SE2051203A1

SE2051203A1 - Method and arrangement for controlling a hybrid vehicle powertrain during regenerative braking

Info

Publication number: SE2051203A1
Application number: SE2051203A
Authority: SE
Inventors: Alexander Stamp; Andreas Szilassy; Christian Wessel
Original assignee: Scania Cv Ab
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2022-04-17
Also published as: SE544453C2; DE102021125205A1

Abstract

A control device (100) and a method of controlling a hybrid vehicle powertrain (2) are provided. The hybrid vehicle powertrain (2) comprises a combustion engine (3), and an electrical motor (4) operable to perform regenerative braking of the vehicle powertrain (2) to charge an energy storage device (5). The method comprises a step of, in response to a prediction that at the point in time of initiation of a braking event, a state of charge of the energy storage device (5) will be above a first state of charge threshold value at which a desired regenerative braking power of the vehicle powertrain (2) for a braking event can be provided, starting (S110) the combustion engine (3) so as to enable active engine braking during at least a portion of the braking event. The disclosure also relates to a computer program, a computer-readable medium as well as a vehicle (1) comprising the control device (100).

Description

CONTROL DEVICE AND METHOD OF CONTROLLING A HYBRID VECHILE POWERTRAIN, COMPUTERPROGRAM, COMPUTER-READABLE MEDIUM AND VEHICLE TECHNICAL FIELD The present disclosure relates in general to a method of controlling a hybrid vehicle powertrain and acontrol device configured to control a hybrid vehicle powertrain. The present disclosure furtherrelates in general to a computer program and a computer readable medium. The present disclosure further relates in general to a vehicle.

BACKGROUND The strive to reduce emissions and improve fuel economy has led to the development of hybridvehicle powertrains comprising one propulsion unit in the form of a combustion engine and anotherpropulsion unit in the form of an electrical motor. The electrical motor is powered by an energystorage device, such as a pack of batteries. ln such vehicle powertrains, electrical energy can berecovered during certain operating conditions of the vehicle, for example by means of regenerativebraking. During regenerative braking, the electrical motor is operated as a generator whereby kineticenergy of the vehicle is converted into electrical energy used to charge the energy storage device.Regenerative braking inter alia has the advantages of reducing wear of service brakes of the vehicleand reducing the fuel consumption and emissions, especially since the recovered energy can later be used for propulsion of the vehicle by means of the electrical motor.

The ability to use regenerative braking is however limited by the storage capacity of the energystorage device. The storage capacity is normally given by a predetermined maximum threshold value.During a braking event, the energy storage device may be charged to the predetermined maximumthreshold value and cannot accept any additional energy without the risk of overcharging anddamaging the energy storage device. Therefore, when the capacity of the energy storage device is ator above the predetermined maximum threshold value, regenerative braking cannot be used for slowing down the vehicle during a braking event. ln addition to regenerative braking and/or use of service brakes, a vehicle may be braked by means of one or more auxiliary brakes. Examples of such auxiliary brakes include retarder, compression release brake and exhaust brake. A vehicle may also be braked by dragging during which the kinetic energy of the vehicle is used for dragging the engine, which in turn slows down the vehicle.

EP 2 127 987 A1 discloses a braking method with energy recovery for a hybrid traction vehicle, which,according to a requested braking target regulates the intervention of an engine-generator and theconnection or disconnection of an endothermic engine from the transmission line. An overall brakingaction is carried out by various contributions (such as a regenerative brake, an exhaust engine brake,a decompression brake, a retarder, or engine dragging) that may be added up and that may vary intime. ln accordance with the method, a braking torque overall value is continuously calculated on thebasis of the current driving conditions and the braking torque sources are used accordingly, with a priority given to regenerative braking in order to recover energy.

SUMMARY The object of the present invention is to provide an improved control of a hybrid vehicle powertrain in conjunction with a braking event.

The object is achieved by the su bject-matter of the appended independent claim(s). ln accordance with the present disclosure, a method of controlling a hybrid vehicle powertrain isprovided. The method is performed by a control device. The hybrid vehicle powertrain comprises acombustion engine, and an electrical motor powered by an energy storage device. The electricalmotor is operable to perform regenerative braking of the vehicle powertrain to charge the energystorage device. The method comprises, in response to a prediction that, at a first point in time, astate of charge of the energy storage device will be above a first state of charge threshold value atwhich a desired regenerative braking power of the vehicle powertrain for a braking event can beprovided, starting the combustion engine so as to enable active engine braking during at least aportion of the braking event. The first point in time corresponds to the point in time of initiation of the braking event.

Regenerative braking of the vehicle powertrain is an efficient way of recovering energy so as tocharge an energy storage device which is configured to power an electric motor of the hybrid vehiclepowertrain. However, state of charge of the energy storage device may limit the ability to use regenerative braking during a braking event. The present method enables an efficient usage of regenerative braking when possible at the same time as ensuring that the vehicle powertrain may besufficiently braked also in situations where the possible regenerative braking power may beinsufficient. The fact that the combustion engine is started in response to a prediction that thecapacity of the energy storage device, at the initiation of the braking event, will be insufficient forallowing regenerative braking for the braking event ensures that the combustion engine is readilyavailable when active engine braking may be needed or desired during the braking event. This in turnreduces the risk of the vehicle undesira bly accelerating during the time it takes to start thecombustion engine and activate active engine braking. The present method also enables overriding aconventional start-and-stop functionality of the combustion engine which may be configured to holdthe combustion engine in a turned-off state when the combustion engine is not needed for providing a driving torque for the purpose of propelling the vehicle.

