SE1551396A1 - A method for controlling a powertrain of a motor 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 application of less driving force or more braking force in comparison with a reference mode of operation, 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 smaller 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 controllinq a powertrain of a motor 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 acruise control which adjusts the speed to topographical data, or amode in which the driver is controlling the vehicle in a specific wayso 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, such that the benefits of an ACC system can be combinedwith the benefits of other fuel-economising systems. Anotherobjective is to improve the driving comfort when travelling behinda lead vehicle and provide a way of avoiding sudden braking in such situations.

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 application of less driving force or morebraking force in comparison with a reference mode of operation isactuated at a predetermined point in time, wherein the simulationcomputes data relating to the size of an expected gap d_simbetween the vehicles during an upcoming time period, (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 the expected gapd_sim is smaller than a preset smallest allowable gap d_min duringat least a part of said upcoming time period, (f) given that said set of predefined actuation conditions is fulfilled, actuating said potential mode of operation.

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 application of less driving force or more braking force in comparison with a reference mode of operation during at least a part of the upcoming time period, and preferably during an initialpart of said upcoming time period. The reference mode ofoperation is preferably one in which the powertrain is controlled so that a specified gap d_set to the lead vehicle is maintained. lf the gap between the vehicles is expected to become smallerthan the predefined smallest allowable gap d_min, i.e. the motorvehicle is expected to come closer to the lead vehicle than desired,the simulated mode of operation is immediately actuated. lnpractice, this may result in that brakes are applied, e.g. wheelbrakes, a retarder, an exhaust brake, etc., or in that the vehicle ismotored or coasted instead of propelled forward with a positivedriving force applied via the powertrain. The simulation revealswhether the motor vehicle is at risk of coming too close to the leadvehicle at some point during the upcoming time period, even if thesimulated mode of operation is actuated. However, if the simulatedpotential mode of operation is not actuated and the powertrain iscontinuously controlled according to the reference mode ofoperation, the motor vehicle will come even closer to the leadvehicle and will need to be braked later on, potentially wastingmore kinetic energy than would be the case if the simulatedpotential mode of operation is immediately actuated. By means ofthe method according to the invention, the fuel efficiency of thevehicle can thereby be improved. At the same time, the drivingcomfort is improved, since sudden braking is prevented. Byrepeating data collection and simulation with a certain frequency,it can be checked continuously whether a switch to a mode ofoperation involving increased braking force or reduced driving force is necessary.

The point in time at which the motor vehicle is at risk of comingtoo close to the lead vehicle may be after an initial time period during which the gap to the lead vehicle is acceptable.

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. Thesimulation is based on a potential mode of operation, which in thiscase is a mode of operation that involves application of less drivingforce or more braking force in comparison with a reference modeSeveral of operation. different modes of operation may be simulated simultaneously.

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 gapd_min can be set in dependence on the specified gap d_set. lf abraking 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.ln this way, situations in which the brakes have to be applied bythe ACC system are prevented. Of course, also safety aspectsinfluence the size of the smallest allowable gap d_min. Comparing the simulated gap to the preset smallest allowable gap is a fast and efficient way of deciding whether the vehicle is at risk of coming too close to the lead vehicle.

According to one embodiment of the invention, the powertrain is inthe reference mode of operation controlled by an adaptive cruisecontrol, such that the speed of the motor vehicle is regulated tomaintain a specified gap d_set to the lead vehicle. This is veryuseful, since the adaptive cruise control is commonly used tocontrol the powertrain when driving behind a lead vehicle. ln thisembodiment, such a mode of operation can be used to control thepowertrain while continuously checking whether it would bepreferable to actuate a mode of operation involving less drivingforce or more braking force, and temporarily depart from the reference mode of operation if this is judged as useful.

According to one embodiment of the present invention, saidpotential mode of operation involves at least one of motoring ofthe motor vehicle, coasting of the motor vehicle, reducing anengine torque, reducing the driving force by shifting to a highergear, and braking of the motor vehicle. Braking may be achievedby applying e.g. wheel-brakes, a retarder, an exhaust brake, etc.The current mode of operation of the powertrain may be used todetermine which modes of operation that are to be simulated. Eachsimulated mode of operation may involve more than one of the listed ways of operating the powertrain.

