion engine 4 may be controlled to ignite when the internalcombustion engine 4 has reached a predetermined rotational speed, suitablyan idling speed. The control unit 18 may control the internal combustion engine4 such that it ignites at a certain internal combustion engine rotational speednoe. The internal combustion engine 4 is thereby started. ln step d) a secondsignal S2 is detected, which indicates that the clutch 12 should be controlled forconnecting the internal combustion engine 4 to the electric machine 14. Thesecond signal may be generated after shifting of gears and when the rotationalspeed of the electric engine is low. ln step e) the clutch 12 is controlled inresponse to the detected second signal S2 for connecting the internalcombustion engine 4 to the electric machine 14. ln response to the detectedfirst signal S1 the internal combustion engine 4 is started. Depending on therotational speed of the electric machine 14 and the next coming drivingconditions of the vehicle 1 it may be more and less suitable to connect theinternal combustion engine 4 to the powertrain 2. lf the rotational speed of theelectric machine 14 is increased due to shifting of gears in the gearbox it ismost likely that the rotational speed of the electric machine 14 is decreasedduring shifting of gears. Thus, it is not suitable to connect the internalcombustion engine 4 to the powertrain 2 when the rotational speed of theelectric machine 14 has been increased, because the rotational speed of theinternal combustion engine 4 will then increase from a low level to a high levelin a short period of time. Thereafter, the rotational speed of the internalcombustion engine 4 will decrease to a low level due to shifting of gears. Suchincrease of the rotational speed of the internal combustion engine 4 is notcomfortable for the driver and passengers in the vehicle 1. Also, an undesired increase of fuel consumption may take place as a result of the increase of therotational speed of the internal combustion engine 4. ln order to avoid theseshortcomings a second signal S2 is generated and detected, which indicatesthat the clutch 12 should be controlled for connecting the internal combustion engine 4 to the electric machine 14.

After step c) and before step d) the method further comprises the step of: f) running the internal combustion engine 4 at idle speed. When the first signalS1 has been detected and the internal combustion engine 4 has been started,the internal combustion engine 4 may be running at a rotational speed thatsubstantially corresponds to the idle speed nidie until it is suitable to connect theinternal combustion engine 4 to the powertrain 2.

The internal combustion engine 4 is in step c) started when the speed of theelectric machine 14 is predicted to reach a rotational synchronizing speed nsyncafter changing gear ratio in the gearbox 6. Also, it may be suitable to delay thestart of the internal combustion engine 4 even if the first signal is detectedearlier. Thus, fuel may be saved. The point of time when the second signal S2is generated may occur shortly after the internal combustion engine 4 hasbeen started.

Thus, according to the invention the internal combustion engine 4 may bestarted immediately after receiving the first signal S1 or the start of the internalcombustion engine 4 may be delayed to start just prior to, or when the second signal S2 is received.

According to an embodiment of the invention, the internal combustion engine 4is in step c) started by means of the starter motor 22 arranged at the internalcombustion engine 4. The clutch 12 is open when starting the internalcombustion engine 4 by means of the starter motor 22. Thus, the internalcombustion engine 4 may be started independent of the condition of theelectric machine 14 or the driving condition of the vehicle 1. 16 According to a further embodiment of the invention the internal combustionengine 4 is in step c) started by controlling the clutch 12 such that it providesclutch torque TC generated by the electric machine 14. The clutch 12 may becontrolled so that it reaches a partly engaged state corresponding to the clutchtorque Tc for starting the internal combustion engine 4. The provided clutchtorque Tc depends on the degree of clutch engagement. The more engagedthe clutch 12 is, the greater clutch torque Tc may be provided and transferredto the internal combustion engine 4. When the clutch 12 is completelyengaged, the transferred torque to the internal combustion engine 4 is thesame as the torque provided by the electric machine 14, less any torqueprovided to the drive wheels 8. The control unit 18 may control the clutch 12,such that the clutch torque TC for starting the internal combustion engine 4 is provided.

The clutch torque TC depends on the degree of clutch engagement. The moreengaged the clutch 12 is the greater clutch torque TC may be provided andtransferred to the internal combustion engine 4. A certain clutch state thuscorresponds to a certain clutch torque TC. The control unit 18 suitably controlsthe clutch 12 such that a partly engaged state is achieved and the clutch 12slips, whereby the crank shaft 16 of the internal combustion engine 4 will startrotating and a clutch torque TC is thus transferred to the internal combustionengine 4. The provided clutch torque TC will thus increase the speed of theinternal combustion engine 4. The clutch torque TC provided for starting theinternal combustion engine 4 may be gradually increased.

