SE543827C2

SE543827C2 - Method and control device to control vehicle speed

Info

Publication number: SE543827C2
Application number: SE1850885A
Authority: SE
Inventors: Afram Kourie; Anders Björkman; Frank Mohr; Marcus Engman; Richard Boström
Original assignee: Scania Cv Ab
Priority date: 2018-07-11
Filing date: 2018-07-11
Publication date: 2021-08-03
Also published as: SE1850885A1; DE102019004368A1

Abstract

The present invention relates to a method performed by a control device (50) of a vehicle (1) for controlling that the vehicle reaches a set speed, wherein the method is adapted to be performed when the vehicle (1) is travelling on a road comprising one or more road sections having a downhill slope (RSD) followed by a curved road section (RSC), wherein the vehicle (1) comprises an automatic or semi-automatic transmission, the method comprising steps of:- determining (s101) a target set speed vtarget for the vehicle (1) at a predetermined location (xi) before the curved road section (RSC), based at least on a radius of the curved road section and a weight of the vehicle (1), - selecting (s102) a gear to decelerate the vehicle speed towards the target set speed vtarget at the predetermined location (x1), wherein the gear is selected based at least on the weight of the vehicle, a current speed of the vehicle and a height difference between a current position of the vehicle and the curved road section (RSC), and- controlling (s103) the transmission to engage the selected gear.

Description

1 Method and control device to control vehicle speed TECHNICAL FIELD The present invention relates to a method performed by a control device of a vehicle forcontrolling that the vehicle reaches a set speed as defined in the appended claims. Thepresent invention also relates to a control device configured to control that the vehiclereaches the set speed, and to a vehicle comprising the control device as defined in theappended claims. Further, the present invention relates to a computer program and a computer-readable medium as defined in the appended claims.BACKGROUND ART An automatic speed control system, also referred to as a cruise control, is a system forregulating the speed of a motor vehicle, which may be a passenger car or a heavy vehicle, e.g.a truck or bus. Simple automatic speed control systems are configured to maintain a desiredset speed for the vehicle by increasing or decreasing the amount of power applied by theengine. The automatic speed control system may be activated/deactivated and operated bymeans of an operating device and/or an interface, which may be situated close to the steeringwheel of the vehicle. lt is also usual that the automatic speed control system in an activated state is deactivated by the driver depressing the brake pedal or the clutch pedal.

Driving a heavy vehicle on long tiovrnhiii roads with inany curves, such as mountain roads, canbe very clemanding for a driver. To he able to adiust the speed ofthe vehicie to a faster traffic,the vehicie is often driven at high speeds on straight sections of the road vrith a dovvnhiiisiope, and very siovvly through curves. This makes it often difficuit to utiiize vehicles cruisecontroi system, vvhich may be for example a specific type adapted for clownhiil speed control(ÛHSC), and the driver rnay end up using hrakes manualiy instead, For example vvheel frictionbrakes, such as drum or disc brakes, rnay deteriorate faster during such manual use, wherehyfrequerit service is required. Tnerefore, there is a desire to decrease the need to use wheel friction brake-s. 2US2017/0ï59805A1 describes a predictive transmission of a vehieie which takes ihto account aroad shape. However, despite existing systems, there is stiii a need to improve the controi ofthe venicie when the vehicle is travelling on a road comprising one or more road sections having a downhill slope followed by a curved road section.SUMMARY OF THE INVENTION During recent years, the automatic speed control systems have been developed to decreasethe need for manual interference by the driver or operator of the vehicle. However, there isstill a need to develop the control systems of vehicles, especially when the vehicle is travellingon is travelling on a road comprising one or more road sections having a downhill slopefollowed by a curved road section. Especially, it wouid he desirabie to enabie efficient driverassistance oh roads having road sections having a downhiii siope foiiovved by a curve, whiie the safety ofthe driver, the vehicie and the surrounding traffic is not cornprtimisetïi. lt is an objective ofthe present invention to provide a method and control device to controlthe speed ofthe vehicle on a road comprising one or more road sections having a downhillslope followed by a curved road section, in such a way that manual interventions of the driveror operator of the vehicle are minimized or not required, while the vehicle speed is controlled in a safe way.

Also, it is an objective to decrease the use of wheel friction brakes, and thus decrease the need for service and maintenance for the brakes.

