Method and control arrangement for controlling a speed of a vehicle

Abstract

The present invention relates to a method performed by a control arrangement (120) for controlling a speed of a vehicle (100), the vehicle (100) comprising:a power source(101) for providing a propelling torque to at least one drive wheel (111-114) of the vehicle (100);at least one brake system for applying a brake torque to at least one wheel of the vehicle;driver manoeuvrable accelerator means (301) for requesting a propelling torque from the power source (101), the driver manoeuvrable accelerator means (301) being manoeuvrable in a movement region (A-B) between a first end position (A) and a second end position (B), the method comprising, when the position of the driver manoeuvrable accelerator means (301) is maintained within a first subregion of the movement region (A-B) for at least a first period of time:controlling torque applied to the at least one drive wheel of the vehicle such that the speed of the vehicle is maintained at or below a first vehicle speed. The invention also relates to a control arrangement and a vehicle.

Description

AThe invention relates to a method and a control arrangement for controlling a speed of a vehicle. The invention also relates to a computer program, a computer-readable medium and a vehicle comprising a control arrangement.BackgroundThe following background description does not necessarily constitute prior art.With regard to vehicles in general, and at least to some extent heavy / commercial vehicles, such as trucks, buses and the like in particular, there are various important aspects that contribute to the general perception of the overall vehicle performance.For example, fuel / energy efficiency and reduction of exhaust emissions are important aspects, where such aspects often emanate from governmental concerns in pollution and air quality, e.g. in urban areas, which has also led to the adoption of various emission standards and rules in many jurisdictions. Also, alternatives to sole use of conventional combustion engine technology have been developed, such as, e.g., hybrid electric vehicles or battery electric vehicles.Furthermore, with regard to commercial vehicles, such as, e.g., trucks and city buses, vehicles of this kind may be used for a large percentage of the day, for instance in shifts or for work related purposes, and the vehicles may also be used e.g. by a driver for relatively long consecutive periods of time. Therefore, in addition to addressing, e.g., energy consumption, efforts are also made to make the driving of the vehicle comfortable to the driver. Such driver comfort may comprise, e.g., economical aspects, but may also comprise vehicle behaviour or safety when being driven. One example of vehicle functionality that may provide driver comfort is the use of cruise controls functions.It is an object of the invention to provide a method and a control arrangement for mitigating or solving drawbacks of conventional solutions. In particular, an object of the invention is to provide a method performed by a control arrangement for controlling a speed of a vehicle in a situation where no cruise control function in general is activated by a driver.According to a first aspect of the invention, the aforementioned and further objects are achieved through a method performed by a control arrangement for controlling a speed of a vehicle, the vehicle comprising:a power source for providing a propelling torque to at least one drive wheel of the vehicle;at least one brake system for applying a brake torque to at least one wheel of the vehicle;driver manoeuvrable accelerator means for requesting a propelling torque from the power source, the driver manoeuvrable accelerator means being manoeuvrable in a movement region between a first end position and a second end position, the method comprising, when the position of the driver manoeuvrable accelerator means is maintained within a first subregion of the movement region for at least a first period of time:controlling torque applied to the at least one drive wheel of the vehicle such that the speed of the vehicle is maintained at or below a first vehicle speed.As was mentioned above, drivers of, e.g., heavy vehicles may spend a lot of time in the vehicle, for which reason driver comfort is an important factor. For example, efforts may be made to improve the driver environment, e.g., in terms of ergonomics and noise attenuation. The vehicle may also comprise cruise control functionality that allows a driver to activate a cruise control, e.g., at a preferred speed of the vehicle, where such cruise control functionality may also, e.g., adapt the speed of the vehicle to the speed of a vehicle in front. However, such cruise control functionality is in general activated when driving on highways, or other roads where traffic may be sparse and where it may be expected to maintain the same speed of the vehicle for longer periods of time, since frequent activation and deactivation of such systems may be perceived as cumbersome in other situations.According to the invention, it is provided a solution that may activate a speed control functionality, which, as explained below, may also be a cruise control functionality, in a vehicle comprising a power source for providing a propelling torque and at least one brake system for applying a brake torque, in situations where no such request is actively performed by the driver but where such activation may still increase driver comfort. The vehicle comprises driver manoeuvrable accelerator means, such as an accelerator, for requesting a propelling torque from the power source, where the driver manoeuvrable accelerator means are manoeuvrable in a movement region between a first end position and a second end position.According to the invention, it is established, e.g. by determining, whether the position of the driver manoeuvrable accelerator means is maintained within a first subregion of the movement region for at least a first period of time. The first period of time may be any suitable period of time, such as, for example, a period of time in the interval 1-10 seconds, or in the interval 2-8 seconds, or in the interval 3-7 seconds. The period of time may also be in any other suitable time interval. According to aspects of the invention, the first period of time may be configurable by the driver, e.g., within predetermined maximum and minimum periods of time. According to aspects of the invention, the first period of time may, alternatively or in addition, be based, e.g., on the current speed of the vehicle, where longer or shorter periods may be used for comparatively lower speeds in relation to comparatively higher speeds of the vehicle.When the driver manoeuvrable accelerator means has been maintained within the first subregion of the movement region for the first period of time, the torque applied to the at least one drive wheel of the vehicle is controlled such that the speed of the vehicle is maintained at or below a first vehicle speed, i.e., does not exceed the first vehicle speed. In this way, a function may be activated that ensures that the vehicle speed will not exceed the first speed, where the first speed may be determined according to the below. Thereby, it can be ensured that the vehicle will not exceed the first speed in situations when driving conditions are such that the driver aims to maintain a particular speed, but where still the speed may vary irrespective of this as is oftentimes the case during regular driving. For example, the invention may prevent increase in speed through