SE541747C2

SE541747C2 - A method and a system for adjusting vehicle speed

Info

Publication number: SE541747C2
Application number: SE1651531A
Authority: SE
Inventors: Erik Holma; Karl Redbrandt
Original assignee: Scania Cv Ab
Priority date: 2016-11-23
Filing date: 2016-11-23
Publication date: 2019-12-10
Also published as: SE1651531A1; DE102017010532A1

Abstract

A method and a system for temporarily adjusting vehicle speed of a motor vehicle having a reference speed regulating cruise control configured to control the vehicle speed, the method comprising:- while controlling the vehicle speed using the cruise control, receiving a signal generated at an initiative of the driver and at a point in time determined by the driver, said signal indicating that a temporary departure from a reference speed (v_ref) demanded by the cruise control from a powertrain of the motor vehicle is desired,- in response to the receipt of said signal, setting a temporary reference speed (v_ref_temp) above the reference speed, anddemanding the temporary reference speed from the powertrain until a defined termination condition is fulfilled.

Description

A method and a system for adjusting vehicle speed TECHNICAL FIELD OF THE INVENTION The present invention relates to a method and a system for adjusting vehicle speed of a motor vehicle having a cruise control configured to control the vehicle speed. The invention also relates to a computer program, a computer readable medium and a motor vehicle.

BACKGROUND AND PRIOR ART The cost of fuel for motor vehicles, e.g. cars, trucks and buses, represents a significant expense for the owner or user of the vehicle. A wide variety of different systems have therefore been developed for reducing fuel consumption, e.g. fuel-efficient engines and fuel-economising cruise controls.

A driver of a motor vehicle with a cruise control usually selects a set speed v_set. The set speed v_set is the speed which the driver wishes the motor vehicle to maintain on a level road. The cruise control then demands a reference speed v_ref from the powertrain of the vehicle, which reference speed v_ref is thereby used to control the engine and/or the electric motor. The set speed v_set may thus be seen as an input signal to the cruise control, while the reference speed v_ref may be seen as an output signal from the cruise control. Typically, the reference speed v_ref is determined based on the set speed v_set.

Traditional cruise controls (CC) maintain a constant reference speed v_ref, which corresponds to the set speed v_set requested by the driver. The value of the reference speed v_ref is here changed only when the user adjusts the set speed v_set while driving.

Today there are also cruise controls, so-called economical cruise controls, such as Scania Ecocruise and similar cruise controls, which estimates the current driving resistance and also have knowledge about the historical driving resistance. An experienced driver who drives a motor vehicle without a cruise control may reduce fuel consumption by adjusting the driving to the characteristics of the road ahead, so that unnecessary braking and/or fuel-consuming acceleration may be avoided. In a further development of these economical cruise controls, the ambition is to mimic the experienced driver's adjustment of driving the motor vehicle based on knowledge about the road ahead, so that fuel consumption may be kept at a level as low as possible, with driving time and comfort taken into consideration.

One example of such a further development of an economical cruise control is a look-ahead cruise control (LACC), i.e. a strategic cruise control using knowledge about road sections ahead, i.e. knowledge about the appearance of the road ahead, in order to determine an appropriate reference speed v_ref. Here, the reference speed v_ref is thus permitted to differ somewhat from the set speed v_set selected by the driver in order to achieve a more fuel-efficient driving. For example, by taking topographic information about the road section ahead of the vehicle into account, the speed may be temporarily increased before e.g. an uphill slope, so that downshifting to a lower transmission gear can be avoided or delayed. In this way, fuel consumption can be reduced. Also information about road curvature and legal speed limits along the road section ahead of the vehicle can be taken into account.

With many fuel-economising cruise controls, there is a risk that the driver of the vehicle feels that the behaviour of the vehicle does not always coincide with the intentions of the driver. Due to the lack of a sense of control of the vehicle speed, the driver may be tempted to switch off the cruise control. This may cause the total fuel consumption to rise, and it is therefore desirable that the driver feels in control of the of the cruise control while the vehicle is driven in a fuel-efficient way.

WO2012158098 describes a method and a system for adjusting vehicle speed of a motor vehicle having a cruise control. According to the method, the driver can in one step adjust the set speed v_set to a value related to a current actual vehicle speed when the reference speed v_ref of the vehicle is different from the present set speed v_set. This method allows the driver to more easily control the set speed v_set of the vehicle.

SUMMARY OF THE INVENTION It would be desirable to provide a method and a system that offers an increased sense of control to a driver of a motor vehicle having a reference speed regulating cruise control configured to control the vehicle speed.

