SE2250498A1

SE2250498A1 - Method and control arrangement for controllring a speed of a vehicle in a downhill road section

Info

Publication number: SE2250498A1
Application number: SE2250498A
Authority: SE
Inventors: Gustav Lindberg; Martin Jakobsson; Mikael Ögren; Mikael Alenius
Original assignee: Scania Cv Ab
Priority date: 2022-04-26
Filing date: 2022-04-26
Publication date: 2023-10-27
Also published as: DE102023107815A1

Abstract

A method performed by a control arrangement for controlling a speed of a vehicle, the vehicle being configured to maintain a first maximum speed when driving downhillThe method comprises when the vehicle is to travel a downhill road section:determining whether the first maximum to be maintained in the downhill road section exceeds a speed threshold value, andapplying, by means of a brake system, a brake force in the downhill road section prior to the speed of the vehicle reaches the first maximum speed, to instead maintain a second speed when the first maximum speed exceeds the speed threshold value, the second speed being lower than the first maximum speed.By reducing the speed in the downhill road section, air resistance acting of the vehicle is reduced. Air resistance represents a complete loss of energy in a vehicle and cannot be recovered. Thus, by reducing the speed in the downhill road section, air resistance losses are reduced, and increased energy efficiency may be obtained.The invention relates also to a control arrangement, a vehicle comprising the control arrangement, a computer program and a computer-readable medium.

Description

METHOD AND CONTROL ARRANGEMENT FOR CONTROLLRING A SPEED OF A VEHICLE IN A DOWNHILL ROAD SECTION Technical field The invention relates to a method and a control arrangement for controlling a speed of a vehicle travelling in a downhill road section.

The invention also relates to a computer program and a computer-readable medium and a vehicle comprising such a control arrangement.

Background The following background description constitutes a description of the background to the invention, which does not, however, necessarily have to constitute prior art.

One of the major global challenges today is reducing the negative impacts of road transportation on the environment due to greenhouse gas emissions. Moreover, the efficiency of a vehicle's energy consumption is one of the major factors influencing the cost, performance, and competitiveness of the vehicle. This has led to an increased interest in solutions aiming to improve energy efficiency in vehicles.

Vehicles, including heavy motor vehicles, such as trucks and busses may vary in speed when travelling on a road section. Typically, vehicles are accelerated on downhill road sections by their great train weight, which conversely often act to decelerate them on uphill road sections. Today, the speed of vehicles is often controlled automatically by means of speed control systems. Usually a driver of the vehicle selects a set speed, which is often automatically maintained. Automatic speed control is often conducted in vehicles by two interacting systems, a cruise control system which demands torque from an engine system to maintain a selected speed, and a downhill speed control system which prevents the vehicle from developing excessive speed, particularly on downhill road sections.

Such an automatic speed control is often comfortable for the driver, who does not need to maintain a selected speed manually by means of accelerator and/or brake pedal. lO Moreover, automatic speed control often provides increased energy efficiency compared to manual speed control. An optimized and energy efficient speed control is an important factor contributing to improved vehicle economy.

Summaﬂ lt is an objective of the present invention to provide a method and a control arrangement for mitigating or solving drawbacks of conventional solutions. ln particular an objective of the present invention is to provide a control arrangement for controlling a speed of a vehicle travelling on a downhill road section wherein an improved energy efficiency in the vehicle is obtained.

According to a first aspect of the invention, aforementioned and further objectives are achieved through a method performed by a control arrangement for controlling a speed of a vehicle, the vehicle being configured to maintain a first maximum speed when driving downhill, the method comprising, when the vehicle is to travel a downhill road secüon: determining whether the first maximum speed to be maintained in the downhill road section exceeds a speed threshold value, and applying, by means of a brake system, a brake force in the downhill road section prior to the speed of the vehicle reaches the first maximum speed, to instead maintain a second speed when the first maximum speed exceeds the speed threshold value, the second speed being lower than the first maximum speed.

The invention relates thus to a method for automatically controlling the speed of a vehicle travelling on a downhill road section. As in conventional solutions, the vehicle is configured to maintain a predefined maximum downhill speed, here referred to as the first maximum speed. The predefined maximum downhill speed is usually selected by the driver of the vehicle and should not be exceeded.

While maintaining the predefined maximum downhill speed, the vehicle is exposed to various forces. Some forces, like gravity force, accelerate the vehicle and some forces, like friction forces and air resistance forces, retard the vehicle. The size of air lO resistance depends on the vehicle speed and increases exponentially with increased vehicle speed. ln vehicles provided with a regenerative brake system, some of the energy from the applied brake force may be recovered if the brake force is applied by means of the regenerative brake system. Air resistance on the other hand, represent a complete loss of energy, i.e., energy which cannot be recovered.

The invention controls the speed of the vehicle such that, if the predefined maximum downhill speed, i.e., the first maximum speed, exceeds a speed threshold value, instead of maintaining the predefined maximum downhill speed as in previously known methods, a second speed, lower than the predefined maximum downhill speed, is maintained in the downhill road section by applying a brake force. By reducing the speed in the downhill road section, air resistance acting of the vehicle is reduced. Thus, by reducing the speed in the downhill road section, air resistance losses are reduced.

Moreover, since air resistance acts to retard the vehicle, the reduced air resistance is compensated by the applied brake force required to maintain the second speed. Thus, instead of energy being consumed by air resistance and lost, some of the energy may be recovered, for example by maintaining the speed of the vehicle in the downhill road section by means of a regenerative brake system. Thereby, increased energy efficiency may be obtained in the vehicle.

