SE539521C2

SE539521C2 - Method and control unit for adjusting a gap between vehicles

Info

Publication number: SE539521C2
Application number: SE1550721A
Authority: SE
Inventors: Alam Assad
Original assignee: Scania Cv Ab
Priority date: 2015-06-04
Filing date: 2015-06-04
Publication date: 2017-10-03
Also published as: DE102016006523A1; SE1550721A1; BR102016009677A2

Description

METHOD AND CONTROL UNIT FOR ADJUSTING A GAP BETWEEN VEHICLES TECHNICAL FIELD This document discloses a method and a control unit. More particularly, a method and a control unit is described, for adjusting a gap between a follower vehicle and a preceding vehicle on a road, in order to reduce air drag and avoid braking.

BACKGROUND Under normal circumstances, the air drag of a vehicle is proportional to the square of the vehicle's velocity. This means that a reduction in speed from 90 km/h to 80 km/h reduces air drag by around 20 percent. A fact that might not be very well known to the common person is the effect of reduced air drag by staying close to a preceding vehicle.

An Adaptive Cruise Control (ACC) enables both of the above mentioned techniques for reducing air drag, and thereby also fuel consumption, by utilising radar, lidar, and/ or camera information for keeping the distance between vehicles and thereby allowing for a lower cruising speed than the preset speed reduces air drag when a forward vehicle is present, and also by staying closer to a forward vehicle may reduce air drag due to the aerodynamic effects.

Hence, by operating several vehicles in a chain formation, also known as platooning or convoy, a substantial fuel reduction can be obtained through automated systems.

Even though automated control systems already exist, such as the ACC, that allows for a small inter-vehicle spacing, they make no assumptions about the preceding vehicle characteristics OR assume that information regarding the preceding vehicle characteristics is known through, for example, Vehicle-to-Vehicle (V2V) communication.

When no assumptions are made with respect to the preceding vehicle, a lot of scenarios can occur that will reduce the fuel saving potential or even increase the fuel consumption compared to when the vehicle is operating alone. Such scenarios occur for example over varying topographies, where the engine power or vehicle mass have a strong impact on the vehicle dynamics.

If the preceding vehicle has a relatively strong engine, with respect to its mass, it will be able to maintain its speed over an uphill segment. If the follower vehicle has a weak engine, with respect to its mass, the distance between the preceding vehicle and the follower vehicle will then increase over the uphill segment. Hence, the gap will then have to be closed after the uphill to regain the air drag reduction. The gap is commonly reduced as soon as possible by maximum fuel injection (to obtain a high engine torque) and thereby achieving a high velocity to catch up. However, when the gap is closed, in most cases, the speed of the preceding vehicle is matched by braking, which is fuel-inefficient.

Braking commonly occurs over downhill segments as well, when a heavier follower vehicle is tracking a lighter preceding vehicle. Over the downhill segment, the preceding vehicle will start to coast, i.e. cut off the fuel injection, in order not to accelerate too fast. The follower vehicle, being heavier, will accelerate faster and will have to brake in order to match the acceleration and/ or speed of the preceding vehicle. This is pure waste, since the energy obtained from fuel combustion is lost through frictional heat in the brake discs.

Thereby energy is unnecessarily wasted. Also, the brakes are unnecessarily used, which may lead to early replacement due to wear.

Even though the characteristics of the preceding vehicle can be conveyed through wireless information if wireless antennas are fitted, the information can be erroneous due to uncertainties in sensor information. Therefore, there is a strong need of classifying the characteristics/ behaviour of the preceding vehicle relative to the follower vehicle, to improve the fuel reduction possibilities of the automated control strategy for vehicle following, i.e. platooning.

The described problems will appear on any vehicles. However, the problems will increase with weight, both for the preceding vehicle and the following vehicle. Thus in particular heavy vehicles like trucks, busses etc., are affected.

In some previously known solutions, a regulating strategy for driving a following vehicle is known. A number of acceleration values for a target vehicle may be determined on the basis of input values, which input values take the form of, or are derived from, a detected distance between the vehicle and the target vehicle. Thereby the target vehicle may be categorised Into type, such as truck, passenger car, motorcycle etc.; weight; and/ or engine power. However, no guidance is given to the driver to proactively use this information for adjusting the distance between the vehicle and the target vehicle, based on this information, in order to avoid braking and thereby save energy.

In some other previously known solutions, a method is provided in a following vehicle for adjusting the speed of the vehicle in order to keep the distance constant to the target vehicle. No adjustment of the distance depending on the road slope is made. Further, no prediction of the road slope is made in order to proactively adjust the speed of the follower vehicle in order to avoid braking at the follower vehicle.

According to yet some previously known solutions, the follower vehicle collects information concerning the target vehicle. Based on this collected information, it may be determined which distance to keep between the vehicles. However, the solution is completely static. Once the inter-vehicular distance is determined, it is kept, irrespectively of any differences in slope.

As these described scenarios, and similar variants of them, will lead to increased fuel consumption, it is desirable to find a solution.

SUMMARY It is therefore an object of this invention to solve at least some of the above problems and adjust a gap between a follower vehicle and a preceding vehicle in order to reduce air drag and avoid braking.

According to a first aspect of the invention, this objective is achieved by a method for adjusting a gap between a follower vehicle and a preceding vehicle on a road, in order to reduce air drag and avoid braking. The method comprises determining a road slope of the road on which the vehicles are driving, as either an uphill road slope or downhill road slope. Further the method also comprises classifying the preceding vehicle as either stronger or weaker than the follower vehicle when driving in an uphill road slope, or as either heavier or lighter than the follower vehicle when driving in a downhill road slope based on said road slope. The method additionally comprises determining geographical position of the vehicle. In addition the method further comprises determining driving direction of the vehicles. Also the method further comprises predicting an ahead road slope of the road ahead of the vehicles in the determined driving direction, as either an uphill road slope, or a downhill road slope, in the determined driving direction, by extracting road slope data associated with a geographical position situated ahead of the determined geographical position of the vehicle in the determined driving direction of the vehicles, from a database. Additionally the method further comprises adjusting the gap between the follower vehicle and the preceding vehicle by: reducing the gap to the preceding vehicle when an uphill road slope is predicted and the preceding vehicle is classified as stronger; maintaining the gap to the preceding vehicle when an uphill road slope is predicted and the preceding vehicle is classified as weaker; increasing the gap to the preceding vehicle when a downhill road slope is predicted and the preceding vehicle is classified as lighter; or maintaining the gap to the preceding vehicle when a downhill road slope is predicted and the preceding vehicle is classified as heavier.