slightly increased pedal depression, or decreased driving resistance. Consequently, it may be ensured, e.g., that the vehicle speed will not exceed a currently prevailing speed limit even if, e.g., the driving resistance is reduced. Furthermore, a reduction in speed through reduced pedal level is not prevented.According to the invention, the control system of the vehicle, e.g., by means of a control arrangement, may take over control of the actual torque that is applied to the wheels of the vehicle in order to ensure that the speed of the vehicle is maintained at or below, and hence does not exceed, the first speed. In this way the driver may focus less on maintaining a particular speed and, e.g., focus more on the overall traffic situation.According to aspects of the invention, the driver manoeuvrable means is an accelerator pedal, where torque from the power source is requested by depressing the accelerator pedal. Flence, the invention is applicable to conventional driving using an accelerator pedal.According to aspects of the invention, the first vehicle speed is determined to a speed being different from the current speed of the vehicle. Hence, the control of the vehicle speed according to the invention may activate at the currently prevailing speed, but the speed of the vehicle may be controlled such that it does not exceed a speed, lower or higher, that differs from the currently prevailing speed, and, e.g., that it is likely that the driver strives to maintain.According to aspects of the invention, the method comprises to determine the first vehicle speed to a closest 10 km / h, or a closest 5 km / h in relation to the current speed of the vehicle, and / or to a currently prevailing speed limit, and maintaining the speed of the vehicle at or below the first vehicle speed by controlling torque applied to the at least one wheel of the vehicle. According to aspects of the invention, the speed is controlled to a closest lower or higher speed that fulfils the above requirements.According to aspects of the invention, the controlling of the speed of the vehicle at or below the first vehicle speed comprises to reduce the torque applied to the at least one drive wheel by the power source in relation to a request for torque from the power source that corresponds to the present position of the driver manoeuvrable accelerator means. In this way, the applied torque can be adapted to the prevailing conditions, and in particular to situations when driving resistance reduces. According to aspects of the invention, the torque applied to the at least one drive wheel by the power source may be successively reduced when the driving resistance successively decreases, so as to maintain the speed of the vehicle speed at or below the first vehicle speed. Hence, the applied torque can be successively reduced under the control of the control arrangement even to a situation corresponding to a fully released accelerator means while still the driver controllable accelerator means are maintained within the subregion.According to aspects of the invention, the torque being applied by the power source when controlling vehicle speed according to aspects of the invention may also be higher than the torque that the current position of the driver manoeuvrable accelerator means correspond to, and hence strive to maintain speed also when the driving resistance increases. According to aspects of the invention, the speed of the vehicle may instead be allowed to reduce in such situations.According to aspects of the invention, the torque applied to the at least one wheel of the vehicle is controlled such that the speed of the vehicle is maintained at or below the first vehicle speed in situations when other driver activatable vehicle cruise control systems are not active. Hence, it may be provided a solution that automatically activates a speed control function in situations when driver activatable cruise control functions otherwise are not activated, and in particular when a driver has not requested activation of a cruise control.According to aspects of the invention, torque applied to the at least one wheel of the vehicle may be controlled such that vehicle speed is maintained at or below the first vehicle speed for as long as the driver manoeuvrable accelerator means is maintained within the subregion of the movement region following the first period of time. Hence, the control of the speed of the vehicle according to the invention may be continued for as long as this condition is fulfilled, and according to aspects of the invention, the maintaining of the speed of the vehicle at or below the first speed is ended when the driver manoeuvrable accelerator means is manoeuvred to a position outside the first subregion. This may hence provide a straightforward method for determining when to end the control of the speed of the vehicle according to the invention. According to aspects of the invention, the first speed may be kept as maximum speed limit for a predetermined period of time following the ending of the maintaining of the speed of the vehicle at or below the first speed. Thereby, the speed is allowed to decrease at will of the driver, but at the same time it may be prevented that a release of the accelerator pedal ending the control according to the invention causes an undesired increase in vehicle speed, e.g., due to a reduced driving resistance.According to aspects of the invention, the maintaining of the speed of the vehicle at or below the first speed is ended when the driver manoeuvrable accelerator means is depressed by a first extent, or released by a first extent within a predetermined period of time. Hence, the control of the speed of the vehicle may be ended also when the driver makes a sudden change of the position of the accelerator means, which may be seen as an indication from the driver that the vehicle no longer is to maintain a current speed.According to aspects of the invention, the maintaining of the speed of the vehicle at or below the first speed is ended when the driver manoeuvrable accelerator means is depressed by a first extent, but not when released by a first extent, hence requiring, e.g., the application of a brake pedal to end the functionality when releasing the accelerator pedal.According to aspects of the invention, the first subregion of the movement region of the driver manoeuvrable accelerator means is determined in dependence of the current position of the driver manoeuvrable accelerator means when the first period of time commences. Different prevailing conditions may cause that different positions of the driver controllable accelerator means may be required to maintain the same speed in dependence of, e.g., current load of the vehicle, and the current driving resistance. Such differences may be accounted for by determining the subregion in dependence, of, e.g., a depression of an accelerator pedal that is required to maintain the speed for which the determination commences.According to aspects of the invention, the method further comprises to only apply torque to the at least one wheel of the vehicle by means of the power source when controlling the torque to maintain the speed of the vehicle at the first vehicle speed. Hence, according to aspects of the invention, the speed of the vehicle is only controlled utilizing torque applied by the power source. According to an example where the power source is an internal combustion engine, there is consequently no other brake torque than the possibly inherent brake torque of the power source. However, according to aspects of the invention, a brake