Furthermore, the braking of the vehicle to maintain the second speed according to the invention can take place over a longer period of time compared to maintaining the first maximum speed. This means that the brake force required to maintain the speed of the vehicle is reduced, since the energy required to maintain the second speed by means of a brake force is spread over a longer time. Thereby, the second speed may be maintained also in steep downhill road sections, where maintaining the first vehicle speel was not possible for example due to lack of available brake force in the brake system. lO lt is to be understood that the speed threshold value is here a speed below which the air resistance does not significantly affect the energy efficiency of the vehicle. ln an embodiment of the invention, the method further comprises, when the first maximum speed to be maintained in the downhi|| road section does not exceed the speed threshold value: applying a brake force in the downhi|| road section when the speed of the vehicle reaches the first maximum speed to maintain the first maximum speed.

Thus, the speed of the vehicle may be allowed to deviate from the predefined maximum downhi|| speed level, here referred to as the first maximum speed only in situations when it is determined that a significant amount of energy may be saved, i.e., when the predetermined maximum downhi|| speed exceeds the speed threshold value.

Hereby, unnecessary vehicle speed decrease in downhi|| road sections is avoided so that the trip time is not unnecessarily adversely affected. ln an embodiment of the invention, the method further comprises, when the vehicle approaches the end of the downhi|| road section: reducing the brake force to accelerate the vehicle to a speed exceeding the second speed at the end of the downhi|| road section.

By reducing the brake force in the final part of the downhi|| road section, the speed of the vehicle will be increased resulting in the vehicle leaving the downhi|| road section with an increased kinetic energy. The increased kinetic energy may be used instead of energy stored in fuel or a battery on a road section following the downhi|| which may lead to decreased energy consumption compared to if no speed increase was performed. Hereby, the energy efficiency of the vehicle is further increased. ln an embodiment of the invention, the reducing of the brake force to accelerate the vehicle to a speed exceeding the second speed at the end of the downhi|| road section comprises accelerating the vehicle to a speed between the second speed and the first maximum speed or to a speed being equal to or exceeding the first maximum speed. lO The amount of available kinetic energy in the end of the downhill road section which may be utilized instead of energy stored in fuel or a battery on a road section following the downhill may depend on the magnitude of the increased speed level at the end of the downhill road section. By utilizing the method of the invention, the amount of available kinetic energy at the end of the downhill road section may be controlled. ln an embodiment of the invention, the first maximum speed is a downhill control speed the vehicle being configured to brake and maintain the vehicle at the downhill control speed when reached.

Thus, the invention may be implemented in the downhill speed control and utilized in vehicles driving on downhill road sections.

Hereby, the energy efficiency of the downhill speed control may be improved in situations when the downhill control speed exceeds a speed threshold value. Moreover, controlling the vehicle speed by means of a downhill speed control may lead to increased use of the energy saving functionality according to the invention. ln an embodiment of the invention, the speed threshold value is at least partly based on air resistance acting on the vehicle.

Hereby, the size of the speed threshold may be set based on the effect of air resistance on a specific vehicle. The speed threshold value may, for example, correspond to a speed above which air resistance losses exceed a level which is acceptable from an energy consumption aspect. ln an embodiment of the invention, the brake system is a regenerative brake system. By using the regenerative brake system to apply a brake force when maintaining a vehicle speed in a downhill road section, energy may be recovered in the vehicle. Hereby, the energy efficiency of the vehicle is further increased. lO Furthermore, since, as previously explained, the brake force required to maintain the speed of the vehicle is reduced, the regeneration will take place at a lower mean power since the brake force will be applied during a longer period of time. Energy recovery is generally more efficient when performed at lower power. Thus, regeneration of the regenerative brake system may be optimized such that more energy is recovered. ln an embodiment of the invention, the second speed is based on at least one of: - a preconfigured parameter, - a driver setting, - a set speed of a cruise control system, - the first maximum speed, - the speed threshold value, - a traffic situation in the downhill road section, or - a regenerative brake system capacity when the brake system is a regenerative brake system.

Thus, a secure and reliable method for controlling the speed of the vehicle is obtained where the speed of the vehicle maintained in the downhill road section may be determined based on one or more parameters or conditions reflecting the driving situation in which the vehicle currently is present. ln an embodiment of the invention, the second speed is a speed corresponding to or being lower than a set speed of a cruise control system.

Hereby, a speed increase from the set speed of the vehicle is avoided. lncreased speed in downhill road sections can be perceived as unpleasant by the vehicle driver who might prefer keeping a steady speed when driving. Hereby, increased driver comfort may be obtained. Controlling the speed of the vehicle according to the method of the invention may result in a more even speed of the vehicle and improved traffic flow.

Moreover, by maintaining a speed corresponding to, or lower than, the set speed of the cruise control in the downhill road section, which usually corresponds to current lO legal speed limits, may reduce the risk of speeding and speeding fines. Hereby, increased driver comfort may be obtained. ln an embodiment of the invention, the speed of the vehicle is controlled to maintain a set speed, lower than the first maximum speed by means of a cruise control system, the method further comprising prior to the vehicle entering the downhill road section: reducing the speed of the vehicle from the set speed, such that the vehicle enters the downhill road section at a reduced vehicle speed.

By reducing the speed of the vehicle from the set speed, such that the vehicle enters the downhill road section at a reduced vehicle speed, the duration when the vehicle is accelerated in the downhill road section by means of gravity in increased. Thereby, reduced energy consumption is achieved. ln an embodiment of the invention, the method further comprises, when the vehicle enters the downhill road section with a speed lower than the second speed and when the brake system is a regenerative brake system: applying, by means of the regenerative brake system a brake force in the downhill road section wherein the brake force allows the vehicle to accelerate up to the second speed.

Hereby, the acceleration of the vehicle up to the second speed can take place over a longer period of time. The energy required to provide the brake force during the acceleration may be recovered and the peak brake force required during the acceleration may be reduced. Thus, increased energy efficiency may be obtained in the vehicle.