Said desired regenerative braking power of the vehicle powertrain for the braking event maycomprise a predicted regenerative braking power required to meet a requirement of apredetermined downhill speed control velocity during the braking event. Thereby, the braking powerneeded to avoid the vehicle at any time during the braking event having a higher velocity than apredetermined downhill speed control velocity is considered. This enables an improved control ofthe vehicle powertrain to avoid unwanted acceleration and enables the method to be integrated into a downhill speed control system, if desired.

The method may further comprise a step of determining a second point in time at which thecombustion engine should be started, and starting the combustion engine at said second point intime. Thereby, it is ensured that the combustion engine is readily available for active engine braking when needed or desired.

The method may further comprise a step of determining a third point in time at which active enginebraking is to be initiated, and initiating active engine braking at said third point in time. Thereby, therecovery of energy by means of regenerative braking may be efficiently used while at the same time avoiding the risk of undesired acceleration of the vehicle during the braking event.

The third point in time may correspond to a point in time at which the state of charge of the energystorage device is estimated to reach a predetermined second state of charge threshold value.

Thereby, the ability to use regenerative braking during the braking event may be fully utilized at thesame time as sufficient braking power of the vehicle powertrain for the whole braking event may be ensured.

The method may comprise the steps of:based on map and topographic data, predicting an energy profile of the braking eventto meet a requirement of a predetermined downhill speed control velocity during thebraking event;based on said energy profile, estimating an amount of charge of the energy storagedevice resulting from the braking event in case of regenerative braking;based on a current state of charge of the energy storage device, estimating the stateof charge of the energy storage device at the first point in time; andbased on the estimated state of charge at the first point in time and the estimatedamount of charge of the energy storage device resulting from the braking event in case ofregenerative braking, predicting whether or not the state of charge of the energy storagedevice at the first point in time will be above the first state of charge threshold value.Thereby, a reliable prediction of whether or not the vehicle powertrain may be braked byregenerative braking during the whole braking event can be provided. This in turn ensures that thecombustion engine is only started in case there is an expected need of active engine braking. ln otherwords, an unnecessary start of the combustion engine, which would result in an increase in fuel consumption and emissions, can be avoided.

The method may further comprise a step of determining whether a current state of charge of theenergy storage device can be reduced prior to the first point in time, and, if possible, controlling thevehicle powertrain accordingly so as to discharge the energy storage device prior to the initiation ofthe braking event. Thereby, the possibility to utilize regenerative braking during the braking event may be further improved.

The method may further comprise controlling the temperature of the energy storage device for thepurpose of increasing regenerative braking power available during the braking event. Thereby, the possibility to utilize regenerative braking during the braking event may be further improved.

The present disclosure further relates to a computer program comprising instructions which, when executed by a control device, cause the control device to carry out the method as described above.

The present disclosure further relates to a computer-readable medium comprising instructionswhich, when executed by a control device, cause the control device to carry out the method as described above.

Moreover, in accordance with the present disclosure a control device configured to control a hybridvehicle powertrain is provided. The hybrid vehicle powertrain comprises a combustion engine, andan electrical motor powered by an energy storage device. The electrical motor is opera ble to performregenerative braking of the vehicle powertrain to charge the energy storage device. The controldevice is configured to, in response to a predication that, at a first point in time, a state of charge ofthe energy storage device will be above a first state of charge threshold value at which a desiredregenerative braking power of the vehicle powertrain for the braking event can be provided, startthe combustion engine so as to enable active engine braking during at least a portion of the braking event. The first point in time corresponds to the point in time of initiation of the braking event.

The control device has the same advantages as described above with regard to the corresponding method of controlling a hybrid vehicle powertrain.

The desired regenerative braking power of the vehicle powertrain for the braking event maycomprise a predicted regenerative braking power required to meet a requirement of a predetermined downhill speed control velocity during the braking event.

The control device may further be configured to: based on map and topographic data, predict an energy profile of the braking event tomeet a requirement of a predetermined downhill speed control velocity during the brakingevent based on said energy profile, estimate an amount of charge of the energy storagedevice resulting from the braking event in case of regenerative braking; based on a current state of charge of the energy storage device, estimate the state ofcharge at the first point in time; and based on the estimated state of charge at the first point in time and the estimatedamount of charge of the energy storage device resulting from the braking event in case ofregenerative braking, predicting whether or not the state of charge of the energy storage device at the first point in time will be above the first state of charge threshold value.

The control device may further be configured to determine whether or not the state of charge of theenergy storage device can be reduced prior to the first point in time to thereby increase the amount of regenerative braking power available for the braking event, and, if possible, control the vehicle powertrain accordingly so as to discharge the energy storage device prior to initiation of the braking eVent.

The control device may further be configured to control the temperature of the energy storage device for the purpose of increasing regenerative braking power available during the braking event.

