WO2015047177A1

WO2015047177A1 - Method and system for a common driving strategy for vehicle platoons

Info

Publication number: WO2015047177A1
Application number: PCT/SE2014/051117
Authority: WO
Inventors: Kuo-Yun LIANG; Henrik Pettersson; Jonas Mårtensson; Karl Henrik JOHANSSON; Assad ALAM
Original assignee: Scania Cv Ab
Priority date: 2013-09-30
Filing date: 2014-09-26
Publication date: 2015-04-02
Also published as: SE537618C2; SE1351128A1; DE112014003989T5

Abstract

A method and a system to control a vehicle platoon that comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit and a unit for wireless communication. The method comprises to provide a driving profile for at least one vehicle f_k in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein the driving profile contains target values b, and associated positions p, for the vehicle f_k along the road horizon, to determine a position-based driving strategy for the vehicles in the vehicle platoon, based on at least the driving profile for the vehicle f_k, after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy.

Description

Method and system for a common driving strategy for vehicle platoons

Technical area

The present invention relates to a system and a method to control a vehicle platoon. The vehicle platoon comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit and a unit for wireless

communication.

Background to the invention

The intensity of traffic is high on major roads in Europe, and it is expected to increase. The increased transport of people and goods not only gives rise to traffic problems in the form of traffic queues, it also requires ever-increasing amounts of energy, which eventually gives rise to the emission of, for example, greenhouse gases. One possible contribution to solving these problems is to allow vehicles to be driven closer together in what are known as "vehicle platoons". The term

"vehicle platoon" is here used to denote a number of vehicles with short distances between them, being driven as a single unit. The short distances lead to it being possible for more traffic to use the road, and the energy consumption for an individual vehicle will be reduced since the drag is reduced. The vehicles in the vehicle platoon are driven with at least one of an automated control of the speed of the vehicle and an automated control of its direction. This leads to vehicle drivers such as truck drivers being subject to a reduced load, accidents based on erroneous human decisions being reduced, and the possibility of reducing fuel consumption. Studies show that the fuel consumption of the leading vehicle in the vehicle platoon can be reduced by 2 to 10%, and that of the following vehicle by 15 to 20%, from the fuel consumption of a vehicle driving alone. This is the case in conditions in which the distance between the vehicles is 8-16 metres and the speed at which they travel is 80 km/h. The reduced fuel consumption gives a corresponding reduction in the emission of CO2.

Drivers are already using this well-known fact, which has a reduced traffic safety as a consequence. One fundamental question related to vehicle platoons is how the time gap between vehicles can be reduced from the recommended 3 seconds to a value between 0.5 and 1 second, without affecting traffic safety. With distance sensors and cameras, the reaction time of the driver can be eliminated. This is a type of technology that is already being used today by systems such as ACC (adaptive cruise control) and LKA (lane-keeping assistance). One limitation, however, is that distance sensors and cameras require a clear view of the target, and this makes it difficult to detect events that lie more than a pair of vehicles ahead in the queue. A further limitation is that the cruise-control system cannot act proactively, i.e., the cruise-control system cannot react to events that occur further in advance in the traffic that are going to affect the traffic rhythm.

One possibility to enable vehicles to act proactively is to arrange that the vehicles communicate and exchange information. One development of the IEEE-standard 802.1 1 for WLAN (wireless local area networks) known as "802.1 1 p" makes possible the wireless transfer of information between vehicles, and between vehicles and infrastructure. Different types of information, such as vehicle parameters and strategies, can be transmitted to and from the vehicles. The development of communication technology, thus, has made it possible to design vehicles and infrastructure that can interact and act proactively. Vehicles can be controlled as a unit and thus a shorter distance between them, and better global traffic flow, are made possible.

Many vehicles today are equipped also with a cruise-control system in order to make it easier for the driver to drive the vehicle. The desired speed can in this case be set by the driver by, for example, a regulator in the dashboard, and a cruise-control system in the vehicle subsequently influences a control system such that it accelerates and brakes the vehicle as appropriate, in order to maintain the desired speed. If the vehicle is equipped with an automatic gear-change system, the gear in which the vehicle is being driven is changed, such that the vehicle can maintain the desired speed.

When the cruise-control system is used in hilly terrain, the cruise-control system will attempt to maintain the preset speed along uphill sections. This sometimes has the consequence that the vehicle accelerates over the crown of the hill and possibly into a subsequent downhill section such that it subsequently must be braked in order not to exceed the preset speed, and this constitutes a manner of driving a vehicle that is wasteful of fuel. By varying the speed of the vehicle in hilly terrain, fuel can be saved, compared with the fuel consumption of a vehicle with a conventional cruise-control system. If the topology that lies ahead is made known through the vehicle having map data and positioning equipment, such systems can be made more robust, and they can change the speed of the vehicle before events have occurred. This is achieved with what is known as "look-ahead cruise control", abbreviated as "LAC".

