TECHNICAL FIELD

The invention relates to a method for controlling a vehicle combination. Moreover, the present invention relates to each one of a computer program, a computer readable medium, a control unit and a vehicle combination.

The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as haulers, cars and the like.

BACKGROUND

A vehicle combination generally comprises a tractor and a trailer. Traditionally, the tractor provides the propulsion force for the vehicle combination and the tractor as well as the trailer may be provided with brakes in order to ensure that the vehicle combination can be appropriately braked.

However, it is currently contemplated to use vehicle combinations in which each one of the tractor and the trailer comprises motion support devices for propelling as well as braking the vehicle combination. To this end, though purely by way of example, each one of the tractor and the trailer may be furnished with a set of electric motors. Such electric motors may be connected to electric storage systems, such as batteries.

Apart from being able to propel the vehicle combination with small or even zero CO2 emissions, the electric motors may have the advantage that they can be used for regenerative braking wherein energy generated during braking by means of the electric motors can be transformed to electric energy to be stored in selected electric storage system(s).

Moreover, for other variants of vehicle combinations not necessarily comprising electric motors, there may be a need for controlling the force distribution amongst the motion support devices of the tractor and the trailer. As a non-limiting example, it may be desired to use only a limited number of service brakes at the time in order to ensure that other services brakes may be sufficiently cooled. As may be realized from the above, it is desired to control the motion support devices of the tractor and the trailer, respectively, in an appropriate manner in order to arrive at desired force distributions.

SUMMARY

An object of the invention is to provide a method that can control the force distribution amongst a tractor and a trailer in an appropriate manner.

The object is achieved by a method according to claim 1.

As such, the present invention relates to a method for controlling a vehicle combination. The vehicle combination comprises a tractor and a trailer. The tractor comprises a set of tractor wheels and the trailer comprises a set of trailer wheels. The tractor comprises a set of tractor motion support devices, comprising at least one tractor motion support device, connectable to the set of tractor wheels to thereby be adapted to provide at least a tractor force. The tractor force is at least one of a tractor propulsion force and a tractor brake force. The trailer comprises a set of trailer motion support devices, comprising at least one trailer motion support device, connectable to the set of trailer wheels to thereby be adapted to provide at least a trailer force. The trailer force is at least one of a trailer propulsion force and a trailer brake force.

The method comprises:

- receiving a request that a desired force imparted on the vehicle combination should be provided by the set of motion support devices of a unique dedicated unit of the vehicle combination, the unique dedicated unit being either the tractor or the trailer;

- upon determining that the desired force imparted on the vehicle combination can be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the predetermined set of safety requirements comprising at least one safety requirement, operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force, otherwise operating one or more of the tractor motion support devices as well as one or more of the trailer motion support devices in order to provide the desired force imparted on the vehicle combination. As used herein, the term “operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force” is intended to encompass that the set of motion support devices of the unique dedicated unit alone are operated so as to provide the desired force. Put differently, the term “operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force” is intended to encompass that the set of motion support devices of the tractor or trailer(s) not being the unique dedicated unit is not operated.

The above method implies an appropriate manner for determining when and how the set of motion support devices only of one unit of a vehicle combination can be used for providing a desired force.

Optionally, the predetermined set of safety requirements of the vehicle combination comprises a lateral acceleration safety condition requiring that, for each one of the set of motion support devices of the unique dedicated unit, a longitudinal force produced by the motion support device must be equal to or lower than a longitudinal force limit value being determined by means of a longitudinal force limit function being a function of at least a lateral acceleration of the unique dedicated unit.

Purely by way of example, the longitudinal force limit values for each motion support device of the unique dedicated unit, i.e. the tractor or the trailer, can be summarized in order to obtain a longitudinal force limit value for the unique dedicated unit.

Optionally, the longitudinal force limit function is a function using a value proportional to the lateral acceleration of the unique dedicated unit as input and provides a value proportional to a normalized longitudinal force, being the longitudinal force divided by a total vertical load imparted on the wheel or wheels connected to the motion support device and the friction value indicative of the friction between the wheel or wheels connected to the motion support device and the ground supporting the unique dedicated unit, as output.

