SE1551398A1 - A method for controlling a powertrain of a vehicle - Google Patents

Abstract

A method for controlling a powertrain of a motor vehicle travelling behind a lead vehicle, comprising the steps of: (a) collecting data relating to a road gradient along an expected travelling route, (b) collecting data relating to a present size of a gap between the vehicles, (c) collecting data relating to a speed of the lead vehicle, (d) performing a simulation based on said data and on the presumption that a potential mode of operation of the powertrain, involving coasting of the motor vehicle, is actuated, wherein the simulation computes data relating to an expected gap between the vehicles during an upcoming time period, (e) checking if the simulated data from step (d) fulfill a predefined actuation condition, which is fulfilled when the expected gap is larger than a preset smallest allowable gap, (f) given that the actuation condition is fulfilled, actuating said potential mode of operation.(Fig. 1)

Description

A method for control/ina a powertrain of a vehicle TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for controlling apowertrain of a motor vehicle travelling behind a lead vehicle. Theinvention further relates to a computer program, a computerprogram product, an electronic control unit, and a motor vehicle.By a motor vehicle is here intended a vehicle which is powered byan internal combustion engine and/or by an electric motor. lnparticular, but not exclusively, the method is intended for use in a heavy motor vehicle such as a truck or a bus.

A mode of operation of the powertrain is here intended to beunderstood as e.g. a mode in which the powertrain is controlled bya cruise control, such as an adaptive cruise control (ACC) or afuel-economising cruise control, or a mode in which the driver iscontrolling the vehicle in a specific way so as to e.g. maintain a particular distance to a lead vehicle travelling ahead of the vehicle.

By a gap is herein intended a gap between the present vehicle and the lead vehicle in terms of either distance or time.

By coasting is to be understood running the motor vehicle forwardwithout transmitting any power via the powertrain, such as bymeans of disengaging a clutch of the vehicle or by putting the gearbox in a neutral position.

By motoring is to be understood running the vehicle forward witha gear engaged, but with no driving force applied by the powertrain.

BACKGROUND AND PRIOR ART The cost of fuel for motor vehicles, e.g. cars, trucks and buses,represents a significant expense for the owner or user of thevehicle. A wide variety of different systems have therefore beene.g.cruise controls. fuel-efficientSuch economising cruise controls aim to reduce fuel consumption by developed for reducing fuel consumption, engines and fuel-economising fuel-adjusting the driving to the characteristics of the road ahead, sothat unnecessary braking and/or fuel-consuming acceleration maybe avoided. For example, by taking topographic information aboutthe road section ahead of the vehicle into account, the speed maybe temporarily increased before e.g. an uphill slope, so thatdownshifting to a lower transmission mode can be avoided ordelayed. ln this way, a total energy consumption can be reduced.Also information about road curvature and legal speed limits along the road section ahead of the vehicle can be taken into account.

One of the main factors affecting the energy consumption of avehicle, in particular at high speeds and for large motor vehicleshaving a large front area, is air resistance. A way to reduce the airresistance, and thereby the energy consumption, is therefore todrive behind a lead vehicle, i.e. another vehicle travelling aheadof the present vehicle, and exploit the so-called slipstream effect.When two or more vehicles are involved in a so-called convoy, i.e. when trailing vehicles drive relatively proximate to lead vehicles, the fuel consumption of said vehicles can be reduced by, for example, 5-15%.

Modern motor vehicles can be equipped with radar technology tomeasure a distance to a lead vehicle. Some vehicles can also beequipped with a control system to automatically maintain aspecified gap d_set to a lead vehicle, as long as the speed of thevehicle does not exceed a set speed, such as a legal speed limit.Such a control system is usually referred to as an Adaptive CruiseControl (ACC), a Radar Cruise Control, or an Autonomous CruiseControl system. According to one example, such a system cancomprise an actuating device with which the driver can manuallyset a position that corresponds to a given gap to a lead vehicle.Such an actuating device can e.g. have five different positions thatcorrespond to discrete increments of distance to the lead vehiclebetween 10 and 75 meters, corresponding to time gaps within therange of 1-4 seconds. This system is usually automated in thetrailing vehicle. Alternatively, a driver of the trailing vehicle can choose to drive at a given distance to the lead vehicle.

An ACC system can e.g. be configured to maintain the specifiedgap d_set by application of the necessary driving force or brakingforce, i.e. so that a driving force is applied if the gap becomeslarger than the specified gap d_set, and so that brakes are appliedas soon as the gap becomes smaller than d_set. However, an ACCsystem may also be configured to maintain the specified gap d_setonly by controlling the driving force transmitted by the powertrain.ln this case, a braking gap d_brake may be defined, at whichbrakes of the vehicle are applied. The braking gap d_brake is set to be smaller than the specified gap d_set, so that if the vehicle comes closer to the lead vehicle than the specified gap d_set, butnot closer than the braking gap d_brake, the vehicle is motored.Only if this is not sufficient, and the vehicle comes closer thand_brake, the brakes are applied. The brakes may be e.g. wheel- brakes, a retarder, an exhaust brake, etc.