The situation, however, becomes more complex when a fuel-optimal driving strategy is to be drawn up for a complete vehicle platoon. Additional aspects must be considered, such as retention of the optimal distance, physically possible speed profiles for all vehicles with different masses, and engine capacities. One additional aspect for a vehicle platoon during travel through varying topography is that the leading vehicle, when it has lost speed in an uphill section, resumes its preset speed after the hill. The following vehicles, which then are still present in the uphill section, will be forced to accelerate while travelling uphill, which is not fuel-efficient. Nor is it always possible, which means that gaps will be created in the vehicle platoon, which gaps must, in turn, be closed. This creates oscillations in the vehicle platoon. A similar behaviour is observed also in downhill sections, when the leading vehicle starts to accelerate in the downhill section due to its large mass. The following vehicles are in this case compelled to accelerate before they reach the downhill section, since they attempt to maintain constant the distance to vehicles in front. After the downhill section, the leading vehicle starts to decelerate in order to return to the preset speed. The following vehicles, which then are still present in the downhill section, will be compelled to brake in order to avoid causing a collision, which braking is not fuel-efficient.

A similar problem arises when driving around bends. With respect to an individual vehicle, it is possible to calculate the maximum speed that the vehicle should have in the bend. The maximum speed is based on such factors as driver comfort, centre of gravity, risk of tipping, degree of curvature, etc., through the use of a predictive cruise-control system. It is, however, not obvious how a vehicle platoon should take the bend. In the case in which the leading vehicle needs to decelerate from its preset speed in order to be able to take the bend, it will return to its preset speed after the bend. The following vehicles, which then are still present in the bend, will be compelled to accelerate in the bend, which may not be possible without exposing the vehicles to risks, such as the risk of leaving the carriageway. A number of documents describe control strategies for vehicle platoons.

JP2010176353 mentions the problem of keeping a vehicle platoon together when the road has a gradient. The control strategy that is applied uses an acceleration error at the road gradient. US2013/0041576 describes various methods of driving a vehicle platoon, and describes in general that other measures to optimise fuel consumption can be used.

The object of the invention is to provide a system that can control in a more efficient manner than previously suggested solutions a vehicle platoon in the event of variations in the design of the carriageway ahead, such as at least one of hills and bends.

Summary of the invention

According to a first aspect, the object described above is at least partially achieved through a method to control a vehicle platoon that comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit and a unit for wireless communication. The method comprises to provide a driving profile for at least one vehicle f_k in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein the driving profile contains target values b, and associated positions p, for the vehicle f_k along the road horizon, to determine a position-based driving strategy for the vehicles in the vehicle platoon based at least on the driving profile for the vehicle f_k, after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy. Thus, all vehicles in the vehicle platoon will principally follow the same driving profile with the same target values b, at the same points p,. This means that the driving strategy is not time-based. When each vehicle f_k is at point p, or within point p., the vehicles that follow will receive target value b,. An appropriate control unit in the vehicle subsequently controls the vehicle according to the target value bi. This means that the problem with unnecessary braking in downhill sections or impossible accelerations in uphill sections is avoided. The driving strategy is thus based on an optimal speed profile for the complete vehicle platoon, which speed profile is point-based. When driving in hills or around bends, small changes in distances will thus be permitted in order to achieve optimal fuel consumption.

When driving around bends, an increase in speed of the leader vehicle after a bend is avoided from being followed at the same time by the other vehicles during the bend, which may both be experienced as uncomfortable for the driver and involve a risk of tipping and other safety risks. Instead, the change of speed of the leader vehicle is followed by the other vehicles at the same position along the road at which the leader vehicle carried out the change in speed. The other vehicles will in this way also leave the bend before they again increase the speed.

By establishing a common driving profile that applies to the complete vehicle platoon, a well organised vehicle platoon is achieved in which consideration is taken of what is best for the complete vehicle platoon when driving in a hill and in a bend, or when driving in a hill or in a bend. The vehicles can be kept together, which has been shown to give savings in fuel compared to dividing the vehicle platoon. The common profile is drawn up by, for example, calculating an optimal LAC speed profile for each individual vehicle. After this, it is determined which vehicle must carry out the largest changes in speed in order to drive in a fuel- efficient manner in the hill ahead, and the driving profile of this vehicle becomes the common selected driving profile. The selected driving profile can be

transmitted to all vehicles in the platoon and followed by each individual vehicle. Each vehicle in the vehicle platoon can in this way follow the same driving profile that has been started from the same point along the road, i.e. not at the same time.