Optionally, the longitudinal force limit function uses the lateral acceleration of the unique dedicated unit divided by a friction reference value, as input, the friction reference value being a friction value, indicative of the friction between the set of wheels of the unique dedicated unit and the ground supporting the unique dedicated unit, multiplied by an acceleration value corresponding to acceleration due to gravity. Optionally, the longitudinal force limit function is a step function such that: for values of the lateral acceleration of the unique dedicated unit divided by the friction reference value being equal to or smaller than a predetermined threshold as input, the output is set to a fixed nonzero value of the normalized longitudinal force, and for values of the lateral acceleration of the unique dedicated unit divided by a friction reference value being greater than the predetermined threshold as input, the output is set to zero.

Optionally, the predetermined set of safety requirements of the vehicle combination comprises a longitudinal slip safety condition requiring that a detected longitudinal slip value for at least a selected subset of the set of wheels for the unique dedicated unit is below a predetermined threshold.

Optionally, the predetermined set of safety requirements of the vehicle combination comprises a state determination condition requiring that for a predetermined vehicle state, a difference between a vehicle state measured value, relating to a measured value indicative of the predetermined vehicle state, and a vehicle state expected value, relating to an expected value indicative of the predetermined vehicle state, is within a predetermined state range.

Optionally, the vehicle state expected value is determined using a vehicle model of the vehicle combination, preferably the vehicle state expected value is determined using a vehicle model as well as a tire model of the set of tractor wheels and/or the set of trailer wheels.

Optionally, the predetermined vehicle state is a yaw rate of the unique dedicated unit.

Optionally, the predetermined vehicle state is an articulation angle or articulation angular rate between the tractor and the trailer.

Optionally, the predetermined vehicle state is a side slip angle of the unique dedicated unit.

Optionally, the predetermined vehicle state is a side slip angle of at least a selected subset of the set of wheels for the unique dedicated unit. Optionally, the desired force imparted on the vehicle is a propulsion force.

Optionally, the desired force imparted on the vehicle is a brake force.

Optionally, the vehicle combination comprises one or more additional trailers or dollies, each additional trailer comprising a set of additional trailer motion support devices, comprising at least one additional trailer motion support device, connectable to the set of additional trailer wheels to thereby be adapted to provide at least an additional trailer force, the additional trailer force being at least one of an additional trailer propulsion force and an additional trailer brake force. The method comprises:

- receiving a request that a desired force imparted on the vehicle combination should be provided by the set of motion support devices of a unique dedicated unit of the vehicle combination, the unique dedicated unit being either the tractor, the trailer or one of the one or more additional trailers;

- upon determining that the desired force imparted on the vehicle combination can be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the predetermined set of safety requirements comprising at least one safety requirement, operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force, otherwise operating one or more of the tractor motion support devices, as well as one or more of the trailer motion support devices and/or one or more of the additional trailer motion support devices of one or more of the one or more additional trailers, in order to provide the desired force imparted on the vehicle combination.

A second aspect of the present invention relates to a computer program comprising program code means for performing the steps of the method according to the first aspect of the present invention when the program is run on a computer.

A third aspect of the present invention relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of the method according to the first aspect of the present invention when the program product is run on a computer. A fourth aspect of the present invention relates to a control unit for controlling a vehicle, the control unit is configured to perform the steps of the method according to the first aspect of the present invention.

A fifth aspect of the present invention relates to a vehicle combination comprising a control unit according to the fourth aspect of the present invention.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 is a schematic top view of a vehicle combination;

Fig. 2 is a flow chart illustrating an embodiment of the method of the invention;

Fig. 3 is diagram relating to an embodiment of the invention;

Fig. 4 is diagram relating to another embodiment of the invention, and

Fig. 5 is diagram illustrating a load envelope for a vehicle combination.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

FIG. 1 shows an example vehicle combination 10 of the type considered in this disclosure.

As may be gleaned from Fig. 1 , the vehicle combination 10 comprises a tractor 12 and a trailer 14. The tractor 12 comprises a set of tractor wheels 16, 18, 20, 22 and the trailer comprises a set of trailer wheels 26, 28, 32, 34. In the Fig. 1 embodiment of a vehicle combination 10, the set of tractor wheels 16, 18, 20, 22 comprises four wheels and the set of trailer wheels 26, 28, 32, 34 comprises six wheels. However, it is of course contemplated that each one of the set of tractor wheels and the set of trailer wheels may contain any number of wheels in various embodiments of the vehicle combination 10

