WO2016186560A1

WO2016186560A1 - Method and system for adjusting the acceleration of a vehicle along a route

Info

Publication number: WO2016186560A1
Application number: PCT/SE2016/050454
Authority: WO
Inventors: Linus Bredberg; Jonny Andersson
Original assignee: Scania Cv Ab
Priority date: 2015-05-20
Filing date: 2016-05-19
Publication date: 2016-11-24
Also published as: BR112017022471B1; EP3297885A4; EP3297883A1; BR112017022470B1; BR112017022470A2; BR112017022471A2; EP3297885A1; WO2016186561A1

Abstract

The present invention relates to a method for adjusting the acceleration of a vehicle travelling along a route, comprising the steps of continuously detecting (S1 ) the presence of speed-limiting features along the vehicle's route and, when speed-limiting features are detected, of determining (S2) the acceleration required for reaching a prescribed target speed at such a detected coming speed-limiting feature. The method is characterised in that where a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance, and the vehicle's speed is initially below said target speed, the step of determining (S2a) required acceleration involves the step of determining braking strategy based on characteristics of said downhill section of the route. The present invention relates also to a system for adjusting the acceleration of a vehicle travelling along a route. The present invention relates also to a motor vehicle. The present invention also relates to a computer programme and a computer programme product.

Description

METHOD AND SYSTEM FOR ADJUSTING THE ACCELERATION OF A

VEHICLE ALONG A ROUTE

TECHNICAL FIELD The invention relates to a method for adjusting the acceleration of a vehicle travelling along a route according to the preamble of claim 1 . The invention relates to a system for adjusting the acceleration of a vehicle travelling along a route. The invention relates also to a motor vehicle. The invention also relates to a computer programme and a computer programme product. BACKGROUND

Cruise controls and similar driver supports are becoming increasingly intelligent. Various systems currently on the market use map data to run the vehicle in a fuel economising way but are only suited to seeing what the topography looks like, which in practice makes them suitable functions for use on motorways and similar roads.

Today's systems are based entirely on a set-value vehicle speed set by the driver. Cruise controls based on topology are only allowed to deviate from that speed by a certain percentage or km/h. Should the vehicle concerned have to use a minor road with bends and speed limits, it is appropriate to switch off the cruise control, since the driver will him/herself still need to brake ahead of bends. On minor roads with many bends, it is also difficult for a driver to drive optimally from a fuel economy perspective, since it is often hard to judge what will happen beyond the next bend.

US20040068359 refers to a predictive cruise control which uses the vehicle's current location and the terrain ahead to save fuel and improve driving comfort. Its calculations include such aspects as road curvature and whether the vehicle is travelling uphill or downhill. One strategy is to prevent unnecessary braking and be able to maintain optimum driving in order to be able to save fuel.

OBJECTS OF THE INVENTION

One object of the present invention is to propose a method and a system for adjusting the acceleration of a vehicle travelling along a hilly route which make safe and comfortable driving of the vehicle possible at speed-limiting features such as bends.

A further object of the present invention is to propose a method and a system for adjusting the acceleration of a vehicle travelling along a hilly and bendy route which increase driver acceptance for driving of the vehicle.

SUMMARY OF THE INVENTION

These and other objects indicated by the description set out below are achieved by means of a method, a system, a motor vehicle, a computer programme and a computer programme product of the kinds indicated in the introduction which further present the features indicated in the characterising parts of the attached independent claims. Preferred embodiments of the method and the system are defined in the attached dependent claims.

The invention achieves the objects with a method for adjusting the acceleration of a vehicle travelling along a route, comprising the steps of continuously detecting the presence of speed-limiting features along the vehicle's route and responding to their detection by determining the acceleration required for reaching a prescribed target speed at such a detected coming speed-limiting feature. The method is characterised in that when a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance and the vehicle's speed is initially below said target speed, the step of determining required acceleration involves the step of determining braking strategy based on characteristics of said downhill section of the route and/or on the vehicle's setting with regard to desired degree of driving comfort.

Improved driving of the vehicle on hilly itineraries with speed-limiting features such as bends is thus made possible. This applying of braking strategy based on characteristics of the downhill section of the route, such as length and degree and kind of gradient, enables smart use of the vehicle's braking devices such as auxiliary brakes, e.g. retarders, in order thereby to increase driver acceptance of this driving of the vehicle. Safe and comfortable driving of the vehicle in cases where speed-limiting features follow a downhill section of the route and hence at speed-limiting features which follow hillcrest driving with a subsequent downhill run is thus made possible. It is thus also made possible to adjust acceleration in order to reach prescribed target speed so that fuel economy is also catered for and trade-off between performance and fuel economy depending on how far before the speed-limiting feature a chosen braking strategy involving certain braking processes is initiated. The possibility of vehicle setting with regard to desired degree of comfort when the vehicle is travelling on a downhill section of the route enables the driver to ensure comfort by seeing to it that braking processes corresponding to comfortable driving are always achieved, or fast and accordingly more sporty driving by seeing it to that a more sporty braking process with briefer but more powerful braking action for faster movement is always achieved. In one variant chosen braking strategies are presented for the driver. Presentation may be by any suitable presentation means. The braking strategy is presented in one variant visually. Visual presentation of braking strategy is provided in one variant by a visual presentation means in the form of a display unit visible to the driver, which in one variant is situated in the vehicle's instrument panel. Visual presentation of braking strategy in one variant is by a visual presentation means in the form of a so-called head-up display, i.e. by information superimposed on the windscreen. The braking strategy is presented in one variant acoustically, i.e. by an acoustic presentation means in the form of any suitable sound unit. Presentation may thus be by any suitable presentation means.

In one embodiment of the method said characteristics of said downhill section of the route comprise gradient and/or length. This makes it possible for the braking strategy to be adjusted with suitable braking processes so that on a relatively short and/or steep section of the route a positively accelerating braking process is activated relatively early on the downhill section, a braking process with a braking action which in principle results in a lack of acceleration when the vehicle is travelling along said section of the route and a vehicle speed close to said target speed is reached early, and on a relatively long and/or level section of the route a negatively accelerating braking process/retarding braking process is activated relatively late on the downhill section.

In one embodiment of the method the step of determining braking strategy further comprises taking vehicle speed and/or running resistance into account. This makes it possible to determine a more correct required acceleration and consequently more correct braking strategy. Thus the braking strategy may be further adjusted with suitable braking processes so that at a relatively high speed and/or a relatively large negative running resistance a positively accelerating braking process is activated relatively early on the downhill section of the route, a braking process with a braking action which in principle results in lack of acceleration when the vehicle is travelling along said section of the route when a vehicle speed close to said target speed is reached early, and at a relatively low speed and/or a relatively low running resistance a negatively accelerating braking process/retarding braking process is activated relatively late on the downhill section of the route.

In one embodiment of the method said braking strategy involves a first braking process involving the step of activating a braking action which results in positively accelerating movement of the vehicle along said section of the route. This braking process is well suited to a relatively short and/or steep section of the route and/or to a relatively high speed and/or a relatively large negative running resistance and results in comfortable driving while maintaining good fuel saving. This braking strategy may also correspond to a vehicle setting with regard to desired high degree of comfort.

In one embodiment of the method said braking strategy involves a second braking process involving the step of activating a braking action which in principle results in lack of acceleration when the vehicle is travelling along said section of the route. This braking process is well suited to when the vehicle is travelling along said section of the route and reaches early a vehicle speed close to said target speed, and results in comfortable driving while maintaining good fuel saving. This braking strategy may also correspond to a vehicle setting with regard to desired high degree of comfort.

In one embodiment of the method said braking strategy involves a third braking process involving the steps of initially allowing the vehicle to freewheel and thereafter activating a braking action which results in negatively accelerating movement of the vehicle along said section of the route. This braking process is well-suited to a relatively long and/or level section of the route and/or to low speed and/or to a relatively low negative running resistance, and results in good fuel saving and time-efficient driving. This braking process may also correspond to a vehicle setting with regard to desired fast travel and accordingly lower degree of comfort.

In one embodiment of the method said first braking process is employed where said section of the route is relatively short and/or relatively steep, said third braking process is employed where said section of the route is relatively long and/or there is relatively little gradient, and said second braking process is employed when a vehicle speed close to said target speed is reached early. In one embodiment of the method the step of determining the acceleration required for reaching a prescribed speed at a speed-limiting feature takes place continuously. Required acceleration being determined continuously provides assurance that prescribed speed will be reached safely and comfortably. It also provides assurance that no required acceleration in the form of retardation will be missed.

In one embodiment of the method said speed-limiting features comprise bends on the route, where speed is prescribed on the basis of the vehicle's maximum permissible lateral acceleration. Safe driving of the vehicle is thus made possible in that its speed is adjusted on bends.

In one embodiment of the method said speed-limiting features involve speed limit changes along the vehicle's route. This provides assurance that adjustment to speed limits along the vehicle's route will take place safely and comfortably. In one embodiment of the method the step of determining the acceleration required for reaching a prescribed speed at a coming speed-limiting feature involves the step of continuously determining running resistance along the vehicle's route. This makes it possible to determine a more correct required acceleration and accordingly a more correct choice of braking strategy on the downhill section of the route. It also makes it possible for the vehicle to be driven more fuel economising, e.g. in that hills such as said downhill section of the route may be used for freewheeling, positively accelerating braking, braking with in principle lack of acceleration and retarding braking, depending on the degree of negative running resistance, thereby making it possible not only to avoid unnecessary braking for acceleration in the form of retardation and unnecessary application of power for positive acceleration but also at the same time to achieve further improvement of comfort.

