SE540825C2 - A method and a system 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.

Description

A method and a system for controlling a powertrain of a vehicle TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for controlling a powertrain of a motor vehicle travelling behind a lead vehicle. The invention further relates to a computer program, a computer program product, an electronic control unit, and a motor vehicle. By a motor vehicle is here intended a vehicle which is powered by an internal combustion engine and/or by an electric motor. In particular, 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 be understood as e.g. a mode in which the powertrain is controlled by a cruise control, such as an adaptive cruise control (ACC) or a fuel-economising cruise control, or a mode in which the driver is controlling 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 forward without transmitting any power via the powertrain, such as by means 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 with a 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 the vehicle. A wide variety of different systems have therefore been developed for reducing fuel consumption, e.g. fuel-efficient engines and fuel-economising cruise controls. Such fueleconomising cruise controls aim to reduce fuel consumption by adjusting the driving to the characteristics of the road ahead, so that unnecessary braking and/or fuel-consuming acceleration may be avoided. For example, by taking topographic information about the road section ahead of the vehicle into account, the speed may be temporarily increased before e.g. an uphill slope, so that downshifting to a lower transmission mode can be avoided or delayed. In 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 a vehicle, in particular at high speeds and for large motor vehicles having a large front area, is air resistance. A way to reduce the air resistance, and thereby the energy consumption, is therefore to drive behind a lead vehicle, i.e. another vehicle travelling ahead of 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 to measure a distance to a lead vehicle. Some vehicles can also be equipped with a control system to automatically maintain a specified gap d_set to a lead vehicle, as long as the speed of the vehicle does not exceed a set speed, such as a legal speed limit. Such a control system is usually referred to as an Adaptive Cruise Control (ACC), a Radar Cruise Control, or an Autonomous Cruise Control system. According to one example, such a system can comprise an actuating device with which the driver can manually set a position that corresponds to a given gap to a lead vehicle. Such an actuating device can e.g. have five different positions that correspond to discrete increments of distance to the lead vehicle between 10 and 75 meters, corresponding to time gaps within the range of 1-4 seconds. This system is usually automated in the trailing 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 specified gap d_set by application of the necessary driving force or braking force, i.e. so that a driving force is applied if the gap becomes larger than the specified gap d_set, and so that brakes are applied as soon as the gap becomes smaller than d_set. However, an ACC system may also be configured to maintain the specified gap d_set only by controlling the driving force transmitted by the powertrain. In this case, a braking gap d_brake may be defined, at which brakes 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, but not closer than the braking gap d_brake, the vehicle is motored. Only if this is not sufficient, and the vehicle comes closer than d_brake, the brakes are applied. The brakes may be e.g. wheelbrakes, a retarder, an exhaust brake, etc.

However, driving behind a lead vehicle also results in that normal fuel saving systems, such as certain fuel-economising cruise controls, cannot be fully utilised due to the risk of coming too close to the lead vehicle, regardless of whether the motor vehicle is driven with an activated ACC system or not. Certain fuel saving systems and functions are therefore deactivated when driving behind 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 It is a primary objective of the present invention to achieve an, in at least some aspect, improved way of controlling a powertrain in a motor vehicle when driving behind a lead vehicle, such that the energy consumption of the motor vehicle is minimised. In particular, it is an objective to provide a method for controlling a powertrain such that fuel-economising systems can be used also in certain situations as the vehicle is travelling behind a lead vehicle 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 the primary objective is achieved by means of the method as defined in claim 1. The method comprises the steps of: (a) collecting data relating to a road gradient along an expected travelling route ahead of the motor vehicle, (b) collecting data relating to a present size of a gap between the 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 on the presumption that a potential mode of operation of the powertrain, involving coasting of the motor vehicle, is actuated at a first point in time t_0, wherein the simulation computes data relating to the size of an expected gap d_sim between the vehicles during an upcoming time period following said first point in time t_0, (e) checking if the simulated data from step (d) fulfill a set of predefined actuation conditions including at least one predefined actuation condition C1, which is fulfilled when an expected gap d_sim is larger than a preset smallest allowable gap d_min during said upcoming time period, (f) given that said set of predefined actuation conditions is fulfilled, actuating said potential mode of operation at said first point in time t_0.