According to a second aspect, the invention relates to a control arrangement for controlling a speed of a vehicle, the vehicle being configured to maintain a first maximum speed when driving downhill, the control arrangement being configured to, when the vehicle is to travel a downhill road section: determine whether the first maximum speed to be maintained in the downhill road section exceeds a speed threshold value, and lO apply, by means of the brake system, a brake force in the downhill road section prior to the speed of the vehicle reaches the first maximum speed, to instead maintain a second speed when the first maximum speed exceeds the speed threshold value, the second speed being lower that the first maximum speed. lt will be appreciated that all the embodiments described for the method aspects of the invention are applicable also to at least one of the control arrangement aspects of the invention. Thus, all the embodiments described for the method aspects of 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 mentioned above for the methods and their embodiments.

According to a third aspect of the invention, aforementioned and further objectives are achieved through a vehicle comprising the control arrangement of the second aspect. The vehicle may for example be a bus, a truck, or a car.

According to a fourth 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 the first aspect.

According to a fifth 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 the first aspect.

The above-mentioned features and embodiments of the method, the control arrangement, the vehicle, the computer program, and the computer-readable medium, respectively, may be combined in various possible ways providing further advantageous embodiments.

Further advantageous embodiments of the method, the control arrangement, the vehicle, the computer program, and the computer-readable medium according to the lO present invention and further advantages with the embodiments of the present invention emerge from the detailed description of embodiments.

Brief description of the drawinqs Embodiments of the invention will be i||ustrated 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 embodiments of the present invention may be implemented; Figure 2a shows a flow chart ofa method for controlling a speed of a vehicle according to embodiments of the invention; Figure 2b shows a flow chart ofa method for controlling a speed of a vehicle according to further embodiments of the invention; Figure 3a illustrates the principle of one embodiment of the invention in one driving situation; Figure 3b illustrates the principle of further embodiment of the invention in a driving situation; Figure 4 shows a control arrangement, in which a method according to any one of the herein described embodiments may be implemented.

Detailed description A traditional downhill speed control system brakes the vehicle automatically when a downhill control speed vdhsc is reached. The downhill speed control system may, for example, regulate the speed of vehicles on downhill road sections on which they are accelerated by their own weight. The downhill control speed vdhsc is often equal to the set speed vsei for the cruise control system plus an offset speed. Normally the offset speed may vary between 3 and 15 km/h. When a vehicle reaches a downhill road section, the vehicle may be accelerated by gravity to a speed exceeding the set speed lO lO vsei for the cruise control system. When the downhill control speed vdhsc is reached, a brake force is applied such that the downhill control speed vdhsc is maintained.

However, it has been realized that current downhill brake systems may not be fully energy optimal for vehicles driving in downhill road sections. lt is thus an objective of the present invention to provide a method and a control arrangement for controlling a speed of a vehicle when driving downhill such that these problems are at least partly solved.

Now turning to Figure 1, which schematically illustrates a vehicle 100 that will be used to explain the herein presented embodiments. lt should be noted that only the units/devices/entities of the vehicle 100 useful for understanding the invention are illustrated in Figure 1. The vehicle 100 in Figure 1 comprises a driveline/drivetrain 110 configured to transfer a torque/power between at least one drive unit 101 and drive wheels 111, 112 of the vehicle 100. The at least one drive unit 101 may include an internal combustion engine which, in a customary fashion, may be connected via an output shaft 102 of the drive unit 101, to a clutch 103, and via the clutch also to a gearbox 105. The torque provided by the drive unit 101 is then provided to an input shaft 104 of the gearbox 105. A propeller shaft 106, connected to an output shaft of the gearbox 105, drives the drive wheels 111, 112 via a central gear 107, such as e.g. a customary differential, and drive shafts 108, 109 connected with the central gear 107. ln addition, the vehicle 100 may include one or more electrical machines for providing power to the drive wheels 111, 112 of the vehicle 100 and may thus for example be a so-called hybrid vehicle. ln another example, the drive unit 101 does not include an internal combustion engine but only at least one electrical machine for providing power to the drive wheels 111, 112, whereby the vehicle 100 may be a pure electrical vehicle. The at least one electrical machine may be arranged essentially anywhere, as long as power is provided to one or more of the drive wheels 111, 112, for example adjacent to one or more of the wheels, or in any other conventional way as is understood by a skilled person. The lO ll at least one electrical machine may be provided with electrical power from a battery system 113 included in the electrical motor system of the vehicle 100.

The driveline/drivetrain 110 and its components may be controlled by the vehicle's control system via at least one control arrangement 120 wherein the disclosed invention may be implemented. The at least one control arrangement 120 is, for example, responsible for one or a plurality of cruise control functions for automatically controlling the speed of the vehicle. These cruise control functions can be of various types. ln one example, a cruise control function may be ofa conventional type arranged to maintain a speed set by the driver or the system.

The control arrangement 120 may be distributed on several control units configured to control different parts of the vehicle 100. The control arrangement 120 may e.g. include a determining unit 121 and an applying unit 122 arranged for performing the method steps of the disclosed invention as is explained further. The control arrangement 120 will be described in further detail in Figure 4.

The vehicle 100 may further include at least one sensor 140, e.g. one or more cameras and/or one or more radar equipment located at suitable positions within the vehicle 100.

Further, the vehicle 100 may comprise a positioning system/unit 150. The positioning unit 150 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 may comprise a GPS receiver.

The vehicle 100 may further include at least one communication device 160 arranged for communication with at least one entity 170 external to the vehicle 100, such as e.g. an infrastructure entity, an external server, a positioning information entity and/or at least one communication entity of another vehicle. lO 12 According to various embodiments of the invention, the at least one communication device 160 may be essentially any device transferring information to and/or from the vehicle 100, and the at least one entity 170 external to the vehicle 100 may be essentially any external entity communicating with the vehicle 100, i.e. with the at least one communication device 160, for the transfer of the information to and/or from the vehicle 100. The at least one communication device 160 may be a vehicle-to-vehicle V2V communication device, a vehicle-to-infrastructure V2l communication device, a vehicle-to-everything V2X communication device, and/or a wireless communication device such that communication between the vehicle 100 and the at least one external entity 170 is achieved/provided.