According to a second aspect of the invention, this objective is achieved by a control unit in a follower vehicle, for adjusting a gap between a follower vehicle and a preceding vehicle on a road, in order to reduce air drag and avoid braking. The control unit is configured for determining a road slope of the road on which the vehicles are driving, as either an uphill road slope or downhill road slope. Further the control unit is configured for classifying the preceding vehicle as either stronger or weaker than the follower vehicle when driving in an uphill road slope, or as either heavier or lighter than the follower vehicle when driving in a downhill road slope based on said road slope. In addition the control unit is configured for determining geographical position of the vehicle. Further the control unit is configured for determining driving direction of the vehicles. The control unit is furthermore configured for predicting an ahead road slope of the road ahead of the vehicles in the determined driving direction, as either an uphill road slope, or a downhill road slope, in the determined driving direction, by extracting road slope data associated with a geographical position situated ahead of the determined geographical position of the vehicle in the determined driving direction of the vehicles, from a database. Additionally, the control unit is configured for adjusting the gap between the follower vehicle and the preceding vehicle by: reducing the gap to the preceding vehicle when an uphill road slope is predicted and the preceding vehicle is classified as stronger; maintaining the gap to the preceding vehicle when an uphill road slope is predicted and the preceding vehicle is classified as weaker; increasing the gap to the preceding vehicle when a downhill road slope is predicted and the preceding vehicle is classified as lighter; or maintaining the gap to the preceding vehicle when a downhill road slope is predicted and the preceding vehicle is classified as heavier.

Thanks to the described aspects, by classifying the preceding vehicle as stronger, weaker, heavier and/ or lighter, based on how it behaves during uphill and downhill driving in relation to the follower vehicle, it is possible to predict how it will behave also in an ahead uphill and downhill road section. By also predicting an ahead road slope in uphill or downhill, measures can be taken before arriving to the road slope in order to adjust the gap between the vehicles before the hill, in order to make the follower vehicle avoid having to brake, while keeping the gap between the vehicles enough large for keeping the air drag as low as possible. Thereby energy is saved, both by avoid braking with the follower vehicle, and also by not allowing the distance between the vehicles to grow so big that no air drag reduction is achieved. Thereby fuel consumption is reduced, while maintaining a safe distance to the preceding vehicle. Other advantages and additional novel features will become apparent from the subsequent detailed description.

FIGURES Embodiments of the invention will now be described in further detail with reference to the accompanying figures, in which:Figure 1illustrates a follower vehicle and a preceding vehicle according to an embod iment of the invention;Figure 2Aillustrates a follower vehicle and a preceding vehicle according to an embod iment of the invention;Figure 2Billustrates a follower vehicle and a preceding vehicle according to an embod iment of the invention;Figure 3Aillustrates graphs over a follower vehicle and a preceding vehicle driving downhill, in an embodiment;Figure 3Billustrates graphs over a follower vehicle and a preceding vehicle driving uphill, in an embodiment;Figure 4Aillustrates a follower vehicle interior according to an embodiment;Figure 4Billustrates a follower vehicle interior according to an embodiment;Figure 5is a flow chart illustrating an embodiment of the method;Figure 6is an illustration depicting a system according to an embodiment.

DETAILED DESCRIPTION Embodiments of the invention described herein are defined as a method and a control unit, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Figure 1illustrates a scenario with a follower vehicle100,driving in a driving direction 105, following a preceding vehicle110.There is a gap t between the follower vehicle 100 and the preceding vehicle 110, when driving on the road120.

The vehicles 100, 110 may comprise e.g. a truck, a bus, a car, a motorcycle or any similar vehicle or other means of conveyance. The vehicles 100, 110 may comprise vehicles of the same, or different types. Further, the vehicles 100, 110 may be driver controlled or driverless autonomously controlled vehicles in different embodiments. However, for enhanced clarity, the vehicles 100, 110 are subsequently described as having a driver.

The follower vehicle 100 and the preceding vehicle 110 may be organised in a platoon or vehicle convoy, wherein the vehicles are driving in coordination after each other with only a small distance t between the vehicles, such as some decimetres or some meters, such as e.g. 20-40 meters. However, the inter-vehicular distance or gap t may be a variable time gap e.g. between 0.1-3 seconds, or any other appropriate time interval.

Further, the gap t between the vehicles 100, 110 may vary with the speed of the vehicles 100, 110, as the time gap t will create length distances of different length in different vehicle speeds (except when driving at very low speed, approaching a stationary condition, where a certain minimum distance in length may be desired). Thus the gap t may be e.g. some centimetres, some decimetres, some meters or some tenths of meters in some embodiments. In other embodiments, the gap t may be e.g. some fractions of a second such as e.g. some tenths of a second.

The low gap t between the vehicles 100, 110, in comparison with the normal distance kept between non-coordinated vehicles, leads to reduced air drag for the vehicles 100,110, leading to reduced energy consumption.

The gap t may be adjusted by a control unit, which may comprise e.g. an Adaptive Cruise Control (ACC) system (sometimes also referred to as an Autonomous Intelligent Cruise Control (AiCC) system, or similar. The control unit may adjust the gap t when driving in hilly terrain, in particular when the vehicles 100, 110 have different driving properties, such as heavier/ lighter and/ or stronger/ weaker.

The distance t to the preceding vehicle 110 may be measured by e.g. a radar unit, a lidar unit, a camera or similar equipment in some embodiments, configured for emitting radio waves and receiving reflexions of the emitted radio waves, reflected by the preceding vehicle 110. By continuously or at certain time intervals measuring the distance t to the preceding vehicle 110 and also continuously or at certain time intervals determine the speed of the vehicle 100, e.g. from the speedometer of the vehicle 100, or from a Global Positioning System (GPS) receiver in the vehicle 100. Thereby, the gap t may be calculated by dividing the measured distance in length with the determined speed.

According to some alternative embodiments, another on-board rangefinder sensor may be used instead of the radar unit, such as e.g. a laser rangefinder, an ultrasonic sensor emitting an ultrasonic wave and detecting and analysing the reflections, or other similar devices.