Thus, in the method according to the invention, an expected gap d_sim to the lead vehicle during an upcoming time period is simulated, and depending on the size of the expected gap, it is determined whether or not to actuate a mode of operation which involves 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 of disengaging a clutch of the vehicle or putting the gearbox in a neutral position.

If the gap between the vehicles is expected to be larger than the predefined smallest allowable gap d_min during the upcoming time period or road section, the simulated mode of operation is actuated. In practice, this is useful when coasting the vehicle might be fuel-economically advantageous and involves reducing a braking force, or increasing a relative speed with respect to the lead vehicle. The simulation reveals if the gap between the vehicles is likely to exceed the smallest allowable gap d_min, and if so, the vehicle is set to coasting so that fuel efficiency of the vehicle can be improved. Coasting is often advantageous from a fuel economy perspective, and it is therefore useful to be able to switch to a mode of operation in which the vehicle is coasted when this is possible. Using the method according to the invention, the mode of operation of the powertrain will automatically be switched to one which involves coasting when this is possible without coming too close to the lead vehicle. By repeating data collection and simulation with a certain frequency, it can be checked continuously whether a switch to a mode of operation involving coasting is possible.

The upcoming time period during which the expected gap d_sim must exceed the smallest allowable gap d_min in order for condition 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. In other words, if the expected gap d_sim is at any point in time during said time period smaller than the smallest allowable gap d_min, condition C1 is not considered fulfilled and the simulated potential mode of operation is not actuated. The upcoming time period may e.g. be set based on a length of a total time period or road section for which the simulation is carried out, or based on a behaviour of the simulation.

The step of collecting data relating to a speed of the lead vehicle may comprise e.g. estimating the speed of the lead vehicle for an upcoming time period, or receiving data from the lead vehicle relating to its foreseen speed variation. In the simplest case, the current speed of the lead vehicle is measured or estimated and an assumption is made that the lead vehicle will maintain constant speed. It is also possible to base an estimation of the future speed of the lead vehicle on its present speed and acceleration, as measured or communicated. The future speed profile of the lead vehicle may also be simulated in the present (trailing) motor vehicle using estimations of mass and engine torque of the lead vehicle.

The simulation performed in the method according to the invention is preferably in the form of a so called full vehicle simulation over an expected travelling route ahead of the motor vehicle. The simulation is repeated with a certain frequency, such as a frequency of 1 Hz. In each simulation, several parameters may be determined, 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 motor vehicle with a gearbox of the powertrain in a neutral position, or with a clutch disengaged. Several different modes of operation may be simulated simultaneously. The simulation may be performed over a longer time period, or road section, than the upcoming time period used when checking if the predefined set of actuation conditions is fulfilled.

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

The smallest allowable gap d_min, which of course can be defined in terms of either time or distance, should usually not be adjustable by the driver of the motor vehicle. In the case where the motor vehicle is controlled by an adaptive cruise control, such that the speed of the motor vehicle is regulated to maintain a specified gap d_set to the lead vehicle, the smallest allowable gap d_min is set to be smaller than d_set. Preferably, the smallest allowable gap d_min can be set in dependence on the specified gap d_set. If a braking gap d_brake is also defined, the smallest allowable gap d_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 smallest allowable gap d_min.

According to the invention, 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. The part of the upcoming time period during which the expected gap d_sim must be smaller than the largest allowable gap d_max can be predefined and may e.g. be a time period starting after an initial delay. By defining a largest allowable gap d_max, there is no risk that the vehicle is set to coasting if this leads to a too large gap between the vehicles, so that the benefits from travelling behind a lead vehicle can no longer be achieved.

