SE540496C2 - A method for controlling a powertrain of a vehicle, a control unit therefore and a vehicle comprising the control unit - 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) based on said data, simulating how the gap is expected to develop if a driving force or a braking force applied by the powertrain is adjusted with respect to a reference driving force or a reference braking force that would be applied in a reference mode of operation of the powertrain,(e) based on said simulation, setting a status of the simulated force adjustment to allowable or non-allowable, and(f) controlling the powertrain based on said status.

Description

A method for controlling a powertrain of a vehicle, a control unit therefore and a vehicle comprising the control unit 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.

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) based on said data, simulating how the size of said gap is expected to develop if a driving force or a braking force applied by the powertrain is adjusted with respect to a reference driving force or a reference braking force that would be applied in a reference mode of operation of the powertrain, (e) based on said simulated results for a predetermined upcoming time period or road section, setting a status of said simulated adjustment of the driving force or the braking force to allowable or non-allowable, and (f) controlling the powertrain based on said status.

The method according to the invention enables simulation of e.g. a mode of operation of the powertrain that could be advantageous from a fuel economy perspective and, based on the size of the gap to the lead vehicle that this mode of operation would cause in the near future, deciding whether the simulated mode of operation is allowable or not. If the status is set to non-allowable, the potential mode of operation cannot be selected. If the status is set to allowable, it is possible, but not necessary, to select the simulated mode of operation. The simulated mode of operation can here be any kind of mode of operation that involves a difference in either driving force applied by the powertrain, braking force applied, or both, with respect to a reference mode of operation of the powertrain. Thus, fuel-economising modes of operation may be allowed as long as the gap to the lead vehicle is not expected to become too small. The method may advantageously be combined with a fuel-economising function or system, in such a way that the fuel-economising function or system is allowed to control the powertrain as long as the status of the simulated adjustment of the driving force or braking force is not set to non-allowable. In this way, fuel can be saved on one hand by travelling behind a lead vehicle, and on one hand by allowing fuel-saving modes of operation as long as certain conditions relating to the size of the gap to the lead vehicle are fulfilled.

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 to base an estimation of the future speed of the lead vehicle on its present speed and acceleration, as measured or communicated.

In the reference mode of operation, the powertrain may e.g. be controlled by an adaptive cruise control system (ACC), by another system in the vehicle, or by a driver of the vehicle, e.g. in such a way that the vehicle maintains a desired distance to the lead vehicle. In the reference mode of operation, 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 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, engine speed, engine torque, gap to the lead vehicle, time, travelled distance, etc. Several potential force adjustments may be simulated simultaneously, so that the status of each of those adjustments will be set to allowable or nonallowable. Such potential force adjustments may e.g. result from activation of another fuel-saving system. If allowable, the other fuel-saving system may be allowed to temporarily control the powertrain. If non-allowable, the powertrain will be controlled according to e.g. the reference mode of operation, or in another allowable way.

According to an embodiment of the invention, step (d) comprises simulating how the size of said gap is expected to develop if more driving force or less braking force is applied with respect to said reference mode of operation during at least a part of said upcoming time period and/or road section. For example, at the end of a downhill road section during which brakes have been applied in order to maintain a given gap to the lead vehicle, e.g. by an adaptive cruise control system, the reference mode of operation of the powertrain may involve continuously applying brakes also during the upcoming road section so that the given gap is maintained. However, from a fuel economy perspective, it may be desirable to release the brakes and instead coast the vehicle with the gearbox in a neutral position or with a clutch disengaged in order to take advantage of the gained momentum, even if this would lead to a decreased gap between the vehicles. This would mean a speed increase, and a reduction in braking force, in comparison with continued driving with applied brakes, i.e. the reference mode of operation. In this situation, also driving the vehicle with the powertrain in motoring mode, i.e. with a gear engaged but with no driving force applied and with no fuel consumption of the engine, would involve a speed increase, and a reduced braking force, in comparison with the reference mode of operation.

According to one embodiment of the invention, the powertrain is in the reference mode of operation 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. This is very useful, since the adaptive cruise control system is commonly used to control the powertrain when driving behind a lead vehicle. In this embodiment, such a mode of operation can be used to control the powertrain while continuously checking whether operations suggested by other fuel-saving systems would be allowable. Other fuel-saving systems are preferably systems which would be active if the motor vehicle was not travelling behind a lead vehicle.

According to another embodiment of the present invention, step (e) includes comparing the simulated size of the gap to a preset smallest allowable gap d_min. In this way, unnecessary braking can be prevented since the simulation reveals whether the motor vehicle, with a shift to a simulated higher driving force or lower braking force, is at risk of coming too close to the lead vehicle. 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. 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 another embodiment of the present invention, said status is set to non-allowable if the simulated size of the gap is smaller than said smallest allowable gap d_min. Thus, any mode of operation that would result in a too small gap between the vehicles cannot be selected, even if such a mode of operation would be expected to lead to a temporarily reduced energy consumption during the upcoming road section. This prevents undesired braking in order to maintain a necessary security gap to the lead vehicle, which would lead to a waste of energy rather than energy savings.