Thereby, in some embodiments, firstly a classification is made by the follower vehicle 100 concerning the preceding vehicle 110. The classification may be performed by e.g. the aid of radar-, lidar-, and/ or camera information. These type of sensors (radar-, lidar-, and/ or camera) are available in most modern heavy duty vehicles already, for other purposes.

Also, the classification may in some embodiments be improved by utilising additional map data, which can provide information regarding the slope of the current segment that the vehicles 100, 110 are traversing. By measuring the relative speed, acceleration, and/ or distance t to the preceding vehicle 110 over a road segment 120 it can be deduced whether the preceding vehicle 110 is heavier, lighter, stronger, and/ or weaker than the own vehicle 100, see Table 1, in uphill and downhill, respectively.

Image available on "Original document" Classification over uphill segments: The behaviour of the preceding vehicle 110 can be measured through the radar, lidar, and/ or camera when travelling over an uphill segment. If the follower vehicle 100 has a maximum fuel injection over the uphill segment to obtain maximum torque while dropping in speed, it detect that it is travelling over a steep uphill segment. If the preceding vehicle 110 is not dropping in speed, the preceding vehicle 110 is classified as beingstronger.On the other hand, if the speed of the preceding vehicle 110 is dropping faster, the preceding vehicle 110 is classified as beingweaker.

Classification over downhill segments: The behaviour of the preceding vehicle 110 can be measured through the radar, lidar, and/ or camera when travelling over a downhill segment. If the follower vehicle 100 is travelling over a downhill segment, such that it increases in speed even though it is coasting/ eco-rolling, the downhill is detected and considered as steep. Then if the preceding vehicle 110 is accelerating faster, it is classified asheavier.On the other hand, if the follower vehicle 100 is accelerating faster such that the distance between the vehicles 100, 110 decreases, the preceding vehicle 110 is classified aslighter.

The expressions coasting and eco-rolling may herein be utilised interchangeably, even if they have a slightly different meaning. Coasting means that the powertrain is connected, the gear is engaged and the engine helps to slow down the vehicle 100, 110. Eco-rolling means that the gear is in neutral, the powertrain is disengaged and thus can roll longer in downhill, which may be fuel efficient in some cases.

It is to be noted that the respective classifications stronger, weaker, heavier and/ or lighter is a classification of the behaviour of the preceding vehicle 110 in uphill/ downhill respectively, independently of the reason and not necessarily a classification of the actual weight and/ or engine capacity, but may be a result of friction etc.

The detection of the behaviour for the preceding vehicle 110 can be done over several hilly segments. Each time a classification is done over a certain hill segment, it may be saved and stored in a memory. The next time a road segment of the same type (uphill/ downhill) is encountered, the previously saved result may be re-evaluated and hopefully confirmed. If the result is contradictive, another evaluation is made over the next suitable segment. The evaluation may be conducted a sufficient or necessary number of times, until the characteristics of the preceding vehicle 110 can be classified and confirmed.

When the classification is made, a suitable icon or text may be displayed in the instrument cluster or on any other suitable interface. By informing the driver of the preceding vehicle type/ classification, the control strategies (explained below) will make sense and be more acceptable.

The classification mentioned above may be based on map information in some embodiments. Such map information comprising the slope of the road, the classification can be made by analytical calculations. In other words, the mass and engine power can be estimated with the aid of map data by determining the geographical position of the vehicles 100, 110 and then extract the road slope at the determined geographical position of the vehicles 100, 110, in some embodiments. However, in other embodiments the road slope may be determined based on map information by the preceding vehicle 110 and sent to the follower vehicle 100.

Further in some embodiments, the classification of the preceding vehicle 110 may be based on direction of the road slope, according to the map information at the geographical position of the vehicles 100, 110, i.e. uphill or downhill, and/ or inclination size of the road slope.

In different embodiments, the road slope data may be stored in a database in the preceding vehicle 110, in a database in the follower vehicle 100, or in a vehicle external entity such as a server, which keeps track of any of the vehicles 100, 110.

A suitable fuel-efficient control strategy when the vehicles 100, 110 are driving in uphill may comprise classifying the preceding vehicle 110 asstrongerthe gap t before entering an uphill may be reduced, since it is known that the gap t will increase over the uphill segment. If the preceding vehicle 110 is classified asweaker,no prior action is necessary before entering the uphill. It is just known that the distance t can be maintained over the uphill segment for fuel-efficiency.

In downhill, when the preceding vehicle 110 is classified asheavier,a calculation may be made (i.e. a prediction is made given that map data is available) with respect to how much the speed is likely to increase over the downhill segment. If the predicted speed profile stays within the road speed limits or the limits set by the driver, the distance is maintained to the preceding vehicle 110 by injecting fuel over the downhill segment. On the other hand, if the preceding vehicle 110 is classified aslighter,the distance t may be increased prior to the downhill. The follower vehicle 100 will accelerate faster over the downhill segment and then the distance t to the preceding vehicle 100 may be reduced. By increasing the gap t before the downhill and then catching up over (and/ or after) the downhill, braking of the follower vehicle 100 can be avoided and thus the fuel consumption is reduced.

Further by using the determined geographical position of the vehicles 100,110 for predicting an ahead road slope of the road 120 ahead of the vehicles 100,110 by extracting road slope data associated with a geographical position situated ahead of the determined geographical position of the vehicle 100 in the determined driving direction 105 of the vehicles 100, 110, from a database, the distance t between the vehicles 100, 110 may be adjusted before arriving to the uphill/ downhill. Thereby a proactive inter-vehicular distance adjustment may be made.

The main advantage by classifying the type of the preceding vehicle 110 according to Table 1 and then automatically adjust the gap t to the preceding vehicle 110 is that a significant fuel reduction can be obtained and the brake ware will be reduced. Another advantage is that currently available on-board sensors can be utilised for the classification, i.e. there is no requirement on having V2V-communication for the classification or control. However, V2V-communication may be used for the mentioned purposes of classification and control. In this case the parameters for the preceding vehicle 110 can be sent through wireless communication. The classification through radar-, lidar-, and/ or camera-information may then be used to verify that the received parameters are correct.