According to the invention, said set of predefined actuation conditions comprises a predefined actuation condition C3, which is fulfilled when the expected gap d_sim is in a range between the smallest allowable gap d_min and the largest allowable gap d_max during at least a preset minimum time period ?t_min. This prevents unnecessary rapid switches between modes of operation when no significant energy gains can be expected. The minimum time period ?t_min can be determined based on factors such as transient losses arising when switching to and from coasting, 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 of the lead vehicle and the size of the gap can thereby be obtained. Simulations of a future speed profile usually take topographic data into account and may also take traffic data etc. into account. Such simulation methods are known and often carried out in the vehicle for 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 of predefined actuation conditions comprises a predefined actuation condition C4, which is fulfilled when the simulated speed v_sim is within a preset allowable speed range between a smallest allowable speed v_min and a largest allowable speed v_max. It is thereby avoided that the vehicle is set to coasting when the speed of the vehicle is either too large or too small for this to be energy efficient and/or desirable.

According to another embodiment of the invention, step (d) further comprises performing at least one simulation based on the presumption that said potential mode of operation 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 first point in time t_0, wherein the simulation computes data relating to an expected gap d_sim_delay between the vehicles. A supplementary simulation is thus 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 previously discussed simulation. The same collected data are used as a basis for the simulation, and the simulations are performed simultaneously. The supplementary simulation thus reveals if any advantages can be achieved by delaying a switch of modes of operation until the later point in time t_1, or if the first point in time t_0 is suitable for making this switch. This embodiment is particularly advantageous when the computing power available for simulation 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 of predefined actuation conditions comprises a predefined actuation condition C5, which is fulfilled when an expected gap d_sim_delay is smaller than said smallest allowable gap d_min. When the smallest allowable gap d_min is smaller than the expected gap d_sim and larger than the expected gap d_sim_delay, d_sim_delay < d_min < d_sim, the conditions are optimal for actuating a mode of operation that includes coasting. If actuation is delayed, the motor vehicle will be at risk of coming too close to the lead vehicle and braking will be necessary. If on the other hand coasting is initiated as both the expected gaps d_sim and d_sim_delay are larger than the smallest allowable gap d_min, the vehicle 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 of the motor vehicle is initially controlled so as to maintain a specified gap d_set to the lead vehicle, wherein said specified gap d_set is larger than the smallest allowable gap d_min. This may preferably be achieved using an adaptive cruise control (ACC) system, which is commonly used to control the powertrain when driving behind a lead vehicle. The ACC system can in this embodiment be used to control the powertrain to drive at the specified gap d_set, while it is continuously checked whether a temporary abandonment of this control 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 of predefined actuation conditions comprises a predefined actuation condition C6, which is fulfilled when, at a point in time during the upcoming time period, a difference between the expected gap d_sim and a specified gap d_set is smaller than a first predefined threshold value, and a difference between an expected speed v_sim and an expected speed of the lead vehicle v_lead is smaller than a second predefined threshold value. In this case, the conditions are perfect for “docking” with the lead vehicle at the specified gap d_set at the given point in time. The specified gap d_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 potential mode of operation comprises coasting the vehicle during a predetermined initial time period, and thereafter motoring the vehicle at a highest available gear. Thus, if the motor vehicle is at risk of coming too close to the lead vehicle if the vehicle is coasted during a longer time period, advantages associated with coasting may be obtained by actuating a mode of operation involving coasting followed by motoring.

According to another aspect of the invention, at least the primary objective is achieved by a computer program comprising computer program 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 a non-transitory data storage medium which can be read by a computer and on which the program code of the proposed computer program is stored.