However, driving behind a lead vehicle also results in that normalfuel saving systems, such as certain fuel-economising cruisecontrols, cannot be fully utilised due to the risk of coming too closeto the lead vehicle, regardless of whether the motor vehicle isdriven with an activated ACC system or not. Certain fuel savingsystems and functions are therefore deactivated when drivingbehind a lead vehicle. The fuel saving effects obtained by driving behind a lead vehicle can thereby not be fully accounted for.

SUMMARY OF THE INVENTION lt is a primary objective of the present invention to achieve an, inat least some aspect, improved way of controlling a powertrain ina motor vehicle when driving behind a lead vehicle, such that theenergy consumption of the motor vehicle is minimised. lnparticular, it is an objective to provide a method for controlling apowertrain such that fuel-economising systems can be used alsoin certain situations as the vehicle is travelling behind a leadvehicle and such that the benefits of an ACC system can be combined with the benefits of other fuel-economising systems.

According to a first aspect of the present invention, at least theprimary objective is achieved by means of the method as definedin claim 1. The method comprises the steps of: (a) collecting data relating to a road gradient along an expectedtravelling route ahead of the motor vehicle, (b) collecting data relating to a present size of a gap betweenthe motor vehicle and the lead vehicle, (c) collecting data relating to a speed of the lead vehicle, (d) performing at least one simulation based on said data and onthe presumption that a potential mode of operation of thepowertrain, involving coasting of the motor vehicle, is actuated ata first point in time t_O, wherein the simulation computes datarelating to the size of an expected gap d_sim between the vehiclesduring an upcoming time period following said first point in timet_O, (e) checking if the simulated data from step (d) fulfill a set ofpredefined actuation conditions including at least one predefinedactuation condition C1, which is fulfilled when an expected gapd_sim is larger than a preset smallest allowable gap d_min duringsaid upcoming time period, (f) given that said set of predefined actuation conditions isfulfilled, actuating said potential mode of operation at said first point in time t_O.

Thus, in the method according to the invention, an expected gapd_sim to the lead vehicle during an upcoming time period issimulated, and depending on the size of the expected gap, it isdetermined whether or not to actuate a mode of operation whichinvolves coasting of the motor vehicle, i.e. running the vehicle forward without transmitting any power via the powertrain, during at least a part of the upcoming time period or road section.Coasting may be achieved in different ways, such as by means ofdisengaging a clutch of the vehicle or putting the gearbox in a neutral position. lf the gap between the vehicles is expected to be larger than thepredefined smallest allowable gap d_min during the upcoming timeperiod or road section, the simulated mode of operation isactuated. ln practice, this is useful when coasting the vehicle mightbe fuel-economically advantageous and involves reducing abraking force, or increasing a relative speed with respect to thelead vehicle. The simulation reveals if the gap between thevehicles is likely to exceed the smallest allowable gap d_min, andif so, the vehicle is set to coasting so that fuel efficiency of thevehicle can be improved. Coasting is often advantageous from afuel economy perspective, and it is therefore useful to be able toswitch to a mode of operation in which the vehicle is coasted whenthis is possible. Using the method according to the invention, themode of operation of the powertrain will automatically be switchedto one which involves coasting when this is possible withoutcoming too close to the lead vehicle. By repeating data collectionand simulation with a certain frequency, it can be checkedcontinuously whether a switch to a mode of operation involving coasting is possible.

The upcoming time period during which the expected gap d_simmust exceed the smallest allowable gap d_min in order forcondition C1 to be considered fulfilled may be predefined.Condition C1 is preferably considered fulfilled only if the expected gap d_sim exceeds the smallest allowable gap d_min during the entire predefined upcoming time period. ln other words, if theexpected gap d_sim is at any point in time during said time periodsmaller than the smallest allowable gap d_min, condition C1 is notconsidered fulfilled and the simulated potential mode of operationis not actuated. The upcoming time period may e.g. be set basedon a length of a total time period or road section for which theor based on a behaviour of the simulation is carried out, simulation.

The step of collecting data relating to a speed of the lead vehiclemay comprise e.g. estimating the speed of the lead vehicle for anupcoming time period, or receiving data from the lead vehiclerelating to its foreseen speed variation. ln the simplest case, thecurrent speed of the lead vehicle is measured or estimated and anassumption is made that the lead vehicle will maintain constantspeed. lt is also possible to base an estimation of the future speedof the lead vehicle on its present speed and acceleration, asmeasured or communicated. The future speed profile of the leadvehicle may also be simulated in the present (trailing) motorvehicle using estimations of mass and engine torque of the lead vehicle.