In one embodiment of the method the step of continuously detecting speed- limiting features along the vehicle's route takes place on the basis of a predetermined distance horizon and/or time horizon ahead of the vehicle along the route. This makes it possible to adjust acceleration, involving choice of braking strategy before driving on the downhill section of the route, catering for comfort, performance and fuel economy depending on how far before the speed-limiting feature the braking strategy in the form of braking processes on the downhill section of the route is initiated, i.e. depending on the distance horizon and/or time horizon ahead of the vehicle along the route. This detecting of speed-reducing features such as bends along a predetermined distance horizon and/or time horizon ahead of the vehicle along the route facilitates the determination of braking strategy, which may take place before the vehicle reaches the downhill section of the route which precedes a speed-limiting feature.

In one embodiment the method comprises the step of prescribing speed in the form of a speed profile along the vehicle's route and continuously executing said speed profile by continuous determination of said required acceleration. The possibility of safe and comfortable driving of the vehicle at speed-limiting features is thus further improved.

In one embodiment the method comprises the step of controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset which is adjusted so that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical and a relatively smaller offset in the case of those which are safety-critical. This makes it possible in a flexible way to adjust the driving of the vehicle for fuel economy at speed-limiting features which are not safety-critical, e.g. speed limit changes along the vehicle's route, and to ensure safe driving at safety-critical speed-limiting features such as bends. Thus controlling the vehicle's speed accordingly achieves more comfortable driving of the vehicle in that braking at non-critical speed-limiting features can be avoided. For speed-limiting features which are not safety-critical the driver may him/herself be allowed to set desired offsets, e.g. depending on desired ride comfort and fuel economy when the vehicle is in motion. The vehicle's speed will accordingly be allowed to vary relative to the target speed within certain limits up to a speed greater than the target speed by said offset. This is particularly advantageous in hilly terrain. On a downhill run a vehicle may for example be allowed to travel at above target speed in order to save fuel. The limit, i.e. said offset, is set separately for the permissible variation, particularly the variation upwards towards greater speed, depending on speed-limiting features.

In one embodiment the method comprises the step, in cases where the third braking process is employed, of adjusting the vehicle's speed so that target speed is reached on a prescribed section before entering a bend along the vehicle's route, and in cases where the first or second braking process is employed, of adjusting the vehicle's speed so that target speed is reached on a section pertaining to target speed. This makes reassuringly safe and comfortable driving possible in that the target speed is reached at a time or distance before the target speed required at the bend in cases where the prevailing vehicle speed is above target speed, and efficient driving of the vehicle so that correct target speed is reached at the bend in cases where the prevailing vehicle speed is at or below target speed. The embodiments for the system present advantages corresponding to those of the embodiments for the method mentioned above.

DESCRIPTION OF DRAWINGS

The present invention will be better understood by reading the detailed description set out below in conjunction with the attached drawings, in which the same reference notations are used for similar items throughout the various views, and

Fig. 1 schematically illustrates a motor vehicle according to an embodiment of the present invention, Fig. 2 schematically illustrates a system for adjusting the acceleration of a vehicle travelling along a route according to an embodiment of the present invention,

Fig. 3a schematically illustrates a curvature profile, Fig. 3b schematically illustrates speed profiles for the curvature profile in Fig. 3a,

Fig. 4a schematically illustrates a topology profile for a route involving bend sections,

Fig. 4b schematically illustrates speed profiles for the topology profile in Fig. 4a,

Fig. 5a schematically illustrates a curvature profile in the form of a roundabout,

Fig. 5b schematically illustrates speed profiles for the curvature profile in Fig. 5a, Fig. 6a schematically illustrates a speed profile when negotiating bends, representing target speed and permissible speed above target speed with certain offsets according to an embodiment of the present invention,

Fig. 6b schematically illustrates a speed profile at speed limit changes, representing target speed and permissible speed above target speed with certain offsets according to an embodiment of the present invention,

Fig. 7 schematically illustrates a block diagram of a method for adjusting the acceleration of a vehicle travelling along a route according to an embodiment of the present invention, and

Fig. 8 schematically illustrates a computer according to an embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

The term "link" refers herein to a communication link which may be a physical line such as an opto-electronic communication line, or a non-physical line such as a wireless connection, e.g. a radio link or microwave link. The term "acceleration" refers herein to both positive and negative acceleration, i.e. acceleration in the form of increasing speed and acceleration in the form of decreasing speed, i.e. retardation.

The term "positively accelerating braking process" and the term "braking action which results in positively accelerating movement of the vehicle" refer herein to a braking process on a downhill section of the route which has positively accelerating effects on the vehicle's running resistance whereby a braking action is activated so that the vehicle is braked to such an extent that its acceleration affected in a positively accelerating way by the downhill section is reduced, but the acceleration is still positive so that the vehicle's speed increases along the downhill section.

The term "braking action which in principle results in lack of acceleration" refers herein to a braking process on a downhill section of the route which has positively accelerating effects on the vehicle's running resistance whereby a braking action is activated so that the vehicle is braked to such an extent that its acceleration affected in a positively accelerating way by the downhill section is reduced so that an in principle uniform speed is reached, i.e. the vehicle's speed neither increases nor decreases with such braking action when travelling along the downhill section.

The term "vehicle setting with regard to desired degree of driving comfort" refers herein to a setting of the vehicle which in one variant is applied/desired by the driver and corresponds to a braking strategy, whereby a desired high degree of comfort results in braking strategy according to certain braking processes with relatively longer and braking action with relatively less braking force and desired lower degree of comfort and accordingly faster movement of the vehicle results in a certain braking process with relatively briefer braking action with relatively greater braking force. Setting for desired high degree of comfort is in one variant called comfort mode. Desired fast driving with accordingly lower degree of comfort is in one variant called sport mode. The term "vehicle setting with regard to desired degree of driving comfort" is a setting of the vehicle which in one variant consequently represents a manual setting for desired degree of comfort, which may be applied by the driver or another operator.

The term "continuously determining", e.g. in the expression "continuously determining the acceleration required for reaching prescribed target speed at a coming speed-limiting feature" refers herein to stepless determination or stepped determination, i.e. determination taking place at a certain repeated interval which may be regular and may be time-based or distance-based.

The term "speed-limiting features" refers herein to any features along the vehicle's route which call for speed limitation of the vehicle. Speed-limiting features comprise bends along the route. Speed-limiting features comprise speed limits along the route. Speed-limiting features comprise a feature such as a bend or a speed limit following a downhill run and causing the vehicle's driving on the downhill section of the route to be acted upon in order to be able to reach the target speed which the feature following the downhill run entails. Speed-limiting features might also comprise other features such as road narrowings, roadworks along the route, obstacles such as speed obstacles along the route, deteriorated road surface, increased traffic density/queuing risk etc. The term "target speed" refers herein to a speed pertaining to a speed- limiting feature such as a safety-critical speed-limiting feature, e.g. a bend, or a non safety-critical speed-limiting feature, e.g. a speed limit.

The term "offset" refers herein to an upper limit on how far the vehicle's speed is allowed to exceed a target speed pertaining to a speed-limiting feature. Said offset may be any desired value. For a safety-critical speed- limiting feature it may be between 0.2 and 3 km/h, preferably between 0.3 and 2 km/h. Said offset for a non safety-critical speed-limiting feature may be between 1 and 30 km/h. The term "controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset" refers herein to the speed being allowed to vary relative to the target speed within certain limits up to a speed which is greater than the target speed by said offset. Fig. 1 schematically illustrates a motor vehicle 1 according to an embodiment of the present invention. The exemplifying vehicle 1 is a heavy vehicle in the form of a truck. It may alternatively be any suitable vehicle such as a bus or car. The vehicle is provided with a system I according to the present invention. Fig. 2 schematically illustrates a block diagram of a system I for adjusting the acceleration of a vehicle travelling along a route according to an embodiment of the present invention.

The system I comprises an electronic control unit 100.

The system I comprises means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route.

Said speed-limiting features comprise bends on the route. Said speed- limiting features comprise speed limit changes along the vehicle's route.

The means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route involves in one variant a map information unit 1 12 providing map data on characteristics of the carriageway along the route comprising speed-limiting features in the form of bends and speed limit changes along the route. The means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route involves in one variant means 1 14 for determining the vehicle's location. The means 1 14 for determining the vehicle's location comprises a geographical position determination system for continuously determining the vehicle's location along the route. An example of a geographical position determination system may be GPS.

The map information unit 1 12 and the means 1 14 for determining the vehicle's location are in one variant part of means 1 1 0a for determining the vehicle's route, which means for determining the route is adapted to providing predetermined characteristics of the carriageway along the route comprising speed-limiting features in the form of bends and speed limit changes along the route. Said map data from the map information unit 1 12 comprise also characteristics of the carriageway along the vehicle's route comprising topography. The topography of the carriageway comprises downhill sections of the route.

The map information unit 1 12 and the means 1 14 for determining the vehicle's location thus make it possible to continuously detect the vehicle's location and characteristics of the carriageway comprising speed-limiting features in the form of bends and speed limit changes along the route and topography along the route comprising uphill sections, hillcrests and downhill sections.