The objectives above are attained by a method as described in the appended eiaims. Themethod is performed by a controi device of a vehicie, and controls that the vehicle reaches aset speed, and the method is adapted to be performed when the vehicle is travelling on a roadcomprising one or more road sections having a downhill slope followed by a curved roadsection. The vehicle comprises an automatic or semi-automatic transmission. The method comprises steps of: - determining a target set speed vtarget for the vehicle at a pre-determinedlocation before the curved road section, based at least on a radius of the curved road section and a weight of the vehicle, 3-- selecting a gear to decelerate the vehicle speed towards the target set speedvtarget at the predetermined location before the curved road section, whereinthe gear is selected based at least on the weight of the vehicle, a current speedof the vehicle and a height difference between a current position ofthe vehicleand the curved road section, and - controlling the transmission to engage the selected gear.

By determining a target speed before the curved road section at a pre-determined locationand by selecting a gear that decelerates the vehicle towards the target speed, the need for manual use of brakes ofthe vehicle can be reduced.

Generally the vehicle obtains a higher speed on road sections having a downhill slope. Thus,the vehicle may be for example coasted at least partly on these road sections, wherebyeconomic operation of the vehicle can be provided. By using the braking torque provided bythe gear selection, the speed of the vehicle can be decelerated while the wear of the wheel friction brakes is reduced and the driving economy can be further improved.

The step of determining the target speed vtarget may include calculation based on a pre-determined maximum vehicle sideways acceleration for the vehicle, an optional slope of thecurved road section and optionally a current speed limit. ln this way, the safety is furtherimproved and the risk for the vehicle tipping reduced. The speed limit may be optional, since itis often higher than the speed allowed by the sideways acceleration ofthe vehicle. However, ifthe speed limit is lower than the speed allowed by the sideways acceleration ofthe vehicle, it needs to be considered.

The step of selecting a gear may be further based on kinetic energy provided by the slope ofthe road section having a downhill slope (RSD) and a pre-determined braking distance. Forexample, by choosing a short braking distance it may be possible to increase the averagespeed ofthe vehicle. Thus, in some embodiments, the pre-determined braking distance maybe chosen to be a shortest possible distance and/or time required to reach the target setspeed vtarget. On the other hand, ifthe braking distance is longer than the shortest possible, a smoother braking, and thus better comfort for the driver can be provided. 4The method may further comprise a step of calculating, in addition to the braking torqueprovided by the gear selection in step, an additional braking torque required to reach thetarget speed vtarget in addition to the braking torque protficied by the gear selection step. in this vvay, the safety of the vehicle is further intproved.

The additional braking torque may be provided by an auxiiiary brake being a retarder, and/oran electric brake, and/or by adjusting a compression release brake and/or an exhaust gasbrake. By using an auxiliary brake, or by adjusting the compression release brake and/or anexhaust gas brake, the use of wheel friction brakes may be reserved for more forceful braking situations. ln the method, the pre-determined location can be selected based on map data. By using map data, accuracy of the ntethod can be intproved.

The step of selecting the gear can be based on gear data provided by simulation ofdeceleration of the vehicle with different gear choices, wherein at least the weight of thevehicle, the braking distance and the slope of the road are variables considered in thesimulation. By using simulation data, the specific road on a planned route and vehicle data canbe considered, and accurate control ofthe vehicle obtained. The target speed and/or thebraking distance may thus be pre-determined, whereby a need for demanding calculation during the operation of the vehicle is not necessary or is at least reduced.

To improve the safety of the vehicle, wheel friction brakes may be additionally used to reach the target speed vtarget.

The present invention also relates to a computer program, which computer programcomprises program code for causing a control device or a computer connected to the control device to perform the steps as defined above.

Further, the present invention relates to a computer-readable medium comprising a programcode stored on the computer-readable medium for performing the method steps as definedabove, when said computer program is run on a control device or a computer connected to the control device. 5Also, the objectives and the advantages described above in connection with the method areattained with a corresponding control device according to the appended claims and as described below.

The control device is configured to control that the vehicle reaches a set speed, the vehiclebeing configured to travel on a road comprising one or more road sections having a downhillslope followed by a curved road section, wherein the vehicle comprises an automatic or semi- automatic transmission. The control unit is configured to: -determine a target set speed vtarget for the vehicle at a pre-determinedlocation before the curved road section, based at least on a radius of the curvedroad section and a weight of the vehicle , - select a gear to decelerate the vehicle speed towards the target set speedvtarget at the predetermined location before the curved road section, whereinthe gear is selected based at least on the weight of the vehicle, a current speedof the vehicle and a height difference between a current position ofthe vehicleand the curved road section, and - control the transmission to engage the selected gear.

The target speed vtarget can be calculated based on a pre-determined maximum vehiclesideways acceleration for the vehicle, an optional slope ofthe curved road section and optionally a current speed limit.

The control device may be configured to select the gear based on the kinetic energy providedby the slope ofthe road section having a downhill slope and a pre-determined brakingdistance. The pre-determined braking distance may be a shortest possible distance and/or time required to reach the target set speed vtarget.