The present disc|osure further re|ates to a vehicle comprising the control device configured to control a hybrid vehicle powertrain as described above. The vehicle may further comprise a hybrid vehicle powertrain as described above.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 schematically illustrates a side view of a vehicle, Fig. 2 schematically illustrates a vehicle when approaching a downhill stretch of a road and abraking event associated with the downhill stretch is identified, Fig. 3 represents a flowchart schematically illustrating a method for controlling a hybridvehicle powertrain according to a first exemplifying embodiment of the presentdisc|osure, Fig. 4 represents a flowchart schematically illustrating a method for controlling a hybridvehicle powertrain according to a second exemplifying embodiment of the presentdisc|osure, Fig. 5 schematically illustrates a device that may constitute, comprise or be a part of a control device configured to control a hybrid vehicle powertrain.

DETAILED DESCRIPTION The invention will be described in more detail below with reference to exemplifying embodimentsand the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and/or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.

Engine braking may be considered to constitute any form of action for braking a vehicle which utilizesthe com bustion engine of the vehicle to provide a braking effect and thereby slow down the vehicle.ln the present disclosure, the term ”active engine braking" is considered to mean engine brakingwherein the engine is actively controlled and operated for achieving the braking power. Examples ofactive engine braking include exhaust braking, compressive release braking (CRB) and variable vanebraking (VVB). Active engine braking may alternatively be denominated ”engine endurance braking".The term ”active engine braking", as used herein, is thus not considered to encompass dragging ofthe engine, which however may be considered to constitute a passive form of engine braking. Enginebraking via engine dragging occurs when the accelerator is released and the driving wheels of the vehicle remain connected with the combustion engine via the gearbox.

A braking event is in the present disclosure considered to mean an event during which braking isperformed, with a constant or varying total braking torque, from one or more brakes, in order to control the velocity of a vehicle. ln accordance with the present disclosure, a method of controlling a hybrid vehicle powertrain isprovided. More specifically, the present disclosure relates to a method of controlling a hybrid vehiclepowertrain in conjunction with a braking event. The method is started before the hybrid vehiclereaches an identified upcoming braking event. The hybrid vehicle powertrain comprises a firstpropulsion unit in the form of a combustion engine, and a second propulsion unit in the form of anelectrical motor. The electrical motor is powered by an energy storage device. The electrical motormay also function as a generator. Thereby, the electrical motor may, when desired, be operable toperform regenerative braking of the vehicle powertrain to charge the energy storage device. Thevehicle powertrain may comprise more than one electrical motor configured to act as a propulsionunit and as a generator, if desired. For example, a second electrical motor may be powered by theenergy storage device and opera ble to charge the energy storage device. Alternatively, the secondelectrical motor may be powered by a second energy storage device and configured to charge the second energy storage device during regenerative braking.

At the start of the method, the combustion engine is in a non-operated state. ln other words, thecom bustion engine is turned off at the start of the method. The com bustion engine may at this stage be connected or disconnected, for example by means of a clutch, from the driveline of the vehicle powertrain. The method of controlling a hybrid vehicle powertrain according to the presentdisclosure may comprise a step of identifying an upcoming braking event. The method comprises astep of starting the combustion engine so as to enable active engine braking during at least a portionof the braking event. Said start of the combustion engine is performed in response to a predictionthat, at a first point in time, the state of charge of the energy storage device will be above a firststate of charge threshold value at which a desired regenerative braking power of the vehiclepowertrain for the whole upcoming braking event can be provided. The first point in timecorresponds to the point in time of initiation of the braking event. The method may further comprisea step of activating active engine braking when the combustion engine has been started. The methodmay further comprise a step of controlling the point in time of activation of the active enginebraking, the duration of the active engine braking and the braking power provided by the activebraking power so as to recover a desired amount of energy by means of regenerative braking duringthe braking event. The desired amount of energy to be recovered may for example correspond to acharge of the energy storage device up to a predetermined maximum state of charge (the storage capacity) of the energy storage device.

Thereby, the combustion engine is started in case it is predicted that the vehicle powertrain cannotbe sufficiently braked by means of regenerative braking for the whole upcoming braking event due toina bility to recover the whole amount of energy associated with the braking event by charging of theenergy storage device, due to the expected state of charge at the initiation of the upcoming brakingevent. By starting the combustion engine, active engine braking can be used for braking the vehiclepowertrain during a desired portion of the braking event. Active engine braking may thereafter beperformed simultaneously with regenerative braking during the whole or part of the braking event.Alternatively, active engine braking and regenerative braking may thereafter be performed separatefrom each other during different portions of the braking event. Thereby, regenerative braking maybe used efficiently to recover as much energy as possible during the braking event. At the same time,it is ensured that the vehicle powertrain may be efficiently braked during the whole braking event inorder to minimize the risk of unwanted acceleration of the vehicle powertrain during the brakingevent. This in turn increases the safety in operation of a vehicle comprising the hybrid vehicle powertrain.

Hybrid vehicle powertrains today may often be operated so as to turn off the combustion enginewhen it is not needed for providing driving torque and restarting the combustion engine again whenneeded for providing driving torque. There may be several reasons for turning off the com bustion engine when it is not needed for providing driving torque, such as for the purpose of preserving energy and/or reducing noise. One example of a situation when the combustion engine may beturned off is during freewheeling. ln such a case, fuel consumption and emissions may be reducedcompared to a case of freewheeling with the combustion engine running at idle speed (and thegearbox being in neutral). Therefore, for example during a long downhill stretch, the combustionengine may be in turned off state since sufficient propulsion may be provided by the gravity force.The combustion engine may also be turned off when driving torque is to be provided by the electricalmotor only. ln order to further reduce energy losses, the combustion engine may even in somesituations be disconnected from the rest of the powertrain (i.e. the driveline) to thereby avoid energylosses resulting from the combustion engine being dragged. For example, a cruise control may beconfigured to turn off the combustion engine during a downhill stretch. The present methodoverrides such a conventional control and starts the combustion engine, although not needed for thepropulsion of the vehicle, in order to enable it to be utilized for active engine braking during a braking event.