The invention gives a driving strategy that ensures that the vehicle platoon is held together, i.e. it minimises disturbances in the form of gaps being created and closed due to saturation of control signals. The invention can manage variations in topography with few and simple control actions. Through the invention, a manner to determine a common regulatory for the vehicles in the vehicle platoon is achieved that does not require such heavy calculations and is thus more suitable to be implemented in real time than other calculation solutions.

According to a second aspect, the object described above is achieved, at least partially, through a system to control a vehicle platoon. The vehicle platoon comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit and a unit for wireless communication. The system comprises further an analysis unit that is configured to: receive a driving profile for at least one vehicle fk in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein the driving profile contains target values b, and associated positions p, for the vehicle fk along the road horizon; to determine a position-based driving strategy for the vehicles in the vehicle platoon, based on at least the driving profile for the vehicle f^ after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy.

According to a third aspect, the object is at least partially achieved through a computer program P at a system, where the said computer program P comprises program code in order to cause the system to carry out any one of the method steps that are described in this application.

According to a fourth aspect, the object is at least partially achieved through a computer program product comprising a program code stored on a medium that can be read by a computer in order to carry out any one of the method steps described in this application. Preferred embodiments are described in the dependent claims and in the detailed description. Brief description of the attached drawings

The invention will be described below with reference to the attached drawings, of which:

Figure 1 shows an example of a vehicle platoon that is travelling up a hill.

Figure 2 shows an example of a vehicle platoon that is travelling around a bend. Figure 3 shows an example of a vehicle in a vehicle platoon.

Figures 4A-4D show different examples of the design of the system.

Figure 5 shows a flow diagram for the method according to one embodiment of the invention. Detailed description of preferred embodiments of the invention

Definitions

LAC (look-ahead cruise control): a cruise-control system that uses information about the topography of the road ahead, and calculates an optimal driving profile in the form of a speed trajectory for a vehicle. Also known as a "predictive cruise- control system".

LAP (look-ahead cruise control for platoons): a cooperative cruise-control system that uses information about the topography of the road ahead, and calculates an optimal driving trajectory for all vehicles in a vehicle platoon. Also known as a "predictive cruise-control system for vehicle platoons". The regulatory strategy is determined by, for example, dynamic programming.

v_k: the speed of vehicle f_k in the vehicle platoon with N vehicles.

dk,k+i - the distance between vehicle fk and the vehicle behind it f_k+i in the vehicle platoon.

<¾: the gradient at vehicle f,.

V2V-communication (vehicle-to-vehicle): wireless communication between vehicles, also known as vehicle-to-vehicle communication. V2l-communication (vehicle-to-infrastructure): wireless communication between vehicles and infrastructure, such as road junctions and computer systems.

Figure 1 shows a vehicle platoon with N heavy vehicles f_k that is driving with small spaces d_k, _k+i between the vehicles, driving up a hill. The gradient at vehicle f_k when it drives over the hill is shown as <¾. Each vehicle f_k may be equipped with a receiver and a transmitter for wireless signals, partially shown with an aerial. The vehicles f_k in the vehicle platoon can thus communicate with each other through V2V-communication or through other means such as, for example, mobile communication units, through an application in a communication unit, or through a server. They can communicate also with infrastructure in the form of V2I- communication. The different vehicles f_k have different masses m_k.

Figure 2 shows a vehicle platoon with N=6 heavy vehicles f, that, similarly to the example shown in Figure 1 , is driving with small spaces d_{k k}+i between the vehicles, but which is, instead, driving around a bend. Also in this case is each vehicle f, equipped with a receiver and a transmitter 2 (Figure 3) for wireless signals, and can communicate through V2V-communication and V2I- communication. The bend is shown here with a radius of curvature r.

Each of the vehicle platoons has a leader vehicle, i.e. the first vehicle fi . Each vehicle f_k in the vehicle platoon has, for example, a unique vehicle identity and a vehicle platoon identity that is common for the complete vehicle platoon, in order to be able to maintain knowledge of which vehicles are members of the vehicle platoon. Data that are transmitted wirelessly between the vehicles in the vehicle platoon can be tagged with these identities such that the vehicle of origin of the data that are received can be determined.