The control device may be configured to calculate additional braking torque required to reachthe target speed vtarget. The control device may be configured to activate an auxiliary brake,vvhich may be a retarder and/or an electric brake, if additional braking torque is requiredand/or to adjust a compression release brake and/or an exhaust gas brake to increase braking torque. 6 The pre-determined location can be selected based on map data.

The control device can be configured to select the gear based on gear data provided bysimulation of deceleration of the vehicle with different gear choices, wherein the weight of the vehicle, the braking distance and the slope ofthe road are considered in the simulation.

The control device may be configured to engage or require use of wheel friction brakes to reach the target speed vtarget The present invention also relates to a vehicle, which comprises control device or the computer-readable medium as described above.

Further objects, features and advantages of the present invention are described below in the detailed description.BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects and advantages of it, thedetailed description set out below should be read together with the accompanying drawings,in which the same reference notations denote similar items in the various diagrams, and in which: Fig. 1 schematically illustrates a vehicle comprising a control device ofthe present disclosure;Fig. 2 schematically illustrates a part of a powertrain for the vehicle in Fig. 1; Fig. 3 schematically illustrates a road section RS having a downhill slope; Fig. 4 schematically shows the vehicle of Fig. 1 travelling on a road comprising one or more road sections having a downhill slope followed by a curved road section; Fig. 5 schematically illustrates a flow chart for a method for controlling that the vehicle reaches a set speed according to an embodiment; and Fig. 6 schematically illustrates a control device according to an embodiment.

DETAILED DESCRIPTION Generally, when heavy vehicles, such as trucks, are travelling on downhill roads having manycurved road sections, there is a need to adjust the speed ofthe vehicle due to the varyingcurvature of the road. The speed is often adapted to be low through the curved road sectionsand higher on the downhill sections ofthe road, especially when the downhill sections areessentially straight, to adjust the vehicle speed to faster traffic of the road, such as passengercars. This may lead to that many drivers use brakes manually to adjust the braking torque,since it is generally experienced as an easier manoeuvre than adjusting a set speed of anautomatic speed control system of the vehicle, such as a downhill speed control (DHSC)system of the vehicle. Thus, it is an objective of the present disclosure to provide a methodand control device to control the speed ofthe vehicle in such a way that manual interventionsof the driver or operator ofthe vehicle are minimized or not required, while the vehicle speedis controlled in a safe way. Also, it is an objective to decrease the use of wheel friction brakes, and thus decrease the need for service and maintenance ofthe brakes.

Fig. i. schematically shows a side view of a heavy vehicle 1,, which is a 'truclg cemprising apewer unit 2, which may he an internal cemhustien engine. Generally, in the presentdisclosure besides the vehicle being a truck, the vehicle could be any other type of a heavyvehicle, such as a hus. The vehicle 1 further comprises a gearbox 6 connected to the drivingwheels 8 ef the vehicle ii. The vehicle may be a hybrid vehicle comprising a power unitincluding an electric machine (not shown) to produce moving force to the vehicle in additionto the internal combustion engine 2. Wheel friction brakes are connected to the wheels of the vehicle (not shown).

Fig. 2 schematically shows parts of a powertrain for the vehicle 1. The powertrain comprisesthe power unit 2, which in this case is mechanically connected by a shaft to a first end of agearbox 6 via a clutch device 4. The gearbox 6 has its second end mechanically connected by apropeller shaft 5 to a differential gear 3 associated with a driving axle. The driving axle comprises left and right drive shafts 7 which drive the powered driving wheels 8.

By this well-known arrangement, the mechanical work of the power unit 2 is transferred, via anumber of transmission devices such as clutch device 4, gearbox 6, propeller shaft 5, differential gear 3 and drive shafts 7, to the powered driving wheels 8 for propulsion of the 8vehicle 1. The gearbox 6 is a transmission device, which has a number of forward gears forpropelling the vehicle 1 forwards and usually also one or more reverse gears. The number of forward gears varies but twelve forward gears are for example usual in trucks.

The transmission ratio of a powertrain may vary, enabling it to assume various ratios (i.e.various transmission ratio configurations). The various ratios depend inter alia on the gearcurrently engaged in the gearbox 6 and on the ratio ofthe differential gear 3. The powertraincan assume a number of different discrete transmission ratios and/or have a continuous rangeof ratios, and the gearbox 6 box may be e.g. an automatic gearbox with so-called converters orit may be another type of gearbox with continuously variable transmissions. The vehicle of thepresent disclosure has an automatic or semi-automatic transmission, and can thereforeassume a number of different discrete transmission ratios and/or have continuous ranges of ratios. ln addition, the vehicle 1 comprises or is connected to a control device 50 comprising one ormore electronic control units (ECUs). The purpose of said control device is to control/regulateone or more functions in the vehicle 1, e.g. the speed, by means of one or more actuatorswhich may be related to various functions in the vehicle 1, such as engine control, gearchanging, cruise control, suspension configuration, etc. The control device 50 may use anumber of different parameters, e.g. current engine speed, current accelerator pedal position,current engine torque, data from various sensors and map data to control the various functions of the vehicle 1.