Figure 2Aillustrates an example of a scenario where the vehicles 100, 110 presented in Figure 1 have arrived to a hilly region, driving in uphill.

Thus the preceding vehicle 110 is driving uphill, at a road slope a of the road 120 ahead of the follower vehicle 100 in the driving direction 105.

The road slope a may in some embodiments be determined at different geographical positions ahead of the vehicle 100 in the driving direction 105, such as e.g. just in front of the vehicle 100, somewhere between the vehicle 100 and the preceding vehicle 110, at the geographical position of the preceding vehicle 110, or at a geographical position in front of the preceding vehicle 110 in different embodiments. The road slope a may be determined by extracting road slope direction and/ or size from a database, associated with the geographical position of the follower vehicle 100, and/ or the preceding vehicle 110.

The gap t may be adjusted by maintaining or prolonging the gap t before arriving at the uphill, when the preceding vehicle 110 is classified as weaker than the follower vehicle 100. The time gap t may be prolonged by e.g. 1-15% in some non-limiting embodiments. In some embodiments, the time gap t may be adjusted linearly with the size of the road slope a ahead of the vehicle 100, within predetermined limits. Such limits may be e.g. 85%-115%, or similar, in some embodiments. Thereby, it is avoided that the follower vehicle 100 has to brake in order to keep a minimum distance t to the preceding vehicle 110.

Further, the gap t may be adjusted by reduction before arriving at the uphill, when the preceding vehicle 110 is classified as stronger than the follower vehicle 100. The time gap t may be decreased by e.g. 1-15% in some non-limiting embodiments. In some embodiments, the time gap t may be adjusted linearly with the size of the road slope a ahead of the vehicle 100, within predetermined limits. Such limits may be e.g. 85%-115%, or similar, in some embodiments. Thereby, the follower vehicle 100 can reduce the gap t to the preceding vehicle 110 and thereby reduce air drag, as the preceding vehicle 110 successively will prologue the gap t when driving in the uphill.

Figure 2Billustrates an example of a scenario where the follower vehicle 100 and the preceding vehicle 110 just has passed a hill and has started to drive downhill at the slope a.

Thus the preceding vehicle 110 is driving downhill, at a road slope a of the road 120 ahead of the follower vehicle 100 in the driving direction 105.

The gap t may be adjusted by prolongation before arriving at the downhill, when the preceding vehicle 110 is classified as lighter than the follower vehicle 100. The time gap t may be prolonged by e.g. 1-15% in some non-limiting embodiments. In some embodiments, the time gap t may be adjusted linearly with the size of the road slope a ahead of the vehicle 100, within predetermined limits. Such limits may be e.g. 85%-115%, or similar, in some embodiments. Thereby, it is avoided that the follower vehicle 100 has to brake in order to keep a minimum distance t to the preceding vehicle 110.

Further, the gap t may be adjusted by maintaining or reducing the gap t before arriving at the downhill, when the preceding vehicle 110 is classified as heavier than the follower vehicle 100. The time gap t may be decreased by e.g. 1-15% in some non-limiting embodiments. In some embodiments, the time gap t may be adjusted linearly with the size of the road slope a ahead of the vehicle 100, within predetermined limits. Such limits may be e.g. 85%-115%, or similar, in some embodiments. Thereby, the follower vehicle 100 can reduce the gap t to the preceding vehicle 110 and thereby reduce air drag, as the preceding vehicle 110 successively will prolong the gap t when driving in the downhill.

Figure 3Aillustrates an example of the previously described scenario in Figure 2B, wherein the vehicles 100, 110 are approaching a downhill at an ahead road slope -B and the preceding vehicle 110 is classified as lighter than the follower vehicle 100.

When the vehicles 100, 110 are approaching the downhill, the follower vehicle 100 may reduce the vehicle velocity by coasting before arriving at the downhill, as illustrated in the velocity/ distance diagram. Thereby the gap t is increased. As the vehicles 100,110 are driving in the downhill, the heavier follower vehicle 100 is gradually increasing velocity in relation to the preceding vehicle 110 when the vehicles 100, 110 are coasting or eco-rolling. When the vehicles 100, 110 has passed the downhill, the follower vehicle 100 may hold a bit higher velocity in order to decrease the gap t.

In the engine torque graph at the bottom of the page, the engine torque of the preceding vehicle 110 is illustrated. The preceding vehicle 110 is coasting down the downhill.

Figure 3Billustrates an example of the previously described scenario in Figure 2A, wherein the vehicles 100, 110 are approaching an uphill at an ahead road slope B driving in uphill and the preceding vehicle 110 is classified as stronger than the follower vehicle 100.

When the vehicles 100,110 are approaching the uphill, the follower vehicle 100 may increase the vehicle velocity before arriving at the uphill, as illustrated in the velocity/ distance diagram, in relation to the preceding vehicle 110. Thereby the gap t is decreased. As the vehicles 100,110 are driving in the uphill, the weaker follower vehicle 100 is gradually decreasing velocity in relation to the preceding vehicle 110. When the vehicles 100, 110 has passed the uphill, the follower vehicle 100 holds a lower velocity in order to increase the gap t.

In the engine torque graph at the bottom of the page, the engine torque of the preceding vehicle 110 is illustrated. The preceding vehicle 110 is driving at maximum engine torque during a passage of the uphill.

Figure 4Aillustrates an interior view of the scenario in Figure 1, or Figures 2A-2B, as it may be perceived by the driver of the follower vehicle 100.

The follower vehicle 100 thus follow the preceding vehicle 110 at a gap t. The vehicle 100 comprises a control unit410configured for adjusting the gap t between the follower vehicle 100 and the preceding vehicle 110, in order to reduce air drag and avoid braking. The control unit 410 may be part of an ACC system of the follower vehicle 100, or may be configured to control the ACC system of the follower vehicle 100.

In some embodiments, an optional display420may be comprised in the follower vehicle 100, connected to the control unit 410. Thereby, information such as e.g. current size of the gap t, current road slope a ahead of the follower vehicle 100, geographical position of the follower vehicle 100, etc.

Further, the follower vehicle 100 comprises a positioning unit430.The positioning unit 430 may be based on a satellite navigation system such as the Navigation Signal Timing and Ranging (Navstar) Global Positioning System (GPS), Differential GPS (DGPS), Galileo, GLONASS, or the like. Thus the positioning unit 430 may comprise a GPS receiver.