The proposed invention will now be described with reference to a method 200, as disclosed in Figure 2a. Thus, in Figure 2a, a method 200 performed by a control arrangement for controlling a speed of a vehicle, such as the vehicle 100, is disclosed. The vehicle 100 may, according to the method 200, be configured to maintain a first maximum speed when driving downhill. The method is performed when the vehicle is to travel a downhill road section. ln a first step 210 of the method 200 in Figure 2a, it is determined whether the first maximum speed to be maintained in the downhill road section exceeds a speed threshold value. ln a second step 220 of the method 200, a brake force is applied by means of a brake system in the downhill road section prior to the speed of the vehicle 100 reaches the first maximum speed, to instead maintain a second speed when the first maximum speed exceeds the speed threshold value, the second speed being lower than the first maximum speed. lt is to be understood that the speed threshold value may relate to a speed above which air resistance losses contribute to deteriorated energy efficiency in the vehicle as will be explained further. lO 13 The size of air resistance acting on the vehicle 100 can be determined using the following formula: 1 Ra =š> where: p is a specific weight of the air [kg/m3], cx is a drag coefficient, S is the size of the front area of the vehicle [m2], v is the speed of the vehicle [m/s].

Air resistance depends thus on the vehicle speed. More specifically, from the formula above it may be seen that air resistance increases proportionally to the square of the vehicle speed. As an example, doubling the speed will increase the air resistance losses four times. Maintaining a low speed by means of a regenerative brake will reduce the overall losses increasing the energy efficiency of the vehicle. As previously explained, since air resistance acts to retard the vehicle, when the vehicle speed is reduced in a downhill road section, the reduced air resistance will result in decreased retarding force acting on the vehicle. This reduced retarding force needs to be compensated by applying a brake force such that the reduced speed of the vehicle is maintained. Thus, instead of energy being consumed by air resistance and lost, some of the energy may be recovered, for example by maintaining the speed of the vehicle in the downhill road section by means of a regenerative brake system. Thus, increased energy efficiency may be obtained in the vehicle.

The method 200 as well as further embodiments of the invention may be further explained based on the non-limitative example in Figure 3a. Figure 3a illustrates a driving scenario comprising the vehicle 100 where the method 200 and further embodiments of the invention may be applied. The xfehicâe 100 is driving throtigh a route Wraere the altitude of the route is shown at the top of the figure. Figure 3a also shows a plot of the vehicle's speed when driving through the route, the speed plot denoted as "speed" in the lower section of the figure as well as a plot of a brake force applied by means of a brake system in the vehicle 100 to achieve the illustrated speed in the downhill road section. The plot of the brake force is denoted as "brake force" in lO 14 the middle section of Figure 3a. The driving situation illustrated in Figure 3a is described in terms of positions such as P1, P2, etc.

Thus, Figure 3a shows the vehicle 100 approaching a downhill road section ofthe route 310 at an original speed. The speed of the vehicle 100 in Figure 3a may in one example, be controlled by means of a cruise control system configured to maintain a set speed vsei. The set speed vsei may, in one example, be set by the driver of the vehicle 100. ln another example, the set speed vsei may be set automatically according to conventional methods, based e.g., on legal speed limits along the route of the vehicle 100, and the curvature of the road section in front of the vehicle. ln one example, such an automatic setting of the target speed may be done by speed sign recognition in the vehicle.

As previously explained the vehicle 100 is configured to maintain a first maximum speed v1 when driving downhill. ln similar fashion as the set speed vsei, the first maximum speed v1 may be set by the driver of the vehicle 100 or set automatically for example as the set speed vsei for the cruise control system plus an offset speed. A parameter representing the first maximum speed v1 may be available in the vehicles control system. ln an embodiment, the first maximum speed v1 is a downhill control speed vdhsc of a downhill speed control onboard the vehicle 100. The vehicle 100 may thus be configured to brake and maintain the vehicle 100 at the downhill control speed vdhsc when the downhill control speed vdhsc has been reached. This embodiment provides thus a connection to the downhill speed control and its use on downhill road sections.

At the first position P1, the vehicle enters the downhill road section 310 where the vehicle 100 is accelerated by gravity from its original speed.

Previous known automatic downhill speed controls base their function on how an actual speed of the vehicle is related to the predefined maximum downhill speed in such a way that a brake force is applied when the predefined maximum downhill speed is reached. The brake force is then continued to be applied so that the predefined lO maximum downhill speed is maintained. Thus, as illustrated in Figure 3a, when the vehicle 100 has reached the first maximum speed vi in the downhill road section 310, i.e., at a third position P3, a brake force Fi is activated to maintain that first maximum speed vi. The brake force Fi is then continuously applied until the vehicle 100 has reached the end of the downhill road section at a fourth position P4. Thus, the first maximum speed vi is maintained throughout the entire stretch of the downhill road section 310 as is illustrated in Figure 3a by the dashed plots of "speed" and "brake force" between the positions P3 and P4. At the end of the downhill road section 310, i.e., at the fourth position P4, the brake force Fi is released (0 brake force in Figure 3a) so that the vehicle speed can again decrease to reach the original speed maintained prior to entering the downhill road section at the sixths position P6. The prior art thus brakes the vehicle 100 between the third position P3 and the fourth position P4.