torque of the at least one brake system may also be applied in order to maintain the speed of the vehicle at the first speed. This may allow control according to the invention, e.g., in case the inclination of the road is such that the vehicle otherwise would accelerate. In case the power source comprises, e.g., an exhaust brake or compression brake, brake torque may be applied using such braking means. Brake torque may also be applied by the power source in case the power source is an electrical machine.According to aspects of the invention, the method comprises, when the vehicle enters a downhill stretch of road, to maintain the vehicle speed at or below the first vehicle speed when the driver manoeuvrable accelerator means is positioned in the subregion of the movement region of the driver manoeuvrable accelerator means, wherein the vehicle speed is maintained at least partly through application of a brake torque by means of the at least one brake system. Hence, the invention may be utilized also when going downhill, where the vehicle speed may be maintained at or below the first speed for as long as the driver manoeuvrable accelerator means is positioned in the subregion of the movement region of the driver manoeuvrable accelerator means. In case the driver releases the driver manoeuvrable accelerator means in such a situation, the first vehicle speed limit may be maintained, since a release of the accelerator means in general will indicate a desire to maintain or reduce speed, and not increase speed.According to aspects of the invention, the torque applied to the at least one drive wheel of the vehicle is controlled such that the speed of the vehicle is maintained at the first vehicle speed. In this way, in principle, a cruise control function is provided, that is automatically activated when a particular criterion is fulfilled. Thereby, the speed of the vehicle may be controlled to be maintained at the first speed, e.g., in situations when driving conditions are such that the driver aims to maintain a particular speed by maintaining the driver manoeuvrable accelerator means within the first movement region, but where still the speed may vary as is oftentimes the case during regular driving.Hence, it may be provided a solution that automatically activates a not only a speed control function but also a cruise control in situations when driver activatable cruise control functions otherwise are not activated, and in particular when a driver has not requested activation of a cruise control. The activation may be indicated to the driver through, e.g., visual or sound indication, or through vibration.According to a further aspect, the invention relates to a control arrangement for controlling the speed of a vehicle when the accelerator means are maintained within a subregion of an overall movement region of the accelerator means. It will be appreciated that all that has been described for the method aspects of the invention is applicable also to control arrangement aspects of the invention. Thus, all the aspects described for methods according to the invention may be performed by the control arrangement, which may also be a control device, i.e., a device. The control arrangement and its embodiments have advantages corresponding to the advantages discussed above with regard to the various aspects of methods according to the invention.According to another aspect of the invention, aforementioned and further objectives are achieved through a vehicle comprising a control arrangement according to aspects of the invention.According to a further aspect, the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to aspects of the invention.According to an aspect, the invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to aspects of the invention.Further advantageous aspects of the method, the control arrangement, the vehicle, the computer program, and the computer-readable medium according to the invention will emerge from the detailed description.Brief description of the drawingsAspects of the invention will be illustrated in more detail below, along with the enclosed drawings, where similar references are used for similar parts, and where:Figure 1 shows a schematic view illustrating an exemplary vehicle in which aspects of the invention may be implemented;Figure 2A shows a flow chart illustrating a method according to aspects of the invention;Figure 2B shows a flow chart illustrating methods according to further aspects of the invention;Figure 3 illustrates an exemplary accelerator pedal;Figure 4 illustrates a method of controlling the speed of a vehicle according to aspects of the invention;Figure 5 illustrates a method of controlling the speed of a vehicle when travelling downhill according to other aspects of the invention;Figure 6 shows a control arrangement, in which a method according to any one of the aspects described herein may be implemented.Detailed descriptionFigure 1 schematically shows an exemplary heavy vehicle 100, such a truck or a bus, which will be used to explain aspects according to the invention. The invention, however, is not limited for use in vehicles as the one illustrated in Figure 1, but may also be used in essentially any vehicle fulfilling the general requirements set out in the claims.The vehicle 100, as schematically illustrated in Figure 1, comprises a pair of drive (i.e. driven) wheels 111, 112 and at least one other pair of non-driven wheels 113, 114. The vehicle 100 furthermore comprises a drivetrain configured to transfer torque between at least one power source 101, and the drive wheels 111, 112. The at least one power source 101 may comprise an internal combustion engine, at least one electrical machine, or any combination thereof. According to the present example, the power source 101 is an internal combustion engine.The internal combustion engine 101 is, in a manner known per se, connected to a gearbox 103 via an output shaft 102 of the engine 101, and a clutch 106. The torque provided by the internal combustion engine 101 is provided to an input shaft 109 of the gearbox 103. A propeller shaft 107, connected to an output shaft of the gearbox 103, propels the drive wheels 111, 112 via a central gear 108, such as, e.g., a differential gear, and drive shafts 104, 105.The vehicle 100 also comprises a, e.g., hydraulic, service brake system 150 constituting a friction brake system and comprising brake discs, or drums, 151, 152, 153, 154, with associated brake linings, or brake shoes, 155, 156, 157, 158 acting on the discs, or drums, to provide a brake torque through friction in a manner known per se, e.g., through influence of a hydraulic pressure, when the vehicle 100 is to be subjected to a brake torque.The hydraulic pressure, or brake pressure, is controlled by a control arrangement 120 forming part of vehicle control system, and according to the present non-limiting example through an electronic brake system (EBS) control unit 121. The EBS 121 may be configured to control the brake pressure of the service brake system based, inter alia, on received requests for brake torque. Such requests may, for example, constitute driver requests, where the driver may request a brake torque through driver maneuverable means such as a brake pedal. The EBS 121 may also receive brake requests through other means, such as, for example, a cruise control system of the vehicle.The vehicle 100 furthermore comprises at least one auxiliary brake system, where such auxiliary brake systems may comprise, e.g., an exhaust brake system and / or a retarder brake system 160 that may apply brake