The geographical position of the follower vehicle 100 may be determined continuously or at certain predetermined or configurable time intervals according to various embodiments.

Positioning by satellite navigation is based on distance measurement using triangulation from a number of satellites440-1, 440-2, 440-3, 440-4.The satellites 440-1, 440-2, 440-3, 440-4 continuously transmit information about time and date (for example, in coded form), identity (which satellite 440-1, 440-2, 440-3, 440-4 which broadcasts), status, and where the satellite 440-1, 440-2,440-3,440-4 are situated at any given time. GPS satellites 440-1,440-2, 440-3, 440-4 sends information encoded with different codes, for example, but not necessarily based on Code Division Multiple Access (CDMA). This allows information from an individual satellite 440-1,440-2,440-3,440-4 distinguished from the others' information, based on a unique code for each respective satellite 440-1, 440-2, 440-3, 440-4. This information can then be transmitted to be received by the appropriately adapted positioning unit 430 in the follower vehicle 100.

Distance measurement can according to some embodiments comprise measuring the difference in the time it takes for each respective satellite signal transmitted by the respective satellites 440-1, 440-2, 440-3, 440-4, to reach the positioning unit 430. As the radio signals travel at the speed of light, the distance to the respective satellite 440-1, 440-2, 440-3, 440-4 may be computed by measuring the signal propagation time.

The positions of the satellites 440-1, 440-2, 440-3, 440-4 are known, as they continuously are monitored by approximately 15-30 ground stations located mainly along and near the earth's equator. Thereby the geographical position, i.e. latitude and longitude, of the follower vehicle 100 may be calculated by determining the distance to at least three satellites 440-1, 440-2, 440-3, 440-4 through triangulation. For determination of altitude, signals from four satellites 440-1, 440-2, 440-3, 440-4 may be used according to some embodiments. Having determined the geographical position of the follower vehicle 100, and also determined the driving direction 105 of the follower vehicle 100, the control unit 410 may extract a road slope a at a geographical position of the road 120 ahead of the follower vehicle 100 in the determined driving direction 105. As stated before, the road slope a may be determined e.g. at the follower vehicle 100, just in front of the follower vehicle 100, somewhere between the follower vehicle 100 and the preceding vehicle 110, at the geographical position of the preceding vehicle 110, or at a geographical position in front of the preceding vehicle 110 in different embodiments, based on road slope data such as road slope direction and/ or size, associated with geographical positions in a database. This position, i.e. the geographical position in front of the follower vehicle 100 where the road slope a is determined, may be configurable by the driver in some embodiments, and may be dependent of the speed of the follower vehicle 100, such that low speed is associated with a short distance ahead and high speed is associated with a long distance ahead, in some embodiments.

The road slope a at the geographical position of the road 120 may be extracted from a database450.The database 450 may be situated within the follower vehicle 100 in some embodiments, or alternatively the database 450 may be external to the follower vehicle 100, and accessible by the control unit 410. Such external database 450 may be situated in the preceding vehicle 110, or in a vehicle external entity such as a server, keeping track of the follower vehicle 100 and/ or the preceding vehicle 110.

In the database 450, different geographical positions are stored associated with a respective road slope value a, which may be extracted by using a geographical position and a direction as input values.

Figure 4Balso illustrates an example of an alternative embodiment of the follower vehicle 100, previously discussed in conjunction with the presentation of Figure 4A.

In this embodiment, the preceding vehicle 110 has a wireless transmitter470.The wireless transmitter 470 is configured for transmitting wireless signals, to be received by a wireless receiver480in the vehicle 100.

The wireless signal may be e.g. a Vehicle-to-Vehicle (V2V) signal, or any other wireless signal based on, or at least inspired by wireless communication technology such as Wi-Fi, Wireless Local Area Network (WLAN), Ultra Mobile Broadband (UMB), Bluetooth (BT), or infrared transmission to name but a few possible examples of wireless communications. According to some embodiments, the road slope a may be measured by the preceding vehicle 110. The road slope a at the geographical position of the preceding vehicle 110 may be determined continuously, or at certain intervals, and transmitted via the wireless transmitter 470, to be received by the wireless receiver 480 in the follower vehicle 100.

Figure 5illustrates an example of a method500according to an embodiment. The flow chart in Figure 5 shows the method 500 for use in a control unit 410 of a vehicle 100, for adjusting a gap t between a follower vehicle 100 and a preceding vehicle 110 on a road 120, in order to reduce air drag and avoid braking.

The size of the gap t between the follower vehicle 100 and the preceding vehicle 110 may be determined based on a measurement made by a measurement unit 460 comprising a radar, lidar and/ or camera situated in the front part of the follower vehicle 100, or by vehicle positioning data of a positioning unit 430, and/ or wireless communication between the follower vehicle 100 and the preceding vehicle 110.

The mentioned wireless signal may be based on, or at least inspired by wireless communication technology such as V2V, Wi-Fi, Wireless Local Area Network (WLAN), Ultra Mobile Broadband (UMB), Bluetooth (BT), or infrared transmission to name but a few possible examples of wireless communications.

The vehicle 100 may be any arbitrary kind of means for conveyance, such as a truck, a bus or a car.

In order to correctly be able to adjust the gap t, the method 500 may comprise a number of steps501-507.However, some of these steps 501-507 may be performed solely in some alternative embodiments, like e.g. step 507. Further, the described steps 501-507 may be performed in a somewhat different chronological order than the numbering suggests. The method 500 may comprise the subsequent steps:Step 501comprises determining a road slope a, -a of the road 120 on which the vehicles 100, 110 are driving, as either an uphill road slope a or downhill road slope a, to direction (uphill/ downhill) and/ or size. The road slope a, -a of the road 120 may be extracted from a database 450, where the road slope a, -a is stored associated with a geographical position of the preceding vehicle 110, and/ or the follower vehicle 100.

Step 502comprises classifying the preceding vehicle 110 as either stronger or weaker than the follower vehicle 100 when driving in an uphill road slope a, or as either heavier or lighter than the follower vehicle 100 when driving in a downhill road slope -a, based on sadi road slope a, -a.