To better address this concern, a method and a system as defined in the independent claims are provided.

According to an aspect, a method for temporarily adjusting vehicle speed of a motor vehicle having a reference speed regulating fueleconomising cruise control configured to control the vehicle speed v is provided. The method comprises: - while controlling the vehicle speed using the cruise control, receiving a signal generated at an initiative of a driver of the motor vehicle and at a point in time determined by the driver, said signal indicating that a temporary departure from a reference speed v_ref demanded by the cruise control from a powertrain of the motor vehicle is desired, wherein the reference speed (v_ref) is initially similar to an adapted speed (v_adapted) determined by the cruise control based on a set speed (v_set) requested by the driver, - in response to the receipt of said signal, setting a temporary reference speed v_ref temp above the reference speed v_ref, and - demanding the temporary reference speed v_ref_temp from the powertrain until a defined termination condition is fulfilled.

According to another aspect, a system for temporarily adjusting vehicle speed v in a motor vehicle having a reference speed regulating cruise control configured to control the vehicle speed is provided. The system comprises a control unit configured to: - receive a signal generated at an initiative of the driver and at a point in time determined by the driver, said signal indicating that a temporary departure from a reference speed v_ref demanded by the cruise control from a powertrain of the motor vehicle is desired, - in response to the receipt of said signal, set a temporary reference speed v_ref temp above the reference speed v_ref, and - demand the temporary reference speed v_ref_temp from the powertrain until a defined termination condition is fulfilled.

The proposed method and system allow temporary adjustment of the vehicle speed at the initiative of the driver and at a point in time determined by the driver. The driver thereby feels an increased sense of control of the vehicle speed in comparison with other methods and systems in which he/she can only accept or reject suggestions to adjust the vehicle speed made by the cruise control or by other systems within the vehicle. The proposed method and system are thereby likely to have a positive influence on the driver’s acceptance of fuel-economising cruise controls. Overall, this is beneficial for the fuel consumption of the vehicle since the driver will be more inclined to use the cruise control if he/she feels more in control.

According to the invention, the driver can provide a signal (e.g. to a control unit) indicating that a temporary departure from the reference speed v_ref is desired. The reference speed v_ref is herein to be understood as the reference speed v_ref currently demanded from the powertrain as the driver provides the signal. In the absence of a signal from the driver indicating that a temporary departure from the reference speed v_ref is desired, the cruise control would typically continue to use the reference speed v_ref to control the powertrain during the upcoming road section.

As the signal is received (e.g. in the control unit), a temporary reference speed v_ref temp above the reference speed v_ref is set. The temporary reference speed v_ref_temp is thereafter demanded from the powertrain until the termination condition is fulfilled. The temporary reference speed may either be set to a specific target value in one step following reception of the signal, or it may be incrementally increased until the target value is reached.

It is to be understood that, in order to reach and/or maintain the desired temporary reference speed v_ref_temp, a positive driving torque may usually have to be applied by the powertrain of the vehicle. Speed controls are often configured to, on one hand demand a reference speed v_ref from the powertrain while a positive driving torque is applied by the powertrain, and on the other hand, control braking of the vehicle to a braking speed when the vehicle travels downhill, and brakes have to be applied not to exceed a desirable vehicle speed. The proposed method and system are focused on control of the reference speed v_ref, and not on control of the braking speed. The present aspects are particularly useful in situations in which the vehicle would normally loose speed if a fuel economising cruise control is used, such as in an uphill slope.

The received signal does not necessarily have to be the exact signal generated by the driver. It may also be a signal which is derived from the signal generated by the driver, but which has been converted by another unit within the vehicle.

For example, the system may form part of a reference speed regulating cruise control or be a separate system which may be used in combination with such a cruise control.

The reference speed v_ref and/or the temporary reference speed v_ref_temp may of course be demanded from a control unit that in turn controls the powertrain, but for simplicity, this has herein been described in terms of the reference speed v_ref and the temporary reference speed v_ref_temp being demanded from the powertrain.

Preferred embodiments of the invention are disclosed in the dependent claims.

According to one embodiment, the method further comprises, given that said termination condition is fulfilled, controlling the speed v of the motor vehicle toward the reference speed v_ref. Hence, as the termination condition is fulfilled, the reference speed v_ref may again be demanded from the powertrain.