Moreover, as indicated in Fig. 1 , the tractor 12 comprises a set of tractor motion support devices 36, 38, 40, 42 comprising at least one tractor motion support device, connectable to the set of tractor wheels 16, 18, 20, 22 to thereby be adapted to provide at least a tractor force. The tractor force is at least one of a tractor propulsion force and a tractor brake force. In the Fig. 1 embodiment, the set of tractor motion support devices 36, 38, 40, 42 comprises two electric motors 36, 38, each one of which being connected to a dedicated wheel 16, 20. However, the set of tractor motion support devices 36, 38 may also or instead comprise an internal combustion engine (not shown). Moreover, in embodiments of the vehicle combination, a single motor, engine or other type of propulsion device may be connected to or more wheels via a shaft or axle for instance. Although the Fig. 1 implementation of the tractor 12 comprises two electric motors 36, 38, each one of which being connected to a dedicated front wheel 16, 20 it is also contemplated that other implementations of the tractor 12 may comprise one or more propulsion unit (not shown) connected to the real wheels 18, 22 of the tractor 12.

Additionally, in the Fig. 1 embodiment, the set of tractor motion support devices 36, 38, 40, 42 comprises services brakes 40, 42 each one of which being connected to a dedicated wheel 18, 22. Moreover, other implementations of the tractor 12 may comprise service brakes arranged at wheels also being connected to a propulsion unit, such as one of the electric motors 36, 38 mentioned hereinabove.

It should be noted that the implementation of the tractor 12 and the set of tractor motion support devices 36, 38, 40, 42 illustrated in Fig. 1 merely serve as an example and that other implementations of the tractor 12 may have other configurations of the set of tractor motion support devices 36, 38, 40, 42.

Moreover, as indicated in Fig. 1 , the trailer comprises a set of trailer motion support devices 44, 46, 48, comprising at least one trailer motion support device, connectable to the set of trailer wheels 26, 28, 32, 34 to thereby be adapted to provide at least a trailer force. The trailer force is at least one of a trailer propulsion force and a trailer brake force. The implementation of the set of trailer motion support devices 44, 46, 48 illustrated in Fig. 1 comprises a propulsion device 44, which for instance may be implemented as an electric motor or an internal combustion engine, which is connected to two wheels via a shaft 50. The implementation of the set of trailer motion support devices 44, 46, 48 illustrated in Fig. 1 comprises services brakes 46, 48, each one of which being connected to a dedicated wheel 28, 24. In implementations of the trailer 14, each wheel axle, possibly each wheel, is connected to a service brake.

It should be noted that the implementation of the trailer 14 and the set of trailer motion support devices 44, 46, 48 illustrated in Fig. 1 merely serve as an example and that other implementations of the trailer 14 may have other configurations of the set of trailer motion support devices 44, 46, 48.

Moreover, as indicated in Fig. 1 , the tractor 12 has a tractor longitudinal extension in a tractor longitudinal direction LTR, a tractor lateral extension in a tractor lateral direction TTR and a tractor vertical extension in a tractor vertical direction VTR. The tractor longitudinal direction LTR corresponds to an intended direction of travel of the tractor 12 when the vehicle combination 10 is travelling straight ahead. The tractor vertical direction VTR corresponds to a direction of a normal to a planar surface supporting the tractor 12 and the tractor lateral direction TTR is perpendicular to each one of the tractor longitudinal direction LTR and the tractor vertical direction VTR.

In a similar vein, the trailer 14 has a trailer longitudinal extension in a trailer longitudinal direction LTL, a trailer lateral extension in a trailer lateral direction TTL and a trailer vertical extension in a trailer vertical direction VTL. The trailer longitudinal direction LTL corresponds to an intended direction of travel of the trailer 14 when the vehicle combination 10 is travelling straight ahead. The trailer vertical direction VTL corresponds to a direction of a normal to a planar surface supporting the trailer 14 and the trailer lateral direction TTL is perpendicular to each one of the trailer longitudinal direction LTL and the trailer vertical direction VTL.