According to step 210 of the method 200, it is instead determined whether the first maximum speed vi exceeds the speed threshold value vill when the vehicle is to travel the downhill road section 310. ln an embodiment, the speed threshold value vill may relate to air resistance acting on the vehicle. As previously mentioned, the energy required to overcome air resistance to obtain a required speed cannot be recovered. ln one example, the speed threshold value vill may be a predetermined parameter preconfigured in the vehicle's control system and correspond to a speed level where acceptable energy efficiency in obtained in downhill drive. ln another example, the speed threshold value vill may be obtained dynamically taking into consideration user's input related to required energy efficiency in the vehicle e.g., a preferred performance mode of the vehicle. Thus, the speed threshold value vill may be set lower if the vehicle is driving in economy mode where optimized energy consumption is prioritized, compared to when the vehicle is driving in sport mode where increased power is required. lO 16 Determining whether the first maximum speed v1 exceeds the speed threshold value vill may be done by comparing the parameters representing the first maximum speed v1 the speed threshold value vill available in the vehicle control system. lf it is determined that the first maximum speed v1 exceeds the speed threshold value vill, a second speed vz, lower that the first maximum speed v1, is instead maintained in the downhill road section 310 according to step 220 of the method 200. Thus, as illustrated in Figure 3a, a brake force F2 is applied at a second position P2 when the vehicle 100, accelerated by gravity in the downhill road section 310, has reached the second speed v2. The brake force Fz may then be applied until the vehicle 100 reaches the end of the downhill road section 310 at the fourth position P4 to maintain the second speed v2 throughout the entire stretch of the downhill road section 310. When the vehicle 100 is travelling in the downhill road section, the vehicles potential energy is converted to kinetic energy. When a brake force is applied to maintain a constant speed in the downhill road section the kinetic energy is kept constant while the potential energy of the vehicle decreases. Thus, the amount of energy converted in the downhill road section is the same regardless of the speed of the vehicle. However, as previously explained, at lower speeds the air resistance losses are reduced.

The brake force Fz may be applied by means of a brake system in the vehicle 100 or by means of a combination of one or more brake systems in the vehicle. Example of brake systems which may be used for retarding the vehicle 100 are auxiliary brakes, e.g., a retarder, an exhaust brake etc. ln an embodiment, the brake system may be a regenerative brake system so that a portion of the energy used when applying the brake force F2 is regenerated. lf the brake force F2 is applied by means of regenerative brake, more energy may be recovered when lower speeds are maintained compared to higher speeds due to reduced air resistance losses. Thus, applying regenerative brakes to maintain the speed ofthe vehicle according to the invention may result in improved energy efficiency in the vehicle. Othervvise, if the brake force is applied by a brake other than a regenerative brake, the brake energy is lost to friction and is not recovered. lO 17 ln an example, when the brake system is a regenerative brake system, the second speed vz may be based on a regenerative brake system capacity. The second speed vz may for example be selected to a speed that can be maintained in the downhill road section solely by means of the regenerative brake system.

Moreover, as previously explained, the braking of the vehicle 100 to maintain the second speed vz according to the invention can take place over a longer period of time compared to maintaining the first maximum speed v1. Thus, as illustrated in Figure 3a, the second speed v2 is maintained in the vehicle between the position P2 and the position P4 by applying the brake force F2. lt should be noted that, since the second speed v2 is lower than the first maximum speed v1, the travelling time between the position P2 and the position P4 will take longer time compared to when the first maximum speed v1 is maintained according to previous known method. This means that the brake force required to maintain the speed of the vehicle is reduced, since the energy required to maintain the second speed by means of a brake force is spread over a longer time. ln case the brake force is applied by means of a regenerative brake system, the regeneration will take place at a lower mean power. Energy recovery is generally more efficient when performed at lower power. Thus, regeneration of the regenerative brake system may be optimized such that more energy is recovered.

Othervvise, if the brake force is applied by means of a non-regenerative brake system, maintaining a lower speed by applying a reduced brake force may have the advantage that the reduced speed may be maintained also in steep downhill road sections where a higher speed was not possible to maintain due to lack of available brake capacity in the vehicle. ln an embodiment, the second speed vz may be based on one or more parameters. ln one example, the second speed v2 may be based on a preconfigured parameter. The second speed v2 may, for example, be preconfigured in the vehicle 100 and correspond to a calibrated, static speed value corresponding to a speed level where acceptable lO 18 energy efficiency in obtained in downhill drive. The second speed v2 may in one example correspond to a speed level of 70 km/h. ln another example, the second speed vz may be based on a driver setting. The driver setting may in one example correspond to input related to required energy efficiency in the vehicle e.g., a preferred performance mode of the vehicle. Thus, the second speed vz may be set lower if the vehicle is driving in economy mode where optimized energy consumption is prioritized, compared to when the vehicle is driving in sport mode where increased power is required. ln yet another example, the second speed v2 may be based on the set speed vsei of the cruise control system i.e., the original speed maintained prior to entering the downhill road section 310 at the position P1 in Figure 3. Generally, the second speed vz may be based on aspects like drivability, acceptance to driver, driver comfort to mention a few. ln an embodiment, the second speed vz may be a speed corresponding to or being lower that the set speed vsei of the cruise control system. Usually, the set speed vsei of the cruise control system may correspond to the legal speed limit valid on the road section the vehicle 100 is currently traveling on. Thus, maintaining the set speed vsei in the downhill road section reduces the risk of speeding and speeding fines. Thus, the second speed v2 may, in one example be set to a value corresponding to the set speed vsei of the cruise control system. ln another example the second speed vz may be set to a level which is more favourable for regeneration with the regenerative brake system, making it possible for more of the brake energy to be recovered by the regenerative brake system. ln yet another example, the second speed vz may be based on the speed threshold value vill. The second speed vz maybe set such that the speed threshold value vih is not exceeded. ln one example the second speed v2 maybe set to a value corresponding to the threshold value vm. ln yet another example, the second speed vz may be based on a traffic situation in the downhill road section 310. The second speed v2 may for example be based on the presence of vehicles in front of the vehicle 100. When the second speed vz is based lO 19 on the presence of vehicles in front of the vehicle 100, the one or more camera or the one or more radar systems may be used to determine a speed of, and/or a distance from, a vehicle in front. The second speed vz may for example be set such that the risk of running into, or coming too close to, other vehicles in front of the vehicle 100 is eliminated. ln another example, the second speed vz may be set to enable the vehicle 100 to follow the vehicle in front at a distance allowing a reduction of air resistance. ln situations where air resistance can be reduced by following another vehicle, a second speed vz exceeding the speed threshold value vill may be allowed. ln yet another example, the second speed v2 may be based on the available brake capacity of the brake system in the vehicle. The available braking capacity may be the brake force available in the downhill road section. ln one example, the second speed vz may be a speed which can be maintained in the downhill road section by mean of a brake system in the vehicle. ln another example, the second speed vz may be a speed which can be maintained in the downhill road section solely by means of the regenerative brake system in the vehicle. The available brake capacity may depend on different factors such as for example the weight of the vehicle 100, the inclination of the downhill road section, to mention a few. The available brake capacity in the vehicle may be determined according to conventional methods, for example based on a simulated vehicle speed of the vehicle in the downhill road section.