According to a further aspect of the invention, at least the primary objective is achieved by an electronic control unit of a motor vehicle comprising an execution means, a memory connected to the execution means and a data storage medium which is connected 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 primary objective is achieved by a motor vehicle comprising the proposed electronic 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 an embodiment 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. 3a is another graph schematically showing results of a simulation carried out in a method according to an embodiment of the invention, Fig. 3b is yet another graph schematically showing results of a simulation carried out in a method according to an embodiment of the invention, Fig. 4 schematically shows a control unit according to the invention, and Fig. 5 schematically shows a vehicle according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 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 gradient along an expected travelling route ahead of the motor vehicle, as will be further described later on. A second step S2 comprises collecting data relating to a present size of a gap between the motor vehicle and the lead vehicle. A third step S3 comprises collecting data relating to a speed of the lead vehicle. Data relating 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 simulation based on the data collected in steps S1-S3 and on the presumption that a potential mode of operation of the powertrain, which mode of operation involves coasting of the motor vehicle, is actuated at a point in time t_0. The simulation computes data relating to the size of an expected gap d_sim between the vehicles during an upcoming time period following the point in time t_0. That is, it is simulated how the size of the gap between the vehicles is expected to develop if a potential mode of operation is actuated at the point in time t_0. The potential mode of operation involves coasting of the motor vehicle at least during a part of the upcoming time period. For example, the potential mode of operation may involve initial coasting of the motor vehicle, and thereafter motoring 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 predefined actuation conditions includes at least one predefined actuation condition C1, which is considered fulfilled when the expected gap d_sim is larger than a preset smallest allowable gap d_min during said upcoming time period, preferably during the entire upcoming time period, the duration of which can be defined in advance. Thus, in the step S5, the simulated expected gap d_sim between the vehicles is compared to the preset smallest allowable gap d_min, acting as a threshold value. If it is found that the gap is likely to exceed the smallest allowable gap d_min during the upcoming time period if the potential mode of operation is actuated, the actuation condition C1 is considered fulfilled. The set of predefined actuation conditions may further include other conditions, such as an actuation condition C2 that the expected gap d_sim must be smaller than a preset largest allowable gap d_max during at least a part of the upcoming time period. A condition C3, which is fulfilled when the expected gap d_sim is in a range between the smallest allowable gap d_min and the largest allowable gap d_max during at least a preset minimum time period ?t_min, and a condition C4, which is fulfilled when a simulated speed v_sim is within a preset allowable speed range between a smallest allowable speed v_min and a largest allowable speed v_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 mode of operation at the point in time t_0, given that the predefined actuation conditions have been fulfilled. Otherwise, in case the actuation conditions have not been fulfilled, steps S1-S5 can preferably be repeated. In the simplest case, the potential mode of operation is actuated given that condition C1 is fulfilled. In principle, this means that the motor vehicle is coasted given that it is not at risk of coming too close to the lead vehicle. Step S6 ends 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 is here to be understood as that the steps are carried out with a predetermined frequency as long as the vehicle is travelling forward. The frequency of data collection and the frequency of simulation are not necessarily identical and can e.g. be in the order of 100 Hz.

Data relating to the road gradient may in step S1 be collected in various different ways. The road gradient may be determined on the basis of map data, e.g. from digital maps containing topographical information, in combination with positioning information, e.g. GPS (global positioning system) information. The positioning information may be used to determine the location of the vehicle relative to the map data so that the road gradient can be extracted from the map data. Various present-day cruise control systems use map data and positioning information. Such systems may then provide the map data and positioning information required for the method according to the present invention, thereby minimising the additional complexity involved in determining the road gradient.

The road gradient may be obtained on the basis of a map in conjunction with GPS information, from radar information, from camera information, of information from another vehicle, from positioning information and road gradient information stored previously on board, or from information obtained from traffic systems related to the expected travelling route. In systems where there is information exchange between vehicles, road gradients estimated by one vehicle may also be made available to other vehicles, 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 the vehicles 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 be collected e.g. by measuring the speed or by communication with the lead vehicle and from this information determining an expected speed of the lead vehicle during travel along the upcoming road section. This step may e.g. comprise measuring a current speed of the lead vehicle and making an assumption about its speed during the upcoming road section or time period, such as assuming that the lead vehicle will maintain a constant speed. The assumption may also be based on knowledge about e.g. the road gradient 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 the expected gap d_sim in step S4 is usually performed in steps by simulating an expected future speed profile of the motor vehicle, and therefrom determining the development of the size of the gap by comparison with the data relating to the speed of the lead vehicle. In the simulation of the future speed profile, the potential mode of operation is assumed to be actuated at the point in time t_0. 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_lead - v_sim)<*>??, wherein v_lead is the speed of the lead vehicle, v_sim is the simulated speed of the motor vehicle, and wherein ?? is the time step used in the simulation.