Moreover, the tractor 12 and the trailer 14 are generally, and as exemplified Fig. 1 , pivotally connected to each other in a pivot point 52. Purely by way of example, such a pivot point 52 may be implemented by a so called fifth wheel. As such, when the vehicle combination 10 is operated there may be an articulation angle cp between the tractor longitudinal direction LTR and the trailer longitudinal direction LTL. Moreover, Fig. 1 illustrates that the vehicle combination comprises a control unit 54 for controlling the vehicle combination 10. In the Fig. 1 embodiment, the control unit 54 is located in the tractor 12 but the control unit 54 may also be located in other positions, such as the trailer 14. The control unit 54 is adapted to communicate with the set of tractor motion support devices 36, 38, 40, 42 and the set of trailer motion support devices 44, 46, 48 in order to control the operation of the vehicle combination 10. To this end, the control unit 54 may be connected to the set of tractor motion support devices 36, 38, 40, 42 and the set of trailer motion support devices 44, 46, 48 via wires (not shown), via a CAN bus system (not shown), via ethernet, via a wireless system (not shown) or any combination of the above possibilities.

The present invention will be presented hereinbelow in relation to a method for controlling a vehicle combination 10. However, it should be noted that the below information is equally applicable to the above-mentioned control unit 54.

As such, the present invention relates to a method for controlling a vehicle combination 10. As intimated above, the vehicle combination 10 comprises a tractor 12 and a trailer 14. The tractor 12 comprises a set of tractor wheels 16, 18, 20, 22 and the trailer comprises a set of trailer wheels 26, 28, 32, 34. The tractor comprises a set of tractor motion support devices 36, 38, 40, 42, comprising at least one tractor motion support device, connectable to the set of tractor wheels 16, 18, 20, 22 to thereby be adapted to provide at least a tractor force. The tractor force is at least one of a tractor propulsion force and a tractor brake force. The trailer comprises a set of trailer motion support devices 44, 46, 48, comprising at least one trailer motion support device, connectable to the set of trailer wheels 26, 28, 32, 34 to thereby be adapted to provide at least a trailer force. The trailer force is at least one of a trailer propulsion force and a trailer brake force.

With reference to Fig. 2, the method comprises:

Receiving a request that a desired force imparted on the vehicle combination 10 should be provided by the set of motion support devices of a unique dedicated unit of the vehicle combination, the unique dedicated unit being either the tractor or the trailer (S10). As a nonlimiting example, such a request may be issued from an operator, for instance using an actuating device such as a lever, knob or touch-screen (not shown), or from an autonomous drive system (not shown).

Purely by way of example, such a request may be implemented as one of the following:

- Imparting a desired braking force on the vehicle combination 10 by the set of motion support devices of the tractor 12 only. Such an implementation may for instance be desired when employing regenerative braking of the tractor 12 in order to charge one or more electric energy storage devices (not shown) of the tractor.

- Imparting a desired propulsion force on the vehicle combination 10 by the set of motion support devices of the trailer 14 only. Such an implementation may for instance be desired when energy storage means associated with the set of tractor motion support devices 36, 38, 40, 42 has a low amount of energy.

- Imparting a desired braking force on the vehicle combination 10 by the set of motion support devices of the trailer only. Such an implementation may for instance be desired when employing regenerative braking of the trailer 14 in order to charge one or more electric energy storage devices (not shown) of the trailer.

- Imparting a desired propulsion force on the vehicle combination 10 by the set of motion support devices of the tractor 14 only. Such an implementation may for instance be desired when energy storage means associated with the set of trailer motion support devices 46, 48, 50 has a low amount of energy.

Irrespective of the selected unique dedicated unit and the reasons for selecting that unique dedicated unit, the method further comprises:

Upon determining that the desired force imparted on the vehicle combination can be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the predetermined set of safety requirements comprising at least one safety requirement (S12), operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force (S14), otherwise operating one or more of the tractor motion support devices as well as one or more of the trailer motion support devices in order to provide the desired force imparted on the vehicle combination (S16). Generally, it should be noted that upon determining that the desired force imparted on the vehicle combination cannot be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the method preferably comprises operating the set of motion support devices of the unique dedicated unit so as to provide a reduced force having a smaller absolute value than the absolute value of the desired force. Preferably, such a reduced force is determined by determining the force with the largest absolute value that can be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination. The remaining load, viz the difference between the desired force and the reduced force can thereafter be provided by the set of motion support devices of the tractor 12 or trailer 14 not being the unique dedicated unit.

However, it is also contemplated that in embodiments of the method of the invention, determining that the desired force imparted on the vehicle combination cannot be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the method may comprise determining a predetermined force distribution of the forces provided by the set of motion support devices of the tractor 12 and the trailer 14 in order to arrive at the desired force.

Hereinbelow, various implementations of the safety requirement will be presented.