As discussed above, the combustion engine is started in response to a prediction that, at the point intime of initiation of the braking event, the state of charge of the energy storage device will be abovea first state of charge threshold value. The first state of charge threshold value corresponds to a stateof charge at which a desired regenerative braking power of the vehicle powertrain for the brakingevent can be provided. The first state of charge threshold value is thus not a static threshold value,but will thus vary over time depending on for example how the hybrid vehicle powertrain is operated and the properties of the road on which the vehicle is travelling. ln general, it is desired to utilize regenerative braking as much as possible in order to recover asmuch energy as possible. Therefore, the desired regenerative braking power of the vehiclepowertrain for the braking event may correspond to the total needed braking power for the brakingevent. ln other words, the desired regenerative braking power may correspond to the braking powerneeded from regenerative braking if only regenerative braking would be utilized for the brakingevent. The desired regenerative braking power may alternatively correspond to the braking powerneeded from regenerative braking in case, for example, the combustion engine is simultaneously dragged in order to assist in the braking of the vehicle.

Vehicles, especially heavy vehicles, are today often equipped with a downhill speed control system.Such a downhill speed control system may for example be integrated into a cruise control. A downhillspeed control system is configured to automatically brake the vehicle powertrain when a preselected downhill speed is reached. The purpose therefore is to avoid the vehicle reaching too high velocity, primarily on downhill stretches. ln such a case, the desired regenerative braking power of the vehiclepowertrain for the braking event, as discussed above, may comprise a predicted regenerative brakingpower required to meet the requirement of a predetermined downhill speed control velocity duringthe braking event. ln other words, the desired regenerative braking power may be the braking powerneeded in order to avoid a travelling speed, at any point during the braking event, above the predetermined downhill speed control velocity of a downhill speed control system.

As mentioned above, the combustion engine is started in response to a prediction that, at theinitiation of the braking event, the state of charge of the energy storage device will be above a firststate of charge threshold value at which a desired regenerative braking power for the braking eventcan be provided. The method may thus comprise a step of predicting whether or not the state ofcharge of the energy storage device, at the first point in time (i.e. the point in time of initiation of thebraking event), will be above a first state of charge threshold value at which a desired regenerativebraking power of the vehicle powertrain for the future braking event can be provided. For thepurpose of making such a prediction of whether or not the state of charge will be above the firststate of charge threshold value, a state of charge of the energy storage device at the point in time ofinitiation of the braking event may be estimated. This may be performed based on the current stateof charge of the energy storage device and an estimated change in state of charge of the energystorage device up to the point in time of initiation of the braking event. Such a change in state ofcharge may be estimated in consideration of how the vehicle powertrain is currently operatedand/or is to be operated until the point in time of initiation of the braking event. The estimation ofthe change in state of charge may be performed in accordance with any previously known methodtherefore. By way of example, it may be based on stored data relating to change in state of charge ofenergy storage devices in other vehicles received for example via a vehicle-to-anything (V2X)communication system or stored historical data relating to change in state of charge of the energy storage device when the vehicle has been travelling the same route on previous occasions.

Moreover, for the purpose of predicting whether or not the state of charge of the energy storagedevice, at the first point in time, will be above a first state of charge threshold value, an estimation ofa charge of the energy storage device which would result from regenerative braking during theupcoming braking event may be made. This may be performed by predicting an energy profile of thebraking event. The energy profile may for example be predicted based on map and topographic data,or be based on data received via a V2X communication system. The energy profile may further takeinto consideration factors, such as weight of the vehicle. The travelling speed of the vehicle at the start of the braking event may also be taken into consideration. Furthermore, a target speed of the 11 vehicle (which may vary during the course of the braking event) may also be taken into considerationfor the prediction of the energy profile. The energy profile may also, in case a predetermineddownhill speed control velocity has been set, be predicted so as to meet the requirement of thepredetermined downhill speed control velocity. From the predicted energy profile, the amount ofcharge which would result from regenerative braking during the braking event may be estimated.This may then be compared to the estimated charge at the point in time of initiation of the brakingevent and the capacity of the energy storage device for the purpose of determining whether or notthe hybrid vehicle powertrain may be braked by means of regenerative braking during the wholebraking event. ln other words, it may be predicted whether or not the state of charge of the energystorage device at the point in time of initiation of the upcoming braking event will be above the firststate of charge threshold value based on the estimated state of charge at the point in time ofinitiation of the upcoming braking event and the estimated amount of charge which would result from regenerative braking during the upcoming braking event.