Figure 3 shows an example of a vehicle f, in the vehicle platoon and illustrates how it may be equipped. The vehicle f_k is equipped with a positioning unit 1 that can determine the position of the vehicle f_k. The positioning unit 1 may be, for example, configured to receive signals from a global positioning system such as GNSS (Global Navigation Satellite System), for example GPS (Global Positioning System), GLONASS, Galileo or Compass. Alternatively, the positioning unit 1 may be configured to receive signals from, for example, one or several detectors in the vehicle that measure relative distances to, for example, a road junction, vehicles in the surroundings, or similar entities, with known positions. Based on the relative distances, the positioning unit 1 can subsequently determine the position of the vehicle fk. A detector may be configured also to detect a signature in, for example, a road junction, wherein the signature represents a certain position. The positioning unit 1 may in this case be configured to determine its position through detection of the signature. The positioning unit 1 may instead be configured to determine the signal strength of one or several signals from several base stations or road junctions, or base stations and road junctions, etc., with known positions, and in this way to determine the position of the vehicle fk by triangulation. The position of the vehicle fk can in this way be determined. Of course, the

technologies described above may be combined in order to determine the position of vehicle fk. The positioning unit 1 is configured to generate a positioning signal that contains the position of the vehicle fk, and to transmit this signal to one or several units in the vehicle fk. The vehicle fk is, as has been mentioned above, equipped also with a unit 2 for wireless communication. The unit 2 is configured to function as receiver and transmitter of wireless signals. The unit 2 can receive at least one of wireless signals from other vehicles and wireless signals from infrastructure around the vehicle fk, and it can transmit at least one of wireless signals to other vehicles and wireless signals to infrastructure around the vehicle fk. The wireless signals can comprise vehicle parameters from other vehicles, for example their mass, torque developed, speed, and also more complex information such as, for example, the currently used driving profile, driving strategy, etc. The wireless signals may contain also information about the surroundings, such as the gradient a of the road, the radius of curvature r, etc. The vehicle fk may be equipped also with one or several detectors 3 in order to detect the surroundings, for example a radar unit, a laser unit, a gradient gauge, etc. These detectors are generally labelled in Figure 3 as a detector unit 3, but they may be constituted by several different detectors located at different locations in the vehicle. The detector unit 3 is configured to determine a parameter, such as a relative distance, speed, gradient, lateral acceleration, rotation, etc., and to generate a detector signal that contains the parameter. The detector unit 3 is further configured to transmit the detector signal to one or several units in the vehicle fk. The vehicle may be equipped also with a map unit that can provide map information about the road ahead. The map unit may, for example, be a part of the positioning unit 1 . The driver may, for example, specify a final position and the map unit can then, given that it has knowledge of the current position of the vehicle, provide relevant map data about the road ahead between the current position and the final destination.

The vehicle fk communicates internally between its various units through, for example, a bus, such as a CAN bus (controller area network), which uses a message-based protocol. Examples of other communication protocols that can be used are TTP (time-triggered protocol), Flexray, etc. Signals and data as described above can in this way be exchanged between various units in the vehicle fk. Signals and data can instead be transferred in a wireless manner, for example, between the various units. There is also a system 4, fully or partially in the vehicle fk, that will be described below with reference to Figures 4A-4D, which show various examples of the system 4. The dashed lines in the drawings indicate that this is a case of the wireless transfer of data. The system 4 is generally for the purpose of controlling the vehicle platoon, and to establish a common driving strategy for the complete vehicle platoon, based on information about the road ahead. The system 4 thus implements a type of cooperative cruise-control system, an LAP, for the vehicle platoon. The system 4 is useful for the vehicle platoon in particular when it is driving in a hill or around a bend, or in a hill and around a bend. By establishing a common driving profile that applies to the complete vehicle platoon, a well organised vehicle platoon is achieved in which consideration is taken of what is best for the complete vehicle platoon when driving in a hill and in a bend, or when driving in a hill or in a bend. The system 4 comprises an analysis unit 7 that is configured to receive a driving profile for at least one vehicle fk in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein the driving profile contains target values b, for the vehicle fk at positions p, along the road horizon. This driving profile may have been determined by, for example, an existing cruise-control system, such as an LAC or other form of predictive cruise-control system, and passed to the analysis unit 7. The target values b, may be, for example, target speeds v,, target accelerations a,, or target separation distances d,. The analysis unit 7 is further configured to determine a position-based driving strategy for the vehicles in the vehicle platoon, based on at least the driving profile for the vehicle fk. The vehicles in the vehicle platoon are subsequently controlled according to the driving strategy. According to one embodiment, the analysis unit 7 is configured to generate a driving strategy signal that indicates the position-based driving strategy, and to transmit the driving strategy signal through the unit 2 to all vehicles in the vehicle platoon, after which the vehicles in the vehicle platoon are controlled according to the driving strategy. According to another embodiment, the vehicles in the vehicle platoon are controlled according to the driving strategy as this is determined, which will be explained in more detail below.