If the computing power is limited in the vehicle, the frequency with which simulations can be repeated is also limited. In this case, it is possible to make an additional simulation simultaneously with the previously discussed simulation. This additional simulation is based on the presumption that the potential mode of operation of the powertrain is actuated at a point in time t_1, which point in time t_1 is delayed with respect to the point in time t_0. The additional simulation computes data relating to an expected gap d_sim_delay between the vehicles, i.e. the development of the gap between the vehicles given that the same potential mode of operation is actuated at the later point in time t_1. The set of predefined actuation conditions may in this case comprise a predefined actuation condition C5, which is fulfilled when the expected gap d_sim_delay is smaller than the smallest allowable gap d_min. In other words, both conditions C1 and C5 are fulfilled if the gap between the vehicles is expected to be smaller than the smallest allowable gap d_min if the potential mode of operation is actuated at the point in time t_1, but larger if it is actuated at the point in time t_0.

The set of predefined actuation conditions may also comprise a predefined actuation condition C6, which is considered fulfilled when, at a point in time during the upcoming time period, a difference between the expected gap d_sim and a specified gap d_set is smaller than a first predefined threshold value, and a difference between an expected speed v_sim and an expected speed of the lead vehicle v_lead is smaller than a second predefined threshold value.

In one example, the method according to an embodiment of the invention is carried out in a motor vehicle travelling along a road section behind a lead vehicle. In a present mode of operation, the powertrain of the motor vehicle is controlled by an ACC system. The speed of the vehicle is therefore automatically adjusted to maintain a specified gap d_set to the lead vehicle. As the vehicle drives along the road section, data relating to the road gradient along the expected travelling route ahead of the motor vehicle are continuously collected using a map in conjunction with a GPS system (step S1) . Simultaneously, data relating to the present size between the motor vehicle and the lead vehicle are collected using radar technology (step S2). Data relating to the speed of the lead vehicle are also collected (step S3), which data are obtained by determining a present speed of the lead vehicle, and making an assumption that the lead vehicle will be travelling at a constant speed. All the collected data are stored in a database.

In a processing unit of the vehicle, the collected data are used to continuously, i.e. at a set frequency of e.g. 1 Hz, simulate how the size of the gap between the vehicles is expected to develop during an upcoming time period for a number of different scenarios (step S4) in which a potential mode of operation of the powertrain involving coasting of the motor vehicle is initiated at a point in time t_0. After the simulation, it is assessed whether a number of preset actuation conditions are fulfilled (step S5). If all preset actuation conditions are fulfilled, the potential mode of operation is actuated (step S6).

In the example, shown in fig. 2, the motor vehicle is travelling on a downhill road section at a set speed v_set, corresponding to a specified gap d_set to a lead vehicle, as the motor vehicle approaches an uphill road section. Brakes are engaged during the downhill road section to maintain the specified gap d_set. The lead vehicle is assumed to travel at a constant speed v_lead. Simulations of the expected gap d_sim carried out with a certain frequency during travel along the downhill road section have so far revealed that the preset actuation condition C1 has not been fulfilled, since the vehicle has been at risk of coming too close to the lead vehicle if a mode of operation involving coasting was to be actuated. In the graph, the dashed lines show results of a simulation carried out on a first occasion T1, wherein the upper graph shows the simulated expected speed v_sim_1 of the motor vehicle and the lower graph shows the simulated expected gap d_sim_1, which is clearly smaller than the smallest allowable gap d_min during a part of the upcoming time period. The potential mode 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, the simulations are repeated on an occasion T2. The simulated speed v_sim_2 and the simulated gap d_sim_2 are shown as solid lines in fig. 2. The simulations carried out on occasion T2, and a subsequent comparison with the predefined set of actuation conditions, reveal that the simulated expected gap d_sim exceeds the preset smallest allowable gap d_min if the brakes are disengaged and the mode of operation involving coasting is actuated. Therefore, the simulated potential mode of operation is actuated, resulting in a speed increase in comparison with the initial mode of operation, in which the powertrain is controlled by the ACC system. In a continuation of the inventive method, it is continuously evaluated whether to continue controlling the powertrain in the actuated mode of operation or whether to switch to another mode of operation, such as controlling the powertrain using the ACC system.