The method may also comprise a step of determining a second point in time at which thecombustion engine should be started, and starting the combustion engine at said second point intime. Depending on the circumstances, the second point in time, i.e. the point in time at which thecombustion engine should be started, may be before the first point in time, correspond to the firstpoint in time (i.e. the point in time of initiation of the braking event), or even be after the first pointin time. ln other words, the combustion engine may be started before the start of the braking event,at the start of the braking event or during the braking event. The process of starting the com bustionengine takes some time (depending on the configuration of the combustion engine, usually in theorder of a few seconds), which means that the combustion engine should be started before activeengine braking is actually needed. ln case the combustion engine is not started prior to a desire for orneed of active engine braking, there might be an undesired acceleration of the vehicle as a result oflack of sufficient braking power during the start-up process of the combustion engine. This may also in turn result to a need of higher braking power when the active engine braking is ready for use.

During the time between the point in time at which the combustion engine has been started and thepoint in time at which active engine braking is desired or needed, the combustion engine may bedragged. This in turn provides a braking force of the vehicle powertrain, which in turn may reducethe later need of braking power from active engine braking. By way of example, the combustionengine may be started before initiation of the braking event and be allowed to be dragged by thevehicle powertrain. This in turn provides a braking force which for example could be compensated by the electrical motor thus requiring more power from the energy storage device. Thereby, the state of 12 charge of the energy storage device will decrease more compared to for example a case of thecombustion engine being turned-off and disconnected from the driveline of the powertrain. Thereby,the energy storage device will be able to accept more charge during the braking event and the abilityto use regenerative braking is therefore improved. At the same time, the combustion engine will beready for use in active engine braking when needed. Alternatively, if the energy loss caused by thedragging of the combustion engine is not allowed to be compensated by a driving torque of theelectrical motor, the travelling speed of the vehicle will be reduced before the point in time ofinitiation of the braking event. This in turn results in lower braking power needed during the braking event and thus also results in better usage of regenerative braking during the braking event.

The method may also comprise a step of determining a third point in time at which active enginebraking is to be initiated, and initiating active engine braking at said third point in time. The thirdpoint in time may be immediately after the combustion engine has been started or after a certainperiod of time after starting the combustion engine. The third point in time may correspond to apoint in time, during the braking event, at which the state of charge of the energy storage device isestimated to reach a predetermined second state of charge threshold value. The second state ofcharge threshold value may for example correspond to the maximum storage capacity of the energystorage device or a preselected percentage thereof, but is not limited thereto. ln case the third pointin time corresponds to a time at which the state of charge of the energy storage device is estimatedto reach the predetermined second state of charge threshold value, the hybrid vehicle powertrainwill in the beginning of the braking event not be braked by active engine braking but by means of regenerative bra king.

The method may further comprise a step of determining whether a current state of charge of theenergy storage device can be reduced prior to the point in time of initiation of the braking event. Thismay be performed in response to the prediction that, at the initiation of braking event, the state ofcharge of the energy storage device will be above the first state of charge threshold value. lf it ispossible to reduce the current state of charge of the energy storage device prior to the point in timeof initiation of the braking event, the method may comprise controlling the hybrid vehicle powertrainaccordingly so as to discharge the energy storage device prior to the initiation of the braking event.This may in turn improve the ability to use regenerative braking during the braking event since, at thetime of initiation of the braking event, the state of charge of the energy storage device will be lowerthan the state of charge at the point in time of the initial prediction. The method may in such a casecomprise a step of making a new prediction as regards the state of charge of the energy storage device at the first point in time (i.e. at the initiation of the braking event). ln case the new prediction 13 reveals that the state of charge of the energy storage device will still above the first state of chargethreshold value, the combustion engine is started so as to enable active engine braking during atleast a portion of the braking event. ln case the new prediction reveals that the state of charge of theenergy storage device will be below the first state of charge threshold value, the step of starting thecombustion engine may be avoided which in turn reduces the fuel consumption and exhaust emissions. ln certain situations, it may be advantageous to reduce the travelling speed of the vehicle before thepoint in time of initiation of the identified upcoming braking event (which could be the point in timeat which the vehicle is expected to reach a downhill stretch of the road) since this may enable abetter usage of regenerative braking during the identified upcoming braking event (in this example,the downhill stretch). For example, it may be predicted that, in case the travelling speed of thevehicle would be reduced by a certain amount, the state of charge of the energy storage device atthe point in time when the vehicle reaches the start of the downhill stretch would allow regenerativebraking during the whole braking event. This could for example be due to the possibility of allowing acertain increase in travelling speed of the vehicle during the braking event. ln such a case, actualbraking of the vehicle powertrain could be commenced before the point in time of initiation of theoriginally identified braking event, i.e. the point in time at which the vehicle reaches the start of thedownhill stretch. This means that the actual point in time at which the braking event is initiated willoccur prior to the point in time of initiation of the originally identified braking event. Thus, inaccordance with one exemplifying embodiment, the method may comprise the steps of: identifying an upcoming braking event; in response to a prediction that, at a point in time of initiation of the identified brakingevent, the state of charge of the energy storage device will be above a first state of charge thresholdvalue at which a desired regenerative braking power of the vehicle powertrain for the identifiedbraking event can be provided, starting the combustion engine at a second point in time which isprior to the point in time of initiation of the identified braking event; when the combustion engine has been started, activating active engine braking so asto brake the vehicle powertrain prior to the point in time of initiation of the identified braking event;and initiating regenerative braking of the vehicle powertrain at the time of initiation of the identified braking event or at a point time of duration of the identified braking event.