The classification of the preceding vehicle 110 may be made by determining the preceding vehicle 110 to be stronger than the follower vehicle 100 when the gap t is prolonged, when driving in the uphill road slope a. Further the classification of the preceding vehicle 110 may be made by determining the preceding vehicle 110 to be weaker than the follower vehicle 100 when the gap t is shortened, when driving in the uphill road slope a. In addition the classification of the preceding vehicle 110 may be made by determining the preceding vehicle 110 to be heavier than the follower vehicle 100 when the gap t is prolonged, when driving in the downhill road slope -a. Also, the classification of the preceding vehicle 110 may be made by determining the preceding vehicle 110 as lighter than the follower vehicle 100 when the gap t is shortened, when driving in the downhill road slope -a.

In some embodiments, the weight and engine power of the preceding vehicle 110 may be determined at the preceding vehicle 110 and provided to the follower vehicle 100 via a wireless communication interface, which information may be utilised for classifying the preceding vehicle 110, by comparison with the weight and engine power of the follower vehicle 100. The weight of the follower vehicle 100 may be measured by a weight sensor in the follower vehicle 100, or by measuring the acceleration of the follower vehicle 100 and comparing with stored reference values, and engine power may be retrieved from a memory in some embodiments.

The classification of the preceding vehicle 110 may be repeated over a plurality of road slopes a, -a of the road 120 at different geographical positions in some embodiments.

Step 503comprises determining geographical position of the follower vehicle 100.

The geographical position may be determined based on GPS positioning in some embodiments, or positioning based on any other satellite navigation system.

Step 504comprises determining driving direction 105 of the vehicles 100, 110.

The driving direction 105 of the vehicles 100, 110 may be determined based on the location of the destination of the journey, or by extrapolating the driving direction based on previously determined geographical positions of the vehicles 100, 110 and possibly knowledge of the road direction, e.g. from stored map data.

Step 505comprises predicting an ahead road slope B of the road 120 ahead of the vehicles 100, 110 in the determined 504 driving direction 105, as either an uphill road slope B, or a downhill road slope -B, in the determined 504 driving direction 105.

The ahead road slope B of the road 120 is predicted 505 by extracting road slope data associated with a geographical position situated ahead of the determined 503 geographical position of the vehicle 100 in the determined 504 driving direction 105 of the vehicles 100, 110, from a database 450.

The database 450 may comprise road slope data at different geographical positions along roads. The database 450 may be comprised in the vehicle 100, or may alternatively be situated external to the vehicle 100 and accessible via a wireless interface from the vehicle 100.

The prediction may be made at a distance ahead of the vehicle 100 appropriate for vehicle 100 to adjust the distance t between the vehicles 100, 110. This ahead distance may be different for different velocities of the vehicle 100, in some embodiments. Said distance may in some embodiments be a part of a second or a number of seconds (when the distance is given in time) or some meters, such as e.g. 10, 50 or 100 meters, or a multiple thereof (when the distance is given in length).

Step 506comprises adjusting the gap t between the follower vehicle 100 and the preceding vehicle 110 by: reducing the gap t to the preceding vehicle 110 when an uphill road slope B is predicted 505 and the preceding vehicle 110 is classified 502 as stronger. Alternatively, the gap t may be adjusted by maintaining the gap t to the preceding vehicle 110 when an uphill road slope B is predicted 505 and the preceding vehicle 110 is classified 502 as weaker. Furthermore, the gap t may be adjusted by increasing the gap t to the preceding vehicle 110 when a downhill road slope -B is predicted 505 and the preceding vehicle 110 is classified 502 as lighter. The gap t may further alternatively be adjusted by maintaining the gap t to the preceding vehicle 110 when a downhill road slope -B is predicted 505 and the preceding vehicle 110 is classified 502 as heavier.

The adjustment of the gap t may be made in proportion to the size of the predicted 505 ahead road slope B, -B.

By keeping the variable gap t in uphill when the preceding vehicle 110 is weaker, or has a lower weight/ power ratio than the follower vehicle 100, it is avoided that the follower vehicle 100 has to brake in order to avoid collision, as the weaker preceding vehicle 110 will slack in comparison with the follower vehicle 100 in the uphill. The follower vehicle 100 may instead eco-roll or coast and thereby adjust the velocity of the follower vehicle 100 for keeping the variable gap t. In the opposite situation, in case the preceding vehicle 110 is stronger or has a higher weight/ power ratio than the follower vehicle 100 the variable time gap t may be maintained or even decreased, as the follower vehicle 100 may lag in comparison with the preceding vehicle 110 in the uphill.

Step 507which may be performed only in some embodiments, comprises informing the driver of the follower vehicle 100 about the adjusted 506 gap t between the follower vehicle 100 and the preceding vehicle 110.

Thereby the vehicles 100,110 in a group of vehicles, and the distance t between the vehicles 100, 110 may be adjusted based on different predicted ahead road slopes B, -B.

Figure 6illustrates an embodiment of a system600in a vehicle 100. The system 600 is configured for adjusting a variable gap t between a follower vehicle 100 and a preceding vehicle 110 on a road 120, in order to reduce air drag and avoid braking.

The system 600 may perform at least some of the previously described steps 501-507 according to the method 500 described above and illustrated in Figure 5 for adjusting a variable gap t between the follower vehicle 100 and the preceding vehicle 110.

The system 600 may comprise an Adaptive Cruise Control (ACC), sometimes also referred to as autonomous or radar cruise control, i.e. a cruise control system for vehicles that automatically adjusts the vehicle speed to maintain and adjust the gap t between the vehicles 100, 110. Thus the system 600 may attempt to keep a certain distance t to the preceding vehicle 110 ahead, upon activation of the system 600.

For a better performance/ security of the system 600 when driving in hilly terrain, an adaptation of the gap t is sometimes made, depending on the slope of the road. In downhill the gap t may be set a little longer when the preceding vehicle 110 is heavier, in uphill the gap t may be set a little shorter when the preceding vehicle 110 is stronger. The estimation of the slope may be made by a slope sensor in the following vehicle 100 in some embodiments.

The system 600 comprises a measurement unit 460, comprising a radar, lidar and/ or camera situated in the front part of the follower vehicle 100. Further the system 600 comprises a positioning unit 430, configured for determining geographical position of the follower vehicle 100. Also, the system 600 comprises a database 450 configured for storing road slope data associated with geographical positions. The database 450 may be comprised in the vehicle 100, or may alternatively be situated external to the vehicle 100 and accessible via a wireless interface from the vehicle 100.