The means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route involves in one variant camera means 1 1 6. The camera means 1 16 is adapted to detecting characteristics of the carriageway comprising speed-limiting features in the form of bends and speed limit changes along the route. The camera means 1 16 is adapted to detecting the shape of the extent of the carriageway involving curvature of the carriageway and/or road markings in order thus to determine curvature of the carriageway along which the vehicle is travelling. The camera means 1 16 is adapted to detecting topography of the carriageway comprising uphill sections, hillcrests and downhill sections. The camera means 1 16 is adapted to detecting road signs along the vehicle's route comprising speed limit signs and to determining speed limit changes along the route by recognising speed limit signs. The camera means may comprise one or more cameras for the detection.

The means 1 10 for detecting the presence of speed-limiting features along the vehicle's route comprises in one variant communication means for communication between the vehicle and other vehicles or between the vehicle and other units in order to communicate speed-limiting features such as the end of a queue or the like.

The means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route comprises means for detecting them on the basis of a predetermined distance horizon and/or time horizon ahead of the vehicle along its route. In one embodiment the means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route comprises means for detecting them on the basis of a predetermined distance horizon ahead of the vehicle along the route, which horizon constitutes a suitable window in the form of a distance from the vehicle's current location and forwards along the route. The distance horizon in one embodiment is of the order of several hundred metres, e.g. about 500 metres ahead of the vehicle along its route.

The distance horizon depends in one variant on the vehicle speed. The distance horizon depends in one variant on comfort considerations, fuel economy considerations and driving efficiency considerations, i.e. how time- efficient the driving of the vehicle is. Setting the distance horizon relatively shorter will require a quicker negative acceleration/retardation at the location of a speed-limiting feature, enabling more time-efficient driving of the vehicle. Setting the distance horizon relatively longer will require a slower negative acceleration/retardation at the location of a speed-limiting feature, enabling more comfortable driving and/or better fuel economy.

Setting the distance horizon relatively shorter is required in cases where the speed-limiting feature is preceded by a downhill run before which the vehicle is brought to a speed lower than the target speed for the speed-limiting feature may affect the choice of braking strategy, i.e. which braking process is possible.

The system in one variant comprises means 120 for regulating desired distance horizons for desired driving of the vehicle, which horizons correspond to desired driving modes such as economy mode, comfort mode or high power mode. The means for regulating desired distance horizons involves in one embodiment an operating device for doing so.

The system I comprises means 130 for continuously determining the vehicle's speed. The means 1 30 for continuously determining the vehicle's speed in one variant comprises speedometer devices.

The system I comprises means 140 for responding to detected speed-limiting features by determining the acceleration required for reaching prescribed target speed at a coming speed-limiting feature.

The means 140 for determining the acceleration required for reaching prescribed target speed at a detected coming speed-limiting feature is arranged for continuous determination. Continuously determining the acceleration required for reaching prescribed target speed at a coming speed-limiting feature makes it possible to achieve a speed profile which is more suitable from a driving perspective. The means 140 for determining the acceleration required for reaching prescribed target speed at a coming speed-limiting feature on the basis of a predetermined distance horizon ahead of the vehicle along its route is based in one variant on the following equations: 1 ) v = v₀ + a * t in which v is the speed which corresponds to the prescribed speed at a coming speed-limiting feature, v₀ is present speed, a is the required acceleration and t the time to the location of the speed-limiting feature. Equation 1 ) is based on a time horizon. In calculations where determination is based on a predetermined distance horizon, t(s) needs to be solved according to

2) t = ^

The distance s is arrived at by ^ a*t²

3) 5 = v₀ * t +—

Inserting equation 2) in equation 3) and resolving the required acceleration a arrives at

4) a = ^

' 2*S in which v₀ consequently is present speed, i.e. the speed at the beginning of the simulation, and v the prescribed speed according to a coming speed- limiting feature after the distance s. The required acceleration a may thus be determined on the basis of the prescribed speed v, present speed v₀ and the distance s to the speed-limiting feature.

The means 140 for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature involves means 142 for continuously determining running resistance along the route.

The means 142 for continuously determining running resistance along the vehicle's route involves with advantage means 142a for determining gradient resistance. The means 142a for determining gradient resistance is provided with or is part of means for determining topology along the route, i.e. any carriageway gradients along the vehicle's.

The means 142a for determining gradient resistance involves in one variant a map information unit providing map data on characteristics of the carriageway along the vehicle's route, involving topology along the route, and means for determining the vehicle's location, in one variant comprising a geographical position determination system, e.g. GPS, for continuously determining the vehicle's location along the route. The map information unit and the means for determining the vehicle's location take the form in one variant of the map information unit 1 12 and the means 1 14 for determining the vehicle's location.

The means 142 for continuously determining running resistance along the vehicle's route involves with advantage means 142b for determining friction characteristics of the vehicle's powertrain. The means 142b for determining friction characteristics of the vehicle's powertrain is provided with means for determining wheel speed differences during driving/braking, so-called slip. Slip is determined by determining wheel speed differences, e.g. by sensor devices measuring wheel rotation speeds.

The means 142 for continuously determining running resistance along the vehicle's route involves with advantage means 142c for determining air resistance. The means 142c for determining air resistance is provided with modelling means for estimating the air resistance by means of air resistance coefficients and vehicle characteristics comprising frontal area and the vehicle speed squared. The means 142c for determining air resistance is provided in one variant with sensor devices for measuring air coming in towards the vehicle, taking into account vehicle geometry such as air deflection devices intended to reduce air resistance.

The means 142 for continuously determining running resistance along the vehicle's route involves with advantage means 142d for determining rolling resistance. The means 142d for determining rolling resistance is provided with modelling means for estimating the rolling resistance by means of vehicle characteristics comprising the vehicle's number of axles, vehicle weight and, where applicable, type of tyres. The means 142 for determining running resistance F_res is provided with calculation means. The calculation means is arranged in one variant to determine an average value of the acceleration contribution a_resavg which the running resistance generates over a current distance horizon s which may be the distance from the vehicle to the coming speed-limiting feature. This calculation is as follows:

^Ό) ^uresavg ~ _stm

The total acceleration required a_tof thus becomes v) ^atot V^s) — ^a O-resavg ~

The required acceleration may thus be determined on the basis of an average running resistance. Unnecessary retardation of the vehicle may thus be avoided.

The means 140 for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature comprises in one variant means 144 for determining required braking retardation. Required braking retardation a_brake is determined in a similar way by ) ^abrake(s) ⁼ ~_s ^ ^max (0, &resavg) in which Vbr_ake might in one variant be a modified prescribed speed/target speed. The last-named maximum expression max(0, a_resavg) uses any braking force from the running resistance in an effective way and braking does not take place unnecessarily. brake is used to be able to distinguish between the prescribed speed v and the braking speed, i.e. a speed of the vehicle which calls for braking action. The prescribed speed v may be a reference speed. The reference speed is for example set at 50 km/h before a 50 section, but a downhill run will cause the vehicle to roll at over 50 km/h. The braking speed V_brake may then for example be set at 60 km/h so that the vehicle is allowed to roll and no brake activation takes place until it reaches 60 km/h, resulting in better fuel economy.

When a detected speed-limiting feature is preceded by a downhill section of the route with positively accelerating effects on the vehicle's running resistance and the vehicle's speed is initially below said target speed, e.g. when the vehicle before a downhill section of the route throttles the fuel supply so that the vehicle rolls and therefore saves fuel by reducing speed before the downhill section to below the target speed pertaining to the speed- limiting feature, braking strategy according to the present invention may be used to thus improve the vehicle's driving. Figs. 4a and 4b illustrate an example of such a scenario and various braking strategies.

The means 140 for determining required acceleration is provided accordingly with means 146 for determining braking strategy. The means 146 for determining braking strategy involves determination on the basis of characteristics of said downhill section of the route. The means 146 for determining braking strategy based on characteristics of said downhill section might be part of the means 144. The means 146 for determining braking strategy involves determination on the basis of vehicle setting with regard to desired degree of driving comfort. The vehicle setting may be a setting for high degree of comfort, also called comfort mode, or a setting for faster driving with accordingly lower degree of comfort, also called sport mode. The vehicle setting is in one variant applied by the driver for desired comfort when driving inter alia on a downhill section of the route. The means 146 for determining braking strategy is arranged in one variant to determine braking strategy taking into account both characteristics of said downhill section and vehicle setting with regard to desired driving comfort.

Said characteristics of the downhill section of the route comprise gradient and/or length. The means 146 for determining braking strategy based on characteristics of said downhill section of the route involves means 146a for determining gradients of the downhill section. The means 146a for determining gradients of the downhill section comprises in one embodiment a map information unit. The means 146a for determining gradients of the downhill section comprises in one embodiment camera means.

The means 146 for determining braking strategy based on characteristics of said downhill section of the route involves means 146b for determining its length. The means 146b for determining the length of the downhill section comprises in one embodiment a map information unit. The means 146b for determining the length of the downhill section of the route comprises in one embodiment camera means.