The applied brake force F2 regulates thus the speed of the vehicle 100 on the downhill road section 310 where the vehicle 100 is accelerated by its own weight.

At the end of the downhill road section 310, i.e., at the fourth position P4, the brake force F2 is released (0 brake force in Figure 3a) so that the vehicle 100 speed may again decrease to reach the original speed of the vehicle. This is illustrated in Figure 3a by the solid plots of "speed" and "brake force" between the positions P2 and P5. ln addition to the method steps 210 - 220 described with reference to Figure 2a the method according to the invention may, in embodiments, comprise further optional steps. Embodiments of the invention will now be explained more in detail with reference to Figure 2b. Figure 2b discloses a flowchart of the method 200 comprising the method lO steps 210 - 220 described with reference to Figure 2a and further optional steps. lt should be noted that the method steps illustrated in Figure 2b and described herein do not necessarily have to be executed in the order illustrated in Figure 2b. The steps may essentially be executed in any suitable order, as long as the physical requirements and the information needed to execute each method step is available when the step is executed.

The method steps 202 - 224 of the method 200 in Figure 2b will be explained referencing to Figure 3b. Figure 3b illustrates a non-limitative example of speed control in a vehicle 100 in the same driving scenario as in Figure 3a, where the embodiments of the method 200 are illustrated. Thus, Figure 3b shows the vehicle 100 approaching a downhill road section 310.

As previously explained, the method of the invention is executed when the vehicle 100 is to travel a downhill road section 310. Thus, in step 202 of method 200 in Figure 2b, it is determined whether the vehicle 100 is approaching a downhill road section. ln one example, it may be determined that the vehicle 100 is approaching a downhill road section if a downhill road section is detected in front of the vehicle 100 and along the planned route of the vehicle 100. Approaching a downhill road section may be detected according to a number of known ways all included within the scope of the invention. For example, a downhill road section may be detected on the basis of map data, e.g. from digital maps available in the vehicle 100 including e.g. topographical information, in combination with positioning information, e.g. GPS information. The positioning information may be used to determine the location of the vehicle relative to the map data so that the road section information may be extracted from the map data. Moreover, the downhill road section may be detected by means of one or more sensors 140 which may be included in the vehicle 100 such as one or more camera or one or more radar. ln another example, the downhill road section may be detected by means of at least one other vehicle 170 in front the vehicle 100 and communicated, e.g., via the at least one communication device 160 to the vehicle 100 using V2V communication. The downhill road section may also be detected by a nearby infrastructure device and communicated to the vehicle 100 using e.g. V2l communication. lO 21 Thus, the vehicle 100 driving along the route illustrated at the top of Figure 3b may detect the approaching downhill road section 310. lf it is determined that the vehicle 100 is approaching a downhill road section 310 i.e., 'Yes' in step 202, the method 200 continues to step 210, and if no downhill road section is detected, i.e., 'No' in step 202, the method 200 returns back to step 202, or is ended. ln step 210 of the method 200, it is determined, as previously described, if the first maximum speed v1 exceeds the speed threshold value vm. lf it is determined that the first maximum speed v1 exceeds the speed threshold value vill i.e., 'Yes' in step 210, the method 200 continues to step 214. Otherwise, i.e., 'No' in step 210, the method 200 continues to step 212. ln an optional step 212 of the method 200, the speed of the vehicle 100 is, in an embodiment, controlled according to previous known methods as previously described with reference to Figure 3a. This embodiment is also illustrated in Figure 3b. Thus, when it has been determined that first maximum speed v1 is equal to, or is lower than the speed threshold value vill, the brake force F1 is applied in the downhill road section 310 when the speed of the vehicle reaches the first maximum speed v1 at the fourth position P4 in Figure 3b such that the first maximum speed v1 is maintained. The speed maintained in the downhill road section is thus only decreased when significant amount of energy may be saved. ln an embodiment, as previously explained, the speed of the vehicle approaching the downhill road section is controlled to maintain a set speed vsei, lower than the first maximum speed v1 by means of a cruise control system. ln an optional step 214 of the method 200, prior to the vehicle 100 entering the downhill road section 310 the speed of the vehicle is reduced, as illustrated in Figure 3b, between the position P1 and P2 from the set speed vsei maintained by the vehicle 100 to a reduced speed va, such that the vehicle 100 enters the downhill road section 310 lO 22 at the reduced vehicle speed va. The reduced vehicle speed vs may be equal to a fixed proportion of the maintained set speed vsei or may be set based on an offset of the set speed vsei. For example, if the set speed vsei maintained by the vehicle 100 prior to the position P1 in Figure 3b is 80km/h, the vehicle speed may be reduced by an offset of 5km/h to a speed of 75km/h prior to entering the downhill road section at the position P1.