Furthermore the system 600 comprises a control unit 410 configured for determining a road slope a, -a of the road 120 on which the vehicles 100, 110 are driving, as either an uphill road slope a or downhill road slope -a. In addition, the control unit 410 is configured for classifying the preceding vehicle 110 as either stronger or weaker than the follower vehicle 100 when driving in an uphill road slope a, or as either heavier or lighter than the follower vehicle 100 when driving in a downhill road slope -a, based on said road slope a, -a. The control unit 410 is also configured for determining geographical position of the vehicle 100. Furthermore the control unit 410 is also configured for determining driving direction 105 of the vehicles 100, 110. In addition the control unit 410 is also configured for predicting an ahead road slope B of the road 120 ahead of the vehicles 100, 110 in the determined driving direction 105, as either an uphill road slope B, or a downhill road slope -B, in the determined driving direction 105, by extracting road slope data associated with a geographical position situated ahead of the determined geographical position of the vehicle 100 in the determined driving direction 105 of the vehicles 100, 110, from a database 450. Also, the control unit 410 is further configured for adjusting the gap t between the follower vehicle 100 and the preceding vehicle 110 by: reducing the gap t to the preceding vehicle 110 when an uphill road slope B is predicted and the preceding vehicle 110 is classified as stronger; maintaining the gap t to the preceding vehicle 110 when an uphill road slope B is predicted and the preceding vehicle 110 is classified as weaker; increasing the gap t to the preceding vehicle 110 when a downhill road slope -B is predicted and the preceding vehicle 110 is classified as lighter; or maintaining the gap t to the preceding vehicle 110 when a downhill road slope -B is predicted and the preceding vehicle 110 is classified as heavier.

In some further embodiments, the control unit 410 may also be configured for informing the driver of the follower vehicle 100 about the adjusted gap t between the follower vehicle 100 and the preceding vehicle 110.

In some further embodiments, the control unit 410 may also be configured for classification of the preceding vehicle 110 by: determining the preceding vehicle 110 to be stronger than the follower vehicle 100 when the gap t is prolonged, when driving in the uphill road slope a; determining the preceding vehicle 110 to be weaker than the follower vehicle 100 when the gap t is shortened, when driving in the uphill road slope a; determining the preceding vehicle 110 to be heavier than the follower vehicle 100 when the gap t is prolonged, when driving in the downhill road slope -a; or determining the preceding vehicle 110 as lighter than the follower vehicle 100 when the gap t is shortened, when driving in the downhill road slope -a.

Also, the control unit 410 may also be configured for adjusting the gap t in proportion to the size of the ahead road slope B.

Further the control unit 410 may also be configured for determining the weight and engine power of the preceding vehicle 110 at the preceding vehicle 110 and provided to the follower vehicle 100 via a wireless communication interface.

Additionally, the control unit 410 may also be configured for determining the size of the gap t between the follower vehicle 100 and the preceding vehicle 110 based on a measurement made by a measurement unit 460 comprising a radar, lidar and/ or camera situated in the front part of the follower vehicle 100, or by vehicle positioning data of a positioning unit 430, and/ or wireless communication between the follower vehicle 100 and the preceding vehicle 110.

The control unit 410 may also be configured for classification of the preceding vehicle 110 is repeated over a plurality of road slopes a, -a of the road 120 at different geographical positions.

Further, the control unit 410 may further be configured for linearly adjusting the variable time gap t, with the size of the road slope a, B within predetermined limits, in some embodiments.

The control unit 410 may comprise a receiving circuit610configured for receiving a signal from a sensor 130, a positioning unit 430 and a database 450.

The control unit 410 may also comprise a processor620configured for performing at least some of the calculating or computing of the control unit 410. Thus the processor 620 may be configured for performing the method according to at least some of the steps 501-507. Such processor 620 may comprise one or more instances of a processing circuit, i.e. a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones enumerated above.

Furthermore, the control unit 410 may comprise a memory625in some embodiments. The optional memory 625 may comprise a tangible, physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory 625 may comprise integrated circuits comprising silicon-based transistors. The memory 625 may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

Further, the control unit 600 may comprise a signal transmitter630.The signal transmitter 630 may be configured for transmitting a control signal over a wired or wireless interface in some embodiments.

The previously described steps 501-507 to be performed in the control unit 410 may be implemented through the one or more processors 620 within the control unit 410, together with computer program product for performing at least some of the functions of the steps 501-507. Thus a computer program product, comprising instructions for performing the steps 501 - 507 in the control unit 410 may perform the method 500 comprising at least some of the steps 501-507 for adjusting a gap t between a follower vehicle 100 and a preceding vehicle 110 on a road 120, in order to reduce air drag and avoid braking, when the computer program is loaded into the one or more processors 620 of the control unit 410.

The computer program product mentioned above may be provided for instance in the form of a tangible data carrier carrying computer program code for performing at least some of the step 501-507 according to some embodiments when being loaded into the one or more processors 620 of the control unit 410. The data carrier may be, e.g., a hard disk, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. The computer program product may furthermore be provided as computer program code on a server and downloaded to the control unit 410 remotely, e.g., over an Internet or an intranet connection.

Further, some embodiments may comprise a vehicle 100, comprising the system 600, configured for adjusting a variable gap t between a follower vehicle 100 and a preceding vehicle 110 on a road 120, in order to reduce air drag and avoid braking by the follower vehicle 100.

The terminology used in the description of the embodiments as illustrated in the accompanying drawings is not intended to be limiting of the described method 500; the control unit 410; the system 600, the computer program or the vehicle 100. Various changes, substitutions or alterations may be made, without departing from invention embodiments as defined by the appended claims.

As used herein, the term "and/ or" comprises any and all combinations of one or more of the associated listed items. The term "or" as used herein, is to be interpreted as a mathematical OR, i.e., as an inclusive disjunction; not as a mathematical exclusive OR (XOR), unless expressly stated otherwise. In addition, the singular forms "a", "an" and "the" are to be interpreted as "at least one", thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" or "comprising", specifies the presence of stated features, actions, integers, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, elements, components, or groups thereof. A single unit such as e.g. a processor may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/ distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms such as via Internet or other wired or wireless communication system.