The simulation performed in the method according to the inventionis preferably in the form of a so called full vehicle simulation overan expected travelling route ahead of the motor vehicle. Thesimulation is repeated with a certain frequency, such as afrequency of 1 Hz. ln each simulation, several parameters may bedetermined, such as speed v_sim, engine speed, engine torque,gap d_sim to the lead vehicle, time, travelled distance, etc. The simulation is based on a potential mode of operation, which in this case is a mode of operation that involves coasting of the motorvehicle with a gearbox of the powertrain in a neutral position, orwith a clutch disengaged. Several different modes of operationmay be simulated simultaneously. The simulation may beperformed over a longer time period, or road section, than theupcoming time period used when checking if the predefined set of actuation conditions is fulfilled.

When the method is initiated, the powertrain can be controlled byan adaptive cruise control system (ACC), by another system in thevehicle, or by a driver of the vehicle. The powertrain is preferablyoperated manually or automatically to maintain a specified gapd_set to the lead vehicle and to apply the necessary driving forceor braking force to achieve this. This means that gear shifting, fuelinjection, braking, etc., is controlled in order to maintain thespecified gap d_set. Also a braking gap d_brake may be defined,in which case brakes are automatically applied if the gap betweenthe vehicles becomes smaller than the braking gap d_brake. lf thegap between the vehicles is between d_brake and d_set, the ACCsystem in this case controls the powertrain such that the vehicle is motored.

The smallest allowable gap d_min, which of course can be definedin terms of either time or distance, should usually not be adjustableby the driver of the motor vehicle. ln the case where the motorvehicle is controlled by an adaptive cruise control, such that thespeed of the motor vehicle is regulated to maintain a specified gapd_set to the lead vehicle, the smallest allowable gap d_min is setto be smaller than d_set. Preferably, the smallest allowable gap d_min can be set in dependence on the specified gap d_set. lf a braking gap d_brake is also defined, the smallest allowable gapd_min is preferably set to be smaller than the specified gap d_set,but larger than the braking gap d_brake, d_brake < d_min < d_set.Of course, also safety aspects influence the size of the smallestallowable gap d_min.

According to an embodiment of the invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C2, which is fulfilled when the expected gap d_sim issmaller than a preset largest allowable gap d_max during at leasta part of said upcoming time period. The part of the upcoming timeperiod during which the expected gap d_sim must be smaller thanthe largest allowable gap d_max can be predefined and may e.g.be a time period starting after an initial delay. By defining a largestallowable gap d_max, there is no risk that the vehicle is set tocoasting if this leads to a too large gap between the vehicles, sothat the benefits from travelling behind a lead vehicle can no longer be achieved.

According to another embodiment of the invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C3, which is fulfilled when the expected gap d_sim is ina range between the smallest allowable gap d_min and the largestallowable gap d_max during at least a preset minimum time periodAt_min. This prevents unnecessary rapid switches between modesof operation when no significant energy gains can be expected.The minimum time period At_min can be determined based onfactors such as transient losses arising when switching to and fromcoasting, driving comfort, and component wear arising when switching modes of operation.

According to another embodiment of the invention, said step (d)comprises simulating a future speed profile of the motor vehicle,and based thereon computing the size of said expected gap d_sim.The speed profile is compared to the data relating to the speed ofthe lead vehicle and the size of the gap can thereby be obtained.Simulations of a future speed profile usually take topographic datainto account and may also take traffic data etc. into account. Suchsimulation methods are known and often carried out in the vehiclefor other reasons, and this is therefore a suitable way of simulating the size of the gap during the upcoming time period.

According to another embodiment of the invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C4, which is fulfilled when the simulated speed v_sim iswithin a preset allowable speed range between a smallestallowable speed v_min and a largest allowable speed v_max. lt isthereby avoided that the vehicle is set to coasting when the speedof the vehicle is either too large or too small for this to be energy efficient and/or desira ble.

According to another embodiment of the invention, step (d) furthercomprises performing at least one simulation based on thepresumption that said potential mode of operation of thepowertrain is actuated at a later point in time t_1, which later pointin time t_1 is delayed with respect to the first point in time t_O,wherein the simulation computes data relating to an expected gapd_sim_delay between the vehicles. A supplementary simulation isthus performed in which the actuation of the potential mode of operation is carried out at a later point in time t_1 than in the 11 previously discussed simulation. The same collected data are usedas a basis for the simulation, and the simulations are performedsimultaneously. The supplementary simulation thus reveals if anyadvantages can be achieved by delaying a switch of modes ofoperation until the later point in time t_1, or if the first point in timet_O is suitable for making this switch. This embodiment isparticularly advantageous when the computing power available forsimulation is limited, so that the frequency with which simulations can be carried out is consequently limited.