Another example is shown in fig. 3a. In this example, a motor vehicle 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 the motor vehicle approaches a downhill road section followed by an uphill road section. As the vehicle is travelling along the level road section, an ACC system is used to control a powertrain of the vehicle and a driving force is applied via the powertrain. At one occasion, data is collected according to step S1-S3, and a simulation according to step S4 is carried out, simulating that a mode of operation in which the motor vehicle is coasted is actuated at the time t_0. The simulated expected speed v_sim and the simulated expected gap d_sim are shown with dashed lines in the upper and lower graphs, respectively. Simultaneously, it is simulated that coasting of the vehicle would instead be initiated at the time t_1, which is delayed with respect to t_0. The simulated expected speed v_sim_delay and the simulated expected gap d_sim_delay are shown with solid lines in the upper and lower graphs, respectively. As can be seen from the graphs, coasting the vehicle will involve an initial speed reduction followed by a speed increase as the vehicle gains momentum on the downhill road section, and a subsequent speed reduction as the vehicle comes onto the uphill road section. Initiating coasting at the time t_0 means that the smallest allowable gap d_min will be exceeded during the entire upcoming time period, so that the predefined actuation condition C1 is fulfilled. If instead initiating coasting at t_1, the motor vehicle will come too close to the lead vehicle. Thus, both predefined conditions C1 and C5 are fulfilled. In the shown example, 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, at which the expected speed v_sim of the motor vehicle coincides with the speed v_lead of the lead vehicle, and at which the expected gap d_sim coincides with the specified gap d_set. Thus, the conditions for docking with the lead vehicle at the point in time t_C6 are optimal if initiating coasting at the point in time t_0. In this example, coasting of the vehicle is therefore initiated immediately after the simulations and a subsequent comparison with the predefined set of actuation conditions have been carried out, i.e. at a point in time corresponding to t_0.

In yet another example, shown in fig. 3b, a motor vehicle is approaching a lead vehicle. A powertrain of the motor vehicle is in this example initially controlled using a cruise control system to maintain a set speed, and a driving force is applied via the powertrain. As the motor vehicle approaches the lead vehicle, it is simulated how a switch to coasting would affect the gap between the vehicles if initiated at a point in time t_0 (dashed lines) or if initiated at a later point in time t_1 (solid lines), delayed with respect 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 to the lead vehicle and it may be necessary to brake. Thus, a switch to coasting is carried out at the time t_0. The vehicle can thereby be 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 controlling the powertrain of a motor vehicle according to the present invention may be implemented in a computer program which, when executed in a computer, causes the computer to conduct the method. The computer program usually takes the form of a computer program product which comprises a suitable digital storage medium on which the computer program is stored. Said computer-readable digital storage medium comprises a suitable memory, e.g. ROM (read-only memory), PROM (programmable read-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 a vehicle provided with an execution means 401 which may take the form of substantially any suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), or a circuit with a predetermined specific function (application specific integrated circuit, ASIC). The execution means 401 is connected to a memory unit 402 which is situated in the control unit 400. A data storage medium 403 is also connected to the execution means and provides the execution means with, for example, the stored program code and/or stored data which the execution means needs to enable it to do calculations. The execution means is also adapted to storing partial or final results of calculations in the memory unit 402.