The means 146a and/or the means 146b is in one variant part of or provided with the map information unit 1 12. The means 146a and/or the means 146b in one variant is part of or provided with the camera means 1 1 6. The means 146 for determining braking strategy further comprises means 146c for determining vehicle speed with a view to taking vehicle speed into account. The means 146c for determining vehicle speed comprises in one embodiment a speedometer. The means 146c in one variant is part of or provided with the means 130 for determining the vehicle's speed. The means 146 for determining braking strategy further comprises means 146d for determining running resistance with a view to taking running resistance into account. The means 146d in one variant is part of or provided with the means 142 for continuously determining running resistance. The system I comprises means 150 for determining a maximum permissible lateral acceleration. The means 150 for determining a maximum permissible lateral acceleration involves determination of a predetermined maximum permissible lateral acceleration based on normal suppositions with regard to vehicle characteristics such as the vehicle's length, width, equipment, cargo distribution, centre of gravity and axle pressure and/or environmental characteristics such as effective traffic lane width, carriageway friction characteristics, visibility and carriageway proportioning characteristics. The predetermined maximum permissible lateral acceleration in one embodiment is of the order of 2 m/s². The maximum permissible lateral acceleration takes the form accordingly of a predetermined maximum permissible lateral acceleration. In an alternative or supplementary variant the electronic control unit 100 has stored data on the maximum permissible lateral acceleration.

The system I comprises means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route.

The means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route comprises with advantage means 1 62 for prescribing speed on the basis of the vehicle's maximum permissible lateral acceleration. The means 1 62 for prescribing speed on the basis of the vehicle's maximum permissible lateral acceleration comprises determination of a maximum vehicle speed on the basis of maximum permissible lateral acceleration. The prescribed speed thus corresponds to the maximum vehicle speed. Vehicle speed here means longitudinal vehicle speed.

The means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route comprises with advantage means 1 64 for prescribing speed on the basis of speed limit changes along the route.

The system I comprises means for prescribing speeds in the form of a speed profile along the vehicle's route. In one embodiment the means 160 for prescribing speed on the basis of coming speed-limiting features along the route comprises the means for prescribing speed in the form of a speed profile along the route. The means 160 is consequently arranged to prescribe speed in the form of a speed profile along the route.

The system I further comprises means for continuously executing said prescribed speed profile by continuous determination of said required acceleration. In one embodiment the means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route comprises the means for continuously executing said speed profile by continuous determination of said required acceleration. The means 160 is consequently arranged to continuously execute said speed profile by continuous determination of said required acceleration.

Determination of maximum vehicle speed and hence prescribed speed/speed profile on the basis of maximum permissible lateral acceleration uses information about the curvature of the carriageway along the vehicle's route, using the following equation:

04) 00 = . \ ^alat,max (s)/c(s) \ in which the V_max(s) is the maximum speed over the distance s ahead of the vehicle, ai_at,_max(s) is the maximum permissible lateral acceleration over the distance s ahead of the vehicle and c(s) is the curvature over the distance s ahead of the vehicle. The system I comprises in one variant means 170 for determining whether an initial required acceleration determined by the means 140 is negative, i.e. requiring retardation of the vehicle, or positive, i.e. requiring speed increase in the form of positive acceleration, which means 170 also involves taking into account whether the initial acceleration a_mw is negative or positive and accordingly distinguishes negative initial required acceleration from positive. This may be done in one variant as follows: i) Initial acceleration demand negative a-now = min (a_now, a(s ) ii) Initial acceleration demand positive anow ^{= sa}t (min (O-now, a(s)),0.10)

Initial acceleration demand positive as per ii) means that the vehicle initially tends to increase speed. The means 170 is so arranged that, in cases where a speed-limiting feature arises within a predetermined time which is relatively short and negative acceleration is required for reaching it, depending on the current situation, it ensures instead that present speed is maintained and instead waits for this speed decrease in order thereby to avoid accelerating in cases where it is known that braking will be necessary within a short time. For example, a_now might be determined according to ii) over a predetermined distance which is below the distance horizon, such a predetermined distance in one variant being of the order of 50m. In cases where a speed decrease is required to meet a speed-limiting feature within, for example, 100m or 5 seconds, the acceleration may still be set to 0 until the requirement for negative acceleration becomes so great that dragging of the engine becomes necessary.

In hillcrest driving where the vehicle's speed before the crest is reduced by reduced application of power/throttling of fuel supply so that the vehicle's speed before a downhill section of the route is below the target speed pertaining to a speed-limiting feature after the downhill section, the initial acceleration demand will be positive and braking strategy according to the present invention may with advantage be employed.

The system I comprises means 1 80 for activating the braking strategy determined by the means 146. The means 180 for activating braking strategy is arranged to activate a braking action for a braking process associated with the braking strategy determined. The braking strategy comprises a first braking process, a second braking process and a third braking process. The first braking process involves activating a braking action which results in positively accelerating movement of the vehicle along the section of the route. The second braking process involves activating a braking action which in principle results in lack of acceleration during the vehicle's movement along said section of the route. The third braking process involves allowing the vehicle to freewheel so that a speed greater than the target speed is reached, followed by activation of a braking action which results in negatively accelerating movement of the vehicle along the route.

In the aforesaid braking processes according to the present invention, activation of braking action involves using suitable brake devices of the vehicle. One embodiment uses the vehicle's auxiliary brakes, e.g. retarders. One embodiment uses the vehicle's service brakes. One embodiment uses both auxiliary brakes and service brakes of the vehicle.

The first braking process involves means 1 82 for activating a braking action which results in positively accelerating movement of the vehicle along the section of the route. The means 182 for activating a braking action according to the first braking process is arranged to activate braking action relatively early along the downhill section of the route and with braking action such that the target speed is reached at the speed-limiting feature.

The second braking process involves means 184 for activating a braking action which in principle results in lack of acceleration during the vehicle's movement along the section of the route. The means 1 84 for activating a braking action according to the second braking process is arranged to activate braking action relatively early along the downhill section of the route and with braking action such that the target speed is reached at the speed- limiting feature. The third braking process involves means 186a for initially allowing the vehicle to freewheel, and means 186b for activating thereafter a braking action which results in negatively accelerating movement of the vehicle along the section of the route. The means 186b for activating a braking action according to the third braking process is arranged to activate braking action relatively late along the downhill section of the route after the vehicle has been allowed to freewheel up to a speed above target speed and with braking action such that the vehicle is retarded so that target speed is reached at the speed-limiting feature. The first braking process is intended to be employed where the section of the route is relatively steep and/or relatively short. It is normally employed relatively briefly. In one embodiment the length of the downhill section of the route for employing the first braking process is of the order of 50-200 metres, in one variant about 1 00 metres. The first braking process may also depend on vehicle setting and accordingly on a setting desired by the driver for the movement of the vehicle whereby driver setting for the first braking process corresponds to a comfort setting or comfort mode with high degree of comfort.

The second braking process is intended to be employed where a vehicle speed close to said target speed is reached early. In one variant it is also employed relatively briefly. In one variant it is employed on lengths of the order of 300, which may of course be longer or shorter. The second braking process may also be employed depending on vehicle setting and accordingly on a setting desired by the driver for the movement of the vehicle whereby driver setting for the second braking process also corresponds to a comfort setting or comfort mode with high degree of comfort.

The third braking process is intended to be employed where the section of the route is relatively long and/or there is relatively little gradient. It may also be employed depending on vehicle setting and accordingly on a setting desired by the driver for the movement of the vehicle whereby driver setting of the vehicle for the third braking process corresponds to a sport setting or sport mode to cater for a desire to travel more quickly and consequently with a lower degree of comfort.

The means 146 for determining braking strategy based on vehicle setting with regard to desired degree of driving comfort involves in one variant determining braking strategy so that a vehicle setting with regard to high degree of comfort results in the first or second braking process normally being adopted, and a vehicle setting with regard to faster and accordingly more sporty driving results in the third braking process being adopted. In cases where the vehicle travelling along a route comes to a downhill section where the running resistance is found to be negative and the vehicle is consequently found to roll with positive acceleration, where the presence of speed-limiting features is continuously detected along the route, where detection is based on a predetermined distance horizon and/or time horizon ahead of the vehicle along the route and where the speed is prescribed in the form of a speed profile which is executed by continuous determination of required acceleration, the distance to the location of the speed-limiting feature may be determined by simulating various scenarios.

This involves determining whether it is a case for the first braking process to be applied by activating a braking action which results in positively accelerating movement of the vehicle along the section of the route.

The average time for the manoeuvre, given present speed v₀, distance s and acceleration a, is as follows: i) if a == 0 t = s/v₀ ii) if a > 0 v₀ VQ 2S

t = +

a a² a iii) if a < 0

If t is below the given threshold value, i.e. if t < T(v), the desired braking profile may be applied. It is normally not desirable to commence braking until a certain time, e.g. 1 0-20 seconds, before the speed-limiting feature. This may also depend on the extent of the section of the route, the visibility distance on the section of the route, i.e. how far the driver can see, and the nature of the road and any other parameters which may be supposed to affect the driver's driving. If the visibility is good, braking may take place sooner than in bad visibility. The system I comprises means 1 90 for determining whether prevailing vehicle speed is above target speed. The means for determining whether prevailing vehicle speed is above target speed involves means for comparing prevailing vehicle speed with target speed.