According to another embodiment of the invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C5, which is fulfilled when an expected gap d_sim_delayis smaller than said smallest allowable gap d_min. When thesmallest allowable gap d_min is smaller than the expected gapthan the d_sim_delay < d_min < d_sim, the conditions are optimal for d_sim and larger expected gap d_sim_delay,actuating a mode of operation that includes coasting. lf actuationis delayed, the motor vehicle will be at risk of coming too close tothe lead vehicle and braking will be necessary. lf on the other handcoasting is initiated as both the expected gaps d_sim andd_sim_delay are larger than the smallest allowable gap d_min, thevehicle may be at risk of coming too far from the lead vehicle if coasting is initiated.

According to another embodiment of the invention, the speed ofthe motor vehicle is initially controlled so as to maintain a specifiedgap d_set to the lead vehicle, wherein said specified gap d_set islarger than the smallest allowable gap d_min. This may preferably be achieved using an adaptive cruise control (ACC) system, which 12 is commonly used to control the powertrain when driving behind alead vehicle. The ACC system can in this embodiment be used tocontrol the powertrain to drive at the specified gap d_set, while itis continuously checked whether a temporary abandonment of thiscontrol can be made by instead actuating the simulated mode of operation, which may in the given situation be more fuel-efficient.

According to another embodiment of the invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C6, which is fulfilled when, at a point in time during theupcoming time period, a difference between the expected gapd_sim and a specified gap d_set is smaller than a first predefinedthreshold value, and a difference between an expected speedv_sim and an expected speed of the lead vehicle v_lead is smallerthan a second predefined threshold value. ln this case, theconditions are perfect for “docking” with the lead vehicle at thespecified gap d_set at the given point in time. The specified gapd_set is preferably the specified gap d_set which an ACC system of the motor vehicle is set to maintain to the lead vehicle.

According to another embodiment of the invention, said potentialmode of operation comprises coasting the vehicle during apredetermined initial time period, and thereafter motoring thevehicle at a highest available gear. Thus, if the motor vehicle is atrisk of coming too close to the lead vehicle if the vehicle is coastedduring a longer time period, advantages associated with coastingmay be obtained by actuating a mode of operation involving coasting followed by motoring. 13 According to another aspect of the invention, at least the primaryobjective is achieved by a computer program comprising computerprogram code for causing a computer to implement the proposed method when the computer program is executed in the computer.

According to a further aspect of the invention, at least the primaryobjective is achieved by a computer program product comprisinga non-transitory data storage medium which can be read by acomputer and on which the program code of the proposed computer program is stored.

According to a further aspect of the invention, at least the primaryobjective is achieved by an electronic control unit of a motorvehicle comprising an execution means, a memory connected tothe execution means and a data storage medium which isconnected to the execution means and on which the computer program code of the proposed computer program is stored.

According to a further aspect of the invention, at least the primaryobjective is achieved by a motor vehicle comprising the proposedelectronic control unit. The motor vehicle may preferably be a truck or a bus.

Other advantageous features as well as advantages of the present invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will in the following be described with reference to the appended drawings, in which: Fig.

Fig.

Fig.

Fig.

Fig.

Fig. 3a 3b 14 is a flow chart showing a method according to an embodiment of the invention, is a graph schematically showing results of a simulationcarried out in a method according to an embodiment of the invention, is another graph schematically showing results of asimulation carried out in a method according to an embodiment of the invention, is yet another graph schematically showing results of asimulation carried out in a method according to an embodiment of the invention, schematically shows a control unit according to the invenüon,and schematically shows a vehicle according to the invenüon.

DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION A method according to an embodiment of the present invention is schematically shown in the flow chart in fig. 1. The method is initiated in a motor vehicle as the vehicle is travelling forward behind a lead vehicle. Typically, a powertrain of the motor vehicle is initially controlled by an adaptive cruise control (ACC) system so that the vehicle maintains a specified gap d_set, in terms of either time or distance, to the lead vehicle.

A first step S1 comprises collecting data relating to a road gradientalong an expected travelling route ahead of the motor vehicle, aswill be further described later on. A second step S2 comprisescollecting data relating to a present size of a gap between themotor vehicle and the lead vehicle. A third step S3 comprisescollecting data relating to a speed of the lead vehicle. Data relatingto the road gradient, the gap and the speed of the lead vehicle are stored on a data storage medium.

A fourth step S4 comprises performing at least one simulationbased on the data collected in steps S1-S3 and on thepresumption that a potential mode of operation of the powertrain,which mode of operation involves coasting of the motor vehicle, isactuated at a point in time t_O. The simulation computes datarelating to the size of an expected gap d_sim between the vehiclesduring an upcoming time period following the point in time t_O.That is, it is simulated how the size of the gap between the vehiclesis expected to develop if a potential mode of operation is actuatedat the point in time t_O. The potential mode of operation involvescoasting of the motor vehicle at least during a part of the upcomingtime period. For example, the potential mode of operation mayinvolve initial coasting of the motor vehicle, and thereaftermotoring of the motor vehicle on a high gear. Several potential modes of operation may be simulated simultaneously.