torque to the gearbox output shaft and / or propeller shaft 107. Retarder brake systems are common and may, e.g., be of an electric or hydraulic type. The vehicle 100 may also be configured to provide auxiliary brake torque through an increase of engine brake torque by changing gear in the gearbox 103 to increase the speed of rotation of the internal combustion engine 101 to thereby increase internal losses of the internal combustion engine 101.The drivetrain, including the internal combustion engine 101, clutch 106 and gearbox 103, as well as other components of the powertrain, may also be controlled by a control unit 123 in the vehicle control system via a control arrangement 120 comprising control units 121, 122, 123. The control arrangement 120 may, as is known per se, be distributed over a plurality of control units configured to control different parts of the vehicle 100, and a vehicle may hence comprise a substantial amount of control units and also control arrangements. The control arrangement 120 and / or any other suitable control arrangement, may further be configured to control any other units / devices / entities of the vehicle 100. The illustration of Figure 1 is hence only exemplary, and various other configurations exist. The control arrangement 120 will be described more in detail with reference to Figure 5 below.The vehicle 100 may also comprise a positioning system / unit 140. The positioning unit 140 may be based on a satellite navigation system such as the Navigation Signal Timing and Ranging (Navstar), Global Positioning System (GPS), Differential GPS (DGPS), Galileo, GLONASS, or the like. Thus, the positioning unit 140 may comprise a GPS receiver. The positioning system 140 may be utilized to determine prevailing and upcoming speed limits along the travel path of the vehicle. The vehicle may also comprise, e.g., traffic sign identification means to identify, e.g., a currently prevailing speed limit. Figure 1 also illustrates an accelerator pedal 301.It should also be understood that the powertrain of the vehicle 100 may be of various other different designs than the one illustrated in Figure 1 without departing from the scope of the invention, and in particular comprise an electrical machine and associated components such as a battery etc. in addition or as an alternative to the internal combustion engine 101.As has been mentioned above, aspects of the invention provides a method for controlling the speed of a vehicle in particular situations. As was also mentioned, heavy vehicles, such as the vehicle 100 according to the illustrated example, in general comprises one or more cruise control functions, where oftentimes such cruise control functions are used in situations where traffic is sparse, such as on highways and other roads where traffic conditions are such that a constant speed may be maintained. However, there exists various situations in which cruise control functions in general are not used. For example, this applies to roads where there may be traffic, or where the prevailing speed limits may regularly change so that a driver might find it inconvenient to regularly activate and deactivate a cruise control function.According to the invention, it is provided a method for controlling the speed of the vehicle that may automatically activate and deactivate a speed control function in dependence of the driver manoeuvring of driver controllable accelerator means such as an accelerator pedal. Aspects of the invention will be described with reference to a method 200, schematically illustrated in Figure 2A. The method 200 may be carried out by any one or more suitable control arrangements of the vehicle, such as the control arrangement 120.The method comprises, when the position of the driver manoeuvrable accelerator means is maintained within a first subregion of the movement region for at least a first period of time, controlling torque applied to the at least one drive wheel of the vehicle such that the speed of the vehicle is maintained at a first vehicle speed, step 210.In this way, the speed of the vehicle may be controlled to be maintained at or below a particular speed in a situation when the driver has maintained the accelerator pedal within a subregion of the overall movement region of the accelerator pedal, where this is then used as an indicator that the driver has the aim of keeping the speed of the vehicle essentially constant. The control system of the vehicle may then take over actual torque control, such that the vehicle speed is maintained at or below the first speed, with the result that the driver may concentrate less on maintaining an exact speed and more on surrounding traffic, thereby alleviating the driving efforts and increasing driver comfort. In particular, the invention provides for a control of the torque applied to the at least one wheel of the vehicle in situations when vehicle cruise control systems in general are not active, which may be the case, e.g., when vehicle speed is frequently changing. According to the invention, the torque may be controlled following any such change in vehicle speed without requiring any driver effort, and with the only requirement that the accelerator pedal is maintained within a particular subregion of the overall movement region for a predetermined period of time. The speed of the vehicle may be controlled such that it is ensured that the speed does not exceed the first vehicle speed. This may, for example, be utilized to ensure that even if the vehicle speed varies during the control according to the invention, the speed may be maintained below, e.g., a prevailing speed limit so that the driver need not focus on such aspects of the driving. The control of the speed of the vehicle according to the invention is ended in step 220 when the accelerator is manoeuvred to a position outside the subregion of the overall movement region of the accelerator pedal.Aspects of the invention will be explained more in the detailed with reference to Figure 2B and Figures 3-4.Figure 2B illustrates a further exemplary method 200 according to aspects of the invention. The method 200 starts in step 205, where it is determined whether the accelerator pedal is positioned within a predetermined subregion of the movement region of the accelerator pedal.Figure 3 illustrates an exemplary operator manoeuvrable accelerator means for requesting torque in the form of an accelerator pedal 301. The figure illustrates the actual accelerator pedal 301, which is movable in a movement region between a fully released state, indicated by dashed line “A”, and a fully depressed state, indicated by dashed line “B”.The figure also illustrates that the accelerator pedal 301 currently is depressed to an extent represented by depression angle “a”, where the current state of the accelerator pedal 301, e.g., may be determined using an angle sensor such as angle sensor 302. It is to be understood that according to the present example, the accelerator pedal 301 is not physically linked, e.g., to means for requesting torque from the internal combustion engine 101. Instead, signals from the angle sensor 302 indicating the current accelerator pedal position is used by the vehicle control system, e.g. by a suitable control unit of the control arrangement 120 illustrated in Figure 1, to request torque from the internal combustion engine 101, and as will be described further below, in a variable dependency of the current position of the accelerator pedal 301.Figure 3 also illustrates dotted lines 303, 304 which exemplifies border positions of a subregion β, which may