Thus, a driving profile for an individual vehicle fk can be achieved through the use of a previously determined driving profile designed by a predictive cruise-control system located in the vehicle or other external unit. Predictive cruise control is a predictive control plan that has knowledge about some of the disturbances, in this case the topography of the road, that lie ahead. An optimisation is carried out with respect to a criterion, which optimisation involves a predicted behaviour of the system. An optimal solution is here sought for the problem along a limited road horizon, which is obtained by truncating the horizon of the complete driving session. The road horizon is typically of length 2 km. The objective of the optimisation is to minimise the energy and the time required for the driving session, while the speed of the vehicle is held within a predetermined interval. The optimisation can be carried out using, for example, MPC (model predictive control) or an LQR (linear quadratic regulator) with respect to minimising fuel consumption and time in a cost function/ , based on a non-linear dynamics model and fuel consumption model for the vehicle f_k, limitations on the input control signals, and limitations on the maximum absolute deviation, for example 5 km/h, from the speed limit for the road. One example of how such an optimisation can be carried out is described in "Look-ahead control of heavy vehicles", E.

Hellstrom, Linkoping University, 2010. A vehicle model that describes the principal forces that influence a vehicle in motion are described in that publication, according to: ct"

where « describes the gradient of the road, ¾ and are characteristic coefficients, s describes the force of gravity, .¾ is the air density, ¾ is the wheel radius, and , ' , " are constants specific for the transmission and gearing.

The accelerating mass of the vehicle ^m* (^m«/ ** ^11> 1^ l^) depends on the gross mass ^ , wheel inertia engine inertia is , the gear ratio and efficiency of the gearbox⁵ ί* *!* and the final gear ratio and efficiency ^lf^{r t "} .

The predictive cruise-control system LAC increases the speed of the vehicle in advance when approaching a steep uphill section, and thus the vehicle at least partially obtains a higher mean speed when the vehicle travels along the steep uphill section. In the same manner, the speed is reduced before the vehicle enters a steep downhill section. The speed of the vehicle can be allowed to fall to a minimum in an uphill section and to regain the lost speed until after the vehicle has passed the crown, i.e. now on a flat road. If the uphill section is followed by a downhill section, the speed can be maintained at a lower level in the uphill section in order to avoid having to brake in the downhill section as the speed of the vehicle becomes too high, and instead to exploit the potential energy that the vehicle obtains from its weight in the downhill section. Both time and fuel can be saved in this way.

A low gradient of the road ^G can be described according to

a, < a <€t_u (2) where

(3)

(4)

¾ is the steepest gradient at which the speed can be maintained in an uphill section with maximum engine torque, and ¾ is the steepest gradient in which a heavy vehicle can maintain a constant speed through coasting, without requiring to brake. Steep hills are defined as segments of road with a gradient outside of the interval in (2).

According to one embodiment, the system 4 comprises at least one horizon unit 5 and one driving profile unit 6. The horizon unit 5 is configured to determine a road horizon for at least one vehicle fk in the vehicle platoon with the aid of positional data and map data for a road ahead, which road horizon contains one or several properties of the road ahead. The road horizon can be divided into several road segments. One property may be, for example, that a road segment in the road horizon is classified as a steep uphill or downhill section with a gradient outside of the interval in (2). The driving profile unit 6 is configured to determine a driving profile for at least one vehicle fk in the vehicle platoon based on properties of the road horizon, wherein the driving profile contains one or several target values b, and the associated positions p, for the vehicle fk along the road horizon. The target values b, may be, for example, target speeds v,, target accelerations a,, or target separation distances d,. Thus the system 4 may be configured to determine independently one or several driving profiles for the vehicles in the vehicle platoon, by, for example, the driving profile unit 6 determining an optimal driving speed profile in the same manner as the LAC described above. The function of the system 4 may be configured to come into operation when the road demonstrates special properties, such as, for example, a steep gradient or a small radius of curvature (a tight bend). These properties are reflected in the driving profile that is drawn up through the target values b, that have been generated, and also as properties in the road horizon. The vehicles in the vehicle platoon normally obey a road speed limit, also known as a "preset speed" v_set, which is the highest speed that the speed limit for the road allows. It may be appropriate on hills, in bends, etc. to change the speed in order to achieve improved fuel economy or to improve or maintain safety. It may be appropriate in a bend to reduce the speed, if the radius of curvature is small . An equation that expresses the maximum vehicle speed that can be used, based on the mass of the vehicle and the radius of curvature of the bend, can be used to calculate the maximum speed of the vehicle in the bend. The LAC calculates at least one of fuel-optimal target values and time-optimal target values b,, for example target speeds v,, at positions p, and these target speeds v, can differ from the preset speed v_set in order to achieve economic or safe driving, or economic and safe driving. The analysis unit 7 is configured according to one embodiment to compare the target speeds v, with a preset speed v_set and to determine a difference Δν between v, and v_set- The analysis unit 7 is further configured to compare Δν with a threshold value, and to initiate determination of the position- based driving strategy should Δν exceed the threshold value. The vehicle platoon can in this way be controlled according to the common driving strategy in selected situations or along special road segments, while in other cases the vehicles in the vehicle platoon can be controlled based on their customary driving profiles. When the vehicle platoon in its entirety has left the bend or has reached the top or bottom of the hill, all the vehicles in the vehicle platoon can return to their customary driving profiles. Figure 4A shows an example of the system 4, where the system 4 is located in the vehicle fk, for example, the leader vehicle fi . The system 4 can in this case be a part of a control unit in the vehicle fi . The system 4 is shown here to comprise a horizon unit 5 and a driving profile unit 6 that provide a driving profile for the vehicle fi to the analysis unit 7. Map data and positional are then transmitted through, for example, the internal network in the vehicle fi to the horizon unit 5. Alternatively, an existing LAC in the vehicle fi can provide a driving profile for the vehicle fi to the analysis unit 7. The system 4 can be located instead in an external unit such as, for example, a road junction or a computer system. In this case, positional data, etc. can be transmitted by V2I to the external unit.