A fifth step S5 comprises checking if the simulated data from step S4 fulfill a set of predefined actuation conditions. This set of 16 predefined actuation conditions includes at least one predefinedactuation condition C1, which is considered fulfilled when theexpected gap d_sim is larger than a preset smallest allowable gapd_min during said upcoming time period, preferably during theentire upcoming time period, the duration of which can be definedin advance. Thus, in the step S5, the simulated expected gapd_sim between the vehicles is compared to the preset smallestallowable gap d_min, acting as a threshold value. lf it is found thatthe gap is likely to exceed the smallest allowable gap d_min duringthe upcoming time period if the potential mode of operation isactuated, the actuation condition C1 is considered fulfilled. Theset of predefined actuation conditions may further include otherconditions, such as an actuation condition C2 that the expectedgap d_sim must be smaller than a preset largest allowable gapd_max during at least a part of the upcoming time period. Acondition C3, which is fulfilled when the expected gap d_sim is ina range between the smallest allowable gap d_min and the largestallowable gap d_max during at least a preset minimum time periodAt_min, and a condition C4, which is fulfilled when a simulatedspeed v_sim is within a preset allowable speed range between asmallest allowable speed v_min and a largest allowable speedv_max, may further be defined. The set of predefined actuation conditions may comprise all or some of these conditions C2-C4.

A sixth step S6 comprises actuating the simulated potential modeof operation at the point in time t_O, given that the predefinedactuation conditions have been fulfilled. Otherwise, in case theactuation conditions have not been fulfilled, steps S1-S5 canpreferably be repeated. ln the simplest case, the potential mode of operation is actuated given that condition C1 is fulfilled. ln 17 principle, this means that the motor vehicle is coasted given thatit is not at risk of coming too close to the lead vehicle. Step S6ends the method according to the invention. The decision to coast the vehicle is thereafter continuously reevaluated.

All steps S1-S5 are preferably carried out continuously, which ishere to be understood as that the steps are carried out with apredetermined frequency as long as the vehicle is travellingforward. The frequency of data collection and the frequency ofsimulation are not necessarily identical and can e.g. be in the orderof 100 Hz.

Data relating to the road gradient may in step S1 be collected invarious different ways. The road gradient may be determined one.g.information, in the basis of map data, from digital maps containing topographical combination with positioninginformation, e.g. GPS (global positioning system) information. Thepositioning information may be used to determine the location ofthe vehicle relative to the map data so that the road gradient canbe extracted from the map data. Various present-day cruise controlsystems use map data and positioning information. Such systemsmay then provide the map data and positioning informationrequired for the method according to the present invention, therebyminimising the additional complexity involved in determining the road gradient.

The road gradient may be obtained on the basis of a map inconjunction with GPS information, from radar information, fromcamera information, of information from another vehicle, frominformation and positioning road gradient information stored 18 previously on board, or from information obtained from trafficsystems related to the expected travelling route. ln systems wherethere is information exchange between vehicles, road gradientsestimated by one vehicle may also be made available to othervehicles, either directly or via an intermediate unit such as a data base or the like.

The data relating to the present size of the gap between thevehicles may in step S2 be collected using e.g. radar technology,camera information, map data in combination with GPS (global positioning system) technology, or the like.

Data relating to a speed of the lead vehicle may in step S3 becollected e.g. by measuring the speed or by communication withthe lead vehicle and from this information determining an expectedspeed of the lead vehicle during travel along the upcoming roadsection. This step may e.g. comprise measuring a current speedof the lead vehicle and making an assumption about its speedduring the upcoming road section or time period, such as assumingthat the assumption may also be based on knowledge about e.g. the road lead vehicle will maintain a constant speed. Thegradient along the upcoming road section, and/or on a present acceleration of the lead vehicle.

The simulation which computes data relating to the size of theexpected gap d_sim in step S4 is usually performed in steps bysimulating an expected future speed profile of the motor vehicle,and therefrom determining the development of the size of the gapby comparison with the data relating to the speed of the lead vehicle. ln the simulation of the future speed profile, the potential 19 mode of operation is assumed to be actuated at the point in timet_O. The simulated gap d_sim to the lead vehicle for an index k+1 can be simulated as: d_sim_k+1 = d_sim_k + (v_|ead - v_sim) * öT, wherein v_ lead is the speed of the lead vehicle, v_sim is thesimulated speed of the motor vehicle, and wherein öT is the time step used in the simulation. lf the computing power is limited in the vehicle, the frequency withwhich simulations can be repeated is also limited. ln this case, itis possible to make an additional simulation simultaneously withthe previously discussed simulation. This additional simulation isbased on the presumption that the potential mode of operation ofthe powertrain is actuated at a point in time t_1, which point in timet_1 is delayed with respect to the point in time t_O. The additionalsimulation computes data relating to an expected gap d_sim_delaybetween the vehicles, i.e. the development of the gap between thevehicles given that the same potential mode of operation isactuated at the later point in time t_1. The set of predefinedactuation conditions may in this case comprise a predefinedactuation condition C5, which is fulfilled when the expected gapd_sim_delay is smaller than the smallest allowable gap d_min. lnother words, both conditions C1 and C5 are fulfilled if the gapbetween the vehicles is expected to be smaller than the smallestallowable gap d_min if the potential mode of operation is actuatedat the point in time t_1, but larger if it is actuated at the point in time t_O.