According to one embodiment of the present invention, saidpotential mode of operation involves braking of the motor vehiclefollowed by motoring of the motor vehicle. By braking before motoring, a speed difference between the vehicles is quickly reduced. The total motoring time, during which no fuel is consumed, can thereby be increased in comparison with asituation in which the vehicle is first motored, and thereafterbraked when coming too close to the lead vehicle. The overall energy consumption can thereby be reduced.

According to one embodiment of the present 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 an initialpart of said upcoming time period. lt is thus ensured that areduction in driving force or an increase in braking force will notbe at risk of removing the motor vehicle too far from the leadvehicle, such that e.g. overtaking vehicles may enter between the vehicles.

According to one embodiment of the present invention, step (d)comprises performing at least two simulations, wherein one of saidsimulations is based on the presumption that said potential modeof operation of the powertrain is actuated at a first point in timet O, presumption and another one of said simulations is based on the 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. Thesame collected data are used as a basis for the simulation, andthe simulations are performed simultaneously. The additionalsimulation reveals if any advantages can be achieved by delayinga switch of modes of operation until the later point in time t_1, orif the first point in time t_O is suitable for making this switch. This embodiment is particularly advantageous when the computing 11 power available for simulation is limited, so that the frequency with which simulations can be carried out is consequently limited.

According to one embodiment of the present invention, said set ofpredefined actuation conditions comprises a predefined actuationcondition C3, which is fulfilled when an expected gap d_sim_O,computed based on the presumption that the potential mode ofoperation is actuated at the first point in time t_O, is larger thansaid smallest allowable gap d_min during the upcoming timeperiod, and when an expected gap d_sim_1, computed based onthe presumption that the potential mode of operation is actuatedat the later point in time t_1, is smaller than said smallest allowablegap d_min during at least a part of said upcoming time period,preferably wherein step (f) is carried out at a point in time beforesaid later point in time t_1, such as at a point in time correspondingto said first point in time t_O. ln this embodiment, the risk of comingtoo close to the lead vehicle can be avoided, since the simulationsreveal that he vehicle will come too close if the potential mode ofoperation including more braking force or less driving force isactuated after a delay. By actuating the potential mode ofoperation immediately, or at a point in time before said later pointin time t_1, such a situation is prevented. ln one embodiment, anoptimal point in time for actuating the potential mode of operation,occurring between the first point in time t_O and the later point intime t_1, can be determined and the potential mode of operation can be actuated at that optimal point in time.

According to one embodiment of the present invention, step (d)comprises simulating a future speed profile of the motor vehicle, and based thereon computing the size of said expected gap d_sim. 12 The simulated speed profile is compared to the data relating to thespeed of the lead vehicle and the size of the gap can thereby beobtained. Simulations of a future speed profile usually taketopographic data into account and may also take traffic data etc.into account. Such simulation methods are known and oftencarried out in the vehicle for other reasons, and this is therefore asuitable way of simulating the size of the gap during the upcoming time period.

Preferably, said set of predefined actuation conditions comprisesa predefined actuation condition C4, which is fulfilled when asimulated speed v_sim is larger than a smallest allowable speedv_min during the upcoming time period. lt can in this way beavoided that the speed of the vehicle drops below a desired minimum speed.

According to one embodiment of the present invention, the speedof the motor vehicle is initially controlled so as to maintain aspecified gap d_set to the lead vehicle, wherein said specified gapd_set is larger than the smallest allowable gap d_min. This maypreferably be achieved using an adaptive cruise control (ACC)system, which is commonly used to control the powertrain whendriving behind a lead vehicle. The ACC system can in thisembodiment be used to control the powertrain to drive at thespecified gap d_set, while it is continuously checked whether atemporary abandonment of this control should be made by insteadactuating the simulated mode of operation, which may in the given situation be more fuel-efficient. 13 According to one embodiment of the present invention, step (d)comprises simulating a future speed profile of the motor vehicle,and said set of predefined actuation conditions comprises apredefined actuation condition C5, which is fu|fi||ed when, at apoint in time during the upcoming time period, a differencebetween the expected gap d_sim and a specified gap d_set issmaller than a first predefined threshold value, and a differencebetween an expected speed v_sim and an expected speed of thelead vehicle v_lead is smaller than a second predefined thresholdvalue. ln this case, the conditions are perfect for “docking” withthe lead vehicle at the specified gap d_set at the given point intime. The specified gap d_set is preferably the specified gap d_setwhich an ACC system of the motor vehicle is set to maintain to the lead vehicle.