According to the present disclosure, the control device is configured to control that the vehiclereaches a set speed when travelling on a road comprising one or more road sections having adownhill slope followed by a curved road section. The set speed is reached at a predeterminedlocation before the curved road section, e.g. at the end of the road section having a downhillslope or at the entry into the curved road section, which is preceded by the road section having a downhill slope.

The road sections having a downhill slope generally have slope defined by a height differencebetween two points on the road. ln an illustrative and non-limiting example, the road mayhave a height difference from the highest point to the lowest point of the road from at least m up to over 3000 meters, but is not limited thereto. The length ofthe road may vary and 9may comprise one or more road sections having a downhill slope followed by a curved roadsection. The road may comprise several, such as from 2 to about 100 or more road sections having a downhill slope followed by a curved road section, but is not limited thereto.

The control device and/or the method may be activated to operate according to the methodor mode of the present disclosure over a specified road length comprising one or more roadsections having a downhill slope followed by a curved road section. As an example, thespecified road length may be 50 m or more, e.g. up to 300 km or more, but is not limited tosuch lengths. The control device may comprise means to activate the method when the roadbegins and to deactivate the method when the road ends. For example, the control systemmay be configured to perform the method and thus choose a driving mode according to thepresent disclosure, i.e. to control that the vehicle reaches a set speed, when the vehiclearrives at a certain point in a route. Alternatively, the operator of the vehicle may activate thedriving mode manually. This is advantageous since the mode may be chosen to be used only on specific roads.

The downhill road sections may have a certain respective height difference resulting in arespective slope or angle as well as being of different lengths. The respective slope may beexpressed in different ways. For example, the slope may be expressed as a ratio or gradient ofthe rise to the coverage, as a slope in percentage or as a slope in degrees indicative of a relationship between the length and height difference ofthe downhill section.

To illustrate a height difference and slope of a road section RS having a downhill slope,reference is made to Fig. 3. RS illustrates a road section RS having a downhill slope. The rise R,i.e. height difference, is illustrated as a vertical leg of a right triangle and the coverage C is illustrated as a horizontal leg ofthe triangle.

As a numerical example, the height difference can be measured to R=3m and the coverage C of the road section can be C=36m. The slope can be expressed in following ways:- The resulting slope gradient is 3:36, i.e. 1:12.- ln percentage, the slope is 3/36*100%=8.3%.

- The angle of the slope can be calculated from the equation tan 6 = 3/36; whereby 9 = tan'1(3/36) = 4.760. Thus, the slope angle is 4.76 O.

The angle ofthe road section RS having a downhill slope is more than 0 degrees.

As mentioned above, at least one road section having a downhill slope is followed by a curvedroad section. Each curved road section has a respective curve radius. The curve radius may beobtained from map data and/or it may be obtained by means of a sensing apparatus, e.g. agyro sensor, earth magnetic equipment and/or a camera providing picture data of the road ahead of the vehicle.

The road section with the downhill slope may be a substantially straight road section, or it mayhave a slight curve radius, but the curve radius is smaller than the curve radius of the curvedroad section, which follows the road section having the downhill slope. The curve radius of theroad section with the downhill slope can be zero, i.e. the road is straight. lfthere is a slightcurve, the curve radius can be for example at least 5-10 times larger than the curve radius ofthe ofthe curved road section which follows the road section having the downhill slope, but isnot limited thereto. The length of the curved road section can be shorter than the length ofthe road section having a downhill slope, and can be for example at least 5-10 times shorterthan the preceding downhill road section, but is not limited thereto. The curved road sectionmay have a downhill slope and the slope ofthe curved road section may set a limitation on themaximum speed of the vehicle in the curve. The downhill slope of a curved section can be smaller than the slope of the preceding road section having a downhill slope.

The data relating to the slope and the curve radius may be directly obtained from map data,which contains topographical information. Alternatively or additionally, the data relating tothe slope and the curve radius may be data saved in the control device during a previousoperation of the vehicle or another vehicle on the road in a route. The control device may alsobe configured to calculate the slope based on map data providing information relating to rise,coverage and the travelled distance. As mentioned above, specific sensors configured to sensethe road shape ahead ofthe vehicle can be used. The map data may be provided by anyknown means and may be for example a Global Positioning system (GPS) device orcorresponding device. The GPS can provide high density map data and may be arranged to communicate with one or several satellites via radio signals. 11According to an embodiment, the road comprising one or more road sections having adownhill slope (RSD) followed by a curved road section is a mountain road. By a mountainroad is meant a road going around the side of a mountain or a road going up and over a mountain.