The set of predefined actuation conditions may also comprise apredefined actuation condition C6, which is considered fulfilledwhen, at a point in time during the upcoming time period, adifference between the expected gap d_sim and a specified gapd_set is smaller than a first predefined threshold value, and adifference between an expected speed v_sim and an expectedspeed of the lead vehicle v_lead is smaller than a second predefined threshold value. ln one example, the method according to an embodiment of theinvention is carried out in a motor vehicle travelling along a roadsection behind a lead vehicle. ln a present mode of operation, thepowertrain of the motor vehicle is controlled by an ACC system.The speed of the vehicle is therefore automatically adjusted tomaintain a specified gap d_set to the lead vehicle. As the vehicledrives along the road section, data relating to the road gradientalong the expected travelling route ahead of the motor vehicle arecontinuously collected using a map in conjunction with a GPSsystem (step S1). Simultaneously, data relating to the present sizebetween the motor vehicle and the lead vehicle are collected usingradar technology (step S2). Data relating to the speed of the leadvehicle are also collected (step S3), which data are obtained bydetermining a present speed of the lead vehicle, and making anassumption that the lead vehicle will be travelling at a constant speed. All the collected data are stored in a database. ln a processing unit of the vehicle, the collected data are used tocontinuously, i.e. at a set frequency of e.g. 1 Hz, simulate how thesize of the gap between the vehicles is expected to develop during an upcoming time period for a number of different scenarios (step 21 S4) in which a potential mode of operation of the powertraininvolving coasting of the motor vehicle is initiated at a point in timet_O. After the simulation, it is assessed whether a number of presetactuation conditions are fulfilled (step S5). lf all preset actuationconditions are fulfilled, the potential mode of operation is actuated(step S6). ln the example, shown in fig. 2, the motor vehicle is travelling ona downhill road section at a set speed v_set, corresponding to aspecified gap d_set to a lead vehicle, as the motor vehicleapproaches an uphill road section. Brakes are engaged during thedownhill road section to maintain the specified gap d_set. The leadvehicle is assumed to travel at a constant speed v_lead.Simulations of the expected gap d_sim carried out with a certainfrequency during travel along the downhill road section have so farrevealed that the preset actuation condition C1 has not beenfulfilled, since the vehicle has been at risk of coming too close tothe lead vehicle if a mode of operation involving coasting was tobe actuated. ln the graph, the dashed lines show results of asimulation carried out on a first occasion T1, wherein the uppergraph shows the simulated expected speed v_sim_1 of the motorvehicle and the lower graph shows the simulated expected gapd_sim_1, which is clearly smaller than the smallest allowable gapd_min during a part of the upcoming time period. The potentialmode of operation is therefore not actuated in response to the assessment carried out in step S5.

Now, as the uphill road section approaches even more, thesimulations are repeated on an occasion T2. The simulated speed v_sim_2 and the simulated gap d_sim_2 are shown as solid lines 22 in fig. 2. The simulations carried out on occasion T2, and asubsequent comparison with the predefined set of actuationconditions, reveal that the simulated expected gap d_sim exceedsthe preset smallest allowable gap d_min if the brakes aredisengaged and the mode of operation involving coasting isactuated. Therefore, the simulated potential mode of operation isactuated, resulting in a speed increase in comparison with theinitial mode of operation, in which the powertrain is controlled bythe ACC system. ln a continuation of the inventive method, it iscontinuously evaluated whether to continue controlling thepowertrain in the actuated mode of operation or whether to switchto another mode of operation, such as controlling the powertrain using the ACC system.