Claims

1. A method (500) for adjusting a gap (t) between a follower vehicle (100) and a preceding vehicle (110) on a road (120), in order to reduce air drag and avoid braking, which method (500) comprises: determining (501) a road slope (a, -a) of the road (120) on which the vehicles (100, 110) are driving, as either an uphill road slope (a) or downhill road slope (-a); utilising map information for classifying (502) the preceding vehicle (110) as either stronger or weaker than the follower vehicle (100) when driving in an uphill road slope (a), or as either heavier or lighter than the follower vehicle (100) when driving in a downhill road slope (-a) based on said road slope (a, -a) and the behaviour of the preceding vehicle; determining (503) geographical position of the vehicle (100); determining (504) driving direction (105) of the vehicles (100, 110); predicting (505) an ahead road slope (B) of the road (120) ahead of the vehicles (100, 110) in the determined (504) driving direction (105), as either an uphill road slope (B), or a downhill road slope (-B), in the determined (504) driving direction (105), by extracting road slope data associated with a geographical position situated ahead of the determined (503) geographical position of the vehicle (100) in the determined (504) driving direction (105) of the vehicles (100, 110), from a database (450); and adjusting (506) the gap (t) between the follower vehicle (100) and the preceding vehicle (110) by: reducing the gap (t) to the preceding vehicle (110) when an uphill road slope (B) is predicted (505) and the preceding vehicle (110) is classified (502) as stronger; maintaining the gap (t) to the preceding vehicle (110) when an uphill road slope (B) is predicted (505) and the preceding vehicle (110) is classified (502) as weaker; increasing the gap (t) to the preceding vehicle (110) when a downhill road slope (-B) is predicted (505) and the preceding vehicle (110) is classified (502) as lighter; or maintaining the gap (t) to the preceding vehicle (110) when a downhill road slope (-B) is predicted (505) and the preceding vehicle (110) is classified (502) as heavier.

2. A control unit (410) in a follower vehicle (100), for adjusting a gap (t) between a follower vehicle (100) and a preceding vehicle (110) on a road (120), in order to reduce air drag and avoid braking, wherein the control unit (410) is configured for: determining a road slope (a, -a) of the road (120) on which the vehicles (100, 110) are driving, as either an uphill road slope (a) or downhill road slope (-a); utilising map information for classifying the preceding vehicle (110) as either stronger or weaker than the follower vehicle (100) when driving in an uphill road slope (a), or as either heavier or lighter than the follower vehicle (100) when driving in a downhill road slope (-a) based on said road slope (a, -a) and the behaviour of the preceding vehicle; determining geographical position of the vehicle (100); determining driving direction (105) of the vehicles (100, 110); predicting an ahead road slope (B) of the road (120) ahead of the vehicles (100, 110) in the determined driving direction (105), as either an uphill road slope (B), or a downhill road slope (-B), in the determined driving direction (105), by extracting road slope data associated with a geographical position situated ahead of the determined geographical position of the vehicle (100) in the determined driving direction (105) of the vehicles (100, 110), from a database (450); and configured for adjusting the gap (t) between the follower vehicle (100) and the preceding vehicle (110) by: reducing the gap (t) to the preceding vehicle (110) when an uphill road slope (B) is predicted and the preceding vehicle (110) is classified as stronger; maintaining the gap (t) to the preceding vehicle (110) when an uphill road slope (B) is predicted and the preceding vehicle (110) is classified as weaker; increasing the gap (t) to the preceding vehicle (110) when a downhill road slope (-B) is predicted and the preceding vehicle (110) is classified as lighter; or maintaining the gap (t) to the preceding vehicle (110) when a downhill road slope (-B) is predicted and the preceding vehicle (110) is classified as heavier.

3. The control unit (410) according to claim 2, further configured for classifying the preceding vehicle (110) by: determining the preceding vehicle (110) to be stronger than the follower vehicle (100) when the gap (t) is prolonged, when driving in the uphill road slope (a); determining the preceding vehicle (110) to be weaker than the follower vehicle (100) when the gap (t) is shortened, when driving in the uphill road slope (a); determining the preceding vehicle (110) to be heavier than the follower vehicle (100) when the gap (t) is prolonged, when driving in the downhill road slope (-a); or determining the preceding vehicle (110) as lighter than the follower vehicle (100) when the gap (t) is shortened, when driving in the downhill road slope (-a).

4. The control unit (410) according to any of claim 2 or claim 3 wherein the control unit (410) is further configured for adjusting the gap (t) in proportion to the size of the predicted ahead road slope (B).

5. The control unit (410) according to any of claims 2-4, wherein the control unit (410) is further configured for receiving the weight and engine power of the preceding vehicle (110) via a wireless communication interface, from the preceding vehicle (110).

6. The control unit (410) according to any of claims 2-5, wherein the control unit (410) is further configured for determining the size of the gap (t) between the follower vehicle (100) and the preceding vehicle (110), based on a measurement made by a measurement unit (460) comprising a radar, lidar and/ or camera situated in the front part of the follower vehicle (100), or by vehicle positioning data of a positioning unit (430), and/ or wireless communication between the follower vehicle (100) and the preceding vehicle (110).

7. The control unit (410) according to any of claims 2-6, wherein the control unit (410) is further configured for classifying the preceding vehicle (110) repeatedly over a plurality of road slopes (a, -a) of the road (120).

8. The control unit (410) according to any of claims 2-7, wherein the control unit (410) is further configured for informing the driver of the follower vehicle (100) about the adjusted gap (t) between the follower vehicle (100) and the preceding vehicle (110).

9. A computer program comprising program code for performing a method (500) according to claim 1 when the computer program is executed in the control unit (410), according to any of claims 2-8.

10. A system (600) for adjusting a gap (t) between a follower vehicle (100) and a preceding vehicle (110) on a road (120), in order to reduce air drag and avoid braking, wherein the system (600) comprises: a control unit (410) according to any of claims 2-8; a measurement unit (460), comprising a radar, lidar and/ or camera situated in the front part of the follower vehicle (100); a positioning unit (430), configured for determining geographical position of the follower vehicle (100); and a database (450) configured for storing road slope data associated with geographical positions.

11. A vehicle (100) comprising a system (600) according to claim 10.