The system I comprises means 200 for responding to prevailing vehicle speed exceeding target speed by adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the route. The prescribed section before the beginning of a bend along the route and said section at the bend represents accordingly a certain distance s_prea/_m. See Figs. 3a and 3b described below. The system I comprises means 210 for determining said prescribed section before the beginning of a bend along the vehicle's route.

The means 210 for determining said prescribed section before the beginning of a bend along the route comprises means 212 for determining said prescribed section on the basis of a prescribed absolute anticipation relative to the section pertaining to the target speed. The distance s_prea,_m corresponding to the distance between the bend section and the section before the beginning of the bend is determined here as a predetermined distance, e.g. 20 metres.

The means 210 for determining said prescribed section before the beginning of a bend along the vehicle's route comprises means 214 for determining said prescribed section on the basis of a retardation from a prevailing vehicle speed to said target speed. The distance s_prea,_m corresponding to the distance between the bend section and the section before the beginning of the bend is determined in one variant as a function of a speed, e.g. a coming speed limit, i.e. the target speed, and may accordingly be referred to a time f_prea,_m at which the vehicle should thus reach this speed corresponding to the time i_prea,_m before the speed begins to apply. This involves determining s_prea,_m as follows, Vd_eSired being the desired speed: spreaim ^desired * tpreaim

The means 210 for determining said prescribed section before the beginning of a bend along the vehicle's route comprises means 21 6 for determining said prescribed section on the basis of a section of the speed profile pertaining to retardation before said bend.

The means 216 for determining said prescribed section before the beginning of a bend along the vehicle's route on the basis of a section of the speed profile pertaining to retardation before said bend comprises means 216a for responding to cases where the section of the speed profile pertaining to retardation before said bend is at a predetermined location before the section pertaining to the target speed by placing a ceiling on corresponding distance and/or time before the beginning of the bend. The means 216a for responding to cases where the section of the speed profile pertaining to retardation before said bend is at a predetermined location before the section pertaining to the target speed by placing a ceiling on the corresponding distance and/or time before the beginning of the bend comprises accordingly means for determining whether the section of the speed profile pertaining to retardation before said bend is at a predetermined location before the section pertaining to the target speed.

In adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the route, the required acceleration in the form of retardation a_tof thus in one variant becomes

The retardation by adjustment of the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the route may take place earlier, i.e. being initiated sooner than retardation to reach target speed on the bend, and/or more strongly so that the vehicle is retarded over a shorter distance to the speed on the prescribed section.

The system I comprises means 220 for responding to prevailing vehicle speed being below or equal to target speed by adjusting the vehicle's speed so that target speed is reached on the section pertaining to target speed. The system I comprises means 230 for controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset.

The means 230 for controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset comprises means 232 for adjusting said offset so that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical and a relatively smaller offset is allowed in the case of those which are safety-critical.

Safety-critical speed-limiting features comprise speed limits during hillcrest driving. Speed-limiting features which are not safety-critical comprise speed limit changes along the vehicle's route. At a non safety-critical speed-limiting feature comprising speed limit change along the vehicle's route the system I is configured to allow the driver him/herself to apply offsets to a desired level above target speed. Safety-critical speed-limiting features also comprise in one variant other features such as road narrowings, roadworks along the vehicle's route, obstacles such as speed obstacles along the route, deteriorated road surface, increased traffic density/queuing risk etc.

The electronic control unit 100 is signal-connected via a link 10 to the means 1 10 for continuously detecting the presence of speed-limiting features along the vehicle's route. The electronic control unit is arranged to receive via the link 1 0 a signal from the means 1 10 which represents data on speed-limiting features such as bends and/or speed limit changes.

The electronic control unit 100 is signal-connected via a link 10a to the means 1 10a which involves the map information unit 1 12 and the means 1 14 for determining the vehicle's location. The electronic control unit is arranged to receive via the link 10a a signal from the means 1 1 0a which represents map data on speed-limiting features in the form of bends and speed limit changes along the vehicle's route and location data on the positions of bends relative to the vehicle.

The electronic control unit 100 is signal-connected to the camera means 1 16 via a link 1 6. The electronic control unit is arranged to receive via the link 16 a signal from the camera means 1 1 6 which represents data on speed-limiting features comprising data on carriageway bends along the vehicle's route and data on speed changes along the route.

The electronic control unit 100 is signal-connected via a link 20 to the means 120 for regulating desired distance horizons for desired movement of the vehicle. The electronic control unit is arranged to receive via the link 20 a signal from the means 120 which represents data on desired distance horizons.

The electronic control unit 100 is signal-connected via a link 30 to the means 130 for continuously determining the vehicle's speed. The electronic control unit is arranged to receive via the link 30 a signal from the means 130 for continuously determining the vehicle's speed which represents data on current vehicle speed.

The electronic control unit 100 is signal-connected via a link 40a to the means 140 for responding to detection of speed-limiting features by determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature. The electronic control unit is arranged to receive via the link 40a a signal from the means 140 which represents data on required acceleration for reaching at speed-limiting features detected the speed appropriate to them. The electronic control unit 100 is signal-connected to the means 142 for continuously determining running resistance along the vehicle's route via a link 42. The electronic control unit is arranged to receive via the link 42 a signal from the means 142 which represents running resistance data.

The electronic control unit 100 is signal-connected to the means 142a for determining gradient resistance via a link 42a. The electronic control unit is arranged to receive via the link 42a a signal from the means 142a which represents data on carriageway gradients along the vehicle's route. The electronic control unit 100 is signal-connected to the means 142b for determining friction characteristics of the vehicle's powertrain via a link 42b. The electronic control unit is arranged to receive via the link 42b a signal from the means 142b which represents data on friction characteristics of the vehicle's powertrain.

The electronic control unit 1 00 is signal-connected to the means 142c for determining air resistance via a link 42c. The electronic control unit is arranged to receive via the link 42c a signal from the means 142c which represents air resistance data for the vehicle on the carriageway along its route.

The electronic control unit 100 is signal-connected to the means 142d for determining rolling resistance via a link 42d. The electronic control unit is arranged to receive via the link 42d a signal from the means 142d which represents rolling resistance data for the vehicle on the carriageway along its route.

The electronic control unit 100 is signal-connected via a link 40b to the means 140 for responding to detection of speed-limiting features by determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature. The electronic control unit is arranged to send via the link 40b a signal to the means 140 which represents data on current vehicle speed, data on speed-limiting features and data on distances to speed-limiting features, and running resistance data.

The electronic control unit 100 is signal-connected to the means 144 for determining required braking retardation via a link 44. The electronic control unit is arranged to receive via the link 44 a signal from the means 144 which represents data on required braking retardation.

The electronic control unit 100 is signal-connected via a link 46:1 to the means 146 for determining braking strategy inter alia on the basis of characteristics of said downhill section of the route. The electronic control unit is arranged to send via the link 46:1 a signal to the means 146 which represents data on characteristics of the section of the route, comprising length and/or gradient, obtained from the means 1 12 and/or the means 1 1 6, and/or data on vehicle speed obtained from the means 130 and/or data on running resistance obtained from the means 142.

The electronic control unit 100 is signal-connected to the means 146a for determining gradients on the downhill section of the route via a link 46a. The electronic control unit is arranged to receive via the link 46a a signal from the means 146a which represents data on gradients on the section of the route. The electronic control unit 100 is signal-connected to the means 146b for determining the length of the downhill section of the route via a link 46b. The electronic control unit is arranged to receive via the link 46b a signal from the means 146b which represents data on the length of the section of the route.

The electronic control unit 100 is signal-connected via a link 46c to the means 146c for determining vehicle speed with a view to taking vehicle speed into account. The electronic control unit is arranged to receive via the link 46c a signal from the means 146c which represents data on current vehicle speed.

The electronic control unit 100 is signal-connected via a link 46d to the means 146d for determining running resistance with a view to taking running resistance into account. The electronic control unit is arranged to receive via the link 46d a signal from the means 146d which represents running resistance data.

The electronic control unit 100 is signal-connected via a link 46:2 to the means 146 for determining braking strategy. The electronic control unit is arranged to receive via the link 46:2 a signal from the means 146 which represents data on braking strategy determined, which may be any from among the first braking process, the second braking process or the third braking process and depends on determined characteristics of the downhill section of the route, vehicle speed and/or running resistance.

The electronic control unit 100 is signal-connected via a link 50 to the means 150 for determining a maximum permissible lateral acceleration. The electronic control unit is arranged to receive via the link 50 a signal from the means 150 which represents data on maximum permissible lateral acceleration.

The electronic control unit 100 is signal-connected via a link 60a to the means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route. The electronic control unit is arranged to send via the link 60a a signal to the means 160 which represents data on speed-limiting features such as bends and/or speed limit changes.

The electronic control unit 100 is signal-connected via a link 60b to the means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route. The electronic control unit is arranged to receive via the link 60b a signal from the means 160 which represents speed data on prescribed speeds pertaining to a speed profile, and data on executing the speed profile.

The electronic control unit 100 is signal-connected via a link 62a to the means 1 62 for prescribing speed on the basis of the vehicle's maximum permissible lateral acceleration and carriageway bends along the vehicle's route. The electronic control unit is arranged to send via the link 62a a signal to the means 1 62 which represents data on maximum permissible lateral acceleration and data on bends along the vehicle's route. The electronic control unit 100 is signal-connected via a link 62b to the means 162 for prescribing speed on the basis of bends and the vehicle's maximum permissible lateral acceleration. The electronic control unit is arranged to receive via the link 62b a signal from the means 162 which represents data on determined maximum vehicle speed taking bends and maximum permissible lateral acceleration into account.