exemplify a subregion of the movement region of the accelerator pedal in which the speed of the vehicle is controlled according to aspects of the invention when the accelerator pedal is positioned therein. That is, when the accelerator pedal, as in the present state of Figure 3, is depressed to a position within the subregion β of the movement region A-B, torque applied to the drive wheels will, given a time constraint, be determined according to the invention.It is to be noted in this regard, that the subregion β of the movement region A-B of the accelerator pedal in general need not be predetermined, but may instead be determined in dependence of the current position of the driver manoeuvrable accelerator means when the first period of time commences. Alternatively, the subregion β of the movement region A-B of the accelerator pedal may be determined in dependence of the current speed of the vehicle. The subregion β may also be configured to depend on, e.g., the current road conditions such as road inclination, and the weight of the vehicle, since, e.g., the weight of a vehicle may differ to a large extent from one time to another, in particular when it comes to heavy vehicles.The invention may be utilized for various different prevailing speeds of the vehicle, and the accelerator position may be depressed to different extents in dependence of the particular speed, and also independence of other parameters as described, that the driver intends to maintain. The subregion β may therefore be determined in dependence of such variations, and, e.g., be determined around a currently prevailing position of the accelerator pedal when the timer commences, where, e.g., the first period of time may be configured to start when the vehicle acceleration is below a predetermined acceleration, or when the vehicle speed reaches a speed that lies within a predetermined difference from a currently prevailing speed limit, which may be determined, e.g., through the use of a navigation system and / or means for identifying traffic signs as is known per se. The subregion β may be determined, e.g., as a predetermined portion of the total movement region A-B, and hence a predetermined angular interval of the overall angular interval γ (see Figure 3) that the movement region A-B encompasses.According to the present invention, the actual torque being applied to the drive wheels of the vehicle may hence depend not only on the accelerator pedal position, but also the control of the speed of the vehicle being performed by the vehicle control system. A particular depression of the accelerator pedal, such as the situation illustrated in Figure 3, may therefore result in different levels of applied torque, e.g., in dependence of the current driving conditions.In step 210 it is determined whether the accelerator pedal 301 has been maintained within the subregion β of the movement region A-B of the accelerator pedal 301 for a first period of time. The method returns to step 205 for as long as this is not the case to again determine whether the accelerator pedal 301 is maintained within the subregion β whereas, when it is determined that this is the case, the method continues to step 215. In step 215 it is determined a first vehicle speed to be maintained, or not exceed, by the vehicle 100, where this first speed may be determined in dependence of the current speed of the vehicle 100.According to aspects of the invention, the first speed is determined to the speed that the vehicle is presently maintaining when the first period of time has lapsed. However, the first speed may also be determined according to various other criteria, and may, e.g., be determined to a closest 10 km / h, i.e. the closest even 10 km / h in relation to the current vehicle speed, or a closest 5 km / h in relation to the current speed of the vehicle, where the result may be a speed being both higher and lower than the current speed of the vehicle. That is, the vehicle control system may be configured to decelerate or accelerate the vehicle to such a speed in case the vehicle speed slightly exceeds, or is below, such a determined speed.The first speed may also be determined as a currently prevailing speed limit, which, as was mentioned, can be deduced, e.g., from a satellite navigation system comprising speed limit data, and / or traffic sign identification. The first speed of the vehicle may hence be determined to a speed being different from the current speed of the vehicle 100.The method then continues to step 216, where, according to aspects of the invention the speed of the vehicle is controlled such that it does not exceed the first speed. That is, the speed of the vehicle may be allowed to vary, e.g., due to variations in the driving resistance, but where the speed is not allowed to exceed the first speed. According to aspects of the invention, the speed of the vehicle is maintained at the first vehicle speed, hence acting as a cruise control function. The speed of the vehicle is controlled by controlling torque applied to the at least one drive wheel of the vehicle, where this control may comprise to control the torque applied by the internal combustion engine 101 as was mentioned.In particular, the controlling of the speed of the vehicle 100 to the first vehicle speed may comprise to reduce the torque applied to the at least one drive wheel by the internal combustion engine in relation to the actual request for torque from the internal combustion engine that the present position of the accelerator pedal otherwise would result in. Thereby, e.g., the torque applied by the internal combustion engine can be successively reduced in case the driving resistance successively decreases, so that the speed of the vehicle may be maintained at the first vehicle speed as much as possible without requiring any effort from the driver in situations where driving resistance reduces. Conversely, the control according to the invention may be configured to more and more increase torque applied to the vehicle drive wheels in case, e.g., the driving resistance is increasing. According to aspects of the invention, the applied torque is not increased to a level higher than what would otherwise be requested at the current position of the accelerator pedal when controlling the speed of the vehicle, but only reduced in case needed.An exemplary situation according to the invention is illustrated in Figure 4. Figure 4 illustrates four graphs, where the uppermost graph schematically illustrates the inclination on the road upon which the vehicle 100 is traveling. According to the present example, the vehicle travels on a stretch of road where the road inclination is slightly varying over time. The second graph from above illustrates the torque applied by the internal combustion engine 101. The third graph from above illustrates the accelerator pedal position, and the lowermost graph illustrates the vehicle speed over time.According to the present example, the internal combustion engine 101 is controlled according to the accelerator pedal position for as long as the accelerator pedal position has not been maintained in the subregion of the movement region A-B of the accelerator pedal for the first period of time. At time t0 the vehicle 100 is set in motion by the driver depressing the accelerator pedal 301, and the speed of the vehicle 100 increases during the time interval between time t0 and t1 At time t11 the accelerator pedal 301 is manoeuvred to a position falling within a subregion β of the movement region, where the subregion β may have been determined according to the above. The