The clutch 12 is disengaged when the internal combustion engine 4 has beenstarted. Since the speed of the electric machine 14 may be different from theidle speed of the internal combustion engine 4 the clutch 12 is disengaged andthe internal combustion engine 4 runs independently of the electric machine14and waits for a suitable moment to be connected to the powertrain 2. 17 According to an aspect of the invention the electric machine 14 is controlledsuch that the torque Te provided by the electric machine 14 is increased withadditional torque Te by the electric machine 14, wherein the additional torqueTe corresponds to the provided clutch torque Te. When starting the internalcombustion engine 4 by means of the electric machine 14, the clutch torque Teand the torque Te provided by the electric machine 14 are counteracting. Whenthe clutch 12 slips, the crank shaft 16 will have a braking effect on the inputshaft 17 connected to the electric machine 14. The torque Te provided by theelectric machine 14, i.e. the output torque on the propeller shaft 10 in thiscase, will thereby be reduced. The torque Te provided by the electric machine14 to propelling the vehicle 1 must therefore be increased with additionaltorque Te for compensating the clutch torque Te needed for starting the internalcombustion engine 4. The torque for propelling the vehicle 1 will as a result be maintained.

The first signal S1 in step b) is generated when the torque Te provided by theelectric machine 14 cannot be maintained or is not enough for the drivingcharacteristics demanded by the vehicle 1. The electric power for the electricmachine 14, which ie stored in the energy storage 19 may be empty or at a iovvievei or the driver of the vehicie t demands higher output tordoe to the driving vvheeie 8 than may be deiivered by the eiectric machine ie.

The second signal S2 in step d) may be generated when the torque Teprovided by the electric machine 14 cannot be maintained or is not enough forthe driving characteristics demanded by the vehicle 1. The second signal S2 instep d) may alternatively be generated when a suitable rotational speed isprovided by the electric machine 14 to the input shaft 17 of the gearbox 6, e.g.when the rotational speed to the input shaft 17 is lowered in connection with shifting gears in the gearbox 6, as discussed above and below. ln a situation that the eiectricai power in the energy storage 'i9 is running out ina very short period of time or When the driver ot the vehicie i irrimediateiy 18 demands higher output tprdue to the driving vvheeis 8 than rnay be deiiveredby the electric machine 14 the internal combustion engine 4 may be connectedto the powertrain 2 immediately even though it may not be comfortable for thedriver or the passengers in the vehicle 1.

Fig. 4a shows a diagram of rotational speed variations during a method forstarting an internal combustion engine 4 according to the invention. Fig. 4bshows a diagram of torque variations during a method for starting an internalcombustion engine 4 according to the invention. The method for starting aninternal combustion engine 4 is described in Figure 3 and is here furtherillustrated by the diagrams over the speed variations and torque variationsover time measured in seconds. The upper solid curve in fig. 4a represents therotational speed of the electric machine 14. The dashed curve in fig. 4arepresents a rotational speed of the internal combustion engine 4 according tothe prior art, and which should be avoided according to the present invention.The lower dotted curve in fig. 4a represents the rotational speed of the internalcombustion engine 4 when started shortly after the first signal S1 is detected.This will occur at time t1 indicated in fig. 4a. The lower fat marked curve in fig.4a represents the rotational speed of the internal combustion engine 4 whenthe start is delayed after the first signal S1 is detected. lf the internal combustion engine 4 is started and connected to the powertrain2 shortly after the first signal S1 has been detected, and if the rotational speedof the electric machine 14 is increased due to shifting of gears in the gearbox6, it is likely that the rotational speed of the electric machine 14 is decreasedduring shifting of gears. Thus, it is not suitable to connect the internalcombustion engine 4 to the powertrain 2 when the rotational speed of theelectric machine 14 has been increased, because the rotational speed of theinternal combustion engine 4 will then increase from a low level to a high levelin a short period of time. Thereafter, the rotational speed of the internalcombustion engine 4 will decrease to a low level due to shifting of gears. Suchincrease of the rotational speed of the internal combustion engine 4 is not 19 comfortable for the driver and passengers in the vehicle 1 due to the soundgenerated by the internal combustion engine 4. Also, an undesired increase offuel consumption may take place as a result of the increase of the rotationalspeed of the internal combustion engine 4.