The electronic control unit 100 is signal-connected via a link 64a to the means 164 for prescribing speed on the basis of speed limit changes along the vehicle's route. The electronic control unit is arranged to send via the link 64a a signal to the means 164 which represents data on required longitudinal acceleration for coming speed limit changes.

The electronic control unit 100 is signal-connected via a link 64b to the means 164 for prescribing speed on the basis of speed limit changes along the vehicle's route. The electronic control unit is arranged to receive via the link 64b a signal from the means 164 which represents data on prescribed speeds pertaining to speed limit changes.

The electronic control unit 100 is signal-connected via a link 70 to the means 170 for determining whether an initially required acceleration is negative or positive. The electronic control unit is arranged to receive via the link 70 a signal from the means 170 which represents data on negative/positive acceleration.

The electronic control unit 100 is signal-connected via a link 80 to the means 180 for activating the braking strategy determined by the means 146. The electronic control unit is arranged to send via the link 80 a signal to the means 180 which represents data on activation of braking strategy determined.

The electronic control unit 100 is signal-connected via a link 82 to the means 182 for activating a braking action according to the first braking process which results in positively accelerating movement of the vehicle along the section of the route. The electronic control unit is arranged to send via the link 82 a signal to the means 1 82 which represents data on activation of braking action according to the first braking process. The electronic control unit 100 is signal-connected via a link 84 to the means 184 for activating a braking action which in principle results in lack of acceleration during movement of the vehicle along the section of the route. The electronic control unit is arranged to send via the link 84 a signal to the means 184 which represents data on activation of braking action according to the second braking process.

The electronic control unit 100 is signal-connected to the means 186a for initially allowing the vehicle to freewheel via a link 86a. The electronic control unit is arranged to send via the link 86a a signal to the means 186a which represents data on having the vehicle freewheel along the downhill section of the route for a certain distance and/or time and/or up to a certain speed above target speed.

The electronic control unit 100 is signal-connected via a link 86b to the means 1 86b for thereafter activating a braking action which results in negatively accelerating movement of the vehicle along its route. The electronic control unit is arranged to send via the link 86b a signal to the means 1 86b which represents data on activation of braking action according to the third braking process.

The electronic control unit 100 is arranged to process said data on speed- limiting features, data on desired distance horizons, speed data and running resistance data from the means 142 and to send said data to the means 140 for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature.

The means 140 for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature is arranged to process said data from the electronic control unit 100 in order thereby to determine the required acceleration.

The means 160 for prescribing speed on the basis of coming speed-limiting features along the vehicle's route is arranged to process said data on speed- limiting features such as bends and/or speed limit changes and lateral acceleration data in order to determine speeds pertaining to a speed profile, and to send to the electronic control unit speed data on prescribed speeds pertaining to a speed profile and data for executing the speed profile. The electronic control unit 100 is arranged in one embodiment to process said data on speed-limiting features, data on desired distance horizons, speed data and running resistance data from the means 142 and data on characteristics of the section of the route comprising at least one from among data on gradients on the section of the route, data on the length of the section of the route, data on current vehicle speed and running resistance data in order to determine braking strategy involving which braking process is to be employed. The electronic control unit 100 then sends the chosen braking strategy to the means 182, 1 84, 186a, 186b of the means 180 which is adapted to activating braking action for the braking process determined. The electronic control unit 100 is signal-connected via a link 90a to the means 1 90 for determining whether prevailing vehicle speed is above target speed. The electronic control unit is arranged to send via the link 90a a signal to the means 190 which represents data on prevailing speed and data on target speed. The means 190 for determining whether prevailing vehicle speed is above target speed is arranged to compare said speed data and target speed data in order thereby to determine data on whether prevailing vehicle speed is above target speed.

The electronic control unit 100 is signal-connected via a link 90b to the means 1 90 for determining whether prevailing vehicle speed is above target speed. The electronic control unit is arranged to receive via the link 90b a signal from the means 190 which represents data on whether prevailing vehicle speed is above target speed. The electronic control unit 1 00 is signal-connected via a link 200a to the means 200 for adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route. The electronic control unit is arranged to send via the link 200a a signal to the means 200 which represents data that prevailing vehicle speed is above target speed.

The electronic control unit 1 00 is signal-connected via a link 200b to the means 200 for adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route. The electronic control unit is arranged to receive via the link 200b a signal from the means 200 which represents data on adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route.

The electronic control unit 1 00 is signal-connected via a link 21 0a to the means 210 for determining said prescribed section before the beginning of a bend along the vehicle's route. The electronic control unit is arranged to receive via the link 210a a signal from the means 210 which represents data on the determined prescribed section before the beginning of a bend.

The electronic control unit 1 00 is signal-connected via a link 21 2a to the means 212 for determining said prescribed section before the beginning of a bend along the vehicle's route on the basis of a prescribed absolute anticipation relative to the section pertaining to target speed. The electronic control unit is arranged to receive via the link 212a a signal from the means 212 which represents data on the determined prescribed section before the beginning of a bend.

The electronic control unit 1 00 is signal-connected via a link 214a to the means 214 for determining said prescribed section before the beginning of a bend along the vehicle's route on the basis of a retardation from a prevailing vehicle speed to said target speed. The electronic control unit is arranged to receive via the link 214a a signal from the means 214 which represents data on the determined prescribed section before the beginning of a bend.

The electronic control unit 100 is signal-connected via a link 216x to the means 216 for determining said prescribed section before the beginning of a bend along the vehicle's route on the basis of a section of the speed profile pertaining to retardation before said bend. The electronic control unit is arranged to receive via the link 216x a signal from the means 216 which represents data on the determined prescribed section before the beginning of a bend. The electronic control unit 100 is signal-connected via a link 220a to the means 220 for adjusting the vehicle's speed so that target speed is reached on the section pertaining to target speed. The electronic control unit is arranged to send via the link 220a a signal to the means 220 which represents data that prevailing vehicle speed is below or equal to target speed.

The electronic control unit 1 00 is signal-connected via a link 220b to the means 220 for adjusting the vehicle's speed so that target speed is reached on the section pertaining to target speed. The electronic control unit is arranged to receive via the link 220b a signal from the means 220 which represents data on adjusting the vehicle's speed so that target speed is reached on the section pertaining to target speed.

The electronic control unit 1 00 is signal-connected via a link 230a to the means 230 for controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset. The electronic control unit is arranged to receive via the link 230a a signal from the means 230 which represents data on speed associated with target speed and greater than target speed by a certain offset.

The electronic control unit 1 00 is signal-connected via a link 232a to the means 232 for adjusting said offset so that a relatively larger offset is allowed in the case of a speed-limiting feature which is not safety-critical and a relatively smaller offset in the case of a safety-critical speed-limiting feature. The electronic control unit is arranged to send via the link 232a a signal to the means 232 which represents data on types of speed-limiting feature, i.e. safety-critical features such as bends or non safety-critical features such as speed limit changes along the vehicle's route.

The electronic control unit 1 00 is signal-connected via a link 232b to the means 232 for adjusting said offset so that a relatively larger offset is allowed at a non safety-critical speed-limiting feature and a relatively smaller offset is allowed at a safety-critical speed-limiting feature. The electronic control unit is arranged to receive via the link 232b a signal from the means 232 which represents data as to what offset of the vehicle speed greater than target speed the vehicle should be controlled with on the basis of whether the speed-limiting feature is safety-critical or not. In one embodiment the system I comprises presentation means, not depicted, for presenting chosen braking strategy to the driver. Presentation may be by any suitable presentation means. The presentation means comprises in one variant visual presentation means. The visual presentation means comprises in one variant a display unit visible to the driver which in one variant is situated in the vehicle's instrument panel. The visual presentation means comprises in one variant a so-called head-up display for information superimposed on the windscreen. The presentation means comprises in one variant acoustic presentation means in the form of any suitable sound unit. Fig. 3a schematically illustrates a curvature profile in the form of an S bend with a first bend d with a radius of curvature r1 and a second bend c2 with a radius of curvature r2. Fig. 3b schematically illustrates speed profiles for the curvature profile in Fig. 3a determined by the system I according to the present invention. The speed-limiting feature thus takes the form of first and second bends.

The dotted line in Fig. 3b represents a reference speed profile based on the required acceleration determined for reaching prescribed speed. The reference speed profile thus represents the speed demand sent to the vehicle's engine on the basis of the required acceleration. Accordingly, positive acceleration is demanded between the first and second bends to increase the vehicle's speed before demanding, close to the second bend, negative acceleration to retard the vehicle to a speed appropriate to the bend and pertaining to permissible lateral acceleration.

The broken line in Fig. 3b represents the vehicle's actual speed. It thus constitutes the executed speed profile based on the required acceleration determined on the basis of speed-limiting features in the form of the bends taking into account running resistance, i.e. how the vehicle's speed is controlled on the basis of required acceleration. Accordingly the vehicle is accelerated between the first and second bends to increase its speed before being retarded, close to the second bend, to a speed appropriate to the bend and pertaining to permissible lateral acceleration. The continuous line in Fig. 3b depicts a speed profile based on maximum permissible lateral acceleration. It thus represents a speed profile based on the speed-limiting feature.