According to one embodiment of the present invention, steps (a)-(e) are carried out continuously at a predetermined frequencyduring forward travel of the motor vehicle. By repeating datacollection and simulation with a certain frequency, it can bechecked continuously whether a switch to a mode of operationinvolving application of more braking force or less driving force is desirable.

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 primary objective is achieved by a computer program product comprising 14 a 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. 1 is a flow chart showing a method according to anembodiment of the invention,Fig. 2 is a graph schematically showing results of a simulation carried out in a method according to an embodiment of the invention, Fig. 3 is another graph schematically showing results of asimulation carried out in a method according to anembodiment of the invention, Fig. 4 schematically shows a control unit according to theinvenüon,and Fig.5 schematically shows a vehicle according to the invenüon.

DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION A method according to an embodiment of the present invention isschematically shown in the flow chart in fig. 1. The method isinitiated in a motor vehicle as the vehicle is travelling forwardbehind a lead vehicle. Typically, a powertrain of the motor vehicleis initially controlled by an adaptive cruise control (ACC) systemso 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 comprises collecting data relating to a speed of the lead vehicle. Data relating 16 to 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 application of less driving forceor more braking force in comparison with a reference mode ofoperation, is actuated at a predetermined point in time. Thesimulation computes data relating to the size of an expected gapd_sim between the vehicles during an upcoming time periodfollowing the predetermined point in time. That is, it is simulatedhow the size of the gap between the vehicles is expected todevelop if a potential mode of operation is actuated at thepredetermined point in time. The potential mode of operationinvolves application of less driving force or more braking force withrespect to a reference mode of operation at least during a part ofthe upcoming time period. For example, the potential mode ofoperation may involve initial braking of the motor vehicle, andthereafter motoring of the motor vehicle. The potential mode ofoperation can e.g. include at least one of motoring of the motorvehicle, coasting of the motor vehicle, reducing an engine torque,reducing the driving force by shifting to a higher gear, and brakingof the motor vehicle. Several potential modes of operation may be simulated simultaneously.

Typically, the reference mode of operation is a case in which thepowertrain is 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. 17 A fifth step S5 comprises checking if the simulated data from stepS4 fulfill a set of predefined actuation conditions. This set ofpredefined actuation conditions includes at least one predefinedactuation condition C1, which is considered fulfilled when theexpected gap d_sim is smaller than a preset smallest allowablegap d_min during at least a part of said upcoming time period.Thus, in the step S5, the simulated expected gap d_sim betweenthe vehicles is compared to the preset smallest allowable gapd_min, acting as a threshold value. lf it is found that the gap islikely to fall below the smallest allowable gap d_min at some pointin time during the upcoming time period if the potential mode ofoperation is actuated, the actuation condition C1 is consideredfulfilled. The set of predefined actuation conditions may furtherinclude other conditions, such as an actuation condition C2 thatthe expected gap d_sim must be smaller than a preset largestallowable gap d_max during an initial part of the upcoming timeperiod. Also other actuation conditions may be defined, as will be further described later on.

A sixth step S6 comprises actuating the simulated potential modeof operation, given that the predefined actuation conditions havebeen fulfilled. Otherwise, in case the actuation conditions have notbeen fulfilled, steps S1-S5 can preferably be repeated. ln thesimplest case, the potential mode of operation is actuated giventhat condition C1 is fulfilled. ln principle, this means that thedriving force is reduced or the braking force is increased given thatthe motor vehicle is at risk of coming too close to the lead vehicle during the upcoming time period. Step S6 ends the method 18 according to the invention. The decision to adjust the driving force or braking force 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 trave||ingforward. 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, frompositioning information and road gradient information storedpreviously on board, or from information obtained from traffic systems related to the expected trave||ing route. ln systems where 19 there 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 leadvehicle. ln the simulation of the future speed profile, the potential mode of operation is assumed to be actuated at the predetermined point in time. 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_|ead 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 two simulations simultaneously. One of thesimulations is based on the presumption that the potential modeof operation of the powertrain is actuated at a point in time t_O.The other simulation is based on the presumption that the samepotential mode of operation of the powertrain is actuated at a pointin time t_1, which point in time t_1 is delayed with respect to thepoint in time t_O. This simulation computes data relating to anexpected gap d_sim_1 between the vehicles, i.e. the developmentof the gap between the vehicles given that the same potentialmode of operation is actuated at the later point in time t_1. Theset of predefined actuation conditions may in this case comprise apredefined actuation condition C3. This condition is consideredfulfilled when an expected gap d_sim_O, computed based on thepresumption that the potential mode of operation is actuated at thepoint in time t_O, is larger than the smallest allowable gap d_minduring the upcoming time period, and when an expected gapd_sim_1, computed based on the presumption that the potentialmode of operation is actuated at the point in time t_1, is smaller than the smallest allowable gap d_min during at least a part of the 21 upcoming time period. lf this condition is fulfilled, the potentialmode of operation is actuated at a point in time corresponding tothe point in time t_O, i.e. immediately after the simulation isperformed. Both conditions C1 and C3 are considered fulfilled ifthe gap between the vehicles is expected to be smaller than thesmallest allowable gap d_min if the potential mode of operation isactuated at 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 C4, which is fulfilled when asimulated speed v_sim is larger than a smallest allowable speed v_min during the upcoming time period.