speed of the vehicle is also only slowly changing.At time t2, the accelerator pedal has been maintained within the subregion β for a predetermined period of time, which may be any suitable period of time, such as, for example, a time in the interval 1-10 seconds or in any other suitable time interval. Therefore, at time t2, the control system of the vehicle 100 assumes control of the internal combustion engine 101, and controls torque applied to the drive wheels of the vehicle based on the current vehicle speed, and in particular in order to maintain the speed of the vehicle below a particular speed, which may be determined according to the above. According to the present example, the speed that is not to be exceeded is a speed Vseti that is slightly higher than the current speed of the vehicle 100 when the control commences. It is to be noted in this regard that although the driver requests a torque from the internal combustion engine using the accelerator pedal, the actual torque applied by the vehicle control system may, and in general will, differ from the requested torque in order to maintain the speed at the speed vset1. The torque may be continuously controlled to ensure that the vehicle maintains a speed that does not exceed the desired speed, and this is also performed between time t2 and time t3, where the speed of the vehicle slightly varies but does not exceed the set speed. The amount to which the torque from the internal combustion engine 101 is increased or decreased during the control will depend on the prevailing conditions, e.g., in terms of road inclination, and vehicle speed, and not on the currently prevailing position of the accelerator pedal for as long as this is within the subregion β. In step 217 it is continuously determined whether the accelerator pedal 301 is within the subregion β, and the control of the speed of the vehicle is maintained for as long as this is the case by returning to step 216. As was mentioned, according to aspects of the invention the torque is not controlled to a level exceeding the request for torque that corresponds to the current position of the accelerator pedal.Slightly before time t3 the driver performs a manoeuvre with the accelerator pedal 301 that causes the accelerator pedal position to leave the subregion β at time t3. According to the present example, the driver depresses the accelerator pedal further to accelerate the vehicle, but the situation could equally well be that the driver instead releases the accelerator pedal 301, and thereby would exit the subregion β by releasing the pedal to a position outside the subregion β. The control of the torque applied by the internal combustion engine 101 according to the invention is then also ended at time t3, step 220, and the torque applied by the internal combustion engine 101 is instead controlled according to the pedal position. The maintaining of the speed of the vehicle 100 at the first speed may hence be ended when the accelerator pedal 301 is manoeuvred to a position outside the subregion β, whereas the vehicle speed is maintained at the first vehicle speed vset1 for as long as the accelerator pedal is maintained within the subregion β following the first period of time.It is in general not desired that the vehicle suddenly accelerates when the accelerator pedal is released. According to aspects of the invention, therefore, it is ensured that the torque requested from the internal combustion engine 101 when ending the control according to the invention does not exceed the torque being applied when maintaining the speed of the vehicle. For example, when commencing the control of the speed of the vehicle, the vehicle may be driven in a slight uphill section of road with a relatively high torque demand as result. The driving resistance may then reduce as the control is ongoing, with the result that the required torque for maintaining the speed of the vehicle may be substantially reduced. If in such a situation the driver would release the accelerator pedal to a position where the control according to the invention is ended, and control of torque in accordance with the position of the accelerator pedal be resumed, this may result in a sudden acceleration in a situation where at least no increase in speed is expected. According to aspects of the invention it may therefore be ascertained that when ending the control of the speed of the vehicle, the torque being requested by the internal combustion engine does not exceed the torque being currently requested when ending the control of the speed of the vehicle. In this way sudden unexpected acceleration can be avoided. This additional control may be maintained, e.g., until the driver has fully released the accelerator pedal, or driving conditions and / or accelerator pedal position changes to a situation where the accelerator position no longer corresponds to a higher request for torque than currently is requested.In addition to ending the control of the torque applied by the internal combustion engine 101 according to the invention, the control may also be ended, e.g., in case the accelerator pedal 301 is very rapidly changing position, where the derivative of the speed of change of the position of the accelerator pedal may be used to determine whether to end the control according to the invention.When the control according to the invention is ended in step 220, the method of Figure 2B may return to step 205 to again determine whether the accelerator pedal 301 is within a subregion of the movement region A-B. With further reference to Figure 4, the vehicle is accelerated between times t3 and t4, and at time it is again determined whether the accelerator pedal is within a predetermined subregion of the movement region, in this case a subregion β2 which differs from the subregion β, e.g., due to the vehicle maintaining a higher speed. At time t5 the accelerator pedal 301 has been maintained within the subregion during the predetermined period of time, and control of the speed of the vehicle according to the invention is resumed, where in this case the speed is controlled such that it does not exceed a slightly lower speed vset2, where the speed of the vehicle is maintained at a speed not exceeding the speed vset2 until the driver releases the accelerator pedal at time t6, and thereby leaves the subregion β2 and control according to the invention again is ended.Figure 5 illustrates a further exemplary aspect of the invention for a situation which is relatively similar to the embodiment of Figure 4 until time t3, but where in difference to Figure 4 the control of the speed of the vehicle is configured to maintain the speed of the vehicle at the speed vsetl, and hence act as a cruise control function. The speed of the vehicle may hence be controlled through suitable control such that the speed vsetl is maintained irrespective of the current accelerator pedal position for as long as the accelerator pedal is maintained within the subregion of the movement region. In difference to the situation in Figure 4, the control according to the invention is not interrupted by the driver at time t3. Instead, the driver continues to maintain the accelerator pedal within the subregion while the vehicle encounters a downhill stretch of road. The driver, as was mentioned, maintains the accelerator pedal within the subregion, and the control system of the vehicle continues to control the speed of the vehicle.At first, the torque applied by the internal combustion engine is reduced to zero, time t4, but given the road inclination, the reduction to zero of the