Fig. 4a schematically illustrates a topology profile for a route involving bend sections. The route starts with an uphill section followed by a hillcrest and a downhill section. The downhill section is followed by a speed-limiting feature in the form of a bend section. The bend section might for example correspond to the bend d illustrated in Fig. 3a with radius of curvature r1 .

The section of the route has a certain characteristic with a gradient a and a length L. The gradient a may vary and any such variation is also catered for. Fig. 4b schematically illustrates speed profiles for the topology profile in Fig. 4a.

The thick continuous line in Fig. 4b represents a speed profile based on maximum permissible lateral acceleration. The thin continuous line in Fig. 4b represents the vehicle's actual speed. It thus constitutes the executed speed profile based on the required acceleration determined on the basis of the speed-limiting feature in the form of the bend involving topology comprising the gradient and extent of the downhill section of the route, the vehicle's speed and running resistance, i.e. how the vehicle's speed is controlled on the basis of required acceleration.

Action in the form of reduced application of power before crossing the hillcrest, i.e. throttling of the vehicle's fuel supply, so that its speed is allowed to drop to a predetermined extent relative to a reference speed before the hillcrest so that the vehicle's speed initially on the downhill section is below the target speed for the speed-limiting feature in the form of the bend section, results in the vehicle consuming less fuel.

When the vehicle is travelling close to the downhill section of the route before the speed-limiting feature, suitable braking strategy is determined on the basis of characteristics of the downhill section, comprising gradient and extent. The speed of the vehicle and the running resistance on the downhill section are also taken into account.

The downhill section of the route has a positively accelerating effect on the vehicle's running resistance.

The broken line represents a first braking process according to the braking strategy, whereby a braking action is activated early on the downhill section of the route and results in positively accelerating movement of the vehicle along said section so that the vehicle is accelerated by positive braking, from a speed below the prescribed target speed pertaining to the speed-limiting feature in the form of the bend section, to a speed pertaining to target speed. Any suitable braking device of the vehicle may be activated for such positively accelerating braking action. In one embodiment the vehicle's auxiliary brakes, e.g. its retarders and/or service brakes, are activated. The chain-dotted line represents a second braking process according to the braking strategy, whereby a braking action is activated relatively early along the downhill section of the route, here somewhat later than activation of braking action according to the first braking process, such that braking action according to the second braking process does in principle result in lack of acceleration during movement of the vehicle along said section of the route. Braking action according to the second braking process is activated accordingly when the vehicle's speed corresponds to the prescribed target speed pertaining to the speed-limiting feature in the form of the bend section and maintains target speed by said braking action on the downhill section of the route as far as the bend section. Any suitable braking device of the vehicle may be activated for such positively accelerating braking action. In one embodiment the vehicle's auxiliary brakes, e.g. its retarders and/or service brakes, are activated.

Where the first or second braking process is employed, one embodiment adjusts the vehicle's speed so that target speed is reached on the section pertaining to target speed.

The dotted line represents a third braking process according to the braking strategy, whereby initially the vehicle is allowed to freewheel for a certain distance along the downhill section of the route, resulting in positive acceleration so that the vehicle reaches a speed above the prescribed target speed pertaining to the speed-limiting feature in the form of the bend section, followed by activation of a braking action which results in negatively accelerating movement of the vehicle along said section of the route. Any suitable braking device of the vehicle may be activated for such positively accelerating braking action. In one embodiment the vehicle's service brakes are activated.

In one embodiment the vehicle's speed is adjusted when the third braking process is employed so that target speed is reached on a prescribed section Spreaim before the beginning of the bend section of the route. Such an embodiment is described above with reference to Fig. 2 and below with reference to Figs. 5a-b.

When employing the third braking process, the vehicle's speed is controlled in one embodiment such that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset which is so adjusted that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical, such as a speed limit, and a relatively smaller offset is allowed in the case of safety-critical speed-limiting features such as the bend section according to Figs. 4a-b. Such an embodiment is described above with reference to Fig. 2 and below with reference to Figs. 6a-b.

The first braking process is employed with advantage where said section of the route is relatively short and/or relatively steep. The second braking process is employed with advantage where a vehicle speed close to said target speed is reached early. The second braking process is also employed where said section of the route is relatively short and/or relatively steep. The third braking process is employed where said section of the route is relatively long and/or there is relatively little gradient.

Fig. 5a schematically illustrates a curvature profile in the form of a roundabout with a certain radius of curvature. The vehicle is travelling on a carriageway and intending to negotiate the roundabout by executing a left turn represented by the arrow A.

Fig 5b schematically illustrates speed profiles for the curvature profile in Fig. 5a determined by the system I according to the present invention. Accordingly a speed profile is determined on the basis of prevailing vehicle speed and comprising a target speed based on a maximum permissible lateral acceleration of the vehicle associated with a coming section P1 of the bend, here the roundabout, on the route. In cases where the prevailing vehicle speed v₀ is above the target speed v, the vehicle's speed is adjusted so that the target speed is reached on a prescribed section P2 before the beginning of the bend, in the form of the roundabout, on the vehicle's route.

In cases where the prevailing vehicle speed is below or equal to the target speed, the vehicle's speed is adjusted so that target speed is reached on the section pertaining to target speed.

The continuous line in Fig. 5b thus represents the speed profile determined on the basis of maximum permissible lateral acceleration.

The broken line in Fig. 5b represents the desired speed profile for the vehicle whereby the target speed v is reached on the prescribed section P2 before the beginning of the bend, section P2 being a distance s_{prea m} before section P1 of the bend.

Fig. 5b illustrates how the prescribed section P2 is determined before the beginning of the bend in the vehicle's route on the basis of a section of the speed profile based on maximum permissible lateral acceleration which pertains to retardation before said bend, i.e. in the region for initiation of retardation according to the speed profile.

The chain-dotted line in Fig. 5b represents an undesired speed profile.

Fig. 6a schematically illustrates a speed profile when negotiating a bend representing target speed v_max and permissible speed v_max>brake above target speed by a certain offset v_0ffSet1 according to an embodiment of the present invention. Fig. 6b schematically illustrates a speed profile at a speed limit change representing target speed v_max and permissible speed v_max,_brake above target speed by a certain offset v₀ff_Set₂ according to an embodiment of the present invention. Fig. 7 schematically illustrates a block diagram of a method for adjusting the acceleration of a vehicle travelling along a route according to an embodiment of the present invention.

In one embodiment the method for adjusting the acceleration of a vehicle travelling along a route comprises a first step S1 in which the presence of speed-limiting features along the vehicle's route is continuously detected.

In one embodiment the method for adjusting the acceleration of a vehicle travelling along a route comprises a second step S2 in which at detected speed-limiting features the acceleration required for reaching a prescribed target speed at such a detected coming speed-limiting feature is determined. In one embodiment the step of determining the required acceleration, where a speed-limiting feature detected is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance, and the vehicle's speed is initially below said target speed, comprises the step S2a of determining braking strategy based on characteristics of said downhill section of the route and/or on the basis of vehicle setting with regard to desired degree of driving comfort.

In one embodiment of the method said characteristics of said downhill section of the route comprise gradient and/or length.

In one embodiment of the method the step of determining braking strategy further comprises taking vehicle speed and/or running resistance into account.

In one embodiment of the method said braking strategy involves a first braking process involving the step of activating a braking action which results in positively accelerating movement of the vehicle along the section of the route.

In one embodiment of the method said braking strategy involves a second braking process involving the step of activating a braking action which in principle results in lack of acceleration during movement of the vehicle along the section of the route.

In one embodiment of the method said braking strategy involves a third braking process involving the steps of initially allowing the vehicle to freewheel and thereafter activating a braking action which results in negatively accelerating movement of the vehicle along the section of the route.

In one embodiment of the method said first braking process is employed where the section of the route is relatively short and/or relatively steep, said third braking process is employed where the section of the route is relatively long and/or there is relatively little gradient, and said second braking process is employed where a vehicle speed close to said target speed is reached early.

In one embodiment of the method the step of determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature takes place continuously.

In one embodiment of the method said speed-limiting features comprise bends on the route, where speed is prescribed on the basis of the vehicle's maximum permissible lateral acceleration.

In one embodiment of the method said speed-limiting features comprise speed limit changes along the vehicle's route.

In one embodiment of the method the step of determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature involves the step of continuously determining running resistance along the vehicle's route.

In one embodiment of the method the step of continuously detecting the presence of speed-limiting features along the vehicle's route on the basis of a predetermined distance horizon and/or time horizon ahead of the vehicle along the route takes place.

In one embodiment the method comprises the step of prescribing speed in the form of a speed profile along the vehicle's route and continuously executing said speed profile by continuous determination of said required acceleration.

In one embodiment the method comprises the step of controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than target speed by a certain offset which is so arranged that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical and a relatively smaller offset is allowed in the case of safety-critical speed-limiting features.

In one embodiment the method comprises the step, in cases where the third braking process is employed, of adjusting the vehicle's speed so that target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route and, in cases where the first or second braking process is employed, of adjusting the vehicle's speed so that target speed is reached on the section pertaining to target speed.