The set of predefined actuation conditions may also comprise apredefined actuation condition C5, 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 vehicle drives along the road section, data relating to the road gradient 22 along 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 duringan upcoming time period for a number of different scenarios (stepS4) in which a potential mode of operation of the powertraininvolving application of less driving force or more braking force incomparison with the present mode of operation, is initiated at apredetermined point in time. After the simulation, it is assessedwhether a number of preset actuation conditions are fulfilled (stepS5). lf all preset actuation conditions are fulfilled, the potential mode of operation is actuated (step S6). ln the example, shown in fig. 2, a motor vehicle is travelling on alevel road section at a set speed v_set, corresponding to a setdistance d_set to a lead vehicle, as the motor vehicle approachesa downhill road section followed by an uphill road section. As thevehicle is travelling along the level road section, an ACC systemis used to control a powertrain of the vehicle and a driving force isapplied via the powertrain. Data is collected according to step S1- S3, and a simulation according to step S4 is carried out, simulating 23 that a mode of operation in which the motor vehicle is coasted,thus involving application of less driving force, is actuated at a firstpoint in time t_O. The simulated expected speed v_sim_O and thesimulated expected gap d_sim_O are shown with dashed lines inthe upper and lower graphs, respectively. Simultaneously, it issimulated that coasting of the vehicle would instead be initiated ata later point in time t_1, which is delayed with respect to t_O. Thesimulated expected speed v_sim_1 and the simulated expectedgap d_sim_1 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, while if coasting is initiatedat the time t_1, the motor vehicle will come too close to the leadvehicle at one point during the upcoming time period. ConditionC1 is thus fulfilled. Moreover, condition C3 is fulfilled, since thegap between the vehicles is expected to be smaller than thesmallest allowable gap d_min if coasting is initiated at the firstpoint in time t_1, but larger if it is actuated at the later point in timet O. ln the shown example, a largest allowable gap d_max has alsobeen defined, which the simulated expected gap d_sim is notallowed to exceed during an initial part of the upcoming time period(condition C2). This condition is fulfilled. Furthermore, a conditionC5 is fulfilled at the point in time t_C5, at which the expected speed v_sim of the motor vehicle coincides with the speed v_lead of the 24 lead vehicle, and at which the expected gap d_sim coincides withthe specified gap d_set. Thus, the conditions for docking with thelead vehicle at the point in time t_C5 are optimal if initiatingcoasting at the point in time t_O. ln this example, coasting of thevehicle is therefore initiated immediately after the simulations anda subsequent comparison with the predefined set of actuationin time conditions have been carried out, i.e. at a point corresponding to the first point in time t_O. ln another example, shown in fig. 3, a motor vehicle is approachinga lead vehicle. A powertrain of the motor vehicle is in this exampleinitially controlled using a cruise control system to maintain a setspeed, and a driving force is applied via the powertrain. As themotor vehicle approaches the lead vehicle, it is simulated how aswitch to coasting would affect the gap between the vehicles ifinitiated at a first point in time t_O (dashed lines) or if initiated ata later point in time t_1 (solid lines), delayed with respect to t_O.As can be seen, if initiating coasting immediately, the vehicle willbe at no risk of coming too close to the lead vehicle, but if waitinguntil the time t_1, the vehicle will come too close to the lead vehicleand it may be necessary to brake. Thus, a switch to coasting iscarried out at the time t_O. The vehicle can thereby be coasteduntil it reaches a desired gap to the lead vehicle, after which thepowertrain may be controlled using an ACC system. ln the shownexample, the conditions for docking with the lead vehicle areoptimal when the speed of the lead vehicle v_lead and the speedof the motor vehicle v_sim_O are expected to coincide. At thispoint, the expected gap d_sim_O between the vehicles is just above the smallest allowable gap d_min.