According to one embodiment, the signal is generated solely at the initiative of the driver without suggestion from the cruise control or from any other system within the motor vehicle. The driver may thereby be in better control over the signal generation, and may experience a better control over the vehicle, which in turn may increase usage of the cruise control. For example, the cruise control may be an economising cruise control, and increased usage thereof may result in lowered fuel consumption. With the present embodiment, the driver may not merely accept or reject suggestions given by the cruise control or by another system, but may take the initiative of adjusting the reference speed v_ref whenever he/she feels urged to do so.

The cruise control is in other words a fuel-economising cruise control such as a look-ahead cruise control or similar, in which the cruise control demands a speed from the powertrain which may differ slightly from the set speed depending on road conditions, traffic, etc.

According to one embodiment, the temporary reference speed v_ref_temp is set in dependence on how an initial actual vehicle speed v_initial, at which the motor vehicle travels upon receipt of said signal, relates to the set speed v_set. The temporary reference speed v_temp that is demanded from the powertrain following receipt of a signal from the driver may thereby be adapted depending on the initial actual vehicle speed. For example, depending on the initial actual vehicle speed, the temporary reference speed may be set above or below the set speed v_set as will be further described below.

According to one embodiment, if said initial actual vehicle speed v_initial exceeds the set speed v_set, the temporary reference speed v_ref_temp is set to one of the initial actual vehicle speed v_initial and a predetermined value above the set speed v_set. The driver may thereby be allowed to temporarily maintain a vehicle speed above the set speed v_set, while a definition of an upper limit for the temporary reference speed v_ref_temp is facilitated.

According to one embodiment, if said initial actual vehicle speed v_initial is similar to the set speed v_set, the temporary reference speed v_ref_temp is set to a predetermined value above the set speed v_set. By an initial actual vehicle speed v_initial that is similar to the set speed v_set is herein intended an initial actual vehicle speed v_initial which is equal to or which does not differ from the set speed v_set by more than ±2 %, preferably ±1 %, or by more than 1 km/h.

According to one embodiment, if said initial actual vehicle speed v_initial is below the set speed v_set, the temporary reference speed v_ref_temp is set to a value that is similar to the initial actual vehicle speed v_initial. The driver can thereby prevent the vehicle speed from dropping further before e.g. a downhill slope in which a fuel-economising cruise control may normally set a reference speed v_ref below the set speed v_set. Thus, in this embodiment, the initial actual vehicle speed v_initial is below the set speed v_set but above the reference speed v_ref. By a value that is similar to the initial actual vehicle speed v_initial is herein intended a value that is equal to or does not differ from the initial actual vehicle speed by more than ±2 %, preferably ±1 %, or by more than 1 km/h.

According to one embodiment, the method further comprises collecting data relating to conditions along an expected travelling route ahead of the motor vehicle. Such road conditions may be e.g. road inclination, traffic conditions, detected vehicles travelling ahead of the vehicle, etc.

According to one embodiment, the method further comprises to, based on said data, determine whether the desired temporary reference speed v_ref_temp is allowable, wherein the temporary reference speed v_ref_temp is only demanded from the powertrain if the temporary reference speed v_ref_temp is found to be allowable. The risk of dangerous or otherwise undesirable situations can thereby be reduced based on e.g. road conditions.

According to one embodiment, the method further comprises to, based on said data, determine whether the termination condition is fulfilled. The termination condition may be defined so that it is fulfilled if e.g. the traffic conditions change or if the road inclination assumes a certain predetermined value, or similar.

According to one embodiment, the termination condition is defined so that it is considered fulfilled if an end of a preset time period is reached and/or if a current actual vehicle speed v_vehicle becomes similar to the set speed v_set and/or if a signal from the driver is received. These termination conditions can be set in independence on road conditions, traffic data etc. By a current actual vehicle speed similar to the set speed is herein intended a current actual vehicle speed that is equal to the set speed v_set or that does not differ from the set speed v_set by more than ±2 %, preferably ±1 %, or by more than 1 km/h.

According to one embodiment, said signal is obtained from an input means provided in connection with an accelerator pedal of the motor vehicle, such that the driver can provide said signal by tapping the accelerator pedal. The driver can thereby more easily and more intuitively generate the signal. Alternative input means may include a button, a microphone, a touch-panel, etc.

The invention also relates to a computer program comprising instructions which, when the computer program is executed by a computer, causes the computer to carry out the proposed method and to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the proposed method.

It will be appreciated that all the embodiments described with reference to the method aspect of the present invention are applicable also for the system aspect of the present invention. That is, the system may be configured to perform any one of the method steps of the above described embodiments.