According to the example that is schematically illustrated in Figure 4A, the analysis unit 7 determines that it is the driving profile for the vehicle fi that is the selected driving profile for the complete vehicle platoon. The driving strategy is passed to the vehicles in the vehicle platoon through a wireless signal. The driving strategy comprises, for example, a message that means that all the vehicles in the vehicle platoon except the leader vehicle are to measure how the vehicle in front of them in the vehicle platoon behaves, and to adapt their own speed accordingly, in order to maintain the distance d,_{, j} between the vehicles. The vehicles can use, for example, radar to determine the speed of the vehicle in front. The vehicles in the vehicle platoon will in this way follow the speed profile of the leader vehicle fi without it being necessary that they are aware of the speed profile themselves.

According to one embodiment, the vehicles in the vehicle platoon are arranged in a certain order, such that the most limited vehicle is located at the front of the vehicle platoon as the leader vehicle fi , and the remaining vehicles are arranged in a descending order such that the least limited vehicle is located at the rear of the vehicle platoon. It is possible in this manner to ensure that all vehicles in the vehicle platoon can follow the driving profile of the leader vehicle. The most limited vehicle is, for example, the vehicle that has the greatest mass or at lowest available engine torque, or a combination of both. According to one embodiment, the analysis unit 7 is configured to receive a driving profile for each one of several vehicles in the vehicle platoon. The analysis unit 7 is, according to this embodiment, configured to analyse the driving profiles in order to determine one selected driving profile as position-based driving strategy for the vehicles in the vehicle platoon. The selected driving profile can subsequently be passed, for example, to all vehicles in the vehicle platoon, after which each individual vehicle in the vehicle platoon will follow the same selected driving profile at the same positions. Before the driving profile is passed to the vehicles, the positions p, in the driving profile can be mapped to actual positions along the road ahead, such that the vehicles in vehicle platoons can be controlled, with respect to, for example, their speed, according to target values b, at the same actual positions along the road. This is the case for all embodiments described in this application.

Different ways of determining a selected driving profile are available. The selected driving profile can, for example, be determined to be the driving profile that has been determined for the most limited vehicle in the vehicle platoon. Examples of the most limited vehicle have been described above. The most limited vehicle can also be determined to be the vehicle that has the largest speed fluctuations in its driving profile in and close to, or in or close to, an approaching hill or curve, or hill and curve. In order to determine which driving profile is thus to become the selected driving profile, the analysis unit 7 is configured to determine a difference Δν for each driving profile that indicates the largest difference between a maximum speed v_max and a minimum speed v_min, to compare the difference Δν for the different driving profiles with each other and to determine a selected driving profile that has the largest difference Δν based on the comparison. The maximum speed v_max is one of the speed targets v, in the driving profile, and the minimum speed v_min is one of the target speeds v, in the driving profile in and close to, or in or close to, an approaching hill or curve, or hill and curve. Figure 4B shows an example of the system 4, in which a driving profile is determined for each vehicle, in each vehicle f_k. The driving profiles are

subsequently transmitted to the analysis unit 7 in order to determine a position- based driving strategy based on one selected driving profile. The analysis unit 7 is in this case located in an external unit, and the various driving profiles are transmitted to the analysis unit through V2l-communication. After the analysis unit 7 has determined one selected driving profile, the driving strategy is passed to the vehicles in the vehicle platoon through V2l-communication, thus through one or several wireless signals. The driving strategy comprises, for example, a message that means that all the vehicles in the vehicle platoon except the leader vehicle are to measure how the vehicle in front of them in the vehicle platoon behaves, and to adapt their own speed accordingly, in order to maintain the distance d,_{, j} between the vehicles. The vehicles can use, for example, radar to determine the speed of the vehicle in front. The driving strategy comprises also a message to the leader vehicle fi that it is to follow the selected driving profile, and the actual driving profile, in cases in which it is not already the driving profile of the leader vehicle. The vehicles in the vehicle platoon will in this way come to follow the selected speed profile without themselves needing to be aware which of the vehicles' speed profiles they are following. Alternatively, the selected driving profile can be passed to all vehicles in the vehicle platoon, after which each individual vehicle in the vehicle platoon will follow the same selected driving profile.