Another example is shown in fig. 3a. ln this example, a motorvehicle is travelling on a level road section at a set speed v_set,corresponding to a set distance d_set to a lead vehicle, as themotor vehicle approaches a downhill road section followed by anuphill road section. As the vehicle is travelling along the level roadsection, an ACC system is used to control a powertrain of thevehicle and a driving force is applied via the powertrain. At oneoccasion, data is collected according to step S1-S3, and asimulation according to step S4 is carried out, simulating that amode of operation in which the motor vehicle is coasted is actuatedat the time t_O. The simulated expected speed v_sim and thesimulated expected gap d_sim are shown with dashed lines in theupper and lower graphs, respectively. Simultaneously, it issimulated that coasting of the vehicle would instead be initiated atthe time t_1, which is delayed with respect to t_O. The simulated expected speed v_sim_delay and the simulated expected gap 23 d_sim_de|ay are shown with solid lines in the upper and lowergraphs, respectively. As can be seen from the graphs, coasting thevehicle will involve an initial speed reduction followed by a speedincrease as the vehicle gains momentum on the downhill roadsection, and a subsequent speed reduction as the vehicle comesonto the uphill road section. lnitiating coasting at the time t_Omeans that the smallest allowable gap d_min will be exceededduring the entire upcoming time period, so that the predefinedactuation condition C1 is fulfilled. lf instead initiating coasting att_1, the motor vehicle will come too close to the lead vehicle. Thus,both predefined conditions C1 and C5 are fulfilled. ln the shownexample, a largest allowable gap d_max has also been defined,which the simulated expected gap d_sim is not allowed to exceed.Furthermore, a condition C6 is fulfilled at the point in time t_C6, atwhich the expected speed v_sim of the motor vehicle coincideswith the speed v_lead of the lead vehicle, and at which theexpected gap d_sim coincides with the specified gap d_set. Thus,the conditions for docking with the lead vehicle at the point in timet_C6 are optimal if initiating coasting at the point in time t_O. lnthis example, coasting of the vehicle is therefore initiatedimmediately after the simulations and a subsequent comparisonwith the predefined set of actuation conditions have been carried out, i.e. at a point in time corresponding to t_O. ln yet another example, shown in fig. 3b, a motor vehicle isapproaching a lead vehicle. A powertrain of the motor vehicle is inthis example initially controlled using a cruise control system tomaintain a set speed, and a driving force is applied via thepowertrain. As the motor vehicle approaches the lead vehicle, it is simulated how a switch to coasting would affect the gap between 24 the vehicles if initiated at a point in time t_0 (dashed lines) or ifinitiated at a later point in time t_1 (solid lines), delayed withrespect to t_0. As can be seen, if initiating coasting immediately,the vehicle will be at no risk of coming too close to the lead vehicle,but if waiting until the time t_1, the vehicle will come too close tothe lead vehicle and it may be necessary to brake. Thus, a switchto coasting is carried out at the time t_0. The vehicle can therebybe coasted until it reaches a desired gap to the lead vehicle, after which the powertrain may be controlled using an ACC system.

One skilled in the art will appreciate that a method for controllingthe powertrain of a motor vehicle according to the presentinvention may be implemented in a computer program which, whenexecuted in a computer, causes the computer to conduct themethod. The computer program usually takes the form of acomputer program product which comprises a suitable digitalstorage medium on which the computer program is stored. Saidcomputer-readable digital storage medium comprises a suitablememory, e.g. ROM (read-only memory), PROM (programmableread-only memory), EPROM (erasable PROM), flash memory,EEPROM (electrically erasable PROM), a hard disc unit, etc.

Fig. 4 depicts schematically an electronic control unit 400 of avehicle provided with an execution means 401 which may take theform of substantially any suitable type of processor ormicrocomputer, e.g. a circuit for digital signal processing (digitalsignal processor, DSP), or a circuit with a predetermined specificASIC). The execution means 401 is connected to a memory unit 402 which is function (application specific integrated circuit, situated in the control unit 400. A data storage medium 403 is also connected to the execution means and provides the executionmeans with, for example, the stored program code and/or storedit to do calculations. The execution means is also adapted to storing data which the execution means needs to enable partial or final results of calculations in the memory unit 402.

The control unit 400 is further provided with respective devices411, 412, 413, 414 for receiving and sending input and outputsignals. These input and output signals may comprise waveforms,pulses or other attributes which the input signal receiving devices411, 413 can detect as information and which can be converted tosignals which the execution means 401 can process. Thesesignals are then supplied to the execution means. The outputsignal sending devices 412, 414 are arranged to convert signalsreceived from the execution means 401, in order to create, e.g. bymodulating them, output signals which can be conveyed to other parts of the vehicle and/or other systems on board.

Each of the connections to the respective devices for receivingand sending input and output signals may take the form of one ormore from among a cable, a data bus, e.g. a CAN (controller areanetwork) bus, a MOST (media orientated systems transport) busor some other bus configuration, or a wireless connection. Oneskilled in the art will appreciate that the aforesaid computer maytake the form of the execution means 401 and that the aforesaid memory may take the form of the memory unit 402.