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 alsoconnected 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 devices 26 411, 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 ofunits (ECUs), components on board the vehicle. electronic control or controllers, and variousSuch 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 provided 27 with 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 (15)

1 _
1. A method for controlling a powertrain of a motor vehicle travelling behind a lead vehicle, comprising: (a) (b) (C)(d) (e) (f)
2. 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 application of less driving forceor more braking force in comparison with a reference modeof operation is actuated at a predetermined point in time,wherein the simulation computes data relating to the sizeof an expected gap d_sim between the vehicles during anupcoming time period, 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 smaller than a preset smallestallowable gap d_min during at least a part of saidupcoming time period, given that said set of predefined actuation conditions is fulfilled, actuating said potential mode of operation. The method according to claim 1, wherein the powertrain in the reference mode of operation is controlled by an adaptive cruise control system, such that the speed of the motor vehicle is regulated to maintain a specified gap d_set to the lead vehicle. 29
3. 3. The method according to claim 1 or 2, wherein said potentialmode of operation involves at least one of motoring of the motorvehicle, coasting of the motor vehicle, reducing an engine torque,reducing the driving force by shifting to a higher gear, and brakingof the motor vehicle.
4. 4. The method according to any one of the preceding claims,wherein said potential mode of operation involves braking of the motor vehicle followed by motoring of the motor vehicle.
5. 5. The method according to any one of the preceding claims,wherein said set of predefined actuation conditions comprises apredefined actuation condition C2, which is fulfilled when theexpected gap d_sim is smaller than a preset largest allowable gap d_max during an initial part of said upcoming time period.
6. 6. The method according to any one of the preceding claims,wherein step (d) comprises performing at least two simulations,wherein one of said simulations is based on the presumption thatsaid potential mode of operation of the powertrain is actuated at afirst point in time t_O, and another one of said simulations is basedon the presumption that said potential mode of operation of thepowertrain is actuated at a later point in time t_1, which later point in time t_1 is delayed with respect to the point in time t_O.
7. 7. The method according to claim 6, wherein said set ofpredefined actuation conditions comprises a predefined actuationcondition C3, which is fulfilled when an expected gap d_sim_O, computed based on the presumption that the potential mode of operation is actuated at the first point in time t_O, is larger thansaid smallest allowable gap d_min during the upcoming timeperiod, and when an expected gap d_sim_1, computed based onthe presumption that the potential mode of operation is actuatedat the first point in time t_1, is smaller than said smallest allowablegap d_min during at least a part of said upcoming time period,preferably wherein step (f) is carried out at a point in time beforesaid later point in time t_1, such as at a point in time corresponding to said first point in time t_O.
8. 8. 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 saidexpected gap d_sim, preferably wherein said set of predefinedactuation conditions comprises a predefined actuation conditionC4, which is fulfilled when a simulated speed v_sim is larger thana smallest allowable speed v_min during the upcoming time penod.
9. 9. 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.
10. 10. The method according to any one of the preceding claims,wherein step (d) comprises simulating a future speed profile of themotor vehicle, and wherein said set of predefined actuationconditions comprises a predefined actuation condition C5, which is fulfilled when, at a point in time during the upcoming time period, 31 a difference 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.
11. 11. The method according to any one of the preceding claims, (HHS) predetermined frequency during forward travel wherein steps are carried out continuously at aof the motor vehicle.
12. 12. A computer program comprising computer program code forcausing a computer to implement a method according to any oneof the claims 1-11 when the computer program is executed in the computer.
13. 13. A computer program product comprising a non-transitorydata storage medium which can be read by a computer and onwhich the program code of a computer program according to claim 12 is stored.
14. 14. 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 12 is stored.
15. 15. A motor vehicle (500) comprising an electronic control unit(400, 510) according to claim14.