Figure 4C shows a further example, in which the analysis unit 7 in the system 4 is located in a vehicle, here the leader vehicle fi . As is the case also in the example in Figure 4B, a driving profile is determined for each of the vehicles, in each of the vehicles f_k. The driving profiles are transmitted by V2V communication to the analysis unit 7 in order to determine a position-based driving strategy based on one selected driving profile. After the analysis unit 7 has determined one selected driving profile, the driving strategy is passed to the vehicles in the vehicle platoon through V2V-communication, thus through one or several wireless signals, and it is passed as a message or a signal to the vehicle f_k in which the analysis unit 7 is located, in this case fi . The driving strategy can in this case be the same as those in the example that is illustrated in Figure 4B. The vehicles in the vehicle platoon subsequently control their speed according to the selected driving profile. Figure 4D shows an example of how a position-based strategy can be

sequentially determined. Each vehicle f_k is here equipped with an analysis unit 7_k, or a part of the analysis unit 7. The final vehicle†N determines its driving profile, and transmits it to the analysis unit 7_N-i in the vehicle f_N-i that lies immediately in front of it. The vehicle f_N-i determines its driving profile and the two driving profiles are compared in the analysis unit 7_N-i in order to determine which of the driving profiles is the most limited. Thus the analysis unit 7 is here configured to sequentially compare differences Δν. The way in which this may be carried out has previously been described. The most limited driving profile of the two is subsequently transmitted onwards to the next vehicle ΪΝ-2 that lies immediately in front, for continued comparison. After a final comparison in the leader vehicle, a selected driving profile that requires the greatest changes in speed has been determined. The leader vehicle follows this selected driving profile, and the other vehicles in the vehicle platoon follow the speed of the vehicle immediately in front of them in the vehicle platoon without further communication, through, for example, radar detection, as has been previously explained. As an alternative, the other vehicles in the vehicle platoon can be informed of the same selected driving profile, which they subsequently follow.

The analysis unit 7, the driving profile unit 6 and the horizon unit 5 may comprise or be constituted by one or several processor units and one or several memory units. A processor unit may be constituted by a CPU (central processing unit). The memory unit may comprise a transient or a non-transient memory or it may comprise a transient and a non-transient memory, such as flash memory or RAM (random access memory). The processor unit may be a part of a computer or a computer system, for example an ECU (electronic control unit), in a vehicle 2. Figure 5 shows a flow diagram for a method to control the vehicle platoon that has been described above. The method may be implemented as program code in a computer program P. The computer program is shown in Figures 4A-4D as a part in the analysis unit 7, and thus the computer program P is stored at a memory unit that may be a part of the analysis unit 7. The program code can cause the system 4 to carry out any one of the steps according to the method when it is run on a processor unit in the system 4. The method will now be explained with reference to the flow diagram in Figure 5. The method comprises to receive a driving profile for at least one vehicle fk in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein the driving profile contains target values b, and associated positions p, for the vehicle fk along the road horizon (A1 ). The target values b, may be, for example, target speeds v,, target accelerations a,, or target separation distances d,. According to one embodiment, the method comprises to provide a driving profile for each one of several vehicles in the vehicle platoon. A driving profile can be obtained by, for example, determining a road horizon for at least one vehicle fk in the vehicle platoon with the aid of positional data and map data for a road ahead, which road horizon contains one or several properties of the road ahead, and by determining a driving profile for at least one vehicle fk in the vehicle platoon based on properties of the road horizon, wherein the driving profile contains target values b, and the associated positions p, for the vehicle fk along the road horizon. The method comprises also the determination of a position-based driving strategy for the vehicles in the vehicle platoon, based on at least the driving profile for the vehicle fk (A2). The vehicles in the vehicle platoon are subsequently controlled according to the position-based driving strategy (A3). According to one embodiment, the step (A3) comprises the passing of the position-based driving strategy to all vehicles in the vehicle platoon, after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy. According to one embodiment, (A1 ) comprises analysis of the driving profiles in order to determine one selected driving profile as position-based driving strategy for the vehicles in the vehicle platoon. The analysis can be carried out through, for example, when the driving profile comprises target speeds v,, determining a difference Δν for each driving profile that indicates the largest difference between a maximum speed v_max and a minimum speed v_min, comparing the differences Δν for the various driving profiles with each other, and determining a selected driving profile that has the largest difference Δν based on the comparison. According to one embodiment, the step of comparing the difference Δν occurs sequentially, for example in each vehicle.