Fig. 4 i||ustrates schematically an example ofthe type of a road comprising several roadsections having a downhill slope, an example of which is depicted as RSD. The illustrated roadis a mountain road. The downhill road section RSD is followed by a curved road section RSC.Only one of each type of road sections is provided with a reference sign for the sake of clarity.Fig. 4 shows a vehicle 1, which is travelling on the road section having a downhill slope, RSD.The vehicle 1 comprises an automatic or semi-automatic transmission. The control device ofthe vehicle is configured to control the speed of the vehicle. ln the context of the presentdisclosure, the control device is configured to determine a target set speed vtarget for thevehicle at a pre-determined location. The target speed may be pre-determined and the controlsystem may be configured to use this pre-determined speed when determining the speed. Thepre-determined location is before the curved road section RSC, and is located on, at the end ofor after the road section having a downhill slope, RSD. The location is depicted with X1 in Fig.4, and is located on the road section having the downhill slope before the vehicle enters thecurved road section RSC. The pre-determined location X1 can be selected based on map dataor the previously saved route data, and is selected such that vtarget Es reached or approached ata location vvhich provides safe ririving in the curved road section RSC. The surrounding traffic ispreferahly affected mänimally, and therefore the location X1 for the vtarget rhay be chosen asclose to the end of the road section having a downhill slope and the begtnning of the curved road section RSC as possible.

The target set speed vtarget for the vehicle is based at least on a radius of the curved roadsection RSC, a current speed ofthe vehicle and a weight ofthe vehicle. The target speed vtargetmay be calculated such that it is a maximum speed of the vehicle before entering the curvewithout a risk for the vehicle tipping over. As explained above, the radius may be obtainedfrom map data. The map data including the topographical data or parts thereof, from whichalso the slope data can be obtained, may be stored in the control device of the vehicle. Thisdata may be utilized when setting the target set speed vtarget. The target set speed may be set already when planning a route for the vehicle, whereby the speed ofthe vehicle at specific 12 road sections is pre-determined at the start of the route. Adjustment of the speed may benecessary during the trip depending e.g. on the traffic and weather conditions, and the controldevice may be configured to adjust the pre-determined set speed based on current trafficand/or weather data. The target speed vtarget may be determined by using any knowntechnology, and may be calculated based on a pre-determined maximum vehicle sidewaysacceleration for the vehicle, an optional slope of the curved road section and optionally acurrent speed limit. The speed limit needs to be considered in cases when it is lower than the speed associated with maximum allowable sideways acceleration of the vehicle.

To reach the target speed, the control device is configured to select a gear strategy that is ableto decelerate the vehicle speed towards the target set speed vtarget at the predeterminedlocation before the curved road section. The gear or gears are selected based at least on theweight of the vehicle, a current speed ofthe vehicle and a height difference, i.e. a slope,between a current position ofthe vehicle and the predetermined location before the curvedroad section. The vehicle may be operated such that the speed on the road sections having adownhill slope, RSD, is increased up to a speed limit ofthe road, e.g. by letting the vehiclecoast. By using the curve radius map data, the gear shifting strategy may determine the needto downshift during the travel along the RSD based not only on the slope of the downhill road section, but the curve radius of the upcoming RSC as well.

The control device is configured to control the transmission to engage the selected gear.Further, the control device may be configured to select the gear based on the kinetic energyprovided by the slope ofthe road and a braking distance. The braking distance is depicted asSbr in Fig. 4. The braking distance may be pre-determined. lt may be chosen such that a slowdeceleration of the vehicle from a downhill speed Vdh to the target speed vtarget is obtained,whereby no sudden deceleration is experienced and the safety and comfort for the driver andthe surrounding traffic is improved. ln this way the braking distance may be chosen to belonger than a required minimum distance. ln some cases, there is a need to decelerate thevehicle fast, whereby the braking distance is chosen and/or pre-determined to be a shortestpossible distance and/or time required to reach the target set speed vtarget. ln this way, theaverage speed of the vehicle may be increased compared to a scenario with a long braking distance, and it is possible to follow the faster traffic travelling on the road a longer distance 13than with the braking distance providing a smooth braking. When determining the braking distance, air resistance of the vehicle and a friction coefficient may also be taken into account.