When the first signal S1 at time t1 has been detected and the internalcombustion engine 4 has been started, the internal combustion engine 4 maybe running on idle speed nidie until it is suitable to connect the internalcombustion engine 4 to the powertrain 2. Depending on the rotational speed ofthe electric machine 14 and the next coming driving conditions of the vehicle 1,it may be more and less suitable to connect the internal combustion engine 4to the powertrain 2. lf the rotational speed of the electric machine 14 isincreased due to shifting of gears in the gearbox it is most likely that therotational speed of the electric machine 14 is decreased during shifting ofgears. Thus, it is not suitable to connect the internal combustion engine 4 tothe powertrain 2 when the rotational speed of the electric machine 14 hasbeen increased, because the rotational speed of the internal combustionengine 4 will then increase from a low level to a high level in a short period oftime. Thereafter, the rotational speed of the internal combustion engine 4 willdecrease to a low level due to shifting of gears. ln order to avoid theseshortcomings a second signal S2 is generated and detected, which indicatesthat the clutch 12 should be controlled for connecting the internal combustionengine 4 to the electric machine 14. The second signal S2 may be generatedwhen a suitable rotational speed is provided by the electric machine 14 to theinput shaft 17 of the gearbox 6, e.g. when the rotational speed to the inputshaft 17 is lowered in connection with shifting gears in the gearbox 6.Alternatively, the second signal S2 may be generated when the torque Teprovided by the electric machine 14 cannot be maintained or is not enough for the driving characteristics demanded by the vehicle 1.

The starting of the internal combustion engine 4 may alternatively be delayedto a suitable moment for the starting of the internal combustion engine 4. This suitable moment occurs at time tg, which is shown in figure 4a. The lower fatmarked curve represents the rotational speed nb of the internal combustionengine 4 when the start is delayed after the first signal S1 is detected. Theinternal combustion engine 4 may be connected to the powertrain 2 when therotational speed of the electric machine 14 is substantially equal to a rotationalsynchronizing speed nsync after changing gear ratio in the gearbox 6. This willoccur at time te, in fig. 4a. lt may be suitable to delay the start of the internalcombustion engine 4 even if the first signal S1 is detected at the earlier time t1.Thus, fuel may be saved. The time t2 when the internal combustion engine 4 isstarted may be before shifting gears in the gearbox 6 is predicted to take placeand when the rotational speed of the electrical machine 14 is lowered inconnection with the shifting of gears in the gearbox 6. Also, it may be suitableto connect the internal combustion engine 4 to the powertrain 2 shortly afterthe internal combustion engine 4 has been started. The second signal S2,which is generated shortly after the internal combustion engine 4 has beenstarted indicates that the clutch 12 should be controlled for connecting the internal combustion engine 4 to the electric machine 14.

Figure 4b shows a diagram of the torque variations during the method forstarting an internal combustion engine 4 according to the invention. The slim solid curve in fig. 4b represents the torque provided by the electric machine 14.

The lower dashed curve in fig. 4b represents torque provided by the internalcombustion engine 4 which should be avoided. The dotted curve in fig. 4brepresents torque provided by the internal combustion engine 4 when startedshortly after the first signal S1 is detected. This will occur at time t1 indicated infig. 4b. The torque generated by the internal combustion engine 4 issubstantially steady when the internal combustion engine 4 is running at idlespeed nidie. When the second signal S2 is generated and detected, the clutch12 is controlled for connecting the internal combustion engine 4 to the electricmachine 14. The torque generated by the internal combustion engine 4 followsthe fat marked curve in fig. 4b after the second signal S2 has been generated. 21 The fat marked curve in fig. 4b represents also torque provided by the internalcombustion engine 4 when the start is delayed after the first signal S1 isdetected. At t2, when the internal combustion engine 4 is started, the torquegenerated by the internal combustion engine 4 increases up to the point oftime when the clutch 12 is controlled at S2. Again, the torque generated by theinternal combustion engine 4 follows the fat marked curve in fig. 4b after thesecond signal S2 has been generated. The curve combined with dashes anddots represents the torque provided by the electric machine 14 when the internal combustion engine 4 is started at t2.