In one embodiment the method comprises the step of presenting chosen braking strategy to the driver. The presentation of braking strategy may be visual and/or acoustic. It may be by any suitable presentation means such as visual presentation means and/or acoustic presentation means.

Fig. 8 is a diagram of one version of a device 500. The control unit 100 described with reference to Fig. 2 may in one version comprise the device 500 which itself comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

A proposed computer programme P comprises routines for adjusting the acceleration of a vehicle travelling along a route according to the innovative method. The programme P comprises routines for continuously detecting the presence of speed-limiting features along the vehicle's route. The programme comprises routines for responding to detected speed-limiting features by determining the acceleration required for reaching a prescribed target speed at such a detected coming speed-limiting feature. The programme comprises, where a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance and the vehicle's speed is initially below said target speed, routines for determining the required acceleration, involving determination of braking strategy based on characteristics of said downhill section of the route and/or on vehicle setting with regard to desired degree of driving comfort. The programme comprises routines for effecting the embodiments of the method in accordance with Fig. 7. The programme may be stored in an executable form or in compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit conducts a certain part of the programme stored in the memory 560 or a certain part of the programme stored in the read/write memory 550. The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit via a data bus 51 1 . The read/write memory 550 is adapted to communicating with the data processing unit via a data bus 514. The links associated with the control unit 100 may for example be connected to the data port.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 will be prepared to conduct code execution as described above. The signals received on the data port may be used by the device 500 for continuously detecting the presence of speed-limiting features along the vehicle's route. The signals received on the data port may be used by the device 500 to respond to detected speed- limiting features by determining the acceleration required for reaching the prescribed target speed at such a detected coming speed-limiting feature. The signals received on the data port may, where a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance and the vehicle's speed is initially below said target speed, be used by the device 500 for determining the required acceleration, involving determination of braking strategy based on characteristics of said downhill section of the route and/or on the basis of vehicle setting with regard to desired degree of driving comfort. The signals received on the data port may be used by the device 500 to effect the embodiments of the method according to Fig. 7.

Parts of the methods herein described may be conducted by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed. The above description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive, nor to restrict the invention to the variants described. Many modifications and variations will obviously suggest themselves to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and their practical applications and thus make it possible for one skilled in the art to understand the invention for different embodiments and with the various modifications appropriate to the intended use.

Claims

1 . A method for adjusting the acceleration of a vehicle (1 ) travelling along a route, comprising the steps of continuously detecting (S1 ) the presence of speed-limiting features along the vehicle's route and, when speed-limiting features are detected, of determining (S2) the acceleration required for reaching a prescribed target speed at such a detected coming speed-limiting feature, characterised in that where a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance, and the vehicle's speed is initially below said target speed, the step of determining (S2a) required acceleration involves the step of determining braking strategy based on characteristics of said downhill section of the route and/or on vehicle setting with regard to desired degree of driving comfort.

2. A method according to claim 1 , in which said characteristics of said downhill section of the route comprise gradient and/or length.

3. A method according to claim 1 or 2, in which the step of determining braking strategy further involves taking vehicle speed and/or running resistance into account.

4. A method according to any one of the foregoing claims, in which said braking strategy involves a first braking process involving the step of activating a braking action which results in positively accelerating movement of the vehicle along said section of the route.

5. A method according to any one of the foregoing claims, in which said braking strategy involves a second braking process involving the step of activating a braking action which in principle results in lack of acceleration during movement of the vehicle along said section of the route.

6. A method according to any one of the foregoing claims, in which said braking strategy involves a third braking process involving the steps of initially allowing the vehicle to freewheel and thereafter activating a braking action which results in negatively accelerating movement of the vehicle along said section of the route.

7. A method according to claim 6, in which said first braking process is employed where said section of the route is relatively short and/or relatively steep, said third speed-limiting feature is employed where said section of the route is relatively long and/or there is relatively little gradient, and said second braking process is employed where a vehicle speed close to said target speed is reached early.

8. A method according to any one of the foregoing claims, in which the step of determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature takes place continuously.

9. A method according to any one of the foregoing claims, in which said speed-limiting features comprise bends on the route, and speed is prescribed on the basis of the vehicle's maximum permissible lateral acceleration.

10. A method according to any one of the foregoing claims, in which said speed-limiting features comprise speed limit changes along the vehicle's route.

1 1 . A method according to any one of the foregoing claims, in which the step of determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature involves the step of continuously determining running resistance along the vehicle's route.

12. A method according to any one of the foregoing claims, in which the step of continuously detecting the presence of speed-limiting features along the vehicle's route takes place on the basis of a predetermined distance horizon and/or time horizon ahead of the vehicle along the vehicle's route.

13. A method according to any one of the foregoing claims, comprising the step of prescribing speed in the form of a speed profile along the vehicle's route and continuously executing said speed profile by continuous determination of said required acceleration.

14. A method according to any one of the foregoing claims, comprising the step of controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset which is so adjusted that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical and a relatively smaller offset is allowed in the case of safety-critical speed-limiting features.

15. A method according to any one of claims 6-14, comprising the steps, in cases where the third braking process is employed, of adjusting the vehicle's speed so that the target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route and, in cases where the first or second braking process is employed, of adjusting the vehicle's speed so that the target speed is reached on the section pertaining to the target speed.

16. A system (I) for adjusting the acceleration of a vehicle (1 ) travelling along a route, comprising means (1 10) for continuously detecting the presence of speed-limiting features along the vehicle's route, and means (140) for, when speed-limiting features are detected, determining the acceleration required for reaching a prescribed target speed at such a detected coming speed- limiting feature, characterised in that where a detected speed-limiting feature is preceded by a downhill section of the route which has positively accelerating effects on the vehicle's running resistance, and the vehicle's speed is initially below said target speed, the means (140) for determining required acceleration involves means (146) for determining braking strategy based on characteristics of said downhill section of the route and/or on vehicle setting with regard to desired degree of driving comfort.

17. A system according to claim 16, in which said characteristics of said downhill section of the route comprise gradient and/or length, and the means (146) for determining braking strategy involves means (146a) for determining the gradient of the section of the route and/or means (146b) for determining the length of the section of the route.

18. A system according to claim 16 or 17, in which the means (146) of determining braking strategy further involves means (146c) for determining vehicle speed and/or means (146d) for determining running resistance with a view to taking vehicle speed and/or running resistance into account.

19. A system according to any one of claims 16-18, in which said braking strategy involves a first braking process involving means (182) for activating a braking action which results in positively accelerating movement of the vehicle along said section of the route.

20. A system according to any one of claims 16-19, in which said braking strategy involves a second braking process involving means (184) for activating a braking action which in principle results in lack of acceleration during movement of the vehicle along said section of the route.

21 . A system according to any one of claims 16-19, in which said braking strategy involves a third braking process means (1 86a) for initially allowing the vehicle to freewheel and means (186b) for thereafter activating a braking action which results in negatively accelerating movement of the vehicle along said section of the route.

22. A system according to claim 21 , in which said first braking process is intended to be employed where said section of the route is relatively short and/or relatively steep, said third speed-limiting feature is intended to be employed where said section of the route is relatively long and/or there is relatively little gradient, and said second braking process is intended to be employed where a vehicle speed close to said target speed is reached early.

23. A system according to any one of claims 16-22, in which the means (140) for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature takes place continuously.

24. A system according to any one of claims 16-23, in which said speed- limiting features comprise bends on the route, and there is accordingly means (160) for prescribing speed on the basis of the vehicle's maximum permissible lateral acceleration.

25. A system according to any one of claims 16-24, in which said speed- limiting features comprise speed limit changes along the vehicle's route.

26. A system according to any one of claims 16-25, in which the means (140) for determining the acceleration required for reaching prescribed speed at a coming speed-limiting feature involves means (142) for continuously determining running resistance along the vehicle's route.

27. A system according to any one of claims 16-26, in which the means (1 10) for continuously detecting the presence of speed-limiting features along the vehicle's route involves means for said determination on the basis of a predetermined distance horizon and/or time horizon ahead of the vehicle along the vehicle's route.

28. A system according to any one of the foregoing claims, comprising means for prescribing speed in the form of a speed profile along the vehicle's route and means for continuously executing said speed profile by continuous determination of said required acceleration.

29. A system according to any one of the foregoing claims, comprising means (230) for controlling the vehicle's speed so that a speed associated with said target speed is allowed to be greater than the target speed by a certain offset, comprising means (232) for adjusting said offset so that a relatively larger offset is allowed in the case of speed-limiting features which are not safety-critical and a relatively smaller offset is allowed in the case of safety-critical speed-limiting features.

30. A system according to any one of claims 21 -29, comprising means (21 2), in cases where the third braking process is employed, for adjusting the vehicle's speed so that the target speed is reached on a prescribed section before the beginning of a bend along the vehicle's route, and means (214), in cases where the first or second braking process is employed, for adjusting the vehicle's speed so that the target speed is reached on the section pertaining to the target speed.

31 . A vehicle provided with a system (I) according to any one of claims 16- 30.

32. A computer programme (P) for adjusting the acceleration of a vehicle travelling along a route, which programme (P) comprises programme codes which, when run by an electronic control unit (1 00) or another computer (500) connected to the electronic control unit (100), enable the electronic control unit (1 00) to perform steps according to claims 1 -7.

33. A computer programme product provided with a digital storage means which stores the computer programme according to claim 32.