In a first implementation, the predetermined set of safety requirements of the vehicle combination comprises a lateral acceleration safety condition requiring that, for each one of the set of motion support devices of the unique dedicated unit, a longitudinal force F _x produced by the motion support device must be equal to or lower than a longitudinal force limit value being determined by means of a longitudinal force limit function being a function of at least a lateral acceleration ay of the unique dedicated unit.

The lateral acceleration a _y extends in the later direction of the unique dedicated unit, viz the tractor lateral direction TTR for the tractor 12 and the trailer lateral direction TTL for the trailer 14. The lateral acceleration a _y may be measured using an acceleration sensor (not shown) located in the unique dedicated unit, viz the tractor 12 or the trailer 14. The longitudinal force F _x may be a propulsion force or a braking force.

Purely by way of example, the longitudinal force limit function may be a function using a value proportional to the lateral acceleration a _y of the unique dedicated unit as input and provides a value proportional to a normalized longitudinal force F _x /pF _z , being the longitudinal force F _x divided by a total vertical load F _z imparted on the wheel or wheels connected to the motion support device and the friction value p indicative of the friction between the wheel or wheels connected to the motion support device and the ground supporting the unique dedicated unit, as output.

Moreover, though again by way of example, the longitudinal force limit function uses the lateral acceleration a _y of the unique dedicated unit divided by a friction reference value pg as input, the friction reference value being a friction value p, indicative of the friction between the set of wheels of the unique dedicated unit and the ground supporting the unique dedicated unit, multiplied by an acceleration value g corresponding to acceleration due to gravity.

With reference to Fig 3, the longitudinal force limit function may be a step function such that:

- for values of the lateral acceleration a _y of the unique dedicated unit divided by the friction reference value pg being equal to or smaller than a predetermined threshold as input (the threshold is indicated by reference c in Fig. 3), the output is set to a fixed non-zero value of the normalized longitudinal force, and

- for values of the lateral acceleration of the unique dedicated unit divided by a friction reference value being greater than the predetermined threshold as input, the output is set to zero.

It should be noted that the longitudinal force limit function need not be a step function. To this end, reference is made to Fig. 4 illustrating an implementation in which the longitudinal force limit function is a continuous function.

Irrespective of how the longitudinal force limit function is implemented, the longitudinal force limit value can be determined for each motion support device of the unique dedicated unit, for instance following the below procedure. A lateral acceleration a _y of the unique dedicated unit, viz the tractor 12 or the trailer 14, may be determined. Such a lateral acceleration value a _y may for instance be determined using an accelerometer (not shown). Moreover, a value indicative of the friction value p indicative of the friction between the wheel or wheels connected to the motion support device and the ground supporting the unique dedicated unit may be determined. Such a friction value p may be determined using any known procedure, such as using a sensor (such as a camera) for monitoring the condition of the ground onto which the unique dedicated unit is travelling and/or by using a brush model or using a slip value associated with the wheel or wheels. Furthermore, the total vertical load currently imparted on the wheel or wheels connected to is motion support device is determined, for instance using information obtainable from the suspension device or devices connected to the wheel or wheels.

The lateral acceleration value a _y and the friction value p can be used as input to a longitudinal force limit function, for instance as exemplified hereinabove with reference to Fig. 3 or Fig. 4, in order to arrive at value of a normalized longitudinal force F _x /pF _z . The longitudinal force limit value F _x may then be determined by multiplying the normalized longitudinal force F _x /pF _z by the friction value p and the total vertical load F _z currently imparted on the wheel or wheels connected to is motion support device.

The above procedure can be carried out for each motion support device of the unique dedicated unit, i.e. the tractor 12 or the trailer 14, and the longitudinal force limit values F _x can thereafter be summarized in order to arrive at a total longitudinal force limit value associated with the unique dedicated unit.

Instead of, or in addition to the above-mentioned lateral acceleration safety condition, the predetermined set of safety requirements of the vehicle combination may comprise a longitudinal slip safety condition requiring that a detected longitudinal slip value for at least a selected subset of the set of wheels for the unique dedicated unit is below a predetermined threshold. As such, the unique dedicated unit, i.e. the tractor 12 or the trailer 14, may be equipped with means for determining a longitudinal slip value for at least a selected subset of the set of wheels associated with the unique dedicated unit. Thereafter, each determined longitudinal slip value may be compared to a predetermined threshold in order to ensure that no excessive slipping occurs for any one of the selected subset of the set of wheels. In response to verifying that no excessive slipping occurs, the longitudinal slip safety condition may be deemed to have been met or fulfilled. Instead of, or in addition to the above-mentioned safety conditions, the predetermined set of safety requirements of the vehicle combination may comprise a state determination condition requiring that for a predetermined vehicle state, a difference between a vehicle state measured value, relating to a measured value indicative of the predetermined vehicle state, and an vehicle state expected value, relating to an expected value indicative of the predetermined vehicle state, is within a predetermined state range.