A target torque Tiargei is indicated with the horizontal upper dashed line, whichhas a step between tz and te, in fig. 4b. However, the target torque Tiargei can also be substantially equal to the torque before shifting gears.

The foregoing description of the preferred embodiments of the presentinvention is provided for illustrative and descriptive purposes. lt is not intendedto be exhaustive or to restrict the invention to the variants described. l\/lanymodifications and variations will obviously be apparent to one skilled in the art.The embodiments have been chosen and described in order best to explainthe principles of the invention and its practical applications and hence make itpossible for specialists to understand the invention for various embodimentsand with the various modifications appropriate to the intended use.

Claims

22 Claims

1. A method for starting an internal combustion engine (4) in a parallel hybridpowertrain (2) in a vehicle (1) comprising an electric machine (14), a clutch(12) arranged between the electric machine (14) and the internal combustionengine (4) and a gearbox (6) with an input shaft (17) connected to the electricmachine (14), the method comprises the steps of: a) providing torque (Te) by the electric machine (14) to the powertrain (2); b) detecting a first signal (S1) indicating that the internal combustion engine (4)should be started; c) starting the internal combustion engine (4) in response to the detected firstsignal (S1); d) detecting a second signal (S2) indicating that the clutch (12) should becontrolled for connecting the internal combustion engine (4) to the electricmachine (14); and e) controlling the clutch (12) in response to the detected second signal (S2) forconnecting the internal combustion engine (4) to the electric machine (14).

2. The method according to claim 2, wherein after step c) and before step d)the method further comprises the step of:f) running the internal combustion engine (4) at idle speed (nidie).

3. The method according to claim 1, wherein the internal combustion engine(4) in step c) is started when the speed of the electric machine (14) is predictedto reach a rotational synchronizing speed (nsync) after changing gear ratio in the gearbox (6).

4. The method according to any of the preceding claims, wherein in step c) theinternal combustion engine (4) is started by means of a starter motor (22) arranged at the internal combustion engine (4).

5. The method according to claim 4, wherein the clutch is open during the internal combustion engine (4) is started in step c). 23

6. The method according to any of claims 1 - 3, wherein in step c) the internalcombustion engine (4) is started by controlling the clutch (12) such that itprovides a clutch torque (TC) generated by the electric machine (14) for starting the internal combustion engine (4).

7. The method according to claim 6, wherein the clutch (12) is disengagedwhen the internal combustion engine (4) has started.

8. The method according to claim 6, wherein the electric machine (14) iscontrolled such that the torque (TC) provided by the electric machine (14) isincreased with an additional torque (TC), wherein the additional torque (TC) corresponds to the provided clutch torque (TC).

9. The method according to claim 8, wherein the clutch torque (TC) and thetorque (TC) provided by the electric machine (14) are counteracting.

10. The method according to any of claims 6 - 9, wherein the clutch (12) instep c) is controlled so that the clutch (12) reaches a partly engaged statecorresponding to the clutch torque (TC) for starting the internal combustion engine (4).

11. The method according to any of the preceding claims, wherein the firstsignal (S1) in step b) is generated when the torque (TC) provided by the electricmachine (14) cannot be maintained or is not enough for the driving characteristics demanded by the vehicle (1).

12. The method according to any of the preceding claims, wherein the secondsignal (S2) in step d) is generated when the torque (TC) provided by the electricmachine (14) cannot be maintained or is not enough for the driving characteristics demanded by the vehicle (1). 24

13. The method according to any of claims 1 - 11, wherein the second signal(S2) in step d) is generated when the speed of the electric machine (14) ispredicted to reach a rotational synchronizing speed (nsync) after changing gear ratio in the gearbox (6).

14. A vehicle with a parallel hybrid powertrain (2), characterized in that thepowertrain (2) comprises an internal combustion engine (4) which is started according to the method in any of the claims 1-13.

15. A computer program (P), wherein said computer program comprisesprogramme code for causing an electronic control unit (18) or a computer (20)connected to the electronic control unit (18) to perform the steps according to any of the claims 1-13.

16. A computer programme product comprising a programme code stored on acomputer-readable medium for performing the method steps according to anyof claims 1-13, when said computer programme is run on an electronic controlunit (18) or a computer (20) connected to the electronic control unit (18).