The method may further comprise a step of controlling the temperature of the energy storage device for the purpose of increasing the regenerative braking power available during the braking event. Said 14 step of contro||ing the temperature of the energy storage device may comprise pre-cooling or pre-heating the energy storage device prior to the point in time of initiation of the braking event, but isnot limited thereto. The ability to charge and discharge an energy storage device is dependent of thetemperature of the energy storage device. Therefore, the temperature of the energy storage significantly impacts the performance.

The step of contro||ing the temperature of the energy storage device for the purpose of increasingthe regenerative braking power available during the braking event may comprise increasing thetemperature of the energy storage device and/or decreasing the temperature of the energy storagedevice depending on the circumstances, such as ambient temperature, current temperature of theenergy storage device, point in time at which the step is performed (prior to the braking event, at thestart of the braking event and/or during the braking event), an expected change of temperature ofthe energy storage device during the braking event, whether the energy storage device is, when thestep is performed, charging or discharging, and/or the charge/discharge rate. By way of example, thestep of contro||ing the temperature of the energy storage device may be conducted as part of thecontro||ing of the hybrid vehicle powertrain so as to discharge the energy storage device prior to theinitiation of the braking event. By discharging the energy storage device prior to the braking event,the regenerative braking available during the braking event may be increased. According to anotherexample, the step of contro||ing the temperature for the purpose of increasing regenerative brakingpower during the braking event may comprise cooling the energy storage device to reduce the charging rate thereof during the braking event.

The performance of the herein described method of contro||ing a hybrid vehicle powertrain may begoverned by programmed instructions. These programmed instructions typically take the form of acomputer program which, when executed in or by a control device, cause the control device to effectdesired forms of control action. Such instructions may typically be stored on a computer-readable medium.

The present disclosure further relates to a control device configured to control a hybrid vehiclepowertrain, such as the hybrid vehicle powertrain described above. The control device may beconfigured to perform any one of the steps of the herein described method of contro||ing a hybridvehicle powertrain. More specifically, the control device is configured to, in response to a predicationthat, at a point in time of initiation of a braking event (above also called a first point in time), a stateof charge of the energy storage device will be above a first state of charge threshold value at which a desired regenerative braking power of the vehicle powertrain for the braking event can be provided, start the combustion engine so as to enable active engine braking during at least a portion of the braking event.

The control device may comprise one or more control units. ln case of the control device comprisinga plurality of control units, each control unit may be configured to control a certain function or acertain function may be divided between more than one control units. The control device may be acontrol device of the hybrid vehicle powertrain. The control device may be arranged in a vehiclecomprising the hybrid vehicle powertrain. Alternatively, parts of the control device may, if desired, be arranged remote from the vehicle.

Figure 1 schematically illustrates a side view of an example of a vehicle 1. The vehicle 1 may be aheavy vehicle, e.g. a truck or a bus, but is not limited thereto. The vehicle 1 comprises a hybridvehicle powertrain 2 comprising a first propulsion unit in the form of an internal combustion engine3, and a second propulsion unit in the form of an electrical motor 4. The electrical motor 4 ispowered by an energy storage device 5, for example a pack of batteries. The electrical motor 4 mayin some situations function as a generator and thereby charge the energy storage device 5. ln otherwords, the electrical motor 4 is opera ble to perform regenerative braking of the vehicle powertrainto charge the energy storage device 5. The hybrid vehicle powertrain 2 may further comprise agearbox 6. The gearbox 6 may be connected to the driving wheels 7 of the vehicle powertrain 2 viaan output shaft 8 of the gearbox 6. The vehicle may further comprise a control device 100 configuredto control the hybrid vehicle powertrain 3. The control device 100 may be configured tocommunicate with a remote control center, control devices of other vehicles, and/or control units ofthe infrastructure, via any previously communication system therefore, such as a V2X communication system, for the purpose of exchanging various forms of data.

For the purpose of illustrating one possible situation and the result of the method according to thepresent disclosure, Figure 2 schematically illustrates a hybrid vehicle, such as the vehicle 1 shown inFigure 1, when approaching a downhill stretch of a road. At the point in time to, an upcoming brakingevent is identified, and it may be determined that the braking event is expected to start at a time t1.The upcoming braking event may be expected to end at the point in time tand. When the upcomingbraking event has been identified, a prediction may be made as to whether regenerative braking maybe utilized for the whole upcoming braking event. ln case it is predicted that the state of charge ofthe energy storage device at t1 is sufficiently low to provide the desired regenerative braking powerfor the braking event, the vehicle powertrain may be controlled to perform regenerative braking during the braking event. However, in case it is predicted that the state of charge of the energy 16 storage device, at the time t1, will be above a state of charge at which a desired regenerative brakingpower of the vehicle powertrain for the braking event can be provided, the combustion engine isstarted in accordance with the present method. The combustion engine may for example be startedat a point in time t; prior to t1. Thereby, the combustion engine will be available for active enginebraking at any time during the braking event as desired. The combustion engine may also be startedat t1 or at a time between t1 and tend. Activation of active engine braking may be performed after thecombustion engine has been started and based on the expected state of charge at time t1 as well asthe charge of the energy storage device resulting from regenerative braking during the brakingevent. By way of example, active engine braking may be desired during a portion of the brakingevent, such as between time t; and time t4. lt should here be recognized that regenerative brakingshould be prioritized for the purpose of recovering as much energy as possible, and the active enginebraking is merely intended to supplement the regenerative braking to ensure that sufficient brakingpower is available at all times during the braking event. However, in the unlikely event that theenergy storage device is essentially fully charged at t1, active engine braking could be used alone for the whole braking event.