torque of the internal combustion engine, and the engine braking that in general thereby is applied due to internal losses of the internal combustion engine, does not provide a brake torque that is sufficient to maintain the speed of the vehicle at the desired speed. The speed of the vehicle therefore also starts to increase above the set speed vset1. At time t4, therefore, a brake torque is applied by at least one brake system of the vehicle 100. This brake torque may be applied by any suitable brake system, such as the service brake system or by one or more of the oftentimes present auxiliary brake systems.The brake torque is illustrated by a negative torque in the figure. The applied brake torque is first controlled to exceed a brake torque -TB in order to reduce the speed of the vehicle, and from time t5 a brake torque -TB is applied that is capable of maintaining the speed of the vehicle at the set speed vset1. The brake torque -TB, and thereby vehicle speed vsetl , is maintained for as long as the driver of the vehicle maintains the accelerator pedal within the movement region β.Slightly before time t6 the driver commences to release the accelerator pedal, and at time t6 the accelerator pedal is moved outside the subregion β, and at time t7 the accelerator pedal is fully released. In principle, the control of the vehicle speed according to the invention is ended when the accelerator pedal leaves the subregion β, but if the vehicle control system would suddenly stop applying the brake torque -TB applied by the one or more brake systems in this situation, the vehicle would suddenly, and possibly unexpectedly, start to accelerate, with potentially dangerous situations arising. Therefore, according to the illustrated example, the applied brake torque -TB is maintained also when the driver releases the accelerator pedal, e.g., until the driver depresses the brake pedal to an extent corresponding to a higher brake torque than the brake torque -TB already applied by the vehicle control system. In case the driver instead depresses the accelerator pedal, the applied brake torque may be controlled to successively reduce to, again, avoid sudden changes in applied brake torque.According to the invention, it is hence provided a method for facilitating driving in situations when a driver normally may not find it worth activating a cruise control function.According to an aspect of the invention, it is provided a control arrangement 120 for carrying out the method according to the invention, and hence to control the speed of a vehicle 100.The control arrangement 120, includes a control unit 121 arranged to, in a situation where the driver maintains the accelerator pedal within a predetermined subregion of the overall movement region of the accelerator pedal, control the speed of the vehicle such that the speed is maintained at or below a set speed.The control arrangement 120, e.g. a device or a control device, according to the invention may be configured to perform all aspects that have been described with regard to methods of the invention.Hence the control arrangement 120 is provided with the above-described advantages for the various aspects of the invention. The invention also relates to a vehicle 100 including the control arrangement 120.Figure 6 illustrates a control arrangement 600 / 120, which may be utilized to carry out the invention. The control arrangement 600 / 120 comprises a computing unit 601, which can be constituted by essentially any suitable type of processor or microcomputer, e.g., a circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit having a predetermined specific function (Application Specific Integrated Circuit, ASIC). The computing unit 601 is connected to a memory unit 602 arranged in the control arrangement 600 / 120, which memory unit provides the computing unit 601 with, e.g., the stored program code and / or the stored data which the computing unit 601 requires to be able to perform computations. The computing unit 601 is also arranged to store partial or final results of computations in the memory unit 602.In addition, the control arrangement 600 / 120 is provided with devices 611, 612, 613, 614 for receiving and transmitting input and output signals. These input and output signals can contain waveforms, impulses, or other attributes which, by the devices 611, 613 for the reception of input signals, can be detected as information and can be converted into signals which can be processed by the computing unit 601. These signals are then made available to the computing unit 601. The devices 612, 614 for the transmission of output signals are arranged to convert signals received from the computing unit 601 in order to create output signals by, e.g., modulating the signals, which can be transmitted to other parts of and / or systems in the vehicle 100.Each of the connections to the devices for receiving and transmitting input and output signals can be constituted by one or more of a cable; a data bus, such as a Controller Area Network CAN bus, a Media Orientated Systems Transport MOST bus, or some other bus configuration; or by a wireless connection. A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 601 and that the above- stated memory can be constituted by the memory unit 602.Control systems in modern vehicles commonly comprise communication bus systems consisting of one or more communication buses for linking a number of electronic control units, ECU's, or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units and the responsibility for a specific function can be divided amongst more than one control unit. Vehicles of the shown type thus often comprise significantly more control units than are shown in Figure 1, which is well known to the person skilled in the art within this technical field.In a shown embodiment, the invention may be implemented by the one or more above mentioned control units 121-123. The invention can also, however, be implemented wholly or partially in one or more other control units being present in the vehicle 100, or in one or more control unit dedicated to the invention.Here and in this document, units are often described as being arranged for performing steps of the method according to the invention. This also includes that the units are designed to and / or configured to perform these method steps.The control units 121-123 are in Figure 1 illustrated as forming part of one unit. These and other units may, however, be logically separated but physically implemented in the same unit or can be both logically and physically arranged together. These units may, e.g., correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by a processor / computing unit 601 when the units are active and / or are utilized for performing its method step, respectively.The person skilled in the art will appreciate that the embodiments described herein for controlling braking of a vehicle may also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product 603 stored on a non-transitory / non-volatile digital storage medium, in which the computer program is incorporated in the computer-readable medium of the computer program product. The computer-readable medium comprises a suitable memory, such as, e.g.: Read-Only Memory ROM, Programmable Read-Only Memory PROM, Erasable PROM EPROM, Flash memory, Electrically Erasable PROM EEPROM, a hard disk unit, etc.Finally, the invention is not limited to the above-described embodiments, but the invention relates to, and encompasses, all of the different embodiments that are included within the scope of the independent claims.