The control device is configured to select the gear based on gear data provided by simulationof deceleration of the vehicle with different gear choices. The simulation may use analgorithm, which calculates suitable gears needed to decelerate the vehicle to reach the targetspeed at the end of the road section with downhill slope, RSD, and the braking power ortorque available at each gear given the current situation. The weight ofthe vehicle, brakingdistance, slope, friction coefficient of the road and air resistance may be variables consideredin the simulation. By simulating different options for gear choices, the option that provides thelowest engine speed and which is able to provide sufficient braking torque and/or power ischosen as the most suitable gear. ln this way economic driving may be achieved while the speed control may be performed in a comfortable and safe way. lf the slope ofthe road is large, e.g. the angle is 22° or more, it may be difficult to reach thetarget speed by only selecting a gear, or alternatively, a long braking distance is required.However, the selected gear controls the vehicle speed towards the target speed. By ”towards”is thus meant that the target speed is at least approached, or in some cases completelyreached. lf the braking torque provided by the gear is not sufficient to completely reach thetarget speed, additional braking torque may be provided to reach the target speed. ln thatcase, the control device is configured to caicuiate additional braking torque, besides thebraking torque provided by rneans of the gear selection, required te reach the target speedvtarget. The control device may be configured to activate an auxiiiary brake, wiiich can be aretarder and/or an electric brake, if additional braking torque is required. Alternatively oradditionally, the control device may be configured to adjust a compression release brakeand/or an exhaust gas brake to increase braking torque. The compression release brake andthe exhaust gas brake are activated during the gear selection, but can be adjusted to provide adetermined braking torque. After determination ofthe braking distance, the control devicemay be configured to engage or require the use of one or more auxiliary brakes. The use ofwheel friction brakes is generally avoided if possible, but may be engaged if needed, e.g. if thebraking torque ofthe available auxiliary brakes, or the adjusted compression release and/ orexhaust gas brakes is not sufficient to decelerate the vehicle to the target speed vtarget at the pre-determined location. 14The above-mentioned objectives are also attained by a method as defined in the appendedclaims. Thus, accordingly the present method is aimed for controlling that a vehicle reaches aset speed. The method is to be performed by the control device described above and isadapted to be performed when the vehicle is travelling on a road comprising one or more road sections having a downhill slope followed by a curved road section.

Reference is made to Fig. 5 showing the steps of the method. The method is performed by thecontrol device as described above, and reference is thus made also to the description ofthecontrol device, details ofwhich are fully applicable also for the description of the methodbelow. The first step of the method comprises determining (s101) a target set speed vtarget forthe vehicle at a pre-determined location before the curved road section, based at least on aradius ofthe curved road section and a weight ofthe vehicle. The pre-determined location canbe selected based on map data, and the determination is performed by the control device as defined above.

The next comprises selecting (s102) a gear to decelerate the vehicle speed towards the targetset speed vtarget at the predetermined location before the curved road section. The gear isselected based at least on the weight ofthe vehicle, a current speed ofthe vehicle and a height difference between a current position of the vehicle and the curved road section.The next step comprises controlling (s103) the transmission to engage the selected gear.

By performing the method in the described way, it is possible to reduce driver interventionswhen driving on downhill roads comprising several curved road sections and preceded by roadsections having a downhill slope. For example, in some embodiments, the driver does notneed to adjust the set speed or braking torque during driving, since the target speed and/orthe braking torque can be pre-determined and are thus given. The method can be performedsuch that the function of it is activated in the control device of the vehicle when the downhillroad begins. Thus, the driver may focus on steering of the vehicle, and no interference in the speed regulation by means of manual use of brakes is required. ln the method, in the step of determining (s101) the target speed vtarget, the speed can becalculated based on a pre-determined maximum vehicle sideways acceleration for the vehicle,an optional slope of the curved road section and optionally a current speed limit. The target speed is calculated such that there is no risk for the vehicle tipping over, whereby the maximum vehicle sideways acceleration for the vehicle is considered. This is important forexample in cases where the speed limit in the curve is higher than the speed of the maximumvehicle sideways acceleration of the vehicle allows. Also, the speed may be adapted such thatit is comfortable to the driver and/or passenger of the vehicle and follows the surrounding traffic as much as possible.