According to another aspect, the invention relates to a motor vehicle comprising a system as defined in any one of the above described embodiments. For example, the motor vehicle may be powered by an internal combustion engine and/or by an electric motor. In particular, but not exclusively, the method and system may be used in a heavy motor vehicle such as a truck or a bus.

Other advantageous features as well as advantages of embodiments of the present invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will in the following be further described by means of example with reference to the appended drawings, wherein Fig. 1 is a flow chart illustrating a method according to an embodiment of the invention, Fig. 2 is a graph schematically illustrating vehicle speed in an exemplary embodiment of the method according to the invention, and Fig. 3 is a graph schematically illustrating vehicle speed in another exemplary embodiment of the method according to the invention Fig. 4 is a schematic illustration of a motor vehicle according to an embodiment of the invention, and Fig. 5 schematically shows a control unit for carrying out the method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION A method according to an embodiment of the invention is illustrated in a flowchart in fig. 1. The method is carried out in a motor vehicle, such as a bus or a truck, having a reference speed regulating cruise control that controls vehicle speed v.

As the method is started in a step 101 , the vehicle speed v is controlled using the cruise control. A driver of the motor vehicle has selected a set speed v_set, which is requested from the cruise control. The cruise control in turn demands a reference speed v_ref from a powertrain of the vehicle. The motor vehicle at this point travels at an initial speed v_initial which may differ from the set speed v_set and the reference speed v_ref depending on road conditions, configurations of the cruise control, etc.

In a step 102, at any point in time determined by the driver, a signal is received which has been generated at an initiative of the driver. The signal indicates that a temporary departure from the reference speed v_ref demanded by the cruise control is desired.

In a step 103, in response to the receipt of the signal, a temporary reference speed v_ref_temp is set. A termination condition may be defined in this step, or a predefined termination condition may be used. The temporary reference speed v_ref_temp is above the reference speed v_ref that would be demanded from the powertrain if the driver had not provided the signal, and may be set depending on how the initial actual vehicle speed v_initial relates to the set speed v set.

In a step 104, the temporary reference speed v_ref_temp is demanded from the powertrain instead of the reference speed v_ref. Normally, this involves requesting a positive driving torque from the powertrain of the vehicle in order to reach and/or maintain the temporary reference speed v_ref_temp. If the temporary reference speed v_ref differs from the initial speed v_initial, the new reference speed v_ref_temp may be set to a target value immediately, in a single step, or it may be adjusted gradually until a target value for the reference speed v_ref_temp is reached.

In a step 105, it is assessed whether the termination condition is fulfilled. If the termination condition is found to be fulfilled, the cruise control returns to automatic control of the vehicle speed, e.g. by controlling the vehicle speed to the reference speed v_ref. If the termination condition is not yet fulfilled, the temporary reference speed v_ref_temp continues to be demanded from the powertrain.

In an example, a heavy motor vehicle having a cruise control controlling vehicle speed has just travelled down a downhill slope. The motor vehicle is therefore initially moving forward at an initial actual vehicle speed v_initial above the set speed v_set currently requested by the driver. As the vehicle moves onto a steep uphill road section, the vehicle speed could potentially drop to a value below the set speed v_set, partly because of the weight of the vehicle and partly since the cruise control would allow the speed to drop if there is a downhill road section following the uphill road section, on which downhill road section the vehicle speed is expected to increase to the set speed v_set without having to apply a positive driving torque. However, the driver taps the accelerator pedal and thereby signals that he/she wishes to temporarily maintain the initial actual vehicle speed v_initial and that a temporary speed v_ref_temp, higher than the reference speed v_ref that would otherwise be used, should be demanded from the powertrain until a termination condition is fulfilled. The motor vehicle could lose speed when travelling on the uphill road section regardless of the reference speed demanded from the powertrain, but this process can be delayed by the driver’s signal. When the current actual vehicle speed has dropped to the set speed v_set due to the natural speed reduction, the termination condition is considered fulfilled and the cruise control goes back to requesting the reference speed v_ref from the powertrain.