Purely by way of example, the vehicle state expected value may be determined using a vehicle model of the vehicle combination, preferably the vehicle state expected value is determined using a vehicle model as well as a tire model of the set of tractor wheels and/or the set of trailer wheels.

For instance, predetermined vehicle state is a yaw rate of the unique dedicated unit. A yaw rate is generally associated with a speed of rotation around and axis extending in the vertical direction of the unique dedicated unit.

As another non-limiting example, the predetermined vehicle state may be an articulation angle cp, the the above presentation of the articulation angle cp with reference to Fig. 1 , or articulation angular rate <p between the tractor 12 and the trailer 14.

Moreover, the predetermined vehicle state may be a side slip angle of the unique dedicated unit.

Furthermore, the predetermined vehicle state may be a side slip angle of at least a selected subset of the set of wheels for the unique dedicated unit.

It should be noted that the embodiments of the method according to the present invention may use a combination of state determination conditions as exemplified above.

As has been intimated above, the desired force imparted on the vehicle may be a propulsion force or a brake force.

It should also be noted that the present invention is not limited to a vehicle combination 10 comprising a tractor and a single trailer. As such, in embodiment of the method, the vehicle combination comprises one or more additional trailers, each additional trailer comprising a set of additional trailer motion support devices, comprising at least one additional trailer motion support device, connectable to the set of additional trailer wheels to thereby be adapted to provide at least an additional trailer force, the additional trailer force being at least one of an additional trailer propulsion force and an additional trailer brake force.

The method comprises:

- receiving a request that a desired force imparted on the vehicle combination should be provided by the set of motion support devices of a unique dedicated unit of the vehicle combination, the unique dedicated unit being either the tractor, the trailer or one of the one or more additional trailers;

- upon determining that the desired force imparted on the vehicle combination can be provided by the set of motion support devices of the unique dedicated unit whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination, the predetermined set of safety requirements comprising at least one safety requirement, operating the set of motion support devices of the unique dedicated unit only so as to provide the desired force, otherwise operating one or more of the tractor motion support devices, as well as one or more of the trailer motion support devices and/or one or more of the additional trailer motion support devices of one or more of the one or more additional trailers, in order to provide the desired force imparted on the vehicle combination.

Finally, Fig. 5 illustrates a force envelope 56 for a vehicle combination 10 comprising a first and second motion support device. For each one of the motion support devices, the Fig. 5 force envelope presents a limit for normalized longitudinal force F _x ,i/pF _z ,i or F _x ,2/pF _z ,2 as discussed hereinabove as a function of the lateral acceleration a _y of the unit concerned, viz the tractor 12 or the trailer 14, divided by the above-mentioned friction reference value pg.

As may be gleaned from Fig. 5, the envelope can be used for determining a maximum combined longitudinal load that can be provided by the first and second motion support devices whilst fulfilling each safety requirement in a predetermined set of safety requirements of the vehicle combination. Thus, the Fig. 5 envelope can be used for identifying one or more suitable pairs for the longitudinal forces provided by the first and second motion support devices. Needless to say, the Fig. 5 envelope can be extended so as to include a plurality of motion support devices exceeding two such that an envelope is generated for each motion support device in a vehicle combination 10. Moreover, the longitudinal force limit value for each motion support device of the tractor 12 may be summarized in order to arrive at a longitudinal force limit value for the longitudinal force that currently can be produced by all the motion support devices of the tractor 12. In a similar vein, the longitudinal force limit value for each motion support device of the trailer 14 may be summarized in order to arrive at a longitudinal force limit value for the longitudinal force that currently can be produced by all the motion support devices of the trailer 14.

The longitudinal force limit value for all the motion support devices of the tractor and the trailer, respectively, can thereafter be used in order to determine suitable combinations of the longitudinal forces provided by the tractor 12 and the trailer 14.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.