Further, in the method, the step of selecting (s102) a gear is further based on the kineticenergy provided by the slope ofthe road and a pre-determined braking distance. The largerthe slope is and the longer the braking distance and the weight ofthe vehicle are, the larger isthe kinetic energy provided. Therefore, the larger the kinetic energy is, the larger is thebraking torque needed. Alternatively or additionally, the braking distance is increased. Forexample in a situation where it is calculated that a maximum braking torque is required, the pre-determined braking distance can be adjusted so that the target speed vtarget is reached. ln some cases, the braking torque provided by the gear selection is not sufficient to reach thetarget speed, whereby the method may further comprise a step of caicuiating (slüii) anadditional braking torque required to reach the target speed vtarget, i.e. a braking torque inaddition to the braking torque provided by the gear seiection in step (slíiâ), The additionalbraking torque is provided by an auxiiiary brake which can be a retarder, and/or an electricbrake. Additionally or alternatively a compression release brake and/or an exhaust gas brakecan be adjusted to provide a determined braking torque. The adjustment can be based on thecalculation of the required additional braking torque. The control device may comprise acontroller configured to adjust the compression release brake and/or an exhaust gas brakeaccordingly. ln some cases when more forceful braking is required wheel friction brakes canbe additionally used to reach the target speed vtarget. The step of selecting s102 the gear isbased on gear data provided by simulation of deceleration ofthe vehicle with different gearchoices, wherein at least the weight of the vehicle, the braking distance and the slope ofthe road are variables considered in the simulation.

The method steps are performed by means ofthe control device 50 described above. Thecontrol device can be an independent control device or connected to the power unit 2, whichmay be for example an internal combustion engine, and thus being a control unit of the engineor the vehicle. Data required for the method is provided by connecting the control unit 50 by means of cables or link, which may be a wireless connection to the gearbox and other devices, 16such as GPS or other sensors and/or computers providing simulation data, as shown by dotted lines in Fig. 2.

Fig. 5 schematically illustrates a control device 50. The control device 50 may be or comprise acomputer. The control device is connected to the gearbox and other devices in the vehicle bymeans a link. The term ”link” refers herein to a communication link which may be a physicalconnection such as an optoelectronic communication line, or a non-physical connection suchas a wireless connection, e.g. a radio link or microwave link. The device 50 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 program, e.g. anoperating system, is stored for controlling the function of the device 50. The device 50 furthercomprises a bus controller, a serial communication port, I/O means, an A/D converter, a timeand 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.

According to the present disclosure, there is also provided a computer program P whichcomprises routines for performing the method for controlling that a vehicle reaches a setspeed, when the vehicle is travelling on a road comprising one or more road sections having adownhill slope followed by a curved road section. The computer program may be activated bythe driver or the operator of the vehicle, or the control system can be configured to start theprogram when map data provides information about a road comprising one or more roadsections having a downhill slope followed by a curved road section according to pre-determined conditions. The computer program P comprises routines for determining (s101) atarget set speed vtarget for the vehicle at a pre-determined location before the curved roadsection, based at least on a radius of the curved road section and a weight ofthe vehicle. Thecomputer program P comprises also routines for selecting (s102) a gear to decelerate thevehicle speed towards the target set speed vtarget at the predetermined location before thecurved road section, wherein the gear is selected based at least on the weight ofthe vehicle, acurrent speed ofthe vehicle and a height difference between a current position ofthe vehicleand the curved road section. Further, the computer program P comprises routines forcontrolling (s103) the transmission to engage the selected gear. Additionally, the computerprogram P may comprise routines for calcuåating (síüli), in addition to the brakirig torque provided by the gear selection in step (s102), an additional braking torque required to reach 17the target speed vtarget. The program P may be stored in an executable form or in a 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 meansthat the data processing unit 510 effects a certain part of the program stored in the memory 560 or a certain part of the program stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. Thenon-volatile memory 520 is intended for communication with the data processing unit 510 viaa data bus 512. The separate memory 560 is intended to communicate with the dataprocessing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the secondmemory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the control device 50 by means ofthe data processing unit 510 which runs the program stored in the memory 560 or theread/write memory 550. When the device 50 runs the program, methods herein described are executed.

The present disclosure also relates to a vehicle comprising the control device 50 describedabove. Alternatively, the vehicle comprises a computer-readable medium comprising aprogram code stored on the computer-readable medium for performing the method steps asdefined above, when said computer program is run on the control device 50 or a computer connected to the control device 50.

The foregoing description of the present invention is provided for illustrative and descriptivepurposes. lt is not intended to be exhaustive or to restrict the invention to the variantsdescribed. Many modifications and variations will obviously be apparent to one skilled in theart within the scope ofthe appended claims. The embodiments have been chosen anddescribed in order best to explain the principles of the invention and its practical applicationsand hence make it possible for a skilled person to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

18CLAll\/IS

1. A method performed by a control fievice (50) of a veliicie (1) for controlling that the vehiclereaches a set speed, wherein the method is adapted to be performed when the vehicle (1) istravelling on a road comprising one or more road sections having a downhill slope (RSD)followed by a curved road section (RSC), wherein the vehicle (1) comprises an automatic or semi-automatic transmission, the method comprising steps of: - determining (s101) a target set speed vtarget for the vehicle (1) at a pre-determined location (X1) before the curved road section (RSC), based at least ona radius ofthe curved road section and a weight of the vehicle (1), - selecting (s102) a gear to decelerate the vehicle speed towards the target setspeed vtarget at the predetermined location (X1), wherein the gear is selectedbased at least on the weight ofthe vehicle, a current speed of the vehicle and aheight difference between a current position of the vehicle and the curved roadsection (RSC), and - controlling (s103) the transmission to engage the selected gear.