The speed reduction from the set speed vsei to the reduced speed vs may be carried out according to any conventional speed reduction methods, all included within the scope of the invention. ln one example, the speed of the vehicle 100 may be reduced by applying a brake force by means of a brake system in the vehicle. ln another example, the speed may be reduced by reducing or terminating of the applied propelling power by freewheeling or dragging. ln electrical vehicles, the speed reduction may be achieved by shutting of the electrical machine providing the propelling power to the drive wheels 111, 112 of the vehicle 100. By reducing the set speed vsei prior to the vehicle 100 reaching the downhill road section 310, the acceleration of the vehicle 100 in the downhill road section due to gravity may take place over a longer time compared to if the set speed is not reduced. Thereby, further energy efficiency may be achieved when driving downhill. ln an optional step 216 of the method 200, when the vehicle 100 enters the downhill road section 310, as illustrated in Figure 3b, at the position P2, with a speed lower than the second speed v2 and when the brake system is a regenerative brake system, a brake force Fa may, in an embodiment, be applied in the downhill road section. The brake force Fa may allow the vehicle to accelerate up to the second speed vz. The brake force may be applied by means of the regenerative brake system. By applying a brake force by means of the regenerative brake system when the vehicle accelerates in the downhill road section 310 energy may be recovered and further energy efficiency may be achieved when driving downhill. ln an embodiment no brake force is applied in this stage. lO 23 ln step 220 ofthe method 200, a brake force F2 is applied when the speed of the vehicle has reached the second speed v2, at the position P3 in Figure 3b, to maintain the second speed vz, as previously explained with reference to Figure 3a. ln an optional step 222 of the method 200, following step 220, it is determined if the vehicle is approaching the end of the downhill road section 310. Determining that the vehicle 100 is approaching the end of a downhill road section may be carried out according to conventional methods, based on e.g., map data in combination with positioning information, by means of one or more sensors 140 in the vehicle and/or by means of V2V or V2l communication. lf it is determined that the vehicle 100 is approaching the end of the downhill road section 310, i.e., 'Yes' in step 222, the method 200 continues to step 224. OthenNise, the method returns to step 220 where the brake force is continuously applied to maintain the second speed v2. ln an optional step 224 of the method 200, when the vehicle 100 is approaching the end of the downhill road section 310 the applied brake force F2 is released (0 brake force in Figure 3b). ln an embodiment, the brake force F2 may be reduced as illustrated in Figure 3b at the position P5 when the vehicle 100 is approaching the end of the downhill road section 310 to accelerate the vehicle 100 to a speed vsch exceeding the second speed v2 at the end of the downhill road section, i.e. at the position P7 in Figure 3b. ln one example, the position P5 where the brake force F2 is reduced to accelerate the vehicle 100 in the end of the downhill road section 310 may be determined according to conventional methods using e.g. Newton's laws of motion so that the speed vsch is reached at the end of the downhill road section. lncreasing the speed of the vehicle in the final part of the downhill road section 310 may have the result that the vehicle will leave the downhill road section, at the position P7 in Figure 3b, with an increased kinetic energy. The increased kinetic energy may be used instead of energy stored in fuel or a battery on a road section following the lO 24 downhill which may lead to decreased energy consumption compared to the embodiment where the second speed vz is maintained until the very end of the downhill slope 310 as illustrated in Figure 3a. The amount of available kinetic energy in the end of the downhill road section will at least depend on the magnitude of the increased speed level. By utilizing the method of the invention, the magnitude of the increased speed level may be controlled in a number of different ways. For example, the magnitude of the increased speed level may be controlled to optimize energy efficiency, acceptability to the driver of the vehicle, acceptability to other road users and/or driver comfort.

The speed vsch may e.g., be selected by the driver of the vehicle, or automatically according to conventional methods. ln an embodiment, as illustrated in Figure 3b, the speed vsch may be a speed equal to or exceed the first maximum speed v1. ln a further embodiment, the speed vsch may be a speed between the second speed vz and the first maximum speed vi. The speed vsch may in one example correspond to a speed level that the vehicle should not exceed e.g., due to one or more performance limitations in the vehicle, or to a speed limit that should not be exceeded on the road section where the vehicle is travelling. ln one example, the speed vsch may be based on the set speed vsei for the cruise control system, and may correspond to the set speed level vsei, plus an offset value. ln one example, the speed vsch may be based on a period of time that the vehicle will exceed the set speed level vsei.

When the vehicle 100 reaches the end of the downhill road section 310 at the position P7, the vehicle speed starts to decrease to reach its original speed at the position P8.

According to an aspect of the invention, a control arrangement 120 for controlling a speed of a vehicle 100 is presented. The control arrangement 120 includes means 121 arranged for determining whether the first maximum speed v1 to be maintained in the downhill road section exceeds a speed threshold value vill. Moreover, the control arrangement 120 includes means 122 arranged for applying, by means of a brake system, a brake force in the downhill road section prior to the speed of the vehicle 100 reaches the first maximum speed v1, to instead maintain a second speed vz when the lO first maximum speed v1 exceeds the speed threshold value vill, the second speed vz being lower than the first maximum speed v1.

The control arrangement 120, e.g. a device or a control device according to the invention may be arranged for performing all of the above, in the claims, and in the herein described embodiments method steps. The control arrangement 120 is hereby provided with the above-described advantages for each respective embodiment.

The invention is also related to a vehicle 100 including the control arrangement 120.