Claims

1. A method performed by a control device for controlling a speed of a vehicle (100), wherein the vehicle (100) comprises:a power source (104) for providing a propulsive torque to at least one drive wheel (111-114) of the vehicle (100);at least one braking system for applying a braking torque to at least one wheel of the vehicle;a driver-operable accelerator means (301) for requesting a propulsive torque from the power source (104), wherein the driver-operable accelerator means (301) is an accelerator pedal operable in a range of motion (A-B) between a first end position (A) and a second end position (B),wherein the method comprises, when the position of the driver-operable accelerator means (301) is maintained within a first sub-range of the range of motion (A-B) for at least a first period of time: determining a first vehicle speed to the nearest 10 km / h, or to the nearest 5 km / h relative to a current speed of the vehicle, and / or to a current prevailing speed limit; and controlling torque applied to the at least one drive wheel of the vehicle so that the vehicle speed does not exceed the first speed, while not preventing a reduction in the vehicle speed by a reduced accelerator pedal level, as long as the driver-operable accelerator means is maintained within the first sub-range after the first period of time, optionally plus a predetermined period of time if the driver-operable accelerator means is released.

2. The method of claim 1, wherein controlling the torque applied to the at least one drive wheel of the vehicle such that the vehicle speed does not exceed the first vehicle speed comprises: reducing the torque applied by the power source to the at least one drive wheel relative to a torque request from the power source corresponding to the current position of the driver-operable accelerator means (301).

3. The method of claim 2, further comprising:gradually reducing the torque applied by the power source to the at least one drive wheel as a driving resistance gradually decreases, to maintain the vehicle speed at or below the first vehicle speed.

4. Method according to any one of claims 1-3, further comprising:controlling torque applied to at least one wheel of the vehicle so that the vehicle speed does not exceed the first vehicle speed in situations where other cruise control systems in the vehicle that can be activated by the driver are not active.

5. A method according to any one of claims 1-4, further comprising the step of:terminate holding the vehicle speed at or below the first speed when the driver-operable accelerator means (301) is depressed to a first extent, or released to a first extent within a predetermined period of time.

6. A method according to any one of claims 1-5, further comprising:determining the first sub-range of the range of motion of the driver-operable accelerator means (301) depending on the current position of the driver-operable accelerator means (301) when the first time period begins.

7. Method according to any one of claims 1-6, further comprising, when the vehicle enters a downhill section of the road:maintaining the vehicle speed at or below the first vehicle speed when the driver-operable accelerator means (301) is positioned in the sub-range of the range of motion of the driver-operable accelerator means (301), wherein the vehicle speed is maintained at least in part by applying a braking torque by means of the at least one braking system.

8. Control device for controlling a speed of a vehicle (100), the vehicle (100) comprising:a power source (104) for providing a propulsive torque to at least one wheel (111-114) of the vehicle (100);at least one brake system for applying a braking torque to at least one wheel of the vehicle; a driver-operable accelerator means (301) for requesting a propulsion torque from the power source (104), wherein the driver-operable accelerator means (301) is an accelerator pedal and can be operated in a range of motion (A-B) between a first end position (A) and a second end position (B), wherein the control device is designed so that, when the position of the driver-operable accelerator means (301) is maintained within a first sub-range of the range of motion (A-B) for at least a first period of time:determine a first vehicle speed to the nearest 10 km / h, or the nearest 5 km / h in relation to a current speed of the vehicle, and / or to a current prevailing speed limit; and control torque applied to at least one wheel of the vehicle so that the vehicle speed does not exceed the first vehicle speed, while not preventing a reduction in vehicle speed by reducing the accelerator pedal level, as long as the driver-operable accelerator means is maintained within the first sub-range after the first period of time, optionally plus a predetermined period of time if the driver-operable accelerator means is released.

9. Vehicle (100) comprising a control device according to claim 8.

10. A computer program comprising instructions which, when executed by a computer included in a control device according to claim 8, causes the computer to perform the method according to any one of claims 1 to 7.

11. Computer-readable medium comprising instructions that, when executed by a computer included in a control device according to claim 8, cause the computer to perform the method (200) according to any one of claims 1 to 7.