According to one embodiment, the method comprises one step before step A1 or A2 that comprises, when the driving profile comprises target speeds v,, comparing the target speeds v, with a preset speed v_set and determining a difference Δν between v, and v_set, comparing Δν with a threshold value and initiating

determination of a position-based driving strategy should Δν exceed the threshold value.

Other embodiments that also can be applied as method have been described in association with the description of the system. The invention includes also a computer program product comprising the program code P stored on a medium that can be read by a computer in order to carry out the method steps described above. The computer program product may be, for example, a CD disk.

The present invention is not limited to the embodiments described above. Various alternatives, modifications and equivalents can be used. For this reason, the embodiments named above do not limit the scope of the invention, which is defined by the attached patent claims.

Claims

1 . A system (4) to control a vehicle platoon that comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit (1 ), a unit (2) for wireless communication, wherein the system (4) comprises an analysis unit (7) that is configured to:

- receive a driving profile for each one of several vehicles fk in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein each driving profile contains target values b, and associated positions p, for the relevant vehicle fk along the road horizon;

- analyse the said driving profiles in order to determine a selected driving profile as position-based driving strategy for the vehicles in the vehicle platoon, after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy.

2. The system according to claim 1 , wherein the analysis unit (7) is configured to:

- generate a driving strategy signal that indicates the position-based driving strategy, and

- transmit the driving strategy signal to all vehicles in the vehicle platoon, after which the vehicles in the vehicle platoon are controlled according to the position-based driving strategy.

3. The system (4) according to claim 1 , wherein the target values b, are target speeds v,, and the analysis unit (7) is configured to:

- determine a difference Δν for each driving profile that indicates the largest difference between a maximum speed v_max and a minimum speed v_min;

- compare the differences Δν for the various driving profiles with each other;

- determine a selected driving profile that has the largest difference Δν based on the comparison.

4. The system (4) according to claim 3, wherein the analysis unit (7) is configured to compare the differences Δν sequentially.

5. The system (4) according to any one of the preceding claims, wherein the target values b, are target speeds v,, and the analysis unit (7) is configured to:

- compare the target speeds v, with a preset speed v_set and to determine a difference Δν between v, and v_set;

- compare Δν with a threshold value, and to initiate determination of the position-based driving strategy should Δν exceed the threshold value.

6. The system (4) according to any one of the preceding claims, that comprises:

- a horizon unit (5), configured to determine a road horizon for at least one vehicle fk in the vehicle platoon with the aid of positional data and map data for a road ahead, which road horizon contains one or several properties of the road ahead;

- a driving profile unit (6), configured to determine a driving profile for at least one vehicle fk in the vehicle platoon, based on properties of the road horizon, wherein the driving profile contains target values b, and associated positions p, for the vehicle fk along the road horizon.

7. A method to control a vehicle platoon that comprises at least one leader vehicle and one further vehicle, each of which has a positioning unit (1 ) and a unit (2) for wireless communication, wherein the method comprises to:

- provide a driving profile for each one of several vehicles fk in the vehicle platoon along a road horizon for the road ahead of the vehicle, wherein each driving profile contains target values b, and associated positions p, for the relevant vehicle fk along the road horizon;

8. The method according to claim 7, that comprises the passing of the position-based driving strategy to all vehicles in the vehicle platoon.

9. The method according to claim 7, wherein the target values b, are target speeds v, and the analysis comprises to:

10. The method according to claim 9, wherein the step of comparing differences Δν takes place sequentially.

1 1 . The method according to any one of claims 7 to 10, wherein the target values b, are target speeds v, and method further comprises to:

- compare Δν with a threshold value, and to initiate the determination of a position-based driving strategy should Δν exceed the threshold value.

12. The method according to any one of claims 7 to 10, which comprises to provide a driving profile through:

- determining a road horizon for at least one vehicle fk in the vehicle platoon with the aid of positional data and map data for a road ahead, which road horizon contains one or several properties of the road ahead;

- determining a driving profile for at least one vehicle fk in the vehicle platoon based on properties of the horizon, wherein the driving profile contains target values b, and associated positions p, for the vehicle fk along the road horizon.

13. A computer program (P) at a system (4), where the said computer program (P) comprises program code in order to cause the system (4) to carry out any one of the steps according to claims 7 to 12.

14. A computer program product comprising a program code stored on a medium that can be read by a computer in order to carry out the method steps according to any one of claims 7 to 12.