Figure 3 represents a flow chart schematically illustrating a first exemplifying embodiment of themethod for controlling a hybrid vehicle powertrain according to the present disclosure. The methodcomprises a step S110 of starting the combustion engine so as to enable active engine braking duringat least a portion of a current or upcoming braking event. The step S110 is performed in response toa prediction that, at the initiation of the braking event, the state of charge of the energy storagedevice will be above a first threshold value at which a desired regenerative braking of the hybridvehicle powertrain for the braking event can be provided. The method may further comprise a step S120 of initiating active engine braking.

Figure 4 represents a clow chart schematically illustrating a second exemplifying em bodiment of themethod for controlling a hybrid vehicle powertrain according to the present disclosure. The methodcomprises a step S101 of estimating a state of charge at the point in time of initiation of an upcomingbraking event. The step S101 may for example comprise determining the current state of charge ofthe energy storage device and estimating any charge/discharge of the energy storage deviceresulting from the operating of the vehicle powertrain up to the point in time of initiation of thebraking event. The method also comprises a step S102 of predicting an energy profile of the brakingevent, for example based on map and topographic data or based on information received via a vehicle-to-anything (V2X) communication system. The method further comprises a step S103 of, 17 based on the energy profile of step S102, estimating an amount of charge of the energy storage device which would result from the braking event in case of regenerative braking. lt should here be recognized that although step S101 is illustrated to be performed before step S102 and step S103, step S101 may be performed after or in parallel with steps S102 and/or S103.

The method further comprises a step S104 of predicting/determining whether or not the state ofcharge of the energy storage device at the point in time of initiation of the braking event will beabove a first state of charge threshold. The first state of charge threshold corresponds to a state ofcharge threshold at which a desired regenerative braking power of the vehicle powertrain for abraking event can be provided. ln case it is predicted that the state of charge the state of charge ofthe energy storage device, at the point in time of initiation of the braking event, will be below or atsaid first state of charge threshold value, the present method may be ended. Thereby, combustionengine may remain in a turned-off state and the hybrid vehicle powertrain braked by regenerativebraking during the braking event. However, in case it is predicted that the state of charge of theenergy storage device, at the point in time of initiation of the braking event, will be above said first state of charge threshold value, the method proceeds subsequent step/steps.

The method may, in response to a prediction/determination in step S104 that the state of charge ofthe energy storage device will be above the first state of charge threshold value, further comprise astep S105 of determining whether the current state of charge of the energy storage device can bereduced prior to the point in time of initiation of the braking event. lf it is possible to reduce the stateof charge of the energy storage device prior to the point in time of initiation of the braking event, themethod may comprise a step of controlling S106 the hybrid vehicle powertrain accordingly so as toreduce the state of charge of the energy storage device. The method may after step S106 has beeninitiated be returned to the beginning of the method such that steps S101-S105 are repeated. ln case the state of charge cannot be reduced, the method proceeds to step S110. ln step S110, the combustion engine is started so as to enable active engine braking during at least aportion of a current or upcoming braking event. Step S110 of starting the combustion engine, isperformed in response to a prediction from step S104 that, at the initiation of the braking event, thestate of charge of the energy storage device will be above the first state of charge threshold value atwhich a desired regenerative braking power of the hybrid vehicle powertrain for the braking eventcan be provided. The method may thereafter further comprise a step S120 of initiating active engine bra king. 18 Figure 5 schematically illustrates an exemplifying embodiment of a device 500. The control device100 described above may for example comprise the device 500, consist of the device 500, or be comprised in the device 500.

The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/writememory 550. The non-volatile memory 520 has a first memory element 530 in which a computerprogram, e.g. an operating system, is stored for controlling the function of the device 500. The device500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, atime and date input and transfer unit, an event counter and an interruption controller (not depicted).

The non-volatile memory 520 has also a second memory element 540.

There is provided a computer program P that comprises instructions for controlling a hybrid vehiclepowertrain. Said hybrid vehicle powertrain comprises a combustion engine and an electrical motor.The electrical motor is operable to perform regenerative braking of the hybrid vehicle powertrain tocharge the energy storage device. The computer program comprises instructions for, in response to apredication that, at a first point in time, a state of charge of the energy storage device will be above afirst state of charge threshold value at which a desired regenerative braking power of the vehiclepowertrain for a braking event can be provided, starting the combustion engine so as to enableactive engine braking during at least a portion of the braking event. The first point in time corresponds to the point in time of initiation of the braking event.

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.

The data processing unit 510 may perform one or more functions, i.e. the data processing unit 510may effect a certain part of the program P stored in the memory 560 or a certain part of the program P stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus512. The separate memory 560 is intended to communicate with the data processing unit 510 via adata bus 511. The read/write memory 550 is adapted to communicate with the data processing unit510 via a data bus 514. The communication between the constituent components may be implemented by a communication link. A communication link may be a physical connection such as 19 an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.