Control communication systems in modern vehicles generally comprise a bus system consisting of one or more communication buses for connecting together a number of 26 electronic control units (ECUs), or controllers, and various components on board the vehicle. Such a control system maycomprise a large number of control units and the responsibility for a specific function may be divided between two or more of them. ln the embodiment depicted, the present invention is implementedin the control unit 400 but might also be implemented wholly orpartly in one or more other control units already on board thevehicle or a control unit dedicated to the present invention.Vehicles of the type here concerned are of course often providedwith significantly more control units than shown here, as one skilled in the art will surely appreciate.

The present invention according to one aspect relates to a motorvehicle 500 which is schematically shown in Fig. 5. The motorvehicle 500 comprises an engine 501 forming part of a powertrain502 which drives driving wheels 503, 504. The motor vehicle 500further comprises an exhaust treatment system 505, and a controlunit 510, which corresponds to the above-mentioned control unit400 in Fig. 4, and which is arranged to control the function in the engine 501.

The invention is of course not in any way restricted to theembodiments described above. On the contrary, many possibilitiesto modifications thereof will be apparent to a person with ordinaryskill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims (14)

1 _

1. A method for controlling a powertrain of a motor vehicle travelling behind a lead vehicle, comprising the steps of: (a) (b) (C)(d) (e) (f)

2. collecting data relating to a road gradient along anexpected travelling route ahead of the motor vehicle,collecting data relating to a present size of a gap betweenthe motor vehicle and the lead vehicle, collecting data relating to a speed of the lead vehicle,performing at least one simulation based on said data andon the presumption that a potential mode of operation ofthe powertrain, involving coasting of the motor vehicle, isactuated at a first point in time t_O, wherein the simulationcomputes data relating to the size of an expected gapd_sim between the vehicles during an upcoming timeperiod following said first point in time t_O, checking if the simulated data from step (d) fulfill a set ofpredefined actuation conditions including at least onepredefined actuation condition C1, which is fulfilled whenthe expected gap d_sim is larger than a preset smallestallowable gap d_min during said upcoming time period,given that said set of predefined actuation conditions isfulfilled, actuating said potential mode of operation at said first point in time t_O. The method according to claim 1, wherein said set of predefined actuation conditions comprises a predefined actuation condition C2, which is fulfilled when the expected gap d_sim is smaller than a preset largest allowable gap d_max during at least a part of said upcoming time period. 28

3. The method according to claim 2, wherein said set ofpredefined actuation conditions comprises a predefined actuationcondition C3, which is fulfilled when the expected gap d_sim is ina range between the smallest allowable gap d_min and the largestallowable gap d_max during at least a preset minimum time period At_min.

4. The method according to any one of the preceding claims,wherein step (d) comprises simulating a future speed profile of themotor vehicle, and based thereon computing the size of said expected gap d_sim.

5. The method according to claim 4, wherein said set ofpredefined actuation conditions comprises a predefined actuationcondition C4, which is fulfilled when a simulated speed v_sim iswithin a preset allowable speed range between a smallest allowable speed v_min and a largest allowable speed v_max.

6. The method according to any one of the preceding claims,wherein step (d) further comprises performing at least onesimulation based on the presumption that said potential mode ofoperation of the powertrain is actuated at a later point in time t_1,which later point in time t_1 is delayed with respect to the firstpoint in time t_O, wherein the simulation computes data relating to an expected gap d_sim_delay between the vehicles.

7. The method according to claim 6, wherein said set of predefined actuation conditions comprises a predefined actuation 29 condition C5, which is fulfilled when the expected gap d_sim_de|ay is smaller than said smallest allowable gap d_min.

8. The method according to any one of the preceding claims,wherein the speed of the motor vehicle is initially controlled so asto maintain a specified gap d_set to the lead vehicle, wherein saidspecified gap d_set is larger than the smallest allowable gap d_min.

9. The method according to any one of claims 4-8, wherein saidset of predefined actuation conditions comprises a predefinedactuation condition C6, which is fulfilled when, at a point in timeduring the upcoming time period, a difference between theexpected gap d_sim and a specified gap d_set is smaller than afirst predefined threshold value, and a difference between anexpected speed v_sim and an expected speed of the lead vehicle v_lead is smaller than a second predefined threshold value.

10. The method according to any one of the preceding claims,wherein said potential mode of operation comprises coasting thevehicle during a predetermined initial time period, and thereafter motoring the vehicle at a highest available gear.

11. A computer program comprising computer program code forcausing a computer to implement a method according to any oneof the claims 1-10 when the computer program is executed in the computer.

12. A computer program product comprising a non-transitory data storage medium which can be read by a computer and on which the program code of a computer program according to claim 11 is stored.

13. An electronic control unit (400) of a motor vehicle comprisingan execution means (401), a memory (402) connected to theexecution means (401) and a data storage medium (403) which isconnected to the execution means (401) and on which thecomputer program code of a computer program according to claim 11 is stored.

14. A motor vehicle (500) comprising an electronic control unit(400, 510) according to claim13.