According to another embodiment of the present invention, step (d) comprises simulating how the size of said gap is expected to develop if more driving force is applied without shifting gears.

Here, one of the gears is engaged and a positive driving force is transmitted via the powertrain to drive the vehicle forward. It is sometimes desirable to increase the speed momentarily in order to be able to save fuel later on, depending on the topography. The method can in this embodiment be used to check if such a speed increase is allowed.

According to another embodiment of the present invention, step (d) comprises simulating how the size of said gap is expected to develop if more driving force is applied by shifting to a lower gear. This may be relevant e.g. in uphill slopes in which a constant speed can be maintained by shifting to a lower gear.

According to another embodiment of the present invention, step (d) comprises simulating how the size of said gap is expected to develop if the vehicle is set to coasting. Coasting may be advantageous at e.g. the end of a downhill slope as previously discussed. Coasting may in this case be achieved in different ways, such as by means of disengaging a clutch of the vehicle or putting the gearbox in a neutral position.

According to another embodiment of the present invention, step (d) comprises simulating how the size of said gap is expected to develop if less braking force is applied by applied brakes, and/or if applied brakes are released. The brakes may be e.g. wheelbrakes, a retarder, an exhaust brake, etc. Releasing the brakes in order to increase the speed slightly on a downhill road section may be desirable to gain momentum, and it is therefore relevant to simulate such a force adjustment to determine whether it is allowable or not. Of course, simulations in which the wheel-brakes but not the retarder are released or similarly may also be carried out.

According to another embodiment of the present invention, step (d) comprises simulating a future speed profile of the motor vehicle if the driving force or the braking force applied by the powertrain is adjusted with respect to the reference driving force or the reference braking force. This 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 present invention, said upcoming time period or road section is selected based on a length of a total time period or road section for which said simulation is carried out. The time period or road section can be set to the entire time period for which the simulation is carried out, but may also be set as e.g. a percentage of said time period or road section. This is a simple way of setting a time period or road section that should be taken into account when setting a status of said simulated adjustment of the driving force or the braking force to allowable or non-allowable.

According to another embodiment of the present invention, said upcoming time period or road section is set based on a behaviour of the simulation in step (d). For example, the time period or road section can be set based on whether and when a set maximum gap d_max between the vehicles is exceeded. This way of determining said upcoming time period or road section is more flexible than setting a fixed time period or road section.

According to another embodiment of the present invention, said upcoming time period or road section is set based on a duration of the time period during which the adjusted driving force or braking force applied by the powertrain is expected to differ from the corresponding reference driving force or braking force, as indicated by the simulation in step (d). Thus, the upcoming time period or road section that should be taken into account in step (e) is based on when the potential adjustment in driving force or braking force is expected to be aborted, i.e. when the vehicle is expected to return to the reference mode of operation or similarly.

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 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 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. 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 simulating how the size of the gap between the vehicles is expected to develop in the case where a driving force or a braking force applied by the powertrain is adjusted with respect to a reference driving force or a reference braking force that would be applied in a reference mode of operation of the powertrain. As a basis for the simulation, the data collected in steps S1-S3 are used. Several cases may be simulated simultaneously, corresponding to different adjustments of said forces. For the present invention, the most important cases to simulate are the cases in which the driving force is increased or in which the braking force is decreased, depending on the force applied in the reference mode of operation. Typically, the reference mode of operation is a case in which the powertrain 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.

In a fifth step S5, a status of the simulated adjustment, or of each of the simulated adjustments, of the driving force or the braking force is/are set to allowable or non-allowable. The status is set based on the simulated results, i.e. the expected development of the size of the gap for each simulated force adjustment, during an upcoming predetermined time period or road section. Preferably, the simulated size of the gap d_sim for each simulated case is compared to a minimum gap d_min. The motor vehicle is not allowed to come closer to the lead vehicle than the minimum gap d_min, so the status of any force adjustment expected to result in a smaller gap d_min, in terms of either time or distance, is set to non-allowed. In practice, the non-allowed force adjustments will thus be either increments in driving force or reductions in braking force with respect to the reference mode of operation.

A sixth step S6 comprises controlling the powertrain based on said status. In other words, the powertrain is controlled such that nonallowable force adjustments cannot be initiated, while allowed force adjustments can be, but will not necessarily be, initiated.

All steps S1-S6 are preferably carried out continuously, which is here to be understood as that the steps are carried out at 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 of the size of the gap 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 driving force or the braking force applied by the powertrain is adjusted with respect to the reference driving force or the reference braking force that would be applied in the reference mode of operation of the powertrain. 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 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). Such scenarios include most importantly scenarios in which the driving force applied by the powertrain is increased with respect to the driving force that would be applied when the powertrain is controlled by the ACC system, and/or in which a braking force is reduced with respect to the braking force that would be applied when the powertrain is controlled by the ACC system. After the simulation, a status of each simulated force adjustment is set to allowed or non-allowed, depending on whether the simulated force adjustment will result in that the motor vehicle comes too close to the lead vehicle (step S5). The minimum allowable gap between the vehicles is defined as the smallest allowable gap d_min, which is a preset value that the simulated size of the gap is compared to. Any value falling below d_min will result in the status of the corresponding force adjustment being set to non-allowable. The powertrain is controlled so that no nonallowable force adjustments are being carried out (step S6).