When data are received on the data port 599, they may be stored temporarily in the second memoryelement 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

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

Claims

1. A method of controlling a hybrid vehicle powertrain (2), the method performed by a controldevice (100),the hybrid vehicle powertrain (2) comprising: a combustion engine (3), an electrical motor (4) powered by an energy storage device (5), wherein the electrical motor (4) is operable to perform regenerative braking of thevehicle powertrain (2) to charge the energy storage device (5),the method comprising: in response to a predication that, at a first point in time (t1), a state of charge of theenergy storage device (5) will be above a first state of charge threshold value at which adesired regenerative braking power of the vehicle powertrain (2) for a braking event can beprovided, starting (S110) the combustion engine (3) so as to enable active engine brakingduring at least a portion of the braking event, wherein the first point in time (t1) corresponds to the point in time of initiation of the braking event. The method according to claim 1, wherein said desired regenerative braking power of thevehicle powertrain (2) for the braking event comprises a predicted regenerative brakingpower required to meet a requirement of a predetermined downhill speed control velocity during the braking event. The method according to any one of claims 1 or 2, further comprising a step of determining asecond point in time (tg) at which the combustion engine (2) should be started, and starting the combustion engine (2) at said second point in time (tg). The method according to any one of the preceding claims, further comprising a step ofdetermining a third point in time (tg) at which active engine braking is to be initiated, and initiating (S120) active engine braking at said third point in time (tg). The method according to claim 4, wherein the third point in time (tg) corresponds to a pointin time at which the state of charge of the energy storage device is estimated to reach a predetermined second state of charge threshold value. 10. 21 The method according to any one of the preceding claims, further comprising the steps of: based on map and topographic data, predicting (S102) an energy profile of the brakingevent to meet a requirement of a predetermined downhill speed control velocity during thebraking event; based on said energy profile, estimating (S103) an amount of charge of the energystorage device (5) resulting from the braking event in case of regenerative braking; based on a current state of charge of the energy storage device (5), estimating (S101)the state of charge of the energy storage device at the first point in time (t1); and based on the estimated state of charge at the first point in time (t1) and the estimatedamount of charge of the energy storage device (5) resulting from the braking event in case ofregenerative braking, predicting (S104) whether or not the state of charge of the energystorage device (5) at the first point in time (t1) will be above the first state of charge threshold value. The method according to any one of the preceding claims, further comprising a step ofdetermining (S105) whether a current state of charge of the energy storage device (5) can bereduced prior to the first point in time (tl), and, if possible, controlling (S106) the hybridvehicle powertrain (2) accordingly so as to discharge the energy storage device (5) prior to initiation of the braking event (t1). The method according to claim any one of the preceding claims, further comprisingcontrolling the temperature of the energy storage device (5) for the purpose of increasing regenerative braking power available during the braking event. The method according to any one of the preceding claims, wherein the step of starting (S110)the combustion engine is performed at or prior to the point in time of initiation of the braking event (t1). A computer program comprising instructions which, when executed by a control device(100), cause the control device (100) to carry out the method according to any one of the preceding claims. 11. 1

2. 1

3. 1

4. 22 A computer-readable medium comprising instructions which, when executed by a controldevice (100), cause the control device (100) to carry out the method according to any one of claims 1 to 9. A control device (100) configured to control a hybrid vehicle powertrain (2),the hybrid vehicle powertrain (2) comprising: a combustion engine (3), an electrical motor (4) powered by an energy storage device (5), wherein the electrical motor (4) is operable to perform regenerative braking of thevehicle powertrain (2) to charge the energy storage device (5), wherein the control device (100) is configured to, in response to a predication that, ata first point in time (t1), a state of charge of the energy storage device (5) will be above a firststate of charge threshold value at which a desired regenerative braking power of the vehiclepowertrain (2) for a braking event can be provided, start the combustion engine (3) so as toenable active engine braking during at least a portion of the braking event, wherein the first point in time (t1) corresponds to the point in time of initiation of the braking event. The control device (100) according to claim 12, wherein said desired regenerative brakingpower of the vehicle powertrain (2) for the braking event comprises a predicted regenerativebraking power required to meet a requirement of a predetermined downhill speed control velocity during the braking event. The control device (100) according to any one of claims 12 and 13, further configured to based on map and topographic data, predict an energy profile of the braking event tomeet a requirement of a predetermined downhill speed control velocity during the brakingevent based on said energy profile, estimate an amount of charge of the energy storagedevice (5) resulting from the braking event in case of regenerative braking; based on a current state of charge of the energy storage device (5), estimate the stateof charge at the first point in time; and based on the estimated state of charge at the first point in time and the estimatedamount of charge of the energy storage device (5) resulting from the braking event in case ofregenerative braking, predicting whether or not the state of charge of the energy storage device at the first point in time (t1) will be above the first state of charge threshold value. 23 1

5. The control device (100) according to any one of claims 12 to 14, further configured todetermine whether or not the state of charge of the energy storage device (5) can bereduced prior to the first point in time (t1) to thereby increase the amount of regenerativebraking power available for the braking event, and, if possible, control the vehicle powertrain(2) accordingly so as to discharge the energy storage device (5) prior to initiation of the braking event (tl).1

6. The control device (100) according to claim 15, further configured to control the temperatureof the energy storage device (5) for the purpose of increasing regenerative braking power available during the braking event. 1

7. A vehicle (1) comprising the control device (100) according to any one of claims 12 to 16.