The control unit 400 is further provided with respective devices 411, 412, 413, 414 for receiving and sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 411, 413 can detect as information and which can be converted to signals which the execution means 401 can process. These signals are then supplied to the execution means. The output signal sending devices 412, 414 are arranged to convert signals received from the execution means 401, in order to create, e.g. by modulating 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 receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media orientated systems transport) bus or some other bus configuration, or a wireless connection. One skilled in the art will appreciate that the aforesaid computer may take the form of the execution means 401 and that the aforesaid memory may take the form of the memory unit 402.

Control systems in modern vehicles generally comprise a communication bus system consisting of one or more communication buses for connecting together a number of electronic control units (ECUs), or controllers, and various components on board the vehicle. Such a control system may comprise a large number of control units and the responsibility for a specific function may be divided between two or more of them.

In the embodiment depicted, the present invention is implemented in the control unit 400 but might also be implemented wholly or partly in one or more other control units already on board the vehicle or a control unit dedicated to the present invention. Vehicles of the type here concerned are of course often provided 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 motor vehicle 500 which is schematically shown in Fig. 5. The motor vehicle 500 comprises an engine 501 forming part of a powertrain 502 which drives driving wheels 503, 504. The motor vehicle 500 further comprises an exhaust treatment system 505, and a control unit 510, which corresponds to the above-mentioned control unit 400 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 the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims (11)

1. 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 ahead of the motor vehicle, (b) collecting data relating to a present size of a gap between the 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 on the presumption that a potential mode of operation of the powertrain, involving coasting of the motor vehicle, is actuated at a first point in time t_0, wherein the simulation computes data relating to the size of an expected gap d_sim between the vehicles during an upcoming time period following said first point in time t_0, (e) checking if the simulated data from step (d) fulfill a set of predefined actuation conditions including at least one predefined actuation condition C1, which is fulfilled when the expected gap d_sim is larger than a preset smallest allowable gap d_min during said upcoming time period, (f) given that said set of predefined actuation conditions is fulfilled, actuating said potential mode of operation at said first point in time t_0, 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, and - a predefined actuation condition C3, which is fulfilled when the expected gap d_sim is in a range between the smallest allowable gap d_min and the largest allowable gap d_max during at least a preset minimum time period ?t_min.

2. The method according to claim 1, wherein step (d) comprises simulating a future speed profile of the motor vehicle, and based thereon computing the size of said expected gap d_sim.

3. The method according to claim 2, wherein said set of predefined actuation conditions comprises a predefined actuation condition C4, which is fulfilled when a simulated speed v_sim is within a preset allowable speed range between a smallest allowable speed v_min and a largest allowable speed v_max.

4. The method according to any one of the preceding claims, wherein step (d) further comprises performing at least one simulation based on the presumption that said potential mode of operation 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 first point in time t_0, wherein the simulation computes data relating to an expected gap d_sim_delay between the vehicles, and wherein said set of predefined actuation conditions comprises a predefined actuation condition C5, which is fulfilled when the expected gap d_sim_delay is smaller than said smallest allowable gap d_min.

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

6. The method according to any one of claims 2-5, wherein said set of predefined actuation conditions comprises a predefined actuation condition C6, which is fulfilled when, at a point in time during the upcoming time period, a difference between the expected gap d_sim and a specified gap d_set is smaller than a first predefined threshold value, and a difference between an expected speed v_sim and an expected speed of the lead vehicle v_lead is smaller than a second predefined threshold value.

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

8. A computer program comprising computer program code for causing a computer to implement a method according to any one of the claims 1-7 when the computer program is executed in the computer.

9. 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 8 is stored.

10. An electronic control unit (400) of a motor vehicle comprising an execution means (401) , a memory (402) connected to the execution means (401) and a data storage medium (403) which is connected to the execution means (401) and on which the computer program code of a computer program according to claim 8 is stored.

11. A motor vehicle (500) comprising an electronic control unit (400, 510) according to claim 10.