In the example, the motor vehicle is travelling on a down-hill road section at a set speed v_set, corresponding to a specified gap d_set to a lead vehicle, at the time t_0. The lead vehicle is assumed to drive at a constant speed v lead. The ACC system controls the powertrain to a motoring mode, i.e. with a gear engaged but with no driving force applied. In practice, a braking force is applied by the powertrain. In the simulation carried out in step S4, as shown in fig. 2, a scenario is simulated in which the speed v_sim of the motor vehicle is increased by reduction of the braking force by means of coasting the vehicle with the gearbox in a neutral position. In this way, momentum would be gained in order to potentially save fuel further ahead. The simulations carried out on a first occasion T1 computes the speed v_sim_1 and the gap d_sim_1 (dashed lines). However, in the simulation it is found that the potential force adjustment would lead to that the smallest allowable gap d_min would be violated, i.e. the simulated gap d_sim_1 < d_min at a later point in time. The status is therefore set to non-allowable and the powertrain continues to be controlled by the ACC system. On a subsequent occasion T2, new data are collected and the simulation is repeated, computing a speed v_sim_2 and a gap d_sim_2 (dash-dotted lines). At this point, putting the gearbox in the neutral position is found to be allowable, since the simulated gap d_sim_2 will in this case not be smaller than the smallest allowable gap d_min. The powertrain may therefore, if desirable, be controlled so that the gearbox is put in the neutral position. This may e.g. be carried out if considered to be fuel-economic. On a subsequent occasion (not shown), the simulation is repeated once more, etc.

Fig. 3 shows another example in which a motor vehicle is travelling behind a lead vehicle with a gear engaged in the gear box and with a positive driving force applied by the powertrain. As the vehicle is approaching an uphill road section, it is simulated, on two occasions T1 and T2, how an increase in driving force would affect the size of the gap between the vehicles, given that the lead vehicle travels at a constant speed v_lead. As seen in fig. 3, such an increased driving force is expected to lead to an initial speed raise followed by a speed reduction as the vehicle comes onto the uphill road section. The expected speed v_sim_1 as simulated on the occasion T1 is shown with a dashed line and the expected speed v_sim_2 as simulated on the occasion T2 is shown with a solid line. On the first occasion T1, it is found that the increased driving force is non-allowable, since the simulated gap d_sim_1 (dashed line) becomes smaller than the smallest allowable gap d_min. On the later occasion T2, it is found that the simulated gap d_sim_2 (solid line) exceeds d_min during the entire upcoming time period, and the status of the force adjustment is set to allowable.

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 (15)

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) based on said data, simulating how the size of said gap is expected to develop if a driving force or a braking force applied by the powertrain is adjusted with respect to a reference driving force or a reference braking force that would be applied in a reference mode of operation of the powertrain, (e) based on said simulated results for a predetermined upcoming time period or road section, setting a status of said simulated adjustment of the driving force or the braking force to allowable or non-allowable, and (f) controlling the powertrain based on said status.

2. The method according to claim 1, wherein step (d) comprises simulating how the size of said gap is expected to develop if more driving force or less braking force is applied with respect to said reference mode of operation during at least a part of said upcoming time period and/or road section.

3. The method according to claim 1 or 2, 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.

4. The method according to any one of the preceding claims, wherein step (e) includes comparing the simulated size of the gap to a preset smallest allowable gap d_min.

5. The method according to claim 4, wherein said status is set to non-allowable if the simulated size of the gap is smaller than said smallest allowable gap d_min.

6. The method according to any one of claims 2-5, wherein step (d) comprises simulating how the size of said gap is expected to develop if more driving force is applied without shifting gears, or if more driving force is applied by shifting to a lower gear.

7. The method according to any one of claims 2-5, wherein step (d) comprises simulating how the size of said gap is expected to develop if the vehicle is set to coasting, if less braking force is applied by applied brakes, and/or if applied brakes are released.

8. The method according to any one of the preceding claims, wherein step (d) comprises simulating a future speed profile of the motor vehicle if the driving force or the braking force applied by the powertrain is adjusted with respect to the reference driving force or the reference braking force.

9. The method according to any one of the preceding claims, wherein said upcoming time period or road section is set based on a length of a total time period or road section for which said simulation is carried out.

10. The method according to any one of claims 1-8, wherein said upcoming time period or road section is set based on a behaviour of the simulation in step (d).

11. 1 1 . The method according to any one of claims 1-8, wherein said upcoming time period or road section is set based on a duration of the time period during which the adjusted driving force or braking force applied by the powertrain is expected to differ from the reference driving force or braking force, as indicated by the simulation in step (d).

12. A computer program comprising computer program code for causing a computer to implement a method according to any one of the claims 1-11 when the computer program is executed in the computer.

13. 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 12 is stored.

14. 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 12 is stored.

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