Now turning to Figure 4 which illustrates the control arrangement 400/120, which may correspond to or may include the above-mentioned control units 121 and 122 i.e. the control unit performing the method steps of the disclosed invention. The control arrangement 400/120 comprises a computing unit 401, 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 401 is connected to a memory unit 402 arranged in the control arrangement 400/120, which memory unit provides the computing unit 401 with, e.g., the stored program code and/or the stored data which the computing unit 401 requires to be able to perform computations. The computing unit 401 is also arranged to store partial or final results of computations in the memory unit 402. ln addition, the control arrangement 400/120 is provided with devices 411, 412, 413, 414 for receiving and transmitting input and output signals. These input and output signals can contain waveforms, impulses, or other attributes which, by the devices 411, 413 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 401. These signals are then made available to the computing unit 401. The devices 412, 414 for the transmission of output signals are arranged to convert signals received from the computing unit 401 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. lO 26 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 CAN bus (Controller Area Network bus), a MOST bus (Media Orientated Systems Transport 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 401 and that the above- stated memory can be constituted by the memory unit 402.

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 Figures 1 and 4, which is well known to the person skilled in the art within this technical field. ln a shown embodiment, the invention may be implemented by the above-mentioned control units 121 and 122. The invention can also, however, be implemented wholly or partially in one or more other control units already in the vehicle 100, or in some 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 and 122 are in Figure 1 illustrated as separate units. These units may, however, be logically separated but physically implemented in the same unit or can be both logically and physically arranged together. The 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 401 when the unit is active and/or is utilized for performing its method step. 27 The person skilled in the art will appreciate that the herein described embodiments for controlling an engine 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 403 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.: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit, etc. The invention is not limited to the above-described embodiments. lnstead, the invention relates to, and encompasses all different embodiments being included within the scope of the independent claims.

Claims

1. A method (200) performed by a control arrangement for controlling a speed of a vehicle (100), the vehicle being configured to maintain a first maximum speed (v1) when driving downhill, the method comprising, when the vehicle is to travel a downhill road section (310): determining (210) whether the first maximum speed (v1) to be maintained in the downhill road section (310) exceeds a speed threshold value (vill), and applying (220), by means of a brake system, a brake force in the downhill road section (310) prior to the speed of the vehicle (100) reaches the first maximum speed (v1), to instead maintain a second speed (vz) when the first maximum speed (v1) exceeds the speed threshold value (vill), the second speed (vz) being lower than the first maximum speed (v1).

2. Method (200) according to claim 1, further comprising, when the first maximum speed (v1) to be maintained in the downhill road section (310) does not exceed the speed threshold value (vm): applying (212) a brake force in the downhill road section (310) when the speed of the vehicle (100) reaches the first maximum speed (v1) to maintain the first maximum speed (v1).

3. Method (200) according to any of claims 1 or 2, the method further comprising when the vehicle (100) approaches the end of the downhill road section (310): reducing (224) the brake force to accelerate the vehicle (100) to a speed exceeding the second speed (v2) at the end of the downhill road section (310).

4. Method (200) according to claim 3, wherein reducing (224) the brake force to accelerate the vehicle (100) to a speed exceeding the second speed (vz) at the end of the downhill road section (310) comprises accelerating the vehicle (100) to a speed between the second speed (v2) and the first maximum speed (v1) or to a speed being equal to or exceeding the first maximum speed (v1). lO

5. Method (200) according to any one of the preceding claims, wherein: the first maximum speed (v1) being a downhill control speed, (vdhsc), the vehicle being configured to brake and maintain the vehicle at the downhill control speed (vdhsc) when reached.

6. Method (200) according to any one of the preceding claims, wherein the speed threshold value (vill) is at least partly based on air resistance acting on the vehicle (100).

7. Method (200) according to any one of the preceding claims, wherein the brake system is a regenerative brake system.

8. Method (200) according to any one of the preceding claims, wherein the second speed (vz) is based on at least one of: - a preconfigured parameter, - a driver setting, - a set speed (vsei) of a cruise control system, - the first maximum speed (v1), - the speed threshold value (vin), - a traffic situation in the downhill road section (310), or - a regenerative brake system capacity when the brake system is a regenerative brake system.

9. Method (200) according to any one of the preceding claims, wherein the second speed (vz) is a speed corresponding to or being lower than a set speed (vsei) of a cruise control system.

10. Method (200) according to any one of the preceding claims, wherein the speed of the vehicle is controlled to maintain a set speed (vsei), lower than the first maximum speed (v1) by means of a cruise control system, the method further comprising prior to the vehicle (100) entering the downhill road section (310): reducing (214) the speed of the vehicle (100) from the set speed (vsei), such that the vehicle enters the downhill road section (310) at a reduced vehicle speed (va). lO

11. Method (200) according to any one of the preceding claims, further comprising when the vehicle enters the downhill road section (310) with a speed lower than the second speed (v2) and when the brake system is a regenerative brake system: applying (216), by means of the regenerative brake system a brake force in the downhill road section (310) wherein the brake force allows the vehicle to accelerate up to the second speed (vz).

12. A control arrangement (120) for controlling a speed of a vehicle (100), the vehicle being configured to maintain a first maximum speed (v1) when driving downhill, the control arrangement (120) being configured to, when the vehicle is to travel a downhill road section (310): determine (210) whether the first maximum speed (v1) to be maintained in the downhill road section (310) exceeds a speed threshold value (vill), and, apply (220), by means of the brake system, a brake force in the downhill road section (310) prior to the speed of the vehicle (100) reaches the first maximum speed (v1), to instead maintain a second speed (vz) when the first maximum speed (v1) exceeds the speed threshold value (vill), the second speed (vz) being lower that the first maximum speed (v1).

13. A vehicle (100) comprising a control arrangement (120) according to claim

14. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method (200) according to any one of the claims 1 to

15. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method (200) according to any one of the claims 1 to 11.