In another example, illustrated in fig. 2, a motor vehicle having a cruise control controlling vehicle speed v travels on a flat road as it approaches an uphill road section. Prior to position A, the actual vehicle speed v_vehicle is in this case essentially equal to the set speed v_set requested by the driver as shown in fig. 2, showing speed v and altitude h of the vehicle as a function of distance. At position A, just before the motor vehicle approaches the steep uphill road section, the driver taps the accelerator pedal and thereby signals that he/she wishes to temporarily increase the vehicle speed v. A target value for a temporary reference speed v_ref_temp above the initial actual vehicle speed v_initial, which is the actual vehicle speed v_vehicle at position A, is therefore set. The temporary reference speed v_ref_temp is gradually increased until it reaches the target value at the position B, as the motor vehicle moves onto the uphill road section. The motor vehicle therefore moves onto the uphill road section with an increased actual vehicle speed v_vehicle. As it climbs up the hill, its actual vehicle speed v_vehicle decreases until it reaches v_set at the position C. The termination condition is thereby considered fulfilled.

In another example, illustrated in fig. 3, a motor vehicle having a cruise control controlling vehicle speed v travels on a flat road as it approaches a downhill road section. Prior to position A, the actual vehicle speed v_vehicle is in this case lower than the set speed v_set requested by the driver as shown in fig. 3, showing speed v and altitude h of the vehicle as a function of distance. At position A, just before the motor vehicle approaches the downhill road section, the driver taps the accelerator pedal and thereby signals that he/she wishes to maintain the current actual vehicle speed v_vehicle, i.e. not to allow the vehicle speed to be further reduced before the downhill road section. A temporary reference speed v_ref_temp equalling the initial actual vehicle speed v_initial, i.e. the actual vehicle speed v_vehicle at position A, is therefore set. The temporary reference speed v_ref_temp is higher than the reference speed v_ref that would otherwise be demanded. The motor vehicle therefore moves onto the downhill road section starting at position B with an increased actual vehicle speed v vehicle. As it descends, its actual vehicle speed v vehicle increases until it reaches the set speed v_set. It continues to increase until, at position C, the termination condition is considered fulfilled.

Data relating to road conditions may be collected and used for evaluating whether a desired temporary reference speed v_ref_temp is allowable, or to evaluate whether the termination condition is fulfilled. Such data may be collected in various different ways and may relate to road gradient, traffic conditions, information about a vehicle travelling ahead of the vehicle, weather conditions, etc. A road gradient may be determined on the basis of map data, e.g. from digital maps containing topographical information, in combination with positioning information, e.g. GPS (global positioning system) information. The positioning information may be used to determine the location of the vehicle relative to the map data so that the road gradient can be extracted from the map data. Various present-day cruise control systems use map data and positioning information. Such systems may then provide the map data and positioning information required for the method according to embodiments of the present invention.

The road gradient may be obtained on the basis of a map in conjunction with GPS information, from radar information, from camera information, of information from another vehicle, from positioning information and road gradient information stored previously on board, or from information obtained from traffic systems related to the expected travelling route. In systems where there is information exchange between vehicles, road gradients estimated by one vehicle may also be made available to other vehicles, either directly or via an intermediate unit such as a data base or the like.

A motor vehicle 1 having a reference speed regulating cruise control 2 configured to control the vehicle speed and further having a system 3 for temporarily adjusting vehicle speed v is shown in fig. 4. The motor vehicle 1 comprises an engine 4 forming part of a powertrain 5 which drives driving wheels 6, 7. The motor vehicle 1 further comprises an exhaust treatment system 8. The system 3 for temporarily adjusting vehicle speed comprises a control unit configured to receive a signal as described above, generated at an initiative of the driver and at a point in time determined by the driver, indicating that a temporary departure from a reference speed v_ref currently demanded by the cruise control from the powertrain is desired. In response to the signal, the control unit is configured to set a temporary reference speed v_ref_temp above the reference speed v_ref and to define a termination condition. The control unit is further configured to demand the temporary reference speed v_ref_temp from the powertrain until the termination condition is fulfilled.

One skilled in the art will appreciate that a method for temporarily adjusting vehicle speed of a motor vehicle according to an embodiment of the present invention may be implemented in a computer program which, when executed in a computer, causes the computer to conduct the method. The computer program usually takes the form of a computer program product which comprises a suitable digital storage medium on which the computer program is stored. Said computer-readable digital storage medium comprises a suitable memory, e.g. ROM (readonly memory), PROM (programmable read-only memory), EPROM (erasable PROM), flash memory, EEPROM (electrically erasable PROM), a hard disc unit, etc.

Fig. 5 illustrates very schematically an electronic control unit 30 comprising an execution means 31 , such as a central processor unit (CPU), for executing a computer program. The execution means 31 communicates with a memory 32, for example of the type RAM, through a data bus 33. The control unit 30 comprises also a non-transitory data storing medium 34, for example in the form of a Flash memory or a memory of the type ROM, PROM, EPROM or EEPROM. The execution means 31 communicates with the data storing medium 34 through the data bus 33. A computer program comprising computer program code for implementing a method according to an embodiment of the invention is stored on the data storing medium 34.