2. The method according to claim 1, wherein determining (s101) the target speed vtarget iscalculated based on a pre-determined maximum vehicle sideways acceleration for the vehicle (1), an optional slope of the curved road section (RSC) and optionally a current speed limit.

3. The method according to claim 1 or 2, wherein selecting (s102) a gear is further based onthe kinetic energy provided by the slope ofthe road section having a downhill slope (RSD) and a pre-determined braking distance (Sbr).

4. The method according to claim 3, wherein in the pre-determined braking distance (Sbr) is a shortest possible distance and/or time required to reach the target set speed vtarget.

5. The method according to any one ofthe preceding claims, wherein the method furthercomprises a step of calcdlating (s101)) an additional braking torque required to reach thetarget speed vtarget, in addition to the braking torque provided by the gear selection in step (sTíÜZ).

6. 195. The method according to claim 5, wherein the additional braking torque is provided by anauxiiiary brake being a retarder, and/or an electric brake, and/or by adjusting a compression release brake and/or an exhaust gas brake.

7. The method according to any one ofthe preceding claims, wherein the pre-determined location is selected based on map data.

8. The method according to any one ofthe preceding claims, wherein the step of selecting(s102) the gear is based on gear data provided by simulation of deceleration of the vehicle (1)with different gear choices, wherein at least the weight ofthe vehicle, the braking distanceand the slope of the road section having a downhill slope (RSD) are variables considered in the simulation.

9. The method according to any ofthe preceding claims, wherein wheel friction brakes are additionally used to reach the target speed vtarget.

10. A computer program (P), wherein said computer program comprises program code forcausing a control device (50) or a computer connected to the control device (50) to perform the steps according to any of the claims 1-9.

11. A computer-readable medium comprising a program code stored on the computer-readable medium for performing the method steps according to any of claims 1-9, when saidcomputer program is run on a control device (50) or a computer connected to the control device.

12. A control device (50) configured to control that the vehicle reaches a set speed, the vehiclebeing configured to travel on a road comprising one or more road sections having a downhillslope (RSD) followed by a curved road section (RSC), wherein the vehicle comprises anautomatic or semi-automatic transmission, the control unit being configured to:- determine a target set speed vtarget for the vehicle at a pre-determinedlocation (X1) before the curved road section (RSC), based at least on a radius of the curved road section (RSC) and a weight of the vehicle (1), -- select a gear to decelerate the vehicle (1) speed towards the target set speedvtarget at the predetermined location (X1) before the curved road section (RSC),wherein the gear is selected based at least on the weight ofthe vehicle, acurrent speed ofthe vehicle and a height difference between a current positionof the vehicle and the curved road section, and - control the transmission to engage the selected gear.

13. The control device (50) of claim 12, wherein the target speed vtarget is calculated based on apre-determined maximum vehicle sideways acceleration for the vehicle, an optional slope of the curved road section and optionally a current speed limit.

14. The control device (50) according to claim 12 or 13 configured to select the gear based onthe kinetic energy provided by the slope ofthe road section having a downhill slope (RSD) and a pre-determined braking distance (Sbr).

15. The control device (50) according to claim 14, wherein the pre-determined brakingdistance (Sbr) is a shortest possible distance and/or time required to reach the target set speed Vtarget-

16. The control device (50) according to any one ofthe preceding claims 12-15, wherein thecontrol device is configured to calculate additional braking torque required to reach the target

17. Vtarggt. i? The control device (50) according to claim 16, wherein the control device is configured toactivate an auxiiiary brake, *which Es a retarder and/or an electric brake, if additional brakingtorque is required and/or to adjust a compression release brake and/or an exhaust gas brake to increase braking torque.

18. The control device (50) according to any one ofthe preceding claims 12-17, wherein the pre-determined location (X1) is selected based on map data.

19. 2119. The control device according to any one ofthe preceding claims 12-18, wherein thecontrol device is configured to select the gear based on gear data provided by simulation ofdeceleration of the vehicle with different gear choices, wherein the weight of the vehicle, the braking distance and the slope ofthe road are variables considered in the simulation.

20. The control device according to any one ofthe preceding claims 12-19, wherein the control device is configured to engage or require use of wheel friction brakes to reach the target speed vtarget

21. A vehicle (1), comprising the control device of any of claims 12-20 or the computer- readable medium of claim 11.