The invention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with skill in the art without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method for temporarily adjusting vehicle speed (v) of a motor vehicle (1) having a reference speed regulating fueleconomising cruise control (2) configured to control the vehicle speed, the method comprising: - while controlling the vehicle speed (v) using the cruise control (2), receiving a signal generated at an initiative of a driver of the motor vehicle (1) and at a point in time determined by the driver, said signal indicating that a temporary departure from a reference speed (v_ref) demanded by the cruise control (2) from a powertrain (5) of the motor vehicle (1) is desired, wherein the reference speed (v_ref) is initially similar to an adapted speed (v_adapted) determined by the cruise control (2) based on a set speed (v_set) requested by the driver, - in response to the receipt of said signal, setting a temporary reference speed (v_ref temp) above the reference speed (v_ref), and - demanding the temporary reference speed (v_ref_temp) from the powertrain (5) until a defined termination condition is fulfilled.

2. The method according to claim 1, further comprising: - given that said termination condition is fulfilled, controlling the speed (v) of the motor vehicle (1) toward the reference speed (v_ref).

3. The method according to claim 1 or 2, wherein said signal is generated solely at the initiative of the driver without suggestion from the cruise control (2) or from any other system within the motor vehicle (1).

4. The method according to any one of the preceding claims, wherein the temporary reference speed (v_ref_temp) is set in dependence on how an initial actual vehicle speed (v_initial), at which the motor vehicle (1) travels upon receipt of said signal, relates to the set speed (v set).

5. The method according to claim 4, wherein, if said initial actual vehicle speed (v_initial) exceeds the set speed (v_set), the temporary reference speed (v_ref_temp) is set to one of the initial actual vehicle speed (v_initial) and a predetermined value above the set speed (v set).

6. The method according to claim 4 or 5, wherein, if said initial actual vehicle speed (v_initial) is similar to the set speed (v_set), the temporary reference speed (v_ref_temp) is set to a predetermined value above the set speed (v_set).

7. The method according to any one of claims 4-6, wherein, if said initial actual vehicle speed (v_initial) is below the set speed (v_set), the temporary reference speed (v_ref_temp) is set to a value that is similar to the initial actual vehicle speed (v_initial).

8. The method according to any one of the preceding claims, wherein the termination condition is defined so that it is considered fulfilled: - if an end of a preset time period is reached, and/or - if a current actual vehicle speed (v_vehicle) becomes similar to the set speed (v_set), and/or - if a signal from the driver is received.

9. The method according to any one of the preceding claims, further comprising: - collecting data relating to conditions along an expected travelling route ahead of the motor vehicle (1).

10. The method according to claim 9, further comprising: - based on said data, determining whether the temporary reference speed (v_ref_temp) is allowable, wherein the temporary reference speed (v_ref_temp) is only demanded from the powertrain (5) if the temporary reference speed (v_ref_temp) is found to be allowable.

11. The method according to claim 9 or 10, further comprising: - based on said data, determining whether the termination condition is fulfilled.

12. The method according to any one of the preceding claims, wherein said signal is obtained from an input means provided in connection with an accelerator pedal of the motor vehicle (1), such that the driver can provide said signal by tapping the accelerator pedal.

13. A computer program comprising instructions which, when the computer program is executed by a computer, causes the computer to carry out the method according to any one of the preceding claims.

14. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1-12.

15. A system (3) for temporarily adjusting vehicle speed (v) in a motor vehicle (1) having a reference speed regulating fueleconomising cruise control (2) configured to control the vehicle speed, said system (3) comprising a control unit configured to: - receive a signal generated at an initiative of a driver of the motor vehicle (1) and at a point in time determined by the driver, said signal indicating that a temporary departure from a reference speed (v_ref) demanded by the cruise control (2) from a powertrain (5) of the motor vehicle (1) is desired, wherein the reference speed (v_ref) is initially similar to an adapted speed (v_adapted) determined by the cruise control (2) based on a set speed (v_set) requested by the driver, - in response to the receipt of said signal, set a temporary reference speed (v_ref temp) above the reference speed (v_ref) , and - demand the temporary reference speed (v_ref_temp) from the powertrain (5) until a defined termination condition is fulfilled.

16. A motor vehicle (1) comprising a system (3) according to claim 15.